Alumina modified sodium vanadate cathode for aqueous zinc-ion batteries

Aqueous zinc-ion batteries (ZIBs) have great prospects for widespread application in massive scale energy storage. By virtue of the multivalent state, open frame structure and high theoretical specific capacity, vanadium (V)-based compounds are a kind of the most developmental potential cathode materials for ZIBs. However, the slow kinetics caused by low conductivity and the capacity degradation caused by material dissolution still need to be addressed for large-scale applications. Therefore, sodium vanadate Na_(2)V_(6)O_(16)·3H_(2)O (NVO) was chosen as a model material, and was modified with alumina coating through simple mixing and stirring methods. After Al_(2)O_(3) coating modification, the rate capability and long-cycle stability of Zn//NVO@Al_(2)O_(3) battery have been significantly improved. The discharge specific capacity of NVO@Al_(2)O_(3) reach up to 228 mAh/g (at 4 A/g), with a capacity reservation rate of approximately 68% after 1000 cycles, and the Coulombic efficiency (CE) is close to 100%. As a comparison, the capacity reservation rate of Zn//NVO battery is only 27.7%. Its superior electrochemical performance is mainly attributed to the Al2O3 coating layer, which can increase zinc-ion conductivity of the material surface, and to some extent inhibit the dissolution of NVO, making the structure stable and improving the cyclic stability of the material. This paper offers new prospects for the development of cathode coating materials for ZIBs.

Structures of sodium vanadate solution under different conditions

Combined with Fourier transform infrared spectroscopy（FTIR） analysis of sodium vanadate solution,the relationship between conductivity and structure was investigated by measuring the electric conductivity of the solution under different alkali concentrations and molar ratios of NaOH to V2O5. Results suggest that the polymerization vanadium acid radical ions gradually transform into monomer with the solution diluting. When the solution is diluted to a certain extent,only the vanadium acid radical ion with V-OH chemical bond exists in the solution. At NaOH concentration of below 105.21 g·L^（-1）,the vanadate anions mainly exist in the form of vanadium acid radical ion with V-OH chemical bond and the ion transference number is approximately from 0.58 to 0.82. In the medium NaOH concentration range of 105.21-117.03 g·L^（-1）, the vanadate anions mostly exist in the form of vanadium acid radical ion with V-OH and V-O-V chemical bonds and the ion transference number is approximately 3.29. At NaOH concentration of above 117.03 g·L^（-1）, vanadate anions exist in the form of vanadium acid radical ion with V-OH and V-O-V chemical bonds.

Sodium vanadium oxides:From nanostructured design to high-performance energy storage materials

Developing high-capacity and low-cost cathode materials for metal-ion rechargeable batteries is the mainstream trend and is also the key to providing breakthroughs in making high-energy rechargeable batteries.Vanadium has a variety of valence states and can form a variety of vanadate structures.As a typical positive electrode material,vanadate has abundant ion adsorption sites,a unique“pillar”framework,and a typical layered structure.Therefore,it has the advantages of high specific capacity and excellent rate performance,possessing the prospect of being a large-capacity energy storage material.In this review,we focus on applications of sodium vanadium oxides(NVO)in electrical energy storage(EES)devices and summarize sodium vanadate materials from three aspects,including crystal structure,electrochemical performance,and energy storage mechanism.The recent progress of NVO-based highperformance energy storage materials along with nanostructured design strategies was provided and discussed as well.This review is intended to serve as general guidance for researchers to develop desirable sodium vanadate materials.