Reorganizing Helmholtz Adsorption Plane Enables Sodium Layered-Oxide Cathode Beyond High Oxidation Limits.

Sodium layered-oxides (Nax TMO2 ) sustain severe interfacial stability issues when subjected to battery applications. Particularly at high potential, the oxidation limits including transition metal dissolution and SEI reformation are intertwined upon the cathode, resulting in poor cycle ability. Herein, by rearranging the complex and structure of Helmholtz absorption plane adjacent to Nax TMO2 cathodes, the mechanism of constructing stable cathode/electrolyte interphase to push up oxidation limits is clarified. The strong absorbent fluorinated anions replace the solvents into the inner Helmholtz plane, thereby reorganizing the Helmholtz absorption structure and spontaneously inducing an anion-dominated interphase to envelop more active sites for layered oxides. More importantly, such multi-component cathode/electrolyte interphase proves effective for long-term durability of a series of manganese-based oxide cathodes, which achieves 1500-cycles lifetime against high oxidation voltage limit beyond 4.3 V. This work unravels the key role of breaking high-oxidation limits in attaining higher energy density of layered-oxide systems. This article is protected by copyright. All rights reserved.

Constructing Stable Anion-Tuned Electrode/Electrolyte Interphase on High-Voltage Na3 V2 (PO4 )2 F3 Cathode for Thermally-Modulated Fast-Charging Batteries.

Constructing stable electrode/electrolyte interphase with fast interfacial kinetics is vital for fast-charging batteries. Herein, we investigate the interphase that forms between a high-voltage Na3 V2 (PO4 )2 F3 cathode and the electrolytes consisting of 3.0, 1.0, or 0.3 M NaClO4 in an organic carbonate solvent (47.5 : 47.5 : 5 mixture of EC: PC: FEC) during charging up to 4.5 V at 55 °C. It is found that a higher anion/solvent ratio in electrolyte solvation structure induces anion-dominated interphase containing more inorganic species and more anion derivatives (Cx ClOy ), which leads to a larger interfacial Na+ transport resistance and more unfavorable gas evolution. In comparison, a low anion/solvent ratio derives stable anion-tuned interphase that enables better interfacial kinetics and cycle ability. Importantly, the performance of a failed cathode is restored by triggering the decomposition of Cx ClOy species. This work elucidates the role of tuning interphase in fast-charging batteries.