Li Ni0.5Mn1.5O4/Ag for electrochemical lithium recovery from brine and its optimized performance via response surface methodology

The surging demand for lithium (Li) necessitates development of high-throughput Li+ recovery processes to maintain sustainable Li supply. Electrochemical Li+ recovery is an attractive option as it can achieve fast Li+ recovery with low energy consumption. However, it requires highly effective electrode materials with good stability in aqueous environment. In this study, delithiated Li1−xNi0.5Mn0.5O4 (NMO) was investigated as Li+ capturing electrode paired with silver (Ag) for electrochemical Li+ recovery. Material and electrochemical characterizations confirm the stability of NMO/Ag in aqueous phase and NMO selectivity towards Li+. Using brine as Li+ feed source, NMO/Ag electrochemically captured Li+ (NMO reduction) and Cl−(Ag oxidation) at an applied current (C-rate) and operation time (min step−1). The captured ions were subsequently released as LiCl in a recovery solution by reversing the current polarity. Response surface methodology using central composite design successfully optimized the process by operating it at C-rate = 1.05C for t = 20 min step−1. At these conditions, NMO/Ag required only 1.29–1.44 W h mol−1 Li+ to recover 1.259 mmol Li+ g−1 NMO at 98.14% Li+ purity. In cycled experiments (n = 50), NMO/Ag steadily accumulated Li+ in the receiving solution without experiencing electrode deterioration. Additionally, NMO/Ag effectively separated Li+ from other cations such as Na+, Mg2+, K+ and Ca2+ in brine. This establishes the potential of NMO/Ag for energy-efficient electrochemical Li+ recovery with fast production rate.