Re-investigating the structure-property relationship of the solid electrolytes Li 3-x In1-x Zr x Cl6 and the impact of In-Zr(iv) substitution.

Chloride-based solid electrolytes are considered interesting candidates for catholytes in all-solid-state batteries due to their high electrochemical stability, which allows the use of high-voltage cathodes without protective coatings. Aliovalent Zr(iv) substitution is a widely applicable strategy to increase the ionic conductivity of Li3M(iii)Cl6 solid electrolytes. In this study, we investigate how Zr(iv) substitution affects the structure and ion conduction in Li3-x In1-x Zr x Cl6 (0 ≤ x ≤ 0.5). Rietveld refinement using both X-ray and neutron diffraction is used to make a structural model based on two sets of scattering contrasts. AC-impedance measurements and solid-state NMR relaxometry measurements at multiple Larmor frequencies are used to study the Li-ion dynamics. In this manner the diffusion mechanism and its correlation with the structure are explored and compared to previous studies, advancing the understanding of these complex and difficult to characterize materials. It is found that the diffusion in Li3InCl6 is most likely anisotropic considering the crystal structure and two distinct jump processes found by solid-state NMR. Zr-substitution improves ionic conductivity by tuning the charge carrier concentration, accompanied by small changes in the crystal structure which affect ion transport on short timescales, likely reducing the anisotropy.

High entropy liquid electrolytes for lithium batteries.

High-entropy alloys/compounds have large configurational entropy by introducing multiple components, showing improved functional properties that exceed those of conventional materials. However, how increasing entropy impacts the thermodynamic/kinetic properties in liquids that are ambiguous. Here we show this strategy in liquid electrolytes for rechargeable lithium batteries, demonstrating the substantial impact of raising the entropy of electrolytes by introducing multiple salts. Unlike all liquid electrolytes so far reported, the participation of several anionic groups in this electrolyte induces a larger diversity in solvation structures, unexpectedly decreasing solvation strengths between lithium ions and solvents/anions, facilitating lithium-ion diffusivity and the formation of stable interphase passivation layers. In comparison to the single-salt electrolytes, a low-concentration dimethyl ether electrolyte with four salts shows an enhanced cycling stability and rate capability. These findings, rationalized by the fundamental relationship between entropy-dominated solvation structures and ion transport, bring forward high-entropy electrolytes as a composition-rich and unexplored space for lithium batteries and beyond.

Li5NCl2: A Fully-Reduced, Highly-Disordered Nitride-Halide Electrolyte for Solid-State Batteries with Lithium-Metal Anodes.

Most highly Li-conducting solid electrolytes (σRT > 10-3 S cm-1) are unstable against lithium-metal and suffer from detrimental solid-electrolyte decomposition at the lithium-metal/solid-electrolyte interface. Solid electrolytes that are stable against lithium metal thus offer a direct route to stabilize lithium-metal/solid-electrolyte interfaces, which is crucial for realizing all-solid-state batteries that outperform conventional lithium-ion batteries. In this study, we investigate Li5NCl2 (LNCl), a fully-reduced solid electrolyte that is thermodynamically stable against lithium metal. Combining experiments and simulations, we investigate the lithium diffusion mechanism, different synthetic routes, and the electrochemical stability window of LNCl. Li nuclear magnetic resonance (NMR) experiments suggest fast Li motion in LNCl, which is however locally confined and not accessible in macroscopic LNCl pellets via electrochemical impedance spectroscopy (EIS). With ab-initio calculations, we develop an in-depth understanding of Li diffusion in LNCl, which features a disorder-induced variety of different lithium jumps. We identify diffusion-limiting jumps providing an explanation for the high local diffusivity from NMR and the lower macroscopic conductivity from EIS. The fundamental understanding of the diffusion mechanism we develop herein will guide future conductivity optimizations for LNCl and may be applied to other highly-disordered fully-reduced electrolytes. We further show experimentally that the previously reported anodic limit (>2 V vs Li+/Li) is an overestimate and find the true anodic limit at 0.6 V, which is in close agreement with our first-principles calculations. Because of LNCl's stability against lithium-metal, we identify LNCl as a prospective artificial protection layer between highly-conducting solid electrolytes and strongly-reducing lithium-metal anodes and thus provide a computational investigation of the chemical compatibility of LNCl with common highly-conducting solid electrolytes (Li6PS5Cl, Li3YCl6, ...). Our results set a framework to better understand and improve highly-disordered fully-reduced electrolytes and highlight their potential in enabling lithium-metal solid-state batteries.

Investigation of Structure, Ionic Conductivity, and Electrochemical Stability of Halogen Substitution in Solid-State Ion Conductor Li3YBr x Cl6-x.

Li3YX6 (X = Cl, Br) materials are Li-ion conductors that can be used as solid electrolytes in all solid-state batteries. Solid electrolytes ideally have high ionic conductivity and (electro)chemical compatibility with the electrodes. It was proven that introducing Br to Li3YCl6 increases ionic conductivity but, according to thermodynamic calculations, should also reduce oxidative stability. In this paper, the trade-off between ionic conductivity and electrochemical stability in Li3YBr x Cl6-x halogen-substituted compounds is investigated. The compositions of Li3YBr1.5Cl4.5 and Li3YBr4.5Cl1.5 are reported for the first time, along with a consistent analysis of the whole Li3YBr x Cl6-x (x = 0-6) tie-line. The results show that, while Br-rich materials are more conductive (5.36 × 10-3 S/cm at 30 °C for x = 4.5), the oxidative stability is lower (∼3 V compared to ∼3.5 V). Small Br content (x = 1.5) does not affect oxidative stability but substantially increases ionic conductivity compared to pristine Li3YCl6 (2.1 compared to 0.049 × 10-3 S/cm at 30 °C). This work highlights that optimization of substitutions in the anion framework provide prolific and rational avenues for tailoring the properties of solid electrolytes.

Entropy-Driven Liquid Electrolytes for Lithium Batteries.

Developing liquid electrolytes with higher kinetics and enhanced interphase stability is one of the key challenges for lithium batteries. However, the poor solubility of lithium salts in solvents sets constraints that compromises the electrolyte properties. Here, it is shown that introducing multiple salts to form a high-entropy solution, alters the solvation structure, which can be used to raise the solubility of specific salts and stabilize electrode-electrolyte interphases. The prepared high-entropy electrolytes significantly enhance the cycling and rate performance of lithium batteries. For lithium-metal anodes the reversibility exceeds 99%, which extends the cycle life of batteries even under aggressive cycling conditions. For commercial batteries, combining a graphite anode with a LiNi0.8 Co0.1 Mn0.1 O2 cathode, more than 1000 charge-discharge cycles are achieved while maintaining a capacity retention of more than 90%. These performance improvements with respect to regular electrolytes are rationalized by the unique features of the solvation structure in high-entropy electrolytes. The weaker solvation interaction induced by the higher disorder results in improved lithium-ion kinetics, and the altered solvation composition leads to stabilized interphases. Finally, the high-entropy, induced by the presence of multiple salts, enables a decrease in melting temperature of the electrolytes and thus enables lower battery operation temperatures without changing the solvents.

Clarifying the Relationship between the Lithium Deposition Coverage and Microstructure in Lithium Metal Batteries.

Improving the reversibility of lithium metal batteries is one of the challenges in current battery research. This requires better fundamental understanding of the evolution of the lithium deposition morphology, which is very complex due to the various parameters involved in different systems. Here, we clarify the fundamental origins of lithium deposition coverage in achieving highly reversible and compact lithium deposits, providing a comprehensive picture in the relationship between the lithium microstructure and solid electrolyte interphase (SEI) for lithium metal batteries. Systematic variation of the salt concentration offers a framework that brings forward the different aspects that play a role in cycling reversibility. Higher nucleation densities are formed in lower concentration electrolytes, which have the advantage of higher lithium deposition coverage; however, it goes along with the formation of an organic-rich instable SEI which is unfavorable for the reversibility during (dis)charging. On the other hand, the growth of large deposits benefiting from the formation of an inorganic-rich stable SEI is observed in higher concentration electrolytes, but the initial small nucleation density prevents full coverage of the current collector, thus compromising the plated lithium metal density. Taking advantages of the paradox, a nanostructured substrate is rationally applied, which increases the nucleation density realizing a higher deposition coverage and thus more compact plating at intermediate concentration (∼1.0 M) electrolytes, leading to extended reversible cycling of batteries.

A Water-Free In Situ HF Treatment for Ultrabright InP Quantum Dots.

Indium phosphide quantum dots are the main alternative for toxic and restricted Cd-based quantum dots for lighting and display applications, but in the absence of protecting ZnSe and/or ZnS shells, InP quantum dots suffer from low photoluminescence quantum yields. Traditionally, HF treatments have been used to improve the quantum yield of InP to ∼50%, but these treatments are dangerous and not well understood. Here, we develop a postsynthetic treatment that forms HF in situ from benzoyl fluoride, which can be used to strongly increase the quantum yield of InP core-only quantum dots. This treatment is water-free and can be performed safely. Simultaneous addition of the z-type ligand ZnCl2 increases the photoluminescence quantum yield up to 85%. Structural analysis via XPS as well as solid state and solution NMR measurements shows that the in situ generated HF leads to a surface passivation by indium fluoride z-type ligands and removes polyphosphates, but not PO3 and PO4 species from the InP surface. With DFT calculations it is shown that InP QDs can be trap-free even when PO3 and PO4 species are present on the surface. These results show that both polyphosphate removal and z-type passivation are necessary to obtain high quantum yields in InP core-only quantum dots. They further show that core-only InP QDs can achieve photoluminescence quantum yields rivalling those of InP/ZnSe/ZnS core/shell/shell QDs and the best core-only II-VI QDs.

Improving Li-ion interfacial transport in hybrid solid electrolytes.

The development of commercial solid-state batteries has to date been hindered by the individual limitations of inorganic and organic solid electrolytes, motivating hybrid concepts. However, the room-temperature conductivity of hybrid solid electrolytes is still insufficient to support the required battery performance. A key challenge is to assess the Li-ion transport over the inorganic and organic interfaces and relate this to surface chemistry. Here we study the interphase structure and the Li-ion transport across the interface of hybrid solid electrolytes using solid-state nuclear magnetic resonance spectroscopy. In a hybrid solid polyethylene oxide polymer-inorganic electrolyte, we introduce two representative types of ionic liquid that have different miscibilities with the polymer. The poorly miscible ionic liquid wets the polymer-inorganic interface and increases the local polarizability. This lowers the diffusional barrier, resulting in an overall room-temperature conductivity of 2.47 × 10-4 S cm-1. A critical current density of 0.25 mA cm-2 versus a Li-metal anode shows improved stability, allowing cycling of a LiFePO4-Li-metal solid-state cell at room temperature with a Coulombic efficiency of 99.9%. Tailoring the local interface environment between the inorganic and organic solid electrolyte components in hybrid solid electrolytes seems to be a viable route towards designing highly conducting hybrid solid electrolytes.

High Stability of Methanol to Aromatic Conversion over Bimetallic Ca,Ga-Modified ZSM-5.

The production of valuable aromatics and the rapid catalyst deactivation due to coking are intimately related in the zeolite-catalyzed aromatization reactions. Here, we demonstrate that these two processes can be decoupled by promoting the Ga/HZSM-5 aromatization catalyst with Ca. The resulting bimetallic catalysts combine high selectivity to light aromatics with extended catalyst lifetime in the methanol-to-aromatics process. Evaluation of the catalytic performance combined with detailed catalyst characterization suggests that the added Ca interacts with the Ga-LAS, with a strong effect on the aromatization processes. A genetic algorithm approach complemented by ab initio thermodynamic analysis is used to elucidate the possible structures of bimetallic extraframework species formed under reaction conditions. The promotion effect of minute amounts of Ca is attributed to the stabilization of the intra-zeolite extraframework gallium oxide clusters with moderated dehydrogenation activity.

A Direct View on Li-Ion Transport and Li-Metal Plating in Inorganic and Hybrid Solid-State Electrolytes.

ConspectusDriven by the intrinsic safety and potential to achieve higher energy densities, solid-state Li-metal batteries are intensively researched. The ideal solid electrolyte should possess a high conductivity, should have electrochemical stability both toward the Li-metal anode and to high voltage cathodes, should suppress dendrites, should provide flexibility to deal with the volumetric changes of the electrodes, and should be easy to process. This challenging combination is to date not fulfilled by any solid electrolyte, be it organic, inorganic, or even a hybrid of the two. Pushing the development of solid electrolytes toward reversible room temperature operation when used in tandem with Li-metal anodes demands an understanding of critical processes that determine the properties of the solid electrolyte. These include the complex Li-ion transport as well as the Li-metal plating processes. This already presents the first experimental hurdle as the ability to directly and noninvasively monitor the Li-ion kinetics, Li densities, and Li chemistries, under in/situ or operando, is not trivial.The scope of this Account is the investigation and improvement of solid electrolytes, with the emphasis on the possibilities offered by solid-state NMR and neutron depth profiling as direct probes for the study of critical processes that involve Li ions and Li metal. Solid-state NMR allows us to unravel the complex interface chemical environment and the diffusion processes both in the bulk solid electrolyte and in the interface environment. These studies shed light on the role of interface composition, wetting and space-charge layers, on the macroscopic battery performance. Another technique that enables probing Li directly is operando neutron depth profiling, which allows us to determine the Li density as a function of depth. It provides a noninvasive and effectively nondestructive tool to examine delamination, irreversible reactions and dendrite formation during plating/stripping. Results demonstrate that it is very challenging to maintain the contact between Li metal and the SE during cycling, especially for the "anode-less" or "anode-free" configuration under low-pressure conditions. A perspective is provided on the potential improvement of the Li-ion transport, dendrite suppression, and preventing Li-metal-solid-electrolyte delamination as well as on the potential role of solid-state NMR and NDP techniques to guide these developments.

High dielectric barium titanate porous scaffold for efficient Li metal cycling in anode-free cells.

Li metal batteries are being intensively investigated as a means to achieve higher energy density when compared with standard Li-ion batteries. However, the formation of dendritic and mossy Li metal microstructures at the negative electrode during stripping/plating cycles causes electrolyte decomposition and the formation of electronically disconnected Li metal particles. Here we investigate the use of a Cu current collector coated with a high dielectric BaTiO3 porous scaffold to suppress the electrical field gradients that cause morphological inhomogeneities during Li metal stripping/plating. Applying operando solid-state nuclear magnetic resonance measurements, we demonstrate that the high dielectric BaTiO3 porous scaffold promotes dense Li deposition, improves the average plating/stripping efficiency and extends the cycling life of the cell compared to both bare Cu and to a low dielectric scaffold material (i.e., Al2O3). We report electrochemical tests in full anode-free coin cells using a LiNi0.8Co0.1Mn0.1O2-based positive electrode and a LiPF6-based electrolyte to demonstrate the cycling efficiency of the BaTiO3-coated Cu electrode.

Quantification of the Li-ion diffusion over an interface coating in all-solid-state batteries via NMR measurements.

A key challenge for solid-state-batteries development is to design electrode-electrolyte interfaces that combine (electro)chemical and mechanical stability with facile Li-ion transport. However, while the solid-electrolyte/electrode interfacial area should be maximized to facilitate the transport of high electrical currents on the one hand, on the other hand, this area should be minimized to reduce the parasitic interfacial reactions and promote the overall cell stability. To improve these aspects simultaneously, we report the use of an interfacial inorganic coating and the study of its impact on the local Li-ion transport over the grain boundaries. Via exchange-NMR measurements, we quantify the equilibrium between the various phases present at the interface between an S-based positive electrode and an inorganic solid-electrolyte. We also demonstrate the beneficial effect of the LiI coating on the all-solid-state cell performances, which leads to efficient sulfur activation and prevention of solid-electrolyte decomposition. Finally, we report 200 cycles with a stable capacity of around 600 mAh g-1 at 0.264 mA cm-2 for a full lab-scale cell comprising of LiI-coated Li2S-based cathode, Li-In alloy anode and Li6PS5Cl solid electrolyte.

Synthesis and Structure-Property Relationships of Polyimide Covalent Organic Frameworks for Carbon Dioxide Capture and (Aqueous) Sodium-Ion Batteries.

Covalent organic frameworks (COFs) are an emerging material family having several potential applications. Their porous framework and redox-active centers enable gas/ion adsorption, allowing them to function as safe, cheap, and tunable electrode materials in next-generation batteries, as well as CO2 adsorption materials for carbon-capture applications. Herein, we develop four polyimide COFs by combining aromatic triamines with aromatic dianhydrides and provide detailed structural and electrochemical characterization. Through density functional theory (DFT) calculations and powder X-ray diffraction, we achieve a detailed structural characterization, where DFT calculations reveal that the imide bonds prefer to form at an angle with one another, breaking the 2D symmetry, which shrinks the pore width and elongates the pore walls. The eclipsed perpendicular stacking is preferable, while sliding of the COF sheets is energetically accessible in a relatively flat energy landscape with a few metastable regions. We investigate the potential use of these COFs in CO2 adsorption and electrochemical applications. The adsorption and electrochemical properties are related to the structural and chemical characteristics of each COF, giving new insights for advanced material designs. For CO2 adsorption specifically, the two best performing COFs originated from the same triamine building block, which-in combination with force-field calculations-revealed unexpected structure-property relationships. Specific geometries provide a useful framework for Na-ion intercalation with retainable capacities and stable cycle life at a relatively high working potential (>1.5 V vs Na/Na+). Although this capacity is low compared to conventional inorganic Li-ion materials, we show as a proof of principle that these COFs are especially promising for sustainable, safe, and stable Na-aqueous batteries due to the combination of their working potentials and their insoluble nature in water.

Revealing High Na-Content P2-Type Layered Oxides as Advanced Sodium-Ion Cathodes.

Layered Na-based oxides with the general composition of NaxTMO2 (TM: transition metal) have attracted significant attention for their high compositional diversity that provides tunable electrochemical performance for electrodes in sodium-ion batteries. The various compositions bring forward complex structural chemistry that is decisive for the layered stacking structure, Na-ion conductivity, and the redox activity, potentially promising new avenues in functional material properties. In this work, we have explored the maximum Na content in P2-type layered oxides and discovered that the high-content Na in the host enhances the structural stability; moreover, it promotes the oxidation of low-valent cations to their high oxidation states (in this case Ni2+). This can be rationalized by the increased hybridization of the O(2p)-TM(3d-eg*) states, affecting both the local TM environment as well as the interactions between the NaO2 and TMO2 layers. These properties are highly beneficial for the Na storage capabilities as required for cathode materials in sodium-ion batteries. It leads to excellent Na-ion mobility, a large storage capacity (>100 mAh g-1 between 2.0-4.0 V), yet preventing the detrimental sliding of the TMO2 layers (P2-O2 structural transition), as reflected by the ultralong cycle life (3000 (dis)charge cycles demonstrated). These findings expand the horizons of high Na-content P2-type materials, providing new insights of the electronic and structural chemistry for advanced cathode materials.

Clarifying the relationship between redox activity and electrochemical stability in solid electrolytes.

All-solid-state Li-ion batteries promise safer electrochemical energy storage with larger volumetric and gravimetric energy densities. A major concern is the limited electrochemical stability of solid electrolytes and related detrimental electrochemical reactions, especially because of our restricted understanding. Here we demonstrate for the argyrodite-, garnet- and NASICON-type solid electrolytes that the favourable decomposition pathway is indirect rather than direct, via (de)lithiated states of the solid electrolyte, into the thermodynamically stable decomposition products. The consequence is that the electrochemical stability window of the solid electrolyte is notably larger than predicted for direct decomposition, rationalizing the observed stability window. The observed argyrodite metastable (de)lithiated solid electrolyte phases contribute to the (ir)reversible cycling capacity of all-solid-state batteries, in addition to the contribution of the decomposition products, comprehensively explaining solid electrolyte redox activity. The fundamental nature of the proposed mechanism suggests this is a key aspect for solid electrolytes in general, guiding interface and material design for all-solid-state batteries.

Review of Recent Development of In Situ/Operando Characterization Techniques for Lithium Battery Research.

The increasing demands of energy storage require the significant improvement of current Li-ion battery electrode materials and the development of advanced electrode materials. Thus, it is necessary to gain an in-depth understanding of the reaction processes, degradation mechanism, and thermal decomposition mechanisms under realistic operation conditions. This understanding can be obtained by in situ/operando characterization techniques, which provide information on the structure evolution, redox mechanism, solid-electrolyte interphase (SEI) formation, side reactions, and Li-ion transport properties under operating conditions. Here, the recent developments in the in situ/operando techniques employed for the investigation of the structural stability, dynamic properties, chemical environment changes, and morphological evolution are described and summarized. The experimental approaches reviewed here include X-ray, electron, neutron, optical, and scanning probes. The experimental methods and operating principles, especially the in situ cell designs, are described in detail. Representative studies of the in situ/operando techniques are summarized, and finally the major current challenges and future opportunities are discussed. Several important battery challenges are likely to benefit from these in situ/operando techniques, including the inhomogeneous reactions of high-energy-density cathodes, the development of safe and reversible Li metal plating, and the development of stable SEI.

Facile Synthesis toward the Optimal Structure-Conductivity Characteristics of the Argyrodite Li6PS5Cl Solid-State Electrolyte.

The high Li-ion conductivity of the argyrodite Li6PS5Cl makes it a promising solid electrolyte candidate for all-solid-state Li-ion batteries. For future application, it is essential to identify facile synthesis procedures and to relate the synthesis conditions to the solid electrolyte material performance. Here, a simple optimized synthesis route is investigated that avoids intensive ball milling by direct annealing of the mixed precursors at 550 °C for 10 h, resulting in argyrodite Li6PS5Cl with a high Li-ion conductivity of up to 4.96 × 10-3 S cm-1 at 26.2 °C. Both the temperature-dependent alternating current impedance conductivities and solid-state NMR spin-lattice relaxation rates demonstrate that the Li6PS5Cl prepared under these conditions results in a higher conductivity and Li-ion mobility compared to materials prepared by the traditional mechanical milling route. The origin of the improved conductivity appears to be a combination of the optimal local Cl structure and its homogeneous distribution in the material. All-solid-state cells consisting of an 80Li2S-20LiI cathode, the optimized Li6PS5Cl electrolyte, and an In anode showed a relatively good electrochemical performance with an initial discharge capacity of 662.6 mAh g-1 when a current density of 0.13 mA cm-2 was used, corresponding to a C-rate of approximately C/20. On direct comparison with a solid-state battery using a solid electrolyte prepared by the mechanical milling route, the battery made with the new material exhibits a higher initial discharge capacity and Coulombic efficiency at a higher current density with better cycling stability. Nevertheless, the cycling stability is limited by the electrolyte stability, which is a major concern for these types of solid-state batteries.

Accessing the bottleneck in all-solid state batteries, lithium-ion transport over the solid-electrolyte-electrode interface.

Solid-state batteries potentially offer increased lithium-ion battery energy density and safety as required for large-scale production of electrical vehicles. One of the key challenges toward high-performance solid-state batteries is the large impedance posed by the electrode-electrolyte interface. However, direct assessment of the lithium-ion transport across realistic electrode-electrolyte interfaces is tedious. Here we report two-dimensional lithium-ion exchange NMR accessing the spontaneous lithium-ion transport, providing insight on the influence of electrode preparation and battery cycling on the lithium-ion transport over the interface between an argyrodite solid-electrolyte and a sulfide electrode. Interfacial conductivity is shown to depend strongly on the preparation method and demonstrated to drop dramatically after a few electrochemical (dis)charge cycles due to both losses in interfacial contact and increased diffusional barriers. The reported exchange NMR facilitates non-invasive and selective measurement of lithium-ion interfacial transport, providing insight that can guide the electrolyte-electrode interface design for future all-solid-state batteries.

Understanding the Electrochemical Formation and Decomposition of Li2O2 and LiOH with Operando X-ray Diffraction.

The lithium air, or Li-O2, battery system is a promising electrochemical energy storage system because of its very high theoretical specific energy, as required by automotive applications. Fundamental research has resulted in much progress in mitigating detrimental (electro)chemical processes; however, the detailed structural evolution of the crystalline Li2O2 and LiOH discharge products, held at least partially responsible for the limited reversibility and poor rate performance, is hard to measure operando under realistic electrochemical conditions. This study uses Rietveld refinement of operando X-ray diffraction data during a complete discharge-charge cycle to reveal the detailed structural evolution of Li2O2 and LiOH crystallites in 1,2-dimethoxyethane (DME) and DME/LiI electrolytes, respectively. The anisotropic broadened reflections confirm and quantify the platelet crystallite shape of Li2O2 and LiOH and show how the average crystallite shape evolves during discharge and charge. Li2O2 is shown to form via a nucleation and growth mechanism, whereas the decomposition appears to start at the smallest Li2O2 crystallite sizes because of their larger exposed surface. In the presence of LiI, platelet LiOH crystallites are formed by a particle-by-particle nucleation and growth process, and at the end of discharge, H2O depletion is suggested to result in substoichiometric Li(OH)1-x , which appears to be preferentially decomposed during charging. Operando X-ray diffraction proves the cyclic formation and decomposition of the LiOH crystallites in the presence of LiI over multiple cycles, and the structural evolution provides key information for understanding and improving these highly relevant electrochemical systems.