Abstract: An electrolyte formulation for use in photoelectrochemical devices is disclosed comprising a thickening agent, wherein the thickening agent is dissolved in the electrolyte. The thickening agent may be polymeric.

Abstract: The present invention is drawn to a high power electrochemical energy storage device in a bipolar configuration, comprising at least n stackable cells (20) in bipolar configuration wherein subgroups of m cells are electronically monitored (63). The storage cells (20) have a lithium ion insertion anode (24) and a lithium ion insertion cathode (26), a separator (36), an electrolyte system (36), and a leak-proof seal structure (51). A number of embodiments are disclosed, characterized by a favorable range of m values, in combination with the anode-to-cathode capacity ratio, electrolyte conductivity, and other battery key features, thereby providing a high power device providing long cycle life and excellent power performance over many thousand charge and discharge cycles while minimizing the cost for electronic monitoring.