Negative plate, preparation method and battery

Abstract

The invention provides a negative plate, a preparation method and a battery. The negative plate comprises a negative current collector; the active material layer is arranged on the surface of the negative electrode current collector, the active material layer comprises negative electrode active materials, a conductive agent, a binder and a conductive network, the conductive network is formed between adjacent negative electrode active materials and between adjacent negative electrode active materials and negative electrode current collector, and the conductive network comprises 3, 4-ethylenedioxythiophene and pyrrole; the conductive network is obtained through polymerization by a pulse current method; according to the invention, a conductive network formed by copolymerization of EDOT and pyrrole is introduced, so that the electrochemical performance and the structural stability of the electrode are remarkably improved, the electrode has excellent electron transmission capability, the contact resistance is effectively reduced, and the cycle life is remarkably prolonged.

Description

Technical Field

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

[0002] In the field of lithium-ion batteries, especially for applications requiring high energy density (such as electric vehicles and consumer electronics), silicon-containing materials are considered important candidates for next-generation anodes due to their high theoretical specific capacity (e.g., pure silicon can reach approximately 4200 mAh / g). However, silicon-containing materials experience severe volume expansion (up to 300% or more) during charge and discharge, leading to particle pulverization, electrode structure collapse, and repeated rupture and regeneration of the solid electrolyte interphase (SEI) film, resulting in rapid capacity decay and shortened cycle life.

[0003] To alleviate the above problems, existing technologies generally use silicon-carbon composite materials as the negative electrode active material, and directly mix conductive additives (such as carbon black, conductive graphite, carbon nanotubes (CNTs) or graphene) into the slurry to improve the overall conductivity of the electrode. A typical process includes: mixing silicon-containing materials, conductive agents, and binders in a certain proportion to form a slurry, then coating it onto a copper foil current collector, and finally drying and rolling it to form a negative electrode sheet.

[0004] However, this traditional approach has the following significant drawbacks: uneven dispersion of the conductive agent, forming local "dead zones"; the conductive agent (especially nanomaterials such as CNTs) is prone to agglomeration, making it difficult to achieve uniform dispersion in the slurry, resulting in some active particles not being effectively connected, forming "blind zones" for electron transport, and reducing material utilization.

[0005] Even with ideal conductive agent distribution, the contact between the conductive agent and the active particles is still mainly "point-to-point," resulting in a small contact area and high interfacial resistance. Under high current or long-cycle conditions, contact failure is likely to occur. Therefore, overcoming the aforementioned technical problems and defects has become a key issue that needs to be addressed. Summary of the Invention

[0006] To address the problem that the active particles of the negative electrode are not effectively connected in existing silicon negative electrode sheets, this invention provides a negative electrode sheet, its preparation method, and a battery.

[0007] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows: The first aspect of the present invention provides a negative electrode sheet, comprising: Negative electrode current collector; An active material layer is disposed on the surface of the negative electrode current collector; the active material layer includes a negative electrode active material, a conductive agent, a binder, and a conductive network; the negative electrode active material includes a silicon-containing material; the negative electrode active material and the conductive agent are mixed together and bonded together by the binder; the conductive network is formed between adjacent negative electrode active materials and between adjacent negative electrode active materials and the negative electrode current collector; the polymer monomers of the conductive network include 3,4-ethylenedioxythiophene and pyrrole; the conductive network is obtained by pulsed current polymerization.

[0008] Optionally, the thickness of the conductive network is 0.5-2 μm.

[0009] Optionally, the conductive network is a three-dimensional mesh structure with a porosity of 30%–70%.

[0010] Optionally, the molar ratio of the 3,4-ethylenedioxythiophene to the pyrrole is (1-5):(1-5).

[0011] Optionally, the total mass of the negative electrode active material, the binder, and the conductive agent is taken as 100%, wherein the mass percentage of the negative electrode active material is 90.5%-93.5%; the mass percentage of the binder is 6%-9.2%; and the mass percentage of the conductive agent is 0.3%-0.5%.

[0012] Optionally, the silicon-containing material includes one or more of silicon particles, silicon suboxide, and silicon-carbon materials.

[0013] Optionally, the silicon-containing particles are selected from silicon-carbon materials, wherein the silicon content in the silicon-carbon materials is 40%-60% by mass.

[0014] A second aspect of the present invention provides a method for preparing a negative electrode sheet, comprising the following steps: The negative electrode active material, conductive agent, and binder are mixed into a slurry and coated onto the surface of the negative electrode current collector. The polymeric electrolyte forms a conductive network between adjacent negative electrode active materials and between adjacent negative electrode active materials and negative electrode current collectors using a pulsed current method. The polymeric electrolyte includes 3,4-ethylenedioxythiophene and pyrrole.

[0015] Optionally, in the polymerization electrolyte, the concentration of 3,4-ethylenedioxythiophene is 0.01-0.1 mol / L; And / or, in the polymerization electrolyte, the concentration of the pyrrole is 0.01-0.1 mol / L.

[0016] Optionally, in the polymerization electrolyte, the molar ratio of 3,4-ethylenedioxythiophene to pyrrole is 1:5 to 5:1.

[0017] Optionally, the polymerization electrolyte further includes potassium chloride, wherein the concentration of potassium chloride in the polymerization electrolyte is 0.05-0.5 mol / L.

[0018] Optionally, the polymeric electrolyte further includes a pH adjuster, which includes one or more of perchloric acid, sulfuric acid, hydrochloric acid, p-toluenesulfonic acid, and trifluoromethanesulfonic acid.

[0019] Optionally, the pH value of the polymer electrolyte is 0.1-2.

[0020] Optionally, an Ag / AgCl electrode is used as a reference electrode in the pulsed current method; and / or, a Pt electrode is used as a counter electrode in the pulsed current method.

[0021] Optionally, during the pulsed current method, the current is 0.2-10 mA / cm. 2 ; And / or, the current deposition time is 1-10 seconds; And / or, the current pause time is 1-10 seconds; And / or, the total time for the pulsed current method is 100-1200s.

[0022] A third aspect of the present invention provides a battery comprising a positive electrode, a negative electrode, and a separator, wherein the negative electrode is the negative electrode described above, or a negative electrode prepared by the method described above.

[0023] According to the negative electrode sheet provided by the present invention, an active material layer is formed on the surface of the negative electrode current collector, and a conductive network formed by copolymerization of 3,4-ethylenedioxythiophene and pyrrole is introduced into the active material layer. This conductive network is generated by in-situ polymerization using a pulsed current method and is precisely distributed between adjacent silicon-containing negative electrode active material particles and at the interface between the negative electrode active material and the negative electrode current collector. This significantly improves the electrochemical performance and structural stability of the electrode. The conductive polymer formed by copolymerization of EDOT and pyrrole combines the high conductivity of PEDOT with the good electrochemical activity and adhesion of polypyrrole (PPy). The synergistic effect of the two makes the conductive network not only have excellent electron transport capability, but also firmly anchor the active particles and the current collector, effectively reducing contact resistance. Moreover, the silicon-containing negative electrode active material undergoes drastic volume changes (up to 300%) during charging and discharging, which can easily lead to electrode pulverization and peeling. The conductive network in this invention possesses excellent flexibility and mechanical adaptability, capable of encapsulating silicon-based particles and buffering their stress and strain, maintaining the structural integrity of the active material layer, and significantly extending cycle life. Furthermore, the conductive network penetrates the interior of the active material layer and extends to the negative electrode current collector interface, forming a two-dimensional electron transport channel between particles and between particles and the current collector, greatly improving the overall conductivity uniformity of the electrode and enabling the battery to maintain high capacity output even under high-rate charge and discharge conditions. Employing a pulsed current polymerization process, EDOT and pyrrole copolymerization can be selectively induced in conductively weak areas (such as particle gaps and interfaces) without damaging the silicon material, forming a conductive network of moderate thickness and uniform distribution. This method avoids problems such as residual oxidant and uneven film formation in traditional chemical oxidative polymerization. Attached Figure Description

[0024] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a schematic diagram of the conductive network of the negative electrode sheet provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the conductive network of the negative electrode sheet provided by existing technology; The reference numerals in the accompanying drawings are as follows: 100 - Negative electrode current collector; 2 - Silicon-containing material; 21 - Silicon particles; 22 - Porous carbon skeleton; 23 - Surface carbon coating; 31 - Effective conductive agent; 32 - Ineffective conductive agent; 33 - Conductive network. Detailed Implementation

[0026] To make the technical problems solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0027] In the description of this invention, it should be understood that the terms "longitudinal," "radial," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0028] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0029] In one embodiment, the first aspect of the present invention provides a negative electrode sheet, comprising: Negative electrode current collector 100; An active material layer is disposed on the surface of the negative electrode current collector 100. The active material layer includes a negative electrode active material, a conductive agent, a binder, and a conductive network 33. The negative electrode active material includes a silicon-containing material. The negative electrode active material and the conductive agent are mixed together and bonded together by the binder. The conductive network 33 is formed between adjacent negative electrode active materials and between adjacent negative electrode active materials and the negative electrode current collector 100. The polymer monomers of the conductive network 33 include 3,4-ethylenedioxythiophene and pyrrole. The conductive network 33 is obtained by pulsed current polymerization.

[0030] Traditional negative electrode sheets have active material layers formed on both sides. The active material layers include negative electrode active material, conductive agent and binder. The negative electrode active material includes silicon-containing material 2. Some conductive agent particles adsorbed at the connection of silicon-containing material 2 are effective conductive agents 31; some conductive agent particles cannot be effectively adsorbed at the connection of silicon-containing material 2, forming ineffective conductive agents 32. Ineffective conductive agents 32 cannot play an effective electrical connection role between silicon-containing materials 2, forming many ineffective conductive networks. During cycling, the expansion of silicon-containing material 2 will also cause some conductive networks to break and lose conductivity.

[0031] like Figures 1-2 As shown, this invention provides an active material layer on the surface of the negative electrode current collector 100, and introduces a conductive network 33 formed by the copolymerization of 3,4-ethylenedioxythiophene (EDOT) and pyrrole into this active material layer. This conductive network 33 is generated through in-situ polymerization using a pulsed current method and is precisely distributed between adjacent silicon-containing negative electrode active material particles and at the interface between the negative electrode active material and the negative electrode current collector 100. This significantly improves the electrochemical performance and structural stability of the electrode. The conductive polymer formed by the copolymerization of EDOT and pyrrole combines the high conductivity of EDOT with the good electrochemical activity and adhesion of polypyrrole (PPy). The synergistic effect of these two components enables the conductive network 33 to not only possess excellent electron transport capabilities but also firmly anchor the active particles and the current collector, effectively reducing contact resistance. Furthermore, the silicon-containing negative electrode active material undergoes drastic volume changes (up to 300%) during charging and discharging, which can easily lead to electrode pulverization and peeling. In this invention, the conductive network 33 possesses excellent flexibility and mechanical adaptability, capable of encapsulating silicon-based particles and buffering their stress and strain, maintaining the structural integrity of the active material layer, and significantly extending cycle life. Furthermore, the conductive network 33 penetrates the interior of the active material layer and extends to the interface of the negative electrode current collector 100, forming a two-dimensional electron transport channel between particles and between particles and the current collector, greatly improving the overall conductivity uniformity of the electrode and enabling the battery to maintain high capacity output even under high-rate charge and discharge conditions. Employing a pulsed current polymerization process, EDOT and pyrrole copolymerization can be selectively induced in conductively weak areas (such as particle gaps and interfaces) without damaging the silicon material, forming a conductive network 33 of moderate thickness and uniform distribution. This method avoids problems such as residual oxidant and uneven film formation in traditional chemical oxidative polymerization.

[0032] In one embodiment, the thickness of the conductive network 33 is 0.5-2 μm.

[0033] Specifically, the thickness of the conductive network 33 is any single value or a range of any two values ​​among 0.5μm, 1μm, 1.5μm or 2μm; in a preferred embodiment, the thickness of the conductive network 33 is 1-1.5μm.

[0034] When the thickness of the conductive network 33 is 0.5–2 μm, it can effectively construct a continuous and dense three-dimensional conductive path, significantly reducing the interfacial resistance, while maintaining good flexibility and interfacial bonding with the active material layer. This improves the overall conductivity of the electrode while avoiding mechanical stress concentration or volume expansion caused by excessive film thickness. When the thickness of the conductive network 33 is less than 0.5 μm, the conductive network 33 may be discontinuous or incompletely covered, making it difficult to form an effective electron transport channel, resulting in increased interfacial impedance and decreased rate performance and cycle stability. When the thickness of the conductive network 33 is greater than 2 μm, although the conductivity is further enhanced, the excessively thick polymer layer increases the proportion of inactive materials in the electrode, reducing the overall energy density. At the same time, the thick film is prone to cracking, peeling, or internal stress accumulation during charge and discharge, which can damage the structural integrity and long-term cycle performance of the electrode.

[0035] In one embodiment, the conductive network 33 is a three-dimensional mesh structure with a porosity of 30%–70%.

[0036] The present invention employs a pulsed current method, which facilitates the uniform nucleation and growth of polymerizable monomers 3,4-ethylenedioxythiophene and pyrrole between adjacent negative electrode active materials and between adjacent negative electrode active materials and negative electrode current collector 100, avoiding dense stacking and forming a three-dimensional network structure with a certain porosity.

[0037] Specifically, the porosity of the three-dimensional mesh structure is any one value or a range of any two values ​​from 40%, 43%, 46%, 49%, 52%, 55%, 58%, 61%, 64%, 67%, or 70%; in a preferred embodiment, the porosity of the three-dimensional mesh structure is 40%-60%.

[0038] When the porosity of the three-dimensional network structure is 30%–70%, it exhibits excellent ion transport capabilities. (Li) + Low diffusion resistance is beneficial for high-rate charge and discharge; the silicon-containing material 2 expands in volume by about 300% during lithiation, and the three-dimensional network structure provides "reserved space," significantly increasing the electrode / electrolyte contact area; this helps improve the electrode's specific capacity. However, when the porosity of the three-dimensional network structure is less than 30%, ion transport is severely restricted, failing to buffer the huge volume expansion of the silicon-containing material 2. The small specific surface area makes it difficult for the electrolyte to penetrate deep into the silicon / polymer interface, resulting in uneven lithiation / delithiation reactions concentrated on the surface area. When the porosity of the three-dimensional network structure is greater than 70%, it leads to discontinuous conductive network 33, extremely low mechanical strength, and easy collapse or detachment. Excessively high specific surface area causes excessive growth of the SEI film, consuming Li. + And the electrolyte; an excessively thick or porous coating "dilutes" the silicon content; the overall mass / volume capacity of the electrode decreases.

[0039] In one embodiment, the molar ratio of 3,4-ethylenedioxythiophene to pyrrole in the polymerization electrolyte is 1:5-5:1.

[0040] Specifically, the molar ratio of 3,4-ethylenedioxythiophene to pyrrole is any one value or a range of any two values ​​from 1:5, 1:4, 1:3, 1:2, 1:1, 2:5, 2:3, 2:1, 3:5, 3:4, 3:2, 3:1, 4:5, 4:3, 4:1, 5:4, 5:3, 5:2, or 5:1; in a preferred embodiment, the molar ratio of 3,4-ethylenedioxythiophene to pyrrole is 1:3 to 3:1.

[0041] When the molar ratio of 3,4-ethylenedioxythiophene to pyrrole is 1:5–5:1, the two monomers can be effectively copolymerized during electrochemical polymerization to form a conductive network with uniform structure and good compatibility 33. Within this range, PEDOT provides excellent environmental stability and high conductivity, while PPy contributes rapid redox response and high doping capability. The synergistic effect of the two significantly improves the overall electrochemical performance of the conductive network 33, including low interfacial impedance, high electronic conductivity, and good mechanical flexibility. When the molar ratio of 3,4-ethylenedioxythiophene to pyrrole is less than 1:5 (i.e., pyrrole excess), the polymerization product is mainly polypyrrole. Although the initial conductivity is high, PPy is prone to peroxidation degradation during long-term cycling, leading to a decrease in film stability. At the same time, excess pyrrole may trigger homopolymerization side reactions, reduce the regularity of the copolymer structure, cause film brittleness and poor adhesion, and thus affect the cycle life and interfacial contact of the electrode. When the molar ratio of 3,4-ethylenedioxythiophene to pyrrole is greater than 5:1 (i.e., EDOT excess), the polymerization system tends to generate a structure dominated by PEDOT. Although it has excellent chemical and electrochemical stability, its polymerization kinetics are slow, and PEDOT alone has high film density and low porosity, which is not conducive to ion diffusion.

[0042] In one embodiment, the total mass of the negative electrode active material, binder, and conductive agent is taken as 100%, the mass percentage of the negative electrode active material is 90.5%-93.5%, the mass percentage of the binder is 6%-9%, and the mass percentage of the conductive agent is 0.3%-0.5%.

[0043] Specifically, the mass percentage of silicon-containing material 2 is any one value or a range of any two values ​​selected from 90.5%, 91%, 91.5%, 92%, 92.5%, 93%, or 93.5%; in a preferred embodiment, the mass percentage of silicon-containing material 2 is 91.5%-92.5%.

[0044] Specifically, the mass percentage of the adhesive is any one value or a range of any two values ​​selected from 6%, 7%, 8% or 9%; in a preferred embodiment, the mass percentage of the adhesive is 7%-8%.

[0045] Specifically, the mass percentage content of the conductive agent is any one value or a range of any two values ​​selected from 0.3%, 0.4%, or 0.5%; in a preferred embodiment, the mass percentage content of the conductive agent is 0.4%-0.5%.

[0046] When the mass percentage of the negative electrode active material is 90.5%-93.5%, the mass percentage of the binder is 6%-9%, and the mass percentage of the conductive agent is 0.3%-0.5%, it has the effect of balancing energy density and electrode thickness expansion. When the negative electrode active material, binder, and conductive agent do not meet the above ranges, it will lead to problems such as low energy density, excessive thickness expansion, excessive internal resistance, and poor rate performance.

[0047] In one embodiment, the silicon-containing material 2 includes one or more of silicon particles, silicon suboxide, and silicon-carbon materials; the selection of the above-mentioned silicon-containing material 2 takes into account both high specific capacity and cycle stability.

[0048] In one embodiment, the silicon-containing particles are selected from silicon-carbon materials, wherein the silicon content in the silicon-carbon materials is 40%-60% by mass.

[0049] Specifically, the silicon content in the silicon-carbon material is any one value or a range of any two values ​​from 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58%, or 60%; in a preferred embodiment, the silicon content in the silicon-carbon material is 45%-55%.

[0050] When the silicon content in silicon-carbon materials is 40%-60% by mass, the energy density and the cyclic expansion of silicon-carbon particles can be relatively balanced. When the silicon content in silicon-carbon materials is less than 40% by mass, the energy density of silicon-carbon materials will be too low. When the silicon content in silicon-carbon materials is greater than 60% by mass, the silicon-carbon particles will expand too much, affecting the cyclic thickness expansion rate and capacity retention rate.

[0051] like Figure 2 As shown, preferably, the structure of the silicon-carbon material of this application includes a porous carbon skeleton 22, silicon particles 21 and a carbon coating layer 23, with the silicon particles 21 embedded inside the porous carbon skeleton 22 and the porous carbon skeleton 22 covered with a carbon coating layer 23.

[0052] Using silicon-carbon materials can improve electronic conductivity: compensate for the low intrinsic conductivity of silicon; inhibit particle agglomeration and pulverization, and maintain structural integrity during cycling; stabilize the SEI film, reduce direct exposure of silicon to the electrolyte, and suppress excessive side reactions; and reserve expansion space (especially in porous or flexible carbon structures) to accommodate changes in silicon volume.

[0053] In one embodiment, the binder includes one or more of sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), sodium alginate, polyacrylic acid (PAA), polyimide (PI), or combinations thereof.

[0054] In one embodiment, the conductive agent includes one or more of carbon black (such as SuperP), acetylene black, Ketjen black, graphene, carbon nanotubes (CNTs), carbon fibers, expanded graphite, or combinations thereof.

[0055] In one embodiment, a second aspect of the present invention provides a method for preparing a negative electrode sheet, comprising the following steps: The negative electrode active material, conductive agent, and binder are mixed into a slurry and coated onto the surface of the negative electrode current collector. The polymer electrolyte forms a conductive network 33 between adjacent negative electrode active materials and between adjacent negative electrode active materials and negative electrode current collector 100 by means of pulsed current method. The polymer electrolyte includes 3,4-ethylenedioxythiophene and pyrrole.

[0056] This invention provides a conductive network 33 between adjacent negative electrode active materials and between adjacent negative electrode active materials and negative electrode current collectors. The conductive network 33 is formed by copolymerization of 3,4-ethylenedioxythiophene (EDOT) and pyrrole, which can effectively stabilize the interface between the negative electrode and the electrolyte, suppress side reactions, and improve battery cycle life. Moreover, the conductive network 33 formed by the copolymerization of EDOT and pyrrole has both good electronic conductivity and certain ion transport capability, which helps to reduce interface impedance and improve battery rate performance and charge / discharge efficiency. Furthermore, the active material layer provides basic electrochemical activity, while the conductive network 33 plays a conductive role. The synergistic effect of the two significantly improves the overall capacity retention and cycle stability of the negative electrode.

[0057] In one embodiment, the concentration of 3,4-ethylenedioxythiophene in the polymerization electrolyte is 0.01-0.1 mol / L.

[0058] Specifically, the concentration of 3,4-ethylenedioxythiophene is any one value or a range of any two values ​​selected from 0.01 mol / L, 0.015 mol / L, 0.02 mol / L, 0.025 mol / L, 0.03 mol / L, 0.035 mol / L, 0.04 mol / L, 0.045 mol / L, 0.05 mol / L, 0.055 mol / L, 0.06 mol / L, 0.065 mol / L, 0.07 mol / L, 0.075 mol / L, 0.08 mol / L, 0.085 mol / L, 0.09 mol / L, 0.095 mol / L, or 0.1 mol / L; in a preferred embodiment, the concentration of 3,4-ethylenedioxythiophene is 0.01-0.05 mol / L.

[0059] When the concentration of 3,4-ethylenedioxythiophene is 0.01-0.1 mol / L, it can polymerize on the negative electrode surface using a constant current pulsed current method to form a uniform, dense, and highly conductive network 33. Synergistic copolymerization with pyrrole effectively regulates the electronic structure and ion transport properties of the polymer, improving interface stability and the reversibility of the pulsed current method. Within this concentration range, the polymerization rate is moderate, which is beneficial for obtaining a functional layer with controllable thickness, strong adhesion, and good mechanical flexibility, thereby significantly improving the cycle performance and rate capability of the battery. When the concentration of 3,4-ethylenedioxythiophene is less than 0.01 mol / L, it leads to excessively low monomer concentration, resulting in a slow polymerization rate or difficulty in achieving polymerization. Ineffective film formation; the formed polymer layer is too thin or even discontinuous, unable to effectively cover the surface of the active material layer, resulting in insufficient interfacial protection; leading to increased electrode / electrolyte interfacial impedance, inhibiting ion / electron transport, and reducing overall battery performance; when the concentration of 3,4-ethylenedioxythiophene is greater than 0.1 mol / L, it will lead to excessively high monomer concentration, triggering violent or non-uniform polymerization, easily forming a rough, porous or even powdery polymer layer; excessive cross-linking or side reactions may accompany the polymerization process, reducing the flexibility of the film and its adhesion to the substrate; a thick and loose coating will hinder lithium-ion diffusion, increase interfacial resistance, and may peel off or break during cycling, thereby damaging electrode stability and cycle life.

[0060] In one embodiment, the concentration of pyrrole in the polymerization electrolyte is 0.01-0.1 mol / L.

[0061] Specifically, the concentration of pyrrole is any one value or a range of any two values ​​selected from 0.01 mol / L, 0.015 mol / L, 0.02 mol / L, 0.025 mol / L, 0.03 mol / L, 0.035 mol / L, 0.04 mol / L, 0.045 mol / L, 0.05 mol / L, 0.055 mol / L, 0.06 mol / L, 0.065 mol / L, 0.07 mol / L, 0.075 mol / L, 0.08 mol / L, 0.085 mol / L, 0.09 mol / L, 0.095 mol / L, or 0.1 mol / L; in a preferred embodiment, the concentration of pyrrole is 0.01-0.02 mol / L.

[0062] When the concentration of pyrrole is 0.01-0.1 mol / L, it can effectively copolymerize with 3,4-ethylenedioxythiophene (EDOT) to form a copolymer coating with uniform structure, high conductivity, and certain hydrophilicity. The introduction of pyrrole can enhance the redox activity and ion exchange capacity of the polymer, which helps to improve the lithium-ion transport kinetics at the negative electrode interface. Within this concentration range, the copolymerization reaction rate is moderate, which is conducive to obtaining a dense, flexible, and strongly adherent functional layer, thereby synergistically enhancing the cycle stability and rate performance of the electrode. When the concentration of pyrrole is less than 0.01 mol / L, the pyrrole monomer content will be too low, making it difficult to effectively participate in the copolymerization reaction, and the proportion of pyrrole units in the copolymer will be insufficient. The resulting polymer layer is mainly dominated by PEDOT and lacks the hydrophilicity and interfacial wettability advantages brought by pyrrole, which may reduce the electrolyte wetting effect. The overall film layer has a single function and limited inhibition of interfacial side reactions, and cannot fully exert the synergistic effect of the EDOT / Py copolymer. When the concentration of pyrrole is greater than 0.1 mol / L, it will cause pyrrole to be easily oxidized and polymerized. Excessive concentration will cause rapid homopolymerization or local overpolymerization, resulting in a rough coating, high brittleness, easy cracking or peeling. High concentration of pyrrole may inhibit the effective incorporation of EDOT, destroy the regularity of the copolymer structure, and reduce the electronic conductivity and long-term stability of the film. An excessively thick or non-uniform polymer layer will hinder the lithium-ion diffusion path, increase the interfacial impedance, and thus deteriorate the cycle performance and rate capability of the battery.

[0063] In one embodiment, the polymerization electrolyte further includes potassium chloride, and the concentration of potassium chloride in the polymerization electrolyte is 0.05-0.5 mol / L.

[0064] Specifically, the concentration of potassium chloride is any one value or a range of any two values ​​selected from 0.05 mol / L, 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.25 mol / L, 0.3 mol / L, 0.35 mol / L, 0.4 mol / L, 0.45 mol / L, or 0.5 mol / L; in a preferred embodiment, the concentration of potassium chloride is 0.05-0.1 mol / L.

[0065] When the concentration of potassium chloride is 0.05–0.5 mol / L, the electrolyte exhibits suitable ionic conductivity and electrochemical stability, effectively supporting the homogeneous electrochemical copolymerization of EDOT and pyrrole monomers. Within this concentration range, K... + and Cl - Ions, acting as inert supporting electrolytes, not only reduce solution resistance and improve current efficiency, but also shield local electric field inhomogeneities on the electrode surface, promoting dense and uniform deposition of conductive polymer films, thereby obtaining composite polymer layers with high conductivity, good adhesion, and controllable thickness. When the concentration of potassium chloride is below 0.05 mol / L, the ionic strength of the electrolyte is insufficient, leading to a significant increase in solution resistance. This can easily cause voltage spikes, local overpolymerization, or film discontinuities during constant current polymerization. Simultaneously, limited mass transfer may cause uneven polymerization rates, forming porous, loose, or even broken conductive networks, severely affecting the electrochemical performance and mechanical integrity of the membrane. When the concentration of potassium chloride is above 0.5 mol / L, although the solution conductivity further increases, excessively high ionic strength may compress the double layer and inhibit monomer adsorption and directional alignment at the electrode interface, thus reducing polymerization efficiency. Furthermore, high concentrations of Cl... - Under strongly acidic conditions (such as an HClO4 system with pH=1), it may participate in side reactions or affect doped anions (such as ClO4). - The embedding of [a substance] leads to a decrease in polymer doping, a reduction in conductivity, and may even cause film roughness or peeling.

[0066] In one embodiment, the polymerization electrolyte further includes a pH adjuster, which includes one or more of perchloric acid, sulfuric acid, hydrochloric acid, p-toluenesulfonic acid, and trifluoromethanesulfonic acid. The use of the above-mentioned pH adjuster can promote the formation of cationic free radicals of EDOT and pyrrole (Py) monomers, which is beneficial to oxidative polymerization; provide a high concentration of H⁺ to enhance the conductivity of the solution; and inhibit side reactions (such as monomer hydrolysis and peroxidation).

[0067] In one embodiment, the pH of the polymer electrolyte is 0.1-2.

[0068] Specifically, the pH value of the polymerization electrolyte is any one value or a range of any two values ​​from 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9 or 2; in a preferred embodiment, the pH value of the polymerization electrolyte is 0.5-1.5.

[0069] When the pH of the polymerization electrolyte is 0.1–2, the system is in a strongly acidic environment, which is conducive to the protonation of 3,4-ethylenedioxythiophene (EDOT) and pyrrole (Py) monomers, improving their solubility and electrochemical activity in the aqueous phase. Simultaneously, the strongly acidic conditions effectively suppress side reactions of the monomers during polymerization (such as peroxidation or hydrolysis), promoting the formation of a dense copolymer film with high doping density and high conductivity. Furthermore, H… + As a charge-compensating ion, it can work synergistically with perchlorate (ClO4) - Doping with anions such as [H+] embeds them into the polymer chain, improving the electrochemical reversibility and interfacial stability of the membrane, thereby obtaining a conductive network with high conductivity, good adhesion, and excellent cycling performance. When the pH of the polymerization electrolyte is higher than 2 (i.e., the acidity decreases), the degree of monomer protonation decreases, the polymerization driving force decreases, leading to a slower polymerization rate, incomplete film formation, or a loose film layer. Simultaneously, under weakly acidic or neutral conditions, pyrrole is prone to non-electrochemical oxidative self-polymerization, generating irregular particulate polymers, disrupting the membrane's uniformity. The oxidation potential of PEDOT may also increase, causing asynchronous polymerization of the two monomers, making effective copolymerization difficult, ultimately resulting in poor conductivity and high interfacial impedance of the composite membrane. When the pH of the polymerization electrolyte is lower than 0.1 (i.e., the acidity is too strong, such as [H+]), the polymerization is affected by the following: + At 1M, although monomer activity is further enhanced, excessively high H+ levels... + Concentration levels can corrode the working electrode (especially the surface of metal current collectors or active materials) and exacerbate the oxidizing properties of the perchloric acid (HClO4) system, triggering excessive oxidative degradation of monomers or polymer chains; furthermore, extremely acidic environments may lead to the degradation of ClO4. - Decreased doping efficiency may cause excessive protonation of the polymer, leading to embrittlement and reducing the mechanical flexibility and long-term electrochemical stability of the film.

[0070] In one embodiment, an Ag / AgCl electrode is used as a reference electrode in the pulsed current method; and / or, a Pt electrode is used as a counter electrode in the pulsed current method.

[0071] Using Ag / AgCl electrodes in Cl-containing - The aqueous solution exhibits a highly reversible electrode reaction (AgCl + e⁻). - ⇌Ag+Cl - Its open-circuit potential is affected by temperature and Cl. -The concentration has minimal impact, providing a stable and reliable potential reference during long-term polymerization, which is beneficial for monitoring real-time potential changes of the working electrode (silicon anode) and ensuring process consistency. Furthermore, the polymerization electrolyte contains KCl (e.g., 0.05 mol / L) as a supporting electrolyte, providing the necessary Cl- for the Ag / AgCl electrode. - Environment, avoid Cl - Insufficient concentration can cause electrode potential drift or failure, thus ensuring the reliability of the reference performance.

[0072] Using a Pt electrode as the counter electrode, Pt has excellent electronic conductivity, which can efficiently conduct current, reduce ohmic losses, and facilitate precise control of pulse current output.

[0073] In one embodiment, during the pulsed current method, the current is 0.2-10 mA / cm. 2 ; And / or, the current deposition time is 1-10 seconds; And / or, the current pause time is 1-10 seconds; And / or, the total time for the pulsed current method is 100-1200s.

[0074] Specifically, the current in the pulsed current method is 0.2 mA / cm. 2 0.9mA / cm 2 1.6mA / cm 2 2.3mA / cm 2 3mA / cm 2 3.7mA / cm 2 4.4 mA / cm 2 5.1 mA / cm 2 5.8 mA / cm 2 6.5mA / cm 2 7.2mA / cm 2 7.9 mA / cm 2 8.6 mA / cm 2 9.3 mA / cm 2 or 10mA / cm 2 The value is any one point or a range of any two points; in a preferred embodiment, the current in the pulse current method process is 2-7 mA / cm. 2 .

[0075] When the current in the pulsed current method is 0.2–10 mA / cm 2At this time, controllable and uniform electrochemical copolymerization can be achieved on the electrode surface, effectively balancing the polymerization rate and film quality. Within this current density range, the monomers (EDOT and pyrrole) have sufficient time to diffuse to the electrode interface and undergo orderly oxidative polymerization, forming a dense, continuous, and well-adhered conductive network 33; simultaneously, the "deposition-relaxation" cycle in pulse mode helps dissipate local heat, alleviate concentration polarization, and promote the growth of doped anions (such as ClO4). - The embedding of ) results in a conductive network 33 with high conductivity, low interfacial impedance, and good mechanical flexibility. When the current is below 0.2 mA / cm 2 At this time, insufficient polymerization driving force leads to a slow deposition rate and low film formation efficiency; it is difficult to form a continuous conductive network 33 under a limited number of pulse cycles, resulting in a film layer that is too thin or incomplete, which cannot effectively reduce the electrode interface resistance and affects the rate performance and cycle stability of the device; when the current is higher than 10mA / cm 2 When the electrode interface reaction is too intense, the monomer consumption rate far exceeds its diffusion replenishment rate, leading to severe concentration polarization and local overpolymerization. This can easily result in a rough, porous film, or even dendritic or powdery deposits, reducing the film's density and adhesion. At the same time, high current may cause side reactions in the solvent (such as water) (such as hydrogen evolution or oxygen evolution), damaging the polymerization environment, causing film structure defects and uneven doping, ultimately leading to decreased conductivity and shortened cycle life.

[0076] Specifically, the current deposition time in the pulse current method process is any one value or a range of any two values ​​from 1s, 2s, 3s, 4s, 5s, 6s, 7s, 8s, 9s or 10s; in a preferred embodiment, the current deposition time in the pulse current method process is 3-7s.

[0077] When the current deposition time in the pulsed current method is 1-10 s, the monomers (3,4-ethylenedioxythiophene and pyrrole) have sufficient time to undergo oxidation, nucleation, and chain growth on the electrode surface, while avoiding localized over-consumption of concentration or heat accumulation caused by continuous current supply. Within this time window, combined with an appropriate pause period, a dynamic balance between polymerization reaction and diffusion mass transfer can be achieved, thereby forming a dense, uniform, strongly adherent, and highly conductive network 33. This deposition time range balances film formation efficiency and film quality, making it suitable for constructing high-performance interface modification layers on the surface of active materials. When the current deposition time is less than 1 second, the charge provided by each pulse is insufficient, making it difficult to effectively induce sufficient oxidative polymerization of monomers. The sparse nucleation sites lead to discontinuous and incomplete film growth, or even the formation of only island-like polymer particles, failing to construct an effective three-dimensional conductive pathway and significantly weakening its role in reducing interfacial impedance and enhancing electron transport capability. When the current deposition time is longer than 10 seconds, the monomers at the electrode / electrolyte interface are rapidly depleted and cannot be replenished in time, causing severe concentration polarization. At the same time, continuous current supply causes local temperature increases, which may trigger side reactions (such as solvent decomposition, polymer peroxidation degradation, etc.). This can lead to a loose film structure, increased roughness, and even cracks or peeling. In addition, excessively long deposition times can easily cause uncontrolled film thickness, increase the proportion of inactive materials, and reduce the overall energy density of the electrode.

[0078] Specifically, the current pause time in the pulse current method process is any one value or a range of any two values ​​from 1s, 2s, 3s, 4s, 5s, 6s, 7s, 8s, 9s, or 10s; in a preferred embodiment, the current pause time in the pulse current method process is 3-7s.

[0079] When the current pause time in the pulsed current method is 1-10s, the electrode / electrolyte interface has sufficient time for the redistribution of matter and charge: depleted monomers can diffuse back from the bulk solution to the electrode surface, byproducts can migrate, effectively alleviating concentration polarization and ohmic polarization, avoiding local overpolymerization, thereby promoting uniform nucleation and orderly growth in the next pulse, and finally forming a dense, continuous, strongly adherent and highly conductive network.33 When the current pause time is less than 1 second, the interfacial mass transfer recovery is insufficient, the monomer concentration gradient continues to accumulate, causing the polymerization reaction in subsequent pulse cycles to concentrate on locally highly active sites, easily forming dendritic and multi-layered polymer networks. Pore ​​or particulate deposition occurs; simultaneously, heat and byproducts cannot be effectively dissipated, which may lead to film structure defects, uneven doping, or internal stress concentration, reducing the mechanical stability and cycle durability of the film; when the current pause time is longer than 10 seconds, although mass transfer is sufficient, the overall deposition efficiency decreases significantly, making it difficult to achieve the target film thickness under the same number of cycles; more seriously, the deposited polymer chains may be partially dedoped or structurally relaxed under long-term no-current conditions, weakening their conductivity; in addition, excessively long pauses will prolong the process cycle, reduce production efficiency, and in extreme cases may lead to partial dissolution or passivation of the initial nucleation layer, affecting the continuity of the film layer.

[0080] Specifically, the total time of the pulse current method is any one value or a range of any two values ​​from 100s, 200s, 300s, 400s, 500s, 600s, 700s, 800s, 900s, 1000s, 1100s, or 1200s; in a preferred embodiment, the total time of the pulse current method is 60-600s.

[0081] When the total time of the pulsed current method is 100-1200 s, a conductive network 33 with moderate thickness, dense structure and continuous structure can be controllably deposited on the electrode surface. Within this cycle range, the polymerization process has both good repeatability and process flexibility: the resulting highly conductive network can effectively reduce the electrode / electrolyte interface impedance, improve electron transport efficiency, and buffer the volume change of active material during charge and discharge, thereby significantly improving the rate performance and cycle stability of the electrode; when the total time of the pulsed current method is less than 100 s, the total deposited charge is insufficient, resulting in an excessively thin or discontinuous polymer film, which cannot form an effective three-dimensional conductive path; when the total time of the pulsed current method exceeds 1200 s, the film thickness continues to increase, although the conductivity may be slightly improved, the proportion of inactive material increases significantly, reducing the overall energy density of the electrode.

[0082] In one embodiment, a third aspect of the present invention provides a battery comprising a positive electrode, a negative electrode, and a separator, wherein the negative electrode is the aforementioned negative electrode or a negative electrode prepared by the aforementioned method for preparing a negative electrode.

[0083] Specifically, the positive electrode sheet includes a positive current collector and positive active material layers disposed on both sides of the positive current collector. The positive active material layers include a positive active substance, which includes the aforementioned positive electrode material, or a positive electrode material prepared by the aforementioned method for preparing the positive electrode material.

[0084] Specifically, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active material layer can be disposed on either or both of the two opposite surfaces of the positive current collector.

[0085] In some embodiments, the positive current collector can be a metal foil or a composite current collector. For example, aluminum foil can be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy on the polymer material substrate. Exemplarily, the polymer material can be selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc. In some embodiments, the positive electrode active material layer further includes a conductive agent; as an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0086] In some embodiments, the positive electrode active material layer further includes a binder. As examples, the binder may include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, and tetrafluoroethylene-hexafluoropropylene copolymer.

[0087] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0088] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive electrode active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0089] Specifically, the separator can be any separator material suitable for lithium-ion batteries in the art, such as, but not limited to, one or more combinations of single-layer polypropylene, single-layer polyethylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester and natural fibers.

[0090] The battery in this application also includes an electrolyte, which may be one or more of a gel electrolyte, a solid electrolyte, and an electrolyte solution, including lithium salts and non-aqueous solvents.

[0091] In some embodiments, the battery is prepared as follows: the positive electrode, separator, and negative electrode are wound or stacked in sequence to form an electrode assembly, which is then placed in, for example, an aluminum-plastic film, injected with electrolyte, formed, and packaged to produce a lithium-ion battery.

[0092] The beneficial effects of the present invention will be further illustrated below with reference to the embodiments.

[0093] To make the inventive objectives, technical solutions, and beneficial effects of this invention clearer, the invention is further described in detail below with reference to embodiments. However, it should be understood that the embodiments of this invention are merely for illustrative purposes and not for limiting the invention, and the embodiments are not limited to those given in the specification. Materials not specified in the embodiments were prepared under conventional conditions or according to the conditions recommended by the material supplier.

[0094] Furthermore, it should be understood that the one or more method steps mentioned in this invention do not preclude the existence of other method steps before or after the combination steps, or the insertion of other method steps between these explicitly mentioned steps, unless otherwise stated. It should also be understood that the combination connection relationship between one or more devices / apparatus mentioned in this invention does not preclude the existence of other devices / apparatus before or after the combination of devices / apparatus, or the insertion of other devices / apparatus between these explicitly mentioned devices / apparatus, unless otherwise stated. Moreover, unless otherwise stated, the numbering of each method step is merely a convenient tool for identifying each method step, and not for limiting the order of the method steps or limiting the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention.

[0095] In the following embodiments, the reagents, materials and instruments used, unless otherwise specified, are commercially available or can be obtained through synthesis methods known in the art.

[0096] Table 1 shows the design of negative electrode parameters for Examples 1-17 and Comparative Examples 1-3; Example 1 This embodiment illustrates the negative electrode sheet and battery disclosed in this invention; it includes the following operational steps: Preparation of negative electrode: The first negative electrode slurry was prepared by mixing silicon-containing porous carbon-supported silicon, binder, and conductive agent in a ratio of 92:7.5:0.5. The first negative electrode slurry is coated onto the negative electrode current collector copper foil on a coating machine, dried, and rolled to obtain a rolled electrode sheet; Preparation of polymerization electrolyte: Dissolve 0.05M KCl in aqueous solution, and after stirring and dissolving, add HClO4 to adjust the pH to 1. Add 0.01M EDOT (3,4-ethylenedioxythiophene) and 0.01M Py (pyrrole), and stir evenly to form polymerization electrolyte; The rolled electrode sheet was placed in the prepared polymerization electrolyte, with Ag / AgCl as the reference electrode and Pt as the counter electrode. Polymerization was carried out using a pulsed current method with a current of 5 mA / cm². 2 The current is deposited for 5 seconds, paused for 5 seconds, and repeated 50 times to form a conductive network. The polymerized electrode sheets are washed with deionized water and dried to serve as negative electrode sheets. Preparation of positive electrode: Lithium cobalt oxide, single-walled carbon nanotubes, conductive carbon black SP, and binder PVDF are mixed in a ratio of 97.3:0.5:1.0:1.2 to prepare a positive electrode slurry. The positive electrode slurry is then coated onto the surface of the positive electrode current collector on a coating machine. After drying, rolling, die-cutting, and other processes, a positive electrode sheet that meets the requirements is obtained.

[0097] Electrolyte preparation: Lithium hexafluorophosphate (LiPF6) was dissolved in a mixed solvent consisting of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a mass ratio of 1:2:1 to obtain an electrolyte with a concentration of 1 mol / L.

[0098] Preparation of the diaphragm: PE porous polymer film is used as the membrane substrate; Battery manufacturing: The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The electrodes are then stacked in the same manner to form a battery cell. The battery cell is placed into a pre-formed battery casing, and the electrolyte is injected into the baked and dried battery cell. After vacuum sealing, settling, and formation processes, the battery is obtained.

[0099] Example 2-17 Examples 2-17 illustrate the negative electrode and battery disclosed in this invention, including most of the operating steps in Example 1, with the following differences: The parameters of the negative electrode shown in Table 1 are used.

[0100] Comparative Examples 1-3 Comparative Examples 1-3 are used to illustrate the negative electrode sheet and battery disclosed in this invention, including most of the operating steps in Example 1, the difference being: The parameters of the negative electrode shown in Table 1 are used.

[0101] Performance testing The following performance tests were performed on the batteries prepared in Examples 1-17 and Comparative Examples 1-3: Internal resistance test: Test the 1KHz AC impedance of the positive and negative terminals of the battery cell.

[0102] Battery rate performance test: At 25℃, charge at 0.5C to 4.5V, cut off at 0.05C, and then discharge at 0.2C to 3.0V as the initial capacity; then charge at 0.5C to 4.5V, cut off at 0.05C, and then discharge at 2C to 3.0V as the rate discharge capacity; Capacity percentage = 2C discharge capacity / initial capacity.

[0103] Cyclic performance test: At 25℃, charge at 0.5C to 4.2V, cut off at 0.05C, and then discharge at 0.5C to 3.0V as the initial capacity. Repeat the cycle until the capacity retention rate decays to 80% of the initial capacity, and record the number of cycles.

[0104] The test results are shown in Table 2.

[0105] Table 2 Battery performance using pulse current method Comparing Example 1 and Comparative Example 1, it can be seen that when only pyrrole is used as a monomer for polymerization, compared with composite polymers, the conductivity is reduced, and the overall cell conductivity, rate capability, and cycle performance are further slightly reduced.

[0106] Comparing Example 1 and Comparative Example 2, it can be seen that when only 3,4-ethylenedioxythiophene is used as a monomer for polymerization, the conductivity of the composite polymer is reduced, and the overall cell conductivity, rate capability, and cycle performance are slightly reduced. Comparing Example 1 and Comparative Example 3, it can be seen that without using 3,4-ethylenedioxythiophene and pyrrole polymer as a bridge, the battery's conductivity, rate performance, and cycle performance deteriorate significantly.

[0107] Comparing Examples 1-5, it can be seen that in the polymer electrolyte, when the concentration of 3,4-ethylenedioxythiophene is 0.01-0.1 mol / L, it exhibits lower internal resistance, higher rate performance, and better cycle performance. When the concentration of 3,4-ethylenedioxythiophene is less than 0.01 mol / L, the conductive polymer layer is thin, which leads to increased internal resistance, reduced rate performance, and reduced cycle performance. When the concentration of 3,4-ethylenedioxythiophene is greater than 0.1 mol / L, the conductive polymer layer is thicker, improving conductivity, but this results in reduced cycle performance and reduced rate performance.

[0108] Comparing Examples 1-2 and Examples 6-8, it can be seen that in the polymer electrolyte, when the concentration of pyrrole is 0.01-0.1 mol / L, it has lower internal resistance, higher rate performance, and better cycle performance. When the concentration of pyrrole is less than 0.01 mol / L, the conductive polymer layer is thin, which leads to increased internal resistance, reduced rate performance, and reduced cycle performance. When the concentration of pyrrole is greater than 0.1 mol / L, it has lower internal resistance, but the rate performance and cycle performance deteriorate significantly.

[0109] Comparing Examples 1, 3, 6-7, and 9, it can be seen that in the polymer electrolyte, when the molar ratio of 3,4-ethylenedioxythiophene to pyrrole is 0.2-5, it exhibits lower internal resistance, higher rate performance, and better cycle performance. When the molar ratio of 3,4-ethylenedioxythiophene to pyrrole is less than 0.2, the conductive polymer layer is thin, which leads to reduced conductivity, lower rate performance, and lower cycle performance. When the molar ratio of 3,4-ethylenedioxythiophene to pyrrole is greater than 5, the conductive polymer layer is thicker, improving conductivity, but excessive thickness leads to reduced cycle performance and lower rate performance.

[0110] Comparing Examples 1 and 10-13, it can be seen that when the concentration of potassium chloride is 0.05-0.5 mol / L, a conductive polymer film can be uniformly formed, resulting in a battery with lower internal resistance, higher rate performance, and better cycle performance. When the concentration of potassium chloride is less than 0.05 mol / L, the conductive polymer film is not fully formed, leading to deterioration in conductivity, rate performance, and cycle performance. When the concentration of potassium chloride is greater than 0.5 mol / L, the conductive polymer film is not densely formed, resulting in deterioration in conductivity, rate performance, and cycle performance.

[0111] Comparing Examples 1 and 14-17, it can be seen that when the pH value of the polymerization electrolyte is 0.1-2, it has lower internal resistance, higher rate performance, and better cycle performance. When the pH value of the polymerization electrolyte is less than 0.1, oligomers are easily formed, affecting the polymer properties, reducing conductivity, increasing internal resistance, reducing rate performance, and reducing cycle performance. When the pH value of the polymerization electrolyte is greater than 2, the pH value is too high, and nucleophilic OH⁻ will attack cationic free radicals, hindering polymerization, reducing conductivity, increasing internal resistance, reducing rate performance, and reducing cycle performance.

[0112] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A negative electrode sheet, characterized in that, include Negative electrode current collector; An active material layer is disposed on the surface of the negative electrode current collector. The active material layer includes a negative electrode active material, a conductive agent, a binder, and a conductive network. The negative electrode active material includes a silicon-containing material. The negative electrode active material and the conductive agent are mixed together and bonded together by the binder. The conductive network is formed between adjacent negative electrode active materials and between adjacent negative electrode active materials and the negative electrode current collector. The polymer monomers of the conductive network include 3,4-ethylenedioxythiophene and pyrrole. The conductive network is obtained by pulsed current polymerization.

2. The negative electrode sheet according to claim 1, characterized in that, The thickness of the conductive network is 0.5-2 μm.

3. The negative electrode sheet according to claim 1, characterized in that, The conductive network is a three-dimensional mesh structure with a porosity of 30%–70%.

4. The negative electrode sheet according to claim 1, characterized in that, The molar ratio of 3,4-ethylenedioxythiophene to pyrrole is (1-5):(1-5).

5. The negative electrode sheet according to claim 1, characterized in that, The total mass of the negative electrode active material, the binder, and the conductive agent is taken as 100%. The mass percentage of the negative electrode active material is 90.5%-93.5%; the mass percentage of the binder is 6%-9%; and the mass percentage of the conductive agent is 0.3%-0.5%.

6. The negative electrode sheet according to claim 1, characterized in that, The silicon-containing material includes one or more of silicon particles, silicon suboxide, and silicon-carbon materials.

7. The negative electrode sheet according to claim 6, characterized in that, The silicon-containing particles are selected from silicon-carbon materials, and the silicon content in the silicon-carbon materials is 40%-60% by mass.

8. The method for preparing the negative electrode sheet according to any one of claims 1-7, characterized in that, Includes the following steps: The negative electrode active material, conductive agent, and binder are mixed into a slurry and coated onto the surface of the negative electrode current collector. The polymeric electrolyte forms a conductive network between adjacent negative electrode active materials and between adjacent negative electrode active materials and negative electrode current collectors using a pulsed current method. The polymeric electrolyte includes 3,4-ethylenedioxythiophene and pyrrole.

9. The method for preparing the negative electrode sheet according to claim 8, characterized in that, In the polymerization electrolyte, the concentration of 3,4-ethylenedioxythiophene is 0.01-0.1 mol / L; And / or, in the polymerization electrolyte, the concentration of the pyrrole is 0.01-0.1 mol / L.

10. The method for preparing the negative electrode sheet according to claim 8, characterized in that, The polymerization electrolyte also includes potassium chloride, and the concentration of potassium chloride in the polymerization electrolyte is 0.05-0.5 mol / L.

11. The method for preparing the negative electrode sheet according to claim 8, characterized in that, The polymer electrolyte also includes a pH adjuster, which includes one or more of perchloric acid, sulfuric acid, hydrochloric acid, p-toluenesulfonic acid, and trifluoromethanesulfonic acid.

12. The method for preparing the negative electrode sheet according to claim 8, characterized in that, The pH value of the polymer electrolyte is 0.1-2.

13. The method for preparing the negative electrode sheet according to claim 8, characterized in that, The pulsed current method uses an Ag / AgCl electrode as a reference electrode; and / or, the pulsed current method uses a Pt electrode as a counter electrode.

14. The method for preparing the negative electrode sheet according to claim 8, characterized in that, During the pulsed current method, the current is 0.2-10 mA / cm. 2 ; And / or, the current deposition time is 1-10 seconds; And / or, the current pause time is 1-10 seconds; And / or, the total time for the pulsed current method is 100-1200s.

15. A battery, characterized in that, It includes a positive electrode, a negative electrode, and a separator, wherein the negative electrode is the negative electrode as described in any one of claims 1-7, or the negative electrode prepared by the method described in any one of claims 8-14.

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