At this time I would say that the electric car industry as a whole is too new to be able to invest in it as a sector. There are only a handful of companies that focus solely on electric cars to create a moderately diverse portfolio, let alone a mutual fund. You can invest in mutual funds that include EV stocks as part of an auto sector or clean energy play, for example, but there's just not enough for an EV-only fund at this point.
At this point, perhaps the best you can do if you want an exclusively EV portfolio is add some exposure to the companies that are the biggest players in the market and review the market periodically to see if any additional investments could be made to improve your diversification. Look at EV-only car makers, battery makers, infrastructure providers, etc. to get a decent balance of stocks.
I would not put any more than 10% of your entire investment portfolio into any one stock, and not more than 20% or so in this sector.