Lithium dendrite (filament) propagation through ceramic electrolytes, leading to short-circuits at high rates of charge, is one of the greatest barriers to realising high energy density all-solidstate lithium anode batteries. Utilising in-situ X-ray computed tomography coupled with spatially mapped X-ray diffraction, the propagation of cracks and the propagation of lithium dendrites through the solid electrolyte have been tracked in a Li/Li6PS5Cl/Li cell as a function of the charge passed. On plating, cracking initiates with spallation, conical "pothole"-like cracks that form in the ceramic electrolyte near the surface with the plated electrode. The spallations form predominantly at the lithium electrode edges where local fields are high. Transverse cracks then propagate from the spallations across the electrolyte from the plated to the stripped electrode. Lithium ingress drives the propagation of the spallation and transverse cracks by widening the crack from the rear, i.e. the crack front propagates ahead of the Li. As a result, cracks traverse the entire electrolyte before the Li arrives at the other electrode and therefore before a short-circuit occurs.

Transmission electron microscopy (TEM) has long been an essential tool for understanding the structure of materials. Over the past couple of decades, this venerable technique has undergone a number of revolutions, such as the development of aberration correction for atomic level imaging, the realization of cryogenic TEM for imaging biological specimens, and new instrumentation permitting the observation of dynamic systems in situ . Research in the latter has rapidly accelerated in recent years, based on a silicon-chip architecture that permits a versatile array of experiments to be performed under the high vacuum of the TEM. Of particular interest is using these silicon chips to enclose fluids safely inside the TEM, allowing us to observe liquid dynamics at the nanoscale. In situ imaging of liquid phase reactions under TEM can greatly enhance our understanding of fundamental processes in fields from electrochemistry to cell biology. Here, we review how in situ TEM experiments of liquids can be performed, with a particular focus on microchip-encapsulated liquid cell TEM. We will cover the basics of the technique, and its strengths and weaknesses with respect to related in situ TEM methods for characterizing liquid systems. We will show how this technique has provided unique insights into nanomaterial synthesis and manipulation, battery science and biological cells. A discussion on the main challenges of the technique, and potential means to mitigate and overcome them, will also be presented.

attractive for future grid-level energy storage applications. Metallic Zn, as the ideal anode for AZBs, has the highest theoretical capacity (5851 mAh mL −1 ). It is also non-toxic, non-flammable, abundant, and has good electrical conductivity and water stability. [1][2][3][4][5] However, conventional metallic Zn anodes suffer from severe dendrite formation during cycling, causing serious problems like poor reversibility, voltage hysteresis, increased parasitic reactions, shorting-induced battery failures, and other issues. [1,3,6] These dendritic structures, either rarefied needle, or non-planar platelet deposits, preferentially form at irregular or defective areas of the electrode where the localized current density is highest and the initial nucleation event is most likely, [7] and is exacerbated by cycling at high current densities and capacities. [8,9] Strategies for controlling and suppressing dendritic growth have revolved around manipulating the electrolyte, typically by inclusion of additives, [10][11][12][13][14][15] or by engineering the electrode into a high-surface-area sponge, [16][17][18] or with a protective surface coating, [19] in order to suppress dendrite formation.Despite being one of the most promising candidates for grid-level energy storage, practical aqueous zinc batteries are limited by dendrite formation, which leads to significantly compromised safety and cycling performance. In this study, by using single-crystal Zn-metal anodes, reversible electrodeposition of planar Zn with a high capacity of 8 mAh cm −2 can be achieved at an unprecedentedly high current density of 200 mA cm −2 . This dendrite-free electrode is well maintained even after prolonged cycling (>1200 cycles at 50 mA cm −2 ). Such excellent electrochemical performance is due to single-crystal Zn suppressing the major sources of defect generation during electroplating and heavily favoring planar deposition morphologies. As so few defect sites form, including those that would normally be found along grain boundaries or to accommodate lattice mismatch, there is little opportunity for dendritic structures to nucleate, even under extreme plating rates. This scarcity of defects is in part due to perfect atomic-stitching between merging Zn islands, ensuring no defective shallow-angle grain boundaries are formed and thus removing a significant source of non-planar Zn nucleation. It is demonstrated that an ideal high-rate Zn anode should offer perfect lattice matching as this facilitates planar epitaxial Zn growth and minimizes the formation of any defective regions.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adma.202202552.

All-solid-state batteries with a Li anode and ceramic electrolyte have the potential to deliver a step change in performance compared with today's Li-ion batteries 1,2 . However, Li dendrites (filaments) form on charging at practical rates, penetrate across the ceramic electrolyte leading to short-circuit and cell failure 3,4 . Previous models of dendrite penetration have generally focused on a single process for dendrite initiation and propagation, with Li driving the crack at its tip [5][6][7][8][9] . Here we show that initiation and propagation are separate processes.

Multivalent cation rechargeable batteries, including those based on Ca, Mg, Al, etc., have attracted considerable interest as candidates for beyond Li-ion. Recent developments have realized promising electrolyte compositions for rechargeable Ca batteries; however, an in-depth understanding of the Ca plating and stripping behavior, and the mechanisms by which adverse dendritic growth may occur, remains underdeveloped. In this work, via in-situ transmission electron microscopy, we have captured the real-time nucleation, growth, and dissolution of Ca, the formation of dead Ca, and demonstrated the critical role of current density and the solid-electrolyte interphase layer in controlling the plating morphology. In particular, the interface was found to influence Ca deposition morphology, and can lead 2 to Ca dendrite growth under unexpected conditions. These observations allow us to propose a model explaining the preferred conditions for reversible and efficient Ca plating.Multivalent cation batteries based on Mg, Ca, Al, etc. have attracted significant interest as potential candidates to replace Li-ion batteries in recent years. [1][2][3][4][5] These metallic anodes have much higher natural metal abundancy, and are reported to be much less prone to dendrite formation compared with metallic Li anode, [3][4][5][6][7][8][9][10][11] potentially due to their lower self-diffusion barriers. 1,12,13 The Ca-ion system has demonstrated significant potential. It has a comparable volumetric capacity to Li, and compared with other multivalent systems like Mg, it also has the advantages of higher earth abundance, lower reductive potential and lower charge density. 1 Despite this, the development of Ca-ion batteries has been slow in part due to issues with the anode, where most studied electrolytes react with metallic Ca, rapidly forming surface passivation layers comprised of CaCl2, Ca(OH)2, or CaCO3, that block Ca ion diffusion and make further plating impossible. [14][15][16][17] However, recent breakthroughs in electrolyte research have brought renewed interest in Ca-ion batteries. [18][19][20][21] These works have demonstrated promising Ca-based electrolytes that are capable of continuous plating and stripping with relatively high efficiency at moderately elevated 17 or room-temperatures. 4,11,22 While most previous studies demonstrated fairly smooth plating morphology, [3][4][5][6][7][8][9][10][11] a recent paper by Davidson et al. 23 showed that dendrites do grow in Mg-ion electrolyte. This challenges the widely accepted belief that multivalent systems do not form dendrites easily. Since research into Ca-ion electrolytes is at an early stage, little work has been done to systematically study their plating and stripping processes. This study explores the electroplating morphology and mechanism within the Ca-ion system via in situ transmission electron microscopy (TEM) to evaluate the feasibility of employing metallic Ca anodes, and to provide a deeper understanding of this system for future optimization.

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The solid electrolyte interphase (SEI), a complex layer that forms over the surface of electrodes exposed to battery electrolyte, has a central influence on the structural evolution of the electrode during battery operation. For lithium metallic anodes, tailoring this SEI is regarded as one of the most effective avenues for ensuring consistent cycling behavior, and thus practical efficiencies. While fluoride‐rich interphases in particular seem beneficial, how they alter the structural dynamics of lithium plating and stripping to promote efficiency remains only partly understood. Here, operando liquid‐cell transmission electron microscopy is used to investigate the nanoscale structural evolution of lithium electrodeposition and dissolution at the electrode surface across fluoride‐poor and fluoride‐rich interphases. The in situ imaging of lithium cycling reveals that a fluoride‐rich SEI yields a denser Li structure that is particularly amenable to uniform stripping, thus suppressing lithium detachment and isolation. By combination with quantitative composition analysis via mass spectrometry, it is identified that the fluoride‐rich SEI suppresses overall lithium loss through drastically reducing the quantity of dead Li formation and preventing electrolyte decomposition. These findings highlight the importance of appropriately tailoring the SEI for facilitating consistent and uniform lithium dissolution, and its potent role in governing the plated lithium's structure.

Lithium-rich disordered rocksalts such as Li 1.3 Nb 0.3 Mn 0.4 O 2 and Li 2 MnO 2 F are being investigated as high energy density cathodes for next generation Li-ion batteries. They can support the (de) lithiation of lithium ions over large compositional ranges while preserving the same overall structure. Here, we present a new Ni-rich oxyfluoride cathode, Li 2 NiO 2 F, with a disordered rocksalt structure. Li 2 NiO 2 F and can deliver a discharge capacity of 200 mAh g −1 at an average voltage of 3.2 V.