Non-aqueous electrolyte and lithium ion battery

Abstract

In order to overcome the problems of destroying the positive electrode in the overcharge environment of the lithium ion battery and the cycle performance deterioration under the low temperature condition in the prior art, a non-aqueous electrolyte and a lithium ion battery are provided, which comprise an additive, an organic solvent and a lithium salt, the additive comprises lithium bis(trimethylsilyl) phosphate and heptafluorobutyrylimidazole; the non-aqueous electrolyte satisfies the following conditions: 0.5 <= A <= 3, 0.5 <= B <= 3; wherein A% is the mass percentage content of lithium bis(trimethylsilyl) phosphate in the non-aqueous electrolyte; B% is the mass percentage content of heptafluorobutyrylimidazole in the non-aqueous electrolyte. The non-aqueous electrolyte provided by the application satisfies the following conditions: 0.5 <= A <= 3, 0.5 <= B <= 3, the combination of lithium bis(trimethylsilyl) phosphate and heptafluorobutyrylimidazole can effectively exert the synergistic effect of the two, and the infiltration and overcharge resistance performance of the electrolyte are considered.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of chemical energy storage devices, and particularly relates to a non-aqueous electrolyte and a lithium ion battery. BACKGROUND

[0002] Lithium ion batteries are widely used in consumer electronics and power batteries due to their high specific energy, good fast charging and discharging capacity, and small self-discharge. However, when the lithium ion battery is overcharged, transition metals (cobalt, nickel, iron, manganese, etc.) in the positive electrode material are easily dissolved out, causing the structure of the positive electrode material to be damaged, and oxygen is released and reacts violently with the electrolyte, which can easily cause safety accidents when the battery is overcharged. In a low temperature environment, the electrolyte has poor wettability due to increased viscosity, which can easily deteriorate the performance of the battery in low temperature cycling.

[0003] Generally, the wettability and the liquid retention amount of the battery cell can be increased to improve the low temperature cycling performance of the battery, but traditional wetting agents such as fluorobenzene and the like can easily decompose at high voltage, and increasing the liquid retention amount can increase the overall thickness of the battery cell, affecting the appearance of the battery and reducing the volume energy density of the battery. In order to solve the above technical problems, it is urgent to develop a new type of lithium ion electrolyte. SUMMARY

[0004] In view of the problems of destroying the positive electrode in the overcharged environment of the lithium ion battery and the deterioration of the cycling performance under low temperature conditions in the prior art, a non-aqueous electrolyte and a lithium ion battery are provided.

[0005] The technical solution adopted by the application to solve the above technical problems is as follows:

[0006] In one aspect, the application provides a non-aqueous electrolyte, comprising an additive, an organic solvent and a lithium salt, wherein the additive comprises lithium bis(trimethylsilyl) phosphate and heptafluorobutyrylimidazole.

[0007] The non-aqueous electrolyte satisfies the following conditions:

[0008] 0.5≤A≤3, 0.5≤B≤3;

[0009] Wherein, A% is the mass percentage content of lithium bis(trimethylsilyl) phosphate in the non-aqueous electrolyte;

[0010] B% is the mass percentage content of heptafluorobutyrylimidazole in the non-aqueous electrolyte.

[0011] Optionally, the non-aqueous electrolyte satisfies the following conditions:

[0012] 0.33≤A / B≤3.

[0013] Optionally, the non-aqueous electrolyte satisfies the following conditions:

[0014] 0.38≤B / X;

[0015] Xg / Ah is the liquid retention amount of the non-aqueous electrolyte.

[0016] Optionally, the liquid retention amount of the non-aqueous electrolyte is 1.1≤X≤2.5.

[0017] Optionally, the mass percentage of the organic solvent in the electrolyte is 55%-85%.

[0018] Optionally, the mass percentage of the lithium salt in the electrolyte is 8%-16%.

[0019] Optionally, the organic solvent includes one or more of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, diphenyl carbonate, methyl acetate, methyl propionate, methyl butyrate, ethyl acetate, propyl acetate, ethyl butyrate, propyl propionate, γ-butyrolactone, 1,3-dioxolane, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

[0020] In another aspect, the application provides a lithium ion battery, which includes a positive electrode, a negative electrode, and the non-aqueous electrolyte.

[0021] Optionally, the positive electrode includes a positive electrode active material layer and a positive electrode current collector, the positive electrode active material layer includes a positive electrode active material, and the positive electrode active material includes one or more of lithium iron phosphate, lithium iron manganese phosphate, and LiNi x Co y Mn (1-x-y) M z O2, (0.3≤x≤0.9, x+y<1, 0≤z<0.08, M is Al, Mg, Zr Ti).

[0022] Optionally, the negative electrode includes a negative electrode active material layer and a negative electrode current collector, the negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes one or more of natural graphite, artificial graphite, mesophase carbon microbeads, hard carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel-structured Li4Ti5O 12 , Li-Al alloy.

[0023] The application has the following beneficial effects:

[0024] The non-aqueous electrolyte provided by the application comprises the additive lithium bis(trimethylsilyl)phosphate, which helps to form a phosphoric acid-rich interface film on the surface of the negative electrode, which helps to improve the conduction rate of lithium ions, and the trimethylsilyl functional group in the lithium bis(trimethylsilyl)phosphate reacts with acidic substances such as HF and POF3 generated by the non-aqueous electrolyte at high voltage, thereby achieving the effect of removing high-voltage byproducts and improving the overcharge resistance of the battery; in addition, the low-polarity perfluorocarbon chain in the heptafluorobutyrylimidazole additive in the non-aqueous electrolyte has good affinity with the non-polar separator, which can increase the wettability of the separator, promote Li+ to pass through the separator and uniformly deposit on the surface of the negative electrode, thereby effectively improving the low-temperature performance of the battery, and also reducing the free electrolyte and the thickness of the battery, and the imidazole group in the heptafluorobutyrylimidazole additive can effectively remove trace amounts of H2O and HF in the electrolyte and inhibit the dissolution of the positive electrode metal ions, thereby improving the overcharge resistance of the battery; since the impedance of the imidazole group film formed on the surface of the negative electrode is relatively high, it will deteriorate the low-temperature performance, and the phosphoric acid-rich interface film formed by the lithium bis(trimethylsilyl)phosphate can effectively make up for the above problems; the inventors have found that when the non-aqueous electrolyte satisfies the following conditions: 0.5≤A≤3, 0.5≤B≤3, the lithium bis(trimethylsilyl)phosphate and the heptafluorobutyrylimidazole can effectively exert the synergistic effect of the two, and the wettability and overcharge resistance of the electrolyte are taken into account. DETAILED DESCRIPTION

[0025] In order to make the technical problems, technical solutions and beneficial effects of the application clearer, the application will be further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the application and not to limit the application.

[0026] The application provides a non-aqueous electrolyte, comprising an additive, an organic solvent and a lithium salt, wherein the additive comprises lithium bis(trimethylsilyl)phosphate and heptafluorobutyrylimidazole.

[0027] The non-aqueous electrolyte satisfies the following conditions:

[0028] 0.5≤A≤3, 0.5≤B≤3;

[0029] A% is the mass percentage content of lithium bis(trimethylsilyl)phosphate in the non-aqueous electrolyte;

[0030] B% is the mass percentage content of heptafluorobutyrylimidazole in the non-aqueous electrolyte.

[0031] The non-aqueous electrolyte provided by the application comprises the additive lithium bis(trimethylsilyl)phosphate, which helps to form a phosphoric acid-rich interface film on the surface of the negative electrode. This type of interface film helps to improve the conduction rate of lithium ions. In addition, the trimethylsilyl functional group in the lithium bis(trimethylsilyl)phosphate reacts with acidic substances such as HF and POF3 generated by the non-aqueous electrolyte at high voltage, thereby removing high-voltage byproducts and improving the overcharge resistance of the battery. Furthermore, the low-polarity perfluorocarbon chain in the heptafluorobutyrylimidazole additive in the non-aqueous electrolyte has good affinity with the non-polar separator, which can increase the wettability of the separator, promote the passage of Li+ through the separator and uniform deposition on the surface of the negative electrode, thereby effectively improving the low-temperature performance of the battery, while also reducing the amount of free electrolyte and the thickness of the battery. The imidazole group in the heptafluorobutyrylimidazole additive can effectively remove trace amounts of H2O and HF in the electrolyte and inhibit the dissolution of metal ions in the positive electrode, thereby improving the overcharge resistance of the battery. Since the impedance of the film formed by the imidazole group on the surface of the negative electrode is relatively high, it will worsen the low-temperature performance. The phosphoric acid-rich interface film formed by the lithium bis(trimethylsilyl)phosphate can effectively compensate for the above problems. The inventors have found that when the non-aqueous electrolyte satisfies the following conditions: 0.5≤A≤3, 0.5≤B≤3, the lithium bis(trimethylsilyl)phosphate and the heptafluorobutyrylimidazole can effectively exert a synergistic effect, taking into account the wettability and overcharge resistance of the electrolyte.

[0032] Specifically, the lithium bis(trimethylsilyl)phosphate (LiTMSP) helps to form a phosphoric acid-rich interface film on the surface of the negative electrode. This interface film helps to improve the conduction rate of lithium ions in the battery, and the improvement effect is more significant than that of the traditional film-forming additives such as vinyl sulfate (DTD) and lithium difluorophosphate (LiPO2F2). In addition, the trimethylsilyl (TMS) functional group in the lithium bis(trimethylsilyl)phosphate additive reacts with acidic substances such as HF and POF3 generated by the non-aqueous electrolyte at high voltage (4.9 V), thereby removing high-voltage byproducts and improving the overcharge resistance of the battery.

[0033] Specifically, the mass percentage of the lithium bis(trimethylsilyl)phosphate can be 0.5%, 0.6%, 0.8%, 1.0%, 1.5%, 1.7%, 2.0%, 2.3%, 2.5%, or 3.0%.

[0034] Specifically, the additive heptafluorobutyrylimidazole (HFBMZ) has the advantages of two derivatives, on the one hand, the low-polarity perfluorocarbon chain (-CF2CF2CF3) has good affinity with the non-polar separator (polypropylene), which can increase the wettability of the separator, promote Li+ to pass through the separator and be uniformly deposited on the negative electrode surface, thus effectively improving the low-temperature performance of the battery, and also reducing the free electrolyte to reduce the thickness of the battery, on the other hand, the imidazole group in heptafluorobutyrylimidazole can effectively remove trace amounts of H2O and HF in the electrolyte, inhibit the dissolution of metal ions in the positive electrode, and thus improve the overcharge resistance of the battery; in addition, since the impedance of the film formed by the imidazole group on the negative electrode surface is relatively high, which will deteriorate the low-temperature performance of the battery, at this time, the lithium bis(trimethylsilyl) phosphate additive forms a phosphoric acid-rich interface film which can effectively compensate for the deterioration of the low-temperature performance of the battery caused by the high-impedance interface film formed by the imidazole group.

[0035] Specifically, the mass percentage content of heptafluorobutyrylimidazole can be 0.5%, 0.6%, 0.8%, 1.0%, 1.5%, 1.7%, 2.0%, 2.3%, 2.5% or 3.0%.

[0036] In some embodiments, the non-aqueous electrolyte satisfies the following condition:

[0037] 0.33≤A / B≤3.

[0038] In some embodiments, the non-aqueous electrolyte satisfies the following condition:

[0039] 0.38≤B / X;

[0040] wherein X g / Ah is the liquid retention amount of the non-aqueous electrolyte.

[0041] Specifically, when the liquid retention amount of the non-aqueous electrolyte satisfies 0.38≤B / X, the absolute content of the non-aqueous electrolyte is increased, which can increase the contact between the non-aqueous electrolyte and the active material, improve the low-temperature cycle performance of the battery, and in addition, the imidazole group of the heptafluorobutyrylimidazole can effectively capture the by-products in the case of overcharge with increased content of non-aqueous electrolyte, thus playing a role in improving the overcharge performance.

[0042] Specifically, X g / Ah is the liquid retention amount of the non-aqueous electrolyte, which refers to the amount of electrolyte actually retained inside the battery.

[0043] In some embodiments, the liquid retention amount of the non-aqueous electrolyte is 1.1≤X≤2.5.

[0044] It should be noted that when the battery is at low temperature, the viscosity of the electrolyte increases, and the electrolyte does not fully penetrate the battery cell separator, pole piece, etc., which leads to insufficient contact between the electrolyte and the pole piece active material, and thus the cycle performance of the battery under low temperature conditions is deteriorated. When the absolute liquid retention of the battery is increased, the contact opportunity between the electrolyte and the pole piece and the separator can be increased, which can improve the cycle performance of the battery at low temperatures. However, when the liquid retention is increased, if the electrolyte is not fully penetrated on the separator and the pole piece, a large amount of electrolyte will be free around the battery shell, causing the battery to swell, increasing the overall thickness of the battery, thereby reducing the overall volume energy density of the battery, affecting terminal installation, and at the same time, increasing the battery liquid retention will increase the battery safety risk, because too much electrolyte will also lead to aggravated side reactions and deteriorate battery safety performance.

[0045] Specifically, in this application, through a large amount of preliminary research, it was found that when the liquid retention volume of the non-aqueous electrolyte is limited to the range of 1.1≤X≤2.5, the heptafluorobutyrylimidazole and the liquid retention volume can be controlled to maintain a relatively appropriate ratio, which is beneficial to promoting the low-temperature cycle performance of the battery.

[0046] Specifically, the liquid retention capacity of the non-aqueous electrolyte can be 1.1g / Ah, 1.2g / Ah, 1.3g / Ah, 1.4g / Ah, 1.5g / Ah, 1.6g / Ah, 1.7g / Ah, 2.0g / Ah, 2.1g / Ah, 2.2g / Ah, 2.3g / Ah, 2.4g / Ah or 2.5g / Ah.

[0047] In some embodiments, based on the mass of the electrolyte being 100%, the mass percentage of the organic solvent is 55% to 85%; specifically, the mass percentage of the organic solvent can be 55%, 60%, 65%, 70%, 75%, 80% or 85%.

[0048] In some embodiments, the organic solvent includes one or more of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methylpropyl carbonate, diphenyl carbonate, methyl acetate, methyl propionate, methyl butyrate, methyl acetate, ethyl acetate, propyl acetate, ethyl butyrate, propyl propionate, γ-butyrolactone, 1,3-dioxolane, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

[0049] Specifically, in a preferred embodiment, the organic solvent is selected from one or more of ethylene carbonate (EC), propylene carbonate (PC), propyl propionate (EP) and diethyl carbonate (DEC).

[0050] In some embodiments, based on 100% by mass of the electrolyte, the mass percentage of the lithium salt is 8% to 16%.

[0051] Specifically, the lithium salt includes at least one of lithium hexafluorophosphate, lithium difluoro(oxalato)borate, lithium bis(oxalato)borate, lithium difluorodicyanophosphate, lithium tetrafluoroborate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide and lithium difluorophosphate; in preferred embodiments, the lithium salt is selected from lithium hexafluorophosphate (LiPF6).

[0052] In another embodiment of the present application, a lithium ion battery is provided, which includes a positive electrode, a negative electrode and the non-aqueous electrolyte solution.

[0053] The lithium ion battery further includes a separator, which is arranged between the positive electrode and the negative electrode to prevent short circuit caused by direct contact of the positive electrode and the negative electrode; specifically, the separator can be a porous sheet or non-woven fabric with excellent liquid retention, and can be a resin or glass fiber separator, the material of the resin or glass fiber separator including but not limited to polyolefin, aromatic polyamide, polytetrafluoroethylene, polyether sulfone.

[0054] The lithium ion battery further includes a battery shell, which is used to accommodate the electrode assembly composed of the positive electrode, the negative electrode and the separator and the electrolyte; specifically, the battery shell includes but is not limited to a hard shell or a soft shell; when the battery shell is a hard shell, it can be a hard plastic shell, an aluminum shell or a steel shell; when the battery shell is a soft shell, it can be a soft package, such as a bag-type soft package, the material of the soft package can be plastic materials such as polypropylene, polybutylene terephthalate and polybutylene succinate; in addition, the shape of the lithium ion battery is not particularly limited, and can be cylindrical, square or any other shape.

[0055] In some embodiments, the positive electrode includes a positive electrode active material layer and a positive electrode current collector, the positive electrode active material layer includes a positive electrode active material, the positive electrode active material includes one or more of lithium iron phosphate, lithium manganese iron phosphate and LiNi x Co y Mn (1-x-y) M z O2, (0.3≤x≤0.9, x+y<1, 0≤z<0.08, M is Al, Mg, Zr Ti) material.

[0056] Specifically, the positive electrode active material layer further includes a positive electrode binder and a positive electrode conductive agent, the positive electrode binder, the positive electrode conductive agent and the positive electrode active material are blended to obtain the positive electrode active material slurry, the positive electrode active material slurry is coated on the positive electrode current collector to form the positive electrode active material layer; the positive electrode current collector is not particularly limited, and can be one of aluminum, stainless steel, nickel plating layer, titanium, tantalum and other metal materials and carbon cloth, carbon paper and other carbon materials.

[0057] Specifically, the positive electrode binder is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, nitrocellulose; the positive electrode conductive agent is selected from at least one of natural graphite, artificial graphite, acetylene black, needle coke, carbon nanotubes, graphene and other carbon materials.

[0058] Specifically, the positive electrode active material slurry is coated on at least one side of the positive electrode current collector.

[0059] In some embodiments, the negative electrode comprises a negative electrode active material layer and a negative electrode current collector, the negative electrode active material layer comprises a negative electrode active material, the negative electrode active material comprises one or more of natural graphite, artificial graphite, mesocarbon microbeads, hard carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel-structured Li4Ti5O12, Li-Al alloy. 12

[0060] Specifically, the negative electrode active material layer further comprises a negative electrode binder and a negative electrode conductive agent, the negative electrode binder, the negative electrode conductive agent and the negative electrode active material are blended to obtain the negative electrode active material slurry, the negative electrode active material slurry is coated on the negative electrode current collector to form the negative electrode active material layer; the negative electrode current collector is not particularly limited, and the negative electrode current collector can be one of copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foamed nickel, foamed copper or composite current collector.

[0061] Specifically, the negative electrode binder is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, nitrocellulose; the negative electrode conductive agent is selected from at least one of natural graphite, artificial graphite, acetylene black, needle coke, carbon nanotubes, graphene and other carbon materials. Specifically, the negative electrode binder is the same as or different from the positive electrode binder, and the negative electrode conductive agent is the same as or different from the positive electrode conductive agent.

[0062] Specifically, the negative electrode active material slurry is coated on at least one side of the negative electrode current collector.

[0063] The application is further illustrated by the following examples.

[0064] Table 1

[0065]

[0066]

[0067] Example 1

[0068] ​The embodiment is used for explaining the non-aqueous electrolyte and the lithium ion battery disclosed by the application, and includes the following operation steps.

[0069] Preparation of the positive electrode sheet

[0070] The positive electrode active material lithium cobaltate, the conductive agent acetylene black (Super P) and the polyvinylidene fluoride (PVDF) binder are mixed uniformly at a mass ratio of 97:1.5:1.5, and are uniformly dispersed in 1-methyl-2-pyrrolidone (NMP) to prepare a uniform black slurry. After the mixed slurry is coated on both sides of the aluminum foil current collector, the positive electrode sheet is obtained after baking, rolling, and cutting.

[0071] Preparation of the negative electrode sheet

[0072] The negative electrode active material graphite, the conductive agent acetylene black (Super P), the thickening agent CMC and the binder SBR are mixed uniformly at a mass ratio of 94:2:1.2:2.8, and are uniformly dispersed in deionized water to prepare a uniform black slurry. After the mixed slurry is coated on both sides of the aluminum foil current collector, the negative electrode sheet is obtained after baking, rolling, and cutting.

[0073] Preparation of the electrolyte

[0074] a. The vinyl carbonate (EC), the propylene carbonate (PC), the propyl propionate (EP) and the diethyl carbonate (DEC) are mixed and stirred according to a mass ratio of 10:20:40:30 to form a mixed solvent, water is removed by using a molecular sieve to obtain an organic solvent for standby, 1M LiPF6 is added and uniformly mixed to obtain a mixture A;

[0075] b. The additive is added to the mixture A obtained in step a, and the type and specific amount of the additive are shown in Table 1 to obtain the electrolyte.

[0076] Preparation of the battery

[0077] The prepared positive electrode sheet, the separator and the negative electrode sheet are stacked in order, the separator is placed between the positive and negative electrode sheets, the bare cell is obtained after winding and tab welding, and the bare cell is packaged in an aluminum plastic film to obtain the battery.

[0078] Examples 2-23

[0079] Examples 2-23 are used for explaining the non-aqueous electrolyte and the lithium ion battery disclosed by the application, and include most of the operations in Example 1, and the difference is that:

[0080] The types of the additives, the amounts of the additives and the relationship between the additives and the liquid storage capacity shown in Examples 2-23 in Table 1 are used.

[0081] Comparative Examples 1-13

[0082] Comparative Examples 1-13 were used to compare the non-aqueous electrolyte and lithium ion battery disclosed in the present application, including most of the operations in Example 1, except that:

[0083] The additive type, additive amount, and the relationship between the additive and the electrolyte amount shown in Comparative Examples 1-13 in Table 1 were used.

[0084] Performance test

[0085] The above-prepared Examples 1-23 and Comparative Examples 1-13 were subjected to the following performance tests:

[0086] Battery performance test:

[0087] 0°C cycle test:

[0088] The test method was as follows: the lithium ion battery was charged to 4.5 V at 1C in a constant-temperature oven at 0±2°C, with a cutoff current of 0.05C, and then discharged to 3 V at 1C. The above conditions were repeated for multiple charge-discharge cycles, and the capacity retention rate after 600 cycles was calculated. There were 5 batteries in each group.

[0089] Capacity retention rate (%) = discharge capacity (mAh) corresponding to the cycle number / discharge capacity (mAh) of the third week cycle * 100%

[0090] The capacity retention rate of 5 batteries in each group after different cycle times was averaged and recorded in Table 1.

[0091] Overcharge test:

[0092] The test method was as follows: the lithium ion battery was continuously charged to 12 V at 1C in a constant-temperature oven at 25±2°C, without a cutoff current. The battery was considered to pass if it did not catch fire or explode.

[0093] The pass rate of 20 batteries in each group was recorded in Table 2.

[0094] Table 2

[0095]

[0096]

[0097] From the test results of Table 1, it can be seen that the test results of Examples 1-23 are all better than those of the comparative examples; among them, no additive described in the application is added in Comparative Example 1, and the LiTMSP and HFBMZ are not added at the same time in Comparative Examples 2-3, and the test results show that, compared with Comparative Example 1, when the LiTMSP and HFBMZ are not added at the same time, the 0℃ cycle performance and overcharge resistance of the battery cannot be improved, and only when both of them are added at the same time can the 0℃ cycle performance and overcharge resistance of the battery be obviously improved; according to Comparative Example 4 and Comparative Examples 10-13, compared with the traditional film-forming additive and wetting agent for reducing interface impedance, the combination of LiTMSP and HFBMZ has more obvious advantages, because LiPO2F2 (lithium difluorophosphate) and vinyl sulfate (DTD) as the traditional film-forming additive for reducing interface impedance have relatively poor improvement on the conduction rate of lithium ions compared with the additive described in the application, and fluorobenzene additives are not resistant to high pressure, and imidazole additives have large impedance, so the above test results show that the combination of LiTMSP and HFBMZ can play a synergistic effect to improve the low-temperature cycle performance and overcharge resistance; compared with Comparative Examples 5-7 and Examples 1-7, when the content of LiTMSP and HFBMZ is too high, the low-temperature cycle performance of the battery deteriorates, because when the additive content is too high, the viscosity of the electrolyte will increase sharply, which will obviously deteriorate the rate performance of the battery, and when the content of LiTMSP and HFBMZ increases within a certain range, the low-temperature cycle performance and overcharge resistance of the battery are improved; from the data of Comparative Examples 5-7 and Examples 1-7, when 0.5≤A≤3 and 0.5≤B≤3, the additive cost and the comprehensive performance of the battery can be better balanced; according to the test results of Examples 1-11, when the content of LiTMSP relative to HFBMZ is too high, the wetting and overcharge resistance of the electrolyte cannot be effectively balanced, and when the content is too low, the negative effect of the imidazole group on the high impedance at the interface cannot be reached, so when 0.33≤A / B≤3 and 0.5≤A≤3 and 0.5≤B≤3, the synergistic effect of the two can be better played; according to the test results of Examples 12-17, when the HFBMZ and the liquid retention amount maintain a certain ratio and the battery liquid retention is improved, the low-temperature cycle performance of the battery can be obviously improved, and the overcharge resistance is not obviously deteriorated, because the increase of the absolute content of the electrolyte can increase the contact between the electrolyte and the active material of the electrode sheet, and the imidazole group of HFBMZ can effectively capture the overcharge by-products generated by the increase of the electrolyte content, thereby improving the overcharge resistance; according to the test results of Examples 18-23, when the HFBMZ is too low relative to the liquid retention, the electrolyte has poor separation membrane wetting, and too much electrolyte is in a free state, which will greatly increase the thickness of the battery, affecting the product appearance and volume energy density of the battery.When the HFBMZ is too low relative to the liquid retention amount, increasing the liquid retention amount of the non-aqueous electrolyte will significantly deteriorate the thermal shock performance, and the battery cycle performance is not significantly improved. According to the above data, when 0.38≤B / X is satisfied, the HFBMZ can improve the battery wettability and overcharge resistance at the same time. In summary, when the additive lithium bis(trimethylsilyl)phosphate and heptafluorobutyrylimidazole are used together in the non-aqueous electrolyte provided by the application, the synergistic effect of the two can be effectively exerted. When 0.38≤B / X is satisfied, the absolute content of the non-aqueous electrolyte is increased, which can increase the contact between the non-aqueous electrolyte and the active material, improve the low-temperature cycle performance of the battery, and in addition, the imidazole group of the heptafluorobutyrylimidazole can effectively capture the by-products under the condition of overcharge with increased content of the non-aqueous electrolyte, thereby playing a role in improving the overcharge performance.

[0098] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A nonaqueous electrolyte, characterized by comprising: The additives include lithium bis(trimethylsilyl)phosphate and heptafluorobutyrylimidazole. The nonaqueous electrolyte satisfies the following conditions: 0.5≤A≤3, 0.5≤B≤3. A% is the mass percentage content of lithium bis(trimethylsilyl)phosphate in the nonaqueous electrolyte. B% is the mass percentage content of heptafluorobutyrylimidazole in the nonaqueous electrolyte.

2. The nonaqueous electrolyte according to claim 1, wherein The nonaqueous electrolyte satisfies the following conditions: 0.33≤A / B≤3.

3. The nonaqueous electrolyte according to claim 1, wherein The nonaqueous electrolyte satisfies the following conditions: 0.38≤B / X. X g / Ah is the liquid retention of the nonaqueous electrolyte.

4. The nonaqueous electrolyte according to claim 1, wherein The liquid retention of the nonaqueous electrolyte is 1.1≤X≤2.

5.

5. The nonaqueous electrolyte according to claim 1, wherein The mass percentage content of the organic solvent is 55% to 85% based on the mass of the electrolyte.

6. The nonaqueous electrolyte according to claim 1, wherein The mass percentage content of the lithium salt is 8% to 16% based on the mass of the electrolyte.

7. The nonaqueous electrolyte according to claim 1, wherein The organic solvent includes one or more of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, diphenyl carbonate, methyl acetate, methyl propionate, methyl butyrate, methyl acetate, ethyl acetate, propyl acetate, ethyl butyrate, propyl propionate, γ-butyrolactone, 1,3-dioxolane, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

8. A lithium-ion battery, characterized by The nonaqueous electrolyte includes a positive electrode, a negative electrode, and the nonaqueous electrolyte according to any one of claims 1 to 7.

9. The lithium-ion battery of claim 8, wherein, The positive electrode includes a positive electrode active material layer including a positive electrode active material including lithium iron phosphate, lithium manganese iron phosphate, and LiNi x Co y Mn (1-x-y) M z O2 material; the LiNi x Co y Mn (1-x-y) M z O2: 0.3≤x≤0.9, x+y<1, 0≤z<0.08, M is Al, Mg, Zr Ti.

10. The lithium-ion battery of claim 8, wherein, The negative electrode includes a negative electrode active material layer and a negative electrode current collector, the negative electrode active material layer includes a negative electrode active material, the negative electrode active material includes one or more of natural graphite, artificial graphite, mesophase microcarbon, hard carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel-structured lithiated TiO2-Li4Ti5O 12 , Li-Al alloy.

Images