The Preparation And Properities Of Novel Electrolyte For Sodium Battery

The rapid development of smart homes,electric vehicles,household grids and smart grids in lithium-ion battery dominated energy storage market has stimulated diversified development of battery systems.Among various candidates,sodium?Na?has attracted numerous attention due to its similar physicochemical properties to lithium?Li?as well a s its natural abundance and low cost,which is suitable for the application of low-cost and long lifespan large-scale energy storage systems.Considering the demand for high energy density energy storage systems,Na metal battery has been regarded as a mor e promising battery system compared with sodium-ion battery due to its ultra-high theoretical specific capacity and low redox potential.Our work is based on promoting the energy density of sodium metal batteries,which focuses on high capacity sulfur cathode to compose room-temperature sodium-sulfur?Na-S?battery and high discharge voltage platform dual-ion system to constitute sodium-graphite?Na-G?battery.In the room-temperature Na-S battery system,the multifunctional sulfur cathode was fabricated by mixing the multiporous carbon fibers prepared by electrospinning and potassium hydroxide activation method with sodium carboxymethyl cellulose?CMCNa?.The carbon fiber network with abundant microporous structure can provide improved conductivity and phys ical confinement towards sodium polysulfide?Na PS?.Moreover,the stronger viscosity of CMCNa can more effectively maintain the integrity of the cathode structure.Therefore,the specific capacity of Na-S batteries was significantly enhanced.The room-temperature Na-S battery with high electrochemical performances and enhanced safety is employed by a“cocktail optimized”electrolyte system,containing highly concentrated bis?trifluoromethane?sulfonimide sodium salt?Na TFSI?,fluoroethylene carbonate?FEC?as co-solvents,and indium triiodide?In I₃?as an additive.The solubility of Na PS was efficiently suppressed via the high salt concentration and FEC-rich solvent.Meanwhile,the Na metal anode was effectively protected by a fluorine?F?-rich stable SEI film.In addition,In I₃additive not only promotes the conversion of the irreversible Na ₂S,but also forms an indium metal protective layer on the anode.The as-developed Na-S batteries exhibited outstanding performances with a specific capacity of 927 m Ah g^-1 at0.1 C after 200 cycles and a specific capacity of 647.6 m Ah g^-1 at 0.5 C and 581.3m Ah g^-1 at 1 C after 500 cycles.In the Na-G battery system,the electrolyte has been optimized to realize an improved electrichemcal performance and the failure mec hanism of this system under small current density has been carefully inverstigated.The novel high-voltage gel polymer electrolyte is developed by in-situ polymerizing the ethoxylated pentaerythritol tetraacrylate monomer in presence of the optimized electrolyte,which contains FEC as co-solvent and 1,3-propanesultone as additive.The as-synthesized electrolyte not only exhibits high resistance against oxidation and constructs thin and stable protective layers on the electrode surfaces,but also facilitates the homogeneous cation/anion fluxes and suppresses the growth of Na dendrites,thus conduces stable insertion/deposition of ions into/on the cathode/anode electrodes.Consequently,the obtained dual-ion Na metal batteries exhibit excellent cycling stability with a specific capacity of 78 m Ah g^-1after1000 cycle with a high voltage window of 4.4 V.