| ABSTRACT:This thesis combining the basic features of Li-ion batteries with charging indexes puts forward an optimized charging curve based on polarization voltage characteristics, and considers the influence of temperature.Firstly charging time, charging capacity, the rate of CC-CV, internal resistance and other factors are studied in different conditions such as at different charging rates and different constant voltage. Aiming at the problem that calculating CV charging time is difficult, the rule of CV turning point is studied at different charge rates. The calculation formula of CC-CV charging time is modified.The Li-ion batteries polarization voltage characteristics are mainly studied, including the polarization time constant, the polarization rate characteristic, the polarization SOC characteristic, polarization dynamic characteristics. The time constant is decomposed into two orders of magnitude representing two Li-ion reaction processes. A linear model of polarization voltage varying with charging rates is established. The concept of polarization rate coefficient is proposed. The reason of the polarization voltage versus SOC is analyzed. The polarization voltage dynamic characteristics are researched including the lagging effect and the overshoot effect. Polarization voltage model in the full range of SOC is given.Then based on the polarization voltage model, considering increasing the charging speed and reducing polarization, a polarization charging curve is put forward taking time constant as the charging time length and polarization voltage as the limit. Computer simulations are carried with different internal resistances, time constants and voltage limits. Do charging experiments to verify the results.Finally considering the temperature in the process of charging, based on the experimental data and the simulation analysis of temperature change at different charging rates, initial charging SOC the charging curve is supplemented. |
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