Sandwiching Defect-Rich TiO_2−δ Nanocrystals into a Three-Dimensional Flexible Conformal Carbon Hybrid Matrix for Long-Cycling and High-Rate Li/Na-Ion Batteries

Abstract

Developing flexible power sources is crucially important to fulfill the need for wearable electronic devices, but state-of-the-art flexible electrodes cannot meet the requirements of practical applications because of their heavy weight and unsatisfactory mechanical properties. Here, we highlight a design strategy for constructing a novel robust three-dimensional (3D) flexible electrode with a unique sandwichlike N-doped carbon sponge/TiO2−δ/reduced graphene oxide (NCS/TiO2−δ/RGO) configuration. In this electrode architecture, ultrafine defect-rich TiO2−δ nanocrystals are spatially sandwiched by a 3D conformal carbon hybrid matrix, where the 3D porous NCS provides an interconnected open diffusion channel for efficient ionic accessibility while the conformal RGO coating layer serves as an additional upper current collector, resulting in a double continuous conductive network for fast electronic transport and guaranteeing excellent electrochemical reaction kinetics. Hence, the as-built NCS/TiO2−δ/RGO flexible electrodes exhibit high-rate capabilities and long-cycling life in lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs), and they also exhibit outstanding thermal stability under cycling at 55 °C. More remarkably, a flexible soft-package full battery based on a NCS/TiO2−δ/RGO anode and a LiNi1/3Co1/3Mn1/3O2 (for LIBs) or Na0.67Fe0.3Mn0.3Co0.4O2 (for SIBs) cathode shows stable electrochemical characteristics under bending and folding, holding great potential for flexible energy storage devices.

Interfacial Modulation of a Self-Sacrificial Synthesized SnO2@Sn Core–Shell Heterostructure Anode toward High-Capacity Reversible Li+ Storage

“…With the ever-increasing energy demands for portable mobile devices, electronic vehicles (EVs), and smart grids, the development of reversible systems as power sources with the merits of high energy density, great stability, and security is urgently needed. − Among diverse systems, secondary lithium ion batteries (LIBs) composed of various intercalated cathodes and a graphite anode gradually bloom their way to practical applications. − Unfortunately, the output of LIBs touches the bottleneck owing to the limited theoretical capacity of the graphite-based anode (372 mA h g –1 ). − More effort has been devoted to seeking and developing alternative high-capacity anodes, such as metal alloys, metal oxides/sulfides, silicon, and their derivatives. − In particular, the Sn anode shows the advantages of high theoretical capacity (992 mA h g –1 ) based on the alloying mechanism with Li + to form the maximum Li 4.4 Sn, abundant resources, low cost, and high safety. ,− However, the tough obstacles in Sn anodes prevent further commercialization: (1) the huge volumetric variation of around 300% during lithiation/delithiation, resulting in the possible detachment from the electrode or the loss of electrical contact between active materials and the conductive matrix; (2) the repeated cracking and formation of a fragile solid electrolyte interphase (SEI) layer, causing the depletion of the finite electrolyte; and (3) the collapse and detachment of conductive Sn from the matrix, inducing the hardness of effective electronic transfer. These interconnected dissatisfactory factors contribute to the depressive capacity, cycling durance, and even battery failure in practical applications. − …”

Free-standing hybrid films comprising of ultra-dispersed titania nanocrystals and hierarchical conductive network for excellent high rate performance of lithium storage

“…On the other hand, TiO2 has advantages including low cost, availability, and environmental friendliness, which can allow the large-scale manufacture of TiO2 anodes for Li-ion batteries. Thus, TiO2 has attracted increasing attention as a promising material for Li-ion batteries [10][11][12][13][14][15][16][17][18][19][20][21][22][23]. The electrochemical performance of TiO2, particularly the high rate capacity, is determined by the chemical diffusivity of Li in TiO2, which mainly depends on two factors: electronic conductivity of TiO2 electrodes and diffusivity of Li ions in TiO2 [24].…”

“…The electrochemical performance of TiO2, particularly the high rate capacity, is determined by the chemical diffusivity of Li in TiO2, which mainly depends on two factors: electronic conductivity of TiO2 electrodes and diffusivity of Li ions in TiO2 [24]. To increase the electronic conductivities of TiO2 electrodes, the composites are typically fabricated by incorporating conductive components such as graphene [9,10,[13][14][15]22], graphitic carbon [16], activated carbon fabric [25], and carbon nanotubes (CNTs) [26]. To increase the diffusivity of Li ions in TiO2, nanostructure engineering is an effective strategy to decrease the diffuse distance of Li ions by designing mesoporous TiO2 with a porous structure [8,19,24,27], TiO2 nanoparticles/nanocrystals [13][14][15]17], and hollow nanostructures [16,18,21,28].…”