A Hybrid Solid-State Battery with a Panoramic-Scale Stack of Bulk Electrodes and a Thin-Film Electrolyte

All-solid-state batteries (ASSBs) have attracted attention as next-generation energy storage systems by their thermal stability and higher-energy-density potential. However, thick solid electrolytes in conventional ASSBs remain a key bottleneck, simultaneously increasing stack thickness and limiting ion-transport efficiency. Here, we develop a hybrid ASSB by depositing a thin-film electrolyte on a bulk anode substrate and stacking a thick cathode sheet. The thin-film electrolyte was deposited by co-sputtering with a Li₂O capping layer. After thermal annealing in Ar, it formed a pure cubic-phase Li_6.4La₃Zr_1.4Ta_0.6O₁₂ film with a uniform thickness of 2.5 µm and an out-of-plane Li-ion conductivity of 1.91 × 10^-2 mS cm^-1 at room temperature. A pore-gradient, well-compacted anode substrate (9.01% porosity) was fabricated via high-speed mixing and cold pressing, followed by thin-film sputtering deposition and infrared-based rapid annealing to integrate the bulk substrate and the thin-film electrolyte. A hybrid ASSB employing a 60 µm-thick cathode sheet exhibited stable cycles, delivering an initial charge capacity of 102.96 mAh g^-1 and a discharge capacity of 52.59 mAh g^-1, while maintaining a robust electrode-electrolyte interface after cycling. This work demonstrates the successful operation of a hybrid architecture, offering a new design strategy that integrates bulk electrodes with thin-film electrolytes toward high-energy-density ASSBs.