In Operando Small-Angle X-ray Scattering Investigation of Nanostructured Polymer Electrolyte for Lithium-Ion Batteries

Electrochemical energy storage still presents one of the biggest challenges that society has to face by developing alternative lithium-ion batteries (LIBs) as they already satisfy important preconditions by providing the highest energy and power densities of all battery systems. Nowadays, the employed liquid electrolytes in LIBs do not merge the world's increasing demand of safely working batteries. Here, we use a lithium salt-doped diblock copolymer electrolyte:poly(styrene)-block-poly(ethylene oxide)/bis(trifluoromethane) lithium salt, denoted PS-b-PEO/LiTFSI, as a solid-state electrolyte. The evolving nanoscale morphology of the electrolyte material in a capillary-based LIB cell is investigated using in operando small-angle X-ray scattering (SAXS). The electrolyte is sandwiched between two opposing electrodes inside of a glass capillary and investigated during cycling at 90 °C while the X-ray beam is oriented orthogonally to the ionic current. Lithium iron phosphate (LFP) is used as a cathode, while both lithium-metal and graphite anode materials are used for the investigation of the solid-state electrolytes. The ill-defined structured lithium-ion containing block copolymer electrolyte seems morphologically more favorable for cell performance, and this is independent of the choice of anode material due to better electrode/electrolyte compatibility.