Kostiantyn V. Kravchyk

X-ray photoelectron spectroscopy (XPS) has revealed many possible Li-induced interfacial reactions in solid-state electrolytes (SSEs), but most in situ studies form Li|electrolyte interfaces through non-electrochemical Li deposition, including evaporation, sputtering, or electron-beam-induced deposition. These routes may introduce additional energy that activates reaction pathways not accessed during electrochemical Li plating. Here, we use lab-based operando XPS to directly evaluate oxide solid-state electrolyte stability during electrochemical Li formation. Using this approach, we find sharply different responses for two representative oxide SSEs: NASICON-type Li1+xAlxTi2–x(PO4)3 (LATP) is reduced upon Li plating, forming a Li+/Ti3+-rich mixed-conducting interphase that partially relaxes through coupled ionic–electronic redistribution, whereas garnet-type Li7La3Zr2O12 (LLZO) shows no spectroscopically resolvable Zr or La reduction. This work represents the first direct operando XPS evaluation of SSE stability against electrochemically plated Li metal.

Unveiling interfacial dynamics in solid‐state batteries under operando conditions remains a major challenge in solid‐state battery research, largely due to the limited temporal resolution of conventional analytical techniques. Here, we introduce a laboratory‐based operando x‐ray photoelectron spectroscopy (XPS) methodology employing a snapshot spectral acquisition mode that enables real‐time tracking of interfacial chemistry in solid‐state battery systems. The approach is demonstrated by monitoring electrochemical lithiation occurring in Sb and Cu films deposited on the surface of the Li _6.25 Al _0.25 La ₃ Zr ₂ O ₁₂ solid‐state electrolyte (SSE). Understanding these processes is critical for developing effective SSE/Li interfacial layers that improve the cycling stability of lithium metal anodes and for advancing anode‐free solid‐state battery architectures. When combined with the static in‐situ non‐destructive depth‐profiling capabilities of hard x‐ray photoelectron spectroscopy (HAXPES), this methodology has strong potential to become a key analytical approach for probing buried interfaces in solid‐state batteries under operando conditions.

Maintaining a stable interface between sulfide solid-state electrolytes and layered oxide cathodes remains a major challenge limiting the performance of all-solid-state batteries. Atomic layer deposition (ALD) of lithium niobate (LNO) on layered oxide cathodes is widely used to stabilize these interfaces, yet the early-stage growth of LNO remains poorly understood and strongly influenced by precursor chemistry. Here, we demonstrate substrate-enhanced ALD growth of LNO on single-crystal LiNi0.82Mn0.07Co0.11O2 (NMC) achieved using commercial lithium–niobium precursor chemistry, enabling complete surface encapsulation with conformal LNO coatings thinner than 8 nm. The resulting ultrathin LNO coatings increase the discharge capacity of Li6PS5Cl-NMC all-solid-state batteries by up to 20% while maintaining good rate capability. The improved electrochemical performance is attributed to the suppressed electrochemical decomposition of the Li6PS5Cl solid-state electrolyte during cycling, as evidenced by X-ray photoelectron spectroscopy, highlighting the importance of controlling the early-stage ALD growth of LNO.

The growing demand for high energy density electrochemical energy storage necessitates energy vectors that maximize the number of electrons transferred per formula unit of active material. Herein, we introduce electrochemically coupled oxygen atom transfer (OAT) as a new paradigm to harness the energy of p-block oxoanions in a Li–metal solid-state battery. Using carbon-supported Fe nanoparticles in a dual role of OAT catalyst and conversion-type cathode active material, we demonstrate the eight-electron anion reduction of ClO4– at >50% conversion, delivering a capacity of 1150 mA h g–1 and an energy density of 1950 W h kg–1. We further demonstrate strategies to enhance the energy density at the electrode level, establishing a foundation for oxoanion-based anion redox in battery systems.

Lithium dendrite growth at the lithium–solid-state electrolyte (SSE) interface, driven by void formation, remains a major barrier to the deployment of Li metal solid-state batteries. Here, we reveal a mechanism of lateral lithium flux that explains how interfacial layers (ILs) along the Li/SSE interface enable suppression of void formation, thereby preventing dendrite growth. Using Li₃Sb as a model IL and Li₇La₃Zr₂O₁₂ as a benchmark SSE, we directly visualize and quantify lateral lithium transport, demonstrating that ILs mitigate void formation by defocusing the local current density. This mechanism accounts for the cycling stability of IL-functionalized Li/SSE interfaces and provides design principles for safe, high-energy-density Li metal solid-state batteries.

All-solid-state batteries are widely regarded as the next frontier in electrochemical energy storage, offering the potential to surpass the energy density and safety limits of conventional lithium-ion batteries. Among the factors governing their performance, paramount are the choice and functionality of the solid-state electrolyte (SSE) as a catholyte within the composite positive electrode. This perspective critically examines the applicability and potential of the three most intensively studied inorganic SSE families, namely oxides, sulfides, and chlorides, as catholytes. We discuss their respective advantages, limitations, and compatibility with common cathode active materials, as well as the remaining knowledge gaps. We then assess whether any of the current SSE classes can be employed as a stand-alone SSE for all-solid-state batteries, or whether composite architectures combining multiple SSEs will ultimately be required.

High-power lithium-ion batteries (LIBs) rely on highly ionically and electronically conductive cathode active materials (CAMs). While oxospinels meet these criteria and are therefore widely employed in state-of-the-art LIBs, we demonstrate that halospinels offer greatly enhanced transport properties and enable the incorporation of earth-abundant transition metals, such as iron. Using spinel-type Li_2–x FeCl₄ (0 < x ≤ 1, LFC) as a model CAM in an all-solid-state battery (ASSBs), we show that its intrinsically high ionic-electronic conductivity enables the fabrication of cathodes composed of micron-sized CAM particles with high areal capacity (>2 mA h cm^–2) at practical current densities (0.5 mA cm^–2) over 200 cycles. Our findings position LFC as a promising CAM, paving the way for cost-effective, high-performance ASSBs.

Understanding thermal transport in solid electrolytes is essential for improving the performance, reliability, and safety of all-solid-state batteries. Garnet-type lithium-ion conductors are promising candidates for solid electrolytes, yet their thermal-transport mechanisms remain poorly understood. Here, we connect the lattice and ion dynamics of single-crystal garnet-type Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12 to its intrinsically low thermal conductivity. Our study reveals that the single crystals grown by the floating-zone method exhibit remarkably low glasslike thermal conductivity. Using first-principles calculations and inelastic-neutron-scattering measurements, we identify both the acoustic and numerous optical phonon modes, which stem from the complex crystal structure of the material. Notably, a low-energy optical branch exhibits an avoided crossing with acoustic phonons near 7 meV. These optical modes can enhance the scattering of heat-carrying acoustic phonons and reduce thermal conductivity. Furthermore, the calculated Grüneisen parameters are large, especially for the vibrational modes around 6 meV, indicating strong anharmonicity, with a noticeable contribution from lithium-ion vibrations. A two-channel thermal-transport model is employed to describe the weak temperature dependence of the thermal conductivity, which can be attributed to the substantial contribution of diffuson transport facilitated by the abundance of optical phonons and intrinsic anharmonicity. These results offer valuable insights into the thermal transport in a broad class of ionic conductors of interest for energy conversion and storage applications.