Electrolyte and lithium ion battery

Abstract

The invention discloses an electrolyte and a lithium ion battery in the technical field of secondary lithium batteries. The electrolyte comprises 13-15 parts of a lithium salt, 70-75 parts of an organic solvent and 10-27 parts of an additive, wherein the additive is prepared from the following raw materials in parts by mass: 3 to 5 parts of fluorobenzene, 3 to 5 parts of 1, 3-propane sultone, 3 to 5 parts of fluoroethylene carbonate, 0 to 1 part of allyl-1, 3-sultone, 0 to 1 part of ethylene sulfate, 1 to 5 parts of adiponitrile, 0.5 to 1 part of ethylene glycol bis (propionitrile) ether, 0.5 to 2 parts of 1, 3, 6-hexanetrinitrile, 1 to 3 parts of biphenyl and 2 to 4 parts of cyclohexylbenzene; according to the electrolyte and the lithium ion battery provided by the invention, the thermal runaway phenomenon of the lithium ion battery under the 2C6V charging condition can be effectively prevented, and other external protection measures do not need to be added.

Description

Technical Field

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

[0002] Lithium-ion batteries with excellent performance such as high energy density, long life and high safety face a negative correlation between energy and safety issues in large-scale applications. High-rate charging and high-voltage overcharge tests can easily lead to battery overcharge. When overcharged, lithium ions are deintercalated from the positive electrode and acquire electrons at the negative electrode to form deposited lithium. The formation of lithium dendrites may puncture the battery separator and cause internal short circuits. At the same time, excessive delithiation of the positive electrode material will cause its structure to collapse and release extremely high reactivity, which will cause violent redox reactions and release a lot of heat. Coupled with the Joule heat generated during the charging process, the battery temperature will rise rapidly. Under high temperature conditions, the battery may undergo thermal decomposition reactions, thereby causing thermal runaway and causing safety accidents. Therefore, this series of problems makes lithium-ion batteries have great safety hazards.

[0003] During the certification process of lithium-ion batteries, one of the tests is the UL2054 test, which includes an assessment of abuse and overcharging, and requires passing the 2C6V certification standard, that is, when the upper limit of the battery charging voltage is 6V, the lithium-ion battery is charged at a current twice the nominal capacity of the battery, and there is no thermal runaway phenomenon. This standard focuses on the safety and reliability of the battery under various fault conditions, and is an internationally recognized authoritative standard for evaluating the safety of the battery. However, it is very difficult for lithium batteries to avoid thermal runaway under the 2C / 6V standard without protection. Summary of the invention

[0004] The purpose of the present invention is to overcome the deficiencies in the prior art and to provide an electrolyte and a lithium ion battery, which can effectively prevent the thermal runaway phenomenon of the lithium ion battery under 2C6V charging conditions.

[0005] To achieve the above object, the present invention is implemented by adopting the following technical solutions:

[0006] In one aspect, the present invention provides an electrolyte solution, comprising the following raw materials in parts by weight: 13 to 15 parts of a lithium salt, 70 to 75 parts of an organic solvent, and 10 to 27 parts of an additive;

[0007] The additive is composed of the following raw materials in parts by mass: 3-5 parts of fluorobenzene, 3-5 parts of 1,3-propane sultone, 3-5 parts of fluoroethylene carbonate, 0-1 parts of propenyl-1,3-sultone, 0-1 parts of vinyl sulfate, 1-5 parts of adiponitrile, 0.5-1 parts of ethylene glycol bis(propionitrile) ether, 0.5-2 parts of 1,3,6-hexanetrinitrile, 1-3 parts of biphenyl and 2-4 parts of cyclohexylbenzene.

[0008] Furthermore, the lithium salt is lithium hexafluorophosphate.

[0009] Furthermore, the molar concentration of the lithium hexafluorophosphate is 1.0-1.3 mol / L.

[0010] Furthermore, the organic solvent consists of diethyl carbonate, ethylene carbonate, propylene carbonate and propyl propionate.

[0011] Furthermore, the organic solvent is composed of the following raw materials in parts by mass: 3-5 parts of diethyl carbonate, 3-4 parts of ethylene carbonate, 2-3 parts of propylene carbonate, and 3-5 parts of propyl propionate.

[0012] In a second aspect, the present invention provides a lithium-ion battery comprising the above-mentioned electrolyte.

[0013] Furthermore, the lithium-ion battery comprises a positive electrode, a negative electrode and an electrolyte, wherein the electrolyte is located between the positive electrode and the negative electrode.

[0014] Furthermore, the positive electrode current collector is an aluminum foil, and the aluminum foil is covered with a coating, wherein the coating is composed of lithium cobalt oxide, conductive carbon black SP and polyvinylidene fluoride PVDF, and the mass ratio of lithium cobalt oxide, SP and polyvinylidene fluoride is 96~98%:0~2%:0.5~1%;.

[0015] Furthermore, the negative electrode current collector is a copper foil, and the copper foil is covered with a coating, wherein the coating is composed of artificial graphite, conductive carbon black SP, styrene-butadiene rubber SBR and sodium carboxymethyl cellulose CMC, and the mass ratio of active material, SP, SBR and CMC is 95-96:0-0.5:1-1.5:0.5-1;

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] The present invention provides an electrolyte and a lithium ion battery, wherein the electrolyte is composed of the following raw materials in parts by mass: 13-15 parts of a lithium salt, 70-75 parts of an organic solvent and 10-27 parts of an additive; wherein the additive is composed of the following raw materials in parts by mass: 3-5 parts of fluorobenzene, 3-5 parts of 1,3-propane sultone, 3-5 parts of fluoroethylene carbonate, 0-1 part of propenyl-1,3-sultone, 0-1 part of vinyl sulfate, 1-5 parts of adiponitrile, 0.5-1 part of ethylene glycol bis(propionitrile) ether, 0.5-2 parts of 1,3,6-hexanetrinitrile, 1-3 parts of biphenyl and 2-4 parts of cyclohexylbenzene; the present invention provides an electrolyte and a lithium ion battery, which can effectively prevent the thermal runaway phenomenon of the lithium ion battery under 2C6V charging conditions without adding other protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a temperature curve diagram of the lithium ion battery provided in Comparative Example 1 of the present invention during the 2C6V test;

[0019] Figure 2 is a temperature curve diagram of the lithium-ion battery provided in Example 1 of the present invention during the 2C6V test;

[0020] Figure 3 It is a temperature curve diagram of the lithium ion battery provided in Comparative Example 2 of the present invention during the 2C6V test;

[0021] Figure 4 is a temperature curve diagram of a lithium-ion battery provided in Example 2 of the present invention during a 2C6V test;

[0022] Figure 5 It is a temperature curve diagram of the lithium ion battery provided in Comparative Example 3 of the present invention during the 2C6V test;

[0023] Figure 6 It is a temperature curve diagram of the lithium ion battery provided in Comparative Example 4 of the present invention during the 2C6V test;

[0024] Figure 7 It is a temperature curve diagram of the lithium ion battery provided in Comparative Example 5 of the present invention during the 2C6V test;

[0025] Figure 8 It is a temperature curve diagram of the lithium ion battery provided in Comparative Example 6 of the present invention during the 2C6V test. DETAILED DESCRIPTION

[0026] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention.

[0027] Example 1

[0028] This embodiment provides an electrolyte and a lithium-ion battery.

[0029] The electrolyte consists of a lithium salt, an organic solvent and an additive, wherein the lithium salt is lithium hexafluorophosphate with a molar concentration of 1.0-1.3 mol / L and a mass ratio of 14%, that is, the mass of the lithium hexafluorophosphate is 14 g, the organic solvent consists of 20 g of diethyl carbonate, 16.5 g of ethylene carbonate, 12 g of propylene carbonate and 20.2 g of propyl propionate, and the additive consists of 4.5 g of fluorobenzene, 3.5 g of 1,3-propane sultone, 4.5 g of fluoroethylene carbonate, 0.5 g of allyl-1,3-sultone, 0.5 g of vinyl sulfate, 2 g of adiponitrile, 0.8 g of ethylene glycol bis(propionitrile) ether, 1 g of 1,3,6-hexanetrinitrile and 3 g of biphenyl.

[0030] The battery provided in this embodiment consists of a positive electrode, a negative electrode and an electrolyte, wherein the electrolyte is located between the positive electrode and the negative electrode, and the nominal capacity of the battery is 450 mAh.

[0031] The positive electrode of the battery uses aluminum foil as the current collector, and the surface of the current collector is coated with a positive electrode coating by a coating machine. The positive electrode coating consists of lithium cobalt oxide, a conductive agent and a binder, wherein the conductive agent is SP and the binder is PVDF. In the positive electrode coating, the mass ratio of lithium cobalt oxide: SP: PVDF is 97:2:1. The lithium cobalt oxide is purchased from Beijing Dangsheng New Materials, model 15A (4.35V). The negative electrode of the battery uses copper foil as the current collector, and the surface of the current collector is coated with a negative electrode coating by a coating machine. The positive electrode coating consists of active materials, conductive agents, binders and thickeners, wherein the active material is a graphite negative electrode material QCG-X purchased from Shanghai Shanshan New Energy, the conductive agent is SP, the binder is SBR, and the thickener is CMC. In the negative electrode coating, the mass ratio of active materials: SP: SBR: CMC is 97:0.5:1.5:1. The electrolyte of the battery uses the electrolyte provided in Example 1.

[0032] Example 2

[0033] This embodiment provides an electrolyte and a lithium ion battery. Different from Embodiment 1, in this embodiment, the additive consists of 4.5 g of fluorobenzene, 3.5 g of 1,3-propane sultone, 4.5 g of fluoroethylene carbonate, 0.5 g of propenyl-1,3-sultone, 0.5 g of vinyl sulfate, 2 g of adiponitrile, 0.8 g of ethylene glycol bis(propionitrile) ether, 1 g of 1,3,6-hexanetrinitrile, 2 g of biphenyl and 3 g of cyclohexylbenzene.

[0034] Comparative Example 1

[0035] This comparative example provides an electrolyte and a lithium ion battery. Different from Example 1, in this comparative example, the additive consists of 4.5 g of fluorobenzene, 3.5 g of 1,3-propane sultone, 4.5 g of fluoroethylene carbonate, 0.5 g of propenyl-1,3-sultone, 0.5 g of vinyl sulfate, 2 g of adiponitrile, 0.8 g of ethylene glycol bis(propionitrile) ether and 1 g of 1,3,6-hexanetrinitrile.

[0036] Comparative Example 2

[0037] This comparative example provides an electrolyte and a lithium ion battery. Different from Example 1, in this comparative example, the additive consists of 4.5 g of fluorobenzene, 3.5 g of 1,3-propane sultone, 4.5 g of fluoroethylene carbonate, 0.5 g of propenyl-1,3-sultone, 0.5 g of vinyl sulfate, 2 g of adiponitrile, 0.8 g of ethylene glycol bis(propionitrile) ether, 1 g of 1,3,6-hexanetrinitrile, 2 g of biphenyl and 3 g of cyclohexylbenzene.

[0038] Comparative Example 3

[0039] This comparative example provides an electrolyte and a lithium ion battery. Different from Example 1, in this comparative example, the additive consists of 4.5 g of fluorobenzene, 3.5 g of 1,3-propane sultone, 4.5 g of fluoroethylene carbonate, 0.5 g of propenyl-1,3-sultone, 0.5 g of vinyl sulfate, 2 g of adiponitrile, 0.8 g of ethylene glycol bis(propionitrile) ether, 1 g of 1,3,6-hexanetrinitrile and 3 g of tert-amylbenzene.

[0040] Comparative Example 4

[0041] This comparative example provides an electrolyte and a lithium ion battery. Different from Example 1, in this comparative example, the additive consists of 4.5 g of fluorobenzene, 3.5 g of 1,3-propane sultone, 4.5 g of fluoroethylene carbonate, 0.5 g of propenyl-1,3-sultone, 0.5 g of vinyl sulfate, 2 g of adiponitrile, 0.8 g of ethylene glycol bis(propionitrile) ether, 1 g of 1,3,6-hexanetrinitrile and 3 g of tert-butylbenzene.

[0042] Comparative Example 5

[0043] This comparative example provides an electrolyte and a lithium ion battery. Different from Example 1, in this comparative example, the additive consists of 4.5 g of fluorobenzene, 3.5 g of 1,3-propane sultone, 4.5 g of fluoroethylene carbonate, 0.5 g of propenyl-1,3-sultone, 0.5 g of vinyl sulfate, 2 g of adiponitrile, 0.8 g of ethylene glycol bis(propionitrile) ether, 1 g of 1,3,6-hexanetrinitrile and 3 g of 2,4-difluorobiphenyl.

[0044] Comparative Example 6

[0045] This comparative example provides an electrolyte and a lithium ion battery. Different from Example 1, in this comparative example, the additive consists of 4.5 g of fluorobenzene, 3.5 g of 1,3-propane sultone, 4.5 g of fluoroethylene carbonate, 0.5 g of propenyl-1,3-sultone, 0.5 g of vinyl sulfate, 2 g of adiponitrile, 0.8 g of ethylene glycol bis(propionitrile) ether, 1 g of 1,3,6-hexanetrinitrile and 3 g of p-fluorotoluene.

[0046] 1.2 g of the electrolyte provided in Example 1-2 and Comparative Example 1-5 were taken respectively, and the water content, hydrogen fluoride concentration, conductivity and viscosity data of the electrolyte provided in Example 1-2 and Comparative Example 1-6 were obtained. The test method is shown in the standard: SJ / T11723-2018, and the test results are shown in Table 1.

[0047] Table 1

[0048] Moisture (ppm) HF(ppm) Conductivity (mS / cm) Viscosity (cPs) Comparative Example 1 1.4 20.4 6.76 5.34 Example 1 3.1 57.6 6.50 5.35 Comparative Example 2 2.0 48.3 6.28 5.31 Example 2 1.9 46.0 6.15 5.31 Comparative Example 3 2.3 40.2 6.39 5.24 Comparative Example 4 2.4 54.3 6.47 5.22 Comparative Example 5 2.2 45.2 6.43 5.47 Comparative Example 6 2.8 42.4 6.83 5.07

[0049] The lithium ion batteries provided in Examples 1-2 and Comparative Examples 1-6 were subjected to formation and capacity separation treatments, respectively. The formation process is shown in Table 2, and the capacity separation process is shown in Table 3.

[0050] Table 2

[0051] Step Working status Working time (min) Current (mA) Upper limit voltage (mV) Surface pressure (kg / cm2) Pressure (kg) Temperature (℃) 1 Hibernation 5 5 500 80 2 Constant current charging 30 90 3400 5 500 80 3 Hibernation 1 5 500 80 4 Constant current charging 85 225 4100 8 800 80 5 Hibernation 1 8 800 80

[0052] Table 3

[0053] Step How it works Programmable current (mA) End voltage(mV) Programmable voltage (mV) End current (mA) Limit time (min) 1 Hibernation 2 2 Constant current charging 90 4350 30 3 Constant current charging 450 4350 60 4 Constant current charging 225 4350 30 5 Constant voltage charging 4350 23 60 6 Hibernation 5 7 Constant current discharge 225 3000 150 8 Hibernation 5 9 Constant current charging 315 3890 80 10 Constant voltage charging 3890 23 120 11 Hibernation 5

[0054] Subsequently, the lithium ion batteries provided in Examples 1-2 and Comparative Examples 1-6 after formation and capacity separation were subjected to a 2C6V test, i.e., they were charged with a current twice the nominal capacity of the battery until the charging voltage of the battery was 6V, and then maintained for 7 hours. If the battery did not catch fire, explode or burn, it passed the test. The test environment temperature was 20-30°C and the humidity was 20-80%RH. The test results are shown in Table 4.

[0055] Table 4

[0056] Explosion phenomenon Fire phenomenon Combustion phenomenon The maximum temperature of the battery during the test Comparative Example 1 √ √ √ 176℃ Example 1 × × × 83℃ Comparative Example 2 √ √ √ 721℃ Example 2 × × × 89℃ Comparative Example 3 √ √ √ 487℃ Comparative Example 4 √ √ √ 313℃ Comparative Example 5 √ √ √ 718℃ Comparative Example 6 √ √ √ 743℃

[0057] The temperature curves of the lithium ion batteries provided in Examples 1-2 and Comparative Examples 1-6 during the 2C6V test are as follows: Figure 1-Figure 8 As shown by Figure 1-Figure 8As shown in Table 4, the lithium-ion batteries provided in Examples 1-2 all passed the 2C6V test. During the test, the batteries did not catch fire, explode or burn, and the highest temperature of the batteries during the test was only 83°C and 89°C. The lithium-ion batteries provided in Comparative Examples 1-6 caught fire, exploded and burned during the test, which proves that the electrolyte formula provided by the present invention can effectively prevent thermal runaway of the battery.

[0058] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation methods. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Under the enlightenment of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the purpose of the present invention and the claims, which all fall within the protection of the present invention.

Claims

1. An electrolyte, characterized in that: The invention is composed of the following raw materials in parts by weight: 13 to 15 parts of lithium salt, 70 to 75 parts of organic solvent and 10 to 27 parts of additives; The additive is composed of the following raw materials in parts by mass: 3-5 parts of fluorobenzene, 3-5 parts of 1,3-propane sultone, 3-5 parts of fluoroethylene carbonate, 0-1 parts of propenyl-1,3-sultone, 0-1 parts of vinyl sulfate, 1-5 parts of adiponitrile, 0.5-1 parts of ethylene glycol bis(propionitrile) ether, 0.5-2 parts of 1,3,6-hexanetrinitrile, 1-3 parts of biphenyl and 2-4 parts of cyclohexylbenzene.

2. The electrolyte according to claim 1, characterized in that: The lithium salt is lithium hexafluorophosphate.

3. The electrolyte according to claim 2, characterized in that: The molar concentration of the lithium hexafluorophosphate is 1.0-1.3 mol / L.

4. The electrolyte according to claim 1, characterized in that: The organic solvent consists of diethyl carbonate, ethylene carbonate, propylene carbonate and propyl propionate.

5. The electrolyte according to claim 4, characterized in that: The organic solvent is composed of the following raw materials in parts by mass: 3-5 parts of diethyl carbonate, 3-4 parts of ethylene carbonate, 2-3 parts of propylene carbonate, and 3-5 parts of propyl propionate.

6. A lithium ion battery, characterized in that: The electrolyte comprising the electrolyte according to any one of claims 1 to 5.

7. The lithium-ion battery according to claim 6, characterized in that: The lithium ion battery comprises a positive electrode, a negative electrode and an electrolyte, wherein the electrolyte is located between the positive electrode and the negative electrode.

8. The lithium-ion battery according to claim 6, characterized in that: The positive electrode current collector is an aluminum foil, and the aluminum foil is covered with a coating, wherein the coating is composed of lithium cobalt oxide, conductive carbon black SP and polyvinylidene fluoride PVDF, and the mass ratio of lithium cobalt oxide, SP and polyvinylidene fluoride is 96-97:0-2:0.5-1.

9. The lithium-ion battery according to claim 6, characterized in that: The negative electrode current collector is a copper foil, which is covered with a coating, wherein the coating is composed of artificial graphite, conductive carbon black SP, styrene-butadiene rubber SBR and sodium carboxymethyl cellulose CMC, and the mass ratio of active material, SP, SBR and CMC is 95-96:0-0.5:1-1.5:0.5-1.

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