Cobalt Oxide 2D Nanosheets Formed at a Polarized Liquid|Liquid Interface toward High-Performance Li-Ion and Na-Ion Battery Anodes

Cobalt oxide (Co3O4)-based nanostructures have the potential as low-cost materials for lithium-ion (Li-ion) and sodium-ion (Na-ion) battery anodes with a theoretical capacity of 890 mAh/g. Here, we demonstrate a novel method for the production of Co3O4 nanoplatelets. This involves the growth of flower-like cobalt oxyhydroxide (CoOOH) nanostructures at a polarized liquid|liquid interface, followed by conversion to flower-like Co3O4 via calcination. Finally, sonication is used to break up the flower-like Co3O4 nanostructures into two-dimensional (2D) nanoplatelets with lateral sizes of 20-100 nm. Nanoplatelets of Co3O4 can be easily mixed with carbon nanotubes to create nanocomposite anodes, which can be used for Li-ion and Na-ion battery anodes without any additional binder or conductive additive. The resultant electrodes display impressive low-rate capacities (at 125 mA/g) of 1108 and 1083 mAh/g, for Li-ion and Na-ion anodes, respectively, and stable cycling ability over >200 cycles. Detailed quantitative rate analysis clearly shows that Li-ion-storing anodes charge roughly five times faster than Na-ion-storing anodes.

Graphene nanowalls grown on copper mesh

Graphene nanowalls (GNWs) can be described as extended nanosheets of graphitic carbon where the basal planes are perpendicular to a substrate. Generally, existing techniques to grow films of GNWsare based on plasma-enhanced chemical vapor deposition (PECVD) and the use of diverse substrate materials (Cu, Ni, C, etc) shaped as foils or filaments. Usually, patterned films rely on substrates priorly modified by costly cleanroom procedures. Hence, we report here the characterization, transfer and application of wafer-scale patterned GNWsfilms that were grown on Cu meshes using low-power direct-current PECVD. Reaching wall heights of ∼300 nm, mats of vertically-aligned carbon nanosheets covered square centimeter wire meshes substrates, replicating well the thread dimensions and the tens of micrometer-wide openings of the meshes. Contrastingly, the same growth conditions applied to Cu foils resulted in limited carbon deposition, mostly confined to the substrate edges. Based on the wet transfer procedure turbostratic and graphitic carbon domains co-exist in the GNWsmicrostructure. Interestingly, these nanoscaled patterned films were quite hydrophobic, being able to reverse the wetting behavior of SiO2surfaces. Finally, we show that the GNWscan also be used as the active material for C-on-Cu anodes of Li-ion battery systems.

Over-Stoichiometric Metastabilization of Cation-Disordered Rock Salts

Cation-disordered rock salts (DRXs) are well known for their potential to realize the goal of achieving scalable Ni- and Co-free high-energy-density Li-ion batteries. Unlike in most cathode materials, the disordered cation distribution may lead to more factors that control the electrochemistry of DRXs. An important variable that is not emphasized by research community is regarding whether a DRX exists in a more thermodynamically stable form or a more metastable form. Moreover, within the scope of metastable DRXs, over-stoichiometric DRXs, which allow relaxation of the site balance constraint of a rock salt structure, are particularly underexplored. In this work, these findings are reported in locating a generally applicable approach to "metastabilize" thermodynamically stable Mn-based DRXs to metastable ones by introducing Li over-stoichiometry. The over-stoichiometric metastabilization greatly stimulates more redox activities, enables better reversibility of Li deintercalation/intercalation, and changes the energy storage mechanism. The metastabilized DRXs can be transformed back to the thermodynamically stable form, which also reverts the electrochemical properties, further contrasting the two categories of DRXs. This work enriches the structural and compositional space of DRX families and adds new pathways for rationally tuning the properties of DRX cathodes.

Novel Low-Strain Layered/Rocksalt Intergrown Cathode for High-Energy Li-Ion Batteries

Both layered- and rocksalt-type Li-rich cathode materials are drawing great attention due to their enormous capacity, while the individual phases have their own drawbacks, such as great volume change for the layered phase and low electronic and ionic conductivities for the rocksalt phase. Previously, we have reported the layered/rocksalt intergrown cathodes with nearly zero-strain operation, while the use of precious elements hinders their industrial applications. Herein, low-cost 3d Mn4+ ions are utilized to partially replace the expensive Ru5+ ions, to develop novel ternary Li-rich cathode material Li1+x[RuMnNi]1-xO2. The as-designed Li1.15Ru0.25Mn0.2Ni0.4O2 is revealed to have a layered/rock salt intergrown structure by neutron diffraction and transmission electron microscopy. The as-designed cathode exhibits ultrahigh lithium-ion reversibility, with 0.86 (231.1 mAh g-1) out of a total Li+ inventory of 1.15 (309.1 mAh g-1). The X-ray absorption spectroscopy and resonant inelastic X-ray scattering spectra further demonstrate that the high Li+ storage of the intergrown cathode is enabled by leveraging cationic and anionic redox activities in charge compensation. Surprisingly, in situ X-ray diffraction shows that the intergrown cathode undergoes extremely low-strain structural evolution during the charge-discharge process. Finally, the Mn content in the intergrown cathodes is found to be tunable, providing new insights into the design of advanced cathode materials for high-energy Li-ion batteries.

Charge Storage Mechanism in Electrospun Spinel-Structured High-Entropy (Mn0.2 Fe0.2 Co0.2 Ni0.2 Zn0.2 )3 O4 Oxide Nanofibers as Anode Material for Li-Ion Batteries

High-entropy oxides (HEOs) have emerged as promising anode materials for next-generation lithium-ion batteries (LIBs). Among them, spinel HEOs with vacant lattice sites allowing for lithium insertion and diffusion seem particularly attractive. In this work, electrospun oxygen-deficient (Mn,Fe,Co,Ni,Zn) HEO nanofibers are produced under environmentally friendly calcination conditions and evaluated as anode active material in LIBs. A thorough investigation of the material properties and Li+ storage mechanism is carried out by several analytical techniques, including ex situ synchrotron X-ray absorption spectroscopy. The lithiation process is elucidated in terms of lithium insertion, cation migration, and metal-forming conversion reaction. The process is not fully reversible and the reduction of cations to the metallic form is not complete. In particular, iron, cobalt, and nickel, initially present mainly as Fe3+ , Co3+ /Co2+ , and Ni2+ , undergo reduction to Fe0 , Co0 , and Ni0 to different extent (Fe < Co < Ni). Manganese undergoes partial reduction to Mn3+ /Mn2+ and, upon re-oxidation, does not revert to the pristine oxidation state (+4). Zn2+ cations do not electrochemically participate in the conversion reaction, but migrating from tetrahedral to octahedral positions, they facilitate Li-ion transport within lattice channels opened by their migration. Partially reversible crystal phase transitions are observed.

Diagnosis of Current Flow Patterns Inside Fault-Simulated Li-Ion Batteries via Non-Invasive, In Operando Magnetic Field Imaging

With the growing popularity of Li-ion batteries in large-scale applications, building a safer battery has become a common goal of the battery community. Although the small errors inside the cells trigger catastrophic failures, tracing them and distinguishing cell failure modes without knowledge of cell anatomy can be challenging using conventional methods. In this study, a real-time, non-invasive magnetic field imaging (MFI) analysis that can signal the battery current-induced magnetic field and visualize the current flow within Li-ion cells is developed. A high-speed, spatially resolved MFI scan is used to derive the current distribution pattern from cells with different tab positions at a current load. Current maps are collected to determine possible cell failures using fault-simulated batteries that intentionally possess manufacturing faults such as lead-tab connection failures, electrode misalignment, and stacking faults (electrode folding). A modified MFI analysis exploiting the magnetic field interference with the countercurrent-carrying plate enables the direct identification of defect spots where abnormal current flow occurs within the pouch cells.

Self-Reinforced Inductive Effect of Symmetric Bipolar Organic Molecule for High-Performance Rechargeable Batteries

Herein, the self-reinforced inductive effect derived from coexistence of both p- and n-type redox-active motifs in a single organic molecule is presented. Molecular orbital energy levels of each motif are dramatically tuned, which leads to the higher oxidation and the lower reduction potentials. The self-reinforced inductive effect of the symmetric bipolar organic molecule, N,N'-dimethylquinacridone (DMQA), is corroborated, by both experimental and theoretical methods. Furthermore, its redox mechanism and reaction pathway in the Li+ -battery system are scrutinized. DMQA shows excellent capacity retention at the operating voltage of 3.85 and 2.09 V (vs Li+ /Li) when used as the cathode and anode, respectively. Successful operation of DMQA electrodes in a symmetric all-organic battery is also demonstrated. The comprehensive insight into the energy storage capability of the symmetric bipolar organic molecule and its self-reinforced inductive effect is provided. Thus, a new class of organic electrode materials for symmetric all-organic batteries as well as conventional rechargeable batteries can be conceived.

Stable Operation Induced by Plastic Crystal Electrolyte Used in Ni-Rich NMC811 Cathodes for Li-Ion Batteries

The LiNi0.8Mn0.1Co0.1O2 (NMC811) cathode material has been of significant consideration owing to its high energy density for Li-ion batteries. However, the poor cycling stability in a carbonate electrolyte limits its further development. In this work, we report the excellent electrochemical performance of the NMC811 cathode using a rational electrolyte based on organic ionic plastic crystal N-ethyl-N-methyl pyrrolidinium bis(fluorosulfonyl)imide C2mpyr[FSI], with the addition of (1:1 mol) LiFSI salt. This plastic crystal electrolyte (PC) is a thick viscous liquid with an ionic conductivity of 2.3 × 10-3 S cm-1 and a high Li+ transference number of 0.4 at ambient temperature. The NMC811@PC cathode delivers a discharge capacity of 188 mA h g-1 at a rate of 0.2 C with a capacity retention of 94.5% after 200 cycles, much higher than that of using a carbonate electrolyte (54.3%). Moreover, the NMC811@PC cathode also exhibits a superior high-rate capability with a discharge capacity of 111.0 mA h g-1 at the 10 C rate. The significantly improved cycle performance of the NMC811@PC cathode can be attributed to the high Li+ conductivity of the PC electrolyte, the stable Li+ conductive CEI film, and the maintaining of particle integrity during long-term cycling. The admirable electrochemical performance of the NMC811|C2mpyr[FSI]:[LiFSI] system exhibits a promising application of the plastic crystal electrolyte for high voltage layered oxide cathode materials in advanced lithium-ion batteries.

Operando Electrochemical Liquid Cell Scanning Transmission Electron Microscopy Investigation of the Growth and Evolution of the Mosaic Solid Electrolyte Interphase for Lithium-Ion Batteries

The solid electrolyte interphase (SEI) is a key component of a lithium-ion battery forming during the first few dischage/charge cycles at the interface between the anode and the electrolyte. The SEI passivates the anode-electrolyte interface by inhibiting further electrolyte decomposition, extending the battery's cycle life. Insights into SEI growth and evolution in terms of structure and composition remain difficult to access. To unravel the formation of the SEI layer during the first cycles, operando electrochemical liquid cell scanning transmission electron microscopy (ec-LC-STEM) is employed to monitor in real time the nanoscale processes that occur at the anode-electrolyte interface in their native electrolyte environment. The results show that the formation of the SEI layer is not a one-step process but comprises multiple steps. The growth of the SEI is initiated at low potential during the first charge by decomposition of the electrolyte leading to the nucleation of inorganic nanoparticles. Thereafter, the growth continues during subsequent cycles by forming an island-like layer. Eventually, a dense layer is formed with a mosaic structure composed of larger inorganic patches embedded in a matrix of organic compounds. While the mosaic model for the structure of the SEI is generally accepted, our observations document in detail how the complex structure of the SEI is built up during discharge/charge cycling.

High-Rate One-Dimensional α-MnO2 Anode for Lithium-Ion Batteries: Impact of Polymorphic and Crystallographic Features on Lithium Storage

Manganese dioxide (MnO2) exists in a variety of polymorphs and crystallographic structures. The electrochemical performance of Li storage can vary depending on the polymorph and the morphology. In this study, we present a new approach to fabricate polymorph- and aspect-ratio-controlled α-MnO2 nanorods. First, δ-MnO2 nanoparticles were synthesized using a solution plasma process assisted by three types of sugars (sucrose, glucose, and fructose) as reducing promoters; this revealed different morphologies depending on the nucleation rate and reaction time from the molecular structure of the sugars. Based on the morphology of δ-MnO2, the polymorphic-transformed three types of α-MnO2 nanorods showed different aspect ratios (c/a), which highly affected the transport of Li ions. Among them, a relatively small aspect ratio (c/a = 5.1) and wide width of α-MnO2-S nanorods (sucrose-assisted) induced facile Li-ion transport in the interior of the particles through an increased Li-ion pathway. Consequently, α-MnO2-S exhibited superior battery performance with a high-rate capability of 673 mAh g-1 at 2 A g-1, and it delivered a high reversible capacity of 1169 mAh g-1 at 0.5 A g-1 after 200 cycles. Our findings demonstrated that polymorphs and crystallographic properties are crucial factors in the electrode design of high-performance Li-ion batteries.

Superb Li-Ion Storage of Sn-Based Anode Assisted by Conductive Hybrid Buffering Matrix

Although Sn has been intensively studied as one of the most promising anode materials to replace commercialized graphite, its cycling and rate performances are still unsatisfactory owing to the insufficient control of its large volume change during cycling and poor electrochemical kinetics. Herein, we propose a Sn-TiO2-C ternary composite as a promising anode material to overcome these limitations. The hybrid TiO2-C matrix synthesized via two-step high-energy ball milling effectively regulated the irreversible lithiation/delithiation of the active Sn electrode and facilitated Li-ion diffusion. At the appropriate C concentration, Sn-TiO2-C exhibited significantly enhanced cycling performance and rate capability compared with its counterparts (Sn-TiO2 and Sn-C). Sn-TiO2-C delivers good reversible specific capacities (669 mAh g-1 after 100 cycles at 200 mA g-1 and 651 mAh g-1 after 500 cycles at 500 mA g-1) and rate performance (446 mAh g-1 at 3000 mA g-1). The superiority of Sn-TiO2-C over Sn-TiO2 and Sn-C was corroborated with electrochemical impedance spectroscopy, which revealed faster Li-ion diffusion kinetics in the presence of the hybrid TiO2-C matrix than in the presence of TiO2 or C alone. Therefore, Sn-TiO2-C is a potential anode for next-generation Li-ion batteries.

Design and Performance of a New Zn0.5Mg0.5FeMnO4 Porous Spinel as Anode Material for Li-Ion Batteries

Due to the low capacity, low working potential, and lithium coating at fast charging rates of graphite material as an anode for Li-ion batteries (LIBs), it is necessary to develop novel anode materials for LIBs with higher capacity, excellent electrochemical stability, and good safety. Among different transition-metal oxides, AB2O4 spinel oxides are promising anode materials for LIBs due to their high theoretical capacities, environmental friendliness, high abundance, and low cost. In this work, a novel, porous Zn0.5Mg0.5FeMnO4 spinel oxide was successfully prepared via the sol-gel method and then studied as an anode material for Li-ion batteries (LIBs). Its crystal structure, morphology, and electrochemical properties were, respectively, analyzed through X-ray diffraction, high-resolution scanning electron microscopy, and cyclic voltammetry/galvanostatic discharge/charge measurements. From the X-ray diffraction, Zn0.5Mg0.5FeMnO4 spinel oxide was found to crystallize in the cubic structure with Fd3¯m symmetry. However, the Zn0.5Mg0.5FeMnO4 spinel oxide exhibited a porous morphology formed by interconnected 3D nanoparticles. The porous Zn0.5Mg0.5FeMnO4 anode showed good cycling stability in its capacity during the initial 40 cycles with a retention capacity of 484.1 mAh g-1 after 40 cycles at a current density of 150 mA g-1, followed by a gradual decrease in the range of 40-80 cycles, which led to reaching a specific capacity close to 300.0 mAh g-1 after 80 cycles. The electrochemical reactions of the lithiation/delithiation processes and the lithium-ion storage mechanism are discussed and extracted from the cyclic voltammetry curves.

NbO2 a Highly Stable, Ultrafast Anode Material for Li- and Na-Ion Batteries

Anode materials with fast charging capabilities and stability are critical for realizing next-generation Li-ion batteries (LIBs) and Na-ion batteries (SIBs). The present work employs a simple synthetic strategy to obtain NbO2 and studies its applications as an anode for LIB and SIB. In the case of the LIB, it exhibited a specific capacity of 344 mAh g-1 at 100 mA g-1. It also demonstrated remarkable stability over 1000 cycles, with 92% capacity retention. Additionally, it showed a unique fast charging capability, which takes 30 s to reach a specific capacity of 83 mAh g-1. For the SIB, NbO2 exhibited a specific capacity of 244 mAh g-1 at 50 mA g-1 and showed 70% capacity retention after 500 cycles. Furthermore, detailed density functional theory reveals that various factors like bulk and surface charging processes, lower ion diffusion energy barriers, and superior electronic conductivity of NbO2 are responsible for the observed battery performances.

A Multifunctional Interlocked Binder with Synergistic In Situ Covalent and Hydrogen Bonding for High-Performance Si Anode in Li-ion Batteries

Silicon has garnered significant attention as a promising anode material for high-energy density Li-ion batteries. However, Si can be easily pulverized during cycling, which results in the loss of electrical contact and ultimately shortens battery lifetime. Therefore, the Si anode binder is developed to dissipate the enormous mechanical stress of the Si anode with enhanced mechanical properties. However, the interfacial stability between the Si anode binder and Cu current collector should also be improved. Here, a multifunctional thiourea polymer network (TUPN) is proposed as the Si anode binder. The TUPN binder provides the structural integrity of the Si anode with excellent tensile strength and resilience due to the epoxy-amine and silanol-epoxy covalent cross-linking, while exhibiting high extensibility from the random coil chains with the hydrogen bonds of thiourea, oligoether, and isocyanurate moieties. Furthermore, the robust TUPN binder enhances the interfacial stability between the Si anode and current collector by forming a physical interaction. Finally, the facilitated Li-ion transport and improved electrolyte wettability are realized due to the polar oligoether, thiourea, and isocyanurate moieties, respectively. The concept of this work is to highlight providing directions for the design of polymer binders for next-generation batteries.

In Situ Li-Plating Diagnosis for Fast-Charging Li-Ion Batteries Enabled by Relaxation-Time Detection

The Li-plating behavior of Li-ion batteries under fast-charging conditions is elusive due to a lack of reliable indicators of the Li-plating onset. In this work, the relaxation time constant of the charge-transfer process (τCT ) is proposed to be promising for the determination of Li-plating onset. A novel pulse/relaxation test method enables rapid access to the τCT of the graphite anode during battery operation, applicable to both half and full batteries. The diagnosis of Li plating at varying temperatures and charging rates enriches the cognition of Li-plating behaviors. Li plating at low temperatures and high charging rates can be avoided because of the battery voltage limitations. Nevertheless, after the onset, severe Li plating evolves rapidly under harsh charging conditions, while the Li-plating process under benign charging conditions is accompanied by a simultaneous Li-intercalation process. The quantitative estimates indicate that Li plating at high temperatures/high charging rates leads to more irreversible capacity losses. This facile method with rational scientific principles can provide inspiration for exploring the safe boundaries of Li-ion batteries.

The Influence of TiO2 Nanoparticles Morphologies on the Performance of Lithium-Ion Batteries

Anode materials based on the TiO2 nanoparticles of different morphologies were prepared using the hydrothermal method and characterized by various techniques, such as X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), and N2 absorption. The TiO2 nanoparticles prepared were used as anode materials for lithium-ion batteries (LIBs), and their electrochemical properties were tested using discharging/charging measurements. The results showed that the initial morphology of the nanoparticles plays a minor role in battery performance after the first few cycles and that better capacity was achieved for TiO2 nanobelt morphology. The sharp drop in the specific capacity of LIB during their first cycles is examined by considering changes in the morphology of TiO2 particles and their porosity properties in terms of size and connectivity. The performance of TiO2 anode materials has also been assessed by considering their phase.

Probing the Formation of Cathode-Electrolyte Interphase on Lithium Iron Phosphate Cathodes via Operando Mechanical Measurements

Interfacial instabilities in electrodes control the performance and lifetime of Li-ion batteries. While the formation of the solid-electrolyte interphase (SEI) on anodes has received much attention, there is still a lack of understanding the formation of the cathode-electrolyte interphase (CEI) on the cathodes. To fill this gap, we report on dynamic deformations on LiFePO4 cathodes during charge/discharge by utilizing operando digital image correlation, impedance spectroscopy, and cryo X-ray photoelectron spectroscopy. LiFePO4 cathodes were cycled in either LiPF6, LiClO4, or LiTFSI-containing organic liquid electrolytes. Beyond the first cycle, Li-ion intercalation results in a nearly linear correlation between electrochemical strains and the state of (dis)-charge, regardless of the electrolyte chemistry. However, during the first charge in the LiPF6-containing electrolyte, there is a distinct irreversible positive strain evolution at the onset of anodic current rise as well as current decay at around 4.0 V. Impedance studies show an increase in surface resistance in the same potential window, suggesting the formation of CEI layers on the cathode. The chemistry of the CEI layer was characterized by X-ray photoelectron spectroscopy. LiF is detected in the CEI layer starting as early as 3.4 V and LixPOyFz appeared at voltages higher than 4.0 V during the first charge. Our approach offers insights into the formation mechanism of CEI layers on the cathode electrodes, which is crucial for the development of robust cathodes and electrolyte chemistries for higher-performance batteries.

Isotropic Microstrain Relaxation in Ni-Rich Cathodes for Long Cycling Lithium Ion Batteries

Developing isotropic-dominated microstrain relaxation is a vital step toward the enhancement of cyclic performance and thermal stability for high-energy-density Ni-rich cathodes. Here, a microstructure engineering strategy is employed for synthesizing the elongated primary particles radially aligned Ni-rich cathodes only by regulating the precipitation rates of cations and the distributions of flow field. The as-obtained cathode also exhibits an enlarged lattice distance and highly exposed (003) plane. The high aspect ratio and favorable atomic arrangement of primary particles not only enable isotropic strain relaxation for effectively suppressing microcrack formation and propagation, but also facilitate Li-ion diffusion with greatly reduced Li/Ni mixing. Consequently, it shows obvious superiority in the high-rate, long-cycle life, and thermal stability compared with the conventional counterparts. After modification, an exceptionally long life is achieved with a capacity retention of 90.1% at 1C and 84.3% at 5C after 1500 cycles within 3.0-4.3 V in a 1.5-Ah pouch cell. This work offers a universal strategy to achieve isotropic strain distribution for conveniently enhancing the durability of Ni-rich cathodes.

Osmotically Delaminated Silicate Nanosheet-Coated NCM for Ultra-Stable Li+ Storage and Chemical Stability Toward Long-Term Air Exposure

To ensure the safety and performance of lithium-ion batteries (LIBs), a rational design and optimization of suitable cathode materials are crucial. Lithium nickel cobalt manganese oxides (NCM) represent one of the most popular cathode materials for commercial LIBs. However, they are limited by several critical issues, such as transition metal dissolution, formation of an unstable cathode-electrolyte interphase (CEI) layer, chemical instability upon air exposure, and mechanical instability. In this work, coating fabricated by self-assembly of osmotically delaminated sodium fluorohectorite (Hec) nanosheets onto NCM (Hec-NCM) in a simple and technically benign aqueous wet-coating process is reported first. Complete wrapping of NCM by high aspect ratio (>10 000) nanosheets is enabled through an electrostatic attraction between Hec nanosheets and NCM as well as by the superior mechanical flexibility of Hec nanosheets. The coating significantly suppresses mechanical degradation while forming a multi-functional CEI layer. Consequently, Hec-NCM delivers outstanding capacity retention for 300 cycles. Furthermore, due to the exceptional gas barrier properties of the few-layer Hec-coating, the electrochemical performance of Hec-NCM is maintained even after 6 months of exposure to the ambient atmosphere. These findings suggest a new direction of significantly improving the long-term stability and activity of cathode materials by creating an artificial CEI layer.

Review of the Scalable Core-Shell Synthesis Methods: The Improvements of Li-Ion Battery Electrochemistry and Cycling Stability

The demand for lithium-ion batteries has significantly increased due to the increasing adoption of electric vehicles (EVs). However, these batteries have a limited lifespan, which needs to be improved for the long-term use needs of EVs expected to be in service for 20 years or more. In addition, the capacity of lithium-ion batteries is often insufficient for long-range travel, posing challenges for EV drivers. One approach that has gained attention is using core-shell structured cathode and anode materials. That approach can provide several benefits, such as extending the battery lifespan and improving capacity performance. This paper reviews various challenges and solutions by the core-shell strategy adopted for both cathodes and anodes. The highlight is scalable synthesis techniques, including solid phase reactions like the mechanofusion process, ball-milling, and spray-drying process, which are essential for pilot plant production. Due to continuous operation with a high production rate, compatibility with inexpensive precursors, energy and cost savings, and an environmentally friendly approach that can be carried out at atmospheric pressure and ambient temperatures. Future developments in this field may focus on optimizing core-shell materials and synthesis techniques for improved Li-ion battery performance and stability.

A Laser-Induced Mo2 CTx MXene Hybrid Anode for High-Performance Li-Ion Batteries

MXenes, a fast-growing family of two-dimensional (2D) transition metal carbides/nitrides, are promising for electronics and energy storage applications. Mo2 CTx MXene, in particular, has demonstrated a higher capacity than other MXenes as an anode for Li-ion batteries. Yet, such enhanced capacity is accompanied by slow kinetics and poor cycling stability. Herein, it is revealed that the unstable cycling performance of Mo2 CTx is attributed to the partial oxidation into MoOx with structural degradation. A laser-induced Mo2 CTx /Mo2 C (LS-Mo2 CTx ) hybrid anode has been developed, of which the Mo2 C nanodots boost redox kinetics, and the laser-reduced oxygen content prevents the structural degradation caused by oxidation. Meanwhile, the strong connections between the laser-induced Mo2 C nanodots and Mo2 CTx nanosheets enhance conductivity and stabilize the structure during charge-discharge cycling. The as-prepared LS-Mo2 CTx anode exhibits an enhanced capacity of 340 mAh g-1 vs 83 mAh g-1 (for pristine) and an improved cycling stability (capacity retention of 106.2% vs 80.6% for pristine) over 1000 cycles. The laser-induced synthesis approach underlines the potential of MXene-based hybrid materials for high-performance energy storage applications.

Modified Viologen- and Carbonylpyridinium-Based Electrodes for Organic Batteries

Efficient electrochemical energy storage has been identified as one of the most pressing needs for a sustainable energy economy. Inorganic battery materials have traditionally been the center of attention, with the current state-of-the-art device being the lithium-ion battery. Recent pursuits have led to organic materials for their beneficial chemistry and properties, but suitable materials for organic batteries are still few and far between. This Spotlight on Applications highlights two intriguing pyridinium-based organic materials, modified viologens and carbonylpyridiniums, that have both been successfully employed in electrode materials for solid-state Li-ion-type organic batteries (LOBs). We first provide an overview of the inherent electronic properties of each building block and how they can effectively be modified while maintaining or enhancing their desirable electrochemical properties for practical applications. We then describe a range of different material designs for a battery context and their application in various organic device settings, with some examples showing competitive performance with traditional Li-ion batteries.

Surface-Diluted LiMn6 Superstructure Units Utilizing PO4 3- Confined Ni-Doping Sites to Stabilize Li-Rich Layered Oxides

Serious capacity and voltage degradation of Li-rich layered oxides (LLOs) caused by severe interfacial side reactions (ISR), structural instability, and transition metal (TM) dissolution during charge/discharge need to be urgently resolved. Here, it is proposed for the inaugural time that the confinement effect of PO4 3- dilutes the LiMn6 superstructure units on the surface of LLOs, while deriving a stable interface with phosphate compounds and spinel species. Combining theoretical calculations, diffraction, spectroscopy, and micrography, an in-depth investigation of the mechanism is performed. The results show that the modified LLO exhibits excellent anionic/cationic redox reversibility and ultra-high cycling stability. The capacity retention is increased from 72.4% to 95.4%, and the voltage decay is suppressed from 2.48 to 1.29 mV cycle-1 after 300 cycles at 1 C. It also has stable long cycling performance, with capacity retention improved from 40.2% to 81.9% after 500 cycles at 2 C. The excellent electrochemical performance is attributed to the diluted superstructure units on the surface of LLO inhibiting the TM migration in the intralayer and interlayer. Moreover, the stable interfacial layers alleviate the occurrence of ISR and TM dissolution. Therefore, this strategy can give some important insights into the development of highly stable LLOs.

Two-Dimensional MXenes Derived from Medium/High-Entropy MAX Phases M2 GaC (M = Ti/V/Nb/Ta/Mo) and their Electrochemical Performance

Two-dimensional (2D) transition metal carbides and/or nitrides, MXenes, are prepared by selective etching of the A-site atomically thin metal layers from their MAX phase precursors. High entropy MXenes, the most recent subfamily of MXenes, are in their infancy and have attracted great interest recently. They are currently synthesized mainly through wet chemical etching of Al-containing MAX phases, while various MAX phases with A-sites elements other than Al have not been explored. It is important to embody non-Al MAX phases as precursors for the high entropy MXenes synthesis to allow for new compositions. In this work, it is reported on the design and synthesis of Ga-containing medium/high entropy MAX phases and then their corresponding medium/high entropy MXenes. Gallium atomic layer etching is carried out using a Lewis acid molten salt (CuCl2). The as-prepared (Ti1/4 V1/4 Nb1/4 Ta1/4 )2 CTx exhibits a Li+ specific capacity of ≈400 mAh g-1 . For (Ti1/5 V1/5 Nb1/5 Ta1/5 Mo1/5 )2 CTx a specific capacity of 302 mAh g-1 is achieved after 300 cycles, and high cycling stability is observed at high current densities. This work is of great significance for expanding the family members of MXenes with tunable chemistries and structures.

Construction of Carbon Nanofiber-Wrapped SnO2 Hollow Nanospheres as Flexible Integrated Anode for Half/Full Li-Ion Batteries

SnO2 is deemed a potential candidate for high energy density (1494 mAh g-1) anode materials for Li-ion batteries (LIBs). However, its severe volume variation and low intrinsic electrical conductivity result in poor long-term stability and reversibility, limiting the further development of such materials. Therefore, we propose a novel strategy, that is, to prepare SnO2 hollow nanospheres (SnO2-HNPs) by a template method, and then introduce these SnO2-HNPs into one-dimensional (1D) carbon nanofibers (CNFs) uniformly via electrospinning technology. Such a sugar gourd-like construction effectively addresses the limitations of traditional SnO2 during the charging and discharging processes of LIBs. As a result, the optimized product (denoted SnO2-HNP/CNF), a binder-free integrated electrode for half and full LIBs, displays superior electrochemical performance as an anode material, including high reversible capacity (~735.1 mAh g-1 for half LIBs and ~455.3 mAh g-1 at 0.1 A g-1 for full LIBs) and favorable long-term cycling stability. This work confirms that sugar gourd-like SnO2-HNP/CNF flexible integrated electrodes prepared with this novel strategy can effectively improve battery performance, providing infinite possibilities for the design and development of flexible wearable battery equipment.