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 Li_3−xIn_1−xZr_xCl₆ (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.

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The use of “water-in-salt” electrolyte (WISE) (i. e., a highly concentrated aqueous solution) in rechargeable batteries has received increasing attention due to the significantly expanded electrochemical window compared to the limited voltage of conventional aqueous electrolytes. It enables the use of more positive/negative electrode material couples in aqueous batteries, resulting in an enhanced output voltage. However, one of the challenges is to identify promising anode materials for the “water-in-salt” Li-ion batteries (WIS-LIBs). Herein we for the first time demonstrate that MoS₃, an amorphous chain-like structured transitional metal trichalcogenide, is promising as anode in the WIS-LIBs. In this work, hollow MoS₃ nanospheres were synthesized via a scalable room-temperature acid precipitation method. When applied in WIS-LIBs, the prepared MoS₃ achieved a high specific capacity of 127 mAh/g at the current density of 0.1 A/g and good stability over 1000 cycles. During operation, MoS₃ underwent irreversible conversion to Li₂MoO₄ (with H₂S and H₂ evolution) during the initial Li ion uptake, and was then converted gradually to a more stable and reversible Li_xMoO_y (2≤y≤4)) phase along cycling. Amorphous Li-deficient Li_x-mMoO_y/MoO_z was formed upon delithiation. Nevertheless, MoS₃ outperformed MoO₃ in WIS-LIBs, which could be accredited to its initial one-dimensional molecular structure and the amorphous nature of the delithiated product facilitating charge transport. These results demonstrated a novel routine for synthesizing metal sulfides with hollow structures using a template-based method and push forward the development of metal sulfides for aqueous energy storage applications.

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The influence of space-charge layers on the ionic charge transport over cathode-solid electrolyte interfaces in all-solid-state batteries remains unclear because of the difficulty to unravel it from other contributions to the ion transport over the interfaces. Here, we reveal the effect of the space-charge layers by systematically tuning the space-charge layer on and off between Li _xV ₂O ₅ and Li _1.5Al _0.5Ge _1.5(PO ₃) ₄ (LAGP), by changing the Li _xV ₂O ₅ potential and selectively measuring the ion transport over the interface by two-dimensional (2D) NMR exchange. The activation energy is demonstrated to be 0.315 eV for lithium-ion exchange over the space-charge-free interface, which increases dramatically to 0.515 eV for the interface with a space-charge layer. Comparison with a space-charge model indicates that the charge distribution due to the space-charge layer is responsible for the increased interface resistance. Thereby, the present work provides selective and quantitative insight into the effect of space-charge layers over electrode-electrolyte interfaces on ionic transport.

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Current Li-ion batteries dominate the market but face great challenges with respect to safety, cost and the higher energy and power densit requirements of electrical vehicles and stationary energy storage. Relevant for mobile electrical transport, Li-O2 batteries in theory offer the highest specific energy among all the lithium electrochemical energy storage systems. Research efforts have been made to address the challenges that impede the functioning of this battery, which include low round trip efficiency, low specific capacity and poor cycling stability. To understand the origin of these issues, attaining a deeper understanding of the mechanism behind the electrochemical reactions is of vital importance. This also forms the foundation for exploring ideal oxygen cathodes and better electrolytes. The aqueous zinc batteries are another potential candidate for large scale electric energy storage owing to its low-cost, high operational safety, and environmental benignity. However, it is not easy to find a suitable insertion cathode for ZIBs, because the electrostatic interaction between divalent Zn ions. The development of host materials for ZIBs is still in its infancy, and in-depth understanding of the electrochemical processes involved is paramount at this early stage. The focus of this thesis is on attaining mechanistic insight into the electrochemical processes occurring in working Li-O2 and aqueous zinc batteries, which guides the choice/design of proper electrode materials for these next generation battery systems. @en

Rechargeable aqueous zinc-ion batteries (ZIBs) are promising for cheap stationary energy storage. Challenges for Zn-ion insertion hosts are the large structural changes of the host structure upon Zn-ion insertion and the divalent Zn-ion transport, challenging cycle life and power density respectively. Here a new mechanism is demonstrated for the VO ₂ cathode toward proton insertion accompanied by Zn-ion storage through the reversible deposition of Zn ₄ (OH) ₆ SO ₄ ·5H ₂ O on the cathode surface, supported by operando X-ray diffraction, X-ray photoelectron spectroscopy, neutron activation analysis, and density functional theory simulations. This leads to an initial discharge capacity of 272 mAh g ⁻¹ at a current density of 3.0 A g ⁻¹ , of which 75.5% is maintained after 945 cycles. It is proposed that the competition between proton and Zn-ion insertion in the VO ₂ host is determined by the solvation energy of the salt anion and proton insertion energetics, where proton insertion has the advantage of minimal structural distortion leading to a long cycle life. As the discharge kinetics are capacitive for the first half of the process and diffusion limited for the second half, the VO ₂ cathode takes the middle road possessing both fast kinetics and high practical capacities revealing a reaction mechanism that provides new perspective for the development of aqueous ZIBs.

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The original HTML version of this Article omitted to list Zhengcao Li as a corresponding author. Correspondingly, the original PDF version of this Article incorrectly stated that ‘Correspondence and requests for materials should be addressed to M.W. (email: m.wagemaker@tudelft.nl)’, instead of the correct ‘Correspondence and requests for materials should be addressed to Z.L. (email: zcli@tsinghua.edu.cn) or to M.W. (email: m.wagemaker@tudelft.nl)’. This has been corrected in both the PDF and HTML versions of the Article.

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Electrical mobility demands an increase of battery energy density beyond current lithium-ion technology. A crucial bottleneck is the development of safe and reversible lithium-metal anodes, which is challenged by short circuits caused by lithium-metal dendrites and a short cycle life owing to the reactivity with electrolytes. The evolution of the lithium-metal-film morphology is relatively poorly understood because it is difficult to monitor lithium, in particular during battery operation. Here we employ operando neutron depth profiling as a noninvasive and versatile technique, complementary to microscopic techniques, providing the spatial distribution/density of lithium during plating and stripping. The evolution of the lithium-metal-density-profile is shown to depend on the current density, electrolyte composition and cycling history, and allows monitoring the amount and distribution of inactive lithium over cycling. A small amount of reversible lithium uptake in the copper current collector during plating and stripping is revealed, providing insights towards improved lithium-metal anodes.

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For practical application of lithium-oxygen batteries, one of the challenges is the development of efficient bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in cathode. In this work, perovskite Sr _0.9 Y _0.1 CoO _3-δ nanorods are synthesized by an electrospinning method. The performance of the Li-O ₂ cell with Sr _0.9 Y _0.1 CoO _3-δ catalysts is better than that of the cell only with Super-P. Furthermore, modification of CoO nanoparticles on the cathode can provide an obviously improved electrochemical performance with a reduced voltage gap (∼80-140 mV), which is ascribed to the superior catalytic activity of CoO nanoparticles toward OER. All of these results demonstrate that the perovskite Sr _0.9 Y _0.1 CoO _3-δ is an efficient bifunctional electrocatalyst for lithium-oxygen batteries, and the incorporation of CoO nanoparticles is an effective approach for improving the cathode performance as well.

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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.

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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.@en

The high theoretical energy density of Li-O₂ batteries as required for electrification of transport has pushed Li-O₂ research to the forefront. The poor cyclability of this system due to incomplete Li₂O₂ oxidation is one of the major hurdles to be crossed if it is ever to deliver a high reversible energy density. Here we present the use of nano seed crystallites to control the size and morphology of the Li₂O₂ crystals. The evolution of the Li₂O₂ lattice parameters during operando X-ray diffraction demonstrates that the hexagonal NiO nanoparticles added to the activated carbon electrode act as seed crystals for equiaxed growth of Li₂O₂, which is confirmed by scanning electron microscopy energy-dispersive X-ray spectroscopy (SEM-EDX) elemental maps also showing preferential formation of Li₂O₂ on the NiO surface. Even small amounts of NiO (∼5 wt %) particles act as preferential sites for Li₂O₂ nucleation, effectively reducing the average size of the primary Li₂O₂ crystallites and promoting crystalline growth. This is supported by first principle calculations, which predict a low interfacial energy for the formation of NiO-Li₂O₂ interfaces. The eventual cell failure appears to be the consequence of electrolyte side reactions, indicating the necessity of more stable electrolytes. The demonstrated control of the Li₂O₂ crystallite growth by the rational selection of appropriate nano seed crystals appears to be a promising strategy to improve the reversibility of Li-air electrodes.

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