Organic Negative Electrode Materials for Metal‐Ion and Molecular‐Ion Batteries: Progress and Challenges from a Molecular Engineering Perspective

Abstract

Thanks to their versatility and flexibility, EOMs have shown broad applicability as bulky solid [3] or dissolved [4,5] active material, in aqueous [6][7][8] or non-aqueous electrolyte, [9][10][11] for portable and stationary batteries, respectively. In practice, OEMs are explored as main active materials in LIBs, [12] beyond Li systems (e.g., hydrogen, [13,14] Na-ion, [15][16][17][18][19] K-ion, [20][21][22][23][24] and multivalent batteries like magnesium, [25,26] zinc, [27] or aluminum [28,29] ) and also redox flow batteries; [30] or as supporting active materials such as redox mediators for Li-O 2 batteries, [31] Li-source sacrificial materials for Li-ion capacitor [32] and redox electrolytes for high-energy supercapacitors. [33] In contrast to the state-of-the-art inorganic materials, whose reactivity is based on redox of transition metal center and consequently Li + de/insertion, [34,35] the redox reaction of EOMs is based on the charge state change of the redox moiety, [12] for which the charge compensation during redox can be either made by cations, referring to n-type systems, or by anions, belonging then to p-type system, according to the proposed Hünig's classification. [36,37] The richness of organic chemistry coupled with molecular modifications have provided thus far a plethora of molecules and architectures operating within a large potential window with high specific capacities, extended cycling stability and high cycling rate. This has enabled building a broad database of electroactive compounds for both positive and negative electrode applications. Organic positive electrode materials (OPEMs) certainly benefit from larger attention since there are more possibilities to explore, for example, conducting polymers, [38,39] nitroxides, and other stable organic radicals, [40][41][42][43] sulfur compounds, [11] as well as conjugated amines, [44][45][46] conjugated sulfonamides, [47] nitro-aromatics, [48] and carbonyls. [49,50] The latter being certainly the most explored category owing to major advances attained so far but also to opportunities for further improvements to attain simultaneously high energy and power densities combined with good cycling stability. [12] On the opposite side, the chemical library is less rich for organic negative electrode materials (ONEMs), primarily due to much focus on positive electrode chemistries, for which many issues and strategies are to be addressed and explored, respectively. Today, the ONEMs database counts fewer redox families as OPEMs one, with also less specific chemistries within each class. To cite some: the most studied conjugated dicarboxylates, [51] Hückel-stabilized Schiff base, [52] nitrogen-redox azo

Revealing the Solid-State Electrochemistry of Conjugated Oximates: Towards a New Functionality for Organic Batteries

“…Organic electrode materials are emerging as potential candidates for electrochemical energy storage applications with most appealing features such as natural abundance, sustainability and lower environmental footprints. [1][2][3][4] The modern battery technologies are heavily dependent on transition metal oxides electrode materials which are procured after extensive mining and expensive synthesis protocols such as energy consuming high temperature processing. Moreover, material cost, handling and recycling encourage the efforts towards development of organic electrode materials.…”

Chemical Upcycling of PET Waste towards Terephthalate Redox Nanoparticles for Energy Storage

“…A common approach to improve the cycling stability of the redox-active small molecules is to covalently bond them to a polymer backbone in order to reduce their solubility into the electrolyte. Consequently, redox polymers have attracted a lot of attention as electrode materials for energy storage application, due to their inherent features such as enhanced cycling stability, high rate performance, processability (i.e., extrusion, roll-to-roll and 2D/3D-printing processes), flexibility, recyclability and their potential to be derived from biomass resources [8][9][10][11][12]. In addition, redox polymers are considered as a promising alternative to the scarce inorganic electrode materials that are currently used in Li-ion battery technology [13,14], as they are essentially composed of naturally abundant elements (i.e., carbon, hydrogen, oxygen, nitrogen and sulphur) [10].…”

“…The design of redox polymers with lower redox potential, which is appealing in term of the energy density output of the electrochemical devices, is a more challenging task, with so far less diversity available in terms of redox chemistry. Most organic anode materials reported to date are based on conjugated dicarboxylates, Schiff bases, conjugated azo groups and viologens moieties [12]. Finally, redox polymers can be designed using a wide range of polymerization methods such as free-radical polymerization, controlled radical polymerization or emulsion polymerization, allowing high tuneability of their macromolecular architecture to suit application requirements.…”

N‐doped carbon nanotube sponges and their excellent lithium storage performances

“…[ 1–3 ] Ever since Sony Co. commercialized the world's first LIBs with a tailor‐made carbon negative electrode, [ 4 ] great efforts have been devoted to exploring novel energy storage materials. [ 5–20 ] Graphite is commonplace among commercial LIBs because of low redox potential, good stability and electrical conductivity. The electrochemical de/lithiation process, known as de/intercalation, is the mechanism through which graphite is able to store lithium.…”

“…The rapidly evolving market of electrically powered vehicles and portable electronics drives a great demand for electrochemical energy storage devices with enhanced tailor-made carbon negative electrode, [4] great efforts have been devoted to exploring novel energy storage materials. [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] Graphite is commonplace among commercial LIBs because of low redox potential, good stability and electrical conductivity. The electrochemical de/lithiation process, known as de/intercalation, is the mechanism through which graphite is able to store lithium.…”