The rated capacity of lithium polymer battery means total quantities of electricity or energy that can be withdrawn from a fully charged cell under specified conditions of discharge current. Rated capacity express by ampere-hours (Ah) or milliampere-hours (mAh) and energy quantity express by watt-hour (Wh)
Wh = Rated capacity (Ah) ¡¿ Average voltage until discharge end voltage (V)
Ah = Specified discharge current (A) ¡¿ Continuous discharge times until discharge end voltage (h)
2) What¡¯s Cycle Life of the battery?
Generally, the capacity of secondary battery decreases as it continues charging and discharging. At the begining, the capacity contains 1000 mAh, however as we charge and discharge for several times, it gets reduced as 980, 950, 900 mAh gradually. In general, cycle life is defined as the numbers of charging and discharging until the initial capacity decreases to its 60~80 %. For example, if the cycle life is 500 times, people think that battery should be replaced after using it 500 times. However, this is not true. 500 times means that under the condition of 100 % D.O.D. is short for depth of discharge. If the battery has the capacity of 1000mAh, cycle life counts by 100% charging/discharging (in other word 100% DOD) of its full capacity 1000mAh. But, in reality, it is general that we recharge it after using its capacity only 70-80 %. Under the condition of 80 % D.O.D, the cycle life increases by several-fold. Cycle life is the performance indicator that is based on this definition. Kokam SLPB's characteristics in various discharge condition have been shown on below graph and table.
Characteristics of cycle life based on the Depth of Discharge (D.O.D)
ITEMS
Criteria
Calculated
Cycle Life
Description
Remarks
DOD100%1)
Until 80%
of Initial Discharge Capacity
> 1,400 cycles
-
Base on
real test
DOD80%2)
> 2,500 cycles
Fitting function
: y = -(0.98E-7)x2-(5.46E-3)x+100
Expected
Cycle times
DOD20%3)
> 11,500 cycles
Fitting function
: y = -(1.697E-3)x +100.07
Expected
Cycle Times
1) Full Discharge 2)Partial Discharge 3)Shallow Discharge
Characteristics of cycle life based on the 100% D.O.D
Characteristics of cycle life based on the 80% D.O.D
Characteristics of cycle life based on the 20% D.O.D
