Negative electrode sheet, cylindrical battery, battery pack and electric tool

Abstract

Provided in the present invention are a negative electrode sheet, a cylindrical battery, a battery pack and an electric tool. With regard to the negative electrode sheet provided in the present invention, the thickness of a silicon-based negative electrode active material on a negative electrode current collector is controlled by adjusting the areal density and compaction density of the negative electrode sheet, thereby improving the electrical conductivity of the negative electrode sheet while ensuring the lithium storage capacity thereof. In view of the strong market demand for cylindrical steel-shell batteries and constraints to size, safety and cost, the cylindrical battery which is provided in the present invention and uses the above negative electrode sheet, taking an 18650 cylindrical battery as an example, realizes ideal high capacity and high rate of the battery simultaneously by means of structural optimization, system improvement and manufacturing process improvement, thereby significantly enhancing the energy density and power output capability of the battery, providing a more efficient and reliable energy solution for the market and having broad application prospects and a high market value.

Description

A negative electrode sheet, a cylindrical battery and battery pack, and power tools.

[0001] This application claims priority to Chinese Patent Application No. 202411621903.1, filed on November 14, 2024, entitled "A negative electrode sheet, a cylindrical battery and a battery pack, and an electric tool", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This invention relates to the field of battery technology, and in particular to a negative electrode sheet, a cylindrical battery and battery pack, and power tools. Background Technology

[0003] Lithium-ion batteries have become the preferred power source in the energy storage electronics industry due to their high capacity and high energy density. In recent years, with continuous technological advancements, various industries have placed higher demands on the capacity, energy density, and safety performance of lithium-ion batteries. The performance of lithium-ion batteries depends on factors such as the positive electrode material, negative electrode material, separator, electrolyte, and battery structure design. Among these, improving the performance of the negative electrode material is a key factor in enhancing overall battery performance. Currently, most lithium-ion batteries on the market use graphite-based negative electrode materials, but the theoretical lithium storage capacity of graphite-based negative electrode materials is relatively low, which can no longer meet the overall improvement requirements of lithium-ion batteries.

[0004] Against this backdrop, using silicon-based materials as the anode material can theoretically improve lithium storage capacity, thus significantly increasing the energy density of lithium-ion batteries, making it the optimal choice at present. However, while using silicon-based materials as the anode material can theoretically improve lithium storage capacity, it also presents the following problems: First, the huge volume expansion effect of silicon-based materials causes silicon particles to easily break and detach from the current collector during cycling, resulting in a short battery cycle life; Second, silicon-based materials have poor conductivity, causing the anode active material to pulverize and crack during battery charge-discharge cycles, with the anode active material and conductive agent detaching together. Simultaneously, the SEI (Sediment Ion) is repeatedly generated, continuously consuming lithium ions, leading to increased internal resistance, high heat generation, rapid capacity decline, poor fast charge-discharge capability, and inability to improve the battery's charge-discharge rate. Currently, the most mature cylindrical lithium-ion batteries on the market are 18650 batteries. They either have a capacity between 1200mAh and 3000mAh, and the maximum continuous cycle discharge rate can reach 6C, but their capacity is small and the single discharge time is short, which cannot meet the needs of customers for long-term power use; or they have a capacity between 3000mAh and 4000mAh, but their maximum continuous cycle discharge rate is only 3C. When used in many power tools, the 3C discharge rate cannot meet the power demand.

[0005] Chinese Patent Publication No. CN108258236B discloses a high-specific-capacity, high-cycle-life 18650 cylindrical lithium battery. Its positive electrode uses NCA material with a thickness of 142μm-146μm; the negative electrode uses SiC material with a thickness of 145μm-152μm. This design utilizes high-nickel-content nickel-cobalt-aluminum NCA as the positive electrode material and silicon-carbon SiC as the negative electrode material to improve the battery capacity of the 18650 battery. Although the discharge capacity of a single cell is ≥3400mAh, the battery can only achieve discharge rates of 0.2C, 0.5C, and 1C, meaning its discharge performance cannot meet the requirements for high discharge rates.

[0006] Chinese Patent Publication No. CN113659218B also discloses a high-capacity and high-rate cylindrical lithium-ion battery. Its positive electrode uses a ternary material with a thickness of 118±2μm; the negative electrode uses a silicon suboxide / graphite composite with a thickness of (90-94)±2μm. However, the specification states that while ensuring high capacity, the cylindrical lithium-ion battery reduces the thickness of the positive and negative electrodes by lowering their areal density to achieve a high-rate 8C discharge. However, in this embodiment, while achieving high-rate discharge, the battery capacity is only 2600mAh, failing to reach a high capacity of over 3500mAh.

[0007] Japanese Patent Publication No. JP2701347B2 also discloses a non-aqueous electrolyte secondary battery. This secondary battery is composed of a positive electrode, a separator, and a negative electrode wound together. The thickness of the double-sided active material layer (A) in the positive electrode is 80μm-250μm; the thickness of the double-sided active material layer (B) in the negative electrode is 80μm-250μm; the A / B ratio is between 0.6 and 1.5; and (A+B) is between 250μm and 500μm. This secondary battery is suitable for lithium-ion batteries with graphite negative electrodes. However, for silicon-based negative electrode batteries, due to the significant expansion of the material, excessively thick negative electrode layers can easily lead to electrode cracking, causing battery failure.

[0008] Therefore, when the positive electrode uses ternary materials as active materials and the negative electrode uses silicon-based materials as active materials, how to improve the battery capacity of lithium-ion batteries and how to achieve high-rate discharge performance (3C discharge / 6C discharge) so that the capacity and rate performance can reach a relatively balanced state are technical problems that urgently need to be solved by those skilled in the art. Summary of the Invention

[0009] The purpose of this invention is to address the shortcomings of existing lithium-ion batteries that use ternary materials as the active material for the positive electrode and silicon-based materials as the active material for the negative electrode, which cannot simultaneously achieve high capacity (above 3.5Ah) and high rate (6C discharge). This invention provides a negative electrode, a cylindrical battery and battery pack, and a power tool, aiming to alleviate the problems of expansion, poor conductivity, and inability to achieve high-rate discharge of silicon-based negative electrode materials.

[0010] In a first aspect, the present invention provides a negative electrode sheet, comprising a negative electrode current collector, a negative electrode tab disposed on the negative electrode current collector, and a negative electrode silicon-based active material;

[0011] The negative electrode current collector includes a first surface and a second surface arranged along its own thickness direction;

[0012] The negative electrode silicon-based active material is coated on the first surface of the negative electrode current collector to form a first coated surface and a first uncoated surface, wherein the thickness of the first coated surface is 20μm-35μm;

[0013] The negative electrode silicon-based active material is coated on the second surface of the negative electrode current collector to form a second coated surface and a second uncoated surface, wherein the thickness of the second coated surface is 20μm-35μm.

[0014] In one embodiment, the negative electrode silicon-based active material contains silicon, and the silicon content in the negative electrode silicon-based active material is 40-65% by mass.

[0015] In one embodiment, the specific capacity of the negative electrode silicon-based active material is ≥1200mAh / g.

[0016] In one embodiment, the areal density of the negative electrode sheet is 4.0-4.5 mg / cm³. 2 .

[0017] In one embodiment, the compaction density of the negative electrode sheet is 0.6-1.0 g / cm³. 3 .

[0018] In one embodiment, the compaction density of the negative electrode sheet is 0.8 g / cm³. 3 .

[0019] In one embodiment, the area of ​​the first coated surface is larger than the area of ​​the second coated surface.

[0020] In one embodiment, the area of ​​the first coated surface is 1.05-1.1 times the area of ​​the second coated surface.

[0021] In one embodiment, the negative electrode tab includes a first tab and a second tab, which are spaced apart along the length of the negative electrode current collector and located on a first uncoated surface and a second uncoated surface, respectively.

[0022] In one embodiment, the negative current collector has two first and second sides arranged parallel to each other along the width direction;

[0023] The first electrode tab includes a first conductive sheet welded to the second uncoated surface and extending outward from the first side, and two first insulating sheets respectively attached to the first uncoated surface and the second uncoated surface and extending outward from the first side; the projection surfaces of the two first insulating sheets on the negative electrode current collector overlap each other, and the first conductive sheet is located between the two first insulating sheets.

[0024] In one embodiment, the distance between the first conductive sheet and the side of the second coated surface is 45mm-65mm.

[0025] In one embodiment, the width of the first insulating sheet is 1.5-2.5 times the width of the first conductive sheet.

[0026] In one embodiment, the first insulating sheet extends outward along the first side for a length of 0.5 mm to 3 mm.

[0027] In one embodiment, the second tab is a second conductive sheet welded to the first coated surface and extending outward from the second side.

[0028] In one embodiment, the distance between the second conductive sheet and the side of the first coated surface is 15mm-20mm.

[0029] In one embodiment, the first conductive sheet extends outward along the first side for a length of A, and the second conductive sheet extends outward along the first side for a length of B. The length relationship between the two should satisfy the following condition: A > B and AB > 8 mm.

[0030] In one embodiment, the width of the second conductive sheet is 0.5-1 times the width of the first conductive sheet.

[0031] In one embodiment, the negative electrode tab includes a main electrode tab disposed on a first uncoated surface or a second uncoated surface and a plurality of secondary electrode tabs disposed on the first uncoated surface and / or the second uncoated surface, the plurality of secondary electrode tabs being arranged at intervals along the length direction of the negative electrode current collector.

[0032] In one embodiment, the main electrode tab and the plurality of the secondary electrode tabs extend outward based on the negative current collector, and the main electrode tab and the plurality of the secondary electrode tabs extend outward in the same direction based on the negative current collector.

[0033] In one embodiment, the main electrode tab extends outward based on the negative current collector by a greater length than the secondary electrode tab extends outward based on the negative current collector.

[0034] The beneficial effects of the negative electrode sheet provided by this invention are as follows: by controlling the areal density and compaction density of the negative electrode sheet, the thickness of the negative electrode silicon-based active material on the negative electrode current collector is controlled, reducing the adverse effects caused by the expansion of the negative electrode silicon-based active material due to charging and discharging. Under the premise of ensuring the lithium storage capacity of the negative electrode sheet, the thickness of the coating is reduced as much as possible to reduce the migration distance of lithium ions during charging and discharging, improve the migration resistance of lithium ions during charging and discharging, reduce the internal resistance of the negative electrode sheet, and achieve the purpose of increasing the current and improving the conductivity of the negative electrode sheet.

[0035] Secondly, the present invention also provides a cylindrical battery, including a casing, a cap, an electrolyte disposed within the casing, and a cylindrical core, wherein the cylindrical core includes a positive electrode, a separator, and the aforementioned negative electrode.

[0036] In one embodiment, the positive electrode includes a positive current collector, a positive electrode tab disposed on the positive current collector, and a positive active material; the positive active material is LiNi. x Co y Mn 1-x-y The material of O2 (where x and y take values ​​between 0 and 1).

[0037] In one embodiment, the areal density of the positive electrode sheet is 28-33 mg / cm³. 2 .

[0038] In one embodiment, the compaction density of the positive electrode sheet is 3.2-3.8 g / cm³. 3 .

[0039] In one embodiment, the positive current collector includes a third surface and a fourth surface disposed along its own thickness direction;

[0040] The positive electrode active material is coated on the third surface of the positive electrode current collector to form a plurality of third coating surfaces, and a first blank area is formed between two adjacent third coating surfaces. The thickness of the third coating surface is 35μm-55μm.

[0041] The positive electrode active material is coated on the fourth surface of the positive electrode current collector to form a plurality of fourth coating surfaces, and a second blank area is formed between two adjacent fourth coating surfaces. The thickness of the fourth coating surface is 35μm-55μm.

[0042] In one embodiment, the positive current collector has two parallel third and fourth sides along the width direction;

[0043] The positive electrode tab includes several third conductive sheets welded to the first blank area and extending outward from the third side, and several pairs of second insulating sheets respectively attached to the first blank area and the second blank area and extending outward from the third side;

[0044] The projection surfaces of each pair of second insulating sheets on the positive current collector coincide, and the third conductive sheet is located between the two second insulating sheets.

[0045] In one embodiment, the third surface of the positive current collector is provided with two third coating surfaces and a first blank area, the two third coating surfaces are symmetrically arranged on both sides of the first blank area, and the fourth surface of the positive current collector is provided with two fourth coating surfaces and a second blank area; the positive electrode tab includes a third conductive sheet welded to the first blank area and a pair of second insulating sheets.

[0046] In one embodiment, the width of the positive electrode tab of the positive electrode sheet is the same as the width of the negative electrode tab.

[0047] In one embodiment, the width of the first blank area and the second blank area is at least 2 mm larger than the width of the positive electrode tab.

[0048] In one embodiment, the area of ​​the second insulating sheet is larger than the area of ​​the first blank area or the second blank area of ​​the positive current collector.

[0049] In one embodiment, during winding, the first coated surface of the negative electrode sheet faces the third coated surface of the positive electrode sheet, and the length of the first coated surface is greater than the length of the positive current collector of the positive electrode sheet.

[0050] In one embodiment, the second insulating sheet extends outward along the third side for a length of 2mm-4mm, and the second insulating sheet extends outward along the fourth side for a length of 0.2mm-1.0mm.

[0051] In one embodiment, the cylindrical core is assembled inside the housing, and the diameter of the cylindrical core is 0.96-0.99 of the inner diameter of the housing.

[0052] In one embodiment, the length of the negative electrode is 1190mm-1205mm; the length of the positive electrode is 1081mm-1091mm.

[0053] In one embodiment, the amount of electrolyte injected is 5.6g-6.2g.

[0054] In one embodiment, the cylindrical battery retains a discharge capacity of more than 97% when charged at 0.2C and discharged at 3C, and the temperature rise is 20-35°C.

[0055] In one embodiment, the cylindrical battery retains more than 95% of its discharge capacity when charged at 0.2C and discharged at 6C, and the temperature rise is 45-65°C.

[0056] In one embodiment, the cylindrical battery has a capacity greater than 3500mAh.

[0057] The beneficial effects of the cylindrical battery provided by this invention are as follows: Using the aforementioned negative electrode sheet, taking an 18650 cylindrical battery as an example, by optimizing the structure, improving the system, and the manufacturing process, the battery achieves both high capacity and high rate of return simultaneously, resulting in a significant improvement in energy density and power output. This provides the market with a more efficient and reliable energy solution, possessing broad application prospects and market value. By using the aforementioned negative electrode sheet, while increasing the lithium-ion capacity of the negative electrode sheet, the migration distance of lithium ions during battery charge-discharge cycles is shortened. This allows the cylindrical battery to maintain a capacity of over 3500mAh while maintaining a discharge capacity retention rate of over 97% and a temperature rise controlled within 20-35℃ when charged at 0.2C and discharged at 3C. Furthermore, when charged at 0.2C and discharged at 6C, the discharge capacity retention rate is over 95% and the temperature rise is controlled within 45-65℃.

[0058] Thirdly, the present invention also provides a battery pack comprising two or more of the above-described cylindrical batteries, wherein the two or more cylindrical batteries are electrically connected in series or in parallel.

[0059] The beneficial effect of the battery pack provided by the present invention is that by using the above-mentioned high-capacity, high-rate cylindrical battery, the overall electrical performance of the battery pack is improved, and a high-capacity and high-rate battery pack is achieved.

[0060] Fourthly, the present invention also provides an electric tool including the battery pack described above.

[0061] The beneficial effect of the power tool provided by the present invention is that by using the above-mentioned high-capacity and high-rate battery pack, the working stability of the power tool is improved. Attached Figure Description

[0062] Figure 1 is a schematic diagram of the structure of the first surface of the negative current collector of a negative electrode sheet provided by the present invention;

[0063] Figure 2 is a schematic diagram of the structure of the second surface of the negative current collector of a negative electrode sheet provided by the present invention;

[0064] Figure 3 is a cross-sectional view of the negative current collector of a negative electrode sheet provided by the present invention;

[0065] Figure 4 is a three-dimensional structural diagram of a cylindrical battery provided by the present invention;

[0066] Figure 5 is a schematic diagram of the structure of the third surface of the positive electrode sheet in a cylindrical battery provided by the present invention;

[0067] Figure 6 is a cross-sectional view of the positive current collector of the positive electrode sheet in a cylindrical battery provided by the present invention;

[0068] Figure 7 is a battery performance test diagram of Embodiment 1 of a cylindrical battery provided by the present invention.

[0069] Explanation of reference numerals in the attached drawings: 100-cylindrical battery, 30-separator, 40-cap, 50-casing; 10-negative electrode, 11-negative current collector; 111-first surface, 111A-first coated surface, 111B-first uncoated surface; 112-second surface, 112A-second coated surface, 112B-second uncoated surface; 113-first side, 114-second side; 12-first tab, 121-first conductive sheet, 121A-first ultrasonic solder mark, 122-first insulating sheet; 13-second tab, 131-second conductive sheet, 131A-second ultrasonic solder mark; 20-Positive electrode sheet, 21-Positive current collector, 211-Third surface, 211A-Third coating surface, 211B-First blank area, 212-Fourth surface, 212A-Fourth coating surface, 212B-Second blank area, 213-Third side, 214-Fourth side, 22-Positive electrode tab, 221-Third conductive sheet, 221A-Third ultrasonic solder mark, 222-Second insulating sheet. Detailed Implementation

[0070] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0071] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0072] The "scope" disclosed in this invention is defined by a lower limit and an upper limit. A given scope is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific scope. This method of defining a scope includes endpoints and allows for arbitrary combinations; that is, any lower limit can be combined with any upper limit to form a scope.

[0073] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0074] Unless otherwise specified, all technical features and optional technical features of this invention can be combined to form new technical solutions.

[0075] Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially.

[0076] Silicon-based materials are commonly used negative electrode active materials in the field of lithium battery technology. Due to their inherent characteristics, they exhibit significant volume expansion during full-charge and discharge processes. During the research and development process, the inventors of this application discovered that silicon-based materials suffer from insufficient conductivity due to volume expansion. Therefore, when using silicon-based materials as negative electrode active materials, the inventors of this application control the areal density and compaction density of the active material on the current collector to control the thickness of the negative electrode active material layer. By reducing the migration distance of lithium ions during charge and discharge, the migration resistance of lithium ions during charge and discharge is improved. This reduces internal resistance and enhances the conductivity of the negative electrode sheet 10, thereby maximizing the battery's discharge rate while maintaining battery capacity, achieving a balance between high capacity and high rate of discharge.

[0077] Figures 1-3 show schematic diagrams of the structure of a negative electrode sheet 10 provided by the present invention. In this invention, the length direction of the negative electrode sheet 10 is defined as X, the width direction as Y, and the thickness direction as Z. It should be understood that the above definitions of directions are for the convenience of describing the present invention, and the directions defined by the present invention can be understood based on the relative positions of the figures and the actual product. It is understood that the length direction, width direction, and thickness direction of the negative electrode current collector 11 and the negative electrode silicon-based active material are the same as those of the negative electrode sheet 10. Figures 1 and 2 show the negative electrode sheet 10 along its length direction X in one embodiment of the present invention, and Figure 3 shows the negative electrode sheet 10 along its thickness direction Z in one embodiment of the present invention.

[0078] As shown in Figure 1, the negative electrode sheet 10 provided by the present invention includes a negative electrode current collector 11, a negative electrode tab disposed on the negative electrode current collector 11, and a negative electrode silicon-based active material. The negative electrode current collector 11 includes a first surface 111 and a second surface 112 disposed along its thickness direction Z. The negative electrode silicon-based active material provided by the present invention is disposed on both the first surface 111 and the second surface 112 of the negative electrode current collector 11.

[0079] As shown in Figure 1, a first coated surface 111A and a first uncoated surface 111B are formed on the first surface 111 of the negative electrode current collector 11 by coating a silicon-based negative electrode active material. The first coated surface 111A, containing the silicon-based negative electrode active material, is formed on the first surface 111. The thickness D1 of the first coated surface 111A is the thickness of the active material formed after the silicon-based negative electrode active material is coated and rolled on the surface of the negative electrode current collector 11. The first uncoated surface 111B is also provided on the first surface 111. In the region of the first uncoated surface 111B of the first surface 111, there is no silicon-based negative electrode active material. The first uncoated surface 111B is the surface of the negative electrode current collector 11 itself.

[0080] Meanwhile, as shown in Figure 2, a second coated surface 112A and a second uncoated surface 112B are formed on the second surface 112 of the negative electrode current collector 11 by coating a silicon-based negative electrode active material. The second coated surface 112A, containing the silicon-based negative electrode active material, is formed on the second surface 112. The thickness D2 of this second coated surface 112A is the thickness of the active material formed after the silicon-based negative electrode active material is coated and rolled on the surface of the negative electrode current collector 11. A second uncoated surface 112B is also provided on the second surface 112. Within the region of the second uncoated surface 112B on the second surface 112, there is no silicon-based negative electrode active material. This second uncoated surface 112B is the surface of the negative electrode current collector 11 itself.

[0081] To better control the stability of the negative electrode silicon-based active material on the negative electrode current collector 11 during battery cycling and to improve the conductivity of the negative electrode silicon-based active material, the thickness D1 of the first coating surface 111A of the negative electrode sheet 10 in this invention is 20μm-35μm; the thickness D2 of the second coating surface 112A is 20μm-35μm. By controlling the thickness D1 (thickness D2) of the active material on the negative electrode sheet 10 to 20μm-35μm, the overall thickness of the negative electrode sheet 10 is significantly reduced compared to the thickness of traditional negative electrode sheets. The thickness of the negative electrode silicon-based active material disposed on the first surface 111 and the second surface 112 of the negative electrode current collector 11 provided by the present invention can be the same or different. That is, the thickness D1 of the first coating surface 111A and the thickness D2 of the second coating surface 112A can be the same, or the thickness D1 of the first coating surface 111A can be greater than the thickness D2 of the second coating surface 112A, or the thickness D1 of the first coating surface 111A can be less than the thickness D2 of the second coating surface 112A. The thickness D1 of the negative electrode silicon-based active material on the first surface 111 or the thickness D2 of the negative electrode silicon-based active material on the second surface 112 can be adjusted individually as needed, and the thickness of the negative electrode silicon-based active material on both surfaces can be adjusted individually, but the thickness of a single surface of each negative electrode current collector 11 is still controlled between 20μm and 35μm.

[0082] The thickness of the negative electrode sheet 10 provided by this invention is the sum of the thickness D1 of the first coating surface 111A, the thickness of the negative electrode current collector 11, and the thickness D2 of the second coating surface 112A. In this embodiment, the negative electrode current collector 11 is made of copper foil with a thickness of 8 μm. Therefore, the thickness of the negative electrode sheet 10 provided by this invention is between 48 μm and 78 μm, which is 50%-70% less than the thickness of negative electrode sheets made of negative electrode active materials used in the prior art. The negative electrode current collector 11 can also be made of copper foil with a thickness of 10 μm, 12 μm, or 15 μm. The thickness of the negative electrode current collector 11 is not limited here and can be adjusted according to actual needs. The thickness of the negative electrode sheet 10 provided by this invention can be adapted to different materials of the negative electrode current collector 11.

[0083] If the thickness D1 or D2 of the monolayer of the silicon-based active material on the first surface 111 or the second surface 112 of the negative electrode current collector 11 is less than 20 μm, the single-cell battery using the negative electrode 10 will not meet the high-capacity requirements, and the capacity of the single-cell battery will be less than 3500 mAh. Conversely, if the thickness D1 or D2 of the monolayer of the silicon-based active material on the first surface 111 or the second surface 112 of the negative electrode current collector 11 is greater than 35 μm, the resistance of the single-cell battery using the negative electrode 10 will be too high, making it impossible to achieve a 6C rate discharge. Therefore, controlling the thickness D1 (or D2) of the silicon-based active material on both sides of the negative electrode current collector 11 of the negative electrode 10 can achieve a balanced control of the capacity and rate of the battery cell using the negative electrode 10.

[0084] In one embodiment, the specific capacity of the silicon-based active material in the negative electrode sheet 10 provided by the present invention is ≥1200mAh / g. Through material selection, material ratio, and control of the processing technology, the specific capacity of the silicon-based active material is ≥1200mAh / g to ensure the energy density of the silicon-based active material. The silicon-based active material in the negative electrode sheet 10 provided by the present invention serves as the main lithium storage component in the battery, enabling lithium-ion insertion and extraction during charging and discharging. Therefore, different selections of this silicon-based active material directly affect the lithium storage capacity of the entire lithium-ion battery, i.e., the capacity of the individual cell. By controlling the specific capacity of the silicon-based active material in the individual cell, the capacity of the individual cell using the negative electrode sheet 10 provided by the present invention can be increased, reaching a capacity greater than 3500mAh.

[0085] In one embodiment, the negative electrode 10 provided by the present invention contains silicon in its silicon-based active material, thereby providing the negative electrode 10 with greater lithium storage capacity. The silicon content in the silicon-based active material is 40-65% by mass, for example, 40%, 45%, 50%, 55%, 60%, 65%, or any value between any two of the above ranges. The silicon-based active material provided by the present invention can be silicon-carbon, silicon suboxide, or a composite material of silicon-carbon and graphite, or a composite material of silicon suboxide and graphite. When silicon-carbon or silicon suboxide is used as the silicon-based active material, the silicon content is 50-65% by mass. When a silicon-based material (silicon-carbon or silicon suboxide) and graphite composite material is used, the silicon content is 40-55% by mass.

[0086] In one embodiment, the areal density of the negative electrode 10 is 4.0-4.5 mg / cm³. 2For example, the areal density of the negative electrode 10 is 4.0 mg / cm³. 2 4.1 mg / cm 2 4.2 mg / cm 2 4.3 mg / cm 2 4.4 mg / cm 2 4.5 mg / cm 2 Or any value between any two of the above ranges. By controlling the areal density per unit area of ​​the negative electrode 10, the lithium storage capacity of the negative electrode silicon-based active material can be regulated, thereby enabling the negative electrode 10 using the negative electrode silicon-based active material to have a high content of active material, and enabling the single cell using the negative electrode 10 to have a high battery capacity.

[0087] The areal density per unit area of ​​the negative electrode 10 mentioned in this invention refers to the mass of a certain thickness of negative electrode silicon-based active material per unit area (the ratio of the mass to the area of ​​the negative electrode silicon-based active material). The method for measuring the areal density per unit area of ​​the negative electrode 10 is as follows: Step 1. Use a sampler to weigh a circular piece of foil of a predetermined area from an empty foil sheet to obtain the foil weight; Step 2. Use a sampler to weigh a circular electrode of the same size from a double-sided coated electrode sheet, subtract the foil weight from Step 1, and divide by the circular area to obtain the double-sided areal density; Steps 1-2 can be repeated to obtain the actual areal density at different positions of the negative electrode 10 and then take the average value.

[0088] When the areal density of the negative electrode 10 is greater than 4.5 mg / cm³ 2 At this point, the areal density of the silicon-based active material for the negative electrode is relatively high, making the material processing more difficult, and the internal resistance of the negative electrode 10 increases, resulting in a decrease in rate performance. When the areal density of the negative electrode 10 is less than 4.0 mg / cm³... 2 At this time, the areal density of the silicon-based active material of the negative electrode is relatively low, resulting in insufficient lithium storage capacity and reduced energy density, which cannot meet the requirements of high-capacity batteries. In this embodiment, the areal density of the negative electrode sheet 10 is 4.2 mg / cm³. 2 .

[0089] In one embodiment, the compaction density of the negative electrode 10 is 0.6-1.0 g / cm³. 3 For example, the compaction density of the negative electrode 10 is 0.6 g / cm³. 3 0.7g / cm 3 0.8g / cm 3 0.9g / cm 3 1.0g / cm 3Or any value between any two of the above ranges. By controlling the compaction density of the negative electrode 10, parameters such as porosity and effective pore size can be controlled to improve the electronic and ion conduction performance of the negative electrode 10. If the compaction density of the negative electrode 10 is too high, it is easy to cause excessive stress within the negative electrode 10, resulting in particle breakage within the negative electrode silicon-based material and affecting the electrode performance. If the compaction density of the negative electrode 10 is too low, the gaps within the active material will be too large, increasing resistance and affecting the ion transport rate. The compaction density is adaptively adjusted according to the different selections of silicon-based materials in the negative electrode silicon-based active material. When silicon-carbon material is selected as the main negative electrode material for the negative electrode 10, the compaction density of the negative electrode 10 is controlled at 0.8 g / cm³. 3 Ideally, this allows for effective control of the thickness D1 of the silicon-based active material on the first coating surface 111A and the thickness D2 of the second coating surface 112A, ensuring that the thickness remains within the designed dimensional range and meets the requirements of high-capacity and high-rate batteries. When silicon suboxide is selected as the main negative electrode material for the negative electrode sheet 10, the compaction density of the negative electrode sheet 10 is controlled at 1.0 / cm². 3 Ideally, the thickness should be controlled within the designed size range to meet the requirements of high-capacity and high-rate batteries.

[0090] The inventors of this application utilize the principle of interaction between the compaction density and the areal density of the negative electrode sheet 10. By controlling the compaction density and areal density of the negative electrode sheet 10, the thickness of the silicon-based active material on the negative electrode current collector 11 is controlled, thereby achieving a balanced control of the conductivity, lithium storage performance, and rate capability of the negative electrode sheet 10. In this embodiment, the compaction density of the negative electrode sheet 10 is 0.8 g / cm³. 3 Meanwhile, the areal density of the negative electrode 10 is 4.2 mg / cm³. 2 This allows the thickness D1 of the first coating surface 111A of the first surface 111 of the negative electrode current collector 11 and the thickness D2 of the second coating surface 112A of the second surface 112 of the negative electrode current collector 11 on the negative electrode sheet 10 provided by the present invention to be controlled between 20μm and 35μm. This achieves a balance between energy density and rate performance, satisfying both the requirements of high-capacity batteries and high-rate charge / discharge performance. Consequently, the negative electrode sheet 10 using the aforementioned silicon-based active material can achieve a relative balance between battery capacity and battery rate. Under the premise that the unit areal density of the negative electrode sheet 10 remains constant, the greater the compaction density, the smaller the thickness D1 of the first coating surface 111A (the thickness D2 of the second coating surface 112A), and vice versa.

[0091] When the compaction density of the negative electrode 10 is greater than 1.0 g / cm³ 3 When the silicon-carbon particles in the silicon-based active material of the negative electrode break down, the lithium storage capacity and conductivity of the negative electrode 10 will be affected. When the compaction density of the negative electrode 10 is less than 0.6 g / cm³... 3 At this time, the silicon-based active material of the negative electrode is loosely packed and the layer thickness increases, which is not conducive to the cyclic migration of lithium ions during battery charging and discharging. The internal resistance of the negative electrode 10 increases and the conductivity decreases.

[0092] In the negative electrode 10 provided by the present invention, the area of ​​the first coating surface 111A of the first surface 111 of the negative electrode 10 is larger than the area of ​​the second coating surface 112A of the second surface 112. During the winding process of the battery cell, the second surface 112 is located on the outer side of the winding, and the first surface 111 is located on the inner side of the winding, that is, the first coating surface 111A faces the positive electrode 20, and the second coating surface 112A faces the housing 50. Therefore, in order to ensure that the active material layers between the positive electrode 20 and the negative electrode 10 can make full use of the spatial interaction during winding, the surface area of ​​the active material layer on the first surface 111 located on the inner side of the winding (the first coating surface 111A) should be fully utilized. However, the active material layer on the second surface 112 located on the outer side of the winding is opposite to the steel shell at the end of the winding. For cost-saving considerations, the second surface 112 near the end of the winding does not need to be coated with active material. Therefore, the area of ​​the first coating surface 111A is larger than the area of ​​the second coating surface 112A.

[0093] In one embodiment, the area of ​​the first coating surface 111A is 1.05-1.1 times the area of ​​the second coating surface 112A. For example, in the negative electrode sheet 10, the area of ​​the first coating surface 111A is 1.05, 1.06, 1.07, 1.08, 1.09, 1.1 times the area of ​​the second coating surface 112A, or any value between any two of the above ranges. As shown in Figures 1 and 2, the negative electrode silicon-based active material coated on the first surface 111 and the second surface 112 of the negative electrode sheet 10 has the same dimension in the width direction Y, and both completely coat the width direction of the negative electrode current collector 11. The dimension of the negative electrode silicon-based active material in the length direction X on the first surface 111 is different from the dimension of the negative electrode silicon-based active material in the length direction X on the second surface 112. The dimension coated on the first surface 111 is larger than the dimension coated on the second surface 112, and the area of ​​the first coating surface 111A is controlled to be between 1.05-1.1 times the area of ​​the second coating surface 112A. By controlling the difference in the coating area of ​​the negative electrode 10 on the first surface 111 and the second surface 112, the silicon-based active material of the negative electrode can be saved on the one hand, and the assembly ratio can be controlled by adjusting the two coating areas on the other hand. If the ratio of the area of ​​the first coating surface 111A to the area of ​​the second coating surface 112A exceeds 1.1, the coating area of ​​the first coating surface 111A increases. The area of ​​the coating edge will be opposite to the steel shell at the shell after the shell is assembled, and will not interact with the positive electrode 20. This will result in excessive coating material, which is not conducive to cost control. If the ratio of the area of ​​the first coating surface 111A to the area of ​​the second coating surface 112A is less than 1.05, the purpose of controlling the assembly ratio cannot be achieved.

[0094] Meanwhile, in order to improve the conductivity of the negative electrode 10 provided by the present invention, the negative electrode 10 provided by the present invention can adopt a bipolar structure design or a multipolar structure design to improve the conductivity of the negative electrode 10.

[0095] In one embodiment, as shown in Figures 1-3, the negative electrode 10 adopts a bipolar tab structure design. The negative electrode tabs on the negative electrode 10 include a first tab 12 and a second tab 13. The bipolar tab structure design can further improve the discharge rate of the battery cell using the negative electrode 10, thereby meeting the requirements of high-rate (3C / 6C discharge).

[0096] As shown in Figures 1 and 2, in this embodiment, the first tab 12 and the second tab 13 of the negative electrode sheet 10 are spaced apart along the length direction X of the negative electrode current collector 11 and are respectively located on the first uncoated surface 111B and the second uncoated surface 112B. That is, the first tab 12 and the second tab 13 are located on different surfaces along the thickness direction Z of the negative electrode current collector 11. During the winding process of the negative electrode sheet 10, the second tab 13 is located at the front end of the winding, and the first tab 12 is located at the rear end of the winding. When the winding is completed, the second tab 13 is located at the center of the core, while the first tab 12 is located on the periphery of the core. The negative electrode 10 adopts a bipolar tab design and, in conjunction with the control of the thickness of the negative electrode silicon-based active material coated on both sides of the negative electrode current collector 11, can reduce the migration path of lithium ions inside the negative electrode 10, reduce the internal resistance of the negative electrode 10, thereby increasing the current of the negative electrode 10, and further improving the conductivity of the negative electrode 10, so that the single cell using the negative electrode 10 of the present invention can achieve high rate (3C / 6C) discharge.

[0097] As shown in Figures 1 and 2, the negative electrode current collector 11 provided by the present invention has two parallel first side edges 113 and second side edges 114 along the width direction Y. The first tab 12 and second tab 13 of the negative electrode sheet 10 provided by the present invention are both arranged perpendicular to the first side edge 113 of the negative electrode current collector 11. The first tab 12 is disposed on the second surface 112, and the second tab 13 is disposed on the first surface 111. The first tab 12 and the second tab 13 are located on different surfaces of the negative electrode current collector 11.

[0098] Specifically, the first tab 12 includes a first conductive sheet 121 welded to the second uncoated surface 112B and extending outward from the first side 113. The first conductive sheet 121 is fixed to the second uncoated surface 112B of the second surface 112 of the negative electrode current collector 11 by ultrasonic welding, achieving both a fixed connection and an electrical connection with the negative electrode current collector 11, forming a first ultrasonic weld mark 121A. The first tab 12 is the main current-flow channel on the negative electrode sheet 10 provided by this invention. The first tab 12 is located at the end of the winding of the negative electrode sheet 10; during winding, the first tab 12 is located at the outer end of the winding core.

[0099] The first tab 12 of the negative electrode sheet 10 provided by the present invention further includes two first insulating sheets 122 respectively attached to the first uncoated surface 111B and the second uncoated surface 112B, and extending outward from the first side 113. The two first insulating sheets 122 are respectively located on the first surface 111 and the second surface 112 of the negative electrode current collector 11, and both first insulating sheets 122 are located on the blank area not coated by the negative electrode silicon-based active material. The two first insulating sheets 122 completely cover all areas of the first conductive sheet 121 on the negative electrode current collector 11. As shown in Figures 1 and 2, the projection surfaces of the two first insulating sheets 122 on the negative electrode current collector 11 overlap, and the first conductive sheet 121 is located between the two first insulating sheets 122. The first insulating sheet 122 is made of polyimide (PI) material and is attached to completely cover the area of ​​the first conductive sheet 121 on the negative electrode current collector 11, thereby preventing the first conductive sheet 121 from contacting and short-circuiting with the positive electrode sheet 20 during the winding process. To ensure that the two first insulating sheets 122 completely cover the first conductive sheet 121, the width A2 of the first insulating sheet 122 is 1.5-2.5 times the width A1 of the first conductive sheet 121. Generally, to meet the overcurrent requirements of the tab, the width A1 of the first conductive sheet 121 is 3mm-6mm, and correspondingly, the width A2 of the first insulating sheet 122 is between 4.5mm-15mm. In this embodiment, the first conductive sheet 121 is a 4mm wide copper-plated nickel tab. The first insulating sheet 122 is an 8mm wide PI electrode protective tape.

[0100] In one embodiment, to ensure that the first conductive sheet 121 does not short-circuit when the first tab 12 is wound around the negative electrode 10, the length H1 of the first insulating sheet 122 extending outward along the first side 113 is 0.5mm-3mm. If the length H1 is less than 0.5mm, the first conductive sheet 121 is prone to short-circuiting by touching the positive current collector 21 or the negative current collector 11 during winding. If the length H1 is greater than 3mm, it is not conducive to the electrical connection between the first tab 12 and the second tab 13. In this embodiment, the outward extension length H1 of the first insulating sheet 122 is 1mm, which ensures that the first conductive sheet 121 is insulated from the current collector during winding and does not hinder the electrical connection between the first conductive sheet 121 and the second tab 13.

[0101] In the negative electrode 10 provided by this invention, the first conductive sheet 121 is located at the end of the winding of the negative electrode 10. Therefore, the distance L1 between the first conductive sheet 121 and the side of the second coating surface 112A is 45mm-65mm. The distance L1 between the first conductive sheet 121 and the side of the second coating surface 112A is approximately the outer diameter of the outermost ring when the battery cell is wound, defining the distance L1 between the first conductive sheet 121 and the second coating surface 112A. This distance L1 is related to the thickness (D1 and / or D2) of the active material layer on the negative electrode 10. The greater the thickness (D1 and / or D2) of the active material layer of the negative electrode 10, the greater the distance L1; conversely, the smaller the thickness (D1 and / or D2) of the active material layer of the negative electrode 10, the smaller the distance L1. By controlling this distance L1, the position of the first tab 12 at the end of the negative electrode sheet 10 is determined, and the edge position of the coating area of ​​the second coating surface 112A is also determined, ensuring that when the negative electrode sheet 10 is wound for the last turn, the second surface 112 of the last turn is as close as possible to the second uncoated surface 112B. In this embodiment, the distance L1 between the first conductive sheet 121 and the side of the second coating surface 112A is 55mm.

[0102] In one embodiment, as shown in FIG1, the second tab 13 is a second conductive sheet 131 welded to the first coating surface 111A and extending outward from the first side 113. The second conductive sheet 131 is welded and fixed to the negative electrode current collector 11 to form a second ultrasonic weld mark 131A. The second tab 13 is located at the foremost end of the negative electrode sheet 10 during winding. The second tab 13 is an auxiliary tab added to the negative electrode sheet 10 provided by the present invention to increase the current carrying capacity. After winding, the second conductive sheet 131 will be directly fixedly connected to the first conductive sheet 121 by welding to achieve electrical connection.

[0103] In one embodiment, the width A3 of the second conductive piece 131 in the negative electrode 10 provided by the present invention is 0.5-1 times the width A1 of the first conductive piece 121. If the width A3 of the second conductive piece 131 is too small, it cannot meet the overcurrent requirement of the discharge rate, and the sum of the current between the first conductive piece 121 and the second conductive piece 131 cannot meet the high-rate charge and discharge requirements of the negative electrode 10. If the width A3 of the second conductive piece 131 is too large, it exceeds the rate requirement and is not conducive to cost control. In this embodiment, the first conductive piece 121 is a copper-plated nickel tab with a width of 4 mm. The second conductive piece 131 is a copper-plated nickel tab with a width of 3 mm. The width A3 of the second conductive piece 131 is 0.75 times the width A1 of the first conductive piece 121.

[0104] To ensure the stability of the electrical connection of the bipolar tab structure in the negative electrode 10, the first conductive sheet 121 of the negative electrode 10 provided by this invention extends outward along the first side 113 by a length of A, and the second conductive sheet 131 extends outward along the first side 113 by a length of B. The length relationship between the two should satisfy the following conditions: A > B and AB > 8 mm. The first conductive sheet 121 is located on the outside of the winding core after winding, and the second conductive sheet 131 is located at the center of the winding core. It is necessary to first weld the second conductive sheet 131 to the first conductive sheet 121, and then weld the first conductive sheet 121 to the housing 50 to achieve electrical connection. Therefore, to ensure the stability of the welding between the first conductive sheet 121 and the second conductive sheet 131, the length of the first conductive sheet 121 extending outward from the negative electrode current collector 11 is A, which is 16 mm in this embodiment, and the length of the second conductive sheet 131 extending outward from the negative electrode current collector 11 is B, which is 6 mm in this embodiment. The first conductive sheet 121 extends by a length A greater than the second conductive sheet 131 extends by a length B, and the difference in the distance between the two extends by 10mm, so as to ensure that the first electrode 12 and the second electrode 13 have enough overlap space for welding and fixing.

[0105] As shown in Figure 1, the distance L2 between the second conductive sheet 131 and the side of the first coating surface 111A is 15mm-20mm. This distance L2 determines the starting position of the first coating surface 111A on the first surface 111 and provides sufficient space for the first insulating sheet 122 of the first electrode 12 to be attached. In this embodiment, the distance L2 between the second conductive sheet 131 and the side of the first coating surface 111A is 17mm.

[0106] In one embodiment, the negative electrode 10 provided by the present invention can also adopt a multi-tab structure design. The negative electrode tabs on the negative electrode 10 include a main tab (not shown in the figure) disposed on a first uncoated surface 111B or a second uncoated surface 112B, and a plurality of secondary tabs (not shown in the figure) disposed on the first uncoated surface 111B and / or the second uncoated surface 112B, with the plurality of secondary tabs arranged at intervals along the length Y direction of the negative electrode current collector 11. The multi-tab structure design of the negative electrode 10 provided by the present invention can further improve the discharge rate of the battery cell using the negative electrode 10, thereby meeting the requirements of high rate (3C / 6C discharge) or even ultra-high rate (9C).

[0107] In one embodiment, when the negative electrode sheet 10 provided by the present invention adopts a multi-tab structure design, the main tab and several secondary tabs extend outward based on the negative electrode current collector 11, and the main tab and several secondary tabs extend outward in the same direction based on the negative electrode current collector 11, that is, the main tab and several secondary tabs extend towards one side of the negative electrode current collector 11 in the width direction. When the negative electrode sheet 10 provided by the present invention is wound into a cylindrical core, several secondary tabs and the main tab are located on the same side of the negative electrode current collector 11.

[0108] In one embodiment, the negative electrode sheet 10 provided by the present invention adopts a multi-tab structure design. The length of the main tab extending outward based on the negative electrode current collector 11 is greater than the length of the secondary tab extending outward based on the negative electrode current collector 11. That is, the length of the main tab outside the negative electrode current collector 11 is greater than the length of the secondary tab outside the negative electrode current collector 11. After the negative electrode sheet 10 is wound, all the secondary tabs are stacked together to form a negative electrode tab, which is then aligned with the main tab and fixed together by ultrasonic welding to form a negative electrode tab. The negative electrode tab is then fixedly connected to the battery casing 50.

[0109] The present invention provides a negative electrode sheet 10, which controls the thickness of the negative electrode silicon-based active material on the negative electrode current collector 11 by controlling the areal density and compaction density of the negative electrode sheet 10. This reduces the adverse effects caused by the expansion of the negative electrode silicon-based active material due to charging and discharging. While ensuring the lithium storage capacity of the negative electrode sheet 10, the thickness of the coating is minimized as much as possible to reduce the migration distance of lithium ions during charging and discharging, improve the migration resistance of lithium ions during charging and discharging, reduce the internal resistance of the negative electrode sheet 10, and achieve the purpose of increasing the current. Combined with the structure design of the negative electrode with bipolar or multipolar tabs, the conductivity of the negative electrode sheet 10 is improved.

[0110] Secondly, the present invention also provides a cylindrical battery 100. Figure 4 shows a three-dimensional structural schematic diagram of the cylindrical battery 100 provided by the present invention. The cylindrical battery 100 provided by the present invention includes a housing 50, a cap 40, an electrolyte disposed within the housing 50, and a cylindrical core. The housing 50 is a cylindrical steel shell with a vertically continuous structure, and the cylindrical core and electrolyte are both disposed inside the housing 50. The cap 40 is located at the top end of the housing 50 along its length and is used to seal the upper and lower openings of the housing 50. The cap 40 is electrically connected to the positive electrode tab 22 of the positive electrode 20, and the negative electrode tab of the negative electrode 10 is electrically connected to the end of the housing 50.

[0111] Further, as shown in Figure 4, the cylindrical core includes a positive electrode 20, a separator 30, and the aforementioned negative electrode 10. The cylindrical battery 100 provided by this invention uses the aforementioned negative electrode 10. In this embodiment, the negative electrode 10 adopts a double-tab structure design. The second tab 13 of the wound negative electrode 10 is welded to the first tab 12 and fixed to the housing 50 by welding the first tab 12. Before being fixed to the housing 50, the first tab 12 and the second tab 13 on the negative electrode 10 are first fixed by ultrasonic welding to form a negative electrode tab, and then fixed to the housing 50 by resistance welding.

[0112] The cylindrical battery 100 provided by this invention has a cylindrical core assembled inside a housing 50. The diameter of the cylindrical core is 0.96-0.99 times the inner diameter of the housing 50. The larger the ratio of the core's diameter to the inner diameter of the housing 50, the larger the assembly ratio of the cylindrical battery 100. By increasing this assembly ratio, the structural strength of the cylindrical core can be improved, thereby enhancing the mechanical properties of the negative electrode 10 and positive electrode 20 in the cylindrical core during formation and battery charge-discharge cycles. In the cylindrical battery 100 provided by this invention, the ratio between the diameter of the cylindrical core and the inner diameter of the housing 50 is the ratio between the unformed cylindrical core and the housing 50. During battery processing, after the cylindrical core is installed in the housing 50, and the cylindrical battery 100 is sealed and formed, both the negative electrode 10 and the positive electrode 20 of the cylindrical core will expand.

[0113] In one embodiment, the cylindrical battery 100 provided by the present invention further includes a positive electrode 20. Figure 5 shows a schematic diagram of the structure of the positive electrode 20 provided in the cylindrical battery 100 of the present invention. The positive electrode 20 includes a positive current collector 21, a positive electrode tab 22 disposed on the positive current collector 21, and a positive active material.

[0114] The positive current collector 21 in the positive electrode sheet 20 provided by the present invention includes a third surface 211 and a fourth surface 212 disposed along its own thickness direction Z; the positive active material is disposed on the third surface 211 and the fourth surface 212, that is, the positive active material is respectively located on two opposite surfaces of the positive current collector 21. The positive active material in the positive electrode sheet 20 provided by the present invention has the chemical formula LiNi. x Co y Mn 1-x-y The material of O2 (where x and y take values ​​from 0 to 1).

[0115] In one embodiment, the areal density of the positive electrode 20 is 28-33 mg / cm³. 2 For example, the areal density of the positive electrode 20 is 28 mg / cm³.2 29mg / cm 2 30mg / cm 2 31mg / cm 2 32mg / cm 2 33mg / cm 2 Or any value between any two of the above ranges. By controlling the areal density per unit area of ​​the positive electrode 20, the battery capacity of a single cell can be regulated. When the areal density per unit area of ​​the positive electrode 20 is greater than 33 mg / cm³, the battery capacity of the single cell can be controlled. 2 When the areal density of the positive electrode 20 is too high, the assembly ratio is greater than 1, resulting in a battery size larger than the cylindrical battery 100 steel casing size. When the areal density of the positive electrode 20 is less than 23 mg / cm³... 2 At this time, the assembly ratio is too low, resulting in insufficient utilization of the internal space of the cylindrical battery 100's steel casing. In this embodiment, the areal density of the positive electrode 20 is 30 mg / cm³. 2 This results in a larger capacity for the positive electrode 20 using the aforementioned positive electrode active material and the cylindrical battery 100 provided by the present invention.

[0116] In one embodiment, the compaction density of the positive electrode 20 is 3.2-3.8 g / cm³. 3 For example, the compaction density of the positive electrode 20 is 3.2 g / cm³. 3 3.3g / cm 3 3.4g / cm 3 3.5g / cm 3 3.6g / cm 3 3.7g / cm 3 3.8g / cm 3 Or any value between any two of the above ranges. By controlling the compaction density of the positive electrode 20, the thickness of the active material layer on the positive electrode 20 can be controlled. If the compaction density of the positive electrode 20 is too high, on the one hand, it will reduce the absorption capacity of the electrolyte, thus affecting the battery capacity; on the other hand, it will limit the rapid transport capacity of lithium ions. If the compaction density of the positive electrode 20 is too low, it will reduce the overall energy density of the single cell and fail to meet the high capacity requirements.

[0117] In one embodiment, the positive electrode active material of the cylindrical battery 100 provided by the present invention is coated on the third surface 211 of the positive electrode current collector 21 to form a plurality of third coating surfaces 211A, and a first blank area 211B is formed between two adjacent third coating surfaces 211A. The positive electrode active material is coated on the fourth surface 212 of the positive electrode current collector 21 to form a plurality of fourth coating surfaces 212A, and a second blank area 212B is formed between two adjacent fourth coating surfaces 212A. The number of third coating surfaces 211A and fourth coating surfaces 212A on the positive electrode current collector 21 is related to the arrangement of the positive electrode tabs 22, that is, the first blank area 211B between two adjacent third coating surfaces 211A and the second blank area 212B between two adjacent fourth coating surfaces 212A are both used to arrange the positive electrode tabs 22. The positive electrode tabs 22 adopt a single tab, double tab or multi tab structure design, which is determined by the actual needs of the cylindrical battery 100 provided by the present invention.

[0118] In one embodiment, the thickness D3 of the third coating surface 211A in the positive electrode sheet 20 of the cylindrical battery 100 provided by the present invention is the thickness of the positive electrode active material formed on the positive electrode current collector 21 after coating and rolling. The thickness of the third coating surface 211A on the positive electrode sheet 20 is 35μm-55μm. The first blank area 211B is the uncoated area, that is, the surface of the positive electrode current collector 21 itself. Furthermore, the positive electrode active material is coated on the fourth surface 212 of the positive electrode current collector 21 to form two fourth coating surfaces 212A, and a second blank area 212B is formed between the two fourth coating surfaces 212A. The two fourth coating surfaces 212A are symmetrically arranged on both sides of the second blank area 212B, and the thickness D4 of the fourth coating surface 212A is 35μm-55μm. The structures on the third surface 211 and the fourth surface 212 of the positive electrode sheet 20 are the same. The thickness D4 of the fourth coating surface 212A is the thickness of the positive electrode active material formed on the positive electrode current collector 21 after coating and rolling. The thickness D3 of the third coating surface 211A and the thickness D4 of the fourth coating surface 212A can be the same or different, and the thickness can be adjusted according to actual needs. However, the thickness D3 of the third coating surface 211A and the thickness D4 of the fourth coating surface 212A are both controlled between 35μm and 55μm.

[0119] In the cylindrical battery 100 provided by this invention, the thickness of the positive electrode 20 is the sum of the thickness D3 of the third coating surface 211A, the thickness D4 of the fourth coating surface 212A, and the thickness of the positive current collector 21. In this embodiment, the positive current collector 21 is made of aluminum foil with a thickness of 15 μm. Therefore, in the cylindrical battery 100 provided by this invention, the thickness of the positive electrode 20 is between 85 μm and 125 μm. The positive current collector 21 can also be made of aluminum foil with a thickness of 10 μm, 12 μm, or 20 μm. The thickness of the positive current collector 21 is not limited here and can be adjusted according to actual needs. The thickness of the positive electrode 20 provided by this invention can be adapted to different materials of the positive current collector 21.

[0120] If the thickness D3 (D4) of the positive electrode active material on the positive electrode current collector 21 is less than 35 μm, it cannot meet the requirements for high battery capacity. If the thickness D3 (D4) of the positive electrode active material on the positive electrode current collector 21 is greater than 55 μm, the effective utilization rate of the positive electrode active material will be reduced, affecting the charge and discharge efficiency of the battery. The electrolyte cannot penetrate into the interior of the electrode, resulting in a decrease in the electrochemical reaction rate and thus reducing the actual capacity of the single cell.

[0121] In one embodiment, as shown in FIG5, in the cylindrical battery 100 provided by the present invention, the positive electrode current collector 21 has two parallel third side 213 and fourth side 214 along the width direction Y. During winding, the third side 213 of the positive electrode current collector 21 and the second side 114 of the negative electrode current collector 11 are located on the same side, and the fourth side 214 of the positive electrode current collector 21 and the first side 113 of the negative electrode current collector 11 are located on the same side.

[0122] In one embodiment, the positive electrode tab 22 of the positive electrode plate 20 in the cylindrical battery 100 provided by the present invention includes a plurality of third conductive sheets 221 welded to the first blank area 211B and extending outward from the third side 213. The number of third conductive sheets 221 in the positive electrode tab 22 is determined according to the actual current carrying capacity required by the cylindrical battery 100. The positive electrode plate 20 provided by the present invention also includes a plurality of pairs of second insulating sheets 222 respectively attached to the first blank area 211B and the second blank area 212B and extending outward from the third side. The second insulating sheets 222 appear in pairs, and the projection surfaces of each pair of second insulating sheets 222 on the positive current collector 21 overlap with each other, with the third conductive sheet 221 located between a pair of second insulating sheets 222. A pair of second insulating sheets 222 are respectively disposed on the third surface 211 and the fourth surface 212 of the positive electrode current collector 21, and each second insulating sheet 222 completely covers the first blank area 211B or the second blank area 212B. The number of second insulating sheets 222 on the positive electrode plate 20 is related to the number of third conductive sheets 221, with one pair of second insulating sheets 222 cooperating with one third conductive sheet 221. Each pair of second insulating sheets 222 is attached to one third conductive sheet 221, covering the connection between the third conductive sheet 221 and the positive electrode current collector 21 from both sides of the positive electrode current collector 21.

[0123] In this embodiment, as shown in FIG5, the third surface 211 is provided with two third coating surfaces 211A and a first blank area 211B; the two third coating surfaces 211A are symmetrically arranged on both sides of the first blank area 211B. That is, the first blank area 211B is located between the two third coating surfaces 211A, and the two third coating surfaces 211A have the same structure. Correspondingly, in this embodiment, the fourth surface 212 is provided with two fourth coating surfaces 212A and a second blank area 212B, and the two fourth coating surfaces 212A are symmetrically arranged on both sides of the second blank area 212B. That is, the first blank area 211B is located between the two fourth coating surfaces 212A, and the two second blank areas 212B have the same structure.

[0124] In this embodiment, the third conductive sheet 221 of the positive electrode 20 in the cylindrical battery 100 is first ultrasonically welded to the positive current collector 21 to form a third ultrasonic weld mark 221A. Then, a pair of second insulating sheets 222 are attached from the two sides of the positive current collector 21 to the uncoated areas of the positive current collector 21, completely covering the two uncoated areas of the positive current collector 21. In this embodiment, the second insulating sheet 222 is made of insulating tape with a width of 10mm. Furthermore, as shown in FIG5, in this embodiment, the positive electrode 20 adopts a single tab structure, and the tab in the positive electrode 20 is centrally located, that is, the positive tab 22 on the positive electrode 20 is located in the center of the positive current collector 21. After winding, the positive tab 22 of the positive electrode 20 is welded to the cap 40. The positive electrode 20 is provided with only one tab, and the tab is directly fixed to the cap 40 by laser welding.

[0125] The width of the positive electrode tab 22 of the positive electrode 20 provided by this invention is the same as the width of the negative electrode tab of the negative electrode 10. That is, the width A4 of the third conductive piece 221 in the positive electrode 20 is the same as the width A1 of the first conductive piece 121 in the negative electrode 10. In this embodiment, the third conductive piece 221 in the positive electrode 20 is an aluminum tab with a width of 4mm. The tab width A4 of the third conductive piece 221 of the positive electrode 20 is the same as the tab width A1 of the first conductive piece 121 of the negative electrode, in order to meet the high current requirements of the cylindrical battery 100.

[0126] To meet the welding and fixing requirements between the positive electrode tab 22 and the positive current collector 21, the width of the first blank area 211B and the second blank area 212B is at least 2mm larger than the width of the positive electrode tab 22. The width A5 of the first blank area 211B and the second blank area 212B of the positive electrode sheet 20 is 7mm, which is 3mm larger than the third conductive sheet 221, and 1.5mm is reserved on each side of the positive electrode tab 22.

[0127] In one embodiment, to ensure that the positive electrode tab 22 does not come into contact with the negative electrode 10 during winding and cause a short circuit, the area of ​​the second insulating sheet 222 is larger than the area of ​​the first blank area 211B or the second blank area 212B of the positive current collector 21. That is, the width A6 of the second insulating sheet 222 is greater than the width A5 of the first blank area 211B. Furthermore, the width A6 of the second insulating sheet 222 should be greater than the width of the second blank area 212B. Specifically, the width A6 of the second insulating sheet 222 is 2mm-5mm larger than the width A5 of the first blank area 211B. In this embodiment, the width A6 of the second insulating sheet 222 is 10mm, and the width A5 of the first blank area 211B is 7mm.

[0128] In one embodiment, the second insulating sheet 222 in the positive electrode 20 extends from both ends of the third side 213 and the fourth side 214 of the positive current collector 21. The length C of the second insulating sheet 222 extending outward along the third side 213 is 2mm-4mm, as shown in Figure 5. In this embodiment, the length C of the second insulating sheet 222 extending outward along the third side 213 is 2.5mm. The length D of the second insulating sheet 222 extending outward along the fourth side 214 is 0.2mm-1.0mm, as shown in Figure 5. In this embodiment, the length D of the second insulating sheet 222 extending outward along the fourth side 214 is 0.5mm.

[0129] In one embodiment, during winding, the first coating surface 111A of the negative electrode 10 faces the side of the positive electrode 20, and the length L3 of the first coating surface 111A is greater than the length L4 of the positive current collector 21 of the positive electrode 20, so that the active material layer on the negative electrode 10 can completely cover the active material layer of the positive electrode 20 during winding.

[0130] In one embodiment, the length of the negative electrode 10 in the cylindrical battery 100 provided by the present invention is 1190mm-1205mm; for example, the length of the negative electrode 10 in the cylindrical battery 100 provided by the present invention is 1190mm, 1193mm, 1195mm, 1196mm, 1198mm, 1200mm, 1202mm, 1204mm, 1105mm, or any value between any two of the above-mentioned ranges. In one embodiment, the length of the positive electrode 20 in the cylindrical battery 100 provided by the present invention is 1081mm-1091mm; for example, the length of the positive electrode 20 in the cylindrical battery 100 provided by the present invention is 1181mm, 1183mm, 1185mm, 1186mm, 1188mm, 1190mm, 1191mm, or any value between any two of the above-mentioned ranges. The cylindrical battery 100 provided by this invention has a capacity ratio (N / P ratio) of 1.03-1.05 between the positive electrode 20 and the negative electrode 10. The lengths of the negative electrode 10 and the positive electrode 20 in the cylindrical battery 100 provided by this invention meet the packaging dimensions of an 18650 battery and are suitable for the requirements of an 18650 cylindrical battery 100.

[0131] In one embodiment, the electrolyte injection volume is 5.6g-6.2g. For example, the electrolyte injection volume in the cylindrical battery 100 provided by the present invention is 5.6g, 5.7g, 5.8g, 5.9g, 6.0g, 6.1g, 6.2g, or any value between any two of the above ranges. The electrolyte injection volume is related to the assembly ratio of the cylindrical battery 100. The assembly ratio of the cylindrical battery 100 provided by the present invention is 0.96-0.99. The higher the assembly ratio, the lower the corresponding electrolyte injection volume; the lower the assembly ratio, the higher the corresponding electrolyte injection volume. When the electrolyte injection volume is below 5.6g, the capacity of the cylindrical battery 100 will decrease because insufficient electrolyte will prevent the active materials inside the battery from being fully utilized, the positive electrode capacity from being fully utilized, and lithium plating may occur at the negative electrode, thereby reducing the usable capacity of the battery. When the electrolyte injection volume is above 6.2g, the cap 40 will flip during charging and discharging.

[0132] As shown in Figure 7, the cylindrical battery 100 provided by this invention, when charged at 0.2C and discharged at 3C, retains a discharge capacity of more than 97% with a temperature rise of 20-35℃. When charged at 0.2C and discharged at 6C, it retains a discharge capacity of more than 95% with a temperature rise of 45-65℃.

[0133] The cylindrical battery 100 provided by this invention adopts the aforementioned negative electrode 10. Taking the 18650 cylindrical battery 100 as an example, by optimizing the structure, improving the system, and manufacturing process, the battery achieves both high capacity and high rate of return simultaneously, resulting in a significant improvement in battery energy density and power output capability. This provides the market with a more efficient and reliable energy solution, with broad application prospects and market value. By adopting the aforementioned negative electrode 10, the lithium-ion capacity of the negative electrode 10 is increased while the migration distance of lithium ions during the battery charge-discharge cycle is shortened. This allows the cylindrical battery 100 to maintain a capacity of over 3500mAh while maintaining a discharge capacity retention rate of over 97% and a temperature rise controlled within 20-35℃ when charging at 0.2C and discharging at 3C. When charging at 0.2C and discharging at 6C, the discharge capacity retention rate is over 95% and the temperature rise is controlled within 45-65℃.

[0134] In addition, the present invention also provides a battery pack comprising two or more of the aforementioned cylindrical batteries 100, wherein the two or more cylindrical batteries 100 are electrically connected in series or in parallel. The specific number of cylindrical batteries 100 included in the battery pack can be adaptively selected by those skilled in the art based on the actual application of the battery pack and the battery capacity.

[0135] The battery pack provided by the present invention uses the above-mentioned high-capacity, high-rate cylindrical battery 100, which improves the overall electrical performance of the battery pack and achieves a high-capacity, high-rate battery pack.

[0136] In addition, the present invention also provides a power tool including the aforementioned battery pack. This power tool includes at least one of the cylindrical battery 100 or battery pack provided by the present invention. The cylindrical battery 100 or battery pack can be used as a power source for the power tool, or as an energy storage unit for the power tool. This power tool includes, but is not limited to: mobile devices (e.g., mobile phones, tablets, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric trucks, electric golf carts, electric scooters, etc.), electric boats, and electric equipment (lighting tools, electric shavers, electric repair tools, electric screwdrivers, electric lawnmowers, etc.).

[0137] The present invention provides an electric tool that uses the aforementioned high-capacity, high-rate battery pack, thereby improving the working stability of the electric tool.

[0138] The present invention will be further described in detail below with reference to embodiments and comparative examples.

[0139] The following describes embodiments of this application. The facts described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Specific techniques or conditions are not specified in the embodiments; they are performed according to techniques or conditions described in the literature in the art or according to product instructions. All reagents used, or those whose manufacturers are not specified, are conventional products that can be obtained commercially.

[0140] 100 cylindrical batteries

[0141] Example 1:

[0142] (1) Preparation of negative electrode 10:

[0143] Silicon carbon was used as the silicon-based active material for the negative electrode. It was mixed with binders PAA, CNT, and graphene in deionized water at a mass ratio of 91.27:1:2:2 to form a uniform negative electrode slurry. The slurry was prepared at a concentration of 4.2 mg / cm³. 2The areal density is double-coated on the first surface 111 and the second surface 112 of a copper foil with a thickness of 8μm and a length of 1190mm. The coating length of the first surface 111 is 1145mm, with a blank length of 10mm at one end and a blank length of 35mm at the other end. The coating length of the second surface 112 is 1091mm, with a blank length of 64mm at one end and a blank length of 35mm at the other end. After cold pressing, it is cut into an electrode sheet with a width of 59mm, a thickness of 60μm, and a length of 1090mm. A second electrode tab 13 is welded to the first uncoated surface 111B of the first surface 111 of the negative electrode sheet 10 (35mm). After welding the first electrode tab 12 to the second uncoated surface 112B of the second surface 112 of the negative electrode sheet 10 (10mm), a negative electrode sheet 10 with a negative electrode silicon-based active material attached to the surface is obtained. The specific capacity of the negative electrode silicon-based active material in the negative electrode sheet 10 is 1280mAh / g.

[0144] (2) Preparation of positive electrode 20:

[0145] Using NCM811 as the positive electrode active material, it was mixed with binder PVDF and conductive agents SP, SWCNT, and MWCNT in NMP at a mass ratio of 96:1.14:1.5:0.06:0.8 to prepare a positive electrode slurry. The slurry was prepared at a concentration of 30 mg / cm³. 2 The areal density is determined by coating the positive electrode slurry on both sides of an aluminum foil with a thickness of 15μm and a length of 1082mm. A 7mm blank area is left in the middle of the front side of the positive electrode sheet along the length direction. The positive electrode sheet is then cold-pressed and cut into a positive electrode sheet with a width of 57±1mm, a thickness of 103μm, and a length of 1082mm. Positive electrode tabs 22 are then welded into the blank area to obtain a positive electrode sheet 20 with positive electrode active material attached to the surface.

[0146] (3) Preparation of diaphragm 30

[0147] The membrane selected is a 30mm thick membrane with a thickness of 16μm, made of a three-layer polypropylene / polyethylene / polypropylene (PP / PE / PP) membrane, with a length of 265mm and a width of 61mm.

[0148] (4) Preparation of electrolyte

[0149] In an argon-filled glove box (moisture < 10 ppm, oxygen < 10 ppm), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and fluoroethylene carbonate (FEC) were mixed in a mass ratio of DEC:EMC:EC:FEC = 40:30:15:15 to obtain an organic solvent. Lithium salt LiPF6 was then dissolved in the mixed organic solvent to prepare a 1.0 mol / L solution. Triphenyl phosphate (TPP) and 2,6-di-tert-butyl-p-cresol (BHT) were then added and mixed thoroughly to obtain the electrolyte.

[0150] (5) Assembly of cylindrical battery 100

[0151] (a): Place the prepared negative electrode 10 and positive electrode 20 into a vacuum oven and bake to remove moisture;

[0152] (b): The baked negative electrode 10, positive electrode 20, and separator 30 are stacked in the order of "separator / negative electrode / separator / positive electrode" and wound into a cylindrical core. When winding, first wind one end of the second tab 13 connected to the negative electrode 10, while ensuring that the first coating surface 111A of the negative electrode 10 completely covers the third coating surface 211A of the positive electrode 20.

[0153] (c): Assemble the cylindrical core according to the ratio of the diameter of the cylindrical core to the inner diameter of the housing 50 being 0.98, and fit the cylindrical core into the housing 50.

[0154] (d): First, weld the second electrode tab 13 of the negative electrode to the first electrode tab 12 to form the negative electrode tab, and then weld the negative electrode tab to the bottom of the steel shell;

[0155] (e): The positive electrode tab 22 is soldered to the cap 40 to form a semi-finished battery cell;

[0156] (f): Baking the semi-finished battery cells, injecting 6.0g of electrolyte according to the liquid injection process, sealing and wetting, charging and forming, and assembling into 18650 type batteries.

[0157] Examples 2-4:

[0158] Examples 2-4 illustrate a cylindrical battery 100 disclosed in this invention, including most of the operations in Example 1, except that the assembly ratio of the cylindrical battery 100 is different in Examples 2-4, that is, the ratio between the diameter of the core and the inner diameter of the casing 50 in the cylindrical battery 100 is different. Specifically, the assembly ratio in Example 2 is 0.96, the assembly ratio in Example 3 is 0.97, and the assembly ratio in Example 4 is 0.99. The specific parameters are based on the data shown in Table 1 for each example.

[0159] Examples 5-9:

[0160] Examples 5-9 illustrate a cylindrical battery 100 disclosed in this invention, including most of the operations in Example 1, except that the different selection of materials in the negative electrode silicon-based active material in Examples 5-9 leads to different mass percentage contents of silicon. Specifically, when silicon-carbon and graphite are used as negative electrode silicon-based active materials, the different contents of silicon-carbon in the negative electrode silicon-based active material result in different mass percentage contents of silicon. Alternatively, when silicon suboxide is used as the negative electrode silicon-based active material, the mass percentage contents of silicon also differ. The specific parameters are based on the data shown in Table 1 for each example.

[0161] Examples 10-12:

[0162] Examples 10-12 illustrate a cylindrical battery 100 disclosed in this invention, including most of the operations in Example 1, except that the compaction density of the silicon-based active material of the negative electrode is different in Examples 10-12, resulting in different thicknesses of the 10 layers of the negative electrode sheet. The specific parameters are based on the data shown in Table 1 for each example.

[0163] Examples 13-14:

[0164] Examples 13-14 illustrate a cylindrical battery 100 disclosed in this invention, including most of the operations in Example 1, except that the compaction density of the positive electrode 20 is different in Examples 13-14, resulting in different layer thicknesses of the positive electrode 20. The specific parameters are based on the data shown in Table 1 for each example.

[0165] Comparative Examples 1-2:

[0166] Comparative Examples 1-2 are used to illustrate the cylindrical battery 100 disclosed in this invention, including most of the operations in Example 1. The difference is that the materials selected in the negative electrode silicon-based active material in Comparative Examples 1-2 are different, resulting in different mass percentage contents of silicon in the negative electrode silicon-based active material. The specific parameters are based on the data shown in Table 1 for each example.

[0167] Comparative Examples 3-4:

[0168] Comparative Examples 3-4 are used to illustrate the cylindrical battery 100 disclosed in this invention, including most of the operations in Example 1. The difference is that the compaction density of the silicon-based active material of the negative electrode is different in Comparative Examples 3-4, which causes the thickness of the 10 layers of the negative electrode sheet to vary. The specific parameters are based on the data shown in Table 1 for each example.

[0169] Comparative Examples 5-6:

[0170] Comparative Examples 5-6 are used to illustrate a cylindrical battery 100 disclosed in this invention, including most of the operations in Example 1. The difference is that the compaction density of the positive electrode active material in Comparative Examples 5-6 is different, which causes the thickness of the 20 layers of positive electrode sheet to vary. The specific parameters are based on the data shown in Table 1 for each example.

[0171] Comparative Example 7:

[0172] Comparative Example 7 is used to illustrate a cylindrical battery 100 disclosed in this invention. It includes most of the operations in Example 1, except that the assembly ratio of the cylindrical battery 100 in Comparative Example 7 has been adjusted. The specific parameters are based on the data shown in Table 1 for each embodiment.

[0173] II. Performance testing of the cylindrical battery 100 obtained by the above preparation method.

[0174] (1) 0.2C discharge test method and battery capacity test

[0175] At an ambient temperature of 25℃, the battery was charged to 4.25V at a rate of 0.2C, then charged at a constant voltage until fully charged. After standing for 30 minutes, the battery was discharged to 2.3V at a rate of 0.2C. The discharge temperature rise and capacity utilization were recorded, and the discharge capacity was recorded as the nominal capacity of the cell.

[0176] (2) 3C discharge test method

[0177] At an ambient temperature of 25°C, the battery was charged to 4.25V at a rate of 0.2C, then charged at a constant voltage until fully charged. After resting for 30 minutes, it was discharged to 2.3V at a rate of 3C. The discharge temperature rise and capacity utilization were recorded.

[0178] (3) 6C discharge test method

[0179] At an ambient temperature of 25°C, the battery was charged to 4.25V at a rate of 0.2C, then charged at a constant voltage until fully charged. After resting for 30 minutes, it was discharged to 2.3V at a rate of 6C. The discharge temperature rise and capacity utilization were recorded.

[0180] III. Analysis of Test Results for Each Embodiment and Comparative Example

[0181] Cylindrical batteries 100 of each embodiment and comparative example were prepared according to the above method, and various performance parameters were measured. The results are shown in Table 1 below.

[0182] Table 1:

[0183] Figure 7 shows the electrical performance parameters of the cylindrical battery 100 prepared in Example 1 of the present invention. A comprehensive analysis of Figure 7 and the results of Example 1 in Table 1 shows that the cylindrical battery 100 prepared in Example 1 of the present invention exhibits the best overall performance. In Example 1, the silicon content in the silicon-based active material of the negative electrode is 65%, and the compaction density of the negative electrode sheet 10 is controlled at 0.8 g / cm³. 3 At that time, the coating thickness of the negative electrode silicon-based active material layer on the negative electrode 10 was approximately 26 μm, thus controlling the single-layer coating thickness of the negative electrode 10 to be between 20 μm and 35 μm. Meanwhile, the compaction density of the positive electrode 20 was 3.4 g / cm³. 3 At this time, the coating thickness of the positive electrode active material on the positive electrode sheet 20 is about 44 μm, so that the single-layer coating thickness of the positive electrode sheet 20 is controlled between 35 μm and 55 μm. Furthermore, under the above parameters, the cylindrical battery 100 fabricated with an assembly ratio of 0.98 not only meets the high-capacity requirement (battery capacity exceeding 3.5 Ah), reaching a capacity of 3.66 Ah, but also meets the high-rate requirement, exhibiting good electrical performance in both 3C and 6C discharge tests. Specifically, when charging at 0.2C and discharging at 3C, the discharge capacity retention rate is 98%, and the temperature rise is 22.4℃. When charging at 0.2C and discharging at 6C, the discharge capacity retention rate is 96%, and the temperature rise is 45.6℃.

[0184] In Examples 2-14 of this invention, different selections of silicon-based active materials for the negative electrode, and adjustments to parameters such as the silicon content ratio, negative electrode compaction density, and positive electrode compaction density, all ensured the high rate and high capacity requirements of the cylindrical battery 100. As can be seen from the test results in Table 1, compared to Comparative Examples 1-7, the cylindrical batteries 100 in Examples 2-14 showed better performance in performance tests (0.2C discharge, 3C discharge, 6C discharge) and battery capacity. The cylindrical batteries 100 in Comparative Examples 1-7 either failed to meet the high capacity requirement or the high rate requirement.

[0185] In the test results of Comparative Example 1, due to the use of a composite material of silicon-carbon and graphite in the silicon-based active material of the negative electrode, and the high graphite content, the silicon content in the silicon-based active material of the negative electrode is less than 40%, which leads to a reduction in the lithium storage capacity of the negative electrode in the cylindrical battery 100 of Comparative Example 1. In Comparative Example 1, not only is the battery capacity unable to meet the high capacity requirement (battery capacity exceeding 3.5Ah), but the layer thickness of its negative electrode sheet 10 is 83μm, and the thickness of a single layer of negative electrode active material is also greater than 35μm.

[0186] In the test results of Comparative Example 2, since the silicon-based active material of the negative electrode is made of silicon particles, the silicon content in the negative electrode active material is 92%. Although the battery capacity of 4.41Ah can meet the high capacity requirements of the battery, it cannot meet the high rate requirements when testing electrical performance parameters. During the 3C discharge test, the temperature rise reached 54.7℃, and it could not complete the 6C discharge test.

[0187] In the test results of Comparative Example 3, although the battery capacity was greatly improved due to the excessive compaction density of the negative electrode sheet 10, the layer thickness of the negative electrode sheet 10 was 46μm, and the thickness of a single layer of negative electrode active material was less than 20μm, which could not meet the requirements of high rate. Specifically, its electrical performance test results were poor, with a temperature rise of 38.3℃ during 3C discharge and 67.2℃ during 6C discharge, indicating excessively high discharge temperature rise.

[0188] In the test results of Comparative Example 4, due to the low compaction density of the negative electrode sheet 10, its battery capacity is only 3.08Ah, which cannot meet the requirements of high capacity (battery capacity exceeding 3.5Ah). Furthermore, the layer thickness of its negative electrode sheet 10 is 92μm, and the thickness of a single layer of negative electrode active material is also greater than 35μm.

[0189] In the test results of Comparative Example 5, due to the low compaction density of the positive electrode 20, the battery capacity was only 3.39Ah, which could not meet the requirements for high capacity (battery capacity exceeding 3.5Ah).

[0190] In the test results of Comparative Example 6, due to the excessive compaction density of the positive electrode 20, although the battery capacity met the requirements for high capacity, it could not meet the requirements for high rate. Specifically, its electrical performance test results were poor, with a temperature rise of 45.2℃ during 3C discharge and 68.4℃ during 6C discharge, indicating excessively high discharge temperature rise.

[0191] In the test results of Comparative Example 7, the battery capacity decreased due to the reduced assembly ratio of the cylindrical battery 100, with a capacity of only 3.37Ah, which could not meet the demand for high capacity (battery capacity exceeding 3.5Ah).

[0192] The above are merely preferred embodiments of the present invention and are 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 by, It includes a negative electrode current collector, a negative electrode tab disposed on the negative electrode current collector, and a negative electrode silicon-based active material; The negative electrode current collector includes a first surface and a second surface arranged along its own thickness direction; The negative electrode silicon-based active material is coated on the first surface of the negative electrode current collector to form a first coated surface and a first uncoated surface, wherein the thickness of the first coated surface is 20μm-35μm; The negative electrode silicon-based active material is coated on the second surface of the negative electrode current collector to form a second coated surface and a second uncoated surface, wherein the thickness of the second coated surface is 20μm-35μm; The negative electrode silicon-based active material contains silicon, and the mass percentage of silicon in the negative electrode silicon-based active material is 40-65%. The unit area density of the negative electrode sheet is 4.0-4.5 mg / cm 2 ; The compacted density of the negative electrode sheet is 0.6-1.0 g / cm 3 .

2. The negative electrode sheet according to claim 1, wherein The specific capacity of the silicon-based anode active material is ≥1200mAh / g.

3. The negative electrode sheet according to claim 1, wherein The compacted density of the negative electrode tab is 0.8 g / cm 3 .

4. The negative electrode sheet according to claim 1, wherein The area of ​​the first coated surface is larger than the area of ​​the second coated surface.

5. The negative electrode sheet according to claim 4, wherein The area of ​​the first coated surface is 1.05-1.1 times the area of ​​the second coated surface.

6. The negative electrode sheet according to claim 1, wherein The negative electrode tab includes a first tab and a second tab, which are spaced apart along the length of the negative electrode current collector and located on the first uncoated surface and the second uncoated surface, respectively.

7. The negative electrode sheet according to claim 6, wherein The negative electrode current collector has two parallel first and second sides along its width. The first electrode tab includes a first conductive sheet welded to the second uncoated surface and extending outward from the first side, and two first insulating sheets respectively attached to the first uncoated surface and the second uncoated surface and extending outward from the first side; the projection surfaces of the two first insulating sheets on the negative electrode current collector overlap each other, and the first conductive sheet is located between the two first insulating sheets.

8. The negative electrode sheet according to claim 7, wherein The distance between the first conductive sheet and the side of the second coated surface is 45mm-65mm.

9. The negative electrode sheet according to claim 7, wherein The width of the first insulating sheet is 1.5-2.5 times the width of the first conductive sheet.

10. The negative electrode sheet according to claim 7, wherein The first insulating sheet extends outward along the first side for a length of 0.5mm-3mm.

11. The negative electrode sheet according to claim 7, wherein The second electrode tab is a second conductive sheet that is welded to the first coated surface and extends outward from the second side.

12. The negative electrode sheet according to claim 11, wherein The distance between the second conductive sheet and the side of the first coated surface is 15mm-20mm.

13. The negative electrode sheet according to claim 11, wherein The first conductive sheet extends outward along the first side for a length of A, and the second conductive sheet extends outward along the first side for a length of B. The length relationship between the two should satisfy the following condition: A > B and AB > 8mm.

14. A negative electrode sheet as described in claim 11, characterized in that, The width of the second conductive sheet is 0.5 to 1 times the width of the first conductive sheet.

15. The negative electrode sheet of claim 1, wherein The negative electrode tab includes a main electrode tab disposed on the first uncoated surface or the second uncoated surface, and a plurality of secondary electrode tabs disposed on the first uncoated surface and / or the second uncoated surface, wherein the plurality of secondary electrode tabs are arranged at intervals along the length direction of the negative electrode current collector.

16. The negative electrode sheet according to claim 15, wherein The main electrode tab and several secondary electrode tabs extend outward based on the negative electrode current collector, and the main electrode tab and several secondary electrode tabs extend outward in the same direction based on the negative electrode current collector.

17. The negative electrode sheet according to claim 16, wherein The main electrode tab extends outward based on the negative electrode current collector by a greater length than the secondary electrode tab extends outward based on the negative electrode current collector.

18. A cylindrical battery characterized by comprising: It includes a housing, a cap, an electrolyte disposed within the housing, and a cylindrical core, wherein the cylindrical core includes a positive electrode, a diaphragm, and a negative electrode as described in any one of claims 1-17.

19. A cylindrical battery as claimed in claim 18, wherein the positive electrode is a lithium cobaltate electrode. The positive electrode tab comprises a positive electrode current collector, a positive electrode tab provided on the positive electrode current collector, and a positive electrode active material; the positive electrode active material is a material with a chemical formula of LiNi x Co y Mn 1-x-y O2, wherein the value range of x, y is 0-1.

20. A cylindrical battery as claimed in claim 19, wherein the positive electrode is a lithium cobaltate electrode. The unit area density of the positive electrode sheet is 28-33 mg / cm 2 .

21. A cylindrical battery as claimed in claim 19, wherein the positive electrode is made of a mixture of lithium cobaltate and lithium nickelate. The compacted density of the positive electrode plate is 3.2-3.8 g / cm 3 .

22. A cylindrical battery as claimed in claim 19, wherein the positive electrode is made of a lithium cobaltate, the negative electrode is made of a lithium metal, and the electrolyte is a lithium hexafluorophosphate solution. The positive current collector includes a third surface and a fourth surface arranged along its own thickness direction; The positive electrode active material is coated on the third surface of the positive electrode current collector to form a plurality of third coating surfaces, and a first blank area is formed between two adjacent third coating surfaces. The thickness of the third coating surface is 35μm-55μm. The positive electrode active material is coated on the fourth surface of the positive electrode current collector to form a plurality of fourth coating surfaces, and a second blank area is formed between two adjacent fourth coating surfaces. The thickness of the fourth coating surface is 35μm-55μm.

23. A cylindrical battery as claimed in claim 22, wherein the positive electrode is a lithium cobaltate electrode. The positive current collector has two parallel third and fourth sides along its width. The positive electrode tab includes several third conductive sheets welded to the first blank area and extending outward from the third side, and several pairs of second insulating sheets respectively attached to the first blank area and the second blank area and extending outward from the third side; The projection surfaces of each pair of second insulating sheets on the positive current collector coincide, and the third conductive sheet is located between the two second insulating sheets.

24. A cylindrical battery as claimed in claim 23, wherein the positive electrode is a lithium cobaltate electrode. The third surface of the positive current collector is provided with two third coating surfaces and a first blank area, and the two third coating surfaces are symmetrically arranged on both sides of the first blank area. The fourth surface of the positive current collector is provided with two fourth coating surfaces and a second blank area. The positive electrode tab includes a third conductive sheet welded to the first blank area and a pair of second insulating sheets.

25. A cylindrical battery as claimed in claim 22, wherein the positive electrode is made of a lithium cobaltate compound. The width of the positive electrode tab of the positive electrode plate is the same as the width of the negative electrode tab.

26. A cylindrical battery as claimed in claim 22, wherein the positive electrode is made of a lithium cobaltate compound. The width of the first blank area and the second blank area is at least 2 mm larger than the width of the positive electrode tab.

27. A cylindrical battery as claimed in claim 23, wherein the positive electrode is made of a lithium cobaltate, the negative electrode is made of a lithium metal, and the electrolyte is a lithium hexafluorophosphate solution. The area of ​​the second insulating sheet is larger than the area of ​​the first blank area or the second blank area of ​​the positive current collector.

28. A cylindrical battery as claimed in claim 22, wherein the cathode is made of lithium cobalt oxide. During winding, the first coating surface of the negative electrode sheet faces the third coating surface of the positive electrode sheet, and the length of the first coating surface is greater than the length of the positive current collector of the positive electrode sheet.

29. A cylindrical battery as claimed in claim 23, wherein the cathode is made of lithium cobalt oxide. The second insulating sheet extends outward along the third side for a length of 2mm-4mm, and the second insulating sheet extends outward along the fourth side for a length of 0.2mm-1.0mm.

30. A cylindrical battery as claimed in claim 18, wherein the positive electrode is made of a lithium cobaltate, the negative electrode is made of a lithium metal, and the electrolyte is a lithium hexafluorophosphate solution. The cylindrical core is assembled inside the housing, and the diameter of the cylindrical core is 0.96-0.99 times the inner diameter of the housing.

31. A cylindrical battery as claimed in claim 18, wherein the cathode is made of lithium cobalt oxide. The length of the negative electrode is 1190mm-1205mm; the length of the positive electrode is 1081mm-1091mm.

32. A cylindrical battery as claimed in claim 31, wherein the cathode is a lithium cobaltate cathode. The amount of electrolyte injected is 5.6g-6.2g.

33. A cylindrical battery as claimed in claim 18, wherein the cathode is made of lithium cobalt oxide. The cylindrical battery retains a discharge capacity of more than 97% when charged at 0.2C and discharged at 3C, with a temperature rise of 20-35℃.

34. A cylindrical battery as claimed in claim 18, wherein the cathode is made of lithium cobalt oxide. The cylindrical battery retains more than 95% of its discharge capacity when charged at 0.2C and discharged at 6C, with a temperature rise of 45-65℃.

35. A cylindrical battery as claimed in claim 18, wherein the cathode is made of lithium cobalt oxide and the anode is made of lithium metal. 35 The capacity of the cylindrical battery is greater than 3500mAh.

36. A battery pack, comprising: It includes two or more cylindrical batteries as described in any one of claims 18-35, wherein the two or more cylindrical batteries are electrically connected in series or in parallel.

37. A power tool characterized by Includes the battery pack as described in claim 36.

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