Composite negative electrode active material and its manufacturing method, and negative electrode plate, secondary battery, and power consumption device including the same

Abstract

The present application provides a composite negative electrode active material and a method for producing the same, as well as a negative electrode plate, a secondary battery, and a power consumption device including the same. The composite negative electrode active material includes a negative electrode active material substrate and a conductive polymer layer located on the surface of the negative electrode active material substrate, and the cyclic voltammetry curve of the composite negative electrode active material has an oxidation peak in the range of 3.2V to 3.6V and a reduction peak in the range of 2.1V to 2.6V. The composite negative electrode active material according to the present application can combine low volume expansion, high gram capacity, and high initial coulombic efficiency, and can further provide a secondary battery with low volume expansion, high energy density, and long cycle life.

Description

[Technical field]

[0001] The present application relates to the field of battery technology, and in particular to a composite negative electrode active material and a manufacturing method thereof, as well as a negative electrode plate, a secondary battery, and a power consuming device including the same. [Background technology]

[0002] In recent years, secondary batteries have been widely used in energy storage power systems such as hydroelectric, thermal, wind and solar power plants, as well as in many fields such as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. During the charge and discharge process of secondary batteries, the absorption and release of lithium ions in the electrode active material causes a change in the volume of the electrode active material, which in turn causes the battery to expand and contract. The expansion of the battery has become an important factor affecting the safety performance and electrochemical performance of secondary batteries. In particular, the volume expansion of the negative electrode active material affects the cycle life and capacity characteristics of secondary batteries. Summary of the Invention

[0003] The present application aims to provide a composite negative electrode active material and a method for producing the same, as well as a negative electrode plate, a secondary battery, and a power consuming device including the same, which can provide a secondary battery with low volume expansion, high gram capacity, and high initial coulombic efficiency, and can provide a secondary battery with low volume expansion, high energy density, and long cycle life.

[0004] A first aspect of the present application provides a composite negative electrode active material, the composite negative electrode active material including a negative electrode active material substrate and a conductive polymer layer located on a surface of the negative electrode active material substrate, wherein a cyclic voltammetry curve of the composite negative electrode active material has an oxidation peak in a range of 3.2 V to 3.6 V and a reduction peak in a range of 2.1 V to 2.6 V.

[0005] The cyclic voltammetry curve of the composite negative electrode active material is obtained by testing in the following manner: (1) providing a negative electrode plate containing the composite negative electrode active material; (2) using a metal lithium sheet as a counter electrode, a 1 mol / L lithium hexafluorophosphate as a solute for the electrolyte, a 1:1 volumetric mixture of ethylene carbonate and dimethyl carbonate as a solvent, and glass fiber as a separator; and assembling the negative electrode plate and the battery into a button cell in a glove box filled with argon gas; placing the packaged button cell in the glove box and leaving it for more than 12 hours to age it; (3) using an electrochemical workstation to perform a cyclic voltammetry test on the obtained button cell to obtain a cyclic voltammetry curve of the composite negative electrode active material, where the scanning voltage is 2.0V to 4.3V and the scanning speed is 0.1mV / s.

[0006] The inventors of the present application have discovered through extensive research that by providing a conductive polymer layer on the surface of a negative electrode active material substrate and causing the cyclic voltammetry curve of the composite negative electrode active material to have an oxidation peak in the range of 3.2 V to 3.6 V and a reduction peak in the range of 2.1 V to 2.6 V, the resulting composite negative electrode active material can be made to have low volume expansion, high gram capacity, and high initial coulombic efficiency.

[0007] Different from the conventional conductive carbon layer coating layer, the present application adopts a conductive polymer layer coating layer, so that the coating layer has low rigidity and good flexibility, and is not easily broken during charging and discharging of the secondary battery, thereby continuously protecting the negative active material substrate, avoiding direct contact between the negative active material substrate and the electrolyte, and avoiding the continuous consumption of active lithium ions and the continuous growth and thickening of the SEI film and the by-reaction product layer. The conductive polymer layer of the present application includes a conductive polymer and is different from the conventional conductive polymer (such as polyaniline, polypyrrole, polythiophene, etc.), because the conductive polymer adopted in the conductive polymer layer of the present application can make the composite negative active material have high oxidation peak potential and reduction peak potential, so that the conductive polymer layer of the present application further has a lithium storage function, which on the one hand can share the lithium storage current and reduce the destruction of the negative active material substrate caused by the current, and on the other hand can share the lithium absorption stress of the negative active material substrate and increase the energy density of the secondary battery. In addition, the conductive polymer layer of the present application is also advantageous in reducing the lithium ion concentration on the negative electrode side and reducing the concentration polarization, so that after the composite negative electrode active material of the present application is applied to a secondary battery, the secondary battery can have low volume expansion, high energy density and long cycle life.

[0008] In any embodiment of the present application, the cyclic voltammetry curve of the composite negative electrode active material has an oxidation peak in the range of 3.3 V to 3.55 V. This allows the composite negative electrode active material to have a suitable lithium release function, which is favorable for increasing the gram capacity and initial coulombic efficiency of the composite negative electrode active material, and is favorable for increasing the energy density of the secondary battery.

[0009] In any embodiment of the present application, the cyclic voltammetry curve of the composite negative electrode active material has a reduction peak in the range of 2.2 V to 2.45 V. This allows the composite negative electrode active material to have a suitable lithium storage function, which is favorable for increasing the gram capacity and initial coulombic efficiency of the composite negative electrode active material, and is favorable for increasing the energy density of the secondary battery.

[0010] In any embodiment of the present application, the oxidation peak potential of the cyclic voltammetry curve of the composite negative electrode active material is greater than the oxidation peak potential of the cyclic voltammetry curve of the negative electrode active material substrate, and optionally, the difference between the oxidation peak potential of the cyclic voltammetry curve of the composite negative electrode active material and the oxidation peak potential of the cyclic voltammetry curve of the negative electrode active material substrate is 2.4 V to 2.8 V, and further optionally, 2.5 V to 2.75 V. This allows the composite negative electrode active material to have an appropriate lithium release function, which is further advantageous for increasing the gram capacity and initial coulombic efficiency of the composite negative electrode active material, and further advantageous for increasing the energy density of the secondary battery.

[0011] In any embodiment of the present application, the reduction peak potential of the cyclic voltammetry curve of the composite negative electrode active material is greater than the reduction peak potential of the cyclic voltammetry curve of the negative electrode active material substrate, and optionally, the difference between the reduction peak potential of the cyclic voltammetry curve of the composite negative electrode active material and the reduction peak potential of the cyclic voltammetry curve of the negative electrode active material substrate is 1.5 V to 2.1 V, and further optionally, 1.7 V to 1.95 V. This allows the composite negative electrode active material to have an appropriate lithium storage function, which is further advantageous for increasing the gram capacity and initial coulombic efficiency of the composite negative electrode active material, and further advantageous for increasing the energy density of the secondary battery.

[0012] In any embodiment of the present application, the composite negative electrode active material has an infrared spectrum of 1396±41 cm -1 The first absorption peak is at a wave number of 1782±53 cm -1 and optionally a ratio of heights of the first absorption peak to the second absorption peak is 1.75±0.1. -1 It has a CN stretching vibration peak at 1782 ± 53 cm -1 It has a C=O stretching vibration peak at the position.

[0013] In any embodiment of the present application, the conductive polymer layer includes a conductive polymer, the conductive polymer includes a polyimide, the polyimide has a ketone carbonyl group in the main chain structure, and the molar ratio of the ketone carbonyl group C=O to the imide ring C(=O)-NC(=O) is 0.5 or more, optionally 0.5 to 2, and further optionally 0.5 to 1. This contributes to the cyclic voltammetry curve of the composite negative electrode active material having an appropriate oxidation peak potential and reduction peak potential, on the one hand, it can quickly store lithium, share the lithium storage current, and reduce the destruction of the negative electrode active material substrate caused by the current, and on the other hand, it can share the lithium absorption stress of the negative electrode active material substrate, and increase the energy density of the secondary battery. Furthermore, it is advantageous for reducing the lithium ion concentration on the negative electrode side and reducing the concentration polarization.

[0014] In any embodiment of the present application, the polyimide is obtained by polymerizing a dianhydride monomer having a ketone carbonyl group C=O in the main chain structure and a diamine monomer, which contributes to the cyclic voltammetry curve of the composite negative electrode active material having appropriate oxidation peak potential and reduction peak potential.

[0015] In an optional embodiment of the present application, the monomer unit of the polyimide is as shown in Formula 1: [ka] X represents at least one selected from the group consisting of an alkyl group having a ketone carbonyl group C=O in its main chain structure, an alicyclic group, an aliphatic heterocyclic group, an aromatic group, and a heteroaromatic group, and Y represents a chain aliphatic diamine monomer residue, an alicyclic diamine monomer residue, or an aromatic diamine monomer residue.

[0016] In any embodiment of the present application, optionally, X is [ka] represents one of the groups R1 and R2 are each independently Ra represents a substituted or unsubstituted C0-C12 divalent alkyl group, a C3-C12 divalent alicyclic group, a C1-C12 divalent aliphatic heterocyclic group, a C6-C30 divalent aromatic group, or a C2-C30 divalent heteroaromatic group, p represents 0, 1, 2, 3, or 4; R a each occurrence independently represents at least one of a halogen atom, a C1-C6 alkyl group, a C1-C6 alkoxy group, and a C1-C6 halogenalkyl group, and # represents a bonding position.

[0017] In any embodiment of the present application, optionally, Y is [ka] represents one of the groups R3 to R 12 are each independently R a represents a substituted or unsubstituted C1-C12 divalent alkyl group, a C3-C12 divalent alicyclic group, a C1-C12 divalent aliphatic heterocyclic group, a C6-C30 divalent aromatic group, or a C2-C30 divalent heteroaromatic group; R b each occurrence independently represents -O-, -S-, or -C(=O)-; R a represents at least one of a halogen atom, a C1 to C6 alkyl group, a C1 to C6 alkoxy group, and a C1 to C6 halogenalkyl group, and # represents a bonding position.

[0018] In any embodiment of the present application, optionally, Y is [ka] [ka] represents one of the groups # represents a bond position, p independently represents 0, 1, 2, 3 or 4 at each occurrence, R a Each occurrence independently represents at least one of a halogen atom, a C1-C6 alkyl group, a C1-C6 alkoxy group, and a C1-C6 halogenalkyl group.

[0019] In any embodiment of the present application, the weight average molecular weight of the conductive polymer is from 30,000 to 100,000, which allows the conductive polymer layer to have good flexibility, covering effect, and electrolyte swelling resistance.

[0020] In any embodiment of the present application, the glass transition temperature of the conductive polymer is 220° C. to 260° C., and optionally 240° C. to 260° C., so that the conductive polymer layer can have good flexibility, covering effect, and electrolyte swelling resistance.

[0021] In any embodiment of the present application, the conductive polymer layer has a thickness of 50 nm or less, optionally 10 nm or less, and further optionally 0.1 nm to 7 nm, which allows the conductive polymer layer to have good flexibility, covering effect, and electrolyte swelling resistance, and is also advantageous in that the composite negative electrode active material has a high gram capacity and a high initial coulombic efficiency.

[0022] In any embodiment of the present application, the composite negative active material has an average particle size of 3 μm to 15 μm, optionally 5 μm to 10 μm, and further optionally 5 μm to 8 μm, which is favorable for improving the lithium ion and electron transport properties, thereby further improving the dynamic performance of the secondary battery.

[0023] In any embodiment of the present application, the negative electrode active material substrate comprises at least one selected from a prelithiated or non-prelithiated carbon-based material, a silicon-based material, and a tin-based material. Optionally, the carbon-based material comprises at least one selected from graphite, soft carbon, and hard carbon, optionally, the silicon-based material comprises at least one selected from elemental silicon, silicon oxide, and silicon alloy, and optionally, the tin-based material comprises at least one selected from elemental tin, tin oxide, and tin alloy.

[0024] In any embodiment of the present application, the negative electrode active material substrate is a prelithiated silicon oxide, which can further increase the energy density of the secondary battery.

[0025] In any embodiment of the present application, the prelithiated silicon oxide comprises a silicon oxide substrate core, a lithium silicate intermediate layer located on the surface of the silicon oxide substrate core, the lithium silicate intermediate layer comprising lithium silicate grains and silicon and / or silicon dioxide nano-grains, and a carbon coating layer located on the surface of the lithium silicate intermediate layer. Optionally, the lithium silicate grains comprise Li2SiO3 grains. This can improve the capacity of the secondary battery and reduce the volume expansion of the composite negative electrode active material, thereby improving the safety performance and cycle life of the secondary battery.

[0026] In any embodiment of the present application, the mass ratio of the lithium silicate crystal grains to the silicon and / or silicon dioxide nanocrystal grains in the lithium silicate intermediate layer is (10-50):(50-90).

[0027] In any embodiment of the present application, the lithium silicate interlayer has a thickness of ≦35 nm, optionally between 15 nm and 35 nm, which can increase the initial coulombic efficiency and gram capacity of the composite anode active material.

[0028] In any embodiment of the present application, the carbon coating layer has a thickness of ≦25 nm, optionally 15 nm to 25 nm, which can increase the conductivity of the composite anode active material and can also prevent residual lithium from dissolving into the anode slurry and electrolyte.

[0029] A second aspect of the present application provides a method for producing the composite negative electrode active material of the first aspect of the present application, the method including: Step S1 of providing a negative electrode active material substrate, a dianhydride monomer having a ketone carbonyl group C=O in a main chain structure, a diamine monomer, and a solvent, optionally the diamine monomer including at least one selected from a chain aliphatic diamine monomer, an alicyclic diamine monomer, and an aromatic diamine monomer; Step S2 of dissolving the diamine monomer in the solvent to obtain a solution in which the diamine monomer is dissolved; and Step S3 of immersing the negative electrode active material substrate in the solution in a shielding gas atmosphere. Step S3 includes adding and stirring to uniformly mix, then adding and stirring to uniformly mix a dianhydride monomer having a ketone carbonyl group C=O in the main chain structure, and performing a polymerization reaction, and after completion of the reaction, washing and drying to obtain a prepolymer, and step S4 includes imidizing the prepolymer obtained in S3 in a shielding gas atmosphere, and after completion of the reaction, obtaining a composite negative electrode active material, wherein the composite negative electrode active material includes a negative electrode active material substrate and a conductive polymer layer located on the surface of the negative electrode active material substrate, and a cyclic voltammetry curve of the composite negative electrode active material has an oxidation peak in the range of 3.2V to 3.6V and a reduction peak in the range of 2.1V to 2.6V.

[0030] The present application uses an in-situ polymerization method to prepare a composite negative active material, which can make the thickness of the conductive polymer layer more uniform and has a better adhesion effect between the conductive polymer layer and the negative active material substrate. In the preparation method of the present application, the dianhydride monomer and diamine monomer having a ketone carbonyl group C=O in the main chain structure are used as raw materials, which is also advantageous for making the conductive polymer layer have good flexibility, so that the negative active material substrate can be continuously protected and the secondary battery can have a longer cycle life.

[0031] In any embodiment of the present application, the imidization reaction in S4 employs a stepwise incubation process.

[0032] In any embodiment of the present application, optionally, the stepwise incubation process includes a first stage of increasing the temperature to 100±15°C at a rate of 3°C / min to 5°C / min and incubating for 1 hour to 1.5 hours, a second stage of increasing the temperature to 150±15°C at a rate of 3°C / min to 5°C / min and incubating for 1 hour to 1.5 hours, a third stage of increasing the temperature to 200±15°C at a rate of 3°C / min to 5°C / min and incubating for 1 hour to 1.5 hours, a fourth stage of increasing the temperature to 250±15°C at a rate of 3°C / min to 5°C / min and incubating for 1 hour to 1.5 hours, and a fifth stage of increasing the temperature to 300±15°C at a rate of 3°C / min to 5°C / min and incubating for 1 hour to 1.5 hours.

[0033] The stepwise heat-insulating process described above can optimally match the volatilization of the solvent, the imidization temperature, and the motion of the conductive polymer molecular chains, which is advantageous in promoting the conductive polymer molecular chains to be regularly arranged to form a crystal structure.

[0034] In any embodiment of the present application, the molar ratio of the diamine monomer to the dianhydride monomer having a ketone carbonyl group C=O in the main chain structure is ≧2:1, optionally (2.1-2.8):1.

[0035] In any embodiment of the present application, the solvent is an aprotic polar solvent, optionally comprising at least one selected from N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone.

[0036] In an optional embodiment of the present application, the dianhydride monomer having a ketone carbonyl group C=O in the main chain structure is [ka] and R1 and R2 are each independently R arepresents a substituted or unsubstituted C0-C12 divalent alkyl group, a C3-C12 divalent alicyclic group, a C1-C12 divalent aliphatic heterocyclic group, a C6-C30 divalent aromatic group, or a C2-C30 divalent heteroaromatic group, p represents 0, 1, 2, 3, or 4; R a Each occurrence independently represents at least one of a halogen atom, a C1-C6 alkyl group, a C1-C6 alkoxy group, and a C1-C6 halogenalkyl group.

[0037] In any embodiment of the present application, optionally, the dianhydride monomer having a ketone carbonyl group C=O in the main chain structure is [ka] The compound includes at least one selected from the following compounds:

[0038] In an optional embodiment of the present application, the diamine monomer is [ka] and R3 to R 12 are each independently R a represents a substituted or unsubstituted C1-C12 divalent alkyl group, a C3-C12 divalent alicyclic group, a C1-C12 divalent aliphatic heterocyclic group, a C6-C30 divalent aromatic group, or a C2-C30 divalent heteroaromatic group; R b each occurrence independently represents -O-, -S-, or -C(=O)-; R a represents at least one of a halogen atom, a C1 to C6 alkyl group, a C1 to C6 alkoxy group, and a C1 to C6 halogenalkyl group.

[0039] In any embodiment of the present application, optionally, the diamine monomer is [ka] [ka] and p independently represents 0, 1, 2, 3, or 4 at each occurrence; R a Each occurrence independently represents at least one of a halogen atom, a C1-C6 alkyl group, a C1-C6 alkoxy group, and a C1-C6 halogenalkyl group.

[0040] In any embodiment of the present application, optionally, the diamine monomer is [ka] [ka] The compound includes at least one selected from the following compounds:

[0041] In any embodiment of the present application, the negative electrode active material substrate comprises at least one selected from a prelithiated or non-prelithiated carbon-based material, a silicon-based material, and a tin-based material, and is optionally a prelithiated silicon oxide.

[0042] In any embodiment of the present application, optionally, the prelithiated silicon oxide comprises a silicon oxide substrate core, a lithium silicate intermediate layer located on the surface of the silicon oxide substrate core and including lithium silicate grains and silicon and / or silicon dioxide nano-grains, and a carbon coating layer located on the surface of the lithium silicate intermediate layer. Optionally, the lithium silicate grains comprise Li2SiO3 grains.

[0043] A third aspect of the present application provides a negative electrode plate, the negative electrode plate including a negative electrode current collector and a negative electrode film layer located on a surface of the negative electrode current collector, wherein the negative electrode film layer includes a composite negative electrode active material of the first aspect of the present application or a composite negative electrode active material produced by the method of the second aspect of the present application, and a mass percentage of the composite negative electrode active material in the negative electrode film layer is 1% to 99%, optionally 5% to 30%, based on a total mass of the negative electrode film layer.

[0044] A fourth aspect of the present application provides a secondary battery including the negative electrode plate of the third aspect of the present application.

[0045] A fifth aspect of the present application provides a power consuming device including the secondary battery of the fourth aspect of the present application.

[0046] The composite anode active material according to the present application can provide low volume expansion, high gram capacity and high initial coulombic efficiency, and can provide a secondary battery with low volume expansion, high energy density and long cycle life. The power consumption device according to the present application includes the secondary battery according to the present application, and therefore has at least the same advantages as the secondary battery. [Brief description of the drawings]

[0047] In order to more clearly describe the technical solutions of the embodiments of the present application, the following briefly introduces the drawings that need to be used in the embodiments of the present application. It is obvious that the drawings described below are only some embodiments of the present application, and those skilled in the art can obtain other drawings based on the drawings without paying creative efforts. [Figure 1] FIG. 1 is a schematic diagram of one embodiment of a secondary battery of the present application. [Diagram 2] FIG. 2 is an exploded schematic view of an embodiment of the secondary battery of FIG. 1. [Diagram 3] FIG. 1 is a schematic diagram of one embodiment of a battery module of the present application. [Figure 4] FIG. 1 is a schematic diagram of one embodiment of a battery pack of the present application. [Diagram 5] 5 is an exploded schematic view of the embodiment of the battery pack shown in FIG. 4. [Figure 6] 1 is a schematic diagram of an embodiment of a power consuming device in which the secondary battery of the present application is used as a power source. [Figure 7] 2 shows infrared spectra of composite negative electrode active materials prepared in Example 1 and Comparative Example 1. [Figure 8]2 is a gel permeation chromatography (GPC) image of a conductive polymer layer in the composite negative electrode active material produced in Example 1. [Figure 9] 1 is a scanning electron microscope (SEM) image of the composite negative electrode active material prepared in Example 1. [Figure 10] 1 is a transmission electron microscope (TEM) image of the composite negative electrode active material prepared in Example 4. [Figure 11] 4 is a cyclic voltammetry curve of the negative electrode active material produced in Example 3. [Figure 12] 4 is a scanning electron microscope (SEM) image of a cross section of the composite negative electrode active material after the capacity of the secondary battery produced in Example 1 has decayed to 80% of the first cycle discharge capacity. [Figure 13] 1 is a scanning electron microscope (SEM) image of a cross section of a composite negative electrode active material after the capacity of a secondary battery produced in Comparative Example 1 has decayed to 80% of the first cycle discharge capacity. In the drawings, the drawings are not necessarily drawn to scale. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0048] Hereinafter, the embodiments specifically disclosing the composite negative electrode active material and the manufacturing method thereof, as well as the negative electrode plate, secondary battery, and power consumption device including the composite negative electrode active material and the manufacturing method thereof according to the present application will be described in detail with appropriate reference to the drawings. However, unnecessary detailed description may be omitted. For example, detailed description of well-known matters and duplicated description of structures that are actually the same may be omitted. This is to avoid the following description becoming unnecessarily long and to allow those skilled in the art to easily understand. It should be noted that the drawings and the following description are provided to allow those skilled in the art to fully understand the present application, and are not intended to limit the subject matter described in the claims.

[0049] The "ranges" disclosed in this application are defined in the form of lower and upper limits, and a given range is defined by selecting one lower limit and one upper limit, and the selected lower and upper limits define the boundaries of the particular range. Such defined ranges may be inclusive or exclusive of the end values, and may be arbitrarily combined, i.e., any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, it is understood that ranges of 60-110 and 80-120 are also envisaged. It is noted that if 1 and 2 are listed as the minimum range values, and 3, 4, and 5 are listed as the maximum range values, then the ranges 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5 are all envisaged. In this application, unless otherwise specified, a numerical range "a-b" represents a shorthand representation of any combination of real numbers a-b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed herein, and "0-5" is just a shorthand for combinations of these numbers. Also, expressing a parameter as an integer ≧2 is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0050] Unless otherwise specified, all the embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution, and such technical solution should be considered to be included in the disclosure content of the present application.

[0051] Unless otherwise stated, all technical features and optional technical features of the present application can be combined with each other to form a new technical solution, and such technical solution should be deemed to be included in the disclosure content of the present application.

[0052] Unless otherwise stated, all steps in this application may be performed in sequence or randomly, and preferably in sequence. For example, the method includes steps (a) and (b) means that the method may include steps (a) and (b) performed in sequence, or may include steps (b) and (a) performed in sequence. For example, the method may further include step (c) as stated above means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), may include steps (a), (c) and (b), may include steps (c), (a) and (b), etc.

[0053] Unless otherwise specified, the terms "comprise" and "include" referred to in this application may be open ended or closed ended. For example, the terms "comprise" and "include" may further include or include other ingredients not listed, or may include or include only the ingredients listed.

[0054] Unless otherwise stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, "A or B" is satisfied in the following cases: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) but B is true (or exists); and A and B are both true (or exist).

[0055] As used in this application, the terms "plurality" and "multiple types" mean two or more than two.

[0056] In this application, when a bond traverses a ring or ring systems, it is meant that the bond may be attached at any accessible position on the ring or ring systems.

[0057] At various places in the present specification, substituents of compounds are disclosed in groups or ranges. It is expressly intended that such descriptions include each individual subcombination of the members of these groups and ranges. For example, the term "C1-C6 alkyl group" is expressly intended to individually disclose C1, C2, C3, C4, C5, C6, C1-C6, C1-C5, C1-C4, C1-C3, C1-C2, C2-C6, C2-C5, C2-C4, C2-C3, C3-C6, C3-C5, C3-C4, C4-C6, C4-C5 and C5-C6 alkyl groups.

[0058] The term "alicyclic group" refers to carbocyclic ring systems of aliphatic character, including alkyl, alkenyl, and alkynyl groups, which may be monocyclic or polycyclic (e.g., fused, bridged, spiro) in structure. Illustrative examples of alicyclic groups include, but are not limited to, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclopentenyl, cyclohexynyl, and cyclohexenyl groups.

[0059] The term "aliphatic heterocyclic group" means an alicyclic group in which one or more atoms in the ring is an element other than carbon, such as N, O, S, etc. Examples of aliphatic heterocyclic groups include, but are not limited to, ethylene oxide groups and aziridine groups.

[0060] The term "aromatic group" refers to a carbocyclic ring system having aromatic character, which may be monocyclic, polycyclic or fused ring in structure. Illustrative examples of aromatic groups include, but are not limited to, phenyl, biphenyl (e.g., diphenyl, terphenyl), diphenylmethane, naphthyl, and indenyl groups.

[0061] The term "heteroaromatic group" means an aromatic group in which one or more atoms in the ring is an element other than carbon, such as N, O, S, etc. Examples of heteroaromatic groups include, but are not limited to, pyrrole, furan, thienyl, pyridyl, pyrimidinyl, pyridazine, pyrazinyl, benzofuranyl, and benzothienyl groups.

[0062] Unless otherwise explained, terms used in this application have the known meanings commonly understood by those of ordinary skill in the art.

[0063] Unless otherwise specified, the numerical values ​​of each parameter mentioned in this application can be measured by various test methods commonly used in the art, for example, by the test method according to this application.

[0064] A secondary battery is also called a rechargeable battery or storage battery, and refers to a battery that can continue to be used by activating the active material through a charging method after the battery is discharged. During the charging and discharging process of a battery, lithium ions are absorbed and released by going back and forth between the positive and negative plates, and a separator is installed between the positive and negative plates, and mainly plays a role in preventing short circuits between the positive and negative electrodes and allows lithium ions to pass through. The positive plate includes a positive electrode collector and a positive electrode film layer, and the positive electrode film layer is generally formed by applying a positive electrode slurry on the positive electrode collector, drying and cold pressing, and the positive electrode slurry is generally formed by dispersing components such as a positive electrode active material, a conductive agent, and an adhesive in a solvent and stirring them uniformly. The negative electrode plate includes a negative electrode current collector and a negative electrode film layer. The negative electrode film layer is generally formed by applying a negative electrode slurry onto the negative electrode current collector, drying, and cold pressing. The negative electrode slurry is generally formed by dispersing components such as a negative electrode active material, a conductive agent, and an adhesive in a solvent and uniformly stirring the mixture.

[0065] During the initial charging of the secondary battery, a solid electrolyte interface (SEI) film is formed on the surface of the negative active material, which can protect the negative electrode and prevent direct contact between the negative active material and the electrolyte, thereby reducing the decomposition of the electrolyte and the consumption of active lithium ions. However, when the secondary battery is charged, the negative active material particles undergo a corresponding volume expansion as charging progresses, and the SEI film on the surface cannot withstand the large volume expansion and is cracked, resulting in exposure of fresh negative active material to the electrolyte, which in turn causes the electrolyte to be continuously decomposed, the active lithium ions to be continuously consumed, and the SEI film and the by-reaction product layer to continuously grow and become thicker.

[0066] In order to reduce the volume expansion of the negative active material, a commonly adopted strategy at present is to coat the surface of the negative active material with a conductive carbon layer. The conductive carbon layer can not only avoid the direct contact between the negative active material and the electrolyte, but also play a role in suppressing the volume expansion of the negative active material. However, the carbonaceous precursor for forming the conductive carbon layer is prone to agglomerate the negative active material during the coating process to form large-sized secondary particles, which reduces the compaction density of the negative active material, and also requires an additional crushing process due to the large size of the negative active material particles, which on the one hand increases energy consumption and on the other hand reduces the uniformity of the size distribution of the negative active material particles. In addition, the conductive carbon material in the conductive carbon layer is generally amorphous carbon, which is a material with short-range order and no long-range order, and has high rigidity, which causes the conductive carbon layer to crack and even to be crushed during the charge and discharge of the secondary battery. After the conductive carbon layer is cracked, fresh negative active material is exposed to the electrolyte, which causes the electrolyte to be continuously decomposed and the active lithium ions to be continuously consumed, leading to the continuous growth and thickening of the SEI film and the by-reaction product layer, and further increasing the charge transfer impedance of the secondary battery and decreasing the rapid charge / discharge efficiency and capacity.

[0067] Therefore, coating the surface of the negative electrode active material with a conductive carbon layer cannot effectively improve the volume expansion and capacity development of the negative electrode active material, and further, it is difficult to provide a secondary battery with low volume expansion, high energy density, and long cycle life.

[0068] Through extensive research, the inventors of the present application have provided a new composite negative electrode active material which has low volume expansion, high gram capacity and high initial coulombic efficiency, and can provide a secondary battery with low volume expansion, high energy density and long cycle life.

[0069] Composite negative electrode active material Specifically, a first aspect of the present application provides a composite negative electrode active material, the composite negative electrode active material including a negative electrode active material substrate and a conductive polymer layer located on a surface of the negative electrode active material substrate, wherein a cyclic voltammetry curve of the composite negative electrode active material has an oxidation peak in a range of 3.2 V to 3.6 V and a reduction peak in a range of 2.1 V to 2.6 V.

[0070] In this application, the "conductive polymer layer" can completely or partially cover the negative electrode active material substrate.

[0071] The inventors of the present application have discovered through extensive research that by providing a conductive polymer layer on the surface of a negative electrode active material substrate and causing the cyclic voltammetry curve of the composite negative electrode active material to have an oxidation peak in the range of 3.2 V to 3.6 V and a reduction peak in the range of 2.1 V to 2.6 V, the resulting composite negative electrode active material can be made to have low volume expansion, high gram capacity, and high initial coulombic efficiency.

[0072] Different from the conventional conductive carbon layer coating layer, the present application adopts a conductive polymer layer coating layer, so that the coating layer has low rigidity and good flexibility, and is not easily broken during charging and discharging of the secondary battery, thereby continuously protecting the negative active material substrate, avoiding direct contact between the negative active material substrate and the electrolyte, and avoiding the continuous consumption of active lithium ions and the continuous growth and thickening of the SEI film and the by-reaction product layer. The conductive polymer layer of the present application includes a conductive polymer and is different from the conventional conductive polymer (such as polyaniline, polypyrrole, polythiophene, etc.), because the conductive polymer adopted in the conductive polymer layer of the present application can make the composite negative active material have high oxidation peak potential and reduction peak potential, so that the conductive polymer layer of the present application further has a lithium storage function, which on the one hand can share the lithium storage current and reduce the destruction of the negative active material substrate caused by the current, and on the other hand can share the lithium absorption stress of the negative active material substrate and increase the energy density of the secondary battery. In addition, the conductive polymer layer of the present application is also advantageous in reducing the lithium ion concentration on the negative electrode side and reducing the concentration polarization, so that after the composite negative electrode active material of the present application is applied to a secondary battery, the secondary battery can have low volume expansion, high energy density and long cycle life.

[0073] In some embodiments, the cyclic voltammetry curve of the composite negative electrode active material has an oxidation peak in the range of 3.3 V to 3.55 V. This allows the composite negative electrode active material to have a suitable lithium release function, which is favorable for increasing the gram capacity and initial coulombic efficiency of the composite negative electrode active material, and is favorable for increasing the energy density of the secondary battery.

[0074] In some embodiments, the cyclic voltammetry curve of the composite negative electrode active material has a reduction peak in the range of 2.2 V to 2.45 V. This allows the composite negative electrode active material to have a suitable lithium storage function, which is favorable for increasing the gram capacity and initial coulombic efficiency of the composite negative electrode active material, and is favorable for increasing the energy density of the secondary battery.

[0075] In some embodiments, the oxidation peak potential of the cyclic voltammetry curve of the composite negative electrode active material is greater than the oxidation peak potential of the cyclic voltammetry curve of the negative electrode active material substrate, and optionally, the difference between the oxidation peak potential of the cyclic voltammetry curve of the composite negative electrode active material and the oxidation peak potential of the cyclic voltammetry curve of the negative electrode active material substrate is 2.4 V to 2.8 V, and further optionally, 2.5 V to 2.75 V. This allows the composite negative electrode active material to have an appropriate lithium release function, which is further advantageous for increasing the gram capacity and initial coulombic efficiency of the composite negative electrode active material, and further advantageous for increasing the energy density of the secondary battery.

[0076] In some embodiments, the reduction peak potential of the cyclic voltammetry curve of the composite negative electrode active material is greater than the reduction peak potential of the cyclic voltammetry curve of the negative electrode active material substrate, and optionally, the difference between the reduction peak potential of the cyclic voltammetry curve of the composite negative electrode active material and the reduction peak potential of the cyclic voltammetry curve of the negative electrode active material substrate is 1.5 V to 2.1 V, and further optionally, 1.7 V to 1.95 V. This allows the composite negative electrode active material to have an appropriate lithium storage function, which is further advantageous for increasing the gram capacity and initial coulombic efficiency of the composite negative electrode active material, and further advantageous for increasing the energy density of the secondary battery.

[0077] Cyclic voltammetry curves of the composite negative electrode active material and the negative electrode active material substrate may be obtained by testing in the following manner.

[0078] (1) A negative electrode plate is provided that includes a composite negative electrode active material or a negative electrode active material substrate.

[0079] (2) A button battery is manufactured by using a metallic lithium sheet as the counter electrode, 1 mol / L lithium hexafluorophosphate (LiPF6) as the solute for the electrolyte, a 1:1 volumetric mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) as the solvent, and glass fiber as the separator, and assembling the negative electrode plate and the button battery in a glove box filled with argon gas (water and oxygen contents both below 0.1 ppm), and then placing the packaged button battery in the glove box and leaving it to stand for 12 hours or more to age it.

[0080] (3) Test by cyclic voltammetry method. Use an electrochemical workstation (such as Shanghai Chenhua CHI 660 electrochemical workstation) to perform cyclic voltammetry test on the obtained button battery, and obtain the cyclic voltammetry curves of the composite negative active material and the negative active material substrate, respectively, where the scanning voltage of the composite negative active material is 2.0V to 4.3V (if it is less than 2.0V, no peak appears), the scanning voltage of the negative active material substrate is 0V to 2.0V (if it is greater than 2.0V, no peak appears), and the scanning speed is 0.1mV / s.

[0081] It should be noted that the above-mentioned cyclic voltammetry test for the composite negative electrode active material and the negative electrode active material substrate may be performed by sampling during the manufacturing process of the negative electrode plate, or by sampling from a manufactured secondary battery.

[0082] In one embodiment, the negative plate in the above step (1) may be manufactured according to the following steps: the composite negative active material or the negative active material substrate, acetylene black, and polyvinylidene fluoride (PVDF) are thoroughly mixed in a mass ratio of 7:2:1, and then added to N-methylpyrrolidone (NMP) and mixed uniformly to obtain a slurry, which is uniformly coated on a copper foil and dried in a vacuum drying oven at 120° C. for 12 hours to obtain a negative plate.

[0083] When sampling the manufactured secondary battery for testing, the sampling may be performed according to the following method, for example.

[0084] The secondary battery is discharged (for safety reasons, secondary batteries are generally fully discharged), and then the secondary battery is removed. The negative plate is taken out and immersed in dimethyl carbonate (DMC) for a certain time (e.g., 2 hours to 10 hours), and then the negative plate is taken out and dried at a certain temperature and time (e.g., 60°C, 4 hours). After drying, the negative plate is taken out, and the dried negative plate is assembled into a button battery using the above method. A cyclic voltammetry test is performed to obtain a cyclic voltammetry curve of the composite negative active material.

[0085] The secondary battery is discharged (for safety reasons, secondary batteries are generally fully discharged), and then the secondary battery is removed. The negative plate is taken out and immersed in N,N-dimethylformamide (DMF) for a certain period of time (e.g., 12 hours or more) to remove the conductive polymer layer on the surface of the composite negative active material. The negative plate is then taken out and dried at a certain temperature and time (e.g., 60°C, 4 hours). After drying, the negative plate is taken out and the dried negative plate is assembled into a button battery using the above method. A cyclic voltammetry test is performed to obtain the cyclic voltammetry curve of the negative active material substrate.

[0086] In some embodiments, the composite negative electrode active material has an infrared spectrum with a wavenumber of 1396±41 cm -1 The first absorption peak is at a wave number of 1782±53 cm -1 and optionally a ratio of heights of the first absorption peak to the second absorption peak is 1.75±0.1. -1 It has a CN stretching vibration peak at 1782 ± 53 cm -1 It has a C=O stretching vibration peak at the position.

[0087] In the present application, infrared spectroscopy can be performed on the composite negative active material using instruments and methods known in the art, for example, an infrared spectrometer (e.g., a Thermo Fisher Nicolet iS10 Fourier transform infrared spectrometer) is used to test according to GB / T 6040-2019 infrared spectroscopy method.

[0088] In this application, the ratio of the heights of a first absorption peak to a second absorption peak may be in terms of the original peak heights or the baseline corrected peak heights.

[0089] In some embodiments, the conductive polymer layer comprises a conductive polymer including polyimide (PI), and the polyimide has a ketone carbonyl group in its main chain structure, and the molar ratio of the ketone carbonyl group C=O to the imide ring C(=O)-NC(=O) is 0.5 or more. When the polyimide has an appropriate content of ketone carbonyl group C=O in its main chain structure, it contributes to the cyclic voltammetry curve of the composite negative electrode active material having an appropriate oxidation peak potential and reduction peak potential, which on the one hand can rapidly store lithium, share the lithium storage current, and reduce the destruction of the negative electrode active material substrate caused by the current, and on the other hand can share the lithium absorption stress of the negative electrode active material substrate, thereby increasing the energy density of the secondary battery. In addition, when the polyimide has an appropriate content of ketone carbonyl group C=O in its main chain structure, it is further advantageous to reduce the lithium ion concentration on the negative electrode side and the concentration polarization.

[0090] In some embodiments, optionally, the molar ratio of the ketone carbonyl group C=O to the imide ring C(=O)-NC(=O) in the main chain structure of the polyimide is from 0.5 to 2, and further optionally from 0.5 to 1. This can prevent the oxidation peak potential of the cyclic voltammetry curve of the composite negative electrode active material from shifting to a too high voltage, which may result in inability to release some lithium ions.

[0091] In some embodiments, the polyimide is optionally obtained by polymerizing a dianhydride monomer having a ketone carbonyl group C=O in its main chain structure and a diamine monomer. The diamine monomer may or may not have a ketone carbonyl group C=O in its main chain structure. This contributes to the cyclic voltammetry curve of the composite negative electrode active material having appropriate oxidation peak potential and reduction peak potential.

[0092] In this application, "polyimide" refers to a polymer having an imide ring, C(=O)-NC(=O), in its main chain structure, and "ketone carbonyl group" refers to a carbonyl group in which both ends of the carbonyl group are directly bonded to carbon atoms, for example, both ends of the carbonyl group may optionally be directly bonded to carbon elements in an alkyl group, an alicyclic group, an aliphatic heterocyclic group, an aromatic group, a heteroaromatic group, etc.

[0093] In some embodiments, the polyimide monomer unit is as shown in Formula 1: [ka] X represents at least one of the group consisting of an alkyl group having a ketone carbonyl group C=O in the main chain structure, an alicyclic group, an aliphatic heterocyclic group, an aromatic group, and a heteroaromatic group, and Y represents a chain aliphatic diamine monomer residue, an alicyclic diamine monomer residue, or an aromatic diamine monomer residue. Chain aliphatic diamine is a general term for diamine compounds in which two amino groups (-NH2) are bonded to one chain hydrocarbon compound and its derivatives, alicyclic diamine is a general term for diamine compounds in which two amino groups (-NH2) are bonded to one alicyclic compound and its derivatives, and aromatic diamine is a general term for diamine compounds in which two amino groups (-NH2) are bonded to one aromatic compound and its derivatives. Diamine monomer residue refers to the remaining group after a diamine compound loses two amino groups (-NH2).

[0094] In some embodiments, optionally, X is [ka] represents one of the groups R1 and R2 are each independently R a represents a substituted or unsubstituted C0-C12 divalent alkyl group, a C3-C12 divalent alicyclic group, a C1-C12 divalent aliphatic heterocyclic group, a C6-C30 divalent aromatic group, or a C2-C30 divalent heteroaromatic group, p represents 0, 1, 2, 3, or 4; R a each occurrence independently represents at least one of a halogen atom, a C1-C6 alkyl group, a C1-C6 alkoxy group, and a C1-C6 halogenalkyl group, and # represents a bonding position.

[0095] In the present application, when R1 and / or R2 are a C0 divalent alkyl group, this represents that R1 and / or R2 are absent, i.e. [ka] teeth, [ka] may be also possible.

[0096] In some embodiments, optionally, Y is [ka] represents one of the groups R3 to R 12 are each independently R a represents a substituted or unsubstituted C1-C12 divalent alkyl group, a C3-C12 divalent alicyclic group, a C1-C12 divalent aliphatic heterocyclic group, a C6-C30 divalent aromatic group, or a C2-C30 divalent heteroaromatic group; R b each occurrence independently represents -O-, -S-, or -C(=O)-; R a represents at least one of a halogen atom, a C1 to C6 alkyl group, a C1 to C6 alkoxy group, and a C1 to C6 halogenalkyl group, and # represents a bonding position.

[0097] In some embodiments, optionally, Y is [ka] [ka] represents at least one of the groups # represents a bond position, p independently represents 0, 1, 2, 3 or 4 at each occurrence, R a Each occurrence independently represents at least one of a halogen atom, a C1-C6 alkyl group, a C1-C6 alkoxy group, and a C1-C6 halogenalkyl group.

[0098] In Formula 1, the heteroatoms in the aliphatic heterocyclic group and the heteroaromatic group may include at least one selected from N, O, and S, and optionally, the heteroatom in the heteroaromatic group is N. The halogen atoms and the halogen atoms in the halogenalkyl group may include at least one selected from F, Cl, and Br.

[0099] In some embodiments, the weight-average molecular weight of the conductive polymer is 30,000 to 100,000. When an oligomer is used as the conductive polymer of the present application and its weight-average molecular weight is within an appropriate range, the conductive polymer layer can have good flexibility, covering effect, and electrolyte swelling resistance. The following situations can be effectively avoided. If the weight-average molecular weight of the conductive polymer is too small, it may dissolve in the electrolyte and furthermore the covering effect may not be obtained. If the weight-average molecular weight of the conductive polymer is too large, the flexibility of the conductive polymer layer may be deteriorated by changing from an oligomer to a high polymer, and the problem of cracking may easily occur.

[0100] In this application, the weight average molecular weight of the conductive polymer has a meaning known in the art, and can be measured by using instruments and methods known in the art. For example, the composite negative active material or a negative electrode plate containing the same can be immersed in N,N-dimethylformamide (DMF) to dissolve the conductive polymer in DMF, and the solution can be collected with a syringe, and the weight average molecular weight can be measured by gel permeation chromatography (GPC), high performance liquid chromatography (HPLC), etc.

[0101] In some embodiments, the conductive polymer has a glass transition temperature (Tg) of ≦260° C., optionally 220° C. to 260° C., and further optionally 240° C. to 260° C. When the conductive polymer of the present application has an appropriate Tg, the conductive polymer layer can have good flexibility, covering effect, and electrolyte swelling resistance.

[0102] In this application, the glass transition temperature of the conductive polymer has a meaning known in the art, and can be measured by using instruments and methods known in the art. For example, the composite negative active material or a negative plate containing the same can be immersed in N,N-dimethylformamide (DMF) to dissolve the conductive polymer in DMF, and heated to volatilize the DMF to obtain a conductive polymer test sample, and the glass transition temperature can be measured by differential scanning calorimetry with reference to GB / T 29611-2013. A Mettler-Toledo DSC-3 type differential scanning calorimeter can be used as the test instrument.

[0103] In some embodiments, the conductive polymer layer has a thickness of 50 nm or less, optionally 10 nm or less, and further optionally 0.1 nm to 7 nm. When the conductive polymer layer has a thickness within a suitable range, the conductive polymer layer can have good flexibility, covering effect and electrolyte swelling resistance, and is also advantageous in that the composite negative electrode active material has a high gram capacity and a high initial coulombic efficiency.

[0104] In the present application, the thickness of the conductive polymer layer has a meaning known in the art and can be measured by using instruments and methods known in the art, for example, by a transmission electron microscope, which can more accurately determine the boundary region between the conductive polymer layer and the negative active material substrate. In order to ensure the accuracy of the test results, the thicknesses of a plurality of (for example, 30 or more) different positions in a TEM photograph obtained by using a transmission electron microscope on a sample to be tested (for example, a composite negative active material or a negative plate containing the same) can be randomly measured, and the average value of the measurements can be used as the thickness of the conductive polymer layer.

[0105] In some embodiments, the composite negative electrode active material has an average particle size of 3 μm to 15 μm, optionally 5 μm to 10 μm, and further optionally 5 μm to 8 μm. When the average particle size of the composite negative electrode active material is within an appropriate range, it is favorable to enhance the lithium ion and electron transport properties, thereby further enhancing the kinetic performance of the secondary battery.

[0106] In the present application, the average particle size of the composite negative electrode active material has a meaning known in the art, and can be measured by adopting instruments and methods known in the art. For example, a scanning electron microscope (e.g., ZEISS Sigma 300) is used to measure the composite negative electrode active material or a negative electrode plate containing the same to obtain an SEM image. A test area having a length of 100 μm and a width of 100 μm is randomly selected from the SEM image, and the lengths of the longest diagonals of all the composite negative electrode active material particles in the test area are statistically calculated to obtain a particle size distribution curve. The particle size corresponding to the particle size distribution percentage reaching 50% can be regarded as the average particle size of the composite negative electrode active material.

[0107] In some embodiments, the negative electrode active material substrate comprises at least one selected from a carbon-based material, a silicon-based material, and a tin-based material, which may or may not be prelithiated. Optionally, the carbon-based material comprises at least one selected from graphite, soft carbon, and hard carbon. Optionally, the silicon-based material comprises at least one selected from elemental silicon, silicon oxide, and silicon alloy. Optionally, the tin-based material comprises at least one selected from elemental tin, tin oxide, and tin alloy.

[0108] In some embodiments, optionally, the negative electrode active material substrate comprises at least one selected from a silicon-based material, a tin-based material, which may or may not be prelithiated.

[0109] Carbon-based materials are the most commonly used negative electrode active materials for secondary batteries, but their theoretical gram capacity is low, so their potential for improving the energy density of secondary batteries is very limited. Silicon-based and tin-based materials have the advantage of having a high theoretical gram capacity, which can increase the energy density of secondary batteries, but they have the disadvantages of severe volume expansion, being easily pulverized, and having low initial coulombic efficiency. By covering the surfaces of the silicon-based material and the tin-based material with the conductive polymer layer of the present application, the volume expansion of the silicon-based material and the tin-based material can be suppressed; the conductive polymer layer of the present application has good flexibility and is not easily broken during charging and discharging of the secondary battery, so that the silicon-based material and the tin-based material can be continuously protected, and the continuous consumption of active lithium ions and the continuous growth and thickening of the SEI film and the by-reaction product layer can be avoided, so that the secondary battery can have both high energy density and long cycle life; and the conductive polymer used in the conductive polymer layer of the present application can also quickly store and release lithium, so as to compensate for the shortcomings of the low initial coulombic efficiency of the silicon-based material and the tin-based material, so that the secondary battery can have better capacity performance.

[0110] In some embodiments, optionally, the negative electrode active material substrate is a prelithiated silicon oxide. Compared with a non-prelithiated silicon oxide, the prelithiated silicon oxide has a higher first coulombic efficiency, thereby further increasing the energy density of the secondary battery.

[0111] In some embodiments, optionally, the prelithiated silicon oxide comprises a silicon oxide substrate core, a lithium silicate intermediate layer, and a carbon coating layer, the lithium silicate intermediate layer being located on a surface of the silicon oxide substrate core and comprising lithium silicate grains and silicon and / or silicon dioxide nanograins, and the carbon coating layer being located on a surface of the lithium silicate intermediate layer.

[0112] In some embodiments, the prelithiated silicon oxide may further include residual lithium, for example, at least one selected from LiOH, Li, LiH, Li2O, and Li2CO3. The residual lithium is a lithium-containing material that is not completely reacted during the prelithiation of the silicon oxide, and is a material generated during the prelithiation of the silicon oxide. The residual lithium may dissolve and dissolve in a solvent (e.g., water) during the preparation of the negative electrode slurry, which may increase the pH of the negative electrode slurry. The increase in pH may reduce the viscosity of the negative electrode slurry and the adhesive strength of the negative electrode plate. Furthermore, the residual lithium may react with the solvent in the electrolyte during charging and discharging of the secondary battery to generate flammable hydrogen gas, which may cause serious safety concerns.

[0113] In further research, the inventors of the present application found that the conductive polymer used in the conductive polymer layer of the present application has the function of quickly storing and releasing lithium, which can not only compensate for the shortcoming of silicon oxide having a low initial coulombic efficiency, but also avoid the contact reaction between the residual lithium that has not been completely reacted during the prelithiation process and the electrolyte, thereby further improving the cycle life of the secondary battery. In addition, the conductive polymer layer of the present application can protect the carbon coating layer in the prelithiated silicon oxide and effectively prevent it from cracking or shattering.

[0114] In some embodiments, optionally, the lithium silicate grains include Li2SiO3 grains, which can improve the capacity of the secondary battery and reduce the volume expansion of the composite negative electrode active material, thereby improving the safety performance and cycle life of the secondary battery.

[0115] In some embodiments, the content of elemental silicon in the prelithiated silicon oxide may be between 50 wt% and 70 wt%.

[0116] In some embodiments, the prelithiated silicon oxide may be a commercial product, or may be optionally prepared by the following method: mixing silicon oxide with a Li precursor and heat treating, and mixing with a carbonaceous precursor and heat treating in a shielding atmosphere to obtain a prelithiated silicon oxide. Optionally, the Li precursor comprises at least one selected from LiOH, Li, LiH, Li2O, and Li2CO3. Optionally, the carbonaceous precursor comprises at least one selected from asphalt, phenolic resin, epoxy resin, starch, glucose, and cellulose.

[0117] In some embodiments, the mass ratio of the lithium silicate grains to the silicon and / or silicon dioxide nanograins in the lithium silicate intermediate layer is (10-50):(50-90), such as 10:90, 15:85, 20:80, 25:75, 30:70, 35:65, 40:60, 45:55, 50:50, or any range of values ​​therein or greater.

[0118] In some embodiments, the lithium silicate interlayer has a thickness of ≦35 nm, optionally between 15 nm and 35 nm, which can increase the initial coulombic efficiency and gram capacity of the composite negative electrode active material.

[0119] In some embodiments, the carbon coating layer has a thickness of ≦25 nm, optionally between 15 nm and 25 nm, which can enhance the electrical conductivity of the composite anode active material and can also inhibit the leaching of residual lithium into the anode slurry and electrolyte.

[0120] In some embodiments, the composite anode active material includes an anode active material substrate and a conductive polymer layer located on a surface of the anode active material substrate, wherein a cyclic voltammetry curve of the composite anode active material has an oxidation peak in the range of 3.2V to 3.6V and a reduction peak in the range of 2.1V to 2.6V, the anode active material substrate is a prelithiated silicon-based material, and optionally a prelithiated silicon oxide, the conductive polymer layer includes a conductive polymer, and the conductive polymer includes a polyimide, and a monomer unit of the polyimide is represented by the following formula 1: X represents at least one of the group consisting of an alkyl group having a ketone carbonyl group C=O in its main chain structure, an alicyclic group, an aliphatic heterocyclic group, an aromatic group, and a heteroaromatic group, Y represents a chain aliphatic diamine monomer residue, an alicyclic diamine monomer residue, or an aromatic diamine monomer residue, and the weight average molecular weight of the conductive polymer is 30,000 to 100,000. As a result, the composite negative electrode active material can have low volume expansion, high gram capacity and high initial coulombic efficiency, and can better provide a secondary battery with low volume expansion, high energy density and long cycle life. [ka]

[0121] Manufacturing method A second aspect of the present application provides a method of making the composite negative electrode active material of the first aspect of the present application by an in situ polymerization process.

[0122] Specifically, the method includes steps of: providing a negative electrode active material substrate, a dianhydride monomer having a ketone carbonyl group C=O in its main chain structure, a diamine monomer, and a solvent in step S1; dissolving the diamine monomer in the solvent to obtain a solution in which the diamine monomer is dissolved; and adding the negative electrode active material substrate to the solution in which the diamine monomer is dissolved in a shielding gas atmosphere, stirring and mixing the solution to be homogeneous; and adding the dianhydride monomer having a ketone carbonyl group C=O in its main chain structure, stirring and mixing the solution to be homogeneous. and step S4, in a shielding gas atmosphere, imidizing the prepolymer obtained in S3 and obtaining a composite negative electrode active material after the reaction is completed, wherein the composite negative electrode active material includes a negative electrode active material substrate and a conductive polymer layer located on the surface of the negative electrode active material substrate, and a cyclic voltammetry curve of the composite negative electrode active material has an oxidation peak in the range of 3.2 V to 3.6 V and a reduction peak in the range of 2.1 V to 2.6 V.

[0123] In some embodiments, the imidization reaction in S4 employs a stepwise incubation process.

[0124] Optionally, the stepwise incubation process includes a first stage of increasing the temperature to 100±15°C at a rate of 3°C / min to 5°C / min and maintaining the temperature for 1 hour to 1.5 hours, a second stage of increasing the temperature to 150±15°C at a rate of 3°C / min to 5°C / min and maintaining the temperature for 1 hour to 1.5 hours, a third stage of increasing the temperature to 200±15°C at a rate of 3°C / min to 5°C / min and maintaining the temperature for 1 hour to 1.5 hours, a fourth stage of increasing the temperature to 250±15°C at a rate of 3°C / min to 5°C / min and maintaining the temperature for 1 hour to 1.5 hours, and a fifth stage of increasing the temperature to 300±15°C at a rate of 3°C / min to 5°C / min and maintaining the temperature for 1 hour to 1.5 hours.

[0125] The stepwise heat-insulating process described above can optimally match the volatilization of the solvent, the imidization temperature, and the motion of the conductive polymer molecular chains, which is advantageous in promoting the conductive polymer molecular chains to be regularly arranged to form a crystal structure.

[0126] In the stepwise incubation process of the present application, the first step is mainly for volatilizing the solvent in the system, and the second to fourth steps are mainly for stepwise polycondensation to gradually increase the degree of imidization, which can ensure that the imidization reaction is more gentle.

[0127] In some embodiments, the molar ratio of the diamine monomer to the dianhydride monomer having a ketone carbonyl group C=O in the main chain structure is ≧2:1, optionally (2.1-2.8):1.

[0128] In some embodiments, the solvent may be an aprotic polar solvent, optionally including at least one selected from N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), and N-methylpyrrolidone (NMP).

[0129] In some embodiments, the dianhydride monomer having a ketone carbonyl group C=O in the main chain structure is [ka] and R1 and R2 are each independently R a represents a substituted or unsubstituted C0-C12 divalent alkyl group, a C3-C12 divalent alicyclic group, a C1-C12 divalent aliphatic heterocyclic group, a C6-C30 divalent aromatic group, or a C2-C30 divalent heteroaromatic group, p represents 0, 1, 2, 3, or 4; R a Each occurrence independently represents at least one of a halogen atom, a C1-C6 alkyl group, a C1-C6 alkoxy group, and a C1-C6 halogenalkyl group.

[0130] For example, the dianhydride monomer having a ketone carbonyl group C=O in the main chain structure is [ka] The compound may include at least one selected from the following compounds:

[0131] In some embodiments, the diamine monomer may include at least one selected from an aliphatic diamine monomer, a cycloaliphatic diamine monomer, and an aromatic diamine monomer, and optionally, the diamine monomer is an aromatic diamine monomer.

[0132] In some embodiments, the diamine monomer is [ka] and R3 to R 12 are each independently R a represents a substituted or unsubstituted C1-C12 divalent alkyl group, a C3-C12 divalent alicyclic group, a C1-C12 divalent aliphatic heterocyclic group, a C6-C30 divalent aromatic group, or a C2-C30 divalent heteroaromatic group; R b each occurrence independently represents -O-, -S-, or -C(=O)-; R a represents at least one of a halogen atom, a C1 to C6 alkyl group, a C1 to C6 alkoxy group, and a C1 to C6 halogenalkyl group.

[0133] In some embodiments, the diamine monomer is optionally [ka] [ka] and p independently represents 0, 1, 2, 3, or 4 at each occurrence; R aEach occurrence independently represents at least one of a halogen atom, a C1-C6 alkyl group, a C1-C6 alkoxy group, and a C1-C6 halogenalkyl group.

[0134] By way of example, the diamine monomer may be [ka] [ka] The compound may include at least one selected from the following compounds:

[0135] In some embodiments, the negative electrode active material substrate comprises at least one selected from a prelithiated or non-prelithiated carbon-based material, a silicon-based material, and a tin-based material, and is optionally a prelithiated silicon oxide. Optionally, the prelithiated silicon oxide substrate comprises a silicon oxide substrate core, a lithium silicate intermediate layer, and a carbon coating layer, the lithium silicate intermediate layer being located on a surface of the silicon oxide substrate core and comprising lithium silicate grains and silicon and / or silicon dioxide nano-grains, and the carbon coating layer being located on a surface of the lithium silicate intermediate layer. Optionally, the lithium silicate grains comprise Li2SiO3 grains.

[0136] The present application uses an in-situ polymerization method to prepare a composite negative active material, which can make the thickness of the conductive polymer layer more uniform and has a better adhesion effect between the conductive polymer layer and the negative active material substrate. In the preparation method of the present application, the dianhydride monomer and diamine monomer having a ketone carbonyl group C=O in the main chain structure are used as raw materials, which is also advantageous for making the conductive polymer layer have good flexibility, so that the negative active material substrate can be continuously protected and the secondary battery can have a longer cycle life.

[0137] The manufacturing method of the second aspect of the present application can be used to manufacture a composite negative electrode active material according to any one of the embodiments of the first aspect of the present application. The specific types and contents of each raw material used in the manufacturing process can be referenced to the composite negative electrode active material according to the first aspect of the present application, and will not be described further herein.

[0138] Negative plate A third aspect of the present application provides a negative electrode plate, the negative electrode plate including a negative electrode current collector and a negative electrode film layer located on a surface of the negative electrode current collector, wherein the negative electrode film layer includes a composite negative electrode active material of the first aspect of the present application or a composite negative electrode active material produced by the method of the second aspect of the present application, and a mass percentage of the composite negative electrode active material in the negative electrode film layer is 1% to 99%, optionally 5% to 30%, based on a total mass of the negative electrode film layer.

[0139] The negative electrode current collector has two surfaces opposing each other in a thickness direction thereof, and the negative electrode film layer is disposed on either one or both of the two opposing surfaces of the negative electrode current collector.

[0140] The negative electrode film layer does not exclude other negative electrode active materials than the composite negative electrode active material, and the other negative electrode active materials may be negative electrode active materials for secondary batteries known in the art. For example, the other negative electrode active materials may include at least one selected from natural graphite, artificial graphite, soft carbon, and hard carbon.

[0141] In some embodiments, the negative electrode film layer optionally further includes a negative electrode conductive agent. The present application does not particularly limit the type of the negative electrode conductive agent, and for example, the negative electrode conductive agent may include at least one selected from superconducting carbon, conductive graphite, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0142] In some embodiments, the negative electrode film layer optionally further includes a negative electrode adhesive. The present application is not particularly limited to the type of the negative electrode adhesive, and for example, the negative electrode adhesive may include at least one selected from styrene butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0143] In some embodiments, the negative electrode membrane layer optionally further comprises other auxiliary agents. For example, the other auxiliary agents may include a thickener, such as sodium carboxymethylcellulose (CMC), a PTC thermistor material, and the like.

[0144] In some embodiments, the negative electrode current collector may be a metal foil sheet or a composite current collector. An example of the metal foil sheet may be copper foil. The composite current collector may include a polymeric material base layer and a metal material layer formed on at least one surface of the polymeric material base layer. For example, the metal material may include at least one selected from copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. For example, the polymeric material base layer may include at least one selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0145] The negative electrode film layer is generally formed by coating a negative electrode slurry on a negative electrode current collector, drying, and cold pressing. The negative electrode slurry is generally formed by dispersing a composite negative electrode active material, an optional conductive agent, an optional adhesive, and other optional auxiliary agents in a solvent and stirring the mixture uniformly. The solvent may be, but is not limited to, N-methylpyrrolidone (NMP) or deionized water.

[0146] The negative electrode plate does not exclude additional functional layers other than the negative electrode film layer. For example, in some embodiments, the negative electrode plate of the present application further includes a conductive undercoat (e.g., made of a conductive agent and an adhesive) sandwiched between the negative electrode collector and the negative electrode film layer and disposed on the surface of the negative electrode collector. In other embodiments, the negative electrode plate of the present application further includes a protective layer covering the surface of the negative electrode film layer. secondary battery

[0147] A fourth aspect of the present application provides a secondary battery. A secondary battery is also called a rechargeable battery or a storage battery, and refers to a battery that can be continuously used by activating an active material through a charging method after the battery is discharged. A secondary battery generally includes a positive electrode plate, a negative electrode plate, a separator, and an electrolyte. The present application is not particularly limited with respect to the type of the secondary battery, and for example, the secondary battery may be a lithium ion battery, and in particular, may be a lithium ion secondary battery.

[0148] [Negative plate] The negative electrode plate used in the secondary battery of the present application is any one of the negative electrode plates according to the third aspect of the present application, which allows the secondary battery to have low volume expansion, high energy density and long cycle life.

[0149] [Positive plate] The positive electrode plate includes a positive electrode current collector and a positive electrode film layer that is disposed on at least one surface of the positive electrode current collector and contains a positive electrode active material. For example, the positive electrode current collector has two surfaces that face each other in a thickness direction of the positive electrode current collector, and the positive electrode film layer is disposed on either one or both of the two facing surfaces of the positive electrode current collector.

[0150] The positive electrode active material may adopt a positive electrode active material for secondary batteries known in this field. For example, the positive electrode active material may include at least one of lithium transition metal oxides, lithium-containing phosphates, and their respective modified compounds. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and at least one of their respective modified compounds. Examples of lithium-containing phosphates include, but are not limited to, lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, a composite material of lithium manganese iron phosphate and carbon, and at least one of their respective modified compounds. These positive electrode active materials may be used alone, or two or more of them may be combined and used.

[0151] In some embodiments, in order to further improve the energy density of the secondary battery, the positive electrode active material may include at least one selected from the lithium transition metal oxides and their modified compounds represented by Formula 1. Li a Ni b Co c M d O e A f Formula 1 In Formula 1, 0.8 ≦ a ≦ 1.2, 0.5 ≦ b < 1, 0 < c < 1, 0 < d < 1, 1 ≦ e ≦ 2, 0 ≦ f ≦ 1, M is at least one selected from Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, and B, and A is at least one selected from N, F, S, and Cl.

[0152] In this application, the modified compound of the positive electrode active material may be one obtained by doping modification and / or surface coating modification of the positive electrode active material.

[0153] The positive electrode film layer generally includes a positive electrode active material, an optional adhesive, and an optional conductive agent. The positive electrode film layer is generally formed by applying a positive electrode slurry onto a positive electrode current collector, drying, and cold pressing. The positive electrode slurry is generally formed by dispersing the positive electrode active material, an optional conductive agent, an optional adhesive, and any other components in a solvent and stirring them uniformly. The solvent may be, but is not limited to, N-methylpyrrolidone (NMP).

[0154] For example, the adhesive used in the positive electrode membrane layer may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin. For example, the conductive agent used in the positive electrode membrane layer may include at least one selected from superconducting carbon, conductive graphite, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0155] The positive electrode current collector may be a metal foil sheet or a composite current collector. An example of the metal foil sheet may be aluminum foil. The composite current collector may include a polymeric material base layer and a metal material layer formed on at least one surface of the polymeric material base layer. For example, the metal material may include at least one selected from aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. For example, the polymeric material base layer may include at least one selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0156] [Electrolytes] The electrolyte serves to conduct lithium ions between the positive and negative plates. The present application does not specifically limit the type of electrolyte, and it can be selected according to needs. For example, the electrolyte may be selected from at least one of a solid electrolyte and a liquid electrolyte (i.e., an electrolyte solution).

[0157] In some embodiments, the electrolyte may employ an electrolyte solution, the electrolyte solution including an electrolyte salt and a solvent.

[0158] The present application does not specifically limit the type of electrolyte salt, and it can be selected according to needs. In some embodiments, for example, the electrolyte salt may include at least one selected from lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonimide (LiFSI), lithium bistrifluoromethanesulfonimide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluoro(oxalato)borate (LiDFOB), lithium bis(oxalato)borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluoro(oxalato)borate (LiDFOP) and lithium tetrafluoro(oxalato)phosphate (LiTFOP).

[0159] The present application does not specifically limit the type of solvent, which can be selected according to needs. In some embodiments, for example, the solvent may include at least one selected from ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS), and diethyl sulfone (ESE).

[0160] In some embodiments, the electrolyte solution optionally further includes additives, such as an anode film-forming additive, a cathode film-forming additive, or an additive that can improve some performance of the battery, such as an additive that improves the overcharge performance of the battery, an additive that improves the high temperature performance of the battery, or an additive that improves the low temperature performance of the battery.

[0161] [Separator] A separator is further included in secondary batteries using an electrolyte and some secondary batteries using a solid electrolyte. The separator is placed between the positive and negative plates and plays a role in isolating them. The present application is not particularly limited to the type of separator, and any known separator with a porous structure having good chemical and mechanical stability may be selected.

[0162] In some embodiments, the separator may be made of at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a monolayer film or a multilayer composite film. When the separator is a multilayer composite film, the materials of each layer may be the same or different.

[0163] In some embodiments, the positive plate, the separator and the negative plate can be wound and / or stacked to form an electrode assembly.

[0164] In some embodiments, the secondary battery may include an exterior body, which may be used to package the electrode assembly and the electrolyte.

[0165] In some embodiments, the exterior of the secondary battery may be a hard case, such as a hard plastic case, an aluminum case, a steel case, etc. The exterior of the secondary battery may be a pouch, such as a bag-shaped pouch. The material of the pouch may be at least one of plastic, such as polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0166] The present application is not particularly limited to the shape of the secondary battery, which may be cylindrical, rectangular or any other shape. Figure 1 shows a secondary battery 5 with a rectangular structure as an example.

[0167] In some embodiments, as shown in FIG. 2, the exterior body may include a case 51 and a cover plate 53. The case 51 may include a bottom plate and a side plate connected on the bottom plate, and the bottom plate and the side plate surround and form a receiving cavity. The case 51 has an opening communicating with the receiving cavity, and the cover plate 53 is provided to cover the opening and close the receiving cavity. The positive electrode plate, the negative electrode plate and the separator may form an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is packaged in the receiving cavity. An electrolyte is permeated into the electrode assembly 52. ​​The number of electrode assemblies 52 included in the secondary battery 5 may be one or more, and may be adjusted according to demand.

[0168] The method for manufacturing the secondary battery of the present application is well known. In some embodiments, a secondary battery can be formed by assembling a positive electrode plate, a separator, a negative electrode plate, and an electrolyte. For example, an electrode assembly can be formed by a winding process and / or a stacking process using the positive electrode plate, the separator, and the negative electrode plate, and the electrode assembly is placed in an outer casing, dried, and then an electrolyte is injected, followed by vacuum packaging, standing, chemical formation, shaping, and other processes to obtain a secondary battery.

[0169] In some embodiments of the present application, the secondary battery according to the present application may be assembled into a battery module, and the number of secondary batteries included in the battery module may be multiple, and the specific number may be adjusted based on the application and capacity of the battery module.

[0170] Fig. 3 is a schematic diagram of an example battery module 4. As shown in Fig. 3, in the battery module 4, the multiple secondary batteries 5 may be arranged in sequence along the longitudinal direction of the battery module 4. Of course, they may be arranged in any other manner. Furthermore, the multiple secondary batteries 5 may be fixed with fasteners.

[0171] Optionally, the battery module 4 may further include a housing having an accommodating space, and the multiple secondary batteries 5 are accommodated in the accommodating space.

[0172] In some embodiments, the above battery modules may be further assembled into a battery pack, and the number of battery modules included in the battery pack can be adjusted based on the application and capacity of the battery pack.

[0173] 4 and 5 are schematic diagrams of an example battery pack 1. As shown in FIG. 4 and FIG. 5, the battery pack 1 may include a battery box and a plurality of battery modules 4 installed in the battery box. The battery box includes an upper housing 2 and a lower housing 3, and the upper housing 2 is provided to cover the lower housing 3 and is used to form a sealed space for accommodating the battery modules 4. The plurality of battery modules 4 may be arranged in the battery box according to any manner.

[0174] power consumption equipment A fifth aspect of the present application provides a power consumption device, the power consumption device including at least one of the secondary battery, battery module, or battery pack of the present application. The secondary battery, battery module, or battery pack may be used as a power source for the power consumption device, or may be used as an energy storage unit for the power consumption device. The power consumption device may be, but is not limited to, a mobile device (e.g., a mobile phone, a laptop, etc.), an electric vehicle (e.g., a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship, a satellite, an energy storage system, etc.

[0175] The power consumption device can be selected as a secondary battery, a battery module, or a battery pack depending on the demands of the usage.

[0176] 6 is a schematic diagram of an example power consuming device, such as a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. A battery pack or battery module may be employed to meet the high power and high energy density demands of the power consuming device.

[0177] Another example of the power consuming device may be a mobile phone, a tablet computer, a notebook computer, etc. The power consuming device is generally required to be lightweight and may employ a secondary battery as a power source. EXAMPLES

[0178] The following examples are provided to more specifically describe the contents disclosed in this application, and these examples are used only for illustrative purposes, and it is obvious to those skilled in the art that various modifications and changes can be made within the scope of the contents disclosed in this application. Unless otherwise indicated, all parts, percentages, and ratios reported in the following examples are based on mass, and all reagents used in the examples are commercially available or can be synthesized by common methods, and can be used directly without further processing, and the equipment used in the examples can be commercially available.

[0179] Example 1 (1) Preparation of prelithiated silicon oxide The raw material, a mixture of silicon metal and silicon dioxide, was introduced into a reactor, vaporized at 650°C for 4 hours under a vacuum of 20 Pa, deposited on an adsorption plate, cooled sufficiently, and then removed and pulverized in a ball mill. Silicon oxide particles with an average particle size of 5 μm were obtained by classification screening.

[0180] The silicon oxide particles thus prepared were mixed with LiOH powder to form a mixed powder with a Li / Si molar ratio of 0.7, which was then heat-treated at 600°C for 6 hours in a nitrogen atmosphere and pulverized in a mortar to produce silicon oxide containing a lithium-containing material, with the silicon oxide having an average particle size of 5 μm.

[0181] The silicon oxide thus produced was mixed with 15% by weight of coal-based asphalt (based on the mass of silicon oxide), and then heat-treated at 700°C for 3 hours under an argon atmosphere, cooled to room temperature after completion, and sieved to obtain prelithiated silicon oxide with an average particle size of 5 μm. The outermost layer of the prelithiated silicon oxide is a carbon coating layer with a thickness of about 15 nm, the middle layer is a mixed layer of Li2SiO3 crystal grains and silicon and / or silicon dioxide nanocrystal grains with a thickness of about 30 nm, and the mass ratio of Li2SiO3 crystal grains to silicon and / or silicon dioxide nanocrystal grains is about 25:75, and the core is a mixture of silicon and / or silicon dioxide nanocrystal grains. (2) Manufacturing of composite negative electrode active material

[0182] Under argon atmosphere, 60mg of the prelithiated silicon oxide (average particle size is 5μm) prepared above is immersed in 100mL of N,N-dimethylformamide (DMF) solution in which 30mg of compound 1-1 is dissolved, and stirred for 30min. Then, 30mg of compound 2-1 is added to the above solution, and stirring is continued to carry out polymerization reaction for 12 hours. After the reaction is completed, the obtained precursor is centrifuged and washed three times with DMF at a speed of 8000rpm, and dried in a vacuum drying oven at 80℃ for 12 hours to obtain a prepolymer. The obtained prepolymer is transferred to a tube furnace, and under argon atmosphere, it is heated to 100℃, 150℃, 200℃, 250℃ and 300℃ according to a program, and each is kept warm for 1 hour, and the heating rate is 3℃ / min. After the reaction is completed, a composite negative electrode active material is obtained. [ka] [ka]

[0183] (3) Manufacturing of negative electrodes The composite negative electrode active material prepared above, artificial graphite, carbon black as a conductive agent, styrene butadiene rubber (SBR) as an adhesive, and sodium carboxymethyl cellulose (CMC) as a dispersant were mixed in a mass ratio of 12:85:1:1:1, deionized water was added as a solvent, and the mixture was stirred uniformly to obtain a negative electrode slurry. The obtained negative electrode slurry was mixed at a concentration of 9.7 mg / cm. 2 The paste was uniformly applied to a copper foil negative current collector having a thickness of 7 μm at an areal density of 100 μm, and the resulting mixture was dried, cold pressed, and slit to obtain a negative plate.

[0184] (4) Manufacturing of positive electrodes Positive electrode active material LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM523), polyvinylidene fluoride (PVDF) as an adhesive, and acetylene black as a conductive agent were mixed in a mass ratio of 98:1:1, N-methylpyrrolidone (NMP) was added as a solvent, and the mixture was stirred uniformly under vacuum to obtain a positive electrode slurry. The obtained positive electrode slurry was 13.7 mg / cm 2 The paste was uniformly applied to an aluminum foil positive electrode current collector having a thickness of 13 μm at an areal density of 100 μm, and the resulting mixture was dried at 140° C., cold pressed, and slit to obtain a positive electrode plate.

[0185] (5) Electrolyte production In an argon atmosphere glove box (water and oxygen contents are both 0.1 ppm or less), ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed uniformly as organic solvents in a volume ratio of 3:7, and 12.5% ​​(based on the total mass of the organic solvent) of LiPF6 was dissolved in the organic solvent and stirred uniformly to obtain an electrolyte solution.

[0186] (6) Separator A commercially available PP-PE copolymer microporous membrane (Model No. 20, from Zhuoga Electronics Technology Co., Ltd.) with a thickness of 20 μm and an average pore size of 80 nm was used.

[0187] (7) Manufacture of secondary batteries A positive electrode plate, a separator, and a negative electrode plate were stacked in that order and wound up to obtain an electrode assembly. The electrode assembly was then placed in an outer casing, the above-mentioned electrolyte solution was injected, and the secondary battery was obtained through processes such as packaging, standing, chemical formation, and aging. Examples 2 to 15 and Comparative Examples 3 to 5

[0188] The manufacturing method of the secondary battery is similar to that of Example 1, except that the manufacturing parameters of the composite negative electrode active material are different, as shown in Table 1.

[0189] In Table 1, the molecular formula of each compound is as follows: [ka]

[0190] Comparative Example 1 The method for manufacturing the secondary battery was similar to that of Example 1, except that when manufacturing the negative electrode plate, prelithiated silicon oxide was directly used instead of the composite negative electrode active material prepared in Example 1.

[0191] Comparative Example 2 The method for manufacturing the secondary battery was similar to that of Example 1, except that when manufacturing the negative plate, prelithiated silicon oxide coated with polythiophene was used instead of the composite negative active material prepared in Example 1.

[0192] [Table 1]

[0193] Testing part (1) Conductive polymer weight average molecular weight test The composite negative electrode active material prepared above was immersed in N,N-dimethylformamide (DMF) to dissolve the conductive polymer in DMF, and the solution was collected by a syringe to test the weight average molecular weight of the conductive polymer by gel permeation chromatography, and the testing equipment used was a Tosoh Corporation HLC-8320 GPC half micro gel permeation chromatograph.

[0194] (2) Testing the glass transition temperature (Tg) of conductive polymers The composite negative electrode active material prepared above was immersed in N,N-dimethylformamide (DMF) to dissolve the conductive polymer in DMF, and the DMF was volatilized by heating to obtain a conductive polymer test sample.

[0195] A Mettler-Toledo DSC-3 type differential scanning calorimeter was adopted to test the Tg of the conductive polymer. The test was carried out according to the following steps: about 10 mg of test sample was weighed and placed into a flat-bottomed Al2O3 crucible, shaken flat, covered, and heated from 35°C to 600°C at a rate of 10°C / min, argon gas was adopted as the shielding gas, the purge gas flow rate was 50mL / min, and the shielding gas flow rate was 20mL / min.

[0196] (3) Conductive polymer layer thickness test A TEM photograph of the negative electrode plate was obtained by a Thermo Fisher Talos transmission electron microscope, and the thickness was measured at 30 different positions in the TEM photograph, and the average value was taken as the thickness of the conductive polymer layer.

[0197] (4) Cyclic voltammetry test of composite negative electrode active material A metallic lithium sheet was used as the counter electrode, and the electrolyte used 1 mol / L lithium hexafluorophosphate (LiPF6) as the solute and a 1:1 volumetric mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) as the solvent. Glass fiber was used as the separator, and this was assembled together with the negative electrode plate produced above into a CR2032 button battery in a glove box filled with argon gas (with water and oxygen contents both below 0.1 ppm). The packaged button battery was then placed in the glove box and left to stand for 12 hours or more to age it.

[0198] Using Shanghai Chenhua CHI 660 electrochemical workstation, cyclic voltammetry test was performed on the obtained button battery to obtain the cyclic voltammetry curve of the composite negative electrode active material, where the scanning voltages of Examples 1-15 and Comparative Examples 3-5 are 2.0V-4.3V, the scanning voltage of Comparative Example 1 is 0V-2.0V, the scanning voltage of Comparative Example 2 is 0V-4.0V, and the scanning rate is 0.1mV / s in order to better observe the peak positions. At the same time, the oxidation peak potential and reduction peak potential shown in Table 2 do not take into account the peak positions of artificial graphite.

[0199] (5) Testing the initial gram capacity and initial coulombic efficiency of button batteries At 25℃, the above-prepared CR2032 button battery was first discharged at a constant current of 10mA / g to 0V, and the first cycle discharge capacity of the button battery was recorded. Then, the battery was charged at a constant current of 10mA / g to 2.5V, and the first cycle charge capacity of the button battery was recorded. Initial gram capacity of the button battery (mAh / g) = first cycle charge capacity of the button battery / (mass of composite negative electrode active material + mass of artificial graphite). Initial coulombic efficiency of the button battery (%) = first cycle charge capacity of the button battery / first cycle discharge capacity of the button battery × 100%.

[0200] (6) Cycle performance test of secondary batteries At 25°C, the secondary battery prepared above was charged at a rate of 2C and discharged at a rate of 1C, and a continuous cycle test was performed from 3% SOC to 97% SOC until the capacity of the secondary battery became less than 80% of the discharge capacity at the first cycle, and the number of cycles was recorded. In this application, the capacity retention performance of the secondary battery is evaluated according to the number of cycles when fast charging at a rate of 2C at 25°C, and the higher the number of cycles of the secondary battery, the better the capacity retention performance of the secondary battery.

[0201] [Table 2]

[0202] As can be seen from the test results of Examples 1 to 15 and Comparative Examples 1 to 5, by providing a conductive polymer layer on the surface of the prelithiated silicon oxide and making the cyclic voltammetry curve of the composite negative electrode active material have an oxidation peak in the range of 3.2 V to 3.6 V and a reduction peak in the range of 2.1 V to 2.6 V, the composite negative electrode active material obtained can have both a high gram capacity and a high initial coulombic efficiency, and furthermore, the secondary battery can have a long cycle life.

[0203] 7 shows the infrared spectrum of the composite anode active material prepared in Example 1 and Comparative Example 1. The test equipment is a Thermo Fisher Nicolet iS10 Fourier transform infrared spectrometer, and the test standard is in accordance with GB / T 6040-2019. As can be seen from FIG. 7, the composite anode active material prepared in Example 1 has a 1396±41 cm -1 It has a CN stretching vibration peak at 1782 ± 53 cm -1 This indicates that the surface of the prelithiated silicon oxide was successfully coated with a conductive polymer by the in situ polymerization method according to the present application.

[0204] FIG 8 is a gel permeation chromatography (GPC) image of the conductive polymer layer in the composite anode active material prepared in Example 1. FIG 9 is a scanning electron microscope (SEM) image of the composite anode active material prepared in Example 1. FIG 10 is a transmission electron microscope (TEM) image of the composite anode active material prepared in Example 4. FIG 11 is a cyclic voltammetry curve of the anode active material prepared in Example 3.

[0205] 11, the cyclic voltammetry curve of the composite negative electrode active material according to the present application has an oxidation peak in the range of 3.2 V to 3.6 V and a reduction peak in the range of 2.1 V to 2.6 V. In Comparative Example 1, the prelithiated silicon oxide not coated with a conductive polymer layer does not show an oxidation peak or a reduction peak in the scanning voltage range of 2.0 V to 4.3 V.

[0206] The conductive polymer layer in the composite negative electrode active material prepared in Comparative Examples 2 to 5 adopts a general polythiophene or a polyimide having no ketone carbonyl group in the main chain structure as the conductive polymer, which can improve the initial coulombic efficiency of the button battery and the number of cycles of the secondary battery to a certain extent, but the improvement effect is limited. Possible reasons are that the pre-lithiated silicon oxide has a severe volume expansion, so when the general polythiophene or the polyimide having no ketone carbonyl group in the main chain structure is adopted as the conductive polymer, the pre-lithiated silicon oxide cannot be continuously protected, and when the general polythiophene or the polyimide having no ketone carbonyl group in the main chain structure is adopted as the conductive polymer, the improvement effect of the oxidation peak potential and the reduction peak potential of the cyclic voltammetry curve of the composite negative electrode active material is limited, and the conductive polymer layer has a poor effect of sharing the lithium storage current and the lithium absorption stress, and cannot effectively reduce the destruction of the pre-lithiated silicon oxide particles caused by the current, and the conductive polymer layer also has a poor effect of reducing the concentration polarization on the negative electrode side. Therefore, when a typical polythiophene or a polyimide having no ketone carbonyl group in the main chain structure is used as the conductive polymer, it is difficult to impart a long cycle life to the secondary battery.

[0207] FIG. 12 is a scanning electron microscope (SEM) image of a cross section of the composite negative electrode active material after the secondary battery capacity produced in Example 1 has decayed to 80% of the discharge capacity at the first cycle. FIG. 13 is a scanning electron microscope (SEM) image of a cross section of the composite negative electrode active material after the secondary battery capacity produced in Comparative Example 1 has decayed to 80% of the discharge capacity at the first cycle. As can be seen from FIG. 12 and FIG. 13, the thickness of the by-reaction product layer after cycling of the composite negative electrode active material produced in Example 1 is about 484 nm, while the thickness of the by-reaction product layer after cycling of the prelithiated silicon oxide not covered with the conductive polymer layer adopted in Comparative Example 1 is about 1423 nm. Therefore, the conductive polymer layer in the composite negative electrode active material according to the present application can continue to protect the negative electrode active material substrate, thereby effectively avoiding the continuous consumption of active lithium ions and the continuous growth and thickening of the SEI film and the by-reaction product layer, and further, the secondary battery adopting it can have both high energy density and long cycle life.

[0208] It should be noted that the present application is not limited to the above-mentioned embodiment. The above-mentioned embodiment is an example, and any embodiment having substantially the same configuration as the technical idea and achieving the same effect within the scope of the technical proposal of the present application is included in the technical scope of the present application. In addition, various modifications that a person skilled in the art can make to the embodiment and other forms constructed by combining some of the components in the embodiment are also included in the scope of the present application, within the scope of the purpose of the present application. [Explanation of symbols]

[0209] The symbols are explained as follows: 1 battery pack, 2 upper housing, 3 lower housing, 4 battery module, 5 secondary battery, 51 case, 52 electrode assembly, 53 cover plate.

Claims

1. A composite negative electrode active material comprising: a negative electrode active material substrate; and a conductive polymer layer located on a surface of the negative electrode active material substrate, wherein a cyclic voltammetry curve of the composite negative electrode active material has an oxidation peak in a range of 3.2 V to 3.6 V and a reduction peak in a range of 2.1 V to 2.6 V; The cyclic voltammetry curve of the composite negative electrode active material is obtained by testing in the following manner: (1) providing a negative electrode plate containing the composite negative electrode active material; (2) using a metal lithium sheet as a counter electrode, a 1 mol / L lithium hexafluorophosphate solute for the electrolyte, a 1:1 volume ratio mixture of ethylene carbonate and dimethyl carbonate as the solvent, and glass fiber as a separator; and assembling the negative electrode plate and the counter electrode into a button cell in a glove box filled with argon gas; and placing the packaged button cell in the glove box for more than 12 hours for aging; and (3) using an electrochemical workstation to perform a cyclic voltammetry test on the obtained button cell to obtain a cyclic voltammetry curve of the composite negative electrode active material, in which the scanning voltage is 2.0V-4.3V and the scanning speed is 0.1mV / s.

2. The cyclic voltammetry curve of the composite negative electrode active material has an oxidation peak in the range of 3.3 V to 3.55 V; and / or 2. The composite negative electrode active material of claim 1, wherein a cyclic voltammetry curve of the composite negative electrode active material has a reduction peak in the range of 2.2V to 2.45V.

3. an oxidation peak potential of the cyclic voltammetry curve of the composite negative electrode active material is greater than an oxidation peak potential of the cyclic voltammetry curve of the negative electrode active material substrate, and optionally a difference between the oxidation peak potential of the cyclic voltammetry curve of the composite negative electrode active material and the oxidation peak potential of the cyclic voltammetry curve of the negative electrode active material substrate is 2.4 V to 2.8 V, and further optionally 2.5 V to 2.75 V; and / or 3. The composite negative electrode active material according to claim 1, wherein a reduction peak potential of a cyclic voltammetry curve of the composite negative electrode active material is greater than a reduction peak potential of a cyclic voltammetry curve of the negative electrode active material substrate, and optionally a difference between the reduction peak potential of the cyclic voltammetry curve of the composite negative electrode active material and the reduction peak potential of the cyclic voltammetry curve of the negative electrode active material substrate is 1.5 V to 2.1 V, and further optionally 1.7 V to 1.95 V.

4. The infrared spectrum of the composite negative electrode active material has a wave number of 1396±41 cm －１ The first absorption peak is at a wave number of 1782±53 cm －１ and optionally a ratio of heights of the first absorption peak and the second absorption peak is 1.75±0.

1.

5. the conductive polymer layer comprises a conductive polymer, the conductive polymer comprises a polyimide, the polyimide has a ketone carbonyl group in its main chain structure, and the molar ratio of the ketone carbonyl group C═O to the imide ring C(═O)—N—C(═O) is 0.5 or more, optionally 0.5 to 2, and further optionally 0.5 to 1; Optionally, the polyimide is obtained by polymerizing a dianhydride monomer having a ketone carbonyl group C=O in a main chain structure and a diamine monomer.

6. The monomer unit of the polyimide is as shown in Formula 1: 【Chemistry 1】 X represents at least one selected from the group consisting of an alkyl group having a ketone carbonyl group C═O in its main chain structure, an alicyclic group, an aliphatic heterocyclic group, an aromatic group, and a heteroaromatic group; Y represents a chain aliphatic diamine monomer residue, an alicyclic diamine monomer residue, or an aromatic diamine monomer residue; Optionally, X is 【Chemistry 2】 represents one of the groups R １ , R ２ are each independently R ａ represents a substituted or unsubstituted C0-C12 divalent alkyl group, a C3-C12 divalent alicyclic group, a C1-C12 divalent aliphatic heterocyclic group, a C6-C30 divalent aromatic group, or a C2-C30 divalent heteroaromatic group; p represents 0, 1, 2, 3, or 4; R ａ each occurrence independently represents at least one of a halogen atom, a C1-C6 alkyl group, a C1-C6 alkoxy group, and a C1-C6 halogenalkyl group, and # represents a bonding position; Optionally, Y is 【Chemistry 3】 represents one of the groups R ３ From R １２ are each independently R ａ represents a substituted or unsubstituted C1-C12 divalent alkyl group, C3-C12 divalent alicyclic group, C1-C12 divalent aliphatic heterocyclic group, C6-C30 divalent aromatic group, or C2-C30 divalent heteroaromatic group; R ｂ each occurrence independently represents -O-, -S- or -C(=O)-; R ａ represents at least one of a halogen atom, a C1-C6 alkyl group, a C1-C6 alkoxy group, and a C1-C6 halogenalkyl group; # represents a bonding position; Further optionally, Y is 【Chemistry 4】 【Chemistry 5】 represents one of the groups # represents a bonding position, p represents independently 0, 1, 2, 3 or 4 at each occurrence, R ａ each occurrence independently represents at least one of a halogen atom, a C1-C6 alkyl group, a C1-C6 alkoxy group, and a C1-C6 halogenalkyl group.

7. The weight average molecular weight of the conductive polymer is 30,000 to 100,000, and / or 7. The composite anode active material of claim 5 or 6, wherein the conductive polymer has a glass transition temperature of 220°C to 260°C, optionally 240°C to 260°C.

8. the thickness of the conductive polymer layer is 50 nm or less, optionally 10 nm or less, further optionally 0.1 nm to 7 nm; and / or 8. The composite anode active material of claim 1, wherein the composite anode active material has an average particle size of 3 μm to 15 μm, optionally 5 μm to 10 μm, and further optionally 5 μm to 8 μm.

9. the negative electrode active material substrate comprises at least one selected from a prelithiated or non-prelithiated carbon-based material, a silicon-based material, and a tin-based material; Optionally, the carbon-based material comprises at least one selected from graphite, soft carbon, and hard carbon; Optionally, the silicon-based material comprises at least one selected from elemental silicon, silicon oxide, and silicon alloy; 9. The composite anode active material of claim 1, wherein the tin-based material optionally comprises at least one selected from elemental tin, tin oxides, and tin alloys.

10. The negative electrode active material substrate is a prelithiated silicon oxide, and optionally, the prelithiated silicon oxide comprises: a silicon oxide substrate core; a lithium silicate intermediate layer located on the surface of the silicon oxide substrate core and comprising lithium silicate grains and silicon and / or silicon dioxide nanograins; a carbon coating layer located on a surface of the lithium silicate intermediate layer; Optionally, the lithium silicate grains comprise Li ２ SiO ３ 10. The composite negative electrode active material of claim 9 comprising crystalline grains.

11. the mass ratio of the lithium silicate grains to the silicon and / or silicon dioxide nanograins in the lithium silicate intermediate layer is (10-50):(50-90); and / or the thickness of the lithium silicate intermediate layer is ≦35 nm, optionally between 15 nm and 35 nm; and / or 11. The composite anode active material of claim 10, wherein the carbon coating layer has a thickness of ≦25 nm, optionally from 15 nm to 25 nm.

12. A method for producing the composite anode active material of any one of claims 1 to 11, comprising the steps of: Step S1 of providing a negative electrode active material substrate, a dianhydride monomer having a ketone carbonyl group C=O in a main chain structure, a diamine monomer, and a solvent, optionally including at least one selected from a chain aliphatic diamine monomer, an alicyclic diamine monomer, and an aromatic diamine monomer; Step S2 of dissolving the diamine monomer in the solvent to obtain a solution in which the diamine monomer is dissolved; Step S3 of adding the negative electrode active material substrate to the solution in which the diamine monomer is dissolved in a shielding gas atmosphere, stirring and mixing uniformly, adding the dianhydride monomer having a ketone carbonyl group C=O in the main chain structure, stirring and mixing uniformly, and carrying out a polymerization reaction. After the reaction is completed, the mixture is washed and dried to obtain a prepolymer. and step S4 of imidizing the prepolymer obtained in step S3 in a shielding gas atmosphere to obtain a composite negative electrode active material after the reaction is completed. wherein the composite negative electrode active material includes a negative electrode active material substrate and a conductive polymer layer located on a surface of the negative electrode active material substrate, and a cyclic voltammetry curve of the composite negative electrode active material has an oxidation peak in a range of 3.2 V to 3.6 V and a reduction peak in a range of 2.1 V to 2.6 V.

13. The method of claim 12, wherein the imidization reaction in S4 adopts a stepwise incubation process, and optionally the stepwise incubation process includes: a first stage of increasing temperature to 100±15° C. at a rate of 3° C. / min to 5° C. / min and incubating for 1 hour to 1.5 hours; a second stage of increasing temperature to 150±15° C. at a rate of 3° C. / min to 5° C. / min and incubating for 1 hour to 1.5 hours; a third stage of increasing temperature to 200±15° C. at a rate of 3° C. / min to 5° C. / min and incubating for 1 hour to 1.5 hours; a fourth stage of increasing temperature to 250±15° C. at a rate of 3° C. / min to 5° C. / min and incubating for 1 hour to 1.5 hours; and a fifth stage of increasing temperature to 300±15° C. at a rate of 3° C. / min to 5° C. / min and incubating for 1 hour to 1.5 hours.

14. the molar ratio of the diamine monomer to the dianhydride monomer having a ketone carbonyl group C=O in the backbone structure is ≧2:1, optionally (2.1-2.8):1; and / or The method of claim 12 or 13, wherein the solvent is an aprotic polar solvent, optionally comprising at least one selected from N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone.

15. The dianhydride monomer having a ketone carbonyl group C=O in the main chain structure is 【Chemistry 6】 and R １ , R ２ are each independently R ａ represents a substituted or unsubstituted C0-C12 divalent alkyl group, a C3-C12 divalent alicyclic group, a C1-C12 divalent aliphatic heterocyclic group, a C6-C30 divalent aromatic group, or a C2-C30 divalent heteroaromatic group; p represents 0, 1, 2, 3, or 4; R ａ each occurrence independently represents at least one of a halogen atom, a C1-C6 alkyl group, a C1-C6 alkoxy group, and a C1-C6 halogenalkyl group; Optionally, the dianhydride monomer having a ketone carbonyl group C═O in the backbone structure is 【Chemistry 7】 The method according to any one of claims 12 to 14, comprising at least one compound selected from the group consisting of:

16. The diamine monomer is 【Chemistry 8】 and R ３ From R １２ are each independently R ａ represents a substituted or unsubstituted C1-C12 divalent alkyl group, C3-C12 divalent alicyclic group, C1-C12 divalent aliphatic heterocyclic group, C6-C30 divalent aromatic group, or C2-C30 divalent heteroaromatic group; R ｂ each occurrence independently represents -O-, -S- or -C(=O)-; R ａ represents at least one of a halogen atom, a C1-C6 alkyl group, a C1-C6 alkoxy group, and a C1-C6 halogenalkyl group; Optionally, the diamine monomer is 【Chemistry 9】 【Chemistry 10】 and p independently represents 0, 1, 2, 3, or 4 at each occurrence; R ａ each occurrence independently represents at least one of a halogen atom, a C1-C6 alkyl group, a C1-C6 alkoxy group, and a C1-C6 halogenalkyl group; Further optionally, the diamine monomer is 【Chemistry 11】 【Chemistry 12】 The method according to any one of claims 12 to 15, comprising at least one compound selected from the group consisting of:

17. the negative electrode active material substrate comprises at least one selected from a prelithiated or non-prelithiated carbon-based material, a silicon-based material, and a tin-based material, and is optionally a prelithiated silicon oxide; Optionally, the prelithiated silicon oxide comprises: a silicon oxide substrate core; a lithium silicate intermediate layer located on the surface of the silicon oxide substrate core and comprising lithium silicate grains and silicon and / or silicon dioxide nanograins; a carbon coating layer located on a surface of the lithium silicate intermediate layer; Optionally, the lithium silicate grains comprise Li ２ SiO ３ The method of any one of claims 12 to 16, comprising grains.

18. 18. A negative electrode plate comprising: a negative electrode current collector; and a negative electrode film layer located on a surface of the negative electrode current collector, the negative electrode film layer comprising a composite negative electrode active material according to any one of claims 1 to 11 or a composite negative electrode active material produced by the method of any one of claims 12 to 17, and a mass percentage of the composite negative electrode active material in the negative electrode film layer is from 1% to 99%, optionally from 5% to 30%, based on a total mass of the negative electrode film layer.

19. A secondary battery comprising the negative electrode plate according to claim 18.

20. 20. A power consuming device comprising the secondary battery of claim 19.

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