Transition Metal Dissolution from Single Crystal Li[Ni_1-x-yMn_xCo_y]O₂ and Li[Ni_1-xMn_x]O₂ Positive Electrodes Subjected to Aggresive Conditions

Transition metal dissolution from the positive electrode of Li-ion cells with subsequent deposition on the graphite negative electrode can contribute to the failure of Li-ion cells. The transition metal dissolution from various single crystal Li[Ni1-x-yMnxCoy]O-2 and Li[Ni1-xMnx]O-2 grades and subsequent depostion on the graphite negative electrode is quantified using scanning micro X-ray fluorescence spectroscopy. Graphite negative electrodes were extracted from Li[Ni1-x-yMnxCoy]O-2/graphite (NMC/graphite) and Li[Ni1-xMnx]O-2/graphite (NM/graphite) pouch cells after aggressive charge-discharge or storage protocols at 70 degrees C. In all cases, less than 1 mu g cm(-2) of transition metals were found on the graphite electrode. Most importantly, the amount of transition metals on the negative electrode was the least for Li[Ni0.6Mn0.4]O-2 (NM64), a medium nickel, cobalt-free material, compared to other NMC grades like NMC532, NMC622 and NMC811. Since Li-ion cells with NMC532, NMC622 and NMC811 have demonstrated excellent cycle and calendar life, one can expect that the lifetime of single crystal NM64 cells will not to be affected significantly by transition metal deposition.