Design and Synthesis of a Facile Solution‐Processing and Ultrastable Crosslinkable Branched Nitroxide Polymer

Abstract

A general critical challenge for nitroxide polymers being used as cathode materials is keeping the good solubility during the processing and good solvent resistance during charging and discharging. To address this issue, herein, a new photo‐crosslinkable branched nitroxide polymer is designed and synthesized via reversible addition‐fragmentation chain transfer copolymerization of 2,2,6,6‐tetramethyl‐4‐piperidyl methacrylate, cinnamoyl ethyl methacrylate, and ethylene glycol dimethacrylate, followed by oxidation using 3‐chloroperoxybenzoic acid. The as‐synthesized polymer can dissolve in ethyl alcohol with environmental‐friendly processing, and then can easily change into crosslinked polymer with highly resistance to organic electrolyte after UV irradiation. The crosslinked nitroxide polymer‐based cathode achieves remarkable cycle stability with a capacity retention of 90% over 1000 charge–discharge cycles at 10 C current rate, superior to that of the un‐crosslinked one with capacity retention of 65% over 1000 cycles.

100th Anniversary of Macromolecular Science Viewpoint: Fundamentals for the Future of Macromolecular Nitroxide Radicals

“…99% in another report, measured using UV−vis spectroscopy. 32,37,65 These results demonstrate that the methods used to determine radical loading may give varied results. EPR spectroscopy, UV−vis spectroscopy, and superconducting quantum interference device (SQUID) magnetometry are the most common methods to determine radical loading.…”

“…2 The most common controlled polymerization methods to synthesize nitroxide containing macromolecular radicals are reversible addition−fragmentation chain transfer (RAFT) polymerization, atom transfer radical polymerization (ATRP), anionic ring opening polymerization, a n d r i n g o p e n i n g m e t a t h e s i s p o l y m e r i z a t i o n (ROMP). 5,25,28,37,65,66 Synthetic challenges for macromolecular radicals are to reduce the dispersity, increase the molar mass, and achieve 100% radical loading. The control of dispersity and molar mass are important for preventing dissolution in battery applications and for fundamental polymer physics investigations (e.g., chain conformation, packing, polymer solution thermodynamics), which are highly dependent on the molar mass profile.…”

“…One example of this indirect synthesis is the RAFT polymerization of PTMA or PTMA copolymer using a dithiobenzoate or trithiocarbonate RAFT agent. 5,37,65 The resulting polymers had M n ≤ 24 000 g/ mol and Đ ≤ 1.3. 5,37,65 Besides RAFT polymerization, ATRP has also been demonstrated for the indirect production of PTMA, resulting in M n ≤ 24 700 g/mol and Đ ≤ 1.2.…”

“…5,37,65 The resulting polymers had M n ≤ 24 000 g/ mol and Đ ≤ 1.3. 5,37,65 Besides RAFT polymerization, ATRP has also been demonstrated for the indirect production of PTMA, resulting in M n ≤ 24 700 g/mol and Đ ≤ 1.2. 5,32,67 Finally, single electron transfer-living radical polymerization produced PTMA with M n ≤ 131 000 g/mol and Đ ≤ 1.3, which resulted in the highest molar mass PTMA found in the literature.…”

“…5 Elsewhere, these results were confirmed for mCPBA and H 2 O 2 /NaWO 4 , where it was also shown that side reactions associated with mCPBA led to a significant increase in the dispersity (from 1.3 to 4.3). 65,68 Further, Zhang et al showed that, as the molar mass of the precursor polymer increased (from 14 000 to 131 000 g/mol), the radical yield also increased from 61% to 80% when using H 2 O 2 /NaWO 4 as the oxidant. 68 On the other hand Rostro et al did not observe an increase in radical loading with increasing molar mass when mCPBA was used as the oxidant.…”