Lithium Dendrite in All-Solid-State Batteries: Growth Mechanisms, Suppression Strategies, and Characterizations

Understanding the lithium dendrites growth in garnet-based solid-state lithium metal batteries

Comprehensive SummaryLithium (Li) metal is considered ideal for high‐energy‐density batteries due to its extremely high specific capacity and low electrochemical potential. However, uncontrolled Li dendrite growth and interfacial instability during repeated Li plating/stripping have limited the practical applicability of Li metal batteries (LMBs). Over the past decades, substantial efforts have been devoted to solving the challenges associated with Li metal anodes. Our research team has developed several Li‐carbon (Li‐C) microsphere composites in recent years to suppress the formation of Li dendrites and achieve a decent cycle life. In this account, we summarize our advances in the design and application of Li‐C composites, which include the developments in the structure and chemical composition of high‐specific‐capacity Li‐C composites, strategies for surface passivation of the micro‐spherical Li‐C composites, and applications of the Li‐C composite in next‐generation high‐energy‐density Li‐ion, Li‐air, and solid‐state LMBs. Finally, we discuss future perspectives for developing high‐performance Li metal anodes and endeavors to realize the practical applications of LMBs.What is the most favorite and original chemistry developed in your research group?Accurate control of surface chemistry of battery materials in general, and Li metal in particular, with self‐assembled monolayers (SAM).How do you get into this specific field? Could you please share some experiences with our readers?Li metal is an ideal anode material for rechargeable batteries except that it is extremely reactive towards the environment and that the conversion reaction tends to deposit Li metal into dendrites. My group developed a Li‐C composite by infiltrating molten Li into carbon nanotube microspheres. This composite largely alleviated the dendrite growth problem of Li anode, but the reactivity of Li metal caused the Li‐C microsphere impossible to process outside Ar gloveboxes. A passivation method is needed.I recalled the molecular self‐assembly technique I learned and used in my Ph.D. dissertation, where I used the Au‐thiol SAM chemistry to control the surface chemical interactions between atomic force microscopy (AFM) probes and samples. The question is whether we can find the right chemistry between Li metal and self‐assembling molecules. This was how we started the journey of SAM on Li metal, and later further developed the idea to other battery materials such as high‐Ni NCM cathode, etc. How do you supervise your students?Students first need to build their own knowledge base, a set of scientific concepts and theoretical framework they are comfortable with and a set of experimental skills they are confident in. Then we define research directions together. Once we agree on a direction and the student starts to explore the direction with his/her knowledge and skills, here it comes the most enjoyable part of supervising students: I get to ask questions. It is through addressing questions, students learn to practice critical thinking, polish logic and reasoning, and eventually they observe and ask questions on their own. They become independent.What are your hobbies? What's your favorite book(s)?Jogging and reading. I like many books. To recommend just a couple: Oracle bones by Peter Hessler, and the comic books Calvin and Hobbes.Who influences you mostly in your life?Historical figures: Su Shi and Wang yangming. Scientists: Professors Charles Lieber and Louis Brus.If you have anything else to tell our readers, please feel free to do so.Genuinely interested in other people's interest seems to be the key of making friends; I also recommend it as a chemist's approach to make friends with the earth.

Suppressing lithium dendrites within inorganic solid-state electrolytes

Stabilizing Solid Electrolyte-Anode Interface in Li-Metal Batteries by Boron Nitride-Based Nanocomposite Coating

Rechargeable metal batteries, such as Li metal batteries are considered the “holy grail” of energy storage systems. However, dendritic metal growth and limited Coulombic efficiency (CE) during metal deposition/stripping have prevented their practical applications in rechargeable batteries.1-3 During the last a few years, we have developed several approaches to suppress metal dendrite growth and enhance the Coulombic efficiency (CE) of metal deposition/stripping processes.2-7 Several electrolyte additives, including CsPF6, RbPF6, and trace-amount of H2O (25-50 ppm) have been found to be effective for achieving dendrite-free Li metal deposition in LiPF6-based electrolytes. Furthermore, we have developed a highly concentrated electrolytes composed of the lithium bis(fluorosulfonyl)imide (LiFSI) salt and 1,2-dimethoxyethane (DME) solvent which enables high rate cycling of Li metal anode at high CE (up to 99.1 %) without dendrite growth. It is demonstrated that a Li|Li cell can be cycled at high rates (10 mA cm-2) for more than 6,000 cycles with no increase in the cell impedance and no dendritic Li growth. A Li|Cu cell can be cycled at 4 mA cm-2 for more than 1,000 cycles with an average CE of 98.4%. We also demonstrate that the dendrite growth and CE of Li deposition is strongly depends on several other factors, such as substrate treatment, charge and discharge protocols, and cell pressure. By optimizing the electrolyte compositions and various operating parameters, CE of Li deposition/stripping has been further improved without dendrite growth. In addition to the high CE cycling of Li metal electrode, novel electrolyte was also developed which enables cycling of Na metal anode with an excellent CE (> 99.1%) as compared to a very low CE of less than 30% in conventional electrolytes. Further development of these approaches may lead to long term stable operation of Li and Na metal batteries. Acknowledgements This work was supported by the Joint Center for Energy Storage Research (JCESR), an Energy Innovation Hub funded by the U. S. Department of Energy, Office of Science, Basic Energy Sciences (BES) and by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies, the Advanced Battery Materials Research Programs of the U.S. Department of Energy (DOE). PNNL is operated by Battelle for the DOE under Contract DE-AC05-76RLO1830.

Lithium (Li) metal is an ideal anode material for rechargeable batteries due to its extremely high theoretical specific capacity (3860 mAh/g), low density (0.59 g/cm3) and the lowest negative electrochemical potential (-3.04 V vs. the standard hydrogen electrode, SHE). Li battery based on Li metal anode is expected to have an order of magnitude higher energy density than today's Li-ion battery. This will enhance energy and power capability of battery devices used in portable electronics, hybrid electric cars, aerospace, telecommunication, military, etc.). The Li metal battery will fulfill the high energy demand that cannot be met through the current Li-ion batteries (e.g. all electric transportation or many other applications which require light weight, high energy density, high power density batteries with small battery footprint and safest). But, to date, uncontrolled dendritic Li growth and limited Coulombic efficiency (CE) during Li deposition/stripping of a bulk Li anode, are the main reason behind low cycle life, which has limited their practical applications. Furthermore, the rate of dendrite growth gets amplified when the cell is cycled at high charge-discharge current density, high charge voltage, and high areal discharge. Increasing anode surface area would reduce the effective charge/discharge current. Additionally, thin films and high surface area Li anodes exhibit high ionic and electronic conductivity contributing to the high efficiency of the current collection required for high capacity battery. Although low CE can be partially compensated by an excess amount of Li (at the expense of lower useable Li energy), fire and other hazards associated with the dendrite growth have limited the development of rechargeable Li metal batteries. Most approaches to dendrite prevention focus on improving the stability and uniformity of the solid-electrolyte interface (SEI) on the bulk Li surface by adjusting electrolyte components and optimizing SEI formation additives. It is very difficult to achieve sufficient passivation on Li electrode due to the thermodynamic instability of Li with electrolytes [1,2]. As an alternative, various mechanical barriers have been proposed to block dendrite penetration [3]. These approaches rely on a strong mechanical barrier provided by an SEI film or a separator to suppress Li dendrite penetration but do not change the fundamental, self-amplifying behavior of the dendrite growth. Also, it is hard to find a mechanical barrier material with required shear modulus (required > 109 Pa) with desired conductivity. In other words, these methods did not prevent Li dendrites from growing during long-term cycling at high charge-discharge current density, high charge voltage, and high areal discharge, or hardly improved the CE and safety in Li deposition/stripping which is not suitable for practical rechargeable Li batteries [1]. We have developed a novel ionic-electronic-mechanical membrane (an artificial SEI), which allows long-term Li cycleability and improved safety by reducing dendrite formation. The new artificial SEI is comprised of three different materials to fulfill the desired SEI criteria such as: (a) facilitate uniform Li ion dispersion and deposition on entire Li surface, (b) desired SEI conductivity (c) mechanical separation of Li and electrolyte and flexibility to contain anode volume change during Li stripping and deposition. The combined effect of the invented SEI result into more than 300% increase in number of cycles and 3-4 times increase in usable Li energy density (i.e. high Coulombic efficiency (CE)) of a wet battery composed of protected Li metal anode, liquid electrolyte (e.g. lithium hexafluoro arsenate, LiAsF6) and Li-ion cathode (e.g. lithium cobalt oxide, LCO) for the advancement of a battery beyond the state-of-the-art Li-ion battery. The added advantage of the invented SEI is improved safety due to suppression of dendrite growth by mechanically strong/flexible SEI and controlled, uniform deposition/stripping of Li from Li anode surface. The protected Li anode may be incorporated into wet cell batteries or solid state batteries having transition metal oxide cathodes (more specifically the state-of-the-art Li-ion cathodes) or Sulfur cathode (Li-S battery) or Oxygen cathode (Li-O2 battery). Moreover, similar methodologies can be applied to other rechargeable metal anodes (Na, Al, Mg, etc.) used in batteries.

The Li metal anode is sought-after for its high theoretical capacity (3860 mAh g-1) and low electrochemical potential (-3.04 V versus the standard hydrogen electrode). Nevertheless, the intrinsic instability of the Li metal towards both solid and liquid electrolytes leads to unstable solid electrolyte interphase (SEI) formation and dendritic lithium, causing safety concerns and rapid performance degradation [1]. Among the potential techniques used to protect the Li metal surface and inhibit dendrite growth, molecular layer deposition (MLD) has proven to be an invaluable tool for the development of nanoscale interfacial coatings with unique properties [2]. The layer-by-layer assembly of molecular fragments and conformal coating abilities of MLD yield the ability to tune the chemical and mechanical properties of the Li metal interface. It is believed that the exploration and adoption of new MLD films will open up new avenues for stabilizing the Li metal anode. Herein, we show several examples of high-performance Li metal anodes in liquid and solid-state systems achieved by polymeric coatings synthesized through MLD techniques [3-8]. New hybrid organic-inorganic coatings belonging to the metalcone family are shown to dramatically enhance the Coulombic efficiency and rate capability of Li metal anodes. Furthermore, the rational design and ordering of these coatings coupled with inorganic atomic layer deposition coatings reveal the importance of bilayer type structures in promoting enhanced mechanical properties for suppressing dendrite growth. The stabilizing properties of these advanced thin films are further extended to several next-generation battery systems including Li-S and Li-O2, proving effective when coupled with high energy density cathode materials. Moreover, advanced characterization techniques such as in-situ X-ray absorption spectroscopy, nanoindentation measurements, Rutherford backscattering spectrometry, and time-of-flight secondary ion mass spectrometry are used to reveal the mechanisms behind the electrochemical lithiation processes as well as cycling stability.

Lithium (Li) metal anode has an ultrahigh theoretical capacity of 3860 mAh/g and the lowest electrochemical potential at -3.040 V vs. standard hydrogen electrode, which makes the rechargeable Li metal batteries as the “holy grail” of energy storage systems.1 However, the development and application of rechargeable Li metal batteries has been hindered in the past decades mainly due to two major problems¾the Li dendrite growth on Li anode during repeated charge/discharge processes and the low Coulombic efficiency. Although several approaches have been reported to suppress Li dendrite growth on Li metal, including forming Li alloys, adding electrolyte additives, using blocking electrolyte membranes, and to improve Coulombic efficiency, the enhancement on Li protection so far is not satisfactory. Recently, highly concentrated ether-based electrolyte has been reported to be more compatible with Li metal anode because high concentration of Li+ ions in these electrolytes facilities the fast Li deposition/stripping even at high current density conditions.2,3 However, ether-based electrolytes may not be suitable for use at charge cutoff voltage higher than ~4.0 V due to their poor stability against oxidation. In this work, we report for the first time the significantly improved performances of Li metal batteries using a LiNi1/3Mn1/3Co1/3O2 (NMC) cathode and a conventional carbonate solvent-based electrolyte by an appropriate cycling protocol to generate a transient, highly concentrated Li+ ion solution layer in the vicinity of Li metal surface. The highly concentrated electrolyte formed in the vicinity of Li anode surface facilitates the formation of an SEI layer with considerably enhanced stability. It is demonstrated that a high capacity retention >80% after 500 cycles can be achieved for the moderately high areal-capacity Li metal batteries at an optimized charging/discharging process. Based on the results of morphology observation and the composition characterization of the cycled Li metal anodes, a more profound understanding of the underlying mechanism behind the improved performances has been obtained. The fundamental findings of this work provide new insights for the further development of high energy density and long cycle life Li metal batteries. Details of the investigations will be reported and discussed in the presentation. Acknowledgements This work was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies, the Advanced Battery Materials Research Programs of the U.S. Department of Energy (DOE). The microscopy and spectroscopy measurements were performed at the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the DOE’s Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. References A. Zhanmu, G. Chen, C. Liu, D. Neff, Q. Fang, Z. Yu, W. Xiong, Y. Wang, X. Wang, and B. Z. Jang, Energy Environ. Sci., 5, 5701 (2012). L. Suo, Y.-S. Hu, H. Li, M. Armand, and L. Chen, Nat. Commun., 4, 1481 (2013). J. Qian, W. A. Henderson, W. Xu, P. Bhattacharya, M. Engelhard, O. Borodin, and J.-G. Zhang, Nat. Commun., 6, 6362 (2015).

Li-metal batteries (LMBs) and Na-metal batteries (NMBs) are considered as the promising next-generation battery systems to replace the conventional Li-ion batteries (LIBs) due to their high theoretical energy density. For LMBs and NMBs, Li metal and Na metal are the ultimate choices to achieve their high energy density due to the high specific capacity, low electrochemical potential, and lightweight. However, as alkali metals, both Li and Na metal anodes suffer from serious challenges including 1) Li/Na dendrite formations and short circuits; 2) Low Coulombic efficiency and poor cycling performance; and 3) Infinite volume changes.In this presentation, I will introduce our research that contributed to next-generation LMBs and NMBs via different approaches. i) The interface is one of the key factors for the Li and Na deposition behaviors and battery performances. We developed different approaches, such as atomic layer deposition (ALD), molecular layer deposition (MLD) techniques, and solution-based method to fabricate the artificial interface with significantly improved electrochemical performances and reduced dendrite formation for Li/Na metal anodes. ii) To address another challenge of volume change, we firstly proposed the 3D conductive interlayer concept for Li and Na metal anodes with excellent electrochemical performance under high current density and high capacity. All these ideas have been also further applied to solve the practical issues for different Li and Na metal battery systems.

Rechargeable all-solid-state lithium (Li) metal batteries show improved safety and energy density compared to commercial Li-ion batteries using liquid electrolyte. As the key component of Li metal batteries, ceramic solid-state electrolyte has attracted great interest because of its high ion conductivity and great potential in interfacing with Li metal. Ceramic electrolyte has a more stable interface with Li metal than liquid electrolyte, but chemical reaction and Li dendrite growth at the electrolyte/Li interface are still significant, which causes device degradation and failure by cycling of Li plating and stripping. Unlike ceramic electrolyte, polymer electrolyte has a relatively stable interface with Li metal and better mechanical flexibility. Therefore, we introduced a polymer electrolyte coating to protect the ceramic electrolyte from direct contact with Li metal. The galvanotactic cycling Li plating/striping data on the devices with (without) the coating illustrates increased (decreased) overall conductivity and cyclability of the test cell by the cycling. Nanometer-scale ionic-transport imaging, based on atomic force microscopy, shows that cycling degrades the ceramic-only electrolyte by partially blocking ionic transport in areas; in contrast, cycling on the polymer-coated electrolyte improves ionic conductivity. Compared with the ceramic-only electrolyte, this novel polymer electrolyte coating on ceramic electrolyte shows less degradation when in contact with Li metal.

An optimized 3D polymer alloy interface for durability and safety for Li metal batteries

Li metal anode shows significant potential for advancing high-energy-density and commercially viable lithium batteries due to its high specific capacity and low electrochemical potential. However, thinning Li metal encounters serious challenges owing to its mechanical stickiness and fragility during the mechanical rolling process, which severely restricts its practical utilization. Consequently, most current Li metal batteries rely on excessively thick Li foils, leading to substantial resource waste and undermining the pursuit of high energy density. This review highlights the quantitative design principles of ultrathin Li metal (≤15µm) and elucidates its critical roles in realizing the true potential of Li metal batteries. Emerging strategies for the fabrication of ultrathin Li metal, followed by a critical evaluation of recent advances and persistent challenges in their deployment for both liquid and solid-state batteries, are summarized. A perspective on future directions for ultrathin Li metal is also presented. Ultrathin Li metal anodes are poised to deliver transformative improvements in energy density, unlocking new opportunities for advanced energy storage systems.

Li-metal batteries (LMBs) and Na-metal batteries (NMBs) are considered as the promising next-generation battery systems to replace conventional Li-ion batteries (LIBs) due to their high theoretical energy density [1]. For LMBs and NMBs, Li metal and Na metal are the ultimate choices to achieve their high energy density due to their high specific capacity, low electrochemical potential, and lightweight. However, as alkali metals, both Li and Na metal anodes suffer from serious challenges including 1) Li/Na dendrite formations and short circuits; 2) Low Coulombic efficiency and poor cycling performance; and 3) Infinite volume changes. In this presentation, I will introduce our research that contributed to the design of artificial interfaces for Li and Na metal anode using atomic layer deposition (ALD) and molecular layer deposition (MLD) techniques [2-3]. i) Developing ionic conductive protective layers for Li and Na metal anodes. A two-step strategy is developed to obtain the smooth and stable LiAlOx and NaAlOx artificial layer for Li and Na metal anodes by the post-lithiation process, respectively. The substrate of Li and Na metals are the Li and Na resources during post-treatment [4]. ii) Nano-alloy structure to the nano-laminated structure for Li and Na metal anodes. Through tailoring the compositions of the hybrid interfaces, we realize the nano-alloy structure to the nano-laminated structure. As a result, the nano-alloy interface (1Al2O3-1alucone or 2Al2O3-2alucone) presents the most stable electrochemical performances for both Li and Na metal anodes [5]. iii) An organic-rich or an inorganic-rich interface? We demonstrate the controllable fabrication of the hybrid artificial SEI for Li metal anode with different organic-inorganic ratios. Three typical compositions were realized: organic-rich interface, organic-inorganic-balanced interface and inorganic-rich interface. The different organic-inorganic ratios of the hybrid interfaces result in the tuning of the mechanical properties, lithiophilicity, diffusion kinetics and Li dendrite formation of the Li metal anode [6]. iv) A new hybrid protective layer for the Na metal anode. A metal-doped hybrid polyurea (PU) film with tunable composition, sodiophilic sites and improved stiffness was fabricated by introducing Zn or Al as crosslinkers into the polymer chains and adopted as an artificial SEI for Na metal. Compared to bare Na and pure PU-coated Na, the Na metal anode coated with the metal-doped PU film exhibits significantly improved electrochemical performance [7]. All these ideas have been also further applied to solve the practical issues for different Li and Na metal battery systems.[1] Energy & Environmental Science, 2024, 17, 442-496[2] Chemical Society Reviews, 2024,53, 5428-5488[3] Chemical Society Reviews, 2021, 50, 3889-3956[4] Small, 2022, 18, 2203045[5] Advanced Materials, 2023, 35, 2301414[6] Advanced Functional Materials, 2024, 2406426[7] Advanced Materials, 2024, 2406837

A New General Paradigm for Understanding and Preventing Li Metal Penetration through Solid Electrolytes

Hybrid polyion complex micelles enabling high-performance lithium-metal batteries with universal carbonates