Carboxymethylcellulose Induced the Formation of Amorphous MnO2 Nanosheets With Abundant Oxygen Vacancies for Fast Ion Diffusion in Aqueous Zinc‐Ion Batteries

Abstract Manganese dioxide with high theoretical capacity has drawn a great deal of attention for aqueous zinc‐ion batteries (ZIBs). Nevertheless, their sluggish diffusion kinetics, low electrical conductivity and limited active sites are still hindering the potential application in batteries. Herein, amorphous MnO 2 nanosheets with abundant oxygen vacancies are facilely prepared by using carboxymethylcellulose sodium (CMC) as a capping agent. During the growth process, CMC can preferentially attach to the (003) facet of MnO 2 to guide its crystal growth and morphology. The small nanosheets can expose abundant edge sites, along with the surface oxygen vacancies, to facilitate the insertion/extraction of H + and Zn 2+ in ZIBs. Moreover, the presence of CMC can stabilize the Mn 3+ to inhibit the Jahn–Teller effect in the preparation process. As a result, CMC‐MnO 2 based ZIB can provide a specific capacity of 324 mAh g −1 at 0.5 A g −1 , and achieve 86.2% retention after a long cycle test of 1000 cycles. Furthermore, the energy storage mechanism may be attributed to the insertion/extraction of H + /Zn 2+ , dissolution/deposition of MnO 2 and Zn 4 SO 4 (OH) 6 ·nH 2 O, and irreversible transformation of vermiculite during long cycles. This work may open new perspectives for the development of MnO 2 ‐based cathodes in ZIBs.