ENERGY INSTITUTE Battery Research Group Analysis of Overcharge & Overdischarge Characteristics and Failure Detection of Li – ion Polymer Batteries Cem Kaypmaz 2008 İstanbul

Advanced Batteries Having a Battery Management System (BMS) integrated with cells is necessary and “State Deterimation”, is a critical issue. The in-situ characterization of a battery is an interest for the battery manufacturers, suppliers and the third party users. Independent from the battery chemistry either primary or secondary, batteries are designed to perform an application specific usage. Studies are focused on, Telecommunication, Aerospace, Advanced Electrified Vehicles (EV, HEV, PHEV) and most Military energy storage systems.

Battery State : Aging ? Ref: Jossen et al, 2005

Battery State

SoC State of Charge (SoC): (remaining capacity) / (capacity of fully charged battery) (Cn – Qb) / Cn Cn: nominal capacity Qb: net dicharged charge from a battery since the last SoC FULL 1 > SoC > 0 100% > SoC > 0%

SoH State of Health (SoH): (measured capacity) / (rated capacity) Cm / Cn Cm: measured capacity Cn: nominal capacity 1 > SoH > 0 As per definition, a battery is at its end of lifetime at SoH of 0.8. (Ref: Rand et al, 2004)

SoF State of Function (SoF): Case variable User (or designer) defined May differ according to the operating conditions

Failure Modes - I For many applications and battery types, failure modes of a battery could be listed and summarized as follows: A certain loss of effective capacity loss of active material, loss of conductivity in active mass Increase in internal resistance resulting active power loss electrolyte loss, loss of active surface

Failure Modes - II Increase in self discharge dendrites between the plates, poisoning of the electrolyte Internal short circuit formation of dendrites, Cell open circuit behavior grid corrosion, pasivation

Battery State: Conventional...

Li- ion Polymer Cells KOKAM SLPB Li-ion polymer Typical Capacity 3.3Ah Nominal Voltage 3.7V Life > 500cycles (Ref: KOKAM data sheet, 2008) 4 cells : Cycling Tests 8 cells: Overcharge Tests 8 cells: Overdischarge Tests

Experimental Setup Battery Test System (Cycler) 8 channel, 20V, 3A Frequency Analyser (P/G) 1 Mhz-10μHzs 10V, 20A power booster

Impedance Spectroscopy Changing the frequency of the excitation current gives the ability to detect different battery kinetics. Ref: Barsoukov et al, 2005).

The Model L: The inductive behavior (L) at high frequencies (4-5kHz) RΩ: Pure ohmic resistance of the cell (2-3 kHz) Rsei and Csei : The solid electrolyte interface (sei), a pasivation layer occurring on the anode (2kHz-20Hz) Rct and Cdl : the charge transfer resistance and the double layer capacity (2Hz- 100mHz). ZW: Warburg Impedance, the diffusion behavior of the battery (50mHz to 5 mHz) EMF: is the direct voltage produced inside the battery (Gerschler et al, 2008).

Tests The tests are planned to create abnormal conditions for the cells both in charge and discharge process. Normal operation voltage range of these cells declared by the manufacturer 2,7V – 4,2V and 3.3 Ah. For “failure creation” these limits were passed and the cells were forced to failure. Overcharge Test (OCT) Overdischarge Tests (ODT) Also Cycling Tests (CT) was performed in order to follow up “normal” conditions and parameter changes.

Test Procedures Cycling Test ProcedureOverdicharge Test Procedure Overcharge Test Procedure Balancing (OCT) Test Procedure

Test Results I II III

Test Results I II III IV V

Test Results

Acknowledgements

THANK YOU TUBITAK MRC ENERGY INSTITUE PK. 21, GEBZE,KOCAELİ