Layer‐by‐Layer Na₃V₂(PO₄)₃ Embedded in Reduced Graphene Oxide as Superior Rate and Ultralong‐Life Sodium‐Ion Battery Cathode

Abstract

However, the limited lithium resource in earth is detrimental to the further application due to the possible increasing cost and unstable energy supply. [12][13][14][15] Therefore, there is an urgent demand for developing alternative energy storage devices with low cost while maintaining a comparable performance to LIBs. Among them, sodium-ion batteries (SIBs) have become the worldwide focus owing to abundant resources and low cost. [16][17][18][19] To develop high-performance SIBs, it remains challenging to discover/develop suitable electrode materials (especially cathode) to satisfy the requirement of long-term cycling stability and rate-capability.Owing to larger radius of Na + than that of Li + (0.98 vs 0.69 Å), various cathode materials with large open frameworks, including layered transitionmetal oxides [19][20][21][22][23][24][25] and polyanionic compounds, [2,13,18,[26][27][28][29][30][31][32][33] have been developed for (1) the improved sodium storage capacity, (2) the facilitated Na + diffusion in the lattice, and (3) the restricted structure degradation caused by Na + insertion/extraction. The NASICON (sodium (Na) super ion conductor) Na x M 2 (NO 4 ) 3 (M = transition metal, N = P 5+ , Si 4+ , S 6+ , and Mo 6+ ) structure with 3D large open framework allows for rapid and reversible ion diffusion in the lattice, which is now developed as electrode with promising electrochemical performance. [34] Among these, the Na 3 V 2 (PO 4 ) 3 (NVP) becomes a "shining star" with high sodium diffusion ability and remarkable high energy density (i.e., 400 Wh kg −1 ). [18] However, the high ionic diffusion ability of NVP is accompanied with poor electronic conductivity, [35] which results in the low utilization of active materials even at low rates. In order to obtain remarkable performance of NVP, the hurdles of poor rate capability and cycling stability need to be further addressed. Recently, carbon-coated active nanocrystals embedded in a porous carbon matrix, which demonstrated excellent rate performance and cycling stability for Li 3 V 2 (PO 4 ) 3 cathodes, [36,37] as well as for NVP cathodes. [38][39][40] In general, the porous carbon content is usually high, which may lead to the decrease of tap density and entire cell volumetric energy density. [41,42] Li and co-workers reported adaptive graphene gel films as a highly compact electrode with Na 3 V 2 (PO 4 ) 3 (NVP) is regarded as a promising cathode for advanced sodiumion batteries (SIBs) due to its high theoretical capacity and stable sodium (Na) super ion conductor (NASICON) structure. However, strongly impeded by its low electronic conductivity, the general NVP delivers undesirable rate capacity and fails to meet the demands for quick charge. Herein, a novel and facile synthesis of layer-by-layer NVP@reduced graphene oxide (rGO) nanocomposite is presented through modifying the surface charge of NVP gel precursor. The well-designed layered NVP@rGO with confined NVP nanocrystal in between rGO layers offers high electronic and ionic conductivity as well as sta...

Reduced Graphene Oxide Decorated Na3V2(PO4)3 Microspheres as Cathode Material With Advanced Sodium Storage Performance

“…Furthermore, sodium resource is abundant on earth and the price is cheap. Thus, SIBs are considered as the most promising competitive alternative to LIBs (Jian et al, 2014; Wang H. et al, 2015; Chao et al, 2016; Xu et al, 2016). Developing SIBs with excellent electrochemical performance becomes necessary and challenging.…”

“…Unfortunately, the poor electronic conductivity of the phosphate salt electrode materials also leads to bad rate capacity and cycle performance (Liang et al, 2017). Many methods are applied to improve the electrochemical performance of NVP cathodes, such as cation doping, particle size reduction and conductive materials coating (Qu et al, 2014; Li et al, 2015; Xu et al, 2016; Liang et al, 2017). Among these methods, carbon coating and particle size reduction are the most effective methods.…”

“…The electronic conductivity of cathode materials can be obviously enhanced through grapheme coating. Graphene is also used as a template to diminish the particle size (Fang et al, 2016; Xu et al, 2016). Herein, we report a novel NVP microsphere cathode material.…”

Nanostructured layered vanadium oxide as cathode for high-performance sodium-ion batteries: a perspective

“…7(a)]. [61] The NVP@rGO nanocomposite contains trace amount of rGO and amorphous carbon, yet displays superior electrochemical performance [ Fig. 7(b)].…”

Recent Advances in Sodium-Ion Battery Materials

“…In situ XRD study indicates a typical two-phase reaction between Na 3 V 2 (PO 4 ) 3 and NaV 2 (PO 4 ) 3 during the sodium insertion/extraction [77]. Tremendous efforts have been made to improve the electrochemical properties of Na 3 V 2 (PO 4 ) 3 electrode, including carbon decoration [78][79][80][81], conductive polymer coating [82] and metal ion doping [83][84][85]. And high-performance Na 3 V 2 (PO 4 ) 3 electrodes are reported [86][87][88].…”