Freestanding and Flexible CNT/Si/Metal Electrodes for High Energy Density Lithium-Ion Batteries with Enhanced Electrochemical Performance

In pursuit of meeting the demands for the next generation of high energy density and flexible electronic products, there is a growing interest in flexible energy storage devices. Silicon (Si) stands out as a promising electrode material due to its high theoretical specific capacity (~3579 mA h g^-1), low lithiation potential (~0.40 V), and abundance in nature. We have successfully developed freestanding and flexible CNT/Si/low-melting-point metal (LM) electrodes, which obviate the need for conductive additives, adhesives, and thereby increase the energy density of the device. As an anode material for lithium-ion batteries (LIBs), the CNT/Si/LM electrode demonstrates remarkable cycling stability and rate performance, achieving a reversible capacity of 1871.8 mA h g^-1 after 100 cycles at a current density of 0.2 A g^-1. In-situ XRD and in-situ thickness analysis are employed to elucidate the underlying mechanisms during the lithiation/delithiation. Density functional theory (DFT) calculations further substantiate the mechanism by which LM enhances the electrochemical performance of Si, focusing on the aspects of stress mitigation and reduction of the diffusion energy barrier. This research introduces a novel approach to flexible electrode design by integrating CNT films, LM, and Si, thereby charting a path forward for the development of next-generation flexible LIBs.