Hybrid polymer–ceramic electrolytes are promising candidates for solid-state lithium batteries, yet ion transport across polymerceramic interfaces often limits performance. Here, atomistic molecular-dynamics simulations are used to investigate Li-ion exchange at the Li7La3Zr2O12 (LLZO)–poly(ε-caprolactone) (PCL) interface and to compare directly with LLZO–poly(ethylene oxide) (PEO) at comparable lithium loading. The LLZO–PCL interface exhibits pronounced interfacial structuring, including strong adsorption of carbonyl oxygen atoms at the ceramic surface and a well-defined first Li+ layer. Li-ion transfer across the interface is quantified from transition statistics and analyzed using free-energy profiles along the surface-normal coordinate. At 700 K, LLZO–PCL shows a substantially higher exchange rate than LLZO—PEO (factor 32), primarily due to a significantly lower free-energy barrier for polymer–ceramic transfer, consistent with weaker Li+ coordination in PCL. An overdamped Kramers analysis together with the intra-well autocorrelation function confirms strongly damped local dynamics and suggests differences in effective friction between the minimum and the barrier region. Overall, the results demonstrate that polymer chemistry controls interfacial Li-ion transfer mainly via the barrier height, identifying polymer coordination strength as a key design parameter for reducing interfacial resistance in hybrid solid electrolytes.

ZUSAMMENFASSUNG Lokal hochkonzentrierte Elektrolyte (LHCEs) gelten aufgrund ihrer effektiven Interphasenbildung und der Förderung einer kompakten Li‐Abscheidung als vielversprechende Elektrolytformulierungen für Lithium‐Metall‐Batterien. Ihre praktische Umsetzung wird jedoch häufig durch eine verminderte ionische Leitfähigkeit eingeschränkt. In dieser Studie werden zwei industriell etablierte fluorierte Ether als wirksame Co‐Diluenten untersucht, da sie ein breites elektrochemisches Stabilitätsfenster mit einer niedrigen Viskosität und einer inhärenten Nichtentflammbarkeit verbinden. Die Einbeziehung dieser Komponenten, die üblicherweise als Wärmeträgerflüssigkeiten verwendet werden, führt zu sichereren, weniger entflammbaren Elektrolytformulierungen mit verbesserter Ionenmobilität. Insbesondere zeigt die ternäre Co‐Diluentenformulierung eine verbesserte Ionenmobilität, indem sie die Viskosität des Elektrolyten verringert und gleichzeitig eine übermäßige Ionenagglomeration begrenzt. Aufgrund der verbesserten Ionentransportkinetik werden mit der ternären Co‐Diluentenmischung bei Stromdichten ≥ 1 mA cm −2 geringere Überspannungen und höhere Coulombische Effizienzen erzielt, was in einer anwendungsorientierten Pouchzelle zu einer deutlich verlängerten Lebensdauer im Vergleich zum Basissystem führt. Ergänzende elektrochemische und ex situ Analysen der entnommenen Elektroden zeigen keine erkennbaren Unterschiede der Interphaseneigenschaften, was darauf hindeutet, dass die verbesserte Ionenmobilität die primäre Ursache für die verbesserte Leistungsfähigkeit bei hohen Stromdichten ist.

Abstract Lithium bis(fluorosulfonyl)imide has emerged as a promising alternative to lithium hexafluorophosphate as conducting salt in battery electrolytes due to its favorable physicochemical properties. However, its tendency to promote the dissolution of Al and stainless steel severely limits its practical application, particularly in lithium ion batteries operating above 4 V vs. Li/Li+. Here we show that the dissolution of SUS316 in lithium bis(fluorosulfonyl)imide-based electrolytes is governed by a synergistic mechanism involving trace Cl- impurities and FSI- anions. Cl- initiates localized pitting, while subsequent interactions between FSI- anions and dissolved iron species lead to the formation of soluble complexes, thereby extending the dissolution process. We further demonstrate that the dissolution can be effectively suppressed by adding lithium difluoro(oxalato) borate. The proposed mechanism involves preferential adsorption of oxalate anions at surface of stainless steel, which limits the access of aggressive anions. Additional improvement is achieved by incorporating more dissolution resistive SUS316L components, resulting in ≈300 cycles until 80 % state of health in silicon-graphite | |LiNi0·8Co0·1Mn0·1O2 cells. Furthermore, this improvement has also been confirmed in silicon-graphite | |LiNi0·8Co0·1Mn0·1O2 pouch cells.

We report extensive molecular dynamics simulations of common PEO-LiTFSI electrolytes (PEO = poly(ethylene oxide), LiTFSI = lithium bis(trifluoromethanesulfonyl)imide), covering a broad range of chain lengths (n EO = 2 to 128 ether oxygens per chain) and salt concentrations (r = 1/80 to 2/5 lithium ions per ether oxygen). The obtained systematic and consistent data set reveals the importance of the lithium-ion coordination for the emergence of different chain-length and salt-concentration regimes in lithium-ion transport. Regarding the effect of chain length on cation transport, three regimes are identified. (i) A low-molecular-weight regime (n EO <= 6) with a highly chain-length-specific behavior caused by the great variety of lithium-ion coordination motives and with a sharp regime crossover at the preferred lithium-oxygen coordination number of six. (ii) An intermediate regime characterized by a monotonic decrease of the lithium-ion dynamics caused by the gradually decreasing center-of-mass motion of the polymer chains. (iii) A high-molecular-weight regime featuring chain-length independent ion dynamics after a smooth regime crossover at around n EO approximate to 50 to 100, caused by a transition in the leading transport mechanism away from the polymer's center-of-mass motion to segmental dynamics and chain transfers. The chain-length dependence of the specific volume of polymer electrolytes is governed by chain-end effects like in ordinary polymer melts. Regarding the effect of salt concentration on the cation transport, two regimes are distinguished. (i) A salt-in-polymer regime (r less than or similar to 1/8) with a strong coupling of the cation dynamics to the polymer dynamics due to an almost pure PEO coordination of the lithium ions. (ii) A polymer-in-salt regime (r greater than or similar to 1/8) characterized by a partial decoupling of the cation and polymer dynamics caused by a mixed PEO/TFSI coordination of the lithium ions. A clear crossover from a salt-in-solvent to a solvent-in-salt regime is only observable in electrolytes with a strong preferential binding of the cations to the solvent.

Block-copolymer electrolytes with lamellar microstructure show promising results regarding the ion transport in experiments. Motivated by these observations we study block-copolymers consisting of a polystyrene (PS) block and a poly(ethylene oxide) (PEO) block which were assembled in a lamellar structure. The lamella was doped with various amounts of lithium-bis(trifluoromethane)sulfonimide (LiTFSI) until very high loadings with ratios of EO monomers to cations up to 1:1 were reached. We present insights into the structure and ion transport from extensive Molecular Dynamics simulations. For high salt concentrations most cations are not coordinated by PEO but rather by TFSI and THF. More specifically, LiTFSI partially separates from the PEO domain and forms a network-like structure in the middle of the lamella. This central salt-rich layer plays a decisive role to enable remarkably good cationic mobilities as well as high transport numbers in agreement with the experimental results.

Solid polymer electrolytes (SPEs) based on cross-linked poly(ethylene oxide) (PEO) encompassing lithium salts have gained significant attention as separators in solid-state lithium metal batteries. Here, we employ terahertz time-domain spectroscopy (THz-TDS), as a noninvasive contact-free technique, to investigate the conduction properties of these cross-linked SPEs and unravel their dependencies on the added lithium salt and the sample temperature. The obtained THz conductivity spectra are dominated by THz absorption bands, which we attribute to resonant vibrations within the polymer matrix of the electrolyte. By careful application of Lorentz model, the conductivity spectra have been analyzed, and the relevant polymer vibration modes have been quantitatively assessed. Calculations based on the density functional theory (DFT) were performed to elucidate the possible microscopic mechanisms of these resonant vibrations. This study sheds light on the relevance of polymer matrix vibrations validating the hopping transport of lithium ions in SPEs which ultimately leads to the technologically relevant ionic conduction in the solid-state polymer-based electrolytes.

Understanding lithium (Li) deposition on copper (Cu) substrates is essential for improving the performance and lifetime of zero-excess lithium metal batteries. In this study, Li deposition was investigated under realistic coin-cell conditions using complementary scanning electron microscopy and laser scanning microscopy. A semi-automatic image processing workflow enabled quantitative analysis of Li surface coverage and deposit height as functions of current density and deposited charge. Depending on the applied current, Li morphology evolved from isolated hemispherical islands at low current densities to stripe-like structures aligned with the substrate grooves at higher currents. Deposits on rough, dendritic Cu exhibited more compact and vertically oriented morphologies compared to smooth Cu foil. Based on the experimental observations, a phenomenological geometric model was developed to describe Li growth dynamics. The complex transition from isolated island growth to coalesced film formation was captured by a novel combination of a hemispherical growth model and an Avrami-type model with an effective exponent of , which is consistent with numerical simulations. This geometric framework successfully rationalizes the observed dependence of Li morphology and surface coverage on deposition parameters, providing fundamental insights into Li nucleation and growth mechanisms relevant for anode-free battery design.

Localized high-concentration electrolytes (LHCEs) have been identified as promising electrolyte formulations for lithium metal batteries, due to their effective interphase formation and promotion of compact Li deposition, yet their practical implementation is often limited by reduced ion transport kinetics. In this study, two industrially established fluorinated ethers are identified for the first time in battery research as effective co-diluents as they combine a broad electrochemical stability window with a low viscosity and intrinsic non-flammability. Incorporating these components, commonly used as heat transfer fluids, yields safer, less flammable electrolyte formulations with enhanced ion mobilities. In particular, the ternary co-diluent formulation shows improved ion mobility by reducing the electrolyte's viscosity while limiting excessive ion clustering. Based on the improved electrolyte transport kinetics, lower overvoltages and higher Coulombic efficiencies at current densities ≥ 1 mA cm-2 are achieved with the ternary co-diluent blend, resulting in markedly extended cycle life in an application-oriented zero-excess pouch cell compared with the baseline system. Complementary electrochemical and ex situ analysis of harvested electrodes at moderate current densities reveals no discernible differences in interphase morphology and composition, suggesting enhanced ion mobility as the primary cause of the improved high-rate performance.

Classical molecular dynamics (MD) simulation is the most computationally efficient way to model large molecular systems atomistically for extended periods. However, due to fixed force-field parameters, incorporating on-the-fly quantum reactions is not straightforward. Reactive Step-Based Molecular Dynamics (RSMD) is a simple approach that incorporates quantum reactions by periodically halting the MD simulation and allowing the possibility for reactions at each halt, based on a Poisson-type reaction probability. But, this simple approach cannot capture the simultaneous involvement of diffusion and reaction processes, and because the reaction probability does not include the influence of the diffusion step, errors can be introduced, especially when the diffusion process is not significantly slower than the reaction process. In this work, the efficiency of the RSMD model is increased by reducing these errors and by addressing the influence of the diffusion process on the reaction probability. To reduce these errors, we modify the RSMD mathematical framework by replacing the Trotter splitting employed in previous works with the Strang splitting scheme. To implement these Strang schemes in MD simulations and to scrutinize their validity, we introduce mathematical models involving three and four states, which correspond to two common reaction scenarios: association-dissociation reactions and homogeneous charge transfer reactions, respectively in the presence of diffusion processes. Using these mathematical models, effective reaction probability functions are derived for various diffusion limits, for example, when diffusion processes are extremely fast or extremely slow compared to the reaction processes. All the derived reaction probability functions, in combination with appropriate Strang schemes, are validated for various diffusion regimes with respect to the reaction time scale.

The development of next-generation batteries requires a breakthrough in materials. High throughput experimentation (HTE) is an effective approach to characterize a large number of materials over a broad compositional space in a short time, considerably accelerating the discovery and optimization of materials and their combinations. The main goal is to parallelize automated, repetitive tasks and fully capture data in a findable, accessible, interoperable, reusable (FAIR) fashion, enabling the creation of data libraries. Each HTE facility is unique in its design and nature. To realize full benefits of HTE, careful investment in strategy, hardware and software is required. Well-designed high throughput experiments result in wealth of experimental data, acquired and processed in automated fashion, that creates the foundation for enhanced technical decision making[1]. Acquired datasets have a dual functionality: they enable identification of hit/lead material candidates, in this case electrolyte formulations for given cell chemistries and targeted applications, based on a set of pre-defined criteria (at electrolyte and lab cell level) and key parameter indicators, and serve as “feeding units” for machine learning orchestrated analysis. The integration of HTE with data-driven analysis represents a transformative step in the evolution of materials discovery. The extensive datasets acquired from HTE lays the foundation for optimized design and a comprehensive understanding of electrolytes with data-driven analysis. Through the use of machine learning algorithms, data-driven analysis enables the identification of complex relationships and patterns within the data that may not be apparent using traditional analysis methods[2]. This talk will highlight state-of-the-art achievements along with an assessment of current and future challenges as well as resulting perspectives towards accelerated development of advanced non-aqueous battery electrolytes and their interfaces/interphases in different battery chemistries. References: A. Benayad, D. Diddens, A. Heuer, A. N. Krishnamoorthy, M. Maiti, F. Le Cras, M. Legallais, F. Rahmanian, Y. Shin, H. Stein, M. Winter, C. Wölke, P. Yan, I. Cekic-Laskovic,High-Throughput Experimentation and Computational Freeway Lanes for Accelerated Battery Electrolyte and Interface Development Research , Advanced Energy Materials 2021, 2102678; DOI:10.1002/aenm.202102678 P. Yan, Mirko Fischer, H. Martin, C. Wölke, A. N. Krishnamoorthy, I. Cekic-Laskovic, D. Diddens, M. Winter, A. Heuer, Non-aqueous Battery Electrolytes: High-Throughput Experimentation and Machine Learning-Aided Optimization of Ionic Conductivity, Journal of Materials Chemistry 2024, A 12(30); DOI:10.1039/D3TA06249J

Organic radical batteries (ORBs) based on the TEMPO (2,2,6,6-tetramethylpiperidin-1-yl oxyl) radical have drawn significant attention, owing to their unique redox properties. A key factor influencing ORB's redox properties, i.e., the kinetics of the electron transfer between the TEMPO-TEMPO+ pairs, is the communication between the underlying redox-active states as given by the electronic coupling. However, due to the complex structure, predicting accurate electronic couplings for these pairs is computationally expensive and challenging. In this study, we introduce a machine learning (ML) workflow to predict the electronic coupling for TEMPO-TEMPO+ pairs simply by their specific geometric orientations. For the ML models, a data set was generated through time-dependent density functional theory calculations coupled with the Generalized Mulliken Hush method to assess energies, (transition-)dipole moment, and couplings for specific TEMPO-TEMPO+ configurations obtained from classical molecular dynamics simulations that mimic a realistic electrolyte environment. Our results demonstrate that, among the three ML models-linear regression, kernel ridge regression (KRR), and random forest-the KRR model, with its kernel-based approach, most effectively handles the correlated orientation-based descriptors. Moreover, our SHapley Additive exPlanations (SHAP)-based feature importance analysis indicates that multiple orientation factors jointly influence electronic coupling, rather than any single distance or angle dominating, with each parameter's impact strongly contingent on the values of the others which is in agreement with previous studies computational by the consortium.

Relevant information about the nature of the dynamics of ions in electrolytes can be obtained by studying the nonlinear dependence on an applied electric field. Here we use molecular dynamics (MD) simulations to study the field effects for a polymer electrolyte, i.e. a mixture of PEO with Li-TFSI salt, for a range of different temperatures and salt contents. Specifically, the effects of the electric field on the current and the diffusivities parallel and orthogonal to the electric fields are analyzed. It is argued that the nonlinear effects in the weak-field regime provide information about the nature of the disorder. In contrast, the nonlinear effects in the high-field regime allow one to extract effective hopping distances. They are in close agreement with typical nearest-neighbor length scales obtained from detailed structural analysis and are hardly dependent on the salt content. Furthermore, from the study of the temperature dependence in the high-field regime, effective barrier heights can be determined, which in this regime decrease linearly with increasing field. The disappearance of the effective barriers, estimated by linear extrapolation, occurs close to the fields where the MD simulations start to be numerically unstable. Finally, the interpretation is supported by a comparison with analytically known solutions of disordered hopping models.

High concentrations of conducting salt in electrolyte formulations enhance the agglomeration of ionic species, which has been demonstrated to yield anion-derived electrode-electrolyte interphases and improved reversibility in several battery configurations. However, industrial application of these electrolytes may be limited due to high costs of electrolyte conducting salts. Here, weakly solvating electrolyte solvents with tailored coordination strength have been established as an approach to achieve ionic agglomeration at moderate conducting salt concentrations and without per-fluorinated diluents. However, the inevitable presence of uncoordinated solvent molecules in this electrolyte concept renders them susceptible to oxidative decomposition. Although previous efforts demonstrated fluorination as an effective design strategy to tailor the oxidative stability of weakly solvating electrolytes, the per-fluorinated solvents are toxic and harmful to the environment. Herein, the incorporation of silicon is evaluated as an eco-friendly approach to dispel electron density of the oxygen lone pair. Though steric demand of substituents is already sufficient to tailor the coordination strength, negative hyperconjugation effectively expands the oxidative stability limit of weakly solvating electrolytes. Combining ion agglomeration and intrinsic oxidative stability, the herein introduced weakly solvating electrolyte enables a notable improvement of reversibility under eco-friendly conditions, presenting a valid alternative to fluorinated electrolyte solvents.

Localized high-concentration electrolytes (LHCEs) are based on the immiscibility of a concentrated salt phase and a diluent phase, creating an internal interface. Here, we study LHCEs based on lithium bis(fluorosulfonyl)imide or lithium bis(trifluoromethanesulfonyl)imide as the conducting salt, 1,2-dimethoxyethane as the solvent, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) as the diluent. With increasing dilution, trends of dynamic properties such as ionic conductivity and self-diffusion strongly depend on the anion structure. By analyzing ion coordinations by NMR and Raman spectroscopy, we attributed this to a different interfacial affinity of the anions: TFSI- anions are more likely than FSI- anions to interact with the diluent molecules. This stabilizes the TTE|conducting salt interface, causing a less compact and more mobile conducting salt-rich phase. Furthermore, it leads to a higher degree of ion dissociation, which explains the enhanced molar ionic conductivity found upon dilution of TFSI-based LHCEs, as opposed to FSI-based LHCEs. These differences are most probably due to the larger size and enhanced charge delocalization of the TFSI- anion compared to the FSI- anion, making the interaction with the uncharged TTE molecule more favorable. Thus, understanding local ion coordinations in different electrolyte formulations plays a crucial role in optimizing transport properties.

Nonlinear ion transport in polymer electrolytes provides key information about the underlying energy landscape and transport mechanisms. Molecular dynamics simulations are employed to investigate the field-dependent ion dynamics in poly(ethylene oxide)/LiTFSI mixtures over a range of temperatures and salt concentrations. The electric-field dependence of the current and the parallel and orthogonal diffusivities is analyzed in detail. In the weak-field regime, the nonlinear response reflects the degree and character of energetic disorder, while in the high-field regime, effective hopping distances and barrier heights can be extracted. The resulting hopping lengths agree with the typical nearest-neighbor separations from structural analysis and show little dependence on salt concentration. The apparent linear decrease in the effective activation barriers with increasing field accounts for the onset of unbounded ion motion at high fields. Comparison with analytically tractable hopping models in disordered energy landscapes provides a consistent physical interpretation of both the low- and high-field regimes. Overall, the study demonstrates how hopping models can be employed to quantitatively and conceptually rationalize nonlinear ion dynamics in polymer electrolytes.

Doping is a cornerstone of optimizing cathode active materials, yet how dopants integrate into the lattice and affect structural stability remains a highly debated topic. In this study, we investigated the doping of Lithium Nickel Oxide (LNO) using Monte Carlo simulations based on a cluster expansion framework. Focusing on Ta5+, Nb5+, W6+, and Mo6+ dopants, our simulations incorporated Coulombic interactions and temperature-dependent sampling to analyze dopant distribution across various temperatures. Our analysis revealed distinct clustering trends among the dopants (Ta > Nb > W> Mo), which correlate with their oxygen bond dissociation energies, providing insights into dopant incorporation mechanisms and their impact on structural stability.

In this study, we delve into the complex electron transfer reactions associated with the redox-active (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO), a common component in organic radical batteries (ORBs). Our approach estimates quantum electron-transfer (ET) energies using Density Functional Theory (DFT) calculations by sampling from structures simulated classically. This work presents a comparative study of reorganization energies in ET reactions across different solvents. Furthermore, we investigate how changes in the electrolyte environment can modify the reorganization energy and, consequently, impact ET dynamics. We also explore the relationship between classical and quantum ET energies using linear regression models. Importantly, this comparison between quantum and classical ET energies underscores the role of quantum effects, like charge delocalization, in offering added stabilization post-redox reactions. These effects are not adequately represented by the classical ET energy distribution. Our study shows that, although we find a significant correlation between the ET energies computed by DFT and the classical force field, the regression parameters depend on the solvent, highlighting that classical methods should be benchmarked by DFT before applying them to novel electrolyte materials.

We present molecular dynamics simulations on localized high-concentration electrolytes (LHCE) based on the conducting salt lithium bis(fluorosulfonyl)imide (LiFSI) or lithium bis(trifluoromethanesulfonyl)imide dissolved in the solvent 1,2-dimethoxyethane and diluted to two different degrees with the diluent 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether. Due to the immiscibility of the conducting salt phase (salt + solvent) and the diluent phase, LHCEs feature a complex microstructure of two phases forming an internal interface. In this study, we not only investigate the lithium coordination structure in the conducting salt phase but also the size and composition of its interface to the diluent phase by Voronoi tessellations. Furthermore, we investigate the influence on the ion transport by evaluating Onsager coefficients. We show that an LHCE containing the surface-active anion TFSI- creates an anion-rich internal interface, leading to enhanced ion dissociation and anticorrelated ion movement. On the other hand, the smaller FSI- anion with a more localized charge distribution and less amphiphilic character shows no enrichment at the internal interface, but rather a depletion. By increasing LiFSI concentration, we even observe a solvent-rich internal interface due to a large and branched Li-anion network. Furthermore, the less diffuse interface and enlarged Li-anion network lead to lower ion-ion anticorrelations and a stronger convective flux of the conducting salt phase, which is compensated by a flux of the diluent phase, especially in the higher concentrated LiFSI based LHCE.