Modification Investigation On Sodium Metal Anode

Due to the low cost,high natural abundance and wide distribution of Na,and the low electrochemical potential?-2.73 V vs.standard Hydrogen electrode?and high theoretical specific capacity(1166 mA h g^-1)of Na metal anode,Na metal batteries attract attentions to the construction of high-energy low-cost energy storage systems.However,Na has high reactivity with the electrolyte,leading to the formation of a solid electrolyte interface?SEI?layer between Na and electrolyte.During the repeated Na plating/stripping,Na metal anode shows uneven deposition and a huge volume change,rendering the breaking and re-forming of SEI layer.The consumed Na metal anode and electrolyte lead to low coulombic efficiency?CE?and battery failure.Meanwhile,uneven Na plating results in the growth of dendritic Na,leading to internal short circuit and safety concerns.It is important that restricting the dendritic growth and improving the CE of Na metal anode for developing Na metal batteries.Therefore,the following work has been carried out:?1?3D conductive carbon fiber paper?CFP?has been used as current collector,guiding Na plating,suppressing dendritic Na growth and improving coulombic efficiency during Na repeated plating/stripping.High reversibility with an average CE of 99.5%over 100 cycles has been achieved at the current density of 1 mA cm^-2.The CFP@Na symmetric battery displays low and stable voltage hysteresis over 500 h.Because of the chemical affinity between Na and carbon,Na tends to nucleate on CFP.Thus,3D structure can restrict Na dendritic growth.Due to its 3D connected structure and high electronic conductivity,CFP shows several advantages:providing suitable space for plated Na to mitigate the volume change and enhance the stability of Na metal anode,reducing the local current density and improving the kinetics of Na plating/stripping.In addition,the full battery assembled with a Prussian blue cathode and CFP@Na anode,shows high electrochemical performance.?2?Owing to applying Li-Na hybrid 1,2-Dimethoxyethane-based electrolyte,the Na dendrite is restricted.The electrochemical performance and mechanism of Li and Na metal anode was also investigated.Due to its lower reduction potential,Li⁺cannot be reduced and forms Li⁺electrostatic shield layer to guide Na plating.We also observed the dynamic plating process via in-situ optical microscope that proves the unique Na plating pattern.In addition,Na metal anode shows higher reversibility with an average CE of 99.2%and faster plating kinetics than Li metal anode.We utilized density functional theory calculation to understand the solvation/desolvation of metal-ions,and proved the fast desolvation kinetics of Na⁺.Moreover,LiFePO₄cathode was used to construct an advantage-complementary Li-Na hybrid battery system?LNHB?.During the discharge/charge processes,Li⁺and Na⁺play roles in insertion/extraction into/from the cathode and stripping/plating of the anode.The LNHB,which inherits the high reversibility,stability and fast kinetics of Na metal anode,shows low voltage hysteresis and long-term cycling.