Battery module with pre-formed battery cell thermal barrier

A pre-formed battery cell thermal barrier for a battery module includes a plurality of conductively coupled electrochemical cells and a pre-formed thermal barrier. The battery module can further include a cell holder configured to receive the plurality of conductively coupled electrochemical cells and the pre-formed thermal barrier. The pre-formed thermal barrier includes a cured potting material insertable into a cell-to-cell space in the battery module. The pre-formed thermal barrier includes one or more locking features configured to physically interlock with one or more corresponding locking features of the cell holder.