Stretchable Thermoelectric Fibers with Three-Dimensional Interconnected Porous Network for Low-Grade Body Heat Energy Harvesting.

Electricity generation from body heat has garnered significant interest as a sustainable power source for wearable bioelectronics. In this work, we report stretchable n-type thermoelectric fibers based on the hybrid of Ti3C2Tx MXene nanoflakes and polyurethane (MP) through a wet-spinning process. The proposed fibers are designed with a 3D interconnected porous network to achieve satisfactory electrical conductivity (σ), thermal conductivity (κ), and stretchability simultaneously. We systematically optimize the thermoelectric and mechanical traits of the MP fibers and the MP-60 (with 60 wt % MXene content) exhibits a high σ of 1.25 × 103 S m-1, an n-type Seebeck coefficient of -8.3 µV K-1, and a notably low κ of 0.19 W m-1 K-1. Additionally, the MP-60 fibers possess great stretchability and mechanical strength with a tensile strain of 434% and a breaking stress of 11.8 MPa. Toward practical application, a textile thermoelectric generator is constructed based on the MP-60 fibers and achieves a voltage of 3.6 mV with a temperature gradient between the body skin and ambient environment, highlighting the enormous potential of low-grade body heat energy harvesting.

Regulating Interfacial Ion Migration via Wool Keratin Mediated Biogel Electrolyte toward Robust Flexible Zn-Ion Batteries.

Aqueous Zn-ion batteries (ZIBs) have emerged as a promising energy supply for next-generation wearable electronics, yet they are still impeded by the notorious growth of zinc dendrite and uncontrollable side reaction. While the rational design of electrolyte composition or separator decoration can effectively restrain zinc dendrite growth, synchronously regulating the interfacial electrochemical performance by tackling the physical delamination venture between electrode and electrolyte remains a major obstacle for high-performance wearable aqueous ZIB. Herein, a category of hybrid biogel electrolyte containing carrageenan and wool keratin (CWK) is put forward to regulate the interfacial electrochemistry in aqueous ZIB. Systematic electrochemical kinetics analyses and ex situ scanning electrochemical microscopy (SECM) characterizations achieve comprehensive understanding of the keratin enhanced interfacial Zn2+ redox reaction. Thanks to the keratin triggered selective ion permeability, the as-designed CWK hybrid biogel electrolyte manifests a promoted Zn2+ transference number and excellent reversibility of Zn plating/stripping and outstanding Zn utilization (average Coulombic efficiency ≈98%). More impressively, the CWK hybrid biogel electrolyte also demonstrates cathode side-reaction depression and strengthened interfacial adhesion while assembled into a quasi-solid-state flexible ZIB. This work offers a strategy to synchronously solve concurrent challenges for both of Zn anode and cathode toward realistic wearable aqueous ZIB.

Mechanistic Insights into Fast Charging and Discharging of the Sodium Metal Battery Anode: A Comparison with Lithium.

Na metal anode receives increasing attention as a low-cost alternative to Li metal anode for the application in high energy batteries. Despite extensive research efforts to improve the reversibility and cycle life of Na metal electrodes, their rate performance, i.e. electrochemical plating and stripping of Na metal at high current, is underexplored. Herein, we report that Na metal electrodes, unlike the more widely studied Li metal electrodes which survive high current density up to 20 mA/cm2, cannot be fast charged or discharged in common ether electrolyte. The fast charging, namely metal plating, is comprised by severe side reactions that decompose electrolyte into electrochemically inactive Na(I) solid species. The fast discharging, namely metal stripping, is disabled by local Na removal that deteriorates the electrical contact with the current collector. While the fast charging failure is permanent, the capacity loss from fast discharging can be recovered through a restructuring process at a low discharging current which rebuilds the electrical connection. We further reveal that the unsatisfactory rate performance of Na metal electrodes is associated with intrinsic physicochemical properties of Na. This study delineates the mechanistic origins of Na's limitation in fast plating and stripping, and demonstrates the necessity of improving the charging and discharging rate performance of Na metal electrodes.

Electrocatalysis in Lithium Sulfur Batteries under Lean Electrolyte Conditions.

The presence of electrocatalysis in lithium-sulfur batteries has been proposed but not yet sufficiently verified. In this study, molybdenum phosphide (MoP) nanoparticles are shown to play a definitive electrocatalytic role for the sulfur cathode working under lean electrolyte conditions featuring a low electrolyte/active material ratio: the overpotentials for the charging and discharging reactions are greatly decreased. As a result, sulfur electrodes containing MoP nanoparticles show faster kinetics and more reversible conversion of sulfur species, leading to improvements in charging/discharging voltage profiles, capacity, rate performance, and cycling stability. Taking advantage of the electrocatalytic properties of MoP, high-performance sulfur electrodes were successfully realized that are steadily cyclable at a high areal capacity of 5.0 mAh cm-2 with a challenging electrolyte/sulfur (E/S) ratio of 4 µLE mg-1 S .

High-capacity rechargeable batteries based on deeply cyclable lithium metal anodes.

Discovering new chemistry and materials to enable rechargeable batteries with higher capacity and energy density is of paramount importance. While Li metal is the ultimate choice of a battery anode, its low efficiency is still yet to be overcome. Many strategies have been developed to improve the reversibility and cycle life of Li metal electrodes. However, almost all of the results are limited to shallow cycling conditions (e.g., 1 mAh cm-2) and thus inefficient utilization (<1%). Here we achieve Li metal electrodes that can be deeply cycled at high capacities of 10 and 20 mAh cm-2 with average Coulombic efficiency >98% in a commercial LiPF6/carbonate electrolyte. The high performance is enabled by slow release of LiNO3 into the electrolyte and its subsequent decomposition to form a Li3N and lithium oxynitrides (LiN x Oy)-containing protective layer which renders reversible, dendrite-free, and highly dense Li metal deposition. Using the developed Li metal electrodes, we construct a Li-MoS3 full cell with the anode and cathode materials in a close-to-stoichiometric amount ratio. In terms of both capacity and energy, normalized to either the electrode area or the total mass of the electrode materials, our cell significantly outperforms other laboratory-scale battery cells as well as the state-of-the-art Li ion batteries on the market.

High-Performance Sodium Metal Anodes Enabled by a Bifunctional Potassium Salt.

Developing Na metal anodes that can be deeply cycled with high efficiency for a long time is a prerequisite for rechargeable Na metal batteries to be practically useful despite their notable advantages in theoretical energy density and potential low cost. Their high chemical reactivity with the electrolyte and tendency for dendrite formation are two major issues limiting the reversibility of Na metal electrodes. In this work, we introduce for the first time potassium bis(trifluoromethylsulfonyl)imide (KTFSI) as a bifunctional electrolyte additive to stabilize Na metal electrodes, in which the TFSI- anions decompose into lithium nitride and oxynitrides to render a desirable solid electrolyte interphase layer while the K+ cations preferentially adsorb onto Na protrusions and provide electrostatic shielding to suppress dendritic deposition. Through the cooperation of the cations and anions, we have realized Na metal electrodes that can be deeply cycled at a capacity of 10 mAh cm-2 for hundreds of hours.

A remote controllable fiber-type near-infrared light-responsive actuator.

A novel near-infrared (NIR) light-responsive sodium polyacrylate (PAAS)/graphene oxide (GO) fiber with a torsional pre-deformation structure is reported to realize remote control actuation. The torsional pre-deformed PAAS/GO fiber exhibited various actuation phenomena, under the control of a low powered near-infrared light (50 mW cm-2), such as rotating in a low-temperature range (<25 °C), rolling a distance of 10 times of its diameter within 10 s, and even driving the shape change of a fabric (the weight is as high as 20 times of the fiber itself).

An electrically controllable all-solid-state Au@graphene oxide actuator.

A novel all-solid electrically controllable Au@graphene oxide (GO) actuator with a bilayer structure is reported to address many of the limitations of traditional electrical-driven materials including complicated layouts and high electric fields. Specifically, the obtained Au@GO actuator possesses electrolyte-free, real time controlled actuation and patterning capabilities.