纤维电化学储能器件的研究进展

Research progress of fiber-shaped electrochemical energy storage devices

近20年来,电子设备不断向轻薄化、微型化、柔性化和集成化的方向快速发展,迫切需要相匹配的供能系统,以解决智能通讯、移动医疗等领域的实际应用要求.纤维状储能器件显示出优异的柔性、良好的适应性和集成性,并能通过编织来满足可穿戴设备的供能需求.经过近10年的系统研究,我们提出了通过取向碳纳米管与活性材料复合以制备柔性纤维电极的普适性方法;揭示了纤维电极多尺度取向孔道结构促进电解液浸润和电荷快速传输的机制;研究了复合纤维中三维包缠结构在稳定电极活性材料界面所发挥的关键作用;发展出高性能纤维状锂离子电池,进一步有效拓展至各类柔性纤维电化学储能器件,并通过纺织方法获得集成的柔性储能织物.本综述对上述研究成果进行了总结描述,并对我们近年来在纤维电化学储能器件领域的研究进行了归纳,最后对该领域尚未解决的问题及未来重点研究方向提出展望.

During the past two decades,wearable devices have been broadly used for a variety of fields such as biomedical system,communication and microelectronics.The power system such as lithium-ion batteries is essential to the operation of wearable devices,which should adapt to irregular substrates and sustain complex deformations.A promising strategy is to fabricate high-performance energy storage devices in a fiber shape,e.g.,fber lithium-ion batteries(LIBs).These fiber LIBs with diameters ranging from tens to hundreds of micrometers can be readily integrated with human body and work stably under constant body motions.They can also be woven into breathable fabrics to satisfy the needs of wearable electronics.The key challenges facing fiber LIBs include effective loading of active materials on fiber electrodes,efficient charge transfer along fiber electrodes and interface stability of fiber electrodes under operation and deformation.Fiber electrodes are thus designed with hierarchical and aligned channels to effectively load active materials,so an effective electric field can be established between the fber cathode and anode.Aligned carbon nanotubes(CNTs)can be made with conductive additives and active materials into fiber electrodes by a continuous spinning process.Conventional metal current collectors,binders and conductive agents are not required,and active materials may reach 90%of the electrode by weight.The resulting hierarchically helical CNT fiber electrode shows high flexibility,high strength,and high electrical conductivity.The flexural rigidity is as low as 10^-7 nN/m^2,which is several orders of magnitude lower than those of ordinary synthetic fibers.The specific strength reaches 10^7 Nm/kg,which is higher than those of ordinary synthetic fibers.The conductivity reaches 10^4 S/cm,which can meet the needs of batteries.The aligned CNT composite fiber permits efficient electron transport,where the electrons hop among neighboring CNTs.Besides,due to the capillary force,the electrolyte can penetrate throughout the entire fiber via micrometer-sized and nanometer--sized channels,benefiting ion transport.The twisted CNT bundles firmly bind active materials and prevent their significant volume variations during charge and discharge processes.Therefore,the efficient conductive pathways can be maintained to deliver both high rate and cyclic stability.Fiber LIBs could be fabricated by assembling two fiber electrodes in parallel,twisting or coaxial structure.Gel electrolyte avoids the potential safety risks stemmed from liquid electrolytes.The continuously fiber LIBs show both high flexibility and energy storage capacity.After bending for 100000 cycles,the capacities have been well maintained,and the energy densities exceed 100 Wh/kg.Based on the similar strategy,a series of fiber energy storage devices such as supercapacitors,lithium-sulfur batteries,lithium-air batteries,zinc-ion batteries,zinc-air batteries aund alurinu-air batleries,have been also produced.To summarize,fiber energy storage devices can be woven into flexible fabrics or integrated with energy harvesting devices to satisfy the next-generation electronics.Such a new strategy establishes an efficient avenue to particularly accelerate the development of wearable electronics in the future.