Lithium battery and electrolyte

Abstract

The application discloses a lithium battery electrolyte, which comprises a lithium salt, an organic solvent and an additive, wherein the additive is any one or more of fluoroethylene carbonate, vinylene carbonate, vinyl ethylene carbonate, butanedinitrile, hexanedinitrile and hexanetristriyne. The application also provides a lithium battery. The lithium battery and the electrolyte. The lithium battery electrolyte and the lithium battery provided by the application solve the problem of excessive PS content in the battery, and can ensure that the high-temperature and cycle performance of the battery are taken into account, and the high-temperature performance can reach or be higher than that of a battery containing PS.

Description

Technical Field

[0001] This application relates to the field of lithium battery technology, and in particular to a lithium battery and electrolyte. Background Technology

[0002] With societal development, traditional fossil fuels can no longer meet the needs of production and daily life, while also causing numerous environmental problems. Developing new renewable energy sources has become an inevitable trend. Lithium-ion batteries, due to their advantages such as high energy density, long cycle life, and environmental friendliness, have been widely used in electric vehicles, laptops, and energy storage.

[0003] In recent years, the European Chemicals Agency (ECHA) has implemented a list-based management system for substances that may be carcinogenic, teratogenic, or reproductively toxic, as well as substances that are bioaccumulative and other substances that have serious impacts on humans and the environment, known as Substances of Very High Concern (SVHCs). EU regulations stipulate that if an article placed on the EU market contains any SVHC candidate substance at a concentration >0.1%, EU producers or importers must fulfill the notification and reporting obligations stipulated in the REACH regulation: when an article contains any SVHC candidate substance at a concentration >0.1% and the total amount of that substance entering the EU exceeds 1 tonne per year, EU producers or importers must first notify ECHA before the product can be sold on the EU market.

[0004] To ensure the high-temperature performance of batteries, a certain amount of 1,3-propanesulfonate lactone (PS) is added to conventional electrolytes. The 1,3-propanesulfonate lactone content in the electrolyte of digital batteries is generally ≥3wt%, while that in power batteries is generally ≤2%. This translates to a relatively high content within the battery itself.

[0005] ≥0.1%. Since 1,3-propanesulfonate lactone is a candidate substance for SVHC, most batteries on the market currently do not meet the requirement of having a PS content of ≤0.1%, which has a significant impact on exports; furthermore, the 1,3-propanesulfonate lactone contained in batteries also poses a threat to the environment.

[0006] Therefore, how to develop a lithium-ion battery with low content of 1,3-propanesulfonic acid lactone while meeting the performance requirements is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0007] To solve the above-mentioned technical problems, the first objective of this invention is to provide a lithium battery electrolyte; the second objective of this invention is to provide a lithium battery; the lithium battery electrolyte and lithium battery provided in this application solve the problem of excessive PS content in the battery, while also ensuring that the battery's high-temperature performance and cycle performance are both maintained, and that the high-temperature performance can reach or exceed that of batteries containing PS.

[0008] The technical solution provided by this invention is as follows:

[0009] A lithium battery electrolyte includes: a lithium salt, an organic solvent, and additives.

[0010] The additive is any one or more of the following: fluoroethylene carbonate, ethylene carbonate, ethylene ethylene carbonate, succinic acid nitrile, adiponitrile, and hexanetrionitrile.

[0011] Preferably, the additives include any one or more of fluoroethylene carbonate, ethylene carbonate, and ethylene ethylene carbonate; and any one or more of succinic acid, adiponitrile, and hexanetrionitrile.

[0012] Preferably, the mass ratio of ethylene carbonate:ethylene carbonate:ethylene ethylene carbonate is (5-20):(0-1):(0-1); the mass ratio of succinic anionyl, adiponitrile, and hexanetrionitrile is (0-2):(0-2):(0-3). Preferably, the lithium salt is one or more of lithium hexafluorophosphate, lithium perchlorate, lithium difluorophosphate, and lithium difluorooxalate borate; and / or,

[0013] In the electrolyte, lithium salt accounts for 10-18% of the total mass of the electrolyte, organic solvent accounts for 60-80% of the total mass of the electrolyte, and additives account for 10-30% of the total mass of the electrolyte.

[0014] Preferably, the organic solvent includes carbonates and carboxylic acid esters, wherein the carbonates include cyclic carbonates and chain carbonates.

[0015] Preferably, the mass ratio of cyclic carbonate:chain carbonate:carboxylic acid ester is (10-50):20:(30-70).

[0016] Preferably, the cyclic carbonate includes one or more of ethylene carbonate and propylene carbonate;

[0017] Chain carbonates include one or more of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate;

[0018] Carboxylic acid esters include one or two of propyl acetate, butyl acetate, ethyl propionate, and propyl propionate.

[0019] Preferably, ethylene carbonate accounts for 0-20% of the total mass of the organic solvent.

[0020] Preferably, the cyclic carbonate includes one or both of ethylene carbonate and propylene carbonate;

[0021] The chain carbonate is diethyl carbonate;

[0022] The carboxylic acid ester is propyl propionate. A lithium battery includes a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte is any of the lithium battery electrolytes described above.

[0023] This application provides a lithium battery electrolyte free of 1,3-propanesulfonate lactone (PS) to solve the problem of excessive PS content. As is well known, PS is a high-temperature additive; its addition improves the high-temperature performance of the battery, while its absence challenges this performance. This invention addresses the high-temperature performance problem through the following two improvements:

[0024] First, reduce the content of the solvent EC. Under high voltage, the positive electrode active material decomposes and releases lattice oxygen, which reacts with the highly reducing EC, causing electrolyte decomposition and dissolution of the transition metal in the positive electrode active material, generating gas. The side reactions are exacerbated, especially at high temperatures.

[0025] Secondly, in addition to SN, ADN, and HTCN as nitrile additives, FEC, VC, and VEC are also added to the electrolyte to promote film formation on the negative electrode. Since EC is an excellent solvent for negative electrode film formation, the resulting SEI film is dense and stable, which has a decisive impact on battery performance, especially cycle performance. This invention improves the high-temperature performance of batteries without PS by reducing the EC content. However, reducing the EC content leads to an unstable and dense SEI film, which can easily cause cycle failure. Therefore, by adding FEC / VC / VEC negative electrode film-forming additives, a dense and stable SEI film can be formed on the negative electrode, improving battery cycle performance. The preferred mass ratio of ethylene carbonate:ethylene carbonate:ethylene ethylene carbonate is (5-20):(0-1):(0-1), and a more preferred mass ratio is (10-12):(0.5-1):(0.3-0.5); the mass ratio of succinic anion, adiponitrile, and hexanetrionitrile is (0-2):(0-2):(0-3), and a more preferred mass ratio is (1-1.5):(1-1.5):(2-3).

[0026] By combining the two methods mentioned above, the problem of excessive PS content in batteries is solved, while ensuring that the battery's high-temperature performance and cycle performance are both maintained, and that the high-temperature performance can reach or exceed that of batteries containing PS. Detailed Implementation

[0027] To enable those skilled in the art to better understand the technical solutions in this application, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0028] The abbreviations for substances are as follows:

[0029] Lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium difluorophosphate (LiPO2F2), and lithium difluorooxalate borate (LiODFB);

[0030] Ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC);

[0031] Propyl acetate (PA), butyl acetate (BA), ethyl propionate (EP), propyl propionate (PP);

[0032] Fluorinated ethylene carbonate (FEC), ethylene carbonate (VC), ethylene ethylene carbonate (VEC), succinic anionyl (SN), adiponitrile (ADN), and hexanetrionitrile (HTCN).

[0033] Example 1

[0034] (1) Preparation of positive electrode

[0035] Lithium cobalt oxide (LCO), conductive agent Super-P (conductive carbon black), and binder PVDF (polyvinylidene fluoride) were mixed at a mass ratio of 98:1:1 and dispersed in the organic solvent NMP (N-methylpyrrolidone). The mixture was stirred in a vacuum mixer until stable and homogeneous, forming a positive electrode slurry. The positive electrode slurry was then uniformly coated onto an aluminum foil with a thickness of 12 μm. After drying the aluminum foil at room temperature, it was transferred to a 120°C forced-air oven for 1 hour of drying. Finally, it was cold-pressed and die-cut to form a positive electrode sheet.

[0036] (2) Preparation of negative electrode

[0037] The negative electrode material graphite, conductive agent Super-P (conductive carbon black), SBR (styrene-butadiene rubber), and CMC (sodium carboxymethyl cellulose) were mixed in a mass ratio of 97:0.5:1.5:1 and dispersed in deionized water. The mixture was stirred in a vacuum mixer until stable and homogeneous, forming a negative electrode slurry. The negative electrode slurry was then uniformly coated onto a copper foil with a thickness of 6 μm. After drying the copper foil at room temperature, it was transferred to a 120°C forced-air oven for 1 hour of drying. Finally, it was cold-pressed and die-cut to form a negative electrode sheet.

[0038] (3) Electrolyte preparation

[0039] LiPF6, a mixed organic solvent (EC / PC / DEC / PP = 20 / 10 / 20 / 50), FEC, SN, ADN, HTCN, and LiODFB were mixed and stirred using a vacuum stirrer until stable and homogeneous to obtain the electrolyte. The mass percentages of LiPF6, the mixed organic solvent, FEC, SN, ADN, HTCN, and LiODFB in the total electrolyte were 15%, 73.5%, 7%, 1%, 1%, 2%, and 0.5%, respectively.

[0040] (4) Lithium-ion battery manufacturing

[0041] A bare cell is obtained by stacking positive electrode, negative electrode and separator. After the cell is put into aluminum-plastic film packaging shell, the above electrolyte is injected and then sealed in sequence. After standing, formation, hot and cold pressing and capacity testing, lithium-ion battery is produced.

[0042] Example 2

[0043] Based on Example 1, the solvent ratio was adjusted to EC / PC / DEC / PP = 10 / 10 / 20 / 60, while other parameters remained unchanged.

[0044] Example 3

[0045] Based on Example 1, the solvent ratio was adjusted to EC / PC / DEC / PP = 5 / 10 / 20 / 65, while other parameters remained unchanged.

[0046] Example 4

[0047] Based on Example 1, the solvent ratio was adjusted to PC / DEC / PP = 10 / 20 / 70, while other parameters remained unchanged.

[0048] Example 5

[0049] Based on Example 4, the mass of FEC was adjusted to 8%, the mass of solvent was adjusted to 72.5%, and other parameters remained unchanged.

[0050] Example 6

[0051] Based on Example 4, the mass of FEC was adjusted to 9%, the mass of solvent was adjusted to 71.5%, and other parameters remained unchanged.

[0052] Example 7

[0053] Based on Example 4, the mass of FEC was adjusted to 10%, the mass of solvent was adjusted to 70.5%, and other parameters remained unchanged.

[0054] Example 8

[0055] Based on Example 4, the mass of FEC was adjusted to 15%, the mass of solvent was adjusted to 65.5%, and other parameters remained unchanged.

[0056] Example 9

[0057] Based on Example 4, the mass of FEC was adjusted to 20%, the mass of solvent was adjusted to 60.5%, and other parameters remained unchanged.

[0058] Example 10

[0059] Based on Example 7, 0.5% VC and 0.3% VEC were added, the solvent mass was adjusted to 69.7%, and other parameters remained unchanged.

[0060] Example 11

[0061] Based on Example 7, 1% VC and 0.5% VEC were added, the solvent mass was adjusted to 69.0%, and other parameters remained unchanged.

[0062] Example 12

[0063] Based on Example 10, the LiPF6 concentration was adjusted to 10%, the solvent mass was adjusted to 74.7%, and other parameters remained unchanged.

[0064] Example 13

[0065] Based on Example 10, the LiPF6 concentration was adjusted to 12.5%, the solvent mass was adjusted to 72.2%, and other parameters remained unchanged.

[0066] Example 14

[0067] Based on Example 10, the LiPF6 concentration was adjusted to 17%, the solvent mass was adjusted to 67.7%, and other parameters remained unchanged.

[0068] Example 15

[0069] Based on Example 10, the masses of SN, ADN, and HTCN were adjusted to 1.5%, 1.5%, and 3%, respectively, and the mass of solvent was adjusted to 67.7%, while other parameters remained unchanged.

[0070] Comparative Example 1

[0071] Based on Example 1, 4% PS (1,3-propanesulfonate lactone) was added, the solvent mass fraction was adjusted to 69.5%, and other parameters remained unchanged.

[0072] Comparative Example 2

[0073] Based on Example 1, 3% PS (1,3-propanesulfonate lactone) was added, the solvent mass fraction was adjusted to 70.5%, and other parameters remained unchanged.

[0074] Comparative Example 3

[0075] Based on Example 1, 2% PS (1,3-propanesulfonic acid lactone) was added, the solvent mass fraction was adjusted to 71.5%, and other parameters remained unchanged.

[0076] Comparative Example 4

[0077] Based on Example 1, 0.8% PS (1,3-propanesulfonate lactone) and 1% PST (1,3-propenesulfonate lactone) by mass fraction were added, the solvent mass fraction was adjusted to 71.7%, and other parameters remained unchanged.

[0078] Comparative Example 5

[0079] Based on Comparative Example 1, the solvent ratio was adjusted to EC / PC / DEC / PP = 30 / 10 / 20 / 40, while other parameters remained unchanged.

[0080] Comparative Example 6

[0081] Based on Comparative Example 1, the solvent ratio was adjusted to EC / PC / DEC / PP = 40 / 10 / 20 / 30, while other ratios remained unchanged.

[0082] The lithium batteries prepared in Examples 1-15 and Comparative Examples 1-6 were subjected to performance tests. The test methods are as follows:

[0083] (1) 25℃ ambient temperature cycling experiment

[0084] Before testing, the thickness D0 of the fully charged cell was measured. The battery was placed in an environment of (25±3)℃ and left to stand for 3 hours. When the cell body reached (25±3)℃, the battery was charged at 1C to 4.2V, then at 0.7C to 4.45V, then at a constant voltage of 4.45V to the cutoff current of 0.05C, and then discharged at 0.5C to 3.0V. The initial capacity Q0 was recorded. When the required number of cycles was reached, or the capacity decay rate was less than 70%, or the thickness exceeded the test requirement (thickness change rate > 10%), the discharge capacity of this cycle was taken as the battery capacity Q2, and the capacity retention rate (%) was calculated. The battery was then fully charged, the cell was removed, and left to stand at room temperature for 3 hours. The fully charged thickness D2 was measured, and the thickness change rate (%) was calculated. The results are shown in the table. The calculation formulas used are as follows:

[0085] Thickness change rate (%) = (D2-D0) / D0×100%; Capacity retention rate (%) = Q2 / Q0×100%.

[0086] (2) 45℃ high temperature cycling experiment

[0087] Before testing, the thickness D0 of the fully charged cell was measured. The battery was placed in an environment of (45±3)℃ and left to stand for 3 hours. When the cell body reached (45±3)℃, the battery was charged at a constant current of 0.7C to 4.45V, then charged at a constant voltage of 4.45V to the cutoff current of 0.05C, and then discharged at 0.5C to 3.0V. The initial capacity Q0 was recorded. This cycle was repeated. When the required number of cycles was reached, or the capacity decay rate was less than 70%, or the thickness exceeded the test requirement (thickness change rate > 10%), the discharge capacity of this cycle was taken as the battery capacity Q3, and the capacity retention rate (%) was calculated. The battery was then fully charged, the cell was removed, and left to stand at room temperature for 3 hours. The thickness D3 at this fully charged state was measured, and the thickness change rate (%) was calculated. The results are shown in the table. The calculation formulas used are as follows:

[0088] Thickness change rate (%) = (D3-D0) / D0×100%; Capacity retention rate (%) = Q3 / Q0×100%.

[0089] (3) 60℃ High-Temperature Storage Experiment

[0090] At 25℃, the sorted batteries were charged to 4.45V at 0.7C, then charged at a constant voltage of 4.45V to a cutoff current of 0.05C, then discharged at a constant current of 0.5C to 3.0V, then charged to 4.45V at 0.7C, and then charged at a constant voltage of 4.45V to a cutoff current of 0.05C. The thickness D0 of the fully charged cell was measured. After the fully charged battery was placed in an environment of 60℃ for 60 days, the thickness D4 was measured again, and the thickness change rate (%) was calculated. The results are shown in the table. The calculation formulas used are as follows:

[0091] Thickness change rate (%) = (D4 - D0) / D0 × 100%.

[0092] (4) Low-temperature discharge experiment at 0℃

[0093] At 25℃, the sorted batteries were charged to 4.45V at 0.7C, then charged at a constant voltage of 4.45V to a cutoff current of 0.05C, and then discharged at a constant current of 0.5C to 3.0V. The discharge capacity Q4 was recorded. The batteries were then charged to 4.45V at 0.7C, then charged at a constant voltage of 4.45V to a cutoff current of 0.05C. After being placed in a 0℃ environment for 4 hours, they were discharged at a constant current of 0.5C to 3.0V, and the discharge capacity Q5 was recorded. The discharge capacity retention rate (%) was calculated, and the results are shown in the table. The calculation formulas used are as follows:

[0094] Capacity retention rate (%) = Q5 / Q4 × 100%.

[0095] The results are shown in the table below:

[0096]

[0097]

[0098] As can be seen from the table, the battery prepared using the electrolyte provided by this invention not only solves the problem of excessive PS, but also has excellent electrochemical performance, as detailed below:

[0099] Comparing the results of Comparative Examples 1-3 and Example 1, it was found that the more PS in the electrolyte, the better the cycle performance of the prepared battery at 25℃ / 45℃, and the better the storage performance at 60℃. However, the discharge at 0℃ was slightly worse. This is mainly because PS is a high-temperature additive that forms a CEI film on the positive electrode, which can prevent side reactions between the positive electrode material and the electrolyte, but the impedance increases slightly.

[0100] Comparing the results of Comparative Example 1 and Comparative Example 4, it was found that the battery prepared with low PS content, by adding PST which has better high-temperature performance, has performance comparable to the battery prepared with high PS content, but its low-temperature performance is slightly worse. This is mainly because the impedance of PST forming CEI film is greater than that of PS forming CEI.

[0101] Comparing the results of Comparative Example 1 and Comparative Examples 5-6, it was found that the more EC in the electrolyte, the better the cycle performance of the prepared battery at 25℃ / 45℃, but the storage performance at 60℃ deteriorated significantly, and the discharge at 0℃ was worse. This is mainly because EC is a good negative electrode film-forming solvent, which is beneficial for cycling, but EC is prone to side reactions at high voltage, which is more obvious at high temperature. Therefore, it is not conducive to high temperature. In addition, EC has a large viscosity, which is also not conducive to low temperature.

[0102] Comparing the results of Examples 1-4, it was found that the less EC in the electrolyte, the worse the cycle performance of the prepared battery at 25℃ / 45℃, but the storage performance at 60℃ was significantly improved, and the discharge at 0℃ was better. This is mainly because EC is a good solvent for negative electrode film formation, but EC is prone to some side reactions under high voltage, which is more obvious at high temperature. In addition, EC has a large viscosity. Therefore, reducing the EC content is not conducive to cycling, but is beneficial for high and low temperature.

[0103] Comparative analysis of the results of Examples 4-9 revealed that the higher the FEC content in the electrolyte, the better the cycle performance of the prepared battery at 25℃ / 45℃. When the FEC content was ≤10%, the storage performance at 60℃ and the discharge performance at 0℃ were not significantly different. However, when the FEC content was 15% or 20%, the storage performance at 60℃ and the discharge performance at 0℃ were slightly worse. This is mainly because FEC generates HF at high temperatures, which damages the stability of the SEI film and the material, thus worsening the performance at high temperatures. Furthermore, the higher the FEC content, the thicker the SEI film is formed, resulting in greater impedance, which also leads to worse performance at low temperatures.

[0104] Comparing the results of Examples 7 and 10-11, it was found that adding small amounts of VC and VEC further improved the cycling performance at 25℃ / 45℃ and the storage performance at 60℃, but the discharge performance at 0℃ was slightly worse. This is mainly because VC and VEC are also good negative electrode film-forming additives, which can further form a stable and dense SEI film, and can also form a CEI film on the positive electrode, thus improving cycling and high-temperature performance. Similarly, adding more negative electrode film-forming additives makes the SEI film thicker and the impedance greater, thus worsening the performance at low temperatures. However, further increasing the amount of VC and VEC added did not significantly improve the cycling performance at 25℃ / 45℃ and the storage performance at 60℃, and the low-temperature deterioration was more obvious.

[0105] Comparing the results of Examples 10 and 12-14, it was found that the battery with a higher lithium salt content in the electrolyte had better cycle performance at 25℃ / 45℃ and storage performance at 60℃. However, there was no linearity during discharge at 0℃. This was mainly because the lithium salt concentration was too low, resulting in lower electrolyte conductivity. However, when the lithium salt concentration was too high, the electrolyte viscosity would also increase. Neither of these conditions is conducive to low-temperature discharge.

[0106] Comparing the results of Examples 10 and 15, it was found that increasing the amounts of SN, ADN, and HTCN slightly worsened the cycling performance at 25°C / 45°C, and significantly deteriorated the discharge performance at 0°C. This was mainly due to the excessive addition of nitrile compounds, which significantly increased the electrolyte viscosity, thus hindering the Li... + Transmission is more pronounced at low temperatures and will cause an increase in battery impedance, thus deteriorating cycle and low-temperature performance, but can improve storage at 60°C. This is mainly because nitrile can complex the transition metal ions of the positive electrode, inhibit their dissolution, and reduce the side reactions between the positive electrode material and the electrolyte.

[0107] As can be seen from the above comparison, the embodiments provided in this application solve the problem of excessive PS content in batteries, while also ensuring that the battery's high-temperature performance and cycle performance are both taken into account, and that the high-temperature performance can reach or exceed that of batteries containing PS.

[0108] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A lithium battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, characterized in that, The positive electrode sheet is prepared by the following method: lithium cobalt oxide, conductive agent Super-P, and binder PVDF are mixed in a mass ratio of 98:1:1 and dispersed in organic solvent NMP. The mixture is stirred in a vacuum mixer until it is stable and uniform to form a positive electrode slurry. The positive electrode slurry is uniformly coated on an aluminum foil with a thickness of 12μm. After the aluminum foil is dried at room temperature, it is transferred to a forced-air oven at 120℃ and dried for 1 hour. Then, it is cold-pressed and die-cut to form a positive electrode sheet. The negative electrode sheet is prepared by the following method: graphite, conductive agent Super-P, SBR and CMC are mixed in a mass ratio of 97:0.5:1.5:1 and dispersed in deionized water. The mixture is stirred in a vacuum mixer until it is stable and uniform to form a negative electrode slurry. The negative electrode slurry is uniformly coated on a copper foil with a thickness of 6μm. After the copper foil is dried at room temperature, it is transferred to a forced-air oven at 120℃ and dried for 1 hour. Then, it is cold-pressed and die-cut to form a negative electrode sheet. Electrolyte preparation can be carried out using any of the following methods: LiPF6, a mixed organic solvent PC / DEC / PP = 10 / 20 / 70, and FEC, SN, ADN, HTCN, LiODFB, VC, and VEC were mixed and stirred using a vacuum stirrer until stable and homogeneous to obtain the electrolyte. The mass percentages of LiPF6, the mixed organic solvent, FEC, SN, ADN, HTCN, LiODFB, VC, and VEC in the total electrolyte were 15%, 69.7%, 10%, 1%, 1%, 2%, 0.5%, 0.5%, and 0.3%, respectively. LiPF6, a mixed organic solvent PC / DEC / PP = 10 / 20 / 70, and FEC, SN, ADN, HTCN, LiODFB, VC, and VEC were mixed and stirred using a vacuum stirrer until stable and homogeneous to obtain the electrolyte. The mass percentages of LiPF6, the mixed organic solvent, FEC, SN, ADN, HTCN, LiODFB, VC, and VEC in the total electrolyte were 15%, 69.0%, 10%, 1%, 1%, 2%, 0.5%, 1%, and 0.5%, respectively. LiPF6, a mixed organic solvent PC / DEC / PP = 10 / 20 / 70, and FEC, SN, ADN, HTCN, LiODFB, VC, and VEC were mixed and stirred using a vacuum stirrer until stable and homogeneous to obtain the electrolyte. The mass percentages of LiPF6, the mixed organic solvent, FEC, SN, ADN, HTCN, LiODFB, VC, and VEC in the total electrolyte were 17%, 67.7%, 10%, 1%, 1%, 2%, 0.5%, 0.5%, and 0.3%, respectively.

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