Establishment of PPy-derived carbon encapsulated LiMn2O4 film electrode and its performance for efficient Li+ electrosorption

Abstract Improving the cycle stability and Li+ electrosorption rate of the LiMn2O4 (LMO) film electrode in the selective Li+ electrosorption process is still a considerable challenge. In this work, a novel polypyrrole (PPy) - derived carbon encapsulated material LiMn2O4@Carbon/Nitrogen-4 (LMO@CN-4) was prepared by the three-dimensional in-situ polymerization and high-temperature annealing of PPy on the LMO surface. The LMO@CN-4 film electrode showed a faster Li+ electrosorption rate, higher lithium-ion selectivity, and higher stability than the LMO film electrode. The maximum capacity of the LMO@CN-4 film electrode for Li+ could reach 34.57 mg/g within 40 min in 0.05 mol/L LiCl solution. Even in the simulated concentrated seawater with a low Li+ concentration (0.17 g/L), it could quickly reach adsorption equilibrium and maintain the high selectivity of Li+. The adsorption capacity was about 37.14 mg/g and the separation coefficient of α (Li+/Mg2+), α (Li+/Na+), and α (Li+/Ca2+) was about 228.25, 2110.64, and 1381.89. The carbon encapsulation served as a conductive layer to enhance charge and ion transport. It also provided a buffer layer to prevent the volume collapse of the crystal and the dissolution of Mn. Therefore, the charge and discharge capacity of the LMO@CN-4 film electrode could be maintained at about 80% after 50 cycles at the 1C (148 mAh/g) rate, which was 20% higher than that of the bare LMO. What’s more, the high cycle stability and Li+ electrosorption rate of the modified film electrode also suggested its potential for lithium electrosorption from concentration seawater.