Polyimide material and use thereof

Abstract

A polyimide material and a use thereof. The repeating unit of the polyamide material comprises a specific dianhydride residue and a specific diamine residue, which can ensure that the polyamide material has a porous structure having a pore diameter of less than or equal to 2 nm. The polyamide material is particularly suitable for coating a lithium battery negative electrode active material having a large volume expansion effect, and does not reduce the dynamic performance thereof.

Description

Polyimide materials and their applications

[0001] This application claims priority to the Chinese patent application filed with the State Intellectual Property Office of China on January 31, 2024, with application number 202410144465.8 and application name “Polyimide Materials and Their Applications”, the entire contents of which are incorporated herein by reference. Technical Field

[0002] The present application relates to the field of battery technology, and in particular to a polyimide material and its application. Background Art

[0003] Silicon-based materials have a higher theoretical specific capacity than commercial graphite anode materials and are highly promising anode materials for next-generation, high-energy-density lithium-ion batteries. However, during the lithium extraction and insertion process, silicon-based materials undergo dramatic volume expansion and contraction, leading to particle breakage and pulverization, which in turn results in battery capacity degradation and reduced cycle performance.

[0004] In order to alleviate the volume expansion of silicon-based materials and the related problems it brings, the common practice in the industry is to construct an inorganic carbon coating layer or a polymer coating layer on the surface of the silicon-based material. However, the toughness of the inorganic carbon coating layer is poor, and it will crack or even fall off under the continuous volume change of the silicon-based material, losing its protective effect; and although the toughness of the existing polymer coating material is better than that of the inorganic carbon material, its ion conductivity is poor, and its dense coating on the surface of the silicon-based material will significantly increase the resistance to lithium ion insertion and deinsertion, affecting the specific capacity and rate performance of the silicon-based material. Therefore, it is necessary to provide a coating material and its application that can effectively inhibit the volume expansion of silicon-based materials without reducing their electrochemical performance. Summary of the Invention

[0005] In view of this, an embodiment of the present application provides a polyimide material and its application. The specific structure of the polyimide material can ensure that it has a porous structure with small pores. The polyimide material is particularly suitable for coating negative electrode active materials (such as silicon-based materials) with large volume expansion effects, and can solve the problem that existing coating schemes for negative electrode active materials cannot effectively inhibit their volume expansion without reducing their electrochemical performance.

[0006] In a first aspect, an embodiment of the present application provides a polyimide material, wherein the polyimide material comprises a repeating unit as shown below:

[0007] Wherein, R1 is selected from one or more dianhydride residues represented by the following formulas (I-1) to (I-11):

[0008] R2 is selected from one or more diamine residues represented by the following formulas (II-1) to (II-12):

[0009] wherein each occurrence of R is independently selected from a halogen atom, or a substituted or unsubstituted alkyl group; each occurrence of Z is independently selected from one of an oxygen atom, a sulfur atom, a selenium atom, -C(=O)-, -S(=O)-, and -S(=O)2-; * represents a linking site;

[0010] The polyimide material has a porous structure with a pore diameter less than or equal to 2 nm.

[0011] When R1 and R2 in the repeating units of the above-mentioned polyimide material are selected from the above-mentioned groups, a rigid "twisted center" structure can be introduced into the polyimide molecular chain, so that it has micropores with a size of less than 2 nm, while ensuring that the material has high mechanical strength and modulus. When the polyimide material is used as a coating layer material for coating electrode active materials or lithium supplements in lithium-ion batteries, it can ensure that the coating layer is not easy to break and can better withstand the volume changes of the core material without affecting the electrochemical properties of the core.

[0012] In the embodiment of the present application, the specific surface area of ​​the polyimide material is greater than or equal to 80m 2 / g. The specific surface area of ​​the polyimide material with a pore size below 2nm is controlled at 80m 2 / g or more, which can ensure that the material has enough micropores. When it is used as a coating material, it will not significantly increase the deintercalation and extraction of Li from the core material. + resistance, which will not affect the electrochemical performance of the core material.

[0013] In some embodiments of the present application, the specific surface area of ​​the polyimide material is 80-800m 2 This ensures that the polyimide material, when used as a coating material, will not significantly increase the resistance of the coated core material to the insertion and removal of lithium ions, nor will it reduce the compaction density of the composite material.

[0014] In the embodiment of the present application, the weight average molecular weight of the polyimide material is in the range of 10,000 to 1,000,000. This helps ensure that the polyimide material has good solubility in organic solvents, thereby having better film-forming properties, and can ensure that the material has suitable tensile strength, etc., so that the material can better withstand the volume changes of the core material when used as a coating material.

[0015] A second aspect of the present invention provides the use of the polyimide material described in the first aspect of the present invention for coating negative electrode active materials, coating positive electrode active materials, coating lithium supplements, and preparing electrode binders. In particular, the polyimide material is particularly suitable for coating negative electrode active materials with large volume expansion effects. The negative electrode active materials include one or more of silicon-based materials, phosphorus-based materials, and tin-based materials.

[0016] A third aspect of an embodiment of the present application provides a composite negative electrode material, comprising a core and a coating layer coated on the core, wherein the core comprises a silicon-based material, and the coating layer comprises the polyimide material described in the first aspect of the present application.

[0017] The above-mentioned composite negative electrode material adopts the above-mentioned polyimide material with a specific structure and pores with a pore size of less than 2nm as the coating layer of the silicon-based material. The coating layer has good toughness, which can effectively and durably alleviate the volume expansion of the silicon-based material, inhibit its side reaction with the electrolyte, and ensure the battery's good cycle performance; and the presence of pores with a pore size of less than 2nm in the polyimide material allows lithium ions to be smoothly embedded / ejected from the coating layer, without affecting the rate performance and gram capacity of the core silicon-based material, thereby ensuring the good electrochemical performance of the overall composite negative electrode material.

[0018] In embodiments of the present application, the mass of the coating layer accounts for 0.5%-8% of the total mass of the composite negative electrode material. Controlling the mass proportion of the coating layer within this range can ensure a high gram capacity of the overall composite negative electrode material and help ensure an appropriate thickness and high degree of coating of the coating layer. In some embodiments of the present application, the mass of the coating layer accounts for 1%-5% of the total mass of the composite negative electrode material.

[0019] In the embodiment of the present application, the coating layer has a thickness of 5 nm to 50 nm. The coating layer has an appropriate thickness to ensure that it has a good protection effect on the core material and an effect of suppressing volume expansion, while not excessively affecting the electrochemical performance of the core material.

[0020] In the embodiment of the present application, any area of ​​the surface of the coating layer is 1 μm 2 In the selected area, the coverage of the polyimide material is greater than or equal to 90%. This indicates that the polyimide material has a high degree of coating on the core. Its complete coating on the surface of the silicon-based material can better suppress the volume expansion of the core material and the occurrence of side reactions between the core material and the electrolyte. In addition, when the coating layer has a high degree of coverage, the pores with a diameter of less than 2 nm in the coating layer can reduce the resistance of lithium ions passing through the coating layer.

[0021] In the embodiment of the present application, the elongation at break of the coating layer is greater than 10% and the fracture strength of the coating layer is greater than 50 MPa. These physical properties reflect that the coating layer has good mechanical strength, especially good toughness.

[0022] In an embodiment of the present application, the silicon-based material includes one or more of elemental silicon, silicon alloy, silicon oxide, and silicon-carbon composite material; wherein the silicon-carbon composite material includes a complex of at least one of the elemental silicon, silicon alloy, silicon oxide and carbon material.

[0023] In the embodiment of the present application, the particle size of the silicon-based material is 1 μm-20 μm. The silicon-based material has a suitable particle size to ensure that the diffusion path of lithium ions in it is not too long and the compaction density is high.

[0024] In the embodiment of the present application, the specific capacity of the composite negative electrode material is substantially the same as that of the uncoated silicon-based material. This indicates that the polyimide material used to coat the core of the present application improves the cycling performance while not affecting the capacity of the core silicon-based material.

[0025] A fourth aspect of the present invention provides a method for preparing a composite negative electrode material, comprising the following steps:

[0026] adding the polyimide material described in the first aspect of the present application to a solvent to obtain a polymer solution;

[0027] Mixing the core material with the polymer solution to obtain a mixed slurry; wherein the core material includes a silicon-based material;

[0028] The solvent in the mixed slurry is removed, so that a coating layer containing the polyimide material is formed on the surface of the core material to obtain a composite negative electrode material.

[0029] The composite negative electrode material is prepared by the above preparation method, which has a simple process, is easy to operate, and is suitable for large-scale production. The obtained composite negative electrode material has high structural stability and good electrochemical performance.

[0030] In some embodiments of the present application, the solvent is removed by spray drying. Spray drying the mixed slurry containing the core material and the coating layer material can produce a core-shell composite negative electrode material with better coating effect, which is more suitable for large-scale preparation.

[0031] The fifth aspect of the embodiment of the present application provides a negative electrode plate, which includes a current collector and a negative electrode active material layer arranged on at least one side of the current collector, and the negative electrode active material layer includes the composite negative electrode material described in the fourth aspect of the embodiment of the present application.

[0032] The negative electrode plate adopts the composite negative electrode material as the negative electrode active material. During the battery cycle, the expansion of the plate is suppressed, and the negative electrode plate particles are not easy to pulverize and fall off the plate.

[0033] A sixth aspect of the present application provides a lithium battery comprising a positive electrode plate and the negative electrode plate described in the fifth aspect of the present application. Because the lithium battery utilizes the composite negative electrode material described in the present application, its cycle performance is improved without significantly reducing its capacity, and it can effectively meet the requirements of consumer electronic devices, power vehicles, and the like for lithium batteries with long cycle life and high energy density.

[0034] In a seventh aspect, embodiments of the present application provide an electrical device comprising an electrical component and a power supply component, wherein the power supply component supplies power to the electrical component, and the power supply component comprises the lithium battery described in the sixth aspect of embodiments of the present application. By using the lithium battery provided in embodiments of the present application to power the electrical device, the user experience and market competitiveness of the electrical device can be improved.

[0035] The power-consuming device includes an electronic device or a power-mobile device. In some embodiments, the electronic device includes a housing and the lithium battery and circuit board assembly housed within the housing. The electronic device may be, for example, a mobile phone, a tablet computer, or a wearable electronic device.

[0036] An eighth aspect of the present application provides an energy storage system, comprising at least one battery pack and a battery management system electrically connected to the battery pack, wherein the battery pack includes a plurality of lithium batteries as described in the sixth aspect of the present application. The lithium batteries used in the energy storage system have good cycle performance and rate performance, and a high energy density, thereby enhancing the energy storage characteristics of the energy storage system. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] FIG1 is a schematic structural diagram of a composite negative electrode material provided in an embodiment of the present application.

[0038] FIG2 is a schematic structural diagram of a negative electrode plate provided in an embodiment of the present application.

[0039] FIG3 is a schematic structural diagram of a lithium battery provided in an embodiment of the present application.

[0040] FIG4 is a schematic structural diagram of an electronic device provided in an embodiment of the present application.

[0041] FIG5 is a schematic structural diagram of a power moving device provided in an embodiment of the present application.

[0042] FIG6 is a schematic structural diagram of an energy storage system provided in an embodiment of the present application.

[0043] Figure 7 summarizes the transmission electron microscope photos of the uncoated silicon-carbon composite material (a, c) of Comparative Example 1 and the composite negative electrode material (b, d) prepared in Example 1; wherein, sub-image c is an enlarged view of the selected area in Figure a, and sub-image d is an enlarged view of the selected area in Figure b.

[0044] FIG8 summarizes the thermogravimetric curves of the uncoated silicon-carbon composite material of Comparative Example 1 and the composite negative electrode material prepared in Example 2.

[0045] FIG9 summarizes the first charge and discharge curves of the button-type batteries of Example 3 and Comparative Example 1.

[0046] FIG10 summarizes the cycle performance curves of the button-type batteries of Example 1 and Comparative Example 1; wherein the horizontal axis is the number of cycles, and the vertical axis is the lithium removal capacity retention rate at each number of cycles.

[0047] FIG11 summarizes the rate performance curves of the button cells of Example 1 and Comparative Examples 1-2. DETAILED DESCRIPTION

[0048] The embodiments of the present application will be described below with reference to the accompanying drawings.

[0049] Compared to graphite, silicon-based materials have a higher theoretical specific capacity (4200mAh / g vs 372mAh / g). Using silicon-based materials as battery anode materials helps improve battery energy density. However, silicon-based materials undergo significant volume changes during the charge and discharge process, which can have the following negative effects: Silicon-based material particles break and pulverize, causing structural damage to the anode active material layer and even detachment from the electrode sheet, reducing battery capacity. The breakage and pulverization of silicon-based material particles expose fresh interfaces. Continued contact with the electrolyte triggers the formation, destruction, and regeneration of the SEI (solid electrolyte interface) film, increasing the degree of side reactions between the silicon anode material and the electrolyte, leading to electrolyte consumption and loss of active lithium, ultimately resulting in a loss of battery capacity and reduced cycle performance. To mitigate the volume expansion of silicon-based materials, the coated silicon-based materials developed by the industry either fail to effectively suppress the volume expansion of the silicon-based materials over a long period of time or, while suppressing the volume expansion of the silicon-based materials, significantly reduce the specific capacity and rate performance. In view of this, the present application provides a coated composite negative electrode material that can effectively inhibit the volume expansion of silicon-based materials without significantly reducing their electrochemical performance.

[0050] Please refer to Figure 1, which is a schematic diagram of the structure of a composite negative electrode material provided in an embodiment of the present application. The composite negative electrode material 100 includes a core 10 and a coating layer 20 coated on the core 10, wherein the core 10 includes a silicon-based material and the coating layer 20 includes a polyimide material. The polyimide material includes a repeating unit represented by the following formula (i) and has a porous structure with a pore size of less than or equal to 2 nm:

[0051] Wherein, R1 is selected from one or more dianhydride residues represented by the following formulas (I-1) to (I-11):

[0052] R2 is selected from one or more diamine residues represented by the following formulas (II-1) to (II-12):

[0053] Wherein, each occurrence of R is independently selected from a halogen atom, or a substituted or unsubstituted alkyl group, each occurrence of Z is independently selected from one of an oxygen atom (-O-), a sulfur atom (-S-), a selenium atom (-Se-), a carbonyl group (-C(=O)-), a sulfoxide group (-S(=O)-), a sulfone group (-S(=O)2-), and a methylene group (-CH2); * represents a connection site.

[0054] When R1 and R2 in the repeating units of the polyimide are selected from the aforementioned groups, a rigid "twisted center" structure can be introduced into the molecular chain of the polyimide material, resulting in a microporous structure similar to that of a molecular sieve material, with a pore diameter of less than 2 nm. Furthermore, when R1 and R2 are both aliphatic rings or aromatic structures, the polyimide material implemented in this application can have high mechanical strength and modulus similar to conventional polyimide materials.

[0055] Therefore, the coating layer 20 in the present application includes the above-mentioned specific polyimide material, which has the high mechanical strength and good toughness of ordinary polyimide materials and is easy to form a film. It can form a stable coating layer 20 on the surface of the core material to ensure that the coating layer 20 has good toughness and can withstand a large degree of volume expansion and contraction of the silicon-based material during the process of lithium insertion and extraction without being easily damaged, thereby reducing the expansion of the electrode plate and ensuring the stability of the plate structure; and the coating layer 20 that is not easily damaged can permanently and effectively protect the core material, prevent the core material from contacting the electrolyte, and inhibit the side reaction between the two, thereby improving the cycle stability of the silicon-based material core and reducing capacity loss. More importantly, the micropores of the above-mentioned polyimide material with a pore size of less than 2nm can provide lithium ions (Li + ) transmission, the use of polyimide material with such a microporous structure as the material of the coating layer 20 can ensure that Li +It can be embedded / ejected from such a coating layer 20 more smoothly without significantly increasing the intercalation and deintercalation of the core material. + The resistance will not affect the electrochemical properties of the core material, such as the gram capacity and rate performance.

[0056] Therefore, the composite negative electrode material 100 provided in the embodiment of the present application adopts the above-mentioned material with good toughness and Li + The highly permeable, specialized polyimide material used as the coating layer can address the core material's volume expansion without compromising its rate performance and capacity, thereby improving its cycling stability. Furthermore, the use of the coating layer 20 improves the interface properties of the silicon-based material, reducing its specific surface area. Furthermore, the coating layer material exhibits a higher degree of similarity and compatibility with the binder, resulting in a better bonding between the binder and the composite negative electrode material 100.

[0057] In the embodiment of the present application, the specific surface area of ​​the polyimide material is greater than or equal to 80m 2 / g. The specific surface area of ​​the polyimide material with a pore size below 2nm is controlled at 80m 2 / g or more, which can ensure that the material has enough micropores with a pore size of less than 2 nm. Using such polyimide as the material of the coating layer 20 will not significantly increase the core material's Li + In some embodiments of the present application, the specific surface area of ​​the polyimide material can be greater than or equal to 80m 2 / g to less than or equal to 1000m 2 / g. That is, the specific surface area of ​​the polyimide material is 80m 2 / g-1000m 2 The specific surface area of ​​the polyimide material is controlled in an appropriate range, and a high micropore porosity is provided to ensure that the coating layer 20 has sufficient Li + The transmission channel ensures that the rate performance of the composite negative electrode material 100 is good, and the coating density of the core material will not be reduced due to the high specific surface area of ​​the material, thereby ensuring that the side reaction of the core material is low, which is conducive to the overall high cycle performance of the composite negative electrode material 100; in addition, the compaction density of the composite negative electrode material and the battery energy density will not be reduced due to excessive micropores.

[0058] Specifically, the specific surface area of ​​the polyimide material can be, for example, 90 m 2 / g、100m 2 / g, 200m 2 / g、300m 2 / g、350m 2 / g, 400m 2 / g, 450m 2 / g、500m 2 / g, 560m 2 / g、580m 2 / g、600m 2 / g、610m 2 / g、620m 2 / g、650m 2 / g、680m 2 / g、690m 2 / g、700m 2 / g、720m 2 / g、730m 2 / g、740m 2 / g、750m 2 / g、760m 2 / g、780m 2 / g、790m 2 / g, or 795m 2 In some embodiments, the specific area of ​​the polyimide material is 300m 2 / g-800m 2 / g range, which is more conducive to the composite negative electrode material 100 to better balance good rate performance, high compaction density and good cycle performance.

[0059] The specific surface area of ​​the polyimide material can be measured using the nitrogen adsorption method (also known as the "BET method"). For example, an organic solvent can be used to dissolve the outer coating layer 20 of the composite negative electrode material 100 to obtain the coating layer material—the polyimide material—and then perform the BET test on this material. It should be noted that the pores with a diameter of less than 2 nm are micropores inherent in the polyimide material and are not affected by the state of the material.

[0060] Because the polyimide material is present in the coating layer 20, the coating layer 20 of the embodiment of the present application also has micropores with a pore size of less than or equal to 2 nm. In the present application, the pore size of the polyimide material is less than 2 nm, which is much smaller than the gaps formed by the accumulation of conventional coating layer materials or the spacing distance formed by the conventional discontinuous coating of coating layer materials. Conventional gaps allow the electrolyte to enter the core 10 through these gaps, causing side reactions between the core material and the electrolyte, and reducing the cycle performance of the overall composite material. However, the micropores on the coating layer 20 of the embodiment of the present application are smaller in diameter, and the electrolyte will not enter the core 10 through these micropores.

[0061] In the embodiment of the present application, the specific surface area of ​​the composite negative electrode material 100 is 4-20 m 2 / g range, which can ensure that the coating layer 20 can achieve uniform and sufficient coating of the core 10, and the coating layer 20 has sufficient Li + The transmission channel can ensure the good dynamic performance of the composite negative electrode material 100, and can also alleviate the excessive side reaction with the electrolyte caused by the excessive specific surface area of ​​the composite negative electrode material 100, resulting in the decrease of the first efficiency and the deterioration of the cycle performance. Specifically, the specific surface area is, for example, 5m 2 / g、6m 2 / g、8m 2 / g、9m 2 / g、10m 2 / g、11m 2 / g、12m 2 / g、13m 2 / g、14m 2 / g、15m 2 / g、16m 2 / g、18m 2 / g、19m 2 In some embodiments, the specific surface area of ​​the composite negative electrode material 100 is 5-20 m 2 / g range.

[0062] In the present application, fine control of mechanical properties such as toughness, specific area, pore size, etc. of the polyimide material can be achieved by regulating the structures of R1 and R2 and the degree of polymerization of the repeating unit represented by formula (i).

[0063] In the present application, the halogen atoms include one or more of fluorine, chlorine, bromine and iodine. The substituted or unsubstituted alkyl group is a chain alkyl group, which can be a straight chain alkyl group or a branched chain alkyl group. The substituted or unsubstituted alkyl group can be a substituted or unsubstituted C1~C 20 Alkyl, further may be substituted or unsubstituted C1~C 10Alkyl, or substituted or unsubstituted C1~C6 alkyl, or substituted or unsubstituted C1~C4 alkyl, etc. Wherein, the substituent in the substituted alkyl may include one or more of a halogen atom, an alkoxy group, a substituted or unsubstituted aryl group. For example, the substituted or unsubstituted alkyl may specifically be methyl (-CH3), monofluoromethyl (-CH2F), trifluoromethyl (-CF3), ethyl (-CH2CH3), 1-bromoethyl (-CH(Br)-CH3), n-propyl (-CH2CH2CH3), isopropyl, n-butyl, isobutyl, tert-butyl, benzyl (C6H5-CH2-), etc. In some embodiments, each occurrence of R is independently selected from C1~C4 alkyl substituted or unsubstituted by a halogen atom, that is, a halogenated or unhalogenated C1~C4 alkyl. Wherein, the halogenation may be partially halogenated or fully halogenated. For example, trifluoromethyl is a fully fluorinated methyl group, and monofluoromethyl is a partially fluorinated methyl group.

[0064] In the above formulas, each R may be the same or different groups each time it appears. Each Z may be the same or different groups each time it appears. For example, in some embodiments, the two Rs in formula (I-11) are all methyl or trifluoromethyl. The three Rs in formula (II-1) are all methyl; the four Rs in formula (II-2) and formula (II-3) are all methyl; the two Rs in formula (II-4) are all methyl; the two Rs in formula (II-8) and formula (II-9) are all methyl; the four Rs in formula (II-10) and (II-11) are all methyl; the six Rs in formula (II-12) may all be methyl, or some methyl and others may be fluorine atoms. In some embodiments, the four Zs in formula (I-3), formula (I-6) and formula (I-8) may all be oxygen atoms.

[0065] It should be noted that when R1 is a dianhydride residue and R2 is a diamine residue, the polyimide material implemented in this application has a single repeating unit represented by formula (i). In this case, the material is a homopolymer. When R1 and / or R2 have multiple structures, the polyimide material implemented in this application can have repeating units having multiple different structures conforming to formula (i). In this case, the material is a copolymer.

[0066] In some embodiments of the present application, the polyimide material in the embodiments of the present application may have any of the following structures:

[0067] In the above formulae, n represents the degree of polymerization of the corresponding repeating unit, and each n is greater than 0.

[0068] In the embodiment of the present application, the weight average molecular weight M of the polyimide material is wWithin the range of 10,000 - 1,000,000. The weight-average molecular weight of the polyimide material is within a suitable range, which is beneficial to making the polymer have good solubility in organic solvents, so as to better form a film to achieve a good coating effect on the surface of the inner core 10, and to ensure that the polyimide material has appropriate tensile strength, etc., to ensure that the coating layer 20 can better withstand the volume change of the inner core material. Exemplarily, the M w can be 20,000, 50,000, 100,000, 200,000, 300,000, 400,000, 500,000, 600,000, 700,000, 800,000, or 900,000, etc.

[0069] In the embodiments of the present application, the above polyimide material can be obtained by at least one of the dianhydride monomers corresponding to the above R1 and at least one of the diamine monomers corresponding to the above R2 through a polycondensation reaction at a certain temperature. Further, the dianhydride monomer and the diamine monomer can carry out the polycondensation reaction in the presence of an organic solvent to obtain a reaction solution; after precipitating the reaction solution with a precipitating agent and then performing solid-liquid separation (such as filtration or centrifugation, etc.), the required product is obtained. Among them, the organic solvent can include but is not limited to m-cresol, etc. The precipitating agent can include but is not limited to methanol or ethanol, etc. Among them, the temperature of the polycondensation reaction can be within the range of 150 - 220 °C, for example, specifically 160 °C, 170 °C, 180 °C, 190 °C, 200 °C, 210 °C, etc. The time of the polycondensation reaction can be 6 - 12 h, and further can be 6 - 10 h.

[0070] Among them, the equation for synthesizing the above polyimide material can include:

[0071] Among them, n represents the degree of polymerization of the repeating unit shown in the above formula (i), and n is a value greater than or equal to 1.

[0072] In the embodiments of the present application, the silicon-based material includes one or more of elemental silicon, silicon alloy, silicon oxide, and silicon-carbon composite material. Among them, the elemental silicon can be one or more of single-crystalline silicon particles, polycrystalline silicon particles, polycrystalline silicon nanowires, amorphous silicon particles, etc. Among them, the silicon alloy can include lithium-silicon alloy, and the chemical formula of the lithium-silicon alloy can be expressed as Li x Si, 0 < x ≤ 4.4. Among them, the chemical formula of the silicon oxide can be expressed as SiO x, where \(0 \lt x \lt 2\). Among them, the silicon-carbon composite material includes a composite of at least one of elemental silicon, silicon alloy, silicon oxide (\(SiO_x\), \(0 \lt x \lt 2\)) and a carbon material. The carbon material may include one or more of graphite (such as natural graphite, artificial graphite), soft carbon, hard carbon, porous carbon, etc., but is not limited thereto. Taking the silicon-carbon composite material as a composite of elemental silicon and a carbon material (which can be abbreviated as Si-C) as an example, it may specifically be a core-shell composite in which the surface of elemental silicon is coated with a carbon material, or a composite in which elemental silicon is loaded in a porous carbon framework, etc.

[0073] In the embodiments of the present application, the particle size of the silicon-based material may be \(1\ \mu m - 20\ \mu m\). The silicon-based material has a suitable particle size, which can not only avoid the diffusion path of lithium ions becoming longer and the rate performance of the material deteriorating due to its too large particle size, but also avoid the lower tap density of the material due to its too small particle size.

[0074] Specifically, the particle size of the silicon-based material may be \(2\ \mu m\), \(3\ \mu m\), \(4\ \mu m\), \(5\ \mu m\), \(6\ \mu m\), \(7\ \mu m\), \(8\ \mu m\), \(9\ \mu m\), \(10\ \mu m\), \(11\ \mu m\), \(12\ \mu m\), \(13\ \mu m\), \(14\ \mu m\), \(15\ \mu m\), \(16\ \mu m\), \(17\ \mu m\), \(18\ \mu m\), \(19\ \mu m\), etc. Although in Fig. 1, the inner core 10 is only exemplified as one particle, it can be understood that there may be one or more silicon-based material particles in the inner core 10 wrapped by the coating layer 20.

[0075] In the embodiments of the present application, the thickness of the coating layer 20 is \(5\ nm - 50\ nm\). The thickness of the coating layer 20 can be adaptively adjusted according to the size of the inner core. A coating layer 20 with a suitable thickness can ensure a good protection effect on the inner core material and an effect of suppressing volume expansion, and at the same time does not affect the electrochemical performance of the inner core material. If the thickness of the coating layer 20 is less than \(5\ nm\), it will be difficult for it to withstand the continuous volume change of the inner core material and to continuously prevent the side reaction between the electrolyte and the inner core material. If the thickness of the coating layer 20 is too thick, it will lead to an increase in the migration path of lithium ions in the coating layer 20, resulting in an increase in polarization, a deterioration in the rate performance of the inner core material, and a reduction in the specific capacity of the overall composite negative electrode material. Specifically, the thickness of the coating layer 20 may be, for example, \(8\ nm\), \(10\ nm\), \(15\ nm\), \(20\ nm\), \(22\ nm\), \(25\ nm\), \(30\ nm\), \(35\ nm\), \(40\ nm\), \(45\ nm\) or \(48\ nm\), etc. In some embodiments, the thickness of the coating layer 20 is \(10\ nm - 30\ nm\).

[0076] In the embodiment of the present application, the mass of the coating layer 20 accounts for 0.5%-8% of the total mass of the composite negative electrode material 100. The core material has a high specific capacity and the coating layer material has an extremely low specific capacity. Controlling the mass proportion of the coating layer 20 within this range can ensure that the overall gram capacity of the composite negative electrode material 100 is high, and helps the coating layer material form a coating layer 20 with appropriate thickness and high degree of coating on the surface of the core material. Specifically, the mass of the coating layer 20 can account for 0.55%, 0.6%, 0.8%, 0.9%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 6%, 7%, 7.5%, etc. of the mass of the core 10. In some embodiments, the mass of the coating layer 20 accounts for 1%-5% of the total mass of the composite negative electrode material 100. In this case, the coating layer 20 has a more appropriate thickness and a higher coating integrity, thereby ensuring that it can permanently inhibit core expansion and side reactions in the core, while maintaining a high gram capacity of the composite negative electrode material 100. In some embodiments of the present application, the mass of the polyimide material accounts for 0.5%-8% of the total mass of the composite negative electrode material 100, and can further be in the range of 1%-5%.

[0077] In the embodiment of the present application, any area on the surface of the coating layer 20 is 1 μm 2 In the selected area of ​​the polyimide material, the coverage rate of the polyimide material is greater than or equal to 90%. This parameter can reflect that the core 10 is highly coated with the polyimide material, the core 10 is basically completely coated in the coating layer 20, and the polyimide material is distributed relatively evenly, which greatly suppresses the side reactions between the core material and the electrolyte and the volume expansion of the core material. This parameter can also reflect, to a certain extent, the good film-forming properties of the polyimide material. For example, the coverage rate can be ≥92%, ≥95%, ≥98%, ≥99%, etc. In some embodiments, the coverage rate is 100%. That is, the core 10 is completely coated in the coating layer 20, and no core material is exposed from the coating layer 20.

[0078] In the embodiment of the present application, any area on the surface of the coating layer 20 is 1 μm 2 The mass of the polyimide material on the selected area is 6×10 -15 -6×10 -14 g, that is, in the range of 6 femtograms to 60 femtograms. This can reflect the uniform and complete coating of the polyimide material on the surface of the core 10 implemented in this application, and the micropores of the polyimide material do not affect the dynamic performance of the composite negative electrode material 100.

[0079] In the present application, the coating layer 20 made of the above-mentioned polyimide material has good toughness. In the embodiment of the present application, the elongation at break of the coating layer 20 is above 10%. In some embodiments, the elongation at break of the coating layer 20 is above 30%, above 40%, above 50%, above 60%, above 80%, above 90%, above 100%, or above 110%. In some embodiments, the elongation at break may be in the range of 20%-150%. In the embodiment of the present application, the fracture strength of the coating layer 20 is above 50 MPa, for example, in the range of 50 MPa-200 MPa, and in some embodiments may be in the range of 80-150 MPa. Elongation at break and fracture strength are both indicators for measuring the tensile properties of materials. Among them, elongation at break specifically refers to the ratio of the length ΔL of plastic elongation of the specimen when it is tensilely fractured to the original length L of the specimen. The higher elongation at break reflects that the coating layer 20 of the embodiment of the present application has good toughness and excellent tensile properties. Fracture strength, also known as "tensile strength," refers to the ratio of the tensile force at fracture to the cross-sectional area of ​​the fracture. A higher fracture strength reflects the good toughness and excellent tensile properties of the coating layer 20 of the embodiment of the present application.

[0080] In the embodiment of the present application, the gram capacity of the composite negative electrode material 100 is basically the same as that of the uncoated silicon-based material. In the case where the coating layer 20 adopts the above-mentioned polyimide material implemented in this application, lithium ions can smoothly enter and exit the coating layer 20, and will not significantly affect the gram capacity of the core material. Among them, the gram capacity of the composite negative electrode material 100 (denoted as C1) specifically refers to the ratio of the first delithiation capacity of the button half-cell made by using the composite negative electrode material 100 as the pole piece of the negative electrode active material to the mass of the composite negative electrode material. The gram capacity of the silicon-based material (denoted as C0) specifically refers to the ratio of the first delithiation capacity of the button half-cell made by using the silicon-based material as the pole piece of the negative electrode active material to the mass of the silicon-based material. Among them, the word "basically the same" in some cases means that the relative deviation k of the two gram capacities does not exceed 5%. That is, k = |C1-C0| / C0, k≤5%. Furthermore, k≤2%, k≤1%, k≤0.5%, or k≤0.2%, etc.

[0081] The present invention also provides a method for preparing a composite negative electrode material, comprising the following steps:

[0082] (1) adding a polyimide material to a solvent to obtain a polymer solution; wherein the polyimide material comprises a repeating unit as shown below and has a porous structure with a pore size less than or equal to 2 nm:

[0083] Wherein, R1 is selected from one or more dianhydride residues represented by the following formulas (I-1) to (I-11):

[0084] R2 is selected from one or more diamine residues represented by the following formulas (II-1) to (II-12):

[0085] wherein each occurrence of R is independently selected from a halogen atom, or a substituted or unsubstituted alkyl group; each occurrence of Z is independently selected from one of an oxygen atom, a sulfur atom, a selenium atom, -C(=O)-, -S(=O)-, and -S(=O)2-; * represents a linking site;

[0086] (2) mixing a core material with the polymer solution to obtain a mixed slurry; wherein the core material comprises a silicon-based material;

[0087] (3) removing the solvent from the mixed slurry, so that in the process of removing the solvent, a coating layer containing the polyimide material is formed on the surface of the core material to obtain a composite negative electrode material.

[0088] The preparation method of the composite negative electrode material provided in the embodiments of the present application is to form a structurally stable and complete coating layer on the surface of the core material by mixing a polymer solution of a polyimide material with a specific structure and then removing the solvent. This coating layer has excellent toughness and can well withstand the volume changes of the silicon-based material during lithium insertion and extraction. It also improves the interfacial properties of the silicon-based material and reduces its side reactions with the electrolyte. This preparation method is simple, easy to operate, and suitable for large-scale production. The resulting composite negative electrode material has high structural stability and good electrochemical performance.

[0089] Among them, regarding the material selection range and related property requirements of polyimide materials, silicon-based materials, etc., please refer to the previous description of this application and will not be repeated here.

[0090] In step (1), in order to facilitate the dissolution of the polyimide material, the solvent used is an organic solvent that can dissolve the material. Specifically, the organic solvent can be selected from one or more of N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), tetrahydrofuran (THF), etc. In the embodiment of the present application, the solid content of the polymer solution is 0.5wt%-5wt%. That is, in the polymer solution, the mass concentration of the polyimide material is 0.5wt%-10wt%, for example, specifically 1wt%, 2wt%, 2.5wt%, 3wt%, 4wt%, 4.5wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, etc. A polymer solution of appropriate mass concentration can ensure that the polyimide material is fully dissolved and that the polymer solution has good fluidity, has a good infiltration / penetration effect on the core material, forms a coating layer with a high degree of coating, and ensures that the time for removing the solvent in the subsequent step (3) is not too long.

[0091] In step (2), the core material is generally a solid material. The solid core material is mixed with the polymer solution to obtain a mixed slurry which is a solid-liquid mixture. Based on the fluidity or wettability of the polymer solution, the surface of the core material can be fully adsorbed with the polymer solution so that after the solvent is subsequently removed, the polymer can better form a film on the surface of the core material. In the embodiment of the present application, the solid content of the mixed slurry is 15wt%-40wt%, for example, specifically 20wt%, 25wt%, 30wt%, 35wt%, etc. Controlling the mixed slurry to have a suitable solid content is conducive to controlling the viscosity of the mixed slurry to be appropriate, which is conducive to preparing composite negative electrode material particles with a compact structure during the subsequent solvent removal process. In particular, when the solvent is removed by spray drying, the mixed slurry has a suitable viscosity, which is conducive to ensuring that the atomization difficulty is low, the nozzle is not easily blocked, and the drying effect of the mixed slurry is good and the product yield is high. In addition, controlling the solid content of the mixed slurry can also regulate the thickness of the coating layer and the coating uniformity.

[0092] In some embodiments of the present application, in the mixed slurry of step (2), the mass of the polyimide material accounts for 0.5%-8% of the total mass of the core material and the polyimide material. This helps to form a coating layer of appropriate thickness, good coating uniformity, and high integrity on the surface of the core material after the treatment in step S03, while avoiding reducing the gram capacity of the overall composite negative electrode material.

[0093] In step (3), the removal of the solvent can be carried out at a certain temperature so that the solvent can be volatilized better. During the process of solvent volatilization, the above-mentioned polyimide material can preferably form a coating film on the surface of the core material. It is understandable that the temperature during solvent removal is greater than the volatilization temperature of the solvent. Among them, the method of removing the solvent includes but is not limited to drying by rotary evaporator, drying in a water bath, drying in an oven, or spray drying.

[0094] In one embodiment of the present application, the solvent is removed by spray drying in step (3). The principle of spray drying is to atomize the slurry into mist-like particles, and then rapidly vaporize the solvent in contact with hot air to obtain dry solid particles. The solid particles produced by this method have a uniform surface coating effect and are suitable for large-scale production.

[0095] In the embodiment of the present application, the drying temperature during spray drying is 170°C-250°C. Wherein, "drying temperature" specifically refers to the inlet temperature of the hot gas of the spray tower, and its level directly affects the yield and quality of the dried pellets (i.e., the dried composite negative electrode material). Exemplarily, the drying temperature can be 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 240°C, etc. The feed rate can be 6mL / min, 8mL / min, 10mL / min, 12mL / min, 15mL / min, 18mL / min, 20mL / min, 25mL / min, 30mL / min, 35mL / min, 40mL / min, 50mL / min, 55mL / min, etc.

[0096] The embodiment of the present application also provides a negative electrode plate for a battery, which includes the composite negative electrode material described above in the embodiment of the present application.

[0097] Referring to Figure 2 , the negative electrode sheet 200 provided in the embodiment of the present application includes a negative electrode current collector 201 and a negative electrode active material layer 202 disposed on the negative electrode current collector 201. The negative electrode active material layer 202 includes the composite negative electrode material 100 described above in the embodiment of the present application. The negative electrode active material layer 202 is disposed on one surface or on two opposing surfaces of the negative electrode current collector 201. The composite negative electrode material 100 serves as the negative electrode active material of the negative electrode sheet 200.

[0098] The negative electrode current collector 201 can be a conventional material in the battery field, such as copper foil, carbon-coated copper foil, copper-plated film, or carbon-coated copper-plated film. In some embodiments, the negative electrode active material layer 202 may also include a binder and a conductive agent. The conductive agent in the negative electrode plate 200 is used to improve the plate's electronic conductivity without providing additional capacity or causing additional chemical reactions. Conductive agents are conventionally used in the battery field and include, but are not limited to, at least one of conductive graphite, conductive carbon black, acetylene black, carbon nanotubes, and graphene. Using these conductive agents can reduce the impedance of the negative electrode plate 200 and improve rate performance. The binder in the negative electrode plate 200 serves to bond the negative electrode active material and conductive agent, as well as the negative electrode active material layer 202 and the negative electrode current collector 201. Binders are conventionally used in the battery field and include, but are not limited to, at least one of carboxymethyl cellulose, styrene-butadiene rubber, styrene-acrylic rubber, polyimide, polyacrylic acid, polyacrylonitrile, polyvinyl alcohol, and polyurethane.

[0099] In addition to the aforementioned composite negative electrode material 100 as the negative electrode active material, the negative electrode active material layer 202 may also contain other negative electrode active components, such as a carbon negative electrode material. The carbon negative electrode material may be at least one of graphite, hard carbon, and soft carbon. Graphite includes, but is not limited to, surface-modified or unmodified natural graphite, or surface-modified or unmodified artificial graphite.

[0100] The present application also provides a lithium battery comprising the negative electrode sheet described above in the present application. It is understood that the lithium battery also comprises the composite negative electrode material described above in the present application.

[0101] Referring to Figure 3 , a schematic diagram of the structure of a lithium battery provided in an embodiment of the present application is shown. The lithium battery 300 includes a positive electrode 31, a negative electrode 32, a separator 34 disposed between the positive electrode 31 and the negative electrode 32, an electrolyte 33, and corresponding connecting components and circuits. The negative electrode 32 includes the negative electrode sheet 200 described above in the embodiment of the present application.

[0102] For lithium batteries, it is through lithium ions (Li + ) between the positive electrode 31 and the negative electrode 32 to achieve energy storage and release. The electrolyte 33 is the carrier for the transfer of lithium ions between the positive electrode 31 and the negative electrode 32. The ion-conducting but electronically insulating separator 34 is used to separate the positive electrode 31 and the negative electrode 32 to prevent short circuits. + The positive electrode active material in the positive electrode 31 is released and migrates to the negative electrode 32 through the electrolyte 33 and the separator 34 to achieve the storage of electrical energy. +The negative electrode active material is released from the negative electrode 32 and migrates back to the positive electrode 31 through the electrolyte 33 and the separator 34 to perform external work, that is, release electrical energy to the power load connected to the lithium battery 300.

[0103] The positive and negative active materials are the main parts of the lithium battery that perform the energy storage function and determine the energy density, cycle performance and safety performance of the battery. After determining the positive electrode material system of the battery, the capacity of the negative electrode active material is crucial to the improvement of the energy density of the entire battery. In the embodiment of the present application, the negative electrode 32 of the lithium battery 300 contains at least the above-mentioned composite negative electrode material 100 provided in the embodiment of the present application as the negative electrode active material. The volume expansion effect of the composite negative electrode material 100 is suppressed, the cycle stability is good, the dynamic performance is good and the capacity is high, which enables the lithium battery 300 to have good cycle performance, rate performance and higher battery energy density.

[0104] The lithium battery 300 shown in FIG3 is a liquid battery, which uses an electrolyte as a liquid electrolyte. It is understood that in other embodiments of the present application, the lithium battery can be a solid / semi-solid battery, which includes a positive electrode, a negative electrode, and a solid / semi-solid electrolyte layer located therebetween.

[0105] The lithium batteries provided in the embodiments of this application can be used in consumer electronic devices, mobile devices such as electric vehicles, and other power-consuming devices, as well as energy storage systems, to enhance product competitiveness. Consumer electronic devices include, but are not limited to, mobile phones, tablet computers, laptop computers, and wearable electronic devices.

[0106] The present application also provides an electrical device that uses the lithium battery 300 described above to power it. The electrical device may include an electronic device or a powered mobile device (such as an electric vehicle). The electrical device includes an electrical component and a power supply component, which supplies power to the electrical component. The power supply component includes the lithium battery described above in the present application.

[0107] In the implementation manner of this application, the electronic device can be a mobile phone, a tablet computer, a laptop computer, a wearable device (such as a smart watch, a smart bracelet, smart glasses, etc.), an augmented reality (AR) device, a virtual reality (VR) device, a television, a digital camera, a vehicle-mounted device and other electronic products, and this application does not limit this.

[0108] In some embodiments, referring to FIG4 , an embodiment of the present application provides an electronic device 400. The electronic device 400 includes a housing 401 and a circuit board assembly (not shown in FIG4 ) and a battery 402 housed in the housing 401. The battery 402 can power the electronic device 400, and the battery 402 includes the lithium battery 300 described above in the embodiment of the present application. The battery 402 is electrically connected to the circuit board and can power the circuit board assembly. The circuit board assembly can be one of the electrical components of the electronic device 400. In some embodiments, the housing 401 may include a front cover assembled on the front side of the electronic device and a rear shell assembled on the rear side, and the battery 402 may be fixed on the inside of the rear shell. The electronic device 400 shown in FIG4 can specifically be a mobile phone, etc.

[0109] In some other embodiments, referring to FIG5 , embodiments of the present application provide a powered mobile device 500. Powered mobile device 500 can be any mobile device used for loading, transporting, assembling, disassembling, or security, and can be, for example, various types of vehicles, including but not limited to electric cars, electric buses, electric trucks, electric motorcycles, and electric bicycles. In this embodiment, the powered mobile device 500 is described using an electric car as an example.

[0110] Specifically, the power mobile device 500 may include a vehicle body 501, a mobile component 502 (for example, a wheel), and a drive component. The drive component includes a motor 503 and a battery system 504. The battery system 504 includes the above-mentioned lithium battery 300 provided in the embodiment of the present application. The battery system 504 is housed in the vehicle body 501 (for example, located under the vehicle chassis) and is electrically connected to the motor 503. It can supply power to the motor 503, and the motor 503 then provides power to drive the mobile component 502 to move. The motor 503 is one of the electrical components of the power mobile device 500. The battery system 504 may be a battery pack, which includes a plurality of the above-mentioned lithium batteries 300. The plurality of lithium batteries may be connected in series and parallel to form a battery pack, and at least one battery module and a battery management system may be packaged to form a battery pack.

[0111] The embodiment of the present application further provides an energy storage system, which includes a plurality of the above-mentioned lithium batteries 300 of the embodiment of the present application.

[0112] Referring to Figure 6, the energy storage system 600 includes one or more battery packs 601 (one battery pack is used as an example in Figure 6), and a battery management system 602 electrically connected to the battery pack 601. Each battery pack 601 includes a plurality of the above-mentioned lithium batteries 300 provided in the embodiment of the present application. Among them, the battery pack 601 can be a module composed of multiple lithium batteries 300 connected in series and parallel. The battery management system 602 can be used to monitor the status information of each lithium battery 300 in the battery pack 601, adjust the voltage and temperature of the battery pack, and realize functions such as charge and discharge protection. The battery pack 601 and the battery management system 602 can be packaged to form a battery pack. Among them, the energy storage system 600 shown in Figure 6 can be an electric vehicle energy storage system, a short-term backup power system for a data center, a site energy backup power system, an intelligent photovoltaic energy storage power station, etc.

[0113] The present application also provides a polyimide material, which includes the following repeating units:

[0114] Wherein, R1 is selected from one or more dianhydride residues represented by the following formulas (I-1) to (I-11):

[0115] R2 is selected from one or more diamine residues represented by the following formulas (II-1) to (II-12):

[0116] wherein each occurrence of R is independently selected from a halogen atom, or a substituted or unsubstituted alkyl group; each occurrence of Z is independently selected from one of an oxygen atom, a sulfur atom, a selenium atom, -C(=O)-, -S(=O)-, and -S(=O)2-; * represents a linking site;

[0117] The polyimide material has a porous structure with a pore diameter less than or equal to 2 nm.

[0118] When R1 and R2 in the repeating units of the polyimide material are selected from the aforementioned groups, a rigid "twisted center" structure can be introduced into the polyimide molecular chain, resulting in micropores with a size of less than 2 nm. This ensures that the material has high mechanical strength and modulus. When the polyimide material is used as a coating material for coating electrode active materials or lithium supplements in lithium-ion batteries, the coating layer is less prone to rupture and can better withstand volume changes in the core material without affecting the electrochemical performance of the core. Furthermore, fine-tuning of mechanical properties such as toughness, specific area, and pore size of the polyimide material can be achieved by regulating R1, R2, and the degree of polymerization of the repeating unit represented by formula (i).

[0119] For further description of the structural characteristics, physical properties, etc. of the polyimide material, please refer to the previous description of this application, which will not be repeated here.

[0120] The embodiments of the present application also provide applications of the above-mentioned polyimide materials of the embodiments of the present application in lithium-ion batteries, for example, applications of the above-mentioned polyimide materials in coating negative electrode active materials, coating positive electrode active materials, coating lithium supplements, and preparing electrode binders are provided, but are not limited thereto.

[0121] In the embodiment of the present application, the negative electrode active material includes one or more of silicon-based materials, phosphorus-based materials, and tin-based materials, but is not limited thereto. The volume expansion effect of these negative electrode materials is large, and the above-mentioned polyimide material is particularly required to coat them, so that the polyimide material can effectively suppress the volume expansion effect of these negative electrode active materials while not increasing their resistance to lithium insertion and extraction. Among them, the phosphorus-based material may include one or more of phosphorus element (such as red phosphorus, black phosphorus, white phosphorus), phosphorus-carbon composite materials, etc. The tin-based material may include one or more of elemental tin, tin alloy, tin oxide, etc. For silicon-based materials, please refer to the description above in this application.

[0122] In some embodiments of the present application, the above-mentioned polyimide material can be used to coat the positive electrode active material. The positive electrode active material can be a nickel-containing positive electrode material commonly used in lithium-ion batteries (i.e., a nickel-containing lithium oxide), such as a nickel-cobalt-manganese ternary material or a nickel-cobalt-aluminum ternary material. The polyimide material can isolate water and oxygen and protect the core positive electrode active material. It can improve the stability of the core positive electrode active material in air and water, extend the stable storage time, and prevent deliquesce and water absorption from causing material structure changes and performance degradation. In addition, during the stirring and slurrying process of the positive electrode slurry, the polyimide material also helps stabilize the slurry, avoiding problems such as gelation and coating difficulties caused by the high residual alkali content on the surface of the positive electrode active material and its easy absorption and deterioration. In addition, since the polyimide material has micropores with a pore size of less than 2nm, it will not affect the capacity of the core positive electrode active material or reduce its rate performance. And because the polyimide material has a certain viscosity, it can improve the bonding strength between the composite positive electrode material formed after coating and the binder.

[0123] In other embodiments of the present application, the polyimide material described above can be used to coat a lithium supplement. The lithium supplement is typically a positive electrode supplement. Similarly, the polyimide material described above in the examples of the present application also contributes to the storage stability of the core lithium supplement and the stability of the slurry during slurrying, without affecting the effectiveness of the lithium supplement.

[0124] Furthermore, the polyimide material of the embodiments of the present application also possesses excellent adhesive properties and can be used as an electrode binder, for example, as a binder in the negative active material layer of a negative electrode sheet, or as a binder in the positive active material layer of a positive electrode sheet. Using the polyimide material as a binder can reduce or avoid the addition of conventional binders during the preparation of battery electrode sheets (i.e., positive or negative electrodes), thereby simplifying the electrode sheet preparation process.

[0125] The embodiments of the present application are further described below with reference to a number of embodiments.

[0126] Example 1

[0127] A composite negative electrode material, the preparation method of which comprises the following steps:

[0128] (1) Synthesis of PIM-PI materials:

[0129] Under nitrogen, 10 mmol of the dianhydride monomer CpODA and 10 mmol of the diamine monomer TBDA2 were added to a polymerization flask. The monomers were rinsed off the flask walls with m-cresol to maintain a solids content of 30 wt%. After stirring at room temperature for 30 minutes, the mixture was heated to 80°C and stirred until the monomers were completely dissolved. The mixture was then heated to 180°C and allowed to react at 180°C for 6 hours until imidization of the polymer was complete, yielding a viscous polyimide solution. m-cresol was then added to dilute the solids content to 5 wt%. Heating was stopped and the mixture was allowed to cool to room temperature. The resulting reaction solution was poured into methanol with a magnetic stirrer to precipitate a filamentous white fibrous solid, which was then filtered. The filamentous fiber solid is placed in a Soxhlet extractor and heated under reflux with methanol for 12-48 hours to remove excess meta-cresol. After completion, it is dried at 120°C to obtain a polyimide material with micropores with a pore size of less than 2 nm (abbreviated as PIM-PI material), which is recorded as 1#PIM-PI (also recorded as CpODA-TBDA2).

[0130] The equations involved in synthesizing the above-mentioned 1# PIM-PI material include:

[0131] Among them, the specific surface area of ​​1#PIM-PI was measured by nitrogen adsorption method to be 387m 2 The weight average molecular weight of the 1# PIM-PI is about 114,000.

[0132] (2) Preparation of 1# PIM-PI coated silicon-carbon composite material:

[0133] a. Take 20g of the above 1 # PIM-PI and add it to a beaker, then add 980g of NMP and stir for 2 hours to obtain a completely dissolved polymer solution of 1 # PIM-PI, having a solid content of 2wt%;

[0134] b. Under mechanical stirring, 980g of silicon-carbon composite material powder (purchased from Lanxi Zhide New Energy Materials Co., Ltd., with an average particle size D50 of 8μm) was added in small amounts to a beaker containing the polymer solution, and the powder stuck to the inner wall of the beaker was rinsed with an appropriate amount of NMP, and the solid content was adjusted to 25wt%, and stirred for 4 hours to obtain a uniformly mixed slurry;

[0135] c. Place the mixed slurry in a spray dryer for spray drying and granulation, setting the feed rate to 40 mL / min and the heating temperature to 200°C. After the oxygen content in the spray dryer stabilizes and is less than 3%, turn on the peristaltic pump on the manual working interface, continuously magnetically stir the mixed slurry, start feeding, and simultaneously spray dry to obtain a dried powder material, i.e., a composite negative electrode material, whose core is a silicon-carbon composite material and the surface of the core has a coating layer made of 1# PIM-PI.

[0136] A preparation method for a negative electrode plate includes: mixing 0.85g of the composite negative electrode material prepared in Example 1 with 0.1g of a conductive agent (specifically Super P conductive carbon black) and 0.7g of a modified polyacrylic acid binder solution (purchased from Chengdu Yindi Le Company, with a solid content of 7wt%), adding deionized water for dilution, and stirring thoroughly to obtain a negative electrode slurry; coating the negative electrode slurry on a 10μm thick copper foil current collector (single-sided coating), vacuum drying at 100°C for 12 hours to form a negative electrode active material layer, and then rolling to obtain a negative electrode plate. The compacted density of the negative electrode plate is 1.0g / cm 3 The loading of the composite negative electrode material is about 4 mg / cm 2 .

[0137] A lithium button cell is prepared, comprising: cutting the negative electrode sheet prepared in Example 1 into a disc with a diameter of 13 mm, using a metal lithium sheet as a counter electrode, Celgard 2400 as a separator, and a mixed solution of 1 mol / L LiPF6 in ethylene carbonate (EC) and diethyl carbonate (EMC) (v / v = 1:1) as an electrolyte solution; and assembling the cells into a CR2032 button cell in an argon-filled glove box.

[0138] Example 2

[0139] A composite negative electrode material, the preparation method of which comprises the following steps:

[0140] (1) Synthesis of PIM-PI materials:

[0141] Under nitrogen, the following dianhydride monomer CTB1 (10 mmol) and the following diamine monomer DAPI (10 mmol) were added to a polymerization flask. The monomers were rinsed off the flask walls with m-cresol to maintain a solids content of 30 wt%. After stirring at room temperature for 30 minutes, the mixture was heated to 80°C and stirred until the monomers were completely dissolved. The mixture was then heated to 180°C and allowed to react at 180°C for 6 hours until the imidization of the polymer was complete, yielding a viscous polyimide solution. m-cresol was then added to the mixture to dilute the solids content to 5 wt%. Heating was stopped and the mixture was allowed to cool to room temperature. The resulting reaction solution was poured into methanol with magnetic stirring to precipitate a filamentous white fibrous solid, which was then filtered. The filamentous fibrous solid was placed in a Soxhlet extractor and heated under reflux with methanol for 12-48 hours to remove excess m-cresol. The mixture was then dried at 120°C to yield a PIM-PI material, designated 2# PIM-PI (also designated CTB1-DAPI).

[0142] Among them, the equations involved in synthesizing the above-mentioned 2# PIM-PI material include:

[0143] Among them, the specific surface area of ​​2#PIM-PI was measured by nitrogen adsorption method to be 80m 2 / g; the weight average molecular weight of the 2#PIM-PI is about 406,000.

[0144] (2) Following the method described in Example 1, the surface of the silicon-carbon composite material was coated with 2#PIM-PI to obtain a composite negative electrode material.

[0145] According to the method described in Example 1, the composite negative electrode material prepared in Example 2 was prepared into a negative electrode sheet, and then assembled into a button battery.

[0146] Example 3

[0147] A composite negative electrode material, which differs from Example 1 in that: 3# PIM-PI is used to coat the surface of the silicon-carbon composite material. In the composite negative electrode material prepared in Example 3, the mass of the coating layer still accounts for 2% of the total mass of the composite negative electrode material.

[0148] The synthesis method of 3#PIM-PI comprises the following steps: under nitrogen protection, adding the following hexafluorodianhydride (abbreviated as 6FDA) (10 mmol) and the following diamine monomer 4MTBDA (10 mmol) to a polymerization flask, and rinsing the monomer raw materials from the flask wall with m-cresol to control the solid content of the mixed system to 30 wt%. After stirring at room temperature for 30 minutes, the mixture was heated to 80°C and stirred until the monomer raw materials were completely dissolved. The mixture was then heated to 180°C and reacted at 180°C for 6 hours until the polymer imidization was complete, thereby producing a viscous polyimide solution. Subsequently, m-cresol was added to the system to dilute the solid content to 5 wt%. The heating was stopped and the mixture was cooled to room temperature. The resulting reaction solution was poured into methanol with magnetic stirring to precipitate a filamentous white fiber solid, which was then filtered. The filamentous fiber solid was placed in a Soxhlet extractor and heated under reflux with methanol for 12-48 hours to remove excess m-cresol. After completion, the extract was dried at 120°C to obtain a PIM-PI material, designated as 3#PIM-PI (also designated as 6FDA-4MTBDA).

[0149] Among them, the equations involved in synthesizing the above-mentioned 3# PIM-PI material include:

[0150] Among them, the specific surface area of ​​3#PIM-PI was measured by nitrogen adsorption method to be 584m 2 / g; the weight average molecular weight of the 3#PIM-PI is about 54,000.

[0151] According to the method described in Example 1, the composite negative electrode material prepared in Example 3 was prepared into a negative electrode sheet, and then assembled into a button battery.

[0152] In order to highlight the beneficial effects of the embodiments of the present application, the following comparative examples are provided.

[0153] Comparative Example 1

[0154] A negative electrode active material is an uncoated silicon-carbon composite material.

[0155] According to the method described in Example 1, the uncoated silicon-carbon composite material powder was directly mixed with a conductive agent and a binder to obtain a negative electrode slurry, and the negative electrode slurry was coated on a 10 μm thick copper foil current collector. After vacuum drying and roller pressing, a negative electrode sheet was obtained. The compacted density of the negative electrode sheet was 1.0 g / cm 3 The loading of the composite negative electrode material is about 4 mg / cm 2 .

[0156] According to the method described in Example 1, the negative electrode sheet prepared in Comparative Example 1 was assembled into a CR2032 button battery.

[0157] Comparative Example 2

[0158] A composite negative electrode material, which differs from Examples 1-3 in that: in the composite negative electrode material of Comparative Example 2, the coating layer on the surface of the silicon-carbon composite material is a conventional PI material without micropores; the mass of the coating layer still accounts for 2% of the total mass of the composite negative electrode material.

[0159] The conventional PI material is obtained by reacting p-phenylenediamine monomer with the above-mentioned dianhydride BTDA. The structural formula of the PI can be expressed as:

[0160] The difference between the preparation method of the composite negative electrode material in Comparative Example 2 and that of the aforementioned Examples 1-3 is that: since the conventional PI in Comparative Example 2 cannot be dissolved in polar organic solvents, it is necessary to use the precursor of the conventional PI, polyamic acid, which is mixed with the silicon-carbon material and then spray-dried to form a polyamic acid coating layer on the surface of the silicon-carbon material, and then the polyamic acid is imidized at a temperature above 300°C to obtain a conventional PI coating layer.

[0161] According to the method described in Example 1, the composite negative electrode material prepared in Comparative Example 2 was prepared into a negative electrode sheet and assembled into a button cell.

[0162] Figure 7 summarizes the transmission electron microscope (TEM) photos of the uncoated silicon-carbon composite material (a, c) and the composite negative electrode material (b, d) prepared in Example 1. Among them, small figure c is an enlarged view of the selected area in figure a, and small figure d is an enlarged view of the selected area in figure b. It can be seen from Figure 7 that the embodiment of the present application achieves a uniform and relatively complete coating of the single particle of the silicon-carbon composite material, and the coverage of the PIM-PI coating layer (the lighter gray area indicated by the arrow in the figure is the coating layer) basically reaches 100%, wherein the coating thickness is about 15nm.

[0163] In addition, taking the composite negative electrode material prepared in Example 2 as an example, a thermogravimetric analysis was performed on it, and the measured thermogravimetric curve is shown in Figure 8. Figure 8 also summarizes the thermogravimetric curve of the uncoated silicon-carbon composite material in Comparative Example 1. It can be seen from Figure 8 that after the temperature reaches 700°C, the thermal weight loss ratio of the composite negative electrode material in Example 2 basically no longer decreases, and the thermal weight loss ratio is about 2%, which basically corresponds to the mass loss of the outer layer PIM-PI material. It can be seen that in the composite negative electrode material of Example 2, the coating amount of the PIM-PI material is about 2%, which is basically consistent with the content of the PIM-PI material and the silicon-carbon composite material in the aforementioned mixed slurry. This also indirectly reflects that the PIM-PI material has achieved the coating of the silicon-carbon composite material.

[0164] In order to strongly support the beneficial effects brought about by the technical solutions of the embodiments of the present application, the negative electrode sheets and button batteries of the above embodiments and comparative examples were subjected to various performance tests as shown in Table 1 below, and the results are also summarized in Table 1 below.

[0165] Table 1

[0166] Among them, the test method of the electrode peeling force includes: cutting the negative electrode to be tested into a 2cm×10cm long strip test sample, then adhering 3M double-sided tape to the side of the long strip test sample to be tested, and compacting it with a roller to make the 3M double-sided tape completely fit the test sample. Then, stick the other side of the double-sided tape to the surface of the stainless steel plate, bend one end of the test sample in the opposite direction with a bending angle of 180 degrees, and use a universal material testing machine to clamp the test sample and the stainless steel plate respectively for stretching, and record the critical force value required to separate the negative electrode from the stainless steel plate during stretching in real time. Repeat the tensile test of multiple test samples, and take the average value of the multiple critical force values ​​as the peeling force of the negative electrode.

[0167] The test method for the electrode expansion rate includes: subjecting each lithium-ion button battery to 250 charge and discharge tests, and taking 3 button batteries from each group, respectively, in the first cycle of full charge state (i.e., 100% SOC or fully lithium-intercalated state) and the 250th cycle of 0% SOC (i.e., 100% delithiation) state, disassembling the button batteries and removing the negative electrode plates, cleaning the surface of the negative electrode plates with dimethyl carbonate solvent and drying, then using a screw micrometer to measure the thickness of different areas of the negative electrode plates and taking the average thickness; the difference between the average thickness and the initial thickness of the negative electrode plates is divided by the initial thickness of the negative active material layer in the negative electrode plates (i.e., the difference between the initial thickness of the negative electrode plates and the thickness of the current collector), and the resulting ratio is the expansion rate of the negative electrode plates.

[0168] Electrochemical performance tests were performed on each lithium-ion button cell using a CT2001A blue-electric tester. The method for testing the initial coulombic efficiency of the button cells involved performing an initial charge-discharge test on each button cell at 0.05C over a voltage range of 0.005V-1.0V. The ratio of the initial delithiation capacity to the initial lithium insertion capacity was recorded as the initial coulombic efficiency. The ratio of the initial delithiation capacity to the mass of the negative electrode active material in the negative electrode sheet was recorded as the delithiation gram capacity of the negative electrode active material. Figure 9 summarizes the initial charge-discharge curves for the button cells of Example 3 and Comparative Example 1.

[0169] The test method for cyclic capacity retention includes: subjecting each button cell to 250 cycles of charge and discharge at a charge and discharge rate of 0.2C / 0.5C, and taking the ratio of the delithiation capacity after 250 cycles to the delithiation capacity in the first cycle as the capacity retention rate. The 0.2C ratio refers to a lithium insertion rate of 0.2C for the negative electrode, and the 0.5C ratio refers to a lithium removal rate of 0.5C for the negative electrode. Each cycle involves lithium insertion followed by lithium removal. The relevant test results are summarized in Table 1. Figure 10 summarizes the cycle performance curves of the button cells of Example 1 and Comparative Example 1.

[0170] It can be seen from Table 1 that the embodiment of the present application uses a PIM-PI-coated silicon-based material as the negative electrode active material in the negative electrode sheet. The peeling force of the negative electrode sheet of the embodiment of the present application and Comparative Example 2 is better than that of the comparative example negative electrode sheet made of an uncoated silicon-based material. This may be because the PIM-PI material is coated on the surface of the silicon-based material to form a new interface. Compared with the surface of the silicon-based material, this interface has better compatibility with the binder, so that the binder solution can better infiltrate the interface, achieving a better bonding effect. Furthermore, the negative electrode plates made of silicon-based materials coated with PIM-PI in the present embodiment exhibited significantly lower thickness expansion rates than the negative electrode plates made of uncoated silicon-based materials in Comparative Example 1, both during the first lithium insertion cycle and after 250 cycles. This demonstrates that PIM-PI coating of the silicon-based material significantly inhibits negative electrode plate expansion. This is likely due to the uniform protective layer formed by PIM-PI on the silicon-based material surface, its inherent mechanical strength and toughness, and the PIM-PI's microporous structure, which facilitates the release of core stress and can withstand the large volume expansion and contraction of the silicon-based material, thereby effectively reducing expansion at the electrode layer. Furthermore, even if the silicon-based material breaks and pulverizes during cycling, the PIM-PI coating maintains its integrity, preventing contact between the silicon-based material and the electrolyte, inhibiting the continued formation of SEI and its side reactions during cycling, thereby achieving a high cycle capacity retention rate for the battery. As shown in Table 1 and FIG10 , the capacity retention rate of the button battery prepared using the composite negative electrode material of Example 1 after 250 cycles is 87%, while the capacity retention rate of the button battery prepared using the uncoated silicon-based material of Comparative Example 1 after 250 cycles is only 81%.

[0171] In addition, it can be seen from Table 1 and Figure 9 that the composite negative electrode material provided in the embodiment of the present application (Figure 9 uses Example 3 as an example) has very similar initial gram capacity and initial coulombic efficiency to the uncoated silicon-based material in Comparative Example 1; while the initial gram capacity of the composite negative electrode material in Comparative Example 2 is lower than that in Comparative Example 1. The main reason is that the PIM-PI material has its own Li + transmission channel, will not hinder Li +The coating is electrochemically inert and will not react with Li + If side reactions occur, the use of PIM-PI materials to coat silicon-based materials will not significantly deteriorate the electrochemical properties of silicon-based materials.

[0172] In addition, taking the button cell of Example 1 as an example, it was tested for rate performance along with the button cells of Comparative Examples 1-2. The specific testing method included inserting lithium at 0.2C in each button cell, delithiating at different rates, and taking the ratio of the delithiation capacity at each delithiation rate to the delithiation capacity at 0.2C as the delithiation capacity retention rate at the corresponding rate. The test results are summarized in Figure 11. As can be seen from Figure 11, the rate performance of the composite negative electrode material of the embodiment of the present application is basically consistent with that of Comparative Example 1, while the rate performance of Comparative Example 2 is lower than that of Comparative Example 1.

[0173] This application also uses other PIM-PI materials to coat silicon-based materials to obtain composite negative electrode materials of other embodiments. For details, please refer to Table 2 below.

[0174] Table 2

[0175] Note: In Table 2, Si-C represents a composite of elemental silicon and carbon material. Similar to Example 1, its delithiation capacity at 1V is 1821 mAh / g. In Table 2, SiOx represents silicon oxide, and its delithiation capacity at 1V is approximately 1350 mAh / g.

[0176] From the comparison between the above embodiment 1 and the embodiments 4-6 in Table 2, it can be seen that, under the condition that the coating material is the same, the more the coating amount and the thicker the coating layer, the lower the specific capacity of the composite negative electrode material at the same charge and discharge current density. In addition, from the comparison between the above embodiment 1 and the embodiments 8 and 9 in Table 1, it can be seen that, under the condition that the coating amount is the same and the structural similarity of the coating material is high, the larger the specific surface area of ​​the coating material and the more pores it has, the lower the specific capacity of the composite negative electrode material at the same charge and discharge current density. + The smaller the effect of intercalation and extraction, the higher the specific capacity of the overall composite negative electrode material. In addition, the comparison between Examples 11-13 and the comparison between Examples 26-27 also have similar phenomena.

[0177] The foregoing merely represents exemplary embodiments of the present application, and while the description is relatively specific and detailed, it should not be construed as limiting the scope of the present invention. It should be noted that a person of ordinary skill in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

[0178] It should be noted that the terms "disposed", "connected", "installed", etc. in this application should be understood in a broad sense. For example, they can refer to direct disposition, connection, or installation, or they can refer to indirect disposition, connection, or installation through an intermediate medium. Directional terms mentioned in this application, such as "upper", "lower", "front", "back", "left", "right", "inside", "outside", "front", "back", "bottom", "top", "side", etc., are only used to better and more clearly illustrate and understand this application, and do not indicate or imply that the referred components must have a specific orientation, be constructed and operate in a specific orientation. Therefore, they should not be understood as limitations on this application.

[0179] It should be understood that the terms "first", "second" and other numbers used in this application are only used for the purpose of description and are not intended to limit the scope of this application. In the description of this application, unless otherwise stated, the meaning of "multiple (kinds)" refers to greater than or equal to two (kinds). "At least one (kind)" refers to one (kind) or more (kinds). "At least one of the following (individuals)" or similar expressions refer to any combination of these items, including any combination of single items (individuals) or plural items (individuals). For example, "at least one of a, b, or c", or "at least one of a, b, and c", can all represent: a, b, c, ab (i.e., a and b), ac, bc or abc, where a, b, c can be single or multiple, respectively.

[0180] In addition, the numerical range represented by "-" in this application refers to the range including the numerical values ​​recorded before and after "-" as the minimum and maximum values, respectively. In this application, expressions about parameter ranges, such as "greater than or equal to (≥)", "less than or equal to (≤)", "above...", and "below..." all include the number itself. The numerical values ​​and numerical ranges involved in the embodiments of this application are approximate values. Due to the influence of manufacturing process / testing method, etc., there may be a certain range of errors, which can be considered negligible by those skilled in the art.

Claims

1. A polyimide material, characterized in that: The polyimide material includes the following repeating units: Wherein, R1 is selected from one or more dianhydride residues represented by the following formulas (I-1) to (I-11): R2 is selected from one or more diamine residues represented by the following formulas (II-1) to (II-12): wherein each occurrence of R is independently selected from a halogen atom, or a substituted or unsubstituted alkyl group; each occurrence of Z is independently selected from one of an oxygen atom, a sulfur atom, a selenium atom, -C(=O)-, -S(=O)-, and -S(=O)2-; * represents a linking site; The polyimide material has a porous structure with a pore diameter less than or equal to 2 nm.

2. The polyimide material according to claim 1, wherein The specific surface area of the polyimide material is greater than or equal to 80m 2 / g.

3. The composite negative electrode material according to claim 2, wherein The specific surface area of the polyimide material is 80-800m 2 / g.

4. The polyimide material according to claim 1 or 2, characterized in that: The substituted or unsubstituted alkyl group is a substituted or unsubstituted C1-C 20 Alkyl; the substituent in the substituted alkyl group includes at least one halogen atom.

5. The polyimide material according to any one of claims 1 to 4, characterized in that The weight average molecular weight of the polyimide material is in the range of 10,000 to 1,000,000.

6. Use of the polyimide material according to any one of claims 1 to 5 in coating negative electrode active materials, coating positive electrode active materials, coating lithium supplements, and preparing electrode binders.

7. The use according to claim 6, characterized in that The negative electrode active material includes one or more of silicon-based materials, phosphorus-based materials, and tin-based materials.

8. A composite negative electrode material, characterized in that The composite negative electrode material includes a core and a coating layer coated on the core, wherein the core includes a silicon-based material, and the coating layer includes the polyimide material according to any one of claims 1 to 5.

9. The composite negative electrode material according to claim 8, wherein The specific surface area of the composite negative electrode material is 4-20m 2 / g range.

10. The composite negative electrode material according to any one of claims 8 to 9, characterized in that: The mass of the coating layer accounts for 0.5%-8% of the total mass of the composite negative electrode material.

11. The composite negative electrode material according to claim 10, wherein The mass of the coating layer accounts for 1%-5% of the total mass of the composite negative electrode material.

12. The composite negative electrode material according to any one of claims 8 to 11, wherein The coating layer has a thickness of 5 nm to 50 nm.

13. The composite negative electrode material according to any one of claims 8 to 12, wherein: Any area on the surface of the coating layer is 1 μm 2 In the selected area, the coverage of the polyimide material is greater than or equal to 90%.

14. The composite negative electrode material according to any one of claims 8 to 13, wherein: The elongation at break of the coating layer is above 10%; and the fracture strength of the coating layer is above 50 MPa.

15. The composite negative electrode material according to any one of claims 8 to 14, characterized in that The silicon-based material includes one or more of elemental silicon, silicon alloy, silicon oxide, and silicon-carbon composite material; wherein the silicon-carbon composite material includes a composite of at least one of elemental silicon, silicon alloy, silicon oxide and carbon material.

16. The composite negative electrode material according to any one of claims 8 to 15, characterized in that The particle size of the silicon-based material is 1 μm-20 μm.

17. The composite negative electrode material according to any one of claims 8 to 16, characterized in that: The composite negative electrode material has substantially the same gram capacity as the uncoated silicon-based material.

18. A method for preparing a composite negative electrode material, characterized in that: The following steps are involved: (1) adding the polyimide material according to any one of claims 1 to 5 to a solvent to obtain a polymer solution; (2) mixing a core material with the polymer solution to obtain a mixed slurry; wherein the core material comprises a silicon-based material; (3) removing the solvent from the mixed slurry, so that a coating layer containing the polyimide material is formed on the surface of the core material to obtain a composite negative electrode material.

19. The preparation method according to claim 18, characterized in that The removal of the solvent is specifically carried out by spray drying.

20. A negative electrode plate, characterized in that: The negative electrode plate includes a current collector and a negative electrode active material layer disposed on the current collector, wherein the negative electrode active material layer includes the composite negative electrode material according to any one of claims 8 to 17.

21. A lithium battery, characterized in that: The lithium battery comprises a positive electrode sheet and a negative electrode sheet as claimed in claim 20.

22. An electrical device, characterized in that: The electrical equipment includes an electrical component and a power supply component, the power supply component supplies power to the electrical component, and the power supply component includes the lithium battery as described in claim 21.

23. The electrical equipment according to claim 22, wherein: The electrical equipment includes electronic equipment or a power-moving device.

24. The electrical equipment according to claim 23, wherein: The electronic device includes a housing and the lithium battery and circuit board assembly accommodated in the housing.

25. An energy storage system, characterized in that: The energy storage system includes at least one battery pack and a battery management system electrically connected to the battery pack, and each of the battery packs includes a plurality of lithium batteries as described in claim 21.

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