[Mutual citations with related applications]
[2]
This application claims the benefit of priority based on Korean Patent Application No. 10-2017-0155957 filed on November 21, 2017, and all contents disclosed in the Korean patent application document are included as part of this specification.
[3]
[4]
[Technical field]
[5]
The present invention relates to a positive electrode material for a lithium secondary battery, and a positive electrode and a lithium secondary battery comprising the same.
[6]
Background
[7]
As technology development and demand for mobile devices increase, demand for secondary batteries as an energy source is rapidly increasing. Among these secondary batteries, lithium secondary batteries having high energy density and voltage, long cycle life, and low self-discharge rate have been commercialized and widely used.
[8]
A lithium transition metal composite oxide is used as a positive electrode active material for a lithium secondary battery, and among them , lithium cobalt composite metal oxide such as LiCoO 2 having a high working voltage and excellent capacity characteristics is mainly used. However, LiCoO 2 has very poor thermal properties due to destabilization of the crystal structure due to delithium, and is expensive, and thus has a limitation in mass use as a power source in fields such as electric vehicles.
[9]
As a material for replacing the LiCoO 2 , lithium manganese composite metal oxides (LiMnO 2 or LiMn 2 O 4, etc.), lithium iron phosphate compounds (LiFePO 4, etc.) or lithium nickel composite metal oxides (LiNiO 2, etc.) have been developed. . Among them, research and development of lithium nickel composite metal oxides, which have a high reversible capacity of about 200 mAh/g and are easy to implement a large-capacity battery, have been actively conducted. However, the LiNiO 2 is inferior in thermal stability to LiCoO 2, and when an internal short circuit occurs due to pressure from the outside in a charged state, the positive electrode active material itself decomposes to cause rupture and ignition of the battery. Accordingly , as a method for improving the low thermal stability while maintaining the excellent reversible capacity of the LiNiO 2 , a lithium nickel cobalt manganese oxide in which a part of Ni is substituted with Mn and Co was developed.
[10]
However, in the case of the lithium nickel cobalt manganese oxide, the rolling density of the particles is low. In particular, when the content of Ni is increased to increase capacity characteristics, the rolling density of the particles becomes lower and the energy density decreases. When the electrode was strongly rolled to increase the rolling density, there was a problem that the current collector fractured and a crack in the positive electrode material occurred.
[11]
In addition, in the case of lithium nickel cobalt manganese oxide having a high Ni content, there is a problem in that the structural stability is deteriorated at a high temperature and the electrochemical performance such as a high temperature lifetime is deteriorated.
[12]
Accordingly, there is a need to develop a cathode material having excellent energy density and capacity characteristics and excellent high temperature life characteristics.
[13]
Detailed description of the invention
Technical challenges
[14]
The first technical problem of the present invention is to provide a high-capacity cathode material having excellent high temperature life characteristics.
[15]
The second technical problem of the present invention is to provide a positive electrode and a lithium secondary battery comprising the positive electrode material as described above.
[16]
Task resolution
[17]
In one aspect, the present invention is a positive electrode material comprising a first positive electrode active material represented by the following formula (1) and a second positive electrode active material represented by the following formula (2), wherein the positive electrode material is bimodal comprising large particle size and small particle size It provides a positive electrode material having a particle size distribution, and the difference between the average particle diameter (D 50 ) of the large particle diameter and the small particle size is 3 μm or more.
[18]
[Formula 1]
[19]
Li a [Ni b Co c M 1 d M a e ]O 2
[20]
In Chemical Formula 1, M 1 is Mn, Al, Zr or Mg, and M a is W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, In, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and one or more elements selected from the group consisting of Mo, 0.9≤a≤1.2, 0.8≤b<1, 0.01≤c< 0.2, 0.01≤d<0.2, 0≤e≤0.02.
[21]
[Formula 2]
[22]
Li x [Ni y Co z Mn w M 2 v M b u ]O 2
[23]
In Chemical Formula 2, M 2 is Al, Mg, Zr or Ti, and M b is W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, In, La, Sr , Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo is one or more elements selected from the group consisting of 0.9≤x≤1.2, 0.8≤y<1, 0.01≤z< 0.2, 0.01≤w<0.2, 0.01≤v<0.2, 0≤u≤0.02.
[24]
At this time, the large particle size particles may have an average particle diameter (D 50 ) of 10 μm to 20 μm, and the small particle size particles may have an average particle diameter (D 50 ) of 1 μm to 7 μm.
[25]
In another aspect, the present invention provides a positive electrode current collector, a positive electrode active material layer formed on the positive electrode current collector, and the positive electrode active material layer includes the positive electrode material according to the present invention.
[26]
In another aspect, the present invention, the positive electrode according to the present invention; cathode; A separator interposed between the anode and the cathode; And it provides a lithium secondary battery comprising an electrolyte.
[27]
Effects of the Invention
[28]
The positive electrode material according to the present invention uses lithium composite transition metal oxide having a nickel content of 80% or more, has excellent capacity characteristics, has a bimodal particle size distribution, and has high rolling density and energy density.
[29]
In addition, the positive electrode material according to the present invention has excellent high temperature life characteristics compared to the case of using a single composition of lithium nickel cobalt manganese oxide by mixing two types of lithium composite transition metal oxides having different compositions.
[30]
Brief description of drawings
[31]
1 is a graph showing the high-temperature cycle characteristics of the lithium secondary battery prepared by Examples 1, 2 and Comparative Example 1.
[32]
Best mode for carrying out the invention
[33]
Hereinafter, the present invention will be described in more detail.
[34]
The terms or words used in the specification and claims should not be interpreted as being limited to the ordinary or lexical meaning, and the inventor can appropriately define the concept of terms in order to best describe his or her invention. Based on the principle that it should be interpreted as meanings and concepts consistent with the technical idea of ​​the present invention.
[35]
[36]
In the present specification, the average particle diameter (D 50 ) may be defined as a particle diameter based on 50% of the particle size distribution, and may be measured using a laser diffraction method. Specifically, the average particle diameter (D 50 ), after dispersing the target particles in a dispersion medium, introduced into a commercially available laser diffraction particle size measuring device (for example, Microtrac MT 3000) and irradiated ultrasonic waves of about 28 kHz at an output power of 60 W. Then, the average particle diameter (D 50 ) at 50% of the particle number distribution according to the particle diameter in the measuring device can be calculated.
[37]
In addition, in this specification,% means weight% unless otherwise specified.
[38]
[39]
The present inventors have repeatedly conducted studies to develop a positive electrode material having excellent capacity characteristics, energy density, and high temperature life characteristics, and include two kinds of positive electrode active materials having a specific composition, and have a large particle diameter and small particle size difference of 3 μm or more. When using a positive electrode material having a fine bimodal particle size distribution with a particle size particle, it has been found that the above object can be achieved and the present invention has been completed.
[40]
[41]
Cathode material
[42]
First, the cathode material according to the present invention will be described.
[43]
The positive electrode material according to the present invention includes a first positive electrode active material and a second positive electrode active material having different compositions, and has a bimodal particle size distribution including large particle size and small particle size. At this time, the difference between the average particle diameter (D 50 ) of the large particle diameter and the small particle diameter may be 3 μm or more, preferably 3 μm to 15 μm, and more preferably 3 μm to 10 μm.
[44]
[45]
The first positive electrode active material is a lithium composite transition metal oxide having a nickel content of 80 mol% or more, specifically, a lithium composite transition metal oxide represented by the following [Formula 1].
[46]
[Formula 1]
[47]
Li a [Ni b Co c M 1 d M a e ]O 2
[48]
In Chemical Formula 1, M 1 is Mn, Al, Zr or Mg, and M a is a doping element substituted at a transition metal (Ni, Co and/or M 1 ) site, W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, In, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo It may be the above element.
[49]
The a is a molar ratio of lithium, and 0.9≤a≤1.2, and preferably 1.1≤a≤1.2.
[50]
The b represents a molar ratio of nickel among all transition metals, and may be 0.8≤b<1, preferably 0.8≤b≤0.98.
[51]
The c refers to a molar ratio of cobalt among all transition metals, and may be 0.01≤c<0.2, preferably 0.01≤c≤0.15.
[52]
The d refers to a molar ratio of M 1 among all transition metals , and may be 0.01≤d<0.2, preferably 0.01≤d≤0.15.
[53]
The e is a molar ratio of the doping element M a among all transition metals , and may be 0≤e≤0.02, preferably 0≤e≤0.01.
[54]
Specifically, the first positive electrode active material is Li a [Ni b Co c Mn d ] O 2 , Li a [Ni b Co c Al d ] O 2 , Li a [Ni b Co c Zr d ] O 2 , Li a [Ni b Co c Mg d ]O 2 , Li a [Ni bCo c Mn d Al e ]O 2 , Li a [Ni b Co c Mn d Zr e ]O 2 , Li a [Ni b Co c Mn d Mg e ]O 2, Li a [Ni b Co c Al d Zr e ]O 2 , or Li a [Ni b Co c Al d Mg e ]O 2 , (where a, b, c, d, and e are the same as defined in Formula 1), but are not limited thereto.
[55]
[56]
The second positive electrode active material is a lithium composite transition metal oxide having a nickel content of 80 mol% or more, specifically, a lithium composite transition metal oxide represented by the following [Formula 2].
[57]
[Formula 2]
[58]
Li x [Ni y Co z Mn w M 2 v M b u ]O 2
[59]
In Chemical Formula 2, M 2 is Al, Mg, Zr or Ti, and M b is a doping element substituted at a transition metal (Ni, Co and/or M 1 ) site, W, Cu, Fe, V, Cr , Ti, Zr, Zn, Al, In, Ta, Y, In, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo. It can be an element.
[60]
The x refers to a molar ratio of lithium, and 0.9≤x≤1.2, preferably 1.1≤x≤1.2.
[61]
The y is a molar ratio of nickel, and may be 0.8≤y<1, preferably 0.8≤y≤0.98.
[62]
The z represents a molar ratio of cobalt, and may be 0.01≤z<0.2, preferably 0.01≤z≤0.15.
[63]
The w is a molar ratio of manganese, and 0.01≤w<0.2, and preferably 0.01≤w≤0.1.
[64]
The v refers to the molar ratio of M 2 , and may be 0.01≤v<0.2, preferably 0.01≤v≤0.1.
[65]
The u refers to a molar ratio of the doping element M b among all transition metals , and may be 0≤u≤0.02, preferably 0≤u≤0.01.
[66]
[67]
Specifically, the second positive electrode active material is Li x [Ni y Co z Mn w Al v ]O 2 , Li x [Ni y Co z Mn w Mg v ]O 2 , Li x [Ni y Co z Mn w Zr v ]O 2 , Li x [Ni y Co z Mn w Ti v ]O 2 , Li x [Ni y Co z Mn w Al v Mg u ]O 2 , Li x [Ni y Co z Mn w Al v Zr u ]O 2 , or Li x [Ni y Co z Mn w Al v Ti u ]O 2(Here, x, y, z, w, v are the same as those defined in Formula 2), and the like, but are not limited thereto.
[68]
[69]
Meanwhile, the first positive electrode active material and/or the second positive electrode active material, if necessary, may further include a coating layer on its surface. At this time, the coating layer is Al, Ti, W, B, F, P, Mg, Ni, Co, Fe, Cr, V, Cu, Ca, Zn, Zr, Nb, Mo, Sr, Sb, Bi, Si, and It may include at least one coating element selected from the group consisting of one or more elements selected from the group consisting of S. When the coating layer as described above is formed, contact between the positive electrode active material and the electrolytic solution is blocked, so that side reaction occurrence is suppressed, and thus life characteristics can be improved when applied to the battery, and the filling density of the positive electrode active material can be increased.
[70]
As described above, when a coating element is further included, the content of the coating element in the coating layer may be 100 ppm to 10,000 ppm, preferably 200 ppm to 5,000 ppm, based on the total weight of the positive electrode active material.
[71]
The coating layer may be formed on the entire surface of the positive electrode active material, or may be partially formed. Specifically, when the coating layer is partially formed on the surface of the positive electrode active material, an area of ​​5% or more and less than 100%, preferably 20% or more and less than 100% of the total surface area of ​​the positive electrode active material may be formed.
[72]
[73]
On the other hand, the first positive electrode active material and the second positive electrode active material, the content of the transition metal elements in the active material particles may be constant regardless of the position, the content of one or more metal elements is changed depending on the position inside the particles It might be. For example, the positive electrode active material may have a concentration gradient in which at least one component of Ni, Mn, Co, M 1 and M 2 gradually changes, and the'gradually changing concentration gradient' is the concentration of the components. It means that it exists as a concentration distribution that changes continuously and stepwise in the whole particle or in a specific region.
[74]
[75]
Since the first positive electrode active material and the second positive electrode active material both contain 80 mol% or more of nickel, excellent capacity characteristics can be realized. In addition, according to the research of the present inventors, when the positive electrode active material of [Chemical Formula 1] and the positive electrode active material of [Chemical Formula 2] are mixed as described above, it has been found that the effect of improving the life characteristics at high temperature occurs.
[76]
[77]
On the other hand, the positive electrode material of the present invention, the first positive electrode active material and the second positive electrode active material in a weight ratio of 10: 90 to 90: 10, preferably 20: 80 to 80: 20, more preferably, 30: 70 to 70 : It can be included in a weight ratio of 30. When the mixing ratio of the first positive electrode active material and the second positive electrode active material satisfies the above range, a high electrode density can be obtained.
[78]
[79]
On the other hand, the positive electrode material of the present invention has a bimodal particle size distribution including large particle size and small particle size particles having different average particle sizes (D 50 ). When having a bimodal particle size distribution as described above, it is possible to realize a high rolling density and an energy density while the empty space between large particle size particles is filled with small particle size particles during rolling.
[80]
At this time, the difference between the average particle diameter (D 50 ) of the large particle diameter and the small particle diameter may be 3 μm or more, preferably 3 μm to 15 μm, and more preferably 3 μm to 10 μm. This is because when the difference between the average particle diameter (D 50 ) of the large particle diameter and the small particle diameter satisfies the above range, the small particle diameter particles are well filled between the large particle diameters, and thus the rolling density and energy density improvement effect is excellent.
[81]
Specifically, the large particle diameter may have an average particle diameter (D 50 ) of 10 μm to 20 μm, preferably 11 to 18 μm, and more preferably 12 to 18 μm. In addition, the small particle size particles may have an average particle diameter (D 50 ) of 1 μm to 7 μm, preferably 2 μm to 7 μm, and more preferably 3 μm to 6 μm.
[82]
[83]
Meanwhile, the type of the active material constituting the small particle diameter and the large particle size is not particularly limited, and may be the first positive electrode active material and/or the second positive electrode active material.
[84]
According to one embodiment, in the positive electrode material of the present invention, the first positive electrode active material may constitute large particle diameters, and the second positive electrode active material may constitute small particle diameter particles.
[85]
According to another embodiment, in the positive electrode material of the present invention, the first positive electrode active material may constitute small particle size particles, and the second positive electrode active material may constitute large particle size particles.
[86]
According to another embodiment, the positive electrode material of the present invention may have a bimodal particle size distribution in which at least one of the first positive electrode active material and the second positive electrode active material includes both the large particle size and the small particle size.
[87]
[88]
anode
[89]
Next, the anode according to the present invention will be described.
[90]
The positive electrode according to the present invention includes a positive electrode current collector, a positive electrode active material layer formed on the positive electrode current collector, wherein the positive electrode active material layer includes the positive electrode material according to the present invention, and if necessary, a conductive material and /Or include a binder.
[91]
[92]
At this time, the positive electrode material is the same as described above, and may be included in an amount of 80 to 99% by weight, more specifically 85 to 98.5% by weight based on the total weight of the positive electrode active material layer. When the positive electrode material is included in the above range, it can exhibit excellent capacity characteristics.
[93]
[94]
The positive electrode current collector is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or carbon, nickel, titanium on aluminum or stainless steel surfaces , Surface treatment with silver or the like can be used. In addition, the positive electrode current collector may have a thickness of usually 3 to 500 μm, and may form fine irregularities on the current collector surface to increase the adhesive force of the positive electrode material. For example, it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics.
[95]
[96]
The conductive material is used to impart conductivity to the electrode, and in the battery configured, it can be used without particular limitation as long as it has electronic conductivity without causing chemical changes. Specific examples include graphite such as natural graphite and artificial graphite; Carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, summer black, and carbon fiber; Metal powders or metal fibers such as copper, nickel, aluminum, and silver; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Or conductive polymers, such as polyphenylene derivatives, etc. are mentioned, and 1 type of these or mixtures of 2 or more types can be used. The conductive material may be included in an amount of 0.1 to 15% by weight based on the total weight of the positive electrode active material layer.
[97]
[98]
The binder serves to improve adhesion between the positive electrode active material particles and the adhesion between the positive electrode active material and the current collector. Specific examples of the binder include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose Woods (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, Styrene butadiene rubber (SBR), fluorine rubber, or various copolymers thereof, and one or a mixture of two or more of them may be used. The binder may be included in 0.1 to 15% by weight relative to the total weight of the positive electrode active material layer.
[99]
[100]
The positive electrode of the present invention can be manufactured according to a conventional positive electrode manufacturing method except that the positive electrode material according to the present invention is used as a positive electrode active material. Specifically, a positive electrode mixture prepared by dissolving or dispersing a positive electrode material, a binder, and/or a conductive material in a solvent may be coated on a positive electrode current collector, followed by drying and rolling.
[101]
The solvent may be a solvent generally used in the art, dimethyl sulfoxide (dimethyl sulfoxide, DMSO), isopropyl alcohol (isopropyl alcohol), N-methylpyrrolidone (NMP), acetone (acetone) or water And the like, and among these, one kind alone or a mixture of two or more kinds can be used. The amount of the solvent used may be such that the positive electrode mixture can be adjusted to have an appropriate viscosity in consideration of the coating thickness, production yield, workability, etc. of the positive electrode mixture, and is not particularly limited.
[102]
[103]
In addition, in another method, the positive electrode may be produced by casting the positive electrode mixture on a separate support, and then laminating the film obtained by peeling from the support on the positive electrode current collector.
[104]
[105]
Lithium secondary battery
[106]
Next, the lithium secondary battery according to the present invention will be described.
[107]
The lithium secondary battery of the present invention includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the positive electrode is the same as the positive electrode according to the present invention described above. Therefore, hereinafter, a detailed description of the anode will be omitted and only the rest of the configuration will be described.
[108]
[109]
The negative electrode includes a negative electrode current collector and a negative electrode active material layer positioned on the negative electrode current collector.
[110]
The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surfaces Carbon, nickel, titanium, silver or the like, aluminum-cadmium alloy, or the like may be used. In addition, the negative electrode current collector may have a thickness of usually 3 μm to 500 μm, and, like the positive electrode current collector, may form fine irregularities on the surface of the current collector to enhance the bonding force of the negative electrode active material. For example, it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics.
[111]
[112]
The negative active material layer optionally includes a binder and a conductive material together with the negative active material.
[113]
As the negative electrode active material, various negative electrode active materials used in the art may be used, and are not particularly limited. Specific examples of the negative electrode active material include artificial graphite, natural graphite, graphitized carbon fibers, carbonaceous materials such as amorphous carbon; Metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy or Al alloy; SiO β (0 <β <2), SnO 2, A metal oxide capable of doping and dedoping lithium, such as vanadium oxide and lithium vanadium oxide; Or a complex containing the metal compound and the carbonaceous material, such as a Si-C composite or a Sn-C composite, and the like, or any one or a mixture of two or more thereof may be used. In addition, a metal lithium thin film may be used as the negative electrode active material. In addition, both low-crystalline carbon and high-crystalline carbon may be used as the carbon material. Soft carbon and hard carbon are typical examples of low crystalline carbon, and amorphous or plate-like, scaly, spherical or fibrous natural graphite or artificial graphite, and kissy graphite are examples of high crystalline carbon. graphite), pyrolytic carbon, mesophase pitch based carbon fibers, meso-carbon microbeads, mesophase pitches, and petroleum or coal tar pitch derived cokes).
[114]
Meanwhile, the negative electrode active material may be included in an amount of 80% to 99% by weight based on the total weight of the negative electrode active material layer.
[115]
[116]
The binder is a component that assists in bonding between the conductive material, the active material, and the current collector, and is usually added in an amount of 0.1 to 10% by weight based on the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoro Roethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluorine rubber, and various copolymers thereof.
[117]
[118]
The conductive material is a component for further improving the conductivity of the negative electrode active material, and may be added in an amount of 10% by weight or less, preferably 5% by weight or less based on the total weight of the negative electrode active material layer. The conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, graphite such as natural graphite or artificial graphite; Carbon blacks such as 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 powder, aluminum powder, 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.
[119]
[120]
The negative electrode active material layer is prepared by applying and drying a negative electrode active material, and optionally a negative electrode material prepared by dissolving or dispersing a binder and a conductive material in a solvent on a negative electrode current collector, or casting the negative electrode material material on a separate support. Then, it can be produced by laminating a film obtained by peeling from this support onto the negative electrode current collector.
[121]
[122]
On the other hand, in the lithium secondary battery, the separator separates the negative electrode from the positive electrode and provides a passage for lithium ions, and is usually used as a separator in a lithium secondary battery. It is desirable to have low resistance and excellent electrolyte-moisturizing ability. Specifically, porous polymer films such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer and ethylene/methacrylate copolymer, etc. A laminate structure of two or more layers of may be used. In addition, a conventional porous non-woven fabric, for example, a high-melting point glass fiber, a polyethylene terephthalate fiber or the like may be used. In addition, a coated separator containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure.
[123]
[124]
Further, as the electrolyte used in the present invention, an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, and the like that can be used in a lithium secondary battery may be used, and are not particularly limited. .
[125]
Specifically, the electrolyte may include an organic solvent and a lithium salt.
[126]
The organic solvent may be used without particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent, methyl acetate (methyl acetate), ethyl acetate (ethyl acetate), γ-butyrolactone (γ-butyrolactone), ε-caprolactone (ε-caprolactone), such as ester-based solvents; Ether-based solvents such as dibutyl ether or tetrahydrofuran; Ketone solvents such as cyclohexanone; Aromatic hydrocarbon-based solvents such as benzene and fluorobenzene; Dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate (propylene carbonate, PC) and other carbonate-based solvents; Alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; Nitriles such as Ra-CN (Ra is a straight-chain, branched or cyclic hydrocarbon group having 2 to 20 carbon atoms, and may include a double bond aromatic ring or ether bond); Amides such as dimethylformamide; Dioxolanes such as 1,3-dioxolane; Alternatively, sulfolanes may be used. Of these, carbonate-based solvents are preferred, Cyclic carbonate (for example, ethylene carbonate or propylene carbonate) having a high ionic conductivity and high dielectric constant that can improve the charge and discharge performance of the battery, and low viscosity linear carbonate-based compounds (for example, ethylmethyl carbonate, dimethyl Mixtures of carbonate or diethyl carbonate) are more preferred. In this case, the mixture of the cyclic carbonate and the chain carbonate in a volume ratio of about 1: 1 to 9 may be used to exhibit excellent electrolyte performance.
[127]
[128]
The lithium salt may be used, without limitation, those which are commonly used in a lithium secondary battery electrolyte, such as Li in the lithium salt cationic + anionic, and include the F - , Cl - , Br - , I - , NO 3 - , N (CN) 2 - , BF 4 - , ClO 4 - , AlO 4 - , AlCl 4 - , PF 6 - , SbF 6 - , AsF 6 - , BF 2 C 2 O 4 - , BC 4 O 8 - , PF 4 C 2 O 4 - , PF 2 C 4 O 8 - , (CF 3 ) 2 PF 4 - , (CF 3 ) 3 PF 3 - , (CF 3 ) 4 PF 2 - , (CF 3 ) 5 PF - , (CF 3) 6 P - , CF 3 SO 3 - , C 4 F 9 SO 3 - , CF 3 CF 2 SO 3 - , (CF 3 SO 2 ) 2 N - , (FSO 2 ) 2 N - , CF 3 CF 2 ( CF 3 ) 2 CO - , (CF 3SO 2 ) 2 CH - , (SF 5 ) 3 C - , (CF 3 SO 2 ) 3 C - , CF 3 (CF 2 ) 7 SO 3 - , CF 3 CO 2 - , CH 3 CO 2 - , SCN - And (CF 3 CF 2 SO 2 ) 2And at least one selected from the group consisting of N − . Specifically, the lithium salt is LiCl, LiBr, LiI, LiClO 4 , LiBF 4 , LiB 10 Cl 10 , LiPF 6 , LiCF 3 SO 3 , LiCH 3 CO 2 , LiCF 3 CO 2 , LiAsF 6 , LiSbF 6 , LiAlCl 4 , LiAlO 4 , and LiCH 3 SO 3LiBTI (lithium bisperfluoroethanesulfonimide, LiN(SO 2 C 2 F 5 ) 2 ), LiFSI (lithium fluorosulfonyl) commonly used in electrolytes of lithium secondary batteries. Electrolytic salts such as lithium imide salts represented by imide, LiN(SO 2 F) 2 ), and LiTFSI (lithium (bis)trifluoromethanesulfonimide, LiN(SO 2 CF 3 ) 2 ) can be used without limitation. Specifically, the electrolyte salt is LiPF 6 , LiBF 4 , LiCH 3 CO 2 , LiCF 3 CO 2 , LiCH 3 SO 3 , LiFSI, LiTFSI, and LiN(C 2 F 5 SO 2 ) 2 .
[129]
The lithium salt may be appropriately changed within a range that can be normally used, but may be specifically included in the electrolyte in an amount of 0.8 M to 3M, and specifically 0.1M to 2.5M.
[130]
[131]
In addition to the electrolyte components, various additives may be used in the electrolyte for the purpose of improving the life characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery. Such additives include, for example, haloalkylene carbonate compounds such as difluoroethylene carbonate; Or pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N -Substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol or aluminum trichloride may be included, and the additives may be used alone or in combination. At this time, the additive may be included in an amount of 0.1 to 5% by weight based on the total weight of the electrolyte.
[132]
[133]
The lithium secondary battery according to the present invention as described above can be usefully used in portable devices such as mobile phones, notebook computers, digital cameras, and electric vehicle fields such as hybrid electric vehicles (HEV).
[134]
Accordingly, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided.
[135]
The battery module or battery pack includes a power tool; An electric vehicle including an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); Alternatively, it can be used as a power supply for any one or more of medium and large-sized devices in a power storage system.
[136]
The external shape of the lithium secondary battery of the present invention is not particularly limited, but may be a cylindrical shape, a square shape, a pouch shape or a coin shape using a can.
[137]
The lithium secondary battery according to the present invention can be used not only for a battery cell used as a power source for a small device, but also as a unit battery in a medium-to-large battery module including a plurality of battery cells.
[138]
Mode for carrying out the invention
[139]
Hereinafter, examples will be described in detail to specifically describe the present invention. However, the embodiments according to the present invention can be modified in many different forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to more fully describe the present invention to those skilled in the art.
[140]
[141]
Example 1
[142]
LiNi 0 having an average particle diameter (D 50 ) of 5 μm . 8 Co 0 . 1 Mn 0 . 1 O 2 and LiNi 0.83 Co 0.11 Mn 0.04 Al 0.02 O 2 having an average particle diameter (D 50 ) of 15 μm were mixed at a weight ratio of 30:70 to form a positive electrode material A.
[143]
The positive electrode material A, carbon black conductive material, and PVdF binder prepared above were mixed in a weight ratio of 96:2:2, and mixed in an NMP solvent to prepare a positive electrode material mixture. The positive electrode mixture was applied to an aluminum foil having a thickness of 12 μm, dried, and roll-pressed to prepare a positive electrode.
[144]
On the other hand, as a negative electrode active material, graphite, a carbon conductive material (SuperC65), and a PVdF binder were mixed in a weight ratio of 95.6:0.75:3.65, and added to NMP as a solvent to prepare a negative electrode mixture. The negative electrode mixture was coated on a copper foil having a thickness of 20 μm, dried, and then roll-pressed to prepare a negative electrode.
[145]
The positive electrode and the negative electrode prepared above were stacked together with a polyolefin separator to prepare an electrode assembly, and then placed in a battery case and mixed with ethylene carbonate:propyl propionate:diethyl carbonate in a 3:1:6 mixed solvent weight of 100 Lithium secondary battery was prepared by injecting 1 M of LiPF 6 , 0.5 parts by weight of vinylene carbonate (VC), 1.0 parts by weight of electrolyte, and 1 part of propane sulfone (PS).
[146]
[147]
Example 2
[148]
LiNi 0 having an average particle diameter (D 50 ) of 15 μm . 8 Co 0 . 1 Mn 0 . 1 O 2 and LiNi 0.83 Co 0.11 Mn 0.04 Al 0.02 O 2 having an average particle diameter (D 50 ) of 5 μm were mixed at a weight ratio of 70:30 to form a positive electrode material B.
[149]
A lithium secondary battery was manufactured in the same manner as in Example 1, except that the positive electrode material B prepared as described above was used instead of the positive electrode material A.
[150]
[151]
Example 3
[152]
LiNi 0 having an average particle diameter (D 50 ) of 10 μm . 8 Co 0 . 1 Mn 0 . 1 O 2 and LiNi 0.83 Co 0.11 Mn 0.04 Al 0.02 O 2 having an average particle diameter (D 50 ) of 5 μm were mixed at a weight ratio of 70:30 to form a cathode material C.
[153]
A lithium secondary battery was manufactured in the same manner as in Example 1, except that the positive electrode material C prepared as described above was used instead of the positive electrode material A.
[154]
[155]
Example 4
[156]
LiNi 0 having an average particle diameter (D 50 ) of 13 μm . 8 Co 0 . 1 Mn 0 . 1 O 2 and LiNi 0.83 Co 0.11 Mn 0.04 Al 0.02 O 2 having an average particle diameter (D 50 ) of 5 μm were mixed in a weight ratio of 70: 30 to form a cathode material D.
[157]
A lithium secondary battery was manufactured in the same manner as in Example 1, except that the positive electrode material D prepared as described above was used instead of the positive electrode material A.
[158]
[159]
Example 5
[160]
LiNi 0 having an average particle diameter (D 50 ) of 15 μm . 85 Co 0 . 1 Mn 0 . 05 O 2 and LiNi 0.83 Co 0.11 Mn 0.05 Mg 0.01 O 2 having an average particle diameter (D 50 ) of 5 μm were mixed at a weight ratio of 70: 30 to form a cathode material E.
[161]
A lithium secondary battery was manufactured in the same manner as in Example 1, except that the positive electrode material E prepared as described above was used instead of the positive electrode material A.
[162]
[163]
Comparative Example 1
[164]
LiNi 0 having an average particle diameter (D 50 ) of 15 μm . 8 Co 0 . 1 Mn 0 . 1 O 2 and LiNi 0.8 Co 0.1 Mn 0.1 O 2 having an average particle diameter (D 50 ) of 5 μm were mixed at a weight ratio of 70:30 to form a cathode material F.
[165]
A lithium secondary battery was manufactured in the same manner as in Example 1, except that the positive electrode material F prepared as described above was used instead of the positive electrode material A.
[166]
[167]
Comparative Example 2
[168]
LiNi 0 with an average particle diameter (D 50 ) of 6 μm . 8 Co 0 . 1 Mn 0 . 1 O 2 and LiNi 0.83 Co 0.11 Mn 0.04 Al 0.02 O 2 having an average particle diameter (D 50 ) of 8 μm were mixed at a weight ratio of 70:30 to form a cathode material G.
[169]
A lithium secondary battery was manufactured in the same manner as in Example 1, except that the positive electrode material G prepared as described above was used instead of the positive electrode material A.
[170]
[171]
Comparative Example 3
[172]
LiNi 0 having an average particle diameter (D 50 ) of 15 μm . 8 Co 0 . 1 Mn 0 . 1 O 2 and LiNi 0.83 Co 0.11 Mn 0.04 Al 0.02 O 2 having an average particle diameter (D 50 ) of 15 μm were mixed at a weight ratio of 70:30 to form a cathode material H.
[173]
A lithium secondary battery was manufactured in the same manner as in Example 1, except that the positive electrode material H prepared as described above was used instead of the positive electrode material A.
[174]
[175]
Comparative Example 4
[176]
LiNi 0 having an average particle diameter (D 50 ) of 5 μm . 8 Co 0 . 1 Mn 0 . 1 O 2 and LiNi 0.83 Co 0.11 Mn 0.04 Al 0.02 O 2 having an average particle diameter (D 50 ) of 5 μm were mixed at a weight ratio of 30:70 to form a cathode material I.
[177]
A lithium secondary battery was manufactured in the same manner as in Example 1, except that the positive electrode material I prepared as described above was used instead of the positive electrode material A.
[178]
[179]
Comparative Example 5
[180]
LiNi 0 having an average particle diameter (D 50 ) of 5 μm . 6 Co 0 . 2 Mn 0 . 2 O 2 and LiNi 0.83 Co 0.11 Mn 0.04 Al 0.02 O 2 having an average particle diameter (D 50 ) of 15 μm were mixed at a weight ratio of 30:70 to form a cathode material J.
[181]
A lithium secondary battery was manufactured in the same manner as in Example 1, except that the positive electrode material J prepared as described above was used instead of the positive electrode material A.
[182]
[183]
Comparative Example 6
[184]
LiNi 0 having an average particle diameter (D 50 ) of 5 μm . 8 Co 0 . 1 Mn 0 . 1 O 2 and LiNi 0.6 Co 0.2 Mn 0.2 O 2 having an average particle diameter (D 50 ) of 15 μm were mixed at a weight ratio of 30:70 to form a cathode material K.
[185]
A lithium secondary battery was manufactured in the same manner as in Example 1, except that the positive electrode material K prepared as described above was used instead of the positive electrode material A.
[186]
[187]
Experimental Example 1
[188]
The capacity retention rate at 100 cycles and 200 cycles while charging and discharging the lithium secondary batteries prepared in Examples 1 to 5 and Comparative Examples 1 to 6 in the range of 2.5 V to 4.2 V at 0.3 C/0.3 C at 45° C. ( %) and the rate of increase in resistance (%) were measured. Table 1 shows the measurement results. In addition, Figure 1 shows a graph showing the cycle characteristics of the lithium secondary battery prepared by Examples 1, 2 and Comparative Example 1.
[189]
[Table 1]
100 cycles 200 cycles
Capacity retention rate (%) Resistance increase rate (%) Capacity retention rate (%) Resistance increase rate (%)
Example 1 92.5 9.6 88.5 18.8
Example 2 92.4 14.0 88.6 23.7
Example 3 90.8 19.8 85.9 30.5
Example 4 91.2 16.9 86.4 27.4
Example 5 90.3 21.4 85.2 34.2
Comparative Example 1 90.4 23.2 84.8 37.4
Comparative Example 2 87.1 29.2 80.0 44.3
Comparative Example 3 86.9 29.8 79.4 44.9
Comparative Example 4 85.4 30.7 78.7 46.1
Comparative Example 5 88.1 27.7 82.2 39.7
Comparative Example 6 88.2 27.3 82.4 40.8
[190]
As shown in [Table 1] and FIG. 1, the difference between the average particle diameter (D 50 ) of large particle size and small particle size particles containing two positive electrode active materials satisfying the composition of the present invention is 3 μm or more and bimodal distribution. Secondary batteries of Examples 1 to 5 using the positive electrode material having a better high-temperature cycle characteristics than the secondary batteries of Comparative Examples 1 to 6, in particular, as the number of cycles increases, the difference in capacity characteristics and resistance increase rate You can see that is bigger.
Claim
[Claim 1]
A positive electrode material comprising a first positive electrode active material represented by the following Chemical Formula 1 and a second positive electrode active material represented by the following Chemical Formula 2, wherein the positive electrode material has a bimodal particle size distribution including large particle size particles and small particle size particles, A positive electrode material having a difference between the average particle diameter (D 50 ) of light particles and small particle diameters of 3 µm or more. [Formula 1] Li a [Ni b Co c M 1 d M a e ] O 2 In Formula 1, The M 1 Is Mn, Al, Zr or Mg, The M a W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, In, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo The above elements are 0.9≤a≤1.2, 0.8≤b<1, 0.01≤c<0.2, 0.01≤d<0.2, and 0≤e≤0.02. [Formula 2] Li x [Ni y Co zMn w M 2 v M b u ]O 2 In Formula 2, M 2 is Al, Mg, Zr or Ti, and M b is W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, In, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and one or more elements selected from the group consisting of Mo, wherein 0.9≤x≤1.2 , 0.8≤y<1, 0.01≤z<0.2, 0.01≤w<0.2, 0.01≤v<0.2, 0≤u≤0.02.
[Claim 2]
The positive electrode material according to claim 1, wherein the large particle diameter has an average particle diameter (D 50 ) of 10 μm to 20 μm.
[Claim 3]
The cathode material according to claim 1, wherein the small particle size particles have an average particle diameter (D 50 ) of 1 μm to 7 μm.
[Claim 4]
The positive electrode material according to claim 1, wherein the first positive electrode active material is the small particle size particle, and the second positive electrode active material is the large particle size particle.
[Claim 5]
The positive electrode material according to claim 1, wherein the first positive electrode active material is the large particle size, and the second positive electrode active material is the small particle size particle.
[Claim 6]
The positive electrode material according to claim 1, wherein at least one of the first positive electrode active material and the second positive electrode active material has a bimodal particle size distribution including the large particle size and the small particle size.
[Claim 7]
The positive electrode material according to claim 1, wherein the first positive electrode active material and the second positive electrode active material are contained in a weight ratio of 10:90 to 90:10.
[Claim 8]
According to claim 1, At least one of the first positive electrode active material and the second positive electrode active material, Al, Ti, W, B, F, P, Mg, Ni, Co, Fe, Cr, V, Cu, Ca, A cathode material comprising a coating layer comprising at least one coating element selected from the group consisting of one or more elements selected from the group consisting of Zn, Zr, Nb, Mo, Sr, Sb, Bi, Si, and S.
[Claim 9]
The method of claim 1, wherein in Formula 1, M 1 , and the Mn, M 2 in the formula 2 of the positive electrode material is Al.
[Claim 10]
The cathode material according to claim 1, wherein a difference between the average particle diameter (D 50 ) of the large particle diameter and the small particle diameter is 3 μm to 15 μm.
[Claim 11]
A positive electrode current collector, including a positive electrode active material layer formed on the positive electrode current collector, the positive electrode active material layer is a positive electrode comprising the positive electrode material of any one of claims 1 to 10.
[Claim 12]
The anode of claim 11; cathode; A separator interposed between the anode and the cathode; And lithium secondary battery comprising an electrolyte.