Stable Lithium-Carbon Composite Enabled by Dual-Salt Additives

Lithium metal is regarded as the ultimate negative electrode material for secondary batteries due to its high energy density.However,it suffers from poor cycling stability because of its high reactivity with liquid electrolytes.Therefore,continuous efforts have been put into improving the cycling Coulombic efficiency(CE)to extend the lifespan of the lithium metal negative electrode.Herein,we report that using dual-salt additives of LiPF_(6) and LiNO_(3) in an ether solvent-based electrolyte can significantly improve the cycling stability and rate capability of a Li-carbon(Li-CNT)composite.As a result,an average cycling CE as high as 99.30% was obtained for the Li-CNT at a current density of 2.5 mA cm^(-2) and an negative electrode to positive electrode capacity(N/P)ratio of 2.The cycling stability and rate capability enhancement of the Li-CNT negative electrode could be attributed to the formation of a better solid electrolyte interphase layer that contains both inorganic components and organic polyether.The former component mainly originates from the decomposition of the LiNO_(3) additive,while the latter comes from the LiPF_(6)-induced ring-opening polymerization of the ether solvent.This novel surface chemistry significantly improves the CE of Li negative electrode,revealing its importance for the practical application of lithium metal batteries.

Revisiting the capacity-fading mechanism of P2-type sodium layered oxide cathode materials during high-voltage cycling

P2-type sodium layered oxide cathode (Na_(2/3)Ni_(1/3)Mn_(2/3)O_(2)P2-NNMO) has attracted great attention as a promising cathode material for sodium ion batteries because of its high specific capacity. However, this material suffers from a rapid capacity fade during high-voltage cycling. Several mechanisms have been proposed to explain the capacity fade, including intragranular fracture caused by the P2-O2 phase transion, surface structural change, and irreversible lattice oxygen release. Here we systematically investigated the morphological, structural, and chemical changes of P2-NNMO during high-voltage cycling using a variety of characterization techniques. It was found that the lattice distortion and crystal-plane buckling induced by the P2-O2 phase transition slowed down the Na-ion transport in the bulk and hindered the extraction of the Na ions. The sluggish kinetics was the main reason in reducing the accessible capacity while other interfacial degradation mechanisms played minor roles. Our results not only enabled a more complete understanding of the capacity-fading mechanism of P2-NNMO but also revealed the underlying correlations between lattice doping and the moderately improved cycle performance.

Engineering Pt heterogeneous catalysts for accelerated liquid–solid redox conversion in Li-S batteries

The shuttle effect caused by soluble lithium polysulfides (LiPSs) deteriorates multiphase transformation reaction kinetics of sulfur species,and gives rise to an unserviceable lithium-sulfur (Li-S) battery.Catalysis,as a process optimization approach,offers an option to eliminate the intrinsic issues.However,exploring and understanding the role of catalysts on electrode reaction remains critical bottlenecks,particularly as they are prone to continuous evolution under complex dynamic environment.Herein,platinum nanoparticles loaded on MXene nanosheets,as sulfur host,and the action of catalysts on the reaction process are investigated via ex-situ monitors upon solid–liquid–solid chemical transformation of sulfur species.These traces confirm that the high performance originates from electron transfer between catalysts and LiPSs,which lowers the nucleation barrier from liquid LiPSs to solid Li_(2)S/Li_(2)S_(2).Further,the accelerated liquid–solid conversion can alleviate the accumulation of LiPSs,and boost the reaction kinetics in Li-S batteries.The findings corroborate the electronic modulation between catalysts and LiPSs,which is a generalizable strategy to optimize energy conversion efficiency of Li-S batteries.

Quantitative measurement of the charge carrier concentration using dielectric force microscopy

The charge carrier concentration profile is a critical factor that determines semiconducting material properties and device performance.Dielectric force microscopy(DFM)has been previously developed to map charge carrier concentrations with nanometer-scale spatial resolution.However,it is challenging to quantitatively obtain the charge carrier concentration,since the dielectric force is also affected by the mobility.Here,we quantitative measured the charge carrier concentration at the saturation mobility regime via the rectification effect-dependent gating ratio of DFM.By measuring a series of n-type GaAs and GaN thin films with mobility in the saturation regime,we confirmed the decreased DFM-measured gating ratio with increasing electron concentration.Combined with numerical simulation to calibrate the tip–sample geometry-induced systematic error,the quantitative correlation between the DFM-measured gating ratio and the electron concentration has been established,where the extracted electron concentration presents high accuracy in the range of 4×10^(16)–1×10^(18)cm^(-3).We expect the quantitative DFM to find broad applications in characterizing the charge carrier transport properties of various semiconducting materials and devices.

CO_(2)electrolysis:Advances and challenges in electrocatalyst engineering and reactor design

Electrochemical reduction of CO_(2)(CO_(2)RR)coupled with renewable electrical energy is an attractive way of upgrading CO_(2)to value-added chemicals and closing the carbon cycle.However,CO_(2)RR electrocatalysts still suffer from high overpotential,and the complex reaction pathways of CO_(2)RR often lead to mixed products.Early research focuses on tuning the binding of reaction intermediates on electrocatalysts,and recent efforts have revealed that the design of electrolysis reactors is equally important for efficient and selective CO_(2)RR.In this review,we present an overview of recent advances and challenges toward achieving high activity and high selectivity in CO_(2)RR at ambient conditions,with a particular focus on the progress of CO_(2)RR electrocatalyst engineering and reactor design.Our discussion begins with three types of electrocatalysts for CO_(2)RR(noble metalbased,none-noble metal-based,and metal-free electrocatalysts),and then we examine systems-level strategies toward engineering specific components of the electrolyzer,including gas diffusion electrodes,electrolytes,and polymer electrolyte membranes.We close with future perspectives on catalyst development,in-situ/operando characterization,and electrolyzer performance evaluation in CO_(2)RR studies.

Solid polymer electrolyte-based high areal capacity all-solid-state batteries enabled with ceramic interlayers

Solid polymer electrolytes(SPEs)based all-solid-state batteries(ASSBs)have attracted extensive attention as a promising candidate for next-generation energy storage systems.Typical ASSBs require high fabrication pressure to achieve high areal capacity,under which,however,SPEs struggle and risk damage or failure due to their low mechanical strength.There is also a lack of study on complex stress and strain SPEs experience during ASSB cell assembly processes.Here,ceramic solid electrolytes are selected as interlayers to address the stress-strain conditions during assembling.As a result,high areal capacity ASSBs with a LiCoO2 loading of 12 mg·cm^(-2) were assembled with SPE-based composite electrolytes.Around 200 cycles were carried out for these cells at a current density of 1 mA·cm^(-2) under room temperature.The capacity decay of the battery at 200 cycles is observed to be as low as 0.06% per cycle.This work identifies a critical issue for application of SPEs in ASSBs and provides a potential strategy for the design of SPE-based ASSBs with high specific energy and long cycle life.

Review—Lithium Carbon Composite Material for Practical Lithium Metal Batteries

Comprehensive Summary Lithium(Li)metal is considered ideal for high-energy-density batteries due to its extremely high specific capacity and low electrochemical potential.However,uncontrolled Li dendrite growth and interfacial instability during repeated Li plating/stripping have limited the practical applicability of Li metal batteries(LMBs).Over the past decades,substantial efforts have been devoted to solving the challenges associated with Li metal anodes.Our research team has developed several Li-carbon(Li-C)microsphere composites in recent years to suppress the formation of Li dendrites and achieve a decent cycle life.In this account,we summarize our advances in the design and application of Li-C composites,which include the developments in the structure and chemical composition of high-specific-capacity Li-C composites,strategies for surface passivation of the micro-spherical Li-C composites,and applications of the Li-C composite in next-generation high-energy-density Li-ion,Li-air,and solid-state LMBs.Finally,we discuss future perspectives for developing high-performance Li metal anodes and endeavors to realize the practical applications of LMBs.

Moisture stable and ultrahigh-rate Ni/Mn-based sodium-ion battery cathodes via K^(+)decoration

As one of the most promising cathodes for sodium-ion batteries(SIBs),the layered transition metal oxides have attracted great attentions due to their high specific capacities and facile synthesis.However,their applications are still hindered by the problems of poor moisture stability and sluggish Na^(+)diffusion caused by intrinsic structural Jahn–Teller distortion.Herein,we demonstrate a new approach to settle the above issues through introducing K^(+)into the structures of Ni/Mn-based materials.The physicochemical characterizations reveal that K^(+)induces atomic surface reorganization to form the birnessite-type K_(2)Mn_(4)O_(8).Combining with the phosphate,the mixed coating layer protects the cathodes from moisture and hinders metal dissolution into the electrolyte effectively.Simultaneously,K^(+)substitution at Na site in the bulk structure can not only widen the lattice-spacing for favoring Na^(+)diffusion,but also work as the rivet to restrain the grain crack upon cycling.The as achieved K^(+)-decorated P2-Na_(0.67)Mn_(0.75)Ni_(0.2)5O_(2)(NKMNO@KM/KP)cathodes are tested in both coin cell and pouch cell configurations using Na metal or hard carbon(HC)as anodes.Impressively,the NKMNO@KM/KP||Na half-cell demonstrates a high rate performance of 50 C and outstanding cycling performance of 90.1%capacity retention after 100 cycles at 5 C.Furthermore,the NKMNO@KM/KP||HC fullcell performed a promising energy density of 213.9 Wh·kg^(−1).This performance significantly outperforms most reported state-ofthe-art values.Additionally,by adopting this strategy on O3-NaMn_(0.5)Ni_(0.5)O_(2),we further proved the universality of this method on layered cathodes for SIBs.

Highly stable lithium anode enabled by self-assembled monolayer of dihexadecanoalkyl phosphate

Li has been considered as the ultimate anode material for high energy density secondary Li batteries.However,its practical application has been limited due to its low Coulombic efficiency(CE)and the formation of lithium dendrites.Recently,we have developed a microspherical Li-carbon nanotube(Li-CNT)composite material passivated with octadecylphosphonic acid(OPA)self-assembled monolayer(SAM)exhibiting suppressed lithium dendrite formation and improved environmental/electrochemical stability.In this work,we demonstrated the significantly enhanced passivation effects of a SAM using dihexadecanoalkyl phosphate(DHP),a molecule that is comprised of double hydrophobic alkyl chains and forms a denser SAM on surfaces with large curvature.As a result,the DHP SAM delivers superior environmental and electrochemical stability to the OPA passivated Li-CNT material.In specific,the DHP passivated Li-CNT composite(DHP-Li-CNT)delivers a high CE of 99.25%under a 33.3%depth of discharge(DOD)at 1 C,when it is paired with a LiFePO4 cathode.The evolution of the SAM during cycling and the effects of DOD and current density on the CE of the DHP-Li-CNT anode have also been investigated.The improved SAM passivation constitutes an important step in achieving the goal of practically applicable Li anodes.

The structure-performance correlation of bulk-heterojunction organic solar cells with multi-length-scale morphology

We build a general multi-length-scale morphology model with mixing phase and pure phase fibril structure,and simulate corresponding organic solar cells performance.Systematical multi-length-scale morphology optimization process by changing the proportion of mixing phase and pure phase in different period width cases shows a clear correlation between period width and device performance that a smaller period width with appropriate proportion of mixing phase and fibril structure is advantageous to achieve high-performance devices.Experiments on multiple donor/acceptor blends have been carried out by varying the composition and processing condition,which afford good structure-performance correlation that supports the model prediction.It is demonstrated that building such a multi-length-scale morphology merging the synergistic effects of mixing and pure phases is indeed an imperative avenue to improve device efficiency.

Unraveling the Effect of Solvent Additive and Fullerene Component on Morphological Control in Organic Solar Cells

The manipulation of the morphology of the active layers is crucial for improving the performance of organic photovoltaic(OPV)devices. In particular, the development of non-fullerene acceptors(NFAs) has led to a large number of new materials with more complex interactions. Therefore, the investigation on the morphology control mechanism is the key aspect in providing guidance for material design and device optimization. In this study, the film morphology optimization using 1,8-diiodooctane(DIO) additive and a ternary fullerene acceptor strategy have been carried out based on the PCE10:ITIC blends. It is seen that suitable amount of DIO helps to increase the crystallization of the blended thin film. However, excessive DIO elevates the crystallization-induced phase separation and the domain size can exceed the exciton diffusion length, leading to efficiency drop. The addition of fullerene acceptor can improve the carrier transport of the blends, and its presence could retard the excessive phase separation induced by DIO additive. Under the joint optimization of the solvent additive and PCBM acceptor,the film morphology achieves a balance between crystallization and phase separation scales, the exciton diffusion and carrier transport are also optimized, and the short-circuit current(JSC) and fill factor(FF) of the device can be improved significantly.

Atomic-resolution characterization on the structure of strontium doped barium titanate nanoparticles

Ferroelectric barium titanate nanoparticles(BTO NPs)may play critical roles in miniaturized passive electronic devices such as multi-layered ceramic capacitors.While increasing experimental and theoretical understandings on the structure of BTO and doped BTO have been developed over the past decade,the majority of the investigation was carried out in thin-film materials;therefore,the doping effect on nanoparticles remains unclear.Especially,doping-induced local composition and structure fluctuation across single nanoparticles have yet to be unveiled.In this work,we use electron microscopy-based techniques including high-angle annular dark-field scanning transmission electron microscopy(HAADF-STEM),integrated differential phase contrast(iDPC)-STEM,and energy dispersive X-ray spectroscopy(EDX)mapping to reveal atomically resolved chemical and crystal structure of BTO and strontium doped BTO nanoparticles.Powder X-ray diffraction(PXRD)results indicate that the increasing strontium doping causes a structural transition from tetragonal to cubic phase,but the microscopic data validate substantial compositional and microstructural inhomogeneities in strontium doped BTO nanoparticles.Our work provides new insights into the structure of doped BTO NPs and will facilitate the materials design for next-generation high-density nano-dielectric devices.

Chemical Electron Microscopy(CEM)for Heterogeneous Catalysis at Nano:Recent Progress and Challenges

Chemical electron microscopy(CEM),a toolbox that comprises imaging and spectroscopy techniques,provides dynamic morphological,structural,chemical,and electronic information about an object in chemical environment under conditions of observable performance.CEM has experienced a revolutionary improvement in the past years and is becoming an effective characterization method for revealing the mechanism of chemical reactions,such as catalysis.Here,we mainly address the concept of CEM for heterogeneous catalysis in the gas phase and what CEM could uniquely contribute to catalysis,and illustrate what we can know better with CEM and the challenges and future development of CEM.

Enhancing the Intermolecular Interactions of Ladder-Type Heteroheptacene-Based Nonfullerene Acceptors for Efficient Polymer Solar Cells by Incorporating Asymmetric Side Chains

Asymmetric nonfullerene acceptors(NFAs)possess larger dipole moments and stronger intermolecular bonding energy than their symmetric counterparts thereby making them promising candidates for high-performance polymer solar cells(PSCs).Herein,we report twoefficient acceptor–donor–acceptor(A–D–A)type NFAs(M14 and M18)with asymmetric side chains that show enhanced intermolecular interactions compared with their corresponding counterparts(M17 and M19)based on symmetric side chains.Furthermore,M14 and M18 exhibit elevated lowest unoccupiedmolecular orbitals and smallerπ–πstacking distances in comparison with M17 and M19,respectively.In combination with the benchmark polymer donor of PM6,the PM6:M14 blend affords superior charge transport properties,and more importantly,an increased power conversion efficiency(PCE)of 15.49%in comparison with the M17-based counterpart(13.01%PCE).Similarly,the asymmetric M18-based blend also shows a higher PCE of 13.00%than the M19-based blend(11.55%).Through further interface engineering,the bestperforming M14-based device delivers an enhanced PCE of 16.46%,which represents a record value among all asymmetric A–D–A type NFAs.Our results provide new insights into the design of asymmetric NFAs with enhanced intermolecular interactions for highperformance PSCs.