With the same energy consumption, under the same volume and weight of the battery pack being strictly limited, the maximum mileage of a new energy electric vehicle depends mainly on the battery energy density.
Endurance ability = Available capacity ÷Energy consumption
What is Energy Density?
Energy density is the amount of energy stored per unit of volume or weight. The energy density is the amount of electrical energy released per unit volume or weight of the battery. The energy density of battery can be divided into two dimensions: weight energy density and volume energy density.
Battery weight energy density = Battery capacity X Discharge platform/weight, the basic unit is Wh/kg (watt hours/kg)
Battery volume energy density = Battery capacity × Discharge platform/volume, basic unit is WH/L (W/L)
Thee higher the energy density of a battery, the more electricity is stored per unit volume or weight.
What is a Single Cell Energy Density?
The energy density of the battery often points to two different concepts, one is the single cell energy density, one is the battery system energy density.
The cell is the smallest unit of a battery system. M cells to form a module, N modules to form a battery pack, which is the Escooter and vehicle battery basic structure.
Single cell energy density, as the name implies is the energy density of a single cell.
According to the Made in China 2025, the development plan of the power battery is made clear: by 2020, the energy density of the battery will reach 300 Wh/kg; by 2025, the energy density of the battery will reach 400 Wh/kg; and by 2030, the energy density of the battery will reach 500 Wh/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 energy amount stored per weight or volume of the whole battery system after the unit combination is completed. Because the battery system contains battery management system(BMS), thermal management system, high and low voltage circuits occupy part of the weight of the battery system and internal space, so the energy density of the battery system is lower than the single energy density.
System Energy Density = Battery system electricity/Battery system weight or Battery system volume
What On Earth Restricts The Energy Density Of Lithium ion Batteries?
The battery chemistry material system is the main factor
In general, the four components of a lithium battery are critical: the anode, the cathode, the electrolyte, and the diaphragm. The positive and negative pole is the place where the chemical reaction takes place, and its important position can be seen.
Most of the existing lithium-ion battery cathode materials are mainly graphite, with a theoretical capacity of 372mAh/g. The theoretical capacity of anode material lifepo4 is only 160mAh/g, while that of NCM material is about 200mAh/g.
According to the bucket theory, the water level is determined by the shortest part of the barrel, and the lower limit of the energy density of the lithium-ion battery depends on the anode material.
The voltage platform of lithium iron phosphate is 3.2 V, and the index of NCM is 3.7V. the difference between the two is 16% .
Of course, in addition to the chemical system, the level of production processes such as compaction density, foil thickness, etc. , will also affect the energy density. Generally speaking, the higher the compaction density is, the higher the capacity of the battery is in the 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.
The biggest advantage of the NCM lithium battery is its high energy density, its energy storage density is usually above 200 Wh/kg, compared to the lithium iron phosphate 90-120 Wh/kg, this performance is more friendly to the lightweight design.
Our Hot sell 72V 30Ah, 60V 60Ah Electric scooter battery and 36V 15Ah, 48V 20Ah Ebike lithium battery are assembled with NCM lithium battery. So this can explains, why most Ebike Lithium battery, E-scooter lithium battery is more prone to apply NCM battery. In the same volume, NCM battery can fulfill larger capacity.
What can you do to increase your energy density
The adoption of new material system, the fine adjustment of lithium battery structure and the improvement of manufacturing capability are the three stages of R & D engineers. Next, we will explain from the cell and the system two dimensions.
The energy density of the monomer depends mainly on the breakthrough of the chemical system.
01 increase battery size
Battery manufacturers can increase cell capacity by increasing the size of the original battery. The most familiar example: Tesla, the first electric car to use the Panasonic 18650 Battery, is getting a new 21700 battery.
02 Chemical System Revolution
As mentioned earlier, the energy density of a battery is controlled by the anode and cathode material. At present, the energy density of cathode materials is much higher than that of anode materials, so it is necessary to upgrade the anode materials to improve the energy density.
High Nickel Anode
NCM material refers to Nickel Cobalt Lithium Manganate Oxide family, we can change the ratio of Nickel, Cobalt, Manganese to change the performance of batteries.
The higher the nickel content, the higher the specific capacity of the cell. In addition, because of the scarcity of cobalt resources, increasing the proportion of nickel will reduce the use of cobalt.
Silicon Carbon Cathode
The specific capacity of silicon-based cathode materials can reach 4200mAh/g, which is much higher than the theoretical specific capacity of graphite cathode materials of 372mAh/g.
Currently, the use of silicon carbon composite materials to enhance the energy density of batteries, has been recognized as one of the lithium-ion battery development direction. Tesla’s Model 3 uses a silicon carbon cathode.
In the future, if you want to go one step further —— to break through the 350WH/kg single cell level, the industry may need to focus on lithium metal negative battery systems, but this also means that the whole battery production process changes and refinement.
03 System Energy Density: Improved Pack Efficiency
The battery pack a tests the ability of the battery “Siege lions”to line up individual cells and modules to make the most of every inch of space on the premise of safety.Battery pack “slimming”there are several main ways.
Optimize the layout
From the aspect of external dimensions, the internal arrangement of the system can be optimized to make the internal parts of the battery pack more compact and efficient.
Under the premise of ensuring the stiffness, strength and structural reliability, the weight reduction design is realized by simulation calculation. Through this technology, topology optimization and shape optimization can be realized, and finally help to realize the lightweight of the battery case.
This technology is most focus applied during custom lithium battery, especially large battery pack, take our 72V 200Ah electric vehicle battery pack for example, through this technology can reduce the weight by about 10%.
The integrated design of the whole vehicle and the overall design of the structure of the whole vehicle, as far as possible to share structural components, such as anti-collision design, to achieve the ultimate lightweight.
Battery is a very comprehensive product, you want to improve one aspect of performance, may be at the expense of other aspects of performance, this is the understanding of battery design and development. Therefore, the energy density is not the only measure of the battery quality, but one of the measure of the battery pack.
SmartPropel Original Writer:Nancy