The origin of this revelation are Bloomberg's unofficial sources.
LG Chem is expected to supply Tesla with 21700 cylindrical cells, produced in Nanjing, some 200 miles (320 km) west of Shanghai.
Separately, Tesla is reportedly still in talks with CATL, which also might become a supplier. The report doesn't say anything about negotiations with Panasonic, which was the main battery supplier for Tesla so far.
Production of the base version of Model 3 is promised to start by the end of this year.
LG Chem batteries also to be used for the base version of Tesla Model Y, once production of those will be launched in the future.