The electrochemical and spectroelectrochemical properties of ZnO thin films prepared by reactive pulsed laser deposition in oxygen ambient have been investigated. The as-deposited and lithiated ZnO thin films were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy techniques. The discharge and charge measurement indicates that the reversible capacities of the as-deposited ZnO thin-film electrodes are more than one Li per Zn atom with an initial capacity of less than 2.75 Li per Zn atom, and more than 0.75 Li per Zn atom could not be explained by the alloying process of ZnO reaction with Li. The evolution of the in situ absorbance spectra exhibits a marked boundary of lithiating 2Li per Zn atom and provides a hint about two different lithiation reactions occurring during charging of the ZnO/Li cell. A new reaction mechanism of lithium with ZnO involving both the classical alloying process and the oxidation/reduction of nanosized metal is proposed.

Hard carbons, an important category of amorphous carbons, are non‐graphitizable and are widely accepted as the most promising anode materials for emerging sodium‐ion batteries (SIBs)， because of their changeable low‐potential charge/discharge plateaus. However, their microstructures are not fixed and are difficult to accurately demonstrate as graphites do. The successful use of hard carbons in SIBs revives the interest to clearly picture their complicated microstructures that are in close relevance to sodium storage. In this review, the past definitions and structural models of hard carbons are revisited first, and a renewed understanding of their sodium storage is presented. Three critical structural features are highlighted for hard carbons, namely crystallites, defects, and nanopores, which are directly responsible for the presence of the low‐potential plateaus and their reversible extension. The impact of these structural features upon the sodium storage is then deeply discussed and sieving carbons is finally proposed as an ideal configuration of carbon anode for superhigh sodium storage. This review is expected to offer a clear picture of hard carbons, and help realize a truly rational design of high‐capacity carbon anodes, driving the industrialization of SIBs, and more promisingly open up a window for exploring their possible new uses.