Lithium secondary battery

Abstract

The present invention provides a lithium secondary battery comprising: a positive electrode; a negative electrode; and an electrolyte, wherein the positive electrode includes a positive electrode active material layer, the positive electrode active material layer includes a positive electrode active material, the positive electrode active material includes a lithium metal oxide including excess lithium and represented by chemical formula 1, the negative electrode includes a negative electrode active material layer, and the negative electrode active material layer includes a silicon-based negative electrode active material.

Description

lithium secondary battery

[0001] The present invention relates to a lithium secondary battery.

[0002]

[0003] As lithium secondary batteries expand their applications from small electronic devices to electric vehicles and power storage devices, the demand for high energy density and excellent lifespan characteristics is increasing day by day.

[0004] However, in order to simultaneously achieve high energy density and excellent lifespan characteristics, the energy density of the positive and negative electrodes themselves must be excellent, and the combination between the positive and negative electrodes must be appropriate, which presents various practical difficulties.

[0005] For example, when using a silicon-based (SiOx, Si / C, Si) anode, the material itself can provide a high specific capacity, but the actual energy density is very low and the cycle life characteristics are also very poor due to the deterioration of the active material caused by the relatively high initial irreversible capacity or the limitation of the anode operating voltage. In order to fill this irreversible capacity characteristic or compensate for the anode operating voltage, a sacrificial anode material is sometimes used in addition to the traditional anode material, but it is difficult to apply in practice due to side reactions, gas generation, and transition metal elution. In addition, manganese-based lithium-rich layered anode active material (Li) which is being studied as a next-generation anode material 1+x M 1-x In the case of O2), it can provide a high initial discharge capacity due to the oxygen oxidation / reduction reaction at the first charge / discharge, but compared to the first charge / discharge, the discharge capacity drops significantly to 2 / 3 from the second charge / discharge due to the use of a relatively low upper limit potential. Therefore, the energy density per volume consumed by the cathode in the actual cell is very high when using a graphite cathode, and the actual usable energy density is very low at 450-500 Wh / L.

[0006] To address the above-mentioned imbalance between the positive and negative electrodes, a lithium secondary battery system using manganese-based layered lithium-rich oxide and silicon-based anode active materials has recently been proposed. This system was able to play a complementary role to some extent, as the high charge capacity of the positive electrode during the first charge was supported by the high irreversible capacity of the silicon anode. However, this system has a problem in that the initial efficiency of the negative electrode is too high compared to the initial efficiency of the positive electrode, which greatly lowers the critical point at which the silicon-based anode active material can withstand degradation. Therefore, only a very limited amount of silicon-based anode active material can be added, less than 5 wt% of the total anode active material. This reduction in the amount of silicon-based anode active material results in a decrease in the energy density of the battery.

[0007] Therefore, the task of finding the optimal combination of positive and negative electrode materials to simultaneously maximize the energy density of lithium secondary batteries and achieve excellent lifespan characteristics is still required.

[0008]

[0009] Accordingly, one object of the present invention is to provide a lithium secondary battery including a combination of a positive electrode and a negative electrode capable of simultaneously maximizing energy density and achieving excellent life characteristics.

[0010]

[0011] One embodiment of the present invention provides a lithium secondary battery comprising a positive electrode; a negative electrode; and an electrolyte, wherein the positive electrode comprises a positive electrode active material layer, the positive electrode active material layer comprises a positive electrode active material, and the positive electrode active material comprises a lithium metal oxide having a lithium-excess composition represented by the following chemical formula 1, and the negative electrode comprises a negative electrode active material layer, and the negative electrode active material layer comprises a silicon-based negative electrode active material.

[0012] [Chemical Formula 1]

[0013] Li 1+x (Ni a M1 b M2c ) 1-x O2

[0014] In the above chemical formula 1, 0.02≤x≤0.1, 0.75≤a≤0.98, 0.02≤b≤0.25, 0≤c≤0.1, a+b+c=1, M1 is a buffer metal element, which may be Ti, Nb, W, Zr, V, Cr, Mo, Ta, or a combination thereof, and M2 is a doping element, which may be Al, B, Y, Co, Mn, Fe, Cu, Zn, Ga, Ge, Ru, Rh, Sn, Sb, Re, Ir, Pt, Pb, Bi, Na, K, Rb, Cs, Ca, Sr, Ba, Mg, Si, Sc, or a combination thereof.

[0015] The absolute value of the initial efficiency difference between the positive and negative electrodes may be 3% or less.

[0016] The lithium metal oxide may have a ratio of the peak intensity of the (003) plane to the peak intensity of the (104) plane (I(003) / I(104)) of 0.7 to 1.6 when analyzed by X-ray diffraction.

[0017] The above lithium metal oxide may have a c-axis lattice constant of 14.2 to 14.5 Å.

[0018] The initial efficiency of the above anode can be 80 to 93%.

[0019] The above silicon-based negative electrode active material may be silicon, silicon oxide, a silicon-carbon composite, or a combination thereof.

[0020] The above negative electrode active material layer may further include a carbon-based negative electrode active material.

[0021] The above carbon-based negative electrode active material may be natural graphite, artificial graphite, or a combination thereof.

[0022] The above silicon-based negative electrode active material is silicon, silicon oxide, or a combination thereof, and the weight ratio of the silicon-based negative electrode active material and the carbon-based negative electrode active material (silicon-based negative electrode active material:carbon-based negative electrode active material) may be 2:98 to 20:80.

[0023] The initial efficiency of the above cathode can be 87 to 92%.

[0024] The above lithium secondary battery may have an N / P ratio of 100 to 130%.

[0025] The above positive electrode active material may have an average particle diameter (D50) of 3 to 12 μm.

[0026] The above positive electrode active material has a BET specific surface area of ​​1 to 10 m 2 / g may be.

[0027] The above positive electrode may have an electrode density of 3.0 to 4.0 g / cc.

[0028] The above silicon-based negative electrode active material may have an average particle diameter (D50) of 3 to 8 μm.

[0029] The above cathode may have an electrode density of 1.5 to 1.8 g / cc.

[0030]

[0031] A lithium secondary battery according to one embodiment of the present invention includes a positive electrode including a positive electrode active material of a novel composition and a negative electrode including a negative electrode active material having an optimal combination thereof, thereby not only maximizing energy density but also improving life characteristics.

[0032]

[0033] Figure 1 is a conceptual diagram of a positive electrode active material according to the present invention.

[0034] Figure 2 is a conceptual diagram of a lithium secondary battery according to the present invention.

[0035]

[0036] The terms first, second, and third, etc., are used to describe, but are not limited to, various parts, components, regions, layers, and / or sections. These terms are used only to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Accordingly, a first part, component, region, layer, or section described below may be referred to as a second part, component, region, layer, or section without departing from the scope of the present invention.

[0037] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the present invention. As used herein, the singular forms "singular" and "comprising" include plural forms as well, unless the context clearly dictates otherwise. The word "comprising" as used herein specifies a particular feature, region, integer, step, operation, element, and / or component, but does not exclude the presence or addition of other features, regions, integers, steps, operations, elements, and / or components.

[0038] When a part is referred to as being "on" or "over" another part, it can be directly on or over the other part, or there may be other parts intervening. Conversely, when a part is referred to as being "directly on" another part, there are no other parts intervening.

[0039] Although not defined otherwise, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with the relevant technical literature and the present disclosure, and are not to be construed as ideal or overly formal unless otherwise defined.

[0040] Also, unless otherwise stated, % means weight%, and 1 ppm is 0.0001 weight%.

[0041] In this specification, the term "combination(s) thereof" described in the expression in the Makushi format means one or more mixtures or combinations selected from the group consisting of the components described in the expression in the Makushi format, and means including any one or more selected from the group consisting of said components.

[0042] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement them. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0043]

[0044] To maximize the energy density and lifespan characteristics of lithium secondary batteries, the energy density and lifespan characteristics of the positive and negative electrodes themselves must first be excellent. Furthermore, even if the performance of the positive and negative electrodes themselves is excellent, an improper combination of the two can lead to rapid deterioration of the battery's lifespan characteristics.

[0045] The inventors of the present invention have completed the present invention as a result of extensive research on the optimal combination of positive and negative electrodes to maximize the energy density and lifespan characteristics of a lithium secondary battery from the above-mentioned viewpoint.

[0046] A lithium secondary battery according to one embodiment of the present invention includes a positive electrode; a negative electrode; and an electrolyte, and more specifically, may further include a positive electrode; a negative electrode; an electrolyte; and a separator interposed between the positive electrode and the negative electrode.

[0047] The above lithium secondary battery may optionally further include a battery container that houses the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0048] Below, each component of a lithium secondary battery is described in more detail.

[0049]

[0050] 1. Bipolar

[0051] The above positive electrode may include a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector.

[0052] At this time, the positive electrode active material layer includes a positive electrode active material, and the positive electrode active material includes a lithium metal oxide having a lithium-excess composition represented by chemical formula 1.

[0053] [Chemical Formula 1]

[0054] Li 1+x (Ni a M1 b M2 c ) 1-x O2

[0055] In the above chemical formula 1, 0.02≤x≤0.1, 0.75≤a≤0.98, 0.02≤b≤0.25, 0≤c≤0.1, a+b+c=1, M1 is a buffer metal element such as Ti, Nb, W, Zr, V, Cr, Mo, Ta or a combination thereof, and M2 is a doping element such as Al, B, Y, Co, Mn, Fe, Cu, Zn, Ga, Ge, Ru, Rh, Sn, Sb, Re, Ir, Pt, Pb, Bi, Na, K, Rb, Cs, Ca, Sr, Ba, Mg, Si, Sc or a combination thereof.

[0056] By including a lithium metal oxide having a lithium-excess composition represented by the above chemical formula 1 as the positive electrode active material, the energy density and life characteristics of the battery can be maximized.

[0057] Figure 1 is a conceptual diagram of a cathode active material according to the present invention. Hereinafter, with reference to Figure 1, the principles by which the cathode active material according to the present invention can maximize the energy density and lifespan characteristics of a battery will be described in more detail.

[0058] The lithium metal oxide represented by chemical formula 1 contains an excess amount of lithium, nickel, and buffer metal elements compared to a conventional cathode material having a typical composition.

[0059] Since the lithium metal oxide contains excess lithium and nickel, not only nickel-based cation oxidation / reduction reactions but also anion (oxygen) oxidation / reduction reactions can be utilized, thereby improving the capacity characteristics and energy density of the battery.

[0060] In addition, since the lithium metal oxide contains a buffer metal element, at least a portion of the lithium lattice sites in the lithium layer are replaced by some of the buffer metal elements, thereby improving the structural stability of the positive electrode active material. Accordingly, anisotropic shrinkage and expansion of the active material during charge and discharge are suppressed, enabling the implementation of excellent cycle characteristics. In addition, the buffer metal elements of the elements listed above prefer to be located in the lithium layer rather than the transition metal layer, which, combined with the substitution of some of the nickel ions in the transition metal layer into the lithium layer due to the introduction of an excessive amount of lithium, causes a disordered cation mixing structure. This disordered cation mixing structure facilitates the movement of lithium ions, which can also contribute to improving capacity and energy density.

[0061] More specifically, the lithium metal oxide having a lithium-excess composition according to the present invention can have a basic skeleton structure in which lithium layers containing lithium and transition metal layers containing a transition metal, such as nickel, are alternately laminated. At this time, the buffer metal elements listed above introduced into the lithium metal oxide may prefer the lithium layer site over the transition metal layer site, so that at least a portion of the lithium sites in the lithium layer may be replaced by the buffer metal element. In addition, the introduction of excess lithium may promote the substitution of nickel ions in the transition metal layer into the lithium layer. In addition, at the same time, the introduction of excess lithium may cause some of the lithium ions in the lithium layer to be replaced into the transition metal layer.

[0062] That is, the lithium metal oxide according to the present invention may have a structure in which lithium ions, nickel ions, and buffer metal elements are randomly mixed between the lithium layer and the transition metal layer.

[0063] In the conventional layered lithium metal oxide with a typical composition, only lithium exists in the lithium layer, and only the transition metal exists in the transition metal layer, or even if some lithium and transition metal exchange occurs, this generally reduces electrochemical activity. Therefore, the development of cathode materials has been directed toward minimizing this mutual exchange. More specifically, even in cathode materials with a typical composition, among transition metals, nickel cations, have similar ionic radii to lithium ions, so there are cases where nickel cations in the transition metal layer occupy lithium sites in the lithium layer, which is commonly referred to as cation mixing. However, when nickel cations occupy lithium sites in the lithium layer, they hinder lithium ion movement, resulting in deterioration of electrochemical characteristics such as reduced capacity and charge / discharge efficiency. Therefore, conventional technology has been developed toward minimizing this cation mixing ratio.

[0064] On the other hand, the lithium metal oxide according to the present invention may have a structure in which lithium in the lithium layer and nickel ions and buffer metal elements in the transition metal layer are randomly mixed with each other. Accordingly, unlike the general two-dimensional movement of lithium ions through the lithium layer, the lithium ions can three-dimensionally move (i.e., insertion and de-insertion) not only through the lithium layer but also through the transition metal layer during charging and discharging, thereby maximizing the lithium ion movement efficiency. As a result, the capacity characteristics and energy density of the battery can be improved. In other words, the position exchange between lithium and nickel generally reduces electrochemical activity, but the present invention facilitates lithium ion movement through the random position exchange of buffer metal elements other than lithium and nickel, thereby maximizing the capacity characteristics and energy density of the battery.

[0065] In order to realize a structure in which lithium in the lithium layer and buffer metal elements and nickel in the transition metal layer are mixed in an appropriately disordered manner, it is necessary to introduce an excess amount of lithium into the lithium metal oxide and an appropriate amount of buffer metal elements. In addition, the existence and degree of this cation disordered mixing structure can be confirmed by obtaining a ratio of the peak intensity of the (003) plane to the peak intensity of the (104) plane (I(003) / I(104)) in the range according to the present invention during X-ray diffraction analysis, as described below.

[0066] The buffer metal element may be Ti, Nb, W, Zr, V, Cr, Mo, Ta, or a combination thereof. The buffer metal elements listed above are transition metal elements that do not have valence electrons in d orbitals. When the transition metal does not have valence electrons in d orbitals, it may have a doping preference into the lithium layer rather than the transition metal layer.

[0067] In addition, the lithium transition metal oxide according to the present invention may be a compound of a solid solution phase in which Li2M1O3 (M1 is a buffer metal element) having a monoclinic structure and LiMO2 (M is Ni and other doping elements) having a rhombohedral structure are mixed.

[0068]

[0069] Hereinafter, the composition of the lithium metal oxide according to the present invention will be described in more detail.

[0070] The lithium metal oxide according to the present invention is represented by the following chemical formula 1.

[0071] [Chemical Formula 1]

[0072] Li 1+x (Ni a M1 b M2 c ) 1-x O2

[0073] In the above chemical formula 1, 0.02≤x≤0.1, 0.75≤a≤0.98, 0.02≤b≤0.25, 0≤c≤0.1, a+b+c=1, M1 is a buffer metal element such as Ti, Nb, W, Zr, V, Cr, Mo, Ta or a combination thereof, and M2 is a doping element such as Al, B, Y, Co, Mn, Fe, Cu, Zn, Ga, Ge, Ru, Rh, Sn, Sb, Re, Ir, Pt, Pb, Bi, Na, K, Rb, Cs, Ca, Sr, Ba, Mg, Si, Sc or a combination thereof.

[0074] In the lithium metal oxide of the above chemical formula 1, lithium may be included in an amount corresponding to 1+x, wherein x may be 0.02≤x≤0.1 or 0.03≤x≤0.06. If x is too small, lithium substitution in the transition metal layer hardly occurs, making it impossible to implement the aforementioned disordered mixed structure, and thus the effect of improving capacity and energy density may be minimal. If x is too large, a problem of phase stability may occur due to excessive occurrence of anion (oxygen) oxidation / reduction reactions, which may deteriorate the life characteristics.

[0075] In the lithium metal oxide of the above chemical formula 1, nickel may be included in an amount corresponding to a, i.e., 0.75≤a≤0.98 or 0.85≤a≤0.94. If a is too small, the nickel-based cation oxidation / reduction reaction may not be sufficiently utilized, which may result in a decrease in capacity and energy density. If a is too large, the content of the buffer metal element is reduced accordingly, and thus the effects of introducing the buffer metal element on improving life characteristics, capacity characteristics, and energy density may be minimal.

[0076] In the lithium metal oxide of the above chemical formula 1, M1 may be included in a content corresponding to b, that is, 0.02≤b≤0.25 or 0.06≤b≤0.15. At this time, M1 may be a buffer metal element such as Ti, Nb, W, Zr, V, Cr, Mo, Ta or a combination thereof. If b is too small, the effect of improving the life characteristics, capacity characteristics and energy density due to the introduction of the buffer metal element may be minimal. If b is too large, the content of the buffer metal element may become too large, and the disordered mixing between the buffer metal element, nickel and lithium may occur excessively, thereby deteriorating the layered crystal structure and, consequently, deteriorating the life characteristics, capacity characteristics and energy density.

[0077] In the lithium metal oxide of the above chemical formula 1, M2 may be included in a content corresponding to c, that is, 0≤c≤0.1. At this time, M2 may be a doping element such as Al, B, Y, Co, Mn, Fe, Cu, Zn, Ga, Ge, Ru, Rh, Sn, Sb, Re, Ir, Pt, Pb, Bi, Na, K, Rb, Cs, Ca, Sr, Ba, Mg, Si, Sc or a combination thereof. The content of the doping element may be appropriately selected and controlled to implement the doping effect within a range that does not deteriorate the electrochemical characteristics.

[0078] Meanwhile, the lithium metal oxide may not contain cobalt and manganese. Conventional cathode materials with typical compositions include cobalt and / or manganese in addition to nickel at appropriate levels to achieve superior capacity and lifespan characteristics by improving the structural stability of the active material. On the other hand, the lithium metal oxide according to the present invention can achieve superior electrochemical characteristics even without cobalt and manganese by introducing excess lithium, nickel, and buffer metal elements. However, it should be noted that the lithium metal oxide according to the present invention does not completely exclude the possibility of using cobalt and manganese.

[0079]

[0080] Hereinafter, the X-ray diffraction analysis properties of lithium metal oxide according to the present invention will be described in more detail.

[0081] The lithium metal oxide according to the present invention may have a ratio of the peak intensity of the (003) plane to the peak intensity of the (104) plane (I(003) / I(104)) in an X-ray diffraction analysis, and more specifically, may have a ratio of 0.9 to 1.5. The ratio of the peak intensity of the (003) plane to the peak intensity of the (104) plane (I(003) / I(104)) may indicate the degree of the mixing ratio of transition metal cations within the lithium layer, and a smaller value indicates a larger mixing ratio of transition metal cations within the lithium layer. The lithium metal oxide according to the present invention may have a smaller ratio of the peak intensity of the (003) plane to the peak intensity of the (104) plane (I(003) / I(104)) than that of a conventional cathode material having a typical composition due to the increased substitution amount of nickel and buffer metal elements in the lithium layer due to the introduction of an excess of lithium and the introduction of buffer metal elements other than nickel. However, if the ratio of the peak intensity of the (003) plane (I(003) / I(104)) is too small, it means that the content of the buffer metal element is excessive, and cation mixing may occur excessively, which may deteriorate the life characteristics, capacity characteristics, and energy density.

[0082] In addition, the lithium metal oxide according to the present invention may have a c-axis lattice constant of 14.2 to 14.5 Å. In the composition of the lithium metal oxide according to the present invention, the c-axis lattice constant may vary depending on the amount of the buffer metal element introduced, and when the c-axis lattice constant satisfies the above range, the effects of improving the lifespan, capacity, and energy density of the battery due to the introduction of the buffer metal element may be preferably implemented.

[0083]

[0084] Meanwhile, the lithium metal oxide according to the present invention may have a secondary particle form formed by agglomeration of a plurality of primary particles. The “secondary particle” refers to an aggregate, i.e., a secondary structure, formed by agglomeration of tens to hundreds of primary particles through physical or chemical bonding between the primary particles without an intentional agglomeration or assembly process for the primary particles. The “primary particle” refers to the smallest particle unit that can be distinguished as a single lump when observing the cross-section of the positive electrode active material through a scanning electron microscope (SEM), and may be formed of a single crystal grain or a plurality of crystal grains. The “crystal grain” refers to a distinct region in which atoms within the primary particle form a lattice structure with a certain direction.

[0085]

[0086] The above-mentioned positive electrode active material may have an average particle diameter (D50) of secondary particles of 3 to 12 μm. If the average particle diameter (D50) of the positive electrode active material is too small, the positive electrode mixture density may become too small. If the average particle diameter (D50) of the positive electrode active material is too large, the capacity and rate characteristics of the positive electrode active material may deteriorate. Therefore, from the viewpoint of maximizing the energy density and rate characteristics of the battery, it may be appropriate when the average particle diameter (D50) of the positive electrode active material satisfies the above range. In the present specification, the average particle diameter (D50) may be defined as a particle diameter corresponding to 50% of the volume accumulation amount in the particle diameter distribution curve of the particles. The above-mentioned average particle diameter (D50) may be measured using, for example, a laser diffraction method.

[0087] The above positive electrode active material has a BET specific surface area of ​​1 to 10 m 2 / g. If the BET specific surface area of ​​the positive active material is too small, the lithium ion migration area may be reduced, making it difficult to achieve sufficient capacity and rate characteristics. If the BET specific surface area of ​​the positive active material is too large, there may be a decline in life characteristics due to side reactions with the electrolyte. In this specification, the specific surface area of ​​the active material can be measured using the BET method (Surface area and Porosity analyzer) (Micromeritics, ASAP2020) for the active material powder.

[0088]

[0089] If the composition of the positive electrode active material satisfies the chemical formula 1 according to the present invention, the method for manufacturing the positive electrode active material is not particularly limited.

[0090] For example, in one embodiment, the raw materials containing each element that constitutes the positive electrode active material composition, i.e., nickel raw material, buffer metal raw material, lithium raw material, and other doping raw materials, can be mixed in a solid state in a stoichiometric ratio according to the composition of Chemical Formula 1, and then sintered to manufacture the positive electrode active material.

[0091] The above nickel raw material may be, but is not necessarily limited to, Ni(OH)2, NiO, Ni2O3 or a combination thereof.

[0092] The buffer metal raw material may be an oxide, hydroxide, carbonate, sulfate, phosphate, or a combination thereof containing a buffer metal element according to the present invention. In this case, the buffer metal element may be Ti, Nb, W, Zr, V, Cr, Mo, or Ta. For example, the buffer metal raw material may be TiO2, Ti(OH)2, Ti(CO3)2, Ti2(CO3)3, Ti[OCH(CH3)2]4, etc., but is not necessarily limited thereto.

[0093] The lithium raw material may be lithium-containing sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide, or oxyhydroxide, and is not particularly limited as long as it can be dissolved in water. Specifically, the lithium raw material may be, but is not limited to, Li2CO3, LiNO3, LiNO2, LiOH, LiOHㆍH2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, Li3C6H5O7, or a combination thereof.

[0094]

[0095] In another embodiment, a precursor may be formed by mixing a nickel raw material, a buffer metal raw material, and a solvent, spray drying the mixture, and then mixing the precursor with a lithium raw material and calcining the mixture. In this case, each of the nickel raw material, the buffer metal raw material, and the lithium raw material may be added in a stoichiometric ratio according to the composition of Chemical Formula 1.

[0096] The above nickel raw material may be, but is not necessarily limited to, Ni(OH)2, NiO, Ni2O3 or a combination thereof.

[0097] The buffer metal raw material may be an oxide, hydroxide, carbonate, sulfate, phosphate, or a combination thereof containing a buffer metal element according to the present invention. In this case, the buffer metal element may be Ti, Nb, W, Zr, V, Cr, Mo, or Ta. For example, the buffer metal raw material may be TiO2, Ti(OH)2, Ti(CO3)2, Ti2(CO3)3, Ti[OCH(CH3)2]4, etc., but is not necessarily limited thereto.

[0098] The solvent may be, but is not necessarily limited to, water, ethanol, or a combination thereof.

[0099] The precursor formed by the above spray drying may be, but is not necessarily limited to, a hydroxide, a carbonate, a hydroxide / oxide complex, a carbonate / oxide complex, or a combination thereof.

[0100] The above spray drying may be spraying and drying using a spray dryer.

[0101] The lithium raw material may be lithium-containing sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide, or oxyhydroxide, and is not particularly limited as long as it can be dissolved in water. Specifically, the lithium raw material may be, but is not limited to, Li2CO3, LiNO3, LiNO2, LiOH, LiOHㆍH2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, Li3C6H5O7, or a combination thereof.

[0102]

[0103] In another embodiment, a precursor containing nickel and buffer metal raw materials may be formed by a conventional wet co-precipitation reaction using a nickel raw material and a buffer metal raw material, and then the lithium raw material may be mixed and calcined to produce the precursor.

[0104] The precursor formed by the above coprecipitation reaction may be, but is not necessarily limited to, a hydroxide, a carbonate, or a combination thereof.

[0105] The lithium raw material may be lithium-containing sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide, or oxyhydroxide, and is not particularly limited as long as it can be dissolved in water. Specifically, the lithium raw material may be, but is not limited to, Li2CO3, LiNO3, LiNO2, LiOH, LiOHㆍH2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, Li3C6H5O7, or a combination thereof.

[0106]

[0107] Meanwhile, the positive electrode current collector is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the positive electrode current collector may typically have a thickness of 3 to 500 μm, and fine unevenness may be formed on the surface of the positive electrode current collector to increase the adhesive strength of the positive electrode active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0108] Additionally, the positive electrode active material layer may further include a binder and / or a conductive material together with the positive electrode active material described above.

[0109] The above binder serves to improve the adhesion between positive electrode active material particles and the adhesive strength between the positive electrode active material and the positive electrode current collector. Specific examples thereof include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof, but is not limited thereto. The binder may be included in an amount of 1 to 30 wt% based on the total weight of the positive electrode active material layer.

[0110] The conductive material is used to provide conductivity to the electrode, and in the battery to be formed, as long as it does not cause a chemical change and has electronic conductivity, it can be used without any particular restrictions. Specific examples include graphite such as natural graphite or 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 powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like. One type alone or a mixture of two or more types may be used among these, but the present invention is not limited thereto. The conductive material may typically be included in an amount of 1 to 30 wt% based on the total weight of the positive electrode active material layer.

[0111] The above positive electrode can be manufactured according to a conventional positive electrode manufacturing method, except that the above positive electrode active material is used.

[0112] Specifically, the positive electrode can be manufactured by applying a composition for forming a positive electrode active material layer, including the positive electrode active material described above and optionally a binder, a conductive agent, or a solvent, on a positive electrode current collector, followed by drying and rolling. At this time, the types and contents of the positive electrode active material, binder, and conductive agent are as described above.

[0113] The solvent may be a solvent generally used in the relevant technical field, such as dimethylsulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. One of these may be used alone or a mixture of two or more thereof may be used. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, taking into account the coating thickness and manufacturing yield of the slurry, and to have a viscosity that can exhibit excellent thickness uniformity when applied thereafter for manufacturing the positive electrode.

[0114] Alternatively, the positive electrode may be manufactured by casting the composition for forming the positive electrode active material layer on a separate support, and then laminating the resulting film on a positive electrode current collector by peeling it off from the support.

[0115]

[0116] Meanwhile, the positive electrode may have an electrode density of 3.0 to 4.0 g / cc. If the positive electrode density is too low, the energy density of the battery may decrease. If the positive electrode density is too high, the secondary particles may be destroyed, which may lower the life characteristics, or the electrolyte may be difficult to impregnate into the electrode, which may cause a decrease in capacity.

[0117]

[0118] 2. Cathode

[0119] The above negative electrode may include a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector.

[0120] At this time, the negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes a silicon-based negative electrode active material.

[0121] Since silicon-based negative electrode active materials have higher theoretical capacity than carbon-based negative electrode active materials and have a faster reaction rate with lithium, energy density and rapid charging performance can be improved when silicon-based negative electrode active materials are included in the negative electrode.

[0122] The above silicon-based negative electrode active material may be silicon, silicon oxide, a silicon-carbon composite, or a combination thereof. The silicon oxide may be, for example, SiO x (0 <x≤2)일 수 있다.

[0123] The above silicon-based negative electrode active material may further include a carbon coating layer on the particle surface, if necessary. In this case, the amount of carbon coating may be 20 wt% or less, and more specifically, 0.1 to 20 wt%, based on the total weight of the silicon-based negative electrode active material. When a carbon coating is applied, the electrical conductivity of the silicon surface is improved, thereby improving the uniformity of the SEI layer and improving the initial efficiency and lifespan characteristics.

[0124] The above carbon coating layer can be formed through methods such as dry coating, wet coating, chemical vapor deposition (CVD), physical vapor deposition (PVD), and atomic layer deposition (ALD).

[0125] FIG. 2 is a conceptual diagram of a lithium secondary battery according to the present invention. Referring to FIG. 2, at this time, the absolute value of the initial efficiency difference between the positive electrode and the negative electrode may be 3% or less, and more specifically, 2.8% or less. Since the initial efficiency difference between the positive electrode and the negative electrode is sufficiently small as in the above range, the irreversible capacities of the positive and negative electrodes are largely matched, thereby maximizing the available range of active materials that can participate in charge and discharge within the cell, thereby enabling a large capacity to be utilized, and since continuous use of both ends (low SOC of a large positive electrode and high SOC of a negative electrode) with very high impedance resistances at the positive and negative electrodes during a cycle can be avoided, the life characteristics can be maximized. Accordingly, the combination between the positive and negative electrodes is optimized, so that the energy density and life characteristics of the battery can be maximized.

[0126] From the perspective of appropriately realizing the initial efficiency difference between the positive and negative electrodes mentioned above, the negative electrode active material layer may optionally further include a carbon-based negative electrode active material, if necessary. Accordingly, by appropriately adjusting the mixing weight ratio of the silicon-based negative electrode active material and the carbon-based negative electrode active material as the negative electrode active material, the initial efficiency difference between the positive and negative electrodes according to the present invention can be more easily realized within the range according to the present invention.

[0127] For example, the silicon-based negative electrode active material may be silicon, silicon oxide, or a combination thereof, and at this time, the weight ratio of the silicon-based negative electrode active material and the carbon-based negative electrode active material (silicon-based negative electrode active material: carbon-based negative electrode active material) may be 2:98 to 20:80, and more specifically, 3:97 to 12:88. When the mixing weight ratio of the silicon-based negative electrode active material and the carbon-based negative electrode active material satisfies the above range, the initial efficiency difference between the positive electrode and the negative electrode composed of the positive electrode active material according to the present invention can be easily implemented within the range according to the present invention. Accordingly, the energy density and life characteristics of the battery can be maximized.

[0128] Alternatively, the silicon-based negative electrode active material may be a silicon-carbon composite, and in this case, by appropriately controlling the composite ratio between silicon and carbon, the initial efficiency difference between the positive electrode and the negative electrode composed of the positive electrode active material according to the present invention can be implemented within the range according to the present invention.

[0129] In addition, the silicon-based negative electrode active material may have an average particle diameter (D50) of 3 to 8 μm. If the average particle diameter (D50) of the silicon-based negative electrode active material is too small, dispersion may not occur during the mixing step, resulting in uneven swelling due to uneven distribution within the electrode, which may adversely affect the life characteristics. If the average particle diameter (D50) of the silicon-based negative electrode active material is too large, there may be problems such as a decrease in rate characteristics due to deterioration of electrical characteristics and a deterioration in life characteristics due to large local swelling within the electrode.

[0130] The above carbon-based negative electrode active material may be, for example, natural graphite, artificial graphite, or a combination thereof, but is not necessarily limited thereto.

[0131] Accordingly, the positive electrode composed of the positive electrode active material according to the present invention may have an initial efficiency of 80 to 93% or 85 to 93%. Furthermore, the negative electrode composed of the negative electrode active material according to the present invention may have an initial efficiency of 87 to 92%.

[0132] In addition, the lithium secondary battery according to one embodiment of the present invention may have an N / P ratio of 100 to 130%. In this specification, “N / P ratio” means the ratio of the discharge capacity of the negative electrode to the discharge capacity of the positive electrode. If the N / P ratio of the lithium secondary battery is too small, there may be a problem of battery deterioration due to lithium precipitation at the negative electrode region. If the N / P ratio of the lithium secondary battery is too large, there may be a problem of reduced energy density.

[0133]

[0134] The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, the negative electrode current collector can typically have a thickness of 3 to 500 ㎛, and like the positive electrode current collector, fine unevenness can be formed on the surface of the current collector to strengthen the bonding strength of the negative electrode active material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc.

[0135] The negative electrode active material layer may optionally include a binder and a conductive material together with the negative electrode active material. As an example, the negative electrode active material layer may be manufactured by applying a composition for forming a negative electrode active material layer comprising the negative electrode active material and optionally a binder and a conductive material onto a negative electrode current collector and drying the composition, or by casting the negative electrode forming composition onto a separate support and then laminating the resulting film onto a negative electrode current collector by peeling the film off from the support.

[0136] Examples of the binder include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylic acid, polyacrylamide, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof may be used. The above binder may be included in an amount of 1 to 20 wt%, 2 to 20 wt%, or 2 to 10 wt% based on the total weight of the negative electrode active material layer.

[0137] Examples of the conductive material include spherical or flaky graphite; carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, carbon fiber, single-walled carbon nanotube, multi-walled carbon nanotube, and the like; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and one of these may be used alone or a mixture of two or more thereof. The conductive material may be included in an amount of 0.1 to 30 wt%, 0.1 to 20 wt%, or 0.1 to 10 wt% based on the total weight of the negative electrode active material layer.

[0138]

[0139] In addition, the negative electrode may have an electrode density of 1.5 to 1.8 g / cc. If the negative electrode density is too low, the energy density of the battery may decrease. If the negative electrode density is too high, there may be problems of deterioration of life characteristics due to the aggravation of side reactions caused by destruction of secondary particles and increased surface exposure, and the impossibility of electrolyte impregnation caused by surface blockage.

[0140]

[0141] 3. Electrolyte

[0142] The above electrolyte may include, but is not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0143] Specifically, the organic liquid electrolyte may include an organic solvent and a lithium salt.

[0144] The organic solvent may be used without any 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 may include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; Carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (wherein R is a C2 to C20 linear, branched, or cyclic hydrocarbon group, and may include a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used. Among these, a carbonate solvent is preferable, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery and a linear carbonate compound having low viscosity (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate, etc.) is more preferable.In this case, the performance of the electrolyte may be improved when the cyclic carbonate and the chain carbonate are mixed and used in a volume ratio of about 1:1 to about 1:9.

[0145] The lithium salt may be used without any particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2. LiCl, LiI, or LiB(C2O4)2. It is preferable that the concentration of the lithium salt be used within the range of 0.1 to 5.0 M. When the concentration of the lithium salt is within the above range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively.

[0146] In addition to the electrolyte components, the electrolyte may also contain, for example, haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexamethylphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol or aluminum trichloride, fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinylethylene carbonate (VEC), ethylene sulfate (ESa), lithium difluorophosphate (LiPO2F2), lithium bisoxalatoborate (LiBOB), lithium tetrafluoroborate (LiBF4), One or more additives such as lithium difluorooxalatoborate (LiDFOB), lithium difluorobisoxalatophosphate (LiDFBP), lithium tetrafluorooxalatophosphate (LiTFOP), lithium methylsulfate (LiMS), lithium ethylsulfate (LiES), propanesultone (PS), propenesultone (PRS), succinonitrile (SN), adiponitrile (AND), 1,3,6-hexanetricarbonitrile (HTCN), 1,4-dicyano-2-butene (DCB), fluorobenzene (FB), ethyldi(pro-2-y-1-yl) phosphate (EDP), and 5-methyl-5-propazyloxylcarbonyl-1,3-dioxane-2-one (MPOD) may be further included. At this time, the additive may be included in an amount of 0.1 to 5 wt% based on the total weight of the electrolyte.

[0147]

[0148] 4. Separator

[0149] The above separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Any separator commonly used as a separator in lithium secondary batteries can be used without any particular restrictions. In particular, a separator having low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may be used. In addition, a coated separator containing a ceramic component or a polymer material to secure heat resistance or mechanical strength may be used, and may optionally be used in a single-layer or multi-layer structure.

[0150]

[0151] Hereinafter, embodiments of the present invention will be described in more detail through examples. However, the following examples are merely preferred embodiments of the present invention, and the present invention is not limited to the following examples.

[0152]

[0153] Example 1

[0154] (1) Positive electrode manufacturing

[0155] (Preparation of positive electrode active material) Ni prepared using coprecipitation reaction 0.95 Ti 0.05 (OH)2 composition hydroxide precursor and LiOH·H2O as lithium raw material were weighed and mixed so that the molar ratio of lithium to the entire metal in the precursor (Li / Me) was 1.05 (+0.01, additional amount considering lithium volatile content), and then calcined at a temperature of 700℃ for 10 hours in an O2 atmosphere to obtain Li 1.024 Ni 0.927 Ti 0.049A cathode active material with an O2 composition was manufactured.

[0156] (After positive electrode manufacturing), the positive electrode active material: conductive material (carbon black, denka black): binder (PVDF, KF1100) = 95.5:1.5:2.5 wt% were mixed, and NMP (N-Methyl-2-pyrrolidone) was added to adjust the viscosity so that the solid content was about 70%, thereby manufacturing a positive electrode active material slurry. The manufactured slurry was applied onto a positive electrode current collector sheet, dried, and then rolled to manufacture a positive electrode.

[0157] (2) Cathode manufacturing

[0158] (Preparation of negative electrode active material) SiO x A negative electrode active material was prepared by mixing silicon oxide and graphite (artificial graphite) in a 3:97 wt% ratio. At this time, SiO x The average particle diameter (D50) of silicon oxide was 6 μm.

[0159] (Cathode manufacturing) After that, the above-mentioned negative electrode active material:conductive material (Super-C65):carboxymethylene cellulose (CMC):styrene-butadiene-styrene (SBR) = 95:1:1.5:2.5 wt% were mixed in water to prepare an aqueous negative electrode slurry. The prepared slurry was applied onto a negative electrode current collector sheet, dried, and then rolled to prepare a negative electrode.

[0160]

[0161] Example 2

[0162] In the preparation stage of the positive electrode active material, Ni 0.9 Ti 0.1 Using a hydroxide precursor with a composition of (OH)2, Li / Me ratio was adjusted to 1.1 (+0.01, additional amount considering lithium volatile matter). 1.048 Ni 0.857 Ti 0.095 Using a positive electrode active material with an O2 composition, and in the negative electrode active material preparation stage, SiO xA positive electrode and a negative electrode were manufactured in the same manner as in Example 1, except that silicon oxide and graphite (artificial graphite) were mixed in a 6:94 wt% ratio.

[0163]

[0164] Example 3

[0165] In the preparation stage of the positive electrode active material, Ni 0.85 Ti 0.15 Using a hydroxide precursor with a composition of (OH)2, Li / Me ratio was adjusted to 1.5 (+0.01, additional amount considering lithium volatile matter). 1.070 Ni 0.791 Ti 0.140 Using a positive electrode active material with an O2 composition, and in the negative electrode active material preparation stage, SiO x A positive electrode and a negative electrode were manufactured in the same manner as in Example 1, except that silicon oxide and graphite (artificial graphite) were mixed in a 10:90 wt% ratio.

[0166]

[0167] Example 4

[0168] In the preparation stage of the positive electrode active material, Ni 0.8 Ti 0.2 Using a hydroxide precursor with a composition of (OH)2, Li / Me ratio was adjusted to 1.2 (+0.01, additional amount considering lithium volatile matter). 1.091 Ni 0.727 Ti 0.182 Using a positive electrode active material with an O2 composition, and in the negative electrode active material preparation stage, SiO x A positive electrode and a negative electrode were manufactured in the same manner as in Example 1, except that silicon oxide and graphite (artificial graphite) were mixed in a ratio of 15:85 wt%.

[0169]

[0170] Comparative Example 1

[0171] In the preparation stage of the positive electrode active material, Li is prepared according to the usual manufacturing method. 1.13 [Ni0.35 Mn 0.65 ] 0.87 Using a positive electrode active material with an O2 composition, and in the negative electrode active material preparation stage, SiO x A positive electrode and a negative electrode were manufactured in the same manner as in Example 1, except that silicon oxide and graphite (artificial graphite) were mixed in a 6:94 wt% ratio.

[0172]

[0173] Comparative Example 2

[0174] In the preparation stage of the positive electrode active material, LiNi is prepared according to the conventional manufacturing method. 0.6 Co 0.2 Mn 0.2 A positive electrode and a negative electrode were manufactured in the same manner as in Example 1, except that a positive electrode active material of O2 composition was used and, in the negative electrode active material preparation step, SiOx silicon oxide and Graphite (artificial graphite) were mixed to a ratio of 6:94 wt%.

[0175]

[0176] Comparative Example 3

[0177] In the preparation stage of the positive electrode active material, LiNi is prepared according to the conventional manufacturing method. 0.8 Co 0.1 Mn 0.1 A positive electrode and a negative electrode were manufactured in the same manner as in Example 1, except that a positive electrode active material of O2 composition was used and, in the negative electrode active material preparation step, SiOx silicon oxide and Graphite (artificial graphite) were mixed to a ratio of 6:94 wt%.

[0178]

[0179] Comparative Example 4

[0180] In the preparation stage of the positive electrode active material, Ni 0.7 Ti 0.3 Using a hydroxide precursor with a composition of (OH)2, Li / Me ratio was adjusted to 1.3 (+0.01, additional amount considering lithium volatile matter). 1.13 Ni 0.609 Ti0.261 Using a positive electrode active material with an O2 composition, and in the negative electrode active material preparation stage, SiO x A positive electrode and a negative electrode were manufactured in the same manner as in Example 1, except that silicon oxide and graphite (artificial graphite) were mixed in a 6:94 wt% ratio.

[0181]

[0182] Comparative Example 5

[0183] In the positive electrode active material preparation step, a hydroxide precursor with a composition of Ni(OH)2 is used, and the Li / Me ratio is adjusted to 1.0 (+0.01, additional input considering lithium volatile matter) to use a positive electrode active material with a composition of LiNiO2, and in the negative electrode active material preparation step, SiO x A positive electrode and a negative electrode were manufactured in the same manner as in Example 1, except that silicon oxide and graphite (artificial graphite) were mixed in a 6:94 wt% ratio.

[0184]

[0185] Reference examples 1 to 4

[0186] A positive electrode and a negative electrode were manufactured in the same manner as in Example 1, except that the composition of the positive electrode active material and the negative electrode active material was changed as shown in Table 1 below.

[0187]

[0188] Reference Example 5

[0189] In the negative electrode active material preparation stage, SiO x A positive electrode and a negative electrode were manufactured in the same manner as in Example 2, except that silicon oxide and graphite (artificial graphite) were mixed in a ratio of 0:100 wt%.

[0190]

[0191] Reference Example 6

[0192] In the negative electrode active material preparation stage, SiO xA positive electrode and a negative electrode were manufactured in the same manner as in Example 2, except that silicon oxide and graphite (artificial graphite) were mixed in a 30:70 wt% ratio.

[0193]

[0194] Tables 1 and 2 below are tables summarizing the compositions of the positive electrode active materials and negative electrode active materials of the examples, comparative examples, and reference examples, and the results of the XRD property evaluation of the positive electrode active materials according to Experimental Example 1 described below.

[0195] Cathode active material composition xabcI(003) / I(104)cLattice constant (Å)Average particle size (D50, μm)Example 1Li 1.024 Ni 0.927 Ti 0.049 O20.0240.950.0501.5314.2412Example 2Li 1.048 Ni 0.857 Ti 0.095 O20.0480.90.101.4114.3212Example 3Li 1.070 Ni 0.791 Ti 0.140 O20.070.850.1501.1714.3812 Example 4Li 1.091 Ni 0.727 Ti 0.182 O20.0910.80.200.814.4412Comparative Example 1Li 1.13 [Ni 0.35 Mn 0.65 ] 0.87 O20.130.3500.651.6814.2612Comparative Example 2LiNi 0.6 Co 0.2 Mn 0.2 O200.600.41.714.2612Comparative Example 3LiNi 0.8 Co 0.1 Mn 0.1 O200.800.21.6814.2412 Comparative Example 4Li 1.13 Ni 0.609 Ti 0.261 O20.130.70.300.5914.5312Comparative example 5LiNiO201001.6414.2112Reference example 1Li 1.024 Ni 0.927 Ti 0.049O20.0240.950.0501.5314.2412 Reference Example 2Li 1.091 Ni 0.727 Ti 0.182 O20.0910.80.200.814.4412 Reference Example 3Li 1.091 Ni 0.727 Ti 0.182 O20.0910.80.200.814.4412 Reference Example 4Li 1.091 Ni 0.727 Ti 0.182 O20.0910.80.200.814.4412 Reference Example 5Li 1.048 Ni 0.857 Ti 0.095 O20.0480.90.101.4114.3212 Reference Example 6Li 1.048 Ni 0.857 Ti 0.095 O20.0480.90.101.4114.3212

[0196] Negative active material composition Example 1 SiOx:C=3:97 Example 2 SiOx:C=6:94 Example 3 SiOx:C=10:90 Example 4 SiOx:C=15:85 Comparative Example 1 SiOx:C=6:94 Comparative Example 2 SiOx:C=6:94 Comparative Example 3 SiOx:C=6:94 Comparative Example 4 SiOx:C=6:94 Comparative Example 5 SiOx:C=6:94 Reference Example 1 SiOx:C=15:85 Reference Example 2 SiOx:C=3:97 Reference Example 3 SiOx:C=6:94 Reference Example 4 SiOx:C=10:90 Reference Example 5 SiOx:C=0:100 Reference Example 6 SiOx:C=30:70

[0197] Tables 3 and 4 below are tables summarizing the results of evaluation of the positive electrode active material, positive and negative electrode properties, and electrochemical characteristics of full-cell batteries according to Experimental Examples 1, 2, and 3 described below.

[0198] AnodeAnode Initial efficiency difference between the anode and cathode (%)Initial charge capacity (mAh / g)Initial discharge capacity (mAh / g)Initial efficiency (%)Electrode density (g / cc)Initial charge capacity (mAh / g)Initial discharge capacity (mAh / g)Initial efficiency (%)Electrode density (g / cc)Example 1262.6242.492.33.6412.3376.291.21.651.1Example 2272.6244.089.53.6428.7388.190.51.651.0Example 3282.1245.787.13.6441.2394.089.31.652.2Example 4295.2251.285.13.6461.5405.387.81.652.7Comparative Example 1292.0269.792.43.0428.7388.190.51.651.9Comparative Example 2201.8180.689.53.6428.7388.190.51.651.0Comparative Example 3226.0206.391.33.6428.7388.190.51.650.8Comparative Example 4300.9249.883.03.5428.7388.190.51.657.5Comparative Example 5251.7234.393.13.6428.7388.190.51.652.6Reference Example 1262.6242.492.33.6461.5405.387.81.654.5Reference Example 2295.2251.285.13.6428.7388.191.21.656.1Reference Example 3295.2251.285.13.6441.2394.090.51.655.4Reference Example 4295.2251.285.13.6461.5405.389.31.654.2Reference Example 5272.6244.089.53.6387.0360.393.11.653.6 Reference example 6272.6244.089.53.6489.1412.384.31.655.2

[0199] Full Cell Electrochemical Characteristics N / P Ratio Energy Density (Wh / L) Lifetime Characteristics (%) Example 1 105813.497 Example 2 105816.297 Example 3 105820.596 Example 4 105830.196 Comparative Example 1 105566.098 Comparative Example 2 105600.295 Comparative Example 3 105706.893 Comparative Example 4 105746.2 drop Comparative Example 5 105686.3 drop Reference Example 1 105772.593 Reference Example 2 105782.194 Reference Example 3 105784.592 Reference Example 4 105788.591 Reference Example 5 105798.3 drop Reference Example 6 105799.1 drop

[0200]

[0201] Experimental Example 1: Evaluation of positive electrode active material and positive electrode properties

[0202] (1) Evaluation of the I(003) / I(104) peak intensity ratio and c-axis lattice constant of the positive electrode active material

[0203] The I(003) / I(104) peak intensity ratio and c-axis lattice constant were evaluated by analyzing the X-ray diffraction pattern, applying the peak broadening and Scherrer equation of XRD data.

[0204] (2) Evaluation of the average particle size (D50) of the positive electrode active material

[0205] For the active material powder, the particle size corresponding to 50% of the cumulative volume was measured using the laser diffraction method.

[0206] (3) Evaluation of initial bipolar efficiency

[0207] The positive electrodes and electrolytes manufactured in the examples, comparative examples, and reference examples were used in a solution of 1M LiPF6in EC:EMC=3:7 (vol%), with 1.0 vol% VC and 0.5 wt% LiBF4 added to the total amount of the electrolyte, and a half coin cell was manufactured using a PP separator and a lithium negative electrode (200 μm, Honzo metal).

[0208] After aging at 25°C for 12 hours, a charge-discharge test was conducted at 45°C. To evaluate the initial capacity, 200 mAh / g was used as the reference capacity, and the battery was charged to 4.65 V at a constant current of 0.1 C, then switched to a constant voltage and charged until the end current reached 0.05 C. After a rest time of 10 minutes after charging, the battery was discharged to 2.5 V at a constant current of 0.1 C, using 200 mAh / g as the reference capacity.

[0209] (4) Evaluation of positive electrode density

[0210] After measuring the thickness of the electrode, the volume was calculated and divided by the weight of the mixture to evaluate the positive electrode density.

[0211]

[0212] Experimental Example 2: Evaluation of Cathode Properties

[0213] (1) Evaluation of initial cathode efficiency

[0214] The negative electrodes and electrolytes manufactured in the examples, comparative examples, and reference examples were used in a solution of 1M LiPF6in EC:EMC=3:7 (vol%), with 1.0 vol% VC and 0.5 wt% LiBF4 added to the total amount of the electrolyte, and a half coin cell was manufactured using a PP separator and a lithium counter electrode (200 μm, Honzo metal).

[0215] After aging at 25℃ for 12 hours, a charge-discharge test was conducted at 45℃. For the initial capacity evaluation, 200 mAh / g was used as the reference capacity, and the battery was charged to 4.6 V at a constant current of 0.1C, then switched to constant voltage and charged until the end current reached 0.005C. After a rest time of 10 minutes after charging, the battery was discharged to 1.5 V at a constant current of 0.1C, using 200 mAh / g as the reference capacity.

[0216] (2) Evaluation of negative electrode density

[0217] After measuring the thickness of the electrode, the volume was calculated and divided by the weight of the mixture to evaluate the negative electrode density.

[0218]

[0219] Experimental Example 3: Evaluation of Full-Cell Battery Electrochemical Characteristics

[0220] The positive and negative electrodes manufactured in the examples, comparative examples, and reference examples, and the electrolyte were 1M LiPF6in EC:EMC=3:7 (vol%), with 1.0 vol% VC and 0.5 wt% LiBF4 added to the total amount of the electrolyte, and a pouch-type full cell was manufactured using a PP separator.

[0221] (1) N / P Ratio Evaluation

[0222] The N / P Ratio was evaluated by converting the measured cell capacity to the total discharge capacity of the cathode in the full cell.

[0223] (2) Energy density evaluation

[0224] After full-cell fabrication, the energy density was evaluated by converting the average voltage and capacity into battery volume, reflecting the electrode density and the thickness of the auxiliary materials used for each material. Here, electrode density was calculated using the electrode weight per unit area and the thickness at maximum rolling.

[0225] (3) Life characteristics evaluation

[0226] After full cell manufacturing, it was charged to 4.6 V at a constant current of 0.5 C at 45°C, then switched to constant voltage and charged until the end current reached 0.05 C. After a rest time of 10 minutes after charging, it was discharged at a constant current of 0.5 C until it reached 2.5 V. Under these charge / discharge cycle conditions, 30 charge / discharge cycles were performed, and the capacity retention rate of the 30th cycle was calculated compared to the first cycle.

[0227]

[0228] Referring to Tables 1 to 4, in the case of Examples 1 to 4, in which the composition of the positive electrode active material, the composition of the negative electrode active material, and the difference in initial efficiency between the positive and negative electrodes satisfied the range according to the present invention, it was confirmed that both the energy density and life characteristics of the full cell were implemented very excellently. In addition, it was confirmed that the positive electrode active materials of Examples 1 to 4 were obtained with a smaller I(003) / I(104) peak intensity ratio than those of Comparative Examples 1 to 4, which are conventional positive electrode active material compositions.

[0229] On the other hand, in Comparative Example 1 using a conventional positive electrode active material with a conventional lithium and manganese excess composition, and Comparative Examples 2 and 3 using a conventional positive electrode active material with a conventional NCM-based lithium metal oxide composition, it was confirmed that the battery energy density and life characteristics were significantly lower than those of the examples.

[0230] In the case of Comparative Example 4, an excess of lithium and a buffer metal element, Ti, were introduced, but as a result of introducing too much Ti, the I(003) / I(104) peak intensity ratio was obtained too small, the battery energy density was lower than in the example, and in particular, it was confirmed that the life characteristics were greatly deteriorated to the level of a drop.

[0231] In the case of Comparative Example 5, which is a conventional LiNiO2 composition, it was confirmed that the battery energy density was lower than that of the example, and in particular, the life characteristics were significantly deteriorated to the level of a drop.

[0232] In the case of Reference Examples 1 to 4, even if the positive electrode active material and the negative electrode active material themselves were appropriate, the combination was inappropriate, resulting in an excessively large initial efficiency difference between the positive electrode and the negative electrode, and it was confirmed that the battery energy density and life characteristics were deteriorated compared to the examples.

[0233] In the case of Reference Examples 5 and 6, the mixing weight ratio of silicon oxide and artificial graphite in the negative electrode active material was not properly controlled, resulting in an excessively large initial efficiency difference between the positive and negative electrodes, resulting in a decrease in battery energy density compared to the examples, and in particular, it was confirmed that the life characteristics were significantly deteriorated to the level of a drop.

[0234]

[0235] Although the preferred embodiments of the present invention have been described above, the present invention is not limited thereto, and various modifications can be made within the scope of the patent claims, the detailed description of the invention, and the attached drawings, and it is obvious that this also falls within the scope of the present invention.

[0236] Accordingly, the actual scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A lithium secondary battery comprising a positive electrode; a negative electrode; and an electrolyte, The above positive electrode includes a positive electrode active material layer, the positive electrode active material layer includes a positive electrode active material, and the positive electrode active material includes a lithium metal oxide having a lithium excess composition represented by the following chemical formula 1, The above negative electrode comprises a negative electrode active material layer, and the negative electrode active material layer comprises a silicon-based negative electrode active material, a lithium secondary battery: [Chemical Formula 1] The 1+x (Nor a M1 b M2 c ) 1-x O2 In the chemical formula 1, 0.02≤x≤0.1, 0.75≤a≤0.98, 0.02≤b≤0.25, 0≤c≤0.1, and a+b+c=1. M1 is a buffer metal element selected from the group consisting of Ti, Nb, W, Zr, V, Cr, Mo, Ta or a combination thereof, and M2 is a doping element selected from the group consisting of Al, B, Y, Co, Mn, Fe, Cu, Zn, Ga, Ge, Ru, Rh, Sn, Sb, Re, Ir, Pt, Pb, Bi, Na, K, Rb, Cs, Ca, Sr, Ba, Mg, Si, Sc or a combination thereof.

2. In paragraph 1, A lithium secondary battery, wherein the absolute value of the initial efficiency difference between the positive electrode and the negative electrode is 3% or less.

3. In paragraph 1, A lithium secondary battery, wherein the lithium metal oxide has a ratio of the peak intensity of the (003) plane to the peak intensity of the (104) plane (I(003) / I(104)) of 0.7 to 1.6 when analyzed by X-ray diffraction.

4. In paragraph 1, A lithium secondary battery wherein the lithium metal oxide has a c-axis lattice constant of 14.23 to 14.5 Å.

5. In paragraph 1, A lithium secondary battery having an initial efficiency of 80 to 93% of the above cathode.

6. In paragraph 1, A lithium secondary battery wherein the silicon-based negative electrode active material is silicon, silicon oxide, a silicon-carbon composite or a combination thereof.

7. In paragraph 1, A lithium secondary battery, wherein the negative electrode active material layer further comprises a carbon-based negative electrode active material.

8. In paragraph 7, A lithium secondary battery wherein the carbon-based negative electrode active material is natural graphite, artificial graphite or a combination thereof.

9. In paragraph 7, A lithium secondary battery wherein the silicon-based negative electrode active material is silicon, silicon oxide or a combination thereof, and a weight ratio of the silicon-based negative electrode active material and the carbon-based negative electrode active material (silicon-based negative electrode active material:carbon-based negative electrode active material) is 2:98 to 20:

80.

10. In paragraph 1, A lithium secondary battery having an initial efficiency of the above cathode of 87 to 92%.

11. In paragraph 1, The above lithium secondary battery is a lithium secondary battery having an N / P ratio of 100 to 130%.

12. In paragraph 1, A lithium secondary battery wherein the positive electrode active material has an average particle diameter (D50) of 3 to 12 μm.

13. In paragraph 1, The above cathode active material has a BET surface area of ​​1 to 10 m 2 / g lithium secondary battery.

14. In paragraph 1, The above positive electrode is a lithium secondary battery having an electrode density of 3.0 to 4.0 g / cc.

15. In paragraph 1, A lithium secondary battery wherein the silicon-based negative electrode active material has an average particle diameter (D50) of 3 to 8 μm.

16. In paragraph 1, The above negative electrode is a lithium secondary battery having an electrode density of 1.5 to 1.8 g / cc.

Images