A negative electrode additive, a preparation method and application thereof

Abstract

The application discloses a negative electrode additive and a preparation method and application thereof, and relates to the technical field of batteries, in particular to a negative electrode additive and a preparation method and application thereof. The preparation method of the negative electrode additive comprises the following steps: (1) uniformly mixing a conductive polymer monomer and an organic sodium salt in a solvent to obtain a mixture; (2) adding an initiator solution to the mixture prepared in the step (1) and stirring, and then filtering, washing and drying to obtain the negative electrode additive. The negative electrode additive prepared by the above preparation method is rich in sodium ions and has good conductivity. The composite material formed by mixing the negative electrode additive with hard carbon can be used as a negative electrode material to construct a sodium ion battery. The capacity and the initial coulomb efficiency of the sodium ion battery are effectively improved, and the problem that the capacity of the hard carbon negative electrode attenuates rapidly during the cycle process is effectively solved, so that the cycle stability of the battery is improved.

Description

Technical Field

[0001] This invention relates to the field of battery technology, specifically to a negative electrode additive, its preparation method, and its application. Background Technology

[0002] Due to their abundant resources and high cost-effectiveness, sodium-ion batteries (SIBs) have shown unprecedented potential as an alternative to lithium-ion batteries, especially in electric vehicles (EVs) and large-scale power systems. Hard carbon is a preferred candidate material for the anode of commercial SIBs due to its low cost, large interlayer spacing, and suitable redox potential. The disordered crystal arrangement and large interlayer spacing of hard carbon provide space for storing large amounts of charge; however, this disordered structure leads to the consumption of large amounts of active sodium during charge and discharge, forming an SEI film that causes irreversible depletion, resulting in low initial coulombic efficiency (ICE) and poor cycle stability. Furthermore, the inherently poor conductivity of hard carbon further limits its rate performance and cycle performance, impacting its commercial applications.

[0003] Current methods for improving the initial efficiency of hard carbon batteries mainly include pre-sodiumization, carbon material surface coating, and electrolyte optimization. However, these methods still have limitations. Surface coating generally requires depositing an inert layer or carbon layer on the carbon surface using atomic layer deposition technology to reduce surface activity. This method requires complex operations and equipment. Electrolyte regulation has shown that ether-based electrolytes have high initial efficiency, but poor cycle stability. Pre-sodiumization involves introducing exogenous sodium into the battery system in a suitable manner and form, by introducing excess Na. + The formation of a stable SEI can simultaneously compensate for Na. + To prevent electrolyte loss and continued decomposition, current pre-sodiuming technologies primarily employ electrode-level pre-sodiuming. This process requires additional steps, equipment, and environmental space, significantly increasing manufacturing time and equipment costs, hindering commercialization. Therefore, there is still a need to develop green, simple, effective, and controllable methods to improve the performance of hard carbon materials. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a negative electrode additive, its preparation method, and its application. A highly conductive negative electrode additive rich in sodium ions is prepared by the self-polymerization of conductive polymer monomers in the presence of an organic sodium salt. This negative electrode additive and hard carbon can be mixed by ball milling to prepare a composite negative electrode material. Compared to a hard carbon negative electrode, the composite negative electrode material containing the negative electrode additive can improve the conductivity of the negative electrode and compensate for the sodium content during the formation of the SEI film. + This reduces the loss of energy, thus enabling sodium-ion batteries constructed from this composite anode material to possess high capacity, high initial coulombic efficiency, and excellent cycle stability.

[0005] Specifically, the following technical solutions are provided:

[0006] The first aspect of this invention provides a method for preparing a negative electrode additive, comprising the following steps:

[0007] (1) Add the conductive polymer monomer and organic sodium salt to the solvent and mix evenly to obtain a mixture;

[0008] (2) Add an initiator solution to the mixture prepared in step (1), stir, filter and dry to obtain the negative electrode additive.

[0009] Further, in step (1), the conductive polymer monomer is aniline, pyrrole, or thiophene.

[0010] Further, in step (1), the organic sodium salt is selected from one or more of disodium diaminetetraacetate, disodium glutarate, sodium benzoate, and disodium phthalate.

[0011] Further, in step (1), the solvent is selected from one or more of water, ethanol, ethylene glycol, N-methylpyrrolidone, dimethylformamide, and toluene.

[0012] Further, in step (1), the mass ratio of the conductive polymer monomer to the organic sodium salt is (1-3):1, for example 1:1, 2:1, 3:1, etc., including but not limited to the mass ratios listed above.

[0013] Further, in step (2), the initiator solution is obtained by dissolving the initiator in a solvent. Preferably, the initiator is ammonium persulfate, and the solvent contains water.

[0014] Further, in step (2), the ratio of the molar amount of the conductive polymer monomer in the mixture to the molar amount of the initiator in the initiator solution is 1:(1-4), for example 1:1, 1:2, 1:3, 1:4, etc., including but not limited to the ratios listed above.

[0015] Further, in step (2), the initiator solution is added dropwise to the mixture, and during the dropwise addition process: the temperature is preferably -15 to 5°C, and the dropwise addition time is preferably 1 to 24 hours.

[0016] Furthermore, in step (2), the stirring time is preferably 2-4 hours.

[0017] Furthermore, in step (2), the drying temperature is preferably 80-100℃, and the drying time is preferably 4-5h.

[0018] Furthermore, the preparation method further includes a step of washing the filtered product; the washing solvent is preferably ethanol and / or water.

[0019] A second aspect of the present invention provides a negative electrode additive, which is prepared by the preparation method described in the first aspect.

[0020] A third aspect of the present invention provides a composite anode material comprising hard carbon and the anode additives described in the second aspect.

[0021] Furthermore, the hard carbon is prepared by the following method, specifically including the following steps:

[0022] S1. The carbon source is subjected to a first calcination treatment under a protective atmosphere to obtain a carbon precursor;

[0023] S2. The carbon precursor is subjected to a second calcination treatment in the presence of a gas-phase pore-forming agent, and then subjected to a third calcination treatment under a protective atmosphere. The product is then acid-washed and dried to obtain the hard carbon.

[0024] Furthermore, in S1, the carbon source can be selected from one or more of polymer materials, coal materials, and biomass materials. The polymer materials include phenolic resin, polytetrafluoroethylene, epoxy resin, furan resin, etc. The coal materials include anthracite, bituminous coal, lignite, coal tar, etc. The biomass materials include sucrose, glucose, starch, coconut shell, sugarcane, poplar wood, etc.

[0025] Furthermore, the protective atmosphere includes one or more of nitrogen, argon, helium, and krypton.

[0026] Furthermore, in S1, the temperature of the first calcination treatment is 450-550℃, and the time of the first calcination treatment is 3-5h.

[0027] Further, in S2, the gas phase pore-forming agent includes one or more of carbon dioxide, oxygen, air, and water vapor; preferably, the gas phase pore-forming agent is introduced during the heat preservation stage of the second calcination treatment, and the gas flow rate of the gas phase pore-forming agent is preferably 10-100 L / min.

[0028] Furthermore, in S2, the temperature of the second calcination treatment is 800-900℃, and the time of the second calcination treatment is 1-10h.

[0029] Furthermore, in S2, the temperature of the third calcination treatment is 1100-1500℃, and the time of the third calcination treatment is 5-10h.

[0030] Furthermore, the composite negative electrode material is obtained by mixing hard carbon and the negative electrode additive through ball milling; preferably, the ball milling speed is 400-500 rpm and the ball milling time is 6-10 h.

[0031] A fourth aspect of the present invention provides a secondary battery comprising the composite negative electrode material described in the third aspect.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0033] 1. This invention provides a negative electrode additive, which is obtained by in-situ polymerization of conductive polymer monomers in a solution containing organic sodium salt. The negative electrode additive contains an organic sodium salt core and a chain-like polymer shell, thereby giving the prepared negative electrode additive high conductivity while being rich in sodium ions.

[0034] 2. This invention also provides a composite negative electrode material, prepared by mixing the above-mentioned negative electrode additive with hard carbon through ball milling. The negative electrode additive dispersed on the surface of the hard carbon particles can not only effectively improve the electronic conductivity of hard carbon, but also the sodium-rich negative electrode additive can compensate for the Na+ ions during the formation of the SEI film of the negative electrode. + This reduces battery capacity and initial coulombic efficiency by minimizing losses. Simultaneously, the negative electrode additive acts as a protective layer, reducing side reactions between hard carbon and the electrolyte and decreasing irreversible capacity. Furthermore, the polymer layer on the surface of the negative electrode additive helps form a uniform and stable SEI film, thereby improving the battery's cycle stability.

[0035] 3. Sodium-ion batteries constructed using the above-mentioned composite anode materials as anode active materials exhibit high capacity, high coulombic efficiency, and excellent cycle stability. Attached Figure Description

[0036] Figure 1 The graphs show the cyclic performance test results for Example 1 and the comparative example. Detailed Implementation

[0037] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items. "Comprising" or "containing" as used herein means that it may include or contain other components in addition to the stated components. "Comprising" or "containing" as used herein may also be replaced with the closed form "is" or "consisting of".

[0038] As described in the background section, hard carbon has a disordered internal crystal arrangement and large interlayer distance, which provides space for storing a large amount of charge. However, this disordered structure causes it to consume a large amount of active sodium during charging and discharging, forming an SEI film that causes irreversible consumption, resulting in low initial coulombic efficiency (ICE) and poor cycle stability. At the same time, the poor conductivity of hard carbon itself will further limit its rate performance and cycle performance, affecting its commercial application.

[0039] To address the above problems, this invention provides a method for preparing a negative electrode additive, comprising the following steps:

[0040] (1) Add the conductive polymer monomer and organic sodium salt to the solvent and mix evenly to obtain a mixture;

[0041] (2) Add an initiator solution to the mixture prepared in step (1), stir, filter and dry to obtain the negative electrode additive.

[0042] This invention involves in-situ polymerization of conductive polymer monomers in a solution containing organic sodium salts, followed by drying to obtain a negative electrode additive comprising an organic sodium salt core and a chain-like polymer shell. This negative electrode additive is rich in sodium ions and exhibits high conductivity. When used in hard carbon negative electrodes, this additive improves the electronic conductivity of hard carbon, and the sodium-rich additive can compensate for the sodium content during the formation of the SEI film by releasing sodium ions. + This reduces battery capacity and initial coulombic efficiency by minimizing electrolyte loss. Simultaneously, the presence of a polymer shell allows for the slow release of sodium ions from the organic sodium salt, thus improving cycle stability. Furthermore, the polymer layer on the surface of the negative electrode additive helps form a uniform and stable SEI film, further enhancing cycle stability. In addition, the negative electrode additive dispersed on the hard carbon surface acts as a protective layer, reducing side reactions between the hard carbon and the electrolyte and minimizing irreversible capacity. By introducing negative electrode additives into the hard carbon negative electrode, battery capacity, initial coulombic efficiency, and cycle stability can be effectively improved.

[0043] In this invention, the conductive polymer monomer in step (1) is preferably aniline, pyrrole or thiophene, and the polymer formed by polymerizing such monomers has intrinsic conductivity.

[0044] In this invention, the organic sodium salt in step (1) can be one or more of disodium hexamethylenetetraacetate, disodium glutarate, sodium benzoate, and disodium phthalate. Such organic sodium salts can be prepared by ion exchange between an organic compound with a carboxyl group and a water-soluble sodium-containing compound. The organic compound with a carboxyl group includes, but is not limited to, hexamethylenetetraacetic acid, glutarate, benzoic acid, and phthalic acid. The water-soluble sodium-containing compound includes, but is not limited to, sodium carbonate, sodium oxalate, sodium chloride, and sodium sulfate.

[0045] In this invention, the solvent in step (1) can be selected from one or more of water, ethanol, ethylene glycol, N-methylpyrrolidone, dimethylformamide, and toluene, to dissolve the conductive polymer monomer.

[0046] In this invention, in step (1), the organic sodium salt in the mixture is preferably in a supersaturated state, so that the conductive polymer monomer can be polymerized in situ on the surface of the particulate organic sodium salt.

[0047] In this invention, in step (1), the mass ratio of the conductive polymer monomer to the organic sodium salt is (1-3):1, for example 1:1, 2:1, 3:1, etc., including but not limited to the mass ratios listed above.

[0048] In this invention, the initiator solution in step (2) is obtained by dissolving the initiator in a solvent. Preferably, the initiator is ammonium persulfate and the solvent contains water.

[0049] In this invention, in step (2), in order to ensure that the conductive polymer monomer is sufficiently present, the ratio of the molar amount of the conductive polymer monomer in the mixture to the molar amount of the initiator in the initiator solution is preferably 1:(1-4), such as 1:1, 1:2, 1:3, 1:4, etc., including but not limited to the ratios listed above.

[0050] In this invention, in step (2), it is preferable to add the initiator solution dropwise to the mixture. During the dropwise addition process, the temperature is preferably -15 to 5°C and the dropwise addition time is preferably 1 to 24 hours.

[0051] In this invention, the stirring time in step (2) is preferably 2-4 hours, such as 2 hours, 3 hours, 4 hours, etc.

[0052] In this invention, the drying temperature in step (2) is preferably 80-100℃, and the drying time is preferably 4-5h.

[0053] In this invention, the above preparation method further includes a step of washing the filtered product; the washing solvent is preferably ethanol and / or water, so as to remove uncoated organic sodium salts and avoid the organic sodium salts affecting the conductivity of the negative electrode additive.

[0054] The present invention also provides a composite anode material comprising an anode additive and hard carbon prepared by the above preparation method.

[0055] In some preferred embodiments of the present invention, the above-mentioned hard carbon is prepared by the following method, specifically including the following steps:

[0056] S1. The carbon source is subjected to a first calcination treatment under a protective atmosphere to obtain a carbon precursor;

[0057] S2. The carbon precursor is subjected to a second calcination treatment in the presence of a gas-phase pore-forming agent, followed by a third calcination treatment under a protective atmosphere. The product is then acid-washed and dried to obtain the hard carbon.

[0058] Preferably, the carbon source in S1 can be selected from one or more of polymer materials, coal materials and biomass materials. Among them, polymer materials include phenolic resin, polytetrafluoroethylene, epoxy resin, furan resin, etc., coal materials include anthracite, bituminous coal, lignite, coal tar, etc., and biomass materials include sucrose, glucose, starch, coconut shell, sugarcane, poplar wood, etc.

[0059] Preferably, the protective atmosphere in S1 and S2 includes one or more of nitrogen, argon, helium, and krypton.

[0060] Preferably, in S1, the temperature of the first calcination treatment is 450-550℃, and the time of the first calcination treatment is 3-5h.

[0061] Preferably, in S2, the gas phase pore-forming agent includes one or more of carbon dioxide, oxygen, air, and water vapor; the gas phase pore-forming agent is introduced during the heat preservation stage of the second calcination treatment, and the gas flow rate of the gas phase pore-forming agent is preferably 10-100 L / min.

[0062] Preferably, in S2, the temperature of the second calcination treatment is 800-900℃, and the time of the second calcination treatment is 1-10h; the temperature of the third calcination treatment is 1100-1500℃, and the time of the third calcination treatment is 5-10h.

[0063] In this invention, the above-mentioned composite negative electrode material is obtained by mixing hard carbon and negative electrode additives through ball milling. Preferably, the ball milling speed is 400-500 rpm and the ball milling time is 6-10 h, so that the negative electrode additives are uniformly dispersed on the surface of hard carbon.

[0064] The present invention also provides a secondary battery comprising the above-mentioned composite negative electrode material, exhibiting high capacity, high coulombic efficiency and excellent cycle stability.

[0065] The present invention will be further described below with reference to specific embodiments, so that those skilled in the art can better understand and implement the present invention, but the embodiments are not intended to limit the present invention.

[0066] Example 1

[0067] This embodiment relates to the preparation of a negative electrode additive and a composite negative electrode material, and the specific operations are as follows:

[0068] Preparation of negative electrode additives:

[0069] (1) Add water to phthalic acid containing carboxyl groups and stir for 2 hours until dissolved. Then add sodium carbonate to the above solution at a mass ratio of 1:1 to phthalic acid. Stir vigorously at 100°C for 3 hours to complete ion exchange. After filtration, wash with deionized water and dry to obtain sodium phthalate.

[0070] (2) Sodium phthalate was added to NMP solvent and ultrasonically stirred to obtain an organic sodium salt dispersion. Aniline monomer was added to the above dispersion and stirred to obtain a uniformly dispersed mixture (the mass ratio of aniline monomer to sodium phthalate was 2:1).

[0071] (3) Add ammonium persulfate (molar ratio of aniline monomer to ammonium persulfate is 1:2) to the mixture and stir for 2 hours. The highly conductive polymer is formed in situ on the surface of sodium phthalate. The solid is separated by filtration, washed several times with water and ethanol, and then dried in a vacuum drying oven at 80°C for 4 hours. The resulting product is the negative electrode additive.

[0072] Preparation of composite anode materials:

[0073] (1) The starch was placed in a box furnace and carbonized at 500°C for 3 hours under argon atmosphere protection. After completion, the carbonized product was cooled to room temperature and then the carbonized product was pulverized to a median particle size of about 8.0 μm by air jet milling to obtain carbon precursor.

[0074] (2) The carbon precursor was then placed in an activation furnace and heated to 900°C in an argon atmosphere. Then, carbon dioxide gas with a flow rate of 50 L / min was introduced and kept at the temperature for 2 h for activation treatment. After activation treatment, the product was cooled to obtain the activated product. The activated product was placed in a box furnace and heated to 1400°C in an argon atmosphere for 5 h. After being taken out, it was acid-washed with hydrochloric acid and then washed with water until neutral. After drying, it was sieved with a 325-mesh sieve to obtain hard carbon material.

[0075] (3) The above hard carbon material and negative electrode additive are mixed at a mass ratio of 3:1 and ball milled at 400 rpm for 8 hours to make them uniformly mixed, thus preparing the composite negative electrode material.

[0076] Example 2

[0077] This embodiment relates to the preparation of a negative electrode additive and a composite negative electrode material. The only difference from Example 1 is that pyrrole of equal mass is used to replace aniline in Example 1. All other operations are the same, and the corresponding negative electrode additive and composite negative electrode material are obtained.

[0078] Example 3

[0079] This embodiment relates to the preparation of a negative electrode additive and a composite negative electrode material. The only difference from Example 1 is that thiophene of equal mass is used to replace aniline in Example 1. All other operations are the same, and the corresponding negative electrode additive and composite negative electrode material are obtained.

[0080] Example 4

[0081] This embodiment relates to the preparation of a negative electrode additive and a composite negative electrode material. The only difference from Example 1 is that the mass ratio of hard carbon material to negative electrode additive is 4:1. All other operations are the same, and the corresponding negative electrode additive and composite negative electrode material are obtained.

[0082] Example 5

[0083] This embodiment relates to the preparation of a negative electrode additive and a composite negative electrode material. The only difference from Example 1 is that the mass ratio of hard carbon material to negative electrode additive is 5:1. All other operations are the same, and the corresponding negative electrode additive and composite negative electrode material are obtained.

[0084] Comparative Example 1

[0085] This comparative example relates to the preparation of a hard carbon material, and the specific operation is consistent with the preparation of the hard carbon material in Example 1.

[0086] Comparative Example 2

[0087] This embodiment relates to the preparation of a negative electrode additive and a composite negative electrode material, and differs from Example 1 in that:

[0088] Sodium phthalate was prepared as the negative electrode additive. Sodium phthalate was mixed with the hard carbon material prepared in Example 1 at a mass ratio of 1:3 and ball-milled at 400 rpm for 8 hours to ensure uniform mixing, thus preparing the composite negative electrode material.

[0089] Comparative Example 3

[0090] This comparative example relates to the preparation of a negative electrode additive and a composite negative electrode material. The difference from Example 1 is that the negative electrode additive is obtained by directly mixing polyaniline and sodium phthalate in a solid phase, while the rest are the same, resulting in the corresponding composite negative electrode material.

[0091] Application and performance testing

[0092] The composite anode material or hard carbon prepared in the above embodiments and comparative examples is used as the anode active material to construct sodium-ion half-cells. The specific operation is as follows:

[0093] Assembly of a sodium-ion half-cell:

[0094] The composite negative electrode material prepared above was mixed with conductive carbon black (SP):carboxymethyl cellulose (CMC):styrene-butadiene rubber (SBR) at a mass ratio of 95:1:1.5:2.5 until homogeneous. An appropriate amount of water was added and stirred until homogeneous to obtain a negative electrode slurry. This slurry was coated onto copper foil, and the coated electrode was dried in a vacuum drying oven at 80℃ for 12 hours. Simulated battery assembly was performed in an argon-protected Braun glove box. The electrolyte was 1 mol NaPF6-EC / DEC (volume ratio 1:1) + 5% FEC, and a sodium metal sheet was used as the counter electrode. CR2032 button cells were assembled in the glove box.

[0095] Charge-discharge tests were conducted on sodium-ion half-cells constructed with the above-mentioned different negative electrode active materials. The test procedure is as follows:

[0096] First charge capacity and first discharge capacity test: 1) Let stand for 2 hours @ (25±2)℃; 2) Discharge at 0.05C constant current to 0V, let stand for 5 minutes, then discharge at 20μA constant current to 0V to obtain the first discharge capacity; 3) Let stand for 5 minutes; 4) Charge at 0.05C constant current to 2.0V to obtain the first charge capacity; 5) Let stand for 5 minutes.

[0097] Initial Coulomb Efficiency (ICE) = Initial Charge Capacity / Initial Discharge Capacity;

[0098] Cyclic performance test: The sodium-ion half-cell was left to stand at 25℃ for 30 min, charged to 2V at a constant current of 0.05C, left to stand for 5 min, then discharged to 0V at a constant current of 0.05C, and then discharged at a constant voltage of 0V to a current of 0.02C. The discharge capacity at this point was recorded as the discharge capacity of the first cycle. After standing for 10 min, the cycle charge and discharge was performed, and the discharge capacity of the sodium-ion half-cell at the 500th cycle was recorded as the discharge capacity of the 500th cycle. The capacity retention rate of the 500th cycle = discharge capacity of the 500th cycle / discharge capacity of the first cycle.

[0099] The test results are shown in Table 1 below:

[0100] Table 1

[0101]

[0102] As shown in Table 1, compared with Comparative Examples 1 and 2, the negative electrode composite materials prepared in Examples 1, 2, and 3 have higher capacity and initial coulombic efficiency, indicating that the addition of this negative electrode additive compensates for the formation of the SEI film during charging by acting as a sodium source. +While reducing the loss of sodium, this additive can further improve the conductivity of the battery. After 500 charge-discharge cycles, the battery cycle retention rate is also significantly improved. This is because the negative electrode additive can not only replenish the sodium loss caused by the formation of the SEI film by slowly releasing sodium ions, but also the polymer layer on the surface of the negative electrode additive is conducive to the formation of a uniform and stable SEI film, thereby further improving the cycle performance of the battery.

[0103] As can be seen from Examples 1, 4, and 5, as the content of negative electrode additive decreases, the battery's initial efficiency gradually decreases, further confirming that the addition of negative electrode additive is beneficial to improving capacity and initial efficiency.

[0104] Furthermore, as shown in Example 1 and Comparative Example 3, directly mixing polyaniline and sodium phthalate into a solid phase and adding it to the negative electrode as a negative electrode additive has a limited effect on improving the initial coulombic efficiency of the battery, and the cycle performance of the battery actually deteriorates. It is speculated that this is because the organic sodium salt dispersed in the negative electrode affects the conductivity of the negative electrode and the stability of the SEI film, deteriorating the battery impedance and interface stability, thereby leading to a deterioration in the battery cycle performance. However, the core-shell structure negative electrode additive provided by the present invention can effectively improve the initial efficiency and cycle performance of the battery.

[0105] The embodiments described above are merely preferred examples to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the claims.

Claims

1. A method for producing a negative electrode additive, characterized by, The preparation method comprises the following steps: (1) uniformly mixing conductive polymer monomers, organic sodium salt in a solvent to obtain a mixture; the conductive polymer monomers are aniline, pyrrole or thiophene; the organic sodium salt is selected from one or more of disodium ethylenediaminetetraacetate, disodium glutarate, sodium benzoate and disodium phthalate; the solvent is selected from one or more of water, ethanol, ethylene glycol, N-methyl pyrrolidone, dimethylformamide and toluene; (2) adding an initiator solution to the mixture prepared in step (1) and stirring to obtain the negative electrode additive after filtration and drying.

2. The production method according to claim 1, characterized by, In step (1), the mass ratio of the conductive polymer monomers to the organic sodium salt is (1-3):

1.

3. The preparation method according to claim 1, characterized in that, In step (2), the initiator solution is obtained by dissolving an initiator in a solvent; the initiator is ammonium persulfate, and the solvent contains water.

4. The production method according to claim 1 or 3, characterized by, In step (2), the ratio of the molar amount of the conductive polymer monomers in the mixture to the molar amount of the initiator in the initiator solution is 1: (1-4).

5. The preparation method according to claim 1, characterized in that, In step (2), at least one of the following characteristics is included: (1) the initiator solution is added dropwise to the mixture, and during the dropping process: the temperature is -15-5 ℃, and the dropping time is 1-24 h; (2) the stirring time is 2-4 h; (3) the drying temperature is 80-100 ℃, and the drying time is 4-5 h; (4) the preparation method further comprises a step of washing the filtered product; the washing solvent is ethanol and / or water.

6. A negative electrode additive characterized by comprising: Prepared by the preparation method of any one of claims 1-5.

7. A composite negative material, characterized by, The composite negative electrode material comprises hard carbon and the negative electrode additive of claim 6.

8. The composite anode material of claim 7, wherein, The composite negative electrode material is obtained by ball milling the hard carbon and the negative electrode additive; the ball milling speed is 400-500 rpm, and the ball milling time is 6-10 h; The mass ratio of the negative electrode additive to the hard carbon in the composite negative electrode material is 1: (3-5).

9. A secondary battery characterized by comprising: The composite negative electrode material of claim 7 or 8. The composite negative electrode material of claim 7 or 8.

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