Discussion on the trend of cylinder battery in the field of EV post 18650 era

- Nov 05, 2016 -

No matter how much controversy for the small cylindrical electric core for EV, 18650 due to high energy density and high cost, become more and more important choice for passenger cars and logistics vehicles.          

18650 has the advantages of high maturity, consistency, high energy density, high cost, flexible arrangement of; the disadvantage is the number of pack is high, the quality control points. The single electric core greater by the change of interior design, greatly enhance the life of, magnification, also make the Pack more easily, but also can greatly reduce the energy density (volume and weight), reduces the assembly space by using the flexibility of large size battery with high energy density, most of the degree of automation low process bad high cost, poor consistency, and once the terrible consequences of failure.          

At present, the advantages of cylindrical batteries is largely due to the size standard, product maturity and cost competitiveness, and standardization is strong; the larger cylinder 26/32 has failed to become the mainstream; the new size 20/21 is ready, is to measure the balance of various factors and the market itself based on the 18650 existing strengths of both choose.          

What type of lithium batteries is more suitable?          

Unit volume capacity and cycle life, and safety rate is strongly related factors: capacity for every increase of 10%, will reduce the cycle life of about 20%; the capacity for every increase of 10%, the charge discharge rate decreased 30-40%; capacity for every increase of 10%, the temperature rise will increase about 20%, and exponentially increased; energy density safety, the greater the risk.          

18650 with 523+ graphite system, according to the new national standard, 1C 2.4AH has been designed to achieve the ultimate, more high energy density materials (NCA, 811) its stability and process control, is not so easy to imagine. So, it is not easy to use, but expensive......          

Cylindrical 18650 lithium-ion battery development faces many challenges          

The energy density of the battery requirements continue to improve, improve the material cost: A. new materials such as NCA, silicon carbide and other new materials supply chain is not mature, the cost is high, the supply is not stable; B. new material process of environmental requirements, fixed assets investment, huge energy consumption; single low battery capacity, technology PACK group and high cost; single electric core is single, adapt to the most negative bipolar ear structure, and influence on the energy density is more significant; high curvature part of a larger ratio, cycle life is greatly affected; high energy density and high rate charge at the same time requirements, the design space to the limit.          

Large diameter cylindrical lithium ion battery will become the inevitable trend: 20/21 18 is a better choice          

The same volume, the energy density advantage: an appropriate increase in diameter and height can obtain more effective volume.

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