Research And Develop Of The Flame-retardant Additives For Lithium Ion Battery

The main obstacle which puzzles the farther progress of large capacity dynamic lithium ion battery is the safety concern, especially when in abuse conditions, such as overcharge, over-discharge, high temperature and short circuit, the batteries easily catch fire or even explode. The aim of this paper is to improve the safety of dynamic lithium ion battery at the same time not to effect electrochemistry performance of battery as soon as possible.The feasible flame-retardant additives tri(β-chloroethyl) phosphate (TCEP), trimethl phosphate(TMP), tris(2,3-dichloropropyl) phosphate (TDCPP), tripheyl phosphate (TPP), trieresyl phosphate (TCP) can observably reduce the flammability of the electrolyte of 1mol/L LiPF₆/EC+DMC (1:1 in mass), the flame-retardant ability of trimethl phosphate(TMP) is best; the electrochemical influence of 5wt% above flame-retardant additives for the graphite / LiCoO₂ cells (18650) was researched, results show that the electrochemical influence of TCEP for the graphite / LiCoO₂ battery (18650) is least.10wt%TMP as additive of the electrolyte of 1mol/L LiPF₆/EC+DMC for graphite/ LiMn2O4 battery (18650), the decomposition of TMP on the surface of the graphite electrode at the first charge and discharge process will effect the formation of excellent solid electrolyte interface (SEI) layer, which make the capacity of batteries lose rapidly at the cycle progress. While the combination application of TMP and vinylene carbonate (VC) as additives for Li-ion batteries, VC will be firstly reduced and the reduction product polymerize to form excellent solid electrolyte interface (SEI) layer on the surface of graphite electrode, which prevents effectively the decomposition of TMP, not only improves their cycling performance, but also enhances safety of the battery. The electrochemical influence of TMP as additive of the electrolyte of 1mol/L LiPF₆/EC+DMC for the graphite / LiCoO₂ batteries(18650) is more obvious than that of graphite/ LiMn2O4 battery. The additive of 2wt%VC in electrolyte can enhance the coulombic efficiency of graphite / LiCoO₂ and graphite/ LiMn2O4 battery and reduce the electrochemical reaction resistance, which improve the cycle performance of batteries.The effects of electrolyte1mol/L LiPF₆/EC+DMC containing 3 wt %,7.5 wt % and 10 wt % TCEP on the safety and cycle performance of graphite / LiCoO₂ battery was researched. The results show when the electrolyte contains 7.5wt% TCEP, the decomposition voltage of TCEP is 4.7V, it could absorb heat consistently decomposition at the temperature of 250,280 and 320℃, the morphology image of the graphite negative electrode after battery 100 cycles is well, the temperature of battery fluctuated between 147 and 155℃when the ability of resisting high temperature of battery was tested at the oven temperature of 150℃, so TCEP can improve the safety of battery greatly. In addition, researches show that glossy both side copper foil as cathode current collector for Li-ion batteries is excelled than rough both side copper foil in both electrochemical and safety performance..The innovation of this paper is that the combination application of flame-retardant additive TMP and film forming additive vinylene carbonate (VC) is first used as additives for lithium ion battery, at the same time exploits TCEP as new flame-retardant additive for lithium ion battery.