Tackling application limitations of high-safetyγ-butyrolactone electrolytes:Exploring mechanisms and proposing solutions

Developing wide-temperature and high-safety lithium-ion batteries(LIBs)presents significant challenges attributed to the absence of suitable solvents possessing broad liquid range and non-flammability properties.γ-Butyrolactone(GBL)has emerged as a promising solvent;however,its incompatibility with graphite anode has hindered its application.This limitation necessitates a comprehensive investigation into the underlying mechanisms and potential solutions.In this study,we achieve a molecular-level understanding of the perplexing interphase formation process by employing in-situ spectroelectrochemical techniques and density function calculations.Our findings reveal that,even at high salt concentrations,GBL consistently occupies the primary Li^(+)solvation sheath,leading to extensive GBL decomposition and the formation of a high-impedance and inorganic-poor solid-electrolyte interphase(SEI)layer.Contrary to manipulating solvation structures,our research demonstrates that the utilization of filmforming additives with higher reduction potential facilitates the pre-establishment of a robust SEI film on the graphite anode.This approach effectively inhibits GBL decomposition and significantly enhances the battery's lifespan.This study provides the first reported intrinsic understanding of the unique GBLgraphite incompatibility and offers valuable insights for the development of wide-temperature and high-safety LIBs.

Progress in in-situ electrochemical nuclear magnetic resonance for battery research

A thorough understanding of the fundamental electrochemical and chemical processes in batteries is crucial to advancing energy density and power density.However,the characterizations of such processes are complex.In-situ electrochemical nuclear magnetic resonance(EC-NMR)offers the capability to collect real-time data during battery operation,furnishing insights into the local structures and ionic dynamics of materials by monitoring changes in the chemical environment around the nuclei.EC-NMR also has the advantages of being both quantitative and non-destructive.This paper systematically reviews the design of EC-NMR approach,and delves into the applications and progress of EC-NMR concerning battery reaction mechanisms,failure mechanisms,and overall battery systems.The review culminates in a comprehensive summary of the perspective and challenges associated with EC-NMR.

Material design at nano and atomic scale for electrocatalytic CO2 reduction

Electrocatalytic CO2 reduction (ECR) into value-added chemicals offers potential solution for renewable energy as well as global carbon footprint concerns. In this review we introduce the general methods and metrics that are commonly applied in ECR, followed by a discussion of current reaction mechanisms and different pathways. We highlight how size and structure of electrocatalysts affect ECR performance and review recent advances in metalfree and single-atom catalysts. The challenges of ECR are also discussed and optimistic perspectives are made for future work.

Strongly coupled Te-SnS_(2)/MXene superstructure with self-autoadjustable function for fast and stable potassium ion storage

Potassium-ion batteries(PIBs)are a promising candidate for next-generation electric energy storage applications because of the abundance and low cost of potassium.However,the development of PIBs is limited by sluggish kinetics and huge volume expansion of anodes,leading to poor rate capability and cycling stability.Herein,an advanced superstructure anode,including Te-doped SnS_(2) nanosheets uniformly anchored on MXene surface(Te-SnS_(2)/MXene),is rationally designed for the first time to boost K^(+)storage performance.Featuring with strong interface interaction and self-autoadjustable interlayer spacings,the Te-SnS_(2)/MXene can efficiently accelerate electron/ion transfer,accommodate volume expansion,inhibit crack formation,and improve pseudocapacitive contribution during cycling.Thus,the novel Te-SnS_(2)/MXene anode delivers a high reversible capacity(343.2 mAh g^(-1) after 50 cycles at0.2 A g^(-1)),outstanding rate capability(186.4 mAh g^(-1) at 20 A g^(-1)),long cycle stability(165.8 mAh g^(-1)after 5000 cycles at 10 A g^(-1) with a low electrode swelling rate of only 15.4%),and reliable operation in flexible full battery.The present Te-SnS_(2)/MXene becomes among the best transition metal-based anode materials for PIBs reported to date.

Operando X-ray diffraction analysis of the degradation mechanisms of a spinel LiMn2O4 cathode in different voltage windows

The understanding of reaction mechanisms of electrode materials is of significant importance for the development of advanced batteries.The LiMn2O4 cathode has a voltage plateau around 2.8 V(vs.Li^+/Li),which can provide an additional capacity for Li storage,but it suffers from a severe capacity degradation.In this study,operando X-ray diffraction is carried out to investigate the structural evolutions and degradation mechanisms of LiMn2O4 in different voltage ranges.In the range of 3.0-4.3 V(vs.Li^+/Li),the LiMn2O4 cathode exhibits a low capacity but good cycling stability with cycles up to 100 cycles and the charge/discharge processes are associated with the reversible extraction/insertion of Li^+from/into LixMn2O4(0≤x≤1).In the range of 1.4-4.4 V(vs.Li^+/Li),a capacity higher than 200 mAh/g is achieved,but it rapidly decays during the cycling.The voltage plateau around 2.8 V(vs.Li^+/Li)is related to the transformation of the cubic LiMn2O4 phase to the tetragonal Li2Mn2O4 phase,which leads to the formation of cracks as well as the performance degradation.

Understanding oxygen electrochemistry in aprotic Li-O_2 batteries

In the past decade, the aprotic lithium-oxygen(Li-O_2) battery has generated a great deal of interest because theoretically it can store more energy than today's lithium-ion batteries. Although considerable research efforts have been devoted to the R&D of this potentially disruptive technology, many scientific and engineering obstacles still remain to be addressed before a practical device could be realized. In this review, we summarize recent advances in the fundamental understanding of the O_2 electrochemistry in Li-O_2 batteries, including the O_2 reduction to Li_2O_2 on discharge and the reverse Li_2 O_2 oxidation on recharge and factors that exert strong influences on the redox of O_2/Li_2O_2. In addition,challenges and perspectives are also provided for the future study of Li—O_2 batteries.

Confining Li_(2)O_(2) in tortuous pores of mesoporous cathodes to facilitate low charge overpotentials for Li-O_(2) batteries

Achieving low charge overpotentials represents one of the most critical challenges for pursuing highperformance lithium-oxygen(Li-O_(2))batteries.Herein,we propose a strategy to realize low charge overpotentials by confining the growth of lithium peroxide(Li_(2)O_(2))inside mesoporous channels of cathodes(CMK-8).The CMK-8 cathode with tortuous pore structures can extend the diffusion distance of lithium superoxide(LiO_(2))in the mesoporous channels,facilitating the further reduction of LiO_(2) to lithium peroxide(Li_(2)O_(2))inside the pores and preventing them to be diffused out of the pores.Therefore,Li_(2)O_(2) is trapped in the mesoporous channels of CMK-8 cathodes,ensuring a good Li_(2)O_(2)/CMK-8 contact interface.The CMK-8 electrode exhibits a low charge overpotential of 0.43 V and a good cycle life for 72 cycles with a fixed capacity of 500 m Ah g^(-1) at 0.1 A g^(-1).This study proposes a strategy to achieve a low charge overpotential by confining Li_(2)O_(2) growth in the mesoporous channels of cathodes.

Ternary mesoporous cobalt-iron-nickel oxide efficiently catalyzing oxygen/hydrogen evolution reactions and overall water splitting

Among various efficient electrocatalysts for water splitting,CoFe and NiFe-based oxides/hydroxides are typically promising candidates thanks to their extraordinary activities towards oxygen evolution reaction (OER).However,the endeavor to advance their performance towards overall water splitting has been largely impeded by the limited activities for hydrogen evolution reaction (HER).Herein,we present a CoFeNi ternary metal-based oxide (CoFeNi-O) with impressive hierarchical bimodal channel nanostructures,which was synthesized via a facile one-step dealloying strategy.The oxide shows superior catalytic activities towards both HER and OER in alkaline solution due to the alloying effect and the intrinsic hierarchical porous structure.CoFeNi-O loaded on glass carbon electrodes only requires the overpotentials as low as 230 and 278 mV to achieve the OER current densities of 10 and 100 mA·cm-2,respectively.In particular,extremely low overpotentials of 200 and 57.9 mV are sufficient enough for Ni foam-supported CoFeNi-O to drive the current density of 10 mA·cm-2 towards OER and HER respectively,which is comparable with or even better than the already-developed state-of-the-art non-noble metal oxide based catalysts.Benefiting from the bifunctionalities of CoFeNi-O,an alkaline electrolyzer constructed by the Ni foam-supported CoFeNi-O electrodes as both the anode and the cathode can deliver a current density of 10 mA·cm-2 at a fairly low cell-voltage of 1.558 V.In view of its electrocatalytic merits together with the facile and cost-effective dealloying route,CoFeNi-O is envisioned as a promising catalyst for future production of sustainable energy resources.

Enabling an intrinsically safe and high-energy-density 4.5 V-class Li-ion battery with nonflammable electrolyte

Developing nonflammable electrolyte with a wide electrochemical window has become an urgent demand for high-energy-density and high-safe lithium-ion batteries(LIBs).Herein,a fluorinated nonflammable phosphate electrolyte is developed to construct a safe 4.5 V-class LIB(Si-SiC-C/0.35Li2MnO3-0.65LiNi0.5Mn0.5O2).The proposed fluorinated phosphate electrolyte,0.8 M LiPF6/tris(2,2,2-trifluoroethyl)phosphate(TFEP)+5 vol%fluoroethylene carbonate(FEC)+5 vol%vinylene carbonate(VC),is not only completely nonflammable but also exhibits excellent oxidative/reductive stability on 0.35Li2MnO30.65LiNi0.5Mn0.5O2 cathode and Si-SiC-C anode.The in situ differential electrochemical mass spectrometry and X-ray photoelectron spectroscopy proved that TFEP-based electrolyte does not decompose into gases but forms a high-quality electrode-electrolyte interface on cathode surface at high working potential.The 4.5 V-class LIBs using 0.8 M LiPF6 TFEP-based nonflammable electrolyte shed some light on potential application for high-safe and low-cost larger-scale energy storage.

Li_2O_2 oxidation: the charging reaction in the aprotic Li-O_2 batteries

Aprotic Li-O2 battery has attracted a great deal of interest because of its high theoretical energy density that is far beyond what the best Li-ion technologies can achieve.However, the present Li-O2 batteries suffer from the low energy efficiency that is limited mainly by the high overpotentials required to re-oxidize Li2O2, the discharge product. Over the past few years, considerable research efforts have been devoted to the understanding of the Li2O2 oxidation reactions. Here, we summarize the results obtained from the fundamental study of the Li2O2 oxidation, including its morphology, reaction route, kinetics, the initial location upon oxidation and the charge transport within Li2O2. A better mechanistic understanding of the Li2O2 oxidation reaction will provide a solid foundation for the realization of practical Li-O2 cells with a higher energy efficiency.

Tungsten diselenide nanoplates as advanced lithium/ sodium ion electrode materials with different storage mechanisms

Transition-metal dichalcogenides （TMDs） exhibit immense potential as lithium/ sodium-ion electrode materials owing to their sandwich-like layered structures. To optimize their lithium/sodium-storage performance, two issues should be addressed： fundamentally understanding the chemical reaction occurring in TMD electrodes and developing novel TMDs. In this study, WSe2 hexagonal nanoplates were synthesized as lithium/sodium-ion battery （LIB/SIB） electrode materials. For LIBs, the WSe2-nanoplate electrodes achieved a stable reversible capacity and a high rate capability, as well as an ultralong cycle life of up to 1,500 cycles at 1,000 mA·g^-1. Most importantly, in situ Raman spectroscopy, ex situ X-ray diffraction （XRD）, transmission electron microscopy, and electrochemical impedance spectroscopy measurements performed during the discharge-charge process clearly verified the reversible conversion mechanism, which can be summarized as follows： WSe2 ＋ 4Li^＋ ＋ 4e^- ←→ W ＋ 2Li2Se. The WSe2 nanoplates also exhibited excellent cycling performance and a high rate capability as SIB electrodes. Ex situ XRD and Raman spectroscopy results demonstrate that WSe2 reacted with Na^＋ more easily and thoroughly than with Li^＋ and converted to Na2Se and tungsten in the Ist sodiated state. The subsequent charging reaction can be expressed as Na2Se → Se ＋ 2Na^＋＋ 2e^-, which differs from the traditional conversion mechanism for LIBs. To our knowledge, this is the first systematic exploration of the lithium/sodium-storage performance of WSe2 and the mechanism involved.

Intermetallic interphases in lithium metal and lithium ion batteries

A robust electrode-electrolyte interface is the cornerstone for every battery system,as demonstrated in the meandering history of the development of Li-ion batteries(LIBs).In the thrust to replace the graphite anode with more energetic ones in LIBs,the effectual strategy for stabilizing the original graphite-electrolyte interface becomes obsolete and a new anode-electrolyte interface needs reconfiguration.Unfortunately,this interface has become the Achilles'heel for those anodes,such as Li-metal anode(LMA)and Si-based anode owing to their excessive reductivity,enormous volume change,and so forth.Encouragingly,in the last decade,impressive progress has been made on taming these extremely unstable interfaces and on the solid-state batteries(SSBs)that are reported to be less susceptible to parasitic reactions.One of the distinguished strategies is the application of artificial Li-alloying intermetallic interphases onto the surface of LMA,via the direct introduction of foreign metals to the Li anode or indirect hetero-cations doping in the electrolyte,to regulate the Li deposition/stripping behavior,which has markedly improved the stability of the LMA-electrolyte interface.In parallel,the intermetallic interphases are also witnessed to profoundly enhance the anode-solid electrolyte contact and the corresponding charge transfer kinetics in various SSBs.This review will provide a panoramic overview of the application of the intermetallic interphases at the anode-electrolyte interfaces in the lithium metal batteries(LMBs),SSBs,and also derivative works in the conventional LIBs,which will focus on different concepts,methodologies,and understandings from the encircled studies.

Self-supporting, eutectic-like, nanoporous biphase bismuth-tin film for high-performance magnesium storage

Magnesium ion batteries are emerging as promising alternatives to lithium ion batteries because of their advantages including high energydensity,dendrite-free features and low cost.Nevertheless,one of the major challenges for magnesium ion batteries is the kinetically sluggishmagnesium insertion/extraction and diffusion in electrode materials.Aiming at this issue,biphase eutectic-like bismuth-tin film is designedherein to construct a self-supporting anode with interdigitated phase distribution and hierarchically porous structure,and further fabricated bya facile one-step magnetron cosputtering route.As benchmarked with single-phase bismuth or tin film,the biphase bismuth-tin film delivershigh specific capacity (538 mAh/g at 50 mA/g),excellent rate performance (417 mAh/g at 1,000 mA/g) and good cycling stability (233 mAh/gat the 200th cycle).The superior magnesium storage performance of the sputtered bismuth-tin film could be attributed to the synergetic effectof the interdigitated bismuth/tin phase distribution,hierarchically porous structure and biphase buffering matrices,which could increase ionictransport channels,shorten diffusion lengths and reduce total volume changes.

The origin of potential rise during charging of Li-O2 batteries

When aprotic Li-O2 batteries recharge, the solid Li2O2 in the positive electrode is oxidized, which often exhibits a continuous or step increase in the charging potential as a function of the charging capacity, and its origin remains incompletely understood. Here, we report a model study of electro-oxidation of a Li2O2 film on an Au electrode using voltammetry coupled with in situ Raman spectroscopy. It was found that the charging reaction initializes at the positive electrodelLizO2 interface, instead of the previously presumed Li2O2 surface, and consists of two temporally and spatially separated Li2O2 oxidation processes, accounting for the potential rise during charging of Li-O2 batteries. Moreover, the electrode surface-initialized oxidation can disintegrate the Li2O2 film resulting in a loss of Li2O2 into electrolyte solution, which drastically decreases the charging efficiency and highlights the importance of using soluble electro-catalyst for the complete charging of Li-02 batteries.

Defective 1T′-ReSe2 nanosheets vertically grown on elastic MXene for fast and stable potassium ion storage

The sluggish reaction kinetics and poor structure stability of transition metal dichalcogenides(TMDs)-based anodes in potassium-ion batteries(KIBs)usually cause limited rate performance and rapid capacity decay,which seriously impede their application.Herein,we report a vacancy engineering strategy for preparing a class of Te-doped 1T'-ReSe_(2)anchored onto MXene(Te-ReSe_(2)/MXene)as an advanced anode for KIBs with high performance.By taking advantage of the synergistic effects of the defective Te-ReSe_(2)arrays with expanded interlayers and the elastic MXene nanosheets with self-autoadjustable function,the Te-ReSe_(2)/MXene superstructure exhibits boosted K^(+)ion storage performance,in terms of high reversible capacity(361.1 mA h g^(−1)at 0.1 A g^(−1)over 200 cycles),excellent rate capability(179.3 mA h g^(−1)at 20 A g^(−1)),ultra-long cycle life(202.8 mA h g^(−1)at 5 A g^(−1)over 2000 cycles),and steady operation in flexible full battery,presenting one of the best performances among the TMDs-based anodes reported thus far.The kinetics analysis and theoretical calculations further indicate that satisfactory pseudocapacitive property,high electronic conductivity and outstanding K^(+)ion adsorption/diffusion capability corroborate the accelerated reaction kinetics.Especially,structural characterizations clearly elaborate that the Te-ReSe_(2)/MXene undergoes reversible evolutions of an initial insertion process followed by a conversion reaction.

Dealloying-constructed hierarchical nanoporous bismuth-antimony anode for potassium ion batteries

Bi-Sb alloys are appealing anode materials for potassium ion batteries(PIBs)but challenged by their enormous volumetric variation during operation.Herein,a facile one-step dealloying protocol was devised and utilized to prepare the Bi-Sb alloys that manifest an exotic bicontinuous hierarchical nanoporous(np)microstructure ideal for volume-change mitigation and K+transport percolation.The growth mechanism fostering the peculiar morphology of the np-(Bi,Sb)alloys was investigated and clarified via operando X-ray(XRD)and ex-situ scanning electron microscopy(SEM).In particular,the np-Bi6Sb2 electrode,optimized for comprehensive electrochemical performance,achieves decent reversible capacities and a superior lifespan,as benchmarked with the monometallic references and other Bi-Sb alloy electrodes.The(de)potassiation mechanism of the np-(Bi,Sb)alloys was studied by operando XRD and further rationalized by density functional theory(DFT)calculations,whereby a homogeneous(segregation-free)and robust two-step electrochemically-driven phase transformations’catenation of(Bi,Sb)↔K(Bi,Sb)2↔K3(Bi,Sb)was reliably established to substantiate the outstanding reversibility of the np-(Bi,Sb)anodes in PIBs.

Oxygen electrochemistry in Li-O2 batteries probed by in situ surface-enhanced Raman spectroscopy

Surface-enhanced Raman spectroscopy(SERS),as a nondestructive and ultrasensitive single molecular level characterization technique,is a powerful tool to deeply understand the interfacial electrochemistry reaction mechanism involved in energy conversion and storage,especially for oxygen electrochemistry in Li-O2 batteries with unrivaled theoretical energy density.SERS can provide precise spectroscopic identification of the reactants,intermediates and products at the electrode|electrolyte interfaces,independent of their physical states(solid and/or liquid)and crystallinity level.Furthermore,SERS’s power to resolve different isotopes can be exploited to identify the mass transport limitation and reactive sites of the passivated interface.In this review,the application of in situ SERS in studying the oxygen electrochemistry,specifically in aprotic Li-O2 batteries,is summarized.The ideas and concepts covered in this review are also extended to the perspectives of the spectroelectrochemistry in general aprotic metal-gas batteries.

Dual-function redox mediator enhanced lithium-oxygen battery based on polymer electrolyte

The polymer electrolyte based lithium-oxygen battery has showed higher safety than that of organic liquid electrolyte.However,the energy efficiency and cycling stability are still the challenges for the practical application of lithium-oxygen battery.Herein,the 1,4 para benzoquinone has been demonstrated as dual-function redox mediator for promoting both oxygen reduction and oxygen evolution reactions of lithium-oxygen battery with polymer electrolyte,which have been confirmed by the Cyclic Voltammetry and discharge/charge test of battery under O_(2) gas,as well as the theoretical calculations.Furthermore,the composite cathode that in-situ constructed by polymerizing electrolyte precursors with redox me-diator can be beneficial for the electrochemical reactions.Combing composite cathode and lithium ions source,the polymer electrolyte based lithium-oxygen batteries can operate for long lifetime with low charge potentials and good rate performances.Thus,this work has highlighted the promising implementation of lithium-oxygen battery based on polymer electrolyte,in which the dual-function redox mediator are employed for both discharge and recharge processes.