Single-crystalline LiMn2O4 Research Articles

Single-crystalline LiMn2O4 nanoparticles by the gel combustion method assisted by microwave for high-performance lithium-ion battery

Single-crystalline LiMn2O4 nanoparticles by the gel combustion method assisted by microwave for high-performance lithium-ion battery

Mitigating the Jahn-Teller distortion driven by the spin-orbit coupling of lithium manganate cathode

Spinel LiMn2O4 is recognized as one of the most competitive cathode candidates for lithium-ion batteries ascribed to environmentally benign and rich sources. However, the wholesale application of LiMn2O4 is predominately plagued by its severe capacity degradation, mainly associated with the innate Jahn-Teller effect. Herein, single-crystalline LiMn2O4 with Eu3+ doping is rationally designed to mitigate the detrimental Jahn-Teller distortion by tuning the chemical environment of MnO6 octahedra and accommodating localized electron, based on the unique aspheric flexible 4f electron orbit of rare-earth metal ions. Notably, the stretching of MnO6 octahedron stemmed from the Jahn-Teller effect in Eu-doped LiMn2O4 is effectively suppressed, confirmed by theoretical calculation. Meanwhile, the structural stability of the material has been significantly enhanced due to the robust Mn–O band coherency and weakened phase transition, proved by synchrotron radiation absorption spectrum and operando X-ray diffraction. The corresponding active cathode manifests superior long-cycle stability after 300 loops at 2C and displays only a 0.011% capacity drop per cycle even at 5C. Given this, this modification tactic sheds new light on achieving superior long-cycle performances by suppressing distortion in various cathode materials.

Carbon-coated single-crystalline LiMn2O4 nanowires synthesized by high-temperature solid-state reaction with high capacity for Li-ion battery

It is a challenge to synthesize highly crystalline nanomorphologies under high-temperature environments. Here, we report that carbon-coated single-crystal LiMn2O4 nanowires were obtained via a high-temperature solid-state method under air environment using carbon-coated MnO2 as the precursor. Without the coated layer of carbon, the obtained LiMn2O4 is bulk. The carbon layer coating on MnO2 acts as a space-limiting layer to maintain the nanowire morphology of the final product of LiMn2O4 during the reaction. Owing to the merits of the highly crystalline, 1D nanowire morphology and the close-coated thin carbon layer, the produced LiMn2O4@C nanowires deliver large capacity and long-term cycling stability. In addition, the space-limiting role of the carbon layer was also found to function for LiMn2O4@C sphere. It is a general strategy to obtain ternary nanomaterials with high crystallinity.

A simple, low-cost and eco-friendly approach to synthesize single-crystalline LiMn2O4 nanorods with high electrochemical performance for lithium-ion batteries

The single-crystalline LiMn2O4 nanorods were successfully synthesized by a simple, low-cost and eco-friendly approach in which the γ-MnOOH nanorods were prepared through a facile hydrothermal process, in which KMnO4 was reduced by anhydrous alcohol (CH3CH2OH) without adding any template reagent or additional surfactant. The crystal structures and morphologies of synthesized materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. The results showed that the γ-MnOOH nanorods had high crystallinity and well-shaped morphology with an average diameter of 200nm and an average length of 12μm. For the resulting LiMn2O4 nanorods, the electrochemical properties were investigated by galvanostatic charge-discharge test, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). For the optimal LiMn2O4 nanorods, the initial discharge capacity was 123.5mAhg−1 and remained 110.2mAhg−1 after 100 cycles at 1.0C in the voltage range of 3.20∼4.35V. Moreover, the optimal LiMn2O4 nanorods can present superior rate performance, especially the capacity recovery performance as the charge-discharge rate restores to 0.1C from 5.0C. Such excellent electrochemical performance could make them to be the promising cathode material for high performance lithium-ion batteries.

Synthesis of Single-Crystalline LiMn2O4 with Different Dimensional Nanostructures for Li-ion Batteries

Synthesis of Single-Crystalline LiMn2O4 with Different Dimensional Nanostructures for Li-ion Batteries

Single-crystalline LiMn2O4 nanorods as cathode material with enhanced performance for Li-ion battery synthesized via template-engaged reaction

Abstract Single-crystalline LiMn 2 O 4 nanorods with a diameter of ~ 100 nm were synthesized via a template-engaged reaction by using tetragonal β-MnO 2 nanorods as starting material. The investigations on the structures and morphologies of both the precursor and the final product reveal that a minimal structure reconstruction can be responsible for the chemical transformation from tetragonal β-MnO 2 nanorods to cubic LiMn 2 O 4 nanorods. The obtained LiMn 2 O 4 nanorods as cathode material for Li-ion battery exhibit superior high-rate capability and good cycling stability in a potential range of 3.5–4.3 V vs. Li + /Li, which can deliver an initial discharge capacity of 125 mAh g − 1 (> 84% of the theoretical capacity of LiMn 2 O 4 ) at a current rate of 0.5 C, and about 75% of its initial capacity can be remained after 500 charge–discharge cycles at a current rate of 3 C. Importantly, the rod-like nanostructure and single-crystalline nature are also well preserved after prolonging the charge/discharge cycling time at a relatively high current rate, indicating good structural stability of the single-crystalline nanorods during the lithium intercalation/deintercalation processes, and such high-rate capacity and cycling performance can be ascribed to the favorable morphology and the high crystallinity of the obtained LiMn 2 O 4 nanorods.

Synthesis of Single‐Crystalline LiMn2O4 and LiMn1.5Ni0.5O4 Nanocrystals and Their Lithium Storage Properties

Yolk–shell spheres as nanoreactors: Single-crystalline LiMn2O4 and LiMn1.5Ni0.5O4 nanocrystals have been prepared by using yolk–shell spheres as nanoreactors to confine the size of the nanocrystals to a range of 14–19 nm (see scheme). These nanocrystals were subsequently employed as cathode materials and showed high lithium-ion storage capacities and stable charge–discharge cycling, especially at high current densities.

Characteristics of stabilized spinel cathode powders obtained by in-situ coating method

TiO2-coated LiMn2O4 cathode powders are prepared using an in situ spray pyrolysis process. The TiO2-coated LiMn2O4 powders have spherical aggregated structures of nanometer-sized primary particles. The mean sizes of the primary and secondary TiO2-coated LiMn2O4 powders are 55 and 880 nm, respectively. The transmission electron microscopy images of the LiMn2O4 primary particles show a single-crystalline and well-faceted structure. The single-crystalline LiMn2O4 primary particles are uniformly coated with an amorphous TiO2 layer. An immediate reaction of titanium tetraisopropoxide with oxygen forms a small flame at the exit of an alumina tube located in the center part of a quartz reactor. Sudden collisions between TiO2 vapor and submicron-sized composite powders of the Li and Mn components occur to form the TiO2-coated cathode powders. The discharge capacities of the TiO2-coated LiMn2O4 cathode powders are 126 and 109 mAh g−1 in the first and 170 cycles at a current density of 1 C. The capacity retentions of the pure and TiO2-coated LiMn2O4 powders are 69% and 86% of the initial capacity after 170 cycles.

Nanoporous LiMn2O4 nanosheets with exposed {111} facets as cathodes for highly reversible lithium-ion batteries

Control over porosity and exposed highly reactive facets is challenging in the area of materials science. Materials with high porosity and reactivity of exposed facets are favorable candidates in catalysis and energy storage. Here we demonstrate a facile template-free route to synthesize nanoporous LiMn2O4 nanosheets composed of single-crystalline LiMn2O4 nanorods with exposed {111} facets via an in situ lithiation of ultrathin MnO2 nanosheets. Nearly 100% of the initial capacity can be retained after 500 cycles at a 1C discharge rate using the nanoporous nanosheets as a cathode, whereas at a discharge rate of 25C, the capacity retention is about 86% of the initial capacity after 500 cycles. The durable cycling performance and high capacity retention can be attributed to the intrinsic highly oriented crystallinity, two-dimensional (2D) nanoporosity and exposed {111} facet of the nanosheet cathode.

Single-Crystalline LiMn2O4 Nanotubes Synthesized Via Template-Engaged Reaction as Cathodes for High-Power Lithium Ion Batteries

Single-crystalline nanotubes of spinel LiMn2O4 with a diameter of about 600 nm, a wall thickness of about 200 nm and a length of 1–4 μm have been synthesized via a template-engaged reaction using β-MnO2 nanotubes as a self-sacrifice template. In this fabrication, a minimal structural reorganization can be responsible for the chemical transformation from [001]-oriented β-MnO2 template to [110]-oriented LiMn2O4. Galvanostatic charge/discharge measurements indicate that the nanotubes exhibit superior high-rate capabilities and good cycling stability. About 70% of its initial capacity can be retained after 1500 cycles at 5 C rate. Importantly, the tubular nanostructures and the single-crystalline nature of the most LiMn2O4 nanotubes are also well preserved after prolonged charge/discharge cycling at a relatively high current density, indicating good structural stability of the single-crystalline nanotubes during lithium intercalation/deintercalation process. As is confirmed from Raman spectra analyses, no evident microstructural changes occur upon long-term cycling. These results reveal that single-crystalline nanotubes of LiMn2O4 will be one of the most promising cathode materials for high-power lithium ion batteries.

Spinel LiMn2O4 Nanorods as Lithium Ion Battery Cathodes

Spinel LiMn2O4 is a low-cost, environmentally friendly, and highly abundant material for Li-ion battery cathodes. Here, we report the hydrothermal synthesis of single-crystalline beta-MnO2 nanorods and their chemical conversion into free-standing single-crystalline LiMn2O4 nanorods using a simple solid-state reaction. The LiMn2O4 nanorods have an average diameter of 130 nm and length of 1.2 microm. Galvanostatic battery testing showed that LiMn2O4 nanorods have a high charge storage capacity at high power rates compared with commercially available powders. More than 85% of the initial charge storage capacity was maintained for over 100 cycles. The structural transformation studies showed that the Li ions intercalated into the cubic phase of the LiMn2O4 with a small change of lattice parameter, followed by the coexistence of two nearly identical cubic phases in the potential range of 3.5 to 4.3 V.