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Pohjalainen E.,Aalto University | Rauhala T.,Aalto University | Valkeapaa M.,Aalto University | Kallioinen J.,Sachtleben Pigments Oy | Kallio T.,Aalto University
Journal of Physical Chemistry C | Year: 2015

Two different Li4Ti5O12 materials were investigated: smaller primary particle size forming large secondary particle aggregates (LTO-SP, surface area 22 m2/g) and larger primary particle size with less secondary particle aggregates (LTO-LP, surface area 7 m2/g). Both samples were synthesized using the same high temperature solid state synthesis but different end processing, resulting in the same crystalline structure but different particle morphology. At 0.1C measured discharge capacities were close to the theoretical capacity of Li4Ti5O12 (175 mAh/g), and similar capacities were obtained at low C-rates and room temperature for both LTO-SP and LTO-LP. However, higher capacities were obtained with LTO-SP at high C-rates and -20 °C indicating beneficial effect of small particle size and large surface area. Shapes of the charge/discharge curves were different for LTO-SP and LTO-LP, and this is attributed to the large surface area of LTO-SP which affects the electrochemical performance because of different reaction potentials at surface sites versus bulk. © 2015 American Chemical Society. Source

Bjorninen T.,Tampere University of Technology | Babar A.A.,Tampere University of Technology | Ukkonen L.,Tampere University of Technology | Sydanheimo L.,Tampere University of Technology | And 2 more authors.
Progress In Electromagnetics Research C | Year: 2012

The development of a compact metal mountable Radio-Frequency IDentification (RFID) tag antenna on a ceramic substrate based on Barium Titanate is presented. The performance limitations and design trade-offs of metal mountable RFID tag antennas are reviewed and the favorable features of a high-permittivity antenna substrate for the development of antennas for metal mountable RFID tags are discussed. The simulation-based tag antenna design process is outlined and the measured read range of the developed metal mountable tag on conductive platforms of various sizes is presented. Source

Pohjalainen E.,Aalto University | Rasanen S.,Kokkola University Consortium Chydenius | Jokinen M.,Aalto University | Yliniemi K.,Aalto University | And 7 more authors.
Journal of Power Sources | Year: 2013

Less expensive and greener aqueous electrode preparation processes are essential for the market penetration of lithium ion batteries to mid-scale applications. So far only carboxyl methyl cellulose (CMC) binder has been adopted for industrial use to fabricate carbon electrodes without harmful organic solvents but this process is prone to bacterial growth. In this study a new binder candidate, Acryl S020, is introduced for an aqueous preparation process that has been used for preparing Li4Ti5O 12 electrodes for lithium ion batteries. It is shown that with our water based process electrodes with capacities comparable to those electrodes fabricated with the conventional organic solvent based process with the PVDF binder are obtained. Moreover, our lithium titanate electrodes with the Acryl S020 binder show high capacity retention and they can be operated at sub-zero temperatures. Electrodes were also fabricated with pilot-scale gravure printing and slot-die coating methods and they showed stable cycles lives of 500 cycles. © 2012 Published by Elsevier B.V. All rights reserved. Source

Pohjalainen E.,Aalto University | Kallioinen J.,Sachtleben Pigments Oy | Kallio T.,Aalto University
Journal of Power Sources | Year: 2015

Traditionally electrodes for lithium ion batteries are manufactured using carbon additives to increase the conductivity. However, in case of lithium titanate, Li4Ti5O12 (LTO), carbon free electrodes have gathered some interest lately. Therefore two LTO materials synthesized using the same synthesis but different end milling process resulting in materials with different particle size and surface area are compared here using electrodes manufactured with and without carbon additives. Both LTO samples (LTO-SP with small primary particle size and high surface area, and LTO-LP with larger primary particle size and small surface area) produce similar capacities and voltages with or without carbon additives at low C-rates at the room temperature. However, at high C-rates and/or sub-zero temperatures electrodes with carbon additives produce higher capacities and smaller ohmic losses and this behavior is more pronounced for the LTO electrodes with smaller primary particle size and larger surface area. These results show that the feasibility of carbon free LTO electrodes depends on the properties of LTO affecting the morphology of the electrode and consequently, the transport properties. This is most pronounced under conditions where electron and Li+ ion transfer become limiting (high C-rates and low temperature). © 2015 Elsevier B.V. Source

Auvinen S.,Lappeenranta University of Technology | Alatalo M.,Lappeenranta University of Technology | Haario H.,Lappeenranta University of Technology | Vartiainen E.,Lappeenranta University of Technology | And 2 more authors.
Journal of Physical Chemistry C | Year: 2013

Wavelength-dependent refractive index functions (RIFs) of (TiO 2)n nanoparticles (n = 2, 8, 18, 28, or 38) have been calculated by using the data from our previous density functional theory and time-dependent density functional theory photoabsorption calculations. The results show significant blueshifts and increased anisotropy in the RIFs of the nanoparticles, when compared to experimental bulk values. On the basis of the results, we conclude that, in the case of these ultrasmall particles, the RIFs may depend notably on the shape and structure of the cluster and on the other hand the fundamental absorption characteristics do not depend much on the rather limited cluster size range. The results also support the proposition that, in light-scattering measurements, one should not use the bulk RIF to model nanosize particles, at least in the case of TiO2 particles. Our results shed some light into this computationally and experimentally very challenging area of nanoparticle properties. © 2013 American Chemical Society. Source

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