Lithium nickel manganese oxide cathode material, preparation method thereof and electrochemical device

Abstract

The application provides a lithium nickel-manganese oxide positive electrode material, a preparation method thereof and an electrochemical device. The preparation method comprises the following steps: mixing a nickel source, a manganese source and an M source with a solvent to prepare a mixed metal salt solution, and then performing a co-precipitation reaction on the mixed metal salt solution, a complexing agent and a precipitant under the condition that the pH is 8-10.8 and inert gas protection is provided, and after washing and drying, a lithium nickel-manganese oxide precursor doped with M elements is obtained; wherein the M source comprises at least one of Nb, V and Mo elements; the lithium nickel-manganese oxide precursor is mixed with a lithium salt and is subjected to primary sintering to obtain a matrix; and the matrix is mixed with a coating material and is subjected to secondary sintering to obtain the lithium nickel-manganese oxide positive electrode material. The preparation method can realize uniform distribution of elements, and combined with flux sintering, a positive electrode material with round particles, few grain boundary defects and stable structure can be obtained, high-voltage gas production and interface side reactions can be effectively inhibited, and the cycle life and comprehensive performance can be improved.

Description

Technical Field

[0001] This application relates to the field of new energy technology, and in particular to a lithium nickel manganese oxide cathode material, its preparation method and electrochemical device. Background Technology

[0002] Lithium nickel manganese oxide (LiNi) 0.5 Mn 1.5 Lithium nickel manganese oxide (LiNMO) cathode materials have attracted much attention due to their high voltage platform and excellent rate performance. However, in practical applications, LiNMO materials suffer from problems such as severe electrolyte decomposition and gas generation under high voltage, poor structural stability during cycling, and intense interfacial side reactions, leading to rapid capacity decay and limited cycle life.

[0003] To overcome these shortcomings, researchers typically employ methods such as doping, coating, and particle morphology optimization to modify materials. However, existing modification methods struggle to effectively address these multiple issues simultaneously. Summary of the Invention

[0004] In view of this, in order to solve at least one of the above technical problems, it is necessary to provide a method for preparing lithium nickel manganese oxide cathode material.

[0005] In addition, this application also provides a cathode material prepared by the aforementioned preparation method and an electrochemical device using the cathode material.

[0006] In a first aspect, this application provides a method for preparing a lithium nickel manganese oxide cathode material, comprising: mixing a nickel source, a manganese source, and an M source with a solvent to prepare a mixed metal salt solution; then co-precipitating the mixed metal salt solution with a complexing agent and a precipitant under conditions of pH 8-10.8 and inert gas protection; and obtaining an M-doped lithium nickel manganese oxide precursor after washing and drying; wherein the M source includes at least one of Nb, V, and Mo; mixing the lithium nickel manganese oxide precursor with a lithium salt and performing a first sintering to obtain a matrix; and mixing the matrix with a coating material and performing a second sintering to obtain the lithium nickel manganese oxide cathode material.

[0007] Based on the first aspect, in some embodiments of this application, the molar ratio of the nickel source to the manganese source is 1:1.5~3.0; and / or, the molar ratio of the nickel source to the M source is 1:0.002~0.01.

[0008] Based on the first aspect, in some embodiments of this application, the general formula of the lithium nickel manganese oxide precursor is Ni. x Mn y M z (OH)2, wherein 0.20≤x<0.30, 0.70≤y<0.80, and x+y+z=1.

[0009] Based on the first aspect, in some embodiments of this application, in the co-precipitation reaction step, the mixed metal salt solution, complexing agent, and precipitant are dripped into the base liquid in a co-current flow at a rate of 0.05 μL / h to 0.2 μL / h, and the base liquid includes deionized water and complexing agent.

[0010] Based on the first aspect, in some embodiments of this application, the M includes Nb.

[0011] Based on the first aspect, in some embodiments of this application, the primary sintering temperature is 900℃~980℃ and the time is 10h~15h; and / or, the secondary sintering temperature is 650℃~750℃ and the time is 8h~12h.

[0012] Based on the first aspect, in some embodiments of this application, the sphericity of the lithium nickel manganese oxide cathode material is 0.64~1; and / or, the average particle size D50 of the lithium nickel manganese oxide cathode material is 7μm~9μm; and / or, the span value of the lithium nickel manganese oxide cathode material is 0.45~0.65.

[0013] Based on the first aspect, in some embodiments of this application, the span value of the lithium nickel manganese oxide cathode material is 0.45 to 0.65.

[0014] Based on the first aspect, in some embodiments of this application, the coating material includes aluminum phosphate; and / or, the coating amount of the coating material is 0.1% to 0.5% of the total mass of the lithium nickel manganese oxide cathode material.

[0015] Based on the first aspect, in some embodiments of this application, in the step of mixing the lithium nickel manganese oxide precursor with the lithium salt, an N source is further doped, wherein the N element in the N source includes at least one of Ti, Al, Mg, Zr and Mo.

[0016] Based on the first aspect, in some embodiments of this application, the amount of N source added is 0.1% to 0.2% of the total mass of the lithium nickel manganese oxide precursor.

[0017] Secondly, this application provides a lithium nickel manganese oxide cathode material, which is prepared by the aforementioned method for preparing lithium nickel manganese oxide cathode materials.

[0018] Thirdly, this application provides an electrochemical device, including a positive electrode, a negative electrode, and an electrolyte located between the positive electrode and the negative electrode, wherein the positive electrode is made of the aforementioned lithium nickel manganese oxide positive electrode material.

[0019] The method for preparing lithium nickel manganese oxide cathode material provided in this application first introduces Nb through a co-precipitation reaction under an inert atmosphere and a pH value of 8-10.8. 5+ V 5+ Or Mo 6+ High-valence metal ions, by being directly added as dopants during precursor preparation, can achieve atomic-level uniform distribution within and on the surface of precursor particles, thus improving the problem of inhomogeneous doping. Furthermore, these high-valence metal ions tend to form specific hydroxyl complexes, selectively adsorbing onto specific growth surfaces of the precursor crystals, promoting the development of secondary particles into rounded, uniform, near-spherical shapes. During secondary sintering, the uniformly distributed high-valence metal ions also act as fluxes, helping to lower the local melting point of the material, promoting surface melting and mass migration, resulting in more rounded and uniform cathode material particles after sintering. The sharp edges and grain boundary defects on the particle surface are also significantly reduced, thus enhancing the structural stability of the obtained cathode material. Due to the improved particle roundness and reduced grain boundary defects, interfacial side reactions between the cathode material and the electrolyte are effectively suppressed, and the decomposition and gas generation of the electrolyte under high voltage decreases, ultimately improving the high-temperature cycle performance of the battery, resulting in a longer cycle life and better safety performance. Attached Figure Description

[0020] Figure 1 A process flow diagram of the method for preparing lithium nickel manganese oxide cathode material provided in the embodiments of this application.

[0021] Figure 2 Figures (a) to (c) are SEM images of the precursors of Comparative Example 1 and Examples 1-2 of this application, respectively.

[0022] Figure 3 Figures (a) to (d) are SEM images of lithium nickel manganese oxide cathode materials in Comparative Example 1 and Examples 1, 5-6, respectively.

[0023] Figure 4 This is a comparison chart of the first-cycle discharge capacity and efficiency of Examples 1-6 and Comparative Example 1 at 0.1C.

[0024] Figure 5 This is a comparison diagram of the first 60 cycles at 45°C for Examples 1-2, 5 to 7 and Comparative Examples 1-2 of this application. Detailed Implementation

[0025] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the embodiments of this application pertain. The terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the embodiments of this application. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially. The terms "once" and "twice" appearing in this application are only used to distinguish different steps or stages of sintering treatment and are not construed as an absolute limitation on the order or number of times.

[0026] The following describes some embodiments of this application in detail. Unless otherwise specified, the embodiments and features described below can be combined with each other.

[0027] For this purpose, please see Figure 1 This application provides a method for preparing lithium nickel manganese oxide cathode material, comprising the following steps: Step S1, Preparation method of lithium nickel manganese oxide precursor: includes: Step S1.1: Mix the nickel source, manganese source and M source with the solvent according to the target stoichiometric ratio to prepare a homogeneous mixed metal salt solution.

[0028] In some embodiments, the M source includes at least one of elements such as Nb, V, and Mo.

[0029] In some embodiments, M is an Nb element. Using Nb 5+ As a dopant ion, it can form hydroxyl complexes during precursor co-precipitation, selectively adsorb onto specific crystal planes, promote the growth of particles into rounded, uniform spherical shapes, and play a fluxing role during sintering, further improving the roundness and structural stability of cathode materials.

[0030] In some embodiments, the mixing in step S1 includes high-speed mixing and low-speed mixing. The high-speed mixing frequency is 1200 rpm to 1800 rpm and the time is 8 min to 15 min. The low-speed mixing frequency is 500 rpm to 800 rpm and the time is 5 min to 10 min.

[0031] In some embodiments, the nickel source in step S1 includes at least one of Ni(NO3)2, NiSO4, and NiCl2. These nickel salts all have good water solubility and can be fully mixed with the manganese source and M source in solution to form a homogeneous metal salt solution, providing a uniform reaction system for the co-precipitation reaction and facilitating the atomic-level distribution of subsequent doping elements. Preferably, the nickel source in step S1 is Ni(NO3)2.

[0032] In some embodiments, the molar ratio of nickel source to manganese source in step S1 is 1:1.5 to 3.0. Adjusting this molar ratio within the aforementioned suitable range is beneficial for forming a spinel-structured lithium nickel manganese oxide cathode material.

[0033] In some embodiments, the molar ratio of nickel source to M source is 1:0.002 to 0.01. Adjusting this molar ratio within this range allows for the incorporation of an appropriate amount of high-valence metal ions into the precursor lattice, sufficient to stabilize the structure and act as a flux, while maintaining the integrity of the lattice structure. The molar ratio of nickel source to M source can, exemplarily, be 1:0.002, 1:0.005, 1:0.01, or any value within the range of any two of the above values.

[0034] In some embodiments, the manganese source includes at least one of Mn(NO3)2, MnSO4, and MnCl2. These manganese salts can be simultaneously precipitated with nickel ions during the co-precipitation process, ensuring the accuracy of the nickel-manganese ratio in the precursor, thereby obtaining a lithium nickel manganese oxide cathode material with the required stoichiometry. Preferably, the manganese source is Mn(NO3)2.

[0035] In some embodiments, the M source includes at least one selected from Nb₂O₃, V₂O₅, NH₄VO₃, Nb(NO₃)₅, and (NH₄)₂MoO₄. The M source contains high-valence metal elements such as Nb, V, and Mo. These elements can be released as high-valence ions under weakly alkaline conditions and participate in the co-precipitation reaction, allowing the dopant ions to be uniformly embedded in the precursor lattice. This, in turn, strengthens the structure and acts as a flux during subsequent sintering, improving the particle roundness and cycle stability of the cathode material.

[0036] In some embodiments, the precipitant in step S1 includes at least one of NaHCO3 and NaOH, and the complexing agent includes ammonia. The precipitant provides OH⁻ to precipitate the metal ions, and the complexing agent regulates the precipitation rate of the metal ions to ensure the uniformity of co-precipitation.

[0037] In some embodiments, the solvent in step S1 is deionized water. Deionized water can effectively avoid the introduction of impurity ions, ensure the purity of the coprecipitation reaction system, and facilitate the uniform dissolution of metal ions to form a stable mixed salt solution, thereby improving the purity and structural consistency of the coprecipitation product.

[0038] Step S1.2: The mixed metal salt solution is subjected to a co-precipitation reaction with a complexing agent and a precipitating agent.

[0039] Specifically, a base liquid (usually deionized water and a complexing agent, such as ammonia) is added to the reactor, and an inert gas (such as N2) is introduced for protection. Then, the mixed salt solution, precipitant, and complexing agent are slowly added dropwise in a co-current flow at a rate of 0.05 μL / h to 0.2 μL / h, with strict control over pH, temperature, and stirring speed. At this point, Ni... 2+ Mn 2+ The doped M ions react together with OH- to form a coprecipitate product with a uniform distribution of doped elements.

[0040] In some embodiments, in step S2, the pH is 8 to 10.8. This pH range is favorable for Ni. 2+ Mn 2+ Simultaneous precipitation with M ions maintains the spherical morphology of the particles, inhibits Mn oxidation, and prevents the dissolution and loss of M ions under strongly alkaline conditions. For example, the pH value can be 8, 9, 10, 10.8, or any value within the range of any two of the above values.

[0041] In some embodiments, in step S2, the precipitant may be, for example, a NaHCO3 or NaOH solution. The precipitant provides OH-. - It causes metal ions to precipitate as hydroxides. When used in conjunction with a complexing agent, the precipitation rate can be controlled, ensuring that the composition and morphology of the coprecipitated product meet expectations.

[0042] In some embodiments, in step S2, the base solution includes deionized water and a complexing agent. The base solution provides an initial stable environment for the co-precipitation reaction, allowing metal ions to nucleate uniformly at low supersaturation, which is beneficial for obtaining precursor particles with uniform particle size and high sphericity.

[0043] In some embodiments, in step S2, the complexing agent may be, for example, ammonia. Ammonia is capable of reacting with Ni. 2+ Mn 2+ The formation of soluble complex ions regulates the release rate of metal ions, ensuring a stable precipitation reaction and thus improving the uniformity and density of the coprecipitated products.

[0044] Step S1.3: After the reaction is complete, the slurry is aged, and then centrifuged, filtered, and washed multiple times to remove impurity ions (such as Na). + SO4 2- Finally, it is dried in an oven to obtain the lithium nickel manganese oxide precursor. The general formula of the lithium nickel manganese oxide precursor is Ni... x Mn y M z (OH)2, where 0.20≤x<0.30, 0.70≤y<0.80, and x+y+z=1.

[0045] Under these weakly alkaline conditions (pH 8-10.8), Ni2+ Mn 2+ and M ions (such as Nb) 5+ V 5+ Mo 6+ Ni reacts with OH- ions provided by the precipitant to undergo a co-precipitation reaction, forming the corresponding hydroxide or hydroxyl oxide precipitate. The reaction formula can be represented as: Ni 2+ +Mn 2+ +M n ⁺+(2+n / 2)OH-→Ni x Mn y M z (OH)₂ (where n is the valence of M). The addition of a complexing agent can regulate the release rate of metal ions, allowing the precipitation reaction to proceed smoothly. During this co-precipitation process, the doped M ions can selectively adsorb onto specific growth surfaces of the precursor grains, inhibiting the excessively rapid growth of certain crystal planes, thereby promoting the development of secondary precursor particles into rounded, uniform spherical shapes and improving the sphericity and uniformity of the precursor particles. Simultaneously, M ions react with Ni... 2+ Mn 2+ Synchronous and uniform precipitation enables atomic-level uniform distribution of dopant elements inside and on the surface of the particles.

[0046] Meanwhile, by controlling the pH to 8-10.8, this application can ensure the simultaneous and uniform precipitation of the three metal ions and inhibit Mn. 2+ Oxidized to Mn 3+ or Mn 4+ This also prevents the high-valence M ions from forming soluble hydroxyl complexes and being lost under strongly alkaline conditions. If the pH is greater than 10.8, the solution is too alkaline, which will lead to the following problems: First, high-valence M ions are prone to forming soluble hydroxyl complexes and dissolving under strongly alkaline conditions, making them unable to be effectively incorporated into the precursor lattice, resulting in insufficient doping and uneven distribution; second, a strongly alkaline environment will accelerate the incorporation of Mn. 2+ Oxidized to Mn 3+ or Mn 4+ The oxidation of Mn generates high-valence manganese oxides such as MnO2, which destroys the uniformity and spherical morphology of the precursor. At the same time, the oxidation of Mn also interferes with the equilibrium of the co-precipitation reaction, resulting in asynchronous precipitation rates of nickel, manganese and M, which further aggravates the uneven doping and deterioration of particle morphology.

[0047] Therefore, by controlling the pH within the range of 8 to 10.8 during the preparation of the precursor, and by combining the co-current addition of the complexing agent with inert gas protection, the three metal ions can be precipitated simultaneously and uniformly, improving the uniformity of the distribution of doped elements. The resulting precursor particles have rounded morphology and uniform particle size, providing a structural basis for the subsequent sintering preparation of high-performance lithium nickel manganese oxide cathode materials.

[0048] In some embodiments, the sphericity DD of the lithium nickel manganese oxide precursor is ≥0.71. Higher sphericity indicates that the precursor particles are round and uniform, which is beneficial for obtaining a cathode material with stable interfaces and few defects during subsequent sintering. Exemplarily, the sphericity DD can be 0.71, 0.72, 0.73, 0.74, 0.75, or any value within the range of any two of the above values.

[0049] Step S2 involves mixing the lithium nickel manganese oxide precursor with a lithium salt and performing a single sintering process to obtain the matrix. Additionally, nitrogen (N) can be added as a dopant during this single sintering process.

[0050] During a sintering process, Ni in the precursor x Mn y M z (OH)₂ undergoes a solid-state reaction with lithium salts to generate a lithium nickel manganese oxide matrix with a spinel structure. The reaction can be represented as: Ni x Mn y M z (OH)2+Li + +O2→LiNi x Mn y MzO4 + CO2↑ + H2O↑. The high-valence metal ions doped in this process act as fluxes at high temperatures, lowering the local melting point, promoting surface melting and material migration, resulting in more rounded and uniform matrix particles after a single sintering process, and reducing grain boundary defects.

[0051] The specific process of a single sintering includes: Step 1, preparing the nickel-manganese precursor Ni x Mn y M z (OH)₂, lithium salt, and dopant elements are mixed at a Li / Me molar ratio of 1.0–1.15. The mixture is first stirred at 1200–1800 rpm for 8–15 min using a high-speed mixer, followed by stirring at 500–800 rpm for 5–10 min to obtain a dry mix. This mixing method ensures thorough and uniform dispersion of the components, avoiding localized excess or deficiency of lithium. Furthermore, the introduced dopant metal elements can further improve the crystal structure and interfacial stability of the cathode material. For example, the Li / Me molar ratio can be 1.0, 1.05, 1.10, 1.15, or any value within the range of any two of the above values.

[0052] Step 2: The above dry mixture is placed into a crucible and sintered once in air atmosphere at a temperature of 900℃~980℃ for 10h~15h. After the material cools to room temperature, it is collected and then pulverized to a D50 of 7μm~9μm and a Dmax < 25μm to obtain a lithium nickel manganese oxide matrix. This sintering temperature and time range is conducive to the formation of a spinel phase with high crystallinity and complete structure, and the particle size of the matrix is ​​moderate, which can balance energy density and rate performance. For example, the primary sintering temperature can be 900℃, 920℃, 950℃, 980℃, or any value within the range of any two of the above values; the primary sintering time can be 10h, 12h, 13h, 15h, or any value within the range of any two of the above values; and the D50 after pulverization can be 7μm, 8μm, 9μm, or any value within the range of any two of the above values.

[0053] In some embodiments, the amount of material added to a single crucible during a single sintering process is 1.5 kg to 3.0 kg. Controlling the amount of material added within this range helps to ensure the heating rate and oxygen diffusion efficiency of the material inside the crucible, resulting in uniform heating and thorough sintering, thereby obtaining a cathode material with uniform structure and stable performance. If the amount of material added is too large, it will slow down the heating rate and reduce the oxygen diffusion and exchange efficiency, leading to uneven mass and heat transfer and affecting the material performance.

[0054] In some embodiments, the dopant element N includes at least one of Ti, Al, Mg, Zr, and Mo, and the dopant element N is added in the form of one or more of carbonates, hydroxides, or oxides. These dopant elements are added during the lithium mixing stage and can enter the crystal lattice or segregate at the grain boundaries during sintering, thereby stabilizing the crystal structure, suppressing interfacial side reactions, and further improving the cycle stability and high voltage withstand capability of the cathode material.

[0055] In some embodiments, the amount of dopant added is 0.1% to 0.2% of the total mass of the lithium nickel manganese oxide precursor. This range of addition allows the dopant to fully exert its modifying effect, effectively stabilize the crystal structure and suppress interfacial side reactions, while maintaining good capacity performance.

[0056] Step S3: Mix the substrate and the coating material and perform secondary sintering to obtain lithium nickel manganese oxide cathode material.

[0057] Specifically, the matrix and coating material are mixed using a high-speed mixer at 1200 rpm to 1800 rpm for 8 to 15 minutes, and then at 500 rpm to 800 rpm for 5 to 10 minutes to achieve uniform mixing. After secondary sintering, the mixture is cooled to room temperature, collected, dispersed, sieved through a 400-mesh vibrating screen, and iron is removed by an iron remover to finally obtain the lithium nickel manganese oxide cathode material.

[0058] Secondary sintering forms a uniform coating layer on the surface of the cathode material particles. This coating layer isolates the cathode material from direct contact with the electrolyte, reduces interfacial side reactions under high voltage, and suppresses electrolyte decomposition and gas generation, thereby improving the cycle stability and safety of the battery. Simultaneously, the secondary sintering process helps to firmly bond the coating layer to the substrate, preventing coating layer detachment and ensuring stable interfacial performance of the cathode material during long-term charge-discharge processes.

[0059] In some embodiments, the secondary sintering temperature is 650°C to 750°C. This temperature range enables the coating material to form a continuous and uniform coating layer on the surface of the matrix particles, while maintaining an appropriate degree of reactivity and grain size between the coating layer and the matrix. Exemplarily, the secondary sintering temperature can be 650°C, 680°C, 700°C, 720°C, 750°C, or any value within the range of any two of the above values.

[0060] In some embodiments, the secondary sintering time is 8h to 12h. This time range ensures that the coating layer is sufficiently densified and firmly bonded to the substrate, while maintaining the integrity of the coating layer and the stability of the lithium content. For example, the secondary sintering time can be 8h, 9h, 10h, 11h, 12h, or any value within the range of any two of the above values.

[0061] In some embodiments, the coating material comprises aluminum phosphate. Aluminum phosphate has excellent chemical stability and ionic conductivity, and can form a protective layer on the surface of the cathode material, effectively isolating the electrolyte from direct contact with the active material and suppressing side reactions and gas generation under high voltage. It is understood that the coating material may also be other metal phosphates or oxides, but aluminum phosphate is preferred.

[0062] In some embodiments, the amount of coating material added is 0.1% to 0.5% of the total mass of the lithium nickel manganese oxide cathode material. This coating amount range can form a complete and uniform coating layer, while ensuring smooth lithium-ion transport and full capacity release. For example, the coating amount can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, or any value within the range of any two of the above values.

[0063] Because high-valence metal ions are introduced during the precursor co-precipitation process and the pH is controlled at 8-10.8, while utilizing the fluxing effect during sintering, the lithium nickel manganese oxide cathode material obtained by the above-described preparation method of this application has the advantage of good sphericity, which can reach 0.64-1. Higher sphericity indicates more rounded particles, which is beneficial for reducing interparticle friction and stress concentration, reducing interfacial side reactions, and improving cycle stability. For example, the sphericity can be 0.64, 0.70, 0.75, 0.80, 0.85, 0.90, 1.00, or any value within the range of any two of the above values.

[0064] In some embodiments, the average particle size D50 of the lithium nickel manganese oxide cathode material is 7 μm to 9 μm. This particle size range can balance high compaction density and good rate performance while maintaining suitable particle size, which is beneficial for electrode processing and long-term cycling. Exemplarily, D50 can be 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, or any value within the range of any two of the above values.

[0065] In some embodiments, the lithium nickel manganese oxide cathode material obtained by the preparation method described above has a narrow particle size distribution, with a SPAN value of 0.5 to 0.7. This particle size distribution range indicates uniform particle size, which ensures consistent electrode reaction, facilitates maintaining a stable charge-discharge process, and improves the cycle stability of the battery. For example, the SPAN value can be 0.5, 0.55, 0.6, 0.65, 0.7, or any value within the range of any two of the above values.

[0066] This application also provides a lithium nickel manganese oxide cathode material, which is prepared by the aforementioned method for preparing lithium nickel manganese oxide cathode materials. Because the cathode material provided in this application is prepared by the above method, it has advantages such as uniform distribution of doped elements, high particle roundness, few grain boundary defects, good structural stability, low gas production under high voltage, few interfacial side reactions, and long cycle life.

[0067] Compared with existing technologies, the preparation method of lithium nickel manganese oxide cathode material provided in this application has the following advantages.

[0068] 1. The preparation method provided in this application controls the pH to 8~10.8 and introduces high-valence metal ions during the precursor co-precipitation stage to achieve atomic-level uniform distribution of dopant elements. At the same time, the fluxing effect of high-valence metal ions is used during sintering to reduce grain boundary defects, enhance the structural stability of the material, and make the cathode material particles more rounded and uniform, reducing the surface edges and grain boundaries of the particles. This reduces the interfacial side reactions between the material and the electrolyte, suppresses the decomposition and gas generation of the electrolyte under high voltage, and comprehensively improves the cycle life and safety performance of the battery.

[0069] 2. Through the synergistic effect of uniform doping and rounded particles, the initial discharge capacity and coulombic efficiency can be improved, and the high-temperature cycle performance at 45℃ can be significantly improved, enabling the battery to achieve a longer cycle life and better safety performance.

[0070] 3. High-valence M ions have a high charge density and can form strong bonds with oxygen during subsequent sintering, which can act as a pinning agent, suppress cation mixing and lattice distortion during cycling, and enhance the structural stability of the material.

[0071] This application also provides an electrochemical device, including a positive electrode, a negative electrode, and an electrolyte located between the positive and negative electrodes. The positive electrode is made of the aforementioned lithium nickel manganese oxide positive electrode material. Because this electrochemical device uses the aforementioned positive electrode material, it has advantages such as good cycle stability under high voltage, low gas production, excellent safety performance, and long service life.

[0072] The present application will be further described below with reference to specific embodiments and comparative examples.

[0073] Example 1 Step 1: Dissolve 0.01 mol Ni(NO3)2, 0.03 mol Mn(NO3)2 and 0.0005 mol Nb(NO3)5 in 100 mL of deionized water to prepare solutions A, B and C respectively.

[0074] Step 2: Mix solutions A, B, and C, and mechanically stir at 300 rpm in a water bath at 60°C for 30 minutes to ensure uniform mixing. Then, add 10% sodium bicarbonate aqueous solution and 30% ammonia solution dropwise, controlling the pH value to 9, to carry out a co-precipitation reaction.

[0075] Step 3: Centrifuge and filter the precipitate (3500 rpm, 8 min), wash with 60℃ deionized water for 30 min, repeat the washing process, and then dry in a vacuum oven at 100℃ for 8 h to obtain the lithium nickel manganese oxide precursor, whose chemical formula is Ni. 0.25 Mn 0.7 Nb 0.05 (OH)2.

[0076] Step 4: Mix the above precursor with lithium salt (Li2CO3) at a molar ratio of Li / Me = 1.10, and simultaneously add 0.15wt% Al2O3 and 0.1wt% TiO2 dopants. Then perform a sintering process at 925℃ for 12 hours.

[0077] Step 5: After cooling the first sintering product, it is mixed with aluminum phosphate coating material (coating amount is 0.25% of the total mass of the cathode material) using a high-speed mixer (high speed 1400 rpm / 5 min + low speed 700 rpm / 5 min), and then subjected to a second-stage sintering at 700℃ for 10 h. Finally, the sintered product is cooled to room temperature to obtain lithium nickel manganese oxide cathode material with a particle size D50 of 7 μm~9 μm.

[0078] Example 2 The difference from Example 1 is that Nb(NO3)5 in step 1 is replaced with Nb2O5. The remaining steps and parameters are basically the same as in Example 1. The specific process of preparation is as described in Example 1.

[0079] Example 3 The difference from Example 1 is that the amount of Nb(NO3)5 added in step 1 is changed from 0.0005 mol to 0.001 mol, while the other steps and parameters are the same as in Example 1.

[0080] Example 4 The difference from Example 1 is that the amount of Nb(NO3)5 added in step 1 is changed from 0.0005 mol to 0.0002 mol, while the other steps and parameters are the same as in Example 1.

[0081] Example 5 The difference from Example 1 is that Nb(NO3)5 in step 1 is replaced with NH4VO3, while the remaining steps and parameters are the same as in Example 1.

[0082] Example 6 The difference from Example 1 is that Nb(NO3)5 in step 1 is replaced with (NH4)2MoO4, while the remaining steps and parameters are the same as in Example 1.

[0083] Example 7 The difference from Example 1 is that Al2O3 and TiO2 dopants are not added in step 4, while the remaining steps and parameters are the same as in Example 1.

[0084] Comparative Example 1 The difference from Example 1 is that niobium ions are not added (i.e., Nb(NO3)5 is not added), while the other steps and parameters are the same as in Example 1.

[0085] Comparative Example 2 The difference from Example 1 is that the pH value of the coprecipitation reaction is adjusted from 9 to 12, while the other steps and parameters are the same as in Example 1.

[0086] Comparative Example 3 The difference from Example 1 is that the pH value of the coprecipitation reaction is adjusted from 9 to 8, while the other steps and parameters are the same as in Example 1.

[0087] Relevant testing and testing methods for cathode materials and precursors: SEM Morphology Observation: Morphology was characterized using field emission scanning electron microscopy. A small amount of sample was dispersed on the conductive adhesive surface and sputtered with gold at 8mA for 60 seconds. Test parameters were: accelerating voltage 15kV, beam current 100pA, working distance 15mm, high vacuum mode (vacuum degree better than 9.9×10⁻⁶). -3 Pa), secondary electron detector imaging.

[0088] Sphericity test: Sphericity is a quantitative indicator characterizing the roundness of particles, and the result is obtained by identifying particles using MetisVision software. The formula for calculating sphericity DD is: Sphericity DD = Pseudo-circular diameter / Circumscribed circle diameter.

[0089] Average particle size D50: Laser particle size distribution method: First, turn on the instrument to preheat and measure the background value. Then, add the sample (wet method requires adding dispersant and then sonicating, dry method directly inject the sample) to the instrument to the appropriate shading ratio. After laser irradiation, the detector receives the scattered light, and the software automatically calculates and outputs the particle size distribution parameters (such as D10, D50, D90).

[0090] The formula for calculating the particle size distribution SPAN value is: SPAN=(D90-D10) / D50.

[0091] Elemental distribution (uniformity) test: EDS (energy dispersive spectroscopy) test is often used in conjunction with scanning electron microscopy: First, a dry, conductive (non-conductive samples need to be sprayed with gold / carbon) sample is placed in the electron microscope and vacuumed. After selecting a microscopic region, the accelerating voltage (usually 10-20kV) and acquisition time (30-120 seconds) are set. The characteristic X-rays excited by the electron beam are received by the probe and generate an energy spectrum. Elements are identified by peak position (qualitative) and the composition is analyzed by peak intensity ratio (semi-quantitative).

[0092] Preparation and performance testing of the electrochemical device: Electrochemical performance testing was conducted using a CR2025 coin cell. First, the positive electrode material, conductive carbon, and binder polyvinylidene fluoride (PVDF) were mixed at a mass ratio of 90:5:5, and an appropriate amount of N-methylpyrrolidone (NMP) was added to prepare a homogeneous slurry. The slurry was coated onto an aluminum foil current collector, vacuum dried at 115℃±5℃ for 8 hours, compacted, and cut into circular electrode sheets. Using a lithium metal sheet as the counter electrode, a coin cell was assembled in a glove box.

[0093] Constant current charge-discharge tests were conducted using the LAND battery testing system, with a test voltage window of 3.0V to 5.0V. The charge-discharge rate for the initial discharge capacity test was +1C / -1C, and the CV cutoff current was 0.01C. The charge-discharge rate for the 45℃ cycle test was +1C / 1C, and the CV cutoff current was 0.01C.

[0094] Gas production test: The gas production test was conducted using a 2Ah pouch cell to evaluate the stability of lithium nickel manganese oxide cathode material at high temperatures. Fully charged pouch cells were stored at 45°C for 7 days. The volume of gas produced was measured using the immersion volume method (solvent displacement method) based on Archimedes' principle. The results are expressed as the amount of gas produced per unit mass of cathode active material (mL / g).

[0095] Table 1 Note: Sphericity (dd) refers to the sphericity of lithium nickel manganese oxide precursor particles.

[0096] Sphericity (sc) refers to the sphericity of the final lithium nickel manganese oxide cathode material particles.

[0097] Results analysis: Through Figure 2 As can be seen in Figure (a), the precursor particles without metal ion doping have poor particle uniformity and contain a large amount of particle fragments; while Figure 2 (b) Figure and Figure 2 The improved precursor particle morphology in Figure c indicates that the addition of high-valence niobium ions can optimize the precursor structure, giving it a more uniform particle packing morphology.

[0098] Figure 3 (a~d) The SEM morphologies of cathode materials obtained after sintering precursors with different metal M ions were compared. Combined with the powder test results of the precursors and corresponding nickel-manganese cathodes in Table 1, it can be seen that the cathode material obtained after niobium ion doping showed improved particle roundness and crystal structure stability. Its I(311) / I(400) test value was lower, and its sphericity calculation value was higher, with the particles transforming from the original cross-sectioned octahedrons into more rounded near-spherical particles. For vanadium and molybdenum ion-doped precursors, the degree of morphology improvement after sintering differed from that of niobium ion-doped precursors. The reason is that Nb... 5+ As a morphology modifier, it inhibits the excessively rapid growth of certain crystal planes through a "pinning" effect, thereby promoting the particles to tend towards spherical shape and preventing the abnormal growth or agglomeration of secondary particles, resulting in a narrower particle size distribution and a more rounded surface; while V 5+ Mo 6+ Under coprecipitation conditions, it exhibits multiple valence states or readily forms heteropolyacids. Its coprecipitation synchronicity with the main elements (Ni, Mn) is slightly weaker than that with Nb. 5+ This leads to differences in the particle growth process.

[0099] Combined with Table 1 and Figure 4 , Figure 5 A comparative analysis of the electrical performance and gas production of Examples 1-7 and Comparative Example 1 reveals that the nickel-manganese cathode material prepared by introducing an appropriate amount of high-valence metal elements into the precursor exhibits superior electrochemical performance compared to the undoped Comparative Example 1. It also shows higher initial discharge capacity and initial coulombic efficiency, as well as improved high-temperature cycling performance. This indicates that in the nickel-manganese precursor system, doping with high-valence metal elements can enhance the roundness and uniformity of the particles. This is attributed to their controllable hydrolysis behavior during co-precipitation, allowing them to selectively adsorb onto specific crystal faces as morphology modifiers, promoting uniform particle growth and inhibiting abnormal agglomeration. Therefore, the preparation method of the lithium nickel manganese oxide cathode material provided in this application offers advantages such as uniform doping, rounded particles, stable structure, low gas production, and excellent cycling performance.

[0100] The above description describes some specific embodiments of this application, but in actual applications, the application should not be limited to these embodiments. For those skilled in the art, other modifications and alterations made based on the technical concept of this application should fall within the protection scope of this application.

Claims

1. A method for preparing a lithium nickel manganese oxide cathode material, characterized in that, include: A mixed metal salt solution is prepared by mixing a nickel source, a manganese source, and an M source with a solvent. The mixed metal salt solution is then subjected to a co-precipitation reaction with a complexing agent and a precipitating agent under conditions of pH 8-10.8 and inert gas protection. After washing and drying, an M-doped lithium nickel manganese oxide precursor is obtained. The M source includes at least one of Nb, V, and Mo. The lithium nickel manganese oxide precursor is mixed with a lithium salt and sintered once to obtain the matrix; and The matrix and the coating material are mixed and sintered a second time to obtain the lithium nickel manganese oxide cathode material.

2. The method for preparing lithium nickel manganese oxide cathode material according to claim 1, characterized in that, The molar ratio of the nickel source to the manganese source is 1:1.5~3.0; and / or, The molar ratio of the nickel source to the M source is 1:0.002~0.

01.

3. The method for preparing lithium nickel manganese oxide cathode material according to claim 1, characterized in that, The general formula of the lithium nickel manganese oxide precursor is Ni x Mn y M z (OH)2, wherein the 0.20≤x<0.30, 0.70≤y<0.80, and x+y+z=1.

4. The method for preparing lithium nickel manganese oxide cathode material according to claim 1, characterized in that, The primary sintering temperature is 900℃~980℃, and the time is 10h~15h; and / or, The secondary sintering temperature is 650℃~750℃, and the time is 8h~12h.

5. The method for preparing lithium nickel manganese oxide cathode material according to claim 1, characterized in that, The sphericity of the lithium nickel manganese oxide cathode material is 0.64~1; and / or, The average particle size D50 of the lithium nickel manganese oxide cathode material is 7 μm to 9 μm; and / or, The span value of the lithium nickel manganese oxide cathode material is 0.45~0.

65.

6. The method for preparing lithium nickel manganese oxide cathode material according to claim 1, characterized in that, The coating material includes aluminum phosphate; and / or, The amount of coating material added is 0.1% to 0.5% of the total mass of the lithium nickel manganese oxide cathode material.

7. The method for preparing lithium nickel manganese oxide cathode material according to claim 1, characterized in that, In the step of mixing the lithium nickel manganese oxide precursor with the lithium salt, an N source is also doped, wherein the N element in the N source includes at least one of Ti, Al, Mg, Zr and Mo.

8. The method for preparing lithium nickel manganese oxide cathode material according to claim 7, characterized in that, The amount of N source added is 0.1% to 0.2% of the total mass of the lithium nickel manganese oxide precursor.

9. A lithium nickel manganese oxide cathode material, characterized in that, The lithium nickel manganese oxide cathode material is prepared by the method for preparing lithium nickel manganese oxide cathode material according to any one of claims 1 to 8.

10. An electrochemical device, characterized in that, It includes a positive electrode, a negative electrode, and an electrolyte located between the positive electrode and the negative electrode, wherein the positive electrode is made of lithium nickel manganese oxide positive electrode material as described in claim 9.

Images