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

ABSTRACT 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 Li ₂ O capping layer. After thermal annealing in Ar, it formed a pure cubic‐phase Li _6.4 La ₃ Zr _1.4 Ta _0.6 O ₁₂ 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.