| Lithium-ion batteries are widely used in power tools,digital products,aerospace and military fields due to their light weight,high energy density,and no memory effects.Although lithium-ion batteries are widely used,they have potential safety hazards.The most important problem is the combustion and explosion caused by the thermal runaway of the battery.Lithium-ion battery needs to effectively control its thermal runaway during use,thus preventing battery fire and explosion accidents.Therefore,it is necessary to seek the thermal runaway propagation characteristics and laws of lithium-ion battery packs during charging and discharging processes.In this paper,a high-energy density 18650 NCM lithium-ion battery was used as the research object.The NCM lithium-ion battery was studied by advanced experiments and simulation methods such as cone calorimeter?CONE?,battery test system?BTS?and COMSOL.Fire hazard,heat generation and heat dissipation during charging and discharging processes,and thermal runaway propagation characteristics during charge and discharge of NCM lithium-ion battery pack.The main research work of this paper is summarized as follows:?1?The fire hazard of ternary lithium-ion batteries under different states of charge and radiant heat is analyzed.The heat release parameters,smoke parameters,toxicity parameters,and mass loss parameters of 18650 NCM lithium ion battery under radiant heat conditions of0%,25%,50%,75%,100%SOC and 25kW/m2,35kW/m2,50kW/m2 was measured and analyzed by cone calorimeter..A comprehensive evaluation index system for fire hazard of lithium ion batteries was constructed.The fire hazard index of 35 kW/m2 radiant heat and brand 1 battery under 25 kW/m2 was calculated.?2?The heat generation and heat dissipation characteristics of the NCM lithium ion battery during charging and discharging processes were studied.By testing the entropy change characteristics of Li[Ni8Co1Mn1]O2/Li and Graphite/Li CR2025 half-cells respectively,the entropy thermal characteristics of the positive and negative electrodes of NCM811/C lithium-ion battery under different SOC?state of charge?conditions are obtained.Furthermore,the electrochemical-thermal model of NCM811/C lithium-ion battery was established,which used to analyze the exothermic law of NCM811/C lithium-ion battery reaction heat,polarization heat and ohmic heat at different C-rates during charging and discharging processes.?3?The factors affecting the thermal runaway during the charge and discharge processes of NCM lithium-ion batteries were studied.Taking NCM811/C lithium ion battery as the research object,the lithium ion battery was charged and discharged to 50%SOC by 1C and2C under the heating condition of 300W heater by using the self-built lithium ion battery thermal runaway test platform.The battery thermal runaway reaction experiments without electricity was been done under the conditions of 0%,25%,50%,75%and 100%SOC.The results shows that the thermal runaway characteristics of the high-nickel NCM lithium-ion battery during heating and discharge processes.?4?The thermal runaway propagation characteristics of the NCM lithium-ion battery pack during charge and discharge were studied.Taking NCM811/C lithium-ion battery as the research object,the thermal model of NCM lithium-ion battery was established,and the heat generation and heat transfer characteristics of the battery during charging and discharging were analyzed.The NCM811/C was completed by using the self-built experimental platform.The lithium-ion battery pack was heated by the heater to induce thermal runaway of the whole battery pack.The thermal runaway propagation model of the three-dimensional lithium-ion battery was established and verified with the experimental results.The model was extended to3×3 parallel conditions.Under the condition of thermal runaway propagation model,the thermal runaway propagation characteristics of NCM811/C lithium-ion battery pack under the C-rate of 0.2C,0.5C,1C,2C,5C and 8C were analyzed,which the thermal runaway trigger temperature was set as 150?under 5C charging conditions.The thermal runaway propagation characteristics of the battery pack under the trigger temperature of 150°C,200°C,260°C and 300°C were analyzed.The thermal runaway propagation characteristics of the battery pack under the battery spacing of1mm,2mm,3mm and 4mm were analyzed.Those results can provide some guidance to control design of thermal runaway and thermal runaway propagation of lithium-ion batteries and ensuring the safe operation of lithium-ion batteries. |
PDF Full Text Request