Electrolytes For Li-ion Batteries Research Articles

Machine Learning Interatomic Potential to Investigate Fundamentals of Electrolytes for Li-ion Solid-State Batteries

Machine learning and deep learning are used to construct interatomic potential with superior performance by satisfying the accuracy of density functional theory (DFT) calculations while requiring computational resources comparable to those required for classical molecular dynamics simulations. In this study, the machine learning interatomic potential (MLIP) is successfully constructed using moment tensor potential (MTP) for predicting the ionic conductivity of Li-ion solid-state electrolytes with Li-Ge-P-X′ and Li-X″-P-S structures, where X′ = O, S, or Se and X″ = Ge, Si, or Sn. <i>Ab initio</i> molecular dynamics (AIMD) simulations are performed to construct the initial training database for MTP; the constructed MLIP exhibits excellent accuracy with an R<sup>2</sup> value of 0.98 for predicting the potential energy value. The excellent performance of MLIP is further validated by calculating the lattice constant and bulk modulus. Finally, the ionic conductivity is obtained by performing MTP-based molecular dynamics (MD); the predicted value exhibits good agreement with previous AIMD results. Further, MTP-MD evidently runs three orders of magnitude faster than AIMD. The obtained results clearly demonstrate that MLIP can be used to rapidly determine promising solid-state electrolytes with accuracy comparable to that of DFT while greatly reducing the computational cost.

High-voltage ionic liquid-based flexible solid polymer electrolyte for high-performance Li-ion batteries

Ionic liquid–solid polymer electrolyte membrane for sustainable battery technology.

Considering cell volume in dopant screening for improving Li-ion mobility in an amorphous LiPON solid-state electrolyte: an ab initio study.

Engineering of solid electrolytes of Li-ion batteries is carried out for achieving high levels of ionic conductivity and preserving low levels of electrical conductivity. Doping metallic elements into solid electrolyte materials composed of Li, P, and O is quite challenging due to instances of possible decomposition and secondary phase formation. To accelerate the development of high-performance solid electrolytes, predictions of thermodynamic phase stabilities and conductivities are necessary, as they would avoid the need to carry out exhaustive trial-and-error experiments. In this study, we demonstrated theoretical approach to increase the ionic conductivity of amorphous solid electrolyte by doping: cell volume-ionic conductivity relation. Using density functional theory (DFT) calculations, we examined the validity of the hypothetical principle in predicting improvements in stability and ionic conductivity with 6 candidate doping elements (Si, Ti, Sn, Zr, Ce, Ge) in a quaternary Li-P-O-N solid electrolyte system (LiPON) both in crystalline and amorphous phases. The doping of Si into LiPON (Si-LiPON) was indicated to stabilize the system and enhance ionic conductivity based on our calculated doping formation energy and cell volume change. The proposed doping strategies provide crucial guidelines for the development of solid-state electrolytes with enhanced electrochemical performances.

Effects of Li content on stability, electronic and Li-ion diffusion properties of Li<sub>3<i>x</i></sub>La<sub>(2/3)–<i>x</i></sub>†<sub>(1/3)–2<i>x</i></sub>TiO<sub>3</sub> surface

Li<sub>3<i>x</i></sub>La<sub>(2/3)–<i>x</i></sub>†<sub>(1/3)–2<i>x</i></sub>TiO<sub>3</sub>(LLTO) is a promising solid-state electrolyte for Li-ion batteries. We study the effect of Li content on the stability, electronic and Li-ion diffusion properties of LLTO surface based on first-principles and molecular dynamics simulations. We consider both Li-poor and Li-rich LLTO surfaces. The results show that La/O/Li-terminated LLTO (001) is the most stable crystal surface. Further, LLTO (001) surface gives better stability when Li content is 0.17, 0.29, and 0.38 for Li-poor phase, while 0.33, 0.40, and 0.45 for Li-rich phase . Electronic structure calculations infer that in both Li-poor and Li-rich LLTO(001) surfaces there occurs the transition from conductor to semiconductor with the increase of Li content. Besides, we find that Li-ion always keeps a two-dimensional diffusion path for different Li content. As Li content increases from 0.17 to 0.38 for Li-poor LLTO (001) surface, Li-ion diffusion coefficient increases gradually and Li-ion diffusion barrier decreases from 0.58 eV to 0.42 eV. Differently, when Li content increases from 0.33 to 0.45 for Li-rich LLTO(001) surface, it does not follow a monotonic trend for diffusion coefficient nor for diffusion barrier of Li-ion. In this case, Li-ion diffusion coefficient is the largest and Li-ion diffusion barrier is the lowest (0.30 eV) when Li content is 0.40. Thus, our study suggests that by varying Li content, the stability, band gap, and Li-ion diffusion performance of LLTO (001) can be changed favorably. These advantages can inhibit the formation of lithium dendrites on the LLTO (001) surface.

Solvent and catalyst free vitrimeric poly(ionic liquid) electrolytes.

Polymer electrolytes (PEs) are a promising alternative to overcome shortcomings of conventional lithium ion batteries (LiBs) and make them safer for users. Introduction of self-healing features in PEs additionally leads to prolonged life-time of LIBs, thus tackling cost and environmental issues. We here present solvent free, self-healable, reprocessable, thermally stable, conductive poly(ionic liquid) (PIL) consisting of pyrrolidinium-based repeating units. PEO-functionalized styrene was used as a co-monomer for improving mechanical properties and introducing pendant OH groups in the polymer backbone to act as a transient crosslinking site for boric acid, leading to the formation of dynamic boronic ester bonds, thus forming a vitrimeric material. Dynamic boronic ester linkages allow reprocessing (at 40 °C), reshaping and self-healing ability of PEs. A series of vitrimeric PILs by varying both monomers ratio and lithium salt (LiTFSI) content was synthesized and characterized. The conductivity reached 10-5 S cm-1 at 50 °C in the optimized composition. Moreover, the PILs rheological properties fit the required melt flow behavior (above 120 °C) for 3D printing via fused deposition modeling (FDM), offering the possibility to design batteries with more complex and diverse architectures.

Molecular dynamics simulations of fluoroethylene carbonate and vinylene carbonate as electrolyte additives for Li-ion batteries

ABSTRACT Contemporary electrolyte additives have captivated the attention of researchers since additives were reported to play a very crucial role in supporting the formation of an effective solid electrolyte interphase (SEI) in the case of silicon if used as an anode. The choice of a good solvent with additives demonstrates a significant impact on the solvation and diffusivity of lithium ions. Fluoroethylene carbonate (FEC) and Vinylene carbonate (VC) were extensively used additives for increasing the lifespan of Li-ion batteries (LIBs). In the current study, structural, dynamical, and transport properties of six different systems were investigated by applying classical molecular dynamics (MD) simulations. The properties obtained from the simulations suggested system E consisting of DMC, 1M LiPF, and 10% FEC, to be the best medium for the electrolytes for LIBs, since the diffusion coefficient of Li ions and ionic conductivity of LiPF were estimated to be of high values for the system E. However, before the evaluation of the transport properties, the structural properties in terms of radial distribution functions and spatial distribution functions were evaluated for DMC molecules with reference to DMC, Li, and PF ions. The structure data were also found to be in fair agreement with experimental and previous simulation results reported so far. Based on the finding of this study, it was suggested that DMC as a solvent with a 10% FEC additive could be considered a good medium for electrolytes for the improved performance of LIBs compared to VC as an additive to DMC.

A novel garnet-type high-entropy oxide as air-stable solid electrolyte for Li-ion batteries

Li-ion batteries are considered prospective candidates for storage systems because of their high energy density and long cycling life. However, the use of organic electrolytes increases the risk of explosion and fire. Hence, all-solid-state Li-ion batteries have attracted considerable attention because the use of solid electrolytes avoids the combustion of electrolytes and explosions, and enhances the performance of batteries. Garnet-type oxides are commonly used solid electrolytes. The common Ta-doped Li7La3Zr2O12 can react easily with CO2 and H2O in air, and its ionic conductivity decays after contact with air. In this study, a novel garnet-type, high-entropy oxide, Li6.4La3Zr0.4Ta0.4Nb0.4Y0.6W0.2O12 (LLZTNYWO), is successfully synthesized as a solid electrolyte for Li-ion batteries,using a conventional solid-state method. Ta, Nb, Y, and W are used as substitutes for Zr, which significantly increase conductivity, have high stability in air, and a lower sintering temperature. LLZTNYWO achieves higher Li-ion conductivity at 1.16 × 10−4 S cm−1 compared to mono-doped Li6.6La3Zr1.6Ta0.4O12 (6.57 × 10−5 S cm−1), Li6.6La3Zr1.6Nb0.4O12 (2.19 × 10−5 S cm−1), and Li6.2La3Zr1.6W0.4O12 (1.16 × 10−4 S cm−1). Additionally, it exhibits higher ionic conductivity compared to equimolar Li5.8La3Zr0.4Ta0.4Nb0.4Y0.4W0.4O12 (1.95 × 10−5 S cm−1). The Li-ion conductivity of LLZTNYWO remains constant for 30 days in the atmosphere without decay, thereby revealing its excellent air stability. Furthermore, LLZTNYWO exhibits a remarkable electrochemical window of up to 6 V vs Li/Li+ and excellent electrochemical stability against Li metal after cycling at 0.1 mA·cm−2 for 2 h, which indicates that it is a promising solid electrolyte for Li-ion batteries.

Thermal, electrical and electrochemical properties of ionic liquid-doped poly(ethylene oxide)–LiTDI polymer electrolytes for Li-ion batteries

Thermal, electrical and electrochemical properties of ionic liquid-doped poly(ethylene oxide)–LiTDI polymer electrolytes for Li-ion batteries

Understanding the Solvation Structure of Li-Ion Battery Electrolytes Using DFT-Based Computation and 1H NMR Spectroscopy.

Molecular dynamics (MD) simulations, density functional theory (DFT) calculations, and 1H NMR spectroscopy were performed to gain a complementary understanding of the concentrated Li-ion electrolyte system, lithium bis(trifluoromethanesulfonyl)imide (Li[TFSI]) dissolved in tetraglyme. The computational methods provided the concentration dependence of differing solvation structure motifs by reference to changes in the corresponding NMR spectra. By combining both the computational and experimental methodologies, we show that the various solvation structures, dominated by the coordination between the tetraglyme (G4) solvent and lithium cation, directly influence the chemical shift separation of resonances in the 1H NMR spectra of the solvent. Thus, the 1H NMR spectra can be used to predict the fraction of tetraglyme involved in the solvation process, with quantitative agreement with solvation fraction predictions from MD simulation snapshots. Overall, our results demonstrate the reliability of a hybrid computational and experimental methodology to understand the solvation structure and hence transport mechanism of LiTFSI-G4 electrolytes in the low concentration region.

Three-electrode in mono-electrolyte for integrated photo-assisted lithium sulfur battery

The combination of solar cells and rechargeable batteries has been confirmed as a new strategy for the development of solar energy utilization. However, the high charging voltage of Li-ion battery (3.0–4.2 V) and incompatible electrolyte with solar cell is adverse to the combination of photo-assisted rechargeable battery (PRB). In this work, Li–S battery as an energy storage unit is combined with dye-sensitized solar cell to form an integrated three-electrode photo-assisted rechargeable Li–S battery (PRSB). The compatible C/S electrode provides a bridge for realizing the bi-function of photoelectric conversion and storage. In contrast to the dual electrolytes in the previously reported PRBs, lithium bis((trifluoromethyl)sulfonyl)azanide (LiTFSI), namely the highly compatible mono-electrolyte in our newly designed PRSB with three-electrode, facilitates the charge separation and enhances the capacity and stability of integrated photo-assisted rechargeable battery. With the compensation of photogenerated carrier, the charge voltage of PRSB drops 0.12 V and the discharge capacity increases to 885 mAh g−1 under solar charging, indicating that the integrated device is promising to save electric energy and improve the performance of PRBs.

Unveiling the Mystery of Lithium Bis(fluorosulfonyl)imide as a Single Salt in Low-to-Moderate Concentration Electrolytes of Lithium Metal and Lithium-Ion Batteries

This work aims to unveil the mystery about the suitability of using lithium bis(fluorosulfonyl)imide (LiFSI) as a single salt in low-to-moderate concentration electrolytes of Li metal and Li-ion batteries by studying the corrosion behavior of Al and stainless steel (SS) in 3:7 (wt) ethylene carbonate/ethyl methyl carbonate electrolytes. It is found that regardless of LiFSI concentrations (0.8–1.8 m), there is a ∼4.3 V vs Li/Li+ of “threshold potential,” above which Al suffers uncontrollable corrosion. This finding is confirmed in graphite/LiNi0.80Co0.15Al0.05O2 pouch cells, however, none of Li/LiNi0.80Co0.10Mn0.10O2 coin cells can be charged to 4.2 V in the first charge. Post-mortem analysis of the failed coin cells reveals that the failure is due to anodic corrosion of the SS spacer. Further study on two types of spacers, made by SS304 and SS316L, indicates that the SS316L spacer is more corrosion resistant, however, it still cannot support batteries for long-life cycling. The suitability for using LiFSI as a single electrolyte solute in Li-ion batteries can be guaranteed as long as, at the cathode, the charge voltage is strictly limited to the “threshold potential” and the SS components are avoided. This conclusion is further verified by using four different sources of LiFSI.

Ligand Elucidation of Dissolved Transition Metal Ions in Pristine and Degraded Electrolytes in Li-Ion Batteries

During operation of a Li-ion battery, layered transition metal oxides release metal ions into the electrolyte. In addition to capacity loss, dissolved metal ions are mobile in the electrolyte and can deposit at the anode, enhancing Faradaic losses and posing the risk of dendrite formation.[1] In the electrolyte solution, transition metal ions are characterized mainly by their oxidation state and complexation behavior, which dictate the transport through the electrolyte. Additionally, mechanistic insights, indirect information about electrolyte degradation, and design of counter-measures might be extracted thereof. However, particularly the coordination sphere is difficult to access, due to inherently low concentrations and scarcity of suitable analytics.In this work, the coordination sphere of dissolved transition metal ions is selectively probed by pulse Electron Paramagnetic Resonance (pEPR). pEPR selectively addresses isolated paramagnetic ions, masking analytical interference from other species in the battery. Because of its known impact on capacity fade, firstly Mn2+ is analyzed in premixed pristine and degraded electrolyte solutions. Carbonates with high dielectric constants such as ethylene carbonate (EC) are the dominant ligands, accompanied by electrolyte salt anions for charge compensation. If present, trace amounts of electrolyte degradation products such as fluorophosphates selectively form the first coordination sphere. The results from pEPR measurements, that have to be performed on frozen solutions at cryogenic temperatures, agree with paramagnetic NMR results at ambient temperatures. Furthermore, samples from batteries operating with vanadium-based cathodes were investigated. Depending on the storage conditions, V4+ ligands predominantly consist of decomposition products from the electrolyte solvent ethylene carbonate (e.g. ethylene glycol anions) or electrolyte salt LiPF6 (fluorophosphates).[2,3] [1] C. Zhan, T. Wu, J. Lu, K. Amine, Energy Environ. Sci. 2018, 11, 243–257.[2] C. Szczuka, R.-A. Eichel, J. Granwehr, ACS Appl. Energy Mater. 2022, 5, 449–460.[3] C. Szczuka, P. Jakes, R.-A. Eichel, J. Granwehr, Adv. Energy Sustain. Res. 2021, 2, 2100121.

Chemometric and Machine Learning Analysis of Lithium Concentration and Solvation Behavior in Li-Ion Battery Electrolytes

The demand for batteries is rapidly growing across a range of technologies. The increasingly diverse use cases for batteries require various capabilities, particularly requirements for high energy densities, that are currently unmet by traditional Li-ion batteries. Electrolyte stability proves to be a bottleneck for battery advancement towards energy dense chemistries beyond Li-ion, including metal anodes. In situ spectroscopy tools, such as Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, and X-ray spectroscopy, have provided insight into critical molecular-level interactions in batteries during cycling. These in situ tools have yielded continuous improvement of electrolyte properties. Spectroscopy datasets, however, contain many nuances that challenge meaningful human understanding. Artificial intelligence and chemometric tools can be coupled with in situ spectroscopy to find relevant interpretations of spectral datasets and elucidate complex molecular phenomena. In this research, an analysis was performed on FTIR spectroscopy data from an electrolyte composed of LiPF6 in ethylene carbonate (EC) and ethyl methyl carbonate (EMC) to discern solvation behavior using principal component analysis (PCA) and a convolutional neural network (CNN). PCA pinpointed exact band locations of solvation shifting behavior in the IR spectra and improved understanding of the relationship between lithium concentrations and peak changes. The CNN was trained with spectral datasets of electrolytes with known lithium concentrations and then could predict lithium concentrations from spectral datasets with extraordinarily high accuracy. Additionally, the CNN interpreted FTIR spectral datasets from a graphite half-cell with EC/EMC/LiPF6 electrolyte and accurately determined the lithium concentration in the bulk electrolyte. The CNN also observed lithium depletion events (up to 10% lithium depletion) in the graphite anode during fast-charging cycles of the galvanostatic intermittent titration technique. This research breaks new ground on using advanced computational tools for in situ spectroscopic analysis of battery electrolytes and demonstrates an improved understanding of complex molecular-level phenomena in electrolytes.

Characterization and Model-Based Investigation of Lithium-Ion Battery Cell Formation

The formation process of lithium-ion battery cells is one of the main contributors to the overall cell cost [1]. During this process step the solid electrolyte interface (SEI) is initially built. It is agreed upon that the composition and morphology of the SEI influences the safety and aging behaviour of the battery cell. However, the processes behind the initial build-up are not fully understood due to the manifold influencing factors, such as electrolyte composition, electrode structure, temperature, and formation protocol, which all impact the complex nanoscale processes at the interface [2,3,4]. High experimental effort is needed to investigate and optimize this process. Detailed multiscale models based on first principles can provide insights into the SEI formation but require many parameters that are difficult to determine and are also associated with uncertainty [5,6]. Therefore, those approaches are limited in terms of exploration and optimization of the formation process. Hence, there is a need for novel methods that enable to obtain information about the SEI growth and investigate the influential factors to effectively accelerate the development process. Here, we suggest a model-based approach that uses lumped growth models that can quickly be identified by using differential voltage data of formation experiments. Further, models are applied to simulate the impact of the formation protocol on the SEI formation with minimal experimental effort.Firstly, we present a parameter identification process for the applied growth model, which is based on a slow formation protocol and a reference measurement in a 3-electrode setup. The parameterization of the SEI model is conducted by combining coulometry and differential voltage analysis (DVA). Shifts of distinct peaks, i.e. feature, within the anode potential curve during the formation and the reference measurement are used to deduce the capacity loss due to the SEI growth. Using the SEI density and surface area of the electrode, the capacity loss is converted into an effective layer thickness, which is used to fit the parameters of the growth model. Within the SEI model different growth mechanisms can be implemented and compared. It is demonstrated that this approach can show differences in the SEI formation for a variation of electrolyte compositions, i.e. the electrolyte additives as can be seen in Figure 1. Afterwards, a simulation study for different formation protocols is presented. The identified growth model has been coupled with a pseudo-2-dimensional (P2D) model. Simulations are also compared to experimental data for various formation protocols and are shown to be in good agreement. Simulations reveal that the final effective film thickness is only slightly affected by current magnitude and mainly depends on the formation time as well as the anode potential. Furthermore, it can be seen that higher formation currents affect the homogeneity of the SEI across the electrode negatively.To sum up, the DVA analysis of the formation yields information about the SEI growth. This can be used to parametrize SEI growth models and investigate film growth mechanisms for different electrolyte compositions. Coupling growth models with P2D models enables to explore the influence of the formation protocols. To conclude, this novel approach enables to significantly accelerate the optimization of battery cell formation. In future work the approach could be refined to enable application to full cell voltage data, which would allow its use within battery production lines and could support end of line testing.[1] A. Kwade, W. Haselrieder, R. Leithoff, A. Modlinger, F. Dietrich, K. Dröder, Current status and challenges for automotive battery production technologies, Nature Energy, 2018, 3, DOI: 10.1038/s41560-018-0130-3[2] G. E. Blomgren, Liquid electrolytes for lithium and lithium-ion batteries, Journal of Power Sources, 2003, 119, DOI: 10.1016/S0378-7753(03)00147-2[3] S. J. An, J. Li, C. Daniel, D. Mohanty, S. Nagpure, D. L. Wood, The state of understanding of the lithium-ion-battery graphite solid electrolyte interphase (SEI) and its relationship to formation cycling, Carbon, 2016, 105, DOI: 10.1016/j.carbon.2016.04.008.[4] K. Xu, Electrolytes and interphases in Li-ion batteries and beyond, Chemical reviews, 2014, 114(23), DOI: 10.1021/cr500003w.[5] A. Wang, S. Kadam, H. Li, S. Shi, Y. Qi, Review on modeling of the anode solid electrolyte interphase (SEI) for lithium-ion batteries, npj Computational Materials, 2018, 4, DOI: 10.1038/s41524-018-0064-0[6] F. Röder, R. D. Braatz, U. Krewer, Multi-scale simulation of heterogeneous surface film growth mechanisms in lithium-ion batteries, Journal of the Electrochemical Society, 2017, 164 (11), DOI: 10.1149/2.0241711jes. Figure 1

Investigation on Tethered Anion Effects in Solid Polymer Electrolytes for Li-Ion Batteries

Solid polymer electrolytes (SPEs) have been proposed to reduce concentration polarizations within batteries by immobilizing anions to the polymer matrix, which can help stabilize the electrodeposition process and extend Li-ion battery lifetime. Unfortunately, single-ion conducting SPEs continue to suffer from poor conductivity due to coupling with the slow segmental mobility of polymer chains and poor ion pair dissociation. Our group systematically investigated how different tethered anions affect the Li-ion conduction and polymer segmental mobility. Copolymers were synthesized using a common neutral monomer, poly(ethylene glycol) methyl ether methacrylate (PEGMA), with a series of different anionic monomers: 4-styrene sulfonate, 4-styrene phosphonate, 4-styrene TFSI, and methacrylate TFSI. These monomers presented a series of anions of varying strength with the same styrene structure, sulfonate vs. phosphonate vs. TFSI, as well as exploring structural monomer changes for the same TFSI anion, styrene vs. methacrylate, that allows for systematic changing of polymer electrolyte properties. Each copolymer series was further expanded by changing the composition of neutral-to-anionic monomers, ranging from 10-67 mol% anionic. The increased ion exchange capacity of the phosphonate groups led to a high degree of ion aggregation that exhibited hard mechanical properties and very low Li-ion conductivities. Increasing the electron delocalization of the ions from sulfonate to TFSI greatly improved the conductivities and lowered activation energies of ion transport, with methacrylate being slightly better than styrene. Implications of these results will be discussed for next-generation polymer electrolyte design.

High Voltage Electrolytes to Stabilize Ni-Rich Lithium Battery Performance

State-of-the-art (SOA) lithium-ion (Li-ion) batteries are approaching their specific energy density limit (~250 Wh kg−1).1 Layered structured, nickel-rich (Ni-rich or high Ni content) lithium transition metal oxides, e.g., LiNi0.8Mn0.1Co0.1O2 (NMC811), have attracted great interests2 owning to their practically deliverable high specific capacity >200 mAh/g. Coupled with high average discharge voltages (~4V vs. Li/Li+), Ni-rich cathode-based lithium batteries possess a great potential to achieve much higher specific energies, e.g., >350 Wh/kg at cell level targeted for electric drive vehicles,3 than SOA Li-ion batteries. In addition, Ni-rich oxides are economically viable as low-cost battery cathode materials due to their low cobalt content. However, Ni-rich cathode-based Li-ion batteries exhibit a quick capacity degradation upon cycling particularly at high charge cutoff voltages (e.g., 4.5V vs. Li/Li+) and at elevated temperatures. Possible degradation mechanisms of Ni-rich based Li cells include structural changes of the material (large c-axis shrinkage at high potentials)4 and parasitic reactions that arise from the interactions between the electrolytes and highly reactive delithiated cathode surface (due to high oxidation state Ni4+ ions).5,6 Therefore, R&D efforts are needed to tackle technical challenges facing the Ni-rick based Li batteries before they become commercially viable.We will present our efforts of developing high voltage electrolytes to afford stable electrochemical performance of Ni-rich cathode-based Li cells. Figure 1 shows the electrochemical performance of NMC-811 cathode, paired Li metal anode, in conventional Li-ion battery electrolyte (Baseline electrolyte) and the high voltage electrolyte developed in this study, evaluated at C/4 rate during the formation and 1 C rate during cycling, between 2.5V and 4.5V, at room temperature. The cell with the high voltage electrolyte maintained ~80% capacity retention after 400 cycles. In contract, the cell with the baseline electrolyte experieced a large capacity fade with only ~25% capacity retention after 400 cycles. The superior cycle stability of the high votage electrolyte, Ni-rich based cell is attributed to the inharently high-voltage stable, multi-functional. Electrolyte chemical structures and their correlation with the electrochemical stability will be discussed. References Chen, W.; Lei, T.; Qian, T.; Lv, W.; He, W.; Wu, C.; Liu, X.; Liu, J.; Chen, B.; Yan, C.; Xiong, J., Advanced Energy Materials 2018, 8 (12).Jiang, M.; Danilov, D. L.; Eichel, R.-A.; Notten, P. H. L., Advanced Energy Materials 2021, 11 (48), 2103005.Gomez‐Martin, A.; Reissig, F.; Frankenstein, L.; Heidbüchel, M.; Winter, M.; Placke, T.; Schmuch, R., Advanced Energy Materials 2022, 12 (8).Cho, D.-H.; Jo, C.-H.; Cho, W.; Kim, Y.-J.; Yashiro, H.; Sun, Y.-K.; Myung, S.-T., Journal of The Electrochemical Society 2014, 161 (6), A920-A926.Chen, C. H.; Liu, J.; Amine, K., Journal of Power Sources 2001, 96 (2), 321-328.Li, J.; Downie, L. E.; Ma, L.; Qiu, W.; Dahn, J. R., Journal of The Electrochemical Society 2015, 162 (7), A1401-A1408. Acknowledgement This material is based upon work supported by the Naval Air Warfare Center Weapons Division, China Lake, CA under Contract No N6893622C0017. Any opinions, findings and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the Naval Air Warfare Center Weapons Division, China Lake, CA. Figure 1

Ethylene-Carbonate-Free Electrolytes for Rechargeable Li-Ion Pouch Cells at Sub-Freezing Temperatures.

Sub-freezing temperature presents a significant challenge to the survival of current Li-ion batteries (LIBs) as it leads to low capacity retention and poor cell rechargeability. The electrolyte in commercial LIBs relies too heavily on ethylene carbonate (EC) to produce a stable solid electrolyte interphase (SEI) on graphite (Gr) anodes, but its high melting point (36.4°C) severely restricts ion transport below 0°C, causing energy loss and Li plating. Here, a class of EC-free electrolytes that exhibits remarkable low-temperature performance without compromising cell lifespan is reported. It is found that at sub-zero temperatures, EC forms highly resistive SEI that seriously impedes electrode kinetics, whereas EC-free electrolytes create a highly stable, low-impedance SEI through anion decomposition, which boosts capacity retention and eliminates Li plating during charging. Pouch-type LiCoO2 (LCO)|Gr cells with EC-free electrolytes sustain 900 cycles at 25°C with 1 C charge/discharge, and LiNi0.85 Co0.10 Al0.05 O2 (NCA)|Gr cells last 300 cycles at -15°C with 0.3C charge, both among the best-performing in the literature under comparable conditions. Even at -50°C, the NCA|Gr cell with EC-free electrolytes still delivers 76% of its room-temperature capacity, outperforming EC-based electrolytes.

Autonomous optimization of non-aqueous Li-ion battery electrolytes via robotic experimentation and machine learning coupling

Developing high-energy and efficient battery technologies is a crucial aspect of advancing the electrification of transportation and aviation. However, battery innovations can take years to deliver. In the case of non-aqueous battery electrolyte solutions, the many design variables in selecting multiple solvents, salts and their relative ratios make electrolyte optimization time-consuming and laborious. To overcome these issues, we propose in this work an experimental design that couples robotics (a custom-built automated experiment named "Clio”) to machine-learning (a Bayesian optimization-based experiment planner named "Dragonfly”). An autonomous optimization of the electrolyte conductivity over a single-salt and ternary solvent design space identifies six fast-charging non-aqueous electrolyte solutions in two work-days and forty-two experiments. This result represents a six-fold time acceleration compared to a random search performed by the same automated experiment. To validate the practical use of these electrolytes, we tested them in a 220 mAh graphite∣∣LiNi0.5Mn0.3Co0.2O2 pouch cell configuration. All the pouch cells containing the robot-developed electrolytes demonstrate improved fast-charging capability against a baseline experiment that uses a non-aqueous electrolyte solution selected a priori from the design space.

Materials Simulation for the Modulated Arrangement in A-Site Deficient Perovskite-Type Lithium Doped Lanthanum Niobate as Solid Electrolytes for All Solid-State Li Ion Batteries

Materials Simulation for the Modulated Arrangement in A-Site Deficient Perovskite-Type Lithium Doped Lanthanum Niobate as Solid Electrolytes for All Solid-State Li Ion Batteries

PVDF-based electrolyte decorated by Li29Zr9Nb3O40 Li-ion conductor and electrochemical performance of related solid-state batteries

Solid-state Li-ion batteries (LIBs) have recently attracted much attention for their high safety and energy density. Polyvinylidene fluoride (PVDF) is as a potential electrolyte for solid-state LIBs due to its high permittivity, wide voltage window and excellent thermal stability. Here, Y3+-doped Li29Zr9Nb3O40 (LZNO) Li-ionic conductor with room temperature conductivity (σ25) of 1.26 × 10−4 S cm−1 is prepared. LZNO decorated PVDF-based composite solid electrolytes (CSEs) are fabricated. The PVDF-based CSE with 10% (mass ratio) of LZNO shows σ25 of 2.34 × 10−4 S cm−1, and has thermal stability with melting temperature up to 332 °C and voltage window of 4.8 V. The assembled Li(Ni0.8Co0.1Mn0.1)O2|CSE|Li cells show initial specific discharge capacity of 216.7 mAh g−1 at 0.1 C, and exhibit high capacity and cycle performance. LiFePO4|CSE|Li cells display initial specific discharge capacity of 137.4 mAh g−1 at 0.5 C and high cycle performance. Addition of LZNO powder in CSEs can inhibit the dehydrofluorination of PVDF during the charge-discharge of cells, alleviate the deterioration of interface resistance, and greatly improve the specific discharge capacity of cells at high rates.