Jean-Paul Peres

On safety of lithium-ion cells

Abstract Safety of lithium-ion cells is mainly related to thermal reactivity of the components. Active materials play a major role: carbon materials because they directly influence the kinetics of reactions at the negative electrode, positive materials because of their relation with their respective delithiation state. Adequately substituted nickel based materials appear as the most stable positive materials. Electrolyte is mainly concerned through its reactivity with lithium of LixC6 and with O2 generated by the positive materials decomposition. Moreover, non-active materials, in particular binders, also clearly influence thermal stability and consequently safety behaviour of lithium-ion cells.

A new method to study Li-ion cell safety: laser beam initiated reactions on both charged negative and positive electrodes

Abstract The improvement of Li-ion batteries safety in abuse use is one of the key issues for their establishment in future hybrid or electrical vehicles. Such a challenge requires a perfect understanding of phenomena which could occur in abuse situation. A new technique for a better understanding of Li-ion cell safety has been so investigated. Reactions between electrolyte and charged electrodes (positive and negative just recovered from dismantled charged 4/5A cells) have been initiated by a laser beam, having a monitored intensity and time pulse. From such a device, a strong and controlled heating can be generated, in a very short time scale, on a defined electrode surface area. This localized heating, which is supposed to be similar to that could occur from a cell internal short-circuit, is able to initiate “self-propagation reactions” on charged negative and positive electrodes. This new technique has allowed a ranking of charged electrodes in terms of “self-propagation ability”. This range of new data has been compared to results obtained from classical thermal characterization methods (DSC, DTA) and results obtained from normalized abuse tests. Global charged negative and positive electrodes degradation mechanisms have been proposed in good agreement with the whole results. The safety of a done Li-ion cell seems mainly related to active negative and positive active materials, but also to other components of the electrodes, and especially additive carbons and aluminum collector of the positive side.