| Li-ion battery, widely used as the secondary battery, plays an increasinglyimportant role. Following the increasing step of market requirement, computersimulation occupy a increasing proportion，after being brought into the research ofLi-ion battery materials.Density Function Theory (DFT), as the most useful theoretical foundation, hascorrectly explained many thermodynamic and dynamic problem of Li-ion batterymaterials, forecasted materials performances and designed functional materials，withan increasingly prominent role. Nevertheless, There are some weakness exist in thesimulation process with DFT. For example, it only calculates the ground state energyand forecasts the relevant performance. Besides, for the foundation of DFT bases onthe approximation of Born-Oppenheimer, neglects the effect of nucleus on systems.So it accounts for some prediction error.This thesis takes the lattice vibration that is ignored by DFT adopting theapproximation of Born-Oppenheimer as the entry point, and considers thethermodynamic effect from it. Specifically, correcting the predicted delithiationpotential through calculating the lattice vibration. Firstly, calculating the crystal latticevibration spectrum of Li、LiCoO2and Li□CoO2referred in the half-cell ofLiCoO2/Li, then calculating their relevant thermodynamic quantities after getting thedata of the crystal lattice vibration. Finally, based on the formula of predictingdelithiation potential previously, we can calculate the change value of delithiationpotential Vwith gotten thermodynamic quantities.With the first principle correction calculation, we find the Vis-95mV at300K, it means the previous predicted value is on a high side with about0.1V. Besides,as the temperature improves to350K, the Vbecomes113mV,that is consistentwith the case that the capacity would decrease after the temperature rises, and itillustrates that the lattice vibration is one of influence factors making the capacitydecreased as the temperature improves. |
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