Revealing the Role of Internal Strain Behavior on Stabilizing High Voltage LiCoO2‐Based All‐Solid‐State Thin Film Batteries

LiCoO2 (LCO)‐based all‐solid‐state thin film batteries are considered to be one of the most promising storage mediums in on‐chip microelectronic systems owing to their compatible production process and predictable high capacity. However, abundant internal defects and serious lattice distortions are still unsustainable for high‐voltage applications. Herein, the study strategically controls lattice orientation and visualizes the strain relaxation to understand mechanical instabilities unknown in conventional thin‐film configurations, while assessing the effect of lattice strain on the electrochemical performance of all‐solid‐state full cells. Guided by this, a densely arranged TiN/LCO nanosheet with rigid (003) migration channels is tactically constructed on the TiN (200) intermediate layer, in which the fixed CoO6 backbones contribute to protecting host structures from the impact of strain accumulation. Consequently, the additive‐free TiN/LCO||LiPON||Li full cell showcases remarkable cycle stability with capacity retention of 73.7% and 80.1% for 100 and 235 cycles at 0.3 C and 1.4 C in 3.0 to 4.6 V, as well as improved rate capability (67.4 µAh cm−2 µm−1 at 6 C) and commercial availability (power supply for microsensors). This work emphasizes the importance of growth crystallography to regulate lattice strain and internal defects and sheds new light on film cathode design with high energy density.