The effect of C-rate and cycling on Li[Ni۰.۵Co۰.۲Mn۰.۳O۲]/graphite ۱۸۶۵۰ cylindrical Li-ion batteries contains sulfide compounds as electrolyte additive

Herein, the electrochemical performance of Li[Ni۰.۵Co۰.۲Mn۰.۳O۲]/graphite ۱۸۶۵۰ cylindrical cell with sulfide compounds was studied. Nowadays, lithium-ion batteries have attracted a lot of attention as vehicle power supplies such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs) and electric vehicles (EVs). The use of lithium-ion batteries for electronic device creates new requirements for electrode materials, one of the factor is their high energy densities, high life cycle and fast charging and discharging function. To achieve high performance lithium ion batteries, the internal resistance consisting of lithium ion and electron transfer must be reduced. Among several lithium ion and electron transfer processes, lithium ion transfer (charge) at the electrode/electrolyte boundary is a fundamental process of the charge-discharge reaction in lithium ion batteries, however, little attention has been paid to the surface lithium ion transfer mechanism. We investigate the growth mechanism and operation of the SEI layer on the electrode.The results showed that the addition of a mixture of ۱ wt% methylene methyl disulfide (MMDS) and ۱ wt% trisomethyl silyl phosphate (TTSPi) to the electrolyte improved the solid electrolyte layer (SEI) compared to the cell without additive, which increases the capacity and stability of the charge and discharge cycle at different speeds. The rate of increase in capacity were ۱۶۲۹۳, ۲۲۷۵۷, ۲۸۷۱۹, ۲۱۸۹۷, ۱۰۵۵۸ and ۵۴۵۵ mAh respectively for speeds ۰.۲ C, ۰.۵ C, ۱.۰ C, ۱.۵ C, ۲.۰ C and ۲.۵ C for the cell containing additive mixture compared to cell without additive. As seen, the capacity difference increases to a speed of ۱.۵C and then decreases. Then, to evaluate the performance of the SEI layer, after each rate, the impedance of the cells containing additive and without additive was measured. It was observed that the impedance of the cell containing additive was lower for all speeds. The impedance in both cells after ۰.۲C decreases, but by ۰.۵C and higher rates shows an increasing trend, it can be concluded that different rates have different effects on the growth in the SEI layer, such that, lower rate cause more soft and lower changes and higher velocities cause more violent changes. The difference in impedance for cell containing additive compared to cell without additive is initially ۰.۰۷۵۲ ohms/cm۳ and for the speeds mentioned above is ۰.۱۵, ۱.۵۸, ۱.۹۷, ۲.۲۶ and ۲.۷۸ ohms/cm۳, respectively, that shows an increasing trend. It means slower growth of SEI layer resistance in cell containing additive and confirms the improvement of its structure during long cycles and different rates.On the other hand, it was noted that the capacity of the cell containing the additive is always higher, that is almost proportional to the growth behavior of the SEI layer and confirms that the added additive improves the electrochemical performance of the battery by improving the SEI layer and thus facilitating ion transfer mechanism and preventing electrode damage.Studies were also performed on cells with one type of additive, ۱wt% MMDS and ۱wt% TTSPi, but results have shown that these additives alone reduce battery performance which is consistent with results of other articles that study on laboratory cells.Then, cells containing a mixture of ۱ wt% MMSD and ۱ wt% TTSPi were prepared to further study about the effect of high rate on the growth mechanism of the SEI layer. In other words, each cell is affected by only one rate (a cell is affected by medium rate and the other is affected by high rate) and the speed of impedance changes for each velocity is examined.