A team of scientists in the US have developed a new type of electrolyte that could extend the life of lithium metal batteries based on how soap works. With such batteries seen as crucial for improving the performance of electric vehicles, smart phones and other devices, these electrolytes offer complex nanostructures to improve how much energy batteries can store per cycle and how many cycles they last.
Although lithium metal batteries have a much higher energy storage capacity than lithium-ion batteries, standard electrolytes – comprised of low-concentration salt dissolved in a liquid solvent – are not good at allowing an electrical charge to pass between the two terminals to make the necessary electrochemical reaction for converting stored chemical energy to electric energy.
When lathered, soap forms structures called micelles that trap and remove grease and dirt when flushed through with water, with the soap acting as bridge between the water and what is being cleaned. However, as reported in Nature Materials [Efaw et al. Nat. Mater. (2023) DOI: 10.1038/s41563-023-01700-3], a similar thing was shown to happen for a new type of electrolyte called a localized high-concentration electrolyte (LHCE).
There has been interest in LHCEs due to in-situ formation of a stable solid–electrolyte interphases layer on a lithium metal anode, although their microstructures are not well understood. The electrolytes were developed by combining high concentrations of salt in solvent with another liquid called a diluent, which helps to make the electrolyte flow better to maintain the power of the battery. The role of the soap or surfactant is played by the solvent that binds the diluent and the salt, wrapping itself around the higher concentration salt in the center of the micelle.
The micelle-like structures produced were predicted by simulations and then confirmed in experiments. As researcher Bin Li told Materials Today, “Based on the micelle structures and predicted ternary phase diagram, this work can help rational design of advanced electrolytes with complicated chemical interactions and shorten the time of searching for good electrolytes with stable [solid–electrolyte interphases] formed and wider operation temperature windows.”
The study therefore provides a guideline on the desired interactions from the salt, the solvent and the diluent in the electrolyte, what the concentrations should be and how they should be mixed. The team now hope to optimize the impact of electrolyte component choices in LHCEs to control the salt–solvent cluster size, shape and composition, as well as external parameters during operation.
“This work can help rational design of advanced electrolytes with complicated chemical interactions and shorten the time of searching for good electrolytes with stable [solid–electrolyte interphases] formed and wider operation temperature windows.”Bin Li