Battery negative electrode sheet and method for manufacturing the same

Abstract

This invention provides a battery negative electrode sheet and its preparation method. At least one surface of the current collector is provided with an active material layer comprising single-walled carbon nanotubes (SUVs) and silicon-carbon. Grooves are formed on the active material layer, and the depth of the grooves is related to the content of SUVs and silicon-carbon as follows: H = 0.236 × b / w; where H is the groove depth in μm, w% is the mass percentage of SUVs, and b% is the mass percentage of silicon-carbon. This invention forms a synergistic system of "silicon-carbon improving energy density + single-walled carbon nanotubes improving fast-charging performance + grooves mitigating silicon-carbon deformation." By quantitatively defining the relationship between the groove depth and the content of the two core components, the structural stability problem caused by the volume expansion of silicon-carbon materials is solved, and the contradiction between fast-charging performance and energy density brought about by the addition of SUVs is balanced, enabling the negative electrode sheet to simultaneously possess high energy density, excellent fast-charging performance, and long cycle life.

Description

Technical Field

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

[0002] Among the current mainstream cathode materials, lithium iron phosphate and lithium manganese iron phosphate have a specific capacity of 160-165 mA·h / g, close to the theoretical limit of 170 mA·h / g, and there is no significant room for improvement in specific capacity. The specific capacity of high-voltage lithium manganese oxide cathode materials may theoretically be further improved, while lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and lithium-rich manganese-based cathode materials have relatively large room for improvement in specific capacity.

[0003] Currently, graphite is still the main material used in commercial lithium batteries. Graphite anodes have advantages such as high conductivity and high stability, but their theoretical specific capacity is low. The current specific capacity of graphite anodes has reached 365 mA·h / g, which is close to its theoretical maximum value of 372 mA·h / g. If we want to further improve the energy density of power batteries, new breakthroughs in anode materials are also necessary.

[0004] Silicon is currently the anode material with the highest theoretical specific capacity. Lithium forms Li in silicon. 4.4 When Si is used, the specific capacity of silicon is as high as 4200 mA·h / g, which is far higher than the theoretical specific capacity of graphite anode. Its silicon-carbon materials also have a high specific capacity.

[0005] Meanwhile, hard carbon materials have an open interlayer structure and abundant nanopores, which facilitates the rapid insertion / extraction of lithium ions and improves the high-rate charge and discharge capability. Its ion diffusion kinetics are superior to graphite, and it has a higher capacity retention rate and smaller volume change (<10%) at low temperatures (such as -20℃), which can reduce electrode stress and extend cycle life (especially when combined with silicon-carbon).

[0006] While combining high-nickel cathodes with hybrid anodes (graphite, silicon-carbon, hard carbon) can significantly improve battery capacity and energy density, current technology indicates that silicon structural units undergo 300% volume expansion and contraction during charging and discharging. Repeated volume changes easily lead to cracking and pulverization of silicon-containing anode material particles, resulting in poor electrical contact and ion conduction. Simultaneously, the cracks and new fracture surfaces caused by volume changes come into contact with the electrolyte, forming an unstable solid electrolyte interphase (SEI) film, causing reversible capacity loss. The repeated rupture and formation of the SEI film, with its uncontrollable thickness and uniformity, further restricts ion transport and affects the material's conductive network, causing reversible capacity decay and impacting rate and cycle performance. This hinders its development and makes industrialization difficult.

[0007] To address this issue, we propose a battery anode sheet and its preparation method to solve the interface problems and poor rate performance caused by the volume expansion of silicon anodes. Summary of the Invention

[0008] To achieve the above objectives, the present invention adopts the following technical solution: A battery negative electrode includes a current collector. An active material layer is disposed on at least one surface of the current collector. The active material layer comprises single-walled carbon nanotubes and silicon-carbon. A groove is disposed on the active material layer, and the depth of the groove is related to the content of the single-walled carbon nanotubes and silicon-carbon as follows: H = 0.236 × b / w; where H is the groove depth in μm, w% is the mass percentage of single-walled carbon nanotubes in the active material layer (0.1 ≤ w ≤ 3.5), and b% is the mass percentage of silicon-carbon material in the active material layer (4.77 ≤ b ≤ 14.32).

[0009] More preferably, the width D of the groove is 0.02-0.2 mm; the spacing L of the groove is 0.2-2 mm; the D50 of the silicon-carbon material is < 5 μm; and the specific capacity of the silicon-carbon material is ≥ 1650 mAh / g.

[0010] This invention establishes a synergistic system of "silicon-carbon increasing energy density + single-walled carbon nanotubes improving fast-charging performance + grooves mitigating silicon-carbon deformation". By quantitatively defining the relationship between groove depth and the content of the two core components, it solves the structural stability problem caused by the volume expansion of silicon-carbon materials, and balances the contradiction between fast-charging performance and energy density brought about by the addition of single-walled carbon nanotubes, enabling the negative electrode to simultaneously possess high energy density, excellent fast-charging performance, and long cycle life.

[0011] Furthermore, the groove design can further optimize the wettability of the active material layer, facilitating the rapid penetration of electrolyte into the active material layer, improving the lithium-ion transport efficiency, and reducing the amount of electrolyte used. This further optimizes the overall performance of the battery and provides a reliable negative electrode solution for the preparation of high-capacity, fast-charging, and long-cycle batteries.

[0012] A method for preparing a battery negative electrode sheet includes the following steps: Step 1: Add the composite negative electrode active material, binder, conductive agent, and dispersant to deionized water in proportion and disperse them evenly at high speed to obtain the negative electrode slurry; Step 2: Apply the negative electrode slurry onto the negative electrode current collector; Step 3: Remove the deionized water from the coated negative electrode current collector by passing it through a drying oven to obtain a dry negative electrode sheet; Step 4: Roll the negative electrode sheet; Step 5: Cut the negative electrode sheet; Step 6: Perform laser scribing on the negative electrode sheet obtained in Step 5; Step 7: Die-cut the marked electrode sheet.

[0013] Further preferably, the composite negative electrode active material includes graphite, silicon carbide, and hard carbon; the mass percentage of graphite in the composite negative electrode active material is a%, 75≤a≤90; the mass percentage of silicon carbide in the composite negative electrode active material is b%, 5≤b≤15; the mass percentage of hard carbon in the composite negative electrode active material is c%, 5≤c≤10, a%+b%+c%=100%; in the negative electrode sheet, the mass percentage of the composite negative electrode active material is d%, 94.0≤d≤97.0; the mass percentage of the conductive agent is e%, 0.1≤e≤3.5; the mass percentage of the binder is f%, 0.8≤f≤3.5; and the mass percentage of the dispersant is g%, 0.1≤g≤1.5.

[0014] More preferably, the areal density in step 2 is 150–200 g / m³. 2 .

[0015] More preferably, the baking temperature of the negative electrode sheet in step 3 is 80-125°C.

[0016] More preferably, the compaction density in step 4 is 1.35–1.55 g / cm³. 3 .

[0017] More preferably, the thickness of the electrode in step 4 is 100-150 μm.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention combines a graphite-silicon-carbon-hard carbon composite anode with a hierarchical buffer structure and an ultra-high nickel cathode with a highly ionic conductive electrolyte to achieve both high energy density and high fast-charging performance. Laser scribing of the composite anode improves the porosity of the anode sheet, shortens the lithium-ion transport distance, reduces lithium-ion migration resistance, and further enhances the battery's fast-charging performance. By limiting the relationship between the scribing depth and the silicon-carbon content and single-walled carbon nanotube content of the active material layer, the silicon-carbon in the active material layer can overcome the effects of repeated expansion, ensuring the stability of the material surface and preventing cracking and detachment of the anode active material due to silicon-carbon expansion, thus improving the battery's fast-charging and cycle performance. Attached Figure Description

[0019] Figure 1 This is a schematic diagram showing the surface dimensions of the composite negative electrode sheet after laser scribing according to the present invention; Figure 2 This is a schematic diagram showing the cross-sectional dimensions of the composite negative electrode sheet of the present invention. Figure 3 Porosity and tortuosity tables for examples and comparative examples; Figure 4 A table of average rate capability from 0-80% SOC for three-electrode lithium plating boundary testing; Figure 5 Cycle life test graphs of high-energy fast-charging lithium-ion batteries prepared for examples and control examples. Detailed Implementation

[0020] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0021] Reference Figure 1-2 A battery negative electrode sheet, the electrode sheet includes a current collector, an active material layer is disposed on at least one surface of the current collector, the active material layer includes single-walled carbon nanotubes and silicon carbon, and grooves are disposed on the active material layer, the depth of the grooves and the content of single-walled carbon nanotubes and silicon carbon satisfy the following relationship: H=0.236×b / w; In the formula, H is the depth of the laser groove in μm, w% is the mass percentage of single-walled carbon nanotubes in the active material layer, 0.1≤w≤3.5; b% is the mass percentage of silicon-carbon material in the active material layer, 4.77≤b≤14.32.

[0022] In some embodiments, the battery negative electrode uses a current collector as a basic carrier. The current collector, as the core supporting component of the battery electrode, mainly serves to carry the active material and conduct current. Its material can be conventional negative electrode current collector materials such as copper foil, ensuring good conductivity, flexibility, and chemical stability. At least one surface of the current collector is uniformly coated with an active material layer. This active material layer is the core area for realizing the battery's charging and discharging function, responsible for the insertion and extraction of lithium ions. Its composition design directly determines the core performance of the battery. In this solution, the active material layer mainly includes two core components: single-walled carbon nanotubes and silicon-carbon. It can also be supplemented with conventional auxiliary components such as binders and dispersants to ensure the bonding strength, conductivity, and structural integrity of the active material layer.

[0023] In some embodiments, grooves are intentionally formed on the surface of the active material layer. These grooves are fabricated using precise processes such as laser processing. Their depth is not randomly determined, but rather forms a strict quantitative relationship with the mass percentage of single-walled carbon nanotubes and silicon-carbon materials in the active material layer. The specific formula is: H = 0.236 × b / w; where H represents the depth of the laser-cut groove in μm; w% is the mass percentage of single-walled carbon nanotubes in the active material layer, with a value range limited to 0.1 ≤ w ≤ 3.5; and b% is the mass percentage of silicon-carbon materials in the active material layer, with a value range limited to 4.77 ≤ b ≤ 14.32. This quantitative relationship is the optimal matching scheme obtained through extensive experimental verification, enabling balanced optimization of the various performance characteristics of the negative electrode. In some embodiments, silicon-carbon materials, as a high-performance negative electrode active material, have extremely high theoretical specific capacity. However, silicon-carbon materials have a key drawback during battery charge-discharge cycles: significant volume expansion occurs when lithium ions are inserted, and the more lithium ions are inserted, the greater the volume expansion. Conversely, the volume shrinks when lithium ions are extracted. This repeated "expansion-contraction" deformation generates significant internal stress. This solution provides sufficient buffer space for the volume deformation of silicon-carbon materials by designing a groove structure and limiting the groove depth to a direct proportional relationship with the silicon-carbon material content.

[0024] The quantitative relationship H = 0.236 × b / w shows that, with a fixed single-walled carbon nanotube content w, the higher the silicon-carbon material content b, the greater the required groove depth H. This is because a higher silicon-carbon content results in a greater total volumetric deformation during cycling, requiring deeper grooves to accommodate the deformation and release internal stress. This effectively prevents the active material layer from cracking and detaching, ensuring the stability of the negative electrode structure and extending the battery's cycle life. Furthermore, limiting the silicon-carbon material content to the range of 4.77 ≤ b ≤ 14.32 not only fully leverages the energy density-enhancing advantages of silicon-carbon materials but also avoids excessive deformation due to excessive silicon-carbon content, exceeding the groove's buffering capacity, further ensuring the structural reliability of the negative electrode.

[0025] In some embodiments, b% is the mass percentage of silicon-carbon material in the active material layer, 4.77≤b≤14.32; b can be a range of one or any two of 4.77, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, 11.0, 12.0, 13.0, 14.0, and 14.32.

[0026] In some embodiments, single-walled carbon nanotubes possess extremely high conductivity, excellent mechanical properties, and a large specific surface area. Adding them to the active material layer can form a continuous conductive network between the active material particles, significantly reducing the internal resistance of the active material layer and accelerating the transport rate of lithium ions and electrons. This effectively improves the fast-charging performance of the battery, shortens the charging time, and meets the application requirements of fast-charging batteries.

[0027] However, there is a certain balance between the amount of single-walled carbon nanotubes added and the energy density of the battery: single-walled carbon nanotubes themselves do not have the ability to insert / deintercalate lithium ions and are inactive components. If their content is too high, they will occupy the effective space of the active material layer, resulting in a reduction in the content of active materials (silicon carbon, graphite, etc.) per unit volume, which in turn affects the energy density of the battery; if their content is too low, they cannot form a complete conductive network and it is difficult to achieve the effect of improving fast charging performance.

[0028] Based on this, this solution achieves a precise balance between battery fast-charging capability and energy density by limiting the inverse relationship between the groove depth and the single-walled carbon nanotube content. From the relationship H = 0.236 × b / w, it can be seen that with a fixed silicon-carbon material content b, the higher the single-walled carbon nanotube content w, the smaller the required groove depth H. This is because a higher single-walled carbon nanotube content results in better conductivity of the active material layer and stronger fast-charging performance. However, at this higher content, the single-walled carbon nanotubes occupy more space. To avoid the groove being too deep and further occupying the active material space, thus reducing energy density, the groove depth needs to be appropriately reduced. Conversely, a lower single-walled carbon nanotube content results in relatively weaker conductivity, requiring an appropriate increase in groove depth to better mitigate silicon-carbon deformation, while avoiding the buffering effect caused by an excessively shallow groove, thus balancing fast-charging performance and energy density.

[0029] By limiting the content of single-walled carbon nanotubes to the range of 0.1≤w≤3.5, it is possible to ensure the formation of a complete conductive network, which can fully improve the fast charging performance of the battery, while avoiding the decrease in energy density due to excessive content, thus achieving the optimal balance between fast charging performance and energy density.

[0030] In some embodiments, w% is the mass percentage of single-walled carbon nanotubes in the active material layer, 0.1≤w≤3.5; w can be a range of one or any two of 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5.

[0031] The width D of the groove is 0.02-0.2mm; the spacing L of the groove is 0.2-2mm.

[0032] In some embodiments, the width D of the groove is 0.02-0.2 mm; the spacing L of the groove is 0.2-2 mm. The above-mentioned parameters for groove width and spacing, as well as the quantitative relationship of depth, are all optimal matching schemes obtained through extensive experimental verification, which can achieve balanced optimization of various performances of the negative electrode sheet. The specific design principle of its width and spacing is as follows: The width D is limited to 0.02-0.2 mm. On the one hand, it can avoid the insufficient buffer deformation capacity of the groove when the width is too narrow (less than 0.02 mm), which cannot effectively accommodate the volume expansion of silicon-carbon material and is not conducive to electrolyte penetration. On the other hand, it can prevent excessive occupation of the effective area of ​​the active material layer when the width is too wide (greater than 0.2 mm), which would lead to a decrease in battery energy density. At the same time, it can avoid insufficient strength of the groove structure, which would cause cracking of the active material layer. The spacing L is limited to 0.2-2mm. The core is to achieve a balance between buffering effect and structural stability: if the spacing is too dense (less than 0.2mm), the active material layer will be overly segmented, the structural integrity will decrease, and the active material will easily fall off during charging and discharging; if the spacing is too sparse (greater than 2mm), the buffering effect of the groove will not be able to uniformly cover the entire active material layer, and cracking problems caused by silicon carbon expansion will still occur in local areas due to the lack of buffer space.

[0033] In some embodiments, the width D of the wire trough is 0.02-0.2 mm; the width D of the wire trough may be one or a range of any two of the following: 0.02 mm, 0.03 mm, 0.04 mm, 0.05 mm, 0.06 mm, 0.07 mm, 0.08 mm, 0.09 mm, 0.10 mm, 0.11 mm, 0.12 mm, 0.13 mm, 0.14 mm, 0.15 mm, 0.16 mm, 0.17 mm, 0.18 mm, 0.19 mm, and 0.2 mm.

[0034] In some embodiments, the spacing L of the wire grooves is 0.2-2 mm; the spacing L of the wire grooves may be one or a range of any two of the following: 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1.0 mm, 1.1 mm, 1.2 mm, 1.3 mm, 1.4 mm, 1.5 mm, 1.6 mm, 1.7 mm, 1.8 mm, 1.9 mm, 2.0 mm.

[0035] In some embodiments, the silicon-carbon material has a D50 of less than 5 μm and a specific capacity of ≥1650 mAh / g; this fully leverages the high specific capacity of the silicon-carbon material while ensuring its synergistic effect with single-walled carbon nanotubes.

[0036] A method for preparing a battery negative electrode sheet includes the following steps: Step 1: Add the composite negative electrode active material, binder, conductive agent, and dispersant to deionized water in proportion and disperse them evenly at high speed to obtain the negative electrode slurry; Step 2: Apply the negative electrode slurry onto the negative electrode current collector; Step 3: Remove the deionized water from the coated negative electrode current collector by passing it through a drying oven to obtain a dry negative electrode sheet; Step 4: Roll the negative electrode sheet; Step 5: Cut the negative electrode sheet; Step 6: Perform laser scribing on the negative electrode sheet obtained in Step 5; Step 7: Die-cut the marked electrode sheet.

[0037] The composite negative electrode active material includes graphite, silicon carbide, and hard carbon; the mass percentage of graphite in the composite negative electrode active material is a%, 75≤a≤90; the mass percentage of silicon carbide in the composite negative electrode active material is b%, 5≤b≤15; the mass percentage of hard carbon in the composite negative electrode active material is c%, 5≤c≤10, a%+b%+c%=100%; in the negative electrode sheet, the mass percentage of the composite negative electrode active material is d%, 94.0≤d≤97.0; the mass percentage of the conductive agent is e%, 0.1≤e≤3.5; the mass percentage of the binder is f%, 0.8≤f≤3.5; and the mass percentage of the dispersant is g%, 0.1≤g≤1.5.

[0038] The areal density in step 2 is 150–200 g / m³. 2 The baking temperature of the negative electrode sheet in step 3 is 80–125℃; the compaction density in step 4 is 1.35–1.55 g / cm³. 3 The electrode thickness in step 4 is 100–150 μm.

[0039] In some embodiments, step 1 involves adding the composite negative electrode active material, binder, conductive agent, and dispersant to deionized water in a preset ratio and performing high-speed dispersion treatment until the system is uniform, free of lumps, and without obvious stratification, thus obtaining a uniform and stable negative electrode slurry. The composite negative electrode active material includes graphite, silicon carbide, and hard carbon, with the following mass percentages: graphite mass percentage is a% (75≤a≤90), silicon carbide mass percentage is b% (5≤b≤15), and hard carbon mass percentage is c% (5≤c≤10), and a%+b%+c%=100%; the silicon carbide material uses the specifications defined above (D50<5 μm, specific capacity ≥1650 mAh / g), and single-walled carbon nanotubes are included in the conductive agent component. Meanwhile, the mass percentages of each component in the negative electrode sheet are limited as follows: the mass percentage of the composite negative electrode active material is d% (94.0≤d≤97.0), the mass percentage of the conductive agent is e% (0.1≤e≤3.5), the mass percentage of the binder is f% (0.8≤f≤3.5), and the mass percentage of the dispersant is g% (0.1≤g≤1.5), with the total percentage of each component being 100%. The binder adopts a PAA (polyacrylic acid) and SBR (styrene-butadiene rubber) mixed system. The synergistic effect of the two can significantly improve the bonding strength between the active material layer and the current collector, while enhancing the flexibility of the active material layer, better adapting to the volume deformation during the cycling process of silicon-carbon materials, and preventing the active material from falling off. The conductive agent can assist single-walled carbon nanotubes in forming a conductive network. Acetylene black, Ketjen black, etc. are selected to further reduce internal resistance. The dispersant is a non-ionic or anionic dispersant, which effectively prevents the agglomeration of active material particles and improves the stability of the slurry. The high-speed dispersion speed is controlled at 2000-5000 r / min, and the dispersion time is 30-90 min. It can be adjusted appropriately according to the viscosity of the slurry to ensure that all components are fully and evenly mixed.

[0040] In some embodiments, step 2 involves uniformly coating the negative electrode slurry prepared in step 1 onto the surface of the negative electrode current collector using a coating machine. The current collector is a copper foil of suitable thickness (usually 8-12 μm). Before coating, the surface of the copper foil needs to be cleaned to remove oil, impurities, and oxide layers, thereby improving the adhesion between the slurry and the current collector. The coating method can employ conventional coating processes such as blade coating or comma blade coating. The coating density is controlled at 150-200 g / m², and the coating thickness is precisely controlled according to the final active material layer thickness requirements to ensure a smooth coating surface without missed areas, pinholes, or scratches. At least one surface of the current collector is coated. If double-sided coating is required, continuous coating or a two-stage coating process can be used to ensure uniform thickness and density of the coating on both sides.

[0041] In some embodiments, step 3 involves: sending the coated negative electrode current collector into a drying oven, removing deionized water from the slurry through a gradient heating method to obtain a dried negative electrode sheet, wherein the baking temperature of the negative electrode sheet is controlled between 80 and 125°C. The drying process requires precise control to avoid excessively rapid heating, which could lead to surface crusting of the slurry and insufficient evaporation of internal moisture, resulting in defects such as pores and cracks. The gradient heating parameters are typically set as follows: initial temperature around 80°C, holding for 10-20 minutes, then gradually increasing to 100-120°C, holding for 30-60 minutes, and finally increasing to around 125°C, holding for 20-30 minutes. The total drying time is adjusted according to the coating thickness and areal density to ensure that the moisture content of the dried electrode sheet is ≤0.5%, and that the active material layer is tightly bonded to the current collector without warping or detachment. The dried electrode sheet must be cooled to room temperature before proceeding to the next process to avoid structural deformation caused by entering subsequent steps at high temperatures.

[0042] In some embodiments, step 4 involves feeding the dried negative electrode sheet from step 3 into a roller press for rolling. The core purpose of rolling is to increase the compaction density of the active material layer, reduce the porosity within the active material layer, enhance the bonding strength between active material particles and between the active material layer and the current collector, and optimize the thickness uniformity of the electrode sheet, laying the foundation for subsequent groove processing and battery assembly. The compaction density is controlled at 1.35–1.55 g / cm³, the thickness of the rolled electrode sheet is controlled at 100–150 μm, the rolling pressure is controlled at 5–15 MPa, the rolling speed is 1–5 m / min, and the number of rolling cycles is adjusted according to the compaction density and electrode sheet thickness requirements (usually 1–3 times). This ensures that the rolled electrode sheet has a uniform thickness, meets the compaction density requirements, and avoids problems such as active material shedding or current collector damage, while retaining an appropriate amount of porosity to allow space for lithium-ion transport and silicon-carbon material volume deformation.

[0043] In some embodiments, step 5 involves: slitting the negative electrode sheet after rolling in step 4 using a slitting machine. According to the battery's size requirements, the electrode sheet is slitted into blanks of a preset width and length. During the slitting process, the slitting speed and slitting blade precision must be controlled to avoid defects such as burrs, rough edges, and curled edges. The burr height must be controlled within 5 μm to prevent burrs from piercing the separator and causing a short circuit in the battery during subsequent processes. The slitted electrode sheets undergo visual inspection to remove defective products with damaged edges or excessive dimensional deviations, ensuring that the dimensional accuracy of the slitted electrode sheets meets the requirements.

[0044] In some embodiments, step 6 involves feeding the negative electrode sheet obtained from step 5 into a laser scribing machine and performing laser scribing according to the groove parameters defined above to prepare grooves with a preset depth, width, and spacing. The laser scribing process requires precise control. A suitable wavelength laser is selected, and the laser power and scribing speed are precisely adjusted based on the groove depth H (calculated using the formula H=0.236×b / w) and width D (0.02-0.2mm) to ensure uniform groove depth, consistent width, and neat edges, without excessive ablation or active material detachment. The groove spacing L is controlled between 0.2-2mm. During scribing, the grooves must be evenly arranged, parallel or perpendicular to the electrode edge, meeting the design layout requirements. After scribing, the electrode sheet needs to be cleaned to remove dust and debris generated during the scribing process to avoid affecting subsequent processes and battery performance.

[0045] In some embodiments, step 7 involves feeding the electrode sheet marked in step 6 into a die-cutting machine for die-cutting. Based on the final shape requirements of the battery electrode sheet (e.g., round, square), the electrode sheet is die-cut into a preset shape using a die-cutting blade, simultaneously cutting the tab position (if the tab is integrally formed). The die-cutting process must ensure die-cutting accuracy to avoid defects such as dimensional deviations, edge burrs, and cracks. The die-cut electrode sheet undergoes final appearance inspection and performance sampling. It must be free of damage, have intact grooves, and meet dimensional standards. Simultaneously, the thickness, compaction density, and groove parameters of the electrode sheet are sampled to ensure compliance with design requirements. Qualified electrode sheets can then be used in subsequent battery assembly processes.

[0046] The present application will be further described in detail below with reference to specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in this application. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products. Example 1 Step 1: Material preparation: Weigh graphite, silicon carbide, hard carbon, conductive carbon black, single-walled carbon nanotubes, PAA binder, SBR binder, and CMC thickener according to the mass ratio of 76.36:9.545:9.545:1.00:0.15:2.50:0.50:0.40.

[0047] Slurry preparation: The composite negative electrode active material, thickener CMC, and conductive carbon black are dry-mixed to obtain negative electrode dry powder; PAA binder and deionized water are added to the above negative electrode dry powder and stirred thoroughly until completely dissolved to obtain slurry 1 with good kneading state; then single-walled carbon nanotubes are added to the above slurry 1 and stirred under the action of a mechanical stirrer until the mixed system forms a uniform and fluid slurry 2; finally, SBR binder is added to the above slurry 2 and stirred thoroughly to obtain negative electrode slurry.

[0048] Step 2: Coating, apply the negative electrode slurry from Step 1 onto the negative electrode current collector; Step 3: Baking. The negative electrode current collector coated in Step 2 is dried in a drying oven to remove the deionized water, resulting in a dry negative electrode sheet. Step 4: Roll forming, the negative electrode sheet from step 3 is rolled through the rollers; Step 5: Slitting. Use a slitting machine to cut the negative electrode sheet from step 4 into the required size. Step 6: Laser scribing. The negative electrode sheet obtained in step 5 is laser scribed according to the given dimensions. The scribing width D is 0.1 mm, the scribing spacing L is 1 mm, and the scribing depth is 15 μm (b=9.545, w=0.15, then H≈15). Step 7: Die-cutting, die-cutting into negative electrode sheets of the specified size according to the given dimensions. Example 2

[0049] The difference from Example 1 is that the mass ratio of graphite, silicon carbide, hard carbon, conductive carbon black, single-walled carbon nanotubes, PAA binder, SBR binder, and CMC thickener is 76.36:4.77:9.545:1.00:0.15:2.50:0.50:0.40; the scribing width D is 0.1 mm, and the scribing spacing L is 1 mm. The scribing depth is 8 μm (b=4.77, w=0.15, then H≈8); Example 3

[0050] The difference from Example 1 is that the mass ratio of graphite, silicon carbide, hard carbon, conductive carbon black, single-walled carbon nanotubes, PAA binder, SBR binder, and CMC thickener is 76.36:14.32:9.545:1.00:0.15:2.50:0.50:0.40; the scribing width D is 0.1 mm, the scribing spacing L is 1 mm, and the scribing depth is 23 μm (b=14.32, w=0.15, then H≈23). Compare with Example 1 The difference from Example 1 is that the scribing width D is 0.1 mm, the scribing spacing L is 1 mm, and the scribing depth is not calculated according to the formula; the scribing depth is taken as an arbitrary value of 5 μm.

[0051] Compare with Example 2 The difference from Example 1 is that the scribing width D is 0.1 mm, the scribing spacing L is 1 mm, and the scribing depth is not calculated according to the formula; the scribing depth is taken as an arbitrary value of 25 μm.

[0052] Compare with Example 3 The difference from Example 1 is that the negative electrode is not laser-scribed.

[0053] Furthermore, this application does not limit the specific type of positive electrode active material in the positive electrode sheet; it can be a positive electrode active material commonly used in batteries, such as a composite oxide of lithium with at least one of cobalt, nickel, manganese, or combinations thereof. The composite negative electrode sheet obtained in the above embodiments is assembled with the same positive electrode sheet to form a 5Ah soft-pack battery cell to be tested.

[0054] The composite negative electrode sheets prepared in the above three sets of examples and three sets of control examples were tested for porosity and tortuosity. The test results are as follows: Figure 3 As shown, the porosity is improved after laser scribing, especially the improvement is more significant when the laser scribing depth satisfies H=0.236×b / w (Examples 1-3). This provides a "highway" for lithium ions to travel directly from the electrolyte / separator interface to the depth of the electrode. Lithium ions no longer need to rely entirely on a long and tortuous nanoscale pore network, but can quickly penetrate vertically through the laser channels and then enter the surrounding graphite particles with only a very short lateral diffusion. This greatly "straightens" the effective transport path of ions throughout the electrode thickness, thus significantly reducing the effective tortuosity of the electrode. Simultaneously, for silicon-containing systems, it can provide a certain buffer space for their expansion.

[0055] The three-electrode lithium plating boundary test of the obtained high-energy fast-charging lithium-ion battery at 0-80% SOC average rate is as follows: Figure 4 As shown, the average charging rate of the embodiment of the present invention is the highest; the peak 4C rate cycle life test is as follows. Figure 5 As shown, the embodiments of the present invention exhibit significantly better rate charging performance and cycle life, maintaining a retention rate of over 93.00% after 500 cycles. In contrast, Control Example 1, with a shallower etching depth than Example 1, exhibits relatively poor cycle performance and capability. This is because the shallower depth is insufficient to accommodate the volume expansion caused by the silicon system, easily leading to poor electrode interface and further affecting cycle performance. Control Example 2, with a deeper etching depth than Example 1, also exhibits relatively poor cycle performance and capability. This is because excessively deep etching disrupts the delicate balance between mechanical support, conductive network, and ion transport in the negative electrode system.

[0056] This invention achieves both high energy density and high fast-charging performance by using a graphite-silicon-carbon-hard carbon composite negative electrode with a hierarchical buffer structure and a highly ionic conductive electrolyte. Laser scribing of the composite negative electrode sheet increases its porosity, shortens the lithium-ion transport distance, reduces lithium-ion migration resistance, and further enhances the battery's fast-charging performance. The resulting lithium-ion battery achieves both high energy density and fast-charging performance.

[0057] Laser etching, particularly for silicon-containing systems, creates trench structures by laser scribing. This provides a reserved and controllable expansion space for the volume expansion of silicon particles during cycling, fundamentally alleviating expansion stress and preventing the overall electrode structure from cracking or deforming due to internal compression. This is the structural basis for improving cycle life. Simultaneously, the controlled relationship between scribing depth and the silicon-carbon content and single-walled carbon nanotube content of the active material layer allows the silicon-carbon in the active material layer to overcome the effects of repeated expansion, ensuring the stability of the material surface and preventing cracking and detachment of the negative electrode active material due to silicon-carbon expansion. It also provides more ion channels, thereby improving the battery's fast charging and cycle performance. Furthermore, the three-dimensional structure created by etching significantly increases the contact area between the electrode and the electrolyte and creates a better ion transport path. This ensures that lithium ions can reach the interior of the silicon particles more uniformly and quickly for reaction, reducing concentration polarization and thus improving the battery's power performance and active material utilization. Therefore, laser etching can significantly improve the fast charging capability of lithium batteries.

Claims

1. A battery negative electrode sheet, characterized in that, The electrode includes a current collector, and an active material layer is disposed on at least one surface of the current collector. The active material layer comprises single-walled carbon nanotubes and silicon carbon. Grooves are disposed on the active material layer, and the depth of the grooves satisfies the following relationship with the content of the single-walled carbon nanotubes and silicon carbon: H = 0.236 × b / w; In the formula, H is the depth of the laser groove in μm, w% is the mass percentage of single-walled carbon nanotubes in the active material layer, 0.1≤w≤3.5; b% is the mass percentage of silicon-carbon material in the active material layer, 4.77≤b≤14.

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2. The battery negative electrode sheet according to claim 1, characterized in that, The width D of the groove is 0.02-0.2mm; the spacing L of the groove is 0.2-2mm.

3. The battery negative electrode sheet according to claim 1, characterized in that, The silicon-carbon material has a D50 of less than 5 μm.

4. The battery negative electrode sheet according to claim 1, characterized in that, The specific capacity of the silicon-carbon material is ≥1650mAh / g.

5. A method for preparing a battery negative electrode sheet as described in any one of claims 1 to 4, characterized in that, Includes the following steps: Step 1: Add the composite negative electrode active material, binder, conductive agent, and dispersant to deionized water in proportion and disperse them evenly at high speed to obtain the negative electrode slurry; Step 2: Apply the negative electrode slurry onto the negative electrode current collector; Step 3: Remove the deionized water from the coated negative electrode current collector by passing it through a drying oven to obtain a dry negative electrode sheet; Step 4: Roll the negative electrode sheet; Step 5: Cut the negative electrode sheet; Step 6: Perform laser scribing on the negative electrode sheet obtained in Step 5; Step 7: Die-cut the marked electrode sheet.

6. The method for preparing a battery negative electrode sheet according to claim 5, characterized in that, The composite negative electrode active material includes graphite, silicon carbide, and hard carbon; the mass percentage of graphite in the composite negative electrode active material is a%, 75≤a≤90; the mass percentage of silicon carbide in the composite negative electrode active material is b%, 5≤b≤15; the mass percentage of hard carbon in the composite negative electrode active material is c%, 5≤c≤10, a%+b%+c%=100%; in the negative electrode sheet, the mass percentage of the composite negative electrode active material is d%, 94.0≤d≤97.0; the mass percentage of the conductive agent is e%, 0.1≤e≤3.5; the mass percentage of the binder is f%, 0.8≤f≤3.5; and the mass percentage of the dispersant is g%, 0.1≤g≤1.

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7. The method for preparing a battery negative electrode sheet according to claim 5, characterized in that, The areal density in step 2 is 150–200 g / m³. 2 .

8. The method for preparing a battery negative electrode sheet according to claim 5, characterized in that, The baking temperature of the negative electrode sheet in step 3 is 80-125℃.

9. The method for preparing a battery negative electrode sheet according to claim 5, characterized in that, The compaction density in step 4 is 1.35–1.55 g / cm³. 3 .

10. A method for preparing a battery negative electrode sheet according to claim 5, characterized in that, The thickness of the electrode in step 4 is 100-150 μm.

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