Lithium-Ion Battery Power Performance Assessment for the Climb Step of an Electric Vertical Takeoff and Landing (eVTOL) Application.

High power is a critical requirement of lithium-ion batteries designed to satisfy the load profiles of advanced air mobility. Here, we simulate the initial takeoff step of electric vertical takeoff and landing (eVTOL) vehicles powered by a lithium-ion battery that is subjected to an intense 15C discharge pulse at the beginning of the discharge cycle followed by a subsequent low-rate discharge. We conducted extensive electrochemical testing to assess the long-term stability of a lithium-ion battery under these high-strain conditions. The main finding is that despite the performance recovery observed at low rates, the reapplication of high rates leads to drastic cell failure. While the results highlight the eVTOL battery longevity challenge, the findings also emphasize the need for tailored battery chemistry designs for eVTOL applications to address both anode plating and cathode instability. In addition, innovative second-use strategies would be paramount upon completion of the eVTOL services.

Enhancing the Electrochemical Performance of Aqueous Processed Li-Ion Cathodes with Silicon Oxide Coatings.

Lithium-ion battery cathode materials suffer from bulk and interfacial degradation issues, which negatively affect their electrochemical performance. Oxide coatings can mitigate some of these problems and improve electrochemical performance. However, current coating strategies have low throughput, are expensive, and have limited applicability. In this article, we describe a low-cost and scalable strategy for applying oxide coatings on cathode materials. We report synergistic effects of these oxide coatings on the performance of aqueously processed cathodes in cells. The SiO2 coating strategy developed herein improved mechanical, chemical, and electrochemical performance of aqueously processed Ni-, Mn- and Co-based cathodes. This strategy can be used on a variety of cathodes to improve the performance of aqueously processed Li-ion cells.

Sodium Rich Vanadium Oxy-Fluorophosphate - Na3.2 Ni0.2 V1.8 (PO4 )2 F2 O - as Advanced Cathode for Sodium Ion Batteries.

Conventional sodium-based layered oxide cathodes are extremely air sensitive and possess poor electrochemical performance along with safety concerns when operating at high voltage. The polyanion phosphate, Na3 V2 (PO4 )3 stands out as an excellent candidate due to its high nominal voltage, ambient air stability, and long cycle life. The caveat is that Na3 V2 (PO4 )3 can only exhibit reversible capacities in the range of 100 mAh g-1 , 20% below its theoretical capacity. Here, the synthesis and characterizations are reported for the first time of the sodium-rich vanadium oxyfluorophosphate, Na3.2 Ni0.2 V1.8 (PO4 )2 F2 O, a tailored derivative compound of Na3 V2 (PO4 )3 , with extensive electrochemical and structural analyses. Na3.2 Ni0.2 V1.8 (PO4 )2 F2 O delivers an initial reversible capacity of 117 mAh g-1 between 2.5 and 4.5 V under the 1C rate at room temperature, with 85% capacity retention after 900 cycles. The cycling stability is further improved when the material is cycled at 50 °C within 2.8-4.3 V for 100 cycles. When paired with a presodiated hard carbon, Na3.2 Ni0.2 V1.8 (PO4 )2 F2 O cycled with a capacity retention of 85% after 500 cycles. Cosubstitution of the transition metal and fluorine in Na3.2 Ni0.2 V1.8 (PO4 )2 F2 O as well as the sodium-rich structure are the major factors behind the improvement of specific capacity and cycling stability, which paves the way for this cathode in sodium-ion batteries.

Na3 Zr2 Si2 PO12 Solid Electrolyte Membrane for High-Performance Seawater Battery.

Seawater batteries (SWBs) have gained tremendous interest in the electrochemical energy storage research field because of their low cost, natural abundance, and potential use for long-duration energy storage. Advancing a SWB to demonstration projects is plagued by the poor electrochemical performance stemming from the poor interfaces of the solid electrolyte (SE), as well as the structural and chemical instabilities and sluggish ionic transport properties. In this study, the anode compartment of a surrogate SWB is constructed with a Na | SE | hard carbon configuration, and tailored dopants are introduced into the Nasicon-type Na3 Zr2 Si2 PO12 (NZSP) SE membrane. After doping with TiO2 , a much more densely packed pellet with uniformly distributed porous structure is obtained. Changes in surface chemistry and local structure in the bulk are observed, which are believed to contribute to the improved ionic conductivity and higher critical current density of the TiO2 -doped NZSP. Stable cycling performance with reversible capacities based on different Na storage mechanisms are also demonstrated.

Polymorphism of garnet solid electrolytes and its implications for grain-level chemo-mechanics.

Understanding and mitigating filament formation, short-circuit and solid electrolyte fracture is necessary for advanced all-solid-state batteries. Here, we employ a coupled far-field high-energy diffraction microscopy and tomography approach for assessing the chemo-mechanical behaviour for dense, polycrystalline garnet (Li7La3Zr2O12) solid electrolytes with grain-level resolution. In situ monitoring of grain-level stress responses reveals that the failure mechanism is stochastic and affected by local microstructural heterogeneity. Coupling high-energy X-ray diffraction and far-field high-energy diffraction microscopy measurements reveals the presence of phase heterogeneity that can alter local chemo-mechanics within the bulk solid electrolyte. These local regions are proposed to be regions with the presence of a cubic polymorph of LLZO, potentially arising from local dopant concentration variation. The coupled tomography and FF-HEDM experiments are combined with transport and mechanics modelling to illustrate the degradation of polycrystalline garnet solid electrolytes. The results showcase the pathways for processing high-performing solid-state batteries.

Differences in the Interfacial Mechanical Properties of Thiophosphate and Argyrodite Solid Electrolytes and Their Composites.

Interfacial mechanics are a significant contributor to the performance and degradation of solid-state batteries. Spatially resolved measurements of interfacial properties are extremely important to effectively model and understand the electrochemical behavior. Herein, we report the interfacial properties of thiophosphate (Li3PS4)- and argyrodite (Li6PS5Cl)-type solid electrolytes. Using atomic force microscopy, we showcase the differences in the surface morphology as well as adhesion of these materials. We also investigate solvent-less processing of hybrid electrolytes using UV-assisted curing. Physical, chemical, and structural characterizations of the materials highlight the differences in the surface morphology, chemical makeup, and distribution of the inorganic phases between the argyrodite and thiophosphate solid electrolytes.

In situ investigation of water on MXene interfaces.

A continuum of water populations can exist in nanoscale layered materials, which impacts transport phenomena relevant for separation, adsorption, and charge storage processes. Quantification and direct interrogation of water structure and organization are important in order to design materials with molecular-level control for emerging energy and water applications. Through combining molecular simulations with ambient-pressure X-ray photoelectron spectroscopy, X-ray diffraction, and diffuse reflectance infrared Fourier transform spectroscopy, we directly probe hydration mechanisms at confined and nonconfined regions in nanolayered transition-metal carbide materials. Hydrophobic (K+) cations decrease water mobility within the confined interlayer and accelerate water removal at nonconfined surfaces. Hydrophilic cations (Li+) increase water mobility within the confined interlayer and decrease water-removal rates at nonconfined surfaces. Solutes, rather than the surface terminating groups, are shown to be more impactful on the kinetics of water adsorption and desorption. Calculations from grand canonical molecular dynamics demonstrate that hydrophilic cations (Li+) actively aid in water adsorption at MXene interfaces. In contrast, hydrophobic cations (K+) weakly interact with water, leading to higher degrees of water ordering (orientation) and faster removal at elevated temperatures.

Scalable Manufacturing of Hybrid Solid Electrolytes with Interface Control.

Hybrid solid electrolytes are promising alternatives for high energy density metallic lithium batteries. Scalable manufacturing of multi-material electrolytes with tailored transport pathways can provide an avenue toward controlling Li stripping and deposition mechanisms in all-solid-state devices. A novel roll-to-roll compatible coextrusion device is demonstrated to investigate mesostructural control during manufacturing. Solid electrolytes with 25 and 75 wt % PEO-LLZO compositions are investigated. The coextrusion head is demonstrated to effectively process multimaterial films with strict compositional gradients in a single pass. An average manufacturing variability of 5.75 ± 1.2 µm is observed in the thickness across all the electrolytes manufactured. Coextruded membranes with 1 mm stripes show the highest room temperature conductivity of 8.8 × 10-6 S cm-1 compared to the conductivity of single-material films (25 wt %, 1.2 × 10-6 S cm-1; 75 wt %, 1.8 × 10-6 S cm-1). Distribution of relaxation times and effective mean field theory calculations suggest that the interface generated between the two materials possesses high ion-conducting properties. Computational simulations are used to further substantiate the influence of macroscale interfaces on ion transport.

Tortuosity Effects in Garnet-Type Li7La3Zr2O12 Solid Electrolytes.

Intrinsic material microstructure features, such as pores or void spaces, grains, and defects can affect local lithium-ion concentration profiles and transport properties in solid ion conductors. The formation of lithium-deficient or -excess regions can accelerate degradation phenomena, such as dendrite formation, lithium plating, and electrode/electrolyte delamination. This paper evaluates the effects pores or void spaces have on the tortuosity of a garnet-type Li7La3Zr2O12 solid electrolyte. Synchrotron X-ray tomography is used to obtain three-dimensional reconstructions of different electrolytes sintered at temperatures between 1050 and 1150 °C. The magnitude of the electrolyte tortuosity and the tortuosity directional anisotropy is shown to increase with sintering temperature. Electrolytes with highly anisometric tortuosity have lower critical current densities. Alignment or elimination of pores within an electrolyte or composite cathode may provide a means for achieving higher critical current densities and higher power densities in all solid-state batteries.

The Role of Adventitious Carbon in Photo-catalytic Nitrogen Fixation by Titania.

Photo-catalytic fixation of nitrogen by titania catalysts at ambient conditions has been reported for decades, yet the active site capable of adsorbing an inert N2 molecule at ambient pressure and the mechanism of dissociating the strong dinitrogen triple bond at room temperature remain unknown. In this work in situ near-ambient-pressure X-ray photo-electron spectroscopy and density functional theory calculations are used to probe the active state of the rutile (110) surface. The experimental results indicate that photon-driven interaction of N2 and TiO2 is observed only if adventitious surface carbon is present, and computational results show a remarkably strong interaction between N2 and carbon substitution (C*) sites that act as surface-bound carbon radicals. A carbon-assisted nitrogen reduction mechanism is proposed and shown to be thermodynamically feasible. The findings provide a molecular-scale explanation for the long-standing mystery of photo-catalytic nitrogen fixation on titania. The results suggest that controlling and characterizing carbon-based active sites may provide a route to engineering more efficient photo(electro)-catalysts and improving experimental reproducibility.