Failure Modes of Flexible LiCoO2 Cathodes Incorporating Polyvinylidene Fluoride Binders with Different Molecular Weights

Understanding the mechanical failure modes of lithium-ion battery [Li-ion batteries (LIBs)] electrodes is exceptionally important for enabling high specific energy and flexible LIB technologies. In this work, the failure modes of lithium cobalt oxide (LCO) cathodes under repeated bending and the role of the polymer binder in improving the mechanical durability of the LCO electrodes for use in flexible LIBs are investigated. Mechanical and electrochemical evaluations of LCO electrodes (areal capacity of ≥2.5 mA h cm-2) employing poly(vinylidene fluoride) (PVDF) binder were carried out, followed by extensive optical and electron microscopies. We find that the molecular weight (MW) of the PVDF significantly influenced the surface and bulk microstructure of the LCO electrodes, particularly the distribution of carbon additive and binder, which plays a crucial role in affecting the mechanical and electrochemical properties of the electrodes. Multiple mechanical failure modes (e.g., surface scratches and microcracks) observed in the LCO electrodes subjected to repeated bending originated from the use of low MW PVDF; these failure modes were successfully mitigated by using a high MW PVDF. Remarkably, the optimized flexible LCO electrode incorporating high MW PVDF showed comparable discharge capacity retention during galvanostatic cycling after repeated bending (7000 cycles at 50 mm bending diameter) to electrodes not subjected to the repeated bending. This study highlights the importance of carrying out a comprehensive investigation of the failure mechanisms in flexible electrodes, which identified the pivotal role of the PVDF MW in the electrode microstructure and its effects on the electrode resilience to failure during repeated bending.

Ionic liquids: environmentally sustainable materials for energy conversion and storage applications

Ionic liquids (ILs), often known as green designer solvents, have demonstrated immense application potential in numerous scientific and technological domains. ILs possess high boiling point and low volatility that make them suitable environmentally benign candidates for many potential applications. The more important aspect associated with ILs is that their physicochemical properties can be effectively changed for desired applications just by tuning the structure of the cationic and/or anionic part of ILs. Furthermore, these eco-friendly designer materials can function as electrolytes or solvents depending on the application. Owing to the distinctive properties such as low volatility, high thermal and electrochemical stability, and better ionic conductivity, ILs are nowadays immensely used in a variety of energy applications, particularly in the development of green and sustainable energy storage and conversion devices. Suitable ILs are designed for specific purposes to be used as electrolytes and/or solvents for fuel cells, lithium-ion batteries, supercapacitors (SCs), and solar cells. Herein, we have highlighted the utilization of ILs as unique green designer materials in Li-batteries, fuel cells, SCs, and solar cells. This review will enlighten the promising prospects of these unique, environmentally sustainable materials for next-generation green energy conversion and storage devices. Ionic liquids have much to offer in the field of energy sciences regarding fixing some of the world's most serious issues. However, most of the discoveries discussed in this review article are still at the laboratory research scale for further development. This review article will inspire researchers and readers about how ILs can be effectively applied in energy sectors for various applications as mentioned above.

Quantification of the Carbon-Coating Effect on the Interfacial Behavior of Graphite Single Particles

The effect of carbon coating on the interfacial charge transfer resistance of natural graphite (NG) was investigated by a single-particle measurement. The microscale carbon-coated natural graphite (NG@C) particles were synthesized by the simple wet-chemical mixing method using a phenolic resin as the carbon source. The electrochemical test results of NG@C using the conventional composite electrodes demonstrated desirable rate capability, cycle stability, and enhanced kinetic property. Moreover, the improvements in the composite electrodes were confirmed with the electrochemical parameters (i.e., charge transfer resistance, exchange current density, and solid phase diffusion coefficient) analyzed by a single-particle measurement. The surface carbon coating on the NG particles reduced the interfacial charge transfer resistance (Rct) and increased the exchange current density (i0). The Rct decreased from 81-101 (NG) to 49-67 Ω cm2 (NG@C), while i0 increased from 0.25-0.32 (NG) to 0.38-0.52 mA cm-2 (NG@C) after the coating process. The results suggested both electrochemically and quantitatively that the outer uniformly coated surface carbon layer on the graphite particles can improve the solid-liquid interface and other kinetic parameters, therefore enhancing the rate capabilities to obtain the high-power anode materials.

Black phosphorene/SnSe van der Waals heterostructure as a promising anchoring anode material for metal-ion batteries

Black phosphorene (BP) is a glowing two-dimensional semiconducting layer material for cutting-edge microelectronics, with high carrier mobility and thickness-dependent band gap. Here, based on van der Waals (vdW)-corrected first-principles approaches, we investigated stacked BP/tin selenide (BP/SnSe) vdW heterostructure as an anode material for metal ion batteries, which exhibits a significant theoretical capacity, along with relatively durable binding strength compared to the constituent BP and SnSe monolayers. Our calculations demonstrated that the Li/Na adatom favors insertion into the interlayer region of BP/SnSe vdW heterostructure owing to synergistic interfacial effect, resulting in comparable diffusivity to the BP and SnSe monolayers. Subsequently, the theoretical specific capacities for Li/Na are found to be as high as 956.30 mAhg-1and 828.79 mAhg-1, respectively, which could be attributed to the much higher storage capacity of Li/Na adatoms in the BP/SnSe vdW heterostructure. Moreover, the electronic structure calculations reveal that a large amount of charge transfer assists in semiconductor-to-metallic transition upon lithiation/sodiation, ensuring good electrical conductivity. These simulations verify that the BP/SnSe vdW heterostructure has immense potential for application in the design of metal-ion battery technologies.

Lithiophilic Zn3N2-Modified Cu Current Collectors by a Novel FCVA Technology for Stable Anode-Free Lithium Metal Batteries

Anode-free lithium metal batteries (AFLMBs) offer high-energy-density battery systems, but their commercial viability is hindered by irregular lithium dendrite growth and "dead Li" formation caused by current collector defects. This study employed filtered cathode vacuum arc (FCVA) technology to fabricate Cu current collectors (CCs) with a lithiophilic Zn3N2 film. This advanced preparation process ensures an evenly distributed film that reduces the nucleation overpotential, homogenizes the interfacial electric field during plating/stripping processes, inhibits lithium dendrite growth, and forms a stable solid-electrolyte interphase (SEI). Our results show that the advanced Zn3N2@Cu CCs exhibit superior performance with a high CE of above 99.3% after 230 cycles at a current density of 0.5 mA cm-2 and an area capacity of 1 mAh cm-2. Additionally, Li-Zn3N2@Cu||Li-Zn3N2@Cu symmetrical cells had a longer stable cycle time of over 1000 h than that of Li||Li and Li-Cu||Li-Cu symmetrical cells at a current density of 1 mA cm-2 and an area capacity of 2 mAh cm-2. Compared with bare Cu CCs, the capacity retention rate is increased from 14.9 to 63.1% after 100 cycles with a 0.5C rate in the AFLMBs with LFP as the cathode. This work provides a pioneering, eco-friendly, and effective solution for the fabrication of anode CCs in AFLMBs, addressing a significant challenge in their commercial application.

Alkyl-C60 liquid electrets as deformable mechanoelectric generators

Special attention is being paid to the potential applicability of various soft electronics in deformable/wearable devices. These devices must be constantly connected to energy sources to ensure their uninterrupted operation. Electrets, which are capable of retaining quasi-permanent electric charges inside or on the surface of materials, are expected to be a battery-less power source. Here, we present a strategy for harvesting the charges in alkyl-C60 liquids. Suitable substitution of bulky yet flexible branched long-alkyl chains generated C60-mono-adducts and regioisomeric bis-adducts as room-temperature solvent-free liquids. These alkyl-C60 liquids were negatively poled by the corona-discharging and soaked in nylon fabric. The liquid of the C60 bis-adduct exhibited better charge retention in comparison to the liquid of the C60 mono-adduct. This suggests that the bulky long-alkyl chains provided proper insulation for the C60 core and charge trapping in the liquid. This charge-trapping behaviour and the inherent fluidity of the alkyl-C60 liquids enabled their fabrication into deformable mechanoelectric generator (MEG) devices. The MEG exhibited applicability as a deformable micropower source or vibration sensor by generating output voltage pulses even under folded/twisted/rolled conditions. The alkylated-liquid-based MEGs worked at frequencies similar to human body motion, showing promising potential for body motion sensors and healthcare applications.

Effect of lithium doping on the structural, conduction mechanism and dielectric property of MnNbO4

The development of multifunctional materials is an exceptional research area, which is aimed at enhancing the versatility of materials according to their wide fields of application. Special interest was devoted here to lithium (Li)-doped orthoniobate ANbO₄ (A = Mn), in particular, the new material Li_0.08Mn_0.92NbO₄. This compound was successfully synthesized by a solid-state method and characterized using various techniques, including X-ray diffraction (XRD), which confirmed the successful formation of an ABO₄ oxide with an orthorhombic structure and the Pmmm space group. The morphology and elemental composition were analyzed by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The vibrational study (Raman) at room temperature confirmed the existence of the NbO₄ functional group. The effects of frequency and temperature on the electrical and dielectric properties were studied using impedance spectroscopy. In addition, the diminishing of the radius of semicircular arcs in the Nyquist plots (-Z'' vs. Z') showed the semiconductor behavior of the material. The electrical conductivity followed Jonscher's power law and the conduction mechanisms were identified. The electrical investigations showed the dominant transport mechanisms in the different frequency and temperature ranges, proposing the correlated barrier hopping (CBH) model in the ferroelectric phase and the paraelectric phase. The temperature dependence in the dielectric study revealed the relaxor ferroelectric nature of Li_0.08Mn_0.92NbO₄, which correlated the frequency-dispersive dielectric spectra with the conduction mechanisms and their relaxation processes. The results demonstrate that Li-doped Li_0.08Mn_0.92NbO₄ could be used both in dielectric and electrical applications.

Electrolyte contact changes nano-Li4Ti5O12 bulk properties via surface polarons

It is of general interest to combine the faradaic processes based high energy density of a battery with the non-faradaic processes based high power density of a capacitor in one cell. Surface area and functional groups of electrode materials strongly affect these properties. For the anode material Li₄Ti₅O₁₂ (LTO), we suggest a polaron based mechanism that influences Li ion uptake and mobility. Here we show electrolytes containing a lithium salt induce an observable change in the bulk NMR relaxation properties of LTO nano particles. The longitudinal ⁷Li NMR relaxation time of bulk LTO can change by almost an order of magnitude and, therefore, reacts very sensitively to the cation and its concentration in the surrounding electrolyte. The reversible effect is largely independent of the used anions and of potential anion decomposition products. It is concluded that lithium salt containing electrolytes increase the mobility of surface polarons. These polarons and additional lithium cations from the electrolyte can now diffuse through the bulk, induce the observed enhanced relaxation rate and enable the non-faradaic process. This picture of a Li⁺ ion equilibrium between electrolyte and solid may help with improving the charging properties of electrode materials.

Chemical Vapor Transport Synthesis of Fibrous Red Phosphorus Crystal as Anodes for Lithium-Ion Batteries

Red phosphorus (RP) is considered to be the most promising anode material for lithium-Ion batteries (LIBs) due to its high theoretical specific capacity and suitable voltage platform. However, its poor electrical conductivity (10^-12 S/m) and the large volume changes that accompany the cycling process severely limit its practical application. Herein, we have prepared fibrous red phosphorus (FP) that possesses better electrical conductivity (10^-4 S/m) and a special structure by chemical vapor transport (CVT) to improve electrochemical performance as an anode material for LIBs. Compounding it with graphite (C) by a simple ball milling method, the composite material (FP-C) shows a high reversible specific capacity of 1621 mAh/g, excellent high-rate performance and long cycle life with a capacity of 742.4 mAh/g after 700 cycles at a high current density of 2 A/g, and coulombic efficiencies reaching almost 100% for each cycle.

Recent advances in dendrite-free lithium metal anodes for high-performance batteries

With the merits of high energy density, light weight, and low electrode potential, lithium metal anodes (LMAs) have lately sparked worldwide attention in the field of batteries. However, their low Coulombic efficiency, tremendous volume expansion, and serious dendrite growth make lithium metal batteries (LMBs) unsuitable for a wide variety of applications. Moreover, when lithium dendrite crosses the electrolyte and reaches the cathode material, it may cause short circuit and safety issues for batteries. Herein, to accelerate the development of LMBs, we give a brief summary of the dendrite growth mechanisms in both liquid and solid systems of electrolytes. In particular, various modification approaches to dendrite-free lithium metal batteries are discussed. Furthermore, advanced in situ characterization techniques for the real-time observation of lithium dendrite growth are presented. To address the application issues, various potential research routes for improving the performance of LMBs are provided as well.

Operando Monitoring of Local pH Value Changes at the Carbon Electrode Surface in Neutral Sulfate-Based Aqueous Electrochemical Capacitors

The operando monitoring of pH during the charging and discharging of an electrochemical capacitor in an aqueous neutral salt solution is presented. Proper knowledge of transient and limiting pH values allows for a better understanding of the phenomena that take place during capacitor operation. It also enables the proper assignment of the reaction potentials responsible for water decomposition. It is shown that the pH inside the capacitor is strongly potential-dependent and different for individual electrodes; therefore, the values of the evolution potentials of hydrogen and oxygen cannot be precisely calculated based only on the initial pH of the electrolyte. The operando measurements indicate that the pH at the positive electrode reaches 4, while at the negative electrode, it is 8.5, which in theory could shift the theoretical operating voltage well beyond 1.23 V. On the other hand, high voltage cannot be easily maintained since the electrolyte of both electrode vicinities is subjected to mixing. Operando gas monitoring measurements show that the evolution of electrolysis byproducts occurs even below the theoretical decomposition voltage. These reactions are important in maintaining a voltage-advantaged pH difference within the cell. At the same time, the electrochemical quartz crystal microbalance (EQCM) measurements indicated that the ions governing the pH (OH^-) that initially accumulated in the vicinity of the positive electrode enter the carbon porosity, losing their pH-governing abilities. pH fluctuations in the cell are important and play a vital role in the description of its performance during the cyclability at a given voltage. This is especially noticeable in cell floating at 1.3 V, where the pH difference between electrodes is the highest (6 units). The increase of the electrode separation distance acts similarly to the introduction of a semipermeable membrane toward the increase of the capacitor cycle life. During floating at 1.6 V, where the pH difference is not as high anymore (4 units), the influence of separation in terms of electrode stability, although present, is less notable.

Tailoring the Solvation Sheath of Cations by Constructing Electrode Front-Faces for Rechargeable Batteries

Solvent molecules within the solvation sheath of cations (e.g., Li⁺ , Na⁺ , Zn²⁺ ) are easily to be dehydrogenated especially when coupled with high-voltage cathodes, and lead to detrimental electrolytes decompositions which finally accelerate capacity decays of rechargeable batteries. Tremendous efforts are devoted to tackle with this long-lasting issue. Among them, salt-concentrated strategies are frequently employed to tailor the solvation sheath of cations and improve the stabilities of electrolytes. However, the cost challenges caused by adding extra dose of expensive salts, additives/cosolvents in preparing highly concentrated electrolytes, hinder their further utilizations to some extent. Introducing porous materials-based electrode front-faces on the surface of electrodes even within dilute electrolytes can transfer the high-energy-state desolvated solvents from the reactive electrodes to the nonconductive porous material surfaces, thus eliminate the contact chances between desolvated solvents and electrode materials, and greatly reduce solvents-related decomposition issues. Herein, recent advances in using electrode front-faces to tailor the solvation sheath of metal ions for rechargeable batteries are discussed. Finally, perspectives to the future challenges and opportunities of constructing electrode front-faces to tailor the solvation sheath of cations by constructing electrode front-face for rechargeable batteries are provided.

Review of metal oxides as anode materials for lithium-ion batteries

Lithium-ion batteries with a stable circulation capacity, high energy density and good safety are widely used in automobiles, mobile phones, manufacturing and other fields. MOs due to their large theoretical capacity, simple processing and abundant reserves, and used as anode materials for LIBs, have attracted much attention. Three electrochemical mechanisms of MOs are reviewed in this paper. In addition, research progress of MOs and prospects for their further applications in LIBs are summarized.

Revisiting Polytetrafluorethylene Binder for Solvent-Free Lithium-Ion Battery Anode Fabrication

Solvent-free (SF) anodes with different carbon materials (graphite, hard carbon, and soft carbon) were fabricated to investigate the stability of different anodes with polytetrafluorethylene (PTFE) degradation. The graphite anode with large volume variation during the charge/discharge process showed poor cycle life performance, while hard carbon and soft carbon with low-volume expansion showed good cycle life. The SF hard carbon electrodes with a high loading of 10.7 mg/cm2 revealed good long-term cycling performance similar to conventional slurry-casting (CSC) electrodes. It demonstrated nearly 90% capacity retention after 120 cycles under a current of 1/3 C with LiNi0.5Co0.2Mn0.3O2 (NCM523) as cathode in coin cell. The rate capability of the high-loading SF electrodes also is comparable to the CSC electrodes. The high stability of SF hard carbon and soft carbon anodes was attributed to its low-volume variation, which could maintain their integrity even though PTFE was defluorinated to amorphous carbon irreversibly. However, the reduced amorphous carbon cannot tolerate huge volume variation of graphite during cycling, resulting in poor stability.

Active material and interphase structures governing performance in sodium and potassium ion batteries

Development of energy storage systems is a topic of broad societal and economic relevance, and lithium ion batteries (LIBs) are currently the most advanced electrochemical energy storage systems. However, concerns on the scarcity of lithium sources and consequently the expected price increase have driven the development of alternative energy storage systems beyond LIBs. In the search for sustainable and cost-effective technologies, sodium ion batteries (SIBs) and potassium ion batteries (PIBs) have attracted considerable attention. Here, a comprehensive review of ongoing studies on electrode materials for SIBs and PIBs is provided in comparison to those for LIBs, which include layered oxides, polyanion compounds and Prussian blue analogues for positive electrode materials, and carbon-based and alloy materials for negative electrode materials. The importance of the crystal structure for electrode materials is discussed with an emphasis placed on intrinsic and dynamic structural properties and electrochemistry associated with alkali metal ions. The key challenges for electrode materials as well as the interface/interphase between the electrolyte and electrode materials, and the corresponding strategies are also examined. The discussion and insights presented in this review can serve as a guide regarding where future investigations of SIBs and PIBs will be directed.

Triallyl Isocyanurate as an Efficient Electrolyte Additive for Layered Oxide Cathode Material-Based Lithium-Ion Batteries with Improved Stability under High-Voltage

In this study, a new electrolyte additive 1,3,5-tri-2-propenyl-1,3,5-triazine-2,4,6-(1H, 3H, 5H)-trione (TAIC) for lithium-ion batteries is reported. The additive is introduced as a novel electrolyte additive to enhance electrochemical performances of layered lithium nickel cobalt manganese oxide (NCM) and lithium cobalt oxide (LiCoO₂) cathodes, especially under a higher working voltage. Encouragingly, we found protective films would be formed on the cathode surface by the electrochemical oxidation, and the stability of the cathode material-electrolyte interface was greatly promoted. By adding 0.5 wt.% of TAIC into the electrolyte, the battery exhibited outstanding performances. The thickness swelling decreased to about 6% after storage at 85 °C for 24 h, while the capacity retention of cycle-life performances under high temperature of 45 °C after the 600th cycle increased 10% in comparison with the batteries without TAIC. Due to its specific function, the additive can be used in high energy density and high voltage lithium-ion battery systems.

Search for New Anode Materials for High Performance Li-Ion Batteries

Owing to an unmatched combination of power and energy density along with cyclic stability, the Li-ion battery has qualified itself to be the highest performing rechargeable battery. Taking both transportable and stationary energy storage requirements into consideration, Li-ion batteries indeed stand tall in comparison to any other existing rechargeable battery technologies. However, graphite, which is still one of the best performing Li-ion anodes, has specific drawbacks in fulfilling the ever-increasing energy and power density requirements of the modern world. Therefore, further research on alternative anode materials is absolutely essential. Equally important is the search for and enhanced use of right earth abundant materials for battery electrodes so as to bring down the costs of the battery systems. In this spotlight article, we discuss the current research progress in the area of alternative anode materials for Li-ion battery, putting our own research work over the past several years into perspective. Starting from conversion anode systems like oxides and sulfides, to insertion cum alloying systems like transition metal carbides, to molecularly engineered open framework systems like metal organic frameworks (MOFs), covalent organic frameworks (COFs), and organic-inorganic hybrid perovskites (OIHPs), this spotlight provides a complete essence of the recent developments in the area of alternative anodes. The possible and potential impact of these new anode materials is detailed and discussed here.

In Situ Orthorhombic to Amorphous Phase Transition of Nb2O5 and Its Temperature Effect on Pseudocapacitive Behavior

Niobium pentoxide (Nb₂O₅) represents an exquisite class of negative electrode materials with unique pseudocapacitive kinetics that engender superior power and energy densities for advanced electrical energy storage devices. Practical energy devices are expected to maintain stable performance under real-world conditions such as temperature fluctuations. However, the intercalation pseudocapacitive behavior of Nb₂O₅ at elevated temperatures remains unexplored because of the scarcity of suitable electrolytes. Thus, in this study, we investigate the effect of temperature on the pseudocapacitive behavior of submicron-sized Nb₂O₅ in a wide potential window of 0.01-2.3 V. Furthermore, ex situ X-ray diffraction and X-ray photoelectron spectroscopy reveal the amorphization of Nb₂O₅ accompanied by the formation of NbO via a conversion reaction during the initial cycle. Subsequent cycles yield enhanced performance attributed to a series of reversible Nb^V, IV/Nb^III redox reactions in the amorphous Li_xNb₂O₅ phase. Through cyclic voltammetry and symmetric cell electrochemical impedance spectroscopy, temperature elevation is noted to increase the pseudocapacitive contribution of the Nb₂O₅ electrode, resulting in a high rate capability of 131 mAh g^-1 at 20,000 mA g^-1 at 90 °C. The electrode further exhibits long-term cycling over 2000 cycles and high Coulombic efficiency ascribed to the formation of a robust, [FSA]^--originated solid-electrolyte interphase during cycling.

Self-Activated Formation of Hierarchical Co3 O4 Nanoflakes with High Valence-State Conversion Capability for Ultrahigh-Capacity Zn-Co Batteries

Cobalt-based materials are attracting increasing interest in alkaline Zn batteries due to the high theoretical capacity. However, the practical utilization is restricted by the poor microstructure and insufficient valence-state conversion. Herein, a self-activated formation of hierarchical Co₃ O₄ nanoflakes with high valence-state conversion capability is designed. This electrode not only exhibits the optimized microstructure with large reaction surfaces, but also shows excellent valence-state conversion capability. Consequently, this battery delivers an ultrahigh capacity of 481.4 mAh g^-1 and an energy density of 818.3 Wh kg^-1 based on the active material, which shines among reported Co-based materials. Besides, the capacity can retain 41.9% with even 20× current density increases, and it can operate with a capacity decay of 20% after the 1000th cycle. This strategy greatly enhances the performance and durability of integrated air electrodes, raising the attention of boundary design for other electrochemical energy conversion and storage devices.

Pushing Stoichiometries of Lithium-Rich Layered Oxides Beyond Their Limits

Lithium-rich layered oxides (LRLOs) are opening unexplored frontiers for high-capacity/high-voltage positive electrodes in Li-ion batteries (LIBs) to meet the challenges of green and safe transportation as well as cheap and sustainable stationary energy storage from renewable sources. LRLOs exploit the extra lithiation provided by the Li_1.2TM_0.8O₂ stoichiometries (TM = a blend of transition metals with a moderate cobalt content) achievable by a layered structure to disclose specific capacities beyond 200-250 mA h g^-1 and working potentials in the 3.4-3.8 V range versus Li. Here, we demonstrate an innovative paradigm to extend the LRLO concept. We have balanced the substitution of cobalt in the transition-metal layer of the lattice with aluminum and lithium, pushing the composition of LRLO to unexplored stoichiometries, that is, Li_1.2+x (Mn,Ni,Co,Al)_0.8-x O_2-δ. The fine tuning of the composition of the metal blend results in an optimized layered material, that is, Li_1.28Mn_0.54Ni_0.13Co_0.02Al_0.03O_2-δ, with outstanding electrochemical performance in full LIBs, improved environmental benignity, and reduced manufacturing costs compared to the state-of-the-art.

Stabilization of gamma sulfur at room temperature to enable the use of carbonate electrolyte in Li-S batteries

This past decade has seen extensive research in lithium-sulfur batteries with exemplary works mitigating the notorious polysulfide shuttling. However, these works utilize ether electrolytes that are highly volatile severely hindering their practicality. Here, we stabilize a rare monoclinic γ-sulfur phase within carbon nanofibers that enables successful operation of Lithium-Sulfur (Li-S) batteries in carbonate electrolyte for 4000 cycles. Carbonates are known to adversely react with the intermediate polysulfides and shut down Li-S batteries in first discharge. Through electrochemical characterization and post-mortem spectroscopy/ microscopy studies on cycled cells, we demonstrate an altered redox mechanism in our cells that reversibly converts monoclinic sulfur to Li₂S without the formation of intermediate polysulfides for the entire range of 4000 cycles. To the best of our knowledge, this is the first study to report the synthesis of stable γ-sulfur and its application in Li-S batteries. We hope that this striking discovery of solid-to-solid reaction will trigger new fundamental and applied research in carbonate electrolyte Li-S batteries.

Co,N-co-doped graphene sheet as a sulfur host for high-performance lithium-sulfur batteries

To improve the performance of lithium-sulfur (Li-S) batteries, herein, based on the idea of designing a material that can adsorb polysulfides and improve the reaction kinetics, a Co,N-co-doped graphene composite (Co-N-G) was prepared. According to the characterization of Co-N-G, there was a homogeneous and dispersed distribution of N and Co active sites embedded in the Co-N-G sample. The 2D sheet-like microstructure and Co, N with a strong binding energy provided significant physical and chemical adsorption functions, which are conducive to the bonding S and suppression of LiPSs. Moreover, the dispersed Co and N as catalysts promoted the reaction kinetics in Li-S batteries via the reutilization of LiPSs and reduced the electrochemical resistance. Thus, the discharge specific capacity in the first cycle for the Co-N-G/S battery reached 1255.7 mA h g-1 at 0.2C. After 100 cycles, it could still reach 803.0 mA h g-1, with a retention rate of about 64%. This phenomenon proves that this type of Co-N-G composite with Co and N catalysts plays an effective role in improving the performance of batteries and can be further studied in Li-S batteries.

Templated synthesis of 2D TiO2 nanoflakes for durable lithium ions battery

In this work, the 2D TiO2 nanoflakes were prepared by employing MXene as sacrificial template for durable lithium ions batteries (LIBs) anode. Essentially, the high crystalline anatase TiO2 nanoparticles compacted...

A current collect-free Li1.2Ni0.13Co0.13Mn0.54O2flexible film for high-performance lithium-ion batteries

Due to the high demand for more convenient flexible devices, there are more requirements for higher performance of flexible batteries. The layered lithium-rich manganese-based Li_1.2Ni_0.13Co_0.13Mn_0.54O₂cathode material has the advantages of higher energy density, higher discharge capacity and environmentally friendly, so it can be used for high-performance flexible electrode cathode material. Its theoretical capacity can reach more than 250 mAh g^-1, which is higher than most cathode materials currently used in commercialization. Here we synthesize Li_1.2Ni_0.13Co_0.13Mn_0.54O₂(LNCM) cathode, and then use a simple method to make a current collect-free LNCM flexible film. This film has excellent flexibility and electrochemical performance. At 25 mA g^-1, its initial discharge capacity reaches 314.0 mAh g^-1. After 200 cycles of 500 mA g^-1, its capacity retention rate is 82.1%, the attenuation is about 0.08% per cycle. Moreover, by bending at any position of the flexible film, it can still remain intact, and the soft-packaged battery made by the flexible film can still be used under the bending condition and keep the brightness of the LED lamp unchanged. This shows that using Li_1.2Ni_0.13Co_0.13Mn_0.54O₂to make high-performance flexible electrodes is a simple and effective method, which is expected to be practically applied to flexible electronic devices.

Revelation of Mott insulating state in layered honeycomb lattice Li2RuO3

We investigate the role of electron correlation in the electronic structure of honeycomb lattice Li₂RuO₃using photoemission spectroscopy and band structure calculations. Monoclinic Li₂RuO₃having Ru network as honeycomb lattice undergoes magneto-structural transition atT_c∼ 540 K from high temperature phaseC2/mto low temperature dimerized phaseP2₁/m. Room temperature valence band photoemission spectra reveal an insulating ground state with no intensity at Fermi level (E_F). Ru 4dband extracted from high and low photon energy valence band photoemission spectra reveal that the surface and bulk electronic structures are very similar in this system. Band structure calculations using generalized gradient approximation leads to metallic ground state while screened hybrid (YS-PBE0) functional reveals opening up of a gap in almost degenerated_zx/d_yzorbitals, whereasd_xyorbital is already gapped. Ru 3dcore level spectra with prominent unscreened feature provides direct evidence of strong electron correlation among Ru 4delectrons which is also manifested by |E-E_F|²dependence of spectral density of states in the vicinity ofE_Fin the high-resolution spectra, establishing Li₂RuO₃as Mott insulator.

Kinetic 2D Crystals via Topochemical Approach

The designing of novel materials is a fascinating and innovative pathway in materials science. Particularly, novel layered compounds have tremendous influence in various research fields. Advanced fundamental studies covering various aspects, including reactants and synthetic methods, are required to obtain novel layered materials with unique physical and chemical properties. Among the promising synthetic techniques, topochemical approaches have afforded the platform for widening the extent of novel 2D materials. Notably, the synthesis of binary layered materials is considered as a major scientific breakthrough after the synthesis of graphene as they exhibit a wide spectrum of material properties with varied potential applicability. In this review, a comprehensive overview of the progress in the development of metastable layered compounds is presented. The various metastable layered compounds synthesized from layered ternary bulk materials through topochemical approaches are listed, followed by the descriptions of their mechanisms, structural analyses, characterizations, and potential applications. Finally, an essential research direction concerning the synthesis of new materials is indicated, wherein the possible application of topochemical approaches in unprecedented areas is explored.

Microwave-Assisted Coal-Derived Few-Layer Graphene as an Anode Material for Lithium-Ion Batteries

A few-layer graphene (FLG) composite material was synthesized using a rich reservoir and low-cost coal under the microwave-assisted catalytic graphitization process. X-ray diffraction, Raman spectroscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy were used to evaluate the properties of the FLG sample. A well-developed microstructure and higher graphitization degree were achieved under microwave heating at 1300 °C using the S5% dual (Fe-Ni) catalyst for 20 min. In addition, the synthesized FLG sample encompassed the Raman spectrum 2D band at 2700 cm-1, which showed the existence of a few-layer graphene structure. The high-resolution TEM (transmission electron microscopy) image investigation of the S5% Fe-Ni sample confirmed that the fabricated FLG material consisted of two to seven graphitic layers, promoting the fast lithium-ion diffusion into the inner surface. The S5% Fe-Ni composite material delivered a high reversible capacity of 287.91 mAhg-1 at 0.1 C with a higher Coulombic efficiency of 99.9%. In contrast, the single catalyst of S10% Fe contained a reversible capacity of 260.13 mAhg-1 at 0.1 C with 97.96% Coulombic efficiency. Furthermore, the dual catalyst-loaded FLG sample demonstrated a high capacity-up to 95% of the initial reversible capacity retention-after 100 cycles. This study revealed the potential feasibility of producing FLG materials from bituminous coal used in a broad range as anode materials for lithium-ion batteries (LIBs).

An overview of hydroxy-based polyanionic cathode insertion materials for metal-ion batteries

Rechargeable batteries based on Li-ion and post Li-ion chemistry have come a long way since their inception in the early 1980s. The last four decades have witnessed steady development and discovery of myriads of cathode materials taking into account their processing, economy, and performance along with ecological sustainability. Though oxides rule the battery sector with their high energy and power density, polyanionic insertion compounds work as gold mines for designing insertion compounds with rich structural diversity leading to tuneable redox potential coupled with high structural/chemical/thermal stability. The scope of polyanionic compounds can be taken a step further by combining two or more different types of polyanions to get suites of mixed polyanionic materials. While most cathodes are built with metal polyhedra constituted by oxygen (MO_m|XO_m, M = 3d metals, X = P, S, Si, B, W, etc., m = 3-6), in some cases, selected oxygen sites can form bonding with hydrogen to form OH/H₂O ligands. It can lead to the family of hydroxy-based mixed-polyanionic cathode materials. The presence of hydroxy components can affect the crystal structure, local chemical bonding, and electronic, magnetic, diffusivity and electrochemical properties. Employing a mineralogical survey, the current review renders a sneak peek on various hydroxy-based polyanionic cathode materials for Li-ion and post Li-ion batteries. Their crystal structure, and electrochemical properties have been overviewed to outline future research focus and scope for real-life application.

Review of Energy Storage and Energy Management System Control Strategies in Microgrids

A microgrid (MG) is a discrete energy system consisting of an interconnection of distributed energy sources and loads capable of operating in parallel with or independently from the main power grid. The microgrid concept integrated with renewable energy generation and energy storage systems has gained significant interest recently, triggered by increasing demand for clean, efficient, secure, reliable and sustainable heat and electricity. However, the concept of efficient integration of energy storage systems faces many challenges (e.g., charging, discharging, safety, size, cost, reliability and overall management). Additionally, proper implementation and justification of these technologies in MGs cannot be done without energy management systems, which control various aspects of power management and operation of energy storage systems in microgrids. This review discusses different energy storage technologies that can have high penetration and integration in microgrids. Moreover, their working operations and characteristics are discussed. An overview of the controls of energy management systems for microgrids with distributed energy storage systems is also included in the scope of this review.

A low-cost and high-loading viologen-based organic electrode for rechargeable lithium batteries

Organic active materials are regarded as a very promising choice for lithium batteries because of several outstanding advantages such as low-cost, flexible tunability and pollution-free sources. Viologen compounds are attractive two-electron storage materials with low redox potentials, which are mainly used as anolytes in redox flow batteries (RFBs) considering their high solubility in electrolytes. However, due to their relatively large molecular weight and low density, it is difficult to prepare high-loading and stable-cycling electrodes for lithium battery application. In this research, by adopting 4,4'-bipyridine as the raw material and combining salification with a high-energy ball milling method, a low-solubility and high-stability viologen carbon-coated composite, ethyl viologen dihexafluorophosphate-Ketjen black (EV-KB), is synthesized. Then, by optimizing the electrode preparation process, a high-loading viologen-based electrode is successfully prepared. Salification effectively reduces the solubility of viologen compounds in the electrolyte so that the EV-KB composite can be used in lithium batteries. At the same time, it is pointed out that current collectors and slurry solvents play an important role in achieving the high-loading electrode. By deliberately selecting carbon paper as the current collector and ethanol as the solvent, the EV-KB composite organic electrode with a loading up to 1.5-9 mg cm^-2 can achieve a specific capacity of 106-79 mA h g^-1 for 400 stable cycles with a coulombic efficiency of 96% as well as a good rate capability. The synthesis method and electrode preparation optimization process introduced in this paper provide a reference for other types of organic active materials to be used in high-loading lithium batteries.

Preparation of LiFePO4 Powders by Ultrasonic Spray Drying Method and Their Memory Effect

The memory effect of lithium-ion batteries (LIBs) was first discovered in LiFePO₄, but its origin and dependence are still not clear, which is essential for regulating the memory effect. In this paper, a home-made spray drying device was used to successfully synthesize LiFePO₄ with an average particle size of about 1 μm, and we studied the influence of spray drying temperature on the memory effect of LiFePO₄ in LIBs. The results showed that the increasing of spray drying temperature made the memory effect of LiFePO₄ strengthen from 1.3 mV to 2.9 mV, while the capacity decreased by approximately 6%. The XRD refinement and FTIR spectra indicate that the enhancement of memory effect can be attributed to the increment of Li–Fe dislocations. This work reveals the dependence of memory effect of LiFePO₄ on spray drying temperature, which will guide us to optimize the preparation process of electrode materials and improve the management system of LIBs.

Real-time control of dendritic propagation in rechargeable batteries using adaptive pulse relaxation

The non-uniform growth of microstructures in dendritic form inside the battery during prolonged charge-discharge cycles causes short-circuit as well as capacity fade. We develop a feedback control framework for the real-time minimization of such microstructures. Due to the accelerating nature of the branched evolution, we focus on the early stages of growth, identify the critical ramified peaks, and compute the effective time for the dissipation of ions from the vicinity of those branching fingers. The control parameter is a function of the maximum interface curvature (i.e., minimum radius) where the rate of runaway is the highest. The minimization of the total charging time is performed for generating the most packed microstructures, which correlate closely with those of considerably higher charging periods, consisting of constant and uniform square waves. The developed framework could be utilized as a smart charging protocol for safe and sustainable operation of rechargeable batteries, where the branching of the microstructures could be correlated with the sudden variation in the current/voltage.

Computing the frequency fluctuation dynamics of highly coupled vibrational transitions using neural networks

The description of frequency fluctuations for highly coupled vibrational transitions has been a challenging problem in physical chemistry. In particular, the complexity of their vibrational Hamiltonian does not allow us to directly derive the time evolution of vibrational frequencies for these systems. In this paper, we present a new approach to this problem by exploiting the artificial neural network to describe the vibrational frequencies without relying on the deconstruction of the vibrational Hamiltonian. To this end, we first explored the use of the methodology to predict the frequency fluctuations of the amide I mode of N-methylacetamide in water. The results show good performance compared with the previous experimental and theoretical results. In the second part, the neural network approach is used to investigate the frequency fluctuations of the highly coupled carbonyl stretch modes for the organic carbonates in the solvation shell of the lithium ion. In this case, the frequency fluctuation predicted by the neural networks shows a good agreement with the experimental results, which suggests that this model can be used to describe the dynamics of the frequency in highly coupled transitions.