Cathode active material for lithium secondary battery, manufacturing method therefor and lithium secondary battery including same

Abstract

The present invention relates to a cathode active material for a lithium secondary battery, the material being a lithium transition metal oxide containing an excessive amount of lithium, an excessive amount of nickel and a buffer metal element, wherein the lithium transition metal oxide has a lithium to lithium transition metal oxide molar ratio of 1.02 to 1.1 and a nickel to transition metal molar ratio of 0.75 or more, the lithium transition metal oxide has a structure in which a lithium layer and a transition metal layer are alternately stacked, and at least a part of a lithium lattice site in the lithium layer is substituted with a buffer metal element so that anisotropic shrinkage and expansion are suppressed during charging and discharging.

Description

Positive electrode active material for lithium secondary batteries, method for producing the same, and lithium secondary batteries comprising the same

[0001] The present invention relates to a positive electrode active material for a lithium secondary battery, a method for producing the same, and a lithium secondary battery including the same.

[0002]

[0003] As the scope of application of lithium secondary batteries expands from small electronic devices to electric vehicles and power storage devices, the demand for cathode materials with high energy density and excellent lifespan characteristics is increasing.

[0004] For high energy density, conventional nickel-cobalt-manganese ternary NCM cathode materials have adopted the direction of increasing capacity by increasing nickel content, but there is a problem of deterioration in life characteristics due to anisotropic expansion / contraction resulting from increased nickel content.

[0005] In addition, lithium-rich layered cathode materials (Li) are being studied as next-generation cathode materials. 1+x M 1-x -O2) is attracting attention as a next-generation cathode active material candidate due to its high lithium content within the structure and its ability to utilize oxygen redox reactions, which results in very high charge / discharge capacity. However, it has problems such as low discharge capacity in actual use after the activation process, low true density of the active material itself, and poor particle packing due to plate-like crystal growth, resulting in a low actual energy density.

[0006] Therefore, there is a need for a new cathode material that can simultaneously achieve high energy density and excellent lifespan characteristics.

[0007]

[0008] Accordingly, one object of the present invention is to provide a positive electrode active material for a lithium secondary battery of a novel composition capable of simultaneously implementing high energy density and excellent lifespan characteristics, a method for producing the same, and a lithium secondary battery including the same.

[0009]

[0010] One embodiment of the present invention provides a positive electrode active material for a lithium secondary battery, which is a lithium transition metal oxide containing an excess of lithium, nickel, and a buffer metal element, wherein the lithium transition metal oxide has a molar ratio of lithium to the lithium transition metal oxide of 1.02 to 1.1 and a molar ratio of nickel to the transition metal of 0.75 or more, and wherein the lithium transition metal oxide has a structure in which lithium layers and transition metal layers are alternately laminated as a basic skeleton, wherein some of the buffer metal elements in the transition metal layers are substituted into the lithium layers, and some of the lithium ions in the lithium layers are substituted into the transition metal layers, thereby suppressing anisotropic shrinkage and expansion during charging and discharging.

[0011] Additionally, some of the nickel ions in the transition metal layer may be substituted into the lithium layer.

[0012] The above lithium transition metal oxide allows lithium ions to move through the lithium layer and transition metal layer during charging and discharging.

[0013] The above buffer metal element may be a transition metal element that does not have an atomic electron in a d orbital.

[0014] The above buffer metal element may be Ti, Nb, W, Zr, V, Cr, Mo, Ta or a combination thereof.

[0015] The content of the above buffer metal element may be 2 to 25 mol% based on the total mole number of transition metals.

[0016] The content of the above buffer metal element may be 6 to 15 mol% based on the total mole number of transition metals.

[0017] The above lithium transition 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.

[0018] The above lithium transition metal oxide may have a difference between the maximum and minimum values ​​of the c-axis lattice constant of 0.6 Å or less during charging until the termination voltage becomes 4.6 V during the first charging process.

[0019] The above lithium transition metal oxide may have a change rate of the c-axis lattice constant of 5% or less during charging until the termination voltage becomes 4.6 V during the first charging process.

[0020] The above lithium transition metal oxide may have a c-axis lattice constant of 13.8 Å or more after being charged until the termination voltage becomes 4.6 V during the first charging process.

[0021] The above lithium transition metal oxide may have a sphericity of 0.5 or less.

[0022] The above lithium transition metal oxide may not contain cobalt and manganese.

[0023] The above transition metal oxide can be represented by the following chemical formula 1.

[0024] [Chemical Formula 1]

[0025] Li 1+x (Ni a M1 b M2 c ) 1-x O2

[0026] 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, 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.

[0027]

[0028] Another embodiment of the present invention provides a method for producing a cathode active material for a lithium secondary battery, comprising: forming a mixture by mixing a nickel-containing transition metal compound, a buffer metal raw material, and a lithium raw material; and calcining the mixture to form a lithium transition metal oxide, wherein in the forming of the mixture, the amount of the nickel-containing transition metal compound input is 75 mol% or more based on the total number of moles of the nickel-containing transition metal compound and the buffer metal raw material, and the amount of the lithium raw material input is adjusted so that the molar ratio of lithium to the total amount of transition metal contained in the nickel-containing transition metal compound and the buffer metal raw material (Li / Me) is 1.05 to 1.25.

[0029] The above buffer metal raw material may be an oxide, hydroxide, carbonate, sulfate, phosphate, or a combination thereof containing a buffer metal element, or a combination thereof.

[0030] The above nickel-containing transition metal compound may be Ni(OH)2, NiO, Ni2O3, or a combination thereof.

[0031] In the step of forming the mixture, the amount of the buffer metal raw material may be 2 to 25 mol% based on the total number of moles of the nickel-containing transition metal compound and the buffer metal raw material.

[0032] The above firing can be performed at a temperature of 650°C to 900°C.

[0033]

[0034] Another embodiment of the present invention provides a positive electrode for a lithium secondary battery comprising the positive electrode active material described above.

[0035] Another embodiment of the present invention provides a lithium secondary battery including the positive electrode for the lithium secondary battery.

[0036]

[0037] A cathode active material for a lithium secondary battery according to one embodiment of the present invention contains an excess of nickel and an excess of lithium, thereby enabling the use of not only a nickel-based cation oxidation / reduction reaction but also an anion (oxygen) oxidation / reduction reaction, thereby enabling the implementation of capacity characteristics and high energy density.

[0038] In addition, the cathode active material for a lithium secondary battery according to one embodiment of the present invention can improve structural stability by containing a buffer metal element, thereby replacing at least a portion of the lithium lattice sites within the lithium layer with the buffer metal element. Accordingly, anisotropic shrinkage and expansion of the active material during charging and discharging are suppressed, enabling the implementation of excellent life characteristics.

[0039]

[0040] Figure 1 is a conceptual diagram of a positive electrode active material for a lithium secondary battery according to one embodiment of the present invention.

[0041] Figure 2 is a SEM image of a positive electrode active material manufactured according to Example 2.

[0042] Figure 3 is a SEM image of a positive electrode active material manufactured according to Example 3.

[0043] Figure 4 is a SEM image of a positive electrode active material manufactured according to Example 4.

[0044] Figure 5 is an SEM image of a positive electrode active material manufactured according to Comparative Example 1.

[0045] Figure 6 is an SEM image of a positive electrode active material manufactured according to Comparative Example 5.

[0046]

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] Also, unless otherwise stated, % means weight%, and 1 ppm is 0.0001 weight%.

[0052] 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.

[0053] 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.

[0054]

[0055] 1. Positive active material

[0056] Figure 1 is a conceptual diagram of a positive electrode active material for a lithium secondary battery according to one embodiment of the present invention. Hereinafter, the positive electrode active material according to the present invention will be described with reference to Figure 1.

[0057] According to one embodiment of the present invention, a cathode active material for a lithium secondary battery comprises a lithium transition metal oxide containing excess lithium, nickel, and a buffer metal element. Accordingly, excellent capacity, high energy density, and lifespan characteristics can be achieved simultaneously.

[0058] Specifically, since the lithium transition metal oxide contains an excess of lithium and nickel, not only nickel-based cation oxidation / reduction reactions but also anion (oxygen) oxidation / reduction reactions can be utilized, enabling the implementation of capacity characteristics and high energy density.

[0059] In addition, since the lithium transition metal oxide contains a buffer metal element, at least a portion of the lithium lattice sites within the lithium layer may be replaced by some of the buffer metal elements, thereby improving structural stability. Accordingly, anisotropic shrinkage and expansion of the active material during charge and discharge may be suppressed, enabling the implementation of excellent cycle-life characteristics. In addition, since the buffer metal element prefers to be located primarily within the lithium layer, this, coupled with the substitution of some of the nickel ions within the transition metal layer into the lithium layer due to the introduction of excess lithium, induces a disordered cation-mixed structure. This disordered cation-mixed structure may facilitate the movement of lithium ions, thereby contributing to the implementation of high capacity and high energy density.

[0060] More specifically, the lithium transition metal oxide according to the present invention may have a basic skeleton structure in which lithium layers and transition metal layers (represented by nickel) are alternately laminated. At this time, the buffer metal element introduced into the lithium transition metal oxide may prefer a lithium 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 an excess amount of 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 an excess amount of lithium may cause some of the lithium ions in the lithium layer to be replaced into the transition metal layer.

[0061] That is, the lithium transition 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.

[0062] In the conventional layered lithium transition 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, nickel cations among transition metals have similar ionic radii to lithium ions, so there were cases where nickel cations in the transition metal layer occupied lithium sites in the lithium layer, which was 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.

[0063] On the other hand, the lithium transition metal oxide according to the present invention can 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, and at the same time, lithium is contained in an excess amount compared to a conventional general composition. Accordingly, (unlike the general two-dimensional movement of lithium ions through the lithium layer), lithium ions can move three-dimensionally (i.e., insertion and de-insertion) not only through the lithium layer but also through the transition metal layer during charging and discharging, so that the lithium ion movement efficiency can be maximized. 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, so that the capacity characteristics and energy density of the battery can be maximized.

[0064] In order to realize a structure in which lithium in the lithium layer and buffer metal elements in the transition metal layer are randomly mixed with each other, introduction of an excess amount of lithium and introduction of an appropriate amount of buffer metal elements are required. In addition, the existence of such a cation randomly mixed structure can be confirmed by the fact that the ratio of the peak intensity of the (003) plane to the peak intensity of the (104) plane (I(003) / I(104)) obtained in X-ray diffraction analysis is within the range according to the present invention, as described below.

[0065] At this time, the buffer metal element may be a transition metal element that does not have an atomic electron in the d orbital. When the buffer metal element is a transition metal element that does not have an atomic electron in the d orbital, the buffer metal element in the transition metal layer can be easily substituted for a lithium site in the lithium layer.

[0066] The buffer metal element may be, more specifically, Ti, Nb, W, Zr, V, Cr, Mo, Ta or a combination thereof, but is not necessarily limited thereto.

[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 transition metal oxide according to the present invention will be described in more detail.

[0070] The lithium transition metal oxide according to the present invention may have a molar ratio of lithium to the lithium transition metal oxide of 1.02 to 1.1, and more specifically, 1.03 to 1.06. If the molar ratio of lithium is too low, the utilization of the anion (oxygen) oxidation / reduction reaction is reduced, and lithium substitution within the transition metal layer hardly occurs, making it impossible to implement the aforementioned disordered mixed structure, so that the effect of improving the capacity and energy density may be minimal. If the molar ratio of lithium is too high, a problem of phase stability may occur due to excessive occurrence of the anion (oxygen) oxidation / reduction reaction, which may deteriorate the life characteristics. In particular, in the lithium transition metal oxide according to the present invention, the lithium content within the above range may not be added in a small amount in consideration of the amount of lithium volatilized during the actual firing process, but may be adjusted so that the content of lithium within the actual lithium transition metal oxide is introduced within the above range.

[0071] The lithium transition metal oxide according to the present invention may have a molar ratio of nickel to transition metal of 0.75 or greater, and more specifically, 0.80 or greater. When the molar ratio of nickel to transition metal satisfies the above range, nickel-based cation oxidation / reduction reactions can be sufficiently utilized, thereby improving capacity and energy density.

[0072] In addition, the content of the buffer metal element may be 2 to 25 mol% based on the total mole number of transition metals, and more specifically, 6 to 15 mol%. If the content of the buffer metal element is too low, the life characteristics, capacity characteristics, and energy density improvement effects due to the introduction of the buffer metal element may be minimal. If the content of the buffer metal element is too high, the disordered mixing between the buffer metal and lithium may occur excessively, causing the layered crystal structure to deteriorate, which may rather deteriorate the life characteristics, capacity characteristics, and energy density.

[0073]

[0074] Hereinafter, the X-ray diffraction analysis properties of the lithium transition metal oxide according to the present invention will be described in more detail.

[0075] The lithium transition 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, more specifically, 0.9 to 1.5, when analyzed by X-ray diffraction. 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 mixing ratio of transition metal cations in the lithium layer, and a smaller value indicates a larger mixing ratio of transition metal cations in the lithium layer. The lithium transition 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 a conventional positive electrode material having a conventional composition, since a buffer metal element other than nickel is further substituted in the lithium layer. However, if the ratio of peak intensities on the (003) plane (I(003) / I(104)) is too small, it means that the buffer metal element content is excessive, and cation mixing may occur excessively, which may deteriorate the life characteristics, capacity characteristics, and energy density.

[0076] In addition, the lithium transition metal oxide may have a c-axis lattice constant (before charging) of 14.23 to 14.5 Å, more specifically, 14.27 to 14.44 Å. In the composition according to the present invention, the c-axis lattice constant (before charging) may vary depending on the amount of the buffer metal element introduced, and when the c-axis lattice constant satisfies the above range, the aforementioned effect of improving the battery electrochemical characteristics may be preferably implemented.

[0077] Additionally, the lithium transition metal oxide may have a difference between the maximum and minimum values ​​of the c-axis lattice constant during charging of 0.6 Å or less, and more specifically, 0.55 Å or 0.5 Å or less, until the termination voltage becomes 4.6 V during the first charging process.

[0078] In addition, the lithium transition metal oxide may have a change rate of the c-axis lattice constant during charging of 5% or less, and more specifically, 4.5%, 4%, or 3.5% or less, until the end voltage becomes 4.6 V during the first charging process. In the present specification, the change rate of the c-axis lattice constant may mean the percentage (%) of the difference between the maximum value and the minimum value of the c-axis lattice constant during charging.

[0079] Additionally, the lithium transition metal oxide may have a c-axis lattice constant of 13.8 Å or more, and more specifically, 13.85 or 13.9 Å or more, after being charged until the termination voltage becomes 4.6 V during the first charging process.

[0080] More specifically, the increase or decrease in the c-axis lattice constant during charging and discharging of lithium transition metal oxides can represent the degree of anisotropic expansion and contraction. Typically, as charging progresses in lithium transition metal oxides, the c-axis lattice constant tends to increase and then decrease. When charging is fully complete, the c-axis lattice constant after charging may decrease compared to the c-axis lattice constant before charging.

[0081] At this time, the lithium transition metal oxide according to the present invention can reduce the change in the c-axis lattice constant during charging due to the introduction of a buffer metal element. Accordingly, the change trend in the c-axis lattice constant can satisfy the above range. Accordingly, the structural stability of the active material can be improved, thereby improving battery life characteristics.

[0082]

[0083] Meanwhile, the lithium transition metal oxide according to the present invention may have a sphericity of 0.5 or less. Conventional cathode active materials required an additional process to increase the sphericity in order to increase the energy density by improving the electrode density and to improve the initial efficiency and lifespan characteristics by reducing side reactions with the electrolyte. On the other hand, the lithium transition metal oxide according to the present invention has excellent capacity, energy density, and lifespan characteristics due to the introduction of excess lithium, excess nickel, and buffer metal elements, and thus can realize excellent electrochemical characteristics without a separate improvement in sphericity. In the present specification, the sphericity is a numerical expression of the degree to which a particle is close to a sphere, and refers to a value obtained by dividing the perimeter of a circle having the same area as a particle projection shape by the actual perimeter of the particle projection shape using a flow-type particle analyzer. This sphericity can be measured using an analyzer for obtaining an optical image (Fluid Imaging Technologies, Flowcam 8100) and analysis S / W (visual spreadsheet).

[0084] In addition, the lithium transition metal oxide may not contain cobalt and manganese. Conventional cathode active materials have introduced cobalt and manganese in addition to nickel at appropriate levels to improve capacity and cycle life characteristics. On the other hand, the lithium transition metal oxide according to the present invention can realize excellent electrochemical characteristics even without cobalt and manganese by introducing excess lithium, excess nickel, and buffer metal elements. However, it is obvious that the lithium transition metal oxide according to the present invention does not completely exclude the possibility of using cobalt and manganese.

[0085] The above transition metal oxide can be more specifically represented by the following chemical formula 1.

[0086] [Chemical Formula 1]

[0087] Li 1+x (Ni a M1 b M2 c )1-x O2

[0088] 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.

[0089] In the lithium transition 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 life characteristics.

[0090] In the lithium transition 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, nickel-based cation oxidation / reduction reactions cannot 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.

[0091] In the lithium transition 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, causing excessive disordered mixing between the buffer metal and lithium, which may rather deteriorate the life characteristics, capacity characteristics and energy density.

[0092] In the lithium transition 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 and 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. 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.

[0093]

[0094] 2. Method for manufacturing positive electrode active material

[0095] Another embodiment of the present invention provides a method for producing a cathode active material for a lithium secondary battery, comprising: forming a mixture by mixing a nickel-containing transition metal compound, a buffer metal raw material, and a lithium raw material; and calcining the mixture to form a lithium transition metal oxide, wherein in the forming of the mixture, the amount of the nickel-containing transition metal compound input is 75 mol% or more based on the total number of moles of the nickel-containing transition metal compound and the buffer metal raw material, and the amount of the lithium raw material input is adjusted so that the molar ratio of lithium to the total amount of transition metal contained in the nickel-containing transition metal compound and the buffer metal raw material (Li / Me) is 1.05 to 1.25.

[0096] Hereinafter, a method for manufacturing a positive electrode active material for a lithium secondary battery according to another embodiment of the present invention will be described step by step.

[0097]

[0098] First, a mixture is formed by mixing a nickel-containing transition metal compound, a buffer metal raw material, and a lithium raw material.

[0099] At this time, the amount of the nickel-containing transition metal compound to be added may be 75 mol% or more, and more specifically, 80 mol% or more, based on the total moles of the nickel-containing transition metal compound and the buffer metal raw material. Accordingly, the content of nickel in the final product, the lithium transition metal oxide, may be 75 mol% or more or 80 mol% or more based on the total moles of the transition metal. The technical significance of controlling the nickel content in the transition metal is the same as mentioned above, and thus is omitted.

[0100] In addition, the amount of the buffer metal raw material may be 2 to 25 mol% based on the total moles of the nickel-containing transition metal compound and the buffer metal raw material, and more specifically, 6 to 15 mol%. The technical significance of controlling the content of the buffer metal raw material is the same as that of controlling the content of the buffer metal element mentioned above, and thus is omitted.

[0101] In addition, the amount of the lithium raw material input can be adjusted so that the molar ratio of lithium to the total amount of transition metal contained in the nickel-containing transition metal compound and buffer metal raw material (Li / Me) is 1.05 to 1.25. Accordingly, a lithium transition metal oxide having a lithium-excess composition according to the present invention can be formed.

[0102] Meanwhile, the nickel-containing transition metal compound may be Ni(OH)2, NiO, Ni2O3, or a combination thereof, but is not necessarily limited thereto.

[0103] In addition, 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. At this time, 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.

[0104] In addition, 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 Li2CO3, LiNO3, LiNO2, LiOH, LiOHㆍH2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, Li3C6H5O7, or a combination thereof, but is not limited thereto.

[0105]

[0106] Next, the mixture is calcined to form a lithium transition metal oxide.

[0107] At this time, the sintering can be performed at a temperature of 650°C to 900°C. If the sintering temperature is too low, the layered lithium transition metal oxide may not be formed properly. If the sintering temperature is too high, the electrochemical properties may deteriorate due to oversintering.

[0108] Additionally, the above-mentioned calcination can be performed for 3 to 15 hours. If the calcination time is too short, the layered lithium transition metal oxide may not be formed properly. If the calcination time is too long, the electrochemical properties may deteriorate due to over-calcination.

[0109] In addition, the atmosphere during the above firing is not particularly limited, and can be performed in an air or oxygen (O2) atmosphere, for example.

[0110]

[0111] Thus, a lithium transition metal oxide according to the present invention can be formed. In this way, the lithium transition metal oxide according to the present invention can be obtained through a simple process of solid-state mixing and calcination of raw materials without the need for a separate wet co-precipitation process, thereby providing economic advantages.

[0112]

[0113] 3. Cathode ray and lithium secondary battery

[0114] Another embodiment of the present invention provides a positive electrode for a lithium secondary battery comprising the positive electrode active material described above.

[0115] More specifically, the positive electrode may include a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, and including the positive electrode active material described above.

[0116] 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 adhesion of the positive electrode active material. For example, the positive electrode current collector may be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0117] The above-described positive electrode active material layer may include a binder and / or a conductive material together with the above-described positive electrode active material.

[0118] At this time, the binder plays a role of improving the adhesion between the positive electrode active material particles and the adhesive strength between the positive electrode active material and the positive electrode current collector. Specific examples 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 kind alone or a mixture of two or more kinds thereof may be used, 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.

[0119] And, the conductive material is used to provide conductivity to the electrode, and in the battery to be constructed, as long as it does not cause a chemical change and has electronic conductivity, it can be used without any special 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 among these may be used, 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.

[0120] 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.

[0121] 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.

[0122] 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.

[0123] 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.

[0124]

[0125] Another embodiment of the present invention provides a lithium secondary battery including the positive electrode for a lithium secondary battery as described above.

[0126] The above lithium secondary battery may more specifically include a positive electrode; a negative electrode; a separator; and an electrolyte.

[0127] 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.

[0128] The above negative electrode may include a negative electrode current collector and a negative electrode active material layer positioned on the negative electrode current collector.

[0129] 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.

[0130] 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.

[0131] As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples thereof include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and 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, and Al alloy; metallic oxides capable of doping and dedoping lithium, such as SiOβ (0 < β < 2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites comprising the metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or a mixture of two or more of these may be used. In addition, a metallic 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 carbonaceous material. Representative examples of low-crystalline carbon include soft carbon and hard carbon, and representative examples of high-crystalline carbon include natural graphite or artificial graphite in the form of amorphous, plate-like, flaky, spherical, or fiber-like forms, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch derived cokes.

[0132] The above binder and conductive material may be the same as those described above for the positive electrode.

[0133]

[0134] 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.

[0135]

[0136] 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.

[0137] Specifically, the organic liquid electrolyte may include an organic solvent and a lithium salt.

[0138] 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.

[0139] 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 2.0 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.

[0140] In addition to the electrolyte components, the electrolyte may further include one or more additives, such as 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, for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery. At this time, the additives may be included in an amount of 0.1 to 5 wt% based on the total weight of the electrolyte.

[0141] As described above, a lithium secondary battery including a cathode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention, and is therefore useful in portable devices such as mobile phones, laptop computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0142] Accordingly, another embodiment of the present invention provides a battery module including the lithium secondary battery as a unit cell and a battery pack including the same.

[0143] The above battery module or battery pack can be used as a power source for one or more medium- to large-sized devices, such as a power tool; an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0144]

[0145] 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.

[0146]

[0147] Example 1

[0148] (1) Manufacturing of positive electrode active material

[0149] (Mixed) LiOH·H2O powder was mixed using a ball mill so that the molar ratio of lithium to the total amount of transition metal contained in the Ni(OH)2 powder, TiO-2 powder, and Ni(OH)2 powder and TiO-2 powder (Li / Me) was 1.05+0.02 (wherein +0.02 is an additional amount added in consideration of the amount of lithium volatilized during the sintering process, and the same applies to Examples 2 to 4 and Comparative Examples 1, 7, and 8). At this time, the molar ratio of the Ni(OH)2 powder and the TiO2 powder was 95:5.

[0150] (After calcination), the mixture was calcined at a temperature of 700℃ for 10 hours under an O2 atmosphere, and Li 1.024 Ni 0.927 Ti 0.049 A lithium transition metal oxide with an O2 composition was formed.

[0151] (2) Lithium secondary battery manufacturing

[0152] The slurry for manufacturing the electrode plate was mixed with the above-mentioned positive electrode active material: conductive material (carbon black, Denka black): binder (PVDF, KF1100) = 92.5:3.5:4 wt%, and the viscosity was adjusted so that the solid content was approximately 30% by adding NMP (N-Methyl-2-pyrrolidone). The manufactured slurry was coated on a 15 μm thick Al foil using a doctor blade, and then dried and rolled. The electrode loading was 14.6 mg / cm 2 and the rolling density (25℃, 20kN) was 3.1 g / cm 3 It was.

[0153] The electrolyte was 1M LiPF6in EC:EMC=3:7(vol%), with 1.0vol% VC and 0.5wt% LiBF4 added to the total amount of the electrolyte, and a coin cell was manufactured using a PP separator and a lithium negative electrode (200㎛, Honzo metal).

[0154]

[0155] Example 2

[0156] In the mixing step, a positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the molar ratio of lithium to the total amount of transition metal (Li / Me) was set to 1.07+0.02 and the molar ratio of Ni(OH)2 powder to TiO2 powder was set to 93:7.

[0157]

[0158] Example 3

[0159] In the mixing step, the molar ratio of lithium to the total amount of transition metal (Li / Me) was set to 1.10+0.02, and the molar ratio of Ni(OH)2 powder to TiO2 powder was set to 90:10, and the same procedure as Example 1 was followed to manufacture a cathode active material and a lithium secondary battery.

[0160]

[0161] Example 4

[0162] In the mixing step, the molar ratio of lithium to the total amount of transition metal (Li / Me) was set to 1.20+0.02, and the molar ratio of Ni(OH)2 powder to TiO2 powder was set to 80:20, and the same procedure as Example 1 was followed to manufacture a cathode active material and a lithium secondary battery.

[0163]

[0164] Comparative Example 1

[0165] In the mixing step, the molar ratio of lithium to the total amount of transition metal (Li / Me) was set to 1.30+0.02, and the molar ratio of Ni(OH)2 powder to TiO2 powder was set to 70:30, and the same procedure as Example 1 was followed to manufacture a cathode active material and a lithium secondary battery.

[0166]

[0167] Comparative Example 2

[0168] In the mixing step, the molar ratio of lithium to the total amount of transition metal (Li / Me) was set to 1.40+0.02, and the molar ratio of Ni(OH)2 powder to TiO2 powder was set to 60:40, and the positive electrode active material and lithium secondary battery were manufactured in the same manner as in Example 1.

[0169]

[0170] Comparative Example 3

[0171] In the mixing step, the molar ratio of lithium to the total amount of transition metal (Li / Me) was set to 1.00+0.02, and the molar ratio of Ni(OH)2 powder to TiO2 powder was set to 100:0, and the same procedure as Example 1 was followed to manufacture a cathode active material and a lithium secondary battery.

[0172]

[0173] Comparative Example 4

[0174] Li(Ni) by conventional wet precipitation method 0.6 Co 0.2- Mn 0.2 ) A lithium transition metal oxide cathode active material having an O2 composition was manufactured, and a lithium secondary battery was manufactured in the same manner as in Example 1.

[0175]

[0176] Comparative Example 5

[0177] Li(Ni) by conventional wet precipitation method 0.8 Co 0.1 Mn 0.1 ) A lithium transition metal oxide cathode active material having an O2 composition was manufactured, and a lithium secondary battery was manufactured in the same manner as in Example 1.

[0178]

[0179] Comparative Example 6

[0180] Li(Ni) by conventional wet precipitation method 0.9 Co 0.05- Mn 0.05) A lithium transition metal oxide cathode active material having an O2 composition was manufactured, and a lithium secondary battery was manufactured in the same manner as in Example 1.

[0181]

[0182] Comparative Example 7

[0183] Li by conventional wet precipitation method 1.13 (Ni 0.3 Mn 0.57 ) A lithium transition metal oxide cathode active material having an O2 composition was manufactured, and a lithium secondary battery was manufactured in the same manner as in Example 1.

[0184]

[0185] Comparative Example 8

[0186] A nickel-titanium hydroxide precursor aqueous solution was prepared by adding NiSO4, a nickel precursor, and TiSO4, a titanium precursor, to water in a molar ratio of 94:06. While stirring the aqueous solution, a sodium hydroxide aqueous solution was slowly added dropwise while stirring to neutralize the precursor aqueous solution, thereby producing nickel-titanium hydrate, Ni. 0.94 Ti 0.06 (OH)2 was precipitated. LiOH was mixed with the precursor thus obtained at a molar ratio of 1.02 and calcined in an oxygen atmosphere at 755°C for 30 hours.

[0187]

[0188] Experimental Example 1: SEM image of positive electrode active material

[0189] SEM (scanning electron microscope) images of the positive electrode active materials manufactured according to Examples 2 to 4, Comparative Example 1, and Comparative Example 5 were observed, and are shown in FIGS. 2 to 6, respectively.

[0190] Referring to FIGS. 2 to 6, it was confirmed that the positive electrode active materials according to Examples 2 to 4 and Comparative Example 1 had a lower degree of sphericity of particles compared to the conventional positive electrode material of a typical composition manufactured through a wet co-precipitation process.

[0191] On the other hand, it was confirmed that the positive electrode active material according to Comparative Example 5 had a good degree of sphericity as a result of being manufactured through a wet co-precipitation process.

[0192]

[0193] Experimental Example 2: Evaluation of the properties of positive electrode active materials

[0194] (1) Evaluation of the I(003) / I(104) peak intensity ratio by X-ray diffraction analysis

[0195] After measuring the X-ray diffraction phenomenon using an XRD measuring device (X-ray diffractometer), the (003) and (104) diffraction peak intensity ratio (I(003) / I(104)) was obtained from the diffraction pattern results.

[0196] (2) Evaluation of the c-axis lattice constant change profile during the first charging process

[0197] For each of the comparative examples, after manufacturing a coin half-cell, the cell was charged until the end voltage reached 4.7 V, and the electrodes were collected to evaluate the c-axis lattice constant change profile. The c-axis lattice constant before charging, the maximum c-axis lattice constant during charging, and the c-axis lattice constant (minimum value) after charging were evaluated. Here, the maximum value was selected as 4.4 V after confirming the voltage at which the maximum value was shown based on the in-situ XRD results. In addition, the amount of change in the c-axis lattice constant was evaluated through the difference between the maximum and minimum values ​​of the c-axis lattice constant, and the rate of change in the c-axis lattice constant was evaluated through the percentage of the amount of change in the c-axis lattice constant with respect to the maximum value of the c-axis lattice constant.

[0198] (3) Evaluation of sphericity

[0199] The sphericity was evaluated by dividing the perimeter of a circle with the same area as the particle projection shape by the actual perimeter of the particle projection shape using a flow particle analysis device. At this time, the measurement was performed using an analyzer for optical image acquisition (Fluid Imaging Technologies, Flowcam 8100) and analysis S / W (visual spreadsheet).

[0200] Overall composition xabc Example 1Li 1.024 Ni 0.927 Ti 0.049 O20.0240.950.050Example 2Li 1.034 Ni 0.899 Ti 0.068 O20.0340.930.070Example 3Li 1.048 Ni 0.857 Ti 0.095 O20.0480.900.100 Example 4Li 1.091 Ni 0.727 Ti 0.182 O20.0910.800.200Comparative example 1Li 1.13 Ni 0.609 Ti 0.261 O20.130.700.300 Comparative Example 2Li 1.167 Ni 0.5 Ti 0.333 O20.1670.600.400Comparative Example 3LiNiO201.000.000Comparative Example 4Li(Ni 0.6 Co 0.2- Mn 0.2 )O200.600.4Comparative example 5Li(Ni 0.8 Co 0.1 Mn 0.1 )O200.800.2Comparative example 6Li(Ni 0.9 Co 0.05 Mn 0.05 )O200.900.1Comparative example 7Li 1.13 (Ni 0.3 Mn 0.57 )O20.130.3400Comparative example 8LiNi 0.94 Ti 0.06 O200.940.060

[0201] (In Table 1, x, a, b, c are the chemical formulas of lithium transition metal oxides Li 1+x (Ni a Ti b M2 c ) 1-x It is a value based on the assumption that O2 and a+b+c=1. In this case, M2 is a doping element other than Ti, which is a buffer metal element.)

[0202] I(003) / I(104) c-axis lattice constant before charging (Å) maximum c-axis lattice constant during charging (Max) (Å) c-axis lattice constant after charging (Min) (Å) change in c-axis lattice constant during charging (Max-Min) (Å) change in c-axis lattice constant during charging (%) sphericity Example 11.54 14.27 14.41 13.91 0.53.47% 0.4 Example 21.41 14.33 14.39 13.99 0.42.78% 0.4 Example 31.19 14.39 14.44 14.14 0.32.08% 0.4 Example 40.83 14.44 14.48 14.32 0.16 1.10% 0.4 Comparative example 10.5914.5314.5614.380.161.24%0.4Comparative Example 20.3714.6214.6314.450.181.23%0.4Comparative Example 31.6414.2114.3913.351.047.23%0.4Comparative Example 41.714.2614.4713.630.845.81%0.9Comparative Example 51.6814.2414.4313.550.886.10%0.9Comparative Example 61.6614.2214.4213.411.017.00%0.9Comparative Example 71.6814.2614.4514.050.42.77%0.9Comparative example 81.3614.3514.4114.040.372.57%0.9

[0203] Referring to Tables 1 and 2, it was confirmed that in the case of Examples and Comparative Examples 1 and 2 where excess lithium, nickel, and a buffer metal element (Ti) were introduced, the I(003) / I(104) values ​​were smaller than those of the cathode material with a normal composition. Through this, it was confirmed that the lithium transition metal oxide into which excess lithium, nickel, and a buffer metal element (Ti) were introduced had a disordered mixing structure in which a large amount of nickel and a buffer metal element were mixed in the lithium site within the lithium layer. In addition, it was confirmed that the amount and rate of change in the c-axis lattice constant were small, and as a result of minimizing shrinkage during charging, a large c-axis lattice constant value was obtained after charging. However, in the case of Comparative Examples 1 and 2, the amount of lithium and a buffer metal element (Ti) introduced was too large, resulting in excessive cation disorder mixing, so that the I(003) / I(104) peak intensity ratio was smaller than in the Example, and the c-axis lattice constant before charging was larger than in the Example.

[0204] On the other hand, in the case of Comparative Examples 3 to 6, which are normal compositions, or Comparative Example 7, which is an excess lithium composition without the introduction of a buffer metal element, it was confirmed that the I(003) / I(104) value was obtained large because cation disorder mixing did not occur well. In addition, in the case of Comparative Examples 3 to 6, which are normal compositions, it was confirmed that the amount and rate of change in the c-axis lattice constant were large, and as a result of the large shrinkage during charging, the c-axis lattice constant value after charging was obtained small.

[0205]

[0206] Experimental Example 3: Evaluation of Electrochemical Characteristics of Lithium Secondary Battery

[0207] (1) 1 st and 2 nd Cycle discharge capacity evaluation

[0208] After manufacturing a lithium secondary battery half cell, it was aged at 25°C for 12 hours and then 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 4.6 V at a constant current of 0.1 C. Then, the battery was 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 at a constant current of 0.1 C with a reference capacity of 200 mAh / g until the battery reached 2.5 V. After that, 2 nd The cycle discharge capacity was evaluated.

[0209] (2) Evaluation of rollable electrode density

[0210] By adjusting the gap of the rolling mill, the damage to the electrode uncoated area was checked and the rollable electrode density was evaluated.

[0211] (3) Average voltage evaluation

[0212] The average voltage was evaluated by integrating the area of ​​the lower part of the discharge profile and dividing it by the discharge capacity.

[0213] (4) Life characteristics evaluation (45℃, 50 cycles)

[0214] After fabricating a lithium secondary battery half-cell, it was charged to 4.6 V at a constant current of 0.5 C at 45°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, it was discharged at a constant current of 0.5 C until it reached 2.5 V. Under these charge-discharge cycle conditions, 50 charge-discharge cycles were performed, and the capacity retention rate of the 50th cycle was calculated compared to the first cycle.

[0215] (5) Battery energy density evaluation

[0216] A secondary battery was designed using a pouch-type battery design, and the energy density was evaluated by converting the average voltage and capacity, and the battery volume, reflecting the density of the electrodes using each material. Here, the electrode density was converted using the electrode weight per unit area and the thickness that appears at maximum rolling.

[0217]

[0218] Half cellFull cell1st cycleDischarge capacity(mAh / g)2nd cycleDischarge capacity(mAh / g)Rollable electrode density(g / cc)Average voltage(V)Lifespan(%, 50 cycles)Energy density(Wh / L)Example 1239.7237.73.43.794.4783.4Example 2242240.93.43.7196.9790.5Example 3244.1243.73.43.797.8799.1Example 4246.3243.33.43.6993.6797.2Comparative example 1249.8232.53.43.788.1747.5Comparative example 2252.5230.13.43.6886.3742.1Comparative example 3234.3210.63.43.6432.7680.7Comparative example 4180.6180.53.43.6995.7600.2Comparative example 5206.6206.33.43.6786.9706.8Comparative example 6227.7225.83.43.6573.2733.5Comparative example 7269.7208.62.93.6192.8566Comparative example 8215.3192.53.43.52drop612.6

[0219] Referring to Table 3, it was confirmed that the examples in which excess lithium, nickel, and buffer metal elements (Ti) were introduced showed excellent overall performances in terms of capacity, rollable electrode density, average voltage, life characteristics, and energy density.

[0220] Comparing Examples 1 to 4 and Comparative Examples 1 to 2, it was confirmed that the electrochemical characteristics were more preferably implemented when the lithium excess amount and the amount of buffer metal element introduced were more appropriately controlled. This can be interpreted as a result of excessive cation disorder mixing occurring due to the introduction of excessive amounts of lithium and titanium in the case of Comparative Examples 1 and 2. In addition, it was confirmed that the I(003) / I(104) peak intensity ratio and the c-axis lattice constant before charging resulted in values ​​exceeding the range according to the present invention.

[0221] On the other hand, in the case of Comparative Example 3 with LiNiO2 composition, it was confirmed that the life characteristics and energy density were significantly lower.

[0222] Additionally, in the case of Comparative Examples 4 to 6, which are conventional nickel-cobalt-manganese compositions, it was confirmed that the capacity, lifespan, and energy density were reduced.

[0223] In addition, in the case of Comparative Example 7, which has a lithium-excess composition but no buffer metal is introduced, 2 nd It was confirmed that the discharge capacity, rollable electrode density, and energy density were significantly reduced, and the average voltage and life characteristics were deteriorated.

[0224] In addition, in the case of Comparative Example 8, which cannot be considered a lithium-excess composition, although the nickel and titanium contents for the entire transition metal are similar to the range according to the present invention, it was confirmed that the capacity characteristics, average voltage, life characteristics, and energy density were all significantly deteriorated compared to the examples.

[0225] In addition, it was confirmed that the positive electrode active material of the embodiment exhibited superior overall electrochemical performance compared to the comparative example, despite having a lower sphericity as examined in the previous experimental examples 1 and 2. Through this, it was confirmed that the positive electrode active material of the present invention with a novel composition possesses superior electrochemical performance without a separate process for improving sphericity, and thus also has an advantage in process economy.

[0226]

[0227] 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.

[0228] Accordingly, the actual scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A lithium transition metal oxide containing an excess of lithium, nickel and buffer metal elements, The above lithium transition metal oxide has a molar ratio of lithium to the lithium transition metal oxide of 1.02 to 1.1, and a molar ratio of nickel to the transition metal of 0.75 or more. The lithium transition metal oxide has a basic skeleton structure in which lithium layers and transition metal layers are alternately laminated, and some of the buffer metal elements in the transition metal layer are substituted into the lithium layer, and some of the lithium ions in the lithium layer are substituted into the transition metal layer, thereby suppressing anisotropic shrinkage and expansion during charging and discharging. Cathode active material for lithium secondary batteries.

2. In paragraph 1, A cathode active material for a lithium secondary battery, wherein some of the nickel ions in the transition metal layer are substituted into the lithium layer.

3. In paragraph 1, The above lithium transition metal oxide is a cathode active material for a lithium secondary battery through which lithium ions move through the lithium layer and transition metal layer during charging and discharging.

4. In paragraph 1, The above buffer metal element is a positive electrode active material for a lithium secondary battery, which is a transition metal element that does not have an atomic electron in the d orbital.

5. In paragraph 1, The above buffer metal element is a cathode active material for a lithium secondary battery, which is Ti, Nb, W, Zr, V, Cr, Mo, Ta or a combination thereof.

6. In paragraph 1, A positive electrode active material for a lithium secondary battery having a content of the buffer metal element of 2 to 25 mol% based on the total mole number of transition metals.

7. In paragraph 1, A positive electrode active material for a lithium secondary battery having a content of the buffer metal element of 6 to 15 mol% based on the total mole number of transition metals.

8. In paragraph 1, The above lithium transition metal oxide is a cathode active material for a lithium secondary battery, wherein the ratio of the peak intensity of the (003) plane to the peak intensity of the (104) plane (I(003) / I(104)) upon X-ray diffraction analysis is 0.7 to 1.

6.

9. In paragraph 1, The above lithium transition metal oxide is a cathode active material for a lithium secondary battery, wherein the difference between the maximum and minimum values ​​of the c-axis lattice constant during charging is 0.6 Å or less until the termination voltage becomes 4.6 V during the first charging process.

10. In paragraph 1, The above lithium transition metal oxide is a cathode active material for a lithium secondary battery, wherein the change rate of the c-axis lattice constant during charging is 5% or less until the termination voltage becomes 4.6 V during the first charging process.

11. In paragraph 1, The above lithium transition metal oxide is a cathode active material for a lithium secondary battery having a c-axis lattice constant of 13.8 Å or more after being charged until the termination voltage becomes 4.6 V in the first charging process.

12. In paragraph 1, The above lithium transition metal oxide is a cathode active material for a lithium secondary battery having a sphericity of 0.5 or less.

13. In paragraph 1, The above lithium transition metal oxide is a cathode active material for a lithium secondary battery that does not contain cobalt and manganese.

14. In paragraph 1, The above lithium transition metal oxide is a cathode active material for a lithium secondary battery represented by the following chemical formula 1: [Chemical Formula 1] Li 1+x (Ni 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.

15. A step of forming a mixture by mixing a nickel-containing transition metal compound, a buffer metal raw material, and a lithium raw material; and Comprising a step of calcining the above mixture to form a lithium transition metal oxide, In the step of forming the mixture, the amount of the nickel-containing transition metal compound input is 75 mol% or more based on the total mole number of the nickel-containing transition metal compound and the buffer metal raw material, and the amount of the lithium raw material input is adjusted so that the molar ratio of lithium to the total amount of transition metal contained in the nickel-containing transition metal compound and the buffer metal raw material (Li / Me) is 1.05 to 1.

25. A method for producing a cathode active material for a lithium secondary battery.

16. In paragraph 15, A method for manufacturing a positive electrode active material for a lithium secondary battery, wherein the buffer metal raw material is an oxide, hydroxide, carbonate, sulfate, phosphate or a combination thereof containing a buffer metal element.

17. In paragraph 15, In the step of forming the above mixture, A method for producing a cathode active material for a lithium secondary battery, wherein the amount of the buffer metal raw material input is 2 to 25 mol% based on the total mole number of the nickel-containing transition metal compound and the buffer metal raw material.

18. A positive electrode for a lithium secondary battery comprising the positive electrode active material of any one of claims 1 to 14.

19. A lithium secondary battery comprising the positive electrode for a lithium secondary battery of Article 18.

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