Preparation method of low-tortuosity electrode sheet and low-tortuosity electrode sheet and battery

Abstract

This application discloses a method for preparing a low-torsion electrode sheet, as well as the low-torsion electrode sheet and battery. The method includes: preparing a first electrode slurry and a second electrode slurry, both of which include a composite additive, the composite additive including a pore-forming agent and a surfactant; coating the first electrode slurry and the second electrode slurry onto at least one side of a current collector to form a stacked first electrode slurry layer and a second electrode slurry layer, and drying to obtain a low-torsion electrode sheet; through the synergistic effect of the specific composite additive composed of the pore-forming agent and the surfactant, not only can through-holes perpendicular to the current collector be formed inside the double-layer electrode, reducing the tortuosity of the electrode sheet to below 1.5, effectively improving the fast-charging performance of the battery; at the same time, the surfactant can optimize the interfacial compatibility of the upper and lower slurries, avoid defects such as thick edges and shrinkage patterns during the coating process, improve the bonding strength of the upper and lower electrodes, and improve the battery capacity retention rate.

Description

Technical Field

[0001] This application relates to the field of lithium battery technology, and in particular to a method for preparing a low-torsion electrode sheet, as well as the low-torsion electrode sheet and the battery. Background Technology

[0002] As a core component in the new energy field, lithium-ion batteries' charge / discharge rate, cycle life, and energy density are closely related to their electrode structure. Dual-layer coating technology, by sequentially or simultaneously coating two layers of slurry with different functions onto the current collector, can achieve both high energy density and high power density in the electrodes, and has become an important technological direction for improving battery performance.

[0003] However, existing double-layer electrode coating technologies using traditional slurry formulations result in electrodes with disordered internal pore structures. This leads to extremely tortuous lithium-ion transport paths within the electrode, resulting in a tortuosity typically exceeding 3.0. This highly tortuous pore structure not only significantly prolongs ion transport distance and increases concentration polarization but also raises the electrode interface impedance, thus limiting the battery's fast-charging performance and cycle stability.

[0004] Current solutions to this problem mostly focus on adjusting the type or ratio of active materials and using trial and error to optimize electrode formulations, failing to address the root cause of low ion transport efficiency. Although attempts have been made to prepare porous electrodes using a single pore-forming agent, the lack of targeted design for bilayer structures makes it difficult for a single pore-forming agent to effectively connect the upper and lower pores, and it easily leads to problems such as weak interfacial bonding and uneven pore distribution.

[0005] Therefore, developing an electrode that can form vertical through-holes and has low tortuosity is of great significance for improving the performance of lithium-ion batteries. Summary of the Invention

[0006] This application aims to solve at least one of the technical problems existing in the prior art. To this end, this application proposes a method for preparing a low-torsion electrode sheet, as well as a low-torsion electrode sheet and a battery, so as to achieve the formation of vertical through-holes in the electrode and produce a low-torsion electrode.

[0007] In a first aspect, this application provides a method for preparing a low-torsion electrode sheet, comprising: A first electrode slurry and a second electrode slurry are prepared, both of which include a composite additive, which includes a pore-forming agent and a surfactant. A first electrode slurry layer and a second electrode slurry layer are coated on at least one side of the current collector to form a stacked first electrode slurry layer and a second electrode slurry layer, and then dried to obtain a low-torsion electrode sheet.

[0008] In some embodiments, the mass ratio of the pore-forming agent to the surfactant is 1:(0.1-0.5).

[0009] In some embodiments, after forming the first electrode slurry layer and the second electrode slurry layer, the electrode sheet with low tortuosity is obtained by segmented drying. The segmented drying process includes drying at 50℃-90℃ for 90min-200min, followed by drying at 130℃-160℃ for 60min-120min.

[0010] In some embodiments, the surfactant includes a nonionic surfactant; the pore-forming agent includes modified thermally decomposable polymer microspheres, and the thermal decomposition and volatilization temperature of the pore-forming agent is 130°C-150°C.

[0011] In some embodiments, the D50 of the thermally decomposable polymer microspheres is 5 μm-20 μm.

[0012] In some embodiments, the pore-forming agent and the surfactant are of the same type and in the same mass ratio in both the first electrode slurry and the second electrode slurry.

[0013] In some embodiments, the first electrode paste comprises the following components in parts by weight: 70-85 parts of active material, 5-10 parts of conductive agent, 2-5 parts of binder, 3-12 parts of composite additive, and 30-50 parts of solvent; and / or, The second electrode slurry comprises the following components by mass: 75-90 parts of active material, 3-8 parts of conductive agent, 2-4 parts of binder, 2-8 parts of composite additive, and 30-50 parts of solvent.

[0014] Secondly, this application provides a low-torsional-degree electrode sheet, which is prepared by the method for preparing a low-torsional-degree electrode sheet as described in any one of the first aspects.

[0015] In some embodiments, the tortuosity τ of the low-torsuosity electrode sheet is ≤1.5.

[0016] Thirdly, this application also provides a battery, including a positive electrode, a negative electrode, a separator, and an electrolyte, wherein at least one of the positive electrode and the negative electrode is a low-torsional electrode sheet prepared by the low-torsional electrode sheet preparation method as described in any one of the first aspects.

[0017] The above-described one or more embodiments of this application have at least one or more of the following beneficial effects: This application provides a method for preparing a low-torsion electrode sheet, as well as the low-torsion electrode sheet and a battery. A first electrode slurry and a second electrode slurry are coated on at least one side of a current collector to form a stacked first electrode slurry layer and a second electrode slurry layer. Both the first and second electrode slurries include a composite additive composed of a pore-forming agent and a surfactant. Drying yields a low-torsion electrode sheet. Through the synergistic effect of the specific composite additive composed of the pore-forming agent and the surfactant, through-holes perpendicular to the current collector are formed inside the double-layer electrode formed after the first and second electrode slurry layers are dried, reducing the tortuosity of the electrode sheet to below 1.5, shortening the ion transport path, improving lithium-ion transport efficiency, reducing electrode interface impedance, and effectively improving the battery's fast-charging performance. Simultaneously, the surfactant optimizes the interfacial compatibility of the upper and lower slurry layers, reduces surface tension differences, avoids defects such as thick edges and shrinkage patterns during coating, improves the bonding strength between the upper and lower electrode layers, and enhances the battery capacity retention rate.

[0018] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Detailed Implementation

[0019] Some embodiments of this application are described below. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of this application and are not intended to limit the scope of protection of this application.

[0020] As described in the background section, thick electrodes employing double-layer coating technology can balance high energy density and high power density, making it an important technological direction for improving battery performance. However, existing thick electrodes use traditional slurry formulations, resulting in disordered internal pore structures and tortuous lithium-ion transport paths within the electrode. The tortuosity of the electrode is typically above 3.0, severely restricting the battery's fast-charging performance and cycle stability. To address this issue, current solutions mostly focus on adjusting the type or ratio of active materials and using trial-and-error methods to optimize the electrode formulation. However, these approaches still struggle to achieve effective interconnection between the upper and lower pore layers and are prone to problems such as weak interface bonding and uneven pore distribution.

[0021] To this end, this application creatively proposes a method for preparing a low-torsion electrode sheet, as well as a low-torsion electrode sheet and a battery. By adding a composite additive composed of a pore-forming agent and a surfactant to the electrode slurry used to manufacture two active material layers, through-holes perpendicular to the current collector can be formed inside the prepared double-layer electrode, reducing the tortuosity of the electrode sheet to less than 1.5, effectively improving the fast-charging performance of the battery. At the same time, the surfactant can optimize the interfacial compatibility of the upper and lower slurries and improve the battery capacity retention rate.

[0022] The present application will be described in detail below through specific embodiments.

[0023] Specifically, this application provides a method for preparing a low-torsion electrode sheet, comprising: S1. Prepare a first electrode slurry and a second electrode slurry. Both the first electrode slurry and the second electrode slurry include composite additives, which include pore-forming agents and surfactants.

[0024] S2. Coat the surface of at least one side of the current collector with a first electrode slurry and a second electrode slurry to form a stacked first electrode slurry layer and a second electrode slurry layer, and dry to obtain a low-torsion electrode sheet.

[0025] By introducing composite additives into both the first and second electrode slurries, a continuous network of pores extending from the surface of the second electrode slurry layer to the bottom of the first electrode slurry layer can be constructed along the electrode thickness direction, avoiding the drawback of a single pore-forming agent only forming isolated pores. Surfactants can optimize the interfacial compatibility of the upper and lower slurry layers, reduce surface tension differences, minimize coating defects such as edge thickening, pinholes, and ripples during the coating process, and improve the interfacial bonding strength between the upper and lower slurry layers.

[0026] In some embodiments, the mass ratio of the pore-forming agent to the surfactant is 1:(0.1-0.5). Optionally, the mass ratio of the pore-forming agent to the surfactant can be 1:0.1, 1:0.13, 1:0.2, 1:0.25, 1:0.3, 1:0.32, 1:0.4, 1:0.47, 1:0.5, or any ratio within the above range. Due to space limitations and for the sake of brevity, this application will not exhaustively list the specific ratios included in the range.

[0027] A mass ratio of pore-forming agent to surfactant within the range of 1:(0.1-0.5) ensures optimal synergistic effect between the two. Too low a surfactant ratio will fail to adequately improve the dispersibility and interfacial wettability of the pore-forming agent, while too high a ratio may lead to decreased slurry stability or introduce excessive residue, resulting in coating defects.

[0028] This application does not impose specific limitations on the coating method of the first electrode slurry and the second electrode slurry in step S2. As long as the first electrode slurry and the second electrode slurry can be applied to the current collector to form a wet film with a layered structure, whether it is a one-time drying and forming or a step-by-step drying and forming, whether it is wet-state lamination or dry-state recoating, it falls within the protection scope of this invention. For example, a double-layer slit extrusion coating die can be used to extrude the two layers of slurry simultaneously; the first electrode slurry can be coated first, and the second slurry can be coated after it is not completely dry or completely dry; multiple coating steps can also be used to complete the process. As long as a wet film with a double-layer structure can be formed, any coating method falls within the protection scope of this invention.

[0029] The drying step in S2 is used to remove the solvent from the first and second electrode slurry layers, allowing the coating to cure. The drying temperature and time are determined based on the type of solvent in the first and second electrode slurry layers and the coating thickness: for oily solvents such as NMP, the drying temperature is typically 80℃-150℃; for aqueous solvent systems, the drying temperature is typically 50℃-120℃. Drying can be performed using any method known in the art, such as forced-air drying, infrared drying, or vacuum drying.

[0030] In some embodiments, after forming the stacked first electrode slurry layer and the second electrode slurry layer, a segmented drying process is performed to obtain a low-torsion electrode sheet. The segmented drying includes drying at 50°C-90°C for 90-200 minutes, followed by drying at 130°C-160°C for 60-120 minutes. Optionally, the temperature of the first stage of segmented drying can be 50°C, 55°C, 60°C, 63°C, 70°C, 78°C, 80°C, 81°C, 90°C, or any value within the above temperature range. The drying time can be 90 minutes, 110 minutes, 125 minutes, 140 minutes, 150 minutes, 178 minutes, 192 minutes, 200 minutes, or any value within the above time range. Due to space limitations and for the sake of brevity, this application will not exhaustively list all the specific values ​​included in the range. The temperature of the second stage of segmented drying can be 130℃, 134℃, 140℃, 143℃, 150℃, 155℃, 160℃, or any value within the above temperature range. The drying time can be 60min, 76min, 83min, 92min, 100min, 117min, 120min, or any value within the above time range. Due to space limitations and for the sake of brevity, this application will not exhaustively list the specific values ​​included in the range.

[0031] Using segmented drying to control the solvent evaporation rate can prevent coating cracking or surface defects.

[0032] In some embodiments, the surfactant includes a nonionic surfactant; the pore-forming agent includes modified thermally decomposable polymer microspheres, wherein the thermal decomposition and volatilization temperature of the pore-forming agent is 130°C-150°C. The modification treatment includes at least one of copolymerization modification or molecular weight reduction treatment to lower the thermal decomposition temperature of the polymer microspheres to 130°C-150°C, allowing them to fully decompose and volatilize during segmented drying, forming a vertically interconnected pore structure. Optionally, the thermal decomposition and volatilization temperature of the pore-forming agent can be 130°C, 134°C, 135°C, 140°C, 145°C, 147°C, 150°C, or any value within the above temperature range. For space limitations and for the sake of brevity, this application will not exhaustively list all specific values ​​within the range.

[0033] The selected pore-forming agent undergoes thermal decomposition into small gaseous molecules during the second stage of segmented drying, escaping and leaving pores in their original positions, thus forming vertically penetrating channels within the electrode layer. Using a thermally decomposable pore-forming agent simplifies the process, resulting in more regular and interconnected channels with no residual solvent, leading to more stable battery cycling. In contrast, soluble pore-forming agents require solvent immersion for dissolution, which can easily cause channel deformation, poor interconnectivity, and solvent residue.

[0034] The pore-forming agent includes, but is not limited to, modified polylactic acid (PLA) microspheres, modified polycaprolactone (PCL) microspheres, modified polymethyl methacrylate (PMMA) microspheres, and modified polystyrene (PS) microspheres. The thermal decomposition temperature of the pore-forming agent is adapted to the drying process or subsequent heat treatment process of the first and second electrode slurry layers, meaning it can fully decompose and volatilize within a temperature range of 130℃-150℃, while the active materials, conductive agents, and binders in the electrodes are not significantly affected. The main products of the above-mentioned thermally decomposable pore-forming agent after decomposition will volatilize, and the remaining small amount of low-molecular-weight lipids will not undergo side reactions with the electrolyte used in the battery. Preferably, the pore-forming agent is selected from at least one of modified polylactic acid (PLA) microspheres and modified polycaprolactone (PCL) microspheres.

[0035] The surfactant is used to adjust the surface tension of the first electrode slurry and the second electrode slurry, improve the dispersibility of the pore-forming agent in the first electrode slurry and the second electrode slurry, and optimize the interfacial wettability of the two slurries. This application does not specifically limit the type of surfactant; the surfactant can be any nonionic surfactant known in the art suitable for lithium-ion battery slurries. As an example and not a limitation, the surfactant includes at least one of the following: sorbitan fatty acid esters (Span series such as Span-20, Span-40, Span-60, Span-80, etc.), polyoxyethylene sorbitan fatty acid esters (Tween series such as Tween-20, Tween-40, Tween-60, Tween-80, etc.), and alkylphenol polyoxyethylene ethers (OP series). Appropriate surfactant types and amounts can be selected through conventional experiments according to the slurry system and process requirements, as long as the purpose of improving the dispersibility of the pore-forming agent and optimizing the interfacial wettability is achieved. The nonionic surfactants selected in this application do not thermally decompose or volatilize under the drying parameters of this application. They not only optimize interfacial compatibility during the coating stage, but also remain inside the electrode to continuously reduce the interfacial tension between the electrode and the electrolyte, improve the wettability of the electrolyte, facilitate lithium-ion transport, and work synergistically with the vertically penetrating pores to improve battery performance.

[0036] The introduction of surfactants reduces the interfacial tension between the pore-forming agent and the slurry system, preventing microsphere aggregation and ensuring the uniformity of pore distribution; it also reduces the surface tension difference between the first electrode slurry layer and the second electrode slurry layer, allowing the two slurry layers to fuse well at the coating interface without mixing, forming a strong interlayer bond and effectively reducing interfacial impedance.

[0037] In some embodiments, the D50 of the thermally degradable polymer microspheres is 5 μm-20 μm. Optionally, the D50 of the thermally degradable polymer microspheres can be 5 μm, 7.2 μm, 9.5 μm, 10 μm, 12.3 μm, 15 μm, 18.6 μm, 20 μm, or any value within the above particle size D50 range. Due to space limitations and for the sake of brevity, this application will not exhaustively list the specific values ​​included in the range.

[0038] The microsphere size of 5μm-20μm is matched with the particle size of the electrode active material and the electrode thickness: if the pore-forming agent particle size is too small, it is difficult to form through-holes, and can only increase micropores; if the particle size is too large, it may lead to a decrease in the strength of the electrode structure or a decrease in the proportion of active material. Microspheres of 5μm-20μm can ensure the integrity of the electrode structure, form vertical through-holes of appropriate diameter, and provide a low-torsion transport path for lithium ions.

[0039] The types and mass ratios of pore-forming agents and surfactants in the first electrode slurry can be the same as or different from those in the second electrode slurry.

[0040] In some embodiments, the pore-forming agent and the surfactant are of the same type and in the same mass ratio in both the first electrode slurry and the second electrode slurry.

[0041] The first and second electrode slurry layers use composite additives with the same composition and mass ratio, ensuring that the pore-forming agent has a consistent decomposition temperature and pore-forming behavior in both layers, and that the surfactants have the same molecular structure and diffusion characteristics. This allows the first and second electrode slurry layers to form pores simultaneously during the drying process, avoiding interlayer stress caused by differences in pore-forming temperature. Furthermore, the strong interdiffusion ability of the same surfactant molecules at the interface of the two wet films creates a more uniform interface transition layer, enhancing interlayer bonding strength and ensuring the consistency of the through-pores.

[0042] In some embodiments, the first electrode paste comprises the following components in parts by weight: 70-85 parts of active material, 5-10 parts of conductive agent, 2-5 parts of binder, 3-12 parts of composite additive, and 30-50 parts of solvent; and / or, the second electrode paste comprises the following components in parts by weight: 75-90 parts of active material, 3-8 parts of conductive agent, 2-4 parts of binder, 2-8 parts of composite additive, and 30-50 parts of solvent.

[0043] This application does not impose any particular limitation on the polarity of the electrode sheet. The low-torsion electrode sheet provided in this application can be applied to both positive and negative electrodes. Correspondingly, this application does not limit the type of active material: the active material is either a positive electrode active material or a negative electrode active material; the binder, conductive agent, and solvent are any materials known in the art that can be used in the electrode system.

[0044] In some embodiments, the method further includes: rolling the electrode sheet.

[0045] Further rolling the dried electrode sheet can adjust the electrode thickness and compaction density, thereby increasing the volumetric energy density.

[0046] While the rolling process increases the volumetric energy density of the compacted electrode, the pore structure, which is pre-constructed by the pore-forming agent and has a vertical orientation, can maintain its continuous shape after rolling. This avoids the problems of pore collapse and increased tortuosity caused by rolling of traditional electrodes, and ultimately achieves a low-resistance transmission channel with tortuosity τ≤1.5.

[0047] This application also provides a low-torsional-degree electrode sheet, which is prepared by the low-torsional-degree electrode sheet preparation method described in any one of the above embodiments.

[0048] In some embodiments, the tortuosity τ of the low-torsuosity electrode sheet is ≤1.5.

[0049] This application also provides a battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein at least one of the positive electrode and the negative electrode is a low-torsional electrode sheet prepared by a method for preparing a low-torsional electrode sheet as described in any one of the first aspects.

[0050] In some embodiments, the positive electrode includes a low-torsion electrode sheet, and the first electrode slurry layer and the second electrode slurry layer form a positive electrode layer after drying.

[0051] In some examples, the active material is a positive electrode active material, including compounds that can reversibly insert and deintercalate lithium ions.

[0052] In some embodiments, the positive electrode active material comprises one or more transition metal cations, such as manganese (Mn), nickel (Ni), cobalt (Co), chromium (Cr), iron (Fe), vanadium (V), and combinations thereof.

[0053] In some embodiments, the positive electrode active material is one of layered oxides, spinel oxides, and polyanionic compounds.

[0054] In some embodiments, the layered oxides (e.g., rock salt layered oxides) include LiCoO2 (LCO) and LiNi. x Mn y Co 1-x-y O2 (where 0 ≤ x ≤ 1 and 0 ≤ y ≤ 1), LiNi 1-x-y Co x Al y O2 (where 0 ≤ x ≤ 1 and 0 ≤ y ≤ 1), LiNi x Mn 1-x O2 (where 0≤x≤1) and xLi2MnO3·(1-x)LiTMO2 (where M is one of Mn, Ni, and Co; 0≤x≤1).

[0055] In some embodiments, the spinel oxide includes LiMn2O4 (LMO) and LiNi. 0.5 Mn 1.5 O4.

[0056] In some embodiments, the polyanionic compound includes a phosphate, such as LiFePO4, LiMnPO4, Li3V2(PO4)3, or LiMn. x Fe 1-x At least one of PO4 (0 < x < 1) and its doped derivatives.

[0057] In some embodiments, the polyanionic compound includes a silicate, which includes Li2FeSiO4.

[0058] In some implementations, the mass of the positive electrode active material accounts for 60% to 95% of the mass of the positive electrode layer.

[0059] The binder in the positive electrode layer can improve the bonding between the positive electrode active material particles and also improve the bonding between the positive electrode layer and the current collector in the positive electrode.

[0060] In some embodiments, non-limiting examples of adhesives include polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc.

[0061] It is understood that when the positive electrode layer is prepared using a dry method, the binder should include at least a fibrous binder, including but not limited to one or more of polytetrafluoroethylene, polyvinylidene fluoride (PVDF), polyvinylidene fluoride hexafluoropropylene, polypropylene, polyethylene, and polyimide.

[0062] In some embodiments, the binder accounts for 0.1% to 20% of the mass of the positive electrode layer.

[0063] The conductive agent in the positive electrode layer imparts conductivity to the electrode. The conductive agent can include any conductive material, as long as it does not cause a chemical change.

[0064] In some embodiments, the conductive agent includes carbon-based materials, metals and their derivatives, conductive polymers, and MXenes, etc. Among them, carbon-based materials include, but are not limited to, natural graphite, artificial graphite, graphene, carbon black, acetylene black, Ketjen black, superconducting carbon black, carbon nanotubes, carbon fibers, etc. Metals and their derivatives include, but are not limited to, metal powders, metal fibers, metal nanowires, etc., and metals include, but are not limited to, copper, nickel, aluminum, silver, etc. Conductive polymers include, but are not limited to, polypyrrole, PEDOT:PSS, and polyaniline.

[0065] In some embodiments, the conductive agent accounts for 0.1% to 20% of the mass of the positive electrode layer.

[0066] In some embodiments, the positive electrode layer also includes a fast ion conductor to improve the ionic conductivity of the positive electrode layer. This application does not limit the type of fast ion conductor; it can be an oxide solid electrolyte, a sulfide solid electrolyte, a halide solid electrolyte, a lithium salt, etc.

[0067] In some embodiments, the mass of the fast ion conductor accounts for 1% to 20% of the mass of the positive electrode layer; preferably 5% to 20%.

[0068] In some embodiments, the current collector in the positive electrode includes a metallic material that can conduct electrons, including but not limited to at least one of aluminum, nickel, tin, copper, and stainless steel.

[0069] In some embodiments, the current collector in the positive electrode includes at least one of aluminum foil, carbon-coated aluminum foil, stainless steel foil, nickel foam, and porous metal.

[0070] In some embodiments, the negative electrode includes a low-torsion electrode sheet, and the first electrode slurry layer and the second electrode slurry layer form a negative electrode layer after drying.

[0071] In some examples, the active material is a negative electrode active material. This application does not have any particular restrictions on the negative electrode active material, as long as it is a substance that can electrochemically adsorb and release s-block metal ions such as lithium ions, sodium ions, potassium ions, and magnesium ions. For example, carbonaceous materials, metal compound materials, or their oxides, carbides, nitrides, silicides, sulfides, phosphides, etc. These substances can be used alone, or two or more can be used in combination at will.

[0072] In some embodiments, the negative electrode active material includes a carbon material, specifically one or more of the following: graphite, needle coke, amorphous carbon, carbon-containing mesophase, carbon fiber, and carbon materials with low graphitization. Graphite may include natural graphite, artificial graphite, etc. Alternatively, materials obtained by coating these materials with carbon materials, such as amorphous carbon or graphitides, may also be used. Amorphous carbon includes, but is not limited to, particles obtained by sintering a monolithic mesophase, and particles obtained by sintering a carbon precursor after a non-melting treatment. Examples of carbonaceous particles with low graphitization include particles obtained by sintering organic matter at temperatures typically below 2500°C.

[0073] In some embodiments, elemental metals and metal compounds may also be selected as negative electrode active materials, such as compounds containing metals or metalloids such as Li, Ag, Al, Bi, Cu, Ga, Ge, In, Ni, Pb, Sb, Si, Sn, Sr, and Zn.

[0074] In some embodiments, when the negative electrode active material is a non-metallic material such as carbon material, the binder in the first electrode slurry layer and the second electrode slurry layer can be an aqueous binder, such as sodium hydroxymethyl cellulose, styrene-butadiene latex, polyacrylic acid, acrylic copolymers, cyclodextrin, or one or more of these. When an aqueous solvent is used as the liquid medium for forming the negative electrode slurry, it is preferable to use a thickener for slurry formation. The thickener is usually used to adjust the viscosity of the slurry.

[0075] The material and shape of the separator used in the battery of this application are not particularly limited, and can be any technology disclosed in the prior art.

[0076] In some embodiments, the diaphragm comprises a polymer or inorganic material formed from a material stable to the electrolyte of this application.

[0077] In some embodiments, the diaphragm may include a substrate layer and a surface treatment layer. The substrate layer is a nonwoven fabric, membrane, or composite membrane with a porous structure, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide.

[0078] In some embodiments, the electrolyte includes a lithium salt and an electrolyte solvent.

[0079] In some embodiments, the lithium salt includes, but is not limited to: lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis(trifluoromethanesulfonyl)imide LiN(CF3SO2)2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2) (LiFSI), lithium bis(oxalateborate)borate LiB(C2O4)2 (LiBOB), or lithium difluorooxalateborate LiBF2(C2O4) (LiDFOB).

[0080] In some embodiments, the electrolyte solvent may be selected from one or more of ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0081] In some embodiments, the electrolyte also includes additives. These additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance characteristics, such as additives that improve battery overcharge performance, high-temperature performance, and low-temperature performance.

[0082] In some embodiments, the aforementioned additives include 1,3-propanesulfonyl lactone, 1,4-butanesulfonyl lactone, propenyl-1,3-sulfonyl lactone, vinyl sulfate, and 4... At least one of the following: methyl vinyl sulfate, propylene sulfate, saturated phosphate compounds and unsaturated phosphate compounds, tris(trimethylsilane) phosphate, tris(trimethylsilane) borate, tris(triethylsilane) borate, succinic acid nitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrionitrile, adiponitrile, heptanonitrile, octanilide, nonadionitrile, and sebaconitrile.

[0083] The present application will be further described in detail below with reference to embodiments. It should be noted that the following embodiments are for illustrative purposes only and are not intended to limit the scope of protection claimed in this application.

[0084] Example 1: In this example, "parts" and "g" have a corresponding relationship, that is, 1 part corresponds to 1g. In this example, the positive electrode uses a low-torsion electrode sheet, and the components and mass percentages are as follows: First positive electrode slurry: 85 parts of positive electrode active material NCM811, 7 parts of conductive agent Super P, 3 parts of binder PVDF, 5 parts of composite additive (PLA+Span-80, mass ratio 1:0.2), and 35 parts of solvent NMP.

[0085] Second positive electrode slurry: 88 parts of positive electrode active material NCM811, 5 parts of conductive agent Super P, 3 parts of binder PVDF, 4 parts of composite additive (PLA+Span-80, mass ratio 1:0.2), and 35 parts of solvent NMP.

[0086] Preparation method: (1) Preparation of composite additive dispersion: Weigh 10g of pretreated PLA microspheres (D50 particle size 10μm, thermal decomposition and volatilization temperature 130℃-150℃) and 2g of Span-80, add 20g of NMP solvent, stir at 25℃ for 40min to obtain a uniform dispersion.

[0087] (2) Preparation of the first positive electrode slurry: Weigh 85g of NCM811, 7g of Super P, and 3g of PVDF, add 13.33g of the above composite additive dispersion and 26.67g of NMP solvent, and stir at 1200r / min for 70min; (3) Preparation of the second positive electrode slurry: Weigh 88g of NCM811, 5g of Super P, and 3g of PVDF, add 10.67g of composite additive dispersion and 28.33g of NMP solvent, and stir at 1200r / min for 70min.

[0088] (4) Using a double-layer slit extrusion coating machine, the first positive electrode slurry prepared in step (2) and the second positive electrode slurry prepared in step (3) are simultaneously coated onto an aluminum foil current collector with a thickness of 12 μm. The coating speed is 1 m / min, and the coating thickness of the first electrode slurry layer (bottom layer) is controlled to be 100 μm, and the coating thickness of the second electrode slurry layer (top layer) is controlled to be 50 μm. During the coating process, the appearance of the coating is observed, and it is observed whether the coating surface is flat and uniform, and whether there are coating defects such as edge thickening, shrinkage cavities, and ripples.

[0089] (5) Place the coated electrode in a forced-air drying oven for segmented drying. First, dry at 60°C for 150 min to remove most of the solvent, then raise the temperature to 130°C and dry for 70 min to allow the solvent and pore-forming agent to evaporate and complete the coating curing.

[0090] (6) The dried electrode sheets are rolled using a roller press, and the compaction density is controlled to be 3.0 g / cm³. 3 This yields the final positive electrode sheet.

[0091] Example 2: In this example, "parts" and "g" have a corresponding relationship, that is, 1 part corresponds to 1g. In this example, the negative electrode uses a low-torsion electrode sheet, and the components and mass percentages are as follows: First negative electrode slurry: 80 parts of graphite, 8 parts of Super P, 4 parts of PVDF, 8 parts of composite additive (PCL+Tween-80, mass ratio 1:0.3), and 45 parts of NMP solvent.

[0092] Second negative electrode slurry: 86 parts of negative electrode active material graphite, 6 parts of conductive agent Super P, 3 parts of binder PVDF, 5 parts of composite additive (PCL+Tween-80, mass ratio 1:0.3), and 45 parts of solvent NMP.

[0093] The preparation method is the same as in Example 1, except that the pore-forming agent is pretreated PCL microspheres (thermal decomposition and volatilization temperature is 130℃-150℃), the surfactant is Tween-80, the current collector is copper foil, the drying parameters are 70℃ for 140 min and 130℃ for 65 min, and the compaction density is 1.6 g / cm³. 3 The final negative electrode is obtained.

[0094] Example 3: In this example, both the positive and negative electrodes are low-torsion electrode sheets, and the types and mass ratios of surfactants and pore-forming agents in the electrode sheets are the same as in Example 1.

[0095] Example 4: The difference between this example and Example 1 is that the mass ratio of pore-forming agent to surfactant is adjusted to 1:0.1.

[0096] Example 5: The difference between this example and Example 1 is that the mass ratio of pore-forming agent to surfactant is adjusted to 1:0.5.

[0097] Example 6: The difference between this example and Example 1 is that the pore-forming agent is pretreated PS microspheres (thermal decomposition and volatilization temperature is 130℃-150℃), and the surfactant is AEO-3.

[0098] Comparative Example 1: In this comparative example, both the positive and negative electrodes are electrode sheets without composite additives.

[0099] Comparative Example 2: The difference between this comparative example and Example 1 is that only PLA microsphere pore-forming agent is added to the positive electrode active material layer, and no surfactant is added.

[0100] Comparative Example 3: The difference between this comparative example and Example 1 is that the mass ratio of pore-forming agent to surfactant is 1:0.8.

[0101] Comparative Example 4: The difference between this comparative example and Example 1 is that only the same pore-forming agent and surfactant with the same composition and mass ratio are added to the first electrode slurry, and no composite additives are added to the second electrode slurry layer.

[0102] The batteries using the target electrodes prepared according to the above embodiments and comparative examples were subjected to battery cycle tests, and the test methods are as follows: Test temperature: 25℃±2℃.

[0103] 1. Characterization of lithium-ion diffusion coefficient: Using the obtained target electrode as the working electrode, a CR2023 type Li half-cell was assembled and EIS test was performed with an amplitude of 5mV and a frequency of 10. -2 -10 6 Hz, combined with formula Calculate the lithium-ion diffusion coefficient. Where V0 m Let be the molar volume of the active material, E be the open-circuit potential, and x be the amount of lithium intercalated in the active material. Here, denoted as Warburg coefficient, A as electrode area, and F as Faraday constant.

[0104] 2. Tortuousness characterization: Using the obtained target electrode as the working electrode, a CR2023 type symmetrical cell was assembled and EIS test was performed with an amplitude of 5mV and a frequency of 10. -2 -10 6 Hz, combined with formula Calculate the tortuosity of the electrode. Where d is the electrode thickness, ε is the electrode porosity, A is the electrode area, and r... ion denoted as ionic resistance, and k as electrolyte conductivity.

[0105] 3. 2C rate charging performance test: Using the obtained target electrode as the working electrode, a CR2032 type Li half cell was assembled. Constant current and constant voltage charging was performed at 0.33C and 2C respectively. The 2C charging capacity retention rate was obtained as: 2C constant current charging capacity / 0.33C constant current charging capacity, which reflects the 2C rate charging capability.

[0106] 4. Cyclic performance test: Using the obtained target electrode as the working electrode, a CR2032 type Li half cell was assembled.

[0107] ① Charge at 1C to the termination voltage (4.4V), cut-off current 0.05C, and let stand for 30 minutes; ② Discharge at 1C until the final discharge voltage (2.8V), and let stand for 30 minutes.

[0108] Repeat cycles ① to ②, record the discharge capacity from the 1st to the 5th cycle, and calculate the average value as the initial discharge capacity; Continue the cycle until the 500th cycle, and record the discharge capacity of the 500th cycle; Battery capacity retention after 500 cycles = Discharge capacity of the 500th cycle / Initial discharge capacity 100%.

[0109] 5. Interface Impedance Test: Using the obtained target electrode as the working electrode, a CR2023 type Li half-cell was assembled and subjected to EIS testing with an amplitude of 5mV and a frequency of 10. -2 -10 6 Hz, combined with equivalent circuit fitting, yields the charge transfer impedance R corresponding to the semicircle in the mid-frequency region. ct This is the interface impedance.

[0110] The test results are shown in the table below: As can be seen from the table above, only by adding composite additives to both the first electrode slurry layer and the second electrode slurry layer can coating defects such as edge thickening, pinholes, and ripples be reduced during the coating process. This also improves the lithium-ion diffusion coefficient, reduces tortuosity and interfacial impedance, and enhances rate performance and cycle performance. Furthermore, when the mass ratio of pore-forming agent to surfactant is limited to 1:(0.1-0.5), the tortuosity is lower and the battery performance is better.

[0111] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0112] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0113] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A method for preparing a low-torsion electrode sheet, characterized in that, include: A first electrode slurry and a second electrode slurry are prepared, both of which include a composite additive, which includes a pore-forming agent and a surfactant. A first electrode slurry layer and a second electrode slurry layer are coated on at least one side of the current collector to form a stacked first electrode slurry layer and a second electrode slurry layer, and then dried to obtain a low-torsion electrode sheet.

2. The method for preparing a low-torsion electrode sheet according to claim 1, characterized in that, The mass ratio of the pore-forming agent to the surfactant is 1:(0.1-0.5).

3. The method for preparing a low-torsion electrode sheet according to claim 1, characterized in that, After forming the first electrode slurry layer and the second electrode slurry layer, the electrode sheet with low tortuosity is obtained by segmented drying. The segmented drying process includes drying at 50℃-90℃ for 90min-200min, followed by drying at 130℃-160℃ for 60min-120min.

4. The method for preparing a low-torsion electrode sheet according to claim 3, characterized in that, The surfactant includes a nonionic surfactant; the pore-forming agent includes modified thermally decomposable polymer microspheres, and the thermal decomposition and volatilization temperature of the pore-forming agent is 130℃-150℃.

5. The method for preparing a low-torsion electrode sheet according to claim 4, characterized in that, The D50 of the thermally decomposable polymer microspheres is 5μm-20μm.

6. The method for preparing a low-torsion electrode sheet according to claim 1, characterized in that, In both the first electrode slurry and the second electrode slurry, the pore-forming agent and the surfactant are of the same type and in the same mass ratio.

7. The method for preparing a low-torsion electrode sheet according to claim 1, characterized in that, The first electrode paste comprises the following components by mass parts: 70-85 parts of active material, 5-10 parts of conductive agent, 2-5 parts of binder, 3-12 parts of composite additive, and 30-50 parts of solvent; and / or, The second electrode paste comprises the following components by mass: 75-90 parts of active material, 3-8 parts of conductive agent, 2-4 parts of binder, 2-8 parts of composite additive, and 30-50 parts of solvent.

8. A low-torsion electrode sheet, characterized in that, It is prepared by the method for preparing a low-torsional-degree electrode sheet according to any one of claims 1-7.

9. The low-torsion electrode sheet according to claim 8, characterized in that, The tortuosity τ of the low-torsional-degree electrode sheet is ≤1.

5.

10. A battery, characterized in that, The device includes a positive electrode, a negative electrode, a separator, and an electrolyte, wherein at least one of the positive electrode and the negative electrode is prepared using the low-torsivity electrode preparation method as described in any one of claims 1-7.

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