Positive electrode active materials, batteries and their preparation methods

Abstract

This application discloses a positive electrode active material, a battery, and a method for preparing the same. The positive electrode active material comprises porous secondary particles and satisfies the following characteristic: 4≤BET×TD×(Dv90-Dv10)≤14, where BET represents the specific surface area of ​​the positive electrode active material in m². 2 / g, TD represents the tap density of the positive electrode active material, in g / cm³. 3 Dv90 represents the particle size value (in μm) corresponding to a cumulative volume distribution percentage of 90% for the positive electrode active material, and Dv10 represents the particle size value (in μm) corresponding to a cumulative volume distribution percentage of 10% for the positive electrode active material. This application improves low-temperature power performance by controlling the particle morphology, size, and pore structure of the positive electrode active material; and by rationally controlling the particle morphology, particle size distribution, and tap density of the positive electrode active material, it achieves an increase in the volumetric energy density of the battery.

Description

Technical Field

[0001] This application relates to the field of new energy technology, specifically to a positive electrode active material, a battery, and a method for preparing the same. Background Technology

[0002] Batteries, such as lithium-ion batteries, have been widely used in various fields due to their advantages such as high specific energy, good power performance, low self-discharge, and long cycle life. Currently, the positive electrode active materials used in electric vehicle batteries are mainly ternary cathode active materials, but their raw materials (such as cobalt sulfate and lithium salts) are expensive. To further reduce the cost of electric vehicles, increasing the volumetric energy density of lithium-ion batteries can reduce the space occupied by battery modules in the vehicle, which is of positive significance for the lightweight development and cost reduction of new energy vehicles. Furthermore, the operating environment of electric vehicle batteries is becoming increasingly harsh, especially cold weather, which severely tests battery performance. Therefore, it is necessary to improve the low-temperature performance of batteries, particularly their low-temperature power performance. Summary of the Invention

[0003] Technical issues

[0004] This application provides a positive electrode active material, a battery, and a method for preparing the same, which solves the problems of poor low-temperature power and low volumetric energy density of batteries prepared from current positive electrode active materials.

[0005] Technical solutions

[0006] According to the positive electrode active material provided in the first aspect of this application, the positive electrode active material includes secondary particles with pores. The positive electrode active material satisfies the following characteristic: 4≤BET×TD×(Dv90-Dv10)≤14, where BET represents the specific surface area of ​​the positive electrode active material in m². 2 / g, TD represents the tap density of the positive electrode active material, in g / cm³. 3 Dv90 represents the particle size value corresponding to a cumulative volume distribution percentage of 90% for the positive electrode active material, in μm; Dv10 represents the particle size value corresponding to a cumulative volume distribution percentage of 10% for the positive electrode active material, in μm. The positive electrode active material contains lithium nickel cobalt manganese oxide, which contains nickel, cobalt, and manganese elements. The sum of the molar amounts of nickel, cobalt, and manganese is taken as 1, and the nickel content is greater than 0.3%. The maximum pore size of the positive electrode active material is D... max nm, satisfying: 800≤D max ≤2200.

[0007] Optionally, in other embodiments of this application, 0.4≤BET≤3.5; 1.2≤TD≤2.6; 4≤Dv90≤18; 1.5≤Dv10≤6.

[0008] Optionally, in other embodiments of this application, the positive electrode active material satisfies at least one of the following characteristics:

[0009] (a) The full width at half maximum (FWHM) of the pore size distribution of the positive electrode active material is D. HW nm, satisfying: 150≤D HW ≤450;

[0010] (b) Porosity P of the positive electrode active material c Satisfying: 45% ≤ P c ≤75%;

[0011] (c) The compacted density of the positive electrode active material powder is P d g / cm 3 The condition 2.8 ≤ P is satisfied. d ≤3.4.

[0012] The method for preparing the positive electrode active material according to the second aspect of this application includes:

[0013] Mix any one of the manganese or aluminum sources with a nickel or cobalt source, add a precipitant and a complexing agent, and react to obtain a ternary material precursor.

[0014] The ternary material precursor, the M element source and the lithium source are mixed and sintered for the first time. After cooling and crushing, the material containing the M element is obtained.

[0015] The positive electrode active material is obtained by mixing the material containing element M and the coating element source and then performing a second sintering.

[0016] Optionally, in other embodiments of this application, the nickel source includes at least one of nickel sulfate, nickel acetate, or nickel nitrate.

[0017] Optionally, in other embodiments of this application, the cobalt source includes at least one of cobalt sulfate, cobalt acetate, or cobalt nitrate.

[0018] Optionally, in other embodiments of this application, the manganese source includes at least one of manganese sulfate, manganese acetate, or manganese nitrate.

[0019] Optionally, in other embodiments of this application, the aluminum source includes at least one of aluminum sulfate, aluminum acetate, or aluminum nitrate.

[0020] Optionally, in other embodiments of this application, the source of element M includes at least one of zirconium nitrate, tungsten nitrate, aluminum nitrate, titanium nitrate, strontium nitrate, magnesium nitrate, yttrium nitrate, cerium nitrate, indium nitrate, niobium nitrate, lanthanum nitrate, antimony nitrate, vanadium nitrate, zinc nitrate, copper nitrate, chromium nitrate, iron nitrate, tungsten oxide, or zirconium oxide.

[0021] Optionally, in other embodiments of this application, the lithium source includes at least one of lithium hydroxide, lithium carbonate, lithium acetate, or lithium nitrate.

[0022] Optionally, in other embodiments of this application, the coating element source includes one or more of aluminum nitrate, titanium nitrate, cobalt nitrate, tungsten nitrate, yttrium nitrate, silicon oxide, boron oxide, phosphorus pentoxide, or aluminum oxide.

[0023] Optionally, in other embodiments of this application, the coating element source accounts for 0.3wt% to 0.7wt% of the mass percentage of the material containing element M.

[0024] Optionally, in other embodiments of this application, the precipitant includes a sodium hydroxide solution and the complexing agent includes ammonia.

[0025] Optionally, in other embodiments of this application, the temperature of the first sintering is 600-1000°C, and the time of the first sintering is 3-16 hours.

[0026] Optionally, in other embodiments of this application, the temperature of the second sintering is 400-700°C, and the time of the second sintering is 1-9 hours.

[0027] The battery provided according to the third aspect of this application includes a positive electrode sheet, the positive electrode sheet including a positive current collector and a positive active material layer disposed on the positive current collector, the positive active material layer including the above-described positive active material or the positive active material prepared by the above-described preparation method.

[0028] Optionally, in other embodiments of this application, the positive electrode active material layer satisfies at least one of the following characteristics:

[0029] (i) The actual active area of ​​the positive electrode active material layer is A cm. 2 Satisfying: 4×10 4 ≤A≤2×10 5 ;

[0030] (ii) Compacted density PD g / cm³ of the positive electrode active material layer 3 The condition is satisfied that 2.4 ≤ PD ≤ 3.5.

[0031] (iii) Porosity P of the positive electrode active material layer s Satisfy: 20% ≤ P s ≤40%.

[0032] The electrical device provided according to the fourth aspect of this application includes the aforementioned battery.

[0033] Beneficial effects

[0034] The positive electrode active material according to the embodiments of this application has at least the following technical effects:

[0035] 1) By reasonably controlling the particle morphology, particle size distribution and tap density of the positive electrode active material, the powder compaction density can be effectively improved, thereby improving the electrode compaction ability and achieving the effect of increasing the volumetric energy density of the battery, without deteriorating the power, cycle and storage gas generation performance.

[0036] 2) By controlling the particle morphology, particle size and pore structure of the positive electrode active material, the specific surface area and porosity of the material can be controlled, the effective contact area between the positive electrode active material and the electrolyte can be increased, the ion transport, electron transport and electrolyte diffusion rate can be optimized, and the battery power performance can be improved, especially the low temperature power performance. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 This is an electron microscopy characterization image of the surface morphology of the positive electrode active material obtained in Example 2 of this application;

[0039] Figure 2 This is an electron microscopy characterization image of the cross-sectional morphology of the positive electrode active material obtained in Example 2 of this application. Detailed Implementation

[0040] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0041] In this specification, the range of values ​​indicated by “~” represents the range containing the minimum and maximum values ​​recorded before and after “~”, respectively.

[0042] This application provides a positive electrode active material, a battery, and a method for preparing the same. These are described in detail below. It should be noted that the order of description of the following embodiments is not intended to limit the preferred order of the embodiments.

[0043] The first aspect of this application provides a positive electrode active material, comprising secondary particles with pores. The I value of the positive electrode active material satisfies the following characteristic: 4 ≤ I = BET × TD × (Dv90 - Dv10) ≤ 14, where BET represents the specific surface area of ​​the positive electrode active material in m². 2 / g, TD represents the tap density of the positive electrode active material, in g / cm³. 3 Dv90 represents the particle size value corresponding to a cumulative volume distribution percentage of 90% for the positive electrode active material, in μm; Dv10 represents the particle size value corresponding to a cumulative volume distribution percentage of 10% for the positive electrode active material, in μm. Low-temperature discharge power performance is mainly affected by the positive electrode sheet of the battery. Therefore, this application improves the low-temperature power performance and volumetric energy density of the battery made using this positive electrode active material by controlling the particle morphology, particle size, particle size distribution, tap density, and pore structure.

[0044] In some embodiments of this application, 4.5 ≤ I ≤ 11.7. For example, it can be a range of 4.5, 4.8, 5.1, 5.6, 6.1, 6.3, 6.9, 7.3, 7.8, 8.1, 8.6, 9.3, 9.7, 10.5, 11.7, or any two of these numbers. In some embodiments of this application, 5.1 ≤ I ≤ 9.7. In some embodiments of this application, 5.6 ≤ I ≤ 8.6. When the value of I is within this range, the particle morphology, particle size, particle size distribution, tap density, and pore structure of the positive electrode active material are all in a superior state, which can further improve the low-temperature power performance of the battery and further increase the volumetric energy density of the battery.

[0045] Currently, at the material and battery design level, methods to improve the energy density of lithium-ion batteries mainly include increasing the nickel content in ternary materials, increasing the upper voltage limit, and improving the compaction capability of the electrodes. While the first two methods can improve the specific capacity of the materials, they can lead to varying degrees of battery performance degradation, such as reduced thermal stability, increased side reactions with the electrolyte, and increased gas production. Increasing the compaction density of the electrodes can improve the volumetric energy density of the battery, but it results in easily broken particles, leading to more interfacial side reactions, high gas production, and poor long-term lifespan. Therefore, this application achieves a battery with high energy density and good low-temperature power performance by controlling the particle morphology, particle size, particle size distribution, tap density, and pore structure of the positive electrode active material, while ensuring low gas production and good long-term performance.

[0046] In some embodiments of this application, 0.4 ≤ BET ≤ 3.5. For example, it can be 0.4, 0.8, 1.1, 1.2, 1.4, 1.8, 2.0, 2.3, 2.8, 3.0, 3.5, or a range of any two values ​​therein. In some embodiments of this application, 0.4 ≤ BET ≤ 2.7. By controlling the BET of the positive electrode active material, the effective contact area between the positive electrode active material and the electrolyte can be better controlled, the side reactions between the positive electrode active material and the electrolyte can be controlled, and the power performance of the battery can be improved. The value of BET can be tested using a specific surface area analyzer (model: TristarⅡ3020).

[0047] In some embodiments of this application, 1.2 ≤ TD ≤ 2.6. For example, it can be a range of 1.2, 1.3, 1.4, 1.5, 1.8, 2.1, 2.2, 2.6, or any two of these values. In some embodiments of this application, 1.3 ≤ TD ≤ 2.2. In some embodiments of this application, 1.5 ≤ TD ≤ 2.1. By reasonably controlling the tap density of the positive electrode active material, the powder compaction density can be effectively improved, thereby improving the compaction ability of the positive electrode sheet and achieving the effect of increasing the volumetric energy density of the battery. The tap density test can refer to GB / T5162-2021 Determination of Tap Density of Metal Powders.

[0048] In some embodiments of this application, 4 ≤ Dv90 ≤ 18; for example, it can be a range of 4.7, 4.8, 4.9, 5.0, 5.2, 5.4, 5.5, 5.8, 10, 15, or any two of these values. In some embodiments of this application, 4.9 ≤ Dv90 ≤ 15. In some embodiments of this application, 5.0 ≤ Dv90 ≤ 10. 1.5 ≤ Dv10 ≤ 6; for example, it can be a range of 1.5, 1.8, 2.1, 2.2, 2.4, 2.5, 2.6, 2.7, 2.8, 5, or any two of these values. In some embodiments of this application, 1.5 ≤ Dv10 ≤ 5. In some embodiments of this application, 1.8 ≤ Dv10 ≤ 2.8. Controlling a suitable particle size distribution can alleviate the problem of particle breakage during rolling and reduce the occurrence of interfacial side reactions. Dv90, Dv50, and Dv10 are tested using a Malvern laser particle size analyzer.

[0049] In some embodiments of this application, 2≤Dv50≤8, where Dv50 represents the particle size value corresponding to a cumulative volume distribution percentage of 50% for the positive electrode active material, in μm.

[0050] In some embodiments of this application, the maximum pore size D of the positive electrode active material is... max nm, satisfying: 800≤D max≤2200; for example, it can be a range of 850, 1100, 1200, 1400, 1500, 1700, 1800, 1900, 2000, or any two of these values. In some embodiments of this application, 850≤D max ≤2000. In some embodiments of this application, 1100≤D max ≤1900. When the value of I is within the above range, and the maximum pore size of the positive electrode active material meets the above conditions, the pore structure, particle morphology, particle size, particle size distribution, and tap density of the positive electrode active material are controlled within a more suitable range, so that the battery has higher energy density and better low-temperature power performance.

[0051] In some embodiments of this application, the full width at half maximum (FWHM) D of the pore size distribution of the positive electrode active material is... HW nm, satisfying: 150≤D HW ≤450; for example, it can be a range of 160, 200, 300, 400, 450, or any two of these values. In some embodiments of this application, 160≤D HW ≤380. In some embodiments of this application, 160≤D HW ≤300.

[0052] In some embodiments of this application, the porosity P of the positive electrode active material c Satisfying: 45% ≤ P c ≤75%; for example, it can be a range of 46%, 53%, 54%, 56%, 58%, 62%, 63%, 65%, 66%, 67%, 72%, or any two of these values. In some embodiments of this application, 53% ≤ P c ≤72%. In some embodiments of this application, 56% ≤P c ≤67%. When the porosity P of the positive electrode active material... c Within the aforementioned range, the contact area between the positive electrode active material and the electrolyte can be controlled within a more optimal range, resulting in better overall battery performance.

[0053] In some embodiments of this application, the powder compaction density P of the positive electrode active material d g / cm 3 The condition 2.8 ≤ P is satisfied. d ≤3.4; for example, it can be a range of 2.9, 3.0, 3.1, 3.2, 3.3, or any two of these values. In some embodiments of this application, 2.9 ≤ P d ≤3.3.

[0054] The pore size distribution and porosity of the positive electrode active material were measured using mercury porosimetry. The compaction density P... dThe compaction density meter was used for testing, and the testing process can refer to the national standard GB / T 24533-2019. This application controls the specific surface area and porosity of the material by controlling the particle morphology, particle size and pore structure, thereby increasing the effective contact area between the positive electrode active material and the electrolyte, optimizing ion transport, electron transport and electrolyte diffusion rate, and improving battery power performance, especially low-temperature power performance. By controlling the appropriate particle size distribution and compressive strength of the positive electrode active material, the problem of particle breakage during rolling can be effectively alleviated, the interfacial side reactions of the battery can be improved, gas production can be reduced and long-term life can be improved.

[0055] In some embodiments of this application, the positive electrode active material comprises nickel, cobalt and Me, with the molar amount of nickel, cobalt and Me being 1, and the content of nickel being greater than or equal to 0.3, wherein Me is selected from at least one of Mn or Al.

[0056] In some embodiments of this application, the positive electrode active material comprises nickel, cobalt and Me, with the molar amount of nickel, cobalt and Me being 1, and the content of nickel being greater than or equal to 0.5, wherein Me is selected from at least one of Mn or Al.

[0057] In some embodiments of this application, the positive electrode active material comprises nickel, cobalt, and me, with the molar amount of nickel, cobalt, and me being 1. The nickel content is less than or equal to 0.7, wherein me is selected from at least one of Mn or Al. When the porous positive electrode active material satisfies 4≤BET×TD×(Dv90-Dv10)≤14, controlling the nickel content within the above range can further improve the stability of the positive electrode active material structure, enabling the battery to have better ion transport and electron transport, and better mitigate problems such as decreased thermal stability, intensified side reactions with the electrolyte, and increased gas production, resulting in better overall battery performance.

[0058] In some embodiments of this application, the positive electrode active material contains an element M, which includes at least one of Y, Nb, In, La, Zr, Ce, W, Al, Ti, Sr, Mg, Sb, V, Zn, Cu, Cr, or Fe.

[0059] In some embodiments of this application, the positive electrode active material contains element M, which contains at least one of Y, Nb, In, La, Zr or Ce, and at least one of W, Al, Ti, Sr, Mg, Sb, V, Zn, Cu, Cr or Fe.

[0060] In some embodiments of this application, the positive electrode active material contains element M, which includes W, and at least one of Y, Nb, In, La, Zr, Ce, Al, Ti, Sr, Mg, Sb, V, Zn, Cu, Cr or Fe.

[0061] Furthermore, the lithium nickel cobalt manganese oxide contains nickel, cobalt and manganese elements. With the sum of the molar amounts of nickel, cobalt and manganese elements being 1, the nickel content is greater than 0.3%.

[0062] Furthermore, the positive electrode active material includes materials with the chemical formula Li x Ni y Co z Me k M p O2 particles, wherein Me is selected from at least one of Mn or Al, M includes at least one of Y, Nb, In, La, Zr, Ce, W, Al, Ti, Sr, Mg, Sb, V, Zn, Cu, Cr or Fe, and 0.8≤x≤1.1, 0.3<y<1, 0<z<1, 0<k<1, 0≤p≤0.1.

[0063] In some embodiments of this application, the surface of the positive electrode active material particles further includes a coating material, which comprises a coating element, including at least one of Al, Ti, Co, W, Y, Si, B, P, or F. The coating material is applied to the surface of the positive electrode active material. Specifically, a dry coating method (high-temperature solid-state method) is used to coat the surface of the positive electrode active material, and the surface of the positive electrode active material is partially or completely covered with a coating layer formed by the coating material. For example, the area of ​​the coating layer in contact with the positive electrode active material accounts for 50%, 60%, 70%, 80%, 90%, or 100% of the surface area of ​​the positive electrode active material. Adding a coating material to the surface of the positive electrode active material improves its structural stability and rate performance.

[0064] In some embodiments of this application, the positive electrode active material particles have a surface region and a central region adjacent to the surface region. The surface region contains at least one of Al, Ti, Co, W, Y, Si, B, P, or F, and the central region contains an element M, which includes Zr and W. While the porous positive electrode active material satisfies 4 ≤ I = BET × TD × (Dv90 - Dv10) ≤ 14, the presence of an element M in the central region and a coating element on the surface of the positive electrode active material allows for superior particle morphology and particle size distribution when used in the positive electrode sheet. Furthermore, adjusting the composition of the element M and the coating element, and selecting more optimal elements, can further optimize the structure of the positive electrode active material, resulting in better overall battery performance.

[0065] Accordingly, a second aspect of this application provides a method for preparing a positive electrode active material, comprising: mixing any one of a manganese source or an aluminum source with a nickel source or a cobalt source, adding a precipitant and a complexing agent, and reacting to obtain a ternary material precursor; mixing the ternary material precursor, an M element source, and a lithium source and performing a first sintering, cooling and crushing to obtain a material containing the M element; mixing the material containing the M element and a coating element source and performing a second sintering to obtain the positive electrode active material. This application optimizes the crystal nucleation rate and growth rate by changing process parameters such as pH value, complexing agent concentration, and synthesis atmosphere during the precursor preparation process. This application also controls the sintering temperature, sintering time, and crushing intensity. Since the control of pore structure is very sensitive to the above parameters, it is necessary to perform precise multi-stage control of the above process parameters.

[0066] Furthermore, the positive electrode active material contains Li x Ni y Co z Me k M p A compound of O2, wherein Me is selected from at least one of Mn or Al, M includes at least one of Y, Nb, In, La, Zr, Ce, W, Al, Ti, Sr, Mg, Sb, V, Zn, Cu, Cr or Fe, and 0.8≤x≤1.1, 0.3<y<1, 0<z<1, 0<k<1, 0≤p≤0.1.

[0067] In some embodiments of this application, the nickel source includes at least one of nickel sulfate, nickel acetate, or nickel nitrate; and / or, the cobalt source includes at least one of cobalt sulfate, cobalt acetate, or cobalt nitrate; and / or, the manganese source includes at least one of manganese sulfate, manganese acetate, or manganese nitrate; and / or, the aluminum source includes at least one of aluminum sulfate, aluminum acetate, or aluminum nitrate; and / or, the M element source includes at least one of zirconium nitrate, tungsten nitrate, aluminum nitrate, titanium nitrate, strontium nitrate, magnesium nitrate, yttrium nitrate, cerium nitrate, indium nitrate, niobium nitrate, lanthanum nitrate, antimony nitrate, vanadium nitrate, zinc nitrate, copper nitrate, chromium nitrate, iron nitrate, tungsten oxide, or zirconium oxide; and / or, the lithium source includes at least one of lithium hydroxide, lithium carbonate, lithium acetate, or lithium nitrate; and / or, the coating element source includes at least one of aluminum nitrate, titanium nitrate, cobalt nitrate, tungsten nitrate, yttrium nitrate, silicon oxide, boron oxide, phosphorus pentoxide, or aluminum oxide.

[0068] In some embodiments of this application, the precipitant includes a sodium hydroxide solution and the complexing agent includes ammonia.

[0069] Furthermore, the ternary precursor, the M element source, and the lithium source are mixed and sintered. The sintering temperature can be 600–1000℃, 700–900℃, or 800–880℃, and the temperature is increased to this temperature at a rate of 5–50℃ / min. The sintering time can be 3–16 hours, 5–15 hours, or 8–10 hours.

[0070] Furthermore, the material containing element M and the coating element source are mixed and sintered. The sintering temperature can be 400-700℃, 450-600℃, or 500-550℃; the sintering time can be 1-9 hours, 2-8 hours, or 3-7 hours.

[0071] In specific implementation, the preparation methods of positive electrode active materials include:

[0072] (1) Weigh any one of the nickel source, cobalt source, manganese source or aluminum source according to a certain molar ratio, dissolve them in deionized water, and synthesize the precursor by controlling the process conditions such as ammonia concentration, pH value, stirring speed, reaction time and reaction temperature. For example, the pH value can be controlled to be 10 to 13.

[0073] (2) The precursor obtained in step (1) is mixed evenly with the M element source and the lithium source, sintered in an oxygen atmosphere, cooled to room temperature and then crushed to obtain a material containing the M element.

[0074] (3) Mix the material containing element M and the coating element source evenly, and sinter at 400-700℃ for 1-9 hours in air atmosphere to obtain positive electrode active material.

[0075] Furthermore, a third aspect of this application provides a battery including a positive electrode sheet, the positive electrode sheet including a positive current collector and a positive active material layer disposed on the positive current collector, the positive active material layer including the above-mentioned positive active material or the positive active material prepared by the above-mentioned preparation method.

[0076] In some embodiments of this application, the actual active area of ​​the positive electrode active material layer is A cm. 2 Satisfying: 4×10 4 ≤A≤2×10 5 For example, it can be 4.5 × 10 4 6.5×10 4 7.6×10 4 8×10 4 9×10 4 1×10 5 Or a range consisting of any two of these values. In some embodiments of this application, 6.5 × 10 4 ≤A≤1×10 5In some embodiments of this application, 7.6 × 10 4 ≤A≤9×10 4 The true active area refers to the effective area that can participate in electrochemical reactions. The true active area of ​​the positive electrode active material layer is related to the pore structure, pore size distribution, specific surface area, and compressive strength of the positive electrode active material. The combined effect of these material parameters and the compaction density of the positive electrode active material layer will cause changes in the true active area.

[0077] In some embodiments of this application, when the temperature is -20°C and the battery state of charge (SOC) is 30%, the discharge power per unit volume of the positive electrode active material layer is PW / cm². 3 8≤P≤30; for example, it can be 8.9, 14, 15, 16, 22, 23, 24, 25, 29 or any two of these values. In some embodiments of this application, 8.9≤P≤29; in some embodiments of this application, 15≤P≤25. The relationship between the low-temperature, low-SOC discharge power P0 of the battery and the actual active area A satisfies: 0.6≤1000P0 / A≤1, d, P=P0×PD / m, P0W represents the discharge power of the battery under the stated conditions; PD g / cm 3 This indicates the compaction density of the positive electrode active material layer; mg indicates the weight of the positive active material layer.

[0078] In some embodiments of this application, the compaction density of the positive electrode active material layer is PD g / cm³. 3 The condition is satisfied that 2.4 ≤ PD ≤ 3.5, and for example, it can be a range of 2.6, 2.8, 3.0, 3.1, 3.3, or any two of these values. In some embodiments of this application, 2.6 ≤ P s ≤3.1; Porosity P of the positive electrode active material layer s Satisfy: 20% ≤ P s ≤40%, for example, can be a range of 22%, 23%, 25%, 26%, 27%, 28%, 30%, 35%, or any two of these values. In some embodiments of this application, 22% ≤ P s ≤35%; in some embodiments of this application, 25% ≤P s ≤30%.

[0079] In practice, the aforementioned positive electrode active material or the positive electrode active material prepared by the aforementioned method is stirred evenly with a conductive agent, binder, and solvent, and then processed into a positive electrode sheet through processes such as sieving, coating, rolling, slitting, and cutting. The corresponding properties and parameters of the positive electrode sheet can also be controlled by changing the rolling parameters. As long as the positive electrode active material layer of this application can be controlled to meet the aforementioned characteristics, it is acceptable.

[0080] Specifically, the battery includes a positive electrode, a negative electrode, a separator, and an electrolyte, with the positive electrode being the aforementioned positive electrode. In practice, the aforementioned positive electrode, along with the negative electrode, separator, and electrolyte, is assembled into a lithium-ion battery. The negative electrode material used can be one or more of the following: artificial graphite, natural graphite, mesophase carbon microspheres, amorphous carbon, lithium titanate, or silicon-carbon alloy. The negative electrode material also needs to possess characteristics such as high compaction density, high specific capacity, and high volumetric capacity.

[0081] In some embodiments, the electrolyte comprises an organic solvent, which may contain linear esters and cyclic esters, wherein the mass percentage of linear esters is greater than the mass percentage of cyclic esters. The cyclic esters may contain ethylene carbonate (EC) and / or propylene carbonate (PP), and the linear esters may contain at least one of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), or diethyl carbonate (DEC). In some embodiments, the solvent of the electrolyte comprises EC, EMC, and DEC. In some embodiments, the mass ratio of EC, EMC, and DEC is (10–25):(10–25):(51–75). In some embodiments, the preparation of the electrolyte comprises: dissolving thoroughly dried lithium salt in an organic solvent in an argon-atmosphere glove box with a water content <10 ppm, mixing thoroughly to obtain the electrolyte. The concentration of the lithium salt is 0.8–1.3 mol / L.

[0082] In some embodiments, the lithium salt can be LiPF6 (lithium hexafluorophosphate), LiBF4 (lithium tetrafluoroborate), etc.

[0083] In some embodiments, the preparation of the separator includes: selecting a polypropylene membrane with a thickness of 9–18 μm as the separator. There are no particular limitations on the separator; any known porous separator with electrochemical and mechanical stability can be selected.

[0084] A fourth aspect of this application provides an electrical device including the battery described above.

[0085] In some embodiments, the electrical device used in this application is, but is not limited to, a backup power supply, a motor, an electric vehicle, an electric motorcycle, a power-assisted bicycle, a bicycle, power tools, a large household storage battery, etc.

[0086] The following description is based on specific embodiments.

[0087] Example 1

[0088] This embodiment provides a method for preparing positive electrode active material and positive electrode sheet.

[0089] The preparation of positive electrode active materials includes the following steps:

[0090] 1) Weigh out nickel sulfate, cobalt sulfate and manganese sulfate according to the elemental molar ratio Ni:Co:Mn = 0.5:0.2:0.3 and dissolve them separately in deionized water. Transport each metal solution to the reaction vessel through pipeline to form a mixed metal solution. Introduce nitrogen gas as a protective gas. Add NaOH aqueous solution as a precipitant and ammonia water as a complexing agent to the mixed metal solution. Adjust the ammonia water concentration and pH value of the solution in stages. React for 10 hours to obtain the precursor.

[0091] 2) Mix the precursor, lithium carbonate, tungsten oxide and zirconium oxide evenly, control the lithium ratio to be 1.1:1, and the weight percentages of tungsten oxide and zirconium oxide to the precursor are 0.6 wt% and 0.37 wt%, respectively.

[0092] 3) Transfer the mixed materials to the sintering process, which includes two stages: the first stage is sintering at 600℃ for 6 hours; the second stage is sintering at 880℃ for 10 hours.

[0093] 4) Crush the sintered material, and then mix the crushed material with alumina evenly. The weight ratio of alumina to crushed material is 0.5 wt%.

[0094] 5) Transfer the mixed materials to the sintering process. The sintering temperature is 450℃ and the sintering time is 8 hours to obtain the positive electrode active material.

[0095] 6) The positive electrode active material, conductive agent, and binder are mixed at a mass ratio of 97:1.5:1.5, then stirred with solvent until homogeneous. The mixture is then subjected to processes such as sieving, coating, rolling, slitting, and cutting to obtain the positive electrode sheet. The specific parameters of the obtained positive electrode active material and positive electrode sheet are shown in Tables 1 and 2.

[0096] The preparation methods of the positive electrode active material and positive electrode sheet in Examples 2-8, 14-18 and Comparative Examples 1-3 are roughly the same as in Example 1. The difference lies in that Examples 2-8 and Comparative Examples 1-3 change the relevant parameters in the preparation steps of the positive electrode active material, and Examples 14-18 also change the nickel-cobalt-manganese ratio, such as process parameters like pH value, ammonia concentration, and synthesis atmosphere. This allows control over the pore size distribution, porosity, and specific surface area of ​​the positive electrode active material, resulting in a positive electrode active material with predetermined parameter characteristics. Using this type of positive electrode active material to prepare positive electrode sheets, positive electrode sheets with predetermined parameter characteristics can be obtained. Specific parameters are shown in Tables 1 and 2. Among them, Comparative Examples 1-3 illustrate cases where the specific surface area, pore size, and porosity parameters are outside the range of this application, and they cannot achieve the expected true active area of ​​the positive electrode active material layer.

[0097] Examples 19-22 use the same positive electrode active material, conductive agent, and binder as in Example 1. The difference is that the rolling parameters in the electrode preparation process are changed in Examples 19-22. By controlling the compaction density of the positive electrode, the porosity and actual active area of ​​the positive electrode can be controlled, and a positive electrode with predetermined parameter characteristics can be obtained. The specific parameters are shown in Table 1 and Table 2.

[0098] Compared with Example 1, Examples 9-13 differ in the different M element and coating elements, but the material pore size distribution, specific surface area and I value are guaranteed to be within an appropriate range. Specific material parameters and electrode parameters are shown in Table 1 and Table 2.

[0099] The method for testing the true active area A of the positive electrode active material layer is as follows:

[0100] 1) Adjust the battery to the specified SOC (e.g., 30% SOC);

[0101] 2) Transfer the battery with the SOC adjusted to the glove box for disassembly. Use the sample preparation mold of the symmetrical battery to cut the positive electrode sheet for sample preparation (the positive electrode sheet sample size is 46x28mm). Pour in an appropriate amount of high-purity anhydrous dimethyl carbonate (DMC) to soak and clean. Replace the DMC every 8 hours and clean it continuously for 3 times. After drying for 12 hours, make a symmetrical battery from the positive electrode sheet.

[0102] 3) Perform EIS testing on the symmetrical cell. Read the frequency f corresponding to the maximum radius from the EIS test curve (Nyquist plot), and then use the formula ω... max =2πf, the angular velocity ω is calculated. max ;

[0103] 4) Fit the EIS of the symmetrical cell to obtain the charge transfer impedance R. ct The specific value;

[0104] 5) Using the formula A = 1 / 20ω max R ct Calculations were performed to obtain the actual active area A of the electrode.

[0105] Table 1

[0106]

[0107]

[0108] Table 2

[0109]

[0110] The lithium-ion batteries of Examples 1-22 and Comparative Examples 1-3 were subjected to low-temperature power, high-temperature storage, and high-temperature gas generation tests. The low-temperature power test procedure was as follows: after adjusting the battery to 30% SOC, it was placed at -20℃ to stabilize the battery surface temperature. It was then discharged at a certain power P0 W for 10 seconds. A successful test was considered when the terminal voltage was 2.21-2.26V, and this P0 W was considered the battery's low-temperature discharge power. The high-temperature storage test procedure was as follows: the battery was charged to 4.3V and stored in a 60℃ constant temperature chamber. The residual capacity was tested every 30 days, and the battery was fully charged again before storage. The calculation method was as follows: the initial capacity Q0 was tested before storage in the chamber; after every 30 days, the battery was removed from the chamber, cooled, and the residual capacity Q was tested. "Q / Q0 × 100%" represents the battery's storage capacity retention rate. The high-temperature gas generation test procedure was as follows: three battery samples were taken, charged to 4.3V, and stored in a 60℃ constant temperature chamber. The battery volume was tested every 15 days using the water displacement method. Charge the battery fully at 1C every 30 days. The calculation method is as follows: test the initial volume V0 using the water displacement method, remove the battery from the temperature chamber every 15 days, cool it down, and test the battery volume V using the water displacement method. "(V / V0-1)×100%" is the high-temperature storage volume expansion rate.

[0111] Performance data are shown in Table 3:

[0112] Table 3

[0113]

[0114] Examples 1-8 and Comparative Examples 1-3 compared material-related parameters with different pore size distributions. As the pore size D of the positive electrode active material increased... max Increased aperture distribution half-width D HW Increase the porosity P of the positive electrode active material c By increasing the size of the electrode and then using the same electrode and battery manufacturing process, the actual active area A of the positive electrode active material layer increases, thus improving the low-temperature power performance of the battery.

[0115] Examples 1 and 19-22, and Examples 14-18, compared the relevant parameters of positive electrode active material layers with different compaction densities. As the compaction density and porosity P of the positive electrode active material layer increased... s The change in the positive electrode active material layer affects the actual active area A, and the low-temperature power of the battery is also affected. This indicates that there is a suitable I value, Ps and compaction density working together to achieve better low-temperature power performance.

[0116] Examples 1 and 9-10 compared the material-related parameters of different M elements. When the positive electrode active material has two M elements, especially when it contains W, the battery has better overall performance than when it has only one M element.

[0117] Examples 1 and 11-12 compared the material-related parameters of different coating elements. The changes and replacements of the coating elements had no significant impact on the pore size distribution and porosity of the positive electrode active material, and had no significant impact on the electrical performance of the battery.

[0118] like Figure 1 The image shown is an electron microscopy characterization image of the surface morphology of the positive electrode active material obtained in Example 2 of this application; as shown... Figure 2 The image shown is an electron microscopy characterization test image of the cross-sectional morphology of the positive electrode active material obtained in Example 2 of this application.

[0119] This application enables the positive electrode active material layer to have a high actual active area without affecting the processing of the slurry and positive electrode sheet. This increases the effective contact area between the positive electrode active material and the electrolyte, optimizes ion transport, electron transport, and electrolyte diffusion rates, and improves the power performance of the battery cell, especially its low-temperature power performance. The positive electrode active material prepared by this application has superior particle size distribution and compressive strength, which can effectively alleviate the problem of particle breakage during rolling, improve the interfacial side reactions of the battery, reduce gas production, and improve long-term lifespan. The positive electrode active material and positive electrode sheet of this application have superior compaction ability, which can ensure the weight of active material per unit volume, thereby ensuring the unit volume capacity of the battery.

[0120] The above provides a detailed description of the positive electrode active material, battery, and preparation method thereof provided in this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A positive electrode active material, characterized in that, The positive electrode active material comprises secondary particles, the secondary particles having pores, and the positive electrode active material satisfies the following characteristics: 5.8≤BET×TD×(Dv90-Dv10)≤12.3, Wherein, BET represents the specific surface area of ​​the positive electrode active material, in m². 2 / g, TD represents the tap density of the positive electrode active material, in g / cm³. 3 Dv90 represents the particle size value corresponding to a cumulative volume distribution percentage of 90% for the positive electrode active material, in μm; Dv10 represents the particle size value corresponding to a cumulative volume distribution percentage of 10% for the positive electrode active material, in μm; 0.98≤BET≤3.02; 1.28≤TD≤2.23; 4.71≤Dv90≤5.89; 1.81≤Dv10≤2.83; The positive electrode active material comprises lithium nickel cobalt manganese oxide, which contains nickel, cobalt and manganese elements, with the sum of the molar amounts of nickel, cobalt and manganese elements being 1, and the content of nickel element being greater than 0.

3. The maximum pore size of the positive electrode active material is D. max nm, satisfying: 850≤D max ≤2000; The full width at half maximum (FWHM) of the pore size distribution of the positive electrode active material is D. HW nm, satisfying: 150≤D HW ≤450; The porosity P of the positive electrode active material c Satisfy: 45% ≤ P c ≤75%; The compacted density of the positive electrode active material is P. d g / cm 3 The condition 2.8 ≤ P is satisfied. d ≤3.

4.

2. The method for preparing the positive electrode active material according to claim 1, characterized in that, The preparation method includes: Mix any one of the manganese or aluminum sources with a nickel or cobalt source, add a precipitant and a complexing agent, and react to obtain a ternary material precursor. The ternary material precursor, the M element source and the lithium source are mixed and sintered for the first time. After cooling and crushing, the material containing the M element is obtained. The material containing element M and the coating element source are mixed and sintered a second time to obtain the positive electrode active material.

3. The method for preparing the positive electrode active material according to claim 2, characterized in that, The nickel source includes at least one of nickel sulfate, nickel acetate, or nickel nitrate; and / or, The cobalt source includes at least one of cobalt sulfate, cobalt acetate, or cobalt nitrate; and / or, The manganese source includes at least one of manganese sulfate, manganese acetate, or manganese nitrate; and / or, the aluminum source includes at least one of aluminum sulfate, aluminum acetate, or aluminum nitrate; and / or, The source of element M includes at least one of zirconium nitrate, tungsten nitrate, aluminum nitrate, titanium nitrate, strontium nitrate, magnesium nitrate, yttrium nitrate, cerium nitrate, indium nitrate, niobium nitrate, lanthanum nitrate, antimony nitrate, vanadium nitrate, zinc nitrate, copper nitrate, chromium nitrate, iron nitrate, tungsten oxide, or zirconium oxide; and / or, The lithium source includes at least one of lithium hydroxide, lithium carbonate, lithium acetate, or lithium nitrate; and / or, The coating element source includes one or more of aluminum nitrate, titanium nitrate, cobalt nitrate, tungsten nitrate, yttrium nitrate, silicon oxide, boron oxide, phosphorus pentoxide, or aluminum oxide.

4. The method for preparing the positive electrode active material according to claim 2, characterized in that, The coating element source accounts for 0.3 wt% to 0.7 wt% of the mass percentage of the material containing element M; and / or, The precipitant includes a sodium hydroxide solution, and the complexing agent includes ammonia.

5. The method for preparing the positive electrode active material according to claim 2, characterized in that, The temperature of the first sintering is 600–1000°C, and the time of the first sintering is 3–16 hours; and / or, The temperature of the second sintering is 400-700℃, and the time of the second sintering is 1-9 hours.

6. A battery, comprising a positive electrode, characterized in that, The positive electrode sheet includes a positive current collector and a positive active material layer disposed on the positive current collector, wherein the positive active material layer includes the positive active material as described in claim 1 or the positive active material prepared by any one of claims 2 to 5.

7. The battery according to claim 6, characterized in that, The positive electrode active material layer satisfies at least one of the following characteristics: (i) The actual active area of ​​the positive electrode active material layer is A cm. 2 Satisfying: 4×10 4 ≤A≤2×10 5 ; (ii) The compaction density of the positive electrode active material layer is PD g / cm³. 3 The condition is satisfied that 2.4 ≤ PD ≤ 3.

5. (iii) The porosity P of the positive electrode active material layer s Satisfy: 20% ≤ P s ≤40%.

8. An electrical device comprising the battery as described in claim 6 or 7.

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