Researchers develop production methods that strike balance between performance and cost-effectiveness.
Lithium-ion batteries are a popular type of rechargeable battery commonly found in portable electronics and electric or hybrid cars. Traditionally, lithium-ion batteries contain a graphite anode, but silicon has recently emerged as a promising anode substitute because it is the second most abundant element on earth and has a theoretical capacity of 3600 milliamp hours per gram (mAh/g), almost 10 times the capacity of graphite. The capacity of a lithium-ion battery is determined by how many lithium ions can be stored in the cathode and anode. Using silicon in the anode increases the battery's capacity dramatically because one silicon atom can bond up to 3.75 lithium ions, whereas with a graphite anode six carbon atoms are needed for every lithium atom.
The USC Viterbi team developed a cost-effective (and therefore commercially viable) silicon anode with a stable capacity above 1100 mAh/g for extended 600 cycles, making their anode nearly three times more powerful and longer lasting than a typical commercial anode.
Up until recently, the successful implementation of silicon anodes in lithium-ion batteries faced one big hurdle: the severe pulverization of the electrode due to the volume expansion and retraction that occurs with the use of silicon. Last year, the same team led by USC Viterbi electrical engineering professor Chongwu Zhou developed a successful anode design using porous silicon nanowires that allowed the material to expand and contract without breaking, effectively solving the pulverization problem.
This solution yielded a new problem, however: the method of producing nanostructured silicon was prohibitively expensive for commercial adoption.
Undeterred, graduate student Mingyuan Ge and other members of Zhou's team built on their previous work to develop a cost-efficient method of producing porous silicon particles through the simple and inexpensive methods of ball-milling and stain-etching. "Our method of producing nanoporous silicon anodes is low-cost and scalable for mass production in industrial manufacturing, which makes silicon a promising anode material for the next generation of lithium-ion batteries," said Zhou. "We believe it is the most promising approach to applying silicon anodes in lithium-ion batteries to improve capacity and performance."