3D WO3 nanostructuration for high power energy storage micro-devices

The key technical challenge in developing high-performance micro-energy storage systems based on thin films that offer enhanced rate performance and cycling stability is to find low-energy, time-consuming methodologies for depositing thick, conformal films on complex 3D architectures. This work addresses this challenge by presenting a chemical solution deposition approach based on spin coating, which can deposit WO 3 thin films with a thickness ranging from 100 to 500 nm on high-aspect-ratio 3D silicon substrates. Combining an optimized 3D substrate with a high AEF and an optimized film thickness results in the electrodes exhibiting a 30-fold increase in capacity compared to 2D planar counterparts, in line with the area enlargement factor. Electrochemical evaluations demonstrate stable capacity of 320 μAh cm −2 , even when the potential is limited to prevent conversion reactions. Furthermore, a capacity of 82 μAh cm −2 is retained at a high current density of 500 μA cm −2 . The improved rate capability is attributed to the expanded surface area of the 3D electrode, the reversible Li + intercalation mechanism and the nanoscale WO 3 structure, which minimize Li ion paths.