Modified lithium nickel manganese oxide cathode material, preparation method thereof and secondary battery

Abstract

This invention provides a modified lithium nickel manganese oxide cathode material, its preparation method, and a secondary battery. The preparation method includes the following steps: first, mixing lithium, nickel, manganese, ruthenium, and magnesium sources to obtain a mixture; subjecting the mixture to a first ball milling treatment to obtain a semi-precursor material; then pre-sintering the mixture to obtain a first precursor material; subjecting the first precursor material to a second ball milling treatment to obtain a second precursor material; then subjecting the second precursor material to a first sintering treatment to obtain a third precursor material; finally, subjecting the third precursor material to a second sintering treatment and annealing treatment sequentially to obtain the modified lithium nickel manganese oxide cathode material. This invention improves the structural stability, ion diffusion performance, and electronic conductivity of the prepared lithium nickel manganese oxide cathode material by employing elemental doping combined with optimized preparation methods, thereby improving the overall electrochemical performance of the secondary battery.

Description

Technical Field

[0001] This invention belongs to the field of cathode material technology, specifically relating to a modified lithium nickel manganese oxide cathode material, its preparation method, and a secondary battery. Background Technology

[0002] In recent years, the rapid development of industries such as electric vehicles has greatly increased the demand for lithium-ion batteries, and cobalt, as an indispensable component in commercially available lithium-ion batteries, has also seen a significant increase in demand. However, the scarcity and high price of cobalt have significantly increased the cost of batteries. Therefore, developing low-cost cobalt-free cathode materials is crucial. Among these, spinel lithium nickel manganese oxide (LiNi) is a promising candidate. 0.5 Mn 1.5 O4 is considered one of the potential candidates to replace cobalt-based cathode materials due to its low cost, environmental friendliness, and high theoretical voltage (~4.7V).

[0003] Currently, spinel lithium nickel manganese oxide still faces the following two problems in practical applications: (1) rapid capacity decay: the structure is unstable during cycling and is prone to collapse, leading to the dissolution of manganese ions and rapid capacity decay; (2) high-temperature performance degradation: its thermal stability is insufficient, posing certain safety hazards. Although traditional modification methods (such as coating, single-element doping, etc.) can alleviate the above problems to a certain extent, it is difficult to achieve a comprehensive improvement in high capacity, high rate performance and long cycle life at the same time.

[0004] Therefore, there is an urgent need in this field to develop a modified lithium nickel manganese oxide cathode material and its preparation method to solve the above problems. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a modified lithium nickel manganese oxide cathode material, its preparation method, and a secondary battery thereof. By employing elemental doping combined with optimized preparation methods, the present invention improves the structural stability, ion diffusion performance, and electronic conductivity of the prepared lithium nickel manganese oxide cathode material, thereby enhancing the overall electrochemical performance of the secondary battery.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing a modified lithium nickel manganese oxide cathode material, the method comprising the following steps:

[0008] S1. Mix lithium source, nickel source, manganese source, ruthenium source and magnesium source to obtain a mixture; subject the mixture to a first ball milling process to obtain a semi-step precursor material;

[0009] S2. The semi-step precursor material is pre-sintered to obtain a first precursor material; the first precursor material is ball-milled a second time to obtain a second precursor material.

[0010] S3. The second precursor material is subjected to a first sintering treatment to obtain the third precursor material;

[0011] S4. The third precursor material is subjected to a second sintering and annealing treatment in sequence to obtain the modified lithium nickel manganese oxide cathode material.

[0012] This invention utilizes a combination of a low-cost, high-temperature solid-state method and elemental doping to prepare a modified lithium nickel manganese oxide cathode material with small particle size and uniform composition distribution. This not only effectively ensures product consistency and structural stability but also broadens ion diffusion channels. Therefore, this modified lithium nickel manganese oxide cathode material exhibits high capacity, high rate performance, and long cycle life when used in secondary batteries. Specific performance characteristics are as follows:

[0013] (1) This invention enhances the binding ability of nickel ions, manganese ions and oxygen by doping the lithium nickel manganese oxide cathode material, thereby reducing the number of oxygen defects formed during sintering. At the same time, the valence electrons formed by the doping elements and the disordered Fd-3m space group structure in lithium nickel manganese oxide work together to change the local electron cloud distribution, effectively suppressing Jahn-Teller lattice contraction, thereby improving the structural stability of the lithium nickel manganese oxide cathode material.

[0014] (2) The modified lithium nickel manganese oxide cathode material prepared by this invention has a crystal morphology that changes from a regular octahedron to a polygonal octahedron, which suppresses the impurity phase Li x Ni 1-x The formation of O enhances the diffusion ability of metal ions and forms a stable solid electrolyte interlayer (such as a stable compound containing nickel-manganese-ruthenium-oxygen), which is beneficial to comprehensively improve the rate performance and cycle performance of lithium nickel manganese oxide cathode materials.

[0015] (3) Compared with the co-precipitation method for preparing cathode precursors, this invention uses multiple ball milling and staged sintering to ensure uniform composition, thereby solving the technical problem that traditional ruthenium doping has weak diffusion ability and is prone to segregation on the material surface, making it unable to enter the bulk phase. In addition, the subsequent annealing treatment reduces lattice oxygen defects and Mn introduced during high-temperature sintering. 3+ The content of ions, and also some Mn 3+ The ions can be re-oxidized to Mn 4+ The addition of ions further improves the disorder of the material structure, ultimately resulting in a lithium nickel manganese oxide cathode material with excellent comprehensive performance.

[0016] Preferably, with the total molar amount of nickel in the nickel source and manganese in the manganese source being 100%, the molar percentage content of ruthenium is 0.1%-2%, for example, it can be 0.1%, 0.2%, 0.5%, 0.8%, 1% or 2%, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable. In this invention, a portion of the doped ruthenium transition metal element is enriched at the grain boundaries, acting as a pinning agent, effectively suppressing the Mn content caused by lithium ion insertion and extraction from the lattice. 3+ The Jahn-Teller effect. Another aspect of this invention involves doping ruthenium onto the surface of the lithium nickel manganese oxide cathode material to form a stable passivation layer.

[0017] Preferably, with the total molar amount of nickel in the nickel source and manganese in the manganese source being 100%, the molar percentage of magnesium is 0.1%-5%, for example, it can be 0.1%, 0.2%, 0.5%, 1%, 1.5%, 2%, 3%, or 5%, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable. This invention, by doping with magnesium ions, advantageously improves the capacity and rate performance of lithium nickel manganese oxide cathode materials.

[0018] In this invention, by adjusting the content range of ruthenium and magnesium, lithium nickel manganese oxide cathode materials can simultaneously achieve a comprehensive improvement in high capacity, high rate performance, and long cycle life.

[0019] Preferably, in step S1, the molar ratio of lithium in the lithium source, nickel in the nickel source, manganese in the manganese source, ruthenium in the ruthenium source, and magnesium in the magnesium source is (0.95-1.05):(0.45-0.55):(1.45-1.55):(0.001-0.02):(0.001-0.05), for example, 0.95:0.45:1.45: The values ​​0.001:0.001, 1:0.46:1.46:0.005:0.005, 1.01:0.49:1.47:0.01:0.03, 1.02:0.5:1.5:0.015:0.02, or 1.05:0.55:1.55:0.02:0.05, etc., are not limited to the listed values; other unlisted values ​​within this range also apply.

[0020] Preferably, in step S1, the first ball milling process includes dry ball milling.

[0021] Preferably, in step S1, the rotational speed of the first ball milling process is 380 r / min-420 r / min, for example, it can be 380 r / min, 390 r / min, 400 r / min, 410 r / min or 420 r / min, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0022] Preferably, in step S1, the time for the first ball milling treatment is 10h-14h, for example, it can be 10h, 11h, 12h, 13h or 14h, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0023] Preferably, in step S2, the temperature of the pre-firing treatment is 300℃-400℃, and the time of the pre-firing treatment is 4h-6h.

[0024] Specifically, the temperature of the pre-firing treatment can be, for example, 300℃, 320℃, 350℃, 380℃ or 400℃; the time of the pre-firing treatment can be, for example, 4h, 4.5h, 5h, 5.5h or 6h; it is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0025] Preferably, in step S2, the second ball milling process includes dry ball milling.

[0026] Preferably, in step S2, the rotation speed of the second ball milling process is 500 r / min-600 r / min, for example, it can be 500 r / min, 520 r / min, 550 r / min, 580 r / min or 600 r / min, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0027] Preferably, in step S2, the second ball milling process takes 6-8 hours, for example, 6 hours, 6.5 hours, 7 hours, 7.5 hours, or 8 hours, and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0028] Preferably, in step S2, the second ball milling process is carried out until the particle size D... 50 The particle size is 0.1µm-2µm, for example, it can be 0.1µm, 0.2µm, 0.5µm, 0.8µm, 1µm, 1.2µm, 1.5µm or 2µm, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0029] In this invention, by adjusting the conditions of the second ball milling process to a higher rotation speed, the segregation and agglomeration of ruthenium are reduced, which is beneficial to achieving the dual effects of effective bulk doping and surface coating, thereby obtaining a cathode precursor material with small particle size and uniform element distribution.

[0030] Preferably, in step S3, the temperature of the first sintering treatment is 600℃-700℃, and the time of the first sintering treatment is 5h-7h.

[0031] Specifically, the temperature of the first sintering treatment can be, for example, 600℃, 620℃, 650℃, 680℃ or 700℃; the time of the first sintering treatment can be, for example, 5h, 5.5h, 6h, 6.5h or 7h, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0032] Preferably, in step S3, after the first sintering treatment is completed, a third ball milling treatment is also included.

[0033] Preferably, the rotation speed of the third ball milling process is 300 r / min to 600 r / min, for example, it can be 300 r / min, 400 r / min, 500 r / min or 600 r / min, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0034] Preferably, the third ball milling treatment time is 6h-8h, for example, it can be 6h, 6.5h, 7h, 7.5h or 8h, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0035] Preferably, in step S4, the temperature of the second sintering treatment is 850℃-1050℃, and the time of the second sintering treatment is 4h-15h.

[0036] Specifically, the temperature of the second sintering treatment can be, for example, 850℃, 900℃, 950℃, 1000℃ or 1050℃; the time of the second sintering treatment can be, for example, 4h, 6h, 8h, 10h, 12h or 15h, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0037] Preferably, in step S4, the annealing temperature is 500℃-800℃, and the annealing time is 6h-24h.

[0038] Specifically, the annealing temperature can be, for example, 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, or 800℃; the annealing time can be, for example, 6h, 8h, 10h, 12h, 15h, 18h, 20h, 22h, or 24h, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0039] In this invention, by controlling the annealing conditions, lattice oxygen defects in lithium nickel cobalt manganese oxide cathode materials are further repaired, while some Mn is also removed. 3+ The ions can be re-oxidized to Mn 4+ ion.

[0040] In a second aspect, the present invention provides a modified lithium nickel manganese oxide cathode material, which is prepared by the preparation method of the modified lithium nickel manganese oxide cathode material as described in the first aspect.

[0041] Preferably, with the total molar amount of transition metal elements in the modified lithium nickel manganese oxide cathode material being 100%, the molar percentage content of manganese in the modified lithium nickel manganese oxide cathode material is 70%-80%, for example, it can be 70%, 72%, 75%, 78% or 80%, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0042] Thirdly, the present invention provides a secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein the active material of the positive electrode comprises the modified lithium nickel manganese oxide positive electrode material as described in the second aspect.

[0043] In this invention, the electrolyte includes at least one of liquid electrolyte, gel electrolyte or solid electrolyte.

[0044] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] This invention provides a modified lithium nickel manganese oxide cathode material. Utilizing a combination of a low-cost, high-temperature solid-state method and elemental doping, a modified lithium nickel manganese oxide cathode material with small particle size and uniform composition distribution is prepared. This not only effectively ensures product consistency and structural stability but also broadens the ion migration path. Therefore, when used in secondary batteries, this modified lithium nickel manganese oxide cathode material exhibits high capacity, high rate performance, and long cycle life. Specific performance characteristics are as follows:

[0047] (1) This invention enhances the binding ability of nickel ions, manganese ions and oxygen by doping the lithium nickel manganese oxide cathode material, thereby reducing the number of oxygen defects formed during sintering. At the same time, the valence electrons formed by the doping elements and the disordered Fd-3m space group structure in lithium nickel manganese oxide work together to change the local electron cloud distribution, effectively suppressing Jahn-Teller lattice contraction, thereby improving the structural stability of the lithium nickel manganese oxide cathode material.

[0048] (2) The modified lithium nickel manganese oxide cathode material prepared by this invention has a crystal morphology that changes from a regular octahedron to a polygonal octahedron, which suppresses the impurity phase Li x Ni 1-x The formation of O enhances the diffusion ability of metal ions and forms a stable solid electrolyte interlayer, which is beneficial to comprehensively improving the rate performance and cycle performance of lithium nickel manganese oxide cathode materials.

[0049] (3) This invention employs multiple ball milling and staged sintering methods to ensure uniform composition. Furthermore, the subsequent annealing treatment reduces lattice oxygen defects and Mn introduced during high-temperature sintering. 3+ The content of ions, and also some Mn 3+ The ions can be re-oxidized to Mn 4+ The addition of ions further improves the disorder of the material structure, ultimately resulting in a lithium nickel manganese oxide cathode material with excellent comprehensive performance. Attached Figure Description

[0050] Figure 1 The image shown is a SEM image of the modified lithium nickel manganese oxide cathode material prepared in Example 1, with a magnification of 1500x.

[0051] Figure 2 The image shown is a SEM image of the modified lithium nickel manganese oxide cathode material prepared in Example 1, with a magnification of 1000x. Detailed Implementation

[0052] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be considered as specific limitations thereof.

[0053] Example 1

[0054] This embodiment provides a modified lithium nickel manganese oxide cathode material and its preparation method, the preparation method including the following steps:

[0055] S1. Lithium carbonate, nickel oxide, manganese oxide, ruthenium oxide, and magnesium oxide are placed in a mixing container in a molar ratio of Li, Ni, Mn, Ru, and Mg of 1.03:0.49:1.47:0.01:0.03 and mixed evenly to obtain a mixture. The mixture is then placed in a ball mill for a first dry ball milling at a speed of 400 r / min for 12 h to obtain a semi-step precursor material.

[0056] S2. The semi-step precursor material is pre-fired at 350℃ for 5 hours to obtain the first precursor material; the first precursor material is then subjected to a second dry ball milling to a particle size of D. 50 The particle size was 1µm, and the second dry ball milling was carried out at a speed of 550r / min for 7h to obtain the second precursor material.

[0057] S3. The second precursor material is sintered for the first time at a temperature of 650℃ for 6 hours to obtain the third precursor material; the third precursor material is then subjected to a third dry ball milling at a speed of 560 r / min for 7 hours.

[0058] S4. The third precursor material, after the third dry ball milling, is subjected to a second sintering at 980℃ for 10 hours. After the second sintering, it is annealed at 600℃ for 12 hours to obtain the annealed product. The annealed product is then crushed using a coarse roller and further pulverized using an air jet mill to obtain the following... Figures 1-2 The modified lithium nickel manganese oxide cathode material shown has a total molar content of nickel and manganese of 100%, wherein the molar percentage of magnesium is 1.5% and the molar percentage of ruthenium is 0.5%.

[0059] Example 2

[0060] This embodiment provides a modified lithium nickel manganese oxide cathode material and its preparation method, the preparation method including the following steps:

[0061] S1. Lithium carbonate, nickel oxide, manganese oxide, ruthenium oxide, and magnesium oxide are placed in a mixing container in a molar ratio of Li, Ni, Mn, Ru, and Mg of 1.02:0.49:1.47:0.02:0.02 and mixed evenly to obtain a mixture. The mixture is then placed in a ball mill for a first dry ball milling at a speed of 380 r / min for 14 h to obtain a semi-step precursor material.

[0062] S2. The semi-step precursor material is pre-fired at 300℃ for 6 hours to obtain the first precursor material; the first precursor material is then subjected to a second dry ball milling to a particle size of D. 50 The particle size was 0.5µm, and the second dry ball milling was carried out at a speed of 500r / min for 8h to obtain the second precursor material.

[0063] S3. The second precursor material is sintered for the first time at a temperature of 600℃ for 7 hours to obtain the third precursor material; the third precursor material is then subjected to a third dry ball milling at a speed of 500 r / min for 8 hours.

[0064] S4. The third precursor material, which has undergone a third dry ball milling, is subjected to a second sintering at a temperature of 850°C for 15 hours. After the second sintering, it is annealed at a temperature of 500°C for 24 hours to obtain an annealed product. The annealed product is crushed by a coarse roller and then pulverized by an air jet mill to obtain the modified lithium nickel manganese oxide cathode material, wherein the total molar content of nickel and manganese is 100%, the molar percentage content of magnesium is 1%, and the molar percentage content of ruthenium is 1%.

[0065] Example 3

[0066] This embodiment provides a modified lithium nickel manganese oxide cathode material and its preparation method, the preparation method including the following steps:

[0067] S1. Lithium carbonate, nickel oxide, manganese oxide, ruthenium oxide, and magnesium oxide are placed in a mixing container in a molar ratio of Li, Ni, Mn, Ru, and Mg of 1.04:0.48:1.45:0.02:0.05 and mixed evenly to obtain a mixture. The mixture is then placed in a ball mill for a first dry ball milling at a speed of 420 r / min for 10 h to obtain a semi-step precursor material.

[0068] S2. The semi-step precursor material is pre-fired at 400℃ for 4 hours to obtain the first precursor material; the first precursor material is then subjected to a second dry ball milling to a particle size of D. 50 The particle size was 2µm, and the second dry ball milling was carried out at a speed of 600 r / min for 6 h to obtain the second precursor material.

[0069] S3. The second precursor material is sintered for the first time at a temperature of 700℃ for 5 hours to obtain the third precursor material; the third precursor material is then subjected to a third dry ball milling at a speed of 480 r / min for 6 hours.

[0070] S4. The third precursor material, which has undergone a third dry ball milling, is subjected to a second sintering at a temperature of 1050°C for 4 hours. After the second sintering, it is annealed at a temperature of 800°C for 6 hours to obtain an annealed product. The annealed product is crushed by a coarse roller and then pulverized by an air jet mill to obtain the modified lithium nickel manganese oxide cathode material, wherein the total molar content of nickel and manganese is 100%, the molar percentage content of magnesium is 2.5%, and the molar percentage content of ruthenium is 1%.

[0071] Example 4

[0072] The difference between this embodiment and Embodiment 1 is that in step S1, lithium carbonate, nickel oxide, manganese oxide, ruthenium oxide, and magnesium oxide are placed in a mixing container in a molar ratio of Li, Ni, Mn, Ru, and Mg of 1.03:0.48:1.46:0.03:0.03 and mixed evenly to obtain a mixture. The total molar content of nickel and manganese is 100%, and the molar percentage content of magnesium and ruthenium is 1.5%. All other aspects are the same as in Embodiment 1.

[0073] Example 5

[0074] The difference between this embodiment and Embodiment 1 is that in step S1, lithium carbonate, nickel oxide, manganese oxide, ruthenium oxide, and magnesium oxide are placed in a mixing container in a molar ratio of Li, Ni, Mn, Ru, and Mg of 1.03:0.48:1.45:0.04:0.03 and mixed evenly to obtain a mixture. The total molar content of nickel and manganese is 100%, the molar percentage of magnesium is 1.5%, and the molar percentage of ruthenium is 2%. All other aspects are the same as in Embodiment 1.

[0075] Example 6

[0076] The difference between this embodiment and Embodiment 1 is that in step S1, lithium carbonate, nickel oxide, manganese oxide, ruthenium oxide, and magnesium oxide are placed in a mixing container in a molar ratio of Li, Ni, Mn, Ru, and Mg of 1.03:0.48:1.45:0.01:0.06 and mixed evenly to obtain a mixture. The total molar content of nickel and manganese is 100%, the molar percentage of magnesium is 3%, and the molar percentage of ruthenium is 0.5%. All other aspects are the same as in Embodiment 1.

[0077] Example 7

[0078] The difference between this embodiment and Embodiment 1 is that in step S1, lithium carbonate, nickel oxide, manganese oxide, ruthenium oxide, and magnesium oxide are placed in a mixing container in a molar ratio of Li, Ni, Mn, Ru, and Mg of 1.03:0.47:1.44:0.01:0.08 and mixed evenly to obtain a mixture. The total molar content of nickel and manganese is 100%, the molar percentage of magnesium is 4%, and the molar percentage of ruthenium is 0.5%. All other aspects are the same as in Embodiment 1.

[0079] Example 8

[0080] The difference between this embodiment and embodiment 1 is that in step S2, the pre-firing temperature is 250°C and the time is 5 hours, while all other aspects are the same as in embodiment 1.

[0081] Example 9

[0082] The difference between this embodiment and embodiment 1 is that in step S2, the pre-firing temperature is 450°C and the time is 5 hours, while all other aspects are the same as in embodiment 1.

[0083] Example 10

[0084] The difference between this embodiment and Embodiment 1 is that, in step S2, the first precursor material is subjected to a second dry ball milling until the particles reach a density of D. 50 The particle size was 1µm, the second dry ball milling speed was 400r / min, and the time was 7h. Everything else was the same as in Example 1.

[0085] Example 11

[0086] The difference between this embodiment and Embodiment 1 is that, in step S2, the first precursor material is subjected to a second dry ball milling until the particles reach a density of D. 50 The particle size was 1µm, the second dry ball milling speed was 700r / min, and the time was 7h. Everything else was the same as in Example 1.

[0087] Comparative Example 1

[0088] The difference between this comparative example and Example 1 is that step S1 is adjusted as follows: lithium carbonate, nickel oxide, manganese oxide and ruthenium oxide are placed in a mixing container in a molar ratio of Li, Ni, Mn and Ru of 1.03:0.49:0.147:0.04 and mixed evenly to obtain a mixture. Everything else is the same as in Example 1.

[0089] Comparative Example 2

[0090] The difference between this comparative example and Example 1 is that step S1 is adjusted as follows: lithium carbonate, nickel oxide, manganese oxide and magnesium oxide are placed in a mixing container in a molar ratio of Li, Ni, Mn and Mg of 1.03:0.49:0.147:0.04 and mixed evenly to obtain a mixture. Everything else is the same as in Example 1.

[0091] Comparative Example 3

[0092] The difference between this comparative example and Example 1 is that step S2 is adjusted to: no pre-firing treatment is performed, and the semi-step precursor material is directly subjected to a second dry ball milling to particle size D. 50 The particle size was 1µm, and the second dry ball milling was carried out at a speed of 550r / min for 7h to obtain the precursor material. All other aspects were the same as in Example 1.

[0093] Comparative Example 4

[0094] The difference between this comparative example and Example 1 is that step S2 is adjusted to: no second dry ball milling is performed, and the semi-step precursor material is directly pre-fired at a temperature of 350°C for 5 hours to obtain the precursor material. All other aspects are the same as in Example 1.

[0095] Test conditions

[0096] The modified lithium nickel manganese oxide cathode material provided in the above embodiments and comparative examples was used to prepare cathode sheets, which were then assembled into coin-type lithium-ion batteries. The preparation method is as follows:

[0097] The modified lithium nickel manganese oxide cathode material, conductive carbon black, and polyvinylidene fluoride binder provided in the above embodiments and comparative examples were mixed in a mass ratio of 8:1:1, and then N-methylpyrrolidone solvent was added to prepare a cathode slurry. The cathode slurry was coated onto aluminum foil, and after drying and rolling, a cathode sheet was obtained. The lithium metal sheet was used as the anode sheet. The electrolyte composition was: lithium hexafluorophosphate with a concentration of 1 mol / L, and a mixture of ethylene carbonate and diethyl carbonate with a volume ratio of 1:1 as the solvent. The cathode shell, anode sheet, electrolyte, polypropylene separator, electrolyte, cathode sheet, current collector, and cathode shell were stacked and pressed together in sequence to form a coin cell lithium-ion battery.

[0098] The prepared coin-type lithium-ion batteries were subjected to electrochemical performance tests at voltages ranging from 3.5V to 4.9V. The discharge capacity and initial coulombic efficiency at room temperature and 1C were tested, as well as the capacity retention rate after 100 cycles at 1C and the discharge specific capacity at 3C.

[0099] The test results are shown in Table 1.

[0100] Table 1

[0101]

[0102]

[0103] As can be seen from Table 1, by controlling the content of ruthenium and magnesium doping in Examples 1-3 within a reasonable range and optimizing the preparation process, the present invention obtains a modified lithium nickel manganese oxide cathode material with high initial coulombic efficiency, good rate performance, and good cycle performance.

[0104] Examples 4-7 show that the Ru and Mg doping content exceeds the preferred range, resulting in lower capacity and poorer rate performance. Examples 8-9 show that the pre-calcination temperature exceeds the preferred range, leading to a deterioration in the overall performance of the prepared modified lithium nickel manganese oxide cathode material. Similarly, Examples 10-11 show that the second dry ball milling speed exceeds the preferred range, resulting in lower capacity, cycle performance, and rate performance of the prepared modified lithium nickel manganese oxide cathode material.

[0105] Compared to Examples 1-3, Comparative Examples 1-2, which did not incorporate the combination of ruthenium and magnesium, resulted in modified lithium nickel manganese oxide cathode materials with poorer cycle stability. The absence of pre-calcination in Comparative Example 3 and the omission of a second dry ball milling in Comparative Example 4 both led to very poor overall performance of the modified lithium nickel manganese oxide cathode materials. Therefore, by employing the specific embodiments of this invention, lithium nickel manganese oxide cathode materials with excellent comprehensive performance can be obtained.

[0106] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a modified lithium nickel manganese oxide cathode material, characterized in that, The preparation method includes the following steps: S1. Mix lithium source, nickel source, manganese source, ruthenium source and magnesium source to obtain a mixture; subject the mixture to a first ball milling process to obtain a semi-step precursor material; S2. The semi-step precursor material is pre-sintered to obtain a first precursor material; the first precursor material is ball-milled a second time to obtain a second precursor material. S3. The second precursor material is subjected to a first sintering treatment to obtain the third precursor material; S4. The third precursor material is subjected to a second sintering and annealing treatment in sequence to obtain the modified lithium nickel manganese oxide cathode material.

2. The preparation method according to claim 1, characterized in that, With the total molar amount of nickel in the nickel source and manganese in the manganese source being 100%, the molar percentage of ruthenium is 0.1%-2%.

3. The preparation method according to claim 1, characterized in that, With the total molar amount of nickel in the nickel source and manganese in the manganese source being 100%, the molar percentage of magnesium is 0.1%-5%.

4. The preparation method according to claim 1, characterized in that, In step S1, the molar ratio of lithium in the lithium source, nickel in the nickel source, manganese in the manganese source, ruthenium in the ruthenium source, and magnesium in the magnesium source is (0.95-1.05):(0.45-0.55):(1.45-1.55):(0.001-0.02):(0.001-0.05).

5. The preparation method according to claim 1, characterized in that, In step S1, the first ball milling process includes dry ball milling; And / or, in step S1, the rotational speed of the first ball milling process is 380 r / min-420 r / min; And / or, in step S1, the first ball milling treatment takes 10-14 hours.

6. The preparation method according to claim 1, characterized in that, In step S2, the temperature of the pre-firing treatment is 300℃-400℃, and the time of the pre-firing treatment is 4h-6h; And / or, in step S2, the second ball milling process includes dry ball milling; And / or, in step S2, the rotational speed of the second ball milling process is 500 r / min-600 r / min; And / or, in step S2, the second ball milling treatment takes 6-8 hours; And / or, in step S2, the second ball milling process is carried out until the particles reach a D... 50 The particle size is 0.1µm-2µm.

7. The preparation method according to claim 1, characterized in that, In step S3, the temperature of the first sintering treatment is 600℃-700℃, and the time of the first sintering treatment is 5h-7h. And / or, in step S3, after the first sintering treatment is completed, a third ball milling treatment is also included.

8. The preparation method according to claim 7, characterized in that, The rotational speed of the third ball milling process is 300 r / min-600 r / min; The third ball milling process takes 6-8 hours.

9. The preparation method according to claim 1, characterized in that, In step S4, the temperature of the second sintering treatment is 850℃-1050℃, and the time of the second sintering treatment is 4h-15h. And / or, in step S4, the annealing temperature is 500℃-800℃, and the annealing time is 6h-24h.

10. A modified lithium nickel manganese oxide cathode material, characterized in that, The modified lithium nickel manganese oxide cathode material is prepared by the method described in any one of claims 1-9.

11. The modified lithium nickel manganese oxide cathode material according to claim 10, characterized in that, With the total molar amount of transition metal elements in the modified lithium nickel manganese oxide cathode material being 100%, the molar percentage content of manganese in the modified lithium nickel manganese oxide cathode material is 70%-80%.

12. A secondary battery, characterized in that, The secondary battery includes a positive electrode, a negative electrode, and an electrolyte, wherein the active material of the positive electrode includes the modified lithium nickel manganese oxide positive electrode material as described in claim 10 or 11.

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