Cathode Materials For Li Batteries Research Articles

(Invited) In-Operando ftir Study on the Redox Behavior of Sulfurized Polymers As Cathode Material for Li-S Batteries

Sulfurized polymers are an attractive cathode active material, promising to overcome the intransigent polysulfide shuttle effect sulfur cathodes face via the anchoring of sulfur by a carbon-sulfur (C-S) bond. Both sulfur-diisopropenylbenzene copolymers (SDIB) and sulfurized polyacrylonitrile (SPAN) contain C-S bonds which should function in this way, however, their performance in ether electrolytes still exhibit capacity fade associated with the polysulfide shuttle. We investigate this anchoring effect using in-operando ATR-FTIR spectroscopy to develop a molecular level understanding of the polysulfide speciation reaction in sulfurized polymers and cathode level molecular changes. We find that in SDIB copolymers with sulfur wt % of 80 and 30 wt %, the C–S bond is not active in the voltage window of Li–S batteries (1.8-2.6V vs Li/Li+).In SPAN, however, we found that the C-S bond is active in the typical voltage window (1-3V vs Li/Li+) contributing to the evolution of polysulfide species in electrolyte with low concentrations of lithium nitrate (LiNO3), however this effect is mitigated when higher concentrations of LiNO3 are used. We attributed the mitigation of the polysulfide shuttle to the formation of a cathode electrolyte interface (CEI), composed of lithium fluoride, established via ex-situ XPS studies on cycled cathodes. Additionally, we observed the reversible behavior of the C-S bond in IR at ~680 cm-1 in electrolytes with high concentration of LiNO3, as opposed to the irreversible behavior of the bond in electrolyte with low concentrations of LiNO3. Moreover, we observed the lithiation of the cyclized PAN backbone, identified by the elimination of the aromatic region of the IR spectrum after the first cycle.

Doped Ceria Nanomaterials: Preparation, Properties, and Uses.

Doping is a powerful strategy for enhancing the performance of ceria (CeO2) nanomaterials in a range of catalytic, photocatalytic, biomedical, and energy applications. The present review summarizes recent developments in the doping of ceria nanomaterials with metal and non-metal dopants for selected applications. The most important metal dopants are grouped into s, p, d, and f block elements, and the relevant synthetic methods, novel properties, and key applications of metal doped ceria are collated and critically discussed. Non-metal dopants are similarly examined and compared with metal dopants using the same performance criteria. The review reveals that non-metal (N, S, P, F, and Cl) doped ceria has mainly been synthesized by calcination and hydrothermal methods, and it has found applications mostly in photocatalysis or as a cathode material for LiS batteries. In contrast, metal doped ceria nanomaterials have been prepared by a wider range of synthetic routes and evaluated for a larger number of applications, including as catalysts or photocatalysts, as antibacterial agents, and in devices such as fuel cells, gas sensors, and colorimetric detectors. Dual/co-doped ceria containing both metals and non-metals are also reviewed, and it is found that co-doping often leads to improved properties compared with single-element doping. The review concludes with a future outlook that identifies unaddressed issues in the synthesis and applications of doped ceria nanomaterials.

氟化高浓电解液实现无水氟化铜正极的可逆循环

Anhydrous copper(II) fluoride (CuF2) has a high specific capacity of 528 mA h g−1 with an operating voltage of 3.55 V vs. Li/Li+, achieving a high gravimetric energy density of 1874 W h kg−1, which makes it a promising cathode candidate for next-generation rechargeable lithium (Li) batteries. However, the notorious dissolution of Cu during charging triggers the rapid failure of the CuF2 cathode, impeding its development. In this work, the reversibility of the anhydrous CuF2 electrode was enabled via the use of a fluorinated high-concentration (FHC) electrolyte to effectively suppress the dissolution of Cu. With the FHC electrolyte, the CuF2-Ketjen Black nanocomposite cathode delivered a reversible capacity of 228 mA h g−1 after 30 cycles, which nearly tripled that of the baseline electrolyte. Thus, the strategy of electrolyte engineering is proposed to harness CuF2 as a high-capacity cathode material for Li batteries.

Novel Strategy for the Formulation of High-Energy-Density Cathodes via Porous Carbon for Li-S Batteries.

Porous carbon is considered an attractive host material for high-energy sulfur electrodes. This study concerns the design of a porous carbon-based sulfur electrode for the formulation of high-energy Li-S batteries. The porous carbon is impregnated with up to 80 vol.% of sulfur and a reduction in both the conductive agent and binder content. Therefore, less solvent can be used during slurry casting to inhibit crack formation following electrode drying. In addition, the utilization of two distinct electrically conducting networks enables reduced battery polarization, resulting in a battery with a capacity of 690 mAh g-1 (even after 100 cycles). Finally, pouch cells are prepared to characterize the practical performance of the optimized cathode. This yields a capacity of 741 mAh and a cathode energy density of 1001 Wh kg-1 . These findings are expected to guide the further development of high-energy-density cathode materials for Li-S batteries.

Identification of linear scaling relationships in polysulfide conversion on α-In2Se3-supported single-atom catalysts.

Developing highly active single-atom catalysts (SACs) for suppressing the shuttle effect and enhancing the kinetics of polysulfide conversion is regarded as an important approach to improve the performance of Li-S batteries. However, the adsorption behaviors of polysulfides and the catalytic properties of host materials remain obscure due to the lack of mechanistic understanding of the structure-performance relationship. Here, we identify that the adsorption energies of polysulfides on 3d transition-metal atoms supported by two-dimensional α-In2Se3 with downward polarization (TM@In2Se3) are highly correlated with the d-band centers of the TM atoms. Introduction of the TM atoms on the α-In2Se3 surface improves the electrical conductivity and meanwhile, significantly enhances the adsorption strength of polysulfides and suppresses the shuttle effect. A mechanistic study of polysulfide conversion on TM@In2Se3 shows that the Li2S2 dissociation is the potential-determining step with low activation energies, indicating that TM@In2Se3 can accelerate the kinetics of polysulfide conversion. Electronic structure analysis shows that the kinetics of the potential-determining step on TM@In2Se3 is related to the TM-S interaction in Li2S2-adsorbed TM@In2Se3. A linear scaling relationship between activation energy and the integrated crystal orbital Hamilton population of TM-S in the potential-determining step on TM@In2Se3 is identified. Based on the evaluation of stability, conductivity and activity, we concluded that Ti@In2Se3, V@In2Se3, and Fe@In2Se3 are the promising cathode materials for Li-S batteries. Our findings provide a fundamental understanding of the intrinsic link between the electronic structure and catalytic activity for polysulfide conversion and pave a way for the rational design of SAC-based cathodes for Li-S batteries.

Reactive Spray Drying Approach Towards rGO As Matrix Material for the Cathode of Li-S Batteries

Lithium-sulfur batteries represent a promising alternative to the classical Li-ion technology, particularly due to the high specific energy density combined with the good environmental sustainability of sulfur. Compared to state-of-the-art cathode materials for Li-ion batteries (LiB), which usually contain cobalt and/or manganese, sulfur is less toxic and much more abundant [1]. Additionally, the theoretical capacity of 1.675 mAh g-1 is more than eight times higher than typical cathode materials as Lithium-Nickel-Mangan-Cobalt-Oxide (NMC), Lithium-Cobalt-Oxide (LCO) or Lithium-Iron-Phosphate (LFP) [1,2]. One of the main challenges of sulfur is the so-called “shuttle effect” [1,3]. During lithiation soluble intermediates (polysulfides) migrate to the anode side, further react and precipitate, resulting in a continuous loss of active material and capacity. Next to that, the poor electrical conductivity (5∙10-30 S cm-1) does not allow the utilization of pure sulfur as cathode material [1].To improve the low conductivity, carbon-containing composites have been proposed as cathode material for Li-S batteries for several decades. One possible carbon matrix material is reduced graphene oxide (rGO) [4]. The reduced form of partially oxidized graphite (graphite oxide; GO) is a graphene-like material with high potential for a scale-up to mass production.In our group, we have developed a new synthesis method to rapidly reduce GO using a reactive spray drying technique, where most functional groups can be removed from GO within seconds. The rapid thermal processing leads to a reduced and exfoliated rGO, which still contains small amounts of epoxy groups within the carbon lattice. These remaining oxygen atoms influence the conjugated π-bonds of the graphene-like matrix and thus change the polarity of the surface. A thermal post-treatment for 2 h in Ar/H2 can further reduce the remaining functional groups leading to a highly non-polar surface.It is assumed that oxygen-containing groups (e.g. epoxy and hydroxy) result in a varying adsorption behavior of the polysulfides, affecting the unwanted “shuttle effect” and thus influencing the electrochemical performance [5]. Here, we show the impact of remaining functional groups in rGO on the electrochemical performance of S-rGO composites as cathode material vs. Li/Li+. We compare untreated GO to reactive spray dried and additionally (thermally) post-treated rGO. Furthermore, we analyze the composites in terms of asymmetric and symmetric bonding vibrations as well as crystallinity using FT-IR, RAMAN and XRD.[1] Baikalov, N. et al., Frontiers Energy Research 2020, 8, 207[2] Su, Y.-S. et al., Nature Communications 2013, 4, 2985[3] Ren, W. et al., Energy Storage Materials 2019, 23, 707-732[4] Shastri, M. et al., Ceramics International 2021, 47, 10, B, 14790-14797[5] Ji, L. et al., Journal of the American Chemical Society 2011, 133, 18522-18525

Binary Fe/Mn-Based Nanocomposites as Li-Free Cathode Materials for Li Batteries Assembled in Charged State

Li-ion batteries play important roles in this mobile society. The ever-increasing demand for energy storage, particularly from electric vehicles, requires next-generation Li batteries with higher energy density and better safety. In contrast to existing Li-ion batteries using lithiated cathodes and Li-free anodes, we explore Li-free cathodes coupled with lithium/lithiated anodes in order to construct new Li batteries assembled in a charged state. Two highly promising Li-free cathode materials of 1-D FeOF nanorods and 2-D monolayer MnO2 nanosheets are integrated to make FeOF@MnO2 nanocomposites. FeOF nanorods are sandwiched by monolayer MnO2 nanosheets where FeOF nanoparticles could prevent the restacking of the monolayer MnO2 nanosheets and the presence of monolayer MnO2 nanosheets could enhance the electrical integration of the FeOF nanorods. Synergistic effects of the binary Fe/Mn-based cathodes can lead to both high voltage and high capacity, compared to individual components. Electrochemical evaluation reveals that binary Fe/Mn-based Li-free cathodes demonstrate promising performances and are worthy of further investigation and optimization.

BiFeO3 Coupled Polysulfide Trapping in C/S Composite Cathode Material for Li-S Batteries as Large Efficiency and High Rate Performance

We demonstrated the efficient coupling of BiFeO3 (BFO) ferroelectric material within the carbon–sulfur (C-S) composite cathode, where polysulfides are trapped in BFO mesh, reducing the polysulfide shuttle impact, and thus resulting in an improved cyclic performance and an increase in capacity in Li-S batteries. Here, the built-in internal field due to BFO enhances polysulfide trapping. The observation of a difference in the diffusion behavior of polysulfides in BFO-coupled composites suggests more efficient trapping in BFO-modified C-S electrodes compared to pristine C-S composite cathodes. The X-ray diffraction results of BFO–C-S composite cathodes show an orthorhombic structure, while Raman spectra substantiate efficient coupling of BFO in C-S composites, in agreement with SEM images, showing the interconnected network of submicron-size sulfur composites. Two plateaus were observed at 1.75 V and 2.1 V in the charge/discharge characteristics of BFO–C-S composite cathodes. The observed capacity of ~1600 mAh g−1 in a 1.5–2.5 V operating window for BFO30-C10-S60 composite cathodes, and the high cyclic stability substantiate the superior performance of the designed cathode materials due to the efficient reduction in the polysulfide shuttle effect in these composite cathodes.

Improving Cycling Stability of Vanadium Sulfide (VS4) as a Li Battery Cathode Material Using a Localized High-Concentration Carbonate-Based Electrolyte

Improving Cycling Stability of Vanadium Sulfide (VS₄) as a Li Battery Cathode Material Using a Localized High-Concentration Carbonate-Based Electrolyte

High-Resolution Atomic Absorption Spectrometry Combined With Machine Learning Data Processing for Isotope Amount Ratio Analysis of Lithium.

An alternative method for lithium isotope amount ratio analysis based on a combination of high-resolution atomic absorption spectrometry and spectral data analysis by machine learning (ML) is proposed herein. It is based on the well-known isotope shift of approximately 15 pm for the electronic transition 22P←22S at around the wavelength of 670.8 nm, which can be measured by the state-of-the-art high-resolution continuum source graphite furnace atomic absorption spectrometry. For isotope amount ratio analysis, a scalable tree boosting ML algorithm (XGBoost) was employed and calibrated using a set of samples with 6Li isotope amount fractions, ranging from 0.06 to 0.99 mol mol-1, previously determined by a multicollector inductively coupled plasma mass spectrometer (MC-ICP-MS). The calibration ML model was validated with two certified reference materials (LSVEC and IRMM-016). The procedure was applied toward the isotope amount ratio determination of a set of stock chemicals (Li2CO3, LiNO3, LiCl, and LiOH) and a BAM candidate reference material NMC111 (LiNi1/3Mn1/3Co1/3O2), a Li-battery cathode material. The results of these determinations were compared with those obtained by MC-ICP-MS and found to be metrologically comparable and compatible. The residual bias was -1.8‰, and the precision obtained ranged from 1.9 to 6.2‰. This precision was sufficient to resolve naturally occurring variations, as demonstrated for samples ranging from approximately -3 to +15‰. To assess its suitability to technical applications, the NMC111 cathode candidate reference material was analyzed using high-resolution continuum source atomic absorption spectrometry with and without matrix purification. The results obtained were metrologically compatible with each other.

Effect of Sulfur Chain Length on the Electrochemical Performance of Sulfur-Rich Copolymers in Li-S Batteries

Lithium-Sulfur battery is considered to be a promising next-generation candidate because of its high theoretical capacity of ~1675 mAh/g compared to current commercial batteries. However, there are challenges related to the long-term cycling of these batteries, originating from the formation of soluble lithium polysulfides species and their subsequent shuttling. Recently, we synthesized a sulfur-rich copolymer/ carbon nanofiber cathode material for Li-S batteries. The formation of a C-S bond in these sulfur-rich copolymers results in formation of organo-lithium polysulfides (OPs) instead of lithium polysulfides (PS). The copolymer is synthesized using inverse vulcanization reaction, where sulfur powder reacts with a monomer, here 1,3-di-isopropenyl benzene (DIB), at high temperatures. In this study, we varied the DIB monomer concentration, and three samples with different sulfur/DIB wt% were synthesized. We characterized these three different samples using XRD, DSC, and FTIR. The XRD results show that the sulfur-rich copolymer transitions from a crystalline material to a completely amorphous composite. Moreover, FTIR results show a redshift in the C-S peak of the sulfur-rich copolymer with increasing the monomer wt%. These results confirm that the molecular structure of the sulfur-rich copolymer is changed as a result of changing S/DIB wt ratio in the synthesis of sulfur-rich copolymers. We believe that by increasing the monomer to sulfur ratio in such copolymers, the sulfur chain length becomes shorter. Figure 1 shows the cyclic voltammetry (CV) obtained using these three different cathodes. As can be seen from this figure, two reduction peaks at ~2.3 and ~2 V represent the formation of higher and lower order Ps and OPs. However, with further increase in DIB concentration, the first reduction peak at ~2.3V disappears. We hypothesize that the disappearance of the first reduction peak can be attributed to the existence of a short sulfur chain length. To investigate the hypothesis, an in situ cell consisted of two different cathodes, one cathode with a low (sample 1) and another with a high DIB wt% (sample 2), were built on the FTIR to simultaneously collect IR spectra and CVs. The FTIR results show a redshift from 695 cm-1 to 705 cm-1 in the C-S bond for sample 1 with higher sulfur chain length (lower monomer wt%). This shift is attributed to the formation of organopolysulfides. Moreover, as the cell was discharged, multiple peaks between the lithium polysulfide region (510 to 480 cm-1) appeared, which confirms the formation of high and low order lithium polysulfides. On the other hand, when sample 2 with lower sulfur chain length (high monomer wt%) was tested, the C-S peak shifted from 704 cm-1 to 706 cm-1 only. The smaller C-S peak shift in sample 2 compared to sample 1 confirms the existence of short-chain polysulfides. Moreover, there was no lithium polysulfide peaks observed in the polysulfide region for sample 2, which confirms that the formation of loose lithium polysulfide is avoided. Figure 1

Synergistic effect of cerium oxide with core-shell structure embedded in porous carbon for high-performance lithium-sulfur batteries

Lithium-sulfur batteries are known as the most prospective secondary batteries for their high specific capacity. Nevertheless, lithium-sulfur batteries still face difficulties such as low cycle life and shuttle effect. To solve these problems, we designed S/Core-shell CeO2/porous carbon as a kind of cathode material for Li-S batteries by template method. CA as the carbon source of the porous carbon and the core-shell CeO2 had a synergistic effect which played physical and chemical adsorption for polysulfides roles. XRD, SEM, and TEM tested the crystalline structure and core-shell structure of the material, combined with XPS to demonstrate the element valence states of Ce, C, and S. The initial discharge specific capacity of S/CS-CeO2/PC composite cathode reached 1242.6 mA h g−1 at 0.25 C. The average coulombic efficiency was 92.36 % after 500 cycles, with only 0.015 % attenuation per cycle. S/CS-CeO2/PC exhibited good electrochemical performance, cycle life, and stability.

Recent progress in organic Polymers-Composited sulfur materials as cathodes for Lithium-Sulfur battery

• Organic polymer cathode materials for Li-S batteries are reviewed. • Several challenges of organic polymers-based materials are analyzed with respect to their Li-S batteries performance. • The possible further research directions for overcoming the challenges are also proposed. With a theoretical specific capacity of 1675 mAh g −1 and an energy density of 2600 W h g −1 , environmentally friendly lithium-sulfur batteries (LSBs) have been considered to be one of the most promising candidates for the next generation of high energy density storage devices, which are expected to meet the requirements of transportation vehicles and power grid energy storage. However, LSBs still have several technical challenges hindering their practical applications. One of the challenges is the dissolution of the cathode sulfur and polysulfides caused shuttle effect which can significantly reduce their cycle-life. To mitigate the challenges, conductive organic polymers have been explored for holders to encapsulate sulfur and inhibit the dissolution of polysulfides into the electrolyte, as well as increase both the electric and ionic conductivities of the corresponding cathodes. This paper reviews the recent progress in conductive organic polymers-composited sulfur materials as cathodes for LSBs in terms of their synthesis, characterization, functional mechanisms and performance validation/optimization. The reviewed polymers include polyacrylonitrile (PAN), polyaniline (PANI), polythiophene (PTh), polypyrrole (PPy), pypercrosslinked polymers (HCPs), etc. Several technical challenges of these organic polymers-based materials are analyzed with respect to their LSB performance, and several possible further research directions for overcoming the challenges are also proposed for further development toward practical applications.

Hollow urchin-like Al-doped α-MnO2−x as advanced sulfur host for high-performance lithium-sulfur batteries

An urchin-like hollow Al-doped α-MnO2−x microsphere is prepared by a facile hydrothermal method and exhibited effective regulation for the dissolution of polysulfides from the Li-S cathode. After Al doping, the conductivity of MnO2 has been greatly improved, and made the traditional MnO2 morphology changed. These Al-doped α-MnO2−x/S microspheres are found to exhibit high initial discharge capacity of 1017 mAh g−1 under sulfur content up to 73 wt% at 1 C and they exhibit a favorable cycle stability of 694 mAh g−1 at 3 C after 300 cycles. These excellent characteristics make this composite a promising cathode material for Li-S batteries.

In Situ FTIR Study on Organo-Polysulfide Evolution in CNF/Sulfur-Copolymer Cathodes for Li-S Batteries: Effect of Sulfur Chain Length on the Electrochemical Performance

Lithium-Sulfur batteries offer five times more energy density compared to conventional Li-ion batteries. However, there are challenges related to long term cycling of these batteries. Recently, we synthesized a sulfur-rich copolymer/ carbon nanofiber cathode material for Li-S batteries. The formation of a C-S bond in these sulfur-rich copolymers results in the formation of organo-lithium polysulfides (OPs), instead of lithium polysulfides (PS). In the present work, we demonstrate in situ FTIR spectroscopy as a tool to investigate the C-S bond and lithium polysulfide evolution in sulfur-rich copolymer-based Li-S batteries. The copolymer is synthesized using inverse vulcanization reaction, where sulfur powder reacts with a monomer, here 1,3-diisopropenylbenzene (DIB), at high temperatures. In this study, we varied the DIB monomer concentration and three samples with differen sulfur/DIB wt% were synthesized. Figure 1 shows the cyclic voltammetry (CV) obtained using the three different cathodes. As it can be seen from this fugure two reduction peaks at ~2.3 and 2 V represent the formation of higher and lower order Ps and OPs. However, with further increase in DIB concentration, the first reduction peak at ~2.3V disappears. We hypothesize that the disappearance of the first reduction peak can be attributed to the existence of short sulfur chain length. To investigate the hypothesis, an in situ cell consisted of two different cathodes, one cathode with a low (sample 1) and another with a high DIB wt% (sample 2), were built on the FTIR to simultaneously collect IR spectra and CVs. Our results show that the C-S bond located at ~695 cm-1 in sample 1 shifts to higher wavenumbers (~705cm-1) as we discharge the cell. The shift to higher wavenumbers shows that the formation of OPs, strengthens the C-S bonds which originates from having Li, with lower electronegativity (0.98 VS. 2.58), instead of S. However, when we tested the sample 2 cell, the C-S cyclic shift, happens between ~704 to ~706 cm-1, only. The smaller C-S peak shift in sample 2 compared to sample 1 is attributed to the existence of the short chain length sulfur. Figure 1

Tuning the Morphology and Electronic Properties of Single-Crystal LiNi0.5Mn1.5O4−δ: Exploring the Influence of LiCl–KCl Molten Salt Flux Composition and Synthesis Temperature

Single-crystal materials have played a unique role in the development of high-performance cathode materials for Li batteries due to their favorable chemomechanical stability. The molten salt synthesis method has become one of the most prominent techniques used to synthesize single-crystal layered and spinel materials. In this work, the molten salt synthesis method is used as a technique to tune both the morphology and Mn3+ content of high-voltage LiNi0.5Mn1.5O4 (LNMO) cathodes. The resulting materials are thoroughly characterized by a suite of analytical techniques, including synchrotron X-ray core-level spectroscopy, which are sensitive to the material properties on multiple length scales. The multidimensional characterization allows us to build a materials library according to the molten salt phase diagram as well as to establish the relationship among synthesis, material properties, and battery performance. The results of this work show that the Mn3+ content is primarily dependent on the synthesis temperature and increases as the temperature is increased. The particle morphology is mostly dependent on the composition of the molten salt flux, which can be tailored to obtain well-defined octahedrons enclosed by (111) facets, plates with predominant (112̅) facets, irregularly shaped particles, or mixtures of these. The electrochemical measurements indicate that the Mn3+ content has a larger contribution to the battery performance of LNMO than do morphological characteristics and that a significant amount of Mn3+ could become detrimental to the battery performance. However, with similar Mn3+ contents, morphology still plays a role in influencing the battery cycle life and rate performance. The insights of molten salt synthesis parameters on the formation of LNMO, with deconvolution of the roles of Mn3+ and morphology, are crucial to continuing studies in the rational design of LNMO cathode materials for high-energy Li batteries.

Synthesis and Characterization of a Composite Cathode Material (Li2S@rGO) for Li-S Batteries Made By in Situ Electrochemical Conversion of MoS2@rGO

Lithium disulfide (Li2S) could be used as cathode material for high-energy-density lithium–sulfur (Li–S) batteries, having a large theoretical specific capacity (1166 mAh g–1). However, the material has low conductivity. Additionally, soluble lithium polysulfide species can be formed during cell operation in carbonate-based electrolytes resulting in a poor cycling stability. In this work, Li2S particles are wrapped in reduced graphene oxide (Li2S@rGO) to produce cathode materials for Li–S batteries in carbonate-based electrolytes. First GO is produced by a modified Hummers method. Then, rGO is reduced hydrothermally on MoS2 particles. The composite is then fully lithiated and irreversible decomposed at 0.01 V vs. Li/Li+ to produce a Li2S@rGO with a high Li2S (loading of ≈5 mg cm–2). The material is characterized by SEM, TEM, EDXS, N2 isotherm and XRD (before and after cell cycling). The material is then used as cathode with Li foil as counter electrode. The system is mounted as coin cells (CR2025) in an Ar filled glove box, filled with 1 M LiPF6 in ethylene carbonate/dimethyl carbonate (EC/DMC; 1:1 v/v). The cells are sealed and then cycled in air (constant temperature and humidity). The electrochemical properties are investigated using galvanostatoc charge/discharge cycles, cyclic voltammetry and electrochemical impedance spectroscopy measurements. The cathode material exhibits a high initial capacity: 1401 mAh g–1 (based on S weight) at 0.1 C. Besides, it shows a good capacity retention (411 mAh g–1 at 2 C after 150 cycles) and excellent Coulombic efficiency (≈99.5%). The material could be used in high-loading Li2S cathodes for high-performance Li–S batteries without the disadvantage of polysulfide formation.

Ultrasmall Iron Fluoride Nanoparticles Embedded in Graphitized Porous Carbon Derived from Fe‐Based Metal Organic Frameworks as High‐Performance Cathode Materials for Li Batteries

AbstractIron‐based metal organic framework (MOF) MIL‐53 is used as a precursor and self‐template to synthesize a 3D porous carbon/FeF3 ⋅ 0.33 H2O composite in situ. We find that the organic ligands in iron‐containing MOFs can convert into highly graphitized carbon with the catalysis of central Fe atoms. The FeF3 ⋅ 0.33 H2O nanoparticles formed after fluorination and dehydration are surrounded by highly graphitized carbon. In the composite, the graphitized 3D porous carbon can provide passageways for electron transport and ultrasmall FeF3 ⋅ 0.33 H2O nanoparticles facilitate the diffusion of Li ions. The composite shows excellent performance for the Li storage. A capacity of 86 mAh g−1 can be reached at an ultra‐high rate of 20 C. Even after 300 charge−discharge cycles at 5 C, the capacity remains at 113 mAh g−1.

The effect of cerium oxide addition on the electrochemical properties of lithium-sulfur batteries

The effects of various CeO2 additions on the electrochemical properties of lithium-sulfur batteries have been studied over synthesizing the sulfur-host matrix with unique surface appearance. It has been revealed that the appropriate additions of CeO2 (0.70–3.65 wt%) to the porous carbon were beneficial to enhance the cycle performance. The polar metal oxide CeO2 can chemically adsorb the sulfur species and promote redox reaction through catalysis properties. Meanwhile, the porous carbon can enhance the conductivity of cathode and form a favorable physical barrier to block the diffusion of polysulfide with abundant pore structures. As results, the CS-CeO2 composite (with 1.84 wt% CeO2) exhibits significantly improved electrochemical performance as a cathode material for Li-S batteries. The initial discharge capacity of assembled battery is as high as 1434.1 mAh g−1 at 0.05 C and the discharge capacity retains 873.6 mAh g−1 with a low decay rate of 0.077% per cycle after 200 cycles at 0.2 C. When the area sulfur content is as high as 4.53 mg cm−2, the CS-Ce2 cathode still retains a discharge capacity of 572.3 mAh g−1 at 1 C after 100 cycles.

Enhancing the performance of sulfurized polyacrylonitrile cathode by in-situ wrapping

Sulfurized Polyacrylonitrile (S-PAN) has garnered extensive attention as cathode materials for LiS batteries in recent years because of its advantages such as high sulfur utilization efficiency, high Coulombic efficiency and low self-discharge rate. However, it is difficult to effectively balance the conflict between a high S loading (> 45wt%) and cycling stability for S-PAN. In this work, we employed an in situ wrapping method to improve the cycling performance of high-S-content S-PAN. Compared with the unwrapped S-PAN, the capacity retention ratio of the wrapped S-PAN cathode increased from 38% to 62% after 100cycles at 0.25C. The analyzed results suggested that the wrapping layer on the high-S-content S-PAN may compose a mixture of sulfide, inorganic LiBxOy and some organic compounds.