Despite progress in solid-state battery engineering, our understanding of the chemo-mechanical phenomena that govern electrochemical behaviour and stability at solid-solid interfaces remains limited ...compared to at solid-liquid interfaces. Here, we use operando synchrotron X-ray computed microtomography to investigate the evolution of lithium/solid-state electrolyte interfaces during battery cycling, revealing how the complex interplay among void formation, interphase growth and volumetric changes determines cell behaviour. Void formation during lithium stripping is directly visualized in symmetric cells, and the loss of contact that drives current constriction at the interface between lithium and the solid-state electrolyte (Li
SnP
S
) is quantified and found to be the primary cause of cell failure. The interphase is found to be redox-active upon charge, and global volume changes occur owing to partial molar volume mismatches at either electrode. These results provide insight into how chemo-mechanical phenomena can affect cell performance, thus facilitating the development of solid-state batteries.
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GEOZS, IJS, IMTLJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK, ZAGLJ
Transformations at interfaces between solid-state electrolytes (SSEs) and lithium metal electrodes can lead to high impedance and capacity decay during cycling of solid-state batteries, but the links ...between structural/chemical/mechanical evolution of interfaces and electrochemistry are not well understood. Here, we use in situ X-ray computed tomography to reveal the evolution of mechanical damage within a Li1+x Al x Ge2–x (PO4)3 (LAGP) SSE caused by interphase growth during electrochemical cycling. The growth of an interphase with expanded volume drives fracture in this material, and the extent of fracture during cycling is found to be the primary factor causing the impedance increase, as opposed to the resistance of the interphase itself. Cracks are observed to initiate near the edge of the lithium/LAGP interface, which agrees with simulations. The chemomechanical effects of interphase growth studied here are expected to play a role in a variety of SSE materials, and this work is a step toward designing durable interfaces.
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IJS, KILJ, NUK, PNG, UL, UM
The interfaces between many solid-state electrolytes (SSEs) and lithium metal are (electro)chemically unstable, and improved understanding of how interfacial transformations influence ...electrochemical degradation is necessary to stabilize these interfaces and therefore enable a wider range of viable SSEs for batteries. Here, the (electro)chemical reaction processes that occur at the interface between Li1.4Al0.4Ge1.6(PO4)3 (LAGP) electrolyte and lithium are studied using in situ transmission electron microscopy and ex situ techniques. The reaction of lithium with LAGP causes amorphization and volume expansion, which induce mechanical stress and fracture of the SSE along with a massive increase in impedance. The evolved interphase has a nonuniform morphology at high currents, which causes accelerated chemo-mechanical failure. This work demonstrates that the current-dependent nature of the reaction at the SSE/Li interface plays a crucial role in determining chemo-mechanical degradation mechanisms, with implications for understanding and controlling degradation in a wide variety of SSE materials with unstable interfaces.
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IJS, KILJ, NUK, PNG, UL, UM
Alloy anodes for lithium-ion batteries feature greater specific capacity than conventional graphite electrodes and could enable batteries with higher energy density. However, large volumetric and ...structural changes during cycling limit performance. Such transformations are expected to be particularly problematic in solid-state batteries, where volume changes can exacerbate chemomechanical degradation of the all-solid structure. Here, we synthesize porous metal foils with bicontinuous porosity by chemical dealloying of Li–In and Li–Sn alloys in dry methanol. Porous indium foils are directly used as the anode in both solid-state and liquid-electrolyte cells, and they exhibit improved capacity and cycle life in solid-state batteries compared to dense indium foil with similar mass loading. Furthermore, capacity retention with cycling of the porous electrodes is much better in solid-state cells than in liquid cells. This performance enhancement is due to improved accommodation of volume changes while minimizing surface side reactions throughout the porous electrode. These results highlight the promise of porous metals for solid-state batteries.
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IJS, KILJ, NUK, PNG, UL, UM
Ultrathin topological insulator membranes are building blocks of exotic quantum matter. However, traditional epitaxy of these materials does not facilitate stacking in arbitrary orders, while ...mechanical exfoliation from bulk crystals is also challenging due to the non-negligible interlayer coupling therein. Here we liberate millimeter-scale films of the topological insulator Bi2Se3, grown by molecular beam epitaxy, down to 3 quintuple layers. We characterize the preservation of the topological surface states and quantum well states in transferred Bi2Se3 films using angle-resolved photoemission spectroscopy. Leveraging the photon-energy-dependent surface sensitivity, the photoemission spectra taken with 6 and 21.2 eV photons reveal a transfer-induced migration of the topological surface states from the top to the inner layers. By establishing clear electronic structures of the transferred films and unveiling the wave function relocation of the topological surface states, our work lays the physics foundation crucial for the future fabrication of artificially stacked topological materials with single-layer precision.
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IJS, KILJ, NUK, PNG, UL, UM
Exploration of novel resistive switching materials attracts attention to achieve neuromorphic computing that can surpass the limit of the current Von-Neumann computing for the time of Internet of ...Things (IoT). Battery materials priorly used to serve as an electrode or electrolyte have demonstrated metal-insulator transitions upon an electrical biasing due to resulting compositional change, which is desirable property for future resistive switching devices. For example, it has been suggested that solid-state electrolyte amorphous lithium lanthanum titanate (a-LLTO) changes in electronic conductivity depending on oxygen content. In this work, switching behavior of a-LLTO was investigated at both bulk- and nano-scale by employing a range of voltage sweep techniques, ultimately establishing a stable and optimal operating condition within the voltage window of − 3.5 V to 3.5 V. This voltage range effectively balances the desirable trait of a substantial resistance change by three orders of magnitude with the imperative avoidance of LLTO decomposition. Experiment and computation with different LLTO composition shows that LLTO has two distinct conductivity states due to Ti reduction. The distribution of these two states is discussed using simplified binary model, implying the conductive filament growth during low resistance state. Consequently, our study deepens understanding of LLTO electronic properties and encourages the interdisciplinary application of battery materials for resistive switching devices.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The use of solid-state electrolytes (SSEs) within batteries is a promising strategy to safely access the high capacity of lithium metal anodes. However, most SSEs with practical ionic conductivity ...are chemically unstable in contact with lithium metal, which is detrimental to battery performance. Lithium aluminum germanium phosphate (LAGP) is an SSE with high ionic conductivity (10−4-10−3 S cm−1) and good environmental stability, but it forms an amorphous interphase region that continuously grows in contact with Li, leading to chemo-mechanical failure within solid-state batteries. Here, we find that thin (∼30 nm) chromium interlayers deposited between the lithium electrode and LAGP extend cycle life to over 1000 h at moderate current densities (0.1-0.2 mA cm−2), compared to ∼30 h without protection. This significantly improved stability occurs because the metallic interlayer alters the trajectory of interphase formation and the nature of the electrochemical reaction at the interface. This work shows the promise of interface engineering for a variety of SSE materials within solid-state batteries, while emphasizing the necessity of understanding how protection layers affect dynamic evolution of interfaces.
Exploration of novel resistive switching materials attracts attention to replace conventional Si-based transistors and to achieve neuromorphic computing that can surpass the limit of the current ...Von-Neumann computing for the time of Internet of Things (IoT). Materials priorly used to serve in batteries have demonstrated metal-insulator transitions upon an electrical biasing due to resulting compositional change. This property is desirable for future resistive switching devices. Amorphous lithium lanthanum titanate (a-LLTO) was originally developed as a solid-state electrolyte with relatively high lithium ionic conductivity and low electronic conductivity among oxide-type solid electrolytes. However, it has been suggested that electric conductivity of a-LLTO changes depending on oxygen content. In this work, the investigation of switching behavior of a-LLTO was conducted by employing a range of voltage sweep techniques, ultimately establishing a stable and optimal operating condition within the voltage window of -3.5 V to 3.5 V. This voltage range effectively balances the desirable trait of a substantial resistance change by three orders of magnitude with the imperative avoidance of LLTO decomposition. This switching behavior is also confirmed at nanodevice of Ni/LLTO/Ni through in-situ biasing inside focused-ion beam/scanning electron microscope (FIB-SEM). Experiment and computation with different LLTO composition shows that LLTO has two distinct conductivity states due to Ti reduction. The distribution of these two states is discussed using simplified binary model, implying the conductive filament growth during low resistance state. Consequently, our study deepens understanding of LLTO electronic properties and encourages the interdisciplinary application of battery materials for resistive switching devices.
Ultrathin topological insulator membranes are building blocks of exotic quantum matter. However, traditional epitaxy of these materials does not facilitate stacking in arbitrary orders, while ...mechanical exfoliation from bulk crystals is also challenging due to the non-negligible interlayer coupling therein. Here we liberate millimeter-scale films of topological insulator Bi\(_2\)Se\(_3\), grown by molecular beam epitaxy, down to 3 quintuple layers. We characterize the preservation of the topological surface states and quantum well states in transferred Bi\(_{2}\)Se\(_{3}\) films using angle-resolved photoemission spectroscopy. Leveraging the photon-energy-dependent surface sensitivity, the photoemission spectra taken with \(6\) eV and \(21.2\) eV photons reveal a transfer-induced migration of the topological surface states from the top to the inner layers. By establishing clear electronic structures of the transferred films and unveiling the wavefunction relocation of the topological surface states, our work paves the physics foundation crucial for the future fabrication of artificially stacked topological materials with single-layer precision.
Solid-state batteries could enable improved energy density and enhanced safety compared to Li-ion batteries. The interfaces between many solid-state electrolytes (SSEs) and lithium metal are ...(electro)chemically unstable, however, and we lack a detailed understanding of how interfacial transformations relate to electrochemical degradation during cycling. Here, we characterize the (electro)chemical reaction processes that occur at the interface between Li
1.4
Al
0.4
Ge
1.6
(PO
4
)
3
(LAGP) and lithium using
in-situ
transmission electron microscopy and
ex-situ
techniques, and we show that the growth of a new phase at the interface is intrinsically linked to chemo-mechanical degradation of the cell. Lithium insertion into LAGP at the interface drives the transformation to form an amorphous phase with expanded volume. In symmetric Li/LAGP/Li cells, the evolution of mechanical stress due to this transformation ultimately causes fracture of the SSE and an associated impedance increase. The morphology of the transformed interphase layer is highly dependent on the applied current density, and the interphase morphology significantly influences mechanical stability. Unlike many other SSEs (such as garnets), cell failure is not dictated by short circuiting. Instead, failure in LAGP is governed by the major increase in impedance as cracks are formed and continue to grow. This work shows that the nature of the reaction at the SSE/Li interface plays a crucial role in determining chemo-mechanical degradation mechanisms, with implications for understanding degradation in the whole class of SSE materials with unstable interfaces.
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