WO2024093082A1

WO2024093082A1 - Coated positive electrode material and preparation method therefor, and lithium-ion battery

Info

Publication number: WO2024093082A1
Application number: PCT/CN2023/080217
Authority: WO
Inventors: 陈希文; 刘伟健; 阮丁山; 李长东; 罗翠苹; 许帅军
Original assignee: 广东邦普循环科技有限公司; 湖南邦普循环科技有限公司
Priority date: 2022-11-04
Filing date: 2023-03-08
Publication date: 2024-05-10
Also published as: FR3141812A1; CN115763684A

Abstract

Disclosed are a coated positive electrode material and a preparation method therefor, and a lithium-ion battery. The method comprises the following steps: (1) coating the surface of a polycrystalline positive electrode material with a coating agent by using a spray coating method; and (2) tempering the polycrystalline positive electrode material obtained in step (1) to prepare the coated positive electrode material. The coated positive electrode material prepared in the present application has high compaction density, so that the volumetric energy density of a battery is improved. In addition, the surface of primary single crystal particles, the surface of secondary polycrystalline particles and grain boundaries of the secondary polycrystalline particles of the polycrystalline positive electrode material are all coated with the coating agent, so that the contact between the positive electrode material and an electrolyte is effectively avoided, and the cycle performance of the positive electrode material is improved.

Description

A coated positive electrode material and preparation method thereof and lithium ion battery

Technical Field

The embodiments of the present application relate to the technical field of positive electrode materials, for example, a coated positive electrode material and a preparation method thereof, and a lithium-ion battery.

Background technique

The lithium battery industry has been seeking higher capacity, more stable and safer battery cathode materials. High nickel ternary materials have always been a hot topic in the industry due to their high capacity. Although there are mature products on the market, high nickel ternary materials still have many problems compared to other mainstream cathode materials. For example, high nickel ternary materials have poor cycle stability, unstable structure, high sensitivity to the environment and poor safety.

Compared with single crystal materials, high nickel polycrystalline materials are easier to achieve high capacity and excellent rate performance. However, since high nickel polycrystalline materials are secondary spheres composed of many small primary single crystal particles, when modified by coating, the internal particles cannot contact the coating agent, resulting in the coating agent playing a greater role in the early stage of the battery cycle, but in the later stage of the battery cycle, the electrolyte infiltrates into the part of the positive electrode material sphere without the coating agent, which will cause the battery's cycle performance to deteriorate rapidly. The existing methods mainly improve this through surface doping, but surface doping has the disadvantage of uneven distribution, and it is easy to form an inactive layer on the surface of the positive electrode material, resulting in a significant decrease in the electrochemical performance of the battery.

For example, CN114975985 A discloses a Ti-Cr co-doped high-voltage spinel positive electrode material and a preparation method thereof, the preparation method comprising mixing raw materials including a lithium source, a nickel source, a manganese source, a titanium source, a chromium source, a solvent and a dispersant to obtain a slurry; drying the slurry to obtain a solid powder, and then pre-sintering the solid powder to obtain a precursor; and secondary sintering the precursor to obtain a Ti-Cr co-doped high-voltage spinel positive electrode material. For example, CN111106343 A discloses a lanthanum and fluorine co-doped high-nickel ternary positive electrode material and a preparation method and application thereof, the preparation method comprising the following steps: preparing a nickel source, a cobalt source, and a manganese source into a solution, and adding a precipitant to obtain a precipitate. Then, the lanthanum source, the fluorine source and the precursor are uniformly mixed in ethanol, and the solvent is evaporated. The treated precursor is mixed with a lithium salt, and a lanthanum and fluorine co-doped high-nickel ternary material is synthesized by pre-sintering and sintering. For example, CN111072074 A discloses a method for preparing an indium-doped nickel cobalt manganese oxide material, comprising weighing raw materials according to a stoichiometric ratio, preparing a microemulsion, adding the raw materials into deionized water, stirring evenly, adding the raw materials into the microemulsion, ultrasonically dispersing, freeze-drying the solution, and sintering the treated raw materials to obtain an indium-doped nickel cobalt manganese oxide positive electrode material.

When the positive electrode material is modified by the above-mentioned doping method, there is a disadvantage of uneven distribution of the doping material, and it is impossible to ensure that the dopant is evenly distributed inside the positive electrode material, thereby affecting the electrochemical performance of the battery. Therefore, it is necessary to develop a positive electrode material with high capacity and excellent rate performance.

Summary of the invention

The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

The embodiment of the present application proposes a coated positive electrode material, a preparation method thereof and a lithium-ion battery. The preparation method of the coated positive electrode material comprises the following steps: (1) coating the surface of a polycrystalline positive electrode material with a coating agent by a spray coating method; (2) preparing the coated positive electrode material by tempering the polycrystalline positive electrode material obtained in step (1).

In a first aspect, an embodiment of the present application provides a method for preparing a coated positive electrode material, the method comprising the following steps:

(1) coating the coating agent onto the surface of the polycrystalline positive electrode material by a spray coating method;

(2) The polycrystalline positive electrode material obtained in step (1) is tempered to obtain the coated positive electrode material.

In this application, the coating agent is uniformly coated on the surface of the polycrystalline positive electrode material by utilizing the uniformity advantage of spray coating, and the coating agent can also enter the internal grain boundary of the polycrystalline positive electrode material. During the tempering process, the coating agent reacts with the residual lithium at the grain boundary of the polycrystalline positive electrode material and the positive electrode material, and the coating and doping of the positive electrode material can be modified together; in addition, the coating agent reacts with the residual lithium at the grain boundary of the polycrystalline positive electrode material and the positive electrode material to depolymerize the primary single crystal particles in the polycrystalline positive electrode material, and the surface of the primary single crystal particles is also coated with the coating agent, which further improves the cycle performance of the prepared positive electrode material. Compared with the traditional method of separating particles by mechanical dissociation, the method of separating particles in this application is more accurate and effective, and does not damage the material, ensuring that the defects inside the material will not increase.

The preparation method of the present application is relatively simple and low-cost, and the process involved in the present application can be completed by making simple modifications to the existing production line, which is conducive to achieving scale.

In the present application, the prepared coated positive electrode material has a graded appearance of primary single crystal particles and secondary polycrystalline particles, which greatly improves the compaction density of the positive electrode material and can achieve a higher volume energy density. The release of the primary single crystal particles also increases the capacity of the positive electrode material. In addition, the coating agent can be more evenly coated on the surface of the primary single crystal particles, the surface of the secondary polycrystalline particles, and the crystal structure of the secondary polycrystalline particles. The interface is located at the bottom of the electrolyte, which fully avoids the contact between the positive electrode material and the electrolyte, and improves the cycle performance of the positive electrode material.

In the present application, the amount of single crystal particles released at one time can be controlled. The extent of the reaction at the grain boundaries of the polycrystalline positive electrode material can be controlled by regulating the content of the coating agent, the annealing temperature and the annealing time. The uniformity of the coating of the coating agent can be controlled by regulating parameters such as the stirring speed and the spraying speed during the spray coating process, thereby affecting the contact area between the coating agent and the positive electrode material, affecting the number of reactive sites, and thus affecting the extent of the reaction at the grain boundaries of the polycrystalline positive electrode material. The amount of single crystal particles released at one time can be controlled by regulating the above parameters.

Preferably, the capping agent comprises a metal boride.

Preferably, the metal boride comprises at least one of Co _a B, ZrB ₂ and MgB ₂ , wherein 3 ≥ a ≥ 1, for example, a may be 1, 1.5, 2, 2.5 or 3.

Preferably, the polycrystalline positive electrode material is a polycrystalline ternary positive electrode material.

Preferably, the composition of the polycrystalline ternary cathode material includes Li(Ni _x Co _y Mn _1-xy )O ₂ , wherein 0＜x＜1, 0＜y＜1, for example x＝0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 or 0.9, 0＜y＜1, for example y＝0.1, 0.2, 0.25, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 or 0.9.

Preferably, 0.6≤x<1, 0.1<y<0.3.

Preferably, the mass ratio of the polycrystalline positive electrode material to the coating agent is 1:(0.0003-0.05), and “0.0003-0.05” can be, for example, 0.0003, 0.0005, 0.0008, 0.001, 0.002, 0.003, 0.004, 0.005, 0.01, 0.02, 0.03, 0.04 or 0.05, preferably 1:(0.0003-0.02).

In the present application, if the content of the coating agent is large, the thickness of the coating layer will be relatively thick, and more metal borides will be doped on the surface of the polycrystalline positive electrode material, resulting in reduced activity on the surface of the polycrystalline positive electrode material. Excessive boron elements will form Li-B-Me-O compounds (Me is Ni, Co or Mn) in the positive electrode material. Too much of this compound will lead to a decrease in the capacity and cycle performance of the positive electrode material. If the content of the coating agent is small, a mixed morphology of primary single crystal particles and secondary polycrystalline particles cannot be formed in the positive electrode material, and the thickness of the coating layer will be small and the doping amount will be small, all of which will affect the electrochemical properties of the positive electrode material.

Preferably, the spray coating method in step (1) comprises:

(a) mixing a coating agent and a dispersant to form a suspension;

(b) spraying the polycrystalline positive electrode material with the suspension described in step (a).

Preferably, the dispersant comprises at least one of water or a hydroalcoholic solution.

Preferably, the spraying speed is 0.2-50 mL/s, for example 0.5 mL/s, 1 mL/s, 1.5 mL/s, 2mL/s, 5mL/s, 10mL/s, 15mL/s, 20mL/s, 25mL/s, 30mL/s, 35mL/s, 40mL/s, 45mL/s, or 50mL/s.

In the present application, if the spraying speed is relatively low, the preparation time of the coated positive electrode material will be prolonged, thereby resulting in the loss of resources and being detrimental to the actual production work. If the spraying speed is relatively high, the coating agent will be unevenly coated, and the coating agent will agglomerate in the prepared coated positive electrode material, thereby affecting the electrochemical properties of the coated positive electrode material.

In one embodiment of the present application, the coating agent in step (a) accounts for 0.3%-10% of the mass of the dispersant.

Preferably, in step (b), the polycrystalline positive electrode material is sprayed under stirring conditions.

Preferably, the linear speed of the stirring is 1-15 m/s, for example, 1 m/s, 3 m/s, 5 m/s, 7 m/s, 9 m/s, 11 m/s, 13 m/s or 15 m/s.

Preferably, the stirring time is 0.5-5 min, for example 1 min, 2 min, 3 min, 4 min or 5 min.

Preferably, the polycrystalline positive electrode material is stirred for 3-5 minutes, such as 3 minutes, 4 minutes or 5 minutes, after spraying is completed.

The purpose of continuing stirring is to ensure that the coating agent can be evenly coated on the surface of the polycrystalline positive electrode material.

Preferably, the tempering temperature in step (2) is 300-700°C, for example, 300°C, 400°C, 500°C, 600°C or 700°C.

Preferably, the tempering time in step (2) is 3-10 h, such as 3 h, 5 h, 7 h or 9 h.

A higher tempering temperature or a longer tempering time will allow all coating agents to enter the grain boundaries of the polycrystalline positive electrode material, resulting in the disappearance of the coating layer on the surface of the polycrystalline positive electrode material, leading to the deterioration of the positive electrode material cycle performance. At the same time, the higher temperature will also have a certain impact on the positive electrode material itself, especially in high-nickel materials, high-temperature tempering will aggravate the lithium-nickel mixing, thereby causing the deterioration of the positive electrode material crystal structure; a lower tempering temperature or a shorter tempering time cannot fully play the role of the coating agent, the number of single crystal particles at a time cannot meet the requirements, and the volume density of the material is slightly improved. At the same time, a lower tempering temperature or a shorter tempering time will also cause the coating agent to not react sufficiently with the positive electrode material or residual lithium, resulting in a decrease in the binding force between the coating agent and the positive electrode material, and the required reaction product is not sufficient to be doped into the surface of the positive electrode material, so the stability of the positive electrode material cannot be significantly improved.

Preferably, the coated positive electrode material is screened after the tempering step.

Exemplarily, the mesh size of the sieving includes but is not limited to 400 mesh.

Taking the ternary cathode material Li(Ni _x Co _y Mn _1-xy )O ₂ as an example, where 0＜x＜1, 0＜y＜1, this application An exemplary method for preparing the coated positive electrode material comprises the following steps:

(1) mixing the coating agent and deionized water so that the coating agent is evenly dispersed in the deionized water to form a coating suspension, pouring the coating suspension into a spray tank and continuously and slightly stirring to prevent sedimentation, thereby obtaining a coating liquid;

(2) pouring Li(Ni _x Co _y Mn _1-xy )O ₂ into a mixing device and starting stirring at a linear speed of 1-15 m/s and a stirring time of 0.5-5 min to ensure that Li(Ni _x Co _y Mn _1-xy )O ₂ is fully dispersed in the cavity of the mixing device;

(3) Turn on the spray system and control the spray speed of the coating liquid to 0.2-50 mL/s until all the coating liquid is sprayed;

(4) After closing the spray system, continue stirring for 3-5 minutes to ensure that the coating agent can be evenly coated on the surface of the polycrystalline positive electrode material;

(5) putting the positive electrode material obtained in step (4) into a sagger and placing it into a kiln for tempering and further modification, the tempering temperature is 300-700° C., and the tempering time is 3-10 h;

(6) After the positive electrode material in step (5) is taken out of the furnace, it is screened to prepare a coated positive electrode material.

In the second aspect, an embodiment of the present application provides a coated positive electrode material prepared by the method described in the first aspect of the present application, wherein the coated positive electrode material includes primary single crystal particles and secondary polycrystalline particles, wherein the surface of the primary single crystal particles, the surface of the secondary polycrystalline particles and the grain boundaries of the secondary polycrystalline particles are all coated with a coating layer.

The mixed morphology of primary single crystal particles and secondary polycrystalline particles in the coated positive electrode material in the present application greatly improves the compaction density of the positive electrode material, thereby improving the volume energy density of the battery; in addition, the coating layer of the coated positive electrode material in the present application is not only limited to the surface of the secondary polycrystalline particles, but the surface of the primary single crystal particles, the surface of the secondary polycrystalline particles and the grain boundaries of the secondary polycrystalline particles are coated with the coating layer, which fully avoids the direct contact between the electrolyte and the positive electrode material in the later stage of the battery cycle, thereby improving the cycle performance of the positive electrode material.

In the present application, primary single crystal particles and secondary polycrystalline particles are both polycrystalline positive electrode materials. Primary single crystal particles refer to primary particles with single crystal morphology, and secondary polycrystalline particles refer to secondary particles with polycrystalline morphology. The secondary polycrystalline particles are composed of primary single crystal particles. The primary single crystal particles can be obtained by depolymerizing the secondary polycrystalline particles in the polycrystalline positive electrode material.

Preferably, the average particle size of the primary single crystal particles is 100-500 nm, for example, 100 nm, 150 nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm or 500nm.

Preferably, the average particle size of the secondary polycrystalline particles is 7-12 μm, for example, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm or 12 μm.

In a third aspect, an embodiment of the present application provides a lithium-ion battery, wherein the positive electrode of the lithium-ion battery includes the coated positive electrode material described in the second aspect of the present application.

The lithium-ion battery assembled using the coated positive electrode material described in the second aspect of the present application has a higher capacity and better cycle performance.

Compared with the related art, the embodiments of the present application have the following beneficial effects:

(1) The embodiment of the present application can evenly coat the coating agent on the surface of the polycrystalline positive electrode material through the spray coating method, and the coating agent can penetrate into the grain boundaries of the polycrystalline positive electrode material. During the tempering process, redox reactions occur at the grain boundaries of the polycrystalline positive electrode material. On the one hand, dual modification of the positive electrode material by doping and coating can be achieved, and on the other hand, the primary single crystal particles in the polycrystalline positive electrode material can be dissociated without damage. Compared with the traditional method of dissociating particles by mechanical dissociation, the method of dissociating the polycrystalline positive electrode material in the present application is more accurate and effective, and does not damage the material, thereby ensuring that the defects inside the material will not increase.

(2) The preparation method of the embodiment of the present application is relatively simple and low-cost. The process involved in the present application can be completed by simply modifying the existing production line, which is conducive to achieving scale.

(3) The coated positive electrode material prepared in the embodiment of the present application has a mixed morphology of primary single crystal particles and secondary polycrystalline particles. This morphology greatly improves the compaction density of the positive electrode material, thereby improving the volume energy density of the battery, and due to the release of the primary single crystal particles, the capacity of the positive electrode material is improved. In addition, the surface of the primary single crystal particles, the surface of the secondary polycrystalline particles, and the grain boundaries of the secondary polycrystalline particles of the coated positive electrode material prepared in the present application are coated with a coating agent, thereby effectively avoiding the contact between the positive electrode material and the electrolyte during the cycle of the battery, thereby improving the cycle performance of the positive electrode material.

Other aspects will be apparent upon reading and understanding the drawings and detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are used to provide further understanding of the technical solution of this article and constitute a part of the specification. Together with the embodiments of the present application, they are used to explain the technical solution of this article and do not constitute a limitation on the technical solution of this article.

FIG. 1 shows the coated positive electrode materials in Examples 1-7 and the uncoated positive electrode materials in Comparative Example 1. X-ray photoelectron spectroscopy (XPS) spectrum of B 1s of LiNi _0.8 Co _0.1 Mn _0.1 O ₂ cathode material;

FIG2 is a scanning electron microscope (SEM) image of the positive electrode materials in Examples 1-7 and Comparative Examples 1-3;

FIG3 is a graph showing the cycle performance of soft-pack batteries assembled with the positive electrode materials in Examples 1-7 and Comparative Examples 1-3 at 45° C. and a current density of 1C.

Detailed ways

The technical solution of the present application is further described below through specific implementation methods. Those skilled in the art should understand that the embodiments are only to help understand the present application and should not be regarded as specific limitations of the present application.

Example 1

This embodiment provides a method for preparing a coated positive electrode material LiNi _0.8 Co _0.1 Mn _0.1 O ₂ @CoB, comprising the following steps:

(1) Prepare raw materials, take 8 kg of high-nickel polycrystalline ternary positive electrode material LiNi _0.8 Co _0.1 Mn _0.1 O ₂ as the substrate material, take 200 mL of deionized water as the dispersant, and take 54.49 g of CoB as the coating agent.

(2) Pour the coating agent CoB into water and stir it thoroughly to form a coating suspension. Pour the coating suspension into the spray tank and continue to stir it slightly. Prepare the spray system to ensure that its flow rate meets the requirements.

(3) Pour the substrate material LiNi _0.8 Co _0.1 Mn _0.1 O ₂ into a mixing device and start stirring at a linear speed of 3 m/s for 1 min to ensure that LiNi _0.8 Co _0.1 Mn _0.1 O ₂ is fully dispersed in the cavity of the mixing device.

(4) Turn on the spray system and spray at a rate of 5 mL/s until all the coating liquid is sprayed. After turning off the spray system, continue stirring for 3 min to further ensure that CoB is evenly coated on the surface of LiNi _0.8 Co _0.1 Mn _0.1 O ₂ .

(5) After completing the above steps, the material obtained in step (4) is loaded into a sagger and placed in a kiln for tempering for further modification. The tempering temperature is 700° C. and the tempering time is 4 h.

(6) After being taken out of the furnace, the resulting product was passed through a 400-mesh sieve to obtain the coated positive electrode material LiNi _0.8 Co _0.1 Mn _0.1 O ₂ @CoB.

The average particle size of the primary single crystal particles in the coated positive electrode material of this embodiment is 310 nm, and the average particle size of the secondary polycrystalline particles is 9.2 μm. According to calculation, the mass of CoB is 0.68% of the mass of LiNi _0.8 Co _0.1 Mn _0.1 O ₂ .

Example 2

This embodiment provides a method for preparing a coated positive electrode material LiNi _0.8 Co _0.1 Mn _0.1 O ₂ @CoB. The following steps are involved:

(3) Pour the substrate material LiNi _0.8 Co _0.1 Mn _0.1 O ₂ into a mixing device and start stirring at a linear speed of 2 m/s for 1 min to ensure that LiNi _0.8 Co _0.1 Mn _0.1 O ₂ is fully dispersed in the cavity of the mixing device.

(4) Turn on the spray system and spray at a rate of 0.5 mL/s until all the coating liquid is sprayed. After turning off the spray system, continue stirring for 3 min to further ensure that CoB is evenly coated on the surface of LiNi _0.8 Co _0.1 Mn _0.1 O ₂ .

(5) After completing the above steps, the material obtained in step (4) is loaded into a sagger and placed in a kiln for tempering and further modification. The tempering temperature is 450° C. and the tempering time is 6 h.

The average particle size of the primary single crystal particles in the coated positive electrode material of this embodiment is 330 nm, and the average particle size of the secondary polycrystalline particles is 11.0 μm. After calculation, the mass of CoB is 0.68% of the mass of LiNi _0.8 Co _0.1 Mn _0.1 O ₂ .

Example 3

(1) Prepare raw materials, take 8 kg of high-nickel polycrystalline ternary positive electrode material LiNi _0.8 Co _0.1 Mn _0.1 O ₂ as the substrate material, take 40 mL of deionized water as the dispersant, and take 6.81 g of CoB as the coating agent.

(3) Pour the substrate material LiNi _0.8 Co _0.1 Mn _0.1 O ₂ into a mixing device and start stirring at a linear speed of 8 m/s for 1 min to ensure that LiNi _0.8 Co _0.1 Mn _0.1 O ₂ is fully dispersed in the cavity of the mixing device.

(4) Turn on the spray system and spray at a rate of 0.2 mL/s until all the coating liquid is sprayed. After turning off the spray system, continue stirring for 3 min to further ensure that CoB is evenly coated on LiNi _0.8 Co _0.1 Mn _0.1 O ₂ s surface.

(5) After completing the above steps, the material obtained in step (4) is loaded into a sagger and placed in a kiln for tempering for further modification. The tempering temperature is 300° C. and the tempering time is 8 h.

The average particle size of the primary single crystal particles in the coated positive electrode material of this embodiment is 320 nm, and the average particle size of the secondary polycrystalline particles is 10 μm. According to calculation, the mass of CoB is 0.085% of the mass of LiNi _0.8 Co _0.1 Mn _0.1 O ₂ .

Example 4

(1) Prepare raw materials, take 8 kg of high-nickel polycrystalline ternary positive electrode material LiNi _0.8 Co _0.1 Mn _0.1 O ₂ as the substrate material, take 360 mL of deionized water as the dispersant, and take 102.16 g of CoB as the coating agent.

(3) Pour the substrate material LiNi _0.8 Co _0.1 Mn _0.1 O ₂ into a mixing device and start stirring with a stirring paddle linear speed of 5 m/s and a stirring time of 1 min to ensure that LiNi _0.8 Co _0.1 Mn _0.1 O ₂ is fully dispersed in the cavity of the mixing device.

(5) After completing the above steps, the material obtained in step (4) is loaded into a sagger and placed in a kiln for tempering for further modification. The tempering temperature is 500° C. and the tempering time is 5 h.

The average particle size of the primary single crystal particles in the coated positive electrode material of this embodiment is 320 nm, and the average particle size of the secondary polycrystalline particles is 9.0 μm. According to calculation, the mass of CoB is 1.28% of the mass of LiNi _0.8 Co _0.1 Mn _0.1 O ₂ .

Example 5

This embodiment provides a method for preparing a coated positive electrode material LiNi _0.8 Co _0.1 Mn _0.1 O ₂ @Co ₂ B. The method comprises the following steps:

(1) Prepare raw materials, take 8 kg of high-nickel polycrystalline ternary positive electrode material LiNi _0.8 Co _0.1 Mn _0.1 O ₂ as the substrate material, take 240 mL of deionized water as the dispersant, and take 92.71 g of Co ₂ B as the coating agent.

(2) Pour the coating agent Co ₂ B into water and stir thoroughly to form a coating suspension. Pour the coating suspension into a spray tank and continue to stir slightly. Prepare the spray system to ensure that its flow rate meets the requirements.

(3) Pour the substrate material LiNi _0.8 Co _0.1 Mn _0.1 O ₂ into a mixing device and start stirring at a linear speed of 5 m/s for 1 min to ensure that LiNi _0.8 Co _0.1 Mn _0.1 O ₂ is fully dispersed in the cavity of the mixing device.

(4) Turn on the spray system and spray at a rate of 3 mL/s until all the coating liquid is sprayed. After turning off the spray system, continue stirring for 3 min to further ensure that Co ₂ B is evenly coated on the surface of LiNi _0.8 Co _0.1 Mn _0.1 O ₂ .

(6) After being taken out of the furnace, the product was passed through a 400-mesh sieve to obtain a coated positive electrode material LiNi _0.8 Co _0.1 Mn _0.1 O ₂ @Co ₂ B.

The average particle size of the primary single crystal particles in the coated positive electrode material of this embodiment is 350 nm, and the average particle size of the secondary polycrystalline particles is 9.0 μm. According to calculation, the mass of Co ₂ B is 1.16% of the mass of LiNi _0.8 Co _0.1 Mn _0.1 O ₂ .

Example 6

This embodiment provides a method for preparing a coated positive electrode material LiNi _0.8 Co _0.1 Mn _0.1 O ₂ @ZrB ₂ , comprising the following steps:

(1) Prepare raw materials, take 8 kg of high-nickel polycrystalline ternary positive electrode material LiNi _0.8 Co _0.1 Mn _0.1 O ₂ as the substrate material, take 160 mL of deionized water as the dispersant, and take 46.05 g of ZrB ₂ as the coating agent.

(2) Pour the coating agent _ZrB2 into water and stir thoroughly to form a coating suspension. Pour the coating suspension into the spray tank and continue to stir slightly. Prepare the spray system to ensure that its flow rate meets the requirements.

(4) Turn on the spray system and spray at a rate of 2 mL/s until all the coating liquid is sprayed. After turning off the spray system, continue stirring for 3 min to further ensure that ZrB ₂ is evenly coated on LiNi _0.8 Co _0.1 Mn _0.1 O ₂ s surface.

(6) After being taken out of the furnace, the product was passed through a 400-mesh sieve to obtain a coated positive electrode material LiNi _0.8 Co _0.1 Mn _0.1 O ₂ @ZrB ₂ .

The average particle size of the primary single crystal particles in the coated positive electrode material of this embodiment is 370 nm, and the average particle size of the secondary polycrystalline particles is 12 μm. According to calculation, the mass of ZrB ₂ is 0.58% of the mass of LiNi _0.8 Co _0.1 Mn _0.1 O ₂ .

Example 7

This embodiment provides a method for preparing a coated positive electrode material LiNi _0.8 Co _0.1 Mn _0.1 O ₂ @MgB ₂ , comprising the following steps:

(1) Prepare raw materials, take 8 kg of high-nickel polycrystalline ternary positive electrode material LiNi _0.8 Co _0.1 Mn _0.1 O ₂ as the substrate material, take 80 mL of deionized water as the dispersant, and take 28.63 g of MgB ₂ as the coating agent.

(2) Pour the coating agent _MgB2 into water and stir thoroughly to form a coating suspension. Pour the coating suspension into the spray tank and continue to stir slightly. Prepare the spray system to ensure that its flow rate meets the requirements.

(4) Turn on the spray system and spray at a rate of 1 mL/s until all the coating liquid is sprayed. After turning off the spray system _, continue stirring for 3 _min to further ensure that _MgB2 is evenly coated on _the surface of _{LiNi0.8Co0.1Mn0.1O2} .

(6) After being taken out of the furnace, the product was passed through a 400-mesh sieve to obtain a coated positive electrode material LiNi _0.8 Co _0.1 Mn _0.1 O ₂ @MgB ₂ .

The average particle size of the primary single crystal particles in the coated positive electrode material of this embodiment is 320 nm, and the average particle size of the secondary polycrystalline particles is 10.5 μm. According to calculation, the mass of MgB ₂ is 0.36% of the mass of LiNi _0.8 Co _0.1 Mn _0.1 O ₂ .

Example 8

This embodiment provides a method for preparing a coated positive electrode material LiNi _0.6 Co _0.2 Mn _0.2 O ₂ @CoB. The following steps are involved:

(1) Prepare raw materials, take 8 kg of high-nickel polycrystalline ternary positive electrode material LiNi _0.6 Co _0.2 Mn _0.2 O ₂ as the substrate material, take 700 mL of deionized water as the dispersant, and take 160 g of CoB as the coating agent.

(3) Pour the substrate material LiNi _0.6 Co _0.2 Mn _0.2 O ₂ into the mixing equipment and start stirring. The stirring paddle linear speed is 10 m/s and the stirring time is 4 min to ensure that LiNi _0.6 Co _0.2 Mn _0.2 O ₂ is fully dispersed in the cavity of the mixing equipment.

(4) Turn on the spray system and spray at a rate of 30 mL/s until all the coating liquid is sprayed. After turning off the spray system, continue stirring for 3 min to further ensure that CoB is evenly coated on the surface of LiNi _0.6 Co _0.2 Mn _0.2 O ₂ .

(5) After completing the above steps, the material obtained in step (4) is loaded into a sagger and placed in a kiln for tempering for further modification. The tempering temperature is 600° C. and the tempering time is 10 h.

(6) After being taken out of the furnace, the product was passed through a 400-mesh sieve to prepare the coated positive electrode material LiNi _0.6 Co _0.2 Mn _0.2 O ₂ @CoB

The average particle size of the primary single crystal particles in the coated positive electrode material of this embodiment is 380 nm, and the average particle size of the secondary polycrystalline particles is 11.0 μm. After calculation, the mass of CoB is 2.0% of the mass of LiNi _0.6 Co _0.2 Mn _0.2 O ₂ .

Example 9

The only difference from Example 1 is that the mass of CoB is 5.5% of LiNi _0.8 Co _0.1 Mn _0.1 O ₂ , and the average particle size of the primary single crystal particles in the coated positive electrode material of this example is 330 nm, and the average particle size of the secondary polycrystalline particles is 9.8 μm.

Example 10

The only difference from Example 1 is that the tempering temperature is 800° C., the average particle size of the primary single crystal particles in the coated positive electrode material of this example is 340 nm, and the average particle size of the secondary polycrystalline particles is 10.5 μm.

Embodiment 11

The only difference from Example 1 is that the tempering time is 2 h. The average particle size of the primary single crystal particles in the coated positive electrode material of this example is 320 nm, and the average particle size of the secondary polycrystalline particles is 9.0 μm.

Example 12

The only difference from Example 1 is that the tempering time is 12 h, and the average particle size of the primary single crystal particles in the coated positive electrode material of this example is 340 nm, and the average particle size of the secondary polycrystalline particles is 9.5 μm.

Example 13

The only difference from Example 1 is that the spray system is turned on and spraying is performed at a speed of 55 mL/s. The average particle size of the primary single crystal particles in the coated positive electrode material of this example is 360 nm, and the average particle size of the secondary polycrystalline particles is 10 μm.

Comparative Example 1

The positive electrode material of this comparative example is an uncoated LiNi _0.8 Co _0.1 Mn _0.1 O ₂ (NCM811) positive electrode material, which is a polycrystalline positive electrode material.

(1) 1 kg of ternary precursor Ni _0.8 Co _0.1 Mn _0.1 (OH) ₂ and 0.46 kg of LiOH were weighed and mixed by ball milling to obtain a mixed material A;

(2) A mixture A was sintered in a sintering furnace at 750° C. for 12 h in an oxygen environment. After cooling, the sintered product was sieved with 400 mesh to prepare a positive electrode material B (LiNi _0.8 Co _0.1 Mn _0.1 O ₂ ).

Comparative Example 2

In this comparative example, CoB is coated on the surface of LiNi _0.8 Co _0.1 Mn _0.1 O ₂ by a liquid phase coating method, wherein the mass of the coating layer CoB is 0.68% of the mass of the positive electrode material LiNi _0.8 Co _0.1 Mn _0.1 O ₂ .

The preparation method of the positive electrode material in Comparative Example 2 comprises the following steps:

(1) Weigh 1 kg of ternary precursor Ni _0.8 Co _0.1 Mn _0.1 (OH) ₂ and 0.46 kg of LiOH and mix them by ball milling to obtain a mixed material A;

(2) sintering a mixture A at 750° C. for 12 h in an oxygen environment in a sintering furnace, and sieving the sintered product with 400 mesh after cooling to prepare a positive electrode material B (LiNi _0.8 Co _0.1 Mn _0.1 O ₂ );

(3) Weigh 500 g of the positive electrode material B, cobalt nitrate hexahydrate and sodium borohydride, dissolve the cobalt nitrate hexahydrate in 800 mL of ethanol under the protection of nitrogen, and stir well to obtain a suspension X; dissolve the sodium borohydride in 200 mL of ethanol under the protection of nitrogen, and stir well to obtain a solution Y;

(4) Solution Y was uniformly added to suspension X, and the mixture was stirred for 2 h under nitrogen protection. After stirring, the mixture was filtered and the obtained solid was washed twice with 100 mL of ethanol. The washed solid was vacuum dried at 120 °C for 6 h to prepare a liquid-coated ternary cathode material.

Comparative Example 3

In this comparative example, CoB is coated on the surface of LiNi _0.8 Co _0.1 Mn _0.1 O ₂ by a dry-mix coating method, wherein the mass of the coating layer CoB is 0.68% of the mass of the positive electrode material LiNi _0.8 Co _0.1 Mn _0.1 O ₂ .

The preparation method of the positive electrode material in Comparative Example 3 comprises the following steps:

(1) Prepare raw materials, take 8 kg of high-nickel polycrystalline ternary positive electrode material LiNi _0.8 Co _0.1 Mn _0.1 O ₂ as the substrate material, take 200 mL of deionized water as the dispersant, and take 54.49 g of CoB as the coating agent;

(2) Pour the high-nickel polycrystalline ternary cathode material and the coating agent into a mixing device, and start stirring, with the stirring paddle linear speed of 3 m/s and the stirring time of 1 min to ensure that the high-nickel polycrystalline ternary cathode material and the coating agent are fully dispersed in the cavity of the mixing device;

(3) After the stirring is completed, the material in step (2) is loaded into a sagger and placed in a kiln for tempering at a tempering temperature of 700°C for a holding time of 4 hours;

(4) After being taken out of the furnace, the product was passed through a 400-mesh sieve to prepare the positive electrode material in Comparative Example 3.

Comparative Example 4

The only difference from Example 1 is that the tempering step is not performed in this comparative example.

Comparative Example 5

The only difference from Example 1 is that the coating agent is replaced by boron oxide instead of CoN.

Comparative Example 6

The positive electrode material of this comparative example is an uncoated LiNi _0.6 Co _0.2 Mn _0.2 O ₂ (NCM622) positive electrode material, which is a polycrystalline positive electrode material.

(1) 1 kg of ternary precursor Ni _0.6 Co _0.2 Mn _0.2 (OH) ₂ and 0.46 kg of LiOH were weighed and mixed by ball milling to obtain a mixed material B;

(2) A mixture B was sintered in a sintering furnace at 880° C. for 12 h in an oxygen environment. After cooling, the sintered product was sieved with 400 mesh to prepare a positive electrode material B (LiNi ₀₆ Co _0.2 Mn _0.2 O ₂ ).

Figure 1 is the XPS spectrum of B 1s of the coated positive electrode materials in Examples 1-7 and the uncoated LiNi _0.8 Co _0.1 Mn _0.1 O ₂ positive electrode material in Comparative Example 1. It can be seen from the figure that the characteristic peak of B 1s is detected in the coated positive electrode materials in Examples 1-7, indicating that the surfaces of the coated positive electrode materials in Examples 1-7 are all coated with metal borides.

FIG2 is a SEM image of the positive electrode materials in Examples 1-7 (ag in FIG2 ) and Comparative Examples 1-3 (hj in FIG2 ). It can be seen from the figure that the primary single crystal particles of the positive electrode materials prepared by the method in the embodiment of the present application are released from the secondary polycrystalline particles, and the coating agent covers the surface of each released primary single crystal particle, and a protective layer is formed on the surface of the primary single crystal particles and the secondary polycrystalline particles, thereby avoiding the accelerated deterioration of battery performance due to the increase in the specific surface area of the positive electrode material, and also avoiding the contact between the positive electrode material and the electrolyte. However, the positive electrode materials in Comparative Examples 1-3 did not have the phenomenon of primary single crystal particles being released from the secondary polycrystalline particles.

Performance testing:

The powder compaction density of the positive electrode materials in Examples 1-13 and Comparative Examples 1-6 was tested using Sansi UTM7305. The results are shown in Table 1.

The positive electrode materials prepared in Examples 1-13 and Comparative Examples 1-6 were assembled into soft-pack batteries and their electrochemical performance was tested.

Assembly of soft pack batteries:

(1) Preparation of positive electrode sheet: Using N-methylpyrrolidone (NMP) as a solvent, the positive electrode materials prepared in Examples 1-13 and Comparative Examples 1-6, the binder polyvinylidene fluoride, and the conductive agent Supper P were mixed in NMP at a mass ratio of 92:4:4, and the slurry obtained after mixing evenly was coated on the positive electrode collector to prepare a electrode sheet;

(2) Electrolyte: The electrolyte was E20, purchased from Shenzhen Xinzhoubang Technology Co., Ltd.

(3) Negative electrode: The active material of the negative electrode is graphite, wherein graphite: Supper P: sodium carboxymethyl cellulose (CMC): styrene butadiene latex (SBR): NMP = 92:0.5:1.5:4:2.

Testing of soft pack batteries:

The 0.33C first-week formation capacity of the soft-pack batteries assembled with the positive electrode materials in Examples 1-7, Examples 9-13 and Comparative Examples 1-5 and the capacity retention rate after 200 cycles at a current density of 1C (voltage window of 2.8-4.25V) were tested at 45°C. The test results are shown in Table 1.

Table 1

The 0.33C first-week formation capacity of the soft-pack batteries assembled with the positive electrode materials in Example 8 and Comparative Example 6 and the capacity retention rate after 200 cycles at a current density of 1C (voltage window of 3.0-4.40V) were tested at 45°C. The test results are shown in Table 2.

Table 2

analyze:

It can be seen from the data of the embodiments and the comparative examples that the first-week formation capacity of the soft-pack battery assembled with the positive electrode material in the embodiments of the present application, the powder compaction density of the positive electrode material and the capacity retention rate of the soft-pack battery are higher than those of the soft-pack battery assembled with the positive electrode material in the comparative example, indicating that the positive electrode material modification method proposed in the embodiments of the present application can increase the compaction density of the positive electrode material, increase the capacity of the positive electrode material and improve the cycle performance of the positive electrode material.

It can be seen from the data of Example 1 and Examples 9-10 that when the content of the coating agent is high or the tempering temperature is high, the capacity and cycle performance of the positive electrode material will be affected to a certain extent.

It can be seen from the data of Example 1 and Examples 11-12 that a longer or shorter tempering time will affect the capacity and cycle performance of the positive electrode material.

It can be seen from the data of Example 1 and Example 13 that when the spray coating speed is fast, the capacity and cycle performance of the positive electrode material will be affected. This is mainly because when the spray coating speed is fast, it will affect the uniformity of the positive electrode material coating, thereby affecting the capacity and cycle performance of the positive electrode material.

Comparative Example 2 adopts a liquid phase synthesis method to achieve in-situ coating on the surface of the positive electrode material. From the data in the table, it can be seen that the positive electrode material in Comparative Example 2 is better than the positive electrode material in Comparative Example 1 in pressure There are improvements in actual density and cycle performance, but the compaction density of the positive electrode material in Comparative Example 2 is not as good as that of the positive electrode material prepared in Example 1 of the present application. At the same time, the raw materials and methods used in Comparative Example 2 are difficult to scale up. This is because the in-situ coating method in Comparative Example 2 not only requires an inert atmosphere environment, but also requires high-cost and flammable ethanol as a solvent to participate in the reaction, which greatly increases the cost of production and the difficulty of production scale-up. The process involved in the example of the present application can be completed by simple modification on the basis of the existing production line.

It can be seen from the data of Example 1 and Comparative Example 3 that the capacity retention rate of the positive electrode material in Comparative Example 3 after 200 cycles is significantly lower than that of the positive electrode material in Example 1, and the compaction density of the positive electrode material in Comparative Example 3 is also lower than that of the positive electrode material in Example 1. Therefore, the volume energy density of the positive electrode material in Comparative Example 3 will be lower.

It can be seen from the data of Example 1 and Comparative Example 4 that the tempering step in the embodiment of the present application has a great influence on the performance of the positive electrode material. If tempering is not performed, it will not only affect the capacity and cycle performance of the positive electrode material, but also reduce the powder compaction density of the positive electrode material.

It can be seen from the data of Example 1 and Comparative Example 5 that if the coating agent is replaced by boron oxide from metal boride, the capacity and cycle performance of the positive electrode material cannot be improved, and the powder compaction density of the positive electrode material cannot be increased.

It can be seen from the data of Example 8 and Comparative Example 6 that if the NMC811 positive electrode material is replaced with the NCM622 series positive electrode material, the same effect of improving the cycle performance and compaction density of the positive electrode material can be obtained, indicating that the positive electrode material modification method involved in the present application is suitable for polycrystalline ternary positive electrode materials of various proportions.

Figure 3 shows the cycle performance of the soft-pack battery assembled with the positive electrode materials in Examples 1-7 of the present application and Comparative Examples 1-3 at 45°C and a current density of 1C. It can be seen from the figure that the positive electrode materials in Examples 1-7 of the present application have a higher capacity retention rate. This is because the primary single crystal particles in the positive electrode materials prepared in the examples of the present application are released from the secondary polycrystalline particles, and the surfaces of the released primary single crystal particles and the grain boundaries of the secondary polycrystalline particles are coated with a coating agent, rather than just coating the surfaces of the secondary polycrystalline particles. This comprehensive coating is beneficial to improving the performance of the positive electrode material. If only the surface of the secondary polycrystalline particles is coated, as the cycle proceeds, the uncoated parts of the secondary polycrystalline particles will contact the electrolyte and undergo side reactions, thereby causing the battery cycle performance to deteriorate. At the same time, since the released primary single crystal particles are very small, they can be coated on the surface of the secondary polycrystalline particles. This structure can be regarded as forming another coating on the surface of the secondary polycrystalline particles, which can prevent more electrolyte from entering the interior of the positive electrode material. Therefore, it also slows down the performance deterioration of the positive electrode material during the cycle and improves the cycle performance of the positive electrode material.

The applicant declares that the present application uses the above-mentioned embodiments to illustrate the detailed methods of the present application, but the present application is not limited to the above-mentioned detailed methods, that is, it does not mean that the present application must rely on the above-mentioned detailed methods to be implemented. The technicians in the relevant technical field should understand that any improvement to the present application, the equivalent replacement of the raw materials of the product of the present application, the addition of auxiliary components, the selection of specific methods, etc., all fall within the scope of protection and disclosure of the present application.

Claims

A method for preparing a coated positive electrode material comprises the following steps:

(1) coating the coating agent onto the surface of the polycrystalline positive electrode material by a spray coating method;

(2) The polycrystalline positive electrode material obtained in step (1) is tempered to obtain the coated positive electrode material.
The method of claim 1, wherein the capping agent comprises a metal boride.
The method according to claim 2, wherein the metal boride comprises at least one of Co a B, ZrB 2 and MgB 2 , wherein 3 ≥ a ≥ 1.
The method according to any one of claims 1 to 3, wherein the polycrystalline positive electrode material is a polycrystalline ternary positive electrode material.
The method according to claim 4, wherein the composition of the polycrystalline ternary cathode material comprises Li(Ni x Co y Mn 1-xy )O 2 , wherein 0＜x＜1, 0＜y＜1;

Preferably, 0.6≤x<1, 0.1<y<0.3.
The method according to any one of claims 1 to 5, wherein the mass ratio of the polycrystalline positive electrode material to the coating agent is 1:(0.0003-0.05), preferably 1:(0.0003-0.02).
The method according to any one of claims 1 to 4, wherein the spray coating method in step (1) comprises:

(a) mixing a coating agent and a dispersant to form a suspension;

(b) spraying the polycrystalline positive electrode material with the suspension described in step (a).
The method of claim 7, wherein the dispersant comprises at least one of water or a hydroalcoholic solution;

Preferably, the spraying speed is 0.2-50 mL/s.
The method according to claim 7 or 8, wherein in step (b), the polycrystalline positive electrode material is sprayed under stirring;

Preferably, the linear speed of the stirring is 1-15 m/s;

Preferably, the stirring time is 0.5-min.
The method according to any one of claims 7 to 9, wherein the polycrystalline positive electrode material is stirred for 3 to 5 minutes after spraying is completed.
The method according to any one of claims 1 to 10, wherein the tempering temperature in step (2) is 300-700° C.;

Preferably, the tempering time in step (2) is 3-10 hours;

Preferably, the coated positive electrode material is screened after the tempering step.
A coated positive electrode material prepared by the method described in any one of claims 1 to 11, wherein the coated positive electrode material comprises primary single crystal particles and secondary polycrystalline particles, wherein the surface of the primary single crystal particles, the surface of the secondary polycrystalline particles and the grain boundaries of the secondary polycrystalline particles are all coated with a coating layer.
The coated positive electrode material according to claim 12, wherein the average particle size of the primary single crystal particles is 100-500nm.
The coated positive electrode material according to claim 12 or 13, wherein the average particle size of the secondary polycrystalline particles is 7-12 μm.
A lithium-ion battery, wherein the positive electrode of the lithium-ion battery comprises the coated positive electrode material according to any one of claims 12 to 14.