Pseudocapacitance has been confirmed to significantly improve the rate capability and cycling durability of electrode materials. However, rational design and controllable synthesis of intercalation pseudocapacitive materials for sodium-ion batteries (SIBs) still remain greatly challenging. Herein, a core−shell TiO 2 -based anode composed of S-, Co-, and N-doped amorphous TiO 2 /C framework cores and ultrathin anatase TiO 2 nanosheet shells (SCN-TC@UT) was synthesized using Ti-based metal−organic frameworks (Ti-MOFs) as self-sacrificing templates coupled with a solvothermal sulfidation process. Thanks to heteroatom doping, integration of carbon species, and 2D nanosheet coating, the kinetic properties of SCN-TC@UT have been significantly improved. As a consequence, the anode achieves ultrahigh capacitive contributions up to 90.9 and 96.3% of the total capacity at scan rates of 5 and 10 mV s −1 and delivers unprecedented capacities of 211, 201, and 100 mA h g −1 at 1, 5, and 30 C (1 C=335 mA g −1 ) for over 800, 2000, and 18,000 cycles, respectively. Even at an ultrahigh rate of 50 C, the anode can still deliver a capacity of 108 mA h g −1 . This work demonstrates the most efficient TiO 2 -based anode ever reported for SIBs and holds great potential in directing the development of amorphous materials for intercalation pseudocapacitance.

TiO2 is the most promising anode material for lithium-/sodium-ion batteries (LIBs/SIBs) for grid-scale energy storage. However, the use of TiO2 anodes is greatly restricted by the low theoretical capacity, inferior electrical conductivity, and slow ion diffusion. In this study, nitrogen-doped carbon-coated TiO2/TiF3 heterostructure nanoboxes with a hierarchically porous yolk–shell structure were successfully fabricated and demonstrated impressive electrochemical performance when employed as anodes for LIBs and SIBs. Specifically, this anode delivers a high lithium storage capacity of 245 mA h g–1 at 100 mA g–1 after 100 cycles and excellent rate capability up to 5000 mA g–1 with a capacity of 71 mA h g–1. In addition, it also delivers a considerable sodium storage capacity of 112 mA h g–1 at 50 mA g–1 after 100 cycles. The enhanced lithium and sodium storage performance is attributed to the TiO2/TiF3 heterostructure that improves both specific capacity and charge transfer, conductive carbon frameworks, and hierarchically porous yolk–shell structure with open diffusion channels.

High rate and long-life sodium-ion batteries (SIBs) are highly desirable for stationary energy storage applications. However, the practical implementations of SIBs are strictly restricted due to the shortage of satisfactory anode materials. In this study, a Fe and N co-doped amorphous TiO 2 /C composite synthesized by an MOF-derived approach fulfills the demands of kinetics and durability by stimulating intercalation pseudocapacitance. Unlike traditional crystalline materials whose pseudocapacitance behaviors are highly dependent on the surface area and the crystal structure, the amorphous TiO 2 /C composite shows fast Na + intercalation/deintercalation independent of the surface area, and it can deliver impressive capacities, decent rate capability, and excellent cyclability. The electrochemical analysis shows that intercalation pseudocapacitance is responsible for the prominent sodium storage performance of the amorphous TiO 2 /C composite. This work demonstrates that Na + intercalation can be realized in amorphous structures and is beneficial for the development of extrinsic pseudocapacitive materials.

Electrochemical activation has been confirmed to be a powerful strategy to improve the Zn2+ storage activity of MnO2-based cathodes. A pivotal challenge of electrochemical activation is the poor cycling stability of activated cathodes upon Zn2+ (de)­intercalation due to the dissolution of active materials in the electrolyte, the structural degeneration of pristine cathode materials, and the complicated dynamic electrochemical process. In this study, we report a novel doping-induced static activation method to induce the formation of active Zn3V2O7(OH)2­·2H2O (ZVO) on the surface of a highly V-doped MnO2 (VMO) cathode by simply placing the cathode in an aqueous ZnSO4 electrolyte for 10 days. Our method not only significantly improves the Zn2+ storage activity of the pristine VMO cathode but also successfully tackles these problems of electrochemical activation. The activated cathode (VMO/ZVO) delivers a significantly increased initial capacity of 262 mA h g–1 and a high capacity retention of 99% after 100 cycles based on a H+/Zn2+ synergetic pseudocapacitive mechanism. The proposed static activation strategy holds great potential in the fabrication of high-activity cathodes for aqueous Zn-ion batteries.

Zn 2+ intercalation pseudocapacitance is a desirable reaction mechanism to achieve high-energy and high-power-density aqueous zinc-ion batteries (AZIBs). However, engineering an intercalation pseudocapacitive cathode for AZIBs remains challenging owing to the sluggish Zn 2+ diffusion kinetics and low electrical conductivity of cathode materials. Here, a novel Mn 0.26 V 2 O 5 •nH 2 O nanoribbon cathode synthesized by a facile ionpreintercalated/-doped strategy is reported for intercalation pseudocapacitive Zn 2+ storage. The preintercalated Mn ions greatly increase the interlayer spacing of V 2 O 5 , providing enough space and active sites for Zn 2+ diffusion and accommodation. Meanwhile, the Mn doping-induced high electrical conductivity and water-lubricated channels promote both the electron transfer and Zn 2+ diffusion to guarantee the occurrence of intercalation pseudocapacitance. In addition, the nanoribbons have a small surface area of 11 m 2 g −1 due to the structural stacking, which reduces the surface capacitance and is able to shed light on the intercalation pseudocapacitive mechanism. The as-built cathode harvests a high capacity of 484 mA h g −1 at 0.1 A g −1 and an admirable capacity retention of 95% after 500 cycles, as well as an excellent rate capability of 212 mA h g −1 at 5.0 A g −1 . This proposed strategy has great implications in the design of intercalation pseudocapacitive materials for AZIBs and beyond.