Factors which limit the cycle life of rechargeable lithium (metal) batteries

Failure mechanisms due to high charging rates of rechargeable lithium batteries comprised of Li metal anodes, Li_0.3MnO₂ cathodes (tunneled structure), and electrolyte solutions based on the combination of 1-3-dioxolane (DN), LiAsF₆, and tributylamine (antipolymerization stabilizer) were explored with the aid of postmortem analysis. It was found that at high charging rates, lithium deposition produces small grains, which are too reactive toward the electrolyte solution, in spite of the excellent passivation of lithium in this solution. In practical batteries such as AA cells with spirally wound configurations, the amount of solution is relatively small, and the solution is spread throughout the battery in a thin layer. Therefore, upon cycling, the Li-solution reactions deplete the amount of the solution below a critical value, so that only part of the active materials continues to function. This leads to a pronounced increase in the internal resistance of these batteries, which fail as a result of their high impedance and the decrease in the effective working electrodes area. Another failure mechanism relates to the extremely high charge-discharge current densities developed as the active electrode area decreases. These high currents, developed after prolonged cycling, lead to the formation of dendrites that short-circuit the battery, thus terminating its life.