Self-Supporting Fiber-Anchor-Encapsulated MnCN₂@Cyclized-PAN Anode for High-Performance Flexible Li-Ion Batteries

MnCN₂ has rich and wide interlayer channels, making it a potentially high-capacity fast-charging anode material for Li-ion batteries. However, intrinsic metastability causes severe chemical and structural deterioration, suppressing capacity output and cycle reversibility. Here, an anchor-encapsulation strategy is proposed for stabilizing surface chemistry and bulk structure and developing an in situ synthesis process for constructing a fiber-encapsulated composite anode. Electrospinning is adopted to realize large-area fabrication of self-supporting electrode and uses the polyacrylonitrile cyclization to achieve chemical anchoring design. The obtained structure features highly oriented MnCN₂ nano-crystallines embedded within cyclized-polyacrylonitrile frameworks, forming a fiber-anchor-encapsulated MnCN₂@cPAN. Systematic studies disclose synergistic physical and chemical interactions between cPAN and MnCN₂. Chemical anchoring facilitates fast electron and ion transport and also stable interface, and compact encapsulation alleviates volume change and electrolyte's erosion. Because of the improvement on electrical, chemical, and volumetric properties, the composite design enables promising electrochemical performance, including a large initial capacity of 825 mAh g⁻¹ at 0.1 C, a high-rate capability of 335 mAh g⁻¹ at 10 C, and a remarkable capacity retention of 80% after 800 cycles at 1 C. It demonstrates a great potential for Li-ion batteries, where LiNi_0.8Mn_0.1Co_0.1O₂//MnCN₂@cPAN pouch-cell exhibits an excellent cycle performance of 86% capacity retention after 100 cycles.