Facet-Controlled LiMn(2)O(4)/C as Deionization Electrode with Enhanced Stability and High Desalination Performance

HIGHLIGHTS: First report of a lithium-ion battery cathode as a deionization electrode for desalination. A novel approach to suppress manganese dissolution by exposing the (111) facet is proposed. Excellent desalination performance by the LiMn(2)O(4)/C cathode. The material achieves an ultrahigh desalination capacity of 117.3 mg g(−1) at 1.0 V and a longer cycle life (200 cycles without capacity decay) with minor manganese dissolution during the cycling test in 10 mM aqueous LiCl solution. ABSTRACT: Battery materials as emerging capacitive deionization electrodes for desalination have better salt removal capacities than traditional carbon-based materials. LiMn(2)O(4), a widely used cathode material, is difficult to utilize as a deionization electrode due to its structural instability upon cycling and Mn dissolution in aqueous-based electrolytes. Herein, a facile and low-cost ball-milling routine was proposed to prepare a LiMn(2)O(4) material with highly exposed (111) facets. The prepared electrode exhibited relatively low dissolution of Mn during cycling, which shows its long cycle stability. In the hybrid capacitive deionization system, the LiMn(2)O(4)/C electrode delivered a high desalination capacity of 117.3 mg g(−1) without obvious capacity decay at a voltage of 1.0 V with a 20 mM initial salt concentration. In addition, the exposed (111) facets significantly alleviated Mn ion dissolution, which also enhanced the structural steadiness. [Image: see text] SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s40820-022-00897-3.