Study On The Material Structure And Reliability Of Secondary Lithium Ion Battery

The secondary lithium ion battery has been widely used on portable electronic equipment due to high energy density,high power density,long cycling life and no obvious memory effect since 1995 when the secondary Li-ion battery began its commercialization.It also plays an important role in our daily life.But its safety reliability in daily life is always being challenged by a series of accidents or extreme situations since it is not only an energy storage material but also frequently used in daily life.Two kinds of Li-ion battery,which are commonly used in civil electronic equipment,were selected,i.e.prismatic Al-shell battery?replaceable?and Al-pouch battery?non-replaceable?.Both kinds of battery are composed by LiCoO₂ as positive material,PE as separator and graphite-2H as negative material.They both have similar rating capacity?-1500 mAh?.Material structure analysis,special reliability simulation,like discharging with different rate under 0?,external short,charging/discharging after dropping and thermal run away,were performed in this study.The purpose of this study is to characterize negative material,to prove thermal stability improvement if the separator coated with ceramic particles,to improve people's safety awareness during using wearable electronics powered by Li-ion battery.Charge/discharge capacity drop obviously during or after working in low-temperature?0??.Lithium plating,internal resistance?IR?increase and swollen occurred for the prismatic Al-shell battery after cycling under low-temperature while no lithium plating or swollen were observed for the Al-pouch Li-ion battery.According to the analysis,the mainly reason for this phenomena was the particle shape and particle size of the graphite.Obvious and stable blocking temperature was observed for both kinds of batteries during external short.The blocking temperature related to the shutdown temperature of separator.Simultaneourly the batteries were slightly swollen,which was caused by the breakdown of electrolyte.The Al-pouch battery with ceramic coated separator had a higher blocking temperature.During ARC test,the breakdown temperature of electrolyte of both batteries was almost the same,while the internal short temperature was quite different,which was mainly caused by different separator.No obvious IR increase,abnormal cycling,internal shorting were observed after multiple shock during dropping test.That said the manufacture processing of Li-ion battery has been more and more mature in these years.No obvious positive/negative particles'falling down,internal damage happened after multiple shock perpendicular to the rolling direction.But because of the strength difference of packing materials,Al-pouch deformed a lot after multiple shocking and it almost caused to leakage.