Analysis of heat generation due to open-circuit voltage hysteresis in lithium-ion cells

For the application of lithium-ion batteries, the thermal management is an important aspect, as the temperature is one of the main parameters for the behavior of Li-ion batteries. Several mechanisms influence the thermal behavior of Li-ion batteries, which can be split into reversible and irreversible losses. In literature, mostly Joule heat and reversible heat due to the entropy is discussed. With upcoming new active materials like silicon, which exhibits a significant charge-direction dependent voltage hysteresis, the losses due to the hysteresis become a more prominent factor. In this paper, we show the influence of the hysteresis losses for the most common active materials, which exhibit a voltage hysteresis. With a detailed analysis of calorimeter measurements, a true equilibrium potential can be calculated. The results show, that the equilibrium potential is not in the middle between both open-circuit voltage (OCV) curves as most of the heat due to hysteresis is generated during charging, which can have a significant influence on the thermal behavior of Li-ion batteries. For pure graphite cells 63 % and for silicon-graphite composite cells even 75 % of the hysteresis heat is generated while charging.