MoSe_(2)@N, P-C composites for sodium ion battery

The conversion reaction-based anode materials of sodium ion batteries have relatively high capacity;however,the application of these materials is limited by their structural collapse due to the poor structure stability.In this work,MoSe_(2) nanosheets were synthesized by a solvothermal method.An organic solvent was intercalated into the MoSe_(2) materials to enlarge the interlayer spacing and improve the conductivity of the material.The MoSe_(2) material was coated with an organic pyrolysis carbon and then a uniform carbon layer was formed.The surface carbon hybridization of the nanosheet materials was realized by the introduction of heteroatoms during the sintering process.The as-prepared MoSe_(2)@N,P-C composites showed a superior rate performance as it could maintain the integrity of the morphology and structure under a high current density.The composites had a discharge specific capacity of 302.4 mA·h/g after 100 cycles at 0.5 A/g,and the capacity retention rate was 84.96%.

Unraveling the stabilization mechanism of solid electrolyte interface on ZnSe by rGO in sodium ion battery

Transition metal selenides have been widely studied as anode materials of sodium ion batteries(SIBs),however,the investigation of solid-electrolyte-interface(SEI)on these materials,which is critical to the electrochemical performance of SIBs,remains at its infancy.Here in this paper,ZnSe@C nanoparticles were prepared from ZIF-8 and the SEI layers on these electrodes with and without reduced graphene oxide(rGO)layers were examined in details by X-ray photoelectron spectroscopies at varied charged/discharged states.It is observed that fast and complicated electrolyte decomposition reactions on ZnSe@C leads to quite thick SEI film and intercalation of solvated sodium ions through such thick SEI film results in slow ion diffusion kinetics and unstable electrode structure.However,the presence of rGO could efficiently suppress the decomposition of electrolyte,thus thin and stable SEI film was formed.ZnSe@C electrodes wrapped by rGO demonstrates enhanced interfacial charge transfer kinetics and high electrochemical performance,a capacity retention of 96.4%,after 1000 cycles at 5 A/g.This study might offer a simple avenue for the designing high performance anode materials through manipulation of SEI film.

Spherical FeF3·0.33H2O/MWCNTs nanocomposite with mesoporous structure as cathode material of sodium ion battery

FeF3·0.33H2O crystallizes in hexagonal tungsten bronze structure with more opened hexagonal cavities are considered as next generation electrode materials of both lithium ion battery and sodium ion battery.In this paper the mesoporous spherical FeF3·0.33H2O/MWCNTs nanocomposite was successfully synthesized via a one-step solvothermal approach. Galvanostatic measurement showed that the performances of sodium ion batteries（SIBs） using FeF3·0.33H2O/MWCNTs as cathode material were highly dependent on the morphology and size of the as-prepared materials. Benefitting from the special mesoporous structure features, FeF3·0.33H2O/MWCNTs nanocomposite exhibits much better electrochemical performances in terms of initial discharge capacity（350.4 mAh g-1） and cycle performance（123.5 mAh g-1 after 50 cycles at 0.1 C range from 1.0 V to 4.0 V） as well as rate capacity（123.8 mAh g-1 after 25 cycles back to 0.1 C）. The excellent electrochemical performance enhancement can be attributed to the synergistic effect of the mesoporous structure and the MWCNTs conductive network, which can effectively increase the contact area between the active materials and the electrolyte, shorten the Na＋ diffusion pathway,buffer the volume change during cycling/discharge process and improve the structure stability of the FeF3·0.33H2O/MWCNTs nanocomposite.

Facile synthesis of MoS_2/graphite intercalated composite with enhanced electrochemical performance for sodium ion battery

MoS2 is a promising anode material for sodium ion batteries owing to its two-dimensional layered structure and high specific capacity. But it still exhibits a poor cycle stability and limited rate capability for Na＋ storage because of its poor electrical conductivity and structural instability. In this work, MoS2/graphite composite is fabricated by mechanically delaminated and restacked MoS2 and graphite to form two-dimensional composite layers. The graphite sheets will improve electrical conductivity and prevent the aggregation as well as structure collapse of the MoS2 layers during charge-discharge process. The MoS2/graphite composite exhibits excellent Na＋ storage properties. It delivers a high discharge specific capacity of 358.2 mAh/g at a current density of 100 mA]g in the first discharge process and with capacity retention of 68.1% after 800 cycles （retains 244 mAh/g）. The average discharge specific capacities retain 250.9 and 225.4 mAh/g corresponding to the current densities of 100 and 1000 mA]g, showing excellent rate capability. The improved electrochemical performance is attributed to the improved electrical conductivity and structural stability after composition of graphite sheets. The study demonstrates a new research strategy for improving sodium ion storage properties of Mo52.

Engineering optimization approach of nonaqueous electrolyte for sodium ion battery with long cycle life and safety

Electrolyte design strategies are closely related to the capacities, cycle life and safety of sodium–ion batteries. In this study, we aimed to optimize electrolyte with the focus on engineering aspects. The basic physicochemical properties including ionic conductivity, viscosity,wettability and thermochemical stability of the electrolytes using Na PF6 as the solute and the mixed solvent with different components of EMC,DMC or DEC in PC or EC were systematically measured. Ah pouch cell with NaNi_(1/3)Fe_(1/3)Mn_(1/3)O_(2)/hard carbon electrodes was used to evaluate the performance of the prepared electrolytes. By using the Inductive Coupled Plasma Emission Spectrometer(ICP), X-ray photoelectron spectroscopy(XPS), Thermogravimetric-differential scanning calorimetry(TG-DSC) and Accelerating Rate Calorimeter(ARC), we show that an optimized electrolyte can effectively promote the formation of a protective interfacial layer on two electrodes, which not only retards parasitic reactions between the electrodes and electrolyte but also suppresses dissolution of metal ions from the cathode. With an optimized electrolyte, a NaNi_(1/3)Fe_(1/3)Mn_(1/3)O_(2)/hard carbon cell can attain 56.16% capacity retention under the low temperature of -40℃, and can be able to retain 80%capacity retention after more than 2500 cycles while presenting excellent thermal safety.

Fe_(3)O_(4)/Fe/FeS Tri-Heterojunction Node Spawning N-Carbon Nanotube Scaffold Structure for High-Performance Sodium-Ion Battery

The Fe-based anode of sodium-ion batteries attracts much attention due to the abundant source,low-cost,and high specific capacity.However,the low electron and ion transfer rate,poor structural stability,and shuttle effect of NaS_(2)intermediate restrain its further development.Herein,the Fe_(3)O_(4)/Fe/FeS tri-heterojunction node spawned N-carbon nanotube scaffold structure(FHNCS)was designed using the modified MIL-88B(Fe)as a template followed by catalytic growth and sulfidation process.During catalytic growth process,the reduced Fe monomers catalyze the growth of N-doped carbon nanotubes to connect the Fe_(3)O_(4)/Fe/FeS tri-heterojunction node,forming a 3D scaffold structure.Wherein the N-doped carbon promotes the transfer of electrons between Fe_(3)O_(4)/Fe/FeS particles,and the tri-heterojunction facilitates the diffusion of electrons at the interface,to organize a 3D conductive network.The unique scaffold structure provides more active sites and shortens the Na^(+)diffusion path.Meanwhile,the structure exhibits excellent mechanical stability to alleviate the volume expansion during circulation.Furthermore,the Fe in Fe_(3)O_(4)/Fe heterojunction can adjust the dband center of Fe in Fe_(3)O_(4)to enhance the adsorption between Fe_(3)O_(4)and Na2S intermediate,which restrains the shuttle effect.Therefore,the FHNCS demonstrates a high specific capacity of 436 mAh g^(-1)at 0.5 A g^(-1),84.7%and 73.4%of the initial capacities are maintained after 100 cycles at 0.5 A g^(-1)and 1000 cycles at 1.0 A g^(-1).We believe that this strategy gives an inspiration for constructing Fe-based anode with excellent rate capability and cycling stability.

Enabling High-Performance Sodium Battery Anodes by Complete Reduction of Graphene Oxide and Cooperative In-Situ Crystallization of Ultrafine SnO_(2)Nanocrystals

The main bottleneck against industrial utilization of sodium ion batteries(SIBs)is the lack of high-capacity electrodes to rival those of the benchmark lithium ion batteries(LIBs).Here in this work,we have developed an economical method for in situ fabrication of nanocomposites made of crystalline few-layer graphene sheets loaded with ultrafine SnO_(2)nanocrystals,using short exposure of microwave to xerogel of graphene oxide(GO)and tin tetrachloride containing minute catalyzing dispersoids of chemically reduced GO(RGO).The resultant nanocomposites(SnO_(2)@MWG)enabled significantly quickened redox processes as SIB anode,which led to remarkable full anode-specific capacity reaching 538 mAh g^(−1)at 0.05 A g^(−1)(about 1.45 times of the theoretical capacity of graphite for the LIB),in addition to outstanding rate performance over prolonged charge–discharge cycling.Anodes based on the optimized SnO_(2)@MWG delivered stable performance over 2000 cycles even at a high current density of 5 A g^(−1),and capacity retention of over 70.4%was maintained at a high areal loading of 3.4 mg cm^(−2),highly desirable for high energy density SIBs to rival the current benchmark LIBs.

Phase-engineering modulation of Mn-based oxide cathode for constructing super-stable sodium storage

The Mn-based oxide cathode with enriched crystal phase structure and component diversity can provide the excellent chemistry structure for Na-ion batteries.Nevertheless,the broad application prospect is obstructed by the sluggish Na^(+)kinetics and the phase transitions upon cycling.Herein,we establish the thermodynamically stable phase diagram of various Mn-based oxide composites precisely controlled by sodium content tailoring strategy coupling with co-doping and solid-state reaction.The chemical environment of the P2/P'3 and P2/P3 biphasic composites indicate that the charge compensation mechanism stems from the cooperative contribution of anions and cations.Benefiting from the no phase transition to scavenge the structure strain,P2/P'3 electrode can deliver long cycling stability(capacity retention of 73.8%after 1000 cycles at 10 C)and outstanding rate properties(the discharge capacity of 84.08 mA h g^(-1)at 20 C)than P2/P3 electrode.Furthermore,the DFT calculation demonstrates that the introducing novel P'3 phase can significantly regulate the Na^(+)reaction dynamics and modify the local electron configuration of Mn.The effective phase engineering can provide a reference for designing other high-performance electrode materials for Na-ion batteries.

Innovative Mn_(3-x)O_(4-y)@NCA design:Leveraging Mn/O vacancies and amorphous architecture for enhanced sodium-ion storage

Manganese-based oxide electrode materials suffer from severe Jahn-Teller(J-T)distortion,leading to severe cycle instability in sodium ion storage.However,it is difficult to adjust the electron at d orbitals exactly to a low spin state to eliminate orbital degeneracy and suppress J-T distortion fundamentally.This article constructed concentration-controllable Mn/O coupled vacancy and amorphous network in Mn_(3)O_(4) and coated it with nitrogen-doped carbon aerogel(Mn_(3-x)O_(4-y)@NCA).The existence of Mn/O vacancies has been confirmed by scanning transmission electron microscopy(STEM)and positron annihilation lifetime spectroscopy(PALS).Atomic absorption spectroscopy(AAS)and X-ray photoelectron spectroscopy(XPS)determine the most optimal ratio of Mn/O vacancies for sodium ion storage is 1:2.Density functional theory(DFT)calculations prove that Mn/O coupled vacancies with the ratio of 1:2could exactly induce a low spin states and a d~4 electron configuration of Mn,suppressing the J-T distortion successfully.The abundant amorphous regions can shorten the transport distance of sodium ions,increase the electrochemically active sites and improve the pseudocapacitance response.From the synergetic effect of Mn/O coupled vacancies and amorphous regions,Mn_(3-x)O_(4-y)@NCA exhibits an energy density of 37.5 W h kg^(-1)and an ultra-high power density of 563 W kg^(-1)in an asymmetric supercapacitor.In sodium-ion batteries,it demonstrates high reversible capacity and exceptional cycling stability.This research presents a new method to improve the Na^(+)storage performance in manganese-based oxide,which is expected to be generalized to other structural distortion.

Layered SnS sodium ion battery anodes synthesized near room temperature

In this report, we demonstrate a simple chemical bath deposition approach for the synthesis of layered SnS nanosheets （typically 6 nm or -10 layers thick） at very low temperature （40℃）. We successfully synthesized SnS/C hybrid electrodes using a solution-based carbon precursor coating with subsequent carbonization strategy. Our data showed that the ultrathin carbon shell was critical to the cycling stability of the SnS electrodes. As a result, the as-prepared binder-free SnS/C electrodes showed excellent performance as sodium ion battery anodes. Specifically, the SnS/C anodes delivered a reversible capacity as high as 792 mAh-g-1 after 100 cycles at a current density of 100 mA·g-1 They also had superior rate capability （431 mAh.g-1 at 3,000 mA.g-1） and stable long-term cycling performance under a high current density （345 mAh-g-1 after 500 cycles at 3 A.g-1）. Our approach opens up a new route to synthesize SnS-based hybrid materials at low temperatures for energy storage and other applications. Our process will be particularly useful for chalcogenide matrix materials that are sensitive to high temperatures during solution synthesis.

Solid-state NMR study on sodium intercalation at low voltage window for Na_(3)V_(2)(PO_(4))_(3) as an anode

In-situ XRD,^(31)P NMR and ^(23)Na NMR were used to analyze the interaction behavior of Na_(3)V_(2)(PO_(4))_(3) at low voltage,and then a new intercalation model was proposed.During the transition from Na_(3)V_(2)(PO_(4))_(3) to Na_(4)V_(2)(PO_(4))_(3),Na ions insert into M1,M2 and M3 sites simultaneously.Afterwards,during the transition of Na_(4)V_(2)(PO_(4))_(3)to Na_(5)V_(2)(PO_(4))_(3),Na ions mainly insert into M3 site.

Cu_2GeS_3 derived ultrafine nanoparticles as high-performance anode for sodium ion battery

Germanium based sulfides are potentially attractive as anode material for sodium ion batteries but rarely investigated. Herein, we firstly investigated Na^＋storage properties of pristine Cu2GeS3（PCGS） and found an effective strategy to improve its performance by a single lithiation/delithiation cycle obtaining ultrafine nanoparticle copper germanium sulfide（NCGS）. The lithiation/delithiation process leads to the formation of a stable Li-containing solid electrolyte interphase film and a significant improvement of sodiation kinetics. Therefore, the NCGS anode delivers favorable capacity retention and better rate capability compared with that of a PCGS whether in the half cell or in the full cell,showing great promise for energy storage application.

DFT study of solvation of Li+/Na+ in fluoroethylene carbonate/vinylene carbonate/ethylene sulfite solvents for lithium/sodium-based battery

Choosing suitable solvent is the key technology for the electrochemical performance of energy storage device.Among them,vinylene carbonate(VC),fluoroethylene carbonate(FEC),and ethylene sulfite(ES)are the potential organic electrolyte solvents for lithium/sodium battery.However,the quantitative relation and the specific mechanism of these solvents are currently unclear.In this work,density functional theory(DFT)method is employed to study the lithium/sodium ion solvation in solvents of VC,ES,and FEC.We first find that 4VC-Li+,4VC-Na+,4ES-Li+,4ES-Na+,4FEC-Li+,and 4FEC-Na+are the maximum thermodynamic stable solvation complexes.Besides,it is indicated that the innermost solvation shells are consisted of 5VC-Li+/Na+,5ES-Li+/Na+,and 5FEC-Li+/Na+.It is also indicated that the Li+solvation complexes are more stable than Na+complexes.Moreover,infrared and Raman spectrum analysis indicates that the stretching vibration of O=C peak evidently shifts to high frequency with the Li+/Na+concentration reducing in nVC-Li+/Na+and nFEC-Li+/Na+solvation complexes,and the O=C vibration peak frequency in Na+solvation complexes is higher than that of Li+complexes.The S=O stretching vibration in nES-Li+/Na+solvation complexes moves to high frequency with the decrease of the Li+/Na+concentration,the S=O vibration in nES-Na+is higher than that in nES-Li+.The study is meaningful for the design of new-type Li/Na battery electrolytes.

Watermelon-like multicore-shell Fe(PO_(3))_(2)@carbon nanocapsule anode to construct an all iron phosphate-based sodium ion battery

Rechargeable sodium ion battery(SIB)has attracted much attention recently.However,the deficiency of high-performance electrode materials limits its commercial development.Exploring new cost-effective,high safe electrode materials and full battery matching technology is an important direction of future research.In this work,a novel watermelon-like multicore-shell Fe(PO_(3))_(2)@C nanocapsule anode material is designed via a facile and eco-friendly process for high performance SIB.Fe(PO_(3))_(2)@C composite anode exhibits remarkable electrochemical performances for SIB,showing high sodium storage capacity(452 mAh·g^(-1) at 0.2 A·g^(-1)),good rate(235 mAh·g^(-1) at 10 A·g^(-1)),stable long-term cycling life(210 mAh·g^(-1) over 2,000 cycles under 5 A·g^(-1)),and superior high-low temperature performance.Furthermore,a new type all iron-based phosphate full battery with high specific capacity is constructed,which can output initial capacity of 309 mAh·g^(-1) and a high energy density of 254,107,and 82 Wh·kg^(-1) at the power density of 186,917,and 1,640 W·kg^(-1) at room temperature.The exceptional performance of multicoreshell Fe(PO_(3))_(2)@C nanocapsule structure can be ascribed to the large specific surface,good structure stability,high conductivity,as well as the multiple layer protection for superior electron/ion transportation.

Bipolar electrode architecture enables high-energy aqueous rechargeable sodium ion battery

Aqueous rechargeable sodium ion batteries(ARSIBs),with intrinsic safety,low cost,and greenness,are attracting more and more attentions for large scale energy storage application.However,the low energy density hampers their practical application.Here,a battery architecture designed by bipolar electrode with graphite/amorphous carbon film as current collector shows high energy density and excellent rate-capability.The bipolar electrode architecture is designed to not only improve energy density of practical battery by minimizing inactive ingredient,such as tabs and cases,but also guarantee high rate-capability through a short electron transport distance in the through-plane direction instead of in-plane direction for traditional cell architecture.As a proof of concept,a prototype pouch cell of 8 V based on six Na_(2)MnFe(CN)_(6)||NaTi_(2)(PO_(4))_(3)bipolar electrodes stacking using a“water-in-polymer”gel electrolyte is demonstrated to cycle up to 4,000 times,with a high energy density of 86 Wh·kg^(−1)based on total mass of both cathode and anode.This result opens a new avenue to develop advance high-energy ARSIBs for grid-scale energy storage applications.

Extending the solid solution range of sodium ferric pyrophosphate:Off‐stoichiometric Na_(3)Fe(2.5)(P_(2)O_(7))_(2)as a novel cathode for sodium‐ion batteries

Iron‐based pyrophosphates are attractive cathodes for sodium‐ion batteries due to their large framework,cost‐effectiveness,and high energy density.However,the understanding of the crystal structure is scarce and only a limited candidates have been reported so far.In this work,we found for the first time that a continuous solid solution,Na_(4−α)Fe_(2+α)_(2)(P_(2)O_(7))_(2)(0≤α≤1,could be obtained by mutual substitution of cations at center‐symmetric Na3 and Na4 sites while keeping the crystal building blocks of anionic P_(2)O_(7) unchanged.In particular,a novel off‐stoichiometric Na_(3)Fe(2.5)(P_(2)O_(7))_(2)is thus proposed,and its structure,energy storage mechanism,and electrochemical performance are extensively investigated to unveil the structure–function relationship.The as‐prepared off‐stoichiometric electrode delivers appealing performance with a reversible discharge capacity of 83 mAh g^(−1),a working voltage of 2.9 V(vs.Na^(+)/Na),the retention of 89.2%of the initial capacity after 500 cycles,and enhanced rate capability of 51 mAh g^(−1)at a current density of 1600 mA g^(−1).This research shows that sodium ferric pyrophosphate could form extended solid solution composition and promising phase is concealed in the range of Na_(4−α)Fe_(2+α)_(2)(P_(2)O_(7))_(2),offering more chances for exploration of new cathode materials for the construction of high‐performance SIBs.

The safety aspect of sodium ion batteries for practical applications

Sodium-ion batteries(SIBs)with advantages of abundant resource and low cost have emerged as promising candidates for the next-generation energy storage systems.However,safety issues existing in electrolytes,anodes,and cathodes bring about frequent accidents regarding battery fires and explosions and impede the development of high-performance SIBs.Therefore,safety analysis and high-safety battery design have become prerequisites for the development of advanced energy storage systems.The reported reviews that only focus on a specific issue are difficult to provide overall guidance for building high-safety SIBs.To overcome the limitation,this review summarizes the recent research progress from the perspective of key components of SIBs for the first time and evaluates the characteristics of various improvement strategies.By orderly analyzing the root causes of safety problems associated with different components in SIBs(including electrolytes,anodes,and cathodes),corresponding improvement strategies for each component were discussed systematically.In addition,some noteworthy points and perspectives including the chain reaction between security issues and the selection of improvement strategies tailored to different needs have also been proposed.In brief,this review is designed to deepen our understanding of the SIBs safety issues and provide guidance and assistance for designing high-safety SIBs.

A review of anode materials for sodium ion batteries

Lithium-ion batteries(LIBs)are used in electric vehicles and portable smart devices,but lithium resources are dwindling and there is an increasing demand which has to be catered for.Sodium ion batteries(SIBs),which are less costly,are a promising replacement for LIBs because of the abundant natural reserves of sodium.The anode of a SIB is a necessary component of the battery but is less understood than the cathode.This review outlines the development of various types of anodes,including carbonbased,metallic and organic,which operate using different reaction mechanisms such as intercalation,alloying and conversion,and considers their challenges and prospects.Strategies for modifying their structures by doping and coating,and also modifying the solid electrolyte interface are discussed.In addition,this review also discusses the challenges encountered by the anode of SIBs and the solutions.

Experimental and computational optimization of Prussian blue analogues as high-performance cathodes for sodium-ion batteries:A review

In this review,we discuss the electrochemical properties of Prussian blue(PB)for Na^(+)storage by combining structural engineering and electrolyte modifications.We integrated experimental data and density functional theory(DFT)in sodium-ion battery(SIB)research to refine the atomic arrangements and crystal lattices and introduce substitutions and dopants.These changes affect the lattice stability,intercalation,electronic and ionic conductivities,and electrochemical performance.We unraveled the intricate structure-electrochemical behavior relationship by combining experimental data with computational models,including first-principles calculations.This holistic approach identified techniques for optimizing PB and Prussian blue analog(PBA)structu ral properties for SIBs.We also discuss the tuning of electrolytes by systematically adjusting their composition,concentration,and additives using a combination of molecular dynamics(MD)simulations and DFT computations.Our review offers a comprehensive assessment of strategies for enhancing the electrochemical properties of PB and PBAs through structural engineering and electrolyte modifications,combining experimental insights with advanced computational simulations,and paving the way for next-generation energy storage systems.

Defect-rich N/O-co-doped porous carbon frameworks as anodes for superior potassium and sodium-ion batteries

Carbon with its high electrical conductivity,excellent chemical stability,and structure ability is the most promising an-ode material for sodium and potassium ion batteries.We developed a defect-rich porous carbon framework(DRPCF)built with N/O-co-doped mesoporous nanosheets and containing many defects using porous g-C_(3)N_(4)(PCN)and dopamine(DA)as raw materials.We prepared samples with PCN/DA mass ratios of 1/1,2/1 and 3/1 and found that the one with a mass ratio of 2/1 and a carbonization temperature of 700℃ in an Ar atmosphere(DRPCF-2/1-700),had a large specific surface area with an enormous pore volume and a large number of N/O heteroatom active defect sites.Because of this,it had the best pseudocapacitive sodium and potassium ion stor-age performance.A half battery of Na//DRPCF-2/1-700 maintained a capacity of 328.2 mAh g^(-1) after being cycled at 1 A g^(-1) for 900 cycles,and a half battery of K//DRPC-2/1-700 maintained a capacity of 321.5 mAh g^(-1) after being cycled at 1 A g^(-1) for 1200 cycles.The rate capability and cycling stability achieved by DRPCF-2/1-700 outperforms most reported carbon materials.Finally,ex-situ Raman spectroscopy analysis result confirms that the filling and removing of K^(+)and Na^(+)from the electrochemically active defects are responsible for the high capacity,superior rate and cycling performance of the DRPCF-2/1-700 sample.