Fully Understand the Energy Density of Power Batteries

The battery life of electric vehicles depends entirely on it! Fully understand the "energy density" of power batteries

It's all about energy density when it comes to the range of electric vehicles! Understanding the power battery's "energy density" in-depth.

As new energy vehicles become more popular, the issue of electric vehicle range has become increasingly prominent. The higher the range, the more likely consumers are to approve it. And the range of an electric vehicle is related to an important battery parameter: energy density. Generally speaking, the higher the energy density of a power battery, the longer the range of an electric vehicle. So, what exactly is the energy density of a power battery?

The energy density of a battery refers to the amount of electricity released per unit volume or mass of the battery on average. Battery energy density = battery capacity × discharge platform/battery thickness/battery width/battery length, with the basic unit being Wh/kg (watt-hours per kilogram). Before understanding the energy density of a power battery, it is necessary to understand the composition of a power battery.

Power batteries mainly include cells, modules, battery packs, etc. Cells are the smallest unit of a battery system. M cells constitute a module, and N modules constitute a battery pack. They are connected through various controllers and electrical devices to form the power system of an electric vehicle.

Cells are mainly composed of positive and negative electrodes, separators, electrolytes, etc. Lithium-ion batteries for electric vehicles are divided into lithium manganese oxide batteries, lithium iron phosphate batteries, nickel-cobalt lithium-ion batteries, and nickel-cobalt-manganese lithium-ion batteries based on positive electrode materials.

The so-called "iron battery" commonly referred to by people refers to a lithium iron phosphate battery, which uses lithium iron phosphate as the positive electrode material; the popular "ternary lithium battery" refers to a battery that uses nickel-cobalt-manganese lithium or nickel-cobalt-aluminum lithium as the positive electrode material.

Cells cannot be used directly and can only be used directly after adding a protection circuit and protective casing and combining them to form a module. In most cases, a single module cannot provide enough electricity for long-distance driving of a car. Therefore, multiple modules need to be combined and equipped with a single-cell battery monitoring and management device to form a power battery pack.

As a result, there are two ways to measure the energy density of power batteries: the energy density of the battery unit (cell) and the energy density of the battery system (the entire power battery system).

The energy density of the battery unit refers to the energy density at the cell level. For example, "Made in China 2025" once released a development plan that aims for a battery energy density of 300Wh/kg by 2020, 400Wh/kg by 2025, and 500Wh/kg by 2030, which refers to the energy density at the individual cell level.

The so-called energy density of the battery system refers to the ratio of the entire battery system's power to its weight or volume after the cell combination is completed. Because the internal battery management system, thermal management system, high and low voltage circuits, etc., occupy part of the battery system's weight and internal space, the energy density of the battery system is lower than that of the energy density of the battery unit.

For instance, using the battery manufacturer CATL as an example, they announced that their mass-produced lithium iron phosphate battery unit's energy density has reached 190Wh/kg and will potentially reach 200Wh/kg. In contrast, the corresponding energy density of the system is only 160Wh/kg. Its current experimental stage 811 soft pack battery's energy density per unit cell has exceeded 300Wh/kg. However, the corresponding energy density of the system is only 200Wh/kg.

The high or low energy density of the battery often directly determines the range of electric vehicles. So, how can we increase the energy density of power batteries? There are mainly two directions:

 1.   Increase the energy density of the cell unit:

Regarding individual cells, the battery's positive and negative electrode materials, production processes, etc., all affect energy density. Thus, it is necessary to adopt more reasonable positive and negative electrode materials, as well as better production processes. For example, the reason for the significant difference in energy density between ternary lithium batteries and lithium iron phosphate batteries is due to their use of different positive electrode materials. Generally, there is limited room for improvement in the energy density of lithium iron phosphate batteries at the unit cell level, while ternary lithium batteries have more room for improvement. This is also an important reason why many car brands choose to install ternary lithium batteries.

  2.  Increase the energy density of the battery system:

The energy density of the battery system is a very important performance parameter of electric vehicles. In cases where the energy density of the battery unit has already been determined, how to optimize the space and layout of the battery system, conduct lightweight design on the battery power system or even the entire vehicle, etc., have become research directions for many car brands. For example, Fudi's recently released "Blade Battery" essentially reduces structural parts and optimizes space utilization efficiency. Ternary lithium battery manufacturers are also continuing to invest and explore in this field.

Overall, whether it is a lithium iron phosphate battery or a ternary lithium battery, by optimizing space utilization efficiency and improving materials to achieve an increase in range, the effect is still very remarkable in the industry.