If an electric car is not used for a long time, the battery will "starve to death"?

Audit Expert: Wang Jinlu, Director of Power Supply R&D, Shenzhen Lingkang Technology Co., Ltd.

Friends who use electric vehicles will find that after long-term use, the battery life of the electric vehicle will become shorter and shorter each time it is fully charged. What's more, when the battery is not used for a long time, it will be out of power and cannot be charged.

Why does the amount of power a battery can store decrease? How can we prevent the battery from storing less power or even becoming unable to be charged?

1

How is the battery consumed?

Common types of electric vehicle batteries on the market include lead-acid batteries, lithium batteries, graphene batteries , etc. Today, I will take you to learn about the lead-acid batteries that are most widely used in electric vehicles today.
Compared with other batteries, lead-acid batteries are low-priced, recyclable, and highly safe. Theoretically, the service life of lead-acid batteries is about 2 years, and they can withstand about 400 deep charges and deep discharges .

Source of Lead-acid Batteries for Automobiles｜Electric Network

To understand how battery power is consumed, we first need to understand how lead-acid batteries work.

As shown in the figure below, batteries generally have two plates, an anode and a cathode. When the battery is charging and discharging, the electrolyte will react chemically with the active substances on the cathode and anode plates, causing electrons to circulate back and forth between the anode and cathode , being released or absorbed, thereby charging and discharging the battery.

Schematic diagram of zinc-copper battery Source: Wikipedia The anode and cathode of a lead-acid battery are composed of lead dioxide (PbO₂) and lead (Pb) respectively, and the electrolyte is dilute sulfuric acid. The battery converts electrical energy into chemical energy when charging, and converts chemical energy into electrical energy by discharging when in use.

The electrodes of the chemical total reaction lead-acid battery are stacked with many small electrode particles. In the process of continuous transfer of lead acid ions, the electrode structure will not be damaged under ideal conditions. But in fact, due to various non-ideal factors, when electrons enter and exit the electrodes, they will inevitably collide with the electrodes, or produce other electrochemical reactions, which will damage the electrode plates and cause the battery to gradually deactivate.

2

Why are batteries becoming less durable?

One is the battery itself.

The voltage characteristic of lead-acid batteries is that as time accumulates, the battery gradually releases electrical energy. However, in the later stage of discharge, the battery voltage has a sudden drop waveform. If the battery continues to discharge at this time, it will cause over-discharge of the battery. Over time, the internal balance consistency of the battery deteriorates , and the battery becomes less and less durable.

Some people are used to charging their electric vehicles only after they have used up all the electricity. This may seem like "timely" charging, but it is very harmful to the battery. This is because deep discharge can easily cause the inside of the battery to salt, which can cause the battery to deform and swell , creating safety hazards.

The battery industry standard requires a 70% discharge for the battery's cycle life, which means a 10A battery is discharged at 5A for 84 minutes. This also means that the shallower the battery discharge depth, the longer the battery's cycle life and the longer the battery's service life.

Second, the temperature of the charging environment

According to the ideal conditions in the laboratory, the charging temperature is best carried out at room temperature, that is, 25 degrees Celsius . However, electric vehicles are often charged outdoors, which leads to problems such as insufficient or overcharged batteries under extreme conditions in summer or winter. These problems are factors that lead to increasingly weak batteries.

Source: pexels

In addition, it is also related to the decadmium and sulfate deposition of lead-acid batteries. Although cadmium is added to traditional lead-acid batteries, it can improve the performance and service life of the battery, but cadmium will cause great pollution to the environment. Therefore, for the sake of environmental protection, major lead-acid battery manufacturers will no longer add cadmium to the batteries they produce in the future. The lack of cadmium has led to a decline in various performances to varying degrees, including the attenuation of battery life.

In addition, the battery begins to sulfide after it is discharged. If it is not charged in time, the sulfide crystals will accumulate and gradually form coarse crystals . General chargers are powerless against these coarse crystals, which will gradually cause the battery capacity to decrease and shorten the battery life. Therefore, in addition to charging every day, you should also pay attention to charging as soon as possible after use to keep the battery in a full state as much as possible.

3

How to use batteries correctly?

Like ordinary batteries, lead-acid batteries also need to be used in a proper way. Only by using the battery correctly can the battery last longer.

1. How to avoid the situation where the battery is empty and cannot be charged?

When the battery is not used for a long time, the battery plates will be sulfided, which will cause the battery to be empty and unable to be charged. Therefore , when the device is not used for a long time, it is necessary to remove the battery of the device , which can effectively extend the battery life.

Turn off the leakage protector. When the electric vehicle is in normal operation, if the circuit is overloaded or short-circuited, the leakage protector can reduce the occurrence of electric shock accidents and protect personal safety, but it can be turned off when the electric vehicle is not running. After turning off the leakage protector, the entire system is in a power-off state. When the battery is in a powerless state, there is no electrochemical reaction inside the battery, and the sulfide state will stop , which can protect the battery to a certain extent.

Charge regularly. When you don’t use your electric vehicle for a long time, you need to charge the device regularly to keep the active substances on the electrodes in the battery active and slow down the battery’s decay.

2. What are the precautions for daily use of batteries?

If you need to store the device for a long time, it is best to keep the battery power at around 50%, which is the best storage state for the battery.

Use the original charger. The original charging equipment is the most suitable and stable. Other chargers will inevitably have mismatch problems.

Do not charge the battery until it is extremely low, but connect the charger when it is at 30%. You do not need to charge it to 100% each time, more than 80% is enough. If you charge it to 100% each time, the battery voltage will increase, which will put pressure on the battery.

Image source | Baidu Encyclopedia

If the charging sequence is incorrect, it will cause a large impact voltage, that is, surge voltage. The correct charging sequence should be to connect the socket plug first, and then connect the data cable to the electric vehicle, which can reduce the surge voltage.

Charge in a suitable environment. An overly cold or overheated environment can easily affect the electrochemical reaction speed inside the battery, causing excessive or insufficient electrochemical reactions, so try to avoid using electric vehicles in extreme ambient temperatures.

We must use electric vehicle batteries in a scientific and correct way, and pay attention to the correct charging method in daily life. At the same time, we must also believe that the development of battery technology will further improve battery performance.