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We have investigated the fundamental impacts of network cross-linking density on organic cathode performance. Current battery technologies rely on transition metal oxide cathodes that suffer from significant availability, cost, environmental, and humanitarian drawbacks. This reality has inspired the exploration of organic cathode materials that host high theoretical capacities, are environmentally friendly, and are tunable by molecular design. These desirable features are typically accompanied by undesirable instability during battery cycling due to solubility in electrolyte, leading to diminished capacities. Cross-linking polymer electrodes presents one strategy to address dissolution challenges. Here, we synthesized variably cross-linked naphthalene diimide (NDI)-based networks to systematically study the effect of cross-linking density on organic electrode battery performance. NDI-networks were cast as composite electrodes, manufactured into coin cells with lithium metal anodes, and evaluated by galvanostatic cycling. We observed that increased cross-linking facilitated reversible redox-access to NDI units in the network, which correlated to increased stability and capacities. Cathodes with optimized cross-linking host an initial capacity of 106 mA h g−1 and >75% capacity retention after 100 cycles with a C/10 rate. This contrasts with uncross-linked materials, which rapidly diminished in performance due to dissolution in the electrolyte, and more densely cross-linked materials, which suffered from limited ionic accessibility. These findings demonstrate that (1) cross-linking can improve organic electrode performance and (2) there are tradeoffs between cycling stability, capacity, and overall energy storage performance with cross-linking density. Future investigations will explore how network design and processing conditions can be leveraged to co-optimize organic cathode performance across these important metrics. [ABSTRACT FROM AUTHOR]

Rapidly synthesizing high‐quality two‐dimensional covalent organic frameworks (2D COFs) is crucial for their practical applications. While strategies such as slow monomer addition have been developed based on an empirical understanding of their formation process, quantitative guidance remains absent, which prohibits precise optimizations of the experimental conditions. Here, we use a machine‐learning approach that overcomes the challenges associated with bottom‐up model derivation for the non‐classical 2D COF crystallization processes. The resulting model, referred to as NEgen1, establishes correlations among the induction time, nucleation rate, growth rate, bond‐forming rate constants, and common solution synthesis conditions for 2D COFs that grow by a nucleation‐elongation mechanism. The results elucidate the detailed competition between the nucleation and growth dynamics in solution, which has been inappropriately described previously by classical, empirical models with assumptions invalid for 2D COF polymerization. By understanding the dynamic processes at play, the NEgen1 model reveals a simple strategy of gradually increasing monomer addition speed for growing large 2D COF crystals. This insight enables us to rapidly synthesize large COF‐5 colloids, which could only be achieved previously by prolonged reaction times or by introducing chemical modulators. These results highlight the potential for systematically improving the crystal quality of 2D COFs, which has wide‐reaching relevance for many of the applications where 2D COFs are speculated to be valuable. [ABSTRACT FROM AUTHOR]

Electrolysis is an emerging approach to polymer postpolymerization modification, deconstruction, and depolymerization. Electrochemical reactions are particularly appealing for macromolecular transformations because of their high selectivity, ability to be externally monitored, and intrinsic scalability. Despite these desirable features and the recent resurgent use of small-molecule electrochemical reactions, the development of macromolecular electrolysis has been limited. Herein, we highlight recent examples of polymer transformations driven by heterogeneous redox chemistry. Throughout our exploration of macromolecular electrolysis, we provide our perspective on opportunities for continued investigation in this nascent field. Specifically, we highlight how targeted reaction development through deeper mechanistic insight will expand the scope of materials that can be (de)constructed with electrochemical methods. As this insight is developed, we expect macromolecular electrolysis to emerge as a high-functioning and complementary tool for macromolecular functionalization and deconstruction.