The recyclability of solid-state lithium batteries has taken a positive turn following developments by a team at Lawrence Berkeley National Laboratory.
The team has designed electrolytes that are viscoelastic solids at battery operating temperatures (-40° to 45°C) yet are viscoelastic liquids above 100°C. This enables the fabrication of high-quality SSBs and the recycling of their cathodes at end-of-life.
Solid-state batteries (SSBs) using supramolecular organo-ionic (ORION) electrolytes with lithium metal anodes and either LFP or NMC cathodes were operated for hundreds of cycles at 45°C with less than 20% capacity fade.
Using a low-temperature solvent process the cathode was isolated from the electrolyte and the team demonstrated that refurbished cells recover 90% of their initial capacity and sustain it for an additional 100 cycles with 84% capacity in their second life.
SSBs remain one of the most sought-after lithium technologies due the improved safety and increased energy density. However, the manufacturing of SSBs remains a challenge due to the difficulty in creating conformal interfaces between the solid electrolyte and the active materials in the electrodes. Further, the deconstruction presents difficulties due to the adhesive character of interphases formed during high temperature, high pressure manufacturing processes.
In their paper, published in Science Advances, the team show that a tetrafunctional zwitterionic supramolecular building unit (SBU) networks both lithium salts and solvates, creating from them organo-ionic lithium-ion conductors. In the liquidus state ORION conductors have excellent wetting characteristics for both the lithium metal anodes and porous cathodes of either LFP or NMC532 active materials. The SSBs can be made with conformal interfaces to both electrodes using low-intensity thermal processing.
ORION conductors feature both structural lithium ions, essential for solidification, alongside mobile lithium ions, essential for conductivity. These characteristics are broadly tuneable through choice of salts, stoichiometry, and SBUs.
The data in the report indicate that ORION conductors are versatile in their ability to exploit a low-temperature solid-liquid phase transformation and favourable wetting characteristics to fabricate all-solid-state lithium metal cells that are rechargeable for hundreds of cycles. Owing to the remarkably slow area-specific impedance rise over time the team reasoned it might be also feasible to deconstruct the all-solid-state cells, taking advantage of the solubility of ORION conductors, and close the loop in direct cathode recycling.