Electrostatic Control of Li+ Density and Transport Rate in Double-Gated van der Waals Devices.

Ion transport in crystalline hosts is controlled by an applied potential that simultaneously sets ionic distribution and transport rate, restricting operation to a one-dimensional control space. Here we show that the transport rate of Li+ ions in double-gated van der Waals devices can be modulated while the system occupies fixed ionic-density states. We measure the ionic current along the van der Waals interfaces between hexagonal boron nitride and graphene or MoS2 while simultaneously monitoring the in-plane electronic response. The ionic current exhibits pronounced hysteresis, with plateaus marking discrete ionic-density states balanced by electronic charge, while an independently tunable electrochemical-potential drop controls the ionic transport rate. The devices sustain over 1,000 switching cycles and function as hybrid ionic-electronic transistors capable of logic operations and memory retention, with ON/OFF ratios exceeding 2 orders of magnitude. This work demonstrates a two-dimensional control space for ions intercalated in layered materials.