Lithium battery cathode material, method for preparing the same, and use

Abstract

This disclosure relates to lithium battery cathode materials, methods for preparing the same, and their use, and to the technical field of lithium batteries. The ability of a polycrystalline cathode material to resist the occurrence of internal cracks during the cycling process is evaluated by its burst strength. A lithium battery cathode material is provided, which has a burst strength that meets a specific range, possesses high-strength crystals and grain boundaries, improves the stability of the material structure, effectively suppresses the diffusion of internal cracks to the interface, and thereby improves the cycling stability and lifespan of the material.

Description

[Technical Field]

[0001] This disclosure relates to the technical field of lithium batteries, and more specifically to lithium battery cathode materials, methods for preparing them, and their use.

[0002] Cross-reference of related applications This disclosure claims priority based on a Chinese patent application filed with the China Patent Administration on 9 July 2024, application number 2024109102998, titled "Lithium Battery Cathode Material, Method for Preparation thereof, and Use thereof," the entire contents of which are incorporated into this disclosure by reference. [Background technology]

[0003] With the rapid development of lithium-ion batteries, ternary cathode materials have also developed dramatically. Ternary cathode materials have advantages such as high specific capacity, reasonable price, low toxicity, and abundant resources. However, ternary materials also have many problems. Nickel-rich ternary materials in particular have problems such as poor battery cycle performance, multi-stage phase changes during the charge and discharge process, large volume changes during charge and discharge that easily generate residual stress, and the risk of mechanical rupture.

[0004] To improve the tap density of ternary materials while simultaneously suppressing surface side reactions, ternary materials are prepared as secondary particles with densely packed primary particles. This significantly reduces contact between the primary particles and the electrolyte, thereby reducing the occurrence of interfacial side reactions. However, the use of secondary particles presents new challenges. First, secondary particles require an extremely dense arrangement of primary particles, particularly a dense interface. This effectively blocks contact between the internal primary particles and the electrolyte, but synthesizing these dense secondary particles is extremely difficult. Furthermore, during the charge-discharge process, the secondary particles expand and contract in volume, increasing internal stress. Over long cycles, this stress accumulates, gradually leading to the formation of microcracks inside and on the surface of the secondary particles, ultimately causing the entire secondary particle to rupture.

[0005] The mechanical rupture of ternary cathode materials proceeds as follows: During the charging process, Li + As Li is desorbed, the interlayer distance of the ternary material gradually increases. This is mainly due to Li + This is because the interlayer electrostatic repulsion force increases after delithiation. When a high delithium state is reached, the interlayer distance contracts. This contraction is due to the excess Li + It is thought that this is due to structural slippage caused by the desorption of oxygen from between layers, or that the interlayer electrostatic repulsion decreases as oxygen participates in oxidation-reduction reactions, resulting in a reduction in the interlayer distance. During the discharge process, the change in interlayer distance is the exact opposite of that during the charging process. In one charge-discharge cycle, the layered material experiences four expansions and contractions, inevitably generating residual stress due to the volume change. The accumulation of residual stress causes microcracks to form at the grain boundaries between particles, increasing contact with the electrolyte and accelerating interfacial side reactions. This further accelerates the expansion of the microcracks, ultimately leading to particle rupture, a decrease in battery capacity, and ultimately, battery failure. From the above, it can be seen that the final rupture of polycrystalline ternary cathode material particles is related to the deformation of the unit cell and the deterioration of the grain boundaries of the ternary cathode material. Since both the unit cell and grain boundaries affect the susceptibility of crack formation during the use of the cathode material, it is extremely important to provide a cathode material that simultaneously possesses high-strength crystals and grain boundaries.

[0006] Therefore, there is currently an urgent need to provide cathode materials that simultaneously possess high-strength crystals and grain boundaries, thereby enhancing the material's ability to resist the occurrence of internal cracks during the cycling process, and further improving the material's cycling stability and lifespan.

[0007] In light of the above, we submit this disclosure. [Overview of the project]

[0008] This disclosure aims to provide lithium battery cathode materials, methods for preparing them, and their uses in order to enhance the material's ability to resist the occurrence of internal cracks during the cycling process, and to further improve the material's cycling stability and lifespan.

[0009] This disclosure will be implemented as follows:

[0010] In the first aspect, the present disclosure provides a lithium battery cathode material, and the fracture strength of this lithium battery cathode material is 4 MPa to 15 MPa.

[0011]

Number

[0012] St represents the crushing strength, which is measured by an indentation test and has the unit of MPa.

Number

Number

[0013] <00​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​ [Number] refers to the shear strain measured in the static state before initial charging.

[0017] a and c represent the unit cell parameters.

[0018] In an optional embodiment, the fracture strength of the lithium battery cathode material is 6 MPa to 15 MPa.

[0019] St = 2.8×P / (πd 2 ) is obtained.

[0020] P represents the maximum press force value immediately before the sudden drop point of the press force in the indentation test, and the unit is mN.

[0021] d represents the particle size of the lithium battery cathode material, and the unit is μm.

[0022] [Number] The value of is 0.2 to 0.3, and [Number] The value of is 0.01 to 0.20, and the value of St is from 90 MPa to 140 MPa.

[0023] c and a are obtained by X-ray diffractometer XRD test.

[0024] In an optional embodiment, the general formula of the lithium battery cathode material is Li x Ni a Co b M c M’ 1-a-b-c A y O 2-y is as follows.

[0025] In the general formula, M is selected from at least one of Al and Mn.

[0026] M' is selected from at least one of the following: Zr, Sr, Mo, Ba, W, B, Ti, Mg, Li, Si, Ca, Cu, La, Ce, Bi, In, Al, Nb, Y.

[0027] A is chosen from at least one of P and F.

[0028] 0.95≦x<1.1, a>0, b>0, c>0, 0.95≦(a+b+c)≦1, 0≦y≦0.01.

[0029] In a second aspect, the disclosure further provides a method for preparing lithium battery cathode materials, the method comprising the step of preparing a lithium battery cathode material that satisfies burst strength requirements.

[0030] In an optional embodiment, the process involves: preparing a precursor core by performing a coprecipitation reaction using a nickel salt, a cobalt salt, and an M salt; mixing the precursor core with a reinforcing solution and firing it to obtain a reinforcing precursor core; performing a coprecipitation reaction using a nickel salt, a cobalt salt, an M salt, and a first doping element compound to grow a shell based on the reinforcing precursor core to obtain a ternary precursor having a core-shell structure; and mixing the ternary precursor with a lithium source and firing it, or mixing the ternary precursor with a second doping element compound and a lithium source. The process includes a step of mixing and calcining a supply, wherein a reinforcing aid is obtained by calcining the raw materials in the reinforcing solution, the reinforcing aid is selected from at least one of LiAlO2, LiMn2O4, and LiCoPO4, the doping element contained in the first doping element compound is selected from at least one of Ti, Al, Zr, and Mg, and the doping element contained in the second doping element compound is selected from at least one of Zr, Sr, Mo, Ba, W, B, Ti, Mg, Li, F, Si, Ca, Cu, La, P, Ce, Bi, In, Nb, and Y.

[0031] In an optional embodiment, the primary particles of the precursor core are arranged radially and have a porosity of 4% to 12%.

[0032] In an optional embodiment, the preparation of the precursor core includes the step of placing a base liquid in a reaction vessel and passing a first mixed metal salt solution, a first precipitant solution, and a first complexing agent solution through the base liquid to carry out a coprecipitation reaction, wherein the preparation of the precursor core satisfies at least one of features A1 to E1.

[0033] Feature A1: Controls the reaction temperature of the coprecipitation reaction to 75°C to 95°C.

[0034] Feature B1: Controls the reaction pH of the coprecipitation reaction to 10.5-11.5.

[0035] Feature C1: The supply of reactants is stopped when the particle size D50 reaches 2 μm to 17 μm.

[0036] Feature D1: The coprecipitation reaction is carried out in an inert gas atmosphere, and the rotation speed during the reaction is 400 rpm to 800 rpm.

[0037] Feature E1: After the coprecipitation reaction is complete, aging is performed, followed by alkaline solution washing, water washing, and drying in that order.

[0038] In an optional embodiment, the preparation of the precursor core satisfies at least one of features F1 to K1.

[0039] Feature F1: The first complexing agent solution is an aqueous ammonia solution with a mass fraction of 18% to 22%, and the ammonia concentration in the reaction vessel is controlled to 3 g / L to 7 g / L during the precipitation process.

[0040] Feature G1: The total molar concentration of metal ions in the first mixed metal salt solution is 1.8 M to 2.2 M, and the flow rate of the first mixed metal salt solution is 400 L / h to 500 L / h.

[0041] Feature H1: The molar ratio of nickel, cobalt, and M in the first mixed metal salt solution is (35-98):(1-35):(1-35).

[0042] Feature I1: The salt in the first mixed metal salt solution is selected from one of the following: nitrate, chloride, or sulfate.

[0043] Feature J1: The first precipitating agent solution is a sodium hydroxide solution with a mass fraction of 30% to 34%.

[0044] Feature K1: The ammonia concentration in the base solution is 4.5 g / L to 5.5 g / L, and the pH is 11.8 to 12.2.

[0045] In an optional embodiment, the preparation of the reinforced precursor core involves mixing the precursor core with the reinforcement solution, sonicating it, reacting it for 10 to 60 minutes under conditions of a temperature of 100°C to 150°C and a pressure of 10 MPa to 20 MPa, then performing solid-liquid separation, and calcining the resulting solid.

[0046] In an optional embodiment, the preparation of the reinforced precursor core satisfies at least one of features A2 to F2.

[0047] Feature A2: The reinforcing solution further contains a thickening agent, and the viscosity of the reinforcing solution can be adjusted from 5 mPa·s to 8 mPa·s by adjusting the amount of the thickening agent.

[0048] Feature B2: If Feature A2 is met, the thickener is selected from at least one of carbomer, xanthan gum, gelatin, and starch.

[0049] Feature C2: The dosage of the reinforcing solution corresponding to 1 g of precursor core is 90 mL to 110 mL.

[0050] Feature D2: Control the ultrasonic treatment time from 10 to 60 minutes.

[0051] Feature E2: The firing temperature is controlled to 600°C to 700°C, and the firing time to 3 to 8 hours.

[0052] Feature F2: The solid components are dried at 80°C to 120°C for 5 to 10 hours, then baked.

[0053] In an optional embodiment, the preparation of a ternary precursor having a core-shell structure includes the steps of adding a reinforced precursor core to a base liquid in a reaction vessel, and passing a second mixed metal salt solution, a second precipitant solution, and a second complexing agent solution through the reaction vessel to carry out a coprecipitation reaction, wherein the second mixed metal salt solution contains a nickel salt, a cobalt salt, an M salt, and a first doped element compound, and by controlling the addition rate of the second mixed metal salt solution, the addition rates of nickel, cobalt, and the M element during the reaction process are controlled to be lower than the addition rates during the preparation of the precursor core.

[0054] In an optional embodiment, the preparation of a ternary precursor having a core-shell structure satisfies at least one of features A3 to I3.

[0055] Feature A3: The total molar concentrations of nickel, cobalt, and element M in the second mixed metal salt solution are 1.8M to 2.2M, the flow rate of the second mixed metal salt solution is 100 L / h to 200 L / h, and the pH of the second mixed metal salt solution is controlled to 2 to 5.

[0056] Feature B3: The total molar amount of metal is calculated from the total molar amounts of nickel, cobalt, and element M, and the ratio of the total molar amount of metal in the reinforcing precursor core to the total molar amount of metal in the second mixed metal salt solution is (4-12):1.

[0057] Feature C3: The molar ratio of nickel, cobalt, and element M in the second mixed metal salt solution is (30-60):(20-35):(20-35).

[0058] Feature D3: The reaction temperature for the coprecipitation reaction is 75°C to 95°C, and the reaction pH is 10.8 to 11.2.

[0059] Feature E3: The second complexing agent solution is an aqueous ammonia solution with a mass fraction of 18% to 22%, and the ammonia concentration in the reaction vessel is controlled to 3 g / L to 7 g / L during the precipitation process.

[0060] Feature F3: The first doped element compound is selected from at least one of titanium disulfate, sodium metaaluminate, zirconium nitrate, zirconium acetate, zirconium sulfate, magnesium sulfate, and magnesium nitrate.

[0061] Feature G3: The base liquid in the reaction vessel is water, and the second precipitant solution is a sodium hydroxide solution with a mass fraction of 30% to 40%.

[0062] Feature H3: The coprecipitation reaction is carried out in an inert gas atmosphere, and the rotation speed during the reaction is 300 rpm to 500 rpm.

[0063] Feature I3: After the addition of the second mixed metal salt solution is complete, the reaction is continued for another 0.5 to 2.0 hours, followed by solid-liquid separation. The resulting solid is then washed with water and dried.

[0064] In an optional embodiment, the step of mixing a ternary precursor, a second doped element compound, and a lithium source and calcining them satisfies at least one of features A4 to F4.

[0065] Feature A4: The molar ratio of nickel, cobalt, and the total amount of M element in the ternary precursor to the lithium content in the lithium source is 1:(1.05~1.1).

[0066] Feature B4: The lithium source is selected from lithium hydroxide.

[0067] Feature C4: The second doped element compound is selected from at least one of oxides, fluorides, carbonates, hydroxides, nitrides, borides, and nitrates.

[0068] Feature D4: The firing process involves a primary firing at 400°C to 500°C for 2 to 6 hours, followed by a secondary firing at 750°C to 850°C for 10 to 15 hours.

[0069] Feature E4: Firing is performed in an oxygen-containing atmosphere.

[0070] Feature F4: Sintering is performed after mixing the ternary precursor, the second doped element compound, and the lithium source, and then polishing the mixture.

[0071] In a third aspect, the Disclosure further provides a positive electrode piece which comprises a lithium battery positive electrode material according to any of the above embodiments or a lithium battery positive electrode material prepared by a preparation method according to any of the above embodiments.

[0072] In the fourth aspect, the present disclosure further provides a lithium battery which includes a positive electrode piece according to the above embodiment.

[0073] This disclosure has the following beneficial effects: By constructing a formula for calculating burst strength, we can evaluate the ability of polycrystalline cathode materials to resist the occurrence of internal cracks during the cycling process. We comprehensively consider the effects of the unit cell and grain boundaries to ensure that the burst strength satisfies a specific numerical range. Cathode materials whose burst strength satisfies a specific numerical range possess high-strength crystals and grain boundaries, improving the stability of the material structure, effectively suppressing the diffusion of internal cracks to the interface, and ultimately improving the cycling stability and lifespan of the material.

[0074] To more clearly describe the technical modes of the embodiments in this disclosure, the drawings necessary for describing the embodiments are briefly described below. The drawings described are only a selection of embodiments of this disclosure and do not limit the scope. Those skilled in the art can obtain other relevant drawings based on these drawings without inventive ability. [Brief explanation of the drawing]

[0075] [Figure 1] This is an ionic cross-sectional view of the cathode material according to Example 1. [Figure 2] This is an ion cross-sectional view of the cathode material according to Comparative Example 1. [Figure 3] This is a cross-sectional view of the cathode material according to Example 1. [Figure 4] This is a cross-sectional view of the cathode material according to Comparative Example 2. [Figure 5]This shows the XRD spectra of the precursor core and precursor material according to Example 1. [Figure 6] These are TEM and EDS images of the cathode material according to Example 1, where (a) is the TEM image and (b) is the EDS image. [Figure 7] These are TEM and EDS images of the cathode material according to Example 4, where (a) is the TEM image and (b) is the EDS image. [Modes for carrying out the invention]

[0076] To clarify the purpose, technical modes, and advantages of the embodiments of this disclosure, the technical modes in the embodiments of this disclosure will be described clearly and completely below. In the embodiments, where specific conditions are not specified, it is possible to perform the experiments under conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, it is possible to use commercially available conventional products.

[0077] The embodiments of this disclosure provide a lithium battery cathode material, which is a polycrystalline material formed by the aggregation of primary particles into secondary particles. The general formula for the lithium battery cathode material is Li x Ni a Co b M c M' 1-a-b-c A y O 2-y That is the case.

[0078] The explanation of each parameter in the general formula is as follows:

[0079] M is selected from at least one of Al and Mn, and M can be any one or two of the above.

[0080] M' is selected from at least one of Zr, Sr, Mo, Ba, W, B, Ti, Mg, Li, Si, Ca, Cu, La, Ce, Bi, In, Al, Nb, and Y, and M' can be one or more of the above.

[0081] A is selected from at least one of P and F, and can be any one or two of the above.

[0082] x, y, a, b, and c are expressed in moles, and 0.95 ≤ x < 1.1, where x can be specifically 0.95, 0.96, 0.97, 0.98, 0.99, 1.00, 1.03, 1.05, 1.08, 1.10, etc.

[0083] a>0, b>0, c>0, and 0.95≦(a+b+c)≦1, so a+b+c can be 0.95, 0.96, 0.97, 0.98, 0.99, 1.00, etc. When a+b+c=1, the element M' is not present.

[0084] 0 ≤ y ≤ 0.01, and the value of y can be 0.000, 0.003, 0.005, 0.008, 0.010, etc. If the value of y is 0, the positive electrode material does not contain element A.

[0085] The inventors found that the ability of a cathode material to resist the occurrence of internal cracks during the cycling process is determined by both crystal strength and grain boundary strength, and that this relationship can be expressed by the following equation.

[0086]

number

[0087] St represents the crushing strength, measured by an indentation test, and its unit is MPa. The crushing strength of the material is calculated from the pressure obtained from the maximum press force value just before the point of steepest decrease in press force during the test, and St = 2.8 × P / (πd 2 ) where P represents the maximum pressing force value just before the point of steepest decrease in pressing force, and its unit is mN. d represents the particle size of the lithium battery positive electrode material, and its unit is μm.

[0088]

number

number

[0089]

number

number

[0090]

number

number

number

number

[0091] c represents the unit cell parameter, and a represents the unit cell parameter. c and a are determined by X-ray diffraction (XRD) testing.

[0092] The burst strength of the lithium battery cathode material according to the embodiments of this disclosure is 4 MPa to 15 MPa, preferably 6 MPa to 15 MPa, and may be, for example, 4 MPa, 5 MPa, 6 MPa, 7 MPa, 8 MPa, 9 MPa, 10 MPa, 11 MPa, 12 MPa, 13 MPa, 14 MPa, 15 MPa, etc., but may be any value between the adjacent values ​​above.

[0093]

number

[0094]

number

[0095] The St value is between 90 MPa and 140 MPa, for example, 90 MPa, 100 MPa, 110 MPa, 120 MPa, 130 MPa, 140 MPa, etc.

[0096] This disclosure provides parameter indicators for bursting strength, enabling a comprehensive evaluation of various factors that cause internal cracks in cathode materials, such as the crystal structure itself and grain boundary strength.

number

number

[0097] Unit cell deformation is an inherent property of the material and is usually addressed by improving chemical bond strength through elemental doping. Regarding the problem of grain boundary degradation, improvements are typically made by controlling the grain shape of primary particles, their morphology after aggregation, and by elemental doping. The inventors further provide a method for preparing lithium battery cathode materials, satisfying the requirements for product burst strength through elemental doping and core-shell structure. The specific preparation steps are as follows.

[0098] The embodiments of this disclosure provide a method for preparing lithium battery cathode material, which includes the following steps.

[0099] S1: Preparation of the precursor core A precursor core is prepared by coprecipitation reaction using a nickel salt, a cobalt salt, and an M salt (i.e., a salt containing element M in the general formula). The M salt can be a manganese salt, but it can also be an aluminum salt.

[0100] In some embodiments, the primary particles of the precursor core are radially arranged, and the porosity is 4% to 12% (e.g., 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, etc.). The radial arrangement of primary particles and the maintenance of a constant porosity contribute to stress release, as well as to suppressing the formation of grain boundary cracks during the cycle process of the cathode material and mitigating irreversible phase changes from the layered phase to the rock salt phase, thereby improving the structural stability of the ternary cathode material.

[0101] In some examples, the preparation of the precursor core includes the following steps: A base liquid is placed in a reaction vessel, and a first mixed metal salt solution, a first precipitant solution, and a first complexing agent solution are passed through the base liquid to carry out a coprecipitation reaction in an inert gas atmosphere, with the reaction temperature controlled to 75°C to 95°C, the reaction pH to 10.5 to 11.5, and the rotation speed to 400 rpm to 800 rpm. As the particles gradually grow, the supply of reactants is stopped when the particle size D50 reaches 2 μm to 17 μm. After the coprecipitation reaction is complete, aging is performed, followed by washing with an alkaline solution, washing with water, and drying in that order. Residual sodium sulfur can be removed by washing with an alkaline solution, residual alkaline solution on the surface can be removed by washing with water, and moisture can be removed by drying. After drying, sieving is performed to obtain a precursor core that satisfies the particle size requirements.

[0102] Specifically, the reaction temperature for the coprecipitation reaction is 75°C, 80°C, 85°C, 90°C, 95°C, etc., the pH is 10.5, 10.8, 11.0, 11.2, 11.5, etc., and the rotation speed can be 400 rpm, 500 rpm, 600 rpm, 700 rpm, 800 rpm, etc. The particle size of the product is measured during the reaction, and the particle size D50 at the end of the reaction is controlled to 2 μm, 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 17 μm, etc. The inert gas atmosphere may be nitrogen gas, but is not limited to this. Alkaline solution washing is performed using a hot dilute alkaline solution to effectively remove residual sodium sulfur.

[0103] In some examples, the first complexing agent solution is an aqueous ammonia solution with a mass fraction of 18% to 22%, and the ammonia concentration in the reaction vessel during the precipitation process is adjusted to 3 g / L to 7 g / L by adjusting the rate of addition of the first complexing agent solution. The first precipitating agent solution is a sodium hydroxide solution with a mass fraction of 30% to 34%, and the pH of the reaction system is controlled to satisfy the requirements by adjusting the rate of addition of the first precipitating agent solution. Specifically, the mass fraction of the aqueous ammonia solution may be 18%, 20%, 22%, etc., the ammonia concentration in the reaction vessel during the precipitation process may be 3 g / L, 4 g / L, 5 g / L, 6 g / L, 7 g / L, etc., and the mass fraction of the sodium hydroxide solution may be 30%, 31%, 32%, 33%, 34%, etc.

[0104] In some examples, the molar ratio of nickel, cobalt, and M in the first mixed metal salt solution is (35-98):(1-35):(1-35). The total molar concentration of metal ions in the first mixed metal salt solution is 1.8M-2.2M, and the flow rate of the first mixed metal salt solution is 400 L / h-500 L / h. By further adjusting the composition, concentration, and addition rate of the first mixed metal salt solution, the deposition rate can be controlled, and a porous morphology can be formed in the precursor core.

[0105] Specifically, in the first mixed metal salt solution, the molar ratio of nickel, cobalt, and element M may be 35:30:35, 40:30:30, 50:20:30, 60:20:20, 70:10:20, 80:10:10, 90:5:5, 98:1:1, etc. The total molar concentration of metal ions in the first mixed metal salt solution refers to the total concentration of nickel, cobalt, and element M, and may be 1.8M, 1.9M, 2.0M, 2.1M, 2.2M, etc. The flow rate of the first mixed metal salt solution may be 400 L / h, 420 L / h, 450 L / h, 480 L / h, 500 L / h, etc.

[0106] Furthermore, the salts in the first mixed metal salt solution are selected from one of nitrates, chlorides, or sulfates, and may, for example, all be nitrates or any one of the above salts. Nickel nitrate, cobalt nitrate, and manganese nitrate (or aluminum nitrate) are used as raw materials.

[0107] In some examples, the base solution can be prepared using an aqueous ammonia solution and a sodium hydroxide solution. To satisfy the reaction conditions for coprecipitation, the ammonia concentration in the base solution is 4.5 g / L to 5.5 g / L, and the pH is 11.8 to 12.2. Specifically, the ammonia concentration in the base solution may be 4.5 g / L, 5.0 g / L, 5.5 g / L, etc., and the pH may be 11.8, 11.9, 12.0, 12.1, 12.2, etc. The volume of the base solution occupies 60% to 80% of the volume of the reaction vessel.

[0108] S2: Preparation of reinforced precursor core A precursor core is mixed with a reinforcing solution, and after calcination, a reinforcing agent is introduced to obtain a reinforced precursor core. The introduced reinforcing agent is selected from at least one of LiAlO2, LiMn2O4, and LiCoPO4, and the introduced reinforcing agent may be one or more of the above. The grain boundaries of the primary particles of the precursor core are reinforced by the sol-gel method, thereby increasing the grain boundary strength of the primary particles.

[0109] In some examples, the preparation of the reinforcing precursor core includes the following steps: The precursor core and reinforcing solution are mixed and sonicated for 10 to 60 minutes, then reacted for 10 to 60 minutes under conditions of a temperature of 100°C to 150°C and a pressure of 10 MPa to 20 MPa, and after the reaction is complete, solid-liquid separation is performed and the resulting solid is calcined. The reaction is carried out under high temperature and high pressure conditions, and the solvent is vaporized by heating to pressurize the reaction solution and ensure that the precursor core is completely immersed.

[0110] Specifically, the time for mixing the precursor core and reinforcing solution and ultrasonic treatment can be 10, 20, 30, 40, 50, or 60 minutes. High-temperature, high-pressure reactions can be carried out in a general high-pressure reaction vessel, with reaction temperatures of 100°C, 110°C, 120°C, 130°C, 140°C, or 150°C, reaction pressures of 10 MPa, 13 MPa, 15 MPa, 18 MPa, or 20 MPa, and reaction times under pressure maintenance controlled to 10, 20, 30, 40, 50, or 60 minutes.

[0111] The reinforcing agent can be obtained by calcining the raw materials in the reinforcing solution. For example, if the reinforcing agent is LiMn2O4, the raw materials may be manganese acetate and lithium hydroxide.

[0112] In some examples, the reinforcing solution further contains a thickening agent, and the viscosity of the reinforcing solution is adjusted to 5 mPa·s to 8 mPa·s by adjusting the amount of the thickening agent. The higher the viscosity, the more easily the reinforcing solution remains in the pores of the precursor core, and further crystallization occurs during the calcination process. That is, if the viscosity is too low, the doping amount will also be low. If the viscosity is too high, penetration into the pores becomes difficult, and the doping amount will also be low. The thickening agent is selected from at least one of carbomer, xanthan gum, gelatin, and starch, and the thickening agent may be one or more of the above. The amount of reinforcing solution corresponding to 1 g of precursor core is 90 mL to 110 mL, for example, 90 mL, 95 mL, 100 mL, 105 mL, or 110 mL.

[0113] In some examples, the firing temperature is controlled to 600°C to 700°C and the firing time to 3 to 8 hours. After firing, a reinforcing agent can be introduced into the precursor core to increase the grain boundary strength of the primary particles. Specifically, the firing temperature may be 600°C, 620°C, 650°C, 680°C, 700°C, etc., and the firing time may be 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, etc.

[0114] In some examples, the solids are dried at 80°C to 120°C for 5 to 10 hours before firing to thoroughly remove surface moisture. Specifically, the drying temperature can be 80°C, 90°C, 100°C, 110°C, 120°C, etc., and the drying time can be 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, etc.

[0115] S3: Preparation of a ternary precursor having a core-shell structure Coprecipitation reactions are carried out using nickel salts, cobalt salts, M salts, and primary doped element compounds to grow a shell based on a reinforced precursor core, thereby obtaining a ternary precursor having a core-shell structure.

[0116] In some examples, the preparation of a ternary precursor having a core-shell structure includes the following steps: A reinforced precursor core is added to a base liquid in a reaction vessel, and a coprecipitation reaction is carried out by passing a second mixed metal salt solution, a second precipitant solution, and a second complexing agent solution through the reaction vessel. The second mixed metal salt solution contains a nickel salt, a cobalt salt, an M salt, and a first dope element compound. By controlling the addition rate of the second mixed metal salt solution, the addition rates of nickel, cobalt, and the M element during the reaction process are controlled to be lower than the addition rates during the preparation of the precursor core. Reducing the addition rate of the second mixed metal salt solution controls the coprecipitation reaction rate, contributing to the securing of a denser shell.

[0117] Furthermore, the molar ratio of nickel, cobalt, and element M in the second mixed metal salt solution is (30-60):(20-35):(20-35). The preparation of a dense shell with low Ni content and doped elements contributes to reducing contact with the electrolyte. In addition, element doping and low Ni content contribute to improving the strength and stability of the crystal structure, increasing its ability to resist strain and suppressing the diffusion of internal cracks to the interface. The total molar concentration of nickel, cobalt, and element M in the second mixed metal salt solution is 1.8M-2.2M. Before adding to the reaction vessel, acid is added to adjust the pH of the second mixed metal salt solution to 2-5 to prevent precipitate formation. During the precipitation process, the second mixed metal salt solution can be slowly added dropwise to the reaction vessel using a peristaltic pump, and the flow rate of the second mixed metal salt solution is controlled to 100 L / h-200 L / h.

[0118] Specifically, the molar ratio of nickel, cobalt, and element M in the second mixed metal salt solution may be 30:35:35, 40:30:30, 50:25:25, 60:20:20, etc. The total molar concentrations of nickel, cobalt, and element M in the second mixed metal salt solution may be 1.8M, 1.9M, 2.0M, 2.1M, 2.2M, etc. Before being placed in the reaction vessel, the pH of the second mixed metal salt solution may be 3.5, 3.8, 4.0, 4.2, 4.5, etc. The flow rate of the second mixed metal salt solution may be 100 L / h, 120 L / h, 150 L / h, 180 L / h, 200 L / h, etc.

[0119] Furthermore, the total molar amount of metal is calculated from the total molar amounts of nickel, cobalt, and element M, and the ratio of the total molar amount of metal in the reinforcing precursor core to the total molar amount of metal in the second mixed metal salt solution is (4-12):1. By adjusting the dosage of the core and shell, the ratio of core to shell can be adjusted to improve the electrochemical performance of the material. Specifically, the ratio of the total molar amount of metal in the reinforcing precursor core to the total molar amount of metal in the second mixed metal salt solution can be 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, etc.

[0120] The doped element in the first doped element compound is selected from at least one of Ti, Al, Zr, and Mg, and the doped element in the first doped element compound may be any one or more of the above. The first doped element compound is selected from at least one of titanium disulfate, sodium metaaluminate, zirconium nitrate, zirconium acetate, zirconium sulfate, magnesium sulfate, and magnesium nitrate, and the first doped element compound may be any one or more of the above. The dose is adjusted according to the amount of doping of the doped element.

[0121] In some examples, the base liquid in the reaction vessel is water, and the volume of water in the reaction vessel may be 15% to 25% of the volume of the reaction vessel. The second precipitating agent solution is a sodium hydroxide solution with a mass fraction of 30% to 40%. The pH during the reaction is adjusted to 10.8 to 11.2 by adjusting the rate of addition of the second precipitating agent solution. The second complexing agent solution is an aqueous ammonia solution with a mass fraction of 18% to 22%, and the ammonia concentration in the reaction vessel is controlled to 3 g / L to 7 g / L during the precipitation process. Specifically, the mass fraction of the sodium hydroxide solution may be 30%, 32%, 34%, 36%, 38%, 40%, etc., and the pH during the reaction may be 10.8, 10.9, 11.0, 11.1, 11.2, etc. The mass fraction of the ammonia aqueous solution is 18%, 19%, 20%, 21%, 22%, etc., and the ammonia concentration in the reaction vessel during the precipitation process can be 3g / L, 4g / L, 5g / L, 6g / L, 7g / L, etc.

[0122] In some examples, the precipitation process is carried out in an inert gas atmosphere (e.g., nitrogen gas). To ensure the reaction proceeds at a uniform rate, the reaction temperature for the coprecipitation reaction is set to 75°C to 95°C, and the rotation speed during the reaction is set to 300 rpm to 500 rpm. Specifically, the reaction temperatures may be 75°C, 80°C, 85°C, 90°C, 95°C, etc., and the rotation speed during the reaction may be 300 rpm, 400 rpm, 500 rpm, etc.

[0123] Furthermore, after the addition of the second mixed metal salt solution is complete, the reaction is continued for another 0.5 to 2.0 hours (for example, 0.5 hours, 1.0 hours, 1.5 hours, 2.0 hours, etc.), after which solid-liquid separation is performed, the obtained solid is washed with water and dried to obtain a precursor having a dense shell.

[0124] S4: Preparation of ternary cathode material A ternary precursor, a second doped element compound, and a lithium source are mixed and calcined to obtain a ternary cathode material.

[0125] The doping element in the second doping compound is selected from at least one of Zr, Sr, Mo, Ba, W, B, Ti, Mg, Li, F, Si, Ca, Cu, La, P, Ce, Bi, In, Nb, and Y, and the doping element in the second doping compound may be any one or more of the above. The second doping compound is selected from at least one of oxides, fluorides, carbonates, hydroxides, nitrides, borides, and nitrates, and the second doping compound may be any one or more of the above. The requirement for the amount of doping of the doping element is satisfied by adjusting the dose of the second doping compound.

[0126] In some embodiments, the lithium source may be, but is not limited to, lithium hydroxide. The molar ratio of nickel, cobalt, and the total amount of M element in the ternary precursor to the lithium content in the lithium source is 1:(1.05~1.1), and can be 1:1.05, 1:1.06, 1:1.07, 1:1.08, 1:1.09, 1:1.10, etc.

[0127] In some embodiments, firing is performed in an oxygen-containing atmosphere. The firing process involves first performing a primary firing at 400°C to 500°C for 2 to 6 hours, followed by a secondary firing at 750°C to 850°C for 10 to 15 hours. A uniform lithium battery cathode material is obtained through this two-stage firing process, where low-temperature and high-temperature firing are performed sequentially. Specifically, the oxygen-containing atmosphere may, but is not limited to, an oxygen gas atmosphere. The primary firing temperature may be 400°C, 420°C, 450°C, 480°C, 500°C, etc., and the primary firing time may be 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, etc. The secondary firing temperature may be 750°C, 780°C, 800°C, 820°C, 850°C, etc., and the secondary firing time may be 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, etc.

[0128] In some embodiments, calcination is performed after mixing and polishing the ternary precursor, the second doped element compound, and the lithium source. Polishing helps to more uniformly mix the raw materials, which contributes to improving the uniformity of the cathode material.

[0129] The lithium battery cathode materials prepared in the embodiments of this disclosure have high burst strength and a core-shell structure. The core has primary particles arranged radially and has a constant porosity. The shell is dense, has a low Ni content, and contains doped elements.

[0130] Embodiments of the present disclosure further provide a positive electrode piece comprising the lithium battery positive electrode material described above. The positive electrode piece comprises a positive electrode active coating layer, and the lithium battery positive electrode material is present in the positive electrode active coating layer.

[0131] Embodiments of the present disclosure further provide a lithium battery which includes the positive electrode piece, a negative electrode piece, an electrolyte, a separator, etc., to form a complete battery structure, and has excellent cycle performance.

[0132] Specifically, the types of the negative electrode, electrolyte, and separator are not limited. During the charging and discharging process of a secondary battery, active ions move back and forth between the positive and negative electrode pieces, being inserted and removed, while the electrolyte plays a role in ion conduction between the positive and negative electrode pieces.

[0133] In other embodiments, instead of a secondary battery, a form such as a battery module or battery pack may be adopted.

[0134] Embodiments of this disclosure provide devices including the above-described secondary batteries, battery modules, and battery packs, which may function as a power source for the device or as an energy storage unit for the device. These devices may, but are not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, and energy storage systems.

[0135] The features and performance of this disclosure will be described in more detail below with reference to examples.

[0136] This disclosure provides cathode materials shown in Tables 1 and 2 and evaluates the burst strength of said cathode materials. Furthermore, its cycle performance and electrochemical performance are tested, and the results are shown in Table 3. The methods for evaluating the strength and testing the performance of the cathode materials prepared in the examples and comparative examples are as follows.

[0137] (1) Observe the overall and cross-sectional microstructure of the material using a JEOL JSM-6490LV scanning electron microscope. To obtain the complete cross-sectional morphology of the sample, cut the sample using focused ion beam spectroscopy. For porosity analysis of the ion cross-section, measure the porosity of the ion cross-section using NanoMeasurer software.

[0138] (2) The active material is coated onto an ultrathin aluminum foil, a molded cell with a Be window is assembled, and then in-situ XRD measurements are performed using an EMPYREAN type XRD diffractometer. The measurements are performed as follows: The cell is charged and discharged at a current density of 0.1C, the 2θ range of the X-ray scan is 10 to 60°, and each scan period is 600 s. The values ​​of the unit cell parameters c and a of the cell during the charging process under a voltage of 3 to 4.5V, and the values ​​of the unit cell parameters c and a after 10 cycles are recorded.

number

[0139] (3) Particle size: Measured using an MS3000 laser particle size analyzer.

[0140] (4) Tap density shall be measured in accordance with the TD:GB / T21354-2008 method for measuring tap density of powder products.

[0141] (5) BET specific surface area: The specific surface area of ​​the material is determined by analyzing the data from the medium- and low-pressure stages of the nitrogen gas adsorption / desorption curve using the BET formula. The test was performed using an Autosorb IQ2 automatic specific surface area porosimetry analyzer manufactured by Anton Paar GmbH in Austria, and the BET (BET) of the cathode material during initial charging was determined. 0 (and notation) and the BET after 100 charge-discharge cycles of the positive electrode material (BET t The following parameters (indicated as) are measured and calculated. The method for collecting samples after cycling is as follows: After cycling, the battery is flexibly disassembled and the electrode pieces are removed. The electrode pieces are immersed in DMSO and stirred until the electrode powder is completely detached. The electrode powder is washed five times with ethanol and then dried at 60°C until quantifiable. The carbon material and positive electrode material in the electrode powder are separated using a magnetic separator, and the separated positive electrode material is used as the test sample.

[0142] (6) For chemical composition analysis, a PE Avio200 inductively coupled plasma emission spectrometer (ICP-OES) is used.

[0143] (7) The sample is evaluated using an FEI Titan Cubed G2 60-300 transmission electron microscope. First, the local diffraction pattern of the material is obtained by limited-field electron diffraction (SAED) to determine the crystal structure. Next, a high-resolution atomic arrangement image is acquired in high-angle annular dark-field imaging (HAADF-STEM) mode, and then the elemental distribution of the material is qualitatively and quantitatively analyzed using an EDS detector.

[0144] (8) Crushing strength measurement: The prepared powder is dispersed in NMP by ultrasonic treatment, and the resulting dispersion is dropped onto a 2cm x 2cm smooth silicone sheet and dried with a heating lamp to obtain a well-dispersed sample. The sample is observed with an optical microscope, and particles spaced 100 μm or more apart are selected on the silicone sheet. An indentation test of the labeled particles is performed using a CSM UNHT nanoindenter with a 100 μm diameter flat indenter head, and a relationship curve between press force and displacement is obtained. In real-time monitoring of the indentation test, a sharp drop in press force is used as the criterion for determining particle pulverization. The crushing strength (St) of the particles is calculated using equation (1) with the maximum press force P just before the sharp drop in press force, and n particles are extracted from each sample and tested, and the average crushing strength is calculated using equation (2).

number

[0145] Formula (1) St = 2.8 × P / (πd 2 )

[0146] Formula (2)

number

[0147] St represents the crushing strength, in units of MPa. P represents the maximum pressing force value just before the point of sharp drop in pressing force, in units of mN. d represents the particle size of the lithium battery cathode material, in units of μm.

number

[0148] (9) Electrochemical performance: Rate performance tests will be conducted using the LANHE CT2001A battery test system.

[0149] Electrode preparation method: Weigh ternary cathode material, conductive carbon black, and PVDF in a mass ratio of 8:1:1, polish thoroughly, transfer to a bottle, add an appropriate amount of NMP solvent, and stir with a stirrer for 24 hours to form a uniform slurry. Apply the prepared slurry uniformly to clean aluminum foil using a wet film applicator, and load at a rate of 2.5 ± 0.05 mg / cm³. 2 After controlling the temperature, the material is dried in a 100°C vacuum drying oven for 24 hours until no more material adheres. Then, the electrode pieces are placed in a hydraulic press and roll-rolled at a pressure of 6 MPa.

[0150] Button battery assembly: The positive electrode piece is further punched out into a circular electrode piece with a diameter of 12 mm. Then, a metallic lithium circular piece is used as the negative electrode, Celgard 2300 as the separator, and a 1 M LiPF6 solution (solvent is a mixed solution of EMC, DC, and DMC in a volume ratio of 1:1:1) is used as the electrolyte to assemble a CR2032 type button battery.

[0151] Tables 1, 2, and 3 show the parameters of the samples prepared in the examples and comparative examples, such as particle size D50, TD, BET, and crush strength, and the calculated burst strength is shown in Table 2.

[0152] [Table 1]

[0153] [Table 2]

[0154] [Table 3]

[0155] From the data in Tables 1, 2, and 3, the greater the burst strength of the positive electrode material, the greater the rate of change in the specific surface area of ​​the material (BET). t / BET 0 It can be seen that the ) becomes smaller. This indicates that the greater the burst strength of the material, the greater its ability to resist the occurrence of microcracks during charge-discharge cycles, resulting in superior cycle stability. The burst strength of the comparative example exceeds the limiting range of this application, which is the cause of the significantly reduced cycle performance.

[0156] Example 1 This example uses lithium battery cathode material (LiN i0.761 Co 0.11 Mn 0.123 Ti 0.006 A method for preparing O2) is provided, corresponding to the product of Example 1 above, and includes the following steps.

[0157] (1) Preparation of precursor core Metal sulfates were weighed with nickel, cobalt, and manganese in a molar ratio of 8:1:1 and dissolved in deionized water to form a metal salt solution with a total molar concentration of 2M metal ions. 70 vol% coprecipitation base solution was added to the reaction vessel, adjusting the ammonia concentration of the base solution to 5 g / L and the pH to 12 ± 0.2. The metal salt solution, sodium hydroxide solution (30 wt%) as a precipitating agent, and aqueous ammonia solution (20 wt%) as a complexing agent were simultaneously added to the reaction vessel via a supply pump through a nitrogen gas supply. The temperature was raised to 85°C and the coprecipitation reaction was carried out at a stirring speed of 600 rpm. During the reaction, the flow rate of the aqueous ammonia solution was adjusted to stabilize the ammonia concentration at 4 g / L, the flow rate of the sodium hydroxide solution was adjusted to stabilize the reaction pH at 11, and the flow rate of the metal salt solution was adjusted to 450 L / h. The reaction conditions were maintained and the reaction continued until the D50 particle size reached 8 μm. After that, the supply of reactants was stopped and the mixture was aged for 12 hours. After aging, the slurry was washed with a 60 g / L NaOH solution at 80°C to remove residual sodium sulfur, then washed with pure water at 80°C, dried at 120°C for 12 hours, and sieved to obtain a ternary precursor core (porosity 8.44%).

[0158] (2) Preparation of reinforcement precursors A reinforcing solution was prepared. The reinforcing solution was an aqueous solution containing 2 wt% manganese acetate, 0.15 wt% lithium hydroxide, and 1.5 wt% starch, with a viscosity of 6.5 mPa.s.

[0159] The precursor core obtained in step (1) was placed in the reinforcing solution, with a solid-liquid ratio of 1 g to 100 mL between the precursor core and the reinforcing solution. After sonication for 30 minutes, a reaction solution was obtained, which was placed in a high-pressure reaction vessel. The solvent was vaporized by heating and the reaction solution was pressurized. The heating temperature was controlled to 100°C to 110°C and the pressure to 15 MPa to ensure that the precursor core was completely immersed. After maintaining the pressure for 30 minutes, the reaction solution was filtered. The solid obtained by filtration was dried at 100°C for 8 hours, then calcined at 650°C for 6 hours, and cooled to obtain a reinforced precursor core.

[0160] (3) Preparation of a ternary precursor having a core-shell structure Nickel, cobalt, and manganese sulfates and titanium disulfate were dissolved in deionized water, and an acid was added to adjust the pH to 4 to form a metal salt solution. The molar ratio of nickel, cobalt, and manganese in the nickel, cobalt, and manganese salts in the metal salt solution was 50:30:20, the molar concentration of the first doped element compound was 0.11 M, and the total molar concentration of nickel, cobalt, and manganese ions in the metal salt solution was 2 M. The ratio of the total molar amounts of nickel, cobalt, and manganese in the reinforced precursor core prepared in step (2) to the total molar amounts of nickel, cobalt, and manganese in the metal salt solution was 8:1.

[0161] 20% by volume of deionized water was placed in the reaction vessel, nitrogen gas was passed through, and the reinforced precursor core obtained in step (2) was added. The metal salt solution was slowly added dropwise to the reaction vessel at a rate of 150 L / h using a peristaltic pump while stirring. The pH of the reaction mixture was adjusted to 11 ± 0.2 with sodium hydroxide solution and ammonia water, and the ammonia concentration was 5 g / L. After the dropwise addition was complete, the reaction was allowed to proceed for 1 hour, followed by pressure filtration, washing with pure water at 80°C, and then drying at 120°C for 12 hours to obtain a ternary precursor having a core-shell structure.

[0162] (4) Preparation of ternary cathode materials The ternary precursor obtained in step (3) was mixed with lithium hydroxide, polished, and then calcined to obtain a ternary cathode material. Its chemical formula is LiN i0.761 Co 0.11 Mn 0.123 Ti 0.006 The material used was O2. A ternary precursor and a lithium source were added so that the molar ratio of Li / (Ni+Co+Mn) was 1.05. The calcination conditions were as follows: the temperature was raised to 450°C at a rate of 1°C / min in an oxygen gas atmosphere and held for 4 hours, and then the temperature was raised to 800°C at a rate of 2°C / min and held for 12 hours.

[0163] Example 2 The difference from Example 1 is that step (1) is as follows.

[0164] Metal sulfates were weighed with nickel, cobalt, and manganese in a molar ratio of 8:1:1 and dissolved in deionized water to form a metal salt solution with a total molar concentration of 2M metal ions. 60 vol% coprecipitation base solution was added to the reaction vessel, adjusting the ammonia concentration of the base solution to 5.5 g / L and the pH to 12 ± 0.2. The metal salt solution, sodium hydroxide solution (30 wt%) as a precipitating agent, and aqueous ammonia solution (20 wt%) as a complexing agent were simultaneously added to the reaction vessel via a supply pump through nitrogen gas. The temperature was raised to 75°C, and the coprecipitation reaction was carried out at a stirring speed of 800 rpm. During the reaction, the flow rate of the aqueous ammonia solution was adjusted to stabilize the ammonia concentration at 7 g / L, the flow rate of the sodium hydroxide solution was adjusted to stabilize the reaction pH at 11, and the flow rate of the metal salt solution was adjusted to 450 L / h. The reaction conditions were maintained, and the reaction continued until the D50 particle size reached 8 μm. After that, the supply of reactants was stopped, and the mixture was aged for 12 hours. After aging, the slurry was washed with a 60 g / L NaOH solution at 80°C to remove residual sodium sulfur, then washed with pure water at 80°C, dried at 120°C for 12 hours, and sieved to obtain a ternary precursor core (porosity 4.13%).

[0165] Example 3 The difference from Example 1 is that step (1) is as follows.

[0166] Metal sulfates were weighed with nickel, cobalt, and manganese in a molar ratio of 8:1:1 and dissolved in deionized water to form a metal salt solution with a total molar concentration of 2M metal ions. 80 vol% coprecipitation base solution was added to the reaction vessel, adjusting the ammonia concentration of the base solution to 4.5 g / L and the pH to 12 ± 0.2. The metal salt solution, sodium hydroxide solution (30 wt%) as a precipitating agent, and aqueous ammonia solution (20 wt%) as a complexing agent were simultaneously added to the reaction vessel via a supply pump through a nitrogen gas supply. The temperature was raised to 95°C and the coprecipitation reaction was carried out at a stirring speed of 800 rpm. During the reaction, the flow rate of the aqueous ammonia solution was adjusted to stabilize the ammonia concentration at 3 g / L, the flow rate of the sodium hydroxide solution was adjusted to stabilize the reaction pH at 11, and the flow rate of the metal salt solution was adjusted to 450 L / h. The reaction conditions were maintained and the reaction continued until the D50 particle size reached 8 μm. Afterward, the supply of reactants was stopped and the mixture was aged for 12 hours. After aging, the slurry was washed with a 60 g / L NaOH solution at 80°C to remove residual sodium sulfur, then washed with pure water at 80°C, dried at 120°C for 12 hours, and sieved to obtain a ternary precursor core (porosity 11.85%).

[0167] Example 4 The only difference from Example 1 is that some conditions in steps (2) to (4) are different, specifically as follows.

[0168] In step (2), the reinforcing solution is an aqueous solution containing 2 wt% aluminum isopropoxide and 0.24 wt% lithium hydroxide, with a viscosity of 5.8 mPa.s. The solid-liquid ratio of the precursor core to the reinforcing solution is 1 g:100 mL. Drying was carried out at 100°C for 8 hours, and calcination was carried out at 600°C for 5 hours.

[0169] In step (3), nickel, cobalt, and manganese sulfates and magnesium sulfate were dissolved in deionized water, and an acid was added to adjust the pH to 4 to form a metal salt solution. The molar ratio of nickel, cobalt, and manganese in the nickel, cobalt, and manganese salts in the metal salt solution was 60:20:20, the concentration of magnesium sulfate was 0.018 M, and the total molar concentration of nickel, cobalt, and manganese ions in the metal salt solution was 2 M. The ratio of the total molar amounts of nickel, cobalt, and manganese in the reinforcing precursor core to the total molar amounts of nickel, cobalt, and manganese in the metal salt solution was 8:1. 20% by volume of deionized water was placed in the reaction vessel, nitrogen gas was passed through, and the reinforcing precursor core obtained in step (2) was added. The metal salt solution was slowly added to the reaction vessel at a rate of 100 L / h using a peristaltic pump while stirring. The pH of the reaction mixture was adjusted to 11 ± 0.2 with sodium hydroxide solution and ammonia water, and the ammonia concentration was 3 g / L. After the dropwise addition was complete, the mixture was reacted for 1 hour, then filtered under pressure, washed with pure water at 80°C, and dried at 120°C for 12 hours to obtain a ternary precursor having a core-shell structure.

[0170] In step (4), the ternary precursor and lithium source were added so that the molar ratio of Li / (Ni+Co+Mn) was 1.05. The calcination conditions were as follows: heating to 500°C at a rate of 1°C / min in an oxygen gas atmosphere and holding for 4 hours, and then heating to 750°C at a rate of 2°C / min and holding for 12 hours.

[0171] Example 5 The only difference from Example 1 is that some conditions in steps (2) to (4) are different, specifically as follows.

[0172] In step (2), the reinforcing solution is an aqueous solution containing 2 wt% cobalt acetate, 0.75 wt% lithium acetate, 1.1 wt% phosphoric acid, and 1.8 wt% carbomer 940, with a viscosity of 7.4 mPa.s. The solid-liquid ratio of the precursor core to the reinforcing solution is 1 g:100 mL. Drying was carried out at 100°C for 8 hours, and calcination was carried out at 700°C for 10 hours.

[0173] In step (3), nickel, cobalt, and manganese sulfates and zirconium acetate were dissolved in deionized water, and an acid was added to adjust the pH to 5 to form a metal salt solution. The molar ratio of nickel, cobalt, and manganese in the nickel, cobalt, and manganese salts in the metal salt solution was 60:20:20, the concentration of zirconium acetate was 0.04 M, and the total molar concentration of nickel, cobalt, and manganese ions in the metal salt solution was 2 M. The ratio of the total molar amounts of nickel, cobalt, and manganese in the reinforcing precursor core to the total molar amounts of nickel, cobalt, and manganese in the metal salt solution was 4:1. 20 vol% deionized water was placed in the reaction vessel, nitrogen gas was passed through, and the reinforcing precursor core obtained in step (2) was added. The metal salt solution was slowly added to the reaction vessel at a rate of 150 L / h using a peristaltic pump while stirring. The pH of the reaction mixture was adjusted to 11±0.2 with sodium hydroxide solution and aqueous ammonia, and the ammonia concentration was 5 g / L. After the addition of the solution dropwise was complete, the reaction was allowed to proceed for 1 hour, followed by pressure filtration, washing with pure water at 80°C, and drying at 120°C for 12 hours to obtain a ternary precursor having a core-shell structure.

[0174] In step (4), the ternary precursor and lithium source were added so that the molar ratio of Li / (Ni+Co+Mn) was 1.05. The calcination conditions were as follows: heating to 500°C at a rate of 1°C / min in an oxygen gas atmosphere and holding for 4 hours, and then heating to 850°C at a rate of 2°C / min and holding for 12 hours.

[0175] Example 6 The only difference from Example 1 is that some conditions in steps (2) to (4) are different, specifically as follows.

[0176] In step (2), the reinforcing solution is an aqueous solution containing 2 wt% aluminum isopropoxide and 0.24 wt% lithium hydroxide, with a viscosity of 5.8 mPa.s. The solid-liquid ratio of the precursor core to the reinforcing solution is 1 g:100 mL. Drying was carried out at 100°C for 8 hours, and calcination was carried out at 700°C for 10 hours.

[0177] In step (3), nickel, cobalt, and manganese sulfates and titanium disulfate were dissolved in deionized water, and an acid was added to adjust the pH to 4 to form a metal salt solution. The molar ratio of nickel, cobalt, and manganese in the nickel, cobalt, and manganese salts in the metal salt solution was 33:33:34, the concentration of titanium disulfate was 0.1 M, and the total molar concentration of nickel, cobalt, and manganese ions in the metal salt solution was 2 M. The ratio of the total molar amounts of nickel, cobalt, and manganese in the reinforcing precursor core to the total molar amounts of nickel, cobalt, and manganese in the metal salt solution was 12:1. 20% by volume of deionized water was placed in the reaction vessel, nitrogen gas was passed through, and the reinforcing precursor core obtained in step (2) was added. The metal salt solution was slowly added to the reaction vessel at a rate of 200 L / h using a peristaltic pump while stirring. The pH of the reaction mixture was adjusted to 11 ± 0.2 with sodium hydroxide solution and ammonia water, and the ammonia concentration was 7 g / L. After the dropwise addition was complete, the mixture was reacted for 1 hour, then filtered under pressure, washed with pure water at 80°C, and dried at 120°C for 12 hours to obtain a ternary precursor having a core-shell structure.

[0178] In step (4), the ternary precursor and lithium source were added so that the molar ratio of Li / (Ni+Co+Mn) was 1.05, and the amount of B element doping in the boron oxide was 0.2%. The calcination conditions were as follows: heating to 500°C at a rate of 1°C / min in an oxygen gas atmosphere and holding for 4 hours, and then heating to 850°C at a rate of 2°C / min and holding for 12 hours.

[0179] Example 7 The difference from Example 1 is that in step (2), the reinforcing solution is an aqueous solution containing 2 wt% aluminum isopropoxide, 0.24 wt% lithium hydroxide, and 0.62 wt% starch, with a viscosity of 6.5 mPa.s.

[0180] Example 8 The difference from Example 1 is that in step (2), the reinforcing solution is an aqueous solution containing 2 wt% cobalt acetate, 0.75 wt% lithium acetate, 1.1 wt% phosphoric acid, and 0.79 wt% starch, with a viscosity of 6.5 mPa.s.

[0181] Example 9 The difference from Example 1 is that in step (2), the reinforcing solution is an aqueous solution containing 2 wt% manganese acetate and 0.15 wt% lithium hydroxide, with a viscosity of 1.62 mPa.s.

[0182] Example 10 The difference from Example 1 is that in step (2), the reinforcing solution is an aqueous solution containing 2 wt% manganese acetate, 0.15 wt% lithium hydroxide, and 2.12 wt% starch, with a viscosity of 7.92 mPa.s.

[0183] Comparative Example 1 (Porosity is less than 4%) The difference from Example 1 is that step (1) is as follows.

[0184] Metal sulfates were weighed with nickel, cobalt, and manganese in a molar ratio of 8:1:1 and dissolved in deionized water to form a metal salt solution with a total molar concentration of 2M metal ions. 50 vol% coprecipitation base solution was added to the reaction vessel, adjusting the ammonia concentration of the base solution to 4 g / L and the pH to 11.5 ± 0.2. The metal salt solution, sodium hydroxide solution (30 wt%) as a precipitating agent, and aqueous ammonia solution (20 wt%) as a complexing agent were simultaneously added to the reaction vessel via a supply pump through nitrogen gas. The temperature was raised to 85°C and the coprecipitation reaction was carried out at a stirring speed of 600 rpm. During the reaction, the flow rate of the aqueous ammonia solution was adjusted to stabilize the ammonia concentration at 3 g / L, the flow rate of the sodium hydroxide solution was adjusted to stabilize the reaction pH at 10, and the flow rate of the metal salt solution was adjusted to 450 L / h. The reaction conditions were maintained and the reaction continued until the D50 particle size reached 8 μm. After that, the supply of reactants was stopped and the mixture was aged for 12 hours. After aging, the slurry was washed with a 60 g / L NaOH solution at 80°C to remove residual sodium sulfur, then washed with pure water at 80°C, dried at 120°C for 12 hours, and sieved to obtain a ternary precursor core (porosity 2.2%).

[0185] Comparative Example 2 (Primary particles are granular) The difference from Example 1 is that step (1) is as follows.

[0186] Metal sulfates were weighed with nickel, cobalt, and manganese in a molar ratio of 8:1:1 and dissolved in deionized water to form a metal salt solution with a total molar concentration of 2M metal ions. 50 vol% coprecipitation base solution was added to the reaction vessel, adjusting the ammonia concentration of the base solution to 5 g / L and the pH to 12 ± 0.2. The metal salt solution, sodium hydroxide solution (30 wt%) as a precipitating agent, and aqueous ammonia solution (20 wt%) as a complexing agent were simultaneously added to the reaction vessel via a supply pump through nitrogen gas. The temperature was raised to 50°C, and the coprecipitation reaction was carried out at a stirring speed of 300 rpm. During the reaction, the flow rate of the aqueous ammonia solution was adjusted to stabilize the ammonia concentration at 6 g / L, the flow rate of the sodium hydroxide solution was adjusted to stabilize the reaction pH at 11, and the flow rate of the metal salt solution was adjusted to 500 L / h. The reaction conditions were maintained, and the reaction continued until the D50 particle size reached 8 μm. After that, the supply of reactants was stopped, and the mixture was aged for 12 hours. After aging, the slurry was washed with a 60 g / L NaOH solution at 80°C to remove residual sodium sulfur, then washed with pure water at 80°C, dried at 120°C for 12 hours, and sieved to obtain a ternary precursor core (porosity 6.7%).

[0187] Comparative Example 3 (Precursor shell not formed) The difference from Example 1 is that step (3) is omitted, and step (4) is as follows.

[0188] A ternary cathode material was obtained by mixing a ternary precursor, lithium hydroxide, and titanium oxide, polishing the mixture, and then firing it. The ternary precursor and lithium source were added so that the molar ratio of Li / (Ni+Co+Mn) was 1.05, and the amount of Ti doping in the titanium oxide was 0.2%. The firing conditions were as follows: heating to 450°C at a rate of 1°C / min in an oxygen gas atmosphere for 4 hours, and then heating to 800°C at a rate of 2°C / min for 12 hours.

[0189] Comparative Example 4 (No grain boundary reinforcement was performed) The only difference from Example 1 is that step (2) was omitted.

[0190] Result analysis: Figures 1 and 2 show ionic cross-sectional views of the cathode materials prepared in Example 1 and Comparative Example 1. The core-shell structure can be confirmed, and Example 1 shows a higher porosity.

[0191] Figures 3 and 4 show cross-sectional views of Example 1 and Comparative Example 2. It was confirmed that the primary particles in Example 1 were distributed radially, while the primary particles in Comparative Example 2 were granular.

[0192] Figure 5 shows the XRD spectra of the precursor core and precursor material prepared in Example 1. The spectra matched the PDF (Powder Diffraction File), there were no impurity phases on the surface, and clear cracks were observed at the (006) and (012) peaks, as well as the (018) and (110) peaks in all samples, confirming that the layered structure of the surface samples was good.

[0193] Figures 6 and 7 show TEM and EDS images of the cathode materials prepared in Examples 1 and 4. Concentrations of Mn and Al elements were observed at the grain boundaries composed of primary particles, confirming that the reinforcing agent was effectively distributed near the grain boundaries and reinforced the primary particles.

[0194] The foregoing description is merely a preferred embodiment of the Disclosure and does not limit the Disclosure. Those skilled in the art may have various modifications and changes to the Disclosure. Any modifications, equivalent substitutions, or improvements made, as long as they do not deviate from the spirit and principles of the Disclosure, are within the scope of the Disclosure. [Industrial applicability]

[0195] This disclosure evaluates the ability of polycrystalline cathode materials to resist the occurrence of internal cracks during the cycling process by constructing a formula for calculating burst strength. The influence of the unit cell and grain boundaries is comprehensively considered to ensure that the burst strength satisfies a specific numerical range. Cathode materials whose burst strength satisfies this specific numerical range possess high-strength crystals and grain boundaries, improving the stability of the material structure, effectively suppressing the diffusion of internal cracks to the interface, and ultimately improving the material's cycling stability and lifespan. The measuring devices for each parameter in the burst strength formula are all common testing equipment, easy to operate, and suitable for industrial applications.

Claims

1. The burst strength is 4 MPa to 15 MPa. [Math 1] And so, St represents the crushing strength, measured by an indentation test, and its unit is MPa. [Math 2] This represents the average crushing strength, and its unit is MPa. [Math 3] Therefore, n is the sample size, and n ≥ 10. [Math 4] This refers to the maximum change in shear strain during the initial charging process. [Math 5] And so, [Math 6] This refers to the change in shear strain after 10 charge-discharge cycles, where t = 10. [Number 7] This refers to the shear strain measured in a static state after 10 charge-discharge cycles. [Number 8] This refers to the shear strain measured in a static state before initial charging. a and c represent unit cell parameters. A lithium battery cathode material characterized by the following features.

2. The burst strength of the lithium battery positive electrode material is 6 MPa to 15 MPa. St=2.8×P / (πd ２ ) and P represents the maximum pressing force value immediately before the point of steepest decrease in pressing force during the indentation test, and its unit is mN. d represents the particle size of the lithium battery positive electrode material, with the unit being μm. [Number 9] The value is between 0.2 and 0.

3. [Number 10] The value of is 0.01 to 0.20, and the value of St is 90 MPa to 140 MPa. c and a are determined by X-ray diffraction (XRD) testing. The lithium battery cathode material according to feature 1.

3. The general formula for the lithium battery cathode material is Li ｘ Ni ａ Co ｂ M ｃ M' １－ａ－ｂ－ｃ A ｙ O ２－ｙ And, In the general formula, M is selected from at least one of Al and Mn. M' is selected from at least one of Zr, Sr, Mo, Ba, W, B, Ti, Mg, Li, Si, Ca, Cu, La, Ce, Bi, In, Al, Nb, Y. A is selected from at least one of P and F. 0.95 ≤ x < 1.1, a > 0, b > 0, c > 0, 0.95 ≤ (a + b + c) ≤ 1, 0 ≤ y ≤ 0.

01. The lithium battery cathode material according to claim 1 or 2.

4. This includes a step of preparing a lithium battery cathode material that meets the requirements for burst strength. A method for preparing a lithium battery cathode material according to any one of claims 1 to 3.

5. The process involves a coprecipitation reaction using nickel salts, cobalt salts, and M salts to prepare a precursor core, The process involves mixing the aforementioned precursor core with a reinforcing solution, firing it, and then obtaining a reinforcing precursor core. A step of performing a coprecipitation reaction using a nickel salt, a cobalt salt, an M salt, and a first-doped element compound to grow a shell based on the reinforced precursor core and obtain a ternary precursor having a core-shell structure, The process includes mixing the ternary precursor and a lithium supply source and firing, or mixing the ternary precursor, a second doped element compound, and a lithium supply source and firing, The raw materials in the reinforcing solution are fired to obtain a reinforcing aid, and the reinforcing aid is selected from at least one of LiAlO ２ , LiMn ２ O ４ , LiCoPO ４ . The doped element contained in the first doped element compound is selected from at least one of Ti, Al, Zr, and Mg. The doping element contained in the second doped element compound is selected from at least one of Zr, Sr, Mo, Ba, W, B, Ti, Mg, Li, F, Si, Ca, Cu, La, P, Ce, Bi, In, Nb, and Y. The preparation method according to feature 4.

6. The primary particles of the precursor core are arranged radially and have a porosity of 4% to 12%. The preparation method according to feature 5.

7. The preparation of the precursor core includes the step of placing a base liquid in a reaction vessel and passing a first mixed metal salt solution, a first precipitant solution, and a first complexing agent solution through the base liquid to carry out a coprecipitation reaction. The preparation of the precursor core is as follows: Feature A: Controlling the reaction temperature of the coprecipitation reaction to 75°C to 95°C. １ and, Feature B: Controlling the reaction pH of the coprecipitation reaction to 10.5-11.5 １ and, Feature C: Stop supplying reactants when the particle size D50 reaches 2 μm to 17 μm. １ and, The coprecipitation reaction is carried out in an inert gas atmosphere, and the rotation speed during the reaction is 400 rpm to 800 rpm. Feature D １ and, Feature E: After the coprecipitation reaction is complete, aging is performed, followed by washing with an alkaline solution, washing with water, and drying in that order. １ and, A １ ~E １ at least one of the following The preparation method according to claim 5 or 6, characterized by the features described herein.

8. The preparation of the precursor core is as follows: The first complexing agent solution is an aqueous ammonia solution with a mass fraction of 18% to 22%, and is characterized by controlling the ammonia concentration in the reaction vessel to 3 g / L to 7 g / L during the precipitation process. １ and, The total molar concentration of metal ions in the first mixed metal salt solution is 1.8 M to 2.2 M, and the flow rate of the first mixed metal salt solution is 400 L / h to 500 L / h. Feature G １ and, The molar ratio of nickel, cobalt, and M in the first mixed metal salt solution is (35-98):(1-35):(1-35), characteristic H １ and, The salt in the first mixed metal salt solution is selected from one of nitrates, chlorides, or sulfates. Feature I １ and, The first precipitating agent solution is characterized by being a sodium hydroxide solution with a mass fraction of 30% to 34%. １ and, The ammonia concentration in the base solution is 4.5 g / L to 5.5 g / L, and the pH is 11.8 to 12.

2. Feature K １ and, Feature F １ ~Features K １ at least one of the following The preparation method according to feature 7.

9. The preparation of the reinforced precursor core includes the steps of mixing the precursor core with the reinforcement solution, ultrasonically treating it, reacting it for 10 to 60 minutes under conditions of a temperature of 100°C to 150°C and a pressure of 10 MPa to 20 MPa, then performing solid-liquid separation, and calcining the resulting solid. The preparation method according to any one of claims 5 to 8, characterized by the features described herein.

10. The preparation of the reinforced precursor core is as follows: The reinforcing solution further contains a thickening agent, and by adjusting the amount of the thickening agent, the viscosity of the reinforcing solution can be set to 5 mPa·s to 8 mPa·s. ２ and, If feature A2 is satisfied, the thickener is selected from at least one of carbomer, xanthan gum, gelatin, and starch. Feature B ２ and, Characteristic C: The amount of the reinforcing solution corresponding to 1 g of the precursor core is 90 mL to 110 mL. ２ and, Feature D: Controlling the ultrasonic treatment time from 10 to 60 minutes. ２ and, Feature E: Controlling the firing temperature to 600°C to 700°C and the firing time to 3 to 8 hours. ２ and, The aforementioned solid content is dried at 80°C to 120°C for 5 to 10 hours, and then fired. ２ and, Feature A ２ ~Features F ２ at least one of the following The preparation method according to feature 9.

11. The preparation of the ternary precursor having the core-shell structure includes the steps of adding the reinforcing precursor core to a base liquid in a reaction vessel, and passing a second mixed metal salt solution, a second precipitant solution, and a second complexing agent solution through the reaction vessel to carry out a coprecipitation reaction. The second mixed metal salt solution contains a nickel salt, a cobalt salt, an M salt, and a first doped element compound. By controlling the addition rate of the second mixed metal salt solution, the addition rates of nickel, cobalt, and the M element during the reaction process are controlled to be lower than the addition rates used during the preparation of the precursor core. The preparation method according to any one of claims 5 to 10, characterized by the features described herein.

12. The preparation of the ternary precursor having the core-shell structure is as follows: The total molar concentration of nickel, cobalt, and element M in the second mixed metal salt solution is 1.8 M to 2.2 M, the flow rate of the second mixed metal salt solution is 100 L / h to 200 L / h, and the pH of the second mixed metal salt solution is controlled to 2 to 5. ３ and, The total molar amount of metal is calculated from the total molar amounts of nickel, cobalt, and element M, and the ratio of the total molar amount of metal in the reinforcing precursor core to the total molar amount of metal in the second mixed metal salt solution is (4-12):

1. Feature B ３ and, Characteristic C: The molar ratio of nickel, cobalt, and element M in the second mixed metal salt solution is (30-60):(20-35):(20-35). ３ and, The reaction temperature for the coprecipitation reaction is 75°C to 95°C, and the reaction pH is 10.8 to 11.

2. Feature D ３ and, The second complexing agent solution is an aqueous ammonia solution with a mass fraction of 18% to 22%, and features E that controls the ammonia concentration in the reaction vessel to 3 g / L to 7 g / L during the precipitation process. ３ and, The first doped element compound is characterized by being selected from at least one of titanium disulfate, sodium metaaluminate, zirconium nitrate, zirconium acetate, zirconium sulfate, magnesium sulfate, and magnesium nitrate. ３ and, The base liquid in the reaction vessel is water, and the second precipitant solution is a sodium hydroxide solution with a mass fraction of 30% to 40%. ３ and, The coprecipitation reaction is carried out in an inert gas atmosphere, and the rotation speed during the reaction is 300 rpm to 500 rpm. ３ and, After the addition of the second mixed metal salt solution, the reaction is continued for another 0.5 to 2.0 hours, followed by solid-liquid separation, and the resulting solid is washed with water and dried. Feature I ３ and, Feature A ３ ~Feature I ３ at least one of the following The preparation method according to feature 11.

13. The process of mixing the ternary precursor, the second doped element compound, and the lithium supply source and calcining them is as follows: Characteristic A: The molar ratio of nickel, cobalt, and the total amount of M element in the ternary precursor to the lithium content in the lithium source is 1:(1.05 to 1.1). ４ and, The lithium source is selected from lithium hydroxide. (Feature B) ４ and, The second doped element compound is characterized by being selected from at least one of oxides, fluorides, carbonates, hydroxides, nitrides, borides, and nitrates. ４ and, The aforementioned firing process is characterized by first performing a primary firing at 400°C to 500°C for 2 to 6 hours, followed by a secondary firing at 750°C to 850°C for 10 to 15 hours. ４ and, Firing is performed in an oxygen-containing atmosphere (Feature E) ４ and, The calcination is carried out after mixing the ternary precursor, the second doped element compound, and the lithium supply source and polishing the mixture, characteristic F. ４ and, Feature A ４ ~Features F ４ at least one of the following The preparation method according to any one of claims 5 to 12.

14. The lithium battery cathode material includes the lithium battery cathode material described in any one of claims 1 to 3 or the lithium battery cathode material prepared by the preparation method described in any one of claims 4 to 13. A positive electrode piece characterized by the following features.

15. Includes the positive electrode piece described in claim 14 A lithium battery characterized by the following features.

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