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

Abstract

The present application discloses a positive electrode active material and a preparation method therefor, a positive electrode sheet, a battery, and an electric device. The BET specific surface area of the positive electrode active material after being soaked in an acidic solution is 1.75 m2 / g-4 m2 / g, the porosity of the positive electrode active material after being soaked in the acidic solution is 2.6%-6.5%, the weight ratio of the positive electrode active material to the acidic solution is 1:10, the pH value of the acidic solution is 5.5, and the soaking time is 2 h. Therefore, the positive electrode active material provided in the present application has both high compaction density and excellent cycle performance.

Description

Cathode active material, preparation method thereof, cathode sheet, battery, and electric device TECHNICAL FIELD

[0001] The present application relates to the field of batteries, in particular to a cathode active material, a preparation method thereof, a cathode sheet, a battery, and an electric device. BACKGROUND

[0002] A lithium-rich manganese-based cathode material has become a research hotspot in the field of lithium-ion battery cathodes due to its high specific capacity and high energy density. The lithium-rich manganese-based cathode material contains Ni, Co, and Mn elements, has a specific capacity of more than 240 mAh / g, an average voltage of higher than 3.5 V, and an energy density higher than that of layered LiMO2, spinel-type LiMn2O4, and olivine-type LiFePO4. Therefore, the lithium-rich manganese-based cathode active material is considered as an optimal material for the next generation of lithium-ion battery cathode active materials. However, the cathode active material in the related art cannot balance its cycle performance and volumetric energy density.

[0003] SUMMARY

[0004] The present application aims to at least partially solve one of the technical problems in the related art.

[0005] The first aspect of the present application provides a cathode active material, the cathode active material being a secondary particle formed by agglomeration of primary particles, the secondary particle having pores, the BET specific surface area of the cathode active material after being soaked in an acid solution being 1.75 m 2 / g-4 m 2 / g, the porosity of the cathode active material after being soaked in the acid solution being 2.6%-6.5%, the weight ratio of the cathode active material to the acid solution being 1:10, the pH of the acid solution being 5.5, and the soaking time being 2 h. Thus, the cathode active material proposed in the present application can have a large specific surface area while maintaining a low porosity after being soaked in an acid solution, thereby improving the energy density and cycle performance of the battery.

[0006] According to some embodiments of the present application, the average pore diameter of the pores of the secondary particle of the cathode active material after being soaked in the acid solution is 9 nm-25 nm. Thus, the cathode active material can have a large specific surface area while maintaining a low porosity, thereby improving the tap density of the cathode active material.

[0007] According to some embodiments of the present application, the proportion of pores with a pore diameter less than or equal to 10 nm is 50%-80%. Thus, the specific surface area of the cathode active material is improved, and the cycle performance of the battery is improved.

[0008] According to some embodiments of the present application, the compaction density of the positive electrode active material is 2.7 g / cm3-3.2 g / cm3. 3 -3.2 g / cm3 3 In this way, the energy density of the battery is improved.

[0009] According to some embodiments of the present application, the positive electrode active material satisfies: η = FWHM(104) / FWHM(003), 1.75 ≤ η ≤ 2.8, optionally, 1.85 ≤ η ≤ 2.1, wherein FWHM(104) is the half-peak width of the diffraction peak (104) of the X-ray diffraction spectrum, the 2θ value corresponding to the diffraction peak (104) is 43.5°-45.5°, FWHM(003) is the half-peak width of the diffraction peak (003) of the X-ray diffraction spectrum, the 2θ value corresponding to the diffraction peak (003) is 17.5°-19.5°. In this way, the integrity of the positive electrode active material lattice is improved, and the cycle stability of the positive electrode active material is improved.

[0010] According to some embodiments of the present application, the positive electrode active material comprises a compound represented by Formula I:

[0011] Li 1+δ (Ni x(1-a) Co y(1-a) Li(1-2x-y)(1-a) / 3Mn(2-x-y)(1-a) / 3M 1 a M 2 b )O (2+δ / 2) N n Formula I,

[0012] wherein 0.02 ≤ δ ≤ 0.08, 0.25 ≤ x ≤ 0.45, 0 ≤ y ≤ 0.1, 0 ≤ a ≤ 0.035, 0 ≤ b ≤ 0.04, 0 ≤ n ≤ 0.04, M 1 comprises at least one of Al, Zr, Y, Mg, Ti, W, Si, Yb, Nb, Sc, Ca, La, Sr, Y, M 2 comprises at least one of B, Mg, Al, Ti, V, Sr, Y, Zr, Nb, Mo, Sc, Cr, La, Sr, W, N comprises at least one of F, S, P, O.

[0013] According to some embodiments of the present application, the positive electrode active material satisfies at least one of the following conditions: 0.03 ≤ δ ≤ 0.06; 0.001 ≤ a ≤ 0.02; 0.001 ≤ b ≤ 0.02; 0 ≤ n ≤ 0.02.

[0014] According to some embodiments of the present application, at least part of the surface of the secondary particles has a coating layer; preferably, the coating layer comprises the M 2The element. Thus, the transition corrosion of the electrolyte to the positive active material is reduced, and the cycle performance of the battery is improved.

[0015] The second aspect of the application provides a method for preparing a positive active material, the method comprising: mixing a Ni source, a Co source, a Mn source, a complexing agent, and a precipitating agent to form a first mixed solution, stirring the first mixed solution, co-precipitating, drying, and obtaining a lithium-rich manganese-based precursor, wherein the pH of the first mixed solution is 9-11.5, and the stirring speed is 500 rpm-900 rpm; mixing the lithium-rich manganese-based precursor, a lithium source, and a M 1 source to perform first sintering to obtain a first process product; mixing the first process product, a M 2 source, and a solvent to form a second mixed solution, the solid-liquid ratio of the first process product to the solvent being 0.5 g / mL-3 g / mL, performing solid-liquid separation, drying the solid-phase material to obtain a second process product; and performing second sintering on the second process product, the temperature of the second sintering being less than or equal to the temperature of the first sintering, to obtain the positive active material.

[0016] Thus, by setting the pH of the first mixed solution and the stirring speed within the above ranges, the primary particles of the positive active material also have good multi-directionality. By controlling the solid-liquid ratio in the process of forming the second mixed solution, the soluble residual substances in the tiny pores between the primary particles can be discharged to the outside of the secondary particles, more micropores are formed in the interior of the secondary particles, and the crystal lattice structure is not damaged, thereby obtaining a positive active material with excellent cycle performance and high volumetric energy density.

[0017] According to some embodiments of the application, the solid-liquid ratio of the first process product to the solvent is 1.0 g / mL-3 g / mL.

[0018] According to some embodiments of the application, the method satisfies at least one of the following conditions: the temperature of the second mixed solution is 5°C-35°C; and the mixing time of the first process product, the M 2 source, and the solvent is 30 s-1200 s, which can be optionally 60 s-600 s. Thus, micropores can be effectively obtained without damaging the crystal lattice structure of the positive active material.

[0019] According to some embodiments of the application, 1.12≤n (Li) / (n (Ni) +n (Co) +n (Mn) +n (M1) )≤1.49. Thus, the integrity of the crystal lattice of the positive active material is improved, and the cycle stability of the positive active material is improved.

[0020] According to some embodiments of the present application, 0≤n (M2) / (n (Ni) +n (Co) +n (Mn) +n (M1) )≤0.04, optionally, 0.001≤n (M2) / (n (Ni) +n (Co) +n (Mn) +n (M1) )≤0.02. Thus, the appropriate coating on the surface of the positive active material can not only reduce the corrosion of the electrolyte on the positive active material and improve the cycle performance, but also improve the conductivity of the secondary particles and the capacity of the positive active material.

[0021] According to some embodiments of the present application, the method satisfies at least one of the following conditions: the temperature of the first sintering is T1, and satisfies 800℃≤T1≤980℃; the time of the first sintering is t1, and satisfies 5h≤t1≤15h; the heating rate of the first sintering is V1, and satisfies 1.3℃ / min≤V1≤10℃ / min. Thus, a better crystal structure can be obtained.

[0022] According to some embodiments of the present application, the method satisfies at least one of the following conditions: the temperature of the second sintering is T2, and satisfies 300℃≤T2≤800℃; the time of the second sintering is t2, and satisfies 6h≤t2≤20h. Thus, a better crystal structure can be obtained.

[0023] The third aspect of the present application provides a positive electrode sheet, comprising the positive active material provided by the first aspect of the present application or the positive active material prepared by the method provided by the second aspect of the present application.

[0024] The fourth aspect of the present application provides a battery, comprising the positive electrode sheet provided by the third aspect of the present application.

[0025] The fifth aspect of the present application provides a power utilization device, comprising the battery provided by the fourth aspect of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0026] The above and / or additional aspects and advantages of the present application will become apparent and be readily understood from the following description, taken in conjunction with the following drawings, in which:

[0027] FIG. 1 shows a flowchart of a method for preparing a positive active material according to an embodiment of the present application. DETAILED DESCRIPTION

[0028] The embodiments of the present invention are described in detail below. These embodiments are exemplary and are only used to explain the present invention, and should not be construed as limiting the invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0029] For lithium-rich manganese-based cathode active materials, increasing their specific surface area allows for more thorough contact between the active material and the electrolyte, promoting interfacial reactions and improving battery cycle performance. However, increasing the specific surface area of ​​lithium-rich manganese-based cathode active materials in related technologies is accompanied by increased porosity. Increased porosity leads to a decrease in the compaction density of the lithium-rich manganese-based cathode active material, sacrificing battery energy density. In other words, it is impossible to obtain lithium-rich manganese-based cathode active materials that simultaneously possess high energy density and excellent cycle performance.

[0030] The first aspect of this application provides a positive electrode active material, which is a secondary particle formed by the agglomeration of primary particles. The secondary particles have pores, and the BET specific surface area of ​​the positive electrode active material after immersion in an acidic solution is 1.75 m². 2 / g-4m 2 / g, the porosity of the positive electrode active material after soaking in the acidic solution is 2.6%-6.5%, the weight ratio of the positive electrode active material to the acidic solution is 1:10, the pH of the acidic solution is 5.5, and the soaking time is 2h.

[0031] During battery operation, the positive electrode active material is fully wetted by the electrolyte, and the interior of the secondary particles is eroded by the electrolyte, thus creating new pores. The porosity and specific surface area of ​​the positive electrode active material increase with the appearance of these new pores. The BET and porosity of the positive electrode active material after immersion in an acidic solution, as proposed in this application, can accurately reflect the properties of the tested material in the electrolyte. By ensuring that the BET specific surface area and porosity of the positive electrode active material after immersion in an acidic solution are within the aforementioned range, this application implies that during battery operation, after the positive electrode active material is fully wetted by the electrolyte, it can maintain a large specific surface area while keeping the porosity low. This shortens the diffusion path of lithium ions within the positive electrode active material and increases its specific capacity.

[0032] The specific surface area of the positive electrode active material after soaking in the acidic solution is large, which can make the positive electrode active material contact with the electrolyte more fully, promote the interface reaction between the positive electrode active material and the electrolyte, and improve the cycle performance of the battery. At the same time, since the porosity of the positive electrode active material after being fully infiltrated by the electrolyte still maintains at a low level, during the stages of coating and rolling of the electrode sheet, it is not necessary to adopt a smaller compaction density in order to pursue that the positive electrode active material has a larger specific surface area, that is to say, the positive electrode active material can have a larger specific surface area during the cycle process of the battery without reducing the compaction density of the positive electrode sheet, and thus a battery with excellent cycle performance and high energy density is obtained.

[0033] For example, the BET specific surface area of the positive electrode active material after soaking in the acidic solution can be 1.75 m 2 / g-4 m 2 / g, for example, can be 1.75 m 2 / g, 2 m 2 / g, 2.5 m 2 / g, 3 m 2 / g, 3.5 m 2 / g, 4 m 2 / g, etc., or can be a range consisting of any of the above values.

[0034] In the present application, the test method of the BET specific surface area is as follows: the positive electrode active material is soaked in an acidic solution for 2 h, the weight ratio of the positive electrode active material to the acidic solution is 1:10, the pH of the acidic solution is 5.5, after soaking, vacuum drying is performed at 120°C, and a specific surface area tester of Tristar 3020 model of Micromeritics Company is used for testing.

[0035] For example, the porosity of the positive electrode active material after soaking in the acidic solution can be 2.6%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, etc., or can be a range consisting of any of the above values.

[0036] In the present application, the porosity of the positive electrode active material can be tested by a specific surface area tester of Tristar 3020 model of Micromeritics Company.

[0037] According to some embodiments of the present application, the average pore size of the pores of the positive electrode active material secondary particles after soaking in an acid solution is 9 nm-25 nm. For example, it can be 9 nm, 13 nm, 17 nm, 21 nm, 25 nm, etc., or a range formed by any of the above values. As can be seen, the average pore size of the positive electrode active material is small, the porosity is small, and the specific surface area is large, so that the positive electrode active material with high compaction density and excellent cycle performance can be obtained.

[0038] In the present application, the specific surface area tester of Model Tristar 3020 of Micromeritics Company is used for testing, and the BJH method is used to calculate the pore size distribution during desorption.

[0039] According to some embodiments of the present application, the pore size ratio of the pore size less than or equal to 10 nm is 50%-80%. For example, it can be 50%, 60%, 70%, or 80%, etc., or a range formed by any of the above values. The smaller the pore size, the larger the specific surface area of the positive electrode active material, and the more small-sized pores, so that the specific surface area of the positive electrode active material can be increased, the interfacial reaction between the positive electrode active material and the electrolyte can be promoted, and the cycle performance of the battery can be improved.

[0040] It should be noted that the pore size ratio of the pore size less than or equal to 10 nm refers to the ratio of the total specific surface area of the pore size less than or equal to 10 nm to the total specific surface area of the secondary particles.

[0041] According to some embodiments of the present application, the positive electrode active material satisfies: η = FWHM(104) / FWHM(003), 1.75≤η≤2.8, wherein FWHM(104) is the half-peak width of the diffraction peak (104) of the X-ray diffraction spectrum, the 2θ value corresponding to the diffraction peak (104) is 43.5°-45.5°, FWHM(003) is the half-peak width of the diffraction peak (003) of the X-ray diffraction spectrum, and the 2θ value corresponding to the diffraction peak (003) is 17.5°-19.5°. For example, η can be 1.75, 1.8, 2, 2.2, 2.4, 2.6, 2.8, etc., or a range formed by any of the above values.

[0042] The symmetry of the (003) plane in the X-ray diffraction spectrum of the positive electrode material is more obvious than that of the (104) plane. When the ratio of FWHM(104) / FWHM(003) is within the range defined in the present application, it indicates that part of the Li atoms are distributed in the transition metal layer of the crystal lattice, i.e., the Li atoms with a content of (1-2x-y)(1-a) / 3 in formula I enter the crystal lattice. The positive electrode active material of the present application has better crystal lattice integrity and more excellent cycle stability. According to some specific embodiments of the present application, 1.85≤η≤2.1.

[0043] In the present application, FWHM (104) and FWHM (003) can be tested by X-ray diffractometer of Smart Lab 9KW model of Japan Rigaku Corporation.

[0044] According to some embodiments of the present application, the compaction density of the positive electrode active material can be 2.7 g / cm 3 -3.2 g / cm 3 . For example, it can be 2.7 g / cm 3 , 2.8 g / cm 3 , 2.9 g / cm 3 , 3 g / cm 3 , 3.1 g / cm 3 , 3.2 g / cm 3 , etc., or can be a range consisting of any of the above values. In this way, the energy density of the battery is improved.

[0045] According to some embodiments of the present application, the compaction density of the positive electrode active material can be tested by a Japanese Mitsubishi Powder Impedance Measurement System.

[0046] According to some embodiments of the present application, the positive electrode active material comprises a compound represented by Formula I:

[0047] Li 1+δ (Ni x(1-a) Co y(1-a) Li(1-2x-y)(1-a) / 3Mn(2-x-y)(1-a) / 3M 1 a M 2 b )O (2+δ / 2) N n Formula I,

[0048] wherein 0.02≤δ≤0.08, 0.25≤x≤0.45, 0≤y≤0.1, 0≤a≤0.035, 0≤b≤0.04, 0≤n≤0.04, M 1 comprises at least one of Al, Zr, Y, Mg, Ti, W, Si, Yb, Nb, Sc, Ca, La, Sr, Y, M 2 comprises at least one of B, Mg, Al, Ti, V, Sr, Y, Zr, Nb, Mo, Sc, Cr, La, Sr, W, and N comprises at least one of F, S, P, O.

[0049] As an example, δ can be 0.002, 0.004, 0.006, 0.008, etc., or can be a range consisting of any of the above values. According to some specific embodiments of the present application, 0.03≤δ≤0.06.

[0050] As an example, x can be 0.25, 0.3, 0.35, 0.4, 0.45, etc., or can be a range consisting of any of the above values.

[0051] As an example, y can be 0, 0.03, 0.05, 0.07, 0.1, etc., or can be a range consisting of any of the above values.

[0052] As an example, a can be 0, 0.01, 0.02, 0.03, 0.035, etc., or can be a range consisting of any of the above values. According to some embodiments of the present application, 0.001≤a≤0.02.

[0053] As an example, b can be 0, 0.01, 0.02, 0.03, 0.04, etc., or can be a range consisting of any of the above values. According to some embodiments of the present application, 0.001≤b≤0.02.

[0054] As an example, n can be 0, 0.005, 0.01, 0.015, 0.02, etc., or can be a range consisting of any of the above values. According to some embodiments of the present application, 0≤n≤0.02.

[0055] The second aspect of the present application provides a method for preparing a positive electrode active material, the method comprising: mixing a Ni source, a Co source, a Mn source, a complexing agent, and a precipitating agent to form a first mixed solution, stirring the first mixed solution, co-precipitating, drying to obtain a lithium-rich manganese-based precursor, wherein the pH of the first mixed solution is 9-11.5, and the stirring speed is 500 rpm-900 rpm; mixing the lithium-rich manganese-based precursor, a lithium source, and a M 1 source to perform first sintering to obtain a first process product; mixing the first process product, a M 2 source, and a solvent to form a second mixed solution, the solid-liquid ratio of the first process product to the solvent being 0.5 g / mL-3 g / mL, performing solid-liquid separation, drying the solid phase material to obtain a second process product; performing second sintering on the second process product, the temperature of the second sintering being less than or equal to the temperature of the first sintering, to obtain the positive electrode active material. In this way, by controlling the pH and stirring speed of the co-precipitation process and the solid-liquid ratio in the process of forming the second mixed solution, the soluble residual substances in the tiny pores between primary particles and between primary particles can be discharged to the outside of secondary particles, so that more micropores are formed in the inside of secondary particles, while the crystal lattice structure is not damaged, thereby obtaining a positive electrode active material with excellent cycle performance and high volume energy density.

[0056] The method is described in detail below, and with reference to FIG. 1, the method comprises:

[0057] S10: mixing a Ni source, a Co source, a Mn source, a complexing agent, and a precipitant to form a first mixed solution, stirring the first mixed solution, co-precipitating, drying to obtain a lithium-rich manganese-based precursor

[0058] According to some embodiments of the present application, a Ni source, a Co source, a Mn source, a complexing agent, and a precipitant are mixed to form a first mixed solution, co-precipitating to obtain a slurry, and the slurry is sequentially aged, pressure-filtered, and dried to obtain a lithium-rich manganese-based precursor.

[0059] According to some embodiments of the present application, the precipitant includes at least one of NaOH, KOH, and LiOH.

[0060] According to some embodiments of the present application, the pH of the first mixed solution can be 9-11.5, for example, can be 9, 9.5, 10, 10.5, 11, 11.5, or can be a range consisting of any of the above values.

[0061] According to some embodiments of the present application, the stirring speed can be 500 rpm-900 rpm, for example, can be 500 rpm, 600 rpm, 700 rpm, 800 rpm, 900 rpm, or can be a range consisting of any of the above values.

[0062] By setting the pH of the first mixed solution and the stirring speed in the above ranges, the lithium-rich manganese-based precursor has good multidirectionality and high tap density, so that the primary particles of the positive electrode active material also have good multidirectionality, and during battery cycling, the positive electrode active material can have more micropores after being soaked in the electrolyte, that is, the positive electrode active material has a larger specific surface area when the porosity is increased less, and thus a battery with excellent cycle performance and high energy density is obtained.

[0063] According to some embodiments of the present application, the temperature during the co-precipitation reaction can be 50°C-80°C, for example, can be 50°C, 60°C, 70°C, 80°C, or can be a range consisting of any of the above values.

[0064] According to some embodiments of the present application, the co-precipitation reaction time is 30h-100h, for example, can be 30h, 50h, 70h, 90h, 100h, or can be a range consisting of any of the above values.

[0065] S20: mixing the lithium-rich manganese-based precursor, a lithium source, and M 1 According to some embodiments of the present application, the lithium source can include at least one of lithium carbonate and lithium hydroxide.

[0066] According to some embodiments of the present application, the M1 source including at least one of an oxide of M 1 , a sulfide of M 1 , a fluoride of M 1 , a hydroxide of M 1 , a carbonate of M 1 .

[0067] According to some embodiments of the present application, 0≤n (M1) / (n (Ni) +n (Co) +n (Mn) )≤0.04, for example, can be 0, 0.01, 0.02, 0.03, 0.04, etc., or can be a range consisting of any of the above values. According to some specific embodiments of the present application, 0.001≤n (M1) / (n (Ni) +n (Co) +n (Mn) )≤0.02.

[0068] According to some embodiments of the present application, the temperature of the first sintering is T1, and satisfies 800℃≤T1≤980℃, for example, can be 800℃, 840℃, 880℃, 920℃, 960℃, 980℃, etc., or can be a range consisting of any of the above values.

[0069] According to some embodiments of the present application, the temperature of the first sintering is T1, and satisfies 800℃≤T1≤980℃, for example, can be 800℃, 840℃, 880℃, 920℃, 960℃, 980℃, etc., or can be a range consisting of any of the above values.

[0070] According to some embodiments of the present application, the time of the first sintering is t1, and satisfies 5h≤t1≤15h, for example, can be 5h, 7h, 9h, 11h, 13h, 15h, etc., or can be a range consisting of any of the above values.

[0071] Thus, by making T1, V1, t1 of the first sintering in the above range, primary particles can be generated uniformly at the same time, so as to obtain more micropore structures among the primary particles.

[0072] According to some embodiments of the present application, 1.12≤n (Li) / (n (Ni) +n (Co) +n (Mn) +n (M1) )≤1.49. Thus, the integrity of the lattice of the positive electrode active material is improved, and the cycle stability of the positive electrode active material is improved. Wherein, n is the molar amount of the corresponding element.

[0073] As an example, n (Li) (Ni) (Co) (Mn) (M1) may be 1.12, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.49, etc., or can be a range consisting of any of the above values. Wherein n is the molar amount of the corresponding element.

[0074] S30: mixing the first process product, M 2 source, and the solvent to form a second mixed solution, the solid-liquid ratio of the first process product to the solvent being 0.5 g / mL-3 g / mL, solid-liquid separation, drying the solid phase material to obtain a second process product

[0075] According to some embodiments of the present application, the first process product, M 2 source is sequentially added to an aqueous solution to form a second mixed solution, and solid-liquid separation is performed to obtain a solid phase material, and the second process product is obtained after drying the solid phase material.

[0076] It should be noted that when there is no M 2 element in the positive active material, there is no need to add M 2 source.

[0077] According to some embodiments of the present application, the solid-liquid ratio of the first process product to the solvent can be 0.5 g / mL, 1 g / mL, 1.5 g / mL, 2 g / mL, 2.5 g / mL, 3 g / mL, etc., or can be a range consisting of any of the above values.

[0078] According to some specific embodiments of the present application, the solid-liquid ratio of the first process product to the solvent is 1.0 g / mL-3 g / mL.

[0079] According to some embodiments of the present application, the temperature of the second mixed solution can be 5℃-35℃. For example, it can be 5℃, 10℃, 15℃, 20℃, 25℃, 30℃, 35℃, etc., or can be a range consisting of any of the above values.

[0080] According to some embodiments of the present application, the mixing time of the first process product, the M 2 source, and the solvent is 30s-1200s, for example, it can be 30s, 100s, 300s, 500s, 700s, 900s, 1100s, 1200s, etc., or can be a range consisting of any of the above values. According to some specific embodiments of the present application, the mixing time of the first process product, the M 2 source, and the solvent is 60s-600s. ​​​​

[0081] Thus, by making the solid-liquid ratio, the temperature of the second mixed solution, and the mixing time in the above ranges, the primary particles and the filler in the micropores between the primary particles are washed away and discharged outside the secondary particles, while the crystal structure is not destroyed.

[0082] According to some embodiments of the present application, 0≤n (M2) / (n (Ni) +n (Co) +n (Mn) +n (M1) )≤0.04, for example, can be 0, 0.01, 0.02, 0.03, 0.04, etc., or can be a range consisting of any of the above values. According to some specific embodiments of the present application, 0.001≤n (M2) / (n (Ni) +n (Co) +n (Mn) +n (M1) )≤0.02. Wherein, n is the molar amount of the corresponding element.

[0083] According to some embodiments of the present application, the M 2 source includes at least one of an oxide of M 2 , a sulfide of M 2 , a fluoride of M 2 , a hydroxide of M 2 , a carbonate of M 2 , a hydroxyl oxide of M 2 .

[0084] S40: performing second sintering on the second process product, the temperature of the second sintering being less than or equal to the temperature of the first sintering, to obtain the positive electrode active material

[0085] According to some embodiments of the present application, the second sintering is performed on the second process product in an oxygen-containing atmosphere, and after the sintered product is screened and iron is removed, the positive electrode active material is obtained.

[0086] According to some embodiments of the present application, the temperature of the second sintering is T2, and satisfies 300℃≤T2≤800℃, for example, can be 300℃, 400℃, 500℃, 600℃, 700℃, 800℃, etc., or can be a range consisting of any of the above values.

[0087] According to some embodiments of the present application, the time of the second sintering is t2, and satisfies 6h≤t2≤20h. For example, can be 6h, 10h, 14h, 18h, 20h, etc., or can be a range consisting of any of the above values.

[0088] Therefore, by setting the temperature and time of the second sintering in the above range, the pore structure in the secondary particles can be better preserved, and the risk of the closed pores of the primary particles being closed after re-sintering can be reduced.

[0089] In summary, the positive electrode active material provided in the present application has the following advantages:

[0090] (1) The positive electrode active material provided in the present application has a large specific surface area after being in contact with the electrolyte while maintaining a low porosity, thereby shortening the diffusion path of lithium ions in the positive electrode active material and improving the gravimetric capacity of the positive electrode active material.

[0091] (2) The large specific surface area of the positive electrode active material allows the positive electrode active material to be in full contact with the electrolyte, promotes the interfacial reaction between the positive electrode active material and the electrolyte, and improves the cycle performance of the battery.

[0092] (3) After the simulation of the electrolyte infiltration process, the average pore size of the positive electrode active material is small, which allows the positive electrode active material to have a large specific surface area at a low porosity, thereby obtaining a positive electrode active material with high tap density and excellent cycle performance.

[0093] (4) In the process of preparing the lithium-rich manganese-based precursor, by controlling the pH of the first mixed solution and the stirring speed, the lithium-rich manganese-based precursor has good multidirectionality and high tap density, so that the primary particles of the positive electrode active material also have good multidirectionality. During the battery cycle process, the positive electrode active material can be soaked in the electrolyte to obtain more micropores, i.e., the positive electrode active material has a large specific surface area at a low porosity, thereby obtaining a battery with excellent cycle performance and high energy density.

[0094] (5) In the process of preparing the positive electrode active material, by controlling the solid-liquid ratio of the first process product and the solvent, the soluble residual substances in the micropores between the primary particles can be discharged to the outside of the secondary particles during the formation of the second process product, so that more micropores are formed in the interior of the secondary particles without damaging the lattice structure, thereby obtaining a positive electrode active material with excellent cycle performance and high volumetric energy density.

[0095] (6) The positive electrode active material provided in the present application has good lattice integrity, which can further improve the cycle performance of the battery.

[0096] The third aspect of the present application provides a positive electrode tab, which comprises the positive electrode active material provided in the first aspect of the present application or the positive electrode active material prepared by the method provided in the second aspect of the present application.

[0097] The fourth aspect of the present application provides a battery comprising the positive electrode plate provided in the third aspect of the present application. Thus, the battery has a high volumetric energy density and cycle performance.

[0098] The fifth aspect of the present application provides a power consumption device comprising the battery provided in the fourth aspect of the present application.

[0099] Embodiments of the present application are described in detail below. The embodiments described below are exemplary and are only used to explain the present application and cannot be understood as a limitation of the present application. If a specific technology or condition is not specified in the embodiments, the technology or condition described in the literature in the art or according to the product instruction is used. If the manufacturer of the reagent or instrument is not specified, it is a conventional product that can be obtained by purchase.

[0100] Example 1

[0101] 1. Preparation of a positive electrode active material

[0102] (1) Under the protection of nitrogen, nickel sulfate, cobalt sulfate, manganese sulfate (molar ratio Ni:Co:Mn = 33:5:62), 25% ammonia water, and a precipitant were passed into a reaction kettle in a parallel flow manner to perform a co-precipitation reaction, the precipitant was a 2 mol / L NaOH aqueous solution, the co-precipitation reaction temperature was 60°C, the rotation speed was 550 rpm, the time was 50 h, the pH was 10.2, and after natural cooling to room temperature, crushing and sieving were performed to obtain a lithium-rich manganese-based precursor;

[0103] (2) The lithium-rich manganese-based precursor, lithium carbonate, and TiO2 were mixed to perform a first sintering, the sintering atmosphere was air, the heating rate V1 was 5°C / min, t1 was 10 h, T1 was 880°C, and after natural cooling to room temperature, crushing and sieving were performed to obtain a first process product;

[0104] (3) The first process product, deionized water, and AlF were mixed to form a second mixed solution, the solid-liquid ratio of the first process product to deionized water was 2 g / mL, the temperature of the second mixed solution was 12°C, the mixing time was 300 s, and after pressure filtration and vacuum drying, a second process product was obtained;

[0105] (4) The second process product was subjected to a second sintering in an air atmosphere, T2 was 440°C, t2 was 8 h, and after sieving and iron removal treatment, natural cooling to room temperature was performed to obtain Li 1.05 (Ni 0.286 Co 0.043 Li 0.126 Mn 0.538 Ti 0.007 )Al 0.012 O 2.025 F 0.012 .

[0106] 2. Preparation of positive electrode sheet

[0107] The positive electrode active material Li 1.05 (Ni 0.286 Co 0.043 Li 0.126 Mn 0.538 Ti 0.007 )Al 0.012 O 2.025 F 0.012 , polyvinylidene fluoride (PVDF) and acetylene black were mixed in a mass ratio of 90:5:5 with an appropriate amount of N-methyl pyrrolidone (NMP) to form a uniform slurry. The slurry was coated on an aluminum foil and dried, and then formed into a positive electrode sheet with a diameter of 12 mm and a thickness of 120 μm by stamping under a pressure of 100 MPa. The positive electrode sheet was then placed in a vacuum drying oven and dried at 120°C for 12 h.

[0108] 3. Preparation of negative electrode sheet

[0109] The negative electrode used a Li metal sheet with a diameter of 17 mm and a thickness of 1 mm.

[0110] 4. Separator film

[0111] A polyethylene porous film with a thickness of 25 μm.

[0112] 5. Electrolyte

[0113] An equal volume mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) with 1 mol / L LiPF6 as the electrolyte.

[0114] 6. Assembly of battery

[0115] The positive electrode sheet, separator film, negative electrode sheet and electrolyte were assembled into a 2025 type button cell in an Ar glove box with a water content and oxygen content of less than 5 ppm.

[0116] The preparation process of the positive electrode active material in Examples 2-9 and Comparative Examples 1-3 is shown in Table 1, and the method of preparing the battery from the positive electrode active material is the same as in Example 1, with the differences shown in Table 1.

[0117] Comparative Example 1

[0118] The preparation process of the positive electrode active material was the same as in Example 1, except that the pH of the first mixed solution was 9.0 and the rotation speed was 400 rpm.

[0119] Comparative Example 2

[0120] The positive electrode active material was prepared according to the procedure of Example 1, except that the pH of the first mixture was 11.8 and the rotation speed was 950 rpm.

[0121] Comparative Example 3

[0122] The positive electrode active material was prepared according to the procedure of Example 1, except that the solid-liquid ratio of the first process product to deionized water was 5 g / mL.

[0123] Performance test

[0124] 1. BET specific surface area

[0125] In the present application, the testing method of BET specific surface area is as follows: the positive electrode active material is soaked in an acidic solution for 2 h, the weight ratio of the positive electrode active material to the acidic solution is 1:10, the pH of the acidic solution is 5.5, after soaking, drying is performed at 120°C in a vacuum atmosphere, and testing is performed using a specific surface instrument of Tristar 3020 model of Micromeritics Company.

[0126] 2. Porosity

[0127] The pore volume is obtained by testing using a specific surface instrument of Tristar 3020 model of Micromeritics Company, and the skeletal volume is obtained by a true density instrument of AccuPyc 1345 model of Micromeritics Company. Porosity = pore volume / (pore volume + skeletal volume) x 100%

[0128] 3. Average pore size

[0129] Obtained by testing using a specific surface instrument of Tristar 3020 model of Micromeritics Company.

[0130] 4. Proportion of pore size less than or equal to 10 nm

[0131] The pore size distribution is obtained by testing using a specific surface instrument of Tristar 3020 model of Micromeritics Company, wherein the proportion of pore size less than or equal to 10 nm.

[0132] 5. Compaction density

[0133] Obtained by testing using a Japan Mitsubishi powder impedance testing system.

[0134] 6. XRD

[0135] The X-ray diffractometer of Smart Lab 9KW model of Rigaku Corporation of Japan was used for the measurement, and the FWHM of the (003) peak was calculated at 2θ of 17.5°-19.5°, and the FWHM of the (104) peak was calculated at 2θ of 43.5°-45.5°.

[0136] 7. Initial discharge specific capacity

[0137] The initial discharge specific capacity was obtained by charging the positive electrode at a current density of 25 mA / g to a cut-off voltage of 4.55 V after the open circuit voltage was stabilized for 2 h after the button cell was prepared, and then discharging to a cut-off voltage of 2.5 V at the same current density, after the constant voltage charging cut-off current was 0.05 C.

[0138] 8. Discharge average voltage

[0139] The discharge average voltage = discharge energy during discharge / discharge capacity during discharge.

[0140] 9. Volume energy density

[0141] The volume energy density = compacted density of powder x initial discharge specific capacity x discharge average voltage.

[0142] 10. Cycle capacity retention rate

[0143] After the button cell was discharged for the first time, the current density of the positive electrode was changed to 250 mAh / g, the charging cut-off voltage was 4.55 V, the constant voltage charging cut-off current was 0.05 C, and then discharged to a cut-off voltage of 2.5 V at the same current density, after 2 times of 0.1 C charge-discharge, the initial cycle capacity was obtained. The 50th cycle capacity was obtained after 50 cycles. The cycle capacity retention rate = 50th cycle capacity / initial cycle capacity x 100%.

[0144] The test results of the positive electrode active material and the battery in Example 1-Example 9, Comparative Example 1-Comparative Example 3 are shown in Table 2.

[0145] Compared with Example 1-Example 9 and Comparative Example 1-Comparative Example 3, it can be seen that, in the process of preparing the positive electrode active material, by controlling the pH of the first mixed solution, the stirring speed and the solid-liquid ratio of the first process product and the solvent, the average pore size of the positive electrode active material prepared after soaking in the acidic solution is smaller, the proportion of pores less than 10 nm is larger, the positive electrode active material has smaller porosity and larger BET specific surface area, the first discharge specific capacity, the average discharge voltage, the volume energy density and the cycle capacity retention rate of the battery are all higher, which shows that the positive electrode active material proposed in the application can not only improve the volume energy density of the battery, but also make the contact between the positive electrode active material and the electrolyte more sufficient during the charging and discharging process of the battery, thereby promoting the interfacial reaction between the positive electrode active material and the electrolyte and improving the cycle performance of the battery.

[0146] Compared with Example 1 and Comparative Example 1, it can be seen that, if the stirring speed is too small, although the specific surface area of the positive electrode active material is larger, the porosity is also larger, resulting in lower volume energy density of the battery.

[0147] Compared with Example 1 and Comparative Example 2, it can be seen that, if the stirring speed is too large, the BET specific surface area and the porosity of the positive electrode active material are both smaller, resulting in lower first discharge capacity of the battery.

[0148] Compared with Example 1 and Comparative Example 3, it can be seen that, if the solid-liquid ratio of the first process product and the solvent is too large, the BET specific surface area and the porosity of the positive electrode active material are both larger, and the battery with higher volume energy density, first discharge specific capacity and cycle capacity retention rate cannot be obtained.

[0149] It can be seen from Example 1, Example 7-Example 9 that, in the process of preparing the positive electrode active material, by adjusting the amount of lithium source (i.e. n (Li) / (n (Ni) +n (Co) +n (Mn) +n (M1) ), the Li content in the positive electrode active material can be controlled, and then the ratio of FWHM(104) / FWHM(003) can be controlled, to obtain a positive electrode active material with better lattice integrity, thereby improving the cycle capacity retention rate of the battery.

[0150] Although the embodiments of the application have been shown and described above, it should be understood that the above embodiments are exemplary and should not be construed as limiting the application, and those skilled in the art can make changes, modifications, replacements and variations to the above embodiments within the scope of the application.

Claims

1. A positive electrode active material, wherein, The positive electrode active material is secondary particles formed by agglomeration of primary particles, the secondary particles having pores, the BET specific surface area of the positive electrode active material after immersion in an acidic solution is 1.75 m 2 / g-4 m 2 / g, the porosity of the positive electrode active material after immersion in the acidic solution is 2.6%-6.5%, the weight ratio of the positive electrode active material and the acidic solution is 1:10, the pH of the acidic solution is 5.5, and the immersion time is 2 h.

2. The positive electrode active material according to claim 1, wherein The average pore size of the pores of the positive electrode active material secondary particles is 9 nm to 25 nm after the positive electrode active material secondary particles are soaked in an acid solution.

3. The positive electrode active material according to claim 2, wherein The proportion of the pores with a pore size of less than or equal to 10 nm is 50% to 80%.

4. The positive electrode active material according to any one of claims 1 to 3, wherein The compacted density of the positive electrode active material is 2.7 g / cm 3 - 3.2 g / cm 3 .

5. The positive electrode active material according to claim 4, wherein The positive electrode active material satisfies: η = FWHM(104) / FWHM(003), 1.75 ≤ η ≤ 2.8, and optionally, 1.85 ≤ η ≤ 2.1, wherein FWHM(104) is a half-peak width of a diffraction peak (104) of an X-ray diffraction spectrum, the diffraction peak (104) corresponding to a 2θ value of 43.5° to 45.5°, and FWHM(003) is a half-peak width of a diffraction peak (003) of the X-ray diffraction spectrum, the diffraction peak (003) corresponding to a 2θ value of 17.5° to 19.5°.

6. The positive electrode active material according to claim 1, wherein The positive electrode active material includes a compound represented by Formula I: Li 1+δ (Ni x(1-a) Co y(1-a) Li(1-2x-y)(1-a) / 3Mn(2-x-y)(1-a) / 3M 1 a M 2 b )O (2+δ / 2) N n Formula I, wherein 0.02≤δ≤0.08, 0.25≤x≤0.45, 0≤y≤0.1, 0≤a≤0.035, 0≤b≤0.04, 0≤n≤0.04, M 1 comprising at least one of Al, Zr, Y, Mg, Ti, W, Si, Yb, Nb, Sc, Ca, La, Sr, Y, M 2 comprising at least one of B, Mg, Al, Ti, V, Sr, Y, Zr, Nb, Mo, Sc, Cr, La, Sr, W, N comprising at least one of F, S, P, O.

7. The positive electrode active material according to claim 6, wherein At least one of the following conditions is satisfied: 0.03 ≤ δ ≤ 0.06; 0.001 ≤ a ≤ 0.02; 0.001 ≤ b ≤ 0.02; 0 ≤ n ≤ 0.

02.

8. The positive electrode active material according to claim 6, wherein At least part of the surface of the secondary particles has a coating layer; preferably, the coating layer comprises the M 2 elements.

9. A method for producing a positive electrode active material, wherein, Comprising: mixing a Ni source, a Co source, a Mn source, a complexing agent, and a precipitating agent to form a first mixed solution, stirring the first mixed solution, co-precipitating, and drying to obtain a lithium-rich manganese-based precursor, wherein a pH of the first mixed solution is 9 to 11.5, The stirring speed is 500 rpm to 900 rpm. sintering the lithium-rich manganese-based precursor, the lithium source, M 1 a first process product by mixing the lithium-rich manganese-based precursor, the lithium source, M The first process product, M 2 The first process product, M 2 The first process product, M 2 The first process product, M 2 The first process product, M 2 The first process product, M 2 The first process product, M 2 The first process product, M 2 The first process product, M 2 The first process product, M 2 The first process product, M 2 The first process product, M < The first process product is subjected to a second sintering, the temperature of the second sintering being less than or equal to the temperature of the first sintering, to obtain the positive electrode active material.

10. The method of claim 9, wherein, The solid-liquid ratio of the first process product to the solvent is 1.0 g / mL to 3 g / mL.

11. The method of claim 9, wherein, At least one of the following conditions is satisfied: The temperature of the second mixed solution is 5°C to 35°C. The first process product, the M 2 The mixing time of the source and the solvent is 30s-1200s, optionally 60s-600s.

12. The method of claim 9, wherein, 1.12≤n (Li) / (n (Ni) +n (Co) +n (Mn) +n (M1) )≤1.

49.

13. The method of claim 9, wherein, 0 ≤ n (M2) / (n (Ni) +n (Co) +n (Mn) +n (M1) ) ≤ 0.04, optionally 0.001 ≤ n (M2) / (n (Ni) +n (Co) +n (Mn) +n (M1) ) ≤ 0.

02.

14. The method of claim 9, wherein, At least one of the following conditions is satisfied: The temperature of the first sintering is T1, and 800°C ≤ T1 ≤ 980°C is satisfied; The time of the first sintering is t1, and 5h ≤ t1 ≤ 15h is satisfied; The temperature rising rate of the first sintering is V1, and 1.3°C / min ≤ V1 ≤ 10°C / min is satisfied.

15. The method of claim 9, wherein, At least one of the following conditions is satisfied: The temperature of the second sintering is T2, and 300°C ≤ T2 ≤ 800°C is satisfied; The time of the second sintering is t2, and 6h ≤ t2 ≤ 20h is satisfied.

16. A positive electrode sheet, wherein, The positive electrode active material comprises the positive electrode active material of any one of claims 1 to 8 or the positive electrode active material prepared by the method of any one of claims 9 to 15.

17. A battery, wherein, The positive electrode tab comprises the positive electrode tab of claim 16.

18. An electrical device, comprising: The battery comprises the battery of claim 17.

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