Spider silk binder for Si-based anode in lithium-ion batteries

Silicon (Si) has attracted attention for use in lithiumion batteries due to its high theoretical capacity and its natural abundance. However, significant change in the volume of Si electrodes during repeated cycles causes dramatic capacity degradation and reduces the benefits of its attractive qualities. Here, it is reported for the first time that a derivative of natural spider silk is effective for retaining the capacity and decreasing the volume expansion of Si for use in Li-ion batteries as electrodes. Relative to the Si-electrode with polyvinylidene fluoride (SPVDF), the Si-electrode containing binder with the dissolved spider silk (SWS) cells achieved significant enhanced capacities with cycling stability during repeated cycles. The SWS electrode at 250 mA g(-1) showed the discharge/charge capacities of 3642/1938 mAh g(-1) at 1st cycle, 1789/1541 mAh g(-1) at 2nd cycle and then reduced to 1142/1054 mAh g(-1) at the 5th cycle. However, the capacities of the SPVDF electrode were 3903/ 2694 mAh g(-1), 1455/1211 mAh g(-1), and 458/435 mAh g(-1). Furthermore, the discharge capacity of SWS was 333 mAh g(-1) at the 38th cycle, but that of SPVDF showed 323 mAh g(-1) at the 7th cycle. Such superior performance with good cycling ability may be attributed to the unique properties of spider silk: the folded crystal layer with semi-amorphous structure, the superior properties of viscosity and adhesion, and the close stacking by the protein blocks as well as the side chain R-group of crystal beta-sheet. The combination of these characteristics was able to restrain the deleterious change in the volume of Si materials substantially, and to provide superior electrochemical characteristics of lithium ions. (C) 2020 The Authors. Published by Elsevier Ltd.