New Electrolyte Preparation And Properties Of The Lithium Salt 2 Fluoboric Acid Oxalate Research

Lithium difluoro(oxalato)borate (LiODFB) is considered to replaced LiPF6electrolyte salt according to its excellent high-low temperature performance, wide working temperature, good thermal stability. With the equipment of electrochemical workstation, belt battery test system, X-ray diffraction, infrared spectrometer, nuclear magnetic resonance instrument, trace moisture meter and high-low temperature and humidity&heat experiment equipment, etc, the preparation、purification and characterization of LiODFB were systematically studied, the physical&chemical properties of LiODFB salt and its electrolyte (1mol/L LiODFB EC+DMC+EMC=1:1:1) were analyzed, a further exploration on the LiODFB electrolyte’s excellent high&low temperature performance and the compatibility between the electrolyte and LTO electrode was studied. Draw the following main conclusions:(1)LiODFB is synthesized by LiC2O4and BF3O (C2H5)2for material, DMC as solvent, with the by-products of LiBF4. The solubility of LiODFB and LiBF4in DMC is7.77g and16.49g. High purity of LiODFB (purity>99.9%) was gain by crystallization method to effectively separated LiODFB and LiBF4.The thermal decomposition temperature (247℃) of LiODFB is obviously superior to the LiPF6(200℃). In the environment of25℃,50%humidity, LiODFB hydrolyzes slowly, but LiPF6would absorb the moisture and generate HF and LiF quickly. With the exposed LiODFB and LiPF6samples for electrolyte salt, the discharge capacity and capacity retention rate of LiFePO4/G batteries turns poor as the exposed time increased. LiODFB battery keeps significantly better capacity retention than LiPF6when the salt was exposed2,3,4h.(2)LiODFB electrolyte has better electrolyte conductivity in-20℃to0℃than LiPF6electrolyte, but between0℃to70℃it is on the contrary. The thermal decomposition reaction of LiODFB appears in250℃, which is higher than LiPF6electrolyte’s (120℃). At room temperature, the electrodes such as LiFePO4, LiNi1/3Mn1/3Co1/3O2and LiMn2O4, have obviously better stability in the LiODFB electrolyte than in the LiPF6electrolyte. During-20-60℃, LiODFB electrolyte and its stability to the aluminum foil are superior to the LiPF6electrolyte.(3)At-20℃,LiODFB battery has excellent recycling CV performance and the first charge-discharge performance superior to LiPF6battery. LiODFB has excellent cycle performance at60℃, with its capacity retention of78%, higher than LiPF6battery’35%. In the LiODFB battery, a compact uniform SEI film would be formed, but film formed in LiPF6battery is rough and loose, then the decomposition products HF generated by LiPF6would destroy the SEI, which would reduce the battery performance.(4)At room temperature and60℃, LTO/Li batteries have good CV performance,他the first charge-discharge performance of LiODFB battery and LiPF6battery is not significant. Both of their rate and cycle performance are basically consistent at room temperature, but LiODFB battery has the capacity retention of90.3%, which is significantly higher than LiPF6battery’74.7%at60℃. So LiODFB electrolyte and LTO are compatible, what’s they has a wonderful high temperature performance than LiPF6electrolyte.The above research laid the foundation to the preparation of the industrialization of LiODFB, at the same time, it provide the reference for the LiODFB’s application.