Investigation On The Thermal And Electrochemical Performance Of Nickel Rich Nickel Cobalt Manganese Oxide Composite Materials For Lithium Ion Cell

Heat production of lithium ion batteries is one of the main reasons for the safety of batteries.In this paper we studied the thermoelectric chemical performance of LiNi_0.5Co_0.2Mn_0.3O₂ battery using electrochemical-calorimetry and cyclic voltammetry,and evaluated the thermal and electrical performance of different kinds of cathode materials battery,finally the Mg doped LiNi_0.5Co_0.2Mn_0.3O₂ materials were calculation by first principles.1.The thermo-electric properties of LiNi_0.5Co_0.2Mn_0.3O₂ materials cell were studied by electrochemical-calorimetry method and cyclic voltammetry.It was found that ambient temperature and rate were the key factors which affect the capacity and quantity of heat of cell.With the increase of ambient temperature and rate,first discharge specific capacity reduce,voltage plateau reduce and its scope is narrowed and battery heat release increases.At low rate?0.2 C?,heat flow have many obvious exothermic peaks which mainly originate from the heat of electrode reaction.While at higher rate?0.5 C?1.0 C?2.0 C?,the battery polarization increases and polarization heat dominates.XRD diffraction peak position and intensity of LiNi_0.5Co_0.2Mn_0.3O₂ battery were accord with the standard fingerprints.From the SEM diagram,the surface morphology of the LiNi_0.5Co_0.2Mn_0.3O₂ battery increased with rate and temperature.Using data obtained from electrochemical-calorimetry at different conditions thermodynamic parameters were calculated.Chemical reaction entropy ?r Sm and Gibbs free energy change ?rGm were 1.781 J mol-1 k-1 and-9.16 kJ mol-1;2.The electrochemical and thermodynamic properties of LiNi_0.5Co_0.2Mn_0.3O₂,LiFePO4,LiMn2O4 and LiMnO2 materials at 50? were compared.The discharge specific capacity of all kinds of different cathode materials decreased with rate,LiMnO2 battery was the smallest,than is LiFePO4 battery,LiNi_0.5Co_0.2Mn_0.3O₂ battery was maximum;The absolute value of heat release LiNi_0.5Co_0.2Mn_0.3O₂ battery is minimum,LiMnO2 cell is maximum.At 0.2 C,heat release of batteries from small to large order was for LiNi_0.5Co_0.2Mn_0.3O₂,LiMn2O4 and LiFe PO4 and LiMnO2.At 2 C,LiFe PO4 battery is the largest,LiNi_0.5Co_0.2Mn_0.3O₂ battery was the smallest.The reaction enthalpy change ?H of various cathode materials batteries duringthe process of charge-discharge increased with the charge and discharge rate.At 0.2C,reaction enthalpy change ?H of LiFe PO4 battery was minimum and LiMnO2 cell was maximum.At 2.0 C,reaction enthalpy change of LiMn2O4 cell is the smallest and LiNi_0.5Co_0.2Mn_0.3O₂ battery is the largest.We can conclude that at lower rate,the safety hazard caused by heat release is relatively small,at higher rate,the safety hazard caused by heat release of LiNi_0.5Co_0.2Mn_0.3O₂ battery are more than other materials;3.Based on the density functional theory?DFT?with the generalized gradient approximation?GGA?in the PW91,the first principles calculations of LiNi_0.5Co_0.2Mn_0.3O₂ and Mg doped LiNi_0.5Co_0.2Mn_0.3O₂ were carried out.We draw the following conclusions: Mg doping does not change the basic structure and basic electrical properties of LiNi_0.5Co_0.2Mn_0.3O₂ materials,and the doped materials are still semiconductors.Therefore,a certain amount of Mg doping is beneficial to the system;Mg doping can effectively reduce the energy of the system and the band gap and help to improve the stability of the material.When the doping amount was 5%,band gap was 0.702 eV and was the minimum;Therefore,we must consider the appropriate amount of doping.