Preparation And Properties Of Solid Electrolytes For Secondary Batteries Based On Seaweed Polysaccharide Fibers

The development of new clean energy and efficient energy storage devices is the fundamental way to solve the current energy crisis and environmental problems.Lithium secondary battery,as a kind of energy storage equipment,has been widespread in daily life owing to its excellent electrochemical performance.Unfortunately,its further applications in long-range electric vehicles and large energy storage power stations are limited owing to the defects of low energy density and poor security.Therefore,it is urgent to develop new lithium secondary batteries with high performance and safety.At present,it has been widely considered as a feasible strategy to improve the energy density and safety of lithium secondary batteries by using solid-state electrolyte instead of liquid electrolyte with poor safety.Among the numerous solid-state electrolytes,polymer electrolyte has been considered as a promising alternative to traditional liquid electrolyte due to it high flexibility,low electrolyte/electrode interface resistance,easy machinability and low cost.However,all-solid-state polymer electrolytes(SPEs)often show low ionic conductivity at room temperature and poor stability.Gel polymer electrolytes(GPEs)exhibit high ionic conductivity at room temperature,while the defects of weak mechanical strength and poor dendrite inhibition ability limit their practical application.Hence,designing a novel SPE and GPE with high-performance and good security to solve these problems is imperative.In this paper,a novel SPE and GPE was prepared by solution casting and electrospinning technique based on polysaccharide fiber derived from seaweed biomass as the internal skeleton for polymer electrolyte.Their morphology,physicochemical properties and electrochemical performances were characterized by various physical and chemical methods.Meanwhile,their application in lithium secondary battery was further studied.(1)A self-supporting SPE was prepared by a simple solution casting method,where PEO was as the polymer matrix,Li TFSI as the lithium salt and alginate fiber as the skeleton.The obtained SPE shows good tensile strength(3.71 MPa),excellent dimensional thermal stability(close to 120?)and wide electrochemical stability window(ESW>5.2 V vs.Li/Li⁺)due to the introduction of alginate fiber skeleton and the formation of internal crosslinking network.Moreover,abundant oxygen-containing functional groups in alginate molecules can provide new pathways for the migration of lithium ions.Hence,the SPE shows a satisfactory ionic conductivity(?=6.57×10^-4 S/cm),high lithium-ion transference number(t⁺_Li=0.45)and good interface compatibility with lithium metal at 80?.When assembled into Li Fe PO₄/SPE/Li all-solid-state lithium battery,it exhibits high discharge specific capacity(122.5 m Ah/g,1 C)and good cycle stability(capacity retention rate is more than 94.0%after 100 cycles)at 80?.(2)A porous alginate nanofiber skeleton was prepared by electrospinning using sodium alginate and PEO as materials.The obtained optimal sample exhibits a high electrolyte uptake of 279%and excellent dimensional thermal stability(over 150?).After gelatinization,the obtained GPE keeps excellent mechanical strength(tensile strength is up to 20.33 MPa).Thanks to the existence of electrostatic attraction between the molecular chain in the alginate nanofibers and the solvent molecules in the electrolyte,the GPE exhibits high ionic conductivity(?=1.54×10^-3 S/cm),excellent lithium-ion transference number(t⁺_Li=0.46)and outstanding electrochemical stability(ESW>5.4 V vs.Li/Li⁺)at room temperature.The excellent electrochemical performance improves the inhibition ability of GPE on lithium dendrite effectively,which enables the assembled Li/GPE/Li symmetric cell to cycle steadily for 1000 h at 0.1 m A/cm².When it is matched with cathode of Li Ni_1/3Co_1/3Mn_1/3O₂,it shows a good discharge specific capacity(122.9 m Ah/g,0.5C).After 300 cycles,it still keeps a good specific capacity of 90 m Ah/g.