| 1. |
- Araujo, Rafael B., et al.
(författare)
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First-principles investigation of Li ion diffusion in Li2FeSiO4
- 2013
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Ingår i: Solid State Ionics. - : Elsevier BV. - 0167-2738 .- 1872-7689. ; 247, s. 8-14
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Tidskriftsartikel (refereegranskat)abstract
- We have studied the Li-ion migration and the electrochemical performance of Li2FeSiO4 in the monoclinic crystal structure with P2(1) symmetry and the related delithiated system LiFeSiO4. For this purpose, the framework of the density functional theory within the generalized gradient approximation in conjunction with the climbing image nudged elastic band method was used. Addition of the Hubbard term was also considered in the Kohn-Sham Hamiltonian to better model the d electrons of the metal ions in this material. The calculated activation energies for Li ion migration are found to decrease by around 20% with the Hubbard term inclusion in the chosen diffusion pathways of Li2FeSiO4. Regarding the delithiated structure, the activation energies were found to be sensitive to the Hubbard term addition, however no general behavior such as in the lithiated structure was found. Furthermore, the diffusion coefficients were calculated considering temperatures of 300 K, 500 K, and 700 K.
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| 2. |
- Araujo, Rafael B., et al.
(författare)
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Insights in the electronic structure and redox reaction energy in LiFePO4 battery material from an accurate Tran-Blaha modified Becke Johnson potential
- 2015
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Ingår i: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 118:12
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Tidskriftsartikel (refereegranskat)abstract
- The main goals of this paper are to investigate the accuracy of the Tran-Blaha modified Becke Johnson (TB-mBJ) potential to predict the electronic structure of lithium iron phosphate and the related redox reaction energy with the lithium deintercalation process. The computed electronic structures show that the TB-mBJ method is able to partially localize Fe-3d electrons in LiFePO4 and FePO4 which usually is a problem for the generalized gradient approximation (GGA) due to the self interaction error. The energy band gap is also improved by the TB-mBJ calculations in comparison with the GGA results. It turned out, however, that the redox reaction energy evaluated by the TB-mBJ technique is not in good agreement with the measured one. It is speculated that this disagreement in the computed redox energy and the experimental value is due to the lack of a formal expression to evaluate the exchange and correlation energy. Therefore, the TB-mBJ is an efficient method to improve the prediction of the electronic structures coming form the standard GGA functional in LiFePO4 and FePO4. However, it does not appear to have the same efficiency for evaluating the redox reaction energies for the investigated system.
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| 3. |
- Araujo, Rafael B., et al.
(författare)
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Lithium transport investigation in LixFeSiO4 : A promising cathode material
- 2013
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Ingår i: Solid State Communications. - : Elsevier BV. - 0038-1098 .- 1879-2766. ; 173, s. 9-13
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we investigate lithium mobility in both Li 2FeSiO4 and its half-lithiated state LiFeSiO4 considering an orthorhombic crystal structure. We find that the calculated activation energy of Li+ ions hopping between adjacent equilibrium sites predicts two least hindered diffusion pathways in both materials. One of them is along the [100] direction characterizing an ionic diffusion in a straight line and the other follows a zig-zag way between the Fe-Si-O layers. We also show that diffusion of Li+ ions in the half-lithiated structure follows the same behavior as in the lithiated structure. As a whole, the activation energies for the investigated compounds present a greater value compared with the activation energies in currently used materials such as LiFePO4. The results were calculated in the framework of density functional theory in conjunction with the climbing image nudged elastic band method. The Hubbard term was added to the Kohn-Sham Hamiltonian to overcome the delocalization problem of d electrons. Furthermore, the diffusion coefficients were calculated for both structures considering temperatures ranging from 300 to 700 K.
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| 4. |
- Castro, Mayara Simões de Oliveira, et al.
(författare)
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Understanding peer feedback contributions using natural language processing
- 2023
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Ingår i: Responsive and sustainable educational futures. - : Springer Nature. ; , s. 399-414
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Konferensbidrag (refereegranskat)abstract
- Peer feedback has been widely used in computer-supported collaborative learning (CSCL) setting to improve students’ engagement with massive courses. Although the peer feedback process increases students’ self-regulatory practice, metacognition, and academic achievement, instructors need to go through large amounts of feedback text data which is much more time-consuming. To address this challenge, the present study proposes an automated content analysis approach to identify relevant categories in peer feedback based on traditional and sequence-based classifiers using TF-IDF and content-independent features. We use a data set from an extensive course (N = 231 students) in the setting of engineering higher education. In particular, a total of 2,444 peer feedback messages were analyzed. The CRF classification model based on the TF-IDF features achieved the best performance. The results illustrate that the ability to scale up the automatic analysis of peer feedback provides new opportunities for student-improved learning and improved teacher support in higher education at scale.
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| 5. |
- Kehoe, Laura, et al.
(författare)
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Make EU trade with Brazil sustainable
- 2019
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 364:6438, s. 341-
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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