Comprehensive Analysis on Dynamic Heat Generation of LiNi1/3Co1/3Mn1/3O2 Coin Cell under Overcharge

To meet the requirement of fast charging and high energy density of lithium ion battery, it is critical to further study the impact of current and voltage on the heat generation. In this work, dynamic heat generation of LiNi1/3Co1/3Mn1/3O2 coin cell under different current rates and overcharge voltages is investigated in detail using an in-situ micro-calorimetry. Polarization is the main factor causing rapid increase of heat generation at high current rate. The internal resistance and entropy coefficient show a great consistency of tendency and magnitude between irreversible and total heat. The excessive delithiation accelerates the polarization of electrode and the oxidation of electrolyte, leading to larger amount of heat generation. Besides, the heat release rate of charging process gets a steep increase as the cutoff voltage exceeds 4.5 V. Under the voltage range of 2.8-4.9 V, the heat generation from abusive range contributes more than 58% to the whole process. With the degradation of electrochemical performance, crystal structure and thermal stability also become worse after 50 cycles under higher cutoff voltage. These results provide basic data for the design of current rate and voltage range and the improvement of thermal management system. (C) 2019 The Electrochemical Society.