Negative pole piece, battery and preparation method

Abstract

In order to solve the problem that the volume expansion of a silicon-containing negative electrode plate in the prior art affects the electrochemical performance, the invention provides a negative electrode plate, a battery and a preparation method. The negative electrode piece comprises a negative electrode current collector and a negative electrode material layer, the negative electrode material layer comprises a negative electrode active material layer and a gel protection layer, the negative electrode active material layer is arranged on at least one surface of the negative electrode current collector, net-shaped gaps are formed in the surface of the negative electrode active material layer, and the negative electrode active material layer is divided into a plurality of blocky structures by the net-shaped gaps; the average area S of the surface of the block structure is 50 [mu] m < 2 > < = S < = 1000 [mu] m < 2 >; and gel protection layers are arranged on the surfaces of the net-shaped gaps and the surface of the negative electrode active material layer. By limiting the average area of the surface of the blocky structure and arranging the gel protection layers on the surface of the netted gap and the surface of the negative electrode active material layer, the volume expansion of the silicon-based material is effectively buffered, the integrity of the SEI film is maintained, the dynamic damage of the SEI film is reduced, and the cycle stability of the battery is improved.

Description

Technical Field

[0001] This invention belongs to the field of secondary battery technology, specifically relating to a negative electrode sheet, a battery, and a preparation method thereof. Background Technology

[0002] Lithium-ion batteries, due to their high energy density, long cycle life, and low self-discharge rate, have become the primary power source for modern portable electronic devices, electric vehicles, and energy storage systems. Current lithium-ion batteries mainly use graphite-based materials as the negative electrode. However, with the continuous upgrading of portable electronic devices and electric vehicles, the demand for higher energy density lithium-ion batteries is increasing. The theoretical specific capacity of graphite-based negative electrode materials is only 372 mAh / g, which is insufficient to meet the development needs of high-energy-density lithium-ion batteries.

[0003] Among common traditional anode materials, silicon-based anodes possess a theoretical specific capacity 10 times that of graphite (4200 mAh / g) and a lower lithium intercalation potential (~0.2 V vs. Li). + / Li). Although silicon has a high theoretical specific capacity, when forming a Li-Si alloy, silicon particles expand to 300% of their original volume. This drastic volume change causes the SEI film formed during the formation process to rupture. During battery use, the SEI film will undergo continuous local damage and repair. However, repairing the SEI film will cause further consumption of lithium ions in the battery, further increasing the irreversible loss of battery capacity and reducing the battery's cycle life and lifespan.

[0004] Therefore, there is an urgent need for a negative electrode that reduces irreversible capacity loss in batteries, thereby improving their cycle life. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to address the issue that the large volume expansion of existing silicon-containing negative electrode sheets affects their electrochemical performance. The present invention provides a negative electrode sheet, a battery, and a preparation method thereof.

[0006] To address the aforementioned technical problems, this invention provides a negative electrode sheet, comprising a negative electrode current collector and a negative electrode material layer. The negative electrode material layer includes a negative electrode active material layer and a gel protective layer. The negative electrode active material layer is disposed on at least one side of the negative electrode current collector. A mesh-like gap is formed on the surface of the negative electrode active material layer, dividing the negative electrode active material layer into multiple block structures. The average surface area S of the block structures is 50 μm. 2 ≤S≤1000μm 2 ; The gel protective layer is provided on both the surface of the mesh slits and the surface of the negative electrode active material layer.

[0007] Preferably, the average surface area S of the block structure is 50 μm. 2 ≤S≤100μm 2 .

[0008] Preferably, the ratio of the depth of the mesh slits to the thickness of the negative electrode active material layer is 0.1-0.5:1.

[0009] Preferably, the negative electrode active material layer includes a negative electrode active material, which includes silicon. Assuming the total silicon and carbon content in the negative electrode material layer is 100%, the mass content of silicon in the negative electrode active material layer within the total silicon and carbon content is w1, where w1 is 85%-98.4%. The gel protective layer includes carbon elements, and the mass content of carbon elements in the gel protective layer in the total amount of silicon and carbon elements is w2, where w2 is 1.6%-15%.

[0010] Preferably, gaps are provided between the gel protective layers disposed on the surface of the mesh slits.

[0011] Preferably, the gel protective layer comprises a gel polymer, which includes at least one of the following structural units: hexafluorobutyl acrylate (HFBA), ethylene glycol dimethacrylate (EGDMA), polyethylene glycol dimethacrylate (PEGDMA), methyl methacrylate (MMA), 1,3-dioxolane (DOL), 1,3-dioxane (DOX), polyethylene glycol acrylate (PEGDA), and glycidyl acrylate (GMA).

[0012] Preferably, the negative electrode sheet further includes an SEI layer, which is disposed on the surface of the negative electrode active material layer and located between the negative electrode active material layer and the gel protective layer; The SEI layer includes at least one of lithium-containing fluorides, oxides, nitrides, and halides.

[0013] Secondly, this application provides a battery comprising a negative electrode sheet as described in any of the above claims, or a negative electrode sheet prepared by any of the above claims.

[0014] Thirdly, this application provides a method for preparing the battery as described above, comprising the following steps: A silicon-containing anode active material is placed on the anode current collector to form a silicon-containing coating, thus obtaining the initial anode sheet. The negative electrode initial plate, the positive electrode plate, and the separator are assembled into a battery cell; A first electrolyte is injected into the battery cell for formation. After reaching the discharge state, the gas and the first electrolyte in the battery cell are extracted. A mesh-like gap is formed on the surface of the silicon-containing coating. A second electrolyte is injected into the battery cell, the second electrolyte comprising a first electrolyte and a polymerizable monomer. The battery cell is heated, and the polymerizable monomer polymerizes to form a gel protective layer on the silicon-containing coating surface and the mesh gap surface. The battery cell undergoes a second formation process, followed by degassing and encapsulation to obtain the battery.

[0015] Preferably, the first electrolyte comprises a lithium salt, an additive, and a solvent, wherein the concentration of the lithium salt is 1-1.2M.

[0016] Preferably, the polymerizable monomer includes at least one of hexafluorobutyl acrylate (HFBA), ethylene glycol dimethacrylate (EGDMA), polyethylene glycol dimethacrylate (PEGDMA), methyl methacrylate (MMA), 1,3-dioxolane (DOL), 1,3-dioxane (DOX), polyethylene glycol acrylate (PEGDA), and glycidyl acrylate (GMA).

[0017] Preferably, the mass content of the polymerizable monomer in the second electrolyte is 1%-40%.

[0018] In this application, the mesh-like gaps formed on the surface of the negative electrode active material layer divide the negative electrode active material layer into multiple block structures, and the average surface area S of the block structures is limited to 50 μm. 2 ≤S≤1000μm 2 Within this range, space is provided for the expansion of the negative electrode active material, thus preventing the SEI film formed on the surface from rupturing due to the expansion of the negative electrode active material layer in the thickness direction during battery operation. Simultaneously, the gel protective layer set on the surface of the mesh-like gaps and the negative electrode active material layer effectively buffers the volume expansion of the silicon-based material, maintaining the integrity of the SEI film. This offers advantages such as stabilizing the negative electrode surface structure, reducing dynamic damage to the SEI film, reducing capacity decay, and improving battery cycle stability. In particular, multiple blocky structures allow the negative electrode active material layer to form more lithium intercalation sites in advance. Even if some lithium intercalation sites fail, the intercalation of active lithium can still be guaranteed, minimizing the formation of new SEI films during cycling. Furthermore, the new lithium intercalation pathways can reduce expansion in the thickness direction, improving the battery's cycle life. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the structure of the negative electrode sheet provided in one embodiment of this application; Figure 2 This is a flowchart illustrating the changes in the negative electrode sheet in a battery preparation method provided in one embodiment of this application.

[0020] Explanation of reference numerals in the attached figures: 1. Negative electrode current collector; 2. Negative electrode active material layer; 21. Mesh gaps; 22. Block structure; 3. Gel protective layer. Detailed Implementation

[0021] 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 embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0022] One embodiment of this application provides a negative electrode sheet, including a negative electrode current collector 1 and a negative electrode material layer. The negative electrode material layer includes a negative electrode active material layer 2 and a gel protective layer 3. The negative electrode active material layer 2 is disposed on at least one side of the negative electrode current collector 1. A mesh-like gap 21 is formed on the surface of the negative electrode active material layer 2, which divides the negative electrode active material layer 2 into multiple block structures 22. The average surface area S of the block structures 22 is 50 μm. 2 ≤S≤1000μm 2 ; The gel protective layer 3 is provided on the surface of the mesh slits 21 and the surface of the negative electrode active material layer 2.

[0023] In this application, the mesh-like gaps 21 formed on the surface of the negative electrode active material layer 2 divide the negative electrode active material layer 2 into multiple block structures 22, and the average surface area S of the block structure 22 is limited to 50 μm. 2 ≤S≤1000μm 2 Within this range, space is provided for the expansion of the negative electrode active material, thereby preventing the SEI film formed on the surface from rupturing due to the expansion of the negative electrode active material layer 2 in the thickness direction during battery operation. The average surface area of ​​the bulk structure 22 is less than 50 μm. 2 Excessive formation of bulk structures 22 increases the contact area with the electrolyte, leading to the formation of an excessively thick SEI film, which consumes electrolyte and lithium source, increases side reactions, and reduces battery cycle life; the average surface area of ​​the bulk structures 22 is greater than 1000 μm. 2 If there are too few block structures, the number of mesh gaps 21 will also be relatively small, thus failing to provide expansion space for the negative electrode active material, which will easily cause the SEI film formed on the surface to break, consuming electrolyte and lithium source. At the same time, if there are too few block structures 22, more lithium intercalation sites cannot be formed, affecting the charging speed.

[0024] Meanwhile, the gel protective layer 3 disposed on the surface of the mesh gaps 21 and the surface of the negative electrode active material layer 2 effectively buffers the volume expansion of the silicon-based material, maintains the integrity of the SEI film, and has the advantages of stabilizing the negative electrode surface structure, reducing dynamic damage to the SEI film, reducing capacity decay, and improving battery cycle stability. In particular, the multiple block structures 22 enable the negative electrode active material layer 2 to form more lithium intercalation sites in advance, ensuring the intercalation of active lithium even when some lithium intercalation sites fail, minimizing the formation of new SEI films during cycling, and the new lithium intercalation path can reduce expansion in the thickness direction, thereby improving the cycle life of the battery.

[0025] In lithium-ion batteries, silicon-based anode materials are prone to rupture of the solid electrolyte interface film due to volume expansion during charging and discharging, leading to irreversible capacity loss and reduced cycle life. The multiple mesh-like gaps 21 formed on the surface of the anode active material layer 2 refer to the micro-gap structure created on the surface of the anode active material layer 2. These gaps can be achieved through charging and discharging methods, primarily to provide local buffer space during lithium intercalation of the silicon-based material, preventing stress concentration from causing overall damage to the anode active material layer 2. Furthermore, the gel protective layer 3 set on the surface of the mesh-like gaps 21 and the surface of the anode active material layer 2 refers to an elastic polymer layer covering the exposed area of ​​the active material. This layer can be achieved through impregnation coating, spraying, spin coating processes, or in-situ polymerization. For example, the anode sheet can be immersed in an acrylate precursor solution and heat-treated to form a protective layer, or a cross-linked polymer film can be generated on the surface through vapor deposition. This layer primarily utilizes the adaptive properties of the gel material to maintain surface continuity and prevent the electrolyte from directly contacting the active material. Therefore, this application constructs a mesh-like gap structure 21 on the surface of the negative electrode active material layer 2 and covers it with a gel protective layer 3. This allows the deformation caused by volume expansion to be absorbed by the mesh-like gap structure 21, while the gel protective layer 3 remains intact during deformation, effectively blocking electrolyte erosion and reducing the repeated damage and repair process of the solid electrolyte interface film. Specifically, the negative electrode current collector 1 serves as a basic support to provide an electron conduction path. The negative electrode active material layer 2 adheres to the surface of the current collector to form an electrochemical reaction interface. The bulk structure 22 enables the negative electrode active material layer 2 to form more lithium intercalation sites in advance. The synergistic effect of the mesh-like gap structure 21, the bulk structure 22, and the gel protective layer 3 ensures the structural stability of the silicon-based material during volume changes and the cycle life of the battery.

[0026] Specifically, the average surface area of ​​the block structure 22 includes, but is not limited to, 50 μm. 2 100μm 2 150μm 2 200μm 2 250μm 2 300μm 2 350μm 2 400μm2 450μm 2 500μm 2 550μm 2 600μm 2 650μm 2 700μm 2 750μm 2 800μm 2 850μm 2 900μm 2 950μm 2 or 1000μm 2 .

[0027] In one specific implementation, the negative electrode active material layer 2 can be specifically composed of a silicon-based composite material, such as a mixture containing silicon particles and graphite, and mesh-like gaps 21 can be formed on the surface of the negative electrode active material layer 2 to accommodate volume changes. Therefore, this structure can effectively address the volume expansion problem of silicon-based materials in practical applications.

[0028] In a preferred embodiment, the average surface area S of the block structure 22 is 50 μm. 2 ≤S≤100μm 2 .

[0029] In some embodiments, the ratio of the depth of the mesh slits 21 to the thickness of the negative electrode active material layer 2 is 0.1-0.5:1.

[0030] The depth of the mesh gap 21 refers to the vertical distance from the surface of the negative electrode active material layer 2 to the bottom of the mesh gap 21, which can be measured using laser scanning or microscopy. The thickness of the negative electrode active material layer refers to the overall thickness of the negative electrode active material layer 2, which can be measured using a micrometer or optical measurement methods. Specifically, the depth of the mesh gap 21 can be measured using a scanning electrode cross-section SEM method, and the thickness of the negative electrode active material layer 2 can also be measured using a scanning electrode cross-section SEM method. The ratio of the mesh gap 21 depth to the negative electrode active material layer thickness is limited to the above range to ensure that during the charging and discharging process of the silicon-based material, the mesh gap 21 can provide a precisely matched buffer space to absorb volume expansion stress while maintaining the mechanical integrity of the electrode structure.

[0031] Specifically, the solution of this application, by limiting the ratio, enables the mesh gaps 21 to dynamically adapt to volume changes when the silicon-based material undergoes charging and discharging expansion. This avoids the mesh gaps 21 being too shallow due to an excessively small ratio, which would prevent the stress from being fully released and thus prevent the gel protective layer 3 from cracking due to local stress concentration. At the same time, it avoids the mesh gaps 21 being too deep due to an excessively large ratio, which would weaken the structural strength of the negative electrode active material layer. This ensures that the electrode maintains sufficient mechanical stability and energy density during cycling, thereby maintaining the continuity of the SEI film and reducing the occurrence of interfacial side reactions.

[0032] Specifically, the ratio of the depth of the mesh gap 21 to the thickness of the negative electrode active material layer 2 includes, but is not limited to, 0.1:1, 0.2:1, 0.3:1, 0.4:1 or 0.5:1.

[0033] Furthermore, in some embodiments described above in this application, a ratio of silicon content w1 in the negative electrode active material layer 2 to carbon content w2 in the gel protective layer 3 is proposed to optimize the volume expansion control of silicon-based materials. However, in its implementation, if the silicon content is too high, the volume expansion during charging and discharging will be excessive, making it impossible for the gel protective layer 3 to effectively constrain deformation, resulting in repeated rupture and repair of the SEI film. If the silicon content is too low, the high capacity advantage cannot be fully utilized. At the same time, an imbalance in the carbon content in the gel protective layer 3 will weaken its mechanical buffering capacity or reduce the utilization rate of the active material, thereby exacerbating irreversible capacity loss and shortening the battery cycle life. If the carbon content in the gel protective layer 3 is too low, the gel protective layer 3 will not cover completely, reducing its protective effect on the negative electrode active material layer 2. If the carbon content in the gel protective layer 3 is too high, it will easily cause a decrease in battery energy density and affect lithium-ion insertion / extraction, resulting in a decrease in battery charge / discharge rate performance.

[0034] In some embodiments, the negative electrode active material layer 2 includes a negative electrode active material, which includes silicon. Assuming the total silicon and carbon content in the negative electrode material layer is 100%, the mass content of silicon in the negative electrode active material layer 2 is w1, where w1 is 85%-98.4%. The gel protective layer 3 includes carbon elements, and the mass content of carbon elements in the gel protective layer 3 in the total amount of silicon and carbon elements is w2, where w2 is 1.6%-15%.

[0035] The mass content of carbon element w2 can be achieved by designing the molecular structure of carbon-containing polymerizable monomers or by controlling the degree of polymerization. The purpose is to provide the elastic modulus and mechanical strength required for the gel protective layer 3.

[0036] The solution in this application, through the aforementioned proportional relationship, enables the negative electrode active material layer 2 and the gel protective layer 3 to form a dynamically synergistic mechanical balance system. This effectively alleviates the volume expansion stress of the silicon-based negative electrode during cycling, reduces the irreversible consumption of the SEI film, thereby lowering the battery's capacity decay rate and extending its cycle life. When silicon expands in volume during charging and discharging, the gel protective layer 3 absorbs stress and limits the deformation amplitude through its elastic network structure, preventing excessive expansion of the mesh gaps 21 that could lead to protective layer failure. Simultaneously, the proportional relationship ensures that the carbon content is within the optimized range, avoiding both loss of buffering capacity due to excessively low carbon content and dilution of the active material ratio due to excessively high carbon content. This maintains the long-term stability of the mesh gap 21 structure and inhibits the repeated damage and regeneration of the SEI film on the surface of the negative electrode active material layer 2.

[0037] The mass content of silicon in the total silicon and carbon content in the negative electrode active material layer 2 can be obtained by EDS scanning, and the mass content of carbon in the total silicon and carbon content in the gel protective layer 3 can be obtained by EDS scanning.

[0038] The silicon content is within the aforementioned range to ensure a sufficiently high silicon content to provide high specific capacity, while avoiding excessive silicon content that could lead to drastic volume expansion and repeated SEI film rupture. This controls the volume expansion of the silicon-based anode during charge and discharge, preventing structural damage due to excessive stress. The carbon content w2 in the gel protective layer 3 is also within the aforementioned range to form a protective layer with appropriate mechanical strength and ionic conductivity. This ensures the gel protective layer 3 has sufficient mechanical support to cover the surface and mesh gaps 21, inhibiting electrolyte penetration, maintaining SEI film stability, and reducing lithium ion consumption during the repair process. The selection of w1 and w2 ranges is interrelated, jointly optimizing the energy density and cycle stability of the anode sheet and addressing the capacity decay problem of silicon-based anodes during long-term use.

[0039] Specifically, w1 includes, but is not limited to, 85%, 87%, 92%, or 98.4%. w2 includes, but is not limited to, 1.6%, 2.5%, 5%, 10%, or 15%.

[0040] In some embodiments, gaps are provided between the gel protective layers 3 disposed on the surface of the mesh gaps 21. If the gel protective layers 3 completely cover the surface of the mesh gaps 21 without gaps, they may not be able to adapt to the drastic volume changes of the silicon-based material during charge-discharge cycles, causing the protective layers to crack due to stress concentration. This leads to repeated damage and repair of the SEI film, resulting in irreversible lithium-ion consumption and battery capacity loss. The solution of this application provides gaps between the gel protective layers 3 on the surface of the mesh gaps 21. When the negative electrode active material layer 2 expands due to charge-discharge cycles, the gaps allow the protective layers to move and deform locally, dispersing mechanical stress.

[0041] In some embodiments, the gel protective layer 3 comprises a gel polymer, which includes at least one of the following structural units: hexafluorobutyl acrylate (HFBA), ethylene glycol dimethacrylate (EGDMA), polyethylene glycol dimethacrylate (PEGDMA), methyl methacrylate (MMA), 1,3-dioxolane (DOL), 1,3-dioxane (DOX), polyethylene glycol acrylate (PEGDA), and glycidyl acrylate (GMA). A gel polymer is a polymeric material with a three-dimensional network structure, which can be formed by in-situ polymerization of polymerizable monomers, specifically through free radical polymerization, photoinitiated polymerization, or thermal polymerization. Its purpose is to provide high elasticity and self-healing ability to adapt to volume changes.

[0042] In some embodiments, the negative electrode sheet further includes an SEI layer, which is disposed on the surface of the negative electrode active material layer 2 and located between the negative electrode active material layer 2 and the gel protective layer 3; The SEI layer includes at least one of lithium-containing fluorides, oxides, nitrides, and halides.

[0043] By setting the SEI layer on the surface of the negative electrode active material layer 2 and forming a stacked structure with the gel protective layer 3, the volume expansion stress generated by the silicon-based negative electrode during battery charging and discharging is first absorbed by the SEI layer. At the same time, if the gel protective layer 3 splits, the lithium-containing fluorides, oxides and other components in the SEI layer can stabilize the interfacial chemical environment, reduce the lithium ion consumption caused by the continuous decomposition of the electrolyte, and ensure that the SEI layer maintains its structural integrity during cycling.

[0044] As a specific implementation method, the solution of this application is implemented as follows: an SEI layer composed of lithium fluoride and lithium oxide is formed on the surface of the negative electrode active material layer 2 by electrochemical deposition, and the SEI layer uniformly covers the surface of the active material particles.

[0045] One embodiment of this application also provides a battery including the negative electrode sheet as described in any of the above claims. By using the aforementioned negative electrode sheet, the destruction process of the solid electrolyte interface film is effectively suppressed, the irreversible consumption of lithium ions is reduced, thereby improving the cycle life of the battery.

[0046] An embodiment of this application also provides a method for preparing a battery, comprising the following steps: A silicon-containing negative electrode active material is placed on the negative electrode current collector 1 to form a silicon-containing coating, thus obtaining the initial negative electrode sheet. The negative electrode initial plate, the positive electrode plate, and the separator are assembled into a battery cell; A first electrolyte is injected into the battery cell for formation. After reaching the discharge state, the gas and the first electrolyte in the battery cell are extracted. A mesh-like gap 21 is formed on the surface of the silicon-containing coating. A second electrolyte is injected into the battery cell. The second electrolyte includes the first electrolyte and a polymerizable monomer. The battery cell is heated, and the polymerizable monomer polymerizes to form a gel protective layer 3 on the surface of the silicon-containing coating and the surface of the mesh gap 21. The battery cell undergoes a second formation process, followed by degassing and encapsulation to obtain the battery.

[0047] By tightly coupling the controllable mesh-like gaps 21 induced during the initial formation process with the in-situ polymerized gel protective layer 3, a buffer structure that dynamically adapts to volume expansion is constructed on the silicon-based anode surface. This effectively maintains the integrity of the solid electrolyte interface film, suppresses its repeated rupture and repair during cycling, and achieves the effect of reducing irreversible lithium-ion consumption and significantly improving battery cycle life. Specifically, this method utilizes the volume expansion kinetics generated during the initial formation to form the mesh-like gaps 21, reserving precise buffer space for the subsequent gel protective layer 3. Simultaneously, by a secondary injection of electrolyte containing polymerizable monomers and heating polymerization, the gel protective layer 3, based on the geometry of the mesh-like gaps 21, covers the active material exposure area in situ. Its flexible characteristics can dynamically adapt to volume changes during charging and discharging, avoiding interface failure caused by stress concentration. As a result, the stability of the solid electrolyte interface film is enhanced, direct contact between the electrolyte and the active material is effectively blocked, irreversible capacity loss is significantly reduced, and ultimately, substantial improvement in battery cycle performance is achieved.

[0048] In some embodiments, the first electrolyte comprises a lithium salt, an additive, and a solvent, wherein the concentration of the lithium salt is 1-1.2M.

[0049] Among them, lithium salts include, but are not limited to, lithium hexafluorophosphate LiPF6, lithium hexafluoroarsenate LiAsF6, lithium tetrafluoroborate LiBF4, lithium hexafluoroantimonyate LiSbF6, lithium bis(trifluoromethanesulfonate imide)LiTFSI or LiN(SO2CF2)2, lithium trifluoromethanesulfonate LiCF3SO3, lithium bis(fluorosulfonyl)imide LiFSI or LiN(SO2CF3)2, lithium perchlorate LiClO4, lithium iodide LiI, and lithium bis(fluorosulfonyl)imide magnesium Li2Mg(N(SO2CF3)2)2. Additives refer to auxiliary components used to improve the performance of the electrolyte. They can be achieved using additives such as vinylene carbonate and fluoroethylene carbonate. Their purpose is to promote the formation of a dense and stable solid electrolyte interphase (SEI) film on the negative electrode surface. Solvents refer to the liquid medium that dissolves lithium salts and additives. They can be achieved using a mixture of organic solvents such as ethylene carbonate and dimethyl carbonate. Their purpose is to provide a suitable ion migration environment and reaction conditions. Lithium salt concentration refers to the molar concentration of lithium salt in the electrolyte. It is limited to the above range. Its purpose is to balance the ionic conductivity and viscosity of the electrolyte, avoiding a concentration that is too low, resulting in a thin and easily broken SEI film, or a concentration that is too high, resulting in an uneven film layer.

[0050] In some embodiments, the polymerizable monomer includes at least one of hexafluorobutyl acrylate (HFBA), ethylene glycol dimethacrylate (EGDMA), polyethylene glycol dimethacrylate (PEGDMA), methyl methacrylate (MMA), 1,3-dioxolane (DOL), 1,3-dioxane (DOX), polyethylene glycol acrylate (PEGDA), and glycidyl acrylate (GMA).

[0051] In some embodiments, the mass content of the polymerizable monomer in the second electrolyte is 1%-40%.

[0052] By controlling the mass content of polymerizable monomers in the second electrolyte within the range of 1%-40%, during the heating polymerization step, the polymerizable monomers can fully diffuse to the surface of the negative electrode active material layer 2 and the mesh gaps 21 based on the characteristics of the electrolyte system and react uniformly, thereby generating a continuous gel protective layer 3 with appropriate mechanical strength. This content range optimizes the dissolution and polymerization kinetics of monomers in the electrolyte, enabling the gel protective layer 3 to not only closely adhere to the negative electrode structure to suppress mechanical damage to the negative electrode active material layer, but also maintain the ion conduction efficiency of the electrolyte, avoiding protective layer coverage defects caused by too low monomer concentration or electrolyte performance degradation caused by too high concentration.

[0053] Specifically, the mass content of polymerizable monomers in the second electrolyte includes, but is not limited to, 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, or 40%.

[0054] The present invention will be further illustrated by the following examples.

[0055] The present invention specifically describes the negative electrode sheet, battery, and preparation method disclosed herein.

[0056] Example 1 1) Preparation of the positive electrode sheet: 97.8% of the positive electrode active material lithium cobalt oxide, 1% of the positive electrode conductive agent conductive carbon black, and 1.2% of the binder PVDF were added to N-methylpyrrolidone and stirred to prepare a positive electrode slurry. The positive electrode slurry was then coated on both surfaces of the positive electrode current collector Al foil, and after drying, cold pressing, and slitting, the positive electrode sheet was obtained.

[0057] 2) First electrolyte: EC / DMC / EMC are mixed in a 1:1:1 ratio as a solvent, with 1M lithium hexafluorophosphate (LiPF6) and 1% vinylene carbonate (VC) added. Second electrolyte: EC / DMC / EMC are mixed in a 1:1:1 ratio as a solvent, with 1M lithium hexafluorophosphate (LiPF6), 1% vinylene carbonate (VC), 5% hexafluorobutyl acrylate (HFBA), and 3% thermal initiator azobisisobutyronitrile (AIBN).

[0058] 3) Lithium-ion battery manufacturing: Silicon-containing active materials are deposited onto copper foil via physical vapor deposition to form a silicon-containing coating with a thickness of 15 μm, thus obtaining the initial negative electrode sheet.

[0059] The separator, positive electrode, and initial negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation, thus forming an electrode assembly. The electrode assembly is placed in the outer packaging, and the first electrolyte is injected. It is then charged at 1C to 4.2V and discharged at 0.5C to 3V at 45°C under a clamping pressure of 5MPa for formation. After reaching the discharge state, the gas and the first electrolyte in the cell are extracted.

[0060] A second electrolyte is injected into the battery cell. The second electrolyte includes the first electrolyte and a polymerizable monomer. The battery cell is heated to 60°C for 8 hours, during which the polymerizable monomer polymerizes.

[0061] The battery cell undergoes secondary formation, gas extraction, and encapsulation to obtain the battery.

[0062] The parameters of the negative electrode are shown in Table 1 and Table 2.

[0063] Examples 2-7, Comparative Example 1, Comparative Example 2 Examples 2-7 are largely the same as Example 1, except that the parameters in Table 1 are used.

[0064] Table 1 Examples 8-18 Examples 8-18 are largely the same as Example 1, except that they use the formulations in Table 2.

[0065] Table 2 Comparative Example 3 Comparative Example 3 and Example 1 share most of the same steps, except that: Silicon-containing active materials are deposited onto copper foil via physical vapor deposition to form a silicon-containing coating, thus obtaining the initial negative electrode sheet.

[0066] The separator, positive electrode, and initial negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation, thus forming an electrode assembly. The electrode assembly is placed in an outer package, and a second electrolyte is injected into the battery cell. The second electrolyte includes the first electrolyte and a polymerizable monomer. The battery cell is heated to 60°C for 8 hours, during which the polymerizable monomer polymerizes.

[0067] The battery is obtained by secondary formation of the battery cell, degassing, and packaging.

[0068] The negative electrode active material layer has a mesh-like gap, and there is no gel protective layer on the surface of the mesh-like gap. The average surface area of ​​the block structure is 500 μm. 2 .

[0069] Comparative Example 4 Comparative Example 4 and Example 1 share most of the same steps, except that: A silicon-containing active material is deposited onto copper foil via physical vapor deposition to form a silicon-containing coating with a silicon content of 100%, resulting in the initial negative electrode sheet. A mesh-like slit pattern 21, 20 μm wide, 25 μm long, and 4 μm deep, is then formed on the silicon-containing coating using laser etching. This mesh-like slit pattern creates multiple blocky structures on the silicon-containing coating, with an average surface area of ​​500 μm². 2 .

[0070] The separator, positive electrode, and initial negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation, thus forming an electrode assembly. The electrode assembly is placed in an outer package, and a second electrolyte is injected into the battery cell. The second electrolyte includes the first electrolyte and a polymerizable monomer. The battery cell is heated to 60°C for 8 hours, during which the polymerizable monomer polymerizes.

[0071] The battery cell undergoes secondary formation, gas extraction, and encapsulation to obtain the battery.

[0072] Comparative Example 5 Comparative Example 5 and Example 1 share most of the same steps, except that: Silicon-containing active materials are deposited onto copper foil via physical vapor deposition to form a silicon-containing coating, thus obtaining the initial negative electrode sheet.

[0073] The separator, positive electrode, and initial negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation, thus forming an electrode assembly. The electrode assembly is placed in the outer packaging, and the first electrolyte is injected. It is then charged at 1C to 4.2V and discharged at 0.5C to 3V at 45°C under a clamping pressure of 5MPa for formation. After reaching the discharge state, the gas and the first electrolyte in the cell are extracted.

[0074] The first electrolyte is injected into the cell again to perform secondary formation, followed by degassing and encapsulation to obtain the battery.

[0075] The negative electrode active material layer has a mesh-like gap, and there is no gel protective layer on the surface of the mesh-like gap. The average surface area of ​​the block structure is 500 μm. 2 .

[0076] Electrical performance testing: The negative electrode sheets and batteries prepared in the above embodiments and comparative examples were tested as follows.

[0077] 1. 25℃ Cyclic Test: After the battery was placed in a constant temperature test chamber at 25℃±2℃ for 1 hour, it was charged to 4.2V with a constant current and constant voltage of 1C and the cutoff current was 0.05C. Then it was discharged to 3V with a constant current of 1C and the discharge capacity was recorded. The cycle number was recorded until the capacity retention rate reached 80% of the initial capacity.

[0078] 2. Rate performance test: At 25℃, charge at 0.5C to 4.2V, cut off at 0.05C, and then discharge at 0.2C to 3.0V as the initial capacity; then charge at 0.5C to 4.2V, 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.

[0079] Fill the test results obtained from the examples and comparative examples into Table 2.

[0080] Table 2 The test results from Examples 1-7 and Comparative Examples 1-2 show that the average surface area S of the blocky structure is 50 μm. 2 -1000μm 2 When the ratio of the depth of the mesh-like gaps to the thickness of the negative electrode active material layer is in the range of 0.1-0.5:1, the battery exhibits good capacity retention and rate performance. The bulk area is less than 50 μm.2 Alternatively, if the crack depth is too large, resulting in a ratio of the mesh gap depth to the thickness of the negative electrode active material layer greater than 0.5:1, although the ion channels increase and the rate performance improves, the surface side reactions of the negative electrode material layer also increase, reducing cycle performance. (Block area greater than 1000 μm) 2 If the crack depth is too small, such that the ratio of the depth of the mesh gap to the thickness of the negative electrode active material layer is less than 0.1:1, the space for silicon expansion is smaller, the cycle performance deteriorates, the ion channels are reduced, and the rate performance is decreased.

[0081] The results of Examples 8-18 show that when the mass content of carbon in the gel protective layer is within the range of 2.5%-15% of the total silicon and carbon elements, the content of polymerizable monomers is moderate, the gap surface and the surface of the active material layer are completely covered, and the cycle performance and rate performance of the battery are good. When w2 is less than 1.6%, the content of polymerizable monomers is too low, the gap surface is poorly covered or even incompletely covered, the cycle performance deteriorates but the rate performance increases. When w2 is greater than 15%, the content of polymerizable monomers is too high, which affects the ion channels, and both cycle performance and rate performance decrease.

[0082] The results of Example 1 and Comparative Example 3 show that Comparative Example 3 did not generate cracks in advance, and the gel polymer only formed on the surface of the active material layer, resulting in poor cycling performance and reduced rate performance due to the reduction of ion channels. The results of Example 1 and Comparative Example 4 show that although laser etching can create similar cracks in Comparative Example 4, these cracks are inconsistent with the natural texture of cyclic expansion and contraction. In subsequent cycles, some silicon layers will crack again, and the SEI film will continuously break and repair itself during cycling, resulting in reduced cycling performance. The results of Example 1 and Comparative Example 5 show that the secondary injection does not contain polymerizable monomers and cannot form a gel protective layer. The SEI film has low stability during cycling, resulting in reduced cycling performance.

[0083] 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, The device includes a negative electrode current collector and a negative electrode material layer. The negative electrode material layer comprises a negative electrode active material layer and a gel protective layer. The negative electrode active material layer is disposed on at least one side of the negative electrode current collector. A mesh-like gap is formed on the surface of the negative electrode active material layer, which divides the negative electrode active material layer into multiple block structures. The average surface area S of the block structures is 50 μm². 2 ≤S≤1000μm 2 ; The gel protective layer is provided on both the surface of the mesh slits and the surface of the negative electrode active material layer.

2. The negative electrode sheet according to claim 1, characterized in that, The average surface area S of the blocky structure is 50 μm. 2 ≤S≤100μm 2 .

3. The negative electrode sheet according to claim 1, characterized in that, The ratio of the depth of the mesh-like gaps to the thickness of the negative electrode active material layer is 0.1-0.5:

1.

4. The negative electrode sheet according to claim 1, characterized in that, The negative electrode active material layer includes a negative electrode active material, which includes silicon. Assuming the total silicon and carbon content in the negative electrode material layer is 100%, the mass content of silicon in the negative electrode active material layer within the total silicon and carbon content is w1, where w1 is 85%-98.4%. The gel protective layer includes carbon elements, and the mass content of carbon elements in the gel protective layer in the total amount of silicon and carbon elements is w2, where w2 is 1.6%-15%.

5. The negative electrode sheet according to claim 1, characterized in that, The gel protective layers on the surface of the mesh slits have gaps between them.

6. The negative electrode sheet according to claim 1, characterized in that, The gel protective layer comprises a gel polymer, which includes at least one of the following structural units: hexafluorobutyl acrylate, ethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, methyl methacrylate, 1,3-dioxolane, 1,3-dioxane, polyethylene glycol acrylate, and glycidyl acrylate.

7. The negative electrode sheet according to claim 1, characterized in that, The negative electrode sheet further includes an SEI layer, which is disposed on the surface of the negative electrode active material layer and located between the negative electrode active material layer and the gel protective layer; The SEI layer includes at least one of lithium-containing fluorides, oxides, nitrides, and halides.

8. A battery, characterized in that, Includes the negative electrode sheet as described in any one of claims 1-7.

9. The method for preparing a battery as described in claim 8, characterized in that, Includes the following steps: A silicon-containing anode active material is placed on the anode current collector to form a silicon-containing coating, thus obtaining the initial anode sheet. The negative electrode initial plate, the positive electrode plate, and the separator are assembled into a battery cell; A first electrolyte is injected into the battery cell for formation. After reaching the discharge state, the gas and the first electrolyte in the battery cell are extracted. A mesh-like gap is formed on the surface of the silicon-containing coating. A second electrolyte is injected into the battery cell, the second electrolyte comprising a first electrolyte and a polymerizable monomer. The battery cell is heated, and the polymerizable monomer polymerizes to form a gel protective layer on the silicon-containing coating surface and the mesh gap surface. The battery cell undergoes a second formation process, followed by degassing and encapsulation to obtain the battery.

10. The preparation method according to claim 9, characterized in that, The first electrolyte comprises lithium salt, additives and solvent, wherein the concentration of lithium salt is 1-1.2M.

11. The preparation method according to claim 9, characterized in that, The polymerizable monomers include at least one of hexafluorobutyl acrylate, ethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, methyl methacrylate, 1,3-dioxolane, 1,3-dioxane, polyethylene glycol acrylate, and glycidyl acrylate.

12. The preparation method according to claim 9, characterized in that, The mass content of the polymerizable monomer in the second electrolyte is 1%-40%.

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