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.

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Carbon fibrous materials are the promising candidate for the anode of flexible sodium-ion batteries and potassium-ion batteries due to the structural advantages. However, the progress of mechanically robust anode materials with high electrochemical properties is still unsatisfactory for the flexible electrodes. Herein, the comprehensive design of the morphology with unique multi-channel hollow 1D/1D carbon nanotube/carbon nanofiber network and the lattice structure of carbon with S/N co-doping has been proposed. Benefiting from the enlarged interlayer spacing and the flexible fibrous network, the S/N doped carbon nanotube/carbon nanofiber composites (CNT/SNCF) possess not only high conductivity but also good structural stability during sodiation and potassiation processes. When used as anode materials in SIBs and PIBs, the free-standing CNT/SNCF electrodes exhibit high discharge capacities (274.1 and 212.5 mA h g–1 at 1 A/g after 1000 cycles, respectively), superior cycle stability (150.4 and 100.1 mA h g–1 at 5 A/g after 5000 cycles, respectively) and rate performance (109.3 mA h g–1 at 10 A/g and 108.7 mA h g–1 at 5 A/g, respectively), showing great prospects in flexible energy storage devices.

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.