Asymmetric Membranes Containing Micron-Size Silicon for High Performance Lithium Ion Battery Anode

Micron-size Si anode is notorious for having extremely poor cycle life. It is mainly caused by the large volume change (∼300%) and poor mechanical strength of the Si electrode. Satisfying methods to address this issue are seriously lacking in literature. In this study, novel single-layer, double-layer and triple-layer asymmetric membranes containing micron-size silicon have been fabricated using a simple phase inversion method to dramatically improve its cyclability. The electrochemical performance of these asymmetric membranes as lithium ion battery anodes are evaluated and compared to pure micron-size Si powders and carbonaceous asymmetric membranes. All three types of asymmetric membrane electrodes demonstrate significantly enhanced stability as compared to pure Si powders. The single-layer asymmetric membrane has the largest capacity degradation due to the loss of pulverized Si powders from the membrane surface, only 40% of whose capacity can be retained in 100 cycles. But this performance is still much better than pure micron-size silicon electrode. After being coated with nanoporous carbonaceous layers on both sides of a single-layer asymmetric membrane to make a triple-layer asymmetric membrane (sandwich structure), the capacity retention is notably increased to 88% in 100 cycles at 610 mAh g−1 and 0.5C. The enhanced stability is attributed to the extra nanoporous coatings that can prevent the fractured Si powders from being leached out and allow facile lithium ion diffusions. Such a novel, efficient and scalable method may provide beneficiary guidance for designing high capacity lithium ion battery anodes with large volume change issues.