High-Rate One-Dimensional α-MnO₂ Anode for Lithium-Ion Batteries: Impact of Polymorphic and Crystallographic Features...

Manganese dioxide (MnO₂) exists in a variety of polymorphs and crystallographic structures. The electrochemical performance of Li storage can vary depending on the polymorph and the morphology. In this study, we present a new approach to fabricate polymorph- and aspect-ratio-controlled α-MnO₂ nanorods. First, δ-MnO₂ nanoparticles were synthesized using a solution plasma process assisted by three types of sugars (sucrose, glucose, and fructose) as reducing promoters; this revealed different morphologies depending on the nucleation rate and reaction time from the molecular structure of the sugars. Based on the morphology of δ-MnO₂, the polymorphic-transformed three types of α-MnO₂ nanorods showed different aspect ratios (c/a), which highly affected the transport of Li ions. Among them, a relatively small aspect ratio (c/a = 5.1) and wide width of α-MnO₂-S nanorods (sucrose-assisted) induced facile Li-ion transport in the interior of the particles through an increased Li-ion pathway. Consequently, α-MnO₂-S exhibited superior battery performance with a high-rate capability of 673 mAh g^-1 at 2 A g^-1, and it delivered a high reversible capacity of 1169 mAh g^-1 at 0.5 A g^-1 after 200 cycles. Our findings demonstrated that polymorphs and crystallographic properties are crucial factors in the electrode design of high-performance Li-ion batteries.