Pushing the Limit of Flexible Batteries

Alongside the rapid development of flexible and wearable electronics, the search for reliable, safe, and high-energy rechargeable flexible batteries (FBs) has become a research hotspot in recent years. Although there are some prototype FBs exhibited by the industry and a rapidly increasing number of publications reported by academia, most demonstrations are shown on a laboratory scale, and it is still difficult to find real implementation of the technology in the market. This perspective aims to discuss and analyze the key metrics, including energy density, flexibility, and safety, that are critical to pushing FBs to a commercially viable level, with a special focus on the lithium batteries and zinc batteries most reported in the literature. We first compare the figure of merit of FBs (fb_FOM) of existing lithium-based and zinc-based FBs with the requirement for market applications. We then analyze the most desired cell configurations toward high flexibility, followed by systematic discussions on features and materials selection toward high energy density FBs. Third, we discuss strategies to enhance battery safety. An outlook of the future developments needed to address the gaps between the state-of-the-art demonstrations and real applications is provided at the end of this article.