Electrolyte composition, application thereof and lithium ion battery

Abstract

The invention discloses an electrolyte composition, application thereof and a lithium ion battery. The electrolyte composition comprises a first electrolyte and a second electrolyte, the first electrolyte comprises a base solution, vinylene carbonate, methylene methanedisulfonate, ammonium perfluorooctane sulfonate and 1, 3, 6-hexane trinitrile, and the second electrolyte comprises a base solution, vinylene carbonate and fluoroethylene carbonate, the basic solution is a mixed solvent in which lithium salt is dissolved, and the mixed solvent comprises at least two of ethylene carbonate, propylene carbonate and diethyl carbonate. The electrolyte composition can be applied to preparation of a lithium ion battery for supplementing lithium. The invention also discloses a lithium ion battery comprising the electrolyte composition, a positive pole piece containing a lithium supplement agent, a negative pole piece containing a lithium supplement agent and a diaphragm. According to the electrolyte composition, the lithium supplement agent can play a better lithium supplement role, the 45 DEG C cycle performance of the lithium supplement battery is obviously improved, and the 45 DEG C cycle capacity is kept at 94% or above.

Description

Technical Field

[0001] The invention relates to an electrolyte and an application thereof, and in particular to an electrolyte composition for a lithium-supplemented lithium-ion battery and an application thereof and a lithium-ion battery. Background Art

[0002] Lithium replenishment technology for lithium-ion batteries is an important means to improve battery energy density. During the formation process of lithium-ion batteries, SEI growth on the negative electrode surface consumes active lithium, resulting in battery energy loss. Lithium replenishment technology can compensate for active lithium and achieve the effect of improving the energy density of lithium-ion batteries. In recent years, positive electrode lithium replenishment technology has begun to attract people's attention and research. Positive electrode lithium replenishment is achieved by adding lithium replenishment materials to the positive electrode of lithium-ion batteries. During the battery charging process, the lithium replenishment materials decompose and release active lithium to compensate for the irreversible active lithium loss caused by the growth of negative electrode SEI. Although lithium replenishers can compensate for the first irreversible capacity loss of the battery, lithium replenishers will produce a large amount of free metal ions and highly active singlet oxygen during the cycle process. Among them, metal ions will not only react with the electrolyte, but also destroy the structural stability of the negative electrode sheet; compared with active oxygen, highly active singlet oxygen has stronger oxidizing properties and is more difficult to adsorb. It will catalyze electrolyte reactions and produce a large amount of gas, resulting in poor battery cycle performance. Summary of the invention

[0003] Purpose of the invention: The purpose of the present invention is to provide an electrolyte composition to solve the problem that lithium supplement agents reduce the cycle performance of batteries. Another purpose of the present invention is to propose an application of an electrolyte composition in the preparation of lithium-ion batteries to solve the problem of how to prepare lithium-supplemented lithium-ion batteries. The third purpose of the present invention is to provide a lithium-supplemented lithium-ion battery with good cycle performance.

[0004] Technical solution: The electrolyte composition described in the present invention comprises a first electrolyte and a second electrolyte, wherein the first electrolyte comprises a base liquid, vinylene carbonate, methylene disulfonate, ammonium perfluorooctane sulfonate and 1,3,6-hexanetrinitrile, and the second electrolyte comprises a base liquid, vinylene carbonate and fluoroethylene carbonate, wherein the base liquid is a mixed solvent in which a lithium salt is dissolved, and the mixed solvent includes at least two of vinyl carbonate, propylene carbonate and diethyl carbonate.

[0005] The present invention uses a first electrolyte for a first injection and a second electrolyte for a second injection to improve the 45°C cycle performance of a lithium-supplemented lithium-ion battery. After screening the electrolyte formula, it was found that the combination of perfluorooctane sulfonic acid ammonium (PFOSA) and 1,3,6-hexanetrinitrile (HTCN) in the first electrolyte participates in the formation of a dense and stable solid electrolyte interface film, which can improve the thermal stability and ionic conductivity of the interface; the second electrolyte uses a high concentration of vinylene carbonate (VC) and fluoroethylene carbonate (FEC) to ensure the stability of the battery cell during the 45°C cycle.

[0006] Preferably, the first electrolyte contains the following components in mass fractions: 92.5-97.5% base liquid, 1-3% vinylene carbonate, 0.5-1.5% methylene disulfonate, 0.5-1.5% ammonium perfluorooctane sulfonate and 0.5-1.5% 1,3,6-hexanetrinitrile; the second electrolyte contains the following components in mass fractions: 84.5-89.5% base liquid, 10-14% vinylene carbonate and 0.5-1.5% fluoroethylene carbonate.

[0007] Preferably, the lithium salt is LiPF6 and LiFSI in a molar ratio of 3-5:1, and the mixed solvent is a mixture of ethylene carbonate, propylene carbonate and diethyl carbonate in a mass ratio of 1-2:1-2:1-2.

[0008] Preferably, the final concentration of LiPF6 in the base solution is 0.3-1.0 mol / L, and the final concentration of LiFSI is 0.1-0.3 mol / L.

[0009] The present invention further applies the above electrolyte composition to prepare a lithium ion battery, and the specific preparation method comprises the following steps:

[0010] (1) winding, assembling, baking, welding and sealing the positive electrode sheet, negative electrode sheet and separator containing the lithium supplement agent, and then injecting the first electrolyte to obtain a battery cell to be formed;

[0011] (2) After the battery cell is formed, the second electrolyte is injected into the battery cell, and the lithium-ion battery is obtained after packaging.

[0012] Preferably, the volume ratio of the first electrolyte to the second electrolyte is 80-90:10-20.

[0013] Preferably, in step (2), the formation method is: charging to 3.0V with a current rate of 0.1C; charging to 3.65V with a current rate of 0.16C; charging to 4.2V with a current rate of 0.05C; and discharging to 3.2V with a current rate of 0.2C.

[0014] Preferably, in step (1), the preparation method of the positive electrode sheet containing the lithium supplement agent is:

[0015] (1) Add the following raw materials in percentage by weight into a stirring tank: 94.3% lithium iron phosphate positive electrode material, 2% lithium-rich nickel oxide, 2% conductive agent, and 1.7% binder, and then add N-methylpyrrolidone and stir to prepare a positive electrode slurry;

[0016] (2) The positive electrode slurry is coated on both sides of the aluminum foil, and then baked, rolled, and cut into pieces to form positive electrode sheets;

[0017] The preparation method of the negative electrode plate is as follows:

[0018] (1) Add the following raw materials in percentage by weight into a stirring tank: 96% graphite, 2% conductive agent, 1% binder, and 1% thickener, and then add water and stir at high speed to prepare a negative electrode slurry;

[0019] (2) The negative electrode slurry is coated on both sides of the copper foil, which is then baked, rolled, and cut into pieces to form negative electrode sheets.

[0020] Another aspect of the present invention provides a lithium ion battery comprising the above electrolyte composition, a positive electrode sheet containing a lithium supplement, a negative electrode sheet and a separator.

[0021] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0022] 1. The electrolyte composition of the present invention can make the lithium replenishing agent play a greater role in replenishing lithium, and significantly improve the 45°C cycle performance of the lithium replenishing battery, and the 45°C cycle capacity is maintained at more than 94%.

[0023] 2. The present invention adopts a staged formation process for the lithium-supplemented battery cell to ensure that the electrode is fully infiltrated with the electrolyte and better discharge the formed gas, and implements a one-two injection scheme of different electrolytes. The first injection can better help the lithium-supplemented battery to form a stable interface film; the second injection can better prevent the membrane of the battery cell from rupturing during the cycle process, ensuring the long-cycle performance of the battery cell is stable. DETAILED DESCRIPTION

[0024] The technical solution of the present invention is further described below.

[0025] Embodiment 1: An electrolyte composition comprises a first electrolyte and a second electrolyte, wherein the first electrolyte comprises the following components in mass fractions: 95% base liquid, 2% vinylene carbonate, 1% methylene disulfonate, 1% ammonium perfluorooctane sulfonate and 1% 1,3,6-hexanetrinitrile; the second electrolyte comprises the following components in mass fractions: 87% base liquid, 12% vinylene carbonate and 1% fluoroethylene carbonate.

[0026] The base liquid is a mixed solvent in which LiPF6 with a final concentration of 0.8 mol / L and LiFSI with a final concentration of 0.2 mol / L are dissolved, and the mixed solvent is composed of ethylene carbonate (EC), propylene carbonate (EMC) and diethyl carbonate (DEC) in a mass ratio of 25:50:25.

[0027] The preparation methods of the first electrolyte and the second electrolyte are as follows:

[0028] (1) In an argon-protected glove box, LiPF6 and LiFSI are dissolved in a mixed solvent to obtain a base solution, and vinylene carbonate (VC), methylene disulfonate (MMDS), ammonium perfluorooctane sulfonate (PFOSA) and 1,3,6-hexanetrinitrile (HTCN) are added to the base solution according to the formula, and the mixture is mixed evenly to prepare a first electrolyte.

[0029] (2) Taking the base liquid in step (1), adding vinylene carbonate (VC) and fluoroethylene carbonate (FEC) into the base liquid according to the formula, and mixing them evenly to prepare a second electrolyte.

[0030] The first electrolyte and the second electrolyte are used to prepare a lithium ion battery, and the method is as follows:

[0031] (1) adding lithium iron phosphate (LFP) positive electrode material: lithium supplement (lithium-rich nickel oxide, LNO): conductive agent (SP): binder (5120) in a ratio of 94.3%: 2%: 2%: 1.7% (% refers to mass percentage) into a stirring tank, using N-methylpyrrolidone (NMP) as a solvent, and then stirring to prepare a positive electrode slurry;

[0032] (2) Prepare the positive electrode slurry at a single surface density of 260 mg / 1540.25 mm 2 It is double-sided coated on aluminum foil according to the standard, and then baked, rolled, and cut into pieces to make positive electrode sheets.

[0033] (3) adding graphite: conductive agent (SP): binder (SBR): thickener (CMC) in a ratio of 96%: 2%: 1.0%: 1% (% refers to mass percentage) into a stirring tank, using deionized water as a solvent, and then stirring at a high speed to prepare a negative electrode slurry;

[0034] (4) Prepare the negative electrode slurry at a single surface density of 130 mg / 1540.25 mm 2 The negative electrode is double-sided coated on the copper foil according to the standard, and then baked, rolled and cut into pieces to make the negative electrode sheet.

[0035] (5) winding, assembling, baking, welding and sealing the positive electrode sheet, the negative electrode sheet and the PE separator, and then injecting 85% of the total volume of the rated electrolyte into the first electrolyte at one time to prepare a battery cell to be formed;

[0036] (6) The battery to be formed is formed, and the formation process is as follows: charging to 3.0V at a current rate of 0.1C; charging to 3.65V at a current rate of 0.16C; charging to 4.2V at a current rate of 0.05C; and discharging to 3.2V at a current rate of 0.2C;

[0037] (7) The formed battery cell is cut open in a glove box, and a second electrolyte of 15% of the rated electrolyte total volume is injected for a second time, and then packaged to obtain a lithium-ion battery.

[0038] Embodiment 2: The rest is the same as Embodiment 1, except that:

[0039] The first electrolyte contains the following components in mass fraction: 97.5% base liquid, 1% vinylene carbonate, 0.5% methylene disulfonate, 0.5% ammonium perfluorooctane sulfonate and 0.5% 1,3,6-hexanetrinitrile; the second electrolyte contains the following components in mass fraction: 89.5% base liquid, 10% vinylene carbonate (VC) and 0.5% fluoroethylene carbonate.

[0040] The base solution is a mixed solvent in which LiPF6 with a final concentration of 0.3 mol / L and LiFSI with a final concentration of 0.1 mol / L are dissolved.

[0041] Injecting 80% of the total volume of the rated electrolyte into the first electrolyte at one time to prepare the battery cell to be formed;

[0042] A second electrolyte accounting for 20% of the total volume of the rated electrolyte is injected for a second time, and then the battery is packaged to obtain a lithium-ion battery.

[0043] Embodiment 3: The rest is the same as Embodiment 1, except that:

[0044] The first electrolyte contains the following components in mass fractions: 92.5% base liquid, 3% vinylene carbonate, 1.5% methylene disulfonate, 1.5% ammonium perfluorooctane sulfonate and 1.5% 1,3,6-hexanetrinitrile; the second electrolyte contains the following components in mass fractions: 84.5% base liquid, 14% vinylene carbonate (VC) and 1.5% fluoroethylene carbonate.

[0045] The base solution is a mixed solvent in which LiPF6 with a final concentration of 1.0 mol / L and LiFSI with a final concentration of 0.3 mol / L are dissolved.

[0046] Injecting 90% of the total volume of the rated electrolyte into the first electrolyte at one time to prepare the battery cell to be formed;

[0047] A second electrolyte accounting for 10% of the total volume of the rated electrolyte is injected for a second time, and then the battery is packaged to obtain a lithium-ion battery.

[0048] Comparative Example 1: The rest is the same as Example 1, except that:

[0049] Only vinylene carbonate (VC) and methylene methane disulfonate (MMDS) were added to the base solution and mixed evenly to prepare electrolyte 1.

[0050] 100% of the rated total electrolyte volume of electrolyte 1 is injected once, and a lithium ion battery is obtained after formation without secondary injection.

[0051] Comparative Example 2: The rest is the same as Example 1, except that:

[0052] Only vinylene carbonate (VC), methylene methane disulfonate (MMDS) and ammonium perfluorooctane sulfonate (PFOSA) were added to the base solution and mixed evenly to prepare electrolyte 2.

[0053] 100% of the rated total electrolyte volume of electrolyte 2 is injected once, and a lithium ion battery is obtained after formation without secondary injection.

[0054] Comparative Example 3: The rest is the same as Example 1, except that:

[0055] Only vinylene carbonate (VC), methylene disulfonate (MMDS) and 1,3,6-hexanetrinitrile (HTCN) were added to the base solution and mixed evenly to prepare electrolyte 3.

[0056] The electrolyte 3 of 100% of the rated total electrolyte volume is injected once, and a lithium ion battery is obtained after formation without secondary injection.

[0057] Comparative Example 4: The rest is the same as Example 1, except that:

[0058] The first electrolyte of 100% of the rated total electrolyte volume is injected once, and a lithium-ion battery is obtained after formation without secondary injection.

[0059] Comparative Example 5: The rest is the same as Example 1, except that:

[0060] The second electrolyte of 100% of the total volume of the rated electrolyte is injected at one time, and a lithium-ion battery is obtained after formation without secondary injection.

[0061] The lithium-ion batteries prepared in Examples 1-3 and Comparative Examples 1-5 were subjected to cycle tests at 45°C, with a voltage range of (2.5-3.65V), 1C charging and 1C discharging, and 3 parallel samples were made at the same time. The results are as follows:

[0062] Table 1 Performance test results of batteries assembled with different electrolytes

[0063]

[0064] The results in Table 1 show that the cycle performance of the lithium-ion battery obtained by injecting the first electrolyte or the second electrolyte alone is poor, and the problem of the reduction of the battery cycle performance by the lithium supplement cannot be solved. Only when the first electrolyte and the second electrolyte are used together can better cycle performance be obtained, reversing the negative effects of the lithium supplement. In addition, the core component formula of the first electrolyte and the second electrolyte is helpful to improve the cycle performance of the lithium supplement battery.

[0065] Embodiment 4: The rest is the same as Embodiment 1, except that:

[0066] Taking the injection volume ratio of the first electrolyte and the second electrolyte as a variable, different lithium-ion battery samples were prepared and the cycle performance was tested. The results are as follows:

[0067] Table 2 Effect of the injection volume ratio of the first electrolyte and the second electrolyte on battery performance

[0068]

[0069]

[0070] The results in Table 2 show that the first electrolyte and the second electrolyte can only effectively improve the battery cycle performance degradation caused by the lithium supplement when the volume ratio is appropriate. Too high or too low volume ratio will lead to a decrease in the battery cycle performance.

Claims

1. An electrolyte composition, characterized in that: The invention comprises a first electrolyte and a second electrolyte, wherein the first electrolyte comprises a base liquid, vinylene carbonate, methylene disulfonate, ammonium perfluorooctane sulfonate and 1,3,6-hexanetrinitrile, and the second electrolyte comprises a base liquid, vinylene carbonate and fluoroethylene carbonate, wherein the base liquid is a mixed solvent in which a lithium salt is dissolved, and the mixed solvent comprises at least two of vinyl carbonate, propylene carbonate and diethyl carbonate.

2. The electrolyte composition according to claim 1, characterized in that: The first electrolyte contains the following components in mass fraction: 92.5-97.5% base liquid, 1-3% vinylene carbonate, 0.5-1.5% methylene disulfonate, 0.5-1.5% ammonium perfluorooctane sulfonate and 0.5-1.5% 1,3,6-hexanetrinitrile; the second electrolyte contains the following components in mass fraction: 84.5-89.5% base liquid, 10-14% vinylene carbonate and 0.5-1.5% fluoroethylene carbonate.

3. The electrolyte composition according to claim 1, characterized in that: The lithium salt is LiPF6 and LiFSI in a molar ratio of 3-5:1, and the mixed solvent is a mixture of ethylene carbonate, propylene carbonate and diethyl carbonate in a mass ratio of 1-2:1-2:1-2.

4. The electrolyte composition according to claim 3, characterized in that: The final concentration of LiPF6 in the base solution is 0.3-1.0 mol / L, and the final concentration of LiFSI is 0.1-0.3 mol / L.

5. Use of the electrolyte composition according to any one of claims 1 to 4 in the preparation of lithium ion batteries.

6. The use according to claim 5, characterized in that: The steps include: (1) winding, assembling, baking, welding and sealing the positive electrode sheet, negative electrode sheet and separator containing the lithium supplement agent, and then injecting the first electrolyte to obtain a battery cell to be formed; (2) After the battery cell is formed, the second electrolyte is continuously injected, and the lithium-ion battery is obtained after packaging.

7. The use according to claim 6, characterized in that: The volume ratio of the first electrolyte to the second electrolyte is 80-90:10-20.

8. The use according to claim 6, characterized in that: In step (2), the formation method is: charging to 3.0V with a current rate of 0.1C; charging to 3.65V with a current rate of 0.16C; charging to 4.2V with a current rate of 0.05C; and discharging to 3.2V with a current rate of 0.2C.

9. The use according to claim 6, characterized in that: In step (1), the preparation method of the positive electrode sheet containing the lithium supplement agent is: (1) Add the following raw materials in percentage by weight into a stirring tank: 94.3% lithium iron phosphate positive electrode material, 2% lithium-rich nickel oxide, 2% conductive agent, and 1.7% binder, and then add N-methylpyrrolidone and stir to prepare a positive electrode slurry; (2) The positive electrode slurry is coated on both sides of the aluminum foil, and then baked, rolled, and cut into pieces to form positive electrode sheets; The preparation method of the negative electrode plate is as follows: (1) Add the following raw materials in percentage by weight into a stirring tank: 96% graphite, 2% conductive agent, 1% binder, and 1% thickener, and then add water and stir at high speed to prepare a negative electrode slurry; (2) Coating the negative electrode slurry on both sides of the copper foil, baking, rolling and cutting into negative electrode sheets.

10. A lithium ion battery comprising the electrolyte composition according to any one of claims 1 to 4, a positive electrode sheet containing a lithium supplement, a negative electrode sheet and a separator.

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