Using Na7V4(P2O7)4(PO4) with superior Na storage performance as bipolar electrodes to build a novel high-energy-density symmetric sodium-ion full battery

Symmetric sodium ion full batteries with high energy density are expected to become promising storage devices. Na 7 V 4 (P 2 O 7 ) 4 (PO 4 )/C can be assembled into a high energy density symmetric full battery due to 3.85 V operating voltage as a cathode and 0.94 V operating voltage as an anode. Here, the as-prepared Na 7 V 4 (P 2 O 7 ) 4 (PO 4 )/C-GA (graphene aerogel) displays excellent electrochemical behavior as both cathode and anode . As the cathode, it can deliver a reversible capacity of 91.4 mA h g −1 at 1C (1C = 92.8 mA h g −1 ) and even shows 74 mA h g −1 capacity at 100C. Meanwhile, an ultra-long cycling property is obtained (77.2% capacity retention after 5000 cycles at 20C). As the anode, it can output 92.4 mA h g −1 at 25 mA g −1 and has a 79.2% capacity retention after 300 cycles at 50 mA g −1 . Interestingly, the symmetric full battery assembled with NVPP/C-GA outputs an initial 81.9 mA h g −1 capacity, a high 2.84 V working voltage, and 232.6 Wh kg −1 energy density at 25 mA g −1 . Therefore, our work shows potential application prospects of the symmetric full battery with Na 7 V 4 (P 2 O 7 ) 4 (PO 4 )/C-GA in energy storage systems .