Prussian blue analogues are actively explored as low cost and high capacity cathodes for Na ion batteries; however, their applications are hindered by low capacity utilization and poor cyclability of these compounds. Here we show that this problem can be solved by controlling the purity and crystallinity of the Prussian blue lattices. As a model compound, single-crystal Fe III Fe III (CN) 6 nanoparticles are synthesized and found to have a sufficiently high capacity of 120 mA h g À1 , an exceptional rate capability at 20 C and superior cyclability with 87% capacity retention over 500 cycles, showing great promise for Na ion battery applications. More significantly, these results provide a new insight into the intercalation chemistry of Prussian blue analogues and open new perspectives to develop Na storage cathodes for widespread applications of electric energy storage.

Current battery systems have severe cost and resource restrictions, difficultly to meet the large scale electric storage applications. Herein, we report an all-organic Na-ion battery using p-dopable polytriphenylamine as cathode and n-type redox-active poly(anthraquinonyl sulphide) as anode, excluding the use of transition-metals as in conventional electrochemical batteries. Such a Na-ion battery can work well with a voltage output of 1.8 V and realize a considerable specific energy of 92 Wh kg−1. Due to the structural flexibility and stability of the redox-active polymers, this battery has a superior rate capability with 60% capacity released at a very high rate of 16 C (3200 mA g−1) and also exhibit an excellent cycling stability with 85% capacity retention after 500 cycles at 8 C rate. Most significantly, this type of all-organic batteries could be made from renewable and earth-abundant materials, thus offering a new possibility for widespread energy storage applications.

Organic Na-host materials have are now actively pursued as an attractive alternative to conventional transition-metal compounds for development of sustainable sodium ion batteries; however, most of the organic compounds reported so far suffer from their low reversible capacity and poor cyclability. Here, we report a simple perylene diimide, 3,4,9,10-perylene-bis(dicarboximide) (PTCDI), which demonstrates remarkable electrochemical performances as an organic cathode for Na-ion batteries. With the high density of redox-active carbonyl groups in a stable π-conjugated structure, the PTCDI molecule can undergo a two-electron redox reaction with reversible insertion/extraction of 2 Na(+) ions per molecular unit, demonstrating a high capacity of 140 mAh g(-1), a strong rate performance with a reversible capacity of 103 mAh g(-1) at 600 mA g(-1) (5 C,1 C = 120 mA g(-1)) and a long-term cyclability with 90% capacity retention over 300 cycles. Because this PTCDI material is commercially available and nontoxic, it may serve as a new alternative cathode for Na-ion battery applications.

A redox-active and water-insoluble polyimide, poly-(naphthalene four formyl ethylenediamine), demonstrates a high capacity of 130 mA h g(-1), a strong rate capability at 10 C rate and an excellent capacity retention of 91.2% over 1000 cycles, offering a low cost and environmentally benign anode for aqueous Na-ion batteries.

Graphene-wrapped organic nanoflowers are synthesized from ultrasonic treatment of a simple microsized disodium salt (Na212H6O4) and graphene, which demonstrates a greatly enhanced electrochemical capacity, rate capability and cycling stability as organic Na(+) storage anode. This work suggests an effective architecture to make organic materials electrochemically energetic and stable for energy storage applications.