There are three primary packaging forms of the lithium-ion battery, namely cylinder, square and soft package. Different packaging structures mean different characteristics, and they have their advantages and disadvantages. From the market development trend in recent years, the proportion of soft pack batteries is higher and higher, experts predict that the market share of soft pack battery is expected to exceed 50% in the future.
Cylindrical cell: mature production technology, high yield
There are many cylindrical lithium-ion batteries models, such as 14650, 17490, 18650, 21700, 26500, etc. The cylindrical lithium-ion battery production process is mature, PACK cost is low, battery product yield and battery PACK consistency is high; Due to the large heat dissipation area of the battery pack, its heat dissipation performance is better than that of the square battery. The cylindrical battery is convenient for the combination of various forms and is suitable for the full layout of electric vehicle space design. Cylindrical batteries, however, are usually made of steel or aluminum, which are heavy and have relatively low specific energy. At present, there are mature production companies in China, Japan, South Korea and the United States, such as SANYO, SONY, LG, Wanxiang A123 and so on.
With the further expansion of the electric vehicle market and the continuous improvement of the range requirements, vehicle companies have put forward higher requirements on the energy density, manufacturing cost, cycle life and additional product attributes of lithium-ion batteries. On the premise that great breakthroughs have not been made in the field of raw materials, appropriately increasing the volume of cylindrical batteries to obtain more battery capacity has become an exploratory direction. At present, Tesla has started the large-scale production of 21700 batteries and plans to use them in tesla Model3. If they pass the test on other tesla models, they will replace all the 18650 batteries previously used. Tesla’s approach may lead to a “21700 trend” around the world.
Prismatic cell: too many models, difficult to unify the process
The shell of the prismatic battery cell is mostly aluminum alloy, stainless steel, and other materials, and the inner winding or overlapping process is adopted. The protection purpose of the cell is better than that of the aluminum-plastic film battery (i.e., the soft package battery), and the safety of the cell is also greatly improved compared with the cylindrical battery.
The aluminum shell of the lithium-ion battery is developed based on a steel shell. Compared with steel shell, aluminum shell becomes the mainstream of lithium-ion battery shell due to its lightweight, safety, and the resulting performance advantages. At present, the aluminum shell of lithium-ion battery is still developing towards the technical direction of high hardness and lightweight, which will supply more superior lithium-ion battery products for the market. Currently, kukheon Tech, Samsung SDI, Risen and Youngdeok Times are the manufacturers of primatic batteries.
Because prismatic batteries can be customized to the size of the product, there are thousands of models on the market, and because there are so many, the process is difficult to unify. Square batteries have no problem in ordinary electronic products, but for industrial equipment products with multiple series and parallel connections, it is best to use standardized cylindrical lithium-ion batteries, so that the production process is guaranteed and it is easier to find replacement batteries in the future.
The pouch cell: the future market share is expected to exceed 50%
There is little difference between the key materials used in the pouch lithium-ion battery — anode material, anode material and diaphragm — and the traditional steel-shell and aluminum-shell lithium-ion battery. The biggest difference lies in the flexible packaging material (aluminum-plastic composite film), which is the most critical and technically difficult material in the pouch lithium-ion battery. Soft packaging materials are usually divided into three layers, that is, the outer resistance layer (generally nylon BOPA or PET formed of the outer protective layer), the resistance layer (middle layer aluminum foil) and the inner layer (multi-functional high barrier layer).
Soft pack battery packaging materials and structure make it has a series of advantages, such as good safety performance, soft pack battery in the structure of aluminum plastic film packaging, safety problems, soft pack battery will generally blow open, rather than like steel shell or aluminum shell cell explosion; The weight of the pouch battery is 40% lighter than that of the steel shell lithium-ion battery of the same capacity, and 20% lighter than that of the aluminum shell lithium-ion battery. Small internal resistance, soft pack battery internal resistance is smaller than lithium-ion battery, can greatly reduce the battery power consumption; The cycle performance is good, the cycle life of the soft battery is longer, 100 times of cycle attenuation is 4% ~ 7% less than that of the aluminum shell; Flexible design, shape variable arbitrary shape, can be thinner, can be customized according to customer needs, the development of new cell models.
The disadvantage of flexible battery is poor consistency, high cost and easy leakage. The high cost can be solved by large-scale production, and the leakage can be solved by improving the quality of aluminum-plastic film. The company that produces soft pack battery has many fluorine many, China aviation lithium, wanxiang, CITIC Guoan, micro-macro power and so on.
In the area of digital consumer electronics products related to the requirements of the battery toward the trend of small volume, lightweight, soft bag instead of the acceleration of rectangular aluminum shell, soft package of polymer lithium-ion battery with its excellent comprehensive performance, in smartphones, tablets, wearable equipment widely used in consumer electronics, And the rise rate is far higher than the average level of lithium-ion battery industry.
In addition, the application of power lithium-ion battery is also accelerating. According to the survey, BaiC, Changan, Dongfeng and other domestic high-end new energy passenger cars have begun to use pouch power lithium-ion battery. According to statistics, in 2015, the output of square, cylindrical and flexible lithium-ion batteries in China was 17GWh, 10.1GWh and 19.8GWh, accounting for 36.4%, 21.5% and 42.3%, respectively, and the proportion of flexible batteries has exceeded square and cylindrical.
In the first three quarters of 2016, influenced by the market fluctuations of new energy vehicles and other factors, the output of square and cylindrical batteries declined to varying degrees from the previous quarter. Only the output of soft battery rose from the previous quarter. The output of domestic soft battery reached 13Gwh in the first three quarters, of which, the third quarter rose by 20%. In recent years, domestic mainstream electric vehicle enterprises such as Dongfeng, Zotye, BaiC New Energy have also begun to try pouch power lithium-ion battery, Shanghai Kanai New Energy, Shandong Hengyu and other companies have also begun to invest in pouch power lithium-ion battery production lines.
In general, the cylindrical, square and flexible package batteries have their own advantages and disadvantages. Each battery has its own leading field, for example, square battery has more lithium iron phosphate, while flexible package battery has more terpolymer. With the introduction of new subsidy policies for new cars, the system energy density of batteries has become an important evaluation index. For example, the new subsidy policy requires that the driving mileage of pure electric buses should not be less than 200 km, the energy density of the battery system should be higher than 85Wh/kg, and the proportion of the total mass of the battery system to the total mass of the vehicle should not be higher than 20%. All these indicate that the subsidy is shifting to the direction of the three-way battery with lighter weight and higher range. The capacity of three flexible battery is 10~15% higher than the steel shell lithium battery of the same size specification, and 5~10% higher than the aluminum shell battery, and the weight is lighter than the steel shell battery and aluminum shell battery of the same capacity specification. Therefore, the subsidy new policy is more favorable for three flexible battery. In view of the advantages of pouch batteries, industry experts expect that with the development of battery routes, the penetration rate of pouch batteries in the new energy vehicle market will continue to improve, and the proportion of pouch batteries in various types of batteries is expected to exceed 50% in the future.