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 and a binder, the binder is used for bonding the adjacent negative electrode active material, and the negative electrode active material comprises silicon-containing particles; the conductive carbon layer is arranged on the surface, far away from the negative electrode current collector, of the active material layer, and the conductive carbon layer forms a continuous layer on the surfaces of the adjacent negative electrode active materials and the surface of the binder between the adjacent negative electrode active materials; the active material layer containing the silicon particles is arranged on the negative electrode current collector, the active material layer does not contain a conductive agent, the proportion of the negative electrode active material is higher, and the specific capacity of the electrode and the volume / weight energy density of the battery are effectively improved; by arranging the conductive carbon layer, traditional point-to-point particle contact is upgraded to face-to-face contact; the electronic conduction interface area is obviously increased, the contact resistance is reduced, and the overall electrode conductivity is 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-carbon 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 particles, 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 agent and active particles is still mainly "point-to-point," resulting in a small contact area and high interfacial resistance. This makes the contact prone to failure under high current or long cycling conditions. To ensure sufficient conductivity, 5–10 wt% or even higher of conductive agent is usually added, which directly dilutes the proportion of active material and reduces the overall specific capacity of the electrode and the energy density of the battery. 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 and a binder. The binder is used to bond adjacent negative electrode active materials. The negative electrode active material includes silicon-containing particles. A conductive carbon layer is disposed on the surface of the active material layer away from the negative electrode current collector, and the conductive carbon layer forms a continuous layer on the surfaces of adjacent negative electrode active materials and the surface of the binder therebetween.

[0008] Optionally, the porosity of the active material layer is 20% to 50%.

[0009] Optionally, the conductive carbon layer is formed on the surface of the active material layer by chemical vapor deposition.

[0010] Optionally, the carbon source gas used in the chemical vapor deposition process includes one or more of methane, acetylene, ethylene, and propylene.

[0011] Optionally, the reaction temperature of the chemical vapor deposition process is 500℃~900℃.

[0012] Optionally, the thickness of the conductive carbon layer is 0.5-5 μm.

[0013] Optionally, the silicon-containing particles include one or more of silicon particles, silicon suboxide, and silicon-carbon materials.

[0014] 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.

[0015] Optionally, the adhesive includes one or more of polyimide, phenolic resin, polyacrylonitrile, polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, polyvinyl alcohol, epoxy resin, polybenzoxazole, polyaryletherketone, asphalt precursors, lignin, or derivatives thereof.

[0016] Optionally, the total mass of the active material layer is taken as 100%, the silicon-containing particles account for 91%-94% of the mass of the active material layer, and the binder accounts for 6%-9% of the mass of the active material layer.

[0017] A second aspect of the present invention provides a method for preparing a negative electrode sheet, comprising the following steps: The active material layer is formed on the surface of the negative electrode current collector; The conductive carbon layer is formed on the surface of the active material layer by chemical vapor deposition.

[0018] 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.

[0019] According to the negative electrode sheet provided by the present invention, by setting an active material layer containing silicon particles on the negative electrode current collector, the active material layer does not contain conductive additives and has a higher proportion of negative electrode active material; thereby, while ensuring or even exceeding the conductivity performance of traditional electrodes, the electrode specific capacity and battery volumetric / weight energy density are effectively improved; by setting a conductive carbon layer on the surface of the active material layer away from the negative electrode current collector, a conductive film is formed on the surface of the active material layer, upgrading the traditional "point-to-point" particle contact to "face-to-face" surface contact; significantly increasing the electron conduction interface area, reducing contact resistance, and improving the overall electrode conductivity; even under high-rate charge and discharge, a stable and efficient electron transport channel can still be maintained. In addition, silicon particles expand significantly in volume during charge and discharge, which easily leads to particle pulverization and repeated SEI film rupture; the conductive carbon layer has both mechanical buffering and conductive functions, inhibiting the shedding of negative electrode active material, stabilizing the SEI interface; reducing repeated SEI film rupture, reducing irreversible lithium loss, and significantly extending cycle life. Attached Figure Description

[0020] 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.

[0021] 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: Negative electrode current collector, 2-silicon particles; 21-silicon particles; 22-porous carbon skeleton; 23-surface carbon coating; 31-effective conductive agent; 32-ineffective conductive agent; 33-effective conductive network. Detailed Implementation

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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 and a binder. The binder is used to bond adjacent negative electrode active materials. The negative electrode active material includes silicon-containing particles 2. A conductive carbon layer is disposed on the surface of the active material layer away from the negative electrode current collector 100. The conductive carbon layer forms a continuous layer on the surfaces of adjacent negative electrode active materials and the surface of the binder between them.

[0026] 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 negative electrode active material, conductive agent and binder. Some conductive agent particles adsorbed at the connection of silicon particles 2 are effective conductive agents 31; some conductive agent particles cannot be effectively adsorbed at the connection of silicon particles 2, forming ineffective conductive agents 32. Ineffective conductive agents 32 cannot play an effective electrical connection role between silicon particles 2, forming many ineffective conductive networks. During cycling, the expansion of silicon particles 2 will also cause some conductive networks to break and lose conductivity.

[0027] like Figure 1As shown, the present invention provides an active material layer containing silicon particles 2 on the negative electrode current collector 100. The active material layer does not contain conductive additives and has a higher proportion of negative electrode active material. Thus, while ensuring or even surpassing the conductivity of traditional electrodes, it effectively improves the electrode specific capacity and battery volumetric / weight energy density.

[0028] This invention forms a conductive film on the surface of the active material layer away from the negative electrode current collector 100 by depositing a conductive carbon layer on the surface of the active material layer. This upgrades the traditional "point-to-point" particle contact to "face-to-face" surface contact, forming an effective conductive network 33. It significantly increases the electron conduction interface area, reduces contact resistance, and improves the overall electrode conductivity. Even under high-rate charge and discharge, it can maintain a stable and efficient electron transport channel. In addition, silicon-containing particles 2 expand significantly during charge and discharge, which can easily lead to particle pulverization and repeated SEI film rupture. The conductive carbon layer has both mechanical buffering and conductive functions, inhibiting the shedding of the negative electrode active material and stabilizing the SEI interface. It reduces repeated SEI film rupture, reduces irreversible lithium loss, and significantly extends cycle life. In summary, this technology, through its innovative dual-layer structure design, fundamentally solves the core problems of poor conductivity and low cycle stability of silicon-based anodes. Without sacrificing energy density, it 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.

[0029] like Figure 1 As shown, in one embodiment, the porosity of the active material layer is 20% to 50%.

[0030] Specifically, the porosity of the active material layer is any one value or a range of any two values ​​from 20%, 25%, 30%, 35%, 40%, 45%, or 50%; in a preferred embodiment, the porosity of the active material layer is 25%-45%.

[0031] After being rolled, the active material layer forms multiple micropores. When the porosity of the active material layer is 20%–50%, it provides sufficient wetting space and a continuous ion transport network for the electrolyte, which is beneficial for the rapid insertion / extraction of lithium ions during high-rate charging and discharging, significantly improving the battery's fast-charging capability and power density; it also buffers the volume expansion of silicon-containing particles, improving cycle stability; and it enhances the effective coverage and conductivity of the conductive carbon layer. When the porosity of the active material layer is less than 20%, the electrode is too dense, making it difficult for the electrolyte to fully penetrate. The diffusion path of lithium ions in the solid phase becomes longer and the resistance increases, leading to a decrease in rate performance and severe polarization. An overly smooth or closed surface is detrimental to the formation of a good interface between the conductive carbon layer and the active material layer. When the porosity of the active material layer is greater than 50%, it reduces the number of silicon-containing particles that can be accommodated per unit volume of the electrode, thereby reducing the volumetric energy density and gravimetric energy density of the battery, which is not conducive to the design requirements of high-energy-density batteries. Excessive porosity weakens the physical contact between active particles and between particles and current collectors, resulting in a discontinuous electronic conductive network, which in turn increases the internal resistance of the electrode. The mechanical strength decreases, and the electrode is prone to powder shedding or structural loosening. The conductive carbon layer is difficult to form a continuous and dense conductive film, which weakens the "face-to-face" conductivity enhancement effect.

[0032] like Figure 1 As shown, in one embodiment, the conductive carbon layer is formed on the surface of the active material layer by chemical vapor deposition.

[0033] Forming a conductive carbon layer on the surface of the active material layer via chemical vapor deposition (CVD) avoids the interfacial impedance introduced by binders / solvents. Traditional conductive slurries require the addition of binders (such as PVDF) and solvents (such as NMP), resulting in an insulating or high-resistance interfacial layer on the surface of the active particles after drying. The conductive carbon layer formed by CVD is pure carbon, without additives, directly forming a clean, low-resistance electronic pathway with the active material layer. Furthermore, during CVD, the carbon precursor gas can diffuse and adsorb uniformly onto the active material. The material layer surface contour achieves conformal coverage, enabling the formation of a continuous carbon film even in uneven or porous areas. The conductive carbon layer acts like a "conductive skin," encapsulating and interconnecting the originally isolated silicon-containing particles. On the active material layer, the conductive carbon layer mainly covers the surface framework without significantly blocking ion channels. If a slurry spray is used, the conductive carbon layer can easily clog surface pores, hindering electrolyte penetration. Moreover, the high chemical inertness of conductive carbon can suppress excessive decomposition of the electrolyte on the high specific surface area silicon surface. At the same time, as part of the SEI, it helps to form a more stable interface.

[0034] In one embodiment, the carbon source gas used in the chemical vapor deposition process includes one or more of methane, acetylene, ethylene, and propylene.

[0035] One or more of methane, acetylene, ethylene, and propylene are used as carbon precursors to form a conductive carbon layer on the surface of the active material layer through chemical vapor deposition. The conductive carbon layer is pure carbon without additives and directly forms a clean and low-resistance electronic pathway with the active material layer.

[0036] In one embodiment, the reaction temperature of the chemical vapor deposition process is 500°C to 900°C.

[0037] Specifically, the reaction temperature of the chemical vapor deposition process is any one value or a range of any two values ​​among 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, 800℃, 850℃ or 900℃; in a preferred embodiment, the reaction temperature of the chemical vapor deposition process is 600℃ to 800℃.

[0038] When the reaction temperature of the chemical vapor deposition process is between 500℃ and 900℃, it promotes the complete decomposition of carbon precursors, and low-hydrogen, high-sp can be obtained at 500–900℃. 2 Hybridized conductive carbon significantly improves electronic conductivity; it can deposit amorphous / graphite-like microcrystalline carbon with both good conductivity and flexibility; when the reaction temperature of the chemical vapor deposition process is less than 500℃, the carbon source gas will be incompletely decomposed, easily forming amorphous carbon or polymer residues with high hydrogen content and poor conductivity; the deposited carbon structure is too disordered and has poor conductivity; when the reaction temperature of the chemical vapor deposition process is greater than 900℃, it will lead to excessive graphitization of the conductive carbon layer, losing its buffering capacity against silicon expansion.

[0039] like Figure 1 As shown, in one embodiment, the thickness of the conductive carbon layer is 0.5-5 μm.

[0040] Specifically, the thickness of the conductive carbon layer is any one value or a range of any two values ​​selected from 0.5μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm or 5μm; in a preferred embodiment, the thickness of the conductive carbon layer is 0.5-2μm.

[0041] When the thickness of the conductive carbon layer is 0.5-5 μm, a continuous, dense, and highly conductive carbon network can be formed, effectively buffering the volume expansion of silicon-containing particles. Lithium ions can quickly embed into the negative electrode active material through the micropores or edge paths of the conductive carbon layer, ensuring high rate performance. The low mass percentage of the conductive carbon layer (typically <3 wt%) results in minimal dilution effect on the electrode specific capacity. Cycle life and power performance are significantly improved with almost no sacrifice in energy density. However, when the thickness of the conductive carbon layer is less than 0.5 μm, the layer becomes too thin, making it prone to pinholes, breaks, or partially uncovered areas. This prevents effective bridging of all active particles, leading to partial defects. It remains a high-resistivity "dead zone"; the enhancement effect of electronic conduction is limited, and the mechanical protection effect is insufficient; when the thickness of the conductive carbon layer is greater than 5μm, the excessively thick and dense conductive carbon layer will block the pores on the electrode surface, prolong the diffusion path of lithium ions from the electrolyte to the active material, increase concentration polarization, and lead to a decrease in initial efficiency; the rate performance deteriorates significantly (especially the capacity drops sharply when charging and discharging above 2C); the low-temperature performance deteriorates; it will also increase the proportion of inactive materials, reduce energy density, and the thick conductive carbon layer is prone to cumulative stress under the repeated action of silicon volume changes, which will cause the conductive carbon layer to crack or debond from the underlying layer, thereby destroying the conductive path and accelerating cycle decay.

[0042] like Figure 1 As shown, in one embodiment, the silicon-containing particles 2 include one or more of silicon particles, silicon suboxide, and silicon-carbon materials; the selection of the above-mentioned silicon-containing particles 2 takes into account both high specific capacity and cycle stability.

[0043] like Figure 1 As shown, in one embodiment, the silicon-containing particles are selected from silicon-carbon materials, and the silicon content in the silicon-carbon materials is 40%-60% by mass.

[0044] 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%.

[0045] 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.

[0046] 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.

[0047] The use of the aforementioned 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.

[0048] In one embodiment, the binder includes one or more of the following: polyimide (PI), phenolic resin (PF), polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyacrylic acid (PAA), polyvinyl alcohol (PVA), epoxy resin, polybenzoxazole (PBO), polyarylether ketone (such as PEEK), bituminous precursors, lignin, or derivatives thereof.

[0049] The above-mentioned binder not only provides good adhesion during the coating stage of forming the active material layer, but also partially or completely carbonizes it during the CVD process to form a dual carbon network that works in synergy with the CVD conductive carbon layer; it improves the overall mechanical strength and conductivity of the electrode; and it avoids cracking or peeling of the active material layer due to binder volatilization.

[0050] In one embodiment, the total mass of the active material layer is 100%, the silicon particles 2 account for 91%-94% of the mass of the active material layer, and the binder accounts for 6%-9% of the mass of the active material layer.

[0051] Specifically, the mass percentage of silicon-containing particles 2 in the active material layer is any one value or a range of any two values, namely 91%, 92%, 93%, or 94%; in a preferred embodiment, the mass percentage of silicon-containing particles 2 in the active material layer is 92%-93%.

[0052] When the mass percentage of silicon-containing particles 2 in the active material layer is 91%-94%, it has the effect of balancing energy density and electrode thickness expansion. When the mass percentage of silicon-containing particles 2 in the active material layer is less than 91%, it will lead to excessively low energy density. When the mass percentage of silicon-containing particles 2 in the active material layer is greater than 94%, it will lead to increased cycle thickness expansion rate and reduced capacity retention rate.

[0053] Specifically, the adhesive accounts for any one of the following mass percentages of the active material layer: 6%, 7%, 8%, or 9%, or a range of any two of these values; in a preferred embodiment, the adhesive accounts for 7%-8% of the active material layer by mass.

[0054] When the binder accounts for 6%-9% of the mass percentage of the active material layer, it has the effect of balancing energy density and thickness expansion. When the binder accounts for less than 6% of the mass percentage of the active material layer, it will result in insufficient binder content, which will not be able to restrain the thickness expansion of silicon carbon particles, resulting in a large cycle thickness expansion rate and rapid capacity decay. When the binder accounts for more than 9% of the mass percentage of the active material layer, it will result in low active material content, low energy density, and excessive binder will increase electrode impedance, increase polarization, and affect cycle capacity decay.

[0055] A second aspect of the present invention provides a method for preparing a negative electrode sheet, comprising the following steps: An active material layer is formed on the surface of the negative electrode current collector 100; A conductive carbon layer is formed on the surface of the active material layer by chemical vapor deposition.

[0056] This invention forms a conductive film on the surface of the active material layer away from the negative electrode current collector 100 by depositing a conductive carbon layer on the surface of the active material layer, thereby upgrading the traditional "point-to-point" particle contact to "face-to-face" surface contact. This significantly increases the electron conduction interface area, reduces contact resistance, and improves the overall electrode conductivity. Even under high-rate charge and discharge, it can maintain a stable and efficient electron transport channel. In addition, silicon-containing particles 2 expand significantly during charge and discharge, which can easily lead to particle pulverization and repeated SEI film rupture. The conductive carbon layer has both mechanical buffering and conductive functions, inhibiting the shedding of the negative electrode active material and stabilizing the SEI interface. This reduces repeated SEI film rupture, reduces irreversible lithium loss, and significantly extends cycle life. In summary, this technology, through its innovative dual-layer structure design, fundamentally solves the core problems of poor conductivity and low cycle stability of silicon-based anodes. Without sacrificing energy density, it 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] Specifically, the negative electrode sheet includes a negative electrode current collector 100 and a negative electrode active material layer, with the negative electrode active material layer coated on both sides of the negative electrode current collector 100.

[0065] Specifically, the negative electrode current collector 100 is selected from a metal material that can conduct electrons. Preferably, the negative electrode current collector 100 includes metals such as stainless steel, Al, Ni, tin, copper, nickel, titanium, and iron, or their alloys. In a more preferred embodiment, the negative electrode current collector 100 is selected from copper foil.

[0066] Specifically, the negative electrode active material layer includes: negative electrode active material, conductive agent, and binder; In one embodiment, the negative electrode active material includes one or more of natural graphite, artificial graphite, hard carbon, silicon materials, and lithium metal materials; the conductive agent includes one or more of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers; and the binder includes one or more of styrene-butadiene rubber, polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl butyral, waterborne acrylic resin, polyacrylic acid, carboxymethyl cellulose, and carboxymethyl cellulose modified materials.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] While the exemplary embodiments described above use lithium-ion batteries as examples, those skilled in the art will understand after reading this application that, without departing from the spirit of this application, specific examples of the battery can include all types of primary or secondary batteries. In particular, the battery is a lithium secondary battery, including lithium metal secondary batteries, lithium-ion secondary batteries, lithium polymer secondary batteries, or lithium-ion polymer secondary batteries.

[0071] The beneficial effects of the present invention will be further illustrated below with reference to the embodiments.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] Table 1 shows the design of the negative electrode parameters for Examples 1-15 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 carbon powder and binder (carboxymethyl cellulose + styrene-butadiene rubber) in a ratio of 92:8. The first negative electrode slurry is coated onto the negative electrode current collector copper foil on a coating machine, and then rolled to obtain the active material layer. Methane is used as the carbon source gas to form a conductive carbon layer on the surface of the active material layer by chemical vapor deposition. The thickness of the conductive carbon layer is 2 μm, and the reaction temperature of the chemical vapor deposition process is 500℃~900℃.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] Example 2-15 Examples 2-15 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.

[0080] Comparative Example 1 Comparative Example 1 is used to illustrate the negative electrode sheet and battery disclosed in this invention, including most of the operating steps in Example 1, except that: Preparation of negative electrode: The first negative electrode slurry was prepared by mixing silicon-carbon powder and binder (carboxymethyl cellulose + styrene-butadiene rubber) in a ratio of 92:8. Conductive carbon black is prepared into a second negative electrode slurry; The first negative electrode slurry and the second negative electrode slurry are sequentially coated onto the negative electrode current collector copper foil on a coating machine. After drying, rolling, die cutting and other processes, a negative electrode sheet that meets the requirements is obtained.

[0081] Comparative Example 2 Comparative Example 2 is used to illustrate the negative electrode sheet and battery disclosed in this invention, including most of the operating steps in Example 2, except that: Preparation of negative electrode: A negative electrode slurry was prepared by mixing silicon carbon powder, binder (carboxymethyl cellulose + styrene-butadiene rubber) and single-walled carbon nanotubes in a ratio of 92:7:1. The first negative electrode slurry is coated onto the negative electrode current collector copper foil on a coating machine. After drying, rolling, die cutting and other processes, a negative electrode sheet that meets the requirements is obtained.

[0082] Performance testing The following performance tests were performed on the batteries prepared in Examples 1-15 and Comparative Examples 1-2: Internal resistance test: Test the 1kHz AC impedance of the positive and negative terminals of the battery cell. 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.

[0083] 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.

[0084] The test results are shown in Table 2.

[0085] Table 2 Battery Electrochemical Performance Comparing Example 1 and Comparative Example 1, it can be seen that Example 1 has lower internal resistance, higher rate performance and cycle performance. This is because the conductive carbon layer is formed on the surface of the active material layer by chemical vapor deposition, which can avoid the interface impedance introduced by the binder / solvent. Traditional sprayed conductive paste requires the addition of binder (such as PVDF) and solvent (such as NMP), which will form an insulating or high-resistance interface layer on the surface of the active particles after drying.

[0086] Comparing Example 1 and Comparative Example 2, it can be seen that Example 1 has lower internal resistance, higher rate performance and cycle performance. This is because by setting a conductive carbon layer on the surface of the active material layer away from the negative electrode current collector, a conductive film is formed on the surface of the active material layer, upgrading the traditional "point-to-point" particle contact to "face-to-face" surface contact; significantly increasing the electronic conduction interface area, reducing contact resistance, and improving the overall electrode conductivity.

[0087] Comparing Examples 1-5, it can be seen that when the content of active material increases, the internal resistance decreases and the rate performance improves, but the cycle performance decreases due to the greater expansion of the electrode. When the binder content increases, the cycle performance improves, but the internal resistance increases and the rate performance decreases. The battery has the best overall performance when the mass percentage of silicon particles in the active material layer is 91%-94% and the mass percentage of binder in the active material layer is 6%-9%.

[0088] Comparing Example 1 with Examples 6-9, it can be seen that as the porosity of the active material layer increases, the internal resistance of the battery increases; when the porosity of the active material layer is 20% to 50%, the battery has higher rate performance and cycle performance; when the porosity of the active material layer is less than 20%, or when the porosity of the active material layer is greater than 50%, the rate performance and cycle performance of the battery will deteriorate.

[0089] Comparing Example 1 with Examples 10-13, it can be seen that as the thickness of the conductive carbon layer increases, the internal resistance of the battery decreases; when the thickness of the conductive carbon layer is 0.5-5 μm, the battery has higher rate performance and cycle performance; when the thickness of the conductive carbon layer is less than 0.5 μm, or when the thickness of the conductive carbon layer is greater than 5 μm, the rate performance and cycle performance of the battery deteriorate.

[0090] Comparing Example 1 with Examples 14-15, it can be seen that Example 1 has lower internal resistance, higher rate performance and cycle performance. This is because the use of nano-silicon particles results in large volume expansion and high activity, which significantly reduces cycle performance. In addition, silicon itself has poor conductivity and poor rate performance. The use of silicon suboxide particles reduces activity, but the expansion is still large, and the surface oxide layer leads to increased internal resistance, which deteriorates rate performance and cycle performance.

[0091] This invention provides an active material layer containing silicon particles on the negative electrode current collector. This active material layer does not contain conductive additives and has a higher proportion of active material in the negative electrode. As a result, it effectively improves the electrode specific capacity and battery volumetric / weight energy density while ensuring or even surpassing the conductivity of traditional electrodes.

[0092] This invention forms a conductive film on the surface of the active material layer away from the negative electrode current collector by depositing a conductive carbon layer on the surface of the active material layer, thereby upgrading the traditional "point-to-point" particle contact to "face-to-face" surface contact. This significantly increases the electron conduction interface area, reduces contact resistance, and improves the overall electrode conductivity. Even under high-rate charge and discharge, it can maintain a stable and efficient electron transport channel. In addition, silicon-containing particles expand significantly during charge and discharge, which can easily lead to particle pulverization and repeated SEI film rupture. The conductive carbon layer has both mechanical buffering and conductive functions, inhibiting the shedding of the negative electrode active material, stabilizing the SEI interface, reducing repeated SEI film rupture, reducing irreversible lithium loss, and significantly extending cycle life. In summary, this technology, through its innovative dual-layer structure design, fundamentally solves the core problems of poor conductivity and low cycle stability of silicon-based anodes. Without sacrificing energy density, it 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.

[0093] 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 and a binder. The binder is used to bond adjacent negative electrode active materials. The negative electrode active material includes silicon-containing particles. A conductive carbon layer is disposed on the surface of the active material layer away from the negative electrode current collector, and the conductive carbon layer forms a continuous layer on the surfaces of adjacent negative electrode active materials and the surface of the binder therebetween.

2. The negative electrode sheet according to claim 1, characterized in that, The porosity of the active material layer is 20% to 50%.

3. The negative electrode sheet according to claim 2, characterized in that, The conductive carbon layer is formed on the surface of the active material layer by chemical vapor deposition.

4. The negative electrode sheet according to claim 3, characterized in that, The carbon source gas used in the chemical vapor deposition process includes one or more of methane, acetylene, ethylene, and propylene.

5. The negative electrode sheet according to claim 3, characterized in that, The reaction temperature of the chemical vapor deposition process is 500℃~900℃.

6. The negative electrode sheet according to claim 1, characterized in that, The thickness of the conductive carbon layer is 0.5-5 μm.

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

8. The negative electrode sheet according to claim 7, 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.

9. The negative electrode sheet according to claim 1, characterized in that, The binder includes one or more of the following: polyimide, phenolic resin, polyacrylonitrile, polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, polyvinyl alcohol, epoxy resin, polybenzoxazole, polyaryletherketone, asphalt precursors, lignin, or derivatives thereof.

10. The negative electrode sheet according to claim 1, characterized in that, With the total mass of the active material layer as 100%, the silicon-containing particles account for 91%-94% of the mass of the active material layer; and the binder accounts for 6%-9% of the mass of the active material layer.

11. The method for preparing the negative electrode sheet according to any one of claims 1-10, characterized in that, Includes the following steps: The active material layer is formed on the surface of the negative electrode current collector; The conductive carbon layer is formed on the surface of the active material layer by chemical vapor deposition.

12. 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 1-10, or the negative electrode prepared by the method for preparing the negative electrode as described in claim 11.

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