| The rapid developments for portable electronic devices and electric vehicles raise an urgent need for rechargeable batteries with high energy density,alkali metal batteries have received great attention.Sodium metal has higher theoretical capacity(1166 mAh g-1)、lower redox potential(-2.714 V)、abundant reserves and low cost,which makes it the most ideal anode material for nextgeneration energy storage systems.However,sodium metal anode has high reactivity and is easy to react with the electrolyte,forming an unstable solid electrolyte(SEI)layer.In addition,sodium dendrites will generate during uneven sodium plating/stripping process.The generation of sodium dendrites will cause problems such as unlimited volume expansion and capacity decay.It may also pierce the diaphragm,which will result in internal short circuits and cause safety hazards.The growth of sodium dendrites has always been the biggest challenge faced of sodium metal anodes,which greatly hinders the commercial development of sodium metal batteries.In this work,metal organic phosphine framework(MOPFs)glass is used as a protective layer to modify the commercial copper current collector to control the sodium metal deposition behavior and effectively improve the stability of the sodium metal anode.Firstly,using 1,2-bis(diphenylphosphine)ethane(DPPE)and cobalt chloride as raw materials,MOPFs were prepared through coordination reactions.MOPFs have a crystalline polygonal rod-like structure,with Co atoms coordinated with 4 P atoms.Then,MOPFs were coated on the surface of the copper current collector,and the MOPFs glass modified copper foil electrode was successfully prepared by the method of melting and quenching treatment.MOPFs glass has an amorphous structure,inherits the coordination mode of MOPFs,and forms a uniform coating on the surface of the copper foil.Finally,the modified Cu foil electrode can reduce the sodium nucleation overpotential,improve the deposition/stripping behavior of sodium on the current collector,inhibit the growth of sodium dendrites and show good electrochemical performance.Under the charge-discharge conditions with a current density of 1.0 mA cm-2 and a capacity of 1.0 mA h cm-2,the sodium metal half-cell has a stable coulombic efficiency of-99.5%for more than 700 cycles;The sodium metal symmetric battery can be cycled stably for more than 2000 h at surface capacities of 2-5.0 mA h cm-2 and a stripping depth of 100%;it is matched with NVP cathode to form a full battery,showing excellent rate performance and long cycle stability.In addition,this work also characterizes the surface structure of the modified copper foil electrode after cycling,and explores the protection mechanism of the MOPFs glass layer on the current collector.This work provides a new idea for the preparation of rechargeable batteries with high energy density,and further promotes the development of the field of energy storage and conversion. |
