London (Reuters) - The uptrend in demand for metals such as copper used in electric vehicles is intact despite doubts raised by the slowdown in EV sales, but estimating numbers is difficult as the market is evolving, commodity trader IXM's head of refined metal said.

Sales of electric vehicles have slowed for reasons including a lack of charging infrastructure and concerns about resale values.

"The electric vehicle industry is new. There are a lot of variables including penetration rates and battery chemistries which makes forecasting demand a guessing game," Tom Mackay said.

"Growth in electric vehicle sales is slowing, but sales are still increasing. It varies from region to region, but overall growth is strong and the demand story for metals is healthy."

According to consultancy Rho Motion, sales of battery EVs and plug-in hybrid EVs rose 32% last year to 13.63 million units, while in the first and second quarters of this year sales were down 25% and up 22% respectively from the previous quarters.

Copper is used in electric vehicle wiring. It is also used in the batteries, which typically contain lithium and depending on the chemistry nickel and cobalt.

"There have been some impressive technological advances in LFP (lithium ion phosphate) chemistry. Some LFP batteries can go for 1,000 kilometres and some can charge up to 80% in 10 minutes," said Mackay, who manages the copper cathode, zinc, lead nickel, cobalt and lithium books at the Swiss-based trader.

LFP batteries were developed for the Chinese market to provide a cheaper alternative to nickel cobalt manganese (NCM). But earlier LFP batteries could not be used for long distances.

"People still believe Western world battery demand will still be predominantly NCM, if only because of the higher value of recycling NCM batteries," Mackay said.

"Recyclability is a very important factor for automakers when deciding what chemistries to use."

Mackay added that the number of people working at IXM globally is lower than before, around 440.

"Focus has been on the quality of people. We exited the aluminium business because it wasn't providing the return we require from the resources."

(Reporting by Pratima Desai; editing by Emelia Sithole-Matarise)