How many times of 18650 lithium battery cycle life generally?

With the promotion of social energy conservation and environmental protection, more and more environmentally friendly products have been applied to the market. In the battery industry, the ternary lithium battery quickly occupied the market with numerous advantages and gradually replaced the traditional lead-acid battery. For the traditional battery, the ternary lithium battery has the advantages of long life, energy saving, no pollution, low maintenance cost, complete charge and discharge, light weight, etc. It is said that the life of the ternary lithium battery is long and to what extent?

Ternary lithium battery

What is a ternary lithium battery?

In nature, lithium is a light metal with a small atomic mass*, and its atomic weight is 6.94 g/mol, ρ = 0.53 g/cm3. Lithium is chemically active, and it is easy to lose electrons to be oxidized to Li+. Therefore, the standard electrode potential is negative, -3.045V, and the electrochemical equivalent * is small, 0.26g/Ah. These characteristics of lithium determine that it is a kind of Very high energy material. The ternary lithium battery refers to a lithium secondary battery using three kinds of transition metal oxides of nickel, cobalt and manganese as a positive electrode material. It fully integrates the good cycle performance of lithium cobaltate, the high specific capacity of lithium nickelate and the high safety and low cost of lithium manganite. It synthesizes nickel by molecular level mixing, doping, coating and surface modification. A multi-element synergistic composite lithium intercalation oxide and cobalt manganese. It is a lithium ion rechargeable battery that has been widely studied and applied.

Ternary lithium battery life

The so-called lithium battery life means that after the battery has been used for a period of time, the capacity is attenuated to 70% of the nominal capacity (room temperature 25 ° C, standard atmospheric pressure, and battery capacity discharged at 0.2 C), and the end of life can be considered. In the industry, the cycle life is generally calculated by the number of cycles in which the lithium battery is fully charged. During the process of use, irreversible electrochemical reactions occur inside the lithium battery, resulting in a decrease in capacity, such as decomposition of the electrolyte, deactivation of the active material, collapse of the positive and negative structures, and reduction in the number of lithium ion insertion and deintercalation. . Experiments have shown that higher rate discharges result in faster attenuation of the capacity. If the discharge current is lower, the battery voltage will approach the equilibrium voltage and release more energy.

The theoretical life of a ternary lithium battery is about 800 cycles, which is medium in commercial rechargeable lithium batteries. lithium iron phosphate is about 2000 times, and lithium titanate is said to reach 10,000 cycles. At present, the mainstream battery manufacturers promise more than 500 times in the ternary battery specifications produced by them (charge and discharge under standard conditions), but after the batteries are assembled into battery packs, due to consistency problems, mainly voltage and internal The resistance cannot be exactly the same, and its cycle life is about 400 times. The manufacturer recommends that the SOC use window be 10%~90%. It is not recommended to carry out deep charge and discharge. Otherwise, it will cause irreversible damage to the positive and negative structures of the battery. If it is calculated by shallow charge and shallow release, the cycle life is at least 1000 times. In addition, if the lithium battery is often discharged in a high rate and high temperature environment, the battery life will be greatly reduced to less than 200 times.

Lithium batteries have a service life of only two to three years.

Lithium batteries are generally capable of charging and discharging 300-500 times. It is best to partially discharge the lithium battery instead of completely discharging it, and try to avoid frequent full discharge. Once the battery is off the production line, the clock begins to move. Lithium batteries last for only two to three years, whether you use them or not.

A "lithium battery" is a type of battery using a lithium metal or a lithium alloy as a negative electrode material and using a non-aqueous electrolyte solution. Lithium metal batteries were first proposed and studied by Gilbert N. Lewis in 1912. In the 1970s, MS Whittingham proposed and began to study lithium-ion batteries. Due to the very active chemical properties of lithium metal, the processing, storage and use of lithium metal are very demanding on the environment. Therefore, lithium batteries have not been used for a long time. With the development of science and technology, lithium batteries have become the mainstream.

Lithium batteries can be roughly divided into two categories: lithium metal batteries and lithium ion batteries. Lithium-ion batteries do not contain metallic lithium and are rechargeable. The fifth-generation lithium-metal battery of rechargeable batteries was born in 1996, and its safety, specific capacity, self-discharge rate and performance price ratio are better than lithium-ion batteries. Due to its own high technical requirements, only a few companies in the country are producing such lithium metal batteries.

Use of lithium ion batteries

This part is the focus of this article. We will talk about it in three points.

1. How to charge a new battery

In the use of lithium batteries, it should be noted that after the battery is placed for a period of time, it enters a sleep state. At this time, the capacity is lower than the normal value, and the use time is also shortened. However, the lithium battery is easy to activate, as long as it is 3-5 times normal charging and discharging.

The battery cycle activates the battery and restores normal capacity. Due to the characteristics of the lithium battery itself, it is determined that it has almost no memory effect. Therefore, the new lithium battery in the user's mobile phone does not require special methods and equipment during the activation process. Not only in theory, but from my own practice, it is best to use a standard method of charging this "natural activation" method from the beginning.

For the "activation" problem of lithium batteries, there are many sayings: charging time must be more than 12 hours, repeated three times in order to activate the battery. This statement that "the first three charges have to be charged for more than 12 hours" is obviously a continuation of nickel batteries (such as nickel cadmium and nickel hydride). So this kind of statement can be said to be misinformation at the beginning. The charge and discharge characteristics of lithium and nickel batteries are very different, and it is very clear to tell you that all the serious formal technical information I have reviewed emphasizes that overcharge and over discharge will make lithium batteries, especially liquid lithium. Ion batteries cause great damage. Therefore, charging is preferably done in accordance with standard time and standard methods, especially for ultra-long charging of more than 12 hours. Usually, the charging method described in the mobile phone manual is a standard charging method suitable for the mobile phone.

In addition, the lithium battery phone or charger will automatically stop charging after the battery is fully charged, there is no so-called “turbulent” charging that the nickel battery charger has for 10 hours. In other words, if your lithium battery is full, it will be white charger on the charger. And none of us can guarantee that the characteristics of the battery's charge and discharge protection circuit will never change and the quality will be foolproof, so your battery will be on the edge of danger for a long time. This is another reason why we oppose long charging.

In addition, on some mobile phones, after charging for more than a certain period of time, if you do not remove the charger, then the system will not stop charging, and will start the discharge-charge cycle. Perhaps the manufacturer of this approach has its own purpose, but it is clearly unfavorable for the life of the battery and the phone/charger. At the same time, long charging takes a long time and often needs to be carried out at night. In the case of China's power grid, the voltage at night is high in many places and fluctuates greatly. As mentioned earlier, lithium batteries are very delicate, and they are much less resistant to fluctuations in charge and discharge than nickel, which in turn poses additional risks.

In addition, another aspect that cannot be ignored is that lithium batteries are also not suitable for over-discharge, and over-discharge is also disadvantageous for lithium batteries. This leads to the following problem.

2. When should I start charging during normal use?

In our forum, we can often see this statement, because the number of charge and discharge is limited, so the battery of the mobile phone should be recharged as much as possible. But I found an experimental table on the charge and discharge cycle of lithium-ion batteries. The data on cycle life are listed below:

Cycle life (10% DOD): >1000 times

Cycle life (100% DOD): >200 times