Solid State Li Metal/LMO Batteries based on Ternary Triblock Copolymers and Ionic Binders

Triblock copolymers containing an ionophilic polymerized ionic liquid block, sandwiched between two ionophobic polystyrene blocks, were investigated as solid polymer electrolytes (SPE) to simultaneously provide mechanically robust, free-standing membranes with high lithium conductivity and an optimized electrolyte composition. The conductivity reached 8 × 10–5 S cm–1 and 6.5 × 10–4 S cm–1 at 30 and 80 °C, respectively, with an anodic stability above 4.5 V. Highly stable Li metal symmetric cycling was demonstrated, with an overpotential of 130 mV for over 300 h at 50 °C at a current density of 0.5 mA cm–2/0.5 mAh cm–2. Attempts were also made to incorporate the SPE as the binder in an LMO cathode formulation. The best cell performance, however, was obtained when substituting the SPE in the LMO cathode formulation with a PMA solid-state gel electrolyte, resulting in a high-performance solid-state Li|polymer eletrolyte|LMO device with stable cycling at C/5, and an impressive capacity retention (i.e., 105 mAh g–1 after 150 cycles at 0.1 mA cm–2) with a Coulombic efficiency around 99.4%

Formulation and Characterization of PS-Poly(ionic liquid) Triblock Electrolytes for Sodium Batteries

Solvent-free solid polymer electrolytes (SPE) are gaining more attention to develop postlithium battery technologies due to the safety and performance benefits of solid-state batteries. In this work, we present a new SPE for a sodium metal battery based on high salt concentration polymer electrolyte membranes comprising mixed anions, polymerized ionic liquid (PIL), block copolymer (BCP) polystyrene-b-poly­(diallydimethylammonium)­bis­(trifluoromethanesulfonyl)­imide-b-polystyrene (PS-b-PDADMATFSI-b-PS) and NaFSI salt. The maximum salt concentration incorporated was up to 1:2 mol ratio (PIL block: NaFSI). The ionic conductivity was 10–3 S cm–1 at 70 °C for 1:2 composition, and the anion diffusion as measured by 19F NMR decreased. FTIR measurement indicates that the ion coordination in the polymer–salt mixtures changes with composition. The storage modulus as measured by dynamic mechanical analysis (DMA) was observed in the range 300 MPa at −40 °C to 35.8 MPa at 70 °C. The optimized electrolyte (1:2 mol ratio) membrane was investigated for its long-term stability against Na metal cycling with Na/Na symmetrical cells demonstrating stable Na plating/stripping behavior at 0.2 mA cm–2 at 70 °C. Finally, an Na|NaFePO4 cell cycled with a specific capacity of 118 mAh g–1 at C-rate C/20 at 70 °C and a good Coulombic efficiency (98%), showing the promising potential of these solvent-free triblock copolymer electrolytes in Na metal batteries