little volume change during cycling. [15,16] It should be noted that albeit with high theoretic capacities, small organic molecules are often subjected to dissolution in the electrolyte at their charged or discharged states, and thereby suffer from very poor cyclability. [16] Poly merization through covalent bonding represents an effective strategy to suppress their dissolution. [17][18][19] A number of conjugated polymers (such as covalent organic frameworks or COFs) with different building units and topologies have been accordingly explored. [20][21][22][23][24][25] They often have low structural crystallinity and unsatisfactory cycling stability limited to a few hundreds of cycles.In addition to covalent bonding, some organic building blocks (such as those containing carboxylic acid or amine functionalities) may also self-assemble through weak hydrogen bonding to form ordered two-dimensional (2D) or three-dimensional (3D) frameworks known as hydrogen bonded organic frameworks (HOFs). [26][27][28][29] They generally have great structural crystallinity, large surface areas and porosity, and have been widely investigated for gas separation, sensing, proton conduction and so on. [26,27,30] Unfortunately, their potentials in electrochemical energy storage are elusive since the weak hydrogen bonds would be disrupted in common organic electrolytes, eventually leading to the collapse of ordered frameworks. [27,30] The construction of chemically stable HOFs remains a challenging task, and necessitates the design of novel linker units capable of forming multi-site hydrogen bonds.To this end, we here introduce diaminotriazole (DAT) as the linker unit for the first time in the construction of chemically stable HOFs. DAT is a nitrogen-rich heterocycle that can potentially forms multiple hydrogen bonds. Its reaction with dianhydride gives rise to imide building blocks that further selfassemble in solution to form 2D HOF molecular sheets. Owing to the multi-site hydrogen bond interactions (eight H-bonds per building blocks), the resultant product is highly robust in spite of its ultrathin thickness of ∼1 nm, and has diminished solubility in most polar or non-polar organic solvents. When evaluated as the cathode material of SIBs, HOF molecular sheets deliver a large capacity, and most surprisingly, outstanding cycling performance of >10,000 cycles at 1 A g −1 that is far from attainable with conventional organic electrode materials in our best knowledge. This impressive electrochemical performance is afforded by the high chemical stability and fast Na + diffusion There has been growing research interest in hydrogen bonded organic frameworks (HOFs) by virtue of their great structural crystallinity, large surface areas and porosity. Their potential in electrochemical applications, unfortunately, remains elusive because weak hydrogen bonds would dissociate in solution that eventually compromises the structural integrity. Herein, it is demonstrated that this issue may be overcome by designing and introducing multisite hydrogen bo...

No abstract

Potassium-ion batteries have attracted considerable attentions as an emerging energy storage solution due to the abundance of potassium resources. The current development of potassium-ion batteries is, however, largely impeded by...

The search of electrode materials for highly reversible electrochemical sodium/potassium-ion storage is central to sodium/ potassium-ion batteries. Organic electrode materials have recently emerged as potential candidates by virtue of their functional diversity and tunability. Unfortunately, their long-term cyclability remains a challenge because of the structural instability and dissolution issue in common organic electrolytes. Herein, we report a quinone-based polymer [poly(benzobisthiazole-dione), PBTD] as a promising cathode material for sodium/potassium-ion storage. It is prepared from the selective amine−aldehyde condensation reaction and features extended π-conjugation along the molecular chain and diminished solubility in electrolytes. This polymeric electrode material exhibits excellent cycle performances with 93% of the initial capacity retained after 2000 cycles for sodium-ion batteries and a specific capacity of 87 mA h g −1 retained after 1500 cycles for potassium-ion batteries.

Organic electrode materials hold unique advantages for electrochemical alkali-ion storage but cannot yet fulfill their potential. The key lies in the design of structurally stable candidates that have negligible solution solubility and can withstand thousands of cycles under operation. To this end, we demonstrate here the preparation of dimensionally stable polyimide frameworks from the two-dimensional cross-linking of tetraaminobenzene and dianhydride. The product consists of hierarchically assembled nanosheets with thin thickness and abundant porosity. Its robust molecular frameworks and advantageous nanoscale features render our polymeric material a promising cathode candidate for both sodium-ion and potassium-ion batteries. Most strikingly, an extraordinary cycle life of up to 6000 cycles at 2 A g −1 is demonstrated, outperforming most of its competitors. Theoretical simulations support the great activity of our polymeric product for the electrochemical alkali-ion storage.