Li-Ion batteries are the most widely manufactured batteries in the world. If you don't think it is that common you surely wont believe that 40% of the worlds batteries are Lithium Ion. They are used in Laptop, Power tools, robots, electric vehicles, solar grids and almost all devices that requires to store energy.
currently lithium ion battery mainly comes/makes from China, china should make at least 80% of the total lithium batteries.
This Chinese manufacturer does all kinds of Lithium batteries and is also doing custom builds:
BENZO Energy Technology Co.,Ltd
Their online website: www.benzoenergy.com
They are a professional lithium battery manufacturer Chinese.
They can customize the 18650 lithium battery you need according to your requirements.