Samples of Li _x CoO ₂ (0.5≤x≤1) have been prepared by electrochemical deintercalation from high temperature LiCoO ₂ and are characterized by X-ray diffraction, electrical measurements and ⁷ Li MAS NMR spectroscopy. X-Ray diffraction studies as a function of x are in good agreement with literature data and suggest that the two-phase domain for 0.75≤x≤0.94 is not due to structural reasons. Electrical conductivity and thermoelectronic power measurements evidence a gradual change in the electronic properties from localised to delocalised electrons upon lithium deintercalation. ⁷ Li MAS NMR suggests that the metal-non metal transition is the driving force for the existence of the biphasic domain.

Considering the natural abundance and low cost of sodium resources, sodium‐ion batteries (SIBs) have received much attention for large‐scale electrochemical energy storage. However, smart structure design strategies and good mechanistic understanding are required to enable advanced SIBs with high energy density. In recent years, the exploration of advanced cathode, anode, and electrolyte materials, as well as advanced diagnostics have been extensively carried out. This review mainly focuses on the challenging problems for the attractive battery materials (i.e., cathode, anode, and electrolytes) and summarizes the latest strategies to improve their electrochemical performance as well as presenting recent progress in operando diagnostics to disclose the physics behind the electrochemical performance and to provide guidance and approaches to design and synthesize advanced battery materials. Outlook and perspectives on the future research to build better SIBs are also provided.

This paper describes the preparation of Na_xVO₂ phases by means of electrochemical deintercalation. The curves V = f(x) show that the process is reversible up to x = 0.5 and they indicate the presence of multiple single phase domains in the range 1 < x < 0.5. Two single phases have been successfully isolated for Na_1/2VO₂ and Na_2/3VO₂ compositions; we report here the first X-ray powder diffraction measurements of these phases. They present a O’3-type monoclinic distortion of the O3 rhombohedral phase observed for Na₁VO₂. The evolution of cell parameters with sodium deintercalation is comparable with other A_xMO₂ layered oxides.

Cathode materials are critical to the energy density, power density and safety of sodium-ion batteries (SIBs). Herein, we performed a comprehensive study to elucidate and exemplify the interplay mechanism between phase structures, interfacial microstrain and electrochemical properties of layered-structured Na_xNi_1/3Co_1/3Mn_1/3O₂ cathode materials for high voltage SIBs. The electrochemical test results showed that Na_xNi_1/3Co_1/3Mn_1/3O₂ with an intergrowth P2/O3/O1 structure demonstrates better electrochemical performance and better thermal stability than Na_xNi_1/3Co_1/3Mn_1/3O₂ with P2/O3 binary-phase integration and Na_xNi_1/3Co_1/3Mn_1/3O₂ where only the P phase is dominant. This result is caused by the distinct interfacial microstrain development during the synthesis and cycling of the P2/O3/O1 phase. In operando high energy X-ray diffraction further revealed that the intergrowth P2/O1/O3 cathode can inhibit the irreversible P2–O2 phase transformation and simultaneously improve the structure stability of the O3 and O1 phases during cycling. We believe that interfacial microstrain can serve as an indispensable bridge to guide future design and synthesis of high performance SIB cathode materials and other high energy battery materials.