Why is the self discharge of lithium battery?

Released on Mar. 23, 2022

Why is the self discharge of lithium battery?

A lithium polymer battery (lithium polymer battery) is a type of rechargeable battery. It is based on lithium-ion technology. It is made with polymer electrolytes instead of traditional liquid electrolytes. Lithium batteries provide higher specific energy than traditional lithium batteries. They are very light, which is why they are used in products where weight is a key feature, such as mobile phones or radio-controlled aircraft.

Li-polymer batteries follow in the footsteps of their predecessors, lithium-ion and lithium-metal batteries. A lot of research has been done in this field since the 1980s. It wasn't until 1991 that Sony released the first commercial cylindrical lithium-ion battery. This was the starting point for later achievements in this field.

Lithium polymer battery has excellent performance. They are smaller, lighter and have a higher power capacity than lithium-ion batteries. They are considered valuable upgrades to lithium-ion batteries. Most LiPo batteries cannot be charged more than 300 times. Many manufacturers claim that their Li-polymer batteries can last for two or even three years. This is somewhat equivalent to about 300 charge cycles. Over time, Li-polymer batteries will lose their ability to charge continuously. Unfortunately, this is an irreversible process. The lithium polymer battery will continue to deteriorate until it can no longer be charged.

Why is your Li-polymer battery self-discharging?

To fully understand what's really going on inside a LiPo battery, we need to know the chemistry behind it. Everything that happens inside a battery is a chemical reaction. The negative electrode is a graphite material, "the same material as in a pencil". The anode electrolyte is made of lithium transition metal oxide material. In a healthy lithium polymer battery, ions flow freely between the two plates, the cathode "negative" and the anode "positive." This flow is what creates the energy. When charging a battery, the ions are forced to change paths, flowing from the cathode to the anode, which is known as battery backflow.

Over time, this process -- reverse flow -- wears down the cathode, reducing battery capacity. With high-end Li-polymer batteries, after you reach 1,000 charge cycles, the capacity drops to 20% of its original capacity. To fully visualize the process, imagine that every time you charge an electronic device, your maximum battery life is reduced by a few seconds. Take into account that discharging and charging the battery in erratic weather conditions can drastically shorten the life of the battery.

What is the self-discharge rate of LiPo batteries?

All batteries based on lithium technology experience what is known as self-discharge. Self-discharge is defined as a phenomenon in which a chemical reaction occurs inside a battery, reducing the battery's capacity. This chemical reaction occurs without any connection between the electrodes, nor any external factor or circuit. Self-discharge reduces the shelf life of the battery, which in turn results in an initial full charge when the battery is placed in the device. Depending on the battery type, determine the self-discharge time. The self-discharge rate of lithium polymer batteries is estimated to be around 5% per month. This is a very low rate compared to the 30% monthly self-discharge rate of NiMH batteries. And nickel-cadmium batteries with a monthly self-discharge rate of 20%.

Do Li-polymer batteries need to be fully discharged?

In short, the answer is no. You do not need to fully discharge Li-polymer batteries before use, during storage, or for any reason. Lithium batteries have no charge memory. Also, you must discharge the LiPo battery in a professional manner or you will be in serious danger. It is very dangerous to discharge a Li-polymer battery below its discharge rate.

For a better understanding, let's discuss the concept of discharge rate. The discharge rating indicates the rate at which a LiPo battery can be safely discharged without damaging the battery. The discharge rate depends on the capacity of the battery, which is why it is represented by a number followed by the letter C, which stands for capacity.

For example, let's say you have a LiPo battery with a capacity of 5 amps. The battery showed a discharge rate of 50C. To calculate it, just multiply 50 by the capacity 5 and the result is 250A. So 250A is the discharge rating of the battery.

There are some safety rules you must follow when charging and discharging Li-polymer batteries. Be aware that failure to follow these safety tips can have disastrous consequences:

Never pick up a Li-polymer battery by its wires. The wires may come off the solder joints. Always pick it up with its body.

When charging, please charge in a fireproof place. It is best to use a LiPo safety bag.

Do not charge the battery immediately after use, please wait for it to cool down.

It is recommended that you charge the battery at a rate of 1C or less.

Never leave the battery unattended while charging. Check regularly to make sure there is no heat or swelling.

Never attempt to charge a damaged Li-polymer battery, as it may cause a fire or explosion.

Before charging, make sure the number and type of batteries match the numbers on the charger.

Avoid overcharging the battery.

Do not leave lithium polymer batteries in the sun or in a car with high temperatures.

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