Synthesis of Porous Si Particles by Metal-assisted Chemical Etching for Li-ion Battery Application

As an anode for Li-ion batteries, Si has a high theoretical capacity but suffers from dramatic volume variations during cycles of lithiation/de-lithiation (LID). Attempt is made to increase cycle stability of Si electrode by incorporating pre-set voids into the electrode matrix to partially accommodate volume expansion. A metal-assisted chemical etching (MACE) method, in which Si is partially etched in the solution containing AgNO3 and HF, has been evaluated for synthesize porous Si particles. It has been found that the particle porosity exhibits complex dependence on etching time, oxidant concentration and temperature. Porous Si particles containing predominantly mesopores have been produced by the MACE method, but the maximum porosity has been limited to be ca. 25%. The resulting porous Si is subsequently coated with a C layer and subjected to cycles of electrochemical LID. The C-coated porous Si electrode exhibits high capacity and remarkably improved cycle stability as compared with non-porous Si electrode.