Electrolyte for lithium manganate lithium ion battery and preparation method of electrolyte

Abstract

The invention discloses an electrolyte for a lithium manganate lithium ion battery and a preparation method thereof, and the electrolyte comprises the following components in percentage by mass: 70-90% of an organic solvent, 5-20% of a lithium salt and 0.5-10% of an additive, the organic solvent is formed by mixing cyclic carbonate and chain carbonate according to the mass ratio of (10-30): (70-90); the lithium salt adopts one or more of lithium hexafluorophosphate (LiPF), lithium tetrafluoroborate (LiBF) and lithium bis (trifluoromethane sulfonimide) (LiTFSI), and the concentration of the lithium salt is 0.8 to 1.5 mol / L; the additives comprise a manganese ion complexing agent, a film forming accelerant and an antioxidant. In the invention, the manganese ion inhibition effect is as follows: the complexing agent and Mn (II) ions form a stable complex, so that the concentration of free Mn (II) in the electrolyte is reduced by more than 80%, migration and deposition of the free Mn (II) to the negative electrode are inhibited, and the dissolution amount of the Mn element of the positive electrode is reduced by 65% after 500 times of circulation at 45 DEG C.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to an electrolyte for lithium manganate lithium ion batteries and a preparation method thereof. Background Art

[0002] In lithium manganate -In graphite lithium-ion battery systems, the problem of manganese dissolution caused by crosstalk between positive and negative electrodes seriously restricts battery performance. During charging, The manganese element in the positive electrode material dissolves from the crystal lattice in the form of Mn(II) ions and enters the electrolyte, and then migrates to the surface of the graphite negative electrode by free diffusion. These manganese ions may be in the form of metallic manganese ( ) form or participate in the formation of solid electrolyte interface film (SEI), which has a dual impact on battery performance: on the one hand, the embedded SEI Metal particles act as electron conductors, destroying the electronic insulation of SEI, triggering continuous reduction and decomposition of the electrolyte, and accelerating SEI degradation; on the other hand, the dissolved Mn(II) ions destroy the positive electrode lattice structure, reduce the reversible lithium storage sites, and at the same time undergo ion exchange with Li⁺ between graphite layers, causing the collapse of the graphite layered structure, and ultimately causing rapid decay of battery capacity.

[0003] The existing conventional electrolyte system is difficult to inhibit the dissolution and migration of manganese elements. The main defects include: lack of complex capture ability for Mn(II) ions, unable to prevent crosstalk between the positive and negative electrodes; insufficient stability of the SEI film structure, difficult to resist Interfacial side reactions caused by deposition; the electrolyte has poor redox stability and is prone to synergistic decomposition with dissolved manganese ions at high temperatures. Therefore, developing a new electrolyte that can effectively inhibit manganese crosstalk is of great significance to improving the life of lithium manganese oxide batteries. Summary of the Invention

[0004] Based on the technical problems existing in the background technology, the present invention proposes an electrolyte for lithium manganese oxide lithium ion batteries and a preparation method thereof. By adding a manganese ion complexing agent and a SEI film optimizer, the dissolution and migration of manganese elements are inhibited, the stability of the SEI film is improved, thereby improving the cycle life and high-temperature performance of the battery.

[0005] The present invention provides an electrolyte for lithium manganate lithium ion batteries, comprising an organic solvent, a lithium salt and an additive, wherein the mass percentage of the organic solvent is 70-90%, the mass percentage of the lithium salt is 5-20%, and the mass percentage of the additive is 0.5-10%. The organic solvent is composed of a mixture of cyclic carbonate and chain carbonate in a mass ratio of 10-30:70-90; The lithium salt is lithium hexafluorophosphate ( ), lithium tetrafluoroborate ( ), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), with a concentration of 0.8-1.5 mol / L; The additives include manganese ion complexing agents, film-forming promoters and antioxidants.

[0006] As a preferred solution of the present invention, the cyclic carbonate is one or both of ethylene carbonate (EC) and propylene carbonate (PC).

[0007] As a preferred solution of the present invention, the chain carbonate is one or more of dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC).

[0008] As a preferred solution of the present invention, the manganese ion complexing agent is one or more of ethylenediaminetetraacetic acid (EDTA), disodium EDTA, citric acid, and tartaric acid.

[0009] As a preferred solution of the present invention, the added amount of the manganese ion complexing agent is 0.5-5% of the total mass of the electrolyte, which stabilizes the Mn(II) ions through coordination bonds and inhibits their migration.

[0010] As a preferred solution of the present invention, the film-forming promoter is a mixture of fluoroethylene carbonate (FEC) and tris(2,2,2-trifluoroethyl)phosphite (TTFEP) in a mass ratio of 1:1-3.

[0011] As a preferred solution of the present invention, the addition amount of the film-forming promoter is 0.5-4% of the total mass of the electrolyte, which promotes the formation of a dense SEI film rich in LiF and phosphate.

[0012] As a preferred solution of the present invention, the antioxidant is phenothiazine (PTZ).

[0013] As a preferred solution of the present invention, the antioxidant is added in an amount of 0.1-2% of the total mass of the electrolyte to inhibit the oxidative decomposition of the electrolyte caused by manganese ions at high temperatures.

[0014] The present invention also provides a method for preparing an electrolyte for a lithium manganate lithium ion battery, comprising the following components: Organic solvent: EC-15g, EMC-30g, DMC-45g; Lithium salts: -14g; Additives: disodium EDTA-1.5g, FEC-1g, TTFEP-2g, PTZ-1g; The preparation steps are as follows: Mix the organic solvent and add , stir until completely dissolved, then add disodium EDTA, FEC, TTFEP, and PTZ in sequence, and continue stirring for 2 hours until uniform and transparent to obtain the electrolyte.

[0015] The beneficial effects of the present invention are: 1. Manganese ion inhibition effect: The complexing agent forms a stable complex with Mn(II) ions, reducing the concentration of free Mn(II) in the electrolyte by more than 80%, inhibiting its migration and deposition to the negative electrode. After 500 cycles at 45°C, the dissolution of Mn elements in the positive electrode is reduced by 65%.

[0016] 2. Improved SEI film stability: The composite SEI generated by the synergistic effect of FEC and TTFEP effectively blocks Mn 0 Due to the interfacial side reaction caused by deposition, after 1000 cycles at 1C at 25°C, the battery capacity retention rate of the battery using the electrolyte of the present invention reached more than 85%, which is 10-25 percentage points higher than that of the conventional electrolyte (capacity retention rate 70%); after storage at 55°C for 180 days, the capacity recovery rate reached 85-90%, which is significantly better than the control group without adding a complexing agent by 10-20%. DETAILED DESCRIPTION

[0017] The present invention will be further explained below with reference to specific embodiments.

[0018] This embodiment provides an electrolyte for a lithium manganate lithium-ion battery, comprising an organic solvent, a lithium salt, and an additive, wherein the mass percentage of the organic solvent is 70-90%, the mass percentage of the lithium salt is 5-20%, and the mass percentage of the additive is 0.5-10%. The organic solvent is composed of a mixture of cyclic carbonate and chain carbonate in a mass ratio of 10-30:70-90; The lithium salt is lithium hexafluorophosphate ( ), lithium tetrafluoroborate ( ), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), with a concentration of 0.8-1.5 mol / L; The additives include manganese ion complexing agents, film-forming promoters and antioxidants.

[0019] In this embodiment, the cyclic carbonate is one or both of ethylene carbonate (EC) and propylene carbonate (PC), and the chain carbonate is one or more of dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC).

[0020] In this embodiment, the manganese ion complexing agent is one or more of ethylenediaminetetraacetic acid (EDTA), disodium EDTA, citric acid, and tartaric acid. The manganese ion complexing agent is added in an amount of 0.5-5% of the total mass of the electrolyte, stabilizing the Mn(II) ions through coordination bonds and inhibiting their migration. The film-forming promoter is fluoroethylene carbonate (FEC) and tris(2,2,2-trifluoroethyl) phosphite (TTFEP) in a mass ratio of 1:1-3. The film-forming promoter is added in an amount of 0.5-4% of the total mass of the electrolyte, promoting the formation of a dense SEI film rich in LiF and phosphate. The antioxidant is phenothiazine (PTZ), and the antioxidant is added in an amount of 0.1-2% of the total mass of the electrolyte, inhibiting the oxidative decomposition of the electrolyte caused by manganese ions at high temperatures. Example 1

[0021] The electrolyte formula is as follows: Organic solvent: EC-15g, EMC-30g, DMC-45g; Lithium salts: -14g; Additives: disodium EDTA-1.5g, FEC-1g, TTFEP-2g, PTZ-1g; The preparation method is as follows: Mix the organic solvent and add , stir until completely dissolved, then add disodium EDTA, FEC, TTFEP, and PTZ in sequence, and continue stirring for 2 hours until uniform and transparent. Example 2

[0022] The electrolyte formula is as follows: Organic solvent: PC-20g, DEC-30g, EMC-40g; Lithium salts: -12g, LiTFSI-2g; Additives: citric acid-2g, FEC-1.5g, TTFEP-1.5g, PTZ-0.5g. Example 3

[0023] The electrolyte formula is as follows: Organic solvent: EC-10g, DMC-60g, DEC-30g; Lithium salts: -10g, -5g; Additives: EDTA-3g, FEC-2g, PTZ-1g.

[0024] Comparative Example 1 The electrolyte formula is as follows: Organic solvent: EC-15g, EMC-30g, DMC-45g; Lithium salts: -14g; Additives: FEC-1g, TTFEP-2g, PTZ-1g (no complexing agent added).

[0025] Performance testing: The above electrolyte was injected into a 26650 lithium manganese oxide-graphite battery cell (capacity 4.0Ah) and the following tests were performed: 1. Cycle test: 1C charge / 1C discharge at 25°C, cycle 1000 times, and record the capacity retention rate; 2. Manganese dissolution test: After 5000 cycles at 25°C, the Mn element dissolution amount of the positive electrode material was detected by ICP-MS; High temperature storage recovery rate: Store at 55°C for 180 days and record the recovery rate.

[0026] The test results are shown in the following table:

[0027] The above data show that the examples with the addition of manganese ion complexing agents significantly improved the battery performance compared with the comparative examples, among which Example 3 had the best comprehensive performance, verifying the synergistic inhibitory effect of the complexing agent and the film-forming agent.

[0028] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. An electrolyte for lithium manganate lithium ion battery, comprising an organic solvent, a lithium salt and an additive, characterized in that: The mass percentage of the organic solvent is 70-90%, the mass percentage of the lithium salt is 5-20%, and the mass percentage of the additive is 0.5-10%; The organic solvent is composed of a mixture of cyclic carbonate and chain carbonate in a mass ratio of 10-30:70-90; The lithium salt is one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, and lithium bis(trifluoromethanesulfonyl)imide, with a concentration of 0.8-1.5 mol / L; The additives include manganese ion complexing agents, film-forming promoters and antioxidants.

2. The electrolyte for lithium manganate lithium ion battery according to claim 1, characterized in that: The cyclic carbonate is one or both of ethylene carbonate and propylene carbonate.

3. The electrolyte for lithium manganate lithium ion battery according to claim 1, characterized in that: The chain carbonate is one or more of dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate.

4. The electrolyte for lithium manganate lithium ion battery according to claim 1, characterized in that: The manganese ion complexing agent is one or more of ethylenediaminetetraacetic acid, disodium EDTA, citric acid, and tartaric acid.

5. The electrolyte for lithium manganate lithium ion battery according to claim 4, characterized in that: The added amount of the manganese ion complexing agent is 0.5-5% of the total mass of the electrolyte.

6. The electrolyte for lithium manganate lithium ion battery according to claim 1, characterized in that: The film-forming accelerator is a mixture of fluoroethylene carbonate and tris(2,2,2-trifluoroethyl)phosphite in a mass ratio of 1:1-3.

7. The electrolyte for lithium manganate lithium ion battery according to claim 6, characterized in that: The added amount of the film-forming promoter is 0.5-4% of the total mass of the electrolyte.

8. The electrolyte for lithium manganate lithium ion battery according to claim 1, characterized in that: The antioxidant is phenothiazine.

9. The electrolyte for lithium manganate lithium ion battery according to claim 8, characterized in that: The added amount of the antioxidant is 0.1-2% of the total mass of the electrolyte.

10. A method for preparing an electrolyte for a lithium manganate lithium ion battery, characterized in that: Includes the following ingredients: Organic solvent: EC-15g, EMC-30g, DMC-45g; Lithium salts: -14g; Additives: disodium EDTA-1.5g, FEC-1g, TTFEP-2g, PTZ-1g; The preparation steps are as follows: Mix the organic solvent and add , stir until completely dissolved, then add disodium EDTA, FEC, TTFEP, and PTZ in sequence, and continue stirring for 2 hours until uniform and transparent to obtain the electrolyte.

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