A cylindrical battery and an electrochemical device including the same

Abstract

The application relates to the field of battery materials, in particular to a cylindrical battery and an electrochemical device comprising the same. The cylindrical battery provided by the application controls the ratio of m and C in the range of 1-3.5, so that the proportion of the mass of the organic component in the electrolyte relative to the battery capacity is moderate. Under the "breathing effect" of the silicon negative electrode, the amount of electrolyte discharged during extrusion is limited, the electrolyte can fully wet the interface, and the side reaction and uneven flow caused by excessive electrolyte are avoided, so that the balance between liquid retention and liquid control is achieved, and the high-temperature and fast-charging cycle performance of the battery is effectively improved.

Description

Technical Field

[0001] This application relates to the field of battery materials, specifically to a cylindrical battery and an electrochemical device including the cylindrical battery. Background Technology

[0002] With the rapid development of electric vehicles and portable electronic devices worldwide, the market has placed unprecedented dual demands on the performance of lithium-ion batteries: higher energy density for longer driving range and faster charging speed for improved efficiency.

[0003] Traditional graphite anode systems are gradually approaching their theoretical energy limit, making them insufficient to meet future demands. Against this backdrop, the evolution of battery technology clearly points to more active electrode materials. Among these, high-capacity silicon anode materials are considered the next-generation mainstream technology direction for achieving breakthroughs in energy density. While silicon anodes can be used to improve battery energy density, their unique alloying and lithium intercalation mechanism causes significant volume expansion during charging and discharging (expansion exceeds 300% after lithium intercalation).

[0004] Cylindrical batteries feature a high-strength cylindrical steel casing. Their uniform circular structure effectively constrains the internal core, acting like a robust "pressure vessel" capable of withstanding higher internal pressure. This limits the volume expansion of the negative electrode during charging and discharging, especially for silicon anodes. Due to insufficient expansion space, the expansion compresses the pores between internal particles, causing electrolyte to be squeezed out. Repeated cycles result in low lithium-ion content at the electrode edges, leading to severe concentration polarization. This not only accelerates capacity decay but also severely limits fast-charge cycle performance. To mitigate the edge effect of cylindrical batteries, the residual electrolyte level can be reduced. However, a prolonged state of low electrolyte levels also affects cycle life. Furthermore, silicon anodes are not conducive to maintaining the integrity of the SEI film, leading to continuous side reactions at the negative electrode interface that consume electrolyte, further impacting cycle life. Summary of the Invention

[0005] This application provides a cylindrical battery and an electrochemical device including the cylindrical battery, which aims to solve the problems of poor battery fast charging and high-temperature cycle life.

[0006] To this end, in a first aspect, this application provides a cylindrical battery, including an electrolyte, an electrode assembly, and a casing, wherein the casing contains the electrolyte and the electrode assembly, the electrolyte includes an organic component, the mass of the organic component in the electrolyte is mg, and the capacity of the cylindrical battery is C Ah, wherein C and m satisfy the following relationship: 1≤m / C≤3.5; The organic components include chain esters and cyclic carbonates. Based on the total mass of the electrolyte, the mass percentage of the cyclic carbonates is S1, and the mass percentage of the chain esters is S2. S1 and S2 satisfy the following relationship: 1.2≤S2 / S1≤6. The electrode assembly includes a negative electrode sheet, the negative electrode sheet includes a negative current collector and a negative active layer covering at least one side of the negative current collector, the negative active layer includes a negative active material, the negative active material includes a silicon-based material; the surface of the negative active layer includes at least one groove, the groove has a depth of 5μm to 30μm and a width of 0.01mm to 0.3mm.

[0007] In some implementations, 30 ≤ m ≤ 55.

[0008] In some implementations, 15 ≤ C ≤ 40.

[0009] In some implementations, 5% ≤ S1 ≤ 40%.

[0010] In some implementations, 40% ≤ S2 ≤ 80%.

[0011] In some embodiments, the cyclic carbonate includes one or more of ethylene carbonate, propylene carbonate, and fluoroethylene carbonate.

[0012] In some embodiments, the chain ester includes one or more of dimethyl carbonate, ethyl methyl carbonate, ethyl acetate, ethyl propionate, and methyl acetate.

[0013] In some embodiments, the minimum distance between the groove and the edge of the negative electrode sheet in the length direction of the groove is 1mm to 2mm.

[0014] In some embodiments, the distance between two adjacent grooves is 0.5 mm to 3 mm.

[0015] In some embodiments, the length direction of the groove is perpendicular to the length direction of the negative electrode sheet.

[0016] In some embodiments, the depth of the groove is a fraction of the thickness of one side of the negative electrode active material layer. In some embodiments, the negative electrode active material also includes graphite.

[0017] In some embodiments, the mass content of silicon-based material in the negative electrode active material is 2%-40%.

[0018] In some embodiments, the mass content of silicon in the negative electrode active layer is 'a', where 1% ≤ a ≤ 20%; The electrolyte includes fluorinated organic compounds, and the mass percentage of the fluorinated organic compounds is S3 based on the total mass of the electrolyte; wherein, S3 and a satisfy the following relationship: 0.3≤S3 / a≤4.

[0019] In some implementations, 4% ≤ a ≤ 15%.

[0020] In some implementations, 1% ≤ S3 ≤ 20%.

[0021] In some embodiments, the fluorinated organic compound includes one or more of fluoroethylene carbonate, difluoroethylene carbonate, trifluoropropylene carbonate, methyltrifluoroethyl carbonate, and ethyl trifluoroacetate.

[0022] In some embodiments, the electrolyte includes a first lithium salt and a second lithium salt. The first lithium salt includes lithium hexafluorophosphate, and the mass content of the first lithium salt is L1, which is 6% ≤ L1 ≤ 15% based on the total mass of the electrolyte. The second lithium salt includes one or both of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide, and the mass content of the second lithium salt is L2, which is 0.1% ≤ L2 ≤ 8% based on the total mass of the electrolyte.

[0023] In some embodiments, the electrolyte includes a second lithium salt, which includes one or both of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethyl)sulfonyl)imide. The mass content of the second lithium salt is L2 based on the total mass of the electrolyte. The electrolyte includes a boron-containing additive, and the mass percentage of the boron-containing additive is S5 based on the total mass of the electrolyte. S5 and L2 satisfy the following relationship: 0.02≤S5 / L2≤0.4.

[0024] In some embodiments, the boron-containing additive includes one or more of lithium tetrafluoroborate, lithium bis(oxalate)borate, lithium bis(oxalate)borate, and tris(trimethylsilyl)borate.

[0025] In some implementations, 0.1% ≤ L2 ≤ 8%.

[0026] In some implementations, 0.1% ≤ S5 ≤ 2%.

[0027] In some embodiments, the electrode assembly includes a positive electrode sheet, the positive electrode sheet includes a positive current collector and a positive active layer covering at least one side of the positive current collector, the positive active layer includes a positive active material, the positive active material includes a high-nickel ternary material, and the mass content of nickel element is w based on the mass of the positive active layer; the electrolyte includes ethylene carbonate, and the mass percentage of ethylene carbonate is S4 based on the total mass of the electrolyte; wherein w and S4 satisfy the following relationship: 0% ≤ S4 ≤ 70% - w.

[0028] In some embodiments, the electrode assembly includes a positive electrode sheet, which includes a positive current collector, a first positive active material layer, and a second positive active material layer. The positive current collector has a first surface and a second surface. The first positive active material layer is disposed on the first surface, and the second positive active material layer is disposed on the second surface. The first positive active material layer has a plurality of recesses spaced apart. The second positive active material layer has a plurality of protrusions corresponding to the recesses. The minimum distance between the recesses and the edge of the positive electrode sheet is 2 mm to 7 mm.

[0029] In some embodiments, an elastic coating is provided on the inner side of the housing. The elastic coating comprises a polymer, which includes one or more of epoxy resin, phenolic resin, polyimide, polyethylene, polypropylene, polyvinylidene fluoride, polytetrafluoroethylene, and polyurethane.

[0030] In some embodiments, the diaphragm includes a base membrane and a heat-resistant layer located on at least one side of the base membrane, wherein the thickness of the base membrane is 5 μm to 15 μm and the thickness of the heat-resistant layer is 1 μm to 5 μm.

[0031] In some embodiments, the thickness of the elastic coating is 5 μm to 100 μm; In some embodiments, the high-nickel ternary material includes one or two of lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide; In some implementations, 45% ≤ w ≤ 58%; In some embodiments, the heat-resistant layer includes heat-resistant particles, the composition of which is selected from one or more of boehmite, alumina, barium sulfate, magnesium oxide, magnesium hydroxide, silicon dioxide, tin dioxide, titanium dioxide, barium titanate, melamine cyanurate, 1,3,5-triazine-2,4,6-triamine, and melamine thiocyanate. In some embodiments, the diaphragm further includes an adhesive coating layer located on the surface of the base film and / or the heat-resistant layer.

[0032] In a second aspect, this application provides an electrochemical device comprising the cylindrical battery described in any one of the first aspects.

[0033] The technical solution of this application has the following advantages: 1. This application provides a cylindrical battery, including an electrolyte, an electrode assembly, and a casing. The casing contains the electrolyte and the electrode assembly. The electrolyte includes an organic component, the mass of which is mg. The capacity of the cylindrical battery is CAh, wherein C and m satisfy the following relationship: 1 ≤ m / C ≤ 3.5. The organic component includes chain esters and cyclic carbonates. Based on the total mass of the electrolyte, the mass percentage of the cyclic carbonates is S1, and the mass percentage of the chain esters is S2, wherein S1 and S2 satisfy the following relationship: 1.2 ≤ S2 / S1 ≤ 6. The electrode assembly includes a negative electrode sheet, the negative electrode sheet includes a negative current collector and a negative electrode active layer covering at least one side of the negative current collector. The negative electrode active layer includes a negative electrode active material, the negative electrode active material being a silicon-based material. The surface of the negative electrode active layer includes at least one groove, the groove having a depth of 5 μm to 30 μm and a width of 0.01 mm to 0.3 mm. The cylindrical battery cell provided in this application achieves a suitable ratio of organic components in the electrolyte to battery capacity by controlling the m / C ratio within the range of 1 to 3.5. Under the "breathing effect" of the silicon anode, the amount of electrolyte discharged during compression is limited, ensuring that the electrolyte can adequately wet the interface without aggravating side reactions and uneven flow due to excessive amounts. This balance between electrolyte retention and control effectively improves the battery's high-temperature and fast-charge cycle performance. Furthermore, by controlling the S2 / S1 ratio to be maintained between 1.2 and 6, the chain ester-dominated structure provides low viscosity and high fluidity, allowing the electrolyte to quickly penetrate and uniformly cover the pores of the tightly wound electrode and separator in the cylindrical battery structure, thus achieving high wettability. The surface of the anode active layer includes at least one groove to provide expansion space for the anode. During charging and discharging, the silicon anode expands and contracts. These grooves, acting as buffer spaces and guide channels, effectively absorb the lateral expansion stress of the electrode, preventing the pores between particles from being completely squeezed and sealed. They also strongly guide the electrolyte to flow back quickly into the electrode, replenishing the lithium-ion transport medium in a timely manner and significantly reducing concentration polarization. The groove width and depth design ensures channel effectiveness without compromising structural integrity. Ultimately, this, in conjunction with the low-viscosity electrolyte, ensures the dynamic balance of the electrolyte during the "breathing" process, significantly improving cycle stability.

[0034] Additional aspects and advantages of the embodiments described in this application will be described and shown in part in the following description, or illustrated by practice of the embodiments of this application. Detailed Implementation

[0035] The following embodiments are provided to better understand this application and are not limited to the preferred embodiments described herein. They do not constitute a limitation on the content and scope of protection of this application. Any product that is the same as or similar to this application, derived by anyone under the guidance of this application or by combining features of this application with other prior art, falls within the scope of protection of this application.

[0036] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0037] Furthermore, the technical features involved in the different embodiments of this application described below can be combined with each other as long as they do not conflict with each other.

[0038] Those skilled in the art will understand that cylindrical batteries have a cylindrical steel shell with extremely high mechanical strength. Its uniform circular structure can effectively constrain the internal core, acting like a robust "pressure vessel" that can withstand higher internal gas pressure. This better suppresses deformation caused by gas production, especially in the face of the huge volume expansion of the silicon anode during charging and discharging. It can prevent deformation of the external structure of the battery and improve the safety of the battery.

[0039] In silicon-doped cylindrical batteries, the active material at the negative electrode expands during charging, causing the electrolyte to flow out of the negative electrode. During discharging, the electrolyte flows in from the outside. During repeated cycles, insufficient expansion space at the negative electrode leads to the expansion compressing the pores between internal particles, causing electrolyte with lower lithium-ion content to flow towards the edges. This ultimately results in low lithium-ion content at the electrode edges, leading to severe concentration polarization. To address this, this application provides a cylindrical battery and an electrochemical device including the cylindrical battery, which can improve the problems of uneven electrolyte distribution, concentration polarization, and unstable negative electrode interface, thereby significantly improving the battery's fast charging and high-temperature cycle life. The technical solution adopted in this application is described below.

[0040] In a first aspect, the cylindrical battery provided in this application includes an electrolyte, an electrode assembly, and a casing. The casing contains the electrolyte and the electrode assembly. The electrolyte includes an organic component, the mass of which is mg. The capacity of the cylindrical battery is CAh, where C and m satisfy the following relationship: 1 ≤ m / C ≤ 3.5. The organic component includes chain esters and cyclic carbonates. Based on the total mass of the electrolyte, the mass percentage of the cyclic carbonate is S1, and the mass percentage of the chain ester is S2, where S1 and S2 satisfy the following relationship: 1.2 ≤ S2 / S1 ≤ 6. The electrode assembly includes a negative electrode sheet, which includes a negative current collector and a negative active layer covering at least one side of the negative current collector. The negative active layer includes a negative active material, which includes a silicon-based material. The surface of the negative active layer includes at least one groove, the depth of which is 5 μm to 30 μm and the width of which is 0.01 mm to 0.3 mm.

[0041] On the one hand, to improve the problems of uneven electrolyte distribution and concentration polarization, the cylindrical cell provided in this application controls the ratio of m to C within the range of 1 to 3.5, so that the mass ratio of organic components in the electrolyte to the battery capacity is moderate. Under the "breathing effect" of the silicon anode, the amount of electrolyte discharged during compression is limited, ensuring that the electrolyte can fully wet the interface without aggravating side reactions and uneven flow due to excess. A balance is achieved between liquid retention and liquid control, thereby effectively improving the high-temperature and fast-charge cycle performance of the battery. When m / C>3.5, the organic components in the electrolyte are too large relative to the capacity. Under the "breathing effect" of the silicon anode, the excess free electrolyte is violently squeezed out and absorbed, aggravating the electrolyte flow at the edge of the electrode, resulting in uneven lithium-ion concentration and increased concentration polarization of lithium ions between the middle and edge of the anode. The specific reason is that when the silicon anode expands during charging, the amount of organic components in the electrolyte is appropriate, and the amount of liquid discharged during compression is limited. However, if the battery contains excessive electrolyte, a large amount of liquid will be forcefully expelled during compression. Similarly, excess electrolyte fills the gaps between the electrodes and is forcefully pushed outward by the expanding negative electrode, resulting in a more intense outward flow and causing a large amount of electrolyte to be squeezed out. Simultaneously, the negative electrode is charging, and lithium ions continuously embed into silicon from the electrolyte. The squeezed-out electrolyte has a relatively low lithium salt content. When discharging, the negative electrode releases lithium ions, and the electrolyte with a lower lithium ion concentration flows from the outside to the center. This repeated movement causes the lithium ion content in the electrolyte at the edges to decrease, while the lithium ion content in the center increases. When m / C < 1, the organic components in the electrolyte are too insufficient relative to the capacity, failing to adequately wet the electrodes, leading to localized "dry areas" (manifested as black spots). The lithium ion transport path is interrupted, and the internal resistance increases sharply. This not only accelerates capacity decay but also causes a voltage "plummet" in the later stages of cycling due to interface runaway, resulting in deteriorated cycle performance. This ratio range is precisely to ensure that the electrolyte can adequately wet the interface without exacerbating side reactions and uneven flow due to excessive amounts. For example, 1≤m / C≤3.5 can be 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, or any two of the above values.

[0042] On the other hand, to further alleviate the concentration polarization problem, this application controls the S2 / S1 ratio to be maintained between 1.2 and 6. The chain ester-dominated structure provides low viscosity and high fluidity, which allows the electrolyte to quickly penetrate and uniformly cover the pores of the tightly wound electrode and separator in the cylindrical battery structure, thereby achieving high wettability. When the silicon anode experiences a "breathing effect," this low viscosity characteristic allows the extruded electrolyte to flow more smoothly in the external space and quickly flow back into the electrode interior due to capillary force when the anode contracts, replenishing the lithium-ion transport channels in a timely manner, thus effectively alleviating the concentration polarization caused by uneven electrolyte distribution. If S2 / S1 < 1.2, the overall viscosity of the electrolyte will increase, the wetting rate will slow down, and the backflow resistance during the breathing process will be large, which is not conducive to the rapid migration of ions. If S2 / S1 > 6, although the viscosity is lower, the insufficient cyclic carbonate will weaken its ability to form a stable solid electrolyte interphase (SEI) film at the interface between the negative electrode (especially the silicon surface) and the positive electrode. This will lead to continuous consumption of active materials during cycling, repeated rupture and reconstruction of the SEI film, and ultimately cause accelerated capacity decay and decreased cycling performance. For example, S2 / S1 can be 1.2, 1.5, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 4, 4.2, 4.5, 5, 6, or within any two of the above values.

[0043] Furthermore, to further accelerate the rapid return of the electrolyte to the electrode, the surface of the negative electrode active layer in this application includes at least one groove (e.g., laser wire etching can be used to etch the groove on the negative electrode surface), providing expansion space for the negative electrode. During charging and discharging, the silicon negative electrode expands and contracts. These grooves, acting as reserved buffer spaces and guide channels, effectively absorb the lateral expansion stress of the electrode and prevent the pores between particles from being completely squeezed and sealed. More importantly, when the negative electrode contracts, the capillary force and low-resistance path formed by the grooves strongly guide the electrolyte to rapidly return to the interior of the electrode, replenishing the lithium-ion transport medium in a timely manner and significantly reducing concentration polarization. The groove width and depth design ensures channel effectiveness without compromising structural integrity. The ultimate effect is that, in conjunction with the low-viscosity electrolyte, it jointly ensures the dynamic balance of the electrolyte during the "breathing" process, improving cycle stability and fast-charge cycle performance. For example, the depth of the groove can be 5μm, 7μm, 9μm, 12μm, 15μm, 18μm, 20μm, 22μm, 25μm, 28μm, 30μm or within any two of the above values, and the width can be 0.01mm, 0.02mm, 0.05mm, 0.08mm, 0.1mm, 0.12mm, 0.15mm, 0.2mm, 0.25mm, 0.28mm, 0.3mm or within any two of the above values.

[0044] In summary, this application effectively limits the magnitude of the "breathing effect" by controlling 1≤m / C≤3.5 and 1.2≤S2 / S1≤6. Combined with the setting of grooves with specific thickness and depth on the surface of the negative electrode active layer, it establishes an efficient channel for the rapid extrusion and reflux of the electrolyte during the expansion and contraction process, which greatly improves the uneven distribution of electrolyte and alleviates concentration polarization, thereby enhancing the fast charging and high-temperature cycling performance of the battery.

[0045] In the embodiments of this application, the method for testing the mass of organic components in the electrolyte of the battery is as follows: First, the battery is discharged at a constant current rate of 1C to 2.5V to obtain an empty battery. The mass of the empty battery is weighed as m1. Then, the battery casing is opened to expose the core. First, all accessories and the core are placed in a forced-air drying oven at 200°C for 48 hours to bake out a large amount of organic components. Then, all accessories and the core are placed in a vacuum drying oven with a desiccant (phosphorus pentoxide) at a pressure of -0.09MPa and a temperature of 200°C for baking. At the same time, a vacuum pump is used to evacuate the air and extract the volatilized organic matter. The desiccant is replaced every 2 hours. After baking for 24 hours, the color of the desiccant is observed. If there is no color change, it means that the organic matter has been dried. If there is still color change, continue baking until the desiccant no longer changes color. After drying, all accessories and the core are taken out and weighed as m2. The mass of organic matter in the battery is calculated as m = m1 - m2.

[0046] In the embodiments of this application, the method for testing the capacity of the cylindrical battery is as follows: using the current of the battery's rated capacity, the battery is subjected to 1C / 1C charge-discharge cycles at 25°C. The test process is as follows: first, 1C constant current charging to 4.25V, then constant voltage charging, with a cutoff current of 0.05C, and finally 1C constant current discharging to 2.5V. This cycle is repeated three times, and the battery capacity of the third cycle is taken as the capacity of the cylindrical battery, denoted as CAh.

[0047] In the embodiments of this application, the method for determining the content of organic components such as fluorinated organics, cyclic carbonates, chain esters, and boron-containing additives in the electrolyte is as follows: the free electrolyte obtained from the battery is used as a sample (either directly taken out or impregnated with a solvent) and tested by gas chromatography (GC) or gas chromatography-mass spectrometry (GC-MS).

[0048] In the embodiments of this application, the method for testing the mass content of lithium salts (including first lithium salt and second lithium salt) in the electrolyte is as follows: the free electrolyte obtained from the battery is used as a sample (either directly taken out or impregnated with a solvent) and detected by ion chromatography analysis.

[0049] In the embodiments of this application, the method for obtaining an electrolyte sample by solvent impregnation is as follows: 50g of chromatographically pure acetonitrile is added to the battery cell, the core is soaked, ultrasonic extraction is performed for 15-30 minutes, and the sample is left to stand at room temperature for 1 hour to obtain the electrolyte sample.

[0050] In some implementations, 30 ≤ m ≤ 55. For example, m can be 30, 35, 38, 40, 42, 45, 47, 49, 50, 52, 55 or within any two of these values.

[0051] In some implementations, 15 ≤ C ≤ 40. For example, C can be 15, 20, 25, 28, 30, 32, 35, 37, 38, 39, 40, or any two of the above values.

[0052] In some implementations, 5% ≤ S1 ≤ 40%. For example, S1 can be 5%, 6%, 8%, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, 35%, 40%, or within any two of the above values.

[0053] In some implementations, 40% ≤ S2 ≤ 80%. For example, S2 can be 40%, 42%, 45%, 47%, 49%, 50%, 52%, 55%, 58%, 60%, 65%, 70%, 75%, 80%, or within any two of the above values.

[0054] In some embodiments, the cyclic carbonate includes one or more of ethylene carbonate, propylene carbonate, and fluoroethylene carbonate.

[0055] In some embodiments, the chain ester includes one or more of dimethyl carbonate, ethyl methyl carbonate, ethyl acetate, ethyl propionate, and methyl acetate.

[0056] In some embodiments, the minimum distance between the groove and the edge of the negative electrode sheet along the length of the groove is 1mm to 2mm. For example, this minimum distance can be 1mm, 1.1mm, 1.2mm, 1.3mm, 1.4mm, 1.5mm, 1.6mm, 1.8mm, 1.9mm, 2mm, or any two of these values. By setting the minimum spacing within the above range, appropriate top and bottom margins are provided, avoiding the risk of powder shedding or short circuits caused by fragile edge structures, and further improving high-temperature and fast-charging cycle performance.

[0057] In some embodiments, the spacing between two adjacent grooves is 0.5mm to 3mm. For example, the spacing between two adjacent grooves can be 0.5mm, 0.8mm, 1.0mm, 1.2mm, 1.5mm, 1.8mm, 2mm, 2.2mm, 2.5mm, 2.6mm, 2.8mm, 3mm, or within any two of these values. This spacing setting achieves uniform current flow, further improving high-temperature and fast-charging cycle performance.

[0058] In some embodiments, the length direction of the groove is perpendicular to the length direction of the negative electrode sheet.

[0059] In some embodiments, the depth of the groove is 1 / 5 to 1 / 2 of the thickness of one side of the negative electrode active material layer. For example, the depth of the groove is 1 / 5, 1 / 4, 1 / 3.5, 1 / 3, 1 / 2.5, 1 / 2 of the thickness of one side of the negative electrode active material layer, or within any two of the above values.

[0060] In some embodiments, the negative electrode active material also includes graphite.

[0061] In some embodiments, the mass content of silicon-based material in the negative electrode active material is 2%-40%. For example, the mass content of silicon-based material in the negative electrode active material is 2%, 4%, 6%, 8%, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 30%, 35%, 40%, or within any two of the above values. For example, the silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, and silicon alloys.

[0062] In some embodiments, the mass content of silicon in the negative electrode active layer is a, wherein 1%≤a≤20%; the electrolyte includes fluorinated organic matter, and the mass percentage of the fluorinated organic matter is S3 based on the total mass of the electrolyte; wherein S3 and a satisfy the following relationship: 0.3≤S3 / a≤4.

[0063] Silicon-based materials undergo significant volume expansion after lithium intercalation (theoretically, silicon expands by up to 300%), which repeatedly tears the solid electrolyte interfacial film on its surface. This results in continuous exposure of fresh silicon surface, constant consumption of electrolyte and active lithium, and rapid capacity decay. Fluorinated organic compounds (such as FEC) within the aforementioned content range can preferentially reduce on the silicon particle surface, forming a LiF-rich SEI film with high mechanical strength and stable interfacial energy. This application controls the ratio of S3 to a to ensure a dynamic balance between the fluorine source supply required for forming a stable interface and the surface area of ​​silicon and its degree of damage, further improving the high-temperature cycling performance of the battery. When the silicon content a is high, the content of fluorinated organic compounds S3 is correspondingly increased to generate a sufficient amount of LiF-rich film to cover more silicon surface and resist stronger expansion stress. If the S3 / a ratio is too low (<0.3), the protective film formed will be incomplete and unable to effectively suppress the continuous growth of SEI and lithium consumption; if the ratio is too high (>4), excessive fluorine-containing organic matter will decompose excessively, producing an overly thick interface film that increases ion transport impedance, and the generated HF will etch the positive electrode surface, causing gas production and leading to a decrease in high-temperature performance. For example, 'a' can be 1%, 2%, 4%, 6%, 8%, 10%, 12%, 15%, 18%, 20%, or any two of the above values. For example, S3 / a can be 0.3, 0.32, 0.35, 0.4, 42, 0.45, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.5, 2, or any two of the above values.

[0064] In the embodiments of this application, the method for determining the mass content of silicon in the negative electrode active layer is as follows: To accurately measure the silicon content of the negative electrode, the electrode must first be cleaned and dried in an argon-filled glove box to remove residual electrolyte. An appropriate amount of sample is weighed and placed in a polytetrafluoroethylene digestion vessel. A mixture of hydrofluoric acid and nitric acid is added for sealed microwave digestion, allowing silicon to be completely converted into soluble fluorosilicic acid. After cooling, the solution is transferred to a plastic volumetric flask and diluted to volume with dilute nitric acid. Finally, inductively coupled plasma optical emission spectrometry (ICP-OES) or an inductively coupled plasma mass spectrometry (ICP-MS) instrument is used to select characteristic spectral lines of silicon for quantitative analysis. The precise content is calculated using a standard curve method. Plastic containers must be used throughout the process to prevent silicon adsorption loss.

[0065] In some implementations, 1% ≤ S3 ≤ 20%. For example, S3 can be 1%, 2%, 4%, 6%, 8%, 10%, 12%, 15%, 18%, 20%, or a range consisting of any two of the above values.

[0066] In some embodiments, the fluorinated organic compound includes one or more of fluoroethylene carbonate, difluoroethylene carbonate, trifluoropropylene carbonate, methyltrifluoroethyl carbonate, and ethyl trifluoroacetate.

[0067] In some embodiments, the electrolyte includes a first lithium salt and a second lithium salt. The first lithium salt includes lithium hexafluorophosphate, and the mass content of the first lithium salt is L1, which is 6% ≤ L1 ≤ 15% based on the total mass of the electrolyte. The second lithium salt includes one or both of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide, and the mass content of the second lithium salt is L2, which is 0.1% ≤ L2 ≤ 8% based on the total mass of the electrolyte.

[0068] The first lithium salt (LiPF6) and the second lithium salt (LiFSI and / or LiTFSI) are used in combination to construct a highly efficient and stable lithium-ion transport system by leveraging their synergistic effect. The LiPF6 content (L1) is controlled between 6% and 15%, which facilitates the formation of a dense LiF-AlF3 passivation layer on the aluminum current collector surface, effectively preventing electrochemical corrosion under high voltage. The key role of the second lithium salt (L2 content 0.1% to 8%) is its large-volume anionic structure. On the one hand, it significantly increases the lithium-ion transference number, accelerating ion conduction to directly address local concentration polarization caused by the "breathing effect" and promoting electrolyte reflux. On the other hand, its excellent thermal stability avoids the problem of HF generation from the decomposition of LiPF6 at high temperatures, thus protecting the highly active interfaces of the positive and negative electrodes from acid corrosion and comprehensively improving the battery's high-temperature cycling and storage performance. For example, L1 can be 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 15%, or within any two of these values. For example, L2 can be 0.1%, 0.2%, 0.5%, 0.8%, 1%, 2%, 4%, 6%, 8%, or within any two of the above values.

[0069] In some embodiments, the electrolyte includes a second lithium salt, which includes one or both of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethyl)sulfonyl)imide. The mass content of the second lithium salt is L2 based on the total mass of the electrolyte. The electrolyte includes a boron-containing additive, and the mass percentage of the boron-containing additive is S5 based on the total mass of the electrolyte. S5 and L2 satisfy the following relationship: 0.02≤S5 / L2≤0.4.

[0070] The second lithium salt decomposes under high temperature or high voltage to produce highly corrosive anions (e.g., LiFSI generates FSI). -These substances can damage the passivation film on the aluminum current collector and steel shell surface, initiating continuous corrosion and dissolution (e.g., LiFSI forming aluminum trifluorosulfonate). Added boron-containing additives (such as LiBF4) preferentially oxidize on the current collector surface, forming a dense and stable boron-containing passivation layer. This physicochemical barrier effectively prevents contact between the corrosive medium and the metal substrate, thereby inhibiting the corrosion effect of LiFSI. This application controls the ratio of S5 to L2 within the range of 0.02 to 4, promoting electrolyte reflux while ensuring the stability of the battery structure, further improving the battery's cycle performance and safety performance. For example, S5 / L2 can be 0.02, 0.04, 0.06, 0.08, 0.1, 0.12, 0.15, 0.2, 0.22, 0.25, 0.3, 0.32, 0.35, 0.4, or within any two of the above values.

[0071] In some embodiments, the boron-containing additive includes one or more of lithium tetrafluoroborate, lithium bis(oxalate)borate, lithium bis(oxalate)borate, and tris(trimethylsilyl)borate. In some implementations, 0.1% ≤ S5 ≤ 2%. For example, S5 can be 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.5%, 2%, or any two of the above values.

[0072] In one optional embodiment, the electrolyte of this application may further include some conventional additives in the art, such as one or more of vinyl sulfate, vinylene carbonate, triargyl phosphate, 1,3-propanesulfonate lactone, 1,3,6-hexanetrionitrile, and lithium difluorophosphate.

[0073] In one alternative embodiment, the mass percentage of the aforementioned conventional additives in the art is 0.5%-2% based on the total mass of the electrolyte.

[0074] In some embodiments, the electrode assembly includes a positive electrode sheet, the positive electrode sheet includes a positive current collector and a positive active layer covering at least one side of the positive current collector, the positive active layer includes a positive active material, the positive active material includes a high-nickel ternary material, and the mass content of nickel element is w based on the mass of the positive active layer; the electrolyte includes ethylene carbonate, and the mass percentage of ethylene carbonate is S4 based on the total mass of the electrolyte; wherein w and S4 satisfy the following relationship: 0% ≤ S4 ≤ 70% - w.

[0075] The combination of high-nickel ternary materials and silicon-carbon anode materials can effectively improve the energy density of batteries. When high-nickel materials (such as those with a Ni content ≥90%) are charged to a high voltage state, the nickel element in their crystal lattice (especially the unstable Ni) 4+Electrolyte (EC) has extremely strong oxidizing properties, catalyzing the oxidative decomposition of EC molecules (whose H atoms in their ring structure come into contact with the positive electrode and readily lose electrons). This process generates a large amount of CO2 and other gases, consumes active lithium, leading to battery gas production, swelling, increased internal pressure, and damage to the positive electrode interface structure. This is the main reason for accelerated battery capacity decay, especially the deterioration of high-temperature long-cycle performance. Therefore, by strictly limiting the relationship between EC content (S4) and w, the severe oxidation side reaction of EC molecules at the highly active positive electrode interface is avoided. Essentially, this cuts off the main reactants of this critical side reaction pathway, reducing electrolyte oxidative decomposition on the positive electrode side at its source. The ultimate effect is a significant improvement in the battery's gas production suppression capability and cycle life retention at high temperatures. For example, S4 can be 0%, 6%, 8%, 10%, 12%, 14%, 15%, 18%, 19%, 20%, 22%, 25%, or within any two of the above values.

[0076] In the embodiments of this application, the method for determining the mass content of nickel in the positive electrode active layer is as follows: To accurately measure the nickel content of the positive electrode, the battery must first be disassembled in a glove box. The positive electrode is then cleaned with dimethyl carbonate to remove the electrolyte and dried. An appropriate amount of sample is weighed and placed in a digestion vessel. A mixture of hydrochloric acid and nitric acid (or aqua regia) is added, and if necessary, a small amount of hydrofluoric acid is added to aid dissolution. Microwave high-temperature closed digestion is performed until the solution is clear and transparent. After cooling, the solution is transferred to a volumetric flask and diluted to volume with dilute nitric acid. Finally, inductively coupled plasma optical emission spectrometry (ICP-OES) or an inductively coupled plasma mass spectrometry (ICP-MS) is used to select the characteristic spectral line of nickel (e.g., 231.604 nm), and quantitative analysis is performed using the standard curve method. A blank experiment is also performed to correct for background interference to ensure data accuracy.

[0077] In some embodiments, the electrode assembly includes a positive electrode sheet, which includes a positive current collector, a first positive active material layer, and a second positive active material layer. The positive current collector has a first surface and a second surface. The first positive active material layer is disposed on the first surface, and the second positive active material layer is disposed on the second surface. The first positive active material layer has a plurality of recesses spaced apart. The second positive active material layer has a plurality of protrusions corresponding to the recesses. The minimum distance between the recesses and the edge of the positive electrode sheet is 2mm to 7mm. For example, the minimum distance between the recesses and the edge of the positive electrode sheet can be 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, or within any two of the above values. The embossed shape is arbitrary and can be one or more of the following: circular, triangular, quadrilateral, pentagonal, striped, or irregular patterns.

[0078] The design of recessed and raised portions (creating a dense uneven structure on the electrode surface through embossing) increases the specific surface area and porosity of the electrode. This not only improves the electrolyte wetting speed and retention, but also facilitates the uniform migration of lithium ions. Furthermore, these embossed points enhance the bonding force between the active material layer and the current collector. During long-term battery cycling, especially under the overall stress caused by positive electrode volume changes and the negative electrode's "breathing effect," these points effectively disperse and absorb stress, preventing the active material from peeling off the current collector, thus maintaining structural integrity and improving cycle life. The reason for leaving the edge areas unembossed is that the electrode edges are where mechanical stress and shear force are most concentrated. Embossing would weaken the mechanical strength of the current collector, significantly increasing the risk of micro-cracks, burrs, or even breakage during slitting and winding, easily leading to internal short circuits. Maintaining smooth edges ensures the mechanical integrity and safety of the electrode, eliminating the risk of short circuits caused by edge damage at the source.

[0079] In some embodiments, the depth of the recess is 1μm-40μm, for example, 1μm, 3μm, 5μm, 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm or within any two of the above values.

[0080] In some embodiments, the height of the protrusion is 1μm-40μm, for example, 1μm, 3μm, 5μm, 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm or within any two of the above values.

[0081] In some embodiments, the width of the recess is 0.5mm-6mm, for example, 0.5mm, 1mm, 2mm, 3mm, 4mm, 5mm, 6mm or within any two of the above values.

[0082] In some embodiments, the width of the protrusion is 0.5mm-6mm, for example, 0.5mm, 1mm, 2mm, 3mm, 4mm, 5mm, 6mm or within any two of the above values.

[0083] In some embodiments, the spacing between the recesses can be 0.5mm-8mm, for example, 0.5mm, 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm or within any two of the above values.

[0084] In some embodiments, the spacing between the protrusions can be 0.5mm-8mm, for example, 0.5mm, 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm or within any two of the above values.

[0085] In some embodiments, an elastic coating is provided on the inner side of the housing. The elastic coating comprises a polymer, which includes one or more of epoxy resin, phenolic resin, polyimide, polyethylene, polypropylene, polyvinylidene fluoride, polytetrafluoroethylene, and polyurethane.

[0086] The design of the elastic coating facilitates the construction of a physical barrier layer that combines insulation, corrosion resistance, and mechanical buffering. The polymer materials used in this coating (such as epoxy resin and polyolefins) effectively prevent direct contact between the electrolyte and the steel casing, fundamentally preventing chemical erosion of the steel casing by corrosive substances. Simultaneously, during battery cycling, this elastic coating effectively absorbs and buffers the periodic stresses generated by the "breathing effect" of the silicon-carbon negative electrode and the volume changes of the positive electrode, avoiding direct mechanical compression between the core and the rigid steel casing. This protects the structural integrity of the electrodes and separator while reducing the risk of internal short circuits due to stress concentration.

[0087] In some embodiments, the diaphragm includes a base film and a heat-resistant layer located on at least one side of the base film. The thickness of the base film is 5 μm to 15 μm, and the thickness of the heat-resistant layer is 1 μm to 5 μm. For example, the thickness of the base film can be 5 μm, 7 μm, 8 μm, 9 μm, 10 μm, 12 μm, 13 μm, 14 μm, 15 μm, or within any two of these values. The thickness of the heat-resistant layer is 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, or within any two of these values.

[0088] The use of a base film with a relatively large thickness ensures that the separator maintains a stable and unobstructed transmission channel under long-term cycling and mechanical compression, while also reserving a safe physical buffer space. The thicker base film firstly provides crucial longitudinal space for the expansion of the silicon anode, directly alleviating the compression of the electrode sheet caused by the "breathing effect" and preventing severe reduction in porosity between particles, which could lead to a large outflow of electrolyte. The ceramic layer (such as Al2O3) coated on the base film primarily acts as a thermal barrier, effectively preventing the separator from shrinking and melting during localized overheating, thus preventing direct contact between the positive and negative electrodes and preventing thermal runaway, greatly improving safety performance.

[0089] In some embodiments, the thickness of the elastic coating is 5 μm to 100 μm. Examples include 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 80 μm, 90 μm, 100 μm, or any two of the above values.

[0090] In some embodiments, the high-nickel ternary material includes one or both of lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide.

[0091] In some implementations, 45% ≤ w ≤ 58%. For example, w can be 45%, 47%, 50%, 52%, 54%, 56%, 58%, or any two of the above values.

[0092] In some embodiments, the heat-resistant layer includes heat-resistant particles, the composition of which is selected from one or more of boehmite, alumina, barium sulfate, magnesium oxide, magnesium hydroxide, silicon dioxide, tin dioxide, titanium dioxide, barium titanate, melamine cyanurate, 1,3,5-triazine-2,4,6-triamine, and melamine thiocyanate.

[0093] In some embodiments, the diaphragm further includes an adhesive layer located on the surface of the base film and / or the heat-resistant layer. The adhesive layer (such as PVDF) can soften at a certain temperature and bond with the electrode sheet, fixing the relative position of the core, enhancing structural stability, and sealing pores through adhesion under extreme conditions such as needle punching, further suppressing the occurrence of internal short circuits.

[0094] The content of the negative electrode active material is ≥96% based on the mass of the negative electrode active material layer. For example, the content of the negative electrode active material is 96%, 97%, 98%, 99%, or within any two of the above values.

[0095] In some embodiments, the positive electrode active material layer or the negative electrode active layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), styrene-butadiene rubber, polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins. In some embodiments, optionally, the binder accounts for 0.5%-3% of the total weight of the positive electrode active material layer. Optionally, the binder accounts for 0.5%-3% of the total weight of the negative electrode active material layer.

[0096] In some embodiments, the positive electrode active material layer or the negative electrode active layer may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from carbon nanotubes, acetylene black, carbon black, Ketjen black, graphene, and carbon nanofibers.

[0097] In some embodiments, the conductive agent may optionally comprise 0.5%-5% of the total weight of the positive electrode active material layer.

[0098] In some embodiments, the positive electrode active material layer or the negative electrode active layer may optionally include a thickener. As an example, the thickener may include sodium carboxymethyl cellulose.

[0099] In some embodiments, the thickener may optionally comprise 0.1%-2% of the total weight of the positive electrode active material layer.

[0100] The electrolyte used in the battery described in this application may include any technology disclosed in the prior art.

[0101] Secondly, this application provides an electrochemical device comprising the battery cell described in any of the first aspects.

[0102] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in this application. In all embodiments and comparative examples of this application, the unit wt% represents the mass percentage content.

[0103] In the following embodiments of this application, a lithium-ion secondary battery is used as an example to illustrate the corresponding technical solutions and effects. However, the solutions described in this application can still be applied to other feasible battery systems.

[0104] Example 1 This embodiment provides a cylindrical battery, the preparation method of which is as follows: (1) Preparation of positive electrode Lithium nickel cobalt manganese oxide (molecular formula: LiNi) 0.9 Co 0.05 Mn 0.05 O2), polyvinylidene fluoride binder, and conductive agent (acetylene black) were added to a vacuum mixer in a mass ratio of 97:1.2:1.8. N-methylpyrrolidone (NMP) was then added, and the mixture was thoroughly mixed under vacuum until a uniform, free-flowing positive electrode slurry with a solid content of 55 wt% was formed. This positive electrode slurry was then uniformly coated onto a 10 μm thick aluminum foil, with a single-sided surface density of 16 mg / cm². 2 After drying and rolling, an electrode sheet with a positive active material layer thickness of 47µm is obtained. After slitting and punching, the positive electrode sheet is obtained.

[0105] (2) Preparation of negative electrode Graphite, silicon carbide, styrene-butadiene rubber, sodium carboxymethyl cellulose, acetylene black, and carbon nanotubes were added to a vacuum mixer in a mass ratio of 81.5:14.5:2:1:0.9:0.1. Deionized water was added, and the mixture was thoroughly mixed under vacuum to form a homogeneous, free-flowing negative electrode slurry with a solid content of 45 wt%. The silicon carbide material contained 50% silicon by mass.

[0106] The above-mentioned negative electrode slurry was uniformly coated on both surfaces of a carbon-coated copper foil with a thickness of 5 μm, with a single-sided surface density of 7 mg / cm³. 2 The electrode sheet is dried and rolled to control the thickness of the negative electrode active material layer on one side to be 47µm. Then, a groove structure is formed on both sides of the negative electrode active material layer using laser wire bonding to obtain the negative electrode sheet. The grooves are perpendicular to the length of the negative electrode sheet, have a depth of 10µm (1 / 4.7 of the thickness of the negative electrode active material layer on one side), a width of 0.1mm, and a spacing of 1mm between adjacent grooves.

[0107] (3) Preparation of electrolyte In an argon-filled glove box with a water content <0.1 ppm and an oxygen content <0.1 ppm, add 5% ethylene carbonate (EC), 7% propylene carbonate (PC), 8% fluoroethylene carbonate (FEC), 8% ethyl methyl carbonate (EMC), and 55% dimethyl carbonate (DMC) by weight of the total electrolyte. Then, add thoroughly dried lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI) to the above solution, controlling their mass fractions in the electrolyte to 10% and 5%, respectively. Finally, add 0.2% lithium tetrafluoroborate, 1% ethylene sulfate, and 0.8% lithium difluorophosphate by weight of the total electrolyte, and stir until homogeneous to obtain the desired electrolyte.

[0108] (4) Preparation of cylindrical batteries The positive electrode sheet (width 83.5 mm, length 6.5 m) obtained in step (1), the negative electrode sheet (width 86.5 mm, length 6.6 m) obtained in step (2), and the separator (a separator with 9 μm polyethylene as the substrate, coated with 1 μm polytetrafluoroethylene on both sides and 1 μm alumina ceramic on one side) are wound together to obtain a bare cell. One bare cell is welded to the tab by connecting piece and placed in the cylindrical battery shell (cylindrical steel shell). The electrolyte prepared in step (3) is injected into the dried and qualified cell, and the injection volume is controlled to be 50 g. After standing, aging, formation, second sealing, aging, sorting and other processes, a 4695 cylindrical battery (diameter 46 mm, height 95 mm) is obtained.

[0109] The preparation methods of the cylindrical batteries in Examples 2-9 and Comparative Examples 1-2 are basically the same as those in Example 1. The difference is that the amount of electrolyte injected is adjusted to make m different and / or the battery size is adjusted to make C different, as shown in Table 1.

[0110] The preparation methods of the cylindrical batteries in Examples 10-11 and Comparative Examples 3-4 are basically the same as those in Example 1. The difference is that the content of at least one of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, methyl ethyl carbonate, and dimethyl carbonate in the electrolyte is adjusted to make the S2 / S1 ratio different, as shown in Table 2. Specifically, in Example 10, the mass content of ethylene carbonate is 4%, the mass content of propylene carbonate is 5%, the mass content of fluoroethylene carbonate is 5%, the mass content of methyl ethyl carbonate is 9%, and the mass content of dimethyl carbonate is 60% based on the total mass of the electrolyte.

[0111] In Example 11, based on the total mass of the electrolyte, the mass content of ethylene carbonate was 7%, the mass content of propylene carbonate was 9%, the mass content of fluoroethylene carbonate was 11%, the mass content of methyl ethyl carbonate was 7%, and the mass content of dimethyl carbonate was 49%.

[0112] In Comparative Example 3, based on the total mass of the electrolyte, the mass content of ethylene carbonate was 3%, the mass content of propylene carbonate was 4%, the mass content of fluoroethylene carbonate was 4%, the mass content of methyl ethyl carbonate was 9%, and the mass content of dimethyl carbonate was 63%.

[0113] In Comparative Example 4, based on the total mass of the electrolyte, the mass content of ethylene carbonate was 10%, the mass content of propylene carbonate was 15%, the mass content of fluoroethylene carbonate was 16%, the mass content of methyl ethyl carbonate was 5%, and the mass content of dimethyl carbonate was 37%.

[0114] The preparation methods of the cylindrical batteries in Examples 12 and 13 are basically the same as those in Example 1. The difference is that the mass ratio of graphite to silicon carbon used in the preparation of the negative electrode is different, which makes a different, and thus S3 / a is different, as shown in Table 3.

[0115] The preparation method of the cylindrical battery in Example 14 is basically the same as that in Example 12. The difference is that the mass ratio of fluoroethylene carbonate in the electrolyte is adjusted to make S3 / a different, as shown in Table 3. The mass ratio of the above substances is changed by adaptively adjusting the mass ratio of dimethyl carbonate in the electrolyte.

[0116] The preparation methods of the cylindrical batteries in Examples 15 and 19 are basically the same as those in Example 13. The difference is that the mass ratio of fluoroethylene carbonate in the electrolyte is adjusted to make S3 / a different, as shown in Table 3. The mass ratio of the above substances is changed by adaptively adjusting the mass ratio of dimethyl carbonate in the electrolyte.

[0117] The preparation method of the cylindrical battery in Example 16 is basically the same as that in Example 1. The difference is that the mass ratio of fluoroethylene carbonate in the electrolyte and / or the mass ratio of graphite to silicon carbon used in the preparation of the negative electrode are adjusted to make S3 / a different, as shown in Table 3. The mass ratio of the above substances is changed by adaptively adjusting the mass ratio of dimethyl carbonate in the electrolyte.

[0118] The preparation method of the cylindrical battery in Example 17 is basically the same as that in Example 15. The difference is that the mass ratio of graphite to silicon carbon used in the preparation of the negative electrode is different, which makes a different, and thus S3 / a is different, as shown in Table 3.

[0119] The preparation method of the cylindrical battery in Example 18 is basically the same as that in Example 14. The difference is that the mass ratio of graphite to silicon carbon used in the preparation of the negative electrode is different, which makes a different, and thus S3 / a is different, as shown in Table 3.

[0120] The preparation method of the cylindrical battery in Examples 20-30 is basically the same as that in Example 1. The difference is that the mass content of at least one of lithium hexafluorophosphate, second lithium salt, and boron-containing additive in the electrolyte is adjusted to make L1, L2, S5 and / or S5 / L2 different. The mass ratio of the above substances is changed by adaptively adjusting the mass ratio of dimethyl carbonate in the electrolyte, as shown in Table 4.

[0121] The preparation methods of the cylindrical batteries in Examples 31-32 are basically the same as those in Example 1, except that the types of positive electrode active materials are different. In Example 31, LiNi was used. 0.8 Co 0.1 Mn 0.1 The positive electrode active material for O2, as used in Example 32, has the molecular formula LiNi. 0.95 Co 0.03 Mn 0.02 O2 is the positive electrode active material.

[0122] The preparation method of the cylindrical battery in Examples 33-34 is basically the same as that in Example 1. The difference is that the mass content of ethylene carbonate in the electrolyte (S4) is adjusted differently, as shown in Table 5. The mass ratio of the above substances is changed by adaptively adjusting the mass ratio of dimethyl carbonate in the electrolyte.

[0123] The preparation method of the cylindrical battery in Examples 35-36 is basically the same as that in Example 1, except that the depth and width of the groove on the negative electrode active layer are adjusted, as shown in Table 6.

[0124] The preparation method of the cylindrical battery in Example 37 is basically the same as that in Example 1, except that the positive electrode sheet is embossed using a special roller with protrusions during the preparation process. The depth of the recesses is 20 μm, the width of the recesses is 2 mm, the spacing between the recesses is 2 mm, the height of the protrusions is 20 μm, the width of the protrusions is 2 mm, the spacing between the protrusions is 2 mm, and the minimum distance between the recesses and the edge of the positive electrode sheet is 2 mm.

[0125] The preparation method of the cylindrical battery in Example 38 is basically the same as that in Example 37. The difference is that the minimum distance between the recess and the edge of the positive electrode is different during the preparation process. In this example, the minimum distance is adjusted to 7mm.

[0126] The preparation method of the cylindrical battery in Example 39 is basically the same as that in Example 1, except that an elastic coating is provided on the inner side of the outer shell, and the elastic coating includes epoxy resin.

[0127] The preparation method of the cylindrical battery in Comparative Example 5 is basically the same as that in Example 1, except that laser wire bonding is not performed in the preparation of the negative electrode.

[0128] The preparation methods of the cylindrical batteries in Comparative Examples 6 and 7 are basically the same as those in Example 1. The difference is that the depth and / or width of the grooves obtained by laser wire cutting are adjusted in the preparation of the negative electrode sheet, as shown in Table 6.

[0129] Table 1

[0130] Table 2

[0131] Table 3

[0132] Table 4

[0133] Table 5

[0134] Table 6

[0135] Test case The lithium-ion batteries prepared in each embodiment and comparative example were subjected to the following tests: 1. High-temperature cycling performance At 45℃, the battery was charged at 0.33C to the upper limit voltage of 4.25V, and then discharged at 0.33C to the lower limit voltage of 2.75V. This cycle was repeated twice, and the discharge capacity of the second discharge was selected as the initial discharge capacity C0 Ah. The battery was then charged at a constant current rate of 1C0 to the upper limit voltage of 4.25V, followed by constant voltage charging to the 0.05C cutoff point. After resting for 30 minutes, the battery was discharged at a 1C0 rate to the lower limit voltage of 2.75V. This cycle was repeated 1000 times, and the discharge capacity C(1000T) was recorded. The discharge capacity retention rate was calculated as C(1000T) / C0*100%.

[0136] 2. Fast charging cycle performance test At 25°C, the battery was charged to the upper limit voltage of 4.25V at 0.33C and discharged to the lower limit voltage of 2.75V at 0.33C. This cycle was repeated twice, and the discharge capacity of the second discharge was selected as the initial discharge capacity C0 Ah. Then perform a stepped charging process on the battery: first, charge at a constant current rate of 1C0 to 10% SOC, then charge at a rate of 5C0 to 50% SOC, then charge at a rate of 4C0 to 65% SOC, then charge at a rate of 3C0 to 75% SOC, then charge at a rate of 2C0 to 90% SOC, then charge at a rate of 1C0 to the upper limit voltage of 4.25V, and then charge at a constant voltage to the 0.05C cutoff point. Let it stand for 30 minutes, and then discharge at a rate of 1C0 to the lower limit voltage of 2.75V. Repeat this cycle 1500 times, read the discharge capacity C(1500T), and calculate the capacity retention rate = C(1500T) / C0*100%.

[0137] Table 7 Performance Test Results

[0138] As can be seen from the results in the table above, compared with Comparative Examples 1 to 7, the embodiments of this application can not only effectively improve the fast charging cycle performance of the battery, but also improve the high-temperature cycle performance of the battery.

[0139] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this application.

Claims

1. A cylindrical battery, characterized in that, The device includes an electrolyte, an electrode assembly, and a housing. The housing contains the electrolyte and the electrode assembly. The electrolyte includes an organic component, the mass of which is mg. The capacity of the cylindrical battery is C Ah, where C and m satisfy the following relationship: 1 ≤ m / C ≤ 3.

5. The organic components include chain esters and cyclic carbonates. Based on the total mass of the electrolyte, the mass percentage of the cyclic carbonates is S1, and the mass percentage of the chain esters is S2. S1 and S2 satisfy the following relationship: 1.2≤S2 / S1≤6. The electrode assembly includes a negative electrode sheet, the negative electrode sheet includes a negative current collector and a negative active layer covering at least one side of the negative current collector, the negative active layer includes a negative active material, the negative active material includes a silicon-based material; the surface of the negative active layer includes at least one groove, the groove has a depth of 5μm to 30μm and a width of 0.01mm to 0.3mm.

2. The cylindrical battery according to claim 1, characterized in that, 30≤m≤55； And / or, 15≤C≤40; And / or, 5% ≤ S1 ≤ 40%; And / or, 40%≤S2≤80%; And / or, the cyclic carbonate includes one or more of ethylene carbonate, propylene carbonate, and fluoroethylene carbonate; And / or, the chain ester includes one or more of dimethyl carbonate, ethyl methyl carbonate, ethyl acetate, ethyl propionate, and methyl acetate; And / or, the minimum distance between the groove and the edge of the negative electrode sheet in the length direction of the groove is 1mm to 2mm; And / or, the distance between two adjacent grooves is 0.5mm to 3mm; And / or, the length direction of the groove is perpendicular to the length direction of the negative electrode sheet; And / or, the depth of the groove is 1 / 5 to 1 / 2 of the thickness of one side of the negative electrode active material layer; And / or, the negative electrode active material further includes graphite; And / or, the mass content of silicon-based material in the negative electrode active material is 2%-40%.

3. The cylindrical battery according to claim 1, characterized in that, The mass content of silicon in the negative electrode active layer is a, wherein 1%≤a≤20%; The electrolyte includes fluorinated organic compounds, and the mass percentage of the fluorinated organic compounds is S3 based on the total mass of the electrolyte; wherein, S3 and a satisfy the following relationship: 0.3≤S3 / a≤4.

4. The cylindrical battery according to claim 3, characterized in that, 4%≤a≤15%； And / or, 1% ≤ S3 ≤ 20%; And / or, the fluorinated organic compound includes one or more of fluoroethylene carbonate, difluoroethylene carbonate, trifluoropropylene carbonate, methyltrifluoroethyl carbonate, and ethyl trifluoroacetate.

5. The cylindrical battery according to claim 1, characterized in that, The electrolyte includes a first lithium salt and a second lithium salt. The first lithium salt includes lithium hexafluorophosphate, and the mass content of the first lithium salt is L1, which is 6% ≤ L1 ≤ 15% based on the total mass of the electrolyte. The second lithium salt includes one or both of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethyl)sulfonyl)imide, and the mass content of the second lithium salt is L2, which is 0.1% ≤ L2 ≤ 8% based on the total mass of the electrolyte.

6. The cylindrical battery according to claim 1, characterized in that, The electrolyte includes a second lithium salt, which includes one or both of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethyl)sulfonyl)imide. The mass content of the second lithium salt is L2 based on the total mass of the electrolyte. The electrolyte includes a boron-containing additive. The mass percentage of the boron-containing additive is S5 based on the total mass of the electrolyte. S5 and L2 satisfy the following relationship: 0.02≤S5 / L2≤0.

4.

7. The cylindrical battery according to claim 6, characterized in that, The boron-containing additives include one or more of lithium tetrafluoroborate, lithium bis(oxalate)borate, lithium bis(oxalate)borate, and tris(trimethylsilyl)borate. And / or, 0.1% ≤ L2 ≤ 8%; And / or, 0.1%≤S5≤2%.

8. The cylindrical battery according to any one of claims 1-7, characterized in that, The cylindrical battery satisfies at least one of the following: A. The electrode assembly includes a positive electrode sheet, the positive electrode sheet includes a positive current collector and a positive active layer covering at least one side of the positive current collector, the positive active layer includes a positive active material, the positive active material includes a high-nickel ternary material, and the mass content of nickel element is w based on the mass of the positive active layer; the electrolyte includes ethylene carbonate, and the mass percentage of ethylene carbonate is S4 based on the total mass of the electrolyte; wherein w and S4 satisfy the following relationship: 0%≤S4≤70%-w; B. The electrode assembly includes a positive electrode sheet, which includes a positive current collector, a first positive active material layer, and a second positive active material layer. The positive current collector has a first surface and a second surface. The first positive active material layer is disposed on the first surface, and the second positive active material layer is disposed on the second surface. The first positive active material layer has a plurality of recesses spaced apart. The second positive active material layer has a plurality of protrusions corresponding to the recesses. The minimum distance between the recesses and the edge of the positive electrode sheet is 2mm to 7mm. C. An elastic coating is provided on the inner side of the outer shell. The elastic coating includes a polymer, which includes one or more of epoxy resin, phenolic resin, polyimide, polyethylene, polypropylene, polyvinylidene fluoride, polytetrafluoroethylene, and polyurethane. D. The diaphragm includes a base membrane and a heat-resistant layer located on at least one side of the base membrane, wherein the thickness of the base membrane is 5μm to 15μm and the thickness of the heat-resistant layer is 1μm to 5μm.

9. The cylindrical battery according to claim 8, characterized in that, The thickness of the elastic coating is 5μm~100μm; And / or, the high-nickel ternary material includes one or both of lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide; And / or, 45% ≤ w ≤ 58%; And / or, the heat-resistant layer includes heat-resistant particles, the composition of which is selected from one or more of boehmite, alumina, barium sulfate, magnesium oxide, magnesium hydroxide, silicon dioxide, tin dioxide, titanium dioxide, barium titanate, melamine cyanurate, 1,3,5-triazine-2,4,6-triamine, and melamine thiocyanate. And / or, the diaphragm further includes an adhesive layer located on the surface of the base film and / or the heat-resistant layer.

10. An electrochemical device, characterized in that, Includes the cylindrical battery as described in any one of claims 1-9.

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