CN108172901A - A kind of additive of high-voltage lithium-ion battery electrolyte - Google Patents

Abstract

The invention belongs to the technical field of electrolyte systems of lithium-ion batteries, and in particular relates to an electrolyte additive for high-voltage lithium-ion batteries. An additive for the electrolyte of a high-voltage lithium ion battery, the electrolyte includes an electrolyte additive, an electrolyte lithium salt, and an organic solvent, the electrolyte additive is trimethylsilyl trimethylsiloxy acetate, the electrolyte lithium salt is lithium hexafluorophosphate, and the organic solvent It is a mixture of ethylene carbonate and diethyl carbonate. The additive of the present invention greatly improves the cycle performance and high rate performance of the lithium battery under the conditions of 500 cycles and a high rate of 5C.

Description

A kind of additive of high-voltage lithium-ion battery electrolyte

technical field

The invention belongs to the technical field of electrolyte systems of lithium-ion batteries, and in particular relates to an additive for electrolytes of high-voltage lithium-ion batteries.

Background technique

As a new type of green high-energy battery, lithium-ion batteries are widely used in mobile phones, cameras, notebooks, etc. Portable devices such as computers. The organic electrolyte is an important part of the lithium-ion battery, which plays the role of transferring charge between the positive and negative electrodes in the battery. The electrolyte is generally composed of electrolyte lithium salt and organic solvent. At present, the electrolyte lithium salt used in lithium-ion batteries is lithium hexafluorophosphate, and the organic solvents are EC (ethylene carbonate), PC (propylene carbonate), DMC (dimethyl carbonate), DEC (diethyl carbonate), EMC (carbonic acid Methyl ethyl ester) and a mixed solution of two or more cyclic carbonates. The formula composition, water content, hydrofluoric acid, and metal impurity ion content of the electrolyte affect the high and low temperature performance, capacity, service life, and safety of the battery.

Lithium hexafluorophosphate is exothermic when it is added to an organic solvent. If there is a small amount of water in the electrolyte, it will cause a hydrolysis reaction of lithium hexafluorophosphate. The reaction formula is LiPF6+H ₂ O→LiF+POF ₃ +2HF. The higher the water content in the electrolyte, the higher the LiF and HF content. On the one hand, LiF will cause the electrode/electrolyte interface impedance for lithium-ion batteries and increase the internal resistance of the battery. On the other hand, HF will react with the SEI film on the electrode surface, resulting in the continuous reduction of battery specific capacity and cycle efficiency, until the entire battery is damaged. When the water content in the electrolyte exceeds 0.1%, it will completely destroy the lithium-ion battery. In addition, when the voltage is higher than 4.2V, the electrolyte will be oxidized and decomposed, which will deteriorate the high-voltage cycle performance of the lithium battery and greatly shorten the service life of the lithium-ion battery.

Therefore, conventional aqueous high-voltage electrolytes have the disadvantages of low battery cycle performance and capacity retention, and cannot meet people's needs for lithium-ion batteries with high capacity retention.

Contents of the invention

The object of the present invention is to overcome the relatively poor defect of prior art lithium battery cycle performance and provide a kind of additive of high voltage lithium ion battery electrolyte.

An additive for the electrolyte of a high-voltage lithium-ion battery, the electrolyte includes an electrolyte additive, an electrolyte lithium salt, and an organic solvent, the electrolyte additive is trimethylsilyl trimethylsiloxy acetate, and the electrolyte lithium The salt is lithium hexafluorophosphate, and the organic solvent is a mixture of ethylene carbonate and diethyl carbonate.

Preferably, in the electrolytic solution, the mass content of trimethylsilyl trimethylsiloxy acetate is 0.5%-1.5%.

Preferably, in the electrolytic solution, the mass content of trimethylsilyl trimethylsiloxy acetate is 1%.

Preferably, the concentration of the electrolyte lithium salt solution is 1 mol/L.

Preferably, the volume ratio of ethylene carbonate to diethyl carbonate is 1:1.

Beneficial effects of the present invention: (1) The additive of the present invention can effectively improve the cycle performance and rate performance of the lithium battery under the conditions of 500 cycles and a high rate of 5C, which is different from the prior art (cycle of 100 cycles and rate of 2C). big difference. Most importantly, the improvement of this battery performance is only added to the high-voltage lithium-ion battery electrolyte for the additive of the present invention, i.e., trimethylsilyl trimethylsiloxy acetate, rather than a class of battery electrolyte additives. Because the battery electrolyte additive also needs to consider the compatibility with electrolyte, consider the stability factor of electrolyte solute; (2) the invention provides a kind of electrolyte additive namely trimethylsilyl trimethylsiloxy acetate, The additive can directly react with the water in the electrolyte, that is, remove water from the source (electrolyte), and there is no relevant report so far. When the additive of the present invention reacts with water, the reaction mechanism is different from that of the prior art. The present invention breaks carbonyl oxygen and oxygen bonds in the additive to generate fat and acid to prevent HF from being produced, while the prior art is to break Si-O to generate Si-F to reduce the HF concentration; (3) the present invention removes On the other hand, it reduces the side reactions in the electrolyte, prevents the generation of HF in the electrolyte, reduces the corrosion degree of the electrode active material and the current collector, and significantly improves the cycle stability of the battery; ( 4) The additive of the present invention has good compatibility with the electrolyte. The carbonyl group in the additive belongs to the Lewis base, which can stabilize the lithium salt lithium hexafluorophosphate in the electrolyte, reduce the decomposition of lithium hexafluorophosphate, thereby reduce the thickness of the SEI film and enhance the cycle stability of the lithium-ion battery.

Description of drawings

Fig. 1 is the lithium battery 1a of the present invention, lithium battery 2a, lithium battery 3a, the performance test comparison curve of lithium battery 4a under magnification 1C;

Fig. 2 is a performance test comparison curve of the lithium battery 2a of the present invention and the lithium battery 4a at a high rate of 5C;

Figure 3 is a linear sweep voltammetry (LSV) test chart.

Detailed ways

The present invention will be further described below in conjunction with specific examples.

Example 1

Preparation of lithium ion battery electrolyte 1: dissolve lithium hexafluorophosphate in an organic solvent to obtain a 1mol/L lithium salt solution, stir, the organic solvent is a mixture of ethylene carbonate and diethyl carbonate, ethylene carbonate and diethyl carbonate The volume ratio is 1:1, and trimethylsilyl trimethylsiloxy acetate with a mass content of 0.5% is added to the lithium salt solution to prepare lithium-ion battery electrolyte solution 1.

Preparation of lithium battery 1a: Celgard 2400 diaphragm is used, the positive electrode material of the battery is Li _1.2 Ni _0.2 Mn _0.6 O ₂ , the negative electrode material of the battery is metal lithium sheet, and the lithium ion battery electrolyte 1 is used to assemble a button Formula lithium-rich battery, as lithium battery 1a.

Example 2

Preparation of Lithium-ion battery electrolyte 2: This example is basically the same as the preparation method of Lithium-ion battery electrolyte 1 in Example 1, the difference is that this example is an additive, namely trimethylsilyltrimethylsiloxyacetic acid The mass content of the ester is 1%, and the lithium-ion battery electrolyte 2 is prepared.

Preparation of lithium battery 2a: This embodiment is basically the same as the preparation method of lithium battery 1a in Example 1. The difference is that this embodiment uses lithium ion battery electrolyte 2 and assembles it into a button-type lithium-rich battery. Battery 2a.

Example 3

Preparation of Lithium-ion battery electrolyte 3: This example is basically the same as the preparation method of Lithium-ion battery electrolyte 1 in Example 1, the difference is that this example is an additive, namely trimethylsilyltrimethylsiloxyacetic The mass content of the ester is 1.5%, and the lithium-ion battery electrolyte 3 is obtained.

Preparation of lithium battery 3a: This embodiment is basically the same as the preparation method of lithium battery 1a in Example 1. The difference is that this embodiment uses lithium-ion battery electrolyte 3 and assembles it into a button-type lithium-rich battery. Battery 3a.

comparative example

Preparation of Lithium-ion battery electrolyte solution 4: This example is basically the same as the preparation method of Lithium-ion battery electrolyte solution 1 in Example 1, the difference is that this step in Example 1 is removed: "into the lithium salt solution Adding mass content is 0.5% trimethylsilyl trimethylsiloxy acetate ", and finally obtain lithium-ion battery electrolyte 4.

Preparation of lithium battery 4a: This embodiment is basically the same as the preparation method of lithium battery 1a in Example 1. The difference is that this embodiment adopts lithium ion battery electrolyte 4 and assembles it into a button-type lithium-rich battery. Battery 4a.

High-voltage lithium-ion battery cycle performance test:

Test conditions: the positive electrode material of the battery is Li _1.2 Ni _0.2 Mn _0.6 O ₂ , the negative electrode material of the battery is metal lithium sheet; the battery diaphragm is Celgard 2400 diaphragm. At 25°C, activated at 0.1C, with a voltage of 2-4.8V, cycled for 500 cycles, and tested the cycle performance of the high-voltage lithium ion battery after 1C (c=250mA·g ^-1 ) formation.

As shown in FIG. 1 , FIG. 1 is a performance test comparison curve of the lithium battery 1a, the lithium battery 2a, the lithium battery 3a, and the lithium battery 4a of the present invention at a rate of 1C. In the lithium ion battery electrolyte 4 obtained in the comparative example, when circulating 297 circles, the lithium battery 4a was damaged; in the lithium ion battery electrolyte 1, the lithium ion battery electrolyte 2, the lithium ion battery electrolyte 3, when the cycle After 500 cycles, the specific capacity of lithium battery 1a is 60mAh·g ^-1 , and the capacity retention rate is 39%; the specific capacity of lithium battery 2a is 108mAh·g ^-1 , and the capacity retention rate is 64%; the specific capacity of lithium battery 3a is It was 79mAh·g ^-1 , and the capacity retention rate was 47%. Specifically, see Table 1.

Table 1 Performance test comparison of lithium battery 1a, lithium battery 2a, lithium battery 3a, and lithium battery 4a

From Table 1, it can be seen that under high pressure (2-4.8V) conditions, using the electrolyte additive of the present invention, after 500 cycles, the lithium battery still has a high capacity retention rate, which can effectively improve the lithium ion battery. cycle performance and rate performance. And do not add electrolytic solution additive of the present invention in contrast, when circulating 297 times, lithium battery 4a damages.

Fig. 2 is a performance test comparison curve of the lithium battery 2a of the present invention and the lithium battery 4a at a high rate of 5C. At a high rate of 5C, the specific capacity of the lithium battery 2a prepared in Example 2 was 107mAh·g ^-1 , while the specific capacity of the lithium battery 4a was 70mAh·g ^-1 in the control without adding the electrolyte additive of the present invention.

After comparison, it is found that after adding the additive of the present invention, the cycle performance and high rate performance of the battery are significantly improved.

Figure 3 is a linear sweep voltammetry (LSV) test chart.

LSV test conditions: use glassy carbon electrode as working electrode, silver wire as reference electrode, platinum electrode as counter electrode, test at 2-4.8V, scan rate 0.1mv·S ^-1 . Put the three electrodes in the electrolyte, from 2V to 4.8V, respectively scan the electrolyte solution (2) with 1% additive and the electrolyte solution (1) without additive. In Fig. 3, no obvious oxidation peak is found in the electrolyte (2) curve of 1% additive, which proves that the present invention does not break the Si-O bond. That is, when the additive of the present invention reacts with the water in the electrolyte, the carbonyl oxygen and the oxygen bond are broken to generate fat and acid to prevent the production of HF. However, in the prior art, Si-O is broken to generate Si-F to reduce the concentration of HF. , different from the prior art; prior art such as Sang Hoo Lim, Woosuk Cho, Young-Jun Kim, Taeeun Yim: Insight into the electrochemical behaviors of 5V-class high-voltage batteries composed of lithium-rich layered oxide with multifunctional additive, Journal of Power Sources 336(2016) 466. In the LSV test chart of Fig.1.(b), the blue curve has a very obvious oxidation peak, which is due to the breakage of the Si-O bond.

The above are only some embodiments of the present invention, and are not intended to limit the present invention in any form. Any simple modifications made to the above-mentioned embodiments according to the technical essence of the present invention, equivalent changes and modifications, all belong to the technical solution of the present invention within range.

Claims (5)

1. An additive for a high-voltage lithium-ion battery electrolyte, characterized in that: said electrolyte comprises electrolyte additive, electrolyte lithium salt, organic solvent, and said electrolyte additive is trimethylsilyltrimethylsiloxyacetic acid ester, the electrolyte lithium salt is lithium hexafluorophosphate, and the organic solvent is a mixture of ethylene carbonate and diethyl carbonate. 2. The additive for the electrolyte of the high-voltage lithium-ion battery according to claim 1, characterized in that: in the electrolyte, the mass content of trimethylsilyl trimethylsiloxy acetate is 0.5%-1.5%. 3. The additive for the electrolyte of the high-voltage lithium-ion battery according to claim 1, characterized in that: in the electrolyte, the mass content of trimethylsilyl trimethylsiloxy acetate is 1%. 4. The additive for the electrolyte solution of the high-voltage lithium-ion battery according to claim 1, characterized in that: the concentration of the electrolyte lithium salt solution is 1mol/L. 5. The additive for the electrolyte of the high-voltage lithium-ion battery according to claim 1, wherein the volume ratio of the ethylene carbonate to diethyl carbonate is 1:1.