Energy Vault Holdings Inc. shares were down more than 18% at around 11:10 a.m. ET in the company's first day of trading on the New York Stock Exchange.

The energy storage upstart, previously named Energy Vault Inc., made its public debut on Feb. 14, following the completion of its merger with Novus Capital Corp. II, a special purpose acquisition company. The common stock and warrants of the combined company trade under the ticker symbols NRGV and NRGV WS, respectively.

Energy Vault Holdings raised approximately $235 million in gross proceeds through the transaction, it announced in a Feb. 14 news release.

Based in Westlake Village, Calif., Energy Vault is one of a host of companies raising significant funds to compete with lithium-ion battery storage and provide longer-lasting solutions, both in terms of storage duration and product lifespan, to help reliably integrate growing volumes of intermittent renewable energy into power grids.

"The proceeds enabled by this transaction, coupled with the additional strategic partnerships we have signed with some of the largest energy and industrial leaders across the globe provide a significant runway for us to drive shareholder value and execute against our growth strategy," Energy Vault Holdings CEO Robert Piconi said.