Single-crystal positive electrode material and preparation method therefor, and lithium-ion battery

Abstract

A single-crystal positive electrode material and a preparation method therefor, and a lithium-ion battery. The single-crystal positive electrode material comprises: a core layer, the core layer comprising an oxide composed of Li, Ni and a doping element A; and a shell layer, the shell layer covering at least part of the surface of the core layer and comprising a compound composed of a coating element L, wherein the core layer has an LiTMO2 layered structure. The single-crystal positive electrode material comprises a single primary particle; the average single crystal size D of the single-crystal positive electrode material ranges from 1.3 μm to 3.0 μm; Dmin of the single-crystal positive electrode material is greater than 1.1 μm; 1.0 < D50 / D < 2.0; and after 400 cycles at a test voltage of 3.0-4.35 V and 45°C, the proportion of a fatigue impurity phase of the single-crystal positive electrode material does not exceed 10%. By improving the preparation process of a single-crystal positive electrode material, the production efficiency is improved, and the cost is reduced; and the cycle and gas production performance of the material are improved by means of improving the single-crystal separation degree.

Description

Single crystal positive electrode material and preparation method thereof, lithium ion battery

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on December 6, 2023, with application number 202311663075.3 and application name “A single crystal positive electrode material, its preparation method, and lithium-ion battery”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the technical field of lithium-ion batteries, and specifically to a single-crystal positive electrode material and a preparation method thereof, and a lithium-ion battery. Background Art

[0003] In recent years, new energy sources have developed rapidly, and lithium-ion batteries have attracted much attention due to their low cost, simple preparation methods, and excellent performance. During the sintering process of lithium-ion batteries, the phase structure of the material changes, and defects such as cation mixing, voids, and impurity phases will appear, thereby affecting the material's cycle performance and gas production. Summary of the Invention

[0004] Therefore, the present application provides a single crystal positive electrode material and its preparation method, and a lithium ion battery, which improves production efficiency and reduces costs by improving the single crystal positive electrode material preparation process, and improves the material cycle performance and gas production by increasing the single crystal separation.

[0005] To this end, the first object of the present application is to provide a single crystal positive electrode material;

[0006] The second object of the present application is to provide a method for preparing a single crystal positive electrode material;

[0007] The third object of this application is to provide a lithium-ion battery;

[0008] To achieve the first object of the present application, the present application provides a single crystal positive electrode material, the single crystal positive electrode material comprising: a core layer, the core layer comprising an oxide composed of Li, Ni, and a doping element A; a shell layer, the shell layer covering at least a portion of the surface of the core layer, and the shell layer comprising a compound composed of a coating element L; wherein the core layer is a LiTMO2 layered structure; the single crystal positive electrode material comprises a single primary particle; the average single crystal size D of the single crystal positive electrode material is in the range of 1.3 μm-3.0 μm; the D of the single crystal positive electrode material min >1.1μm; 1.0<D50 / D<2.0; after 400 cycles at a test voltage of 3.0-4.35V and 45°C, the fatigue impurity phase of the single crystal positive electrode material does not exceed 10%; the doping element A includes at least one of Zr, Al, W, Sr, Ti, Mg, Ca, Y, Nb, Mo, and Ce; and the coating element L includes at least one of Li, Al, Ti, Mg, W, and B.

[0009] Compared with the existing technology, the technical effects achieved by adopting this technical solution are as follows: the core layer includes an oxide composed of Li, Ni, and doping element A, Ni is conducive to single crystal growth, and Li moves from the intercalation material electrode with higher chemical potential to the electrode with lower potential, forming current for output use; the doping element A can replace part of the transition metal elements to form a more stable metal-oxygen bond, making the structural changes smaller, and can inhibit the release of oxygen during the cycle; the core layer includes a single primary particle, and the larger single crystal primary particles can better hinder electrolyte corrosion and show higher circulation and gas production performance.

[0010] The shell layer covers at least a portion of the surface of the core layer. The shell layer includes a compound composed of the coating element L. The shell layer can resist corrosion from the electrolyte and increase the service life of the single crystal positive electrode material.

[0011] The average single crystal size D of the single crystal positive electrode material refers to the average diameter of the single crystal; the D of the single crystal positive electrode material min It refers to the minimum particle size of the single crystal positive electrode material, that is, the smallest particle size among all particles in the single crystal positive electrode material; D50 of the single crystal positive electrode material refers to the median particle size of the single crystal, that is, the particle size corresponding to when the cumulative particle size distribution percentage of the single crystal positive electrode material reaches 50%; the separation degree Z of the single crystal positive electrode material is obtained by D50 / D. When the separation degree range falls within 1.0<Z<2.0, the single crystal particles can be relatively separated, and the obtained single crystal material has the best performance.

[0012] During the cycle, the positive electrode material will undergo surface oxygen evolution and transition metal migration, causing structural changes on the surface of the material, transforming from the initial layered structure to a rock salt phase or a spinel-like phase. The existence of this surface reconstruction layer not only directly increases the material impedance, but also limits the lattice "breathing" of the adjacent active phase, inhibiting the capacity of the active phase. The above-mentioned reconstruction layer and its adjacent damaged active phase are collectively referred to as fatigue phases. If the structural damage of the cycled material is relatively light, its fatigue phase content is low and the capacity loss is also small. Therefore, after 400 cycles at a test voltage of 3.0-4.35V and 45°C, the fatigue impurity phase of the single crystal positive electrode material does not exceed 10%. At this time, the cycle performance of the single crystal positive electrode material is the best.

[0013] Furthermore, the precursor, lithium salt and dopant are first mixed and pre-sintered to obtain the first oxide. By promoting the early entry of lithium ions into the single crystal positive electrode material, the formation of the metastable spinel phase is suppressed, thereby reducing the Li / Ni mixing and impurity phase formation of the single crystal positive electrode material; at the same time, the doping energy barrier is reduced, and the stabilizing effect of the doping elements on the structure is improved.

[0014] In one technical solution of the present application, the separation degree of the single crystal positive electrode material is 1.0<Z<1.3, and the separation degree is calculated by D50 / D. At this time, the single crystal particles are relatively separated, and the performance of the obtained single crystal material is better.

[0015] In one technical solution of the present application, the D50 particle size of the core layer ranges from 2 μm to 6 μm.

[0016] In one technical solution of the present application, the thickness of the shell layer is 1 nm-100 nm.

[0017] The D50 particle size of the core layer and the thickness of the shell layer within the above ranges can achieve an appropriate degree of agglomeration and coating of the positive electrode material, thereby increasing the single crystal formation rate, reducing and repairing material damage caused by dissociation, and improving the electrochemical performance of the material. It will be understood that the D50 of the core layer of the single crystal positive electrode material of the present invention is on the micron level, while the shell layer thickness is on the nanometer level. Therefore, the D50 of the core layer of the single crystal positive electrode material is almost the same as the D50 of the single crystal positive electrode material.

[0018] To achieve the second purpose of this application, the present application provides a method for preparing a single crystal positive electrode material.

[0019] The single crystal positive electrode material comprises: a core layer, the core layer comprises an oxide composed of Li, Ni, and a doping element A; a shell layer, the shell layer covers at least a portion of the surface of the core layer, and the shell layer comprises a compound composed of a coating element L; wherein the core layer is a LiTMO2 layered structure; the single crystal positive electrode material comprises a single primary particle; the average single crystal size D of the single crystal positive electrode material ranges from 1.3 μm to 3.0 μm; the D of the single crystal positive electrode material min >1.1μm; 1.0<D50 / D<2.0; doping element A includes at least one of Zr, Al, W, Sr, Ti, Mg, Ca, Y, Nb, Mo, and Ce; coating element L includes at least one of Li, Al, Ti, Mg, W, and B;

[0020] The preparation method comprises the following steps:

[0021] S100, mixing a precursor, a lithium salt, and a dopant containing a doping element A, and performing a pre-sintering process to obtain a first oxide;

[0022] S200, mixing the first oxide with a co-solvent and performing a pre-dissociation treatment to obtain a first dissociated product;

[0023] S300, performing a sintering process and a dissociation process on the first dissociated product in sequence to obtain a second oxide;

[0024] S400: mixing the second oxide and the coating agent containing the coating element L again, and performing a secondary sintering process to obtain a single crystal positive electrode material;

[0025] Among them, the pre-sintering process and the primary sintering process are both carried out by two-stage sintering.

[0026] Compared with the existing technology, the technical effect achieved by adopting this technical solution is as follows: first, the precursor, lithium salt and dopant are mixed and pre-sintered to obtain the first oxide, and the formation of metastable spinel phase is suppressed by promoting lithium ions to enter the single crystal positive electrode material in advance, thereby reducing the Li / Ni mixing and impurity phase formation of the single crystal positive electrode material; at the same time, the doping energy barrier is reduced, and the stabilizing effect of the doping element on the structure is improved; and in the pre-sintering treatment, the heating rate of the first temperature zone is higher than the heating rate of the second temperature zone, the temperature of the first temperature zone is lower than the temperature of the second temperature zone, and the time of the first temperature zone is less than the time of the second temperature zone; first, the temperature is raised to the dehydration temperature of the lithium salt and the precursor at a faster speed, and maintained for a period of time so that the adsorbed water and crystallization water are largely removed from the material, the density of the material is increased, and the effective lithium salt and the precursor are in close contact; then a low heating rate and a certain holding time are maintained so that the lithium ions can fully enter the layered structure of the precursor to avoid the generation of impurity phases caused by overburning.

[0027] Secondly, the first oxide is mixed with the co-solvent and then pre-dissociated to obtain a first dissociated product. Through the dissociation treatment, the degree of material aggregation is reduced in advance, the sintering uniformity of the material is improved, and the lithium salt is fully reacted with the material to improve the lithiation effect; the subsequent material crushing strength can be reduced, the damage to the primary particles and the generation of fine powder can be avoided, the roundness of the material can be improved, and the subsequent steps can also be strengthened, so that the long cycle performance of the single crystal positive electrode material is further enhanced; at the same time, the pyrolysis temperature is lowered, the volatilization of the lithium salt and the heat energy consumption are reduced, the cost is reduced, and the material performance is improved.

[0028] The first dissociation product is subjected to a sintering treatment and a dissociation treatment to obtain a second oxide. Due to the dehydration effect of the reaction between the precursor and the lithium salt, the material density increases, and the charging amount can be increased during the first high-temperature sintering, thereby greatly improving the production capacity; at the same time, the lower sintering temperature can reduce lithium volatilization, reduce lithium loss, and save costs; and in the first sintering treatment, the heating rate of the first temperature zone is higher than the heating rate of the second temperature zone, the temperature of the first temperature zone is lower than the temperature of the second temperature zone, and the time of the first temperature zone is less than the time of the second temperature zone. First, the first temperature zone is heated at a fast rate. The rate is raised to a given temperature for pre-sintering treatment, which can save sintering time and reduce costs; then the temperature is raised at a second temperature zone at a heating rate lower than that of the first temperature zone and maintained at the sintering temperature, so that the material is fully lithiated and grows, and the crystallinity is further improved; and the dissociation treatment can increase the specific surface area of ​​the second oxide, so that it has a better coating effect during the secondary sintering treatment, and the second oxide obtained by the pre-dissociation treatment and then the dissociation treatment has uniform particle size, is not easy to produce fine powder, and has high roundness. Finally, the single crystal positive electrode material obtained has good performance.

[0029] Finally, through the secondary sintering treatment of the second oxide of the coating agent, a passivation layer resistant to electrolyte corrosion is formed on the shell, thereby obtaining a single crystal positive electrode material with excellent comprehensive performance, improving the stability of the material, and extending the service life of the coated single crystal positive electrode material.

[0030] In addition, experiments have shown that the lithium salt of the present invention can be at least one of LiOH·H2O, Li2CO3, LiOH, and LiNO3; preferably, LiOH·H2O is the best lithium salt, which is better than Li2CO3 in improving the capacity retention rate after 400 cycles, reducing the volume growth rate after 35 days, and the proportion of fatigue phase.

[0031] In one technical solution of the present application, the first dissociation product XPS detects Ni 3+ The peak area accounts for 60%-85%.

[0032] Compared with the existing technology, the technical effect achieved by adopting this technical solution is: since the reaction of TM(OH)2+O2→TMOOH+H2O occurs at 350℃, while the crystal water of LiOH·H2O begins to evaporate at 125℃, with a melting point of 478℃; if the pre-calcination temperature is too high, the TMOOH structure will prematurely undergo the TM3O4 structure transformation, affecting the Li + Embedding causes the intermediate spinel structure phase to account for a large proportion, which ultimately affects the proportion of the layered structure phase in the finished product; and when the pre-firing temperature is low, the precursor pyrolysis and lithiation reaction are slowed down, which cannot increase the proportion of the layered phase structure and reduce the effect of Li / Ni mixing. 3+ The peak area accounts for 60%-85%, and the pre-dissociation product with the best structure can be obtained, which is beneficial to the subsequent lithiation sintering and improves the material performance.

[0033] In one technical solution of the present application, the second oxide XPS detects Ni 3+ The peak area accounts for 80%-95%.

[0034] Compared with the existing technology, the technical effect achieved by adopting this technical solution is: the second oxide XPS detection of Ni 3+ When the peak area accounts for 80%-95%, the proportion of LiTMO2 layered structure can be calculated to be 90%-98% through XRD peak separation. This result proves that after one sintering treatment, the proportion of LiTMO2 layered phase structure in the positive electrode material increases, the effect of Li / Ni mixing decreases, the generation of impurity phase and fatigue phase is reduced, and the doping effect is improved.

[0035] In one technical solution of the present application, the water content of the first dissociation product is less than 2%.

[0036] Compared with the existing technology, the technical effect achieved by adopting this technical solution is: the water content of the first dissociation product is less than 2%, and the material density is increased through the dehydration of the precursor and the lithium salt, which is beneficial to the charging amount in the subsequent sintering process.

[0037] In one technical solution of the present application, the bulk density of the first dissociated product is increased by 10%-30% compared with the first oxide.

[0038] Compared with the existing technology, the technical effects achieved by adopting this technical solution are: through pre-dissociation treatment, the loose density of the first dissociated product is increased by 10%-30% compared with the first oxide, thereby improving the degree of agglomeration and reducing sintering energy consumption; during the high-temperature growth process of the single crystal, the doping ions can be more evenly contacted with the single crystal particles, achieving a more uniform doping distribution; reducing the damage to the material structure and the increase of fine powder caused by crushing, improving the integrity of the single crystal, and improving the material properties.

[0039] In one technical solution of the present application, in S100: the heating rate of a temperature zone of the pre-sintering is 3°C / min-8°C / min, the temperature is 130°C-250°C, and the time is 2h-5h.

[0040] In one technical solution of the present application, in S100: the heating rate of the second temperature zone is 1°C / min-4°C / min, the temperature is 400°C-600°C, and the time is 5h-10h.

[0041] Compared with the existing technology, the technical effect achieved by adopting the above technical scheme is: in S100, the heating rate of the first temperature zone of pre-sintering is 3℃ / min-8℃ / min, the temperature is 130℃-250℃, and the time is 2h-5h; the heating rate of the second temperature zone is 1℃ / min-4℃ / min, the temperature is 400℃-600℃, and the time is 5h-10h. First, the temperature is raised to the dehydration temperature of the lithium salt and the precursor at a faster speed, and maintained for a period of time so that the adsorbed water and crystallized water are largely removed from the material, the density of the material is increased, and the effective lithium salt and the precursor are in close contact; then a lower heating rate and a certain holding time are maintained so that the lithium ions can fully enter the layered structure of the precursor to avoid the generation of impurity phases caused by overburning.

[0042] In one technical solution of the present application, in S100 , the molar ratio of the precursor, the lithium salt, and the dopant is 1:1:(0.001-0.01).

[0043] When the molar ratio of the precursor, lithium salt and dopant is 1:1:(0.001-0.01), the product performance is the best, the ratio is optimal, and it is also convenient for subsequent processing.

[0044] In one technical solution of the present application, in S200 : the temperature of the pre-dissociation treatment is 150° C.-300° C., and the time of the pre-dissociation treatment is 0.3 h-3.4 h.

[0045] Compared with the existing technology, the technical effect achieved by adopting this technical solution is: in S200, the temperature of the pre-dissociation treatment is 150℃-300℃, and the time of the pre-dissociation treatment is 0.3h-3.4h. Through the pre-dissociation treatment, the single crystal particles can be promoted to self-dissociate at a lower temperature, the degree of agglomeration can be improved and the sintering energy consumption can be reduced; at the same time, during the high-temperature growth process of the single crystal, the doping ions can be more evenly contacted with the single crystal particles, achieving a more distributed doping distribution; reducing the damage to the material structure and the increase of fine powder caused by crushing, improving the integrity of the single crystal, and improving the material properties.

[0046] In one technical solution of the present application, in S200: the molar ratio of the first oxide to the co-solvent is 1:(0.01-0.2).

[0047] When the molar ratio of the first oxide to the co-solvent is 1:(0.01-0.2), the obtained product has the best performance and the best ratio.

[0048] In one technical solution of the present application, in S300: the heating rate of a temperature zone in a primary sintering treatment is 4°C / min-8°C / min, and the temperature is 500°C-600°C.

[0049] In one technical solution of the present application, in S300: the heating rate of the second temperature zone is 2°C / min-5°C / min, the temperature is 600°C-1000°C, and the time is 5h-10h.

[0050] Compared with the existing technology, the technical effect achieved by adopting the above technical scheme is: in S300, the heating rate of the first temperature zone of the primary sintering treatment is 4℃ / min-8℃ / min, and the temperature is 500℃-600℃; the heating rate of the second temperature zone is 2℃ / min-5℃ / min, and the temperature is 600℃-1000℃, and the time is 5h-10h. First, the first temperature zone is heated to the given temperature of the pre-sintering treatment at a rapid heating rate, which can save sintering time and reduce costs; after reaching the given temperature of the pre-sintering treatment, the temperature is immediately heated at a heating rate of the second temperature zone lower than that of the first temperature zone and maintained at the sintering temperature for a period of time, which can promote the full lithiation and growth of the material and further improve the crystallinity.

[0051] In one technical solution of the present application, in S400 , the secondary sintering treatment temperature is 300° C.-600° C., the heating rate is 2° C. / min-6° C. / min, and the time is 6 h-12 h.

[0052] In one technical solution of the present application, in S400 , the molar ratio of the second oxide to the coating agent is 1:(0.0001-0.01).

[0053] Compared with the existing technology, the technical effect achieved by adopting the above technical scheme is: the secondary sintering treatment temperature is 300℃-600℃, the heating rate is 2℃ / min-6℃ / min, the time is 6h-12h, and the molar ratio of the second oxide to the coating agent is 1:(0.0001-0.01). The obtained product has the best performance effect and the optimal ratio.

[0054] To achieve the third objective of the present application, the present application provides a lithium-ion battery comprising a single crystal positive electrode material prepared by any of the above-mentioned preparation methods. The battery thus includes the beneficial effects of any of the above-mentioned technical solutions, which will not be elaborated here.

[0055] By adopting the technical solution of this application, the following technical effects can be achieved:

[0056] (1) Through pre-sintering treatment, the precursor TM(OH)2 will lose water during the sintering process to generate a layered TMOOH structure and a spinel TM3O4 structure. At the same time, Li undergoes interfacial diffusion and is embedded into the layered structure, thereby generating a LiTMO2 structure. Doping elements with a small radius also enter at the same time to complete site occupation. In addition, through the two-stage pre-sintering process parameters, the embedding of lithium ions in the transition phase can be promoted, the proportion of layered structures in the transition phase can be increased, thereby improving the order of the layered structure of the finished material and reducing the degree of Li / Ni mixing; at the same time, it is also beneficial to the effective embedding of doping elements, reducing the doping energy barrier, improving the stability of the finished doping structure, and reducing internal stress and lattice mismatch rate;

[0057] (2) Pre-dissociation treatment can promote the self-dissociation of single crystal particles at a lower temperature, improve the degree of agglomeration and reduce sintering energy consumption; at the same time, during the high-temperature growth process of single crystals, the doping ions can be more evenly contacted with the single crystal particles, achieving a more uniform doping distribution; reducing the damage to the material structure and the increase of fine powder caused by crushing, improving the integrity of the single crystal and improving the material properties;

[0058] (3) The preparation method of the present application can improve the production capacity of a single sintering and improve the utilization rate of thermal energy; and increase the proportion of LiTMO2 in the material, reduce the generation of impurity phases and fatigue phases, and improve the doping effect; the two-stage sintering reduces the volatilization of lithium salts; finally, due to the dehydration of the precursor and lithium salt, the material density increases, and the charging amount can be increased during the single high-temperature sintering, thereby significantly improving the production capacity. At the same time, the lower sintering temperature can reduce lithium volatilization during pre-lithiation, reduce lithium loss, and save costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] To more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings to be used in describing the embodiments. Obviously, the drawings described below are only some embodiments of the present application, and those skilled in the art can derive other drawings based on these drawings without inventive effort.

[0060] FIG1 is a morphology diagram of a single crystal positive electrode material after pre-sintering treatment during the preparation process provided in an embodiment of the present application;

[0061] FIG2 is one of the morphology images of a single crystal cathode material provided in an embodiment of the present application;

[0062] FIG3 is a second morphology diagram of a single crystal cathode material provided in an embodiment of the present application;

[0063] FIG4 is a line graph showing the cycle performance of Examples 1-4 and Comparative Examples 1-2;

[0064] FIG5 is a line graph showing the volume growth rates of Examples 1-4 and Comparative Examples 1-2. DETAILED DESCRIPTION

[0065] To make the above-mentioned purposes, features, and advantages of this application more obvious and easy to understand, the technical solutions in the embodiments of this application are clearly and completely described. Obviously, the described embodiments are only part of the embodiments of this application, not all of them. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of this application.

[0066] In recent years, new energy sources have developed rapidly. Lithium-ion batteries have attracted much attention due to their low cost, simple preparation methods, and excellent performance. During the sintering process of lithium-ion batteries, the phase structure of the material changes, and defects such as cation mixing, voids, and impurity phases will appear, thereby affecting the material's cycle performance and gas production.

[0067] Therefore, the present application provides a single crystal positive electrode material and a preparation method thereof, and a lithium ion battery, which improves production efficiency and reduces costs by improving the preparation process of the single crystal positive electrode material, and improves the material cycle performance and gas production.

[0068] This embodiment provides a method for preparing a single crystal positive electrode material, the preparation method comprising the following steps:

[0069] S100, mixing a precursor, a lithium salt, and a dopant containing a doping element A, and performing a pre-sintering process to obtain a first oxide;

[0070] S200, mixing the first oxide with a co-solvent and performing a pre-dissociation treatment to obtain a first dissociated product;

[0071] S300, performing a sintering process and a dissociation process on the first dissociated product in sequence to obtain a second oxide;

[0072] S400: The second oxide is mixed again with the coating agent containing the coating element L, and subjected to a secondary sintering treatment to obtain a single crystal positive electrode material.

[0073] Preferably, the reaction of TM(OH)2+O2→TMOOH+H2O is at 350°C; at the same time, the crystallization water of LiOH·H2O begins to evaporate at 125°C, and the melting point is 478°C; and when the temperature exceeds 300°C, TM(OH)2 and TMOOH will transform into the spinel phase TM3O4. Two-thirds of the TM still occupy the octahedral position, but one-third migrates to the tetrahedral position. At this time, defects such as cation mixing, voids, and impurity phases will appear in the positive electrode material, affecting the material performance. Therefore, in S100, the precursor, lithium salt and dopant containing doping element A are mixed and pre-sintered to obtain the first oxide. The pre-sintering treatment adopts two-stage sintering to promote the lithium ions to enter the layered structure in advance, inhibit the formation of metastable spinel phase, and increase the proportion of layered structure in the transition phase, thereby reducing the Li / Ni mixing and impurity phase formation of the finished material and improving the order of the layered structure of the material; at the same time, the doping energy barrier is reduced, the stabilizing effect of the doping element on the structure is improved, the stability of the finished doping structure is improved, and the internal stress and lattice mismatch rate are reduced.

[0074] Furthermore, the heating rate of the first temperature zone of pre-sintering is 3°C / min-8°C / min, the temperature is 130°C-250°C, and the time is 2h-5h; the heating rate of the second temperature zone is 1°C / min-4°C / min, the temperature is 400°C-600°C, and the time is 5h-10h. First, the temperature is raised to the dehydration temperature of the lithium salt and the precursor at a relatively fast speed, and maintained for a period of time so that the adsorbed water and crystallized water are largely removed from the material, the density of the material is increased, and the effective lithium salt and the precursor are in close contact; then a low heating rate and a certain holding time are maintained so that the lithium ions can fully enter the layered structure of the precursor to avoid the generation of impurity phases caused by overburning.

[0075] Preferably, the dopant M includes at least one of ZrO2, Al2O3, Al(OH)3, WO6, H2WO4, SrO, TiO2, MgO, CaCO3, Ca(OH)2, Y2O3, Nb2O5, MoO3, and CeO2; and the molar ratio of the precursor, lithium salt, and dopant A is 1:1:(0.001-0.01).

[0076] Preferably, the first oxide is mixed with the co-solvent and then subjected to a pre-dissociation treatment to obtain a first dissociated product; the pre-dissociation treatment can reduce the degree of material aggregation in advance, improve the sintering uniformity of the material, and even if the lithium salt fully reacts with the material, improve the lithiation effect; it can reduce the subsequent material crushing strength, avoid primary particle damage and fine powder generation, improve the roundness of the material, and enhance the coating effect, so that the long cycle performance of the single crystal material is further enhanced; at the same time, the pyrolysis temperature is reduced, the volatilization of the lithium salt and the heat energy consumption are reduced, and the cost is reduced;

[0077] In general, if there is no pre-dissociation treatment step, the first oxide is directly subjected to a sintering treatment and then a dissociation treatment, which can easily cause damage to the primary particles and the generation of fine powder, and the particles of the second oxide are of different sizes when the dissociation treatment is carried out. However, in this embodiment, the first oxide is mixed with a solvent and then a pre-dissociation treatment is carried out before the first sintering treatment. The solvent can open the first oxide to increase its solubility and improve the degree of single crystal agglomeration. Therefore, during the first sintering treatment, the particle size obtained after the dissociation treatment of the second oxide is more uniform and the specific surface area of ​​the particles is large, thereby improving the doping and subsequent crushing effects and improving the material properties.

[0078] Furthermore, the mixing treatment temperature is 150°C-300°C, the mixing treatment is carried out in a high-speed mixer at a stirring speed of 1000rpm-4000rpm for 0.3h-3.4h, the molar ratio of the first oxide to the co-solvent is 1:(0.01-0.2), and the co-solvent L includes at least one of LiNO3, Li2SO4, and LiO2.

[0079] Furthermore, the pre-dissociation treatment can optimize the mixing process, control the degree of dissociation of the polycrystalline precursor, and add grain refiners to prepare positive electrode materials with good comprehensive performance, high compaction density, and coexistence of polycrystalline, single-crystal-like, and single-crystal morphologies, and different D50 agglomeration states.

[0080] Preferably, coarse LiOH·H2O particles can be used to reduce the lithium salt crushing process and save costs.

[0081] Preferably, the first dissociation product is subjected to a sintering treatment to obtain the first oxide. Due to the dehydration effect of the reaction between the precursor and the lithium salt, the material density increases, and the charging amount can be increased during the high-temperature sintering, thereby greatly improving the production capacity and thus improving the thermal energy utilization rate; at the same time, the lower sintering temperature can reduce lithium volatilization, reduce lithium loss, and save costs.

[0082] The heating rate of the first temperature zone of the primary sintering treatment is 4℃ / min-8℃ / min, and the temperature is 500℃-600℃; the heating rate of the second temperature zone is 2℃ / min-5℃ / min, and the temperature is 600℃-1000℃, and the time is 5h-10h. First, the first temperature zone is heated to the given temperature of the pre-sintering treatment at a rapid heating rate, which can save sintering time and reduce costs; after reaching the given temperature of the pre-sintering treatment, the temperature is immediately raised at a heating rate of the second temperature zone lower than that of the first temperature zone and maintained at the sintering temperature for a period of time, so that the material is fully lithiated and grows, and the crystallinity is further improved.

[0083] Furthermore, pre-sintering and secondary sintering can use a rotary kiln (a cylindrical container with a built-in propeller to push the material), which has a short sintering cycle, a large material handling capacity, and convenient loading, but the sintering temperature is not high enough;

[0084] Primary sintering and secondary sintering can be carried out in a track kiln (rectangular container, charging sagger placed on the track, track rotating to send samples), the sintering cycle is long, the sagger needs to be loaded, the handling is troublesome, but the temperature is relatively stable;

[0085] Furthermore, the positive electrode is mixed again with a coating agent containing the coating element L and subjected to a secondary sintering process to obtain a single-crystalline positive electrode material. Through the secondary sintering process of the coating agent and the single-crystalline positive electrode material, a passivation layer resistant to electrolyte corrosion is formed on the outer shell, thereby obtaining a single-crystalline positive electrode material with excellent overall performance, improving the stability of the material, and extending the service life of the coated single-crystalline positive electrode material.

[0086] Preferably, the secondary sintering treatment temperature is 300℃-600℃, the heating rate is 2℃ / min-6℃ / min, and the time is 6h-12h; the molar ratio of the second oxide to the coating agent is 1:(0.0001-0.01), and the coating agent includes at least one of Al2O3, TiO2, MgO, WO3, H2WO4, B2O3, AlF3, and MgF2.

[0087] Furthermore, the cathode material includes a core-shell two-layer structure.

[0088] The chemical formula of the core layer is Li y Ni a Co b Mn c M d , where 1.0≤y≤1.10, 0.5≤a<1, 0≤b≤0.4, 0≤c≤0.4, 0<d<0.1, and the D50 range of the core layer is 2μm-6μm;

[0089] The shell layer covers at least a portion of the surface of the core layer. The shell layer is a passivation layer containing a coating element L. The thickness of the shell layer is 1 nm to 100 nm.

[0090] Example 1

[0091] This embodiment provides a single crystal positive electrode material and a preparation method thereof, and the specific operation steps are as follows:

[0092] S100, NM7525 precursor, LiOH·H2O, ZrO2, and WO6 were mixed in a molar ratio of 1:1:0.001:0.001, and then heated to 200°C at 5°C / min in an oxygen atmosphere, maintained for 2 hours, and then heated to 550°C at 2°C / min and maintained for 8 hours, and pre-sintered to obtain the first oxide, as shown in Figure 1;

[0093] S200, adding the first oxide and LiNO3 in a molar ratio of 1:0.05 into a 220°C constant temperature high-speed mixer and stirring at a speed of 2500 rpm for 80 minutes for pre-dissociation treatment to obtain a first dissociated product;

[0094] S300, heating the first dissociated product to 550° C. at a rate of 5° C. / min in an oxygen atmosphere, then heating the product to 880° C. at a rate of 3° C. / min and holding the temperature for 8 hours, performing a primary sintering treatment, and dissociating the product by air flow milling to obtain a second oxide; and controlling the D50 thereof to be within a range of 2 μm-6 μm;

[0095] S400. Mix the positive electrode material and Al2O3 in a molar ratio of 1:0.01, then heat the mixture to 450°C at a heating rate of 3°C / min in an oxygen atmosphere and maintain for 8 hours to obtain a single crystal positive electrode material, as shown in Figure 2-3.

[0096] Example 2

[0097] This embodiment provides a single crystal positive electrode material and a preparation method thereof, wherein the preparation method is similar to that of Example 1, except that in S100, Al(OH)3 and TiO2 are used as dopants, the temperature is raised to 200°C at 5°C / min in an oxygen atmosphere and maintained for 1.5 hours, then the temperature is raised to 700°C at 2°C / min and maintained for 8 hours, and a pre-sintering treatment is performed to obtain the first oxide, and the second-stage sintering temperature is increased.

[0098] Example 3

[0099] This embodiment provides a single crystal positive electrode material and a preparation method thereof, wherein the preparation method is similar to that of Example 1, except that in S100, H2WO4 and MgO are used as dopants, the temperature is raised to 200°C at 5°C / min in an oxygen atmosphere and maintained for 1.5 hours, then the temperature is raised to 550°C at 2°C / min and maintained for 10 hours, and a pre-sintering treatment is performed to obtain the first oxide, and the second-stage holding time is increased.

[0100] Example 4

[0101] This embodiment provides a single crystal positive electrode material and a preparation method thereof, wherein the preparation method is similar to that of Example 1, except that in S200, pre-lithiated powder A and LiNO3 are added to a 300°C constant temperature high-speed mixer in a molar ratio of 1:0.05 and stirred at 3000 rpm for 60 minutes for pre-dissociation treatment to obtain a first dissociated product, and the dissociation process parameters are adjusted.

[0102] Example 5

[0103] This embodiment provides a single crystal positive electrode material and a preparation method thereof, wherein the preparation method refers to Example 1, except that in S100, Ca(OH)2 and CeO2 are used as dopants and NCM811 precursor is used; in S300, the first dissociated product is heated to 500°C at 5°C / min in an oxygen atmosphere, and then heated to 700°C at a rate of 3°C / min and maintained for 8 hours for a single sintering treatment.

[0104] Example 6

[0105] This embodiment provides a single crystal positive electrode material and a preparation method thereof, wherein the preparation method is similar to that of Example 1, except that in S100, an NM7525 precursor, LiOH·H2O, Nb2O5, and CaCO3 are mixed in a molar ratio of 1:1:0.001:0.01, and then heated to 130°C in an oxygen atmosphere at a rate of 3°C / min and held for 5 hours, and then heated to 400°C at a rate of 1°C / min and held for 10 hours, and pre-sintered to obtain a first oxide;

[0106] In S200, the first oxide and Li2SO4 are added to a 150°C constant temperature high-speed mixer at a molar ratio of 1:0.01 and stirred at 1000 rpm for 200 minutes;

[0107] In S300, the temperature was increased to 500 °C at 4 °C / min, then increased to 600 °C at 2 °C / min and maintained for 10 h;

[0108] In S400, the single crystal cathode material and TiO2 are mixed in a molar ratio of 1:0.01, and then the temperature is increased to 300°C at a heating rate of 2°C / min in an air atmosphere and kept at this temperature for 12 hours to obtain a coated single crystal cathode material.

[0109] Example 7

[0110] This embodiment provides a single crystal positive electrode material and a preparation method thereof, wherein the preparation method is similar to that of Example 1, except that in S100, an NM7525 precursor, LiOH·H2O, Y2O3, and MoO3 are mixed in a molar ratio of 1:1:0.01:0.001, and then the mixture is heated to 250°C at 8°C / min in an oxygen atmosphere and held for 2 hours, and then heated to 600°C at 4°C / min and held for 5 hours, and pre-sintered to obtain a first oxide.

[0111] In S200, the first oxide and LiO2 are added to a 300°C constant temperature high-speed mixer at a molar ratio of 1:0.2 and stirred at 4000 rpm for 20 minutes;

[0112] In S300, the temperature was raised to 600 °C at 8 °C / min, then raised to 1000 °C at 5 °C / min and held for 5 h;

[0113] In S400, the single crystal cathode material and WO3 are mixed in a molar ratio of 1:0.0001, and then the temperature is raised to 600°C at a heating rate of 6°C / min in an air atmosphere, and kept at this temperature for 6 hours to obtain a coated single crystal cathode material.

[0114] Comparative Example 1

[0115] This embodiment provides a single crystal positive electrode material and a preparation method thereof, wherein the preparation method is similar to that of Example 1, except that step S100 is omitted. That is, an NM7525 precursor, LiOH·H2O, ZrO2, and WO6 are first mixed in a molar ratio of 1:1:0.001:0.001, and then the mixture and LiNO3 are added in a molar ratio of 1:0.05 to a 220°C constant temperature high-speed mixer and stirred at 2500 rpm for 80 minutes for pre-dissociation treatment to obtain a first dissociated product; then steps S300 and S400 of Example 1 are performed.

[0116] Comparative Example 2

[0117] This embodiment provides a single crystal positive electrode material and a preparation method thereof, wherein the preparation method is similar to that of Example 1, except that there is no step S200, i.e., no pre-dissociation process. A first oxide is obtained by step S100 of Example 1, and then the first oxide is heated to 550°C at a rate of 5°C / min in an oxygen atmosphere, and then heated to 880°C at a rate of 3°C / min and maintained for 8 hours, subjected to a sintering treatment, and dissociated by air flow milling to obtain a second oxide; and its D50 is controlled to be in the range of 2μm-6μm; and then step S400 of Example 1 is performed.

[0118] Cycling performance test: The above battery was cycled 400 times in the 3.0V-4.35V test window, 45°C, 1C charge and discharge conditions. The cycling performance of Examples 1-5 and Comparative Examples 1-2 at 3.0V-4.35V is shown in Figure 4.

[0119] Volume growth rate test: The volume of flatulence is calculated using the water displacement method. Place the battery with no flatulence in a water tank (with a recharging process, and the tabs must be well protected). Use an electronic density tester to measure the weight of the water displacement, and then convert the volume to obtain the volume expansion. The specific steps are as follows:

[0120] 1. Batteries were prepared using the positive electrode materials of the above examples and comparative examples. The fully charged batteries, with their tabs securely protected, were slowly placed in a 70°C water tank. After 30 seconds, the weight of the water drained from the tank was measured and divided by the medium density to obtain the initial battery volume (V0).

[0121] 2. After drying, place the battery in an insulated box and store it at 70°C for 7 days;

[0122] 3. Protect the battery tabs after high-temperature storage and slowly place them in a 70°C water tank. After waiting for 30 seconds, measure the weight of the water discharged from the tank and divide it by the medium density to obtain the battery volume V7. The volume growth rate after 7 days can be calculated by (V7-V0) / V0×100%;

[0123] 4. After drying the battery, fully charge it at 4.35V and store it in an insulated box at 70℃ for another 7 days;

[0124] 5. Repeat steps 3-4 to obtain the volume growth rate under high temperature storage for different days.

[0125] Fatigue phase ratio test: Disassemble the fully charged battery after cycling, scrape the powder off the positive electrode and send it for XRD testing (micro sample stage + internal standard method); then intercept the peak data, use peak separation software to separate and fit the peaks, and obtain the relative content of fatigue phase and active phase.

[0126] Single crystal cathode material parameter detection: Malvern 3000 equipment is used to detect the D min and D50; the particle size was measured once on the scanning electron microscope (SEM) image at 3K by software or manually to obtain the average single crystal size D, and the separation Z was obtained according to Z = D50 / D; the particle profile of the single crystal positive electrode material was linearly scanned using energy dispersive X-ray spectroscopy (EDS) to detect the thickness of the shell; the specific results can be seen in Table 2.

[0127] Detection of parameters related to intermediate products in the preparation process of single crystal cathode materials: X-ray photoelectron spectroscopy (XPS) technology was used to detect Ni 3+Peak area ratio, second oxide Ni 3+ Peak area ratio; the water content of the first dissociation product was detected using a coulometric moisture meter; the bulk density of the first oxide and the first dissociation product was detected using an FS4-2 Scott bulk density meter; the specific results can be seen in Table 3.

[0128] The data of rate performance, volume growth rate, and fatigue phase ratio of Examples 1-7 and Comparative Examples 1-2 are compared, as shown in Table 1:

[0129] Table 1

[0130] The parameters of the single crystal positive electrode materials of Examples 1-7 and Comparative Examples 1-2 are shown in Table 2:

[0131] Table 2

[0132] The parameters of the intermediate products in the preparation process of the single crystal positive electrode materials of Examples 1-7 and Comparative Examples 1-2 are shown in Table 3:

[0133] Table 3

[0134] By comparing Examples 1-7 with Comparative Examples 1-2, it can be seen that Example 2 has a better dehydration effect, but the higher temperature results in a smaller increase in the proportion of the transition layered structure phase, and the structural order in the final product is reduced; Example 3 extends the pre-firing holding time, which is beneficial to further increase the bulk density and promote phase generation; Example 4 appropriately adjusts the dissociation process parameters and can still achieve better performance parameters; Example 5 proves that the preparation method of the present application is also applicable to the preparation of other ternary single crystal system samples; Examples 6 and 7 prove that better performance parameters can still be obtained by using different process conditions within the scope specified by the present invention.

[0135] Compared with Example 1, Comparative Example 1 does not have a pre-sintering process, which proves that the pre-sintering process can increase the proportion of the layered structure of the lithium material, reduce the generation of impurity phases, and improve the subsequent doping and crushing effects.

[0136] Compared with Example 1, Comparative Example 2 does not have a pre-dissociation process, which proves that the pre-dissociation process is beneficial to improving the material doping effect, improving the subsequent crushing effect and the integrity of the single crystal particles, thereby improving the material performance.

[0137] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A single crystal positive electrode material, wherein: The single crystal positive electrode material comprises: A core layer, the core layer comprising an oxide composed of Li, Ni, and a doping element A; A shell layer, wherein the shell layer covers at least a portion of the surface of the core layer, and the shell layer comprises a compound composed of a coating element L; Wherein, the core layer is a LiTMO2 layered structure; The single crystal positive electrode material comprises a single primary particle; the average single crystal size D of the single crystal positive electrode material ranges from 1.3 μm to 3.0 μm; the D of the single crystal positive electrode material min >1.1μm; 1.0<D50 / D<2.0; after 400 cycles at a test voltage of 3.0-4.35V and 45°C, the fatigue impurity phase of the single crystal positive electrode material does not exceed 10%; The doping element A includes at least one of Zr, Al, W, Sr, Ti, Mg, Ca, Y, Nb, Mo, and Ce; and the coating element L includes at least one of Li, Al, Ti, Mg, W, and B.

2. The single crystal positive electrode material according to claim 1, wherein: The separation degree of the single crystal positive electrode material is 1.0<Z<1.3, and the separation degree is calculated by D50 / D.

3. The single crystal positive electrode material according to claim 1, wherein: The D50 particle size of the core layer ranges from 2 μm to 6 μm.

4. The single crystal positive electrode material according to claim 1 or 3, wherein: The thickness of the shell layer is 1nm-100nm.

5. A method for preparing a single crystal positive electrode material, wherein: The preparation method comprises the following steps: S100, mixing a precursor, a lithium salt and a dopant containing a doping element A, and performing a pre-sintering treatment to obtain a first oxide; S200, mixing the first oxide with a co-solvent and performing a pre-dissociation treatment to obtain a first dissociated product; S300, subjecting the first dissociated product to a sintering process and a dissociation process in sequence to obtain a second oxide; S400: mixing the second oxide with the coating agent containing the coating element L again, and performing a secondary sintering process to obtain a single crystal positive electrode material; Wherein, the pre-sintering process and the primary sintering process are both performed by two-stage sintering.

6. The preparation method according to claim 5, wherein: The first dissociation product XPS detected Ni 3+ The peak area accounts for 60%-85%.

7. The preparation method according to claim 5 or 6, wherein: The second oxide XPS detection Ni 3+ The peak area accounts for 80%-95%.

8. The preparation method according to claim 5, wherein The water content of the first dissociation product is less than 2%.

9. The preparation method according to claim 5 or 8, wherein: The bulk density of the first dissociated product is increased by 10%-30% compared with the first oxide.

10. The preparation method according to claim 5, wherein: In the S100 , the heating rate of a temperature zone of the pre-sintering is 3° C. / min-8° C. / min, the temperature is 130° C.-250° C., and the time is 2h-5h.

11. The preparation method according to claim 5 or 10, wherein: In the S100, the heating rate of the second temperature zone is 1°C / min-4°C / min, the temperature is 400°C-600°C, and the time is 5h-10h.

12. The preparation method according to claim 5, 10 or 11, wherein: In the S100 , the molar ratio of the precursor, the lithium salt and the dopant is 1:1:(0.001-0.01).

13. The preparation method according to claim 4, wherein: In the S200 , the temperature of the pre-dissociation treatment is 150° C.-300° C., and the time of the pre-dissociation treatment is 0.3 h-3.4 h.

14. The preparation method according to claim 5 or 13, wherein: In the S200: the molar ratio of the first oxide to the co-solvent is 1:(0.01-0.2).

15. The preparation method according to claim 5, wherein: In the S300 , the heating rate of a temperature zone in the primary sintering treatment is 4° C. / min-8° C. / min, and the temperature is 500° C.-600° C.

16. The preparation method according to claim 5 or 15, wherein: In the S300 , the heating rate of the second temperature zone is 2° C. / min-5° C. / min, the temperature is 600° C.-1000° C., and the time is 5h-10h.

17. The preparation method according to claim 5, wherein: In the S400, the secondary sintering treatment temperature is 300°C-600°C, the heating rate is 2°C / min-6°C / min, and the time is 6h-12h.

18. The preparation method according to claim 5 or 17, wherein: In the S400, the molar ratio of the second oxide to the coating agent is 1:(0.0001-0.01).

19. A lithium ion battery, characterized in that: It comprises the single crystal positive electrode material as described in any one of claims 1 to 4 or the single crystal positive electrode material prepared by the preparation method as described in any one of claims 5 to 18.

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