Abstract of doctoral thesis - Koutsouvelis Dionisios

"Optimization of Li type batteries efficiency"

Lithium batteries (Li) offer high power and energy density per unit volume and mass but are sensitive on the way they are operated and handled. Incorrect operation may lead to unacceptable conditions. They can be damaged, explode or even release hazardous materials.
These batteries are sensitive of their charge and discharge rate as well as their Depth Of Discharge (DoD). They can easily be destroyed when fully discharged and dangerous when inappropriately charged or discharged.
Electric cars as well as hybrid power stations with energy storage are some examples of systems that require these batteries to operate at their limits.
Reliability and safety of lithium batteries is often questioned and continuous monitoring of parameters that govern their correct operation is required.
Charge / discharge temperature is a factor that affects operation of Lithium batteries, their longevity as well as the number of charge and discharge cycles. Use of these batteries at unacceptable temperatures, causes premature faults and makes them dangerous. For example, charging a battery at temperatures below 0 ° C results in the formation of metallic lithium in the anode plate, which will eventually pass the battery separator and cause a short circuit in the battery and its ignition.
Allowable power discharge and available power of the lithium battery are parameters particularly affected by the operating temperature. It is of vital importance to create and preserve optimum operating temperature conditions in order to maximize the performance of these two parameters.
Li batteries, usually formed by serially connected cells, are greatly affected by cell balancing. When the serially connected cells are not balanced, i.e. they are in a different SOC (SOC = State Of Charge), then discharge is ended prematurely due to the strict limitation of the allowable lowest voltage on the cell.
The purpose of this doctoral thesis shall be:
• investigation and study of the parameters that affect Lithium battery operation and their contribution to improving battery performance. This shall be accomplished through extensive testing and analysis of these parameters
• development of smart algorithms for calculating the Lithium batteries SOC (State Of Charge) with methods that make its calculation more reliable.
• design and development of units that provide optimal operating temperature conditions with innovative techniques, ensuring better performance, longevity and safety of operation
• Development of innovative methods and techniques
 to reduce power loss during charging / discharging of Lithium batteries
 for cell balancing of Lithium batteries
 Safety algorithms to improve Lithium battery safety