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

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AbstractIncreasing 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 LiNi0.5Mn0.3Co0.2O2 (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.