Investigation Of The Thermal And Electrochemical Performance Of LiMn₂O₄ Battery

Lithium ion battery has attracted extensive attention around the world ever since it was invented. In a few decades, lithium-ion battery have undergone a few technological revolutions, from small energy equipment to large power energy installations, in which lithium-ion battery plays an important role. But its wide application is limited to safety performance, especially the safety of hybrid lithium-ion battery. This paper focused on the research of thermoelectric chemical properties for LiMn2O4 battery with electrochemical-calorimetry equipment under different charge-discharge rates at 40 ℃ and 50 ℃, and the thermal analysis of the LiMnO2 battery at 50 ℃ was investigated. The dynamics properties for LiMn2O4 battery was investigated by cyclic voltammetry and electrochemical impedance spectroscopy and the structure for LiMn2O4 cathode material before and after charge and discharge was detected by means of XRD and SEM. There are some important conclusions as followed:1. LiMn2O4 battery showed no voltage plateau during discharge, and the capacity decreased with increasing temperature and increasing rates. The higher the temperature, the greater the rates, the larger the polarization of the internal battery. The discharge capacity for LiMn2O4 battery with 0.1 C rates at 50 ℃ and 40 ℃ was 100 and 108 mAh g-1, respectively.2. Heat flow curve for LiMn2O4 battery at 40 ℃ and 50 ℃ showed that an obvious endothermic peaks existed during charge at 0.1 C. The conclusion was that reversible heat was the main heat generation at low rates, while irreversible heat was dominated during-charge and discharge when the rates increased to 0.2 C. Heat production was increased with increasing temperature and rate. The value of △rSm at 0.1C under 40 ℃ and 50 ℃ was 0.442 J mol-1 K-1 and 0.022 J mol-1 K-1, respectively, and the ArGm at 0.1 C under 40 ℃ and 50 ℃ was-4.794 kJ mol-1 and -5.925 kJ mol-1, respectively.3. Comparing electrochemical and thermodynamic properties for LiMn2O4 and LiMnO2, it was showed that LiMnO2 battery has a higher specific capacity and a worser security than LiMn2O4, which displayed that the specific capacity at 0.1 C was 148.5 mAh g-1 for LiMnO2 battery and its heat production was 2-3 times than LiMn2O4 at the same charge-discharge rate.4. It can be seen that the structure of LiMn2O4 was damaged during charge and discharge at high rate from XRD diffraction pattern, resulting in a Li2MnO3 and MnO2 impurities. SEM showed that LiMn2O4 particles appeared agglomeration and manganese dissolved under high charge and discharge rate.5. Cyclic Voltammetry showed that LiMn2O4 battery has no good reversibility. AC impedance test showed diffusion coefficient reached to the maximum when voltage change between 3.8 V to 4.0 V at 0.1 C for LiMnn2O4 battery. The DLi+ is 1.898×10-13 cm2/s. Fully charged lithium ion diffusion coefficient was 1-2 orders of magnitude than fully discharged state. Rct after fully discharged was smaller than fully charged.