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 a negative electrode active material, a conductive agent, a binder and a conductive polymer layer, the conductive polymer layer is formed on the surfaces of the negative electrode active material and the conductive agent and forms a continuous surface, and the conductive polymer layer comprises 3, 4-ethylenedioxythiophene and sodium polystyrenesulfonate; the conductive polymer layer can effectively stabilize the interface between the negative electrode and the electrolyte, inhibit the side reaction of the electrolyte or the growth of metal dendrites, and prolong the cycle life of the battery; sodium polystyrenesulfonate is water-soluble, so that a 3, 4-ethylenedioxythiophene and sodium polystyrenesulfonate compound can be stably dispersed in water and effectively deposited on the surfaces of the adjacent negative electrode active material and the conductive agent, a conductive polymer layer is constructed on the battery negative electrode, and the electrochemical performance and the cycle stability can be remarkably improved.

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 polymer layer; 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 polymer layer is formed on the surfaces of adjacent negative electrode active materials and the conductive agent to form a continuous surface; the monomers of the conductive polymer layer include 3,4-ethylenedioxythiophene and sodium polystyrene sulfonate.

[0008] Optionally, the conductive polymer layer is obtained by polymerization using a constant current method.

[0009] Optionally, the thickness of the conductive polymer layer is 0.5-2 μm.

[0010] Optionally, the molar ratio of the 3,4-ethylenedioxythiophene to the sodium polystyrene sulfonate 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%; 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. A conductive polymer layer is formed by depositing a polymer electrolyte on the surfaces of adjacent negative electrode active materials and conductive agents using a constant current method. The polymer electrolyte includes 3,4-ethylenedioxythiophene and sodium polystyrene sulfonate.

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

[0016] Optionally, the polymerization electrolyte further includes lithium perchlorate, wherein the concentration of lithium perchlorate in the polymerization electrolyte is 0.05-0.5 mol / L.

[0017] Optionally, the polymeric electrolyte further includes a pH adjuster, which includes one or more of hydrochloric acid, perchloric acid, sulfuric acid, p-toluenesulfonic acid, and trifluoromethanesulfonic acid.

[0018] Optionally, the pH value of the polymer electrolyte is 0.1-2.

[0019] Optionally, an Ag / AgCl electrode is used as a reference electrode in the constant current method; and / or, a Pt electrode is used as a counter electrode in the constant current method.

[0020] Optionally, during the constant current method, the current is 0.2-10 mA / cm. 2 ; and / or, the deposition time is 10-600 s.

[0021] 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.

[0022] According to the negative electrode sheet provided by the present invention, a conductive polymer layer is formed on the surface of adjacent negative electrode active materials and conductive agents. The conductive polymer layer is formed by copolymerization of 3,4-ethylenedioxythiophene (EDOT) and sodium polystyrene sulfonate (NaPSS). This effectively stabilizes the interface between the negative electrode and the electrolyte, inhibits electrolyte side reactions or metal dendrite growth, and improves battery cycle life. Moreover, the conductive polymer layer formed by copolymerization of EDOT and sodium polystyrene sulfonate has both good electronic conductivity and certain ion transport capacity, which helps to reduce electrode / electrolyte interface impedance and improve battery rate performance and charge / discharge efficiency. In addition, the conductive polymer layer has certain mechanical strength and uniform ion flux regulation capability, which can inhibit the formation of lithium dendrites to a certain extent and improve battery safety. At the same time, sodium polystyrene sulfonate... It is water-soluble. NaPSS, acting as a dopant and dispersant, enables the 3,4-ethylenedioxythiophene and sodium polystyrene sulfonate complex to be stably dispersed in water, forming a colloidal solution. This solution is then effectively deposited on the surfaces of adjacent negative electrode active materials and conductive agents. Constructing such a conductive polymer layer on the negative electrode of a battery or supercapacitor can significantly improve electrochemical performance and cycle stability. Furthermore, the conductive polymer layer is formed by in-situ polymerization on the surfaces of adjacent negative electrode active materials and conductive agents using a constant current method. This achieves uniform, dense, and robust coating, effectively preventing the detachment of negative electrode active materials, conductive agents, or binders, and enhancing the integrity of the electrode structure. The active material layer provides basic electrochemical activity, while the conductive polymer layer plays a dual role of protection and conductivity. The synergistic effect of the two significantly improves the overall capacity retention and cycle stability of the negative electrode. Attached Figure Description

[0023] 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.

[0024] 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 the prior art of this invention; 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 polymer layer. Detailed Implementation

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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 polymer layer 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 polymer layer 33 is formed on the surfaces of adjacent negative electrode active materials and conductive agents to form a continuous surface. The polymer monomers of the conductive polymer layer 33 include 3,4-ethylenedioxythiophene and sodium polystyrene sulfonate.

[0029] like Figure 2 As shown, a negative electrode active material layer is formed on both sides of a conventional negative electrode sheet. The negative electrode active material layer includes a negative electrode active material, a conductive agent, and a binder. The negative electrode active material includes a silicon-containing material 2. Some conductive agent particles adsorbed at the connection points of the silicon-containing material 2 are effective conductive agents 31; some conductive agent particles cannot be effectively adsorbed at the connection points of the silicon-containing material 2, forming ineffective conductive agents 32. The 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 the silicon-containing material 2 will also cause some conductive networks to break and lose conductivity.

[0030] like Figure 1 As shown, this invention provides a conductive polymer layer 33 on the surfaces of adjacent negative electrode active materials and conductive agents. The conductive polymer layer 33 is formed by copolymerizing 3,4-ethylenedioxythiophene (EDOT) and sodium polystyrene sulfonate (NaPSS). This effectively stabilizes the interface between the negative electrode and the electrolyte, suppresses electrolyte side reactions or metal dendrite growth, and improves battery cycle life. Furthermore, the conductive polymer layer 33 formed by the copolymerization of EDOT and sodium polystyrene sulfonate possesses both good electronic conductivity and a certain ion transport capability, which helps reduce electrode / electrolyte interface impedance and improve battery rate performance. In addition to improving charge and discharge efficiency, the conductive polymer layer 33 possesses certain mechanical strength and uniform ion flux regulation capabilities, which can suppress the formation of lithium dendrites to a certain extent and enhance battery safety. Meanwhile, sodium polystyrene sulfonate is water-soluble, and NaPSS, as a dopant and dispersant, enables the 3,4-ethylenedioxythiophene and sodium polystyrene sulfonate complex to be stably dispersed in water, forming a colloidal solution, and effectively deposited on the surface of adjacent negative electrode active materials and conductive agents. Constructing such a conductive polymer layer 33 on the negative electrode of a battery or supercapacitor can significantly improve electrochemical performance and cycle stability.

[0031] In summary, this technology, through its encapsulated double-layer structure design, achieves efficient construction of the conductive network and long-term stability of the electrode structure, demonstrating significant technological advancement and promising prospects for industrial application.

[0032] In one embodiment, the conductive polymer layer 33 is obtained by constant current polymerization.

[0033] A conductive polymer layer 33 is formed by in-situ polymerization on the surfaces of adjacent negative electrode active materials and conductive agents using a constant current method. This achieves uniform, dense, and robust coating, effectively preventing the detachment of negative electrode active materials, conductive agents, or binders, and enhancing the integrity of the electrode structure. The active material layer provides basic electrochemical activity, while the conductive polymer layer 33 plays a dual role of protection and conductivity. The synergistic effect of the two significantly improves the overall capacity retention and cycle stability of the negative electrode. In one embodiment, the thickness of the conductive polymer layer 33 is 0.5-2 μm.

[0034] Specifically, the thickness of the conductive polymer layer 33 is any one 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 polymer layer 33 is 1-1.5μm.

[0035] When the thickness of the conductive polymer layer 33 is 0.5-2μm, it can form a continuous, dense and flexible conductive network on the surface of adjacent negative electrode active materials and conductive agents. This not only effectively improves the electronic conductivity, but also fully buffers the mechanical stress caused by the volume expansion (>300%) of silicon during charging and discharging, preventing particle pulverization and electrode structure collapse. At the same time, it allows lithium ions to migrate rapidly, thereby significantly improving the cycle stability, coulombic efficiency and rate performance of the negative electrode. When the thickness of the conductive polymer layer 33 is less than 0.5 μm, the conductive polymer layer 33 is too thin, making it difficult to completely cover the negative electrode active material. The negative electrode active material exposed in local areas is prone to uncontrollable side reactions in the electrolyte, leading to repeated rupture and regeneration of the solid electrolyte interphase (SEI) film, resulting in continuous consumption of active lithium, increased internal resistance, and ultimately rapid capacity decay and shortened cycle life. When the thickness of the conductive polymer layer 33 is greater than 2 μm, the excessive thickness of the conductive polymer layer 33 will significantly increase the lithium ion diffusion path, increase the interfacial transport impedance, inhibit electrode reaction kinetics, and lead to a decrease in rate performance. At the same time, the excessively thick conductive polymer layer 33 is prone to microcracks, wrinkles, or even peeling due to the accumulation of internal stress during silicon volume changes, losing its protective effect on the silicon-containing material 2 and accelerating electrode failure instead.

[0036] In one embodiment, the molar ratio of 3,4-ethylenedioxythiophene to sodium polystyrene sulfonate is (1-5):(1-5).

[0037] Specifically, the molar ratio of 3,4-ethylenedioxythiophene to sodium polystyrene sulfonate 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 sodium polystyrene sulfonate is ((1-3):(3-1).

[0038] When the molar ratio of 3,4-ethylenedioxythiophene to sodium polystyrene sulfonate is (1-5):(1-5), PSS Providing sufficient counter-anions ensures that the polymer chains formed by 3,4-ethylenedioxythiophene are electrically neutral in the oxidative doping state, preventing precipitation or uneven sedimentation during the polymerization of 3,4-ethylenedioxythiophene. The conductive polymer layer 33 formed by 3,4-ethylenedioxythiophene and sodium polystyrene sulfonate is dense and continuous, possessing both flexibility and adhesion, and effectively deposited on the surface of adjacent negative electrode active materials and conductive agents. When the molar ratio of 3,4-ethylenedioxythiophene to sodium polystyrene sulfonate is less than 1:5, the excess of sodium polystyrene sulfonate leads to an excessively high proportion of insulating components in the resulting conductive polymer layer 33, resulting in a significant decrease in conductivity. When the molar ratio of 3,4-ethylenedioxythiophene to sodium polystyrene sulfonate is greater than 5:1, the relative excess of 3,4-ethylenedioxythiophene makes it easy to generate insoluble aggregates during polymerization, resulting in a loose conductive polymer layer 33 with poor adhesion and reduced electrolyte stability.

[0039] 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%.

[0040] 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%.

[0041] 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%.

[0042] 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%.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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%.

[0047] When the silicon content in a silicon-carbon material is 40%-60% by mass, it can relatively balance the energy density and the cyclic expansion of silicon-carbon particles. When the silicon content is less than 40%, the energy density of the silicon-carbon material will be too low. When the silicon content is greater than 60%, the silicon-carbon particles will expand excessively, affecting the cyclic thickness expansion rate and capacity retention rate.

[0048] like Figure 1-2 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.

[0049] 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.

[0050] 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.

[0051] In one embodiment, the conductive agent includes one or more of carbon black (such as Super P), acetylene black, Ketjen black, graphene, carbon nanotubes (CNTs), carbon fibers, expanded graphite, or combinations thereof.

[0052] 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 is deposited on the surfaces of adjacent negative electrode active materials and conductive agents by a constant current method to form a conductive polymer layer 33. The polymer electrolyte includes 3,4-ethylenedioxythiophene and sodium polystyrene sulfonate.

[0053] This invention forms a conductive polymer layer 33 on the surface of adjacent negative electrode active materials and conductive agents. The conductive polymer layer 33 is formed by copolymerization of 3,4-ethylenedioxythiophene (EDOT) and sodium polystyrene sulfonate. First, 3,4-ethylenedioxythiophene is a conjugated monomer that undergoes oxidative polymerization under a positive potential (or constant current) applied at the anode to generate the conductive polymer PEDOT. NaPSS dissociates into PSS in water. - and Na + During electropolymerization, the PEDOT chains are in a cationic state (positively charged due to oxidative doping), requiring counterbalancing anions to maintain electroneutrality; PSS - As a macromolecular dopant, it is embedded between PEDOT chains to form a stable conductive polymer layer 33; at the same time, PSS has good water solubility and film-forming properties, which enables PEDOT to be stably dispersed in the aqueous system and avoids precipitation or aggregation.

[0054] In one embodiment, the concentration of 3,4-ethylenedioxythiophene in the polymerization electrolyte is 0.01-0.1 mol / L.

[0055] 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 0.01-0.08 mol / L.

[0056] When the concentration of 3,4-ethylenedioxythiophene is 0.01-0.1 mol / L, the monomer supply is sufficient but not excessive, enabling controllable and uniform heterogeneous nucleation and growth on the electrode surface; forming a smooth, strongly adherent conductive polymer layer 33; the PEDOT chains are fully connected, and PSS provides effective doping and dispersion, thus giving it good conductivity; when the concentration of 3,4-ethylenedioxythiophene is less than 0.01 mol / L, it will lead to insufficient monomer supply, resulting in discontinuous and incomplete coverage of the conductive polymer layer 33, significantly reducing conductivity and interface protection effect; when the concentration of 3,4-ethylenedioxythiophene is greater than 0.1 mol / L, it is easy to initiate homogeneous polymerization in the solution phase, producing insoluble aggregates, causing the conductive polymer layer 33 to be loose and have poor adhesion, and reducing the stability of the electrolyte.

[0057] In one embodiment, the concentration of sodium polystyrene sulfonate in the polymerization electrolyte is 0.01-0.1 mol / L.

[0058] Specifically, the concentration of sodium polystyrene sulfonate 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 sodium polystyrene sulfonate is 0.01-0.08 mol / L.

[0059] When the concentration of sodium polystyrene sulfonate is 0.01-0.1 mol / L, provide an appropriate amount of PSS. - Doping with anions effectively balances PEDOT + The positive charge of the chain forms a stable conductive polymer layer 33; it maintains good water solubility and colloidal stability, preventing EDOT or PEDOT from agglomerating and precipitating; PSS acts as a polymer template, guiding PEDOT to deposit orderly on the electrode surface, promoting the uniform formation of the conductive polymer layer 33; when the concentration of sodium polystyrene sulfonate is less than 0.01 mol / L, insufficient doping anions lead to the precipitation and aggregation of PEDOT during polymerization, resulting in a discontinuous conductive polymer layer 33 with poor adhesion. When the concentration of sodium polystyrene sulfonate is greater than 0.1 mol / L, excessive insulating sodium polystyrene sulfonate encapsulates the conductive phase, significantly reducing the conductivity of the conductive polymer layer 33 and hindering ion transport, thus affecting electrochemical performance.

[0060] In one embodiment, the polymerization electrolyte further includes lithium perchlorate (LiClO4), and the concentration of lithium perchlorate in the polymerization electrolyte is 0.05-0.5 mol / L.

[0061] Specifically, the concentration of lithium perchlorate 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 lithium perchlorate is 0.1-0.4 mol / L.

[0062] When the concentration of lithium perchlorate is 0.05-0.5 mol / L, within this range, lithium perchlorate effectively improves the solution conductivity as a supporting electrolyte, inhibits film "bursting" or irregular growth caused by charge accumulation, and promotes uniform electrodeposition of poly(3,4-ethylenedioxythiophene) films. When the concentration of lithium perchlorate is less than 0.05 mol / L, the ionic strength is insufficient, the solution resistance is high, and the film layer is uneven. When the concentration of lithium perchlorate is greater than 0.5 mol / L, the improvement in conductivity tends to saturate (ion mobility is limited by viscosity); high concentrations of ClO4... - It has strong oxidizing properties and may cause side reactions on the electrode surface (especially at high potentials); perchlorate can coexist with organic matter (such as EDOT, PEDOT) for a long time, and there is a potential explosion hazard under dry or heated conditions.

[0063] In one embodiment, the polymerization electrolyte further includes a pH adjuster, which includes one or more of hydrochloric acid, perchloric acid, sulfuric acid, p-toluenesulfonic acid, and trifluoromethanesulfonic acid. Using the above-mentioned pH adjuster can improve the protonation degree of EDOT and promote its oxidative polymerization; enhance the ionization degree of PSS and improve the doping efficiency; suppress side reactions (such as peroxidation degradation) and obtain a denser and more conductive polymer layer 33.

[0064] In one embodiment, the pH of the polymer electrolyte is 0.1-2.

[0065] 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.

[0066] When the pH of the polymerization electrolyte is 0.1-2, under these strongly acidic conditions, the 3,4-ethylenedioxythiophene monomer readily undergoes efficient electrochemical oxidative polymerization. Simultaneously, polystyrene sulfonic acid is fully protonated and embedded as an effective dopant within the poly(3,4-ethylenedioxythiophene) backbone, resulting in a dense, highly conductive, and strongly adherent conductive polymer layer 33. When the pH of the polymerization electrolyte is less than 0.1, it corrodes the electrode substrate (especially copper and aluminum), causing partial hydrolysis or degradation of the PSS backbone. When the pH of the polymerization electrolyte is greater than 2, the EDOT polymerization rate decreases significantly, and the onset potential shifts positively. Water oxidation (oxygen evolution) easily occurs, leading to a porous and loose membrane. The PSS doping efficiency decreases, the PEDOT chains become disordered, and the conductivity drops sharply (often <0.01 S / cm). The conductive polymer layer 33 is easily peeled off, resulting in poor reproducibility.

[0067] In one embodiment, an Ag / AgCl electrode is used as a reference electrode in the constant current method; and / or, a Pt electrode is used as a counter electrode in the constant current method.

[0068] Using Ag / AgCl electrodes in Cl-containing environments - The aqueous solution exhibits a highly reversible electrode reaction (AgCl + e⁻) - ⇌Ag + Cl - Its open-circuit potential is affected by temperature and Cl. - With minimal impact from concentration, it provides 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.

[0069] 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 constant current output.

[0070] In one embodiment, during the constant current method, the current is 0.2-10 mA / cm. 2 ; and / or, the deposition time is 10-600 s.

[0071] Specifically, the current in the constant current method process 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 27.2mA / 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 value or a range of any two point values; in a preferred embodiment, the current in the constant current method process is 1.6-2.3 mA / cm. 2 μm.

[0072] When the current in the constant current method is 0.2-10 mA / cm 2 Within this range, 3,4-ethylenedioxythiophene can achieve uniform and dense electrochemical polymerization on the electrode surface, forming a highly conductive and well-adhered conductive polymer layer 33; the current density during the galvanostatic process is less than 0.2 mA / cm². 2 When the deposition rate is too slow, the conductive polymer layer 33 becomes discontinuous and incompletely covered; when the current density during the constant current method is greater than 10 mA / cm², the deposition rate is too slow. 2 When this occurs, it can easily trigger oxygen evolution side reactions and homogeneous polymerization in the solution phase, resulting in a loose, porous, and easily detached conductive polymer layer 33, which seriously affects electrochemical performance and cycle stability.

[0073] Specifically, the deposition time in the constant current method process is any one value or a range of any two values ​​from 10s, 50s, 100s, 150s, 200s, 250s, 300s, 350s, 400s, 450s, 500s, 550s, or 600s; in a preferred embodiment, the deposition time in the constant current method process is 50-300s.

[0074] When the deposition time in the galvanostatic process is 10-600s, a conductive polymer layer 33 with moderate thickness, dense structure, and good electrochemical activity can be formed on the electrode surface within this range. When the deposition time in the galvanostatic process is less than 10s, the conductive polymer layer 33 will be discontinuous and unable to effectively cover the substrate, resulting in insufficient interface protection and conductivity. When the deposition time in the galvanostatic process is greater than 600s, the conductive polymer layer 33 will be too thick, which will easily cause internal stress cracking and hinder ion transport, thereby reducing electrochemical performance and cycle stability.

[0075] 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.

[0076] 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 positive active material, which includes the aforementioned positive electrode material, or a positive electrode material prepared by the aforementioned method for preparing positive electrode material.

[0077] Specifically, the positive electrode current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode active material layer can be disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] The beneficial effects of the present invention will be further illustrated below with reference to the embodiments.

[0086] 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.

[0087] 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 combined steps, or the insertion of other method steps between these explicitly mentioned steps, unless otherwise stated. It should also be understood that the combined 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 combined 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 defining 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.

[0088] 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.

[0089] Table 1. Design of negative electrode parameters for Examples 1-17 and Comparative Examples 1-2; 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 the polymerization electrolyte: Dissolve 0.05M LiClO4 in an aqueous solution. After stirring and dissolving, add 0.01M EDOT (3,4-ethylenedioxythiophene) and 0.01M NaPSS (sodium polystyrene sulfonate). Stir until homogeneous, then adjust the pH to 1 with HCl to form the polymerization electrolyte. The rolled electrode sheet was placed in the prepared polymerization electrolyte, with Ag / AgCl as the reference electrode, and polymerization was carried out using a constant current method at 5 mA / cm². 2 The current is deposited for 300 seconds to form a conductive polymer layer on the surface of the adjacent negative electrode active material and conductive agent; 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.

[0090] 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 molar ratio of 1:2:1 to obtain an electrolyte with a concentration of 1 mol / L.

[0091] 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.

[0092] 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.

[0093] Comparative Examples 1-2 Comparative Examples 1-2 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.

[0094] Performance testing The following performance tests were performed on the batteries prepared in Examples 1-17 and Comparative Examples 1-2: Internal resistance test: Test the 1KHz AC impedance of the positive and negative terminals of the battery cell.

[0095] 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.

[0096] 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.

[0097] The test results are shown in Table 2.

[0098] Table 2 Battery Electrochemical Performance Comparing Example 1 and Comparative Example 1, it can be seen that when only sodium polystyrene sulfonate is used as a monomer for polymerization, compared with composite polymers, its conductivity is reduced and its internal resistance is increased; the battery rate performance and cycle performance are further slightly reduced.

[0099] Comparing Example 1 and Comparative Example 2, it can be seen that without using 3,4-ethylenedioxythiophene and sodium polystyrene sulfonate polymer as a bridge, the conductivity, rate performance, and cycle performance of the battery deteriorate significantly.

[0100] 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.

[0101] Comparing Examples 1-2 and Examples 6-8, it can be seen that in the polymer electrolyte, when the concentration of sodium polystyrene sulfonate is 0.01-0.1 mol / L, it has lower internal resistance, higher rate performance, and better cycle performance. When the concentration of sodium polystyrene sulfonate 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 sodium polystyrene sulfonate is greater than 0.1 mol / L, it has even lower internal resistance, but the rate performance and cycle performance deteriorate significantly.

[0102] 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 sodium polystyrene sulfonate 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 sodium polystyrene sulfonate is less than 0.2, the conductive polymer layer is thin, leading to reduced conductivity, lower rate performance, and lower cycle performance. When the molar ratio of 3,4-ethylenedioxythiophene to sodium polystyrene sulfonate is greater than 5, the conductive polymer layer is thicker, improving conductivity, but excessive thickness can lead to reduced cycle performance and lower rate performance.

[0103] Comparing Examples 1 and 10-13, it can be seen that when the concentration of lithium perchlorate 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 lithium perchlorate 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 lithium perchlorate 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.

[0104] 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.

[0105] In summary, this technology, through its innovative dual-layer structure design, achieves efficient construction of the conductive network and long-term stability of the electrode structure, demonstrating significant technological advancement and promising prospects for industrial application.

[0106] The above description is only 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 polymer layer. 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 polymer layer is formed on the surfaces of adjacent negative electrode active materials and the conductive agent to form a continuous surface. The monomers of the conductive polymer layer include 3,4-ethylenedioxythiophene and sodium polystyrene sulfonate. The conductive polymer layer is obtained by constant current polymerization.

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

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

4. 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%.

5. 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.

6. The negative electrode sheet according to claim 5, characterized in that, The silicon-containing material is selected from silicon-carbon materials, and the silicon content in the silicon-carbon materials is 40%-60% by mass.

7. The method for preparing the negative electrode sheet according to any one of claims 1-6, 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. A conductive polymer layer is formed by depositing a polymer electrolyte on the surfaces of adjacent negative electrode active materials and conductive agents using a constant current method. The polymer electrolyte includes 3,4-ethylenedioxythiophene and sodium polystyrene sulfonate.

8. The method for preparing the negative electrode sheet according to claim 7, characterized in that, In the polymerization electrolyte, the concentration of 3,4-ethylenedioxythiophene is 0.01-0.1 mol / L; And / or, in the polymer electrolyte, the concentration of sodium polystyrene sulfonate is 0.01-0.1 mol / L.

9. The method for preparing the negative electrode sheet according to claim 7, characterized in that, The polymer electrolyte also includes lithium perchlorate, wherein the concentration of lithium perchlorate in the polymer electrolyte is 0.05-0.5 mol / L.

10. The method for preparing the negative electrode sheet according to claim 7, characterized in that, The polymer electrolyte also includes a pH adjuster, which includes one or more of hydrochloric acid, perchloric acid, sulfuric acid, p-toluenesulfonic acid, and trifluoromethanesulfonic acid.

11. The method for preparing the negative electrode sheet according to claim 7, characterized in that, The pH value of the polymer electrolyte is 0.1-2.

12. The method for preparing the negative electrode sheet according to claim 7, characterized in that, The constant current method uses an Ag / AgCl electrode as a reference electrode; and / or, the constant current method uses a Pt electrode as a counter electrode.

13. The method for preparing the negative electrode sheet according to claim 7, characterized in that, During the constant current method, the current is 0.2-10 mA / cm. 2 ; and / or, the deposition time is 10-600 s.

14. 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 1-6, or the negative electrode prepared by the method described in any one of claims 7-13.

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