Discharge characteristic analysis of lithium-sulfur batteries considering the discontinuous deposit and transport-limited effects

The modeling research plays a crucial role in grasping the reaction mechanisms and forecasting the performance of lithium-sulfur (Li–S) batteries. A transient Li–S battery model including continuity, transportation, and reaction kinetics by simultaneously considering the discontinuous deposit of discharge product Li₂S and the transport limitation in the concentrated electrolyte, is developed to reveal the discharge phenomena. The effects of operating conditions and electrolyte and electrode properties on the discharge behaviors including voltage-capacity curve, energy density, profiles of solid product (ɛ_Li2S) and porosity (ɛ) at the cathode are quantitatively studied. It is found that low discharge rate is beneficial to the discharge capacity and utilization of cathode sulfur. Enhancing precipitate (S₈) solubility K_{sp, S8} and ionic diffusivity D_i improves voltage plateau and specific energy to varying degrees; the promotion of voltage plateau will be inconspicuous as electrode conductivity σ is enlarged over 0.1 S/m. With the rise of ɛ from 0.5 to 0.9, the specific capacity and the specific energy are expanded by around 5 times. When lengthening L_ca from 20 μm to 60 μm, the specific capacity ascends from 944.5 to 991.5 mAh/g_-S, whereas the growth rate of specific capacity and specific energy decreases gradually; the practical total energy almost increases linearly with thickness, yielding a 218.75% enhancement. With a certain period of relaxation, the recovered cell capacity after the high discharge rate is higher than that after the low discharge rate. This work may guide in designing electrodes and electrolytes and provide performance regulation strategies for Li–S batteries.