Tailoring a facile electronic and ionic pathway to boost the storage performance of Fe3O4 nanowires as negative electrode for supercapacitor application.

Today, high-energy applications are devoted to boosting the storage performance of asymmetric supercapacitors. Importantly, boosting the storage performance of the negative electrodes is a crucial topic. Fe3O4-based active materials display a promising theoretical storage performance as a negative electrode. Thus, to get a high storage performance of Fe3O4, it must be tailored to have a higher ionic and electronic conductivity and outstanding stability. Functionalized graphite felt (GF) is an excellent candidate for tailoring Fe3O4 with a facile ionic and electronic pathway. However, the steps of the functionalization of GF are complex and time-consuming as well as the energy loss during this step. Thus, the in-situ functionalization of the GF surface throughout the synthesis of Fe3O4 active materials is proposed herein. Fe3O4 is electrodeposited at the in-situ functionalized GF surface with the crystalline nanowires-like structure as revealed from the various analyses; SEM, TEM, Mapping EDX, XPS, XRD, wettability test, and Raman analysis. Advantageously, the synthetic approach introduces full homogeneous and uniform coverage of the large surface area of the GF. Thus, Fe3O4 nanowires with high ionic and electronic conductivity are characterized by a higher storage performance. Interestingly, Fe3O4/GF possesses a high specific capacity of 1418 mC cm-2 at a potential scan rate of 10 mV s-1 and this value retained to 54% at a potential scan rate of 50 mV s-1 at an extended potential window of 1.45 V. Remarkably, the diffusion-controlled reaction is the main contributor of the storage of Fe3O4/GF electrode as revealed by the mechanistic studies.

Anodic Electrolysis Strategy Enabled Fe/FeCl2 Electrode for Scalable Fe/FeCl2-Graphite Molten Salt Battery.

The Fe/FeCl2-Graphite molten salt battery is a promising technology for large-scale energy storage, offering a long lifespan, a low operating temperature (<200 °C), and cost efficiency. However, its practical applications are hindered by the lack of a scalable preparation approach and insufficient redox stability in the Fe/FeCl2 electrode. Our study introduces an electrochemical anodic electrolysis (EAE) strategy, employing the anodic process (Fe → Fe2+) in an Al|AlCl3/NaCl/LiCl|Fe electrolysis system for the Fe/Fe2+ negative electrode in the Fe/FeCl2-Graphite battery. The EAE strategy forms an oxidized film, preventing incipient dissolution in the electrolyte and addressing redox stability issues with FeCl2 as the active substance. The Fe/Fe2+ negative electrode prepared by the EAE strategy exhibits a stabilized capacity of 0.72 mAh/cm2 after 7000 cycles at 5 mA/cm2, with a lower polarization level (∼29 mV) compared to FeCl2 as the active component. The flexibility of the EAE strategy is validated in both galvanostatic and potentiostatic processes, with a discharge capacity of 14 mAh after 1000 cycles, a capacity retention rate of 85%, and a Coulombic efficiency of 98% in the potentiostatic anodic electrolysis Fe/Fe2+ electrode. The scalability and reliability of the EAE strategy are further demonstrated in capacity-expanded Fe/FeCl2-Graphite batteries, reaching a discharge capacity of 155.1 mAh after 1000 cycles at 130 mA, with a capacity retention rate of 94%. For the first time, we showcased an EAE approach capable of producing Fe/Fe2+ electrodes at a rate of about 68.6 m2 per day. Additionally, we successfully assembled an Fe/FeCl2-Graphite battery at about a 0.42 ampere-hour level, paving the way for the scalable application of Fe/FeCl2-Graphite batteries.

Facilely Fabricating F-Doped Fe3N Nanoellipsoids Grown on 3D N-Doped Porous Carbon Framework as a Preeminent Negative Material.

Transition metal nitride negative electrode materials with a high capacity and electronic conduction are still troubled by the large volume change in the discharging procedure and the low lithium ion diffusion rate. Synthesizing the composite material of F-doped Fe3N and an N-doped porous carbon framework will overcome the foregoing troubles and effectuate a preeminent electrochemical performance. In this study, we created a simple route to obtain the composite of F-doped Fe3N nanoellipsoids and a 3D N-doped porous carbon framework under non-ammonia atmosphere conditions. Integrating the F-doped Fe3N nanoellipsoids with an N-doped porous carbon framework can immensely repress the problem of volume expansion but also substantially elevate the lithium ion diffusion rate. When utilized as a negative electrode for lithium-ion batteries, this composite bespeaks a stellar operational life and rate capability, releasing a tempting capacity of 574 mAh g-1 after 550 cycles at 1.0 A g-1. The results of this study will profoundly promote the evolution and application of transition metal nitrides in batteries.

Design and Synthesis Strategy of MXenes-Based Anode Materials for Sodium-Ion Batteries and Progress of First-Principles Research.

MXenes-based materials are considered to be one of the most promising electrode materials in the field of sodium-ion batteries due to their excellent flexibility, high conductivity and tuneable surface functional groups. However, MXenes often have severe self-agglomeration, low capacity and unsatisfactory durability, which affects their practical value. The design and synthesis of advanced heterostructures with advanced chemical structures and excellent electrochemical performance for sodium-ion batteries have been widely studied and developed in the field of energy storage devices. In this review, the design and synthesis strategies of MXenes-based sodium-ion battery anode materials and the influence of various synthesis strategies on the structure and properties of MXenes-based materials are comprehensively summarized. Then, the first-principles research progress of MXenes-based sodium-ion battery anode materials is summarized, and the relationship between the storage mechanism and structure of sodium-ion batteries and the electrochemical performance is revealed. Finally, the key challenges and future research directions of the current design and synthesis strategies and first principles of these MXenes-based sodium-ion battery anode materials are introduced.

Use of Hydrothermal Carbonization to Improve the Performance of Biowaste-Derived Hard Carbons in Sodium Ion-Batteries.

Over the last years, hard carbon (HC) has been the most promising anode material for sodium-ion batteries due to its low voltage plateau, low cost and sustainability. In this study, biomass waste (spent coffee grounds, sunflower seed shells and rose stems) was investigated as potential material for hard carbon preparation combining a two-step method consisting of on hydrothermal carbonization (HTC), to remove the inorganic impurities and increase the carbon content, and a subsequent pyrolysis process. The use of HTC as pretreatment prior to pyrolysis improves the specific capacity in all the materials compared to the ones directly pyrolyzed by more than 100 % at high C-rates. The obtained capacity ranging between 210 and 280 mAh g-1 at C/15 is similar to the values reported in literature for biomass-based hard carbons. Overall, HC obtained from sunflower seed shell performs better than that obtained from the other precursors with an initial Coulombic efficiency (ICE) of 76 % and capacities of 120 mAh g-1 during 1000 cycles at C with a high capacity retention of 86-93 %.

Silicon-Based Solid-State Batteries: Electrochemistry and Mechanics to Guide Design and Operation.

Solid-state batteries (SSBs) are promising alternatives to the incumbent lithium-ion technology; however, they face a unique set of challenges that must be overcome to enable their widespread adoption. These challenges include solid-solid interfaces that are highly resistive, with slow kinetics, and a tendency to form interfacial voids causing diminished cycle life due to fracture and delamination. This modeling study probes the evolution of stresses at the solid electrolyte (SE) solid-solid interfaces, by linking the chemical and mechanical material properties to their electrochemical response, which can be used as a guide to optimize the design and manufacture of silicon (Si) based SSBs. A thin-film solid-state battery consisting of an amorphous Si negative electrode (NE) is studied, which exerts compressive stress on the SE, caused by the lithiation-induced expansion of the Si. By using a 2D chemo-mechanical model, continuum scale simulations are used to probe the effect of applied pressure and C-rate on the stress-strain response of the cell and their impacts on the overall cell capacity. A complex concentration gradient is generated within the Si electrode due to slow diffusion of Li through Si, which leads to localized strains. To reduce the interfacial stress and strain at 100% SOC, operation at moderate C-rates with low applied pressure is desirable. Alternatively, the mechanical properties of the SE could be tailored to optimize cell performance. To reduce Si stress, a SE with a moderate Young's modulus similar to that of lithium phosphorous oxynitride (∼77 GPa) with a low yield strength comparable to sulfides (∼0.67 GPa) should be selected. However, if the reduction in SE stress is of greater concern, then a compliant Young's modulus (∼29 GPa) with a moderate yield strength (1-3 GPa) should be targeted. This study emphasizes the need for SE material selection and the consideration of other cell components in order to optimize the performance of thin film solid-state batteries.

Electrochemical Investigation of Calcium Substituted Monoclinic Li3 V2 (PO4 )3 Negative Electrode Materials for Sodium- and Potassium-Ion Batteries.

Herein, the electrochemical properties and reaction mechanism of Li3-2 x Cax V2 (PO4 )3 /C (x = 0, 0.5, 1, and 1.5) as negative electrode materials for sodium-ion/potassium-ion batteries (SIBs/PIBs) are investigated. All samples undergo a mixed contribution of diffusion-controlled and pseudocapacitive-type processes in SIBs and PIBs via Trasatti Differentiation Method, while the latter increases with Ca content increase. Among them, Li3 V2 (PO4 )3 /C exhibits the highest reversible capacity in SIBs and PIBs, while Ca1.5 V2 (PO4 )3 /C shows the best rate performance with a capacity retention of 46% at 20 C in SIBs and 47% at 10 C in PIBs. This study demonstrates that the specific capacity of this type of material in SIBs and PIBs does not increase with the Ca-content as previously observed in lithium-ion system, but the stability and performance at a high C-rate can be improved by replacing Li+ with Ca2+ . This indicates that the insertion of different monovalent cations (Na+ /K+ ) can strongly influence the redox reaction and structure evolution of the host materials, due to the larger ion size of Na+ and K+ and their different kinetic properties with respect to Li+ . Furthermore, the working mechanism of both LVP/C and Ca1.5 V2 (PO4 )3 /C in SIBs are elucidated via in operando synchrotron diffraction and in operando X-ray absorption spectroscopy.

Preparation of NH4Cl-Modified Carbon Materials via High-Temperature Calcination and Their Application in the Negative Electrode of Lead-Carbon Batteries.

The performance of lead-acid batteries could be significantly increased by incorporating carbon materials into the negative electrodes. In this study, a modified carbon material developed via a simple high-temperature calcination method was employed as a negative electrode additive, and we have named it as follows: N-doped chitosan-derived carbon (NCC). The performance of this material was compared with a control battery containing activated carbon (AC). X-ray diffraction (XRD), scanning electron microscopy (SEM) and Raman spectroscopy were engaged in analyzing the crystal structure and morphology of the material. Afterwards, the electrochemical and battery performance was examined through cyclic voltammetry (CV), linear voltammetry (LSV) and constant current charge-discharge testing. Markedly, the electrode plate containing 1 wt.% NCC indicates the highest specific capacity (106.48 F g-1) as compared to the control battery, which is 1.56 times higher than the AC electrode plate and 4.75 times higher than the blank electrode plate. The linear voltammetry shows that the hydrogen precipitation current density of the 1 wt.% NCC electrode plate is only -0.028 A cm-2, a much higher value than that of the AC electrode plate. In addition, the simulated battery containing 1 wt.% NCC has a cycle life of 4324 cycles, which is 2.36 times longer than that of the same amount of additive AC battery (1834 cycles) and 5.34 times longer than that of the blank battery (809 cycles). In summary, NCC carbon has the advantage of extending the life of lead-acid batteries, rendering it a promising candidate for lead-acid battery additives.

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

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

Boosting Pseudocapacitive Behavior of Supercapattery Electrodes by Incorporating a Schottky Junction for Ultrahigh Energy Density.

Pseudo-capacitive negative electrodes remain a major bottleneck in the development of supercapacitor devices with high energy density because the electric double-layer capacitance of the negative electrodes does not match the pseudocapacitance of the corresponding positive electrodes. In the present study, a strategically improved Ni-Co-Mo sulfide is demonstrated to be a promising candidate for high energy density supercapattery devices due to its sustained pseudocapacitive charge storage mechanism. The pseudocapacitive behavior is enhanced when operating under a high current through the addition of a classical Schottky junction next to the electrode-electrolyte interface using atomic layer deposition. The Schottky junction accelerates and decelerates the diffusion of OH‒/K+ ions during the charging and discharging processes, respectively, to improve the pseudocapacitive behavior. The resulting pseudocapacitive negative electrodes exhibits a specific capacity of 2,114 C g-1 at 2 A g-1 matches almost that of the positive electrode's 2,795 C g-1 at 3 A g-1. As a result, with the equivalent contribution from the positive and negative electrodes, an energy density of 236.1 Wh kg-1 is achieved at a power density of 921.9 W kg-1 with a total active mass of 15 mg cm-2. This strategy demonstrates the possibility of producing supercapacitors that adapt well to the supercapattery zone of a Ragone plot and that are equal to batteries in terms of energy density, thus, offering a route for further advances in electrochemical energy storage and conversion processes.

Coordinatively Cross-Linked Binders for Silicon-Based Electrodes for Li-Ion Batteries: Beneficial Impact on Mechanical Properties and Electrochemical Performance.

A simple and versatile preparation of Zn(II)-poly(carboxylates) reticulated binders by the addition of Zn(II) precursors (ZnSO4, ZnO, or Zn(NO3)2) into a preoptimized poly(carboxylic acids) binder solution is proposed. These binders lead systematically to a significantly improved electrochemical performance when used for the formulation of silicon-based negative electrodes. The formation of carboxylate-Zn(II) coordination bonds formation is investigated by rheology and FTIR and NMR spectroscopies. Mechanical characterizations reveal that the coordinated binder offers a better electrode coating cohesion and adhesion to the current collector, as well as higher hardness and elastic modulus, which are even preserved in the presence of a carbonate solvent (i.e., in battery operation conditions). Ultimately, as shown from operando dilatometry experiments, the electrode expansion during lithiation is reduced, mitigating electrode mechanical failure. Such coordinatively reticulated electrodes outperform their uncoordinated counterparts with an improved capacity retention of over 30% after 60 cycles.

Toward Improving the Thermal Stability of Negative Electrode Materials: Differential Scanning Calorimetry and In Situ High-Temperature X-ray Diffraction/X-ray Absorption Spectroscopy Studies of Li2ZnTi3O8 and Related Compounds.

Negative electrode materials with high thermal stability are a key strategy for improving the safety of lithium-ion batteries for electric vehicles without requiring built-in safety devices. To search for crucial clues into increasing the thermal stability of these materials, we performed differential scanning calorimetry (DSC) and in situ high-temperature (HT)-X-ray diffraction (XRD)/X-ray absorption (XAS) up to 450 °C with respect to a solid-solution compound of Li4/3-2x/3ZnxTi5/3-x/3O4 with 0 ≤ x ≤ 0.5. The DSC profile of fully discharged x = 0.5 (Li2ZnTi3O8) with a LiPF6-based electrolyte could be divided into three temperature (T) regions: (i) T ≤ 250 °C for ΔHaccumi, (ii) 250 °C < T ≤ 350 °C for ΔHaccumii, and (iii) T > 350 °C for ΔHaccumiii, where ΔHaccumn is the accumulated change in enthalpy in region n. The HT-XRD/XAS analyses clarified that ΔHaccumi and ΔHaccumii originated from the decomposition of solid electrolyte interphase (SEI) films and the formation of a LiF phase, respectively. Comparison of the DSC profiles with x = 0 (Li[Li1/3Ti5/3]O4) and graphite revealed the operating voltage, i.e., amount of SEI films, and stability of the crystal lattice play significant roles in the thermal stability of negative electrode materials. Indeed, the highest thermal stability was attained at x = 0.25 using this approach.

Visualization of Electrolyte Reaction Field Near the Negative Electrode of a Lead Acid Battery by Means of Amplitude/Frequency Modulation Atomic Force Microscopy.

The precise observation of a solid-liquid interface by means of frequency modulation atomic force microscopy (FM-AFM) was performed, demonstrating its applicability to a study on lead acid batteries using an electrochemical test cell for in-liquid FM-AFM embedded with a specialized cantilever holder. The consistency and reproducibility of each surface profile observed via amplitude modulation AFM and FM-AFM were verified properly in a strong acidic electrolyte. In terms of FM-AFM, the ability to observe remarkable changes in the force mapping is the most beneficial, especially near the negative electrode surface. The localization of lignosulfonate (LS) added into the electrolyte as an expander could be visualized since this characteristic force mapping was captured when LS was added to electrolyte.

Bismuth oxyformate microspheres assembled by ultrathin nanosheets as an efficient negative material for aqueous alkali battery.

A negative electrode with high capacity and rate capability is essential to match the capacity of a positive electrode and maximize the overall charge storage performance of an aqueous alkali battery (AAB). Due to the 3-electron redox reactions within a wide negative potential range, bismuth (Bi)-based compounds are recognized as efficient negative electrode materials. Herein, hierarchically structured bismuth oxyformate (BiOCOOH) assembled by ultrathin nanosheets was prepared by a solvothermal reaction for application as negative material for AAB. Given the efficient ion diffusion channels and sufficient exposure of the inner surface area, as well as the pronounced 3-electron redox activity of Bi species, the BiOCOOH electrode offered a high specific capacity (Cs, 229 ± 4 mAh g-1 at 1 A g-1) and superior rate capability (198 ± 6 mAh g-1 at 10 A g-1) within 0 âˆ¼ -1 V. When pairing with the Ni3S2-MoS2 battery electrode, the AAB delivered a high energy density (Ecell, 217 mWh cm-2 at a power density (Pcell) of 661 mW cm-2), showing the potential of such a novel BiOCOOH negative material in battery-type charge storage.

Optical Study of the Surface Film Formed during Li-Metal Deposition and Dissolution Investigated by Surface Plasmon Resonance Spectroscopy.

The features of the electrode surface film during Li-metal deposition and dissolution cycles are essential for understanding the mechanism of the negative electrode reaction in Li-metal battery cells. The physical and chemical property changes of the interface during the initial stages of the reaction should be investigated under operando conditions. In this study, we focused on the changes in the optical properties of the electrode surface film of the negative electrode of a Li-metal battery. Cu-based electrochemical surface plasmon resonance spectroscopy (EC-SPR) was applied because of its high sensitivity to optical phenomena on the electrode surface and its stability against Li-metal deposition. The feature of SPR reflectance dip depends on the optical properties of the electrode surface; namely, the wavelength and depth of the reflectance dip directly connected the refractive index and extinction coefficient (color of electrode surface film), which was confirmed by reflectance simulation. In the operando EC-SPR experiment, various changes in optical properties were clearly observed during the cycles. In particular, the change in the extinction coefficient was more remarkable at the second process than the first process of Li-metal deposition. By electrochemical quartz-crystal microbalance (EQCM) measurements, surface film formation was confirmed during the first Li-metal deposition process. The remarkable change in the extinction coefficient is based on the color change of the surface film, which is caused by the chemical condition change during Li-metal deposition cycles.

Strategies for Harnessing High Rate and Cycle Performance from Graphite Electrodes in Potassium-Ion Batteries.

Potassium-ion batteries (PIBs) have been lauded as the next-generation energy storage systems on account of their high voltage capabilities and low costs and the high abundance of potassium resources. However, the practical utility of PIBs has been heavily encumbered by severe K metal dendrite formation, safety issues, and insufficient electrochemical performance during operations─indeed critical issues that underpin the need for functional electrolytes with high thermal stability, robust solid-electrolyte interphase (SEI)-forming capabilities, and high electrochemical performance. In a bid to establish a knowledge framework for harnessing high rate capabilities and long cycle life from graphite negative electrodes, this study presents the physical properties and electrochemical behavior of a high K+ concentration inorganic ionic liquid (IL) electrolyte, K[FSA]-Cs[FSA] (FSA- = bis(fluorosulfonyl)amide) (54:46 in mol), at an intermediate temperature of 70 °C. This IL electrolyte demonstrates an ionic conductivity of 2.54 mS cm-1 and a wide electrochemical window of 5.82 V. Charge-discharge tests performed on a graphite negative electrode manifest a high discharge capacity of 278 mAh g-1 (0.5 C) at 70 °C, a high rate capability (106 mAh g-1 at 100 C), and a long cyclability (98.7% after 450 cycles). Stable interfacial properties observed by electrochemical impedance spectroscopy during cycling are attributed to the formation of sulfide-rich all-inorganic SEI, which was examined through X-ray photoelectron spectroscopy. The performance of the IL is collated with that of an N-methyl-N-propylpyrrolidinium-based organic IL to provide insight into the synergism between the highly concentrated K+ electrolyte at intermediate temperatures and the all-inorganic SEI during electrochemical operations of the graphite negative electrode.

Wet-Chemical Synthesis of TiO2/PVDF Membrane for Energy Applications.

To satisfy the ever-increasing energy demands, it is of the utmost importance to develop electrochemical materials capable of producing and storing energy in a highly efficient manner. Titanium dioxide (TiO2) has recently emerged as a promising choice in this field due to its non-toxicity, low cost, and eco-friendliness, in addition to its porosity, large surface area, good mechanical strength, and remarkable transport properties. Here, we present titanium dioxide nanoplates/polyvinylidene fluoride (TiO2/PVDF) membranes prepared by a straightforward hydrothermal strategy and vacuum filtration process. The as-synthesized TiO2/PVDF membrane was applied for energy storage applications. The fabricated TiO2/PVDF membrane served as the negative electrode for supercapacitors (SCs). The electrochemical properties of a TiO2/PVDF membrane were explored in an aqueous 6 M KOH electrolyte that exhibited good energy storage performance. Precisely, the TiO2/PVDF membrane delivered a high specific capacitance of 283.74 F/g at 1 A/g and maintained capacitance retention of 91% after 8000 cycles. Thanks to the synergistic effect of TiO2 and PVDF, the TiO2/PVDF membrane provided superior electrochemical performance as an electrode for a supercapacitor. These superior properties will likely be used in next-generation energy storage technologies.

Bifunctional iron molybdate as highly effective heterogeneous electro-Fenton catalyst and Li-ion battery anode.

Three-dimensional materials have attracted considerable interest in energy and environmental remediation fields. Iron molybdate (FMO) materials have prepared via a facile hydrothermal technique with glycerol assistance, and their structural and chemical composition confirmed using various physico-chemical techniques. The prepared bi-functional material is a strong candidate for energy storage and electrocatalytic degradation of Methylene blue and Congo red. Experimental results confirmed the synthesized FMO-10 catalyst was extremely efficient for methylene blue and Congo red breakdown, achieving 91 % and 96 % degradation in 36 h, respectively. This high catalytic activity was attributed to FMO significant visible light absorption, and reactive OH formation from H2O2 synergistically triggered by both Fe3+ and MoO42-. Prepared FMO samples demonstrated excellent potential as negative electrode material for lithium ion batteries. Electrode specific capacity initially dropped then rebounded to 1265 mAh g-1 after 100 cycles at 100 mA g-1 change rate between 0.01 and 3.0 V.

Thermal Behavior of Li1+x[Li1/3Ti5/3]O4 and a Proof of Concept for Sustainable Batteries.

An in-depth understanding of the thermal behavior of lithium-ion battery materials is valuable for two reasons: one is to devise strategies for inhibiting the risk of catastrophic thermal runaway and the other is to respond to the increasing demand for sustainable batteries using a direct regeneration method. Li1+x[Li1/3Ti5/3]O4 (LTO) is regarded as a suitable negative electrode under the type of severe conditions that cause this thermal runaway, such as in ignition systems for automobiles. Thus, in this study, we used differential scanning calorimetry to systematically analyze lithiated LTO combined with ex situ and in situ high-temperature X-ray diffraction measurements. The observed thermal reactions with a LiPF6-based electrolyte were divided into three processes: (i) the decomposition of the initially formed solid electrolyte interphase below 200 °C, (ii) the formation of a LiF phase at 200 °C ≤ T ≤ 340 °C, and (iii) the formation of a TiO2 phase at T > 340 °C. Because the enthalpy change in process (ii) mainly contributed to the total heat generation, fluorine-free Li salts and/or stabilization of the LTO lattice may be effective in coping with the thermal runaway. Even in various lithiated states, a direct regeneration method returned the discharge capacity of LTO to ∼90% of its initial value, if we ignore the contributions from the electrochemically inactive LiF and TiO2 rutile phases. Hence, it can be concluded that the recycling performance of LTO is far superior to those of lithium transition metal oxides for a positive electrode, whose delithiated states easily convert into electrochemical-inactive phases at high temperatures.

Influence of the Polyacrylic Acid Binder Neutralization Degree on the Initial Electrochemical Behavior of a Silicon/Graphite Electrode.

The role of the physicochemical properties of the water-soluble polyacrylic acid (PAA) binder in the electrochemical performance of highly loaded silicon/graphite 50/50 wt % negative electrodes has been examined as a function of the neutralization degree x in PAAH1-xLix at the initial cycle in an electrolyte not containing ethylene carbonate. Electrode processing in the acidic PAAH binder at pH 2.5 leads to a deep copper corrosion, resulting in a significant electrode cohesion and adhesion to the current collector surface, but the strong binder rigidity may explain the big cracks occurring on the electrode surface at the first cycle. The nonuniform binder coating on the material surface leads to an important degradation of the electrolyte, explaining the lowest initial Coulombic efficiency and the lowest reversible capacity among the studied electrodes. When processed in neutral pH, the PAAH0.22Li0.78 binder forms a conformal artificial solid electrolyte interphase layer on the material surface, which minimizes the electrolyte reduction at the first cycle and then maximizes the initial Coulombic efficiency. However, the low mechanical resistance of the electrode and its strong cracking explain its low reversible capacity. Electrodes prepared at intermediate pH 4 combine the positive assets of electrodes prepared at acidic and neutral pH. They lead to the best initial performance with a notable areal capacity of 7.2 mA h cm-2 and the highest initial Coulombic efficiency of around 90%, a value much larger than the usual range reported for silicon/graphite anodes. All data obtained with complementary characterization techniques were discussed as a function of the PAA polymeric chain molecular conformation, microstructure, and surface adsorption or grafting, emphasizing the tremendous role of the binder in the electrode initial performance.