A battery

Abstract

The embodiment of the application provides a battery, which comprises a positive electrode sheet, a diaphragm, a negative electrode sheet and an electrolyte, the positive electrode sheet, the diaphragm and the negative electrode sheet are laminated and wound to form a roll core; the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer located on at least one side surface of the positive electrode current collector; the roll core comprises circular arc segments and flat segments located between the circular arc segments, the positive electrode active material layer in the circular arc segment comprises a first region, and the first region comprises a plurality of recesses; the depth b of the recesses is 0.005 mm to 0.04 mm, and the width c of the recesses is 0.01 mm to 0.8 mm; the electrolyte comprises 1,2,4-butanetricarbonitrile; and the mass content a of the 1,2,4-butanetricarbonitrile in the electrolyte is 0.1 wt% to 5 wt%. The battery has high structural stability, low internal high-temperature cycle gas production and good high-temperature cycle performance.

Description

Technical Field

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

[0002] With the rapid development of new energy vehicles, consumer electronics, and energy storage systems, lithium-ion batteries, as core energy storage devices, directly affect the energy density, cycle life, and safety of these devices. Due to their advantages such as high energy density, high manufacturing efficiency, and controllable cost, wound-type cells have become the mainstream structural form for high-voltage lithium cobalt oxide batteries.

[0003] However, during long-term battery cycling, the curved area of ​​the wound cell suffers from poor electrolyte penetration due to stress concentration caused by electrode bending and electrolyte surface tension. This wettability defect leads to poor contact between the positive electrode active material and the current collector, obstructing the lithium-ion transport path and causing problems such as capacity decay and increased polarization. Simultaneously, the insufficient structural stability of the curved area may accelerate microcrack propagation under high temperature or high-rate cycling, leading to electrode breakage or internal short circuits, severely impacting battery safety. Furthermore, high-voltage lithium cobalt oxide batteries are prone to gas generation at high temperatures, further reducing cycle life and reliability.

[0004] Therefore, how to solve the problems of poor wetting in the arc area, interface stress concentration and high-temperature gas generation while ensuring the structural strength of the cell has become a key technical bottleneck for improving the performance of high-energy-density lithium-ion batteries. Summary of the Invention

[0005] This invention provides a battery that, while ensuring the structural strength of the battery cell, effectively solves the problems of wetting and gas generation caused by stress concentration at the arc of the battery, and improves the high-temperature cycling gas generation problem and cycle performance of the battery.

[0006] This invention provides a battery comprising a positive electrode, a separator, a negative electrode, and an electrolyte. The positive electrode, separator, and negative electrode are stacked and wound to form a core. The positive electrode includes a positive current collector and a positive active material layer located on at least one side surface of the positive current collector. The core includes an arc segment and a straight segment located between the arc segments. The positive active material layer within the arc segment includes a first region, which includes a plurality of recesses.

[0007] The depth b mm of the recess is 0.005 mm to 0.04 mm, and the width c mm of the recess is 0.01 mm to 0.8 mm.

[0008] The electrolyte comprises 1,2,4-butanetrionitrile; the mass content (a) of the 1,2,4-butanetrionitrile in the electrolyte is 0.1 wt% to 5 wt%.

[0009] In some embodiments of the present invention, the battery satisfies: 0.05

[0010] And / or, 0.003

[0011] In some embodiments of the present invention, the battery satisfies at least one of the following conditions:

[0012] (1) Along the width direction of the positive electrode, the distance d mm between the edge of the first region and the edge of the adjacent positive electrode is 0.2 mm to 5 mm;

[0013] (2) Along the length of the positive electrode, the size e mm of the first region is 4 mm to 18 mm;

[0014] (3) The distance between two adjacent recesses is 0.03mm to 2mm.

[0015] In some embodiments of the present invention, the electrolyte further includes a fluorocarboxylic acid ester, and the battery satisfies at least one of the following conditions:

[0016] (1) The fluorocarboxylic acid ester has a mass percentage of 2wt% to 65wt% in the electrolyte; preferably, the fluorocarboxylic acid ester has a mass percentage of 10wt% to 55wt% in the electrolyte;

[0017] (2) The fluorocarboxylic acid esters include one or more of 2-fluoro-1-ethanol acetate, 2,2-difluoroethyl acetate, 2,2,2-trifluoroethyl acetate, 3-fluoro-1-propanol acetate, 2,2-difluoroethyl propionate, and (2,2,2-trifluoroethyl) propionate.

[0018] In some embodiments of the present invention, the electrolyte further includes fluorosulfonamide, wherein the fluorosulfonamide accounts for 2wt% to 30wt% of the mass of the electrolyte.

[0019] In some embodiments of the present invention, the fluorosulfonamide comprises one or more compounds represented by formulas I-1 to I-13:

[0020] Formula I-1 Formula I-2 Formula I-3

[0021] Formula I-4 Formula I-5 Formula I-6

[0022] Formula I-7 Formula I-8 Formula I-9 ​​

[0023] Formula I-10 Formula I-11 Formula I-12

[0024] Formula I-13.

[0025] In some embodiments of the present invention, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer located on at least one side surface of the negative electrode current collector, the negative electrode active material layer includes a negative electrode active material, the negative electrode active material includes a silicon-based material, and the battery satisfies at least one of the following conditions:

[0026] (1) The silicon element in the silicon-based material accounts for 2wt% to 30wt% of the mass of the anode active material layer;

[0027] (2) The Dv50 of the silicon-based material is 1μm~15μm;

[0028] (3) The silicon-based material includes at least one of silicon-carbon material, silicon-oxygen material, elemental silicon, and silicon alloy.

[0029] In some embodiments of the present invention, the negative electrode sheet includes a safety coating located between the negative electrode current collector and the negative electrode active material layer, the safety coating including a conductive agent, and the battery satisfies at least one of the following conditions:

[0030] (1) The thickness fμm of the safety coating is 0.1μm~5μm;

[0031] (2) The battery satisfies: 5 ≤ f / a ≤ 1500;

[0032] (3) The conductive agent includes one or more of carbon black, carbon nanotubes, and graphene.

[0033] In some embodiments of the present invention, the positive electrode active material layer includes a positive electrode active material, and the positive electrode active material includes lithium cobalt oxide.

[0034] In some embodiments of the present invention, the charging cut-off voltage of the battery is not lower than 4.5V.

[0035] The battery provided in this invention improves electrolyte wettability and alleviates interfacial stress concentration by setting a recess in the positive electrode active material layer of the arc segment of the core and simultaneously introducing an electrolyte system containing 1,2,4-butanetrionitrile. It also suppresses high-temperature side reaction gas generation. Thus, while ensuring the structural strength of the cell, it effectively solves the wettability and gas generation problems caused by arc stress concentration in high-energy-density lithium-ion batteries, reduces high-temperature cycle gas generation, and improves the high-temperature cycle performance of the battery. Attached Figure Description

[0036] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0037] Figure 1 A schematic diagram illustrating the provision of a winding core for an embodiment of the present invention;

[0038] Figure 2 A schematic diagram of the positive electrode sheet is provided for an embodiment of the present invention.

[0039] Explanation of reference numerals in the attached figures:

[0040] 1: Arc segment; 2: Straight segment; 3: First region; 4: Positive electrode active material layer; 5: Positive electrode current collector; 6: Positive electrode sheet; 7: Negative electrode sheet.

[0041] The accompanying drawings have illustrated specific embodiments of the invention, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the invention in any way, but rather to illustrate the concept of the invention to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0043] To improve the electrolyte wettability of the arc-shaped region of the wound battery cell, the inventors of this application attempted to use a method of physically drilling holes in the corresponding region of the positive electrode. This method aims to optimize the wetting effect by introducing a microporous structure to increase the electrolyte transport channels and local storage capacity. However, research has found that this method has drawbacks: First, excessive physical drilling can damage the structural integrity of the electrode, leading to a decrease in its mechanical strength and tensile properties. This makes the arc-shaped region prone to microcracks due to stress concentration during electrochemical cycling, thus affecting long-term reliability. Second, the drilling edges, under the stress of repeated expansion and contraction of the active material, are prone to become paths for crack propagation, which may eventually lead to electrode breakage. Third, this solution fails to effectively alleviate the interfacial stress problem caused by electrode bending in the arc-shaped region. Under high-temperature cycling conditions, side reactions intensify, and gas generation remains a prominent issue. In addition, the inventors of this application also attempted to use nitrile additives (such as 1,3,6-hexanetrionitrile, butadionitrile, etc.) to stabilize the cathode structure. However, it was found that such additives have limited chelating ability due to the relatively loose spatial arrangement of their cyano groups, which limits their ability to suppress gas generation under high voltage conditions. Furthermore, they may have an adverse effect on the overall performance of the battery by increasing the electrolyte impedance.

[0044] Therefore, it is urgent to address the issues of electrolyte wetting and gas generation caused by stress concentration in the arc region of the battery, in order to improve the high-temperature cycling gas generation problem and high-temperature cycling performance of the battery.

[0045] Based on this, embodiments of the present invention provide a battery, including a positive electrode, a separator, a negative electrode, and an electrolyte. The positive electrode, separator, and negative electrode are stacked and wound to form a core. The positive electrode includes a positive current collector and a positive active material layer located on at least one side surface of the positive current collector. The core includes an arc segment and a straight segment located between the arc segments. The positive active material layer within the arc segment includes a first region, which includes a plurality of recesses. The depth bmm of the recesses is 0.005mm-0.04mm, and the width cmm of the recesses is 0.01mm-0.8mm. The electrolyte includes 1,2,4-butanetrionitrile. The mass content a of 1,2,4-butanetrionitrile in the electrolyte is 0.1wt%-5wt%.

[0046] When the battery of the present invention includes the above-described structure and composition, it can effectively improve the problems of electrolyte wetting and gas generation caused by stress concentration in the arc region of the battery while ensuring the structural strength of the cell, thereby improving the high-temperature cycling gas generation problem and high-temperature cycling performance of the battery.

[0047] In detail, the embodiments of the present invention provide several recesses in the first region of the positive electrode active material layer in the arc segment of the core, controlling the depth of the recesses to 0.005mm~0.04mm and the width to 0.01mm~0.8mm, while limiting the mass content of 1,2,4-butanetrionitrile (BTCN) in the electrolyte to 0.1wt%~5wt%. This recessed structure can effectively increase the electrolyte retention in the arc region, improve the wetting effect of the electrolyte in this region, and ensure that 1,2,4-butanetrionitrile can fully play its role in the arc region. By controlling the 1,2,4-butanetrionitrile content, recess depth, and width within the above ranges, the recesses in the arc region can improve the performance of the arc region. The electrolyte retention capacity ensures sufficient 1,2,4-butanetrionitrile to function effectively. However, the stress on the electrode in the bending region is greater than that in the straight region. When grooves are added to the bending region, the structural strength of the bending region deteriorates, and gas generation becomes more severe. This leads to a higher risk of breakage in the later stages of cycling. The multiple cyano groups of the added 1,2,4-butanetrionitrile have a more compact spatial configuration, resulting in better complexation of the positive electrode metal ions. This ensures a more stable and dense passivation film, reduces gas generation, improves the mechanical strength of the protective film, and enhances the structural stability of the positive electrode. This suppresses the positive electrode breakage problem in the arc region of the battery and improves the high-temperature cycling gas generation and high-temperature cycling performance of the battery.

[0048] The embodiments of this invention can use conventional testing methods and instruments in the art to test the depth and width of the recesses, as well as the mass content (a) of 1,2,4-butanetrionitrile in the electrolyte. For example, the depth (b) and width (c) of the recesses can be observed and measured in the first region of the arc segment of the positive electrode using scanning electron microscopy (SEM) or laser confocal microscopy. The mass content (a) of 1,2,4-butanetrionitrile in the electrolyte can be quantitatively detected using gas chromatography-mass spectrometry (GC-MS) or high-performance liquid chromatography (HPLC) with external standard method. Specifically, the battery can be completely discharged and disassembled. The positive electrode can be separated and dried. Then, the first region of the arc segment of the positive electrode can be observed using scanning electron microscopy (SEM) or laser confocal microscopy. The depth and width of at least 20 recesses can be randomly measured, and the average value is taken to obtain the depth (b) and width (c) of the recesses. When specifically testing the mass content 'a' of 1,2,4-butanetrionitrile in the electrolyte, the battery can be completely discharged and disassembled, and the electrolyte sample can be taken for testing using gas chromatography-mass spectrometry or high performance liquid chromatography.

[0049] Some embodiments of the present invention, such as Figure 1 and Figure 2As shown, the battery includes a positive electrode 6, a separator, a negative electrode 7, and an electrolyte. The positive electrode 6, the separator, and the negative electrode 7 are stacked and wound to form a core. The positive current collector has a positive active material layer 4 on at least one side surface. The core includes an arc segment 1 and a straight segment 2 located between the arc segments 1. The positive active material layer 2 within the arc segment 1 includes a first region 3, and the first region 3 includes a plurality of recesses.

[0050] For example, the value of the depth b of the recess is, for example, a range of 0.005 mm, 0.01 mm, 0.015 mm, 0.018 mm, 0.02 mm, 0.025 mm, 0.03 mm, 0.04 mm or any combination thereof. The depth of the recess has the conventional meaning in the art, referring to the vertical distance from the lowest point in the recess to the surface of the positive electrode.

[0051] For example, the width c of the recess can be 0.01mm, 0.05mm, 0.1mm, 0.2mm, 0.3mm, 0.4mm, 0.5mm, 0.6mm, 0.7mm, 0.8mm, or any combination thereof. When the projection of the recess onto the thickness of the positive electrode is a regular circle, the width of the recess is the diameter of the regular circle. When the projection of the recess onto the thickness of the positive electrode is not a "regular circle", the diameter of the recess is the equivalent diameter of a circle with the same area as the irregular circle. When the recess is a linear groove on the positive electrode, the width is the width of the linear groove.

[0052] The mass content 'a' of 1,2,4-butanetrionitrile in the electrolyte is, for example, a range of 0.1 wt%, 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, or any combination thereof.

[0053] In some embodiments of the present invention, 0.03

[0054] ​In some embodiments of the present invention, 0.003

[0055] Through collaborative control 0.03

[0056] The first region described above can be prepared using methods conventional in the art, such as laser drilling, mechanical punching, etching, ultrasonic drilling, or molding. The specific preparation method can be selected according to actual needs.

[0057] In some embodiments of the present invention, the battery satisfies at least one of the following conditions:

[0058] (1) Along the width direction of the positive electrode, the distance dmm between the edge of the first region and the edge of the adjacent positive electrode is 0.2mm~5mm;

[0059] (2) Along the length of the positive electrode, the size of the first region is 4mm~18mm;

[0060] (3) The distance between two adjacent recesses is 0.03mm~2mm.

[0061] In some embodiments, the size e of the first region and the distance d between the edge of the first region and the edge of the adjacent positive electrode are as follows: Figure 2 As shown.

[0062] ​​In some embodiments, the distance *d* between the edge of the first region and the edge of the adjacent positive electrode sheet along the width direction of the positive electrode sheet can better improve the structural stability of the positive electrode arc region, help reduce powder shedding from the positive electrode active layer, further improve the stress state of the positive electrode sheet, further improve the overall structural reliability of the electrode sheet, and further reduce the tendency of the electrode sheet to break. For example, the value of *d* is, for example, a range of 0.2 mm, 0.5 mm, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, or any combination thereof. Specifically, the distance *d* is the vertical distance from the edge of the concave portion closest to the edge of the positive electrode sheet to the corresponding edge of the positive electrode sheet along the width direction of the positive electrode sheet.

[0063] In some embodiments, the dimension emm of the first region along the length of the positive electrode sheet is 4mm to 18mm. This better ensures sufficient wetting of the electrolyte in the arc-shaped region, further optimizes the structural stability of the positive electrode sheet, better balances electrode strength and wetting performance, and further improves the overall cycle performance of the battery and suppresses gas generation during high-temperature cycling. For example, the value of e is, for instance, 4mm, 6mm, 8mm, 10mm, 12mm, 14mm, 16mm, 18mm, or any combination thereof. Specifically, along the length of the positive electrode sheet, the farthest distance between the edges of the recesses closest to the two ends of the first region is the dimension e of the first region.

[0064] In some embodiments, the spacing between two adjacent recesses is 0.03 mm to 2 mm, which can better ensure the uniform wetting of electrolyte in the arc-shaped region, further optimize the structural stability of the electrode in the arc-shaped region, better balance the electrolyte retention effect and the overall strength of the electrode, and is more conducive to improving the cycle performance of the battery. For example, the spacing between two adjacent recesses is, for example, a range of 0.03 mm, 0.1 mm, 0.5 mm, 1 mm, 1.5 mm, 2 mm, or any combination thereof. More specifically, the spacing between two adjacent recesses refers to the shortest distance between the edges of the orthographic projections of two adjacent recesses on the surface of the positive electrode.

[0065] The embodiments of the present invention can use conventional testing methods and instruments in the art to test the distance d between the edge of the first region and the edge of the adjacent positive electrode, the size e of the first region, and the spacing between two adjacent recesses, for example, by using a laser confocal microscope, a scanning electron microscope, or an optical microscope in conjunction with image analysis software for measurement.

[0066] In some embodiments of the present invention, the electrolyte further includes fluorocarboxylic acid esters, and the battery satisfies at least one of the following conditions:

[0067] (1) The mass percentage of fluorocarboxylic acid ester in the electrolyte is 2wt%~65wt%; preferably, the mass percentage of fluorocarboxylic acid ester in the electrolyte is 10wt%~55wt%;

[0068] (2) Fluorocarboxylic acid esters include one or more of 2-fluoro-1-ethanol acetate, 2,2-difluoroethyl acetate, 2,2,2-trifluoroethyl acetate, 3-fluoro-1-propanol acetate, 2,2-difluoroethyl propionate, and (2,2,2-trifluoroethyl) propionate.

[0069] In some embodiments of the present invention, the fluorocarboxylic acid ester has a mass percentage of 2wt% to 65wt% in the electrolyte. It can be used in conjunction with 1,2,4-butanetrionitrile to modify and fill the passivation layer of the positive electrode, increasing the LiF content in the passivation layer, making the passivation layer denser and with higher mechanical strength, better stabilizing the structure of the positive electrode, accelerating the desolvation rate of lithium, further improving the impedance increase problem caused by nitrile components, and thus further improving the overall battery performance. For example, the mass percentage of the fluorocarboxylic acid ester in the electrolyte is, for example, 2wt%, 10wt%, 20wt%, 30wt%, 40wt%, 50wt%, 60wt%, 65wt%, or any combination thereof. Preferably, the mass percentage of the fluorocarboxylic acid ester in the electrolyte is 10wt% to 55wt%, which provides better results.

[0070] In some embodiments, the fluorocarboxylic acid ester includes one or more of 2-fluoro-1-ethanol acetate, 2,2-difluoroethyl acetate (DFEA), ethyl 2,2,2-trifluoroacetate, 3-fluoro-1-propanol acetate, 2,2-difluoroethyl propionate, and (2,2,2-trifluoroethyl) propionate. Preferably, the fluorocarboxylic acid ester includes 2,2-difluoroethyl acetate, which provides better results.

[0071] In some embodiments of the present invention, the fluorosulfonamide has a mass percentage of 2wt% to 30wt% in the electrolyte. This facilitates the detachment of fluorine atoms from the negative electrode to form a high-quality, tightly packed LiF protective layer, further reducing the problem of gas generation at the negative electrode. The formation of an S-containing organic-inorganic cross-linked network and Li3N through the sulfonyl groups helps adapt to changes in the volume of the negative electrode, further improving the lithium-ion transport rate and thus enhancing the overall cycle performance of the battery. For example, the mass percentage of fluorosulfonamide in the electrolyte may be 2wt%, 5wt%, 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, or any combination thereof.

[0072] In some embodiments of the present invention, fluorosulfonamides include one or more compounds represented by formulas I-1 to I-13:

[0073] Formula I-1 Formula I-2 Formula I-3

[0074] Formula I-4 Formula I-5 Formula I-6

[0075] Formula I-7 Formula I-8 Formula I-9

[0076] Formula I-10 Formula I-11 Formula I-12

[0077] Formula I-13. When the electrolyte of the present invention includes the above-described components, the effect of improving high-temperature gas generation in the battery is further improved, and the cycle performance of the battery is further enhanced.

[0078] The embodiments of the present invention can use conventional testing methods and instruments in the art to test the content and type of fluorocarboxylic acid esters and fluorosulfonamides in the above-mentioned electrolyte. For example, gas chromatography-mass spectrometry (GC-MS) or high performance liquid chromatography (HPLC) with external standard method can be used for quantitative detection. The specific testing methods are as described above and will not be repeated here.

[0079] In some embodiments of the present invention, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer located on at least one side surface of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material, which includes a silicon-based material. The battery satisfies at least one of the following conditions:

[0080] (1) The mass percentage of silicon in the anode active material layer of the silicon-based material is 2wt%~30wt%;

[0081] (2) The Dv50 of silicon-based materials is 1μm~15μm;

[0082] (3) Silicon-based materials include at least one of silicon-carbon materials, silicon-oxygen materials, elemental silicon, and silicon alloys.

[0083] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer located on at least one side surface of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material, which is a silicon-based material. The mass percentage of silicon in the silicon-based material within the negative electrode active material layer is 2 wt% to 30 wt%, which can further improve the energy density and cycle performance of the battery. For example, the mass percentage of silicon in the silicon-based material within the negative electrode active material layer is, for example, 2 wt%, 5 wt%, 10 wt%, 20 wt%, 30 wt%, or any combination thereof.

[0084] In some embodiments, the negative electrode active material further includes a carbon-based material, which includes at least one of graphite, hard carbon, and soft carbon. Preferably, the carbon-based material includes graphite.

[0085] This invention allows for the testing of silicon content in the negative electrode active material layer using conventional testing methods and instruments. For example, the content can be calculated using ash content testing and EDS testing results. EDS testing: The battery is discharged to 0% SOC, disassembled, and the negative electrode is removed. The negative electrode containing the silicon-carbon composite material is treated with an argon ion polisher to obtain its cross-section. The cross-section is then tested using a scanning electron microscope in backscatter mode at a magnification of 10K. A single silicon-based material particle is selected, and EDS is used to test the location points within the particle. The silicon content (wt%) at these points is calculated using standard-free analysis. EDS sampling tests are performed on the silicon content at five points in different regions within a single particle. The average value is calculated as the silicon content of the single particle. The silicon content of 10 different silicon-based materials is statistically analyzed, and the average value is taken as the silicon content of the silicon-based material. Ash content test: After discharging the lithium-ion secondary battery to 0% SOC, the negative electrode sheet is disassembled and soaked in dimethyl carbonate (DMC) solvent for 12 hours, followed by rinsing with DMC to remove the lithium salt adhering to the negative electrode sheet. After drying, the electrode sheet is subjected to high-temperature treatment at 400℃ in an inert atmosphere for 2 hours (e.g., in a tube furnace under nitrogen or argon atmosphere). The negative electrode active material layer can then be peeled off from the current collector, and the negative electrode active material is collected. In the silicon content test, a thermogravimetric analyzer (e.g., a TGA550 thermogravimetric analyzer) is used. The sample amount is 5~15mg. Under an air or oxygen atmosphere, the temperature is increased from room temperature to 900℃ at a rate of 10℃ / min, and held at 900℃ for 40 minutes. This allows the non-silicon components in the active layer of the negative electrode material to volatilize while the silicon is fully oxidized to silicon dioxide. The weight percentage at the end of the entire test process is the ash content of the negative electrode active layer. Ignoring the mass percentage of trace impurities that may exist in the ash, and treating all the ash as silicon dioxide, the mass of silicon in the negative electrode active material can be calculated using the following formula: Mass percentage of silicon in the negative electrode active material layer = 7 × mass of ash / (15 × mass of test sample).

[0086] In some embodiments, the Dv50 of the silicon-based material is 1 μm to 15 μm, which is beneficial for improving the overall stability of the negative electrode, further mitigating the volume expansion and contraction effect of the silicon-based material during charge and discharge, better maintaining the integrity of the electrode structure, and improving the high-temperature cycle gas generation and high-temperature cycle performance of the battery. For example, the Dv50 of the silicon-based material is, for example, a range of 1 μm, 3 μm, 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, or any combination thereof.

[0087] The embodiments of the present invention can use conventional testing methods and instruments in the art to test the Dv50 (referring to the volume median particle size, i.e. the particle size corresponding to 50% of the cumulative volume distribution of the particles) of silicon-based materials, such as a laser particle size analyzer.

[0088] In some embodiments, silicon-based materials include at least one of silicon-carbon materials, silicon-oxygen materials, elemental silicon, and silicon alloys.

[0089] In some embodiments, the silicon-based material includes a silicon-carbon material, which includes a porous carbon matrix and silicon material deposited on the porous carbon matrix.

[0090] In some embodiments of the present invention, the negative electrode sheet includes a safety coating located between the negative electrode current collector and the negative electrode active material layer, the safety coating including a conductive agent, and the battery satisfies at least one of the following conditions:

[0091] (1) The thickness fμm of the safety coating is 0.1μm~5μm; the battery satisfies 5≤f / a≤1500;

[0092] (2) Conductive agents include one or more of carbon black, carbon nanotubes, and graphene.

[0093] In some embodiments, the thickness f of the safety coating is 0.1 μm to 5 μm, which can better form a physical barrier between the negative electrode active material and the copper foil, thus mitigating the corrosive effect of 1,2,4-butanetrionitrile on the copper foil and suppressing the expansion of the negative electrode active layer. This further protects the structural integrity of the copper foil, thereby improving the overall structural stability of the cell and further improving the high-temperature cycling and gas generation issues of the battery. For example, the value of f is, for instance, a range of 0.1 μm, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, or any combination thereof.

[0094] In some embodiments, the battery satisfies 5 ≤ ​​f / a ≤ 1500, which can better synergize the effects of the safety coating and 1,2,4-butanetrionitrile, and is more conducive to balancing the protective performance of the copper foil and the internal impedance characteristics of the battery, further optimizing the interface stability of the electrodes, thereby better improving the battery cycle and safety performance, and facilitating the efficient matching of coating protection and electrolyte function. For example, the value of f / a is, for example, a range of 5, 10, 20, 30, 50, 70, 100, 150, 200, 250, 300, 400, 500, 600, 800, 1000, 1200, 1500, or any combination thereof. In the embodiments of the present invention, when calculating the value of f / a, the value of a is substituted into its specific value, and f needs to be converted to the corresponding unit before being substituted into the value for calculation. For example, when a is 1.5wt% and f is 1μm, the value of f / a is 1 / 0.015 ≈ 66.67.

[0095] In some embodiments, the conductive agent includes one or more of carbon black, carbon nanotubes, and graphene, which can better improve the conductivity of the negative electrode and improve the cycle performance of the battery.

[0096] The safety coating can be prepared using conventional methods in the art, for example, by mixing a conductive agent (such as at least one of conductive carbon black, graphene, and carbon nanotubes), a binder, and a solvent, and then preparing a uniformly dispersed slurry by high-speed stirring or grinding, and then coating the slurry onto at least one side of the negative electrode current collector.

[0097] The thickness f of the safety coating can be tested using conventional testing methods and instruments in the art, such as scanning electron microscope (SEM), laser confocal microscope, white light interferometer or protractor for cross-sectional observation and measurement; if the thickness of the safety coating is uneven, the arithmetic mean of multiple measurement points is taken as the value of the thickness f.

[0098] In some embodiments of the present invention, the positive electrode active material layer includes a positive electrode active material, which includes lithium cobalt oxide, thereby further improving the battery's operating voltage and better enhancing the battery's application scenarios.

[0099] In some embodiments, the charging cutoff voltage of the battery is greater than or equal to 4.53V, for example, it can be any one of 4.53V, 4.54V, 4.55V, 4.56V, 4.57V, 4.58V or 4.6V.

[0100] In this embodiment of the invention, the battery includes an electrolyte, a battery cell, and a casing for encapsulating the battery cell. The electrolyte is injected into the battery cell within the casing. The battery cell includes a positive electrode, a negative electrode, and a separator located between the positive and negative electrode. The battery cell is a wound battery cell, meaning that the battery cell is formed by stacking and winding the positive electrode, separator, and negative electrode.

[0101] As mentioned above, the positive electrode sheet includes a positive current collector and a positive active material layer located on at least one side surface of the positive current collector. Specifically, the positive active material layer can be provided on one side surface in the thickness direction of the positive current collector, or positive active material layers can be provided on both opposite sides surface in the thickness direction of the positive current collector.

[0102] The positive electrode active material layer includes positive electrode active material, positive electrode conductive agent and positive electrode binder. In the positive electrode active material layer, the mass percentage of positive electrode active material can be 70% to 99%, the mass fraction of positive electrode conductive agent can be 0.5% to 15%, and the mass fraction of positive electrode binder can be 0.5% to 15%.

[0103] In this embodiment of the invention, the positive electrode conductive agent in the positive electrode active layer can be a conventional conductive material in the art. For example, the positive electrode conductive agent in the positive electrode active layer may include one or more of conductive carbon black, conductive graphite, carbon nanotubes (CNTs), carbon fibers, graphene, acetylene black, and Ketjen black.

[0104] In this embodiment of the invention, the positive electrode binder in the positive electrode active layer can be a conventional bonding material in the art. For example, the positive electrode binder in the positive electrode active layer may include one or more of polyvinylidene fluoride (PVDF), polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, etc.

[0105] The embodiments of the present invention may employ conventional positive current collectors in the art, for example, positive current collectors may include aluminum foil.

[0106] Specifically, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer located on at least one side surface of the negative electrode current collector. Specifically, the negative electrode active material layer can be provided on one side surface of the negative electrode current collector, or negative electrode active material layers can be provided on both opposite sides of the negative electrode current collector in the thickness direction.

[0107] Specifically, the negative electrode active material layer may include a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder. For example, the negative electrode active material may include graphite, and the negative electrode conductive agent may include one or more of conductive carbon black, carbon nanotubes (CNT), acetylene black, graphene, Ketjen black, and carbon fiber. The negative electrode binder may include one or more of sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate.

[0108] The embodiments of the present invention may employ conventional negative electrode current collectors in the art, for example, negative electrode current collectors include copper foil.

[0109] The electrolyte in this embodiment of the invention can be the electrolyte described above. The electrolyte also includes a solvent, which includes at least one of propyl propionate, ethyl propionate, propyl acetate, methyl butyrate, ethyl butyrate, methyl propionate, ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, fluorobenzene, and fluoroether.

[0110] In this embodiment of the invention, the electrolyte further includes lithium salts, including at least one of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium hexafluorophosphate, lithium difluorophosphate, lithium tetrafluoroborate, lithium bis(oxalate)borate, and lithium difluorooxalateborate.

[0111] In this embodiment of the invention, the electrolyte also includes other additives, including at least one of fluoroethylene carbonate, difluoroethylene carbonate, vinylene carbonate, 1,3-propanesulfonate lactone, and vinyl sulfate.

[0112] In this embodiment of the invention, the separator is used to separate the positive and negative electrode plates, preventing short circuits caused by contact between them. Conventional separators in the art can be used in this embodiment, and there are no particular limitations. For example, the separator material can be one or more of the following: high-density polyethylene, ultra-high-density polyethylene, low-density polyethylene, linear low-density polyethylene, high-density polypropylene, ultra-high-density polypropylene, polyimide, and polyvinylidene fluoride.

[0113] In this embodiment of the invention, the battery cell can be packaged using conventional housing materials in the art, such as flexible packaging materials like aluminum-plastic film, but is not limited thereto.

[0114] This invention also provides a battery pack comprising at least two of the above-described batteries, which has advantages corresponding to the electrolyte described above, and will not be elaborated further.

[0115] This invention also provides an electrical device including the battery described above. This electrical device has advantages corresponding to the electrolyte described above, which will not be elaborated further.

[0116] The electrical equipment used in the embodiments of this invention can be conventional electrical equipment in the art, such as power equipment (e.g., electric vehicles, electric cars), electronic devices (e.g., mobile phones, tablets, laptops, digital cameras, etc.), wearable devices (e.g., watches, bracelets, VR glasses, etc.), energy storage power stations, etc., and there are no particular limitations. The technical solution of this invention will be further described below with reference to specific embodiments.

[0117] Example 1

[0118] The battery in this embodiment is prepared by the following method:

[0119] 1) Preparation of positive electrode sheet

[0120] Lithium cobalt oxide (LiCoO2), a positive electrode active material, polyvinylidene fluoride (PVDF), a positive electrode binder, superP, and carbon nanotubes (CNTs) were mixed in a mass ratio of 96:2:1.5:0.5. N-methylpyrrolidone (NMP) was added, and the mixture was stirred under vacuum until it formed a homogeneous and fluid positive electrode slurry. The positive electrode slurry was uniformly coated onto both surfaces of an aluminum foil. The coated aluminum foil was dried, then rolled and slit. All the positive electrode active layer was removed from a specific area of ​​the positive electrode sheet to form a positive electrode tab groove. The positive electrode tabs were welded into the positive electrode tab groove to obtain the desired positive electrode sheet. The first region of the arc segment of the dried positive electrode sheet is processed by laser drilling to obtain a concave part of the arc segment. The distance d mm between the edge of the first region and the edge of the adjacent positive electrode sheet is 3 mm. The size e mm of the first region along the length of the positive electrode sheet is 10 mm. The depth b mm of the concave part is 0.01 mm, the diameter is 0.4 mm, and the distance between two adjacent concave parts is 1 mm.

[0121] 2) Preparation of negative electrode sheet

[0122] Conductive agent (conductive carbon black) and binder styrene-butadiene rubber / sodium carboxymethyl cellulose were mixed evenly at a mass ratio of 7:2.5:0.5. Deionized water was added, and the mixture was stirred or ground at high speed to form a uniformly dispersed slurry. The slurry was then coated on both sides of the negative electrode current collector, and after drying and other post-treatments, a copper foil with a safety coating was obtained. Alternatively, negative electrode active materials artificial graphite, silicon carbide, sodium carboxymethyl cellulose (CMC-Na), styrene-butadiene rubber, conductive carbon black (SP), and single-walled carbon nanotubes (SWCNTs) were mixed at a mass ratio of 74.5:20:2.5:1.5:1:0.5. Deionized water was added, and a negative electrode slurry was obtained under vacuum stirring. The negative electrode slurry was uniformly coated on the surface of the safety coating facing away from the negative electrode current collector, and then air-dried at room temperature. It was then transferred to an 80°C oven for drying for 10 hours, and finally cold-pressed and slit to obtain the negative electrode sheet.

[0123] 3) Preparation of electrolyte

[0124] In an argon-filled glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), the solvents EC / PC / PP were mixed thoroughly at a mass ratio of 1:1:1. Then, 12 wt% of fully dried lithium hexafluorophosphate (LiPF6), fluorocarboxylic acid esters, fluorosulfonamides, 8 wt% fluoroethylene carbonate, and 2.5 wt% 1,3-propanesulfonate lactone were rapidly added based on the total mass of the electrolyte. The specific amounts of fluorocarboxylic acid esters and fluorosulfonamides added are shown in Table 1. After thorough mixing, the electrolyte was tested for moisture and free acid and found to be within acceptable limits to obtain the desired electrolyte.

[0125] 4) Preparation of lithium-ion batteries

[0126] The positive electrode sheet from step 1), the negative electrode sheet from step 2), and the separator (specifically a PP separator) are stacked in the order of positive electrode sheet, separator and negative electrode sheet, and then wound to obtain a battery cell. The battery cell is placed in an outer packaging aluminum foil, and the electrolyte from step 3) is injected into the outer packaging. After vacuum sealing, standing, formation, shaping and sorting, a lithium-ion battery is obtained.

[0127] The lithium-ion batteries obtained in the examples and comparative examples were subjected to tests such as normal and high temperature cycling performance. The test results are shown in Table 3.

[0128] The differences between Examples 2-21, Comparative Examples 1-5 and Example 1 are as follows: the depth b of the recess, the width c of the recess, the mass content a of 1,2,4-butanetrionitrile in the electrolyte, the value of a / b, the value of a / c, the distance d between the edge of the first region and the edge of the adjacent positive electrode, the size e of the first region, the spacing between two adjacent recesses, the type of fluorocarboxylic acid ester, the mass percentage of fluorocarboxylic acid ester in the electrolyte (referred to as fluorocarboxylic acid ester mass percentage in the table), the type of fluorosulfonamide, the mass percentage of fluorosulfonamide in the electrolyte (referred to as fluorosulfonamide mass percentage in the table), the mass percentage of silicon element in the silicon-based material in the negative electrode active material layer (referred to as silicon element percentage in the table), the type of silicon-based material (in the examples and comparative examples where silicon-based material is " / " in Table 2, the negative electrode active material only includes artificial graphite of the same mass as the negative electrode active material of Example 1), the Dv50 of the silicon-based material, the thickness f of the safety coating, the value of f / a, and the specific type of conductive agent are shown in Tables 1 and 2. In the electrolytes of the embodiments and comparative examples of the present invention, the increase or decrease of fluorocarboxylic acid esters and fluorosulfonamide components were made up to the corresponding ratio by solvent (the solvent includes EC / PC / PP compounded in a mass ratio of 1:1:1), while other components in the electrolyte remained unchanged.

[0129]

[0130]

[0131] 1) High-temperature circulating gas production test and high-temperature circulating test

[0132] The batteries prepared in the above examples and comparative examples were placed in an environment of 45±1℃ and left to stand for 180 min. They were then discharged at a constant current of 0.5C to 2.75V, left to stand for 30 min, and then charged at a constant current and constant voltage of 0.2C to 4.53V with a cutoff current of 0.05C. After standing for 30 min, they were discharged at a constant current of 0.2C to 2.75V. The discharge capacity C0 and the thickness H0 were recorded. After standing for 30 min, this constituted one cycle. The above operation was repeated. When the cycle reached 300 cycles, the discharge capacity Cn of the 300th cycle and the battery thickness H1 were recorded.

[0133] The high-temperature cycling capacity retention rate was (Cn / C0) × 100%. The test results are recorded in Table 3.

[0134] The thickness change rate is used to represent the high-temperature circulating gas generation test: the thickness change rate is (H1-H0) / H0, and the results are shown in Table 3.

[0135] 2) Positive electrode fragment band test

[0136] The battery that had undergone 300 high-temperature cycles was then cycled for another 500 cycles, for a total of 800 cycles. After this, the battery was disassembled to check whether the aluminum foil in the arc section of the positive electrode was broken. Five batteries were tested each time. If no breakage was found, the battery was considered to have passed. The result was recorded as the number of batteries that passed / the total number of batteries tested. For example, if all five batteries passed without any breakage, the result would be recorded as 5P / 5T.

[0137]

[0138] As shown in Table 3, compared with the comparative example, the embodiments of the present invention, by setting a recess in the positive electrode active material layer of the arc segment of the core and simultaneously introducing an electrolyte system containing 1,2,4-butanetrionitrile, can reduce the high-temperature cycle gas generation of the battery and improve the high-temperature cycle performance of the battery while ensuring the structural strength of the cell.

[0139] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A battery, characterized in that, The device includes a positive electrode, a separator, a negative electrode, and an electrolyte. The positive electrode, separator, and negative electrode are stacked and wound to form a core. The positive electrode includes a positive current collector and a positive active material layer located on at least one side surface of the positive current collector. The core includes an arc segment and a straight segment located between the arc segments. The positive active material layer within the arc segment includes a first region, which includes a plurality of recesses. The depth b mm of the recess is 0.005 mm to 0.04 mm, and the width c mm of the recess is 0.01 mm to 0.8 mm. The electrolyte comprises 1,2,4-butanetrionitrile; the mass content (a) of the 1,2,4-butanetrionitrile in the electrolyte is 0.1 wt% to 5 wt%.

2. The battery according to claim 1, characterized in that, The battery satisfies: 0.05 and / or 0.

003. The battery satisfies at least one of the following conditions: (1) Along the width direction of the positive electrode, the distance dmm between the edge of the first region and the edge of the adjacent positive electrode is 0.2mm~5mm; 3. The battery according to claim 1 or 2, characterized in that, (2) Along the length of the positive electrode, the size e mm of the first region is 4 mm to 18 mm; (3) The distance between two adjacent recesses is 0.03mm to 2mm. The electrolyte further includes fluorocarboxylic acid esters, and the battery satisfies at least one of the following conditions: (1) The fluorocarboxylic acid ester has a mass percentage of 2wt% to 65wt% in the electrolyte; preferably, the fluorocarboxylic acid ester has a mass percentage of 10wt% to 55wt% in the electrolyte; 4. The battery according to any one of claims 1-3, characterized in that, (2) The fluorocarboxylic acid esters include one or more of 2-fluoro-1-ethanol acetate, 2,2-difluoroethyl acetate, 2,2,2-trifluoroethyl acetate, 3-fluoro-1-propanol acetate, 2,2-difluoroethyl propionate, and (2,2,2-trifluoroethyl) propionate. The electrolyte also includes fluorosulfonamide, which accounts for 2 wt% to 30 wt% of the electrolyte by mass. The fluorosulfonamide includes one or more of the compounds shown in Formulas I-1 to I-13:

5. The battery according to any one of claims 1-4, characterized in that, The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer located on at least one side surface of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material, which includes a silicon-based material. The battery satisfies at least one of the following conditions:

6. The battery according to claim 5, characterized in that, (1) The silicon element in the silicon-based material accounts for 2wt% to 30wt% of the mass of the anode active material layer; Formula I-1 Formula I-2 Formula I-3 Formula I-4 Formula I-5 Formula I-6 Formula I-7 Formula I-8 Formula I-9 Formula I-10 Formula I-11 Formula I-12 Formula I-13.

7. The battery according to claim 1, characterized in that, (2) The Dv50 of the silicon-based material is 1μm~15μm; (3) The silicon-based material includes at least one of silicon-carbon material, silicon-oxygen material, elemental silicon, and silicon alloy. The negative electrode includes a safety coating located between the negative electrode current collector and the negative electrode active material layer, the safety coating including a conductive agent, and the battery satisfies at least one of the following conditions: (1) The thickness fμm of the safety coating is 0.1μm~5μm; 8. The battery according to claim 7, characterized in that, (2) The battery satisfies: 5 ≤ f / a ≤ 1500; (3) The conductive agent includes one or more of carbon black, carbon nanotubes, and graphene. ​ ​ 9. The battery according to claim 1, characterized in that, The positive electrode active material layer includes a positive electrode active material, which includes lithium cobalt oxide.

10. The battery according to any one of claims 1-9, characterized in that, The charging cutoff voltage of the battery is not lower than 4.53V.

Images