Structural Design And Performance Optimization Of PEO-based Solid State Electrolytes

For the next generation of energy storage batteries（e.g.,lithium-sulfur batteries,lithium-oxygen-air batteries）,the use of solid-state electrolytes instead of liquid-state ones becomes a growing trend.Solid-state electrolytes offer a new strategy for lithium metal cathodes,which are relatively stable to lithium metal and slow down the generation of lithium dendrites to some extent.The utilization of solid electrolytes in batteries not only solves the normal safety problem,but also achieves high energy density due to the matching to the high voltage and high capacity cathodes.However,the conventional poly（ethylene oxide）（PEO）-based solid electrolytes exhibit a semi-crystalline state at room temperature,which have many shortcomings such as low ionic conductivity at room temperature,poor mechanical properties,narrow electrochemical stability window,which limits the application of SPE.Therefore,the development of PEO-based solid electrolytes becomes a challenge for the near future.Herein,the grafted block copolymers were constructed with the alternating copolymer styrene-maleic anhydride as the backbone and soft segment as side chains to obtain solid-state polymer electrolytes（SMA-g-PEG-SPE）with a nanophase separated structure,which performed high ion transport and excellent mechanical properties at room temperature.In our structural design,PEO chains are used as soft segments to achieve lithium ion transport,and SMA copolymers are used as hard segments to provide high mechanical strength and high voltage performance.On the one hand,the existence of the nanophase-separated structure disrupts the regular arrangement of PEG segments,thereby increasing the proportion of amorphous regions in the electrolyte;on the other hand,the support of the hard segments SMA improves the film-forming properties of PEG.At room temperature,SMA-g-PEG-SPE has high ionic conductivity,which can reach to 10^-4 S/cm^-1.At the same time,SMA-g-PEG-SPE has good interface stability for lithium metal anode,with an electrochemical stability window of 5 V.The Li|SMA-g-PEG-SPE|Li symmetric cell performed excellent cycling stability for more than 1500 h without short circuit at 0.1 m A cm^-2.Moreover,at 0.2 C and25°C,the Li|SMA-g-PEG-SPE|Li Fe PO₄ full cell could run stably for 400cycles,the first cycle discharge capacity can reach 143.7 m Ah g^-1,and the Coulombic efficiency is 97.99%.It shows that SMA-g-PEG-SPE has good interfacial contact with lithium metal cathode and Li Fe PO₄ cathode and has great application potential in solid-state lithium batteries.In order to further improve the mechanical properties of solid polymer electrolytes（SPEs）,SPE with an interpenetrating network structure was prepared by heat polymerization via Thiol-ene click chemistry.The effects of different synthesis conditions such as the molar ratios of polyethylene glycol diacrylate 1000（PEGDA1000）,maleic anhydride modifiedβ-cyclodextrin（MAH-β-CD）,and Pentaerythritol Tetra（3-mercaptopropionate）（PETMP）on the polymeric film property were compared and optimized.When the content of PEGDA is 35%,the content of PETMP is 20%,and the content of MAH-β-CD is 35%,the solid polymer electrolyte(P₃₅P₂₀CD₃₅)has the best performance.The introduction of MAH-β-CD and PETMP molecules increased the crosslinking sites（C-S-C）and lowered the glass transition temperature,which improved the lithium ion transference number（0.46）and mechanical properties（strain up to 210%）of P₃₅P₂₀CD₃₅.The LFP full cell assembled P₃₅P₂₀CD₃₅showed a capacity retention of 82.1%and an average Coulomb efficiency of99.1%after 450 cycles at 0.7 C and 60°C.And the Li|P₃₅P₂₀CD₃₅|Li symmetric cell operated safely for 3000 h without short circuit at a current density of 0.1 m A cm^-2.