No description available.

No description available.

Recently, Electric Vehicles (EVs) have received extensive consideration since they offer a more sustainable and greener transportation alternative compared to fossil-fuel propelled vehicles. Lithium-ion batteries are increasingly being considered in EVs due to their high energy density, slow loss of charge when not in use, and for lack of hysteresis effect. Conventionally, the batteries are connected in series to achieve the load voltage requirements. However, for the batteries with intrinsic discrepancies or different initial states, cell balancing is a concern because it is the weakest cell that determines the empty point for the battery and an undercharged series cell will shorten the lifetime of the entire pack. The imbalance potential of the battery behaves as the way of State-of-Charge (SOC) mismatch and it’s also temperature dependent. Therefore, in this thesis, an active cell balancing optimization was proposed and conducted in MATLAB to optimize battery unused capacity and thermal effect simultaneously based on bi-directional balancing system and pre-estimated SOC. The bi-directional balancing system was physically built based on “Fly-back” converter to compare balancing performance in discharging, idle, and plug-in charging mode. Moreover, a battery combined model worked collaboratively with robust state and parameter estimation strategies, namely Extended Kalman Filter (EKF) and Smooth Variable Structure Filter (SVSF) in order to estimate SOC for cell balancing. As a result, the proposed method can effectively optimize SOC mismatch around 2.5%. Meanwhile, more uniform temperature was achieved and the maximum temperature can be reduced about 7 ℃. / Thesis / Master of Applied Science (MASc)

No description available.

No description available.

This study investigates the economic benefits of installing a lithium-ion battery storage (lithium iron phosphate, LFP and lithium titanate, LTO) at an electric bus fast charging station.  It is conducted on a potential electric bus system in the Swedish city Västerås, and based on the existing bus schedules and routes as well as the local distribution system. The size of the energy storage as well as the maximum power outtake from the grid is optimized in order to minimize the total annual cost of the connection. The assessment of the distribution system shows that implementing an electric bus system based on opportunity charging in Västerås does not cause over-capacity in the 10 kV grid during normal feeding mode. However, grid reinforcements might become necessary to guarantee potential backup feeding modes. Batteries are not a cost effective option to decrease grid owner investments in new transformers. However, battery energy storage have the possibility to decrease the annual cost of connecting a fast charging station to the low-voltage grid. The main advantage of the storage system is to decrease the fees to the grid owner. Of the studied batteries, LTO is the most cost effective solution because of its larger possible depth-of-discharge for a given cycle life. The most important characteristics, that determine if a fast charging station could benefit economically from an energy storage, is the bus frequency. The longer the time in between buses and the higher the power demand, the more advantageous is the energy storage.

We are today experiencing an increasing demand for high energy density storage devices like the lithium-ion battery for applications in portable electronic devices, electric vehicles (EV) and as interim storage for renewable energy. High capacity retention and long cycle life are prerequisites, particularly for the EV market. The key for a long cycle life is the formation of a stable solid-electrolyte interphase (SEI) layer on the surface of the negative electrode, which typically forms on the first cycles due to decomposition reactions at the electrode-electrolyte interface. More control over the surface layer can be gained when the layer is generated prior to the battery operation. Such a layer can be tailored more easily and can reduce the loss of lithium inventory considerably. In this context, water-soluble electrode binders, e.g. sodium carboxymethyl cellulose (CMC-Na) and poly(acrylic acid) (PAA), have proven themselves exceptionally useful. Since the binder is a standard component in composite electrodes anyway, its integration into the electrode fabrication process is easily accomplished. This thesis work investigates the parameters that govern binder distribution in elec-trode coatings, control the stability and electrochemical performance of the elec-trode and that determine the composition of the surface layer. Several commonly used electrode materials (graphite, silicon and lithium titanate) have been applied in order to study the impact of the binder on the electrode morphology and the differ-ent electrode-electrolyte interfaces. The results are correlated with the electrochemi-cal performance and with the SEI composition obtained by in-house and synchro-tron-based photoelectron spectroscopy (PES). The results demonstrate that the poor swellability of these water-soluble binders leads to a protection of the active material, given that the surface coverage is high and the binder evenly distributed. Although on the laboratory scale electrode formu-lations with a high binder content are common, they have little practical use in commercial devices due to the high content of inactive material. As the binder con-tent is decreased, complete surface coverage is more difficult to achieve and the binder distribution is more strongly coupled to the particle-binder interactions during the preparation process. Moreover, it is demonstrated in this thesis how these inter-actions are related to the surface area of the electrode components applied, the surface composition and the electrochemistry of the electrode. As a result of the smaller binder contents the benefits provided by CMC-Na and PAA at the electrode surface are compromised and the performance differs less distinctly from electrodes fabricated with the conventional binder, i.e. poly(vinylidene difluoride) (PVdF). Composites of alloying and conversion materials, on the other hand, typically em-ploy binders in larger amounts. Despite the frequently noted resiliency to volume expansion, which is also a positive side effect of the poor swellability of the binder in the electrolyte, the protection of the surface and the formation of a more stable interface are the major cause for the improved electrochemical behaviour, com-pared to electrodes employing PVdF binders.

We consider the prediction algorithm and performance evaluation for prognostics and health management (PHM) problems, especially the prediction of remaining useful life (RUL) for the milling machine cutter and lithium ‐ ion battery. We modeled battery as a voltage source and internal resisters. By analyzing voltage change trend during discharge, we made the prediction of battery remain discharge time in one discharge cycle. By analyzing internal resistance change trend during multiple cycles, we were able to predict the battery remaining useful time during its life time. We showed that the battery rest profile is correlated with the RUL. Numerical results using the realistic battery aging data from NASA prognostics data repository yielded satisfactory performance for battery prognosis as measured by certain performance metrics. We built a battery test platform and simulated more usage pattern and verified the prediction algorithm. Prognostic performance metrics were used to compare different algorithms.

Thesis advisor: Dunwei Wang / In this work, we present our findings regarding the low-temperature, solid-state conversion of Cu₂S nanowires to Cu₂S/Cu₅FeS₄ rod-in-tube structures, Cu₂S/ZnS segmented nanowires, and a full conversion of Cu₂S nanowires to ZnS nanowires. These conversion reactions occur at temperatures as low as 105 degrees Celsius, a much lower temperature than those required for reported solid-state reactions. The key feature of the Cu₂S nanowires that enables such low conversion temperatures is the high ionic diffusivity of the Cu⁺ within a stable S sublattice. The second portion of this work will focus on the oxide-stabilization and utilization of TiSi₂ nanonets as a lithium-ion battery anode. This nanostructure, first synthesized in our lab, was previously demonstrated to possess a lithium storage capacity when cycled against a metallic Li electrode. However, with subsequent lithiation and delithiation cycles, the TiSi₂ nanonet structure was found to be unstable. By allowing a thin oxide layer to form on the surface of the nanonet, we were able to improve the capacity retention of the nanonets in a lithium-ion half-cell; 89.8% of the capacity of the oxide-coated TiSi₂ was retained after 300 cycles compared to 62.3% of the capacity of as-synthesized TiSi₂ nanonets after 300 cycles. The layered structure of C49 TiSi₂ exhibited in the nanonets allows for a specific capacity greater than 700 mAh g(-1), and the high electrical conductivity of the material in conjunction with the layered structure confer the ability to cycle the anode at rates of up to 6C, i.e., 10 minute charge and discharge cycles, while still maintaining more than 75% of the capacity at 1C, i.e., 1 hour charge and discharge cycles. / Thesis (MS) — Boston College, 2013. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

Current demands on lithium ion battery (LIB) technology include high capacity retention over a life time of many charge and discharge cycles. Maximizing battery longevity is still a major challenge partly due to electrode degradation as a function of repeated cycling. The intercalation of lithium ions into an active material causes the development of stress and strain in active electrode materials which can result in fracture and shifting that can in turn lead to capacity fade and eventual cell failure. The processes leading to active material degradation in cycling LIBs has been studied using a combination of acoustic emission (AE) and in situ X-ray diffraction (XRD) techniques. Safe, low cost custom electrochemical cells were designed and developed for use in battery AE and XRD experiments. These tools were used to monitor the time of material fracture through AE and link these events to lattice strain and phase composition as determined by XRD. Both anode and cathode materials were studied with an emphasis on graphite, silicon, and Li(Mn1.5Ni0.5)O4, and tin. A thermal analogy model for lithiation/delithiation induced fracture of spherical particles capable of predicting when AE should be detected in a cell containing a composite silicon electrode. The results of this work were used to develop an understanding of when and how active materials are degrading as well as to suggest methods of improving their performance and operational longevity.