Anodes for Li-ion batteries based on p-Si with self-organized macropores

The practical application of microstructured anodes produced by the electrochemical etching of single-crystal silicon is limited by their cost. The proposed approach will make it possible to reduce the cost for several reasons: less stringent requirements to the quality of the initial material due to the replacement of n-Si with p-Si, the exclusion of operations that are aimed at the formation of nucleation centers, and the repeated use of a silicon substrate. The formation of random macropores in 10-20 Omega cm p-Si (100) in a 4% solution of hydrofluoric acid in dimethylformamide is studied and the role of chemical etching is revealed. The dependences on the current density are obtained for the etching rate, morphology of the porous layers, effective valence, pore density, and average pore diameter. The part played by chemical dissolution in the electrolyte is determined. A technology is developed for the deposition of 50-mu-thick porous layers. This technology combines successive detachments of several membranes from the same substrate and provides enhanced porosity (similar to 70%). The electrochemical characteristics of anodes formed from these membranes are examined, and 120+ test cycles are performed in the mode with the charge capacity limited to 1000 mA h/g at a current of 0.2 A/g.