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One of the inherent challenges with Li-S batteries is polysulfide dissolution, in which soluble polysulfide species can contribute to the active material loss from the cathode and undergo shuttling reactions inhibiting the ability to effectively charge the battery. Prior theoretical studies have proposed the possible benefit of defective 2 D MoS2 materials as polysulfide trapping agents. Herein the synthesis and thorough characterization of hydrothermally prepared MoS2 nanosheets that vary in layer number, morphology, lateral size, and defect content are reported. The materials were incorporated into composite sulfur-based cathodes and studied in Li-S batteries with environmentally benign ether-based electrolytes. Through directed synthesis of the MoS2 additive, the relationship between synthetically induced defects in 2 D MoS2 materials and resultant electrochemistry was elucidated and described.

Molybdenum(IV) sulfide (MoS2) has generated significant interest as an electroactive material for Li-ion batteries because of its high theoretical capacity, good rate capability, and minimal volume...

Solid state batteries are an emerging alternative to traditional liquid electrolyte cells that provide potential for safe and high-energy density power sources. This report describes a self-forming, solid state battery based on the Li/I2 couple using an LiI-rich LiI(3-hydroxypropionitrile)2 electrolyte (LiI–LiI(HPN)2). As the negative and positive active materials are generated in situ, the solid electrolyte–current collector interfaces play a critical role in determining the electrochemical response of the battery. Herein, we report the investigation of solid electrolyte–current collector interfaces with a self-forming LiI–LiI(HPN)2 solid electrolyte and the role of varying interface design in reducing resistance during cycling.

Fe3O4 nanoparticles (NPs) with an average size of 8-10 nm have been successfully functionalized with various surface-treatment agents to serve as model systems for probing surface chemistry-dependent electrochemistry of the resulting electrodes. The surface-treatment agents used for the functionalization of Fe3O4 anode materials were systematically varied to include aromatic or aliphatic structures: 4-mercaptobenzoic acid, benzoic acid (BA), 3-mercaptopropionic acid, and propionic acid (PA). Both structural and electrochemical characterizations have been used to systematically correlate the electrode functionality with the corresponding surface chemistry. Surface treatment with ligands led to better Fe3O4 dispersion, especially with the aromatic ligands. Electrochemistry was impacted where the PA- and BA-treated Fe3O4 systems without the -SH group demonstrated a higher rate capability than their thiol-containing counterparts and the pristine Fe3O4. Specifically, the PA system delivered the highest capacity and cycling stability among all samples tested. Notably, the aromatic BA system outperformed the aliphatic PA counterpart during extended cycling under high current density, due to the improved charge transfer and ion transport kinetics as well as better dispersion of Fe3O4 NPs, induced by the conjugated system. Our surface engineering of the Fe3O4 electrode presented herein, highlights the importance of modifying the structure and chemistry of surface-treatment agents as a plausible means of enhancing the interfacial charge transfer within metal oxide composite electrodes without hampering the resulting tap density of the resulting electrode.

Mixed transition metal oxides, such as Ni0.8Mn0.1Co0.1O2 (NMC811), are intended to combine the high capacity of nickel oxides, the rate capability of cobalt oxides, and the structural stability of manganese oxides to meet the capacity and power demands of electric vehicles and commercial portable electronics. However, the capacity fade mechanisms in Ni-rich chemistries (x >y+z in NixMnyCozO2) can be elusive due to factors at the crystallographic, particle, or electrode level. In this study, bulk and surface x-ray spectroscopy characterization of NMC cathodes was used to explore cathode degradation mechanisms as influenced by cycling protocol, namely current rate and upper voltage limits. Soft x-ray absorption spectroscopy (sXAS) was used to probe the surface of recovered NMC electrodes via transition metal L-edge and O K-edge spectroscopy. The effect of rate and upper voltage potential under charge will be discussed to illustrate the versatility of sXAS for NMC cathode electrode characterization.

While the focus of research related to the design of robust, high-performance Li-ion batteries relates primarily to the synthesis of active particles, the binder plays a crucial role in stability and ensures electrode integrity during volume changes that occur with cycling. Conventional polymeric binders such as poly(vinylidene difluoride) generally do not interact with active particle surfaces and fail to accommodate large changes in particle spacing during cycling. Thus, attention is now turning toward the exploration of interfacial interactions between composite electrode constituents as a key element in ensuring electrode stability. Recently, a poly[3-(potassium-4-butanoate)thiophene] (PPBT) binder component, coupled with a polyethylene glycol (PEG) surface coating for the active material was demonstrated to enhance both electron and ion transport in magnetite-based anodes, and it was established that the PEG/PPBT approach aids in overall battery electrode performance. Herein, the PEG/PPBT system is used as a model polymeric binder for understanding cation effects in anode systems. As such, the potassium ion was replaced with sodium, lithium, hydrogen, and ammonium through ion exchange. The potassium salt exhibited the most stable electrochemical performance, which is attributed to the cation size and resultant electrode morphology that facilitates ion transport. The lithium analogue demonstrated an initial increase in capacity but was unable to maintain this performance over 100 cycles; while the sodium-based system exhibited initially lower capacity as a result of slow reaction kinetics, which increased as cycling progressed. The parent carboxylic acid polymer and its ammonium salt were notably inferior. The results exploring the effect of ion exchange creates a framework for understanding how cations associated directly with the polymer impact electrochemical performance and aid in the overall design of binders for composite Li-ion battery anodes.

Newer, more demanding energy storage systems require high energy density along with high power and fast charge rates. Conventional battery electrode fabrication techniques are often limited by how much active material they can hold in the case of slurry-cast electrodes and how much of the electrode can be utilized in the case of dense pelletized electrodes. Thick porous electrode fabrication techniques have been developed as a way to obtain a higher active mass loading and an architecture which enables ionic and electronic transport. The homogeneity of the phase distribution of lithiated LVO in thick (∼500 μm) porous electrodes (TPEs) designed to facilitate both ion and electron transport was determined using synchrotron-based operando energy dispersive X-ray diffraction (EDXRD). Probing 3 positions in the TPE while cycling at a fast rate of 1C revealed a homogeneous phase transition across the thickness of the electrode at the 1st and 95th cycles. Continuum modelling indicated homogenous lithiation across the electrode upon discharge at 1C consistent with the EDXRD results and ascribed decreasing accessible active material to be the cause of loss in delivered capacity between the 1st and 95th cycles. The model was supported by the observation of significant particle fracture by SEM consistent with loss of electrical contact. The absence of the beta phase peaks in the EDXRD over extended cycling are consistent with electrochemical accessibility of only part of the active material. Overall, the combination of operando EDXRD, continuum modeling, and ex situ measurements enabled a deeper understanding of lithium vanadium oxide transport properties under high rate extended cycling within a thick highly porous electrode architecture.