Lithium metal anodes offer high theoretical capacities (3,860 milliampere-hours per gram)1, but rechargeable batteries built with such anodes suffer from dendrite growth and low Coulombic efficiency (the ratio of charge output to charge input), preventing their commercial adoption2,3. The formation of inactive ('dead') lithium- which consists of both (electro)chemically formed Li+ compounds in the solid electrolyte interphase and electrically isolated unreacted metallic Li0 (refs 4,5)-causes capacity loss and safety hazards. Quantitatively distinguishing between Li+ in components of the solid electrolyte interphase and unreacted metallic Li0 has not been possible, owing to the lack of effective diagnostic tools. Optical microscopy6, in situ environmental transmission electron microscopy7,8, X-ray microtomography9 and magnetic resonance imaging10 provide a morphological perspective with little chemical information. Nuclear magnetic resonance11, X-ray photoelectron spectroscopy12 and cryogenic transmission electron microscopy13,14 can distinguish between Li+ in the solid electrolyte interphase and metallic Li0, but their detection ranges are limited to surfaces or local regions. Here we establish the analytical method of titration gas chromatography to quantify the contribution of unreacted metallic Li0 to the total amount of inactive lithium. We identify the unreacted metallic Li0, not the (electro)chemically formed Li+ in the solid electrolyte interphase, as the dominant source of inactive lithium and capacity loss. By coupling the unreacted metallic Li0 content to observations of its local microstructure and nanostructure by cryogenic electron microscopy (both scanning and transmission), we also establish the formation mechanism of inactive lithium in different types of electrolytes and determine the underlying cause of low Coulombic efficiency in plating and stripping (the charge and discharge processes, respectively, in a full cell) of lithium metal anodes. We propose strategies for making lithium plating and stripping more efficient so that lithium metal anodes can be used for next-generation high-energy batteries.

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Quantifying inactive lithium in lithium metal batteries

Inactive lithium (Li) formation is the immediate cause of capacity loss and catastrophic failure of Li metal batteries. However, the chemical component and the atomic level structure of inactive Li have rarely been studied due to the lack of effective diagnosis tools to accurately differentiate and quantify Li+ in solid electrolyte interphase (SEI) components and the electrically isolated unreacted metallic Li0, which together comprise the inactive Li. Here, by introducing a new analytical method, Titration Gas Chromatography (TGC), we can accurately quantify the contribution from metallic Li0 to the total amount of inactive Li. We uncover that the Li0, rather than the electrochemically formed SEI, dominates the inactive Li and capacity loss. Using cryogenic electron microscopies to further study the microstructure and nanostructure of inactive Li, we find that the Li0 is surrounded by insulating SEI, losing the electronic conductive pathway to the bulk electrode. Coupling the measurements of the Li0 global content to observations of its local atomic structure, we reveal the formation mechanism of inactive Li in different types of electrolytes, and identify the true underlying cause of low Coulombic efficiency in Li metal deposition and stripping. We ultimately propose strategies to enable the highly efficient Li deposition and stripping to enable Li metal anode for next generation high energy batteries.

Quantifying Inactive Lithium in Lithium Metal Batteries

Lithium metal anodes have attracted much attention as candidates for high-energy batteries, but there have been few reports of long cycling behaviour, and the degradation mechanism of realistic high-energy Li metal cells remains unclear. Here, we develop a prototypical 300 Wh kg−1 (1.0 Ah) pouch cell by integrating a Li metal anode, a LiNi0.6Mn0.2Co0.2O2 cathode and a compatible electrolyte. Under small uniform external pressure, the cell undergoes 200 cycles with 86% capacity retention and 83% energy retention. In the initial 50 cycles, flat Li foil converts into large Li particles that are entangled in the solid-electrolyte interphase, which leads to rapid volume expansion of the anode (cell thickening of 48%). As cycling continues, the external pressure helps the Li anode maintain good contact between the Li particles, which ensures a conducting percolation pathway for both ions and electrons, and thus the electrochemical reactions continue to occur. Accordingly, the solid Li particles evolve into a porous structure, which manifests in substantially reduced cell swelling by 19% in the subsequent 150 cycles. Much has been said about the high-energy, long-lasting potential of Li metal batteries, and yet little has been demonstrated at the cell scale. Here, Jun Liu and colleagues demonstrate a Li metal pouch cell with a 300 Wh kg−1 energy density and a 200-cycle lifetime.

https://www.nature.com/articles/s41560-019-0390-6.pdf?proof=t

High-energy lithium metal pouch cells with limited anode swelling and long stable cycles

Lithium-ion batteries (LIBs) possess several advantages over other types of viable practical batteries, including higher operating voltages, higher energy densities, longer cycle lives, lower rates of self-discharge and less environmental pollution Therefore, LIBs have been widely and successfully applied in portable electronic devices and industrial fields However, the rapidly increasing demands of new energy vehicles have also quickly increased the performance requirements of LIBs, including the need for higher power densities, greater capacity densities and better safety As battery designs gradually standardize, improvements in LIB performances mainly depend on the technical progress in key electrode materials such as positive and negative electrode materials, separators and electrolytes For LIB performances to meet the rising requirements, many studies on the structural characteristics and morphology modifications of electrode/separator/electrolyte materials with different synthesis methods have been conducted In this review, recent progress of LIBs is reviewed with a focus on positive electrode materials, negative electrode materials, separators and electrolytes in terms of energy density, power density, life-cycle and safety To accelerate the research and development and to overcome the challenges of LIB technology and application, several possible research directions are also discussed to further improve LIB performances

Recent progress in advanced electrode materials, separators and electrolytes for lithium batteries

Lithium, the lightest and most electronegative metallic element, has long been considered the ultimate choice as a battery anode for mobile, as well as in some stationary applications. The high electronegativity of Li is, however, a double-edged sword—it facilitates a large operating voltage when paired with essentially any cathode, promising a high cell-level energy density. It is also synonymous with a high chemical reactivity and low reduction potential. The interfaces a Li metal anode forms with any other material (liquid or solid) in an electrochemical cell are therefore always mediated by one or more products of its chemical or electrochemical reactions with that material. The physical, crystallographic, mechanical, electrochemical, and transport properties of the resultant new material phases (interphases) regulate all interfacial processes at a Li metal anode, including electrodeposition during battery recharge. This Review takes recent efforts aimed at manipulating the structure, composition, and physical properties of the solid electrolyte interphase (SEI) formed on an Li anode as a point of departure to discuss the structural, electrokinetic, and electrochemical requirements for achieving high anode reversibility. An important conclusion is that while recent reports showing significant advances in the achievement of highly reversible Li anodes, e.g. as measured by the coulombic efficiency (CE), raise prospects for as significant progress towards commercially relevant Li metal batteries, the plateauing of achievable CE values to around 99 ± 0.5% apparent from a comprehensive analysis of the literature is problematic because CE values of at least 99.7%, and preferably >99.9% are required for Li metal cells to live up to the potential for higher energy density batteries offered by the Li metal anode. On this basis, we discuss promising approaches for creating purpose-built interphases on Li, as well as for fabricating advanced Li electrode architectures for regulating Li electrodeposition morphology and crystallinity. Considering the large number of physical and chemical factors involved in achieving fine control of Li electrodeposition, we believe that achievement of the remaining ∼0.5% in anode reversibility will require fresh approaches, perhaps borrowed from other fields. We offer perspectives on both current and new strategies for achieving such Li anodes with the specific aim of engaging established contributors and newcomers to the field in the search for scalable solutions.

Regulating electrodeposition morphology of lithium: towards commercially relevant secondary Li metal batteries

Meniscus‐Guided Printing Meniscus‐guided micro‐printing of Prussian Blue is realized by the localized crystallization of FeFe(CN)6 on the substrate confined by the ink meniscus and thermal reduction of the crystallized FeFe(CN)6. This strategy is capable of being used as an electrochromic display to give real‐time directions on an augmented reality (AR) smart contact lens device. More details can be found in article number 2205588 by Im Doo Jung, Seung Kwon Seol, and co‐workers.

Meniscus‐Guided Micro‐Printing of Prussian Blue for Smart Electrochromic Display (Adv. Sci. 3/2023)

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Im Doo Jung

Papers

Meniscus‐Guided Micro‐Printing of Prussian Blue for Smart Electrochromic Display (Adv. Sci. 3/2023)

Virtual reality-based assembly-level design for additive manufacturing decision framework involving human aspects of design