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

Abstract

The application claims a high-nickel positive electrode material and a preparation method thereof, and a lithium ion battery, to improve the cycle performance of the high-nickel positive electrode material. The high-nickel positive electrode material is a secondary particle composed of primary particles; in the primary particles, the content of surface Si elements is greater than the content of internal Si elements, and the mass percentage of Sr elements contained on the surface is greater than or equal to 2.5wt%; wherein the molecular expression of the high-nickel positive electrode material is Li a Ni b Co c Mn d Sr f Zr g Si h O i ; 1≤a≤1.1, 0.8≤b≤1, 0≤c≤0.2, 0≤d≤0.2, 0

Description

Technical Field

[0001] This application relates to the field of secondary battery cathode materials technology, and in particular to a high-nickel cathode material and its preparation method, and lithium-ion batteries. Background Technology

[0002] For lithium-ion batteries, their energy density is closely related to the performance of their cathode materials. Among the many cathode materials, high-nickel materials stand out because they exhibit a capacity close to the theoretical specific capacity during charge-discharge cycles.

[0003] With the increase of nickel content in high-nickel materials, the reversible capacity increases almost linearly. However, at the same time, the capacity decay and high thermal instability of high-nickel materials also show an exacerbated trend. This is because during lithium-ion battery cycling, the high proportion and high activity of Ni in the high-nickel material located at the positive electrode... 4+ High-nickel materials readily undergo side reactions with the electrolyte to form inert salt-rock phase NiO, increasing positive electrode impedance and the electrochemically inert region, leading to a decline in electrochemical performance. Furthermore, the H2-H3 phase transition in high-nickel materials causes anisotropic strain accumulation, resulting in microcracks and exposing the interior of the high-nickel material, thus exacerbating the aforementioned side reactions between the high-nickel material and the electrolyte. Therefore, high-nickel materials currently suffer from low cycle performance. Summary of the Invention

[0004] This application provides a high-nickel cathode material and its preparation method, as well as a lithium-ion battery, to improve the cycle performance of the high-nickel cathode material.

[0005] In a first aspect, embodiments of this application provide a high-nickel cathode material, wherein the high-nickel cathode material is a secondary particle composed of primary particles; in the primary particles, the content of Si element on the surface is greater than the content of Si element inside, and the mass percentage of Sr element contained on the surface is greater than or equal to 2.5 wt%; wherein,

[0006] The molecular formula of the high-nickel cathode material is Li a Ni b Co c Mn d Sr f Zr g Si h O i ; 1≤a≤1.1, 0.8≤b≤1, 0≤c≤0.2, 0≤d≤0.2, 0<f≤0.01, 0<g≤0.01, 0<h≤0.01, 1.98≤i≤2.02, and b+c+d+f+g+h=1.

[0007] One possible implementation is 0.003 ≤ f ≤ 0.01.

[0008] In one possible implementation, the mass percentage of Sr element contained in the surface is the ratio of the mass of Sr element obtained from point-by-point scanning of the test points to the sum of the masses of all elements at the test points.

[0009] In one possible implementation, the Si element content in the primary particles decreases from the surface to the center.

[0010] In one possible implementation, the difference between the Si element content on the surface and the Si element content at the center of the primary particle is greater than or equal to 0.6 wt%; wherein the surface Si element content and the center Si element content are both obtained by point scanning.

[0011] In one possible implementation, the surface of the primary particles contains 0.5-0.8 wt% Si.

[0012] In one possible implementation, the mass percentage of Si element contained in the surface is the ratio of the mass of Si element obtained by point-to-point scanning of the test points to the sum of the masses of all elements at the test points.

[0013] The amount or mass percentage of Si and Sr on the surface of the primary particles were obtained by point scanning; the amount or mass percentage of Si and Sr inside the primary particles were also obtained by point scanning.

[0014] In one possible implementation, the surface of the primary particle comprises silicon oxide and lithium silicate; in the XPS test spectrum of the primary particle, the peak area of ​​the silicon oxide is smaller than the peak area of ​​the lithium silicate.

[0015] In one possible implementation, the silicon oxide comprises SiO2, and the lithium silicate comprises Li8SiO6, Li4SiO4, Li2SiO3, Li6Si2O7, Li2Si2O5, or Li2Si5O. 11 At least one of them.

[0016] In one possible implementation, the silicon oxide is SiO2; the lithium silicate is composed of Li8SiO6, Li4SiO4, Li2SiO3, Li6Si2O7, Li2Si2O5, and Li2Si5O. 11 At least one of the components.

[0017] In one possible implementation, the mass percentage of Sr element contained on the surface of the primary particles is 2.0-3.2 wt%.

[0018] In one possible implementation, the mass percentage of Sr element contained within the primary particle is less than or equal to 0.1 wt%.

[0019] In one possible implementation, the mass percentage of Sr element contained inside the primary particle is the ratio of the mass of Sr element obtained by point scanning of test points at a preset depth to the sum of the masses of all elements at the test points at the preset depth; the preset depth indicates the depth in the direction from the surface of the primary particle toward the geometric center of the primary particle.

[0020] Secondly, embodiments of this application provide a method for preparing the high-nickel cathode material described in the first aspect and any possible implementation, comprising:

[0021] In an oxygen-containing atmosphere, the precursor Ni x Co y Mn z A mixture of TM, lithium source, and zirconium source is subjected to a first sintering, and the intermediate obtained from the first sintering is subjected to a second sintering with a mixture of silicon source and strontium source to obtain the high-nickel cathode material; TM is the salt anion of the precursor, x≤1, y≤0.2, z≤0.2;

[0022] In the second sintering process, the holding time after heating to the target temperature is 3-5 hours, and the cooling rate after holding is greater than or equal to 7℃ / min; the target temperature is 620-680℃.

[0023] One possible implementation is that the precursor Ni b Co c Mn d After the first sintering of the mixture of TM, lithium source, and zirconium source, it also includes:

[0024] The intermediate is washed with water and dried so that the mass percentage of lithium carbonate on the surface of the intermediate is less than 0.2 wt% and the water content of the intermediate is less than 0.5 wt%.

[0025] In one possible implementation, during the second sintering process, when the sintering temperature is in the heating range from 400°C to the target temperature, the heating rate in the heating range is less than or equal to 3°C / min.

[0026] In one possible implementation, the target temperature for the first sintering is 750-850°C; in the first sintering, when the sintering temperature is greater than 500°C, the heating rate is less than or equal to 3°C / min, and the cooling rate is less than or equal to 2°C / min.

[0027] Thirdly, embodiments of this application provide a lithium-ion battery, comprising:

[0028] The high-nickel cathode material described in the first aspect and any possible embodiment.

[0029] The one or more technical solutions provided in the embodiments of this application have at least the following beneficial effects:

[0030] Firstly, because the primary particles in this high-nickel cathode material contain Si both on the surface and inside, Si can form high-energy Si-O bonds with O in the bulk phase, thus playing a role in oxygen fixation during charge-discharge. Furthermore, the decreasing Si content from the surface to the center of the primary particles contributes to the high energy density and good stability of the high-nickel material, avoiding the capacity reduction and increased side reactions caused by the majority of Si being distributed on the surface of the primary particles. Secondly, the Sr enriched on the surface of the primary particles significantly enhances the grain boundaries between them, thereby significantly mitigating the occurrence and deepening of microcracks caused by phase transition stress during charge-discharge, which exacerbates side reactions between the electrolyte and the cathode material. Thus, through the synergistic effect of these two elements, the cycle stability of this high-nickel cathode material is significantly increased.

[0031] Furthermore, on the surface of the primary particles of this high-nickel positive material, Si is coated in the form of silicon oxide and lithium silicate. Since silicon oxide and lithium silicate have relatively stable properties, they can significantly reduce the high proportion of highly active Ni within the primary particles. 4+ Side reactions with the electrolyte further enhance the stability of the cathode material. Attached Figure Description

[0032] Figure 1 A high-magnification SEM image of primary particles of a high-nickel cathode material secondary particles provided in an embodiment of this application;

[0033] Figure 2 SEM image of the high-nickel cathode material of Example 1 provided in this application;

[0034] Figure 3 XRD pattern of the high-nickel cathode material of Example 1 provided in this application;

[0035] Figure 4a TEM-HAADF image of a slice of the high-nickel cathode material of Example 1 provided in this application;

[0036] Figure 4b The Sr element distribution map obtained by TEM-EDS testing of the slice of Example 1 provided in this application embodiment;

[0037] Figure 4c The Si elemental distribution map obtained by TEM-EDS testing of the slices from Example 1 provided in this application embodiment;

[0038] Figure 4dThe Zr elemental distribution map obtained by TEM-EDS testing of the slices from Example 1 provided in this application embodiment;

[0039] Figure 5 XPS test image of the high-nickel cathode material of Example 1 provided in this application. Detailed Implementation

[0040] To address the issue of low stability in existing high-nickel cathode materials, this application provides a high-nickel cathode material in which the Si content on the surface of the primary particles is higher than the Si content inside, and the surface is enriched with Sr, with the Sr content on the surface being at least greater than or equal to 2.5 wt%. On one hand, the Si-O bonds formed by Si in the primary particles have high bond energy, thus stabilizing lattice oxygen and preventing the structural stability of the cathode material from being affected by severe lattice contraction and expansion during charge-discharge, thereby improving its cycle stability. On the other hand, the enrichment of Sr on the surface of the primary particles strengthens the grain boundaries between them, alleviating the problem of microcracks caused by stress in the cathode material during charge-discharge; thus, the cycle stability of the cathode material is further improved.

[0041] The following provides a detailed description of a high-nickel cathode material, its preparation method, and a lithium-ion battery based on embodiments of this application. It should be noted that the embodiments described below are merely some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0042] This invention provides a high-nickel cathode material, which is composed of secondary particles formed from primary particles. Both the primary and secondary particles have a near-spherical morphology. (Please refer to...) Figure 1-2 .

[0043] The Si content on the surface of the primary particle is greater than the Si content inside the primary particle, and the mass percentage of Sr is greater than or equal to 2.5 wt%.

[0044] The molecular formula for this cathode material is Li. a Ni b Co c Mn d Sr f Zr g Si h O i .

[0045] Where 1≤a≤1.1, 0.8≤b≤1, 0≤c≤0.2, 0≤d≤0.2, 0<f≤0.01, 0<g≤0.01, 0<h≤0.01, 1.98≤i≤2.02, and b+c+d+f+g+h=1.

[0046] Alternatively, 0.003 ≤ f ≤ 0.01. For example, f = 0.00332.

[0047] The Si content on the surface and inside of the primary particles, as well as the Sr content within the primary particles, are determined using secondary particles as the smallest unit. That is, the content is determined by testing at least 10 primary particles at the corresponding test depth and calculating the average value based on the test results; thus, the content of each element at each location can be used to indicate the distribution of each element on the primary particles in at least one secondary particle.

[0048] During testing, samples can be prepared by FIB (Focused Ion Beam) slicing, and then scanned at depth using TEM-EDS (Transmission Electron Microscope and Energy Dispersive Spectrometer) at the points corresponding to that depth. The Si element content at each scan point is determined by this method as the ratio of the mass of Si to the mass of all elements at that scan point.

[0049] When testing the Si or Sr content on the surface, the testing depth for primary particles is set to no more than 10 nm in the direction from the surface profile towards the center. The surface Sr content test is used as an example for illustration:

[0050] First, arbitrarily select N secondary particles and slice them. Then, randomly select one slice from the multiple slices of each secondary particle.

[0051] Then, M primary particles were randomly selected from each slice, and the Sr element at the same depth on the surface of the M primary particles was tested.

[0052] Finally, for each secondary particle slice, the average value of the Sr element content data on the surface of M primary particles is calculated, and the average value of the Sr element content on the surface of N primary particles is calculated.

[0053] Where N is a natural number greater than or equal to 2, and M is a natural number greater than or equal to 10, and N and M can be different.

[0054] Furthermore, within the primary particles, the Si element content decreases from the surface to the center, exhibiting a gradient distribution. This center indicates the geometric center of the primary particle.

[0055] In some embodiments, the mass percentage of Si element contained at any point on the surface of the primary particle is 0.5-0.8 wt%.

[0056] In some embodiments, the difference between the surface Si content and the central Si content in a primary particle is greater than or equal to 0.6 wt%.

[0057] The surface Si content and the central Si content were obtained by a single particle spot scan (i.e., spot scan) using the aforementioned TEM-EDS.

[0058] The test points mentioned above are the test points for spot scanning. Thus, in the Si element spot scanning data obtained by spot scanning test points at different depths of any primary particle in any secondary particle, the Si element content shows a pattern of first decreasing and then increasing as the spot scanning depth increases; and before the increase, that is, the scan depth corresponding to the minimum Si element content is the center position of the primary particle.

[0059] Furthermore, the substances corresponding to the Si element on the surface of the aforementioned primary particles include silicon oxide and lithium silicate, and in the XPS test spectrum of the primary particles, the peak area of ​​silicon oxide is smaller than that of lithium silicate.

[0060] The peak areas mentioned above are the areas of the peaks obtained by intersecting the baseline. It can be seen that the silica content on the surface of primary particles is lower than the lithium silicate content. The relative contents of silica and lithium silicate were obtained through XPS analysis, calculated and compared using silicon as a baseline.

[0061] The silicon oxide mentioned above is SiO2; the lithium silicate mentioned above includes Li8SiO6, Li4SiO4, Li2SiO3, Li6Si2O7, Li2Si2O5, and Li2Si5O. 11 At least one of the following. Alternatively, lithium silicate is composed of Li8SiO6, Li4SiO4, Li2SiO3, Li6Si2O7, Li2Si2O5, and Li2Si5O. 11 At least one of the components.

[0062] When performing XPS testing on the surface of particles to determine the distribution of silicon oxide and lithium silicate, the testing depth can be 3-10 nm.

[0063] Furthermore, in the cathode material provided in this application embodiment, the surface of the primary particles is enriched with Sr elements. That is, the Sr element content on the surface of the primary particles is much greater than the Sr element content inside the primary particles.

[0064] In some embodiments, the mass percentage of Sr on the surface of the primary particle is 2.0 wt% to 3.2 wt%. Furthermore, the interior of the primary particle contains almost no Sr, with the Sr content at any point within it being 0 or close to 0. Specifically, the mass percentage of Sr at any point within the primary particle is less than or equal to 0.1 wt%.

[0065] Based on the same inventive concept, this application also provides a method for preparing the aforementioned positive electrode material, which includes the following steps:

[0066] In an oxygen-containing atmosphere, the precursor Ni x Co y Mn z A mixture of TM, lithium source, and zirconium source is subjected to a first sintering, and the intermediate obtained from the first sintering is subjected to a second sintering with a mixture of silicon source and strontium source to obtain the aforementioned cathode material.

[0067] In the second sintering process, the holding time after reaching the target temperature is 3-5 hours. The cooling rate is greater than or equal to 7℃ / min; preferably 15-20℃ / min. This is to ensure that Si element forms a gradient distribution with decreasing content on the surface and inside the primary particles, and that Sr element is enriched on the surface of the primary particles. The target temperature is 620-680℃.

[0068] Specifically, the target temperature for the first sintering is 750-850℃, and the holding time is 7-9 hours. Furthermore, in the first sintering, the higher the temperature, the lower the heating and cooling rates. In the first sintering, the heating rate from room temperature to 500℃ is greater than the heating rate from 500-800℃. Similarly, the cooling rate from 500℃ to room temperature is greater than the heating rate from 800-500℃, thus promoting the full diffusion and uniform distribution of Zr elements within the bulk phase of the intermediate obtained in the first sintering process.

[0069] In some embodiments, during the first sintering process, when the sintering temperature is greater than 500°C, the heating rate is less than or equal to 3°C / min, and the cooling rate is less than or equal to 2°C / min.

[0070] In the second sintering process, the target temperature is 620-680℃. Furthermore, in the second sintering process, by controlling the heating rate in the higher temperature range, the Si element is controlled to enter the particulate phase in a gradient manner; and before entering this high temperature range, a relatively high heating rate can be used to improve the preparation efficiency.

[0071] In some embodiments, when the temperature rises to 400°C, the heating rate is reduced until the target temperature is reached. Specifically, the temperature can be increased at a rate of 5°C / min within the temperature range from room temperature to 400°C, and within the temperature range from 400°C to the target temperature, the heating rate is reduced to a rate of less than or equal to 3°C / min until the target temperature is reached.

[0072] In addition, the sintering atmosphere of the first and second sintering processes is an oxygen-rich atmosphere, for example, the oxygen content can be 80% or 90%.

[0073] In the above precursor, TM is a salt anion, for example, it can be O. 2- CO3 2- , and OH - One or more of them.

[0074] The lithium source can be Li2CO3 and / or LiOH·H2O.

[0075] The zirconium source can be one or more of oxides, hydroxides, sulfates, silicates, halides, and phosphates.

[0076] The silicon source can be one or more of the following silicate compounds: silicon dioxide (SiO2), orthosilicic acid (H4SiO4), metasilicic acid (H2SiO3), and disilicate (H2Si2O5). The strontium source can be one or more of the following: SrO, SrCO3, Sr(OH)2, Sr(NO3)2, strontium oxalate, and strontium acetate.

[0077] The aforementioned precursor Ni x Co y Mn z In a mixture of TM, lithium source, and zirconium source, multiple precursors can be added. The amount of each precursor added is determined by ensuring that the total amount of Ni, Co, and Mn elements is equal to the content of the corresponding elements in the cathode material. Similarly, for lithium source, zirconium source, silicon source, and strontium source, multiple forms of compounds can be added simultaneously, and the total amount added is determined based on the content of the corresponding elements in the cathode material.

[0078] The intermediate D obtained from the first sintering above 50 It can be 10.0±1.0μm.

[0079] Furthermore, to reduce the impact of residual alkali (Li2CO3, LiOH) on the cathode material, the residual alkali can be removed by washing with water after the first sintering and before the second sintering. Specifically, the intermediate obtained from the first sintering is washed with water for 2 minutes at a 1:1 mass ratio and then dried, or filtered and dried, so that the mass percentage of lithium carbonate on the surface of the intermediate (i.e., the intermediate after washing and drying) is less than 0.2 wt%, the mass fraction of lithium hydroxide is less than 0.4 wt%, and the water content of the intermediate is less than 0.5 wt%.

[0080] Based on the same inventive concept, this application also provides a lithium-ion battery, which includes the aforementioned high-nickel cathode material.

[0081] Because Si-O bonds have strong bond energy, the Si elements on the surface and inside the primary particles in the aforementioned cathode material are distributed in a gradient manner. On the one hand, this can stabilize the lattice oxygen in the bulk phase of the cathode material, thus effectively alleviating the lattice contraction and lattice expansion phenomena of the cathode material during charging and discharging, thereby improving the cycle stability of the cathode material.

[0082] On the other hand, the silicon oxide and lithium silicate corresponding to the surface Si element can form a coating layer on the surface of the primary particles, thereby mitigating the side reactions between the electrolyte and the cathode material during the charging-discharging process, thus increasing the cycle stability of the cathode material.

[0083] In this way, the lifespan of the lithium-ion battery is also improved.

[0084] Furthermore, since the Sr element on the surface of primary particles can enhance grain boundaries, it can significantly alleviate the phenomenon of microcracks appearing on the surface of primary particles due to stress during charging and discharging, thereby further improving the cycle stability of the cathode material. Correspondingly, the lifespan and safety of lithium-ion batteries are also further improved.

[0085] The following detailed description is provided through specific embodiments.

[0086] (I) Preparation of cathode materials

[0087] Example 1

[0088] S1, Ni 0.85 Co 0.05 Mn 0.10( OH)2, lithium hydroxide monohydrate, and zirconium oxide according to the chemical formula Li 1.03 Ni 0.84788 Co 0.0498 8Mn 0.09975 Zr 0.0025 O2 was weighed and stirred at 300 rpm for 120 min. The mixed material was then loaded into a sagger and heated to 500°C in a roller kiln at a rate of 5°C / min, then to 800°C at a rate of 2°C / min, and held at that temperature for 8 h. The sintering atmosphere was oxygen (oxygen concentration ≥80%). Subsequently, the material was cooled to 600°C at a rate of 1°C / min, and then cooled to room temperature at a rate of 15°C / min to obtain the primary sintered material.

[0089] S2. Crush the primary sintering material, D 50The particle size was controlled at 10.0±1.0μm, then washed with water at a mass ratio of 1:1 for 2 minutes, followed by pressure filtration and drying. The residual alkali Li2CO3 content on the surface of the dried material was 0.1-0.2wt%, the residual alkali LiOH content was 0.1-0.3wt%, and the moisture content was 0.1-0.4wt%.

[0090] S3. Weigh the dried material with silicon dioxide (calculated as silicon) and strontium oxide (calculated as strontium) in a mass percentage ratio of 0.994:0.003:0.003. Mix the materials at 300 rpm for 120 min, then place them in a roller kiln and heat to 400°C at a rate of 5°C / min. Then heat to 650°C at a rate of 2°C / min and hold for 3 h. Finally, cool to room temperature at a rate of 15°C / min to obtain the secondary sintered material. After sieving, iron removal, and packaging, the cathode material is obtained.

[0091] See the SEM image of the cathode material. Figure 2 The XRD pattern of this cathode material can be found in [reference needed]. Figure 3 See the TEM-HAADF image of the cross-section of this cathode material. Figure 4a For Sr, Si, and Zr elements, please refer to [the relevant documentation]. Figures 4b-4d The XPS test results of this cathode material, as well as the peak-separated SiO2 and lithium silicate, can be found in [reference needed]. Figure 5 .

[0092] Example 2

[0093] S1, Ni 0.85 Co 0.05 Mn 0.10 (OH)₂, lithium hydroxide monohydrate, and zirconium oxide according to the chemical formula Li 1.03 Ni 0.84788 Co 0.04988 Mn 0.09975 Zr 0.0025 O2 was weighed and stirred at 300 rpm for 120 min. The mixed material was then loaded into a sagger and heated to 500°C in a roller kiln at a rate of 5°C / min, then to 780°C at a rate of 2°C / min, and held at that temperature for 9 h. The sintering atmosphere was oxygen (oxygen concentration ≥80%). Subsequently, the material was cooled to 600°C at a rate of 1°C / min, and then cooled to room temperature at a rate of 15°C / min to obtain the primary sintered material.

[0094] S2. Crush the primary sintering material, D 50The particle size was controlled at 10.0±1.0μm, then washed with water at a mass ratio of 1:1 for 2 minutes, followed by pressure filtration and drying. The residual alkali Li2CO3 content on the surface of the dried material was 0.1-0.2wt%, the residual alkali LiOH content was 0.1-0.3wt%, and the moisture content was 0.1-0.4wt%.

[0095] S3. Weigh the dried material with silicon dioxide (calculated as silicon) and strontium carbonate (calculated as strontium) in a mass percentage ratio of 0.994:0.003:0.003. Mix the materials at 300 rpm for 120 min, then place them in a roller kiln and heat to 400°C at a rate of 5°C / min. Then heat to 640°C at a rate of 2°C / min and hold for 3 h. Finally, cool to room temperature at a rate of 15°C / min to obtain the secondary sintered material. After sieving, iron removal, and packaging, the cathode material is obtained.

[0096] Example 3

[0097] S1, Ni 0.85 Co 0.05 Mn 0.10( OH)2, lithium hydroxide monohydrate, and zirconium oxide according to the chemical formula Li 1.03 Ni 0.84788 Co 0.0498 8Mn 0.09975 Zr 0.0025 O2 was weighed and stirred at 300 rpm for 120 min. The mixed material was then loaded into a sagger and heated to 500°C in a roller kiln at a rate of 5°C / min, then to 800°C at a rate of 2°C / min, and held at that temperature for 8 h. The sintering atmosphere was oxygen (oxygen concentration ≥80%). Subsequently, the material was cooled to 600°C at a rate of 1°C / min, and then cooled to room temperature at a rate of 10°C / min to obtain the primary sintered material.

[0098] S2. Crush the primary sintering material, D 50 The particle size was controlled at 10.0±1.0μm, then washed with water at a mass ratio of 1:1 for 2 minutes, followed by pressure filtration and drying. The residual alkali Li2CO3 content on the surface of the dried material was 0.1-0.2wt%, the residual alkali LiOH content was 0.1-0.3wt%, and the moisture content was 0.1-0.4wt%.

[0099] S3. Weigh the dried material with silicon dioxide (calculated as silicon) and strontium oxide (calculated as strontium) in a mass percentage ratio of 0.994:0.003:0.003. Mix the materials at 300 rpm for 120 min, then place them in a roller kiln and heat to 400°C at a rate of 5°C / min. Then heat to 650°C at a rate of 2°C / min and hold for 3 h. Finally, cool to room temperature at a rate of 10°C / min to obtain the secondary sintered material. After sieving, iron removal, and packaging, the cathode material is obtained.

[0100] Comparative Example 1

[0101] S1, Ni 0.85 Co 0.05 Mn 0.10( OH)2, lithium hydroxide monohydrate, and zirconium oxide according to the chemical formula Li 1.03 Ni 0.84788 Co 0.0498 8Mn 0.09975 Zr 0.0025 O2 was weighed and stirred at 300 rpm for 120 min. The mixed material was then loaded into a sagger and heated to 500°C in a roller kiln at a rate of 5°C / min, then to 800°C at a rate of 2°C / min, and held at that temperature for 8 h. The sintering atmosphere was oxygen (oxygen concentration ≥80%). Subsequently, the material was cooled to 600°C at a rate of 1°C / min, and then cooled to room temperature at a rate of 15°C / min to obtain the primary sintered material.

[0102] S2. Crush the primary sintering material, D 50 The particle size was controlled at 10.0±1.0μm, then washed with water at a mass ratio of 1:1 for 2 minutes, followed by pressure filtration and drying. The residual alkali Li2CO3 content on the surface of the dried material was 0.1-0.2wt%, the residual alkali LiOH content was 0.1-0.3wt%, and the moisture content was 0.1-0.4wt%.

[0103] S3. Weigh the dried material with silicon dioxide (calculated as silicon) and strontium oxide (calculated as strontium) in a mass percentage ratio of 0.994:0.003:0.003. Mix at 300 rpm for 120 min, then place in a roller kiln and heat to 400°C at a rate of 5°C / min. Then heat to 700°C at a rate of 2°C / min and hold for 3 h. Finally, cool to room temperature at a rate of 15°C / min to obtain the secondary sintered material. After sieving, iron removal, and packaging, the cathode material is obtained.

[0104] Comparative Example 2

[0105] S1, Ni 0.85 Co 0.05 Mn 0.10(OH)2, lithium hydroxide monohydrate, and zirconium oxide according to the chemical formula Li 1.03 Ni 0.84788 Co 0.0498 8Mn 0.09975 Zr 0.0025 O2 was weighed and stirred at 300 rpm for 120 min. The mixed material was then loaded into a sagger and heated to 500°C in a roller kiln at a rate of 5°C / min, then to 800°C at a rate of 2°C / min, and held at that temperature for 8 h. The sintering atmosphere was oxygen (oxygen concentration ≥80%). Subsequently, the material was cooled to 600°C at a rate of 1°C / min, and then cooled to room temperature at a rate of 15°C / min to obtain the primary sintered material.

[0106] S2. Crush the primary sintering material, D 50 The particle size was controlled at 10.0±1.0μm, then washed with water at a mass ratio of 1:1 for 2 minutes, followed by pressure filtration and drying. The residual alkali Li2CO3 content on the surface of the dried material was 0.1-0.2wt%, the residual alkali LiOH content was 0.1-0.3wt%, and the moisture content was 0.1-0.4wt%.

[0107] S3. Weigh the dried material with silicon dioxide (calculated as silicon) and strontium oxide (calculated as strontium) in a mass percentage ratio of 0.994:0.003:0.003. Mix the materials at 300 rpm for 120 min, then place them in a roller kiln and heat to 400°C at a rate of 5°C / min. Then heat to 650°C at a rate of 2°C / min and hold for 3 h. Finally, cool to room temperature at a rate of 5°C / min to obtain the secondary sintered material. After sieving, iron removal, and packaging, the cathode material is obtained.

[0108] Comparative Example 3

[0109] S1, Ni 0.85 Co 0.05 Mn 0.10 (OH)₂, lithium hydroxide monohydrate, and zirconium oxide according to the chemical formula Li 1.03 Ni 0.84788 Co 0.04988 Mn 0.09975 Zr 0.0025 O2 was weighed and stirred at 300 rpm for 120 min. The mixed material was then loaded into a sagger and heated to 500°C in a roller kiln at a rate of 5°C / min, then to 800°C at a rate of 2°C / min, and held at that temperature for 8 h. The sintering atmosphere was oxygen (oxygen concentration ≥80%). Subsequently, the material was cooled to 600°C at a rate of 1°C / min, and then cooled to room temperature at a rate of 15°C / min to obtain the primary sintered material.

[0110] S2. Crush the primary sintering material, D 50 The particle size was controlled at 10.0±1.0μm, then washed with 1:1 water for 2 minutes, followed by pressure filtration and drying. The resulting dried material had a residual alkali Li2CO3 content of 0.1-0.2wt%, a residual alkali LiOH content of 0.1-0.3wt%, and a moisture content of 0.1-0.4wt%.

[0111] S3. Weigh the dried material with silicon dioxide (calculated as silicon) and strontium oxide (calculated as strontium) in a mass percentage ratio of 0.994:0.003:0.003. Mix the materials at 300 rpm for 120 minutes. After the materials are evenly mixed, place them in a roller kiln and heat to 300°C at a rate of 5°C / min, hold at that temperature for 3 hours, and then cool to room temperature at a rate of 15°C / min to obtain the secondary sintered material. After screening, iron removal, and packaging, the finished high-nickel ternary material is obtained.

[0112] Comparative Example 4

[0113] S1, Ni 0.85 Co 0.05 Mn 0.10( OH)2, lithium hydroxide monohydrate, and zirconium oxide according to the chemical formula Li 1.03 Ni 0.84788 Co 0.0498 8Mn 0.09975 Zr 0.0025 O2 was weighed and stirred at 300 rpm for 120 min. The mixed material was then loaded into a sagger and heated to 500°C in a roller kiln at a rate of 5°C / min, then to 800°C at a rate of 2°C / min, and held at that temperature for 8 h. The sintering atmosphere was oxygen (oxygen concentration ≥80%). Subsequently, the material was cooled to 600°C at a rate of 1°C / min, and then cooled to room temperature at a rate of 15°C / min to obtain the primary sintered material.

[0114] S2. Crush the primary sintering material, D 50 The particle size was controlled at 10.0±1.0μm, then washed with water at a mass ratio of 1:1 for 2 minutes, followed by pressure filtration and drying. The residual alkali Li2CO3 content on the surface of the dried material was 0.1-0.2wt%, the residual alkali LiOH content was 0.1-0.3wt%, and the moisture content was 0.1-0.4wt%.

[0115] S3. Weigh the dried material with silicon dioxide (calculated as silicon) and strontium oxide (calculated as strontium) in a mass percentage ratio of 0.994:0.003:0.003. Mix the materials at 300 rpm for 120 min, then place them in a roller kiln and heat to 400°C at a rate of 5°C / min. Then heat to 650°C at a rate of 2°C / min and hold for 1 hour. Finally, cool to room temperature at a rate of 15°C / min to obtain the secondary sintered material. After sieving, iron removal, and packaging, the cathode material is obtained.

[0116] (II) Testing of Cathode Materials

[0117] 1) The content of Si and Sr elements in the particles of each embodiment and comparative example was tested.

[0118] The following describes the testing methods for Si and Sr content, as well as the relative content of SiO2 and lithium silicate corresponding to Si: First, samples are prepared by FIB slicing to obtain slices with a thickness of 30-100 nm. Then, the Si and Sr content is obtained by TEM-EDS point scanning (the scanning depth can be selected within the range of 500 nm), and the testing depth is controlled to be the primary particle surface, 1 / 4 depth, and the primary particle center.

[0119] When testing the Si or Sr content on the surface of a single particle, the test depth is 2 nm, 1 / 4 of the depth and the center are the calculated test depths, and the error of the test position does not exceed 5 nm.

[0120] Furthermore, the relative contents of silicon oxide and lithium silicate were obtained by XPS testing. After calibrating the spectrum with the C1s peak at 284.8 eV, the results were calculated and compared with silicon as the reference.

[0121] During testing, two secondary particles were randomly selected and sliced. The cross-section of each slice passed through the geometric center of a primary particle. On the side of the slice containing the geometric center, ten primary particles were randomly selected for testing, and the average value was calculated. Table 1 shows the specific test data and calculation results for Example 1.

[0122] Table 1

[0123]

[0124]

[0125] Similar to Example 1, Table 2 shows the average values ​​of Si, Sr, silicon oxide, and lithium silicate content at the test points of the particles in the other examples and comparative examples besides Example 1.

[0126] Table 2

[0127]

[0128] As shown in Table 1-2, when the cooling rate of the secondary sintering is 15℃ / min, the decreasing distribution of Si element in the primary particles and the distribution of Sr element on the surface of the primary particles are particularly prominent, especially in Comparative Example 2 and Comparative Example 3.

[0129] 2) Fabrication of pouch cells using the cathode materials in the examples and comparative examples:

[0130] Positive electrode powder, conductive agent Super-P, and binder PVDF were mixed in a mass ratio of 94.5:3:2.5, and an appropriate amount of NMP solution was added to form a slurry. This slurry was then coated onto a positive electrode sheet made of aluminum foil, dried, and baked in a vacuum oven at 120°C for 12 hours. Finally, using this positive electrode sheet, negative electrode sheet (artificial graphite), separator (PP / PE / PP), and electrolyte (1.0M LiPF6 EC / DMC / EMC (1:1:1 volume ratio) solution), an 800mAh soft-pack battery was assembled.

[0131] To avoid randomness, five pouch cells were prepared under the same conditions. Specific capacity was tested at 2.8–4.25V and 1C; the test data are shown in Table 3.

[0132] Table 3

[0133] Unit: mAh / g

[0134] Battery 1 Battery 2 Battery 3 Battery 4 Battery 5 average value Example 1 188.7 188.5 188.9 188.2 187.6 188.4 Example 2 189.0 188.2 188.5 188.3 188.8 188.4 Example 3 188.8 188.9 188.1 188.4 188.5 188.5 Comparative Example 1 188.4 188.9 188.3 187.8 188.1 188.3 Comparative Example 2 188.7 189.2 188.6 188.1 188.4 188.6 Comparative Example 3 188.5 188.1 188.2 188.5 189.1 188.5 Comparative Example 4 187.8 188.9 188.5 188.6 188.1 188.4

[0135] The cycle retention rate of the pouch cell was tested after 300 cycles at 25°C under conditions of 2.8–4.25V and 1C. Test data are shown in Table 4.

[0136] Table 4

[0137] unit:%

[0138] Battery 1 Battery 2 Battery 3 Battery 4 Battery 5 average value Example 1 94.3 94.5 94.6 93.9 94.6 94.4 Example 2 94.6 94.8 94.7 94.6 93.7 94.5 Example 3 94.6 94.3 94.4 94.0 94.1 94.3 Comparative Example 1 93.6 92.4 92.5 92.2 92.2 92.6 Comparative Example 2 92.5 92.0 92.3 93.3 93.2 92.7 Comparative Example 3 91.1 91.3 91.8 91.5 90.9 91.3 Comparative Example 4 91.7 91.8 91.1 91.9 92.2 91.7

[0139] As shown in Tables 3-4, the high-nickel cathode materials in Examples 1-3 have better cycle retention rates than the comparative examples because the Si content decreases from the surface to the center of the primary particles, and the Si content at the center is not zero; and the Sr content on the surface of the primary particles is high.

[0140] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A high-nickel cathode material, characterized in that, The high-nickel cathode material is a secondary particle composed of primary particles; the primary particles contain Si elements on both the surface and inside; in the primary particles, the surface Si element content is greater than the internal Si element content, and the mass percentage of Sr element contained on the surface is greater than or equal to 2.5 wt%; the surface Sr element content is greater than the internal Sr element content; when testing the surface Si element or Sr content, the test depth of the primary particle is set to no more than 10 nm in the direction from the surface contour towards the center; the center is the geometric center of the primary particle; the interior refers to the region in the primary particle whose depth from the surface exceeds one-quarter of the diameter of the primary particle; wherein, The molecular formula of the high-nickel cathode material is Li a Ni b Co c Mn d Sr f Zr g Si h O i ; 1≤a≤1.1, 0.8≤b≤1, 0≤c≤0.2, 0≤d≤0.2, 0<f≤0.01, 0<g≤0.01, 0<h≤0.01, 1.98≤i≤2.02, and b+c+d+f+g+h=1.

2. The high-nickel cathode material as described in claim 1, characterized in that, In the primary particles, the Si content decreases from the surface to the center.

3. The high-nickel cathode material as described in claim 1, characterized in that, The mass percentage of Si element contained on the surface of the primary particles is 0.5-0.8 wt%.

4. The high-nickel cathode material according to any one of claims 1-3, characterized in that, The surface of the primary particle comprises silicon oxide and lithium silicate; in the XPS test spectrum of the primary particle, the peak area of ​​silicon oxide is smaller than that of lithium silicate.

5. The high-nickel cathode material as described in claim 1, characterized in that, The mass percentage of Sr element contained on the surface of the primary particles is 2.0-3.2 wt%.

6. The high-nickel cathode material according to any one of claims 1-3, 5, characterized in that, The mass percentage of Sr element contained in the primary particle is less than or equal to 0.1 wt%.

7. A method for preparing the high-nickel cathode material according to any one of claims 1-6, characterized in that, include: In an oxygen-containing atmosphere, the precursor Ni x Co y Mn z A mixture of TM, lithium source, and zirconium source is subjected to a first sintering, and the intermediate obtained from the first sintering is subjected to a second sintering with a mixture of silicon source and strontium source to obtain the high-nickel cathode material; TM is the salt anion of the precursor, x≤1, y≤0.2, z≤0.2; In the second sintering process, the holding time after heating to the target temperature is 3-5 hours, and the cooling rate after holding is greater than or equal to 7℃ / min; the target temperature is 620-680℃.

8. The method as described in claim 7, characterized in that, The precursor Ni x Co y Mn z After the first sintering of the mixture of TM, lithium source, and zirconium source, it also includes: The intermediate is washed with water and dried so that the mass percentage of lithium carbonate on the surface of the intermediate is less than 0.2 wt% and the water content of the intermediate is less than 0.5 wt%.

9. The method as described in claim 7, characterized in that, In the second sintering process, when the sintering temperature is in the heating range from 400°C to the target temperature, the heating rate in the heating range is less than or equal to 3°C / min.

10. A lithium-ion battery, characterized in that, include: The high-nickel cathode material according to any one of claims 1-6.

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