Cross-Linking of Sugar-Derived Polyethers and Boronic Acids for Renewable, Self-Healing, and Single-Ion Conducting Organogel Polymer Electrolytes

This report describes the synthesis and characterization of organogels by reaction of a diol-containing polyether, derived from the sugar d-xylose, with 1,4-phenylenediboronic acid (PDBA). The cross-linked materials were analyzed by infrared spectroscopy (FT-IR), thermal gravimetric analysis (TGA), scanning electron microscopy (FE-SEM), and rheology. The rheological material properties could be tuned: gel or viscoelastic behavior depended on the concentration of polymer, and mechanical stiffness increased with the amount of PDBA cross-linker. Organogels demonstrated self-healing capabilities and recovered their storage and loss moduli instantaneously after application and subsequent strain release. Lithiated organogels were synthesized through incorporation of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) into the cross-linked matrix. These lithium–borate polymer gels showed a high ionic conductivity value of up to 3.71 × 10–3 S cm–1 at 25 °C, high lithium transference numbers (t+ = 0.88–0.92), and electrochemical stability (4.51 V). The gels were compatible with lithium-metal electrodes, showing stable polarization profiles in plating/stripping tests. This system provides a promising platform for the production of self-healing gel polymer electrolytes (GPEs) derived from renewable feedstocks for battery applications.


Cross-linking and monosubstitution of PDBA
Scheme S1 Reaction of dp-poly(D-1) and 1,4-phenylenediboronic acid (PDBA) can afford cross-linked or monosubstituted products, or those containing a combination of both.

Figure S1
Annotated 1 H NMR spectrum of IPXF in chloroform-d.

Figure S2
Annotated 13 C{ 1 H} NMR spectrum of IPXF in chloroform-d.       Annotated 1 H NMR spectrum of dp-poly(D-1) in chloroform-d. A 91% deprotected sample has been chosen to demonstrate the protected vs. deprotected proton environments.

Figure S13
Vial inversion tests of reactions between a 0.409 mol L -1 dp-poly(D-1) solution in DMSO with increasing equiv. of PDBA. Equiv. of PDBA from left to right: 0.05, and 0.125. Vial labels show the theoretical maximum percentage crosslinking, i.e the percentage of polymer hydroxy groups that would be functionalised if all added PDBA reacted.

Figure S14
Vial inversion tests of reactions between a 0.072 mol L -1 dp-poly(D-1) solution in DMSO with increasing equiv. of PDBA. Equiv. of PDBA from left to right: 0.25, 0.50, and 1.00. Vial labels show the theoretical maximum percentage cross-linking, i.e the percentage of polymer hydroxyl groups that would be functionalised if all added PDBA reacted. S12

pH Stability
Figure S15 Vial inversion tests of organogels made with a 0.144 mol L -1 dp-poly(D-1) solution in DMSO with 0.5 equiv. of PDBA upon addition of small amount of acid or base. From left to right: original organogel; organogel after addition of 1 mol L -1 HCl; organogel after addition of 1 mol L -1 NaOH; partial reformation of gel after addition of 1 mol L -1 HCl to basic gel mixture. S13

5.1
Frequency sweep of 0.287 mol L -1 dp-poly(D-1), 0.25 PDBA equiv. Figure S19 LEFT: Dynamic frequency sweep of organogel made from dp-poly(D-1) and PDBA with a polymer concentration of 0.287 mol L -1 and 0.25 equiv. of PDBA. Annotations show the crossover frequency and modulus. RIGHT: Photograph of the organogel used in rheological studies.

5.3
Frequency sweep of 0.287 mol L-1 dp-poly(D-1), 1.00 PDBA equiv. Figure S21 LEFT: Dynamic frequency sweep of organogel made from dp-poly(D-1) and PDBA with a polymer concentration of 0.287 mol L -1 and 1.00 equiv. of PDBA. Annotations show the crossover frequency and modulus. RIGHT: Photograph of the organogel used in rheological studies.

5.7
Frequency sweep of 0.409 mol L -1 dp-poly(D-1), 1.00 PDBA equiv. Figure S25 LEFT: Dynamic frequency sweep of organogel made from dp-poly(D-1) and PDBA with a polymer concentration of 0.409 mol L -1 and 1.00 equiv. of PDBA. Annotations show the crossover frequency and modulus. RIGHT: Photograph of the organogel used in rheological studies.

Figure S26
Dynamic strain sweep of organogel made from dp-poly(D-1) and PDBA with a polymer concentration of 0.144 mol L -1 and 0.50 equiv. of PDBA conducted at 1 Hz. Annotations show crossover modulus and critical % strain.

5.10
Strain ramp of 0.144 mol L -1 dp-poly(D-1), 0.50 PDBA equiv. with LiTFSI Figure S28 Change in moduli during a strain ramp, measured at a frequency of 1 Hz, of a lithiated organogel made from dppoly(D-1), PDBA, and LiTFSI (0.144 mol L -1 ) with a polymer concentration of 0.144 mol L -1 and 0.50 equiv. of PDBA. The percentage strain was increased from 0.007 % to 100 %, then strain was released and the moduli were measured at 0.007 % strain. Annotation shows the point of moduli crossover.

5.13
Strain ramp of 0.287 mol L -1 dp-poly(D-1), 0.50 PDBA equiv. with LiTFSI Figure S31 Change in moduli during a strain ramp, measured at a frequency of 1 Hz, of a lithiated organogel made from dppoly(D-1), PDBA, and LiTFSI (0.144 mol L -1 ) with a polymer concentration of 0.287 mol L -1 and 0.50 equiv. of PDBA. The percentage strain was increased from 0.007 % to 100 %, then strain was released and the moduli were measured at 0.007 % strain. Annotation shows the point of moduli crossover.

Table S1
Bulk resistance (Rb) and ionic conductivity (σ) values of a lithiated organogel made from dp-poly(D-1), PDBA, and LiTFSI (0.144 mol L -1 ) with a polymer concentration of 0.287 mol L -1 and 0.50 PDBA equiv. Values are averaged over five measurements. The thickness of the gel used was 3.21 mm.