Separators　or　electrolyte　membranes　are　recognized　as　the　key　components　to　guarantee　ion　transport　in　rechargeable　batteries.　However,　the　ever‐growing　applications　of　the　battery　systems　for　diverse　working　environments　bring　new　challenges,　which　require　advanced　battery　membranes　with　high　thermal　stability,　excellent　mechanical　strength,　high　voltage　tolerance,　etc.　Therefore,　it　is　highly　desirable　to　design　novel　methods/concepts　to　solve　the　current　challenges　for　battery　membranes　through　understanding　the　mechanism　of　novel　phenomena　and　electrochemical　reactions　in　battery　systems　working　under　unconventional　conditions.　Recently,　the　new　emerging　Janus　separators　or　electrolyte　membranes　with　two　or　more　distinct　chemical/physical　properties　arising　from　their　asymmetric　structure　and　composition,　are　promising　to　address　the　above　challenges　via　rational　design　of　their　targeted　functionalities.　To　this　end,　in　this　review,　we　first　briefly　cover　the　current　challenges　of　the　traditional　battery　membrane　for　battery　devices　working　in　unconventional　conditions.　Then,　the　state‐of‐art　developments　of　the　rational　design　of　Janus　membranes　to　overcome　the　above　challenges　for　diverse　battery　applications　are　summarized.　Finally,　we　outline　these　latest　developments,　challenges,　and　future　potential　directions　of　the　Janus　membrane.　Our　review　is　aimed　to　provide　basic　guidance　for　developing　functional　separators　or　electrolyte　membranes　for　advanced　batteries.