How many times can a lithium-ion battery be charged and discharged?

Cycle life is commonly calculated by the number of full discharge cycles of a lithium-ion battery. In the process of use, an irreversible electrochemical reaction occurs inside the lithium battery, resulting in a decrease in capacity, such as decomposition of the electrolyte, deactivation of the active material, and collapse of the positive and negative structures, resulting in intercalation. such as a decrease in the number of deintercalated and deintercalated lithium ions.

According to different materials, the existing power batteries on the market are mainly lithium iron phosphate batteries, ternary lithium batteries (including NCA and NCM), lithium manganate batteries, lithium cobalt oxide batteries, nickel metal hydride batteries, titanium Lithium oxide batteries, etc. Among them, lithium iron phosphate battery is the mainstream battery type in China's electric vehicle market, but in recent years, the market growth rate is obviously inferior to ternary lithium battery.

The theoretical life of a ternary lithium battery is about 800 cycles, which is medium among commercially available lithium secondary batteries. Lithium iron phosphate is about 2,000 cycles, while lithium titanate is said to be capable of 10,000 cycles.

Current mainstream battery manufacturers promise 500 or more cycles (charging and discharging under standard conditions) for ternary batteries, but it is not possible to make the resistance values ??completely the same, and the cycle life is about 400 cycles.

We recommend that the SOC use window is 10%~90%. It is not recommended to perform deep charging and discharging, otherwise it will cause irreversible damage to the positive and negative structure of the battery. When calculated with shallow charging and shallow discharging, the cycle life is at least 1000 times. In addition, when lithium batteries are frequently discharged in high-rate and high-temperature environments, battery life is significantly reduced to less than 200 times.

There are three things to keep in mind when using lithium-ion batteries:

1. How to charge a new battery

If you use a lithium battery, please note that the battery will enter a dormant state after a certain amount of time, resulting in a lower capacity and shorter usage time than usual. Lithium batteries, however, are easily rejuvenated as long as 3 to 5 normal charge/discharge cycles can rejuvenate the battery and restore its normal capacity. Due to the characteristics of the lithium battery itself, there is almost no memory effect. Therefore, the user's new lithium battery does not require any special methods or equipment during the activation process. From my own practice as well as theory, this "natural rejuvenation" is best charged in a standard way from the beginning.

2. When should charging start in normal use?

Lithium batteries should be charged as often as possible due to their limited number of charge/discharge cycles. However, I found an experimental table on charge/discharge cycles for lithium-ion batteries. Data on cycle life are listed as follows:

Cycle life (10%DOD): >1000 times

Cycle life (100%DOD): >200 times

The principle of charging when the battery runs out should not be taken to extremes. There is a word as widely circulated as long charging. So, the saying goes, "It's best to let your machine's battery run out as much as possible and use auto-shutdown." This practice is really just a practice with nickel batteries, the purpose is to avoid memory effects, and unfortunately, it is also prevalent in lithium batteries. After being warned that the battery is low, there have been cases of people continuing to use the device without charging until it automatically shuts off. As a result, the example machine did not respond during subsequent charging and booting and had to be sent to customer service for overhaul. This is actually because the battery voltage is too low due to over-discharging to allow normal charging and power on.

3. The Right Approach to Lithium Batteries

In summary, the most important tips for charging and discharging lithium batteries in use are:

1. Follow standard charging times and procedures for the first three charges.

2. When the machine prompts that the power is too low, please start charging in time.

3. No special method is required to activate the lithium battery. Lithium batteries naturally rejuvenate with normal use of the machine. Sticking to the popular “first three 12-hour long charge triggers” method doesn’t really work.

Therefore, the pursuit of 12 hours of long charging and the use of lithium batteries for automatic shutdown are all wrong. If you have done something wrong in the past, correct it in time. It's never too late.