Computer simulation of positive electrode operation in lithium-ion battery: Optimization of active mass composition

Abstract

The work of the positive electrode (cathode) of a lithium-ion battery is simulated. The model of equally sized grains of three types: the intercalating agent grains with a volume fraction g, the electrolyte grains with a volume fraction g _i, and the carbon black grains with a volume fraction g _e is studied. The optimal composition of cathode active mass providing maximum specific capacity of cathode is determined. It is shown that a fraction of carbon black grains should be as small as possible: g _e = 0.35. The variation in the fraction of intercalating agent grains within the allowable limits (0 ≤ g ≤ 0.3) changes the main parameters of cathode active mass: a fraction of electrochemically active intercalating agent grains g* (g* < g); a specific surface area S, on which the electrochemical process proceeds; and the conductivity k* by lithium ions in the ionic percolation cluster, which forms in the cathode active mass. The parameters g* and S decrease and parameter k* steeply increases with decreasing g. Therefore, in the range of possible values of g, specific capacity of cathode reaches the maximum value at g = g _opt. The value of g _opt is determined under the galvanostatic mode of cathode discharge. The cathode working parameters: the active layer thickness, discharge time, specific capacity, and potential at the cathode active layer/interelectrode space interface at the instant of discharge completion are calculated in relation to a fraction of intercalating agent grains g.