Cathode Materials Titanium Oxide For The Rechargeable Mg²⁺/Li⁺ Hybrid Batteries

Rechargeable magnesium battery is a potential candidate for the application in heavy load storage due to a high energy density,a high theoretical specific capacity,the safety to handle,a low cost and environmental friendliness of metallic magnesium.However,the divalent magnesium ions show a low Mg²⁺intercalation level for most of the cathode materials because of the small ion radius,high charge density and serious solvation,which limits the development of cathode materials of rechargeable magnesium batteries.Rechargeable Mg²⁺/Li⁺hybrid batteries contain a magnesium anode,a Li⁺intercalation cathode material and a hybrid magnesium-lithium-ion electrolyte.The combination of rechargeable magnesium batteries and lithium-ion batteries not only takes the advantages of rechargeable magnesium batteries,but also solves the dilemma of the limited Mg²⁺intercalation materials by using Li⁺intercalation materials.In this work,different polymorphs of titanium oxide were used as the cathode materials of rechargeable Mg²⁺/Li⁺hybrid batteries for the first time.The electrochemical performance of these batteries as well as the possible electrochemical reaction mechanism were discussed.?1?A rechargeable Mg²⁺/Li⁺hybrid battery contained a commercial nano-sized TiO₂?anatase?cathode,a 0.5 mol L^-1 Mg?BH₄?₂+1.5 mol L^-1LiBH₄/TG electrolyte and a magnesium anode was assembled.The hybrid battery showed an excellent cycling ability and reversibility.The discharge capacity was up to 155.8 mAh/g at the rate of 0.2 C at the first cycle and still maintained 135.5 mAh/g at the 500th cycle,which showed87%capacity retention.Meanwhile,the Coulombic efficiency was as high as 99.9%except the initial several cycles.Furthermore,the hybrid battery had an excellent rate capability with a discharge capacity of 125,115,97.9 mAh/g at the rate of 1 C,1.5 C,2 C,respectively.In addition,more than 1900 cycles with little capacity fade was maintained.?2?1D mesoporous TiO₂?B?nanoflake was prepared by a hydrothermal process followed by heat-treatment.A high-performance Mg²⁺/Li⁺hybrid battery with the synthesized TiO₂?B?nanoflakes as the cathode,Mg as the anode,and 0.5 mol L^-1 Mg?BH₄?₂+1.5 mol L^-1LiBH₄/TG as the electrolyte has been developed.The hybrid battery showed an excellent cycling ability and reversibility.The initial discharge capacity was 197.3 mAh/g at the rate of 0.1 C and the overall average capacity was 185 mAh/g with a 0.03 mAh/g capacity fade each cycle and a nearly 100%Coulombic efficiency.In addition,the battery showed an excellent rate capacity with¹30 mAh/g at 1 C up to 3000 cycles and¹15 mAh/g at 2 C up to 6000 cycles.The capacity of the Mg²⁺/Li⁺hybrid battery was dominated by pseudo-capacitive reactions,and the Coulombic efficiency was effectively enhanced by the presence of Mg²⁺ions.