Highly Conductive, Ionic Liquid-Based Polymer Electrolytes

Abstract

In this manuscript is reported a thermal and impedance spectroscopy investigation carried out on quaternary polymer electrolytes, to be addressed as separators for lithium solid polymer batteries, containing large amount of the N-methyl-N-propylpyrrolidinium bis(fluorosulfonyl)imide ionic liquid. The target is the development of Li + conducting membranes with enhanced ion transport even below room temperature. Polyethylene oxide and polymethyl methacrylate were selected as the polymeric hosts. A fully dry, solvent-free procedure was followed for the preparation of the polymer electrolytes, which were seen to be self-consistent and handled even upon prolonged storage periods (more than 1 year). Appealing ionic conductivities were observed especially for the PEO electrolytes, i.e., 1.6 × 10 −3 and 1.5 × 10 −4 S cm −1 were reached at 20 and −20 • C, respectively, which are ones the best, if not the best ion conduction, never detected for polymer electrolytes. Lithium polymer batteries (LPBs) are considered excellent candidates for the next generation power sources because they combine high energy density and flexible characteristics with the safety issue of the solvent-free electrolytes.1 Nevertheless, the performance of LPBs is limited by the low ionic conductivity of the solvent-free polymer electrolytes at room temperature as the polymeric host is manly crystalline (i.e., resulting in slow motion of the Li + active specie). 2For instance, polyethylene oxide-(PEO) based electrolytes exhibit suitable conduction values (≥10 −4 S cm −1 ) for practical applications only above 65• C, e.g., where the amorphous phase is predominant and allows remarkably higher mobility to the lithium ions.3-5 Therefore, several approaches 6 were attempted aiming to decrease the content of crystalline phase (particularly, P(EO) 6 LiX) 3-5 in polymer electrolytes, e.g., branched and/or cross-linked hosts, blended polymer matrices, large counter anion lithium salts, addition of additives (organic compounds, oligomers, ceramic fillers).One of the most promising approaches is represented by the incorporation of ionic liquids (ILs) into the polymer electrolytes. 6 In the last years it was successfully demonstrated 6 that incorporation of N-alkyl-N-methylpyrrolidinium (PYR 1A , where the subscripts indicate the number of carbon atoms of the pyrrolidinium cation alkyl chains) perfluorosulfonylimide (PFSI) ILs enhances the room temperature ionic conductivity of solid polymer electrolytes (SPEs) above 10 −4 Scm −1 and improves the compatibility with respect to the lithium anode.However, faster ion transport properties are needed, especially in devices (operating at high current rates) for applications (i.e., automotive) requiring higher power density values. In the frame of the MARS-EV project 7 we have properly designed and developed SPEs based on PEO and polymethyl methacrylate (PMMA), i.e., considered ones of the most suitable materials as host for polymer electrolytes, 6 and incorporating large fraction of N-methyl-N-propylpyrrolidinium bis(f...

A multiple electrolyte concept for lithium-metal batteries

“…Therefore, the DSC behavior indicates that cross-linking likely slows down the crystallization kinetics, preventing the crystallization upon cooling at about 30 °C and favoring an amorphous metastable phase at low temperatures. This behavior has been already observed in PEO-based, IL-containing ternary electrolyte [37].…”

“…Furthermore, the lower melting temperature and heat of fusion (∆H) of the cl-TPE compared to the TPE (∆H is 18.2 J g −1 and 16.6 J g −1 for the TPE and cl-TPE samples, respectively) suggest a slight increase of amorphous fraction after cross-linking, which is expected to have minor effects on the ion transport properties. However, possible effects of the particular DSC protocol herein employed and of the thermal history of the samples cannot be excluded [37].…”

Ionic liquid‐based organic–inorganic hybrid electrolytes: Impact of in situ obtained and dispersed silica

“…Figure (ii) shows the room temperature ionic conductivity of PINa 10 IL x hybrid electrolytes with their respective glass transition temperature ( T g ). The IL addition leads to an increase in the amorphous phase of the hybrid electrolyte which favors the segmental motion of the polymer chains or increases the chain flexibility . This fact has been evidenced by a lowering in T g value with addition of IL up to 15 wt% (discussed in DSC studies).…”

Preparation and performance study of a PVDF–LATP ceramic composite polymer electrolyte membrane for solid-state batteries

“…[5][6][7] All-solid-state Li-ion batteries, where the ammable liquid electrolyte is replaced by solid state electrolytes, offer the possibility to solve the safety issues of traditional Li-ion batteries arising from the leakage of ammable organic liquid electrolytes, and in some cases a large electrochemical stability window compared to conventional organic electrolytes. [8][9][10] In past studies, many kinds of crystalline lithium solid electrolyte have been reported and widely applied in solid-state batteries, such as the garnet structure Li 7 La 3 Zr 2 O 12 (LLZO), 11 the perovskite structure Li 0.5 La 0.5 TiO 3 (LLTO), 12 the LISICON structure Li 14 Zn(GeO 4 ) 4 (LZGO), 13 the NASICON structure Li 1.5 -Al 0.5 Ge 1.5 (PO 4 ) 3 (LAGP), 14,15 Li 1.4 Al 0.4 Ti 1.6 (PO 4 ) 3 (LATP), 16,17 and so on. Among the above-mentioned solid electrolytes, NASICON-type ceramics, Li 1+x Al x Ti 2Àx (PO 4 ) 3 , have received much attention because of their comparatively higher lithium ion conductivity at room temperature and air-stability, as well as their relatively low cost for synthesis.…”