Study On Preparation And Properties Of Cathode Materials For Aqueous Zinc Ion Batteries

Aqueous zinc ion battery is a safe,green,and pollution-free new energy with the special advantages of low cost and high safety in large-scale energy storage systems.The cathode materials are dominant in characterizing performance.At present,there are several problems on the cathode materials,such as,low specific capacity and poor stability.Herein,this research work mainly focuses on developing suitable cathode materials to achieve the goal of better discharge specific capacity and cycle stability of aqueous zinc ion batteries,providing a reference for understanding its energy storage mechanism.The details are listed as follows:Generally,the transition metal sulfides in aqueous zinc ion batteries exhibits relatively poor specific discharge capacity,among which the unmodified Mo S₂ only is about 10 m Ah g^-1.However,Mo S₂ is a two-dimensional graphene-like material with tunable electrochemical properties from semiconductor to metal phase,exhibiting promising research value in aqueous zinc ion batteries.Here,a doping strategy is employed to introduce P,N,and O elements into Mo S₂ to replace S atoms,and then the1T/2H phase heterostructures with different contents of oxygen defects and 1T-Mo S₂ are constructed by adjusting the temperature.It is found that the O-doping and low temperature（140℃）can promote the structure transition from 2H-Mo S₂ to 1T-Mo S₂ and thus increase the contents of 1T-Mo S₂ with good conductivity.Moreover,the Mo S₂-O·2.75H₂O sample has the high-content oxygen defects and large interlayer spacing（9.68（?））,which is conducive to the rapid insertion/extraction of Zn²⁺in the MoS₂-O·2.75H₂O cathode.Zn//MoS₂-O·2.75H₂O battery exhibits the best electrochemical performance with a specific capacity of 197.5 m Ah g^-1 at 0.1 A g^-1,about 20 times that of unmodified Mo S₂.Notiablely,V-based oxides cathode materials can achieve high discharge specific capacity in aqueous zinc ion batteries,but they are easy to suffer from the structural collapse during charge-discharge cycle and exhibit poor cycling stability.Herein,an intercalated V-based oxides Mn_0.2V₈O₂₀·1.12H₂O（Mn VO）with interlayer water and Mn²⁺is synthesized via doping strategy.Mn²⁺combines with oxygen in VO₆ octahedron of V-based oxides layers to form the solid pillars,so that the V-based oxides provide a large interlayer spacing（10.3（?））and prevent the structural collapse of cathode material during charge-discharge processes.This enables the Zn//Mn VO battery output a specific capacity of 306.4 m Ah g^-1 at 0.1 A g^-1 and maintain 86.4%of the capacity after 1000 cycles at 2.0 A g^-1.For comparison,the V-based oxide without Mn-doping can only maintain 70.6%after1000 cycles.The high specific capacity and good cycle stability of Mn VO cathode indicate that the Zn//Mn VO battery has broad application prospects in the field of energy storage.