Lithium-ion battery electrolyte, lithium-ion battery

Abstract

This invention provides a lithium-ion battery electrolyte and a lithium-ion battery. The lithium-ion battery electrolyte comprises a lithium salt, a first organic solvent, and additives; wherein the first organic solvent has the structure shown in the formula, where R1-R6 each independently represent H or a halogen. Applying the lithium-ion battery electrolyte of this invention to a lithium-ion battery can enable the battery to exhibit better chemical performance and stability, and can avoid thermal runaway at high temperatures, thus demonstrating excellent safety performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of lithium ion batteries, in particular to a lithium ion battery electrolyte and a lithium ion battery. BACKGROUND

[0002] As a rechargeable battery, lithium ion battery has high specific energy, high voltage, no memory effect, good environmental protection, long service life and other advantages, and is widely used as a power source for portable electronic products. However, when the lithium battery is subjected to heat shock or overcharge and short circuit, etc., it is easy to cause thermal runaway phenomenon, resulting in fire and explosion accidents. Especially when the lithium ion battery is applied to large-capacity power sources such as electric vehicles, the safety problems caused thereby are particularly serious.

[0003] Generally, the electrolyte of lithium ion battery is mainly composed of lithium salt, organic solvent and additive. Among them, the commonly used organic solvent is alkyl carbonate compound, but this kind of compound has a low flash point, so it is easy to burn and cause frequent safety accidents. Therefore, as a way to improve the safety of lithium ion battery, the research on preparing electrolyte with high safety has attracted widespread attention. Based on this, it is urgent to provide a lithium ion battery electrolyte to solve the problem of poor safety of lithium ion battery due to thermal runaway phenomenon under high temperature in the prior art. SUMMARY

[0004] The main purpose of the present application is to provide a lithium ion battery electrolyte and a lithium ion battery to solve the problem of poor safety of lithium ion battery due to thermal runaway phenomenon under high temperature in the prior art.

[0005] In order to achieve the above purpose, according to one aspect of the present application, a lithium ion battery electrolyte is provided; the lithium ion battery electrolyte comprises lithium salt, first organic solvent and additive; wherein the first organic solvent is a compound having the structure shown in formula (I);

[0006]

[0007] In formula (I), R1-R6 each independently represents H or halogen.

[0008] Further, in formula (I), R1-R6 each independently represents H or F.

[0009] Further, the first organic solvent is selected from one or more of the following compounds:

[0010]

[0011] Further, the weight content of the first organic solvent in the lithium ion battery electrolyte is 0.1-15wt%, preferably 5-10wt%.

[0012] Further, the lithium ion battery electrolyte further comprises a second organic solvent; preferably, the second organic solvent is a carbonate-based organic solvent; more preferably, the carbonate-based organic solvent is a cyclic carbonate compound and / or a chain carbonate compound; further preferably, the cyclic carbonate compound is selected from one or more of ethylene carbonate, propylene carbonate or γ-butyrolactone L; the chain carbonate compound is selected from one or more of dimethyl carbonate, diethyl carbonate or methyl ethyl carbonate; further more preferably, the weight content of the second organic solvent in the lithium ion battery electrolyte is 30-60wt%.

[0013] Further, the organic solvent further comprises a third organic solvent; preferably, the third organic solvent is an ether-based organic solvent; more preferably, the ether-based organic solvent is a cyclic ether compound and / or a chain ether compound; further preferably, the cyclic ether compound is selected from one or more of tetrahydrofuran, 2-methyltetrahydrofuran or 1,3-dioxolane; the chain ether compound is selected from one or more of dimethoxymethane, 1,2-dimethoxyethane or diglyme; further more preferably, the weight content of the third organic solvent in the lithium ion battery electrolyte is 10-30wt%.

[0014] Further, the lithium salt is selected from one or more of lithium hexafluorophosphate, lithium bisfluorosulfonylimide, lithium bis(trifluoromethylsulfonyl)imide, lithium trifluoromethylsulfonate, lithium tetrafluoroborate, lithium bisfluorooxalato borate or lithium bisoxalato borate.

[0015] Further, the weight content of the lithium salt in the lithium ion battery electrolyte is 10-15wt%.

[0016] Further, the additive is selected from one or more of vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, 1,3-propane sultone, 1,4-butane sultone, 1,3-(1-propene) sultone, vinyl sulfite, vinyl sulfate, tris(trimethylsilyl) phosphate or tris(trimethylsilyl) borate; preferably, the weight content of the additive in the lithium ion battery electrolyte is 1-10wt%, further preferably 3-8wt%.

[0017] Further, the lithium ion battery electrolyte comprises 13-15wt% of the lithium salt, 5-10wt% of the first organic solvent, 50-55wt% of the second organic solvent, 20-25wt% of the third organic solvent and 4-8wt% of the additive; wherein the first organic solvent is The second organic solvent is ethylene carbonate, methyl ethyl carbonate and diethyl carbonate, and the weight ratio of ethylene carbonate, methyl ethyl carbonate and diethyl carbonate is 4-6:30-32:15-16; the third organic solvent is 1,2-dimethoxyethane; the additive is vinylene carbonate and fluoroethylene carbonate, and the weight ratio of vinylene carbonate and fluoroethylene carbonate is 1:4-6; and the lithium salt is lithium hexafluorophosphate.

[0018] In order to achieve the above-mentioned purpose, according to one aspect of the present application, a lithium ion battery is provided, comprising a positive electrode, a negative electrode, a separator and an electrolyte, wherein the electrolyte is the lithium ion battery electrolyte as described above.

[0019] The lithium ion battery electrolyte of the present application is applied to a lithium ion battery, and shows good chemical performance and stability, and can avoid thermal runaway phenomenon under high temperature, and has excellent safety performance. DETAILED DESCRIPTION

[0020] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The present application will be described in detail below with reference to the embodiments.

[0021] As described in the background section, the lithium ion battery in the prior art has the problem of poor safety due to thermal runaway phenomenon under high temperature. In order to solve this problem, the present application provides a lithium ion battery electrolyte, which comprises a lithium salt, a first organic solvent and an additive; wherein,

[0022] The first organic solvent is a compound having the structure shown in formula (I):

[0023]

[0024] In formula (I), R1-R6 each independently represents H or halogen.

[0025] The present application uses the above-mentioned organic solvent with specific structure to form the electrolyte of the lithium ion battery, which can promote the formation of an oil film layer on the surface of the positive electrode and the negative electrode of the lithium ion battery under high temperature conditions, which hinders the transmission of lithium ions and electrons, thereby inhibiting the violent side reaction between the positive and negative electrode materials and the electrolyte, and further avoiding the occurrence of thermal runaway phenomenon of the lithium ion battery, so as to greatly improve the safety of the battery on the basis of meeting the excellent electrical performance of the battery.

[0026] In a preferred embodiment, in order to further improve the thermal stability of the organic solvent in the lithium ion battery electrolyte, promote the formation of an oil film layer on the positive and negative electrode surfaces under high temperature conditions, thereby avoiding the occurrence of thermal runaway phenomenon of lithium ion battery. Preferably, in formula (I), R1-R6 each independently represents H or F. In order to further promote the first organic solvent in the lithium ion battery electrolyte under high temperature conditions to form a more stable oil film layer on the positive and negative electrode surfaces to prevent the transmission of lithium ions and electrons, thereby further inhibiting the occurrence of side reactions between the positive and negative electrode materials and the electrolyte, and further avoiding the occurrence of thermal runaway phenomenon of lithium ion battery. Preferably, the structure of the first organic solvent can be any one of the following structures:

[0027]

[0028] In order to further improve the chemical properties and thermal stability of lithium ion battery, preferably the weight content of the first organic solvent in the lithium ion battery electrolyte is 0.1-15wt%, more preferably 5-10wt%, for example, it can be 5wt%, 6wt%, 7wt%, 8wt%, 9wt% or 10wt%.

[0029] In a preferred embodiment, the lithium ion battery electrolyte further comprises a second organic solvent; the second organic solvent is a carbonate-based organic solvent. Based on this, the solubility of lithium salt in the electrolyte can be further improved, and the liquid temperature range is wider, thereby effectively improving the stability and chemical properties of the battery, and avoiding the occurrence of thermal runaway phenomenon. Preferably, the carbonate-based organic solvent is a cyclic carbonate compound and / or a chain carbonate compound. In order to further improve the ability of the lithium ion electrolyte to transport lithium ions and electrons, promote the chemical properties and stability of the lithium ion battery, preferably the cyclic carbonate compound is selected from one or more of ethylene carbonate (EC), propylene carbonate (PC) or γ-butyrolactone (GBL), and preferably the chain carbonate compound is selected from one or more of dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC). Further preferably, the weight content of the second organic solvent in the lithium ion battery electrolyte is 50-70wt%, for example, it can be 50wt%, 55wt%, 60wt%, 65wt%, 70wt%.

[0030] In a preferred embodiment, the lithium ion battery electrolyte further comprises a third organic solvent; the third organic solvent is an ether-based organic solvent. Based on this, the conductivity of the electrolyte can be further improved, and it has a lower dielectric constant and a lower viscosity coefficient, thereby effectively improving the stability and chemical properties of the battery and avoiding the occurrence of thermal runaway. Preferably, the ether-based organic solvent is a cyclic ether compound and / or a chain ether compound. In order to further improve the conductivity of the lithium ion electrolyte and promote the chemical properties and stability of the lithium ion battery, preferably the cyclic ether compound is selected from one or more of tetrahydrofuran (THF), 2-methyltetrahydrofuran (2Me-THF), or 1,3-dioxolane (DOL), and preferably the chain ether compound is selected from one or more of dimethoxymethane (DMM), 1,2-dimethoxyethane (DME), or diglyme (DG). It is further preferred that the weight content of the third organic solvent in the lithium ion battery electrolyte is 30-50 wt%, for example, it can be 30 wt%, 35 wt%, 40 wt%, 45 wt% or 50 wt%.

[0031] In order to further improve the electrochemical performance of the battery, preferably the lithium salt is selected from one or more of lithium hexafluorophosphate (LiPF6), lithium bisfluorosulfonylimide (LiFSI), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium trifluoromethylsulfonate (LiSO3CF3), lithium tetrafluoroborate (LiBF4), lithium bisfluorooxalate borate (LiDFOB), or lithium bisoxalate borate (LiBOB), and it is further preferred that the weight content of the lithium salt in the lithium ion battery electrolyte is 10-15 wt%, for example, it can be 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt% or 15 wt%.

[0032] In a preferred embodiment, in order to promote the formation of a more excellent SEI film in the lithium ion battery, thereby improving the cycle performance and chemical properties of the lithium ion battery, and further improving the occurrence of thermal runaway in the lithium ion battery, preferably the additive in the electrolyte is selected from one or more of vinylene carbonate (VC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), 1,3-propane sultone (PS), 1,4-butane sultone (BS), 1,3-(1-propene) sultone (PST), vinyl sulfite (DTD), vinyl sulfate (ES), tris(trimethylsilyl)phosphate (TMSP), or tris(trimethylsilyl)borate (TMSB). In order to further promote the chemical properties and thermal stability of the lithium ion battery, preferably the weight content of the additive in the lithium ion battery electrolyte is 1-10 wt%, more preferably 3-8 wt%, for example, it can be 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt% or 8 wt%.

[0033] In order to further improve the comprehensive performance of the battery, in a preferred embodiment, the lithium ion battery electrolyte comprises 13-15 wt% of lithium salt, 5-10 wt% of the first organic solvent, 50-55 wt% of the second organic solvent, 20-25 wt% of the third organic solvent and 4-8 wt% of the additive; wherein the first organic solvent is propylene carbonate; the second organic solvent is ethylene carbonate, methyl ethyl carbonate and diethyl carbonate, and the weight ratio of ethylene carbonate, methyl ethyl carbonate and diethyl carbonate is 4-6:30-32:15-16; the third organic solvent is 1,2-dimethoxyethane; the additive is vinylene carbonate and fluoroethylene carbonate, and the weight ratio of vinylene carbonate and fluoroethylene carbonate is 1:4-6; and the lithium salt is lithium hexafluorophosphate.

[0034] It is supplemented herein that the above-mentioned first organic solvent of the present application can be directly obtained by commercial purchase or prepared according to the existing conventional technical solutions. For example, in some embodiments, squalene can be used to perform an addition reaction with HF gas under the catalysis of Raney nickel, different fluorosqualene derivatives are obtained with different reaction times, and then H2 addition reaction is performed to finally obtain a fluorosqualane derivative. The molar ratio of the initial reactant squalene to HF is 1:10, and after 30 min of reaction, H2 addition is performed to obtain The molar ratio of the initial reactant squalene to HF is 1:10, and after 2 h of reaction, H2 addition is performed to obtain The molar ratio of the initial reactant squalene to HF is 1:10, and after 4 h of reaction, H2 addition is performed to obtain The molar ratio of the initial reactant squalene to HF is 1:10, and after 8 h of reaction, H2 addition is performed to obtain The molar ratio of the initial reactant squalene to HF is 1:10, and after 12 h of reaction, H2 addition is performed to obtain The molar ratio of the initial reactant squalene to HF is 1:10, and after 24 h of reaction, H2 addition is performed to obtain

[0035] Another aspect of the present application also provides a lithium ion battery, which comprises a positive electrode, a negative electrode, a separator and an electrolyte, wherein the electrolyte is the above-mentioned lithium ion battery electrolyte. The lithium ion battery has good chemical performance and stability, can avoid thermal runaway phenomenon under high temperature conditions, and has excellent safety performance.

[0036] The present application will be further described in detail below in combination with specific embodiments, which cannot be understood as limiting the scope of the present application.

[0037] Example 1

[0038] The composition and weight content of the lithium ion electrolyte are as follows: wherein the first organic solvent (CAS No. 111-01-3) has the structural formula:

[0039]

[0040] The weight content of squalane is 5 wt%; the lithium salt is LiPF6, and the weight content of LiPF6 is 14 wt%; the carbonate organic solvent is EC, EMC and DEC, and the weight contents thereof are 5.25 wt%, 31.5 wt% and 15.75 wt% respectively, and the total weight content of the carbonate organic solvent is 52.5 wt%; the ether-based organic solvent is DME, and the weight content of DME is 22.5 wt%; the additives are VC and FEC, and the weight contents thereof are 1 wt% and 5 wt% respectively, and the total weight content of the additives is 6 wt%.

[0041] The lithium ion battery comprises a positive electrode, a negative electrode, a separator and the above-mentioned electrolyte solution, wherein the positive electrode material is LiNi 0.8 Co 0.1 Mn 0.1 O2, the negative electrode material is a silicon-based material (25% SiO x +75% artificial graphite), and the separator material is a PP / PE composite porous film.

[0042] Example 2

[0043] The difference from Example 1 is that the structural formula of the first organic solvent is:

[0044]

[0045] Example 3

[0046] The difference from Example 1 is that the structural formula of the first organic solvent is:

[0047]

[0048] Example 4

[0049] The difference from Example 1 is that the structural formula of the first organic solvent is:

[0050]

[0051] Example 5

[0052] The difference from Example 1 is that the structural formula of the first organic solvent is:

[0053]

[0054] Example 6

[0055] The difference from Example 1 is only that the structure of the first organic solvent is:

[0056]

[0057] Example 7

[0058] The difference from Example 1 is only that the structure of the first organic solvent is:

[0059]

[0060] Example 8

[0061] The difference from Example 1 is only that the weight content of the first organic solvent is 10wt%.

[0062] Example 9

[0063] The difference from Example 1 is only that the weight content of the first organic solvent is 15wt%.

[0064] Example 10

[0065] The difference from Example 1 is only that the weight content of the first organic solvent is 0.1wt%.

[0066] Example 11

[0067] The difference from Example 1 is only that the weight content of the first organic solvent is 20wt%.

[0068] Comparative Example 1

[0069] The difference from Example 1 is only that the first organic solvent is not added.

[0070] Performance test:

[0071] (1) First coulombic efficiency test of lithium ion battery

[0072] Formation stage: after the lithium ion battery of the example and the comparative example is placed at high temperature for 24h, it is charged at 45℃ with a constant current of 0.02C to a voltage of 3.0V, then charged with a constant current of 0.05C to a voltage of 3.2V, and then charged with a constant current of 0.1C to a voltage of 3.8V to end the formation.

[0073] The difference from Example 1 is only that the structure of the first organic solvent is:

[0074] Finally, record the charge capacity D1 of the formation and disassembly stage and the discharge capacity D2 of the disassembly stage. Test 6 lithium ion batteries in each group and take the average value. The first coulomb efficiency of the lithium ion battery (%) = (D1 / D2) x 100%.

[0075] (2) Hot box test of lithium ion battery

[0076] Take the lithium ion battery of the example and the comparative example, and charge it at a constant current of 0.33C to a voltage of 4.25V, and then charge it at a constant voltage of 4.25V to a current less than 0.05C. Then, take the lithium ion battery in a full state and place it in a 60℃ oven for 2-16h; the oven is heated to 130℃ at a heating rate of 2℃ / min, and is kept for 30min. Finally, the oven is heated to 200℃ at a heating rate of 2℃ / min, and is kept for 30min before being naturally cooled to room temperature. If a fire or explosion occurs during the heating process, the battery is determined to be invalid, and if no fire or explosion occurs, it is determined to be passed.

[0077] The test results are shown in Table 1 below:

[0078] Table 1

[0079]

[0080] From the above description, it can be seen that the above-mentioned examples of the present application achieve the following technical effects:

[0081] From the test results of Examples 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 and Comparative Example 1, it can be found that the addition of the first organic solvent in the lithium ion electrolyte can significantly improve the thermal stability of the lithium ion battery, thereby avoiding the occurrence of thermal runaway phenomenon under high temperature conditions, and further improving the safety performance of the lithium ion battery. And the addition of the first organic solvent does not have a negative impact on the chemical performance of the battery while improving its safety performance.

[0082] From the test results of Examples 1, 2, 3, 5 and Examples 4, 6, it can be found that when the weight content of the first organic solvent added in the lithium ion electrolyte is 5wt%, the test effect of the battery is better when squalane derivative 3 (Example 4) or squalane derivative 5 (Example 6) is used, which can further improve the thermal stability of the lithium ion battery and avoid the occurrence of thermal runaway phenomenon.

[0083] From the test results of Example 1, 9 and Example 8, it can be found that when the weight content of the first organic solvent added in the lithium ion electrolyte is 10wt% (such as Example 8), the test effect of the battery is better, and when the weight content of the first organic solvent added in the lithium ion electrolyte is 5wt% (such as Example 1) and 15wt% (such as Example 9), the battery hot box test results are 200℃ for 3min failure, 200℃ for 18min failure, respectively.

[0084] From the test results of Example 1, 8, 9, 10 and Example 11, it can be found that when the weight content of the first organic solvent added in the lithium ion electrolyte is within the range of 0.1-15wt% (such as 5% of Example 1, 10% of Example 8, 15% of Example 9 and 0.1% of Example 10), the lithium ion battery electrolyte prepared therefrom has better test effect in battery electric box test, which can further improve the thermal stability of the lithium ion battery and avoid the occurrence of thermal runaway phenomenon. When the weight content of the first organic solvent added in the lithium ion electrolyte is within the range of 5-10wt%, the initial efficiency and the thermal stability of the battery are better, and the comprehensive performance is better. When the weight content of the first organic solvent added in the lithium ion electrolyte is outside the range of 0.1-15wt% (20% of Example 11), the initial efficiency is greatly reduced, and the battery performance is poor.

[0085] The above only describes the preferred embodiments of the present application and is not used to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A lithium-ion battery electrolyte, characterized in that, The lithium ion battery electrolyte comprises a lithium salt, a first organic solvent and an additive; wherein The first organic solvent is selected from one or more of the following compounds: ； The weight content of the first organic solvent in the lithium ion battery electrolyte is 0.1-15wt%.

2. The electrolyte for lithium ion batteries according to claim 1, characterized in that, The weight content of the first organic solvent in the lithium ion battery electrolyte is 5-10wt%.

3. The electrolyte for lithium ion batteries according to claim 1, characterized in that, The lithium ion battery electrolyte further comprises a second organic solvent.

4. The electrolyte for lithium-ion batteries according to claim 3, characterized in that, The second organic solvent is a carbonate organic solvent.

5. The electrolyte for lithium-ion batteries according to claim 4, characterized in that, The carbonate organic solvent is a cyclic carbonate compound and / or a chain carbonate compound.

6. The electrolyte for lithium-ion batteries according to claim 5, characterized in that, The cyclic carbonate compound is selected from one or more of vinyl carbonate, propylene carbonate or gamma-butyrolactone L; and the chain carbonate compound is selected from one or more of dimethyl carbonate, diethyl carbonate or methyl ethyl carbonate.

7. The electrolyte for lithium ion batteries according to claim 3, characterized in that, The weight content of the second organic solvent in the lithium ion battery electrolyte is 30-60wt%.

8. The electrolyte for lithium ion batteries according to claim 1, characterized in that, The lithium ion battery electrolyte further comprises a third organic solvent.

9. The electrolyte for lithium ion batteries according to claim 8, characterized in that, The third organic solvent is an ether-based organic solvent.

10. The electrolyte for lithium ion batteries according to claim 9, characterized in that, The ether-based organic solvent is a cyclic ether compound and / or a chain ether compound.

11. The electrolyte for lithium ion batteries according to claim 10, characterized in that, The cyclic ether compound is selected from one or more of tetrahydrofuran, 2-methyltetrahydrofuran or 1,3-dioxolane; and the chain ether compound is selected from one or more of dimethoxymethane, 1,2-dimethoxyethane or diethylene glycol dimethyl ether.

12. The electrolyte for lithium ion batteries according to claim 8, characterized in that, The weight content of the third organic solvent in the lithium ion battery electrolyte is 10-30wt%.

13. The electrolyte for lithium-ion batteries according to claim 1, characterized in that, The lithium salt is selected from one or more of lithium hexafluorophosphate, lithium bisfluorosulfonylimide, lithium bis(trifluoromethylsulfonyl)imide, lithium trifluoromethylsulfonate, lithium tetrafluoroborate, lithium bisfluorooxalato borate or lithium bisoxalato borate.

14. The electrolyte for lithium-ion batteries according to claim 1, characterized in that, The weight content of the lithium salt in the lithium ion battery electrolyte is 10-15wt%.

15. The electrolyte for lithium-ion batteries according to claim 1, characterized in that, The additive is selected from one or more of vinylene carbonate, vinyl ethylene carbonate, fluorinated vinyl carbonate, 1,3-propane sultone, 1,4-butane sultone, 1,3-(1-propylene) sultone, vinyl sulfite, vinyl sulfate, tris(trimethylsilyl) phosphate or tris(trimethylsilyl) borate.

16. The electrolyte for lithium-ion batteries according to claim 1, characterized in that, The weight content of the additive in the lithium ion battery electrolyte is 1-10wt%.

17. The lithium-ion battery electrolyte of claim 16, wherein, The weight content of the additive in the lithium ion battery electrolyte is 3-8wt%.

18. The electrolyte for lithium-ion batteries according to claim 1, characterized in that, The lithium ion battery electrolyte comprises 13-15wt% of the lithium salt, 5-10wt% of the first organic solvent, 50-55wt% of the second organic solvent, 20-25wt% of the third organic solvent and 4-8wt% of the additive. The first organic solvent is ; the second organic solvent is ethylene carbonate, methyl ethyl carbonate and diethyl carbonate, and the weight ratio of ethylene carbonate, methyl ethyl carbonate and diethyl carbonate is 4-6:30-32:15-16; the third organic solvent is 1,2-dimethoxyethane; the additive is vinylene carbonate and fluoroethylene carbonate, and the weight ratio of vinylene carbonate and fluoroethylene carbonate is 1:4-6; and the lithium salt is lithium hexafluorophosphate.

19. A lithium-ion battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, characterized in that, The electrolyte is the lithium ion battery electrolyte according to any one of claims 1-18.

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