Heteroatom doped carbon materials have recently demonstrated an outstanding sodium storage ability and are being considered as the most promising candidates as anodes for sodium ion batteries.

Prussian blue (PB) with concave centers is synthesized successfully through a hydrothermal method with the assistance of acid. In this study, the role of the acid is investigated systematically by adjusting the reaction temperature and time, using different kinds and amounts of acid, and changing the amount of PVP surfactant added. It is found that the acid can not only trigger the chemical reaction to form cubic PB, but also act as an etching reagent to tailor the morphology. The as-obtained cubic PB with concave centers demonstrates a superior cycle stability and rate performance, which can achieve a capacity of 107 mA h g at 0.2 A g . The corresponding capacity retention is 74 % after 500 cycles relative to the second cycle. Even at a current density of 5 A g , the specific capacity remains at 82 mA h g . Furthermore, the full cell, using PB as the cathode and hard carbon as the anode, exhibits a high capacity of 70 mA h g at 0.1 A g , and can power an LED light successfully. This work provides new insights into the role of acid in tailoring the morphology of PB, and opens a new avenue toward the design of unique structures to improve sodium storage.

The composite cathode material of the conductive polymer polyaniline (PANI)-coated spinel structural LiNi 0.5 Mn 1.5 O 4 (LNMO) for high-voltage lithium-ion batteries has been successfully synthesized by an in situ chemical oxidation polymerization method. The electrode of the LNMO–PANI composite material shows superior rate capability and excellent cycling stability. A capacity of 123.4 mAh g –1 with the capacity retention of 99.7% can be maintained at 0.5C after 200 cycles in the voltage range of 3.0–4.95 V (vs Li/Li + ) at room temperature. Even with cycling at 5C, a capacity of 65.5 mAh g –1 can still be achieved. The PANI coating layer can not only reduce the dissolution of Ni and Mn from the LNMO cubic framework into the electrolyte during cycling, but also significantly improve the undesirable interfacial reactions between the cathode and electrolyte, and markedly increase the electrical conductivity of the electrode. At 55 °C, the LNMO–PANI composite material exhibits more superior cyclic performance than pristine, that is, the capacity retention of 94.5% at 0.5C after 100 cycles vs that of 13.0%. This study offers an effective strategy for suppressing the decomposition of an electrolyte under the highly oxidizing (>4.5 V) and elevated temperature conditions.

Carbonaceous materials are one of the most promising anode materials for sodium-ion batteries, because of their abundance, stability, and safe usage. However, the practical application of carbon materials is hindered by poor specific capacity and low initial Coulombic efficiency. The design of porous structure and doping with heteroatoms are two simple and effective methods to promote the sodium storage performance. Herein, the N, P co-doped porous carbon materials are fabricated using renewable and biodegradable gelatin as carbon and nitrogen resource, phosphoric acid as phosphorus precursor and polystyrene nanospheres as a template. The product can deliver a reversible capacity of 230 mA h g at a current density of 0.2 A g , and even a high capacity of 113 mA h g at 10 Ag . The enhanced sodium storage performance is attributed to the synergistic effect of the porosity and the dual-doping of nitrogen and phosphorus.

The nitrogen-doped 3D bubble-like porous graphene (N-3DPG) is a promising candidate for apllication in sodium ion batteries for large-scale electrochemical energy storage.