Theory of Electrochemical Memory: Application to Short‐Circuit Memory in Electrochromic Displays

We introduce the concept of electrochemical memory and discuss it in relation to electrochromism. We show that the electrochemical memory could be created by the dynamics of the ion‐electrolyte interaction during the ion‐insertion process. To calculate the electrochemical memory we introduce a small‐polaron model of ion transfer at the electrochemical interface and derive general, analytical expressions for the probability of transitions. We apply these expressions to a Langmuir‐type macroscopic model of the electrochromic reaction. Under these assumptions, we establish lower limits of the breakdown voltage necessary for short‐circuit memory with threshold in an electrochromic display cell. We also derive a simple expression for the maximum memory in terms of the intrinsic response time of the electrochromic cell. For response times ∼10 msec and breakdown voltages ∼2V, the maximum memory would be ∼20 min at room temperature. Finally, we calculate the electrolyte reorganization energy required to achieve the maximum memory. Its value lies in the range 1.5 ↔ 2.0 eV. In applying these results to displays, we find that the number of lines which could be sequentially matrix addressed in an electrochromic display matrix spans the range 10 ↔ 10 5 . In contrast to the current notion, this proves that direct matrix addressing of electrochromic displays is theoretically possible.