Large-Scale Nanofiber Manufacturing| Radially unfolded nanosheets inpolyacrylonitrile nanofibers: A biomimeticsconstruct of high-performance anode forlithium-ion batteries

Shaanxi Normal University Zhang Hang & Hunan University Professor Zhang Guanhua: Biomimetic Design of Neuron-like Structured Electrode Materials Achieved Through Radial Unfolding of Nanosheets in Polyacrylonitrile Fibers

Lithium-ion batteries (LIBs), with advantages such as high output voltage, long cycle life, safety, and pollution-free operation, remain core devices in the development of future energy storage technologies as the current mainstream electrochemical energy storage products in the market. As one of the key components of LIBs, commercial graphite anodes have reached their theoretical limits and can hardly meet the growing demands of our era. Additionally, traditional energy storage devices generally possess mechanical rigidity and cannot meet the societal need for wearable flexible products. Therefore, the development and utilization of lightweight carbon-based fiber electrode materials represent a highly promising research field.

One-dimensional nanofiber nonwoven membranes fabricated via electrospinning technology are crucial for advancing the field of flexible freestanding electrode materials. Benefiting from graphene's unique structure and surface properties, two-dimensional architectures exhibit abundant reactive sites, rapid ion diffusion kinetics, excellent electron transport characteristics, and unique anisotropic mechanical properties in energy storage applications, making them ideal structural-functional units for composite materials. Consequently, effectively constructing two-dimensional morphologies within nanofibers to develop structurally integrated fiber electrodes that combine both one-dimensional and two-dimensional features holds significant scientific importance and practical value for advancing LIB development.

Recently, inspired by the structural characteristics and functional behaviors of neurons, Assistant Researcher Zhang Hang from Shaanxi Normal University and Professor Zhang Guanhua from Hunan University collaborated to propose a biomimetic neuron-like fiber electrode design. Through electrospinning technology, they achieved the radial unfolding of two-dimensional metal-organic frameworks within polyacrylonitrile fibers, constructing a neuron-like structured fiber electrode (NRN-ONFs) featuring a "one-dimensional conductive skeleton (axon-like) + two-dimensional active units (soma-like)." This biomimetic structure simultaneously addresses three major challenges in fiber electrodes: insufficient active interfaces, sluggish electron/ion transport, and accumulated volume strain, effectively enhancing the rate performance and cycling stability of LIBs during charge/discharge processes. It provides a novel paradigm for high-performance flexible lithium-ion battery anodes. The related research was published in the journal Carbon under the title "Radially unfolded nanosheets in polyacrylonitrile nanofibers: a biomimetics construct of high-performance anode for lithium-ion batteries."

Fig. 1. Schematic of morphological and functional characteristics of neuron-like structured fiber electrodes, and morphology images of neuron-like electrode materials.

Fig. 2. Preparation process and structural characterization of neuron-like structured fiber electrodes.

Scanning electron microscopy and transmission electron microscopy characterizations reveal that the NRN-ONFs fiber electrode exhibits an interconnected morphology of one-dimensional and two-dimensional structures, with active metal oxides uniformly distributed within the two-dimensional architecture. By introducing two-dimensional units while maintaining the original three-dimensional network skeleton of interpenetrating one-dimensional fibers, the design innovatively separates reaction centers from conduction pathways, effectively improving the electron/ion transport efficiency and volume strain accommodation of the electrode material during electrochemical lithium storage. This enhancement benefits the rate capability and cycling stability of LIBs during charge/discharge processes.

Fig. 3. Lithium-ion battery performance of neuron-like structured fiber electrodes.

Thanks to the unique composition distribution and structural design of the neuron-like structured fiber electrode, the NRN-ONFs anode delivers a first-cycle reversible capacity of 1424.56 mAh g⁻¹ at 0.1 A g⁻¹, retaining 1087.66 mAh g⁻¹ after 300 cycles. Even at a high rate of 6.4 A g⁻¹, it maintains a reversible capacity of 300.51 mAh g⁻¹. When paired with an NCM 811 cathode to assemble a full cell, it demonstrates a high capacity retention rate of 97.2% after 70 cycles, showcasing excellent practical application potential.

Fig. 4. Kinetic analysis of neuron-like structured fiber electrodes.

In-situ electrochemical impedance spectroscopy (EIS) and distribution of relaxation times (DRT) analyses reveal that NRN-ONFs can form a stable solid electrolyte interphase (SEI) film during cycling. Galvanostatic intermittent titration technique (GITT) measurements indicate the excellent lithium-ion diffusion capability (DLi⁺) of NRN-ONFs, ensuring electrode reaction kinetics under superior rate performance. Even when directly used as freestanding electrodes, NRN-ONFs maintain outstanding electrochemical performance, offering a potential solution for lightweight, high-energy-density electrode materials in wearable devices.