The gliding of transition-metal slabs in layered Na containing oxides would limit the battery performance in several crucial aspects.

Attempts to utilize lithium-ion batteries (LIBs) in large-scale electrochemical energy storage systems have achieved initial success, and solid-state LIBs using metallic lithium as the anode have also been well developed. However, the sharply increased demands/costs and the limited reserves of the two most important metal elements (Li & Co) for LIBs have raised concerns about future development. Sodium-ion batteries (SIBs) equipped with advanced cobalt-free cathodes show great potential in solving both “lithium panic” and “cobalt panic”, and have made remarkable progress in recent years. In this review, we comprehensively summarize the recent advances of high-performance cobalt-free cathode materials for advanced SIBs, systematically analyze the conflicts of structural/electrochemical stability with intrinsic insufficiencies of cobalt-free cathode materials, and extensively discuss the strategies of constructing stable cobalt-free cathode materials by making full use of non-cobalt transition-metal elements and suitable crystal structures, all of which aim to provide insights into the key factors (e.g., phase transformation, particle cracks, crystal defects, lattice distortion, lattice oxygen oxidation, morphology, transition-metal migration/dissolution, and the synergistic effects of composite structures) that can determine the stability of cobalt-free cathode materials, provide guidelines for future research, and stimulate more interest on constructing high-performance cobalt-free cathode materials.

Two principles of component regulation and pre-desolvation and derived strategies for achieving dehydrated zinc-ion solvation structures are systematically reviewed.

The inner Helmholtz plane and thus derived solid-electrolyte interphase (SEI) are crucial interfacial structure to determine the electrochemical stability of Zn-ion battery (ZIB). In this work, we demonstrate that introducing β-cyclodextrins (CD) as anion-receptors into Zn(OTf)₂ aqueous electrolyte could significantly optimize the Zn anode SEI structure for achieving stable ZIB. Specifically, β-CD with macrocyclic structure holds appropriate cavity size and charge distribution to encase OTf^- anions at the Zn metal surface to form β-CD@OTf^- dominated inner Helmholtz structure. Meanwhile, the electrochemically triggered β-CD@OTf^- decomposition could in situ convert to the organic-inorganic hybrid SEI (ZnF₂/ZnCO₃/ZnS‒(C-O-C/^*CF/^*CF₃)), which could efficiently hinder the Zn dendrite growth with maintain the proper SEI mechanical strength stability to guarantee the long-term stability. The thus-derived Zn | |Zn pouch cell (21 cm² size) with β-CD-containing electrolyte exhibits a cumulative capacity of 6450 mAh⁻² cm⁻² at conditions of 10 mAh cm⁻² high areal capacity. This work gives insights for reaching stable ZIB via electrolyte additive triggered SEI structure regulation.