Bimetallic Ni-Co MOF@PAN modified electrospun separator enhances high-performance lithium-sulfur batteries

Lithium-sulfur(Li-S)batteries with high energy density are considered promising energy storage devices for the next generation.Nevertheless,the shuttle effect and the passive layer between the separator and the electrodes still seriously affect the cycle stability and life.Herein,a bimetallic Ni-Co metal-organic framework(MOF)with adsorption and catalytic synergism for polysulfides was successfully synthesized as an electrospinning separator sandwich for Li-S batteries.Introducing porous Ni-Co MOF coatings into the separator provides more adsorption catalytic sites for polysulfides,prevents their diffusion to the anode,and enhances sulfur utilization.Consequently,the improved Li-S batteries with a Ni-Co MOF@PAN(NCMP)electrospun separator delivered excellent rate performance and outstanding cycle stability,yielding an ultra-high initial capacity of 1560 mA h g^(-1)at 0.1 C.Notably,remarkable Li-S battery performance with a discharge capacity of 794 mA h g^(-1)(84.1%capacity retention)was obtained after500 cycles,while delivering a low capacity decay rate of 0.032%during long-term cycling(up to 500cycles)at 1 C.Surprisingly,even at the current density of 2 C,the capacity attenuation rate of 2000 cycles is only 0.034%per cycle.In addition,compared with the Celgard separator,the NCMP separator also had high thermal stability(keeping the separator outline at 200℃)that ensured battery safety and excellent electrolyte wettability(73%porosity and 535%electrolyte absorption)and significantly enhanced the ionic conductivity and Li^(+) transfer number,and protected the surface integrity of the anode.

Influence of overhanging tool length and vibrator material on electromechanical impedance and amplitude prediction in ultrasonic spindle vibrator

This study presents the development of an ultrasonic transducer with a radius horn for an ultrasonic milling spindle(UMS)system.The ultrasonic transducer was intended to have a working frequency of approximately 30 kHz.Two different materials were considered in the study:stainless steel(SS 316L)and titanium alloy(Ti-6Al-4V).Titanium alloy gave a higher resonance frequency(33 kHz)than stainless steel(30 kHz)under the same preload compression stress.An electromechanical impedance simulation was carried out to predict the impedance resonance frequency for both materials,and the effect of the overhanging toolbar was investigated.According to the electromechanical impedance simulation,the overhanging toolbar length affected the resonance frequency,and the error was less than 3%.Harmonic analysis confirmed that the damping ratio helps determine the resonance amplitude.Therefore,damping ratios of 0.015-0.020 and 0.005-0.020 were selected for stainless steel and titanium alloy,respectively,with an error of less than 1.5%.Experimental machining was also performed to assess the feasibility of ultrasonic-assisted milling;the result was a lesser cutting force and better surface topography of Al 6061.

Tribological properties of hierarchical micro-dimples produced on a cylindrical surface by dual-frequency texturing

An experimental investigation was performed for investigating the tribological performance of micro-dimple surface texture patterns on a cylindrical surface in a realistic operating environment of starved lubrication. Micro-dimples were generated by a dual-frequency surface texturing method, in which a high-frequency (16.3 kHz) three-dimensional (3D) vibration and a low-frequency (230 Hz) one-dimensional (1D) vibration were applied at the tool tip simultaneously, resulting in the generation of the hierarchical micro-dimples in a single step. Rotating cylinder-on-pin tribological tests were conducted to compare the tribological performance of the non-textured reference specimen and micro-dimple samples. The effect of surface textures generated with various shape parameters (long drop and short drop), dimension parameters (length and surface texture density), and operation parameters (load and sliding velocity) on the tribological performance was evaluated. Stribeck curves indicate that the hierarchical micro-dimples exhibit a lower coefficient of friction than the reference specimen in the high contact-pressure regions. It is also observed that variation in the length of a micro-dimple, the shape effect, is the major factor affecting the friction response of the textured surfaces. The generation of additional hydrodynamic pressure and lift effect by hierarchical structures is the main reason for the improved performance of hierarchical micro-dimple surfaces.