Memristive devices based on ion-transfer between two meta-stable phases in an ion intercalated material are provided. In one aspect, a memristive device is provided. The memristive device includes: a first inert metal contact; a layer of a phase separated material disposed on the first inert metal contact, wherein the phase separated material includes interstitial ions; and a second inert metal contact disposed on the layer of the phase separated material. The first phase of the phase separated material can have a different concentration of the interstitial ions from the second phase of the phase separated material such that the first phase of the phase separated material has a different electrical conductivity from the second phase of the phase separated material. A method for operating the present memristive device is also provided.