Li-ion Battery Electrodes Research Articles

MXenes as Li-Ion Battery Electrodes: Progress and Outlook

MXenes as Li-Ion Battery Electrodes: Progress and Outlook

Recent Progress in Design Principles of Covalent Organic Frameworks for Rechargeable Metal-Ion Batteries.

Covalent organic frameworks (COFs) are acknowledged as a new generation of crystalline organic materials and have garnered tremendous attention owing to their unique advantages of structural tunability, frameworks diversity, functional versatility, and diverse applications in drug delivery, adsorption/separation, catalysis, optoelectronics, and sensing, etc. Recently, COFs is proven to be promising candidates for electrochemical energy storage materials. Their chemical compositions and structures can be precisely tuned and functionalized at the molecular level, allowing a comprehensive understanding of COFs that helps to make full use of their features and addresses the inherent drawback based on the components and functions of the devices. In this review, the working mechanisms and the distinguishing advantages of COFs as electrodes for rechargeable Li-ion batteries are discussed in detail. Especially, principles and strategies for the rational design of COFs as advanced electrode materials in Li-ion batteries are systematically summarized. Finally, this review is structured to cover recent explorations and applications of COF electrode materials in other rechargeable metal-ion batteries.

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.

Highly Reversible Ti/Sn Oxide Nanocomposite Electrodes for Lithium Ion Batteries Obtained by Oxidation of Ti3 Al(1-x) Snx C2 Phases.

Among the materials for the negative electrodes in Li-ion batteries, oxides capable of reacting with Li+ via intercalation/conversion/alloying are extremely interesting due to their high specific capacities but suffer from poor mechanical stability. A new way to design nanocomposites based on the (Ti/Sn)O2 system is the partial oxidation of the tin-containing MAX phase of Ti3 Al(1-x) Snx O2 composition. Exploiting this strategy, this work develops composite electrodes of (Ti/Sn)O2 and MAX phase capable of withstanding over 600 cycles in half cells with charge efficiencies higher than 99.5% and specific capacities comparable to those of graphite and higher than lithium titanate (Li4 Ti5 O12 ) or MXenes electrodes. These unprecedented electrochemical performances are also demonstrated at full cell level in the presence of a low cobalt content layered oxide and explained through an accurate chemical, morphological, and structural investigation which reveals the intimate contact between the MAX phase and the oxide particles. During the oxidation process, electroactive nanoparticles of TiO2 and Ti(1-y) Sny O2 nucleate on the surface of the unreacted MAX phase which therefore acts both as a conductive agent and as a buffer to preserve the mechanical integrity of the oxide during the lithiation and delithiation cycles.

Green Recovery of Cathode Active Materials from Li-Ion Battery Electrode Scraps Using Propylene Carbonate: A Novel Approach for Direct Recycling

Green Recovery of Cathode Active Materials from Li-Ion Battery Electrode Scraps Using Propylene Carbonate: A Novel Approach for Direct Recycling

Decarboxylative - Dimerization of levulinic acid using spent Li-ion battery electrode material with lithium nickel cobalt manganese oxide as a catalyst

A low cost catalyst prepared by pyrolyzing electrode coating material from spent Li-ion battery cells was shown as an effective catalyst for the decarboxylative - dimerization of levulinic acid to a mixture of C6 and C9 fuel precursors. The highest levulinic acid conversion of 94% was observed with 10% (w/w) catalyst loading under 1.24 MPa H2 at 140 °C, 15 h. A reaction scheme was proposed to explain the novel transformation producing C9 lactone products and C6 unsaturated alcohol product through a decarboxylative pathway followed by the aldol dimerization of levulinic acid.

Measuring microscale mechanical properties of PVdF binder phase and the binder-particle interface using micromechanical testing

In this study, we developed a robust methodology for extracting the mechanical properties of individual components in complex systems such as Li-ion battery electrodes and provided quantitative values that can be used as input for modelling and lifetime estimation of Li-ion batteries. We employed micromechanical testing techniques, including micropillar compression, microcantilever bending, and nanoindentation, to measure the mechanical properties of the PVdF binder phase in the active layer. We discovered that nanoindentation tends to overestimate the modulus due to uncertainty associated with the test volume and initial large compression strains, while the micropillar compression technique provides more accurate modulus data with a narrower spread. Additionally, the yield stress of the binder phase can be evaluated using micropillar compression. Our obtained modulus values were in the range of 2.5–4.4 GPa, and the yield stress was in the range of 162–270 MPa. By microcantilever bending tests, we determined that the binder–particle interface often fails before the binder itself, suggesting that the interface significantly influences the failure mechanics. Overall, our results indicate that the microcantilever bending tests provide moduli estimates that agree with those obtained from micropillar compression tests. We also qualitatively examined the binder-particle and binder-current collector interfaces, further emphasising the significance of our methodology and the obtained quantitative values.

Recent advancements in MXene-based nanocomposites as photocatalysts for hazardous pollutant degradation - A review

The recent expeditious industrialization and urbanization showcase the increasing need for renewable and non-renewable energy and the severe environmental crisis. In this regard, numerous 2-dimensional (2D) nanomaterials have been developed as a facile approach to meet the futuristic energy essentials and to resolve the crisis. In contrast, the newly explored 2D MXenes (transition metal carbide/nitrides/carbonitride) have been employed as an intriguing material for various environmental applications. This development is accredited to their unique properties, which include a vast surface area, strong electrical conductivity, fascinating photophysical properties, high mechanical properties, stability in an aqueous medium, high hydrophilicity, biocompatibility, ease of functionalization, and excellent thermal properties. MXenes act as a potential candidate in water desalination, energy storage devices such as electrodes of Li-ion batteries and pseudo capacitors, hydrogen production, sensors, and wastewater treatment. This review article deliberates the synthesis of MXene and nanocomposites of MXene and their photo-catalytic actions against various toxic pollutants such as organic dyes and heavy metals in wastewater. This review also precises the various preparation methods of MXene-based photocatalyst and the enhanced photocatalytic activity of MXene and MXene-based nanocomposites in wastewater treatment. Also, it details the attempts made to improve the photocatalytic activity of MXene-based nanocomposites in terms of their structural compositions. In addition, the merits and demerits of the MXene-based photocatalysts are deliberated, which may pave the way for future research in this arena.

Understanding the Activation of Anionic Redox Chemistry in Ti4+-Substituted Li2MnO3 as a Cathode Material for Li-Ion Batteries

Layered Li-rich oxides, demonstrating both cationic and anionic redox chemistry being used as positive electrodes for Li-ion batteries, have raised interest due to their high specific discharge capacities exceeding 250 mAh/g. However, irreversible structural transformations triggered by anionic redox chemistry result in pronounced voltage fade (i.e., lowering the specific energy by a gradual decay of discharge potential) upon extended galvanostatic cycling. Activating or suppressing oxygen anionic redox through structural stabilization induced by redox-inactive cation substitution is a well-known strategy. However, less emphasis has been put on the correlation between substitution degree and the activation/suppression of the anionic redox. In this work, Ti4+-substituted Li2MnO3 was synthesized via a facile solution-gel method. Ti4+ is selected as a dopant as it contains no partially filled d-orbitals. Our study revealed that the layered “honeycomb-ordered” C2/m structure is preserved when increasing the Ti content to x = 0.2 in the Li2Mn1–xTixO3 solid solution, as shown by electron diffraction and aberration-corrected scanning transmission electron microscopy. Galvanostatic cycling hints at a delayed oxygen release, due to an improved reversibility of the anionic redox, during the first 10 charge–discharge cycles for the x = 0.2 composition compared to the parent material (x = 0), followed by pronounced oxygen redox activity afterward. The latter originates from a low activation energy barrier toward O–O dimer formation and Mn migration in Li2Mn0.8Ti0.2O3, as deduced from first-principles molecular dynamics (MD) simulations for the “charged” state. Upon lowering the Ti substitution to x = 0.05, the structural stability was drastically improved based on our MD analysis, stressing the importance of carefully optimizing the substitution degree to achieve the best electrochemical performance.

Mitigating water-induced surface degradation in water-based Ni-rich Li-ion battery electrodes

Replacement of the toxic solvent used during manufacturing of cathode electrodes for Li-ion batteries with water is an essential step on the road towards eco-friendly battery production. This study aims to improve the performance of pilot-scale water-based LiNi0.83Co0.12Mn0.05O2 cathodes. The importance of proper electrode treatment before cell assembly to achieve maximum cell performance is demonstrated. Temperatures ranging from room temperature to 170 °C were applied to the electrodes to investigate the impact of residual moisture in pouch cells. Electrochemical cycling showed that despite a much higher amount of residual moisture a low drying temperature was beneficial. X-ray photoelectron spectroscopy indicated that with increasing temperature a phase reconstruction in the near-surface region of the cathode material particles is the cause for the difference in performance. This was further supported by impedance spectroscopy showing growing charge-transfer resistance arcs with higher temperature, which split into two contributions with ongoing cycling. Already temperatures above 100 °C resulted in more pronounced surface reconstruction and stronger impedance increase lowering the long-term cycling stability, while the residual moisture seemed to have only a minor impact. By optimizing the drying temperature, the long-term cycling stability could be improved from 1000 to 1700 cycles before reaching 80% capacity retention.

Engineering robust biopolymer-derived carbon growth of Ni-rich cathode materials for high-performance Li-ion batteries

Nickel-rich ternary layered oxide (NCM811) is one of the most promising electrode materials for next-generation lithium ion batteries, offering high reversibility, ecofriendly, and low cost. However, this type of cathode material also has low thermal stability, phase changes during charge-discharge, and safety concerns, requiring considerable improvement to be commercially viable. This study induced carbon growth on a modified nickel-rich layered oxide NCM811 cathode material as positive electrodes for Li ion batteries, and subsequently performed electrochemical, structural, and post-mortem characterization for the material. Specific capacity retention for the best case cathodes improved to 75 % after 100 cycles at 0.1C rate under atmospheric conditions compared with current standard NCM electrodes. Full cell fabricated using that best case electrodes achieved 220 mAh g−1 initial charge capacity, retaining 81 % charge capacity after 50 cycles. Initial coulombic efficiency and cycle stability for the prepared best case cathode material was enhanced by optimum carbon growth due to the reconstructed layer structure's capacity to inhibit side reactions at the interface and stabilize bulk structure over cycles.

Transition Metal Layer Substitution in Mo2CS2 MXene for Improving Li Ion Surface Kinetics.

We study the adsorption and mobility of a Li ion on the surface of the Mo2CS2 MXene by means of Density Functional Theory. We find that by substituting the Mo atoms of the upper MXene layer with V the mobility of the Li ion can be improved up to 95% while the material retains its metallic character. This fact indicates that MoVCS2 is a promising candidate for anode electrode in Li-ion batteries, where the materials need to be conductive and the Li ion needs to have a small migration barrier.

In-Plane Ordering of Li-Intercalated Turbostratic Graphite for the Negative Electrode of High-Power Long-Life Li-Ion Batteries

Turbostratic carbon graphitized at ca. 2000 °C exhibits low discharge capacity but excellent pulse charge/discharge characteristics and long cycle performance. In this study, to clarify the charge/discharge mechanism, the intercalation process of Li into turbostratic graphite was investigated by operando synchrotron X-ray diffraction and 7Li-NMR spectroscopy. The dataset obtained from both methods was synchronously analyzed by treating it as a function of the LiC x composition estimated from the charge/discharge curves. It was found that both the synchrotron X-ray diffraction profile and 7Li-NMR spectrum dynamically changed in conjunction with the composition and the LiC9-type and LiC6-type in-plane structures formed in turbostratic graphite, as in the case of natural graphite when Li ions intercalate. The domain formed by these in-plane structures was a short-range ordered structure that changed depending on the misorientation angle between the two adjacent graphene sheets, and a stage structure with a periodic distance in the c-axis direction did not form, as in the case of natural graphite.

Deciphering structural changes in LiNixMnyCozO2 cathodes of Li ion batteries during cycling: Experimental and theoretical investigations

Layered oxide material LiNixMnyCozO2 is emerging out as promising cathode for new generation of Li-ion batteries, especially as power sources for electric vehicles and plug-in hybrid vehicles. In this work, structural and electronic changes occurring in LiNixMnyCozO2 (LNMC) cathode materials during charge/discharge cycle of the battery is studied over a wide composition range using in-situ X-ray diffraction (XRD) and in-situ X-ray absorption spectroscopy (XAS) techniques. While in-situ XRD measurements decipher the overall structural changes during the charging/discharging cycles, in-situ element specific XAS measurements reveal site specific information on electronic and local structural changes. It has been found that for the LNMC samples the major charge compensation at the metal site during charging or Li ion de-intercalation is achieved by oxidation of Ni2+ ions without significant change in the oxidation state of Co or Mn ions. It is also found that local structure around Ni undergoes reversible change during charging and discharging cycles whereas local structure around Co or Mn sites show no significant change. Moreover, it has been found that local structural changes at Ni sites in the samples with higher Ni concentrations are much less compared to that in the samples with lower Ni concentrations during charging/discharging cycles, the result being corroborated by ab-initio theoretical simulations also. This is a new finding and would have significant implications in determining the optimum composition of LNMC electrodes of Li ion batteries for commercial applications.

Cation-Driven Assembly of Bilayered Vanadium Oxide and Graphene Oxide Nanoflakes to Form Two-Dimensional Heterostructure Electrodes for Li-Ion Batteries.

Lithium preintercalated bilayered vanadium oxide (LVO or δ-LixV2O5·nH2O) and graphene oxide (GO) nanoflakes were assembled using a concentrated lithium chloride solution and annealed under vacuum at 200 °C to form two-dimensional (2D) δ-LixV2O5·nH2O and reduced GO (rGO) heterostructures. We found that the Li+ ions from LiCl enhanced the oxide/carbon heterointerface formation and served as stabilizing ions to improve structural and electrochemical stability. The graphitic content of the heterostructure could be easily controlled by changing the initial GO concentration prior to assembly. We found that increasing the GO content in our heterostructure composition helped inhibit the electrochemical degradation of LVO during cycling and improved the rate capability of the heterostructure. A combination of scanning electron microscopy and X-ray diffraction was used to help confirm that a 2D heterointerface formed between LVO and GO, and the final phase composition was determined using energy-dispersive X-ray spectroscopy and thermogravimetric analysis. Scanning transmission electron microscopy and electron energy-loss spectroscopy were additionally used to examine the heterostructures at high resolution, mapping the orientations of rGO and LVO layers and locally imaging their interlayer spacings. Further, electrochemical cycling of the cation-assembled LVO/rGO heterostructures in Li-ion cells with a non-aqueous electrolyte revealed that increasing the rGO content led to improved cycling stability and rate performance, despite slightly decreased charge storage capacity. The heterostructures with 0, 10, 20, and 35 wt % rGO exhibited capacities of 237, 216, 174, and 150 mAh g-1, respectively. Moreover, the LVO/rGO-35 wt % and LVO/rGO-20 wt % heterostructures retained 75% (110 mAh g-1) and 67% (120 mAh g-1) of their initial capacities after increasing the specific current from 20 to 200 mA g-1, while the LVO/rGO-10 wt % sample retained only 48% (107 mAh g-1) of its initial capacity under the same cycling conditions. In addition, the cation-assembled LVO/rGO electrodes exhibited enhanced electrochemical stability compared to electrodes prepared through physical mixing of LVO and GO nanoflakes in the same ratios as the heterostructure electrodes, further revealing the stabilizing effect of a 2D heterointerface. The cation-driven assembly approach, explored in this work using Li+ cations, was found to induce and stabilize the formation of stacked 2D layers of rGO and exfoliated LVO. The reported assembly methodology can be applied for a variety of systems utilizing 2D materials with complementary properties for applications as electrodes in energy storage devices.

The impact of ionomeric active binder on Li-ion battery charge–discharge and rate capability, Part I: Electrolyte

Ionically functionalized polymers as active binders in porous electrodes of Li-ion batteries have been studied recently to improve the rate capability of thick electrodes. Li+ ion depletion and the accompanying rapid drop of electric potential act as limiting factors for thick cathodes in Li-ion batteries. We show that the incorporation of lithiated additives containing covalently bound anions, including both ionomers and nanoparticle salts, can enhance the nominal voltage and utilization of Li-ion cathodes. A mathematical model is proposed to describe the influence of the lithiated ionic additives in liquid electrolyte and is implemented. The simulation results elaborate the effect of varying ion-pair dissociability for the ionic additives. A steady state ion concentration gradient is achieved for low current density, but operation at high current density results in Li+ depletion in the electrolyte phase. The use of dissociable ionic additives can overcome this limitation and reduce the potential polarization across the electrolyte. Higher concentration of ionomer ligands can improve performance for poorly dissociable ionic additives. The model validation shows that the potential drop can be lessened when ion-pair dissociation is considered while ion mobility remains unchanged. The modeling technique can be extended to a whole battery cell.

Photolithographic Structuring of Ordered Silicon Micropillar Electrodes for Lithium-Ion Batteries and Electrochemical Performance

Ordered and vertically oriented silicon (Si) micropillar structures, when optimally designed, can accommodate the lithiation-induced volumetric expansion that is limiting the implementation of Si as negative electrodes in Li-ion batteries. As there is not much work in this area, this study is focused on evaluating systematically the potential of Si micropillar electrodes prepared by photolithographic structuring of Si. The specific objective is to determine the effect of micropillar length and the free space around the pillars on the electrochemical performance of the electrode. The Si micropillar electrode with the pillar length of 14 μm showed a high specific capacity (2600 mAh/g) and a high areal capacity (3 mAh/cm2), which were stable for over 100 cycles. However, there was significant capacity degradation in 32 and 48 μm-long Si pillar electrodes due to cracking and electrode damage during cycling. In the 32 μm Si micropillar electrode, a small change in porosity from 69 to 86% caused a substantial increase in specific capacity from 1400 to 2000 mAh/g over 100 cycles, with the areal capacity decreasing from 3 to 2 mAh/cm2. The findings also show the directions for further work for the optimization of Si micropillar electrodes.

Defective graphene decorated with TiO2 nanoparticles as negative electrode in Li-ion batteries

In this work, the performance of novel negative electrodes for Li-ion batteries based on defective graphene synthesized via a scalable thermal exfoliation of graphite oxide and decorated with TiO2 nanoparticles is investigated. Titania polymorphs are interesting as battery electrode materials, owing to their high cycle stability, safety, abundance and negligible solid electrolyte interphase formation and volume changes upon cycling. Defective graphene, on the other hand, can embed TiO2 nanoparticles, forming a conductive hybrid nanocomposite anode material for Li-ion batteries, with improved Li-ion and electron transport, optimising power density. Here we propose two different synthetic approaches for the decoration of graphene with TiO2 nanoparticles: I) a novel chemical route where TiO2 nanoparticles, mainly anatase, were grown on graphene in hydrothermal mild conditions and II) a physical solid-state approach where hydrothermal TiO2 nanoparticles and graphene were mixed together via high energy ball-milling. The synthesized materials were analysed via powder X-ray diffraction, micro-Raman spectroscopy and HR-TEM, while the electrodes were electrochemically tested. Operando synchrotron diffraction was conducted on half-cell to investigate phase transitions in the electrode materials. Even in presence of small amount of graphene, significant improvement in capacity, reversibility, and high-rate capability were observed. In particular, the sample obtained through the addition of 1 wt% of graphene displayed a reversible capacity of more than 180 mA h/g after prolonged and wearing cycling. This result outperforms by 327 % the reversible capacity of pure TiO2 electrode.

Tannic acid as a binder and electronic conductor precursor in silicon electrodes for Li-ion batteries

State of-the-art Si electrodes for Li-ion batteries typically require the addition of an advanced polymeric binder and a conductive carbon additive to the active material in order to circumvolve the issues associated with silicon, namely its poor conductivity in the oxidized state, and its high volume variation upon lithiation which give rise to several failure mechanisms. Here, we demonstrate that both additives can be replaced by a cheap, naturally available, polyphenol, tannic acid (TA). We show that Si/TA electrodes (80/20 wt%), even with a high loading (∼2 mg_Si cm−2), can retain a specific capacity above 2000 mAh g−1 after 50 cycles. This unexpected result appears to result from the irreversible reduction of TA during the first cycle, into a conducting, likely polymeric, species.

Roll-to-roll solvent-free manufactured electrodes for fast-charging batteries

Roll-to-roll solvent-free manufactured electrodes for fast-charging batteries