It is understood that the energy density of a single lithium iron phosphate (LFP) battery cell can reach 157 Wh/kg, but the energy density drops to 100 Wh/kg when cells are assembled into a battery pack. Currently, the energy density of LFP batteries is generally around 150 Wh/kg, and even the better ones are only around 160 Wh/kg, which is significantly lower than the 200 Wh/kg energy density of ternary lithium batteries. The soon-to-be-produced 32131 high-energy-density cylindrical LFP battery has a single-cell energy density of 180 Wh/kg, and passenger vehicles using this battery can achieve a range of over 300 km.
What is energy density?
Energy density refers to the amount of energy stored in a given unit space or mass of matter. The energy density of a battery is the electrical energy released per unit volume or mass of that battery. Battery energy density is generally divided into two dimensions: gravimetric energy density and volumetric energy density.
Battery gravimetric energy density = battery capacity × discharge plateau / weight, with the basic unit being Wh/kg (watt-hours per kilogram).
Battery volumetric energy density = battery capacity × discharge plateau / volume, with the basic unit being Wh/L (watt-hours per liter).
The higher the energy density of a battery, the more electrical energy it can store per unit volume or weight.
What is single-cell energy density?
The energy density of a battery often refers to two different concepts: the energy density of a single cell and the energy density of the battery system.
A battery cell is the smallest unit of a battery system. M battery cells make up a module, and N modules make up a battery pack. This is the basic structure of lithium-ion batteries for automotive power.
Single cell energy density, as the name suggests, is the energy density at the level of a single cell.
According to "Made in my country 2025," the development plan for power lithium-ion batteries is as follows: by 2020, the battery energy density will reach 300Wh/kg; by 2025, the battery energy density will reach 400Wh/kg; and by 2030, the battery energy density will reach 500Wh/kg. This refers to the energy density at the individual cell level.
What is system energy density?
System energy density refers to the ratio of the electrical capacity of the entire battery system (after the individual cells are assembled) to the weight or volume of the entire battery system. Because the battery system contains components such as the battery management system, thermal management system, and high and low voltage circuits, which occupy part of the battery system's weight and internal space, the energy density of the battery system is lower than that of a single cell.
System energy density = Battery system capacity / Battery system weight OR Battery system volume
Batteries are multifaceted products; improving performance in one area may sacrifice performance in others. This is the fundamental understanding behind battery design and development. Power lithium-ion batteries are specifically designed for automotive applications, therefore energy density is not the sole metric for battery quality.
