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.

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.

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.

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.

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.

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 ℃).

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.

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.

Microscopic Understanding of the Ionic Networks of“Water-in-Salt”Electrolytes

“Water-in-salt”electrolytes with excellent electrochemical and physical properties have been extensively investigated.However,the structural understanding of the lithium bis(trifluoromethane sulfonyl)imide(LiTFSI)in water is still lacking.Here,we perform synchrotron X-ray scattering to systemically study the structural variation of TFSI anions in an aqueous solution under a variety of concentrations and temperatures.There are two different solvation structures in the solution:TFSI-solvated structure and TFSI-network.As the concentration increases,the TFSI-solvated structure gradually disappears while the TFSI-network gradually forms.Even at relatively low concentrations,the TFSI-network can be observed.Our experimental results show that these two structures can coexist at a particular concentration,and temperature changes will lead to one structure’s formation or disappearance.Also,the TFSI-network is the key to obtain a stable electrochemical window under relatively high temperatures.