Battery

Abstract

The invention relates to the technical field of batteries, and discloses a battery which comprises a shell, a battery cell and electrolyte. The battery cell comprises a positive pole piece, a diaphragm and a negative pole piece, the negative pole piece comprises a negative pole current collector and a negative pole active material layer, the negative pole active material layer comprises a silicon-based material, the negative pole active material layer is provided with a plurality of first grooves, each first groove comprises a first groove section and a second groove section, and the second groove section is provided with a slope area close to the first groove section; the depth of the second groove section in the thickness direction is gradually reduced from one end close to the first groove section to one end far away from the first groove section; the electrolyte comprises a first cyclic carbonate compound and a second cyclic carbonate compound, and according to the total mass of the electrolyte, the sum X of the mass ratios of the first cyclic carbonate compound and the second cyclic carbonate compound is larger than or equal to 13% and smaller than or equal to 65%. Through the gradient region, the electrolyte fluidity is improved, and the cycle performance of the battery is further improved.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically to batteries. Background Technology

[0002] Batteries are widely used in various devices, such as mobile phones, laptops, electric vehicles, electric cars, electric airplanes, electric ships, electric toy cars, electric toy ships, electric toy airplanes, and power tools.

[0003] With the rapid development of battery technology, higher requirements are being placed on battery cycle performance. Summary of the Invention

[0004] In view of this, the present invention provides a battery to solve the problem of poor battery cycle performance.

[0005] In a first aspect, the present invention provides a battery, comprising: a casing; and a battery cell disposed within the casing, the battery cell comprising a positive electrode, a separator, and a negative electrode, the negative electrode comprising a negative current collector and a negative active material layer disposed on at least one side of the negative current collector along its thickness direction, the negative active material layer comprising a silicon-based material, the negative active material layer having a plurality of first trenches spaced apart; wherein, the first trench comprises a first trench segment and a second trench segment, at least one end of the first trench segment being connected to the second trench segment, the second trench segment having a slope region adjacent to the first trench segment, and the second trench segment extending along the thickness direction... The depth of the direction gradually decreases from the end closer to the first tank section to the end farther away from the first tank section; the electrolyte is disposed inside the shell, and the electrolyte includes a first cyclic carbonate compound and a second cyclic carbonate compound. Based on the total mass of the electrolyte, the sum of the mass percentages X of the first cyclic carbonate compound and the second cyclic carbonate compound is in the range of 13% ≤ X ≤ 65%; the first cyclic carbonate compound includes at least one of fluoroethylene carbonate, vinylene carbonate, and difluoroethylene carbonate, and the second cyclic carbonate compound includes at least one of ethylene carbonate and propylene carbonate.

[0006] In one optional embodiment, the ratio of the mass content percentage of the first cyclic carbonate compound X1 to the mass content percentage of the second cyclic carbonate compound X2, based on the total mass of the electrolyte, is in the range of: 0.1≤X1 / X2≤8.5; the mass content percentage percentage of the first cyclic carbonate compound X1, based on the total mass of the electrolyte, is: 5%≤X1≤25%, preferably 8%≤X1≤20%; and the mass content percentage percentage of the second cyclic carbonate compound X2, based on the total mass of the electrolyte, is: 3%≤X2≤55%.

[0007] In one alternative embodiment, the depth of the second groove segment along the thickness direction gradually decreases from the end closer to the first groove segment to the end farther away from the first groove segment.

[0008] In one optional embodiment, the negative electrode active material layer includes a main region and thinning regions connected to both ends of the main region along the length direction. Along the thickness direction, the thickness of the thinning regions is less than the thickness of the main region, and the second groove segment extends to the thinning regions.

[0009] In one optional implementation, along the length direction, the length of the second groove segment is L1, and the length of the first groove segment is L2, satisfying that L2 > L1; 30μm ≤ L1 ≤ 500μm.

[0010] In one optional embodiment, the angle between the bottom surface of the second groove segment and the bottom surface of the first groove segment is α1, satisfying 90°<α1<150°.

[0011] In one optional implementation, the depth of the first groove segment is H1, which satisfies 2μm < H1 ≤ 40μm.

[0012] In one optional embodiment, along the length direction, the distance between the edge of the first trench on the same side and the edge of the negative electrode active material layer is L3, which satisfies 20mm≤L3≤100mm.

[0013] In one optional embodiment, along the width direction, the distance between the edge of the negative electrode active material layer on the same side and the edge of the first trench closest to the negative electrode active material layer is L4, satisfying that 1mm≤L4≤10mm.

[0014] In one optional embodiment, along the thickness direction, the width of the bottom opening of the first trench near the negative electrode current collector is L6, the width of the top opening of the first trench away from the negative electrode current collector is L7, and the mass percentage of silicon in the negative electrode active material layer is A1, satisfying: 0.6 < L6 / L7 < 1; 30 μm < L6 < 150 μm; 50 μm < L7 < 150 μm; 1.2 < L6 / (L7*A1) < 18, 5% ≤ A1 ≤ 50%.

[0015] In one optional embodiment, the included angle between the bottom surface and the side surface of the first trench is α2, satisfying 90°<α2<130°.

[0016] In an optional embodiment, along the thickness direction, a raised structure is formed at the top notch edge of the first groove away from the negative current collector, and the height of the raised structure protruding from the surface of the negative active material layer is L8, satisfying 0.5 μm < L8 < 13 μm.

[0017] In an optional embodiment, the negative active material layers are provided on both sides of the negative current collector along the thickness direction, and the first grooves are provided on the surfaces of the negative active material layers on both sides; wherein, the distance between the two edges along the length direction of the second groove segment in the first grooves on both sides of the winding tail end of the negative active material layer is L5, satisfying L5 ≤ 1 mm.

[0018] In an optional embodiment, the battery cell is of a wound structure, including a flat region and an arc region. The positive electrode plate includes a positive current collector and a positive active material layer provided on at least one side of the positive current collector along the thickness direction. Along the thickness direction, a second groove is provided in the positive active material layer on the side close to the winding center of the positive electrode plate located in the arc region; the second groove includes a third groove segment and a fourth groove segment, and at least one end of the third groove segment along the winding direction is connected to the fourth groove segment; along the thickness direction, the depth of the fourth groove segment gradually decreases from one end close to the third groove segment to the end away from the third groove segment, and the maximum depth of the fourth groove segment is less than the depth of the third groove segment; wherein, the depth of the third groove segment is H2, satisfying 2 μm < H2 ≤ 40 μm.

[0019] In an optional embodiment, along the winding direction of the positive electrode plate, the length of the fourth groove segment of the second groove is L11, and the total length of the second groove is L12, satisfying 50 μm ≤ L11 ≤ 500 μm, 1 mm ≤ L12 ≤ 10 mm.

[0020] In an optional embodiment, along the winding direction of the positive electrode plate, the fourth groove segment of the second groove extends beyond the junction position of the flat region and the arc region of the positive electrode plate, and the length of the second groove located in the arc region is L13, satisfying L13 ≤ L12 ≤ 2L13.

[0021] Beneficial effects: During cycling, silicon-based materials in the negative electrode active layer often experience severe expansion and contraction, easily exposing fresh material surfaces that react with the electrolyte. These reactions continuously generate new SEI films on the surface of the silicon-based material, reducing the battery's cycle life. However, when the electrolyte includes first cyclic carbonate compounds and second cyclic carbonate compounds, the first cyclic carbonate compounds can participate in the formation of a fluorine-rich SEI film on the surface of the negative electrode silicon-based material. Fluorine-containing SEI films have high interfacial energy, stability, and mechanical strength, which can improve battery cycle life. However, the first cyclic carbonate compounds require sufficient solvation numbers to form a stable and effective fluorine-containing SEI film. The second cyclic carbonate compounds, due to their high dielectric constant, can effectively dissolve and promote the dissociation of lithium salts in the electrolyte, generating a large number of free lithium ions. These free lithium ions undergo solvation with the first cyclic carbonate compounds, allowing them to be more uniformly dispersed and dissolved, laying a good foundation for the formation of a fluorine-rich SEI film.On the other hand, second-cyclic carbonate compounds, due to their excellent solvation ability, are more likely to preferentially enter the first solvation sheath of lithium ions and bind tightly to them, while first-cyclic carbonate compounds may remain more in the outer layer or in a looser binding state. When the electrolyte approaches the negative electrode surface, lithium ions need to be desolvated in order to react on the surface of the silicon-based material. Since the second-cyclic carbonate compounds are more tightly bound to lithium ions, desolvation requires energy. In contrast, the relatively weaker binding of first-cyclic carbonate molecules makes them more prone to reduction reactions, allowing the first-cyclic carbonate compounds to more accurately bind to the negative electrode. Surface decomposition of silicon-based materials effectively constructs a protective SEI film primarily composed of lithium fluoride, reducing its unnecessary consumption in the bulk electrolyte and improving film formation efficiency and quality. Simultaneously, the free radical intermediates generated after the ring-opening of the first cyclic carbonate compound carry strong electron-withdrawing F, raising the reduction barrier of the surrounding second cyclic carbonate compound. This mitigates the problem of excessive loss of the second cyclic carbonate compound during battery cycling, improving battery cycle performance. However, compared to the chain carbonates in the electrolyte, both the first and second cyclic carbonate compounds have higher viscosity and slower flow within the battery, potentially causing cycling issues. To address the issues of electrolyte shortage and slow electrolyte reflux within the cell during cycling, multiple first trenches of varying depths extending along the length of the negative electrode are designed with a slope. This improves the fluidity of the electrolyte, including the first and second cyclic carbonate compounds, during battery cycling, as well as the reflux rate of the electrolyte from the outside to the inside of the battery, thereby improving the battery's cycle performance. By controlling the sum of the mass percentages of the first and second cyclic carbonate compounds in the electrolyte, X, to satisfy 13% ≤ X ≤ 65%, a more efficient topography of the silicon-based negative electrode surface can be ensured. To form a stable SEI film and improve battery cycle performance, the combined mass percentage (X) of the first and second cyclic carbonate compounds is too high. This results in a thicker SEI film, increasing impedance during lithium-ion migration, accelerating capacity decay, and increasing electrolyte viscosity, thus impairing battery cycle performance. Conversely, if X is too low, the surface film formation on the silicon-based negative electrode may be incomplete, leading to insufficient SEI protection. As the silicon-based material expands and contracts during cycling, the electrolyte continuously decomposes, damaging the electrode structure and worsening battery cycle performance. Therefore, a concentration of 13% ≤ X ≤ 65% ensures both a stable SEI film formation on the silicon-based material surface, extending battery cycle life, and improved electrolyte flow, further enhancing battery cycle performance.

[0022] In addition, the first trench can store a relatively abundant electrolyte, improving the ability of positive electrode active materials (such as lithium ions) to be inserted and extracted in the negative electrode active material layer during battery cycling; and it helps lithium ions to be inserted and extracted in the inner layers of the negative electrode active material layer, effectively alleviating the problem of lithium plating on the surface of the negative electrode sheet; the first trench can also release the expansion stress of the silicon-based negative electrode sheet during cycling, alleviate the degree of cell expansion, and reduce the risk of breakage of the positive electrode sheet and / or negative electrode sheet.

[0023] Because the second section of the first trench has a sloped area, eliminating dead zones at both ends of the first trench, even high-viscosity electrolytes can be smoothly transported to and from the first trench during battery cycling, thus improving electrolyte flow performance and effectively enhancing battery cycle performance. Furthermore, dust and particulate matter from silicon-based materials that detach during the processing of the first trench can be quickly removed through the sloped area, preventing residual dust and particulate matter from causing severe self-discharge and rapid capacity decay. Attached Figure Description

[0024] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0025] Figure 1 This is a schematic diagram of the structure of a battery according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the battery cell structure according to an embodiment of the present invention; Figure 3 for Figure 2 A cross-sectional view taken along the cutting line AA. Figure 4 This is a schematic diagram of the front view of the negative electrode sheet of the winding core after it has been unfolded according to an embodiment of the present invention. Figure 5 This is a schematic diagram of the back view of the negative electrode sheet of the winding core after it has been unfolded according to an embodiment of the present invention; Figure 6 This is a schematic diagram of the negative electrode of a laminated battery cell according to an embodiment of the present invention; Figure 7 for Figure 4 A cross-sectional view taken along the cutting line BB. Figure 8 for Figure 6 A cross-sectional view taken along the cutting line CC. Figure 9 for Figure 7 A magnified view of a portion of position D; Figure 10 This is a partially enlarged schematic diagram of another embodiment of the present invention; Figure 11 for Figure 2 Enlarged view of a portion; Figure 12 for Figure 2 A cross-sectional view of another embodiment cut along section line AA; Figure 13 This is a partial cross-sectional view of the positive electrode sheet in an embodiment of the present invention.

[0026] Explanation of reference numerals in the attached figures: 100-battery; 1-Outer casing; 2-Battery cell; 21-Straight area; 22-Circular area; 3-Positive electrode sheet; 31-Positive current collector; 32-Positive active material layer; 321-Second trench; 3211-Third trench section; 3212-Fourth trench section; 4-Septum; 5-Negative electrode sheet; 51-Negative electrode current collector; 521-First trench; 5211-First trench segment; 5212-Second trench segment; 52-Negative electrode active material layer; 522-Main region; 523-Thinning region; 524-Protrusion structure; X - Length direction; Y - Width direction; Z - Thickness direction. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Batteries are widely used in various devices, such as mobile phones, laptops, electric vehicles, electric cars, electric airplanes, electric ships, electric toy cars, electric toy ships, electric toy airplanes, and power tools. With the rapid development of battery technology, higher requirements are being placed on the cycle performance of batteries.

[0029] During battery cycling, the expansion and contraction of the negative electrode silicon-based material are significant, making it prone to side reactions with the electrolyte, such as tearing or bursting the SEI film. This exposes the surface of the silicon-based material, which then reacts with the electrolyte again to form a new SEI film. This process continuously consumes electrolyte, causing capacity decay and reducing the battery's cycle life.

[0030] When a first cyclic carbonate compound and a second cyclic carbonate compound are added to the electrolyte, the second cyclic carbonate compound, due to its high dielectric constant, can effectively dissolve and promote the dissociation of lithium salts in the electrolyte, generating a large number of free lithium ions. These free lithium ions then undergo a solvation reaction with the first cyclic carbonate compound, allowing it to disperse and dissolve more uniformly, forming a stable and effective fluorinated SEI film. This reduces side reactions between the silicon-based material and the electrolyte, improving the battery's cycle life. However, compared to chain carbonates in the electrolyte, the electrolyte containing both the first and second cyclic carbonate compounds has a higher viscosity. This results in poor electrolyte flow during battery cycling, leading to problems such as electrolyte shortages inside or in the middle of the cell, and slow electrolyte reflux. Research has shown that when the trenches on traditional electrodes have a uniform depth and extend along the width of the electrode, dead corners exist at both ends of the uniformly deep trenches. During battery cycling, it is more difficult for the electrolyte with higher viscosity inside the trench to be transported out of the trench through the dead corners at both ends, and it is even more difficult for the electrolyte with higher viscosity outside the trench to return to the trench through the dead corners at both ends. This results in poor electrolyte transport and return capabilities, which adversely affects the battery's cycle performance and may even lead to the risk of lithium plating.

[0031] In this regard, multiple first trenches with sloping zones can improve the flowability of electrolytes, including first and second cyclic carbonate compounds, during battery cycling, as well as the return flow rate of electrolytes from the outside to the inside of the battery during cycling, thereby improving the battery's cycle performance. Furthermore, even electrolytes with high viscosity can be smoothly transported to the outside of the trenches and returned to the inside of the trenches through the sloping zones, improving the electrolyte's flow properties, enhancing battery cycle performance, and reducing the risk of lithium plating.

[0032] The following is combined Figures 1 to 13 The following describes embodiments of the present invention.

[0033] According to an embodiment of the present invention, in a first aspect, a battery 100 is provided, including a housing 1, a battery cell 2 disposed within the housing 1, and an electrolyte. The battery cell 2 includes a positive electrode 3, a separator 4, and a negative electrode 5 sequentially stacked. The negative electrode 5 includes a negative current collector 51 and a negative active material layer 52 disposed on at least one side of the negative current collector 51 along the thickness direction Z. The negative active material layer 52 includes a silicon-based material, and the negative active material layer 52 is provided with a plurality of first trenches 521, which are spaced apart. Each first trench 521 includes a first trench segment 5211 and a second trench segment 5212, with at least one end of the first trench segment 5211 connected to the second trench segment 5212, i.e., the second trench segment 5212 is disposed near the end of the first trench along the extension direction of the first trench. The second trench segment 5212 has a slope region near the first trench segment 5211. The depth of the second groove segment 5212 along the thickness direction Z gradually decreases from the end closest to the first groove segment 5211 (the connection point between the two) towards the end furthest from the first groove segment 5211. Five points are taken sequentially on the second groove segment 5212 from the end closest to the first groove segment 5211 towards the end furthest from the first groove segment 5211. The depth of the first point closest to the first groove segment 5211 is less than the depth of the second point in the middle, and the depth of the second point in the middle is less than the depth of the third point furthest from the first groove segment 5211.

[0034] The first trench 521 can extend along the length direction X or the width direction Y of the negative electrode plate 5, or extend along a direction that forms a certain angle with the width direction Y. The present invention exemplarily illustrates a case where the first trench 521 extends along the length direction X of the negative electrode plate 5, and multiple first trenches 521 are spaced apart along the width direction Y of the negative electrode plate 5.

[0035] The electrolyte comprises a first cyclic carbonate compound and a second cyclic carbonate compound. The sum of the mass percentages (X) of the first and second cyclic carbonate compounds, based on the total mass of the electrolyte, ranges from 13% to 65%. The first cyclic carbonate compound includes at least one of fluoroethylene carbonate, vinylene carbonate, and difluoroethylene carbonate, and the second cyclic carbonate compound includes at least one of ethylene carbonate and propylene carbonate. X can be any value from 13%, 15%, 25%, 30%, 45%, 55%, 60%, and 65%, or any value between two of these.

[0036] Battery 100 can be either a pouch battery or a hard-shell battery. Taking a pouch battery as an example, the outer shell 1 can be an aluminum-plastic film.

[0037] Cell 2 can be a laminated cell or a wound cell.

[0038] The negative electrode active material layer 52 can be formed on one side surface of the negative electrode current collector 51 along the thickness direction Z, or it can be formed on both sides surface of the negative electrode current collector 51. When the negative electrode active material layer 52 is formed on both sides surface of the negative electrode current collector 51, a first trench 521 can be formed on one side of the negative electrode active material layer 52, or a first trench 521 can be formed on both sides of the negative electrode active material layer 52. The negative electrode current collector 51 can be made of copper.

[0039] The positive electrode 3 includes a positive current collector 31 and a positive active material layer 32 disposed on at least one side of the positive current collector 31 along the thickness direction Z. The positive current collector 31 can be aluminum, and the positive active material in the positive active material layer 32 can be lithium cobalt oxide, lithium iron phosphate, ternary lithium, or lithium manganese oxide, etc.

[0040] In this embodiment of the application, when the battery cell is a wound battery cell, the length direction X is the length direction of the negative electrode 5 after it is unfolded. When the wound battery cell is in a wound state, the length direction X is the winding direction of the negative electrode 5.

[0041] The multiple first trenches 521 can be distributed at equal intervals or at unequal intervals along the width direction Y of the negative electrode plate 5. The shapes of the multiple first trenches 521 can be the same or at least partially different.

[0042] For example, the first slot segment 5211 may be connected to one end of the second slot segment 5212 along the length direction X, or the second slot segment 5212 may be connected to both ends of the first slot segment 5211 along the length direction X.

[0043] The second groove segment 5212 has a sloped area, and its average depth is less than that of the first groove segment 5211. The average depth is measured by taking any five points on the surface of the second groove segment 5212, measuring the depth at each point, and calculating the average depth G1. Similarly, taking any five points on the surface of the first groove segment 5211, measuring the depth at each point, and calculating the average depth G2. The sloped area ensures that there are no dead angles at either end of the first groove 521 along its length X. The first groove 521 can be formed by grinding the negative electrode active material layer 52 using rollers.

[0044] In the electrolyte, the larger the sum of the mass percentages (X) of the first and second cyclic carbonate compounds, the more stable the SEI film formed on the silicon-based material surface, thus extending the battery's cycle life. Conversely, the smaller the sum of the mass percentages (X) of the first and second cyclic carbonate compounds, the lower the electrolyte viscosity and the better its fluidity, which improves the battery's cycle performance. Therefore, a concentration of 15% ≤ X ≤ 65% ensures both the formation of a stable SEI film on the silicon-based material surface, extending the battery's cycle life, and improved electrolyte fluidity, thus enhancing the battery's cycle performance.

[0045] The first trench 521 can store a relatively abundant electrolyte, improving the ability of positive electrode active material (such as lithium ions) to be inserted and extracted in negative electrode active material layer 52 during battery cycling. Since the first trench 521 itself has a certain depth and width, on the one hand, it can facilitate the insertion and extraction of lithium ions in the inner layer of negative electrode active material layer 52, effectively alleviating the problem of lithium deposition on the surface of negative electrode sheet 5. On the other hand, the first trench 521 can release the expansion stress of negative electrode sheet 5 with silicon-based material during cycling, alleviate the degree of cell expansion, and reduce the risk of breakage of positive electrode sheet 3 and / or negative electrode sheet 5.

[0046] Because the second section 5212 of the first trench 521 has a sloped area, the sloped area ensures that there are no dead corners at both ends of the first trench 521. In contrast, the trenches on the electrode sheets in the prior art are usually of uniform depth, i.e., without sloped areas, resulting in dead corners at both ends of the trench. These dead corners are not conducive to the flow of electrolyte from the outside to the inside of the cell. At the same time, dust generated during the trench manufacturing process tends to accumulate in these dead corners and is difficult to clean thoroughly. After the electrolyte is injected, the dust in the dead corners will dissolve, resulting in severe self-discharge of the battery and causing poor K value. On the other hand, during battery cycling, even if the electrolyte contains high-viscosity first cyclic carbonate compounds and second cyclic carbonate compounds, it can still be smoothly transported to the first trench 521 and to the internal area of ​​the battery and to other areas except the area where the first trench is located through the sloped area, as well as flow back into the first trench 521, thereby improving the flow performance of the electrolyte. Thus, the cycle performance of the battery can be effectively improved. In addition, silicon-based material dust and particles that fall off during the processing of the first trench 521 can be quickly removed through the slope area, preventing dust and particles from causing severe self-discharge of the battery and resulting in excessively rapid capacity decay.

[0047] In some embodiments, the ratio of the mass content of the first cyclic carbonate compound X1 to the mass content of the second cyclic carbonate compound X2, based on the total mass of the electrolyte, ranges from 0.1 to X1 / X2 to 8.5. X1 / X2 can be any one of 0.1, 0.5, 3, 4.7, 5, 6.3, 7.5, 8, 8.5, or any value between two of them.

[0048] Based on the total mass of the electrolyte, the mass content percentage X1 of the first cyclic carbonate compound is: 5%≤X1≤25%, preferably 8%≤X1≤20%. X1 can be any one or any combination of 5%, 6%, 8%, 10%, 15%, 16%, 17%, 18%, 19%, and 20%.

[0049] Based on the total mass of the electrolyte, the mass content percentage (X2) of the second cyclic carbonate compound is: 3% ≤ X2 ≤ 55%. X1 can be any one of 3%, 6%, 8%, 10%, 15%, 20%, 27%, 35%, 40%, 55%, or any value between two of them.

[0050] The methods for testing the mass content of first- and second-cyclic carbonate compounds include: using GS-MS (gas chromatography-mass spectrometry) to compare the electrolyte sample with the standard sample spectrum or to search the mass spectral library, and then using the commonly used external standard method or internal standard method to plot a standard curve to calculate the component content.

[0051] Reference Figures 7-8 The depth of the second trench segment 5212 along the thickness direction Z gradually decreases from the end closer to the first trench segment 5211 to the end farther away from the first trench segment 5211, making the second trench segment 5212 a gently sloping area. The first trench segment 5211 can be a flat area with relatively uniform depth, while the second trench segment 5212 is a gently sloping area. This structure can further improve the fluidity of the electrolyte from the outside to the inside of the cell, and at the same time further prevent the dust generated during the manufacturing process of the first trench 521 from being difficult to clean, which could lead to severe self-discharge of the battery and cause poor K value.

[0052] In some embodiments, the negative electrode active material layer 52 includes a main region 522 and a thinning region 523 connected to both ends of the main region 522 along the length direction X. Along the thickness direction Z, the thickness of the thinning region 523 is less than the thickness of the main region 522, and the second groove segment 5212 extends to the thinning region 523.

[0053] The main region 522 is the main part of the negative electrode active material layer 52, and its area can be much larger than that of the thinning region 523. The second groove segment 5212 can be partially located in the thinning region 523, or it can be entirely located in the thinning region 523.

[0054] In a wound cell, during the fabrication process of the negative electrode sheet, due to the inertial force of the coating, the negative electrode active material layer 52 of the negative electrode sheet 5 near the winding center at the beginning of the winding and far from the winding center at the end of the winding will form a thinning zone 523 in the winding start section and the winding end section due to the problem of negative electrode slurry flow.

[0055] During battery manufacturing (such as coating, rolling, drying) and charge-discharge cycles, the thinning region 523 may be unable to withstand large mechanical stresses (such as mechanical stresses generated by bending, shearing, volume expansion and contraction). The second groove section 5212 with a slope extends to the thinning region 523. The slope can disperse and absorb local high stresses, significantly reducing the risk of shedding of the negative electrode active material layer 52 located in the thinning region 523 and the risk of breakage of the negative electrode current collector 51 located in the thinning region 523, thereby improving the battery cycle performance and safety.

[0056] It should be noted that, in another embodiment, the second groove segment 5212 may not extend to the thinning region 523, that is, the second groove segment 5212 is a certain distance away from the thinning region 523, which can further reduce the risk of damage and breakage of the thinning region.

[0057] In some embodiments, refer to Figure 6 Along the length direction X, the length of the second slot segment 5212 is L1, and the length of the first slot segment 5211 is L2, satisfying L2 > L1; 30μm ≤ L1 ≤ 500μm. L1 can be any value among 30μm, 60μm, 80μm, 100μm, 200μm, 260μm, 300μm, 400μm, 470μm, and 500μm, or any value between two of them.

[0058] A slope L1 greater than or equal to 30 μm ensures a sufficient length for the slope region of the second tank section 5212, which is beneficial for improving electrolyte flow, enhancing electrolyte transport and return capabilities, and improving battery cycle performance. An excessively long slope region results in insufficient tank depth for many negative electrode active material layers 52, hindering the intercalation and deintercalation speeds of the underlying silicon-based material and lithium ions, and potentially leading to localized lithium plating, thus affecting battery cycle performance. Therefore, a slope L1 less than or equal to 500 μm prevents the slope region of the second tank section 5212 from becoming excessively long, reducing its impact on battery cycle performance.

[0059] In some embodiments, refer to Figure 9The angle between the bottom surface of the second trough segment 5212 and the bottom surface of the first trough segment 5211 is α1, satisfying 90° < α1 < 150°. Angle α1 is the angle between the slope surface of the slope zone and the length direction X, and also represents the slope of the slope zone. α1 can be any value from 91°, 93°, 96°, 100°, 105°, 110°, 120°, 130°, 140°, and 149°, or any value between two of these.

[0060] The above α1 test method: After discharging the battery to 0% SOC, disassemble the battery to obtain the negative electrode sheet. Cut the negative electrode sheet along a plane parallel to the depth direction (Z direction) and perpendicular to the width direction (Y direction) of the first trench to obtain a longitudinal section with a first trench segment and a second trench segment (e.g., Figure 9 As shown in the image, under a scanning electron microscope at 500x magnification, if the bottom and side surfaces of the first groove in the longitudinal section are straight lines, the angle formed by the intersection of the straight line M1 containing the side surface and the straight line M2 containing the bottom surface is α1. If the bottom and side surfaces of the first groove in the longitudinal section are uneven curved surfaces, then under a scanning electron microscope at 500x magnification, draw the first tangent to the curved surface of the bottom surface of the first groove and the second tangent to the curved surface of the side surface of the first groove, and extend the first tangent to the second tangent to form the angle α1. It should be noted that the tangents (first tangent, second tangent) of the curved surfaces mentioned above refer to the tangent of the most outwardly convex surface among the multiple curved surfaces.

[0061] When α1 is greater than 90°, the second tank section 5212 has a certain slope, which is beneficial to improving the fluidity of the electrolyte along the length of the negative electrode sheet, enhancing the electrolyte delivery and return capabilities, and improving the ease of dust particle cleaning. When α1 is less than 150°, the slope of the second tank section 5212 is not too shallow, reducing the impact on battery cycle performance. If the slope is too shallow, the tank depth in some areas of the negative electrode active material layer 52 will be insufficient, which is not conducive to the intercalation and deintercalation speed of the silicon-based material and lithium ions in the lower part of the negative electrode active material layer 52, affecting the battery cycle performance. At the same time, when α1 is greater than 150°, the slope area is too gentle, which is not conducive to the flow of electrolyte to other areas of the battery.

[0062] In some embodiments, refer to Figure 9 The depth of the first groove segment 5211 is H1, which satisfies 2μm < H1 ≤ 40μm. H1 can be any value among 2.1μm, 5μm, 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, and 40μm, or any value between two of them.

[0063] H1 is greater than 2μm, which allows the first groove segment 5211 to store more electrolyte, improving the lithium-ion insertion / extraction capability and speed of silicon-based materials in the negative electrode active material layer 52. An excessively deep first groove segment 5211 can easily lead to insufficient residual thickness of the negative electrode active material layer 52, making it easy to fall off. It can also easily scratch the negative electrode current collector 51 during processing. Therefore, H1 is less than or equal to 40μm, so that the first groove segment 5211 is not too deep, which can reduce the risk of the negative electrode active material layer 52 falling off during battery cycling, and also reduce the risk of scratching the negative electrode current collector 51 during manufacturing.

[0064] In some embodiments, refer to Figure 4 , Figure 5 and Figure 6 Along the length direction X, the distance between the edge of the first trench 521 on the same side and the edge of the negative electrode active material layer 52 is L3, which satisfies 20mm≤L3≤100mm. L3 can be any value among 20mm, 30mm, 40mm, 50mm, 60mm, 70mm, 80mm, 90mm, and 100mm, or any value between two of them.

[0065] Since the negative electrode active material layer 52, which is closer to the edge along the length direction X, is more prone to detachment when compressed, when L3 is greater than or equal to 20 mm, a certain distance is maintained between the edge of the first trench 521 on the same side along the length direction X and the edge of the negative electrode active material layer 52. This prevents the risk of the negative electrode active material layer 52 detaching or even scratching the negative electrode current collector 51 during the processing of the first trench 521, thus improving safety. However, an excessively large distance will reduce the processing length of the first trench 521, decrease its electrolyte storage capacity, and reduce the battery's cycle performance. Therefore, when L3 is less than or equal to 100 mm, the distance between the edge of the first trench 521 on the same side along the length direction X and the edge of the negative electrode active material layer 52 is not too large, thereby improving the electrolyte storage capacity of the first trench 521 and enhancing the battery's cycle performance.

[0066] In some embodiments, refer to Figure 4 , Figure 5 and Figure 6 Along the width direction Y, the distance between the edge of the negative electrode active material layer 52 on the same side and the edge of the first trench 521 closest to the negative electrode active material layer 52 is L4, which satisfies 1mm≤L4≤10mm. L4 can be any value among 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm, and 10mm, or any value between two of them.

[0067] Because the negative electrode active material layer 52 near the edge along the width direction Y is more prone to detachment when squeezed, when L4 is greater than or equal to 1 mm, a certain gap is maintained between the edge of the first trench 521 on the same side along the width direction Y and the edge of the negative electrode active material layer 52. This prevents the negative electrode active material layer 52 from detaching or even scratching the negative electrode current collector 51 during the processing of the first trench 521, or from being too close to the edge of the negative electrode sheet. In such cases, the processing and cutting of the negative electrode sheet 5 may easily result in cutting into the first trench 521, causing more severe powder shedding, or even triggering lithium plating at the edge of the negative electrode sheet, thus improving safety. However, an excessively large gap reduces the processing size of the first trench 521, reduces the area where the first trench 521 is set, and reduces the electrolyte storage capacity of the first trench 521. At the same time, it will also cause the electrolyte storage in the edge area of ​​the negative electrode sheet to be different from that in the area where the trench is set, resulting in different lithium insertion / extraction rates in the two areas, thus causing local lithium plating problems. Therefore, when L3 is less than or equal to 100mm, the distance between the edge of the first trench 521 on the same side along the width direction Y and the edge of the negative electrode active material layer 52 is not too large, ensuring that the area of ​​the first trench 521 on the electrode is as large as possible, thereby improving the liquid storage capacity of the first trench 521 and improving the cycle performance of the battery.

[0068] In some embodiments, along the thickness direction Z, the first trench 521 has a bottom opening near the negative electrode current collector 51 and a top opening away from the negative electrode current collector 51, the width of the top opening being greater than the width of the bottom opening. The width of the bottom opening of the first trench 521 near the negative electrode current collector 51 is L6, and the width of the top opening of the first trench 521 away from the negative electrode current collector 51 is L7, satisfying the following conditions: 0.6 < L6 / L7 < 1; 30 μm < L6 < 150 μm; 50 μm < L7 < 150 μm.

[0069] The L6 and L7 test methods for the first trench: After discharging the battery to 0% SOC, disassemble the battery to obtain the negative electrode sheet. Cut the negative electrode sheet along a cross-section parallel to the depth direction (Z direction) and perpendicular to the length direction (X direction) of the first trench to obtain the cross-section (e.g., Figure 10 As shown in the figure, using a scanning electron microscope magnified to 500x, along the depth direction (Z direction) of the first trench, towards the surface of the negative electrode current collector, take multiple straight lines connecting the left and right side walls of the width direction (Y direction) of the first trench and parallel to the surface of the negative electrode current collector. Among the multiple straight lines, the longest straight line is the one closest to the negative electrode active material layer and furthest from the surface of the negative electrode current collector. The length of this longest straight line is L7. Among the multiple straight lines, the shortest straight line is the one closest to the negative electrode current collector and overlaps with the bottom surface of the trench. The length of this shortest overlapping straight line is L6.

[0070] It should be noted that if the bottom surface of the first trench is an uneven surface, then among the multiple straight lines, there is the shortest straight line that is closest to the negative electrode current collector and passes through the lowest point of the bottom surface of the trench. The length of this shortest straight line is L6.

[0071] L6 / L7 can be any one of the values ​​0.61, 0.7, 0.8, 0.9, or 0.99, or any value in between.

[0072] L6 can be any value among 31μm, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm, 100μm, 130μm, and 149μm, or any value between the two.

[0073] L7 can be any value among 50μm, 60μm, 70μm, 80μm, 90μm, 100μm, 110μm, 120μm, 130μm, and 149μm, or any value between the two.

[0074] The ratio 0.6 < L6 / L7 < 1 ensures that the width of the top opening of the first trench 521, which is away from the negative electrode current collector 51, is larger than the width of the bottom opening of the first trench 521, which is close to the negative electrode current collector 51. The side surface of the first trench 521 is inclined, which not only increases the electrolyte storage capacity but also facilitates the electrolyte's penetration into the interior of the first trench 521 and its diffusion to the surrounding areas without trenches, improving the wetting effect and thus enhancing the battery's cycle performance. Furthermore, it facilitates the removal of negative electrode active material dust and particles generated during processing from the top opening, thereby preventing self-discharge caused by contact between negative electrode active material dust and particles and positive electrode active material. In addition, the inclined surface of the first trench 521, compared to a straight surface, increases the contact area with lithium ions, improving the lithium ion insertion / extraction ability in the negative electrode active material layer 52, further enhancing the battery's cycle performance.

[0075] If the difference between the top and bottom opening widths of the first trench 521 is too large, lithium ions will easily deposit at the bottom of the trench, which is not conducive to the storage of a large amount of electrolyte in the first trench 521 and is detrimental to the storage stability of the electrolyte. If the difference between the top and bottom opening widths of the first trench 521 is too small, excessive material removal will reduce the capacity, and the structure of the negative electrode current collector will be easily damaged when removing the bottom negative electrode active material. Therefore, 0.6 < L6 / L7 < 1 can not only increase the storage capacity of the electrolyte, but also improve the storage stability of the electrolyte, and improve the cycle and safety performance of the battery.

[0076] In some embodiments, refer to Figure 10The angle between the bottom surface and the side surface of the first groove 521 is α2, which satisfies 90°<α2<130°. α2 can be any value among 91°, 95°, 100°, 120°, and 129°, or any value between two of them.

[0077] The above α2 test method: After discharging the battery to 0% SOC, disassemble the battery to obtain the negative electrode sheet. Cut the negative electrode sheet along a cross-section parallel to the depth direction (Z direction) and perpendicular to the length direction (X direction) of the first trench to obtain the cross-section (e.g., Figure 10 As shown in the image, under a scanning electron microscope at 500x magnification, along the width direction (Y direction) of the first trench, if the sidewall of the trench is a straight surface, the angle formed by the intersection of the extended straight line N1 containing the sidewall and the straight line N2 parallel to the surface of the negative electrode current collector is α2. If the sidewall of the trench is an uneven curved surface along the width direction, under a scanning electron microscope at 500x magnification, the angle formed by the intersection of the extended tangent line and the straight line parallel to the surface of the negative electrode current collector is α2. It should be noted that if the sidewall of the trench has multiple protruding curved surfaces, the tangent line refers to the tangent line of the most outwardly protruding curved surface on the sidewall. When α2 is greater than 90°, the top opening of the first trench 521 is larger, which can increase the storage capacity of the electrolyte and facilitate the removal of dust and particulate matter from the negative electrode active material. When α2 is greater than 90°, the trench wall is inclined. During the cycle, the inclined structure can effectively disperse the stress of the silicon-based material in the thickness direction of the negative electrode sheet, thereby reducing the Z-expansion stress in the thickness direction and reducing the powder shedding caused by stress concentration in the Z-direction of the thickness direction. However, an excessively large top opening is not conducive to the storage stability of the electrolyte. Therefore, α2 is less than 130°, which can improve the storage stability of the electrolyte in the first trench 521.

[0078] In some embodiments, the mass percentage of silicon in the negative electrode active material layer 52 is A1, 1.2 < L6 / (L7*A1) < 18, 5% ≤ A1 ≤ 50%.

[0079] L6 / (L7*A1) can be any one of the values ​​1.21, 2, 5, 10, 12, 13, 14, 15, 16, 17, 17.9 or any value between two of them. A1 can be any one of the values ​​5%, 10%, 20%, 30%, 40%, 50% or any value between two of them.

[0080] As mentioned above, the first trench 521 can provide an expansion gap for the cyclic expansion of the negative electrode 5 with silicon-based material, which can release the expansion stress to a certain extent, alleviate the overall expansion of the cell, and reduce the risk of breakage of the positive electrode 3 and / or the negative electrode 5.

[0081] A larger opening in the first trench 521 can better mitigate the cyclic expansion of the silicon-based negative electrode 5. However, a larger opening leads to greater loss of the negative electrode active material, reducing the ratio of negative electrode active material to positive electrode active material (CB value). An excessively low CB value can result in a lack of sufficient lithium-ion insertion sites, leading to lithium plating. Therefore, controlling the ratio between the opening size of the first trench 521 and the silicon content in the negative electrode active material layer 52 to be within the range of 1.2 < L6 / (L7*A1) < 18 can both maximize the mitigation of cyclic expansion and reduce the risk of lithium plating.

[0082] In some embodiments, refer to Figure 10 Along the thickness direction Z, a protruding structure 524 is formed at the top edge of the first trench 521 away from the negative electrode current collector 51. The height of the protruding structure 524 protruding from the surface of the negative electrode active material layer 52 is L8, which satisfies 0.5μm < L8 < 13μm. L8 can be any value among 0.51μm, 1μm, 1.7μm, 3μm, 5μm, 7μm, 8μm, 10μm, 12μm, and 12.9μm, or any value between two of them.

[0083] The top edge of the first trench 521, away from the negative electrode current collector 51, is the boundary between the area where the first trench 521 is located and the area where no trench is located (untreated area) of the negative electrode active material layer 52. A raised structure 524 is formed at this boundary. The raised structure 524 can be continuous along the length direction X.

[0084] With an L8 greater than 0.5 μm, the first trench 521 can hold more electrolyte, and there is a certain liquid storage space between the untreated area and the separator 4, allowing more electrolyte residue to remain on the surface of the untreated area, thereby improving the ability of lithium ions to be inserted and extracted into the negative electrode active material layer 52. If the protrusion structure 524 is too high, it is easy to cause the risk of collapse and detachment after the cell is hot-pressed, which may cause dust, particles, etc. of the negative electrode active material to come into contact with the positive electrode active material, causing internal short circuits and creating safety hazards. With an L8 less than 13 μm, the height of the protrusion structure 524 is not too high, thereby reducing the risk of collapse and detachment of the protrusion structure 524 and eliminating safety hazards.

[0085] In some embodiments, refer to Figure 8The negative electrode current collector 51 has negative electrode active material layers 52 on both sides along the thickness direction Z, and the surfaces of the negative electrode active material layers 52 on both sides are provided with first grooves 521. At one end of the negative electrode sheet 5, the distance between the two edges of the second groove segment 5212 in the first groove 521 on both sides of the negative electrode active material layer 52 along the length direction X is L5, satisfying that L5 ≤ 1 mm. L5 can be any value among 0.01 mm, 0.2 mm, 0.4 mm, 0.6 mm, 0.7 mm, 0.9 mm, and 1 mm, or any value between two of these.

[0086] The battery cell 10 can be either stacked or wound. When the battery cell 10 is wound, one end of the negative electrode 5 is the wound tail end.

[0087] The negative electrode 5, made of silicon-based material, expands and contracts during cycling. The SEI film continuously breaks down and reforms during this expansion and contraction, consuming a large amount of electrolyte. Since the winding tail of the negative electrode 5 is located on the outermost layer of the cell, the combined stresses of expansion and contraction make it most severely affected by the stress caused by the volume change of the silicon-based material. This leads to faster electrolyte consumption at the winding tail of the negative electrode 5. Therefore, the tail of the negative electrode 5 needs to be replenished with electrolyte in a timely manner through the sloping area of ​​the second groove section 5212 to prevent the battery performance from deteriorating rapidly. At this time, if the tops of the grooves on both sides of the negative electrode 5 are far apart, the side of the second groove section 5212 closer to the tail of the negative electrode 5 will receive electrolyte replenishment more quickly. As a result, it can resume participation in the cell cycle more quickly. While the negative electrode 5 expands further on this side, it squeezes the other side, making it more difficult for the electrolyte inside the first groove 521 to flow into the untreated area. As a result, a large area of ​​the active material in the cell loses its activity, causing a loss of cell capacity.

[0088] Furthermore, during the electrolyte injection process, the electrolyte typically enters simultaneously into the first trenches 521 on the surfaces of the negative electrode active material layers 52 on both sides. If L5 is too large, the electrolyte will preferentially be introduced into the first trenches 521 near the winding tail end through the second trench segment 5212, causing the electrolyte to be rapidly absorbed by the first trench 521 on one side. This results in uneven distribution of the electrolyte in the negative electrode active material layers 52 on both sides. The negative electrode active material layer 52 on the side with insufficient electrolyte absorption will then experience lithium plating due to insufficient lithium ion insertion / extraction capacity. Therefore, L5 ≤ 1 mm ensures a smaller distance between the two edges of the second trench segment 5212 on the same side along the length direction X in the first trenches 521 on both sides. This results in a more uniform distribution of the electrolyte in the negative electrode active material layers 52 on both sides, reducing the risk of lithium plating.

[0089] In some embodiments, refer to Figure 11 and Figure 12, the battery cell 2 is a wound structure (winding core), including a flat area 21 and an arc area 22. The positive electrode tab 3 includes a positive current collector 31 and a positive active material layer 32 provided on at least one side of the positive current collector 31 in the thickness direction Z. Along the thickness direction Z, the positive active material layer 32 on the side of the positive electrode tab 3 in the arc area 22 close to the winding center is provided with a second groove 321. The second groove 321 includes a third groove segment 3211 and a fourth groove segment 3212, and at least one end of the third groove segment 3211 in the winding direction is connected to the fourth groove segment 3212. The fourth groove segment 3212 has a slope area close to the third groove segment 3211. Along the thickness direction Z, the depth of the fourth groove segment 3212 gradually decreases from one end close to the third groove segment 3211 to the end far from the third groove segment 3211. Among them, the depth of the third groove segment 3211 is H2, satisfying 2μm < H2 ≤ 40μm. H2 can be any value among 2.1μm, 3μm, 5μm, 10μm, 20μm, 30μm, 40μm or any value between any two of them.

[0090] The fourth groove segment 3212 has a slope area, and the average depth of the fourth groove segment 3212 is less than the average depth of the third groove segment 3211. The measurement methods of the average depth of the fourth groove segment 3212 and the average depth of the third groove segment 3211 can refer to the average depth of the first groove segment and the average depth of the second groove segment in the above text.

[0091] The positive electrode tab 3 located in the arc area 22 can include multiple positive electrode arc areas, and the second groove 321 can be provided in the positive active material layer 32 on the side of at least one positive electrode arc area close to the winding center.

[0092] H2 is greater than 2μm. The second groove 321 has a certain depth, which can balance the ratio (CB value) of the negative active material to the positive active material, thereby improving the risk of lithium plating. At the same time, it can also improve the fluidity of the electrolyte and the wetting effect of the positive active material layer 32. If the depth of the second groove 321 is too large, it is not conducive to the improvement of the battery energy density. Therefore, H2 is less than or equal to 40μm, which is beneficial to the improvement of the battery energy density.

[0093] In some embodiments, refer to Figure 13Along the thickness direction Z, the width of the bottom opening of the second trench 321 on the surface near the positive current collector 31 is L9, and the width of the top opening of the second trench 321 on the surface away from the positive current collector 31 is L10, satisfying 0.6 < L9 / L10 < 1, 30μm < L9 < 150μm, and 50μm < L10 < 150μm. L9 / L10 can be any value from 0.61, 0.7, 0.8, 0.9, 0.99, or any value between two values. L9 can be any value from 31μm, 40μm, 60μm, 100μm, 120μm, 130μm, 140μm, 150μm, or any value between two values. L10 can be any value among 50μm, 60μm, 80μm, 100μm, 120μm, 130μm, 140μm, and 150μm, or any value in between. The measurement methods for L9 and L10 can be the same as those for parameters L6 and L7.

[0094] The ratio 0.6 < L9 / L10 < 1 ensures that the width of the top opening of the second trench 321, which is away from the positive current collector 31, is larger than the width of the bottom opening of the second trench 321, which is close to the positive current collector 31. The side surface of the second trench 321 is inclined, which not only increases the electrolyte storage capacity but also facilitates the electrolyte's penetration into the interior of the second trench 321 and its diffusion to the surrounding areas without trenches, thus improving the wetting effect and improving the cycle performance of the battery. Furthermore, it also facilitates the removal of positive electrode active material dust and particulate matter generated during the processing from the top opening, thereby preventing the positive electrode active material dust and particulate matter from contacting the negative electrode active material and causing self-discharge.

[0095] If the difference between the top and bottom opening widths of the second trench 321 is too large, it will be detrimental to the retention of electrolyte in the second trench 321 and the stability of electrolyte storage. If the difference between the top and bottom opening widths of the second trench 321 is too small, it will lead to excessive material removal, reducing capacity, and it will also easily damage the structure of the positive current collector when removing the bottom positive electrode active material. Therefore, 0.6 < L9 / L10 < 1 can not only increase the electrolyte storage capacity, but also improve the electrolyte storage stability, and improve the cycle life and safety performance of the battery.

[0096] In some embodiments, refer to Figure 13 The angle between the bottom surface and the side surface of the second groove 321 is α3, which satisfies 90° < α3 < 130°. α3 can be any value among 91°, 95°, 100°, 120°, and 129°, or any value in between. The method for measuring α3 can refer to the method for measuring α2 mentioned above.

[0097] When α3 is greater than 90°, the top opening of the second trench 321 is larger, which can increase the storage capacity of the electrolyte and facilitate the removal of dust and particulate matter from the positive electrode active material. When α2 is greater than 90°, the trench wall is inclined. During the cycle, the inclined structure can effectively disperse the expansion stress of the negative electrode silicon-based material along the thickness direction Z, reducing the powder shedding caused by stress concentration in the thickness direction Z. However, an excessively large top opening is not conducive to the storage stability of the electrolyte. Therefore, α3 is less than 130°, which can improve the storage stability of the electrolyte in the first trench 521.

[0098] In some embodiments, refer to Figure 11 Along the winding direction of the positive electrode 3, the length of the fourth groove segment 3212 is L11, and the total length of the second groove 321 is L12, satisfying 50μm≤L11≤500μm and 1mm≤L12≤10mm. L11 can be any value among 50μm, 100μm, 200μm, 250μm, 300μm, 400μm, and 500μm, or any value between two of them. L12 can be any value among 1mm, 3mm, 5mm, 7mm, 8mm, and 10mm, or any value between two of them.

[0099] A slope L11 greater than or equal to 50 μm ensures a sufficient length for the slope region of the fourth cell segment 3212, which is beneficial for improving electrolyte flow, electrolyte transport and return capabilities, and battery cycle performance. However, an excessively long slope region in the fourth cell segment 3212 results in insufficient depth of the positive electrode active material layer 32, which is detrimental to balancing the ratio of negative to positive electrode active material (CB value) and mitigates lithium deposition. Therefore, a slope L1 less than or equal to 500 μm prevents the slope region of the second cell segment 5212 from becoming excessively long, thus facilitating a balance of the ratio of negative to positive electrode active material (CB value) and mitigating lithium deposition.

[0100] In some embodiments, along the winding direction of the positive electrode 3, the positive electrode 3 located in the arc region 22 includes a first positive arc region, the first positive arc region is connected to the first positive straight region, and the fourth groove segment 3212 of the second groove 321 of the first positive arc region extends beyond the boundary position P between the first positive arc region and the first positive straight region. Figure 11 As shown), and the length of the first positive arc region along the winding direction is L13, which satisfies L13≤L12≤2L13.

[0101] The positive electrode 3 located in the arc region 22 has multiple positive arc regions along the stacking direction of the arc region 22. The multiple positive arc regions include a first positive arc region, which can be any one of the multiple positive arc regions.

[0102] Because the thickness of the positive active material layer 32 at the junction of the third groove segment 3211 (normal processing area) and the fourth groove segment 3212 (slope area) of the second groove 321, and at the junction of the fourth groove segment 3212 and the positive active material layer 32 (non-processed area) without grooves, there is a stress change at the junction due to the combined effect of winding stress and expansion stress during the cyclic expansion of the wound cell. Furthermore, the junction of the arc area 22 and the straight area 21 of the wound cell is the most vulnerable part during the cyclic expansion process and is most prone to breakage. If the fourth groove segment 3212 is set at the junction of the arc area 22 and the straight area 21, the stress change will make the originally vulnerable part more prone to breakage. If L12 is too small, less than L13, the amount of positive active material layer 32 in the arc region 22 will be insufficient, failing to achieve the purpose of slow lithium dissolution. If L12 is too large, greater than 2L13, the amount of positive active material layer 32 in the arc region 22 will be excessive, which is not conducive to improving the energy density of the battery. Therefore, the fourth trench segment 3212 of the second trench 321 extends beyond the junction of the flat region 21 and the arc region 22 of the positive electrode sheet 3, with L13≤L12≤2L13. This not only reduces the risk of breakage of the positive electrode sheet 3 of the wound cell at the junction of the arc region 22 and the flat region 21, but also slows down the lithium dissolution problem and is conducive to improving the energy density of the battery.

[0103] Example 1: Battery preparation: I. Preparation of the positive electrode sheet Lithium cobalt oxide (LCO), polyvinylidene fluoride (PVDF), and conductive carbon (SuperP) are dissolved in N-methylpyrrolidone (NMP) at a mass ratio of 98:1:1 and stirred evenly to form a positive electrode slurry. This slurry is then uniformly coated on both sides of the positive electrode current collector 31 along its thickness direction. After drying and rolling, the positive electrode sheet 3 is formed.

[0104] II. Preparation of the negative electrode sheet Silicon-carbon composite material, graphite, conductive carbon black, polyacrylic acid, sodium carboxymethyl cellulose, and styrene-butadiene rubber are mixed in a mass ratio of 43.5:53.5:0.5:1.2:0.4:0.9. After being mixed with deionized water and stirred evenly to form a negative electrode slurry, the slurry is uniformly coated on both sides of the negative electrode current collector 51 along its thickness direction to form a negative electrode active material layer 52. After drying and rolling, a negative electrode sheet 5 is formed. Then, a first groove 521 extending along the length direction X is rolled out on the negative electrode active material layer 52. The first groove 521 includes a first groove segment 5211 and a second groove segment 5212 located at both ends of the first groove segment 5211. The second groove segment 5212 has a slope area close to the first groove segment 5211, and the maximum depth of the second groove segment 5212 is less than the depth of the first groove segment 5211.

[0105] III. Preparation of Electrolyte In an argon-filled glove box with a water content of <0.1 ppm and an oxygen content of <0.1 ppm, the electrolyte is prepared by mixing the following components by mass: 10% of the first cyclic carbonate fluoroethylene carbonate, 25% of the second cyclic carbonate ethylene carbonate (EC), 20% of the second cyclic carbonate (PC), 30% of the second cyclic carbonate (DEC), 3% of the second cyclic carbonate (ADN and HTCN in a 1:1 ratio), 1.5% of the third cyclic carbonate (PS), 10% of the third cyclic carbonate (LiPF6), and 0.5% of the fourth cyclic carbonate (LiPO2F2). After passing physical property testing, the electrolyte is obtained. The total mass of the first cyclic carbonate fluoroethylene carbonate, the second cyclic carbonate, and the second cyclic carbonate is 85%.

[0106] In this electrolyte, the content of the first cyclic carbonate compound is X1, the content of the second cyclic carbonate compound is X2, and the sum of the content of X1 and X2 is X.

[0107] IV. Battery Assembly The negative electrode, the first separator, the positive electrode, and the second separator are stacked in sequence and wound to form a battery cell. The battery cell is then packaged with the casing, and processes such as liquid injection, secondary sealing, formation, and sorting are performed to obtain the battery.

[0108] The battery cells of each embodiment are processed according to Table 1 for other parameters. Specific parameter differences are indicated in the table and will not be detailed here. It should be noted that the relevant parameters of the trenches on the surface of the negative electrode active material layer 52 can be measured by disassembling the battery, removing the corresponding negative electrode plate, and using a scanning electron microscope.

[0109] Table 1: Effects of battery parameter variations on capacity retention, K-value, and energy density

[0110] 800T Cycle Capacity Retention Rate Test Method: The batteries prepared in the above examples and comparative examples were placed in an environment of 25±2℃ and charged at a constant current of 1C until the cutoff current was 0.05C. After the batteries were fully charged, they were left to rest for 5 minutes and then discharged at a constant current of 0.5C until the cutoff voltage was 3.0V. The charging and discharging mechanism was repeated three times. The highest discharge capacity in the first three cycles was recorded as the initial capacity Q0. After 800 cycles, the discharge capacity Q1 of the battery was recorded. The high-temperature capacity retention rate of the battery is Q1 / Q0×100%.

[0111] Energy density testing method: Charge the battery at a current of 0.2C to the limiting voltage, then charge it at a constant voltage until the current drops to 0.02C, and then discharge it at a current of 0.2C until the limiting voltage is reached. The energy discharged is recorded as E. Measure the thickness, width, and length of the battery and calculate their product to obtain the battery volume, recorded as V. The formula for calculating volumetric energy density is VED = E / V.

[0112] K-value defect test method: Charge the battery at 25℃ with a constant current and constant voltage of 1C to 4.0V, cut off at 0.02C (battery charged to 65% SOC), let it stand for 5 minutes, and test the open circuit voltage OCV1 of the battery, in volts (V). Then, leave the battery open-circuit at (25±2)℃ for 48 hours, and test the voltage OCV2 of the battery after the open circuit. Calculate the self-discharge coefficient K value of the battery: K=(OCV1-OCV2) / 48. The normal range of the self-discharge coefficient K value is -0.01 to 0.06. If it exceeds this range, the K value is considered defective, indicating abnormal battery self-discharge. A total of 10 batteries were tested. For example, 6 / 10 means that 6 batteries did not have K-value defects. As shown in Table 1, the batteries with the second slot in Examples 1-16 did not have K-value defects, while the batteries without the second slot in Comparative Example 1 had K-value defects. This shows that the batteries with the second slot in the embodiments of the present invention can effectively prevent abnormal battery self-discharge.

[0113] In Examples 1-16, the 800T cycle capacity retention rate of batteries with X in the range of 13% to 65% is higher than that of batteries in Comparative Examples 2 and 3 where X is not in the range of 13% to 65%. This indicates that when the battery X in the embodiments of the present invention is in the range of 13% to 65%, the cycle performance of the battery can be improved.

[0114] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms "comprising" and "having," and any variations thereof, in the specification, claims, and accompanying drawings of this application, are intended to cover non-exclusive inclusion. In the description of embodiments of this application, technical terms such as "first," "second," etc., are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary or secondary relationship of the indicated technical features. In the description of embodiments of this application, "a plurality of" means two or more, unless otherwise expressly and specifically defined. The reference to "embodiment" herein means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0115] In the description of the embodiments of this application, the technical terms "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "circumferential," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed, operated, or used in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0116] In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of this application according to the specific circumstances.

[0117] Although embodiments of the invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the invention, and such modifications and variations all fall within the scope defined by the appended claims.

Claims

1. A battery (100) characterized in that, Comprise: A shell (1); An electric core (2) arranged in the shell (1), the electric core (2) comprising a positive electrode sheet (3), a separator (4) and a negative electrode sheet (5), the negative electrode sheet (5) comprising a negative electrode current collector (51) and a negative electrode active material layer (52) arranged on at least one side of the negative electrode current collector (51) in the thickness direction (Z), the negative electrode active material layer (52) comprising a silicon-based material, the negative electrode active material layer (52) being provided with a plurality of first grooves (521), the plurality of first grooves (521) being spaced apart; Wherein, the first groove (521) comprises a first groove section (5211) and a second groove section (5212), at least one end of the first groove section (5211) is connected with the second groove section (5212), the second groove section (5212) has a slope area close to the first groove section (5211), the depth of the second groove section (5212) in the thickness direction (Z) gradually decreases from one end close to the first groove section (5211) to one end away from the first groove section (5211); An electrolyte arranged in the shell (1), the electrolyte comprising a first cyclic carbonate compound and a second cyclic carbonate compound, the sum X of the mass content proportions of the first cyclic carbonate compound and the second cyclic carbonate compound in the total mass of the electrolyte ranges from 13% to 65%; the first cyclic carbonate compound comprises at least one of fluoroethylene carbonate and difluoroethylene carbonate, and the second cyclic carbonate compound comprises at least one of ethylene carbonate and propylene carbonate.

2. The battery of claim 1, wherein, The ratio of the mass content proportion X1 of the first cyclic carbonate compound to the mass content proportion X2 of the second cyclic carbonate compound in the total mass of the electrolyte ranges from 0.1 to 8.5; The mass content proportion X1 of the first cyclic carbonate compound in the total mass of the electrolyte ranges from 5% to 25%, preferably from 8% to 20%; The mass content proportion X2 of the second cyclic carbonate compound in the total mass of the electrolyte ranges from 3% to 55%.

3. The battery of claim 1, wherein: The negative electrode active material layer (52) comprises a main body area (522) and a thinned area (523) connected to both ends of the main body area (522) in the length direction (X), the thickness of the thinned area (523) is smaller than the thickness of the main body area (522) in the thickness direction (Z), and the second groove section (5212) extends to the thinned area (523).

4. The battery of claim 1, wherein: In the length direction (X), the length of the second groove section (5212) is L1, and the length of the first groove section (5211) is L2, satisfying L2>L1 and 30 μm≤L1≤500 μm; And / or, An included angle between a groove bottom surface of the second groove segment (5212) and a groove bottom surface of the first groove segment (5211) is α1, and satisfies 90° < α1 < 150°; And / or, A depth of the first groove segment (5211) is H1, and satisfies 2 μm < H1 ≤ 40 μm.

5. The battery of claim 1, wherein, Along the length direction (X), a spacing between edges of the first groove (521) on the same side and edges of the negative active material layer (52) satisfies 20 mm ≤ L3 ≤ 100 mm; and / or, Along the width direction (Y), a spacing between edges of the negative active material layer (52) on the same side and edges of the first groove (521) closest to the negative active material layer (52) satisfies 1 mm ≤ L4 ≤ 10 mm.

6. The battery of claim 1, wherein, Along the thickness direction (Z), the first groove (521) has a bottom notch close to the negative current collector (51) and a top notch away from the negative current collector (51), and a width of the top notch is greater than a width of the bottom notch; and / or, A bottom notch width of the first groove (521) close to the negative current collector (51) is L6, a top notch width of the first groove (521) away from the negative current collector (51) is L7, and a mass percentage of silicon in the negative active material layer (52) is A1, and satisfies 0.6 < L6 / L7 < 1; 30 μm < L6 < 150 μm; 50 μm < L7 < 150 μm; 1.2 < L6 / (L7*A1) < 18, 5% ≤ A1 ≤ 50%; and / or, An included angle between a groove bottom surface and a groove side surface of the first groove (521) satisfies 90° < α2 < 130°.

7. The battery of claim 1, wherein, Along the thickness direction (Z), a top notch edge of the first groove (521) away from the negative current collector (51) is formed with a protruding structure (524), and a height of the protruding structure (524) protruding from a surface of the negative active material layer (52) is L8, and satisfies 0.5 μm < L8 < 13 μm.

8. The battery of claim 1, wherein, The negative current collector (51) is provided with the negative active material layer (52) on both sides along the thickness direction (Z), and surfaces of the negative active material layers (52) on both sides are provided with the first groove (521); and wherein, at one end of the negative electrode plate (5), a distance between two edges of the second groove segment (5212) in the first groove (521) on both sides of the negative active material layer (52) along the length direction (X) satisfies L5 ≤ 1 mm.

9. The battery of claim 1, wherein, The electric core (2) is in a winding structure, comprising a flat area (21) and a circular arc area (22), the positive electrode sheet (3) comprises a positive electrode current collector (31) and a positive electrode active material layer (32) arranged on at least one side of the positive electrode current collector (31) in the thickness direction (Z), and the positive electrode active material layer (32) on the side of the positive electrode sheet (3) in the circular arc area (22) close to the winding center is provided with a second groove (321) in the thickness direction (Z); The second groove (321) comprises a third groove section (3211) and a fourth groove section (3212), and the third groove section (3211) is connected with the fourth groove section (3212) at least at one end in the winding direction; in the thickness direction (Z), the depth of the fourth groove section (3212) gradually decreases from one end close to the third groove section (3211) to one end away from the third groove section (3211); Wherein, the depth of the third groove section (3211) is H2, and satisfies 2μm 10. The battery of claim 9, wherein, in the winding direction of the positive electrode sheet (3), the length of the fourth groove section (3212) is L11, and the total length of the second groove (321) is L12, and satisfies 50μm≤L11≤500μm, 1mm≤L12≤10mm; and / or, in the winding direction of the positive electrode sheet (3), the positive electrode sheet (3) in the circular arc area (22) comprises a first positive electrode circular arc area, the first positive electrode circular arc area is connected with a first positive electrode flat area, the fourth groove section (3212) of the second groove (321) of the first positive electrode circular arc area exceeds the junction position of the first positive electrode circular arc area and the first positive electrode flat area, and the length of the first positive electrode circular arc area in the winding direction is L13, and satisfies L13≤L12≤2L13.

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