At present, lithium-ion batteries are mainly divided into three categories: square, cylindrical and soft-packed. Among them, square and cylindrical casings are mainly made of aluminum alloy, stainless steel and other hard shells, while soft-packed casings are made of aluminum-plastic film. This is their essential difference, performance The main advantages of soft-pack lithium batteries include:

　　(1) Good safety performance: Soft-pack batteries have less electrolyte leakage, and soft-pack batteries will inflate and crack in the event of safety hazards, unlike hard-shell batteries that will explode if the internal pressure is too high;

　　(2) Light weight: Soft-pack batteries are 40% lighter than steel-cased prismatic batteries of the same capacity, and 20% lighter than aluminum-cased prismatic batteries;

　　(3) Large battery capacity: The soft pack saves 20% of the volume, has a capacity 50% higher than that of steel-shell batteries of the same specifications, and is 20-30% higher than that of aluminum-shell batteries;

　　Low temperature lithium iron phosphate battery 3.2V 20A -20℃ charging, -40℃ 3C discharge capacity ≥70%

　　Charging temperature: -20~45℃ -Discharge temperature: -40~+55℃ -40℃ Support maximum discharge rate: 3C -40℃ 3C discharge capacity retention rate ≥70%

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　　(4) Good cycle performance: Soft-pack batteries have a longer cycle life, and the attenuation after 100 cycles is 4% to 7% less than that of aluminum cases;

　　(5) Small internal resistance: The internal resistance of soft-pack batteries is smaller than that of lithium batteries, and the domestic minimum can be less than 35mΩ, which greatly reduces the battery’s self-consumption;

　　(6) Sensitive design: the shape can be customized according to customer needs, and can be made thinner. Ordinary aluminum shells can only be 4mm, and soft bags can be 0.5mm.

　　Functional comparison of three types of batteries:

　　In terms of functions, soft-pack batteries have more comprehensive advantages and have broad future application prospects:

　　Low temperature and high energy density 18650 3350mAh-40℃ 0.5C discharge capacity ≥60%

　　1) Soft-pack batteries are more suitable for portable applications that require high space or thickness, such as 3C consumer electronics products;

　　2) Although prismatic batteries have high single capacity, they are heavy and large, while soft pack batteries have significant advantages in energy density, and now single cells are also developing in the direction of large capacity and high rate, which will be more in line with new technologies. Requirements for mobile power sources in areas such as energy vehicles;

　　3) Although the production process of cylindrical batteries is mature and the energy density advantage is significant, due to the small capacity of a single battery cell, a battery pack with the same capacity requires more cells, such as the battery pack capacity of Tesla Model S It is 85kWh, and there are about 7,000 18650-type cylindrical batteries, which requires very high requirements for the battery management system BMS. The single capacity of the soft-pack battery can be equivalent to more than 10 18650-type cylindrical batteries, and the requirements for BMS are relatively low. Most BMS in China and even around the world have limited supporting capabilities. Large-capacity battery packs do not use cylindrical batteries too much. In addition, cylindrical batteries have poor safety due to their high energy density, and their hard shells cause high internal pressure, so they often explode. events, and pouch batteries offer significant advantages.

　　my country's current mainstream electric vehicle companies are accelerating the use of soft-pack batteries. Passenger car companies such as BAIC and SAIC have begun to experiment with the use of soft-pack batteries, among which Wanxiang A123 and Funeng Technology soft-pack batteries occupy the mainstream. At the same time, domestic ternary soft packaging technology has made significant progress, and the energy density has increased significantly. The trend of soft packaging is on the rise, and power battery companies are increasing their efforts to expand the production of soft packaging in order to seize the opportunity.

　　Facing the huge market temptation, domestic companies are also investing in the lithium battery soft pack business. From January to May 2018, my country's power battery installed capacity reached 12.66Gwh, a year-on-year increase of 247.80%. Among them, the installed capacity of soft-pack power batteries reached 1.43Gwh, a year-on-year increase of 71.98%, and the market share reached 11%. The share dropped by 12 percentage points from January to May last year; the main reason was the installed capacity of CATL and BYD in the first five months. The rapid growth rate has increased the market share of prismatic batteries, while the soft pack and cylindrical batteries have declined. It is predicted that the demand for lithium batteries and the penetration rate of soft packs will increase side by side. In 2020, the penetration rate of soft packs will be about 41%, and the demand for soft pack batteries will reach 59GWh, with a GAGR of 35%.

　　Soft-pack batteries generally have three sealing edges. The heat sealing machine adjusts appropriate temperature, strength, time and other parameters to ensure the sealing effect. The quality of the seal directly affects the safety and life of the battery. Both over-sealing and under-sealing can easily lead to poor quality. The thickness of the seal is a significant indicator of seal quality, and thickness monitoring of the top and side sealing processes is an important means to improve battery quality and safety.

　　Dacheng Precision 2D Offline Laser Thickness Gauge is a model specially designed to provide various thickness measurement solutions at lithium-ion battery production sites. High-precision thickness measurement of samples can be performed in the XY plane. According to different measurement needs, the measurement fixture can be replaced to complete the thickness scanning measurement of the given sample. Each installation position can measure a thickness summary. Placed in the soft pack battery top and side sealing workshop, it is used for offline random inspection of edge sealing thickness and direct judgment of seal quality. Thickness measurement of soft pack battery seals can be easily accomplished on this device.

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