A coated cathode material, a preparation method thereof, and a lithium-ion battery

Abstract

The present invention discloses a coated cathode material, a preparation method thereof, and a lithium-ion battery. The method includes the following steps: (1) coating a coating agent on the surface of a polycrystalline cathode material by means of spray coating; (2) preparing the coated cathode material after tempering the polycrystalline cathode material obtained in step (1). The coated cathode material prepared by the present invention has a relatively high tap density, thereby improving the volumetric energy density of the battery. At the same time, the coating agent is coated on the surface of primary single crystal particles of the polycrystalline cathode material, the surface of secondary polycrystalline particles, and the grain boundaries of secondary polycrystalline particles, effectively avoiding the contact between the cathode material and the electrolyte and improving the cycle performance of the cathode material.

Description

Technical Field

[0001] The present invention relates to the technical field of cathode materials, and relates to a coated cathode material, a preparation method thereof, and a lithium-ion battery. Background Art

[0002] The lithium battery industry has been seeking higher-capacity, more stable, and safer battery cathode materials. High-nickel ternary materials have been a hot topic in the industry due to their high capacity. Although there are already 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, are more sensitive to the environment, and have poor safety.

[0003] Compared with single-crystal materials, high-nickel polycrystalline materials are more likely 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 using the coating method for modification, the internal particles cannot contact the coating agent, resulting in the coating agent playing a greater role in the early stage of battery cycling. However, in the later stage of battery cycling, the electrolyte infiltrates into the part of the cathode material sphere without the coating agent, which will cause the cycle performance of the battery to deteriorate rapidly. The existing methods mainly improve by 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 cathode material, resulting in a significant decrease in the electrochemical performance of the battery.

[0004] For example, CN114975985 A discloses a Ti-Cr co-doped high-voltage spinel cathode material and a preparation method thereof. The preparation method includes 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 cathode material. For example, CN111106343 A discloses a lanthanum and fluorine co-doped high-nickel ternary cathode material, a preparation method thereof, and an application thereof. The preparation method includes the following steps: preparing a solution of a nickel source, a cobalt source, and a manganese source, adding a precipitant to obtain a precipitate. Then, uniformly mixing a lanthanum source, a fluorine source, and the precursor in ethanol and evaporating the solvent. The treated precursor is mixed with a lithium salt, and a lanthanum and fluorine co-doped high-nickel ternary material is synthesized through pre-sintering and sintering. For example, CN111072074 A discloses a preparation method of an indium-doped lithium nickel cobalt manganate material. Weigh the raw materials according to the stoichiometric ratio, prepare a microemulsion, add the raw materials to deionized water, stir evenly, then add them to the microemulsion, disperse ultrasonically, freeze-dry the solution, and sinter the treated raw materials to obtain an indium-doped lithium nickel cobalt manganate cathode material.

[0005] When the cathode material is modified by the above doping method, there is a disadvantage of uneven distribution of the doped substance, and it is impossible to ensure that the dopant is evenly distributed inside the cathode material, thus affecting the electrochemical performance of the battery. Therefore, it is necessary to develop a cathode material with high capacity and excellent rate performance. Summary of the Invention

[0006] In view of the above problems existing in the prior art, the present invention provides a coated cathode material, a preparation method thereof and a lithium-ion battery. The preparation method of the coated cathode material includes the following steps: (1) coating a coating agent on the surface of a polycrystalline cathode material by a spray coating method; (2) preparing the coated cathode material after tempering the polycrystalline cathode material obtained in step (1).

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a preparation method of a coated cathode material, the method including the following steps:

[0009] (1) Coating a coating agent on the surface of a polycrystalline cathode material by a spray coating method;

[0010] (2) Preparing the coated cathode material after tempering the polycrystalline cathode material obtained in step (1).

[0011] In the present invention, the coating agent is evenly coated on the surface of the polycrystalline cathode material by utilizing the uniformity advantage of spray coating, and the coating agent can also enter the internal grain boundaries of the polycrystalline cathode material. During the tempering process, the coating agent reacts with the residual lithium and the cathode material at the grain boundaries of the polycrystalline cathode material, enabling the co-modification of coating and doping of the cathode material; in addition, the reaction of the coating agent with the residual lithium and the cathode material at the grain boundaries of the polycrystalline cathode material can depolymerize the primary single crystal particles in the polycrystalline cathode material, and the coating agent is also coated on the surface of the primary single crystal particles, further improving the cycle performance of the prepared cathode material. And compared with the traditional method of separating particles by mechanical dissociation, the method of separating particles in the present invention is more accurate and effective, and there is no damage to the material, ensuring that the defects inside the material will not increase.

[0012] The preparation method of the present invention is relatively simple and has a low cost. The process involved in the present invention only needs to be simply modified on the basis of the existing production line, which is conducive to large-scale production.

[0013] In the present invention, the prepared coated cathode material has a hierarchical morphology of primary single-crystal particles and secondary polycrystalline particles, which greatly improves the tap density of the cathode material, enables a higher volumetric energy density, and the extraction of primary single-crystal particles also increases the capacity of the cathode material; in addition, the coating agent can be more uniformly coated on the surfaces of primary single-crystal particles, secondary polycrystalline particles, and grain boundaries of secondary polycrystalline particles, fully avoiding the contact between the cathode material and the electrolyte and improving the cycling performance of the cathode material.

[0014] In the present invention, the extraction amount of primary single-crystal particles can be controlled. By adjusting the content of the coating agent, the tempering temperature, and the tempering time, the degree of reaction at the grain boundaries of the polycrystalline cathode material can be controlled; by adjusting parameters such as the stirring speed and spraying speed during the spray coating process, the uniformity of the coating agent coating can be controlled, which affects the contact area between the coating agent and the cathode material and the number of reactive active sites, thereby affecting the degree of reaction at the grain boundaries of the polycrystalline cathode material. The extraction amount of primary single-crystal particles is controlled by adjusting the above parameters.

[0015] Preferably, the coating agent includes metal boride.

[0016] Preferably, the metal boride includes Co a B, ZrB2, and at least one of MgB2, where 3≥a≥1. For example, a can be 1, 1.5, 2, 2.5, or 3.

[0017] Preferably, the polycrystalline cathode material is a polycrystalline ternary cathode material.

[0018] Preferably, the composition of the polycrystalline ternary cathode material includes Li(Ni x Co y Mn 1-x-y )O2, where 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.

[0019] Preferably, 0.6≤x<1, 0.1<y<0.3.

[0020] Preferably, the mass ratio of the polycrystalline cathode material to the coating agent is 1:(0.0003 - 0.05). "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, and preferably 1:(0.0003 - 0.02).

[0021] In the present invention, if the content of the coating agent is relatively large, the thickness of the coating layer will be relatively thick, and a relatively large amount of metal boride will be doped on the surface of the polycrystalline cathode material, resulting in a decrease in the activity on the surface of the polycrystalline cathode material. Moreover, if there is too much boron element, Li-B-Me-O compounds (Me is Ni, Co or Mn) will be formed in the cathode material. The excessive amount of such compounds will lead to a decrease in the capacity and cycling performance of the cathode material; if the content of the coating agent is relatively small, it will not be possible to form a morphology in which primary single crystal particles and secondary polycrystalline particles are mixed in the cathode material, and it will lead to a relatively small thickness of the coating layer and a relatively small doping amount, all of which will affect the electrochemical performance of the cathode material.

[0022] Preferably, the spray coating method in step (1) includes:

[0023] (a) Mix the coating agent and the dispersant to form a suspension;

[0024] (b) Spray the polycrystalline cathode material with the suspension obtained in step (a).

[0025] Preferably, the dispersant includes at least one of water or an aqueous alcohol solution.

[0026] Preferably, the spraying speed is 0.2 - 50 mL / s, such as 0.5 mL / s, 1 mL / s, 1.5 mL / s, 2 mL / s, 5 mL / s, 10 mL / s, 15 mL / s, 20 mL / s, 25 mL / s, 30 mL / s, 35 mL / s, 40 mL / s, 45 mL / s or 50 mL / s.

[0027] In the present invention, if the spraying speed is relatively small, it will prolong the preparation time of the coated cathode material, resulting in resource loss and being unfavorable for actual production work. If the spraying speed is relatively large, the phenomenon of uneven coating of the coating agent will occur, and agglomeration of the coating agent will occur in the prepared coated cathode material, thus affecting the electrochemical performance of the coated cathode material.

[0028] In an embodiment of the present invention, the coating agent in step (a) accounts for 0.3% - 10% of the mass of the dispersant.

[0029] Preferably, the step of spraying the polycrystalline cathode material in step (b) is carried out under stirring conditions.

[0030] Preferably, the linear velocity of the stirring is 1 - 15 m / s, such as 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.

[0031] Preferably, the stirring time is 0.5 - 5 min, such as 1 min, 2 min, 3 min, 4 min or 5 min.

[0032] Preferably, after the spraying of the polycrystalline cathode material is completed, stirring is continued for 3 - 5 min, such as 3 min, 4 min or 5 min.

[0033] The purpose of continuous stirring is to ensure that the coating agent can be uniformly coated on the surface of the polycrystalline cathode material.

[0034] Preferably, the tempering temperature in step (2) is 300 - 700 °C, such as 300 °C, 400 °C, 500 °C, 600 °C or 700 °C.

[0035] Preferably, the tempering time in step (2) is 3 - 10 h, such as 3 h, 5 h, 7 h or 9 h.

[0036] A higher tempering temperature or a longer tempering time will cause all the coating agents to enter the grain boundaries of the polycrystalline cathode material, resulting in the disappearance of the coating layer on the surface of the polycrystalline cathode material, leading to the deterioration of the cycling performance of the cathode material. At the same time, a higher temperature will also have a certain impact on the cathode material itself. Especially in high-nickel materials, high-temperature tempering will exacerbate lithium-nickel mixing, resulting in the deterioration of the crystal structure of the cathode material; a lower tempering temperature or a shorter tempering time cannot fully exert the role of the coating agent, and the number of single-crystal particles cannot meet the requirements, and the volume density of the material increases less. At the same time, a lower tempering temperature or a shorter tempering time will also cause the coating agent not to react sufficiently with the cathode material or residual lithium, resulting in a decrease in the bonding force between the coating agent and the cathode material, and the required reaction products are not sufficient to be doped on the surface of the cathode material, so the stability of the cathode material cannot be significantly improved.

[0037] Preferably, after the tempering step, the coated cathode material is sieved.

[0038] Exemplarily, the mesh number of sieving includes but is not limited to 400 mesh.

[0039] Taking the ternary cathode material Li(Ni x Co y Mn 1-x-y )O2 as an example, where 0 < x < 1, 0 < y < 1, an exemplary preparation method of the coated cathode material of the present invention includes the following steps:

[0040] (1) Mix the coating agent and deionized water so that the coating agent is uniformly dispersed in the deionized water to form a coating suspension. Pour the coating suspension into the spray liquid tank and continuously stir gently to prevent sedimentation to obtain a coating liquid;

[0041] (2) Pour Li(Nix Co y Mn 1-x-y )O₂ is poured into the mixing equipment, and stirring is started. The linear velocity of stirring is 1 - 15 m / s, and the stirring time is 0.5 - 5 min to ensure that Li(Ni x Co y Mn 1-x-y )O₂ is fully dispersed in the cavity of the mixing equipment;

[0042] (3) The spray system is started, and the spray speed of the coating liquid is controlled to be 0.2 - 50 mL / s until all the coating liquid is sprayed out;

[0043] (4) After the spray system is turned off, stirring is continued for 3 - 5 min to ensure that the coating agent can be uniformly coated on the surface of the polycrystalline cathode material;

[0044] (5) The cathode material obtained in step (4) is loaded into a crucible and put into a kiln for tempering for further modification. The tempering temperature is 300 - 700 °C, and the tempering time is 3 - 10 h;

[0045] (6) After the cathode material in step (5) is taken out of the furnace, it is sieved to prepare the coated cathode material.

[0046] In the second aspect, the present invention provides a coated cathode material prepared by the method described in the first aspect of the present invention. The coated cathode material includes primary single-crystal particles and secondary polycrystalline particles. Among them, the surfaces of the primary single-crystal particles, the surfaces of the secondary polycrystalline particles, and the grain boundaries of the secondary polycrystalline particles are all coated with a coating layer.

[0047] In the coated cathode material of the present invention, the morphology of the mixed combination of primary single-crystal particles and secondary polycrystalline particles greatly improves the tap density of the cathode material, thereby increasing the volumetric energy density of the battery; in addition, the coating layer of the coated cathode material in the present invention is not only limited to the surface of the secondary polycrystalline particles, but also the surfaces of the primary single-crystal particles, the surfaces of the secondary polycrystalline particles, and the grain boundaries of the secondary polycrystalline particles are all coated with a coating layer, which fully avoids the direct contact between the electrolyte and the cathode material in the later stage of battery cycling, thereby improving the cycling performance of the cathode material.

[0048] In the present invention, both the primary single-crystal particles and the secondary polycrystalline particles are polycrystalline cathode materials. The primary single-crystal particles refer to primary particles with a single-crystal morphology, and the secondary polycrystalline particles refer to secondary particles with a polycrystalline morphology. The secondary polycrystalline particles are composed of primary single-crystal particles, and the primary single-crystal particles can be obtained by depolymerizing the secondary polycrystalline particles in the polycrystalline cathode material.

[0049] Preferably, the average particle size of the primary single-crystal particles is 100-500 nm, such as 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm or 500 nm.

[0050] Preferably, the average particle size of the secondary polycrystalline particles is 7-12 μm, such as 7 μm, 8 μm, 9 μm, 10 μm, 11 μm or 12 μm.

[0051] In a third aspect, a lithium-ion battery is provided, and the positive electrode of the lithium-ion battery includes the coated positive electrode material described in the second aspect of the present invention.

[0052] The lithium-ion battery assembled using the coated positive electrode material described in the second aspect of the present invention has a higher capacity and better cycle performance.

[0053] Compared with the prior art, the present invention has the following beneficial effects:

[0054] (1) By the method of spray coating, the present invention can uniformly coat the coating agent on the surface of the polycrystalline positive electrode material, and the coating agent can penetrate into the grain boundaries of the polycrystalline positive electrode material. During the tempering process, a redox reaction occurs at the grain boundaries of the polycrystalline positive electrode material. On the one hand, it can achieve dual modification of doping and coating of the positive electrode material, and on the other hand, it can dissociate the primary single-crystal particles in the polycrystalline positive electrode material 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 invention is more precise and effective, and does not damage the material, ensuring that the internal defects of the material will not increase.

[0055] (2) The preparation method of the present invention is relatively simple and has a low cost. The process involved in the present invention only needs to be simply modified on the basis of the existing production line, which is conducive to large-scale implementation.

[0056] (3) The coated positive electrode material prepared by the present invention has a morphology in which primary single-crystal particles and secondary polycrystalline particles are mixed and matched. This morphology greatly improves the tap density of the positive electrode material, thereby increasing the volumetric energy density of the battery. In addition, due to the extraction of the primary single-crystal particles, the capacity of the positive electrode material is increased. Moreover, the surfaces of the primary single-crystal particles, the surfaces of the secondary polycrystalline particles, and the grain boundaries of the secondary polycrystalline particles of the coated positive electrode material prepared by the present invention are all coated with a coating agent, so that the contact between the positive electrode material and the electrolyte can be effectively avoided during the cycling process of the battery, improving the cycle performance of the positive electrode material. Description of the Drawings

[0057] Figure 1 For the coated positive electrode materials in Examples 1-7 and the uncoated LiNi in Comparative Example 1 0.8 Co0.1 Mn 0.1 X-ray photoelectron spectroscopy (XPS) spectrum of B1s of the MnO₂ cathode material;

[0058] Figure 2 Scanning electron microscope (SEM) images of the cathode materials in Examples 1-7 and Comparative Examples 1-3;

[0059] Figure 3 Cycling performance graphs of the soft-pack batteries assembled with the cathode materials in Examples 1-7 and Comparative Examples 1-3 at a current density of 45 °C and 1C. Detailed implementation manners

[0060] The technical solutions of the present invention will be further described below through specific implementation manners. Those skilled in the art should understand that the described embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention.

[0061] Example 1

[0062] This example provides a preparation method of a coated cathode material LiNi 0.8 Co 0.1 Mn 0.1 O₂@CoB, including the following steps:

[0063] (1) Prepare raw materials. Take 8 kg of high-nickel polycrystalline ternary cathode material LiNi 0.8 Co 0.1 Mn 0.1 O₂ as the base material, take 200 mL of deionized water as the dispersant, and take 54.49 g of CoB as the coating agent.

[0064] (2) Pour the coating agent CoB into water and stir well to form a coating suspension. Pour the coating suspension into the spray liquid tank and continuously stir gently, and prepare the spray system to ensure that its flow rate meets the requirements.

[0065] (3) Pour the base material LiNi 0.8 Co 0.1 Mn 0.1 O₂ into the mixing equipment and start stirring. The linear velocity of stirring is 3 m / s, and the stirring time is 1 min to ensure that LiNi 0.8 Co 0.1 Mn 0.1 O₂ is fully dispersed in the cavity of the mixing equipment.

[0066] (4) Start the spray system and spray at a speed of 5 mL / s until all the coating liquid is sprayed out. After closing the spray system, continue to stir for 3 min to further ensure that CoB is evenly coated on LiNi 0.8 Co 0.1Mn 0.1 The surface of O2.

[0067] (5) After completing the above steps, load the material obtained in step (4) into a sagger and put it into a kiln for tempering to further modify it. The tempering temperature is 700 °C and the tempering time is 4 h.

[0068] (6) After taking out of the furnace, sieve through a 400-mesh sieve to prepare the coated cathode material LiNi 0.8 Co 0.1 Mn 0.1 O2@CoB.

[0069] In the coated cathode material of this example, the average particle size of the primary single-crystal particles is 310 nm, and the average particle size of the secondary polycrystalline particles is 9.2 μm. After calculation, the mass of CoB is 0.68% of the mass of LiNi 0.8 Co 0.1 Mn 0.1 O2.

[0070] Example 2

[0071] This example provides a preparation method of a coated cathode material LiNi 0.8 Co 0.1 Mn 0.1 O2@CoB, including the following steps:

[0072] (1) Prepare raw materials. Take 8 kg of high-nickel polycrystalline ternary cathode material LiNi 0.8 Co 0.1 Mn 0.1 O2 as the base material, take 200 mL of deionized water as the dispersant, and take 54.49 g of CoB as the coating agent.

[0073] (2) Pour the coating agent CoB into water and stir well to form a coating suspension. Pour the coating suspension into a spray liquid tank and continuously stir slightly, and prepare a spray system to ensure that its flow rate meets the requirements.

[0074] (3) Pour the base material LiNi 0.8 Co 0.1 Mn 0.1 O2 into a mixing device, and start stirring. The linear velocity of stirring is 2 m / s, and the stirring time is 1 min to ensure that LiNi 0.8 Co 0.1 Mn 0.1 O2 is fully dispersed in the cavity of the mixing device.

[0075] (4) Turn on the spray system and spray at a rate of 0.5 mL / s until all the coating liquid is sprayed out. 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 O2.

[0076] (5) After completing the above steps, load the material obtained in step (4) into a crucible and put it into a kiln for tempering for further modification. The tempering temperature is 450 °C and the tempering time is 6 h.

[0077] (6) After taking out of the furnace, sieve through a 400-mesh sieve to prepare the coated cathode material LiNi 0.8 Co 0.1 Mn 0.1 O2@CoB.

[0078] In the coated cathode material of this example, the average particle size of the primary single-crystal particles 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 O2.

[0079] Example 3

[0080] This example provides a preparation method of a coated cathode material LiNi 0.8 Co 0.1 Mn 0.1 O2@CoB, including the following steps:

[0081] (1) Prepare raw materials. Take 8 kg of high-nickel polycrystalline ternary cathode material LiNi 0.8 Co 0.1 Mn 0.1 O2 as the base material, take 40 mL of deionized water as the dispersant, and take 6.81 g of CoB as the coating agent.

[0082] (2) Pour the coating agent CoB into water and stir well to form a coating suspension. Pour the coating suspension into the spray liquid tank and keep stirring slightly, and prepare the spray system to ensure that its flow rate meets the requirements.

[0083] (3) Pour the base material LiNi 0.8 Co 0.1 Mn 0.1 O2 into the mixing equipment, turn on the stirring, and the linear velocity of stirring is 8 m / s, and the stirring time is 1 min to ensure that LiNi 0.8 Co 0.1 Mn 0.1O2 is fully dispersed in the cavity of the mixing equipment.

[0084] (4) Turn on the spray system and spray at a speed of 0.2 mL / s until all the coating liquid is sprayed out. 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 O2.

[0085] (5) After completing the above steps, load the material obtained in step (4) into a sagger and put it into a kiln for tempering for further modification. The tempering temperature is 300 °C and the tempering time is 8 h.

[0086] (6) After taking out of the furnace, screen through a 400-mesh sieve to prepare the coated cathode material LiNi 0.8 Co 0.1 Mn 0.1 O2@CoB.

[0087] In the coated cathode material of this example, the average particle size of the primary single-crystal particles is 320 nm, and the average particle size of the secondary polycrystalline particles is 10 μm. After calculation, the mass of CoB is 0.085% of the mass of LiNi 0.8 Co 0.1 Mn 0.1 O2.

[0088] Example 4

[0089] This example provides a preparation method of a coated cathode material LiNi 0.8 Co 0.1 Mn 0.1 O2@CoB, including the following steps:

[0090] (1) Prepare raw materials. Take 8 kg of high-nickel polycrystalline ternary cathode material LiNi 0.8 Co 0.1 Mn 0.1 O2 as the base material, take 360 mL of deionized water as the dispersant, and take 102.16 g of CoB as the coating agent.

[0091] (2) Pour the coating agent CoB into water and stir well to form a coating suspension. Pour the coating suspension into the spray liquid tank and keep stirring slightly, and prepare the spray system to ensure that its flow rate meets the requirements.

[0092] (3) Pour the base material LiNi 0.8 Co 0.1 Mn 0.1 O2 into the mixing equipment, and turn on the stirring. The linear velocity of the stirring paddle is 5 m / s, and the stirring time is 1 min to ensure LiNi0.8 Co 0.1 Mn 0.1 O2 is fully dispersed in the cavity of the mixing equipment.

[0093] (4) Turn on the spray system and spray at a rate of 5 mL / s until all the coating liquid is sprayed out. 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 on the surface of O2.

[0094] (5) After completing the above steps, load the material obtained in step (4) into a crucible and put it into a kiln for tempering for further modification. The tempering temperature is 500 °C and the tempering time is 5 h.

[0095] (6) After taking out of the furnace, sieve through a 400-mesh sieve to prepare the coated cathode material LiNi 0.8 Co 0.1 Mn 0.1 O2@CoB.

[0096] In the coated cathode material of this example, the average particle size of the primary single-crystal particles is 320 nm, and the average particle size of the secondary polycrystalline particles is 9.0 μm. After calculation, the mass of CoB is 1.28% of the mass of LiNi 0.8 Co 0.1 Mn 0.1 O2.

[0097] Example 5

[0098] This example provides a preparation method of a coated cathode material LiNi 0.8 Co 0.1 Mn 0.1 O2@Co2B, including the following steps:

[0099] (1) Prepare raw materials. Take 8 kg of high-nickel polycrystalline ternary cathode material LiNi 0.8 Co 0.1 Mn 0.1 O2 as the base material, take 240 mL of deionized water as the dispersant, and take 92.71 g of Co2B as the coating agent.

[0100] (2) Pour the coating agent Co2B into water and stir well to form a coating suspension. Pour the coating suspension into the spray liquid tank and continuously stir gently, and prepare the spray system to ensure that its flow rate meets the requirements.

[0101] (3) Put the base material LiNi 0.8 Co 0.1 Mn 0.1Pour O2 into the mixing equipment and start stirring. The linear velocity of stirring is 5 m / s, and the stirring time is 1 min to ensure that LiNi 0.8 Co 0.1 Mn 0.1 O2 is fully dispersed in the cavity of the mixing equipment.

[0102] (4) Turn on the spray system and spray at a rate of 3 mL / s until all the coating liquid is sprayed out. After turning off the spray system, continue stirring for 3 min to further ensure that Co2B is evenly coated on the surface of LiNi 0.8 Co 0.1 Mn 0.1 O2.

[0103] (5) After completing the above steps, load the material obtained in step (4) into a sagger and put it into a kiln for tempering for further modification. The tempering temperature is 500 °C and the tempering time is 5 h.

[0104] (6) After taking out of the furnace, pass through a 400-mesh sieve to prepare the coated cathode material LiNi 0.8 Co 0.1 Mn 0.1 O2@Co2B.

[0105] In the coated cathode material of this example, the average particle size of primary single-crystal particles is 350 nm, and the average particle size of secondary polycrystalline particles is 9.0 μm. After calculation, the mass of Co2B is 1.16% of the mass of LiNi 0.8 Co 0.1 Mn 0.1 O2.

[0106] Example 6

[0107] This example provides a preparation method of a coated cathode material LiNi 0.8 Co 0.1 Mn 0.1 O2@ZrB2, including the following steps:

[0108] (1) Prepare raw materials. Take 8 kg of high-nickel polycrystalline ternary cathode material LiNi 0.8 Co 0.1 Mn 0.1 O2 as the base material, take 160 mL of deionized water as the dispersant, and take 46.05 g of ZrB2 as the coating agent.

[0109] (2) Pour the coating agent ZrB2 into water and stir well to form a coating suspension. Pour the coating suspension into the spray liquid tank and continuously stir slightly, and prepare the spray system to ensure that its flow rate meets the requirements.

[0110] (3) Pour the base material LiNi0.8 Co 0.1 Mn 0.1 Pour O2 into the mixing equipment and start stirring. The linear velocity of stirring is 5 m / s and the stirring time is 1 min to ensure that LiNi 0.8 Co 0.1 Mn 0.1 O2 is fully dispersed in the cavity of the mixing equipment.

[0111] (4) Turn on the spray system and spray at a rate of 2 mL / s until all the coating liquid is sprayed out. After turning off the spray system, continue stirring for 3 min to further ensure that ZrB2 is evenly coated on the surface of LiNi 0.8 Co 0.1 Mn 0.1 O2.

[0112] (5) After completing the above steps, load the material obtained in step (4) into a crucible and put it into a kiln for tempering for further modification. The tempering temperature is 500 °C and the tempering time is 5 h.

[0113] (6) After taking out of the furnace, sieve through a 400-mesh sieve to prepare the coated cathode material LiNi 0.8 Co 0.1 Mn 0.1 O2@ZrB2.

[0114] In the coated cathode material of this example, the average particle size of primary single-crystal particles is 370 nm, and the average particle size of secondary polycrystalline particles is 12 μm. After calculation, the mass of ZrB2 is 0.58% of the mass of LiNi 0.8 Co 0.1 Mn 0.1 O2.

[0115] Example 7

[0116] This example provides a preparation method of a coated cathode material LiNi 0.8 Co 0.1 Mn 0.1 O2@MgB2, including the following steps:

[0117] (1) Prepare raw materials. Take 8 kg of high-nickel polycrystalline ternary cathode material LiNi 0.8 Co 0.1 Mn 0.1 O2 as the base material, take 80 mL of deionized water as the dispersant, and take 28.63 g of MgB2 as the coating agent.

[0118] (2) Pour the coating agent MgB2 into water and stir well to form a coating suspension. Pour the coating suspension into the spray liquid tank and continuously stir slightly, and prepare the spray system to ensure that its flow rate meets the requirements.

[0119] (3) Pour the base material LiNi 0.8 Co 0.1 Mn 0.1 O2 into the mixing equipment, turn on the stirring, the linear velocity of the stirring is 5 m / s, and the stirring time is 1 min to ensure that LiNi 0.8 Co 0.1 Mn 0.1 O2 is fully dispersed in the cavity of the mixing equipment.

[0120] (4) Turn on the spray system and spray at a speed of 1 mL / s until all the coating liquid is sprayed out. After turning off the spray system, continue stirring for 3 min to further ensure that MgB2 is evenly coated on the surface of LiNi 0.8 Co 0.1 Mn 0.1 O2.

[0121] (5) After completing the above steps, load the material obtained in step (4) into a crucible and put it into a kiln for tempering for further modification. The tempering temperature is 500 °C and the tempering time is 5 h.

[0122] (6) After taking out of the furnace, sieve through a 400-mesh sieve to prepare the coated cathode material LiNi 0.8 Co 0.1 Mn 0.1 O2@MgB2.

[0123] In the coated cathode material of this example, the average particle size of the primary single-crystal particles is 320 nm, and the average particle size of the secondary polycrystalline particles is 10.5 μm. After calculation, the mass of MgB2 is 0.36% of the mass of LiNi 0.8 Co 0.1 Mn 0.1 O2.

[0124] Example 8

[0125] This example provides a preparation method of a coated cathode material LiNi 0.6 Co 0.2 Mn 0.2 O2@CoB, including the following steps:

[0126] (1) Prepare raw materials. Take 8 kg of high-nickel polycrystalline ternary cathode material LiNi 0.6 Co 0.2 Mn 0.2 O2 as the base material, take 700 mL of deionized water as the dispersant, and take 160 g of CoB as the coating agent.

[0127] (2) Pour the coating agent CoB into water and stir well to form a coating suspension. Pour the coating suspension into the spray liquid tank and continuously stir gently, and prepare the spray system to ensure that its flow rate meets the requirements.

[0128] (3) Pour the substrate material LiNi 0.6 Co 0.2 Mn 0.2 O2 into the mixing equipment, start stirring, the linear velocity of the stirring paddle is 10 m / s, and the stirring time is 4 min to ensure that LiNi 0.6 Co 0.2 Mn 0.2 O2 is fully dispersed in the cavity of the mixing equipment.

[0129] (4) Start the spray system and spray at a speed of 30 mL / s until all the coating liquid is sprayed out. 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 O2.

[0130] (5) After completing the above steps, load the material obtained in step (4) into the crucible and put it into the kiln for tempering for further modification. The tempering temperature is 600 °C and the tempering time is 10 h.

[0131] (6) After taking out of the furnace, sieve through a 400-mesh sieve to prepare the coated cathode material LiNi 0.6 Co 0.2 Mn 0.2 O2@CoB

[0132] In the coated cathode material of this example, the average particle size of the primary single-crystal particles 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 O2.

[0133] Example 9

[0134] The difference from Example 1 is only that the mass of CoB is 5.5% of LiNi 0.8 Co 0.1 Mn 0.1 O2. In the coated cathode material of this example, the average particle size of the primary single-crystal particles is 330 nm, and the average particle size of the secondary polycrystalline particles is 9.8 μm.

[0135] Example 10

[0136] It is only different from Example 1 in that the tempering temperature is 800 °C. The average particle size of the primary single-crystal particles in the coated cathode material of this example is 340 nm, and the average particle size of the secondary polycrystalline particles is 10.5 μm.

[0137] Example 11

[0138] It is only different from Example 1 in that the tempering time is 2 h. The average particle size of the primary single-crystal particles in the coated cathode material of this example is 320 nm, and the average particle size of the secondary polycrystalline particles is 9.0 μm.

[0139] Example 12

[0140] It is only different from Example 1 in that the tempering time is 12 h. The average particle size of the primary single-crystal particles in the coated cathode material of this example is 340 nm, and the average particle size of the secondary polycrystalline particles is 9.5 μm.

[0141] Example 13

[0142] It is only different from Example 1 in that the spray system is turned on and spraying is carried out at a speed of 55 mL / s. The average particle size of the primary single-crystal particles in the coated cathode material of this example is 360 nm, and the average particle size of the secondary polycrystalline particles is 10 μm.

[0143] Comparative Example 1

[0144] The cathode material of this comparative example is an uncoated LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811) cathode material, which is a polycrystalline cathode material.

[0145] (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 carry out ball milling and mixing to obtain a first mixed material A;

[0146] (2) Sinter the first mixture A in a sintering furnace in an oxygen environment at 750 °C for 12 h. After cooling, screen the sintered product through a 400-mesh sieve to prepare the cathode material B (LiNi 0.8 Co 0.1 Mn 0.1 O2).

[0147] Comparative Example 2

[0148] This comparative example uses a liquid-phase coating method on LiNi 0.8 Co 0.1 Mn 0.1The surface of O2 is coated with CoB, where the mass of the coating layer CoB is 0.68% of the mass of the cathode material LiNi 0.8 Co 0.1 Mn 0.1 O2.

[0149] The preparation method of the cathode material in Comparative Example 2 includes the following steps:

[0150] (1) Weigh 1 kg of the ternary precursor Ni 0.8 Co 0.1 Mn 0.1 (OH)2 and 0.46 kg of LiOH and carry out ball milling and mixing to obtain a first mixed material A;

[0151] (2) Sinter the first mixture A in a sintering furnace in an oxygen environment at 750 °C for 12 h. After cooling, screen the sintered product through a 400-mesh sieve to prepare the cathode material B (LiNi 0.8 Co 0.1 Mn 0.1 O2);

[0152] (3) Weigh 500 g of the above cathode material B, cobalt hexahydrate nitrate, and sodium borohydride. Dissolve cobalt hexahydrate nitrate in 800 mL of ethanol under the protection of nitrogen and stir well to obtain a suspension X; dissolve sodium borohydride in 200 mL of ethanol under the protection of nitrogen and fully dissolve and stir well to obtain a solution Y;

[0153] (4) Uniformly add solution Y to suspension X and stir for 2 h under the protection of nitrogen; after stirring, carry out suction filtration, wash the obtained solid twice with 100 mL of ethanol, and vacuum dry the washed solid at 120 °C for 6 h to prepare a liquid-phase coated ternary cathode material.

[0154] Comparative Example 3

[0155] In this comparative example, the dry-mixing coating method is used to coat CoB on the surface of LiNi 0.8 Co 0.1 Mn 0.1 O2, where the mass of the coating layer CoB is 0.68% of the mass of the cathode material LiNi 0.8 Co 0.1 Mn 0.1 O2.

[0156] The preparation method of the cathode material in Comparative Example 3 includes the following steps:

[0157] (1) Prepare raw materials, take 8 kg of high-nickel polycrystalline ternary cathode material LiNi 0.8 Co 0.1 Mn 0.1Using O2 as the base material, 200 mL of deionized water was taken as the dispersant, and 54.49 g of CoB was taken as the coating agent;

[0158] (2) Pour the high-nickel polycrystalline ternary cathode material and the coating agent into the mixing equipment, start stirring, the linear velocity of the stirring paddle is 3 m / s, and the stirring time is 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 equipment;

[0159] (3) After the stirring is completed, load the material in step (2) into a crucible and put it into a kiln for tempering. The tempering temperature is 700 °C and the holding time is 4 h;

[0160] (4) After taking out of the furnace, sieve through a 400-mesh sieve to prepare the cathode material in Comparative Example 3.

[0161] Comparative Example 4

[0162] The difference from Example 1 is only that the step of tempering is not carried out in this comparative example.

[0163] Comparative Example 5

[0164] The difference from Example 1 is only that the coating agent is replaced from CoN to boron oxide.

[0165] Comparative Example 6

[0166] The cathode material of this comparative example is the uncoated LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622) cathode material, which is a polycrystalline cathode material.

[0167] (1) Weigh 1 kg of ternary precursor Ni 0.6 Co 0.2 Mn 0.2 (OH)2 and 0.46 kg of LiOH are ball-milled and mixed to obtain a first mixed material B;

[0168] (2) Sinter the first mixture B in a sintering furnace in an oxygen environment at 880 °C for 12 h. After cooling, screen the sintered product through a 400-mesh sieve to prepare the cathode material B (LiNi 06 Co 0.2 Mn 0.2 O2).

[0169] Figure 1 For the coated cathode materials in Examples 1-7 and the uncoated LiNi in Comparative Example 1 0.8 Co 0.1 Mn 0.1XPS spectrum of B1s of O2 positive electrode material. It can be seen from the figure that the characteristic peak of B1s is detected in the coated positive electrode materials of Examples 1-7, indicating that the surface of the coated positive electrode materials in Examples 1-7 is coated with metal boride.

[0170] Figure 2 For Example 1-7 ( Figure 2 ag) and Comparative Examples 1-3 ( Figure 2 The SEM images of the positive electrode materials in Figures hj) show that the primary single crystal particles of the positive electrode material prepared by the method of the present invention are released from the secondary polycrystalline particles. The coating agent covers the surface of each released primary single crystal particle, forming a protective layer on the surface of both the primary single crystal particles and the secondary polycrystalline particles. This avoids the accelerated deterioration of battery performance caused by the increase in the specific surface area of the positive electrode material and also avoids contact between the positive electrode material and the electrolyte. In contrast, the positive electrode materials in Comparative Examples 1-3 did not show the phenomenon of primary single crystal particles being released from the secondary polycrystalline particles.

[0171] Performance testing:

[0172] The powder compaction density of the positive electrode materials in Examples 1-13 and Comparative Examples 1-6 was tested using Sansi Zongheng UTM7305. The results are shown in Table 1.

[0173] The positive electrode materials prepared in Examples 1-13 and Comparative Examples 1-6 were assembled into soft-pack batteries, and their electrochemical properties were tested.

[0174] Assembly of soft pack batteries:

[0175] (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. The slurry obtained after mixing was evenly coated on the positive electrode current collector to prepare a electrode sheet;

[0176] (2) Electrolyte: The electrolyte was E20, purchased from Shenzhen Xinzhoubang Technology Co., Ltd.

[0177] (3) Negative electrode: The active material of the negative electrode is graphite, wherein the ratio of graphite: Supper P: sodium carboxymethyl cellulose (CMC): styrene-butadiene latex (SBR): NMP is 92:0.5:1.5:4:2.

[0178] Soft pack battery testing:

[0179] The first-week formation capacity at 0.33C and the capacity retention rate after 200 cycles at a current density of 1C (voltage window: 2.8 - 4.25V) of the soft-pack batteries assembled with the cathode materials in Examples 1-7, Examples 9-13, and Comparative Examples 1-5 were tested at 45°C. The test results are shown in Table 1.

[0180] Table 1

[0181]

[0182]

[0183] The first-week formation capacity at 0.33C and the capacity retention rate after 200 cycles at a current density of 1C (voltage window: 3.0 - 4.40V) of the soft-pack batteries assembled with the cathode materials in Example 8 and Comparative Example 6 were tested at 45°C. The test results are shown in Table 2.

[0184] Table 2

[0185]

[0186] Analysis:

[0187] It can be seen from the data of the examples and comparative examples that the first-week formation capacity of the soft-pack batteries assembled with the cathode materials in the examples of the present invention, the powder compaction density of the cathode materials, and the capacity retention rate of the soft-pack batteries are all higher than those of the soft-pack batteries assembled with the cathode materials in the comparative examples, indicating that the cathode material modification method proposed in the examples of the present invention can improve the compaction density of the cathode material, increase the capacity of the cathode material, and improve the cycling performance of the cathode material.

[0188] It can be seen from the data of Example 1 and Examples 9-10 that when the content of the coating agent is relatively high or the tempering temperature is relatively high, it will affect the capacity and cycling performance of the cathode material to a certain extent.

[0189] It can be seen from the data of Example 1 and Examples 11-12 that a relatively long or short tempering time will affect the capacity and cycling performance of the cathode material.

[0190] It can be seen from the data of Example 1 and Example 13 that when the spray coating speed is relatively fast, it will affect the capacity and cycling performance of the cathode material. This is mainly because when the spray coating speed is relatively fast, it will affect the uniformity of the coating of the cathode material, thereby affecting the capacity and cycling performance of the cathode material.

[0191] Comparative Example 2 adopted a liquid-phase synthesis method to achieve in-situ coating on the surface of the cathode material. From the data in the table, it can be seen that the cathode material in Comparative Example 2 had some improvements in terms of tap density and cycling performance compared to the cathode material in Comparative Example 1. However, the tap density of the cathode material in Comparative Example 2 was lower than that of the cathode material prepared in Example 1 of the present invention. At the same time, it was very difficult to scale up the raw materials and methods used in Comparative Example 2 because the in-situ coating method in Comparative Example 2 not only required an inert gas atmosphere but also needed high-cost and flammable ethanol as a solvent to participate in the reaction, which greatly increased the production cost and the difficulty of production scale-up. The process involved in the examples of the present invention only required simple modification on the basis of the existing production line to be completed.

[0192] From the data of Example 1 and Comparative Example 3, it can be seen that the capacity retention rate of the cathode material in Comparative Example 3 after 200 cycles was significantly lower than that of the cathode material in Example 1, and the tap density of the cathode material in Comparative Example 3 was also lower than that of the cathode material in Example 1. Therefore, the volumetric energy density of the cathode material in Comparative Example 3 would be lower.

[0193] From the data of Example 1 and Comparative Example 4, it can be seen that the tempering step in the examples of the present invention had a great influence on the performance of the cathode material. If tempering was not carried out, it would not only affect the capacity and cycling performance of the cathode material but also reduce the powder tap density of the cathode material.

[0194] From the data of Example 1 and Comparative Example 5, it can be seen that if the coating agent was replaced from metal boride to boron oxide, it could not improve the capacity and cycling performance of the cathode material well, nor could it increase the powder tap density of the cathode material.

[0195] From the data of Example 8 and Comparative Example 6, it can be seen that if the NMC811 cathode material was replaced with the NCM622 series of cathode materials, the same effect of improving the cycling performance and tap density of the cathode material could be obtained, indicating that the cathode material modification method involved in the present invention was suitable for various proportions of polycrystalline ternary cathode materials.

[0196] Figure 3The cycling performance of the soft-pack batteries assembled with the cathode materials in Examples 1-7 and Comparative Examples 1-3 of the present invention at a current density of 1C and 45°C. As can be seen from the figure, the cathode materials in Examples 1-7 of the present invention have a high capacity retention rate. This is because the primary single-crystal particles in the cathode materials prepared in the examples of the present invention are detached from the secondary polycrystalline particles, and the surfaces of the detached primary single-crystal particles and the grain boundaries of the secondary polycrystalline particles are coated with a coating agent, rather than just coating the surface of the secondary polycrystalline particles. This comprehensive coating is beneficial to improving the performance of the cathode material. If only the surface of the secondary polycrystalline particles is coated, as the cycling progresses, the uncoated part inside the secondary polycrystalline particles will come into contact with the electrolyte and cause side reactions, resulting in the deterioration of the battery cycling performance. At the same time, since the detached primary single-crystal particles are very small and can be coated on the surface of the secondary polycrystalline particles, this structure can be regarded as forming an additional coating on the surface of the secondary polycrystalline particles, which can block more electrolyte from entering the inside of the cathode material. Therefore, it also slows down the performance deterioration of the cathode material during cycling and improves the cycling performance of the cathode material.

[0197] The applicant declares that the present invention uses the above examples to illustrate the detailed method of the present invention, but the present invention is not limited to the above detailed method, that is, it does not mean that the present invention must rely on the above detailed method to be implemented. Those skilled in the art should understand that any improvement to the present invention, the equivalent substitution of each raw material of the product of the present invention, the addition of auxiliary components, the selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A preparation method of a coated cathode material, characterized in that The method comprises the following steps: (1) Coating a coating agent onto the surface of a polycrystalline cathode material by means of spray coating; The spray coating method described in step (1) comprises: (a) Mixing the coating agent and a dispersant to form a suspension; (b) Spraying the polycrystalline cathode material with the suspension described in step (a); the step of spraying the polycrystalline cathode material is carried out under stirring conditions, the linear velocity of the stirring is 1-15 m / s, the stirring time is 0.5-5 min, and stirring continues for 3-5 min after the spraying of the polycrystalline cathode material ends; The coating agent comprises a metal boride, and the mass ratio of the polycrystalline cathode material to the coating agent is 1:(0.0003-0.05); (2) Preparing the coated cathode material by tempering the polycrystalline cathode material obtained in step (1); The temperature of the tempering is 450-700 °C, and the time is 4-6 h; During the tempering process, the coating agent causes the primary single crystal particles in the polycrystalline cathode material to dissociate without damage; The average particle size of the primary single crystal particles is 100-500 nm.

2. The method according to claim 1, characterized in that The metal boride includes at least one of Co a B, ZrB2, and MgB2, where 3 ≥ a ≥ 1.

3. The method according to claim 1, wherein The polycrystalline cathode material is a polycrystalline ternary cathode material.

4. The method according to claim 3, characterized in that The composition of the polycrystalline ternary cathode material includes Li(Ni x Co y Mn 1-x-y )O2, where 0 < x < 1 and 0 < y < 1.

5. The method according to claim 4, wherein The composition of the polycrystalline ternary cathode material includes Li(Ni x Co y Mn 1-x-y )O2, where 0.6 ≤ x < 1 and 0.1 < y < 0.

3.

6. The method according to claim 1, wherein The mass ratio of the polycrystalline cathode material to the coating agent is 1:(0.0003-0.02).

7. The method according to claim 1, wherein The dispersant comprises at least one of water or an aqueous alcohol solution.

8. The method according to claim 1, wherein The spraying speed is 0.2-50 mL / s.

9. The method according to claim 1, wherein After the tempering step, the coated cathode material is sieved.

10. A coated cathode material prepared by the method according to any one of claims 1-9, characterized in that, The coated cathode material comprises primary single crystal particles and secondary polycrystalline particles, wherein a coating layer is coated on the surface of the primary single crystal particles, the surface of the secondary polycrystalline particles, and the grain boundaries of the secondary polycrystalline particles.

11. The coated cathode material according to claim 10, wherein The average particle size of the secondary polycrystalline particles is 7-12 μm.

12. A lithium-ion battery, characterized in that, The positive electrode of the lithium-ion battery comprises the coated cathode material according to any one of claims 10-11.

Images