A preparation method of lithium-rich manganese-based composite positive electrode material, composite positive electrode material and battery

Abstract

The present invention provides a preparation method of a lithium-rich manganese-based composite positive electrode material, a composite positive electrode material, and a battery. The preparation method comprises the following steps: S1. preparing a graphene dispersion, adding a matrix material to the graphene dispersion, and reacting for 5 to 10 hours at a temperature of 70 to 95° C. and a pH of 4 to 6 to obtain a sol; the chemical formula of the matrix material is xLi2MnO3·(1-x)LiNi 0.5 Mn 0.5 O2, x is 0.2 to 0.8; S2. adding the metal oxide to the sol, mixing, and then hydrothermally reacting at 200 to 400°C for 14 to 20 hours to obtain a gel; S3. washing the gel with deionized water, then aging at -20 to -10°C for 20 to 50 hours, and drying to obtain a composite positive electrode material. The preparation method provided by the present invention can further optimize the conductivity, structural stability, and rate performance of the lithium-rich manganese-based positive electrode material, while also effectively suppressing the dissolution of transition metal ions, thereby optimizing the cycle performance of the battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and in particular relates to a preparation method of a lithium-rich manganese-based composite positive electrode material, a composite positive electrode material and a battery. Background Art

[0002] In the context of green development, lithium-ion batteries with low environmental impact have been widely used in 3C electronic products, new energy electric vehicles, and large-scale energy storage. As the main active material of lithium-ion batteries, the low energy density and high cost of cathode materials are the shortcomings that restrict the development of lithium-ion batteries. The anions and cations of lithium-rich manganese-based cathode materials jointly participate in charge compensation and provide 250mAh g -1 The above high specific capacity, and the fact that it contains less precious metal elements such as cobalt and nickel, and is mainly composed of cheap manganese elements, has lower material costs and is a strong candidate for the next generation of lithium-ion battery positive electrode materials.

[0003] However, the current lithium-rich manganese-based cathode materials have the following problems: First, the button cell or full battery assembled with the material has a serious voltage drop during the cycle. Second, due to the precipitation of lattice oxygen, the first cycle coulomb efficiency is low, the first efficiency is ≤85%, and the irreversible capacity is as high as 40-100mAh / g. The charging process of Li + The layered structure of lithium-rich manganese-based cathode materials is broken, causing the material structure to collapse and resulting in poor cycling performance. These issues severely impair the electrochemical performance of lithium-rich manganese-based lithium-ion batteries, hindering their future development and application. Therefore, the sole application of lithium-rich manganese-based cathode materials remains extremely challenging.

[0004] To address this, researchers have proposed numerous methods and strategies to modify lithium-rich manganese-based cathode materials, such as adjusting the composition and structure, surface modification, ion doping, and designing specialized configurations. However, some currently available methods can only improve material performance in certain areas and cannot effectively enhance all aspects of lithium-rich manganese-based cathode materials. Alternatively, they may require complex preparation processes and demanding conditions.

[0005] In view of this, providing a preparation method of a new lithium-rich manganese-based positive electrode material is of great significance for solving the problems existing in the current lithium-rich manganese-based positive electrode materials and improving the electrochemical performance of lithium-rich manganese-based positive electrode materials. Summary of the Invention

[0006] To address the problems and shortcomings of the prior art, the present invention provides a preparation method for a lithium-rich manganese-based composite cathode material, a composite cathode material, and a battery. The preparation method provided by the present invention can further optimize the conductivity, structural stability, and rate capability of the lithium-rich manganese-based cathode material, while also effectively inhibiting the dissolution of transition metal ions, thereby optimizing the battery's cycling performance.

[0007] According to a first aspect of the present invention, a method for preparing a lithium-rich manganese-based composite positive electrode material is provided, characterized in that it comprises the following steps: S1. preparing a graphene dispersion, adding a matrix material to the graphene dispersion, and reacting for 5 to 10 hours at a temperature of 70 to 95°C and a pH of 4 to 6 to obtain a sol; the chemical formula of the matrix material is xLi2MnO3·(1-x)LiNi 0.5 Mn 0.5 O2, the value of x is 0.2 to 0.8; S2. The metal oxide is added to the sol and mixed, and then a hydrothermal reaction is carried out at 200 to 400°C for 14 to 20 hours to obtain a gel; S3. The gel is washed with deionized water, and then aged at -20 to -10°C for 20 to 50 hours, and dried to obtain a composite positive electrode material.

[0008] In the preparation method of the above-mentioned composite positive electrode material, the temperature in S1 can be, for example, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, the pH can be, for example, 4, 5, 6, and the reaction time can be, for example, 5h, 6h, 7h, 8h, 9h, 10h; the temperature of the hydrothermal reaction in S2 can be, for example, 200°C, 250°C, 300°C, 350°C, 400°C, and the reaction time can be, for example, 14h, 17h, 18h, 19h, 20h; the aging temperature in S3 can be, for example, -20°C, -18°C, -15°C, -12°C, -10°C, and the aging time can be, for example, 20h, 25h, 30h, 35h, 40h, 45h, 50h; the above-mentioned reaction conditions are not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0009] Graphene has excellent electrical conductivity, structural strength, and toughness. By preparing a graphene dispersion and then reacting it with a matrix material at a specific temperature and pH, the graphene and matrix material are thoroughly mixed, resulting in a uniform dispersion of the graphene and matrix material in the resulting sol. This allows the graphene to serve as the structural support for the sol, facilitating its full coating with metal oxides, forming a dense, uniform metal oxide coating. This in turn improves the structural stability and electrical conductivity of lithium-rich manganese-based composite cathode materials, effectively inhibiting the dissolution of transition metal ions, and thereby enhancing the cycling performance and rate capability of the composite cathode materials.

[0010] The metal oxide undergoes a hydrothermal reaction with the graphene / matrix material sol at a specific temperature and time, and can form a dense, uniform coating on the surface of the graphene / matrix material, thereby improving the conductivity, structural stability and corrosion resistance of the lithium-rich manganese-based composite positive electrode material, reducing the internal resistance and polarization of the electrode material, and making the material have better cycle performance, high-temperature stability and safety performance. Specifically, the metal oxide has stable chemical properties and does not react with the electrolyte during the charge and discharge cycle. As a coating material, it can improve the stability of the electrode / electrolyte interface, thereby improving the cycle performance and safety of the electrode, while effectively inhibiting the dissolution of transition metal ions. Compared with other inorganic materials that can improve cycle performance, it has a cost advantage. In addition, the metal oxide itself has good conductivity and mechanical strength, and can further improve the conductivity and structural stability of the lithium-rich manganese-based composite positive electrode material, thereby optimizing the cycle performance, high-temperature stability and safety performance of the lithium-rich manganese-based composite positive electrode material.

[0011] Furthermore, aging the gel obtained after the hydrothermal reaction at a relatively low temperature of -20 to -10°C for a certain period of time is conducive to the molecules in the gel being arranged more regularly and tightly, strengthening the gel network structure, and thus optimizing the structural strength of the positive electrode particles, making them less likely to break or collapse during the charge and discharge cycle. At the same time, the chemical composition uniformity and purity of the lithium-rich manganese-based composite positive electrode material are improved, thereby improving the electrochemical performance of the material. More importantly, aging at a relatively low temperature can also improve the uniformity of the particle size and optimize the particle size distribution of the positive electrode particles, so that the positive electrode particles can take into account the performance of all aspects of the material and exhibit better comprehensive electrochemical performance.

[0012] Furthermore, the choice of matrix material generally influences the performance of lithium-rich manganese-based cathode materials. Different compositions often result in different material properties, and this also affects the composite effect of the matrix material with other modifying materials, ultimately impacting the performance improvement of the lithium-rich manganese-based composite cathode material. The general chemical formula for lithium-rich manganese-based matrix materials is xLi2MnO3·(1-x)LiMO2, where M is a transition metal. This can be considered a continuous solid solution of Li2MnO3 and LiMO2. Taking Li2MnO3 and LiMnO2 as examples, the more authoritative view is that when the voltage is less than 4.5V, LiMnO2 undergoes lithium ion deintercalation, while Li2MnO3 does not react, stabilizing the material structure. When the voltage is greater than 4.5V, Li2O deintercalates from Li2MnO3. However, during discharge, this lithium cannot be reintercalated, resulting in irreversible initial capacity loss and low Coulombic efficiency. This structural change deteriorates the cycling performance. Therefore, the selection of LiMO2 (M is a transition metal) in the lithium-rich manganese-based matrix material also has an important influence on its cycle performance. The chemical formula of the matrix material selected in the present invention is xLi2MnO3·(1-x)LiNi 0.5 Mn 0.5 O2, firstly, the transition metals Ni and Mn are introduced into the LiMO2 structure, and secondly, the value of x is controlled within a specific range. Under the combined action of these two, the matrix material is composited with graphene, and after being further coated with metal oxides, it exhibits better electrochemical properties, such as higher conductivity, discharge capacity, cycle capacity retention rate, lower transition metal dissolution, etc.

[0013] Preferably, in S1, when preparing the graphene dispersion, the mass ratio of graphene to water is 0.2 to 5:10; when preparing the sol, the mass ratio of the graphene dispersion to the matrix material is 5 to 20:80 to 95. For example, it can be 5:95, 10:90, 15:85, or 20:80, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable. Controlling the mass ratio of graphene to water within the above range is conducive to the full dispersion of graphene. At the same time, further controlling the mass ratio of the graphene dispersion to the matrix material is conducive to having sufficient water to wet and mix the graphene and the matrix material, thereby forming a relatively uniform sol under certain reaction conditions.

[0014] Preferably, in S1, the D50 of the base material is 2-7 μm, for example, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, or 7 μm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0015] Preferably, in S1, when preparing the graphene dispersion, the sheet diameter of the graphene used is 5 to 10 μm, and the number of layers is 6 to 9 layers. For example, the sheet diameter of the graphene can be 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, and the number of layers can be 6 layers, 7 layers, 8 layers, and 9 layers, but it is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable. Ensuring that the sheet diameter and the number of layers of the graphene are within the above-mentioned numerical range can ensure that the graphene is fully interspersed between the matrix materials to form a relatively uniform sol system. At the same time, it can ensure that the graphene can provide sufficient structural strength to the positive electrode material, ensure that the composite positive electrode material has good structural stability, and make it not easy to break or collapse during the cycle. In addition, in the present invention, the sheet diameter of the graphene is the average sheet diameter.

[0016] Preferably, in S2, the amount of metal oxide added is 1 to 10% of the mass of the matrix material. For example, it can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, but it is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable. Too little metal oxide is not conducive to its coating of graphene / matrix material, and too thin oxide coating layer will lead to a decrease in the protection effect of graphene / matrix material, and cannot effectively prevent the contact and reaction between internal materials and electrolyte, and cannot effectively limit the dissolution of transition metal ions, so it cannot effectively improve the cycle stability of the positive electrode material. At the same time, too thin metal oxide coating layer cannot effectively improve the conductivity of the positive electrode material. Too much metal oxide will cause the coating layer to be too thick, which will cause the transmission path of lithium ions to be too long, which is not conducive to the rapid deintercalation of lithium ions, and therefore is not conducive to the cycle performance of the positive electrode material.

[0017] Preferably, in S2, the D50 of the metal oxide is 50 to 100 nm. For example, it can be 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, 100 nm, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable. Ensuring that the D50 of the metal oxide is within the above range can ensure that the metal oxide is coated on the surface of the graphene / matrix material with a relatively stable binding force, while ensuring that the metal oxide is distributed on the surface of the graphene / matrix material in a more appropriate arrangement, ensuring that the metal oxide coating layer can effectively protect the internal material while also ensuring that there is suitable pores to allow lithium ion deintercalation to have a higher rate, taking into account both protection and lithium ion transmission efficiency.

[0018] It's also important to note that maintaining the graphene sheet diameter, number of layers, and D50 of the metal oxide within a certain numerical range is beneficial for ensuring that the final composite cathode material particle size and particle size distribution are within an appropriate range. This ensures that the composite cathode material has a high specific surface area, allowing for rapid electrolyte wetting and efficient lithium-ion transport. It also prevents particle agglomeration caused by overly small composite cathode material particles, ensuring the subsequent preparation of battery slurry and electrode sheets. However, overly small particles can also increase the degree of side reactions with the electrolyte, which is detrimental to cycling stability.

[0019] Preferably, in S2, the metal oxide includes at least one of vanadium oxide, titanium dioxide, magnesium oxide, aluminum oxide, and chromium oxide. The selection of these metal oxides can effectively improve the conductivity of the lithium-rich manganese-based positive electrode material while effectively inhibiting its lattice oxygen precipitation, improving the structural stability of the material, and helping to improve the specific capacity and cycle performance of the positive electrode material, and reducing voltage decay during the cycle.

[0020] Preferably, in S2, the metal oxide is vanadium oxide, or a combination of aluminum oxide and chromium oxide. These metal oxides or combinations of metal oxides are more conducive to balancing the performance of the lithium-rich manganese-based composite positive electrode material in various aspects. This may be because the composite positive electrode material formed by these metal oxides, the above-mentioned matrix material, and graphene has better structural stability and can withstand greater cyclic stress during the charge and discharge cycle, which is more conducive to the cyclic stability of the positive electrode material, thereby further optimizing the electrochemical performance of the positive electrode material in various aspects.

[0021] Preferably, in S3, during washing, the solid-liquid ratio is 1:4 to 6, and the number of washes is 3 to 5. The solid-liquid ratio can be, for example, 1:4, 1:5, or 1:6, and the number of washes can be, for example, 3, 4, or 5 times, but are not limited to the values ​​listed above, and other values ​​not listed within the numerical range are also applicable.

[0022] Preferably, in S3, the drying method is freeze drying or supercritical drying, and the drying time is 24 to 36 hours. For example, it can be 24 hours, 26 hours, 28 hours, 30 hours, 32 hours, 34 hours, or 36 hours, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable. Freeze drying or supercritical drying is more conducive to maintaining the original structure and properties of the product, reducing the degree of damage to the positive electrode material during the drying process, and ensuring that the positive electrode material can exert better electrochemical performance during the charge and discharge cycle.

[0023] According to a second aspect of the present invention, a composite positive electrode material is provided, characterized in that it is prepared by the above-mentioned preparation method based on the lithium-rich manganese-based composite positive electrode material. The composite positive electrode material prepared by the preparation method provided by the present invention has a higher specific capacity and better cycle performance, can reduce voltage decay during the cycle process, and has higher rate performance and conductivity, and can effectively inhibit the dissolution of transition metal ions.

[0024] According to a third aspect of the present invention, a battery comprises the composite positive electrode material described above. The active material used in the positive electrode sheet of the battery provided by the present invention is the composite positive electrode material prepared by the preparation method of the present invention, effectively improving the battery's discharge capacity and cycle capacity retention rate, thereby optimizing the battery's electrochemical performance.

[0025] In summary, the lithium-rich manganese-based composite positive electrode material prepared by the method provided by the present invention, which respectively composites the matrix material with graphene under specific reaction conditions and then coats the surface of the composite with metal oxide, can effectively improve the conductivity, gram capacity, rate performance and cycle capacity retention rate of the lithium-rich manganese-based positive electrode material, and can also effectively inhibit the dissolution of transition metal elements. Therefore, the preparation method has a good modification effect on the lithium-rich manganese-based positive electrode material, can be used as a new modification route for the current lithium-rich manganese-based positive electrode material, and is of great significance for improving the electrochemical performance of the lithium-rich manganese-based positive electrode material. At the same time, the composite positive electrode material obtained by the preparation method provided by the present invention is relatively light in weight and can reduce the weight of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a SEM image of the composite positive electrode material prepared in Example 1 of the present invention, with a magnification of 10kx.

[0027] Figure 2 This is a SEM image of the composite positive electrode material prepared in Example 1 of the present invention, with a magnification of 50kx.

[0028] Figure 3 This is a test principle diagram for the resistivity test of the composite positive electrode material in the present invention. DETAILED DESCRIPTION

[0029] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0030] Example 1

[0031] 1. Preparation of composite cathode materials

[0032] The composite cathode material in this embodiment was prepared according to the following steps:

[0033] S1. A graphene dispersion was prepared with a graphene / water mass ratio of 2.5:10. The matrix material was added to the graphene dispersion and reacted for 6 h at 90°C and pH 5 to obtain a sol. The mass ratio of the graphene dispersion to the matrix material was 10:90. The graphene flake diameter was 6 μm (average flake diameter) and the number of layers was 6. The chemical formula of the matrix material was xLi2MnO3·(1-x)LiNi 0.5 Mn 0.5 O2, the x value is 0.5, and D50 is 4.5 μm;

[0034] S2. Vanadium oxide (V2O5) was added to the above sol and mixed, and then subjected to a hydrothermal reaction at 300 ° C for 18 hours to obtain a gel; the amount of vanadium oxide added was calculated as 5% of the mass of the matrix material;

[0035] S3. The gel was washed four times with deionized water at a solid-liquid ratio of 1:5, and then aged at -15°C for 35 hours and freeze-dried for 30 hours to obtain a composite positive electrode material.

[0036] like Figure 1 and Figure 2 , are all electron microscope images of the composite positive electrode material prepared in Example 1, where Figure 1 The magnification of the electron microscope is 10kx. Figure 2 The magnification of the electron microscope is 50kx.

[0037] 2. Prepare the battery

[0038] The battery of this embodiment was prepared according to the following steps:

[0039] a. Weigh the materials separately according to the mass ratio of the composite positive electrode material: conductive carbon black (Super P): binder (PVDF) of 93:3:4, use N-methylpyrrolidone (NMP) as solvent, and centrifuge the mixture for 10 minutes to obtain a positive electrode slurry;

[0040] b. Use a coater to coat the positive electrode slurry on aluminum foil with a thickness of 160 μm. After drying at 120°C for 3 hours, the slurry is rolled once on a double-roller roller with a gap of 0.1 mm. The slurry is then transferred to a vacuum drying oven and dried at 120°C for 12 hours to completely remove NMP and residual moisture.

[0041] c. Cut the dried electrode into discs with a diameter of 12 mm as the positive working electrode;

[0042] d. Assemble button cells: CR2032 button cells were assembled in a glove box filled with dry argon using a lithium sheet as the negative electrode, a polypropylene separator as the separator, and an electrolyte consisting of 1 M LiPF6, dimethyl carbonate (DMC) and ethylene carbonate (EC) in a 1:1.1 (mass ratio).

[0043] Example 2

[0044] 1. Preparation of composite cathode materials

[0045] When preparing the composite positive electrode material of this embodiment, the difference from that of Example 1 is that the mass ratio of the graphene dispersion to the matrix material is 3:97. The rest is the same as that of Example 1.

[0046] 2. Prepare the battery

[0047] The preparation of the battery of this embodiment is the same as that of Example 1.

[0048] Example 3

[0049] 1. Preparation of composite cathode materials

[0050] When preparing the composite positive electrode material of this embodiment, the difference from that of Example 1 is that the mass ratio of the graphene dispersion to the matrix material is 25:75. The rest is the same as that of Example 1.

[0051] 2. Prepare the battery

[0052] The preparation of the battery of this embodiment is the same as that of Example 1.

[0053] Example 4

[0054] 1. Preparation of composite cathode materials

[0055] When preparing the composite positive electrode material of this embodiment, the difference from that of Example 1 is that the D50 of the base material is 0.5 μm. The rest is the same as that of Example 1.

[0056] 2. Prepare the battery

[0057] The preparation of the battery of this embodiment is the same as that of Example 1.

[0058] Example 5

[0059] 1. Preparation of composite cathode materials

[0060] When preparing the composite positive electrode material of this embodiment, the difference from that of embodiment 1 is that the D50 of the base material is 10 μm. The rest is the same as that of embodiment 1.

[0061] 2. Prepare the battery

[0062] The preparation of the battery of this embodiment is the same as that of Example 1.

[0063] Example 6

[0064] 1. Preparation of composite cathode materials

[0065] When preparing the composite positive electrode material of this embodiment, the difference from that of Example 1 is that the diameter of the graphene sheet is 15 μm. The rest is the same as that of Example 1.

[0066] 2. Prepare the battery

[0067] The preparation of the battery of this embodiment is the same as that of Example 1.

[0068] Example 7

[0069] 1. Preparation of composite cathode materials

[0070] When preparing the composite positive electrode material of this embodiment, the difference from that of Example 1 is that the diameter of the graphene sheet is 0.8 μm and the number of layers is 12. The rest is the same as that of Example 1.

[0071] 2. Prepare the battery

[0072] The preparation of the battery of this embodiment is the same as that of Example 1.

[0073] Example 8

[0074] 1. Preparation of composite cathode materials

[0075] When preparing the composite positive electrode material of this embodiment, the difference from Example 1 is that the amount of vanadium oxide added is calculated based on the mass of vanadium oxide being 1% of the mass of the base material.

[0076] 2. Prepare the battery

[0077] The preparation of the battery of this embodiment is the same as that of Example 1.

[0078] Example 9

[0079] 1. Preparation of composite cathode materials

[0080] When preparing the composite positive electrode material of this embodiment, the difference from that of Example 1 is that the amount of vanadium oxide added is calculated based on the mass of vanadium oxide being 4% of the mass of the base material.

[0081] 2. Prepare the battery

[0082] The preparation of the battery of this embodiment is the same as that of Example 1.

[0083] Example 10

[0084] 1. Preparation of composite cathode materials

[0085] When preparing the composite positive electrode material of this embodiment, the difference from that of Example 1 is that the amount of vanadium oxide added is calculated based on the mass of vanadium oxide being 8% of the mass of the base material.

[0086] 2. Prepare the battery

[0087] The preparation of the battery of this embodiment is the same as that of Example 1.

[0088] Example 11

[0089] 1. Preparation of composite cathode materials

[0090] When preparing the composite positive electrode material of this embodiment, the difference from that of embodiment 1 is that the amount of vanadium oxide added is calculated based on the mass of vanadium oxide being 10% of the mass of the base material.

[0091] 2. Prepare the battery

[0092] The preparation of the battery of this embodiment is the same as that of Example 1.

[0093] Example 12

[0094] 1. Preparation of composite cathode materials

[0095] When preparing the composite positive electrode material of this embodiment, the difference from that of Example 1 is that the metal oxide is titanium oxide, and the addition amount is 2%. The rest is the same as that of Example 1.

[0096] 2. Prepare the battery

[0097] The preparation of the battery of this embodiment is the same as that of Example 1.

[0098] Example 13

[0099] 1. Preparation of composite cathode materials

[0100] The preparation of the composite positive electrode material of this embodiment is different from that of Example 1 in that the metal oxide is magnesium oxide + chromium oxide, the addition amount is 5%, and the mass ratio of magnesium oxide to chromium oxide is 1:1. The rest is the same as Example 1.

[0101] 2. Prepare the battery

[0102] The preparation of the battery of this embodiment is the same as that of Example 1.

[0103] Example 14

[0104] 1. Preparation of composite cathode materials

[0105] The preparation of the composite positive electrode material of this embodiment is different from that of Example 1 in that the metal oxide is aluminum oxide + chromium oxide, the addition amount is 7%, and the mass ratio of aluminum oxide to chromium oxide is 1:1. The rest is the same as Example 1.

[0106] 2. Prepare the battery

[0107] The preparation of the battery of this embodiment is the same as that of Example 1.

[0108] Example 15

[0109] 1. Preparation of composite cathode materials

[0110] When preparing the composite positive electrode material of this embodiment, the difference from that of Example 1 is that the temperature of the hydrothermal reaction is 250° C. The rest is the same as that of Example 1.

[0111] 2. Prepare the battery

[0112] The preparation of the battery of this embodiment is the same as that of Example 1.

[0113] Example 16

[0114] 1. Preparation of composite cathode materials

[0115] When preparing the composite positive electrode material of this embodiment, the difference from that of Example 1 is that the temperature of the hydrothermal reaction is 350° C. The rest is the same as that of Example 1.

[0116] 2. Prepare the battery

[0117] The preparation of the battery of this embodiment is the same as that of Example 1.

[0118] Comparative Example 1

[0119] 1. Preparation of composite cathode materials

[0120] When preparing the composite positive electrode material of this comparative example, the difference from Example 1 is that the temperature of the hydrothermal reaction is 150° C. The rest is the same as Example 1.

[0121] 2. Prepare the battery

[0122] The preparation of the battery of this comparative example is consistent with that of Example 1.

[0123] Comparative Example 2

[0124] 1. Preparation of composite cathode materials

[0125] When preparing the composite positive electrode material of this comparative example, the difference from Example 1 is that the hydrothermal reaction time is 10 h. The rest is the same as Example 1.

[0126] 2. Prepare the battery

[0127] The preparation of the battery of this comparative example is consistent with that of Example 1.

[0128] Comparative Example 3

[0129] 1. Preparation of composite cathode materials

[0130] When preparing the composite positive electrode material of this comparative example, the difference from Example 1 is that the aging temperature is -30°C. The rest is the same as Example 1.

[0131] 2. Prepare the battery

[0132] The preparation of the battery of this comparative example is consistent with that of Example 1.

[0133] Comparative Example 4

[0134] 1. Preparation of composite cathode materials

[0135] When preparing the composite positive electrode material of this comparative example, the difference from Example 1 is that the aging temperature is 0° C. The rest is the same as Example 1.

[0136] 2. Prepare the battery

[0137] The preparation of the battery of this comparative example is consistent with that of Example 1.

[0138] Comparative Example 5

[0139] 1. Preparation of composite cathode materials

[0140] When preparing the composite positive electrode material of this comparative example, the difference from Example 1 is that the aging time is 15 hours. The rest is the same as Example 1.

[0141] 2. Prepare the battery

[0142] The preparation of the battery of this comparative example is consistent with that of Example 1.

[0143] Comparative Example 6

[0144] 1. Preparation of composite cathode materials

[0145] The preparation of the composite positive electrode material of this comparative example differs from that of Example 1 in that the aging treatment in S3 is not performed, that is, the washed gel is directly dried to obtain the composite positive electrode material.

[0146] 2. Prepare the battery

[0147] The preparation of the battery of this comparative example is consistent with that of Example 1.

[0148] Comparative Example 7

[0149] 1. Preparation of composite cathode materials

[0150] The preparation of the composite positive electrode material of this comparative example differs from that of Example 1 in that the step of mixing the matrix material and the graphene dispersion in S1 is omitted. Instead, the graphene dispersion, matrix material, and vanadium oxide are directly mixed and then subjected to a hydrothermal reaction. The hydrothermal reaction conditions are the same as those of Example 1. The remaining conditions are the same as those of Example 1.

[0151] 2. Prepare the battery

[0152] The preparation of the battery of this comparative example is consistent with that of Example 1.

[0153] Comparative Example 8

[0154] 1. Preparation of composite cathode materials

[0155] When preparing the composite positive electrode material of this comparative example, the difference from Example 1 is that in the base material, the value of x in the chemical formula is 0. The rest is the same as Example 1.

[0156] 2. Prepare the battery

[0157] The preparation of the battery of this comparative example is consistent with that of Example 1.

[0158] Comparative Example 9

[0159] 1. Preparation of composite cathode materials

[0160] When preparing the composite positive electrode material of this comparative example, the difference from Example 1 is that in the base material, the value of x in the chemical formula is 1. The rest is the same as Example 1.

[0161] 2. Prepare the battery

[0162] The preparation of the battery of this comparative example is consistent with that of Example 1.

[0163] Test Case

[0164] 1. Experimental Construction Method

[0165] The composite cathode materials or batteries prepared in all the above examples and comparative examples were subjected to the following performance tests:

[0166] (1) Conductivity test of composite cathode materials

[0167] The powder resistivity of the material is tested and characterized by the following steps: a quantitative sample is added to the material cavity and a four-probe powder resistivity meter is used for pressure testing. Figure 3 The resistivity is calculated using the following formula: ρ = k*U / I (k is the diameter-thickness compensation factor, and U is the voltage).

[0168] (2) Discharge capacity and cycle capacity retention test

[0169] After preparing the battery and letting it rest for 3 hours, charge / discharge tests were performed on a LAND battery testing system at a voltage range of 2.0 to 4.8 V. The battery's discharge specific capacity was recorded at currents of 0.1C, 1C, and 5C, and the capacity retention rate after 100 cycles at a current of 1C was calculated and recorded. The capacity retention rate was calculated as: discharge capacity at the 100th cycle / discharge capacity at the first cycle.

[0170] (3) Transition metal dissolution test

[0171] After the cycle in (2) is completed, the battery is discharged to 0% SOC, the positive electrode sheet is scraped, and the manganese (Mn) content in the positive electrode active material layer is tested by ICP, and the dissolution of the transition metal element Mn is recorded.

[0172] 2. Experimental Results

[0173] The test results of the above-mentioned related properties of the composite positive electrode materials or batteries prepared in all the above embodiments and comparative examples are shown in Table 1.

[0174] Table 1 Test results of composite positive electrode materials or battery performance prepared in Examples and Comparative Examples

[0175]

[0176]

[0177] As shown in Table 1, the lithium-rich manganese-based composite positive electrode material prepared by the method provided by the present invention has a low resistivity and a high discharge specific capacity at 0.1C, 1C, and 5C rates. The capacity retention rate after 100 cycles at 1C can reach more than 83%, and the Mn dissolution amount is no more than 238ppm. Therefore, the lithium-rich manganese-based composite positive electrode material prepared by the present invention has good electrochemical properties and is a positive electrode material with excellent comprehensive performance. It can effectively improve the problems existing in current lithium-rich manganese-based materials.

[0178] In Comparative Example 1, the hydrothermal temperature of the metal oxide and the sol was too low, resulting in insufficient reaction between the metal oxide and the sol. Consequently, the metal oxide was unable to form a dense, uniform coating on the graphene / matrix surface, impairing the structural stability and corrosion resistance of the composite cathode material. This resulted in a decrease in the battery's high-rate (5C) discharge capacity, a decrease in capacity retention, and a significant increase in Mn dissolution. The hydrothermal reaction time in Comparative Example 2 was also too short, resulting in insufficient reaction between the metal oxide and the sol. Consequently, the coating formed was not dense or uniform, similarly leading to a decrease in the battery's high-rate (5C) discharge capacity, a decrease in capacity retention, and a significant increase in Mn dissolution.

[0179] In Comparative Examples 3 and 4, the aging temperatures were too low and too high, respectively. Both of these temperatures were detrimental to grain growth, resulting in poor structural stability of the positive electrode particles or poor particle size distribution, which in turn led to poor performance of the composite positive electrode material. High-rate discharge capacity and capacity retention were significantly reduced, while Mn dissolution was also significantly increased. Comparative Example 5 had a shorter aging time, while Comparative Example 6 was not aged. This resulted in insufficient grain growth, poor structural stability of the positive electrode particles, and uneven particle size distribution. This increased material resistance, significantly reduced high-rate discharge capacity and capacity retention, and significantly increased Mn dissolution.

[0180] In Comparative Example 7, the step of mixing the matrix material and the graphene dispersion in S1 is not carried out. The graphene has poor dispersion during the reaction. At the same time, directly mixing the three materials together to react will also lead to insufficient reaction. The surface coating of the matrix material is not dense and uniform enough, and the improvement effect of the graphene and metal oxide on it cannot be exerted, resulting in a higher material resistivity, worse high-rate performance of the battery, a low capacity retention rate, and a high amount of Mn dissolution.

[0181] In the matrix material of Comparative Example 8, the value of x is 0, and the chemical formula is LiNi 0.5 Mn 0.5 O2, the lithium-rich phase is missing, and the material only has a ternary phase, which reduces the charge and discharge specific capacity and significantly reduces the battery capacity retention rate. In the matrix material of Comparative Example 9, the X value is 1, and the chemical formula is Li2MnO3. The ternary phase is missing, and only the lithium-rich phase is present. The irreversible capacity of the material increases, resulting in a lower high-rate discharge specific capacity, a lower battery capacity retention rate, worse material stability, and a higher amount of Mn dissolution.

[0182] Further comparing Example 1 with Examples 2 and 3, relative to Example 1, the mass ratios of the graphene dispersion to the matrix material in Examples 2 and 3 are respectively lower and higher. In Example 2, the graphene content is small, the graphene framework is incomplete, and it cannot provide good support for the material. At the same time, it causes the conductivity of the composite positive electrode material to decrease, and the amount of Mn dissolution also increases. In Example 3, the graphene content is high, the matrix material content is low, and the discharge capacity is reduced, thereby causing the high-rate discharge capacity of the battery to decrease and the amount of Mn dissolution to increase.

[0183] Comparing Example 1 with Examples 4 and 5, relative to Example 1, the D50 of the matrix materials in Examples 4 and 5 are respectively smaller and larger. The matrix material in Example 4 is smaller, not easy to disperse, and the coating effect is poor. Therefore, the discharge specific capacity and capacity retention rate of the final composite positive electrode material are reduced, and the Mn dissolution amount is also increased; the matrix material in Example 5 is larger, the lithium ion intercalation and deintercalation speed is relatively slow, and the battery charge and discharge speed is reduced, which will also cause the battery discharge capacity and capacity retention rate to decrease, and the Mn dissolution amount is also increased.

[0184] Comparing Example 1 with Examples 6 and 7, relative to Example 1, the graphene sheet diameter in Example 6 is too large, which is not conducive to its full contact and reaction with the matrix material, resulting in a loose connection between the graphene and the matrix material, leading to an increase in the resistivity of the composite positive electrode material, a decrease in the discharge specific capacity, and a decrease in the capacity retention rate, while the amount of Mn dissolution also increases. In Example 7, the graphene sheet diameter is too small and the number of layers is too large, which is not conducive to the long-term and rapid transmission of electrons, nor is it conducive to the rapid deintercalation of lithium ions, thereby causing an increase in the resistivity of the material, resulting in a decrease in the battery discharge specific capacity and capacity retention rate, while the amount of Mn dissolution also increases.

[0185] Comparing Example 1 with Examples 8, 9, 10, and 11, it can be seen that when the mass fraction of the metal oxide is changed, the discharge specific capacity and other properties will be affected to a certain extent. In particular, as in Example 8 and Example 10, the mass fractions of the metal oxide are 1% and 10%, respectively, which are relatively low and high, and the impact on the high-rate discharge capacity will be greater.

[0186] Comparing Example 1 with Examples 12, 13, and 14, it can be seen that changing the type of metal oxide also affects the performance of the material. It should be noted that different types of metal oxides or compoundings have different optimal feed mass fractions, because different metal oxides or compoundings play different roles. It is necessary to select the appropriate feed amount based on the properties of the different metal oxides, the matrix material, and the graphene to maximize the performance of each material and achieve the goal of jointly optimizing the positive electrode material.

[0187] Comparing Example 1 with Examples 15 and 16, it can be seen that the hydrothermal temperature also has a certain impact on the performance of the material, because the hydrothermal temperature is very important for the reaction process, and thus affects the performance of the reaction product. Therefore, further controlling the hydrothermal temperature is of great significance for further improving the performance of the composite positive electrode material.

[0188] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents, but these modifications or replacements are all within the scope of protection of the present invention.

Claims

1. A method for preparing a lithium-rich manganese-based composite positive electrode material, characterized in that: The steps include: S1. Prepare a graphene dispersion, add a matrix material to the graphene dispersion, and react for 5 to 10 hours at a temperature of 70 to 95°C and a pH of 4 to 6 to obtain a sol; the chemical formula of the matrix material is xLi2MnO3·(1-x)LiNi 0.5 Mn 0.5 O2, the value of x is 0.2 to 0.8; S2. adding the metal oxide to the sol and mixing, and then performing a hydrothermal reaction at 200 to 400 ° C for 14 to 20 hours to obtain a gel; S3. The gel is washed with deionized water, and then aged at -20 to -10°C for 20 to 50 hours, and dried to obtain a composite positive electrode material.

2. The method for preparing a lithium-rich manganese-based composite positive electrode material according to claim 1, wherein: In said S1, when preparing said graphene dispersion, the mass ratio of graphene to water is 0.2 to 5:10; When preparing the sol, the mass ratio of the graphene dispersion to the matrix material is 5-20:80-95.

3. The method for preparing a lithium-rich manganese-based composite positive electrode material according to claim 1, wherein: In the step S1, the D50 of the base material is 2 to 7 μm.

4. The method for preparing a lithium-rich manganese-based composite positive electrode material according to claim 1, wherein: In the step S1, when preparing the graphene dispersion, the graphene sheet used has a diameter of 5 to 10 μm and a number of layers of 6 to 9.

5. The method for preparing a lithium-rich manganese-based composite positive electrode material according to claim 1, wherein: In the step S2, the amount of the metal oxide added is 1-10% of the mass of the base material.

6. The method for preparing a lithium-rich manganese-based composite positive electrode material according to claim 1, wherein: In the S2, the D50 of the metal oxide is 50 to 100 nm.

7. The method for preparing a lithium-rich manganese-based composite positive electrode material according to claim 1, wherein: In S2, the metal oxide includes at least one of vanadium oxide, titanium dioxide, magnesium oxide, aluminum oxide, and chromium oxide.

8. The method for preparing a lithium-rich manganese-based composite positive electrode material according to claim 7, wherein: In S2, the metal oxide is vanadium oxide, or a compound of aluminum oxide and chromium oxide.

9. A composite cathode material, characterized in that: The cathode material is prepared by the method for preparing a lithium-rich manganese-based composite cathode material according to any one of claims 1 to 8.

10. A battery, characterized in that: Comprising the composite positive electrode material as claimed in any one of claims 9.

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