Electrolyte additive for improving high-temperature performance of lithium ion battery, electrolyte and lithium ion battery

Abstract

The invention relates to the technical field of lithium ion batteries, in particular to an electrolyte additive for improving the high-temperature performance of a lithium ion battery, an electrolyte and the lithium ion battery, and the electrolyte additive comprises poly (2, 2, 2-trifluoroethyl methacrylate). Compared with a lithium ion battery without poly (2, 2, 2-trifluoroethyl methacrylate), when the electrolyte additive provided by the invention is applied to a lithium ion battery system, the high-temperature storage performance of the lithium ion battery can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to an electrolyte additive, an electrolyte and a lithium ion battery for improving the high temperature performance of a lithium ion battery. Background Art

[0002] The high-temperature storage performance of energy storage lithium-ion batteries is a very important indicator of electrochemical stability, and also determines the application of energy storage batteries in high-temperature scenarios. Therefore, in the electrical performance test, high-temperature storage test (45°C 30 Days) is an indispensable part. Energy storage battery technicians have always been pursuing the development of high-temperature resistant systems. Therefore, how to improve the high-temperature storage performance of lithium-ion batteries is a technical problem that needs to be solved urgently in this field. Summary of the invention

[0003] In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide an electrolyte additive, an electrolyte, and a lithium ion battery for improving the high temperature performance of lithium ion batteries. Compared with lithium ion batteries to which the electrolyte additive of the present invention is not added, the electrolyte additive provided by the present invention can improve the high temperature storage performance of lithium ion batteries when applied to lithium ion battery systems.

[0004] In order to achieve the above object, the present invention adopts the following technical solutions:

[0005] In a first aspect, the present invention provides an electrolyte additive for improving the high temperature performance of a lithium-ion battery, wherein the electrolyte additive comprises poly (2,2,2-trifluoroethyl methylacrylate).

[0006] Compared with a lithium ion battery to which the electrolyte additive of the present invention is not added, the electrolyte additive provided by the present invention can improve the high temperature storage performance of the lithium ion battery when applied to a lithium ion battery system.

[0007] Furthermore, the weight average molecular weight of the poly 2,2,2-trifluoroethyl methylacrylate is 800-1500 g / mol.

[0008] In a second aspect, the present invention provides an electrolyte comprising a lithium salt, a non-aqueous organic solvent and a functional additive, wherein the functional additive comprises the electrolyte additive described in the first aspect.

[0009] Furthermore, the electrolyte additive accounts for no more than 0.5% by mass in the electrolyte;

[0010] And / or, the lithium salt includes at least one of lithium hexafluorophosphate LiPF6 and lithium bis(fluorosulfonyl)imide LiFSi;

[0011] And / or, the mass percentage of the lithium salt in the electrolyte is 10%-20%;

[0012] And / or, the non-aqueous organic solvent includes at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate, and γ-butyrolactone;

[0013] And / or, the mass percentage of the non-aqueous organic solvent in the electrolyte is 68% to 92%;

[0014] And / or, the functional additive further includes other functional additives, the other functional additives include at least one of fluoroethylene carbonate (FEC), 1,3-propane sultone (PS), and vinylene sulfate (DTD), and the mass percentage of the other functional additives in the electrolyte is 5%-10%.

[0015] In a third aspect, the present invention provides a lithium-ion battery, which includes a positive electrode sheet, a negative electrode sheet, a separator disposed between the positive electrode sheet and the negative electrode sheet at intervals, and an electrolyte, and the electrolyte includes the electrolyte described in the second aspect.

[0016] Further, the tap density of the positive electrode sheet is 2.3-2.55 g / cm 3 ;

[0017] And / or, the double-sided areal density of the positive electrode sheet is 360-380 g / m 2 ;

[0018] And / or, the tap density of the negative electrode sheet is 1.3-1.55 g / cm 3 ;

[0019] And / or, the double-sided areal density of the negative electrode sheet is 165-200 g / m 2 .

[0020] Further, the NP ratio of the lithium-ion battery is designed to be 1.05-1.1;

[0021] And / or, the positive electrode sheet includes a positive electrode current collector and a positive electrode active layer, and the positive electrode active layer includes a positive electrode active material, a conductive agent, and a binder;

[0022] And / or, the negative electrode sheet includes a negative electrode current collector and a negative electrode active layer, and the negative electrode active layer includes a negative electrode active material, a conductive agent, and a binder.

[0023] Further, the positive electrode active material includes lithium iron phosphate (LFP);

[0024] And / or, in the positive electrode active layer, the conductive agent includes at least one of carbon black, acetylene black, conductive graphite, carbon fiber, carbon nanotube, and graphene;

[0025] And / or, in the positive electrode active layer, the binder includes at least one of PVDF, polyvinyl alcohol, and polytetrafluoroethylene;

[0026] And / or, in the positive electrode active layer, the mass ratio of the positive electrode active material, the conductive agent, and the binder is (95 - 97):(1 - 2):(2 - 3);

[0027] And / or, the negative electrode active material includes graphite;

[0028] And / or, in the negative electrode active layer, the conductive agent includes at least one of carbon black, acetylene black, conductive graphite, carbon fiber, carbon nanotube, and graphene;

[0029] And / or, in the negative electrode active layer, the binder includes polyacrylic acid PAA;

[0030] And / or, in the negative electrode active layer, the mass ratio of the negative electrode active material, the conductive agent, and the binder is (94 - 96):(1 - 3):(2 - 3);

[0031] And / or, the thickness of the separator is 10 - 15 μm, the thickness of the positive electrode current collector is 14 - 20 μm, and the thickness of the negative electrode current collector is 4.5 - 8 μm.

[0032] Furthermore, the formation current of the lithium-ion battery is not less than 0.1C.

[0033] Furthermore, the formation method of the lithium-ion battery includes the following steps:

[0034] First, perform constant current charging with a current of 0.1 - 0.15C until 10% SOC, then perform constant current charging with a current of 0.2 - 0.4C until 20% SOC, and finally perform constant current charging with a current of 0.5 - 1C until 35% SOC.

[0035] Compared with the prior art, the beneficial effects of the present invention include at least one of the following:

[0036] Compared with a lithium-ion battery without adding the electrolyte additive of the present invention, when the electrolyte additive provided by the present invention is applied to a lithium-ion battery system, it can improve the high-temperature storage performance of the lithium-ion battery. Specific embodiments

[0037] To make the objectives, technical solutions, and advantages of the present invention clearer, the following will, in conjunction with the embodiments of the present invention, clearly and completely describe the technical solutions in the embodiments of the present invention. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention. For the process parameters without specific conditions noted in the following embodiments, they are usually in accordance with conventional conditions.

[0038] In the ranges disclosed in the present invention, the endpoints and any values are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed in the present invention.

[0039] In a first aspect, the present invention provides an electrolyte additive for improving the high-temperature performance of lithium-ion batteries. The electrolyte additive includes poly(2,2,2-trifluoroethyl methacrylate) (PTFEMA).

[0040] Here, the structure of 2,2,2-trifluoroethyl methacrylate is as follows:

[0041]

[0042] Compared with lithium-ion batteries without poly(2,2,2-trifluoroethyl methacrylate) (PTFEMA), when the electrolyte additive provided by the present invention is applied to a lithium-ion battery system, it can improve the high-temperature storage performance of the lithium-ion battery.

[0043] In the above electrolyte additive, as an alternative embodiment, the weight-average molecular weight of the poly(2,2,2-trifluoroethyl methacrylate) is 800 - 1500 g / mol, and for example, it can be 800 g / mol, 1000 g / mol, 1100 g / mol, 1300 g / mol, or 1500 g / mol.

[0044] In a second aspect, the present invention provides an electrolyte. The electrolyte includes a lithium salt, a non-aqueous organic solvent, and a functional additive. The functional additive includes the electrolyte additive described in the first aspect.

[0045] In the above electrolyte, as an alternative embodiment, the mass percentage of the electrolyte additive in the electrolyte is not more than 0.5%, and for example, it can be 0.02%, 0.05%, 0.1%, 0.3%, or 0.5%.

[0046] In the above electrolyte, as an alternative embodiment, the lithium salt includes at least one of lithium hexafluorophosphate LiPF6 and lithium bis(fluorosulfonyl)imide LiFSi.

[0047] In the above electrolyte, as an alternative embodiment, the mass percentage of the lithium salt in the electrolyte is 10% - 20%, for example, it can be 10%, 12%, 14%, 16%, 18% or 20%.

[0048] In the above electrolyte, as an alternative embodiment, the non-aqueous organic solvent includes at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate EMC, ethylene carbonate EC, propylene carbonate, and γ-butyrolactone.

[0049] In the above electrolyte, as an alternative embodiment, the mass percentage of the non-aqueous organic solvent in the electrolyte is 68% - 92%, for example, it can be 68%, 70%, 75%, 80%, 90% or 92%.

[0050] In the above electrolyte, as an alternative embodiment, the functional additive further includes other functional additives, and the other functional additives include at least one of fluoroethylene carbonate FEC, 1,3-propane sultone PS, and vinylene sulfate DTD.

[0051] In the above electrolyte, as an alternative embodiment, the mass percentage of the other functional additives in the electrolyte is 5% - 10%.

[0052] In a third aspect, the present invention provides a lithium-ion battery, which includes a positive electrode sheet, a negative electrode sheet, a separator disposed between the positive electrode sheet and the negative electrode sheet at intervals, and an electrolyte, and the electrolyte includes the electrolyte described in the second aspect.

[0053] In the above lithium-ion battery, as an alternative embodiment, the tap density of the positive electrode sheet is 2.3 - 2.55 g / cm 3 . By using a lower tap density of the positive and negative electrodes, the infiltration and liquid retention of the high-viscosity electrolyte can be ensured, so that the function of the electrolyte additive provided by the present invention can be more effectively exerted to improve the high-temperature storage performance of the battery.

[0054] In the above lithium-ion battery, as an alternative embodiment, the double-sided areal density of the positive electrode sheet is 360 - 380 g / m 2 , for example, it can be 360 g / m 2 , 365 g / m 2 , 370 g / m 2 , 375 g / m 2 or 380 g / m2 PTFEMA has water and oil resistance. In a lithium-ion energy storage battery system with a low areal density of the electrode sheet, it can improve the high-temperature storage stability without loss of electrochemical performance, enabling the lithium-ion battery to have excellent high-temperature storage performance.

[0055] In the above lithium-ion battery, as an alternative embodiment, the tap density of the negative electrode sheet is 1.3 - 1.55 g / cm 3 。

[0056] In the above lithium-ion battery, as an alternative embodiment, the double-sided areal density of the negative electrode sheet is 165 - 200 g / m 2 , for example, it can be 165 g / m 2 、170 g / m 2 、175 g / m 2 、180 g / m 2 、185 g / m 2 、190 g / m 2 、195 g / m 2 or 200 g / m 2 PTFEMA has water and oil resistance. In a lithium-ion energy storage battery system with a low areal density of the electrode sheet, it can improve the high-temperature storage stability without loss of electrochemical performance, enabling the lithium-ion battery to have excellent high-temperature storage performance. In the above lithium-ion battery, as an alternative embodiment, the N / P ratio of the lithium-ion battery is designed to be 1.05 - 1.1, and the N / P ratio refers to the designed value of the ratio of the negative electrode capacity to the positive electrode capacity of the battery. Adopting a smaller N / P ratio design to reduce the potential difference between the positive and negative electrodes can further improve the high-temperature storage performance of the lithium-ion battery.

[0057] In the above lithium-ion battery, as an alternative embodiment, the positive electrode sheet includes a positive electrode current collector and a positive electrode active layer, and the positive electrode active layer includes a positive electrode active material, a conductive agent, and a binder.

[0058] In the above lithium-ion battery, as an alternative embodiment, the positive electrode active material includes lithium iron phosphate LFP.

[0059] In the above lithium-ion battery, as an alternative embodiment, in the positive electrode active layer, the conductive agent includes at least one of carbon black, acetylene black, conductive graphite, carbon fiber, carbon nanotube, and graphene.

[0060] In the above lithium-ion battery, as an alternative embodiment, in the positive electrode active layer, the binder includes at least one of PVDF, polyvinyl alcohol, and polytetrafluoroethylene.

[0061] In the above lithium-ion battery, as an alternative embodiment, in the positive electrode active layer, the mass ratio of the positive electrode active material, the conductive agent, and the binder is (95-97):(1-2):(2-3).

[0062] In the above lithium-ion battery, as an alternative embodiment, the negative electrode sheet includes a negative electrode current collector and a negative electrode active layer, and the negative electrode active layer includes a negative electrode active material, a conductive agent, and a binder.

[0063] In the above lithium-ion battery, as an alternative embodiment, the negative electrode active material includes graphite.

[0064] In the above lithium-ion battery, as an alternative embodiment, in the negative electrode active layer, the conductive agent includes at least one of carbon black, acetylene black, conductive graphite, carbon fiber, carbon nanotube, and graphene.

[0065] In the above lithium-ion battery, as an alternative embodiment, in the negative electrode active layer, the binder includes polyacrylic acid (PAA).

[0066] In the above lithium-ion battery, as an alternative embodiment, in the negative electrode active layer, the mass ratio of the negative electrode active material, the conductive agent, and the binder is (94-96):(1-3):(2-3).

[0067] In the above lithium-ion battery, as an alternative embodiment, the thickness of the separator is 10-15 μm, the thickness of the positive electrode current collector is 14-20 μm, and the thickness of the negative electrode current collector is 4.5-8 μm.

[0068] In the above lithium-ion battery, as an alternative embodiment, the formation current of the lithium-ion battery is not less than 0.1C. In the film formation step of formation and grading, the minimum charge current must be ≥0.1C, otherwise the consumption of PTFEMA will be completed in the first step, and the stability of subsequent high-temperature storage cannot be significantly improved. According to the lithium-ion battery system design provided by the present invention, the new additive PTFEMA can be more effectively applied in the energy storage lithium-ion battery, thereby improving the high-temperature storage performance of the entire system without affecting other electrochemical properties, and making the lithium-ion battery have excellent high-temperature storage performance.

[0069] In the above lithium-ion battery, as an alternative embodiment, the formation method of the lithium-ion battery includes the following steps:

[0070] First, charge at a constant current of 0.1 - 0.15C until 10% SOC, then charge at a constant current of 0.2 - 0.4C until 20% SOC, and finally charge at a constant current of 0.5 - 1C until 35% SOC. In the above lithium-ion battery, as an alternative embodiment, the formation temperature of the lithium-ion battery is 40 - 50°C, for example, it can be 40°C, 45°C or 50°C.

[0071] The present invention will be further described in detail below with specific examples and comparative examples.

[0072] In the following examples and comparative examples:

[0073] The weight-average molecular weight of PTFEMA is 1000 g / mol.

[0074] Example 1

[0075] <Preparation of electrolyte>

[0076] In an inert gas atmosphere with a water content of less than 0.1 ppm and an oxygen content of less than 1 ppm, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed to obtain a basic solvent, and then lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSi), poly(2,2,2-trifluoroethyl methacrylate) PTFEMA, fluoroethylene carbonate FEC, 1,3-propane sultone PS, and vinylene sulfate DTD are added to the basic solvent and mixed evenly to obtain an electrolyte. Among them, based on the mass of the electrolyte, the mass percentage of ethylene carbonate (EC) is 22%, the mass percentage of ethyl methyl carbonate EMC is 52.95%, the mass percentage of fluoroethylene carbonate FEC is 4%, the mass percentage of 1,3-propane sultone PS is 1%, the mass percentage of vinylene sulfate DTD is 2%, the mass percentage of lithium hexafluorophosphate LiPF6 is 10%, the mass percentage of lithium bis(fluorosulfonyl)imide LiFSi is 8%, and the mass percentage of poly(2,2,2-trifluoroethyl methacrylate) PTFEMA is 0.05%.

[0077] <Preparation of negative electrode sheet>

[0078] The artificial graphite of the negative electrode active material, the conductive agent SP, the binder PAA (polyacrylic acid), and carboxymethyl cellulose (CMC) are mixed according to a mass ratio of 96:1:2:1, and deionized water is added as a solvent to prepare a slurry with a solid content of 52 wt%. After being stirred evenly by a vacuum mixer, a negative electrode slurry is obtained. The negative electrode slurry is evenly coated on one surface of a negative electrode current collector copper foil with a thickness of 8 μm and dried at 90 °C to obtain a negative electrode sheet with a single-sided coated negative electrode material layer. Then, the above steps are repeated on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided coated negative electrode material layer. After drying at 85 °C, it is roll-pressed, and then slit and welded with tabs to obtain a negative electrode sheet for use. Among them, the compaction density of the negative electrode sheet is 1.5 g / cm 3 , and the double-sided areal density is 170 g / m 2 , the discharge specific capacity of graphite is 350 mAh / g, and the NP ratio of the negative electrode to the positive electrode is designed to be 1.1.

[0079] <Preparation of the positive electrode sheet>

[0080] The positive electrode active material lithium iron phosphate (LiFePO4), the positive electrode conductive agent SP, and the positive electrode binder polyvinylidene fluoride (PVDF) are mixed according to a mass ratio of 96:2:2, and N-methylpyrrolidone (NMP) is added as a solvent to prepare a slurry with a solid content of 65 wt%. After being stirred evenly by a vacuum mixer, a positive electrode slurry is obtained. The positive electrode slurry is evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 18 μm and dried at 90 °C to obtain a positive electrode sheet with a single-sided coated positive electrode material layer. Then, the above steps are repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coated positive electrode material layer. After drying at 85 °C, it is roll-pressed, and then slit and welded with tabs to obtain a positive electrode sheet for use. Among them, the compaction density of the positive electrode sheet is 2.5 g / cm 3 , and the double-sided areal density is 370 g / m 2 , and the discharge specific capacity of lithium iron phosphate (LiFePO4) is 145 mAh / g.

[0081] <Preparation of the separator>

[0082] A polyethylene (PE) porous membrane with a thickness of 12 μm (provided by Shenzhen Xingyuan Material Technology Co., Ltd.) is used as the separator.

[0083] <Preparation of the lithium-ion battery>

[0084] Stack the positive electrode sheet, separator, and negative electrode sheet prepared in this embodiment in sequence, with the separator placed in the middle of the positive electrode sheet and the negative electrode sheet to play an isolation role, and wind to obtain an electrode assembly. Place the electrode assembly in an aluminum-plastic film packaging bag, remove moisture at 85 °C, inject the electrolyte prepared in this embodiment, and obtain a lithium-ion battery through processes such as vacuum packaging, standing, formation, aging, and grading. Among them, stand for 48 hours. The method of formation includes: at 45 °C and a formation pressure of 300 kgf, first charge at a constant current of 0.1C to 10% SOC, then charge at a constant current of 0.3C to 20% SOC, and finally charge at a constant current of 0.5C to 35% SOC.

[0085] Example 2

[0086] <Preparation of electrolyte>

[0087] The electrolyte provided in this embodiment is the same as that in Example 1, except that the mass percentage content of poly(2,2,2-trifluoroethyl methacrylate) PTFEMA is 0.2%, and the mass percentage content of ethyl methyl carbonate EMC is 52.8%.

[0088] <Preparation of negative electrode sheet>

[0089] The same as in Example 1.

[0090] <Preparation of positive electrode sheet>

[0091] The same as in Example 1.

[0092] <Preparation of separator>

[0093] The same as in Example 1.

[0094] <Preparation of lithium-ion battery>

[0095] Basically the same as in Example 1, except that the electrolyte prepared in this embodiment is used.

[0096] Example 3

[0097] <Preparation of electrolyte>

[0098] The same as in Example 1.

[0099] <Preparation of negative electrode sheet>

[0100] Basically the same as in Example 1, except that the double-sided areal density is 165 g / m 2 , and the NP ratio of the negative electrode to the positive electrode is designed to be 1.05.

[0101] <Preparation of positive electrode sheet>

[0102] Basically the same as in Example 1, except that the double-sided areal density is 380 g / m2 。

[0103] <Preparation of separator>

[0104] Same as Example 1.

[0105] <Preparation of lithium-ion battery>

[0106] Basically the same as Example 1, except that the positive electrode sheet and the negative electrode sheet prepared in this example are used.

[0107] Comparative Example 1

[0108] <Preparation of electrolyte>

[0109] Basically the same as Example 1, except that it does not contain poly(2,2,2-trifluoroethyl methacrylate) (PTFEMA), and the mass percentage content of ethyl methyl carbonate (EMC) is 53%.

[0110] <Preparation of lithium-ion battery>

[0111] Basically the same as Example 1, except that the electrolyte prepared in this comparative example is used.

[0112] Comparative Example 2

[0113] <Preparation of electrolyte>

[0114] Same as Example 1.

[0115] <Preparation of negative electrode sheet>

[0116] Basically the same as Example 1, except that the double-sided surface density of the negative electrode sheet is 255 g / m 2 。

[0117] <Preparation of positive electrode sheet>

[0118] Basically the same as Example 1, except that the double-sided surface density of the positive electrode sheet is 555 g / m 2 。

[0119] <Preparation of separator>

[0120] Same as Example 1.

[0121] <Preparation of lithium-ion battery>

[0122] Basically the same as Example 1, except that the positive electrode sheet and the negative electrode sheet prepared in this comparative example are used.

[0123] Comparative Example 3

[0124] <Preparation of electrolyte>

[0125] Same as Example 1.

[0126] <Preparation of negative electrode sheet>

[0127] It is basically the same as Example 1, except that the binder PAA (polyacrylic acid) is replaced by styrene-butadiene rubber (SBR).

[0128] <Preparation of positive electrode sheet>

[0129] It is the same as Example 1.

[0130] <Preparation of separator>

[0131] It is the same as Example 1.

[0132] <Preparation of lithium-ion battery>

[0133] It is basically the same as Example 1, except that the negative electrode sheet prepared in this comparative example is used.

[0134] Comparative Example 4

[0135] <Preparation of lithium-ion battery>

[0136] It is basically the same as Example 1, except that the formation method includes: at 45 °C and a formation pressure of 300 kgf, first constant current charge at 0.02C to 10% SOC, then constant current charge at 0.3C to 20% SOC, and finally constant current charge at 0.5C to 35% SOC.

[0137] Comparative Example 5

[0138] <Preparation of electrolyte>

[0139] It is the same as Example 1.

[0140] <Preparation of negative electrode sheet>

[0141] It is basically the same as Example 1, except that the double-sided surface density of the negative electrode sheet is 255 g / m 2 , and the binder PAA (polyacrylic acid) is replaced by styrene-butadiene rubber (SBR).

[0142] <Preparation of positive electrode sheet>

[0143] It is basically the same as Example 1, except that the double-sided surface density of the positive electrode sheet is 555 g / m 2 .

[0144] <Preparation of separator>

[0145] It is the same as Example 1.

[0146] <Preparation of lithium-ion battery>

[0147] It is basically the same as Example 1, except that the positive and negative electrode sheets prepared in this comparative example are used.

[0148] Comparative Example 6

[0149] <Preparation of electrolyte>

[0150] It is basically the same as Example 1, except that it does not contain poly(2,2,2-trifluoroethyl methacrylate) PTFEMA, and the mass percentage content of ethyl methyl carbonate EMC is 53%.

[0151] <Preparation of lithium-ion battery>

[0152] It is basically the same as Comparative Example 5, except that the electrolyte prepared in this comparative example is used.

[0153] Performance test

[0154] According to the high-temperature storage (45°C - 100% SOC - 30-day storage) test method of national standard GB44240, the high-temperature storage (45°C - 100% SOC - 30-day storage) performance of the lithium-ion batteries prepared in the examples and comparative examples was tested, and the results are shown in Table 1.

[0155] Table 1

[0156]

[0157] It can be seen at least the following points from Table 1:

[0158] (1) By comparing Examples 1 - 3 with Comparative Example 1 and Comparative Example 5 with Comparative Example 6, it can be known that compared with the lithium-ion batteries without poly(2,2,2-trifluoroethyl methacrylate) (PTFEMA), when the poly(2,2,2-trifluoroethyl methacrylate) (PTFEMA) provided by the present invention is applied to the lithium-ion battery system, the high-temperature storage performance of the lithium-ion battery can be improved.

[0159] (2) By comparing Example 1 with Comparative Examples 2-4, it can be seen that poly(ethyl 2,2,2-trifluoromethacrylate) (PTFEMA) can make the high-temperature storage performance of lithium-ion batteries more excellent under specific areal density, binder, and formation methods. The applicant speculates that the reason may be that PTFEMA has water and oil resistance, and it must be in the corresponding lithium-ion battery energy storage system design to improve the high-temperature stability without loss of electrochemical performance. That is, we need to use a lower areal density and cooperate with a PAA binder with higher binding force to ensure the infiltration and liquid retention of the high-viscosity electrolyte. In the film-forming step of formation and grading, the minimum charging current must be ≥0.1C, otherwise, the consumption of PTFEMA will be completed in the first step, and the stability of subsequent high-temperature storage cannot be significantly improved. Under these system designs, we can use the electrolyte additive PTFEMA provided by the present invention in soft-pack batteries to significantly improve the high-temperature storage performance of the batteries.

[0160] (3) By comparing Example 1 with Comparative Examples 1, 5-6, it can be seen that poly(ethyl 2,2,2-trifluoromethacrylate) (PTFEMA) can better play its performance in the lithium-ion battery system provided by the present invention and significantly improve the high-temperature storage performance of lithium-ion batteries.

[0161] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An electrolyte additive for improving the high-temperature performance of lithium-ion batteries, characterized in that, The electrolyte additive includes poly(ethyl 2,2,2-trifluoromethylacrylate).

2. The electrolyte additive according to claim 1, wherein The poly(ethyl 2,2,2-trifluoromethylacrylate) has a weight-average molecular weight of 800-1500 g / mol.

3. An electrolyte, characterized in that, The electrolyte includes a lithium salt, a non-aqueous organic solvent, and a functional additive, and the functional additive includes the electrolyte additive as claimed in claim 1 or 2.

4. The electrolyte according to claim 3, characterized in that, The mass ratio of the electrolyte additive in the electrolyte is not more than 0.5%; and / or, the lithium salt includes at least one of lithium hexafluorophosphate LiPF6 and lithium bis(fluorosulfonyl)imide LiFSi; and / or, the mass ratio of the lithium salt in the electrolyte is 10%-20%; and / or, the non-aqueous organic solvent includes at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate EMC, ethylene carbonate EC, propylene carbonate, and γ-butyrolactone; and / or, the mass ratio of the non-aqueous organic solvent in the electrolyte is 68% to 92%; and / or, the functional additive further includes other functional additives, and the other functional additives include at least one of fluoroethylene carbonate FEC, 1,3-propane sultone PS, and vinylene sulfate DTD, and the mass ratio of the other functional additives in the electrolyte is 5%-10%.

5. A lithium-ion battery, characterized in that, The lithium-ion battery includes a positive electrode sheet, a negative electrode sheet, a separator disposed between the positive electrode sheet and the negative electrode sheet, and an electrolyte, and the electrolyte includes the electrolyte as claimed in claim 3 or 4.

6. The lithium ion battery according to claim 5, characterized in that, The tap density of the positive electrode sheet is 2.3 to 2.55 g / cm 3 ; and / or, the areal density of both sides of the positive electrode sheet is 360 to 380 g / m 2 ; And / or, the compaction density of the negative electrode sheet is 1.3 to 1.55 g / cm 3 ; and / or, the double-sided areal density of the negative electrode sheet is 165 to 200 g / m 2 .

7. The lithium ion battery according to claim 5, wherein The NP ratio of the lithium-ion battery is designed to be 1.05-1.1; and / or, the positive electrode sheet includes a positive electrode current collector and a positive electrode active layer, and the positive electrode active layer includes a positive electrode active material, a conductive agent, and a binder; and / or, the negative electrode sheet includes a negative electrode current collector and a negative electrode active layer, and the negative electrode active layer includes a negative electrode active material, a conductive agent, and a binder.

8. The lithium ion battery according to claim 7, wherein The positive electrode active material includes lithium iron phosphate LFP; and / or, in the positive electrode active layer, the conductive agent includes at least one of carbon black, acetylene black, conductive graphite, carbon fiber, carbon nanotube, and graphene; and / or, in the positive electrode active layer, the binder includes at least one of PVDF, polyvinyl alcohol, and polytetrafluoroethylene; and / or, in the positive electrode active layer, the mass ratio of the positive electrode active material, the conductive agent, and the binder is (95-97):(1-2):(2-3); and / or, the negative electrode active material includes graphite; and / or, in the negative electrode active layer, the conductive agent includes at least one of carbon black, acetylene black, conductive graphite, carbon fiber, carbon nanotube, and graphene; and / or, in the negative electrode active layer, the binder includes polyacrylic acid PAA; and / or, in the negative electrode active layer, the mass ratio of the negative electrode active material, the conductive agent, and the binder is (94-96):(1-3):(2-3); and / or, the thickness of the separator is 10-15 μm, the thickness of the positive electrode current collector is 14-20 μm, and the thickness of the negative electrode current collector is 4.5-8 μm.

9. The lithium ion battery according to claim 5, characterized in that, The formation current of the lithium-ion battery is not less than 0.1C.

10. The lithium-ion battery according to any one of claims 5-9, characterized in that, The formation method of the lithium-ion battery includes the following steps: First, charge at a constant current with a current of 0.1-0.15C until 10% SOC, then charge at a constant current with a current of 0.2-0.4C until 20% SOC, and finally charge at a constant current with a current of 0.5-1C until 35% SOC.

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