Unveiling the tailorable electrochemical properties of zeolitic imidazolate framework-derived Ni-doped LiCoO_(2) for lithium-ion batteries in half/full cells

As a prevailing cathode material of lithium-ion batteries(LIBs),LiCoO_(2)(LCO)still encounters the tricky problems of structural collapse,whose morphological engineering and cation doping are crucial for surmounting the mechanical strains and alleviating phase degradation upon cycling.Hereinafter,we propose a strategy using a zeolitic imidazolate framework(ZIF)as the self-sacrificing template to directionally prepare a series of LiNi_(0.1)Co_(0.9)O_(2)(LNCO)with tailorable electrochemical properties.The rational selection of sintering temperature imparts the superiority of the resultant products in lithium storage,during which the sample prepared at 700℃(LNCO-700)outperforms its counterparts in cyclability(156.8 mA h g^(-1)at 1 C for 200 cycles in half cells,1 C=275 mA g^(-1))and rate capability due to the expedited ion/electron transport and the strengthen mechanical robustness.The feasibility of proper Ni doping is also divulged by half/full cell tests and theoretical study,during which LNCO-700(167 mA h g^(-1)at 1 C for 100 cycles in full cells)surpasses LCO-700 in battery performance due to the mitigated phase deterioration,stabilized layered structu re,ameliorated electro nic co nductivity,a nd exalted lithium sto rage activity.This work systematically unveils tailorable electrochemical behaviors of LNCO to better direct their practical application.

Correction:Impact of Transition Metal Layer Vacancy on the Structure and Performance of P2 Type Layered Sodium Cathode Material

Following publication of the original article[1],the authors reported that the author Hun-Gi Jung should be affiliated as 3,4 and 5 instead of 4 and 5.The author’s name“A.-Yeon Kim”needed to be updated to“A-Yeon Kim”,removing the period.The correct author’s name and affiliation have been provided in this Correction.The original article[1]has been corrected.

Uniform Metal Sulfide@N-doped Carbon Nanospheres for Sodium Storage: Universal Synthesis Strategy and Superior Performance

Nitrogen-doped carbon-coated transition-metal sulfides(TMS@NCs)have been considered as efficient anodes for sodium-ion batteries.However,the uncontrollable morphology and weak core-shell binding forces significantly limit the sodium storage performance and life.Herein,based on the reversible ring-opening reaction of the epoxy group of the tertiary amino group-rich epoxide cationic polyacrylamide(ECP)at the beginning of hydrothermal process(acidic environment)and the irreversible ring-opening(cross-linking reactions)at the late hydrothermal period(alkaline environment),47 nm-sized ZnS@NCs were prepared via a one-pot hydrothermal process.During this process,the covalent bonds formed between the ZnS core and elastic carbon shell significantly improved the mechanical and chemical stabilities of ZnS@NC.Benefiting from the nanosize,fast ion/electron transfer,and high stability,ZnS@NC exhibited a high reversible capacity of 421.9 mAh g^(−1) at a current density of 0.1 A g^(−1) after 1000 cycles and a superior rate capability of 273.8 mAh g^(−1) at a current density of 5 A g^(−1).Moreover,via this universal synthesis strategy,a series of TMS@NCs,such as MoS_(2)@NC,NiS@NC,and CuS@NC were developed with excellent capacity and cyclability.

Impact of Transition Metal Layer Vacancy on the Structure and Performance of P2 Type Layered Sodium Cathode Material

This study explores the impact of introducing vacancy in the transition metal layer of rationally designed Na_(0.6)[Ni_(0.3)Ru_(0.3)Mn_(0.4)]O_(2)(NRM)cathode material.The incorporation of Ru,Ni,and vacancy enhances the structural stability during extensive cycling,increases the operation voltage,and induces a capacity increase while also activating oxygen redox,respectively,in Na_(0.7)[Ni_(0.2)V_(Ni0.1)Ru_(0.3)Mn_(0.4)]O_(2)(V-NRM)compound.Various analytical techniques including transmission electron microscopy,X-ray absorption near edge spectroscopy,operando X-ray diffraction,and operando differential electrochemical mass spectrometry are employed to assess changes in the average oxidation states and structural distortions.The results demonstrate that V-NRM exhibits higher capacity than NRM and maintains a moderate capacity retention of 81%after 100 cycles.Furthermore,the formation of additional lone-pair electrons in the O 2p orbital enables V-NRM to utilize more capacity from the oxygen redox validated by density functional calculation,leading to a widened dominance of the OP4 phase without releasing O_(2) gas.These findings offer valuable insights for the design of advanced high-capacity cathode materials with improved performance and sustainability in sodium-ion batteries.

MOF-Transformed In_(2)O_(3-x)@C Nanocorn Electrocatalyst for Efficient CO_(2)Reduction to HCOOH

For electrochemical CO_(2) reduction to HCOOH,an ongoing challenge is to design energy efficient electrocatalysts that can deliver a high HCOOH current density(JHCOOH)at a low overpotential.Indium oxide is good HCOOH production catalyst but with low con-ductivity.In this work,we report a unique corn design of In_(2)O_(3-x)@C nanocatalyst,wherein In_(2)O_(3-x)nanocube as the fine grains dispersed uniformly on the carbon nanorod cob,resulting in the enhanced conductivity.Excellent performance is achieved with 84%Faradaic efficiency(FE)and 11 mA cm^(−2)JHCOOH at a low potential of−0.4 V versus RHE.At the current density of 100 mA cm^(−2),the applied potential remained stable for more than 120 h with the FE above 90%.Density functional theory calculations reveal that the abundant oxygen vacancy in In_(2)O_(3-x) has exposed more In^(3+) sites with activated electroactivity,which facilitates the formation of HCOO*intermediate.Operando X-ray absorp-tion spectroscopy also confirms In^(3+) as the active site and the key intermediate of HCOO*during the process of CO_(2) reduction to HCOOH.

Effects of Cr doping on structural and electrochemical properties of Li_(4)Ti_(5)O_(12) nanostructure for sodium-ion battery anode

Sodium-ion batteries are considered as promising alternatives to lithium-ion batteries,owing to their low cost and abundant raw materials.Among the several candidate materials for the anode,spinel-type Li_(4)Ti_(5)O_(12)has potential owing to its superior safety originating from an appropriate operating voltage and the reversible Na^(+)intercalation properties.However,a low diffusion coefficient for Na^(+)and the insulating nature of LTO remains challenging for practical sodium-ion battery systems.Herein,we present a strategy for integrating physical and chemical approaches to achieve superior electrochemical properties in LTO.We demonstrate that carefully controlling the amount of Cr doping is crucial to enhance the electrochemical properties of nanostructured LTO.Optimized Cr doped LTO shows a superior reversible capacity of 110 m Ah g^(-1) after 400 cycles at 1 C,with a three-fold higher capacity(75 m Ah g^(-1))at 10 C compared with undoped LTO material.This suggests that appropriately Cr doped nanostructured LTO is a promising anode material for sodium-ion batteries.

CO_(2)-adsorbent spongy electrode for non-aqueous Li–O_(2) batteries

Regulation of the Li_(2)CO_(3) byproduct is the most critical challenge in the field of non-aqueous Li–O_(2) batteries.Although considerable efforts have been devoted to preventing Li_(2)CO_(3) formation,no approaches have suggested the ultimate solution of utilizing the clean Li_(2)O_(2) reaction instead of that of Li_(2)CO_(3).Even if extremely pure O_(2) is used in a Li–O_(2) cell,its complete elimination is impossible,eventually generating CO_(2) gas during charge.In this paper,we present the new concept of a CO_(2)-adsorbent spongy electrode(CASE),which is designed to trap the evolved CO_(2) using adsorption materials.Various candidates composed of amine functional groups(–NH2)for capturing CO_(2) were screened,with quadrapurebenzylamine(QPBZA)exhibiting superior CO_(2)-adsorbing ability among the proposed candidates.Accordingly,we fabricated the CASE by sandwiching QPBZA between porous carbon layers,which facilitated the transport of gaseous products.The new electrode was demonstrated to effectively capture the evolved CO_(2) during charge,therefore altering the reaction pathways to the ideal case.It is highly advantageous to mitigate the undesirable CO_(2) incorporation in the next discharge,resulting in improved cyclability.This novel concept of a CO_(2)-sponging electrode provides an alternative route to the realization of practically meaningful Li–O_(2) batteries.

KPI-based Real-time Situational Awareness for Power Systems with a High Proportion of Renewable Energy Sources

With the increasing complexity of power systems and the widespread penetration of renewable energy sources(RES),real-time situational awareness for power systems is of great significance for operational scheduling.Considering the impact of RES on power system operations,a situational awareness key performance index(KPI)system for power systems with a high proportion of RES is proposed in this paper,which consists of reserve capacity abundance,ramp resource abundance,center of inertia(COI)frequency deviation,interface power flow margin,synthesized voltage stability,and angle stability margin.Then,the KPIs are synthesized and visualized by the decision tree method and radar chart method,respectively,for monitoring the operation states(i.e,normal,alert,and emergency states)of power systems with a high proportion of RES.Numerical simulations are conducted in a revised New England 16-machine 68-bus power system and an actual CEPRI-RE power system in the northwest region of China with a high proportion of RES.The results show that the proposed KPI-based situational awareness method is able to accurately monitor the real-time state of power systems with a high proportion of RES,and can assist power dispatchers to make effective decisions.

Aggregation induced edge sites actuation of 3D MoSe_(2)/rGO electrocatalyst for high-performing water splitting system

2D materials are regarded as promising electrocatalysts for water splitting because of their advances in providing ample active sites and improving electrochemical reaction kinetics.2D MoSe_(2)has a greater intrinsic electrical conductivity and lower Gibbs free energy for reactant adsorption.However,there is still room for improvement in the electrocatalytic performance of MoSe_(2)for high-performance electrochemical water splitting devices.Herein,the in situ preparation of heterostructure made of covalently bonded MoSe_(2)and rGO is reported.The obtained electrocatalyst contains the aggregated 3D structured MoSe_(2)over rGO,which is covalently bonded together with more edge sites.The active edge sites of MoSe_(2)/rGO are dynamically involved in the electrocatalytic activity while facilitating electron transfer.Hence,the MoSe_(2)/rGO heterostructure requires a low cell voltage of 1.64 V to reach 100 mA cm^(−2)in water splitting with high reaction kinetics.The aggregated MoSe_(2)over rGO with more edge sites exposed by the 3D structure of MoSe_(2)and the interfacial covalent bond in between them provides a favorable electronic structure for the HER and OER with low overpotentials and high current densities and enhances the stability of the electrocatalyst.This work presents an attractive and cost-effective electrocatalyst suitable for industrial-scale hydrogen fuel production.

Understanding fluorine-free electrolytes via small-angle X-ray scattering

Fluorine-free electrolytes have attracted great attention because of its low-cost and environmental friendliness. However, so far, little is known about the solution structures of these electrolytes. Here,we compare the solvation phenomenon of sodium tetraphenylborate(NaBPh_(4)) salt dissolved in organic solvents of propylene carbonate(PC), 1,2-dimethoxyethane(DME), acetonitrile(ACN) and tetrahydrofuran(THF). Small-angle X-ray scattering(SAXS) reveals a unique two-peak structural feature in this saltconcentrated PC electrolyte, while solutions using other solvents only have one scattering peak.Molecular dynamics(MD) simulations further reveal that there are anion-based clusters in addition to the short-range charge ordering in the concentrated NaBPh4/PC electrolyte. Raman spectroscopy confirms the existence of considerable contact ion pairs(CIPs). This work emphasizes the importance of global and local structural analysis, which will provide valuable clues for understanding the structureperformance relationship of electrolytes.

The Transference Number

The performance of rechargeable batteries and other electrochemical systems depends on the rate at which the working ion(often a cation)is transported from one electrode to the other.The cation transference number is an important transport parameter that affects this rate.The purpose of this perspective is to distinguish between approximate and rigorous methods used in the literature to measure the transference number.We emphasize the fact that this parameter is dependent on the reference frame used in the analysis;care must be taken when comparing values obtained from different sources to account for differences in reference frames.We present data obtained from a well-characterized electrolyte.We compare rigorously determined transference numbers in two reference frames with values obtained by an approximate method.We conclude with a qualitative discussion of the relationship between the transference number and salt concentration gradients that are obtained when current is drawn through a battery。

In Situ/Operando(Soft) X-ray Spectroscopy Study of Beyond Lithium-ion Batteries

The lightweight,rechargeable lithium-ion battery is one of the dominant energy storage devices globally in portable electronics due to its high energy density,no memory effect,wide operating voltage,lightweight,and good charge efficiency.However,due to safety concerns,the depletion of lithium reserves,and the corresponding increase of cost,an alternative battery system becomes more and more desirable.To develop alternative battery systems with low cost and high material abundance,for example,sodium,magnesium,zinc,and calcium,it is important to understand the chemical and electronic structure of materials.Soft X-ray spectroscopy,for example,X-ray absorption spectroscopy(XAS),X-ray emission spectroscopy(XES),and resonant inelastic soft X-ray scattering(RIXS),is an element-specific technique with sensitivity to the local chemical environment and structural order of the element of interest.Modern soft X-ray systems enable operando experiments that can be applied to amorphous and crystalline samples,making it a powerful tool for studying the electronic and structural changes in electrode and electrolyte species.In this article,the application of in situ/operando(soft)X-ray spectroscopy in beyond lithium-ion batteries is reviewed to demonstrate how such spectroscopic characterizations could facilitate the interpretation of interfacial phenomena under in situ/operando condition and subsequent development of the beyond lithium-ion batteries.

Solvation Structure and Dynamics of Mg(TFSI)_(2) Aqueous Electrolyte

Using ab initio molecular dynamics(AIMD)simulations,classical molecular dynamics(CMD)simulations,small-angle X-ray scattering(SAXS),and pulsed-field gradient nuclear magnetic resonance(PFG-NMR),the solvation structure and ion dynamics of magnesium bis(trifluoromethanesulfonyl)imide(Mg(TFSI)_(2))aqueous electrolyte at 1,2,and 3 m concentrations are investigated.From AIMD and CMD simulations,the first solvation shell of an Mg;ion is found to be composed of six water molecules in an octahedral configuration and the solvation shell is rather rigid.The TFSI^(-)ions prefer to stay in the second solvation shell and beyond.Meanwhile,the comparable diffusion coefficients of positive and negative ions in Mg(TFSI)_(2)aqueous electrolytes have been observed,which is mainly due to the formation of the stable[Mg(H_(2)O_(6))_(2)]^(+)complex,and,as a result,the increased effective Mg ion size.Finally,the calculated correlated transference numbers are lower than the uncorrelated ones even at the low concentration of 2 and 3 m,suggesting the enhanced correlations between ions in the multivalent electrolytes.This work provides a molecular-level understanding of how the solvation structure and multivalency of the ion affect the dynamics and transport properties of the multivalent electrolyte,providing insight for rational designs of electrolytes for improved ion transport properties.

Quantifying Electrochemical Processes in Batteries and Beyond

The correlation of electrochemical measurements with materials characterization has advanced our understanding of operation and degradation mechanisms in electrochemical energy storage and many other fields.Yet,often these correlations are qualitative,preventing the unambiguous identification of both operational principles and the root causes of performance losses.Here we suggest quantitative approaches to define competing mechanisms and determine their relative contributions.We illustrate the importance of quantitative methodologies over a range of electrochemical systems and highlight the need to consider the effect of the experimental design and measurement itself.These approaches will reveal the most detrimental degradation mechanisms and enable the development of strategies to suppress,stabilize or eliminate them,leading to materials and devices with longer lifetimes,reduced environmental impact,and improved performance.

Fe2N nanoparticles boosting FeNx moieties for highly efficient oxygen reduction reaction in Fe-N-C porous catalyst

Replacing Pt-based electrocatalysts for the oxygen reduction reaction (ORR) with high performance and low-cost non-precious metal catalysts is crucial for the commercialization of fuel cells.Herein,we present a highly efficient Fe-N-C porous ORR electrocatalyst with FeNx moieties promoted by Fe2N nanoparticles derived from Fe-doped zeolitic imidazolate framework.The best-performing Fe-N-C/HPC-NH3 catalyst exhibits a superior ORR activity with an onset (E0) and half-wave (E1/2) potential of 0.945 and 0.803 V (RHE),respectively,which is comparable to those of the commercial Pt/C in acidic media.Probing and acid-leaching experiments prove that FeNx moieties play an important role in the ORR and the Fe2N can further improve the ORR activity.Density functional theory calculation reveals a synergistic effect that the existence of Fe2N weakens the adsorption of ORR intermediates on active sites and lowers the reaction free energy of the potential limiting step,thus facilitating the ORR.Both experimental evidence and theoretical analysis for the enhancement of ORR activity by Fe2N decoration in Fe-N-C catalyst might inspire a new strategy for rational design of high performance non-precious metal catalysts.

Polydopamine-derived N-doped carbon-wrapped Na3V2(PO4)3 cathode H with superior rate capability and cycling stability for sodium-ion I batteries

Na superionic conductor (NASICON)-type Na3V2(PO4)3 (NVP) has been regarded as a promising cathode material for sodium-ion batteries (SIBs). However, NVP suffers from poor cyclability and rate capability because of its intrinsically low electronic conductivity. Herein, we successfully syn thesized N-doped carb on-wrapped Na3V2(PO4)3 (NC@NVP) through the carb on izati on of polydopami ne, which is rich in nitrogen species. The strong adhesion properties of the polydopamine lead to effective and homogeneous wrapping of NVP particles, and it I is further turned into a con ductive N-doped carb on n etwork itself, providi ng facile diffusi on of electr ons and Na+ i ons duri ng battery operation. NC@NVP displays remarkable electrochemical performanee, even under harsh operating conditions, such as a high rate capability (discharge capacity of 70.88, 49.21 mA·h·g^-1 at 50 and 100 C), long-term cycling stability (capacity retention of 94.77% over 1,000 cycles at 20 C), and high-temperature cycling (capacity retention of 92.0% after 500 cycles at 60 ℃).

Phase formation and crystallization of LiMn_(x)Fe_(1-x)PO_(4)-C olivine material with different Mn^(2+)contents fabricated at lower calcination temperatures

LiMn_(x)Fe_(1-x)PO_(4)-C cathode materials for lithium ion batteries were synthesized via solid-state method using Li_(2)CO_(3),MnCO_(3),NH_(4)H_(2)PO_(4),FePO_(4) and sucrose as starting raw materials,followed by high-temperature reduction-annealing.A series of calcination experiments at different temperatures reveal that Mn^(2+)-containing materials exhibit a lower temperature for olivine phase formation,for example LiMn_(0.5)Fe_(0.5)PO_(4) olivine phase forms at 275℃,while manganese-free crystalline LiFePO_(4) generally forms at the required temperature of 350℃.Increasing Mn^(2+) content is found to enhance crystallization degree of LiMn_(x)Fe_(1-x)PO_(4) material prepared at lower calcination temperatures.X-ray photoelectron spectroscopy(XPS)results confirm that Mn valence state(+2)remains unchanged up to~250℃ when calcined in ambient atmosphere.The above-mentioned beneficial effect of manganese on phase formation and crystallization of olivine can be well attributed to the stable nature of Mn^(2+)and its strong propensity to form olivine phases.

Dual impact of superior SEI and separator wettability to inhibit lithium dendrite growth

Lithium metal battery(LMB)is regarded as the most potential energy storage system.However,unfortunately,its large-scale commercial development is hindered due to the uncontrollable dendrite growth problem on its Li-metal anode.The utilization of electrolyte additives is one of the promising strategies to solve the problem mentioned above.An electrolyte additive based on heptafluorobutyric anhydride(HFA)is used to solve the dendrite problem by forming robust inorganic-rich solid electrolyte interphase(SEI)and enhancing the separator wettability.

Analysis on Application of a Current-source Based DFIG Wind Generator Model

Models for simulation are vital for the authenticity of the simulation.Modeling doubly fed induction generation(DFIG)for power system stability analysis has attracted a great deal of research interests in the past few years due to the wide applications of DFIG in wind power generation.The models developed by the wind generator manufacturers are not only complicated,but also proprietary and very specific to their own products.Many simplified generic models have been proposed.Among them,the current-source based model is most widely used for power system stability analysis.The validation work on this model so far has been based on the selected simulation scenarios or limited real measurements.However,there has been no systematic and theoretic analysis on the validity of the current-source based model,which may cause inappropriate applications of this type of model in real engineering practices.This paper presents the conditions for using the current-source based model for power system stability analysis;then examines the model’s validity under symmetrical and asymmetrical fault conditions.Our practices for modeling and validating a real wind farm in North China confirm the validity analysis of this work on the current-source based DFIG model.

Quasi-compensatory effect in emerging anode-free lithium batteries

As electric vehicle(EV)sales grew approximately 50%year-over-year,surpassing 3.2 million units in 2020,the“roaring era”of EV is around the corner.To meet the increasing demand for low cost and high energy density batteries,anode-free configuration,with no heavy and voluminous host material on the current collector,has been proposed and further investigated.Nevertheless,it always suffers from several non-negligible“bottlenecks”,such as fragile solid electrolyte interface,deteriorated cycling reversibility,and uncontrolled dendrite formation.Inspired by the“compensatory effect”of some disabled people with other specific functions strengthened to make up for their inconvenience,corresponding quasi-compensatory measures after anode removal,involving dimensional compensation,SEI robustness compensation,lithio-philicity compensation,and lithium source compensation,have been carried out and achieved significant battery performance enhancement.In this review,the chemistry,challenges,and rationally designed“quasi-compensatory effect”associated with anode-free lithium-ion battery are systematically discussed with several possible R&D directions that may aid,direct,or facilitate future research on lithium storage in anode-free configuration essentially emphasized.