Interface-Engineered Atomic Layer Deposition of 3D Li₄Ti₅O₁₂ for High-Capacity Lithium-Ion 3D Thin-Film Batteries

Upcoming energy-autonomous mm-scale Internet-of-things devices require high-energy and high-power microbatteries. On-chip 3D thin-film batteries (TFBs) are the most promising option but lack high-rate anode materials. Here, Li₄Ti₅O₁₂ thin films fabricated by atomic layer deposition (ALD) are electrochemically evaluated on 3D substrates for the first time. The 3D Li₄Ti₅O₁₂ reveals an excellent footprint capacity of 20.23 µAh cm^-2 at 1 C. The outstanding high-rate capability is demonstrated with 7.75 µAh cm^-2 at 5 mA cm^-2 (250 C) while preserving a remarkable capacity retention of 97.4% after 500 cycles. Planar films with various thicknesses exhibit electrochemical nanoscale effects and are tuned to maximize performance. The developed ALD process enables conformal high-quality spinel (111)-textured Li₄Ti₅O₁₂ films on Si substrates with an area enhancement of 9. Interface engineering by employing ultrathin AlO_x on the current collector facilitates a required crystallization time reduction which ensures high film and interface quality and prospective on-chip integration. This work demonstrates that 3D Li₄Ti₅O₁₂ by ALD can be an attractive solution for the microelectronics-compatible fabrication of scalable high-energy and high-power Li-ion 3D TFBs.