Investigation On LiCo_1/3Ni_1/3Mn_1/3O₂ Cathode Material And Safety Of Lithium-ion Battery

The explosion mechanism and the safety improvement of lithium ion batteries were studied in this paper. Based on this subject, Li_xNi_1/3Co_1/3Mn_1/3O₂ cathode materials with better thermal stability were synthesized and amended by cation and anion replacing or surface coating, the overcharge protection addictives and the flame-retardant addictives were also investigated. The reaction kinetics of Li_xNi_1/3Mn_1/3Co_1/3O₂ cathode was firstly discussed in detail. The M-doped(M=Cl, Br, Zn, Zr, Ge) and Mg₂(PO₄)₃-coated Li_xNi_1/3Co_1/3Mn_1/3O₂ cathode materials were firstly synthesized and studied. The flame-retardant addictives TCEP cooperating with overcharge protection addictives cycleohexyl benzene was firstly adding to the F-type LiMn₂O₄/C dynamic lithium-ion battery.The main heat sources of lithium batteries were tested and the explosion mechanism was analyzed under oven test, overcharge test and short-circuit. The results showed that the explosion of lithium ion battery in oven test was induced by the heat and the air in turn coming from the LixC6/Solvet reacton, electrolyte decomposition and cathode decomposition. The heat and the air coming from the excessiveLixC6/Solvet reacton casued the batteries thermal runawy under the batteries being overcharged .The heat coming from the current may let the batteries reach high temperature in a moment.Li_xNi_1/3Mn_1/3Co_1/3O₂ cathode materials were synthesized via co-precipitation method and the safety was tested.As a result, the material had the better layer structure and good electrochemical performance synthesized under the flowing condition, controlling the pH=11±0.2 at co-precipitation process, sintering 12-20h at 900℃, Li/M ratio in 1.05-1.10. DSC showed that Li_xNi_1/3Mn_1/3Co_1/3O₂ began decomposing at 211℃and reached maximum temperature at 269℃. The safety of of Li1.05Co1/3Ni1/3Mn1/3O2/C 18650 batteries was better than LiCoO₂ /C 18650 batteries under oven test, overcharged test and short circuit. The reaction kinetics of Li_xNi_1/3Mn_1/3Co_1/3O₂ cathode was firstly studied by Eis and the results illuminated that the lithium ion diffused step was the control step of the whole electrochemical reaction kinetics of Li_xNi_1/3Mn_1/3Co_1/3O₂ cathode.The cation and anion doped and surface modified of Li_xNi_1/3Co_1/3Mn_1/3O₂ were studied and the M-doped(M=Cl, Br, Zn, Zr, Ge) and Mg₂(PO₄)₃-coated Li_xNi_1/3Co_1/3Mn_1/3O₂ cathode materials were firstly synthesized and discussed. The results showed that 5%Cl^- or Br^- replacing O^2- of Li_xNi_1/3Co_1/3Mn_1/3O₂ materials especially for Cl^--doped can improve the discharge capacity, high current discharge ability and thermal stability. The discharge capacity order after transition metal Zn²⁺,Fe³⁺,Ti⁴⁺,Zr⁴⁺) doped was Ti⁴⁺-doped >no doped >Zr⁴⁺-doped =Fe³⁺ -doped >Zn²⁺-doped , the rate discharge ability order was Ti⁴⁺-doped> Zr⁴⁺-doped >Zn²⁺-doped no doped >Fe³⁺-doped and the thermal stability order was Ti⁴⁺-doped>Zr⁴⁺-doped>Zn²⁺-doped>Fe³⁺-doped= no doped. Ge⁴⁺or Sn⁴⁺-doped especially Ge⁴⁺-doped enhanced the dynamic performance and thermal stability. Mg3(PO4)2-coating improved high rate discharge capacity and thermal stability.The overcharge protection ability of polymeric additives cyclohexyl benzene (CHB) and biphenyl was studied.The more content cyclohexyl benzene of lithium ion battery made the better overcharge protection ability and the worse cycling performance of batteries, so the best ratio of CHB was 5-7%. 5-7% CHB or biphenyl can resist the batteries with safe-walve explosion ,while can not resist the batteries thermal runaway without safe-valve. Cyclohexyl benzene( 7%) or biphenyl( 5%) using jointly with triethyl amine(2% )can improve the battery overcharge protection ability and prevent the batteries from expanding. But the triethyl amine adding reduced the discharge capacity and increasing the internal resistance.5% biphenyl and 1%VC using jointly not only amended the batteries overcharge protection ability, but also had slightly effect on the electrochemical performance of lithium ion batteries.With batteries structure and manufacturing process mending, the F-type LiMn₂O₄/C dynamic lithium-ion batteries with high safety and high power were firstly manufactured. The results showed that the capacity of the battery with two cathode and two anode paralleling alternately was 5Ah and the capacity holding rate was 92.73% after 50 cycles at 4C rate charge-discharge current density . CHB and TCEP using jointly can improve the battery safety under oven test and overcharge test ,which was firstly brought forword.The electrolyte containing 6%TCEP and 6%CHB and cooper safety-lab on the batteries covers using together could greatly improved the batteries safety and the batteries can not explode or ignite when overcharged at 1C-10V or heated at 150℃oven test.