High-nickel positive electrode material, preparation method thereof, positive electrode and lithium ion battery

Abstract

The present application provides a tungsten-doped high-nickel positive electrode material, which is a spherical or quasi-spherical secondary particle formed by stacking thin flake-like primary particles, the thickness of the thin flake-like primary particles is 50-300 nm, there are gaps between the primary particles, and the size of the gaps is 40-200 nm; the high-nickel positive electrode material has excellent thermal stability, structural stability, high compaction density and good lithium ion diffusion rate, thereby ensuring that the battery has excellent energy density, cycle performance, rate performance and improved service life. The present application also provides a preparation method of the tungsten-doped high-nickel positive electrode material, a high-nickel precursor with a specific morphology is prepared by a coprecipitation method, and the high-nickel precursor is mixed with a lithium source and a certain amount of tungsten source for sintering, so that the morphology of the precursor can be better inherited, and a spherical or quasi-spherical secondary particle positive electrode material formed by stacking thin flake-like primary particles with a certain size according to a certain gap is obtained.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery cathode material technology, specifically relating to high-nickel cathode materials and their preparation methods. Background Technology

[0002] Currently, lithium-ion batteries are widely used in portable electronic products, electric vehicles, energy storage, and many other fields related to renewable energy. However, with increasing demands for the driving range of electric vehicles, more stringent requirements are being placed on the energy density, rate performance, and cycle performance of lithium-ion batteries. Compared to traditional layered oxides (LiCoO2) and perovskite compounds (LiFePO4), high-nickel cathode materials offer higher energy density and lower cost, and can achieve higher capacity by increasing the nickel content, thus dominating the market.

[0003] However, the main problems with high-nickel cathode materials are: (1) Under high-rate conditions, the intergranular crack problem of high-nickel ternary materials will become more prominent, which will cause the secondary particles of the material to break and pulverize, not only exposing the fresh material surface and aggravating the side reactions at the cathode / electrolyte interface, but also the "island" particles generated cannot participate in the redox reaction, ultimately leading to the deterioration of the overall performance of high-nickel ternary materials. (2) During the cycle of the battery, the phenomenon of transition metal ion dissolution will occur, thereby increasing the interfacial impedance of the cathode material and causing problems such as thermal runaway of high-nickel cathode materials.

[0004] Currently, the mainstream modification methods for high-nickel cathode materials are reducing grain size, doping, and coating. Inhomogeneous doping and coating can have negative effects, and current mainstream methods cannot ensure that high-nickel cathode materials maintain high capacity at high rates. Reducing grain size often leads to a decrease in compaction density, which is detrimental to practical applications. Existing modification methods struggle to balance the compaction density, high-rate performance, structural stability, and thermal stability of high-nickel cathode materials. There is an urgent need to develop a high-rate performance, high-compaction high-nickel cathode material. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a high-nickel cathode material, its preparation method, a cathode, and a lithium-ion battery.

[0006] To achieve the above objectives, the present invention proposes the following technical solution: In a first aspect, a high-nickel cathode material is provided, wherein the high-nickel cathode material is a spherical or near-spherical secondary particle formed by stacking thin sheet-like primary particles, wherein the thickness of the thin sheet-like primary particles is 50~300nm, and there are gaps between the primary particles, wherein the size of the gaps is 40~200nm, wherein the size of the gaps is the maximum distance between adjacent thin sheet-like primary particles; the high-nickel cathode material is doped with tungsten.

[0007] Furthermore, the high-nickel cathode material satisfies at least one of the following conditions (a) to (f): (a) The tungsten doping amount in the high-nickel cathode material is 0.7~2wt%; (b) The chemical formula of the high-nickel cathode material is Li(Ni) x Co y Mn 1-x-y ) 1-z W z O2, where 0.8≤x≤0.95, 0≤y≤0.2, 0≤1-xy≤0.2, and 0.007≤z≤0.02; (c) The particle size D50 of the secondary particles is 8~10μm; (d) The diameter of the secondary particles is 0.6~0.8; (e) The compaction density of the high-nickel cathode material is 3.15~3.25 g / cm³. 3 ; (f) The specific surface area of ​​the high-nickel cathode material is 0.4~0.6 m². 2 / g.

[0008] Secondly, it provides methods for preparing high-nickel cathode materials, including: S1. A mixed metal salt solution A and a mixed solution B of precipitant and complexing agent are introduced concurrently into the bottom liquid of the reactor. A co-precipitation reaction is carried out under a protective atmosphere. During the reaction, the pH value is controlled at 10.3~11.7. When the precursor particle size D50 reaches the target particle size and target pitch, the precursor slurry is obtained. S2. Filter, wash and dry the precursor slurry to obtain the precursor; S3. The precursor is mixed with lithium source and WO3, and then sintered at high temperature to obtain high nickel cathode material; the amount of WO3 is 1.0~2.5wt% of the precursor mass.

[0009] Furthermore, the total metal element concentration in the mixed metal salt solution A is 1.5~2 mol / L.

[0010] Furthermore, the mixed metal salt solution A includes nickel salt, manganese salt and cobalt salt; and the molar ratio of nickel, cobalt and manganese in the mixed metal salt is x:y:1-xy, where 0.8≤x≤0.95, 0≤y≤0.2, and 0≤1-xy≤0.2.

[0011] Furthermore, in the mixed solution B, the molar ratio of the precipitant to the complexing agent is (4~13):1; Furthermore, in the mixed solution B, the concentration of the precipitant is 2~10 mol / L.

[0012] Furthermore, the complexing agent is ammonia.

[0013] Furthermore, the precipitant is sodium hydroxide.

[0014] Furthermore, in step S1, the temperature of the coprecipitation reaction is 45~65℃.

[0015] Furthermore, in step S1, the stirring speed of the coprecipitation reaction is 300~700 rpm.

[0016] Furthermore, the bottom liquid of the reaction vessel is an ammonia solution; the concentration of the ammonia solution is 0.5~2 mol / L.

[0017] Furthermore, the temperature of the bottom liquid in the reaction vessel is 45~65℃.

[0018] Furthermore, the volume of the bottom liquid in the reactor is 10-30% of the reactor volume.

[0019] Furthermore, the target particle size D50 is 8~10μm.

[0020] Furthermore, the target axial distance is 0.6 to 0.8.

[0021] Furthermore, the molar ratio of the precursor to lithium in the lithium source is 1:1.02~1.1.

[0022] Furthermore, the lithium source is one or more of lithium hydroxide, lithium carbonate, lithium acetate, and lithium nitrate.

[0023] Further, in step S3, the high-temperature solid-state sintering is a two-stage sintering; the two-stage sintering includes: first heating to 450~500℃ and holding for 5~8h, and then continuing to heat to 700~800℃ and holding for 12~30h.

[0024] Furthermore, the heating rate of the two sintering stages is 2~5℃ / min; furthermore, the sintering atmosphere is a pure oxygen atmosphere.

[0025] Thirdly, a positive electrode is provided, including the aforementioned high-nickel positive electrode material or the high-nickel positive electrode material prepared by the aforementioned preparation method.

[0026] Fourthly, lithium-ion batteries are provided, including the aforementioned positive electrode.

[0027] Compared with the prior art, one or more of the above technical solutions can achieve at least one of the following beneficial effects: A tungsten-doped high-nickel cathode material is provided. This high-nickel cathode material consists of spherical or near-spherical secondary particles formed by stacking thin-film primary particles. The thickness of the thin-film primary particles is 50-300 nm, and there are gaps between the primary particles with a size of 40-200 nm, wherein the size of the gap is the maximum distance between adjacent thin-film primary particles. This high-nickel cathode material has excellent thermal stability, structural stability, high compaction density, and good lithium-ion diffusion rate, thereby ensuring that the battery has excellent energy density, cycle performance, rate performance, and improved lifespan.

[0028] A method for preparing high-nickel cathode materials is provided. A high-nickel precursor with a specific morphology is prepared by co-precipitation. The high-nickel precursor is then mixed with a lithium source and a certain amount of tungsten source and sintered. This method can better inherit the morphology of the precursor and obtain high-nickel cathode materials with spherical or near-spherical secondary particles formed by stacking thin sheet-like primary particles of a certain size with certain gaps. This preparation method has the advantages of strong process controllability, simple operation, and easy industrialization. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 The image shows a SEM image of the high-nickel cathode material precursor prepared in Example 1.

[0031] Figure 2 SEM images of the high-nickel cathode material prepared in Example 1 at different magnifications.

[0032] Figure 3 The image shows the EDS diagram of the high-nickel cathode material prepared in Example 1.

[0033] Figure 4 The figures show the rate performance and cycle performance of the battery assembled with the high-nickel cathode material prepared in Example 1, where (a) is the rate performance at different rates and (b) is the cycle performance.

[0034] Figure 5 The images are SEM images of the high-nickel cathode materials prepared in Examples 2-4, where (a) corresponds to Example 2, (b) corresponds to Example 3, and (c) corresponds to Example 4.

[0035] Figure 6SEM images of the high-nickel cathode materials prepared in Comparative Examples 1-3, where (a) corresponds to Comparative Example 1, (b) corresponds to Comparative Example 2, and (c) corresponds to Comparative Example 3.

[0036] Figure 7 SEM images of the high-nickel cathode material and its precursor prepared in Example 5, where (a) corresponds to the precursor and (b) corresponds to the high-nickel cathode material.

[0037] Figure 8 The images shown are SEM images of the high-nickel cathode material and its precursor prepared in Example 6, where (a) corresponds to the precursor and (b) corresponds to the high-nickel cathode material.

[0038] Figure 9 SEM images of the high-nickel cathode material and its precursor prepared in Comparative Example 4 are shown, where (a) corresponds to the precursor and (b) corresponds to the high-nickel cathode material.

[0039] Figure 10 SEM images of the high-nickel cathode material and its precursor prepared in Comparative Example 5 are shown, where (a) corresponds to the precursor and (b) corresponds to the high-nickel cathode material.

[0040] Figure 11 SEM images of the high-nickel cathode material and its precursor prepared in Comparative Example 6 are shown, where (a) corresponds to the precursor and (b) corresponds to the high-nickel cathode material.

[0041] Figure 12 The images shown are SEM images of the high-nickel cathode material and its precursor prepared in Example 7, where (a) corresponds to the precursor and (b) corresponds to the high-nickel cathode material.

[0042] Figure 13 SEM images of the high-nickel cathode material and its precursor prepared in Example 8, where (a) corresponds to the precursor and (b) corresponds to the high-nickel cathode material. Detailed Implementation

[0043] Through research, the inventors have discovered that a high-nickel cathode material with a spherical or near-spherical secondary particle morphology formed by stacking thin-film primary particles, with certain gaps between the primary particles, and doped with an appropriate amount of tungsten, possesses both good rate performance, thermal stability, and discharge specific capacity.

[0044] Specifically, the present invention provides a thermodynamically stable high-rate, high-nickel cathode material, wherein the high-nickel cathode material is a spherical or near-spherical secondary particle formed by stacking thin sheet-like primary particles, wherein the thickness of the thin sheet-like primary particles is 50~300nm, and there are gaps between the primary particles, wherein the size of the gaps is 40~200nm, wherein the size of the gaps is the maximum distance between adjacent thin sheet-like primary particles; the high-nickel cathode material is doped with tungsten.

[0045] This invention starts with a precursor for high-nickel cathode materials, preparing a precursor with a thin, sheet-like primary particle morphology and certain gaps between the primary particles. During the preparation of the cathode material, an appropriate amount of tungsten doping is applied, allowing the cathode material to better inherit the morphological characteristics of the precursor, resulting in a high-nickel cathode material (50-300 nm) with extremely thin sheet-like primary particles (primary nanosheets). Typically, larger secondary particle sizes in cathode materials can increase the compaction density, but their rate performance is poor. However, the cathode material prepared by this invention, due to the gaps between the primary nanosheets, significantly shortens the lithium-ion diffusion path, increasing the lithium-ion diffusion rate in the bulk phase. This ensures both high compaction density and superior rate performance. Furthermore, the presence of tungsten (W) in the crystal lattice forms stronger WO2 chemical bonds with oxygen, increasing the thermal runaway temperature of the cathode material and giving it excellent thermal stability. Therefore, a high-nickel cathode material with high compaction density, excellent thermal stability, superior cycle stability, and high rate performance is obtained.

[0046] In some preferred embodiments, the high-nickel cathode material satisfies at least one of the following conditions (a) to (f): (a) The tungsten doping amount in the high-nickel cathode material is 0.7~2wt%; (b) The chemical formula of the high-nickel cathode material is Li(Ni) x Co y Mn 1-x-y ) 1-z W z O2, where 0.8≤x≤0.95, 0≤y≤0.2, 0≤1-xy≤0.2, and 0.007≤z≤0.02; (c) The particle size D50 of the secondary particles is 8~10μm, such as 8μm, 8.5μm, 9μm, 9.5μm, 10μm, etc. The large secondary particle size of the high nickel cathode material ensures that the material has a high compaction density and still has excellent rate performance. (d) The diameter of the secondary particles is 0.6~0.8, for example 0.6, 0.62, 0.65, 0.68, 0.7, 0.72, 0.75, 0.78, 0.8, etc.; (e) The compaction density of the high-nickel cathode material is 3.15~3.25 g / cm³. 3 ; (f) The specific surface area of ​​the high-nickel cathode material is 0.4~0.6 m². 2 / g.

[0047] This invention also provides a method for preparing a high-nickel cathode material, comprising: S1. A mixed metal salt solution A and a mixed solution B of precipitant and complexing agent are introduced concurrently into the bottom liquid of the reactor. A co-precipitation reaction is carried out under a protective atmosphere. During the reaction, the pH value is controlled at 10.3~11.7. When the precursor particle size D50 reaches the target particle size and target pitch, the precursor slurry is obtained. S2. Filter, wash and dry the precursor slurry to obtain the precursor; S3. The precursor is mixed with lithium source and WO3, and then sintered at high temperature to obtain high nickel cathode material; the amount of WO3 is 1.0~2.5wt% of the precursor mass, for example 1.0wt%, 1.2wt%, 1.5wt%, 1.8wt%, 2.0wt%, 2.2wt%, 2.5wt%, etc.

[0048] In the above preparation method, a high-nickel precursor with extremely thin primary nanosheets is first prepared. This high-nickel cathode material precursor has a morphology of spherical or near-spherical secondary particles formed by stacking thin-sheet primary particles, with certain gaps between the primary particles. The thickness of the thin-sheet primary particles is 10-50 nm, and the size of the gaps is 20-150 nm. In some embodiments, the high-nickel cathode material precursor is a hydroxide precursor.

[0049] The addition of WO3 slows down atomic migration, allowing the sintered cathode material to still possess an extremely thin primary nanosheet structure (50~300nm). Furthermore, as the WO3 content increases, the nanosheet thickness decreases, and the gaps between primary particles can significantly shorten the lithium-ion diffusion path, increase the lithium-ion diffusion rate in the bulk phase of the material, thereby improving the rate performance and structural stability of the material.

[0050] In some preferred embodiments, the total metal element concentration in the mixed metal salt solution A is 1.5~2 mol / L.

[0051] In some preferred embodiments, the mixed metal salt solution A includes nickel salt, manganese salt and cobalt salt; and the molar ratio of nickel, cobalt and manganese in the mixed metal salt is x:y:1-xy, where 0.8≤x≤0.95, 0≤y≤0.2, and 0≤1-xy≤0.2. In some preferred embodiments, in step S1, the pH value is controlled to be 10.5~11.5 during the reaction process, such as 10.5, 10.8, 11.0, 11.2, 11.5, etc. In some preferred embodiments, the molar ratio of the precipitant to the complexing agent in the mixed solution B is 4 to 13:1, for example, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, etc.

[0052] In some preferred embodiments, the concentration of the precipitant in the mixed solution B is 2~10 mol / L, for example, 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L, 6 mol / L, 7 mol / L, 8 mol / L, 9 mol / L, 10 mol / L, etc.

[0053] In some preferred embodiments, the precipitant is NaOH; the complexing agent is ammonia.

[0054] In some preferred embodiments, in step S1, the temperature of the coprecipitation reaction is 45~65℃, for example 45℃, 50℃, 55℃, 60℃, 65℃, etc.

[0055] In some preferred embodiments, in step S1, the stirring speed of the coprecipitation reaction is 300~700 rpm, such as 300 rpm, 350 rpm, 400 rpm, 450 rpm, 500 rpm, 550 rpm, 600 rpm, 650 rpm, 700 rpm, etc.

[0056] In some preferred embodiments, the bottom liquid of the reaction vessel is an ammonia solution; the concentration of the ammonia solution is 0.5~2 mol / L; In some preferred embodiments, the temperature of the bottom liquid in the reactor is 45~65℃, for example, 45℃, 50℃, 55℃, 60℃, 65℃, etc.

[0057] In some preferred embodiments, the volume of the bottom liquid in the reactor is 10-30% of the reactor volume, for example, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, etc.

[0058] In some preferred embodiments, the target particle size D50 is 8~10μm; the target diameter is 0.6~0.8, for example 0.6, 0.62, 0.65, 0.68, 0.7, 0.72, 0.75, 0.78, 0.80, etc.

[0059] In some preferred embodiments, the molar ratio of the precursor to lithium in the lithium source is 1:1.02~1.1. Optionally, the lithium source is one or more of lithium hydroxide, lithium carbonate, lithium acetate, and lithium nitrate.

[0060] In some embodiments, in step S3, the high-temperature solid-state sintering is a two-stage sintering; the two-stage sintering includes: first heating to 450~500℃ and holding for 5h, then continuing to heat to 700~800℃ and holding for 12h; the heating rate of the two-stage sintering is 2~5℃ / min; the sintering atmosphere is a pure oxygen atmosphere.

[0061] The present invention also provides a positive electrode, including the aforementioned high-nickel positive electrode material or the high-nickel positive electrode material prepared by the aforementioned preparation method.

[0062] The present invention also provides a lithium-ion battery, including the aforementioned positive electrode.

[0063] To facilitate understanding of the present invention, the invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0064] Example 1 (1) Preparation of raw material solutions: Prepare solution A with a total concentration of 2 mol / L by molar ratio of NiSO4•6H2O:MnSO4•4H2O:CoSO4•7H2O=0.9∶0.05∶0.05; prepare solution B with a concentration of 4 mol / L NaOH; prepare solution C with a concentration of 0.5 mol / L ammonia; mix solutions B and C in a volume ratio of 1:1 to obtain solution D.

[0065] (2) Coprecipitation synthesis of precursor: 10L of 0.5mol / L ammonia solution was added to a 50L reactor as the base solution. The temperature was maintained at 55℃ under nitrogen atmosphere protection, and the stirring speed was 700rpm. Solution A was pumped into the reactor at a feed rate of 4mL / min, and solution D was pumped into the reactor at a feed rate of 8mL / min. The pH of the system was controlled at 11.0±0.2 during the reaction. When the spherical particles D50 in the reactor were 8~10μm and uniformly distributed (i.e., the diameter distance D90-D50 / D10 was 0.6~0.8), the solution in the reactor was discharged, filtered, washed with deionized water until the pH of the filtrate was <8, and then dried under vacuum at 80℃ for 12h to obtain the high-nickel cathode material precursor. Its SEM image is shown below. Figure 1 As shown.

[0066] (3) The precursor and LiOH were mixed evenly at a molar ratio of 1:1.05, and then 2wt% WO3 of the precursor was added and ground thoroughly. Stepwise high-temperature solid-state sintering was performed to obtain a high-nickel cathode material. The stepwise high-temperature solid-state sintering was as follows: the heating rate was 5℃ / min, first heated to 450℃ and held for 5h, then heated to 700℃ and held for 12h, and the calcination atmosphere was pure oxygen. The SEM and EDS images of the obtained high-nickel cathode material are shown below. Figure 2 , Figure 3 As shown.

[0067] Combination Figure 1 and Figure 2 It can be seen that the prepared cathode material precursor has primary nanosheets with a thickness of 10-30 nm, and there are gaps between the primary nanosheets with a size of 20-100 nm. The secondary particle size D... 50=8~10μm. The cathode material inherits the structure of the precursor very well. The thickness of the primary nanosheets is 100~200nm, and there are gaps between the primary nanosheets with a size of 70~150nm. These gaps expand the lithium-ion transport channels and improve the rate performance. According to Figure 3 It can be seen that the high-nickel cathode material achieves uniform W doping.

[0068] The high-nickel cathode material obtained in Example 1 was used to prepare a battery according to the following method: The active material: carbon black: PVDF ratio is 8:1:1 by mass. 1.2g of the prepared sample, 0.15g of carbon black and 3.75g of PVDF solution (the solvent in the PVDF solution is NMP and the concentration of PVDF solution is 4wt.%) are manually ground evenly, passed through a 200# sieve and coated on aluminum foil. After drying, the pieces are cut, weighed and assembled into button half-cells.

[0069] The assembled button cell was subjected to the following electrochemical performance tests: Cyclic stability test: At 25°C, first perform 3 cycles at 0.1°C, then perform 100 cycles at 1°C. The test results are shown in Table 1.

[0070] Rate performance test: At 25℃, the circuit was cycled 5 times sequentially at 0.1C, 0.2C, 0.5C, 1C, 2C, and 5C, and finally cycled 5 times at 0.1C. The test results are as follows. Figure 4 As shown in (a) and Table 2.

[0071] Fast charge / discharge test: At 25℃, first, a 0.1C charge / discharge cycle of 3 times was performed, followed by a 5C charge / 2C discharge cycle of 100 times. The test results are as follows. Figure 4 As shown in (b), the battery retains 89.8% of its capacity after 100 cycles of 5C / 2C fast charging and discharging.

[0072] It is worth noting that the high-nickel cathode materials obtained in Examples 2-8 and Comparative Examples 1-6 were also prepared into batteries and subjected to electrochemical performance tests according to the above method. The test results are shown in Tables 1-6.

[0073] The physical performance parameters of the high-nickel cathode materials obtained in Examples 1-8 and Comparative Examples 1-6 were tested using the following methods: Compacted density test: Weigh approximately 1.00g of sample using weighing paper on a balance; place the weighed sample into a mold, and then place the mold with the material in the designated position in the center of the compaction density meter. Apply 3T pressure to the material for compression, and then calculate the material's compacted density using the weight / volume after compression; the test results are shown in Tables 1, 3, and 5.

[0074] Thermal stability test: The sample was cut into small particles, and approximately 0.50 g of the sample was weighed on a balance using weighing paper. The sample was then placed in a high-pressure crucible, which was then placed on a base. The equilibrium temperature was set to 40℃ and held for 1 minute. Then, the temperature was increased from 40℃ to 350℃ on a ramp to obtain the thermal stability test data. The test results are shown in Tables 1, 3, and 5.

[0075] Example 2 The only difference between this embodiment and embodiment 1 is that the amount of WO3 added in step (3) is different; the amount added is 1 wt% of the precursor.

[0076] SEM images of the obtained cathode material are as follows Figure 5 As shown in (a), the thickness of the primary nanosheets in the cathode material is 150~250nm, and the porosity is 50~100nm.

[0077] The thermal stability, compaction density, and cycle stability of the assembled coin cell of the obtained cathode material are shown in Table 1, and the rate performance of the coin cell is shown in Table 2.

[0078] Example 3 The only difference between this embodiment and embodiment 1 is that the amount of WO3 added in step (3) is different, and the amount added is 1.5wt% of the precursor.

[0079] SEM images of the obtained cathode material are as follows Figure 5 As shown in (b), the thickness of the primary nanosheets in the cathode material is 110~220nm, and the porosity is 60~120nm.

[0080] The thermal stability, compaction density, and cycle stability of the assembled coin cell of the obtained cathode material are shown in Table 1, and the rate performance of the coin cell is shown in Table 2.

[0081] Example 4 The only difference between this embodiment and embodiment 1 is that the amount of WO3 added in step (3) is different, and the amount added is 2.5 wt% of the precursor.

[0082] SEM images of the obtained cathode material are as follows Figure 5 As shown in (c), the thickness of the primary nanosheets in the cathode material is 70~150nm, and the porosity is 90~170nm.

[0083] The thermal stability, compaction density, and cycle stability of the assembled coin cell of the obtained cathode material are shown in Table 1, and the rate performance of the coin cell is shown in Table 2.

[0084] Comparative Example 1 The only difference between this comparative example and Example 1 is that WO3 is not added in step (3).

[0085] SEM images of the obtained cathode material are as follows Figure 6 As shown in (a), the thickness of the primary nanosheets in the cathode material is 300~400nm, and no obvious gaps can be observed. The primary particles are tightly packed.

[0086] The thermal stability, compaction density, and cycle stability of the assembled coin cell of the obtained cathode material are shown in Table 1, and the rate performance of the coin cell is shown in Table 2.

[0087] Comparative Example 2 The only difference between this comparative example and Example 1 is that the amount of WO3 added in step (3) is different, and the amount added is 0.5 wt% of the precursor.

[0088] SEM images of the obtained cathode material are as follows Figure 6 As shown in (b), the thickness of the primary nanosheets in the cathode material is 200~350nm, and the porosity is 10~50nm.

[0089] The thermal stability, compaction density, and cycle stability of the assembled coin cell of the obtained cathode material are shown in Table 1, and the rate performance of the coin cell is shown in Table 2.

[0090] Comparative Example 3 The only difference between this comparative example and Example 1 is that the amount of WO3 added in step (3) is different; the amount added is 3 wt% of the precursor.

[0091] SEM images of the obtained cathode material are as follows Figure 6 As shown in (c), the thickness of the primary nanosheets in the cathode material is 50~100nm, and the porosity is 130~250nm.

[0092] The thermal stability, compaction density, and cycle stability of the assembled coin cell of the obtained cathode material are shown in Table 1, and the rate performance of the coin cell is shown in Table 2.

[0093] Table 1. Thermal stability, compaction density, and cycle stability of the cathode materials prepared in Examples 1-4 and Comparative Examples 1-3. Table 2 Rate performance of batteries assembled from cathode materials prepared in Examples 1-4 and Comparative Examples 1-3 As shown in Tables 1 and 2, comparing Examples 1-4 and Comparative Examples 1-3, when WO3 is not added or the amount of WO3 is too small, the primary nanosheets of the cathode material are relatively thick, with very few voids, resulting in poor rate performance and relatively poor thermal stability. With increasing WO3 doping, the thickness of the primary nanosheets of the cathode material gradually decreases, the void size gradually increases, and the number of voids also gradually increases. This significantly shortens the lithium-ion diffusion path, improves the lithium-ion diffusion rate in the bulk phase of the material, thereby improving the rate performance and structural stability of the material. Furthermore, with increasing WO3 doping, the thermal decomposition temperature of the cathode material increases. Analysis suggests this may be due to W entering the crystal lattice and forming stronger WO3 chemical bonds with oxygen, increasing the thermal runaway temperature of the cathode material and giving it excellent thermal stability. However, since WO3 itself cannot contribute to capacity, excessive WO3 will significantly reduce the specific capacity of the cathode material, further affecting its rate performance.

[0094] Based on the data in Tables 1 and 2, it can be concluded that when the doping amount of WO3 is controlled within the range of 1~2.5wt%, the prepared cathode material has both good thermal stability and high compaction density. The assembled battery exhibits excellent cycle performance, demonstrating that the cathode material also has good structural stability.

[0095] Example 5 The only difference between this embodiment and Embodiment 1 is that steps (1) and (2) are different; (1) Preparation of raw material solutions: Prepare solution A with a total concentration of 2 mol / L by molar ratio of NiSO4•6H2O:MnSO4•4H2O:CoSO4•7H2O=0.9∶0.05∶0.05; prepare solution B with a concentration of 2 mol / L NaOH; prepare solution C with a concentration of 0.5 mol / L ammonia; mix solutions B and C in a volume ratio of 1:1 to obtain solution D.

[0096] (2) Coprecipitation synthesis of precursor: 10 L of 0.5 mol / L ammonia solution was added to a 50 L reactor as the base solution, heated to 55 °C, and protected under a nitrogen atmosphere. The stirring speed was 700 rpm. Solution A was pumped into the reactor at a feed rate of 4 ml / min, and solution D was pumped into the reactor at a feed rate of 16 ml / min. The pH of the system was controlled at 11.0 ± 0.2 during the reaction. When the spherical particles D50 in the reactor were 8~10 μm and uniformly distributed, the solution in the reactor was discharged, filtered, washed with deionized water until the pH of the filtrate was < 8, and then dried under vacuum at 80 °C for 12 h to obtain the high-nickel cathode material precursor.

[0097] SEM images of the obtained high-nickel cathode material precursor are shown below. Figure 7 As shown in (a); the SEM image of the obtained high-nickel cathode material is shown in Figure 1. Figure 7 As shown in (b). From Figure 7 It can be seen that the thickness of the primary nanosheets in the precursor is 10~30nm, and the porosity is 30~120nm. The cathode material inherits the structure of the precursor very well. In the cathode material, the thickness of the primary nanosheets is 80~150nm, and the porosity is 100~200nm.

[0098] The thermal stability, compaction density, and cycle stability of the assembled coin cell of the obtained cathode material are shown in Table 3, and the rate performance of the coin cell is shown in Table 4.

[0099] Example 6 The only difference between this embodiment and Embodiment 1 is that steps (1) and (2) are different; (1) Preparation of raw material solutions: Prepare solution A with a total concentration of 2 mol / L by molar ratio of NiSO4•6H2O:MnSO4•4H2O:CoSO4•7H2O=0.9∶0.05∶0.05; prepare solution B with a concentration of 6 mol / L NaOH; prepare solution C with a concentration of 0.5 mol / L ammonia; mix solutions B and C in a volume ratio of 1:1 to obtain solution D.

[0100] (2) Coprecipitation synthesis of precursor: 10 L of 0.5 mol / L ammonia solution was added to a 50 L reactor as the base solution, heated to 55 °C, and protected under a nitrogen atmosphere. The stirring speed was 700 rpm. Solution A was pumped into the reactor at a feed rate of 4 ml / min, and solution D was pumped into the reactor at a feed rate of 5.33 ml / min. The pH of the system was controlled at 11.0 ± 0.2 during the reaction. When the spherical particles D50 in the reactor were 8~10 μm and uniformly distributed, the solution in the reactor was discharged, filtered, washed with deionized water until the pH of the filtrate was < 8, and then dried under vacuum at 80 °C for 12 h to obtain the high-nickel cathode material precursor.

[0101] SEM images of the obtained high-nickel cathode material precursor are shown below. Figure 8 As shown in (a); the SEM image of the obtained high-nickel cathode material is shown in Figure 1. Figure 8 As shown in (b). From Figure 8 It can be seen that the thickness of the primary nanosheets in the precursor is 30-50 nm, and the porosity is 20-80 nm. The cathode material inherits the structure of the precursor very well. In the cathode material, the thickness of the primary nanosheets is 200-250 nm, and the porosity is 40-100 nm.

[0102] The thermal stability, compaction density, and cycle stability of the assembled coin cell of the obtained cathode material are shown in Table 3, and the rate performance of the coin cell is shown in Table 4.

[0103] Comparative Example 4 The only difference between this comparative example and Example 1 is that steps (1) and (2) are different; (1) Preparation of raw material solutions: Prepare solution A with a total concentration of 2 mol / L by molar ratio of NiSO4•6H2O:MnSO4•4H2O:CoSO4•7H2O=0.9∶0.05∶0.05; prepare solution B with a concentration of 8 mol / L NaOH; prepare solution C with a concentration of 0.5 mol / L ammonia; mix solutions B and C in a volume ratio of 1:1 to obtain solution D.

[0104] (2) Coprecipitation synthesis of precursor: 10 L of 0.5 mol / L ammonia solution was added to a 50 L reactor as the base solution. The temperature was maintained at 55 °C under nitrogen atmosphere protection, and the stirring speed was 700 rpm. Solution A was pumped into the reactor at a feed rate of 4 ml / min, and solution D was pumped into the reactor at a feed rate of 4 ml / min. The pH of the system was controlled at 11.0 ± 0.2 during the reaction. When the spherical particles D50 in the reactor were 8~10 μm and uniformly distributed, the solution in the reactor was discharged, filtered, washed with deionized water until the pH of the filtrate was < 8, and then dried under vacuum at 80 °C for 12 h to obtain the high-nickel cathode material precursor. SEM images of the obtained high-nickel cathode material precursor are shown below. Figure 9 As shown in (a); the SEM image of the obtained high-nickel cathode material is shown in Figure 1. Figure 9 As shown in (b). From Figure 9 It can be seen that the primary particles of the precursor are relatively thick sheets. In the cathode material, the thickness of the primary particle sheets is 250~400nm, with no obvious gaps observed, and the primary particles are tightly packed.

[0105] The thermal stability, compaction density, and cycle stability of the assembled coin cell of the obtained cathode material are shown in Table 3, and the rate performance of the coin cell is shown in Table 4.

[0106] Comparative Example 5 The only difference between this comparative example and Example 1 is that steps (1) and (2) are different; (1) Preparation of raw material solutions: Prepare solution A with a total concentration of 2 mol / L by molar ratio of NiSO4•6H2O:MnSO4•4H2O:CoSO4•7H2O=0.9∶0.05∶0.05; prepare solution B with a concentration of 10 mol / L NaOH; prepare solution C with a concentration of 0.5 mol / L ammonia; mix solutions B and C in a volume ratio of 1:1 to obtain solution D.

[0107] (2) Coprecipitation synthesis of precursor: 10 L of 0.5 mol / L ammonia solution was added to a 50 L reactor as the base solution, heated to 55 °C, and protected under a nitrogen atmosphere. The stirring speed was 700 rpm. Solution A was pumped into the reactor at a feed rate of 4 ml / min, and solution D was pumped into the reactor at a feed rate of 3.2 ml / min. The pH of the system was controlled at 11.0 ± 0.2 during the reaction. When the spherical particles D50 in the reactor were 8~10 μm and uniformly distributed, the solution in the reactor was discharged, filtered, washed with deionized water until the pH of the filtrate was < 8, and then dried under vacuum at 80 °C for 12 h to obtain the high-nickel cathode material precursor.

[0108] SEM images of the obtained high-nickel cathode material precursor are shown below. Figure 10 As shown in (a); the SEM image of the obtained high-nickel cathode material is shown in Figure 1. Figure 10 As shown in (b). From Figure 10 It can be seen that the primary particles of the precursor are relatively thick sheets. In the cathode material, the thickness of the primary particle sheets is 300~500nm, with no obvious gaps observed, and the primary particles are tightly packed.

[0109] The thermal stability, compaction density, and cycle stability of the assembled coin cell of the obtained cathode material are shown in Table 3, and the rate performance of the coin cell is shown in Table 4.

[0110] Comparative Example 6 The only difference between this comparative example and Example 1 is that steps (1) and (2) are different; (1) Preparation of raw material solutions: Prepare solution A with a total concentration of 2 mol / L by molar ratio of NiSO4•6H2O:MnSO4•4H2O:CoSO4•7H2O=0.9∶0.05∶0.05; prepare solution B with a concentration of 1 mol / L NaOH; prepare solution C with a concentration of 0.5 mol / L ammonia; mix solutions B and C in a volume ratio of 1:1 to obtain solution D.

[0111] (2) Coprecipitation synthesis of precursor: 10 L of 0.5 mol / L ammonia solution was added to a 50 L reactor as the base solution, heated to 55 °C, and protected under a nitrogen atmosphere. The stirring speed was 700 rpm. Solution A was pumped into the reactor at a feed rate of 4 ml / min, and solution D was pumped into the reactor at a feed rate of 32 ml / min. The pH of the system was controlled at 11.0 ± 0.2 during the reaction. When the spherical particles D50 in the reactor were 8~10 μm and uniformly distributed, the solution in the reactor was discharged, filtered, washed with deionized water until the pH of the filtrate was < 8, and then dried under vacuum at 80 °C for 12 h to obtain the high-nickel cathode material precursor.

[0112] SEM images of the obtained high-nickel cathode material precursor are shown below. Figure 11 As shown in (a); the SEM image of the obtained high-nickel cathode material is shown in Figure 1. Figure 11 As shown in (b). From Figure 11 It can be seen that the primary particles of the precursor are small in size and extremely thin. In the cathode material, the thickness of the primary particle layers is 50~100nm, the porosity is 50~250nm, and the primary particles are loosely arranged.

[0113] The thermal stability, compaction density, and cycle stability of the assembled coin cell of the obtained cathode material are shown in Table 3, and the rate performance of the coin cell is shown in Table 4.

[0114] By comparing Examples 1, 5, 6, 4, 5, and 6, it can be found that the molar ratio of precipitant to complexing agent affects the sheet size of the primary nanosheets of the cathode material precursor. If the molar ratio of precipitant to complexing agent is too high and the amount of complexing agent added is too low, the sheet size of the primary nanosheets of the cathode material precursor will be too large, resulting in excessively thick primary nanosheets of the sintered cathode material, disappearing the voids, reducing the lithium ion transport channels, and causing a decrease in the rate performance and cycle stability of the cathode material. If the molar ratio of precipitant to complexing agent is too low and the amount of complexing agent added is too high, the size of the primary particles of the cathode material precursor will be too small, resulting in a loose arrangement of the primary particles of the sintered cathode material, leading to a decrease in the compaction density of the cathode material.

[0115] Based on the data in Tables 3 and 4, it can be concluded that when the molar ratio of precipitant to complexing agent is controlled within the range of this invention, the prepared cathode material has both good thermal stability and high compaction density. The assembled battery exhibits excellent cycle performance and rate performance, demonstrating that the cathode material also has good structural stability.

[0116] Table 3. Thermal stability, compaction density, and cycle stability of the cathode materials prepared in Examples 5-6 and Comparative Examples 4-6. Table 4. Rate performance of the batteries assembled with the cathode materials prepared in Examples 5-6 and Comparative Examples 4-6 Example 7 The only difference between this embodiment and Example 1 is that in step (2), the pH value of the system is controlled at 10.5±0.2 during the reaction process.

[0117] SEM images of the obtained high-nickel cathode material precursor are shown below. Figure 12 As shown in (a); the SEM image of the obtained high-nickel cathode material is shown in Figure 1. Figure 12As shown in (b), compared with Example 1, the obtained high-nickel cathode material has some larger nanosheets in the precursor, with a primary nanosheet thickness of 10~30nm and a gap size of 20~100nm. The primary nanosheet thickness of the high-nickel cathode material is 170~300nm, and the gap size between the primary nanosheets is 50~100nm.

[0118] The thermal stability, compaction density, and cycle stability of the assembled coin cell of the obtained cathode material are shown in Table 5, and the rate performance of the coin cell is shown in Table 6.

[0119] Example 8 The only difference between this embodiment and Example 1 is that in step (2), the pH value of the system is controlled at 11.5±0.2 during the reaction process.

[0120] SEM images of the obtained high-nickel cathode material precursor are shown below. Figure 13 As shown in (a); the SEM image of the obtained high-nickel cathode material is shown in Figure 1. Figure 13 As shown in (b), compared with Example 1, the obtained high-nickel cathode material has some extremely small nanosheets in the precursor. The thickness of the primary nanosheets in the precursor is 10~20nm, and the porosity is 30~150nm. The thickness of the primary nanosheets in the high-nickel cathode material is 70~150nm, and the porosity is 90~180nm.

[0121] The thermal stability, compaction density, and cycle stability of the assembled coin cell of the obtained cathode material are shown in Table 5, and the rate performance of the coin cell is shown in Table 6.

[0122] Table 5 shows the thermal stability, compaction density, and cycle stability of the cathode materials prepared in Examples 7-8. Table 6. Rate performance of the cathode materials assembled in Examples 7-8 Studies have found that at excessively low pH, the primary particles of the prepared precursor are relatively thick sheets. The primary particles of the cathode material have thicker sheets, resulting in reduced pore size and number. (Li...) + Reduced diffusion channels slow down Li + The transport rate leads to a decrease in the rate performance of the cathode material. When the pH is too high, the transition metal elements precipitate unevenly, resulting in uneven distribution of Ni, Co, and Mn elements in the sintered cathode material, which in turn leads to a decrease in the cycle stability and rate performance of the cathode material. Tables 5 and 6 show that the cathode material obtained at a pH of 10.3~11.7 can have better cycle stability, rate performance, and thermal stability, as well as a higher compaction density.

[0123] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A high-nickel cathode material, characterized in that, The high-nickel cathode material is a spherical or near-spherical secondary particle formed by stacking thin sheet-like primary particles. The thickness of the thin sheet-like primary particles is 50~300nm, and there are gaps between the primary particles. The size of the gaps is 40~200nm. The high-nickel cathode material is doped with tungsten.

2. The high-nickel cathode material as described in claim 1, characterized in that, The high-nickel cathode material satisfies at least one of the following conditions (a) to (f): (a) The tungsten doping amount in the high-nickel cathode material is 0.7~2wt%; (b) The chemical formula of the high-nickel cathode material is Li(Ni) x Co y Mn 1-x-y ) 1-z W z O2, where 0.8≤x≤0.95, 0≤y≤0.2, 0≤1-xy≤0.2, and 0.007≤z≤0.02; (c) The particle size D50 of the secondary particles is 8~10μm; (d) The diameter of the secondary particles is 0.6~0.8; (e) The compaction density of the high-nickel cathode material is 3.15~3.25 g / cm³. 3 ; (f) The specific surface area of ​​the high-nickel cathode material is 0.4~0.6 m². 2 / g.

3. A method for preparing high-nickel cathode materials, characterized in that, include: S1. A mixed metal salt solution A and a mixed solution B of precipitant and complexing agent are introduced concurrently into the bottom liquid of the reactor. A co-precipitation reaction is carried out under a protective atmosphere. During the reaction, the pH value is controlled at 10.3~11.

7. When the precursor particle size D50 reaches the target particle size and target pitch, the precursor slurry is obtained. S2. Filter, wash and dry the precursor slurry to obtain the precursor; S3. The precursor is mixed with lithium source and WO3, and then sintered at high temperature to obtain high nickel cathode material; the amount of WO3 is 1.0~2.5wt% of the precursor mass.

4. The method for preparing the high-nickel cathode material as described in claim 3, characterized in that, The total metal element concentration in the mixed metal salt solution A is 1.5~2 mol / L; The mixed metal salt solution A contains nickel salt, manganese salt, and cobalt salt; and the molar ratio of nickel, cobalt, and manganese in the mixed metal salt is x:y:1-xy, where 0.8≤x≤0.95, 0≤y≤0.2, and 0≤1-xy≤0.

2. In the mixed solution B, the molar ratio of the precipitant to the complexing agent is (4~13):1; In the mixed solution B, the concentration of the precipitant is 2~10 mol / L; The complexing agent is ammonia water; The precipitant is sodium hydroxide.

5. The method for preparing the high-nickel cathode material as described in claim 3, characterized in that, In step S1, the temperature of the coprecipitation reaction is 45~65℃; In step S1, the stirring speed for the coprecipitation reaction is 300~700 rpm.

6. The method for preparing the high-nickel cathode material as described in claim 3, characterized in that, The bottom liquid of the reaction vessel is an ammonia solution; the concentration of the ammonia solution is 0.5~2 mol / L; The temperature of the bottom liquid in the reactor is 45~65℃; The volume of the bottom liquid in the reactor is 10-30% of the reactor volume.

7. The method for preparing the high-nickel cathode material as described in claim 3, characterized in that, The target particle size D50 is 8~10μm; the target diameter is 0.6~0.

8.

8. The method for preparing the high-nickel cathode material as described in claim 3, characterized in that, The molar ratio of the precursor to lithium in the lithium source is 1:1.02~1.1; The lithium source is one or more of lithium hydroxide, lithium carbonate, lithium acetate, and lithium nitrate.

9. The method for preparing the high-nickel cathode material as described in claim 3, characterized in that, In step S3, the high-temperature solid-state sintering is a two-stage sintering; the two-stage sintering includes: first heating to 450~500℃ and holding for 5~8h, and then continuing to heat to 700~800℃ and holding for 12~30h; the heating rate of the two-stage sintering is 2~5℃ / min; the sintering atmosphere is a pure oxygen atmosphere.

10. A positive electrode, characterized in that, This includes the high-nickel cathode material as described in claim 1 or 2, or the high-nickel cathode material prepared by the preparation method described in any one of claims 3 to 9.

11. A lithium-ion battery, characterized in that, Includes the positive electrode as described in claim 10.

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