Room 206 (2nd floor, restricted access)
23 October 2018 - 14h00
An Adaptive Charge Protocol for Lithium-lon Batteries
by Thusitha Asela Bandara from Verimag
Abstract: Lithium ion (Li ion) secondary batteries have become the prevalent technology for a range of electronic devices from consumer gadgets to high-end locomotives and energy storages in smart grids. The proliferation of mobile devices and recent developments in electric vehicles (EVs) have demanded the fast charging of these Li-ion batteries as a crucial factor for their own sustainability and stability. Nonetheless, the fast charging itself is a challenging issue due to a number of reasons. Some of them are the wider and rapidly varying cell chemistries, limitations of advanced electrochemical and electro-physical measurements in practical chargers and the needed assurance in safety, cycle life and the high charge-retention which are known to be declining during the fast charging process. To become a highly available electric power source, mainly three types of approaches can be seen in rechargeable battery industry. These three types can be identified as new cell-chemistries based batteries promising high energy and high power densities, new algorithm based charging methods assuring fast and ultra-fast charging, and new structural design based battery cells improving their performances within certain environmental conditions. Out of all these three, new algorithm based charging methods are very important as other two types also benefits from the same to enhance their charging performances.
This thesis demonstrates the proposed fast charging technique, which is based on non-linear voltammetry (NLV) with the use of a set of adaptation parameters related to the state of charge (SOC) and the state of health (SOH) of the battery. This study only focuses on its application with the Li-ion batteries even we believe that this can also be applied for most of the other rechargeable batteries. The newly developed technique allows non-linear voltage sweeping, with a faster change in voltage when the cell does not like to draw much current at a specific voltage status. Otherwise, it will sweep the voltage more slowly, when the battery is able to draw more current. This self-adjustment indirectly enables a dynamic charging current-profile based on the potential current demands of the battery-cell at each individual point of time with respect to its runtime SOC & SOH. Although this method lets the battery to adjust its own charging current, it will never impose any specific current on the system. Unlike other methods (such as CCCV), the NLV technique doesn’t use any predefined cut-off voltage as the termination condition. This natural charging adjust itself to terminate the process whenever it’s deemed necessary.