Extended Conjugation Acceptors Increase Specific Energy Densities in π-Conjugated Redox Polymers

Abstract

Organic materials are a sustainable alternative to replace inorganic transition metal-based cathodes in rechargeable intercalation batteries. Among the possible redox active organic materials, conjugated polymers with multiple redox sites per repeat unit are expected to afford high energy and power densities while being resistant to dissolution when in contact with battery electrolytes. However, accessing the full capacity of polymeric electrodes while ensuring electrochemical reversibility has been challenging. Using diketopyrrolopyrrole (DPP)-based donor− acceptor (D−A) polymers as model systems and complementary electrochemical experiments and first-principles calculations, we show that conjugated backbone moieties that minimize charge localization on the electron accepting repeat units lead to near theoretical discharge capacities. Further, the capacity enhancement is associated with better rate performance and improved electrochemical stability of the polymer over prolonged cycling. Our work suggests that charge density on the electron accepting moiety is a potential descriptor for rationally designing redox-active polymer electrodes that afford high discharge capacities along with a long cycle life.

Observation of super-Nernstian proton-coupled electron transfer and elucidation of nature of charge carriers in a multiredox conjugated polymer

“…[16][17][18][19][20][21][22] Although traditional redox-active pconjugated polymers are usually conducting polymers such as polyaniline (PANi), polypyrrole (PPy), or poly(3,4ethylenedioxythiophene) (PEDOT) (Chart 1a) 23 or metallopolymers 24 (Chart 1a), current state-of-the-art redox p-conjugated polymers incorporate molecular redox sites into the backbone such as carbonyl group (-C]O-) containing polymers including naphthalene diimide (NDI) based copolymers [16][17][18][19] (Chart 1a) and diketopyrrolopyrrole (DPP) based copolymers (Chart 1a). 21,22 Although a detailed measurement and analysis of the Pourbaix diagram was absent in these previously reported redox p-conjugated polymers, they were assumed to follow the Nernstian response. [16][17][18][19][20][21][22] The ability to store charges with excellent stability and robust reversibility in electrochemically n-doped redox pconjugated polymers 16,25 could also enable fundamental studies to explore the nature of charge carriers (e.g.…”

“…21,22 Although a detailed measurement and analysis of the Pourbaix diagram was absent in these previously reported redox π-conjugated polymers, they were assumed to follow the Nernstian response. 16–22…”

“…), 15 the class of redox p-conjugated polymers contain redox-active sites within the polymer backbone; thus, combining the robust charging/ discharging nature of redox sites with the enhanced electronic charge delocalization and transport along the conjugated polymer backbone. [16][17][18][19][20][21][22] Although traditional redox-active pconjugated polymers are usually conducting polymers such as polyaniline (PANi), polypyrrole (PPy), or poly(3,4ethylenedioxythiophene) (PEDOT) (Chart 1a) 23 or metallopolymers 24 (Chart 1a), current state-of-the-art redox p-conjugated polymers incorporate molecular redox sites into the backbone such as carbonyl group (-C]O-) containing polymers including naphthalene diimide (NDI) based copolymers [16][17][18][19] (Chart 1a) and diketopyrrolopyrrole (DPP) based copolymers (Chart 1a). 21,22 Although a detailed measurement and analysis of the Pourbaix diagram was absent in these previously reported redox p-conjugated polymers, they were assumed to follow the Nernstian response.…”

“…21,22 Although a detailed measurement and analysis of the Pourbaix diagram was absent in these previously reported redox p-conjugated polymers, they were assumed to follow the Nernstian response. [16][17][18][19][20][21][22] The ability to store charges with excellent stability and robust reversibility in electrochemically n-doped redox pconjugated polymers 16,25 could also enable fundamental studies to explore the nature of charge carriers (e.g. electron-polarons, electron-bipolarons, etc.)…”