Their paper “Biomimetic Solid-State Zn2+ Electrolyte for Corrugated Structural Batteries” published in the ACS Nano journal describes lightweight rechargeable Zn/Zn+2 batteries with so much increased safety and impact resistance that they can double up as rugged structural elements. To design their solid electrolyte, the researchers tried to mimic the mechanical and electrical properties of articular cartilage, known for their fibrous content, high resilience to deformation and excellent ionic conductivity.
They Zn2+ solid and non-corrosive electrolyte compound consists of an optimum blend of branched aramid nanofibers (BNA) for the mechanical part, Poly(ethyleneoxide) (PEO) and Zn(CF3SO3)2 as the ion-transport components. The BANFs replicates the fibrous structure of articular cartilage. They serve as the high-strength components of the composite electrolyte and mimic the stiff collagen nanofibers of cartilage, branching out from an original 200-300nm diameter stem into about five to six fork-points whose branches are 50 to 100nm in diameter.
“Multi-point bifurcation of these filaments facilitates the formation of a fibrous 3D network with a large volume fraction of nanoscale pores necessary for ion transport. Similarly to the structure of soft tissues, the efficient entanglement of nanoscale branches lends high stiffness to the material on both macro- and nanoscales needed for the prevention of dendrite growth”, the paper reads.
As for the PEO and Zn(CF3SO3)2, the authors compare their properties to that of the soft proteoglycan portion of natural cartilage. The researchers then optimized the whole PEO : Zn(CF3SO3)2 : BANFs mixture (PZB) with respect to Zn2+ conductivity and mechanical properties, reaching a 9:3:1 ratio for a solid electrolyte now called PZB-931.
The paper then reviews Zn/PZB-931/γ-MnO2 battery prototypes undergoing different deformations such as moulding, stamping and even cutting or stabbing (leak-proof by design) while they retained both their capacity and voltage. Next, they prove such corrugated battery packs could be used as direct replacement for original drone covers, acting both as a structural element and as a supplement power source while being light-enough that their integration would extend the drone’s total flight time.
“The replacement of the traditional alkaline electrolyte with a BANF composite drastically changes the mechanism of ion transport, electrode processes including the dendrite growth and results into a flexible, rechargeable battery with cyclability of over 100 cycles and over 90% charge retention” the authors wrote.
These exceptional mechanical properties combine with charge storage parameters comparable to those of lithium thin film batteries. Hence the authors conclude that such batteries could be designed into a large variety of corrugated shapes adaptable to specific load-bearing conditions, including those found in UAVs. For now, the zinc batteries are best as secondary power sources because they can’t charge and discharge as quickly as their lithium ion equivalent, the researchers plan to figure out a better partner electrode that could improve the speed and longevity of such zinc rechargeable batteries.
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