A Guide To Reusing Old Lithium Batteries
Recycling of lithium-ion batteries: Recent advances and perspectives
BU-808: How to Prolong Lithium-based Batteries
LiPO4 = 9000 cycles at 20% DOD = 1800 full cycles possible at 20% DOD ( MAX )
Karachi 100 Ah 48V LiPO4 = Rs 165,000
20% DOD = 100 Ah x 48v x 0.2 = 960 watt hours = 0.96 KWH
1800 cycles = 1,728 kwh over life
Rs 165,000 / 1728 kwh = Rs 95 per kwh.
Capital cost per kwh = 165,000 / 0.96 kwh = Rs 171,875 per kwh
Actual lifetime of 18650 cells
Eleven new Li-ion were tested on a Cadex C7400 battery analyzer. All packs started at a capacity of 88–94% and decreased to 73–84% after 250 full discharge cycles. The 1500mAh pouch packs are used in mobile phones.
NMC battery In short, NMC batteries offer a combination of Nickel, Manganese and Cobalt. They are sometimes known as Lithium Manganese Cobalt Oxide batteries. NMC batteries have a high specific energy or power. This limitation of either 'energy' or 'power' makes them more common for use in power tools or electric vehicles.
A partial discharge reduces stress and prolongs battery life, so does a partial charge. Elevated temperature and high currents also affect cycle life.
* 100% DoD is a full cycle; 10% is very brief. Cycling in mid-state-of-charge would have best longevity.
Lithium-ion suffers from stress when exposed to heat, so does keeping a cell at a high charge voltage. A battery dwelling above 30°C (86°F) is considered elevated temperature and for most Li-ion a voltage above 4.10V/cell is deemed as high voltage. Exposing the battery to high temperature and dwelling in a full state-of-charge for an extended time can be more stressful than cycling. Table 3 demonstrates capacity loss as a function of temperature and SoC. Temperature 40% Charge 100% Charge 0°C 98% (after 1 year) 94% (after 1 year) 25°C 96% (after 1 year) 80% (after 1 year) 40°C 85% (after 1 year) 65% (after 1 year) 60°C 75% (after 1 year) 60% (after 3 months) Table 3: Estimated recoverable capacity when storing Li-ion for one year at various temperatures Elevated temperature hastens permanent capacity loss. Not all Li-ion systems behave the same.
Most Li-ions charge to 4.20V/cell, and every reduction in peak charge voltage of 0.10V/cell is said to double the cycle life. For example, a lithium-ion cell charged to 4.20V/cell typically delivers 300–500 cycles. If charged to only 4.10V/cell, the life can be prolonged to 600–1,000 cycles; 4.0V/cell should deliver 1,200–2,000 and 3.90V/cell should provide 2,400–4,000 cycles.
On the negative side, a lower peak charge voltage reduces the capacity the battery stores. As a simple guideline, every 70mV reduction in charge voltage lowers the overall capacity by 10 percent. Applying the peak charge voltage on a subsequent charge will restore the full capacity.
In terms of longevity, the optimal charge voltage is 3.92V/cell. Battery experts believe that this threshold eliminates all voltage-related stresses; going lower may not gain further benefits but induce other symptoms(See BU-808b: What causes Li-ion to die?) Table 4 summarizes the capacity as a function of charge levels. (All values are estimated; Energy Cells with higher voltage thresholds may deviate.) Charge Level* (V/cell) Discharge Cycles Available Stored Energy [4.30] [150–250] [110–115%] 4.25 200–350 105–110% 4.20 300–500 100% 4.15 400–700 90–95% 4.10 600–1,000 85–90% 4.05 850–1,500 80–85% 4.00 1,200–2,000 70–75% 3.90 2,400–4,000 60–65% 3.80 See note 35–40% 3.70 See note 30% and less Table 4: Discharge cycles and capacity as a function of charge voltage limit Every 0.10V drop below 4.20V/cell doubles the cycle but holds less capacity. Raising the voltage above 4.20V/cell would shorten the life. The readings reflect regular Li-ion charging to 4.20V/cell. Guideline: Every 70mV drop in charge voltage lowers the usable capacity by about 10%. Note: Partial charging negates the benefit of Li-ion in terms of high specific energy. * Similar life cycles apply for batteries with different voltage levels on full charge. Based on a new battery with 100% capacity when charged to the full voltage.
Experiment: Chalmers University of Technology, Sweden, reports that using a reduced charge level of 50% SOC increases the lifetime expectancy of the vehicle Li-ion battery by 44–130%.