At present, there are three main mainstream lithium battery packaging forms, namely cylindrical, square and soft packaging. Different packaging structures mean different characteristics, and each of them has its own advantages and disadvantages.

1、Round lithium battery

Circular lithium batteries refer to cylindrical lithium batteries. The earliest cylindrical lithium battery is the 18650 lithium battery invented by Japan's SONY Company in 1992. Because the 18650 cylindrical lithium battery has a long history, the market penetration rate is very high. Cylindrical lithium batteries use a fairly mature winding process with a high degree of automation, stable product quality, and relatively low cost. There are many models of cylindrical lithium batteries, such as 14650, 17490, 18650, 21700, 26650, etc. are common. Cylindrical lithium batteries are more popular among Japanese and Korean lithium battery companies, and there are also considerable-scale companies in China producing cylindrical lithium batteries.

With the further expansion of the electric vehicle market and the increasing requirements for cruising range, vehicle manufacturers have put forward higher requirements for power batteries in terms of energy density, manufacturing cost, cycle life and additional product attributes. As long as there has not yet been a huge breakthrough in the field of raw materials, appropriately increasing the size of cylindrical batteries to obtain more battery capacity has become an explorable direction. Currently, Tesla has started large-scale production of 21700 batteries and plans to use them on Tesla Model 3. If tested on other Tesla models, all the 18650 batteries used previously will be replaced. Tesla This approach may lead a "21700 trend" around the world.

2、Square lithium battery

Square lithium batteries usually refer to aluminum-shell or steel-shell square batteries. The popularity of square batteries is very high in China. With the rise of automobile power batteries in recent years, the contradiction between automobile cruising range and battery capacity has become increasingly prominent. Domestic power battery manufacturers Aluminum-shell rectangular batteries with higher battery energy density are mostly used because the structure of rectangular batteries is relatively simple. Unlike cylindrical batteries, which use higher-strength stainless steel as the casing and accessories such as explosion-proof safety valves, the overall accessory weight is higher. Light and relatively high energy density. Square batteries use two different processes: winding and lamination.

However, because prismatic lithium batteries can be customized according to the size of the product, there are thousands of models on the market, and because there are so many models, it is difficult to unify the process. There is no problem in using square batteries in ordinary electronic products, but for industrial equipment products that require multiple series and parallel connections, it is best to use standardized cylindrical lithium batteries. This way the production process is guaranteed and it will be easier to find replacements in the future. Battery.

3、Soft pack lithium battery

The key materials used in soft-pack lithium batteries—positive electrode materials, negative electrode materials, and separators—are not much different from traditional steel-shell and aluminum-shell lithium batteries. The biggest difference lies in the soft packaging material (aluminum-plastic composite film). It is the most critical and technically difficult material in soft-pack lithium batteries. Flexible packaging materials are usually divided into three layers, namely the outer barrier layer (generally an outer protective layer composed of nylon BOPA or PET), the barrier layer (middle layer aluminum foil) and the inner layer (multifunctional high barrier layer).

The packaging materials and structure of soft-pack batteries give them a series of advantages. The Electric Zhijia public account summarizes that, for example, the safety performance of soft-pack batteries is good. The soft-pack batteries are structurally packaged with aluminum-plastic film. When safety problems occur, soft-pack batteries generally It will bulge and crack, instead of exploding like steel or aluminum-cased batteries; it is light in weight, and the weight of soft-pack batteries is 40% lighter than steel-cased lithium batteries of the same capacity, and 20% lighter than aluminum-cased lithium batteries; internal resistance Small, the internal resistance of the soft-pack battery is smaller than that of the lithium battery, which can greatly reduce the self-consumption of the battery; the cycle performance is good, the cycle life of the soft-pack battery is longer, and the attenuation after 100 cycles is 4% to 7% less than that of the aluminum case. ; The design is flexible, the shape can be changed to any shape, it can be thinner, and it can be customized according to customer needs and develop new battery cell models. The disadvantages of soft-pack batteries are poor consistency, high cost, and prone to leakage. High costs can be solved through large-scale production, and liquid leakage can be solved by improving the quality of aluminum plastic films.

4、Comparative analysis of technical characteristics

1. Battery shape: Square lithium batteries can be of any size, so they are incomparable to cylindrical batteries.

2. Rate characteristics: There are process limitations for welding multi-pole tabs of cylindrical lithium batteries, so the rate characteristics are slightly worse than the square multi-pole tab solution.

3. Discharge platform: The same positive electrode material, negative electrode material, and electrolyte are used, so the discharge platform is theoretically the same. However, the internal resistance of the square battery has a slight advantage, so the discharge platform is slightly higher.

4. Product quality: The cylindrical lithium battery process is very mature, the probability of common secondary slitting defects of pole pieces is low, and the winding process is more mature and automated than the lamination process. The lamination process is still using a semi-manual method. Therefore, it has a negative impact on the quality of the battery.

5. Welding of tabs: The tabs of cylindrical lithium batteries are easier to weld than square lithium batteries. Square batteries are prone to false welding, which affects battery quality.

6. PACK into groups: Circular batteries are relatively easier to use, so the PACK solution is simple and has good heat dissipation effect. When packing square batteries, the heat dissipation problem must be solved.

7. Structural features: The chemical activity of the corners of square batteries is poor, and the performance of the battery will decrease significantly after long-term use.

In short, whether cylindrical, prismatic or soft-pack batteries are currently developing rapidly, it is because they have been well used in their respective application fields.

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