Dual graphite battery emerges as a promising renewable energy storage system with merits of a high working voltage, low cost and environment-friendliness. However, energy density is limited because of a low packing density of graphite. We propose for the first time dual carbon fiber batteries (DCFBs) in which carbon fiber functions as both cathode and anode. With a graphite mass loading of ∼30 mg cm⁻² at pitch-based carbon fiber (PCF) cloth, the reversible discharge capacity of PCF-PCF type DCFBs (with PCF cloth cathodes/anodes) can reach 72 mAh g⁻¹ at 0.1 C (1 C corresponding to 80 mAh g⁻¹), resulting in an unprecedentedly high areal capacity of ∼2.2 mAh cm⁻². Unlike the general applicability of commercialized carbon fiber as DCFBs anode, only PCF out of five kinds of commercialized carbon fibers can function as DCFBs cathode. Meanwhile, PCF-PCF type DCFB enables investigation into distinct electrochemical behaviors of Li⁺/PF₆⁻intercalation/deintercalation in PCF. Morphological difference of PCF brought about by Li⁺/PF₆⁻ ions, as found out by ex-situ X-ray diffraction (XRD) and ex-situ scanning electronic microscopy/energy dispersive spectroscopy (SEM/EDS) characterizations, facilitates comprehensive understanding of electrochemical behavior of graphite. This work lays good foundations for future exploration into a new arena of dual ion batteries.

双石墨电池具有工作电压高、成本低、环境友好等优点，成为一种很有前途的可再生能源存储系统。然而，由于石墨的堆积密度低，能量密度受到限制。我们首次提出了双碳纤维电池 (DCFB)，其中碳纤维同时充当阴极和阳极。在沥青基碳纤维 (PCF) 布上的石墨质量负载量为 ~30 mg cm ^-2时，PCF-PCF 型 DCFB（具有 PCF 布阴极/阳极）的可逆放电容量在 0.1时可达到 72 mAh g ^-1 C（1 C 对应于 80 mAh g ^-1），导致空前高的面容量~2.2 mAh cm ^-2. 与商业化碳纤维作为DCFBs阳极的普遍适用性不同，五种商业化碳纤维中只有PCF可以作为DCFBs阴极。同时，PCF-PCF 型 DCFB 能够研究 Li ⁺ /PF ₆ ^-在 PCF 中嵌入/脱嵌的不同电化学行为。异位X射线衍射(XRD)和非原位分析发现Li ⁺ /PF ₆ ⁻离子对PCF的形貌差异扫描电子显微镜/能量色散光谱 (SEM/EDS) 表征，有助于全面了解石墨的电化学行为。这项工作为未来探索双离子电池的新领域奠定了良好的基础。