Encapsulation strategies are widely used for alleviating dissolution and diffusion of polysulfides, but they experience nonrecoverable structural failure arising from the repetitive severe volume change during lithium−sulfur battery cycling. Here we report a methodology to construct an electrochemically recoverable protective layer of polysulfides using an electrolyte additive. The additive nitrogen-doped carbon dots maintain their "dissolved" status in the electrolyte at the full charge state, and some of them function as active sites for lithium sulfide growth at the full discharge state. When polysulfides are present amid the transition between sulfur and lithium sulfide, nitrogen-doped carbon dots become highly reactive with polysulfides to form a solid and recoverable polysulfide-encapsulating layer. This design skilfully avoids structural failure and efficiently suppresses polysulfide shuttling. The sulfur cathode delivers a high reversible capacity of 891 mAh g −1 at 0.5 C with 99.5% coulombic efficiency and cycling stability up to 1000 cycles at 2 C.

A discrete beam transfer matrix method is introduced to enhance the existing approaches for the static and dynamic compliance solutions of curved-axis flexure hinges with variable curvatures and nonuniform profiles. An idea of discretizing curved-axis flexure hinges as a series of constant beam segments parallel to the centroidal axis is developed. As a result, only a concise beam transfer matrix with decoupled longitudinal and transverse components is needed to establish the compliance model. A step-by-step modeling procedure with simple formulas is provided as well qualifying for curved-axis and folded hinges. With this modeling idea, the small-deflection compliance matrix in the common sense of statics and particularly in a viewpoint of frequency-dependent dynamics can be simultaneously obtained. A typical curved-axis flexure hinge available in literature is analyzed and compared as a study case. In addition, the static and dynamic design for a compliant guiding mechanism comprised of folded flexure hinges is efficiently implemented as a case study.

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Ongoing interests in high-speed precision actuation continuously sparks great attention on developing fast amplified piezoelectric actuators (APAs) with compliant mechanisms. A new type of APA with enhanced resonance frequency is herein reported based on a hybrid compliant amplifying mechanism. A two-stage displacement flexure amplifier is proposed by synthesizing the lever-type and semi bridge-type compliant mechanisms in a compact configuration, promising to a well tradeoff between the displacement amplification ratio and dynamic bandwidth. The static and dynamic performances are experimentally evaluated. The resonance frequency of 2.1 kHz, displacement amplification ratio of 6, and step response time of around 0.4 ms are realized with a compact size of 50 mm × 44 mm × 7 mm. Another contribution of this paper is to develop a comprehensive two-port dynamic stiffness model to predict the static and dynamic behaviors of the compliant amplifier. The modeling approach presented here differs from previous studies in that it enables the traditional transfer matrix method to formulate both the kinetostatics and dynamics of compliant mechanisms including serial-parallel branches and rigid bodies.