Lithium electrochemical device

Abstract

According to the lithium electrochemical device provided by the invention, the mass transfer capability of the lithium electrochemical device under different structures can be ensured by regulating and controlling the concentration of the lithium salt in the electrolyte and the single-side positive and negative electrode overhang of the lithium electrochemical device, the lithium salt concentration is ensured to be matched with the single-side positive and negative electrode overhang under the high current density of a quick charge system, and a lithium precipitation window is widened; and meanwhile, the dissociation capability of the lithium salt is improved by regulating and controlling the mass ratio of ethylene carbonate (EC) and propylene carbonate (PC), so that sufficient dissociation capability of the lithium salt can be ensured while the concentration of the lithium salt is matched with the overhang of a single-side positive electrode and a single-side negative electrode under a quick charge system. Besides, the pyrrole compound has high HOMO and LUMO and can be preferentially oxidized to form a film at the positive electrode, a nitrogen-containing inorganic film is generated to improve the stability of the positive electrode, and a polypyrrole substance is generated through current electropolymerization brought by a short circuit point at the limiting temperature, so that further temperature rise of the lithium electrochemical device can be inhibited, and the safety performance of the lithium electrochemical device is improved.

Description

[0001] This disclosure is a divisional application of the invention patent application filed with the Chinese Patent Office with application number 202211042735.1, application date August 29, 2022, entitled "A Lithium-ion Battery Chemical Device". Technical Field

[0002] This invention belongs to the field of lithium-ion battery chemical device technology, specifically relating to a lithium-ion battery chemical device with fast charging and safety features. Background Technology

[0003] With the development of the new energy industry and the increasing market demand for lithium-ion battery performance, high-energy-density fast-charging lithium-ion batteries have become the direction of industry development. As the lifeblood of lithium-ion batteries, electrolyte has a significant impact on fast-charging performance. Lithium salt, as an important component of electrolyte, provides lithium ions while its anions can participate in multiple functions such as electrolyte solubilization, making it an indispensable part of electrolyte research. Summary of the Invention

[0004] Research has found that with the increasing demand for fast charging in lithium-ion battery chemical devices, the lithium salt concentration also needs to be matched accordingly to meet the requirements of fast charging performance. Meanwhile, the structural design of lithium-ion battery chemical devices can also significantly affect their performance. Among these factors, the overhang between the positive and negative electrodes on one side is a key concern in the design of lithium-ion battery chemical devices, as it significantly impacts the cycle performance, safety performance, and fast charging performance. Therefore, how to better match the material system and the structural design of the lithium-ion battery chemical device to achieve better performance has become a key research focus.

[0005] To address the shortcomings of existing technologies, this invention provides a lithium-ion electrochemical device. By adjusting the concentration of lithium salt in the electrolyte, the mass ratio of ethylene carbonate (EC) and propylene carbonate (PC) in the organic solvent, and the single-sided overhang of the positive and negative electrodes, the electrical performance of the lithium-ion electrochemical device is optimized. This significantly improves the room-temperature cycling performance and fast-charging performance of the device, and also solves the lithium plating problem, preventing lithium plating at the negative electrode. Furthermore, by adding pyrrole compounds as additives to the electrolyte, the safety performance of the lithium-ion electrochemical device can be simultaneously enhanced.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A lithium-ion battery chemical device includes a positive electrode, a negative electrode, a separator, and an electrolyte; the electrolyte includes a solvent, an additive, and a lithium salt, the solvent including a first solvent selected from ethylene carbonate (EC) and propylene carbonate (PC).

[0008] The lithium electrochemical device satisfies:

[0009] X / Y≥1;

[0010] 4Z+8≤Y×100≤20;

[0011] Where X is the percentage of the total mass of ethylene carbonate (EC) and propylene carbonate (PC) in the total mass of the electrolyte; Y is the percentage of the mass of lithium salt in the total mass of the electrolyte; and Z is the overhang of the positive and negative electrodes on one side, in mm.

[0012] According to an embodiment of the present invention, the single-sided positive and negative electrode overhang refers to the width of the side of the negative electrode sheet that extends beyond the positive electrode sheet in the width direction, such as... Figure 1 As shown.

[0013] According to an embodiment of the present invention, the positive and negative overhang refers to the width of the portion of the negative electrode sheet that extends beyond the positive and negative electrode sheets in the width direction (i.e., the sum of the widths on both sides). Specifically, the positive and negative overhang is the sum of the two single-sided positive and negative overhangs. Preferably, the two single-sided positive and negative overhangs are the same.

[0014] According to embodiments of the present invention, when the lithium-ion electrochemical device satisfies X / Y≥1 and 4Z+8≤Y×100≤20, the electrical performance of the lithium-ion electrochemical device can be optimized, significantly improving its room-temperature cycling performance and fast-charging performance, and also solving the lithium plating problem. This is because by controlling the ratio of ethylene carbonate (EC) and propylene carbonate (PC) to lithium salt, the lithium-ion electrochemical device can be ensured to have sufficient dissociation capacity to guarantee the solvation capacity of lithium ions under fast-charging conditions. Simultaneously, matching the corresponding concentration of lithium salt to the positive and negative electrode overhangs on one side ensures the consumption of lithium ions at the edges of the positive and negative electrodes under high current density, thereby improving the room-temperature cycling performance and fast-charging performance of the lithium-ion electrochemical device. When the lithium-ion electrochemical device satisfies X / Y<1 or 4Z+8>Y×100>20, the lithium-ion solubilization capability is affected because ethylene carbonate (EC) and propylene carbonate (PC) cannot provide sufficient dissociation capacity. At the same time, under a large single-sided positive and negative electrode overhang, lithium-ion consumption is fast, the lithium salt concentration cannot meet the lithium-ion consumption rate under high current density, lithium is easily deposited at the edge, and fast charging performance cannot be achieved.

[0015] According to an embodiment of the present invention, 5 ≥ X / Y ≥ 1; exemplarily, X / Y is 1, 2, 3, 4 or 5.

[0016] According to embodiments of the present invention, the lithium salt is selected from at least one of lithium hexafluorophosphate (LiPF6), lithium bisfluorosulfonylimide (LiTFSI), and lithium bisfluorosulfonylimide (LiFSI).

[0017] According to an embodiment of the present invention, the mass percentage of the lithium salt to the total mass of the electrolyte is 10wt% to 20wt% (i.e., Y is 10 to 20wt%), for example, 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt%, 16wt%, 17wt%, 18wt%, 19wt%, or 20wt%.

[0018] According to an embodiment of the present invention, the single-sided positive and negative electrode overhang is 0.5mm~3mm (i.e., Z is 0.5mm~3mm), for example, 0.5mm, 0.6mm, 0.7mm, 0.8mm, 0.9mm, 1.0mm, 1.1mm, 1.2mm, 1.3mm, 1.4mm, 1.5mm, 1.6mm, 1.7mm, 1.8mm, 1.9mm, 2.0mm, 2.1mm, 2.2mm, 2.3mm, 2.4mm, 2.5mm, 2.6mm, 2.7mm, 2.8mm, 2.9mm or 3.0mm.

[0019] According to an embodiment of the present invention, the total mass of ethylene carbonate (EC) and propylene carbonate (PC) accounts for 15wt% to 45wt% of the total mass of the electrolyte (i.e., X is 15wt% to 45wt%), for example, 15wt%, 20wt%, 25wt%, 30wt%, 35wt%, 40wt% or 45wt%.

[0020] According to an embodiment of the present invention, the solvent further includes a second solvent, the second solvent being selected from at least one of diethyl carbonate (DEC), ethyl propionate (EP), propyl propionate (PP), ethyl acetate (EA), ethyl butyrate (EB), and γ-butyrolactone (GBL).

[0021] According to an embodiment of the present invention, the total mass of the solvent accounts for 20wt% to 60wt% of the total mass of the electrolyte, for example, 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, 45wt%, 50wt%, 55wt% or 60wt%.

[0022] According to an embodiment of the present invention, the electrolyte further includes a first additive, wherein the first additive is selected from at least one pyrrole compound represented by Formula I:

[0023] Formula I

[0024] R1 is selected from -CN, substituted or unsubstituted C. 1~10 Alkyl, substituted or unsubstituted C 2~10 alkenyl, substituted or unsubstituted C 2~10 Alkyne, substituted or unsubstituted C 6~10 Aryl group, if substituted, the substituent is C. 1~10 Alkyl group, -CN;

[0025] R2, R3, R4, and R5 may be the same or different, and are independently selected from hydrogen atoms, halogens, and substituted or unsubstituted carbon atoms. 6~10 aryl, substituted or unsubstituted C 2~10 Alkenes, substituted or unsubstituted C 1~10 Alkyl, substituted or unsubstituted C 1~10 Alkoxy group, if substituted, the substituent is C. 1~10 alkyl.

[0026] According to an embodiment of the present invention, R1 is selected from -CN, substituted or unsubstituted C. 1~6 Alkyl, substituted or unsubstituted C 2~6 alkenyl, substituted or unsubstituted C 2~6 Alkyne, substituted or unsubstituted C 6~8 Aryl group, if substituted, the substituent is C. 1~6 Alkyl group, -CN;

[0027] R2, R3, R4, and R5 may be the same or different, and are independently selected from hydrogen atoms, halogens, and substituted or unsubstituted carbon atoms. 6~8 aryl, substituted or unsubstituted C 2~6 Alkenes, substituted or unsubstituted C 1~6 Alkyl, substituted or unsubstituted C 1~6 Alkoxy group, if substituted, the substituent is C. 1~6 alkyl.

[0028] According to an embodiment of the present invention, R1 is selected from -CN, substituted or unsubstituted C. 1~3 Alkyl, substituted or unsubstituted C 2~3 alkenyl, substituted or unsubstituted C 2~3 Alkynyl, substituted or unsubstituted phenyl groups; if substituted, the substituent is C. 1~3 Alkyl group, -CN;

[0029] R2, R3, R4, and R5 may be the same or different, and are independently selected from hydrogen atoms, halogens, substituted or unsubstituted phenyl groups, and substituted or unsubstituted C atoms. 2~3 Alkenes, substituted or unsubstituted C 1~3 Alkyl, substituted or unsubstituted C 1~3 Alkoxy group, if substituted, the substituent is C. 1~3 alkyl.

[0030] According to an embodiment of the present invention, R1 is selected from CH3; R2, R3, R4, and R5 are similarly selected from hydrogen atoms.

[0031] According to an embodiment of the present invention, the total mass of the first additive accounts for 0.3 to 3 wt% of the total mass of the electrolyte, for example, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1.0 wt%, 1.2 wt%, 1.5 wt%, 1.7 wt%, 1.8 wt%, 2 wt%, 2.2 wt%, 2.4 wt%, 2.5 wt%, 2.7 wt%, and 3 wt%.

[0032] According to an embodiment of the present invention, the electrolyte further includes a second additive, the second additive being selected from at least one of fluoroethylene carbonate (FEC), vinylene carbonate (VC), 1,3-propanesulfonate lactone (PS), vinyl sulfate (DTD), methanedisulfonate methylene ester (MMDS), propenesulfonate lactone (PST), maleic anhydride, diethanolic anhydride, succinic anhydride, succinic anhydride, succinic nitrile (SN), adiponitrile (ADN), ethylene glycol bis(propionitrile) ether (EGBE), and hexanetrionitrile (HTCN).

[0033] According to an embodiment of the present invention, the total mass of the second additive accounts for a percentage of the total mass of the electrolyte from 0.1 wt% to 15 wt%, for example, 0.1 wt%, 0.2 wt%, 0.5 wt%, 1.0 wt%, 1.2 wt%, 1.5 wt%, 1.7 wt%, 1.8 wt%, 2 wt%, 2.2 wt%, 2.4 wt%, 2.5 wt%, 2.7 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, or 15 wt%.

[0034] According to an embodiment of the present invention, the positive electrode sheet includes a positive current collector and a positive active material layer coated on the positive current collector, wherein the positive active material layer includes a positive active material, a positive conductive agent, and a positive binder. The positive active material may be, but is not limited to, a chemical formula such as Li. a Ni x Co y M z O 2-b N b(where 0.95≤a≤1.2, x>0, y≥0, z≥0, and x+y+z=1, 0≤b≤1, M is selected from Mn and / or Al, and N is selected from one or more combinations of F, P and S) The positive electrode active material may also be, but is not limited to, LiCoO2, LiNiO2, LiVO2, LiCrO2, LiMn2O4, LiCoMnO4, Li2NiMn3O8, LiNi 0.5 Mn 1.5 The positive electrode active material can be one or more combinations thereof, such as O4, LiCoPO4, LiMnPO4, LiFePO4, LiNiPO4, LiCoFSO4, CuS2, FeS2, MoS2, NiS, and TiS2. The positive electrode active material can also be modified. Methods for modifying the positive electrode active material are known to those skilled in the art. For example, coating, doping, and other methods can be used to modify the positive electrode active material. The materials used for modification can be one or more combinations thereof, including but not limited to Al, B, P, Zr, Si, Ti, Ge, Sn, Mg, Ce, and W. The positive electrode current collector is typically a structure or component that collects current. The positive electrode current collector can be any material suitable for use as a positive electrode current collector in lithium-ion electrochemical devices. For example, the positive electrode current collector can be, but is not limited to, metal foil, and more specifically, aluminum foil. Preferably, the electrolyte provided by this invention is more suitable for lithium-ion electrochemical devices using lithium cobalt oxide as the positive electrode active material.

[0035] According to an embodiment of the present invention, the negative electrode sheet includes a negative electrode fluid and a negative electrode active material layer coated on the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder. The negative electrode active material may be one or more of the following, including but not limited to graphite, soft carbon, hard carbon, carbon fiber, mesophase carbon microspheres, silicon-based materials, tin-based materials, lithium titanate, or other metals that can form alloys with lithium. Specifically, the graphite may be selected from one or more of artificial graphite, natural graphite, and modified graphite; the silicon-based material may be selected from one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, and silicon alloys; and the tin-based material may be selected from one or more of elemental tin, tin oxide compounds, and tin alloys. The negative electrode current collector is typically a structure or component that collects current. The negative electrode current collector may be any material suitable for use as a negative electrode current collector in lithium-ion electrochemical devices, for example, the negative electrode current collector may be, but is not limited to, metal foil, and more specifically, may be, but is not limited to, copper foil.

[0036] According to embodiments of the present invention, the separator can be any material suitable for separators in lithium-ion battery chemical devices, for example, it can be one or more of the following: polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester, and natural fibers.

[0037] According to an embodiment of the present invention, the lithium electrochemical device is a battery, preferably a lithium-ion battery.

[0038] Beneficial effects:

[0039] This invention provides a lithium-ion electrochemical device. By controlling the concentration of lithium salt in the electrolyte and the overhang of the positive and negative electrodes on one side, the mass transfer capability of the lithium-ion electrochemical device under different structures can be guaranteed. This ensures that the lithium salt concentration matches the overhang of the positive and negative electrodes on one side under high current density in the fast-charging system, thus broadening the lithium deposition window. Simultaneously, by controlling the mass ratio of ethylene carbonate (EC) and propylene carbonate (PC), the dissociation capability of lithium salt is improved, ensuring that the lithium salt concentration matches the overhang of the positive and negative electrodes on one side while maintaining sufficient lithium salt dissociation capability in the fast-charging system. Furthermore, pyrrole compounds have high HOMO and high LUMO, and can preferentially oxidize and form films at the positive electrode, generating nitrogen-containing inorganic films to improve the stability of the positive electrode. At extreme temperatures, the electropolymerization of polypyrrole substances through the current brought by the short-circuit point can suppress further temperature rise of the lithium-ion electrochemical device, improving its safety performance. Attached Figure Description

[0040] Figure 1 The diagram shows the structure of the positive and negative electrodes; reference numerals: 1 represents a single-sided positive and negative electrode, 2 represents the negative electrode, and 3 represents the positive electrode. Detailed Implementation

[0041] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0042] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0043] In the description of this invention, it should be noted that the terms "first," "second," etc., are used for descriptive purposes only and are not intended to indicate or imply relative importance.

[0044] Methods for preparing lithium-ion batteries include:

[0045] [Preparation of positive electrode sheet]

[0046] Lithium cobalt oxide (LCO), polyvinylidene fluoride (PVDF), conductive carbon black, and single-walled carbon nanotubes were mixed in a weight ratio of 97.2:1.5:1.2:0.1. 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 a current collector aluminum foil. The coated aluminum foil was baked in an oven with five different temperature gradients, and then dried in an oven at 120°C for 8 hours. Finally, it was rolled and slit to obtain the desired positive electrode sheet.

[0047] [Preparation of negative electrode sheet]

[0048] The negative electrode active material graphite, the thickener sodium carboxymethyl cellulose (CMC-Na), the binder styrene-butadiene rubber, and the conductive agent acetylene black were mixed in a weight ratio of 97:1:1:1. Deionized water was added, and the mixture was stirred in a vacuum mixer to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated onto a high-strength carbon-coated copper foil to obtain an electrode sheet. After the obtained electrode sheet was dried at room temperature, it was transferred to an 80°C oven to dry for 10 hours. Then, it was rolled and slit to obtain a negative electrode sheet.

[0049] [Electrolyte Preparation]

[0050] In a glove box filled with inert gas (H2O < 10 ppm, O2 < 5 ppm), ethylene carbonate, propylene carbonate, methyl ethyl carbonate, and diethyl carbonate were mixed. Then, lithium hexafluorophosphate (LiPF6) (based on Y wt% of the total electrolyte weight), 1,3-propanesulfonyl lactone (PS), and fluoroethylene carbonate (FEC) (based on 9 wt% of the total electrolyte weight) were slowly added to the mixed solution. After passing the tests for moisture and free acid, the electrolytes of the examples and comparative examples were obtained.

[0051] [Battery manufacturing]

[0052] The prepared positive electrode, separator (9-micron thick PP film), and negative electrode are stacked in sequence to ensure that the separator is between the positive and negative electrodes to provide isolation. The overhang size of the positive and negative electrodes on one side is tested. The bare cell is placed in an aluminum-plastic film outer packaging. The prepared electrolyte is injected into the dried battery. The battery is then encapsulated, left to stand, formed, shaped, and tested for capacity to complete the preparation of the lithium-ion battery.

[0053] The obtained lithium-ion batteries and their electrolytes were subjected to relevant performance tests.

[0054] (1) Lithium plating status: The lithium-ion battery was charged at 25°C at 1.5C to 4.45V, then charged at 4.45V at a constant voltage to 0.05C, and then discharged at a constant current of 1.0C to 3.0V. After 30 cycles, the lithium plating was observed after disassembly. No lithium plating or lithium plating area <5% was referred to as no lithium plating; lithium plating area between 5% and 20% was referred to as slight lithium plating; and lithium plating area >20% was referred to as severe lithium plating.

[0055] (2) Thermal shock performance: Under 25℃ ambient conditions, discharge to 3.0V with a given current of 0.2C; rest for 5 minutes; charge to 4.45V with a charging current of 0.2C. When the cell voltage reaches 4.45V, switch to 4.45V constant voltage charging until the charging current is less than or equal to the given cutoff current of 0.05C; after resting for 1 hour, put the cell into an oven. The oven temperature rises to 135±2℃ at a rate of 5±2℃ / min and is maintained for 30 minutes before stopping. The judgment criterion is that the cell does not catch fire or explode.

[0056] (3) Room temperature cycle performance: Room temperature cycle performance test: At 25℃, the battery after capacity division is charged to 4.45V at a constant current and constant voltage of 0.7C, and the cutoff current is 0.05C. Then it is discharged to 3.0V at a constant current of 0.5C. This cycle is repeated. After 500 charge-discharge cycles, the capacity retention rate at the 500th cycle is calculated. The calculation formula is as follows:

[0057] 500-week cycle capacity retention (%) = (500-week cycle discharge capacity / initial cycle discharge capacity) × 100%.

[0058] The results of the above performance tests are shown in Tables 1 and 2.

[0059] Table 1. Battery composition and performance test results of Examples 1-6 and Comparative Examples 1-4

[0060]

[0061] Table 2. Battery composition and performance test results for Examples 7-10 and Comparative Examples 5-6

[0062]

[0063] Comparing the test results of Comparative Examples 3-4 and Examples 1-6 in Table 1, it can be seen that a certain ratio between the lithium salt concentration and the overhang of the positive and negative electrodes on one side can ensure interface stability while guaranteeing the fast-charging performance of the battery. In other words, by adjusting the concentration of lithium salt in the electrolyte and the overhang of the positive and negative electrodes on one side of the lithium electrochemical device, the mass transfer capability of the lithium electrochemical device under different structures can be guaranteed, ensuring that the lithium salt concentration matches the overhang of the positive and negative electrodes on one side under high current density in the fast-charging system, thus broadening the lithium deposition window.

[0064] Furthermore, comparing Examples 1-3, the larger the X / Y value, the better the room temperature cycling performance of the battery. It is speculated that the increased amount of cyclic carbonate solvent is conducive to the dissociation of lithium salt and participates in the formation of SEI film, thereby improving interface stability. Therefore, the room temperature cycling performance of the battery is improved.

[0065] Furthermore, comparing Examples 4-6, when the lithium salt concentration remains constant, the room temperature cycle performance of the battery deteriorates as the overhang of the positive and negative electrodes on one side increases. It is speculated that the larger the overhang of the positive and negative electrodes on one side, the greater the lithium salt consumption due to the high current density at the edge of the overhang. Under the same lithium salt conditions, a lower overhang of the positive and negative electrodes on one side consumes less lithium salt and has less impact on the room temperature cycle performance of the battery.

[0066] Furthermore, comparing Example 3 with Comparative Examples 1 and 2, when the X / Y value is <1, significant lithium plating occurs after disassembling the battery, and the battery's room temperature cycling performance deteriorates significantly. It is speculated that the possible reason is the mismatch between the concentration of cyclic carbonate and lithium salt, which significantly deteriorates the battery performance.

[0067] Furthermore, comparing Examples 5-6 with Comparative Examples 3-4, when the X / Y value is ≥1 but not 4Z+8≤Y×100≤20, continuous lithium plating occurs near the edge of the positive and negative electrode overhang on one side. It is speculated that the possible reason is that when the positive and negative electrode overhang and the lithium salt concentration are mismatched, the low lithium salt concentration cannot meet the edge requirements, resulting in continuous lithium plating at the edge.

[0068] Furthermore, comparing Examples 7-10 with Comparative Examples 5-6, the thermal shock performance of the battery was significantly improved as the amount of the first additive increased, indicating that pyrrole compounds can significantly improve the thermal shock performance of the battery. This is mainly because pyrrole compounds can undergo electropolymerization under thermal shock conditions, thereby improving thermal shock stability. Moreover, the effect of pyrrole compounds on thermal shock performance is significantly higher than that of cyclic carbonates, lithium salts, and changes in the positive and negative electrode overhangs.

[0069] In summary, it can be seen that the lithium-ion battery chemical device provided by this invention can improve fast charging performance while enhancing safety performance, demonstrating extremely high application value.

[0070] The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A lithium-ion battery chemical device, characterized in that, The lithium-ion battery chemical device includes a positive electrode, a negative electrode, a separator, and an electrolyte; the electrolyte includes a solvent, additives, and a lithium salt, and the solvent includes a first solvent selected from ethylene carbonate (EC) and propylene carbonate (PC). The lithium electrochemical device satisfies: X / Y≥1; 4Z+8≤Y×100≤20; Where X is the percentage of the total mass of ethylene carbonate (EC) and propylene carbonate (PC) to the total mass of the electrolyte; Y is the percentage of the mass of lithium salt to the total mass of the electrolyte; Z is the overhang of the positive and negative electrodes on one side, in mm; the overhang of the positive and negative electrodes on one side refers to the width of the negative electrode sheet extending beyond the positive electrode sheet in the width direction. Y is 10wt%~20wt%; Z is 0.5mm~3mm; X is 15wt%~45wt%; The electrolyte comprises fluoroethylene carbonate (FEC) and 1,3-propanesulfonate lactone (PS); The positive electrode includes lithium cobalt oxide as the positive electrode active material.

2. The lithium-ion electrochemical device according to claim 1, characterized in that, 3≥X / Y≥1.

3. The lithium-ion electrochemical device according to claim 1, characterized in that, The solvent further includes a second solvent selected from at least one of diethyl carbonate (DEC), ethyl propionate (EP), propyl propionate (PP), ethyl acetate (EA), ethyl butyrate (EB), and γ-butyrolactone (GBL).

4. The lithium-ion electrochemical device according to claim 1, characterized in that, The electrolyte further includes a first additive, the first additive being selected from at least one pyrrole compound represented by Formula I: Formula I Wherein, R1 is selected from -CN, substituted or unsubstituted C1~10 alkyl, substituted or unsubstituted C2~10 alkenyl, substituted or unsubstituted C2~10 alkynyl, substituted or unsubstituted C6~10 aryl, and if substituted, the substituent is C1~10 alkyl or -CN. R2, R3, R4, and R5 may be the same or different, and are independently selected from hydrogen atoms, halogens, substituted or unsubstituted C6-10 aryl groups, substituted or unsubstituted C2-10 olefins, substituted or unsubstituted C1-10 alkyl groups, substituted or unsubstituted C1-10 alkoxy groups, and if substituted, the substituents are C1-10 alkyl groups.

5. The lithium-ion electrochemical device according to claim 4, characterized in that, R1 is selected from -CN, substituted or unsubstituted C1~6 alkyl, substituted or unsubstituted C2~6 alkenyl, substituted or unsubstituted C2~6 alkynyl, substituted or unsubstituted C6~8 aryl, and if substituted, the substituent is C1~6 alkyl or -CN; R2, R3, R4, and R5 may be the same or different, and are independently selected from hydrogen atoms, halogens, substituted or unsubstituted C6-8 aryl groups, substituted or unsubstituted C2-6 alkenes, substituted or unsubstituted C1-6 alkyl groups, substituted or unsubstituted C1-6 alkoxy groups, and if substituted, the substituents are C1-6 alkyl groups.

6. The lithium-ion electrochemical device according to claim 4, characterized in that, The total mass of the first additive accounts for 0.3~3 wt% of the total mass of the electrolyte.

7. The lithium-ion electrochemical device according to claim 1, characterized in that, The electrolyte further includes a second additive selected from at least one of vinylene carbonate (VC), vinyl sulfate (DTD), methane disulfonate (MMDS), propene sulfonate lactone (PST), maleic anhydride, diethanolic anhydride, succinic anhydride, succinic anhydride, succinic anhydride (SN), adiponitrile (ADN), ethylene glycol bis(propionitrile) ether (EGBE), and hexanetrionitrile (HTCN).

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