Probing the charged state of layered positive electrodes in sodium-ion batteries : reaction pathways, stability and opportunities

Sodium-ion batteries have received significant interest as a cheaper alternative to lithium-ion batteries and could be more viable for use in large scale energy storage systems. However, similarly to lithium-ion batteries, their performance remains limited by the positive electrode materials. Layered transition metal oxides, with chemical formula NaxMO2, have been extensively investigated and appear to show the most promise. However, the inability to reversibly extract large amounts of sodium ions from these layered structures, by charging to high voltages, has limited the useful capacity and cycle life of these materials. To address this, numerous studies have attempted to resolve the structural and chemical changes that take place in positive electrode materials upon cycling. This is particularly important at and near the charged state, which is where the materials\u27 structures are highly sodium deficient. Following a brief introduction into the status of sodium-ion battery positive electrodes, this work focuses on the development of knowledge and understanding into the structure of layered oxides at the charged state by highlighting cutting edge characterisation techniques that have been utilised. Finally, a perspective on future development is provided to direct further structural characterisation research which will enable the rational design of new and improved energy storage materials

Exploration of the high temperature phase evolution of electrochemically modified Sc2(WO4)3via potassium discharge

The activation of Sc2(WO4)3via electrochemical discharge against potassium metal is investigated, as well as the subsequent thermal evolution of Sc2(WO4)3. On subsequent heating from 100 to 623 K the discharged electrode exhibits essentially the same thermal expansion as that of the pure powder. Between 673 and 973 K a trigonal K2WO4-type phase (P[3 with combining macron]m1) is formed. Variable-temperature X-ray diffraction data indicates that upon heating from 923 K–1023 K, this phase has a thermal expansion coefficient of −1.90(10) × 10−4 K−1

Advanced Nanoparticle Coatings for Stabilizing Layered Ni‐Rich Oxide Cathodes in Solid‐State Batteries

Improving the interfacial stability between cathode active material (CAM) and solid electrolyte (SE) is a vital step toward the development of high-performance solid-state batteries (SSBs). One of the challenges plaguing this field is an economical and scalable approach to fabricate high-quality protective coatings on the CAM particles. A new wet-coating strategy based on preformed nanoparticles is presented herein. Nonagglomerated nanoparticles of the coating material (≤5 nm, exemplified for ZrO$_{2}$) are prepared by solvothermal synthesis, and after surface functionalization, applied to a layered Ni-rich oxide CAM, LiNi$_{0.85}$Co$_{0.10}$Mn$_{0.05}$O$_{2}$ (NCM85), producing a uniform surface layer with a unique structure. Remarkably, when used in pelletized SSBs with argyrodite Li$_{6}$PS$_{5}$Cl as SE, the coated NCM85 is found to exhibit superior lithium-storage properties (q$_{dis}$ ≈ 204 mAh g$_{NCM85}$$^{-1}$ at 0.1 C rate and 45 °C) and good rate capability. The key to the observed improvement lies in the homogeneity of coating, suppressing interfacial side reactions while simultaneously limiting gas evolution during operation. Moreover, this strategy is proven to have a similar effect in liquid electrolyte-based Li-ion batteries and can potentially be used for the application of other, even more favorable, nanoparticle coatings