Surface Engineering Of Ion Channel On The Anode Of Rechargeable Magnesium Batteries

Rechargeable magnesium batteries（RMBs）are a promising candidate for“post-Li-ion batteries”due to their high capacity,high abundance,and most importantly,dendrite-free Mg metal anode.However,the formation of passivating surface film rather than Mg²⁺-conducting interphase on Mg anode surface has always restricted the development of rechargeable Mg batteries.In the early stage of research on RMBs,most efforts focused on inventing new electrolytes to mitigate the formation of insulating layers.In recent years,the strategy of engineering an artificial Mg²⁺-conductive interphase on the Mg anode surface is worth further developing as it would significantly broaden the selection of electrolytes.On the one hand,the artificial interphase enables the reversible Mg chemistry of RMBs in Mg（TFSI）₂-based electrolytes,which possess high ionic conductivities and oxidation stabilities,in RMBs.On the other hand,the modified Mg anode could be paired with high-voltage and high-capacity cathode,eventually exploiting high-energy magnesium battery chemistries.In this work,we report that an artificial Mg²⁺-conducting interphase can be engineered on the Mg anode surface,which facilitates a reversible Mg deposition/stripping process.The main contents are as follows:（1）To address the problem of surface passivation of Mg metal anode in a conventional electrolyte（Mg（TFSI）₂/DME electrolyte）,we report a Mg²⁺-conducting tin-based artificial layer on Mg anode via a facile and safe method,leading to a long and stable electrochemical performance in Mg（TFSI）₂/DME electrolyte.For the artificial layers,the Sn-based compounds（Mg₂Sn/Sn）provide a fast ion transport conduit for Mg ions,showing a high diffusion coefficient of Mg²⁺,and the insulating halides（Mg Cl₂/Sn Cl₂）offer potential gradient to drive Mg ions to electrodeposit under the coating film.Besides,the interfacial resistance and ion transport activation energy were sharply reduced and fast ion diffusion kinetics was performed on the modified Mg anodes.The symmetric cells with modified Mg electrodes exhibit a quite low overpotential（<0.2 V）and an ultralong lifespan over 1400 h even at a high current density of 6 m A cm^-2.（2）To tackle the problem of poor applicability of magnesium metal anode in conventional ether-based electrolytes,we prepared a modified Mg anode with newly Pero film by doctor-blade coating,thus delivering excellent electrochemical properties even at high current density.The modified magnesium anode with highly crystalline exhibits a fast kinetics upon plating/stripping cycling.The symmetric cell with modified Mg electrode displays a superior rate capability.It can even provide the overpotential of～0.22 V at a high current density of 15 m A cm^-2.Prototype full cells in which modified Mg anodes are paired with titanium carbide cathodes exhibit excellent long-cycle stability for 500 cycles at high rate of 1 A g^-1,enabling the application of magnesium metal anode in ether-based electrolyte.（3）To deal with the problem of surface passivation of Mg anode in conventional carbonate-based electrolyte and its application,a bismuth-based artificial interfacial layer was constructed on the surface of magnesium metal by a facile ion-exchange chemistry leading to highly reversible Mg chemistry in oxidation-resistant electrolytes.The modified Mg electrode can be cycled stably for more than 2500 hours with minimal voltage divergence of～0.2 V at 0.02 m A cm^-2.The strategy is to couple high potential cathodes with the modified Mg anode in hybrid Mg²⁺/Li⁺electrolytes so that it is possible to run full cells in carbonate-based electrolyte.By means of electrochemical analysis and the cryoelectron microscopy studies,the reasons for the reversible deposition dissolution of the modified Mg metal anode in carbonate-based electrolyte were also investigated.