Lithium Transport Research Articles

Molecular Dynamics Analysis of Lithium-Ion Transport Properties in All-Solid-State Lithium-Ion Battery

Lithium-ion batteries have been widely used in electronic products since their commercialization, but the use of liquid electrolytes carries safety risks of electrolyte volatilization, leakage, and corrosion. Meanwhile, solid-state electrolytes have the advantage of high safety performance compared with liquid electrolytes. Therefore, all-solid-state Lithium-ion batteries has become a new research topic. LiNi x Co y Mn z O2 (NCM, x+y+z =1) material have been used as a representative ternary compound cathode material in Lithium-ion batteries. However, understanding the influencing conditions during the transport of Lithium ions in NCM materials is incomplete and difficult to observe experimentally. Therefore, our goal is to understand the factors influencing Lithium-ion transport properties. In this work, molecular dynamics (MD) simulations of NCM materials were used to analyze the transport properties of Lithium-ion.According to Wei's study, we created three patterns for transition metal alignment for LiNi0. 33Co0. 33Mn0. 33O2(NCM333). Then, MD simulations were performed for the three types of NCM333. The Lithium-ion transport properties are considered in different Lithium-ion content rate (100%, 88%, 77%, 66%, 55%, 44%, 33%, and 22%) which represent different state of charge (SOC). The occupied positions of Lithium-ion in the initial NCM structure were randomly constructed for different percentages of Lithium-ion content. According to Zhu's research, we used the Morse potential energy in the LAMMPS as the basis and added the corresponding Coulomb force and long-range repulsive interaction force. In the end, the potential model based on Morse-type interaction, Coulomb interaction and a long-range repulsive interaction were used. The size of the simulation box was 34.74 Å×29.72 Å×28.54 Å. The total number of atoms was 3456. The temperature of the system during the MD simulation was set at 300 K, the timestep was set at 1.0 fs, and the sampling interval for trajectories was 500 steps. To relax the system, a 0.5 ns NPT process was first applied. After 10 ns of NVT process was performed, the size of the simulation box at the final equilibrated state was compared with that of 100% Lithium-ion content. The results showed that the simulation box volume variation was less than 2% in all calculated Lithium-ion content. Radial distribution function (RDF) analysis was also performed using the same conditions, and the results were consistent with Lee's study. These two analyses confirmed the integrity of the structural NCM in the simulation.The mean-squared displacement (MSD) analysis was performed on the NCM333 material throughout the trajectories in the 10 ns NVT process. From the MSD data, all three patterns of NCM333 have very minimal Lithium-ion mean square displacement at 100% Lithium-ion content, and the values of Lithium-ion mean square displacement for each pattern were very close to each other, which was not only consistent with the structural properties of NCM333, but also with the Lee's study. In the simulation of Pattern 1 with different Lithium-ion contents, it can be seen that there was a more significant migration of lithium ions compared to 100% Lithium-ion content, which was also reflected in the mean square displacement data. The mean square displacement data at 88% Lithium-ion content was significantly smaller than those at 55% Lithium-ion content, but all rang of the mean square displacement data were much larger than those at 100% Lithium-ion content. Because at 100% Lithium-ion content, there was no vacancy around the Lithium-ion, so only vibrations occured. When the Lithium-ion content is less than 100%, vacancies appear, so the Lithium-ion occur in vibration and diffusion.The Lithium-ion diffusion coefficient was obtained by linear fitting the MSD data in the region of 2.5ns-5ns. The figure shows the Lithium-ion diffusion coefficients (DLi) of the NCM333 material for different Lithium-ion contents. As shown in the figure, the experimental value is 3.3x10-11cm2/s and the theoretical value of the Wei's study is 5x10-9cm2/s when the Lithium-ion content of NCM333 was 33%. Also the calculated value was approximately one hundredth times larger than the experimental, consistent with the Wei's study. The diffusion coefficient maximum peak exists around 50% Lithium-ion content, which was inconsistent with our prediction. Our predictions suggest that as the Lithium-ion content decreases, more vacancies will occur and therefore the DLi should increase. Further refinement and improvements will be considered to confirm these phenomena. Figure 1

(Invited) Potentiometric Entropy Measurements and Isothermal Operando Calorimetry to Identify the Charging Mechanisms of Battery Materials

This talk presents recent development in potentiometric entropy measurements and isothermal operando calorimetry to gain insight into the charging mechanisms of lithium ion batteries. First, the concept, design, and operation of two unique experimental apparatuses will be presented. Then, the effects of material composition, crystallographic structure, and particle size on the cell’s thermodynamic behavior, polarization, and lithium ion transport will be discussed for different Wadsley-Roth materials (e.g., TiNb2O7, PNb9O25, (W0.2V0.8)3O7) under quasi-equilibrium conditions. Particular attention will be paid to phase transition, lithium ion intercalation and ion ordering in solid solution, and/or two-phase coexistence occurring during charging/discharging. Finally, instantaneous heat generation rates measured by isothermal operando calorimetry at each electrode will be used to identify the causes of energy dissipation and to provide insight into the transport and interfacial phenomena taking place in the electrodes at different states of charge and charging rates. Here, special emphasis will be placed on the contributions of Joule heating associated with resistive losses, heat of mixing due to ion concentration gradient, and reversible entropic changes.

(Invited) High-Nickel Layered Oxide Cathodes: Crack Vs. Surface Reactivity

The appetite for long driving range and high energy density is pushing the nickel content in layered oxide cathodes for lithium-ion batteries. The lying of Ni3+/4+:3d band slightly above the Co3+/4+:3d band enables to extract more lithium during charge without encountering oxygen release from the lattice in high-nickel cathodes compared to that in LiCoO2. However, as the nickel content increases in the lattice, the cells suffer from cycle and thermal instability. The cycle instability has largely been attributed in the literature to the formation of cracks caused by the occurrence of H2-H3 phase transition with large lattice parameter changes during high degree of charge. Several approaches, such as doping with other cations and microstructural control of the primary and secondary particles, have been extensively pursued to overcome the challenges and improve the cycle life.With a systematic investigation of a number of cathode compositions and their characterization after extensive cycling, this presentation will illustrate that surface reactivity of high-nickel cathodes with electrolyte plays a dominant and decisive role on cycle life. Even cathodes like LiNiO2 with 100% Ni without any cation doping or surface coating could be cycled with high capacities over a large number of cycles with an appropriate choice of electrolyte that suppresses surface reactivity. Electrolytes that are stable to slightly higher voltages, even by as low as 100 mV, compared to the conventional electrolytes alter the surface reconstruction pathway on cathode surface in contact with electrolyte. Electrolytes with better high-voltage stability favor the formation of mildly reduced LiNi2O4 spinel on the surface without much oxygen release from the surface. In contrast, electrolytes that have inferior stability to higher voltages lead to a drastic reduction of the cathode surface to highly reduced Ni3O4 spinel and NiO rock salt phases with significant oxygen loss from and volume change on the surface, which could cause crack initiation on the surface, followed by their propagation into the bulk. Interestingly, the fast 3-dimensional lithium-ion and electron transport in spinel LiNi2O4 supports a facile charge transfer through the cathode-electrolyte interphase (CEI), resulting in better cycle life, in contrast to the poor lithium-ion transport in both spinel Ni3O4 and rock salt NiO phases, resulting in poor charge-transfer through the CEI and inferior cycle life. With robust electrolyte formulations with better high-voltage stability, long cycle life could be achieved even with the repeated occurrence of the H2-H3 phase transitions over a large number of cycles.

Electro-Chemo-Mechanical Study of Cathode-Interface-Engineered All-Solid-State Lithium Batteries

All-solid-state lithium batteries (ASSLBs) have been regarded as one of the most promising next-generation batteries in terms of their superior safety and great potential to meet the requirements of high energy and power density.1 However, the performance of ASSLBs based on even state-of-the-art solid electrolytes (SEs) with a high room-temperature ion conductivity of 10−2 S·cm−1 is still inferior to that of commercially available LIBs, because fast solid electrode/electrolyte interfacial lithium-ion transport remains a vital challenge in ASSLBs.2 The sluggish lithium-ion transport across the solid electrode/electrolyte interface mainly results from the electro-chemo-mechanical degradation, such as the space charge layer (SCL), interface reaction generating ionically resistive products, and poor physical contact.3,4 On the cathode side, coating high-voltage cathodes with chemically compatible and stable buffering layers with high ionic conductivity but low electronic conductivity has been widely confirmed to be an effective approach to overcome these problems.However, a mechanistic understanding of the coating functionality remains unresolved, and there is still much room for improvement regarding the methodology and associated material properties.5 Here, from electro-chemo-mechanical perspectives, we have fully studied the improvement mechanism of cathode interface engineering for ASSLBs based on the complementary analyses including calculations (e.g., first-principles, finite element methods), in-situ (e.g., differential phase contrast scanning transmission electron microscopy (DPC-STEM), Raman, electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), galvanostatic intermittent titration technique (GITT)) and ex-situ (X-ray absorption spectra (XAS), X-ray photoelectron spectroscopy (XPS), focused-ion beam scanning electron microscopy (FIB-SEM)) characterizations. We find that discontinuous ferroelectric BaTiO3 coating can effectively suppress the SCL formation and lead to fast continuous interfacial lithium-ion conduction pathways, thus significantly improving the interfacial migration kinetics between cathode materials and the sulfide SEs.6 The bidirectionally compatible NASICON-type LixZr2(PO4)3 (LZPO) buffering layer enables the high-voltage cathode interface (4.5 V LiCoO2/Li6PS5Cl) with high chemical/electrochemical stability and fast Li-ion transport dynamics.7 Additionally, the high Young’s modulus of the coating layer (e.g., LZPO) can remarkably decrease stress inside cathodes and prevent cathode/SE interface separation, which is beneficial to mitigate microcracks in cathodes and cathode/SE interface contact loss, respectively.8 We believe these findings will help advance the fundamental scientific understanding of the coating functionality and the interfacial lithium-ion transport mechanism in ASSLBs, thus shed light on rational electrode/electrolyte interface design for high-rate performance ASSLBs.References Janek, J. & Zeier, W. G. A solid future for battery development. Nat. Energy 1, 16141 (2016).Janek, J. & Zeier, W. G. Challenges in speeding up solid-state battery development. Nat. Energy, doi:10.1038/s41560-023-01208-9 (2023).Banerjee, A., Wang, X., Fang, C., Wu, E. A. & Meng, Y. S. Interfaces and Interphases in All-Solid-State Batteries with Inorganic Solid Electrolytes. Chem. Rev. 120, 6878–6933 (2020).Chen, R., Li, Q., Yu, X., Chen, L. & Li, H. Approaching Practically Accessible Solid-State Batteries: Stability Issues Related to Solid Electrolytes and Interfaces. Chem. Rev. 120, 6820–6877 (2020).Culver, S. P., Koerver, R., Zeier, W. G. & Janek, J. On the functionality of coatings for cathode active materials in thiophosphate-based all-solid-state batteries. Adv. Energy Mater. 9, 1900626 (2019).Wang, L. et al. In-situ visualization of the space-charge-layer effect on interfacial lithium-ion transport in all-solid-state batteries. Nat. Commun. 11, 5889 (2020).Wang, L. et al. Bidirectionally compatible buffering layer enables highly stable and conductive interface for 4.5 V sulfide-based all-solid-state lithium batteries. Adv. Energy Mater. 11, 2100881 (2021).Sun, X. et al. A Bifunctional Chemomechanics Strategy To Suppress Electrochemo-Mechanical Failure of Ni-Rich Cathodes for All-Solid-State Lithium Batteries. ACS Appl. Mater. Interfaces 14, 17674–17681 (2022).

AMIDR: A Complete Pulse Method for Measuring Cathode Solid-State Diffusivity

Lithium transport within cathode material is driven by diffusion. While fast cathode diffusion is desired, solid-state diffusivity is one of the most difficult cell material properties to measure. However, it is an important property to understand as cathode capacity is often limited by poor diffusivity. GITT (Galvanostatic Intermittent Titration Technique) is a common diffusivity measurement method. This technique is accomplished by applying a series of constant current pulses to a cell and analyzing the voltage response. While easy to use, this method only measures near the surface of the active material by assuming that it takes the geometry of a semi-infinite plane. This approximation means that GITT is only accurate when measuring the very initial voltage response. However, the voltage response cannot be analyzed too early as this may amplify error produced by CDL (double layer capacitance) and RI (interface resistance) found at the cathode-electrolyte interface which GITT does not account for. EIS (Electrochemical Impedance Spectroscopy), an AC method, is better suited for distinguishing CDL/RI from diffusivity but also struggles to evaluate diffusivity beyond the surface of active material within a reasonable time frame1. In addition, instruments capable of quality EIS are often cost prohibitive compared to DC cell testers.The voltage responses after the first few moments of a pulse are relevant when evaluating cell behaviour in real-world applications and should be considered to produce comprehensive measurements of diffusivity and its performance impact. AMID (Atlung Method for Intercalant Diffusion) is a multi-rate pulse method produced by this lab which uses a series of pulses, both short/fast and long/slow, and an approximation-free analytical model (developed by Sven Atlung) for diffusion in a spherical particle, not a semi-infinite plane2. However, AMID cannot differentiate diffusion impedance from resistance and therefore requires that resistance be considered negligible. In addition, while AMID mathematics are free of approximations, the typical multi-rate pulse protocol does require that series of pulses be approximated as singular pulses3. Lastly, the multi-rate pulse protocol limits the state-of-charge resolution of diffusivity measurements.AMIDR (Atlung Method for Intercalant Diffusion and Resistance) incorporates a GITT-style single pulse protocol with AMID-style mathematics modified to account for resistance as shown in Figure 1b). AMIDR collects pulse data with a pseudo-logarithmic time distribution. This means that the same number of data points is collected in 0.1-1.0 seconds, 1.0-10 seconds, 10-100 seconds and so on. Unlike GITT which measures diffusivity at an early arbitrary point in a pulse, AMIDR considers the entire length of a pulse comprehensively. Fractional capacity is calculated for each datapoint by dividing the actual capacity with the ideal “impedance-free” capacity expected at that voltage as shown in Fig 1c). These fractional capacity values, normalized from 0-1, are fitted to the modified Atlung model. This modified Atlung model is nearly the same as the original Atlung model except an additional term is added for capacity limited by resistance. Unlike AMID, AMIDR measures both diffusivity and resistance simultaneously by using both as fitting parameters. Lastly, while CDL is usually small enough for RI to behave simply like ohmic resistance on relatively short time scales (>0.1 seconds), AMIDR has the option to account for CDL/RI when relevant such as near the bottom of a complete discharge.AMIDR is a new diffusivity measurement method tailored for cathode material in Li-ion batteries. By combining the advantages of various previous diffusivity methods, AMIDR eliminates many of their concerns and sources of error such as sampling of only the material surface, alternate confounding sources of impedance, and expensive equipment as seen in Figure 1a). When paired with proper cell design (i.e. ultra-low single layer cathode loading to remove pore impedance and reference electrodes to remove anode impedance), AMIDR can produce high resolution diffusivity measurements with improved accuracy and applicability to real-world cell performance.References C. Deng and W. Lu, Journal of Power Sources, 473, 228613 (2020).A. Liu et al., J. Electrochem. Soc., 168, 070503 (2021).M. Doyle, J. Newman, and J. Reimers, Journal of Power Sources, 52, 211–216 (1994). Figure 1. (a) Comparison of various Diffusivity measurements. (b) The modified Atlung model for diffusion in a spherical particle. (c) How pulse data is converted to the unitless Atlung model. Figure 1

Intercalation Pathway in Graphite Particles Analyzed with a Multi-Layer Phase Field Model

Graphite is today the most common negative electrode material in commercial cells, alone or blended with silicon, thanks to its relatively high specific capacity of 372 mAh·g−1, its excellent cycling stability, its low thermodynamic potential, and relatively low cost compared to alternative materials. The increase in the energy densities, power capabilities, and durability of lithium-ion batteries using this conventional cost-effective active material is possible through an optimization of the electrode and material designs. Such optimization requires, however, knowledge of the fundamental mechanisms that govern both the lithium transport inside graphite particles and the electrochemical transfer at the electrolyte / active material interface.Graphite has an ideal lamellar structure made of graphene sheets. During intercalation, the lithium atoms insert between the graphene planes, with almost no lithium transport across the graphene sheets. The interactions between lithium atoms in adjacent galleries leads to the formation of structures with filled layers separated by a number of empty layers, known as stages. Given this phenomenon, graphite active material undergoes phase separation between successions of several stable phases during lithium intercalation. This staging phenomenon influences the critical properties of graphite like its equilibrium potential, lithium diffusion or lithium insertion kinetics.In the present work, we use a Cahn-Hilliard type model, adapted to multi-layered materials1 and study the influence of the parameters in the underlying free-energy models. We focus first on the intra-layer and inter-layer lithium interaction contributions. Free-energy models with increasing complexity of inter-layer interactions are introduced and discussed based on their corresponding phase diagrams. In particular, we show that occurrence of fractional 3/2 stage, observed for potassium or rubidium intercalation in graphite at high pressure, requires an interlayer interaction effective at second neighbor, while a continuous screening effect of the intercalant is necessary to predict the occurrence of stages greater than 2 without the occurrence of the fractional 3/2 stage, as observed for lithium2.The kinetics of stage formation and evolution is also greatly affected by the interaction parameters of the free-energy model. A linear stability analysis (LSA) is performed to investigate the impact of the free energy model parameters on the stage formation dynamics and growth rates. In particular, the LSA shows that stage 2 grows the fastest, even for low lithium filling fraction. In accordance with this result, simulations of spinodal decomposition from moderate homogeneous lithium filling fraction (c=0.3) shows the formation of stage 2 at early times before an evolution towards stage 3 (See figure 1). This higher growth rate of stage 2 seems to have an impact on lithium intercalation pathway. Indeed, during simulations of lithium intercalation in a graphite particle at different C-rates, stage 2 tends to form very early at the electrolyte/particle interface, even when stage 3 and dilute stage 1 dominates inside the particle. The simulation of lithium intercalation also provides access to the effective exchange current density as function of the averaged surface concentration. The presence of the stages at the surface of the particles directly affects this averaged exchange current density. It results in non-symmetric exchange current density profiles, in coherence with operando X-ray micro-diffraction measurement in thick graphite electrodes3.Figure 1: Snapshots of a spinodal decomposition at different times. The initial average filling fraction is c=0.3 and the system has six layers. For each subfigure, top: lithium content in each layer, bottom: coefficients of the Fourier transform used to track the stages Smith, R. B. et al. Intercalation Kinetics in Multiphase-Layered Materials. J. Phys. Chem. C 121, 12505–12523 (2017).Chandesris, M., et al. Thermodynamics and Related Kinetics of Staging in Intercalation Compounds. J. Phys. Chem. C 123, 23711–23720 (2019)Tardif, S. et al. Combining operando X-ray experiments and modelling to understand the heterogeneous lithiation of graphite electrodes. J. Mater. A 9, 4281–4290 (2021) Figure 1

Macroscale Inhomogeneity of Electrochemical Lithium-Metal Plating Triggered by Gas Phase Evolution

Promoting homogenous electrode reactions is essential to suppressing electrode degradation and thus realizing stable energy storage systems. In particular, lithium-metal anodes that undergo drastic morphological change during charging/discharging require strict homogeneity control, more so than conventional intercalation electrodes. Previous studies have mainly focused on the micrometer-scale homogeneity of lithium plating and its control by tailoring the electrolyte chemistry and following the solid-electrolyte interphase formation process. However, the larger-scale, electrode-level homogeneity issue recently emerging for conventional electrodes has received little attention. Here, for the first time, we observe clear electrode-level inhomogeneity during lithium plating that is independent from the micro-scale lithium dendritic growth. Ex-situ and in-situ experiments clearly reveal that this electrode-level inhomogeneity is triggered by gas-generating reactions and the resulting gas-phase (i.e., bubble) evolution that causes localized lithium growth. Experiments using Li|Cu half cells demonstrate that this macroscale inhomogeneity is accompanied by an overpotential increase mainly attributed to limited lithium-ion mass transport through bubbles, as revealed by continuum modeling and simulation. Full-cell experiments using lithium iron phosphate demonstrate that this bubble-inducing macroscale inhomogeneity significantly contributes to decay of the cell capacity and energy density. Our observation of this larger-scale lithium plating inhomogeneity suggests that homogeneity control and its implications for lithium-metal cell performance should be approached from a multi-scale perspective.

Lithium Distribution and Site Disorder in Halide-Substituted Lithium Argyrodites: A Structural and Transport Study

Lithium argyrodite superionic conductor has recently gained significant attention as a potential solid electrolyte for all-solid-state batteries because of its high ionic conductivity and ease of processing. One promising aspect of these materials is the ability to introduce halide (Li6-xPS5-xY1+x, Y = Cl and Br ) into the crystal structure, which can greatly impact the lithium distribution over the wide range of accessible sites and structural site-disorder between the S2₋ and Y₋ anion on Wyckoff 4d site, strongly influences the ionic conductivity. However, the relationship between halide substitution, structural site-disorder, and lithium distribution is not fully understood. In this study, we investigate the effect of halide substitution on lithium argyrodite and engineer site-disorder by changing the synthesis protocol. We reveal the lithium substructure and ionic transport correlations using neutron diffraction, solid-state NMR, and electrochemical impedance spectroscopy, We find that higher ionic conductivity is correlated with a negative charge on the 4d site, as replacing the S2− with Br− leads to a lowered average charge on the 4d site and weaker interactions within the Li+ “cage”, promoting a migration pathway for Li+ ions across the Li+ cage. We also identify a new T4 Li+ site, which enables an alternative jump route (T5–T4–T5) with a lower migration energy barrier. The resulting expansion of Li+ cages and increased connections between cages leads to a maximum ionic conductivity of 8.55 mS cm-1 with higher site-disorder, an improvement of 11-fold compared to lower site-disorder. Overall, this work provides a deeper understanding of the structure-transport correlations in lithium argyrodite, specifically how site-disorder and halide substitution impact the lithium substructure and transport properties.

Nanotwinned Structure in Copper Affects Lithium Deposition Behavior at Electrolyte-Electrode Interface in Anode-Free Lithium Metal Battery

Anode-free lithium metal battery (AFLMB) is one of new promising energy storage systems. In contrast to lithium-ion battery, the negative electrode of AFLMB does not contain any active materials, resulting in a two-fold increase in energy density. As a result, the charging mechanism on the negative electrode in AFLMB is based on electrodeposition of lithium, rather than intercalation of lithium ions. Unfortunately, that causes a series of problems, such as lithium dendrite formation, volume expansion, broken SEI and dead lithium accumulation, leading to the low cycling stability of AFLMB. Consequently, interfacial characteristics of the negative electrode (usually copper) play a critical role in determining the morphology of lithium deposits which largely affects the issues mentioned above. Understanding the mechanism of lithium electrodeposition across the electrode-electrolyte interface is crucial to design a better copper electrode for long-cyclability AFLMB.The interfacial characteristics of copper are mainly influenced by crystal phase, surface roughness and defects. While the effects of crystal phase and surface roughness on lithium electrodeposition have been extensively studied, the role of micro-scale defects has been seldom discussed, despite their potential to strongly influence the surface properties of copper. Therefore, this work focuses on elucidating the elementary process about how the defects on copper affect the lithium nucleation and subsequent growth. Specifically, we use (111)-nanotwinned and (111)-preferred orientation copper foils with the same surface roughness to conduct a series of electrochemical measurements. The presence of nanotwin structure can reduce the grain boundary and atomic step density, a type of the defects with high surface energy, on the copper. Before lithium electrodeposition, solvents and anions in an electrolyte adsorb on the electrode-electrolyte interface to form the electric double layer. During this process, the atomic steps with high surface energy on copper can establish strong adsorption with the substance in the electrolyte. The solvents adsorbed on the defects may hinder the reduction of anion. Accordingly, the (111)-nanotwinned Cu foil with fewer defects induces the formation of LiF-rich solid electrolyte interphase (SEI), which is beneficial to the transportation of lithium ions. In cyclic voltammetry test, the (111)-nanotwinned Cu foil exhibits higher reduction current density of the precipitation of LiF (Fig. 1).For lithium electrodeposition, during the initial stage, lithium adatoms tend to adsorb on the defects with high surface energy on the copper surface, where other adatoms accumulate to form stable nucleus. Subsequently, the nucleus on each nucleation sites might have different growth direction and crystal phase, resulting in a lot of independent lithium grains. In other words, compared to the (111)-preferred orientation substrate, the (111)-nanotwinned Cu foil with less nucleation sites provides more space for the nucleus to grow in 2-D direction, which leads to the lower nucleation overpotential (Fig. 2 a). That result also facilitates the formation of larger lithium grains with smaller surface area exposed to the electrolyte (Fig. 3). As shown in Figure 2 (b), quasi-steady state over-potential of Li plating on the (111)-nanotwinned Cu is generally larger than that on the (111)-preferred orientation Cu foil, which has been ascribed to the high local current density on larger lithium grains. The quasi-steady state overpotential of Li plating on the (111)-preferred orientation Cu foil gradually increased with the cycle number, which might be attributable to the relatively unstable SEI and the accumulation of dead lithium with the GCD cycling. Furthermore, the (111)-nanotwinned Cu foil always exhibits a lower quasi-steady state overpotential of lithium stripping in comparison with the (111)-preferred orientation substrate at each cycle, probably resulting from the uniform Li deposit and the special LiF-rich SEI formation due to the nanotwinned structure. In the cycling stability test (Figure 2 c), for the Cu//Li cell using the (111)-nanotwinned Cu foil, the coulombic efficiency was kept being around 90% in this 160-cycle test. However, for the Cu//Li cell using the (111)-preferred orientation Cu foil, the coulombic efficiency is generally lower than that of the cell using the (111)-nanotwinned Cu foil at the cycle number > 15. In addition, the coulombic efficiency starts to obviously decay at the 135th cycle and becomes lower than 5% at the 160th cycle.To sum up, we proposed a mechanism about how the defects affect the reaction at electrode-electrolyte interface. The nanotwinned columnar grains reduces the atomic density on the copper surface, which effectively reduces the formation of lithium dendrite, the accumulation of dead lithium and broken SEI. The (111)-nanotwinned Cu foil is proved to be a superior substrate for lithium deposition and stripping, significantly improving the Li+/Li redox reversibility and cycling stability. Figure 1

(Invited) Functional Protective Coatings Based on Polysaccharides and Single-Ion Conducting Polymers for Li Metal Batteries

Li metal batteries are regarded as a promising system to overcome the energy density limitations of the current graphite anode Li-ion batteries, by taking advantage of the low reduction potential of lithium metal (-3.04 V vs SHE) and extremely high theoretical capacity (3860 mAh g-1). However, its use is still plagued with challenges that must be solved in order to achieve a successful Li-metal battery operation, that primarily relies on the performance, stability, and reversibility of the anodic side. Those challenges are related to safety concerns, mainly caused by the uncontrolled growth of high surface area lithium (HSAL) and high volumetric expansion. In this sense, to enable the safe use of Li metal, the concept of protective coating has been proposed, enabling to tailor of adequate interphases that can thermodynamically stabilize the lithium metal surface, and therefore improve the lifespan and safety of the battery. The ideal coating should possess a balance between mechanical strength, flexibility, and ionic conductivity, at the time it enables a uniform and efficient transport of lithium ions. Additionally, it must be electronically insulating and possess high chemical and electrochemically stability. In this context, polymeric coatings can offer good flexibility and elasticity which makes them suitable to adapt to the volumetric changes during lithium stripping/deposition cycles. Moreover, they can form uniform films, creating an ideal contact with lithium metal surface. An attractive group of materials that can provide numerous advantages such as high chemical, mechanical and thermal stability, are polysaccharides, aside from being the highly abundant and renewable resource on the Earth, which can be obtained in different forms.Several studies have shown that concentration polarization during battery operation is the main responsible for HSAL generation and limited cycle life, due to the coupled anion-cation movement in the electrolyte. To solve this problem the use of single-ion conducting polymers (SICPs) can result beneficial due to their immobilized anions to a polymeric backbone, which eases lithium ion transport, boosting lithium transference number (𝑡𝐿𝑖+). In addition, the selection of an appropriate polymeric backbone that can withstand volumetric changes, and allow a satisfactory ionic conductivity is essential. In this regard, the use of cellulose is preferred due to their film formation and mechanical properties, lightweight, high abundance, and biodegradability. Herein, a polymeric coating based on cellulose and P(LiMTFSI) single-ion conductor polymer is studied as a protective coating for metallic Li, in order to prevent HSAL initiation and propagation, as well as to enhance electrochemical stability in liquid and solid polymer electrolyte. The coating effectiveness is tested by casting the solution on activated lithium surface and performing lithium stripping/deposition in Li/Cu pouch cells. Additionally, the correlation with its electrochemical and physicochemical properties is performance based on microscopy and spectroscopy technics, to study the most relevant parameters influencing Coulombic Efficiency.

Improvement of Ionic Conductivity in Li7La3Zr2O12 (LLZO) Solid Electrolyte By Doping with Aluminum/Tungsten

Recently, there has been increasing interest in solid electrolytes, which are the most important materials in all-solid-state lithium-ion batteries. Among all solid electrolytes, garnet-type Li7La3Zr2O12 (LLZO) has been proven to be one of the most promising electrolytes due to its high Li+ conductivity, wide potential window, and electrochemical stability towards metallic lithium anode. In particular, cubic garnet-type LLZO solid electrolytes have received a lot of attention for the development of high-performance all-solid-state batteries with safety, energy density, and long cycle life. In this study, we synthesized LLZO solid electrolyte powders with garnet structure and determined the optimal composition and sintering temperature by adding Al/W to form a stable cubic phase.In this study, Al or W-doped LLZO were prepared by a post-doping method. In this process, LLZO powder was first prepared, and then mixed with Al2O3 or WO3 powders to produce doped LLZO ceramic electrolytes, respectively. During this process, the doped ions entered the LLZO lattice, increasing the lithium ion transport channels and promoting lithium ion conductivity. The sintering time, crucible, and sintering temperature were adjusted to investigate the optimal process conditions of the post-doping method. As a result, the doped solid electrolyte exhibited high lithium ion conductivity and low activation energy. Using the high lithium ion conductivity and broad electrochemical stability window of the Al or W doped LLZO SSE, the (NCM622)/(Al or W doped-LLZO) cell delivered a steady cycle for 100 cycles at 0.1C. The Al or W doped-LLZO prepared in this study showed advantages of high conductivity, simple preparation process, high reproducibility, and low cost, which provides technical support and reference for further application of garnet-type SSEs in solid-state batteries with high energy density.

Fluorinated Graphene Fillers for High-Performance Solid-State Lithium Batteries

Solid-state batteries (SSBs) are expected to revolutionize the field of energy storage due to their superior safety and high energy density, which result from the use of lithium metal as the negative electrode. However, the development of solid-state electrolytes (SSEs), the key component of SSBs, is quite crucial. SSEs have high thermal stability, high mechanical strength, and a wide electrochemical window but lack enough ionic conductivity; which is one of the most challenging aspects. Incorporating suitable active or inert fillers in the solid polymer electrolyte matrix is one of several methods adopted to improve the ionic conductivity of pure polymer SSEs. Two-dimensional graphene-based fillers are a promising option as they provide a high surface area for creating an abundant interface with the polymer matrix creating a continuous pathway for lithium-ion transport and simultaneously their robust nature improves the mechanical strength of the electrolyte. Pristine graphene is electronically conducting in nature owing to the continuous sp2 carbon linkages, but the electronic conductivity can be suppressed by disrupting the sp2 bonds by heteroatom functionalization on the graphene. This study investigates the heteroatom functionalization of graphene to obtain various graphene-based fillers such as graphene oxide (GO), reduced graphene oxide (rGO), and fluorinated graphene oxide (FGO) and their effectiveness when introduced into a polymer SSE matrix for LiNi0.8Co0.1Mn0.1O2-based SSBs. FGO filler outperforms others in terms of ionic conductivity, thermal stability, enhanced electrochemical potential window, and compatibility of the SSE. The optimized ratio of FGO fillers in SSE demonstrates excellent electrochemical performance, enabling long-term Li plating/stripping with small overpotential and stable cycling of Li/ LiNi0.8Co0.1Mn0.1O2 full cells. This work highlights the notable potential of FGO materials in improving the comprehensive properties of polymer SSEs and promoting the applications of polymer SSEs in high-performance SSBs.

Enhanced Performances for Solid-State Lithium-Ion Batteries with Llzo Thin Electrolyte and Silicon-Nanowires Electrode

In the past decades, due to an always more electrification and the research of a greener environment, Li-ion Batteries (LIB) have taken an important place in worldwide research. Solid-state batteries (SSBs) have the potential to revolutionize the energy storage industry, offering superior safety and energy density in comparison to traditional LIBs[1, 2]. Our research aims to enhance the performance and safety of solid-state batteries at ambient temperature by incorporating electrodes with high specific capacity with a lithium lanthanum zirconate (LLZO) solid electrolyte.The integration of SiNW electrodes into the solid-state battery architecture offers several advantages. SiNWs are known for their large surface area and superior electrical conductivity and offer a strong platform for efficient lithium-ion transport and cell energy density optimization, theoretically almost 10 times the capacity of graphite[3, 4]. Furthermore, LLZO solid electrolytes are a stable and non-flammable alternative to conventional liquid electrolytes[2, 5], significantly improving battery safety.The main objectives of this study are to investigate the combined effects of silicon nanowires (SiNWs) electrodes and LLZO solid electrolyte and to determine the optimal amount of liquid electrolytes to improve cell safety.In this work, an LLZO thin solid electrolyte tape has been manufactured by casting technique. Precise volumes of liquid electrolyte have been added to the LLZO tape to improve surface contact and ion conductivity. Furthermore, the study will provide a view of the relationship between the quantity of liquid electrolytes introduced and their impact on cell stability and safety.Preliminary results show the preparation of a mechanically stable LLZO tape with high ionic conductivity (>10-4 S cm-1) through an easy and up-scalable procedure. Improvements have been reported in the electrochemical performance of SiNW-LLZO solid-state batteries compared to the relative Li-ion liquid cell.In conclusion, here we developed a new thin solid electrolyte tape with high ionic conductivity, used in solid-state LIBs with silicon nanowires as anode material. Moreover, we standardized a procedure to optimize the use of organic liquid electrolytes as an additive, without omitting the volume or using any excess that could lead to safety issues. This optimization process can contribute to the development of solid-state batteries that are not only high-performance but also safe and reliable for various applications, including electric vehicles and portable electronics. References Wu, F., J. Maier, and Y. Yu, Guidelines and trends for next-generation rechargeable lithium and lithium-ion batteries. Chem Soc Rev, 2020. 49(5): p. 1569-1614.Wang, C., et al., Garnet-Type Solid-State Electrolytes: Materials, Interfaces, and Batteries. Chem Rev, 2020. 120(10): p. 4257-4300.Chan, C.K., et al., High-performance lithium battery anodes using silicon nanowires. Nat Nanotechnol, 2008. 3(1): p. 31-5.Kennedy, T., M. Brandon, and K.M. Ryan, Advances in the Application of Silicon and Germanium Nanowires for High-Performance Lithium-Ion Batteries. Adv Mater, 2016. 28(27): p. 5696-704.Xu, L., et al., Garnet Solid Electrolyte for Advanced All ‐Solid ‐State Li Batteries. Advanced Energy Materials, 2020. 11(2).

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

Ionic Liquid - Glyme Mixtures to Modify Solvation Chemistry, Electrochemical and Physiochemical Properties in Lithium Containing Electrolytes

Pyrrolidinium-based ionic liquids are an intriguing material for lithium-based battery electrolytes due to their inherit non-flammability and large electrochemical windows. Poor lithium-ion transport in ionic liquid-based electrolytes hinder the effectiveness of these electrolytes. Solvate ionic liquids were introduced as a subclass of ionic liquids consisting of high concentrations of lithium salts and glymes. For example, the solvate ionic liquid Li(G4)TFSI is an equimolar ratio of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and tetraethylene glycol dimethyl ether (G4). In this work, pyrrolidinium-based ionic liquids containing short polyether side chains, structurally analogous to glymes, are mixed with equimolar amounts of LiTFSI and varying portions of G4. These tertiary mixtures were evaluated based on the ratio of solvating oxygen to lithium ion ([O]/[Li+]) present in the mixture. Trends in the oxidative stability, conductivity and lithium transference number were evaluated from mixtures of [O]/[Li+] between 5 to 8. Oxidative stability of tertiary mixtures with [O]/[Li+] = 5 showed improved oxidative stability compared to the binary Li(G4)TFSI, while [O]/[Li+] > 5 had diminished oxidative stability. DSC thermal analysis between -85°C to +120°C showed the tertiary mixtures helped suppress the glass transition temperature of Li(G4)TFSI to lower temperatures. Changes in the solvation structures were evaluate using spectroscopic analysis, including Raman spectroscopy. The changes in the solvation chemistry were correlated to the physiochemical and electrochemical properties.

Life Cost Assessment of Using Binders of Sulfide-Based All Solid-State Lithium Batteries for Lithium-Ion Batteries

PVDF is commonly a binder used for cathode materials in generation 3 Li ion batteries due to the good binding ability to active material and the current collector with reasonable electrochemical stability and maintaining facile lithium transport. However, organic solvent N-methyl pyrrolidone (NMP) is required for the preparation of slurry in order to dissolve PVDF [1]. These drawbacks of high cost and environmental issues are worsened by the fact that PVDF can easily react with components of liquid electrolytes with possible formation of LiF leading to the unstable performance [2]. Furthermore, fluorinated polymers are considered an environmental risk and are a major concern for recycling efforts [3]. Therefore, reducing the use of polyvinylidene difluoride binder in combination with toxic and expensive N-methyl pyrrolidone (NMP) organic solvent, resulting in safe use and utilization during the battery manufacturing process, is the aim of this work. Here, the sulfide solid state binders are attractive candidates for the anode and cathode composites from the point of view of environmentally friendly use of materials, low cost, and easy electrode processing with subsequent disposal. This study reports the performance of the cathode and anode materials applied to these types of binders and reference binders of polyvinylidene difluoride (PVDF) for these as-obtained samples for lithium-ion batteries. The obtained cathode and anode materials are analyzed by XRD and SEM methods. The electrochemical performance of the obtained electrodes is tested by galvanostatic cycling, cyclic voltammetry, and electrochemical impedance spectroscopy. The obtained electrodes exhibit stable electrochemical performance due to the better uniform distribution of electrode particles with strong adhesion to the current collector for long cycle life and stable formed SEI layer compared to the PVDF-based sample. In addition, these samples maintain stable cycle life after various rate capabilities due to the facilitated lithium-ion diffusion and electronic conductivity. Acknowledgments This work was supported by the financial support of the Austrian Federal Ministry for Climate Action, Environment, Energy, Mobility, Innovation and Technology.

Fast and Durable Lithium Storage Enabled By Tuning Entropy in Wadsley-Roth Phase Titanium Niobium Oxides

To date, Wadsley−Roth phase materials are one of the most promising intercalation-type hosts for fast lithium transport because of the unique crystalline diffusion channels. However, the volume expansion as well as sluggish ion/electron transport kinetics retards its application in grid scale. In recent years, various strategies have been suggested to further improve the overall performance of micro-sized Wadsley-Roth phase materials, such as oxygen vacancy creation or cation substitution.Lately, entropy tuning has received considerable interest due to the favorable entropy-dominated phase-stabilization and ionic conductivity boosting effects.[1,2] However, it has only been applied in a few materials and the understanding of its function is still limited. It has been suggested that entropy-stabilized Wadsley−Roth shear phases with a more ordered structure would be stable upon electrochemical lithium (de-)insertion without a phase transition, while a more disordered structure would compromise the stability of the active material.[3] Therefore, suitable entropy tuning in entropy-stabilized Wadsley−Roth phase materials remains challenging and detailed knowledge about its effect on crystal structure and lithium storage is still lacking.Here, we have successfully realized entropy-stabilized Wadsley-Roth phase Fe0.4Ti1.6Nb10O28.8 (FTNO) in which the increased entropy, due to iron substitution, leads to a reduced grain size, and therefore, a shortened Li+ diffusion channel length.[4] Secondly, the diffusion coefficient and the reaction rate constant are enhanced leading to a reduced overpotential and an improved rate performance. Benefiting from this, the micro-sized FTNO electrode exhibits an enhanced rate ability of 73.7 mAh·g-1 at 50 C as compared to 37.9 mAh·g-1 for its TNO counterpart. Thirdly, the increased entropy results in an extended cycling durability of FTNO electrode which can deliver a specific capacity of 130.0 mAh g-1 after 6000 cycles at high rate of 10 C. Operando XRD analysis demonstrates a suppression of the a-axis deformation during the first stage of the lithiation process. The mechanism is revealed by DFT calculations and found that Fe-O bond lengths undergo less changes than Ti-O during lithiation. Finally, the potential practical application of FTNO anodes has been demonstrated by successfully constructing fast charging and stable LiFePO4‖FTNO full cells.Our results demonstrate the effectiveness of tuning entropy by iron substitution to stabilize the Wadsley-Roth phase with fast charging ability, which can be extended to other intercalation electrodes for enhanced battery applications.[1] Y. Zeng et al., Science 2022, 378, 1320-1324.[2] R. Zhang et al., Nature 2022, 610, 67-73.[3] A. A. Voskanyan et al., Chem. Mater. 2020, 32, 5301-5308[4] J. Zheng et al., Small, smll.202301967R1, accepted.

Space Charges in Solid State Batteries: Friend, Foe or Fantasy?

Thermodynamics tells us that all materials have an internal energy that determines how they act and react with all matter in the universe. Furthermore, it forces all matter to strive towards equilibrium with its surroundings. For solid-state lithium-ion conductors, the chemical potential of lithium is an important parameter that determines stability and influences conductivity. However, it also implies something deeper. The chemical potential of an element in a solid is determined by the bonds that surround it as well as its concentration. Whereas the former is an intrinsic property of the material, the latter can be altered. When two solids with different chemical potentials are placed in contact, a driving force is created for atoms to migrate across the surface and establish thermodynamic equilibrium by altering their concentration. For semiconductors, in which either only a hole or electron can migrate, something interesting occurs. The migrating entity moves across but the counter-charge cannot, resulting in excess charge at the interface. The migrating partner, unable to return to its original material due to thermodynamics, is now unable to dissipate into the new material due to electrostatics. The result is a thin, charged layer across the interface. Because solid electrolytes conduct lithium cations but no anions or electrons, this ‘space-charge layer’ is also thought to occur in solid-state batteries between electrolyte and electrode. Whereas its size is thought to only be a few nanometres, its (negative) influence could be very large as it can act as barrier for lithium transport across the surface. Yet experimental evidence of its existence is rare and investigation of its behaviour even more so. The space charge between two materials is very thin and chemically almost identical to the bulk. But just like how water can carve the stone, we employ liquids to crack a solid-state problem.We find that when mixing an argyrodite solid electrolyte (Li6PS5Cl) with an ionic liquid (1-Ethyl-3-methylimidazolium bis(trifluoromethyls ulfonyl) imide or EMIN TFSI) , we observe a new chemical environment with NMR (see figure) that cannot be attributed to dissolved precursors. We see an increase in the mobility of lithium ions in the solid electrolyte itself with NMR and an increase in conductivity of the mixture with EIS. Furthermore, exchange of lithium has been confirmed between argyrodite and the mystery environment. What does this all mean? Are we observing the illusive space charge layer? Or are we just staring at an empty promise in the well-known shape of a mysterious peak in a spectrum? Figure 1

Modulating Entropic Driving Forces to Promote Metal Ion Mobility in Ionic Liquids

Ionic liquids and organic ionic plastic crystals promise to provide safer, nonflammable alternatives to the unstable organic electrolytes currently used in commercial batteries. However, the performance of ionic liquids and organic ionic plastic crystals as battery electrolytes has been hindered by poor lithium transport, in large part due to the formation of strong lithium-anion complexes. Similar ion coordination exists in ionic liquids containing dissolved sodium, magnesium, and calcium, suggesting that design of ionic liquids for sodium and multivalent battery chemistries will face similar challenges. In this talk, I will discuss our work on the design and characterization of novel ionic liquid-inspired organic electrolytes that leverage unique self-assembly properties of molecular diamond templates, called “diamondoids,” to promote selective redox ion transport. By leveraging the unique self-assembly properties of diamondoids, we show that metal cation-anion coordination can be reduced, and possibly removed, resulting in enhanced mobility of redox-active cations. Specifically, our investigation of electrolyte phase behavior, vibrational spectra, and magnetic environments demonstrates that metal salt solubility can remain high while metal cation-anion coordination is suppressed. Our results provide a new paradigm for enhancing redox species mobility in ionic liquid-derived electrolytes by engineering cation functional groups to enhance organic cation-anion interactions, suppress metal coordination, and leverage packing mismatches to enhance redox species mobility.

Gradual gradient distribution composite solid electrolyte for solid-state lithium metal batteries with ameliorated electrochemical performance

Composite solid electrolytes (CSEs) have emerged as promising contenders for tackling the safety concerns associated with lithium metal batteries and attaining elevated energy densities. Nonetheless, augmenting ion conductivity and curtailing the growth of lithium dendrites within the electrolyte remain pressing challenges. We have developed CSEs featuring a unique structure, in which Li6.4La3Zr1.4Ta0.6O12 (LLZTO) is distributed in a gradient decline from the center to both sides (GCSE). This distinctive arrangement encompasses heightened polymer content at the edges, thereby enhancing the compatibility between CSEs and electrode materials. Concurrently, the escalated LLZTO content at the center functions to impede the proliferation of lithium dendrites. The uniform gradient distribution state facilitates the consistent and rapid transport of lithium ions. At room temperature, GCSE exhibits an ionic conductivity of 1.5 × 10−4 S cm−1, with stable constant current cycling of lithium for over 1200 h. Furthermore, CR2032 coin batteries with a LiFePO4 (LFP)|GCSE|Li configuration demonstrate excellent rate performance and cycling stability, yielding a discharge capacity of 120 mA h g−1 at 0.5C and retaining 90 % capacity after 200 cycles at 60 °C. Flexible solid electrolytes with gradient structures offer substantial advantages in dealing with ion conductivity and inhibition of lithium dendrites, thereby expected to propel the practical application of lithium metal batteries.