Boston-area start-up Ionic Materials has raised $65 million in its third round of venture funding. Backers include unnamed electronics firms and auto manufacturers. Last month, an alliance of Renault, Nissan, and Mitsubishi Motors identified Ionic Materials as the first investment of their new venture fund. Founded by Tufts University materials scientist Michael Zimmerman, Ionic Materials is developing a solid polymer electrolyte for lithium-ion batteries. It will use the funds for hiring and to meet what it calls “significant market demand” for its material.