Spinel LiMn₂O₄ as a Capacitive Deionization Electrode Material with High Desalination Capacity: Experiment and...

Capacitive deionization (CDI) is a newly developed desalination technology with low energy consumption and environmental friendliness. The surface area restricts the desalination capacities of traditional carbon-based CDI electrodes while battery materials emerge as CDI electrodes with high performances due to the larger electrochemical capacities, but suffer limited production of materials. LiMn₂O₄ is a massively-produced lithium-ion battery material with a stable spinel structure and a high theoretical specific capacity of 148 mAh·g^-1, revealing a promising candidate for CDI electrode. Herein, we employed spinel LiMn₂O₄ as the cathode and activated carbon as the anode in the CDI cell with an anion exchange membrane to limit the movement of cations, thus, the lithium ions released from LiMn₂O₄ would attract the chloride ions and trigger the desalination process of the other side of the membrane. An ultrahigh deionization capacity of 159.49 mg·g^-1 was obtained at 1.0 V with an initial salinity of 20 mM. The desalination capacity of the CDI cell at 1.0 V with 10 mM initial NaCl concentration was 91.04 mg·g^-1, higher than that of the system with only carbon electrodes with and without the ion exchange membrane (39.88 mg·g^-1 and 7.84 mg·g^-1, respectively). In addition, the desalination results and mechanisms were further verified with the simulation of COMSOL Multiphysics.