Nanostructured Mn-based oxides for electrochemical energy storage and conversion
Batteries and supercapacitors as electrochemical energy storage and conversion devices are continuously serving for human life. The electrochemical performance of batteries and supercapacitors depends in large part on the active materials in electrodes. As an important family, Mn-based oxides have shown versatile applications in primary batteries, secondary batteries, metal–air batteries, and pseudocapacitors due to their high activity, high abundance, low price, and environmental friendliness. In order to meet future market demand, it is essential and urgent to make further improvements in energy and power densities of Mn-based electrode materials with the consideration of multiple electron reaction and low molecular weight of the active materials. Meanwhile, nanomaterials are favourable to achieve high performance by means of shortening the ionic diffusion length and providing large surface areas for electrode reactions. This article reviews the recent efforts made to apply nanostructured Mn-based oxides for batteries and pseudocapacitors. The influence of structure, morphology, and composition on electrochemical performance has been systematically summarized. Compared to bulk materials and notable metal catalysts, nanostructured Mn-based oxides can promote the thermodynamics and kinetics of the electrochemical reactions occurring at the solid–liquid or the solid–liquid–gas interface. In particular, nanostructured Mn-based oxides such as one-dimensional MnO2 nanostructures, MnO2–conductive matrix nanocomposites, concentration-gradient structured layered Li-rich Mn-based oxides, porous LiNi0.5Mn1.5O4 nanorods, core–shell structured LiMnSiO4@C nanocomposites, spinel-type Co–Mn–O nanoparticles, and perovskite-type CaMnO3 with micro–nano structures all display superior electrochemical performance. This review should shed light on the sustainable development of advanced batteries and pseudocapacitors with nanostructured Mn-based oxides.