Organic electrode materials represent a promising alternative to conventional inorganic anodes in rechargeable batteries, offering advantages in sustainability, structural diversity, and tunable electrochemical properties. Among these materials, polyketones and Schiff bases have gained attention for their ability to reversibly store alkali metal ions through well-defined redox reactions. Their performance as anodes depends on ion-coordination chemistry, redox potentials, and structural stability during cycling.

Polyketones consist of carbonyl groups linked by aromatic or aliphatic structures, which undergo reversible reduction to enolate forms during lithiation or sodiation. The carbonyl oxygen atoms coordinate with Li+ or Na+ ions, forming stable complexes that enable charge storage. For example, dilithium terephthalate, a representative polyketone, delivers a specific capacity of approximately 300 mAh/g through a two-electron redox process at an average potential of 0.8 V vs. Li+/Li. Schiff bases, featuring imine linkages (-C=N-), exhibit similar ion-coordination behavior, where the nitrogen and adjacent carbon atoms participate in redox reactions. These materials typically operate at potentials between 0.5–1.2 V vs. Li+/Li, making them suitable as anodes.

A critical challenge for organic anodes is their inherent volume change during ion insertion and extraction. Unlike graphite, which experiences minimal expansion (10–15%), polyketones and Schiff bases can undergo volume changes exceeding 50% due to structural rearrangements upon redox reactions. This leads to particle cracking, loss of electrical contact, and rapid capacity fade. Pre-lithiation or pre-sodiation strategies mitigate this issue by introducing an initial metal-ion reservoir into the electrode. For instance, pre-lithiated polyimide anodes demonstrate improved cycling stability, retaining over 80% capacity after 500 cycles compared to untreated counterparts.

The redox behavior of organic anodes contrasts sharply with conventional materials. Graphite anodes operate via intercalation chemistry, where Li+ ions insert between graphene layers at potentials close to 0.1 V vs. Li+/Li, delivering a theoretical capacity of 372 mAh/g. Silicon anodes rely on alloying reactions, offering high capacities (4200 mAh/g for Li22Si5) but suffer from severe volume expansion (300%). Organic materials, while providing moderate capacities (200–600 mAh/g), exhibit lower energy densities due to their higher redox potentials and larger molecular weights. However, their structural flexibility allows for molecular engineering to optimize performance.

Enhancing the electronic conductivity of organic anodes remains a key focus. Many polyketones and Schiff bases are intrinsically insulating, necessitating conductive additives like carbon black or graphene. Composite electrodes with 20–30% conductive carbon demonstrate improved rate capability, achieving capacities above 200 mAh/g at 1C rates. Another approach involves polymerizing redox-active units into conjugated frameworks, which enhances both conductivity and mechanical stability. For example, poly(anthraquinonyl sulfide) maintains a capacity of 220 mAh/g at 2C due to its extended π-conjugation.

Electrolyte compatibility also influences organic anode performance. Conventional carbonate-based electrolytes may decompose at the relatively high operating potentials of organic materials, forming resistive solid-electrolyte interphases (SEI). Ether-based electrolytes, such as 1M LiPF6 in DME/DOL, show better stability by promoting thinner and more ionically conductive SEI layers. Additives like fluoroethylene carbonate further improve SEI properties, reducing irreversible capacity loss in the first cycle from 40% to under 20%.

Long-term cycling stability depends on suppressing dissolution of active material into the electrolyte. Small organic molecules are particularly prone to this issue, leading to active mass loss and capacity fading. Strategies include covalent grafting onto carbon substrates, polymerization into insoluble networks, or using crosslinked binders like poly(acrylic acid). These methods have extended cycle life to over 1000 cycles in some systems, with capacity retention exceeding 70%.

Comparative performance metrics highlight tradeoffs between organic and inorganic anodes:
Material Theoretical Capacity (mAh/g) Average Potential (V) Volume Change (%) Cycle Life (cycles)
Graphite 372 0.1 10–15 1000+
Silicon 4200 0.4 300 100–200
Polyketones 200–600 0.8–1.2 40–60 300–500
Schiff Bases 150–400 0.5–1.0 30–50 200–400

Future development of organic anodes requires addressing energy density limitations while maintaining sustainability benefits. Multi-redox systems incorporating several functional groups per molecule could increase capacity, while nanostructuring may improve rate performance. Hybrid designs combining organic and inorganic components may offer synergistic effects, such as buffering volume changes while leveraging high-capacity redox reactions.

Processing and manufacturing considerations also play a role in practical adoption. Organic materials often require solution-based electrode fabrication rather than the slurry casting used for graphite. This impacts production scalability and cost, though roll-to-roll processing techniques may offset these challenges. The environmental footprint of organic synthesis must be weighed against the mining impacts of conventional anode materials.

In summary, organic anodes based on polyketones and Schiff bases present a viable pathway for sustainable battery development, with distinct ion-coordination mechanisms and tunable electrochemical properties. While they currently lag behind graphite and silicon in energy density and cycle life, ongoing research into molecular design, composite engineering, and electrolyte optimization continues to narrow the performance gap. Their inherent advantages in resource availability and environmental compatibility make them compelling candidates for next-generation energy storage systems.