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

Abstract

Understanding the transport properties of the solid electrolyte interphase (SEI) is a critical piece in the development of lithium ion batteries (LIB) with better performance. We studied the lithium ion diffusivity in the main components of the SEI found in LIB with silicon anodes and performed classical molecular dynamics (MD) simulations on lithium fluoride (LiF), lithium oxide (Li 2 O) and lithium carbonate (Li 2 CO 3 ) in order to provide insights and to calculate the diffusion coefficients of Li-ions at temperatures in the range of 250 K to 400 K, which is within the LIB operating temperature range. We find a slight increase in the diffusivity as the temperature increases and since diffusion is noticeable at high temperatures, Li-ion diffusion in the range of 1300 K to 1800 K was also studied and the diffusion mechanisms involved in each SEI compound were analyzed. We observed that the predominant mechanisms of Li-ion diffusion included vacancy assisted and knock-off diffusion in LiF, direct exchange in Li 2 O, and vacancy and knock-off in Li 2 CO 3 . Moreover, we also evaluated the effect of applied electric fields in the diffusion of Li-ions at room temperature. The continuous demand for smart phones, tablets and other mobile devices has enormously promoted the improvement of Li-ion batteries. Moreover, volatile oil prices, pollution and climate change concerns have further increased the need for energy storage devices for renewable energies and electric vehicles. The latter applications require batteries with even higher energy density, better cycle life, better power performance, lower cost and improved safety.1 Therefore, improving and increasing the fundamental scientific knowledge of lithium ion batteries is essential for their continual advancement.A key component in lithium ion batteries is the solid electrolyte interphase (SEI) film. 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. 25 In silicon anodes, i.e., the huge volume expansion of the anode creates cracks in the SEI layer and generates new surfaces which are freshly exposed to the electrolyte. 26 In both carbon and si...

Quantum critical points in ferroelectric relaxors: Stuffed tungsten bronze K3Li2Ta5OSmith1, Gardner2, Morrison3 et al. 2018Phys. Rev. Materials3020View full textAdd to dashboardCite

“…As suggested for KLN, the two mechanisms seen in KLT are likely to be linked by Li ion motion, although the activation energies reported here are less than 1.27 eV reported for Li ionic conduction in LiTaO 3 [69] but comparable for other TTBs [70] containing Li, with activation energies of around 0.80 eV. At > 0.6 eV the activation energies for KLT are larger than the reported values of 0.15 and 0.12 eV for LiO 2 and Li 2 CO 3 [71,72]. However, for commercial applications, the ionic current per unit weight is a key parameter, and tantalate or niobate tungsten bronzes are not competitive with lighter weight Li oxides, carbonates, or sulfides.…”

Review on modeling of the anode solid electrolyte interphase (SEI) for lithium-ion batteries

“…Vacancy-mediated diffusion mechanisms (knock-off, direct exchange, and hopping) were reported in classical MD simulations of Li 2 CO 3 , LiF, and Li 2 O. 180 Pan et al 179 predicted the ionic conductivity of LiF is at least three orders of magnitude lower than that in Li 2 CO 3 and Li 2 O, and similar conclusions were drawn by Yildirim et al 181 An interesting study by Soto et al 182 showed that the SEI based on Na + is easier for Li + transport, and thus switching the cation Li + vs. Na + in a premade SEI can enhance the Li + conductivity. In addition to that, the low adsorption energy of Li adsorbates on LiF leads to low in-plane diffusion barrier of Li adatoms, 183 which was considered to be beneficial for restraining the Li dendrite growth.…”

Unraveling the Potassium Storage Mechanism in Graphite Foam

“…The vacancy-diffusion mechanism is popular in the processes of Li + insertion into graphite. [65,66] The diffusion coefficient D K here can be estimated by a hopping model with an effective jumping frequency (the details in the Supporting Information). The effective frequency can be obtained by the elementary jump frequencies with their degeneracies.…”