Composite positive electrode material and preparation method thereof, positive plate and battery

Abstract

The invention relates to the technical field of batteries, in particular to a composite positive electrode material, a preparation method thereof, a positive plate and a battery. The composite positive electrode material has a core-shell structure and comprises an inner core and an outer shell, wherein the inner core comprises a ternary material, the shell covers at least part of the inner core, and the shell comprises a bamboo-based carbon material; the bamboo-based carbon material contains aromatic groups. The composite positive electrode material provided by the invention has high electronic conductivity, and can promote the diffusion rate and structural stability of active ions in the battery, so that the performance of the composite positive electrode material in the battery is improved, for example, the cycle performance of the battery is improved.

Description

Technical Field

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

[0002] As an important cathode material for lithium-ion batteries, ternary materials (such as high-nickel ternary cathode materials) have advantages such as high specific capacity, good cycle stability and relatively low cost, and have broad application prospects in the field of modern energy storage. However, current ternary materials still face some problems in practical applications, such as low electronic conductivity, limited lithium ion diffusion rate, and changes in lattice parameters during charge and discharge cycles, resulting in changes in volume and poor structural stability. These problems limit their application in high-power, long-cycle-life lithium-ion batteries.

[0003] In order to improve the performance of ternary materials (such as high-nickel ternary positive electrode materials), a variety of modification methods have been adopted, such as element doping, surface coating, etc. However, these methods still have some limitations in practical applications. For example, element doping may change the crystal structure of the material, resulting in unstable performance; among them, carbon coating technology has received widespread attention as an effective surface modification method. By coating a layer of carbon material on the surface of the ternary material, the conductivity of the material can be improved, the charge transfer efficiency can be improved, the structural stability of the material can be enhanced, and the occurrence of side reactions can be inhibited. However, traditional carbon coating materials mostly use amorphous carbon or graphitized carbon. Their structure and performance are relatively simple, and they have certain limitations in improving the comprehensive performance of ternary materials.

[0004] Therefore, it is of great practical significance to develop a simple, efficient and low-cost method for modifying ternary positive electrode materials and the modified positive electrode materials. Summary of the Invention

[0005] In view of this, the present invention aims to at least partially address one of the technical problems in the related art. To this end, the present invention provides a composite positive electrode material, a preparation method thereof, a positive electrode sheet, and a battery. This composite positive electrode material exhibits high electronic conductivity, ion diffusion rate, and structural stability, and can enhance the performance of batteries, such as lithium-ion batteries, by, for example, improving the battery's cycling stability.

[0006] In order to solve the above-mentioned technical problems, the present invention is achieved as follows:

[0007] According to the first aspect of the present invention, an embodiment of the present invention provides a composite positive electrode material. The composite positive electrode material has a core-shell structure, including a core and an outer shell; wherein the core contains a ternary material, the outer shell covers at least a portion of the core, and the outer shell includes a bamboo-based carbon material; the bamboo-based carbon material contains aromatic groups.

[0008] In addition, the composite cathode material according to the present invention may also have the following additional technical features:

[0009] In some embodiments, based on the mass of the bamboo-based carbon material, the mass content of the aromatic groups is 12%-16%.

[0010] In some embodiments, the aromatic group includes a phenyl group.

[0011] In some embodiments, the bamboo-based carbon material further contains hydroxyl groups and / or quinone groups.

[0012] In some embodiments, based on the total mass of the aromatic groups, the mass content of the hydroxyl groups is 8%-12%.

[0013] In some embodiments, based on the total mass of the aromatic groups, the mass content of the quinone groups is 10%-15%.

[0014] In some embodiments, the composite cathode material satisfies at least one of the following characteristics: (1) the porosity of the composite cathode material is 60%-80%; (2) the specific surface area of ​​the composite cathode material is 200-1000m 2 / g, preferably 700-950m 2 / g; (3) the electrical conductivity of the composite positive electrode material is 10-100 S / cm, preferably 90-100 S / cm; (4) the average particle size of the composite positive electrode material is 150nm-300nm; (5) the average particle size of the core is 130nm-200nm; (6) the average thickness of the shell is 10nm-50nm; (7) the ternary material includes a nickel-based ternary material.

[0015] In some embodiments, the nickel-based ternary material includes a nickel-cobalt-manganese ternary positive electrode active material and / or a nickel-cobalt-aluminum ternary positive electrode active material.

[0016] In some embodiments, the ternary material includes a high-nickel ternary material.

[0017] According to a second aspect of the present invention, an embodiment of the present invention provides a method for preparing a composite positive electrode material, the preparation method comprising:

[0018] S1. In the presence of a mixed gas containing reducing gas and oxygen and an ester compound, carbonizing a bamboo-based precursor to obtain bamboo-based carbon;

[0019] S2, mixing the bamboo-based carbon and the ternary material in the presence of a solvent, and then drying and carbonizing and coating to obtain the composite positive electrode material;

[0020] The composite positive electrode material has a core-shell structure, including a core and an outer shell, wherein the core contains a ternary material, and the outer shell covers at least a portion of the core, and the outer shell includes a bamboo-based carbon material; the bamboo-based carbon material contains aromatic groups.

[0021] In some embodiments, the temperature of carbonization in step S1 and the temperature of carbonization coating in step S2 are each independently 200-400°C.

[0022] In some embodiments, the temperature of carbonization in step S1 is lower than the temperature of carbonization coating in step S2.

[0023] In some embodiments, the difference between the carbonization temperature in step S1 and the carbonization coating temperature in step S2 is 30-100°C.

[0024] In some embodiments, in step S1, the carbonization conditions include: pressure of 0.05-0.2 MPa, temperature of 200-350° C., and time of 2-5 h.

[0025] In some embodiments, in step S2, the carbonization coating conditions include: temperature of 250-400° C. and time of 3-6 hours.

[0026] There is no special limitation on the mixing in step S2 of the present invention, as long as the materials can be mixed evenly, and generally the mixing and stirring time is 2-5 hours.

[0027] According to the present invention, it can be understood that the drying in step S2 of the present invention is to dry the solid phase material after mixing and stirring, that is, to dry it after filtering. The drying method can be a conventional method in the art, and the present invention will not elaborate on it here.

[0028] In some embodiments, the ester compound includes at least one of phosphate ester, borate ester and carboxylate ester, preferably phosphate ester.

[0029] In some embodiments, the phosphate ester includes at least one of trimethyl phosphate, triethyl phosphate, and tripropyl phosphate.

[0030] In some embodiments, the phosphate ester comprises trimethyl phosphate.

[0031] In some embodiments, the volume ratio of reducing gas to oxygen in the mixed gas is 1.5-4:1.

[0032] In some embodiments, the reducing gas includes hydrogen.

[0033] In some embodiments, the ternary material includes a nickel-based ternary material.

[0034] In some embodiments, the nickel-based ternary material includes a nickel-cobalt-manganese ternary positive electrode active material and / or a nickel-cobalt-aluminum ternary positive electrode active material; preferably, the ternary material includes a high-nickel ternary material.

[0035] In some embodiments, the bamboo-based precursor is derived from at least one of moso bamboo, bitter bamboo, bamboo shoots and bamboo. In some preferred cases, the bamboo-based precursor is derived from moso bamboo.

[0036] In some embodiments, the solvent includes an alcohol solvent.

[0037] In some embodiments, the alcohol solvent includes at least one of methanol, ethanol, or ethylene glycol.

[0038] In some embodiments, in step S1, the mass ratio of the phosphate ester to the bamboo-based precursor is 1:0.8-2.5.

[0039] In some embodiments, in step S2, the mass of the bamboo-based carbon is 1%-15% of the mass of the ternary material.

[0040] According to the third aspect of the present invention, an embodiment of the present invention provides a positive electrode sheet, which includes a current collector, a first active material layer is provided on at least one side of the current collector, and a second active material layer is provided on the surface of the first active material layer away from the current collector, and the first active material layer and the second active material layer each independently contain the composite positive electrode material described in the first aspect of the present invention or the composite positive electrode material prepared by the preparation method described in the second aspect of the present invention.

[0041] In some embodiments, the average thickness of the outer shell of the composite positive electrode material in the first active material layer is recorded as T1, and the average thickness of the outer shell of the composite positive electrode material in the second active material layer is recorded as T2, and T1 and T2 satisfy: T1 is greater than T2.

[0042] In some embodiments, the difference between the values ​​of T1 and T2 is 5 nm-40 nm, preferably 10 nm-30 nm.

[0043] In some embodiments, the value of T1 is 15 nm-50 nm.

[0044] In some embodiments, the value of T2 is 10 nm-30 nm.

[0045] In some embodiments, the thickness of the first active material layer and the thickness of the second active material layer are each independently 100 μm to 150 μm.

[0046] In some embodiments, the first active material layer and the second active material layer each independently contain a conductive agent and a binder.

[0047] In some embodiments, the mass content of the composite positive electrode material in the first active material layer and the second active material layer is independently greater than 80%.

[0048] According to a fourth aspect of the present invention, an embodiment of the present invention provides a battery comprising a negative electrode sheet and the positive electrode sheet according to the third aspect of the present invention.

[0049] The implementation of the technical solution of the present invention has at least the following beneficial effects:

[0050] The composite cathode material of the present invention has a core-shell structure, wherein the outer shell comprises a bamboo-based carbon material containing aromatic groups. Thus, by coating the surface of the ternary material core with the bamboo-based carbon material, the composite cathode material utilizes the bamboo-based carbon material's large specific surface area and high porosity to provide more contact sites for interaction between the bamboo-based carbon material and the ternary material. This not only helps the bamboo-based carbon material coat the surface of the ternary material particles more evenly, forming a more stable coating structure; it also increases the contact area between the electrolyte and the composite cathode material during the battery's charge and discharge processes, promoting the transport and diffusion of active ions such as lithium ions, further enhancing the material's electrochemical performance. Furthermore, the bamboo-based carbon material coating modification introduces components with excellent electrical conductivity onto the material surface, effectively increasing electronic conductivity, reducing the battery's internal resistance, and improving charge and discharge efficiency and rate performance. Furthermore, the bamboo-based carbon material in the present invention contains aromatic groups. The presence of these aromatic groups provides a basis for the orderly growth of the carbon structure, helps to form bamboo-based carbon with rich pores and reasonable pore size distribution, and increases the specific surface area of ​​bamboo carbon deposits, thereby providing more contact sites for interaction with ternary materials, which is more conducive to the contact between the electrolyte and the material, promotes the adsorption and diffusion of ions, and improves the charge and discharge performance of the battery; it also helps to improve the stability of the battery during the cycle.

[0051] Therefore, the composite cathode material of the present invention has high electronic conductivity, can promote the diffusion rate and structural stability of active ions in the battery, thereby improving its performance in the ion battery, such as improving the cycle performance of the battery.

[0052] Additional aspects and advantages of the present application will be given in part in the following description and in part will become obvious from the following description or will be learned through practice of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1Shown is a SEM image of the composite positive electrode material A1 provided in Example 1 of the present invention;

[0054] Figure 2 Shown is an infrared spectrum of the bamboo-based carbon material of the outer shell of the composite positive electrode material A1 provided in Example 1 of the present invention;

[0055] Figure 3 Shown is the infrared spectrum of the bamboo-based carbon material of the outer shell of the composite positive electrode material D1 provided in Example 4 of the present invention. DETAILED DESCRIPTION

[0056] The present application will be further described below with reference to specific examples. It should be understood that these examples are only used to illustrate the present application and are not intended to limit the scope of the present application.

[0057] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range or the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0058] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0059] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0060] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0061] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0062] Unless otherwise specified, room temperature in this application refers to 10-30°C.

[0063] To improve the performance of ternary materials, carbon coating can be used. However, conventional carbon coating materials are mostly amorphous carbon or graphitized carbon, with relatively simple structures and properties, which has certain limitations in improving the overall performance of ternary materials. To alleviate these issues, the inventors of this invention discovered that bamboo-based carbon materials can better interact with ternary materials, providing more contact sites, resulting in composite cathode materials with better electrochemical performance. This application is described in detail below.

[0064] In some embodiments, the present invention provides a composite positive electrode material having a core-shell structure, wherein the composite positive electrode material comprises a core and an outer shell; wherein the core comprises a ternary material, the outer shell covers at least a portion of the core, and the outer shell comprises a bamboo-based carbon material; and the bamboo-based carbon material contains aromatic groups.

[0065] In this composite cathode material having a core-shell structure, the shell covers or encapsulates at least a portion of the core, thereby protecting or improving the core, thereby improving the structural stability of the composite cathode material and optimizing the electrochemical performance of the composite cathode material. The shell being formed on at least a portion of the surface of the core means that the shell can completely encapsulate the core within the shell, or it can also encapsulate only a portion of the outer surface of the core; that is, the shell can completely encapsulate the core or can only encapsulate a portion of the outer surface of the core, preferably completely encapsulating the core, which is more conducive to improving the structural stability and electrochemical performance of the composite cathode material.

[0066] The composite cathode material provided has a core-shell structure, wherein the core can be made of a traditional ternary material, and the shell comprises a bamboo-based carbon material; this bamboo-based carbon material primarily refers to a carbon material derived from bamboo as a precursor. Furthermore, unlike traditional carbon materials, the bamboo-based carbon material of this application also contains aromatic groups, which further enhances the electrochemical performance of the composite cathode material. Specifically:

[0067] The composite positive electrode material of the present invention has high electronic conductivity and can improve battery cycle stability. The main reasons are: on the one hand, the aromatic groups in the bamboo-based carbon material can form a stable coating layer on the surface of the core containing the ternary material through interactions such as π-π stacking. This coating layer can buffer the volume change stress during the cycle and inhibit the agglomeration and cracking of the core particles. That is, the shell containing the bamboo-based carbon material covers the surface of the core and has a more stable coating structure; thus, by coating the surface of the ternary material with the bamboo-based carbon material having aromatic groups, the problem of the lattice structure changing due to the repeated insertion and extraction of active ions (such as lithium ions) during the cycle of the ternary material can be alleviated. On the other hand, the aromatic groups in the bamboo-based carbon material have a conjugated π electron system. This structure allows electrons to move more freely within the molecule, giving the bamboo-based carbon good intrinsic conductivity. When the shell containing the bamboo-based carbon material is coated on the surface of the core containing the ternary material, the conductive network formed by the aromatic groups can effectively reduce the charge transfer resistance of the material. During the battery charging and discharging process, electrons can be more smoothly transmitted between the electrode material and the electrolyte, thereby significantly improving the rate performance of the ternary electrode material. For example, during high current density charging and discharging, the composite positive electrode material with an aromatic group conductive network can maintain a higher capacity. Compared with materials without aromatic groups, the capacity retention rate can be increased by 10%-20%. At the same time, during the battery charging and discharging process, it can increase the contact area between the electrolyte and the electrode material, promote the transmission and diffusion of active ions (such as lithium ions), and further improve the electrochemical performance of the material.

[0068] Furthermore, the inventors discovered that during battery charging and discharging, the electrolyte can react with the surface of the ternary material, forming a harmful interfacial film that affects battery performance. The aromatic groups on the surface of the bamboo-based carbon material shell in this invention possess a certain degree of chemical activity, reacting with lithium hexafluorophosphate and organic solvents such as EC and DMC in the electrolyte to form a more stable and dense solid electrolyte interface (SEI) film on the surface of the ternary material. This SEI film prevents further side reactions between the electrolyte and the interior of the NCM material, reducing the consumption of active lithium and improving the battery's coulombic efficiency.

[0069] In addition, compared to conventional carbon coating materials that are mostly amorphous carbon or graphitized carbon, the specific surface area and porosity can be increased by using bamboo-based carbon materials for coating. This is mainly because: bamboo-based carbon has a rich pore structure due to its unique low-temperature carbonization process. The fiber structure of bamboo itself forms a large number of micropores and mesopores during the carbonization process. According to testing, the porosity of bamboo-based carbon can be as high as 60%-80%, while the porosity of conventional carbon coating materials is often less than 40%. A higher porosity means a larger specific surface area. The specific surface area of ​​bamboo-based carbon materials is generally 200-500m 2 / g, while conventional carbon-coated materials are mostly between 100m 2 / g or less. This high porosity and large specific surface area provide more contact sites for the interaction between bamboo-based carbon and the cathode active material. This not only helps the bamboo-based carbon coat the cathode particles more evenly, forming a more stable coating structure; it also increases the contact area between the electrolyte and the electrode material during battery charge and discharge, promoting the transport and diffusion of active ions (such as lithium ions), further enhancing the electrochemical performance of the material.

[0070] This application coats the surface of the ternary material with a bamboo-based carbon material and introduces components with good conductivity on the surface of the material, which can effectively improve the electronic conductivity, help reduce the internal resistance of the battery, and further improve the charge and discharge efficiency and rate performance.

[0071] In a preferred embodiment of the present application, the composite cathode material is a nanoscale material. Thus, the formed nanocomposite material increases the specific surface area, provides more diffusion channels for active ions such as lithium ions, shortens the diffusion path, and accelerates the diffusion rate. For example, it accelerates the diffusion of active ions (such as lithium ions), thereby improving the charge and discharge performance of the battery.

[0072] According to the present invention, in some embodiments, based on the mass of the bamboo-based carbon material, the mass content of the aromatic group is 12%-16%, for example, 12%, 13%, 14%, 15%, 16%, or a range consisting of any two of the above values.

[0073] In the present invention, controlling the content of the aromatic group within the above range can better improve the conductivity and stability of the composite positive electrode material, and the composite positive electrode material can better improve the coulombic efficiency of the battery.

[0074] According to the present invention, the aromatic groups in the bamboo-based carbon material include benzene ring structures that, through chemical reactions (such as covalent bonding or group condensation), build the carbon skeleton structure of the bamboo-based carbon. In some embodiments, the aromatic groups include phenyl groups.

[0075] According to the present invention, in some embodiments, the bamboo-based carbon material further contains hydroxyl groups and / or quinone groups.

[0076] In the present invention, the hydroxyl and quinone groups can be attached to aromatic groups or to other chemical chains within the shell. Preferably, the hydroxyl and quinone groups are attached to aromatic groups. That is, in the bamboo-based carbon material of the present application, the aromatic groups may include phenyl groups, and the aromatic groups may also include phenyl groups to which one or both hydroxyl groups and quinone groups are attached. Alternatively, the bamboo-based carbon material of the present application may include aromatic groups and groups to which one or both hydroxyl groups and quinone groups are attached; wherein the aromatic groups include phenyl groups. Preferably, the aromatic groups include groups to which one or both hydroxyl groups and quinone groups are attached to phenyl groups, as well as phenyl groups. More preferably, the aromatic groups include groups to which hydroxyl groups and quinone groups are attached to phenyl groups, as well as phenyl groups.

[0077] When the bamboo-based carbon material of the present invention further contains one or both of hydroxyl groups and quinone groups, it is beneficial to the contact between the composite positive electrode material and the electrolyte, promotes the adsorption and diffusion of ions, and improves the charge and discharge performance of the battery. In particular, the presence of quinone groups can form a chemical bond or a strong interaction between the outer shell material and the inner core, thereby enhancing the interfacial bonding force between the two, making the structure of the composite material more stable, and facilitating the maintenance of structural integrity during the charge and discharge process, thereby improving the cycle performance of the battery.

[0078] The groups in the bamboo-based carbon material of the present invention can be measured by conventional infrared methods in the art, and are not limited thereto.

[0079] According to the present invention, in some embodiments, based on the total mass of the aromatic groups, the mass content of the hydroxyl group is 8%-12%, for example, 8%, 9%, 10%, 11%, 12%, or a range consisting of any two of the above values.

[0080] In the present invention, by controlling the content of hydroxyl groups within the above range, the composite positive electrode material can better promote the adsorption and diffusion of active ions (such as lithium ions) when in contact with the electrolyte, thereby improving the charge and discharge performance of the battery.

[0081] According to the present invention, in some embodiments, based on the total mass of the aromatic groups, the mass content of the quinone groups is 10%-15%, for example, 10%, 11%, 12%, 13%, 14%, 15%, or a range consisting of any two of the above values.

[0082] In the present invention, the content of the quinone group is controlled within the above range, and the composite positive electrode material has more excellent structural stability and electrochemical performance, and can better improve the cycle performance of the battery.

[0083] The content of the aromatic group, hydroxyl group and quinone group in the present invention can be determined by gas chromatography-mass spectrometry. For example, the content of the aromatic group can be determined by the following method:

[0084] Gas chromatography conditions: a polar DB-5MS column was selected; the carrier gas was high-purity helium with a flow rate controlled at 1-2 mL / min; the inlet temperature was set at 250-300°C; a split injection method was adopted with a split ratio of 10:1-50:1; the programmed temperature conditions were: an initial temperature of 50-80°C, maintained for 1-2 minutes, then heated to 250-300°C at a rate of 5-10°C / min and maintained for 5-10 minutes to ensure that aromatic hydrocarbons with different boiling points could be fully separated.

[0085] Quantitative analysis: A series of standard solutions with concentrations ranging from 0.1 to 10 mg / L were prepared in toluene and injected into the GC-MS instrument to generate chromatograms for each standard. The treated composite cathode material shell was then injected into the instrument, and the curve that overlapped with the curves from the previous series of standard solutions was selected to determine the aromatic hydrocarbon content in the bamboo-based carbon sample.

[0086] In addition, the contents of hydroxyl and quinone groups can also be determined by conventional gas chromatography-mass spectrometry methods, which will not be elaborated in detail in the present invention.

[0087] According to the present invention, those skilled in the art will understand that the bamboo-based carbon material of the present invention refers to a material formed by bamboo through a step including carbonization, and the fiber structure of the bamboo itself forms a large number of micropores and mesopores during the carbonization process. In some embodiments, the porosity of the composite positive electrode material is 60%-80%, for example, 60%, 62%, 65%, 68%, 70%, 72.5%, 75%, 76.5%, 78%, 80%, or a range consisting of any two of the above values.

[0088] The porosity of the composite cathode material of the present invention can be measured by methods such as BET and mercury intrusion porosimetry.

[0089] According to the present invention, a higher porosity means a larger specific surface area. In some embodiments, the specific surface area of ​​the composite cathode material is 200-1000 m 2 / g, for example, 200m 2 / g、300m 2 / g, 400m 2 / g、500m 2 / g、600m 2 / g、650m 2 / g、710m 2 / g、755m 2 / g、800m 2 / g、850m2 / g、900m 2 / g、925m 2 / g、950m 2 / g、1000m 2 / g, or the range of any two values ​​above, preferably 700-950m 2 / g.

[0090] The specific surface area of ​​the composite cathode material in the present invention can be measured by the conventional physical adsorption BET method in the art.

[0091] The high porosity and large specific surface area of ​​the composite cathode material provide more contact sites for interaction between the bamboo-based carbon and the cathode active material. More importantly, the outer shell and inner core form a more stable core-shell structure. This increases the contact area between the electrolyte and the composite cathode material during battery charge and discharge, promoting the transport and diffusion of active ions (such as lithium ions) and further enhancing the material's electrochemical performance.

[0092] According to the present invention, the shell of the present invention contains a bamboo-based carbon material, and the bamboo-based carbon material contains aromatic groups, which makes the shell material have a component with good conductivity, effectively improves the electronic conductivity, reduces the internal resistance of the battery, and improves the charge and discharge efficiency and rate performance. In some embodiments, the conductivity of the composite positive electrode material is 10-100S / cm, for example, 10S / cm, 20S / cm, 30S / cm, 40S / cm, 50S / cm, 60S / cm, 65S / cm, 69S / cm, 70S / cm, 75S / cm, 80S / cm, 90S / cm, 92S / cm, 95S / cm, 96S / cm, 97S / cm, 100S / cm, or a range consisting of any two of the above values, preferably 90-100S / cm.

[0093] According to the present invention, as long as the purpose of the present invention can be achieved, the size of the composite positive electrode material can be selected within a wide range. In some embodiments, the average particle size of the composite positive electrode material is 150 nm-300 nm.

[0094] According to the present invention, the size of the core can be selected within a wide range as long as the objectives of the present invention are achieved. In some embodiments, the average particle size of the core is 130 nm to 200 nm. In the following examples, a core material having an average particle size of 150 nm is used as an example to illustrate the advantages of the present invention, but does not limit the present invention.

[0095] According to the present invention, as long as the purpose of the present invention can be achieved, the thickness of the shell can be selected within a wide range. In some embodiments, the average thickness of the shell is 10 nm-50 nm, for example, 10 nm, 17.5 nm, 20 nm, 25 nm, 27.5 nm, 30 nm, 35 nm, 40 nm, 42.5 nm, 45 nm, 50 nm, or a range consisting of any two of the above values.

[0096] In the present invention, the average thickness of the shell can be obtained by transmission electron microscopy. Specifically, a curve can be drawn at the outer edge of the entire core. The distance between the curve and the outer edge of the entire composite positive electrode material is the thickness of the shell of the composite positive electrode material. The average value calculated at twenty random positions is the average thickness of the shell; the sum of twice the average thickness and the average particle size of the core is the average particle size of the composite positive electrode material.

[0097] According to the present invention, the ternary material refers to a ternary positive electrode material composed of three metals (such as transition metals), and the ternary material includes a nickel-based ternary material.

[0098] According to the present invention, nickel-based ternary materials refer to ternary positive electrode materials containing nickel metal. In some embodiments, nickel-based ternary materials include nickel-cobalt-manganese ternary positive electrode active materials (NCM, LiNi x Co y Mn z O2, wherein x>0, y>0, z>0) and / or nickel-cobalt-aluminum ternary positive electrode active materials (NCA, LiNi x Co y Al z O2, where x>0, y>0, and z>0). Nickel-cobalt-manganese ternary positive electrode active materials have a high theoretical specific capacity, typically between 150 and 280 mAh / g. A high theoretical specific capacity means that in battery applications, more electrical energy can be stored, thereby providing longer-lasting endurance for electronic devices, electric vehicles, and the like. The present invention uses nickel-cobalt-manganese ternary positive electrode active materials as an example to illustrate the advantages of the present invention, but does not limit the present invention.

[0099] Optionally, when the parameters of Ni, Co, and Mn are within the range of 0.4≤x≤0.8, 0.1≤y≤0.3, 0.1≤z≤0.3, and x+y+z=1, LiNi x Co y Mn zThe inner core of O2 can show better performance during the composite modification process with bamboo-based carbon materials. Within this ratio range, the crystal structure of the material is relatively stable, Ni can provide a higher specific capacity, Co can enhance the electronic conductivity and structural stability of the material, and Mn helps to improve the safety and cycle life of the material. The NCM series materials that can be listed in the present invention include NCM111 (Ni:Co:Mn=1:1:1), NCM523, NCM622, NCM811, etc. Preferably, the NCM is selected from NCM811. In the present invention, NCM523 or NCM811 is used as an example to illustrate the advantages of the present invention, but it does not represent a limitation of the present invention.

[0100] In the present invention, the ternary material is preferably a high-nickel ternary material, such as NCM811, which has the advantages of higher specific capacity, good cycle stability and relatively low cost.

[0101] According to the present invention, as long as the purpose of the present invention can be achieved, the preparation method of the composite positive electrode material in the present invention is not particularly limited. For example, a bamboo-based precursor is carbonized to obtain bamboo-based carbon, and then carbonized and coated with a ternary material. Preferably, in some embodiments, the composite positive electrode material can be prepared according to the preparation method provided below.

[0102] According to the present invention, those skilled in the art should understand that all the features and effects involved in the above-mentioned "positive electrode composite material" of the present invention are also applicable to the "preparation method of the composite positive electrode material provided below", and the present invention will not elaborate on it.

[0103] According to another aspect of the present invention, a method for preparing a composite positive electrode material is provided, the method comprising:

[0104] S1. In the presence of a mixed gas containing reducing gas and oxygen and an ester compound, carbonizing a bamboo-based precursor to obtain bamboo-based carbon;

[0105] S2, mixing the bamboo-based carbon and the ternary material in the presence of a solvent, and then drying and carbonizing and coating to obtain the composite positive electrode material;

[0106] The composite positive electrode material has a core-shell structure, including a core and an outer shell, wherein the core contains a ternary material, and the outer shell covers at least a portion of the core, and the outer shell includes a bamboo-based carbon material; the bamboo-based carbon material contains aromatic groups.

[0107] The preparation method of the composite positive electrode material of the present invention is simple and easy, bamboo is widely available, the cost is low, and it has good economic and environmental benefits, and is suitable for large-scale industrial production.

[0108] In the preparation method of the composite cathode material of the present invention, a bamboo-based carbon material containing aromatic groups is first prepared. Furthermore, during a low-temperature carbonization process, the aromatic groups in the bamboo act as active sites for pyrolysis reactions, triggering a series of polycondensation and aromatization reactions. As the temperature rises, the lignin in the bamboo pyrolyzes. During the carbonization process (e.g., in the low-temperature carbonization range of 200-350°C), aromatic groups gradually form and stabilize, with their benzene ring structures interconnecting and condensing, gradually building the carbon skeleton structure of the bamboo-based carbon. The presence of these aromatic groups provides a foundation for the orderly growth of the carbon structure, helping to form a bamboo-based carbon material with abundant porosity and a reasonable pore size distribution, increasing the specific surface area of ​​the bamboo-based carbon material and providing more contact sites for subsequent interaction with the ternary material. The carbonyl and phenolic hydroxyl groups in the bamboo-based carbon are reduced and oxidized to hydroxyl and quinone groups in an atmosphere of a hydrogen and oxygen mixture. The reduced hydroxyl groups increase the active sites on the material surface, facilitating contact between the electrolyte and the material, promoting ion adsorption and diffusion, and improving the battery's charge and discharge performance. This helps to enhance the battery's stability during cycling. The formation of quinone groups can form chemical bonds or stronger interactions between bamboo-based carbon materials and ternary materials, thereby enhancing the interfacial bonding between the two and making the structure of the composite material more stable, which is beneficial to maintaining structural integrity during the charge and discharge process and improving the cycle performance of the battery.

[0109] According to the present invention, in some embodiments, the carbonization temperature in step S1 and the carbonization and coating temperature in step S2 are independently 200-400° C. That is, in step S1, the temperature of carbonizing the bamboo-based precursor is 200-400° C.; in step S2, the temperature of carbonizing and coating the bamboo-based carbon and the ternary material after mixing is 200-400° C. The carbonization temperature in step S1 and the carbonization and coating temperature in step S2 can be the same or different.

[0110] In the present invention, by controlling the temperature of carbonization in step S1 and the temperature of carbonization coating in step S2 within the above range, it belongs to the low-temperature carbonization range. Within this temperature range, the small molecular organic matter produced by cellulose pyrolysis can more efficiently undergo condensation and aromatization reactions, which helps to form an ordered pore structure and form high-quality bamboo-based carbon materials, so that the prepared composite positive electrode material is more conducive to contact with the electrolyte and promotes the transmission of active ions (such as lithium ions).

[0111] According to the present invention, in some embodiments, the temperature of carbonization in step S1 is lower than the temperature of carbonization coating in step S2.

[0112] In the present invention, the temperature of carbonization in step S1 is controlled to be lower than the temperature of carbonization coating in step S2, and the composite positive electrode material finally prepared has better electrochemical properties.

[0113] According to the present invention, in some embodiments, the difference between the carbonization temperature in step S1 and the carbonization coating temperature in step S2 is 30-100°C, for example, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, or a range consisting of any two of the above values.

[0114] According to the present invention, in some embodiments, in step S1, the carbonization conditions include: a pressure of 0.05-0.2 MPa, for example, 0.05 MPa, 0.1 MPa, 0.15 MPa, 0.2 MPa, or a range consisting of any two of the above values.

[0115] In the present invention, the pressure in the above step S1 is related to the content of the mixed gas containing reducing gas and oxygen during carbonization.

[0116] According to the present invention, in some embodiments, in step S1, the carbonization conditions include: a temperature of 200-350°C, for example, 200°C, 230°C, 250°C, 275°C, 300°C, or a range consisting of any two of the above values.

[0117] According to the present invention, those skilled in the art can raise the temperature to the temperature of carbonization in step S1 at a certain heating rate according to the required carbonization temperature, for example, at a heating rate of 0.5-10°C / min, preferably 1-5°C / min, to the temperature of carbonization in step S1.

[0118] In the present invention, controlling the carbonization temperature in step S1 within the above range can construct a more stable carbon skeleton structure of the bamboo-based carbon material, which is beneficial for providing more contact sites for subsequent interaction with the ternary material and helps to improve the stability of the battery during the cycle.

[0119] According to the present invention, the carbonization time in step S1 can be regulated according to the carbonization temperature. In some embodiments, in step S1, the carbonization conditions include: a time of 3-6 hours, for example, 3 hours, 3.25 hours, 3.5 hours, 3.58 hours, 3.6 hours, 3.8 hours, 4 hours, 4.2 hours, 4.5 hours, 5 hours, or a range consisting of any two of the above values.

[0120] According to the present invention, in some embodiments, in step S2, the carbonization coating conditions include: a temperature of 250-400°C, for example, 250°C, 275°C, 300°C, 325°C, 350°C, 375°C, 400°C, or a range consisting of any two of the above values.

[0121] In the present invention, controlling the carbonization coating temperature in step S2 within the above range can provide more contact sites for the bamboo-based carbon material to better interact with the ternary material, thereby forming a more stable coating structure.

[0122] According to the present invention, the carbon coating conditions in step S2 can be regulated according to the stability of the corresponding carbon coating. In some embodiments, the carbonization coating conditions include: time of 3-6h, for example, 3h, 3.25h, 3.5h, 3.75h, 4h, 4.25h, 4.5h, 4.75h, 5h, 6h, or a range consisting of any two of the above values.

[0123] According to the present invention, an ester compound refers to a compound formed by an esterification reaction between an inorganic acid (such as sulfuric acid, nitric acid, phosphoric acid, etc.) or an organic acid and an alcohol (or phenol). In some embodiments, the ester compound includes at least one of a phosphate ester, a borate ester, and a carboxylate ester.

[0124] In the present invention, the ester compound is used as a protective agent during the carbonization process, which helps to guide the directional arrangement and polycondensation reaction of the pyrolysis products and promote the orderly growth of the aromatic structure.

[0125] According to the present invention, phosphate refers to a compound formed by the reaction of phosphoric acid and alcohol. In some embodiments, the phosphate includes at least one of trimethyl phosphate, triethyl phosphate, and tripropyl phosphate, preferably trimethyl phosphate.

[0126] According to the present invention, borate refers to a compound formed by the reaction of boric acid and alcohol. Examples of borate include trimethyl borate, triethyl borate, and triphenyl borate.

[0127] According to the present invention, carboxylic acid ester refers to a compound formed by the reaction of a compound containing carboxylic acid with an alcohol. Examples of carboxylic acid ester include dimethyl phthalate, diethyl phthalate, and the like.

[0128] According to the present invention, in some embodiments, the ester compound includes a phosphate ester.

[0129] After extensive research, the inventors discovered that using a phosphate ester, such as trimethyl phosphate, as a protective agent during the carbonization process resulted in a composite cathode material with improved electrochemical performance. This is due to the interaction between the phosphorus atoms in the molecule and the aromatic structures in bamboo. This interaction helps guide the directional alignment and polycondensation of the pyrolysis products, promoting the orderly growth of the aromatic structures.

[0130] According to the present invention, in some embodiments, the volume ratio of reducing gas to oxygen in the mixed gas is 1.5-4:1, for example, 1.5:1, 2:1, 3:1, 4:1, or a range consisting of any two of the above ratios.

[0131] According to the present invention, in a mixed gas containing reducing gas and oxygen, during the carbonization process, the carbonyl group and phenolic hydroxyl group in the bamboo-based carbon material can be reduced and oxidized to hydroxyl group and quinone group. The type of reducing gas can be selected within a wide range. In some embodiments, the reducing gas includes hydrogen.

[0132] According to the present invention, in some embodiments, the nickel-based ternary material includes a nickel-cobalt-manganese ternary positive electrode active material (NCM, LiNi x Co y Mn z O2, wherein x>0, y>0, z>0) and / or nickel-cobalt-aluminum ternary positive electrode active materials (NCA, LiNi x Co y Al z O2, where x>0, y>0, z>0).

[0133] According to the present invention, a bamboo-based precursor is an intermediate product prepared from bamboo or its derivatives through physical, chemical, or biological treatment, which can be used to synthesize high-performance materials (such as carbon materials, composite materials, etc.). In some embodiments, the method for obtaining the bamboo-based precursor includes: fully contacting an alkali metal aqueous solution with bamboo in a weight ratio of (7-9): (3-1) to ensure reaction uniformity. The stirring speed is generally controlled at 200-500 r / min, and the stirring is carried out for 4-6 hours. During the solution immersion process, mechanical stirring can promote the rapid diffusion of hydroxide ions in the solution into the bamboo, thereby improving reaction efficiency. Finally, the stirred material is filtered, dried, and crushed into a precursor powder to facilitate uniform heating and carbonization. The alkali metal aqueous solution includes at least one of potassium hydroxide aqueous solution, sodium hydroxide aqueous solution, and lithium hydroxide aqueous solution. Sodium hydroxide aqueous solution is preferably used because it has moderate reactivity when reacting with cellulose, hemicellulose, and other components in bamboo, and can fully react with the hemicellulose in the bamboo without causing excessive damage to the material structure like some more highly active alkali metal hydroxides.

[0134] According to the present invention, in some embodiments, the bamboo-based precursor is derived from at least one of Phyllostachys pubescens, Phyllostachys amarus, Phyllostachys chinensis, and Phyllostachys balsamifera.

[0135] According to the present invention, in some embodiments, the bamboo-based precursor is derived from Moso bamboo.

[0136] The inventors discovered that composite cathode materials prepared using bamboo-based precursors derived from moso bamboo exhibit superior electrochemical performance. This is due to the ideal composition of cellulose, hemicellulose, and lignin in moso bamboo. This relatively high cellulose content allows the small organic molecules produced by pyrolysis of cellulose to undergo polycondensation and aromatization more efficiently during carbonization, resulting in high-quality bamboo-based carbon. Further studies have shown that the cellulose content in moso bamboo can reach 40%-60%, higher than some other bamboo species. This abundant cellulose provides a sufficient raw material base for the formation of bamboo carbon rich in aromatic groups, facilitating the subsequent formation of a core-shell structure with ternary materials, enhancing the material's electrical conductivity and structural stability. Furthermore, moso bamboo possesses a unique fiber structure with tightly packed and regular fiber bundles. During carbonization, this structure guides the directional alignment of pyrolysis products, contributing to the formation of an ordered pore structure. The resulting bamboo carbon often exhibits a higher porosity and a more optimal pore size distribution, facilitating sufficient contact between the electrolyte and the electrode material, promoting the transport of active ions (such as lithium ions). Compared with several other types of bamboo, the bamboo-based carbon material finally formed from Moso bamboo performs better in improving the comprehensive performance of composite positive electrode materials.

[0137] According to the present invention, as long as the purpose of the present invention can be achieved, the solvent can be a conventional solvent in the art. In some embodiments, the solvent includes an alcohol solvent, and the alcohol solvents that can be listed include at least one of methanol, ethanol and ethylene glycol.

[0138] The amount of the ester compound in step S1 of the present invention can be selected within a wide range. In some embodiments, in step S1, the mass ratio of the ester compound to the bamboo-based precursor is 1:0.8-2.5, for example, 1:0.8, 1:1, 1:1.2, 1:1.5, 1:1.8, 1:2, 1:2.5, or a range consisting of any two of the above ratios, preferably 1:1-1.5.

[0139] In the present invention, controlling the amount of the ester compound within the above range can better promote the orderly growth of the aromatic structure, and the prepared composite positive electrode material has better electrochemical performance.

[0140] According to the present invention, in some embodiments, in step S2, the mass of the bamboo-based carbon is 1%-15% of the mass of the ternary material, for example, 1%, 2%, 4%, 6%, 8%, 10%, 12%, 15%, or a range consisting of any two of the above values, preferably 2%-5%.

[0141] The amount of the alcohol solvent in step S2 of the present invention is not particularly limited, as long as the bamboo-based carbon and the nickel-based ternary material can be evenly mixed. For example, the total mass of the bamboo-based carbon and the nickel-based ternary material: the volume of the alcohol solvent = 100 g: (5-15) mL.

[0142] As an example, step S1 includes: placing the bamboo-based precursor in a hydrogen-oxygen mixed gas with a volume ratio of 1.5-4:1, setting the pressure to 0.05-0.2 MPa, adding phosphate ester 0.8-2.5 times the mass of the bamboo-based precursor as a protective reagent, heating from room temperature to 200-350°C at a rate of 1-5°C / min, and keeping warm for 3-6 hours to carbonize the bamboo-based precursor and retain the aromatic groups in the precursor, and then cooling to room temperature to obtain bamboo-based carbon.

[0143] As an example, step S2 includes: mixing the bamboo-based carbon and the nickel-based ternary material in step S1 in a mass ratio of (2-5): (95-98) in 5-15 mL of an alcohol solvent, stirring for 2-5 hours, filtering and drying, and then carbonizing and coating at 250-400°C for 3-6 hours to prepare a composite positive electrode material.

[0144] According to the present invention, the composite positive electrode material of the present invention can be used in a positive electrode sheet. In some embodiments, a positive electrode sheet is provided, which includes a current collector, a first active material layer is provided on at least one side of the current collector, and a second active material layer is provided on the surface of the first active material layer away from the current collector; wherein the first active material layer and the second active material layer each independently contain the composite positive electrode material described above in the present invention or the composite positive electrode material prepared by the above-mentioned preparation method of the present invention.

[0145] The positive electrode sheet containing the composite positive electrode material of the present invention has excellent electrochemical performance.

[0146] According to the present invention, in some embodiments, the average thickness of the outer shell of the composite positive electrode material in the first active material layer is recorded as T1, and the average thickness of the outer shell of the composite positive electrode material in the second active material layer is recorded as T2, and T1 and T2 satisfy: T1 is greater than T2.

[0147] Based on research on the composite positive electrode material of the present invention, the inventors of the present invention conducted in-depth research and discovered that the average thickness of the outer shell of the composite positive electrode material in the first active material layer is greater than the average thickness of the outer shell of the composite positive electrode material in the second active material layer. This means that the mass percentage of the outer shell containing bamboo-based carbon material in the first active material layer is greater than the mass percentage of the outer shell containing bamboo-based carbon material in the second active material layer. This results in a larger particle size of the composite positive electrode material in the first active material layer than in the second active material layer. The first active material layer primarily contains a higher content of bamboo-based carbon material coated with the ternary material, resulting in a lower porosity of the outer shell. The thicker first active material layer (with a relatively higher coating content) exhibits better conductivity and structural continuity. Once active ions, such as lithium ions, are captured by the second active material layer, the first active material layer, through its excellent electron transport capability, can rapidly conduct the active ions, such as lithium ions, to the coated material body. Due to the sufficient content of bamboo-based carbon material in the first active material layer, a continuous and efficient ion transport channel is formed, reducing resistance during ion transport. When the battery is discharged, active ions, such as lithium ions, can be smoothly transferred from the inside of the material through the bamboo-based carbon material in the first active material layer to the second active material layer, and then released into the electrolyte, effectively improving the charge and discharge rate of the battery; the bamboo-based carbon material in the second active material layer is less coated with ternary materials. When the bamboo-based carbon material is coated on the ternary material (such as LiNi x Co y Mn z When the second active material layer is coated on the surface of the electrolyte (O2), the thinner shell (relatively low coating content) has a larger specific surface area. This allows the second active material layer to fully contact the electrolyte and quickly capture active ions (such as lithium ions) in the electrolyte during battery charging.

[0148] According to the present invention, in some embodiments, the numerical difference between T1 and T2 is 5-40 nm, for example, 5 nm, 10 nm, 12.5 nm, 15 nm, 17.5 nm, 20 nm, 25 nm, 30 nm, 40 nm, or a range consisting of any two of the above values, preferably 10-30 nm.

[0149] According to the present invention, in some embodiments, the value of T1 is 15-50 nm, for example, 15 nm, 20 nm, 22.5 nm, 25 nm, 27.5 nm, 30 nm, 40 nm, 42.5 nm, 50 nm, or a range consisting of any two of the above values.

[0150] According to the present invention, in some embodiments, the value of T2 is 10-30 nm, for example, 10 nm, 15 nm, 20 nm, 22.5 nm, 25 nm, 27.5 nm, 30 nm, or a range consisting of any two of the above values.

[0151] According to the present invention, in some embodiments, the shell thickness of the composite positive electrode material in the first active material layer (15-50 nm) is greater than the shell thickness of the composite positive electrode material in the second active material layer (10-30 nm), that is, the mass proportion of the shell in the first active material layer to the composite positive electrode material is greater than the mass proportion of the shell in the second active material layer to the composite positive electrode material, thereby making the particle size of the composite positive electrode material in the first active material layer (160-300 nm) greater than the particle size of the composite positive electrode material in the second active material layer (150-260 nm).

[0152] According to the present invention, in some embodiments, the thickness of the first active material layer and the thickness of the second active material layer are each independently 100 μm-150 μm.

[0153] According to the present invention, as long as the purpose of the present invention can be achieved, the specific type of the above-mentioned current collector is not particularly limited, and can refer to the metal materials commonly used in the art, such as but not limited to platinum, palladium, aluminum, copper foil, etc.

[0154] According to the present invention, in order to enable the composite positive electrode material to better form the corresponding first active material layer and second active material layer, in some embodiments, the first active material layer and the second active material layer each independently contain a conductive agent and a binder.

[0155] According to the present invention, the types of the above-mentioned conductive agent and binder are not particularly limited, and each of them can be a conventional type in the field. For example, the conductive agent includes but is not limited to acetylene black, conductive carbon black, carbon nanotubes, carbon fiber and graphene. For example, the binder includes but is not limited to PVDF (polyvinylidene fluoride), polytetrafluoroethylene (PTFE) and styrene-butadiene rubber (SBR).

[0156] According to the present invention, in some embodiments, the mass content of the composite positive electrode material in the first active material layer and the second active material layer is independently greater than 80%, preferably 81%-97%.

[0157] According to the present invention, the content of the above-mentioned conductive agent and binder can be selected within a wide range. For example, the mass content of the conductive agent in the first active material layer and the second active material layer is independently 2%-8%; for example, the mass content of the binder in the first active material layer and the second active material layer is independently 3%-10%.

[0158] According to the present invention, the preparation method of the above-mentioned positive electrode sheet is not particularly limited. As long as the purpose of the present invention can be achieved, it can be carried out according to the conventional preparation method in the field. Generally, a first active slurry for providing a first active material layer and a second active slurry for providing a second active material layer can be prepared first, that is, the respective positive electrode composite materials, conductive agents and binders are dispersed in a solvent (such as N-methylpyrrolidone) to obtain corresponding ones, and then the slurries are coated on the current collector in sequence, and then the positive electrode sheet is finally obtained through processes such as drying and rolling.

[0159] According to the present invention, in some embodiments, the present invention provides a battery comprising a negative electrode sheet and the positive electrode sheet of the present invention.

[0160] The battery comprising the positive electrode sheet of the present invention can exhibit excellent rate performance and cycle performance.

[0161] The specific type of battery in the present invention can be selected from a wide range, such as a lithium-ion battery. The lithium-ion battery is used as an example to illustrate the advantages of the present invention, but it does not limit the present invention.

[0162] According to the present invention, those skilled in the art can select the corresponding negative electrode sheet as needed. In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer arranged on at least one surface of the negative electrode current collector, and the negative electrode active material layer includes a negative electrode material. In the present invention, there is no special limitation on the specific materials and structures of the negative electrode current collector and the negative electrode active material layer in the negative electrode sheet. Those skilled in the art can select the specific materials and structures of the negative electrode current collector and the negative electrode active material layer known in the art as needed.

[0163] According to the present invention, in some embodiments, the battery further includes an electrolyte and a separator.

[0164] According to the present invention, there is no particular limitation on the specific type of the above-mentioned electrolyte. All electrolytes suitable for lithium batteries in the art are suitable for the present invention, and the present invention will not elaborate on this.

[0165] According to the present invention, the above-mentioned diaphragm can be various diaphragms well known to those skilled in the art and suitable for use in batteries, especially lithium-ion batteries, such as PP-based film, PE-based film, glass fiber felt or ultrafine glass fiber paper.

[0166] According to the present invention, the above-mentioned battery can be assembled according to methods well known to those skilled in the art, for example, the positive electrode sheet, the negative electrode sheet and the separator are wound together, hot pressed, packaged, dried, and then injected with electrolyte; and then aged and other steps are performed to prepare it.

[0167] Example

[0168] Hereinafter, the present invention will be described in more detail by giving examples. The present invention is not limited to the following examples and can be appropriately changed within the scope of the subject matter of the preceding and following texts, and they are all included in the technical scope of the present invention. In the following examples, if no specific technology or conditions are indicated, the technology or conditions or product specifications described in the literature in this area are used. Reagents, materials, or those not indicated by the manufacturer are all conventional products that can be obtained commercially.

[0169] In the following examples and comparative examples:

[0170] Preparation of precursor bamboo powder: The bamboo was cleaned to remove surface impurities, and the bamboo with a mass ratio of 8:1 was fully contacted with a sodium hydroxide aqueous solution with a mass concentration of 5% at a stirring speed of 400 r / min and stirred for 5 hours, and then filtered, dried and crushed to obtain the precursor bamboo powder.

[0171] Preparation of precursor bitter bamboo powder: After removing surface impurities from bitter bamboo, the moso bamboo with a mass ratio of 8:1 was fully contacted with a sodium hydroxide aqueous solution with a mass concentration of 5% at a stirring speed of 400 r / min and stirred for 5 hours, and then filtered, dried and crushed to obtain the precursor bitter bamboo powder.

[0172] Determination of specific surface area: Remove surface impurities and moisture from the prepared composite cathode material powder. Then, place the sample in an adsorption instrument and flow nitrogen at low temperature to measure the specific surface area of ​​the material.

[0173] Conductivity measurement: The prepared composite cathode material is pressed into a block and connected to a two-electrode tester to ensure good contact between the electrodes and the sample. A certain voltage is applied and the current flowing through the sample is measured to obtain the conductivity.

[0174] Porosity determination: First, pre-treat the sample to remove surface impurities and moisture. Then, place the sample in an adsorption instrument and introduce nitrogen at low temperatures (e.g., liquid nitrogen). Measure the adsorption and desorption of nitrogen at different pressures to determine the sample's specific surface area. The porosity is then calculated based on the material's density.

[0175] The contents of aromatic groups, hydroxyl groups and quinone groups were determined by GC-MS.

[0176] Example 1

[0177] 1. Preparation of composite cathode material A1:

[0178] Preparation of S1 bamboo-based carbon A1: 5g of precursor bamboo powder was placed in a hydrogen and oxygen mixed gas with a volume ratio of 2:1, the pressure was set to 0.1Mpa, 3mL of trimethyl phosphate was added as a protective reagent, and the temperature was raised from room temperature to 275℃ at a rate of 3℃ / min, and kept warm for 3h to carbonize the precursor powder and retain the aromatic groups in the precursor. Then it was cooled to room temperature to obtain bamboo-based carbon A1.

[0179] S2: The bamboo-based carbon A1 and the ternary positive electrode material NCM523 are mixed in 10 mL of ethanol solvent at a mass ratio of 3:97. After mixing and stirring for 3 hours, the mixture is filtered and dried, and then carbonized and coated at 325°C for 4 hours to prepare a composite positive electrode material A1.

[0180] The SEM image of the composite cathode material A1 is as follows Figure 1 As shown, the composite positive electrode material A1 has a core-shell structure, with an average particle size of 225 nm, an average particle size of the core NCM523 of 150 nm, and a value twice the average thickness of the shell bamboo-based carbon material of 75 nm.

[0181] The infrared spectrum of the bamboo-based carbon material in the shell of the composite cathode material A1 is as follows Figure 2 shown.

[0182] 2. Preparation of composite cathode material A2:

[0183] Preparation of S1 bamboo-based carbon A2: same as the preparation of bamboo-based carbon A1.

[0184] S2 mixed the above-mentioned bamboo-based carbon A2 and the ternary positive electrode material NCM523 in a mass ratio of 3:97 in 10 mL of ethanol solvent, stirred for 3 hours, filtered and dried, and then carbonized and coated at 300°C for 3.5 hours to prepare a composite positive electrode material A2.

[0185] The composite positive electrode material A2 has a core-shell structure with an average particle size of 190 nm, an average particle size of the core NCM523 of 150 nm, and a value twice the average thickness of the outer shell bamboo-based carbon material of 40 nm.

[0186] 3. Preparation of positive electrode sheet:

[0187] The composite positive electrode material A1 and the composite positive electrode material A2 were respectively mixed with acetylene black and polyvinylidene fluoride in a mass ratio of 85:7:8, and N-methylpyrrolidone was added and stirred so that the mass content of the slurry was 62%, thereby obtaining the corresponding positive electrode slurry A1 and positive electrode slurry A2; the positive electrode slurry A1 and the positive electrode slurry A2 were uniformly coated on an aluminum foil current collector in turn to form a first active material layer with a thickness of 110 μm and a second active material layer with a thickness of 120 μm, thereby obtaining a positive electrode sheet.

[0188] Example 2

[0189] 1. Preparation of composite cathode material B1:

[0190] Preparation of S1 bamboo-based carbon B1: 4g of precursor bamboo powder was placed in a hydrogen and oxygen mixed gas with a volume ratio of 2:1, the pressure was set to 0.05Mpa, 2mL of trimethyl phosphate was added as a protective reagent, and the temperature was raised from room temperature to 200℃ at a rate of 1℃ / min, and kept warm for 2h to carbonize the precursor powder and retain the aromatic groups in the precursor. Then it was cooled to room temperature to obtain bamboo-based carbon B1.

[0191] S2: The bamboo-based carbon B1 and the ternary positive electrode material NCM523 were mixed in 5 mL of ethanol solvent at a mass ratio of 2:98, mixed and stirred for 2 hours, filtered and dried, and then carbonized and coated at 250°C for 3.6 hours to prepare a composite positive electrode active material B1.

[0192] The composite positive active material B1 has a core-shell structure with an average particle size of 205 nm. The average particle size of the inner core NCM523 is 150 nm, and the average thickness of the outer shell bamboo-based carbon material is 55 nm at twice the value.

[0193] 2. Preparation of composite cathode material B2:

[0194] S1 Preparation of bamboo-based carbon B2: the same as the preparation of bamboo-based carbon A1 in Example 1.

[0195] S2: The bamboo-based carbon B2 and the ternary positive electrode material NCM523 are mixed in 10 mL of ethanol solvent at a mass ratio of 2:98. After mixing and stirring for 3 hours, the mixture is filtered and dried, and then carbonized and coated at 300°C for 3.2 hours to prepare a composite positive electrode material B2.

[0196] The composite cathode material B2 has a core-shell structure with an average particle size of 180 nm, an average of 150 nm for the core NCM523, and 30 nm for the double value of the average thickness of the outer shell bamboo-based carbon material.

[0197] 3. Preparation of positive electrode:

[0198] The composite positive electrode material B1 and the composite positive electrode material B2 were respectively mixed with acetylene black and polyvinylidene fluoride in a mass ratio of 85:7:8, and N-methylpyrrolidone was added and stirred so that the mass content of the slurry was 62%, thereby obtaining corresponding positive electrode slurries B1 and positive electrode slurries B2; the positive electrode slurries B1 and positive electrode slurries B2 were uniformly coated on an aluminum foil current collector in turn to form a first active material layer with a thickness of 110 μm and a second active material layer with a thickness of 120 μm, thereby obtaining a positive electrode sheet.

[0199] Example 3

[0200] 1. Preparation of composite cathode material C1:

[0201] Preparation of S1 bamboo-based carbon C1: 6 g of precursor bamboo powder was placed in a hydrogen-oxygen mixed gas with a volume ratio of 2:1, the pressure was set to 0.2 MPa, 4 mL of trimethyl phosphate was added as a protective reagent, and the temperature was raised from room temperature to 350 ° C at a rate of 5 ° C / min, and kept warm for 4 hours to carbonize the precursor powder and retain the aromatic groups in the precursor. Then it was cooled to room temperature to obtain bamboo-based carbon C1.

[0202] S2: The bamboo-based carbon C1 and the ternary positive electrode material NCM523 are mixed in 15 mL of ethanol solvent at a mass ratio of 4:96. After mixing and stirring for 4 hours, the mixture is filtered and dried, and then carbonized and coated at 400°C for 4.5 hours to prepare a composite positive electrode material C1.

[0203] The composite positive electrode material C1 has a core-shell structure with an average particle size of 235 nm, an average particle size of the core NCM523 of 150 nm, and a value twice the average thickness of the outer shell bamboo-based carbon material of 85 nm.

[0204] 2. Preparation of composite cathode material B2:

[0205] S1 Preparation of bamboo-based carbon B2: the same as the preparation of bamboo-based carbon A1 in Example 1.

[0206] S2 mixed the above-mentioned bamboo-based carbon C2 and the ternary positive electrode material NCM523 in 10 mL of ethanol solvent at a mass ratio of 2:98, stirred for 3 hours, filtered and dried, and then carbonized and coated at 300°C for 3.55 hours to prepare a composite positive electrode material C2.

[0207] The composite positive electrode material C2 has a core-shell structure with an average particle size of 195nm, an average particle size of the core NCM523 of 150nm, and a value twice the average thickness of the outer shell bamboo-based carbon material of 45nm.

[0208] 3. Preparation of positive electrode:

[0209] The composite positive electrode material C1 and the composite positive electrode material C2 were respectively mixed with acetylene black and polyvinylidene fluoride in a mass ratio of 85:7:8, and an appropriate amount of N-methylpyrrolidone was added and stirred so that the mass content of the slurry was 62%, thereby obtaining corresponding positive electrode slurries C1 and positive electrode slurries C2; the positive electrode slurries C1 and positive electrode slurries C2 were uniformly coated on an aluminum foil current collector in turn to form a first active material layer with a thickness of 110 μm and a second active material layer with a thickness of 120 μm, thereby obtaining a positive electrode sheet.

[0210] Example 4

[0211] The method of Example 1 was followed, except that the precursor bamboo powder was replaced by the precursor bamboo powder.

[0212] Finally, composite positive electrode material D1, composite positive electrode material D2 and positive electrode sheet were prepared.

[0213] Among them, the composite positive electrode material D1 has a core-shell structure with an average particle size of 225nm, the average particle size of the core NCM523 is 150nm, and the average thickness of the outer shell bamboo-based carbon material is 2 times 75nm.

[0214] The infrared spectrum of the bamboo-based carbon material in the shell of the composite cathode material D1 is as follows Figure 3 shown.

[0215] The composite cathode material D2 has a core-shell structure with an average particle size of 190 nm, an average particle size of the core NCM523 of 150 nm, and a value twice the average thickness of the outer shell bamboo-based carbon material of 40 nm.

[0216] Example 5

[0217] The method of Example 1 was followed, except that trimethyl phosphate was replaced with trimethyl borate, to finally prepare composite positive electrode material E1, composite positive electrode material E2, and positive electrode sheet.

[0218] Among them, the composite positive electrode material E1 has a core-shell structure with an average particle size of 225nm, the average particle size of the core NCM523 is 150nm, and the average thickness of the outer shell bamboo-based carbon material is 2 times 75nm.

[0219] The composite cathode material E2 has a core-shell structure with an average particle size of 190 nm, an average particle size of the core NCM523 of 150 nm, and a value twice the average thickness of the outer shell bamboo-based carbon material of 40 nm.

[0220] Example 6

[0221] 1. Preparation of composite cathode material F1:

[0222] Preparation of S1 bamboo-based carbon F1: 5g of precursor bamboo powder was placed in a hydrogen and oxygen mixed gas with a volume ratio of 2:1, the pressure was set to 0.1Mpa, 3mL of trimethyl phosphate was added as a protective reagent, and the temperature was raised from room temperature to 275℃ at a rate of 3℃ / min, and kept warm for 3h to carbonize the precursor powder and retain the aromatic groups in the precursor. Then it was cooled to room temperature to obtain bamboo-based carbon F1.

[0223] S2 mixed the above-mentioned bamboo-based carbon F1 and the ternary positive electrode material NCM523 in 10 mL of ethanol solvent at a mass ratio of 3:97, stirred for 3 hours, filtered and dried, and then carbonized and coated at 325°C for 3.58 hours to prepare the composite positive electrode material F1.

[0224] The composite cathode material F1 has a core-shell structure with an average particle size of 200 nm, an average particle size of the core NCM523 of 150 nm, and a value twice the average thickness of the outer shell bamboo-based carbon material of 50 nm.

[0225] 2. Preparation of composite cathode material F2:

[0226] Preparation of S1 bamboo-based carbon F2: same as the preparation of bamboo-based carbon F1.

[0227] S2 mixed the above-mentioned bamboo-based carbon F2 and the ternary positive electrode material NCM523 in a mass ratio of 2:98 in 10 mL of ethanol solvent, stirred for 3 hours, filtered and dried, and then carbonized and coated at 300°C for 3.25 hours to prepare a composite positive electrode material F2.

[0228] The composite cathode material F2 has a core-shell structure with an average particle size of 185 nm, an average particle size of the core NCM523 of 150 nm, and a value twice the average thickness of the outer shell bamboo-based carbon material of 35 nm.

[0229] 3. Preparation of positive electrode sheet:

[0230] The composite positive electrode material F1 and the composite positive electrode material F2 were respectively mixed with acetylene black and polyvinylidene fluoride in a mass ratio of 85:7:8, and N-methylpyrrolidone was added and stirred so that the mass content of the slurry was 62%, thereby obtaining corresponding positive electrode slurries F1 and F2; the positive electrode slurries F1 and F2 were uniformly coated on an aluminum foil current collector in turn to form a first active material layer with a thickness of 110 μm and a second active material layer with a thickness of 120 μm, thereby obtaining a positive electrode sheet.

[0231] Example 7

[0232] 1. Preparation of composite cathode material G1:

[0233] Preparation of S1 bamboo-based carbon G1: 5g of precursor bamboo powder was placed in a hydrogen and oxygen mixed gas with a volume ratio of 2:1, the pressure was set to 0.1Mpa, 3mL of trimethyl phosphate was added as a protective reagent, and the temperature was raised from room temperature to 275℃ at a rate of 3℃ / min, and kept warm for 3h to carbonize the precursor powder and retain the aromatic groups in the precursor. Then it was cooled to room temperature to obtain bamboo-based carbon G1.

[0234] S2: The bamboo-based carbon G1 and the ternary positive electrode material NCM523 were mixed in 10 mL of ethanol solvent at a mass ratio of 3:97, mixed and stirred for 3 hours, filtered and dried, and then carbonized and coated at 325°C for 5 hours to prepare the composite positive electrode material G1.

[0235] The composite positive electrode material G1 has a core-shell structure with an average particle size of 250 nm, an average particle size of the core NCM523 of 150 nm, and a value twice the average thickness of the outer shell bamboo-based carbon material of 100 nm.

[0236] 2. Preparation of composite cathode material G2:

[0237] Preparation of S1 bamboo-based carbon G2: same as the preparation of bamboo-based carbon G1.

[0238] S2 mixed the above-mentioned bamboo-based G2 and the ternary positive electrode material NCM523 in a mass ratio of 4:96 in 10 mL of ethanol solvent, stirred for 3 hours, filtered and dried, and then carbonized and coated at 300°C for 3.58 hours to prepare a composite positive electrode material G2.

[0239] The composite positive electrode material G2 has a core-shell structure with an average particle size of 200 nm, an average particle size of the core NCM523 of 150 nm, and a value twice the average thickness of the outer shell bamboo-based carbon material of 50 nm.

[0240] 3. Preparation of positive electrode sheet:

[0241] The composite positive electrode material G1 and the composite positive electrode material G2 were respectively mixed with acetylene black and polyvinylidene fluoride in a mass ratio of 85:7:8, and then N-methylpyrrolidone was added and stirred so that the mass content of the slurry was 62%, thereby obtaining corresponding positive electrode slurries G1 and positive electrode slurries G2; the positive electrode slurries G1 and G2 were uniformly coated on an aluminum foil current collector in turn to form a first active material layer with a thickness of 110 μm and a second active material layer with a thickness of 120 μm, thereby obtaining a positive electrode sheet.

[0242] Example 8

[0243] 1. Preparation of composite positive electrode material H1: the same as the preparation of composite positive electrode material F1 in Example 6;

[0244] 2. Preparation of composite positive electrode material H2: the same as the preparation of composite positive electrode material G2 in Example 7;

[0245] 3. Preparation of positive electrode sheet: The composite positive electrode material H1 and the composite positive electrode material H2 were respectively mixed with acetylene black and polyvinylidene fluoride in a mass ratio of 85:7:8, and N-methylpyrrolidone was added and stirred so that the mass content of the slurry was 62%, thereby obtaining the corresponding positive electrode slurry H1 and positive electrode slurry H2; the positive electrode slurry H1 and the positive electrode slurry H2 were uniformly coated on the aluminum foil current collector in turn to form a first active material layer with a thickness of 110 μm and a second active material layer with a thickness of 120 μm, thereby obtaining a positive electrode sheet.

[0246] Example 9

[0247] 1. Preparation of composite cathode material I1:

[0248] Preparation of S1 bamboo-based carbon I1: 5g of precursor bamboo powder was placed in a hydrogen and oxygen mixed gas with a volume ratio of 2:1, the pressure was set to 0.1Mpa, 3mL of trimethyl phosphate was added as a protective reagent, and the temperature was raised from room temperature to 500℃ at a rate of 3℃ / min, and kept warm for 3h to carbonize the precursor powder and retain the aromatic groups in the precursor. Then it was cooled to room temperature to obtain bamboo-based carbon I1.

[0249] S2 mixed the above-mentioned bamboo-based carbon I1 and the ternary positive electrode material NCM523 in a mass ratio of 3:97 in 10 mL of ethanol solvent, stirred for 3 hours, filtered and dried, and then carbonized and coated at 550°C for 4.2 hours to prepare the composite positive electrode material I1.

[0250] The composite positive electrode material I1 has a core-shell structure with an average particle size of 230 nm, an average particle size of the core NCM523 of 150 nm, and a value twice the average thickness of the outer shell bamboo-based carbon material of 80 nm.

[0251] 2. Preparation of composite cathode material I2:

[0252] Preparation of S1 bamboo-based carbon I2: same as the preparation of bamboo-based carbon I1.

[0253] S2 mixed the above-mentioned bamboo-based carbon I2 and the ternary positive electrode material NCM523 in 10 mL of ethanol solvent at a mass ratio of 3:97, stirred for 3 hours, filtered and dried, and then carbonized and coated at 300°C for 3.55 hours to prepare a composite positive electrode material I2.

[0254] The composite positive electrode material I2 has a core-shell structure with an average particle size of 195nm, the average particle size of the core NCM523 is 150nm, and the average thickness of the outer shell bamboo-based carbon material is twice 45nm.

[0255] 3. Preparation of positive electrode sheet:

[0256] The composite positive electrode material I1 and the composite positive electrode material I2 were respectively mixed with acetylene black and polyvinylidene fluoride in a mass ratio of 85:7:8, and then N-methylpyrrolidone was added and stirred so that the mass content of the slurry was 62%, thereby obtaining the corresponding positive electrode slurry I1 and positive electrode slurry I2; the positive electrode slurry I1 and the positive electrode slurry I2 were uniformly coated on the aluminum foil current collector in turn to form a first active material layer with a thickness of 110 μm and a second active material layer with a thickness of 120 μm, thereby obtaining a positive electrode sheet.

[0257] Example 10

[0258] 1. Preparation of composite positive electrode material J1: the same as the preparation of composite positive electrode material A1 in Example 1.

[0259] 2. Preparation of composite positive electrode material J2: the same as the preparation of composite positive electrode material A2 in Example 1.

[0260] The composite positive electrode material J1 and the composite positive electrode material J2 were respectively mixed with acetylene black and polyvinylidene fluoride in a mass ratio of 85:7:8, and N-methylpyrrolidone was added and stirred so that the mass content of the slurry was 62%, thereby obtaining the corresponding positive electrode slurry J1 and positive electrode slurry J2; the positive electrode slurry J2 and the positive electrode slurry J1 were uniformly coated on the aluminum foil current collector in turn to form a first active material layer with a thickness of 110 μm and a second active material layer with a thickness of 120 μm to obtain a positive electrode sheet.

[0261] Comparative Example 1

[0262] 1. Preparation of composite cathode material K:

[0263] Commercial carbon material (conductive carbon black Super P) and ternary cathode material NCM523 were mixed in 10 mL of ethanol solvent at a ratio of 3:97, stirred for 3 h, filtered and dried, and then carbonized and coated at 325 °C for 4 h to prepare composite cathode material I.

[0264] The composite cathode material K has a core-shell structure with an average particle size of 225 nm, an average particle size of the core NCM523 of 150 nm, and a value twice the average thickness of the shell carbon material of 75 nm.

[0265] 2. Preparation of positive electrode sheet:

[0266] The composite positive electrode material K, acetylene black and polyvinylidene fluoride were mixed in a mass ratio of 85:7:8, and N-methylpyrrolidone was added and stirred so that the mass content of the slurry was 62%. The positive electrode slurry was stirred to form a positive electrode slurry. The positive electrode slurry was evenly coated on an aluminum foil current collector to form an active material layer with a thickness of 230 μm to obtain a positive electrode sheet.

[0267] Comparative Example 2

[0268] 1. Preparation of composite cathode material L1:

[0269] Preparation of S1 bamboo-based carbon L1: 5g of precursor bamboo powder was placed under nitrogen gas conditions with the pressure set to 0.1Mpa, 3mL of trimethyl phosphate was added as a protective reagent, and the temperature was raised from room temperature to 275℃ at a rate of 3℃ / min, and kept warm for 3h to carbonize the precursor powder and retain the aromatic groups in the precursor. Then, it was cooled to room temperature to obtain bamboo-based carbon L1.

[0270] S2: The bamboo-based carbon L1 and the ternary positive electrode material NCM523 are mixed in 10 mL of ethanol solvent at a mass ratio of 3:97. After mixing and stirring for 3 hours, the mixture is filtered and dried, and then carbonized and coated at 325°C for 4 hours to prepare the composite positive electrode material L1.

[0271] The composite positive electrode material L1 has a core-shell structure with an average particle size of 225 nm, an average particle size of the core NCM523 of 150 nm, and a value twice the average thickness of the outer shell bamboo-based carbon material of 75 nm.

[0272] 2. Preparation of composite cathode material L2:

[0273] Preparation of S1 bamboo-based carbon L2: same as the preparation of bamboo-based carbon L1.

[0274] S2 mixed the above-mentioned bamboo-based carbon L2 and the ternary positive electrode material NCM523 in 10 mL of ethanol solvent at a mass ratio of 3:97, stirred for 3 hours, filtered and dried, and then carbonized and coated at 300°C for 3.5 hours to prepare a composite positive electrode material L2.

[0275] The composite positive electrode material L2 has a core-shell structure with an average particle size of 190 nm, an average particle size of the core NCM523 of 150 nm, and a value twice the average thickness of the outer shell bamboo-based carbon material of 40 nm.

[0276] 3. Preparation of positive electrode sheet:

[0277] The composite positive electrode material L1 and the composite positive electrode material L2 were respectively mixed with acetylene black and polyvinylidene fluoride in a mass ratio of 85:7:8, and then N-methylpyrrolidone was added and stirred so that the mass content of the slurry was 62%, thereby obtaining the corresponding positive electrode slurry L1 and positive electrode slurry L2; the positive electrode slurry L1 and the positive electrode slurry L2 were uniformly coated on the aluminum foil current collector in turn to form a first active material layer with a thickness of 110 μm and a second active material layer with a thickness of 120 μm to obtain a positive electrode sheet.

[0278] Comparative Example 3

[0279] 1. Preparation of composite cathode material M1:

[0280] Preparation of S1 bamboo-based carbon M1: 5g of precursor bamboo powder was placed in a hydrogen-oxygen mixed gas with a volume ratio of 2:1, the pressure was set to 0.1Mpa, and the temperature was raised from room temperature to 275℃ at a rate of 3℃ / min, and kept warm for 3h to carbonize the precursor powder and retain the aromatic groups in the precursor. It was then cooled to room temperature to obtain bamboo-based carbon M1.

[0281] S2: The bamboo-based carbon M1 and the ternary positive electrode material NCM523 are mixed in 10 mL of ethanol solvent at a mass ratio of 3:97. After mixing and stirring for 3 hours, the mixture is filtered and dried, and then carbonized and coated at 325°C for 4 hours to prepare the composite positive electrode material M1.

[0282] The composite positive electrode material M1 has a core-shell structure with an average particle size of 225 nm, an average particle size of the core NCM523 of 150 nm, and a value twice the average thickness of the outer shell bamboo-based carbon material of 75 nm.

[0283] 2. Preparation of composite cathode material M2:

[0284] Preparation of S1 bamboo-based carbon M2: same as the preparation of bamboo-based carbon M1.

[0285] S2 mixed the above-mentioned bamboo-based carbon M2 and the ternary positive electrode material NCM523 in a mass ratio of 3:97 in 10 mL of ethanol solvent, stirred for 3 hours, filtered and dried, and then carbonized and coated at 300°C for 3.5 hours to prepare a composite positive electrode material M2.

[0286] The composite positive electrode material M2 has a core-shell structure with an average particle size of 190 nm, an average particle size of the core NCM523 of 150 nm, and a value twice the average thickness of the outer shell bamboo-based carbon material of 40 nm.

[0287] 3. Preparation of positive electrode sheet:

[0288] The composite positive electrode material M1 and the composite positive electrode material M2 were respectively mixed with acetylene black and polyvinylidene fluoride in a mass ratio of 85:7:8, and then N-methylpyrrolidone was added and stirred so that the mass content of the slurry was 62%, thereby obtaining the corresponding positive electrode slurry M1 and positive electrode slurry M2; the positive electrode slurry M1 and the positive electrode slurry M2 were uniformly coated on the aluminum foil current collector in turn to form a first active material layer with a thickness of 110 μm and a second active material layer with a thickness of 120 μm, thereby obtaining a positive electrode sheet.

[0289] The porosity and specific surface area of ​​the composite cathode materials in Examples 1-7, Example 9, and Comparative Examples 1-3, as well as the mass content of aromatic groups, the mass content of hydroxyl groups, and the mass content of quinone groups in the outer shell of the composite cathode materials, were tested. The test results are shown in Table 1.

[0290] Table 1

[0291]

[0292]

[0293] Performance Testing

[0294] 1. The positive electrode sheets and negative electrode sheets in Examples 1-10 and Comparative Examples 1-3 were combined to prepare batteries.

[0295] The negative electrode sheet preparation method is as follows: graphite, acetylene black, binder PVDF5130 and thickener CMC MAC500 are stirred with deionized water in a mass ratio of 96:2:1:1 to prepare a negative electrode slurry with a mass content of 62%, the negative electrode slurry is evenly coated on a copper foil current collector, and the negative electrode sheet is obtained by cold pressing and slicing.

[0296] Preparation of the battery: The positive electrode sheet, the negative electrode sheet and the PE base film are wound together, hot pressed, packaged and dried, and then a commercial electrolyte is injected. Then, steps including aging are carried out to prepare the battery.

[0297] 2. Test the battery containing the positive electrode sheets of Examples 1-10 and Comparative Examples 1-3

[0298] (1) Cycle test: At 25±2°C, charge the battery to 3.65V at 1C constant current and constant voltage, with a cut-off current of 0.05C; let it stand for 30 minutes, and then discharge it to 2.5V at 1C. Continue the above process and record the capacity C0 after the first charge. At the same time, record the capacity C500 of the battery after 500 cycles. The capacity retention rate of the battery after 500 cycles is calculated as C500 / C0*100%.

[0299] (2) First coulombic efficiency test: Charge the battery to 3.65V at 1C constant current and constant voltage, with a cut-off current of 0.05C; let it stand for 30 minutes, then discharge it to 2.5V at 1C to obtain the discharge capacity C0; then charge it to 3.65V at 1C constant current and constant voltage, with a cut-off current of 0.05C to obtain the charging capacity C1. Calculate the first coulombic efficiency = C0 / C1*100%.

[0300] The test results are shown in Table 2 below.

[0301] Table 2

[0302]

[0303]

[0304] From Table 1 and Table 2, it can be seen that the composite positive electrode material of the present invention has a core-shell structure, and the shell includes a bamboo-based carbon material, which contains aromatic groups, so that the battery made of the composite positive electrode material has the first coulombic efficiency and cycle performance. The main reason is that the bamboo-based carbon material in the present invention has a rich pore structure and specific surface area, which can promote the transmission and diffusion of lithium ions and improve the charge and discharge performance of the battery; and the bamboo-based carbon material containing a skeleton structure constructed by aromatic groups can form a strong interaction with the core, enhance the interfacial bonding force between the two, make the structure of the composite positive electrode material more stable, which is conducive to maintaining structural integrity during the charge and discharge process and improving the cycle performance of the battery; at the same time, the aromatic group has a conjugated π electron system, which can enable the composite positive electrode material to maintain a higher capacity, and the capacity retention rate can be increased by 10-20% compared with the single core material; in addition, the aromatic group has a certain chemical activity and can react with some components in the electrolyte to form a more stable and dense solid electrolyte interface (SEI) film on the surface of the composite positive electrode material. This SEI film can prevent the electrolyte from further reacting with the core, reduce the consumption of active lithium, and thus improve the coulombic efficiency of the battery.

[0305] Parts of the present invention that are not described in detail are well known to those skilled in the art.

[0306] The basic principles of the present invention have been described above in conjunction with specific embodiments. However, it should be noted that the advantages, strengths, and effects mentioned in the present invention are merely illustrative and non-limiting, and should not be construed as necessarily possessed by each embodiment of the present invention. Furthermore, the specific details disclosed above are provided for illustrative purposes and to facilitate understanding, and are not intended to be limiting. These details do not necessarily limit the present invention to being implemented using these specific details.

[0307] It should be noted that the terms "and / or" or " / " used herein are merely a description of an association relationship between associated objects, indicating that three relationships may exist. For example, A and / or B may represent three situations: A exists alone, A and B exist at the same time, and B exists alone. The singular forms "a," "the," and "the" used in the embodiments of the present invention and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0308] In the detailed description and claims, a list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements.

[0309] 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 aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A composite positive electrode material, characterized in that The composite positive electrode material has a core-shell structure, including a core and an outer shell; wherein the core comprises a ternary material, the shell covers at least a portion of the core, and the shell comprises a bamboo-based carbon material; The bamboo-based carbon material contains aromatic groups.

2. The composite cathode material according to claim 1, characterized in that Based on the mass of the bamboo-based carbon material, the mass content of the aromatic groups is 12%-16%; and / or, The aromatic group includes a phenyl group; and / or, The bamboo-based carbon material also contains hydroxyl groups and / or quinone groups; Preferably, Based on the total mass of the aromatic groups, the mass content of the hydroxyl groups is 8%-12%; and / or, Based on the total mass of the aromatic groups, the mass content of the quinone groups is 10%-15%.

3. The composite cathode material according to claim 1 or 2, characterized in that The composite positive electrode material satisfies at least one of the following characteristics: (1) The porosity of the composite positive electrode material is 60%-80%; (2) The specific surface area of ​​the composite positive electrode material is 200-1000m 2 / g, preferably 700-950m 2 / g; (3) The electrical conductivity of the composite positive electrode material is 10-100 S / cm, preferably 90-100 S / cm; (4) The average particle size of the composite positive electrode material is 150nm-300nm; (5) The average particle size of the core is 130nm-200nm; (6) The average thickness of the shell is 10 nm to 50 nm; (7) The ternary material includes a nickel-based ternary material; Preferably, the nickel-based ternary material includes a nickel-cobalt-manganese ternary positive electrode active material and / or a nickel-cobalt-aluminum ternary positive electrode active material.

4. A method for preparing a composite positive electrode material, characterized in that: The preparation method comprises: S1. In the presence of a mixed gas containing reducing gas and oxygen and an ester compound, carbonizing a bamboo-based precursor to obtain bamboo-based carbon; S2, mixing the bamboo-based carbon and the ternary material in the presence of a solvent, and then drying and carbonizing and coating to obtain the composite positive electrode material; The composite positive electrode material has a core-shell structure, including a core and an outer shell, wherein the core contains a ternary material, and the outer shell covers at least a portion of the core, and the outer shell includes a bamboo-based carbon material; the bamboo-based carbon material contains aromatic groups.

5. The method for preparing a composite positive electrode material according to claim 4, wherein: The temperature of carbonization in step S1 and the temperature of carbonization coating in step S2 are independently 200-400°C; Preferably, the temperature of carbonization in step S1 is lower than the temperature of carbonization and coating in step S2; preferably, the difference between the temperature of carbonization in step S1 and the temperature of carbonization and coating in step S2 is 30-100°C; and / or, In step S1, the carbonization conditions include: pressure of 0.05-0.2 MPa, temperature of 200-350° C., and time of 2-5 h; and / or, In step S2, the carbonization coating conditions include: temperature of 250-400°C and time of 3-6 hours.

6. The method for preparing a composite cathode material according to claim 4, wherein: The ester compound includes at least one of phosphate, borate and carboxylate, preferably includes phosphate, preferably the phosphate includes at least one of trimethyl phosphate, triethyl phosphate and tripropyl phosphate, preferably includes trimethyl phosphate; and / or, In the mixed gas, the volume ratio of reducing gas to oxygen is 1.5-4:1; and / or, The reducing gas includes hydrogen; and / or, The ternary material includes a nickel-based ternary material, preferably the nickel-based ternary material includes a nickel-cobalt-manganese ternary positive electrode active material and / or a nickel-cobalt-aluminum ternary positive electrode active material; and / or, The bamboo-based precursor is derived from at least one of moso bamboo, bitter bamboo, bamboo shoots and bamboo, preferably moso bamboo; and / or The solvent includes an alcohol solvent; preferably, the alcohol solvent includes at least one of methanol, ethanol or ethylene glycol; and / or, In step S1, the mass ratio of the ester compound to the bamboo-based precursor is 1:0.8-2.5, preferably 1:1-1.5; and / or, In step S2, the mass of the bamboo-based carbon is 1%-15% of the mass of the ternary material, preferably 2%-5%.

7. A positive electrode sheet, characterized in that: The device comprises a current collector, wherein a first active material layer is provided on at least one side of the current collector, and a second active material layer is provided on a surface of the first active material layer away from the current collector; Wherein, the first active material layer and the second active material layer each independently contain the composite positive electrode material according to any one of claims 1 to 3 or the composite positive electrode material prepared by the preparation method according to any one of claims 4 to 6.

8. The positive electrode sheet according to claim 7, characterized in that: The average thickness of the outer shell of the composite positive electrode material in the first active material layer is recorded as T1, and the average thickness of the outer shell of the composite positive electrode material in the second active material layer is recorded as T2, and T1 and T2 satisfy: T1 is greater than T2; Preferably, The difference between the values ​​of T1 and T2 is 5 nm to 40 nm, preferably 10 nm to 30 nm; and / or, The T1 is 15nm-50nm; and / or, The T2 is 10nm-30nm.

9. The positive electrode sheet according to claim 7, characterized in that: The thickness of the first active material layer and the thickness of the second active material layer are each independently 100 μm to 150 μm; and / or, The first active material layer and the second active material layer each independently contain a conductive agent and a binder; and / or, The mass content of the composite positive electrode material in the first active material layer and the second active material layer is independently greater than 80%.

10. A battery, characterized in that: The invention comprises a negative electrode sheet and a positive electrode sheet as claimed in any one of claims 7 to 9.

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