Working Thin-Film Solid-State Batteries Designed in a Multilayered Stack to Enhance Energy Density

Solid state batteries (SSBs) are the next devices to substitute conventional lithium-ion batteries by providing increased safety, energy density, and high-power performance. Thin-film SSBs are a particularly interesting technology for implantable biomedical devices and integration with microelectronics. Designing batteries in the micro-scale range with different shapes is now a possibility using techniques from the microelectronics industry and by choosing materials which are compatible with the thin film processing. Here, we describe a thin-film SSB prototype made using two novel and broadly applicable techniques: 1) co-deposition of the cathode from a lithium source and metal oxide source, and 2) shadow masking to produce a “multibattery” in a 3D architecture like a prismatic pouch cell. Using a multilayered stack like this, where the cathode and anode layers are connected on either side in parallel, saves material and improves device energy density.<br/>Thin films of silicon, LiPON, and lithiated vanadium oxide (LVO) were deposited as the anode, electrolyte, and cathode layers to produce a battery with tunable lithium content without breaking vacuum. As a final step, the whole SSB stack was post-annealed at 300 °C. SEM cross-sectional images and EDS confirmed that the interfaces were smooth and that, surprisingly, the devices were electrochemically active even with a thin layer of sputtered LiPON (less than 300 nm). Highly reversible redox peaks were observed when the batteries were cycled under different scan rates in a cyclic voltammetry experiment. Galvanostatic charge and discharge cycling was performed under different current densities, ranging from 0.5C up to 17C. When running 100 cycles of galvanostatic charge and discharge on the SSB at 17C, a coulombic efficiency of 99% was achieved after the 12^th cycle.<br/>Prototypes of this prismatic SSB with different numbers of layers were made using the sputtering tool to judge the scaling of discharge capacity and power performance. Although the single battery devices had a capacity below the theoretical capacity of vanadium oxide, the scaling of the power and energy density is none-the-less encouraging. These prototype “multibatteries” demonstrate the potential of this 3D architecture as next generation energy storage in microelectronic devices.