The voltage window, also known as the operating voltage range, is a crucial parameter in electrochemical devices such as batteries and capacitors. It defines the range of voltages within which the device can safely operate without experiencing degradation or failure. For example, in lithium-ion batteries, the voltage window is determined by the stability of the electrolyte and the electrode materials. A wider voltage window allows for higher energy density and improved performance. However, exceeding this range can lead to safety issues, such as thermal runaway and battery degradation.