Li-ion Battery Electrodes Research Articles

Theoretical prediction of two-dimensional Cr3C2 monolayer and its derivatives as potential electrode of Li-ion batteries

The investigations on Cr3C2 and Cr3C2T2 (T = F, Cl, O, OH) monolayers as promising electrode materials for lithium-ion battery (LIBs) are systematically carried out by Hubbard-corrected density functional theory (DFT + U). It indicates that Cr3C2 monolayer and its derivatives are dynamically and thermally stable. At the same time, the pristine Cr3C2 monolayer exhibits metallic character and the conductivity can be maintained through chemical modification. The lithium diffusion barrier on Cr3C2 monolayer is only 0.024 eV, which can guarantee a fast rate during the charge/discharge process. The storage capacity of Cr3C2 monolayer adsorbing one layer of Li atoms is about 298 mAh/g. It is found that the Cr3C2T2 (T = Cl, O, OH) monolayer can keep at least one layer of Li atoms adsorbed without any structural deformation, and the theoretical capacities are 214, 253 and 250 mAh/g, respectively. The Li storage capacities can be increased exponentially with the more layers of Li atoms adsorbing on the two-dimensional (2D) materials. Thus, Cr3C2 and Cr3C2T2 monolayers are potential electrode materials for LIBs.

Lithium Niobate for Fast Cycling in Li-ion Batteries: Review and New Experimental Results

Li-Nb-O-based insertion layers between electrodes and electrolytes of Li-ion batteries (LIBs) are known to protect the electrodes and electrolytes from unwanted reactions and to enhance Li transport across interfaces. An improved operation of LIBs, including all-solid-state LIBs, is reached with Li-Nb-O-based insertion layers. This work reviews the suitability of polymorphic Li-Nb-O-based compounds (e.g., crystalline, amorphous, and mesoporous bulk materials and films produced by various methodologies) for LIB operation. The literature survey on the benefits of niobium-oxide-based materials for LIBs, and additional experimental results obtained from neutron scattering and electrochemical experiments on amorphous LiNbO3 films are the focus of the present work. Neutron reflectometry reveals a higher porosity in ion-beam sputtered amorphous LiNbO3 films (22% free volume) than in other metal oxide films such as amorphous LiAlO2 (8% free volume). The higher porosity explains the higher Li diffusivity reported in the literature for amorphous LiNbO3 films compared to other similar Li-metal oxides. The higher porosity is interpreted to be the reason for the better suitability of LiNbO3 compared to other metal oxides for improved LIB operation. New results are presented on gravimetric and volumetric capacity, potential-resolved Li+ uptake and release, pseudo-capacitive fractions, and Li diffusivities determined electrochemically during long-term cycling of LiNbO3 film electrodes with thicknesses between 14 and 150 nm. The films allow long-term cycling even for fast cycling with rates of 240C possessing reversible capacities as high as 600 mAhg−1. Electrochemical impedance spectroscopy (EIS) shows that the film atomic network is stable during cycling. The Li diffusivity estimated from the rate capability experiments is considerably lower than that obtained by EIS but coincides with that from secondary ion mass spectrometry. The mostly pseudo-capacitive behavior of the LiNbO3 films explains their ability of fast cycling. The results anticipate that amorphous LiNbO3 layers also contribute to the capacity of positive (LiNixMnyCozO2, NMC) and negative LIB electrode materials such as carbon and silicon. As an outlook, in addition to surface-engineering, the bulk-engineering of LIB electrodes may be possible with amorphous and porous LiNbO3 for fast cycling with high reversible capacity.

2-dimensional biphenylene monolayer as anode in Li ion secondary battery with high storage capacity: Acumen from density functional theory

Energy storage methods are cardinal for the mitigation of intermittency of renewable energy and among many technologies available, Li-ion batteries (LIBs) dominate the market on the account of their significant attributes. However, there is still room for improvement in their performance for high-end applications. Modifying the anode material can significantly affect the overall battery performance. It becomes necessary to discover a satisfactory negative electrode for more productive Li ion batteries. The present density functional theory based work examines the potential of a novel, experimentally fabricated 2D monolayer, Biphenylene having sp2 carbon atoms arranged periodically in four, six, and eight-membered rings, for its application in LIBs as adequate anode. Phonon spectrum and ab initio molecular dynamics (AIMD) signify the dynamic and thermal stability of the nanosheet. The band structures and density of states reveal the metallic nature which is maintained after the Li (adatom) adsorption as well. The mean adsorption energies for subsequent loading of Li over the sheet vary from -0.44 to -0.15 eV. The appreciative interactions between the adatom and the monolayer are well authenticated by charge transfer analysis. The Biphenylene monolayer is observed to offer a low diffusion barrier of 0.23 eV for the Li atoms. High storage capacity of 1302 mAhg−1 (almost 3.5 times higher than that of marketable Graphite), a low voltage of 0.34 V, and low volume changes (less than 3%) are noticed. This comprehensive study authenticates the capability of the 2D carbonous Biphenylene sheet as a suitable LIB negative electrode.

Effects of Butadiene Sulfone as an Electrolyte Additive on the Formation of Solid Electrolyte Interphase in Lithium-Ion Batteries Based on Li4Ti5O12 Anode Materials.

In this study, butadiene sulfone (BS) was selected as an efficient electrolyte additive to stabilize the solid electrolyte interface (SEI) film on the lithium titanium oxide (LTO) electrodes in Li-ion batteries (LIBs). It was found that the use of BS as an additive could accelerate the growth of stable SEI film on the LTO surface, leading to the improved electrochemical stability of LTO electrodes. It can be supported by the BS additive to effectively reduce the thickness of SEI film, and it significantly enhances the electron migration in the SEI film. Consequently, the LIB-based LTO anode in the electrolyte containing 0.5 wt.% BS showed a superior electrochemical performance to that in the absence of BS. This work provides a new prospect for an efficient electrolyte additive for next-generation LIBs-based LTO anodes, especially when discharged to low voltage.

Enhanced Electrochemical Performance of Rare-Earth Metal-Ion-Doped Nanocrystalline Li4Ti5O12Electrodes in High-Power Li-Ion Batteries

A comprehensive and comparative exploration research performed, aiming to elucidate the fundamental mechanisms of rare-earth (RE) metal-ion doping into Li4Ti5O12 (LTO), reveals the enhanced electrochemical performance of the nanocrystalline RE-LTO electrodes in high-power Li-ion batteries. Pristi ne Li4Ti5O12 (LTO) and rare-earth metal-doped Li4-x/3Ti5-2x/3LnxO12 (RE-LTO with RE = Dy, Ce, Nd, Sm, and Eu; x ≈ 0.1) nanocrystalline anode materials were synthesized using a simple mechanochemical method and subsequent calcination at 850 °C. The X-ray diffraction (XRD) patterns of pristine and RE-LTO samples exhibit predominant (111) orientation along with other characteristic peaks corresponding to cubic spinel lattice. No evidence of RE-doping-induced changes was seen in the crystal structure and phase. The average crystallite size for pristine and RE-LTO samples varies in the range of 50-40 nm, confirming the formation of nanoscale crystalline materials and revealing the good efficiency of the ball-milling-assisted process adopted to synthesize nanoscale particles. Raman spectroscopic analyses of the chemical bonding indicate and further validate the phase structural quality in addition to corroborating with XRD data for the cubic spinel structure formation. Transmission electron microscopy (TEM) reveals that both pristine and RE-LTO particles have a similar cubic shape, but RE-LTO particles are better interconnected, which provide a high specific surface area for enhanced Li+-ion storage. The detailed electrochemical characterization confirms that the RE-LTO electrodes constitute promising anode materials for high-power Li-ion batteries. The RE-LTO electrodes deliver better discharge capacities (in the range of 172-198 mAh g-1 at 1C rate) than virgin LTO (168 mAh g-1). Among them, Eu-LTO provides the best discharge capacity of 198 mAh g-1 at a 1C rate. When cycled at a high current rate of 50C, all RE-LTO electrodes show nearly 70% of their initial discharge capacities, resulting in higher rate capability than virgin LTO (63%). The results discussed in this work unfold the fundamental mechanisms of RE doping into LTO and demonstrate the enhanced electrochemical performance derived via chemical composition tailoring in RE-LTO compounds for application in high-power Li-ion batteries.

Time and space resolved operando synchrotron X-ray and Neutron diffraction study of NMC811/Si–Gr 5 Ah pouch cells

Silicon–Graphite blended electrodes in Li-ion batteries have been proposed as a way to harness the high capacity of Si as an anode material, while minimising the negative effects of their large volume expansion. NMC 811 is the current state-of-the-art layered oxide cathode material, where the cobalt content of the cathode has been minimised. These are the two of the most promising materials for achieving electric vehicle targets in terms of performance, cyclability and price, however their degradation mechanism is not fully understood. Here these two materials have been used to manufacture 5 Ah prototype multi-layer pouch cells, which are aged and then studied using two complimentary diffraction techniques. Neutron diffraction has enabled a quantitative analysis of phase transitions in Si–Gr anodes in a pristine and degraded cell, and the alloying behaviour of Si and Li has been inferred by comparison of identical cells with either graphite or Si–Gr anodes. Synchrotron X-ray Diffraction has been used to make an operando 2D map of the cathode and anode lithiation in the pouch cell, as well as to map the volume expansion across the cell. This approach has revealed that degradation entails significant inhomogeneities across both electrodes, linked to the inhomogeneous volume expansion of the Si–Gr anodes.

Computational Design of Cation-Disordered Li3Ta2O5 with Fast Ion Diffusion Dynamics and Rich Redox Chemistry for a High-Rate Li-Ion Battery Anode Material

Disordered rock salt transition-metal oxides have emerged recently as promising electrodes for Li-ion batteries (LIBs). However, only two disordered rock salt (DRX) materials, Li3V2O5 and Li3Nb2O5, have been studied as anodes so far, leaving numerous DRX compounds with vast compositions and exotic battery-related performance unexplored. Here, based on theoretical analyses and calculations, we propose a Ta pentoxide-based DRX anode with rich electrochemical properties, where the thermodynamic stability, average voltage, energy density, redox chemistry, and cation mobility are studied. Our results show that DRX-Li3Ta2O5 can cycle three Li ions at an average voltage of 1.27 V, which is higher than that of DRX-Li3V2O5 (0.73 V) but lower than that of DRX-Li3Nb2O5 (1.76 V), falling in the optimal range for the high rate performance. More importantly, DRX-Li3Ta2O5 exhibits a superhigh volumetric capacity of 1336 mAh cm–3, which surpasses that of graphite, Li4Ti5O12, and DRX-Li3V2O5. Meanwhile, the unique geometry of DRX-Li3Ta2O5 allows Li+ to diffuse rapidly through channels with low diffusion energy barriers, and Ta2O5 is electronically activated by inserting Li+ into the available octahedral sites with enhanced orbital overlapping. Our work expands the family of DRX anode materials with new features.

Superior catalytic effect of titania - porous carbon composite for the storage of hydrogen in MgH2 and lithium in a Li ion battery

A novel nanocomposite (0.2TiO2 + AC) with two promising applications is demonstrated, (i) as an additive for promoting hydrogen storage in magnesium hydride, (ii) as an active electrode material for hosting lithium in Li ion batteries (surface area of activated carbon (AC): 491 m2/g, pore volume: 0.252 cc/g, size of TiO2 particles: 20–30 nm). Transmission electron microscopy study provides evidence that well dispersed TiO2 nanoparticles are enclosed by amorphous carbon nets. A thermogravimetry-differential scanning calorimetry (TG-DSC) study proves that the nanocomposite is thermally stable up to ∼400 °C. Volumetric hydrogen storage tests and DSC studies further prove that a 3 wt% of 0.2TiO2+AC nanocomposite as additive not only lowers the dehydrogenation temperature of MgH2 over 100 °C but also maintains the performance consistency. Moreover, as a working electrode for Li ion battery, 0.2TiO2+AC offers a reversible capacity of 400 mAh/g at the charge/discharge rate of 0.1C and consistent stability up to 43 cycles with the capacity retention of 160 mAh/g at 0.4C. Such cost effective-high performance materials with applications in two promising areas of energy storage are highly desired for progressing towards sustainable energy development.

Competing Ethylene Carbonate Reactions on Carbon Electrode in Li-Ion Batteries

Ethylene carbonate (EC) is the archetype solvent in Li-ion batteries. Still, questions remain regarding the numerous possible reaction pathways of EC. Although the reaction pathway involving direct EC reduction and SEI formation is most commonly discussed, EC ring-opening is often observed, but seldomly addressed, especially with respect to SEI formation. By applying Online Electrochemical Mass Spectrometry, the EC ring-opening reaction on carbon is found to start already at ∼2.5 V vs Li+/Li as initiated by oxygenic carbon surface groups. Later, OH− generated from H2O reduction reaction at ∼1.6 V further propagates EC to ring-open. The EC reduction reaction occurs <0.9 V but is suppressed depending on the extent of EC ring-opening at higher potentials. Electrode/electrolyte impurities and handling conditions are found to have a significant influence on both processes. In conclusion, SEI formation is shown to be governed by several kinetically competing reaction pathways whereby EC ring-opening can play a significant role.

Nanoporous multilayer graphene oxide membrane for forward osmosis metal ion recovery from spent Li-ion batteries

The recovery of Li and rare metals from the spent electrodes of Li-ion batteries (LIBs) is becoming increasingly important. Herein, nanoporous multilayer graphene oxide (NMG) membranes were fabricated via the confined thermal annealing method to achieve Li-ion selectivity. A graphene oxide (GO) membrane was prepared by coating the membrane with an aqueous layer of GO liquid crystal via the scalable bar coating method, followed by hot-pressing. The influence of the GO interlayer spacing and nanopore presence on the ion separation performance was investigated. The NMG membrane shows different ion permeance phenomena depending on ion concentration. The permeation rate of divalent ions (Co, Ni, Mn) through the NMG membrane was faster than that of Li ions in solution with low ionic strength, whereas the membrane was Li-ion selective in mixed ionic solutions or at high ionic strength. This result indicates that electrostatic interaction by oxygen groups is important at low ionic strength, but size exclusion by interlayer spacing and adsorption by nanopore is critical at high ionic strength. The ion permeation mechanisms were further examined based on molecular calculations, which revealed that the binding energies between the divalent ions and nanopores or basal plane of graphene were high, resulting in slow ion permeation. When the NMG membrane was combined in a forward osmosis system, Li-ion can be separated continuously from the mixture solution simulated from the spent Li-battery electrode. This approach shows the high potential of nanoporous multilayer graphene membrane for Li extraction in particular with dense pore structure and around 7 Å of d-spacing.

Covalent organic framework@graphene composite as a high-performance electrode for Li-ion batteries

ABSTRACT As emerging candidates for the electrode materials of next-generation rechargeable batteries, covalent organic frameworks (COFs) have large charge capacity, wide ion diffusion paths and low potential range. However, organic electrodes generally suffer from low conductivity. Graphene (G) possesses great strength, flexibility and has been widely used as a type of conductive additive due to its remarkable electrical conductivity. Here we propose a composite constructed by a certain kind of COF and a pristine G sheet (COF@G), the characteristics of which have been systematically investigated based on density functional theory calculations and molecular dynamics simulations. Results indicate that the COF@G (COF/G, COF/COF/G, COF/G/G) can exhibit good electronic conductivity and ultrahigh capability, which can be used as high-performance electrodes of Li-ion batteries. For Li-ions (Li+), they can provide strong adsorption sites and smooth diffusion channels leading to high specific capacity and good rate capability. More importantly, the coupling interaction of the COF and the G can greatly inhibit the structure changes of the COF during the lithiation process, and the volumetric change rate is less than 23%. Among them, the COF/G is the most suitable for Li+ adsorption and corresponding theoretical capacity can reach 353 mAh/g.

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.

Density Functional Tight-Binding Model for Lithium-Silicon Alloys.

The predictive power of molecular dynamic simulations is mainly restricted by the time scale and model accuracy. Many systems of current relevance are of such complexity that they require addressing both issues simultaneously. This is the case of silicon electrodes in Li-ion batteries, where different LixSi alloys are formed during charge/discharge cycles. While first-principles treatments for this system are seriously limited by the computational cost of exploring its large conformational space, classical force fields are not transferable enough to represent it accurately. Density Functional Tight Binding (DFTB) is an intermediate complexity approach capable of capturing the electronic nature of different environments with a relatively low computational cost. In this work, we present a new set of DFTB parameters suited to model amorphous LixSi alloys. LixSi is the usual finding upon cycling the Si electrodes in the presence of Li ions. The model parameters are constructed with a particular emphasis on their transferability for the entire LixSi composition range. This is achieved by introducing a new optimization procedure that weights stoichiometries differently to improve the prediction of their formation energies. The resulting model is shown to be robust for predicting crystal and amorphous structures for the different compositions, giving excellent agreement with DFT calculations and outperforming state-of-the-art ReaxFF potentials.

Interphase formation with carboxylic acids as slurry additives for Si electrodes in Li-ion batteries. Part 1: performance and gas evolution

Rendering the solid electrolyte interphase and the inter-particle connections more resilient to volume changes of the active material is a key challenge for silicon electrodes. The slurry preparation in a buffered aqueous solution offers a strategy to increase the cycle life and capacity retention of silicon electrodes considerably. So far, studies have mostly been focused on a citrate buffer at pH = 3, and therefore, in this study a series of carboxylic acids is examined as potential buffers for slurry preparation in order to assess which chemical and physical properties of carboxylic acids are decisive for maximizing the capacity retention for Si as active material. In addition, the cycling stability of buffer-containing electrodes was tested in dependence of the buffer content. The results were complemented by analysis of the gas evolution using online electrochemical mass spectrometry in order to understand the SEI layer formation in presence of carboxylic acids and effect of high proton concentration.

Interphase formation with carboxylic acids as slurry additives for Si electrodes in Li-ion batteries. Part 2: a photoelectron spectroscopy study

Preparing aqueous silicon slurries in presence of a low-pH buffer improves the cycle life of silicon electrodes considerably because of higher reversibility of the alloying process and higher resilience towards volume changes during (de)alloying. While the positive effects of processing at low pH have been demonstrated repeatedly, there are gaps in understanding of the buffer’s role during the slurry preparation and the effect of buffer residues within the electrode during cycling. This study uses a combination of soft and hard x-ray photoelectron spectroscopy to investigate the silicon particle interface after aqueous processing in both pH-neutral and citrate-buffered environments. Further, silicon electrodes are investigated after ten cycles in half-cells to identify the processing-dependant differences in the surface layer composition. By tuning the excitation energy between 100 eV and 7080 eV, a wide range of probing depths were sampled to vertically map the electrode surface from top to bulk. The results demonstrate that the citrate-buffer becomes an integral part of the surface layer on Si particles and is, together with the electrode binder, part of an artificial solid-electrolyte interphase that is created during the electrode preparation and drying.

Carbon nanotubes and carbon-coated current collector significantly improve the performance of lithium-ion battery with PEDOT:PSS binder

We report an approach for enhancing performance of PEDOT:PSS binder in Li-ion battery electrodes by introducing small amount of carbon additives. Coating of current collector with carbon increases adhesion and electrical contact to the binder while introduction of carbon nanotubes enhances the electrical contact between the binder particles. The combination of these factors improves rate and cycling capability of the electrode.

Mathematical Modeling of Multiple-Li-Dendrite Growth in Li-ion Battery Electrodes

Lithium dendrite growth in Li-ion batteries is one of the most dangerous phenomena because it can cause inner short circuits and thermal runaways. However, the nucleation and growth of the dendrites are difficult to predict because of their complex behaviors, which depend on several factors such as the charging conditions and electrode-design parameters. In this study, a comprehensive mathematical model has been developed for Li-deposition on Li-ion battery electrodes. The model is based on the Single Particle model (to evaluate the Li-ion concentration fields) combined with dendrite-growth models based on the electrochemical and crystal growth theory. The effect of the SEI thickness distribution, the charging C-rate and cut-off voltage on the growth of dendrite tips have been statistically evaluated, and the risk of short circuit is discussed. The study focuses on the effects of the SEI-thickness distribution on the timing of the SEI breaking and density of the dendrite formation.

Mass Transport in the Stefan-Knudsen Transition Region during Vacuum Drying at Different Pressures in a Porous Structure Resembling Battery Electrodes.

A precise understanding of the mass transport kinetics of water inside the porous structure of battery electrodes is crucial to understanding and optimizing their post-drying process. This process and the moisture management during the production of Li-ion battery electrodes adjust and remove residual water from electrodes and are cost intensive. Furthermore, the amount of residual moisture in the electrode affects device performance. Mass transport phenomena in the Stefan and Knudsen transition affect these processes. In this manuscript, we investigate the mass transport in the interparticle gas phase of a porous structure gravimetrically by a magnetic suspension balance with a conditioned (humidity, temperature, and pressure) measurement cell. Emphasis lies on the pressure, porosity, and mass transport distance dependency of the desorption process. Comparing experimental data with a simulation of the interparticle gas phase shows that the mass transport close to ambient pressure can be described by Stefan diffusion through the porous structure. The experiments show the significance of Knudsen diffusion during the mass transport toward lower pressure. A proposed diffusion-coefficient model describes the Stefan and Knudsen region with a transition function, taking the mass transport phenomena overlap into account by lower and upper limits as transition values.

Battery Cycle Stability in Additive-free MAX(Ti3AlC2) Li-ion Battery Anode

We fabricated an additive-free MAX(Ti3AlC2) phase Li-ion battery (LIB) electrode using the electrophoretic deposition (EPD) method. In this study, MAX, a precursor of MXene, which has recently been receiving great attention as a negative electrode material for LIBs, was manufactured as a coin cell through EPD rather than the conventional slurry system. We excluded the effect of additives on the electrochemical performance, enabling evaluation of the intrinsic electrochemical properties related to battery charging and discharging. As a result, the battery using MAX as an anode material showed a large specific capacity of 148.2 mAh/g in the first discharge and superior cycle stability. Enhanced cycle stability and reversible electrochemical reactions were attributed to activation of faradaic and non-faradaic behavior, i.e., pseudocapacitive behavior, caused by delamination of the MAX(Ti3AlC2) into MXene (Ti3C2). This was confirmed by the decrease in the charge transfer resistance and the increase in total capacitance at the interface, using electrochemical impedance spectroscopy and cyclic voltammetry measurements. In addition, the activation of pseudocapacitive behavior was confirmed by the change in kinetic mechanism, as evidenced from a significant increase in the Li ion diffusivity with cycles. These results demonstrate that MAX(Ti3AlC2) is promising as an anode material for LIBs and at the same time shows potential for tuning electrochemical properties through the electrochemical delamination process.

Rational Design of Nanoelectrodes for Highly Efficient Lithium-Ion Batteries

Li-ion battery is a very promising market. Researchers and scientists are trying to improve further the function of all Li-ion batteries on the account that they still cannot meet the customers' requirements and may not be as competitive as the internal combustion engine on traveling distances. The Nanotechnology application of Li-ion battery electrodes affects the general performance such as capacity, energy density, charging and discharging speed, etc. At the atomic scale, the pulverization problem caused by lithiation also limits the growth of batteries. Nanotechnology may be one of the solutions because the strain the material can sustain at the nanoscale is extremely large. The working mechanism of Li-ion helps to have an overall understanding of how batteries work. Replacing graphite with silicon can greatly enhance the battery's performance, but there are still some problems with replacing the electrode material. There are three different types of applications of nanotechnologies that can solve the problems like pulverization: 0D nanoparticles, 1D nanowires, and 2D nanofilms. Nanotechnology is no longer at a laboratory scale and has taken part in the mass production industry.