What is Energy Density?
Energydensity refers to the amount of energy stored in a certain unit of space or mass of matter. The energy density of a battery is the amount of electricity emitted by the average unit volume or mass of the battery. The energy density of a battery is generally divided into two dimensions: weight energy density and volume energy density.
Battery weight energy density = battery capacity × discharge platform/weight, the basic unit is Wh/kg (watt-hours/kg)
Battery volume energy density = battery capacity ×discharge platform/volume, the basic unit is Wh/L (watt-hours/liter)
The greater the energy density of a battery, the more power can be stored per unit volume or weight.
What is Monomer Energy Density?

The energy density of a battery often refers to two different concepts, one is the energy density of a single cell, and the other is the energy density of a battery system.
A battery cell is the smallest unit of a battery system. M cells form a module, and N modules form a battery pack, which is the basic structure of automotive power batteries.
The energy density of a single cell, as the name suggests, is the energy density at the level of a single cell.
According to the "Made in China 2025", the development plan of power batteries has been clarified: in 2020, the energy density of batteries will reach 300Wh/kg; In 2025, the energy density of the battery will reach 400Wh/kg; In 2030, the energy density of batteries will reach 500Wh/kg. This refers to the energy density at the level of a single cell.

What is System Energy Density?

System energy density refers to the weight or volume of the entire battery system after the combination of monomers to the weight or volume of the entire battery system. Because the battery system contains the battery management system, thermal management system, high and low voltage circuits, etc., which occupy part of the weight and internal space of the battery system, the energy density of the battery system is lower than that of the single body.
System energy density = battery system power / battery system weight OR battery system volume
What exactly limits the energy density of lithium batteries?
The chemistry behind the battery is the main reason.
Generally speaking, the four parts of a lithium battery are very critical: the positive electrode, the negative electrode, the electrolyte, and the diaphragm. The positive and negative electrodes are the places where the chemical reaction takes place, which is equivalent to the second pulse of Ren Du, and its important position can be seen. We all know that the energy density of a battery pack system with ternary lithium as the cathode is higher than that of a battery pack system with lithium iron phosphate as the cathode. Why is that?
The existing anode materials of lithium-ion batteries are mainly graphite, and the theoretical gram capacity of graphite is 372mAh/g. The theoretical gram capacity of lithium iron phosphate, the cathode material, is only 160mAh/g, while the ternary material nickel-cobalt-manganese (NCM) is about 200mAh/g.
According to the barrel theory, the water level is determined by the shortest point of the barrel, and the lower limit of energy density of lithium-ion batteries depends on the cathode material.
The voltage platform of lithium iron phosphate is 3.2V, and the ternary index is 3.7V, compared with the two phases, the energy density is high: a difference of 16%.
Of course, in addition to the chemical system, the level of the production process such as compaction density, foil thickness, etc., will also affect the energy density. Generally speaking, the larger the compaction density, the higher the capacity of the battery in a limited space, so the compaction density of the main material is also regarded as one of the reference indicators of the energy density of the battery.
In the fourth episode of "Great Power Heavy Equipment II", CATL uses 6-micron copper foil to improve the energy density by using advanced technology.
If you can stick to each line, read it all the way to this point. Congratulations, your understanding of batteries has gone up to the next level.

How can we increase energy density?
The adoption of new material system, the fine adjustment of lithium battery structure, and the improvement of manufacturing capacity are the three stages for R&D engineers to "dance with long sleeves". Below, we will explain from the two dimensions of monomer and system.
——The energy density of monomers mainly depends on the breakthrough of the chemical system
1. Increase the size of the battery
Battery manufacturers can achieve the effect of power expansion by increasing the size of the original battery. The most familiar example is that Tesla, the well-known electric vehicle company that pioneered the use of Panasonic 18650 batteries, will replace it with a new 21700 battery.
However, the "fattening" or "growing" of the battery cell is only a symptom, not a cure. The method of drawing wages from the bottom of the kettle is to find the key technology to improve the energy density from the positive and negative electrode materials and electrolyte components that make up the battery cell.
2. Chemical system reform
As mentioned earlier, the energy density of a battery is limited by the positive and negative electrodes of the battery. Since the energy density of the current anode material is much greater than that of the cathode, it is necessary to continuously upgrade the cathode material to improve the energy density.

High nickel cathode
Ternary materials generally refer to the large family of nickel-cobalt-manganese oxides, and we can change the performance of batteries by changing the ratio of nickel, cobalt, and manganese.
In the figure silicon carbon anode
The specific capacity of silicon-based anode materials can reach 4200mAh/g, which is much higher than the theoretical specific capacity of graphite anode of 372mAh/g, so it has become a strong substitute for graphite anode.
At present, the use of silicon-carbon composite materials to improve the energy density of batteries has been recognized as one of the development directions of lithium-ion battery anode materials in the industry. Tesla's Model 3 uses a silicon carbon anode.
In the future, if you want to go one step further - break through the 350Wh/kg threshold of single cells, industry peers may need to focus on lithium metal anode battery systems, but this also means the change and improvement of the entire battery manufacturing process. It can be seen that the proportion of nickel is getting higher and higher, and the proportion of cobalt is getting lower and lower. The higher the nickel content, the higher the specific capacity of the cell. In addition, due to the scarcity of cobalt resources, increasing the proportion of nickel will reduce the amount of cobalt used.
3. System energy density: improve the grouping efficiency of the battery pack
The group of battery packs tests the ability of the battery "siege lions" to arrange the single cells and modules, and it is necessary to maximize the use of every inch of space on the premise of safety.