Structural characteristics of 18650 cylindrical, square, and soft pack lithium batteries.
With the further expansion of the electric vehicle market and the increasing demand for range, vehicle manufacturers have put forward higher requirements for power batteries in terms of energy density, manufacturing cost, cycle life, and additional product attributes. Given the lack of significant breakthroughs in the field of raw materials, increasing the volume of cylindrical batteries appropriately to obtain more battery capacity has become an exploratory direction. At present, Tesla has launched large-scale production of 21700 batteries and plans to use them in Tesla Model 3. If tested on other Tesla models, all 18650 batteries previously used will be replaced. Tesla's approach may lead a "21700 trend" worldwide.
Square hard shell battery: too many models, difficult to unify the process
The shell of square hard shell batteries is mostly made of materials such as aluminum alloy and stainless steel, and the interior adopts winding or laminated technology, which provides better protection for the battery cells than aluminum-plastic film batteries (i.e. soft pack batteries). The safety of the battery cells has also been greatly improved compared to cylindrical batteries.
The aluminum shell of lithium batteries has developed on the basis of steel shells. Compared with steel shells, aluminum shells have become the mainstream of lithium battery casings due to their lightweight, safety, and performance advantages. The aluminum shell of lithium batteries is currently developing towards high hardness and lightweight technology, which will provide the market with more technologically superior lithium battery products. At present, companies producing square hard shell batteries include Guoxuan High tech, Samsung SDI, Lishen, Ningde Times, etc.
Due to the customizable production of square lithium batteries based on product size, there are thousands of models available in the market, but due to the large number of models, it is difficult to standardize the manufacturing process. Square batteries are not a problem to use in ordinary electronic products, but for industrial equipment products that require multiple series or parallel connections, it is best to use standardized cylindrical lithium batteries. This ensures the production process and makes it easier to find replaceable batteries in the future
Soft pack batteries: expected market share to exceed 50% in the future
The key materials used in soft pack lithium batteries - positive electrode materials, negative electrode materials, and separators - are not significantly different from traditional steel and aluminum shell lithium batteries. The biggest difference lies in the soft packaging material (aluminum-plastic composite film), which is the most critical and technically difficult material in soft pack lithium batteries. Soft packaging materials are usually divided into three layers, namely the outer protective layer (usually made of nylon BOPA or PET), the barrier layer (middle layer of 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, such as good safety performance. Soft pack batteries are packaged with aluminum-plastic film in the structure. When safety issues occur, soft pack batteries generally burst and crack, unlike steel or aluminum shell cells that explode; Lightweight, soft pack batteries are 40% lighter than steel shell lithium batteries of the same capacity and 20% lighter than aluminum shell
lithium batteries; Low internal resistance, the internal resistance of soft pack batteries is smaller than that of lithium batteries, which can greatly reduce the battery's self consumption; Good cycling performance, longer cycling life of soft pack batteries, with a 4% to 7% reduction in attenuation after 100 cycles compared to aluminum shells; Flexible design, adjustable shape, can be thinner, can be customized according to customer needs, and new battery cell models can be developed.
The shortcomings of soft pack batteries are poor consistency, high cost, and easy leakage. The high cost can be solved through large-scale production, while the leakage can be resolved by improving the quality of aluminum-plastic film. Enterprises producing soft pack batteries include Duofuduo, AVIC Lithium Battery, Wanxiang, CITIC Guoan, Weihong Power, etc.
