According to the notice on adjusting and improving the financial subsidy policy for the promotion and application of new energy vehicles jointly issued by relevant national departments and the National Development and Reform Commission, the new subsidy has raised the energy density threshold of the power battery system for non fast charging pure electric buses, special vehicles, and other vehicle models, accelerated the elimination of low energy density batteries, and vigorously increased the energy density of batteries.

　　Energy density refers to the amount of energy stored in a certain space or mass of matter. The energy density of a battery is the average unit volume or mass of electrical energy released by the battery. Battery energy density=battery capacity × The basic unit of discharge platform/battery thickness/battery width/battery length is Wh/kg (watt hours/kg).

　　The higher the energy density of a battery, the more electricity stored per unit volume.

　　Regarding the energy density of batteries, we now know that it is the most obvious breakthrough point for the current battery industry, even the electric vehicle industry, to make significant strides forward. However, breaking through it is really difficult!

　　It is reported that the energy density of a battery is basically determined by the positive and negative electrodes of the battery, but only the active materials of the positive and negative electrodes cannot guarantee that the battery can generate electricity. There must be many non active substances, such as conductive aids, adhesives between active powders, isolation films, foil for the negative and positive electrodes, insulation fixed adhesive paper, aluminum plastic film shells or steel aluminum shells, etc.

　　Most of us always intentionally or unintentionally ignore the content of this material, resulting in a significant difference in energy density compared to the facts, misleading people who eat melons. In fact, this part is quite important. Taking the technological progress of the past decade or so, the improvement of battery energy density is mainly achieved by the increase in the proportion of active substances.

　　Another way is to increase the original battery size to achieve the effect of battery capacity expansion.

　　Our most familiar example is that Tesla, a well-known electric vehicle company that was the first to use Panasonic 18650 batteries, will replace them with a new 21700 battery. The reason is not that there are any quality issues with the 18650 battery, but that the single capacity of the 18650 battery is small, generally around 2-4Ah, and there are too many series and parallel connections, resulting in a high probability of single unit failure, which limits its application in the field of electric vehicles.

　　The 21700 battery is larger in size compared to the 18650 battery (diameter 18mm, length 65mm), reaching a diameter of 21mm and a length of 70mm. If you want to think about this issue more vividly, let's take a look at the calculation from HitechEnergy, which only considers the dense stacking of monomers. It can be seen that the volume of 30 units 21700 is 1.1 times that of 40 units 18650, and the mass is 0.97 times.

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