Extra storage capacity in transition metal oxide lithium-ion batteries revealed by in situ magnetometry

Preparation, Characterization, and Electrochemical Performance of the Hematite/Oxidized Multi-Walled Carbon Nanotubes Nanocomposite

In this research work, a hematite (α-Fe₂O₃) nanoparticle was prepared and then mixed with oxidized multi-walled carbon nanotubes (O-MWCNT) to form a stable suspension of an α-Fe₂O₃/O-MWCNTs nanocomposite. Different characterization techniques were used to explore the chemical and physical properties of the α-Fe₂O₃/O-MWCNTs nanocomposite, including XRD, FT-IR, UV-Vis, and SEM. The results revealed the successful formation of the α-Fe₂O₃ nanoparticles, and the oxidation of the MWCNT, as well as the formation of stable α-Fe₂O₃/O-MWCNTs nanocomposite. The electrochemical behaviour of the α-Fe₂O₃/O-MWCNTs nanocomposite was investigated using cyclic voltammetry (CV) and linear sweep voltammetry (LSV), and the results revealed that modification of α-Fe₂O₃ nanoparticles with O-MWCNTs greatly enhanced electrochemical performance and capacitive behaviour, as well as cycling stability.

Perspectives on Iron Oxide-Based Materials with Carbon as Anodes for Li- and K-Ion Batteries

The necessity for large scale and sustainable energy storage systems is increasing. Lithium-ion batteries have been extensively utilized over the past decades for a range of applications including electronic devices and electric vehicles due to their distinguishing characteristics. Nevertheless, their massive deployment can be questionable due to use of critical materials as well as limited lithium resources and growing costs of extraction. One of the emerging alternative candidates is potassium-ion battery technology due to potassium’s extensive reserves along with its physical and chemical properties similar to lithium. The challenge to develop anode materials with good rate capability, stability and high safety yet remains. Iron oxides are potentially promising anodes for both battery systems due to their high theoretical capacity, low cost and abundant reserves, which aligns with the targets of large-scale application and limited environmental footprint. However, they present relevant limitations such as low electronic conductivity, significant volume changes and inadequate energy efficiency. In this review, we discuss some recent design strategies of iron oxide-based materials for both electrochemical systems and highlight the relationships of their structure performance in nanostructured anodes. Finally, we outline challenges and opportunities for these materials for possible development of KIBs as a complementary technology to LIBs.

Robust α-Fe2O3@TiO2 Core–Shell Structures With Tunable Buffer Chambers for High-Performance Lithium Storage

α-Fe2O3 has high potential energy storage capacity and can serve as a green and low-cost anode material for lithium-ion batteries. However, α-Fe2O3 suffers large volume expansion and pulverization. Based on DFT calculations, TiO2 can effectively maintain the integrity of the crystal structure during the discharge/charge process. Well-defined cubic α-Fe2O3 is coated with a TiO2 layer using the hydrothermal method with the assistance of oxalic acid surface treatment, and then α-Fe2O3@TiO2 with tunable buffer chambers is obtained by altering the hydrochloric acid etching time. With the joint efforts of the buffer chamber and the robust structure of the TiO2 layer, α-Fe2O3@TiO2 alleviates the expansion of α-Fe2O3 during the discharge/charge process. The optimized sample (FT-1h) achieves good cycling performance. The reversible specific capacity remains at 893.7 mA h g-1, and the Coulombic efficiency still reaches up to 98.47% after 150 cycles at a current density of 100 mA g−1. Furthermore, the reversible specific capacity can return to 555.5 mA h g−1 at 100 mA g−1 after cycling at a high current density. Hence, the buffer chamber and the robust TiO2 layer can effectively improve the cycling stability and rate performance of α-Fe2O3.

Gradient Architecture Design in Scalable Porous Battery Electrodes

Because it has been demonstrated to be effective toward faster ion diffusion inside the pore space, low-tortuosity porous architecture has become the focus in thick electrode designs, and other possibilities are rarely investigated. To advance current understanding in the structure-affected electrochemistry and to broaden horizons for thick electrode designs, we present a gradient electrode design, where porous channels are vertically aligned with smaller openings on one end and larger openings on the other. With its 3D morphology carefully visualized by Raman mapping, the electrochemical properties between opposite orientations of the gradient electrodes are compared, and faster energy storage kinetics is found in larger openings and more concentrated active material near the separator. As further verified by simulation, this study on gradient electrode design deepens the knowledge of structure-related electrochemistry and brings perspectives in high-energy battery electrode designs.

Low-Tortuosity Thick Electrodes with Active Materials Gradient Design for Enhanced Energy Storage

The ever-growing energy demand of modern society calls for the development of high-loading and high-energy-density batteries, and substantial research efforts are required to optimize electrode microstructures for improved energy storage. Low-tortuosity architecture proves effective in promoting charge transport kinetics in thick electrodes; however, heterogeneous electrochemical mass transport along the depth direction is inevitable, especially at high C-rates. In this work, we create an active material gradient in low-tortuosity electrodes along ion-transport direction to compensate for uneven reaction kinetics and the nonuniform lithiation/delithiation process in thick electrodes. The gradual decrease of active material concentration from the separator to the current collector reduces the integrated ion diffusion distance and accelerates the electrochemical reaction kinetics, leading to improved rate capabilities. The structure advantages combining low-tortuosity pores and active material gradient offer high mass loading (60 mg cm^-2) and enhanced performance. Comprehensive understanding of the effect of active material gradient architecture on electrode kinetics has been elucidated by electrochemical characterization and simulations, which can be useful for development of batteries with high-energy/power densities.

Hollow CoS/C Structures for High-Performance Li, Na, K Ion Batteries

Alkali ion (Li, Na, and K) batteries as a new generation of energy storage devices are widely applied in portable electronic devices and large-scale energy storage equipment. The recent focus has been devoted to develop universal anodes for these alkali ion batteries with superior performance. Transition metal sulfides can accommodate alkaline ions with large radius to travel freely between layers due to its large interlayer spacing. Moreover, the composite with carbon material can further improve electrical conductivity of transition metal sulfides and reduce the electron transfer resistance, which is beneficial for the transport of alkali ions. Herein, we designed zeolitic imidazolate framework (ZIF)–derived hollow structures CoS/C for excellent alkali ion (Li, Na, and K) battery anodes. The porous carbon framework can improve the conductivity and effectively buffer the stress-induced structural damage. The ZIF-derived CoS/C anodes maintain a reversible capacity of 648.9, and 373.2, 224.8 mAh g⁻¹ for Li, Na, and K ion batteries after 100 cycles, respectively. Its outstanding electrochemical performance is considered as a universal anode material for Li, Na, and K ion batteries.

Construction of Novel Bimetallic Oxyphosphide as Advanced Anode for Potassium Ion Hybrid Capacitor

Potassium ion hybrid capacitors (PIHCs) have attracted considerable interest due to their low cost, competitive power/energy densities, and ultra-long lifespan. However, the more sluggish insertion kinetics of battery-type anodes than capacitor-type cathodes in PIHCs seriously limits their practical application. Therefore, developing advanced anodes with high capacitor and suitable K⁺ intercalation is imperative and significant. A novel core-shell structure of NiCo oxide/NiCo oxyphosphide (NCOP) nanowires are designed and constructed in this study via efficient and facile strategy. Combining the merits of the core-shell structure and the massive active sites in the oxyphosphide layer, the as-prepared NCOP composites manifest highly reversible capacitors and outstanding rate capability. Meanwhile, the insertion and conversion potassium storage mechanisms of the NCOP are successfully revealed through in situ X-ray diffraction and density functional theory calculations, respectively. Furthermore, the PIHC was assembled with NCOP anode and borocarbonitride cathode, which displays a large energy density and high-power density, along with an exceptional capacity retention of ≈90% over 10 000 cycles at 1.0 A g^-1 . This work provides the anion regulation strategy for modifying the transition metal oxide and constructing the advancing electrode materials for next-generation energy storage and beyond.

Design of Ordered Mesoporous CeO2-YSZ Nanocomposite Thin Films with Mixed Ionic/Electronic Conductivity via Surface Engineering

Mixed ionic and electronic conductors represent a technologically relevant materials system for electrochemical device applications in the field of energy storage and conversion. Here, we report about the design of mixed-conducting nanocomposites by facile surface modification using atomic layer deposition (ALD). ALD is the method of choice, as it allows coating of even complex surfaces. Thermally stable mesoporous thin films of 8 mol-% yttria-stabilized zirconia (YSZ) with different pore sizes of 17, 24, and 40 nm were prepared through an evaporation-induced self-assembly process. The free surface of the YSZ films was uniformly coated via ALD with a ceria layer of either 3 or 7 nm thickness. Electrochemical impedance spectroscopy was utilized to probe the influence of the coating on the charge-transport properties. Interestingly, the porosity is found to have no effect at all. In contrast, the thickness of the ceria surface layer plays an important role. While the nanocomposites with a 7 nm coating only show ionic conductivity, those with a 3 nm coating exhibit mixed conductivity. The results highlight the possibility of tailoring the electrical transport properties by varying the coating thickness, thereby providing innovative design principles for the next-generation electrochemical devices.

Hydrothermal Preparation and High Electrochemical Performance of NiS Nanospheres as Anode for Lithium-Ion Batteries

Nickel sulfide has been widely studied as an anode material for lithium-ion batteries due to its environmental friendliness, low cost, high conductivity, and high theoretical capacity. A simple hydrothermal method was used to prepare NiS nanospheres materials with the size in the range of 100–500 nm. The NiS nanospheres electrodes exhibited a high reversible capacity of 1402.3 mAh g−1 at 200 mA g−1 after 280 cycles and a strong rate capability of 814.8 mAh g−1 at 0.8 A g−1 and 1130.5 mAh g−1 when back to 0.1 A g−1. Excellent electrochemical properties and the simple preparation method of the NiS nanospheres make it possible to prepare NiS on a large scale as the anode of lithium-ion batteries.

Architecting Hierarchical WO3 Agglomerates Assembled With Straight and Parallel Aligned Nanoribbons Enabling High Capacity and Robust Stability of Lithium Storage

The pursuit of electrochemical energy storage has led to a pressing need on materials with high capacities and energy densities; however, further progress is plagued by the restrictive capacity (372 mAh g⁻¹) of conventional graphite materials. Tungsten trioxide (WO₃)-based anodes feature high theoretical capacity (693 mAh g⁻¹), suitable potential, and affordable cost, arousing ever-increasing attention and intense efforts. Nonetheless, developing high-performance WO₃ electrodes that accommodate lithium ions remains a daunting challenge on account of sluggish kinetics characteristics and large volume strain. Herein, the well-designed hierarchical WO₃ agglomerates assembled with straight and parallel aligned nanoribbons are fabricated and evaluated as an anode of lithium-ion batteries (LIBs), which exhibits an ultra-high capacity and excellent rate capability. At a current density of 1,000 mA g⁻¹, a reversible capacity as high as 522.7 mAh g⁻¹ can be maintained after 800 cycles, corresponding to a high capacity retention of ∼80%, demonstrating an exceptional long-durability cyclic performance. Furthermore, the mechanistic studies on the lithium storage processes of WO₃ are probed, providing a foundation for further optimizations and rational designs. These results indicate that the well-designed hierarchical WO₃ agglomerates display great potential for applications in the field of high-performance LIBs.

Unveiling the Genesis and Effectiveness of Negative Fading in Nanostructured Iron Oxide Anode Materials for Lithium-Ion Batteries

Iron oxide anode materials for rechargeable lithium-ion batteries have garnered extensive attention because of their inexpensiveness, safety, and high theoretical capacity. Nanostructured iron oxide anodes often undergo negative fading, that is, unconventional capacity increase, which results in a capacity increasing upon cycling. However, the detailed mechanism of negative fading still remains unclear, and there is no consensus on the provenance. Herein, we comprehensively investigate the negative fading of iron oxide anodes with a highly ordered mesoporous structure by utilizing advanced synchrotron-based analysis. Electrochemical and structural analyses identified that the negative fading originates from an optimization of the electrolyte-derived surface layer, and the thus formed layer significantly contributes to the structural stability of the nanostructured electrode materials, as well as their cycle stability. This work provides an insight into understanding the origin of negative fading and its influence on nanostructured anode materials.

One-Pot Synthesized Amorphous Cobalt Sulfide With Enhanced Electrochemical Performance as Anodes for Lithium-Ion Batteries

In order to solve the poor cycle stability and the pulverization of cobalt sulfides electrodes, a series of amorphous and crystalline cobalt sulfides were prepared by one-pot solvothermal synthesis through controlling the reaction temperatures. Compared to the crystalline cobalt sulfide electrodes, the amorphous cobalt sulfide electrodes exhibited superior electrochemical performance. The high initial discharge and charge capacities of 2,132 mAh/g and 1,443 mAh/g at 200 mA/g were obtained. The reversible capacity was 1,245 mAh/g after 200 cycles, which is much higher than the theoretical capacity. The specific capability was 815 mAh/g at 800 mA/g and increased to 1,047 mAh/g when back to 100 mA/g, indicating the excellent rate capability. The outstanding electrochemical performance of the amorphous cobalt sulfide electrodes could result from the unique characteristics of more defects, isotropic nature, and the absence of grain boundaries for amorphous nanostructures, indicating the potential application of amorphous cobalt sulfide as anodes for lithium-ion batteries.

A Silicon Monoxide Lithium-Ion Battery Anode with Ultrahigh Areal Capacity

Silicon monoxide (SiO) is an attractive anode material for next-generation lithium-ion batteries for its ultra-high theoretical capacity of 2680 mAh g-1. The studies to date have been limited to electrodes with a relatively low mass loading (< 3.5 mg cm-2), which has seriously restricted the areal capacity and its potential in practical devices. Maximizing areal capacity with such high-capacity materials is critical for capitalizing their potential in practical technologies. Herein, we report a monolithic three-dimensional (3D) large-sheet holey graphene framework/SiO (LHGF/SiO) composite for high-mass-loading electrode. By specifically using large-sheet holey graphene building blocks, we construct LHGF with super-elasticity and exceptional mechanical robustness, which is essential for accommodating the large volume change of SiO and ensuring the structure integrity even at ultrahigh mass loading. Additionally, the 3D porous graphene network structure in LHGF ensures excellent electron and ion transport. By systematically tailoring microstructure design, we show the LHGF/SiO anode with a mass loading of 44 mg cm-2 delivers a high areal capacity of 35.4 mAh cm-2 at a current of 8.8 mA cm-2 and retains a capacity of 10.6 mAh cm-2 at 17.6 mA cm-2, greatly exceeding those of the state-of-the-art commercial or research devices. Furthermore, we show an LHGF/SiO anode with an ultra-high mass loading of 94 mg cm-2 delivers an unprecedented areal capacity up to 140.8 mAh cm-2. The achievement of such high areal capacities marks a critical step toward realizing the full potential of high-capacity alloy-type electrode materials in practical lithium-ion batteries.

High Cycle Stability of Hybridized Co(OH)2 Nanomaterial Structures Synthesized by the Water Bath Method as Anodes for Lithium-Ion Batteries

Cobalt oxides have been intensely explored as anodes of lithium-ion batteries to resolve the intrinsic disadvantages of low electrical conductivity and volume change. However, as a precursor of preparing cobalt oxides, Co(OH)₂ has rarely been investigated as the anode material of lithium-ion batteries, perhaps because of the complexity of hydroxides. Hybridized Co(OH)₂ nanomaterial structures were synthesized by the water bath method and exhibited high electrochemical performance. The initial discharge and charge capacities were 1703.2 and 1262.9 mAh/g at 200 mA/g, respectively. The reversible capacity was 1050 mAh/g after 150 cycles. The reversible capability was 1015 mAh/g at 800 mA/g and increased to 1630 mAh/g when driven back to 100 mA/g. The electrochemical reaction kinetics study shows that the lithium-ion diffusion-controlled contribution is dominant in the energy storage mechanism. The superior electrochemical performance could result from the water bath method and the hybridization of nanosheets and nanoparticles structures. These hybridized Co(OH)₂ nanomaterial structures with high electrochemical performance are promising anodes for lithium-ion batteries.

Preparation of Hollow Core-Shell Fe3O4/Nitrogen-Doped Carbon Nanocomposites for Lithium-Ion Batteries

Iron oxides are potential electrode materials for lithium-ion batteries because of their high theoretical capacities, low cost, rich resources, and their non-polluting properties. However, iron oxides demonstrate large volume expansion during the lithium intercalation process, resulting in the electrode material being crushed, which always results in poor cycle performance. In this paper, to solve the above problem, iron oxide/carbon nanocomposites with a hollow core-shell structure were designed. Firstly, an Fe2O3@polydopamine nanocomposite was prepared using an Fe2O3 nanocube and dopamine hydrochloride as precursors. Secondly, an Fe3O4@N-doped C composite was obtained by means of further carbonization treatment. Finally, Fe3O4@void@N-Doped C-x composites with core-shell structures with different void sizes were obtained by means of Fe3O4 etching. The effect of the etching time on the void size was studied. The electrochemical properties of the composites when used as lithium-ion battery materials were studied in more detail. The results showed that the sample that was obtained via etching for 5 h using 2 mol L-1 HCl solution at 30 °C demonstrated better electrochemical performance. The discharge capacity of the Fe3O4@void@N-Doped C-5 was able to reach up to 1222 mA g h-1 under 200 mA g-1 after 100 cycles.

Metal organic framework-based nanostructure materials: applications for non-lithium ion battery electrodes

Non-lithium ion (e.g., Al3+, Ca2+, K+, Mg2+, Na+, and Zn2+) batteries have emerged as a promising platform for next-generation energy storage systems.

Long life of exceeding 10000 cycles for aluminum-ion batteries based on FeTe2@GO composite as cathode

Iron telluride wrapped with graphene oxide (GO) nanocomposite via a hydrothermal method is introduced as the cathode material for aluminum-ion batteries (AIBs), exhibiting best cyclability ( 120.4 mA h g-1...

Three-dimensional porous structured germanium anode materials for High-Performance Lithium-Ion Full-cell

Germanium (Ge) has a high specific capacity when used as an alloying anode in lithium ion batteries. Despite this, the large volume of expansion that occurs during charging and discharging...

MOF-Derived ZnS/NC yolk-shell Composites for Highly Reversible Lithium Storage

The application of ZnS-based anode materials in lithium-ion batteries (LIBs) has some severe challenges, such as the insulating nature of ZnS, the pronounced polarization caused by conversion reactions and alloying...

Construction of N, P doped 3D dendritic-free lithium metal anode by using silicon-containing lithium metal

Lithium is thought to be an excellent anode material for next-generation Li metal batteries (LMBs). However, some problems with lithium anode often lead to serious safety concerns and catastrophic failures...

(FexNi1−x)4N nanoparticles: magnetism and electrocatalytic properties for the oxygen evolution reaction

(FexNi1−x)4N nanoparticles (NPs) encased within amorphous carbon were prepared by a facile route and the positive effect of nickel doping content on the magnetic and OER catalytic performance of γ′-Fe4N was investigated.

Quasi-anisotropic benefits in electrospun nickel–cobalt–manganese oxide nano-octahedron as anode for lithium-ion batteries

A polyhedral Ni–Co–Mn–O nano-octahedron anode for lithium-ion batteries was synthesized, which demonstrated enhanced lithium storage properties as compared to the nanofiber counterpart.

Ultrahigh-Capacity and Scalable Architected Battery Electrodes via Tortuosity Modulation

A thick electrode with high areal capacity is a straightforward approach to maximize the energy density of batteries, but the development of thick electrodes suffers from both fabrication challenges and electron/ion transport limitations. In this work, a low-tortuosity LiFePO₄ (LFP) electrode with ultrahigh loadings of active materials and a highly efficient transport network was constructed by a facile and scalable templated phase inversion method. The instant solidification of polymers during phase inversion enables the fabrication of ultrathick yet robust electrodes. The open and aligned microchannels with interconnected porous walls provide direct and short ion transport pathways, while the encapsulation of active materials in the carbon framework offers a continuous pathway for electron transport. Benefiting from the structural advantages, the ultrathick bilayer LiFePO₄ electrodes (up to 1.2 mm) demonstrate marked improvements in rate performance and cycling stability under high areal loadings (up to 100 mg cm^-2). Simulation and operando structural characterization also reveal fast transport kinetics. Combined with the scalable fabrication, our proposed strategy presents an effective alternative for designing practical high energy/power density electrodes at low cost.

MXene nanofibers confining MnOx nanoparticles: a flexible anode for high-speed lithium ion storage networks

The electron and ion conductivities of anode materials such as MnO_x affect critically the properties of anodes in Li-ion batteries. Herein, a three-dimensional (3D) nanofiber network (MnO_x-MXene/CNFs) for high-speed electron and ion transport with a MnO_x surface anchored and embedded inside is designed via electrospinning manganese ion-modified MXene nanosheets and subsequent carbonization. Ion transport analysis reveals improved Li⁺ transport on the MnO_x-MXene/CNF electrode and first-principles density functional theory (DFT) calculation elucidates the Li⁺ adsorption and storage mechanism. The surface-anchored MnO_x nanoparticles form extremely strong bonds with the nanofibers, and the internally embedded MnO_x nanoparticles, due to the fiber confinement effect, ensure the structural stability during charging and discharging, achieving the so-called dual stabilization strategies for cyclic fluctuation. By electrospinning, self-restacking of MXene flakes can be prevented, thereby giving rise to a larger surface area and more accessible active sites on the flexible anode. Benefiting from the 3D network with excellent conductivity and stability, at high current densities, the MnO_x-MXene/CNF anode exhibits outstanding electrochemical characteristics. Even after 2000 cycles, a reversible capacity of 1098 mA h g^-1 can be obtained at 2 A g^-1 with only 0.007208% decay rate. The MnO_x-MXene/CNF anode also shows a significant rate performance such as 1268 mA h g^-1 at 2 A g^-1 and 1137 mA h g^-1 at 5 A g^-1 corresponding to an area specific capacity of 2.536 mA h cm^-2 at 4 mA cm^-2 and 2.274 mA h cm^-2 at 10 mA cm^-2, respectively. The results indicate that the MnO_x-MXene/CNF anode has excellent Li-ion storage properties and great commercial potential.

Utilization of Interfacial Charge Storage toward Ultra-high Capacity: Li2SO4 Sealed Micron Sized Iron Oxides as Anode for Lithium Batteries

The interfacial charge storage is derived from spin-polarized electrons stored on the surface of iron metal nanoparticles, and reasonable utilization can achieve a capacity far beyond the traditional conversion mechanism. Generally, iron oxide is easy to crack, pulverize, and fall off due to its poor conductivity and large volume change during cycling, and causes serious side reactions with the electrolyte. Herein, this pulverization phenomenon was intentionally utilized to in situ form nano-sized iron particles and create a large number of Fe/Li₂O interfaces. Specifically, a Li⁺ conductor like Li₂SO₄ was utilized to seal micron sized iron oxides and also work as an aggregation barrier. Thus, the in situ formed nanoparticles were separated from the electrolyte and could provide huge capacity through interfacial charge storage. Therefore, the specific capacity of this unique composite continues to rise upon activation cycling and finally reaches 1708 mA h g^-1, which is more than twice its theoretical capacity based on the conversion mechanism. The gradually increasing interfacial charge storage capacity was also directly confirmed by X-ray photoelectron spectroscopy tests. This novel strategy provides new opportunities for the design and commercialization of advanced energy storage systems.

The Synergetic Effect Induced High Electrochemical Performance of CuO/Cu2O/Cu Nanocomposites as Lithium-Ion Battery Anodes

Due to the high theoretical capability, copper-based oxides were widely investigated. A facile water bath method was used to synthesis CuO nanowires and CuO/Cu₂O/Cu nanocomposites. Owing to the synergetic effect, the CuO/Cu₂O/Cu nanocomposites exhibit superior electrochemical performance compared to the CuO nanowires. The initial discharge and charge capacities are 2,660.4 mAh/g and 2,107.8 mAh/g, and the reversible capacity is 1,265.7 mAh/g after 200 cycles at 200 mA/g. Moreover, the reversible capacity is 1,180 mAh/g at 800 mA/g and 1,750 mAh/g when back to 100 mA/g, indicating the excellent rate capability. The CuO/Cu₂O/Cu nanocomposites also exhibit relatively high electric conductivity and lithium-ion diffusion coefficient, especially after cycling. For the energy storage mechanism, the capacitive controlled mechanism is predominance at the high scan rates, which is consistent with the excellent rate capability. The outstanding electrochemical performance of the CuO/Cu₂O/Cu nanocomposites indicates the potential application of copper-based oxides nanomaterials in future lithium-ion batteries.

Unlocking Rapid Charging and Extended Lifetimes for Li-Ion Batteries Using Freestanding Quantum Conversion-Type Aerofilm Anode

Batteries capable of quick charging as fast as fossil fuel vehicles are becoming a vital issue in the electric vehicle market. However, conversion-type materials promising as a next-generation anode have many problems to satisfy fast charging and long-term cycles due to their low conductivity and large irreversibility despite a high theoretical capacity. Here, we report effective strategies for a SnO₂-based anode to enable rapid-charging, long-cycle, and high reversible capacity. The quantum size of SnO₂ nanoparticles uniformly embedded within a 3D conductive carbon matrix as a prerequisite for high reversible capacity increases the interdiffusion layer and facilitates a highly reversible conversion reaction between Li₂O/Sn and SnO₂. In particular, the Sn-C chemical bond achieves ion-site control and direct electron transfer, enabling boost charging. Further, the robust and porous structure of the binder-free three-dimensional electrode buffers the massive volume expansion during Li insertion/desertion and allows for multidimensional rapid-ion diffusion. As a result, our quantum SnO₂ anode delivers a high reversible capacity of about 753 mAh g^-1 with a 468% capacity increase after 4000 cycles at 10 C. It also presents a gradually increasing capacity up to 548 mAh g^-1 even at 20 C and superior cyclability over 20 000 cycles in capacity stabilization. This study will contribute to designing aerofilm-based conversion-type electrodes for fast charging devices.

A Coral-Like FeP@NC Anode with Increasing Cycle Capacity for Sodium-Ion and Lithium-Ion Batteries Induced by Particle Refinement

We present a coral-like FeP composite with FeP nanoparticles anchored and dispersed on a nitrogen-doped 3D carbon framework (FeP@NC). Due to the highly continuous N-doped carbon framework and a spring-buffering graphitized carbon layer around the FeP nanoparticle, a sodium-ion battery with the FeP@NC composite exhibits an ultra-stable cycling performance at 10 A g^-1 with a capacity retention of 82.0 % in 10 000 cycles. Also, particle refinement leads to a capacity increase during cycling. The FeP nanoparticles go through a refining-recombination process during the first cycle and present a global refining trend after dozens of cycles, which results in a gradually increase in graphitization degree and interface magnetization, and further provides more active sites for Na⁺ storage and contributes to a rising capacity with cycling. The capacity ascending phenomenon can also extend to lithium-ion batteries.

Building Efficient Ion Pathway in Highly Densified Thick Electrodes with High Gravimetric and Volumetric Energy Densities

A common practice in thick electrode design is to increase porosity to boost charge transport kinetics. However, a high porosity offsets the advantages of thick electrodes in both gravimetric and volumetric energy densities. Here we design a freestanding thick electrode composed of highly densified active material regions connected by continuous electrolyte-buffering voids. By wet calendering of the phase-inversion electrode, the continuous compact active material region and continuous ion transport network are controllably formed. Rate capabilities and cycling stability at high LiFePO₄ loading of 126 mg cm^-2 were achieved for the densified cathode with porosity as low as 38%. The decreased porosity and efficient void utilization enable high gravimetric/volumetric energy densities of 330 Wh kg^-1 and 614 Wh L^-1, as well as improved power densities. The versatility of this method and the industrial compatible "roll-to-roll" fabrication demonstrate an important step toward the practical application of thick electrodes.

Immobilizing Redox-Active Tricycloquinazoline into a 2D Conductive Metal-Organic Framework for Lithium Storage

Heteroaromatic-conjugated aromatic molecules have inspired numerous interests in rechargeable batteries like Li-ion batteries, but were limited by low conductivity and easy dissolution in electrolytes. Herein, we immobilize a nitrogen-rich aromatic molecule tricycloquinazoline (TQ) and CuO₄ unit into a two-dimensional (2D) conductive metal-organic framework (MOF) to unlock their potential for Li⁺ storage. TQ was identified redox activity with Li⁺ for the first time. With a synergistic effect of TQ and CuO₄ unit, the 2D conductive MOF, named Cu-HHTQ (HHTQ=2,3,7,8,12,13-hexahydroxytricycloquinazoline), can facilitate the Li⁺ /e^- transport and ensure a resilient electrode, resulting in a high capacity of 657.6 mAh g^-1 at 600 mA g^-1 with extraordinary high-rate capability and impressive cyclability. Our findings highlight an efficient strategy of constructing electrode materials for energy storage with combining multiple redox-active moieties into conductive MOFs.

Atmosphere-sensitive photoluminescence of Co x Fe3-x O4 metal oxide nanoparticles

In this work the photoluminescence (PL) of Co x Fe3-x O4 spinel oxide nanoparticles under pulsed UV laser irradiation (λ exc = 270 nm) is investigated for varying Co/Fe ratios (x = 0.4⋯2.5). A broad emission in the green spectral range is observed, exhibiting two maxima at around 506 nm, which is dominant for Fe-rich nanoparticles (x = 0.4, 0.9), and at around 530 nm, that is more pronounced for Co-rich nanoparticles (x > 1.6). As examinations in different atmospheres show that the observed emission reacts sensitively to the presence of water, it is proposed that the emission is mainly caused by OH groups with terminal or bridging metal-O bonds on the Co x Fe3-x O4 surface. Raman spectroscopy supports that the emission maximum at 506 nm corresponds to terminal OH groups bound to metal cations on tetrahedral sites (i.e., Fe3+), while the maximum around 530 nm corresponds to terminal OH groups bound to metal cations on octahedral sites (i.e., Co3+). Photoinduced dehydroxylation shows that OH groups can be removed on Fe-rich nanoparticles more easily, leading to a conversion process and the formation of new OH groups with different bonds to the surface. As such behavior is not observed for Co x Fe3-x O4 with x > 1.6, we conclude that the OH groups are more stable against dehydroxylation on Co-rich nanoparticles. The higher OH stability is expected to lead to a higher catalytic activity of Co-rich cobalt ferrites in the electrochemical generation of oxygen.

Recent Progress on In Situ/Operando Characterization of Rechargeable Alkali Ion Batteries

The specific chemical and physical evolutions of electrode materials under operating conditions should be understood to optimize their electrochemical performances. The in-situ/operando techniques including Raman spectrum, transmission electron microscope, X-ray diffraction, X-ray absorption spectrum, and magnetization are powerful tools, which can provide the real-time surficial/interfacial changes of electrodes, the transformation of crystal lattice structures, the adjustment of electronic states and even the influence of magnetic properties under operating conditions. In this Review, the advantages and limitations of these in-situ/operando techniques in investigating the inner energy storage mechanisms of various type electrode materials are analyzed. The representative research results such as the ion dependent storage mechanism, step-alloying processes and space charge storage theory are highlighted. In addition, the challenges and opportunities of in-situ/operando characterizations are proposed as well.

Study of the Lithium Storage Mechanism of N-Doped Carbon-Modified Cu2 S Electrodes for Lithium-Ion Batteries

Owing to their high specific capacity and abundant reserve, Cu_xS compounds are promising electrode materials for lithium‐ion batteries (LIBs). Carbon compositing could stabilize the Cu_xS structure and repress capacity fading during the electrochemical cycling, but the corresponding Li⁺ storage mechanism and stabilization effect should be further clarified. In this study, nanoscale Cu₂S was synthesized by CuS co‐precipitation and thermal reduction with polyelectrolytes. High‐temperature synchrotron radiation diffraction was used to monitor the thermal reduction process. During the first cycle, the conversion mechanism upon lithium storage in the Cu₂S/carbon was elucidated by operando synchrotron radiation diffraction and in situ X‐ray absorption spectroscopy. The N‐doped carbon‐composited Cu₂S (Cu₂S/C) exhibits an initial discharge capacity of 425 mAh g⁻¹ at 0.1 A g⁻¹, with a higher, long‐term capacity of 523 mAh g⁻¹ at 0.1 A g⁻¹ after 200 cycles; in contrast, the bare CuS electrode exhibits 123 mAh g⁻¹ after 200 cycles. Multiple‐scan cyclic voltammetry proves that extra Li⁺ storage can mainly be ascribed to the contribution of the capacitive storage.

Pseudocapacitive trimetallic NiCoMn-111 perovskite fluorides for advanced Li-ion supercabatteries

Exploring advanced electrochemical energy storage systems and clarifying their charge storage mechanisms are key scientific frontiers presenting a great challenge. Herein, we demonstrate a novel concept of Li-ion supercabatteries (i.e., Li-ion capacitors/batteries, LICBs), which were realized using a novel trimetallic Ni-Co-Mn perovskite fluoride (K_0.97Ni_0.31Co_0.34Mn_0.35F_2.98, denoted as KNCMF-111 (8^#)) anode and a high-performance activated carbon/LiFePO₄ (AC/LFP) cathode, which makes the boundary between LICs and LIBs less distinctive. Thanks to the pseudocapacitive conversion mechanism of the KNCMF-111 (8^#) anode with superior kinetics and the enhanced capacity of the capacitor/battery hybrid AC/LFP cathode, the designed KNCMF-111 (8^#)//AC/LFP LICBs, integrating the synergistic superiority of pseudocapacitive, capacitive and faradaic characteristics, exhibit remarkable energy/power densities and a long cycle life, indicating a high-efficiency energy storage application. Overall, this work provides new insights into exploring advanced Li-ion supercabatteries and clarifying their charge storage mechanisms based on trimetallic Ni-Co-Mn perovskite fluoride electrode materials, which sheds light on the development of advanced electrochemical energy storage systems and in-depth understanding of their charge storage mechanisms.

Dramatically comprehensive improved electrochemical performances of symmetric and asymmetric supercapacitors under external magnetic field

Recently, magnetic field (MF) has been described as a potential way to improve the properties of electrode materials, which significantly enhances the ion diffusion behavior and material wettability. We first synthezised for the first time a comparable carbon-based electrode material (GCA) including active carbon, reduced graphene and carbon nanotubes through a facile stirring method for further research under MF. Herein, 0.15 T of MF induced by two NdFeB magnets was applied on the supercapacitor devices to enhance the energy density, which increased by about 62% for the symmetric supercapacitor (SSC: from 11.2 to 18.1 W h kg^-1). An asymmetric supercapacitor composed of the prepared GCA as the anode and NiCoFe/NiCoFe-OH as the cathode was also assembled for research. And it was found that the whole electrochemical performance significantly improved (for example, energy density increased by about 22% for the asymmetric supercapacitor, i.e., from 50.6 to 61.4 W h kg^-1).