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What are the methods to increase the energy density of lithium batteries?

by:dcfpower     2021-03-13

The energy density of lithium batteries (Energydensity) refers to the amount of energy stored in a unit of a certain space or mass of matter. The energy density of a battery is the electric energy released by the average unit volume or mass of the battery. The energy density of lithium batteries is generally divided into two dimensions: weight energy density and volume energy density.

Battery weight energy density u003d battery capacity × discharge platform/weight, the basic unit is Wh/kg (watt hour/kg)

Battery volume energy density u003dBattery capacity×discharge platform/volume, the basic unit is Wh/L (watt hour/liter)

The greater the energy density of the battery, the more power stored per unit volume or weight.

What is the energy density of a single battery?

The energy density of batteries often points to two different concepts, one is the energy density of a single cell, and the other is the energy density of the battery system.

The battery cell is the smallest unit of a battery system. M batteries form a module, and N modules form a battery pack. This is the basic structure of a vehicle power battery.

The energy density of a single cell, as the name implies, is the energy density of a single cell level.

According to 'Made in China 2025500Wh/kg. This refers to the energy density of a single cell level.

What is the energy density of the battery system?

System energy density refers to the weight or volume of the entire battery system after the monomer combination is completed. Because the battery system contains battery management system, thermal management system, high and low voltage circuits, etc. occupy part of the weight and internal space of the battery system, the energy density of the battery system is lower than the energy density of the monomer.

System energy densityu003dbattery system power/battery system weight OR battery system volume

What exactly limits the energy density of lithium batteries?

The chemical system behind the battery is the main reason.

Generally speaking, the four parts of a lithium battery pack are very critical: positive electrode, negative electrode, electrolyte, and diaphragm. The positive and negative poles are the places where chemical reactions occur, which are equivalent to the two veins of Ren and Du, and their important status is evident. We all know 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. Why is this?

The current negative electrode materials for lithium-ion batteries are mostly graphite, and the theoretical gram capacity of graphite is 372mAh/g. The theoretical gram capacity of the positive electrode 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 water level is determined by the shortest part of the barrel, and the lower limit of the 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. Comparing the two phases, the energy density is high and the difference is 16%.

Of course, in addition to the chemical system, the production process level, such as compaction density, foil thickness, etc., will also affect the energy density. Generally speaking, the higher 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 for the energy density of the battery.

In the fourth episode of 'Da Guo Heavy Equipment II

If you can insist on reading each line until you reach here. Congratulations, your understanding of batteries has reached a level.

How to increase energy density?

The adoption of new material systems, the fine-tuning of the structure of lithium batteries, and the improvement of manufacturing capabilities are the three stages for Ru0026D engineers to 'long sleeves'. Below, we will explain from the two dimensions of monomer and system.

The energy density of the monomer mainly depends on the breakthrough of the chemical system.

1. Increase the battery size

Battery manufacturers can increase the original battery size to achieve the power The effect of capacity expansion. The most familiar example is that Tesla, a well-known electric car company that was the first to use Panasonic's 18650 battery, will replace it with a new 21700 battery.

But the 'fat' or 'growth' of the battery cell is only a temporary cure, not a permanent cure. The method of drawing salaries from the bottom of the kettle is to find the key technology to increase the energy density from the positive and negative materials that constitute the battery cell and the electrolyte composition.

2. Chemical system reform

As mentioned earlier, the energy density of the battery is restricted by the positive and negative electrodes of the battery. Since the energy density of the current negative electrode material is much greater than that of the positive electrode, increasing the energy density requires continuous upgrading of the positive electrode material.

High nickel cathode

The ternary material generally refers to the large family of nickel cobalt manganese oxide lithium oxide. We can change the battery by changing the ratio of the three elements of nickel, cobalt, and manganese Performance.

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