Lithium batteries are becoming increasingly popular in Campervans and Recreational Vehicles. Is lithium right for your van build?
Explorevanx and MaxWorld Technologies
What is the energy density of a lithium-ion battery?
In this passage, we will learn about the definition of energy density, dimensions of the energy density which are weight and volume. And we will discuss energy density from two general concepts: a single cell and the battery system. Therefore, we will have better understanding of what are limiting the energy density of a lithium battery and how shall we increase it. Lithium batteries are becoming increasingly popular in Campervans and Recreational Vehicles. Is lithium right for your van build?
What is energy density?
The energy density refers to the amount of energy stored in a unit of a particular space or mass matter. The energy density of a battery is generally divided into two dimensions, which are weight and volume.
Battery weight energy density (Wh/kg) = battery capacity×discharge platform/weight
Battery volume energy density (Wh/L) = battery capacity×discharge platform/volume
So, when there is more electricity stored per unit volume or weight, the battery density is greater.
What is the energy density of the monomer?
The energy density of a battery are often considered as two different concepts, one is the energy density of a single cell, and the other is the energy density of the battery system.
The energy density of a single cell is considered as the energy density of a single cell level. While, the battery cell is the smallest unit of a battery system. The battery module is consisted of a certain amount of battery cells and several modules form a battery pack. In order to differentiate the two, we can take "Made in China 2025" document for example. This development plan for motive batteries is defined: in 2020, the battery energy density will reach 300Wh/kg; in 2025, the battery energy density will reach 400Wh/kg; in 2030, the battery energy density will reach 500Wh/kg. Here it refers to the energy density of a single cell level.
What is the system energy density?
The system energy density refers to the weight or volume of the entire battery system after the single cell batteries are combined. Because the battery system contains a 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, therefore, the energy density of the battery system is lower than the energy density of the monomer.
What limits the energy density of lithium batteries?
The chemical system of the battery is the main reason. In most of the case, the four parts of a lithium battery are very critical: a positive electrode, a negative electrode, electrolyte, and diaphragm. The positive and negative poles are the places where chemical reactions take place.
It is well acknowledged that the energy density of the battery pack system with ternary lithium as the positive electrode is higher than that of the battery pack system with lithium iron phosphate as the positive electrode. Most of the anode materials for lithium-ion batteries are graphite, and the theoretical gram capacity of graphite is from 366~372 mAh/g. The theoretical gram capacity of the cathode material lithium iron phosphate is only 160mAh/g, while the ternary material nickel cobalt manganese (NCM) is about 200mAh/g. According to the barrel theory, the lower limit of the energy density of lithium-ion batteries depends on the cathode material, just like the water level is decided by the shortest one of the barrel.
In practice, the voltage platform of lithium iron phosphate is 3.2V, and the ternary index is 3.7V. The difference of the energy density is huge in comparison, which is 16% of difference rate.
In addition to the chemical system, however, the production process level, such as foil thickness, compaction density, etc., will also affect the energy density. Therefore, not only chemical system is influencing the energy density of a battery, but also the material plays an important role.
How to increase energy density?
1. Increase the battery size
2. Changes in the chemical system
3. Improve the efficiency of battery packs ( for system energy density
In addition, we can slim the battery packs by optimizing the layout structure, reducing the weight, choosing low density material and using integrating design.
The purpose of this passage is to give you a new perspective of learning aspects of lithium ion battery and thus get to know the difference between different types of them. After learning the concepts of energy density of a battery, it will not be hard for you to understand that, in the future, if you want to go a step further-breaking the 350Wh/kg threshold for single cells, industry colleagues may need to focus on lithium metal negative battery systems, but this also means that the entire battery manufacturing will meet with the process of changes and improvement. Many companies on Explorevanx’s build directory have begun utilizing lithium batteries, will you?
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