Polymer dispersed ionic liquid electrolytes with high ionic conductivity for ultrastable solid‐state lithium batteries

Abstract

Solid polymer electrolytes (SPEs) have emerged as one of the most promising candidates for building solid‐state lithium batteries due to their excellent flexibility, scalability, and interfacial compatibility with electrodes. However, the low ionic conductivity and poor cyclic stability of SPEs do not meet the requirements for practical applications of lithium batteries. Here, a novel polymer dispersed ionic liquid‐based solid polymer electrolyte (PDIL‐SPE) is fabricated using the in situ polymerization‐induced phase separation (PIPS) method. The as‐prepared PDIL‐SPE possesses both outstanding ionic conductivity (0.74 mS cm−1 at 25°C) and a wide electrochemical window (up to 4.86 V), and the formed unique three‐dimensional (3D) co‐continuous structure of polymer matrix and ionic liquid in PDIL‐SPE can promote the transport of lithium ions. Also, the 3D co‐continuous structure of PDIL‐SPE effectively accommodates the severe volume expansion for prolonged lithium plating and stripping processes over 1000 h at 0.5 mA cm−2 under 25°C. Moreover, the LiFePO4//Li coin cell can work stably over 150 cycles at a 1 C rate under room temperature with a capacity retention of 90.6% from 111.1 to 100.7 mAh g−1. The PDIL‐SPE composite is a promising material system for enabling the ultrastable operation of solid‐state lithium‐metal batteries.

State-of-the-Art of Solid-State Electrolytes on the Road Map of Solid-State Lithium Metal Batteries for E-Mobility

“…145 Shengyu Qin et al ( 2022) reported a novel polymer dispersed ionic liquid solid polymer electrolyte (PDIL-SPE) fabricated with an in situ polymerization-induced phase separation (PIPS) method. 145 The PDIL was prepared by using a sonication dispersion method to disperse an ionic liquid solution of LiTFSI in [EMIM][TFSI] with a monomer solution of MPEGA and PEGDA in MEA, followed by fabrication of the SPE by sandwiching the PDIL between two glass substrates with 200-μm spacers in between and by polymerization with UV irradiation for the curing process. 145 Apart from good flexibility and interfacial compatibility with Li metal, the PDIL-SPE produced high ionic conductivity of 0.74 mS cm −1 at room temperature, over 1000 h of stable lithium plating/stripping in Li//Li symmetrical cells at 0.5 mA cm −2 current density, and an excellent electrochemical performance evaluation with LiFePO 4 as cathode (157.6 and 98.3 mAh g −1 at 0.1 C and 1 C rates, 90.6% capacity retention after 150 cycles at 1 C).…”

“…145 The PDIL was prepared by using a sonication dispersion method to disperse an ionic liquid solution of LiTFSI in [EMIM][TFSI] with a monomer solution of MPEGA and PEGDA in MEA, followed by fabrication of the SPE by sandwiching the PDIL between two glass substrates with 200-μm spacers in between and by polymerization with UV irradiation for the curing process. 145 Apart from good flexibility and interfacial compatibility with Li metal, the PDIL-SPE produced high ionic conductivity of 0.74 mS cm −1 at room temperature, over 1000 h of stable lithium plating/stripping in Li//Li symmetrical cells at 0.5 mA cm −2 current density, and an excellent electrochemical performance evaluation with LiFePO 4 as cathode (157.6 and 98.3 mAh g −1 at 0.1 C and 1 C rates, 90.6% capacity retention after 150 cycles at 1 C). 145 This was contributed to the novel 3D cocontinuous tubular polymer network structure with abundant −O−CH 2 −CH 2 −O− and continuous ionic liquid phase, both serving as a conductive route for fast Li + transport.…”

“…145 Apart from good flexibility and interfacial compatibility with Li metal, the PDIL-SPE produced high ionic conductivity of 0.74 mS cm −1 at room temperature, over 1000 h of stable lithium plating/stripping in Li//Li symmetrical cells at 0.5 mA cm −2 current density, and an excellent electrochemical performance evaluation with LiFePO 4 as cathode (157.6 and 98.3 mAh g −1 at 0.1 C and 1 C rates, 90.6% capacity retention after 150 cycles at 1 C). 145 This was contributed to the novel 3D cocontinuous tubular polymer network structure with abundant −O−CH 2 −CH 2 −O− and continuous ionic liquid phase, both serving as a conductive route for fast Li + transport. 145 Application of IL can also be expanded to surface modifications of inorganic fillers, with one of it being graphene oxide (GO), which widely used in literature as a nano filler for polymer electrolytes.…”

“…Incorporation of IL toward solid polymer electrolyte (SPE) was also reported to improve both the ionic conductivity as well as cyclic stability of the electrolyte, to meet practical requirements of lithium batteries . Shengyu Qin et al (2022) reported a novel polymer dispersed ionic liquid solid polymer electrolyte (PDIL-SPE) fabricated with an in situ polymerization-induced phase separation (PIPS) method .…”

“…26 Incorporation of IL toward solid polymer electrolyte (SPE) was also reported to improve both the ionic conductivity as well as cyclic stability of the electrolyte, to meet practical requirements of lithium batteries. 145 Shengyu Qin et al ( 2022) reported a novel polymer dispersed ionic liquid solid polymer electrolyte (PDIL-SPE) fabricated with an in situ polymerization-induced phase separation (PIPS) method. 145 The PDIL was prepared by using a sonication dispersion method to disperse an ionic liquid solution of LiTFSI in [EMIM][TFSI] with a monomer solution of MPEGA and PEGDA in MEA, followed by fabrication of the SPE by sandwiching the PDIL between two glass substrates with 200-μm spacers in between and by polymerization with UV irradiation for the curing process.…”