So what is this made of if not lithium?

From the linked article

The battery uses a carbon electrode to store hydrogen that has been split from water, and then works as a hydrogen fuel cell to produce electricity

Chatgpt says:

Proton batteries are an emerging energy storage technology that uses hydrogen ions (protons) to store and release energy. They split hydrogen gas into protons and electrons at the anode, with a membrane allowing only protons to pass to the cathode. At the cathode, protons combine with oxygen and electrons to generate electrical energy. Proton batteries offer high energy density and potential environmental benefits but are still in early development and face efficiency and cost challenges compared to traditional batteries

What is the energy density of this? It sounds like a rebrand of a hydrogen fuel cell, which has some limited applications, but has been supplanted by lithium-ion due to hydrogen’s low energy density and the fuel cells/electrolysis combo having poor energy efficiency.

The new proton battery has an energy density of 245 watt hours per kilogram, nearly three times the energy density of the team’s 2018 prototype