Dynamic covalent bonds in a polymer network lead to plasticity, reshapability, and potential recyclability at elevated temperatures in combination with solvent-resistance and better dimensional stability at lower temperatures. Here we report a simple one-step procedure for the catalyst-free preparation and intramolecularly catalyzed stress-relaxation of dynamic polyester networks. The procedure is based on the coupling of branched OH-end functional polyesters (functionality ≥ 3) by pyromellitic dianhydride (PMDA) or 2,5-bis­(methoxy-carbonyl) benzenesulfonic acid resulting in ester linkages with, respectively, a COOH or a SO3H group in a position ortho to the ester bond. This approach leads to an efficient external catalyst-free dynamic polyester network, in which the topology rearrangements occur via a dissociative mechanism involving anhydrides. The SO3H-containing network is particularly interesting, as it shows the fastest stress relaxation and does not suffer from unwanted additional transesterification reactions, as was observed in the COOH-containing network.

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LiNiCoMnO positive electrode materials of lithium ion battery can release a discharge capacity larger than 200 mAh/g at high potential (>4.30 V). However, its inevitable capacity fading, which is greatly related to the structural evolution, reduces the cycling performance. The origin of this capacity fading is investigated by coupled in situ XRD-PITT-EIS. A new phase of NiMnO is discovered on the surface of the LiNiCoMnO upon charging to high voltage, which blocks Li diffusion pathways. Theoretical calculations predict the formation of cubic NiMnO. Moreover, corrosion, cracks, and microstress appear to increase the difficulty of Li transportation, which are attributed to the protection degradation of the interfacial film on the positive electrode material at high voltage. After 50 electrochemical cycles, the increase in degree of crystal defects by low-angle grain boundary, evidenced through HR-TEM, leads to poor Li kinetics, which in turn causes capacity loss. The in situ XRD-PITT-EIS technique can bring multiperspective insights into fading mechanism of the high-voltage positive electrode materials and provide a solution to control or suppress the problem on the basis of structural, kinetic, and electrochemical interfacial understandings.

This work was funded by the Dutch Research Council (NWO), Project No. 731.016.202. We are grateful to Annelore Aerts for her help in mechanical testing of the samples. We thank Dr. Ruth Cardinaels for fruitful discussions.

In Li1.2Ni0.12Co0.15Mn0.53O2 oxide, four lines of lattice fringe from O3 rhombohedral phase are squeezed into two lines from spinel cubic phase at 4.70 V charged state under the effect of microstress.