Impact of Cl Doping on Electrochemical Performance in Orthosilicate (Li₂FeSiO₄): A Density Functional Theory Supported Experimental Approach

Abstract

Safe and high-capacity cathode materials are a long quest for commercial lithium-ion battery development. Among various searched cathode materials, LiFeSiO has taken the attention due to optimal working voltage, high elemental abundance, and low toxicity. However, as per our understanding and observation, the electrochemical performance of this material is significantly limited by the intrinsic low electronic conductivity and slow lithium-ion diffusion, which limits the practical capacity (a theoretical value of ∼330 mAh g). In this report, using first-principles density functional theory based approach, we demonstrate that chlorine doping on oxygen site can enhance the electronic conductivity of the electrode and concurrently improve the electrochemical performance. Experimentally, X-ray diffraction, X-ray photoelectron spectroscopy, and field-emission gun scanning electron microscopy elemental mapping confirms Cl doping in LiFeSiOCl/C (x ≤ 0.1), while electrochemical cycling performance demonstrated improved performance. The theoretical and experimental studies collectively predict that, via Cl doping, the lithium deinsertion voltage associated with the Fe/Fe and Fe/Fe redox couples can be reduced and electronic conductivity can be enhanced, which opens up the possibility of utilization of silicate-based cathode with carbonate-based commercial electrolyte. In view of potential and electronic conductivity benefits, our results indicate that Cl doping can be a promising low-cost method to improve the electrochemical performance of silicate-based cathode materials.

Sorption of CO2 on NaBr co-doped Li4SiO4 ceramics: Structural and kinetic analysis

“…However, faint diffraction peaks of NaBr were identified in SCT-NaBr-0.04, and stronger diffraction peaks of NaBr were also detected in SCT-NaBr-0.1 showing that the Na was not fully dispersed within the lattice. As reported for Cl-doped Li2FeSiO4 [43], both halogen ions (bromide and chloride) tended to be incorporated into the orthosilicate.…”

High Performance and Structural Stability of K and Cl Co-Doped LiNi0.5Co0.2Mn0.3O2 Cathode Materials in 4.6 Voltage

“…In contrast, it is obvious that the coulombic efficiency and initial discharge capacity of KCl-NCM sample is superior to those of NCM. The rate capacity of NCM and KCl-NCM is evaluated in Figures 5B,C, the discharge capacity of NCM samples drops dramatically with the current density increasing, and the discharge capacities of NCM are from 203.9 mAh g −1 at 0.1C to 152.74 and 116.0 mAh g −1 at 3 C and 5 C, which are only 74.9 and 56.9% of the discharge capacity at 0.1 C. However, the discharge capacities of the sample doped with K and Cl at 3 C and 5 C is, respectively, 175 and 162.5 mAh/g, corresponding to 83.7 and 77.7% of its capacity of 209.1 mAh/g at 0.1 C. Apparently, the rate performance of K and Cl substituted sample is remarkably enhanced compare with NCM, which may be due to the fact that K replaces the Li site and increases the diffusion channel of lithium ions because the radius of K + (rK+ = 1.33 Å) is higher than that of Li + (rLi+ = 0.76 Å), in addition, according to the literature (Singh et al, 2017), the doping of Cl plays a role in the improvement of the rate performance because the radius of Cl is larger than the radius of O. Figure 5D demonstrates the cycle performance of two samples at 1 C rate.…”

“…Because of the tangible that the radius of K + (rK+ = 1.33 Å) is much larger than that of Li + (rLi+ = 0.76 Å), we partially replace Li with K into the structure of NCM to reduce the mixing of the cations and improve the lithium ion diffusion coefficient. Simultaneously, we also partially replace O with Cl into the crystal structure because of the covalent radii and the electronegativity of Cl much than O (Singh et al, 2017), moreover, Cl doping is associated with the reinforcement of MnO 6 octahedral in the framework by the strong ionic Mn-Cl, Ni-Cl, and Co-Cl bonds (Kim et al, 2014), which makes the structure more stable and improves cyclic performance. Through the co-doping, cycle performance and rate performance of NCM are markedly improved.…”

High‐Voltage Layered Ternary Oxide Cathode Materials: Failure Mechanisms and Modification Methods†

“…Substituting K for part of Li into the structure of cathode materials could reduce the mixing of the cations, suppress phase transition, and improve the lithium‐ion diffusion coefficient (Figures 14a—j). Simultaneously, because the covalent radii and the electronegativity of Cl are larger than those of O, [ 162 ] the substitution of O by Cl is associated with the reinforcement of MnO 6 octahedral in the framework by the strong ionic Mn—Cl, Ni—Cl and Co—Cl bonds, [ 163 ] which makes the structure more stable. Thus, the impedance was reduced and the electrochemical properties of the material were greatly improved (Figures 14k—n).…”