Search for: All records

Both thin (55μm) composite and thick (350μm) all active material battery porous electrodes were prepared for estimating the diffusion coefficient of Li⁺($D_{{\mathit{Li}}^{+}})$in tellurium (Te) during electrochemical lithiation. Galvanostatic intermittent titration technique (GITT), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) were applied to quantify the chemical lithium solid-state diffusion coefficient within the Te active material in the electrodes. Multiple methods of GITT and EIS were assessed. For the composite Te electrodes, the$D_{{\mathit{Li}}^{+}}$was on the order of 10⁻¹¹cm²s⁻¹from both CV and GITT methods, but 10⁻⁹cm²s⁻¹from EIS. For the thick tellurium electrodes, both GITT and EIS resulted in lithium diffusion coefficient estimates in the range of 10⁻¹¹–10⁻¹²cm²s⁻¹. The general trend across all methods that quantified the diffusion coefficient as a function of lithiation of tellurium was that the$D_{{\mathit{Li}}^{+}}$decreased rapidly when the Te material was initially lithiated. The$D_{{\mathit{Li}}^{+}}$at the phase transition voltage plateau (∼1.7 V, vs Li/Li⁺, where both Te and Li₂Te were expected) had the lowest$D_{{\mathit{Li}}^{+}},$while the$D_{{\mathit{Li}}^{+}}$both before and after the plateau was generally higher. Among all the electrochemical measurements of$D_{{\mathit{Li}}^{+}},$the modified GITT method with modelling the relaxation region resulted in relatively low scatter in the data, provided values as a function of lithiation, and was well suited to thick electrodes with a flat discharge plateau as was the case herein.

 

Lithium-ion batteries have become a widespread energy storage technology, and research continues towards improving battery properties. One route to increase electrode areal active material loading and decrease relative volume fractions of inactive components is to increase electrode thickness, but increasing thickness can impact mechanical stability for conventional composite electrodes. All active material (AAM) electrodes, including those in this work, can mitigate mechanical and transport limitations for very thick lithium-ion electrodes. Such electrodes are free of polymer binders and conductive additives, and processed by pressing electroactive material powder into a porous pellet followed by mild sintering to improve mechanical properties. This study investigated the processing of a more recent material processed into AAM electrodes, TiNb₂O₇, which has relatively high volumetric capacity among reported materials processed into AAM electrodes. The anode material was characterized in AAM electrodes where different processing temperatures were used, resulting in different titanium and niobium containing phases being present. This manuscript provides insights and electrochemical consequences for fabricating AAM electrodes with multicomponent oxide phases.

 

Thick sintered porous tellurium pellets are fabricated and evaluated as cathodes in lithium–tellurium batteries. These electrodes lack inactive binders and conductive additives and have very high areal capacity, which are important attributes for increasing cell energy density. More commonly tellurium in lithium–tellurium batteries is processed via melt impregnation into a conductive host. In contrast, herein, porous sintered electrodes comprising only tellurium material dramatically increase the areal active material loading to 150 mg cm⁻²compared to the typically reported <5 mg cm⁻². A processing route is used on the tellurium powder to reduce the particle size and increase the electroactive area by a factor of 13. With the increased surface area, gravimetric capacity increased for the same current density and retention of capacity at increasing rates has even greater improvement. Thick all active material–sintered tellurium electrodes provide a route toward high volumetric energy density batteries, where the relatively high electronic conductivity of tellurium is expected to be beneficial due to the lack of conductive additives in the electrode system.

 

Recently publications have suggested best practices with regards to techniques and reporting for battery research. One area gaining attention is the need for battery cell replicates. In this perspective, the need for replicates is put into the context of the uncertainty in gravimetric capacity resulting from a component typically assumed as a constant—the current collector mass. The expected variation in reported gravimetric capacity just due to this factor for representative current collectors and battery materials will be discussed, and the additional importance of electrode loading to minimize the impact of this factor will be described.

 

Redox targeting reactions between lithium-ion battery materials and redox shuttles have been proposed to design high energy density redox flow batteries. Designing these batteries would require a deeper understanding of the kinetics of redox targeting reactions and the phase transformation of the materials involved. In this study, the oxidation and reduction of lithium iron phosphate, LiFePO₄, via chemical and electrochemical routes will be compared. Ultraviolet-visible spectroscopy was used as a technique to characterize the extent of chemical lithiation/delithiation during chemical redox of LiFePO₄, while the electrochemical redox was characterized using battery coin cells. The kinetic parameters extracted using the Johnson–Mehl–Avrami–Erofeyev–Kolomogorov model suggested that chemical redox was slower than electrochemical redox within the experimental regimes. Calculated apparent activation energies suggested the limitations in the chemical redox rate were due to different processes than the electrochemical redox. In addition, asymmetry observed for oxidation and reduction of LiFePO₄materials will be discussed. As pairs of solid battery electroactive particles and soluble redox shuttles are designed, tools and analysis such as those in this study will be needed for interrogating and comparing electrochemical and chemical oxidation and reduction of the solid particles to understand and design these systems.

 

In efforts to increase the energy density of lithium-ion batteries, researchers have attempted to both increase the thickness of battery electrodes and increase the relative fractions of active material. One system that has both of these attributes are sintered thick electrodes comprised of only active material. Such electrodes have high areal capacities, however, detailed understanding is needed of their transport properties, both electronic and ionic, to better quantify their limitations to cycling at higher current densities. In this report, efforts to improve models of the electrochemical cycling of sintered electrodes are described, in particular incorporation of matrix electronic conductivity which is dependent on the extent of lithiation of the active material and accounting for initial gradients in lithiation of active material in the electrode that develop as a consequence of transport limitations during charging cycles. Adding in these additional considerations to a model of sintered electrode discharge resulted in improved matching of experimental cell measurements.

 

Multicomponent transition metal oxides are among the most successful lithium-ion battery cathode materials, and many previous reports have described the sensitivity of final electrochemical performance of the active materials to the detailed composition and processing. Coprecipitation of a precursor template is a popular, scalable route to synthesize these transition metal oxide cathode materials because of the homogeneous mixing of the transition metals within the particles, and the morphology control provided by the precursors. However, the deviation of the precursor composition from feed conditions is a challenge that has generally not been reported in previous studies. Using a target final material of the high voltage spinel LiMn 1.5 Ni 0.5 O 4 as an example, we show in this study that the compositional deviation caused by coprecipitation can be significant under certain conditions, impacting the calcined final material structure and electrochemical properties. The study herein provides insights into the role of solution equilibrium and rate of precipitation of the transition metals during precipitate formation on precursor, and thus final active material, composition. Such knowledge is necessary to rationally predict and tune multicomponent battery precursor compositions synthesized via coprecipitation with high levels of accuracy. 

Switching from organic to aqueous solvents for battery electrode processing is desirable due to both safety and cost advantages. Lithium iron phosphate (LFP) is considered a cathode material for aqueous processing due to its demonstrated chemical compatibility with water, in addition to its favorable cost, safety, electrochemical performance, and environmental advantages as a battery active material. All research on LFP stability in water has been conducted in a scenario where LFP is aged in stagnant water, or surrounded by water when confined within a composite electrode. However, a much accelerated degradation in the electrochemical performance of LFP when it is in contact with water and exposed to mechanical agitation is demonstrated. Changes to LFP are probed using a combination of materials characterization methods. Although there are no significant changes to the bulk particle structure and morphology, significant particle surface damage and compositional modifications are observed. These results suggest that the systems where LFP is exposed to agitation in an aqueous environment, such as in aqueous battery electrode processing or in aqueous slurry electrodes, need to be carefully investigated for potential changes to the LFP surface environment under relevant processing conditions.