查看更多>>摘要：Energy density can be substantially raised and even maximized if the bulk of an electrode material is fully utilized.Transition metal oxides based on conversion reaction mechanism are the imperative choice due to either constructing nanostructure or intercalation pseudocapacitance with their intrinsic limitations.However,the fully bulk utilization of transition metal oxides is hindered by the poor understanding of atomic-level conversion reaction mechanism,particularly it is largely missing at clarifying how the phase transformation(conversion reaction)determines the electrochemical performance such as power density and cyclic stability.Herein,α-Fe2O3 is a case provided to claim how the diffusional and diffusionless transformation determine the electrochemical behaviors,as of its conversion reaction mechanism with fully bulk utilization in alkaline electrolyte.Specifically,the discharge product α-FeOOH diffusional from Fe(OH)2 is structurally identified as the atomic-level arch criminal for its cyclic stability deterioration,whereas the counterpart δ-FeOOH is theoretically diffusionless-like,unlocking the full potential of the pseudocapacitance with fully bulk utilization.Thus,such pseudocapacitance,in proof-of-concept and termed as conversion pseudocapacitance,is achieved via diffusionless-like transformation.This work not only provides an atomic-level perspective to reassess the potential electrochemical performance of the transition metal oxides electrode materials based on conversion reaction mechanism but also debuts a new paradigm for pseudocapacitance.
查看更多>>摘要：Smart construction of battery-type anodes with high rate and good mechanical properties is significant for advanced sodium ion capacitors(SICs).Herein,a flexible film consisting of MoO2 subnanoclusters encapsulated in nitrogen-doped carbon nanofibers(MoO2 SCs@N-CNFs)is designed and synthesized via electrospinning toward SICs as anodes.The strong N-Mo interaction guarantees the stable yet uniform dispersion of high loading MoO2 SCs(≈40 wt.％)in the flexible carbonaceous substrate.The sub-nanoscale effect of SCs restrains electrode pulverization and improves the Na+diffusion kinetics,rendering better pseudocapacitance-dominated Na+-storage properties than the nanocrystal counterpart.The MoO2 SCs@N-CNFs paper with mass loadings of 2.2-10.1 mg cm-2 can be directly used as free-standing anode for SICs,which exhibit high reversible gravimetric/areal capacities both in liquid and quasi-solid-state electrolytes.The assembled flexible SICs competitively exhibit exceptional energy density and cycling stability.More significantly,the sub-nanoscale engineering strategy here is promisingly generalized to future electrode design for other electrochemical energy-related applications and beyond.
查看更多>>摘要：We devised a functional form stable composite phase-change materials(PCMs)to achieve a three-dimensional(3D)interconnected porous carbon aerogel structure for encapsulating polyethylene glycol(PEG).A novel homogeneity reinforced carbon aerogel with a well-interconnected porous structure was constructed by combining a flexible carbon resource from biomass guar gum with hard-brittle carbon from polyimide,to overcome severe shrinkage and poor mechanical performance of traditional carbon aerogel.The supporting carbon aerogel-encapsulated PEG produced the novel composite PCMs with good structure stability and comprehensive energy storage performance.The results showed that the composite PCMs displayed a well-defined 3D interconnected structure,and their energy storage capacities were 171.5 and 169.5 J/g,which changed only slightly after 100 thermal cycles,and the composites could maintain the equilibrium temperature at 50.0-58.1 ℃ for about 760.3 s.The thermal conductivity of the composites could reach 0.62 W m-1 K-1,which effectively enhanced the thermal response rate.And the composite PCMs exhibited good leakage-proof performance and excellent light-thermal conversion.The compressive strength of the composite PCMs can improve up to 1.602 MPa.Results indicate that this strategy can be efficiently used to develop novel composite PCMs with improved comprehensive thermal performance and high light-thermal conversion.
查看更多>>摘要：The lithium dendrite and parasitic reactions are two major challenges for lithium(Li)metal anode—the most promising anode materials for high-energy-density batteries.In this work,both the dendrite and parasitic reactions that occurred between the liquid electrolyte and Li-metal anode could be largely inhibited by regulating the Li+-solvation structure.The saturated Li+-solvation species exist in commonly used LiPF6 liquid electrolyte that needs extra energy to desolvation during Li-electrodeposition.Partial solvation induced high-energy state Li-ions would be more energy favorable during the electron-reduction process,dominating the competition with solvent reduction reactions.The Li-symmetric cells that are cycling at higher temperatures show better performance;the cycled lithium metal anode with metallic lustre and the dendrite-free surface is observed.Theoretical calculation and experimental measurements reveal the existence of high-energy state Li+-solvates species,and their concentration increases with temperature.This study provides insight into the Li+-solvation structure and its electrodeposition characteristics.
查看更多>>摘要：Metallic tin(Sn)foil is a promising candidate anode for lithium-ion batteries(LIBs)due to its metallurgical processability and high capacity.However,it suffers low initial Coulombic efficiency and inferior cycling stability due to its uneven alloying/dealloying reactions,large volume change and stress,and fast electrode structural degradation.Herein,we report an undulating LiSn electrode fabricated by a scalable two-step procedure involving mechanical lithography and chemical prelithiation of Sn foil.With the combination of experimental measurements and chemo-mechanical simulations,it was revealed the obtained undulating LiSn/Sn electrode could ensure better mechanical stability due to the pre-swelling state from Sn to LixSn and undulating structure of lithography in comparison with plane Sn,homogenize the electrochemical alloying/dealloying reactions due to the activated surface materials,and compensate Li loss during cycling due to the introduction of excess Li from LixSn,thus enabling enhanced electrochemical performance.Symmetric cells consisting of undulating LiSn/Sn electrode with an active thickness of～5 um displayed stable cycling over 1000 h at 1 mA cm-2 and 1 mAh cm-2 with a low average overpotential of ＜15 mV.When paired with commercial LiNi0.6Co0.2Mn0.2O2(NCM622)cathode with high mass loading of 15.8 mg cm-2,the full cell demonstrated a high capacity of 2.4 mAh cm-2 and outstanding cycling stability with 84.9％capacity retention at 0.5 C after 100 cycles.This work presents an advanced LiSn electrode with stress-regulation design toward high-performance LIBs,and sheds light on the rational electrode design and processing of other high-capacity lithium alloy anodes.
查看更多>>摘要：Electrocatalytic N2 reduction reaction(NRR)represents an appealing solution for sustainable ammonia production,whereas exploring high-efficiency NRR catalysts is highly desired but extremely challenging.Herein,we combine Ti3C2Tx-MXene quantum dots(MQDs)with porous Cu nanosheets to design a novel heterostructured MQDs/Cu as an effective and durable NRR catalyst.Impressively,MQDs/Cu showed a synergistically enhanced NRR activity with an NH3 yield of 78.5 μg h-1 mg-1(-0.5 V)and a Faradaic efficiency of 21.3％(-0.4 V),far superior to pure MQDs and Cu,and outperforming the majority of the state-of-the-art NRR catalysts.Density function theory computations demonstrated that the synergy of MQDs and Cu enabled the creation of interfacial Cu-Ti dimer as dual-active-centers to strongly activate the absorbed N2 and promote the*N2H formation,consequently resulting in the much reduced energy barriers and greatly enhanced NRR performance.
查看更多>>摘要：Carbyne delivers various excellent properties for the existence of the larger number of sp-hybridized carbon atoms.Here,a 3D well-defined porous carbon material germanium-carbdiyne(Ge-CDY)which is comprised of only sp-hybridized carbon atoms bridging by Ge atoms has been developed and investigated.The unique diamond-like structure constructed by linear butadiyne bonds and sp3-hybridized Ge atoms ensures the stability of Ge-CDY.The large percentage of conjugated alkyne bonds composed of sp-C guarantees the good conductivity and the low band gap,which were further confirmed experimentally and theoretically,endowing Ge-CDY with the potential in electrochemical applications.The well-defined 3D carbon skeleton of Ge-CDY provides abundant uniform nanopores,which is suitable for metal ions storage and diffusion.Further half-cell evaluation also demonstrated Ge-CDY exhibited an excellent performance in lithium storage.All those indicating sp-hybridized carbon-based materials can exhibit great potential to possess excellent properties and be applied in the field of energy,electronic,and so on.
查看更多>>摘要：LiNi0.5Co0.2Mn0.3O2 is extensively researched as one of the most widely used commercially materials for Li-ion batteries at present.However,the poor high-voltage performance(≥4.3 V)with low reversible capacity limits its replacement for LiCoO2 in high-end digital field.Herein,three-in-one modification,Na-doping and Al2O3@Li3BO3 dual-coating simultaneously,is explored for single-crystalline LiNi0.5Co0.2Mn0.3O2(N-NCM@AB),which exhibits excellent high-voltage performance.N-NCM@AB displays a discharge-specific capacity of 201.8 mAh g-1 at 0.2 C with a high upper voltage of 4.6 V and maintains 158.9 mAh g-1 discharge capacity at 1 C over 200 cycles with the corresponding capacity retention of 87.8％.Remarkably,the N-NCM@AB llgraphite pouch-type full cell retains 81.2％of its initial capacity with high working voltage of 4.4 V over 1600 cycles.More importantly,the fundamental understandings of three-in-one modification on surface morphology,crystal structure,and phase transformation of N-NCM@AB are clearly revealed.The Na+doped into the Li-O slab can enhance the bond energy,stabilize the crystal structure,and facilitate Li+transport.Additionally,the interior surface layer of Li+-ions conductor Li3BO3 relieves the charge transfer resistance with surface coating,whereas the outer surface Al2O3 coating layer is beneficial for reducing the active materials loss and alleviating the electrode/electrolyte parasite reaction.This three-in-one strategy provides a reference for the further research on the performance attenuation mechanism of NCM,paving a new avenue to boost the high-voltage performance of NCM cathode in Li-ion batteries.
查看更多>>摘要：Low-cost and flexible solid polymer electrolytes are promising in all-solid-state Li-metal batteries with high energy density and safety.However,both the low room-temperature ionic conductivities and the small Li+transference number of these electrolytes significantly increase the internal resistance and overpotential of the battery.Here,we introduce Gd-doped CeO2 nanowires with large surface area and rich surface oxygen vacancies to the polymer electrolyte to increase the interaction between Gd-doped CeO2 nanowires and polymer electrolytes,which promotes the Li-salt dissociation and increases the concentration of mobile Li ions in the composite polymer electrolytes.The optimized composite polymer electrolyte has a high Li-ion conductivity of 5 × 10-4 S cm-1 at 30 ℃ and a large Li+transference number of 0.47.Moreover,the composite polymer electrolytes have excellent compatibility with the metallic lithium anode and high-voltage LiNi0.8Mn0.1Co0.1O2(NMC)cathode,providing the stable cycling of all-solid-state batteries at high current densities.
查看更多>>摘要：Boron hydrides release an abundant amount of hydrogen in the presence of a suitable catalyst.Accelerating bimolecular activation kinetics is the key to designing cost-effective catalysts for borohydride hydrolysis.In this study,the bimolecular activation of a polar O-Co-P site demonstrated superior hydrogen-generation kinetics(turnover frequency,TOF=37 min-1,298 K)and low activation energy(41.0 kJ mol-1)close to that of noble-metal-based catalysts.Through a combination of experiments and theoretical calculations,it was revealed that the activated dangling oxygen atom in the Co-O precursor effectively replaced via surface-phosphorization because of strong electronic interactions between the dangling oxygen and P atoms.This substitution modulated the local coordination environment and electronegativity around the surface Co sites and formed a new polar O-Co-P active site for optimizing the activation kinetics of ammonia borane and water.This strategy based on bimolecular activation may create new avenues in the field of catalysis.
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