Lithium‐rich, Mn‐based layered oxides Li2MnO3‐LiMO2 (M=Ni, Co) have been considered as promising cathode candidates owing to their high capacity. However, the resources shortage and high price of cobalt make it imperious to substitute cobalt with other high‐abundance elements. Here, we synthesized a low‐cost, cobalt‐free, Fe‐substituted oxide material, Li(Li0.16Ni0.19Fe0.18Mn0.46)O2. It exhibited a high reversible capacity of 169.2 mAh g−1 after 100 cycles and maintained an extraordinarily high discharge potential during cycling. X‐ray photoelectron spectroscopy and DFT calculations revealed that super iron FeIV exists in the delithiated state, and oxygen participates in the redox reaction in addition to the Ni2+/Ni4+ and Fe3+/Fe4+ redox couples. The anionic oxidation preferentially occurred on oxygen with a Li−O−Li configuration and with oxidized Fe and Ni coordination.

High‐energy‐density and low‐cost lithium‐ion batteries are sought to meet increasing demand for portable electronics. In this study, a cobalt‐free Li(Li0.17Ni0.17Fe0.17Mn0.49)O2 (LNFMO) cathode material is chosen, owing to the reversible anionic redox couple O2−/O−. The aim is to elucidate the Fe‐substitution function and oxygen redox mechanism of experimentally synthesized Li(Li0.16Ni0.19Fe0.18Mn0.46)O2 by DFT. The redox processes of cobalt‐containing Li(Li0.17Ni0.17Co0.17Mn0.49)O2 (LNCMO) are compared with those of LNFMO. Redox couples including Ni2+/Ni3+/Ni4+, Fe3+/Fe4+ or Co3+/Co4+, and O2−/O− are found, confirmed by a X‐ray photoelectron spectroscopy, and explained by redox competition between O and transition metals. In LNFMO and LNCMO, O ions with an Li‐O‐Li configuration readily participate in oxidation, and the most active O ions are coordinated to Mn4+ and Li+. Oxidation of O in LNCMO is triggered earlier, along with that of Co. Fe substitution activates O ions, contributes additional oxygen redox charge compensation of 0.44 e per formula unit, avoids concentrated accumulation of oxygen oxidation, and improves structural stability. This work provides new scope for designing cobalt‐free, low‐cost, and higher‐energy‐density cathode materials for Li‐ion batteries.

Potassium-and sodium-ion batteries (KIBs and SIBs) have attracted wide attention due to abundant potassium and sodium resources, low cost, and high safety. Therefore, in this work, FeP as an anode material is selected to study diffusions of Na/K using a density functional theory method in order to explain our experimental result that the rate performance of the FeP/C anode material in KIBs is much better than that in SIBs. The rate performance of the FeP/C anode material in KIBs and SIBs is related to diffusion activation energies including interaction energies between Na/K and FeP and migration energy barriers. Our calculations find that diffusion of Na/K in FeP is a multistep one. The most favorable one among various possible diffusion paths is obtained. A migration energy barrier is a key factor to distinguish between K and Na diffusions in FeP. Na−P/K−P bond lengths, consequent binding energies between Na/K and FeP, and local structures of transition states account for migration energy barriers. The calculated result of the larger migration energy barrier for Na in FeP than K in FeP can well explain our experimental phenomenon that the rate performance of FeP/C in KIBs is better than that in SIBs. This work provides a theoretical basis that iron phosphide can be used as a better, low-cost, and higher-energy-density anode material for KIBs.

Binding energies ([Formula: see text], geometric and electronic structures for [[Formula: see text]](O/[[Formula: see text]]) additions of O atom on ([Formula: see text])([Formula: see text] − 10) single-walled carbon nanotubes with di-vacancies are studied using a GGA-PBE method, and defect curvature ([Formula: see text]) is used to predict reactivities of different C—C bonds at defect area. Calculated results show that the C—C bonds can be divided into two types: broken C—C bonds corresponding to adducts with a C—O—C configuration structure and unbroken C—C bonds corresponding to adducts with a closed-3MR structure. [Formula: see text] of O/[[Formula: see text]] additions for the adduct with the C—O—C configuration structure monotonously increases with the increase of [Formula: see text] in any ([Formula: see text],0)([Formula: see text]) tube and decreases with the increase of [Formula: see text] in ([Formula: see text],0)([Formula: see text], 7, 10) tubes. Besides the fact that [Formula: see text] value is mainly determined by the defect curvature, it is also affected by band gaps, bonding characteristic of C—C bonds in the highest occupied molecular orbital (HOMO) and geometric structures. The study would provide a theoretical basis for surface modifications of carbon nanotubes with atomic vacancy defects.