NiMH No. 7

Why are NiMH No. 7 made into round pillars, bread slices, and hard drives?

First of all, we must first realize that the internal components of the three NiMH No. 7 are not much different. They are all lithium-ion batteries. The core difference is that cylindrical and square batteries mainly use metal materials as the shell, while soft-pack lithium-ion batteries use aluminum-plastic film as the packaging shell. Let's talk about them one by one:

■Cylindrical batteries

Suppliers: Panasonic, Sony, Johnson Controls

Used models: Tesla full series, JAC IEV series

Advantages: mature production process, low PACK cost, high battery product yield, good heat dissipation performance

Disadvantages: heavy weight

The cylindrical batteries commonly used in new energy vehicles look very similar to the No. 5 batteries we use in daily life. This type of battery has a long history, very mature production technology, and international standards. The Tesla 21700 we often mention actually refers to its size of 21 mm x 70 mm.

In addition, because of its shape, many cylindrical batteries can leave gaps for heat dissipation when they are arranged together. If you see square batteries are arranged together, there is no gap in the middle.

However, this type of battery has a characteristic that the energy density of the single cell is low. If you want the same capacity, you must carry more batteries, and the metal shell must be used, which leads to a large weight.

■ Square battery

Supplier: Samsung, CATL, Guoxuan High-tech

Used models: BMW i3, Roewe ERX5, NIO ES8, BYD series, GAC Trumpchi New Energy GE3

Advantages: flexible layout, customization, good safety

Disadvantages: large differences in single cells, difficult to unify standards

▲Packaged square battery

The biggest feature of square batteries is that they can be customized according to different cars. To put it simply and crudely, the OEM and supplier can design a set of battery layout methods for a car, but this in disguise increases the human and financial costs of both parties; another problem also arises. The batteries of each car are different, resulting in many square battery models on the market and difficult to unify the process.

Think about it, if you are a second party, is it better to use a ready-made template or to discuss with the customer to make a customized version?

■Soft-pack battery

Supplier: LG Chem, Farasis Energy

Models used: Buick VELITE5, Nissan Leaf, Chery eQ, BAIC New Energy

Advantages: light weight, high energy density

Disadvantages: large differences in monomers, difficult to unify standards, poor mechanical strength

▲Buick VELITE6 soft-pack battery

Soft-pack batteries are also very common in daily life, such as mobile phone batteries. It uses aluminum-plastic film as packaging material, which is obviously lighter than the above two batteries with metal shells; but naturally, it does not protect the battery as well as the above two methods.

■Is the future the world of soft-pack batteries?

The biggest advantage of soft-pack batteries is that they can improve the energy density of power lithium batteries at the existing technical level. According to statistics from Gaogong Lithium Battery, soft-pack batteries are 20% lighter than aluminum-shelled batteries of the same capacity, and have a capacity 50% higher than aluminum-shell batteries of the same size.

The subsidy policy for 2019 is still unclear, but it is certain that the subsidy amount is closely related to the energy density of the battery, and soft-pack batteries have a huge advantage in this regard.

■The localization of aluminum-plastic film is a problem

So why do many manufacturers not use soft-pack batteries? As mentioned earlier, aluminum-plastic film is the biggest difference between soft-pack batteries and the above two types of batteries. After the single-chip battery is assembled, it is sealed with aluminum-plastic film to form a battery. The aluminum-plastic film is used to protect the contents. This thing is also common in daily life, such as the outer packaging of capsules...

The important problem is that aluminum-plastic film is generally monopolized by Japanese manufacturers. Japan's DNP has a market share of nearly 50%, and the remaining Showa Denko can also account for about 25%. The two companies have also issued their own process standards.

▲Aluminum-plastic film manufacturing process (picture from New Materials Network)

However, due to process, equipment and other reasons, some indicators of domestic manufacturers' products cannot reach the Japanese level, such as punching depth, which is about 5 mm for domestic products, while Japan requires 8-12 mm.

Of course, there are also many excellent suppliers in China who are constantly working hard, such as Xinlun Technology (which acquired Japan's T&T aluminum-plastic film business) and Shanghai Zijiang.

■Do battery manufacturers favor soft-pack batteries?

According to the forecast of my country's energy storage network, the domestic soft-pack power lithium battery shipments in 2020 are expected to be 35.9 MWh, with a penetration rate of 38%, an increase of about 30 MWh compared to the shipments of about 5.5 MWh in 2017.

At present, domestic companies such as Farasis Energy, Jiewei Power, and Guoneng Battery have planned additional production of soft-pack batteries.

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