Stepwise Artificial Yarn Muscles with Energy-Free Catch States Driven by Aluminum-Ion Insertion

Present artificial muscles have been suffering from poor actuation step precision and the need of energy input to maintain actuated states due to weak interactions between guest and host materials or the unstable structural changes. Herein, these challenges are addressed by deploying a mechanism of reversible faradaic insertion and extraction reactions between tetrachloroaluminate ions and collapsed carbon nanotubes. This mechanism allows tetrachloroaluminate ions as a strong but dynamic "locker" to achieve an energy-free high-tension catch state and programmable stepwise actuation in the yarn muscle. When powered off, the muscle nearly 100% maintained any achieved contractile strokes even under loads up to 96,000 times the muscle weight. The actuation mechanism allowed the programmable control of stroke steps down to 1% during reversible actuation. The isometric stress generated by the yarn muscle (14.6 MPa in maximum, 40 times that of skeletal muscles) was also energy freely lockable and step controllable with high precision. Importantly, when fully charged, the muscle stored energy with a high capacity of 102 mAh g^-1, allowing the muscle as a battery to power secondary muscles or other devices.

Novel K2Ti8O17 Anode via Na+/Al3+ Co-Intercalation Mechanism for Rechargeable Aqueous Al-Ion Battery with Superior Rate Capability

A promising aqueous aluminum ion battery (AIB) was assembled using a novel layered K₂Ti₈O₁₇ anode against an activated carbon coated on a Ti mesh cathode in an AlCl₃-based aqueous electrolyte. The intercalation/deintercalation mechanism endowed the layered K₂Ti₈O₁₇ as a promising anode for rechargeable aqueous AIBs. NaAc was introduced into the AlCl₃ aqueous electrolyte to enhance the cycling stability of the assembled aqueous AIB. The as-designed AIB displayed a high discharge voltage near 1.6 V, and a discharge capacity of up to 189.6 mAh g⁻¹. The assembled AIB lit up a commercial light-emitting diode (LED) lasting more than one hour. Inductively coupled plasma–optical emission spectroscopy (ICP-OES), high-resolution transmission electron microscopy (HRTEM), and X-ray absorption near-edge spectroscopy (XANES) were employed to investigate the intercalation/deintercalation mechanism of Na⁺/Al³⁺ ions in the aqueous AIB. The results indicated that the layered structure facilitated the intercalation/deintercalation of Na⁺/Al³⁺ ions, thus providing a high-rate performance of the K₂Ti₈O₁₇ anode. The diffusion-controlled electrochemical characteristics and the reduction of Ti⁴⁺ species during the discharge process illustrated the intercalation/deintercalation mechanism of the K₂Ti₈O₁₇ anode. This study provides not only insight into the charge–discharge mechanism of the K₂Ti₈O₁₇ anode but also a novel strategy to design rechargeable aqueous AIBs.

Real-Time Observation of Anion Reaction in High Performance Al Ion Batteries

Recently, aluminum ion batteries (AIBs) have attracted great attention across the globe by virtue of their massive gravimetric and volumetric capacities in addition to their high abundance. Though carbon derivatives are excellent cathodes for AIBs, there is much room for further development. In this study, flexuous graphite (FG) was synthesized by a simple thermal shock treatment, and for the first time, an Al/FG battery was applied as a cathode for AIBs to reveal the real-time intercalation of AlCl₄^- into FG with high flexibility by using in-situ scanning electron microscope (SEM) measurements exclusively. Similarly, in-situ X-ray diffraction (XRD) and in-situ Raman techniques have been used to understand the anomalous electrochemical behavior of FG. It was found that FG adopts a unique integrated intercalation-adsorption mechanism where it follows an intercalation mechanism potential above 1.5 V and an adsorption mechanism potential below 1.5 V. This unique integrated intercalation-adsorption mechanism allows FG to exhibit superior properties, like high capacity (≥140 mAh/g), remarkable long-term stability (over 8000 cycles), excellent rate retention (93 mAh/g at 7.5 A/g), and extremely rapid charging and slow discharging.