3D‐Integrated, Multi‐Functional Carbon Fibers for Stable, High‐Areal‐Capacity Batteries

Abstract Increasing lithium‐ion batteries' (LIBs) electrode areal capacity can boost energy density and lower manufacturing costs, but faces challenges in manufacturing, rate performance, and cycling stability. A conductive framework made of commercial micro‐sized carbon fibers (Cfs) is presented that serves as a host for both the LiNi_0.5Mn_0.3Co_0.2O₂ (NMC 532) cathode and Cfs anode. The Cf framework has multiple functions that offer high electronic conductivity (270 mS cm⁻¹), low tortuosity (1.7), low Li⁺ diffusion resistance (22 Ω), and high thermal conductivity (200 W mK⁻¹). Additionally, the Cf‐integrated electrodes can have an extremely high mass loading of NMC 532 (70 mg cm⁻²) with a theoretical capacity of 14 mAh cm⁻². Thus, the practical full cells assembled with the Cfs‐enabled electrodes exhibit an initial areal capacity of 4.1 mAh cm⁻² and capacity retention of 90.4% at 500 cycles at a cycling rate of C/3, 1.5 mA cm⁻². Data collected from the operando isothermal microcalorimetry suggest that full cells utilizing the Cf anode experience less heat release from side reactions compared to cells utilizing a conventional graphite anode. This present approach is scalable and cost‐effective and can fabricate practical LIBs that boast high areal capacity, rate performance, and a lengthy cycling lifetime.