Review of Research on Anode Materials for Secondary Magnesium Batteries
The development of lithium-ion batteries has driven the development of mobile electronic devices and information industri-alization.However,due to the scarcity of lithium resources and the safety risks of lithium-ion batteries,it is urgent to develop a new generation of energy storage technology that is cheap and secure.Secondary magnesium battery is expected to be used in large-scale en-ergy storage for its low cost,high safety,abundant resources,high energy density and other advantages.The following benefits of mag-nesium metal over alkali metals:the melting point of magnesium is substantially higher than that of lithium,magnesium and its com-pounds are largely non-toxic or have minimal toxicity,thus do not affect the environment.Magnesium is one of the most plentiful ele-ments in the earth's crust,with a crustal abundance of roughly 2.3％.The most important factor is that magnesium metal,which is used in batteries,cannot easily form dendrites during the charging and discharging process.This effectively guarantees the safety of battery.Therefore,electrochemical energy storage technologies using secondary magnesium batteries are particularly promising.Nowa-days,secondary magnesium batteries are still in the preliminary stage of research,in which the selection and optimization of anode ma-terials are especially significant.This work reviewed the advantages,application status,and latest research progress of anode materi-als for secondary magnesium batteries,such as pure magnesium anode materials,alloy anode materials,embedded anode materials,and interfacial film modified anode materials.Pure Mg anode with high theoretical specific capacity,low cost and simple preparation process was the anode materials chosen by most of the researches,however,the high pressure Mg(TFSI)2 electrolyte was not compati-ble with Mg anode and would form passivation film on the surface,which would seriously affect the kinetic behavior during Mg deposi-tion/dissolution and hinder the development of pure Mg anode.In order to widely match various electrolytes and cathode materials,al-loy anodes,interfacial film modified anodes,and embedded anodes were still important choices.Alloy anodes changed the microstruc-ture and phase composition by doping pure Mg metal with other elements,and then improved the performance of Mg anode.Bi,Sb and other elements doping could improve the interaction between Mg(TFSI)2 electrolyte and anode surface,inhibiting the generation of passivation film.And the alloyed electrode could better adapt to the volume expansion during the charging and discharging process and maintain a stable electrochemical reaction process.However,the current research on alloyed anode mainly adopted the exploration of alloying elements and design of alloy composition,and the alloys searched were either insufficient in performance or expensive.It was particularly important to find lower cost and better performance alloyed anode materials by starting from the electrochemical process and the nature of the reaction.Therefore,the development of new modified alloyed anode materials would be one of the important direc-tions for the future development of secondary magnesium battery anode.Based on the interface film modified anode,it was created to electron-insulated and ion-conducting interface"route"might effectively block the breakdown of electrolyte and therefore inhibited the creation of passivation film,and could play the original benefits of pure magnesium.However,the preparation of the interfacial film on the surface of pure magnesium was complicated and expensive at present.Therefore,the optimization of the preparation process and cost control would be the focus of future research in order to achieve industrial-scale application of interface film modified anode.The intercalated anode materials,such as carbon-based anode,had high theoretical capacity and were widely used in lithium-ion and sodi-um-ion batteries,however,the magnesium storage performance of carbon-based materials still could not reach to the theoretical capac-ity.The divalent Mg2+with two units of positive charge in the secondary magnesium battery had a very strong solvent effect,Mg2+ions tended to bind with the anion or solvent group to produce a bigger radius polymerization ion.The large radius ion was evidently unsuit-able for the smaller layer spacing of intercalation type materials,and the co-embedding Mg2+and solvent ions would also destroy the structure of the intercalation type materials,thus limiting the performance of the battery.The anode material had a significant impact on the performance of secondary magnesium batteries.The future research path for anode materials of secondary magnesium batteries would be low cost and good performance.The alloy anode electrode production technique was easy,which might effectively increase the passivation of the negative electrode,but the cost was high.By establishing an interfacial ion route,the interfacial film modified anode might also effectively alleviate electrolyte breakdown and decrease surface passivation,but the cost was expensive and the indus-trial preparation process was difficult.Although the intercalated anode had a significant theoretical capacity,it was still incompatible with secondary magnesium batteries.Finally,alloy anode materials,embedded anode materials,and interfacial film modified anode materials were all predicted to fulfill the aim of high-performance secondary magnesium batteries following further process optimization and performance improvement.
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