An inorganic composite membrane as the separator of Li-ion batteries

Abstract

We studied an inorganic composite membrane as the separator for Li-ion batteries. Being made of mainly CaCO 3 powder and a small amount of polymer binder, the composite membrane has excellent wettability with liquid electrolytes due to its high porosity and good capillarity. Ionic conductivity of the membrane can be easily achieved by absorbing a liquid electrolyte. Additional benefit of such a membrane is that the alkali CaCO 3 can scavenge acidic HF, which is inevitably present in the LiPF 6-based electrolytes used currently in the Li-ion batteries. In this work, we typically evaluated a membrane with the composition of 92:8 (wt.) CaCO 3/Telfon by using a 1.0 m LiPF 6 dissolved in a 3:7 (wt.) mixture of ethylene carbonate (EC) and ethylmethyl carbonate (EMC) as the liquid electrolyte. Ionic conductivity of the electrolyte-wetted membrane was measured to be 2.4 mS cm −1 at 20 °C versus 8.0 mS cm −1 of the liquid electrolyte. With the said membrane as a separator, both Li/graphite and Li/cathode half-cells exhibited good capacity retention. We also found that the Li-ion cell fabricated in this manner not only had stable capacity retention, but also showed good high-rate performance.