The Effect of State of Charge and Charge Rate on the Formation and growth Deposit Layer on the Anode Electrode of the Lithium Ion Battery

The lithium ion battery technology has for the past two decades received a lot of attention because of its high energy density and excellent cycle life compared to other battery chemistries such as lead acid and Ni-Cd. These attributes of the lithium ion battery have positioned it as the preferred portable energy source for most consumer appliances and for electric/hybrid electric vehicles. However, several reported battery failures during its operation, have raised some safety concerns. These failures of the lithium ion batteries are linked to the degradation of its components: electrodes, current collectors, separator and electrolyte. In particular, the carbon-based anode has been associated with many aging mechanisms. The formation of the solid electrolyte interphase (SEI) layer on the surface of the anode electrode prevents further electrolyte decomposition reaction, however, at certain battery operating parameters the SEI breakdown gives way to more electrolyte solvent and salt decomposition reactions to form several species that are non-uniform and electronically insulating on the anode electrode. The research described in this dissertation focuses on investigating the effect of battery potential and charge rate on the decomposition reaction on the anode electrode of a lithium ion polymer battery. This relationship is important for understanding how charging protocols are related to performance degradation. The investigation showed that at high potential and charge rate the metastable species ROCO2Li within the SEI layer decomposes into more stable compounds –Li2CO3 and LiF. This therefore created a defective SEI structure thereby exposing the graphite surface to more electrolyte decomposition reaction. The overall impedance of batteries increased, particularly the charge transfer resistance. This was ii attributed to deposit layer formed at the electrode/electrolyte interface which affected the lithium intercalation kinetics at the interface. A direct link between the capacity fade during cycling and the progressive deposit layer thickness growth resulting from side reaction at the anode was established. Analysis of the crystal structure of the graphite electrode showed an increasing amount of lithium residing in the graphite sheets as the batteries are aged at higher SOC. The “trapped” lithium in the crystal structure of the graphite led to reduction/isolation of recyclable lithium taking part in the electrochemical process. Cycling the batteries at high charge rate of 4C induce some stresses in the electrode matrix during the intercalation/de-intercalation process that led to loss and isolation of carbon particles from the current collector that could make these particles electrochemically inactive. At high potential, the depletion of the recyclable lithium via trapping of lithium in the crystal structure of the graphite, deposit layer formation, and the partial loss of graphite active materials were predominant regardless of the charge rate and these factors contributed to the high capacity loss of the lithium ion batteries

Forcespinning: A new method for the mass production of Sn/C composite nanofiber anodes for lithium ion batteries

The development of nanostructured anode materials for rechargeable Lithium-ion Batteries has seen a growing interest. We herein report the use of a new scalable technique, Forcespinning (FS) to produce binder-free porous Sn/C composite nanofibers with different Sn particle size loading. The preparation process involves the FS of Sn/PAN precursor nanofibers and subsequently stabilizing in air at 280 °C followed by carbonization at 800 °C under an inert atmosphere. The Sn/C composite nanofibers are highly flexible and were directly used as binder-free anodes for lithium-ion batteries. The produced Sn/C composite nanofibers showed an improved discharge capacity of about 724 mA h g− 1 at a current density of 100 mA g− 1 for over 50 cycles compared to most nanofiber electrodes prepared by electrospinning and centrifugal spinning. The FS method clearly produces Sn/C nanofiber composite electrodes that have a high specific capacity and excellent cyclic performance, owing to the unique structure and properties of the nanofibers. The FS technology is thus a viable method for the large scale production of nano/micro fibers for battery electrodes, separators, and other applications. To the best of our knowledge, this is the first time to report results on the use of Forcespinning technology to produce composite nanofiber anodes for lithium-ion batteries

Effect of Polymer Concentration, Rotational Speed, and Solvent Mixture on Fiber Formation Using Forcespinning

Polycaprolactone (PCL) fibers were produced using Forcespinning® (FS). The effects of PCL concentration, solvent mixture, and the spinneret rotational speed on fiber formation were evaluated. The concentration of the polymer in the solvents was a critical determinant of the solution viscosity. Lower PCL concentrations resulted in low solution viscosities with a correspondingly low fiber production rate with many beads. Bead-free fibers with high production rate and uniform fiber diameter distribution were obtained from the optimum PCL concentration (i.e., 12.5 wt%) with tetrahydrofuran (THF) as the solvent. The addition of N, N-dimethylformamide (DMF) to the THF solvent promoted the gradual formation of beads, split fibers, and generally affected the distribution of fiber diameters. The crystallinity of PCL fibers was also affected by the processing conditions, spinning speed, and solvent mixture

Effect of Polymer Concentration Rotational Speed and Solvent Mixture On Fiber Formation Using Forcespinning®

Polycaprolactone (PCL) fibers were produced using Forcespinning® (FS). The effects of PCL concentration, solvent mixture, and the spinneret rotational speed on fiber formation were evaluated. The concentration of the polymer in the solvents was a critical determinant of the solution viscosity. Lower PCL concentrations resulted in low solution viscosities with a correspondingly low fiber production rate with many beads. Bead-free fibers with high production rate and uniform fiber diameter distribution were obtained from the optimum PCL concentration (i.e., 12.5 wt%) with tetrahydrofuran (THF) as the solvent. The addition of N, N-dimethylformamide (DMF) to the THF solvent promoted the gradual formation of beads, split fibers, and generally affected the distribution of fiber diameters. The crystallinity of PCL fibers was also affected by the processing conditions, spinning speed, and solvent mixture

Graphene-Based Nanocomposites for Energy Storage

Since the first report of using micromechanical cleavage method to produce graphene sheets in 2004, graphene/graphene-based nanocomposites have attracted wide attention both for fundamental aspects as well as applications in advanced energy storage and conversion systems. In comparison to other materials, graphene-based nanostructured materials have unique 2D structure, high electronic mobility, exceptional electronic and thermal conductivities, excellent optical transmittance, good mechanical strength, and ultrahigh surface area. Therefore, they are considered as attractive materials for hydrogen (H2) storage and high-performance electrochemical energy storage devices, such as supercapacitors, rechargeable lithium (Li)-ion batteries, Li–sulfur batteries, Li–air batteries, sodium (Na)-ion batteries, Na–air batteries, zinc (Zn)–air batteries, and vanadium redox flow batteries (VRFB), etc., as they can improve the efficiency, capacity, gravimetric energy/power densities, and cycle life of these energy storage devices. In this article, recent progress reported on the synthesis and fabrication of graphene nanocomposite materials for applications in these aforementioned various energy storage systems is reviewed. Importantly, the prospects and future challenges in both scalable manufacturing and more energy storage-related applications are discussed

The effects of material formulation and manufacturing process on mechanical and thermal properties of epoxy/clay nanocomposites

A holistic study was conducted to investigate the combined effect of three different pre-mixing processes, namely mechanical mixing, ultrasonication and centrifugation, on mechanical and thermal properties of epoxy/clay nanocomposites reinforced with different platelet-like montmorillonite (MMT) clays (Cloisite Na+, Cloisite 10A, Cloisite 15 or Cloisite 93A) at clay contents of 3–10 wt%. Furthermore, the effect of combined pre-mixing processes and material formulation on clay dispersion and corresponding material properties of resulting composites was investigated using X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), flexural and Charpy impact tests, Rockwell hardness tests and differential scanning calorimetry (DSC). A high level of clay agglomeration and partially intercalated/exfoliated clay structures were observed regardless of clay type and content. Epoxy/clay nanocomposites demonstrate an overall noticeable improvement of up to 10 % in the glass transition temperature (Tg) compared to that of neat epoxy, which is interpreted by the inclusion of MMT clays acting as rigid fillers to restrict the chain mobility of epoxy matrices. The impact strength of epoxy/clay nanocomposites was also found to increase by up to 24 % with the addition of 3 wt% Cloisite Na+ clays. However, their flexural strength and hardness diminished when compared to those of neat epoxy, arising from several effects including clay agglomeration, widely distributed microvoids and microcracks as well as weak interfacial bonding between clay particles and epoxy matrices, as confirmed from TEM and SEM results. Overall, it is suggested that an improved technique should be used for the combination of pre-mixing processes in order to achieve the optimal manufacturing condition of uniform clay dispersion and minimal void contents

Influence of Nanoclay Dispersion Methods on the Mechanical Behavior of E-Glass/Epoxy Nanocomposites

Common dispersion methods such as ultrasonic sonication, planetary centrifugal mixing and magnetic dispersion have been used extensively to achieve moderate exfoliation of nanoparticles in polymer matrix. In this study, the effect of adding three roll milling to these three dispersion methods for nanoclay dispersion into epoxy matrix was investigated. A combination of each of these mixing methods with three roll milling showed varying results relative to the unmodified polymer laminate. A significant exfoliation of the nanoparticles in the polymer structure was obtained by dispersing the nanoclay combining three roll milling to magnetic and planetary centrifugal mixing methods. This exfoliation promoted a stronger interfacial bond between the matrix and the fiber, which increased the final properties of the E-glass/epoxy nanocomposite. However, a combination of ultrasound sonication and three roll milling on the other hand, resulted in poor clay exfoliation; the sonication process degraded the polymer network, which adversely affected the nanocomposite final properties relative to the unmodified E-glass/epoxy polymer

Lithium Ion Battery Anode Aging Mechanisms

Degradation mechanisms such as lithium plating, growth of the passivated surface film layer on the electrodes and loss of both recyclable lithium ions and electrode material adversely affect the longevity of the lithium ion battery. The anode electrode is very vulnerable to these degradation mechanisms. In this paper, the most common aging mechanisms occurring at the anode during the operation of the lithium battery, as well as some approaches for minimizing the degradation are reviewed

Forcespinning: An Alternative Method to Produce Metal Sulfides/Carbon Composite Nanofibers As Anode Materials for Lithium-Ion and Sodium-Ion Batteries

We present results on the Forcespinning (FS) of SnS2/SnO2/PAN and MoS2/PAN precursors for the mass production of SnS2/SnO2 /carbon and MoS2/C as anode materials for Lithium-ion and Sodium-ion batteries. The binary composite nanofiber electrodes of SnS2/SnO2/C and MoS2/C are produced using a scalable technique (FS) and subsequent thermal treatment (calcination). The composite nanofiber anodes were porous and flexible. The nanofiber preparation process involved the FS of SnS2/SnO2/PAN and MoS2/PAN precursors into nanofibers and subsequent stabilization in air at 280oC and calcination at 800oC under an inert atmosphere. The flexible composite nanofibers were directly used as working electrode in lithium-ion and sodium-ion batteries without a current collector, conducting additives, or binder. The SnS2/C and SnS2/SnO2/C electrodes delivered a specific capacity of 556 mAhg-1 and 965 mAhg-1 respectively during the first sodiation cycle. This initial high capacity is attributed to the irreversible formation of a stable SEI layer and to the porous structure of the Forcespun composite nanofibers. In the subsequent cycles, the SnS2/C electrode exhibited a much stable cycling performance compared to SnS2/SnO2/C i.e. 145 mAhg-1 was maintained after 50 cycles. The MoS2/C composite nanofiber electrodes delivered a good electrochemical performance and Coulombic efficiency when used for Lithium-ion batteries. This study provides a novel and feasible pathway for designing and developing promising anodes and cathodes for high-performance lithium ion and sodium-ion batteries. </jats:p