More that you ever wanted to know! LOL Excerpt from
https://batteryuniversity.com/article/bu-808-how-to-prolong-lithium-based-batteries
Tables 2, 3 and 4 indicate general aging trends of common cobalt-based Li-ion batteries on depth-of-discharge, temperature and charge levels, Table 6 further looks at capacity loss when operating within given and discharge bandwidths. The tables do not address ultra-fast charging and high load discharges that will shorten battery life. No all batteries behave the same. |
Table 2 estimates the number of discharge/charge cycles Li-ion can deliver at various DoD levels before the battery capacity drops to 70 percent. DoD constitutes a full charge followed by a discharge to the indicated state-of-charge (SoC) level in the table.
NMC | LiPO4 | |
---|
Depth of Discharge | Discharge cycles | |
---|
100% DoD | ~300 | ~600 |
80% DoD | ~400 | ~900 |
60% DoD | ~600 | ~1,500 |
40% DoD | ~1,000 | ~3,000 |
20% DoD | ~2,000 | ~9,000 |
10% DoD | ~6,000 | ~15,000 |
Table 2: Cycle life as a function ofdepth of discharge*
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% |
4.13 | 400–700 | 90% |
4.06 | 600–1,000 | 81% |
4.00 | 850–1,500 | 73% |
3.92 | 1,200–2,000 | 65% |
3.85 | 2,400–4,000 | 60% |
Table 4: Discharge cycles and capacity as a function of charge voltage limit