Sodium Storage Performance and Mechanism of MnO<sub>2</sub> with Different Phase Structures (α, β, γ, δ) as Anode Materials for Sodium-Ion Batteries
Wenhan Xu, Jiang Li, Yanwei Li, Jing Zhang, Qize Huang, Jinhuan Yao, Shunhua Xiao, Chenghong Lei
Abstract
An in-depth understanding of the links between the phase structure and electrochemical property is crucial for the advancement of high-performance anode materials. Herein, the sodium storage performance and mechanisms of MnO 2 with four distinct phase structures (α, β, γ, and δ) as anodes are systematically investigated. Among the four materials, the layered δ-MnO 2 nanoflowers exhibit the best sodium storage performances, characterized by a specific capacity of 303.6 mA h g –1 after 100 cycles at 200 mA g –1, cyclability of 247.3 mA h g –1 after 500 cycles at 1000 mA g –1, and high-rate performance of 184.5 mA h g –1 at 3000 mA g –1 . Furthermore, δ-MnO 2 shows the most pronounced pseudocapacitance behavior during discharge/charge processes among the four materials. Ex situ XRD and TEM analyses reveal that the sodium storage reactions of α-, β-, and γ-MnO 2 proceed via a conversion reaction mechanism, while the sodium storage reaction of δ-MnO 2 is controlled by an insertion/deinsertion mechanism. The findings presented in this study may offer insights into the structure regulation and performance promotion of MnO 2 -based anode materials for SIBs.