Highly ion-Conductive solid electrolytes regenerated from spent Li6.5La3Zr1.5Ta0.5O12 via selective delithiation-delithiation

The efficient recycling of spent solid electrolytes represent a promising pathway toward the sustainable development of solid-state batteries (SSBs), a challenge that has remained unaddressed in previous works. Herein, a selective delithiation-relithiation strategy has been proposed to regenerate spent garnet-type Li6.5La3Zr1.5Ta0.5O12 (LLZTO) electrolyte, which involves water extracting active lithium at room temperature followed by thermal relithiation process. The compositional and structural analyses revealed that water leaching cannot only completely remove lithium dendrites in the degraded LLZTO electrolytes, but also induce phase transformation from conventional garnet to a hydrated garnet structure. In the subsequent thermal relithiation process, entropy-driven lithium-ion redistribution can increase the occupancy ratio of octahedral 96h site in the regenerated LLZTO, as demonstrated by the experimental data and theoretical calculation. As a result, the regenerated LLZTO electrolyte showed a superior ionic conductivity of 7.01×10-4 S cm-1 and remarkable cycling stability in full cells, maintaining a high capacity ratio of 92.9% after 200 cycles at 0.5 C. Techno-economic assessment further confirmed the economic viability and reduced environmental footprint of our recycling strategy. This work provided new mechanistic and practical insights into the recycling of spent SSBs.