Electrolyte additive, electrolyte and lithium ion battery

Abstract

The present invention discloses an electrolyte additive, an electrolyte and a lithium ion battery, and relates to the technical field of lithium ion batteries, wherein an electrolyte additive comprises an additive A and an additive B, wherein the additive A is a fluorine-containing lithium salt, and the additive B is one or more of the compounds shown in formula 1 to formula 3. The electrolyte additive of the present application, under the synergistic effect of the additive A and the additive B, can significantly improve the high temperature cycle performance and high temperature storage performance of the lithium ion battery, while effectively reducing the risk of deterioration of the power performance of the lithium ion battery.

Description

Technical Field

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

[0002] Lithium-ion batteries have extremely wide applications in electronic products, the automotive industry, and electrochemical energy storage due to their high energy density, no memory effect, and high operating voltage. In recent years, lithium-ion battery technology has developed rapidly, and energy density has continued to increase, but it still cannot meet the energy density needs of the application end, especially in the automotive industry. Range anxiety caused by short driving range is one of the main problems restricting the rapid development of the electric vehicle industry. At present, a large number of studies are mainly focused on how to improve the energy density of positive electrode active materials, such as by increasing the operating voltage of the battery and increasing the gram capacity of the material by increasing the nickel content in the ternary material. However, these solutions bring an unavoidable problem. Regardless of high voltage or high nickel materials, the surface of the material has extremely high chemical and electrochemical activity when charged. The oxidation and decomposition of the electrolyte on the surface and a series of side reactions will lead to the power attenuation of the battery, the deterioration of the cycle life, and the degradation of high-temperature storage gas production and other performance.

[0003] In order to improve the above problems, a method of adding additives to the electrolyte has emerged in the prior art, such as the patent application number CN102593512B and the application number CN201210032333.3 Lithium-ion battery and its electrolyte. In this patent, titanate is added to the electrolyte, and an oxidation reaction occurs during the first charging process of the battery. The solid part of the oxidation product covers the surface of the positive electrode to form a dense passivation film, which protects the positive electrode, prevents the reaction between the positive electrode and the electrolyte at high temperature, and inhibits the decomposition of the electrolyte by the positive electrode, thereby greatly improving the high-temperature storage performance of the battery. And a high-temperature resistant non-aqueous electrolyte with publication number CN110034333A and application number CN201910303287.8. In this patent, tetrapropyl zirconate is added to the electrolyte. The zirconate undergoes an oxidation reaction during the first charging process of the battery. The solid part of the oxidation product zirconium dioxide covers the surface of the positive electrode to form a dense passivation film, which protects the positive electrode, prevents the reaction between the positive electrode and the electrolyte at high temperature, and inhibits the decomposition of the electrolyte by the positive electrode, thereby greatly improving the high-temperature storage performance of the battery. However, in the above two patents, although the decomposition of the electrolyte can be inhibited and the high-temperature storage performance of the battery can be improved, the dense passivation film formed on the surface of the positive electrode has a higher impedance, causing the power attenuation of the battery cell and leading to the degradation of the power performance of the lithium-ion battery. Summary of the invention

[0004] 1. Technical problem to be solved by the invention

[0005] In view of the technical problem that the prior art improves the high-temperature cycle performance and high-temperature storage performance of lithium-ion batteries while the power performance of lithium-ion batteries deteriorates, the present invention provides an electrolyte additive, an electrolyte and a lithium-ion battery, which can significantly improve the cycle performance and high-temperature storage performance of lithium-ion batteries while effectively reducing the risk of deterioration of the power performance of lithium-ion batteries.

[0006] 2. Technical solution

[0007] To solve the above problems, the technical solution provided by the present invention is:

[0008] An electrolyte additive, comprising an additive A and an additive B, wherein the additive A is a fluorine-containing lithium salt, and the additive B is one or more compounds represented by formula 1 to formula 3.

[0009]

[0010]

[0011] Among them, R 1 -R 51 Each of them can be independently selected from an alkyl group having 1-5 carbon atoms, an unsaturated hydrocarbon group having 2-5 carbon atoms, and an alkoxy group having 1-5 carbon atoms; or the hydrogen in the alkyl group having 1-5 carbon atoms, the unsaturated hydrocarbon group having 2-5 carbon atoms, and the alkoxy group having 1-5 carbon atoms can be partially or completely substituted by one or more of fluorine, chlorine, bromine, cyano, carboxyl, and sulfonic acid groups.

[0012] Optionally, the additive B is selected from tris(trimethylsilyl)aluminate, tris(triethylsilyl)aluminate, tris(tri-n-propylsilyl)aluminate, tris(triisopropylsilyl)aluminate, tris(tri-n-butylsilyl)aluminate, tris(triisobutylsilyl)aluminate, tris(tri-tert-butylsilyl)aluminate, tris(trimethoxysilyl)aluminate, tris(triethoxysilyl)aluminate, tris(tri-n-propoxysilyl)aluminate, tris(triisopropoxysilyl)aluminate, tris(tri-n-butoxysilyl)aluminate, tris(tri-n-butylsilyl)aluminate, tris(tri-methoxysilyl)aluminate, tris(triethoxysilyl)aluminate, tris(tri-n-propoxysilyl)aluminate, tris(tri-isopropoxysilyl)aluminate, tris(tri-n-butoxysilyl)aluminate, tris(tri-n-butyl ... sec-butylsilyl)aluminate, tris(tri-tert-butylsilyl)aluminate, tris(trifluoromethylsilyl)aluminate, tris(trivinylsilyl)aluminate, tris(triethynylsilyl)aluminate, tetrakis(trimethylsilyl)zirconate, tetrakis(triethylsilyl)zirconate, tetrakis(tri-n-propylsilyl)zirconate, tetrakis(triisopropylsilyl)zirconate, tetrakis(tri-n-butylsilyl)zirconate, tetrakis(triisobutylsilyl)zirconate, tetrakis(tri-tert-butylsilyl)zirconate, tetrakis(trimethoxysilyl)zirconate, tetrakis(triethoxysilyl)zirconate tetrakis(tri-n-propoxysilyl) zirconate, tetrakis(tri-isopropoxysilyl) zirconate, tetrakis(tri-n-butoxysilyl) zirconate, tetrakis(tri-sec-butoxysilyl) zirconate, tetrakis(tri-tert-butoxysilyl) zirconate, tetrakis(trifluoromethylsilyl) zirconate, tetrakis(trivinylsilyl) zirconate, tetrakis(triethynylsilyl) zirconate, tetrakis(trimethylsilyl) titanate, tetrakis(triethylsilyl) titanate, tetrakis(tri-n-propylsilyl) titanate, tetrakis(tri-isopropylsilyl) titanate, tetrakis(tri-n-butylsilyl) ) titanate, tetrakis(triisobutylsilyl) titanate, tetrakis(tri-tert-butylsilyl) titanate, tetrakis(trimethoxysilyl) titanate, tetrakis(triethoxysilyl) titanate, tetrakis(tri-n-propoxysilyl) titanate, tetrakis(triisopropoxysilyl) titanate, tetrakis(tri-n-butoxysilyl) titanate, tetrakis(tri-sec-butoxysilyl) titanate, tetrakis(tri-tert-butoxysilyl) titanate, tetrakis(trifluoromethylsilyl) titanate, tetrakis(trivinylsilyl) titanate, tetrakis(triethynylsilyl) titanate or one or more thereof.

[0013] Optionally, the fluorine-containing lithium salt is selected from one of lithium difluorophosphate, lithium difluorobisoxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0014] Optionally, an additive C is also included, and the additive C is selected from one of vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, 1,3-propane sultone, 1,3-propylene sultone, vinyl sulfate, tris(trimethylsilane)borate and tris(trimethylsilane)phosphate. Further, the content of the additive C is 0-5% of the total weight of the electrolyte.

[0015] At the same time, the present application also provides an electrolyte, including a lithium salt, an organic solvent and the electrolyte additive mentioned above.

[0016] Optionally, the content of the additive A is 0.01%-5% of the total weight of the electrolyte, the content of the additive B is 0.01%-10% of the total weight of the electrolyte, and the content of the lithium salt is 6.25-25% of the total weight of the electrolyte. Further, the content of the additive B is 0.1%-5% of the total weight of the electrolyte, and the content of the lithium salt is 6.25-18.8% of the total weight of the electrolyte. Further, the content of the additive B is 0.3%-3% of the total weight of the electrolyte.

[0017] Optionally, the organic solvent is selected from one or more of ethylene carbonate, propylene carbonate, butylene carbonate, pentylene carbonate, fluoroethylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, 1,4-butyrolactone, methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, propyl propionate, and ethyl butyrate.

[0018] Optionally, the lithium salt is selected from LiPF 6 , LiBF 4 、LiN(SO 2 F) 2 、LiClO 4 、LiAsF 6 、LiB(C 2 O 4 ) 2 , LiBF 2 C 2 O 4 、LiN(SO 2 R F ) 2 、LiN(SO 2 F)(SO 2 R F ) in one or more, wherein R F C n F 2n+1 , n = 1-10, further, n is 1-3, R F For-CF 3 , -CF 2 CF 3 or -CF 2 CF 2 CF 3 ; Further, the lithium salt is selected from LiFP 6 、LiN(SO 2 F) 2 、LiN(CF 3 SO 2 ) 2 、LiB(C 2 O 4 ) 2, LiBF 2 C 2 O 4 one or more of; further, the lithium salt is selected from LiPF 6 , LiNSO 2 F 2 , LiBF 2 C 2 O 4 one or more of.

[0019] In addition, the present application also provides a lithium-ion battery, including a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. The separator is disposed between the positive electrode sheet and the negative electrode sheet, and the electrolyte is the electrolyte described in the present application.

[0020] Optionally, the positive electrode sheet includes a positive electrode current collector and a positive electrode active paste layer located on the positive electrode current collector. The positive electrode active paste layer includes a positive electrode active material, and the positive electrode active material is selected from LiCoO 2 , LiNi x A y B (1-x-y) O 2 , LiMPO 4 , Li 1-x’ Q y’ L z’ C (1-y’-z’) O 2 one or more of, where A and B are each independently selected from one of Co, Al, and Mn, and A and B are different, 0 < x < 1, 0 < y < 1, and x + y < 1; M is selected from one or more of Co, Ni, Fe, Mn, and V, 0 < x' < 1, 0 < y' < 1, 0 < z' < 1, and y' + z' < 1; Q, L, and C are each independently selected from one of Co, Ni, Fe, and Mn, and Q, L, and C are different from each other; the negative electrode sheet includes a negative electrode current collector and a negative electrode active paste layer located on the negative electrode current collector. The negative electrode active paste layer includes a negative electrode active material, and the negative electrode active material is selected from metallic lithium, natural graphite, artificial graphite, mesophase carbon microspheres, hard carbon, soft carbon, silicon, silicon-carbon composites, Li-Sn alloys, Li-Sn-O alloys, Sn, SnO, SnO 2 , TiO 2 -Li 4 Ti 5 O 12 one or more of Li-Al alloys.

[0021] 3. Beneficial Effects

[0022] Adopting the technical solution provided by the present invention, compared with the prior art, it has the following beneficial effects:

[0023] (1) An electrolyte additive proposed in the embodiment of the present application, additive A is a fluorine-containing lithium salt, which can be adsorbed on the surface of the positive electrode to form a film, which can effectively block the electrolyte from being continuously oxidized on the surface of the positive electrode, reduce the content of organic components such as alkyl lithium carbonate and lithium alcohol in CEI, and form a low-impedance electrolyte / positive electrode interface film, thereby effectively improving the impedance of the battery, and slightly improving the gas production, thereby effectively improving the high-temperature cycle performance and power performance of the high-voltage lithium-ion battery. At the same time, additive B can undergo an oxidation reaction during the first charging process of the battery, and the oxidation product metal oxide covers the surface of the positive electrode to form a dense passivation film, which plays a role in protecting the positive electrode, preventing the reaction between the positive electrode and the electrolyte at high temperature, and inhibiting the decomposition of the positive electrode on the electrolyte, thereby greatly improving the high-temperature storage performance of the battery, and additive B will also produce decomposition products including trifluoromethylsilane during the decomposition process, and trifluoromethylsilane is beneficial to improving the transmission of lithium ions in the electrolyte, thereby reducing the negative electrode interface impedance, and thus making the increase in battery impedance have no significant change. It can be seen from this that the electrolyte additive of the present application, under the synergistic effect of additive A and additive B, can significantly improve the high-temperature cycle performance and high-temperature storage performance of lithium-ion batteries while causing no significant increase in battery impedance, thereby effectively reducing the risk of lithium-ion battery power performance degradation.

[0024] (2) An electrolyte proposed in an embodiment of the present application can form SEI at the negative electrode by adding C, thereby improving the surface stability of the negative electrode material and further improving the cycle performance of the lithium-ion battery.

[0025] (3) An electrolyte proposed in an embodiment of the present application contains electrolyte additives of additive A and additive B. Under the synergistic effect of additive A and additive B, a passivation film containing metal oxide and fluoride is formed on the surface of the positive electrode, which effectively inhibits the decomposition of solvents and lithium salts on the surface of the positive electrode, and can increase the content of components with good lithium ion transport performance, improve the lithium ion transport performance in the electrolyte, and thus effectively improve the battery impedance, so that the risk of battery power performance degradation can be effectively reduced while significantly improving the cycle performance and high-temperature storage performance of the lithium-ion battery, especially in lithium-ion batteries using high-voltage and high-nickel positive electrode materials.

[0026] (4) A lithium-ion battery proposed in an embodiment of the present application significantly improves the cycle performance and high-temperature storage performance while reducing the risk of battery power performance degradation. Since an electrolyte containing an electrolyte additive is added, a passivation film with excellent performance is formed on the electrode surface through the synergistic effect of additives A and additive B, which inhibits the decomposition of various components in the electrolyte on the electrode surface. As a result, the lithium-ion battery maintains good cycle performance and high-temperature storage performance at high voltage while effectively reducing the risk of lithium-ion battery power performance degradation. DETAILED DESCRIPTION

[0027] For further understanding of the content of the present invention, the technical scheme in the embodiment of the present invention will be clearly and completely described below in conjunction with the embodiment of the present invention. Obviously, the described embodiment is only a part of the embodiment of the present invention, rather than all embodiments. Based on the embodiment in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work premise belong to the scope of protection of the present invention. It should be noted that the reagents, materials and instruments involved in this application, if not otherwise specified, can all be purchased from the market.

[0028] Example 1

[0029] Preparation of positive electrode

[0030] The positive electrode active material is lithium nickel cobalt manganese oxide (LiN i0.5 Mn 0.3 Co 0.2 ), a binder polyvinylidene fluoride (PVDF), and a conductive agent acetylene black Super-P are mixed in a mass ratio of 96:2:2, N-methylpyrrolidone is added, and the mixture is stirred in a vacuum mixer until it is stable and uniform to obtain a positive electrode slurry; the obtained positive electrode slurry is evenly coated on an aluminum foil with a thickness of 12 um, the coated aluminum foil is dried in a blast oven at 120°C, and then cold pressed and slit to obtain a positive electrode sheet.

[0031] Preparation of negative electrode

[0032] The negative electrode active material artificial graphite, the binder styrene butadiene rubber (SBR), the thickener sodium carboxymethyl cellulose (CMC), and the conductive agent acetylene black Super-P are mixed in a mass ratio of 97:1:1, deionized water is added, and the mixture is stirred in a vacuum mixer until it is stable and uniform to obtain a negative electrode slurry; the obtained positive electrode slurry is evenly coated on a copper foil with a thickness of 8 um, the coated copper foil is dried in a blast oven at 120°C, and then cold pressed and slit to obtain a negative electrode sheet.

[0033] Preparation of electrolyte

[0034] In a glove box filled with argon (water content <10ppm, oxygen content <1ppm), ethylene carbonate, ethyl methyl carbonate and diethyl carbonate are mixed in a weight ratio of 1:1:1 to obtain a mixed solution, and then lithium hexafluorophosphate in an amount of 12.5% ​​by weight of the total weight of the electrolyte is evenly mixed into the mixed solution, and then additives are added, wherein the additives include lithium difluorophosphate in an amount of 0.5% by weight of the total weight of the electrolyte and tris(trimethylsilyl)aluminate in an amount of 0.3% by weight of the total weight of the electrolyte, and after stirring evenly, an electrolyte is obtained.

[0035] Preparation of lithium-ion batteries

[0036] The positive electrode sheet, negative electrode sheet and isolation film prepared above are wound to obtain a battery cell, and after the battery cell is placed in a packaging shell, the prepared electrolyte is injected, and then sealed in sequence, and a lithium-ion battery is obtained through processes such as standing, hot and cold pressing, formation, exhaust, packaging, and capacity testing.

[0037] Example 2

[0038] Compared with Example 1, the difference is that the additives in the electrolyte include 0.5% of lithium difluorophosphate and 0.1% of tris(trimethylsilyl)aluminate by weight of the total electrolyte, and the other conditions are the same as those in Example 1.

[0039] Example 3

[0040] Compared with Example 1, the difference is that the additives in the electrolyte include 0.5% of lithium difluorophosphate and 0.5% of tris(trimethylsilyl)aluminate by weight of the total electrolyte, and the other conditions are the same as those in Example 1.

[0041] Example 4

[0042] Compared with Example 1, the difference is that the additives in the electrolyte include 0.5% of lithium difluorophosphate and 1% of tris(trimethylsilyl)aluminate based on the total weight of the electrolyte, and the other conditions are the same as those in Example 1.

[0043] Example 5

[0044] Compared with Example 1, the difference is that in the electrolyte, the additives include 0.5% of lithium difluorophosphate and 2% of tris(trimethylsilyl)aluminate based on the total weight of the electrolyte, and the other conditions are the same as those in Example 1.

[0045] Example 6

[0046] Compared with Example 1, the difference is that in the electrolyte, the additives include lithium difluorophosphate with a content of 0.5% of the total weight of the electrolyte, tris(trimethylsilyl)aluminate with a content of 0.3% of the total weight of the electrolyte and vinylene carbonate with a content of 0.20% of the total weight of the electrolyte, and the other conditions are the same as those in Example 1.

[0047] Example 7

[0048] Compared with Example 1, the difference is that the additives in the electrolyte include 0.5% of lithium difluorophosphate and 0.3% of tetrakis(trimethylsilyl)zirconate based on the total weight of the electrolyte, and the other conditions are the same as those in Example 1.

[0049] Example 8

[0050] Compared with Example 1, the difference is that the additives in the electrolyte include 0.5% of lithium difluorophosphate and 0.3% of tetrakis(trimethylsilyl)titanate by weight of the total electrolyte, and the other conditions are the same as those in Example 1.

[0051] Example 9

[0052] Compared with Example 1, the difference is that the additives in the electrolyte include lithium difluorophosphate with a content of 0.5% of the total weight of the electrolyte, tris(trimethylsilyl)aluminate with a content of 0.1% of the total weight of the electrolyte, and tetrakis(trimethylsilyl)zirconate with a content of 0.2% of the total weight of the electrolyte, and the other conditions are the same as in Example 1.

[0053] Example 10

[0054] Compared with Example 1, the difference is that the additives in the electrolyte include lithium difluorophosphate with a content of 0.5% of the total weight of the electrolyte, tris(trimethylsilyl)aluminate with a content of 0.1% of the total weight of the electrolyte, and tetrakis(trimethylsilyl)titanate with a content of 0.2% of the total weight of the electrolyte, and the other conditions are the same as those in Example 1.

[0055] Embodiment 11

[0056] Compared with Example 1, the difference is that the additives in the electrolyte include 0.5% of lithium difluorophosphate, 0.1% of tris(trimethylsilyl)aluminate, 0.1% of tetrakis(trimethylsilyl)zirconate and 0.1% of tetrakis(trimethylsilyl)titanate, based on the total weight of the electrolyte, and the other conditions are the same as those in Example 1.

[0057] Comparative Example 1

[0058] Compared with Example 1, the difference is that there is no additive in the electrolyte, and the other conditions are the same as those in Example 1.

[0059] Comparative Example 2

[0060] Compared with Example 1, the difference is that the additive in the electrolyte is vinylene carbonate with a content of 0.20% of the total weight of the electrolyte, and the other conditions are the same as those in Example 1.

[0061] Comparative Example 3

[0062] Compared with Example 1, the difference is that the additive in the electrolyte is lithium difluorophosphate with a content of 0.5% of the total weight of the electrolyte, and the other conditions are the same as those in Example 1.

[0063] Comparative Example 4

[0064] Compared with Example 1, the difference is that the additives in the electrolyte include 0.20% of vinylene carbonate and 0.5% of lithium difluorophosphate based on the total weight of the electrolyte, and the other conditions are the same as those in Example 1.

[0065] Comparative Example 5

[0066] Compared with Example 1, the difference is that the additive in the electrolyte is tris(trimethylsilyl)aluminate with a content of 0.3% of the total weight of the electrolyte, and the other conditions are the same as those in Example 1.

[0067] Performance Testing

[0068] Relevant performance tests were performed on the lithium-ion batteries and electrolytes thereof prepared in Examples 1-8 and Comparative Examples 1-4.

[0069] Lithium-ion battery cycle performance test

[0070] The lithium-ion battery is charged to 4.2V at 0.5C constant current at 45°C, then charged at constant voltage to a current ≤ 0.05C, and then discharged to 2.8V at 0.5C constant current. The above is one charge and discharge cycle, and then 300 and 500 cycles are performed under the above conditions, wherein the capacity retention rate (%) of the lithium-ion battery after n cycles = (discharge capacity of the nth cycle / first discharge capacity) × 100%, wherein n is the number of cycles of the lithium-ion battery.

[0071] Lithium-ion battery high temperature storage performance test

[0072] The lithium-ion battery is charged at room temperature at a constant current of 0.5C to 4.2V, and then charged at a constant voltage to a current ≤ 0.05C. The volume of the tested lithium-ion battery is V 0 ; Then put the lithium-ion battery into a 60℃ constant temperature box and store it for 60d and 120d respectively. The volume of the lithium-ion battery taken out for testing on the nth day is recorded as V n ; Volume expansion rate of lithium-ion battery after storage at 60℃ for n days (%) = (V n -V 0 ) / V 0 × 100%, where n is the number of days the lithium-ion battery is stored at 60°C.

[0073] Lithium-ion battery power performance test

[0074] The power performance of a lithium-ion battery is characterized by measuring the direct current internal resistance (DCIR) of the lithium-ion battery at 50% SOC at 25° C., where SOC indicates the state of charge.

[0075] The lithium-ion battery was charged to 4.2V at 0.5C constant current at 25°C, charged to a current ≤ 0.05C at constant voltage, left for 5 minutes, and discharged to 2.8V at 0.5C constant current. The discharge capacity of the lithium-ion battery was recorded, and the discharge capacity was recorded as 100% SOC. The state of charge of the lithium-ion battery was adjusted to the required 50% SOC at 0.5C. After the adjustment, the battery was discharged at a current of 4C for 10 seconds, and the difference between the voltage before discharge and the voltage at the end of discharge was calculated, and the DCIR was calculated by dividing the difference by the current.

[0076] The results of the above performance tests are shown in Table 1.

[0077] Table 1 is the test results of Examples 1-8 and Comparative Examples 1-4

[0078]

[0079] According to the test results in Table 1, it can be seen that: in combination with Examples 1-11 and Comparative Examples 1-5, it can be seen that the electrolyte obtained in the present application contains additive A lithium difluorophosphate and additive B tris(trimethylsilyl)aluminate or tetrakis(trimethylsilyl)zirconate or tetrakis(trimethylsilyl)titanate. The high-temperature cycle performance and high-temperature storage performance of the prepared lithium-ion battery are greatly improved, and the battery internal resistance DCIR is at a relatively low level.

[0080] Specifically, combining the data of Comparative Example 1, Comparative Example 3, Comparative Example 5 and Example 2, it can be seen that compared with Comparative Example 1, if only additive A, that is, lithium difluorophosphate, is added to the electrolyte alone, the high-temperature storage gas production and cycle performance of the lithium-ion battery are slightly improved, but the gas production is still at a relatively high level; if only additive B is added to the electrolyte alone, the high-temperature storage gas production and cycle performance of the lithium-ion battery are improved to a certain extent, but the DCIR is slightly increased; and when additive A and additive B are added at the same time, the high-temperature cycle performance and high-temperature storage performance of the battery are greatly improved, and the DCIR is at a relatively low level. It can be seen that under the synergistic effect of additive A and additive B, a passivation film containing metal oxide and fluoride is formed on the surface of the positive electrode, which effectively inhibits the decomposition of solvents and lithium salts on the surface of the positive electrode, can increase the content of components with good lithium ion transmission performance, and improve the transmission performance of lithium ions in the electrolyte, thereby effectively improving the battery impedance, so that the risk of battery power performance degradation can be effectively reduced while significantly improving the cycle performance and high-temperature storage performance of lithium-ion batteries, especially in lithium-ion batteries using high-voltage and high-nickel positive electrode materials.

[0081] At the same time, combined with the data of Comparative Examples 1 and 2, it can be seen that the addition of the additive vinylene carbonate can form SEI at the negative electrode, improve the surface stability of the negative electrode material, increase its impedance to a certain extent, and the gas production level is equivalent, further improving the cycle performance of the lithium ion battery. At the same time, combined with the data of Comparative Examples 2, Comparative Examples 4 and Example 1 and Example 6, it can be seen that under the premise of adding additives A and additive B at the same time, adding the additive vinylene carbonate, that is, additive C, can further improve the cycle performance of the lithium ion battery.

[0082] It can be seen from this that the electrolyte and lithium-ion battery containing additives A and additive B in the present application can significantly improve the cycle performance and high-temperature storage performance while reducing the risk of battery power performance degradation.

[0083] The above is only a preferred embodiment of the present invention, and is not any formal or substantial limitation of the present invention. It should be pointed out that ordinary technicians in this technical field can make several improvements and supplements without departing from the method of the present invention, and these improvements and supplements should also be regarded as the protection scope of the present invention. Any technician familiar with this profession, without departing from the spirit and scope of the present invention, can make some changes, modifications and evolutions of the technical content disclosed above, which are equivalent embodiments of the present invention; at the same time, any changes, modifications and evolutions of any equivalent changes made to the above embodiments based on the essential technology of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. An electrolyte additive, characterized in that: The invention comprises an additive A and an additive B, wherein the additive A is a fluorine-containing lithium salt, and the additive B is one or more compounds represented by formula 1 or formula 3. 、 Formula 1 ； Formula 3 Among them, R1-R 51 Each of them can be independently selected from an alkane group having 1 to 5 carbon atoms, an unsaturated hydrocarbon group having 2 to 5 carbon atoms, and an alkoxy group having 1 to 5 carbon atoms; or an alkane group having 1 to 5 carbon atoms, and an unsaturated hydrocarbon group having 2 to 5 carbon atoms; The mass ratio of the additive A to the additive is (0.01-10): (0.03-5); The fluorine-containing lithium salt is selected from one of lithium difluorophosphate, lithium difluorobisoxalate phosphate and tetrafluorooxalate phosphate.

2. The electrolyte additive according to claim 1, characterized in that: The additive B is selected from tris(trimethylsilyl)aluminate, tris(triethylsilyl)aluminate, tris(tri-n-propylsilyl)aluminate, tris(triisopropylsilyl)aluminate, tris(tri-n-butylsilyl)aluminate, tris(triisobutylsilyl)aluminate, tris(tri-tert-butylsilyl)aluminate, tris(trimethoxysilyl)aluminate, tris(triethoxysilyl)aluminate, tris(tri-n-propoxysilyl)aluminate, tris(triisopropoxysilyl)aluminate, tris(tri-n-butoxysilyl)aluminate, tris(tri-sec-butoxysilyl)aluminate, tris(tri-tert-butoxysilyl)aluminate, tris(trifluoromethylsilyl)aluminate, tris(trivinylsilyl)aluminate, tris(triethynylsilyl)aluminate Aluminate, tetrakis(trimethylsilyl)zirconate, tetrakis(triethylsilyl)zirconate, tetrakis(tri-n-propylsilyl)zirconate, tetrakis(triisopropylsilyl)zirconate, tetrakis(tri-n-butylsilyl)zirconate, tetrakis(triisobutylsilyl)zirconate, tetrakis(tri-tert-butylsilyl)zirconate, tetrakis(trimethoxysilyl)zirconate, tetrakis(triethoxysilyl)zirconate, tetrakis(tri-n-propoxysilyl)zirconate, tetrakis(triisopropoxysilyl)zirconate, tetrakis(tri-n-butoxysilyl)zirconate, tetrakis(tri-sec-butoxysilyl)zirconate, tetrakis(tri-tert-butoxysilyl)zirconate, tetrakis(trifluoromethylsilyl)zirconate, tetrakis(trivinylsilyl)zirconate, tetrakis(triethynylsilyl)zirconate.

3. The electrolyte additive according to claim 1, characterized in that: The invention also includes an additive C, which is selected from the group consisting of vinylene carbonate, ethylene carbonate, fluoroethylene carbonate, 1,3-propane sultone, 1,3-propylene sultone, vinyl sulfate, tris(trimethylsilane)borate, and tris(trimethylsilane)phosphate.

4. An electrolyte, characterized in that: The electrolyte comprises a lithium salt, an organic solvent and the electrolyte additive according to any one of claims 1 to 3.

5. The electrolyte according to claim 4, characterized in that The content of the additive A is 0.01%-5% of the total weight of the electrolyte, the content of the additive B is 0.01%-10% of the total weight of the electrolyte, and the content of the lithium salt is 6.25-25% of the total weight of the electrolyte.

6. The electrolyte according to claim 4, characterized in that The organic solvent is selected from one or more of ethylene carbonate, propylene carbonate, butylene carbonate, pentyl carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, 1,4-butyrolactone, methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, propyl propionate, and ethyl butyrate.

7. The electrolyte according to claim 4, characterized in that The lithium salt is selected from LiPF6, LiBF4, LiN(SO2F)2, LiClO4, LiAsF6, LiB(C2O4)2, LiBF2C2O4, LiN(SO2R F )2. LiN(SO2F)(SO2R F ) in one or more, wherein R F C n F 2n+1 , n=1-10.

8. A lithium ion battery, characterized in that: The invention comprises a positive electrode sheet, a negative electrode sheet, a separator and the electrolyte according to any one of claims 5 to 7, wherein the separator is arranged between the positive electrode sheet and the negative electrode sheet.

9. The lithium-ion battery according to claim 8, characterized in that: The positive electrode sheet includes a positive electrode current collector and a positive electrode active paste layer located on the positive electrode current collector. The positive electrode active paste layer includes a positive electrode active material, and the positive electrode active material is selected from one or more of LiCoO2, LiNi x A y B (1-x-y) O2, LiMPO4, Li 1-x’ Q y’ L z’ C (1-y’-z’) O2, where A and B are each independently selected from one of Co, Al, and Mn, and A and B are different, 0 < x < 1, 0 < y < 1, and x + y < 1; M is selected from one or more of Co, Ni, Fe, Mn, and V, 0 < x' < 1, 0 < y' < 1, 0 < z' < 1, and y' + z' < 1; Q, L, and C are each independently selected from one of Co, Ni, Fe, and Mn, and Q, L, and C are different from each other; the negative electrode sheet includes a negative electrode current collector and a negative electrode active paste layer located on the negative electrode current collector. The negative electrode active paste layer includes a negative electrode active material, and the negative electrode active material is selected from one or more of metallic lithium, natural graphite, artificial graphite, mesocarbon microbeads, hard carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, TiO2-Li4Ti5O 12 , Li-Al alloy, etc.

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