Modified nickel cobalt lithium manganate positive electrode material and preparation method thereof, lithium ion battery and electric device

Abstract

The invention discloses a modified nickel cobalt lithium manganate positive electrode material which comprises a nickel cobalt lithium manganate positive electrode material matrix and a perovskite coating layer Li [mu] W [alpha] Sr [beta] O [gamma] coating the surface of the nickel cobalt lithium manganate positive electrode material matrix. The preparation method comprises the following steps: mixing a precursor containing nickel, cobalt and manganese elements, a lithium salt, a W-containing compound, a Sr-containing compound and an M-containing compound, carrying out first sintering treatment, crushing and dissociating, mixing with the lithium salt, carrying out second sintering treatment, and screening to obtain the modified nickel cobalt lithium manganate positive electrode material. The invention also discloses a lithium ion battery comprising the positive electrode material and an electric device. According to the invention, the surface of the nickel cobalt lithium manganate positive electrode material substrate is coated with the perovskite coating layer, so that the problems of internal resistance, rate capability and low power of a low-Co material can be improved; the high-temperature cycle capacity retention ratio of the material under high charging cut-off voltage can be improved; and the problems of high-temperature storage internal resistance increase and gas production of the material under high charging cut-off voltage can be improved.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion batteries, and particularly relates to a modified lithium nickel cobalt manganese oxide cathode material and its preparation method, lithium-ion batteries, and electrical devices. Background Technology

[0002] As the development of new energy vehicles has progressed, people's demands for driving range, charging speed, and cost have continued to increase. Therefore, for lithium battery cathode materials, developing high energy density, high power density, and lower cost is crucial. Ternary lithium nickel cobalt manganese oxide (NCO) cathode materials have significant advantages over lithium cobalt oxide in terms of capacity and cost due to their lower Co content, high capacity, and high rate capability. However, the impedance and rate performance of NCO cathode materials gradually deteriorate as the Co content decreases; high-temperature cycle life, storage gas generation performance, and safety performance deteriorate with increasing cutoff voltage and Ni content.

[0003] Currently, existing technologies address the technical problems of lithium nickel cobalt manganese oxide cathode materials through doping modification, but the improvement effect is still unsatisfactory, and the introduction of dopants still leads to problems such as deterioration of material rate capability and impedance performance. Existing technologies also address these problems through coating modification, forming dot-like oxide coatings on the material structure surface to improve the side reaction problem on the cathode material surface. However, oxide coating not only leads to a decrease in impedance and rate capability but also poses a risk of precipitation at high voltage or in the later stages of cycling. For example, non-patent literature (Xinhe Yang, Zicheng Zuo, Haiyan Wang, Quanbin Chen, Hui Zhang, Zhenlei Huang, Borong Wu, Henghui Zhuo, Electrochimica Acta (180) 2015:604-609) confirms that layered materials coated with simple tungsten oxide do not generate stable tungsten compounds, causing them to accumulate on the graphite anode during electrochemical reactions, resulting in poor high-temperature cycling and storage performance.

[0004] Therefore, it is of great significance to study a ternary lithium nickel cobalt manganese oxide cathode material with a stable coating layer on its surface and low interfacial impedance. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the background art above, and to provide a modified lithium nickel cobalt manganese oxide cathode material, its preparation method, lithium-ion battery, and power device.

[0006] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows:

[0007] A modified lithium nickel cobalt manganese oxide cathode material includes a lithium nickel cobalt manganese oxide cathode material matrix and a perovskite coating layer encapsulating the surface of the lithium nickel cobalt manganese oxide cathode material matrix, wherein the chemical formula of the perovskite coating layer is Li. μ W α Sr β O γ Where 0 < μ ≤ 1, the ratio of α to β is 0.3-0.7, and 3 ≤ γ < 6.

[0008] The applicant's research found that, in Li μ W α Sr β O γ In the coating layer, when the α:β ratio is less than 0.3, the coating layer structure is unstable and has no or poor improvement effect on the DCR and stability of the modified nickel cobalt manganese oxide cathode material. When the α:β ratio is greater than 0.7, the formed coating material has fewer oxygen vacancies and has no improvement effect on storage and circulating gas production.

[0009] The aforementioned modified lithium nickel cobalt manganese oxide cathode material, preferably, as determined by XRD analysis, has Li μ W α Sr β O γ The peak intensity of the (111) crystal plane and Li μ W α Sr β O γ The ratio of the peak intensities of the (220) crystal plane is 0.2 < I. (111) / I (220) <1.5; more preferably, 0.4 <I (111) / I (220) <1.3; During the applicant's research process, by testing XRD data, it was found that I (111) / I (220) Within this range, the generated coating material Li can be described. μ W α Sr β O γ Its good crystallinity is beneficial to the gas production performance and rate performance of the material.

[0010] Li μ W α Sr β O γ The peak intensity of the (400) crystal plane and Li μ W α Sr β O γ The ratio of the peak intensities of the (111) crystal plane is 0.1 < I (400) / I (111) <2.0; more preferably, 0.2 <I (400) / I (111) <1.2, During the applicant's research process, by testing XRD data, it was found that I (400) / I (111) Within this range, it can be explained that the resulting coating material Li... μ W α Sr β O γ Its good crystallinity is beneficial to the gas production performance and rate performance of the material.

[0011] The aforementioned modified lithium nickel cobalt manganese oxide cathode material, preferably, as determined by XRD analysis, has Li μ W α Sr β O γ The (111) crystal plane half-width at half-maximum and Li μ W α Sr β O γ The half-maximum-to-width ratio of the (220) crystal plane is 0.5 < K. (111) / K (220) <1.0; further preferred, 0.6 <K (111) / K (220) <0.8; During the applicant's research process, K was found to be <0.8 through testing XRD data. (111) / K (220) Materials within this range exhibit good gas production and rate capability.

[0012] Li μ W α Sr β O γ The (400) crystal plane half-width and Li μ W α Sr β O γ The half-maximum-to-width ratio of the (111) crystal plane is 0.3 < K. (400) / K (111) <1.0; further preferred, 0.4 <K (400) / K (111) <0.7.

[0013] The aforementioned modified lithium nickel cobalt manganese oxide cathode material, preferably, as determined by XRD analysis, has Li μ W α Sr β O γ The ratio of the intensity of the (111) crystal plane peak to the intensity of the (003) crystal plane peak of the modified lithium nickel cobalt manganese oxide cathode material is 0.01 < I. (111) / I (003) <0.05; more preferably, 0.015 < I (111) / I (003)<0.035;

[0014] Li μ W α Sr β O γ The ratio of the full width at half maximum (FWHM) of the (111) crystal plane to that of the (003) crystal plane in the modified nickel-cobalt-manganese oxide cathode material is 1.2 < K. (111) / K (003) <2.2; further preferred, 1.4 < K (111) / K (003) <1.8.

[0015] In the above-mentioned modified lithium nickel cobalt manganese oxide cathode material, preferably, the thickness of the perovskite coating layer is 1-20 nm.

[0016] Preferably, in the above-mentioned modified lithium nickel cobalt manganese oxide cathode material, the chemical formula of the lithium nickel cobalt manganese oxide cathode material matrix is ​​Li. x Ni y Co z Mn 1-y-z-a M a O2, wherein 0.95≤x≤1.2, 0.5≤y<1, 0<z≤0.2, 0<a≤0.02, 0<1-yza≤0.28, and M includes one or more of the elements Mg, Ti, Zr, Ba, W, Nb, Sr, Ta and La.

[0017] Preferably, the modified lithium nickel cobalt manganese oxide cathode material has a powder conductivity ρ of 0.0001 S / cm - 0.02 S / cm under a pressure of 190 MPa.

[0018] As a general inventive concept, the present invention also provides a method for preparing the modified lithium nickel cobalt manganese oxide cathode material as described above, comprising the following steps:

[0019] (1) The precursor containing nickel, cobalt and manganese elements, lithium salt, W-containing compound, Sr-containing compound and M-containing compound are mixed and subjected to a first sintering treatment to obtain sintered products. During the sintering process, some W elements will enter the matrix, while Sr elements are basically unable to enter the matrix due to their large particle radius. Therefore, W and Sr are mainly distributed on the surface of the material.

[0020] (2) The sintered product obtained in step (1) is crushed and dissociated, then mixed with lithium salt, and subjected to a second sintering treatment. After sieving, the modified lithium nickel cobalt manganese oxide cathode material is obtained.

[0021] In the preferred embodiment of the above preparation method, in step (1), the molar ratio of Li to precursor in the lithium salt is 0.95-1.0:1; the mass of W in the W-containing compound accounts for 0.4%-2.0% of the precursor mass, the mass of Sr in the Sr-containing compound accounts for 0.25%-1.6% of the precursor mass, and the molar ratio of W to Sr is 2:5 to 4:5. When the amount of W added is too low, below 0.4%, as the sintering temperature increases, some W will penetrate into the interior of the cathode material, resulting in a low W content on the material surface, making it difficult to form perovskite with the Sr on the surface; when the W content is too high, above 2%, W will inhibit the particle size growth of the cathode material, significantly inhibiting particle size growth, making it difficult to generate the desired cathode material. When the Sr content is too low, below 0.25%, it is difficult to form perovskite minerals with W on the surface; when the Sr content is too high, above 1.6%, there is too much surface coating material, the capacity of the cathode material deteriorates significantly, and the material performance is affected.

[0022] In the above preparation method, preferably, in step (1), the first sintering treatment is carried out in an oxygen or air atmosphere with a gas flow rate of 5m³. 3 / h-30m 3 / h.

[0023] In the above preparation method, preferably, in step (1), the first sintering treatment is a multi-stage sintering: the first stage sintering temperature is T1, the sintering time is t1, and the heating rate is V1; the second stage sintering temperature is T2, the sintering time is t2, and the heating rate is V2; the third stage sintering temperature is T3, the sintering time is t3, and the cooling rate is V3; wherein, 450℃≤T1≤750℃, 850℃≤T2≤950℃, 600℃≤T3≤800℃, 3h≤t1≤8h, 1.5≤t2 / t1≤3, t1≤t3≤t2; 0.5℃ / min≤V1≤1.5℃ / min, 1<V2 / V1≤3, V1≤V3≤V2. The first sintering stage, with its slow heating rate, low isothermal temperature, and short sintering time, facilitates the reaction between lithium salt and the precursor, slows precursor growth, and maintains only partial lithium embedding within the precursor. The second sintering stage features a rapid heating rate, high isothermal temperature, and long sintering time. Rapid heating promotes rapid precursor growth, while the high isothermal temperature and long duration facilitate the growth of the internal structure and full lithium embedding. During this stage, a lithium-deficient perovskite-like coating layer rapidly forms on the material surface, composed of Li, W, and Sr. The third sintering stage, with a moderately lower temperature, slow cooling rate, and moderate isothermal time, further facilitates the embedding of lithium into the lithium-deficient perovskite-like coating layer, thereby increasing the lithium content in the coating layer. If the first sintering process is not configured as described above, such as omitting the first stage, lithium will react rapidly with the precursor, W, and Sr simultaneously, preventing the formation of a uniform coating layer on the material surface. Without the third stage, the resulting perovskite coating layer will suffer from severe lithium deficiency, leading to deterioration of material performance.

[0024] In the above preparation method, preferably, in step (2), the molar ratio of lithium element in the lithium salt to lithium nickel cobalt manganese oxide in the sintered product obtained in step (1) is 0.06-0.2:1.

[0025] In the above preparation method, preferably, in step (2), the second sintering treatment is carried out in an oxygen or air atmosphere with a gas flow rate of 1 m³ / s. 3 / h-5m 3 / h.

[0026] In the preferred embodiment of the above preparation method, in step (2), the sintering temperature of the second sintering treatment is 600℃-850℃, the sintering time is 6h-20h, and the heating rate is 0.2-0.5℃ / min. When the second sintering temperature is below 600℃, lithium is lacking in the sinter, and the perovskite cannot react with lithium. When the sintering temperature is above 850℃, the material particles adhere and agglomerate with each other, requiring further dissociation, which increases costs. Moreover, dissociation also damages the surface coating layer, leading to a deterioration in material performance. The heating rate cannot be too high, otherwise, the added lithium will not be able to fully react with the perovskite coating layer obtained in the first sintering, failing to repair the material surface. The heating rate also cannot be too low, otherwise, the heating time will be too long, resulting in low sintering capacity, high costs, and is not conducive to industrial production.

[0027] In the above preparation method, preferably, the lithium salt is selected from one or more of lithium carbonate, lithium hydroxide, or lithium acetate; the Sr-containing compound includes one or more of strontium oxide, strontium hydroxide, and strontium carbonate; and the W-containing compound includes one or more of tungsten oxide, ammonium metatungstate, and ammonium paratungstate.

[0028] As a general inventive concept, the present invention also provides a lithium-ion battery comprising the modified lithium nickel cobalt manganese oxide cathode material described above or comprising the modified lithium nickel cobalt manganese oxide cathode material prepared by the above preparation method.

[0029] As a general inventive concept, the present invention also provides an electrical device including the aforementioned lithium-ion battery.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] (1) The modified lithium nickel cobalt manganese oxide cathode material of the present invention has a perovskite coating layer including Li, W and Sr elements coated on the surface of the lithium nickel cobalt manganese oxide cathode material matrix. The coating layer has multiple technical effects: it can improve the internal resistance, rate performance and low power of low Co materials; it can improve the high-temperature cycle capacity retention rate of the material under high charging cut-off voltage; it can improve the high-temperature storage internal resistance growth and gas generation problem of the material under high charging cut-off voltage; it can improve the surface properties of the nickel cobalt manganese cathode material, reduce the residual Li content on the material surface, and reduce the side reactions with the electrolyte during the electrochemical process.

[0032] (2) This invention prepares modified lithium nickel cobalt manganese oxide cathode materials by hierarchically controlling the sintering process and combining the use of Sr-containing compounds, W-containing compounds, and additional lithium salts. Under the hierarchical control of the first sintering process, Sr and W elements form lithium-deficient LiW oxide. α Sr β O γThe perovskite compound coating effectively slows down the ingress of W and Sr elements into the material, promoting the formation of lithium-deficient Li on the surface by W and Sr elements. μ W α Sr β O γ The perovskite compound coating stabilizes the surface structure of the material and effectively improves its stability.

[0033] (3) The preparation method of the present invention, through a second high-temperature sintering and the addition of a small amount of lithium salt, not only repairs the lithium-deficient state of Li obtained in the first sintering, but also... μ W α Sr β O γ The perovskite compound coating layer forms a stable lithium-containing perovskite layer on the material surface. It also allows the micro-powder and rock salt phase components on the material surface to react with residual lithium and additional lithium sources on the surface, and integrate with the matrix particles. The two work together to make the material surface more stable and effectively improve the material's interfacial resistance and stability performance.

[0034] (4) In the preparation method of the present invention, W-containing compounds are used. On the one hand, W-containing compounds can form stable lithium-containing coatings, which make them have low impedance and high rate performance. On the other hand, they can also effectively reduce the dissolution of tungsten elements in the electrolyte and promote their tight bonding on the surface of the cathode material. This can effectively improve the stability of the material interface and further enhance the impedance, rate, long cycle and storage characteristics of the cathode material.

[0035] In summary, the modified lithium nickel cobalt manganese oxide cathode material of the present invention exhibits excellent electrochemical performance in terms of capacity, internal resistance, rate capability, cycle life, and storage. Attached Figure Description

[0036] Figure 1 This is a scanning electron microscope (SEM) image of the modified lithium nickel cobalt manganese oxide cathode material prepared in Example 1 of the present invention.

[0037] Figure 2 This is a scanning electron microscope (SEM) image of the modified lithium nickel cobalt manganese oxide cathode material prepared in Comparative Example 2 of this invention.

[0038] Figure 3 This is a transmission electron microscope (TEM) image of the modified lithium nickel cobalt manganese oxide cathode material prepared in Example 1 of this invention.

[0039] Figure 4 This is a transmission electron microscope (TEM) image of the modified lithium nickel cobalt manganese oxide cathode material prepared in Example 2 of the present invention.

[0040] Figure 5 The images show the XRD patterns of the modified lithium nickel cobalt manganese oxide cathode materials prepared in Example 1 and Comparative Examples 1-7 of this invention. Detailed Implementation

[0041] To facilitate understanding of the present invention, the present 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.

[0042] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0043] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0044] Example 1:

[0045] A modified lithium nickel cobalt manganese oxide cathode material of the present invention includes a lithium nickel cobalt manganese oxide cathode material matrix Li. 1.04 Ni 0.686 Co 0.07 Mn 0.24 Zr 0.004 O2 and the perovskite compound coating layer LiWSr2O on the substrate surface 5.5 The coating thickness is 5-16.5 nm.

[0046] The preparation method of the modified lithium nickel cobalt manganese oxide cathode material in this embodiment includes the following steps:

[0047] (1) Weigh 2000g of nickel-cobalt-manganese hydroxide precursor Ni 0.69 Co 0.07 Mn 0.24 (OH)₂ was prepared, and 910g of LiOH·H₂O was weighed out according to a precursor-to-Li molar ratio of 1:1; 11.4g of nano-zirconia was weighed out according to a precursor-to-Zr molar ratio of 1:0.004; 31.89g of nano-tungsten oxide was weighed out according to W as 1.2% of the precursor mass; and 24.9g of nano-strontium oxide was weighed out according to Sr as 1% of the precursor mass. These materials were then weighed and added to a mixing tank and mixed thoroughly. The mixed materials were then placed in an oxygen atmosphere with an oxygen concentration >98% for the first sintering, wherein the oxygen flow rate was 8 m³ / s. 3The first sintering process involves raising the temperature from room temperature to 650℃ at a rate of 0.5℃ / min and holding it at that temperature for 6 hours. Then, the temperature is raised to 930℃ at a rate of 1.5℃ / min and held at that temperature for 18 hours. Finally, the temperature is lowered to 750℃ at a rate of 1℃ / min and held at that temperature for 12 hours. The material is then allowed to cool naturally to room temperature to obtain the sintered material. The sintered material is then crushed and sieved to obtain the sintered product.

[0048] (2) The sintered product obtained in step (1) and LiOH·H2O are mixed evenly according to the molar ratio of lithium nickel cobalt manganese oxide to lithium element in the sintered product being 1:0.15; then the mixture is placed in a kiln for a second sintering. The conditions for the second sintering are: air atmosphere, air flow rate of 3m³ / h. 3 The temperature was increased to 820℃ at a rate of 0.3℃ / min and held for 12 hours. After naturally cooling to room temperature, the solution was passed through a 200-mesh sieve to obtain LiWSr2O. 5.5 Lithium nickel cobalt manganese oxide cathode material coated with perovskite coating.

[0049] The modified lithium nickel cobalt manganese oxide cathode material prepared in this embodiment is shown in the scanning electron microscope (SEM) image. Figure 1 As shown, the cathode material has a distinct coating layer on its surface, with uniform particle distribution and few fine powder particles on the sample surface, and no obvious adhesion phenomenon. The Dv50 value is 3.6 μm.

[0050] At room temperature, 2g of the modified lithium nickel cobalt manganese oxide cathode material prepared in this embodiment was placed in a specific mold for powder compaction testing. The pressure was set to 190MPa and the holding time was 10 seconds. The powder conductivity of the cathode material was measured to be as high as 0.005S / cm.

[0051] Uniform particle dispersion and a uniform coating layer can mitigate the corrosion of the material surface by the electrolyte, while high powder conductivity can improve the internal resistance of the material, thus improving the material's power and gas generation performance. Residual lithium testing shows that the modified nickel-cobalt-manganese oxide cathode material sample prepared in this embodiment has a residual Li content of 0.05% on its surface, which is low and helps to mitigate surface side reactions during cycling.

[0052] The modified lithium nickel cobalt manganese oxide cathode material prepared in this embodiment was tested by transmission electron microscopy (TEM) as follows: Figure 3 As shown, a stable nanoscale LiWSr2O layer is formed on the surface of this cathode material. 5.5The coating layer (the area between the dashed lines represents the coating material) is formed by adjusting the parameters of the multi-stage sintering process in this embodiment. This process can dynamically repair the perovskite, promoting the formation of a stable and uniform nano-layered coating layer on the material surface. Selected area electron diffraction (SAED) analysis shows that the coating material is LiWSr2O. 5.5 The crystal structure is an Fm-3m(225) layered lithium-bearing perovskite mineral. Nano Measurer analysis showed that the coating thickness ranged from 5 to 16.5 nm, with a minimum thickness of 5 nm and a maximum thickness of 16.5 nm. This nanoscale lithium-bearing perovskite coating not only improves the internal resistance of low-Co materials and increases power output, but also prevents electrolyte corrosion and enhances material interface stability. Furthermore, the abundance of oxygen vacancies significantly reduces oxygen release during high-temperature storage, thus improving storage performance.

[0053] The modified lithium nickel cobalt manganese oxide cathode material prepared in this embodiment was tested by X-ray diffraction (XRD) as follows: Figure 5 As shown, in addition to the positions of the diffraction peaks corresponding to those of standard lithium nickel cobalt manganese oxide, it also exhibits characteristic peaks such as (111), (220), and (400). Through automatic identification and analysis using JADE 6.0 and comparison with the PDF card, it was determined that these characteristic peaks represent LiWSr2O. 5.5 The crystal structure here also corresponds to the TEM characterization results; by analyzing the characteristic peaks (111), (220), and (400), their peak intensities are 477.8, 549.8, and 136.7, respectively, and their full width at half maximum (FWHM) are 0.132, 0.180, and 0.099, respectively; among which I (111) / I (220) It is 0.868, I (400) / I (111) K is 0.286. (111) / K (220) K is 0.733. (400) / K (111) The intensity was 0.55. Analysis showed that the characteristic peak intensity of lithium nickel cobalt manganese oxide (003) was 18344.2, and the full width at half maximum (FWHM) was 0.088. (LiWSr2O) 5.5 The ratio of the intensity of the (111) crystal plane peak to the intensity of the (003) crystal plane peak of the modified lithium nickel cobalt manganese oxide cathode material is I (111) / I (003) The value is 0.026, LiWSr2O 5.5 The ratio K of the full width at half maximum (FWHM) of the (111) crystal plane to the FWHM of the (003) crystal plane of the modified nickel cobalt manganese oxide cathode material is K (111) / K (003)The value was 1.5. XRD analysis showed that this application successfully prepared a perovskite-coated lithium nickel cobalt manganese oxide cathode. The material has high crystallinity and forms an ordered layered structure, which significantly improves its gas generation performance and impedance.

[0054] Example 2:

[0055] A modified lithium nickel cobalt manganese oxide cathode material of the present invention includes a lithium nickel cobalt manganese oxide cathode material matrix Li. 1.04 Ni 0.686 Co 0.07 Mn 0.24 Ti 0.004 O2 and the perovskite compound coating layer on the substrate surface (Li) 0.4 W 0.6 SrO3, with a coating thickness of 3-7 nm.

[0056] The preparation method of the modified lithium nickel cobalt manganese oxide cathode material in this embodiment includes the following steps:

[0057] (1) Weigh 2000g of nickel-cobalt-manganese hydroxide precursor Ni 0.69 Co 0.07 Mn 0.24 (OH)₂ was prepared, and 910g of LiOH·H₂O was weighed out according to a precursor-to-Li molar ratio of 1:1; 7.04g of nano-titanium oxide was weighed out according to a precursor-to-Ti molar ratio of 1:0.004; 26.58g of nano-tungsten oxide was weighed out according to W as 1.0% of the precursor mass; and 19.94g of nano-strontium oxide was weighed out according to Sr as 0.8% of the precursor mass. These materials were then weighed and added to a mixing tank and mixed thoroughly. The mixed material was then placed in an oxygen atmosphere with an oxygen concentration >98% for the first sintering, wherein the oxygen flow rate was 8 m³ / s. 3 The first sintering process involves raising the temperature from room temperature to 650℃ at a rate of 0.5℃ / min and holding it at that temperature for 6 hours. Then, the temperature is raised to 930℃ at a rate of 1.5℃ / min and held at that temperature for 18 hours. Finally, the temperature is lowered to 750℃ at a rate of 1℃ / min and held at that temperature for 12 hours. The material is then allowed to cool naturally to room temperature to obtain the sintered material. The sintered material is then crushed and sieved to obtain the sintered product.

[0058] (2) The sintered product obtained in step (1) and LiOH·H2O are mixed evenly according to the molar ratio of lithium nickel cobalt manganese oxide to lithium in the sintered product being 1:0.06; then the mixture is placed in a kiln for a second sintering. The conditions for the second sintering are: air atmosphere, with an air flow rate of 4 m³ / s. 3The temperature was increased to 820℃ at a rate of 0.3℃ / min and held for 12 hours. After naturally cooling to room temperature, the material was passed through a 200-mesh sieve to obtain lithium nickel cobalt manganese oxide cathode material coated with a perovskite coating.

[0059] The modified lithium nickel cobalt manganese oxide cathode material prepared in this embodiment was tested by transmission electron microscopy (TEM). The TEM image is shown below. Figure 4 As shown, a stable nanoscale Li layer is formed on the surface of this cathode material. 0.4 W 0.6 The SrO3 coating, as measured by NanoMeasurer, has a thickness distribution between 3 and 7 nm, with the thinnest part being 3 nm and the thickest part being 7 nm. This nanoscale lithium-containing perovskite coating not only improves the internal resistance of low-Co materials and increases power, but also prevents electrolyte corrosion, improves the material interface stability, and significantly reduces oxygen release during high-temperature storage, thus improving storage performance.

[0060] The modified lithium nickel cobalt manganese oxide cathode material prepared in this embodiment was tested by X-ray diffraction. Besides corresponding to the standard lithium nickel cobalt manganese oxide, its diffraction peak positions also exhibited characteristic peaks such as (111), (220), and (400). Through automatic identification and analysis using JADE 6.0 and comparison with PDF cards, these characteristic peaks were determined to be Li... 0.4 W 0.6 The SrO3 crystal structure here also corresponds to the TEM characterization results; by analyzing the characteristic peaks (111), (220), and (400), their peak intensities are 612.47, 600.46, and 418.32, respectively, and their full width at half maximum (FWHM) are 0.1458, 0.180, and 0.0921, respectively; among which I (111) / I (220) It is 1.02, I (400) / I (111) K is 0.683. (111) / K (220) K is 0.812. (400) / K (111) The intensity was 0.632. Analysis showed that the characteristic peak intensity of lithium nickel cobalt manganese oxide (003) was 19139.6, and the full width at half maximum (FWHM) was 0.090. (Li...) 0.4 W 0.6 The ratio of the intensity of the (111) crystal plane peak of SrO3 to the intensity of the (003) crystal plane peak of the modified nickel cobalt manganese oxide cathode material is I (111) / I (003) Li is 0.032. 0.4 W 0.6 The ratio K of the full width at half maximum (FWHM) of the (111) crystal plane of SrO3 to that of the (003) crystal plane of the modified nickel cobalt manganese oxide cathode material is K (111) / K (003)The value was 1.62. XRD analysis showed that the embodiments of this application successfully prepared a lithium-containing perovskite-coated lithium nickel cobalt manganese oxide cathode. The material has high crystallinity and forms an ordered layered structure, which significantly improves its gas generation performance and impedance.

[0061] Comparative Example 1:

[0062] The only difference between the preparation method of the modified nickel cobalt manganese oxide cathode material in this comparative example and that in Example 1 is the amount of W added in step (1). In step (1) of this comparative example, 7.97g of nano-tungsten oxide was weighed according to the mass of W being 0.3% of the precursor mass. The other process parameters were the same as in Example 1.

[0063] The modified lithium nickel cobalt manganese oxide cathode material prepared in this comparative example was tested by X-ray diffraction (XRD) as follows: Figure 5 As shown, no Li coating layer was found. μ W α Sr β O γ The characteristic peaks indicate that no perovskite coating material is formed when the surface W content is too low.

[0064] Comparative Example 2:

[0065] The only difference between the preparation method of the modified nickel cobalt manganese oxide cathode material in this comparative example and that in Example 1 is the amount of W added in step (1). In step (1) of this comparative example, 55.83g of nano-tungsten oxide was weighed according to the mass of W being 2.1% of the precursor mass. The other process parameters were the same as in Example 1.

[0066] The scanning electron microscope (SEM) images of the modified nickel-cobalt-manganese oxide cathode material in this comparative example are as follows: Figure 2 As shown, excessive W content leads to a lower particle size, increased primary particle agglomeration, and a significant deterioration in the gas production performance of the material.

[0067] The modified lithium nickel cobalt manganese oxide cathode material prepared in this comparative example was tested by X-ray diffraction (XRD) as follows: Figure 5 As shown, no Li coating layer was found. μ W α Sr β O γ The characteristic peaks indicate that when the surface W content is too high, the surface state of the material changes during sintering, making single crystal growth difficult, altering the material interface state, and resulting in the absence of perovskite coating material.

[0068] Comparative Example 3:

[0069] The only difference between the preparation method of the modified nickel cobalt manganese oxide cathode material in this comparative example and that in Example 1 is the amount of Sr added in step (1). In step (1) of this comparative example, 31.89 g of nano tungsten oxide was weighed according to the mass of W element accounting for 1.2% of the precursor mass, and 39.88 g of nano strontium oxide was weighed according to the mass of Sr element accounting for 1.6% of the precursor mass. The other process parameters are the same as those in Example 1.

[0070] The modified lithium nickel cobalt manganese oxide cathode material prepared in this comparative example was tested by X-ray diffraction (XRD) as follows: Figure 5 As shown, no Li coating layer was found. μ W α Sr β O γ The characteristic peaks indicate that when the surface W content is too low or the Sr content is too high, the contents of both are not within the appropriate range, resulting in no perovskite coating material being generated during the reaction.

[0071] Comparative Example 4:

[0072] The preparation method of the modified lithium nickel cobalt manganese oxide cathode material in this comparative example differs from that in Example 1 only in the first sintering procedure in step (1). In this comparative example, the mixed materials are placed in an oxygen atmosphere with an oxygen concentration >98% for the first sintering, wherein the oxygen flow rate is 8m³ / s. 3 The first sintering process involves raising the temperature from room temperature to 800℃ at a rate of 3℃ / min and holding it for 6 hours, then raising it to 930℃ at a rate of 0.3℃ / min and holding it for 18 hours, followed by lowering it to 750℃ at a rate of 5℃ / min and holding it for 12 hours. Finally, the material is allowed to cool naturally to room temperature to obtain the sintered material. The sintered material is then crushed and sieved to obtain the final sintered material. The remaining process parameters are the same as in Example 1.

[0073] The modified lithium nickel cobalt manganese oxide cathode material prepared in this comparative example was tested by X-ray diffraction (XRD) as follows: Figure 5 As shown, no Li coating layer was found. μ W α Sr β O γ The characteristic peaks indicate that the heating rate was too fast during the first sintering process and was not within the appropriate range, which prevented the additives from reacting in time, resulting in no obvious perovskite coating material being formed on the surface.

[0074] Comparative Example 5:

[0075] The preparation method of the modified nickel-cobalt-manganese lithium cathode material in this comparative example differs from that in Example 1 only in step (2). In step (2) of this comparative example, the sintered product obtained in step (1) is directly placed in a kiln for a second sintering. The conditions for the second sintering are: it is carried out in an air atmosphere with an air flow rate of 3 m³ / s. 3 The temperature was increased to 820℃ at a rate of 0.3℃ / min and held for 12 hours. After naturally cooling to room temperature, the material was passed through a 200-mesh sieve to obtain the modified lithium nickel cobalt manganese oxide cathode material.

[0076] The modified lithium nickel cobalt manganese oxide cathode material prepared in this comparative example was tested by X-ray diffraction (XRD) as follows: Figure 5 As shown, no Li coating layer was found. μ W α Sr β O γ The characteristic peaks indicate that lithium replenishment was not performed during the secondary sintering of the surface, resulting in an incomplete structure and poor crystallinity of the coated material, which was therefore not identified by XRD.

[0077] Comparative Example 6:

[0078] The preparation method of the modified lithium nickel cobalt manganese oxide cathode material in this comparative example differs from that in Example 1 only in the heating rate in step (2). The heating rate in step (2) of this comparative example is 3℃ / min, and the other process parameters are the same as those in Example 1.

[0079] The modified lithium nickel cobalt manganese oxide cathode material prepared in this comparative example was tested by X-ray diffraction (XRD) as follows: Figure 5 As shown, no Li coating layer was found. μ W α Sr β O γ The characteristic peaks indicate that the heating rate was too fast and not within the appropriate range during the second sintering process, which prevented the initially formed coating material from being repaired, resulting in an incomplete structure and poor crystallinity, and therefore XRD failed to identify it.

[0080] Comparative Example 7:

[0081] The preparation method of the modified lithium nickel cobalt manganese oxide cathode material in this comparative example differs from that in Example 1 only in the amount of LiOH·H2O added in step (2). In step (2) of this comparative example, the lithium nickel cobalt manganese oxide in the sintering product and the lithium element in LiOH·H2O are mixed in a molar ratio of 1:0.02. The other process parameters are the same as those in Example 1.

[0082] The modified lithium nickel cobalt manganese oxide cathode material prepared in this comparative example was tested by X-ray diffraction (XRD) as follows: Figure 5 As shown, no Li coating layer was found. μ Wα Sr β O γ The characteristic peaks indicate that the lithium content was too low during the second sintering process and was not within the appropriate range, which prevented the initially formed coating material from being repaired, resulting in an incomplete structure and poor crystallinity, and therefore it could not be identified by XRD.

[0083] Electrochemical performance testing:

[0084] Positive electrode sheet: The positive electrode materials prepared in the above embodiments and comparative examples are added to NMP solvent with conductive carbon black, graphite and binder PVDF in a mass ratio of 94:2:2:2. After being mixed evenly, they are coated on Al foil, dried at 120°C for 12 hours, and rolled to prepare a positive electrode sheet.

[0085] Negative electrode sheet: Graphite, conductive carbon black, CMC and SBR are added to NMP solvent in a mass ratio of 97:1:1:1. After being mixed evenly, the mixture is coated onto Cu foil and dried at 120°C for 12 hours. The negative electrode sheet is then prepared by roller drying.

[0086] Assemble the battery: Assemble the above positive electrode with the negative electrode to form a 1.5Ah soft pack battery.

[0087] Electrochemical performance was tested at 25℃ within a voltage window of 2.8-4.4V. The specific test regime was as follows: capacity test: 0.33C charging and 0.33C discharging; high temperature cycling and gas generation test regime: at 45℃, 1C charging to 4.4V, 1C discharging to 2.8V, cycling to 1000 cycles, and calculating capacity retention and gas generation content; high temperature storage gas generation test regime: at 25℃, 1C charging to 4.4V, then placing the battery in a 60℃ constant temperature chamber for 56 days, and calculating the gas generation content using the water displacement method.

[0088] The materials obtained in the above embodiments and comparative examples were assembled into a soft-pack battery. The electrochemical performance data, such as the 0.33C discharge specific capacity, internal resistance at 10% SOC at 25℃ and -20℃, capacity retention after 1000 cycles at 45℃, gas generation after 1000 cycles at 45℃, and gas generation during storage at 60℃, are shown in Table 1. Among them, gas generation after 1000 cycles refers to the difference between the battery volume after 1000 cycles and the initial battery volume, and gas generation during storage at 60℃ refers to the difference between the battery volume after 56 days of storage at 60℃ and the initial battery volume.

[0089] Table 1: Electrochemical data for each example and comparative example

[0090]

[0091] As shown in Table 1, comparing Example 1 and Comparative Example 1, Comparative Example 1 did not form a lithium-containing perovskite coating layer due to insufficient W content. Example 1, with its lithium-containing perovskite coating layer, exhibited better performance, with superior internal resistance, rate capability, and gas generation. Comparing Example 1 and Comparative Example 2, Comparative Example 2's excessive W content made it difficult to form single crystals. While its smaller particle size resulted in significant short-term performance improvement, its gas generation performance deteriorated significantly, failing to meet requirements. Comparing Example 1 and Comparative Example 3, Comparative Example 3's high strontium content led to excessive surface coating material, resulting in significant deterioration in material capacity and short-term performance, failing to meet requirements. Comparing Example 1 and Comparative Example 4, it is evident that the multi-stage sintering process, with its heating rate and sintering time, affects the formation of the lithium-containing perovskite coating layer. This further demonstrates that the sintering process can repair the formation of the lithium-containing perovskite coating layer, thereby improving performance. Comparing Example 1 and Comparative Example 5, Comparative Example 5 did not add additional lithium, resulting in the inability of the secondary sintering to repair the lithium-containing perovskite coating layer. This led to an unstable coating layer structure. Although it improved the material's internal resistance and gas generation performance, the improvement was weaker compared to Example 1. Comparing Example 1 and Comparative Example 6, although lithium was added during the secondary sintering in Comparative Example 6, the heating rate during the secondary sintering was too fast, causing the added lithium to fail to react with the perovskite coating layer and thus fail to repair it, resulting in insufficient improvement in material performance. Comparing Example 1 and Comparative Example 7, although lithium was added during the secondary sintering in Comparative Example 7, the added lithium content was too low, resulting in insufficient reaction with the perovskite coating layer and incomplete repair, resulting in insufficient improvement in material performance.

[0092] The above are merely preferred embodiments of the present invention, and the scope of protection of the present invention is not limited to the above embodiments. For those skilled in the art, improvements and modifications obtained without departing from the inventive concept should also be considered within the scope of protection of the present invention.

Claims

1. A modified lithium nickel cobalt manganese oxide cathode material, characterized in that, It includes a lithium nickel cobalt manganese oxide cathode material matrix and a perovskite coating layer encapsulating the surface of the lithium nickel cobalt manganese oxide cathode material matrix; the chemical formula of the perovskite coating layer is Li. μ W α Sr β O γ Where 0 < μ ≤ 1, the ratio of α to β is 0.3-0.7, and 3 ≤ γ < 6.

2. The modified lithium nickel cobalt manganese oxide cathode material as described in claim 1, characterized in that, According to XRD testing, Li μ W α Sr β O γ The peak intensity of the (111) crystal plane and Li μ W α Sr β O γ The ratio of the peak intensities of the (220) crystal plane is 0.2 < I. (111) / I (220) <1.5; Li μ W α Sr β O γ The peak intensity of the (400) crystal plane and Li μ W α Sr β O γ The ratio of the peak intensities of the (111) crystal plane is 0.1 < I (400) / I (111) <2.

0.

3. The modified lithium nickel cobalt manganese oxide cathode material as described in claim 1, characterized in that, According to XRD testing, Li μ W α Sr β O γ The (111) crystal plane half-width at half-maximum and Li μ W α Sr β O γ The half-maximum-to-width ratio of the (220) crystal plane is 0.5 < K. (111) / K (220) <1.0; Li μ W α Sr β O γ The (400) crystal plane half-width and Li μ W α Sr β O γ The half-maximum-to-width ratio of the (111) crystal plane is 0.3 < K. (400) / K (111) <1.

0.

4. The modified lithium nickel cobalt manganese oxide cathode material as described in claim 1, characterized in that, According to XRD testing, Li μ W α Sr β O γ The ratio of the intensity of the (111) crystal plane peak to the intensity of the (003) crystal plane peak of the modified lithium nickel cobalt manganese oxide cathode material is 0.01 < I. (111) / I (003) <0.05; Li μ W α Sr β O γ The ratio of the full width at half maximum (FWHM) of the (111) crystal plane to that of the (003) crystal plane in the modified lithium nickel cobalt manganese oxide cathode material is 1.2 < K. (111) / K (003) <2.

2.

5. The modified lithium nickel cobalt manganese oxide cathode material according to any one of claims 1 to 4, characterized in that, The thickness of the perovskite coating is 1-20 nm.

6. The modified lithium nickel cobalt manganese oxide cathode material according to any one of claims 1 to 4, characterized in that, The chemical formula of the lithium nickel cobalt manganese oxide cathode material matrix is ​​Li x Ni y Co z Mn 1-y-z-a M a O2, wherein 0.95≤x≤1.2, 0.5≤y<1, 0<z≤0.2, 0<a≤0.02, 0<1-yza≤0.28, and M includes one or more of the elements Mg, Ti, Zr, Ba, W, Nb, Sr, Ta and La.

7. The modified lithium nickel cobalt manganese oxide cathode material according to any one of claims 1 to 4, characterized in that, The modified lithium nickel cobalt manganese oxide cathode material has a powder conductivity ρ of 0.0001 S / cm-0.02 S / cm under a pressure of 190 MPa.

8. A method for preparing a modified lithium nickel cobalt manganese oxide cathode material as described in any one of claims 1 to 7, characterized in that, Includes the following steps: (1) A first sintering treatment was performed on a mixture of a precursor containing nickel, cobalt and manganese, a lithium salt, a W-containing compound, a Sr-containing compound and a M-containing compound to obtain a sintered product. (2) The sintered product obtained in step (1) is crushed and dissociated, then mixed with lithium salt, and subjected to a second sintering treatment. After sieving, the modified lithium nickel cobalt manganese oxide cathode material is obtained.

9. The preparation method according to claim 8, characterized in that, In step (1), the molar ratio of Li to precursor in lithium salt is 0.95-1.0:1, the mass of W in W-containing compound is 0.4%-2.0% of the precursor mass, the mass of Sr in Sr-containing compound is 0.25%-1.6% of the precursor mass, and the molar ratio of W to Sr is (2-4):

5.

10. The preparation method according to claim 8, characterized in that, In step (1), the first sintering treatment is carried out in an oxygen or air atmosphere with a ventilation rate of 5 m³ / s. 3 / h-30m 3 / h.

11. The preparation method according to claim 8, characterized in that, In step (1), the first sintering process is multi-stage sintering: the first stage sintering temperature is T1, the sintering time is t1, the heating rate is V1, the second stage sintering temperature is T2, the sintering time is t2, the heating rate is V2, the third stage sintering temperature is T3, the sintering time is t3, and the cooling rate is V3. Among them, 450℃≤T1≤750℃, 850℃≤T2≤950℃, 600℃≤T3≤800℃, 3h≤t1≤8h, 1.5≤t2 / t1≤3, t1≤t3≤t2; 0.5℃ / min≤V1≤1.5℃ / min, 1<V2 / V1≤3, V1≤V3≤V2.

12. The preparation method according to claim 8, characterized in that, In step (2), the molar ratio of lithium element in the lithium salt to lithium nickel cobalt manganese oxide in the sintered product obtained in step (1) is 0.06-0.2:1; In step (2), the second sintering process is carried out in an oxygen or air atmosphere with a ventilation rate of 1 m³ / s. 3 / h-5m 3 / h; the sintering temperature of the second sintering treatment is 600℃-850℃, the sintering time is 6h-20h, and the heating rate is 0.2-0.5℃ / min.

13. The preparation method according to claim 8, characterized in that, The lithium salt is selected from one or more of lithium carbonate, lithium hydroxide, or lithium acetate; the Sr-containing compound includes one or more of strontium oxide, strontium hydroxide, and strontium carbonate; and the W-containing compound includes one or more of tungsten oxide, ammonium metatungstate, and ammonium paratungstate.

14. A lithium-ion battery, characterized in that, The modified lithium nickel cobalt manganese oxide cathode material includes any one of claims 1 to 7, or includes the modified lithium nickel cobalt manganese oxide cathode material prepared by any one of claims 8 to 13.

15. An electrical appliance, characterized in that, Including the lithium-ion battery as described in claim 14.

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