The Use of Nanoporous Silicon for Advanced Rechargeable Lithium-Ion Batteries

There is great interest in developing rechargeable lithium batteries with higher energy capacities and a longer cycle lifetimes. Currently technology has been mainly based on graphite, which has a lithium capacity of 372 mAh/g. Silicon has very high lithium ion capacity of 4200 mAh/g, and has been suggested as a potential high capacity lithium battery anode material. However, it has been encumbered with serious expansion/ contraction during cycling, increasing internal resistance and resulting in cell failure. Severe silicon pulverization can be triggered by a large volume change (>300%) during lithium alloying (to form LixSi) and de-alloying (to reform Si), which results in electrically disconnected smaller particles. These disconnected particles cause a rapid decrease in cycling stability. Porous silicon structures have been suggested as a potential means to accommodate silicon expansion/contraction while maintaining continuity. We will report on our fabrication of a nanoporous silicon structure by electrochemical etching process. The pores vary from 500 nanometer to 1 micrometer in diameter with a pore depth of 10-50 micrometers. A battery cell is created with these nanoporous silicon samples and the battery is tested using charge and discharge rates between 0.1 to 2.5V with a current of 60 microampere. We find that the specific capacity of the battery cell is 1000Mah/g after 10 cycles with a capacity of 2300 mAh/g for first cycle. This leads to the fact that porous silicon can be utilized as a promising electrode for lithium ion battery technology.