Realizing High-Energy and Stable Wire-Type Batteries with Flexible Lithium–Metal Composite Yarns

High-capacity and omnidirectionally flexible wire-type lithium (Li)–metal batteries represent a feasible technology for the realization of electronic textiles. However, the use of commercially available Li–metal wires as anodes nowadays confronts many electrochemical and mechanical issues such as dendrite formation, low yield strength, and poor fatigue resistance. Here, a flexible and stable Li–metal composite yarn (LMCY) is designed via a fast capillary filling of molten Li into metallic carbon yarn for fabricating high-energy-density and long-lasting wire-type Li–metal batteries. LMCY shows outstanding electrochemical cyclic stability, mechanical strength, flexibility, and durability. Pairing lithium–iron phosphate (LFP) with the LMCY as anode results in a foldable LFP||Li full cell that delivers a high energy density over 290 Wh L⁻¹ and a long lifetime over 800 cycles with a capacity retention of over 50% after 750 charge/discharge cycles. The seamless integration of this wire-shape LFP||Li cell with commercial textiles is demonstrated as a built-in power supply to wearable electronics, while maintaining the excellent breathability of the textiles. LMCYs are also adaptable to other high-performance wire-type batteries, such as lithium–sulfur battery.