Li-ion Battery Electrodes Research Articles

Properties of Layered TMDC Superlattices for Electrodes in Li-Ion and Mg-Ion Batteries.

In this work, we present a first-principles investigation of the properties of superlattices made from transition metal dichalcogenides for use as electrodes in lithium-ion and magnesium-ion batteries. From a study of 50 pairings, we show that, in general, the volumetric expansion, intercalation voltages, and thermodynamic stability of vdW superlattice structures can be well approximated with the average value of the equivalent property for the component layers. We also found that the band gap can be reduced, improving the conductivity. Thus, we conclude that superlattice construction can be used to improve material properties through the tuning of intercalation voltages toward specific values and by increasing the stability of conversion-susceptible materials. For example, we demonstrate how pairing SnS2 with systems such as MoS2 can change it from a conversion to an intercalation material, thus opening it up for use in intercalation electrodes.

High-speed slot-die coating of primer layers for Li-ion battery electrodes: model calculations and experimental validation of the extended coating window depending on coating speed, coating gap and viscosity

In the battery industry, very thin primer layers are used to improve electrode adhesion on substrates or act as blocker layers to prevent corrosion in case of aqueous cathodes. For these material configurations, high-speed coating is mandatory to ensure the economic viability of the process. One way to realize high-speed coating is a set-up including a slot die and a vacuum box to stabilize the coating bead. Knowledge and prediction of the coating window of thin wet film thicknesses is crucial to design the production process. Therefore, the influence of coating gap and viscosity of shear-thinning fluids on the coating window is investigated with the help of various model fluids. In addition, a prediction model for the calculation of the coating window for high-speed slot-die coating with vacuum box is developed. This model is shown to be valid for the prediction of the coating window for the investigated material systems and coating gaps over the investigated range of coating speeds up to 500 m min−1. For a material system, which corresponds to a real material system for adhesive primer coatings, it is possible to reach a target wet film thickness of 20–25 µm. This would correspond to a layer thickness of 0.5 µm for a solid content of 2–2.5 wt%.

Characterization of ultrafast-laser ablation of micro-structures in Li-ion battery anode and cathode materials: Morphology, rate, and efficiency

Characterization of the rate and quality of ultrafast-laser ablation of Li-ion battery (LIB) electrode materials is presented for a collection of common and next-generation electrodes. Laser ablated micro-structures on the surface of LIB electrodes have been shown to provide dramatic enhancement of high-rate capability and electrode wetting. However, industrial adoption is hampered by a lack of data enabling informed choice of laser parameters and predicting process throughput. This work bridges this gap by providing characterization of the ablation process at more laser parameters (laser fluence and number of pulses used) than are currently available in the literature. Further, we expand on previous graphite and lithium iron phosphate (LFP) ablation work by extending ablation characterization to new LIB materials, providing high data resolution and adopting new characterization metrics which are relevant for industrial application of this technology. Ablated pores are characterized by their ablated depth, volume, and how the depth and volume ablation rate changes as a function of pore depth. Finally, we provide a detailed characterization of the morphology of laser ablated micro-structures which informs how material and laser parameters affect the quality of laser-processed electrodes.

Solvent-free NMC electrodes for Li-ion batteries: unravelling the microstructure and formation of the PTFE nano-fibril network

The microstructure and electrochemical performance of solvent-free processed and slurry cast Li(Ni0.6Co0.2Mn0.2)O2 (NMC622) based electrodes for Li-ion batteries has been investigated. In contrast to a moss-like PVDF-based carbon binder domain in slurry cast electrodes, the PTFE binder in solvent-free electrodes had a hierarchical morphology composed of primary fibrils of a few µm in diameter and 100’s µm in length that branched into secondary and then ever finer fibrils, down to diameters of 10s nm or below. A mechanism for the formation of the branch-like morphology observed in PTFE-based solvent-free electrodes is also presented. Even the finest fibrils were confirmed to survive typical cathode cycling conditions. The solvent-free electrodes showed progressive improvement in capacity with increasing charge-discharge rate (up to 150% at 2C) compared with slurry cast equivalents. The capacity of solvent-free electrodes faded 40% slower over 200 cycles at C/3. Impedance analysis showed the solvent-free microstructure enabled reduced charge transfer resistance and ionic resistance, arising from minimal obscuration of the active material surface and no pore blockage.

ZnO-PANI nanocomposite: Enhanced electrochemical performance towards energy storage

In the present investigation a novel nanocomposite composed of Polyaniline (PANI) and Zinc Oxide (ZnO) has been evaluated for its structural, morphological, and electrochemical properties for its application as high-performance Li-ion battery electrode. The X-ray diffraction (XRD) and Furrier transform infrared (FTIR) spectral analysis confirmed the synthesis of ZnO-PANI nanocomposite. The Field emission- scanning electron microscopy (FE-SEM) images confirmed the uniform distribution of ZnO nanoparticle in PANI matrix, while BET surface area analysis revealed a narrow mesoporous pore distribution with high surface area, enhancing its potential for energy storage. The electrochemical assessment using CR2032 coin cells showcased the remarkable performance of the ZnO-PANI nanocomposite as an electrode material for energy storage. Cyclic voltammetry (CV) analysis revealed distinct reduction and reformation peaks related to ZnO and Li+ insertion into the PANI matrix. The nanocomposite displayed a high specific capacity, with an initial discharge capacity of 1052 mA h g−1, followed by stable performance in subsequent cycles. Notably, Coulombic efficiency consistently exceeded 98 % from the 10th cycle, demonstrating excellent performance. The rate capability was equally impressive, delivering discharge capacities from 1052 mA h g−1 at 0.1C to 771 mA h g−1 at 2C. Long-term cycling tests illustrated exceptional capacity retention, with 92.99 % capacity retained after 500 cycles and outstanding Coulombic efficiency consistently above 99 %. In conclusion, the ZnO-PANI nanocomposite exhibits desirable structural and morphological attributes, exceptional electrochemical performance, and potential for advanced energy applications, particularly in Li-ion batteries.

Carbon-doped titanium dioxide (TiO2) as Li-ion battery electrode: Synthesis, characterization, and performance

Development of lithium-ion batteries (Li-ion batteries) with high safety and solidity features has become a main challenge of researchers when practical implementations for large-scale energy storage systems are prioritized. In this work, we introduce a useful and efficient strategy to manufacture a long-standing and high-rate carbon-doped TiO2 (C-TiO2) as an anode material. Titanium (TiO2) and C-TiO2 were successfully prepared through hydrothermal method in order to improve the electrical performance of Li-battery. The structure and thermal properties were investigated by XRD, Raman and TGA; whereas the electrical properties were evaluated by Glvanostatic discharge–charge measurements. The density function theory (DFT) results revealed that TiO2 doped with carbon atoms causes considerable stress inside the crystal lattice of TiO2, and to avoid or minimize this stress the lattice of TiO2 underwent relaxation and then optimized. The performance of the prepared electrodes in Li-battery was analyzed by 100 cycles at different calcination temperatures of 400 and 450 °C. The results also showed the charge capacities of 400 and 500 mAhg−1 at 100 mAg−1.

Results from Exploratory Work in Li-Rich Regions of the AE-Li-Ge Systems (AE = Ca, Sr, Ba)

The compounds AELi2Ge (AE = Ca, Sr and Ba) were synthesized, and their structures were determined as a part of the exploratory work in the Li-rich regions of the respective ternary systems. The three compounds are isostructural, and their crystal structure is analogous with the orthorhombic structure of BaLi2Si and KLi2As (space group Pmmn). The atomic arrangement can be viewed as an intergrowth of corrugated AEGe layers, alternated with slabs of Li atoms, suggestive of the possible application of these phases as electrode materials for lithium-ion batteries. Both experimental electronic density and calculated electronic structure suggest the existence of Li–Li and Li–Ge interactions with largely covalent character. Despite that, the valence electrons can be partitioned as (AE2+)(Li+)2(Ge4–), i.e., the title compounds can be viewed as valence-precise Zintl phases. The band structure calculations for BaLi2Ge show that a bona fide energy gap in the band structure does not exist and that the expected poor metallic behavior is originated from the AEGe sub-lattice and related to hybridization of Ba5d and Ge3p states in the valence band in proximity of the Fermi level. In addition, electrochemical measurements indicate that Li atoms can be intercalated into CaGe with a maximum capacity of 446 mAh/g, close to the theoretical value of 480 mAh/g of CaLi2Ge, which reveals the possibility of this Li-rich compound to be used as an electrode in Li-ion batteries.

Visualization of Lithium Plating Morphologies on Graphite Electrode By O perando X-Ray Tomography

The plating of lithium metal on graphite electrodes in Li-ion batteries is a major factor limiting the fast charging of electric vehicles. Lithium metal plating leads to the growth of dendritic structures that can pierce through the battery’s separator resulting in an internal short circuit and catastrophic failure of the battery. Moreover, the plating of lithium metal on graphite is not reversible, manifesting in poor Coulombic efficiency, severe reduction of the battery’s life expectancy, and safety issues. Understanding how and when plating occurs in Li-ion batteries is crucial in the development of strategies to prevent plating under fast charging conditions. Thus, we have conducted an operando X-ray tomographic microscopy experiment to directly monitor the plating of lithium metal in a Li/Graphite cell when applying electrolytes with the additives vinylene carbonate (VC) and Lithium bis(fluorosulfonyl)imide (LiFSI). The experiment was performed at the ID19 beamline (ESRF, France) where tomographic scans, linked with the lithiation state of graphite, made it possible to gain a strong understanding of the mechanisms behind Li-deposition and stripping at high current rates in addition to understand the effect of the VC and LiFSI additives.

Revisiting Tin Oxide: A Systematic Investigation of Performance As a Function of Particle Size, Dopant and Electrolyte

The reliable application of conversion and alloying materials as high capacity electrodes in Li-ion batteries has been a mostly elusive ambition for nearly 30 years. The most notable successes being the commercialisation of the Tin based Nexelion™ chemistry by Sony in 2005, and the current commercialisation of Si and SiOx materials as anode additives today. Despite the relatively narrow scope of commercialised systems however, the scientific literature remains vibrant on this topic, spurred on by the allure of specific capacities in excess of 1000mAh/g.The limitations of conversion systems are well known: Extremely poor first cycle efficiencies, large voltage hysteresis, wide voltage windows and generally poor cyclability arising from the massive morphological changes during cycling. Nanostructuring is widely regarded as the best route to mitigating these problems, and the literature is accordingly rich with complex and “photogenic” nanostructures and composites demonstrating greatly improved performance. These are however often produced by routes which are difficult to scale.Within the SMICE-Li project we have been revisiting conversion and conversion-alloy materials with an inherently scalable synthesis route: Flame Spray Pyrolysis. This involves the continuous combustion of an atomised spray of combustible precursors and yields an inherently nanoscaled product which can be controllably grown and modified with post-synthesis thermal annealing.We will present the results of a systematic study into doped SnO2 as a function of dopant, particle size, cycling voltage window and electrolyte formulation. Clear differences in cyclability are observed for SnO2 just by altering particle size from ~7nm to ~25nm, but these may be suppressed by the addition of dopants. Clear performance differences between dopants (Ni, Fe, Co, Mn; Ti) are also found, with results replicated across a range of organic-carbonate and ionic liquid electrolyte compositions. For all compositions the Sn-SnO2 Conversion reaction is seen to be the major source of capacity fade, but some dopants stabilise the Sn-LixSn alloy reaction whilst others do not. Restricting the voltage cycling window to limit cycling to only the alloy reaction greatly improves cyclabilty in all compositions, and for the best performing compositions, stable cycling with capacity retention in excess of 450mAh/g is achieved after 300 cycles.

Understanding the Drying Process and Mud Cracking of Li-Ion Battery Electrodes through Synchrotron X-Ray Computed Tomography

The drying process of slurry cast Li-ion battery electrodes is a subject with significant impacts on the performance of the battery but where detailed understanding is lacking(1). Mud cracking, opening of cracks in the surface due to stress from the slurry shrinking as it dries, is the most dramatic phenomenon during the process. Cracks may be detrimental to electrode performance due to delamination, which makes sections of the electrode unusable, or generally poor electrode cohesion. However, cracks could provide channels for ion transport to deeper levels of the electrode, similar to templated electrodes (2) but without the extra manufacturing steps. Cracking is prominent in thick (3-5) or water processed electrodes (3), which are desirable for greater energy density and replacement of the toxic solvent N-methyl pyrrolidone (NMP), respectively. Thus, understanding mud cracking during drying can lead to more energy dense (thicker), greener (without toxic NMP), and better performing electrodes (fast charging).Li-ion electrodes are industrially produced by casting a slurry on a metal foil current collector by a slot die or doctor blade method in a roll-to-roll machine. In the case of the positive electrode this slurry typically contains active metal oxide (e.g. LiNiMnCoO2, LiNi0.6Mn0.2Co0.2O2) particles, polyvinylidene fluoride (PVDF) binder, and carbon black. Drying is composed of three stages illustrated in Fig. 1 a-d, with the binder, carbon black settling and migrating at random (1),(6, 7). Crack formation is thought to occur during the third stage when capillary forces cause stress in the drying slurry opening cracks as solvent menisci form between particles. However, the process of crack nucleation and their 3-dimensional growth has never been directly observed in-situ(1),(4). X-ray computed tomography (Fig. 1 f-j) is able to show the morphology of cracks in an electrode and can be used to characterize properties like delamination, crack volume, crack network connectedness or crack network tortuosity, which can be linked to electrode performance. However, to understand how these crack networks form requires observation of the time evolution of the cracks and the movement of active material particles near the cracks, which requires fast measurements. Here, we present synchrotron x-ray computed tomography of drying electrode which enable the fast measurements required and allows us to more fully explain mud cracking in drying electrodes, and the drying process in general.References Y. S. Zhang, N. E. Courtier, Z. Zhang, K. Liu, J. J. Bailey, A. M. Boyce, G. Richardson, P. R. Shearing, E. Kendrick and D. J. L. Brett, Advanced Energy Materials, 2102233 (2021). C. Huang, M. Dontigny, K. Zaghib and P. S. Grant, Journal of Materials Chemistry A, 7, 21421 (2019). Z. Du, K. M. Rollag, J. Li, S. J. An, M. Wood, Y. Sheng, P. P. Mukherjee, C. Daniel and D. L. Wood, Journal of Power Sources, 354, 200 (2017). B. Lu, C. Ning, D. Shi, Y. Zhao and J. Zhang, Chinese Physics B, 29, 026201 (2020). R. Sahore, D. L. Wood, A. Kukay, K. M. Grady, J. Li and I. Belharouak, ACS Sustainable Chemistry & Engineering, 8, 3162 (2020). S. Jaiser, L. Funk, M. Baunach, P. Scharfer and W. Schabel, Journal of Colloid and Interface Science, 494, 22 (2017). Y. S. Zhang, A. N. Pallipurath Radhakrishnan, J. B. Robinson, R. E. Owen, T. G. Tranter, E. Kendrick, P. R. Shearing and D. J. Brett, ACS Applied Materials & Interfaces, 13, 36605 (2021). Figure 1

(Invited) Challanges with Novel Binders for LiNi0.5Mn1.5O4 li-Ion Battery Electrodes

In the search for high-energy density Li-ion battery electrode materials which are also comparatively sustainanble, LiNi0.5Mn1.5O4 (LNMO) is often targeted as a promising next-generation alternative. While the capacity of LNMO is limited, it has a high operating voltage around 4.7 V vs. Li+/Li, and the spinel structure of the materials renders useful power capacilities. Moreover, it is a cobalt-free cathode. However, fabricating functional electrodes have shown problematic due to inherent instabilities at both bulk and surfaces, where especially operation at elevated temperatures has shown to cause capacity degradation. Problems comprise structural changes, loss of oxygen, and Mn dissolution, often interconnected with each other. One strategy to improve stabilization would be through coatings of the LNMO particles, either inorganic or organic.The polymer binder used for battery processing is inherently an organic coating layer, since it wraps around the particles of the electrodes. Thereby, binders has been shown to being able to add functionalities to electrode materials, e.g. to improve electronic conductivity, add storage capacity or mitigate side-reactions. The binder is at interplay with the reactions causing interphase layer formation. Thereby, changing or taioring the binder can cause direct improvements in cell performance.Poly(vinylidene difluoride) (PVdF) and its many derviates is since long time the standard for Li-ion battery electrodes, despite not being particular sustainable and being dependent on toxic solvents such as N-methyl-2-pyrrolidone (NMP). LNMO is, in this context, no exception. Nevertheless, while PVdF is chemically intert, it provides little other capabilities to the battery electrodes, and other binder systems could improve in this context: either through electochemica performance or through being more sustainable.Here, two other binder systems for LNMO are discussed: polyacrylonitrile (PAN) and polyacrylic acid (PAA). Polynitriles are often promoted as being comparatively stable at higher potentials, while also being ionically conductive, and should therefore in principle add functionalities into the resulting electrodes. PAA, on the other hand, has shown good adhesion and adherence to oxide surfaces, and can thereby form more robust interfacial layers on the cathode. We show here, however, that challenges remain for these alternative binder systems, not least due to the high operating potential of LNMO electrodes which cause side-reactions of both types of alternative binders. These side-reactions are their products are analyzed through a range of methods, e.g. photoelectron spectroscopy, electron microscopy and electroanalytical techniques, thereby providing guidance to the development of novel binders for high-voltage electrodes.

Numerical Simulation of Spatial Atomic Layer Deposition on Moving Substrates with Microgrooves and Porous Structures

The need of ultrathin and highly conformal coatings on large-area microstructure substrates such as photovoltaic cells, flexible displays, and Li-ion battery (LIB) electrodes has driven the development of high-efficient ALD. Spatial ALD is a promising high-throughput technique capable of producing ultrathin films on large substrates, which can reach up to two orders of magnitude faster than temporal ALD. However, spatial ALD is a complex and strong-coupled process of fluid flow, heat and mass transfer, as well as chemical reactions. Compared to the flat substrate, the diffusion process in the microstructures takes longer, limiting the substrate velocity and the deposition rate. In this work, spatial ALD on moving microgroove substrates and porous LIB electrodes are quantitatively studied through the multiscale modelling method by coupling computational fluid dynamics (CFD) with chemical kinetics. Dynamic mesh method is implemented to simulate the ALD reaction with the in-line movement of the substrate. Results show that the vortices always exist in the micro-gap with microgroove substrates. Besides, the top of the microstructure on the first contact with the precursor is the highest, and the surface coverage at the corner on the other side of the microstructure is the lowest. For porous LIB electrodes with large specific surface area, the film coating depth is limited by both the low precursor diffusion rate and the amount of precursor supply. Increasing the carrier gas flow rate increases the film coating depth by increasing the precursor supply over the same time period. Besides, the gas byproduct of ALD remaining at the electrode bottom can be more effectively removed. Quantitative process optimizations of substrate velocity and precursor concentration for different electrode structures are also carried out. It is found that the electrode gradient design with higher porosity on the top is beneficial for obtaining deeper coating depth and higher precursor utilization compared to the inverse gradient design. The present multiscale modeling work provides a comprehensive understanding and important guidance for the industrial application of the spatial ALD process on microstructure substrates.

Operando Ambient Pressure X Ray Photoelectron Spectroscopy for Li-Ion Battery Electrode/Electrolyte Interface Probing

Electrochemical reactions occur at the electrode/electrolyte interface. In lithium-ion batteries, the reversible Li ion insertion/desertion from the interfaces of electrodes gives the capacity of the battery. The surface phase transition and component chemical states change during the lithiation/delithiation in turn hugely effect the further battery capacity and reversibility. In the past decades, many ex-situ characterizations gave some insights of electrode surface behavior after cycling. However, the surface chemistry of electrode relies decisively on the real battery operation condition, e.g. the passive layer formed on the electrode surface changes dramatically with the absence of electrolyte. Therefore it is emerging and necessary to develop operando study for electrode/electrolyte interface probing during battery cycling.X-ray photoelectron spectroscopy (XPS) as a surface sensitive technique detects the photoelectrons ejected from core level with certain pass energy. The binding energy of the electrons give the information of chemical composition and chemical states of the materials. Ambient pressure XPS, developed rapidly in recent years after since it gives possibility of the participation of gas and/ liquid phase, enabling the observation of structure dynamics during chemical reactions, thereby unprecedentedly extended the application of the technique. A method called dip-and-pull is used for operando liquid/solid interface probing. With a typical three-electrode system, the electrode is pulled up from the electrolyte with still contact to liquid to maintain the circuit. A thin film of electrolyte formed with a shape of meniscus at the interface of electrode, electrolyte and atmosphere is probed through. The probing of the electrochemical active surface through the liquid can be achieved with an optimized liquid layer and surface condition.In this study Lithium cobalt oxide (LCO), as the most widely used positive electrode for Li-ion battery with rock salt layered structure optimized for reversible Li intercalation/deintercalation, is used for interface dynamics investigation. As Li is deintercalated from LCO structure, the charge transfer from Li+ to Co-O environment causes a phase change. It was commonly assumed that the charge due to the deintercalation of Li from structure is fully transferred to Co3+, i.e. the loss of one electron contributes to one Co4+ from Co3+ oxidation. However, it is recently reported that the real condition maybe more complicated. The charge transfer from Li+ to Oa- (a<2) might take place especially during high voltage due to the hybrid fermi level of O and Co which might increase the mobility of Oa- and further results in cobalt reduction and oxygen evolution reaction. But the mechanism of structure evolution under corresponding potentials are very unclear. In this study, with the operando probing with APXPS, it is discovered that a native phase of Co2+ may play an unignorable role in the charge transfer, giving some new understandings of phase transition during lithiation/delithiation (see figure 1). With the development of APXPS for battery probing, combining with software data treatment, a clearer picture of phase evolution is possible to be given by time-resolved probing with APXPS. Potentially hidden intermediate states during electrochemical reactions which cannot be given from ex-situ probing are resolved. Figure 1

(Invited) Advanced Photoelectron Spectroscopy on Battery Materials: Lessons Learnt on Silicon- Containing Electrodes

While Silicon (Si) is being incorporated more and more as an active material in commercial lithium-ion batteries, it is still a topic of intense research and the motivation for these research efforts remains unchanged: Silicon’s large volume expansion during cycling leads rapid capacity fading largely associated with changes in the Si surface chemistry and unstable solid electrolyte interphase (SEI). Using advanced photoelectron spectroscopy (PES) characterization, we have investigated crucial interfaces on Si model systems and Si-containing negative electrodes for Li-ion batteries. Here, we focus on two approaches to influence the SEI composition intrinsically: Binders and electrolytes.Starting with pristine Si powders, we studied the effect of carboxylic acids as electrode slurry additives on the Si surface chemistry before and after electrochemical cycling [1] using synchrotron PES depth profiling. Further, we used photoelectron spectroscopy to confirm cross-linking in poly-acrylic acid-based binder for Si electrodes and showed that the cross-linking agent pentaerythritol had no negative effect on the SEI thus attributing improved cycling performance to increased binder cross-linking [2].In silicon/graphite negative electrodes, we used PES to elucidate the influence of fluoroethylene carbonate (FEC) on the degradation phenomena in electrodes with varying silicon content [3]. Finally, photoelectron spectroscopy provided insights into what happens to the SEI on Si-containing electrodes if we replace the classical electrolyte solvent ethylene carbonate with either FEC or glyoxylic acetal-based alternatives [4, 5].[1] F. Jeschull, H.Q. Pham, A. Ghamlouche, P.K. Thakur, S. Trabesinger, J. Maibach, J. Phys. Energy 2023, 5 (2), 025002. https://doi.org/10.1088/2515-7655/acbbee.[2] J. He, C. Das, F. Yang, J. Maibach, Electrochimica Acta 2022, 411, 140038. https://doi.org/10.1016/j.electacta.2022.140038.[3] A. Ghamlouche, M. Müller, F. Jeschull, J. Maibach, J. Electrochem. Soc. 2022. https://doi.org/10.1149/1945-7111/ac4cd3.[4] L. Gehrlein, C. Njel, F. Jeschull, J. Maibach, ACS Appl. Energy Mater. 2022, 5 (9), 10710–10720. https://doi.org/10.1021/acsaem.2c01454.[5] L. Gehrlein, C. Leibing, K. Pfeifer, F. Jeschull, A. Balducci, J. Maibach, Electrochimica Acta 2022, 140642–140642. https://doi.org/10.1016/j.electacta.2022.140642.

Next-Generation Battery Components Derived from Soft Dendritic Colloids

Growing demands for energy storage are causing rapid development of next-generation batteries. Researchers typically use commercially available Li-ion components and processing techniques to investigate new chemistries and cell architectures. Herein, we propose an emerging materials-development platform: shear- driven precipitation of polymeric materials to develop application-specific battery components. In this process, polymer particles with high aspect ratios, called soft dendritic colloids (SDCs), are formed via turbulent solvent-nonsolvent induced phase separation. Two specific component applications are presented.The first application is nano-composite redox active polymer electrodes for Li-ion batteries. Redox polymer electrodes are currently limited by low intrinsic electronic conductivity. As a result, large amounts of conductive additives are added to the composite electrodes, lowering the gravimetric performance. The network forming capabilities of the SDC morphology provides intimate contact between active material and conductive material to enable free-standing electrodes that are produced via simple vacuum filtration. We present cyclic voltammetry and charge/discharge data using poly(2,2,6,6-tetramethyl-1-piperidinyloxy methacrylate) as the SDC material.The second application is composite separator assemblies to mitigate lithium polysulfide shuttling in Li-S batteries. Polysulfide shuttling is considered a technological hurdle plaguing Li-S battery development. Separators can be functionalized to reduce polysulfide shuttling by incorporating additives onto or within the separator matrix, which either bind or repel the soluble species to prevent crossover to the anode. We demonstrate that SDC materials are a promising platform for fabricating nanocomposite separators using a variety of nanomaterials. The nano composite separators show increased thermal stability, cycling stability, and polysulfide rejection as compared to commercial materials.

Modeling of Crystal Structure in Li-Rich Layered Oxides for Rechargeable Lithium Cells

Lithium-Ion Batteries (LIBs) require further development in terms of safety and performance to establish also in the automotive market and new materials at both electrode sides as well as at the electrolyte side are necessary to overcome the state of-the-art and the commercial benchmarks. [1] The positive electrode materials constitute the bottleneck for present LIBs. They are based on layered structures (LiCoO2, NMC, NMA), spinel (LiMn2O4) and olivine LiFePO4, with rather moderate specific capacities (120–180 mAhg−1). [2] Therefore, the resulting specific energies are insufficient to meet market demand. Over-stoichiometric Li-rich layered oxides (LRLOs) are a family of positive electrode materials with promising theoretical electrochemical performance. [3] Indeed, they have received widespread attention due to their extremely high specific capacity (>250 mAhg−1) and low cost. Their extraordinary capacity has been confirmed to originate not only from the redox activities of transition metals, but also from the redox activities of oxygen anions. The crystal structure of LRLOs is an open playground of debate. There are two main hypotheses: a) a two phase nano-domain and b) a single phase solid solution. In this framework, the modeling of the crystal structure is quite challenging. Usually, the description of the structure of LRLOs can be done with rhombohedral or monoclinic unit cell. Nevertheless, the use of convention unit cells leads to a bad representation of the crystal structure because of the missing of structure features in the superstructure region (20<θ<30 in typical diffraction pattern with Cu Kα). In this communication, we demonstrate that extensive defectivities play a key role in the shape and intensity of diffractograms of LRLOs. In particular, we show how the use of supercells or defects (antisite defects and stacking faults) can help in the description of crystal structure of this class of materials.[1] Zubi, G.; Dufo-López, R.; Carvalho, M.; Pasaoglu, G. The Lithium-Ion Battery: State of the Art and Future Perspectives. Renewable and Sustainable Energy Reviews 2018, 89, 292–308.[2] Casas-Cabanas, M.; Ponrouch, A.; Palacín, M.R. Blended Positive Electrodes for Li-Ion Batteries: From Empiricism to Rational Design. Isr J Chem 2021, 61, 26–37.[3] Nie, L.; Chen, S.; Liu, W. Challenges and Strategies of Lithium-Rich Layered Oxides for Li-Ion Batteries. Nano Res 2022.

Influence of Binders on Printability and Battery Performance of Thick 3D-Printed Positive Electrode for Li-Ion Batteries

Nowadays, lithium-ion batteries have been considered to be the superior commercial batteries in the market, thanks to their high energy density (until ca. 250 Wh/kg at cell level) and low fabrication cost (actually < 0.3 Euro/Wh at cell level). However, due to the recent global push for electrification, there is a constant need to further improve battery performance while minimalizing the cost. Besides the development of new battery materials, engineering the electrodes could be a valid solution to meet such demand. By increasing the electrode thickness to 200 µm, the active material loading in the electrode is expected to increase to over 30 wt%, hence enhancing the energy density and limiting the cost at the cell level. Nevertheless, thick electrodes fabricated by conventional coating methods suffer severely from weak mechanical strength and delamination as well as long and highly-tortuous Li-ion diffusion path, sluggish electrochemical kinetics, and poor charge/discharge rate performance. Recently, great attention has gone to 3D printing (additive manufacturing) with the promise to overcome these limitations, thanks to the porous structures of the 3D- printed electrodes.In this work, we present 450 µm thick lithium iron phosphate (LFP) electrodes produced by 3D micro-extrusion with a superior LFP loading of ca. 30 mg/cm2 and a high areal capacity of ca. 4.2 mAh/cm2. Two commercial polymeric binders were employed, including carboxymethyl cellulose (CMC) and poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS). It is concluded that both CMC and PEDOT:PSS are essential to obtain well-printed 3D electrodes. While CMC contributes significantly to the mechanical strength of the 3D-printed LFP electrodes, it is of great importance to add PEDOT:PSS to avoid intra-fiber cracks. Furthermore, the electrodes containing both binders have shown significantly improved specific capacity at different C-rates compared to those formulated from either CMC or PEDOT:PSS. Further analyses give insights into charge transfer resistance, tortuosity and electrical conductivity of the investigated electrodes. Additionally, we highlight the difference in the battery performance of 3D-printed electrodes and their standard doctor-bladed counterparts.Reference(1) Kuang, Y.; Chen, C.; Kirsch, D.; Hu, L. Thick Electrode Batteries: Principles, Opportunities, and Challenges. Adv. Energy Mater. 2019, 9 (33), 1901457. https://doi.org/10.1002/aenm.201901457.

Insights on the Buffer Effect in Blended Positive Electrodes for Lithium Ion Batteries

An approach to improve the performance of positive electrodes for Li-ion batteries that is commonly used by companies is fabricating them using mixtures of different materials (usually 2) with complementary features1. This coexistence, when properly formulated, provides an extra design degree of freedom and gives rise to synergetic effects, allowing blends to perform better than what the rule of mixture predicts. Unfortunately, the internal dynamics of the electrodes are still poorly understood at fundamental level and the optimization of formulations for such blends still mainly depends on empirical studies. One of the important characteristics identified in blends is termed the buffer effect. This occurs when the material exhibiting fastest kinetics can receive an excess of the incoming lithium under high power discharge and subsequently, when the current stops, transfer this excess to the higher capacity material.In this study, the role and extent of this effect is explored for a set of representative materials and the resulting blends resulting from their mixtures. For the measurements we are using a special experimental model-like blended electrode setup reported by Heubner et al.2 slightly adapted to our needs. In this setup, two positive electrodes with different active material, but same active mass, are facing each other, separated by 2 separators with a disk of perforated lithium in the middle. During measurement, current is applied between an electrode and lithium while a potentiostat actively keeps the two positive electrodes at the same potential. Such setup gives us access to the current exchanged between the positive electrodes while keeping them in equal potential at all times, as would happen in a blended electrode with 50% of each material.For the study, 4 cathode active materials were used, LiNi0.5Mn0.3Co0.2O2 (NMC), LiMn2O4 (LMO), LiFePO4 (LFP) and LiFe0.4Mn0.6PO4 (LFMP), and every binary combination of them was measured. The cells after 3 C/10 formation cycles were subjected to a pulsed electrochemical test (1 minute 3C pulses followed by 10 minutes of relaxation). Top figure shows the voltage response of the cell vs. time while the bottom one shows the charge that was transferred between the materials during their relaxations (buffering charge) and while the cell current is equal to zero , for the NMC-LMO blend. We applied the same protocol for all the combinations under study and found out large variations of this buffering ability depending on the blends constituents and their individual electrochemical properties. It is clearly evident that both the magnitude and the direction (sign) of the buffering current varies in the voltage range meaning each material can act as donor or acceptor of the buffering lithium. We believe that this provides a new insight in the internal processes in blended electrodes and brings us one step closer to their rational design. References : Casas‐Cabanas et al. Isr J Chem 61, 26–37 (2021).Heubner et al. J Power Sources 363, 311–316 (2017). Figure 1

Morphology Control of Ball Milled Si-Ti Alloys and a Comparison of Their Surface Reactivity with SiOx

Si-based anode materials have been widely studied due to their higher volumetric capacity compared to graphite.1 However, they can suffer from poor cycling due to severe volume changes, crystallization effects (formation of Li15Si4), an unstable solid electrolyte interphase (SEI) and surface erosion. Alloying Si with an electrochemically inactive material can decrease the volume expansion and lead to better cycling performance. If nanostructured or amorphous Si-based alloys are used, the phase transition due to the crystallization effect is suppressed.1,2 Considering all improvements, Si-based anode materials still experience large surface erosion that continuously increases the surface area of active material particles during cycling. Different studies show that the main causes of surface erosion are the volume changes during cycling and the reaction between the active material and electrolyte.3,4 It is known that higher active material surface area leads to a higher reaction rate with electrolyte. This leads to a larger lithium inventory loss and a decrease in coulombic efficiency (CE), which is undesirable.5 Mechanical milling has long been used to create metal alloys. Cao et al showed that preparing Si-based alloys with a two-step milling method, in which Si is first milled alone with the metal added in the second step, produces Si-M alloys having an amorphous active Si-phase and a reduced surface area compared to conventional one-step milling.5 SiOx has also been extensively studied as an anode material because of reduced volume expansion, less side reactions with electrolyte, and high capacity retention during cycling.6 Despite decades of research to our knowledge, it has yet to be determined how the surface erosion or reactivity of SiOx compares with Si-based alloys with a similar surface area. This fundamental question needs to be answered if Si-based alloys are to be considered as candidates for practical application as negative electrode materials. A barrier to answering this question has been the very different surface areas of Si-based alloys (typically high surface area materials prepared by ball milling) and SiOx, which has a low surface area. Increasing the surface area of SiOx and reducing the surface area of the Si-based alloys using the two-step milling method can provide the opportunity to compare their surface reactivity.In this study, SixTi100-x (x= 85,70, 60) alloys were prepared by ball milling using the one-step and two-step methods, allowing low and high surface area alloys to be synthesized. The results show that reducing alloy surface area results in an increased CE, however, the difference is not pronounced. The surface erosion or reactivity of low surface area Si0.85Ti0.15 was compared with SiOx with a similar surface area. Cycling results show that Si0.85Ti0.15 has a higher CE than SiOx in initial cycles, but SiOx has a markedly higher CE after longer term cycling. These results are verified by direct observations of reduced surface erosion on cycled SiOx alloy particles compared to Si0.85Ti0.15 particles. Figure 1(a) and (b) shows the cross-section SEM images of low surface area Si0.85Ti0.15 and SiOx with a similar surface area after 50 cycles, respectively. The SiOx particles are almost pristine, while the Si0.85Ti0.15 particles are severely eroded. These results imply that the chemistry of SiOx plays a more important role in its good cycling performance than does its low surface area. References. Obrovac, M. N. & Chevrier, V. L. Alloy Negative Electrodes for Li-Ion Batteries. Chem Rev 114, 11444–11502 (2014).Iaboni, D. S. M. & Obrovac, M. N. Li15Si4 Formation in Silicon Thin Film Negative Electrodes. J Electrochem Soc 163, A255 (2016).Chevrier, V. L., Aiken, C. & Krause, L. J. Impact of Electrolyte on the Cycling of Si-Based Materials. in 228th ECS Meeting – Phoenix (2015).4.Krause, L. J., Brandt, T., Chevrier, V. L. & Jensen, L. D. Surface Area Increase of Silicon Alloys in Li-Ion Full Cells Measured by Isothermal Heat Flow Calorimetry. J Electrochem Soc 164, A2277 (2017).Cao, S., Tahmasebi, M. H., Gracious, S., Bennett, J. C. & Obrovac, M. N. Preparation of Low Surface Area Si-Alloy Anodes for Li-Ion Cells by Ball Milling. J Electrochem Soc 169, 060540 (2022).Liu, Y., Charlton, M., Wang, J., Bennett, J. C. & Obrovac, M. N. Si85Fe15Ox Alloy Anode Materials with High Thermal Stability for Lithium Ion Batteries. J Electrochem Soc 168, 110521 (2021). Figure 1

Covalently Joined Electrode Architectures for Extreme Fast Charging Li-Ion Batteries

Li-ion batteries are the backbone of all electric vehicles (EVs) in production today [1]. However, they compete poorly against the few-minute refueling time of fossil fuel powered vehicles [2, 3]. To successfully replace fossil fuel powered vehicles, the EV batteries must support charging rates under the 15-minute mark as determined by the eXtreme Fast Charging (XFC) standard defined by the U.S. Department of Energy [4]. When subjected to XFC charging rates, well-known problems of lithium plating and delamination plague graphite anodes due to local potential gradients and binder degradation respectively [5].Our work replaces the traditional polymer binder with conductive titanium carbide interconnects that covalently join graphite particles as well as bond them to the current collector [6]. This new architecture demonstrates ~400% increase in electrical conductivity compared to traditional architectures with polymer binders while maintaining interparticle integrity and improving adhesion. The adhesion and mechanical properties are provided by conductive chemical bonds mitigating delamination as these novel bonds suffer less mechanical and chemical degradation under high current rates than adhesion provided by polymer binders. The improved conductivity was also utilized to form a solid electrolyte interphase (SEI) at rates up to 4C reducing the ionic impedance of the SEI interface significantly [7]. The improved graphite electrodes can sustain 15-minute charge maintaining 80% of the specific capacity of the graphite particles for 800 cycles at commercially relevant loadings. Our studies introduce an effective strategy to engineer Li-ion battery electrode architectures that simultaneously improve electrical and ionic conductivity mitigating lithium plating and delamination under XFC charging rate needed for the mass adoption of EVs. Habib, A.A., S. Motakabber, and M.I. Ibrahimy. A comparative study of electrochemical battery for electric vehicles applications. in 2019 IEEE International Conference on Power, Electrical, and Electronics and Industrial Applications (PEEIACON). 2019. IEEE.Balali, Y. and S. Stegen, Review of energy storage systems for vehicles based on technology, environmental impacts, and costs. Renewable and Sustainable Energy Reviews, 2021. 135: p. 110185.Andwari, A.M., et al., A review of Battery Electric Vehicle technology and readiness levels. Renewable and Sustainable Energy Reviews, 2017. 78: p. 414-430.Dufek, E.J., et al., Developing extreme fast charge battery protocols–A review spanning materials to systems. Journal of Power Sources, 2022: p. 231129.Ahmed, S., et al., Enabling fast charging–A battery technology gap assessment. Journal of Power Sources, 2017. 367: p. 250-262.Rangom, Y., Covalently Joined Carbonaceous and Mettalloid Powders by Carbide-Based Interconnects and Method of Fabrication for High-Performance Electrodes. 2021: United States preliminary patent #63/248,293.Rangom, Y., T.T. Duignan, and X. Zhao, Lithium-ion transport behavior in thin-film graphite electrodes with SEI layers formed at different current densities. ACS Applied Materials & Interfaces, 2021. 13(36): p. 42662-42669. Figure 1