Negative electrodes for lithium-ion batteries obtained by photoanodization of solar-grade silicon

Negative electrodes for lithium-ion batteries prepared by electrochemical etching of single-crystalline silicon crystals demonstrate a high specific capacity per gram of the material and per unit of nominal anode area as well as a high stability during several hundreds and even thousands of cycles. However, industrial application of such structures is inexpedient in view of the high cost of the material and technology used. In this work we have investigated anodes based on disordered macropores in solar-grade $n$-Si obtained by photoanodization in a 4% HF solution in dimethyl formamide. The use of this organic electrolyte leads to the formation of layers with a porosity higher than in an aqueous electrolyte and ensures spontaneous separation of these layers from the substrate. The anodes have been prepared from macroporous membranes with a thickness of 48–86 $\mu$m and a porosity of 52–75%, and their electrochemical parameters have been studied. It is found that the geometrical parameters of the porous structure and experimental conditions determine the charge and discharge capacity and the cycle life of the anodes. In the regime of the charge capacity limited by 1000 mA h/g and charge/discharge rate $C$/5, the obtained anodes can stably operate during several hundreds of cycles, preserving a high (greater than 98%) Coulombic efficiency.