Browsing by Subject "Electrochemical energy storage"

Now showing 1 - 4 of 4

Open Access
Analysis of errors in zero-free-parameter modeling approach to predict the voltage of electrochemical energy storage systems under arbitrary load
(Electrochemical Society, 2017) Ulgut, Burak; Uzundal, Can Berk; Özdemir, Elif
In a recently published article (J. Electrochem. Soc. 164 (2017) A1274-A1280), we described a new method to predict the voltage response of electrochemical energy storage systems during arbitrary load profiles. Our work shows that the impedance spectrum can be employed in the frequency domain in order to ultimately calculate the time domain behavior of the electrochemical energy storage system. The big advantage of this method is the fact that there are no free parameters and fits throughout. The present work deals with the sources of error in the above-mentioned prediction approach and looks for the effects of the various sources of error. The current analysis concludes that two big contributors to the overall error are the inaccuracies in the DC part of the prediction and the non-linearities that are not modeled by a linear impedance spectrum. Discussions are also made regarding ways to improve the performance of the modeling approach the most and where future work is going to be looking to improve.
Open Access
Lyotropic liquid crystalline mesophases made of salt-acid-surfactant systems for the synthesis of novel mesoporous lithium metal phosphates
(Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim, 2019) Uzunok, Işıl; Kim, J.; Çolak, Tuluhan O.; Kim, D.; Kim, H.; Kim, M.; Yamauchi, Y.; Dağ, Ömer
Mesoporous lithium metal phosphates are an important class of materials for the development of lithium ion batteries. However, there is a limited success in producing mesoporous lithium metal phosphates in the literature. Here, a lyotropic liquid crystalline (LLC) templating method was employed to synthesize the first examples of LiMPO4 (LMP) of Mn(II), Co(II), and Ni(II). A homogeneous aqueous solution of lithium and transition metal nitrate salts, phosphoric acid (PA), and surfactant (P123) can be spin coated or drop‐cast coated over glass slides to form the LLC mesophases which can be calcined into mesoporous amorphous LMPs (MA‐LMPs). The metal salts of Mn(II), Co(II) and Ni(II) produce MA‐LMPs that crystallize into olivine structures by heat treatment of the LLC mesophase. The Fe(II) compound undergoes air oxidation. Therefore, both Fe(II) and Fe(III) precursors produce a crystalline Li3Fe2(PO4)3 phase at over 400 °C. The MA‐LMPs show no reactivity towards lithium, however the crystalline iron compound exhibits electrochemical reactivity with lithium and a good electrochemical energy storage ability using a lithium‐ion battery test.
Open Access
Ultrathin titanium dioxide coatings on carbon nanotubes for stable lithium oxygen battery cathodes
(2016-10) Okur, Faruk
Fossil fuels hold the biggest share in energy sources for a very long time, especially in transportation, because of their appealing properties like very high energy efficiency, easy transport to any place in the world, very straightforward usage principle and they used to be quite abundant. However fossil fuel consumption results into release of harmful greenhouse gasses that causes global warming. On the other hand fossil fuels are not very abundant anymore and as a product that is formed in millions of years, the increasing energy demand worsens the situation. That is why renewable energy sources are more and more pronounced each day in the last half century. Nonetheless, irregular nature of the renewable energy sources makes them highly unpractical. Energy can only be harvested from renewable energy sources in specific time or specific locations, for instance, it is not possible to harvest energy from sun all day long or wind turbines can only be efficient in the places that there is sufficient wind power. This being the case, a clever approach is needed in order to be able to benefit from such convenient energy sources. Energy storage systems are the saviour in this picture since they can be used to store the energy that is produced from renewable energy sources and available when needed. For instance, lithium oxygen (Li-O2) batteries are a very promising candidates for a replacement of fossil fuels in transportation due to their very high theoretical gravimetric energy density. Oxygen is used as active cathode material unwanted side product formations on cathode-electrolyte interface. These side products are accumulating on the cathode surface upon battery cycling and result into drastic capacity fading. Especially carbon based materials are not stable against battery cycling in Li-O2 batteries even tough they have quite profitable features as a cathode material for Li-O2 batteries, such as; high surface area, low weight, high electrical conductivity, good oxygen reduction reaction activity etc. In this thesis study, the motivation is to increase the stability of carbon nanotubes (CNTs) while benefiting from their aforementioned advantages in Li-O2 batteries. In order to achieve this, an ultrathin and uniform titanium dioxide (TiO2) layer is coated on CNT surface by atomic layer deposition method. Prior to TiO2 coating an effective functionalization method is introduced to CNT surfaces to facilitate a uniform coating. Transmission electron microscopy imaging and x-ray diffractometer analysis are performed to observe coating properties. Xray photoelectron spectroscopy analysis and scanning electron microscopy imaging show the subsided side reactions, proving the stability of the TiO2 coated CNT cathode. TiO2 protective layer significantly prevents side product formation due to reduced cathode degradation and shows superior capacity retention compared to pristine CNT cathode upon full capacity battery cycling.
Open Access
Zero-free-parameter modeling approach to predict the voltage of batteries of different chemistries and supercapacitors under arbitrary load
(Electrochemical Society, Inc., 2017) Özdemir, E.; Uzundal, C. B.; Ulgut, B.
Performance modeling of electrochemical energy storage systems is gathering increasingly higher attention in recent years. With the ever increasing power demand of mobile applications, predicting voltage behavior under different load profiles is of utmost importance for communications, automotive and consumer electronics. The ideal modelling approach needs not only to accurately predict the response of the battery, but also be robust, easy to implement and have low computational complexity. We will present a new algorithm that is algebraically straightforward, that has no adjustable parameters and that can accurately predict the voltage response of batteries and supercapacitors. The approach works well in a variety of discharge profiles ranging from simple long DC discharge/charge profiles to pulse schemes based on drive schedules published by regulatory bodies. Our approach is based on Electrochemical Impedance Spectroscopy measurements done on the system to be predicted. The spectrum is used in the frequency domain without any further processing to predict the fast moving portion of the voltage in the frequency domain. DC response is added in through a straightforward lookup table. This widely applicable approach can predict the voltage of with less than 1% error, without any adjustable parameters to a large variety of discharge profiles.