Materials scientists seek to develop better lithium (Li) metal batteries by improving structural stability and reducing dendrite formation that causes battery failure. It is well-known that instability at the metal electrode-electrolyte interface causes lithium dendrite growth, leading to short-circuiting and formation of inactive lithium. New electrolyte designs that control lithium deposition during cycling may solve these issues. Researchers are investigating liquid crystalline (LC) electrolytes under different conditions at MAX IV’s ForMAX beamline to determine whether these electrolytic materials are possible to align on demand. Successful results hold promise to propel the development of Li metal batteries as a next-generation power solution for electric vehicles and energy storage systems.
The study examines a foundational idea that the organised molecular structure and chemistry of LC electrolytes allow for ‘self-healing’ of the battery interfaces whereas conventional solvent-based liquid electrolytes fail. “LC electrolytes introduce an additional energy contribution for dendrite nucleation due to their strong anchoring energy and are therefore expected to supress the growth of dendrites from the electrode-electrolyte interface,” explained Owies Wani, study author and postdoctoral fellow at Aalto University. “Besides, due to their fluid nature, they can potentially flow into the crack formed in the interface upon cycling of the battery and thereby form a new healed interface.”
The experimental phase included structural measurements of sample LC electrolytes with small- and wide-angle X-ray scattering (SWAXS) at ForMAX beamline to look at colloidal and molecular processes with applied stimuli of shear force at different temperatures. A rheometer supplies the force to align the material structure from a polydomain to a monodomain, which potentially creates straight, directed channels for efficient Li ion transport in the battery, thereby boosting ionic conductivity.
The group carried out three simultaneous measurements: rheology, SWAXS and polarized light imaging. “This was instrumental to understand the dynamic shear induced alignment in our LC electrolytes at different length scales,” explained Wani.
The research includes collaboration with the RheoSAX group headed by Professor Roland Kader at Chalmers University of Technology, for setup of the Rheo-PLI-SAXS configuration and assistance with data analysis using their developed analysis protocols.
Further analyses will involve testing the LC electrolytes at HMFL-FELIX in the Netherlands with up to 30 T magnetic fields stimulus and observation of changes in magnetic birefringence with potential alignment.
“Mitigating the long thought-sought after lithium dendrite issue in lithium metal batteries would be a tour de force,” added Patrice Rannou, a co-author of the study, Director of Research at the Institute of Chemistry of CNRS and Deputy-head of the LEPMI/Blue Solutions (BS) Lithium interface Li2 (joint academia/industry) lab in Grenoble (France). “We hypothesize that the dynamic self-assembly of liquid crystalline electrolytes at the electrolyte/electrode interface and the stimuli-responsive directed Li+ cation transport in the bulk of these organized yet fluid electrolytes are advanced levers to decipher the complicated and intricated mechanisms at play, if not solving the problem through a one-stone-for-two-birds fundamental research solution by leveraging the physics of liquid crystals and the electrochemistry of ionic conductors for an energy storage device. It would be instrumental and rewarding to show that fundamental and applied research goes rather hand-in-hand than against each other.”
The study follows the research group’s earlier investigation describing how complexation of cellulose nanocrystals (CNCs) with a specific surfactant leads to formation of a nematic LC phase in organic solvents, unlike its commonly observed cholesteric LC phase.
“We are now building on this observation to develop hybrid LC electrolytes formed by combination of CNCs, surfactants and metal salts that can show externally controllable ion transport and potentially help to stability electrolyte-electrode interface in next generation batteries,” said Wani.
This work advances knowledge for the development of longer lasting, stable, and more energy-dense lithium metal batteries. These aspects are more important than ever for the increasing demands for energy storage and efficient electric vehicles in a circular economy.
