A Dual-Functional Conductive Framework Embedded with TiN-VN Heterostructures for Highly Efficient Polysulfide and Lithium Regulation toward Stable Li–S Full Batteries

Lithium–sulfur (Li–S) batteries are strongly considered as next-generation energy storage systems because of their high energy density. However, the shuttling of lithium polysulfides (LiPS), sluggish reaction kinetics, and uncontrollable Li-dendrite growth severely degrade the electrochemical performance of Li–S batteries. Herein, a dual-functional flexible free-standing carbon nanofiber conductive framework in situ embedded with TiN-VN heterostructures (TiN-VN@CNFs) as an advanced host simultaneously for both the sulfur cathode (S/TiN-VN@CNFs) and the lithium anode (Li/TiN-VN@CNFs) is designed. As cathode host, the TiN-VN@CNFs can offer synergistic function of physical confinement, chemical anchoring, and superb electrocatalysis of LiPS redox reactions. Meanwhile, the well-designed host with excellent lithiophilic feature can realize homogeneous lithium deposition for suppressing dendrite growth. Combined with these merits, the full battery (denoted as S/TiN-VN@CNFs || Li/TiN-VN@CNFs) exhibits remarkable electrochemical properties including high reversible capacity of 1110 mAh g⁻¹ after 100 cycles at 0.2 C and ultralong cycle life over 600 cycles at 2 C. Even with a high sulfur loading of 5.6 mg cm⁻², the full cell can achieve a high areal capacity of 5.5 mAh cm⁻² at 0.1 C. This work paves a new design from theoretical and experimental aspects for fabricating high-energy-density flexible Li–S full batteries.     

In Situ 1D Carbon Chain-Mail Catalyst Assembly for Stable Lithium–Sulfur Full Batteries

The main obstacles for the commercial application of Lithium–Sulfur (Li–S) full batteries are the large volume change during charging/discharging process, the shuttle effect of lithium polysulfide (LiPS), sluggish redox kinetics, and the indisciplinable dendritic Li growth. Especially the overused of metal Li leads to the low utilization of active Li, which seriously drags down the actual energy density of Li–S batteries. Herein, an efficient design of dual-functional CoSe electrocatalyst encapsulated in carbon chain-mail (CoSe@CCM) is employed as the host both for the cathode and anode regulation simultaneously. The carbon chain-mail constituted by carbon encapsulated layer cross-linking with carbon nanofibers protects CoSe from the corrosion of chemical reaction environment, ensuring the high activity of CoSe during the long-term cycles. The Li–S full battery using this carbon chain-mail catalyst with a lower negative/positive electrode capacity ratio (N/P < 2) displays a high areal capacity of 9.68 mAh cm⁻² over 150 cycles at a higher sulfur loading of 10.67 mg cm⁻². Additionally, a pouch cell is stable for 80 cycles at a sulfur loading of 77.6 mg, showing the practicality feasibility of this design.     

Effect of Heterostructure-Modified Separator in Lithium–Sulfur Batteries

Lithium–sulfur (Li–S) batteries with high energy density and low cost are the most promising competitor in the next generation of new energy reserve devices. However, there are still many problems that hinder its commercialization, mainly including shuttle of soluble polysulfides, slow reaction kinetics, and growth of Li dendrites. In order to solve above issues, various explorations have been carried out for various configurations, such as electrodes, separators, and electrolytes. Among them, the separator in contact with both anode and cathode is in a particularly special position. Reasonable design-modified material of separator can solve above key problems. Heterostructure engineering as a promising modification method can combine characteristics of different materials to generate synergistic effect at heterogeneous interface that is conducive to Li–S electrochemical behavior. This review not only elaborates the role of heterostructure-modified separators in dealing with above problems, but also analyzes the improvement of wettability and thermal stability of separators by modification of heterostructure materials, systematically clarifies its advantages, and summarizes some related progress in recent years. Finally, future development direction of heterostructure-based separator in Li–S batteries is given.     

Fatigue lifetime and tearing resistance of AA2198 Al–Cu–Li alloy friction stir welds: Effect of defects

The fatigue strength and failure mechanisms of defect-free (“sound”) and flaw bearing friction stir butt-welds of 3.1 mm-thick AA2198-T8 Al–Li–Cu alloy have been investigated via S–N curves at R = 0.1 using cross weld specimens. The fatigue strength of sound welds is only reduced by 10–15% at the aimed lifetime of 10⁵ cycles compared to the base material. Joint Line Remnant (JLR) bearing welds have a similar fatigue strength as sound welds and the JLR is not the crack initiation site. Kissing Bond (KB) bearing welds that have undergone a weld root polishing show a reduction in fatigue strength by 17% compared to sound welds. For specimens loaded at or above yield strength of the weld nugget the crack systematically initiates from the KB during the first cycle, which is interpreted further using fracture mechanics. The strongest reduction, about 28% in fatigue strength, is found for welds with an initial gap between the parent sheets (GAP welds) along with initiation at intergranular surface microcracks. Kahn tear tests show a reduction in tearing resistance for the flaw bearing welds with a similar ranking as for the fatigue strength.     

单自由度平面闭链机构构型方法的研究

提出了一种关于自由度平面闭链机构的构型方法,即"平面图形构造方法"。利用这种方法进行机构结构综合的主要过程是：先根据机械功能确定运动链的组成成分;再按这些成分构造平面图;最后在平面图上进行机构的构型和变异,并将其中结构最优者转换为机构简图。     

Enhancing Electron Conductivity and Electron Density of Single Atom Based Core–Shell Nanoboxes for High Redox Activity in Lithium Sulfur Batteries

Herein, an integrated structure of single Fe atom doped core-shell carbon nanoboxes wrapped by self-growing carbon nanotubes (CNTs) is designed. Within the nanoboxes, the single Fe atom doped hollow cores are bonded to the shells via the carbon needles, which act as the highways for the electron transport between cores and shells. Moreover, the single Fe atom doped nanobox shells is further wrapped and connected by self-growing carbon nanotubes. Simultaneously, the needles and carbon nanotubes act as the highways for electron transport, which can improve the overall electron conductivity and electron density within the nanoboxes. Finite element analysis verifies the unique structure including both internal and external connections realize the integration of active sites in nano scale, and results in significant increase in electron transfer and the catalytic performance of Fe-N₄ sites in both Li₂S_n lithiation and Li₂S delithiation. The Li–S batteries with the double-shelled single atom catalyst delivered the specific capacity of 702.2 mAh g⁻¹ after 550 cycles at 1.0 C. The regional structure design and evaluation method provide a new strategy for the further development of single atom catalysts for more electrochemical processes.     

奇偶层交错对瓦楞纸板缓冲性能的影响

目的研究在奇偶层交错方式下,交错角度对瓦楞纸板缓冲性能的影响。方法将单瓦楞纸板按奇偶层交错的方式进行多层粘合以制备试样,交错角度分别为0°,30°,45°,60°和90°,采用共面静压、侧向静压和共面冲击的试验方法,对各试样共面和侧向的缓冲性能进行研究。结果与奇偶层不交错的样品相比,在共面静压下,奇偶交错使瓦楞纸板的初始峰应力、平台应力、密实化单位体积变形能和密实化比吸能分别提高了4.15%~9.38%,6.49%~10.39%,5.00%~7.94%和7.43%~10.81%;在沿瓦楞方向侧向静压下,抗压强度和平台应力分别减少了1.18%~14.34%和0.89%~20.66%,密实化比吸能和密实化单位体积变形能与交错角度近似呈二次函数关系。在共面冲击载荷下,当交错角度一定时,总能量吸收与冲击能近似呈一次函数关系。结论奇偶层交错一定角度能改善瓦楞纸板的共面缓冲性能,降低其沿瓦楞方向的侧向缓冲性能。     

Microstructure and mechanical properties of Mg–9Li–3Al–xGd alloys

The influence of gadolinium on the microstructure and mechanical properties of Mg–9Li–3Al alloy was investigated. Results show that the addition of Gd can effectively refine the α-Mg phase and change the morphology of the α-Mg phase. Meanwhile, the Al₃Gd phase is mainly distributed at the boundaries of the α-Mg phase and inside the α-Mg phase. The mechanical property tests reveal that the addition of Gd can effectively improve the mechanical properties of the as cast alloys. When the content of Gd is 2·0%, the tensile strength and yield stress (engineering stress) reach max values of 188 and 174 MPa respectively. When the content of Gd addition is 2·5%, the elongation of the alloy is 15·7%.     

Furnishing Continuous Efficient Bidirectional Polysulfide Conversion for Long-Life and High-Loading Lithium–Sulfur Batteries via the Built-In Electric Field

Most catalysts cannot accelerate uninterrupted conversion of polysulfides, resulting in poor long-cycle and high-loading performance of lithium–sulfur (Li–S) batteries. Herein, rich p-n junction CoS₂/ZnS heterostructures embedded on N-doped carbon nanosheets are fabricated by ion-etching and vulcanization as a continuous and efficient bidirectional catalyst. The p-n junction built-in electric field in the CoS₂/ZnS heterostructure not only accelerates the transformation of lithium polysulfides (LiPSs), but also promotes the diffusion and decomposition for Li₂S the from CoS₂ to ZnS avoiding the aggregation of lithium sulfide (Li₂S). Meanwhile, the heterostructure possesses a strong chemisorption ability to anchor LiPSs and superior affinity to induce homogeneous Li deposition. The assembled cell with a CoS₂/ZnS@PP separator delivers a cycling stability with a capacity decay of 0.058% per cycle at 1.0 C after 1000 cycles, and a decent areal capacity of 8.97 mA h cm⁻² at an ultrahigh sulfur mass loading of 6 mg cm⁻². This work reveals that the catalyst continuously and efficiently converts polysulfides via abundant built-in electric fields to promote Li–S chemistry.     

A High-Performance Li–Mn–O Li-rich Cathode Material with Rhombohedral Symmetry via Intralayer Li/Mn Disordering

The search for new high-performance and low-cost cathode materials for Li-ion batteries is a challenging issue in materials research. Commonly used cobalt- or nickel-based cathodes suffer from limited resources and safety problems that greatly restrict their large-scale application, especially for electric vehicles and large-scale energy storage. Here, a novel Li–Mn–O Li-rich cathode material with symmetry is developed via intralayer Li/Mn disordering in the Mn-layer. Due to the special atomic arrangement and higher symmetry with respect to the C2/m symmetry, the oxygen redox activity is modulated and the Li in the Li-layer is preferentially thermodynamically extracted from the crystal structure instead of Li in the Mn-layer. The as-obtained material delivers a reversible capacity of over 300 mAh g⁻¹ at 25 mA g⁻¹ and rate capability of up to 260 mAh g⁻¹ at 250 mA g⁻¹ within 2.0–4.8 V. The excellent performance is attributed to its highly structural reversibility, mitigation of Jahn–Teller distortion, lower bandgap, and faster Li-ion 2D channels during the lithium-ion de/intercalation process. This material is not only a promising cathode material candidate but also raises new possibilities for the design of low-cost and high-performance cathode materials.