Positive electrode material and preparation method and application thereof

Abstract

The invention relates to the technical field of batteries, in particular to a positive electrode material and a preparation method and application thereof. The positive electrode material comprises a positive electrode material base body, a first coating layer and a second coating layer, the first coating layer is located on the surface of the positive electrode material base body, and the second coating layer is located on the surface of the first coating layer; the first coating layer comprises an ionic conductor layer, and the ionic conductivity of the ionic conductor layer is greater than or equal to 10 <-8 > S / cm; and the second coating layer comprises nitrogen-doped graphene quantum dots. According to the invention, through coordination and cooperation of the first coating layer and the second coating layer, an ion / electron double-conduction composite coating layer is constructed to carry out interface chemical passivation and mechanical protection, so that surface cracks and phase change of a material can be reduced, an exothermic reaction of an electrode and an electrolyte interface can be reduced, and thermal stability is improved; the cycle performance and the rate capability of the positive electrode material can be improved, and the positive electrode material has excellent stability and good fast charging performance at high temperature and high pressure.

Description

Technical Field

[0001] The present invention relates to the field of battery technology, and in particular to a positive electrode material and a preparation method and application thereof. Background Art

[0002] Positive electrode materials play a vital role in new energy batteries and directly affect the battery's energy storage and release capabilities. The problems of existing positive electrode materials include: many side reactions at the interface: the surface of the positive electrode material is prone to side reactions with the electrolyte under high voltage and high temperature, generating Ni 3+ / Ni 4+ Dissolution and thickening of the CEI film lead to accelerated capacity decay and poor cycling stability. Severe gassing at high temperature / high voltage: The lattice oxygen of the material precipitates in a highly delithiated state and reacts with the electrolyte to produce gases such as CO2 and O2, which in turn can cause battery expansion and even thermal runaway. Electron / ion transport imbalance: The intrinsic electronic conductivity of the positive electrode material is poor, making it difficult to achieve both ionic and electronic conductivity through traditional coating. Furthermore, co-coating can easily lead to weak interfacial bonding.

[0003] Therefore, it is urgent to develop a multi-layer synergistic coating strategy to solve the problems of interface stability and charge transfer dynamics of positive electrode materials.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] One object of the present invention is to provide a positive electrode material that, through the synergistic effect of the first coating layer and the second coating layer, precisely controls the chemical composition, interface bonding strength and conductive network structure of the coating layer, so as to simultaneously optimize the chemical stability and conductivity of the positive electrode material and improve the interface impedance and cycle stability.

[0006] Another object of the present invention is to provide a method for preparing a positive electrode material. The method is simple and easy to implement. By combining the various steps, a first and a second coating layer with excellent electrochemical properties are obtained. The two layers are combined to enhance the coating effect and improve the electrochemical properties of the positive electrode material matrix.

[0007] Another object of the present invention is to provide a positive electrode sheet.

[0008] Another object of the present invention is to provide a battery.

[0009] Another object of the present invention is to provide an electrical device.

[0010] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are adopted:

[0011] A positive electrode material comprises a positive electrode material substrate, a first coating layer and a second coating layer, wherein the first coating layer is located on the surface of the positive electrode material substrate, and the second coating layer is located on the surface of the first coating layer; the first coating layer comprises an ion conductor layer, and the ion conductivity of the ion conductor layer is ≥10 -8 S / cm; the second coating layer includes nitrogen-doped graphene quantum dots.

[0012] In some embodiments, the ion conductor layer includes at least one of Li3PO4, LATP, LLZO, LGPS, amorphous chloride, and a copper-based coordination compound.

[0013] In some embodiments, the thickness of the first coating layer is 30-50 nm.

[0014] In some embodiments, the atomic percentage of nitrogen in the second coating layer is C N It is 8% to 12%.

[0015] In some embodiments, the particle size of the nitrogen-doped graphene quantum dots is 1 to 10 nm.

[0016] In some embodiments, the form of nitrogen in the second coating layer includes pyridinic nitrogen, and optionally at least one of pyrrolic nitrogen, graphitic nitrogen, and oxidized nitrogen, and the atomic percentage of pyridinic nitrogen in the total nitrogen element is greater than 65%.

[0017] In some embodiments, the second coating layer has a thickness of 30 to 70 nm.

[0018] In some embodiments, the chemical formula of the positive electrode material matrix is LiNi x Co y Mn (1-x-y) O2, where 0.50≤x≤0.96, 0.005≤y≤0.35, x+y<1.

[0019] In some embodiments, the average particle size of the positive electrode material matrix is 3 to 5 μm.

[0020] In some embodiments, the defect density of the positive electrode material is ≤10 12 cm -2 .

[0021] In some embodiments, the interfacial impedance of the battery corresponding to the positive electrode material is less than 19Ω.

[0022] In some embodiments, the capacity retention rate of the battery corresponding to the positive electrode material after 100 cycles under 1.5C charging and 1C discharging conditions is greater than 90%.

[0023] In some embodiments, the capacity retention rate of the battery corresponding to the positive electrode material after 100 cycles at a cut-off voltage of 4.5V is ≥85%.

[0024] In some embodiments, the capacity retention rate of the positive electrode material corresponding to the battery after 200 cycles at 60° C. is greater than 82%.

[0025] In some embodiments, the gas production of the positive electrode material corresponding to the battery at 60° C. and 4.5V cut-off voltage after 100 cycles is ≤1.35mL / g;

[0026] In some embodiments, the ion mobility of the positive electrode material corresponding to the electrode is 2.3×10 -9 ~3.5×10 -9 .

[0027] The method for preparing the positive electrode material as described above comprises the following steps:

[0028] A dispersion of an ion conductor is sprayed on the surface of a positive electrode material substrate, and a first coating layer is formed after a first sintering to obtain a sintered substrate; a dispersion of nitrogen-doped graphene quantum dots is sprayed on the surface of the sintered substrate, and a second coating layer is formed after a second sintering to obtain a positive electrode material.

[0029] In some embodiments, the ion conductor dispersion includes an ion conductor and an alcohol solvent, and the mass content of the ion conductor is 4% to 7%.

[0030] In some embodiments, the temperature of the first sintering is 280-400° C., and the time of the first sintering is 0.8-2 hours.

[0031] In some embodiments, the ion conductor includes at least one of Li3PO4, LATP, LLZO, LGPS, amorphous chloride, and a copper-based coordination compound.

[0032] In some embodiments, the method for preparing nitrogen-doped graphene quantum dots specifically includes: subjecting a mixed system of a carbon source, a nitrogen source, and water to microwave hydrothermal treatment.

[0033] In some embodiments, the carbon source comprises citric acid, and the nitrogen source comprises urea.

[0034] In some embodiments, the molar ratio of the carbon source to the nitrogen source is 1:(3-5).

[0035] In some embodiments, the microwave power of the microwave hydrothermal treatment is 700-900 W, the temperature of the microwave hydrothermal treatment is 180-220° C., and the time of the microwave hydrothermal treatment is 20-40 min.

[0036] In some embodiments, after the microwave hydrothermal treatment, the process further includes cooling, solid-liquid separation, and drying.

[0037] In some embodiments, the cooling treatment time is 1 to 2 hours, the solid-liquid separation is performed by centrifugal washing, the centrifugal washing speed is 8000 to 12000 rpm, and the centrifugal washing time is 10 to 15 minutes; the drying treatment temperature is 50 to 80°C, and the drying treatment time is 12 to 24 hours.

[0038] In some embodiments, the dispersion of nitrogen-doped graphene quantum dots comprises nitrogen-doped graphene quantum dots and an alcohol solvent, and the mass content of the nitrogen-doped graphene quantum dots is 4% to 8%.

[0039] In some embodiments, the mass ratio of the dispersion of the ion conductor and the dispersion of the nitrogen-doped graphene quantum dots, calculated as ion conductor and nitrogen-doped graphene quantum dots, is (2-4):1;

[0040] In some embodiments, the second sintering temperature is 400-550° C., and the second sintering time is 2-4 hours.

[0041] A positive electrode sheet comprises the positive electrode material or the positive electrode material obtained by the preparation method of the positive electrode material.

[0042] A battery comprises the positive electrode sheet.

[0043] An electrical device comprises the battery.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] (1) The positive electrode material of the present invention is provided with a first coating layer and a second coating layer in sequence on the surface of the positive electrode material matrix. The first coating layer has excellent ionic conductivity, can effectively isolate the positive electrode material matrix from direct contact with the electrolyte, reduce side reactions, promote the uniform transmission of lithium ions at the interface between the positive electrode and the electrolyte, and inhibit the local stress accumulation and microcrack generation on the surface of the positive electrode material matrix caused by uneven lithium ion deintercalation; the second coating layer has excellent electronic conductivity, and the nitrogen-doped graphene quantum dots contained therein form a three-dimensional conductive network on the surface of the first coating layer, which can reduce the charge transfer impedance and buffer the volume change of the positive electrode material matrix during the charging and discharging process; the present invention constructs an ion / electron dual-conducting composite coating layer through the coordinated cooperation of the first coating layer and the second coating layer to perform interface chemical passivation and mechanical protection, which is more conducive to reducing surface cracks and phase changes of the material, reducing exothermic reactions at the interface between the electrode and the electrolyte, improving thermal stability, and improving the cycle performance and rate performance of the positive electrode material. The positive electrode material has excellent stability under high temperature and high pressure and good fast charging performance.

[0046] (2) The preparation method of the positive electrode material of the present invention comprises spraying a dispersion of Li3PO4 on the surface of the positive electrode material substrate, forming a uniform first coating layer after the first sintering to protect the interface of the positive electrode material substrate, and further spraying a dispersion of nitrogen-doped graphene quantum dots on the surface of the first coating layer by spraying. The nitrogen-doped graphene quantum dots can be well combined with the first coating layer, and forming a second coating layer after the second sintering to coordinate with the first coating layer to improve the interface performance of the positive electrode material substrate, improve its conductive performance, and cycle stability. The obtained positive electrode material has excellent high temperature and high pressure performance and excellent fast charging performance.

[0047] (3) The battery of the present invention has excellent cycle stability under high temperature and high pressure and good fast charging capability. DETAILED DESCRIPTION

[0048] The embodiments of the present invention will be described in detail below with reference to the examples, but it will be understood by those skilled in the art that the following examples are merely illustrative of the present invention and should not be construed as limiting the scope of the invention. Where specific conditions are not specified in the examples, the methods were performed according to conventional conditions or the conditions recommended by the manufacturer. Where the manufacturers of the reagents or instruments are not specified, they are all commercially available conventional products.

[0049] According to one aspect of the present invention, the present invention relates to a positive electrode material, comprising a positive electrode material substrate, a first coating layer and a second coating layer, wherein the first coating layer is located on the surface of the positive electrode material substrate, and the second coating layer is located on the surface of the first coating layer; the first coating layer comprises an ion conductor layer, and the ion conductivity of the ion conductor layer is ≥10 -8 S / cm; the second coating layer includes nitrogen-doped graphene quantum dots.

[0050] The positive electrode material of the present invention is provided with a first coating layer and a second coating layer in sequence on the surface of the positive electrode material substrate. The ion conductor layer contained in the first coating layer has excellent ionic conductivity, which can effectively isolate the direct contact between the positive electrode material substrate and the electrolyte, reduce side reactions (such as dissolution of transition metal ions, oxidative decomposition of the electrolyte, etc.), promote the uniform transmission of lithium ions at the interface between the positive electrode and the electrolyte, and inhibit the local stress accumulation and microcrack generation on the surface of the positive electrode material substrate due to uneven lithium ion deintercalation; the second coating layer has excellent electronic conductivity and contains nitrogen-doped graphene quantum dots. The points form a three-dimensional conductive network on the surface of the first coating layer, which can reduce the charge transfer impedance and buffer the volume change of the positive electrode material matrix during the charge and discharge process; the present invention constructs an ion / electron dual-conducting composite coating layer through the coordinated cooperation of the first coating layer and the second coating layer to perform interface chemical passivation and mechanical protection, which is more conducive to reducing the surface cracks and phase changes of the material, and is conducive to reducing the exothermic reaction at the interface between the electrode and the electrolyte, improving thermal stability, and improving the cycle performance and rate performance of the positive electrode material. The positive electrode material has excellent stability under high temperature and high pressure and good fast charging performance. The ionic conductivity of the ion conductor layer of the present invention is greater than or equal to 10 -8 S / cm (e.g. 1.1×10 -8 S / cm, 1.2×10 -8 S / cm, 1.3×10 -8 S / cm, 1.5×10 -8 S / cm, etc.), which can ensure the ion transport performance of the positive electrode material and better achieve interface passivation and structural stabilization to improve the cycle life of the positive electrode material.

[0051] In some embodiments, the ion conductor layer includes Li3PO4, LATP (Li 1.3 Al 0.3 Ti 1.7 (PO4)3)、LLZO(Li7La3Zr2O 12 )、LGPS(Li 10 GeP2S 12 ), an amorphous chloride (such as LiTaCl6), and a copper-based coordination compound (such as copper maleate hydrate). The ion conductor layer of the present invention uses one or more of the above materials in combination, such as a combination of Li3PO4 and LATP, or a combination of LGPS, LiTaCl6, and copper maleate hydrate, which is more conducive to optimizing the ionic conductivity and interfacial stability of the positive electrode material.

[0052] In some embodiments, the thickness of the first coating layer is 30 to 50 nm, for example, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, or any range between the two. The first coating layer of the present invention adopts an appropriate thickness, which is more conducive to ensuring the balance between interface protection and ion transport, and plays a better synergistic role with the second coating layer. If the first coating layer is too thin, the interface protection effect is poor, which is easy to cause side reactions and reduce the cycle stability. If the first coating layer is too thick, it will lead to an increase in lithium ion diffusion resistance and an increase in interface impedance, which will destroy the rate performance and capacity.

[0053] In some embodiments, the atomic percentage of nitrogen in the second coating layer is C N The nitrogen content of the second coating layer is 8% to 12%, for example, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5% or 12%, or any range therebetween. In some embodiments, the nitrogen in the second coating layer is in the form of pyridinic nitrogen, and optionally at least one of pyrrolic nitrogen, graphitic nitrogen and nitrogen oxide, and the atomic percentage of pyridinic nitrogen in the total nitrogen is greater than 65%, for example, 66%, 67%, 68%, 70%, 72%, 75%, 80%, 85%, 90%, or any range therebetween. In nitrogen-doped graphene quantum dots, an appropriate amount of nitrogen atoms replaces the carbon atoms of graphene to form a suitable doping, which can enhance the electron transport capacity; the appropriate content of nitrogen doping forms defects in the graphene lattice, providing more adsorption or reaction sites, improving the interface function of the material, accelerating ion diffusion, inhibiting volume expansion, and improving antioxidant properties; the nitrogen element has an appropriate proportion of pyridinic nitrogen, which preferentially adsorbs on the defect sites on the surface of the single crystal, reducing the interface impedance, which is beneficial to balancing the conductivity and active site density, improving the rate performance and cycle stability of the material, and improving the interface dynamics. If the nitrogen content is too high, high nitrogen doping (especially an increase in the proportion of pyridinic nitrogen) may destroy the conjugated structure of the carbon-based skeleton, causing the N-GQDs layered structure to be distorted or disordered, reducing the mechanical strength of the coating layer, and easily cracking or falling off during the cycle, affecting the bonding strength with the inner layer. Under long-term cycling, high rate or high voltage conditions, the performance may deteriorate due to structural defects and interface side reactions. If the nitrogen content is reduced, the mechanical strength and flexibility of the coating layer will be better, it will not easily crack or fall off during the cycle, the interfacial bonding force with the inner layer and the matrix (such as the positive electrode particles) will be more stable, and the interfacial side reactions will be reduced. However, too low a nitrogen content will lead to limited active sites and kinetic performance, and the electron conduction optimization effect will be limited, which may lead to a slightly lower coulombic efficiency (SEI film formation) in the first week (due to fewer defect sites and slightly poorer uniformity of the SEI film), a reduced density of the electron conduction path in the coating layer, and an increased interface charge transfer impedance (Rct).

[0054] In some embodiments, the nitrogen-doped graphene quantum dots have a particle size of 1 to 10 nm, such as 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, or any range therebetween. The nitrogen-doped graphene quantum dots of the present invention have an appropriate particle size, which facilitates a balance between high specific surface area, stability, and conductivity, and can better coordinate with the first coating layer.

[0055] In some embodiments, the atomic percentage of nitrogen doping is C N and electron mobility μ e Satisfies the relationship: μ e =1000 / [1+0.04·(100·C N -10) 2 ], unit is cm 2 / (V·s). From this formula, it can be seen that the atomic percentage of nitrogen in the present invention is C N is 10%, the electron mobility μ e Can reach a maximum value of 1000cm 2 / (V·s); atomic percentage of nitrogen C N Too large or too small will make the electron mobility μ e Lower, for example, when C N is 8% or 12%, and the electron mobility μ e About 862cm 2 / (V·s). When the atomic percentage of nitrogen C N 8% to 12%, electron mobility μ e 862~1000cm 2 / (V·s). The present invention adjusts the atomic percentage of nitrogen C N Satisfy the appropriate range, thereby ensuring high electron mobility, thereby improving the conductivity of the positive electrode material, increasing the response speed, reducing heat dissipation, and further improving the cycle performance of the battery.

[0056] In some embodiments, the thickness of the second coating layer is 30 to 70 nm, for example, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, or any range therebetween. The second coating layer of the present invention has an appropriate thickness, which is more conducive to ensuring the conductive effect and stability of the second coating layer, and better synergizing with the first coating layer.

[0057] In some embodiments, the chemical formula of the positive electrode material matrix is LiNi x Co y Mn (1-x-y)O2, wherein 0.50≤x≤0.96 (e.g., 0.5, 0.6, 0.7, 0.8, 0.85, 0.9, 0.96, etc.), 0.005≤y≤0.35 (e.g., 0.005, 0.01, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, etc.), and x+y<1.

[0058] In some embodiments, the average particle size of the positive electrode material matrix is 3 to 5 μm, such as 3 μm, 3.5 μm, 4 μm, 4.5 μm or 5 μm, or any range between the two.

[0059] In some embodiments, the defect density of the positive electrode material is ≤10 12 cm-2, for example 10 11 cm-2, 10 10 cm-2, 10 9 The cathode material of the present invention has an appropriate defect density, which has the following advantages: 1) it can reduce the obstruction of the migration path of lithium ions in the lattice and improve the diffusion coefficient; 2) it can reduce the local stress concentration during the charge and discharge process; and 3) it can help inhibit the interface side reactions.

[0060] In some embodiments, the interface impedance of the battery corresponding to the positive electrode material is less than 19Ω, such as 16Ω, 17Ω, 18Ω, 18.5Ω, 18.9Ω, etc. The interface impedance of the positive electrode material of the present invention is relatively low and has good conductivity.

[0061] In some embodiments, the capacity retention rate of the battery corresponding to the positive electrode material after 100 cycles under 1.5C charge and 1C discharge conditions is greater than 90%, for example, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, etc., or any range therebetween. High-rate charge and discharge tests have shown that the positive electrode material of the present invention has excellent fast charging capability and structural durability.

[0062] In some embodiments, the capacity retention rate of the positive electrode material corresponding to the battery after 100 cycles at a cutoff voltage of 4.5V is ≥85%, for example, 85%, 88%, 90%, 95%, etc. The positive electrode material of the present invention has excellent stability under high voltage and electrolyte oxidation resistance.

[0063] In some embodiments, the capacity retention rate of the positive electrode material corresponding to the battery after 200 cycles at 60°C is greater than 82%, such as 83%, 85%, 88%, 95%, etc., or a range therebetween. The positive electrode material of the present invention has excellent high-temperature performance.

[0064] In some embodiments, the gas production of a battery corresponding to the cathode material after 100 cycles at 60°C and a cutoff voltage of 4.5V is ≤1.35 mL / g, for example, 1 mL / g, 1.1 mL / g, 1.2 mL / g, 1.3 mL / g, 1.35 mL / g, etc. Batteries obtained using the cathode material of the present invention have low gas production under high temperature and high pressure.

[0065] In some embodiments, the ion mobility of the positive electrode material corresponding to the electrode is 2.3×10 -9 ~3.5×10 -9 , for example 2.3×10 -9 , 2.5×10 -9 , 3×10 -9 , 3.5×10 -9 The positive electrode material of the present invention has high ion mobility corresponding to the electrode sheet.

[0066] In some embodiments, the bonding strength of the first coating layer and the second coating layer is expressed by the XRD half-peak width: the XRD half-peak width is reduced by 30% (relative to the form of a blend of Li3PO4 and N-GQDs). The positive electrode material of the present invention allows the inner layer (ion conductor layer) to first form a stable interface with the matrix, and the outer layer N-GQDs is then tightly bonded to the ion conductor layer through chemical bonding (such as POC, N-Li bond) or physical adsorption to form a "matrix-ion conductor layer-N-GQDs" gradient interface, forming an ordered double-layer structure, which can improve interface compatibility and significantly reduce interface defects, thereby making the interface bond tighter and the structure more ordered (half-peak width is reduced). During co-blending and coating, due to the uneven mixing of the two materials at the interface, the following may be formed: an amorphous phase or a defect-rich region (resulting in a widened half-peak width); an interface lattice mismatch or stress (aggravating structural disorder).

[0067] In some embodiments, the cathode materials of the present invention can achieve up to three times the electronic conductivity of the cathode material matrix, significantly increase ion migration rate, and significantly reduce gas production at high temperature / high voltage. The cathode materials of the present invention are suitable for solid-state batteries and suppress lithium dendrites (SEM analysis shows no punctures).

[0068] According to another aspect of the present invention, the present invention also relates to a method for preparing the positive electrode material as described above, comprising the following steps:

[0069] A dispersion of an ion conductor is sprayed on the surface of a positive electrode material substrate, and a first coating layer is formed after a first sintering to obtain a sintered substrate; a dispersion of nitrogen-doped graphene quantum dots is sprayed on the surface of the sintered substrate, and a second coating layer is formed after a second sintering to obtain a positive electrode material.

[0070] The preparation method of the positive electrode material of the present invention comprises the following steps: spraying a dispersion of an ion conductor on the surface of a positive electrode material substrate, forming a uniform and dense first coating layer after a first sintering to provide interface protection for the positive electrode material substrate, and further spraying a dispersion of nitrogen-doped graphene quantum dots on the surface of the first coating layer by spraying. The nitrogen-doped graphene quantum dots can be well combined with the first coating layer, and forming a second coating layer after a second sintering to coordinate with the first coating layer to improve the interface performance of the positive electrode material substrate, enhance its electrical conductivity, and cycle stability. The obtained positive electrode material has excellent high-temperature and high-voltage performance, and excellent fast-charging performance.

[0071] In some embodiments, the ion conductor dispersion includes an ion conductor and an alcohol solvent, and the mass content of the ion conductor is 4% to 7%, such as 4%, 5%, 6% or 7%, or any range therebetween.

[0072] In some embodiments, the ion conductor includes at least one of Li3PO4, LATP, LLZO, LGPS, an amorphous chloride, and a copper-based coordination compound. Examples include a combination of Li3PO4 and LATP, or a combination of LGPS, LiTaCl6, and copper maleate hydrate. The use of these ion conductors in the present invention facilitates optimization of the ionic conductivity and interfacial stability of the positive electrode material.

[0073] In some embodiments, the temperature of the first sintering is 280-400°C, for example, 280°C, 290°C, 300°C, 320°C, 350°C, 400°C, etc., or a range between any two thereof. The time of the first sintering is 0.8-2h, for example, 0.8h, 1h, 1.5h or 2h, etc., or a range between any two thereof. The sintering atmosphere of the first sintering is a protective gas, such as nitrogen. The present invention adopts a suitable first sintering temperature and time to ensure that the first coating layer forms a continuous coating layer, avoids cracking (TEM verifies that the interface is seamless), and has better ionic conductivity and cycle stability.

[0074] In some embodiments, the method for preparing nitrogen-doped graphene quantum dots specifically comprises: subjecting a mixed system of a carbon source, a nitrogen source and water to microwave hydrothermal treatment. The carbon source comprises citric acid, and the nitrogen source comprises urea. The microwave power of the microwave hydrothermal treatment is 700 to 900 W, such as 700 W, 750 W, 800 W or 900 W, etc., the temperature is 180 to 220 ° C, such as 180 ° C, 190 ° C, 200 ° C, 220 ° C, etc., and the reaction time is 20 to 40 min, such as 20 min, 25 min, 30 min, 35 min or 40 min, etc. The present invention can obtain nitrogen-doped graphene quantum dots with suitable particle size, excellent conductive properties and good stability through the above-mentioned suitable microwave hydrothermal treatment conditions.

[0075] In some embodiments, after the microwave hydrothermal treatment, the process further includes: cooling treatment, solid-liquid separation and drying treatment. In some embodiments, the cooling treatment time is 1 to 2 hours. In some embodiments, solid-liquid separation is performed by centrifugal washing, the rotation speed of the centrifugal washing is 8000 to 12000 rpm (for example, 8000 rpm, 900 rpm, 10000 rpm or 12000 rpm, etc.), and the centrifugal washing time is 10 to 15 minutes (for example, 10 minutes, 12 minutes or 15 minutes, etc.); the temperature of the drying treatment is 50 to 80°C (for example, 50°C, 60°C, 70°C, 80°C, etc.), and the drying treatment time is 12 to 24 hours (12 hours, 15 hours, 20 hours or 24 hours).

[0076] In some embodiments, the dispersion of nitrogen-doped graphene quantum dots includes nitrogen-doped graphene quantum dots and an alcohol solvent, and the mass content of the nitrogen-doped graphene quantum dots is 4% to 8% (e.g., 4%, 5%, 6%, 7% or 8%, etc.).

[0077] In some embodiments, the method for preparing nitrogen-doped graphene quantum dots comprises the following steps:

[0078] (1) Accurately weigh a certain amount of citric acid and urea in a molar ratio of 1:(3-5) and place them in a reactor lined with polytetrafluoroethylene. Add an appropriate amount of deionized water and stir evenly to form a uniform mixed solution. The amount of deionized water used should be sufficient to completely dissolve the citric acid and urea, generally 1 / 3-1 / 2 of the reactor volume. (2) Microwave hydrothermal treatment: Seal the reactor and place it in a microwave hydrothermal synthesizer. Set the microwave power to 700-900W and the reaction time to 20-40min. Under these conditions, the solution heats up rapidly under the action of microwaves and undergoes a hydrothermal reaction to generate a precursor of nitrogen-doped graphene quantum dots. (3) Cooling and collection: After the reaction is completed, turn off the microwave power and let the reactor cool naturally to room temperature in the synthesizer. The cooling time is 1-2h. After cooling, open the reactor and transfer the reaction product to a centrifuge tube. (4) Washing and purification: Add an appropriate amount of deionized water or ethanol to the centrifuge tube and perform centrifugal washing. The centrifugal speed is generally set to 8000-12000 rpm, and the centrifugation time is 10-15 minutes. Through centrifugation, the nitrogen-doped graphene quantum dots are precipitated at the bottom of the centrifuge tube, while the supernatant contains impurities such as unreacted raw materials and by-products. The supernatant is poured out and the washing steps are repeated 3-5 times until no impurity ions are detected in the supernatant (which can be detected by a conductivity meter or other detection methods). (5) Drying: The washed product is placed in a vacuum drying oven and dried at a temperature of 50-80°C for 12-24 hours to remove moisture and residual washing solvent to obtain a powder sample of nitrogen-doped graphene quantum dots.

[0079] In some embodiments, the mass ratio of the dispersion of the ion conductor and the dispersion of the nitrogen-doped graphene quantum dots, calculated as ion conductor and nitrogen-doped graphene quantum dots, is (2-4):1, for example, 2:1, 2.5:1, 3:1, 3.5:1, or 4:1. The ion conductor and nitrogen-doped graphene quantum dots of the present invention are preferably in a suitable mass ratio to obtain a first coating layer and a second coating layer having suitable thicknesses, thereby ensuring a balance between the ion migration channel and the electron path. The two can better play a synergistic role to improve the coating effect, enhance the cycle stability and rate performance of the positive electrode material under high temperature and high pressure, and improve its fast charging capability. If the mass ratio of the ion conductor and the nitrogen-doped graphene quantum dots is too low (the ion conductor decreases and the N-GQDs increase), the electronic conductivity is enhanced, and the ion conductor layer becomes relatively thinner (if the inner layer is less than 30nm), which may lead to discontinuity of the ion conduction layer, or although the thickness is within the range, the mass ratio decreases, the ion migration channel decreases, and the interface impedance may increase; if the mass ratio of the ion conductor and the nitrogen-doped graphene quantum dots is too high (the ion conductor increases and the N-GQDs decreases), the second coating layer is too thin (<50nm), resulting in an incomplete conductive network and a decrease in electron transmission efficiency, which is especially obvious during high-rate charge and discharge.

[0080] In some embodiments, the second sintering temperature is 400-550°C, for example, 400°C, 450°C, 480°C, 500°C, 550°C, etc. The second sintering time is 2-4 hours, for example, 2 hours, 2.5 hours, 3 hours, 3.5 hours, or 4 hours. The second sintering atmosphere includes a protective gas, such as nitrogen or an inert gas. The present invention adopts an appropriate combination of the second sintering temperature and time to ensure the electrochemical performance of the second coating layer and improve the coating effect.

[0081] The preparation method of the positive electrode material matrix specifically comprises: x Co y Mn (1-x-y) (OH)2 and LiOH·H2O are sintered in an oxygen atmosphere at 750-850°C for 8-15h in an appropriate molar ratio to obtain a positive electrode material matrix.

[0082] According to another aspect of the present invention, the present invention also relates to a positive electrode sheet, comprising the positive electrode material or the positive electrode material obtained by the method for preparing the positive electrode material.

[0083] The positive electrode sheet of the present invention comprises a positive electrode current collector and a positive electrode material layer disposed on at least one side surface of the positive electrode current collector, wherein the positive electrode material layer comprises the positive electrode material.

[0084] According to another aspect of the present invention, the present invention also relates to a battery, comprising the positive electrode sheet.

[0085] The battery of the present invention comprises the above-mentioned positive electrode sheet, negative electrode sheet, separator and electrolyte.

[0086] The battery of the present invention has excellent cycle stability under high temperature and high pressure and good fast charging capability.

[0087] According to another aspect of the present invention, the present invention also relates to an electric device comprising the battery. The electric device of the present invention includes a mobile phone, a laptop computer, an electric car, an electric tool, etc.

[0088] The following is further explained with reference to specific embodiments and comparative examples.

[0089] Example 1

[0090] A method for preparing a positive electrode material comprises the following steps:

[0091] (a) Preparation of positive electrode material matrix: precursor Ni 0.8 Co 0.1 Mn 0.1 (OH)2 and LiOH·H2O (the molar ratio of Li to precursor is 1.05:1) are sintered at 800°C for 12 hours in an oxygen atmosphere to obtain a positive electrode material matrix with an average particle size of 4 μm.

[0092] (b) Preparation of a first coating layer: Disperse the ion conductor Li3PO4 in ethanol (concentration 5%) to obtain an ion conductor solution, and then spray it onto the positive electrode material substrate of step (a) by spraying. Then, perform a first sintering at a temperature of 300°C and a time of 1 hour in a nitrogen atmosphere to form a continuous ion conductor layer with a thickness of 40 nm, thereby obtaining a sintered substrate having a first coating layer.

[0093] (c) Preparation of nitrogen-doped graphene quantum dots, including: (1) Accurately weighing a certain amount of citric acid and urea, controlling the nitrogen doping amount to 10%, placing them in a reactor lined with polytetrafluoroethylene, adding an appropriate amount of deionized water, stirring evenly, and forming a uniform mixed solution. The amount of deionized water used is appropriate to be able to completely dissolve the citric acid and urea. (2) Microwave hydrothermal treatment: Seal the reactor and place it in a microwave hydrothermal synthesizer. Set the microwave power to 800W, the reaction time to 30min, and the temperature to 200°C. Under these conditions, the solution rapidly heats up under the action of microwaves and undergoes a hydrothermal reaction to generate a precursor of nitrogen-doped graphene quantum dots. (3) Cooling and collection: After the reaction is completed, turn off the microwave power and let the reactor cool naturally to room temperature in the synthesizer. The cooling time is 1.5h. After cooling, open the reactor and transfer the reaction product to a centrifuge tube. (4) Washing and purification: Add an appropriate amount of deionized water to the centrifuge tube and perform centrifugal washing at a centrifugal speed of 10,000 rpm for 12 minutes. Through centrifugation, the nitrogen-doped graphene quantum dots are precipitated at the bottom of the centrifuge tube, while the supernatant contains impurities such as unreacted raw materials and by-products. Pour out the supernatant and repeat the washing steps 4 times until no impurity ions are detected in the supernatant (which can be detected by a conductivity meter or other detection methods). (5) Drying: Place the washed product in a vacuum drying oven and dry it at 70°C for 15 hours to remove moisture and residual washing solvent to obtain nitrogen-doped graphene quantum dots with an average size of 5 nm.

[0094] (d) Nitrogen-doped graphene quantum dots were mixed with ethanol (5% by weight) to obtain a nitrogen-doped graphene quantum dot (N-GQDs) dispersion. The N-GQDs dispersion was sprayed onto the surface of the sintered substrate, with the mass ratio of ionic conductor to nitrogen-doped graphene quantum dots being controlled to be 3:1. A second sintering process was then performed at 450°C for 3 hours in a nitrogen atmosphere to form a second coating layer having a three-dimensional conductive network. The total coating thickness of the first and second coating layers was 85 nm, thereby obtaining a positive electrode material.

[0095] Example 2

[0096] A method for preparing a positive electrode material, which differs from Example 1 in that:

[0097] The temperature of the first sintering was 350°C.

[0098] The thickness of the total coating layer was adjusted to 100 nm, the thickness of the first coating layer was 50 nm, and the thickness of the second coating layer was 50 nm.

[0099] Example 3

[0100] A method for preparing a positive electrode material, which differs from Example 1 in that:

[0101] The mass ratio of ion conductor and nitrogen-doped graphene quantum dots is 2:1.

[0102] The thickness of the first cladding layer was adjusted to 40 nm, and the thickness of the second cladding layer was adjusted to 60 nm.

[0103] Example 4

[0104] A method for preparing a positive electrode material, which differs from Example 1 in that:

[0105] The mass ratio of ion conductor and nitrogen-doped graphene quantum dots is 4:1.

[0106] The thickness of the first cladding layer was adjusted to 50 nm, and the thickness of the second cladding layer was adjusted to 37.5 nm.

[0107] Example 5

[0108] A method for preparing a positive electrode material, which differs from Example 1 in that:

[0109] The nitrogen doping amount is controlled to be 12%.

[0110] Example 6

[0111] A method for preparing a positive electrode material, which differs from Example 1 in that:

[0112] The nitrogen doping amount is controlled to be 8%.

[0113] Example 7

[0114] A method for preparing a positive electrode material comprises the following steps:

[0115] (1) Preparation of positive electrode material matrix: precursor Ni 0.8 Co 0.1 Mn 0.1 (OH)2 and LiOH·H2O (the molar ratio of Li to precursor is 1.05) are sintered at 800°C for 12 hours in an oxygen atmosphere to obtain a positive electrode material matrix with an average particle size of 4 μm.

[0116] (2) Preparation of the first coating layer: The ion conductor Li3PO4 is dispersed in ethanol (concentration 5wt%) to obtain an ion conductor solution, which is then sprayed onto the positive electrode material substrate of step (1) by spraying. The first sintering is then performed at a temperature of 280°C and a time of 2 hours in a nitrogen atmosphere to form a continuous ion conductor layer with a thickness of 45nm, thereby obtaining a sintered substrate having a first coating layer.

[0117] (3) Preparation of nitrogen-doped graphene quantum dots. The difference from Example 1 is that the microwave power is 900 W, the reaction time is 20 min, and the temperature is 220 ° C. Nitrogen-doped graphene quantum dots (N-GQDs) are obtained, and the average size of the quantum dots is 8 nm.

[0118] (4) Nitrogen-doped graphene quantum dots were mixed with ethanol (5% by mass) to obtain a nitrogen-doped graphene quantum dot (N-GQDs) dispersion. The N-GQDs dispersion was sprayed onto the surface of the sintered substrate, and the mass ratio of the ion conductor to the nitrogen-doped graphene quantum dots was controlled to be 3:1. A second sintering was then performed at a temperature of 550°C for 2 hours in a nitrogen atmosphere to form a second coating layer of a three-dimensional conductive network. The total coating thickness of the first and second coating layers was 90 nm, thereby obtaining a positive electrode material.

[0119] Example 8

[0120] A method for preparing a positive electrode material comprises the following steps:

[0121] (1) Preparation of positive electrode material matrix: precursor Ni 0.8 Co 0.1 Mn 0.1 (OH)2 and LiOH·H2O (the molar ratio of Li to precursor is 1.05) are sintered at 800°C for 12 hours in an oxygen atmosphere to obtain a positive electrode material matrix with an average particle size of 4 μm.

[0122] (2) Preparation of the first coating layer: The ion conductor Li3PO4 is dispersed in ethanol (concentration 5wt%) to obtain an ion conductor solution, which is then sprayed onto the positive electrode material substrate of step (1) by spraying. The first sintering is then performed at a temperature of 400°C and a time of 0.8h in a nitrogen atmosphere to form a continuous ion conductor layer with a thickness of 40nm, thereby obtaining a sintered substrate having a first coating layer.

[0123] (3) Preparation of nitrogen-doped graphene quantum dots. The difference from Example 1 is that the microwave power is 700 W, the reaction time is 40 min, and the temperature is 180 ° C. Nitrogen-doped graphene quantum dots (N-GQDs) are obtained, and the average size of the quantum dots is 6 nm.

[0124] (3) Nitrogen-doped graphene quantum dots were mixed with ethanol (5% by mass) to obtain a nitrogen-doped graphene quantum dot (N-GQDs) dispersion. The N-GQDs dispersion was sprayed onto the surface of the sintered substrate, with the mass ratio of the ion conductor to the nitrogen-doped graphene quantum dots being controlled to be 3:1. A second sintering process was then performed at a temperature of 400°C for 4 hours in a nitrogen atmosphere to form a second coating layer having a three-dimensional conductive network. The total coating thickness of the first and second coating layers was 95 nm, thereby obtaining a positive electrode material.

[0125] Example 9

[0126] A method for preparing a positive electrode material, which differs from Example 1 in that:

[0127] Replace Li3PO4 in step (b) with LLZO.

[0128] Example 10

[0129] A method for preparing a positive electrode material, which differs from Example 1 in that:

[0130] In step (b), the ion conductors are Li3PO4 and LATP, and the mass ratio of Li3PO4 to LATP is 2:1.

[0131] Example 11

[0132] A method for preparing a positive electrode material, which differs from Example 1 in that:

[0133] In step (b), the ion conductors are Li3PO4, LGPS and LiTaCl6, and the mass ratio of Li3PO4, LGPS and LiTaCl6 is 2:0.5:0.5.

[0134] Comparative Example 1

[0135] A method for preparing a positive electrode material comprises the following steps:

[0136] According to steps (1) and (2) of Example 1, a sintered substrate was obtained.

[0137] The GQDs dispersion was sprayed onto the surface of the sintered substrate, with the mass ratio of Li3PO4:GQDs controlled at 3:1, and then a second sintering was performed at a temperature of 400°C for 4 hours in a nitrogen atmosphere to obtain a second coating layer. The total coating thickness of the first and second coating layers was 85 nm, and a positive electrode material was obtained.

[0138] Comparative Example 2

[0139] A method for preparing a positive electrode material comprises the following steps:

[0140] According to step (1) of Example 1, a positive electrode material matrix was obtained.

[0141] N-GQDs were prepared according to the method of Example 1.

[0142] The positive electrode material matrix, Li3PO4 and N-GQDs were mixed and sintered. The amount of each raw material was the same as that in Example 1. The sintering temperature was 450°C, the time was 3 hours, and the nitrogen atmosphere was used to obtain the positive electrode material.

[0143] Comparative Example 3

[0144] A positive electrode material adopts the positive electrode material matrix of embodiment 1.

[0145] Experimental example

[0146] 1. Performance test of positive electrode materials

[0147] The positive electrode materials in each embodiment and comparative example were tested for defect density and pyridinic nitrogen ratio.

[0148] Defect density test: The defect level of graphene quantum dots (GQDs) is analyzed by Raman spectroscopy, and the ID / IG ratio is calculated and converted into defect density.

[0149] Steps: 1) Use a laser confocal Raman spectrometer (excitation wavelength 532nm, power 1mW), scanning range 1000~3000cm -1 ; 2) Measure the Raman spectrum of the coating surface and extract the D peak (1350cm -1 , defect-related) and G peak (1580 cm -1 , graphitization related) intensity ratio ID / IG; 3) According to the formula Nd=k×(ID / IG) 2 (k is the calibration constant, taken as 5.0×1013cm -2 )Calculate the defect density.

[0150] The performance test results of the positive electrode materials are shown in Table 1.

[0151] Table 1 Performance test results of positive electrode materials

[0152]

[0153]

[0154] 2. Battery performance test

[0155] The batteries prepared from the positive electrode materials of the embodiments and comparative examples respectively include the following steps:

[0156] (A) Preparation of positive electrode

[0157] Formula: active material (positive electrode material in the example): conductive agent (Super P): binder (PVDF) = 85:10:5 (mass ratio).

[0158] Steps: 1) Add active material, Super P, and PVDF to N-methylpyrrolidone (NMP) and stir for 12 h to form a uniform slurry; 2) Use a coater to coat the slurry on aluminum foil (thickness 15 μm) with a coating thickness of 80 μm (wet film); 3) Vacuum dry at 80 ° C for 12 h and compact with a roller press to a compaction density of 3.0 g / cm 3 , cut into discs with a diameter of 12 mm.

[0159] (B) Preparation of negative electrode sheet

[0160] Formula: artificial graphite: conductive agent (Super P): binder (SBR): thickener (CMC) = 95:2:2:1 (mass ratio).

[0161] Steps: 1) Add graphite, Super P, SBR, and CMC to deionized water and stir for 8 hours to form a uniform slurry; 2) Apply the slurry to a copper foil (thickness 10 μm) with a coating thickness of 100 μm (wet film); 3) Dry under vacuum at 90°C for 10 hours and roll to a compacted density of 1.5 g / cm 3 , cut into discs with a diameter of 14 mm.

[0162] (C) Button battery assembly

[0163] Diaphragm: PP / PE composite membrane (thickness 25 μm, porosity 45%, pore size 0.1 μm).

[0164] Electrolyte: solute is 1.2M LiPF6; solvent: ethylene carbonate (EC): diethyl carbonate (DEC): ethyl methyl carbonate (EMC) = 3:3:4 (volume ratio); additive: 1% vinylene carbonate (VC, volume ratio).

[0165] In an argon-filled glove box (H2O, O2 < 1 ppm), CR2032 batteries were assembled in the following order:

[0166] Positive electrode → diaphragm → negative electrode → gasket → spring → stainless steel shell, inject 50μL of electrolyte, seal and let it stand for 24 hours.

[0167] The battery performance test is as follows:

[0168] 1. Interface impedance test

[0169] Electrochemical impedance spectroscopy (EIS) was used to measure the interfacial charge transfer resistance of the battery.

[0170] 1) Incubate the assembled button cell (CR2032) at room temperature for 12 hours. 2) Use an electrochemical workstation (e.g., Solartron 1260) to scan the frequency range from 10 mHz to 100 kHz with an amplitude of 5 mV. 3) Fit an equivalent circuit (Randles model, where R is the interfacial impedance and Warburg impedance fits the diffusion process) and extract the charge transfer resistance, Rct, as the interfacial impedance.

[0171] 2. High temperature / high voltage gas production (mL / g)

[0172] The battery was cycled for 100 cycles at 60°C and a cutoff voltage of 4.5V and placed in a sealed glass container. The gas volume in the container was measured using a gas chromatograph (TCD detector), and the gas production was calculated after deducting the blank value.

[0173] 3. Ion migration rate (cm 2 / s)

[0174] The lithium ion conductivity (σ) of the positive electrode was measured by the AC impedance method, and the formula is σ=L / (R×S), where L is the thickness, R is the resistance, and S is the area. The lithium ion transference number (tLi) was measured by the constant current polarization method. + ), combined with σ, the ion migration rate v = tLi + × σ / (F × c), where F is the Faraday constant and c is the lithium ion concentration.

[0175] 4. Capacity retention test

[0176] (1) Capacity retention after 100 cycles under 1.5C charge and 1C discharge conditions.

[0177] (2) Retention rate after 200 cycles at 60°C.

[0178] (3) Capacity retention after 100 cycles at a cut-off voltage of 4.5 V.

[0179] The test results of battery performance are shown in Table 2.

[0180] Table 2 Battery performance test results

[0181]

[0182]

[0183] As can be seen from Tables 1 and 2, the methods of each embodiment of the present invention obtain a positive electrode material having a first coating layer and a second coating layer, and construct an ion / electron dual-conducting composite coating layer to perform interface chemical passivation and mechanical protection, which is beneficial to reducing surface cracks and phase changes of the material, improving thermal stability, and improving the cycle performance and rate performance of the positive electrode material. The positive electrode material has excellent stability under high temperature and high pressure and good fast charging performance.

[0184] Comparative Example 1 was not nitrogen-doped, and the interfacial impedance of the obtained positive electrode material was relatively high, the gas production at high temperature / high voltage was high, the ion mobility was low, the capacity retention rate under high temperature and high pressure was reduced, and the fast charging capability was weakened.

[0185] In Comparative Example 2, the raw materials were blended and coated, and cracks appeared in the coating layer, resulting in increased interfacial impedance of the positive electrode material, increased gas production at high temperature / high voltage, low ion mobility, reduced capacity retention under high temperature and high pressure, and weakened fast charging capability.

[0186] The positive electrode material matrix of Comparative Example 3 has a large defect density, large interface impedance, increased gas production at high temperature / high voltage, low ion mobility, low capacity retention rate under high temperature and high pressure, and weak fast charging capability.

[0187] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A positive electrode material, characterized in that The positive electrode material substrate comprises a first coating layer and a second coating layer, wherein the first coating layer is located on the surface of the positive electrode material substrate, and the second coating layer is located on the surface of the first coating layer; The first coating layer includes an ion conductor layer, the ion conductivity of the ion conductor layer is ≥10 -8 S / cm; The second cladding layer includes nitrogen-doped graphene quantum dots.

2. The positive electrode material according to claim 1, characterized in that Contains at least one of the following features (1) to (6): (1) The ion conductor layer includes at least one of Li3PO4, LATP, LLZO, LGPS, amorphous chloride, and a copper-based coordination compound; (2) The thickness of the first coating layer is 30 to 50 nm; (3) In the second coating layer, the atomic percentage of nitrogen is C N 8% to 12%; (4) The particle size of the nitrogen-doped graphene quantum dots is 1 to 10 nm; (5) In the second coating layer, the form of nitrogen element includes pyridinic nitrogen, and optionally at least one of pyrrolic nitrogen, graphitic nitrogen and oxidized nitrogen, and the atomic percentage of pyridinic nitrogen in the total nitrogen element is greater than 65%; (6) The thickness of the second coating layer is 30 to 70 nm.

3. The positive electrode material according to claim 1 or 2, characterized in that Contains at least one of the following features (1) to (2): (1) The chemical formula of the positive electrode material matrix is LiNi x Co y Mn (1-x-y) O2, where 0.50≤x≤0.96, 0.005≤y≤0.35, x+y<1; (2) The average particle size of the positive electrode material matrix is 3 to 5 μm.

4. The positive electrode material according to claim 1, characterized in that Contains at least one of the following features (1) to (7): (1) The defect density of the positive electrode material is ≤10 12 cm -2 ; (2) The interfacial impedance of the battery corresponding to the positive electrode material is less than 19Ω; (3) The capacity retention rate of the battery corresponding to the positive electrode material after 100 cycles under 1.5C charging and 1C discharging conditions is greater than 90%; (4) The capacity retention rate of the battery corresponding to the positive electrode material after 100 cycles at a cut-off voltage of 4.5V is ≥85%; (5) The capacity retention rate of the battery corresponding to the positive electrode material after 200 cycles at 60°C is greater than 82%; (6) The gas production of the battery corresponding to the positive electrode material at 60°C and 4.5V cut-off voltage after 100 cycles is ≤1.35mL / g; (7) The ion mobility of the positive electrode material corresponding to the electrode is 2.3×10 -9 ~3.5×10 -9 .

5. The method for preparing a positive electrode material according to any one of claims 1 to 4, characterized in that: The following steps are involved: Spraying a dispersion of an ion conductor on the surface of the positive electrode material substrate, forming a first coating layer after a first sintering to obtain a sintered substrate; The surface of the sintered substrate is sprayed with a dispersion of nitrogen-doped graphene quantum dots, and a second coating layer is formed after a second sintering to obtain a positive electrode material.

6. The method for preparing the positive electrode material according to claim 5, wherein: Contains at least one of the following features (1) to (3): (1) The ion conductor dispersion comprises an ion conductor and an alcohol solvent, wherein the mass content of the ion conductor is 4% to 7%; (2) The temperature of the first sintering is 280-400° C., and the time of the first sintering is 0.8-2 hours; (3) The ion conductor includes at least one of Li3PO4, LATP, LLZO, LGPS, amorphous chloride, and copper-based coordination compounds.

7. The method for preparing the positive electrode material according to claim 5, wherein: Contains at least one of the following features (1) to (4): (1) The preparation method of the nitrogen-doped graphene quantum dots specifically comprises: subjecting a mixed system of a carbon source, a nitrogen source and water to microwave hydrothermal treatment; Preferably, the carbon source comprises citric acid, and the nitrogen source comprises urea; Preferably, the molar ratio of the carbon source to the nitrogen source is 1:(3-5); Preferably, the microwave power of the microwave hydrothermal treatment is 700-900 W, the temperature of the microwave hydrothermal treatment is 180-220° C., and the time of the microwave hydrothermal treatment is 20-40 min; Preferably, after the microwave hydrothermal treatment, the process further comprises: cooling treatment, solid-liquid separation and drying treatment; Preferably, the cooling treatment time is 1 to 2 hours; the solid-liquid separation adopts centrifugal washing, the speed of centrifugal washing is 8000 to 12000 rpm, and the centrifugal washing time is 10 to 15 minutes; the temperature of the drying treatment is 50 to 80° C., and the drying treatment time is 12 to 24 hours; (2) The dispersion of nitrogen-doped graphene quantum dots comprises nitrogen-doped graphene quantum dots and an alcohol solvent, wherein the mass content of the nitrogen-doped graphene quantum dots is 4% to 8%; (3) the mass ratio of the dispersion of the ion conductor and the dispersion of the nitrogen-doped graphene quantum dots, calculated as Li3PO4 and nitrogen-doped graphene quantum dots, is (2-4):1; (4) The temperature of the second sintering is 400-550°C, and the time of the second sintering is 2-4 hours.

8. A positive electrode sheet, characterized in that: The invention relates to a positive electrode material comprising the positive electrode material according to any one of claims 1 to 4 or a positive electrode material obtained by the preparation method of the positive electrode material according to any one of claims 5 to 7.

9. A battery, characterized in that: Including the positive electrode sheet according to claim 8.

10. An electrical device, characterized in that: A battery comprising the battery of claim 9.

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