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

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.