One may wish to increase the cooling capacity of the radiator by adding a coolant to the water. One may also wish to use a tripartite fuel to investigate the effects. Like using any bio ethanol whose exhaust temperature reduction characteristics has been established in the literature
As professor Usman mentioned in detail, you can add nanomaterials into your coolant working fluid in order to increase thermal capacity and heat removal ability.
About battery thermal management, I believe that making battery cooler via active thermal management systems such as air-cooled or liquid-cooled systems are no longer efficient. Nowadays, the most efficient way to cool the battery is benefiting from Phase Change Materials. You can refer to my papers for more technical information.