Carboxymethyl cellulose regulated solvation structures enabling long cyclability in aqueous calcium-ion battery.

Aqueous calcium-ion battery (ACIB) has emerged as a promising candidate for energy storage devices due to its environment friendly, high safety, and cost-effectiveness. However, traditional aqueous calcium salt solutions contain a large number of active free water molecules, which triggers a range of side reactions, such as hydrogen evolution, electrode dissolution, and weak kinetics of Ca2+ diffusion. Here, a green and cost-effective sodium carboxymethyl cellulose (CMC) additive was utilized to change the composition and properties of Ca(NO3)2 electrolyte, which effectively improved the electrochemical performance of the Ca(NO3)2 electrolyte. DFT calculations and MD simulations demonstrated that CMC disrupts the strong hydrogen bond network architecture within the electrolyte through strong carboxylate coordination. Moreover, CMC reconfigures the solvation structure of Ca2+, thereby decreasing the overall rigidity of the solvation shell. Therefore, the assembled battery with MnO2 electrode demonstrates a capacity retention of 70.4% after 4500 cycles at the current density of 1 A g-1, and the full cell used activated carbon as anode exhibits a capacity retention of 96.6% after 190 cycles at 1 A g-1, and the coulombic efficiency is up to 97%. This work provides a low-cost electrolyte additive with an innovative protection strategy for aqueous Ca2+ energy storage devices.