A Pseudo-Two-Dimensional (P2D) Model for FeS2 Conversion Cathode Batteries

Conversion cathode materials are gaining interest for secondary batteries due to their high theoretical energy and power density. However, practical application as a secondary battery material is currently limited by practical issues such as poor cyclability. To better understand these materials, we have developed a pseudo-two-dimensional model for conversion cathodes. We apply this model to FeS2 - a material that undergoes intercalation followed by conversion during discharge. The model is derived from the half-cell Doyle-Fuller-Newman model with additional loss terms added to reflect the converted shell resistance as the reaction progresses. We also account for polydisperse active material particles by incorporating a variable active surface area and effective particle radius. Using the model, we show that the leading loss mechanisms for FeS2 are associated with solid-state diffusion and electrical transport limitations through the converted shell material. The polydisperse simulations are also compared to a monodisperse system, and we show that polydispersity has very little effect on the intercalation behavior yet leads to capacity loss during the conversion reaction. We provide the code as an open-source Python Battery Mathematical Modelling (PyBaMM) model that can be used to identify performance limitations for other conversion cathode materials

Electrochemical Insights on Materials for Next-Generation Batteries

The development of the lithium-ion battery has played an indispensable role in shaping the landscape of portable electronics and emerging electric vehicle industry. While its development has been recognized with a Nobel Prize in 2019, battery technology is far from mature. Since its conception, the battery research landscape has only widened with the rise of electric vehicles and wearable devices, each having a different set of requirements. Therefore, the “next-generation” in the context of this dissertation focuses on two different aspects of the battery field. The first aspect considers the development of high energy density batteries and more specifically the move away from capacity-limited intercalation chemistries. Chapter 3 delves into the interfacial challenges posed by lithium metal anodes during the Li plating/stripping reactions while Chapter 4 visits the complex reaction pathways in FeS2 conversion cathodes to understand charge product formation and identify capacity loss mechanisms. While both Li and FeS2 are commercialized as primary battery electrode materials and have the potential to provide high energy density rechargeable batteries, safety and performance issues have limited their use to primary systems. Ultimately, better understanding of the interfaces and reaction pathways can fuel the design of solutions to improve the performance and safety of these systems. The latter part of the dissertation focuses on the other type of “next-generation” battery, namely, that of miniaturized power sources for IoT technologies. With the vision of an on-chip battery integrated into a device, new materials and processes must be developed to integrate the same semiconductor processing techniques used to make the device to make the batteries as well. Chapter 5 details the development of a conformal, photopatternable separator and the integration of the separator onto various battery architectures. The ability to spatially photopattern a porous separator onto three dimensional architectures provides a path towards high power on-chip batteries. In summary this dissertation aims to provide perspective in the different directions and progress towards the next generation of rechargeable batteries. From better fundamental insights on complex electrochemical pathways to application-driven materials design and development, this dissertation highlights a few of the challenges, discoveries, and advancements of a much larger research landscape of “next-generation” batteries

A three-dimensional analysis of pre-and post-operative running biomechanics in femoroacetabular impingement

M.S. University of Hawaii at Manoa 2014.Includes bibliographical references.Femoroacetabular impingement (FAI) consists of abnormal bony formation that leads to premature contact between the femur and acetabulum during motion1. The proximal femur can be non-spherical (Cam-FAI) leading to abrasion type impacts with the acetabular rim, whereas the femoral neck can be impacted due to acetabular over-coverage-(Pincer-FAI)2,3. The bony deformities lead to pain, intra-articular damage of the acetabular labrum and hyaline cartilage, and early development of osteoarthritis (OA)1. Initial development of FAI first presents in young to middle-aged active populations via insidious groin pain and limited passive flexion, adduction, and IR (IR) (e.g. anterior impingement sign)1-3. Continued activity and maximal ranges of motion during turning, twisting, pivoting, or lateral movements may exacerbate signs and symptoms4. Persistent aggravation may result in decreased strength5,6(e.g. decreased maximal isometric hip flexion, adduction, abduction, and external rotation[ER] strength) pre-operatively compared to controls5. These findings may lead to antalgic walking gait and decreased ability to perform activities of daily living6-10. Pre-operative three-dimensional biomechanical studies involving kinematic and kinetic FAI level walking gait are controversial7-9. Kinematically, FAI patients display significantly lower peak hip extension, adduction, IR, as well as frontal and sagittal hip excursion decreases when compared to controls7. However, in another study, no significant differences were revealed in the transverse plane8. Kinetically, a single study of a mixed (i.e. Cam and Pincer) FAI patients indicated decreases in peak flexion and ER moments7, whereas other studies showed no differences 6,8,9. Though the specific effects of symptomatic FAI on gait differ between studies, every sample showed kinematic deficits. Post-operative patients reported decreased pain and improved functional abilities 6,9,11 however, gait analyses were limited. Following arthroscopic intervention, increased sagittal hip excursion on the involved hip during walking was reported, which was largely due to increased maximal flexion during walking after arthroscopic intervention 9. However, following surgical hip dislocation (SHD) hip frontal excursion decreased both pre-and post-operatively (21.1± 9.4 months), when compared to controls6. Peak hip abduction and IR external moments and peak power generation near toe-off decreased after SHD as well6. The differences in findings may be attributed to the lack of control subjects in the arthroscopic study9, and/or the increased trauma of joint, ligament, and muscle resections utilized in the SHD technique. This increased trauma may lead to larger post-operative strength deficits12, unfortunately, strength has only been evaluated pre-operatively in FAI patients, to our knowledge5. Walking gait and hip strength related changes after FAI surgery are currently debated and unknown. Additionally, FAI patient goals include the desire to return to normal walking and also vigorous activity. To our knowledge, there are no analyses of more impactful motions than walking and stair climbing 13. A longitudinal analysis of running gait in relation to hip strength may elucidate the operative efficacy in FAI patient surgery and follow-up treatment. Therefore, the purpose of this study was to examine the three-dimensional running gait kinematics and kinetics, and hip strength in pre-and 6 months post-operative FAI patients compared to controls

Transition Metal Sulfide Conversion: A Promising Approach to Solid-State Batteries

Rechargeable Li-ion batteries play a critical role in the net zero picture spanning across the automotive industry, grid scale storage, and recycling infrastructure. With the rising demand for lithium-ion batteries in both the electric vehicle and stationary storage sector, challenges regarding resource availability and supply chain are expected. To reduce the inevitable growing pains of the changing global energy storage landscape, other alternative battery materials must be considered. For stationary power sources, the weight and volume requirements are less stringent than their electric vehicle counterparts offering the possibility to look at a wider range of battery chemistries and an opportunity to explore beyond Co- and Ni-based intercalation chemistries. In this Perspective, we explore the opportunity space for all solid-state batteries based on transition metal sulfide conversion chemistries for stationary energy storage applications

Photopatternable hydroxide ion electrolyte for solid-state micro-supercapacitors

International audienceElectrochemical energy storage (EES) devices that provide high power and energy for micropower systems are considered to be essential for developing micro/nano electronics such as nanorobotics, environmental sensors, and connected smart electronics. One promising research direction in this field has been to develop on-chip EES devices whose length scales integrate with those of miniaturized electronic devices. In the work described here, we provide the first report of a hydroxide-ion-conducting solid electrolyte that can be patterned using standard lithography. By combining a negative photoresist with a polymerizable ionic liquid, we obtain a thermally and dimensionally stable, hydroxide-ion-conducting solid electrolyte with a conductivity of 10 mS cm−1. Patterning the solid electrolyte directly on interdigitated vanadium nitride (VN) electrodes enables a scalable fabrication approach for producing high-resolution, solid-state VN micro-supercapacitors (MSC) in both single and multiple devices

Avoiding dendrite formation by confining lithium deposition underneath Li-Sn coatings

The use of interfacial layers to stabilize the lithium surface is a popular research direction for improving the morphology of deposited lithium and suppressing lithium dendrite formation. This work considers a different approach to controlling dendrite formation where lithium is plated underneath an interfacial coating. In the present research, a Li-Sn intermetallic was chosen as a model system due to its lithium-rich intermetallic phases and high Li diffusivity. These coatings also exhibit a significantly higher Li exchange current than bare Li thus leading to better charge transfer kinetics. The exchange current is instrumental in determining whether lithium deposition occurs above or below the Li-Sn coating. High-resolution transmission electron microscopy and cryogenic focused ion beam scanning electron microscopy were used to identify the features associated with Li deposition. Atomic scale simulations provide insight as to the adsorption energies determining the deposition of lithium below the Li-Sn coating.</p

Heat Generation in Electric Double Layer Capacitors with Neat and Diluted Ionic Liquid Electrolytes Under Large Potential Window Between 5 and 80°C

This study investigates the effect of temperature on the heat generation and the associated electrochemical phenomena occurring in IL-based EDLCs. The EDLCs consisted of two identical activated carbon electrodes with neat Pyr14TFSI or Pyr14TFSI diluted in propylene carbonate (PC) as electrolytes. The instantaneous heat generation rate at each electrode was measured by isothermal calorimetry between 5 and 80 °C under constant current cycling and potential window of 2.5 V.First, the instantaneous heat generation rate was similar at each electrode in neat IL. However, it was smaller at the negative electrode in diluted IL and featured endothermic dips growing with increasing temperature > 40 °C due to overscreening effects, ion desolvation, and/or decomposition of PC. The irreversible heat generation was similar in each half-cell and decreased with increasing temperature due to the reduction in internal resistance, particularly with neat IL. The irreversible heat generation exceeded Joule heating in all cases, especially at high temperature and low current. This was attributed to ion desorption and charge redistribution in the porous electrodes. Finally, the reversible heat generation for both electrolytes was larger at the positive than at the negative electrode due to the difference in anion and cation sizes.</div

Investigating the Perovskite Ag1-3xLaxNbO3 as a High-Rate Negative Electrode for Li-Ion Batteries

International audienceThe broader development of the electric car for tomorrow's mobility requires the emergence of new fast-charging negative electrode materials to replace graphite in Li-ion batteries. In this area, the design of new compounds using innovative approaches could be the key to discovering new negative electrode materials that allow for faster charging and discharging processes. Here, we present a partially substituted AgNbO3 perovskite material by introducing lanthanum in the A-site. By creating two vacancies for every lanthanum introduced in the structure, the resulting general formula becomes Ag1-3xLax2xNbO3 (with x <= 0.20 and where is a A-site vacancy), allowing the insertion of lithium ions. The highly substituted Ag0.40La0.200.40NbO3 oxide shows a specific capacity of 40 mAh.g(-1) at a low sweep rate (0.1 mV s(-1)). Interestingly, Ag0.70La0.100.20NbO3 retains 64% of its capacity at a very high sweep rate (50 mV s(-1)) and about 95% after 800 cycles. Ex situ Li-7 MAS NMR experiments confirmed the insertion of lithium ions in these materials. A kinetic analysis of Ag1-3xLax2xNbO3 underlines the ability to store charge without solid-state ion-diffusion limitations. Furthermore, in situ XRD indicates no structural modification of the compound when accommodating lithium ions, which can be considered as zero-strain material. This finding explains the interesting capacity retention observed after 800 cycles. This paper thus demonstrates an alternative approach to traditional insertion materials and identifies a different way to explore not-so common electrode materials for fast energy storage application