The ever-increasing boom in smart yet miniaturized electronics urgently requires on-chip energy storage systems with high performance, safety, flexibility, and robust integration, but 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 anode and activated graphene as cathode. The interdigital LIMCs were fabricated via layer-by-layer mask-assisted deposition of graphene and electrode materials, without metal current collector, additive and polymer binder. The as-assembled LIMCs delivered the record volumetric energy density of 53.5 mWh cm-3. Furthermore, they exhibited outstanding mechanical flexibility without performance degradation under repeated bending, superior electrochemical metrics and safety at high temperature of 80 oC due to high-stable ionogel electrolyte and free of separator, and remarkably modular integration of constructing bipolar cells for boosting high voltage, thereby holding great potential for future flexible and wearable electronics.