The Mechanism of Lithium Deposition in Open-Porous 3D Copper Micro-Foam Electrodes for Zero-Excess Lithium Metal Batteries (ZELMBs) [Mechanismus der Lithium-Abscheidung in offenporigen 3D-Kupfer-Mikroschäumen für überschussfreie Lithium-Metall-Batterien (ZELMBs)]

Ingber, Tjark T. K.; Bela, Marlena M.; Püttmann, Frederik; Dohmann, Jan F.; Bieker, Peter; Börner, Markus; Winter, Martin; Stan, Marian C

Abstract

In zero-excess Lithium metal batteries (ZELMBs), also termed ‘anode-free’ LMBs, Li from the positive electrode is electrodeposited onto a bare current collector instead of the Li metal negative electrode commonly used in LMBs. This enables high theoretical energy density and facile, safe, and low-cost assembly. To tackle Coulombic inefficiencies during Li deposition/dissolution, 3D structured current collectors can be used instead of 2D foil materials. This study elucidates the mechanism of Li deposition in custom-made open-porous 3D Cu micro-foams from nucleation to large scale deposition. For the first time in ZELMBs, surface and sub-surface Li deposits in an open-porous 3D material are compared to deposits on 2D foils using cryogenic focused ion beam scanning electron microscopy (cryo-FIB-SEM). Multiphysics simulations reveal that current density distribution over the large surface area of the Cu micro-foams enables storage of substantial amounts of dendrite-free Li in the open-porous 3D structure of the Cu micro-foams, minimizing detrimental volume changes during Li deposition/dissolution. Electrochemical analysis proves that the Li nucleation overvoltage in the Cu micro-foams is reduced by ≈ 40%. Also, charge/discharge cycling in ZELMBs shows increased Coulombic efficiency, capacity retention, and cycle life. Overall, this work explains how open-porous Cu micro-foam current collectors improve the Li deposition to boost the cycling characteristics of ZELMBs.