Kelsey Bridget Hatzell

Sodium closo-hydridoborates have emerged as promising solid-state electrolytes for Na-ion batteries because of their high ionic conductivity and electrochemical stability. However, their sensitivity to water makes them challenging to scale-up. In this work, we systematically investigate the impact of controlled hydration on the structure, ion transport, and interfacial stability of an anion-mixed hydridoborate, Na4(B10H10)0.5(B12H12)0.5. By exposing the hydridoborate to varying degrees of relative humidity (RH) of 30-70%, we find that hydration at 30% enables retention of its moderate Na-ion conductivity (∼0.7 mS/cm) while higher hydration levels lead to the separation of the two anions ([B10H10] 2− and [B12H12] 2−), resulting in significant disruption in the Na ion conduction pathways. X-ray diffraction (XRD) and solid-state nuclear magnetic resonance (NMR) measurements indicate that hydration leads to the formation of distinct crystalline phases and alters the local ion coordination environments. The hydrated phase at 30% RH reversibly returns the original structure, restoring its ionic conductivity and compatibility with Na metal anodes. These findings provide insights into the role of structural water in Na-ion transport and a practical strategy for the use of moisturesensitive closo-hydridoborates solid state electrolytes.

Impressive electrochemical performance has been demonstrated with sulfide-based solid-state batteries. However, these results are predominantly obtained under high stack pressures—up to hundreds of MPa. While such conditions are valuable for probing fundamental material properties and intrinsic performance limits, the resulting cell metrics are not easily transferable to practical applications. Consequently, there is a growing imperative for application-oriented evaluation of SSBs under more realistic, low-pressure conditions in the single-digit MPa range. In this study, we demonstrate that the assessment of low-pressure performance can be significantly influenced by the chosen cell architecture. By comparing the cycling performance of sulfide-based SSBs—utilizing an NMC composite cathode and an In/(InLi) _x anode with argyrodite-type Li ₆ PS ₅ Cl as electrolyte—in both pouch-cell and press-cell configurations, we reveal significant discrepancies in electrochemical performance at stack pressures ranging from 0 MPa to 25 MPa. Notably, the developed pouch cells exhibit superior electrochemical performance at low stack pressures of 1 MPa compared to their press-cell counterparts despite the same materials used. Using three-electrode pouch cells, we identify In/(InLi) _x anode delamination as a primary low-pressure failure mechanism. Overall, our findings emphasize that a realistic assessment of SSB cell performance requires cell architectures that mirror targeted applications.

Anode-free lithium metal batteries (AFLMBs) represent the ultimate solution to mankind’s quest for the Holy Grail of batteries, where the cell-level energy density is maximized on the assumption that lithium (Li0) must be fully utilized with near 100% Coulombic efficiency. Although substantial progress has been made since the anode-free concept was first proposed, the challenges presented by the most powerful anode material that can be found on the periodic table still remain unresolved due to its extreme reactive nature, which not only makes it impossible to retain 100% reversibility but also induces inhomogeneity during repeated plating/stripping cycles and persistent capacity loss over a long period of time. The isolated study approaches, emphasizing either individual electrolyte components or interphasial chemistry engineering, but mostly focused on the negative-electrode current collector, hinder insight into issues arising when these components are assembled into cells and forced to interface with each other. In this review, we attempt to examine this high-dimensional topic from a panoramic perspective, with the focus placed on the liquid electrolytes. We first outline the fundamental operating principles of key individual battery components, together with practical perspectives for evaluating lithium utilization and reversibility in AFLMBs. We then discuss how these components interact when assembled into full cells, how such interactions give rise to heterogeneous electrochemical and mechanical behaviors, and how these phenomena can be characterized and regulated. It is also outlined that a hierarchical perspective on lithium behavior, spanning from the nano- to cell-scale, is essential to enable plating, stripping, and recovery in AFLMBs. Finally, we present perspectives from leading researchers actively working on the various elements that constitute AFLMBs and integrate these viewpoints to clarify the future research directions of this field. By providing a system-level framework for understanding AFLMBs, this review aims to guide future research efforts and contribute to addressing the broader challenges of sustainable energy storage.

Graphite plays an essential role in energy storage and electrochemical applications; however, the reliance on mining and petroleum-derived precursors in conventional graphite manufacturing presents environmental and economic challenges. Biomass offers a renewable and widely available alternative feedstock for synthetic graphite production. In this study, we explore the graphitization of cellulose as a model biomass precursor, focusing on how graphitization heating conditions influence microstructural evolution and electrochemical behavior. Using rapid Joule heating and conventional thermal treatments, we characterize the resulting biocarbon materials with respect to their crystallinity, grain size, and morphology. Electrochemical testing reveals that heating rate and duration significantly impact capacity retention and rate performance, with faster heating producing smaller grain sizes and improved high-rate capabilities. These findings demonstrate a direct link between processing conditions and electrochemical performance, highlighting biomass-derived graphite as a viable pathway toward distributed graphite production.

We investigate composite solid state blended cathodes composed of lithium iron phosphate (LFP), nickel cobalt manganese oxide (NMC), and halide solid electrolyte for application in all solid state batteries (ASSBs). Electrochemical characterization indicates that the blended cathode integrates the high rate capability of LFP with the high specific capacity of NMC. Synchrotron X‐ray diffraction (XRD) techniques, including spatially resolved operando micro‐diffraction, reveal asymmetric charge distribution, and lithiation gradients across the cathode depth during electrochemical cycling. Complementary thermal modeling demonstrates that the blended cathode generates less heat than pure NMC, thereby enhancing thermal stability. These results highlight the potential of blended cathodes to achieve an optimal balance between performance and safety in ASSBs and provide valuable insights for the design of microstructures for next‐generation solid state battery systems.

Bipolar membranes (BPMs) enable electrochemical systems that operate across large pH gradients; however, high-current operation is often limited by voltage losses whose origins remain difficult to resolve in membrane−electrode assemblies. Here, we combine electrochemical impedance spectroscopy with distribution of relaxation times (EIS–DRT) analysis and operando synchrotron X-ray diffraction to examine interfacial polarization, membrane hydration, and transport in commercial and synthesized BPMs. EIS–DRT isolates the BPM-associated interfacial contribution and shows that the commercial BPM exhibits larger water-dissociation-associated overpotentials than the synthesized BPM. Operando hydration mapping shows that both membranes retain water at the bipolar junction during high-current operation, while anode-adjacent hydration gradients are more pronounced in the commercial membrane. These results indicate that high-current voltage losses are not governed by junction water starvation alone but by coupled interfacial polarization and transport resistances.

Electrolyte composition, concentration, and structure can affect reaction kinetics, ion transport, and heat generation during operation. In liquid electrolyte systems, the properties of ion-solvent and ion-ion interactions strongly affect thermodynamics and electrochemistry. The change in total entropy of the electrolyte when one mole of an ion is added to an electrolyte at a constant temperature and pressure is known as the partial molar entropy of ion solvation and describes broadly how the solvation environment changes with the addition or removal of an ion. Herein, we measure the partial molar entropies of lithium-ion solvation in solid-state systems using potentiometric temperature coefficient measurements. For solid-state systems, we measure positive partial molar entropies of lithium-ion solvation of 43.3 J mol^-1 K^-1 for Li₆PS₅Cl and 26.4 J mol^-1 K^-1 for Li_6.5La₃Zr_1.5T_0.5O₁₂. In contrast, the liquid electrolyte 1 M LiPF₆ in 1:1 vol % EC:DEC exhibits a negative partial molar entropy of -76.0 J mol^-1 K^-1. A one-dimensional analytical model is developed to elucidate how the temperature coefficient is influenced by the multiple interfaces formed when an inorganic single-ion conductor is combined with a binary liquid electrolyte, providing a unified framework for understanding the partial molar entropies of ion solvation across a wide range of electrochemical systems.

In situ exsolution of metal nanoparticles is a promising strategy to prepare electrocatalysts with enhanced activity and resistance to agglomeration for efficient chemical transformations and energy conversion. Achieving a high nucleation density of nanoparticles under mild conditions and understanding how to tailor the process is important for performance of these electrodes in electrochemical cells. Here, we demonstrate facile exsolution of Ni nanoparticles using fluorite-structured (Pr,Ce)O_2-δ as the support oxide, driven by electrochemical potential and aided by the metastability of Ni in the solid solution (elastic driving force). We prepare single-phase oriented thin films of (Pr,Ce,Ni)O_2-δ (NPCO) on (Zr,Y)O_2-δ (YSZ) substrates by pulsed laser deposition. With the aid of a high-throughput electrochemical cell that provides a lateral gradient in Nernst voltage, we apply in situ near-ambient pressure synchrotron X-ray photoelectron spectroscopy and ex situ atomic force microscopy to investigate the impact of electrochemical potential on Ni nucleation density. We find that metallic Ni can be successfully exsolved at 550 °C upon cathodic biasing in 20 mTorr O₂, and its nucleation density increases with increasing electrochemical driving force/decreasing oxygen chemical potential. We further evaluate the electrochemical performance under highly reducing (fuel electrode) conditions by electrochemical impedance spectroscopy. With the exsolved Ni nanoparticles, the surface exchange coefficient of the NPCO is found to be ∼4× higher than for PCO without exsolution. This work confirms mixed conducting fluorites as beneficial host lattices for facile transition-metal exsolution and suggests the possibility for constructing an all ceria-based electrochemical cell with PCO serving as both the cathode and the anode.

Electrochemical energy storage technologies (such as batteries and fuel cells) are vital for powering space devices. There has been tremendous progress in developing various batteries to meet different power demands in both stationary and transporation applications. From rovers to space suits, batteries are ubiquitous in space missions. Space applications however expose batteries to extreme environments which can cause capacity degradation. This review, discusses a range of secondary batteries including traditionally Ag‐Zn/Ni‐based batteries to lithium‐ion batteries and their use applications for space. The battery degradation mechanisms related to electrodes and electrolytes are examined via the lens of: (1) pressure, (2) radiation, (3) gravity, (4) magnetic field, (5) low temperature, and (6) high temperature. Recent improvements that tackle those challenges which are feasible for space applications are discussed. Based on the analysis of external operating environments and literature, we compared different secondary battery technologies’ properties and their resistances to those external environments and offered perspectives on the road forward.