As of my last knowledge update in September 2021, flexible lithium-air (Li-Air) batteries are still a topic of active research and development. Li-Air batteries have the potential to provide high energy densities due to their utilization of oxygen from the air as one of the reactants, but there have been challenges related to their stability, efficiency, and cycle life.
However, there isn't a widely recognized "typical" voltage rating for flexible Li-Air batteries, as their performance characteristics can vary depending on the specific design, materials, and manufacturing processes used by different research groups and companies.
Traditional lithium-ion batteries typically operate around 3.7 to 3.8 volts per cell. Lithium-air batteries, due to their use of oxygen from the air as one of the reactants, theoretically have the potential for higher energy densities, which could result in higher voltages. Some research papers and projects have proposed Li-Air battery designs that aim for higher voltages, potentially in the range of 4 to 5 volts or even higher.
However, it's important to note that the practical development and commercialization of flexible Li-Air batteries are still in progress, and the specifications and performance metrics can vary widely between different research efforts. To get the most accurate and up-to-date information on the voltage rating of a typical flexible Li-Air battery, I recommend checking recent research papers, news articles, or official announcements from reputable sources in the field of battery research and development.