Browsing by Subject "Lithium ion batteries"

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Atomistic simulation of the early stages of solid electrolyte interphase formation in lithium ion batteries
(2019-09-19) Boyer, Mathew J.; Hwang, Gyeong S.; Freeman, Benny D; Manthiram, Arumugam; Ren, Pengyu
Lithium ion batteries have fueled a technological revolution in consumer electronics, power tools, and electric vehicles. Further advancements of this technology to improve charge times and capacity while maintaining safe operability, however, require a deeper fundamental understanding of electrode and electrolyte materials as well as their interfaces. In particular, interfacial stability between the high energy anode and the electrolyte represents one of the greatest hurdles to improving current-generation batteries as well as moving onto next-generation technologies like lithium metal or silicon. Despite the commercial availability of lithium ion batteries for more than a decade, there is no intrinsically stable electrolyte which is able to satisfy the design requirements of a commercial device. Instead, a protective layer formed during the first charge cycle known as the solid electrolyte interphase (SEI) is relied upon to ensure stable operation over subsequent charge/discharge cycles. Despite being critical to battery operability, the SEI and the process by which it forms remains poorly understood. As the SEI is only several to tens of nm thick and decomposes in ambient conditions, its study through experiments presents many challenges. However, computational tools can easily access the size- and time-scales required to elucidate the processes which govern the formation of the SEI. This dissertation presents a computational framework by which reductive decomposition of the electrolyte during the early stages of SEI formation may be studied through atomistic simulations including classical molecular dynamics and density functional theory. Additionally, fundamental descriptions of several reaction and diffusion processes involved in the formation of the SEI from a conventional electrolyte on a graphite electrode are presented. This methodology may be later applied to more complex electrolytes or other electrodes like silicon, but also lays the groundwork for exploring later stages of the SEI formation and growth.
Characterizing the lithiation and failure mechanisms of transition metal phosphates and phosphides for lithium ion batteries
(2015-05) Membreño, Nellymar; Stevenson, Keith J.; Henkelman, Graeme; Webb, Lauren J; Delia, Milliron J; Richard, Crooks M
In this dissertation the lithiation and failure mechanisms of some promising transition metal phosphide and phosphate materials are discussed for application in lithium ion batteries (LIBs). More specifically, the materials investigated include the intercalation cathode Li₃V₂(PO₄)₃ and the conversion anode FeP₂. For FeP₂, a nano amorphous material obtained through a novel, low-temperature synthetic reaction was galvanostatically characterized and the correlation between its morphology and lithiation properties is discussed. For Li₃V₂(PO₄)₃, Raman microscopy and X-ray photoelectron spectroscopy (XPS) are primarily used as the analytical techniques to characterize the bulk and surface chemistry of this material. In the first chapter the advancements and current challenges of LIBs are discussed. A brief overview on the different lithiation mechanisms (intercalation, alloying and conversion) is presented along with the cathode and anodes that historically have been of interest. The potential of Li₃V₂(PO₄)₃ and FeP₂ as next generation LIB electrodes is also discussed. In the second chapter we present the first reports of a nano, amorphous FeP₂ material obtained through a novel, low-temperature reaction between a σ-bonded alkly Fe complex with PH₃. Electrochemical lithiation of nano, amorphous FeP₂ showed superior performance to the bulk, crystalline morphology and a competing lithiation mechanism between classical intercalation and conversion is proposed. The third chapter discusses the monoclinic phase of Li₃V₂(PO₄)₃ which is characterized via Raman microscopy and compared to the spectrum calculated through density functional theory (DFT) providing groundwork for future in situ experiments. The fourth chapter reports on XPS measurements of composite Li₃V₂(PO₄)₃ electrodes after complete intercalation/deintercalation reactions and specifically examines the role that the carbon black additive plays on the interface of the composite electrode and electrolyte. Finally, the fifth chapter presents a novel design for an in situ Raman microscopy test cell for LIBs along with a detailed explanation of the important component and design criteria for optimal scattering and electrochemical measurements. Future in situ Raman microscopy experiments for Li₃V₂(PO₄) and other LIB materials of interest are discussed.
Controlled prelithiation of PbS to Pb/Li₂S for high initial Coulombic efficiency in lithium ion batteries
(2018-12) Guo, Yong, M.A.; Mullins, C. B.
PbS nanoparticle aggregates were synthesized in a simple aqueous reaction at room temperature, and were tested as a lithium ion anode material, with a gravimetric capacity of 374 mAh/g at C/2, and a 0.15% capacity loss per cycle. However, its half cell initial Coulombic efficiency (ICE) was only 40%, due to a combination of irreversible Li₂S and solid electrolyte interface (SEI) formations. A custom controlled prelithiation technique was then applied to the PbS electrodes, converting the active material to Pb/Li₂S, and consolidating the SEI prior to coin cell assembly. This brought the ICE from 40% to >97%, and allowed for immediate cycling of the electrode at high Coulombic efficiency, without further formation cycles. Upon construction of prelithiated Pb/Li₂S vs NCM full cells, an 82% ICE was observed, with the majority of the lithium loss from the NCM. The full cells had a combined electrode capacity of 100 mAh/g at C/2
Hybrid neural net and physics based model of a lithium ion battery
(2011-05) Refai, Rehan; Chen, Dongmei, Ph. D.; Fernandez, Benito R.
Lithium ion batteries have become one of the most popular types of battery in consumer electronics as well as aerospace and automotive applications. The efficient use of Li-ion batteries in automotive applications requires well designed battery management systems. Low order Li-ion battery models that are fast and accurate are key to well- designed BMS. The control oriented low order physics based model developed previously cannot predict the temperature and predicts inaccurate voltage dynamics. This thesis focuses on two things: (1) the development of a thermal component to the isothermal model and (2) the development of a hybrid neural net and physics based battery model that corrects the output of the physics based model. A simple first law based thermal component to predict the temperature model is implemented. The thermal model offers a reasonable approximation of the temperature dynamics of the battery discharge over a wide operating range, for both a well-ventilated battery as well as an insulated battery. The model gives an accurate prediction of temperature at higher SOC, but the accuracy drops sharply at lower SOCs. This possibly is due to a local heat generation term that dominates heat generation at lower SOCs. A neural net based modeling approach is used to compensate for the lack of knowledge of material parameters of the battery cell in the existing physics based model. This model implements a neural net that corrects the voltage output of the model and adds a temperature prediction sub-network. Given the knowledge of the physics of the battery, sparse neural nets are used. Multiple types of standalone neural nets as well as hybrid neural net and physics based battery models are developed and tested to determine the appropriate configuration for optimal performance. The prediction of the neural nets in ventilated, insulated and stressed conditions was compared to the actual outputs of the batteries. The modeling approach presented here is able to accurately predict voltage output of the battery for multiple current profiles. The temperature prediction of the neural nets in the case of the ventilated batteries was harder to predict since the environment of the battery was not controlled. The temperature predictions in the insulated cases were quite accurate. The neural nets are trained, tested and validated using test data from a 4.4Ah Boston Power lithium ion battery cell.
Microwave-assisted synthesis and characterization of inorganic materials for energy applications
(2012-08) Harrison, Katharine Lee; Manthiram, Arumugam
Lithium-ion batteries play a crucial role in portable electronics, but require further innovation for electric vehicle and grid storage applications. To meet this demand, significant emphasis has been placed on developing safe, inexpensive, high energy density cathode materials. LiFePO₄ is a candidate cathode material for electric vehicle and grid storage applications. Vanadium-doped LiFePO₄ cathodes of the form [chemical formula] (0 ≤ x ≤ 0.25) were synthesized here by a facile, low-temperature microwave-assisted solvothermal (MW-ST) method. Such an approach offers manufacturing-energy and cost savings compared to conventional synthesis. Additionally, although [chemical formula] has been synthesized previously by conventional methods, it is shown here that the MW-ST method allows much higher doping levels than can be achieved at conventional temperatures, indicating that metastable phases can be isolated through the low-temperature microwave-assisted synthesis. LiFePO₄ suffers from poor ionic conductivity, but this limitation can be minimized by microwave-assisted synthesis through a tuning of the particle size, allowing for decreased Li⁺ diffusion paths. LiVOPO₄ is another polyanion material with higher energy density than LiFePO₄, but similar ionic conductivity limitations. It has not been previously synthesized by MW-ST. Thus, a MW-ST method was developed here to prepare LiVOPO₄. By varying reaction conditions, three polymorphic modifications of LiVOPO₄ were accessed and the electrochemical performance was optimized. LiVOPO₄ can be further discharged to Li₂VOPO₄, which has been suggested in the literature, but the structural transformation that accompanies this process has not been detailed. To this end, the delithiation process was studied by ex situ XRD measurements to better understand how the second lithium is accommodated. Finally, MW-ST has also been exploited to grow thin films of anatase TiO₂ phase on indium tin oxide (ITO)-coated glass substrates. The microwave field is selectively absorbed by the conductive ITO layer on the glass substrates, leading to ohmic heating. The resulting heated ITO layer acts as a favorable site for nucleation and growth. TiO₂ thin films have widespread applications in the energy and electronics sectors. Such selective microwave-assisted ohmic heating of solid materials within a growth solution represents a promising new avenue for microwave synthesis, which has been minimally explored in the literature.
Nanostructuring silicon and germanium for high capacity anodes in lithium ion batteries
(2012-12) Harris, Justin Thomas; Korgel, Brian Allan, 1969-; Ekerdt, John G.; Hwang, Gyeong S.; Mullins, Charles B.; Stevenson, Keith A.
Colloidally synthesized silicon (Si) and germanium (Ge) were explored as high capacity anode materials in lithium ion batteries. a-Si:H particles were synthesized through the thermal decomposition of trisilane in supercritical n-hexane. Precise control over particle size and hydrogen content was demonstrated. Particles ranged in size from 240-1500 nm with hydrogen contents from 10-60 atomic%. Particles with low hydrogen content had some degree of local ordering and were easily crystallized during Raman spectroscopy. The as-synthesized particles did not perform well as an anode material due to low conductivity. Increasing surface conductivity led to enhanced lithiation potential. Cu nanoparticles were deposited on the surface of the a-Si:H particles through a hydrogen facilitated reduction of Cu salts. The resulting Cu coated particles had a lithiation capacity seven times that of pristine a-Si:H particles. Monophenylsilane (MPS) grown Si nanowire paper was annealed under forming gas to reduce a polyphenylsilane shell into conductive carbon. The resulting paper required no binder or carbon additive and achieved capacities of 804 mA h/g vs 8 mA h/g for unannealed wires. Si and Ge heterostructures were explored to take advantage of the higher inherent conductivity of Ge. Ge nanowires were successfully coated with a-Si by thermal decomposition of trisilane on their surface, forming Ge@a-Si core shell structures. The capacity increased with increasing Si loading. The peak lithiation capacity was 1850 mA h/g after 20 cycles – higher than the theoretical capacity of pure Ge. MPS additives created a thin amorphous shell on the wire surfaces. By incubating the wires after MPS addition the shell was partially reduced, conductivity increased, and a 75% increase in lithiation capacity was observed for the nanowire paper. The syntheses of Bi and Au nanoparticles were also explored. Highly monodisperse Bi nanocrystals were produced with size control from 6-18 nm. The Bi was utilized as seeds for the SLS synthesis of Ge nanorods and copper indium diselenide (CuInSe2) nanowires. Sub 2 nm Au nanocrystals were synthesized. A SQUID magnetometer probed their magnetic behavior. Though bulk Au is diamagnetic, the Au particles were paramagnetic. Magnetic susceptibility increased with decreasing particle diameter.
Silicon and germanium battery materials : exploring new structures, surface treatments, and full cell applications
(2018-05) Adkins, Emily Renee; Korgel, Brian Allan, 1969-; Mullins, Charles B; Manthiram, Arumugam; Hwang, Gyeong S; Yu, Guihua
Lithium ion batteries (LIBs) with higher energy and power density are needed to meet the increasing demands of portable electronic devices, extended-range electric vehicles, and renewable energy storage. Silicon (Si) and germanium (Ge) are attractive anode materials for next generation batteries because they have significantly higher capacities compared with current graphite anodes. One of the challenges Si and Ge face during battery cycling is high volume expansion upon lithiation, which can be accommodated by nanostructuring. LIBs made using Si and Si-Ge type II clathrates exhibited superior reversible cycling performance. This high capacity and stability is due to the type II phase purity of the samples which is a unique feature of the synthetic method used in this study. During cycling, the anode will react with the electrolyte, forming a passivating solid electrolyte interphase (SEI) layer on the surface, which is crucial to stable battery function. The formation of this layer is influenced by the surface chemistry of the active material. Ge NWs with different surface passivations exhibited different battery performance and rate capability. One strategy used to improve the performance of nanostructured Si, is the addition of a surface coating layer. Si nanowires coated with an SiO[subscript x] shell examined using in situ transmission electron microscopy during battery cycling showed reduced volume expansion, at the expense of complete lithiation. When the nanowire is delithiated, pores are observed to form in the amorphized Si due to the SiO[subscript x] shell, which prevents the migration of vacancies formed during delithiation to the nanowire surface. To increase the performance of the LIB, both the anode and cathode capacities must increase. Prelithiation of the Si anode was crucial to improve the capacity and stability of battery cycling for both lithium iron phosphate and sulfur cathodes, and the prelithiation process used strongly influenced battery performance. In a full cell with a sulfur cathode, no sulfides were observed in the Si SEI layer, due to the use of a carbon interlayer. Si-S batteries fully consumed the lithium nitrate electrolyte additive during cycling, resulting in high levels of electrolyte degradation that contaminated the anode and reduced battery stability
Tin-based nanocomposite alloy anodes for lithium-ion batteries
(2014-05) Leibowitz, Joshua Abel; Manthiram, Arumugam
Lithium-alloying anode materials have attracted much attention as an alternative to carbon due to their high theoretical gravimetric capacities (e.g. Li4.4Si: 4200 mAh g-1, Li4.4Sn: 990 mAh g-1, and Li3Sb: 660 mAh g-1). An additional benefit of lithium alloying metals is that some of the react at a higher potentials vs. Li/Li+ than carbon, which can mitigate safety issues caused by solid-electrolyte interface layer formation and lithium plating. One of the most promising lithium -alloying anode materials that are being pursued are Sn-based materials due to their high capacity and tap density. This thesis investigates the synthesis and characterization of Sn-based lithium-ion battery anodes. SnSb-TiC-C and FeSn2-TiC nanocomposite alloy anodes for lithium-ion batteries have been synthesized by a mechanochemical process involving high-energy mechanical milling of Ti/Sn, Ti/M (M = Fe or Sb), and C. Characterization of the nanocomposites formed with x-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) reveals that these alloys are composed of crystalline nanoparticles of FeSn2 and SnSb dispersed in a matrix of TiC and carbon. The SnSb-TiC-C alloy shows an initial gravimetric capacity of 653 mAh g-1 (1384 mAh cm-3), an initial coulombic efficiency of 85%, and a tap density of 1.8 g cm-3. The FeSn2-TiC alloy shows an initial gravimetric capacity of 510 mAh g-1 (1073 mAh cm-3), an initial coulombic efficiency of 71%, and a tap density of 2.1 g cm-3. The TiC-C buffer matrix in the nanocomposite alloy anodes accommodates the large volume change occurring during the charge-discharge process and leads to good cyclability compared to pure FeSn2 and SnSb anodes.