Mi Ru Jo

Tailored Li4Ti5O12 nanofibers with outstanding kinetics for lithium rechargeable batteries

We report on the synthesis of one-dimensional (1D) Li(4)Ti(5)O(12) nanofibers through electrospinning and their outstanding electrochemical performances. Li(4)Ti(5)O(12) with a spinel structure is a promising candidate anode material for lithium rechargeable batteries due to its well-known zero-strain merits. In order to improve the electronic properties of spinel Li(4)Ti(5)O(12), which are intrinsically poor, we processed the material into a nanofiber type of architecture to shorten the Li(+) and electron transport distance using a versatile electrospinning approach. The electrospun Li(4)Ti(5)O(12) nanofiber showed significantly enhanced discharging/charging properties, even at high rates that exceeded 10 C, demonstrating that the nanofiber offers an attractive architecture for enhanced kinetics.

Tailored Oxygen Framework of Li4Ti5O12 Nanorods for High-Power Li Ion Battery

Here we designed the kinetically favored Li4Ti5O12 by modifying its crystal structure to improve intrinsic Li diffusivity for high power density. Our first-principles calculations revealed that the substituted Na expanded the oxygen framework of Li4Ti5O12 and facilitated Li ion diffusion in Li4Ti5O12 through 3-D high-rate diffusion pathway secured by Na ions. Accordingly, we synthesized sodium-substituted Li4Ti5O12 nanorods having not only a morphological merit from 1-D nanostructure engineering but also sodium substitution-induced open framework to attain ultrafast Li diffusion. The new material exhibited an outstanding cycling stability and capacity retention even at 200 times higher current density (20 C) compared with the initial condition (0.1 C).

Na3V2(PO4)3 particles partly embedded in carbon nanofibers with superb kinetics for ultra-high power sodium ion batteries

We here describe the extraordinary performance of NASICON Na3V2(PO4)3-carbon nanofiber (NVP–CNF) composites with ultra-high power and excellent cycling performance. NVP–CNFs are composed of CNFs at the center part and partly embedded NVP nanoparticles in the shell. We first report this unique morphology of NVP–CNFs for the electrode material of secondary batteries as well as for general energy conversion materials. Our NVP–CNFs show not only a high discharge capacity of ∼88.9 mA h g−1 even at a high current density of 50 C but also ∼93% cyclic retention property after 300 cycles at 1 C. The superb kinetics and excellent cycling performance of the NVP–CNFs are attributed to the facile migration of Na ions through the partly exposed regions of NVP nanoparticles that are directly in contact with an electrolyte as well as the fast electron transfer along the conducting CNF pathways.

Comprehensive design of carbon-encapsulated Fe3O4 nanocrystals and their lithium storage properties.

Controlling the bulk and surface structure of metal oxide nanostructures is crucial to obtain superior electronic and electrochemical properties. However, the synthetic or post-treatment techniques for preparing such structures, especially those with complex configurations, still remains a challenge. Herein, we report a completely novel approach-an amorphous carbon coating on the surface coupled with a controlled metal oxidation state in the bulk-via a simple glucose treatment. The bulk and surface structures of iron oxides are controlled by the carbothermal reaction associated with the decomposition of glucose. These novel configurations of iron oxides possess an amorphous carbon layer and ferrous state with high electronic conductivity, which definitely enhances their electrochemical properties compared to pristine iron oxides. Our findings provide an effective solution for the synthesis of complex metal oxide nanostructures, which can pave the way to further expand the electronic or electrochemical applications of metal oxides.

Hollow Sn–SnO2 Nanocrystal/Graphite Composites and Their Lithium Storage Properties

Hollow spheres have been constructed by applying the Kirkendall effect to Sn nanocrystals. This not only accommodates the detrimental volume expansion but also reduces the Li(+) transport distance enabling homogeneous Li-Sn alloying. Hollow Sn-SnO2 nanocrystals show a significantly enhanced cyclic performance compared to Sn nanocrystal alone due to its typical structure with hollow core. Sn-SnO2/graphite nanocomposites obtained by the chemical reduction and oxidation of Sn nanocrystals onto graphite displayed very stable cyclic performance thanks to the role of graphite as an aggregation preventer as well as an electronic conductor.

Polymorphism-induced catalysis difference of TiO2 nanofibers for rechargeable Li–O2 batteries

The polymorphic change of TiO2 nanofiber catalysts from anatase to rutile enabled Li–O2 cells to have higher round-trip efficiency and lower overpotential followed by a better cyclic retention. This is due to enhanced catalytic activity probably associated with the smaller Li+ chemisorption energy and band gap of the rutile phase compared with the anatase phase.

A reduced graphene oxide-encapsulated phosphorus/carbon composite as a promising anode material for high-performance sodium-ion batteries

As a promising anode for sodium ion batteries, phosphorus has captured remarkable interest due to its highest sodium-storage capacity. However, phosphorus suffers from huge volume expansion during discharging and its typical low conductive nature. So, herein, we have realized a phosphorus/carbon composite encapsulated by reduced graphene oxide (P/C@rGO) through a simple spray drying process combined with in situ oxidation of the P/C composite. The rGO coating layer alleviates the volume expansion of phosphorus and improves its electrical conductivity. In addition, a small amount of phosphate species in P/C@rGO enables strong interaction between rGO nanosheets and P/C particles, finally promoting sodium ion transfer and cycling stability. As a result, P/C@rGO shows a high reversible capacity of 2445 mA h gp−1 and maintains 95% of its initial capacity even after 100 cycles.

An improved catalytic effect of nitrogen-doped TiO2 nanofibers for rechargeable Li–O2 batteries; the role of oxidation states and vacancies on the surface

This work deals with nitrogen-doped TiO2 nanofibers with increased ionic conductivity and good catalytic activity, as a potential cathode catalyst for lithium–air battery. The electrochemical enhancement with nitrogen-doped TiO2 in comparison with pristine TiO2 could be realized by the changed electronic properties correlated with the evolution of oxygen vacancies altering the surface oxidation state of TiO2. A discharge capacity greater than 11 000 mA h g−1(carbon) and a cyclic retention more than 25 cycles were achieved with the corresponding nitrogen-doped TiO2 catalyst.

Controlling Solid-Electrolyte-Interphase Layer by Coating P-Type Semiconductor NiOx on Li4Ti5O12 for High-Energy-Density Lithium-Ion Batteries

Li4Ti5O12 is a promising anode material for rechargeable lithium batteries due to its well-known zero strain and superb kinetic properties. However, Li4Ti5O12 shows low energy density above 1 V vs Li(+)/Li. In order to improve the energy density of Li4Ti5O12, its low-voltage intercalation behavior beyond Li7Ti5O12 has been demonstrated. In this approach, the extended voltage window is accompanied by the decomposition of liquid electrolyte below 1 V, which would lead to an excessive formation of solid electrolyte interphase (SEI) films. We demonstrate an effective method to improve electrochemical performance of Li4Ti5O12 in a wide working voltage range by coating Li4Ti5O12 powder with p-type semiconductor NiOx. Ex situ XRD, XPS, and FTIR results show that the NiOx coating suppresses electrochemical reduction reactions of the organic SEI components to Li2CO3, thereby promoting reversibility of the charge/discharge process. The NiOx coating layer offers a stable SEI film for enhanced rate capability and cyclability.

Lithium‐Ion Transport through a Tailored Disordered Phase on the LiNi0.5Mn1.5O4 Surface for High‐Power Cathode Materials

The phase control of spinel LiNi0.5 Mn1.5 O4 was achieved through surface treatment that led to an enhancement of its electrochemical properties. Li(+) diffusion inside spinel LiNi0.5 Mn1.5 O4 could be promoted by modifying the surface structure of LiNi0.5 Mn1.5 O4 through phosphidation into a disordered phase (Fd3m) that allows facile Li(+) transport. Phosphidated LiNi0.5 Mn1.5 O4 showed a significantly enhanced electrochemical performance, even at high rates exceeding 10 C, demonstrating that the improved kinetics (related to the amount of Mn(3+) ) can render LiNi0.5 Mn1.5 O4 competitive as a high-power cathode material for electric vehicles and hybrid electric vehicles.