Electrochemical energy storage (EES) devices integrated with smart functions are highly attractive for powering the next-generation electronics in the coming era of artificial intelligence. In this regard, exploiting functional electrolytes represents a viable strategy to realize smart functions in EES devices. In this review, recent advances in the development of functional electrolytes for smart EES devices like rechargeable batteries and supercapacitors are presented. Various stimulus-responsive electrolytes are first summarized, including temperature-, mechanical force-, voltage-, magnetism-, and light-responsive electrolytes. Emphasis is placed on the working principles of stimulus-responsive electrolytes and their specific problem-solving functions in EES devices. Then, the latest advances in electrochromic and self-healing electrolytes used for smart EES devices are discussed. Finally, key challenges and research opportunities related to functional electrolyte design and smart EES device development are envisioned, with the goal of accelerating further research in this thriving field.