Do lithium-ion batteries need to be fully charged?
Ternary lithium battery and lithium iron phosphate batteries are two types of lithium batteries currently widely used in new energy vehicles. The user manuals of vehicles using ternary lithium batteries will inform users that if they are not running long distances in daily use, try not to use them. The battery is fully charged, but it is advisable to charge it to 80%.
The user manual of lithium iron phosphate models will tell users that it is best to fully charge the battery once a week. They are both lithium batteries, so why are there such significant differences in use? In this article, we will talk about this topic.
Table of Contents
The principle of lithium ion battery
The directed motion of the electrons forms the electric current. The current flows from the positive to the negative, but it is essentially the flow of electrons from the negative to the positive. And many substances in nature have electrons, and if we can artificially control the movement of these electrons, then we can make batteries.
The picture above is the structure of the world’s first battery, which can generate electric current using copper sheets, zinc sheets and salt water. Although we don’t know the specific principle, we can definitely imagine that the reason why it can discharge is that the movement of electrons essentially occurs. Let’s take a look at how zinc and copper generate electric current.
We all know that an atom is composed of a nucleus and an outer shell of electrons. Zinc has two electrons in its outermost shell. Because it is very active, it is more prone to losing electrons. There is an electron in the outermost layer of the nucleus of the copper element. Although it is more inclined to lose electrons, it is not as active as zinc, so copper is more inclined to gain electrons than zinc.
So when we connect the copper sheet and the zinc sheet with wires, the outer electrons of the zinc element will move toward the copper sheet, thus causing directional movement of electrons and generating current.
But such batteries are still unusable. Because zinc loses electrons and becomes positively charged zinc ions, the positive and negative charges attract each other, which attracts the electrons and prevents them from moving further toward copper. Therefore, this structure cannot continue to generate current.
So what can be done to generate stable current? The answer is to add electrolyte. Whenever a zinc atom loses electrons to produce zinc ions, the zinc ions will enter the electrolyte and flow to the copper through the electrolyte. This will prevent the electrons from being adsorbed, allowing the electrons to continue to flow to generate current.
It’s just that this battery is disposable and cannot be recharged. The principle of lithium batteries is the same as above, relying on the migration of electrons to generate current. The difference is that lithium batteries can be recharged.
The cathode of a lithium battery is a lithium compound, such as ternary lithium or lithium iron phosphate, and the anode is graphite. During charging, electrons from the cathode flow from the external circuit to the anode under the attraction of the positive voltage of the power supply. At the same time, the lithium ions generated by the cathode enter the graphite of the anode through the electrolyte.
Why is it not recommended to fully charge ternary lithium battery?
This is mainly related to the characteristics of the cathode material. As mentioned earlier, lithium batteries essentially rely on the back and forth movement of lithium ions and electrons to generate current and store electricity. During charging, electrons and lithium ions are ejected from the cathode and come to the anode. During discharge, lithium ions and electrons are released from the anode and come to the cathode.
If lithium ions flow to the cathode during charging and the cathode still retains the position of lithium ions during discharge, then the battery capacity will be difficult to decay. If lithium ions flow to the cathode during charging, but the vacancies are occupied by other substances, then part of the lithium ions in the cathode will have nowhere to go during discharge, which will cause the battery capacity to decay.
The cathode material of the ternary lithium battery is unstable, and the divalent nickel ions and lithium ions in it have similar diameters. When charging, the lithium ions all run to the anode. At this time, some nickel ions may occupy the position of lithium ions, causing battery capacity to decline.
Therefore, when designing the battery, the number of cathode materials in ternary lithium batteries will be greater than the anode materials. Simply put, it provides more lithium ions and space to store lithium ions, which can ensure the stability of the capacity. But this brings a new problem, that is, the anode does not have so much space to accommodate all the lithium ions in the battery during charging.
This requires caution when charging. Charging should be stopped in time after the anode is full of lithium ions. Otherwise, the lithium ions will continue to move toward the anode, and the anode will no longer have room to accommodate them.
At this time, lithium ions will crystallize, which may affect the lifespan at best, or pierce the diaphragm and cause a short circuit, causing danger. Therefore, it is helpful to reduce this risk by not fully charging each time.
Why do LiFePO4 battery need to be fully charged regularly?
Because the battery voltage is an important basis for the battery management system to judge the battery pack power, the operating voltage range of lithium iron phosphate batteries is particularly narrow, and its voltage changes very little with capacity within a wide range.
For example, the voltage may be the same when the battery power is 30% and 60%. This feature will drive the battery management system crazy, and it cannot judge the battery capacity by voltage at all. Therefore, it needs to be fully charged regularly and let the battery management system calibrate the power.
Moreover, the molecules of the cathode materials of lithium iron phosphate batteries are very tightly arranged, which makes them highly stable, but also limits the movement speed of lithium ions, resulting in low energy density.
However, due to its high stability, when lithium ions flow to the negative electrode during charging, there will be no other substances occupying the position of the lithium ions in the positive electrode, so its lifespan is longer, and it is not as sensitive to overcharging as ternary lithium batteries.
So if you buy a two wheeler electric bike, you must find out what kind of battery the vehicle uses when charging. It is best to read the user manual carefully and follow the prompts to charge the battery, so as to maximize the battery life.
Lucky
Hi, I am Lucky, graduated from a well-known university in China, now mainly engaged in article editing on lithium motorcycle batteries, and the battery swapping station, I am committed to offering services and solutions about battery swap station for various industries.
Do lithium-ion batteries need to be fully charged?
Ternary lithium battery and lithium iron phosphate batteries are two types of lithium batteries currently widely used in new energy vehicles. The user manuals of vehicles using ternary lithium batteries will inform users that if they are not running long distances in daily use, try not to use them. The battery is fully charged, but it is advisable to charge it to 80%.
The user manual of lithium iron phosphate models will tell users that it is best to fully charge the battery once a week. They are both lithium batteries, so why are there such significant differences in use? In this article, we will talk about this topic.
The principle of lithium ion battery
The directed motion of the electrons forms the electric current. The current flows from the positive to the negative, but it is essentially the flow of electrons from the negative to the positive. And many substances in nature have electrons, and if we can artificially control the movement of these electrons, then we can make batteries.
The picture above is the structure of the world’s first battery, which can generate electric current using copper sheets, zinc sheets and salt water. Although we don’t know the specific principle, we can definitely imagine that the reason why it can discharge is that the movement of electrons essentially occurs. Let’s take a look at how zinc and copper generate electric current.
We all know that an atom is composed of a nucleus and an outer shell of electrons. Zinc has two electrons in its outermost shell. Because it is very active, it is more prone to losing electrons. There is an electron in the outermost layer of the nucleus of the copper element. Although it is more inclined to lose electrons, it is not as active as zinc, so copper is more inclined to gain electrons than zinc.
So when we connect the copper sheet and the zinc sheet with wires, the outer electrons of the zinc element will move toward the copper sheet, thus causing directional movement of electrons and generating current.
But such batteries are still unusable. Because zinc loses electrons and becomes positively charged zinc ions, the positive and negative charges attract each other, which attracts the electrons and prevents them from moving further toward copper. Therefore, this structure cannot continue to generate current.
So what can be done to generate stable current? The answer is to add electrolyte. Whenever a zinc atom loses electrons to produce zinc ions, the zinc ions will enter the electrolyte and flow to the copper through the electrolyte. This will prevent the electrons from being adsorbed, allowing the electrons to continue to flow to generate current.
It’s just that this battery is disposable and cannot be recharged. The principle of lithium batteries is the same as above, relying on the migration of electrons to generate current. The difference is that lithium batteries can be recharged.
The cathode of a lithium battery is a lithium compound, such as ternary lithium or lithium iron phosphate, and the anode is graphite. During charging, electrons from the cathode flow from the external circuit to the anode under the attraction of the positive voltage of the power supply. At the same time, the lithium ions generated by the cathode enter the graphite of the anode through the electrolyte.
During discharge, electrons return from the anode to the cathode through an external circuit, while lithium ions return to the cathode from the lithium ion battery electrolyte. This is the principle of charging and discharging of lithium ion battery.
Why is it not recommended to fully charge ternary lithium battery?
This is mainly related to the characteristics of the cathode material. As mentioned earlier, lithium batteries essentially rely on the back and forth movement of lithium ions and electrons to generate current and store electricity. During charging, electrons and lithium ions are ejected from the cathode and come to the anode. During discharge, lithium ions and electrons are released from the anode and come to the cathode.
If lithium ions flow to the cathode during charging and the cathode still retains the position of lithium ions during discharge, then the battery capacity will be difficult to decay. If lithium ions flow to the cathode during charging, but the vacancies are occupied by other substances, then part of the lithium ions in the cathode will have nowhere to go during discharge, which will cause the battery capacity to decay.
The cathode material of the ternary lithium battery is unstable, and the divalent nickel ions and lithium ions in it have similar diameters. When charging, the lithium ions all run to the anode. At this time, some nickel ions may occupy the position of lithium ions, causing battery capacity to decline.
Therefore, when designing the battery, the number of cathode materials in ternary lithium batteries will be greater than the anode materials. Simply put, it provides more lithium ions and space to store lithium ions, which can ensure the stability of the capacity. But this brings a new problem, that is, the anode does not have so much space to accommodate all the lithium ions in the battery during charging.
This requires caution when charging. Charging should be stopped in time after the anode is full of lithium ions. Otherwise, the lithium ions will continue to move toward the anode, and the anode will no longer have room to accommodate them.
At this time, lithium ions will crystallize, which may affect the lifespan at best, or pierce the diaphragm and cause a short circuit, causing danger. Therefore, it is helpful to reduce this risk by not fully charging each time.
Why do LiFePO4 battery need to be fully charged regularly?
Because the battery voltage is an important basis for the battery management system to judge the battery pack power, the operating voltage range of lithium iron phosphate batteries is particularly narrow, and its voltage changes very little with capacity within a wide range.
For example, the voltage may be the same when the battery power is 30% and 60%. This feature will drive the battery management system crazy, and it cannot judge the battery capacity by voltage at all. Therefore, it needs to be fully charged regularly and let the battery management system calibrate the power.
Moreover, the molecules of the cathode materials of lithium iron phosphate batteries are very tightly arranged, which makes them highly stable, but also limits the movement speed of lithium ions, resulting in low energy density.
However, due to its high stability, when lithium ions flow to the negative electrode during charging, there will be no other substances occupying the position of the lithium ions in the positive electrode, so its lifespan is longer, and it is not as sensitive to overcharging as ternary lithium batteries.
So if you buy a two wheeler electric bike, you must find out what kind of battery the vehicle uses when charging. It is best to read the user manual carefully and follow the prompts to charge the battery, so as to maximize the battery life.