1. LITHIUM ION-BATTERIES REFURBISHMENT BY : ANMOL NAYAK UTSAV VASUDEVAN

2. FACTS ABOUT Li-ion Li-ion between 300 and 500 discharge/charge cycles. Self-discharge rate 8% at 21 °C, 15% at 40 °C,31% at 60 °C (per month) Similar to a mechanical device that wears out faster with heavy use, so also does the depth of discharge (DoD) determine the cycle count. shorter the discharge (low DoD), the longer the battery will last. If at all possible, avoid full discharges and charge the battery more often between uses. Partial discharge on Li-ion is fine(This is contarary to the belief that one should completely discharge a phone before recharging it) The below data compares the number of discharge/charge cycles Li-ion can deliver at various DoD levels before the battery capacity drops to 70 percent. The number of discharge cycles depends on many conditions and includes charge voltage, temperature and load currents. A partial discharge reduces stress and prolongs battery life. Elevated temperature and high currents also affect cycle life. 100% DoD50% DoD25% DoD10% DoD 300 – 5001,200 – 1,5002,000 – 2,5003,750 – 4,700(Cycle life) Lithium-ion suffers from stress when exposed to heat, so does keeping a cell at a high charge voltage.

3. Table 3: Estimated recoverable capacity when storing Li-ion for one year at various temperatures Elevated temperature hastens capacity loss. The capacity cannot be restored. Not all Li-ion systems behave the same. 0°C25°C40°C60°C 98%96%85%75% (Roc)(@40% charge) 94%80%65%60%(Roc)(@100% charge) (after 3 months)

4. Table 4: Discharge cycles and capacity as a function of charge Every 0.10V drop below 4.20V/cell doubles the cycle; the retained capacity drops accordingly. Raising the voltage above 4.20V/cell stresses the battery and compromises safety. 4.20 |4.1| | 4.00||3.92| 300 – 500 | 600 – 1,0001|200 – 2,000|2,400 – 4,000| For safety reasons, lithium-ion cannot exceed 4.20V/cell.

6. SUMMARY -the temperatures should be kept around 25 degrees C(cooling pads+temperature sensor) -Dod should be kept low(below 30%) – use external portable chargers with sensors -voltage to which the batteries are charged should be around 3.9-4 V(depending on the device application)