Electrolytic solution additive for improving high and low temperature performance of lithium battery, preparation method of electrolytic solution additive, electrolytic solution and electrochemical device

Abstract

The invention discloses an electrolytic solution additive for improving high and low temperature performance of a lithium battery, a preparation method of the electrolytic solution additive, an electrolytic solution containing the electrolytic solution additive and an electrochemical device. The electrolytic solution additive is shown in the following structural formula defined in the specification, and can relatively improve the discharge capacity retention ratio of a lithium battery containing the electrolytic solution additive at high temperature and low temperature and the cycle capacity retention ratio at high temperature and low temperature.

Description

technical field [0001] The present application relates to the field of lithium batteries, and more specifically, to an electrolyte additive for improving the high and low temperature performance of lithium batteries, a preparation method thereof, an electrolyte containing the electrolyte additive, and an electrochemical device. Background technique [0002] Lithium battery is a secondary battery (rechargeable battery) that mainly relies on lithium ions (Li + ) to work by moving between positive and negative poles. During the charging process of lithium battery, Li + Deintercalation from the positive electrode, intercalation into the negative electrode through the electrolyte, makes the negative electrode in a lithium-rich state, and realizes the conversion of electrical energy into chemical energy, while the discharge process is just the opposite. [0003] Lithium batteries are widely used in 3C consumer batteries, power batteries, and energy storage batteries due to their...

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Problems solved by technology

Among them, lithium hexafluorophosphate (LiPF6) is mostly used as the electrolyte lithium salt in commercial electrolytes, but it is unstable at high temperatures, and generally begins to decompose when it reaches 60°C, producing PF5 and other substances, these substances will destroy the SEI film of the negative electrode and affect the active material of the positive electrode, thus greatly restricting the high temperature performance of the battery

In addition, under low temperature conditions (such as -20°C), the discharge capacity of lithium batteries decreases, and the discharge capacity is even less than 70% of the normal temperature discharge capacity, which also restricts the performance of lithium batteries at low temperatures.

[0005] is currently researching and seeking to replace lithium hexafluorophosphate with other lithium salts, such as lithium tetrafluoroborate (LiBF4), lithium dioxalate borate (LiBOB ), lithium difluorophosphate (LiF2PO2), lithium bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI) The promotion and application of lithium difluorooxalate borate (LiODFB) and lithium difluorobisoxalate phosphate (LiODFP) in lithium batteries have been reported. However, these lithium salts cannot significantly improve the high and low temperature performance of lithium batteries at the same time.

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