Elon Musk hints at a more powerful EV battery ahead of Tesla's Battery Day

Tesla Inc's chief executive Elon Musk has suggested the US electric carmaker may be able to mass produce longer-life batteries with 50% more energy density in three to four years.

"400 Wh/kg with high cycle life, produced in volume (not just a lab) is not far. Probably 3 to 4 years," Musk tweeted on Monday ahead of its anticipated "Battery Day" event where Tesla is expected to reveal how it has improved its battery performance.

Researchers have said the energy density of Panasonic's "2170" batteries used in Tesla's Model 3 is around 260Wh/kg, meaning a 50% jump from the current energy density which is key to achieving a longer driving range.

Tesla said its Battery Day will take place on the same day as its 2020 annual meeting of shareholders on Sept. 22.

The electric car manufacturer also showed a background image where a number of dots are clustered in line formations, sparking speculation among media and fans about what it will reveal at the event.

South Korean battery expert Park Chul-wan said the image may hint at "silicon nanowire anode," a breakthrough technology which can potentially increase both battery energy density and battery life sharply.

Panasonic Corp earlier told Reuters that it plans to boost the energy density of the original "2170" battery cells it supplies to Tesla by 20% in five years.

Tesla is also working with China's Contemporary Amperex Technology Ltd (CATL) to introduce a new low-cost, long-life battery in its Model 3 sedan in China later this year or early next year, with the batteries designed to last for a million miles of use, Reuters reported in May.

A very "limited number of stockholders" will be able to attend the Sept. 22 events due to pandemic-related restrictions, Tesla said, and a lottery will be held to select attendees.