Activating the Extra Redox Couple of Co²⁺/Co³⁺ for a Synergistic K/Co Co-Substituted and Carbon Nanotube-Enwrapped Na₃V₂(PO₄)₃ Cathode with a Superior Sodium Storage Property

Abstract

Na3V2(PO4)3 (NVP) materials have emerged as a promising cathode for sodium ion batteries (SIBs). Herein, NVP is successfully optimized by dual-doping K/Co and enwrapping carbon nanotubes (CNTs) through a sol–gel method. Naturally, the occupation of K and Co in the Na1 sites and V sites can efficiently stabilize the crystal cell and provide the expanded Na+ transport channels. The existence of tubular CNTs could restrict the crystal grain growth and effectively downsize the particle size and provide a shorter pathway for the migration of electrons and ions. Moreover, the amorphous carbon layers combined with the conductive CNTs form a favorable network for the accelerated electronic transportation. Furthermore, the ex situ XPS characterization reveals that an extra redox reaction pair of Co2+/Co3+ is successfully activated at the high voltage range, resulting in superior capacity and energy density property for KC0.05/CNTs composites. Comprehensively, the optimized KC0.05/CNTs electrode exhibits a distinctive electrochemical property. It delivers an initial reversible capacity of 119.4 mA h g–1 at 0.1 C, surpassing the theoretic value for the NVP system (117.6 mA h g–1). Moreover, the KC0.05/CNT electrode exhibits the initial capacity of 113.2 mA h g–1 at 5 C and 105.8 mA h g–1 at 10 C, and the maintained capacities at 500 cycles are 105.8 and 100.8 mA h g–1 with outstanding retention values of 96.6 and 95.3%. Notably, it releases capacities of 99.8 and 84.5 mA h g–1 at 50 and 100 C, and the capacity retention values at 2500 cycles are 66.2 and 58.8 mA h g–1, respectively. What is more, the KC0.05/CNTs//Bi2Se3 asymmetric full cell exhibits a high capacity of 191.4 mA h g–1 at 2.65 V, with the energy density being as high as 507 W h kg–1, demonstrating the eminent practical application potential of KC0.05/CNTs in SIBs.

Ti-Doped Na3V2(PO4)3 Activates Additional Ti3+/Ti4+ and V4+/V5+ Redox Pairs for Superior Sodium Ion Storage

“…In addition, the Na + diffusion coefficient of Ti 0.1 -NVP/C electrode during the charge and discharge process was calculated by eqs 3 and 4. 58,59 Among them, ΔE s and ΔE τ in the formula were obtained from Figure S8(b,c). As shown in Figure S8(d,e), the Na + diffusion coefficient of Ti 0.1 -NVP/C electrode is about 2 × 10 −8 cm 2 s −1 .…”

“…Figure S8a shows the GITT curves of Ti 0 -NVP/C and Ti 0.1 -NVP/C electrodes in the voltage range of 2.0–4.2 V. The overpotentials of the two electrodes in the early stage of cycling are not much different, but as the cycling progresses, the Ti 0.1 -NVP/C electrode exhibits smaller overpotentials, indicating better Na + diffusion kinetics. In addition, the Na + diffusion coefficient of Ti 0.1 -NVP/C electrode during the charge and discharge process was calculated by eqs and . , Among them, Δ E s and Δ E τ in the formula were obtained from Figure S8­(b,c). As shown in Figure S8­(d,e), the Na + diffusion coefficient of Ti 0.1 -NVP/C electrode is about 2 × 10 –8 cm 2 s –1 .…”

Synthesis and Mechanism of Co2+/Sr2+ Codoped Magnetic Lanthanum Cuprate with Excellent Corrosion Resistance

“…The peaks of La 4e), 26 demonstrating that Sr 2+ successfully replaced part of La 3+ . According to a previous report on perovskite, the binding energy of lattice Sr was higher than that of surface Sr. 27 Meanwhile, after doping Co, the Sr 3d orbital convolution peak shifted 0.3 eV to the low binding energy side, which was due to the irregular coordination of Co 2+ with oxygen ions leading to the appearance of Co 3+ (Figure 4f) 28 and also affected the interaction between Sr and O, resulting in a change in the Sr 3d orbital binding energy. Thermogravimetric (TG) testing under a N 2 atmosphere characterized the thermal stability of the material and aided in resolving the crystal structure (Figure 5).…”

Synergistic Modification of Dandelion-Shaped Na3V2(PO4)3 with Triple Superimposed Conductive Networks by Dual-Carbon Sources for High Performance Sodium-Ion Batteries

“…However, the low reversible specific capacity and unstable cyclic properties of cathode materials limit further development of SIBs. Na 3 V 2 (PO 4 ) 3 (NVP), as a phosphate-based cathode material, possesses a high reversible specific capacity (≈117.6 mAh g –1 ) and a stable NASCION framework, which is an ideal cathode material for SIBs. − Nevertheless, the low intrinsic electron conductivity and fragile structure of NVP at high current densities limit its further application. , In order to overcome the above shortcomings, many modification methods have been used to modify NVP in recent years, such as ion doping, − morphology control, − multiphase recombination, − and carbon coating. − Carbon coating has been widely studied and applied because of its low cost, simple processing process, and easy to realize industrialization. Furthermore, additional carbon sources often reveal other benefits such as constructing conductive networks, , controlling particle size, , and controlling morphology. , Zhou et al prepared carbon-coated NVP samples with a core–shell structure by a sol–gel method.…”