Succinonitrile (SN)-based polymer plastic crystal electrolytes (PPCEs) have attracted considerable attention as solid-state electrolytes owing to their high ionic conductivities similar to those of liquid electrolytes, excellent contacts with the electrodes, and good mechanic properties. As a crucial property of a solid-state electrolyte, the ionic conductivity of the PPCE directly depends on the interactions between the constituent parts including the polymer, lithium salt, and SN. A few studies have focused on the effects of polymer–lithium–salt and polymer–SN interactions on the PPCE ionic conductivity. Nevertheless, the impact of the lithium–salt–SN combination on the PPCE ionic conductivity has not been analyzed. In particular, tuning of the lithium-salt–SN interaction to fabricate a subzero PPCE with a high low-temperature ionic conductivity has not been reported. In this study, we design and fabricate five PPCE membranes with different weight ratios of LiN(SO 2 CF 3 ) 2 (LiTFSI) and SN to investigate the effect of the LiTFSI–SN interaction on the PPCE ionic conductivity. The ionic conductivities of the five PPCEs are investigated in the temperature range of –20 to 60 °C by electro-chemical impedance spectroscopy. The interaction is analyzed by Fourier-transform infrared spectroscopy, Raman spectroscopy, and differential scanning calorimetry . The LiTFSI–SN interaction significantly influences the melting point of the PPCE, dissociation of the LiTFSI salt, and thus the PPCE ionic conductivity. By tuning the LiTFSI–SN interaction, a subzero workable PPCE membrane having an excellent low-temperature ionic conductivity (6 × 10 −4 S cm –1 at 0 °C) is obtained. The electro-chemical performance of the optimal PPCE is evaluated by using a LiCoO 2 /PPCE/Li 4 Ti 5 O 12 cell, which confirms the application feasibility of the proposed quasi-solid-state electrolyte in subzero workable lithium-ion batteries.
Ting Zhao,Weijie Kou,Yafang Zhang,Wenjia Wu,Wenpeng Li,Jingtao Wang
Succinonitrile (SN) plastic crystal electrolyte holds great promise for high-performance solid-state lithium metal batteries due to its high ionic conduction. However, the serious side reaction between SN and lithium anode always causes large interfacial resistance , deteriorating the battery capacity. Herein, we penetrated LiTFSI-SN (LSN) electrolyte into the interlayer channels of laminar metal-organic framework (MOF), then an ultra-thin and stable laminar LiTFSI–SN–MOF composite solid-state electrolyte (LSN-MOF CSE) was obtained. We demonstrate that the interlayer nanochannels for LSN electrolyte storage without sacrificing the mobility of SN molecules. Meanwhile, the unsaturated coordination of MOF, induced by Co/Ni metal sites, causes a horizontal arrangement of SN. Therefore, this electrolyte offers a remarkable ionic conductivity of 7.41 × 10 −4 S cm −1 at 25 °C. Moreover, the interlayer nanochannels and covalent interaction of MOF synergistically suppress the migration of SN to lithium anode, thus improving the interface stability of lithium anode. Importantly, the assembled Li symmetrical cell performs stable operation over 800 h under 0.2 mA cm −2 , and the LiFePO 4 /Li cell delivers excellent cycling stability of 148.2 mAh g −1 with a low capacity decay of 0.048% per cycle after 200 cycles under 0.2C and 25 °C.
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