First-principles study: Effect of lithium and sodium intercalation in transition metal phosphates, MPO4 (M: Mn, Fe, Co)

Structural, Electronic, Mechanical, and Thermodynamic Properties of Na Deintercalation from Olivine NaMnPO4: First-Principles Study

“…Equation (2) was used to calculate the average voltage/average potential at each deintercalation stage, which is shown in Figure 4 . The voltage or potential required to remove the Na ions from Na x MnPO 4 ranged between 3.997 and 3.848 V. Moreover, the Na x Mn 2 O 4 potentials are consistent with previously calculated data for Mn-based isostructures olivine LiMnPO 4 [ 26 ] and maricite NaMnPO 4 [ 19 ].…”

“…The positive bulk, shear, and Young’s moduli of Na x MnPO 4 structures are relatively large, implying hardness, great resistance to volume change, deformation, and stiffness, respectively. The elastic characteristics of the maricite NaMnPO 4 polymorph were calculated to be higher than those reported here for the olivine phase by Lethole et al [ 26 ]. Furthermore, our calculated C 11 , C 22 , and C 33 values are much larger than C 44 , C 55 , and C 66 , implying that the materials have strong directional resistance to linear compressions against uniaxial pressures but limited resistance to shear deformations.…”

“…The states near the Fermi level are mostly Mn 3d and O 2p, with just minor contributions from the Na and P states. Due to the smaller band gap, it can be concluded that the spin-up states are primarily insulators (according to theoretical data [ 26 ]), whereas the spin-down states are semiconductors. The partial DOS of deintercalated Na x MPO 4 structures are presented in Figure 3 a–e.…”

“…The nine independent elastic constants (C ij ) of orthorhombic NaMPO 4 structures are shown in Table 3 . For orthorhombic systems, the Born mechanical stability criteria are [ 26 , 27 , 31 , 32 ]: …”

Enhancing the Electrochemical Performance of Olivine LiMnPO4 as Cathode Materials for Li-Ion Batteries by Ni–Fe Codoping

“…35,50 Such a small volume change (less than 7.3%) between lithiated/delithiated phases is generally required to obtain good cycling stability of these compounds, leading to a long life cycle during Li insertion/ extraction. 49 For a better understanding of the volume change, we have investigated the metal−oxygen bond lengths in all structures (see Table 2); the majority of the M−Oi bond lengths tighten with oxidation of the metal ion (M 2+ /M 3+ for lithiated/delithiated), which reflects the shrinking volume in the delithiated phases, whereas Mn−O3 in LMP and LMFP The charge density repartition plays a key role in shrinking the volume during Li-ion extraction. To this aim, charge density analysis was performed using Bader's topological partitioning scheme based on the charge densities generated by Quantum Espresso using the codes provided by Henkelman et al 52,53 Table 3 shows the atomic charges of all atoms in both lithiated and delithiated phases.…”