Title of invention: negative active material for secondary battery, negative electrode including the same, and method for manufacturing the same
Technical field
[One]
This application claims the benefit of priority based on Korean Patent Application No. 10-2019-0006167 filed on January 17, 2019, and all contents disclosed in the documents of the Korean patent application are included as part of this specification.
[2]
The present invention relates to a negative active material for a secondary battery, a negative electrode including the same, and a method of manufacturing the same. In more detail, the present invention relates to an anode active material having improved cycle swelling and high rate charging characteristics, an anode, and a method of manufacturing the same.
Background
[3]
The present invention relates to a negative active material for a secondary battery, a negative electrode including the same, and a method of manufacturing the same. In more detail, the present invention relates to an anode active material having improved cycle swelling and high rate charging characteristics, an anode, and a method of manufacturing the same.
[4]
As the price of energy sources rises due to the depletion of fossil fuels and interest in environmental pollution increases, the demand for eco-friendly alternative energy sources is becoming an indispensable factor for future life. In particular, technology development for mobile devices As the demand and demand increase, the demand for secondary batteries as an energy source is rapidly increasing.
[5]
Typically, in terms of the shape of the battery, there is a high demand for prismatic secondary batteries and pouch-type secondary batteries that can be applied to products such as mobile phones with a thin thickness. In terms of materials, lithium-ion batteries with high energy density, discharge voltage, and output stability, There is high demand for lithium secondary batteries such as lithium ion polymer batteries.
[6]
In general, secondary batteries form a positive electrode and a negative electrode by coating an electrode mixture containing an electrode active material on the surface of a current collector, and form an electrode assembly with a separator interposed therebetween, and then a cylindrical or rectangular metal can or an aluminum laminate sheet. It is mounted inside the pouch-shaped case of the electrode assembly, and is manufactured by mainly injecting or impregnating a liquid electrolyte into the electrode assembly or using a solid electrolyte.
[7]
In addition, secondary batteries are classified according to the structure of the electrode assembly of the anode/separator/cathode structure. Typically, long sheet-shaped anodes and cathodes are wound with a separator interposed between them. Roll (wound type) electrode assembly, stacked (stacked) electrode assembly in which a plurality of anodes and cathodes cut into units of a predetermined size are sequentially stacked with a separator interposed, And a stack/folding electrode assembly in which bi-cells or full cells stacked in a state are wound with a separator sheet.
[8]
Meanwhile, the electrode generates an electric current through the exchange of ions, and the positive electrode and the negative electrode constituting the electrode have a structure in which an electrode active material is coated on an electrode current collector made of metal.
[9]
Among them, in the case of the negative electrode, conventionally, lithium metal was used as the negative electrode in the secondary battery. It is being replaced by a carbon-based compound capable of intercalation and desorption of phosphorus lithium ions.
[10]
The carbon-based compound has a very low discharge potential of about -3V with respect to the standard hydrogen electrode potential, and exhibits excellent electrode life characteristics due to a very reversible charging and discharging behavior due to the uniaxial orientation of the graphene layer. . In addition, since the electrode potential is 0V Li/Li+ when charging Li ions, it can exhibit a potential that is almost similar to that of pure lithium metal, so that higher energy can be obtained when configuring a battery with an oxide-based positive electrode.
[11]
The carbon-based compound includes crystalline carbon and amorphous carbon. Crystalline carbon is representative of graphite carbon such as natural graphite and artificial graphite, and amorphous carbon is heat treated with non-graphitizable carbons (hard carbons) obtained by carbonizing a polymer resin and pitch. And the resulting graphitizable carbons (soft carbons).
[12]
In particular, as a carbon-based material, natural graphite having a high capacity or excellent artificial graphite such as high-temperature properties is used, but artificial graphite exhibits a lower capacity than natural graphite, and the production of negative electrode slurry due to secondary particle formation and coating treatment And poor processability, such as a decrease in electrode adhesion, and poor electrode rolling characteristics. In addition, natural graphite exhibits a swelling phenomenon according to a high degree of orientation or poor fast charging performance, and has a relatively large number of functional groups on the surface compared to artificial graphite, resulting in poor high-temperature characteristics.
[13]
Korean Patent Registration No. 10-1338299 discloses a lithium secondary battery using natural graphite as an anode active material. However, in the case of a negative active material using natural graphite, the mechanical strength of the electrode is weakened, and the cycle swelling and rapid charging performance during charging and discharging are poor. In this case, the electrode may swell during charging and discharging, resulting in a problem such as a reduction in cycle life.
[14]
Therefore, it is necessary to develop a technology for solving the above problems.
Detailed description of the invention
Technical challenge
[15]
The present invention was invented to solve the above problems. In the negative electrode active material using natural graphite, fine powder and coarse powder are removed to make the particle size distribution uniform, and then the surface is modified to form large pores in the natural graphite. An object of the present invention is to provide a negative electrode active material for secondary batteries with improved output and cycle characteristics, swelling characteristics, and rapid charging capability of graphite, a negative electrode including the same, and a method of manufacturing the same.
Means of solving the task
[16]
The negative active material for a secondary battery according to the present invention,
[17]
As a negative active material for secondary batteries manufactured by surface modification of natural graphite,
[18]
In the particle size distribution of the natural graphite, the D max /D min value is 1.6 to 2.1,
[19]
Pores having a diameter of 0.5 to 2.0 μm are formed on the surface.
[20]
In addition, in the negative active material for a secondary battery according to the present invention, the pores may be formed by surface modification by treating the surface of natural graphite with potassium hydroxide (KOH).
[21]
In addition, in the negative active material for a secondary battery according to the present invention, the size of pores formed on the surface may be 0.5 to 1.0 μm.
[22]
In addition, in the negative active material for a secondary battery according to the present invention, the natural graphite may have a spherical shape.
[23]
In addition, in the negative active material for a secondary battery according to the present invention, the average particle diameter (D 50 ) of the natural graphite may be 5 to 15 μm.
[24]
In addition, in the negative active material for a secondary battery according to the present invention, pores may be formed inside the natural graphite.
[25]
In addition, in the negative active material for a secondary battery according to the present invention, the pores formed inside the natural graphite may include 3 to 15 vol% of those having a size of 6 nm or less, and 55 to 85 vol% of those having a size of 60 to 200 nm. .
[26]
In addition, in the negative active material for a secondary battery according to the present invention, the natural graphite may be coated with a carbon-based compound.
[27]
In addition, in the negative active material for a secondary battery according to the present invention, the carbon-based compound may be amorphous carbon.
[28]
In addition, the present invention provides a method for manufacturing a negative active material for a secondary battery, wherein the method for preparing a negative active material for a secondary battery includes a classification step of removing fine powder and coarse powder so that the D max /D min value for natural graphite is 1.6 to 2.1. ; And a surface modification step of treating the classified natural graphite with potassium hydroxide (KOH). It may include.
[29]
In addition, in the method of manufacturing a negative active material for a secondary battery according to the present invention, an annealing step of heating and cooling natural graphite after the surface modification step; It may further include.
[30]
In addition, in the method of manufacturing a negative active material for a secondary battery according to the present invention, in the annealing step, the heat treatment may be performed at 700 to 1000°C.
[31]
In addition, in the method of manufacturing a negative active material for a secondary battery according to the present invention, prior to the classification step, a step of coating natural graphite with a carbon-based compound may be further included.
[32]
In addition, the present invention provides a negative electrode including the negative active material for a secondary battery.
[33]
In addition, the present invention provides a secondary battery including a negative electrode, a positive electrode, a separator interposed between the negative electrode and the positive electrode, and an electrolyte.
Effects of the Invention
[34]
In the present invention, in the negative electrode active material using natural graphite, the particle size distribution is uniform by removing fine powder and coarse powder during the production of the active material, and then by modifying the surface through chemical activation using KOH on the surface of the active material, large pores are increased. The output of the electrode, rapid charging, and cycle swelling performance can be improved.
Brief description of the drawing
[35]
1 is a flow chart showing the flow of a method of manufacturing a negative active material according to an embodiment of the present invention.
Best mode for carrying out the invention
[36]
Terms used in this specification and claims should not be construed as being limited to a conventional or dictionary meaning, and that the inventor can appropriately define the concept of terms in order to describe his own invention in the best way. Based on the principle, it should be interpreted as a meaning and concept consistent with the technical idea of ​​the invention. Therefore, the configuration shown in the embodiments described in the present specification is only one of the most preferred embodiments of the present invention and does not represent all of the technical spirit of the present invention, and various equivalents that can replace them at the time of the present application And it should be understood that there may be variations.
[37]
Throughout this specification, terms such as "comprise" or "have" are intended to designate the presence of features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, but one or more other It is to be understood that it does not preclude the presence or addition of features, numbers, steps, actions, components, parts, or combinations thereof.
[38]
The terms "about", "substantially" and the like used throughout this specification are used as a meaning at or close to the numerical value when manufacturing and material tolerances specific to the stated meaning are presented, and are accurate to aid the understanding of the present application. Or absolute figures are used to prevent unreasonable use of the stated disclosure by unconscionable infringers.
[39]
In the entire specification of the present application, the term "combination(s) thereof" included in the expression of the Makushi form means one or more mixtures or combinations selected from the group consisting of the constituent elements described in the expression of the Makushi form, It means to include at least one selected from the group consisting of the above constituent elements.
[40]
[41]
Hereinafter, the present invention will be described in detail.
[42]
The negative active material for a secondary battery according to the present invention is prepared by surface modification of natural graphite, and has a D max /D min value of 1.6 to 2.1 in the particle size distribution of the natural graphite .
[43]
In general, as the charge/discharge cycle of natural graphite is repeated, a swelling phenomenon may occur due to an electrolyte solution decomposition reaction occurring at the edge of the natural graphite, and charge/discharge efficiency and capacity may be deteriorated. In addition, natural graphite has many internal pores and receives a lot of mechanical stress as the internal pores are clogged during electrode rolling.In particular, internal pores in the active material called micro pores are formed through spheroidization or acid treatment during the manufacturing process. The pores in the active material adversely affect cell performance by excessive side reactions with the electrolyte.
[44]
Therefore, through surface modification of natural graphite with a small particle size and uniform particle size, the output and rapid charging cycle swelling performance can be improved beyond the level of artificial graphite.
[45]
Specifically, the particle size distribution should be uniform in order to improve the performance degradation that may occur when using natural graphite.In the particle size distribution of the natural graphite, the D max /D min value may be 1.6 to 2.1, preferably 1.8 to 2.0 days. I can. Here, D max means the diameter of the largest particle in the order of particle diameter, and D min means the diameter of the smallest particle in the order of particle diameter. The smaller the D max /D min value, the sharper the particle size distribution curve appears.
[46]
If the D max /D min value is less than 1.6, rapid charging performance may deteriorate, such as causing lithium precipitation during charging, and if the D max /D min value exceeds 2.1, it may be difficult to obtain an appropriate density. That is, if the value of D max /D min is out of the above range, there is a problem that the tap density of the active material becomes too low, the thickness of the electrode active material layer becomes thick and the pressability decreases, so there is a disadvantage in realizing a high energy density. have.
[47]
The average particle diameter (D 50 ) of the natural graphite may be 5 to 15 μm, more preferably 9 to 11 μm. The average particle diameter (D 50 ) means the particle diameter at which the accumulation of 50% from the smallest particle in the order of particle diameter. By using natural graphite having an average particle diameter within the above range, it is possible to obtain an advantage of improving the rapid charging capability at a high energy density. When the average particle diameter of the natural graphite exceeds 15 μm, the tap density of the electrode (cathode) and the adhesion characteristics of the active material may decrease, so that the effect of improving the swelling phenomenon of the electrode may decrease. Conversely, when the average particle diameter of natural graphite is less than 5 μm, the initial efficiency of the secondary battery decreases due to an increase in the specific surface area, and battery performance may be deteriorated.
[48]
The particle diameters (D max , D min , D 50 ) of the natural graphite can be measured using, for example, a laser diffraction method. In general, the laser diffraction method can measure a particle diameter of about several mm from a submicron region, and high reproducibility and high resolution results can be obtained. More specifically, the particle size measurement of the spheroidized natural graphite is performed by dispersing spheroidized natural graphite in an ethanol/water solution, and then introducing it into a commercially available laser diffraction particle size measuring device (for example, Microtrac MT 3000), and using ultrasonic waves of about 28 kHz. After irradiating with an output of 60 W, it can calculate based on the particle size distribution in a measuring device.
[49]
Natural graphite according to an embodiment of the present invention has a specific surface area of ​​1.7 m 2 /g to 5.1 m 2 /g, and the tap density may be 1.0 g/cc to 1.5 g/cc, but is not limited thereto.
[50]
Here, the specific surface area is the average specific surface area obtained based on the adsorption isotherm of BET (Brunauer, Emmett, Teller), specifically, nitrogen gas adsorption using a Porosimetry analyzer (Bell Japan Inc, Belsorp-II mini). It can be measured by the BET 6 point method by the distribution method. In addition, the tap density can be measured by performing tapping 2000 times using TAP-2S manufactured by LOGAN, which is a tap density measuring device.
[51]
In addition, the natural graphite used as the negative electrode active material of the present invention may use various types of natural graphite, such as flaky graphite and natural graphite, and a spherical shape is more preferable for improving the compressibility and impregnation of the electrolyte for high rate charge and discharge characteristics of the active material Do. That is, when a negative electrode active material is manufactured using only general scale-like natural graphite, there may be problems such as dropping of the active material from the current collector, bending of the electrode plate, difficulty in controlling the thickness of the electrode plate, low adhesion, and impregnation of the electrolyte solution.
[52]
When natural graphite is spheronized and used, it can be obtained by applying an external mechanical force to general natural graphite and subjecting it to granulation spheroidization. For example, spheroidized natural graphite is spheroidized for 10 to 30 minutes at a rotor speed of 30 m/s to 100 m/s in a spheroidizing device after treating the scaled natural graphite with an acid or a base. It may be manufactured by converting it, and is not limited thereto, and the speed of the rotor and the time of the rotor may be appropriately adjusted in order to control the shape and particle diameter of the natural graphite.
[53]
In addition, pores having a diameter of 0.5 to 2.0 μm may be formed on the surface of the natural graphite, and the pore size may be more preferably 0.5 to 1.0 μm. The size of the surface pores can be obtained from SEM images taken of natural graphite particles. Specifically, from an image obtained by photographing with a scanning microscope (SEM), a number of pores of about 5% of the total number of pores is arbitrarily selected, the diameter thereof is measured, and the average value of the diameter can be defined as the diameter of the pores.
[54]
As described above, micro pores are formed in natural graphite while undergoing spheronization and acid treatment processes, and unnecessary side reactions may occur between the natural graphite and the electrolyte due to the micropores. Accordingly, by reducing side reactions between the natural graphite and the electrolyte by forming large pores having a diameter within the above range on the surface of the natural graphite, the output, rapid charging, and cycle swelling performance of the natural graphite can be improved.
[55]
If the size of the pores formed on the surface is less than 0.5 μm, the size of the pores is small and side reactions between natural graphite and the electrolyte cannot be suppressed. On the contrary, if the pore size exceeds 2.0 μm, the specific surface area of ​​the active material decreases Adhesion may decrease.
[56]
The pores formed on the surface may be formed by modifying the surface of natural graphite by treating potassium hydroxide (KOH). Potassium hydroxide chemically activates the surface of natural graphite. Specifically, the surface of graphite and potassium hydroxide (KOH) undergo the following reaction.
[57]
6KOH + 2C → 2K + 3H 2 + 2K 2 CO 3
[58]
K 2 CO 3 + C → K 2 O + 2CO
[59]
K 2 O+C → CO + 2K
[60]
As can be seen wherein the potassium penetrate inside carbon layer is K while the heat treatment at the activation temperature 2 a form a O and generates upon activation K 2 O is reduced to potassium back through the dehydration reaction, K 2 O is As much as it is reduced, pores are formed on the carbon surface due to the reduction of carbon, and the reduced K penetrates into the carbon, thereby widening the space inside the carbon.
[61]
When the natural graphite is treated with potassium hydroxide, the potassium hydroxide penetrates into the natural graphite, thereby chemically activating the natural graphite and increasing the size of pores formed inside the natural graphite.
[62]
As a result, the pores formed inside the natural graphite may include 3 to 15 vol% of those having a size of 6 nm or less, preferably 5 to 13 vol%, more preferably 5 to 10 vol%. . In addition, the pores formed inside the natural graphite may include 55 to 85 vol% of those having a size between 60 to 200 nm, preferably 60 to 80 vol%, more preferably 70 to 80 vol%%. . In one embodiment of the present invention, the measurement of the distribution according to the size of the pores formed inside the natural graphite was performed using a BEL Sorption equipment of BEL of Japan, and nitrogen gas adsorption as a liquid nitrogen temperature was performed to obtain BET. Plot was done. By analyzing the result with the BJH Method, the ratio of the total volume of internal pores and the volume occupied by pores having a predetermined diameter (those having a size of 6 nm or less and those having a size of 60 to 200 nm) can be calculated. .
[63]
When the distribution according to the size of the pores formed inside the natural graphite is the same as the above range, the specific surface area is reduced enough to reduce unnecessary side reactions between the electrolyte and graphite while maintaining the performance of the electrode and the battery. And cycle characteristics can be improved.
[64]
In the natural graphite, if less than 3 vol% of those having a size of 6 nm or less among the pores formed therein, and those having a size of between 60 to 200 nm exceed 85 vol%, the specific surface area of ​​the negative active material is excessively reduced and the electrode Adhesion decreases, and cycle characteristics may deteriorate. Conversely, when those having a size of 6 nm or less exceed 15 vol%, and those having a size of 60 to 200 nm are less than 55 vol%, micropores in the active material may increase excessively, which is not preferable because side reactions between the electrolyte and the active material may increase.
[65]
In addition, the natural graphite may be coated with a carbon-based compound. By coating natural graphite with a carbon-based compound, it is possible to confirm improvement in rapid charging performance and output performance by increasing the intercalation/desorption rate of lithium ions.
[66]
The carbon-based compound may be amorphous carbon. As an amorphous carbon coating layer is formed on the surface of natural graphite, the hardness of natural graphite is increased, and lithium is easily inserted/desorbed during charging/discharging. Initial efficiency can be expected.
[67]
In the method of forming an amorphous carbon coating layer on the surface of natural graphite according to an embodiment of the present invention, a carbon source and natural graphite are put in a sintering furnace, and, for example, in a temperature range of 300° C. to 1400° C., from about 3 hours to about It can be coated by heat treatment for 15 hours.
[68]
The carbon source may be used without limitation, as long as it generates carbon by heat treatment. For example, coating with pyrolytic carbon using at least one gaseous or liquid carbon source selected from the group consisting of methane, ethane, ethylene, butane, acetylene, carbon monoxide, propane, polyvinyl alcohol and propylene; Or coating by liquid or solid pitch; Or glucose, fructose, galactose, maltose, lactose, sucrose, phenolic resin, naphthalene resin, polyvinyl alcohol resin, urethane resin, polyimide resin, furan resin, cellulose resin, epoxy resin, polystyrene resin, resorcinol resin , Any one selected from the group consisting of fluoroglucinol-based resins, tar, and low molecular weight heavy oils, or a mixture of two of them may be a carbon source, and the pitch may be a coal-based pitch or a petroleum-based pitch.
[69]
The coating amount of the amorphous carbon on the natural graphite may be 0.5 parts by weight to 10 parts by weight, preferably 1 part by weight to 8 parts by weight, more preferably 2 to 7 parts by weight based on 100 parts by weight of natural graphite. If the coating amount of the amorphous carbon is less than 0.5 parts by weight, the hardness of natural graphite decreases and side reactions with the electrolyte may increase. On the contrary, when the coating amount of amorphous carbon exceeds 10 parts by weight, the thickness of the amorphous carbon layer is excessively increased and lithium ions The mobility of the cell is impeded, so the resistance may increase, and the surface becomes hard and the electrode density cannot be increased.
[70]
The present invention also provides a negative electrode for a secondary battery comprising the negative active material.
[71]
The negative electrode may be prepared by applying a negative electrode mixture including a negative electrode active material on a current collector and then drying the negative electrode mixture, and the negative electrode mixture may optionally further include a binder, a conductive material, a filler, and the like, if necessary. In this case, the above-described surface-modified natural graphite may be used as the negative active material.
[72]
In the case of a negative electrode current collector sheet, it is generally made to have a thickness of 3 to 500 µm. Such a negative electrode current collector is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, the surface of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel For example, carbon, nickel, titanium, silver, etc. surface-treated, aluminum-cadmium alloy, and the like may be used. In addition, like the positive electrode current collector, it is possible to strengthen the bonding strength of the negative electrode active material by forming fine irregularities on the surface thereof, and it may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics.
[73]
The conductive material is typically added in an amount of 1 to 30% by weight based on the total weight of the mixture including the positive electrode active material. Such a conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery, and examples thereof include graphite such as natural graphite or artificial graphite; Carbon blacks such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; Conductive fibers such as carbon fibers and metal fibers; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used.
[74]
The binder is a component that assists in bonding of an active material and a conductive material and bonding to a current collector, and is typically added in an amount of 1 to 30% by weight based on the total weight of the mixture including the positive electrode active material. Examples of such a binder include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, recycled cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, poly Propylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butyrene rubber, fluorine rubber, and various copolymers.
[75]
The filler is selectively used as a component that suppresses the expansion of the electrode, and is not particularly limited as long as it is a fibrous material without causing chemical changes to the battery, and examples thereof include olefinic polymerization agents such as polyethylene and polypropylene; Fibrous materials such as glass fiber and carbon fiber are used.
[76]
Other ingredients, such as viscosity modifiers, adhesion promoters, and the like, may be further included optionally or as a combination of two or more. The viscosity modifier is a component that adjusts the viscosity of the electrode mixture so as to facilitate the mixing process of the electrode mixture and the application process on the current collector thereof, and may be added up to 30% by weight based on the total weight of the negative electrode mixture. Examples of such viscosity modifiers include carboxy methylcellulose, polyvinylidene fluoride, and the like, but are not limited thereto. In some cases, the solvent described above may simultaneously serve as a viscosity modifier.
[77]
The adhesion promoter is an auxiliary component added to improve the adhesion of the active material to the current collector, and may be added in an amount of 10% by weight or less relative to the binder, for example, oxalic acid, adipic acid, And formic acid, acrylic acid derivatives, itaconic acid derivatives, and the like.
[78]
[79]
The present invention also provides a secondary battery manufactured by the present method. Specifically, the secondary battery includes two or more electrodes for secondary batteries manufactured according to the present invention, and the electrode assembly is embedded in a battery case, wherein the secondary battery is wound with a separator interposed between the electrodes for secondary batteries. And a non-aqueous electrolyte containing a lithium salt is impregnated with the electrode assembly. The secondary battery electrode may be a positive electrode and/or a negative electrode. In this case, the negative electrode may be the same as described above, and the negative electrode may be assembled into an electrode assembly and then sealed in a battery case together with an electrolyte to be manufactured into a lithium secondary battery through an activation process. The secondary battery may be a cylindrical battery, a prismatic battery, a pouch-type battery, or a coin-type battery, and there is no particular limitation on the shape of the battery.
[80]
The electrode assembly is not particularly limited as long as it has a structure consisting of an anode and a cathode, and a separator interposed therebetween, and for example, a folding type structure, a stack type structure, or a stack/folding type (SNF) structure, or a lamination/stack It may be a type (LNS) structure structure.
[81]
The electrode assembly of the folding-type structure includes at least one anode, at least one cathode, and at least one separator interposed between the anode and the cathode, and the anode, the separator, and the cathode do not cross each other at one end and the other end. It may be a structure that does not.
[82]
In addition, the electrode assembly of the stacked structure includes one or more positive electrodes, one or more negative electrodes, and one or more separators interposed between the positive and negative electrodes, and the positive electrode, the separator, and the negative electrode cross each other at one end and the other end. It can be a structure to
[83]
The electrode assembly of the stack/folding type structure includes at least one anode, at least one cathode, and at least one separator interposed between the anode and the cathode, and the separator includes a first separator and a second separator, One end and the other end of each of the anode, the first separator, and the cathode do not cross each other, and the second separator may have a structure surrounding a side surface of an electrode on which an electrode tab is not formed.
[84]
The electrode assembly of the lamination/stack type structure may include one or more improved electrodes in which a separator is laminated on one or both surfaces. The improved electrode may be implemented in a structure in which, for example, a separator is bonded to one side of an anode or a cathode. In addition, the separator may be implemented in a structure in which both sides of an anode or both sides of a cathode are bonded to each other. In addition, it may be implemented in a structure in which an anode, a separator, and a cathode are bonded to each other while a separator is interposed between the anode and the cathode.
[85]
In the secondary battery according to the present invention, the positive electrode may be prepared by applying an electrode mixture containing a positive electrode active material on a current collector and then drying. The positive electrode mixture may optionally contain a binder, a conductive material, a filler, etc. It can be included more.
[86]
In the present invention, the positive electrode current collector is generally made to have a thickness of 3 to 500 μm. Such a positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes to the battery, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel. Surface treatment of carbon, nickel, titanium, silver, or the like may be used on the surface of. The current collector may increase the adhesion of the positive electrode active material by forming fine irregularities on its surface, and various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics are possible.
[87]
In the present invention, the positive electrode active material is a material capable of causing an electrochemical reaction, as a lithium transition metal oxide, containing two or more transition metals, and, for example, lithium cobalt oxide (LiCoO 2) substituted with one or more transition metals. ), layered compounds such as lithium nickel oxide (LiNiO 2 ); Lithium manganese oxide substituted with one or more transition metals; Formula LiNi 1-y M y O 2 (where M = Co, Mn, Al, Cu, Fe, Mg, B, Cr, Zn or Ga, and including one or more of the above elements, 0.01≤y≤0.7) Lithium nickel-based oxide represented by; Li 1+z Ni 1/3 Co 1/3 Mn 1/3 O 2 , Li 1+z Ni 0.4 Mn 0.4 Co 0.2 O 2Li 1+z Ni b Mn c Co 1-(b+c+d) M d O (2-e) A e (where -0.5≤z≤0.5, 0.1≤b≤0.8, 0.1≤c≤ 0.8, 0≤d≤0.2, 0≤e≤0.2, b+c+d<1, M = Al, Mg, Cr, Ti, Si or Y, and A = F, P or Cl) Lithium nickel cobalt manganese composite oxide; Formula Li 1 + x M 1-y M ' y PO 4-z X z , and (wherein, M = a transition metal, preferably Fe, Mn, Co or Ni, M' = Al, Mg or Ti, X = F, S, or N, and -0.5≦x≦=+0.5, 0≦y≦0.5, 0≦z≦0.1, and the like), but are not limited thereto.
[88]
In the positive electrode, additive materials such as a binder, a conductive material, and a filler are as described above.
[89]
The separator is interposed between the anode and the cathode, and an insulating thin ultrathin having high ion permeability and mechanical strength is used. The pore diameter of the separator is generally 0.01 to 10 µm, and the thickness is generally 5 to 300 µm. Examples of such a separation membrane include olefin-based polymers such as polypropylene having chemical resistance and hydrophobicity; Sheets or non-woven fabrics made of glass fiber or polyethylene are used. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as a separator.
[90]
The lithium salt-containing non-aqueous electrolyte is composed of an electrolyte and a lithium salt, and as the electrolyte, a non-aqueous organic solvent, an organic solid electrolyte, an inorganic solid electrolyte, or the like is used.
[91]
As the non-aqueous organic solvent, for example, N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma -Butyl lactone, 1,2-dimethoxy ethane, tetrahydroxy franc (franc), 2-methyl tetrahydrofuran, dimethylsulfoxide, 1,3-dioxolone, formamide, dimethylformamide, dioxolone , Acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid tryster, trimethoxy methane, dioxolone derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbo Aprotic organic solvents such as nate derivatives, tetrahydrofuran derivatives, ethers, methyl pyropionate, and ethyl propionate may be used.
[92]
Examples of the organic solid electrolyte include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphoric acid ester polymers, poly agitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, A polymerization agent or the like containing an ionic dissociating group may be used.
[93]
As the inorganic solid electrolyte, for example, Li 3 N, LiI, Li 5 NI 2 , Li 3 N-LiI-LiOH, LiSiO 4 , LiSiO 4 -LiI-LiOH, Li 2 SiS 3 , Li 4 SiO 4 , Nitrides , halides, and sulfates of Li such as Li 4 SiO 4 -LiI-LiOH and Li 3 PO 4 -Li 2 S-SiS 2 may be used.
[94]
The lithium salt is a material soluble in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO 4 , LiBF 4 , LiB 10 Cl 10 , LiPF 6 , LiCF 3 SO 3 , LiCF 3 CO 2 , LiAsF 6 , LiSbF 6 , LiAlCl 4 , CH 3 SO 3 Li, (CF 3 SO 2 ) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate and imide.
[95]
In addition, for the purpose of improving charge/discharge properties and flame retardancy, the electrolyte solution includes, for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate triamide, and nitro. Benzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol, aluminum trichloride, etc. may be added. . In some cases, in order to impart non-flammability, a halogen-containing solvent such as carbon tetrachloride and ethylene trifluoride may be further included, and carbon dioxide gas may be further included to improve high-temperature storage characteristics, and FEC (Fluoro-Ethylene Carbonate), PRS (Propene sultone), and the like may be further included.
[96]
In one preferred example, lithium salts such as LiPF 6 , LiClO 4 , LiBF 4 , and LiN(SO 2 CF 3 ) 2 are used in a cyclic carbonate of EC or PC as a highly dielectric solvent and DEC, DMC or EMC as a low viscosity solvent. The lithium salt-containing non-aqueous electrolyte can be prepared by adding it to a mixed solvent of linear carbonate.
[97]
[98]
In addition, the present invention provides a method of manufacturing the negative active material.
[99]
1 is a flow chart showing the flow of a method of manufacturing a negative active material according to the present invention.
[100]
Referring to FIG. 1, the method of manufacturing the negative active material includes a classification step of removing fine powder and coarse powder so that D max /D min value of natural graphite is 1.6 to 2.1; And a surface modification step of treating the classified natural graphite with potassium hydroxide (KOH). It may include.
[101]
The natural graphite in the classification step may be natural graphite obtained by graphitizing natural graphite having a uniform shape and shape through pulverization treatment. The pulverized natural graphite undergoes a graphitization process at a high temperature. By heating the natural graphite at a high temperature, functional groups present on the surface of the natural graphite can be removed, and side reactions with the electrolyte solution at a high temperature can be suppressed.
[102]
The graphitization step may be performed at 2800 to 3200°C, preferably 2900 to 3100°C, and more preferably at about 3000°C. If the temperature is less than 2800°C, the graphitization step is not sufficiently performed due to the low temperature, so that the surface functional groups may not be removed, and if the temperature exceeds 3200°C, natural graphite may be damaged through thermal decomposition, which is not preferable. .
[103]
In addition, the graphitization step may be performed for 8 to 12 hours, preferably 9 to 11 hours. If the time required for the graphitization step is less than 8 hours, the graphitization step is not sufficiently performed, so that the surface functional groups may not be removed.
[104]
In one embodiment of the present invention, prior to the classification step of removing fine and coarse powder, a coating step of coating graphitized natural graphite with a carbon-based compound may be performed. The coating step is a step of coating natural graphite with a carbon-based compound such as amorphous carbon on the surface of natural graphite, increasing the hardness of natural graphite, and repetitive charging/discharging due to easy insertion/desorption of lithium during charging/discharging. It is performed for the purpose of having a high initial efficiency by forming a stable SEI layer with little structural change even at the time, and the weight ratio of the coating layer and the type of carbon-based compound constituting the coating layer are as described above.
[105]
After the graphitization step, the natural graphite may be adjusted to have a D max /D min value of 1.6 to 2.1, preferably 1.8 to 2.0 by passing through a classification step .
[106]
The classification process may be carried out by any method, but it is appropriate to carry out the classification process by an air flow classification process. In the case of performing the air flow classification process, the conditions of the air flow classification process can be appropriately adjusted according to the type of active material or the like.
[107]
The classified natural graphite may be subjected to a surface modification step of treating potassium hydroxide (KOH). As described above, potassium hydroxide chemically activates the surface of natural graphite to form large pores having a diameter of 0.5 to 2.0 µm, preferably 0.5 to 1.0 µm on the surface of natural graphite. By reducing the value, the output, rapid charging, and cycle swelling performance of natural graphite can be improved.
[108]
Specifically, the graphite may be mixed with a potassium hydroxide solution, left to stand at a certain temperature, dried, and then treated with an acidic solution to remove remaining potassium ions and potassium hydroxide, and then washed with distilled water.
[109]
In addition, the method for producing a negative active material according to the present invention includes an annealing step (S50) of heating and cooling natural graphite after the surface modification step; It may further include.
[110]
Specifically, the annealing step may be a process of gradually cooling the surface-modified natural graphite after heat treatment at 700 to 1000°C, preferably 800 to 900°C for 2 to 12 hours. In addition, the annealing step may be performed in an atmosphere of a ball active gas and a mixed gas, wherein the inert gas may be at least one selected from the group including argon, nitrogen, and helium.
[111]
When the annealing temperature is less than 700°C, the annealing effect is not large, and when the temperature exceeds 1000°C, the temperature is too high, and the surface structure of graphite may be destroyed.
[112]
Through the annealing step, impurities that may be included as by-products in natural graphite may be removed, and the pore structure activated by KOH may be stabilized, thereby improving the mechanical properties of graphite.
[113]
[114]
Hereinafter, examples will be described in detail to aid understanding of the present invention. However, the embodiments according to the present invention may be modified in various other forms, and the scope of the present invention should not be construed as being limited by the following examples. Embodiments of the present invention are provided to more completely describe the present invention to those of ordinary skill in the art.
[115]
[116]
[Example 1]
[117]
Preparation of cathode
[118]
Spherical natural graphite (specific surface area: 2.5 m 2 /g, tap density: 1.21 g/cc) graphitized by heating at 3000° C. for 10 hours was prepared. Thereafter, the petroleum pitch and the natural graphite were mixed at a weight ratio of 5:95, put in a sintering furnace, and heat-treated at a temperature of about 1200° C. for 8 hours to coat the natural graphite with amorphous carbon. At this time, the amorphous carbon coating layer was about 4% by weight with respect to the entire coated natural graphite particles, and the average particle diameter (D 50 ) of the coated natural graphite particles was about 12 μm.
[119]
The natural graphite was classified to remove fine and coarse powder so that the D max / D min value was 1.8, and then the natural graphite was mixed with 1M potassium hydroxide solution and left to stand at 1400°C for 6 hours for surface treatment. The surface-treated natural graphite was washed. Subsequently, the natural graphite was heat-treated at 900° C. for 8 hours, and then an annealing process of gradually cooling was performed. As a result, the D max /D min value was 1.8, and pores with a diameter of 0.5 μm were formed on the surface. It is uniform, and it is 0.5㎛ as a result of calculating the average value of the diameters of the selected pores by randomly selecting 10 pores), pores having a size of 6 nm or less inside are 10 vol%, pores having a size of 60 to 200 nm are 70 vol % Formed natural graphite to prepare an active material.
[120]
[121]
The natural graphite was used as a negative electrode active material, SuperC65 as a conductive material, styrene butadiene high part (SBR) as a binder, and carboxymethylcellulose (CMC) as a thickener were mixed in a weight ratio of 96.6:1:1.3:1.1, respectively, and water was added. A slurry was prepared.
[122]
The slurry prepared as described above was coated on a copper foil, and vacuum-dried at about 130° C. for 10 hours to prepare a negative electrode having an area of ​​1.4875 cm 2. At this time, the loading amount of the negative electrode was prepared to be 3.61mAh/cm2.
[123]
[124]
Manufacture of battery cell
[125]
A working electrode (cathode) was prepared by applying the negative active material to a copper foil with a loading amount of 3.61 mAh/cm 2. As a counter electrode (anode), a lithium transition metal composite oxide using NCM622 was used and coated so that the loading amount was 3.2561 mAh/cm 2. An electrode assembly was manufactured by interposing a polyethylene separator between the working electrode and the counter electrode. Then, 1M LiPF 6 was added to a solvent in which 0.5% by weight of a nonaqueous electrolyte additive VC was added in a volume ratio of 1:4 to prepare a nonaqueous electrolyte, and then injected into the electrode assembly. I did. The electrode assembly was put into a case to prepare a coin-type full-cell secondary battery.
[126]
In addition, the negative electrode active material was coated on a copper foil to prepare a working electrode (cathode) so that the loading amount was 3.61 mAh/cm 2 in an area of ​​1.4875 cm 2, and lithium metal having an area of ​​1.7671 cm 2 was used as a counter electrode (anode). . An electrode assembly was manufactured by interposing a polyethylene separator between the working electrode and the counter electrode. Then, 1M LiPF 6 was added to a solvent in which 0.5% by weight of a nonaqueous electrolyte additive VC was added in a volume ratio of 1:4 to prepare a nonaqueous electrolyte, and then injected into the electrode assembly. I did. The electrode assembly was put into a case to prepare a coin-type half-cell secondary battery.
[127]
[128]
[Example 2]
[129]
Preparation of cathode
[130]
Natural graphite having an average particle diameter (D 50 ) of about 12 μm and an amorphous carbon coating layer of about 4% by weight was prepared by coating the spherical natural graphite with graphitization heat treatment and amorphous carbon in the same manner as in Example 1. . Fine powder and coarse powder were removed through classification of the natural graphite, and then the natural graphite was surface-treated with KOH in the same manner as in Example 1, and an annealing process was performed. As a result, D max /D min value is 1.8, pores with a size of 1 μm are formed on the surface, pores with a size of 6 nm or less are formed inside, 5 vol% of pores with a size of 60 to 200 nm are formed, natural graphite with 80 vol% of pores An active material consisting of was prepared.
[131]
The natural graphite was used as a negative electrode active material, SuperC65 as a conductive material, styrene butadiene high part (SBR) as a binder, and carboxymethylcellulose (CMC) as a thickener were mixed in a weight ratio of 96.6:1:1.3:1.1, respectively, and water was added. A slurry was prepared.
[132]
The slurry prepared as described above was coated on a copper foil, and vacuum-dried at about 130° C. for 10 hours to prepare a negative electrode having an area of ​​1.4875 cm 2. At this time, the loading amount of the negative electrode was prepared to be 3.61mAh/cm2.
[133]
[134]
Manufacture of battery cell
[135]
A battery (coin-type full-cell and half-cell battery) was manufactured in the same manner as in Example 1 using the negative active material of Example 2.
[136]
[137]
[Example 3]
[138]
Natural graphite having an average particle diameter (D 50 ) of about 12 μm and an amorphous carbon coating layer of about 4% by weight was prepared by coating the spherical natural graphite with graphitization heat treatment and amorphous carbon in the same manner as in Example 1. . Fine powder and coarse powder were removed through classification of the natural graphite, and then the natural graphite was surface-treated with KOH in the same manner as in Example 1, but no annealing was performed. As a result, the D max /D min value is 2.0, pores with a size of 1 μm are formed on the surface, 15 vol% of pores with a size of 6 nm or less inside, and 60 vol% of pores with a size of 60 to 200 nm are formed. A negative active material consisting of was prepared.
[139]
In addition, a battery (coin type full-cell and half-cell battery) was manufactured in the same manner as in Example 1 using the negative active material.
[140]
[141]
[Example 4]
[142]
Natural graphite having an average particle diameter (D 50 ) of about 12 μm and an amorphous carbon coating layer of about 4% by weight was prepared by coating the spherical natural graphite with graphitization heat treatment and amorphous carbon in the same manner as in Example 1. . Fine powder and coarse powder were removed through classification of the natural graphite, and then the natural graphite was surface-treated with KOH in the same manner as in Example 1, but no annealing was performed. As a result, D max /D min value is 2.0, pores with a size of 2 μm are formed on the surface, pores with a size of 6 nm or less are formed inside, 10 vol% of pores with a size of 60 to 200 nm are formed, natural graphite with 70 vol% of pores A negative active material consisting of was prepared.
[143]
In addition, a battery (coin type full-cell and half-cell battery) was manufactured in the same manner as in Example 1 using the negative active material.
[144]
[145]
[Comparative Example 1]
[146]
Natural graphite having an average particle diameter (D 50 ) of about 12 μm and an amorphous carbon coating layer of about 4% by weight was prepared by coating the spherical natural graphite with graphitization heat treatment and amorphous carbon in the same manner as in Example 1. . Thereafter, the natural graphite was not classified, and the surface of the natural graphite was surface-treated with KOH, but the annealing process was not performed. As a result, the D max /D min value is 2.2, pores with a size of 1 μm are formed on the surface, 15 vol% of pores with a size of 6 nm or less inside, and 60 vol% of pores with a size of 60 to 200 nm are formed. A negative active material consisting of was prepared.
[147]
In addition, a battery (coin type full-cell and half-cell battery) was manufactured in the same manner as in Example 1 using the negative active material.
[148]
[149]
[Comparative Example 2]
[150]
Natural graphite having an average particle diameter (D 50 ) of about 12 μm and an amorphous carbon coating layer of about 4% by weight was prepared by coating the spherical natural graphite with graphitization heat treatment and amorphous carbon in the same manner as in Example 1. . Fine powder and coarse powder were removed through classification of the natural graphite, but the surface of the natural graphite was not treated with KOH, and an annealing process was not performed. As a result, the D max /D min value is 2.0, no pores are formed on the surface, and 20 vol% of pores having a size of 6 nm or less inside are formed, and a negative electrode made of natural graphite with 50 vol% of pores having a size of 60 to 200 nm. An active material was prepared.
[151]
In addition, a battery (coin type full-cell and half-cell battery) was manufactured in the same manner as in Example 1 using the negative active material.
[152]
[153]
[Comparative Example 3]
[154]
Natural graphite having an average particle diameter (D 50 ) of about 12 μm and an amorphous carbon coating layer of about 4% by weight was prepared by coating the spherical natural graphite with graphitization heat treatment and amorphous carbon in the same manner as in Example 1. . The natural graphite was not classified, the surface of the natural graphite was not treated with KOH, and an annealing process was not performed. As a result, the D max /D min value is 2.2, no pores are formed on the surface, 25 vol% of pores with a size of 6 nm or less inside are formed, and a negative electrode made of natural graphite with 40 vol% of pores with a size of 60 to 200 nm An active material was prepared.
[155]
In addition, a battery (coin type full-cell and half-cell battery) was manufactured in the same manner as in Example 1 using the negative active material.
[156]
[157]
[Comparative Example 4]
[158]
Natural graphite having a spherical average particle diameter (D50) of about 12 µm was prepared by heating at 3000°C for 5 hours to graphitize. Thereafter, the natural graphite was not coated with amorphous carbon, and fine powder and coarse powder were removed through classification, and then the surface was treated with KOH in the same manner as in Example 1, but an annealing process was not performed. As a result, the D max /D min value is 2.0, pores with a size of 2 μm are formed on the surface, 30 vol% of pores with a size of 6 nm or less inside, and 50 vol% of pores with a size of 60 to 200 nm are formed. A negative active material consisting of was prepared.
[159]
In addition, a battery (coin type full-cell and half-cell battery) was manufactured in the same manner as in Example 1 using the negative active material.
[160]
[161]
[Comparative Example 5]
[162]
Natural graphite having a spherical average particle diameter (D 50 ) of about 12 μm was prepared by heating at 3000° C. for 5 hours to graphitize . Thereafter, the natural graphite was surface-treated with KOH in the same manner as in Example 1 without coating and classifying amorphous carbon on the natural graphite, but an annealing process was not performed. As a result, the D max /D min value is 2.2, pores with a size of 2 μm are formed on the surface, 35 vol% of pores with a size of 6 nm or less inside, and 40 vol% of pores with a size of 60 to 200 nm are formed. A negative active material consisting of was prepared.
[163]
In addition, a battery (coin type full-cell and half-cell battery) was manufactured in the same manner as in Example 1 using the negative active material.
[164]
[165]
[Comparative Example 6]
[166]
Natural graphite having an average particle diameter (D 50 ) of about 12 μm and an amorphous carbon coating layer of about 4% by weight was prepared by coating the spherical natural graphite with graphitization heat treatment and amorphous carbon in the same manner as in Example 1. . Fine powder and coarse powder were removed from the natural graphite through classification so that the D max /D min value became 1.4, and then the natural graphite was surface-treated with KOH in the same manner as in Example 1, and an annealing process was performed. As a result, pores having a size of 0.5 μm were formed on the surface, and a negative active material made of natural graphite was prepared in which 10 vol% of pores having a size of 6 nm or less and 70 vol% of pores having a size of 60 to 200 nm were formed therein.
[167]
In addition, a battery (coin type full-cell and half-cell battery) was manufactured in the same manner as in Example 1 using the negative active material.
[168]
Table 1 below summarizes and shows the characteristics of each negative active material prepared according to the Examples and Comparative Examples.
[169]
[170]
[Experimental Example 1] Monocell HPPC output 2.5C@SOC 50 TEST
[171]
After charging the monocell type lithium secondary battery so that the SOC value was 50%, the output resistance at room temperature (25°C) was measured according to the HPPC (Hybrid pulse power characterization) test method. Specifically, the output resistance is a lithium secondary battery discharged at 2.5V at 0.33C, charging and discharging for 3 cycles under a 4.2V charging condition, and then discharging the battery at 50% SOC, and then charging at 2.5C for 10 minutes. After that, let it rest for 30 minutes, discharge at 2.5C for 10 minutes, and then rest for 30 minutes, divide the current applied to the voltage change during charging and discharging, and measure the resistance value to measure the HPPC resistance value. Indicated.
[172]
[173]
[Experimental Example 2] Lithium Plating Test
[174]
Using the coin-type half cell prepared above, the half cell was charged and discharged at 1C for 3 cycles, and then charged at 3C for 15 minutes, and the profile was first differentiated. At this time, the inflection point indicated by dQ/dV was identified to quantify the lithium plating SOC (Li-Plating SOC, %), which is the SOC at the time when lithium precipitation occurs on the surface of the negative electrode. The results are shown in Table 2 below.
[175]
[176]
[Experimental Example 3] In-situ SAC Swelling Test
[177]
Using the above manufactured coin-type full cell, the charging range is set so that the SOC is from 0 to 95%, the first cycle is 0.1C, the second cycle is 0.2C, and the third cycle is charged at 0.5C from the 30th cycle. Meanwhile, the change in the thickness of the cathode electrode during charging and discharging was expressed as a swelling ratio (%). The results are shown in Table 2 below.
[178]
[Table 1]
D max /D min Surface pore size (㎛) Presence or absence of KOH treatment Whether or not annealing is performed Pore ​​less than 6nm (vol%) Pore ​​size of 60~200nm (vol%)
Example 1 1.8 0.5 O O 10 70
Example 2 1.8 1.0 O O 5 80
Example 3 2.0 1.0 O X 15 60
Example 4 2.0 2.0 O X 10 70
Comparative Example 1 2.2 1.0 O X 15 60
Comparative Example 2 2.0 X X X 20 50
Comparative Example 3 2.2 X X X 25 40
Comparative Example 4 2.0 2.0 O X 30 50
Comparative Example 5 2.2 2.0 O X 35 40
Comparative Example 6 1.4 0.5 O X 10 70
[179]
[Table 2]
HPPC resistance value (ohm) Li-Plating SOC (%) Swelling Ratio (%)
Example 1 0.62 50 22.0
Example 2 0.63 48 21.8
Example 3 0.65 47 22.3
Example 4 0.68 45 22.9
Comparative Example 1 0.89 38 27.5
Comparative Example 2 0.94 34 29.2
Comparative Example 3 1.01 35 30.8
Comparative Example 4 1.14 29 31.5
Comparative Example 5 1.06 26 33.7
Comparative Example 6 1.11 27 33.5
[180]
As can be seen in Table 2, in Examples 1 to 4, the particle size distribution is uniform and pores are formed on the surface, and a large number of pores having a particle diameter of 60 to 200 nm are formed inside. As a result, it can be seen that the output characteristics and cycle swelling characteristics of the battery are improved compared to Comparative Examples 1, 3, and 5 in which the particle size distribution is not uniform.
[181]
In addition, Examples 1 to 4 improved the output characteristics and cycle swelling characteristics of the battery compared to Comparative Examples 2 and 3 in which no pores were formed on the surface, and the size distribution of the pores formed therein was within the numerical range of the present invention. It can be seen that the output characteristics and cycle swelling characteristics of the battery are improved compared to the external Comparative Examples 2 to 5.
[182]
On the other hand, when comparing Comparative Example 6 in which the value of D max / D min is 1.4 and Example 1 in which the value of D max / D min is 1.8, the value of D max / D min is less than 1.6, so the content of coarse powder is relatively If it is low, it can be seen that it has a negative effect on the output characteristics and cycle swelling characteristics of the battery.
[183]
[184]
The above description is merely illustrative of the technical idea of ​​the present invention, and those of ordinary skill in the art to which the present invention pertains will be able to make various modifications and variations without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are not intended to limit the technical spirit of the present invention, but to explain, and the protection scope of the present invention should be interpreted by the following claims, and all technologies within the scope equivalent thereto. The idea should be construed as being included in the scope of the present invention.
[185]
Claims
[Claim 1]
As a negative active material for secondary batteries manufactured by surface modification of natural graphite, in the particle size distribution of the natural graphite, the D max /D min value is 1.6 to 2.1, and pores having a diameter of 0.5 to 2.0 μm are formed on the surface. A negative active material for a secondary battery, characterized in that.
[Claim 2]
The negative active material for a secondary battery according to claim 1, wherein the pores are formed by surface modification by treating the surface of natural graphite with potassium hydroxide (KOH).
[Claim 3]
The negative active material of claim 1, wherein the pores formed on the surface have a size of 0.5 to 1.0 μm.
[Claim 4]
The negative active material for a secondary battery according to claim 1, wherein the natural graphite has a spherical shape.
[Claim 5]
The negative active material of claim 1, wherein the natural graphite has an average particle diameter (D 50 ) of 5 to 15 μm.
[Claim 6]
The negative active material for a secondary battery according to claim 1, wherein pores are formed in the natural graphite.
[Claim 7]
The anode for a secondary battery according to claim 6, wherein the pores formed in the natural graphite include 3 to 15 vol% of those having a size of 6 nm or less and 55 to 85 vol% of those having a size of 60 to 200 nm. Active material.
[Claim 8]
The negative active material of claim 1, wherein the natural graphite is coated with a carbon-based compound.
[Claim 9]
The negative active material of claim 8, wherein the carbon-based compound is amorphous carbon.
[Claim 10]
A method of preparing a negative active material for a secondary battery, comprising: a classification step of removing fine powder and coarse powder so that a D max /D min value of 1.6 to 2.1 for natural graphite ; And a surface modification step of treating the classified natural graphite with potassium hydroxide (KOH). Method for producing a negative active material for a secondary battery comprising a.
[Claim 11]
11. The method of claim 10, further comprising: an annealing step of cooling the natural graphite after heat treatment after the surface modification step; Method for producing a negative active material for a secondary battery, characterized in that it further comprises.
[Claim 12]
The method of claim 11, wherein in the annealing step, the heat treatment is performed at 700 to 1000°C.
[Claim 13]
11. The method of claim 10, further comprising coating natural graphite with a carbon-based compound before the classification step.
[Claim 14]
A negative electrode comprising the negative active material for a secondary battery according to any one of claims 1 to 9.
[Claim 15]
A secondary battery comprising a negative electrode, a positive electrode, a separator interposed between the negative electrode and the positive electrode, and an electrolyte, wherein the negative electrode is the negative electrode of claim 14.