Yang Zhao

Advances in Wearable Fiber-Shaped Lithium-Ion Batteries

It is highly desirable to develop flexible and efficient energy-storage systems for widely used wearable electronic products. To this end, fiber-shaped lithium-ion batteries (LIBs) attract increasing interest due to their combined superiorities of miniaturization, adaptability, and weavability, compared with conventional bulky and planar structures. Recent advances in the fabrication, structure, mechanism, and properties of fiber-shaped LIBs are summarized here, with a focus on the electrode material. Remaining challenges and future directions are also highlighted to provide some useful insights from the viewpoint of practical applications.

A Shape‐Memory Supercapacitor Fiber

A shape-memory, fiber-shaped supercapacitor is developed by winding aligned carbon nanotube sheets on a shape-memory polyurethane substrate. Despite its flexibility and stretchability, the deformed shapes under bending and stretching can be frozen as expected and recovered to the original state when required. Its electrochemical performances are well-maintained during deformation, at the deformed state and after the recovery.

A Self-Healing Aqueous Lithium-Ion Battery

Flexible lithium-ion batteries are critical for the next-generation electronics. However, during the practical application, they may break under deformations such as twisting and cutting, causing their failure to work or even serious safety problems. A new family of all-solid-state and flexible aqueous lithium ion batteries that can self-heal after breaking has been created by designing aligned carbon nanotube sheets loaded with LiMn2 O4 and LiTi2 (PO4 )3 nanoparticles on a self-healing polymer substrate as electrodes, and a new kind of lithium sulfate/sodium carboxymethylcellulose serves as both gel electrolyte and separator. The specific capacity, rate capability, and cycling performance can be well maintained after repeated cutting and self-healing. These self-healing batteries are demonstrated to be promising for wearable devices.

An All-Solid-State Fiber-Shaped Aluminum–Air Battery with Flexibility, Stretchability, and High Electrochemical Performance

Owing to the high theoretical energy density of metal-air batteries, the aluminum-air battery has been proposed as a promising long-term power supply for electronics. However, the available energy density from the aluminum-air battery is far from that anticipated and is limited by current electrode materials. Herein we described the creation of a new family of all-solid-state fiber-shaped aluminum-air batteries with a specific capacity of 935u2005mAhu2009g(-1) and an energy density of 1168u2005Whu2009kg(-1) . The synthesis of an electrode composed of cross-stacked aligned carbon-nanotube/silver-nanoparticle sheets contributes to the remarkable electrochemical performance. The fiber shape also provides the aluminum-air batteries with unique advantages; for example, they are flexible and stretchable and can be woven into a variety of textiles for large-scale applications.

Aligned carbon nanotube/molybdenum disulfide hybrids for effective fibrous supercapacitors and lithium ion batteries

An aligned carbon nanotube/MoS2 nanosheet hybrid fiber was synthesized to display combined remarkable mechanical, electronic and electrochemical properties. It was used to fabricate flexible fibrous supercapacitors and lithium ion batteries with a high specific capacitance of 135 F cm−3 and a high specific capacity of 1298 mA h g−1, respectively.

Realizing both High Energy and High Power Densities by Twisting Three Carbon‐Nanotube‐Based Hybrid Fibers

Energy storage devices, such as lithium-ion batteries and supercapacitors, are required for the modern electronics. However, the intrinsic characteristics of low power densities in batteries and low energy densities in supercapacitors have limited their applications. How to simultaneously realize high energy and power densities in one device remains a challenge. Herein a fiber-shaped hybrid energy-storage device (FESD) formed by twisting three carbon nanotube hybrid fibers demonstrates both high energy and power densities. For the FESD, the energy density (50u2005mWhu2009cm(-3) or 90u2005Whu2009kg(-1) ) many times higher than for other forms of supercapacitors and approximately 3u2005times that of thin-film batteries; the power density (1u2005Wu2009cm(-3) or 5970u2005Wu2009kg(-1) ) is approximately 140 times of thin-film lithium-ion battery. The FESD is flexible, weaveable and wearable, which offers promising advantages in the modern electronics.

A fiber-shaped aqueous lithium ion battery with high power density

A new fiber-shaped aqueous lithium ion battery is developed using a polyimide/carbon nanotube hybrid fiber as the anode and LiMn2O4/carbon nanotube hybrid fiber as the cathode. This battery outputs a power density of 10u2006217.74 W kg−1, which exceeds that of most supercapacitors, and an energy density of 48.93 W h kg−1, which equals that of thin-film lithium ion batteries. The safety issue generated by flammable organic electrolytes is fundamentally resolved by using an aqueous electrolyte. Compared with the conventional planar structure, the fiber shape also provides some unique and promising advantages, e.g., being three-dimensionally deformable. It can be also woven into a flexible power textile to satisfy a variety of new emerging fields, such as microelectronics and wearable electronics.

Elastic and wearable ring-type supercapacitors

The development of flexible energy storage devices is critical while it remains challenging for wearable electronics. Herein, a new family of elastic and wearable ring-type supercapacitors is fabricated by winding aligned carbon nanotube/poly(3,4-ethyl-enedioxythiophene):poly(styrene sulfonate) composite sheets onto an elastic polymer ring. The supercapacitor delivers a high specific capacitance of 134.8 F g−1 at a current density of 1 A g−1. Importantly, the specific capacitance has been well maintained after expanding and pressing, which endows the supercapacitor with unique advantages, e.g., it can be used for substrates with different sizes and shapes and may satisfy a variety of wearable applications as well as other fields.

Superaligned Carbon Nanotubes Guide Oriented Cell Growth and Promote Electrophysiological Homogeneity for Synthetic Cardiac Tissues

Cardiac engineering of patches and tissues is a promising option to restore infarcted hearts, by seeding cardiac cells onto scaffolds and nurturing their growth in vitro. However, current patches fail to fully imitate the hierarchically aligned structure in the natural myocardium, the fast electrotonic propagation, and the subsequent synchronized contractions. Here, superaligned carbon-nanotube sheets (SA-CNTs) are explored to culture cardiomyocytes, mimicking the aligned structure and electrical-impulse transmission behavior of the natural myocardium. The SA-CNTs not only induce an elongated and aligned cell morphology of cultured cardiomyocytes, but also provide efficient extracellular signal-transmission pathways required for regular and synchronous cell contractions. Furthermore, the SA-CNTs can reduce the beat-to-beat and cell-to-cell dispersion in repolarization of cultured cells, which is essential for a normal beating rhythm, and potentially reduce the occurrence of arrhythmias. Finally, SA-CNT-based flexible one-piece electrodes demonstrate a multipoint pacing function. These combined high properties make SA-CNTs promising in applications in cardiac resynchronization therapy in patients with heart failure and following myocardial infarctions.

Sticky-note supercapacitors

With the rapid development in portable and wearable electronics, it will be of great convenience if flexible supercapacitors can be easily mounted/disassembled from different substrates at our will, which will largely expand their application scenarios. Herein, inspired by a sticky note, a new family of flexible sticky-note supercapacitors with repeated adhesive performance has been developed by employing a novel kind of sticky aligned carbon nanotube array electrode. The sticky-note supercapacitor demonstrated high capacitance and can be easily and repeatedly attached onto various substrates including cloth, glass, paper, plastic and metal. For up to 200 attaching/removing cycles on different substrates, the capacitance of the supercapacitor note can be well maintained at above 99%.