Iron Phosphate Lithium Battery Using The Electrolyte Of High And Low Temperature

LiFePO4 is one of the most promising cathode materials for dynamical battery, and the study of supporting electrolyte for LiFePO4 battery also has practical significance. In this paper, galvanostatic charge-discharge, cyclic voltammetry (CV), electrochemical impedance spectros-copy (EIS), inductively coupled plasma (ICP), energy dispersive spectroscopy (EDS) were used to study the performance of batteries with different lithium salt, solvents, and additives.First of all, we have studied the effect of a new lithium salt, which was called lithium difluoro(oxalato)borate (LiODFB), on the performance of LiFePO4/graphite batteries at high and low temperature. Results showed that, LiODFB used in electrolyte as a lithium salt had no negative effect in LiFePO4/Li cells, and the LiODFB-based electrolyte could restrain iron dissolution from LiFePO4. According to the EIS results, on the one hand, the SEI film formed in LiODFB-based electrolyte had better thermal stability; on the other hand, LiODFB-based electrolyte could restrain iron dissolution from LiFePO4 and prevent the reduction of dissolved iron ions'reducing at anode's surface which decreased the impedance effectively, thereby improve the cycling performance of LiFePO4/graphite batteries at high temperature. LiODFB has a lower charge-transfer resistance, which may be the reason for the good property of battery at low-temperature when LiODFB is added, and the mechanism remains to be studied further.Secondly, the effects of bi-solvent,a new solvent (ethyl propionate) on the performance of LiFePO4/graphite were tested. Compared with other bi-solvent systems, the battery with ethylene carbonate(EC) and diethyl carbonate(DEC) solvent system has the best cycling performance at high temperature, and the battery with EC and ethyl methyl carbonate(EMC) solvent system has the better low temperature discharge property. In the EC+EMC bi-solvent electrolyte, adding some ethyl propionate could increase the battery's low temperature performance, but adding too much ethyl propionate would have some negative impact on the battery's high temperature performance.Finally, the performances of LiFePO4/graphite batteries with two different additives, propane soltone (PS) and fluoroethylene carbonate (FEC), were investigated respectively. The results showed that a smoother and compacter SEI film structure generated by the introduction of the additive PS or FEC to the electrolyte, which could improve the battery's high temperature performance. The results revealed that the flat of battery increased after adding FEC to the electrolyte, and the presence of FEC improved the low temperature discharge property of the battery.