Cycling Capacity Retention Research Articles

Hydrothermal synthesis of β-NiS layer structure nanoparticles for supercapacitor applications

At present, there is a significant research focus on development of sulfide based electrode materials for improving the performance of electrochemical supercapacitor (SC). Nickel sulfide (NiS) electrode materials has emerged attention as a promising candidate due to its high value of specific capacitance and outstanding redox activities. This study includes synthesis, characterization, and a novel electrode material called layer-like NiS that resembles a single-phase (β) is evaluated. At a current density of 3 mA g−1 in 3 M KOH electrolytes, the β-NiS electrode demonstrates an impressive specific capacitance of 780 F g−1 with 92 % cycling capacitance retention after 5000 cycles.

Unlocking Charge Transfer Limitation in NASICON Structured Na3V2(PO4)3 Cathode via Trace Carbon Incorporation

AbstractNASICON‐type cathode with remarkable ionic conductivity is perspective candidate for fast‐charging sodium‐ion battery. However, severely restricted by low electrical conductivity and poor interfacial kinetics, it usually delivers poor charge transfer kinetics. Different from traditional carbon compositing with high carbon contents, herein, a trace carbon incorporation tactic is proposed based on a typical NASICON‐structured Na3V2(PO4)3. First, particle‐growth process of Na3V2(PO4)3 is regulated via incorporating carbon dot, significantly reducing its particle size to shorten charge diffusion path. Second, electrical conductivity of Na3V2(PO4)3 is improved without sacrificing its high electrochemical activity due to the incorporated trace carbon content (0.76 wt.%). Third, Na3V2(PO4)3‐electrolyte interface structure is optimized by abundant functional groups from the incorporated carbon dot, enabling a thin and stable NaF‐rich CEI layer to boost interface kinetics. As a result, carbon dot endows Na3V2(PO4)3 with ultrastable cyclability up to 20 k cycles (capacity retention of 98.4%) and excellent rate capability (up to 200 C) in half cell, as well as high energy density (368.7 Wh kg−1) and fast charging property (≈110.2 s per charging with 250.8 Wh kg−1 input) in full cell. This study carves a new path for developing fast‐charging cathode, as is increasingly desired for present energy storage applications.

Stabilizing LiNi0.8Co0.1Mn0.1O2 cathode by combined moisture and HF digestion/adsorption for high-performance lithium metal batteries

Nickel-rich layered oxide cathodes such as LiNi0.8Co0.1Mn0.1O2 are promising to significantly increase the energy density of lithium metal batteries beyond 350 Wh kg−1. However, serious issues regarding cycle stability still remain when matching with conventional non-aqueous carbonate electrolytes that contain fluorine such as lithium hexafluorophosphate (LiPF6). Hydrolysis of LiPF6 generates corrosive hydrofluoric acid (HF), which destroys the cathode structure and accelerates the cathodic dissolution/anodic deposition of transition metal (TM) ions. Here, we demonstrate that ball milling NCM811 with carbon-coated aluminum nitride (AlN-C) remarkably enhances the capacity retention. AlN-C acts both as a scavenger and as an adsorption center to digest and adsorb H2O and HF, respectively. Thereby, it prevents the dissolution of TM ions, which would result in capacity decay and damage to the lithium metal anode. It is demonstrated that the addition of AlN-C via wet ball milling with NCM811 enables retaining a specific capacity of 149.9 mA h g−1 after 250 cycles (capacity retention: 85.2 %) at 1 C even in a high moisture electrolyte containing ∼0.2 % (v/v) H2O. Therefore, this work shows up a pathway to a rational enhancement of the capacity retention and cycle life of nickel-rich cathodes.

Introducing an Efficient and Eco-Friendly Spray-Drying Process for the Synthesis of NCM Precursor for Lithium-ion Batteries

<p>Ni-rich cathode is one of the promising candidates for high-energy lithium-ion battery applications. Due to its specific capacity, easy industrialization, and good circulation ability, Ni-rich cathode materials have been widely used for lithium-ion batteries. However, due to the limitation of the co-precipitation method, including sewage pollution, and the instability of the long production cycles, developing a new efficient and environmentally friendly synthetic approach is critical. In this study, the Ni<sub>0.91</sub>Co<sub>0.06</sub>Mn<sub>0.03</sub>CO<sub>3</sub> precursor powder was successfully synthesized by an efficient spray-drying method using carbonate compounds as a raw material. This Ni<sub>0.91</sub>Co<sub>0.06</sub>Mn<sub>0.03</sub>CO<sub>3</sub> precursor was calcined by mixing with LiOH·H<sub>2</sub>O (5 wt% excess) at 480°C for 5 hours and then sintered at two different temperatures (780°C/800°C) for 15 hours under an oxygen atmosphere to complete the cathode active material preparation, which is a key component of lithium-ion batteries. As a result, LiNi<sub>0.91</sub>Co<sub>0.06</sub>Mn<sub>0.03</sub>O<sub>2</sub> cathode active material powders were obtained successfully via a simple sintering process on the Ni<sub>0.91</sub>Co<sub>0.06</sub>Mn<sub>0.03</sub>CO<sub>3</sub> precursor powder. Furthermore, the obtained LiNi<sub>0.91</sub>Co<sub>0.06</sub>Mn<sub>0.03</sub>O<sub>2</sub> cathode active material powders were characterized. Overall, the material sintered at 780°C shows superior electrochemical performance by delivering a discharge capacity of 190.76mAh/g at 1<sup>st</sup> cycle (0.1 C) and excellent capacity retention of 66.80% even after 50 cycles.</p>

Various Solvent‐Binder Compositions and their Crystalline Phase for Optimal Screen‐Printing of NMC Cathodes

AbstractThis research examines the compatibility and performance of various solvents and binders in the battery cathode fabrication. The study focused on the applicability of solvents, including DMF, NMP, p‐Xylene, Ethanol, Toluene, Cyrene, and KJCMPA, in conjunction with binders such as PVDF #9300, PVDF #1100, HSV 1810, PVP, Oppanol N150, and Oppanol B15 for NMC‐based slurry formulation. Each solvent‐binder combination was evaluated with NMC material, and those demonstrating optimal solubility, adhesion, and film quality were selected for cathode screen‐printing trials. Results show that the combination of NMP solvent and HSV 1810 binder outperformed other pairings in cycling stability and capacity retention, achieving 87 % capacity retention after 1,000 1C/1C cycles. Comprehensive analyses using SEM, XRD, and FTIR offered insights into the structural and binder phase characteristics of the fabricated cathodes, especially the alterations in binder crystallinity phases (α, β, and γ). The data suggest that the use of the homopolymer HSV 1810, irrespective of the solvent, results in a pronounced presence of the γ‐phase within the binder, which subsequently improves battery performance. Moreover, the findings underscore the importance of the solvent‐binder combinations in enhancing battery performance and longevity.

Structural Evolution of Lithium-Exchanged Na3(VO)2(PO4)2F Cathode under Operation in Sodium Ion Batteries.

Na superionic conductor (NASICON)-type Na3(VO)2(PO4)2F (NVOPF) exhibits excellent cycling stability for high-voltage sodium ion batteries. Various strategies have been developed to form ion-exchanged NVOPF which can enhance the ionic and electronic conductivity. However, the underlying ion transport mechanism and complex structural transitions during battery operation remained uninvestigated. In this work, we prepared lithium-exchanged NVOPF (namely NLVOPF) which shows improved ionic conductivity and increased capacity at high discharging rates. Solid-state nuclear magnetic resonance (SSNMR) revealed the distinctive presence of two kinds of Li-exchanged sites in the NLVOPF, which are attributed to the occupied lithium ions at the Na1 and Na2 sites (namely Li1 and Li2, respectively). The Li1 site was metastably replaced in the first cycle, yet the Li2 site participated in ion insertion/extraction in the subsequent cycles. Our characterizations show that the dynamic doping of lithium in NLVOPF could contribute to the improved cycling stability and capacity retention.

Manipulated Fluoro‐Ether Derived Nucleophilic Decomposition Products for Mitigating Polarization‐Induced Capacity Loss in Li‐Rich Layered Cathode

AbstractElectrolyte engineering is a fascinating choice to improve the performance of Li‐rich layered oxide cathodes (LRLO) for high‐energy lithium‐ion batteries. However, many existing electrolyte designs and adjustment principles tend to overlook the unique challenges posed by LRLO, particularly the nucleophilic attack. Here, we introduce an electrolyte modification by locally replacing carbonate solvents in traditional electrolytes with a fluoro‐ether. By benefit of the decomposition of fluoro‐ether under nucleophilic O‐related attacks, which delivers an excellent passivation layer with LiF and polymers, possessing rigidity and flexibility on the LRLO surface. More importantly, the fluoro‐ether acts as “sutures”, ensuring the integrity and stability of both interfacial and bulk structures, which contributed to suppressing severe polarization and enhancing the cycling capacity retention from 39 % to 78 % after 300 cycles for the 4.8 V‐class LRLO. This key electrolyte strategy with comprehensive analysis, provides new insights into addressing nucleophilic challenge for high‐energy anionic redox related cathode systems.

Manipulated Fluoro-Ether Derived Nucleophilic Decomposition Products for Mitigating Polarization-Induced Capacity Loss in Li-Rich Layered Cathode.

Electrolyte engineering is a fascinating choice to improve the performance of Li-rich layered oxide cathodes (LRLO) for high-energy lithium-ion batteries. However, many existing electrolyte designs and adjustment principles tend to overlook the unique challenges posed by LRLO, particularly the nucleophilic attack. Here, we introduce an electrolyte modification by locally replacing carbonate solvents in traditional electrolytes with a fluoro-ether. By benefit of the decomposition of fluoro-ether under nucleophilic O-related attacks, which delivers an excellent passivation layer with LiF and polymers, possessing rigidity and flexibility on the LRLO surface. More importantly, the fluoro-ether acts as "sutures", ensuring the integrity and stability of both interfacial and bulk structures, which contributed to suppressing severe polarization and enhancing the cycling capacity retention from 39 % to 78 % after 300 cycles for the 4.8 V-class LRLO. This key electrolyte strategy with comprehensive analysis, provides new insights into addressing nucleophilic challenge for high-energy anionic redox related cathode systems.

A Rooted Multifunctional Heterogeneous Interphase Layer Enabled by Surface‐Reconstruction for Highly Durable Sodium Metal Anodes

AbstractSodium plating–stripping with high reversibility is still an intractable challenge for sodium metal‐based batteries due to the fragile natural solid‐electrolyte interphase (SEI) film and severe Na dendrites growth. Herein, a surface reconstruction strategy is proposed and a rooted heterogeneous interlayer derived from in situ reactions between tin selenide and Na metal (abbr. Na/SnSe) is produced to regulate Na+ deposition behavior and impede dendrite growth. The high sodiophilic Na15Sn4 component demonstrates the robust combination and dendrite suppression capability, inhibiting fracture and delamination problems during volume variation. Meanwhile, the superionic Na2Se ingredient contributes to the optimized Na+ conduction efficiency and low nucleation overpotential, enabling uniform distribution of electrical fields and ultimately eliminating Na dendrites. Consequently, the reconfigured multifunctional Na/SnSe interphase realizes a long‐term lifespan over 2400 h at 0.5 mA cm−2/1 mAh cm−2 in symmetric cell with an extremely low voltage hysteresis. Moreover, the assembled Na/SnSe||NaNi1/3Fe1/3Mn1/3O2 pouch cell achieves exceptional cycling stability and capacity retention (90.4 mAh g−1 after 1800 cycles at a high current density of 2 A g−1), exploiting an avenue for designing durable SEI layer and high‐quality sodium metal batteries.

Bio-inspired carbon electrodes for metal-ion batteries.

Carbon has been widely used as an electrode material in commercial metal-ion batteries (MIBs) because of its desirable electrical, mechanical, and physical properties. Still, traditional carbon electrodes suffer from limited mechanical stability and electrochemical performance in MIBs. Drawing inspiration from biological species, the carbon allotropes, such as fullerenes, carbon nanotubes, and graphene, can be engineered into mechanically robust, highly conductive frameworks with enhanced ion storage and transport capabilities for MIBs. Here, we present an assortment of bio-inspired carbon electrodes that have enhanced the cycling stability, capacity retention, and overall performance of MIBs. In addition, mimicking the structure and functionality of biological systems has led to the development of flexible MIBs whose performance does not degrade even when stretched, bent, or twisted. Finite element analysis (FEA) is a useful guide in identifying such bio-inspired carbon frameworks because it can simulate and analyze potential failure scenarios, such as stress build-up or structural collapse in MIBs. This review highlights through several examples that there is much scope for improving carbon-based electrode materials through bio-inspired designs for practical high-performance MIBs.

Spatially restricted deposition of Zn metal in localized-activation 3D electrode enables long-term stable zinc ion batteries

3D structures with organized channels have attracted extensive interest in constructing weak-dendrite anode for Zinc ion batteries (ZIBs). However, the uncontrolled “top-growth” dendrites caused by the unrestricted zinc deposition at all locations of the 3D electrode may eventually trigger a separator failure. Herein, a novel design principle of localized-activation 3D electrodes for spatially restricted deposition of metals is proposed. Based on the principle, a 3D Zn@CuSnAg/SiOC anode with spatially restricted feature (P-G Zn@CuSnAg/SiOC-SR), whose top surface (near separator) is an insulating SiOC and other surfaces are highly reactive Zn@CuSnAg, is fabricated by coupling polymer-derived ceramics (PDCs) 3D printing and surface modified method. Uniquely, the insulated SiOC of the top surface bestows a spatially restricted Zn deposition within the anode and ultimately prevents the upper surface from Zn plating and stripping, eliminating “top-growth” Zn dendrites in the 3D electrode. As expected, the P-G Zn@CuSnAg/SiOC-SR symmetrical battery affords spatially restricted Zn plating/stripping with a superior lifespan over 2100 h at 1.0 mA cm−2 for 0.82 mAh cm−2. Meanwhile, the VO2/C//P-G Zn@CuSnAg/SiOC-SR full battery demonstrates remarkable cyclic stability over 800 cycles (capacity retention: 80.5 %). This work sheds light on the 3D anode design and fabrication for the next-generation long-term stable ZIBs.

Effect of Electrolyte Additives on the Performance of 18650 Cylindrical Ni-Rich Li-Ion Battery Cells

Ni-rich Li-ion batteries have gained a lot of attention in recent years due to their high energy density and low cost. However, these batteries also face some challenges such as poor cycle life, capacity fading, and safety concerns. One way to overcome these issues is by modifying the electrolyte composition through the addition of various additives. Electrolyte additives can affect various aspects of the battery's performance, including its capacity, cycle life, and safety. For example, the addition of certain electrolyte additives can increase the stability of the cathode material, leading to improved cycle life and capacity retention. Other additives can enhance the thermal stability of the battery, which is important for preventing thermal runaway and improving safety. One commonly used electrolyte additive is fluoroethylene carbonate (FEC), which has been shown to improve the cycle life of Ni-rich Li-ion batteries by forming a protective layer on the surface of the cathode material. Another additive, vinylene carbonate (VC), can improve the stability of the electrolyte interface and prevent the decomposition of the electrolyte at high voltages.

Dual-Additive Approach for Tuning Si-Based Anode Interphase Realized By Operando ATR-FTIR

Dual-additive approach for tuning Si-based anode interphase realized by Operando ATR-FTIRMasoud Baghernejad1, Matthias Weiling1, Felix Pfeiffer1, Diddo Diddens1, Lars Frankenstein2, Christian Lechtenfeld2 1Helmholtz-Institute Münster, IEK-12, Forschungszentrum Jülich GmbH, Corrensstraße 46, 48149 Münster, Germany 2MEET Battery Research Center, Institute of Physical Chemistry, University of Münster, Corrensstraße 46, 48149 Münster, GermanySilicon is a promising next-generation anode material, offering a high gravimetric capacity. However, silicon-based anodes suffer from significant volume expansion during lithiation that can cause particle pulverization and capacity fade, continuous solid-electrolyte interphase (SEI) (re-)formation, and constant electrolyte consumption. To alleviate these issues, the effect of 2-Sulfobenzoic anhydride (2-SBA) as an SEI electrolyte additive was investigated through complementary electrochemical and operando spectroscopic techniques.The electrochemical performance was evaluated through galvanostatic charge/discharge cycling. The results show that the optimum concentration of 2-SBA improves the cycling stability and capacity retention of NMC811||AG+20% SiOx (4.5 – 2.8 V) cells to more than 100 cycles compared to 70 cycles with the baseline electrolyte (BE) before cell failure. Introducing lithium difluorophosphate (LiDFP), a common additive for high-voltage applications, to the electrolyte containing 2-SBA further increased the cycle life to 160 cycles. Interestingly, LiDFP alone in the electrolyte did not lead to improved electrochemical performance or longer cycle life of the cells compared to BE, proving a beneficial dual-additive approach of combining inorganic and organic compounds for sufficient SEI formation on AG+20% SiOx anodes. The analysis of the electrochemical performance concludes that the improved SEI structure formed by 2-SBA and LiDFP mitigates pulverization. In this regard, the SEI structure is further analyzed using operando ATR-FTIR spectroscopy.Operando ATR-FTIR spectroscopy proves to be a powerful technique in battery research, particularly for investigating SEI. The ATR mode's surface sensitivity enables studying the composition of the SEI without bulk signal interference. In this work, we employed the internal reflection mode of the ATR-FTIR spectroscopy, for which the electrode of interest has to be IR permeable. Furthermore, by variation of the incident angle of the IR beam, the penetration depth can be varied to obtain an interphase profile from electrode to bulk electrolyte. In this study, the SEI composition on the silicon anode in the presence of BE and the corresponding additives, 2-SBA and LiDFP, was investigated under real-working conditions. The results elucidate that 2-SBA is accumulated and decomposed via ring-opening on the silicon surface to form a stable SEI layer. However, in the presence of LiDFP and 2-SBA, a hybrid organic and inorganic SEI layer is formed, which proves to enhance electrochemical performance and cycle life. The findings of this study provide valuable structural insights into the silicon particle surface for the development of high-voltage silicon-based lithium-ion batteries with Ni-rich cathodes.

Thin, Conformal Carbon-Coating of Silicon-Phosphorus Nanoparticle Agglomerates for Lithium-Ion Battery Anodes

Efforts to further enhance the capabilities of silicon as a lithium-ion battery anode are continuing into the realm of chemical composition. Adding varying amounts of other elements can significantly alter the material properties or side reactions, which influence electrochemical performance. Additionally, tuning the chemical composition combined with surface modifications can better enable application of silicon anodes in other devices such as hybrid supercapacitors.Prior work, among others, has shown different performance enhancement regimes depending on how much phosphorus is added to silicon-containing anodes [1, 2]. In particular, the amount of phosphorus from ppm levels to majority atomic fraction can result in enhancement in the conductivity, diffusivity, or forming altogether a wholly new protective matrix [3]. However, while the rate capability has been enhanced only primarily for delithiation, silicon-phosphorus (SiPx) anodes still suffer from similar capacity degradation issues as pure silicon anodes.In the present work, we attempt to address the capacity degradation issue by using a thin, conformal carbon coating to modify the solid-electrolyte interface (SEI) reaction. Firstly, amorphous nanoparticles of SiPx with a few atomic percent of phosphorus are prepared using silane and phosphine co-pyrolysis. Using an oscillating furnace at 800 degrees Celsius under a low flow of acetylene in Ar carrier gas, we are able to produce consistent, uniform carbon films on nanoparticle agglomerates with select thicknesses between 2 and 10 nm, validated using low voltage scanning transmission electron microscopy (LV-STEM), as shown in Figure 1. By comparing Si- and SiPx-containing anodes in electrochemical half cells, we can reproduce the rate capability results while demonstrating the effect of carbon coating on cycle life and capacity retention. Furthermore, the carbon coating’s effect on volume expansion for Si- and SiPx-containing anodes is studied in situ using an electrochemical dilatometer in half cell configuration.[1] Y. Domi, H. Usui, M. Shimizu, Y. Kakimoto, H. Sakaguchi, ACS Applied Materials & Interfaces 2016, 8, 7125-7132.[2] S. Huang, L.-Z. Cheong, D. Wang, C. Shen, ACS Applied Materials & Interfaces 2017, 9, 23672-23678.[3] F. T. Huld, S. Y. Lai, W. M. Tucho, R. Batmaz, I. T. Jensen, S. Lu, O. E. Eleri, A. Y. Koposov, Z. Yu, F. Lou, ChemistrySelect 2022, 7, e202202857. Figure 1

Investigating the Reaction Mechanism of Vinylene Carbonate Additive in Lithium Ion Batteries Using X-Ray Photoelectron Spectroscopy

The rechargeable Li-ion battery is an enabling technology which facilitates the electrification of the automotive industry and reduces the demand for fossil fuels. During the charge and discharge of a battery, a solid-electrolyte interphase (SEI) forms between the liquid electrolyte and the solid negative electrode as a result of electrolyte degradation. The chemical and physical stability and the functionality of the SEI is a key determining factor of battery performance. The chemical composition of the SEI is mainly controlled by the choice of solvent and salt used, but can be manipulated by the addition of electrolyte additives that influence the electrolyte degradation process.Vinylene carbonate (VC) is an additive used in many commercial Li-ion battery configurations. The addition of a small amount of VC to ethylene carbonate (EC) containing electrolytes has been demonstrated to drastically improve several performance metrics for batteries including cycle life, coulombic efficiencies, capacity retention and thermal stability. The success of VC is widely attributed to its ability to form a thinner, denser and more robust SEI, which better protects the electrode surface and prevents further electrolyte consumption. This improvement in stability has been linked to the presence of poly(VC) in the SEI, but the mechanism by which VC reacts in EC-containing electrolytes is still an area of ongoing study. Whilst computational methods have suggested several potential decomposition pathways of electrolytes containing VC, it is yet to be convincingly demonstrated experimentally. Whilst there is a general consensus about ‘What?’ forms in the SEI on the addition of VC to EC-containing solvent, this work aims to confirm ‘Where?’ these components are in the interface and the currently unanswered questions of ‘How?’ and ‘Why?’ they form.Using highly surface sensitive photoelectron spectroscopy (PES) measurements of the SEI deposited at various potentials, we identify the differences in composition and structure that result from the addition of VC additive to EC-containing electrolytes. The SEI formation is studied using a smooth Au surface as the model working electrode and a fluorine free EC:diethyl carbonate (DEC) (1:9) 1 M LiClO4 electrolyte in an attempt to isolate the impact of VC on the SEI. A potential step procedure allows analysis of the working electrode surface by PES at several progressively more negative potentials on the first charge. Through systematic variation of components such as the concentration of VC, the ratio of EC:DEC and swapping Au for other electrode materials such as Cu or Si, the interaction between VC, EC and the electrode surface is revealed. The differences in SEI composition and structure formed in each environment and at each potential step are correlated to quartz crystal microbalance (QCM) data in order to identify potential reaction mechanisms and formation processes. The results play a key role in understanding the reaction pathway of VC-containing electrolytes and will accelerate development of more efficient electrolyte additives.

A tailored dual-layer electronic shielding interface enables highly stable and dendrite-free solid-state lithium metal batteries

All-solid-state lithium metal batteries (ASSLMBs) have emerged as promising energy storage devices due to their high energy density and enhanced safety features. However, challenges related to Li/electrolyte interface stability and ion transport efficiency hinder the practical implementation of sulfide-based ASSLMBs. In this study, we tailored the Li anode interface from the conventional mosaic structure to dual-layer gradient structure through a simple conversion reaction with an organic fluoride. The dual-layer multifunctional interface consists of a highly flexible and wettable upper layer enriched with organic LiBASF3 compounds and an LiF-rich lower layer with high interfacial energy. Eventually, the glittering integration of targeted surface smoothness, excellent interfacial wettability, and high interfacial energy is verified by experimental and theoretical calculation results. The insulating property of the dual-layer interface can impede electronic tunneling and minimize current leakage into the sulfide solid-state electrolytes. Ultimately, the implementation of interface engineering has shown significant improvements in enhancing the critical current density (CCD, 1.9 mA cm−2) of symmetric batteries, as well as enhancing the long-term cycling stability and capacity retention rate of the FeS2 and LiCoO2 cathodes based full cells.

Multiphase nano Co9S8/CoS encapsulated in N-doped carbon for high capacity sodium-ion battery anode

As anode materials for sodium-ion batteries (SIBs), transition metal sulfides (TMSs) have been widely explored due to their low cost, high theoretical capacity and rich redox reactions. However, poor cycling performance and capacity retention limit the application of materials. In this work, multiphase nano Co9S8/CoS encapsulated in N-doped carbon for high capacity SIBs anode is prepared via a facile two-step strategy: precipitation and heat treatment. When applied as anodes for SIBs, mass capacity of 389.2 mAh g−1 at 0.1 A g−1 after 60 cycles is obtained, and delivered ~300 mAh g−1 from 2nd to 300th cycle without depravation under 1.0 A g−1. In addition, according to the calculation of Na+ diffusion kinetics, it is evident that carbon encapsulation not only helps prevent electrolyte erosion but also enhances the DNa+ of the anode material. The high efficient strategy can be applied to synthesis of other multiphase analogues. Based on theoretical investigations, calculations of band gaps and rebuild energies for other TMSs (i.e., Cu7S4/Cu2S, FeS/Fe21.333O32/Fe3O4, MnS2/MnS, Ni3S2/Ni3C and cubic-ZnS/hexagonal-ZnS), as well as analysis of cyclic data, it can be concluded that Co9S8/CoS@NC material exhibits the highest conductivity and cycle stability.

Superior oxygen-resistance and intrinsic mechanisms of coherent Pd/Pd3Zr@ZrCo structure with excellent cycling durability

As a promising candidate for hydrogen isotopes storage, ZrCo alloy suffers tremendously from the poisoning of impurity gases, especially in oxygen-containing atmospheres, but related effective modification method for long cycling durability is still lacking. In this work, the anti-oxygen-poisoning behaviors and mechanisms of virginal ZrCo and palladium-coated ZrCo with different heating evacuation methods were detailly investigated. Notably, the phase transition occurs during traditional heating evacuation (550 °C for 60 min) with the gradual generation of Pd3Zr from original Pd coating and ZrCo substrate. According to absorption behaviors and degeneration state of O πp-orbital peak from theoretical calculations, O2 undergoes spontaneous dissociation and strong hybridization at the surface of ZrCo and Pd3Zr, especially for ZrCo, while much weak surface absorption is recognized on Pd. Considering the superior anti-poisoning properties but weak substrate anchoring strength of Pd, it’s valuable to reconstruct the Pd/ZrCo interface to generate transition Pd3Zr layer that is less susceptible to hydrogen embrittlement. Accordingly, a coherent structure of Pd/Pd3Zr@ZrCo was successfully obtained by high temperature short time pretreatment (550 °C for 10 min), and its cycling capacity retention in O2-containg hydrogen atmosphere is significantly enhanced from initial 74.87 % after 5 cycles to 90.83 % after 10 cycles, which is superior to Pd-plating hydrogen storage alloys ever reported. The interface reconstruction of coherent structure proposed here can function as a promising strategy for construction of protective layer for all related surface engineering.

Synergistic Effect of Bimetallic MOF Modified Separator for Long Cycle Life Lithium‐Sulfur Batteries

AbstractSevere polysulfide dissolution and shuttling are the main challenges that plague the long cycle life and capacity retention of lithium‐sulfur (Li‐S) batteries. To address these challenges, efficient separators are designed and modified with a dual functional bimetallic metal‐organic framework (MOF). Flower‐shaped bimetallic MOFs (i.e., Fe‐ZIF‐8) with nanostructured pores are synthesized at 35 °C in water by introducing dopant metal sites (Fe), which are then coated on a polypropylene (PP) separator to provide selective channels, thereby effectively inhibiting the migration of lithium polysulfides while allowing homogeneous transport of Li‐ions. The active sites of the Fe‐ZIF‐8 enable electrocatalytic conversion, facilitating the conversion of lithium polysulfides. Moreover, the developed separator can prevent dendrite formation due to the uniform pore size and hence the even Li‐ion transport and deposition. A coin cell using a Fe‐ZIF‐8/PP separator with S‐loaded carbon cathode displayed a high cycle life of 1000 cycles with a high initial discharge capacity of 863 mAh g−1 at 0.5 C and a discharge capacity of 746 mAh g−1 at a high rate of 3 C. Promising specific capacity has been documented even under high sulfur loading of 5.0 mg cm−2 and electrolyte to the sulfur ratio (E/S) of 5 µL mg−1.

New stachydrine-derived ionic liquids enable the formation of robust cathode electrolyte interphase for improving the performance of LiFePO4 battery

In the present study, several new stachydrine-based room temperature ionic liquids ([Cn-Sta] ILs, n = 2, 3, 4 or 5) are prepared, characterized and applied as an electrolyte additive to significantly improve LiFePO4 battery performance. The Sta-based ILs are structurally homologous with the popular pyrrolidinium ILs combining a chiral ester group close to the N+ cationic center, leading to low symmetry for the absence of cold crystallization, a wide liquid range from about −60 °C (glass transition temperature) to 320 °C (thermal decomposition temperature) and a decent electrochemical stability window (∼4.5 V). These ILs are ready to decompose on the surface of LiFePO4 particles to form LiF-rich and robust cathode electrolyte interphase (CEI) passivation layers, according to an aggregate study of electrochemical and morphological evidence. As a result, the ILs are used as an efficient CEI-forming additive to improve the LiFePO4 battery performance, namely higher capacity and cyclic capacity retention, better high-current rate performance and lower initial resistance.