Integrated Design of Homogeneous/Heterogeneous Copper Complex Catalysts to Enable Synergistic Effects on Sulfur and Lithium Evolution Reactions.

Fatal polysulfide shuttling, sluggish sulfur redox kinetics and detrimental lithium dendrites have curtailed the real discharge capacity, working lifespan and safety of lithium-sulfur (Li-S) batteries. Organic small molecule promotors as one type of emerging active catalysts can fulfil the management of the electrochemical species evolution behaviors. Herein, an integrated engineering is organized by synthesizing dual chlorine-bridge enabled binuclear copper complex (Cu2(phen)2Cl2) and its derivative generated in electrolyte (Cu-ETL) as the heterogeneous and homogeneous catalyst, respectively. The well-designed Cu-ETL with a optimized concentration of 0.25 wt.% as a homogeneous enabler offers highly utilized Cu centers and the sufficient interface contact for guiding the Li2S nucleation/decomposition reactions. The Cu2(phen)2Cl2 loaded on carbon spheres as an interlayer (Cu-INT) can break through the catalytic limitation resulting from the saturated concentration of Cu-ETL and thus offers an extended manipulation effect. Benefiting from the synergistic effect, the Li-S battery shows stable cycling at 3 C upon 500 cycles with a capacity degradation rate as low as 0.029% per cycle. Of specific note, an actual cell energy density of 372.1 Wh kg-1 is harvested by a 1.2 Ah-level soft-packaged pouch cell, implying a chance for requiring the demand of high-energy batteries.

Locally boosted Li2S nucleation on VO2 by loading carbon quantum dots for soft-packaged lithium-sulfur pouch cells.

VO2 affords ultrafast polysulfide adsorption on account of its oxidation potential, which matches the sulfur working window (1.7-2.8 V). Nevertheless, its nonconductive surface limits direct sulfur conversion. Herein, we gently load carbon quantum dots on VO2 to increase direct Li2S nucleation by enhanced electron conductivity. As a result, the soft-packaged lithium-sulfur pouch cell yields a capacity retention of 88.8% at 0.5C after 100 cycles and a decay rate of 0.17% per cycle over 200 cycles at 2C. The cell energy density of the multilayer cell is up to 386.1 W h kg-1.

Coupled Ni─Co Dual-Atom Catalyst for Guiding Sulfur and Lithium Evolutions in Lithium-Sulfur Batteries.

The kinetically retarded sulfur evolution reactions and notorious lithium dendrites as the major obstacles hamper the practical implementation of lithium-sulfur batteries (LSBs). Dual metal atom catalysts as a new model are expected to show higher activity by their rational coupling. Herein, the dual-atom catalyst with coupled Ni─Co atom pairs (Ni/Co-DAC) is designed successfully by programmed approaches. The Ni─Co atom pairs alter the local electron structure and optimize the coordination configuration of Ni/Co-DAC, leading to the coupling effect for promoting the interconversion of sulfur and guiding lithium plating/striping. The LSB delivers a remarkable capacity of 818 mA h g-1 at 3.0 C and a low degeneration rate of 0.053% per cycle over 500 cycles. Moreover, the LSB with a high sulfur mass loading of 6.1 mg cm-2 and lean electrolyte dosage of 6.0 µL mgS -1 shows a remarkable areal capacity of 5.7 mA h cm-2.

An Electrolyte Engineered Homonuclear Copper Complex as Homogeneous Catalyst for Lithium-Sulfur Batteries.

Lithium-sulfur (Li-S) batteries suffer from severe polysulfide shuttle, retarded sulfur conversion kinetics and notorious lithium dendrites, which has curtailed the discharge capacity, cycling lifespan and safety. Engineered catalysts act as a feasible strategy to synchronously manipulate the evolution behaviors of sulfur and lithium species. Herein, a chlorine bridge-enabled binuclear copper complex (Cu-2-T) is in situ synthesized in electrolyte as homogeneous catalyst for rationalizing the Li-S redox reactions. The well-designed Cu-2-T provides completely active sites and sufficient contact for homogeneously guiding the Li2S nucleation/decomposition reactions, and stabilizing the lithium working interface according to the synchrotron radiation X-ray 3D nano-computed tomography, small angle neutron scattering and COMSOL results. Moreover, Cu-2-T with the content of 0.25 wt% approaching saturated concentration in electrolyte further boosts the homogeneous optimization function in really operated Li-S batteries. Accordingly, the capacity retention of the Li-S battery is elevated from 51.4% to 86.3% at 0.2 C, and reaches 77.0% at 1.0 C over 400 cycles. Furthermore, the sulfur cathode with the assistance of Cu-2-T realizes the stable cycling under the practical scenarios of soft-packaged pouch cell and high sulfur loading (6.5 mg cm-2 with the electrolyte usage of 4.5 µL mgS -1).

Chlorine bridge bond-enabled binuclear copper complex for electrocatalyzing lithium-sulfur reactions.

Engineering atom-scale sites are crucial to the mitigation of polysulfide shuttle, promotion of sulfur redox, and regulation of lithium deposition in lithium-sulfur batteries. Herein, a homonuclear copper dual-atom catalyst with a proximal distance of 3.5 Å is developed for lithium-sulfur batteries, wherein two adjacent copper atoms are linked by a pair of symmetrical chlorine bridge bonds. Benefiting from the proximal copper atoms and their unique coordination, the copper dual-atom catalyst with the increased active interface concentration synchronously guide the evolutions of sulfur and lithium species. Such a delicate design breaks through the activity limitation of mononuclear metal center and represents a catalyst concept for lithium-sulfur battery realm. Therefore, a remarkable areal capacity of 7.8 mA h cm-2 is achieved under the scenario of sulfur content of 60 wt.%, mass loading of 7.7 mg cm-2 and electrolyte dosage of 4.8 µL mg-1.

Dual-Functional V2 C MXene Assembly in Facilitating Sulfur Evolution Kinetics and Li-Ion Sieving toward Practical Lithium-Sulfur Batteries.

Lithium-sulfur (Li-S) batteries are considered as one of the most promising candidates to achieve an energy density of 500 Wh kg⁻1 . However, the challenges of shuttle effect, sluggish sulfur conversion kinetics, and lithium-dendrite growth severely obstruct their practical implementation. Herein, multiscale V2 C MXene (VC) with a spherical confinement structure is designed as a high-efficiency bifunctional promotor for the evolution of sulfur and lithium species in Li-S batteries. Combining synchrotron X-ray 3D nano-computed tomography (X-ray 3D nano-CT), small-angle neutron scattering (SANS), and first-principle calculations, it is revealed that the activity of VC can be maximized by tuning the scale, and the as-attained functions are conducted as follows: (i) the VC acts as the efficient lithium polysulfide (LiPS) scavenger due to the large number of active sites; (ii) the VC exhibits significantly improved electrocatalytic function for the Li2 S nucleation and decomposition reaction kinetics owing to the scale effect; and (iii) the VC can regulate the dynamic behavior of Li-ions and thus stabilize the lithium plating/stripping effectively on account of the unique ion-sieving effect.

Nitrogen Balance on Ni-N-C Promotor for High-Energy Lithium-Sulfur Pouch Cells.

The viability of lithium-sulfur (Li-S) batteries toward real implementation directly correlates with unlocking lithium polysulfide (LiPS) evolution reactions. Along this line, designing promotors with the function of synchronously relieving LiPS shuttle and promoting sulfur conversion is critical. Herein, the nitrogen evolution on hierarchical and atomistic Ni-N-C electrocatalyst, mainly pertaining to the essential subtraction, reservation and coordination of nitrogen atoms, is manipulated to attain favorable Li-S pouch cell performances. Such rational evolution behavior realizes the "nitrogen balance" in simultaneously regulating the Ni-N coordination environment, Ni single atom loading, abundant vacancy defects, active nitrogen and electron conductivity, and maximizing the electrocatalytic activity elevation of Ni-N-C system. With such merit, the cathode harvests favorable performances in a soft-packaged pouch cell prototype even under high sulfur mass loading and lean electrolyte usage. A specific energy density up to 405.1 Wh kg-1 is harvested by the 0.5-Ah-level pouch cell.

Manipulating the Li-S reaction kinetics via the V8C7/phosphorus defect-integrated carbon promoter.

V8C7/phosphorus defect-integrated carbon (VPC) is proposed as a dual-function promoter for Li-S chemistry. The well-dispersed V8C7 and phosphorus defects exhibit ample polar sites and remarkable electron conductivity. Such rational integration of dual active centers simultaneously suppresses the shuttle effect and propels the Li-S redox reaction kinetics. Therefore, the S/VPC cathode shows an initial capacity of 1090.0 mA h g-1 and a high retention of 83.5% at 0.2C after 100 cycles and a low decay rate of 0.076% at 2C over 600 cycles.

Phosphorization Engineering on Metal-Organic Frameworks for Quasi-Solid-State Asymmetry Supercapacitors.

Porous carbon and metal oxides/sulfides prepared by using metal-organic frameworks (MOFs) as the precursors have been widely applied to the realm of supercapacitors. However, employing MOF-derived metal phosphides as positive and negative electrode materials for supercapacitors has scarcely been reported thus far. Herein, two types of MOFs are used as the precursors to prepare CoP and FeP4 nanocubes through a two-step controllable heat treatment process. Due to the advantages of composition and structure, the specific capacitances of FeP4 and CoP nanocubes reach 345 and 600 F g-1 at the current density of 1 A g-1 , respectively. Moreover, a quasi-solid-state asymmetric supercapacitor is assembled based on charge matching principle by employing CoP and FeP4 nanocubes as the positive and negative electrodes, respectively, which exhibits a high energy density of 46.38 Wh kg-1 at the power density of 695 W kg-1 . Furthermore, a solar-charging power system is assembled by combining the quasi-solid-state asymmetric supercapacitor and monocrystalline silicon plates, substantiating that the device can power the toy electric fan. This work paves a practical way toward the rational design of quasi-solid-state asymmetry supercapacitors systems affording favorable energy density and long lifespan.

The recovery of nano-sized carbon black filler structure and its contribution to stress recovery in rubber nanocomposites.

The hierarchical structural evolution of natural rubber (NR) filled with different contents of nanoscale carbon black (CB) (10 phr-CB10 and 50 phr-CB50) after first loading and recovering for different times was investigated by X-ray nano-CT, wide-angle X-ray scattering (WAXS) and solid state NMR techniques. The CB filler structures as captured by X-ray nano-CT recover gradually with increasing recovering time, but the filler network with different CB contents shows dramatically different structure evolution. For CB10, limited by the filling content, CB particles mainly induces a hydrodynamic effect in spite of deformation or recovering. For CB50, the CB filler forms a 3D connected network, partially destructed during deformation, and the destructed part can be partially recovered during recovery. This suggests that the connected CB filler structure mainly acts as a network reinforcement, whereas the destructed part can induce a hydrodynamic effect. The different effects induced by different CB filling contents are also reflected by the NR matrix, which is reflected by the onset strains εc of strain-induced crystallization (SIC) of NR as captured by WAXS. For CB10, εc remains almost constant, i.e. εc = ca. 1.49, while that of NR with CB50 slightly decreases from initial ca. 1.12 to 0.96 with increasing recovering time up to 50 h. Also, the bound rubber fraction and entangled rubber network remain unchanged after deformation and under different recovery time as detected by the magic sandwich echo (MSE) FID and proton multiple quantum (MQ) NMR. These results demonstrate the key role of the CB filler network in determining the stress-softening behavior of reinforced rubber.

Structure-controlled Co-Al layered double hydroxides/reduced graphene oxide nanomaterials based on solid-phase exfoliation technique for supercapacitors.

High-efficient nanosheets exfoliation and ordered controlled stacking are in urgent need of work for electrochemistry application. Here, we have developed a high-efficient and environmentally-friendly solid-phase method for the exfoliation of Co-Al layered double hydroxide (Co-Al LDH) and graphene oxide (GO). Meanwhile, we found that there is a dynamic structure evolution in the self-assembly process between Co-Al LDH-NS and GO-NS and new theoretical structure models were proposed. With the reduction treatment, the electrochemical test results show that Co-Al LDH/rGO-3 with ideal tiling structure has better electrochemical performance, which provides a specific capacitance of 1492 F g-1 at 1 A g-1 and remains the capacitance retention at approximately 94.3% after 5000 cycles. Moreover, an energy density of 44.6 Wh kg-1 is obtained at a power density of 799.6 W kg-1. The proposed method and the structure-relationship are practically applicable for other 2D materials in the asymmetric supercapacitors.

Controlled Self-Assembled NiFe Layered Double Hydroxides/Reduced Graphene Oxide Nanohybrids Based on the Solid-Phase Exfoliation Strategy as an Excellent Electrocatalyst for the Oxygen Evolution Reaction.

Layered double hydroxides (LDHs), as an effective oxygen evolution reaction (OER) electrocatalyst, face many challenges in practical applications. The main obstacle is that bulk materials limit the exposure of active sites. At the same time, the poor conductivity of LDHs is also an important factor. Exfoliation is one of the most direct and effective strategies to increase the electrocatalytic properties of LDHs, leading to exposure of many active sites. However, developing an efficient exfoliation strategy to exfoliate LDHs into stable monolayer nanosheets is still challenging. Therefore, we report a new and efficient solid-phase exfoliation strategy to exfoliate NiFe LDH and graphene oxide (GO) into monolayer nanosheets and the exfoliating ratios of NiFe LDH and GO can reach up to 10 and 5 wt %, respectively. Based on the solid-phase exfoliation strategy, we accidentally discovered that there is a dynamic evolution process between NiFe-LDH nanosheets (NiFe-LDH-NS) and GO nanosheets (GO-NS) to assemble new NiFe-LDH/GO nanohybrids, i.e., NiFe-LDH-NS could be horizontal bespreading on GO-NS or well-organized standing on GO-NS, or both simultaneously. The electrocatalytic OER property test results show that NiFe-LDH/RGO-3 (NFRG-3) nanohybrids obtained by the reduction treatment of NiFe-LDH/GO-3 (NFGO-3) nanohybrids, in which NiFe-LDH-NS are well-organized standing on GO-NS, have excellent electrocatalytic properties for OER in an alkaline solution (with a small overpotential of 273 mV and a Tafel slope of 49 mV dec-1 at the current density of 30 mA cm-2). The excellent electrocatalytic properties for OER of NFRG-3 nanohybrids could be attributed to the unique three-dimensional arraylike structure with many active sites. At the same time, reduced graphene oxide (RGO) with excellent conductivity can improve the charge-transfer efficiency and synergistically improve OER properties of nanohybrids.

Thermo Sensitivity of Polysiloxane/Silica Nanocomposites Affected by the Structure of Polymer-Filler Interface.

In this work thermo sensitivity was investigated with the bound rubber theory and thermoelasticity theory of the polymer-filler interface interaction between Polymethylvinylsiloxane (PMVS) and nanofillers (fumed and precipitated silica with the primary particle size of 10 nanometres). Bound rubber (the transition phase between PMVS and silica) content was measured by sol-gel analysis and swelling experiments. Results showed that the amount of bound rubber increases steadily with the increases of filler content. But the increasing rate suddenly decreased at certain silica content (between 40 and 50 phr of precipitated silica and between 30 and 40 phr of fumed silica, respectively), which was constant with the thermoelaticity experiment results. The temperature coefficients in low strain uniaxial extension are found to present sudden changing at the same silica content. This observation shows that thermo sensitivity is closely connected with the structure of polymer-filler interface.