Abstract:

Lithium methoxy oligo(oxyethylene) sulfate(LiSA(EO)n) and pentaerythritol tetrakis(2-methoxyethyl-ether)(STEO) were synthesized and used for the preparation of polyethylene oxide(PEO) based polymer electrolytes. All solid-state polymer electrolytes PEO-LiSA(EO)n and PEO-LiClO4 were obtained by the solvent casting method and the ionic conductivities and lithium ion transference numbers were measured by using ac impedance and steady state current methods respectively. The influences of lithium salt structure on lithium ion transference numbers and ionic conductivities of polymer electrolytes were studied. Results showed that, comparing with LiClO4, LiSA(EO)n could enhance the ionic conductivity of polymer electrolytes and ionic conductivity decreased with increasing size of anion of lithium salt. Lithium ion transference numbers increased with increasing size of anion of lithium salt, and achieved a relatively high value of 0.35 when (PEO16+LiSA(EO)2) was used. Composed polymer electrolytes(CPEs) PEO16-LiSAEO-STEO were prepared and the effects of addition of STEO on ionic conductivities were discussed. The experimental results showed that the addition of STEO could improve the ionic conductivity of the composited polymer electrolytes effectively, the ionic conductivity of PEO16-LiSAEO-20%STEO achieved 0.5×10-4 S/cm under 25 ℃. The thermal properties of CPEs were investigated by DSC experiments. Results indicated that the addition of STEO could decrease the melting temperature and crystallinity of CPE, resulting in the improvement of ionic conductivity. The electrochemical stability window of PEO16-LiSAEO-20%STEO exceeded 4.4 V, which ensured the use of PEO16-LiSAEO-STEO as electrolyte materials for all solidstate rechargeable lithium ion batteries.

Key words: polymer electrolyte, lithium sulfate, lithium ion transference number