A lithium electrochemical device

Abstract

The application provides a lithium electrochemical device, by regulating the concentration of lithium salt in the electrolyte and the single-side positive and negative electrode overhang of the lithium electrochemical device, the mass transfer capacity of the lithium electrochemical device under different structures can be ensured, the lithium salt concentration is matched with the single-side positive and negative electrode overhang under the high current density of the fast charging system, and the lithium precipitation window is widened; meanwhile, by regulating the mass ratio of ethylene carbonate (EC) and propylene carbonate (PC), the dissociation capacity of the lithium salt can be improved, the lithium salt concentration can be matched with the single-side positive and negative electrode overhang under the fast charging system, and meanwhile, the lithium salt dissociation capacity is sufficient. In addition, the pyrrole compound has high HOMO and high LUMO, can be preferentially oxidized into a film at the positive electrode, nitrogen-containing inorganic film is generated to improve the stability of the positive electrode, and the current generated by the short circuit point at the limit temperature can generate polypyrrole substances to inhibit the further temperature rise of the lithium electrochemical device, and the safety performance of the lithium electrochemical device is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium electrochemical devices, and particularly relates to a lithium electrochemical device with fast charging performance and safety performance. BACKGROUND

[0002] With the development of the new energy industry, the market demand for the performance of lithium ion batteries is continuously improved, and high-energy-density fast-charging lithium ion batteries have become the development direction of the industry. Electrolyte, as the blood of lithium ion batteries, has an important influence on fast charging performance. Lithium salt, as an important component of electrolyte, provides lithium ions and its anions can participate in electrolyte solvation and other multiple functions, making it an indispensable part of electrolyte research. SUMMARY

[0003] Research has found that, with the continuous improvement of the fast charging demand of lithium electrochemical devices, the lithium salt concentration also needs to be matched accordingly to meet the demand for fast charging performance. At the same time, the structural design of the lithium electrochemical device can significantly affect its performance. Among them, the single-sided positive and negative overhang (single-sided positive and negative electrode tab width difference) is an important concern in the design of lithium electrochemical devices, which has a significant impact on the cycle performance, safety performance and fast charging performance of lithium electrochemical devices. Therefore, how to better match the material system and the structural design of the lithium electrochemical device to achieve better performance of the lithium electrochemical device has become a research focus.

[0004] In order to improve the deficiencies of the prior art, the application provides a lithium electrochemical device, which optimizes the electrical performance of the lithium electrochemical device by regulating 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 positive and negative overhang of the lithium electrochemical device, significantly improves the room temperature cycle performance and fast charging performance of the lithium electrochemical device, and also solves the problem of lithium precipitation of the lithium electrochemical device, avoiding lithium precipitation on the negative electrode. On this basis, by further adding a pyrrole compound as an additive in the electrolyte, the safety performance of the lithium electrochemical device can be improved at the same time.

[0005] The purpose of the application is achieved by the following technical solutions:

[0006] A lithium electrochemical device, the lithium electrochemical device comprising a positive electrode tab, a negative electrode tab, a separator and an electrolyte; the electrolyte comprising a solvent, an additive and a lithium salt, the solvent comprising a first solvent, the first solvent being selected from ethylene carbonate (EC) and propylene carbonate (PC);

[0007] The lithium electrochemical device satisfies:

[0008] X / Y>=1;

[0009] 4Z+8<=Yx100<=20;

[0010] wherein 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 the lithium salt in the total mass of the electrolyte; and Z is the single-side positive and negative electrode overhang, in mm.

[0011] According to an embodiment of the present application, the single-side positive and negative electrode overhang refers to the width of one side of the part of the negative electrode tab that extends beyond the positive and negative electrode tab in the width direction, as shown in Figure 1

[0012] According to an embodiment of the present application, the positive and negative electrode overhang refers to the width of the part of the negative electrode tab that extends beyond the positive and negative electrode tab in the width direction (i.e. the sum of the widths of both sides), and specifically, the positive and negative electrode overhang is the sum of the two single-side positive and negative electrode overhangs, and preferably, the two single-side positive and negative electrode overhangs are the same.

[0013] According to an embodiment of the present application, when the lithium electrochemical device satisfies X / Y≥1, 4Z+8≤Y×100≤20, the electrical performance of the lithium electrochemical device can be optimized, the room temperature cycle performance and the fast charging performance of the lithium electrochemical device can be significantly improved, and the lithium precipitation problem of the lithium electrochemical device can be solved. This is because by controlling the ratio of ethylene carbonate (EC) and propylene carbonate (PC) to the lithium salt, the lithium electrochemical device can ensure sufficient dissociation capacity to ensure the solvation capacity of lithium ions under fast charging conditions, and the single-side positive and negative electrode overhang matching the corresponding concentration of the lithium salt can ensure the consumption of lithium ions by the positive and negative electrode edges under high current density, thereby achieving the improvement of the room temperature cycle performance and the fast charging performance of the lithium electrochemical device. When the lithium electrochemical device satisfies X / Y<1 or 4Z+8>Y×100>20, the ethylene carbonate (EC) and propylene carbonate (PC) cannot provide sufficient dissociation capacity, which affects the solvation capacity of lithium ions, and under the condition of a large single-side positive and negative electrode overhang, the consumption of lithium ions is fast, the lithium salt concentration cannot meet the consumption speed of lithium ions under high current density, and the edges are prone to lithium precipitation, which cannot achieve the fast charging performance.

[0014] According to an embodiment of the present application, 5≥X / Y≥1; and exemplarily, X / Y is 1, 2, 3, 4 or 5.

[0015] According to an embodiment of the present application, the lithium salt is selected from at least one of lithium hexafluorophosphate (LiPF6), lithium bisfluorosulfonylimide (LiTFSI) and lithium bisfluorosulfonylimide (LiFSI).

[0016] ​According to an embodiment of the present application, the lithium salt has a mass percentage of 10wt% to 20wt% (i.e. Y is 10 to 20wt%) of the total mass of the electrolyte, for example 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt%, 16wt%, 17wt%, 18wt%, 19wt% or 20wt%.

[0017] According to an embodiment of the present application, the single-sided positive and negative electrode overhang is 0.5mm to 3mm (i.e. Z is 0.5mm to 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.

[0018] According to an embodiment of the present application, the total mass of the ethylene carbonate (EC) and propylene carbonate (PC) has a mass percentage of 15wt% to 45wt% (i.e. X is 15wt% to 45wt%) of the total mass of the electrolyte, for example 15wt%, 20wt%, 25wt%, 30wt%, 35wt%, 40wt% or 45wt%.

[0019] According to an embodiment of the present application, the solvent further comprises a second solvent selected from at least one of diethyl carbonate (DEC), ethyl propionate (EP), propyl propionate (PP), ethyl acetate (EA), ethyl n-butyrate (EB) and γ-butyrolactone (GBL).

[0020] According to an embodiment of the present application, the total mass of the solvent has a mass percentage of 20wt% to 60wt% of the total mass of the electrolyte, for example 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, 45wt%, 50wt%, 55wt% or 60wt%.

[0021] According to an embodiment of the present application, the electrolyte further comprises a first additive selected from at least one pyrrole compound shown in Formula I:

[0022]

[0023] wherein 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 alkynyl, substituted or unsubstituted C 6～10aryl, if substituted, substituted with C 1～10 alkyl, -CN;

[0024] R2, R3, R4, R5, are the same or different, independently from each other, selected from the group consisting of a hydrogen atom, halogen, substituted or unsubstituted C 6～10 aryl, substituted or unsubstituted C 2～10 alkene, substituted or unsubstituted C 1～10 alkyl, substituted or unsubstituted C 1～10 alkoxy, if substituted, substituted with C 1～10 alkyl.

[0025] According to an embodiment of the present application, R1is selected from the group consisting of -CN, substituted or unsubstituted C 1～6 alkyl, substituted or unsubstituted C 2～6 alkenyl, substituted or unsubstituted C 2～6 alkynyl, substituted or unsubstituted C 6～8 aryl, if substituted, substituted with C 1～6 alkyl, -CN;

[0026] R2, R3, R4, R5, are the same or different, independently from each other, selected from the group consisting of a hydrogen atom, halogen, substituted or unsubstituted C 6～8 aryl, substituted or unsubstituted C 2～6 alkene, substituted or unsubstituted C 1～6 alkyl, substituted or unsubstituted C 1～6 alkoxy, if substituted, substituted with C 1～6 alkyl.

[0027] According to an embodiment of the present application, R1is selected from the group consisting of -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, if substituted, substituted with C 1～3 alkyl, -CN;

[0028] R2, R3, R4, R5, are the same or different, independently from each other, selected from the group consisting of a hydrogen atom, halogen, substituted or unsubstituted phenyl, substituted or unsubstituted C 2～3 alkene, substituted or unsubstituted C 1～3 alkyl, substituted or unsubstituted C 1～3 alkoxy, if substituted, substituted with C 1～3 alkyl.

[0029] According to an embodiment of the present application, R1is selected from the group consisting of CH3; R2, R3, R4, R5, are the same selected from the group consisting of a hydrogen atom.

[0030] According to embodiments of the present application, the first additive is present in an amount of 0.3-3 wt% of the total 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%, 3 wt%.

[0031] According to embodiments of the present application, the electrolyte further comprises a second additive, the first additive is selected from at least one of fluoroethylene carbonate (FEC), vinylene carbonate (VC), 1,3-propane sultone (PS), vinyl sulfate (DTD), methylene methane disulfonate (MMDS), propylene sulfite (PST), maleic anhydride, diglycolic anhydride, succinic anhydride, succinonitrile (SN), adiponitrile (ADN), ethylene glycol bis(propionitrile) ether (EGBE), and hexane trinitrile (HTCN).

[0032] According to embodiments of the present application, the second additive is present in an amount of 0.1-15 wt% of the total electrolyte, 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%.

[0033] According to embodiments of the present application, the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer coated on the positive electrode current collector, the positive electrode active material layer comprising a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder. The positive electrode active material can be a combination of one or more of compounds represented by the chemical formulae Li a Ni x Co y M z O 2-b N b a combination of one or more of compounds represented by the chemical formulae Li 0.5 Mn1.5 O4, LiCoPO4, LiMnPO4, LiFePO4, LiNiPO4, LiCoFSO4, CuS2, FeS2, MoS2, NiS, TiS2, etc. The positive active material can also be modified, and the method for modifying the positive active material is known to those skilled in the art, for example, the positive active material can be modified by coating, doping, etc., and the material used for modification can be one or more combinations of Al, B, P, Zr, Si, Ti, Ge, Sn, Mg, Ce, W, etc. The positive current collector is generally a structure or part for collecting current, and the positive current collector can be various materials suitable for use as a positive current collector of a lithium electrochemical device, for example, the positive current collector can be one or more combinations of metal foils, etc., and more specifically can be one or more combinations of aluminum foils, etc. Preferably, the electrolyte provided by the present application is more suitable for a lithium electrochemical device with lithium cobaltate as the positive active material.

[0034] According to an embodiment of the present application, the negative tab includes a negative fluid and a negative active material layer coated on the negative current collector, and the negative active material layer includes a negative active material, a negative conductive agent, and a negative binder. The negative active material can be one or more of graphite, soft carbon, hard carbon, carbon fiber, mesocarbon microbead, silicon-based material, tin-based material, lithium titanate, or other metal capable of forming an alloy with lithium, etc. Among them, the graphite can be selected from one or more of artificial graphite, natural graphite, and modified graphite; the silicon-based material can be selected from one or more of elemental silicon, silicon oxide compound, silicon-carbon composite, silicon alloy; the tin-based material can be selected from one or more of elemental tin, tin oxide compound, tin alloy. The negative current collector is generally a structure or part for collecting current, and the negative current collector can be various materials suitable for use as a negative current collector of a lithium electrochemical device, for example, the negative current collector can be one or more combinations of metal foils, etc., and more specifically can be one or more combinations of copper foils, etc.

[0035] According to an embodiment of the present application, the separator can be various materials suitable for use as a separator of a lithium electrochemical device, for example, can be one or more combinations of polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester, and natural fiber, etc.

[0036] According to an embodiment of the present application, the lithium electrochemical device is a battery, preferably a lithium ion battery.

[0037] Advantages:

[0038] The application provides a lithium electrochemical device, which can ensure the mass transfer capacity of the lithium electrochemical device under different structures by regulating the concentration of lithium salt in an electrolyte and the single-sided positive and negative electrode overhang of the lithium electrochemical device, ensure the matching of the lithium salt concentration and the single-sided positive and negative electrode overhang under a high current density of a fast-charging system, and expand the lithium precipitation window; meanwhile, the application can improve the dissociation capacity of the lithium salt by regulating the mass ratio of ethylene carbonate (EC) and propylene carbonate (PC), so that the lithium electrochemical device can have sufficient lithium salt dissociation capacity while ensuring the matching of the lithium salt concentration and the single-sided positive and negative electrode overhang under the fast-charging system. In addition, the pyrrole compound has high HOMO and high LUMO, can be preferentially oxidized into a film at the positive electrode, generate a nitrogen-containing inorganic film to improve the stability of the positive electrode, and generate a polypyrrole compound by the current electro-polymerization caused by a short-circuit point under an extreme temperature, so that the further temperature rise of the lithium electrochemical device can be inhibited, and the safety performance of the lithium electrochemical device can be improved. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 FIG. 1 is a structural schematic diagram of the positive and negative electrode sheets; in the figure, 1 represents the single-sided positive and negative electrode overhang, 2 represents the negative electrode sheet, and 3 represents the positive electrode sheet. DETAILED DESCRIPTION

[0040] The application will be described in further detail below with reference to specific examples. It should be understood that the following examples are only illustrative and explanatory of the application, and should not be interpreted as limiting the scope of protection of the application. Any technology achieved based on the above description of the application is included in the scope of protection intended by the application.

[0041] In the following examples, the experimental methods used are conventional methods unless otherwise specified; the reagents, materials, etc. used in the following examples can be obtained from commercial channels unless otherwise specified.

[0042] In the description of the application, it should be noted that the terms "first", "second", etc. are only used for the purpose of description, and do not indicate or imply relative importance.

[0043] The preparation method of the lithium ion battery comprises the following steps:

[0044] [Preparation of positive electrode sheet]

[0045] The positive active material lithium cobalt oxide (LCO), the binder polyvinylidene fluoride (PVDF), the conductive carbon black and the single-walled carbon nanotube are mixed in a weight ratio of 97.2:1.5:1.2:0.1, N-methyl pyrrolidone (NMP) is added, and stirring is performed under the action of a vacuum stirrer until the mixed system becomes a positive electrode slurry with uniform fluidity; the positive electrode slurry is uniformly coated on a current collector aluminum foil; the coated aluminum foil is baked in an oven with five different temperature gradients, and then dried in an oven at 120°C for 8h, and then subjected to rolling and slitting to obtain the required positive electrode sheet.

[0046] [Preparation of negative electrode sheet]

[0047] The negative active material graphite, the thickening agent sodium carboxymethyl cellulose (CMC-Na), the binder styrene-butadiene rubber and the conductive agent acetylene black are mixed in a weight ratio of 97:1:1:1, deionized water is added, and a negative electrode slurry is obtained under the action of a vacuum stirrer; the negative electrode slurry is uniformly coated on a high-strength carbon-coated copper foil to obtain an electrode sheet; the obtained electrode sheet is transferred to a 80°C oven after air drying at room temperature and dried for 10h, and then subjected to rolling and slitting to obtain a negative electrode sheet.

[0048] [Preparation of electrolyte]

[0049] In an inert gas-filled glove box (H2O<10ppm, O2<5ppm), ethylene carbonate, propylene carbonate, methyl ethyl carbonate and diethyl carbonate are mixed, then Ywt% of lithium hexafluorophosphate (LiPF6) and 3wt% of 1,3-propane sultone (PS) and 9wt% of fluoroethylene carbonate (FEC) based on the total weight of the electrolyte are slowly added to the mixed solution, and after passing the water and free acid detection, the electrolyte of the examples and comparative examples is obtained.

[0050] [Manufacture of battery]

[0051] The above prepared positive electrode sheet, separator (9 micron thick PP film) and negative electrode sheet are stacked in order, ensuring that the separator is between the positive and negative electrode sheets to play an isolating role, and the size of the single-sided positive and negative overhang is tested, the bare cell is placed in an aluminum plastic film outer package, the above prepared electrolyte is injected into the dried battery, and the battery is packaged, placed, formed, shaped and tested to complete the preparation of the lithium ion battery.

[0052] The obtained lithium ion battery and its electrolyte are subjected to relevant performance tests.

[0053] (1) Lithium precipitation state: lithium ion battery was charged at 1.5C to 4.45V at 25℃, constant voltage charged at 4.45V to 0.05C, then discharged at 1.0C to 3.0V, cycled 30 times, disassembled to observe the degree of lithium precipitation. No lithium precipitation or lithium precipitation area <5% is called no lithium precipitation; lithium precipitation area between 5% and 20% is called slight lithium precipitation; lithium precipitation area >20% is called severe lithium precipitation.

[0054] (2) Thermal shock performance: discharge at a given current of 0.2C to 3.0V under 25℃ environmental conditions; stand for 5min; charge at a charge current of 0.2C to 4.45V, when the cell voltage reaches 4.45V, change to 4.45V constant voltage charging until the charge current is less than or equal to the given cutoff current of 0.05C; after standing for 1h, put the cell into an oven, increase the oven temperature to 135±2℃ at a speed of 5±2℃ / min, and keep for 30min before stopping, the judgment standard is that the cell does not catch fire and does not explode.

[0055] (3) Normal temperature cycle performance: normal temperature cycle performance test: after discharging, the battery was charged at 0.7C constant current and constant voltage to 4.45V at 25℃, then discharged at 0.5C constant current to 3.0V, and the cycle was repeated, and the capacity retention rate at the 500th cycle was calculated after 500 cycles of charging and discharging, the calculation formula was as follows:

[0056] The 500th cycle capacity retention rate (%) = (the 500th cycle discharge capacity / the first cycle discharge capacity) x 100%.

[0057] The results of the above performance tests are shown in Tables 1 and 2.

[0058] Table 1 Battery composition and performance test results of Examples 1-6 and Comparative Examples 1-4

[0059]

[0060] Table 2 Battery composition and performance test results of Examples 7-10 and Comparative Examples 5-6

[0061]

[0062] From the comparison of the test results of Comparative Examples 3-4 and Examples 1-6 in Table 1, it can be seen that the lithium salt concentration and the single-sided positive and negative overhang in a certain proportion can ensure the stability of the interface and the fast charging performance of the battery; that is, by adjusting the concentration of lithium salt in the electrolyte and the single-sided positive and negative overhang of the lithium electrochemical device, the mass transfer capacity of the lithium electrochemical device under different structures can be ensured, the matching of lithium salt concentration and single-sided positive and negative overhang under high current density of fast charging system is ensured, and the lithium precipitation window is widened.

[0063] Further, compared with Examples 1-3, the greater the value of X / Y, the better the room temperature cycle performance of the battery, and it is speculated that the increase in the amount of cyclic carbonate solvent is conducive to the dissociation of lithium salt, and at the same time participates in the formation of SEI film, thereby improving the interface stability, and thus the room temperature cycle performance of the battery is improved.

[0064] Further, compared with Examples 4-6, when the lithium salt concentration is unchanged, as the unilateral positive and negative overhang increases, the room temperature cycle performance of the battery shows a deterioration trend, and it is speculated that the greater the unilateral positive and negative overhang, the greater the high current density at the edge of the unilateral positive and negative overhang, which consumes more lithium salt, and under the same lithium salt condition, the consumption of lithium salt is small with low unilateral positive and negative overhang, which has little effect on the room temperature cycle performance of the battery.

[0065] Further, compared with Example 3 and Comparative Examples 1-2, when the value of X / Y is <1, obvious lithium precipitation occurs after the battery is disassembled, and the room temperature cycle performance of the battery is significantly deteriorated, and the possible reason is that the cyclic carbonate and the lithium salt concentration are not matched, which significantly deteriorates the battery performance.

[0066] Further, compared with Examples 5-6 and Comparative Examples 3-4, when the value of X / Y is ≥1 and 4Z+8≤Y×100≤20 is not met, continuous lithium precipitation occurs at the edge near the unilateral positive and negative overhang, and the possible reason is that when the positive and negative overhang and the lithium salt concentration are not matched, the low lithium salt concentration cannot meet the edge demand, resulting in continuous lithium precipitation at the edge.

[0067] Further, compared with Examples 7-10 and Comparative Examples 5-6, as the amount of the first additive increases, the thermal shock performance of the battery is significantly improved, indicating that the pyrrole compound can significantly improve the thermal shock performance of the battery, which is mainly because the pyrrole compound can undergo electropolymerization under thermal shock conditions, thereby improving the thermal shock stability, and the influence of the pyrrole compound on the thermal shock performance is significantly higher than that of the cyclic carbonate, the lithium salt and the positive and negative overhang.

[0068] In summary, it can be seen that the lithium electrochemical device provided by the present application can improve the fast charging performance while improving the safety performance, and has extremely high application value.

[0069] The above describes the embodiments of the present application. However, the present application is not limited to the above-mentioned embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A lithium electrochemical device characterized by, The lithium electrochemical device comprises a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte; the electrolyte comprises a solvent, an additive and a lithium salt, the solvent comprises 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; Wherein, 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 the lithium salt in the total mass of the electrolyte; Z is the unilateral positive and negative overhang, unit: mm; the unilateral positive and negative overhang refers to the width of one side of the part of the negative electrode sheet that exceeds the positive electrode sheet in the width direction; Y is 10wt%-20wt%; Z is 0.5mm-3mm; X is 15wt%-45wt%.

2. The lithium electrochemical device of claim 1, wherein, 3≥X / Y≥1.

3. The lithium electrochemical device of claim 1, wherein, The solvent further comprises a second solvent selected from at least one of diethyl carbonate (DEC), ethyl propionate (EP), propyl propionate (PP), ethyl acetate (EA), ethyl n-butyrate (EB) and gamma-butyrolactone (GBL).

4. The lithium electrochemical device of claim 1, wherein, The electrolyte further comprises a first additive selected from at least one pyrrole compound represented by formula I: Formula I wherein R1is selected from -CN, substituted or unsubstituted C 1~10 alkyl, substituted or unsubstituted C 2~10 alkenyl, substituted or unsubstituted C 2~10 alkynyl, substituted or unsubstituted C 6~10 aryl, and if substituted, substituted with C 1~10 alkyl, -CN; R2, R3, R4, R5, are the same or different, independently of each other, selected from the group consisting of a hydrogen atom, a halogen, a substituted or unsubstituted C 6~10 aryl group, a substituted or unsubstituted C 2~10 alkene group, a substituted or unsubstituted C 1~10 alkyl group, a substituted or unsubstituted C 1~10 alkoxy group, if substituted, the substituents are C 1~10 alkyl groups.

5. The lithium electrochemical device of claim 4, wherein, R1is selected from -CN, substituted or unsubstituted C 1~6 alkyl, substituted or unsubstituted C 2~6 alkenyl, substituted or unsubstituted C 2~6 alkynyl, substituted or unsubstituted C 6~8 aryl, and if substituted, with C 1~6 alkyl, -CN; R2, R3, R4, R5, are the same or different, independently of each other, selected from the group consisting of a hydrogen atom, a halogen, a substituted or unsubstituted C 6~8 aryl group, a substituted or unsubstituted C 2~6 alkene group, a substituted or unsubstituted C 1~6 alkyl group, a substituted or unsubstituted C 1~6 alkoxy group, if substituted, the substituents are C 1~6 alkyl groups.

6. The lithium electrochemical device of claim 4, wherein, The percentage of the total mass of the first additive in the total mass of the electrolyte is 0.3-3wt%.

7. The lithium electrochemical device of claim 1, wherein, The electrolyte further comprises a second additive selected from at least one of fluoroethylene carbonate (FEC), vinylene carbonate (VC), 1,3-propane sulfonic acid lactone (PS), ethylene sulfate (DTD), methylene methane disulfonate (MMDS), propylene sulfonic acid lactone (PST), maleic anhydride, diglycolic anhydride, succinic anhydride, butanedinitrile (SN), adipodinitrile (ADN), ethylene glycol bis (propionitrile) ether (EGBE) and hexane trinitrile (HTCN).

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