Electrical and Lithium Ion Dynamics in Three Main Components of Solid Electrolyte Interphase from Density Functional Theory Study

Abstract

Li2CO3, Li2O, and LiF are three important inorganic components that build up the “compact” layer of the solid electrolyte interphase which adhere tightly to the graphite anode of lithium ion batteries. The electrical conductivity and the lithium ion diffusivity within this layer are relevant to the rate performance of the graphite anode. Using density functional theory, the electronic structures of the three compounds are calculated and lithium migration dynamics are simulated using nudged elastic band method. Results show that all three components have insulating electronic structures, while lithium vacancies create some strongly localized holes that do not contribute much to the electronic conduction. Lithium diffusion in Li2CO3 and Li2O can be very fast when lithium vacancies are available. The energy barriers of lithium migration in Li2CO3 (ranges from 0.227 to 0.491 eV) and Li2O (0.152 eV) are comparable to that in graphite with the help of vacancies. However, lithium migration in LiF (energy barrier 0.729 eV) is much slower even when there are lithium vacancies in the lattice.

Multi-Scale Simulation of Heterogeneous Surface Film Growth Mechanisms in Lithium-Ion Batteries

“…We assume that intermediate As can be seen in Figure 3, net reactions considered in the continuum model are direct pathways from the reactants EC, Li + , and e − to the products C 2 H 4 , LC, LEDC, and the desorbed intermediate species Solid components.-The assumed solid products are LC and LEDC, which have been reported as being the main SEI film components. 6,7,12,31,35,36 LC is reported to be the most important component for SEI functionality 13,37 and formed with ECbased electrolytes. 7 A two-layer structure of the SEI is commonly reported, 13,38 with a dense inner film and a porous outer film.…”

“…31 LC forms a crystal structure with a monoclinic lattice system with a = 8.370 Å, b = 4.929 Å, c = 5.870 Å, and β = 117.1…”

Ion Diffusivity through the Solid Electrolyte Interphase in Lithium-Ion Batteries

“…The SEI film is a thin passivating layer that is initially formed, on both anode and cathode surfaces, from the reduction of the electrolyte during the first charging/discharging cycles. [2][3][4][5][6][7][8][9] It consists of a mixture of inorganic and organic products, such as LiF, Li 2 O and LiCO 3 , and (CH 2 OCO 2 Li) 2 , ROCO 2 Li and ROLi, where R is an organic group such as CH 2 , CH 3 , CH 2 CH 2 , CH 2 CH 3 , CH 2 CH 2 CH 3 that depends on the electrolyte solvent.10-24 Proposed structure models suggest that a dense layer of inorganic products is found near the electrode (inner layer) followed by a porous organic layer near the electrolyte/SEI interface (outer layer). [19][20][21] In carbon anodes, the SEI layer prevents further decomposition of the electrolyte by hindering electron transport from the electrode to the electrolyte, and by blocking the travel of solvent molecules to the active surface of the anode, where they can react with lithium ions and electrons.…”

“…The SEI film is a thin passivating layer that is initially formed, on both anode and cathode surfaces, from the reduction of the electrolyte during the first charging/discharging cycles. [2][3][4][5][6][7][8][9] It consists of a mixture of inorganic and organic products, such as LiF, Li 2 O and LiCO 3 , and (CH 2 OCO 2 Li) 2 , ROCO 2 Li and ROLi, where R is an organic group such as CH 2 , CH 3 , CH 2 CH 2 , CH 2 CH 3 , CH 2 CH 2 CH 3 that depends on the electrolyte solvent.…”

“…[77][78][79][80][81][82][83] Only a couple of theoretical studies reported diffusion barriers in Li 2 O at low temperature. 8,75 Chen et al 8 used DFT to investigate the electronic structure and the vacancy-assisted Li diffusion using NEB method; they showed that Li 2 O electronic structure had insulating character and obtained a diffusion barrier of 0.15 eV. Additionally, Guan et.…”