Electro-Chemo-Mechanical Coupling Effects of Al2O3 Coatings on Separators in High Energy Density Lithium Metal Batteries.

As renewable energy and battery-powered technologies become more widespread, high energy-density and high-performing batteries are required to meet society’s needs. While lithium-ion batteries have been the staple, their energy density development has been slow, and at gravimetric energy densities of around 250 Wh/kg, they are approaching their theoretical limit.1 The lithium-metal battery (LMB) is considered a next-generation battery due to high theoretical energy densities (ex: Lithium-Sulfur, 2600 Wh/kg), and lithium metal’s high gravimetric capacity (3860 mAh/g) and low reduction potential (-3.04 V vs S.H.E.). However, commercialization of LMBs has been limited due to various issues.Two properties that dictate the performance of the LMBs are: 1. The composition of the solid electrolyte interphase (SEI), an electronically conducting, yet passivating, layer at the anode-electrolyte interface, and 2. The morphology of the lithium deposited at the anode. Morphological studies focus on creating dense, low surface area, deposits that limit SEI fracturing and the formation of electronically disconnected lithium. SEI quality is improved by incorporating inorganic or anion-rich SEIs, formed from the electrolyte salt, to promote SEIs that are mechanically robust, ionically conducting, and homogeneous. Our group’s previous work aimed to improve LMB performance via both routes by growing resistive Al2O3 coatings on the copper (Cu) current collector using atomic layer deposition (ALD). Defects in the thin film create areas of low resistance that behave like ultramicroelectrodes which encourage radial diffusion of lithium ions to the nuclei promoting lateral growth and producing low surface area, dense, planar lithium deposits. Simultaneously, the Al2O3 coating’s Lewis acidic properties promote the decomposition and subsequent incorporation of inorganic electrolyte species into the SEI.We present a study of how the different interfaces present at the anode in LMBs impact SEI composition and battery performance. To hold the Li nucleation morphology at the anode constant, we deposit metal oxide films of a fixed resistance onto the Cu current collector, generating planar, low surface area, lithium deposits. This experimental design allows us to decouple the effect of the metal oxide thin film-electrolyte interface on SEI quality and battery performance from that of the lithium morphology. First, as shown in Fig. 1a, different metal oxide films of equal resistance, but different thicknesses, are grown via ALD, confirmed by measuring the first-cycle nucleation overpotential. The resistive metal oxides investigated are Al2O3, HfO2, AlHfxOy, and ZrO2. Scanning electron microscopy results indicate that all cells modified with equal resistance metal oxide films exhibit the same low surface area, dense, planar Li nucleation morphology. However, long-term cycling tests show differences in cell performance and life cycle. Subsequently, the composition of the SEI is investigated using X-ray photoelectron spectroscopy (XPS). Through XPS, an elemental atomic ratio analysis is conducted to investigate the relative number of species derived from the anion of the electrolyte versus the solvent of the electrolyte to reflect the anion-derived nature of the SEI. Additionally, high-resolution peaks are used to determine the relative abundance of high-quality SEI species such as lithium fluoride. This analysis confirms that the metal oxide thin film tunes the SEI composition. Additionally, we identify trends present between the SEI quality of the ALD-modified cell and its performance.To further investigate the thin film-electrolyte interface, a set of cells modified with binary stacked metal oxide thin films with two different stack orders were created, as shown in Fig. 1b. Investigating SEI composition and LMB performance, with the morphology fixed by the nucleation overpotential, allowed for deconvolution of the impact of the Cu-thin film interface and thin film-electrolyte interface. Both interfaces can in principle impact the battery’s function because 1. The Cu-thin film interface controls the electron transport to form Lio from Li+ ion during electrodeposition, and 2. The thin film-electrolyte interface can modulate the SEI. Our results indicated that the SEI and performance were both primarily regulated by the thin film-electrolyte interface. Based on our fixed-resistance and binary stack experimental design, we propose that modulation of the SEI composition by the metal oxide coating controls LMB performance when the Li nucleation morphology is fixed. This result suggests the potential for tuning LMB performance by careful selection of the metal oxide interfacial coating. References (1) Cheng, X.-B., et al. Toward Safe Lithium Metal Anode in Rechargeable Batteries: A Review. Chem. Rev. 2017, 117 (15), 10403–10473. https://doi.org/10.1021/acs.chemrev.7b00115.(2) Oyakhire, S. T., et al. Electrical Resistance of the Current Collector Controls Lithium Morphology. Nature Communications 2022, 13 (1), 3986. https://doi.org/10.1038/s41467-022-31507-w. Figure 1

The solid electrolyte interphase (SEI) with lithium fluoride (LiF) is critical to the performance of lithium metal batteries (LMBs) due to its high stability and mechanical properties. However, the low Li ion conductivity of LiF impedes the rapid diffusion of Li ions in the SEI, which leads to localized Li ion oversaturation dendritic deposition and hinders the practical applications of LMBs at high-current regions (>3 C). To address this issue, a fluorophosphated SEI rich with fast ion-diffusing inorganic grain boundaries (LiF/Li3P) is introduced. By utilizing a sol electrolyte that contains highly dispersed porous LiF nanoparticles modified with phosphorus-containing functional groups, a fluorophosphated SEI is constructed and the presence of electrochemically active Li within these fast ion-diffusing grain boundaries (GBs-Li) that are non-nucleated is demonstrated, ensuring the stability of the Li || NCM811 cell for over 1000 cycles at fast-charging rates of 5 C (11mA cm-2). Additionally, a practical, long cycling, and intrinsically safe LMB pouch cell with high energy density (400Wh kg-1) is fabricated. The work reveals how SEI components and structure design can enable fast-charging LMBs.

Secondary electron emission from oxide-coated cathodes

Effect of the dielectric constant of a liquid electrolyte on lithium metal anodes

Dense garnet structured solid electrolytes exhibit great promise for lithium metal batteries owing to its high lithium-ion conductivity, good mechanical and electrochemical properties. However, the rigid interfacial contact between garnet structured electrolyte and electrode stymie their practical application. In this chapter, salient features of various strategies utilized to enhance the room temperature performance of lithium metal battery based on garnet structured solid electrolyte are discussed. In particular, a detailed electrochemical investigation on lithium | garnet interface and cathode | garnet interface with buffer layers for solid-state battery. The application of garnet structured solid electrolyte in suppressing polysulfide shuttling in lithium-sulfur (Li-S) battery is also discussed. It is shown that the cycling performance of lithium metal and Li-S batteries can be greatly improved with the incorporation of garnet structured solid electrolyte.

The stabilization and enhanced performance of lithium metal batteries (LMBs) depend on the formation and evolution of the Solid Electrolyte Interphase (SEI) layer as a critical component for regulating the Li metal electrodeposition processes. This study employs a first-principles kinetic Monte Carlo (kMC) model to simulate the SEI formation and Li+ electrodeposition processes on a lithium metal anode, integrating both the electrochemical electrolyte reduction reactions and the diffusion events giving place to the SEI aggregation processes during battery charge and discharge processes. The model replicates the competitive interactions between organic and inorganic SEI components, emphasizing the influence of the cycling regime. Results indicate that grain boundaries within the SEI facilitate faster lithium-ion transport compared to crystalline regions, crucial for improving the performance and stability of LMBs. The findings underscore the importance of dynamic SEI modeling for further development of next-generation high-energy-density batteries.

Enhanced separator wettability by LiTFSI and its application for lithium metal batteries

The uneven growth of lithium dendrites not only compromise the performance of lithium metal batteries, but also has security risks. In this sutudy, double coating with MgF2 and hydroxypropyl methylcellulose was synthesized on the surface of polyethylene separator through a simple soaking and in‐situ chemical precipitation method, achieve the purpose of protecting lithium metal anode. Utilizing the MgF2/HPMC@PE separator, the Li||Li symmetric cell was capable of cycling for over 1000 hours with a voltage hysteresis of only 11.4 mV, comparing the voltage hysteresis based on the cell use of PE separator increases rapidly after 200 h. Furthermore, the initial discharge capacity of Li||LiNi0.6Co0.2Mn0.2O2(NCM622) is 144.6 mAh g−1 and the capacity retention is 87.2 % after 200 cycles at 1 C, which is higher than that of the PE separator (135.3 mAh g−1, with retention of 74.9 %). All improvements can be credited with the formation of stable solid electrolyte interphase(SEI) film induced by HPMC/MgF2 double coating, which is reduced the Li nucleation overpotential and ultimately promoted uniform Li deposition. This study provides a simple and effective strategy for improving the cycling performance and safety of lithium metal batteries.

Lithium metal batteries (LMBs) have gained significant attention because of their high theoretical energy density. However, under high‐rate charge and discharge conditions, lithium metal anodes are susceptible to dendrite formation, compromising battery safety. Creating multifunctional separators offers an effective and cost‐efficient solution for addressing fast charging and safety challenges in LMBs. This study proposes a method to prepare a functional separator by in situ growing a polydopamine copper chelate (PDA(Cu)) coating on a polypropylene (PP)/polyethylene (PE)/PP separator (PP/PE/PP@PDA(Cu)). The PDA(Cu) exhibits excellent electrolyte wetting properties and ion exclusion effects, contributing to high ionic conductivity (5.02 × 10−⁴ S cm−1) and high lithium‐ion (Li+) transference number (0.776). Owing to its strong adhesion to the lithium metal anode, the coating significantly suppresses the formation of lithium dendrites. The Li||Li symmetric cell with a PP/PE/PP@PDA(Cu) separator demonstrates highly stable lithium plating‐stripping cycles, lasting over 900 h. Additionally, the PDA(Cu) promotes the formation of a stable cathode electrolyte interphase (CEI) film on the LiFePO4 cathode surface. The LiFePO4||Li cell with a PP/PE/PP@PDA(Cu) separator maintains 85.1% of its capacity after 6000 cycles at 10 C. This work paves a novel path for designing separators to enhance the fast‐charging performance of LMBs and solve the challenges of lithium dendrite formation and long cycling life.

The performance of lithium metal batteries is significantly affected by temperature variations, which makes it challenging for them to operate across a wide temperature range. Herein, a wide temperature adaption electrolyte is proposed, enabling excellent electrochemical performance of lithium metal batteries from −40 °C to 60 °C. Large, 5.8 Ah pouch cells employing such an electrolyte achieve high energy density of 503.3 Wh kg−1 at 25 °C with a lifespan of 260 cycles and outstanding energy density of 339 Wh kg−1 at −40 °C. The critical role of the solid electrolyte interphase (SEI) in determining the temperature‐dependent performance of lithium metal batteries is unveiled. It is demonstrated that the LiF‐rich, anion‐derived SEI facilitates Li+ diffusion in SEI. Moreover, accelerated Li+ desolvation at SEI is observed. These two aspects promote the kinetics of lithium metal anodes and further inhibit the dendrite growth at low temperatures. This work showcases the importance of understating the chemistry of SEI to enable wide temperature lithium metal batteries.

The performance of lithium metal batteries is significantly affected by temperature variations, which makes it challenging for them to operate across a wide temperature range. Herein, a wide‐temperature adaption electrolyte is proposed, enabling excellent electrochemical performance of lithium metal batteries from ‐40 °C to 60 °C. Large, 5.8 Ah pouch cells employing such an electrolyte achieve high energy density of 503.3 Wh kg‐1 at 25 °C with a lifespan of 260 cycles and outstanding energy density of 339 Wh kg‐1 at ‐40 °C. The critical role of the solid electrolyte interphase (SEI) in determining the temperature‐dependent performance of lithium metal batteries is unveiled. It is demonstrated that the LiF‐rich, anion‐derived SEI facilitates Li+ diffusion in SEI. Moreover, accelerated Li+ desolvation at SEI is observed. These two aspects promote the kinetics of lithium metal anodes and further inhibit the dendrite growth at low temperatures. This work showcases the importance of understating the chemistry of SEI to enable wide‐temperature lithium metal batteries.

Boosting the performances of lithium metal batteries through in-situ construction of dual-network self-healing gel polymer electrolytes

The long-lasting maintenance of the pore structure achieves the stability of lithium metal batteries

Advances in energy storage (ES) devices have the potential to transform nearly every aspect of society, from transportation to communication to electricity delivery, national defense and domestic security. Among the various prevalent energy storage devices, the most prominent to date are related to electrochemical energy storage (EES) technologies. Several EES technologies are either in existence or have evolved over the years. Among the various systems studied, lithium battery technologies (LBs) have emerged in the forefront as a panacea to the high energy and high power problems facing portable electronics, electric powered vehicle, military applications as well as stand-alone stationary power systems integrated into the electric grid. Despite advances in the anode arena, lithium metal anodes due to the inherent dendrite formation limitations have never attained commercial status. Overcoming these barriers would be a major breakthrough in the search for high energy density anode systems due to its extremely high theoretical specific capacity (~3860 mAh/g) and the lowest negative electrochemical potential (-3.040 V vs. the standard hydrogen electrode). Similarly, pursuit of high energy density rechargeable lithium metal battery (LMB) cathodes have led to sulfur (for a Li-S battery), air electrode (for a Li-air battery) or intercalation compounds (e.g. NbSe3, V2O5) to realize high voltage LMBs exhibiting high energy densities. Li-S batteries, owing to their high theoretical energy density (2600 Wh kg-1)1, is considered as one of the most promising Li metal-based batteries. However, the liquid organic electrolytes, S cathodes and Li metal in current LMBs could not be commercialized globally for high energy applications due to low cycle life and safety issues. The low cycle life, low coulombic efficiency (CE) and safety issue of rechargeable LMBs mainly arises due to the uncontrolled cellular and dendritic growth of Li metal during repeated lithium plating/stripping and formation of unstable solid electrolyte interphase (SEI) and the continuous growth of thick SEI during repeated cycling at the solid liquid interface of organic electrolyte based LMBs. In addition, the large volume expansion (~80%)3 of sulfur accompanying the electrochemical cycling, the low utilization of sulfur resulting from poor room-temperature electronic conductivity of sulfur (~10-15 S/cm) 4 , combined with the shuttle effect of highly soluble polysulfide species in the organic ether-based electrolytes has limited the use of Li-S batteries. To address these challenges facing sulfur cathodes, significant efforts have been made to demonstrate advanced composite cathodes using various carbon materials5, polymers6 and metal-organic framework (MOF) materials7. In addition, solid polymer electrolytes8 and electrolytes additives have also been studied to develop a viable Li-S battery system. Thin-film solid-polymer electrolyte batteries offer the potential for improved safety because of the reduced activity of lithium with the solid electrolyte, flexibility in design as the cell can be fabricated in various sizes and shapes, and high energy density. In this work, we demonstrate the use of a composite polymer electrolyte (CPE) with modified physical and chemical properties in Li-S batteries. These CPEs exhibits superior mechanical properties, excellent room-temperature lithium ion conductivity and low electrolyte: sulfur (E:S) ratio. These CPEs, when used as electrolytes for Li-S batteries, helps prevent both polysulfide dissolution and dendrite formation, in addition to providing very high energy density (~750 Wh/kg). Structural, chemical, physical and electrochemical characterization results validating these properties of the CPEs will be presented and discussed. Acknowledgements: The authors acknowledge the financial support of DOE grant DE-EE 0006825 and DE-EE-0008199, Edward R. Weidlein Chair Professorship funds and the Center for Complex Engineered Multifunctional Materials (CCEMM). References V. S. Kolosnitsyn and E. V. Karaseva, Russian Journal of Electrochemistry, 2008, 44, 506-509.Y. Sun, G. Li, Y. Lai, D. Zeng and H. Cheng, Scientific Reports, 2016, 6, 22048.B. Dunn, H. Kamath and J.-M. Tarascon, Science, 2011, 334, 928-935.M. Edeling, R. W. Schmutzler and F. Hensel, Philosophical Magazine Part B, 1979, 39, 547-550.J. Jin, Z. Wen, G. Ma, Y. Lu and K. Rui, Solid State Ionics, 2014, 262, 170-173.P. J. Hanumantha, B. Gattu, O. Velikokhatnyi, M. K. Datta, S. S. Damle and P. N. Kumta, Journal of The Electrochemical Society, 2014, 161, A1173-A1180.P. M. Shanthi, P. J. Hanumantha, B. Gattu, M. Sweeney, M. K. Datta and P. N. Kumta, Electrochimica Acta, 2017, 229, 208-218.B. A. Boukamp, I. D. Raistrick, C. Ho, Y.-W. Hu and R. A. Huggins, in Superionic Conductors, eds. G. D. Mahan and W. L. Roth, Springer US, Boston, MA, 1976, DOI: 10.1007/978-1-4615-8789-7_65, pp. 417-417.E. Peled, C. Menachem, D. Bar‐Tow and A. Melman, Journal of The Electrochemical Society, 1996, 143, L4-L7.

Lithium metal batteries are considered highly promising candidates for the next-generation high-energy storage system. However, the growth of lithium dendrites significantly hinders their advance, particularly under high current densities, due to the formation of unstable solid electrolyte interphase (SEI) layers. In this study, we demonstrate that molybdenum-based MXenes, including Mo2CTx , Mo2TiC2Tx , and Mo2Ti2C3Tx , form more stable LiF/Li2CO3 SEI layers during lithium plating, compared to the conventional Cu electrode. Among these, the bimetallic Mo2Ti2C3Tx MXene, with its higher fluorine terminations, produces the most stable LiF-rich SEI layer. The formation of this stable inorganic SEI layer significantly reduces the nucleation overpotential for lithium deposition, promotes uniform Li deposition, and suppresses dendrite growth. Consequently, the Mo2Ti2C3Tx substrate achieved prolonged cycling stability of approximately 544 cycles with coulombic efficiency of ~99.79% at high current density of 3 mA cm-2 and capacity of 1 mAh cm-2. In full cells, the Mo2Ti2C3Tx anode, paired with an NCM622 cathode, maintained capacity retention of 70% over 100 cycles with high cathode loading of 10 mg cm-2. Our approach highlights the potential of Mo-based MXenes to improve the performance of lithium metal batteries, making them promising candidates for the next-generation energy storage system.