Synergistic electrochemical catalysis by high-entropy metal phosphide in lithium-sulfur batteries.

The shuttle effect and sluggish redox kinetics of polysulfides have hindered the development of lithium-sulfur batteries (LSBs) as premier energy storage devices. To address these issues, a high-entropy metal phosphide (NiCoMnFeCrP) was synthesized using the sol-gel method. NiCoMnFeCrP, with its rich metal species, exhibits strong synergistic effects and provides numerous catalytic active sites for the conversion of polysulfides. These active sites, possessing significant polarity, can bond with polysulfides. In situ ultraviolet-visible were conducted to monitor the dynamic changes in species and concentrations of polysulfides, validating the ability of NiCoMnFeCrP to facilitate the conversion of polysulfides. The batteries with the NiCoMnFeCrP catalyst as functional separators exhibited minimal capacity decay rates of 0.04 % and 0.23 % after 100 cycles at 0 °C and 60 °C, respectively. This indicates that the NiCoMnFeCrP catalyst possesses good thermal stability. Meanwhile, its area capacity can reach 4.78 mAh cm-2 at a high sulfur load of 4.54 mg cm-2. In conclusion, NiCoMnFeCrP achieves the objective of mitigating the shuttle effect and accelerating the kinetics of the redox reaction, thereby facilitating the commercialization of LSBs.

Enabling Rapid and Stable Sodium Storage via a P2-Type Layered Cathode with High-Voltage Zero-Phase Transition Behavior.

Currently, a major target in the development of Na-ion batteries is the concurrent attainment of high-rate capacity and long cycling stability. Herein, an advanced Na-ion battery with high-rate capability and long cycle stability based on Li/Ti co-doped P2-type Na0.67 Mn0.67 Ni0.33 O2 , a host material with high-voltage zero-phase transition behavior and fast Na+ migration/conductivity during dynamic de-embedding process, is constructed. Experimental results and theoretical calculations reveal that the two-element doping strategy promotes a mutually reinforcing effect, which greatly facilitates the transfer capability of Na+ . The cation Ti4+ doping is a dominant high voltage, significantly elevating the operation voltage to 4.4 V. Meanwhile, doping Li+ shows the function in charge transfer, improving the rate performance and prolonging cycling lifespan. Consequently, the designed P2-Na0.75 Mn0.54 Ni0.27 Li0.14 Ti0.05 O2 cathode material exhibits discharge capacities of 129, 104, and 85 mAh g- 1 under high voltage of 4.4 V at 1, 10, and 20 C, respectively. More importantly, the full-cell delivers a high initial capacity of 198 mAh g-1 at 0.1 C (17.3 mA g-1 ) and a capacity retention of 73% at 5 C (865 mA g-1 ) after 1000 cycles, which is seldom witnessed in previous reports, emphasizing their potential applications in advanced energy storage.

MoO2/t-C3N4 Heterogeneous Materials with Bidirectional Catalysis for the Rapid Conversion of S Species in Li-S Batteries.

Li-S batteries have drawn a lot of attention for their high theoretical specific capacity and significant economic benefits. However, the shuttle effect of polysulfides prevents them from being used widely. To tackle this difficulty, a heterogeneous structure based on tubular carbon nitride with evenly dispersed molybdenum dioxide nanoparticles (MoO2/t-C3N4) as the S host is constructed in this work. As a polar material with a large specific surface area, MoO2/t-C3N4 has a strong anchoring effect on polysulfide. Additionally, the heterogeneous material has excellent bidirectional catalytic ability for the redox process of S species based on the action of the built-in electric field formed by electron directional transfer. Not only does it improve the reaction kinetics of the redox process of the polysulfides but it also prevents polysulfides from accumulating on the surface of the modified material and deactivating it, further improving the utilization of the active material. Thus, MoO2/t-C3N4/S shows the high initial-discharge specific capacity of 812.7 mAh g-1 at the current density of 5C, and the Coulombic efficiency is maintained at more than 95% after 400 charge/discharge cycles. Moreover, MoO2/t-C3N4/S achieved a capacity retention of 89% after 100 cycles at the current density of 0.1C under the high S loading. Therefore, the research results of this work provide a trustworthy reference for the future commercial application of Li-S batteries.

Long-Term Cycling Stability of Porphyrin Electrode for Li/Na Charge Storage at High Temperature.

Bipolar redox organic compounds have been considered as potential next-generation electrode materials due to their sustainability, low cost and tunable structure. However, their development is still limited by the poor cycling stability and low energy density ascribed to high dissolution during cycling and the low conductivity of organic molecules. Herein, porphyrin-based bipolar organics of [5,10,15,20-tetrathienylporphinato] MII (M=2 H, Cu (CuTTP)) are proposed as new stable organic electrodes. Enhanced cycling stability is obtained by a temperature-induced in situ polymerization strategy of porphyrin molecules. The resulting polymer exhibits excellent cycling stability up to 10 00 cycles even at a high current density (1000 mA g-1 ) in organic lithium-/sodium-based charge storage devices at 50 °C. In a symmetrical cell using CuTTP as both cathode and anode material a discharge capacity of 72 mAh g-1 is achieved after 600 cycles at 1000 mA g-1 . This strategy would offer a new approach to developing stable energy storage bipolar materials in organic-based devices at high temperature.

Insight into the Catalytic Role of Defect-Enriched Vanadium Sulfide for Regulating the Adsorption-Catalytic Conversion Behavior of Polysulfides in Li-S Batteries.

The performance promotion of Li-S batteries relies primarily on inhibition of the shuttle effect and improvement of the catalytic-conversion reaction kinetics of polysulfides. Herein, we prepare defect-enriched VS2 nanosheets (VS2-x) as catalysts for Li-S batteries and further study the catalytic mechanism of VS2-x via ex situ X-ray diffraction and in situ UV-vis spectroscopy. A multifunctional S cathode was also obtained by assembling VS2-x on a C cloth to achieve high S loading for Li-S batteries. It was found that VS2-x catalysts undergo a lithiation process in the work voltage of Li-S batteries, and the triggered LiyVS2-x intermediates reciprocate VS2-x with a high catalytic activity so as to enhance the performance of Li-S batteries by promoting the dissociation process of S62- to S3•-. Consequently, Li-S batteries with a C/VS2-x/S cathode deliver a high reversible capacity (1471 mAh g-1 at 0.1 C) and good cycling performance (low fading rate of 0.064% per cycle after 400 cycles). Meanwhile, the CC@VS2-x/S cathode with a high S areal loading of 5.6 mg cm-2 can render a satisfactory areal capacity of 4.22 mAh cm-2 at 0.2 C and a cycle stability of over 100 cycles. Therefore, the study on the catalysis of LiyVS2-x intermediates provides a scientific view for revealing the catalysis mechanism of a sulfide-based electrocatalyst and boosting the development of an electrocatalyst for Li-S batteries.

ZnFe2O4-Ni5P4 Mott-Schottky Heterojunctions to Promote Kinetics for Advanced Li-S Batteries.

The practical progress of lithium-sulfur batteries is hindered by the serious shuttle effect and the slow oxidation-reduction kinetics of polysulfides. Herein, the ZnFe2O4-Ni5P4 Mott-Schottky heterojunction material is prepared to address these issues. Benefitting from a self-generated built-in electric field, ZnFe2O4-Ni5P4 as an efficient bidirectional catalysis regulates the charge distribution at the interface and accelerates electron transfer. Meanwhile, the synergy of the strong adsorption capacity derived from metal oxides and the outstanding catalytic performance that comes from metal phosphides strengthens the adsorption of polysulfides, reduces the energy barrier during the reaction, accelerates the conversion between sulfur species, and further accelerates the reaction kinetics. Hence, the cell with ZnFe2O4-Ni5P4/S harvests a high discharge capacity of 1132.4 mAh g-1 at 0.5C and displays a high Coulombic efficiency of 99.3% after 700 cycles. The ZnFe2O4-Ni5P4/S battery still maintains a capacity of 610.1 mAh g-1 with 84.4% capacity retention after 150 cycles at 0.1C under a high sulfur loading of 3.2 mg cm-2. This work provides a favorable reference and advanced guidance for developing Mott-Schottky heterojunctions in lithium-sulfur batteries.

Porous NiCo2S4 Nanoneedle Arrays with Highly Efficient Electrocatalysis Anchored on Carbon Cloths as Self-Supported Hosts for High-Loading Li-S Batteries.

Lithium-sulfur (Li-S) batteries have attracted all-time attention because of their supernormal high energy density and low cost, whereas they are still plagued by the severe polysulfide shuttling and sluggish sulfur redox reaction kinetics. Moreover, poor sulfur electrochemical utilization and rapid capacity degradation are top concerns in the high-loading Li-S batteries, which severely hinder their practical applications. Herein, a completely novel porous nanoneedle array NiCo2S4 electrocatalyst grown on a nitrogen-sulfur-doped carbon cloth (NSCC) (NiCo2S4@NSCC) is constructed as a 3D self-supported sulfur host for high-loading Li-S batteries, in which the highest sulfur loading reaches 4.9 mg cm-2. The as-prepared NiCo2S4@NSCC with a typical sulfur loading of around 2.0 mg cm-2 provides a high discharge capacity of 1223 mA h g-1 at 0.2 C and long-term cycle stability with a low capacity decay of 0.046% per cycle over 500 cycles at 1 C. Additionally, NiCo2S4@NSCC/S with a high sulfur loading of 4.9 mg cm-2 delivers an excellent reversible areal capacity of 4.4 mA h cm-2 g over 50 cycles. Noting that such superior electrochemical performance of NiCo2S4@NSCC/S with high-loading sulfur is mainly attributed to high electronic conductivity and the abundant porous structure of NSCC to transport electrons and ions fastly and accommodate sulfur as well as robust absorbability and the outstanding catalytic effect of NiCo2S4 to accelerate the capture and conversion of the polysulfide intermediate. Predictably, this work can provide a guideline to efficiently and rationally design the structure of metal-based compounds with catalytic functions for various applications.

Superior Na-Storage Properties of Nickel-Substituted Na2FeSiO4@C Microspheres Encapsulated with the In Situ-Synthesized Alveolation-like Carbon Matrix.

The poor electronic conductivity of Na2FeSiO4 always limits its electrochemical reactivities and no effective solution has been found to date. Herein, the novel Ni-substituted Na2Fe1-xNixSiO4@C nanospheres (50-100 nm) encapsulated with a 3D hierarchical porous skeleton (named as alveolation-like configuration) constructed using in situ carbon are first synthesized via a facile sol-gel method, and the effects of Ni substitution combined with the design of a unique carbon network on Na-storage properties are assessed systematically, focusing on alleviating the inherent defects of the Na2FeSiO4 cathode material. A series of characterization technologies such as X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy and so forth, coupled with the electrochemical measurements and first-principles calculations, are used to explore the structure, morphology and electrochemical behaviors of the as-prepared materials. The results show that the synergism between Ni substitution and the special alveolation-like configuration enables fast Na ions mobility (from 10-14 to 10-12 cm2 s-1), reduces band gap energy (from 2.82 to 1.79 eV) and lowers Na-ion diffusion barriers, finally reciprocating the vigorous electrochemical kinetics of the electrode. Especially, the elaborately designed material-Na2Fe0.97Ni0.03SiO4@C-displays superior Na-storage properties of around 197.51 mA h g-1 (corresponding to 1.43 Na+ intercalation) at 0.1 C within 1.5-4.5 V along with desirable capacity retention (84.44% after 100 cycles), and the rate capability is also markedly enhanced (a capacity of 133.62 mA h g-1 at 2 C). Such the effective methodology employed in this work opens a potential pathway to synthesize the silicate cathode material with excellent electrochemical properties.

Copper Porphyrin as a Stable Cathode for High-Performance Rechargeable Potassium Organic Batteries.

Rechargeable potassium-ion batteries (KIBs) are promising alternatives to lithium-ion batteries for large-scale electrochemical energy-storage applications because of the abundance and low cost of potassium. However, the development of KIBs is hampered by the lack of stable and high-capacity cathode materials. Herein, a functionalized porphyrin complex, [5,15-bis(ethynyl)-10,20-diphenylporphinato]copper(II) (CuDEPP), was proposed as a new cathode for rechargeable potassium batteries. Spectroscopy and molecular simulation studies were used to show that both PF6 - and K+ interact with the porphyrin macrocycle to allow a four-electron transfer. In addition, the electrochemical polymerization of the ethynyl functional groups in CuDEPP resulted in the self-stabilization of the cathode, which was highly stable during cycling. This unique charge storage mechanism enabled CuDEPP to provide a capacity of 181 mAh g-1 with an average potential of 2.8 V (vs. K+ /K). These findings could open a pathway towards the design of new stable organic electrodes for KIBs.

Carbon-Coated Yttria Hollow Spheres as Both Sulfur Immobilizer and Catalyst of Polysulfides Conversion in Lithium-Sulfur Batteries.

Li-S battery has tremendous application prospect on account of the high theoretical specific capacity and large energy density, while its large-scale application is impeded by the severe shuttle effect and the slow electrochemical kinetics of polysulfides conversion. Herein, the Lewis acidic yttria hollow spheres (YHS) are rationally designed as both sulfur immobilizer and catalyst of polysulfides conversion for the advanced Li-S batteries. It can be known that the Lewis acidic yttria can effectively capture the Lewis basic polysulfides and thus mitigate the shuttle effect of Li-S battery; besides, yttria shows the enhanced catalytic effect for the kinetics of interconversion reaction from polysulfides to Li2S. As a result, either as a sulfur host or as the separator coating, yttria plays a vital part in realizing the high specific discharge capacity and good cycle stability for Li-S battery. In particular, Li-S battery with YHS@C/S cathode and YHS/CNT-0.6- modified separator (2.1 mg cm-2 active material loading) shows a good specific discharge capacity of 912.5 mAh g-1 at 0.5C. Even after 200 steady cycles, the discharge specific capacity can keep as 842.3 mAh g-1, and the capacity decay rate is only 0.038% per cycle. When active material areal loading is increased to 4.24 mg cm-2, it still maintains a considerable areal capacity of 3.79 mAh cm-2. In consequence, the synergy of polysulfides confinement and catalytic conversion reaction provides a meaningful exploration for achieving the high performance of Li-S batteries.

Architecture and Performance of the Novel Sulfur Host Material Based on Ti2O3 Microspheres for Lithium-Sulfur Batteries.

Lithium-sulfur batteries are considered as promising next-generation green secondary batteries. Irrespective of the enhancement of the cycling stability or the suppression of polysulfide species shuttle, although much progress has recently been achieved, improving the conductivity of host materials and capturing the sulfide species as far as possible are still hot topics in the research of lithium-sulfur batteries nowadays. Here, we put forward a novel sulfur host architecture based on Ti2O3 microspheres fabricated by magnesiothermic reduction. The Ti2O3 microspheres possess both high electronic conductivity and excellent ability of anchoring lithium polysulfide species. The high electronic conductivity endowed by a narrow band gap can adequately activate insulative sulfur and reduce the battery resistance so that high specific capacity and excellent rate capability can be achieved, while the polar Ti2O3 could afford abundant polar active sites for the absorption of polysulfides for high capacity retention. As a result, Ti2O3 microspheres are applied in the research of lithium-sulfur batteries; excellent electrochemical performance has been revealed. The initial specific capacity is 1245 mAh g-1 at 0.2C, with 91.57% capacity retention after 180 cycles. Even with a high areal loading of 3.6 mg cm-2, an initial capacity of 665 mAh g-1 at 0.5C and a good capacity retention of 70.98% after 300 cycles could be achieved. Apparently, the preparation and application of Ti2O3 microspheres can not only further extend the application field of the Ti-based compound but also boost the electrochemical performance of lithium-sulfur batteries.

Multifunctional Heterostructures for Polysulfide Suppression in High-Performance Lithium-Sulfur Cathode.

The commercialization of lithium-sulfur (Li-S) batteries is greatly hindered due to serious capacity fading caused by the polysulfide shuttling effect. Optimizing the structural configuration, enhancing reaction kinetics of the sulfur cathode, and increasing areal sulfur loading are of great significance for promoting the commercial applications of Li-S batteries. Herein, the multifunctional polysulfide scavengers based on nitrogen, sulfur co-doped carbon cloth (DCC), which is supported by flower-like MoS2 (1T-2H) decorated with BaMn0.9 Mg0.1 O3 perovskite particle (PrNP) and carbon nanotubes (CNTs), namely, DCC@MoS2 /PrNP/CNTs, are delicately designed and synthesized. The physical confinement, chemical coupling, and catalysis conversion for active sulfur are achieved simultaneously in this polysulfide motif. Due to these merits, the as-fabricated self-supported DCC@MoS2 /PrNP/CNTs/S manifests an excellent reversible areal capacity of 4.75 mAh cm-2 with an ultrahigh sulfur loading of 5.2 mg cm-2 at the 50th cycle. The outstanding cycling stability is obtained upon 800 cycles with a large reversible capacity of 871 mAh g-1 and a negligible fading rate of 0.02% per cycle at a rate of 1.0 C, suggesting its promising prospects for the commercial success of high-performance Li-S batteries toward flexible electronic devices and energy storage equipment.

Effects of Nanofiber Architecture and Antimony Doping on the Performance of Lithium-Rich Layered Oxides: Enhancing Lithium Diffusivity and Lattice Oxygen Stability.

Li-rich layered oxides (LLOs) with high specific capacities are favorable cathode materials with high-energy density. Unfortunately, the drawbacks of LLOs such as oxygen release, low conductivity, and depressed kinetics for lithium ion transport during cycling can affect the safety and rate capability. Moreover, they suffer severe capacity and voltage fading, which are major challenges for the commercializing development. To cure these issues, herein, the synthesis of high-performance antimony-doped LLO nanofibers by an electrospinning process is put forward. On the basis of the combination of theoretical analyses and experimental approaches, it can be found that the one-dimensional porous micro-/nanomorphology is in favor of lithium-ion diffusion, and the antimony doping can expand the layered phase lattice and further improve the lithium ion diffusion coefficient. Moreover, the antimony doping can decrease the band gap and contribute extra electrons to O within the Li2MnO3 phase, thereby enhancing electronic conductivity and stabilizing lattice oxygen. Benefitting from the unique architecture, reformative electronic structure, and enhanced kinetics, the antimony-doped LLO nanofibers possess a high reversible capacity (272.8 mA h g-1) and initial coulombic efficiency (87.8%) at 0.1 C. Moreover, the antimony-doped LLO nanofibers show excellent cycling performance, rate capability, and suppressed voltage fading. The capacity retention can reach 86.9% after 200 cycles at 1 C, and even cycling at a high rate of 10 C, a capacity of 172.3 mA h g-1 can still be obtained. The favorable results can assist in developing the LLO material with outstanding electrochemical properties.

Hydrothermal preparation and performance of LiFePO4 by using Li3PO4 recovered from spent cathode scraps as Li source.

A novel process recycling Li from the spent LiFePO4 cathode material has been put forward. The new LiFePO4 sample is synthesized through hydrothermal reaction by using recovered Li3PO4 as Li source and FeSO4·7H2O as Fe source. The morphologies, structure and physicochemical properties of the re-synthesized LiFePO4 cathode material were characterized by Field emission scanning electron microscope (FESEM), X-ray diffraction (XRD), Transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS) and electrochemical measurement. The results showed that the morphology and particle size of re-synthesized LiFePO4 samples become more regular and smaller with the increase of the hydrothermal reaction temperature. Besides, it has been found that the LiFePO4 cathode material synthesized at 200 °C showed excellent electrochemical properties which deliver a high initial capacity of 144.25 mAh/g at the rate of 1 C and high capacity retention of 96.7% after 200 cycles. Therefore, this work provides a new strategy for recovery and recycle of the spent LiFePO4 cathode scraps.

Spinel/Layered Heterostructured Lithium-Rich Oxide Nanowires as Cathode Material for High-Energy Lithium-Ion Batteries.

Lithium-rich oxide material has been considered as an attractive candidate for high-energy cathode for lithium-ion batteries (LIBs). However, the practical applications are still hindered due to its low initial reversible capacity, severe voltage decaying, and unsatisfactory rate capability. Among all, the voltage decaying is a serious barrier that results in a large decrease of energy density during long-term cycling. To overcome these issues, herein, an efficient strategy of fabricating lithium-rich oxide nanowires with spinel/layered heterostructure is proposed. Structural characterizations verify that the spinel/layered heterostructured nanowires are a self-assembly of a lot of nanoparticles, and the Li4Mn5O12 spinel phase is embedded inside the layered structure. When the material is used as cathode of LIBs, the spinel/layered heterostructured nanowires can display an extremely high invertible capacity of 290.1 mA h g-1 at 0.1 C and suppressive voltage fading. Moreover, it exhibits a favorable cycling stability with capacity retention of 94.4% after charging/discharging at 0.5 C for 200 cycles and it shows an extraordinary rate capability (183.9 mA h g-1, 10 C). The remarkable electrochemical properties can be connected with the spinel/layered heterostructure, which is in favor of Li+ transport kinetics and enhancing structural stability during the cyclic process.

Cornlike Ordered Mesoporous Silicon Particles Modified by Nitrogen-Doped Carbon Layer for the Application of Li-Ion Battery.

The cornlike ordered mesoporous silicon (OM-Si) particles modified by the nitrogen-doped carbon layer (OM-Si@NC) are successfully fabricated and used as the anode of lithium-ion battery (LIBs). The influences of the N-doped carbon layer on the structure and electrochemical properties of the OM-Si@NC composite are detailedly investigated by transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectrum, X-ray photoelectron spectroscopy (XPS), and charge/discharge tests. The results reveal that the amorphous N-doped carbon layer can offer the abundant conductive pathways for fast lithium ion transportation and electron transfer, which not only leads to a high specific capacity under high ampere density but also serves as a structural barrier maintaining the whole integrity and settling the mechanical breaking due to the huge volume changes of Si host. Therefore, the as-synthesized OM-Si@NC composite exhibits a high original discharge capacity of 2548 mA h g-1 under 0.2 A g-1 as well as a large reversible capacity of 1336 mA h g-1 under 1 A g-1 after 200 circles. The OM-Si@NC composite prepared by a relatively simple and feasible synthesis method shows excellent electrochemical performances and turns out to be promising for the application of high power LIBs.