Symmetrical Sandwich-Structured SiN/Si/SiN Composite for Lithium-Ion Battery Anode with Improved Cyclability and Rate Capacity

Abstract

Substoichiometric silicon nitride/silicon/substoichiometric silicon nitride (SiN/Si/SiN) composite with a symmetrical sandwich structure is investigated as the anode of thin-film lithium-ion battery. The SiN film between the Si film and electrolyte acts as a clamping layer to suppress the anode volume expansion and stabilize the formation of solid-state interphase, while the SiN film between the Si film and current collector works as a buffer layer to enhance the mechanical strength and electrical contact at the anode/current collector interface. Compared with the pure Si anode, the SiN/Si/SiN anode exhibits improved mechanical stability and keeps intact even after cycling. Consequently, the SiN/Si/SiN anode shows much better cycling stability (1702 mAh g−1 at 0.6 C with a capacity fading rate of 0.1% per cycle) and higher rate performance than the Si anode (3222 mAh g−1 with a fading rate of 0.7% per cycle). Moreover, because the SiN buffer layer can effectively alleviate the stress (caused by anode volume change) accumulated at the anode/current collector interface and also the stress compensation effect can be created by using this symmetrical sandwich structure, the SiN/Si/SiN anode presents higher mechanical stability and thus better electrochemical performance than the anode with a structure of SiN/Si on the current collector.