When lithium-ion batteries charging, their capacity gradually decreases with the number of charge and discharge cycles. The intuitive feeling is the energy is getting less and less. For example, a new smartphone can last a whole day after fully charged. But as you continue using it, a full charge may only last for half a day. This is the battery capacity has degraded over time.

Many factors affect the lifespan of lithium-ion batteries, such as temperature, charge and discharge currents, and cutoff voltage, etc. There are also three main reasons for lithium battery capacity degradation: increased internal resistance and polarization, loss of active electrode materials, and loss of lithium inventory. Different external factors have different effects on these three aspects.

The Impact of Charging Rate on the Lithium-Ion Batteries Life

When charging lithium-ion batteries, the charger has a maximum charging current, but the actual current is determined by the battery itself. The battery’s size, capacity, internal resistance, and age all play a role on current. If the amperes is too high, the following will happen:

• Overcharge: The battery may be overcharged, resulting in reduced performance and lifespan.

• Overheat: High amperes charging generates more heat, accelerate battery aging, and may cause risks like battery bulging and short circuit.

• Shorten battery life: Using the wrong charging current will shorten the lithium battery life.

Test results from Yang Gao show that when the charging rate and cutoff voltage exceed certain values, the capacity degradation rate of lithium batteries increases significantly. To reduce this degradation, you should choose appropriate current and voltage values.

In the experiment, Yang Gao used commercial 18650 batteries. He tested how different charging rates affect the capacity degradation rate.

Data Sources: www.sciencedirect.com/science/article/abs/pii/S0378775317305876

The test results are shown in the figures above. From Figure (A) and (B), we can conclude :

• At 0.5C, the degradation rate is 0.02% for the first 150 cycles, 0.0156% from 150 to 800 cycles, and 0.0214% after 800 cycles.

• At 0.8C, the degradation rate is 0.0243% for the first 150 cycles, 0.175% from 150 to 800 cycles, and 0.0209% after 800 cycles.

• At 1C, the degradation rate is 0.032% for the first 150 cycles, 0.0188% from 150 to 600 cycles, and 0.0271% after 600 cycles.

• At 1.2C, the degradation rate is 0.0472% for the first 100 cycles, 0.0226% from 100 to 400 cycles, and 0.0356% after 400 cycles.

• At 1.5C, the average degradation rate is 0.078%, much higher than at other charging rates.

It is clear that as the charging rate increases, the capacity degradation rate of the lithium battery also increases rapidly.

Additionally, Yang Gao also tested the changes in battery internal resistance under different charging rates and cutoff voltages.

• From figure (C): When the charging rate is below 1C, the change trend of internal resistance almost remains the same throughout battery cycles. But when it exceeds 1C, the internal resistance increases rapidly.

• From Figure (D): When the charging cutoff voltage is 4.3V, the internal resistance increases very quickly. At 4.1V and 4.2V, the internal resistance increases more slowly. This shows a high cutoff voltage reduces the battery’s performance.

Data Sources: www.sciencedirect.com/science/article/abs/pii/S0378775317305876

From the experiments, the tested 18650 battery’s maximum charge rate is 1C and the highest charge cutoff voltage is 4.2V. Exceeding these limits causes a rapid decline in battery performance. When they are lower than 1C and 4.2V, increasing the current and cutoff voltage does not greatly affect the battery capacity degradation rate.

Besides, when the charging current is below 1C, it mainly speeds up the loss of active electrode materials. Using a cutoff voltage lower than 4.2V primarily results in lithium inventory loss. However, when both the charging current and cutoff voltage exceed these two values, there is a significant acceleration in the loss of both active electrode materials and lithium inventory.

What is the Optimal Charging Current for Lithium Batteries of Different Capacities?

The best charging current for lithium batteries is 0.2C. This standard charging current enhances battery performance and extends its lifespan.

What is the Maximum Charging Current of Lithium Batteries?

The maximum charging current for lithium batteries should not exceed 1C. If it’s higher than 1C, the battery temperature becomes too high, seriously harming its cycle life.

What is the Minimum Charging Current of Lithium Batteries?

Too low charging current will make the charging time longer and affect the user experience. For example, a 1500mAh lithium battery takes 3 hours to fully charge at 0.5C, but requires 6 hours at 0.2C and over 11 hours at 0.1C.

To address this, smart chargers can auto-adjust the charging current based on the battery capacity, typically ranging from 0.5 to 1C. Larger capacity lithium batteries can accept higher charging currents.

Here are examples of calculation:

• For a 850mAh 16340 battery, charging at 0.5C means a current of 850mAh x 0.5 = 425mA. A recommended range is 400-500mA, and it takes around 2 hours to fully charge.

• For a higher-capacity 4000mAh 18650 battery, charging at 0.5C means a current of 4000mAh x 0.5 = 2000mA, i e 2A. It also takes about 2 hours to fully charge.

This charging rate balances battery life and user experience quite well. What’s more, some enthusiasts in the diving flashlight forums suggest using 0.2C to 0.5C in hot weather and 1C in cold weather. Many reliable charger manufacturers offer smart chargers with manual adjustment of charge currents. You can choose the optimal charging current according to your battery capacity.

Which XTAR Smart Charger Should I Choose for Different Capacities and Sizes of Lithium Batteries?

Some cheap chargers just use basic charging methods without precise control, often causing batteries to overcharge and overheat. In contrast, high-quality smart chargers can select the optimal charging currents based on battery capacity and health.

XTAR, a globally reliable manufacturer of lithium-ion battery chargers, offers different smart chargers to meet different needs. If you’re looking for an XTAR smart charger for your lithium-ion batteries, which one should you choose?

– Low capacity and small size lithium batteries such as 14500 and 16340.

Their have a maximum capacity of 1200mAh, a charging current of 0.5A is recommended. XTAR Mini Chargers such as MC1 PLUS and MC2 PLUS, are ideal for them. These chargers can auto-adjust the charging current to 0.5A or up to 1A based on the battery size.

– High capacity and big size lithium batteries such as 18650, 21700, and 26650.

For 18650, the capacity range from 2200mAh to 3600mAh with a maximum of 4000mAh. And for 21700 and 26650, it can reach up to 6000mAh. A higher charging rate of 1C is acceptable for them.

Due to their increased capacity and higher price, choosing a more intelligent and multifunctional charger is advisable. A good option are the XTAR Visible Smart Chargers. They allow you to manually select the maximum charging current with 2A or 3A. Additionally, these chargers feature a clear LCD screen that displays real-time charging status and can even test the battery real capacity and internal resistance. Popular models include the VC2SL, VC4SL, and VC8S.

Conclusion

Charging current is a key factor affecting the charging efficiency and lifespan of lithium-ion batteries. Too high amperes will lead to seriously overheat batteries and reduce their life.

To ensure lithium-ion batteries charging safety and extend cycle life, it’s best to use a high-quality smart charger and keep the charging current within the range of 0.5C to 1C.