Negative Electrode Material Research Articles

Conversion-type Ni2.5Co0.5(PO4)2 phosphate as negative electrode material for rechargeable Li-ion batteries

The production of clean energy requires efficient energy storage systems, such as Lithium-ion batteries, to store wind and solar energy. To meet this demand, suitable electrode materials must be chosen. Conversion-type negative electrode materials are considered promising candidates due to their high reversible capacity. In this study, pure Ni2.5Co0.5(PO4)2 (NCP) orthophosphate was synthesized using a solid-state reaction at 900 °C in air and its electrochemical behavior was studied for the first time as a negative electrode material. Carboxymethyl cellulose (CMC) and polyvinylidene fluoride (PVDF) binders were used and the obtained performances were compared. The electrochemical properties were explored over a voltage range of 0.5 – 3.0 V and 0.01 – 3.0 V. The results showed that NCP exhibits the best electrochemical properties, delivering a high reversible discharge capacity of 200 mAh g−1 after 30 cycles at a C/5 current rate over 0.01 – 3.0 V voltage range, using a water-based CMC binder. Additionally, NCP@C delivers a reversible discharge capacity of 211 mAh g−1 after 400 cycles at a 2 C rate with a coulombic efficiency of 100 %

Tin Interlayer at the Li/Li3PS4 Interface for Improved Li Stripping/Plating Performance

Li metal is a promising negative electrode material for the development of all-solid-state batteries with high energy densities. However, the short-circuiting of batteries owing to Li dendrite formation is challenging. To solve this issue, it is crucial to form a suitable interface between the Li metal and solid electrolyte. This study demonstrates that the incorporation of a Sn interlayer at the interface between the Li metal and Li3PS4 (LPS) electrolyte improved the Li stripping/plating performance of all-solid-state Li symmetrical cells. The cycling performance was further enhanced by replacing pure Li metal with a Li–Mg alloy. Galvanostatic cycling tests were conducted on a symmetrical cell of Li–Mg/Sn/LPS/Sn/Li–Mg at a current density of 1.0 mA cm–2 and a temperature of 100 °C. The operation of the cell was stable for 5000 h without short-circuiting. X-ray diffraction (XRD) and scanning electron microscopy (SEM) revealed that Sn film incorporation into the Li or Li–Mg/LPS interface suppressed the reductive LPS decomposition and maintained a stable interface. These findings will facilitate the development of interfacial modifications between Li metal and sulfide solid electrolytes to enhance the cycling performance of all-solid-state Li metal batteries.

Structural and Electrical Properties of Novel Cr/Fe Mixed Transition-Metal Phosphates.

The phosphate KCoCr(PO4)2 and iron-substituted variants KCoCr1-xFex(PO4)2 (x = 0.25, 0.5, and 0.75) were synthesized by a solid-state reaction route, while a high substitution level of Fe was achieved. Their structures were refined using powder X-ray diffraction and indexed in a monoclinic system with a P21/n space group. A 3D framework with six-sided tunnels parallel to the [101] direction was formed in which the K atoms are located. Mössbauer spectroscopy confirms the exclusive presence of octahedral paramagnetic Fe3+ ions, with isomer shifts increasing slightly with x substitution. Electron paramagnetic resonance spectroscopy confirmed the presence of paramagnetic Cr3+ ions. The activation energy, determined by dielectric measurements, shows that the iron-containing samples present higher ionic activity. Relative to the electrochemical activity of K, these materials could be good candidates for positive and/or negative electrode materials for energy storage applications.

Ethyl viologen-functionalized reduced graphene oxide composites for asymmetric ionic liquid-based supercapacitors

The development of pseudocapacitive materials matching ionic liquid (IL) electrolytes can significantly enhance the performance of supercapacitors (SCs). Herein we report an ethyl viologen-functionalized reduced graphene oxide composite (EV-RGO) synthesized by one-step hydrothermal method. In EV-RGO, the ethyl viologen cations are anchored on the RGO sheets through electrostatic interactions, π-π stacking interactions, and cation-π interactions, which makes EV-RGO as an electrode material more stable and reversible during charging and discharging. Meanwhile, the viologen cations with ethyl groups can better function as a spacer to suppress effectively the stacking of RGO sheets and expand their interlayer spacing. In 1-ethyl-3-methylimidazolium tetrafluoroborate (EmimBF4) IL electrolyte, the electrochemical performance of the composite is enhanced due to synergic contributions from electric double-layer capacitance and pseudocapacitance. The pseudocapacitance mechanism is also supported by the results of XPS data. The specific capacitance of the EV-RGO as a negative electrode material for SCs reaches to 222.7 F g−1 at a current density of 0.5 A g−1. An asymmetric SC device (EV-RGO//AC ASC) exhibits an energy density of 64.1 Wh kg−1 at a power density of 888 W kg−1. This work offers an advanced strategy for the fabrication of high-performance SCs using organic molecule-modified graphene composites.

Two-Dimensional Siloxene Nanosheets: Impact of Morphology and Purity on Electrochemistry.

Two-dimensional (2D) siloxene (Si6O3H6) has shown promise as a negative electrode material for Li-ion batteries due to its high gravimetric capacity and superior mechanical properties under (de)lithiation compared to bulk Si. In this work, we prepare purified siloxene nanosheets through the removal of bulk Si contaminants, use ultrasonication to control the lateral size and thickness of the nanosheets, and probe the effects of the resulting morphology and purity on the electrochemistry. The thin siloxene nanosheets formed after 4 h of ultrasonication deliver an average capacity of 810 mA h/g under a 1000 mA/g rate over 200 cycles with a capacity retention of 76%. Interestingly, the purified siloxene shows lower initial capacity but superior capacity retention over extended cycling. The 2D morphology benefit is illustrated where the parent siloxene nanosheet morphology and structure were largely maintained based on operando optoelectrochemistry, in situ Raman, ex situ scanning electron microscopy, and ex situ transmission electron microscopy. Furthermore, the purified siloxene-based electrode free from crystalline Si impurity experiences the least expansion upon (de)lithiation as visualized by cross-section electron microscopy of samples recovered post-cycling.

Rational construction of NiCo double-hydroxide/cobalt hydroxycarbonate as advanced electrode for high performance asymmetric supercapacitor

In this present paper, a novel nickel‑cobalt double hydroxide/cobalt carbonate hydroxide nanosheets composite (NiCo-DH/NSs) with excellent electrochemical performances is successfully constructed through a rational design of the structure and composition. Cobalt carbonate hydroxide (Co2(OH)2CO3) with a nanosheet morphology and low surface energy is firstly prepared by an simple one-step hydrothermal approach. Then the electroconductive NSs are exploited as a substrate for the in-situ growth of metal-organic framework (MOF). The pre-synthesized MOF/NSs composite is further alkali treated to obtain the final composite material by a “crystal-crystal conversion” strategy. Due to proper structure and synergistic effect between two components, the prepared NiCo-DH/NSs as positive electrode material delivers a high specific capacity (586 mAh g−1 at 1 A g−1) and outstanding rate performance (92.15 % capacity retention at 10 A g−1). In addition, a high specific capacitance of negative electrode material (BiOBr microsphere) is also successfully prepared. As a result, the assembled NiCo-DH/NSs//BiOBr asymmetric supercapacitor (ASC) device exhibits ultrahigh energy density of 67.74 Wh kg−1 at power density of 775.03 W kg−1.

Hybrid Machine Learning-Enabled Potential Energy Model for Atomistic Simulation of Lithium Intercalation into Graphite from Plating to Overlithiation.

Graphite is one of the most widely used negative electrode materials for lithium ion batteries (LIBs). However, because of the rapid growth of demands pursuing higher energy density and charging rates, comprehensive insights into the lithium intercalation and plating processes are critical for further boosting the potential of graphite electrodes. Herein, by utilizing the dihedral-angle-corrected registry-dependent potential (DRIP) (Wen et al., Phys. Rev. B 2018, 98, 235404), the Ziegler-Biersack-Littmark (ZBL) potential (Ziegler and Biersack, Astrophysics, Chemistry, and Condensed Matter; 1985, pp 93-129), and the machine learning-based spectral neighbor analysis (SNAP) potential (Thompson et al., J. Comput, Phys. 2015, 285, 316-330), we have successfully trained a hybrid machine learning-enabled potential energy model capable of simulating a wide spectrum of lithium intercalation scenario from plating to overlithiation. Our extensive atomistic simulations reveal the trapping of intercalated lithium atoms close to the graphite edges due to high hopping barriers, resulting in lithium plating. Furthermore, we report a stable dense graphite intercalation compound (GIC) LiC4 with a theoretical capacity of 558 mAh/g, wherein lithium atoms occupy alternating upper/lower graphene hollow sites with a nearest Li-Li distance of 2.8 Å. Surprisingly, following the same lithium insertion manner would allow the nearest Li-Li distance to be retained until the capacity reaches 845.2 mAh/g, corresponding to a GIC of LiC2.6. Hence, the present study demonstrates that the hybrid machine learning approach could further extend the scope of machine learning energy models, allowing us to investigate the lithium intercalation into graphite over a wide range of intercalation capacity to unveil the underlying mechanisms of lithium plating, diffusion, and discovery of new dense GICs for advanced LIBs with high charging rates and high energy densities.

Modification of activation and corrosion properties of LaNi4.5Co0.5 HSA by ball milling with Zn and preferential alkaline leaching

LaNi4.5Co0.5 hydrogen storage alloy (HSA) was modified by 9.4 and 17.1 mass percent Zn additions and ball milling (BM). The amorphous powder was then subjected to alkaline leaching for selective dissolution of amphoteric Zn and thus surface activation. Long-lasting leaching (720 h) of powder in hot 0.5 M KOH solution allowed removal of 75–77% of Zn from the amorphous material. The modified materials revealed evidently faster (over 3 times) activation for hydrogen sorption both from the gaseous (H2) phase and in conditions of electrochemical cycling. Exchange current densities of H2O/H2 system stabilize after 30–40 cycles for untreated and leached materials on similar levels: 70 and 80 mA/g, respectively. Additionally, Zn-rich residues remaining within the powder particles after leaching play the role of an anodic protector which efficiently inhibits electrochemical corrosion degradation of the negative electrode material. As a result, the modified electrode materials do not display any capacity fade during 60 cycles at −0.5C/+0.5C charge/discharge rates.

Engineering of Conformal Electrode Coatings by Atomic Layer Deposition for Aqueous Na-ion Battery Electrodes

The application of atomic layer deposition on active material particles or as conformal layers directly on electrodes is an effective and viable approach for protecting the battery materials from degradation. Al2O3, TiO2, and HfO2 coatings are applied on NaTi2(PO4)3, which is among the most studied negative electrode materials for aqueous Na-ion batteries. The coated electrodes are characterized in terms of electrochemical kinetics, charge capacity retention, and electrochemical impedance spectra. Al2O3, a widely used protective coating in non-aqueous batteries, is shown to be insufficient to suppress parasitic processes and is eventually dissolved by reaction with hydroxide during extended cycling in aqueous Na2SO4. However, this process provides a local buffering effect making the protective action of this coating mainly of chemical nature. TiO2 is found to be very resistant to increase in pH and remains almost intact during electrochemical cycling. However, we provide strong evidence that TiO2 itself is electrochemically active in aqueous electrolytes at negative potentials. The protonation of TiO2 leads to an additional increase in local pH which is detrimental to NaTi2(PO4)3 and results in even faster capacity loss than in uncoated electrodes. Only HfO2 is found to be sufficiently stable and electrochemically inert ALD coating for negative NaTi2(PO4)3 electrodes operating in aqueous electrolytes.

Triple-shelled nickel-cobalt-manganese sulfides hollow spheres for advanced hybrid supercapacitors

To design high-performance hybrid supercapacitors, positive and negative electrode materials with superior electrochemical features are needed. This paper proposes the fabrication of a hybrid supercapacitor using hollow ternary mixed metal sulfides as a positive electrode and iron oxide-decorated nitrogen-doped reduced graphene oxide (Fe3O4/N-rGO) as the negative electrode. Triple-shelled hollow spheres of nickel-cobalt-manganese-sulfides (NCMS) are synthesized using an optimum calcination temperature, followed by post-sulfurization. As the positive electrode, NCMS produced at 350 °C (NCMS-350) displays a high specific capacity of 797 C g−1 (1885 F g−1) at 1 A g−1 with excellent rate capability (79.5% at 20 A g−1). On the other hand, the negative Fe3O4/N-rGO electrode is synthesized hydrothermally without post-calcination and exhibits a maximum specific capacity of 454 C g−1 (378 F g−1) at 1 A g−1. Moreover, the NCMS-350//Fe3O4/N-rGO hybrid device delivers an impressive energy density of 67.9 Wh kg−1 at 474 W kg−1. These promising electrochemical performances provide a facile strategy for optimizing and integrating electrode materials to develop high-performance hybrid supercapacitors for efficient energy storage.

Construction of tunable ZnCoOx/C-PANI electrode materials for high-performance supercapacitors

Polyaniline (PANI) has been widely studied because of its unique physicochemical properties, but its practical significance in supercapacitors is seriously affected by its structural collapse during charging and discharging. We have successfully synthesized transition metal oxide/carbon-polyaniline composite electrode materials by in situ growth of polyaniline using the electrodeposition method with a metal-organic skeleton as a sacrificial template. This method not only can obtain high capacitance materials but also carbon materials provide buffer space during long-term charge/discharge to improve the overall stability. ZnCoOx/C-PANI-3 has a smaller charge transfer resistance and solution resistance compared to other materials, indicating that the interfacial coupling between PANI and ZnCoOx/C shortens the ion transport path between electrolyte and electrode surface, which is beneficial for rapid ion transfer and thus enhances its electrochemical performance. ZnCoOx/C-PANI-3 as an electrode material in the three-electrode system, has remarkable specific capacitance (1055 F.g−1 at a current density of 1 A.g−1) and good cycling stability (85.7% capacitance retention after 10,000 cycles of charge and discharge at high current density). Similarly, the asymmetric supercapacitor (ZnCoOx/C-PANI-3//AC) assembled with ZnCoOx/C-PANI-3 as the positive electrode material and activated carbon as the negative electrode material has a maximum energy density of 42.77 Wh.kg−1 at a power density of 705 W.kg−1 and a remarkable cycle life with a capacitance retention rate of 80% after 5000 cycles. This research opens up new avenues for studying polyaniline/MOF derivatives (transition metal oxide-carbon) composites.

Lithium Niobate for Fast Cycling in Li-ion Batteries: Review and New Experimental Results

Li-Nb-O-based insertion layers between electrodes and electrolytes of Li-ion batteries (LIBs) are known to protect the electrodes and electrolytes from unwanted reactions and to enhance Li transport across interfaces. An improved operation of LIBs, including all-solid-state LIBs, is reached with Li-Nb-O-based insertion layers. This work reviews the suitability of polymorphic Li-Nb-O-based compounds (e.g., crystalline, amorphous, and mesoporous bulk materials and films produced by various methodologies) for LIB operation. The literature survey on the benefits of niobium-oxide-based materials for LIBs, and additional experimental results obtained from neutron scattering and electrochemical experiments on amorphous LiNbO3 films are the focus of the present work. Neutron reflectometry reveals a higher porosity in ion-beam sputtered amorphous LiNbO3 films (22% free volume) than in other metal oxide films such as amorphous LiAlO2 (8% free volume). The higher porosity explains the higher Li diffusivity reported in the literature for amorphous LiNbO3 films compared to other similar Li-metal oxides. The higher porosity is interpreted to be the reason for the better suitability of LiNbO3 compared to other metal oxides for improved LIB operation. New results are presented on gravimetric and volumetric capacity, potential-resolved Li+ uptake and release, pseudo-capacitive fractions, and Li diffusivities determined electrochemically during long-term cycling of LiNbO3 film electrodes with thicknesses between 14 and 150 nm. The films allow long-term cycling even for fast cycling with rates of 240C possessing reversible capacities as high as 600 mAhg−1. Electrochemical impedance spectroscopy (EIS) shows that the film atomic network is stable during cycling. The Li diffusivity estimated from the rate capability experiments is considerably lower than that obtained by EIS but coincides with that from secondary ion mass spectrometry. The mostly pseudo-capacitive behavior of the LiNbO3 films explains their ability of fast cycling. The results anticipate that amorphous LiNbO3 layers also contribute to the capacity of positive (LiNixMnyCozO2, NMC) and negative LIB electrode materials such as carbon and silicon. As an outlook, in addition to surface-engineering, the bulk-engineering of LIB electrodes may be possible with amorphous and porous LiNbO3 for fast cycling with high reversible capacity.

High performance δ-Bi2O3 nanosheets transformed Bi2S3 nanoflakes interconnected nanosheets as negative electrode for supercapacitor applications

Progress of negative electrode for supercapacitors (SCs) is most important topic of the recent advanced technological era for the next generation energy storage devices and applications. Bismuth oxide (δ-Bi2O3) with high specific capacitance has emerged as a promising negative electrode material for SCs. Herein, a facile two-step synthesis strategy has been proposed to fabricate Bi2S3 nanoflakes interconnected nanosheets electrode by the conversion of electro-deposited as-prepared δ-Bi2O3 nanosheets followed by hydrothermal route. From the comparison study, it is concluded that Bi2S3 nanoflakes interconnected nanosheets exhibit ultrahigh specific capacitance (565 F g−1 at 1 A g−1) and exceptional cycling stability (∼98% retention after 2000 cycles) as a negative electrode material. Meanwhile, δ-Bi2O3 nanosheets electrode has only reached to 474 F g−1 at 1 A g−1 with poor retention of ∼46%. The improved and better performance of Bi2S3 nanoflakes interconnected nanosheets electrode is attributed to high conductivity due to sulfurization. The current fabrication strategy would provide valuable insights to prepare Bi-based nano-materials for high-performance energy storage technologies and beyond.

A novel MoP2@Ni2P nanosheet and an individual kelp-based porous carbon for assembly a unique high performance asymmetric supercapacitor

In order to improve the specific capacity and energy density of the asymmetric supercapacitors, it is necessary to design positive and negative electrode materials with special structure and good electrochemical properties. Herein, a novel MoP2@Ni2P nanosheet material is prepared by one-step simple hydrothermal synthesis and low temperature phosphating method, which exhibits excellent specific capacity of 133.6 mAh g−1 at 0.5 A g−1. In addition, a kelp based porous carbon nanosheet material (AKPC) is prepared via swollen the kelp in a sodium chloride solution and then subjected to an activation and carbonization. Because of its biomaterial unique morphology, the carbon material shows ultra-high specific surface area (1197 m2 g−1) and large pore volume, thus possess a high specific capacitance of 180 F g−1 at 0.5 A g−1. Moreover, the above two materials are assembled into a unique asymmetric supercapacitor with operating voltage of 1.65 V, which has demonstrated a high energy density of 31.5 Wh kg−1 and excellent cycling stability with 81 % capacitance retention after 1500 cycles in aqueous electrolyte. The successful preparation of the asymmetric device provides a new idea for the development of high performance electronic devices.

Effect of particle microstructure and the role of proton on the lithium insertion properties of HTiNbO5 electrode material

Layered oxides showing edge-sharing octahedra are promising negative electrode materials for high-power Li-ion batteries. In this sense, we propose the synthesis of the lamellar HTiNbO5 by solid-state (SS), sol-gel (SG) and exfoliation-restacking (NS) syntheses investigating in the same way the charge storage mechanism of this oxide and the influence of the microstructure on material and electrochemical properties. An arsenal of characterization techniques has been used to investigate these three types of particles using X-Ray Diffraction (XRD), electron microscopy, but also by associating mass spectroscopy to thermogravimetric analyses (TGA). Their ability to intercalate lithium has been compared, showing interesting and very similar specific capacities for solid-state and sol-gel synthesis (> 100 mAh.g − 1 at 0.5 A.g − 1). In addition, it was shown that the synthesis giving rise to nanosheet (NS) led to lower performance due to the presence of organic molecules in the interlayer spacing of the 2D lamellar structure. Lastly, in situ XRD evidenced a solid-solution reaction for HTiNbO5, with an initial and irreversible phase change leading to the formation of Li0.4HTiNbO5. Moreover, ex situ1H MAS NMR measurements highlight the essential role of the proton in the charge storage mechanism of HTiNbO5. Thus, this paper demonstrates the interest of HTiNbO5 as a fast negative electrode material for high-power Li-ion batteries as well as the predominant role that the proton can play in the diffusion of lithium ions inside a confined interlayer space.

Regulating surface condition of cotton-derived carbon towards enhanced lithium ion storage behavior

With the advancement of battery technology, graphite as a negative electrode material for commercial lithium-ion batteries (LiBs) is reaching the limit of its capacity, and mesoporous carbon with a larger capacity is regarded as its best alternative. In this paper, waste cotton is used as the carbon source, and KOH and urea are used as pore formers and pore size regulators to prepare uniform mesoporous materials (N-PCC800) with a pore size distribution of 2–5 nm. Compared with the traditional KOH pore-making method, the addition of urea can adjust the pore size upward, thereby increasing the effective number of pores for Li+ insertion. While optimizing the structure, urea can also be used as an additional nitrogen source for the material to enrich the content of heteroatoms and defects, thereby increasing the amount of Li+ adsorbed by porous carbon. As an anode material, N-PCC800 exhibits a stable discharge capacity (1086 mAh g−1 at 100 mA g−1) far exceeding that of graphite. At a current density of 1000 mA g−1, there is still a capacity of 596 mAh g−1 remaining after 1000 cycles, indicating its advantages in rate performance and cycle performance. The optimized pore size and higher nitrogen content endow the carbon material with higher Li+ storage performance, and further kinetic analysis indicates that the increased capacity comes from the increased Li+ insertion. This work proposes a new pore size optimization scheme to obtain high-capacity mesoporous carbon, which provides an effective scheme for the reuse of waste cotton and cotton products and helps achieve the goal of carbon neutrality.

LiAlO2-Modified Li Negative Electrode with Li10GeP2S12 Electrolytes for Stable All-Solid-State Lithium Batteries.

Lithium (Li) metal has an ultrahigh specific capacity in theory with an extremely negative potential (versus hydrogen), receiving extensive attention as a negative electrode material in batteries. However, the formation of Li dendrites and unstable interfaces due to the direct Li metal reaction with solid sulfide-based electrolytes hinders the application of lithium metal in all-solid-state batteries. In this work, we report the successful fabrication of a LiAlO2 interfacial layer on a Li/Li10GeP2S12 interface through magnetic sputtering. As LiAlO2 can be a good Li+ ion conductor but an electronic insulator, the LiAlO2 interface layer can effectively suppress Li dendrite growth and the severe interface reaction between Li and Li10GeP2S12. The Li@LiAlO2 200 nm/Li10GeP2S12/Li@LiAlO2 200 nm symmetric cell can remain stable for 3000 h at 0.1 mA cm-2 under 0.1 mAh cm-2. Moreover, unlike the rapid capacity decay of a cell with a pristine lithium negative electrode, the Li@LiAlO2 200 nm/Li10GeP2S12/LiCoO2@LiNbO3 cell delivers a reversible capacity of 118 mAh g-1 and a high energy efficiency of 96.6% after 50 cycles. Even at 1.0 C, the cell with the Li@LiAlO2 200 nm electrode can retain 95% of its initial capacity after 800 cycles.

Ti3 C2 Tx MXene with High Pseudocapacitive Activity and Large Potential Window in a Mild AlCl3 Aqueous Electrolyte.

MXenes have been extensively explored as supercapacitor electrodes, especially in acidic aqueous electrolytes, where ultrahigh specific capacitance can be achieved; however, their narrow working potential window (≤ 1.0V) limits the acquisition of high energy. Neutral and alkaline electrolytes can be used to extend the working potential window but MXenes in these electrolytes are less pseudocapacitive active, which leads to reduced charge storage. In this study, it is shown that Ti3 C2 Tx MXene in a mild AlCl3 aqueous electrolyte can operate at a wide potential range from 0 to -1.3V versus Hg/Hg2 SO4 and retain high pseudocapacitive activity. Thus, a high capacity of up to 85mAhg-1 is achieved, surpassing its performance in H2 SO4 electrolyte of 78mAhg-1 . More interestingly, most of the capacity is released at a more negative potential range than that in acidic electrolytes, making it more suitable as a negative electrode material. In situ electrochemical quartz crystal microbalance results suggest that the high capacity originates from the pseudocapacitive intercalation/deintercalation of H+ instead of Al3+ , providing the possibility of coupling MXene anodes with proton redox active cathodes to achieve high-energy and high-power devices.

Dual-Phase Coexistence Design and Advanced Electrochemical Performance of Cu2MoS4 Electrode Materials for Supercapacitor Application

The tetragonal layered transition metal copper–molybdenum sulfide Cu2MoS4 (CMS) possesses a high theoretical electrochemical potential because of its abundant redox properties and large layered surface area, which is favorable for ion adsorption/desorption and transport. Cu2MoS4 contains P and I phases, exhibiting different crystal structures, ion transport characteristics, and electrochemical properties accordingly. In this work, for the first time, Cu2MoS4 electrode materials with dual-phase compositions are designed and prepared for supercapacitor application, providing a synergistic effect with high electron transport efficiency and structural stability. Upon an in-depth optimization process, the optimal CMS-4 sample having P and I phases coexisting yields the optimal electrochemical behavior. The CMS-4@carbon cloth (CC) electrode provides a specific capacity of 33.9 mAh g–1 at 1 A g–1, which is 12.6 and 4.0 times higher than the pure P and I phases, respectively. The assembled MnO2@CC//CMS-4@CC supercapacitor exhibits a high energy density of 16.8 Wh kg–1 at 800 W kg–1 power density. The results demonstrate that two-phase coexistence of Cu2MoS4 significantly enhances the electrochemical activities owing to the synergistic effects of P and I phases and provides a promising material for supercapacitor negative electrodes.

Hard Carbon–Sulfide Solid Electrolyte Interface in All-Solid-State Sodium Batteries

Hard carbon is a promising negative electrode material for sodium-ion batteries that operate at low potentials. However, reversible and high-capacity charging and discharging in all-solid-state sodium batteries with hard carbon electrodes using sulfide solid electrolytes have not been reported. This study reports that reductive decomposition of the sulfide solid electrolyte occurs at both the negative composite electrode and the interface between the negative electrode layer and the solid electrolyte layer. In the first cycle, the all-solid-state cell with a composite electrode containing a Na3PS4 solid electrolyte exhibited a large irreversible capacity of 561 mAh g−1 because of the reductive decomposition of Na3PS4 to Na2S and Na3P. The use of a Na3BS3 glass electrolyte with reduction stability can lead to the successful charging and discharging of all-solid-state cell that utilizes hard carbon. This glass electrolyte can serve as a solid electrolyte for the negative composite electrode and as a buffer layer between the negative electrode layer and the solid electrolyte layer. Hence, it can also help suppress the irreversible capacity of the cell to 122 mAh g−1.