Preparation method of high-dispersity small-particle high-nickel single-crystal ternary positive electrode material and secondary battery

Abstract

The invention discloses a preparation method of a high-dispersity small-particle high-nickel single-crystal ternary positive electrode material and a secondary battery, and the preparation method comprises the following steps: mixing a high-nickel polycrystalline ternary positive electrode material of which the particle size of primary particles is in a range of 0.7-1.7 microns with a grain boundary expanding agent, and sintering to enable the grain boundary expanding agent to be diffused to the grain boundary among the primary particles to obtain the high-dispersity small-particle high-nickel single-crystal ternary positive electrode material, a coating material is obtained; and carrying out crushing treatment on the coating material by adopting an airflow crushing process to obtain the high-dispersity small-particle high-nickel single crystal ternary positive electrode material. According to the preparation method, the sintered and shaped high-nickel polycrystalline ternary positive electrode material base material is coated and sintered, the grain boundary expanding agent is diffused to the grain boundary of the primary particles, the combination of the primary particles is weakened, the primary particles are crushed under simple crushing conditions, and the high-dispersity small-particle high-nickel single crystal ternary positive electrode material is prepared.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of battery materials, in particular to a preparation method of high-dispersibility small-particle high-nickel single-crystal ternary positive electrode material and a secondary battery. BACKGROUND

[0002] The ternary positive electrode lithium ion battery has become the preferred technical route for current high-end electric vehicles, long-endurance consumer electronic products, electric tools, unmanned aerial vehicles and electric vertical take-off and landing aircraft (eVTOL) due to its extremely high energy density, excellent rate performance and good comprehensive performance, and further promotes the development of high energy density-high nickel ternary positive electrode material. Meanwhile, the high energy density battery has higher requirements for the tap density of the positive electrode material. The commonly used scheme is to adopt the form of large particles (particle size = 9-15 mu m) and small particles (1-3 mu m) doping, to take the large particles with high inherent tap density as the main body (accounting for 65%-90%), and to let the small particles fill in the gaps of the large particles, so as to maximize the tap density of the mixed positive electrode material and further improve the energy density of the lithium ion battery. Among them, the preparation of single-crystal small particles with good dispersibility has always been a big difficulty in the high tap density mixed material system.

[0003] In the industrialization of high-nickel ternary positive electrode material, the ternary positive electrode material is usually prepared by the process of co-precipitation precursor + solid phase sintering. In this process, the particle size of the single-crystal high-nickel ternary positive electrode material needs to be comprehensively considered in terms of precursor particle size, sintering temperature, and crushing process. In particular, if small-particle single-crystal ternary positive electrode material is prepared for high tap density mixed material, high requirements are put forward for the above three problems. For the conventional particle size of the precursor (D50 = 2-15 mu m), in order to prepare single-crystal ternary positive electrode material with particle size below D50 = 1.5 mu m and without agglomeration (good dispersibility), firstly, the sintering temperature needs to be controlled to make the precursor form agglomerated ternary positive electrode material with small primary particle size, and then the agglomerated ternary positive electrode material is broken by a high-pressure and high-classification air flow crushing system. The smaller the primary particle size of the ternary positive electrode material, the higher the degree of agglomeration, and the more difficult it is to break the agglomeration by the air flow crushing system. The conventional air flow crushing system is difficult to deal with the above problems, and the dispersibility of the small-particle single-crystal ternary positive electrode material is poor. The tap density and specific surface area of the agglomerated ternary positive electrode material are reduced, and it is difficult to release its capacity and rate performance, so it is difficult to achieve higher energy density. SUMMARY

[0004] The application aims to overcome the problems in the prior art and provide a preparation method of high-dispersibility small-particle high-nickel single-crystal ternary positive electrode material and a secondary battery.

[0005] The application solves the technical problems by adopting the following technical solutions.

[0006] The application provides a preparation method of a small-particle high-nickel single-crystal ternary positive electrode material with high dispersity, comprising the following steps: mixing a high-nickel polycrystal ternary positive electrode material with a particle size of primary particles in the range of 0.7-1.7 microns with a grain boundary expander, and then sintering to diffuse the grain boundary expander to the grain boundaries between the primary particles, so as to obtain a coating material; and performing a pulverizing treatment on the coating material by using a gas flow pulverizing process, so as to obtain the small-particle high-nickel single-crystal ternary positive electrode material with high dispersity.

[0007] The application provides a secondary battery comprising the small-particle high-nickel single-crystal ternary positive electrode material with high dispersity obtained by using the above preparation method, wherein the particle size of the small-particle single-crystal high-nickel ternary positive electrode material is 0.7-1.7 microns.

[0008] The application has the following beneficial effects: The application diffuses the grain boundary expander to the grain boundaries between the primary particles by coating and sintering the high-nickel polycrystal ternary positive electrode material with a particle size of primary particles in the range of 0.7-1.7 microns, weakens the combination between the primary particles, and then breaks the primary particles by using a simple pulverizing condition, so as to obtain the small-particle high-nickel single-crystal ternary positive electrode material with high dispersity. BRIEF DESCRIPTION OF DRAWINGS

[0009] In order to more clearly illustrate the technical solutions of the embodiments of the application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some of the embodiments of the application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor.

[0010] Figure 1 SEM images of the precursors used for Examples 1-3; Figure 2 SEM images of the products prepared in Example 1; Figure 3 SEM images of the products prepared in Example 2; Figure 4 SEM images of the products prepared in Example 3; Figure 5 SEM images of the products prepared in Comparative Example 1; Figure 6 SEM images of the products prepared in Comparative Example 2; Figure 7 SEM images of the products prepared in Comparative Example 3; Figure 8 SEM images of the products prepared in Comparative Example 4; Figure 9 SEM images of the products prepared in Comparative Example 5; Figure 10 Figure 1 shows the 45℃ charge-discharge cycle performance of the comparative examples and the example button cells. DETAILED DESCRIPTION

[0011] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below. If specific conditions are not specified in the embodiments, the conventional conditions or the conditions suggested by the manufacturers are adopted. If the manufacturers of the reagents or instruments are not specified, the conventional products that can be purchased in the market are adopted.

[0012] The preparation method of the high-dispersibility small-particle high-nickel single-crystal ternary positive electrode material and the secondary battery provided by the embodiments of the present application will be described in detail below.

[0013] In a first aspect, the present application provides a preparation method of a high-dispersibility small-particle high-nickel single-crystal ternary positive electrode material, which comprises the following steps: mixing a high-nickel polycrystal ternary positive electrode material with a particle size of primary particles in the range of 0.7-1.7 μm with a grain boundary expander, and sintering to diffuse the grain boundary expander to the grain boundaries between the primary particles to obtain a coating material; and performing a pulverization treatment on the coating material by using an airflow pulverization process to obtain a high-dispersibility small-particle high-nickel single-crystal ternary positive electrode material.

[0014] The existing high-nickel ternary positive electrode material structures are roughly divided into the following three types: large-particle polycrystal, medium-particle single crystal, and medium-particle polycrystal-single crystal. Among them: The large-particle polycrystal is a kind of material that is obtained by sintering a precursor at a slightly lower temperature, so that a small part of the grains in the precursor are grown together to form primary particles (particle size ≤0.4 μm) agglomerates. These primary particles agglomerate together to form secondary particles (particle size = 8-15 μm), which retain the spherical morphology of the precursor. Since it is formed by agglomeration of multiple primary particles, it has many obvious grain boundaries. Since the particle size of the primary particles is small and the number of grain boundaries is large, it is easier to release Li + , has higher capacity and rate performance. The retained spherical structure of the precursor makes it easy to accumulate, improves the tap density of the material, and can improve the energy density of the lithium ion battery. However, during the cycle process, the electrolyte is more likely to penetrate into the grain boundaries, causing cracks in the positive electrode material from the grain boundaries, which makes the cycle performance worse.

[0015] The middle particle single crystal material is formed by growing and fusing most of the crystal grains of the precursor into a larger single crystal ternary positive electrode material (particle size = 3-5 μm) through a higher sintering temperature. If there are single crystal particles adhered together, the adhesion between the particles can be opened by simple crushing. Because larger single crystal particles are formed, the material structure is stable, the number of grain boundaries is less, and therefore the cycle life is better. However, due to the longer lithium ion diffusion path caused by the larger single crystal particles, the capacity and rate performance are significantly lower than that of the polycrystalline material. At the same time, the single crystal material is not easy to accumulate due to its irregular shape, and its tap density is lower than that of the polycrystalline material, resulting in a slightly lower energy density of the lithium ion battery prepared.

[0016] The middle particle polycrystalline-single crystal material is formed by growing and fusing part of the crystal grains of the precursor into primary particles (particle size = 0.1-2.0 μm) through a moderate sintering temperature, and these primary particles are agglomerated to form secondary particles (particle size = 3.0-8.0 μm). The secondary particles still inherit the spherical morphology and particle size of the precursor. According to the size of the primary particle size, the smaller particle size is regarded as a polycrystalline material, and the larger primary particle size is regarded as a single crystal material. Because the primary particles of this material are grown and fused into one by the whiskers of the precursor itself, the crystal boundaries are tightly combined and difficult to separate by conventional crushing methods. Its electrochemical performance is similar to that of large particle polycrystalline, with good capacity and rate performance, but poor cycle performance. Commonly, the secondary particle size is controlled at 3.0 μm, and a mixed material is formed with the large particle polycrystalline material, which is filled into the interstitial space of the secondary particles of the large particle polycrystalline material to improve the tap density of the mixed material and the energy density of the battery.

[0017] It is found in practice that the high-nickel polycrystalline ternary positive electrode material with a primary particle size in the range of 0.7-1.7 μm has a weakly combined crystal boundary, and therefore the high-nickel polycrystalline ternary positive electrode material with the above particle size characteristics is mixed with a crystal boundary expander and then sintered, the crystal boundary expander is diffused to the crystal boundary between the primary particles by coating and sintering the sintered high-nickel polycrystalline ternary positive electrode material, the combination between the primary particles is weakened, and the primary particles can be broken by simple crushing.

[0018] In some optional embodiments, the crystal boundary expander is a polyanion salt, including one or more of phosphate, sulfate, silicate, borate, molybdate, and tungstate, more preferably, the crystal boundary expander is any one or more of Li3PO4, AlPO4, Li2SiO3, Li2WO4, Li3BO3, and AlBO3, and preferably the mixing speed of the high-nickel polycrystalline ternary positive electrode material and the crystal boundary expander is 600-1000 rpm, the mixing time is 30-60 min, and the mixing temperature is controlled to be not more than 50°C.

[0019] The application coats and sinter the high-nickel polycrystal ternary positive electrode material substrate by using Li3PO4, AlPO4, Li2SiO3, Li2WO4, Li3BO3, AlBO3 and other polyanion salt grain boundary extenders, diffuses the polyanion group to the grain boundary of the primary crystal grain through sintering. Due to the large ionic radius of the polyanion group, the sintering temperature is controlled, the polyanion group cannot diffuse into the crystal lattice of the high-nickel polycrystal ternary positive electrode material, and only exists at the grain boundary, thereby weakening the bonding effect between different primary particles.

[0020] In some optional embodiments, the addition amount of the grain boundary extender is 1000-10000 ppm, preferably 3000-5000 ppm.

[0021] In some optional embodiments, the sintering temperature is 300-500℃, the heating rate is 2-10℃ / min, the holding sintering time is 6-10h, and the sintering atmosphere is an oxygen atmosphere.

[0022] In some optional embodiments, the grinding gas pressure of the airflow crushing is 0.3-0.45MPa, and the frequency of the classification wheel is 40-140Hz.

[0023] In the application, the primary particles in the coated material with improved adhesion are dispersed by simple crushing conditions, the D50 of the high-nickel polycrystal ternary positive electrode material is significantly reduced, more grain boundaries are released, the specific surface area of the material as a whole is improved, the dispersity of the positive electrode material particles is improved, and the particle size distribution of the positive electrode material is improved. Thus, small-particle high-nickel single-crystal ternary positive electrode material with good dispersity and a particle size of 0.7-1.7μm is obtained.

[0024] In some optional embodiments, the preparation of the high-nickel polycrystal ternary positive electrode material with a particle size of the primary particles in the range of 0.7-1.7μm includes the following steps: mixing a precursor with a median particle size of 2-8μm and a lithium source, and then sintering at a low temperature in an oxygen atmosphere.

[0025] In some optional embodiments, the composition of the precursor is Ni x Co y Mn 1-x-y (OH)2, wherein 0.85≤x≤0.97, 0.02≤y<0.08, the median particle size of the precursor is 2-8μm, preferably 2-4μm; the lithium source includes at least one of lithium carbonate, lithium hydroxide, lithium acetate, lithium nitrate, and lithium dihydrogen phosphate; preferably, the mixing speed of the precursor and the lithium source is 200-900rpm, the mixing time is 30-60min, and the mixing temperature is controlled to be not more than 50℃.

[0026] In some alternative embodiments, the lithium source and the transition metal in the precursor have a molar ratio Li / Me of 0.7-1.03, preferably 0.8-1.01.

[0027] In some alternative embodiments, the sintering temperature is 700-830℃, the heating rate is 2-10℃ / min, the holding time is 6-10h, and the sintering atmosphere is oxygen atmosphere.

[0028] The present application controls the particle size of the primary particles by controlling the sintering temperature. The particle size of the primary particles is in the range of 0.7-1.7μm, between the particle size of the polycrystalline material (≤0.4μm) and the particle size of the single-crystal material (3-5μm) by using a lower sintering temperature.

[0029] In the second aspect, the present application provides a secondary battery comprising the high-dispersibility small-particle high-nickel single-crystal ternary positive electrode material prepared by the preparation method described above, wherein the particle size of the high-dispersibility small-particle single-crystal high-nickel ternary positive electrode material is 0.7-1.7μm.

[0030] The high-dispersibility small-particle single-crystal high-nickel ternary positive electrode material has better capacity, rate performance than the medium-particle single-crystal material and the medium-particle polycrystalline-single-crystal material, and has better cycle performance than the polycrystalline material, and has better comprehensive performance. The high-dispersibility small-particle single-crystal high-nickel ternary positive electrode material has better comprehensive performance than the medium-particle single-crystal material and the medium-particle polycrystalline-single-crystal material, and is more suitable for being mixed with the large-particle polycrystalline material to form a mixed material system, thereby improving the capacity, rate, and cycle performance of the mixed material.

[0031] The present application will be further described below with reference to the examples.

[0032] Example 1 Step 1, ternary precursor A and lithium source B were weighed according to the molar ratio, mixed by using a high-speed mixer, the rotation speed was 600rpm, the mixing time was 30min, and the mixing temperature was controlled to be 20-35℃, to obtain a uniform mixture C; the ternary precursor was Ni x Co y Mn 1-x-y (OH)2, wherein x=0.92, y=0.06, the value particle size was 3μm, and the SEM image was shown in Figure 1 ; the molar ratio Li / Me of the lithium source and the transition metal in the ternary precursor was 1.00; the lithium source was lithium hydroxide; Step 2, the mixture C in step 1 is loaded into a crucible and put into a box furnace, heated to 740℃ at a rate of 3℃ / min in an oxygen atmosphere, and heat treated for 6h. Then cooled, dispersed by a high-speed mixer, to obtain the high-nickel polycrystalline ternary positive electrode material base D, the particle size of the primary particles is 1.0μm; Step 3, AlPO4 powder (grain boundary expander E) accounting for 3000ppm of the mass of the high-nickel polycrystalline ternary positive electrode material base D is added to the high-nickel polycrystalline ternary positive electrode material D prepared in step 2, mixed using a high-speed mixer at a speed of 900rpm for 45min, and the mixing temperature is 20-35℃, to obtain a uniform mixture F.

[0033] Step 4. The mixture F in step 3 is loaded into a crucible and put into a box furnace, heated to 450℃ at a rate of 3℃ / min in an oxygen atmosphere, and sintered for 8h. Then cooled, dispersed by a high-speed mixer, to obtain the coated material G.

[0034] Step 5. The coated material G in step 4 is crushed by a jet mill, using common jet milling parameters, the grinding gas pressure is 0.40MPa, and the classification wheel frequency is 90Hz, to obtain the finished high-dispersibility small-particle high-nickel single-crystal ternary positive electrode material.

[0035] Figure 2 The SEM image of the high-dispersibility small-particle high-nickel single-crystal ternary positive electrode material prepared for Example 1 can be seen: the average size of the sample particles is about 1.0μm.

[0036] Example 2 The high-nickel single-crystal ternary positive electrode material is prepared according to the same operating conditions and steps as in Example 1, except that the sintering temperature in step 2 is 760℃, to obtain the high-nickel polycrystalline ternary positive electrode material base D, the particle size of the primary particles is 1.5μm.

[0037] Figure 3 The SEM image of the high-dispersibility small-particle high-nickel single-crystal ternary positive electrode material prepared for Example 2 can be seen: the average size of the sample particles is about 1.5μm.

[0038] Example 3 The high-nickel single-crystal ternary positive electrode material is prepared according to the same operating conditions and steps as in Example 1, except that the grain boundary expander E in step 3 is Li2WO4.

[0039] Figure 4 The SEM image of the high-dispersibility small-particle high-nickel single-crystal ternary positive electrode material prepared for Example 3 can be seen: the average size of the sample particles is about 1.0μm.

[0040] Comparative Example 1 The large-particle polycrystal high-nickel ternary positive electrode material can be prepared by the following method, using the ternary precursor as Ni x Co y Mn 1-x-y (OH)2, wherein x = 0.92, y = 0.06, wherein the value particle size is 10 μm, mixed with lithium salt and loaded into a sagger, sintered at 710°C for 6h under oxygen atmosphere, to obtain the large-particle polycrystal high-nickel ternary positive electrode material.

[0041] Figure 5 The SEM graph of the large-particle polycrystal high-nickel ternary positive electrode material prepared for Comparative Example 1 can be seen that: the average size of the primary particles of the sample is about 0.3 μm, and the secondary particle size is about 10.0 μm.

[0042] Comparative Example 2 The medium-particle single-crystal high-nickel ternary positive electrode material can be prepared by the following method, using the ternary precursor as in the example, mixed with lithium salt and loaded into a sagger, sintered at 850°C for 6h under oxygen atmosphere, and then obtained by airflow crushing to obtain the medium-particle single-crystal high-nickel ternary positive electrode material.

[0043] Figure 6 The SEM graph of the medium-particle single-crystal high-nickel ternary positive electrode material prepared for Comparative Example 2 can be seen that: the average size of the sample particles is about 2.8 μm.

[0044] Comparative Example 3 The medium-particle single-crystal high-nickel ternary positive electrode material can be prepared by the following method, using the ternary precursor as in the example, mixed with lithium salt and loaded into a sagger, sintered at 770°C for 6h under oxygen atmosphere, and then obtained by airflow crushing to obtain the medium-particle single-crystal high-nickel ternary positive electrode material.

[0045] Figure 7 The SEM graph of the medium-particle single-crystal high-nickel ternary positive electrode material prepared for Comparative Example 3 can be seen that: the average size of the sample particles is about 2.8 μm.

[0046] Comparative Example 4 The medium-particle polycrystal high-nickel ternary positive electrode material can be prepared by the following method, using the ternary precursor as in the example, mixed with lithium salt and loaded into a sagger, sintered at 680°C for 6h under oxygen atmosphere, and then obtained by airflow crushing to obtain the medium-particle polycrystal high-nickel ternary positive electrode material.

[0047] Figure 8 The SEM graph of the medium-particle polycrystal high-nickel ternary positive electrode material prepared for Comparative Example 4 can be seen that: the average size of the sample particles is about 2.8 μm.

[0048] Comparative Example 5 Similar to the steps of Example 1, the only difference is that the sintering temperature in step 2 is 760°C, and the grain boundary expansion agent E in step 3 is replaced by the commonly used metal oxide coating agent Al2O3. The obtained material is a high-nickel ternary positive electrode material with a mesoparticle-like single crystal morphology.

[0049] Figure 9 The SEM image of the high-nickel ternary positive electrode material with a mesoparticle-like single crystal morphology prepared for Comparative Example 5 shows that the primary particle median size of the sample is about 1.5 μm, and the secondary particle median size is about 2.8 μm.

[0050] Comparative Example 6 Similar to the steps of Example 1, the only difference is that the sintering temperature in step 2 is 800°C. A single crystal ternary positive electrode material with a median particle size of 2.1 μm can be obtained.

[0051] Comparative Example 7 Similar to the steps of Example 1, the only difference is that the sintering temperature in step 2 is 680°C. The obtained material is a small-particle polycrystalline ternary positive electrode material with a primary particle median size of 0.4 μm and a secondary particle median size of about 2.8 μm.

[0052] Comparative Example 8 Similar to the steps of Example 1, the only difference is that the amount of grain boundary expansion agent in step 3 is 1000 ppm.

[0053] Comparative Example 9 Similar to the steps of Example 1, the only difference is that the amount of grain boundary expansion agent in step 3 is 10000 ppm.

[0054] Electrochemical performance test The high-nickel single crystal ternary positive electrode materials obtained in Examples 1-3 and Comparative Examples 1-9 were used as battery positive electrode materials to make button cells for electrochemical performance testing. The production method is as follows: a. The high-nickel single crystal positive electrode materials prepared in the examples and comparative examples were stirred to form a uniform dispersion of positive electrode slurry according to the ratio of positive electrode material powder: conductive agent (SP): adhesive (PVDF) = 90:5:5, and the slurry was coated, punched, and vacuum dried; lithium metal sheet was used as the negative electrode material of the counter electrode, and a microporous polypropylene film was used as the battery separator; 1:1 ethylene carbonate (EC) / dimethyl carbonate (DMC) solvent, 1 mol / L LiPF6 as electrolyte, assembled into 2025 type button cells in a glove box filled with dry high-purity argon and left for 8 h; b. The prepared button cell was charged and discharged at 0.2C rate current at ambient temperature 25℃, 2.5-4.25V, and the electrochemical performance of Examples 1-3 and Comparative Examples 1-9 was tested. The first discharge efficiency was calculated, i.e., first efficiency = first discharge specific capacity / first charge specific capacity*100%.

[0055] c. The cycle performance of Examples 1-3 and Comparative Examples 1-5 was tested at 1C charge / 1C discharge at 45℃, 2.5-4.25V, and the capacity retention rate after 50 cycles was calculated, according to the formula: capacity retention rate = 50th discharge specific capacity / first discharge specific capacity*100%.

[0056] The test data is shown in Table 1.

[0057] Table 1. Electrical performance test results

[0058] Table 2. Physicochemical performance test results

[0059] Referring again to the results of Tables 1 and 2 above and Figure 10 It can be seen that, compared with the commonly used large-particle polycrystal high-nickel ternary positive electrode material, medium-particle single-crystal high-nickel ternary positive electrode material, medium-particle single-crystal-like high-nickel ternary positive electrode material and medium-particle polycrystal high-nickel ternary positive electrode material (see Comparative Examples 1-4), the small-particle high-nickel single-crystal ternary positive electrode material prepared by the scheme provided in the embodiments of the present application can have both capacity and cycle performance. Specifically: In Comparative Example 1, a large-particle polycrystal high-nickel ternary positive electrode material was prepared, which had a low sintering temperature and small primary particle size. The secondary particle morphology retained the morphology of the precursor, and the primary particles were combined together by whiskers in the precursor to form a secondary particle ball, and the combination between different primary particles was still very tight. At the same time, there were many primary particles in a secondary particle ball, and even after sintering and crushing, only the surface part of the primary particles could be crushed and fallen off, and a single-crystal small-particle material with good dispersity could not be obtained.

[0060] In Comparative Example 2, a single-crystal high-nickel ternary positive electrode material was prepared, which had a high sintering temperature, so that almost all the whiskers in the precursor were grown and fused together to form a single-crystal particle of the ternary positive electrode material, and the single-crystal particle of the ternary positive electrode material basically retained the size of the precursor particle. The single crystal with large size had small crystal faces and long lithium ion diffusion path, but the structure was stable, so it had the characteristics of low capacity and high cycle.

[0061] Comparative Example 3 is prepared by middle particle single crystal high nickel ternary positive electrode material, compared with Comparative Example 2, the sintering temperature is reduced, so that the size of the primary particle is slightly smaller, and several single crystal particles (primary particles) are contained in one precursor particle. Since no grain boundary expander is used for coating sintering, the combination between the primary particles is still relatively tight, and after crushing, there is still a case of several primary particles sticking together. There are many primary particle grain boundaries that have not been released, and the capacity is significantly lower than the examples. And the electrolyte penetrates along the grain boundary during the cycle, and the difference from the initial state is large, and the cycle performance is slightly lower than the examples.

[0062] Comparative Example 4 is prepared by middle particle polycrystalline high nickel ternary positive electrode material, which is similar to Comparative Example 1, except that the size of the precursor particle is smaller, so the size of the secondary particle formed is smaller. It also has similar capacity and cycle performance to Comparative Example 1. Due to the same sintering temperature, the size of the primary particle is slightly larger, and the capacity is slightly smaller than Comparative Example 1; because the number of primary particles in a single secondary particle is less than Comparative Example 1, the electrolyte is more likely to penetrate into the interior of the secondary particle during the cycle, and the cycle performance is worse than Comparative Example 1.

[0063] Again, referring to the results of Tables 1 and 2 above and Figure 10 It can be seen that: compared with Comparative Examples 1 and 4, the high-temperature cycle stability of the small particle high nickel single crystal ternary positive electrode material prepared by the method of each example is significantly improved. Compared with Comparative Examples 3 and 5, the small particle high nickel single crystal ternary positive electrode material prepared by each example of the present application controls the opening of the grain boundaries between the primary grains, releases more interfaces, effectively improves the capacity and rate performance of the ternary positive electrode material, and at the same time ensures that its cycle performance does not deteriorate obviously. Compared with Comparative Example 2, it can be found that by controlling the particle size of the single crystal in a smaller range (0.7-1.7 μm), the capacity and rate performance can be greatly improved while ensuring a certain high-temperature cycle performance.

[0064] Compared with Example 1, the sintering temperature of Comparative Example 6 is increased, the crystal grains grow further, the grain size increases, the specific surface area decreases, the capacity decreases, and the cycle increases. Compared with Example 1, the sintering temperature of Comparative Example 7 is decreased, the primary particle size is small, even if the coating sintering of the grain boundary expansion agent is performed, the crystal grain between the primary particles cannot be completely opened after crushing, so that the capacity is not released, and the cycle performance is obviously reduced. Compared with Example 1, the amount of the grain boundary expansion agent in Comparative Example 8 is significantly reduced, the combination between the primary particles is not significantly reduced, the primary particles cannot be crushed by crushing, and the morphology of the single crystal is still maintained, the crystal grain is not released, so that the capacity is lower than that of Example 1. In the cycle process, the electrolyte slowly penetrates into the crystal grain, which also leads to the reduction of the cycle performance. Compared with Example 1, the amount of the grain boundary expansion agent in Comparative Example 9 is too high, the surface of the primary particles is covered with too much grain boundary expansion agent, which hinders the diffusion of lithium ions on the surface of the ternary positive electrode material particles, and the capacity decreases. However, the grain boundary expansion agent has the effect of protecting the interface, which slightly improves the cycle performance of the material.

[0065] The above comparison shows that the small-particle high-nickel single-crystal ternary positive electrode material prepared in each embodiment of the present application has excellent comprehensive electrochemical performance.

[0066] The above only describes the preferred embodiments of the present application and is not used to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A method for preparing a highly dispersed, small-particle, high-nickel single-crystal ternary cathode material, characterized in that, The process includes the following steps: mixing high-nickel polycrystalline ternary cathode material with a primary particle size in the range of 0.7-1.7μm with a grain boundary expander and then sintering the mixture to allow the grain boundary expander to diffuse to the grain boundaries between the primary particles, thereby obtaining a coating material; The coating material is pulverized using an airflow pulverization process to obtain a highly dispersed, small-particle, high-nickel single-crystal ternary cathode material.

2. The preparation method according to claim 1, characterized in that, The grain boundary expander is a polyanionic salt, including one or more of phosphates, sulfates, silicates, borates, molybdates, and tungstates. More preferably, the grain boundary expander is any one or more of Li3PO4, AlPO4, Li2SiO3, Li2WO4, Li3BO3, and AlBO3. Preferably, the mixing speed of the high-nickel polycrystalline ternary cathode material and the grain boundary expander is 600-1000 rpm, the mixing time is 30-60 min, and the mixing temperature is controlled not to exceed 50°C.

3. The preparation method according to claim 1, characterized in that, The amount of the grain boundary expander added is 1000-10000ppm, preferably 3000-5000ppm.

4. The preparation method according to claim 1, characterized in that, The sintering temperature is 300-500℃, the heating rate is 2-10℃ / min, the holding time is 6-10h, and the sintering atmosphere is an oxygen atmosphere.

5. The preparation method according to claim 1, characterized in that, The grinding air pressure of the air jet mill is 0.3-0.45MPa, and the classifier wheel frequency is 40-140Hz.

6. The preparation method according to claim 1, characterized in that, The preparation of the high-nickel polycrystalline ternary cathode material with a primary particle size in the range of 0.7-1.7 μm includes the following steps: The precursor with a median particle size of 2-8 μm and the lithium source were mixed and then sintered at low temperature in an oxygen atmosphere.

7. The preparation method according to claim 6, characterized in that, The precursor is composed of Ni x Co y Mn 1-x-y (OH)2, wherein 0.85≤x≤0.97, 0.02≤y<0.08, the median particle size of the precursor is 2-8μm, preferably 2-4μm; the lithium source includes at least one of lithium carbonate, lithium hydroxide, lithium acetate, lithium nitrate, and lithium dihydrogen phosphate; preferably, the mixing speed of the precursor and the lithium source is 200-900rpm, the mixing time is 30-60min, and the mixing temperature is controlled not to exceed 50℃.

8. The preparation method according to claim 7, characterized in that, The molar ratio of the lithium source to the transition metal in the precursor, Li / Me, is 0.7-1.03, preferably 0.8-1.

01.

9. The preparation method according to claim 6, characterized in that, The low-temperature sintering temperature is 700-830℃, the heating rate is 2-10℃ / min, the holding time is 6-10h, and the sintering atmosphere is an oxygen atmosphere.

10. A secondary battery, characterized in that, The invention includes a highly dispersed small-particle high-nickel single-crystal ternary cathode material prepared by the preparation method according to any one of claims 1-9, wherein the particle size of the highly dispersed small-particle high-nickel single-crystal ternary cathode material is 0.7-1.7 μm.

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