Graphite Anode In Lithium-ion Batteries Research Articles

Topology-enhanced mechanical stability of swelling nanoporous electrodes

Materials like silicon and germanium offer a 10-fold improvement in charge capacity over conventional graphite anodes in lithium-ion batteries but experience a roughly threefold volume increase during lithiation, which challenges ensuring battery integrity. Nanoporous silicon, created by liquid-metal-dealloying, is a potentially attractive anode design to mitigate this challenge, exhibiting both higher capacity and extended cycle lifetimes. However, how nanoporous structures accommodate the large volume change is unknown. Here, we address this question by using phase-field modeling to produce nanoporous particles and to investigate their elastoplastic swelling behavior and fracture. Our simulations show that enhanced mechanical stability results from the network topology consisting of ligaments connected by bulbous, sphere-like nodes. The ligaments forcefully resist elongation while the nodes, behaving like isolated spherical particles, experience large stresses driving fracture. However, being smaller compared to a sphere of the same volume as the entire nanoporous particle, the nodes are more protected against fracture.

Gum based functional binder for high-performance artificial graphite anode for lithium-ion batteries

Artificial graphite (AG), in contrast to natural graphite, has received much attention due to its superior rate capabilities and stability under high current density. Although the rate capabilities can be enhanced by employing artificial graphite, there is room for improvement in the cycle retention characteristics of artificial graphite. In particular, further optimization on the binder type on anodes is necessary, as commercially used polyvinylidene fluoride (PVdF) has limitations in long-term cycling stability. Furthermore, PVdF is dissolved in N-Methyl-2-pyrrolidone (NMP), which is not environmentally- and eco-friendly. In this work, we have introduced a water-soluble binder based on deacetylated kondagogu gum (KG) for AG anodes, which are derived from the gum tree. Upon deacetylation, kondagogu gum can be dissolved in water, which can be directly used together with active materials and conductive agents in a slurry. Replacing a PVdF binder with a KG binder results in an enhanced cycle retention and comparable rate capabilities, without the changes in the overall redox reactions with Li+. Postmortem analysis reveals that the improved electrochemical performance of the AG anode contributed to the excellent structural integrity of the KG binder compared with the PVdF binder.

Graphite Nanosheets as a Platform for the Nanosize GeSe2 Anode with Improved Electrode Performance

GeSe2 anode materials possess energy densities higher than those of the commercial graphite anode for lithium-ion batteries (LIBs). However, the limited cycling life and poor inherent conductivity present significant difficulties for their use in various fields. LIBs’ lifetime and capacity density depend on their electrode materials, where structural stability and a slow diffusion control mechanism are crucial factors. In this study, amorphous nanosize GeSe2 uniformly anchored on graphite sheets (GeSe2/G) was prepared using ball milling. For comparison, the cycle performances of pure GeSe2 and GeSe2 with the same ball milling conditions (M-GeSe2) were tested. The results showed that ball milling enabled uniform anchoring of GeSe2 nanoparticles of ∼200 nm on graphite nanosheets without aggregation, where the introduction of graphite not only served as electron transfer layers to effectively improve the electrical conductivity but also assisted in reducing the volume growth and comminution of GeSe2 during Li+ insertion/extraction procedures. When served as anode materials for LIBs, the GeSe2/G nanocomposites showed high Li+ storage properties, i.e., a high reversible capacity of 812.8 mAh g–1 at 0.1 A g–1. After 50 cycles, GeSe2/G still reached 650 mAh g–1, which was much higher than M-GeSe2 (392.3mAh g–1) and GeSe2 (183 mAh g–1). Even at 1 A g–1, the GeSe2/G anode exhibited a high reversible capacity of 409.6 mAh g–1 and remarkable cycling stability, with a high capacity retention of 63% after 300 cycles.

Microsized Silicon/Carbon Composite Anodes through In Situ Polymerization of Phenolic Resin onto Silicon Microparticles for High-Performance Lithium-Ion Batteries

Silicon (Si) has been gradually explored as a next-generation anode material to replace traditional graphite anodes in lithium-ion batteries (LIBs) due to its high specific capacity (3579 mAh g–1 at room temperature). In terms of cost and tap density, silicon microparticles (SiMPs) are more advantageous than silicon nanoparticles (SiNPs) in high energy density LIBs, but they are also plagued by the more serious volume effect. Here, we design a silicon/carbon (Si/C) composite anode through the in situ polymerization of phenolic resin (PF) onto SiMPs, and after pyrolysis, SiMPs are tightly coated with pyrolytic carbon layers. When applied in LIBs, the composite anodes (μSi@PF) exhibit excellent cycling performance (1283 mAh g–1 after 400 cycles at 2 A g–1) and rate performance (a reversible capacity of about 1000 mAh g–1 at 8 A g–1). The full cell with lithium iron phosphate cathodes and μSi@PF anodes can maintain 87.7% capacity retention after 100 cycles. The great electrochemical performance can be ascribed to the rational structure design of μSi@PF in which PF pyrolytic carbon as a shell around SiMPs can accommodate the volume change of SiMPs during cycling and reduce the internal impedance. This is the first attempt to construct Si/C composites by in situ polymerizing PF resin onto SiMPs, and the great performance of Si/C anode provides a reference for the practical application of SiMPs.

Process and Material Analysis of Laser- and Convection-Dried Silicon–Graphite Anodes for Lithium-Ion Batteries

Drying electrodes is very cost-intensive as it is characterized by high energy and space consumption. Laser drying is considered a promising alternative process due to direct energy input and lower operating costs. However, it is unclear whether the same product and process quality can be achieved with laser drying. Silicon–graphite anodes with different silicon contents were processed using either a high-power diode laser or a convection oven. The laser-drying process was investigated using thermography, and the effect of laser drying on the electrode quality was examined using adhesion and residual moisture measurements. Furthermore, thermogravimetric analysis, SEM images and electrical conductivity were used to analyse the laser- and convection-dried anodes. It was shown that silicon–graphite anodes can also be manufactured using laser drying, with a significant reduction in drying time of over 80%.

Effect of Y-doped TiO2(B)/SnO2 1D structured nanocomposite on the performance and capacity of lithium-ion batteries

Because traditional graphite anode for Lithium-ion batteries (LIBs) has low coulombic efficiency, high irreversible capacity and large volume expansion which can no longer satisfy the requirements of high-performance batteries. This article therefore presented the development of an anode material based on structural design to enhance its properties. One-dimension structured nanocomposites of yttrium-doped TiO2(B) nanowires/ SnO2 nanotubes were synthesised at various yttrium concentrations via hydrothermal method. Phase composition, crystal structure, morphologies, and electrochemical properties were evaluated to study the effects of the dopant on performance and capacity of the LIBs. XRD showed the modification in crystalline size and lattice parameters when yttrium was introduced. Electrochemical properties were markedly enhanced by the yttrium-doped nanocomposites, especially for the one with 0.5%mole yttrium (TSY50). The TSY50 offered the highest diffusion coefficient of 2.34×10-10 cm2 /s, reduced the Li-ion diffusion length and the cell resistance, improved the specific capacity, cycle performance and capacity retention, as demonstrated by cycling tests. The prepared yttrium-doped nanocomposite could be considered as a promising material for its application as an anode in LIBs.

Amorphous MnO2-Modified FeOOH Ternary Composite with High Pseudocapacitance As Anode for Lithium-Ion Batteries

The development of high-capacity anodes that are stable at high rates is of immediate interest as a potential alternative to the commercial graphite anode in lithium-ion batteries (LIBs). Conversion-based transition metal oxides, known for their high theoretical capacities, have been extensively studied in this regard. In this work, a ternary FeOOH-rGO-MnO2 composite has been suitably designed to address the limitations of the bare FeOOH anode arising from poor conductivity and volume expansion. A simple low-temperature synthesis method was employed to obtain a uniform distribution of FeOOH nanorods over the rGO matrix, which was further modified with a buffer layer of amorphous MnO2 nanosheets. While cycling at high rates, the modified composite anode delivered capacities of 956, 842, and 688 mAh g–1 at 1, 2, and 5 A g–1, respectively, for 200 cycles along with a cycling stability of 900 mAh g–1 at 1 A g–1 for 100 cycles. Various electrochemical techniques were used to analyze the superior performance of the ternary composite anode. The carbon matrix effectively provides favorable pathways for electron conduction and aids in the stable SEI formation, while the amorphous MnO2 sustains the structural integrity of the electrode by controlling volume expansion. Further, the exceptional stability of the anode at high rates was attributed to the marked increase in capacitive contribution in the FeOOH-rGO-MnO2 ternary composite anode, paving the way for faster electrode kinetics.

Structural transformation induced twinning for enhanced conversion reaction of vacancy-ordered metal oxides with Li ions

Metal oxide anode materials based on conversion reaction usually deliver a capacity much higher than that of commercial graphite anodes in lithium-ion batteries (LIBs), and the porous forms of the materials can effectively alleviate volume change associated with (de)lithiation. In this work, tetragonal γ-Fe2O3, which is a vacancy-ordered superstructure containing large vacancy clusters, is studied as the representative of intrinsic nanoporous metal oxide anode materials of LIBs. γ-Fe2O3 exhibits a reversible capacity higher than the theoretical value in initial cycles, but a steady capacity same as that of α-Fe2O3. In lithiation, γ-Fe2O3 first transforms irreversibly to an ordered rock salt Li1-xFe1+xO2 (LiTiO2 type), and the Li1-xFe1+xO2 is converted reversibly into Li2O and Fe0 upon further lithiation: γ-Fe2O3+Li→Li1-xFe1+xO2+Li ↔ Fe0+Li2O. The alternate stacking of dense tetrahedral layers and porous octahedral layers in γ-Fe2O3 enables the simultaneous formation of Li1-xFe1+xO2 phases with different Li contents in a single particle and triggers structure twinning, accounting for fast reaction and likely high capacity in initial cycles. The structural evolution disclosed in γ-Fe2O3 not only updates the understanding of conversion reactions of vacancy-ordered metal oxides, but also offers an innovative approach for the fabrication of twinning structures in metal oxides including cathode materials.

Recent status, key strategies and challenging perspectives of fast-charging graphite anodes for lithium-ion batteries

The fast-charging technology of graphite anode has a great significance for developing electric vehicle. This review summarizes the current advancements and challenging perspectives of graphite anode for achieving fast-charging lithium-ion batteries.

Rejuvenation of aged graphite anodes from spent lithium-ion batteries via a facile surface treatment strategy.

In this study, we present a facile formic acid treatment to rejuvenate aged graphite anodes from spent lithium-ion batteries (LIBs) without damaging the electrode structure. This method effectively removes the interfacial blocking layer, improving capacity and rate performance. Our approach contributes to sustainable battery recycling strategies for spent graphite anodes in LIBs.

(Digital Presentation) Investigation of Solid Electrolyte Interphase Formation on Highly Oriented Pyrolytic Graphite Anodes in Lithium-Ion Batteries

Lithium-ion batteries (LIBs) are widely used in modern society. Since LIBs represent a substantial fraction and sometimes even majority of the device cost, extending the lifetime of LIBs and understanding their degradation mechanisms draw an increasing attention. Graphite, commonly used as the negative electrode in LIBs, suffers from two main degradation mechanisms: loss of active material and loss of lithium-ion inventory. Formation of the so-called solid electrolyte interphase (SEI) layer is known as the key factor for functioning of the anode. On the one hand, its growth covering the electrode surface slows down Li-ion intercalation. On the other hand, the SEI layer both protects the graphite particles from exfoliation upon intercalation and the electrolyte from decomposition by preventing organic molecules from entering graphite. Due to surface defects of the graphite particles used in common LIBs, it is challenging to observe the SEI layer formation. Therefore, highly oriented pyrolytic graphite (HOPG), which has a perfectly smooth surface, is commonly used in SEI formation experiments.In this work, we have applied electrochemical analysis, as well as morphology and structure characterization to investigate processes involved into the formation of SEI layer.A three-electrode electrochemical cell setup was installed in a glove box under inert argon atmosphere. HOPG was used as the working electrode and lithium metal was employed as both the reference electrode (RE) and counter electrode (CE). The electrolyte was composed of 1M lithium hexafluorophosphate (LiPF6) dissolved in 1:1 v/v mixture of ethylene carbonate (EC) and diethyl carbonate (DEC). Cyclic voltammetry (CV) was performed in voltage ranges of 2, 1.5, and 0.5 V versus Li/Li+. canning Electron Microscopy (Zeiss XB1540) and Atomic Force Microscopy (Ntegra Aura) were used to characterize the morphology and topography of the HOPG electrode after CV. X-ray Photoelectron Spectroscopy (XPS, Phoibos 150 1D-DLD, XR 50, Specs) was employed to measure the elemental composition and structure at the HOPG surface.When the cycling was performed between 3 – 2 V, small particles were observed on the surface of the HOPG, which can be assigned to the deposition of electrolyte. Homogeneous microspheres started to appear when the voltage reached below 1.5 V, which can be attributed to the formation of SEI particles. As the CV range increased, which also meant an increase in the depth of discharge (DOD), the density of microspheres on the surface increased as well. The diameter of the microspheres was found to be around 80 – 100 nm at a low lithiation level, and as the HOPG electrode became fully lithiated, the size of the particles slightly increased. This finding was supported by XPS measurements where the integral of the LixPFy and LixPFyOy peak, which is related to the main constituents of SEI layer, was found to be the largest (57.68% of the full F 1s spectra peak area) in the 3 – 0 V cycle range, while a lower peak (54.56%) was observed in the 3 – 0.5 V range (in the attached Figure).These results provide an indication of how the charging method affects the capacity fade and lifetime of the LIBs. The stage from 0.5 to 0 V on HOPG is approximately equivalent to 80-100% SOC for a full cell. As was found, in this stage, the SEI film grows thicker, thereby aggravating the aging of the cell. The lifetime of LIBs can therefore be extended if cycling at high SOC is avoided. Based on this, our future work will focus on the development of an optimized multi-step fast-charging method, which can reduce degradation and extend the lifetime of commercial lithium-ion batteries. Figure 1

Benefits of Tuned Binder Distribution in Multi-Layered Thick NMC811 Cathodes

Maximizing the electrode thickness is an inevitable target to reach when improving the energy density of Li-ion batteries [1,2]. Unfortunately, the fabrication of electrodes of several hundreds of micrometer thickness is often accompanied by detrimental side-effects. A critical process step in thick electrode production is the drying of the coated layer. During the evaporation of the solvent, light components of the slurry such as binder and carbon black can be dragged to the top of the coating [3,4]. The lack of liquid linkage throughout the layer leads to binder particles being evenly spread across the coating after the drying process is concluded. Inhomogeneous distribution of binder can not only cause delamination, but also negatively influences the Li-ion transport pathways through the electrode. To ensure ideal mechanical stability and satisfactory electrochemical performance, binder migration needs to be suppressed effectively.Multi-layering has proven itself as a technique within aqueous processing to overcome the limitations arising for thick electrodes. Subsequent coating of layers offers opportunities to establish selective material compositions at specific regions within the electrode (Figure 1a). This novel coating method can be considered a steppingstone to further optimize high loading electrodes. We have previously demonstrated that by multi-layering an increase of 40% in adhesion can be achieved compared to single-layer electrodes. Moreover, the assembled cells show superior performances at rate capability tests. Especially for low current densities (0.2C) an increase of up to 20% in specific discharge capacity was reached through multi-layering (Figure 1b) [5].Within aqueous electrode fabrication, the use of sodium carboxy-methyl cellulose (CMC) as binder material is common, due to its role as a thickening agent of the slurry and solubility in water. However, due to its brittleness, the usage of CMC requires additional binders to maintain flexibility of the coating. The ratio of active and inactive materials within the cell is strongly correlated to its capacity and the addition of these binders ultimately results in a decreased energy density of the cell. Besides keeping the particles together, the main purpose of the binder is to guarantee good adhesion to the substrate. Therefore, a high concentration is not necessarily needed at the top of the coating and the overall amount of binder material should be kept at a minimum.Bi-layered cathodes consisting of Ni-rich lithium nickel manganese cobalt oxides (NMC811) as active material were fabricated. The concentration of poly(methyl)acrylate (PMA) binder was changed in the top layer and its effect on structural properties and electrochemical performance was investigated. Water-based processed cathodes with high loadings of more than 8 mAhcm-2 were tested in full cell configurations.Reduction of the binder content leads to an increase in specific discharge capacity of up to 40% compared to single-layered and 25% to unmodified multi-layered electrodes at a C-rate of 1C (Figure 1b). Acknowledgements This work was financially supported by the Austrian Federal Ministry for Climate Action, Environment, Energy, Mobility, Innovation and Technology (bmk).[1] Z. Du, D.L.W. Iii, C.D.S. Kalnaus, J. Li, Understanding limiting factors in thick electrode performance as applied to high energy density Li-ion batteries, J. Appl. Electrochem. 47 (2017) 405–415. https://doi.org/10.1007/s10800-017-1047-4.[2] Y. Kuang, C. Chen, D. Kirsch, L. Hu, Thick Electrode Batteries: Principles, Opportunities, and Challenges, Adv. Energy Mater. 9 (2019). https://doi.org/10.1002/aenm.201901457.[3] F. Font, B. Protas, G. Richardson, J.M. Foster, Binder migration during drying of lithium-ion battery electrodes: Modelling and comparison to experiment, J. Power Sources. 393 (2018) 177–185. https://doi.org/10.1016/j.jpowsour.2018.04.097.[4] M. Müller, L. Pfaffmann, S. Jaiser, M. Baunach, V. Trouillet, F. Scheiba, P. Scharfer, W. Schabel, W. Bauer, Investigation of binder distribution in graphite anodes for lithium-ion batteries, J. Power Sources. 340 (2017) 1–5. https://doi.org/10.1016/j.jpowsour.2016.11.051.[5] L. Neidhart, K. Fröhlich, N. Eshraghi, D. Cupid, F. Winter, M. Jahn, Aqueous Manufacturing of Defect-Free Thick Multi-Layer NMC811 Electrodes, Nanomaterials. 12 (2022) 1–15. https://doi.org/10.3390/nano12030317. Figure 1

Benchmarking the Electrochemical Degradation Behavior of Aluminum Foil Anodes for Lithium-Ion Batteries

Aluminum is an attractive candidate for replacing graphite anodes in lithium-ion batteries because it has high specific capacity (990 mAh g-1), and directly using aluminum foil as the anode structure eliminates the need for slurry-coating processes. However, achieving highly reversible lithiation and delithiation of aluminum is challenging due to volume changes during transformation, sluggish lithium-ion transport through the surface oxide layer, and poor initial Coulombic efficiency which all lead to degradation during cycling. Previous studies have focused on understanding the fundamental electrochemical reaction and material transformation behaviors of aluminum, yet there has not been a focus on how different aluminum alloy compositions behave and degrade under electrochemical cycling conditions. In this work, we carry out comprehensive electrochemical testing to benchmark the performance of three different aluminum alloy foils under different cycling conditions. We found that for foils of constant thickness, all foil compositions exhibit a power-law dependence of cycle life on the areal capacity lithiated per cycle, revealing that degradation is significantly accelerated when high areal capacities are used each cycle. Furthermore, the composition of the aluminum alloy was found to strongly affect the Coulombic efficiency over the first 10 cycles, with higher purity foils exhibiting higher Coulombic efficiency. Finally, ex situ scanning electron microscopy and operando optical microscopy revealed different reaction mechanisms and mechanical degradation behavior amongst the different alloys. Based on understanding these various parameters, we showed how full cells with aluminum anodes can be cycled for hundreds of cycles at relatively low areal capacities. The improved understanding of the behavior of aluminum foil anodes herein paves the way for future work intended to engineer aluminum-based foils with enhanced stability.

Diazotization Grafting Phenol for Improving the Electrochemical Performance of Graphite Anode

Capacity fading resulting from graphite exfoliation is a thorny problem for real application of the graphite anodes in lithium-ion batteries. In this paper, we report on diazotization grafting phenol for graphite flakes to settle this issue, using 4-aminophenol and tert-butyl nitrite as the diazonium reagents. Diazotization grafting phenol enables expansion of graphite interlayer spacing and formation of surface protective layer, yielding modified graphite anodes with improved electrode kinetics, and significantly improved cycling stability. Also, the phenol modifier contributes additional specific capacity to the anode through reversible redox reaction of phenol hydroxyls with Li+ ions. The modified graphite anode with mole percent of 4-aminophenol to graphite being 5% retains a discharge specific capacity of 361 mA h g‒1 after 300 cycles at 1C, presenting capacity retention of 90.5% relative to the initial cycle, much higher than that of 156 mA h g‒1 and 54.2% for pristine graphite.

Multi-scale study on a synergetic multimetal-based selenide anode with nitrogen-doped porous carbon support for high-performance lithium storage

Transition metal selenides (TMSes) are promising substitutes for graphite anode for lithium-ion batteries (LIBs). The deficiency of rational strategies to solve the issues of intrinsic activity, synergistic sites deficiency, and structural simplicity for TMSes restricts their application in LIBs. Herein, a hierarchical multi-metal (Fe, Co) modified nanorod-like selenide with nitrogen-coordinated porous carbon support (CoFeSe/NC) is synthesized to intensify the intrinsic activity and structural stability of the derived material via a well-designed Fe-doped ZnCo-based multi-metal organic framework as a precursor. Profiting from the synergistic effect of the N-coordinated porous carbon support, multi-metal components, and well-retained integrated architecture, the CoFeSe/NC anodes exhibit exceptional electrochemical performances with a discharge capacity retention of 775 mAh g −1 after 50 cycles at 0.2 A g −1 and ultralong cycling stability (423 mAh g −1 at 3 A g −1 up to 1000 cycles). Further detailed kinetic analysis and in situ and ex situ characterizations indicate the improved electrochemical kinetics compared to the single-metal selenides and elucidate the lithium storage mechanism of the CoFeSe/NC anodes. This work is expected to offer a guideline to construct the multi-component material with controllable intrinsic activity and induce the rapid kinetic of high-capability anodes. • A hierarchical multi-metal (Fe, Co) modified nanorod-like selenide are constructed. • Multi-metal selenides exhibit exceptional electrochemical performances. • The superior performance arise from the synergistic effect of the N-coordinated porous carbon and multi-metal components. • The adsorption and storage of Li + ions on CoSeFe/NC is more favorable and abundant than that on CoSe/NC.

Controllable self-assembled flower-like FeS with N-doped carbon coating anchored on S-doped reduced graphene oxide as high-performance lithium-ion battery anode

Iron sulfide (FeS) was supposed to be a suitable substitute for the commonly used graphite anode in lithium-ion batteries due to its higher specific capacity. However, its electrochemical property was severely limited due to its weak conductivity and evident volume change. To address these issues, we successfully construct controllable self-assembled flower-like with N-doped carbon coating FeS anchored on S-doped reduced graphene oxide (FeS/C@rGO) nanocomposites, used the synthesized octahedron iron-based metal-organic framework and graphene oxide composite (Fe-MOF@GO) as the precursor and thioacetamide as the sulfur via high-temperature calcination. The flower-like structure was generated by the controllable self-assembly of FeS nanosheets following an octahedral collapse, which enhanced the contact area between the active material and the electrolyte and improved Li+ transmission efficiency. Furthermore, the N-doped carbon and rGO efficiently inhibits the volume growth and aggregation of FeS nanosheets, resulting in the fabrication of controllable self-assembled flower-like FeS/C@rGO with a stable structure and outstanding rate performance. The discharge capacities of the FeS/C@rGO electrode were 1446.3, 1379.4, 1266.7, 1179.2, 1097.5 and 980.7 mAh g−1 at different current densities of 0.1, 0.2, 0.5, 1.0, 2.0 and 5.0 A g−1, respectively. When the current density returns to 0.1 A g−1, the reversible capacity is restored to 1629.7 mAh g−1. Moreover, the reversible specific capacity of FeS/C@rGO anode was 1428.2 mAh g−1 (130 cycles) at 0.1 A g−1 current density, showing excellent cycling performance.

Effect of Disorder and Doping on Electronic Structure and Diffusion Properties of Li3V2O5

V2O5 in its ω phase (Li3V2O5) with excess lithium is a potential alternative to the graphite anode for lithium-ion batteries at low temperature and fast charging conditions owing to its safer voltage (0.6 V vs Li+/Li(s)) and high lithium transport rate. In-operando cationic disorder, as observed in most ordered materials, can produce significant changes in charge compensation mechanisms, anionic activity, lithium diffusion, and operational voltages. In this work, we report the variation in structural distortion, electronic structure, and migration barrier accompanied by disorder using first-principles calculations. Owing to the segregation of lithium atoms in the disordered state, we observe greater distortion, emergence of metallic behavior, and potential anionic activity from nonbonding oxygen states near the Fermi level. Redox capacity can be tuned by doping with 3d metals, which can adjust the participating cationic states, and by fluorine substitution, which can stabilize or suppress anionic states. Moreover, the suppression of anionic activity is found to decrease structural distortion, which is crucial for mitigating voltage fade and hysteresis. Diffusion barrier calculations in the presence of disorder indicate the activation of the remaining 3D paths for lithium hopping which are unavailable in the ordered configuration, explaining its fast-charging ability observed in experiments.

On the connection between slurry rheology and electrochemical performance of graphite anodes in Lithium-ion batteries

Many current lithium-ion battery anodes are prepared from a slurry containing graphite, polyvinylidene fluoride (PVDF), n-methyl-2-pyrrolidone (NMP), and small amounts of conductive carbon black (CB). The rheology of this four-component slurry is an important indicator of its microstructure, that affects the structure of the dried electrode. This in turn has consequences on the electrochemical performance of the anode. We modulate the rheology of the slurry by choosing three different commercially available carbon blacks that are used in lithium-ion batteries and establish a connection between slurry rheology and electrochemical performance. We show that the storage modulus is the key factor that impacts the electrochemical performance.

Computation-Based Investigation of Motion and Dynamics of Lithium in Phase Separated Silicon-Oxide Anode Materials

Si attracts significant attention as an alternative anode material to replace the conventional graphite anode in lithium-ion batteries (LIBs). Si offers extremely high theoretical energy-storage capacity of 4200 mAh/g for Li4.4Si, while the theoretical energy-storage capacity of graphite is only 372 mAh/g for Li/C6. In addition, Si is abundant, eco-friendly, and non-toxic, and it also has a safe thermodynamic potential with an average voltage of about 0.4 V vs. Li+/Li, making them attractive candidates for LIB anodes. However, the capacity of the Si anode exhibits a relatively high initial charge capacity and then rapidly decreases as the charge/discharge cycle proceeds, hampering its extensive application. This rapid performance degradation can be attributed to the poor connection between the active material and the current collector resulting from the severe volume expansion and contraction of the Si particles during the repeated charge and discharge cycles, respectively.Controlled addition of O to Si is often taken as a viable approach to utilize Si as an anode material. Silicon suboxides (SiOx, 0 < x < 2), compared with Si, offer a low energy capacity but a high stability against volume expansion. As a result, silicon monoxide (SiO) anodes are indeed commercialized by being blended with graphite. However, only low amounts (about 5 wt%) of SiO are blended with graphite because of the poor first cycle efficiency of SiO. During the charge process, SiOx reacts with Li and produces in-situ byproducts such as Li2O and Li-silicates, which are irreversible in following discharge cycles. This irreversible Li consumption is known to decrease the initial Coulombic efficiency (ICE) of SiO, typically below 75%. The low ICE of SiOx along with its inherently poor electronic conductivity leads to poor rate performance and increased capacity decay, hindering its substantial application in LIBs. To realize more extensive application of SiOx for LIB anodes, physical properties of SiOx should be improved in a direction to mitigate the low ICE issue.In this study, we investigate the motion and dynamics of a Li atom in SiOx by performing a series of first principles-based atomistic simulations. To this end, we perform Monte Carlo simulations within a continuous random network model to generate realistic SiOx structures with varying O-to-Si ratios. Then, we implement a density-functional theory calculation-based path sampling scheme to obtain detailed thermodynamic information when a Li atom penetrates a SiO matrix. Subsequent electronic structure analysis reveals that the thermodynamic stability of a Li atom is determined by local Si-O network environment surrounding Li. The identified thermodynamic information regarding the Li dynamics in SiO provides additional insight into the origin and solutions of the low ICE, highlighting the importance of controlling the SiO morphology during the synthesis of SiO. This fundamental understanding can be an important theoretical basis for developing practically applicable high-ICE silicon suboxide-based anode materials. Figure 1

Improving cycle life and rate capability of artificial graphite anode for lithium-ion batteries by agglomeration

For lithium-ion batteries (LIBs), the cycle life and ratecapability are of great importance to make practical use in electric vehicles (EVs). Therefore, it is essential to develop anode materials with excellent cycle life and superior ratecapability. In this work, agglomerated graphite (AG) was prepared by agglomerating small-sized coke particles into big particles and subsequent graphitization. The obtained AG exhibits much-improved cycle life and ratecapability for LIBs in comparison with pristine graphite (PG). Meanwhile, orientation intensity, which is defined as the ratio of (004) peak intensity to (110) peak intensity in graphite anode plates X-ray diffraction pattern (XRD), is proposed to evaluate the cycle performance and ratecapability of graphite for LIBs.