Improved electrochemical performance of the Na3V2(PO4)3 cathode by B-doping of the carbon coating layer for sodium-ion batteriesElectronic supplementary information (ESI) available. See DOI: 10.1039/c5ta03519h

• Main Authors: Shen, Wei, Li, Hui, Wang, Cong, Li, Zhihong, Xu, Qunjie, Liu, Haimei, Wang, Yonggang
• Format: Article
• Language: English
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/c5ta03519h

Boron-doped carbon coating is initially used to improve the electrochemical performance of Na 3 V 2 (PO 4 ) 3 cathode materials of sodium-ion batteries. Based on the precise analysis of Raman spectroscopy, electrochemical impedance spectroscopy and X-ray photoemission spectroscopy, it is found that there are four different B-doping species (B 4 C, BC 3 , BC 2 O and BCO 2 ) in various boron-doped carbon coated Na 3 V 2 (PO 4 ) 3 samples; moreover, different B-doping species in the carbon coated layer have different impacts on the improvement of the electrochemical performance of Na 3 V 2 (PO 4 ) 3 . Compared to lithium-ion batteries, the mechanism of B-doped carbon coating for the improvement of the electrochemical performance in sodium-ion batteries is different. Due to the introduction of the O atom in the carbon coated layer, BC 2 O and BCO 2 significantly increase numerous extrinsic defects and active sites, which could significantly accelerate Na + transport in the carbon layer. Therefore, it is unexpectedly demonstrated that Na 3 V 2 (PO 4 ) 3 /C + B, which consists of the largest total amount of BC 2 O + BCO 2 , exhibits the best electrochemical performance, particularly high-rate performance and cycling stability. As an example, when the discharging rate increases from 0.2 C to 5 C, it delivers 95.8 mA h g −1 to 90.3 mA h g −1 and an amazing capacity retention of 94% is achieved. Boron-doped carbon coated Na 3 V 2 (PO 4 ) 3 is prepared, and different impacts of various carbon-boron species on the improvement of the electrochemical performance for sodium and lithium ion batteries are analyzed and discussed in this work.