The Lithium-ion Battery Electrolyte Anti-overcharge Additive Research

Nowadays, Li-ion Battery is a new green energy storage equipment which have developed quickly. As chemical energy source cell, it is more ideal because of its higher energy density comparing with that of other secondary battery. Its properties directly depend on the choice and preparation of the electrode, electrolyte and separator. Electrolyte is an important part of Li-ion battery, bearing the responsibility of transportation of conductive ions. The effect of electrolyte on the cycle performance, specific capacity, safety and so on is very important. In order to attain to the demand of the application of Li-ion battery, all of the commercial electrolyte are the mixture of some different organic solvent and a little functional additive is added in it for improving the chemical and physical properties because single electrolyte system could not be up to the demand of the application of Li-ion battery. In resent years, because additive is a organic compound which have the advantages of lower consumption and higher improvement for the properties of electrolyte, new additive which have fine electrochemical properties become one of the hot point in the study area of properties of electrolyte.In the introduction of this paper, the present developmental status and application prospect of electrolyte of Li-ion battery were introduced. The anti-overcharge additive which could improve the safety properties of Li-ion battery was summarized emphatically. At the same time, the present developmental status and application prospect of anti-overcharge additive were discussed by category.In the experimental section of this paper, the electrochemical properties of methyl benzoate and ethyl acetate which as the electrolyte additives of Li-ion battery were studied and the effect of them on the anti-overcharge was also investigated by much more test methods, such as recharge cycles test, cyclic voltammetry test, overcharge test and so on. Results showed that the cycles property of blank electrolyte after adding methyl benzoate and ethyl acetate respectively were changed. The cycles property of cell decreased but the specific capacity of that was improved after adding methyl benzoate. The effect of ethyl acetate on the cycles property of cell was unobvious. During the analysis of cyclic voltammetry, it was found that the reduction peak potential of the electrolyte of methyl benzoate was 3.8V. It was lower than the normal working voltage of Li-ion battery. But ethyl acetate had higher redox reaction potential which was 4.25V and 4.5V respectively. In the processing of overcharge property test, It was found that the electrolyte containing methyl benzoate and ethyl acetate respectively had certain ability of anti-overcharge. The effect of additives on the electrolyte and positive plate was investigated and the mechanism of anti-overcharge was determined by the methods of alternating current impedance test and scanning electron microscope. During the analysis of alternating current impedance, it was found that additives certainly affect the impedance of electrolyte. After overcharge, during SEM, it was found that the surface of the positive plate in the electrolyte containing methyl benzoate was covered by a layer of substance. But the surface of the positive plate in the electrolyte containing ethyl acetate was more integrated and no covering.After studying the combination of two additives of methyl benzoate and ethyl acetate, it was found that although the addition of these two additives had some anti-overcharge effect on the batteries under the conditions of 0.5C/4.2V and 0.2C/4.6V, the cycles property was certainly influenced. During the experiment of optimal combination of additives and the alteration of the rate of additives, the cycles property was improved and the effect of anti-overcharge was also attained.The innovations of this paper were the determination of the appropriate additional rate of the methyl benzoate and ethyl acetate which had the effect of anti-overcharge, the deep study of the effect of these two additives on electrolyte, and the investigation of the effect of the combination of methyl benzoate and ethyl acetate on electrolyte.