All-solid-state flexible planar lithium ion micro-capacitors†
The ever-increasing boom in smart, miniaturized electronics has led to an urgent need for on-chip energy storage systems that exhibit high performance, safety, flexibility and robust integration. However, tremendous challenges exist. Here, we demonstrate the first prototype of all-solid-state planar lithium ion micro-capacitors (LIMCs) based on interdigital patterns of lithium titanate nanospheres as the anode and activated graphene as the cathode. The interdigital LIMCs were fabricated via layer-by-layer mask-assisted deposition of graphene and electrode materials, without the need for metal current collectors, additives or polymer binders. The as-assembled LIMCs delivered a record volumetric energy density of 53.5 mW h cm−3. Furthermore, they exhibited outstanding mechanical flexibility without performance degradation under repeated bending, superior electrochemical metrics and safety at a high temperature of 80 °C due to the highly stable ionogel electrolyte and the absence of a separator. Additionally, our microdevices presented remarkable modular integration of the constructed bipolar cells for boosting high voltage and capacitance. Therefore, these LIMCs hold great potential for application in future flexible and wearable electronics.