[One]Cross-Citation with Related Application(s)
[2]This application claims the benefit of priority based on Korean Patent Application No. 2019-0009467 dated January 24, 2019, and all contents disclosed in the literature of the Korean patent application are incorporated as a part of this specification.
[3]
[4]
technical field
[5]
The present invention relates to a lithium secondary battery, and to a lithium secondary battery having improved resistance characteristics.
background
[6]
Recently, interest in energy storage technology is increasing. For example, as the field of application of energy storage technology expands to mobile phones, camcorders, notebook PCs, and even electric vehicles, efforts for research and development of energy storage technology are increasingly taking shape. An electrochemical device is the field receiving the most attention in the field of such energy storage technology, and research on rechargeable batteries capable of charging and discharging among electrochemical devices is being actively conducted.
[7]
Among these secondary batteries, a lithium secondary battery has an advantage that an operating voltage is higher and an energy density is significantly higher than that of a conventional battery using an aqueous solution (electrolyte solution), and thus is widely used in various fields requiring energy storage technology.
[8]
Recently, in particular, as the use of portable devices such as mobile phones increases, the demand for small lithium secondary batteries is rapidly increasing, and research on high voltage and high capacity of small lithium secondary batteries is also being focused.
[9]
In general, in order to increase the voltage and capacity of a small lithium secondary battery, a method of increasing the rolling rate of the electrode or adding more salt to the electrolyte is used. In the case of a small lithium secondary battery, the inside of the battery is Due to the increase in resistance, problems such as sudden power off during use often occur.
[10]
Therefore, in the case of a lithium secondary battery, even when it is driven at a high voltage, there is a need for research on a lithium secondary battery having a reduced internal resistance to suppress a sudden power off phenomenon.
[11]
Prior art literature
[12]
Korean Patent Publication No. 10-2013-0125236
DETAILED DESCRIPTION OF THE INVENTION
technical challenge
[13]
An object of the present invention is to solve the above problems, and to provide a lithium secondary battery capable of suppressing an increase in internal resistance of the battery even under a high temperature condition or a high voltage condition.
means of solving the problem
[14]
According to one embodiment, the present invention provides an anode comprising a first lithium cobalt oxide and a second lithium cobalt oxide having different average particle diameters (D 50 ); an anode including first graphite and second graphite having different average particle diameters (D 50 ); and an electrolyte including a first additive which is a nitrile-based compound, wherein the first lithium cobalt oxide and the second lithium cobalt oxide each independently contain aluminum at a concentration of 2500 ppm to 4000 ppm.
[15]
Meanwhile, the average particle diameter (D 50 ) of the first lithium cobalt oxide may be 1 μm to 4 μm, and the average particle diameter (D 50 ) of the second lithium cobalt oxide may be 5 μm to 15 μm.
[16]
In addition, the average particle diameter (D 50 ) of the first graphite may be 5 μm to 14 μm, and the average particle diameter (D 50 ) of the second graphite may be 15 μm to 25 μm.
[17]
In addition, the first graphite and the second graphite may be artificial graphite.
[18]
The electrolyte may include a lithium salt in a concentration of 1.0M to 1.5M.
[19]
The first additive may be included in an amount of 2 parts by weight to 10 parts by weight based on 100 parts by weight of the electrolyte.
[20]
The first additive may include at least one nitrile-based compound selected from the group consisting of succinonitrile, adiponitrile, butyronitrile, pimelonitrile, and hexanetricarbonitrile.
[21]
The electrolyte may further include a second additive.
[22]
The second additive may be at least one selected from the group consisting of a cyclic sultone-based compound and a cyclic carbonate-based compound in which fluorine is substituted or unsubstituted.
[23]
The second additive may be included in an amount of 10 to 15 parts by weight based on 100 parts by weight of the electrolyte.
[24]
Meanwhile, the driving voltage of the lithium secondary battery according to the present invention may be 4.2V to 4.5V.
Effects of the Invention
[25]
When the lithium secondary battery according to the present invention is used, it is possible to suppress an increase in the internal resistance of the battery even under high-voltage conditions as well as high-temperature conditions, so that sudden power off while the battery is being driven can be prevented in advance .
Brief description of the drawing
[26]
The following drawings attached to the present specification illustrate preferred embodiments of the present invention, and serve to further understand the technical spirit of the present invention together with the above-described content of the present invention, so the present invention is limited to the matters described in those drawings It should not be construed as being limited.
[27]
1 is a graph showing the continuous charging evaluation results according to Experimental Example 1.
[28]
2 is a graph showing a resistance evaluation result according to Experimental Example 2. Referring to FIG.
Best mode for carrying out the invention
[29]
Hereinafter, the present invention will be described in more detail.
[30]
The terms or words used in the present specification and claims should not be construed as being limited to their ordinary or dictionary meanings, and the inventor may properly define the concept of the term in order to best describe his invention. It should be interpreted as meaning and concept consistent with the technical idea of ​​the present invention based on the principle that there is.
[31]
The terminology used herein is used to describe exemplary embodiments only, and is not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly dictates otherwise.
[32]
In the present specification, terms such as "comprise", "comprising" or "having" are intended to designate the presence of an embodied feature, number, step, element, or a combination thereof, but one or more other features or It should be understood that the existence or addition of numbers, steps, elements, or combinations thereof is not precluded in advance.
[33]
In this specification, “particle diameter Dn” means a particle diameter at an n% point of the cumulative distribution of the number of particles according to the particle diameter. That is, D 50 is the particle size at 50% of the cumulative distribution of the number of particles according to the particle size, D 90 is the particle size at 90% of the cumulative distribution of the number of particles according to the particle size, and D 10 is the cumulative distribution of the number of particles according to the particle size. is the particle size at the 10% point of
[34]
The Dn may be measured using a laser diffraction method. Specifically, after dispersing the powder to be measured in the dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (for example, Microtrac S3500) to measure the diffraction pattern difference according to the particle size when the particles pass through the laser beam to measure the particle size distribution to calculate D 10 , D 50 , and D 90 can be measured by calculating the particle diameters at the points used as 10%, 50%, and 90% of the particle number cumulative distribution according to the particle diameter in the measuring apparatus .
[35]
[36]
The lithium secondary battery according to the present invention, the average particle diameter (D 50 ) of different first lithium cobalt oxide and the second lithium cobalt positive electrode comprising an oxide, the average particle diameter (D 50 ) of different first graphite and second graphite It includes an electrolyte including an anode and a first additive that is a nitrile-based compound. In this case, the first lithium cobalt oxide and the second lithium cobalt oxide each independently contain aluminum at a concentration of 2500 ppm to 4000 ppm. Meanwhile, the lithium secondary battery according to the present invention may further include a separator.
[37]
Hereinafter, each component of the lithium secondary battery of this invention is demonstrated.
[38]
[39]
(1) Anode
[40]
First, the positive electrode according to the present invention will be described.
[41]
The positive electrode may be prepared by coating a positive electrode active material slurry including a positive electrode active material, a binder for an electrode, a conductive material for an electrode, and a solvent on a positive electrode current collector.
[42]
The positive electrode current collector is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or carbon on the surface of aluminum or stainless steel. , nickel, titanium, silver, etc. may be used. In this case, the positive electrode current collector may form fine irregularities on the surface to strengthen the bonding force of the positive electrode active material, and may be used in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, a nonwoven body.
[43]
The positive active material is a compound capable of reversible intercalation and deintercalation of lithium, and uses a lithium composite metal oxide including a metal such as cobalt and lithium.
[44]
In the present invention, as the lithium composite metal oxide, the first and second lithium cobalt oxide (LiCoO 2 ) and second lithium cobalt oxide (LiCoO 2 ) having different average particle diameters (D 50 ) are included, and the first and second The lithium cobalt oxide each independently contains aluminum in a concentration of 2500 ppm to 4000 ppm.
[45]
When the first and second lithium cobalt oxides having different average particle diameters (D 50 ) are used, the porosity between active material components may be reduced, and thus energy density may be increased.
[46]
In this case, the average particle diameter (D 50 ) of the first lithium cobalt oxide may be 1 μm to 4 μm, and the average particle diameter (D 50 ) of the second lithium cobalt oxide may be 5 μm to 15 μm. Preferably, the average particle diameter (D 50 ) of the first lithium cobalt oxide is 1 μm to 3 μm, and the average particle diameter (D 50 ) of the second lithium cobalt oxide may be 8 μm to 12 μm. More preferably, the average particle diameter (D 50 ) of the first lithium cobalt oxide may be 2 μm to 3 μm, and the average particle diameter (D 50 ) of the second lithium cobalt oxide may be 10 μm to 12 μm. As described above, when lithium cobalt oxide having each average particle diameter (D 50 ) is mixed and used, it is possible to more effectively minimize the porosity between active material components, thereby improving energy density.
[47]
At this time, the first and second lithium cobalt oxides are doped with aluminum. When aluminum is doped, they are structurally more stable and prevent transformation into a spinel-like structure, thereby suppressing the increase in resistance even under high voltage conditions. have.
[48]
Specifically, the first lithium cobalt oxide and the second lithium cobalt oxide may each be doped with a concentration of 2500 ppm to 4000 ppm, preferably 2600 ppm to 4000 ppm, more preferably 2700 ppm to 4000 ppm of the aluminum. . When the aluminum is doped in the above range to the first lithium cobalt oxide and the second lithium cobalt oxide, a more stable layered structure may be maintained.
[49]
The binder for the electrode is a component that assists in bonding the positive electrode active material and the electrode conductive material and the like to the positive electrode current collector. Specifically, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene (PE) , polypropylene, ethylene-propylene-dienter polymer, sulfonated ethylene-propylene-dienter polymer, styrene-butadiene rubber, styrene-butadiene rubber-carboxymethylcellulose (SBR-CMC), fluororubber, various copolymers, etc. can be heard
[50]
The conductive material for the electrode is a component for further improving the conductivity of the positive electrode active material. The conductive material for the electrode is not particularly limited as long as it has conductivity without causing chemical change in the battery. For example, carbon black, acetylene black (or Denka black), Ketjen black, channel black, furnace black, lamp carbon powder such as black or thermal black; Graphite powder, such as natural graphite, artificial graphite, or graphite with a highly developed crystal structure; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskeys such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; A conductive material such as a polyphenylene derivative may be used. Specific examples of commercially available conductive materials include acetylene black-based Chevron Chemical Company, Denka Singapore Private Limited, Gulf Oil Company, etc.), Ketjenblack, EC series (products of the Armak Company), the Vulcan XC-72 (products of the Cabot Company) and the Super P (products of the Timcal Company).
[51]
The solvent may include an organic solvent such as N-methyl-2-pyrrolidone (NMP), and may be used in an amount having a desirable viscosity when the positive active material and optionally a binder and a conductive material are included. For example, it may be included so that the solid content concentration in the slurry including the positive electrode active material, and optionally the binder and the conductive material is 10 wt% to 60 wt%, preferably 20 wt% to 50 wt%.
[52]
[53]
(2) cathode
[54]
Next, the negative electrode according to the present invention will be described.
[55]
The negative electrode may be prepared by, for example, coating a negative electrode active material slurry including a negative electrode active material, a binder for an electrode, a conductive material for an electrode, a solvent, and the like on an anode current collector.
[56]
The negative electrode current collector is not particularly limited as long as it has high conductivity without causing a chemical change in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel. The surface treated with carbon, nickel, titanium, silver, etc., an aluminum-cadmium alloy, etc. may be used. In addition, like the positive electrode current collector, the bonding strength of the negative electrode active material may be strengthened by forming fine irregularities on the surface, and may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a non-woven body.
[57]
As the anode active material, first graphite and second graphite having different average particle diameters (D 50 ) are used. When two or more types of graphite having different average particle diameters (D 50 ) are used, porosity between active material components may be reduced, and thus energy density may be increased.
[58]
In this case, the average particle diameter (D 50 ) of the first graphite may be 5 μm to 14 μm, and the average particle diameter (D 50 ) of the second graphite may be 15 μm to 25 μm. Preferably, the average particle diameter (D 50 ) of the first graphite is 7 μm to 12 μm, and the average particle diameter (D 50 ) of the second graphite may be 17 μm to 22 μm. More preferably, the average particle diameter (D 50 ) of the first graphite may be 10 μm to 12 μm, and the average particle diameter (D 50 ) of the second graphite may be 19 μm to 22 μm. As described above, when graphite having each average particle diameter (D 50 ) is mixed and used, the energy density can be improved by effectively minimizing the porosity between active material components.
[59]
Meanwhile, artificial graphite may be used as the first and second graphites. In general, in the case of graphite, there is natural graphite or artificial graphite. However, while natural graphite has a plate-like shape, artificial graphite has a round shape, and natural graphite has a structure with more edges (egde), which is highly likely to cause more side reactions than round-shaped artificial graphite. Accordingly, it is preferable to use artificial graphite as the first and second graphite according to the present invention.
[60]
Since the binder for the electrode, the electrode conductive material, and the solvent are the same as those described above, a detailed description thereof will be omitted.
[61]
[62]
(3) electrolyte
[63]
Next, the electrolyte according to the present invention will be described.
[64]
The electrolyte according to the present invention may include a lithium salt, an organic solvent, and a first additive that is a nitrile-based compound. In addition, the electrolyte of the present invention may further include a second additive.
[65]
In this case, the second additive may be at least one selected from the group consisting of a cyclic sultone-based compound and a cyclic carbonate-based compound in which fluorine is substituted or unsubstituted.
[66]
[67]
(i) lithium salt
[68]
First, the lithium salt will be described.
[69]
The lithium salt is used as a medium for transferring ions in the lithium secondary battery. Typically, the lithium salt is LiPF 6 , LiBF 4 , LiSbF 6 , LiAsF 6 , LiClO 4 , LiN(C 2 F 5 SO 2 ) 2 , LiN(CF 3 SO 2 ) 2 , CF 3 SO 3 Li, LiC(CF) 3 SO 2 ) 3 , LiC 4 BO 8 , LiTFSI, LiFSI and LiClO 4It may include at least one compound selected from the group consisting of.
[70]
The lithium salt is preferably contained in the electrolyte at a concentration of 1.0M to 1.5M, preferably 1.05M to 1.45M, and more preferably, 1.1M to 1.4M. When the lithium salt is included in the above range, while minimizing by-products generated by dissolution in the electrolyte, when the battery is driven under high voltage, the SEI (Solid Electrolyte Interphase, SEI) film formed on the electrode interface is prevented from decomposing, thereby preventing the battery It can prevent my resistance from rising.
[71]
[72]
(ii) organic solvents
[73]
Next, the organic solvent will be described.
[74]
In the present invention, the organic solvent is a solvent commonly used in lithium secondary batteries, for example, an ether compound, an ester (Acetate, Propionate) compound, an amide compound, a linear carbonate or a cyclic carbonate compound, a nitrile compound, etc. alone or a mixture of two or more.
[75]
Among them, a carbonate compound that is a cyclic carbonate, a linear carbonate, or a mixture thereof may be typically used.
[76]
Specific examples of the cyclic carbonate compound include ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene There is a single compound or a mixture of at least two or more selected from the group consisting of carbonate, vinylene carbonate, and halides thereof. In addition, specific examples of the linear carbonate compound include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethylmethyl carbonate (EMC), methylpropyl carbonate (MPC) and ethylpropyl carbonate (EPC) A compound selected from the group consisting of or a mixture of at least two or more may be representatively used, but the present invention is not limited thereto.
[77]
In particular, among the carbonate-based compounds, propylene carbonate and ethylene carbonate, which are cyclic carbonates, are highly viscous organic solvents and have a high dielectric constant and thus well dissociate lithium salts in the electrolyte, and may be preferably used in these cyclic carbonates such as ethylmethyl carbonate, diethyl carbonate, or When a low-viscosity, low-dielectric constant linear carbonate such as dimethyl carbonate is mixed in an appropriate ratio, an electrolyte having a high electrical conductivity can be prepared, which can be more preferably used.
[78]
In addition, the esters include methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, α-valerolactone and ε- A single compound selected from the group consisting of caprolactone or a mixture of at least two or more types may be used, but the present invention is not limited thereto.
[79]
[80]
(iii) a first additive
[81]
Next, the first additive, which is a nitrile-based compound, will be described.
[82]
In the case of the first additive, under high voltage/high temperature conditions, it reacts with general additives (eg, vinylene carbonate (VC), etc.) to suppress an increase in internal resistance, prevent a decrease in reversible capacity, and reduce gas generation can do it
[83]
The first additive may be included in an amount of 2 parts by weight to 10 parts by weight, preferably 2 parts by weight to 9 parts by weight, more preferably, 2 parts by weight to 8 parts by weight based on 100 parts by weight of the electrolyte. When the first additive is included within the above range, it is possible to minimize a decrease in the reversible capacity even under a high voltage condition.
[84]
Specifically, the first additive is succinonitrile (Succinonitrile), adiponitrile (Adiponitrile), butyronitrile (Butyronitrile), pimelonitrile (Pimelonitrile), butyronitrile (Butyronitrile) and hexane tricarbonitrile (Hexanetricarbonitrile) It may include one or more nitrile-based compounds selected from the group consisting of.
[85]
[86]
(iv) a second additive
[87]
Meanwhile, the electrolyte according to the present invention may further include a second additive.
[88]
The second additive may be at least one selected from the group consisting of a cyclic sultone-based compound and a cyclic carbonate-based compound in which fluorine is substituted or unsubstituted.
[89]
The second additive may be used without limitation as long as it is a compound that allows the SEI film to be firmly formed on the negative electrode.
[90]
Specifically, as the cyclic sultone-based compound, 1,3-propanesultone (PS) or 1,3-propene sultone (PRS) may be used. In addition, as the fluorine-substituted or unsubstituted cyclic carbonate-based compound, fluoroethylene carbonate (FEC), vinylene carbonate (VC), or vinylethylene carbonate (VEC) may be used.
[91]
In this case, the second additive may be included in an amount of 10 parts by weight to 15 parts by weight, preferably 10 parts by weight to 14 parts by weight, more preferably 10 parts by weight to 13 parts by weight based on 100 parts by weight of the electrolyte. When the second additive is used within the above range, an SEI film can be stably formed on the negative electrode while minimizing the increase in resistance in the battery.
[92]
[93]
(V) additional additives
[94]
In addition, the electrolyte of the present invention is decomposed in a high-output environment to prevent cathodic collapse, or to further improve low-temperature high-rate discharge characteristics, high-temperature stability, overcharge prevention, high-temperature swell improvement effect, and the like. may further include
[95]
As such additional additives, ethylene sulfate (Esa), trimethylene sulfate (TMS), (ethylene glycol bis(2-cyanoethyl) ether (EGPN), lithium difluoro (oxalato) borate) (LIDFOB), lithium difluorophosphate, lithium oxalyl difluoroborate, and at least one selected from the group consisting of LiBF 4 may be mentioned.
[96]
[97]
Meanwhile, the driving voltage of the lithium secondary battery according to the present invention may be 4.2 V to 4.5 V, preferably 4.3 V to 4.5 V, and more preferably 4.4 V to 4.5 V. At this time, even when the driving voltage of the lithium secondary battery is within the above range, a sudden increase in resistance does not occur due to the internal configuration of the battery as described above, so that the power of the battery is not turned off during driving and can operate normally.
[98]
[99]
(4) separator
[100]
Meanwhile, the lithium secondary battery according to the present invention may include a separator, and the separator includes a conventional porous polymer film conventionally used as a separator, for example, ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, A porous polymer film made of a polyolefin-based polymer such as an ethylene/hexene copolymer and an ethylene/methacrylate copolymer can be used alone or by laminating them, and inorganic particles (eg, Al 2 O 3 ) are coated polyolefin-based films. A porous polymer film or a conventional porous nonwoven fabric may be used, for example, a nonwoven fabric made of high melting point glass fiber, polyethylene terephthalate fiber, or the like, but is not limited thereto.
[101]
[102]
Hereinafter, the present invention will be described in more detail through specific examples. However, the following examples are only examples to help the understanding of the present invention, and do not limit the scope of the present invention. It is obvious to those skilled in the art that various changes and modifications can be made within the scope and spirit of the present disclosure, and it is natural that such variations and modifications fall within the scope of the appended claims.
[103]
[104]
[Example]
[105]
1. Example 1 : Preparation of lithium secondary battery
[106]
A positive electrode active material in which the first lithium cobalt oxide having an average particle diameter (D 50 ) of 2.5 μm and the second lithium cobalt oxide having an average particle diameter (D 50 ) of 11 μm is mixed is prepared. In this case, the first lithium cobalt oxide and the second lithium cobalt oxide each contain aluminum at a concentration of 3100 ppm.
[107]
Then, the cathode active material, carbon black as a conductive material, and polyvinylidene fluoride (PVDF) as a binder were mixed in a weight ratio of 97.59:1.1:1.31, and then N-methyl-2-pyrrolidone as a solvent ( NMP) to prepare a cathode active material slurry (solid content: 50 wt%). The positive electrode active material slurry was applied to a 12 μm-thick aluminum (Al) thin film as a positive electrode current collector, dried to prepare a positive electrode, and then a positive electrode was prepared by roll press.
[108]
As an anode active material, an anode active material in which artificial graphite (first graphite) having an average particle diameter (D 50 ) of 11 μm and artificial graphite (second graphite) having an average particle diameter (D 50 ) of 21 μm is mixed is prepared.
[109]
Next, the negative active material, carbon black as a conductive material, and styrene-butadiene rubber-carboxymethylcellulose (SBR-CMC) as a binder were mixed in a weight ratio of 96.65:0.5:2.85, and then added to water as a solvent. to prepare a negative active material slurry (solid content: 60% by weight). The negative electrode active material slurry was applied to a 6 μm-thick copper (Cu) thin film as a negative electrode current collector, dried to prepare a negative electrode, and then roll press was performed to prepare a negative electrode.
[110]
Next, a non-aqueous organic solvent was prepared by dissolving LiPF 6 in an organic solvent having a composition of ethylene carbonate (EC): propylene carbonate (PC): polypropylene = 2:1:7 by volume so as to have a molar concentration of 1.2M. Next, in 82.3 g of a non-aqueous organic solvent, 2 g of succinonitrile (SN) as a first additive, 1 g of hexanetricarbonitrile (HTCN), 4 g of 1,3-propane sultone (PS) as a second additive, fluoro Ethylene carbonate (FEC) 5 g, vinyl ethylene carbonate (VEC) 0.2 g, additionally, (ethylene glycol bis (2-cyanoethyl) ether (EGPN) 5 g, lithium difluoro (oxalato) borate (LIDFOB) 0.5 g was added to prepare an electrolyte.
[111]
Then, the positive electrode, the polyolefin-based porous separator, and the negative electrode were sequentially stacked to prepare an electrode assembly. Thereafter, the electrode assembly was accommodated in a coin-type battery case, and the electrolyte for the lithium secondary battery was injected to prepare a coin-type lithium secondary battery.
[112]
[113]
2. Example 2
[114]
A lithium secondary battery was manufactured in the same manner as in Example 1, except that the second lithium cobalt oxide containing aluminum at a concentration of 3900 ppm, respectively, and the positive electrode active material in which the second lithium cobalt oxide was mixed were used.
[115]
[116]
[Comparative example]
[117]
1. Comparative Example 1
[118]
A lithium secondary battery was manufactured in the same manner as in Example 1, except that second lithium cobalt oxide each containing aluminum at a concentration of 960 ppm and a cathode active material in which second lithium cobalt oxide was mixed were used.
[119]
[120]
2. Comparative Example 2
[121]
As the positive electrode active material, a lithium secondary battery was prepared in the same manner as in Example 1, except that only one lithium cobalt oxide having an average particle diameter (D 50 ) of 16.5 μm and containing aluminum at a concentration of 367 ppm was prepared. .
[122]
[123]
[Experimental example]
[124]
1. Experimental Example 1: Continuous charging evaluation
[125]
Each of the coin-type lithium secondary batteries prepared in Examples 1 and 2 and Comparative Example 1 was activated at 0.7C CC. Thereafter, under constant current-constant voltage (CC-CV) charging conditions at 25° C., it was charged at 0.7C CC/CV to 4.45V, followed by 0.05C current cut, and discharged at 0.2C up to 3.0V under CC conditions.
[126]
Next, charge continuously for 28 days at 0.5C CC/CV up to 4.45V under constant current-constant voltage (CC-CV) charging conditions at high temperature (45℃), and measure the thickness of the battery at intervals of 5 days using a 300gf flat-panel measuring instrument. was measured, and the results are shown in FIG. 1 .
[127]
Referring to FIG. 1 , it can be seen that, when continuously charged, the secondary battery of Comparative Example 1 swells more than the secondary batteries of Examples 1 and 2, and thus the thickness increase rate is large.
[128]
[129]
2. Experimental Example 2: Resistance evaluation at high temperature (45°C) and high voltage (4.45V)
[130]
Each of the coin-type lithium secondary batteries prepared in Examples 1 and 2 and Comparative Examples 1 and 2 was activated at 0.7C CC. Thereafter, under constant current-constant voltage (CC-CV) charging conditions at 25° C., it was charged at 0.7C CC/CV to 4.45V, followed by 0.05C current cut, and discharged at 0.2C up to 3.0V under CC conditions.
[131]
Afterwards, after cutting 1/40C at 0.5C CC/CV to 4.45V under constant current-constant voltage (CC-CV) charging conditions at high temperature (45℃), discharge proceeds. Discharge proceeds at 0.2C until SOC (State Of Charge, SOC) reaches 20%. After 1C discharge at SOC 20% for 10 seconds, discharge proceeds at 0.2C until it becomes 3.0V again. Thereafter, a resistance value (measured with a PNE solution device) was obtained using the current difference and the voltage difference, and the results are shown in FIG. 2 .
[132]
Referring to FIG. 2 , even when the lithium secondary batteries of Examples 1 and 2 are driven at a high temperature and high voltage, it can be seen that the width of the increase in resistance is lower than that of the secondary batteries of Comparative Examples 1 and 2 .

WE CLAIMS

[Claim 1]an anode including a first lithium cobalt oxide and a second lithium cobalt oxide having an average particle diameter (D 50 ); an anode including first graphite and second graphite having different average particle diameters (D 50 ); and an electrolyte including a first additive which is a nitrile-based compound, wherein the first lithium cobalt oxide and the second lithium cobalt oxide each independently contain aluminum at a concentration of 2500 ppm to 4000 ppm.
[Claim 2]
The lithium secondary battery according to claim 1, wherein the average particle diameter (D 50 ) of the first lithium cobalt oxide is 1 μm to 4 μm, and the average particle diameter (D 50 ) of the second lithium cobalt oxide is 5 μm to 15 μm. .
[Claim 3]
The lithium secondary battery of claim 1 , wherein the first graphite has an average particle diameter (D 50 ) of 5 μm to 14 μm, and the second graphite has an average particle diameter (D 50 ) of 15 μm to 25 μm.
[Claim 4]
The lithium secondary battery of claim 1, wherein the first graphite and the second graphite are artificial graphite.
[Claim 5]
The lithium secondary battery according to claim 1, wherein the electrolyte contains a lithium salt at a concentration of 1.0M to 1.5M.
[Claim 6]
The lithium secondary battery of claim 1, wherein the first additive is included in an amount of 2 parts by weight to 10 parts by weight based on 100 parts by weight of the electrolyte.
[Claim 7]
The lithium according to claim 1, wherein the first additive comprises at least one nitrile-based compound selected from the group consisting of succinonitrile, adiponitrile, butyronitrile, pimelonitrile, and hexanetricarbonitrile. secondary battery.
[Claim 8]
The lithium according to claim 1, wherein the electrolyte further comprises a second additive, and the second additive is at least one selected from the group consisting of a cyclic sultone-based compound and a cyclic carbonate-based compound in which fluorine is substituted or unsubstituted. secondary battery.
[Claim 9]
The lithium secondary battery according to claim 8, wherein the second additive is included in an amount of 10 to 15 parts by weight based on 100 parts by weight of the electrolyte.
[Claim 10]
The lithium secondary battery according to claim 1, wherein the driving voltage of the lithium secondary battery is 4.2 V to 4.5 V.