Embedded Lithium-graphite Negative Electrode Charge And Discharge Mechanism And Electrochemical Properties Of The Theory

Li-ion secondary batteries have a great prospect in application and exploitation as an interesting kind of electrical source. Improving and enhancing the electrochemical performance of batteries mainly depends on the change-discharge property of negative electrode materials. Further researches into lithium intercalation graphite (LIG), which is used widely enough as a cathode, is very urgent to us. Cluster models and quantum chemical methods were used to study the charge- discharge mechanism, performance and their relationship with the structure of LIG for the purpose of providing a theoretical ground to the preparation, function improvement and application of materials.It was reported that the mechanism of lithium intercalation into or deintercalation from graphene crystal lattices only explained the interaction with the electrolyte, Li-ion and electrode material that exists only on the surface of graphite. Ab inito and DFT methods explored the charge-discharge process of LIG. The potential energy surface scan tells us that the lithium into or out of the graphene layers is the charge-discharge process of Li-ion secondary batteries which concurs with the continuous charge transfer between lithium and the graphite layers which synchronizes with the shift of the graphite layer stacking sequences between the ABAB type and the relatively stable AAAA type. The calculated storage energies of lithium intercalation into graphite are 177.3264kJ-morl and 128.6233kJ-mor' at the HF/6-31G* and B3LYP/6-31G* levels, respectively, which shows that LIG is also metastable. The result proves that LIG as a negative electrode material has the good charge-discharge reversible cycle and great work longevity.The very low electrode potential of LIG is an another important reason for the good electrochemical performance of Li-ion secondary batteries. We have obtained the electrode potential of six LIGs with the same C3 symmetry and different Li capacity, namely l/6Cmax, 2/6Cmax, 3/6 Cmax, 4/6Cmax, 5/6 Cmax and Cmax, where Cmax is 372Ah kg-1 which approaches toAbstractthe greatest lithum capacity of LIG, vs. Li+/Li as a negative electrode by using the theories of thermodynamics, electrochemistry and DFT. The calculation clearly shows that the electrode potential of LIG decreases sharply with its charge capacity to increase when LIG has lower charge capacity. Surprisingly, enough high charge capacity, calculated 250 Ah kg-1 and experimental 186 Ah kg-1, gives LIG a lowest charge-discharge flat, 0.11v as the calculated value and 0.10v as the experimental value. Therefore, batteries work effectively only when LIG has the pretty high charge capacity. Our theoretical conclusion about electrochemical performance of LIG is strongly consistent with experiments.