Non-aqueous electrolyte and lithium ion battery

Abstract

The application provides a non-aqueous electrolyte and a lithium ion battery. The non-aqueous electrolyte comprises a lithium salt, a non-aqueous organic solvent, a compound A shown in structural formula I and a compound B shown in structural formula II. Wherein R1 and R2 are each independently selected from halogen, a substituted or unsubstituted C1-C6 hydrocarbon group, a CN-containing group or an O-containing group, and R3 and R4 are each independently selected from halogen, a substituted or unsubstituted C1-C6 hydrocarbon group, a CN-containing group, an O-containing group or a ketone-containing group. The SEI film formed by the synergistic effect of the compound A and the compound B has better toughness, so that the electrochemical comprehensive performance of the lithium ion battery is improved.

Description

TECHNICAL FIELD

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

[0002] With the development of transportation and the concept of carbon neutralization, the demand for lithium ion batteries in the field of electric vehicles (EV) has increased dramatically, and there is an urgent need for good performance in terms of energy and power density. At present, the mainstream development route of electric vehicle lithium ion batteries is nickel-cobalt-manganese ternary material combined with silicon-carbon negative electrode. The lithium ion battery with this combination has high energy and power.

[0003] Although the nickel-cobalt-manganese ternary material has advantages such as moderate cost and high specific capacity, it also has some problems, such as poor high-rate stability, poor high-voltage cycle stability, cation mixing, poor high-temperature performance, etc. Moreover, the silicon-carbon negative electrode has a volume expansion of 300% during high-voltage charging and discharging, which causes continuous regeneration of the electrode-electrolyte interface and continuous consumption of the electrolyte, resulting in rapid performance degradation of the battery.

[0004] In addition, as the application range of lithium ion batteries becomes more and more extensive, higher requirements are put forward for the cycle life of lithium ion batteries, especially at high voltage. In order to meet the cycle life requirements of nickel-cobalt-manganese ternary material combined with silicon-carbon negative electrode at high voltage, it is found that a passivation layer, i.e. SEI film, is usually formed on the surface of the negative electrode film during the formation process of the lithium ion battery. The ideal SEI film is dense and stable, which can inhibit further side reactions between the electrode active material and the electrolyte, reduce the consumption of active materials and electrolyte during use, and inhibit the formation of lithium dendrites, thereby improving the cycle performance of the secondary battery.

[0005] Therefore, it is urgent to develop a new non-aqueous electrolyte to form an ideal SEI film to improve the cycle and storage performance of high-voltage lithium ion batteries. SUMMARY

[0006] The purpose of the present application is to provide a non-aqueous electrolyte and a lithium ion battery, wherein the compound A and the compound B of the non-aqueous electrolyte can form an SEI film with better toughness, thereby improving the electrochemical comprehensive performance of the lithium ion battery.

[0007] To achieve the above-mentioned purpose, the present application provides a non-aqueous electrolyte, which comprises a lithium salt, a non-aqueous organic solvent, a compound A as shown in structural formula I and a compound B as shown in structural formula II, wherein R1, R2 are each independently selected from halogen, substituted or unsubstituted C1-C6 hydrocarbon group, CN-containing group or O-containing group, R3, R4 are each independently selected from halogen, substituted or unsubstituted C 11a C1-C6 hydrocarbon group, a CN-containing group, an O-containing group, or a ketone-containing group.

[0008]

[0009] In the electrolyte of the present application, the compound B shown in structural formula II has a bicyclic ether structure, and in the initial formation process, an oxygen-containing polymer is formed at the electrode-electrolyte interface, which has high lithium ion transmission characteristics and can improve the low-temperature and fast-charging performance of the lithium ion battery. However, the oxygen-containing polymer is easily dissolved in the conventional carbonate, resulting in the loss of the interface, the intensification of the electrode-electrolyte side reaction, and the deterioration of the battery performance. The addition of the compound A shown in structural formula I has relatively high oxidation resistance and low solubility to the interface formed by the compound B, which ensures the stability of the interface formed by the compound B. At the same time, the compound A forms a good toughness LiF and a sulfur-containing interface at the negative electrode interface, which can improve the toughness of the negative electrode interface generated by the oxygen-containing polymer layer of the compound B and relieve the interface side reaction caused by the expansion of the silicon negative electrode, block the consumption of the electrolyte, and significantly improve the electrochemical performance of the battery.

[0010] In the compound A of the present application, the substituted or unsubstituted C1-C6 hydrocarbon group refers to a C1-C6 hydrocarbon group without substitution or a C1-C6 hydrocarbon group with substitution. Further, R1 and R2 are each independently selected from halogen, C1-C3 alkyl, C2-C3 alkenyl, C2-C3 alkynyl, halogen-substituted C1-C3 alkyl, halogen-substituted C2-C3 alkenyl, or halogen-substituted C2-C3 alkynyl. The halogen can be fluorine, chlorine, bromine, or iodine, preferably fluorine. The C1-C6 hydrocarbon group refers to an alkyl group with a carbon atom number of 1-6, an alkenyl group with a carbon atom number of 2-6, or an alkynyl group with a carbon atom number of 2-6. The C1-C6 hydrocarbon group can be, but is not limited to, methyl, ethyl, propyl, isopropyl, ethenyl, propenyl, ethynyl, or propynyl. The substituent refers to one or more hydrogen atoms in the hydrocarbon group being replaced by other atoms or groups, which can be halogen (such as fluorine, chlorine, bromine, or iodine), hydroxyl, amino, nitro, alkoxy, or aryl, etc. For example, the methyl group can be replaced by a chlorine atom to form a chloromethyl group (-CH2Cl) or replaced by a hydroxyl group to form a hydroxymethyl group (-CH2OH). The CN-containing group refers to a group containing at least -CN, which can be -CN, -CH2CN, or -CH2-CH2-CN. The O-containing group refers to a group containing at least -O-, which can be a branched alkyl ether group or a cyclic ether group.

[0011] In the R3, R4 of the compound B of the present application, the substituted or unsubstituted C1-C6 hydrocarbon group refers to a C1-C6 hydrocarbon group without substitution or a C1-C6 hydrocarbon group with substitution. Further, R3, R4 are each independently selected from halogen, C1-C3 alkyl, C2-C3 alkenyl, C2-C3 alkynyl, halogen-substituted C1-C3 alkyl, halogen-substituted C2-C3 alkenyl, halogen-substituted C2-C3 alkynyl, cyclic ether group or C2-C3 alkanone group. The halogen can be fluorine, chlorine, bromine, iodine, and preferably fluorine. The C1-C6 hydrocarbon group refers to an alkyl group with carbon atom number of 1-6, an alkenyl group with carbon atom number of 2-6 or an alkynyl group with carbon atom number of 2-6. The C1-C6 hydrocarbon group can be, but is not limited to, methyl, ethyl, propyl, butyl, isopropyl, ethenyl, propenyl, ethynyl, propynyl. The substituent refers to one or more hydrogen atoms in the hydrocarbon group being substituted by other atoms or groups, and the substituent can be halogen (such as fluorine, chlorine, bromine, iodine), hydroxyl, amino, nitro, alkoxy or aryl, etc. For example, the methyl group can be substituted by a chlorine atom to form a chloromethyl group (-CH2Cl) or substituted by a hydroxyl group to form a hydroxymethyl group (-CH2OH). The group containing-CN refers to a group containing at least-CN, which can be-CN, -CH2CN or -CH2-CH2-CN. The group containing-O- refers to a group containing at least-O-, which can be a branched alkyl ether group, a branched alkyl ether group or a cyclic ether group. The group containing ketone refers to a group containing at least ketone, which can be a branched alkyl ketone group, a branched alkyl ketone group or a cyclic ketone group.

[0012] As a preferred technical solution, the compound A is selected from at least one of the compound one to the compound four.

[0013]

[0014] As a preferred technical solution, the compound B is selected from at least one of the compound five to the compound eight.

[0015]

[0016] As a preferred technical solution, the mass percentage of the compound A in the non-aqueous electrolyte is 0.1-20.0%, and the mass percentage of the compound A in the non-aqueous electrolyte is 0.1%-5.0%. As an example, the mass percentage of the compound A in the non-aqueous electrolyte can be, but is not limited to, 0.1%, 0.2%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, 6.0%, 7.0%, 8.0%, 9.0%, 10.0%, 11.0%, 12.0%, 13.0%, 14.0%, 15.0%, 16.0%, 17.0%, 19.0%, 20.0%, and the content of the compound A is not limited to the listed values, and other values not listed in the range are also applicable. The mass percentage of the compound B in the non-aqueous electrolyte is 0.1-5.0%. Preferably, the mass percentage of the compound B in the non-aqueous electrolyte is 0.1%-3.0%. As an example, the mass percentage of the compound B in the non-aqueous electrolyte can be, but is not limited to, 0.1%, 0.2%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, and the content of the compound B is not limited to the listed values, and other values not listed in the range are also applicable.

[0017] As a preferred technical solution, the lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium bisfluorosulfonylimide (LiFSI), lithium bis-trifluoromethylsulfonylimide (LiTFSI), lithium methylsulfate (LiCH3SO3), lithium trifluoromethylsulfate (LiCF3SO3), lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiDFOB), lithium difluorophosphate (LiPO2F2), lithium difluorobis(oxalato)phosphate (LiDFBP), and lithium tetraphenylborate (LiCHB).

[0018] As a preferred technical solution, the mass percentage of the lithium salt in the non-aqueous electrolyte is 10%-25%. Preferably, the mass percentage of the lithium salt in the non-aqueous electrolyte is 10-18%. As an example, the mass percentage of the lithium salt in the non-aqueous electrolyte is 10%, 12%, 14%, 15%, 16%, 18%, 20%, 23%, 25%, and the content of the lithium salt is not limited to the listed values, and other values not listed in the range are also applicable.

[0019] As a preferred technical solution, the non-aqueous organic solvent is at least one of a carbonate compound, a carboxylic acid ester compound, and an ether compound. Further, the carbonate compound includes but is not limited to a cyclic carbonate and / or a chain carbonate, wherein the cyclic carbonate can be but is not limited to ethylene carbonate (EC), propylene carbonate (PCA), and butylene carbonate (BC). The chain carbonate includes but is not limited to dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), and propylene carbonate (PC). The carboxylic acid ester compound includes but is not limited to a cyclic carboxylic acid ester and / or a chain carboxylic acid ester. The cyclic carboxylic acid ester can specifically include but is not limited to at least one of gamma-butyrolactone (GBL), gamma-valerolactone (GVL), and delta-valerolactone (DVL). The chain carboxylic acid ester includes but is not limited to methyl acetate (MA), ethyl acetate (EA), propyl acetate (EP), butyl acetate (BAC), propyl propionate (PP), and butyl propionate (PRB). The ether compound includes a cyclic ether and / or a chain ether. The cyclic ether can specifically include but is not limited to at least one of 1,3-dioxolane (DOL), 1,4-dioxane (DX), crown ether, tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-CH3-THF), and 2-trifluoromethyltetrahydrofuran (2-CF3-THF). The chain ether can specifically include but is not limited to dimethoxymethane (DMM), diethoxymethane (DEM), ethoxymethoxymethane (DCE), ethylene glycol di-n-butyl ether (EDB), and diethylene glycol dimethyl ether (DEGME).

[0020] In another aspect, the present application provides a lithium ion battery with a charging voltage of 4.45 V, comprising a positive electrode material, a negative electrode material, and a non-aqueous electrolyte. The application of the aforementioned non-aqueous electrolyte to the lithium ion battery can effectively improve the cycle performance of the lithium ion battery at high voltage.

[0021] As a preferred technical solution, the positive electrode material includes lithium nickel cobalt manganese oxide, and the chemical formula of the lithium nickel cobalt manganese oxide is LiNi x Co y Mn (1-x-y) M z O2, wherein 0.1≤x<0.9, x+y<1, 0≤z<0.08, and M is at least one of Al, Mg, Zr, and Ti.

[0022] As a preferred technical solution, the negative electrode comprises a negative electrode material, and the negative electrode material comprises at least one of an alkali metal, a carbon-based material, a silicon-based material, and a tin-based material. The alkali metal can comprise lithium metal or a lithium alloy, and the lithium alloy can specifically be at least one of a lithium-silicon alloy, a lithium-sodium alloy, a lithium-potassium alloy, a lithium-aluminum alloy, a lithium-tin alloy, and a lithium-indium alloy. The carbon-based material can comprise at least one of graphite, hard carbon, soft carbon, graphene, and mesocarbon microbeads. The silicon-based material can comprise at least one of elemental silicon, silicon oxide, silicon-carbon composite, and a silicon alloy material. The tin-based negative electrode can comprise at least one of elemental tin, tin-carbon, tin oxide, and a tin alloy material. DETAILED DESCRIPTION

[0023] For the purpose of better illustrating the object, technical solution and beneficial effects of the present application, the present application will be further described below in combination with specific examples. It should be noted that the following description of the method is a further explanation and description of the present application, and should not be regarded as a limitation of the present application.

[0024] If specific conditions are not specified in the examples and comparative examples, the preparation can be performed according to conventional conditions or conditions recommended by the manufacturer. If the reagents or instruments used are not specified by the manufacturer, they are all conventional products that can be obtained on the market.

[0025] Example 1

[0026] 1.1 Preparation of electrolyte:

[0027] In a glove box filled with nitrogen (O2<1 ppm, H2O<1 ppm), a mixed solvent obtained by uniformly mixing diethyl carbonate (DEC), propylene carbonate (PC), ethyl methyl carbonate (EMC), and ethyl acetate (EA) in a mass ratio of 2:2:2:1 was used as an organic solvent, and then compound A and compound B were added to obtain a mixed solution. The mixed solution was sealed, packaged, and frozen in a quick-freezing chamber (-4°C) for 2 h, and then taken out. In a glove box filled with nitrogen (O2<1 ppm, H2O<1 ppm), lithium salt was slowly added to the mixed solution, and the mixture was uniformly mixed to prepare the electrolyte.

[0028] 1.2 Preparation of positive electrode sheet:

[0029] The ternary material LiNi 0.5 Co 0.2 Mn 0.3 Zr 0.03 O2, a conductive agent SuperP, a binder PVDF, and carbon nanotubes (CNT) were uniformly mixed in a mass ratio of 96.5:1.5:1:1 to prepare a lithium ion battery positive electrode slurry with a certain viscosity, which was coated on a current collector aluminum foil, and the coating amount was 324 g / m 2After drying at 85℃, cold pressing is performed; then edge cutting, cutting, and slitting are performed, and after slitting, drying is performed under vacuum conditions at 85℃ for 4h, tab welding is performed, and a positive electrode sheet of a lithium ion battery that meets the requirements is prepared.

[0030] 1.3 Preparation of a negative electrode sheet:

[0031] After mixing artificial graphite and silicon at a mass ratio of 90:10, a slurry is prepared with a ratio of conductive agent Super P, thickening agent CMC, and adhesive SBR (styrene-butadiene rubber emulsion) at a mass ratio of 95:1.5:1.0:2.5, and the mixture is uniformly mixed. After coating the mixed slurry on both sides of a copper foil, drying and rolling are performed to obtain a negative electrode sheet, and a negative electrode sheet of a lithium ion battery that meets the requirements is prepared.

[0032] 1.4 Preparation of a lithium ion battery:

[0033] The positive electrode sheet, negative electrode sheet, and separator prepared according to the above process are subjected to a lamination process to produce a lithium ion battery with a thickness of 4.7mm, a width of 55mm, and a length of 60mm. Vacuum baking is performed at 75℃ for 10h, and the above electrolyte is injected. After standing for 24h, constant current charging is performed at 0.1C (180mA) to 4.45V, and then constant voltage charging is performed at 4.45V until the current decreases to 0.05C (90mA). Then, discharging is performed at 0.2C (180mA) to 3.0V, and the charging and discharging process is repeated twice. Finally, the battery is charged at 0.2C (180mA) to 3.8V, and the preparation of the lithium ion battery is completed.

[0034] The composition and content of the electrolyte of Examples 1-16 and Comparative Examples 1-4 are shown in Table 1. The preparation processes of the lithium ion battery electrolyte, positive electrode sheet, negative electrode sheet, and lithium ion battery of Examples 2-16 and Comparative Examples 1-4 are the same as those of Example 1.

[0035] Table 1 Composition of the electrolyte of the examples and comparative examples

[0036]

[0037] The lithium ion batteries prepared in Examples 1-12 and Comparative Examples 1-3 are subjected to high-temperature cycle performance testing, room-temperature cycle performance testing, low-temperature and fast-charging performance testing under the following conditions, and the results are shown in Table 2.

[0038] (1) Room-temperature cycle performance testing

[0039] Under room-temperature (25℃) conditions, the lithium ion battery is subjected to one cycle of 1.0C / 1.0C charging and discharging (battery discharge capacity is C0), and the upper limit voltage is 4.45V. Then, the battery is subjected to 1.0C / 1.0C charging and discharging for 500 cycles under room-temperature conditions (battery discharge capacity is C1), and the capacity retention rate is calculated.

[0040] Capacity retention rate = (C1 / C0) * 100%

[0041] (2) High temperature cycle test

[0042] The lithium ion battery was subjected to 1.0C / 1.0C charge and discharge (battery discharge capacity was C0) once at an over-high temperature (45°C) with an upper limit voltage of 4.45V, and then subjected to 1.0C / 1.0C charge and discharge 400 times (battery discharge capacity was C1) at a high temperature (45°C), and the capacity retention rate was calculated.

[0043] Capacity retention rate = (C1 / C0) * 100%

[0044] (3) Normal temperature fast charging performance test

[0045] The lithium ion battery was subjected to 1.0C / 1.0C charge and discharge (battery discharge capacity was C0) once at a normal temperature (25°C) with an upper limit voltage of 4.45V, and then subjected to 4.0C / 1.0C charge and discharge 500 times (battery discharge capacity was C1) at a normal temperature, and the capacity retention rate was calculated.

[0046] Capacity retention rate = (C1 / C0) * 100%

[0047] (4) High temperature fast charging performance test

[0048] The lithium ion battery was subjected to 1.0C / 1.0C charge and discharge (battery discharge capacity was C0) once at an over-high temperature (45°C) with an upper limit voltage of 4.45V, and then subjected to 4.0C / 1.0C charge and discharge 400 times (battery discharge capacity was C1) at a normal temperature, and the capacity retention rate was calculated.

[0049] Capacity retention rate = (C1 / C0) * 100%

[0050] (5) Low temperature performance test

[0051] The lithium ion battery was subjected to 0.5C / 0.5 charge and discharge (battery cutoff voltage was 3.0V, and discharge capacity was C0) once at a normal temperature (25°C) with an upper limit voltage of 4.4V (cutoff current 0.05C). Then the battery was charged to 4.4V (cutoff current 0.05C) at a normal temperature (25°C) at 0.5C, and then the battery was transferred to a condition of -20°C and left for 4h, and discharged to 3.0V at 0.5C, and the discharge capacity was C1, and the capacity retention rate was calculated.

[0052] Capacity retention rate = (C1 / C0) * 100%

[0053] Table 2 Test results of lithium ion battery performance of each example and comparative example

[0054]

[0055]

[0056] From the results of Table 2, the electrochemical comprehensive performance of the lithium ion batteries of Examples 1-12 is better, because Examples 1-12 include compounds such as compound A and compound B, compound B has a bicyclic ether structure, and during the initial formation process, an oxygen-containing polymer is formed at the electrode electrolyte interface, the polymer has high lithium ion transport properties, and the low temperature and fast charging performance of the lithium ion battery is improved, but because the oxygen-containing polymer is easily dissolved in conventional carbonate, the interface is lost, the electrode electrolyte side reaction is intensified, and the battery performance is deteriorated. By adding compound A as shown in structural formula I, compound A has relatively high oxidation resistance and low solubility to the interface formed by compound B, which ensures the stability of the interface formed by compound B. At the same time, compound A forms a good toughness LiF and sulfur-containing interface at the negative electrode interface, which can improve the toughness of the negative electrode interface produced by the oxygen-containing polymer layer of compound B to relieve the interface side reaction caused by the expansion of the silicon negative electrode, block the consumption of the electrolyte, and significantly improve the performance of the battery. In Comparative Examples 2 and 3, only compound A or compound B is used, and the complementary synergistic effect cannot be produced, so the cycle and low temperature and fast charging performance cannot be improved at the same time.

[0057] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application and not to limit the scope of protection of the present application, although the present application has been described in detail with reference to the preferred embodiments, but it is not limited to the examples listed in the embodiments, and those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present application.

Claims

1. A non-aqueous electrolyte, comprising a lithium salt, a non-aqueous organic solvent, a compound A of structural formula I, and a compound B of structural formula II, wherein R 1, R 2 are each independently selected from halogen, substituted or unsubstituted C 1-C 6 alkyl, CN, CH 2CN, CH 2-CH 2-CN, branched alkyl ether group, or cyclic ether group, R 3, R 4 are each independently selected from halogen, substituted or unsubstituted C 1-C 6 alkyl, CN, CH 2CN, CH 2-CH 2-CN, branched alkyl ether group, cyclic ether group, branched alkyl ketone group, vinyl ketone group, or cyclic ketone group. wherein R 1, R 2 are each independently selected from halogen, C 1-C 3 alkyl, C 2-C 3 alkenyl, C 2-C 3 alkynyl, halogen-substituted C 1-C 3 alkyl, halogen-substituted C 2-C 3 alkenyl, or halogen-substituted C 2-C 3 alkynyl, R 3, R 4 are each independently selected from halogen, C 1-C 3 alkyl, C 2-C 3 alkenyl, C 2-C 3 alkynyl, halogen-substituted C 1-C 3 alkyl, halogen-substituted C 2-C 3 alkenyl, halogen-substituted C 2-C 3 alkynyl, cyclic ether group, or C 2-C 3 alkyl ketone group.

2. The nonaqueous electrolyte according to claim 1, characterized by The compound A is selected from at least one of compound one to compound four, 3. The nonaqueous electrolyte according to claim 1, characterized by The compound B is selected from at least one of compound five to compound eight, 4. The nonaqueous electrolyte according to claim 1, characterized by The mass percentage of the compound A in the non-aqueous electrolyte is 0.1-20.0%, and the mass percentage of the compound B in the non-aqueous electrolyte is 0.1-5.0%.

5. The nonaqueous electrolyte according to claim 1, wherein The lithium salt comprises at least one of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium bisfluorosulfonylimide, lithium bis-trifluoromethylsulfonylimide, lithium methylsulfonate, lithium trifluoromethylsulfonate, lithium bisoxalate borate, lithium difluorooxalate borate, lithium difluorophosphate, lithium difluorobisoxalate phosphate, lithium tetraphenylborate, and lithium 2-trifluoromethyl-4,5-dicyanimidazole.

6. The nonaqueous electrolyte according to claim 1, wherein The mass percentage of the lithium salt in the non-aqueous electrolyte is 10-25%.

7. The nonaqueous electrolyte according to claim 1, wherein The non-aqueous organic solvent comprises at least one of a carbonate compound, a carboxylic acid ester compound, and an ether compound.

8. The nonaqueous electrolyte according to claim 1, wherein A charging voltage is 4.45 V, comprising a positive electrode material, a negative electrode material, and the non-aqueous electrolyte according to any one of claims 1-8.

9. A lithium-ion battery, characterized by ​ 10. The lithium-ion battery of claim 9, wherein, The positive electrode material includes lithium nickel cobalt manganese oxide, a chemical formula of the lithium nickel cobalt manganese oxide is LiNi x Co y Mn (1-x-y) M z O2, wherein 0.1≤x<0.9, x+y<1, 0≤z<0.08, M is at least one of Al, Mg, Zr and Ti, and the negative electrode material includes at least one of an alkali metal, a carbon-based material, a silicon-based material and a tin-based material.

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