The microwave plasma torch chemical vapor deposition of graphene layers on copper foil for facilitating uniform lithium deposition in lithium metal batteries

Abstract

The utilization of vertically aligned graphene, grown via microwave plasma torch chemical vapor deposition (MPTCVD), on copper (Cu) foil is investigated for its application in “zero-excess” lithium metal batteries (ZELMBs), or the so-called anode-free lithium metal batteries. The graphene layers combining high surface area and defect concentration significantly enhance the affinity of Cu foil with the electrolyte. The vertically aligned structure of graphene layers facilitates efficient reduction of NO₃⁻ and TFSI⁻ but impedes solvent reduction. This leads to a high ratio of the inorganic/organic solid electrolyte interface (SEI), enhancing ionic conductivity and reducing electrolyte consumption. The graphene layers contribute to uniform lithium-ion flux, promoting stable lithium deposition and stripping. In cycling tests for Cu//LFP ZELMBs, the graphene-modified copper (G-Cu) foil exhibits enhanced capacity retention (55%) over 100 cycles, surpassing its untreated counterpart (37.5%) in a 0.25C-charge/0.5C-discharge program. In the Li@Cu//LFP LMBs (Li@Cu: Li-pre-deposited-Cu, N/P = 1), the cell using the G-Cu substrate shows a high-capacity retention of 76.7% after 300 cycles, whereas the cell with an unmodified substrate exhibits only 46.7% retention. A comprehensive analysis of the electrochemical lithium plating/stripping behavior is conducted through a three-electrode system in this work.