In the rising advent of organic Li-ion positive electrode materials with increased energy content, chemistries with high redox potential and intrinsic oxidation stability remain a challenge. Here, we report the solid-phase reversible electrochemistry of the oximate organic redox functionality. The disclosed oximate chemistries, including cyclic, acyclic, aliphatic, and tetra-functional stereotypes, uncover the complex interplay between the molecular structure and the electroactivity. Among the exotic features, the most appealing one is the reversible electrochemical polymerization accompanying the charge storage process in solid phase, through intermolecular azodioxy bond coupling. The best-performing oximate delivers a high reversible capacity of 350 mAh g
−1
at an average potential of 3.0 versus Li
+
/Li
0
, attaining 1 kWh kg
−1
specific energy content at the material level metric. This work ascertains a strong link between electrochemistry, organic chemistry, and battery science by emphasizing on how different phases, mechanisms, and performances can be accessed using a single chemical functionality.
Sodium‐ion batteries are considered as the immediate sustainable alternative to lithium‐ion systems. To reduce the competitiveness gap, improved performances and better understanding of sodium storage, especially of new phases based on sustainable materials, are further required. In this work, we provide advanced investigation of the structure and the electrochemistry of a peculiar off‐stoichiometric iron‐rich phase (Na0.6Fe1.2PO4) for sodium storage. An interesting electrochemical activation phenomenon is described and contrary to conventional ageing processes it is found to significantly enhance the energy and power rate performances.
Sodium and iron make up the perfect combination for the growing demand for sustainable energy storage systems, given the natural abundance and sustainability of the two building block elements. However, most sodium–iron electrode chemistries are plagued by intrinsic low energy densities with continuous ongoing efforts to solve this. Herein, the chemical space of a series of (meta)stable, off‐stoichiometric Fe‐PO
4
‐F phases is analyzed. Some are found to display markedly improved electrochemical activity for sodium storage, as compared to the amorphous or thermodynamically stable phases of equivalent composition. The metastable crystalline Na
1.2
Fe
1.2
PO
4
F
0.6
delivers a reversible capacity of more than 140 mAh g
−1
with an average discharge potential of 2.9 V (vs Na
+
/Na
0
) resulting in a practical specific energy density of 400 Wh kg
−1
(estimated at the material level), outperforming many developed Fe‐PO
4
analogs thus far, with further multiple possibilities to be explored toward improved energy storage metrics. Overall, this study unlocks the possibilities of off‐stoichiometric Fe‐PO
4
‐F cathode materials and reveals the importance to explore the oft‐overlooked metastable or transient state materials for energy storage.
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