Quinone compounds and their derivatives are a class of promising electroactive materials, characterized by high specific capacity, high redox reaction activity, and excellent electrochemical reversibility^[100].

In non-aqueous battery systems, quinone compounds often face the challenge of high solubility due to the use of organic solvents as electrolytes. To address this issue, researchers have employed molecular design strategies. By modifying the composition and structure of the molecules—such as enhancing intermolecular interactions, expanding the molecular framework, and achieving extensive π-conjugation—they have effectively improved the material’s solubility. For example, Fu et al.^[101]used a naphthoquinone (NQ) molecule as a building block, leveraging its strong intramolecular interactions with three different benzenedithiols (1,2-BDT, 1,3-BDT, 1,4-BDT) to construct three highly extended five-benzene-ring structures (1,2-PNQ, 1,3-PNQ, 1,4-PNQ) (Fig. 3a). This approach was designed to mitigate the solubility issues of naphthoquinone molecules. As shown in Fig. 3b, the solubility of unmodified NQ was 12.82 mg·mL^-1; after modification with benzenedithiols, the solubilities of the newly formed materials 1,2-PNQ, 1,3-PNQ, and 1,4-PNQ decreased to 0.07, 0.28, and 0.11 mg·mL^-1, respectively—representing reductions to 1/183, 1/46, and 1/116 of the original value. The underlying reason is that the newly formed materials exhibit larger molecular structures and enhanced intermolecular π–π stacking, which inhibits the dissolution of the molecules in the electrolyte. Among these three molecular structures, 1,4-PNQ possesses the greatest steric hindrance and the highest degree of active-site exposure, resulting in the highest redox activity (Fig. 3c). As illustrated in Fig. 3d, compared with previously reported quinone-based electrode materials, 1,4-PNQ demonstrates nearly 100% carbonyl group utilization in a lithium half-cell. Moreover, due to its unique molecular structure and low solubility, it retains a high capacity of 185 mAh·g^-1after 100 charge–discharge cycles—a roughly 1.8-fold improvement over unmodified NQ under the same conditions. The modified 1,4-PNQ exhibits high carbonyl group utilization in lithium-ion batteries, indicating that batteries using this material can store more energy within the same volume and weight. This makes it particularly valuable for devices requiring high energy density, such as electric vehicles, where the material can be used to develop batteries with longer driving ranges, thereby enhancing vehicle performance.

Through further molecular design, the cyclic stability of the material can be effectively enhanced, resulting in a high capacity retention rate. Popovs et al.^[102]further introduced conjugated naphthoquinone into the core of an electron-deficient hexaazabenzenederivative (HATA), forming a large polyelectronic acceptor organic cathode material, hexaaza-tri anthracene quinone (HATAQ) (Fig. 3e). The resulting polyelectronic acceptor electrode material features an extended π-conjugation system and a greater number of redox-active sites (Fig. 3f). The introduction of conjugated quinone groups expands the molecule’s π-conjugation system, enhancing its electron-affinity capability. At the same time, the molecule forms a stable two-dimensional layered structure via a “lock-and-key” hydrogen-bond network, thereby facilitating the insertion and extraction of lithium ions. As a result, the HATAQ molecule exhibits an exceptionally high lithium-storage capacity. At 0.4 C, this material delivers a capacity of 426 mAh·g^-1, which is higher than that of typical small-molecule organic cathode materials. Even at an ultra-high rate of 19 C, it retains nearly 85% of its initial capacity after 1,000 cycles (Figs. 3g, h). Similarly, Cao et al. used a Schiff base condensation reaction to introduce imidazole units with multiple electron-transfer capabilities and a conjugated structure into naphthoquinone, forming, through core linkage, a C ₃-symmetric trimeric imidazole naphthoquinone derivative with dual redox sites: 2,2,2′-(benzene-1,3,5-triyl)tri(1H-naphtho[2,3-d]imidazole-4,9-dione) (BTNID) (Fig. 3i). A strong π–π orbital interaction between the naphthoquinone and imidazole leads to extensive electron delocalization, providing a high density of reversible C=O/C=N redox-active sites for lithium storage (Fig. 3j). Consequently, this material exhibits a high lithium-storage capacity. Density functional theory (DFT) calculations, as shown in Fig. 3k, indicate that as lithium ions are inserted, the total energy of BTNID gradually decreases, and the structure becomes more stable. The high lithium-storage capacity of BTNID, combined with its C ₃-symmetric structure, enhances the material’s structural stability and capacity retention. When used as a cathode in lithium batteries, the material achieves a specific capacity of up to 483 mAh·g^-1at 0.2 A·g^-1, and even after 3,000 cycles at 10 A·g^-1, it retains 74.8% of its initial capacity—significantly higher than most previously reported results, as illustrated in Fig. 3l ^[103]. In addition to serving as a cathode material for lithium batteries, naphthoquinone can also be used as a cathode material for zinc batteries. Song et al.^[104]combined 2,5-dihydroxy-1,4-benzoquinone (DHBQ) with o-phenylenediamine (oPDA) to form a structure—5,7,12,14-tetraaza-6,13-pentacondensed tetrabenzoquinoline ketone (TAPQ) (Fig. 3m). This structure likewise possesses multiple redox-active sites, including C=O and C=N. DFT simulations have demonstrated an H⁺/Zn²⁺co-insertion mechanism, with H⁺as the primary participant, as shown in Fig. 3n. This mechanism effectively enhances the material’s cycling stability and yields a high capacity retention rate. Within a voltage range of 0.1–1.6 V, TAPQ exhibits a capacity of 270 mAh·g^-1, which is 1.3 times higher than that of DHBQ used alone as an electrode material. At the same time, TAPQ boasts an energy density of 282 Wh·g^-1and a high capacity retention rate of 92% (Figs. 3o, p).

In addition to molecular design, polymerization is also an effective strategy for improving the electrochemical performance of batteries. By linking small-molecule monomers into long-chain polymers, the dissolution of active materials can be reduced, thereby maintaining good cycling stability. Zhao et al.^[105]designed an electrochemical redox couple in which anthraquinone (AQ) serves as a dendrite-free anode material, coupled with the Mn²⁺/MnO₂redox reaction to construct an alkaline–acid battery. In practical applications, to further reduce the solubility of AQ, poly(1,4-anthraquinone) (P14AQ) was synthesized, as shown in Figure 4a. Compared with metal anodes such as zinc and lead, anthraquinone exhibits an exceptionally high current density and does not suffer from dendrite growth (Figure 4b). The structure formed through polymerization not only reduces intermolecular voids but also enhances molecular stability through cross-linking via chemical bonds, thereby significantly suppressing the dissolution of the material in the electrolyte. Testing has shown that P14AQ exhibits an initial discharge specific capacity of 295 mAh·g^-1, which is 5.9 times that of AQ. Using this redox reaction (Figure 4c), a fully decoupled alkaline–acid P14AQ//MnO₂battery was assembled. Figure 4dshows the cycling performance of the battery composed of an MnO₂@HGF cathode and a P14AQ anode. At 20C and a low temperature of -20 ℃, after 100 cycles, the battery still retains a high initial capacity of 300 mAh·g^-1, with a capacity retention rate of 84%. When electric vehicles and many portable electronic devices are operated at low temperatures, battery performance declines significantly. Batteries incorporating P14AQ, however, can maintain high capacity and cycling stability at low temperatures, making them suitable for these applications and potentially extending the service life of such devices.

In conventional batteries, organic solvents are used as electrolytes, resulting in high solubility of quinone compounds when used as electrode materials. Since quinone compounds are generally insoluble in water, using quinone- and derivative-based electrode materials in aqueous batteries can effectively mitigate solubility issues. AQ can also serve as a negative electrode material in various aqueous batteries (Zn²⁺, Mg²⁺, Al³⁺). Ling et al.^[106]used AQ as a research model to analyze its electrochemical redox behavior in various aqueous metal ion electrolytes (H⁺, Li⁺, Na⁺, K⁺, Zn²⁺, Mg²⁺, Ca²⁺, Ba²⁺, Al³⁺) (Fig. 5a). Simulation calculations revealed the free energy level distribution of AQ, with the spin density distribution of the [AQ-Mn ^{n +}]^{（ n -1）+}radical intermediate leading to irreversible redox behavior for Li⁺, Na⁺, K⁺, Ca²⁺, and Ba²⁺. The binding energy between metal ions and AQ anions enables reversible proton-assisted side reactions in Al³⁺, Zn²⁺, and Mg²⁺(Fig. 5b). The performance of this AQ-based negative electrode in aqueous metal ion batteries was investigated; under the same conditions, the electrode exhibited relatively superior performance in aluminum-ion batteries, delivering a reversible capacity of 211.4 mAh·g^-1after 500 cycles at 800 mA·g^-1, with a capacity retention rate of 94.5%. In contrast, the capacity retention rates in magnesium-ion and zinc-ion batteries were only 68.8% and 44.9%, respectively (Fig. 5c).

Although the solubility issues faced by quinone compounds in aqueous battery systems have been effectively alleviated, enhancing the cyclic stability of the electrode remains an urgent challenge. By combining quinone compounds with support structures that exhibit excellent performance, such as MXene, the cyclic stability and rate performance of the electrode can be significantly improved. For example, Lv et al.^[107]constructed a layered composite structure using the organic anthraquinone derivative benz[1,2-b:4,5-b']dithiophene-4,8-dione (BDTO) and Ti₃C₂(MXene) as the cathode material for an aluminum organic battery, thereby effectively enhancing the insertion and extraction capability of Al³⁺(Fig. 6a). Transmission electron microscopy (TEM) images confirmed the formation of the layered composite structure (Fig. 6b). This layered structure effectively reduces the dissolution of BDTO in the electrolyte and provides additional pathways for the diffusion of Al³⁺, leading to significant improvements in both cyclic stability and the ionic diffusion coefficient, as shown in Fig. 6c. By examining the relationship between the scan rate and current density of the redox peaks, it was found that the layered structure facilitates the deintercalation of Al³⁺, thereby enhancing ion diffusion. Various characterization methods and DFT calculations revealed that three C=O groups react with one Al³⁺, thereby defining the battery’s mechanism (Fig. 6d). During the reaction, the C=O groups in the BDTO molecule are partially reduced to C—O—Ti bonds; the formation of these chemical bonds strengthens the interfacial bonding between the two structures, enhancing the stability of the composite. When used as an electrode material, the composite exhibits a high reversible capacity, as shown in Fig. 6e: the reversible capacity of MXene@BDTO reaches 229.8 mAh·g^-1, which is 2.1 times that of BDTO under the same conditions, and it still retains a reversible capacity of 134.9 mAh·g^-1after 500 cycles, whereas the reversible capacity of BDTO drops to only 54.4 mAh·g^-1.

In addition, in aqueous batteries, protons or hydrogen ions can serve as charge carriers, enabling the construction of aqueous proton batteries. Quinone compounds have the ability to absorb protons, and their rational application in proton-based aqueous solution batteries can further enhance cycle stability and rate performance. Zhao et al. introduced a small-molecule benzoquinone derivative (tetraamino-1,4-benzoquinone, TABQ) as the negative electrode material for all-organic aqueous batteries. The strongly electron-donating amino groups effectively narrow the band gap of quinone materials, yielding an electrode material with a lower redox potential (Fig. 7a). The protonation and amorphization of the amino groups facilitate the formation of an intermolecular hydrogen-bond network, which supports Grothuss-type proton conduction within the electrode with a low activation energy of 192.7 meV (Fig. 7b). Electrochemical performance studies of this electrode reveal that, at a current density of 1 A·g^-1, the TABQ negative electrode delivers a specific capacity as high as 307 mAh·g^-1, representing an approximately 1.54-fold improvement over the 200 mAh·g^-1of the conventional electrode material TCBQ (tetrachlorobenzoquinone), and making it one of the highest-performing organic proton electrodes reported to date (Fig. 7c). When used in an all-organic proton battery configuration (TABQ//TCBQ), the battery exhibits exceptional stability, sustaining 3,500 cycles at room temperature and maintaining excellent performance even at sub-zero temperatures (Fig. 7d)^[108]. TCBQ tends to undergo structural degradation after multiple charge–discharge cycles, leading to rapid capacity decay and limiting its use in long-life applications. In contrast, TABQ demonstrates superior stability, effectively addressing this challenge and better meeting the demands of modern energy systems.

Carboxylic acid compounds have advantages such as low cost, abundant resources, environmental friendliness, and high sustainability. At the same time, their molecular structures are highly tunable, making them promising electrode materials^[109]..

Carboxyl-containing compounds as electrode materials give batteries excellent rate performance. Wang et al.^[110]introduced a new organic carboxyl compound, methyl acid organic lithium hexa salt (Li₆C₁₂O₁₂), as the negative electrode for lithium batteries, enabling reversible multi-electron redox reactions (Fig. 8a). The electrostatic potential map of this electrode, shown in Fig. 8b, demonstrates that after the reaction products bind with lithium ions, they generate an electrostatic distribution with a structure similar to symmetry. Combined electrochemical and spectroscopic studies further validate the mechanism of reversible coordination reactions based on carboxyl groups and lithium ions. The rapid and reversible nature of these coordination reactions ensures that the material can still effectively facilitate the insertion and extraction of lithium ions at high rates. Specifically, this negative electrode material not only delivers a reversible capacity of 730 mAh·g^-1at 0.21 A·g^-1but also provides a high reversible capacity of 372 mAh·g^-1at 2 A·g^-1. This electrode enables LiFePO₄//Li₆C₁₂O₁₂all-lithium-ion batteries and graphite//Li₆C₁₂O₁₂all-dual-ion batteries to exhibit high capacity and good cycling stability. Compared with other reported lithium-ion negative electrode materials, this negative electrode material boasts an exceptionally high energy density (Fig. 8c). Song et al.^[111]found that selecting an appropriate electrolyte when using carboxylic acid-based electrodes can significantly enhance the electrode's capacity performance. In the development of carboxyl compound electrodes, various modification strategies have been employed to improve their performance, thereby enabling more optimal applications.

Rational molecular engineering can effectively enhance the conductivity and specific capacity of materials, enabling the efficient application of carboxylate electrode materials. Li et al. used sodium 1,10-phenanthroline-3,8-dicarboxylate (S-PD) as the anode material for sodium-ion batteries. S-PD features a large π-conjugated planar structure with two heteroatoms, N. By extending the molecular conjugation of S-PD, π–π interactions are enhanced, effectively improving electrical conductivity (Fig. 9a).Further studies on this material revealed that, in addition to the carboxylate groups being able to store 2 Na⁺ions, the N atoms on the phenanthroline ring also provide additional active sites for Na⁺storage, enabling a 3Na⁺insertion/extraction process (Fig. 9b). The extension of the molecular structure enhances intermolecular charge-transfer capabilities, while the N atoms on the material also provide additional Na⁺storage sites. Tests have shown that this material exhibits good diffusion properties and fast reaction kinetics; these two mechanisms work together to effectively enhance the material’s specific capacity. After undergoing long-cycle cycling tests at 2 C, the material achieves a discharge capacity of up to 252 mAh·g^-1and a reversible capacity of 126 mAh·g^-1(Fig. 9c)^[112]. Introducing heteroatoms such as nitrogen or sulfur into the conjugated structure allows them to form covalent bonds with carbon atoms, enhancing the structural stability of the material, improving its cycling stability, and increasing its reversible capacity. Chen et al.^[113]designed and synthesized both planar and twisted organic carboxylates by introducing heteroatoms into the conjugated structure and adjusting the positions of carboxylate groups within the aromatic ring, thereby gaining deeper insights into how geometric structure influences the electrochemical performance of carboxylate anodes in sodium-ion batteries (Fig. 9d). The introduction of N atoms not only participates in the molecular conjugation structure but also provides additional Na⁺storage sites, increasing the material’s specific capacity. At the same time, by carefully designing the molecular structure of the material, these two mechanisms act in concert. Studies have shown that the planar structure reduces steric hindrance among molecules, enhances material stability, and endows the material with a higher specific capacity. At a current density of 50 A·g^-1, the initial discharge specific capacity of 2,2′-bipyridine-5,5′-dicarboxylic acid disodium (2255-Na), which has a planar structure, is 210 mAh·g^-1, 4.3 times that of the twisted-structure disodium 2,2′-bipyridine-3,3′-dicarboxylate (2233-Na). Testing of these materials reveals that 2255-Na outperforms other carboxylates in terms of highest specific capacity (210 mAh·g^-1), longest cycle life (2000 cycles), and best rate performance (up to 5 A·g^-1), as shown in Fig. 9e. After 2000 cycles, 2255-Na still maintains a reversible capacity of 123.3 mAh·g^-1under conditions of 1 A·g^-1. In addition, based on the 2255-Na anode, polyaniline (PANI) cathode, and ether-based electrolyte, high-temperature (up to 100 ℃) all-organic batteries have been realized and exhibit excellent electrochemical performance (Fig. 9f). Many carboxylate electrode materials suffer from a significant decline in electrochemical performance when used in high-temperature industrial equipment; however, the excellent high-temperature performance of 2255-Na makes its application in high-temperature environments feasible and suggests tremendous potential for future applications.

To address the issues of low electrical conductivity and leakage in carboxylic acid electrode materials, Bakandritsos et al.^[114]carboxylated conductive graphene to design a densely carboxylated, conductive graphene derivative (graphene acid (GA)) for use as an anode material while maintaining the mechanical and chemical stability of the electrode. By introducing a high density of carboxyl groups onto the graphene framework, multiple lithium ions can be accommodated, significantly increasing the storage sites for lithium ions. Raman measurements and theoretical calculations have revealed that the GA anode exhibits superior charge transport, redox activity, and lithium intercalation properties at the monolayer level, outperforming all previously reported organic anodes (Fig. 10a, b). When the GA anode is compared with other organic anode materials, it demonstrates an actual capacity of 800 mAh·g^-1at 0.05 A·g^-1, far exceeding that of conventional graphene materials (476 mAh·g^-1for monolayer graphene and 330 mAh·g^-1for graphene nanosheets). Moreover, at a high current density of 2.0 A·g^-1, the GA anode still delivers an actual capacity of 174 mAh·g^-1, demonstrating excellent electron transport capabilities and highlighting its potential for practical application in advanced lithium-ion batteries (Fig. 10c).

Similarly, to enhance the conductivity and solvent resistance of carboxylic acid compounds, Hu et al.^[115]employed a SiO₂template-assisted pyrolysis strategy to prepare nitrogen-doped hollow porous carbon bowls (N-HPCBs) as carriers for organic conjugated carboxylic acids (maleic acid, MA), thereby effectively improving the solvent resistance of the organic conjugated carboxylic acid anode (Fig. 11a). As characterized by ¹H nuclear magnetic resonance (NMR), as shown in Fig. 11(b), there exists a strong physical interaction between N-HPCBs and MA, which effectively suppresses the dissolution of MA. Fundamentally, this is because N-HPCBs possess a large specific surface area, a well-optimized pore structure, and a high density of nitrogen defect sites. Through physical confinement and chemical bonding, they can inhibit the dissolution of MA and its redox intermediates (LixMA) while promoting the conversion of LixMA (Fig. 11c). Electrochemical performance tests reveal that the MA@N-HPCB electrode delivers a high reversible specific capacity of 1134.9 mAh·g^-1at 0.1 A·g^-1, whereas pure MA exhibits only 522.8 mAh·g^-1of reversible capacity. Moreover, the MA@N-HPCB electrode demonstrates excellent rate capability and outstanding long-term cycling stability: after 985 cycles at 5 A·g^-1, it still retains a reversible capacity of 328.8 mAh·g^-1, whereas under the same conditions, the reversible capacity of the pure MA electrode drops to 178.6 mAh·g^-1after fewer than 500 cycles (Fig. 11d).

Imines are a class of organic compounds containing a carbon-nitrogen double bond, featuring electroactive functional groups and a large π-electron-deficient framework. They hold potential application value as electrode materials in secondary batteries, with high theoretical specific capacity and flexible structural design^[116].

By optimizing the structure of imine molecules, such as by expanding the π-conjugated system, the electron cloud density within the molecule can be increased, thereby enhancing conductivity and capacity. Wang et al.^[117]carried out terminal acylation and lateral π-system extension on perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA), yielding a perylene-based imine derivative (2PDI) with a larger π-conjugated structure, which improved the cycling performance of aqueous zinc-organic batteries (Fig. 12a). Characterization of 2PDI revealed, through molecular electrostatic potential (MESP) maps, that the oxygen atoms of the carbonyl groups in 2PDI exhibit a high negative electrostatic potential, confirming that the carbonyl groups are the electrochemically active centers in this material. At the same time, 2PDI has a relatively narrow band gap, which can promote intrinsic electronic conductivity. DFT calculations further elucidated the adsorption geometries and binding energies of H⁺and Zn²⁺ions on the 2PDI molecule, indicating that the interaction between Zn²⁺and 2PDI enhances battery stability (Fig. 12b). Thanks to the formed π-conjugated structure, 2PDI, as the cathode material for this battery, exhibits high specific capacity and cycling stability: at a current density of 100 mA·g^-1, it delivers a discharge capacity of 72.8 mAh·g^-1. After 500 cycles, PTCDA retains only 21.2% of its initial capacity, whereas 2PDI, even at a capacity of 3000 mAh·g^-1, still retains 99.4% of its capacity after 50,000 cycles (Fig. 12c).

By compositing imine molecules with conductive materials such as graphene and carbon nanotubes, the conductivity and cycling stability of the material can be effectively enhanced. Feng et al.^[118]integrated two-dimensional polyarylimide (2D-PAI) with carbon nanotubes (CNTs) and used the resulting composite as an organic cathode material in LIBs (Fig. 13a). The integrated polyarylimide hybrid (2D-PAI@CNT) features abundant π-conjugated redox-active naphthalene diimide units and robust cyclic imide bonds, ensuring material stability. Moreover, the high specific surface area and porous structure of 2D-PAI@CNT facilitate rapid diffusion of lithium ions, enabling high utilization of redox-active sites and fast ion diffusion (Fig. 13b). At a current density of 0.1 A·g^-1, the active site utilization of this material reaches 82.9%, which is 3.7 times that of 2D-PAI. In addition, this cathode exhibits high cycling stability: as shown in Fig. 13c, after 8,000 cycles, the capacity retention of the cathode remains at 100%, far exceeding previously reported polyimide electrode materials. In another study, to enhance the conductivity and electrochemical utilization of carbonyl polymers, Zhang et al.^[119]in situ incorporated two-dimensional (2D) graphene as a conductive interlayer between 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTCDA) and 2,6-diaminoanthraquinone (DAQ) nanosheets, yielding a three-dimensional open sandwich structure in which conductive graphene sheets are sandwiched between densely interwoven quinone-containing polyimide nanosheets, resulting in a graphene/carbonyl-enriched polyquinoneimide (PQI@Gr) cathode material (Fig. 13d). This three-dimensional open structure features abundant porous channels that provide short diffusion pathways for lithium ions, while its high specific surface area significantly increases the contact area between carbonyl groups and the electrolyte solution, thereby promoting lithium-ion transport and diffusion and enhancing rate performance. The content of graphene in the composite has different effects on the material's performance; as shown in Fig. 13e, PQI@Gr-3, which contains the highest amount of graphene, exhibits the highest lithium-ion diffusion coefficient. Due to these characteristics, compared with pure PQI, the PQI@Gr cathode offers higher capacity: at 5 A·g^-1, PQI@Gr-3 delivers a capacity of 179.4 mAh·g^-1, which is 1.85 times that of PQI under the same conditions. The superior cycle life and rate performance of this material surpass those of most carbonyl polymer electrodes reported to date (Fig. 13f).

Anhydrides, as compounds with high energy density, have structures that can be flexibly adjusted through chemical means, thereby optimizing their performance in electrochemical applications. Importantly, anhydrides contain stable redox-active functional groups, a characteristic that makes them an ideal choice for electrode materials in metal-ion batteries^[120].In practical applications, anhydrides can be used as monomers in combination with other monomers, or they can be combined with other monomers to form polymers.

Anhydrides are often used as monomers in combination with other monomers for electrode material applications. Yang et al.^[121]incorporated various anhydride monomers into 2,6-diaminoanthraquinone (DAAQ) and successfully synthesized thermally imidized polyimides with different chain structures. Among these, the quinone-containing polyimide (PMAQ) synthesized from phthalic anhydride and DAAQ exhibited a high specific capacity, with PMAQ showing a specific capacity of 160 mAh·g^-1as a cathode material at a current density of 0.05 A·g^-1.

Anhydride monomers, in conjunction with stable organic frameworks, can yield electrode materials with superior performance. By introducing anhydride monomers and combining them with organic frameworks, the structural stability of the material is enhanced, resulting in a higher capacity retention rate. Li et al.^[122]By polymerizing truxene-based triamine with linear anhydrides, two novel polyimide covalent organic frameworks (PI-COFs), COF-JLU85 and COF-JLU86, were synthesized. Covalent organic frameworks can construct more stable elastic structural frameworks and provide open channels for ion transport. Compared with previously used polymer electrode materials, the two materials synthesized by combining the electrode material with this framework exhibit better capacity retention rates, with COF-JLU86 maintaining a capacity retention rate as high as 99.11% after 10,000 cycles at 15 A·g^-1.

Although binding to a stable framework helps enhance the stability of electrode materials and maintain their high capacity, the material’s conductivity remains limited. Therefore, incorporating conductive substrates—such as single-walled carbon nanotubes (SWCNTs) or graphene—into the composite has emerged as an effective strategy for improving conductivity. Wu et al. prepared a delaminated polyimide COF composite (P-COF@SWCNT) on the surface of SWCNTs via in-situ condensation of anhydrides and amines, using it as an anode for potassium-ion batteries (Fig. 14a). The open channels provided by the delaminated structure expose more active sites and shorten the ion diffusion pathways, facilitating K⁺transport. By using single-walled carbon nanotubes as a conductive substrate, this preparation method creates a cross-linked conductive network that facilitates electron transport, ensuring full utilization of electroactive groups. In practical applications, increasing the scan rate reveals a progressively higher capacitance contribution from this electrode, confirming the material’s highly efficient K⁺storage capability (Fig. 14b). DFT calculations, as shown in Fig. 14c, confirm that K⁺participates in the carbonylation of imide groups and naphthalene rings via enolization and π-K⁺interactions. These mechanisms work synergistically to effectively enhance the material’s conductivity, enabling efficient electron transport, accelerating the electrode’s reaction kinetics, and resulting in improved capacity. Before modification, P-COF exhibited an initial capacity of only 121 mAh·g^-1at 0.1 A·g^-1; in contrast, this anode material achieves an initial capacity of 204 mAh·g^-1at 0.7 A·g^-1, and also demonstrates extended stability, as illustrated in Fig. 14d ^[123].

In the molecular structure of conjugated polymers, there is a spatially extended π-bond system. The long-chain structure and the π-conjugated system endow these materials with excellent flexibility and structural diversity, giving them great application potential in organic electrode materials^[137].Among them, three special types of conjugated polymers—donor-acceptor (D-A), acceptor-acceptor (A-A), and donor-acceptor-donor (D-A-D)—have attracted considerable attention in applications due to their unique electronic structures and functional properties.

Donor-acceptor (D-A) polymers consist of alternating electron-donating donor units (D) and electron-withdrawing acceptor units (A). The D-A structure enhances charge transport efficiency, significantly improving the material's conductivity. Ma et al.^[138]prepared a donor-acceptor (D-A) conjugated polymer, poly(dihydrophenazine-thiophene) (pTTPZ), using dihydrophenazine (PZ) and thiophene (TT). The D-A structure in this material enables efficient charge transfer between PZ and TT units, allowing electrons to move more smoothly along the polymer chain and thereby enhancing the material's electrical conductivity. Linear sweep voltammetry (LSV) tests revealed that the electrical conductivity of this D-A material is one order of magnitude higher than that of poly(dihydrobenzophenoxazine) (p-DPPZ) and poly(thieno[3,2-b]thiophene) (p-PATT), which do not contain a D-A acceptor. Furthermore, p-TTPZ exhibits excellent rate performance, maintaining a high capacity of 124.2 mAh·g^-1 even at a high current density of 10 A·g^-1, far exceeding the capacities of p-DPPZ (53.1 mAh·g^-1) and p-PATT (14 mAh·g^-1) under the same conditions.

On the basis of forming a D-A structure, carbon nanostructures can be further introduced. Marcilla et al.^[139]introduced carbon additives (MWCNTs) during the polymerization of D-A type materials RCMPs, forming the composite material IEP-11-Xy, which was further processed into a self-supporting buckypaper electrode, thereby developing high-performance organic electrode materials (Fig. 20a). Carbon nanostructures provide efficient electron transport pathways while enhancing the mechanical stability of the electrode, significantly improving its performance. Studies have found that the discharge capacity of IEP-11@M20, prepared by directly adding MWCNTs via a physical method, is only 30 mAh·g^-1, with an active material utilization rate of just 26% (theoretical capacity is 149 mAh·g^-1). In contrast, IEP-11-M20 prepared using this strategy (containing 20% by weight of MWCNTs) exhibits a high gravimetric capacity of 83.7 mAh·g^-1and a high areal capacity of 6.3 mAh·cm^-2, and maintains a capacity retention rate of over 80% after 1000 cycles, demonstrating significant application potential (Fig. 20b).

In A-A type polymers, both adjacent units in the polymer chain are acceptors, resulting in a narrow band gap that can effectively enhance electrochemical reactivity. However, the lack of donor units leads to lower charge separation efficiency, limiting their practical applications. In D-A-D type polymers, two donors flank a central acceptor in the polymer chain, providing enhanced charge transfer capabilities and enabling higher energy densities when used in materials. Bhosale et al. studied the D-A-D electrode material 2,3,7,8-tetra(4-(3,6-di-tert-butyl-9H-carbazol-9-yl)phenyl)pyrazino[3-g]quinoxaline quinone (DTC-PQx-DTC). The combination of donors and acceptors broadens the potential window of the electrode material, allowing it to operate over a wider voltage range. Tests have shown that in a 1 M H₂SO₄electrolyte, the potential window of DTC-PQx-DTC reaches -0.2 V to 1.0 V, which is broader than that of conventional organic electrode materials^[140].All three types of conjugated polymers possess unique advantages and occupy an important position in the field of organic electrode materials.

MOFs are a class of crystalline porous materials formed through the self-assembly of metal ions or metal clusters with organic ligands. MOFs possess numerous advantages, such as an extremely high specific surface area, tunable pore size and shape by selecting different organic ligands and metal ions, and an environmentally friendly synthesis process. Due to these advantages, MOFs have garnered widespread attention in the field of electrode materials^[141].When applied, MOFs and their derivatives can serve as precursors for preparing electrode materials and function as molecular sieves, thereby yielding electrode materials with excellent performance.

When MOFs are used as precursors for electrode materials, they can serve as templates to prepare electrode materials with high capacity and long cycle stability. Wu et al.^[142]used the imidazole-based zeolite-8 (ZIF-8) as a template to synthesize the cathode material V₂O₃/V₃O₅/Zn₂VO₄@NC composite (referred to as ZnVO-800). During the synthesis process, the porous and hierarchical structure of ZIF-8 was preserved, resulting in a uniform particle size distribution for ZnVO-800, which helps enhance the structural stability of the material. After 3,000 cycles, the ZnVO-800 cathode material exhibited a capacity retention of 90.8%, with a reversible capacity of 100.1 mAh·g^-1. The nanoporous structure of MOFs enables them to function as molecular sieves in applications. In lithium–sulfur batteries, the shuttle effect is a significant issue; using MOFs as molecular sieves can prevent polysulfides from migrating from the cathode to the anode, thereby mitigating the shuttle effect and achieving higher capacity. Luo et al. combined dimethylammonium zinc formate (DMAZF), which possesses an antiferroelectric perovskite structure, with CNTs and sulfur to prepare a DMAZF/CNTs/sulfur electrode. The nanostructure of DMAZF acts as a physical molecular sieve to separate polysulfides and prevent their migration, while Zn²⁺, acting as a Lewis acid site, attracts polysulfides and enhances chemical adsorption. The combined action of these two mechanisms effectively restricts the migration of polysulfides (Fig. 21a). As shown in Fig. 21b, this electrode outperforms two other materials in terms of both capacity and cycle stability. At a sulfur loading of 5 mg·cm^-2, the electrode delivers specific capacities of 1260 and 1007 mAh·g^-1at 0.05 and 0.1 C, respectively. Even at a high sulfur loading of 7 mg·cm^-2, the capacity decay rate is only 0.12% per cycle after 500 cycles at 0.5 C (Fig. 21b)^[143].

COFs are crystalline porous polymeric materials formed by organic molecules connected via covalent bonds, featuring ordered pore structures, large framework structures, and strong covalent bonding, thus enabling diverse applications in electrode materials^[144].It is precisely due to the molecular structure of COFs that, in practical applications, electrode material performance can be enhanced through molecular engineering strategies such as altering conjugation length and chemical doping.

The strong covalent bonds in COFs can link organic building blocks to form 2D structures, yielding electrode materials with high rate capability. Kim et al. combined an organic building block containing an azo group with a thiazole ring to synthesize a two-dimensional covalent organic framework (AZO-1) based on thiazole ring linkages. This structure features an extended π-conjugated system, and the molecular structural modification design enables a two-electron transfer process to occur in a single step, enhancing electron transport efficiency and improving the battery’s rate performance. Testing has shown that AZO-1 can undergo more than 5,000 cycles at a high rate of 10 C, and achieves a high power density of approximately 2800 W·kg^-1 at 40 C^[145].

By adjusting the size of the conjugated units, the cyclic stability of COF electrode materials can be enhanced. Zhang et al.^[146]demonstrated that modulating the size of the conjugated units allows for the tuning of molecular orbital energies, charge transport capabilities, and spin electron densities in the active units of COFs, thereby optimizing the performance of COF electrodes (Fig. 22a).In this study, polyimide COFs based on benzene, naphthalene, and perylene diimide conjugated units were synthesized, designated as Be-PICOF, Na-PICOF, and Pe-PICOF, respectively. Using ENa-PICOF as a representative sample, the redox mechanism of this material in lithium-ion batteries was investigated, as shown in Fig. 22b. Through schematic diagrams and electron paramagnetic resonance (EPR) spectroscopy, the critical role of imine radicals in the redox process was revealed, indicating that the electrochemical performance of the electrode can be improved by adjusting the size of the imine conjugated units. Increasing the size of the imide conjugated units effectively enhances the cyclic stability of the electrode material. EBe-PICOF has the smallest conjugated unit; experimental results (Fig. 22c) show that at 1000 mA·g^-1, after 1200 cycles, EBe-PICOF exhibits rapid capacity decay, whereas ENa-PICOF and EPe-PICOF, with larger conjugated units, still retain 76% and 81% of their initial capacity after 10,000 cycles.

Chemical doping can enhance the electrical conductivity of COF electrode materials, resulting in excellent rate performance. Melle-Franco et al.^[147]used tetrathiafulvalene (TTF) as a building block and phenyl (ph) linkers to synthesize COF electrode materials. Through chemical doping, the number of free charge carriers was increased, thereby enhancing the material’s electrical conductivity. Taking TTF-Ph-COF as an example, iodine doping resulted in higher electrical conductivity, increasing from 2.66 × 10^-8 S·cm^-1before doping modification to 8.50 × 10^-5 S·cm^-1after doping.