Braving the frigid cold of the Chinese winter last December, William Li, chief executive of Chinese automaker NIO, drove for 14 hours from Shanghai to the southern eastern city of Xiamen, allowing viewers to watch him via a livestream on the company’s app. His aim? To demonstrate that the latest version of the company’s ET7 sedan model could complete the 1,000 kilometer journey using a semi-solid-state battery pack — a new technology for NIO that its peers in China and around t