Thermal Safety and Runaway Blocking Mechanism for Lithium-Ion Batteries through Introducing Nanoscale Magnesium Hydroxide into the LiNi0.5Co0.2Mn0.3O2 Cathode

The thermal safety of pouch lithium-ion batteries (LIBs) with a nominal capacity of 2000 mA h is improved by adding nanoscale Mg(OH)2 into the LiNi0.5Co0.2Mn0.3O2 (NCM523) cathode, and the thermal runaway blocking mechanism is elucidated. The safety assessment includes nail penetration, impact, and overcharge tests. The results reveal that the main reasons for the improvement of cell safety can be ascribed to the unique characteristics of Mg(OH)2, including the insulation, compressibility, gas generation, and heat absorption during the thermal runaway process. In particular, adiabatic rate calorimeter measurements indicate that the decomposition of Mg(OH)2 can absorb the internal heat of the cell, resulting in the thermal runaway process of the cell being effectively interrupted and the thermal runaway temperature of the cell being increased from 120 to 176 °C. In addition, it is also shown that Mg(OH)2 in the NCM523 cathode enhances the rate performance and cycle stability of the cell, and the capacity retention rate of the cell is 83% after 300 cycles of 1.0 C, suggesting that this nanoscale Mg(OH)2 as a cathode safety additive has promising prospects in the practical application value in the LIBs.