Positive electrode active material and preparation method therefor, positive electrode sheet, and battery

Abstract

The present application provides a positive electrode active material and a preparation method therefor, a positive electrode sheet, and a battery. The positive electrode active material satisfies the following condition: [Formula 1], wherein I(111), I(222), I(400), and I(440) are all not equal to 0. In the positive electrode active material provided by the present application, by means of formula 1, the degree of exposure of the (222) and (111) crystal planes relative to the (110) and (100) crystal planes is defined, which can improve the lithium-ion conduction rate and dynamic performance of lithium nickel manganese oxide, thereby significantly improving the rate performance and discharge capacity of the corresponding battery.

Description

A positive electrode active material and its preparation method, positive electrode sheet and battery

[0001] This disclosure claims priority to Chinese Patent Application No. 202411997946.X, filed with the Chinese Patent Office on December 31, 2024, entitled "A positive electrode active material and its preparation method, positive electrode sheet and battery", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of battery technology, and more specifically, to a positive electrode active material and its preparation method, a positive electrode sheet, and a battery. Background Technology

[0003] In the new energy industry, the widespread use of electric vehicles has brought great convenience and benefits. However, with the updating and development of technology, the market has put forward higher requirements for electric vehicles, with mileage and charging time being the two key concerns of consumers.

[0004] Spinel lithium nickel manganese oxide (LiMO) possesses high operating voltage and high energy density, along with a stable 3D lithium-ion transport channel, making it a promising candidate for applications in electric vehicles, energy storage systems, and portable electronic devices. However, the commercialization of LiMO is hindered by electrolyte decomposition caused by high operating voltage and crystal structure instability (the Jan Taylor effect). While coating and doping can effectively improve the structural stability of spinel LiMO, these methods significantly reduce the rate performance of LiMO batteries.

[0005] Application content

[0006] This application provides a positive electrode active material that can significantly improve the rate performance and discharge capacity of a battery by limiting the exposure degree of specific crystal faces.

[0007] This application also provides a method for preparing the above-mentioned positive electrode active material, which can prepare the above-mentioned positive electrode active material and has a simple process.

[0008] This application also provides a positive electrode sheet, which, because it includes the above-mentioned positive electrode active material, has the advantages of fast ion transport rate and high charge storage capacity.

[0009] This application also provides a battery that, because it includes the aforementioned positive electrode, has both high rate performance and discharge capacity.

[0010] In a first aspect, this application provides a positive electrode active material, wherein the positive electrode active material satisfies the following formula 1:

[0011] Among them, I(111) I (222) I (400) and I (440) None of them are 0.

[0012] Furthermore, the positive electrode active material includes trivalent manganese ions and tetravalent manganese ions, and the mass ratio of trivalent manganese ions to tetravalent manganese ions increases from the center of the positive electrode active material to the outer surface.

[0013] Furthermore, the chemical composition of the positive electrode active material includes: Li a Ni b Mn c M d O 4-h ;

[0014] Wherein, 1.0≤a≤1.006, 0.495≤b≤0.505, 1.495≤c≤1.505, 0≤d≤0.003, -0.082<h<0.21, b+c=2, and M is selected from at least one of W, Mo, Ta, Nb, V, and Sb.

[0015] Furthermore, the disorder degree of the positive electrode active material is 6%-9%.

[0016] Secondly, this application provides a method for preparing the positive electrode active material as described in the first aspect, comprising the following steps:

[0017] A mixture comprising a nickel-manganese hydroxide precursor and a first lithium source is sintered once in an oxygen-containing atmosphere at a heating rate of 1-5℃ / min to m℃ to obtain an intermediate. The first lithium source is calculated based on lithium element, and the nickel-manganese hydroxide precursor is calculated based on the sum of nickel and manganese elements. The molar ratio of the nickel-manganese hydroxide precursor to the first lithium source is 2:0.8-0.95.

[0018] The mixture comprising the intermediate and the second lithium source is subjected to secondary sintering in an oxygen-containing atmosphere at a heating rate of 1-5℃ / min to n℃ to obtain the positive electrode active material; wherein the molar ratio of the intermediate and the second lithium source is 0.05-0.2, and n is less than m.

[0019] Furthermore, the first lithium source is calculated based on lithium element, and the nickel-manganese hydroxide precursor is calculated based on the sum of nickel and manganese elements, with the molar ratio of the nickel-manganese hydroxide precursor to the first lithium source being 2:0.85-0.9.

[0020] Furthermore, m satisfies: 950≤m≤1050.

[0021] Furthermore, n satisfies: 750≤n≤850.

[0022] Thirdly, this application provides a positive electrode sheet, including a current collector and a positive electrode active layer disposed on at least one surface of the current collector; the positive electrode active layer includes the positive electrode active material as described in the first aspect.

[0023] Fourthly, this application provides a battery including a positive electrode as described in the third aspect.

[0024] The positive electrode active material provided in this application defines the exposure degree of the (222) and (111) crystal planes relative to the (400) and (440) crystal planes by Formula 1, which can improve its lithium-ion conduction rate and charge storage energy, thereby significantly improving the rate performance and discharge capacity of the corresponding battery. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments or related technologies of this disclosure, the accompanying drawings used in the description of the embodiments or related technologies of this disclosure are briefly introduced below. Obviously, the accompanying drawings described below are merely some embodiments of this disclosure. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0026] Figure 1 is a SEM image of the positive electrode active material of Example 1;

[0027] Figure 2 shows the SEM image of the positive electrode active material of Comparative Example 1;

[0028] Figure 3 is a SEM image of the positive electrode active material in Example 2;

[0029] Figure 4 shows the SEM image of the positive electrode active material of Comparative Example 2;

[0030] Figure 5 shows a comparison of the XRD patterns of the positive electrode active materials of Example 1 and Comparative Example 1. Detailed Implementation

[0031] To enable those skilled in the art to better understand the solutions of this application, a further detailed description of this application is provided below. The specific embodiments listed below are merely descriptions of the principles and features of this application; the examples are only for explaining this application and are not intended to limit its scope. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this application.

[0032] Lithium nickel manganese oxide exhibits a spinel octahedral structure, mainly comprising three crystal faces: (100), (110), and (111). Different crystal faces have different lithium-ion transport rates due to variations in atomic density. The (111) face has a higher Ni / Mn atom density, resulting in slower lithium-ion transport, but it is also more stable. The (100) and (110) faces have lower atomic densities than the (111) face, leading to higher lithium-ion transport rates. However, due to their lower atomic density and higher reactivity, the Jan Taylor effect can cause Mn dissolution, resulting in poor stability of the (100) and (110) faces. This application finds that by controlling the polycrystalline faces of the positive electrode active material, its kinetic performance can be comprehensively improved. Specifically, this application adopts the following technical solution:

[0033] In a first aspect, this application provides a positive electrode active material that satisfies the following formula 1:

[0034] Among them, I (111) I (222) I (400) and I (440) None of them are 0.

[0035] It should be noted that in Equation 1, I (111) This refers to the intensity of the diffraction peak on the (111) crystal plane in the XRD pattern of the positive electrode active material, where the intensity is expressed as the height of the diffraction peak. Furthermore, I... (111)+ I (222) I refers to the sum of the diffraction peak intensities of the (111) crystal plane and the (222) crystal plane in the XRD pattern of the positive electrode active material. (400) I (400) +I (440) Similarly. In addition, in the XRD pattern, since the (110) and (100) planes are low-index crystal planes and are at a low 2-Theta angle, they are difficult to identify. The (400) crystal plane is the fourth-order diffraction plane of the (100) crystal plane, and the (440) crystal plane is the fourth-order diffraction plane of the (110) crystal plane. Therefore, this application uses (440) and (400) instead of (110) and (100) for limitation.

[0036] In this application, Equation 1 can define the exposure degree of the (111) and (222) planes relative to the (400) and (440) crystal planes, which helps to improve the rate performance and specific capacity of the positive electrode active material. The reason is that the (100) and (110) crystal planes of the positive electrode active material reflect the truncated angle and truncated edge composition of the particle morphology, respectively, while the (111) and (222) crystal planes reflect the octahedral composition. The atomic arrangement of the (111) crystal plane is relatively dense, the crystal plane is relatively stable, and the Jan Taylor effect is not obvious. The positive electrode active material that satisfies Equation 1 With more truncated morphologies, lithium ion insertion and extraction are easier. Therefore, the rate performance and discharge capacity of the positive electrode active material are significantly improved compared to the traditional octahedral lithium nickel manganese oxide. Moreover, the positive electrode active material that satisfies Formula 1 also reasonably controls the exposure of the (100) and (110) crystal planes relative to the (111) and (222) crystal planes. This can improve the pressure resistance of the material to a certain extent, thereby reducing the problem of particle breakage of the positive electrode active material caused by mechanical stress during coating, which leads to an increase in side reactions and a decrease in cycle performance.

[0037] In some alternative embodiments, the positive electrode active material includes trivalent manganese ions and tetravalent manganese ions, with the mass ratio of trivalent manganese ions to tetravalent manganese ions increasing from the center of the positive electrode active material to the outer surface.

[0038] The increasing mass ratio of trivalent manganese ions to tetravalent manganese ions from the center to the outer surface of the positive electrode active material can also be understood as the increasing ratio of disordered phase to ordered phase structure from the center to the outer surface of the positive electrode active material. In addition, the "increasing" in this application only means that the mass ratio of trivalent manganese ions is increasing. As for whether the increase is regular or in a curve-like manner, this application does not make specific limitations on this.

[0039] As described above, since the positive electrode active material includes trivalent manganese ions, and the trivalent manganese ions increase from the inside to the outside, the positive electrode active material can have better electrochemical activity. Trivalent manganese ions can participate in redox reactions during charge and discharge, thereby contributing to the capacity. At the same time, lithium nickel manganese oxide, which exists in the form of trivalent manganese ions, has a disordered phase structure, and its structure is stable during charge and discharge, thus improving cycle performance.

[0040] The increasing concentration of trivalent manganese ions can be tested using the following methods:

[0041] X-ray photoelectron spectroscopy (XPS) was used for characterization to test the valence state and content of manganese in samples with different etching depths. Based on data fitting, the Mn content was determined. 4+ / Mn 3+ The ratio was used to infer the change in the mass ratio of trivalent manganese ions to tetravalent manganese ions.

[0042] In some embodiments, Mn is located at a distance of 2 nm from the outer surface of the positive electrode active material in the direction from the outer surface to the center. 4+ / Mn 3+ The ratio is defined as C2, and Mn at a distance of 20 nm from the outer surface. 4+ / Mn 3+ The ratio is defined as C1, and C2-C1 satisfies: 0.1≤C2-C1≤0.3.

[0043] In some alternative embodiments, the chemical composition of the positive electrode active material includes: Li a Ni b Mn c M d O 4-h ;

[0044] Wherein, 1.0≤a≤1.006, 0.495≤b≤0.505, 1.495≤c≤1.505, 0≤d≤0.003, -0.082<h<0.21, b+c=2, and M is selected from at least one of W, Mo, Ta, Nb, V, and Sb.

[0045] In some embodiments, the positive electrode active material includes a core and a shell located on the surface of the core, with element M located in the shell of the positive electrode active material. The inclusion of dopant element M in the shell further enhances the electronic and ionic conductivity of the positive electrode active material, thereby improving the rate performance of the battery.

[0046] In some embodiments, when conventional lithium nickel manganese oxide has the same chemical composition as the positive electrode active material described above in this application, the rate performance of the positive electrode active material described above can be improved by 1%-5%, wherein the rate performance W is defined as W = 2C / 0.1C*100.

[0047] In order to further improve the lithium-ion transport and energy storage performance of the positive electrode active material, in a preferred embodiment, d = 0.003.

[0048] Ordered lithium nickel manganese oxide typically possesses a cubic spinel structure with space group P4332, where lithium ions occupy octahedral sites. Disordered lithium nickel manganese oxide, with space group Fd3m, also has a cubic spinel structure, but its nickel and manganese ions are randomly distributed in the lattice. Ordered lithium nickel manganese oxide generally exhibits higher energy density due to its higher voltage plateau, while disordered lithium nickel manganese oxide is more conducive to lithium ion diffusion and transport, thus exhibiting better rate performance. However, excessive disorder leads to severe Chern-Taylor effects, resulting in poor structural chemical stability and deteriorating electrochemical performance. Therefore, it is necessary to control the ratio of ordered to disordered structures. In some optional embodiments, the disorder degree of the positive electrode active material is 6%-9%.

[0049] Among them, the above-mentioned disordered positive electrode active material has more conductive paths, which helps to further improve the electronic conductivity of the positive electrode active material, thereby further improving the rate performance of the battery.

[0050] For example, the disorder of the positive electrode active material is any value of 6%, 7%, 8%, 9%, or any combination thereof.

[0051] In some embodiments, the disorder of the positive electrode active material is tested by the following methods:

[0052] The fully ordered lithium nickel manganese oxide positive electrode active material is assembled into a positive electrode sheet, and then the positive electrode sheet is assembled into a battery cell 1. Then, the positive electrode active material of this application is assembled into a positive electrode sheet in the same way, and then the positive electrode sheet is assembled into a battery cell 2. The proportion of the charging capacity of battery cell 1 at 4.4V in the first cycle to the total charging capacity in the first cycle is defined as X1, and the proportion of the charging capacity of battery cell 2 below 4.4V in the first cycle to the total charging capacity in the first cycle is defined as X2. Then, the disorder degree σ=(X2-X1) / X1.

[0053] Secondly, this application provides a method for preparing a positive electrode active material as described in the first aspect, comprising the following steps:

[0054] A mixture comprising a nickel-manganese hydroxide precursor and a first lithium source is sintered once in an oxygen-containing atmosphere at a heating rate of 1-5℃ / min to m℃ to obtain an intermediate. The first lithium source is calculated based on lithium element, and the nickel-manganese hydroxide precursor is calculated based on the sum of nickel and manganese elements. The molar ratio of the nickel-manganese hydroxide precursor to the first lithium source is 2:0.8-0.95.

[0055] The mixture including the intermediate and the second lithium source is heated to n℃ twice in an oxygen-containing atmosphere at a heating rate of 1-5℃ / min to obtain the positive electrode active material; wherein the molar ratio of the intermediate and the second lithium source is 0.05-0.2, and n is less than m.

[0056] The above preparation method, by controlling the amount of the first lithium source added to the mixture and the temperature of the first sintering, synthesizes a lithium-deficient nickel-manganese spinel intermediate and constructs a polycrystalline morphology. Then, a second lithium source is added, and a second sintering is performed at a lower temperature to complete the synthesis of polycrystalline nickel-manganese spinel with a disordered surface phase. Wherein, if the chemical composition of the positive electrode active material includes: Li a Ni b Mn c M d O 4-hAnd d is not 0. The mixture material for secondary sintering also includes M source. M source has a fluxing effect and can work with the second lithium source to make the (110) and (100) crystal planes of the positive electrode active material easier to form and can control the formation of (111) plane, construct a cross section with high lithium ion diffusion coefficient, and avoid forming (110) and (100) crystal planes that are too wide and too long. At the same time, it will be doped in the interface of lithium nickel manganese oxide. Due to the charge compensation effect, a disordered phase spinel structure will be formed. Meanwhile, the second lithium source is an intermediate lithium supplement, making the surface of the positive electrode material rich in lithium, further improving the lithium ion diffusion coefficient of the positive electrode active material.

[0057] It is understandable that since the above intermediate is lithium-deficient lithium nickel manganese spinel, a second lithium source needs to be added to replenish lithium. As for the amount of the second lithium source to be added, the technician can calculate it based on the difference between the target chemical structure of the finished product and the chemical structure of the intermediate. This application does not make specific limitations on this.

[0058] For example, both the first lithium source and the second lithium source are lithium-containing substances, and they can be the same or different, for example, including at least one of lithium carbonate, lithium hydroxide, lithium acetate, lithium oxalate, and lithium citrate. Preferably, at least one of lithium carbonate and lithium hydroxide is used.

[0059] The aforementioned source M can be a compound of M, preferably an oxide of M.

[0060] The aforementioned nickel-manganese hydroxide precursor is a hydroxide containing Ni and Mn elements, and its chemical formula can be Ni. x Mn y (OH) z , 0.495≤x≤0.505, 1.495≤y≤1.505, z=2, x+y=2.

[0061] In some embodiments, the molecular formula of the above intermediate is: Li a Ni b Mn c O 4-h , where 0.8≤a≤0.95, 0.495≤b≤0.505, 1.495≤c≤1.505, and 0.025<h<0.1.

[0062] In some embodiments, the process further includes cooling and pulverizing steps after primary sintering and / or secondary sintering.

[0063] In some alternative embodiments, the first lithium source is calculated as lithium element, the nickel-manganese hydroxide precursor is calculated as the sum of nickel and manganese elements, and the molar ratio of the nickel-manganese hydroxide precursor to the first lithium source is 2:0.85-0.9.

[0064] The above implementation method can further control the proportion of disordered phase on the surface of the positive electrode active material, thereby further avoiding the collapse of the positive electrode active material structure or the occurrence of irreversible phase transition during cycling.

[0065] To further ensure that the intermediate can be formed into lithium-deficient nickel-manganese spinel, in some alternative embodiments, m satisfies: 950≤m≤1050.

[0066] To further ensure the construction of a positive electrode active material that satisfies Equation 1, in some optional embodiments, n satisfies: 750≤n≤850.

[0067] Thirdly, this application provides a positive electrode sheet, including a current collector and a positive electrode active layer disposed on at least one surface of the current collector; the positive electrode active layer includes the positive electrode active material as described in the first aspect.

[0068] It is understandable that the positive electrode active layer also includes conductive agents and binders.

[0069] In some embodiments, the positive electrode active material layer comprises, by weight percentage: 93–98 wt% positive electrode active material, 2–5 wt% conductive agent, 2–5 wt% binder, and 0–1 wt% dispersant. This system possesses a more complete electronic conductive network and stronger adhesion between particles and between particles and the current collector, which contributes to performance at low temperatures and the stability of the system during long-term cycling.

[0070] For example, the conductive agent may be selected from at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanotubes, metal powder, and graphene; the binder may be selected from at least one of carboxymethyl cellulose, styrene-butadiene rubber, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate; and the dispersant may be selected from at least one of sodium carboxymethyl cellulose, triethylhexyl phosphate, and sodium dodecyl sulfate.

[0071] The thickness, areal density, and thickness of the positive electrode active material layer are not specifically limited in this application. However, in order to balance battery capacity, cycle life, and energy density, in one specific embodiment, the thickness of the positive electrode is 40-120 μm, specifically including but not limited to: 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, etc.; the areal density of the positive electrode is 3-10 mg / cm³. 2 Specifically, including but not limited to: 3.5 mg / cm³ 2 4mg / cm 2 4.5 mg / cm 25mg / cm 2 5.5 mg / cm 2 6mg / cm 2 6.5 mg / cm 2 7mg / cm 2 7.5 mg / cm 2 8mg / cm 2 8.5 mg / cm 2 9mg / cm 2 9.5 mg / cm 2 The thickness of the positive electrode active material layer is 20-60μm, including but not limited to: 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, 55μm, etc.

[0072] Fourthly, this application provides a battery including a positive electrode as described in the third aspect.

[0073] It is understood that the battery in this application may also include a negative electrode, a separator, and an electrolyte.

[0074] This application does not impose any particular limitation on the above-mentioned diaphragm, and any known porous structure diaphragm with electrochemical stability and chemical stability can be selected, for example, it can be at least one of glass fiber, non-woven fabric, polyethylene, polypropylene or polyvinylidene fluoride; the diaphragm can be single layer or multilayer.

[0075] This application does not impose any particular limitation on the electrolyte mentioned above. For example, an electrolyte comprising an organic solvent and an electrolyte salt may be selected. The organic solvent, as the medium for transporting ions in the electrochemical reaction, may be one or more organic solvents known in the art for use in battery electrolytes, such as fluorocarbonates, fluorocarboxylic acid esters, non-fluorocarbonates, fluorocarbonates, non-fluorocarboxylic acid esters, fluorocarboxylic acid esters, fluoroethers, non-fluoroethers, and tetrahydrofuran. The electrolyte salt, as the ion source, may be one or more electrolyte salts known in the art for use in battery electrolytes, such as lithium hexafluorophosphate, bis(trifluoromethanesulfonyl)imide, and lithium bis(fluorosulfonyl)imide.

[0076] The battery of this application can be manufactured using conventional methods in the art. For example, a positive electrode, a separator, and a negative electrode can be stacked sequentially, and then assembled into a cell using a winding or stacking process. After encapsulation and baking, an electrolyte is injected, and the battery is then subjected to hot-pressing and other processes to obtain the final battery. The following specific embodiments further illustrate this application:

[0077] Example 1

[0078] This example provides a positive electrode active material with a chemical composition of Li. 1.003 Ni 0.502 Mn 1.498 O3.793 The positive electrode active material is a single-crystal positive electrode active material, and its structural characteristics are shown in Table 1.

[0079] Its preparation method includes the following steps:

[0080] Ni was weighed according to the Li:(Ni+Mn) molar ratio of 0.9:2. 0.5 Mn 1.5 (OH)4 and Li2CO3, then Ni 0.5 Mn 1.5 (OH)4 and Li2CO3 were added to a high-speed mixer and mixed at a speed of 600 rpm / min for 30 min. The mixture was then calcined in air at a high temperature, with the temperature increased to 1000℃ at a rate of 2℃ / min, and held for 15 h. After natural cooling, it was crushed by a roller crusher and passed through a 325-mesh sieve to obtain lithium-deficient lithium nickel manganese oxide cathode active material (intermediate). The lithium-deficient spinel was weighed before and after crushing, and the loss rate was calculated.

[0081] The crushed lithium-deficient nickel-manganese oxide positive electrode active material and Li2CO3 were added to a high-speed mixer after the loss rate was calculated (to make the molar ratio of Li:(Ni+Mn) = 1.0:2). The mixing speed was 600 rpm / min and the mixing time was 30 min. The mixture was then calcined at high temperature in air atmosphere, with the temperature increased to 800℃ at 2℃ / min and held for 5 h. After natural cooling, it was crushed by a double roller crusher and passed through a 325 mesh sieve to obtain the nickel-manganese oxide positive electrode active material.

[0082] Example 2

[0083] This example provides a positive electrode active material with a chemical composition of Li. 1.004 Ni 0.497 Mn 1.503 W 0.003 O 4.064 The positive electrode active material is a single-crystal positive electrode active material. Other parameters are shown in Table 1.

[0084] Its preparation method includes the following steps:

[0085] Ni was weighed according to the Li:(Ni+Mn) molar ratio of 0.9:2. 0.5 Mn 1.5 (OH)4 and Li2CO3, then Ni 0.5 Mn 1.5(OH)4 and Li2CO3 were added to a high-speed mixer and mixed at a speed of 600 rpm / min for 30 min. The mixture was then calcined at high temperature in air, with the temperature increased to 1000℃ at a rate of 2℃ / min, and held for 15 h. After natural cooling, it was crushed using a roller crusher and passed through a 325-mesh sieve to obtain lithium-deficient lithium nickel manganese oxide cathode active material. The lithium-deficient spinel was weighed before and after crushing, and the loss rate was calculated.

[0086] The crushed lithium-deficient nickel-manganese oxide positive electrode active material, the lithium source with the designed molar ratio, and WO3 with the designed molar ratio were added to a high-speed mixer and mixed at a speed of 600 rpm / min for 30 min. The mixture was then calcined at high temperature in air, with the temperature increased to 800℃ at a rate of 2℃ / min and held for 5 h. After natural cooling, the mixture was crushed by a double-roll crusher and passed through a 325-mesh sieve to obtain the nickel-manganese oxide positive electrode active material.

[0087] Example 3

[0088] This example provides a positive electrode active material with a chemical composition of Li. 1.005 Ni 0.495 Mn 1.505 Nb 0.003 O 3.996 The positive electrode active material is a single-crystal positive electrode active material. Other parameters are shown in Table 1.

[0089] The difference between its preparation method and that of Example 2 is that the M source in the secondary sintering is Nb2O5, and the secondary sintering is carried out at a temperature of 4℃ / min to 750℃ and held for 6h.

[0090] Example 4

[0091] This example provides a positive electrode active material with the chemical composition LiNi. 0.5 Mn 1.5 Mo 0.003 O 4.078 The positive electrode active material is a single-crystal positive electrode active material. Other parameters are shown in Table 1.

[0092] The difference between its preparation method and that of Example 2 is that the M source in the secondary sintering is MoO3, and the secondary sintering is carried out at a temperature of 1℃ / min to 850℃ and held for 5h.

[0093] Example 5

[0094] This example provides a positive electrode active material with the chemical composition Li1.002Ni. 0.497 Mn 1.503 Ta 0.003 O 4.075The positive electrode active material is a single-crystal positive electrode active material. Other parameters are shown in Table 1.

[0095] The difference between its preparation method and that of Example 2 is that the first sintering is carried out by heating to 950°C at 1°C / min and then holding for 15 hours; the M source in the second sintering is Ta2O5.

[0096] Example 6

[0097] This example provides a positive electrode active material with a chemical composition of Li. 1.001 Ni 0.499 Mn 1.501 V 0.003 O 4.005 The positive electrode active material is a single-crystal positive electrode active material. Other parameters are shown in Table 1.

[0098] The difference between its preparation method and that of Example 2 is that the first sintering is carried out by heating to 1050°C at 4°C / min and then holding for 11 hours; the M source in the second sintering is V2O5.

[0099] Example 7

[0100] This example provides a positive electrode active material with a chemical composition of Li. 1.006 Ni 0.503 Mn 1.497 Sb 0.003 O 4.019 The positive electrode active material is a single-crystal positive electrode active material. Other parameters are shown in Table 1.

[0101] The difference between its preparation method and that of Example 2 is that the M source in the secondary sintering is Sb2O3.

[0102] Example 8

[0103] This example provides a positive electrode active material with a chemical composition of Li. 1.002 Ni 0.498 Mn 1.502 W 0.003 O 3.907 The positive electrode active material is a single-crystal positive electrode active material. Other parameters are shown in Table 1.

[0104] The difference between its preparation method and that of Example 2 is that, in the first sintering, Ni is weighed according to the Li:(Ni+Mn) molar ratio of 0.8:2. 0.5 Mn 1.5 (OH)4 and Li2CO3.

[0105] Example 9

[0106] This example provides a positive electrode active material with a chemical composition of Li. 1.003 Ni 0.497 Mn1.503 W 0.003 O 4.055 The positive electrode active material is a single-crystal positive electrode active material. Other parameters are shown in Table 1.

[0107] The difference between its preparation method and that of Example 2 is that, in the first sintering, Ni is weighed according to the Li:(Ni+Mn) molar ratio of 0.85:2. 0.5 Mn 1.5 (OH)4 and Li2CO3.

[0108] Example 10

[0109] This example provides a positive electrode active material with a chemical composition of Li. 1.001 Ni 0.503 Mn 1.497 W 0.003 O 4.082 The positive electrode active material is a single-crystal positive electrode active material. Other parameters are shown in Table 1.

[0110] The difference between its preparation method and that of Example 2 is that, in the first sintering, Ni is weighed according to the Li:(Ni+Mn) molar ratio of 0.95:2. 0.5 Mn 1.5 (OH)4 and Li2CO3.

[0111] Comparative Example 1

[0112] This example provides a positive electrode active material with a chemical composition of Li. 1.002 Ni 0.503 Mn 1.497 O 3.815 The positive electrode active material is a single-crystal positive electrode active material. Other parameters are shown in Table 1.

[0113] Its preparation method includes the following steps:

[0114] Ni was weighed according to the Li:(Ni+Mn) molar ratio of 1:2. 0.5 Mn 1.5 (OH)4 and Li2CO3, then Ni 0.5 Mn 1.5 (OH)4 and Li2CO3 were added to a high-speed mixer and mixed at a speed of 600 rpm / min for 30 min. The mixture was then calcined at high temperature in air, with the temperature increased to 1000℃ at a rate of 2℃ / min, and then held for 15 h. After natural cooling, the mixture was pulverized using a roller crusher and passed through a 325-mesh sieve to obtain lithium nickel manganese oxide cathode active material.

[0115] The single-crystal lithium nickel manganese oxide cathode active material was sintered twice and then mixed in a high-speed mixer at a speed of 600 rpm / min for 30 min. The mixture was then calcined at high temperature in air, with the temperature increased to 800℃ at a rate of 2℃ / min and held for 5 h. After natural cooling, it was crushed by a roller crusher and passed through a 325-mesh sieve to obtain the lithium nickel manganese oxide cathode active material.

[0116] Comparative Example 2

[0117] This example provides a positive electrode active material with a chemical composition of Li. 1.001 Ni 0.5 Mn 1.5 W 0.003 O 4.084 The positive electrode active material is a single-crystal positive electrode active material. Other parameters are shown in Table 1.

[0118] The difference between its preparation method and that of Comparative Example 1 is that WO3 with a molar ratio of Li:(Ni+Mn):M source = 1.0:2:0.003 is added during the secondary sintering.

[0119] Comparative Example 3

[0120] This example provides a positive electrode active material with a chemical composition of Li. 1.003 Ni 0.501 Mn 1.499 Nb 0.003 O 4.020 The positive electrode active material is a single-crystal positive electrode active material. Other parameters are shown in Table 1.

[0121] The difference between its preparation method and that of Comparative Example 1 is that Nb2O5 with a Li:(Ni+Mn):M source molar ratio of 1.0:2:0.003 is added during the secondary sintering.

[0122] Comparative Example 4:

[0123] This example provides a positive electrode active material with a chemical composition of Li. 1.003 Ni 0.504 Mn 1.496 Mo 0.003 O 4.091 The positive electrode active material is a single-crystal positive electrode active material. Other parameters are shown in Table 1.

[0124] The difference between its preparation method and that of Comparative Example 1 is that MoO3 with a Li:(Ni+Mn):M source molar ratio of 1.0:2:0.003 is added during the secondary sintering.

[0125] Comparative Example 5

[0126] This example provides a positive electrode active material with a chemical composition of Li. 1.004 Ni0.505 Mn 1.495 Ta 0.003 O 4.041 The positive electrode active material is a single-crystal positive electrode active material. Other parameters are shown in Table 1.

[0127] The difference between its preparation method and that of Comparative Example 1 is that Ta2O5 with a Li:(Ni+Mn):M source molar ratio of 1.0:2:0.003 is added during the secondary sintering.

[0128] Comparative Example 6

[0129] This example provides a positive electrode active material with a chemical composition of Li. 1.002 Ni 0.499 Mn 1.501 V 0.003 O 4.027 The positive electrode active material is a single-crystal positive electrode active material. Other parameters are shown in Table 1.

[0130] The difference between its preparation method and that of Comparative Example 1 is that V2O5 with a molar ratio of Li:(Ni+Mn):M source = 1.0:2:0.003 is added during the secondary sintering.

[0131] Comparative Example 7

[0132] This example provides a positive electrode active material with a chemical composition of Li. 1.005 Ni 0.501 Mn 1.499 Sb 0.003 O 3.950 The positive electrode active material is a single-crystal positive electrode active material. Other parameters are shown in Table 1.

[0133] The difference between its preparation method and that of Comparative Example 1 is that Sb2O3 with a Li:(Ni+Mn):M source molar ratio of 1.0:2:0.003 is added during the secondary sintering.

[0134] The following tests were performed on the positive electrode active materials of the above embodiments and comparative examples:

[0135] 1. The microstructure of the positive electrode active materials of the above embodiments and comparative examples was observed using SEM. Figure 1 shows the SEM image of the positive electrode active material of Example 1, Figure 2 shows the SEM image of the positive electrode active material of Comparative Example 1, Figure 3 shows the SEM image of the positive electrode active material of Example 2, and Figure 4 shows the SEM image of the positive electrode active material of Comparative Example 2. By comparison, it can be seen that the lithium nickel manganese oxide positive electrode active materials of Examples 1 and 2 exhibit a truncated octahedral structure. There is agglomeration between the particles in Example 1. This is because no fluxing element (M) was added in Example 1, which could not reduce the surface energy of the lithium nickel manganese oxide surface, resulting in poor dispersion of lithium nickel manganese oxide. Moreover, it was impossible to control the orientation repair of the crystal plane of lithium nickel manganese oxide, resulting in excessive exposure of the (100) and (110) crystal planes of the overall material and the appearance of more pores. All of these will affect the electrochemical stability of lithium nickel manganese oxide. Comparative Examples 1-2 show octahedral lithium nickel manganese oxide with smooth surfaces, which are basically in the form of regular octahedrons. The surface energy of lithium nickel manganese oxide is well improved by the addition of fluxing elements. It has good dispersibility and the (100) and (110) crystal planes are oriented and repaired without the generation of pores.

[0136] 2. The crystal structure of the positive electrode active material powder of the above examples and comparative examples was tested using XRD.

[0137] Figure 5 shows the XRD diffraction patterns of Example 1 and Comparative Example 1. Calculations show that the Ig of Example 1 is... (111)+(222) / I (400)+(440) The value of decreased significantly, indicating that the (100) and (110) crystal planes were more exposed. By comparing the XRD diffraction patterns of the examples and comparative examples, it can be seen that lithium nickel manganese oxide with different exposed crystal planes was synthesized by adding fluxing elements.

[0138] 3. X-ray photoelectron spectroscopy (XPS) was used to test the manganese ion content of the positive electrode active material: The positive electrode active materials of the examples and comparative examples were etched, and then the valence state and content of manganese in samples with different etching depths were tested. The Mn content was obtained based on the data fitting. 4+ / Mn 3+ The ratio, specifically, will be used for samples with an etching depth of 2nm, Mn 4+ / Mn 3+ The ratio is defined as C1, and the sample Mn with an etching depth of 20 nm is... 4+ / Mn 3+ The ratio is defined as C2, and the value of C2-C1 is defined as the Mn content in the positive electrode active material. 3+ The degree of gradient change.

[0139] Application Example 1

[0140] The preparation of a positive electrode sheet using the positive electrode active materials of the above embodiments and comparative examples includes the following steps:

[0141] The above-described examples and comparative examples were added to an appropriate amount of NMP at a ratio of positive electrode active material: conductive agent (Super P): binder (PVDF) = 94.5:3:2.5, and mixed into a homogenate using a degassing machine. The mixed slurry was then coated onto both sides of an aluminum foil to obtain a positive electrode sheet with a single-sided areal density of 8 mg / cm³. 2 .

[0142] Application Example 2

[0143] The process of preparing a battery using the above-mentioned positive electrode includes the following steps:

[0144] Lithium-manganese oxide cathode materials from the examples and comparative examples were used as cathode materials to prepare lithium-ion batteries. The lithium-ion battery mainly consists of a cathode sheet, a negative electrode sheet, a separator, and an electrolyte, as described in Application Example 1. The negative electrode sheet is a lithium sheet. The electrolyte is a mixture of dimethyl carbonate, diethyl carbonate, and ethyl carbonate in a volume ratio of 1:1:1, with the addition of 1 mol / L LiPF6. The cathode sheet, separator, and negative electrode sheet are stacked sequentially to obtain a battery cell. The battery cell then undergoes baking, electrolyte injection, formation, and packaging processes to obtain the lithium-ion battery.

[0145] Performance testing:

[0146] The electrical performance of each lithium-ion battery assembled in Application Example 2 was tested separately (results are shown in Table 2): including the following steps:

[0147] CC+CV charge-discharge tests were performed within a voltage window of 3.5–4.85V (vs. Li+ / Li). The specific test steps were as follows: 2 cycles of 0.1C charge-discharge, 100 cycles of 0.33C charge-2C discharge, and 5 cycles of 0.33C charge-3C discharge. The retention rate after 100 cycles was the percentage of the 2C discharge capacity in the 100th cycle to the 2C discharge capacity in the 1st cycle. The 4V plateau percentage was the ratio of the discharge capacity below 4.4V in the first cycle to the total discharge capacity in the first cycle. The 2C / 0.1C rate percentage was the ratio of the 2C discharge capacity in the first cycle to the 0.1C discharge capacity in the first cycle.

[0148] Table 2:

[0149] As shown in Table 1, compared with the comparative example, the battery discharge capacity and rate performance of the embodiment are superior. In terms of the contribution of the 4V platform capacity, the nickel manganese oxide of the embodiment is slightly higher. This may be because the nickel manganese oxide of the embodiment forms more lithium-rich phase and disordered phase nickel manganese oxide at the surface and interface, which is also one of the reasons for the better rate performance and discharge capacity.

[0150] Furthermore, Table 1 shows that the values ​​of C1 and C2 in Examples exhibit significant changes, with a large difference between C2 and C1, indicating that the overall Mn content of the material changes from the outside inwards. 4+ / Mn 3+ The valence state changes significantly, exhibiting a clear gradient. Unlike other embodiments in Example 1, the values ​​of C1 and C2 are significantly smaller, indicating that the coating of high-valence element M causes the surface lithium nickel manganese oxide structure to transform into a disordered phase. Similarly, the difference between C2 and C1 in the comparative example is smaller, indicating that the material as a whole changes from the outside to the inside due to the presence of Mn. 4+ / Mn 3+ The valence state change is small and there is no obvious gradient change, indicating that during the second calcination process, the flux element M diffused and entered the bulk. In the embodiment, the flux element M mainly plays a role in the repair of the oriented crystal plane during the second calcination process. Because it is difficult to undergo Ni / Mn site substitution with lithium-deficient spinel during the repair process, it agglomerates on the material surface.

[0151] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this disclosure, and are not intended to limit them. Although this disclosure has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this disclosure.

Claims

1. A positive electrode active material, characterized in that, The positive electrode active material satisfies the following formula: Among them, I (111) I (222) I (400) and I (440) None of them are 0.

2. The positive electrode active material according to claim 1, characterized in that, The positive electrode active material includes trivalent manganese ions and tetravalent manganese ions, and the mass ratio of trivalent manganese ions to tetravalent manganese ions increases from the center of the positive electrode active material to the outer surface.

3. The positive electrode active material according to claim 2, characterized in that, The chemical composition of the positive electrode active material includes: Li a Ni b Mn c M d O 4-h ; Wherein, 1.0≤a≤1.006, 0.495≤b≤0.505, 1.495≤c≤1.505, 0≤d≤0.003, -0.082<h<0.21, b+c=2, and M is selected from at least one of W, Mo, Ta, Nb, V, and Sb.

4. The positive electrode active material according to claim 2 or 3, characterized in that, The disorder degree of the positive electrode active material is 6%-9%.

5. A method for preparing a positive electrode active material as described in any one of claims 1-4, characterized in that, Includes the following steps: A mixture comprising a nickel-manganese hydroxide precursor and a first lithium source is sintered once in an oxygen-containing atmosphere at a heating rate of 1-5℃ / min to m℃ to obtain an intermediate; wherein the first lithium source is calculated based on lithium element, the nickel-manganese hydroxide precursor is calculated based on the sum of nickel and manganese elements, and the molar ratio of the nickel-manganese hydroxide precursor to the first lithium source is 2:0.8-0.95; The mixture comprising the intermediate and the second lithium source is heated to n℃ twice in an oxygen-containing atmosphere at a heating rate of 1-5℃ / min to obtain the positive electrode active material, where n is less than m.

6. The preparation method according to claim 5, characterized in that, The first lithium source is calculated based on lithium element, the nickel-manganese hydroxide precursor is calculated based on the sum of nickel and manganese elements, and the molar ratio of the nickel-manganese hydroxide precursor to the first lithium source is 2:0.85-0.

9.

7. The preparation method according to claim 5, characterized in that, The condition m satisfies: 950≤m≤1050.

8. The preparation method according to claim 5, characterized in that, The condition n satisfies: 750≤n≤850.

9. A positive electrode plate, characterized in that, It includes a current collector and a positive electrode active layer disposed on at least one surface of the current collector; the positive electrode active layer includes the positive electrode active material according to any one of claims 1-4.

10. A battery, characterized in that, Includes the positive electrode sheet as described in claim 9.

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