![]() ![]() ![]() For the sodium layered oxides, the most prevailing structures applied for SIB cathodes are P2 or O3 phase, where Na + ions are accommodated at “prismatic” or “octahedral” sites, and the stacking sequences of oxygen are “ABBA” for P2 and ABCABC for O3, respectively. This will weaken the O–O repulsion and thereby give rise to moderate interlayer contraction for endurable cycle life. Meanwhile, the redox charge loss of TMs could be compensated persistently by the O 2 p electrons through generating electron holes (i.e., oxygen charge compensation). ] In detail, when most of the lithium ions are extracted from the lattice at high voltage, the interlayer distance is governed heavily by the O–O electrostatic force between the layers. ] A charge compensation mechanism between highly hybridized TM‐3 d and O‐2 p states has been thought to be responsible for this moderate solid solution behavior. Starting from a Li‐intercalated layered structure ( Figure 1a), the framework exhibits a continuously evolved interlayer contraction when deeply charged, which is sustainable for long‐term cycling. The gap between the cycling stabilities of Li‐ and Na‐based layered oxides could be mostly attributed to their diverse structural changes upon Li‐ or Na‐(de)intercalation. Nevertheless, more solutions with artful and in‐depth concepts for fine material design are still urgently desired. ] To improve the cycling stability, substantial efforts with various degree of success have been made including incorporating foreign dopants, [ ] but most of them suffer from severe capacity decay and poor structural stability of Na‐intercalated lattice. ] These materials share common advantages over lithium layered counterparts (e.g., LiCoO 2), such as high energy density, fast ionic diffusion, and good stability in air, [ ![]() ] In analogy to Li‐based layered cathodes that have been widely applied in commercial LIBs, a variety of sodium layered intercalated compounds, for example, sodium layered transition‐metal (TM) oxides (i.e., Na xTMO 2, TM = Ni, Mn, Fe, Cr, V, Ti, etc.), have been extensively explored as cathode materials for SIBs. Especially, the exploration of suitable cathode materials has been the focus of attention, since it is the cathode materials that account for most of the overall costs of the whole cell and determine critical battery performance, such as energy density and cut‐off voltage. [Īpart from the prospect, there are still critical challenges for the widespread usage of SIBs. ] In light of this, the development of sodium‐ion batteries (SIBs), using sodium instead of lithium as charge carriers, shows great promises upon overcoming the economic barriers of LIBs and therefore have attracted significant attention. Contrary to the lithium raw materials, sodium resources are earth‐abundant, distributed worldwide and cost effective. ] With this regard, searching for alternative energy storage chemistries lies at the very heart of global concerns nowadays. ] Despite almost 30 years of commercial success, nevertheless, concerns have recently arisen about the shortage of Li resource and potentially rising costs. ] Among the currently existing energy storage technologies, lithium‐ion batteries (LIBs) are widely applied in portable devices and preferred for powering next‐generation electric vehicles (EVs). As a result, the development of energy storage techniques for sustainable energy sources (e.g., solar, wind, etc.) becomes necessary to a green and recycling society. However, nonrenewable fossil fuels are being exhausted rapidly, and their over‐exploitation and consumption also lead to severe environmental issues. With the growth of the economy, the global demands for energy have significantly increased. This study starts a perspective way of optimizing the sodium layered cathodes by rational structural design coupling electrochemical reactions, which can be extended to widespread battery researches. Accordingly, the cycling stability of the codoped cathode material is improved superiorly over the pristine sample. In this way, the interlayer O-O electrostatic repulsion is weakened upon deeply charging, which strongly affects the systematic total energy that transforms the striking P2–O2 interlayer contraction into a moderate solid‐solution‐type evolution. Herein a Ti/Mg co‐doping strategy for a model P2‐Na 2/3Ni 1/3Mn 2/3O 2 cathode material is put forward to activate charge compensation through highly hybridized O 2 p-TM 3 d covalent bonds. Hence, enabling charge compensation in sodium layered oxides is a fascinating task for extending the cycle life of sodium‐ion batteries. Layered transition‐metal (TM) oxides are ideal hosts for Li + charge carriers largely due to the occurrence of oxygen charge compensation that stabilizes the layered structure at high voltage. ![]()
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