An ionic liquid, a solvent for lithium ion batteries, a lithium ion battery electrolyte, a lithium ion battery, and an electric device

Abstract

The application provides an ionic liquid, a lithium ion battery solvent, a lithium ion battery electrolyte, a lithium ion battery and an electric device, and belongs to the technical field of lithium ion battery manufacturing. The ionic liquid comprises ionic liquid 1 and / or ionic liquid 2, wherein the structural formula of the ionic liquid 1 is as formula I, and the structural formula of the ionic liquid 2 is as formula II. The ionic liquid can exist stably under high-voltage and high-temperature conditions and has relatively high conductivity, so that the corresponding battery has relatively excellent cycle performance when applied under high-voltage and high-temperature conditions, and the problem that the corresponding battery is prone to inflation under high-voltage and high-temperature conditions can be effectively improved.

Description

Technical Field

[0001] This application relates to the field of lithium-ion battery manufacturing technology, and more specifically, to an ionic liquid, a solvent for lithium-ion batteries, a lithium-ion battery electrolyte, a lithium-ion battery, and an electrical device. Background Technology

[0002] Lithium-ion batteries currently dominate the power and energy storage fields, and with technological innovation, efforts are being made to develop lithium-ion batteries that can operate at high voltages (≥4.9V). However, traditional solvents (such as EC, EMC, or DEC) are prone to oxidation and decomposition at high voltages, producing gas and causing severe gas buildup in the corresponding batteries. Based on this, novel fluorinated solvents (such as FEMC, FPC, or FEC) have been proposed. While these fluorinated solvents have high oxidation potentials and can remain stable at high voltages, they suffer from low conductivity and instability at high temperatures, easily decomposing and producing gas, thus affecting the cycle performance of the corresponding batteries under high voltage and high temperature conditions. Therefore, there is an urgent need to develop a new solvent that can remain stable under high voltage and high temperature conditions while also possessing high conductivity. Summary of the Invention

[0003] The purpose of this application is to provide an ionic liquid, a solvent for lithium-ion batteries, a lithium-ion battery electrolyte, a lithium-ion battery, and an electrical device. The ionic liquid can exist stably under high voltage and high temperature conditions and has high conductivity, so that the corresponding battery has excellent cycle performance when used under high voltage and high temperature conditions. At the same time, it can also effectively improve the problem of the corresponding battery easily expanding and bloating under high voltage and high temperature conditions.

[0004] The embodiments of this application are implemented as follows:

[0005] In a first aspect, embodiments of this application provide an ionic liquid, including ionic liquid 1 and / or ionic liquid 2, wherein the structural formula of ionic liquid 1 is as shown in Formula I, and the structural formula of ionic liquid 2 is as shown in Formula II:

[0006]

[0007] In the above technical solution, the ionic liquid has the specific structure described above. The piperidine group in the structure has the advantage of high oxidation potential (i.e., it can exist stably under high voltage). At the same time, the N atom in the piperidine structure can neutralize the acid generated in the electrolyte (helping to improve the problem of decomposition and gas production). Furthermore, difluorooxalate borate and / or tetrafluorooxalate phosphate can form a thermally stable interfacial film on both the positive and negative electrode surfaces (the interfacial film can reduce the direct contact between the ionic liquid and the positive and negative electrodes, also helping to improve the problem of decomposition and gas production), so that the ionic liquid can exist stably under high voltage and high temperature conditions. In addition, the piperidine group in the structure also has the advantage of high conductivity. Therefore, the ionic liquid provided in this application embodiment can exist stably under high voltage and high temperature conditions and has high conductivity, so that the corresponding battery has excellent cycle performance when used under high voltage and high temperature conditions. At the same time, it can also effectively improve the problem of easy gas expansion when the corresponding battery is used under high voltage and high temperature conditions.

[0008] Secondly, embodiments of this application provide a solvent for lithium-ion batteries, including ionic liquids and organic solvents as provided in the first aspect embodiments.

[0009] In the above technical solution, the solvent for lithium-ion batteries contains not only organic solvents but also the ionic liquid provided in the first aspect embodiment. By leveraging the unique advantages of ionic liquids, the solvent for lithium-ion batteries can exist stably under high voltage and high temperature conditions and also have high conductivity. This results in the corresponding battery having superior cycle performance when used under high voltage and high temperature conditions. At the same time, it can also effectively improve the problem of the corresponding battery easily expanding and bloating under high voltage and high temperature conditions.

[0010] In some alternative implementations, the ionic liquid constitutes 30–50% of the solvent by mass.

[0011] In the above technical solution, the mass percentage of ionic liquid in the solvent is limited to a specific range so that the solvent contains a suitable mass percentage of ionic liquid. This results in the battery having better cycle performance when used under high voltage and high temperature conditions, and can also more effectively improve the problem of the battery being prone to gas expansion when used under high voltage and high temperature conditions. At the same time, it can also make the battery have better safety performance.

[0012] In some alternative embodiments, the organic solvent is selected from at least one of fluoroethylene carbonate, difluoroethylene carbonate, trifluoroethyl methyl carbonate, di(2,2,2-trifluoroethyl) carbonate, 3,3,3-trifluoropropylene carbonate, and methyl hexafluoroisopropyl carbonate.

[0013] The above-mentioned technical solutions are applicable to a wide variety of organic solvents, and can provide a large number of feasible solutions, thereby facilitating the promotion and application of the technical solutions provided in this application.

[0014] Thirdly, embodiments of this application provide a lithium-ion battery electrolyte, including the lithium-ion battery solvent, lithium salt, and additives as provided in the second aspect embodiment.

[0015] In the above technical solution, the lithium-ion battery electrolyte includes the lithium-ion battery solvent provided in the second aspect embodiment. Since the solvent contains ionic liquid with a specific structure, the corresponding battery has excellent cycle performance when used under high voltage and high temperature conditions. At the same time, it can also effectively improve the problem of the corresponding battery easily expanding and bloating when used under high voltage and high temperature conditions.

[0016] In some alternative embodiments, the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium bis(fluorosulfonyl)imide, lithium difluorobis(oxalate)phosphate, lithium tetrafluorooxalate phosphate, lithium difluorooxalate borate, lithium bis(trifluoromethylsulfonyl)imide, and lithium bis(oxalate)borate.

[0017] Among the above technical solutions, the technical solutions provided in this application embodiment are applicable to a wide variety of lithium salts and can provide a large number of feasible implementation schemes, thereby facilitating the promotion and application of the technical solutions provided in this application.

[0018] In some alternative implementations, the lithium salt constitutes 10–18% of the electrolyte by mass.

[0019] In the above technical solution, the mass percentage of lithium salt in the electrolyte is limited to a specific range so that the electrolyte has a suitable mass percentage of lithium salt, so that the electrolyte has a better conductivity, and thus the corresponding battery has better cycle performance when used under high voltage and high temperature conditions.

[0020] In some alternative embodiments, the additive is selected from at least one of 1,3-propane sulpholactone, 1,4-butane sulpholactone, propenyl 1,3-sulfonyl lactone, lithium dioxalatoborate, lithium difluorooxalatoborate, lithium tetrafluorooxalatophosphate, lithium difluorooxalatophosphate, tetraethylenesilane, tripropylene phosphate, tetravinyltin, hexamethylene diisocyanate, and difluoropyridine.

[0021] The above-mentioned technical solutions have a wide range of applicable additives and can provide a large number of feasible solutions, which facilitates the promotion and application of the technical solutions provided in this application.

[0022] In some alternative implementations, the additive is present in the electrolyte at a mass percentage of 0.5% to 5%.

[0023] In the above technical solution, the mass percentage of the additive in the electrolyte is limited to a specific range so that the electrolyte has an appropriate mass percentage of additive, so that the corresponding battery has better cycle performance when used under high voltage and high temperature conditions.

[0024] Fourthly, embodiments of this application provide a lithium-ion battery, including a casing, an electrode assembly, and an electrolyte as provided in the third aspect embodiment, wherein the electrode assembly is housed within the casing; and the electrolyte is housed within the casing.

[0025] In the above technical solution, the lithium-ion battery includes the electrolyte provided in the first aspect embodiment. With the unique advantages of the electrolyte, the lithium-ion battery has excellent cycle performance when used under high voltage and high temperature conditions. At the same time, it can also effectively improve the problem of the corresponding battery easily expanding and bloating when used under high voltage and high temperature conditions.

[0026] In some alternative embodiments, the positive electrode active material in the battery positive electrode of the electrode assembly is selected from at least one of lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium nickel manganese oxide, and lithium cobalt oxide.

[0027] The technical solutions provided in the embodiments of this application are applicable to the above-mentioned various positive electrode active material systems, providing more feasible implementation schemes, thereby facilitating the promotion and application of the technical solutions provided in the embodiments of this application.

[0028] In some alternative embodiments, the negative electrode active material in the battery negative electrode assembly is selected from at least one of graphite, soft carbon, hard carbon, silicon, silicon oxides, and silicon-carbon composites.

[0029] The technical solutions provided in the embodiments of this application are applicable to the above-mentioned various negative electrode active material systems, providing more feasible implementation schemes, thereby facilitating the promotion and application of the technical solutions provided in the embodiments of this application.

[0030] Fifthly, embodiments of this application provide an electrical device including a lithium-ion battery as provided in the fourth aspect embodiment. Attached Figure Description

[0031] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1The nuclear magnetic resonance spectrum of ionic liquid 1 provided in Example 1 of this application;

[0033] Figure 2 The nuclear magnetic resonance spectrum of ionic liquid 2 provided in Example 7 of this application;

[0034] Figure 3 A comparison diagram of the oxidation potentials of the electrolytes prepared in Example 5 and Comparative Example 1 provided in this application. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0036] It should be noted that the terms "and / or" in this application, such as "feature 1 and / or feature 2", all refer to the three cases of "feature 1" alone, "feature 2" alone, and "feature 1" plus "feature 2".

[0037] In addition, in the description of this application, unless otherwise stated, "one or more" means two or more; the range of "numerical value a to numerical value b" includes the two endpoints "a" and "b"; and "unit of measurement" in "numerical value a to numerical value b + unit of measurement" represents the "unit of measurement" of both "numerical value a" and "numerical value b".

[0038] The following is a detailed description of an ionic liquid, a solvent for lithium-ion batteries, a lithium-ion battery electrolyte, a lithium-ion battery, and an electrical device according to embodiments of this application.

[0039] In a first aspect, embodiments of this application provide an ionic liquid, including ionic liquid 1 and / or ionic liquid 2, wherein the structural formula of ionic liquid 1 is as shown in Formula I, and the structural formula of ionic liquid 2 is as shown in Formula II:

[0040]

[0041] In this application, the ionic liquid has the specific structure described above. The piperidine group in the structure has the advantage of a high oxidation potential (i.e., it can exist stably under high voltage). Simultaneously, the nitrogen atom in the piperidine structure can neutralize the acid generated in the electrolyte (helping to improve the problem of decomposition and gas production). Furthermore, difluorooxalate borate and / or tetrafluorooxalate phosphate can form a thermally stable interfacial film on both the positive and negative electrode surfaces (the interfacial film can reduce direct contact between the ionic liquid and the positive and negative electrodes, also helping to improve the problem of decomposition and gas production), enabling the ionic liquid to exist stably under high voltage and high temperature conditions. In addition, the piperidine group in the structure also has the advantage of high conductivity. Therefore, the ionic liquid provided in this application embodiment can exist stably under high voltage and high temperature conditions and also has high conductivity, resulting in superior cycle performance of the corresponding battery when used under high voltage and high temperature conditions. At the same time, it can effectively improve the problem of gas expansion that easily occurs when the corresponding battery is used under high voltage and high temperature conditions.

[0042] To better understand the technical solution, specific preparation processes are explained here.

[0043] The preparation process of ionic liquid 1 includes the following steps:

[0044] 0.1 mol of N-methylpiperidine and 0.1 mol of 1-bromomethane were added to 50 g of acetonitrile under a nitrogen atmosphere and mixed. The mixture was then heated under reflux at 80 °C and stirred for 24 h. After the acetonitrile in the mixture evaporated, an orange solid was obtained. The orange solid was mixed with activated carbon in methanol and stirred overnight, then filtered to obtain a yellow solid. The yellow solid was then transferred to a mixture of ethyl acetate and acetonitrile (volume ratio 1:1) for recrystallization to obtain a white intermediate.

[0045] The white intermediate and lithium difluorooxalate borate (LiDFOB) were mixed in deionized water at a molar ratio of 1:1.1. Then, three times the volume of dichloromethane was added to the mixture to cause it to separate into layers. The dichloromethane phase containing crude ionic liquid 1 was collected. The aqueous phase was recovered by using the same amount (i.e., three times the volume of the aqueous phase) of dichloromethane for two weeks to maximize the yield. The dichloromethane phase containing crude ionic liquid 1 was then washed with deionized water for three weeks, and the dichloromethane was removed by rotary evaporation to obtain crude ionic liquid 1 (the presence of bromide ion impurities in crude ionic liquid 1 was determined by mixing it with AgNO3 / HNO3 solution).

[0046] The crude ionic liquid 1 was diluted in dichloromethane and then purified by transferring it to a chromatographic column packed with alumina. The purified substance was then dried under vacuum at 70°C for 12 hours to obtain ionic liquid 1. The main reaction equation for ionic liquid 1 is as follows:

[0047]

[0048] The only difference between the preparation process of ionic liquid 2 and ionic liquid 1 is that lithium difluorooxalate borate (LiDFOB) is replaced with lithium tetrafluorooxalate phosphate (LiOTFP).

[0049] Secondly, embodiments of this application provide a solvent for lithium-ion batteries, including ionic liquids and organic solvents as provided in the first aspect embodiments.

[0050] In this application, the solvent for lithium-ion batteries contains not only organic solvents but also the ionic liquid provided in the first aspect embodiment. By leveraging the unique advantages of ionic liquids, the solvent for lithium-ion batteries can exist stably under high voltage and high temperature conditions and also has high conductivity. This results in the corresponding battery having superior cycle performance when used under high voltage and high temperature conditions. At the same time, it can also effectively improve the problem of the corresponding battery easily expanding and bloating under high voltage and high temperature conditions.

[0051] As an example, the ionic liquid has a mass percentage of 30% to 50% in the solvent, such as, but not limited to, any one of the mass percentages of 30%, 35%, 40%, 45%, and 50%, or a range between any two.

[0052] In this embodiment, the mass percentage of the ionic liquid in the solvent is limited to a specific range so that the solvent contains a suitable mass percentage of ionic liquid. This results in the battery having better cycle performance when used under high voltage and high temperature conditions, and can also more effectively improve the problem of the battery easily expanding and bloating under high voltage and high temperature conditions. At the same time, it can also make the battery have better safety performance.

[0053] It should be noted that there are no restrictions on the types of organic solvents used; they can be selected and set according to conventional practices in the field.

[0054] As an example, the organic solvent is selected from at least one of fluoroethylene carbonate, difluoroethylene carbonate, trifluoroethyl methyl carbonate, di(2,2,2-trifluoroethyl) carbonate, 3,3,3-trifluoropropylene carbonate, and methyl hexafluoroisopropyl carbonate.

[0055] In this embodiment, the technical solution provided by this application is applicable to a wide variety of organic solvents, and can provide a large number of feasible implementation schemes, thereby facilitating the promotion and application of the technical solution provided by this application.

[0056] It should be noted that, for components in the solvent used in lithium-ion batteries that are not specifically specified or limited, their amounts can be set according to conventional selection in the field.

[0057] Thirdly, embodiments of this application provide a lithium-ion battery electrolyte, including the lithium-ion battery solvent, lithium salt, and additives as provided in the second aspect embodiment.

[0058] In this application, the lithium-ion battery electrolyte includes the lithium-ion battery solvent provided in the second aspect embodiment. Since the solvent contains an ionic liquid with a specific structure, the corresponding battery can have excellent cycle performance when used under high voltage and high temperature conditions. At the same time, it can also effectively improve the problem of the corresponding battery easily expanding and bloating when used under high voltage and high temperature conditions.

[0059] It should be noted that there are no restrictions on the type of lithium salt, and it can be selected and set in accordance with the conventional methods in this field.

[0060] As an example, the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium bis(fluorosulfonyl)imide, lithium difluorobis(oxalate) phosphate, lithium tetrafluorooxalate phosphate, lithium difluorooxalate borate, lithium bis(trifluoromethylsulfonyl)imide, and lithium bis(oxalate) borate.

[0061] In this embodiment, the technical solution provided by this application is applicable to a wide variety of lithium salts, and can provide a large number of feasible implementation schemes, thereby facilitating the promotion and application of the technical solution provided by this application.

[0062] As an example, the lithium salt in the electrolyte is 10% to 18% by mass, for example, but not limited to any one of 10%, 12%, 14%, 16% and 18% by mass, or any range between two of them.

[0063] In this embodiment, the mass percentage of lithium salt in the electrolyte is limited to a specific range so that the electrolyte has a suitable mass percentage of lithium salt, which in turn gives the electrolyte excellent conductivity and thus gives the corresponding battery excellent cycle performance when used under high voltage and high temperature conditions.

[0064] It should be noted that there are no restrictions on the types of additives; they can be selected and set in accordance with the conventions in this field.

[0065] As an example, the additive is selected from at least one of 1,3-propane sulpholactone, 1,4-butane sulpholactone, propenyl 1,3-sulfonyl lactone, lithium dioxalatoborate, lithium difluorooxalatoborate, lithium tetrafluorooxalatophosphate, lithium difluorooxalatophosphate, tetraethylenesilane, tripropylene phosphate, tetravinyltin, hexamethylene diisocyanate, and difluoropyridine.

[0066] In this embodiment, the technical solution provided by this application is applicable to a wide variety of additives, and can provide a large number of feasible implementation schemes, thereby facilitating the promotion and application of the technical solution provided by this application.

[0067] As an example, the additive is present in the electrolyte at a mass percentage of 0.5% to 5%, for example, but not limited to any one of 0.5%, 1%, 2%, 3%, 4% and 5% or a range between any two.

[0068] In this embodiment, the mass percentage of the additive in the electrolyte is limited to a specific range so that the electrolyte contains an additive with a suitable mass ratio, thereby enabling the corresponding battery to have superior cycle performance when used under high voltage and high temperature conditions.

[0069] It should be noted that the components and their amounts in the lithium-ion battery electrolyte that are not specifically specified or limited can be set according to conventional selection in the field.

[0070] Fourthly, embodiments of this application provide a lithium-ion battery, including a casing, an electrode assembly, and an electrolyte as provided in the third aspect embodiment, wherein the electrode assembly is housed within the casing; and the electrolyte is housed within the casing.

[0071] In this application, the lithium-ion battery includes the electrolyte provided in the first aspect embodiment. With the unique advantages of the electrolyte, the lithium-ion battery has superior cycle performance when used under high voltage and high temperature conditions.

[0072] As an example, in the positive electrode of the battery electrode assembly, the positive electrode active material is selected from at least one of lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium nickel manganese oxide, and lithium cobalt oxide.

[0073] In this embodiment, the technical solution provided by the present application can be applied to the above-mentioned various positive electrode active material systems, providing more feasible implementation schemes, thereby facilitating the promotion and application of the technical solution provided by the present application.

[0074] As an example, in the negative electrode of the battery electrode assembly, the negative electrode active material is selected from at least one of graphite, soft carbon, hard carbon, silicon, silicon oxides and silicon-carbon composites.

[0075] In this embodiment, the technical solution provided by the present application can be applied to the above-mentioned various negative electrode active material systems, providing more feasible implementation schemes, thereby facilitating the promotion and application of the technical solution provided by the present application.

[0076] It should be noted that for functional components in lithium-ion batteries that are not specifically described or limited, they can be set according to the conventional selection in this field.

[0077] Fifthly, embodiments of this application provide an electrical device including a lithium-ion battery as provided in the fourth aspect embodiment.

[0078] It should be noted that there are no restrictions on the type of electrical equipment, such as mobile phones, portable devices, laptops, electric vehicles, electric cars, ships, electric aircraft, spacecraft, electric toys, energy storage devices, and power tools.

[0079] The features and performance of this application will be further described in detail below with reference to the embodiments.

[0080] Example

[0081] The preparation method of ionic liquid 1 includes the following steps:

[0082] 0.1 mol of N-methylpiperidine and 0.1 mol of 1-bromomethane were added to 50 g of acetonitrile under a nitrogen atmosphere and mixed. The mixture was then heated under reflux at 80 °C and stirred for 24 h. After the acetonitrile in the mixture evaporated, an orange solid was obtained. The orange solid was mixed with activated carbon in methanol and stirred overnight, then filtered to obtain a yellow solid. The yellow solid was then transferred to a mixture of ethyl acetate and acetonitrile (volume ratio 1:1) for recrystallization to obtain a white intermediate.

[0083] A white intermediate and lithium difluorooxalate borate (LiDFOB) were mixed in deionized water at a molar ratio of 1:1.1. Then, three times the volume of dichloromethane was added to the mixture to cause it to separate into layers. The dichloromethane phase containing crude ionic liquid 1 was collected, while the aqueous phase was recovered by using the same amount (i.e., three times the volume of the aqueous phase) of dichloromethane for two weeks to maximize the yield. The dichloromethane phase containing crude ionic liquid 1 was then washed with deionized water for three weeks, and the dichloromethane was removed by rotary evaporation to obtain crude ionic liquid 1.

[0084] The crude ionic liquid 1 was diluted in dichloromethane and then transferred to a chromatographic column packed with alumina for purification. The purified substance was then dried at 70°C for 12 hours under vacuum to obtain ionic liquid 1.

[0085] The preparation method of ionic liquid 2 includes the following steps:

[0086] 0.1 mol of N-methylpiperidine and 0.1 mol of 1-bromomethane were added to 50 g of acetonitrile under a nitrogen atmosphere and mixed. The mixture was then heated under reflux at 80 °C and stirred for 24 h. After the acetonitrile in the mixture evaporated, an orange solid was obtained. The orange solid was mixed with activated carbon in methanol and stirred overnight, then filtered to obtain a yellow solid. The yellow solid was then transferred to a mixture of ethyl acetate and acetonitrile (volume ratio 1:1) for recrystallization to obtain a white intermediate.

[0087] The white intermediate and lithium tetrafluorooxalate phosphate were mixed in deionized water at a molar ratio of 1:1.1. Then, three times the volume of dichloromethane was added to the mixture to cause it to separate into layers. The dichloromethane phase containing crude ionic liquid 2 was collected, while the aqueous phase was recovered by using the same amount (i.e., three times the volume of the aqueous phase) of dichloromethane for two weeks to maximize the yield. The dichloromethane phase containing crude ionic liquid 2 was then washed with deionized water for three weeks, and the dichloromethane was removed by rotary evaporation to obtain crude ionic liquid 2.

[0088] The crude ionic liquid 2 was diluted in dichloromethane and then transferred to a chromatographic column packed with alumina for purification. The purified substance was then dried at 70°C for 12 hours under vacuum to obtain ionic liquid 2.

[0089] The prepared ionic liquid 1 or ionic liquid 2, trifluoroethyl methyl carbonate (FEMC), and fluoroethylene carbonate (FEC) are mixed in a mass ratio of 2:70:28 to obtain a solvent for lithium-ion batteries. Then, additives (tetravinylsilane, propylene 1,3-sulfonyl lactone, and lithium difluorooxalate borate) and lithium salt (lithium hexafluoroborate) are added to the solvent and mixed to obtain an electrolyte. In the electrolyte, the mass percentages of solvent, tetravinylsilane, propylene 1,3-sulfonyl lactone, lithium difluorooxalate borate, and lithium salt are 85.7:0.5:0.3:0.5:13, that is, the mass percentages of solvent:additive:lithium salt in the electrolyte are 85.7:1.3:13.

[0090] The composition and amount of lithium salt and additives in the subsequent embodiments and comparative examples are the same, the only difference being the composition of the solvent, as detailed in Table 1.

[0091] Table 1

[0092] sample Ionic liquid 1 (%) Ionic liquid 2 (%) FEMC (%) FEC (%) Example 1 5 — 70 25 Example 2 10 — 70 20 Example 3 20 — 70 10 Example 4 30 — 70 0 Example 5 50 — 50 0 Example 6 80 — 20 0 Example 7 — 20 70 10 Example 8 — 30 70 0 Example 9 — 50 50 0 Comparative Example 1 — — 50 50 Comparative Example 2 — — 70 30

[0093] It should be noted that "—" indicates no addition.

[0094] Experimental Example 1

[0095] The structure of ionic liquids has been determined.

[0096] Test method:

[0097] The structures of the ionic liquids prepared in Examples 1 and 7 were tested using a nuclear magnetic resonance spectrometer (model: Bruker 400MHz). The specific parameters are as follows: deuterated acetonitrile was used as the solvent, tetramethylsilane was used as the internal standard (δ = 0 ppm), and the compound structures were confirmed by hydrogen nuclear magnetic resonance (1H NMR).

[0098] For the structural determination of ionic liquid 1: The structure of the ionic liquid prepared in Example 1 was tested using a nuclear magnetic resonance spectrometer (model: Bruker 400MHz), and the test results are shown in [the table below]. Figure 1 ,Depend on Figure 1 It can be seen that at the position δ = 3.27 (s, 3H), there is a single peak with 3 H atoms, representing the N-linked CH3 group N-CH3; at the position δ = 3.24 (t, 2H), there are 2 H atoms, splitting into a triplet, representing the N-linked CH2 group N-(CH2)3; at the position δ = 2.98 (s, 2H), there is a single peak with 2 H atoms, representing CH2; at the position near δ = 1.78 (t, 4H), there are 4 H atoms, splitting into a triplet, representing N-(CH2CH2)3; at the positions δ = 1.73~1.61 (m, 2H), there are 2 hydrogen atoms, splitting into multiple peaks, representing multiple symmetrical CH2 groups; at the position δ = 0.91 (t, 3H), there are 3 hydrogen atoms, splitting into a triplet, representing CH3 groups; thus, it is proven that the structural formula of the prepared ionic liquid 1 is Formula I.

[0099] For the structural determination of ionic liquid 2: The structure of the ionic liquid prepared in Example 7 was tested using a nuclear magnetic resonance spectrometer (model: Bruker 400MHz). The test results are shown in […]. Figure 2 ,Depend on Figure 2 It can be seen that at the position δ=3.30(s, 3H), there is a single peak with 3 H atoms, representing the N-linked CH3 group N-CH3; at the position δ=3.22(t, 2H), there are 2 H atoms, splitting into a triplet, representing the N-linked CH2 group N-(CH2)3; at the positions δ=1.8~1.70(m, 2H), there are 2 hydrogens, splitting into a multiplet, representing multiple symmetrical CH2 groups; at the position δ=1.60(d, 2H), there are 2 hydrogens, a doublet, representing multiple symmetrical CH2 groups; at the position δ=0.95(t, 3H), there are 3 hydrogens, splitting into a triplet, representing CH3 groups; thus, it is proven that the structural formula of the prepared ionic liquid 2 is formula II.

[0100] Experimental Example 2

[0101] Oxidation potential test of electrolyte

[0102] Test method: Platinum sheet was used as working electrode and lithium sheet as counter electrode. The platinum electrode electrolytic cell was assembled and the electrolytes of Example 5 and Comparative Example 1 were added respectively. LSV test was performed using an electrochemical workstation with a scanning voltage of 3.0 to 7.0 V.

[0103] Test results are available for reference. Figure 3 ,Depend on Figure 3It can be seen that the oxidation potential in Example 5 is significantly higher than that in Comparative Example 1, indicating that replacing part of the conventional organic solvent in the solvent with an ionic liquid of a specific structure provided in the embodiments of this application can increase the oxidation potential of the solvent, thus making it more advantageous for application under high voltage.

[0104] Experimental Example 3

[0105] Electrical performance testing

[0106] Test method:

[0107] First, the lithium-ion battery electrolytes prepared in Examples 1-9 and Comparative Examples 1-2 were numbered, and then the conductivity of each electrolyte was tested. Then, each electrolyte was assembled into a battery, and the capacity retention rate of each battery sample after 500 cycles at 25°C, the capacity retention rate after 500 cycles at 60°C, the expansion rate after 7 days of storage at 60°C, and the safety performance were tested and statistically analyzed in Table 2.

[0108] The battery assembly is carried out according to the following method:

[0109] S1 was mixed with LiNi at a mass ratio of 96.8:2:1.2 0.5 Mn 1.5 O4 (positive electrode active material), conductive carbon black (conductive agent), and polyvinylidene fluoride (binder) are dispersed in N-methyl-2-pyrrolidone to obtain a positive electrode slurry. Then, the positive electrode slurry is uniformly coated on both sides of an aluminum foil. After drying, rolling, and vacuum drying, aluminum leads are welded on using an ultrasonic welding machine to obtain a positive electrode sheet with a thickness of 125 μm.

[0110] S2 is mixed with graphite (negative electrode active material), conductive carbon black (conductive agent), styrene-butadiene rubber and carboxymethyl cellulose (binder) in a mass ratio of 95:1.5:1.5:2 and dispersed in deionized water to obtain a negative electrode slurry. Then, the negative electrode slurry is coated on both sides of a copper foil. After drying, rolling and vacuum drying, nickel leads are welded on using an ultrasonic welding machine to obtain a negative electrode sheet with a thickness of 125μm.

[0111] S3 prepares a bare cell by winding the prepared positive electrode sheet, negative electrode sheet and PE ceramic separator. Then, the bare cell, the casing and the electrolyte group prepared in Examples 1-9 and Comparative Examples 1-2 are injected into the dried battery. After encapsulation, standing, formation, shaping and capacity testing, the battery is assembled.

[0112] The testing procedures for the relevant electrical properties are as follows:

[0113] (1) Conductivity test:

[0114] Take 50g of electrolyte and put it into a beaker. Then transfer the beaker containing the electrolyte to a 25℃ constant temperature water bath and keep it at 25℃. Measure the conductivity using a conductivity meter.

[0115] (2) Battery capacity retention test at 25°C for 500 cycles:

[0116] The battery was placed at 25°C and charged and discharged at a current of 0.5C within the charge and discharge voltage range of 3.5 to 4.9V. The discharge capacity of the 500th cycle was recorded.

[0117] (3) Battery capacity retention test at 60°C for 100 cycles:

[0118] The battery was placed at 60°C and charged and discharged at a current of 0.5C within the charge and discharge voltage range of 3.5 to 4.9V. The discharge capacity of the 500th cycle was recorded.

[0119] (4) Battery expansion rate test after 7 days of storage at 60℃:

[0120] Charge the battery at 25℃ with a constant current of 0.5C to 4.9V, then charge it at a constant voltage of 4.9V until the cutoff current is 0.05C. Remove the battery and measure its initial thickness as T1 using a thickness tester. Then transfer the battery to 60℃ and leave it for 7 days. Measure its thickness after 7 days using a thickness tester as T2.

[0121] The calculation formula is as follows:

[0122] 500-cycle capacity retention (%) = (500-cycle discharge capacity / 1-cycle discharge capacity) × 100%.

[0123] Expansion rate (%) after 7 days of storage at 60℃ = (T2-T1) / T1×100%.

[0124] (5) Battery safety performance nail penetration test:

[0125] Charge the battery at 25℃ with a constant current of 0.5C to 4.9V, then charge it at a constant voltage of 4.9V until the cutoff current is 0.05C. Remove the battery and fix it on a special needle-piercing device. Use a high-temperature resistant steel needle with a diameter of 5mm (the needle tip has a conical angle of 45°~50°, the surface of the needle is smooth, and there is no rust, oxide layer or oil stains) to penetrate the battery from a direction perpendicular to the battery plates at a speed of 25mm / s. The penetration position is close to the geometric center of the pierced surface. The steel needle stays in the battery and is observed for 1 hour.

[0126] Table 2

[0127]

[0128]

[0129] Referring to Table 2, the test results of Examples 1-9 and Comparative Examples 1-2 show that replacing part of the conventional organic solvent in the solvent with the ionic liquid 1 or ionic liquid 2 with a specific structure provided in the embodiments of this application helps to improve the conductivity of the corresponding solvent. At the same time, it can also enable the corresponding battery to have better cycle performance when used under high voltage and high temperature conditions, and can also effectively improve the problem of the corresponding battery being prone to gas expansion when used under high voltage and high temperature conditions.

[0130] The test results of Examples 1 to 6 show that limiting the amount of ionic liquid in the solvent to a specific range of 30% to 50% helps to better improve the conductivity of the corresponding solvent. At the same time, it can also make the corresponding battery have better cycle performance when used under high voltage and high temperature conditions, and can also more effectively improve the problem of the corresponding battery being prone to gas expansion when used under high voltage and high temperature conditions.

[0131] The test results of Examples 1 to 9 show that when the mass percentage of ionic liquid 1 or ionic liquid 2 in the solvent exceeds 30%, the safety performance of the corresponding battery under high voltage and high temperature conditions can be effectively improved.

[0132] The test results of Examples 3-5 and Examples 7-9 show that the effects of ionic liquid 1 and ionic liquid 2 are basically equivalent, and it is possible to add only one of them or both of them to the solvent at the same time.

[0133] The embodiments described above are some, but not all, of the embodiments of this application. The detailed description of the embodiments of this application is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

Claims

1. A lithium-ion battery electrolyte, characterized in that, It includes solvents for lithium-ion batteries, lithium salts, and additives, wherein the solvent for lithium-ion batteries includes ionic liquid 2 and an organic solvent, and the structural formula of ionic liquid 2 is as shown in Formula II: Formula II.

2. The lithium-ion battery electrolyte according to claim 1, characterized in that, The ionic liquid accounts for 30-50% by mass in the solvent used in lithium-ion batteries.

3. The lithium-ion battery electrolyte according to claim 2, characterized in that, The organic solvent is selected from fluoroethylene carbonate, difluoroethylene carbonate, trifluoroethyl methyl carbonate, and di(2,2,2) fluorocarbonate. Trifluoroethyl carbonate, 3,3,3 At least one of trifluoropropylene carbonate and methyl hexafluoroisopropyl carbonate.

4. The lithium-ion battery electrolyte according to any one of claims 1 to 3, characterized in that, The lithium salt is selected from at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium bis(fluorosulfonyl)imide, lithium difluorobis(oxalate) phosphate, lithium tetrafluorooxalate phosphate, lithium difluorooxalate borate, lithium bis(trifluoromethylsulfonyl)imide, and lithium bis(oxalate) borate.

5. The lithium-ion battery electrolyte according to claim 4, characterized in that, The lithium salt in the electrolyte has a mass percentage of 10-18%.

6. The lithium-ion battery electrolyte according to any one of claims 1 to 3, characterized in that, The additive is selected from 1,3 Propanesulfonyl lactone, 1,4 Butanesulfonyl lactone, propenyl 1,3 At least one of sulfonyl lactone, lithium dioxalate borate, lithium difluorooxalate borate, lithium tetrafluorooxalate phosphate, lithium difluorooxalate phosphate, tetraethylenesilane, tripropylene phosphate, tetravinyltin, hexamethylene diisocyanate, and difluoropyridine.

7. The lithium-ion battery electrolyte according to claim 6, characterized in that, The additive is present in the electrolyte at a mass percentage of 0.5-5%.

8. A lithium-ion battery, characterized in that, include: case; An electrode assembly, the electrode assembly being housed within the housing; as well as The electrolyte as described in any one of claims 1 to 7, wherein the electrolyte is contained within the housing.

9. The lithium-ion battery according to claim 8, characterized in that, In the positive electrode of the electrode assembly, the positive electrode active material is selected from at least one of lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium nickel manganese oxide, and lithium cobalt oxide.

10. The lithium-ion battery according to claim 8, characterized in that, In the negative electrode of the electrode assembly, the negative electrode active material is selected from at least one of graphite, soft carbon, hard carbon, silicon, silicon oxide, and silicon-carbon composite.

11. An electrical appliance, characterized in that, Including the lithium-ion battery as described in any one of claims 8 to 10.

Images