Anode-free lithium metal batteries: a promising flexible energy storage system

The demand for flexible lithium-ion batteries (FLIBs) has witnessed a sharp increase in the application of wearable electronics, flexible electronic products, and implantable medical devices. However, many challenges still remain towards FLIBs, including complex cell manufacture, low-energy density and low-power density. To address these issues, researchers have widely conducted studies on the structure and material design of flexible batteries. Among these efforts, the anode-free lithium metal battery (AFLMB) stands out as a promising solution, offering potential new avenues for research in flexible battery design. The anode-free full cell configuration removes excess lithium and combines the fully lithiated cathode with a bare current collector (CC), which not only simplifies the production process and lowers the cost, but also achieves light weight and high-energy-density. Nevertheless, AFLMBs are still confronted by challenges including diminished coulombic efficiency (CE), shortened cycle longevity, and lithium dendrite growth, which substantially impede the practical application of AFLMBs towards flexible batteries. This review provides an overview of the latest developments in anode-free batteries, particularly focusing on research strategies in electrolyte design and current collector modification. Considering the characteristics of flexible batteries, the article also points out the challenges and feasible research directions for the development of flexible AFLMBs. It is concluded that although there are significant challenges in developing flexible AFLMBs, the design of gel electrolytes and polymer artificial solid electrolyte interphases (SEIs) can expedite practical advancements, aiming to achieve safe, light weight, cost-effective, and high-energy-density flexible batteries.