Comparison of organic and inorganic gelation agents in ethylene carbonate based electrolytes for lithium-ion batteries

Two types of electrolyte which are suitable for lithium-ion batteries are investigated. In both cases the basic electrolyte is a mixture of organic solvents such as ethylene carbonate (EC) and propylene carbonate (PC) or EC and dimethyl carbonate (DMC). The lithium salts applied are LiClO4, LiPF6, LiTFMSI and LiTFMS. Gel-type electrolytes were prepared by adding a few wt.% of highly dispersed silica (HDS) to the liquid electrolyte. If hydrophilic HDS is used, thixotropic gels are formed. The second type of electrolytes are poly(acrylonitrile) (PAN) based. These electrolytes can be prepared as dimensionally stable films. The conductivity of the HDS gel electrolytes is very close to that of the liquid electrolyte. PAN-based electrolytes exhibit lower conductivities than the comparable liquid electrolytes. If a lithium anode is used in a rechargeable battery, PAN-based electrolytes offer significant advantages, since they are efficient to avoid internal short circuits due to lithium dendrite formation. A small test battery of the type lithium/PAN-based electrolyte/LiCoO2 was deep-cycled for about 450 times without any indication of internal shorts.