PDF Publication Title:
Text from PDF Page: 005
Condens. Matter 2021, 6, 22 5 of 9 3.3. Iron Reduction upon Lithium Intercalation The results obtained in the ideal case can be extended to model more realistic cathodic conditions by adding one Li+ ion per additional electron to the system, and then relaxing both the atomic positions and the electronic structure. The gained energy was calculated using the equation ∆Enon-ideal = EMIL-101(Fe)/mLi − EMIL-101(Fe) − mELi,atom (1) in which m is the number of intercalated Li atoms, and EMIL-101(Fe)/mLi, EMIL-101(Fe) and ELi,atom are ZPE-corrected electronic energies of the Li-intercalated MOF, free MOF and free Li atom, respectively. The energy given by Equation (1) can be converted to the voltage with respect to the Li reference anode via the Faraday constant (F) and replacing Li atom energy with the energy of Li metal as shown by Zhou et al. [53] by using the cohesive energy of Li metal Ecoh = ELi,atom – ELi,metal = 1.65 V [54]: V = −(EMIL-101(Fe)/mLi − EMIL-101(Fe) − mELi,metal)/mF = −(∆Enon-ideal − mEcoh,Li)/mF (2) The intercalation geometries and energies are reported in Figure 2 and Figure S2 of the SM. Figure 2 shows that at the B3LYP/def2-TZVP level, the addition of the first electron (i.e., intercalation of the first Li atom) gives a voltage of 2.79 V while the value obtained in the ideal case (without geometrical deformation) is 5.24 V. The reduction peaks in the experimental cyclic voltammogram reported by Shin et al. [12] for MIL-101(Fe) with axial Cl anion (MOF/carbon black weight ratio of 3:7) are at 2.99, 2.59, 2.42, 2.27 and 2.13 V, with respect to the Li/Li+ reference, while the corresponding peaks reported by Yamada et al. [17] for water-bound MIL-101(Fe) (mixed with Ketjen black and PTFE adhesive) are at 2.94, 3.08 and 3.50 V. The value obtained from our more realistic model (2.79 V) is in reasonable agreement with the experimental values but lower than the ideal value of 5.24 V. The difference between the ideal voltage of 5.24 V and the model value of 2.79 V indicates that part of the energy gained in the reduction reaction is lost in deforming the MIL-101(Fe) SBU in the presence of Li atom. A similar deformation effect has been found by Hafiz et al. [14] in their modeling of the FeO6 octahedron in the lithium iron phosphate cathode. The negligible difference between the experimental and theoretical values can be attributed to the sensitivity of the results to axially bound anions and molecules [12] and the matrix composition [17], in addition to the uncertainties inherent in computations (see Figure S2). For the intercalation of the second Li atom, both the ideal and non-ideal cases give the total gained energy of 9.22 eV (i.e., ∆Eideal = ∆Enon-ideal= −9.22 eV), showing no net loss of energy, due to the irreversible restructuring of the MOF model. In this case, the energy used for restructuring helps reach a more stable configuration with the release of energy. Intercalation of the third Li atom, however, releases 13.86 eV energy (∆Eideal= −6.93, but ∆Enon-ideal= −13.86 eV). Clearly, the energy gained is mostly the result of the structural disintegration of the fragment rather than an electron transfer process. In fact, intercalation of three Li atoms can form a Li-O-C ring-like structure on top of the SBUs, resulting in an irreversible destruction and decomposition of the cathode material when the Fe3+ atoms reduce beyond a certain point (e.g., 0.6 Li atoms per unit MIL- 53(Fe) [55]). This is consistent with the X-ray absorption spectroscopy (XAS) and cyclic voltammetry results of Shin et al. [12], showing a decay in the Li insertion capacity caused by irreversible accumulation of lithium. Significant structural distortion around Fe upon Li+ ion-intercalation/Fe-reduction has also been reported in the periodic unit cell modeling study of Combelles et al. on the MIL-53(Fe) MOF [56]. Similarly, other exchange-correlation schemes shown in Figure S2 of the SM yield an energy gain lower than the ideal case upon the addition of the first Li atom, and disintegration of the model structure with the addition of the third Li. However, according to the experimental study of Yamada et al. [17], at some MIL-101(Fe)/carbon mixing ratios, the disintegration does not occur. A possible healingPDF Image | Electrochemical Potential MIL-101(Fe) as Cathode Material in Li-Ion Batteries
PDF Search Title:
Electrochemical Potential MIL-101(Fe) as Cathode Material in Li-Ion BatteriesOriginal File Name Searched:
condensedmatter-06-00022.pdfDIY PDF Search: Google It | Yahoo | Bing
Sulfur Deposition on Carbon Nanofibers using Supercritical CO2 Sulfur Deposition on Carbon Nanofibers using Supercritical CO2. Gamma sulfur also known as mother of pearl sulfur and nacreous sulfur... More Info
CO2 Organic Rankine Cycle Experimenter Platform The supercritical CO2 phase change system is both a heat pump and organic rankine cycle which can be used for those purposes and as a supercritical extractor for advanced subcritical and supercritical extraction technology. Uses include producing nanoparticles, precious metal CO2 extraction, lithium battery recycling, and other applications... More Info
CONTACT TEL: 608-238-6001 Email: greg@infinityturbine.com (Standard Web Page)