General Strategy for Designing Core–Shell Nanostructured Materials for High-Power Lithium Ion Batteries

Abstract

Because of its extreme safety and outstanding cycle life, Li 4 Ti 5 O 12 has been regarded as one of the most promising anode materials for next-generation high-power lithium-ion batteries. Nevertheless, Li 4 Ti 5 O 12 suffers from poor electronic conductivity. Here, we develop a novel strategy for the fabrication of Li 4 Ti 5 O 12 /carbon core−shell electrodes using metal oxyacetyl acetonate as titania and single-source carbon. Importantly, this novel approach is simple and general, with which we have successfully produce nanosized particles of an olivine-type LiMPO 4 (M = Fe, Mn, and Co) core with a uniform carbon shell, one of the leading cathode materials for lithium-ion batteries. Metal acetylacetonates first decompose with carbon coating the particles, which is followed by a solid state reaction in the limited reaction area inside the carbon shell to produce the LTO/C (LMPO 4 /C) core−shell nanostructure. The optimum design of the core−shell nanostructures permits fast kinetics for both transported Li + ions and electrons, enabling high-power performance. KEYWORDS: Lithium ion batteries, Li 4 Ti 5 O 12 , lithium metal phosphates, core−shell structures, anode, cathode L ithium-ion batteries (LIBs), dominating the portable power market, have attracted enormous attention in the last several years for large-scale battery applications, such as electric vehicles (EV) and hybrid electric vehicles (HEV). 1,2 However, further improvements in terms of power densities, safety, and lifetime require new materials or new structures with a higher storage capacity and faster charge and discharge rate and desired potentials. 3−6 Graphitic carbon is commonly used as an anode in commercial LIBs but exhibits poor rate performance due to its low Li diffusion coefficient and presents serious safety issues because of potential solid electrolyte interphase (SEI) film formation. 7−10 As for cathode materials, lithium transition metal oxides suffer from the intrinsic disadvantage of poor thermal stability due to the release of oxygen from the highly delithiated oxide materials. 11 Advanced materials with better safety and excellent rate capability are critical components for the next generation of LIBs.Compared to graphite, spinel Li 4 Ti 5 O 12 (LTO) exhibits a relatively high lithium insertion/extraction voltage of approximately 1.55 V (vs Li/Li + ), which circumvents the formation of the SEI and suppress lithium dendrite deposition on the surface of the anode. 12−14 As a zero-strain insertion material, LTO possesses excellent reversibility and excellent Li-ion mobility in the charge−discharge process. 15−17 As a cathode material, olivine-type LiMPO 4 (M = Fe, Mn, Co, and Ni) compounds which display high Li-ion mobility, superior safety properties, and high electrochemical and thermal stability. 18−23 Therefore, a LiMPO 4 /LTO cell system possessing unique properties would enable a promising rechargeable batteries for large-scale application.However, both materials suffer from poor electronic conductivity (for example: ...

A Facile Surface Reconstruction Mechanism toward Better Electrochemical Performance of Li4Ti5O12 in Lithium‐Ion Battery

“…It suggests that the 10 nm amorphous layer, to some degree, forms a diffusion barrier for Li + between the electrolyte and the spinel LTO phase, which hinders the charge‐transfer process, which apparently becomes rate limiting at large currents. Although the rate performance does not achieve that of carbon‐coated LTO, nano/porous LTO, or other samples based on methods aiming at improving the conductivity,28, 29, 30, 31, 32, 33 these results demonstrate the importance of the surface quality for the performance of electrode materials, giving guidance to design and produce high‐performance materials.…”

High‐Density Microporous Li4Ti5O12 Microbars with Superior Rate Performance for Lithium‐Ion Batteries

“…As the most widely commercialized anode material, the graphite anode suffers from several disadvantages, for instance, severe irreversible lithium dendrites, poor high rate charge capability, formation of a solid electrolyte interface (SEI), and serious safety issues 3, 4, 5, 6. Thus, it cannot satisfy the increasing demand for fast energy storage and large‐scale devices which requires improvement of the battery current densities, cycling stability, safety, and low‐temperature charge properties.…”

“…For instance, metal, carbon, and graphene coating have been shown to increase the surface electronic conductivity of LTO. Nanosized LTO possesses high Li‐ion ionic conductivity, for instance, nanoparticles,3, 19 nanofibers,20, 21 nanosheets,9, 22 nanotubes,23 nanowires,24 nanoarrays,23, 24 and nanoscopic porous frameworks 25. Unfortunately, as LTO particle size decreases to the nanoscale, the specific surface area of the materials increased greatly, which significantly introduces irreversible reactions with the electrolyte solution 26, 27.…”

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

“…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. Xiang et al 21 synthesized an LTO/graphene composite through a sol-gel method using lithium acetate, tetrabutyl titanate and graphene sheets; however, the capacity of as-obtained LTO/graphene decayed from 146 to 110 mAh g − 1 within 100 cycles at a 10 C rate, which may be due to the difficulties with controlling the morphology of LTO/ graphene from the sol-gel method.…”

“…[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…”