Developing
efficient energy storage technologies is at the core
of current strategies toward a decarbonized society. Energy storage
systems based on renewable, nontoxic, and degradable materials represent
a circular economy approach to address the environmental pollution
issues associated with conventional batteries, that is, resource
depletion and inadequate disposal. Here we tap into that prospect
using a marine biopolymer together with a water-soluble polymer to
develop sodium ion battery (NIB) separators. Mesoporous membranes
comprising agarose, an algae-derived polysaccharide, and poly(vinyl
alcohol) are synthesized via nonsolvent-induced phase separation.
Obtained membranes outperform conventional nondegradable NIB separators
in terms of thermal stability, electrolyte wettability, and Na
+
conductivity. Thanks to the good interfacial adhesion with
metallic Na promoted by the hydroxyl and ether functional groups of
agarose, the separators enable a stable and homogeneous Na deposition
with limited dendrite growth. As a result, membranes can operate at
200 μA cm
–2
, in contrast with Celgard and
glass microfiber, which short circuit at 50 and 100 μA cm
–2
, respectively. When evaluated in Na
3
V
2
(PO
4
)
3
/Na half-cells, agarose-based
separators deliver 108 mA h g
–1
after 50 cycles
at C/10, together with a remarkable rate capability. This work opens
up new possibilities for the use of water-degradable separators, reducing
the environmental burdens arising from the uncontrolled accumulation
of electronic waste in marine or land environments.