Norbornene-based polymers have shown promise as solid electrolytes for lithium-based rechargeable electrochemical cells. These polymers are characterized as single-ion conductors.
Single-ion-conducting polymers that can be used in lithium cells have long been sought. Single-ion conductors are preferred to multiple-ion conductors as solid electrolytes because concentration gradients associated with multiple-ion conduction lead to concentration polarization. By minimizing concentration polarization, one can enhance charge and discharge rates.
Norbornene sulfonic acid esters have been synthesized by a ring-opening metathesis polymerization technique, using ruthenium-based catalysts. The resulting polymer structures (see figure) include sulfonate ionomers attached to the backbones of the polymer molecules. These molecules are single-ion conductors in that they conduct mobile Li+ ions only; the —SO3 – anions in these polymers, being tethered to the backbones, do not contribute to ionic conduction.
This molecular system is especially attractive in that it is highly amenable to modification through functionalization of the backbone or copolymerization with various monomers. Polymers of this type have been blended with poly(ethylene oxide) to lend mechanical integrity to free-standing films, and the films have been fabricated into solid polymer electrolytes. These electrolytes have been demonstrated to exhibit conductivity of 2 × 10–5 S·cm (which is high, relative to the conductivities of other solid electrolytes) at ambient temperature, plus acceptably high stability.
This type of norbornene-based polymeric solid electrolyte is in the early stages of development. Inasmuch as the method of synthesis of these polymers is inherently flexible and techniques for the fabrication of the polymers into solid electrolytes are amenable to optimization, there is reason to anticipate further improvements.
This work was done by Iris Cheung and Marshall Smart of Caltech and Surya Prakash, Akira Miyazawa, and Jinbo Hu of the University of Southern California for NASA's Jet Propulsion Laboratory. For more information, download the Technical Support Package (free white paper) at www.techbriefs.com/tsp under the Materials category.
In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to:
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Refer to NPO-41134, volume and number of this NASA Tech Briefs issue, and the page number.
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Norbornene-Based Polymer Electrolytes for Lithium Cells
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Overview
The document titled "Norbornene-Based Polymer Electrolytes for Lithium Cells" (NASA Tech Briefs NPO-41134) outlines advancements in solid polymer electrolytes (SPEs) aimed at improving lithium rechargeable batteries. The research, conducted by NASA's Jet Propulsion Laboratory (JPL) and the University of Southern California (USC), focuses on developing single-ion conducting polymers derived from norbornene-based monomers through a ring-opening metathesis polymerization (ROMP) technique.
The primary goal of this research is to create a solid polymer electrolyte that exhibits high ionic conductivity, chemical stability, and mechanical integrity, addressing the limitations of existing polymer electrolytes, such as poly(ethylene oxide) (PEO). Traditional PEO-based systems have shown marginal conductivity (10^-6 to 10^-5 S/cm) at ambient temperatures and low lithium ion transference numbers, which hinder their performance in lithium-based rechargeable cells. In contrast, the newly developed polynorbornene-based electrolytes demonstrate significantly improved conductivity (2.0 x 10^-5 S/cm at 25°C) and are designed to operate effectively at room temperature.
The document highlights the advantages of single-ion conductors, where ionic conduction is facilitated exclusively by mobile lithium ions, minimizing concentration gradients and polarization issues typically associated with conventional electrolytes. The synthesized polymers incorporate sulfonate ionomers tethered to the polymer backbone, enhancing their ionic conductivity and stability.
The research also emphasizes the potential benefits of SPEs, including increased safety, higher specific energy (over 200 Whr/Kg), greater packaging flexibility, and improved storage and longevity compared to state-of-the-art (SOA) lithium systems. These attributes make SPEs particularly attractive for applications in aerospace and other fields requiring reliable and efficient energy storage solutions.
The document concludes by noting that the technology is still in the early stages of development, with ongoing efforts to optimize polymer synthesis and electrolyte fabrication techniques. The ultimate aim is to demonstrate the utility of these novel polymer electrolytes in experimental lithium rechargeable cells, paving the way for advancements in solid-state battery technology.
