The full cycle safety of high specific energy Li-ion battery
The high-specific energy Li-ion power battery and the safety have always been the focus of research.A 300 W·h/kg power Li-ion battery is prepared using high-nickel ternary materials LiNi0.8 Co0.1 Mn0.1 O2(NCM811)as the cathode active material and graphite-SiOx material as the anode active material,the full cycle safety changes of the batteries are analyzed from production to cycle decay to the capacity retention of 75%.The changes of thermal stability are evaluated by heating tests,the changes in internal short-circuit tolerance are evaluated by nail penetration tests.The mechanism of safety performance changes is analyzed by differential scanning calorimeter(DSC),SEM and four-probe testing.The thermal runaway temperatures of the batteries at 100%(before cycling),80%and 75%capacity retention are 167℃,161℃and 143℃,respectively.The penetration depths while thermal runaway are 1.99 mm,2.52 mm and 3.54 mm,respectively.As the cycles continue,the solid electrolyte interphase(SEI)film on the SiOx anode continues to increase significantly,leading to a decrease in thermal stability and an improvement in its internal short-circuit tolerance.The reduction of electrolytes leads to the decrease of thermal runaway heat release in the later stage of battery life.