As of my last knowledge update in September 2021, flexible lithium-air (Li-Air) batteries were still in the experimental and research stages, and specific voltage ratings might not have been firmly established. However, I can provide some general information about Li-Air batteries.
Lithium-air batteries are known for their potential to provide high energy densities compared to conventional lithium-ion batteries. The theoretical voltage of a lithium-air battery is around 3.5 to 4.0 volts, based on the electrochemical reactions involved. This is because lithium reacts with oxygen from the air to form lithium oxide during discharge, and the voltage is determined by the energy difference between these compounds.
It's important to note that practical implementations of lithium-air batteries can vary significantly due to factors such as electrode materials, electrolyte compositions, and overall design. Also, the flexible nature of the battery could introduce additional complexities that might affect the voltage characteristics. Therefore, if there have been developments in flexible Li-Air batteries since September 2021, I recommend checking the latest research papers, technical documents, or manufacturer information for the most accurate and up-to-date voltage ratings.