Discussion on the development trend of cylindrical 18650 lithium-ion batteries in electric vehicles

Regardless of small cylindrical batteries for the number of controversial EV, 18650 due to high energy density and cost-effective, as more and more passenger cars and logistics vehicles, an important choice. 18650 has the advantage of high maturity, high consistency, energy density, cost, flexible arrangement of high; disadvantage is the number of pack high difficulty, quality control points. The larger single cells can also make the Pack look easier by changing the internal design, dramatically increasing life, magnification, etc., but at the same time significantly reducing energy density (size and weight) and reducing assembly space utilization Flexibility, high-energy-density large-size batteries, most of the low degree of automation, process and other undesirable high cost, consistency is poor, and once the failure of the terrible consequences.

At present, the advantages of cylindrical batteries to a large extent due to size standardization, product maturity and cost competitiveness, and standardization must be strong correlation; larger cylinder 26/32, etc. has been unable to become mainstream; ready to come out of the new size 20/21, the market itself is a balance of many factors and 18650 based on the balance of the existing advantages of choice!

What type of lithium batteries is more suitable?

Capacity per 10% increase in capacity, charge and discharge rate reduced by 30-40%; capacity for each 10% increase in capacity per cycle, life cycle, , The temperature rise will increase by about 20%, and a geometric rise; energy density, the higher the risk of greater security.

Cylindrical 18650 lithium-ion battery development faces many challenges

New materials such as NCA, silicon carbon and other new materials supply chain is not yet mature, high cost, the supply is difficult to stabilize; b. New materials on the environmental requirements of the process, investment in fixed assets High energy consumption; single cell capacity is low, PACK group technical requirements and high cost; single cell up to accommodate single-pole, negative bipolar ear structure, and the energy density is more significant; high curvature ratio Large, cycle life is greatly affected; high-energy density and high-rate charging at the same time, the design space has reached the limit.

Larger-diameter cylindrical lithium-ion batteries will become an inevitable trend: 20/21 relative 18 is a better choice

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

The benefits: 

A. Appropriate to improve the energy density, you can choose conventional materials, stable, cost-effective

B. Can be properly designed to reduce the internal multi-pole internal resistance.

C. The same energy density, you can choose fast-filling characteristics of graphite, improve fast-filling performance

D. High curvature part of the ratio is reduced, to extend the battery cycle life.

E. Single cell capacity increases, reducing the cost of Pack.