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Why Lithium-ion battery cells are small?


Lithium-ion batteries, as an electrochemical device that converts chemical energy into electric energy, is getting greater popularity currently. It is versatile to be utilized in many kinds of applications ranging from consumer electronics like laptops, cameras; military and medical devices to various electric vehicles, and also renewable energy storage system. With a long lifespan, the gradually improving energy density and battery safety, Li-ion battery technology has evolved from a burgeoning stage to growing relatively maturity. But, have you ever consider why the lithium-ion battery cells are small? Why they are not as heavy as lead-acid battery?

Why Lithium-ion battery cells are small?

Cylindrical cells, pouch cells and prismatic cells are three common types of Lithium-ion cells, which is completely different from traditional heavy-weight lead-acid battery. What is the fact? High energy density, as one of the main benefits of lithium-ion battery, is also the significant factor related to why Li-ion battery cells are always small. High energy density means that with the same capacity, lithium-ion battery can be lightweight with compact size compared to lead acid battery. But why they cannot be big enough with more energy? The short answer is safety concern. Thai is, the higher the energy density, the higher the requirement of safety.

Let’s have a look at the energy density of lead acid battery and lithium-ion battery. The energy density of lead acid battery is about 40Wh/kg while the Lithium-ion battery owns a higher energy density of more than 150Wh/kg. If the lithium-ion battery cell is too big enough, the safety control could be hard in case of accident. 

There have been many reports in regards to the effect of heat and penetration of the lithium-ion battery. When lithium-ion batteries are over heated the cells short circuit causing the safety separators to shrink, meld, crack and split which leads to thermal runaway. This will cause rapid reaction within the Lithium-ion battery cell in a short time. If the energy density of lithium-ion battery cell is too high, too much energy cannot be released in a short time, resulting in failure in lithium-ion battery or even explosion. Besides, the energy was wrapped by the lithium-ion battery case, it is hard to deal with by the extinguishing agent in case a fire accident happened. The solution is to isolate the dangerous scene until the energy burned out. Therefore, each battery cell is always small with a specified capacity in order to ensure the battery safety.

Is there hope for safety?

Certainly, with the development of Li-ion technology, multiple safe protections have been designed for lithium-ion batteries. For instance, cylindrical Li-ion cells is equipped with several safe components.

1. Safety valve

Safety valve is a kind of component that can handle the pressure inside the lithium-ion battery so as to prevent it from being exploded. When the gas pressure inside the lithium-ion battery is quickly increased due to short circuit or other problems inside the battery, the safety valve is opened automatically, and a gas inside the battery can be discharged which protect the lithium-ion battery from safety failure. 

2. NTC Thermistor

NTC thermistor is a component that is used to prevent the batteries from being charged at a extreme temperature. Once over current occurs, the resistance will increase quickly after the thermistor reaching a certain temperature, then the current drops down to prevent the temperature from rising further and avoid inherent hazards of battery.

3. Fuse

The lithium-ion battery cells are equipped with fuse. The circuit will be shut down in the event of overcurrent, which protects the battery from damage.

Although Li-ion battery cells are always small to improve safety, it can also be assembled together to meet the high energy requirement of some applications. Different numbers of Li-ion battery cells can be assembled as Li-ion battery packs. Each UFO lithium-ion battery cells is manufactured using the latest technology and stringent quality control, and our LiFePO4 battery pack products are designed to exceed in performance and reliability. 

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