Spinel-type lithium nickel manganese oxide cathode material and preparation method thereof, lithium ion battery

Abstract

This invention belongs to the field of lithium-ion battery technology, and discloses a spinel-type lithium nickel manganese oxide cathode material, its preparation method, and a lithium-ion battery. The spinel-type lithium nickel manganese oxide material contains Mn... 3+ molar amount of Mn 3+ Mn 4+ The ratio of total molar amount is 5% ≤ n(Mn) 3+ / (Mn) 3+ +Mn 4+ The concentration of manganese in the lithium nickel manganese oxide cathode material is ≤12%, which can reduce manganese dissolution and the Jahn-Teller effect, and improve the conductivity of the material, thereby improving the cycle stability of the battery. After uniformly mixing the precursor material and lithium salt, the above-mentioned spinel-type lithium nickel manganese oxide cathode material is obtained by optimizing the sintering process. This process can make full use of existing production systems and equipment.

Description

Technical Field

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

[0002] Lithium-ion batteries play a vital role in power and energy storage due to their advantages such as light weight, high energy density, high power density, and good cycle life. With the increasing market demand for batteries with high energy density, long cycle life, and low cost, spinel-type lithium nickel manganese oxide (LiNi) cathode materials are gaining popularity. 0.5 Mn 1.5 O4, LNMO) is gradually gaining attention. Spinel-type lithium nickel manganese oxide cathode materials have high operating voltages (4.7V vs. Li). + It possesses high specific discharge capacity (146.7 mAh / g) and excellent rate performance (three-dimensional lithium-ion channels). Furthermore, spinel-type lithium nickel manganese oxide cathode materials have a significant cost advantage. However, currently, spinel-type lithium nickel manganese oxide, as a cathode material for lithium-ion batteries, still suffers from structural instability under certain conditions, easily leading to problems such as rapid capacity decay at high temperatures and severe production delays in secondary batteries, thus hindering its application in the power battery market. Summary of the Invention

[0003] To address the problems existing in the prior art, the first objective of this invention is to provide a spinel-type lithium nickel manganese oxide cathode material and its preparation method; the second objective of this invention is to provide a lithium-ion battery.

[0004] To achieve the above objectives, the present invention provides the following specific technical solutions.

[0005] First, this invention provides a spinel-type lithium nickel manganese oxide cathode material, wherein Mn in the material 3+ molar amount and Mn 3+ Mn 4+ The ratio of the total molar amounts is n, n = Mn 3+ / (Mn) 3+ +Mn 4+ ), 5%≤n≤12%.

[0006] In a further preferred embodiment, the spinel-type lithium nickel manganese oxide cathode material has a coating layer, and the coating layer material is a fast ion conductor. More preferably, the coating layer material is at least one selected from lithium zirconium phosphate, lithium phosphate, and lithium titanium aluminum phosphate.

[0007] Secondly, this invention provides a method for preparing a spinel-type lithium nickel manganese oxide cathode material, comprising: After the precursor material and lithium salt are mixed evenly, they are sintered. The precursor material is Ni.0.25 Mn 0.75 (OH)2 or a mixture of Mn2O3 and MnNiO3; The oxygen volume content in the sintering atmosphere is ≥60%; The sintering method includes: first performing a sintering process at 800~1200℃, and then cooling down to 650~750℃ for heat preservation sintering.

[0008] In a further preferred embodiment, the lithium salt is at least one of Li₂CO₃, LiOH, and LiNO₃.

[0009] In a further preferred embodiment, the amounts of the precursor material and lithium salt are determined based on a ratio of 2:1 to 1.05 between the total molar amounts of Ni and Mn in the precursor material and the molar amounts of Li in the lithium salt.

[0010] In a further preferred embodiment, the spinel-type lithium nickel manganese oxide cathode material is further modified by coating, that is, the precursor material, lithium salt and coating agent are mixed evenly and then sintered.

[0011] In a further preferred embodiment, the coating agent includes at least one selected from lithium phosphate, lithium dihydrogen phosphate, and lithium monohydrogen phosphate. Preferably, the coating agent further includes at least one selected from titanium dioxide, aluminum oxide, and zirconium oxide.

[0012] In a further preferred embodiment, the amount of the coating agent is 0.3% to 0.8% of the mass of the precursor material.

[0013] In a further preferred embodiment, the heating rate of the first sintering stage is 5~10℃ / min; the holding time of the first sintering stage is 5~20h.

[0014] In a further preferred embodiment, the cooling rate from the temperature of the first sintering stage to the temperature of the holding sintering stage is 1~3℃ / min; the holding time of the holding sintering stage is 3~10h.

[0015] In a further preferred embodiment, the flow rate of the sintering atmosphere is 50~200 sccm.

[0016] Based on the same inventive concept, the present invention provides a lithium-ion battery, including the aforementioned spinel-type lithium nickel manganese oxide cathode material or the spinel-type lithium nickel manganese oxide cathode material prepared by the aforementioned preparation method.

[0017] In a further preferred embodiment, the N / P ratio of the lithium-ion battery is 0.92~1.06. The N / P ratio in a lithium-ion battery refers to the ratio of the capacity of the negative electrode per unit area to the capacity of the positive electrode per unit area.

[0018] In a further preferred embodiment, the electrolyte of the lithium-ion battery is a high-voltage electrolyte. More preferably, the high-voltage electrolyte includes a fluorinated solvent.

[0019] Furthermore, the fluorinated solvent is selected from at least one of fluorinated cyclic carbonates, fluorinated chain carbonates, fluorinated linear carboxylic esters, and fluorinated ethers.

[0020] Furthermore, the high-voltage electrolyte is a fluorinated high-voltage electrolyte.

[0021] Further preferably, the fluorinated electrolyte contains x% FEC (fluoroethylene carbonate), 85%-x FEMC (methyltrifluoroethyl carbonate), and 15% LiPF6, where x = 20~25%.

[0022] 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: This invention provides 5%≤n(Mn) 3+ / (Mn) 3+ +Mn 4+ Spinel-type lithium nickel manganese oxide cathode material with a content of ≤12% can reduce manganese dissolution and the Jahn-Teller effect in lithium nickel manganese oxide cathode material, thereby improving the cycle stability of the battery.

[0023] Further coating the surface of the spinel-type lithium nickel manganese oxide cathode material with a fast ion conductor coating layer can not only reduce the contact between the lithium nickel manganese oxide cathode material surface and the electrolyte, but also remove trace amounts of water or H2 produced by electrolyte decomposition. + Ni dissolved from the cathode by in-situ precipitation of Li3PO4 2+ Mn 2+ The presence of metal ions reduces the amount of metal ions dissolved from the cathode material, thereby improving the cycle stability of the battery.

[0024] In lithium-ion batteries, the aforementioned spinel-type lithium nickel manganese oxide cathode material of this invention is used as the cathode active material. By designing an N / P ratio of 0.95 to 1.06, the formation of the SEI film and lithium loss are reduced, which slows down the delithiation kinetics of the cathode, reduces the concentration of lithium ions intercalated on the negative electrode surface, reduces the possibility of lithium reduction in the negative electrode, and thus reduces electrolyte decomposition and consumption of active lithium, significantly improving the first coulombic efficiency of the battery.

[0025] The spinel-type lithium nickel manganese oxide cathode material described in this invention, when effectively combined with a specific high-voltage electrolyte, can effectively solve the problems of gas generation and stability of lithium nickel manganese oxide materials during high-temperature cycling.

[0026] This invention obtains specific spinel-type lithium nickel manganese oxide materials by optimizing the sintering process, which can fully utilize existing production systems and equipment. Attached Figure Description

[0027] Figure 1 The image shows the XPS plot of the lithium nickel manganese oxide material obtained in Example 1. Detailed Implementation

[0028] Spinel-type lithium nickel manganese oxide cathode materials inevitably produce Mn under certain process synthesis conditions. 3+ Because Mn 3+ There is only one electron in the high-energy orbital eg, and the uneven arrangement of electrons in the high-energy orbitals will cause a large distortion, making Mn 3+ Inducing Jahn-Teller distortion in the crystal lattice elongates the Z-axis, isolates verticeal oxygen O, disrupts cubic symmetry, and transforms it into a tetragonal structure, making it Lewis basic. Vertex basic oxygen O readily undergoes acid-base neutralization reactions in acidic electrolyte solutions; furthermore, Mn 3+ Its presence can also trigger a disproportionation reaction (2Mn) 3+ →Mn 2+ +Mn 4+ Electron transfer occurs, Mn 3+ Convert to Mn 4+ The generated Mn 4+ It is easily reduced to Mn by solvents. 2+ Dissolved in electrolyte, the dissolved Mn 2+ It easily precipitates on the negative electrode surface, accelerating the decomposition of the electrolyte. Therefore, the Jahn-Teller distortion will bring about drastic structural changes to the material, accelerating the destruction and deactivation of the material structure. Moreover, under high voltage, the electrolyte inevitably decomposes to produce HF. HF reacts with the positive electrode material to produce trace amounts of water. The catalytic effect of these trace amounts of water will exacerbate the decomposition of the electrolyte and the positive electrode material, and repeated cycles will lead to the failure of the positive electrode material.

[0029] In addition, a small amount of Mn 3+ The presence of Mn is beneficial to the improvement of conductivity, and the reason may be: 3+ The presence of Mn, similar to other metal ion doping, distorts the original crystal structure, creating crystal defects and thus increasing the material's conductivity. Based on this, the applicant's research found that Mn 3+ molar amount and Mn 3+ Mn 4+ The ratio of total molar amounts n(Mn) 3+ / (Mn) 3+ +Mn 4+Spinel-type lithium nickel manganese oxide cathode materials with a content of 5-12% exhibit good conductivity while maintaining material stability, and have relatively low manganese leaching, thus meeting the requirements for high-performance spinel-type lithium nickel manganese oxide cathode materials.

[0030] The spinel-type lithium nickel manganese oxide cathode material provided in some embodiments of the present invention has a coating layer, wherein the coating layer is made of a fast ion conductor. In some specific embodiments, the coating layer is made of at least one of lithium zirconium phosphate, lithium phosphate, and lithium titanium aluminum phosphate.

[0031] Coating the surface of spinel-type lithium nickel manganese oxide cathode material with a fast ion conductor can not only reduce the contact between the lithium nickel manganese oxide cathode material surface and the electrolyte, but also remove trace amounts of water or H2 produced by electrolyte decomposition. + Ni dissolved from the cathode by in-situ precipitation of Li3PO4 2+ Mn 2+ The presence of metal ions reduces the amount of metal ions dissolved from the cathode material, thereby improving the cycle stability of the battery.

[0032] Some embodiments of the present invention provide a method for preparing spinel-type lithium nickel manganese oxide cathode material, including: After the precursor material and lithium salt are mixed evenly, they are sintered. The precursor material is Ni. 0.25 Mn 0.75 (OH)2 or a mixture of Mn2O3 and MnNiO3; The oxygen content in the sintering atmosphere is ≥60%; The sintering method includes: first performing a sintering process at 800~1200℃, and then cooling down to 650~750℃ for heat preservation sintering.

[0033] The mixture of Mn2O3 and MnNiO3 described in this invention is Ni 0.25 Mn 0.75 The product of (OH)2 sintering at high temperature in air or oxygen.

[0034] This invention employs a two-stage sintering method, and by optimizing the sintering process, achieves 5%≤n(Mn) 3+ / (Mn) 3+ +Mn 4+ Spinel-type lithium nickel manganese oxide cathode material with a content ≤12%. When the oxygen content in the sintering atmosphere is ≥60%, sintering is first performed at a high temperature (800~1200℃), which is beneficial for shaping and crystal growth; then, it is held at a low temperature (650~750℃) to obtain Mn. 3+ Under aerobic conditions, it is easily converted into Mn. 4+ Low-temperature heat preservation sintering is beneficial for reducing n(Mn) 3+ / Mn3+ +Mn 4+ The content of ).

[0035] In some specific embodiments of the present invention, the lithium salt is at least one selected from Li₂CO₃, LiOH, and LiNO₃. Those skilled in the art may also choose other conventional lithium salts.

[0036] In some specific embodiments of the present invention, the amounts of the precursor material and lithium salt are determined based on a ratio of the total molar amount of Ni and Mn in the precursor material to the molar amount of Li in the lithium salt of 2:1 to 1.05. In the present invention, 5% ≤ n(Mn) 3+ / (Mn) 3+ +Mn 4+ Based on the technical concept of spinel-type lithium nickel manganese oxide cathode material with ≤12% spinel type nickel manganese oxide, the conventional coating process in this field is further applied to mix the coating agent with the precursor material and lithium salt evenly and then sinter to obtain the coated and modified spinel-type lithium nickel manganese oxide cathode material.

[0037] In some specific embodiments of the present invention, the coating agent includes at least one of lithium phosphate, lithium dihydrogen phosphate, and lithium monohydrogen phosphate.

[0038] In some specific embodiments of the present invention, the coating agent further includes at least one of titanium oxide, aluminum oxide, and zirconium oxide.

[0039] In some specific embodiments of the present invention, the heating rate of the first-stage sintering is 5~10℃ / min; the holding time of the first-stage sintering is 5~20h. The effect of the heating rate is relatively small. If the heating rate is too low, the nucleation rate is fast, the growth rate is slow, and the particle size is small; if the heating rate is too high, the growth rate is greater than the nucleation rate, and the particle size is large.

[0040] In some specific embodiments of the present invention, the cooling rate from the sintering temperature to the holding sintering temperature is 1~3℃ / min; the holding time for the holding sintering is 3~10h. The applicant's research has found that the cooling rate has a significant impact and slow cooling is necessary. Too rapid a cooling rate leads to an excessive number of oxygen vacancies, exacerbating the structural mixing of the material, and consequently affecting the Mn content in the material. 3+ Increased content affects structural stability. A lower cooling rate helps reduce structural defects, which is more conducive to the stability of the crystal structure, reduces internal stress in single crystals, and thus improves the cyclic stability of the material.

[0041] In some specific embodiments of the present invention, the flow rate of the sintering atmosphere is 50-200 sccm. If the gas flow rate is too high, it carries away a large amount of heat, resulting in excessive energy consumption for sintering, and also affects the lithium content; if the flow rate is too low, the oxygen content is too low to effectively sinter Mn.3+ Oxidation to Mn 4+ .

[0042] Some embodiments of the present invention also provide a lithium-ion battery, including the aforementioned spinel-type lithium nickel manganese oxide cathode material or the spinel-type lithium nickel manganese oxide cathode material prepared by the aforementioned preparation method.

[0043] Compared to ternary cathode materials and lithium iron phosphate materials, spinel-type lithium nickel manganese oxide has a 50% lower lithium-to-metal ratio, but it has a higher operating voltage, resulting in a relatively higher energy density. Simultaneously, the spinel structure is relatively stable, thus effectively reducing oxygen evolution compared to ternary materials, thereby ensuring the battery's thermal and chemical stability and reducing the risk of thermal runaway. The lower lithium content also effectively improves battery safety. However, due to the high charge / discharge voltage of spinel-type lithium nickel manganese oxide, the high operating voltage accelerates electrolyte decomposition, leading to increased SEI film thickness and impedance, and consequently exacerbating lithium-ion consumption.

[0044] Existing technologies typically replenish lithium lost during the SEI process by adding lithium replenishing agents. This involves adding a small amount of high-capacity material during the cathode slurry preparation process. During charging, Li+ ions are released from the high-capacity material, replenishing the irreversible capacity loss during the initial charge-discharge cycle. However, commonly used lithium replenishing agents, such as lithium iron phosphate, have the characteristic of releasing oxygen at high temperatures, leading to severe gas generation problems in the battery and increasing the amount of metal ions dissolved.

[0045] Based on this, the present invention improves battery performance through battery design, specifically by optimizing the N / P ratio, that is, by achieving an N / P ratio of 0.92 to 1.06 for the negative electrode and positive electrode of the lithium-ion battery. The N / P ratio in a lithium-ion battery refers to the ratio of the negative electrode capacity per unit area to the positive electrode capacity per unit area. By optimizing the N / P value within the above range, while ensuring battery capacity, the possibility of SEI film formation is reduced, lithium loss is decreased, and the positive electrode is kept in an over-discharged state, reducing electrolyte decomposition and improving the stability of the spinel-type lithium nickel manganese oxide positive electrode material, enabling its application at operating voltages of 4.6V or even higher.

[0046] In some specific embodiments of the present invention, the electrolyte of the lithium-ion battery is one of the fluorinated high-voltage electrolytes.

[0047] The application of the spinel-type lithium nickel manganese oxide cathode material described in this invention, in conjunction with the aforementioned high-voltage electrolyte, can further solve the gas generation problem of lithium nickel manganese oxide material during high-voltage cycling.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] Example 1 Weigh the precursor Ni 0.25 Mn 0.75 29.60 kg of (OH)2, 2.041 kg of lithium carbonate, 28.8 g of nano-zirconia, and 30.0 g of nano-lithium phosphate were added into a high-speed mixer, mixed evenly, and then discharged. Using 320*320*180mm saggers, the material was divided into four saggers, with approximately 3.0kg added to each sagger. After the material layer was leveled, holes were punched in it with a large stainless steel handle. The saggers were then placed in a double layer, double row, in the center of the atmosphere box furnace. High-purity oxygen (100% oxygen content) was used at a flow rate of 100 sccm, and the heating rate was controlled at 10℃ / min. The material was sintered at 1000℃ for 20 hours, then cooled to 700℃ at a rate of 2℃ / min and held for 5 hours. After natural cooling to room temperature in the furnace, the sample, i.e., lithium nickel manganese oxide cathode material, was removed.

[0052] Mn content in lithium nickel manganese oxide materials was determined by XPS. 3+ Mn 4+ The content of Mn was specifically determined by XPS testing of single-crystal lithium nickel manganese oxide materials using an Al target. Avantage software was used with Gaussian-Lorentzian as the fitting function to perform peak fitting on the single-crystal lithium nickel manganese oxide samples, including Mn content. 3+ and Mn 4+ Fitting and quantitative analysis of different valence states, the adjusted parameters include: carbon element calibration, peak position, area, FWHM, Gaussian proportion, etc. The percentage content of n is calculated as: S(Mn) 3+ ) / (S(Mn 3+ )+S(Mn 4+ )), S(Mn 3+ ) represents Mn 3+ The corresponding area, S(Mn) 4+ ) represents Mn 4+ The corresponding area. The result is as follows. Figure 1As shown. Calculate n(Mn) 3+ / Mn 3+ +Mn 4+ The value of ) is 6%.

[0053] Compared with Example 1, Examples 2-8 and Comparative Examples 1-6 adjusted the oxygen content in the sintering atmosphere, calcination temperature, heating rate, and cooling rate.

[0054] Table 1 Example 9 Example 9 differs from Example 1 only in that the coating agents nano-zirconia and nano-lithium phosphate are not added to the high-speed mixer. The resulting lithium nickel manganese oxide material has an n(Mn) content that... 3+ / Mn 3+ +Mn 4+ =10%.

[0055] Example 10 The only difference between Example 10 and Example 1 is that the precursor material is 9.60 kg Ni. 0.25 Mn 0.75 The product of calcining (OH)₂ at 700℃ for 5 h is a mixture of Mn₂O₃ and MnNiO₃. The resulting lithium nickel manganese oxide material contains n(Mn) 3+ / Mn 3+ +Mn 4+ =6%.

[0056] As can be seen from the data in the above embodiments and comparative examples, at high temperatures (≥850℃), Mn 4+ The stability is not as good as Mn 3 + Therefore, during high-temperature sintering, n(Mn) 3+ / Mn 3+ +Mn 4+ The value of Mn is relatively high; at 400℃~800℃, 4+ Its stability is higher than that of Mn 3+ Then, during low-temperature sintering, n(Mn) 3+ / Mn 3+ +Mn 4+ The value of Mn is relatively low. However, when the reaction temperature is below 700℃, the crystal growth of lithium nickel manganese oxide is incomplete; under conditions of reduced oxygen concentration, Mn... 3+ Cannot be oxidized to Mn 4+ When cooling from the high-temperature zone to the insulation zone, excessively rapid cooling can easily lead to internal stress in the material, resulting in poor structural stability, surface oxygen loss, and ultimately, n(Mn) degradation. 3+ / Mn 3 + +Mn 4+The content is too high.

[0057] Example 11 The spinel lithium nickel manganese oxide material prepared in Example 1 was used as the positive electrode active material. It was mixed uniformly with a binder and conductive carbon black at a mass ratio of 94:2:4. An appropriate amount of NMP was added and the mixture was stirred uniformly. After stirring, the mixture was filtered through a screen to obtain a positive electrode slurry. The positive electrode slurry was coated onto carbon-coated aluminum foil, dried, and cut into sheets to obtain the positive electrode sheet. Graphite, conductive carbon black, and binders (CMC and SBR) were uniformly mixed at a mass ratio of 94.5:2:3.5. An appropriate amount of pure water was added and the mixture was stirred uniformly. After stirring, the mixture was filtered through a screen to obtain a negative electrode slurry. The negative electrode slurry was coated onto copper foil, dried, and cut into sheets to obtain the negative electrode sheet. The designed N / P ratio was 0.98. Specifically, N / P = specific capacity of negative electrode active material × areal density of negative electrode active material × content ratio of negative electrode active material ÷ (specific capacity of positive electrode active material × areal density of positive electrode active material × content ratio of positive electrode active material), where the specific capacity of negative electrode active material is 335 mAh / g, the areal density of negative electrode is 1.6~1.68 mg / cm², and the content of negative electrode active material is 94.5%; the specific capacity of positive electrode active material is 135 mAh / g, the areal density of positive electrode is 4.0~4.2 mg / cm², and the content of positive electrode active material is 94.0%. The areal density is adjusted by the coating area and coating thickness of the positive and negative electrode slurries to achieve the N / P design. The positive electrode sheet, Celgard 2320 separator, fluorinated electrolyte (the electrolyte contains 20% FEC by mass, 68% FEMC by mass, and 12% LiPF6 by mass), and negative electrode sheet are assembled into a pouch battery.

[0058] Testing the electrical performance of the pouch battery: (1) Formation: At 25°C, the pouch cell is charged at a constant current of 0.3C to a voltage of 4.85V, then charged at a constant voltage of 4.8V to a current of 0.05C. After standing for 5 minutes, the pouch cell is discharged at a constant current of 0.33C to a voltage of 3.5V. This is one charge-discharge cycle. The ratio of the first discharge capacity to the first charge capacity is the first-cycle efficiency.

[0059] (2) High-temperature (45℃) cycle test: After the above formation, the soft-pack battery is charged at 45℃ with a constant current of 0.5C to a voltage of 4.8V, and then charged at a constant voltage of 4.8V to a current of 0.05C. After standing for 5 minutes, the soft-pack battery is discharged at a constant current of 1C to a voltage of 3.5V. This is one charge-discharge cycle. After the battery is repeatedly charged and discharged according to the above method, the remaining reversible discharge capacity is recorded. The charging and discharging is stopped when the capacity is lower than 80% of the maximum capacity, and the number of cycles is recorded.

[0060] (3) 55℃ Full Charge Storage (days): After formation, the soft-pack battery is charged at 25℃ with a constant current of 0.3C to a voltage of 4.8V, and then charged at a constant voltage of 4.8V to a current of 0.05C. The soft-pack battery is then placed at 55℃, and every 7 days it is removed and subjected to a capacity test at 25℃ (discharged at a constant current of 0.33C to a voltage of 3.5V, charged at a constant current of 0.3C to a voltage of 4.8V, then charged at a constant voltage of 4.8V to a current of 0.05C, and then discharged at a constant current of 0.33C to a voltage of 3.5V). It is then fully charged again (charged at a constant current of 0.3C to a voltage of 4.8V, then charged at a constant voltage of 4.8V to a current of 0.05C) and stored at 55℃. The discharge capacity value is extracted until the discharge capacity decays to 80% of the initial value, at which point the storage ends. The total time spent storing the product at 55°C after full charging is the high-temperature full-charge storage time.

[0061] The lithium nickel manganese oxide material in Example 1 was replaced with lithium nickel manganese oxide materials obtained in other examples and comparative examples, and the electrical performance of the pouch battery was tested using different N / P ratios, etc. These are represented by Examples 12-18 and Comparative Examples 7-14, respectively. Relevant data and test results are shown in Table 2.

[0062] Table 2 In lithium nickel manganese oxide cathode materials, n(Mn) 3+ / Mn 3+ +Mn 4+ When the ratio of Mn to N satisfies 5% ≤ n ≤ 12%, the amount of Mn ions dissolved is relatively less, resulting in less electrolyte decomposition and higher high-temperature storage performance and cycle stability of the battery.

[0063] The positive electrode is a three-dimensional lithium insertion / extraction material, while the negative electrode is a one-dimensional lithium insertion / extraction material. If the lithium extraction rate of the positive electrode is too fast and the lithium insertion rate of the negative electrode is too slow, the mismatch between the lithium extraction and insertion rates of the positive and negative electrodes leads to a higher lithium-ion concentration at the negative electrode interface. This increases the possibility of lithium ions being reduced to nano-lithium metal, which in turn exacerbates the decomposition of the electrolyte and increases the thickness of the SEI, resulting in increased battery impedance. In this invention, by rationally optimizing the N / P ratio, for spinel-type lithium nickel manganese oxide cathode material batteries, when the N / P ratio of the lithium nickel manganese oxide cathode material meets the requirement of N / P=0.92~1.06, the cathode is moderately excessive. This avoids the problem of excessive lithium consumption due to the formation of SEI on the negative electrode under high voltage, ensuring the content of active lithium in the cell, avoiding affecting the battery's initial efficiency and cycle performance, and also helping to reduce impedance, thereby improving the battery's initial efficiency and cycle stability. In addition, a suitable N / P ratio can also take into account the cathode delithiation kinetics, reduce the concentration of lithium ion intercalation on the negative electrode surface, reduce the possibility of lithium reduction on the negative electrode, and avoid the problem of severe lithium deposition on the negative electrode surface due to excessive cathode, forming lithium dendrites, causing internal short circuits, and thus reducing the cycle life of the cell. By balancing the effects of active lithium consumption and negative electrode lithium crystallization, the battery's capacity, initial coulombic efficiency, high-temperature storage, and cycle life performance are ensured.

[0064] 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 spinel-type lithium nickel manganese oxide cathode material, characterized in that, Mn in the material 3+ molar amount and Mn 3+ Mn 4+ The ratio of the total molar amounts is n, n = Mn 3+ / (Mn) 3+ +Mn 4+ ), 5%≤n≤12%.

2. The spinel-type lithium nickel manganese oxide cathode material as described in claim 1, characterized in that, The spinel-type lithium nickel manganese oxide cathode material has a coating layer.

3. The spinel-type lithium nickel manganese oxide cathode material as described in claim 2, characterized in that, The coating material is at least one of lithium zirconium phosphate, lithium phosphate, and lithium titanium aluminum phosphate.

4. A method for preparing a spinel-type lithium nickel manganese oxide cathode material, characterized in that, include: After the precursor material and lithium salt are mixed evenly, they are sintered. The lithium salt is at least one selected from Li₂CO₃, LiOH, and LiNO₃, and the precursor material is Ni. 0.25 Mn 0.75 (OH)2 or a mixture of Mn2O3 and MnNiO3; The oxygen volume content in the sintering atmosphere is ≥60%; The sintering method includes: first performing a sintering process at 800~1200℃, and then cooling down to 650~750℃ for heat preservation sintering.

5. The preparation method according to claim 4, characterized in that, The amounts of the precursor material and lithium salt are determined based on a ratio of 2:1 to 1.05 between the total molar amounts of Ni and Mn in the precursor material and the molar amounts of Li in the lithium salt.

6. The preparation method according to claim 4, characterized in that, After the precursor material, lithium salt and coating agent are mixed evenly, they are sintered.

7. The preparation method according to claim 6, characterized in that, The coating agent includes at least one of lithium phosphate, lithium dihydrogen phosphate, and lithium monohydrogen phosphate; preferably, the coating agent further includes at least one of titanium oxide, aluminum oxide, and zirconium oxide; and / or, the amount of the coating agent is 0.3% to 0.8% of the mass of the precursor material.

8. The preparation method according to claim 4, characterized in that, The heating rate of the first sintering stage is 5~10℃ / min; the holding time of the first sintering stage is 5~20h; and / or, The cooling rate from the sintering temperature to the holding sintering temperature is 1~3℃ / min; the holding time for the holding sintering is 3~10h.

9. A lithium-ion battery, characterized in that, Includes the spinel-type lithium nickel manganese oxide cathode material according to any one of claims 1 to 3 or the spinel-type lithium nickel manganese oxide cathode material prepared by the preparation method according to any one of claims 4 to 8.

10. The lithium-ion battery as described in claim 9, characterized in that, The N / P ratio of the lithium-ion battery is 0.92~1.

06.

11. The lithium-ion battery as described in claim 9 or 10, characterized in that, The electrolyte of the lithium-ion battery is a high-voltage electrolyte, which includes a fluorinated solvent.

12. The lithium-ion battery as described in claim 11, characterized in that, The fluorinated solvent is selected from at least one of fluorinated cyclic carbonates, fluorinated chain carbonates, fluorinated linear carboxylic esters, and fluorinated ethers.

Images