Reversible Changes in the Grain Structure and Conductivity in a Block Copolymer Electrolyte

Abstract

We study the phase behavior of a triblock organic-inorganic hybrid copolymer, poly(polyhedral oligomeric silsesquioxane)-b-poly(ethylene oxide)-bpoly(polyhedral oligomeric silsesquioxane) (POSS-PEO-POSS)/ lithium bis(trifluoromethanesulfonyl) imide salt mixture as a function of temperature. The polymer exhibits a lamellar morphology, both in the neat state as well as in the presence of salt. However, the average grain size increases substantially when the electrolyte is heated above 113 o C. The grain structure of this sample changes reversibly with temperature, i.e., smaller grains reappear when the electrolyte is cooled below 113 o C. While annealing block copolymers at high temperatures often leads to an increase in grain size, this change is generally irreversible. The reason for the reversible change in the grain structure of the POSS-PEO-POSS/LiTFSI electrolyte is discussed. The ionic conductivity of the electrolyte also exhibits reversible changes in this temperature window. Knowledge of the grain structure is crucial for understanding ion transport in nanostructured electrolytes.

Ionic Conductivities of Broad Dispersity Lithium Salt-Doped Polystyrene/Poly(ethylene oxide) Triblock Polymers

“…Chintapalli et al first pointed out the importance of grain structure on the ionic conductivities of nSO diblock polymers, whereby increased conductivities were documented in LAM samples with poor long-range translational order derived from rapid thermal quench processing 54 or increased salt loadings. 12 To understand the former observations, they estimated the microphase separated grain sizes (L) in their nSO samples by a 15 and Yuan et al 17 65 Since the principal SAXS peak breadth apparently increases in the order nSO < nSOS < bSOS, which is coincident with the observed trend in σ n (90 °C), we applied the quantitative analysis of Chakraborty et al to the present sample set. 65 More explicitly, we fit the q* peaks in the log[I(q)] versus q data in Figure 2 with a q-dependent fifth-order polynomial background and a Voigt distribution to quantify the peak full width at half-maximum (F) in Å −1 .…”

100th Anniversary of Macromolecular Science Viewpoint: Block Copolymers with Tethered Acid Groups: Challenges and Opportunities

“…Such theoretical efforts played a major role in understanding extensive experimental results on the structure–transport relationship of the charged block copolymers over the past 20 years. ,,,,,,− Mezzenga and co-workers investigated the dependency of the proton conductivity of the PSS- b -PMMA (PMMA; poly­(methyl methacrylate)) on the morphology by varying the molecular weight and sulfonation degree, as schematically depicted in Figure c . The highest normalized proton conductivity of LAM phases was understood by the dominant swelling of PSS domains.…”

“…Based on the effective medium theory of Sax-Ottino and experimental results of Balsara and co-workers, ,− , a morphology factor of 1/3 for the HEX (with cylindrical conducting phases) structure and 2/3 for the LAM structure were determined. Meanwhile, theoretically the highest morphology factor of 1 for the gyroid structure is expected; however, experimental works have reported considerably lower ionic conductivity than that of randomly oriented LAM. , This is because of the small grain sizes and uncontrollable grain orientations in the gyroid, which cause uncertainty in its ion transport efficiency …”

“…Note in passing that the advantageous feature of having a major ionic matrix was also seen for other applications such as a water purification membrane. 112 Based on the effective medium theory of Sax-Ottino 113 and experimental results of Balsara and co-workers, 90,[103][104][105][106][107]114 a morphology factor of 1/3 for the HEX (with cylindrical conducting phases) structure and 2/3 for the LAM structure were determined. Meanwhile, theoretically the highest morphology factor of 1 for the gyroid structure is expected; however, experimental works have reported considerably lower ionic conductivity than that of randomly oriented LAM.…”

Safety-enhanced Polymer Electrolytes with High Ambient-temperature Lithium-ion Conductivity Based on ABA Triblock Copolymers

“…However, in most cases, the mechanical performances of these BCPs are unsatisfactory owing to their low molecular weights and weak chain entanglements. [16] Chemical crosslinking is a natural thought to enhance the mechanical strength. [30−32] However, the restriction on chain mobility by crosslinking will decrease the ionic conductivity severely.…”