In this article, we demonstrated for the first time an ultra-strong bacterial cellulose supported poly(methyl vinyl ether-alt-maleic anhydride) as a multifunctional polymer electrolyte for a 4.45 V-class LiCoO₂ lithium metal battery. Such a polymer electrolyte based LiCoO₂ lithium metal battery delivered significant capacity retention (85% retention after 700 cycles) at 60 °C. A more thorough investigation elucidated that it played multiple roles in enhancing the electro-oxidative resistance and reversible lithium plating/stripping of a LiCoO₂ lithium metal cell. These extraordinary features open up a new avenue for the fabrication of advanced polymer electrolytes for high-voltage lithium metal cells.