Modeling of Lithium Ion Batteries Employing Grand Canonical Monte Carlo and Multiscale Simulation

Abstract

In the current investigation modeling of two half cells (LiMn 2 O 4 cathode and carbon anode) followed by modeling of the complete cell of the battery employing Grand Canonical Monte Carlo simulations to evaluate open circuit potential and energetic of the process involved had been carried out. Current model takes into account the effect of electrolyte and temperature variations on various battery parameters like open circuit potential, cell current, cell voltage and free energy of Li + intercalation/deintercalation. Estimation of open circuit potential (OCV) of Lithium ion batteries becomes vital as it is a crucial parameter in (i) estimating diffusion coefficient of lithium in the electrode material during charge/discharge process, (ii) obtaining entropy of the reaction and internal energy calculations and (iii) understanding thermal runaway problems. The strong dependence of OCV with the state of charge (SOC) of the battery and temperature makes the prediction more difficult. To avoid computational tediousness, Grand Canonical Monte Carlo technique coupled with multiscale simulation is employed to predict experimental OCV of LiMn 2 O 4 cathode material in the presence of electrolyte solution.The lithium-ion battery is an ideal candidate for a wide variety of applications due to its light weight, high energy/power density and operating voltage. Lithium-ion (Li-ion) batteries most commonly used for energy storage in portable electronic devices exhibit numerous advantages compared to other present day battery technologies like lead acid, nickel metal hydrides etc. They provide one of the best energy-to-weight ratios, exhibit no memory effects and experience low self-discharge when not in use. These beneficial properties, as well as decreasing costs, have established Li-ion batteries as a leading candidate for the next generation of automotive and aerospace applications. 1,2 Compounds such as Li x CoO 2 , Li x Mn 2 O 4 , Li x NiO 2 and Li x Ni 0 . 5 Co 0 . 5 O 2 have been investigated recently as the positive materials for lithium batteries. 3 Manganese oxide spinel, in particular, is an attractive candidate for the positive electrodes because of its low cost and environmentally benign characteristics. [2][3][4] The fundamental understanding of the Lithium intercalation reaction in manganese oxide spinel and its effect on the energy of the intercalation reaction are of great interest. Estimation of open circuit potential (OCV) of Lithium ion batteries becomes vital as it is a crucial parameter in (i) estimating diffusion coefficient of lithium in the electrode material during charge/discharge process, (ii) obtaining entropy of the reaction and internal energy calculations and (iii) understanding thermal runaway problems. The strong dependence of OCV with the state of charge (SOC) of the battery and temperature makes the prediction more difficult. To avoid computational tediousness, Grand Canonical Monte Carlo technique coupled with multiscale simulation is employed to predict OCV of Li x Mn 2 O 4 cathode material....

A phenomenological thermodynamic approach for evaluating the energetics involved in the discharge of lithium ion battery

“…(III) DG a/e ¼ free energy change involved in the escape of Li ions from the solid/solution interface (anode/electrolyte). The excess energy required for an ion or electron to escape to vacuum from the solution phase or vice versa is called its surface potential, 22…”

“…where R is the Li-ion radius in Angstroms taken to be 0.9Å, 22 D is the thickness of the anode and considered to be 0.01Å for the calculations. The value of diffusion coefficient for Li ions in graphite is employed as 2.27 Â 10 À13 cm 2 s À1 , 21 that of cathode is 1 Â 10 À13 cm 2 s À1 , 21 and that for the concentration gradients (C ini a -C a a ) and (C ini c -C a c ) before and aer diffusion is assumed to be 0.1.…”

“…For every State of Charge (SoC) of Li-ion intercalation at the cathode, the potential value (V c ) and deintercalation at the anode (V a ) are taken from the literature. 22 DG II and DG III . The values of DG II and DG III obtained are negligible, in the order of 10 À6 to 10 À7 .…”

“…These results are analogous to the potentiostatic or galvanostatic intermittent techniques to determine the diffusion coefficient from the slope of charge versus time graph (Scheme 6). 22…”

“…Since, SEI is electrically insulating and sufficiently thick, it suppresses the decomposition of the electrolyte at the electrode surface. Hence, the actual deintercalation process takes place almost aer 0.2 V. 22 The formation energy of the insoluble Li carbonates and bicarbonates at SEI is calculated here at different porosity values.…”