Nanoscale Porous Framework of Lithium Titanate for Ultrafast Lithium Insertion

Abstract

The rapidly growing demand for electric vehicles and mobile electronics urgently requires the development of electrochemical energy storage systems with both high energy density and high power. [1] Supercapacitors [2] can deliver very high powers, but their attainable energy densities are far lower than those of batteries. [3] Closing the gap between the two main technologies requires the development of materials that can incorporate or liberate a large amount of charge in a very short time. Herein we report the synthesis of fully crystalline interconnected porous frameworks composed of ultrasmall lithium titanate spinel nanocrystals of a few nanometers in size. These frameworks feature a gravimetric capacity of about 175 mA h g À1 at rates of 1-50 C (0.17-8.7 A g À1 ) and can deliver up to 73 % of their maximum capacity at unprecedented high rates of up to 800 C or 140 A g À1 (corresponding to only 4.5 s of charge/discharge) without deterioration up to a thousand cycles. This titanate morphology results in the fastest ever-reported lithium insertion.A key to this performance is the design of a fully crystalline interconnected porous framework composed of ultrasmall spinel nanocrystals of a few nanometers in size. The assembly of nanoscale building blocks into interconnected porous frameworks is a promising strategy to maximize the rate performance and to enhance the power density, and is also possible for materials not accessible by electrodeposition. Nanoscaling greatly increases the interface leading to enhanced charge transfer, and drastically shortens the ion/ electron diffusion pathways by decreasing the grain size of the bulk material. [1b, 4, 5] Lithium titanate Li 4 Ti 5 O 12 (LTO) is widely used as an active material in commercial lithium ion batteries and hybrid electrochemical storage devices [6] owing to its suitable potential, relatively high capacity, and robustness. Although the lithium insertion rate in bulk LTO is intrinsically low, which is due to its low conductivity, recent reports have demonstrated that it can be substantially increased by decreasing the crystal size to the nanometer scale, [6, 7] and several approaches were developed to obtain nanoscaled material. The reported strategies include flash annealing [6] or solid-state reactions of nanosized titania, [7a] which however lead to relatively large crystals of over 30 nm. Lithium titanate with much smaller crystalline domains and enhanced insertion rates can be obtained by solvothermal [7b] and sol-gel reactions. [7c-f,i, 8] However, the power density and especially the cycling stability still need to be improved. High rate capability in combination with excellent cycling stability was achieved for hybrid materials composed of a few nanometersized crystals anchored on a conducting carbon matrix, although at the expense of significantly decreased gravimetric and volumetric capacities owing to a high content of the conducting support. [9,10] A non-supported nanosized and fully crystalline LTO with extremely high insertion/extractio...

Advanced High Energy Density Secondary Batteries with Multi‐Electron Reaction Materials

“…Spinel Li 4 Ti 5 O 12 (LTO) is considered to be a promising anode material for Li‐ion batteries because of its excellent characteristics such as low cost, safety, negligible volume change during the charge–discharge process, and long life cycling 68. The lattice of LTO is a spinel framework structure with the F d 3–m space group, which forms a 3D tunnels with octahedral sites sharing edges 69.…”

Li4Ti5O12/TiO2-SiO2 and Li4Ti5O12/SiO2 composites as an anode material for Li-ion batteries

“…Therefore, the introduction of the TiO 2 -SiO 2 groups into the spinel causes significant stabilization of the capacitance, which positively influences the working life of the electrode. theoretical capacity and superior rate capability [71][72][73][74][75][76][77][78][79][80][81][82][83][84][85][86]. In particular, by using flexible current collectors such as carbon nanotubes and fibers, flexible LTO composite electrodes have been obtained [71,86].…”

“…theoretical capacity and superior rate capability [71][72][73][74][75][76][77][78][79][80][81][82][83][84][85][86]. In particular, by using flexible current collectors such as carbon nanotubes and fibers, flexible LTO composite electrodes have been obtained [71,86]. In addition, combining LTO with conducting metallic nanoparticles can also improve the rate performance of LTO electrodes [87][88][89][90][91][92][93][94].…”

One-step, continuous synthesis of a spherical Li4Ti5O12/graphene composite as an ultra-long cycle life lithium-ion battery anode

“…[4][5][6][7][8] In addition, LTO possesses excellent Li ion insertion and removal reversibility with almost zero volume change during the charge/discharge process. 9,10 However, as demonstrated in previous studies, it is still a challenge to achieve good battery performance at high charge/discharge rates using LTO as the anode material because of the low electrical conductivity (o10 − 13 S cm − 1 ) of LTO, 11,12 and thus there have been many efforts to improve the rate capability and the cycling performance of LTO-based batteries.…”

“…Commonly applied strategies include engineering the proper LTO structure to reduce the transport path length of Li ions and enhancing the electrical conductivity by surface coating or forming composites with carbon-based materials. Along these strategies, LTO has been fabricated into various nanostructures, for example, nanoparticles, 6,8,13 nanofibers/nanowires, 14,15 nanosheets 16,17 and porous networks, 7,10 or integrated with highly conductive carbons. 11,[18][19][20] Because graphene has excellent electrical conductivity, LTO/ graphene composites have received significant attention lately.…”