Theoretical investigation of voltage-time behavior of Li2FeSiO4 as a lithium ion batteries cathode material

Three important challenges in cathode materials of lithium-ion batteries are the energy density, cost, and safety. Orthosilicate base cathodes provide safety considerations due to their high chemical and thermal stability and the presence of non-toxic elements, especially in Li2FeSiO4 and Li2MnSiO4 compounds. However, the other two challenges, those are, the cost and energy density, are the limiting factors for these cathodes. The purpose of this study is to attempt to better understand the mechanisms governing the electrochemical behavior of orthosilicate-based cathode material in order to provide solutions for improving the energy density of the battery. The cathode material used in this study was Pmn21 polymorph from Li2FeSiO4, synthesized by sol-gel nitrate method1-3. Voltage-time (voltage-capacity) behavior obtained from synthesized samples of Li2FeSiO4 cathode was investigated and theoretically analyzed. The relationship between voltagetime behavior and related factors, such as particle size, rate and reaction energy, was presented. The proposed relationship in this study was evaluated using theoretical calculations and experimental data and confirmed in the assumed boundary. Based on theoretical studies and evaluation of the results obtained in this study and similar studies, it was suggested that reducing the size of the grain and the appropriate additive can improve the properties of Orthosilicate-based cathodes of lithium-ion batteries. As a result, the slope of the voltage-time (so voltage-capacity) curve is linearly related to radical of applied current rate. Calculations in this work were performed using the full-potential linear augmented plane wave (FP-LAPW) method as implemented in the WIEN2K code within the framework of density 14th Annual Electrochemistry Seminar of Iran Materials and Energy Research Center (MERC), 12- 13 Dec, 2018 223 functional theory (DFT). The calculations were carried out in two different assumed categories of RMTs (atomic radial). In one of the categories, the RMT belonging to Fe, Li, O, and Si atoms is 1.75, 1.60, 1.42 and 1.42 a.u. It was name RFe = 1.75. In the other hand, the RMT of Fe, Li, O, and Si atoms are 2.00, 1.97, 1.42 and 1.42 a.u., respectively (name RFe = 2.0). The integrals were calculated on the Brillouin region with k-pionts of 4 × 5 × 5 of the Monkhorst-Pack (MP) network for the Pmn21 structure 4-6. The calculations were performed as ferromagnetic (FM) using LSDA, PBE-GGA, LDA + U and GGA + U methods.