Enhanced Anionic Redox Reaction of Na-Layered Li-Containing Mn-Based Cathodes by Cu-Mediated Reductive Coupling Mechanism.

Na-layered Li-containing Mn-based cathodes (NaLiMnO, NLMOs) with additional Na storage ability resulting from the anionic redox reaction (ARR) hold great promise for sodium-ion batteries (NIBs). However, practical applications of NLMOs encounter challenges, such as migration of transition metal Mn, loss of lattice oxygen, and voltage decay during cycling. Here, we show that Cu plays an important role in enhancing the ARR via the reductive coupling mechanism (RCM). Results shows that a Cu/Fe modified NLMO sample delivers a Na storage capacity as high as 174 mA h g at 0.2C, higher than that of a Zn/Fe modified NLMO sample (130 mA h g) and NLMO (154 mA h g). Both in situ and ex situ characterization results indicate that the obvious improvement in the electrochemical performance of the Cu/Fe modified NLMO is due to the additional overlaps between the Cu 3d and O 2p orbitals, which is beneficial for the RCM. As a result, the ARR is enhanced so as to increase the Na storage capacity.