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

Abstract

The application belongs to the technical field of lithium ion battery materials, and discloses a high-nickel single-crystal positive electrode material with a cationic mixed arrangement degree of 1.9% to 3.6% and including single-crystal particles with a sheet-like morphology. A hydroxide precursor material of the high-nickel single-crystal positive electrode material is mixed with a lithium salt and a molten salt to obtain a mixture; the molten salt at least includes lithium nitrate; the mixture is subjected to two-stage sintering in an oxygen atmosphere, first sintering at 400 to 500 DEG C, and then sintering after being heated to 650 to 750 DEG C to obtain a black powder; the black powder is washed with water, dried, mixed with a lithium salt, and then sintered at 500 to 600 DEG C to obtain the high-nickel single-crystal positive electrode material. The high-nickel single-crystal positive electrode material including single-crystal particles with a sheet-like morphology has a low cationic mixed arrangement degree, which is beneficial to improving the reversible capacity and cycle stability of a lithium ion battery. The high-nickel single-crystal positive electrode material with a low cationic mixed arrangement degree is prepared at a low sintering temperature, and the preparation method is simple, reliable, easy to operate, and beneficial to reducing the industrial production cost.

Description

Technical Field

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

[0002] Lithium-ion batteries are widely used in portable electronics, electric vehicles, energy storage, and many other fields related to renewable energy. However, with growing concerns about the driving range of electric vehicles, stricter requirements have been placed on the energy density, rate performance, and cycle performance of lithium-ion batteries. The cathode material of a lithium-ion battery has a significant impact on its electrical performance. Currently, much research focuses on optimizing the fabrication process of high-nickel single-crystal cathode materials to improve the electrical performance of lithium-ion batteries.

[0003] CN116443954A discloses a nickel-cobalt-manganese high-nickel single-crystal cathode material and its preparation method. The method first prepares a nickel-rich hydroxide precursor through co-precipitation; the precursor is then mixed uniformly with KCl and lithium salt in a specific stoichiometric ratio, followed by high-temperature calcination. The resulting mixture is washed multiple times with deionized water, dried, and then subjected to a second high-temperature sintering to obtain the single-crystal nickel-rich layered cathode material. The single-crystal particles prepared by this method exhibit partial agglomeration, and the high sintering temperature inevitably leads to severe cation mixing, affecting the battery's cycle stability.

[0004] CN115432750A discloses a porous honeycomb-shaped single-crystal high-nickel cathode material and its preparation method. The preparation method includes: S1, a first calcination of a high-nickel precursor and a lithium-containing molten salt under a low-oxygen atmosphere; S2, a second calcination of an intermediate material and a lithium-containing compound under a pure oxygen atmosphere, to obtain the porous honeycomb-shaped single-crystal high-nickel cathode material. The material prepared by this method has numerous pores on its surface, increasing the contact area between the electrolyte and the cathode material, leading to more electrolyte decomposition. Furthermore, this method also uses a relatively high sintering temperature, resulting in severe cation mixing and a low reversible discharge capacity.

[0005] CN110844947A discloses a method for preparing a high-nickel single-crystal cathode material and the cathode material in a lithium-ion battery. The preparation method includes: S1, crushing a high-nickel secondary spherical precursor; S2, coating the surface with a solid oxidant; S3, pre-oxidizing the precursor; S4, sintering the precursor with mixed lithium; S5, crushing treatment; and S6, washing and re-sintering. However, this method for preparing a high-nickel single-crystal cathode material is difficult to produce high-nickel single-crystal cathode materials with a high nickel content.

[0006] In general, the single-crystal cathode materials prepared by current processes cannot simultaneously possess the characteristics of high nickel content and low cation mixing degree. Summary of the Invention

[0007] To address the problems existing in the prior art, the main objective of this invention is to provide a high-nickel single-crystal cathode material with low cation mixing degree and its low-temperature preparation process. Secondly, this invention provides a battery.

[0008] To achieve the above objectives, the present invention provides the following specific technical solutions.

[0009] First, this invention provides a high-nickel single-crystal cathode material, the chemical formula of which is LiNi. 1-x- y Co x Mn y O2, 0≤x≤0.1, 0≤y≤0.1, comprising single-crystal particles with a plate-like morphology, wherein the cation mixing degree of the cathode material is 1.9%~3.6%; and the thickness of the single-crystal particles of the cathode material is 50~300nm.

[0010] Secondly, this invention provides a method for preparing the above-mentioned high-nickel single-crystal cathode material, comprising: A hydroxide precursor material for a high-nickel single-crystal cathode is mixed with a lithium salt and a molten salt to obtain a mixture; the molten salt includes at least lithium nitrate. The mixture was sintered in two stages under an oxygen atmosphere. First, it was sintered at 400~500℃, and then the temperature was raised to 650~750℃ to obtain a black powder. The black powder is washed with water, dried, mixed with lithium salt, and then sintered at 500~600℃ to obtain the high-nickel single crystal cathode material.

[0011] In a further preferred embodiment, the general chemical formula of the hydroxide precursor of the high-nickel single-crystal cathode material is Ni. (1-x-y) Co x Mn y (OH)2, where 0≤x≤0.1, 0≤y≤0.1.

[0012] In a further preferred embodiment, the lithium salt is one or both of lithium hydroxide and lithium carbonate.

[0013] In a further preferred embodiment, the molten salt further includes at least one of Li₂SO₄, NaCl, and KCl.

[0014] In a further preferred embodiment, the amount of lithium nitrate in the molten salt is greater than or equal to 50 wt%.

[0015] In a further preferred embodiment, the molar ratio of the hydroxide precursor material of the high-nickel single-crystal cathode material, lithium in the lithium salt, and molten salt in the mixture is 1:1.05~1.2:1.8~3.

[0016] In a further preferred embodiment, the black powder and lithium salt are mixed according to a ratio of 1:0.02 to 0.1 between the total molar amount of transition metals in the dried black powder and the molar amount of Li in the lithium salt. The transition metals referred to in this invention are Ni, Co, and Mn.

[0017] Based on the same inventive concept, the present invention provides a lithium-ion battery comprising the above-mentioned high-nickel single-crystal cathode material.

[0018] Compared with the prior art, the above-described one or more technical solutions of the present invention can achieve at least one of the following beneficial effects: The high-nickel single-crystal cathode material provided by this invention, which includes single-crystal particles with a plate-like morphology, has a low cation mixing degree, which is beneficial to improving the reversible capacity and cycle stability of lithium-ion batteries.

[0019] This invention provides a method for preparing high-nickel single-crystal cathode materials with low cation mixing degree at a lower sintering temperature. The preparation method is simple, reliable, easy to operate, and helps to reduce industrial production costs. Attached Figure Description

[0020] Figure 1 The image shows a SEM image of the high-nickel cathode material prepared in Example 1.

[0021] Figure 2 This is a SEM image of the high-nickel cathode material prepared in Example 2.

[0022] Figure 3 This is a SEM image of the high-nickel cathode material prepared in Example 3.

[0023] Figure 4 This is a SEM image of the high-nickel cathode material prepared in Example 4.

[0024] Figure 5 SEM image of the high-nickel cathode material prepared in Comparative Example 1.

[0025] Figure 6 SEM image of the high-nickel cathode material prepared in Comparative Example 2.

[0026] Figure 7 SEM image of the high-nickel cathode material prepared in Comparative Example 3.

[0027] Figure 8 SEM image of the high-nickel cathode material prepared in Comparative Example 4.

[0028] Figure 9 SEM image of the high-nickel cathode material prepared in Comparative Example 5.

[0029] Figure 10 SEM image of the high-nickel cathode material prepared in Comparative Example 6.

[0030] Figure 11 SEM image of the high-nickel cathode material prepared in Comparative Example 7.

[0031] Figure 12 This is a SEM image of the high-nickel cathode material prepared in Example 5.

[0032] Figure 13 This is a SEM image of the high-nickel cathode material prepared in Example 6.

[0033] Figure 14 This is a SEM image of the high-nickel cathode material prepared in Example 7.

[0034] Figure 15 The image shows a SEM image of the high-nickel cathode material prepared in Example 8.

[0035] Figure 16 The image shows a SEM image of the high-nickel cathode material prepared in Example 9.

[0036] Figure 17 SEM image of the high-nickel cathode material prepared in Example 10. Detailed Implementation

[0037] Cation misalignment refers to the displacement of cations (such as nickel, cobalt, and manganese) in cathode materials during the manufacturing process, occupying positions that would normally belong to lithium ions. This phenomenon typically occurs in cathode materials with high nickel content because divalent nickel ions and lithium ions are similar in size, making misalignment more likely. 2+ and Li + The location has changed, entering Li + Ni layer 2+ It will hinder Li + The diffusion of Li led to the spread of Li + The shuttle rate between lattice layers slows down, increasing Li + Embedded impedance. On the other hand, during charging and discharging, the impedance located in Li... + Ni layer 2+ It will be oxidized to Ni 4+ Due to Ni 4+ The ionic radius is much smaller than that of Li. + This leads to the collapse of the local crystal lattice structure, resulting in irreversible capacity decay.

[0038] Currently, the cation mixing degree of cathode materials is typically around 5%. Generally speaking, the sintering temperature for obtaining high-nickel single-crystal cathode materials cannot be too low, otherwise a single-crystal structure cannot be obtained. Therefore, in existing technologies, higher sintering temperatures are often used to prepare high-nickel single-crystal cathode materials. However, higher sintering temperatures result in a higher cation mixing degree in high-nickel single-crystal cathode materials, which is detrimental to improving the electrical performance of lithium-ion batteries.

[0039] To further improve the structural stability and electrochemical performance of cathode materials, this invention provides a high-nickel single-crystal cathode material with a cation mixing degree of 1.9%~3.6%.

[0040] This invention tests cation mixing degree in the following way: First, XRD tests are performed on the cathode material to be tested, and the raw XRD data are then structurally refined using Fullprof software. The space group of the high-nickel cathode material is R-3m, which is similar to the structure of lithium nickelate LiNiO2. Therefore, this invention uses LiNiO2 as the structural model for the cathode powder material. During the refinement process, the Pseudo-Voigt function is selected as the peak shape function, and the cosine fourier expansion of the parameters is used for background fitting. The order of the refined parameters is as follows: 1. Scale factor; 2. Background parameters; 3. Cell parameters; 4. Zero-point correction; 5. Half-width at half-maximum (WHM); 6. Peak shape function; 7. Thermal vibration factor; 8. Atomic position; 9. Atomic occupancy. The refinement of atomic occupancy and cell parameters abc is the key step in the refinement process. Specifically, a mixing model is constructed for refinement and fitting, assuming Li + After entering the transition metal layer, only nickel sites with a relatively high content are occupied. The structural parameter—atomic occupancy—is refined in detail. Finally, the lithium-nickel mixing degree is obtained by calculating the concentration ratio of Ni atoms at the 3a site. At the same time, the final error parameter R-factor is controlled at around 5% to ensure the reliability of the fitting results.

[0041] Furthermore, the high-nickel single-crystal cathode material provided by this invention comprises single-crystal particles with a plate-like morphology, and the thickness of the single-crystal particles is 50~300 nm. Compared with common single crystals, the high-nickel single-crystal cathode material provided by this invention, comprising plate-like single-crystal particles, shortens the Li... + The transmission distance makes it easier to achieve Li + Extraction / intercalation significantly reduces battery polarization.

[0042] This invention takes a novel approach, employing the following specific method for preparing high-nickel single-crystal cathode materials. Under low-temperature sintering conditions, a high-nickel single-crystal cathode material with low cation mixing degree and comprising single-crystal particles exhibiting a plate-like morphology is prepared, including: A hydroxide precursor material for a high-nickel single-crystal cathode is mixed with a lithium salt and a molten salt to obtain a mixture; the molten salt includes at least lithium nitrate. The mixture was sintered in two stages under an oxygen atmosphere. First, it was sintered at 400~500℃, and then the temperature was raised to 650~750℃ to obtain a black powder. The black powder is washed with water, dried, mixed with lithium salt, and then sintered at 500~600℃ to obtain the high-nickel single crystal cathode material.

[0043] Typically, molten salts, used as high-temperature fluxes and reaction media, shorten the diffusion distance of reactants and enhance their fluidity. Lithium nitrate, as a molten salt, benefits from the low melting point of LiNO3, which facilitates particle growth during low-temperature calcination, and the strong oxidizing properties of LiNO3 inhibit Ni… 2+ The formation of ions reduces cation mixing.

[0044] The mixture was sintered in two stages under an oxygen atmosphere. The first stage was sintering at 400-500℃. Li + The high-nickel polycrystalline cathode material is fully embedded in the precursor to form a layered high-nickel cathode material. Then, it is heated to 650~750℃ for sintering. The secondary polycrystalline particles decompose, and the primary particles undergo Ostwald growth, eventually forming a high-nickel single-crystal cathode material including single-crystal particles with a plate-like morphology.

[0045] The black powder may contain excess molten salt, which is removed by washing with water; then it is dried and mixed with lithium salt, followed by low-temperature sintering. The black powder consists of cathode material and excess molten salt. Washing with water not only removes the excess molten salt but also causes the lithium inside the cathode material to... + The lithium diffuses outward, forming a lithium-deficient phase cathode material. After washing, the black powder is mixed with a small amount of lithium salt. Due to the thinness of the single-crystal cathode material, it can be sintered at low temperature to complete the Li-ion process. + The cathode material is obtained by fully embedding the cathode material.

[0046] In some preferred embodiments, the general chemical formula of the hydroxide precursor of the high-nickel single-crystal cathode material is Ni. (1-x-y) Co x Mn y (OH)2(0≤x≤0.1, 0≤y≤0.1).

[0047] In some preferred embodiments, the lithium salt is one or both of lithium hydroxide and lithium carbonate.

[0048] In some preferred embodiments, the molten salt further includes at least one of Li2SO4, NaCl, and KCl.

[0049] In some preferred embodiments, the molar amount of lithium nitrate in the molten salt is greater than or equal to 50%.

[0050] In some preferred embodiments, the molar ratio of the hydroxide precursor material of the high-nickel single-crystal cathode material, lithium in the lithium salt, and molten salt in the mixture is 1:1.05~1.2:1.8~3.

[0051] In some preferred embodiments, the black powder and lithium salt are mixed according to a ratio of 1:0.02 to 0.1 between the total molar amount of transition metals in the dried black powder and the molar amount of Li in the lithium salt.

[0052] Some embodiments of the present invention provide a lithium-ion battery comprising the above-mentioned high-nickel single-crystal cathode material.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] Example 1 Ni(OH)2, LiOH, and LiNO3 were ground and mixed in a molar ratio of 1:1.2:1.8 to obtain a mixture. The mixture was sintered in two stages under an oxygen atmosphere. First, it was sintered at 450℃ for 5 hours, and then the temperature was raised to 650℃ for 12 hours to obtain a black powder. The black powder was washed with deionized water and then dried under vacuum at 80°C. The black powder and lithium salt were mixed according to a ratio of 1:0.05 between the total molar amount of transition metals in the dried black powder and the molar amount of Li in the lithium salt. The mixture was then sintered at 500°C in an oxygen atmosphere for 5 hours. After sintering, it was cooled to room temperature to obtain a high-nickel single-crystal cathode material.

[0057] Figure 1 The SEM image of the high-nickel single-crystal cathode material obtained in Example 1 shows that the thickness of the single-crystal particles is 100~300nm, and the surface of the single-crystal particles is smooth, proving that the washing has completely removed the excess molten salt, and that the subsequent low-temperature sintering can also facilitate the addition of Li. + It is fully embedded in the high-nickel single-crystal cathode material.

[0058] Example 2 Ni(OH)2, LiOH, LiNO3, and NaCl were ground and mixed in a molar ratio of 1:1.05:1:1 to obtain a mixture. The mixture was sintered in two stages under an oxygen atmosphere. First, it was sintered at 500℃ for 5 hours, and then the temperature was raised to 680℃ for 12 hours to obtain a black powder. The black powder was washed with deionized water and then dried under vacuum at 80°C. The black powder and lithium salt were mixed according to a ratio of 1:0.05 between the total molar amount of transition metals in the dried black powder and the molar amount of Li in the lithium salt. The mixture was then sintered at 600℃ in an oxygen atmosphere for 5 hours. After sintering, it was cooled to room temperature to obtain a high-nickel single-crystal cathode material.

[0059] Figure 2 The image shows the SEM image of the high-nickel single-crystal cathode material obtained in Example 2. It can be seen that the surface of the single-crystal particles is smooth and the thickness is 70~200nm.

[0060] Example 3 Ni(OH)2, LiOH, LiNO3, and Li2SO4 were ground and mixed in a molar ratio of 1:1.05:1:1 to obtain a mixture. The mixture was sintered in two stages under an oxygen atmosphere. First, it was sintered at 500℃ for 5 hours, and then the temperature was raised to 700℃ for 12 hours to obtain a black powder. The black powder was washed with deionized water and then dried under vacuum at 80°C. The black powder and lithium salt were mixed according to a ratio of 1:0.03 between the total molar amount of transition metals in the dried black powder and the molar amount of Li in the lithium salt. The mixture was then sintered at 600℃ in an oxygen atmosphere for 5 hours. After sintering, it was cooled to room temperature to obtain a high-nickel single-crystal cathode material.

[0061] Figure 3 The image shows the SEM image of the high-nickel single-crystal cathode material obtained in Example 3. It can be seen that the surface of the single-crystal particles is smooth and the thickness is 80~200nm.

[0062] Example 4 Ni(OH)2, Li2CO3, and LiNO3 were ground and mixed in a molar ratio of 1:0.6:1.8 to obtain a mixture. The mixture was sintered in two stages under an oxygen atmosphere. First, it was sintered at 450℃ for 5 hours, and then the temperature was raised to 660℃ for 12 hours to obtain a black powder. The black powder was washed with deionized water and then dried under vacuum at 80°C. The black powder and lithium salt were mixed according to a ratio of 1:0.04 between the total molar amount of transition metals in the dried black powder and the molar amount of Li in the lithium salt. The mixture was then sintered at 550℃ in an oxygen atmosphere for 5 hours. After sintering, it was cooled to room temperature to obtain a high-nickel single-crystal cathode material.

[0063] Figure 4 The image shows the SEM image of the high-nickel single-crystal cathode material obtained in Example 4. It can be seen that the surface of the single-crystal particles is smooth and the thickness is 70~250 nm.

[0064] Comparative Example 1 Ni(OH)₂, LiOH, and NaCl were ground and mixed in a molar ratio of 1:1.2:1.8 to obtain a mixture. The mixture was sintered in two stages under an oxygen atmosphere. First, it was sintered at 450℃ for 5 hours, and then the temperature was raised to 650℃ for 12 hours to obtain a black powder. The black powder was washed with deionized water and then dried under vacuum at 80°C. The black powder and lithium salt were mixed according to a ratio of 1:0.05 between the total molar amount of transition metals in the dried black powder and the molar amount of Li in the lithium salt. The mixture was then sintered at 500°C in an oxygen atmosphere for 5 hours. After sintering, it was cooled to room temperature to obtain a high-nickel polycrystalline cathode material.

[0065] Comparative Example 2 Ni(OH)2, LiOH, and Li2SO4 were ground and mixed in a molar ratio of 1:1.2:1.8 to obtain a mixture. The mixture was sintered in two stages under an oxygen atmosphere. First, it was sintered at 450℃ for 5 hours, and then the temperature was raised to 650℃ for 12 hours to obtain a black powder. The black powder was washed with deionized water and then dried under vacuum at 80°C. The black powder and lithium salt were mixed according to a ratio of 1:0.05 between the total molar amount of transition metals in the dried black powder and the molar amount of Li in the lithium salt. The mixture was then sintered at 500°C in an oxygen atmosphere for 5 hours. After sintering, it was cooled to room temperature to obtain a high-nickel polycrystalline cathode material.

[0066] Comparative Example 3 Ni(OH)2, LiOH, Li2SO4, and NaCl were ground and mixed in a molar ratio of 1:1.05:1:1 to obtain a mixture. The mixture was sintered in two stages under an oxygen atmosphere. First, it was sintered at 500℃ for 5 hours, and then the temperature was raised to 680℃ for 12 hours to obtain a black powder. The black powder was washed with deionized water and then dried under vacuum at 80°C. The black powder and lithium salt were mixed according to a ratio of 1:0.05 between the total molar amount of transition metals in the dried black powder and the molar amount of Li in the lithium salt. The mixture was then sintered at 600℃ in an oxygen atmosphere for 5 hours. After sintering, it was cooled to room temperature to obtain a high-nickel polycrystalline cathode material.

[0067] Comparative Example 4 Ni(OH)2 and LiOH were ground and mixed at a molar ratio of 1:1.2 to obtain a mixture. The mixture was sintered in two stages under an oxygen atmosphere. First, it was sintered at 450℃ for 5 hours, and then the temperature was raised to 650℃ for 12 hours to obtain a black powder. The black powder was washed with deionized water and then dried under vacuum at 80°C. The black powder and lithium salt were mixed according to a ratio of 1:0.05 between the total molar amount of transition metals in the dried black powder and the molar amount of Li in the lithium salt. The mixture was then sintered at 500°C in an oxygen atmosphere for 5 hours. After sintering, it was cooled to room temperature to obtain a high-nickel polycrystalline cathode material.

[0068] Comparative Example 5 Ni(OH)2 and LiOH were ground and mixed at a molar ratio of 1:1.2 to obtain a mixture. The mixture was sintered in two stages under an oxygen atmosphere. First, it was sintered at 450℃ for 5 hours, and then the temperature was raised to 850℃ for 12 hours to obtain a black powder. The black powder was washed with deionized water and then dried under vacuum at 80°C. The black powder and lithium salt were mixed according to a ratio of 1:0.05 between the total molar amount of transition metals in the dried black powder and the molar amount of Li in the lithium salt. The mixture was then sintered at 500°C in an oxygen atmosphere for 5 hours. After sintering, it was cooled to room temperature to obtain a high-nickel single-crystal cathode material.

[0069] Comparative Example 6 Ni(OH)2, LiOH, and LiNO3 were ground and mixed in a molar ratio of 1:1.2:1.8 to obtain a mixture. The mixture was sintered at 650°C for 12 hours in an oxygen atmosphere to obtain a black powder. The black powder was washed with deionized water and then dried under vacuum at 80°C. The black powder and lithium salt were mixed according to a ratio of 1:0.05 between the total molar amount of transition metals in the dried black powder and the molar amount of Li in the lithium salt. The mixture was then sintered at 500°C in an oxygen atmosphere for 5 hours. After sintering, it was cooled to room temperature to obtain a high-nickel single-crystal cathode material.

[0070] Comparative Example 7 Ni(OH)2, LiOH, and LiNO3 were ground and mixed in a molar ratio of 1:1.2:1.8 to obtain a mixture. The mixture was sintered in two stages under an oxygen atmosphere. First, it was sintered at 450℃ for 5 hours, and then the temperature was raised to 650℃ for 12 hours to obtain a black powder. The black powder was washed with deionized water, dried under vacuum at 80°C, and then sintered at 500°C in an oxygen atmosphere for 5 hours. After sintering, it was cooled to room temperature to obtain a high-nickel single-crystal cathode material.

[0071] Example 5 Ni 0.99 Mn 0.01 (OH)2, LiOH, and LiNO3 are ground and mixed in a molar ratio of 1:1.1:2.5 to obtain a mixture. The mixture was sintered in two stages under an oxygen atmosphere. First, it was sintered at 480℃ for 5 hours, and then the temperature was raised to 660℃ for 12 hours to obtain a black powder. The black powder was washed with deionized water and then dried under vacuum at 80°C. The black powder and lithium salt were mixed according to a ratio of 1:0.05 between the total molar amount of transition metals in the dried black powder and the molar amount of Li in the lithium salt. The mixture was then sintered at 550℃ in an oxygen atmosphere for 5 hours. After sintering, it was cooled to room temperature to obtain a high-nickel single-crystal cathode material.

[0072] Example 6 Ni 0.8 Co 0.1 Mn 0.1 (OH)2, LiOH, and LiNO3 are ground and mixed in a molar ratio of 1:1.2:3.0 to obtain a mixture; The mixture was sintered in two stages under an oxygen atmosphere. First, it was sintered at 500℃ for 5 hours, and then the temperature was raised to 700℃ for 12 hours to obtain a black powder. The black powder was washed with deionized water and then dried under vacuum at 80°C. The black powder and lithium salt were mixed according to a ratio of 1:0.04 between the total molar amount of transition metals in the dried black powder and the molar amount of Li in the lithium salt. The mixture was then sintered at 600℃ in an oxygen atmosphere for 5 hours. After sintering, it was cooled to room temperature to obtain a high-nickel single-crystal cathode material.

[0073] Example 7 Ni 0.9 Co 0.05 Mn 0.05 (OH)2, LiOH, and LiNO3 are ground and mixed in a molar ratio of 1:1.2:2.8 to obtain a mixture. The mixture was sintered in two stages under an oxygen atmosphere. First, it was sintered at 480℃ for 5 hours, and then the temperature was raised to 690℃ for 12 hours to obtain a black powder. The black powder was washed with deionized water and then dried under vacuum at 80°C. The black powder and lithium salt were mixed according to a ratio of 1:0.05 between the total molar amount of transition metals in the dried black powder and the molar amount of Li in the lithium salt. The mixture was then sintered at 600℃ in an oxygen atmosphere for 5 hours. After sintering, it was cooled to room temperature to obtain a high-nickel single-crystal cathode material.

[0074] Example 8 Ni 0.92 Co 0.04 Mn 0.04 (OH)2, LiOH, and LiNO3 are ground and mixed in a molar ratio of 1:1.1:1.8 to obtain a mixture. The mixture was sintered in two stages under an oxygen atmosphere. First, it was sintered at 480℃ for 5 hours, and then the temperature was raised to 680℃ for 12 hours to obtain a black powder. The black powder was washed with deionized water and then dried under vacuum at 80°C. The black powder and lithium salt were mixed according to a ratio of 1:0.05 between the total molar amount of transition metals in the dried black powder and the molar amount of Li in the lithium salt. The mixture was then sintered at 600℃ in an oxygen atmosphere for 5 hours. After sintering, it was cooled to room temperature to obtain a high-nickel single-crystal cathode material.

[0075] Example 9 Ni 0.96 Co 0.02 Mn 0.02 (OH)2, LiOH, and LiNO3 are ground and mixed in a molar ratio of 1:1.1:2.0 to obtain a mixture; The mixture was sintered in two stages under an oxygen atmosphere. First, it was sintered at 480℃ for 5 hours, and then the temperature was raised to 670℃ for 12 hours to obtain a black powder. The black powder was washed with deionized water and then dried under vacuum at 80°C. The black powder and lithium salt were mixed according to a ratio of 1:0.05 between the total molar amount of transition metals in the dried black powder and the molar amount of Li in the lithium salt. The mixture was then sintered at 580℃ in an oxygen atmosphere for 5 hours. After sintering, it was cooled to room temperature to obtain a high-nickel single-crystal cathode material.

[0076] Example 10 Ni 0.98 Mn 0.02 (OH)2, LiOH, and LiNO3 are ground and mixed in a molar ratio of 1:1.2:1.8 to obtain a mixture. The mixture was sintered in two stages under an oxygen atmosphere. First, it was sintered at 480℃ for 5 hours, and then the temperature was raised to 660℃ for 12 hours to obtain a black powder. The black powder was washed with deionized water and then dried under vacuum at 80°C. The black powder and lithium salt were mixed according to a ratio of 1:0.05 between the total molar amount of transition metals in the dried black powder and the molar amount of Li in the lithium salt. The mixture was then sintered at 550℃ in an oxygen atmosphere for 5 hours. After sintering, it was cooled to room temperature to obtain a high-nickel single-crystal cathode material.

[0077] SEM images of high-nickel cathode materials ( Figures 1-17 The thickness of the single crystal particles was obtained by measurement.

[0078] The cation mixing degree and single crystal particle thickness results of the high-nickel single crystal cathode materials obtained in Examples 1-10 and Comparative Examples 1-7 are shown in Table 1.

[0079] Table 1 When the molten salt does not contain LiNO3, the sintering process of this invention can only produce high-nickel polycrystalline cathode materials with high cation mixing degree, but not high-nickel single-crystalline cathode materials with low cation mixing degree. This may be because the low melting point of LiNO3 facilitates particle growth during calcination, and the strong oxidation of LiNO3 inhibits Ni… 2+ The formation of ions reduces cation mixing.

[0080] As shown in Comparative Example 5, high-temperature sintering can indeed produce high-nickel single-crystal cathode materials when molten salt is not present. However, the cation mixing degree of the cathode material is very high, and the single-crystal thickness is very large.

[0081] When a mixture of Ni(OH)₂, LiOH, and LiNO₃ is sintered using only a single-stage process, a high-nickel single-crystal cathode material with a high degree of cation mixing is also obtained. This may be because during single-stage sintering, Li… + The embedding within the precursor and the growth of single-crystal grains occur simultaneously, leading to the Li + It cannot be well embedded, resulting in the formation of high-nickel single-crystal cathode materials with a high degree of cation mixing.

[0082] If no further lithium replenishment process is performed during the preparation of high-nickel single-crystal cathode materials, a high-nickel single-crystal cathode material with a high cation mixing degree will be obtained. This may be because washing with water not only removes excess molten salt but also leads to the removal of lithium within the cathode material. + It diffuses outwards, forming a lithium-deficient phase cathode material. Ni 2+ It enters its vacancy, further aggravating cation mixing.

[0083] The high-nickel single-crystal cathode materials obtained in Examples 1-10 and Comparative Examples 1-7 were assembled into batteries as follows: The cathode material, acetylene black, and polyvinylidene fluoride were mixed in N-methyl-2-pyrrolidone at a mass ratio of 8:1:1. The paste was coated onto an aluminum foil collector and dried at 80°C for 4 hours. The cathode was then perforated onto a 12 mm diameter disk and vacuum dried at 80°C for 12 hours. The half-cell (CR2032) was assembled in an argon-filled glove box, using 1 M LiPF6 in fluoroethylene carbonate (FEC):trifluoroethyl methyl carbonate (FEMC) = 1:1 (volume ratio) as the electrolyte and lithium metal as the anode.

[0084] Using constant current / constant voltage charging and constant current discharging modes, under different current conditions (1C = 180 mA g) and cutoff voltages of 2.7~4.4 V, the results were obtained. −1 A constant current charge-discharge cycle is obtained.

[0085] The electrochemical performance of the high-nickel single-crystal cathode materials obtained in Examples 1-10 and Comparative Examples 1-7 is shown in Table 2.

[0086] Table 2 As can be seen from Table 2, high-nickel single-crystal cathode materials with low cation mixing degree, including single-crystal particles with a plate-like morphology, can improve the reversible capacity and cycle stability of the battery.

[0087] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A high-nickel single-crystal cathode material, characterized in that, The chemical formula of the high-nickel cathode material is LiNi. 1-x-y Co x Mn y O2, 0≤x≤0.1, 0≤y≤0.1, including single crystal particles with a plate-like morphology; the cation mixing degree of the cathode material is 1.9%~3.6%.

2. The high-nickel single-crystal cathode material as described in claim 1, characterized in that, The thickness of the single-crystal particles of the cathode material is 50~300nm.

3. A method for preparing a high-nickel single-crystal cathode material, characterized in that, include: A hydroxide precursor material for a high-nickel single-crystal cathode is mixed with a lithium salt and a molten salt to obtain a mixture; the molten salt includes at least lithium nitrate. The mixture was sintered in two stages under an oxygen atmosphere. First, it was sintered at 400~500℃, and then the temperature was raised to 650~750℃ to obtain a black powder. The black powder is washed with water, dried, mixed with lithium salt, and then sintered at 500~600℃ to obtain the high-nickel single crystal cathode material.

4. The preparation method according to claim 3, characterized in that, The general chemical formula of the hydroxide precursor of the high-nickel single-crystal cathode material is Ni. (1-x-y) Co x Mn y (OH)2, where 0≤x≤0.1, 0≤y≤0.

1.

5. The preparation method according to claim 3, characterized in that, The lithium salt is one or both of lithium hydroxide and lithium carbonate.

6. The preparation method according to any one of claims 3 to 5, characterized in that, The molten salt also includes at least one of Li2SO4, NaCl, and KCl.

7. The preparation method according to claim 6, characterized in that, The molar content of lithium nitrate in the molten salt is greater than or equal to 50%.

8. The preparation method according to claim 6, characterized in that, The molar ratio of the hydroxide precursor material of the high-nickel single-crystal cathode material, lithium in the lithium salt, and molten salt in the mixture is 1:1.05~1.2:1.8~3.

9. The preparation method according to claim 3, characterized in that, The black powder and lithium salt are mixed according to the ratio of the total molar amount of transition metals in the dried black powder to the molar amount of Li in the lithium salt being 1:0.02~0.

1.

10. A lithium-ion battery, characterized in that, The high-nickel single-crystal cathode material as described in claim 1 or 2, or the high-nickel single-crystal cathode material prepared by the preparation method described in any one of claims 3 to 9.

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