A battery system includes a first battery module, a second battery module, and a thermoresistant spacer disposed between the first battery module and the second battery module. The thermoresistant spacer may be a thermoresistant urethane foam or a silicon pad and may include thermoresistant additives, which may include at least one of melamine resin powder, aerogel particles, and milled oxidized polyacrylonitrile fibers. A flame retardant material may be disposed over at least a surface of the thermoresistant spacer.