Ferroelectric Nanorods as a Polymer Interface Additive for High-Performance Garnet-Based Solid-State Batteries

Sandwiching polymer interlayers between the electrode and solid electrolyte is considered promising in solving the interfacial issues arising from solid-solid contact in garnet-based solid-state batteries, but drawbacks including low ionic conductivity, inferior Li⁺ transference number, and unsatisfying mechanical property of the polymer hindered the practical application of such strategy. To solve the mentioned shortcomings of the polymer interlayer simultaneously, we introduce the ferroelectric material, BaTi₂O₅ (BT) nanorods, into the polymer matrix in this work. By taking full advantage of the plasticization effect and intrinsic spontaneous polarization of the introduced ferroelectric, the polymer's ionic conductivity and Li⁺ transference number have been significantly enhanced. The built-in electric field BT introduced also benefits the modulation of CEI components formed on the cathode particles, further enhancing the battery performance by decreasing cathode degradation. Besides, the BT nanorods' particular high aspect ratio also helps increase the mechanical property of the obtained polymer film, making it more resistant to lithium dendrite growth across the interface. Benefitting from the merits mentioned above, the assembled lithium symmetric cells using garnet SE with the BT-modified polymer interlayer exhibit stable cycling performance (no short circuit after 1000 h under RT) with low polarization voltage. The full battery employing LiFePO₄ as a cathode also presents superior capacity retentions (94.6% after 200 cycles at 0.1 C and 93.4% after 400 cycles at 0.2 C). This work highlights the importance of ferroelectric materials with specific morphology in enhancing the electrochemical performance of polymer-based electrolytes, promoting the practical application of solid-state batteries.