| The electric vehicle industry has witnessed explosive growth at home and abroad based on energy shortage and the country’s emphasis on the new energy industry.Lithiumion power batteries are widely used and the high-Nickel ternary cathode material are gradually favored than Lithium iron phosphate and lithium manganate materials,which are superior in energy density.The demand for driving range further promotes the further application of this material system.However,the safety issues with thermal runaway as the core is gradually highlighted.The following studies were carried out to solve this problem.Firstly,a newly type of EC-free electrolyte was reasonably designed according to the demand of high specific energy power battery.The aim was to construct a stable electrode-electrolyte interface and applied it to single crystal high nickel ternary(nickel cobalt manganese)/graphite anode power battery system.Secondly,in regard to the electrical performance of power battry.A stable electrochemical window can be formed at both conventional and high cut-off voltages.The capacity of the battery with conventional electrolyte was reduced to 738 m Ah after62 cycles,while the the battery with newly electrolyte was 944 m Ah after 500 stable cycles at the conventional cut-off voltage(4.3V).The final discharge capacity of conventional electrolyte and newly electrolyte was 912 m Ah and 1114 m Ah respectively,and the capacity retention rate after 300 cycles was 87.4% and 95% respectively at high cut-off voltage.Furthermore,in regard to the component of power battry.Differential scanning calorimeter was used to verify the heat release.The newly electrolyte can reduce the heat release of the cathode and anode electrode materials by 53% and 36%,respectively and delayed the phase transition temperature of the cathode electrode materials by about118℃.The mass spectrometer proved that the newly electrolyte can produce less O2,CO2 and H2,thus reduced the occurrence of side reactions.The electrode materials under different cycling conditions were qualitatively and quantitatively analyzed by X-ray photoelectron spectroscopy,and the elements of the stable interface layer were obtained.The morphology and distribution of elements were analyzed by Scanning Electron Microscope and Energy Dispersive Spectrometer.It is pointed out that the F,N and S elements produced under the action of the newly electrolyte can construct a more stable interfacial film,inhibit the generation of cracks in the electrode material,and reduce the side reaction between the electrode and the electrolyte.Finally,at the power battery macroscopic monomer level.The thermal runaway suppression effect of the two electrolytes in adiabatic and non-adiabatic environment was investigated by means of Accelerated Rate Calorimeter(ARC)and lateral heating.In an adiabatic environment,thermal analysis was performed by ARC.The newly electrolyte can increase the self-generated heat temperature T1 and the thermal runaway starting temperature T2 by 11.5℃ and 59.6℃ respectively,which has improved the inherent safety of the power battery.The maximum thermal runaway temperature T3 was reduced by 40℃,and the maximum temperature rise rate was reduced by 47%,which can significantly reduce the risk of thermal runaway of this battery system.In the nonadiabatic environment,the new electrolyte can reduce the maximum temperature by 95℃by using side heating to simulate the thermal runaway of the battery cell under real environment.The above research showed that the EC-free electrolyte of this paper had a better electrochemical cycling performance and safety performance than the traditional electrolyte in the application of SC-NCM 811/AG pouch cell.The thermal runaway mechanism of high specific energy power batteries could be explored by the research mode of macroscopic experiment and microscopic characterization at multiple levels and angle,which had a guiding significance for the performance exploration of power batteries of other systems and the development of new electrolytes. |
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