Oriented liquid crystal networks (LCNs) can undergo reversible shape change at the macroscopic scale upon an order–disorder phase transition of the mesogens. This property is explored for developing ...soft robots that can move under external stimuli, such as light in most studies. Herein, electrically driven soft robots capable of executing various types of biomimetic locomotion are reported. The soft robots are composed of a uniaxially oriented LCN strip, a laminated Kapton layer, and thin resistive wires embedded in between. Taking advantage of the combined attributes of the actuator, namely, easy processing, reprogrammability, and reversible shape shift between two 3D shapes at electric power on and off state, the concept of a “Janus” soft robot is demonstrated, which is built from a single piece of the material and has two parts undergoing opposite deformations simultaneously under a uniform stimulation. In addition to complex shape morphing such as the movement of oarfish and sophisticated devices like self‐locking grippers, electrically powered “Janus” soft robots can accomplish versatile locomotion modes, including crawling on flat surfaces through body arching up and straightening down, crawling inside tubes through body stretching and contraction, walking like four‐leg animals, and human‐like two‐leg walking while pushing a load forward.
Soft robots based on liquid crystal polymers are built to possess two parts capable of simultaneous and opposite deformations upon an order–disorder phase transition. This design enables various electrically powered locomotion modes, including moving on flat surface through body arching up–straightening down, crawling in a tunnel‐like tube through body stretching–contraction, four‐leg walking, and two‐leg walking while pushing a load.
The ability to optically reconfigure an existing actuator of a liquid crystal polymer network (LCN) so that it can display a new actuation behavior or function is highly desired in developing ...materials for soft robotics applications. Demonstrated here is a powerful approach relying on selective polymer chain decrosslinking in a LCN actuator with uniaxial LC alignment. Using an anthracene‐containing LCN, spatially controlled optical decrosslinking can be realized through photocleavage of anthracene dimers under 254 nm UV light, which alters the distribution of actuation (crosslinked) and non‐actuation (decrosslinked) domains and thus determines the actuation behavior upon order‐disorder phase transitions. Based on this mechanism, a single actuator having a flat shape can be reconfigured in an on‐demand manner to exhibit reversible shape transformation such as self‐folding into origami three‐dimensional structures. Moreover, using a dye‐doped LCN actuator, a light‐fueled microwalker can be optically reconfigured to adopt different locomotion behaviors, changing from moving in the laser scanning direction to moving in the opposite direction.
Walk along: Selective polymer chain decrosslinking in a liquid crystal polymer network (LCN) actuator is demonstrated. Spatially controlled optical decrosslinking alters the distribution of the actuation (crosslinked) and non‐actuation (decrosslinked) domains, and determines the actuation behavior upon the order–disorder phase transition. By using a dye‐doped LCN actuator, a light‐fueled microwalker can be optically reconfigured.
Lithium metal is recognized as one of the most promising anode materials owing to its ultrahigh theoretical specific capacity and low electrochemical potential. Nonetheless, dendritic Li growth has ...dramatically hindered the practical applications of Li metal anodes. Realizing spherical Li deposition is an effective approach to avoid Li dendrite growth, but the mechanism of spherical deposition is unknown. Herein, a diffusion‐reaction competition mechanism is proposed to reveal the rationale of different Li deposition morphologies. By controlling the rate‐determining step (diffusion or reaction) of Li deposition, various Li deposition scenarios are realized, in which the diffusion‐controlled process tends to lead to dendritic Li deposition while the reaction‐controlled process leads to spherical Li deposition. This study sheds fresh light on the dendrite‐free Li metal anode and guides to achieve safe batteries to benefit future wireless and fossil‐fuel‐free world.
Sphere factor: A diffusion–reaction competition mechanism reveals the principle of spherical Li deposition. By controlling the rate‐determining step of Li deposition, different Li deposition scenarios are revealed, in which the diffusion‐controlled process tends to give dendritic Li deposition while the reaction‐controlled process leads to spherical Li deposition.
Novel main‐chain liquid crystalline Diels—Alder dynamic networks (LCDANs) were prepared that exhibit unprecedented ease for actuator programming and reprocessing compared to existing liquid ...crystalline network (LCN) systems. Following cooling from 125 °C, LCDANs are deformed with aligned mesogens self‐locked at room temperature by slowly formed Diels–Alder (DA) bonds, which allows for the formation of solid 3D actuators capable of reversible shape change, and strip walker and wheel‐capable light‐driven locomotion upon either thermally or optically induced order–disorder phase transition. Any actuator can readily be erased at 125 °C and reprogrammed into a new one under ambient conditions. Moreover, LCDANs can be processed directly from melt (for example, fiber drawing) and from solution (for example, casting tubular actuators), which cannot be achieved with LCNs using exchangeable covalent bonds. The combined attributes of LCDANs offer significant progress toward developing easily programmable/processable LCN actuators.
Liquid crystalline dynamic networks can be shaped into 3D objects at room temperature while being stabilized by slowly formed Diels–Alder‐bonded (DA) cross‐links. The actuators demonstrate thermally or optically induced reversible shape change for the purpose of performing mechanical work or locomotion.
Uncontrolled Li plating in graphite electrodes endangers battery life and safety, driving tremendous efforts aiming to eliminate Li plating. Herein we systematically investigate the boundary of Li ...plating in graphite electrode for safe lithium‐ion batteries. The cell exhibits superior safety performance than that with Li dendrites by defining the endurable amount of uniform Li plating in graphite anode. The presence of “dead Li” can be eliminated owing to the uniform distribution of Li plating, and the average Coulombic efficiency for deposited Li during reversible plating/stripping process is decoupled as high as about 99.5 %. Attributing to the limited Li plating with superior Coulombic efficiency, the LiNi0.5Mn0.3Co0.2O2 | graphite cell achieves a high capacity retention of 80.2 % over 500 cycles. This work sheds a different light on further improving the fast‐charging capability, low‐temperature performance, and energy density of practical lithium‐ion batteries.
The boundary of Li plating in a graphite electrode for safe lithium‐ion batteries is defined. The cell with regulated Li plating exhibits highly reversible Li plating/stripping Coulombic efficiency >99.5 % with superior safety performance, offering a strategy to achieve safe high‐energy fast‐charging lithium‐ion batteries.
Lithium (Li) metal anodes hold great promise for next‐generation high‐energy‐density batteries, while the insufficient fundamental understanding of the complex solid electrolyte interphase (SEI) is ...the major obstacle for the full demonstration of their potential in working batteries. The characteristics of SEI highly depend on the inner solvation structure of lithium ions (Li+). Herein, we clarify the critical significance of cosolvent properties on both Li+ solvation structure and the SEI formation on working Li metal anodes. Non‐solvating and low‐dielectricity (NL) cosolvents intrinsically enhance the interaction between anion and Li+ by affording a low dielectric environment. The abundant positively charged anion–cation aggregates generated as the introduction of NL cosolvents are preferentially brought to the negatively charged Li anode surface, inducing an anion‐derived inorganic‐rich SEI. A solvent diagram is further built to illustrate that a solvent with both proper relative binding energy toward Li+ and dielectric constant is suitable as NL cosolvent.
The introduction of cosolvents with non‐solvating and low‐dielectricity (NL) properties can intrinsically enhance the interaction between anion and Li+ and regulate the solvation structures in electrolytes, which favors an upgraded anion‐derived solid electrolyte interphase (SEI) on lithium metal anodes.
A series of supramolecular assemblies of types Ag8(L)4(PF6)8 and Ag4(L)2(PF6)4, obtained from the tetraphenylethylene (TPE) bridged tetrakis(1,2,4‐triazolium) salts H4‐L(PF6)4 and AgI ions, is ...described. The assembly type obtained dependends on the N‐wingtip substituents of H4‐L(PF6)4. Changes in the lengths of the N4‐wingtip substituents enables controlled formation of assemblies with either Ag4(L)2(PF6)4 or Ag8(L)4(PF6)8 stoichiometry. The molecular structures of selected Ag8(L)4(PF6)8 and Ag4(L)2(PF6)4 assemblies were determined by X‐ray diffraction analyses. While H4‐L(PF6)4 does not exhibit fluorescence in solution, their tetra‐NHC (NHC=N‐heterocyclic carbene) assemblies do upon NHC–metal coordination. Upon irradiation, all assemblies undergo a light‐induced, supramolecule‐to‐supramolecule structural transformation by an oxidative photocyclization involving phenyl groups of the TPE core, resulting in a significant change of the luminescence properties.
Silver links: Tetrakis(1,2,4‐triazolium) salts H4‐L(PF6)4, featuring different N4 substituents, react with Ag2O to give, depending on the length of the N4 alkyl substituent, tetranuclear metallo‐supramolecular assemblies of type Ag4(L)2(PF6)4 or octanuclear assemblies of type Ag8(L)4(PF6)8. Both types of assemblies, upon irradiation, undergo oxidative photocyclization of the central tetrakisarylethylene unit to yield the complexes with a 9,10‐phenyl‐substituted phenanthrene bridge.
A tetrakis(bisurea)‐decorated tetraphenylethene (TPE) ligand (L2) was designed, which, upon coordination with phosphate ions, displays fluorescence “turn‐on” over a wide concentration range, from ...dilute to concentrated solutions and to the solid state. The fluorescence enhancement can be attributed to the restriction of the intramolecular rotation of TPE by anion coordination. The crystal structure of the A4L2 (A=anion) complex of L2 with monohydrogen phosphate provides direct evidence for the coordination mode of the anion. This “anion‐coordination‐induced emission” (ACIE) is another approach for fluorescence turn‐on in addition to aggregation‐induced emission (AIE).
Phosphate ions in a bind: The tetrakis(bisurea)‐decorated tetraphenylethene (TPE) displays fluorescence “turn‐on” over a wide concentration range upon phosphate coordination. The fluorescence enhancement can be attributed to the restriction of the intramolecular rotation of TPE by anion coordination. This “anion‐coordination‐induced emission” (ACIE) is another approach for fluorescence turn‐on.
Liquid crystalline network (LCN) actuator normally deforms upon thermally or optically induced order-disorder phase transition, switching once between two shapes (shape 1 in LC phase and shape 2 in ...isotropic state) for each stimulation on/off cycle. Herein, we report an LCN actuator that deforms from shape 1 to shape 2 and then reverses the deformation direction to form shape 3 on heating or under light only, thus completing the shape switch twice for one stimulation on/off cycle. The deformation reversal capability is obtained with a monolithic LCN actuator whose two sides are made to start deforming at different temperatures and exerting different reversible strains, by means of asymmetrical crosslinking and/or asymmetrical stretching. This desynchronized actuation strategy offers possibilities in developing light-fueled LCN soft robots. In particular, the multi-stage bidirectional shape change enables multimodal, light-driven locomotion from the same LCN actuator by simply varying the light on/off times.
Lithium (Li) metal has been considered a promising anode for next‐generation high‐energy‐density batteries. However, the low reversibility and intricate Li loss hinder the widespread implementation ...of Li metal batteries. Herein, we quantitatively differentiate the dynamic evolution of inactive Li, and decipher the fundamental interplay among dynamic Li loss, electrolyte chemistry, and the structure of the solid electrolyte interphase (SEI). The actual dominant form in inactive Li loss is practically determined by the relative growth rates of dead Li0 and SEI Li+ because of the persistent evolution of the Li metal interface during cycling. Distinct inactive Li evolution scenarios are disclosed by ingeniously tuning the inorganic anion‐derived SEI chemistry with a low amount of film‐forming additive. An optimal polymeric film enabler of 1,3‐dioxolane is demonstrated to derive a highly uniform multilayer SEI and decreased SEI Li+/dead Li0 growth rates, thus achieving enhanced Li cycling reversibility.
The fundamental interplay among Li dynamic loss behavior, electrolyte composition, and the structure of the solid electrolyte interphase (SEI) layer was quantitatively elucidated. The actual dominant form in inactive Li loss is determined by the relative growth rates of dead Li0 and SEI Li+ as the anode interface undergoes processive evolution during cycling. The mechanistic studies shed fresh light on the interfacial dynamics of the Li‐metal anode.
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