Effect of polymer and ceramic morphology on the material and electrochemical properties of electrospun PAN/polymer derived ceramic composite nanofiber membranes for lithium ion battery separators

Electrospun polyacrylonitrile (PAN)/ceramic fibers were created by combining the PAN polymer and various room temperature curable organopolysilazane (OPSZ) precursors in a one step electrospinning process. The resultant PAN/ceramic (70:30 wt%) hybrid fiber mats consisted of well-formed, uniform fibers with evenly distributed ceramic, both in the longitudinal and cross-sections of the fibers. The presence of the tetraethyl orthosilicate (TEOS) pendant chain attached to the polysilazane (PSZ) backbone impacted the ability of the ceramic to form a continuous ceramic network within the polymer network. Results show that the membranes with an interconnected ceramic domain showed superior mechanical and electrochemical properties. The interconnected ceramic domains affect the polymer's ability to crystallize, leading to an increase in amorphous regions within the fiber. The increase in amorphous regions leads to increased electrolyte uptake, superior ionic conductivity and excellent cycling performance. Batteries containing 40 wt% TEOS:PSZ and 20 wt% TEOS:PSZ separators showed greater than 90% capacity retention at a C/5 discharge rates after 100 cycles. C-rate tests show a similar trend with 40 wt% TEOS:PSZ and 20 wt% TEOS:PSZ membranes maintaining greater capacity retention even at high charge rates.