How the service life of lithium-based batteries should be extended

Lithium chemistry is of great interest in battery research, so lithium-ion batteries can argue that lithium can save the future of batteries. We’re pleased because lithium ions have a lot of advantages over other chemicals in a lot of places. Currently, applications are growing and invading a previously dominated market by lead acids, such as backup and load balancing. Lithium electrons also power many satellites.

Lithium-ion batteries aren’t perfect yet, and they’re getting better. In particular, it has improved a lot more than before in terms of life and safety, and its production capacity is also greatly improved. Today, although lithium-ion is used in most devices and consumers are happy, the use of electric vehicles needs to improve before the power source can be accepted by the public.

How to extend battery life as a battery attendant. Each battery system has unique requirements, especially regarding charging speed, discharge depth, load, and adverse temperatures. Examine the causes of capacity loss, how performance is affected by rising internal resistance, what can be done to improve self-discharge, and the battery’s discharge capacity? You may also want to learn the basics of battery testing.


What are the causes of lithium-ion aging?

Lithium-ion batteries are ions moving between positive and negative electrodes. This mechanism should work forever, but performance degrades over time due to cycling, high temperatures, and aging. So manufacturers are very conservative and prescribe 300 to 500 lithium-ion discharge/charge cycles for most consumer products, which is their lifetime.

Lithium ion batteries can assess battery life by counting cycles, but this is not conclusive, as discharge depths can vary. There is no clear standard for what processes consist of (see BU-501: Discharge Basics). Some manufacturers suggest writing the battery replacement date, but this is not practical. Batteries may fail on specified dates due to overuse or improper temperature conditions; However, the date shown on the label is generally much shorter than the lifespan of most battery packs.

Battery performance is generally measured by capacity, a significant health indicator. Other elements, such as internal resistance and self-discharge, are of little use in predicting the end of the life of modern lithium-ion batteries.*

Figure 1 shows a decrease in the capacity of the caDEX lab batteries, which have 11 lithium polymer cycles. The 1500 mA sack batteries are used in mobile phones, where they are first charged at 1500 mA (1C) to 4.20 V/battery and then charged to 0.05 mA (75mA). Then the battery discharge voltage is 1500mA to 3.0V /cell, and the cycle is repeated. In 250 cycles, the capacity loss and performance of the lithium-ion battery were the same as expected.

Figure 1: Capacity drop as part of cycling

Eleven new lithium-ion batteries were tested on the cadet C7400 battery analyzer. All batteries start with an actual capacity of 88-94%, then slowly decline to 73-84% after 250 complete discharge cycles. 1500 mah bag is used on your phone.

Although batteries are supposed to be 100 percent full in the first year of use, they are usually prescribed to be higher than the battery’s actual capacity, and shelf life may also contribute to this loss. In addition, manufacturers often overestimate their batteries, knowing that few users will conduct spot checks. Instead of matching a single battery in a phone or tablet, which is required with multiple battery packs, there will be a broader range of performance. Lower-capacity storms can appear without the consumer’s knowledge.

The number of battery cycles is determined by the discharge depth, just as many mechanical devices accelerate wear after use. The lower the discharge (low voltage), the longer the battery life. If you want to maintain life, recharge your battery more often between uses. Partial combustion of Li-ion is acceptable. Without memory, batteries do not need periodic total releases to increase their life. The exception may be to calibrate the fuel meter on an intelligent battery or smart device regularly (see BU-603: How to Calibrate a ‘smart’ Battery)

The following table shows the capacity loss of cobalt-based lithium-ion batteries concerning pressure. Lithium iron phosphate and lithium titanate have lower voltages and are unsuitable for a given voltage reference.

Note: Show the general aging trend of ordinary cobalt-based lithium-ion batteries in discharge depth, temperature, and charge level. illustrates the capacity loss when operating within a given and discharge bandwidth range. Not addressing ultra-fast charging and high load discharges can shorten battery life. All batteries are the same.

Estimates the number of discharge/charge cycles of lithium-ion batteries at different levels before the battery capacity drops to 70%. After the Dod is fully charged, it discharges to the state of charge (SOC) level specified in the table.

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

Cycle life as a function of discharge depth

Partial discharge and partial charge reduce pressure and help extend battery life. But high temperature and high current can affect cycle life.

*100% DOD is an entire cycle. 10% is concise. When lithium ions have the most extended cycle life, it’s when they’re fully charged.

Lithium ions withstand pressure when exposed to high temperatures and high voltages. Batteries above 30 ° C (86 ° F) are considered high temperatures. But for lithium ions, a voltage of 4.10 V/battery is deemed to be increased. This hows the capacity loss as a function of temperature and SOC.

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)

The estimated recoverable capacity of storing lithium ions at different/elevated temperatures for one year accelerates permanent capacity loss.

Most lithium ions charge to 4.20 V/battery, and cycle life is said to double for every 0.10 V/battery decrease in peak voltage. For example, lithium-ion batteries can charge 4.20V/battery, and typically, lithium-ion batteries can extend life to 300-500 cycles.Charging to 4.10 V /cell provides 600-1,000 cycles, charging to 4.0 V /cell provides 1,200-2,000 cycles, and charging to 3.90 V /cell provides 2,400-4,000 cycles.

On the negative side, the battery’s capacity can be reduced by a lower peak charging voltage. A simple instruction manual states that a 10% reduction in total capacity is caused by a 70 millivolt reduction in charge voltage. Apply the peak charge voltage to a rechargeable battery.

The whole capacitance of the battery is restored. Battery experts believe that this threshold eliminates all voltage-related pressures and that lowering the voltage may not benefit. Still, they can cause other symptoms (see BU-808B: What Causes Lithium-ion death?). This summarizes the capacity as a function of charge level. (All values are estimated; Energy cells with higher voltage thresholds may deviate.)

[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

Discharge cycle and capacity as a function of charge voltage limitation

Drop to less than 4.20 V/cell doubling cycle per 0.10 V, but smaller capacity. Increasing the voltage above 4.20 volts per battery will shorten life. Reading shows regular lithium-ion charge to 4.20 V /cell.

Guideline: Approximately 10% reduction in available capacity is due to each 70mV reduction in charging voltage.

Note: Partial charging negates the benefits of lithium-ion in terms of high specific energy.

Battery life cycles are similar, and batteries have different voltage levels when fully charged.

Is based on a new type of battery that has 100% capacity when fully charged.

Experiment: Chalmers Institute of Technology, Sweden, reports that using 50% soc to reduce charging levels can extend the life of lithium-ion batteries in cars by 44-130%.

Most chargers, such as mobile phones, laptops, tablets, and digital cameras, have a charging voltage of 4.20 V /cell. Because consumers require long running times, the battery allows maximum capacity. On the other hand, industries like satellites and electric vehicles tend to choose lower voltage thresholds because they care more about longevity.

Lithium-ion batteries generally cannot exceed 4.20 V/cell for safety reasons.

Some NMCS are unsafe. Higher voltages increase capacity, but exceeding voltages shortens service life. Figure 5 shows the functional periodic count of charging voltage. At 4.35 V, standard lithium ions reduce the number of cycles by half.

Figure 5: Effect on cycle life at high charge voltages

Higher charge voltages increase capacity, reduce cycle times, reduce battery life and compromise safety.

A standard lithium-ion should not always be maintained at 4.20 V /cell as high voltages, except for the voltage threshold selected for specific applications. Lithium-ion chargers When the charging current is turned off, the battery voltage returns to its average level, similar to relaxing a muscle after strenuous exercise (see BU-409: Charging Lithium Ions).

Figure 6 illustrates the dynamic pressure test (DST), which reflects the loss of the lithium-ion battery when it is circulated at different charging and discharging frequencies. The maximum capacity loss is when the discharge charge reaches 25%. Cycling between 85% and 25% (green) has a longer life and provides more cycles than 100% charge and 50% discharge (dark blue). Battery capacity loss is minimal when charging 75% and discharging 65%. However, the battery is underutilized at this point. Degrades battery performance more slowly under normal conditions than at high voltages and exposure to high temperatures. (Nissan case)


Figure 6: Relationship between capacity loss and charge-discharge bandwidth

Charge-discharge lithium-ion batteries reduce battery utilization and partially extend their life.

  • Case, 1:75-65% soc, provides only 90,000 energy units (EU), but this is the most extended cycle life and uses a 10% battery.
  • Case 2:75-25% soc provides 150,000 EU, has 3000 cycles (up to 90% capacity), uses 50% battery.(Electric battery, new)*
  • Case 3:85-25% SOC delivers 120,000 euros, has 2000 cycles, uses 60% of the battery.
  • Case 4:100 to 25% soCs have 75% battery utilization and extended run time, but life is short. (Cell phones, drones, etc.)

*The period counts in Table 2 and Figure 6 differ. There is no clear explanation other than to assume differences in battery quality and test methods. But there are also differences between low-cost consumer goods and durable industrial grades. Water storage capacity declines more rapidly at elevated temperatures than at 20 ° C.

A complete cycle is required to supply the energy needed for the battery. This is about 250Wh /kg for modern energy cells, but cycle life is affected. All of this is linear; prolonging life reduces the energy by 60%, which is equivalent to adjusting the specific energy density from 250wh/kg to 150wh/kg and turning the particular energy density down. Also harnessing the power of batteries are consumer mobile phones. For industrial devices such as electric cars, batteries are usually at 60% of their actual capacity, which means they are limited to 85% charge and 25% discharge, thus extending their battery life.

Lithium-ion batteries can also improve the internal resistance of lithium-ion batteries by increasing the cycle depth. Figure 7 shows the sharp rise in the 61% cycle depth measured by the DC resistance method (BU-802A: How does rising internal resistance affect performance?). The increase in resistance is permanent.

Figure 7: The internal resistance increases sharply as the lithium-ion cycling depth increases.

Note: The DC and AC methods (green frame) provide different internal resistance readings.

Figure 8 Extrapolating from the data in Figure 6, an extrapolation program is used to extend the predicted cycle life of lithium-ion batteries by assuming that the battery capacity decays linearly with the number of cycles. If this is true, then a lithium-ion battery with 75-25% soc (blue) will fall back to 74% capacity after 14,000 cycles. If the battery is charged to 85% at the same discharge depth (green), its actual power drops to 64% after 14,000 cycles, and to 100% at the same charge depth (black), its ability drops to 48% after the cycle. Natural life expectancy tends to be lower than simulated for reasons not yet explored. (See BU-208: Bicycle Performance)

Figure 8: Prediction modeling of battery life by extrapolation [5]

Lithium-ion batteries are charged to three different SOC levels, and cycle life models are established.Lithium-ion batteries can extend battery life by limiting the range of charges but with less energy delivered.

This reflects the increased weight and initial cost of the battery. Battery manufacturers typically specify a cycle life of 80 dods. This is practical because the battery must retain some reserves even for everyday use (see BU-501: Basics about discharging, “What Constitutes a Discharge Cycle”); the DST (Dynamic Stress Test) cycle count differs from battery type, charge time, loading protocol, and operating temperature. In addition, the numbers that lithium-ion batteries can obtain in laboratory tests are not available in the field.


What can users do to extend battery life?

Environmental conditions, and not just recycling, interfere with the life of lithium-ion batteries. There’s nothing worse than having a fully charged battery at high temperatures. The battery pack will not suddenly die, but the running time will gradually decrease as the running time reduces the battery’s actual capacity.

Electric cars and satellites take advantage of low charging voltage to extend battery life. Similarly, lithium ion batteries can extend laptop batteries by lowering the charging voltage for consumer electronics.

The device should adopt a “long life” mode that keeps the battery voltage at 4.05 V /cell and provides about 80% soc to make this more desirable. One hour before travel, users request “full capacity” mode to charge the battery to 4.20 V /cell.

That raises the question, “Should I disconnect my laptop when it’s not used?” Under normal circumstances, this is not necessary, as lithium ion batteries will not recharge lithium ions after being fully charged. When the battery voltage drops to the point where it needs to be charged, could you do it again? Most users choose not to switch off, which is suitable and safe.

Older computers run hotter than modern laptops, and modern laptops have fewer fires. Ensure good ventilation when operating an electric unit with an air cooling unit, especially on a bed or pillow. Excellent laptops protect the internal components from extending battery life. Most consumer products have energy batteries, which should be charged at 1 degree Celsius or lower, and avoid so-called superfast chargers that can fill a lithium-ion battery in an hour.

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