Enabling efficient guiding of Li diffusion/plating toward high-performance lithium metal batteries by utilizing a gradient Janus interlayer

Lithium metal batteries (LMBs) face significant challenges, including dendrite growth and degradation during cycling. Two effective strategies to address these issues involve utilizing a nano-structured current collector as a lithium host and forming an ideal solid-electrolyte interphase (SEI) as an artificial anode modifier. However, synthesizing an anode modifier that offers high cycling stability and efficient lithium diffusion/storage via a well-controlled deposition method remains challenging. This study presents a binder-free and novel gradient Janus interlayer(GJL) as anode modifier comprising gradient layered composite of fluorinated graphene (FECG) and intrinsic graphene (ECG), deposited through electrophoretic deposition (EPD). The gradient Janus structure provides separate ionic and electronic transport pathways. The top FECG layer with LiF-rich species enhances both electrolyte wettability and lithium ion transport for uniform Li plating, while the underlying ECG layer facilitates efficient electron transfer. Also, a thin CuF₂-riched functional layer is designed to connecting the GJL to the copper substrate, ensures strong adhesion to the copper substrate without using any binder, enabling stable lithium deposition and improved structural integrity. The GJL as anode modifier demonstrates outstanding electrochemical performance, showing a low nucleation overpotential of 42.17 mV and stable polarization over 600 h. After 325 cycles, the Coulombic efficiency reached 97.2 %, indicating excellent stability. In full-cell testing, the specific capacity exceeded 120 mAh/g after 150 cycles, with 72 % capacity retention after 160 cycles. Overall, this innovative composite multilayer ASEI offers a promising solution to overcome the challenges of anode-free lithium metal batteries (AFLB), paving the way for safer and higher-energy-density battery technologies.