Research progress on Na3V2(PO4)2F3-based cathode materials for sodium-ion batteries

Sodium-ion batteries (SIBs) have received significant attention in large-scale energy storage due to their low cost and abundant resources. To obtain high-performance SIBs, many intensive studies about electrode materials have been carried out, especially the cathode material. As various types of cathode material for SIBs, a 3D open framework structural Na₃V₂(PO₄)₂F₃ (NVPF) with Na superionic conductor (NASICON) structure is a promising cathode material owing to its high operating potential and high energy density. However, its electrochemical properties are severely limited by the poor electronic conductivity due to the insulated [PO₄] tetrahedral unit. In this review, the challenges and strategies for NVPF are presented, and the synthetic strategy for NVPF is also analyzed in detail. Furthermore, recent developments of modification research to enhance their electrochemical performance are discussed, including designing the crystal structure, adjusting the electrode structure, and optimizing the electrolyte components. Finally, further research and application for future development of NVPF are prospected.     

Amorphous MnO2 as Cathode Material for Sodium‐ion Batteries

Amorphous MnO₂ has been prepared from the reduction of KMnO₄ in ethanol media by a facile one‐step wet chemical route at room temperature. The electrochemical properties of amorphous MnO₂ as cathode material in sodium‐ion batteries (SIBs ) are studied by galvanostatic charge/discharge testing. And the structure and morphologies of amorphous MnO₂ are investigated by X‐ray diffraction (XRD ), scanning electron microscopy (SEM ), transmission electron microscopy (TEM ) and Raman spectra. The results reveal that as‐synthesized amorphous MnO₂ electrode material exhibits a spherical morphology with a diameter between 20 and 60 nm. The first specific discharge capacity of the amorphous MnO₂ electrode is 123.2 mAh •g⁻¹ and remains 136.8 mAh •g⁻¹ after 100 cycles at the current rate of 0.1 C. The specific discharge capacity of amorphous MnO₂ is maintained at 139.2, 120.4, 89, 68 and 47 mAh •g⁻¹ at the current rate of 0.1 C, 0.2 C, 0.5 C, 1 C and 2 C, respectively. The results indicate that amorphous MnO₂ has great potential as a promising cathode material for SIBs .     

Thin‐film Potentiometric Sensor to Detect CO2 Concentrations Ranging Between 2 % and 100 %

A potentiometric thin‐film sensor to detect CO₂ in a wide range (2–100 %) has been developed. The system has been fabricated depositing a reference electrode of Pt, a solid electrolyte of YSZ (Yttria‐stabilized Zirconia), a sensing phase made of Li₂CO₃ and a working electrode of Au via Physical Vapor Deposition (PVD). Characterization of the different elements has provided the optimal fabrication parameters and the system response for CO₂ concentrations can be measured from 2 to 100 % at 450 °C. The sensor behaves as a non‐Nerstian system and slightly deviates from a linear response with the logarithm of CO₂ until the CO₂ concentration reaches the 30 %. Higher CO₂ amounts make the response divert more from the Nernst law but give a stable and reproducible response to CO₂ in a wide range of concentrations. Based on these promising results the recovery time, stability, repeatability and selectivity of the sensor have been measured. The performance showed by the thin film sensor proves the feasibility of the use of this system for biogas and natural gas applications owing to its very good consistency at low temperature in a wide concentration range.     

Development and implementation of a high temperature electrochemical cell for lithium batteries

An electrochemical cell designed to perform high temperature lithium battery tests has been developed adapting a typical Swagelok^® cell. The high temperature cell is intended to work in a wide temperature range, namely from room temperature up to 300 °C. It has been successfully tested at 250 °C using LiFePO₄ as cathode, LiTFSI as molten salt electrolyte and metallic lithium as anode.     

Robust SnO2−x Nanoparticle‐Impregnated Carbon Nanofibers with Outstanding Electrochemical Performance for Advanced Sodium‐Ion Batteries

The sluggish sodium reaction kinetics, unstable Sn/Na₂O interface, and large volume expansion are major obstacles that impede practical applications of SnO₂‐based electrodes for sodium‐ion batteries (SIBs). Herein, we report the crafting of homogeneously confined oxygen‐vacancy‐containing SnO_2?x nanoparticles with well‐defined void space in porous carbon nanofibers (denoted SnO_2?x/C composites) that address the issues noted above for advanced SIBs. Notably, SnO_2?x/C composites can be readily exploited as the working electrode, without need for binders and conductive additives. In contrast to past work, SnO_2?x/C composites‐based SIBs show remarkable electrochemical performance, offering high reversible capacity, ultralong cyclic stability, and excellent rate capability. A discharge capacity of 565 mAh g^?1 at 1 A g^?1 is retained after 2000 cycles.     

Pseudocapacitive Lithium Storage of Cauliflower-Like CoFe2O4 for Low-Temperature Battery Operation

Binary transition-metal oxides (BTMOs) with hierarchical micro–nano-structures have attracted great interest as potential anode materials for lithium-ion batteries (LIBs). Herein, we report the fabrication of hierarchical cauliflower-like CoFe₂O₄ (cl-CoFe₂O₄) via a facile room-temperature co-precipitation method followed by post-synthetic annealing. The obtained cauliflower structure is constructed by the assembly of microrods, which themselves are composed of small nanoparticles. Such hierarchical micro–nano-structure can promote fast ion transport and stable electrode–electrolyte interfaces. As a result, the cl-CoFe₂O₄ can deliver a high specific capacity (1019.9 mAh g⁻¹ at 0.1 A g⁻¹), excellent rate capability (626.0 mAh g⁻¹ at 5 A g⁻¹), and good cyclability (675.4 mAh g⁻¹ at 4 A g⁻¹ for over 400 cycles) as an anode material for LIBs. Even at low temperatures of 0 °C and −25 °C, the cl-CoFe₂O₄ anode can deliver high capacities of 907.5 and 664.5 mAh g⁻¹ at 100 mA g⁻¹, respectively, indicating its wide operating temperature. More importantly, the full-cell assembled with a commercial LiFePO₄ cathode exhibits a high rate performance (214.2 mAh g⁻¹ at 5000 mA g⁻¹) and an impressive cycling performance (612.7 mAh g⁻¹ over 140 cycles at 300 mA g⁻¹) in the voltage range of 0.5–3.6 V. Kinetic analysis reveals that the electrochemical performance of cl-CoFe₂O₄ is dominated by pseudocapacitive behavior, leading to fast Li⁺ insertion/extraction and good cycling life.     

Temperature effect on the recovery of SO2-Poisoned GC/Nano-Pt electrode towards oxygen reduction

The SO₂ poisoning of Pt nanoparticle (n-Pt) modified glassy carbon (GC/n-Pt) electrode and the recovery of its activity for the oxygen reduction reaction (ORR) were studied using cyclic voltammetry at ambient (25 °C) and elevated (70 °C) temperatures. Recovery of the GC/n-Pt electrode by cycling the potential within the ORR range (1.0 to 0.2 V (standard hydrogen electrode)) in 0.1 M H₂SO₄ was not effective at 25 °C, but at 70 °C the onset potential of the ORR was almost the same as that at the fresh GC/n-Pt electrode. For the two different temperatures used here, the recovery on cycling the potential between 0.4 and 1.7 V was efficient. However, the number of cycles and the amount of charge required for the recovery at 70 °C were the smallest, which is of great interest for the proton exchange membrane fuel cell performance. The recovery using such a wide potential range at 70 °C resulted in an enhancement of the electrocatalytic activity of the GC/n-Pt electrode over a non-poisoned (bare) GC/n-Pt electrode.     

Improved electrochemical performance of nano-crystalline Li2FeSiO4/C cathode material prepared by the optimization of sintering temperature

Li₂FeSiO₄/C cathode materials have been prepared using the conventional solid-state method by varying the sintering temperature (650 °C, 700 °C and 750 °C), and the structure and electrochemical performance of Li₂FeSiO₄/C materials are investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), galvanostatic charge–discharge tests, respectively. The results show that Li₂FeSiO₄ nano-crystals with a diameter of about 6–8 nm are inbedded in the amorphous carbon, and the Li₂FeSiO₄/C material obtained at 700 °C exhibits an initial discharge capacity of 195 mA?h g^?1 at 1/16 C in the potential range of 1.5–4.8 V. The excellent electrochemical performance of Li₂FeSiO₄/C attributes to the improvement of conductivity and reduction of impurity by the optimization of the sintering temperature.     

Revealing performance of 78Li2S-22P2S5 glass ceramic based solid-state batteries at different operating temperatures

78Li₂S-22P₂S₅ are sulfide electrolytes with high lithium-ion conductivity and wide electrochemical windows in the Li₂S-P₂S₅ system, making them attractive solid electrolytes for ASSLBs. However, the role and potential of 78Li₂S-22P₂S₅ solid electrolytes over a wide temperature range are still not fully understood. Therefore, we constructed solid-state batteries with NCM622 as the positive electrode and 78Li₂S-22P₂S₅ glass-ceramics as the electrolyte to investigate in depth the differences in battery performance over a wide temperature range and their intrinsic mechanisms. The in-situ impedance and relaxation time distribution (DRT) demonstrated the electrochemical stability of the electrolyte over a wide temperature range, while the in-situ stacking pressure observed a large volume change during cycling at 60 °C, leading to local solid-solid contact failure and poor cycling stability. This study provides insight into the advantages and problems of 78Li₂S-22P₂S₅ in the wide temperature range as well as a basis for the construction of ASSLBs with high energy density and long cycle life.     

Asymmetric Solvents Regulated Crystallization-Limited Electrolytes for All-Climate Lithium Metal Batteries

Electrolytes that can keep liquid state are one of the most important physical metrics to ensure the ions transfer with stable operation of rechargeable lithium-based batteries at a wide temperature window. It is generally accepted that strong polar solvents with high melting points favor the safe operation of batteries above room temperatures but are susceptible to crystallization at low temperatures (≤−40 °C). Here, a crystallization limitation strategy was proposed to handle this issue. We demonstrate that, although the high melting points of ethylene sulfite (ES, −17 °C) and fluoroethylene carbonate (FEC, ≈23 °C), their mixtures can avoid crystallization at low temperatures, which can be attributed to low intermolecular interactions and altered molecular motion dynamics. A suitable ES/FEC ratio (10 % FEC) can balance the bulk and interface transport of ions, enabling LiNi_0.8Mn_0.1Co_0.1O₂||lithium (NCM811||Li) full cells to deliver excellent temperature resilience and cycling stability over a wide temperature range from −50 °C to +70 °C. More than 66 % of the capacity retention was achieved at −50 °C compared to room temperature. The NCM811||Li pouch cells exhibit high cycling stability under realistic conditions (electrolyte weight to cathode capacity ratio (E/C)≤3.5 g Ah⁻¹, negative to positive electrode capacity ratio (N/P)≤1.09) at different temperatures.     

P2‐NaCo0.5Mn0.5O2 as a Positive Electrode Material for Sodium‐Ion Batteries

As a promising positive electrode material for sodium‐ion batteries (SIBs), layered sodium oxides have attracted considerable attention in recent years. In this work, stoichiometric P2‐phase NaCo_0.5Mn_0.5O₂ was prepared through the conventional solid‐state reaction, and its structural and physical properties were studied in terms of XRD, XPS, and magnetic susceptibility. Furthermore, the P2‐NaCo_0.5Mn_0.5O₂ electrode delivered a discharge capacity of 124.3 mA h g^?1 and almost 100 % initial coulombic efficiency over the potential window of 1.5–4.15 V. It also showed good cycle stability, with a reversible capacity and capacity retention reaching approximately 85 mA h g^?1 and 99 %, respectively, at the 5 C rate after 100 cycles. Additionally, cyclic voltammetry and ex situ XRD were employed to explain the electrochemical behavior at the different electrochemical stages. Owing to the applicable performances, P2‐NaCo_0.5Mn_0.5O₂ can be considered as a potential positive electrode material for SIBs.     

RuO2 electrode surface effects in electrocatalytic oxidation of glucose

We have studied the electrocatalytic activity of RuO₂-PVC film electrodes, fabricated using RuO₂ powders prepared at five different temperatures, viz., 300, 400, 500, 600 and 700°C, for the oxidation of glucose in high alkaline media, 1 to 3 M NaOH. The RuO₂-PVC film electrodes have been first characterized in 1 to 3 M NaOH solution by cyclic voltammetry (CV) and rotating disc electrode (RDE) techniques in a wide potential range −1,100 to 450 mV (SCE), and three redox pairs representing Ru(IV)/Ru(III), Ru(VI)/Ru(IV) and Ru(VII)/Ru(VI) transitions have been identified. The voltammetric peaks at low sweep rates have been analyzed using surface activity theory formulated for interacting electroactive adsorption sites, and interaction terms have been evaluated. The total voltammetric surface charges have been analyzed as per Trassatti’s formalism with respect to their dependence on potential sweep rate, and charges associated with less accessible and more accessible surface sites have been calculated. For glucose oxidation, the results have indicated that RuO₂ (700°C)-PVC electrode shows two oxidation peaks in contrast to RuO₂ (300°C)-PVC electrode. Also, RuO₂ (700°C)-PVC electrode exhibits higher intrinsic electrocatalytic activity than the 300°C electrode, although the former possesses lower electrochemically active surface area. Additionally, kinetic analyses made from RDE results with reference to Michealis–Menten (MM) enzyme catalysis has shown that RuO₂ (700°C) electrode possesses extended glucose-sensing range in terms of MM kinetic constant, K _M , compared to other electrodes. Possible reasons for such differences in the behavior of the electrodes of different temperatures towards glucose oxidation are identified from studies on oxidation of glucose in solutions of different pH, oxidation of different glucose derivatives, and also from physicochemical results from BET, XRD, SEM, DTGA, XPS analysis of RuO₂ powder samples.     

Suppressing the P2–O2 Phase Transition of Na0.67Mn0.67Ni0.33O2 by Magnesium Substitution for Improved Sodium‐Ion Batteries

Room‐temperature sodium‐ion batteries (SIBs) have shown great promise in grid‐scale energy storage, portable electronics, and electric vehicles because of the abundance of low‐cost sodium. Sodium‐based layered oxides with a P2‐type layered framework have been considered as one of the most promising cathode materials for SIBs. However, they suffer from the undesired P2–O2 phase transition, which leads to rapid capacity decay and limited reversible capacities. Herein, we show that this problem can be significantly mitigated by substituting some of the nickel ions with magnesium to obtain Na_0.67Mn_0.67Ni_0.33?xMg_xO₂ (0≤x≤0.33). Both the reversible capacity and the capacity retention of the P2‐type cathode material were remarkably improved as the P2–O2 phase transition was thus suppressed during cycling. This strategy might also be applicable to the modulation of the physical and chemical properties of layered oxides and provides new insight into the rational design of high‐capacity and highly stable cathode materials for SIBs.     

A robust carbon coating of Na3V2(PO4)3 cathode material for high performance sodium-ion batteries

Na₃V₂(PO₄)₃ is a very prospective sodium-ion batteries (SIBs) electrode material owing to its NASICON structure and high reversible capacity. Conversely, on account of its intrinsic poor electronic conductivity, Na₃V₂(PO₄)₃ electrode materials confront with some significant limitations like poor cycle and rate performance which inhibit their practical applications in the energy fields. Herein, a simple two-step method has been implemented for the successful preparation of carbon-coated Na₃V₂(PO₄)₃ materials. As synthesized sample shows a remarkable electrochemical performance of 124.1 mAh/g at 0.1 C (1 C = 117.6 mA/g), retaining 78.5 mAh/g under a high rate of 200 C and a long cycle-performance (retaining 80.7 mAh/g even after 10000 cycles at 20 C), outperforming the most advanced cathode materials as reported in literatures.     

Formation of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–TiO<Subscript>2</Subscript> bilayer using atomic layer deposition and its application to dynamic random access memory

To enhance film conformality together with electrical property suitable for dynamic random access memory (DRAM) capacitor dielectric, the effects of oxidant and post heat treatment were investigated on aluminum and titanium oxide (Al₂O₃–TiO₂) bilayer (ATO) thin film formed by atomic layer deposition method. For the conformal deposition of Al₂O₃ thin film, the O₃ oxidant required a higher deposition temperature, more than 450 °C, while H₂O or combined oxygen sources (H₂O+O₃) needed a wide range of deposition temperatures ranging from 250 to 450 °C. Conformal deposition of the TiO₂ thin film was achieved at around 325 °C regardless of the oxidants. The charge storage capacitance, measured from the ATO bilayer (4 nm Al₂O₃ and 2 nm TiO₂) deposited at 450 °C for Al₂O₃ and 325 °C for TiO₂ with O₃ oxidant on the phosphine-doped poly silicon trench, showed about 15% higher value than that of 5 nm Al₂O₃ single layer thin film without any increase of leakage current. To maintain the improved electrical property of the ATO bilayer for DRAM application, such as enhanced charge capacitance without increase of leakage current, upper electrode materials and post heat treatments after electrode formation must be selected carefully. Dedicated to Professor Su-Il Pyun on the occasion of his 65th birthday.     

Unlocking the Interfacial Adsorption-Intercalation Pseudocapacitive Storage Limit to Enabling All-Climate,High Energy/Power Density and Durable Zn-Ion Batteries

Sluggish storage kinetics and insufficient performance are the major challenges that restrict the transition metal dichalcogenides (TMDs) applied for zinc ion storage, especially at the extreme temperature conditions. Herein, a multiscale interface structure-integrated modulation concept was presented, to unlock the omnidirectional storage kinetics-enhanced porous VSe_2−x⋅n H₂O host. Theory research indicated that the co-modulation of H₂O intercalation and selenium vacancy enables enhancing the interfacial zinc ion capture ability and decreasing the zinc ion diffusion barrier. Moreover, an interfacial adsorption-intercalation pseudocapacitive storage mechanism was uncovered. Such cathode displayed remarkable storage performance at the wide temperature range (−40–60 °C) in aqueous and solid electrolytes. In particular, it can retain a high specific capacity of 173 mAh g⁻¹ after 5000 cycles at 10 A g⁻¹, as well as a high energy density of 290 Wh kg⁻¹ and a power density of 15.8 kW kg⁻¹ at room temperature. Unexpectedly, a remarkably energy density of 465 Wh kg⁻¹ and power density of 21.26 kW kg⁻¹ at 60 °C also can be achieved, as well as 258 Wh kg⁻¹ and 10.8 kW kg⁻¹ at −20 °C. This work realizes a conceptual breakthrough for extending the interfacial storage limit of layered TMDs to construct all-climate high-performance Zn-ion batteries.     

Deciphering an Abnormal Layered‐Tunnel Heterostructure Induced by Chemical Substitution for the Sodium Oxide Cathode

Demands for large‐scale energy storage systems have driven the development of layered transition‐metal oxide cathodes for room‐temperature rechargeable sodium ion batteries (SIBs). Now, an abnormal layered‐tunnel heterostructure Na_0.44Co_0.1Mn_0.9O₂ cathode material induced by chemical element substitution is reported. By virtue of beneficial synergistic effects, this layered‐tunnel electrode shows outstanding electrochemical performance in sodium half‐cell system and excellent compatibility with hard carbon anode in sodium full‐cell system. The underlying formation process, charge compensation mechanism, phase transition, and sodium‐ion storage electrochemistry are clearly articulated and confirmed through combined analyses of in situ high‐energy X‐ray diffraction and ex situ X‐ray absorption spectroscopy as well as operando X‐ray diffraction. This crystal structure engineering regulation strategy offers a future outlook into advanced cathode materials for SIBs.     

In‐Situ Fabrication of Bone‐Like CoSe2 Nano‐Thorn Loaded on Porous Carbon Cloth as a Flexible Electrode for Na‐Ion Storage

Sodium‐ion batteries (SIBs) based on flexible electrode materials are being investigated recently for improving sluggish kinetics and developing energy density. Transition metal selenides present excellent conductivity and high capacity; nevertheless, their low conductivity and serious volume expansion raise challenging issues of inferior lifespan and capacity fading. Herein, an in‐situ construction method through carbonization and selenide synergistic effect is skillfully designed to synthesize a flexible electrode of bone‐like CoSe₂ nano‐thorn coated on porous carbon cloth. The designed flexible CoSe₂ electrode with stable structural feature displays enhanced Na‐ion storage capabilities with good rate performance and outstanding cycling stability. As expected, the designed SIBs with flexible BL?CoSe₂/PCC electrode display excellent reversible capacity with 360.7 mAh g^?1 after 180 cycles at a current density of 0.1 A g^?1.     

Improvement of the proton exchange membrane fuel cell performances by optimization of the hot pressing process for membrane electrode assembly

The present study deals with PEM fuel cells, namely with the optimization of the hot pressing process for membrane electrode assembly (MEA) fabrication. Designs of experiments (DoE) have been used for evaluating the effect of hot pressing parameters (pressure, temperature, and time) on the MEA electrical performances. Full factorial 2³ DoE showed that the most important parameter is the pressing temperature. Surface response methodology indicated a non-monotonous behavior of the MEA electrical performances with respect to the pressing temperature. The MEA electrical performances increased with the pressing temperature in the temperature range from 100 to 115 °C, and decreased significantly in the temperature range from 115 to 130 °C. This behavior was attributed to drastic changes of the Nafion® 112 membrane properties and membrane/electrode interface over this temperature range. Observations of the MEA cross-section structure by scanning electron microscopy confirmed such hypotheses. Thermo-mechanical properties of Nafion® as determined by dynamic scanning calorimetry allowed estimating the glass transition temperature at ca. T _g?≈?117 °C in the conditions of the present study. The higher H₂/air fuel cell performance of ca. 0.8 W cm^?2 was obtained with the optimized pressing temperature for MEA fabrication of ca. 115 °C close to the T _g temperature of Nafion® 112, whereas for higher temperature the structure of the Nafion® membrane and of the membrane–electrode interface is damaged.     

One-step hydrothermal synthesis of LiMn2O4 cathode materials for rechargeable lithium batteries

LiMn₂O₄ cathode materials with high discharge capacity and good cyclic stability were prepared by a simple one-step hydrothermal treatment of KMnO₄, aniline and LiOH solutions at 120–180 °C for 24 h. The aniline/KMnO₄ molar ratio (R) and hydrothermal temperature exhibited an obvious influence on the component and phase structures of the resulting product. The precursor KMnO₄ was firstly reduced to birnessite when R was less than 0.2:1 at 120–150 °C. Pure-phased LiMn₂O₄ was formed when R was 0.2:1, and the LiMn₂O₄ was further reduced to Mn₃O₄ when R was kept in the range of 0.2–0.3 at 120–150 °C. Moreover, LiMn₂O₄ was fabricated when R was 0.15:1 at 180 °C. Octahedron-like LiMn₂O₄ about 300 nm was prepared at 120 °C, and particle size decreased with an increase in hydrothermal temperature. Especially, LiMn₂O₄ synthesized at 150 °C exhibited the best electrochemical performance with the highest initial discharge capacity of 127.4 mAh g⁻¹ and cycling capacity of 106.1 mAh g⁻¹ after 100 cycles. The high discharge capacity and cycling stability of the as-prepared LiMn₂O₄ cathode for rechargeable lithium batteries were ascribed to the appropriate particle size and larger cell volume.