Non-aqueous electrolyte and lithium ion battery

Abstract

The application discloses a non-aqueous electrolyte and a lithium ion battery, wherein the non-aqueous electrolyte comprises a lithium salt, an organic solvent and an additive; the organic solvent comprises a carbonate compound; the additive comprises a compound A and a compound B; the structure of the compound A is shown in the following formula 1; the structure of the compound B is shown in the following formula 2; wherein R1 and R2 are each independently selected from C1-C6 alkyl, halogen and C1-C6 halogen-substituted alkyl; and R3 is selected from C1-C6 alkyl, C2-C6 alkenyl, C2-C6 alkynyl and cyano. The non-aqueous electrolyte of the application can reduce the impedance of the battery and significantly improve the fast-charging capacity and high-low temperature performance of the lithium ion battery by combining the compound A and the compound B.

Description

TECHNICAL FIELD

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

[0002] Since the commercialization of lithium ion batteries, they have been widely used in various fields of daily life and production due to their high energy density, excellent cycle life and low self-discharge rate. Lithium ion batteries not only serve as an important cornerstone for the development of new energy industries, but also play a crucial role in many industries such as electric power, transportation, industry, communication, construction and military, supporting the widespread application of new energy technologies. With the development of these specific application fields, the requirements for the high and low temperature performance, storage performance and fast charging capability of lithium ion batteries are also increasing.

[0003] The electrolyte plays a crucial role in lithium ion batteries, as it serves as a medium for the transport of lithium ions between the positive and negative electrodes. The electrochemical performance of lithium ion batteries is largely related to the electrode / electrolyte interface characteristics. In the prior art, the chemical composition and properties of the electrode / electrolyte interface are usually adjusted by introducing additives into the electrolyte, thereby improving the electrochemical performance of the battery. However, most of the current additives in lithium ion batteries usually exhibit high impedance, which cannot simultaneously consider the fast charging capability and high and low temperature performance of the battery.

[0004] Therefore, there is an urgent need to develop a non-aqueous electrolyte to reduce the impedance of the battery, thereby enabling lithium ion batteries to simultaneously consider fast charging capability and high and low temperature performance. SUMMARY

[0005] In view of the above problems, the purpose of the present application is to provide a non-aqueous electrolyte and a lithium ion battery, which can reduce the impedance of the battery and significantly improve the fast charging capability and high and low temperature performance of the lithium ion battery.

[0006] To achieve the above purpose, the first aspect of the present application provides a non-aqueous electrolyte, comprising a lithium salt, an organic solvent and an additive, the organic solvent comprising a carbonate compound, the additive comprising compound A and compound B, the structure of compound A being shown in formula 1 below, and the structure of compound B being shown in formula 2 below;

[0007]

[0008] wherein R1, R2 are each independently selected from C1-C6 alkyl, halogen, C1-C6 halogen-substituted alkyl; R3 is selected from C1-C6 alkyl, C2-C6 alkenyl, C2-C6 alkynyl, cyano (-C≡N) 。

[0009] Compound A has good oxidation resistance, so introducing compound A into the non-aqueous electrolyte can make the lithium ion battery not easy to produce gas at high temperature and high voltage. However, in practical application, the presence of compound A can deteriorate the fast charging ability of the lithium ion battery, leading to a decrease in the charging rate, thereby limiting the widespread use of the lithium ion battery in application scenarios requiring fast charging. Compound B has a relatively low oxidation potential and can be oxidized on the electrode surface before the solvent, forming a relatively thin interface layer, which has a relatively optimal lithium ion transmission efficiency, thereby helping to reduce the impedance of the battery and improve the fast charging ability and low temperature performance of the lithium ion battery. In addition, compound B contains an alkoxy group, so the alkoxy-containing interface formed by compound B is easy to dissolve in the carbonate solvent, causing the battery interface to be unstable, leading to the deterioration of the high temperature performance of the battery. The inventors of the present application found during the inventive process that the alkoxy-containing interface formed by compound B is not easy to dissolve in the carbonate solvent when compound A is introduced into the carbonate solvent, which is conducive to exerting the protection characteristics of the alkoxy interface on the electrode material, so that the high temperature performance of the lithium ion battery at high voltage is significantly improved. Therefore, the non-aqueous electrolyte of the present application combines compound A and compound B, which can reduce the impedance of the battery and significantly improve the fast charging ability and high and low temperature performance of the lithium ion battery.

[0010] Further, the C1-C6 alkyl of the present application can be, but is not limited to, methyl, ethyl, propyl, butyl, pentyl, hexyl; the halogen can be fluorine (F), chlorine (Cl), bromine (Br), iodine (I); the C1-C6 halogen-substituted alkyl can be, but is not limited to, monofluoromethyl (-CH2F), difluoromethyl (-CHF2), trifluoromethyl (-CF3), 1,1-dichloroethyl (-CHCl2), 2,2,2-trifluoroethyl (-CH2CF3), 2-chloropropyl (-CH2CHClCH3), 3-chloropropyl (-CH2CH2CH2Cl), 1,1,1-trifluorobutyl (-CH2CH2CH2CF3); the C2-C6 alkenyl can be, but is not limited to, vinyl (-C2H3), propenyl (-C3H5), butenyl (-C4H7), pentenyl (-C5H9), hexenyl (-C6H 11 ); the C2-C6 alkynyl can be, but is not limited to, ethynyl (-C≡CH), propynyl (-CH2C≡CH), butynyl (-C4H5), pentynyl (-C5H7), hexynyl (-C6H9).

[0011] Further, the compound A of the present application is selected from at least one of compound A1 to compound A3:

[0012]

[0013] Further, the compound B of the present application is selected from at least one of compound B1 to compound B4:

[0014]

[0015] Specifically, the side chain in compound B2 and compound B3 both contains unsaturated bond, which can polymerize on the surface of the negative electrode, improve the toughness of the negative electrode interface, and further improve the low temperature performance of the lithium ion battery.

[0016] Further, the mass percentage of compound A in the non-aqueous electrolyte is 0.1-10%. Specifically, the mass percentage of compound A in the non-aqueous electrolyte can be, but is not limited to, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 7%, 8%, 9%, 10%.

[0017] Further, the mass percentage of compound B in the non-aqueous electrolyte is 0.1-10%. Specifically, the mass percentage of compound B in the non-aqueous electrolyte can be, but is not limited to, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 6%, 7%, 8%, 9%, 10%.

[0018] Further, the lithium salt in the present application includes at least one of lithium hexafluorophosphate (LiPF6), lithium perchlorate, lithium tetrafluoroborate (LiBF4), lithium bisfluorosulfonylimide (LiFSI), lithium bis-trifluoromethylsulfonylimide, lithium methylsulfate, lithium trifluoromethylsulfate, lithium fluorosulfate, lithium bis-oxalate borate, lithium difluoro-oxalate borate, lithium difluorophosphate, lithium difluoro-bis-oxalate phosphate, lithium diphosphate and lithium lower aliphatic carboxylate. Specifically, the mass percentage of lithium salt in the non-aqueous electrolyte is 5-30%, such as the content of lithium salt can be, but is not limited to, 5%, 10%, 15%, 20%, 25%, 30%; preferably, the mass percentage of lithium salt in the non-aqueous electrolyte is 5-18%.

[0019] Further, the carbonate compound in the present application includes cyclic carbonate and chain carbonate. Specifically, the cyclic carbonate can be, but is not limited to, ethylene carbonate, propylene carbonate, butylene carbonate, pentylene carbonate, vinylene carbonate or their derivatives; the chain carbonate includes, but is not limited to, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, propylene carbonate.

[0020] Further, the organic solvent in the present application also includes at least one of carboxylic acid ester compound and ether compound. By mixing carboxylic acid ester compound, ether compound and carbonate compound, the comprehensive performance of the electrolyte can be further improved. For example, carboxylic acid ester compound can provide higher dielectric constant, ether compound can provide better low temperature performance, and carbonate compound can provide better film forming performance.

[0021] Further, the carboxylic ester of the present application includes at least one of cyclic carboxylic ester and chain carboxylic ester, the cyclic carboxylic ester can specifically include but is not limited to at least one of γ-butyrolactone, γ-valerolactone, δ-valerolactone; the chain carboxylic ester includes but is not limited to methyl acetate, ethyl acetate, propyl acetate, butyl acetate, propyl propionate, butyl propionate.

[0022] Further, the ether compound of the present application includes cyclic ether or 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), 2-trifluoromethyltetrahydrofuran (2-CF3-THF); the chain ether can specifically include but is not limited to dimethoxymethane, diethoxymethane, ethoxymethoxymethane, ethyleneglycol di-n-propyl ether, ethyleneglycol di-n-butyl ether, diethyleneglycol dimethyl ether.

[0023] Further, the non-aqueous electrolyte of the present application further includes an additive, the additive is selected from at least one of vinylene carbonate (VC), vinylene ethylene carbonate (VEC), fluoroethylene carbonate (FEC), vinyl sulfite (ES), 1,3 propanesultone (PS), 1,3-propene sulfite (PES), 1,4-butanesultone (BS), vinyl sulfate (DTD), succinic anhydride (SA), maleic anhydride (MA), 2-methyl maleic anhydride (MMA), methyl carbonic acid-2-propynyl ester, tetraethylenesilane, triallyl isocyanurate, hexamethylene diisocyanate, o-phenanthroline, p-phenylenediisocyanate, 2,4-toluene diisocyanate, N-phenyl bis(trifluoromethanesulfonyl) imide, bisvinyl sulfate, methylsulfonic acid phenyl ester, bisvinyl sulfate, bispropylene sulfite, p-phenylenediamine difluorosulfonate, triallyl phosphate, triallyl phosphate, 2,4-butane sulfite, isocyanatoethyl methacrylate, methanedi sulfonate methylene, tris(trimethylsilyl) borate, tris(trimethylsilyl) phosphate, tris(vinyldimethylsilyl) phosphate. Specifically, the mass percentage of the additive in the non-aqueous electrolyte of the present application is 0.1-5%, such as the additive content can be but is not limited to 0.1%, 0.5%, 1%, 1.6%, 1.9%, 2.6%, 3.2%, 3.8%, 4.3%, 4.8%, 5%. Preferably, the mass percentage of the additive in the non-aqueous electrolyte is 0.1-2%.

[0024] Correspondingly, the second aspect of the present application further provides a lithium ion battery, including a positive electrode, a negative electrode, and further including the above-mentioned non-aqueous electrolyte. The lithium ion battery has lower impedance and better fast charging capacity and high-low temperature performance.

[0025] Further, the active material of the positive electrode of the present application includes at least one of lithium-containing phosphate of olivine structure, lithium transition metal oxide, and their respective modified compounds. Specifically, the lithium-containing phosphate of olivine structure includes, but is not limited to, at least one of lithium iron phosphate (e.g., LiFePO4), a composite of lithium iron phosphate and carbon, lithium manganese phosphate (e.g., LiMnPO4), a composite of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and a composite of lithium manganese iron phosphate and carbon. The lithium transition metal oxide includes, but is not limited to, lithium cobalt oxide (e.g., LiCoO2), lithium nickel oxide (e.g., LiNiO2), lithium manganese oxide (e.g., LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (e.g., LiNi x Co y Mn 1-x-y M z O2, wherein 0.6≤x<0.9, x+y<1, 0≤z<0.08, and M is at least one of Al, Mg, Zr, and Ti). Preferably, the active material of the positive electrode of the present application is LiNi 0.8 Co 0.1 Mn 0.1 Zr 0.03 O2.

[0026] Further, the active material of the negative electrode of the present application includes at least one of carbon-based negative electrode, silicon-based negative electrode, tin-based negative electrode, and lithium negative electrode. The carbon-based negative electrode can include graphite, hard carbon, soft carbon, graphene, mesocarbon microbeads, etc.; the silicon-based negative electrode can include silicon material, oxide of silicon, silicon-carbon composite material, and silicon alloy material, etc.; the tin-based negative electrode can include tin, tin-carbon, tin-oxygen, tin metal compound; and the lithium negative electrode can include metallic lithium or lithium alloy. The lithium alloy can be at least one of lithium-silicon alloy, lithium-sodium alloy, lithium-potassium alloy, lithium-aluminum alloy, lithium-tin alloy, and lithium-indium alloy. DETAILED DESCRIPTION

[0027] For the purpose of further illustrating the objects, technical solutions, and advantages of the present application, a further description will be given with reference to the specific examples. It should be noted that, if the specific conditions are not specified in the examples and comparative examples, the conventional conditions or the conditions recommended by the manufacturers can be used, and the reagents or instruments not specified by the manufacturers are all conventional products available in the market.

[0028] Example 1

[0029] The present example provides a method for preparing a lithium ion battery, comprising the following steps:

[0030] (1) mixing a ternary material LiNi 0.8 Co 0.1 Mn 0.1 Zr 0.03O2, conductive agent Super P, binder PVDF and carbon nanotube (CNT) were mixed in a mass ratio of 96.5:1.5:1:1 to form a slurry of lithium ion battery cathode with a certain viscosity, which was coated on an aluminum foil current collector with a coating amount of 324 g / m 2 After drying at 85℃, cold pressing was performed; then edge cutting, piece cutting and striping were performed, and after striping, drying was performed at 85℃ under vacuum for 4h, and tab welding was performed to produce a required cathode sheet;

[0031] (2) Artificial graphite and silicon were mixed in a mass ratio of 90:10, and then mixed with conductive agent Super P, thickening agent CMC, and binder SBR (styrene-butadiene rubber emulsion) in a mass ratio of 95:1.5:1.0:2.5 to form a slurry, which was coated on both sides of a copper foil, and then dried and rolled to obtain an anode sheet, thereby producing a required anode sheet;

[0032] (3) In a glove box filled with nitrogen (O2<1 ppm, H2O<1 ppm), a mixed solvent obtained by mixing ethylene carbonate (EC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), ethyl propionate (EP) and propyl propionate (PP) in a mass ratio of 2:2:5:2:1 was used as an organic solvent, and then additives and adjuvants were added to obtain a mixed solution. The mixed solution was sealed, packaged and frozen in a quick freezing chamber (-4℃) for 2h, and then taken out. In a glove box filled with nitrogen (O2<1 ppm, H2O<1 ppm), lithium hexafluorophosphate was slowly added to the mixed solution, and then mixed uniformly to obtain a non-aqueous electrolyte;

[0033] (4) The above-mentioned cathode sheet, anode sheet and separator were stacked to produce a lithium ion battery with a thickness of 4.7 mm, a width of 55 mm and a length of 60 mm, which was vacuum baked at 75℃ for 10h, and then injected with the above-mentioned non-aqueous electrolyte. After standing for 24h, the battery was charged to 4.4V at a constant current of 0.1C (180mA), and then charged to a current of 0.05C (90mA) at a constant voltage of 4.4V. Then, the battery was discharged to 3.0V at 0.2C (180mA), and the above-mentioned charging and discharging was repeated twice. Finally, the battery was charged to 3.8V at 0.2C (180mA) to obtain a lithium ion battery.

[0034] The formulations of the non-aqueous electrolytes of Examples 1-17 and Comparative Examples 1-6 are shown in Table 1. The preparation processes of the non-aqueous electrolytes, cathode sheets, anode sheets and lithium ion batteries of Examples 2-17 and Comparative Examples 1-6 are the same as those of Example 1.

[0035] Table 1 Formulations of non-aqueous electrolytes of examples and comparative examples

[0036]

[0037]

[0038] The lithium ion prepared from Examples 1-17 and Comparative Examples 1-6 was subjected to the following performance tests, and the test results are shown in Table 2.

[0039] Impedance test:

[0040] The impedance of the battery after the capacity test was measured using an electrochemical workstation at a frequency range of 0.01-10 Hz to obtain the total impedance value of the lithium ion battery.

[0041] High-temperature storage performance test

[0042] The lithium ion battery was subjected to 0.5C / 0.5C charging and discharging once at room temperature (25°C) (the battery discharge capacity was recorded as C0), and the upper limit voltage was 4.4 V. Then, the battery was charged to 4.4 V under 0.5C constant current and constant voltage conditions, and the thickness of the battery was measured (the thickness was recorded as D0). The battery was placed in a 60°C oven for 30 days, taken out and measured for thickness (the thickness was recorded as D1). The battery was placed in a 25°C environment and subjected to 0.5C discharging (the discharge capacity was recorded as C1). The lithium ion battery was subjected to 0.5C / 0.5C charging and discharging once at room temperature (25°C) (the battery discharge capacity was recorded as C2), and the upper limit voltage was 4.4 V. The capacity retention rate, capacity recovery rate and thickness expansion rate were calculated.

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

[0044] Capacity recovery rate = (C2 / C0)*100%

[0045] Thickness expansion rate = (D1 / D0)*100%

[0046] Normal-temperature cycle performance test

[0047] The lithium ion battery was subjected to 1.0C / 1.0C charging and discharging once at room temperature (25°C) (the battery discharge capacity was C0), and the upper limit voltage was 4.4 V. Then, the battery was subjected to 1.0C / 1.0C charging and discharging for 500 cycles at room temperature (the battery discharge capacity was C1), and the capacity retention rate was calculated.

[0048] Capacity retention rate = (C1 / C0)*100%

[0049] High-temperature cycle performance test

[0050] ​​​The lithium ion battery was subjected to one 1.0C / 1.0C charging and discharging (battery discharge capacity was CO) at an excessively high temperature (45°C) with an upper limit voltage of 4.4V, and then subjected to 1.0C / 1.0C charging and discharging for 400 cycles (battery discharge capacity was C1) at room temperature, and the capacity retention rate was calculated.

[0051] Capacity retention rate = (C1 / CO) * 100%

[0052] Low-temperature performance test :

[0053] The lithium ion battery was subjected to one 0.5C / 0.5 charging and discharging (battery cutoff voltage was 3.0V, and discharge capacity was CO) at room temperature (25°C) with an upper limit voltage of 4.4V (cutoff current was 0.05C). Then the battery was fully charged to 4.4V (cutoff current was 0.05C) at room temperature (25°C) at 0.5C, and then the battery was transferred to a condition of -20°C and left for 4 hours, and then discharged to 3.0V at 0.5C, and the discharge capacity was C1, and the capacity retention rate was calculated.

[0054] Capacity retention rate = (C1 / CO) * 100%

[0055] Rate performance test:

[0056] The lithium ion battery was subjected to 5C rate charging and discharging cycles at room temperature for 5 cycles, i.e. 5C capacity retention rate = fifth cycle discharge capacity / 1C discharge capacity at room temperature.

[0057] Table 2 Performance test results of lithium ion batteries of examples and comparative examples

[0058]

[0059]

[0060] As can be seen from Table 2, compared with Comparative Example 1, Examples 1-17, because the non-aqueous electrolyte comprises compound A and compound B, the lithium ion battery not only has good high-temperature storage and high-temperature cycle performance, but also has good low-temperature performance at -20°C, and also has good fast-charging performance. This is because compound A can prevent the lithium ion battery from generating gas at high temperature and high voltage, and compound B can help to reduce the impedance of the battery and improve the fast-charging capacity and low-temperature performance of the lithium ion battery; importantly, the alkoxyl-containing interface formed by compound B is not easily dissolved in the carbonate solvent containing compound A, which is conducive to the protection of the alkoxyl interface to the electrode material; therefore, the combination of compound A and compound B in the non-aqueous electrolyte of the present application can reduce the impedance of the battery and significantly improve the fast-charging capacity and high-low temperature performance of the lithium ion battery.

[0061] Comparing example 10 and examples 11-14, it can be seen that, on the basis of the additive of the application, further adding the auxiliary agent can further improve the high-temperature storage performance, high-temperature cycle performance, low-temperature performance and lithium ion cycle performance of the lithium ion battery, and the expansion rate is lower.

[0062] Comparing examples 15-17 and examples 11-12, it can be seen that, when the VC / FEC mixed auxiliary agent is used in the electrolyte, the high-temperature performance and low-temperature performance of the lithium ion battery are greatly improved, and the expansion rate is further improved.

[0063] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application, and are not intended 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, it is not limited to the examples listed in the embodiments. 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, an organic solvent, and additives, characterized in that, The organic solvent includes carbonate compounds, the additive includes compound A and compound B, the mass percentage of compound A in the non-aqueous electrolyte is 0.1~10%, the mass percentage of compound B in the non-aqueous electrolyte is 0.1~10%, the structure of compound A is shown in Formula 1 below, and the structure of compound B is shown in Formula 2 below; R1 and R2 are the same and are selected from fluorine and C1~C6 fluorinated alkyl groups; R3 is selected from C1~C6 alkyl, C2~C6 alkenyl, C2~C6 alkynyl, and cyano groups.

2. The non-aqueous electrolyte as described in claim 1, characterized in that, The compound A is selected from at least one of compounds A1 to A3: 。 3. The non-aqueous electrolyte as described in claim 1, characterized in that, The compound B is selected from at least one of compounds B1 to B4: 。 4. The non-aqueous electrolyte as described in claim 1, characterized in that, The lithium salt includes at least one of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium methanesulfonate, lithium trifluoromethanesulfonate, lithium fluorosulfonate, lithium dioxalate borate, lithium difluorooxalate borate, lithium difluorophosphate, lithium difluorobis(oxalate) phosphate, lithium diphosphate, and lower aliphatic carboxylic acids.

5. The non-aqueous electrolyte as described in claim 1, characterized in that, The organic solvent also includes at least one of carboxylic acid esters and ethers.

6. The non-aqueous electrolyte as described in claim 1, characterized in that, It also includes additives selected from vinylene carbonate, vinylene ethylene carbonate, fluoroethylene carbonate, vinyl sulfite, 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, 1,4-butanesulfonate lactone, vinyl sulfate, succinic anhydride, maleic anhydride, 2-methylmaleic anhydride, methyl carbonate-2-propynyl ester, tetraethylenesilane, triallyl isocyanurate, hexamethylene diisocyanate, o-phenanthroline, terephthalic diisocyanate, 2, At least one of the following: 4-toluene diisocyanate, N-phenylbis(trifluoromethanesulfonyl)imide, vinyl disulfate, phenyl methanesulfonate, vinyl disulfate, propylene dispironate, hydroquinone difluorosulfonate, triallyl phosphate, triargyl phosphate, 2,4-butane sulpholol, isocyanate ethyl methacrylate, methylene disulfonate, tri(trimethylsilane)borate, tri(trimethylsilane) phosphate, and tri(vinyldimethylsilane) phosphate.

7. A lithium-ion battery, comprising a positive electrode and a negative electrode, characterized in that, It also includes the non-aqueous electrolyte as described in any one of claims 1 to 6.

8. The lithium-ion battery as described in claim 7, characterized in that, The active materials of the positive electrode include lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds.

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