All Publications

  • Solvation-property relationship of lithium-sulphur battery electrolytes. Nature communications Kim, S. C., Gao, X., Liao, S., Su, H., Chen, Y., Zhang, W., Greenburg, L. C., Pan, J., Zheng, X., Ye, Y., Kim, M. S., Sayavong, P., Brest, A., Qin, J., Bao, Z., Cui, Y. 2024; 15 (1): 1268


    The Li-S battery is a promising next-generation battery chemistry that offers high energy density and low cost. The Li-S battery has a unique chemistry with intermediate sulphur species readily solvated in electrolytes, and understanding their implications is important from both practical and fundamental perspectives. In this study, we utilise the solvation free energy of electrolytes as a metric to formulate solvation-property relationships in various electrolytes and investigate their impact on the solvated lithium polysulphides. We find that solvation free energy influences Li-S battery voltage profile, lithium polysulphide solubility, Li-S battery cyclability and the Li metal anode; weaker solvation leads to lower 1st plateau voltage, higher 2nd plateau voltage, lower lithium polysulphide solubility, and superior cyclability of Li-S full cells and Li metal anodes. We believe that relationships delineated in this study can guide the design of high-performance electrolytes for Li-S batteries.

    View details for DOI 10.1038/s41467-023-44527-x

    View details for PubMedID 38341443

  • Recovery of isolated lithium through discharged state calendar ageing. Nature Zhang, W., Sayavong, P., Xiao, X., Oyakhire, S. T., Shuchi, S. B., Vilá, R. A., Boyle, D. T., Kim, S. C., Kim, M. S., Holmes, S. E., Ye, Y., Li, D., Bent, S. F., Cui, Y. 2024; 626 (7998): 306-312


    Rechargeable Li-metal batteries have the potential to more than double the specific energy of the state-of-the-art rechargeable Li-ion batteries, making Li-metal batteries a prime candidate for next-generation high-energy battery technology1-3. However, current Li-metal batteries suffer from fast cycle degradation compared with their Li-ion battery counterparts2,3, preventing their practical adoption. A main contributor to capacity degradation is the disconnection of Li from the electrochemical circuit, forming isolated Li4-8. Calendar ageing studies have shown that resting in the charged state promotes further reaction of active Li with the surrounding electrolyte9-12. Here we discover that calendar ageing in the discharged state improves capacity retention through isolated Li recovery, which is in contrast with the well-known phenomenon of capacity degradation observed during the charged state calendar ageing. Inactive capacity recovery is verified through observation of Coulombic efficiency greater than 100% on both Li||Cu half-cells and anode-free cells using a hybrid continuous-resting cycling protocol and with titration gas chromatography. An operando optical setup further confirms excess isolated Li reactivation as the predominant contributor to the increased capacity recovery. These insights into a previously unknown pathway for capacity recovery through discharged state resting emphasize the marked impact of cycling strategies on Li-metal battery performance.

    View details for DOI 10.1038/s41586-023-06992-8

    View details for PubMedID 38326593

    View details for PubMedCentralID 8580315

  • High-entropy electrolytes for practical lithium metal batteries NATURE ENERGY Kim, S., Wang, J., Xu, R., Zhang, P., Chen, Y., Huang, Z., Yang, Y., Yu, Z., Oyakhire, S. T., Zhang, W., Greenburg, L. C., Kim, M., Boyle, D. T., Sayavong, P., Ye, Y., Qin, J., Bao, Z., Cui, Y. 2023
  • Environmentally stable and stretchable polymer electronics enabled by surface-tethered nanostructured molecular-level protection. Nature nanotechnology Zheng, Y., Michalek, L., Liu, Q., Wu, Y., Kim, H., Sayavong, P., Yu, W., Zhong, D., Zhao, C., Yu, Z., Chiong, J. A., Gong, H., Ji, X., Liu, D., Zhang, S., Prine, N., Zhang, Z., Wang, W., Tok, J. B., Gu, X., Cui, Y., Kang, J., Bao, Z. 2023


    Stretchable polymer semiconductors (PSCs) are essential for soft stretchable electronics. However, their environmental stability remains a longstanding concern. Here we report a surface-tethered stretchable molecular protecting layer to realize stretchable polymer electronics that are stable in direct contact with physiological fluids, containing water, ions and biofluids. This is achieved through the covalent functionalization of fluoroalkyl chains onto a stretchable PSC film surface to form densely packed nanostructures. The nanostructured fluorinated molecular protection layer (FMPL) improves the PSC operational stability over an extended period of 82 days and maintains its protection under mechanical deformation. We attribute the ability of FMPL to block water absorption and diffusion to its hydrophobicity and high fluorination surface density. The protection effect of the FMPL (~6 nm thickness) outperforms various micrometre-thick stretchable polymer encapsulants, leading to a stable PSC charge carrier mobility of ~1 cm2 V-1 s-1 in harsh environments such as in 85-90%-humidity air for 56 days or in water or artificial sweat for 42 days (as a benchmark, the unprotected PSC mobility degraded to 10-6 cm2 V-1 s-1 in the same period). The FMPL also improved the PSC stability against photo-oxidative degradation in air. Overall, we believe that our surface tethering of the nanostructured FMPL is a promising approach to achieve highly environmentally stable and stretchable polymer electronics.

    View details for DOI 10.1038/s41565-023-01418-y

    View details for PubMedID 37322142

  • Dissolution of the Solid Electrolyte Interphase and Its Effects on Lithium Metal Anode Cyclability. Journal of the American Chemical Society Sayavong, P., Zhang, W., Oyakhire, S. T., Boyle, D. T., Chen, Y., Kim, S. C., Vilá, R. A., Holmes, S. E., Kim, M. S., Bent, S. F., Bao, Z., Cui, Y. 2023


    At >95% Coulombic efficiencies, most of the capacity loss for Li metal anodes (LMAs) is through the formation and growth of the solid electrolyte interphase (SEI). However, the mechanism through which this happens remains unclear. One property of the SEI that directly affects its formation and growth is the SEI's solubility in the electrolyte. Here, we systematically quantify and compare the solubility of SEIs derived from ether-based electrolytes optimized for LMAs using in-operando electrochemical quartz crystal microbalance (EQCM). A correlation among solubility, passivity, and cyclability established in this work reveals that SEI dissolution is a major contributor to the differences in passivity and electrochemical performance among battery electrolytes. Together with our EQCM, X-ray photoelectron spectroscopy (XPS), and nuclear magnetic resonance (NMR) spectroscopy results, we show that solubility depends on not only the SEI's composition but also the properties of the electrolyte. This provides a crucial piece of information that could help minimize capacity loss due to SEI formation and growth during battery cycling and aging.

    View details for DOI 10.1021/jacs.3c03195

    View details for PubMedID 37220230

  • LiH formation and its impact on Li batteries revealed by cryogenic electron microscopy. Science advances Vilá, R. A., Boyle, D. T., Dai, A., Zhang, W., Sayavong, P., Ye, Y., Yang, Y., Dionne, J. A., Cui, Y. 2023; 9 (12): eadf3609


    Little is known about how evolved hydrogen affects the cycling of Li batteries. Hypotheses include the formation of LiH in the solid-electrolyte interphase (SEI) and dendritic growth of LiH. Here, we discover that LiH formation in Li batteries likely follows a different pathway: Hydrogen evolved during cycling reacts to nucleate and grow LiH within already deposited Li metal, consuming active Li. We provide the evidence that LiH formed in Li batteries electrically isolates active Li from the current collector that degrades battery capacity. We detect the coexistence of Li metal and LiH also on graphite and silicon anodes, showing that LiH forms in most Li battery anode chemistries. Last, we find that LiH has its own SEI layer that is chemically and structurally distinct from the SEI on Li metal. Our results highlight the formation mechanism and chemical origins of LiH, providing critical insight into how to prevent its formation.

    View details for DOI 10.1126/sciadv.adf3609

    View details for PubMedID 36961896

  • Revealing the Multifunctions of Li3N in the Suspension Electrolyte for Lithium Metal Batteries. ACS nano Kim, M. S., Zhang, Z., Wang, J., Oyakhire, S. T., Kim, S. C., Yu, Z., Chen, Y., Boyle, D. T., Ye, Y., Huang, Z., Zhang, W., Xu, R., Sayavong, P., Bent, S. F., Qin, J., Bao, Z., Cui, Y. 2023


    Inorganic-rich solid-electrolyte interphases (SEIs) on Li metal anodes improve the electrochemical performance of Li metal batteries (LMBs). Therefore, a fundamental understanding of the roles played by essential inorganic compounds in SEIs is critical to realizing and developing high-performance LMBs. Among the prevalent SEI inorganic compounds observed for Li metal anodes, Li3N is often found in the SEIs of high-performance LMBs. Herein, we elucidate new features of Li3N by utilizing a suspension electrolyte design that contributes to the improved electrochemical performance of the Li metal anode. Through empirical and computational studies, we show that Li3N guides Li electrodeposition along its surface, creates a weakly solvating environment by decreasing Li+-solvent coordination, induces organic-poor SEI on the Li metal anode, and facilitates Li+ transport in the electrolyte. Importantly, recognizing specific roles of SEI inorganics for Li metal anodes can serve as one of the rational guidelines to design and optimize SEIs through electrolyte engineering for LMBs.

    View details for DOI 10.1021/acsnano.2c12470

    View details for PubMedID 36700841

  • Correlating the Formation Protocols of Solid Electrolyte Interphases with Practical Performance Metrics in Lithium Metal Batteries ACS ENERGY LETTERS Oyakhire, S. T., Zhang, W., Yu, Z., Holmes, S. E., Sayavong, P., Kim, S., Boyle, D. T., Kim, M., Zhang, Z., Cui, Y., Bent, S. F. 2023: 869-877
  • Investigating the Cyclability and Stability at the Interfaces of Composite Solid Electrolytes in Li Metal Batteries. ACS applied materials & interfaces Holmes, S. E., Liu, F., Zhang, W., Sayavong, P., Oyakhire, S. T., Cui, Y. 2022


    Despite the fact that much work has been dedicated to finding the ideal additive for composite solid electrolytes (CSEs) for lithium-based solid-state batteries, little is known about the properties of a CSE that enable stable cycling with a lithium metal anode. In this work, we use three CSEs based on lithium nitride (Li3N), a fast lithium-ion conductor, and lithium hydroxide (LiOH) to investigate the properties and interfacial interactions that impact the cyclability of CSEs. We present a method for stabilizing Li3N with a shell of LiOH, and we incorporate Li3N, core-shell particles, and LiOH into CSEs using polyethylene oxide (PEO) and lithium bis(trifluoromethanesulfonyl)imide. Through improved interfacial chemistry, CSEs with core-shell particles have superior electrochemical cycling performance compared to those with unprotected Li3N in symmetric Li-Li cells. This CSE features a high ionic conductivity of 0.66 mS cm-1 at 60 °C, a high critical current density of 1.2 mA cm-2, and a wide voltage window of 0-5.1 V. Full cells with the core-shell CSE and lithium iron phosphate cathodes exhibit stable cycling and high reversible specific capacities in cells as high as 2.5 mAh cm-2. We report that the improved ionic conductivity and amorphous PEO content have a limited effect on the solid-state electrolyte performance, while improving the electrolyte-Li metal anode interface is key to cycling longevity.

    View details for DOI 10.1021/acsami.2c14677

    View details for PubMedID 36416366

  • Correlating Kinetics to Cyclability Reveals Thermodynamic Origin of Lithium Anode Morphology in Liquid Electrolytes. Journal of the American Chemical Society Boyle, D. T., Kim, S. C., Oyakhire, S. T., Vila, R. A., Huang, Z., Sayavong, P., Qin, J., Bao, Z., Cui, Y. 2022


    The rechargeability of lithium metal batteries strongly depends on the electrolyte. The uniformity of the electroplated Li anode morphology underlies this dependence, so understanding the main drivers of uniform plating is critical for further electrolyte discovery. Here, we correlate electroplating kinetics with cyclability across several classes of electrolytes to reveal the mechanistic influence electrolytes have on morphology. Fast charge-transfer kinetics at fresh Li-electrolyte interfaces correlate well with uniform morphology and cyclability, whereas the resistance of Li+ transport through the solid electrolyte interphase (SEI) weakly correlates with cyclability. These trends contrast with the conventional thought that Li+ transport through the electrolyte or SEI is the main driver of morphological differences between classes of electrolytes. Relating these trends to Li+ solvation, Li nucleation, and the charge-transfer mechanism instead suggests that the Li/Li+ equilibrium potential and the surface energy─thermodynamic factors modulated by the strength of Li+ solvation─underlie electrolyte-dependent trends of Li morphology. Overall, this work provides an insight for discovering functional electrolytes, tuning kinetics in batteries, and explaining why weakly solvating fluorinated electrolytes favor uniform Li plating.

    View details for DOI 10.1021/jacs.2c08182

    View details for PubMedID 36318744

  • Resolving Current-Dependent Regimes of Electroplating Mechanisms for Fast Charging Lithium Metal Anodes. Nano letters Boyle, D. T., Li, Y., Pei, A., Vila, R. A., Zhang, Z., Sayavong, P., Kim, M. S., Huang, W., Wang, H., Liu, Y., Xu, R., Sinclair, R., Qin, J., Bao, Z., Cui, Y. 2022


    Poor fast-charge capabilities limit the usage of rechargeable Li metal anodes. Understanding the connection between charging rate, electroplating mechanism, and Li morphology could enable fast-charging solutions. Here, we develop a combined electroanalytical and nanoscale characterization approach to resolve the current-dependent regimes of Li plating mechanisms and morphology. Measurement of Li+ transport through the solid electrolyte interphase (SEI) shows that low currents induce plating at buried Li||SEI interfaces, but high currents initiate SEI-breakdown and plating at fresh Li||electrolyte interfaces. The latter pathway can induce uniform growth of {110}-faceted Li at extremely high currents, suggesting ion-transport limitations alone are insufficient to predict Li morphology. At battery relevant fast-charging rates, SEI-breakdown above a critical current density produces detrimental morphology and poor cyclability. Thus, prevention of both SEI-breakdown and slow ion-transport in the electrolyte is essential. This mechanistic insight can inform further electrolyte engineering and customization of fast-charging protocols for Li metal batteries.

    View details for DOI 10.1021/acs.nanolett.2c02792

    View details for PubMedID 36214378