Olivine-Type MgMn0.5 Zn0.5 SiO4 Cathode for Mg-Batteries: Experimental Studies and First Principles Calculations

The Magnesium Insertion Effects into P2-Type Na2/3 Ni1/3 Mn2/3 O2

A Mg-cell with P2-Na2/3 Ni1/3 Mn2/3 O2 layered oxide cathode provides novel reaction mechanism not observed in Na-cells. The sodium/vacancy ordering and Jahn-Teller effects are suppressed with the insertion of magnesium ion. The Mg-cell exhibits different features when operating between 4.5 and 0.15 V and 3.9 and 0.15 V versus Mg2+ /Mg. To analyze the structural and chemical changes during Mg insertion, the cathode is first charged to obtain the Na1/3 Ni1/3 Mn2/3 O2 compound, which is formally accompanied by an oxidation from Ni2+ to Ni3+ . As structure models Mg1/6 Na1/3 Ni1/3 Mn2/3 O2 and Mg1/12 Na1/2 Ni1/3 Mn2/3 O2 are utilized with a large2 3 a $2\sqrt 3 a$ ×2 3 a $2\sqrt 3 a$ supercell. On discharge, the Mg-cell exhibits a multistep profile which reaches ≈100 mA h g-1 with the valence change from Ni3+ to Ni2+ . Such profile is quite different from its sodium counterpart (230 mA h g-1 ) which exhibits the sodium/vacancy ordering and deleterious presence of Mn3+ . Depending on how the two interlayer spacings are filled by Na and Mg the "staged," "intermediated," and "average" models are analyzed for Mgy Na8 Ni8 Mn16 O48 supercell. This fact suggests differences in the cell performance when Mg is used as counter electrode providing some tips to improve the structure engineering on cathode materials.

Rational Design of Ni-Doped V2O5@3D Ni Core/Shell Composites for High-Voltage and High-Rate Aqueous Zinc-Ion Batteries

Aqueous zinc-ion batteries (ZIBs) have significant potential for large energy storage systems because of their high energy density, cost-effectiveness and environmental friendliness. However, the limited voltage window, poor reaction kinetics and structural instability of cathode materials are current bottlenecks which contain the further development of ZIBs. In this work, we rationally design a Ni-doped V2O5@3D Ni core/shell composite on a carbon cloth electrode (Ni-V2O5@3D Ni@CC) by growing Ni-V2O5 on free-standing 3D Ni metal nanonets for high-voltage and high-capacity ZIBs. Impressively, embedded Ni doping increases the interlayer spacing of V2O5, extending the working voltage and improving the zinc-ion (Zn302+) reaction kinetics of the cathode materials; at the same time, the 3D structure, with its high specific surface area and superior electronic conductivity, aids in fast Zn302+ transport. Consequently, the as-designed Ni-V2O5@3D Ni@CC cathodes can operate within a wide voltage window from 0.3 to 1.8 V vs. Zn30/Zn302+ and deliver a high capacity of 270 mAh g-1 (~1050 mAh cm-3) at a high current density of 0.8 A g-1. In addition, reversible Zn2+ (de)incorporation reaction mechanisms in the Ni-V2O5@3D Ni@CC cathodes are investigated through multiple characterization methods (SEM, TEM, XRD, XPS, etc.). As a result, we achieved significant progress toward practical applications of ZIBs.