Sulfuric acid-controlled electroplating of Sn nano-seeds on Cu current collectors toward stable anode-free lithium metal batteries

초록

Lithium metal batteries offer high energy density, yet their reversibility is severely limited by uneven Li nucleation and dendritic growth on lithiophobic Cu current collectors. Here, we report a bath-acidity-controlled Sn electroplating strategy to construct lithiophilic Sn-modified Cu current collectors (Sn@Cu) and regulate Li deposition behavior. By varying the H2SO4 concentration in a SnSO4-H2SO4 bath, we show that bath acidity governs the nucleation/growth balance of Sn, leading to distinct seed morphologies. The optimized 1.5 M H2SO4 bath yields uniformly dispersed Sn nano-seeds, whereas insufficient or excessive acidity produces coarse or non-uniform deposits. The uniform Sn nano-seed layer decreases the Li nucleation overpotential from 208.2 mV for bare Cu to 107 mV, promotes homogeneous Li plating, and enables stable plating/stripping with similar to 98% Coulombic efficiency over prolonged cycling. Ex situ and in situ impedance analyses reveal suppressed interfacial resistance growth from the early stage of Li plating, and cryogenic SEM confirms denser Li deposits on Sn@Cu than on bare Cu. Full cells further show improved capacity retention. This work establishes bath-acidity-controlled Sn electroplating as a simple current-collector engineering route for stable anode-free lithium metal batteries.

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