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DOE OSTI2024

Lithium Dendrite-Free Li 7 N 2 I-LiOH Solid Electrolytes for High Energy Lithium Batteries

All-solid-state lithium batteries (ASSLBs) hold great potential to improve the safety and energy density of today’s lithium-ion batteries by using non-flammable inorganic solid electrolytes. Solid electrolytes (SEs) are believed to prevent Li dendrite growth because of high mechanical strength and high Li+ transference numbers. Significant advances in SE have been achieved, among which, Li7La3Zr2O12 (LLZO) and Li2S–P2S5 (LPS) are the most promising SEs for bulk-type solid-state lithium batteries because of high ionic conductivities (>10-4 S/cm2). However, in contrast to our expectations, the growth of lithium dendrites is not suppressed but is facilitated in LLZOs and LPSs regardless of dopants, porosity, and crystallinity of the electrolytes. Despite the unity Li transference number and over two-times of shear modulus than that of Li metal, the critical current densities for Li plating and stripping in these SEs are less than 1.0 mA cm-2, which is one-fourth to one-tenth of that in liquid electrolytes at room temperature. The incompatibility between LLZO and LPS with Li metal seriously limits the energy density of all-solid-state batteries. The mechanism for lithium dendrite formation and growth in SEs are still disputable. Lack of understanding of the Li dendrite formation mechanism seriously impeded the development of solid-state lithium batteries. The development of the criterion for Li dendrite suppression is essential for the success of solid electrolyte lithium batteries. In this project, a criterion for Li dendrite suppression will be developed through thermodynamics and kinetics analysis of lithium dendrite nucleation/growth, which will guide the solid-state electrolyte design. Li7N2I-LiOH, Li5NI2-LiOH and Li3YCl6 solid electrolyte with high ionic conductivity and low electronic conductivity were used to validate the criterion for lithium dendrite suppression. Different surface modifications were also explored to enhance the dendrite suppression capability of SSEs.

25 ENERGY STORAGE↗
DOE OSTI2021

Efficient diffusion of superdense lithium via atomic channels for dendrite-free lithium–metal batteries

The non-uniform aggregation of fast-diffused Li on an anode surface would aggravate its tip-effect-induced nucleation/growth, leading to the notorious dendrite growth in Li metal batteries (LMBs). Tuning the Li diffusion on the anode surface has been regarded previously as a mainstream method to induce its uniform deposition, while the diffusion of Li in the anode bulk is usually ignored. In this study, conceptually different from the classic surface modification, we propose a molecular tunnelling strategy to construct atomic channels in graphite bulk, which enables the fast diffusion of superdense Li. Density functional theory calculations and ab initio molecular dynamics simulations prove that the bulk diffusion through atomic channels could become a new and dominating path. Its reversible and efficient diffusion has been further visualized by in situ transmission electron microscopy. As a result, when coupled with high-loading LiFePO 4 cathodes (20 mg cm –2 ), a high areal capacity and 100% capacity retention are achieved over 370 cycles. Through this work a new strategy is developed based on the bulk-diffusion of superdense Li for dendrite-free LMBs, which can be pervasive in other high-performance energy storage systems.

25 ENERGY STORAGE↗
DOE OSTI2020

A Metal Organic Framework Derived Solid Electrolyte for Lithium–Sulfur Batteries

Lithium–sulfur batteries (LSBs) are currently considered as promising candidates for next-generation energy storage technologies. However, their practical application is hindered by the critical issue of the polysulfide-shuttle. Herein, a metal organic framework (MOF)-derived solid electrolyte is presented to address it. The MOF solid electrolyte is developed based on a Universitetet i Oslo (UIO) structure. By grafting a lithium sulfonate (-SO 3 Li) group to the UIO ligand, both the ionic conductivity and the polysulfide-suppression capability of the resulting -SO 3 Li grafted UIO (UIOSLi) solid electrolyte are greatly improved. After integrating a Li-based ionic liquid (Li-IL), lithium bis(trifluoromethanesulfonyl)imide in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, the resulting Li-IL/UIOSLi solid electrolyte exhibits an ionic conductivity of 3.3 × 10 -4 S cm -1 at room temperature. Based on its unique structure, the Li-IL/UIOSLi solid electrolyte effectively restrains the polysulfide shuttle and suppresses lithium dendritic growth. Lithium–sulfur cells with the Li-IL/UIOSLi solid electrolyte and a Li 2 S 6 catholyte show stable cycling performance that preserves 84% of the initial capacity after 250 cycles with a capacity-fade rate of 0.06% per cycle.

25 ENERGY STORAGE↗
DOE OSTI2022

Lithium metal stripping mechanisms revealed through electrochemical liquid cell electron microscopy

An understanding of lithium stripping is as important as that of lithium plating to achieve significant advances in using lithium metal anodes for high-energy rechargeable batteries. However, there have been limited studies on lithium stripping compared to lithium plating. Here we report the lithium stripping mechanisms revealed through in-situ electrochemical liquid cell transmission electron microscopy (TEM). We directly observe and compare the stripping behavior of the in-situ grown lithium dendrites and lithium nanograins covered by a lithium fluoride-rich solid-electrolyte interphase (SEI). Furthermore, we find the sporadic lithium stripping behavior and three important modes that can describe the stripping of individual lithium deposits, regardless of their morphology: (i) symmetric stripping, (ii) surface-preferred asymmetric stripping, and (iii) interface-preferred asymmetric stripping. In addition, SEI chemical mapping with high spatial resolution shows a remarkable SEI loss at the end of the lithium metal stripping, which illustrates the importance of SEI protection in the subsequent cycles.

25 ENERGY STORAGE↗
DOE OSTI2025

A Modified Sand’s Time Incorporating Li-Ion Transport Across the SEI: Basis for Understanding Li Dendrite Formation and Li-Metal Battery Electrolyte Selection

Abstract Understanding the initiation of lithium dendrites remains elusive, largely due to the intricate role of the solid electrolyte interphase (SEI) which forms on the Li surface during electrodeposition. Many studies have utilized the classical Sand’s equation to estimate the onset time when lithium dendrites begin to form. The Sand’s equation provides the time when the cation (Li+) concentration at the electrode-electrolyte interface approaches zero under diffusion-limited conditions in galvanostatic Li electrodeposition. However, recent experimental studies have revealed that the observed lithium dendrite onset time deviates considerably from the Sand’s time. Here, we show that this deviation from classical theory is likely due to the transport of Li+ ions through the SEI - a transport limitation that is much more dominant in controlling dendrite formation. We develop a ‘modified’ Sand's equation, incorporating the SEI layer and the diffusional transport across it to predict Li dendrite onset times. To validate this approach, we conducted Li electrodeposition experiments at various current densities using two distinct organic electrolytes. Analysis of the results demonstrates that the modified Sand's equation provides a more accurate prediction of dendrite onset times, highlighting the importance of incorporating SEI into transport models of Li plating in next-generation rechargeable Li-metal batteries.

Ma, Yuanman (ORCID:0000000200444811)↗
DOE OSTI2021

Engineering Approaches to Dendrite free Lithium Anodes

This is the Final Technical Report of the work that was completed related to development of dendrite free anodes for Li-metal batteries. The report contains full details of all the strategies that were employed to overcome this pernicious problems of dendrite formation of lithium metal during cycling of Li-metal and Li-ion batteries. Various approaches were developed to understand the formation of dendrites and mitigation strategies were then developed to overcome this severe problem. In doing so novel multi-component alloys as well as structurally isomorphous alloys have been developed. In addition coating strategies were also developed to overcome the formation of dendrites. The novel approaches related to development of novel alloys using economic cost effective and scalable approaches. The new approaches will easily advance the science of lithium metal alloys and dendrite free anodes including current collectors. Development of this new technology will have immense benefit to providing new high energy density batteries of tremendous benefit to the public since cost effective and safe high energy density batteries will be possible with this new technology.

25 ENERGY STORAGE↗
DOE OSTI2022

Modification of lithium electrodeposition behavior by variation of electrode distance

Developing a better understanding and control over the lithium electrodeposition behavior will assist with the commercial application of lithium metal anodes for rechargeable batteries. Despite intensive research over the past decade, our understanding of the deposition of lithium is limited. Here a new observation on the effect of distance between the working electrode and the counter electrode for electrochemical lithium deposition behavior is reported. From this fundamental investigation of distance, the high lithium ion concentration regions formed by release of lithium ions from the counter electrode modify the lithium deposition behavior on the working electrode, resulting in the generation of non-uniform lithium dendrites with a thick diversely composed surface film. Alternatively, increasing the distance between the electrodes results in the deposition of a spherical lithium morphology with a thin LiF rich surface film. Here, this fundamental study provides a deeper understanding of correlation between lithium deposition behavior and electrode separation and provides insight to inhibit lithium dendrite formation.

25 ENERGY STORAGE↗
DOE OSTI2021

Dual Function Solid State Battery with Self-Forming Self-Healing Electrolyte and Separator (Final Scientific/Technical Report)

Over the course of this program, we have demonstrated an improved rechargeable Li/I2 battery with reduced impedance, improved cyclability, improved Coulombic Efficiency, and the ability to “self-heal” during shorting events. Multi-year efforts have led to the development and improvements in the composition, fabrication, and preparation of the solid state electrolyte, the role of the interface, and design of appropriate test conditions. These investigations have led to significant improvements in Coulombic efficiency. By systematic development of a composite solid state electrolyte, this system is able to self-form upon charge, thus lending itself to long shelf life before use. The initial project objective was to demonstrate a solid-state rechargeable battery based on a Li-metal anode and iodine cathode with a self-forming, self-healing electrolyte and separator with high gravimetric and volumetric energy density. The final deliverables of this project build on a multi-year effort beginning with materials development and design to generate a suitable solid state electrolyte composite with demonstrated higher ionic conductivity compared to the baseline (LiI). Development in cell design and interface modification leading to the generation of rechargeable solid electrolyte cells with Coulombic efficiency improvements of ~3X over initial tests, as well as demonstration of self-healing behavior, where the cells retained their ability to continue extended cycling after shorting events. The hypothesis put forward as part of the initial concept for the project was that the cell chemistry would be self-healing. For example, if a lithium dendrite formed during charge of the cell and reached the iodine cathode, the reaction of the lithium dendrite with the iodine would consume the tip of the dendrite to form lithium iodide, more of the solid electrolyte. The formation of the solid electrolyte would allow the cell to recover and continue to function. This type of self-healing during cycling has been demonstrated and has the potential to improve on safety considerations that stem from shorting events in other Li- containing systems.

25 ENERGY STORAGE↗
DOE OSTI2020

Design principles for self-forming interfaces enabling stable lithium-metal anodes

Significance It is possible to nearly double the energy density of existing lithium-ion batteries by using lithium metal anodes. However, it has been known for decades that the lithium dendrites and mossy lithium formed during charging (electrodeposition) limit the cycle life of the batteries. It is important to change the growth behavior of lithium metal, which is closely related to the properties of the solid–electrolyte interface (SEI) formed via spontaneous reactions between the lithium metal and the electrolyte. In this experimental-modeling integrated study, we reveal the design principles of the SEI that facilitates the dendrite-free and dense deposition of lithium and demonstrate one of the best cycling performances of lithium metal anode to date under practically relevant conditions.

25 ENERGY STORAGE↗
DOE OSTI2020

Universal chemomechanical design rules for solid-ion conductors to prevent dendrite formation in lithium metal batteries

Dendrite formation during electrodeposition while charging lithium metal batteries compromises their safety. Although high-shear-modulus ( G s ) solid-ion conductors (SICs) have been prioritized to resolve the pressure-driven instabilities that lead to dendrite propagation and cell shorting, it is unclear whether these or alternatives are needed to guide uniform lithium electrodeposition, which is intrinsically density-driven. Here, we show that SICs can be designed within a universal chemomechanical paradigm to access either pressure-driven dendrite-blocking or density-driven dendrite-suppressing properties, but not both. This dichotomy reflects the competing influence of the SIC’s mechanical properties and the partial molar volume of Li + $(V_{\mathrm{Li}^+})$ relative to those of the lithium anode ( G Li and V Li ) on plating outcomes. Within this paradigm, we explore SICs in a previously unrecognized dendrite-suppressing regime that are concomitantly ‘soft’, as is typical of polymer electrolytes, but feature an atypically low $(V_{\mathrm{Li}^+})$ that is more reminiscent of ‘hard’ ceramics. Li plating (1 mA cm -2 ; T = 20 °C) mediated by these SICs is uniform, as revealed using synchrotron hard X-ray microtomography. As a result, cell cycle life is extended, even when assembled with thin Li anodes (~30 µm) and either high-voltage NMC-622 cathodes (1.44 mAh cm -2 ) or high-capacity sulfur cathodes (3.02 mAh cm -2 ).

25 ENERGY STORAGE↗
DOE OSTI2020

NASICON Li 1.2 Mg 0.1 Zr 1.9 (PO 4 ) 3 Solid Electrolyte for an All‐Solid‐State Li‐Metal Battery

Abstract A thin solid electrolyte with a high Li + conductivity is used to separate the metallic lithium anode and the cathode in an all‐solid‐state Li‐metal battery. However, most solid Li‐ion electrolytes have a small electrochemical stability window, large interfacial resistance, and cannot block lithium‐dendrite growth when lithium is plated on charging of the cell. Mg 2+ stabilizes a rhombohedral NASICON‐structured solid electrolyte of the formula Li 1.2 Mg 0.1 Zr 1.9 (PO 4 ) 3 (LMZP). This solid electrolyte has Li‐ion conductivity two orders of magnitude higher at 25 °C than that of the triclinic LiZr 2 (PO 4 ) 3 . 7 Li and 6 Li NMR confirm the Li‐ions in two different crystallographic sites of the NASICON framework with 85% of the Li‐ions having a relatively higher mobility than the other 15%. The anode–electrolyte interface is further investigated with symmetric Li/LMZP/Li cell testing, while the cathode–electrolyte interface is explored with an all‐solid‐state Li/LMZP/LiFePO 4 cell. The enhanced performance of these cells enabled by the Li 1.2 Mg 0.1 Zr 1.9 (PO 4 ) 3 solid electrolyte is stable upon repeated charge/discharge cycling.

Zhou, Qiongyu↗
DOE OSTI2024

Phase Field Modeling of Pressure Induced Densification in Solid Electrolytes

Adoption of dense and homogeneous solid electrolytes can possibly mitigate the propagation of lithium dendrites and enable lithium metal anodes. Application of external pressure helps to minimize the sintering temperature in oxide ceramics and can potentially densify softer sulfide electrolytes even under room temperature conditions. Here, a previously developed phase field-based computational scheme for predicting the high-temperature sintering-induced densification of oxide ceramic solid electrolytes is extended in the present context to capture the influence of external pressure for densifying solid electrolytes. Two different bulk deformation mechanisms, namely, "reorganization" and "creep deformation," are dominant under external pressure, which is different from the surface and grain-boundary diffusion-induced densification of solid electrolytes that occurs during high temperature sintering. External pressure also increases the points of contact between the particles, which further enhances the propensity of diffusion-induced sintering process. Results obtained from simulations indicate that densification under external pressure is independent of the solid electrolyte particle morphology. Finally, a phase map is generated between applied pressure and temperature for achieving complete densification of oxide ceramics, which can possibly guide the synthesis of thin and dense solid electrolyte separators.

25 ENERGY STORAGE↗
DOE OSTI2020

Design rules for liquid crystalline electrolytes for enabling dendrite-free lithium metal batteries

Significance Lithium metal anodes offer a promising approach to improve the energy density of batteries to enable electrification of transportation. Dendrite suppression plagues the safety and cycle life of lithium metal anodes. In this work, we perform a comprehensive analysis of the use of liquid crystalline electrolytes in lithium metal anodes. We report theoretical demonstration of spontaneous stabilization of metal-electrode position using a liquid crystalline electrolyte due to the energy that arises when the molecules of the liquid crystal reorient. Building on this, we develop a comprehensive set of molecular-level design rules that will pave the way toward the realization of this new class of electrolytes for practical lithium metal batteries.

Ahmad, Zeeshan↗
DOE OSTI2023

Developing a model for the impact of non-conformal lithium contact on electro-chemo-mechanics and dendrite growth

Lithium dendrite growth hinders the use of lithium metal anodes in commercial batteries. We present a 3D model to study the mechanical and electrochemical mechanisms that drive microscale plating. With this model, we investigate electrochemical response across a lithium protrusion characteristic of rough anode surfaces, representing the separator as a porous polymer in non-conformal contact with a lithium anode. The impact of pressure on separator morphology and electrochemical response is of particular interest, as external pressure can improve cell performance. We explore the relationships between plating propensity, stack pressure, and material properties. External pressure suppresses lithium plating due to interfacial stress and separator pore closure, leading to inhomogeneous plating rates. For moderate pressures, dendrite growth is completely suppressed, as plating will occur in the electrolyte-filled gaps between anode and separator. In fast-charging conditions and systems with low electrolyte diffusivities, the benefits of pressure are overridden by ion transport limitations.

25 ENERGY STORAGE↗
DOE OSTI2024

Methylation enables the use of fluorine-free ether electrolytes in high-voltage lithium metal batteries

Lithium metal batteries represent a promising technology for next-generation energy storage, but they still suffer from poor cycle life due to lithium dendrite formation and cathode cracking. Fluorinated solvents can improve battery longevity by improving LiF content in the solid-electrolyte interphase; however, the high cost and environmental concerns of fluorinated solvents limit battery viability. Here, for this work, we designed a series of fluorine-free solvents through the methylation of 1,2-dimethoxyethane, which promotes inorganic LiF-rich interphase formation through anion reduction and achieves high oxidation stability. The anion-derived LiF interphases suppress lithium dendrite growth on the lithium anode and minimize cathode cracking under high-voltage operation. The Li + -solvent structure is investigated through in situ techniques and simulations to draw correlations between the interphase compositions and electrochemical performances. The methylation strategy provides an alternative pathway for electrolyte engineering towards high-voltage electrolytes while reducing dependence on expensive fluorinated solvents.

25 ENERGY STORAGE↗
DOE OSTI2023

Incombustible Polymer Electrolyte Boosting Safety of Solid–State Lithium Batteries: A Review

Lithium-ion batteries with their portability, high energy density, and reusability are frequently used in today's world. Under extreme conditions, lithium-ion batteries leak, burn, and even explode. Therefore, improving the safety of lithium-ion batteries has become a focus of attention. Researchers believe using a solid electrolyte instead of a liquid one can solve the lithium battery safety issue. Due to the low price, good processability and high safety of the solid polymer electrolytes, increasing attention have been paid to them. However, polymer electrolytes can also decompose and burn under extreme conditions. Moreover, lithium dendrites are formed continuously due to the uneven charge distribution on the surface of the lithium metal anode. A short circuit caused by a lithium dendrite can cause the battery to thermal runaway. As a result, the safety of polymer solid-state batteries remains a challenge. In this review, the thermal runaway mechanism of the batteries is summarized, and the batteries abuse test standard is introduced. In addition, the recent works on the high-safety polymer electrolytes and the solution strategies of lithium anode problems in polymer batteries are reviewed. Finally, the development direction of safe polymer solid lithium batteries is prospected.

25 ENERGY STORAGE↗