As-prepared LiMn2O4 Research Articles

Utilization of manganese ore waste in development of mesoporous Mn3O4 and spinel LiMn2O4 octahedrons as a cathode for Li-ion battery

Nowadays, research on extracting gainful materials from waste precursors is highly fascinating and possesses excellent economic importance. This contribution validates the utilization of waste manganese sulphate (MnSO4) solution produced during the Mn mining processes for value-added battery materials. Specifically, the nano-sized spherical Mn3O4 particles were prepared using the MnSO4 solution by a controlled crystallization process in high purity, which was subsequently employed to develop efficacious cathode material i.e. LiMn2O4 (LMO) by a scalable solid-state method. The structural and morphological properties of as-prepared Mn3O4 and LiMn2O4 are studied by various characterization techniques like XRD, FTIR, Raman spectroscopy, FE-SEM, FE-TEM, XPS, and BET. The investigation reveals the formation of highly crystalline and phase-pure materials. The well-defined truncated octahedral LMO was successfully demonstrated as cathode electrode materials in the assembly li-ion battery coin cell. The as-prepared pristine, highly crystalline LiMn2O4 exhibited specific charge and discharge capacities of 122 mAhg-1 and 116 mAhg-1, respectively at 0.1C and prolonged stability with 71.4% capacity retention after 900 cycles at the current density of 1C within the potential window of 3.6 to 4.5V. The superior cycling performance of LMO suggests the significance of surface orientation in achieving enhanced electrochemical performance.

Tracking Electrochemical-Cycle-Induced Surface Structure Evolutions of Cathode Material LiMn2O4 with Improved Operando Raman Spectroscopy.

Linking surface structure evolution to the capacity fading of cathode materials has been a problem in lithium ion batteries. Most of the strategies used to solve this problem are focused on the differences between the unaged and aged materials, leading to the loss of intermediate dynamic change information during cycling. Raman spectroscopy is a convenient, nondestructive, and highly sensitive tool for characterizing the surface/near-surface region structure. In this work, we improved an operando Raman system, which is able to record in situ and in real time a series of Raman spectra during charging/discharging cycles and is even able to record very weak Raman peaks without the use of SRES enhancement, which facilitates sample preparation. These series of Raman spectra revealed an inherent correlation between the electrode potential/Li content and the surface structure changes of the as-prepared pure LiMn2O4 film, including the biphase reaction, the evolution of the peroxo O-O bond, and the formation of the Mn3O4 surface phase. They were the first to show that the number of peroxo O-O bonds was decreased with an increasing number of cycles and that this decrease was accompanied by an increase in the Mn3O4 phase. With the help of the data measured by XPS, c-AFM, electrochemical testing equipment, and the calculation based on density functional theory, the causes of the capacity fading of the material are discussed. This work not only showed a direct correlation between the surface structure evolution and the capacity fading of the LiMn2O4 but also could provide an alternative operando Raman system that could be widely used for the in situ characterization of battery electrode materials.

Spinel LiMn2O4 cathode materials for lithium storage: The regulation of exposed facets and surface coating

Minimal Mn dissolution was achieved with surface Mn4+-rich phase-modified truncated octahedral spinel LiMn2O4 with exposed {111} planes, which was synthesized via a simple hydrothermal reaction, followed by high temperature calcination in an oxygen atmosphere. The calcination atmosphere had a significant influence on the formation of the surface Mn4+-rich phase-modified layer; LiMn2O4 without a surface Mn4+-rich phase was obtained by calcination in an air atmosphere. Benefiting from the unique structure, the as-prepared LiMn2O4 exhibited an excellent rate capability and prolonged cycle stability, delivering a discharge capacity of 101 mAh g−1 and capacity retention rates of about 94% and 88% after 500 and 1000 cycles at 1C, respectively, compared to a discharge capacity of 86 mAh g−1 and a capacity retention rate of about 86% after 500 cycles at 1C for the LiMn2O4 prepared in an air atmosphere. The synergistic effect of the unique truncated octahedral morphology of spinel LiMn2O4 with {111} exposed planes and the modification of the surface Mn-rich phase endowed the composite with excellent electrochemical properties.

High capacitance LiMn2O4 microspheres with different microstructures as cathode material for aqueous asymmetric supercapacitors

Asymmetric supercapacitors (ASCS) with a battery-type electrode and a capacitor-type electrode have been regarded as the most promising energy-storage devices with high-energy and high-power densities. In this paper, the porous and hollow LiMn2O4 microspheres were prepared using MnCO3 microspheres as template and subsequently an ASCS with the as-prepared LiMn2O4 as cathode and activated carbon (AC) as anode in Li2SO4 aqueous electrolyte (designated by AC//LiMn2O4 ASCS) was assembled and investigated electrochemically. The results indicate that the porous LiMn2O4 exhibits a higher reversible capacity and rate capability compared to hollow LiMn2O4 microspheres, and delivers a specific capacitance of 536 F g−1 at 1 mV s−1. The assembled AC//porous LiMn2O4 ASCS presents a high energy density of 33.12 Wh kg−1 at the power density of 90 W kg−1. All these might be attributed to the unique microstructure of the as-prepared porous LiMn2O4 microspheres.

Facile synthesis of LiMn2O4 microsheets with porous micro-nanostructure as high-rate cathode materials for Li-ion batteries

Porous LiMn2O4 microsheets with micro-nanostructure have been successfully prepared through a simple carbon gel-combustion process with a microporous membrane as hard template. The crystal structure, morphology, chemical composition, and surface analysis of the as-obtained LiMn2O4 microsheets are characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscope (XPS). It can be found that the as-prepared LiMn2O4 sample presents the two-dimensional (2-D) sheet structure with porous structure comprised with nano-scaled particles. As cathode materials for lithium-ion batteries, the obtained LiMn2O4 microsheets show superior rate capacities and cycling performance at various charge/discharge rates. The LiMn2O4 microsheets exhibit a higher charge and discharge capacity of 137.0 and 134.7 mAh g−1 in the first cycle at 0.5 C, and it remains 127.6 mAh g−1 after 50 cycles, which accounts for 94.7% discharge capacity retention. Even at 10 C rate, the electrode also delivers the discharge capacity of 91.0 mAh g−1 after 300 cycles (93.5% capacity retention). The superior electrochemical properties of the LiMn2O4 microsheets could be attributed to the unique microsheets with porous micro-nanostructure, more active sites of the Li-ions insertion/deinsertion for the higher contact area between the LiMn2O4 nano-scaled particles and the electrolyte, and better kinetic properties, suggesting the applications of the sample in high-power lithium-ion batteries.

Nanoparticle-assembled LiMn2O4 hollow microspheres as high-performance lithium-ion battery cathode

Spinel LiMn2O4 is an attractive cathode material for rechargeable lithium-ion batteries. However, its cycling and rate performance need further improvement. Herein, we present a novel LiMn2O4 hollow microsphere cathode fabricated via a simple solid-state reaction utilizing MnO2 hollow microspheres and LiOHH2O as the reactants. Interestingly, the as-prepared LiMn2O4 hollow microspheres are assembled by LiMn2O4 octahedral nanoparticles with exposed {111} planes, exhibiting abundant void spaces for the stress buffering and larger diffusion coefficient (1.570×10−7cm2s−1) for fast lithium ion transfer as compared to the simply aggregated LiMn2O4 nanoparticles. As a result, the LiMn2O4 hollow microspheres exhibit much improved cycling stability and deliver a specific discharge capacity of 86.3mAhg−1 at a high rate of 10C, higher than that of the aggregated LiMn2O4 (73.9mAhg−1). Our work suggests that the electrochemical performance of LiMn2O4 cathode can be manipulated by the design of unique hollow sphere structure.

Hierarchical LiMn2O4 Hollow Cubes with Exposed {111} Planes as High-Power Cathodes for Lithium-Ion Batteries.

Hierarchical LiMn2O4 hollow cubes with exposed {111} planes have been synthesized using cube-shaped MnCO3 precursors, which are fabricated through a facile co-precipitation reaction. Without surface modification, the as-prepared LiMn2O4 exhibits excellent cyclability and superior rate capability. Surprisingly, even over 70% of primal discharge capacity can be maintained for up to 1000 cycles at 50 C, and with only about 72 s of discharge time the as-prepared materials can deliver initial discharge capacity of 96.5 mA h g(-1). What is more, the materials have 98.4% and 90.7% capacity retentions for up to 100 cycles at 5 C under the temperatures of 25 and 60 °C, respectively. The superior electrochemical performance can be attributed to the unique hierarchical and interior hollow structure, exposed {111} planes, and high-quality crystallinity.

Controllable preparation and superior rate performance of spinel LiMn2O4 hollow microspheres as cathode material for lithium-ion batteries

Spinel LiMn2O4 microspheres and hollow microspheres with adjustable wall thickness have been prepared using controllable oxidation of MnCO3 microspheres precursors and following solid reactions with lithium salts. Scanning electron microscopy (SEM) investigations demonstrate that the microsphere morphology and hollow structure of precursors are inherited. The effect of hollow structure properties of as-prepared LiMn2O4 on their performance as cathode materials for lithium-ion batteries has been studied. Electrochemical performance tests show that LiMn2O4 hollow microspheres with small wall thickness exhibit both superior rate capability and better cycle performance than LiMn2O4 solid microspheres and LiMn2O4 hollow microspheres with thick wall. The LiMn2O4 hollow microspheres with thin wall have discharge capacity of 132.7 mA·h·g-1 at C/10 (14.8 mA·g-1) in the first cycle, 94.1% capacity retention at C/10 after 40 cycles and discharge capacity of 116.5 mAh·g-1 at a high rate of 5C. The apparent lithium-ion diffusion coefficient (Dapp) of as-prepared LiMn2O4 determined by capacity intermittent titration technique (CITT) varies from 10-11 to 10-8.5 cm2·s-1 showing a regular “W” shape curve plotted with test voltages. The Dapp of LiMn2O4 hollow microspheres with thin wall has the largest value among all the prepared samples. Both the superior rate capability and cycle stability of LiMn2O4 hollow microspheres with thin wall can be ascribed to the facile ion diffusion in the hollow structures and the robust of hollow structures during repeated cycling.

One-Pot Hydrothermal Synthesis of LiMn2O4 Cathode Material with Excellent High-Rate and Cycling Properties

The spinel LiMn2O4 was prepared by a one-step hydrothermal method using acetone as the reductant under different hydrothermal temperatures. X-ray diffraction and scanning electron microscopy analysis indicated that optimal LiMn2O4 particles (LMO-120) were synthesized at the temperature of 120°C and the particles were well distributed and about 410 nm in size. Electrochemical performance showed that the as-prepared LiMn2O4 particles exhibited a higher initial discharge capacity than commercial LiMn2O4 (131.5 mAh g−1 versus 115.6 mAh g−1 at 0.2 C). An excellent discharge capacity retention rate of 94.07% was observed after 60 charge–discharge cycles. On the other hand, when cycled at the high rate of 1 C, the optimal LiMn2O4 in this work showed a high discharge capacity of 107.5 mAh g−1 in contrast to only 92.3 mAh g−1 of the commercial LiMn2O4. These results indicate that LMO-120 showed excellent electrochemical performance, especially the prolonged cycling life and high-rate performance, which suggested that this spinel LiMn2O4 has promise for practical application as a high-rate cathode material for lithium ion batteries.

Influences of polyethylene glycol (PEG) on the performance of LiMn2O4 cathode material for lithium ion battery

Spinel phase LiMn2O4 is synthesized by a polyethylene glycol (PEG)-assisted co-precipitation method. The samples are characterized by X-ray diffraction and scanning electron microscopy techniques. The LiMn2O4 samples synthesized have similar morphology and uniform size of about 150–350 nm. The electrochemical measurements show that as-prepared LiMn2O4 nanoparticle sample using PEG with the molecular weight as 4000 (PEG-4000) shows the best cycling performance and highest rate capability among all samples, its initial discharge capacity is 133 mAhg−1 and maintains at 122 mAhg−1 under 0.5 °C after 50 cycles. The loss of its capacity was just 5.1 %. To control the particle size of LiMn2O4 is one of important factors for its application as a cathode material.

Plasma-enhanced low-temperature solid-state synthesis of spinel LiMn2O4 with superior performance for lithium-ion batteries

In this work, for the first time, we develop a plasma-enhanced low-temperature solid-state strategy to prepare LiMn2O4 with low energy consumption and superior performance for Li-ion batteries. The as-prepared LiMn2O4 shows a narrow particle size distribution in the range of 400–450 nm and smaller mean particle size.

High-performance aqueous asymmetric supercapacitor based on spinel LiMn2O4 and nitrogen-doped graphene/porous carbon composite

Spinel LiMn2O4 has been prepared by a facile hydrothermal procedure and the prepared LiMn2O4 exhibits superior electrochemical performance, such as high specific capacitance (409Fg−1 at 2mVs−1) and excellent rate capability (85% retention at 100mVs−1). In order to achieve high energy and power densities, a high-voltage asymmetric supercapacitor (ASC) is successfully assembled using the as-prepared LiMn2O4 as the positive electrode and nitrogen-doped graphene/porous carbon composite as the negative electrode in a Li2SO4 aqueous electrolyte. The optimized ASC delivers a high specific energy of up to 44.3Whkg−1 at a specific power of 595Wkg−1 with an output voltage of 1.8V based on the total weight of the active electrode materials. This novel strategy provides a promising route to design high-performance supercapacitors with high energy density for next-generation storage systems.

Synergistic Enhancement Effect of Al Doping and Highly Active Facets of LiMn2O4 Cathode Materials for Lithium-Ion Batteries

To overcome the poor cycling stability of LiMn2O4 cathode materials without sacrificing the specific capacity, we demonstrate a new strategy for synergistically enhancing their electrochemical performance by combining the advantages of Al doping and the exposure of highly active facets. Specifically, Al doping can suppress Mn dissolution in the electrolyte, leading to an outstanding cycling stability. In addition, the exposure of highly active facets can greatly enhance the specific capacity and rate capability, while also compensating for the capacity loss caused by Al doping. As a consequence, the as-prepared Al-doped LiMn2O4 truncated octahedrons exhibit a far superior performance in both rate capacity and cycling stability than the pure LiMn2O4 octahedrons and the LiMn2O4 truncated octahedrons. Our work is meaningful not only for the synthesis of high-performance LiAl0.1Mn1.9O4 truncated octahedrons, but also for providing new insight into the development of high-performance LiMn2O4 cathode materials.

Improving the Electrochemical Performance of LiMn2O4 by Amorphous Carbon Coating

A novel cyclohexanone hydrothermal method had been firstly adopted to synthesize LiMn2O4, which was then modified with carbon coating through a post-heat treatment. X-ray diffraction (XRD) and scanning electron microscopy (SEM) exhibited that the particles were well-distributed and the primary grains were about 0.8 μm in size. Transmission electron microscope (TEM) indicated the LiMn2O4/C was uniformly coated with a carbon layer about 1.5 nm in thickness. The as-prepared bare LiMn2O4 exhibited a high initial discharge capacity of 127.9 mAh g−1 at 0.1 C, and the specific capacity increased to 138.5 mAh g−1 at 0.1 C by carbon coating. Moreover, it exhibited more excellent cycling maintaining 97.76% of its initial discharge capacity after 100 charge–discharge cycles. All the tests showed that LiMn2O4 with a carbon layer had excellent electrochemical performance, which was attributed to the carbon layer avoiding the core material direct contact with the acidic electrolyte and suppression of Mn+ dissolution into electrolyte.

Combustion-derived nanocrystalline LiMn2O4 as a promising cathode material for lithium-ion batteries

In this study, nanocrystalline LiMn2O4 was synthesized by a simple combustion method and investigated for its utility as the positive electrode of a lithium-ion battery. X-Ray Diffraction characterization demonstrated that a basic crystallized spinel phase was already formed in the primary product from the direct combustion process, while pure phase LiMn2O4 was obtained after further calcination in air at relatively low temperature of 600 °C. Characterization by SEM and HR-TEM as well as BET analysis showed that the LiMn2O4 compound had a primary particle size of 40–80 nm and that those particles were partially sintered to form 0.2–0.8 μm aggregates with few mesopores. The exposed surface area of the aggregates was low and mainly formed by the outer surfaces of the constituent particles, which is beneficial to reducing the interfacial area between the liquid electrolyte and LiMn2O4, thereby effectively mediating the Mn dissolution problem. As a result, the as-prepared LiMn2O4 showed a favorable capacity of 114 mAh g−1 at a current rate of 0.2C and still retained a capacity of 84 mAh g−1 at 5C. After 100 continuous cycles at 0.1C, a capacity of 108 mAh g−1 was still maintained, compared to 120 mAh g−1 at the first cycle. The results demonstrated that combustion synthesis-derived LiMn2O4 is a promising cathode material for lithium ion batteries (LIBs).

Effects of ball milling on the crystal face of spinel LiMn2O4

Lithium manganese oxide (LiMn2O4) cathode materials are synthesized by a facile solid state reaction method using planetary ball-milled mixtures of Li2CO3 and MnO2 as materials. The as-prepared LiMn2O4 is analyzed by XRD, SEM and AAS to investigate the effects of ball milling on the grain size and morphology of LiMn2O4. It is found that ball milling treatment can reduce the (111) surfaces of LiMn2O4 and improve the corresponding electrochemical performance. The LiMn2O4 prepared after 6 h ball-milling shows higher first discharge capacity (129.3 mA h g−1 at 0.5 C) and excellent cycling stability (94.95% after 30 cycles).

One-step hydrothermal synthesis of LiMn2O4 cathode materials for rechargeable lithium batteries

LiMn2O4 cathode materials with high discharge capacity and good cyclic stability were prepared by a simple one-step hydrothermal treatment of KMnO4, aniline and LiOH solutions at 120–180 °C for 24 h. The aniline/KMnO4 molar ratio (R) and hydrothermal temperature exhibited an obvious influence on the component and phase structures of the resulting product. The precursor KMnO4 was firstly reduced to birnessite when R was less than 0.2:1 at 120–150 °C. Pure-phased LiMn2O4 was formed when R was 0.2:1, and the LiMn2O4 was further reduced to Mn3O4 when R was kept in the range of 0.2–0.3 at 120–150 °C. Moreover, LiMn2O4 was fabricated when R was 0.15:1 at 180 °C. Octahedron-like LiMn2O4 about 300 nm was prepared at 120 °C, and particle size decreased with an increase in hydrothermal temperature. Especially, LiMn2O4 synthesized at 150 °C exhibited the best electrochemical performance with the highest initial discharge capacity of 127.4 mAh g−1 and cycling capacity of 106.1 mAh g−1 after 100 cycles. The high discharge capacity and cycling stability of the as-prepared LiMn2O4 cathode for rechargeable lithium batteries were ascribed to the appropriate particle size and larger cell volume.

Electrochemical performance of solid sphere spinel LiMn2O4 with high tap density synthesized by porous spherical Mn3O4

Solid sphere spinel LiMn2O4 materials are synthesized from porous spherical Mn3O4 particles with LiOH·H2O via a high temperature solid-phase reaction. Porous spherical Mn3O4 particles, composed of aggregated crystallites, can be obtained from as-prepared spherical β-MnOOH. The solid sphere spinel LiMn2O4 particles have a high tap-density of 2.67 g·cm−3 and are well-distributed with sizes ranging from 7-9μm. The as-prepared β-MnOOH, Mn3O4 and LiMn2O4 are characterized by X-ray diffraction and scanning electron microscopy. As cathode materials, solid sphere spinel LiMn2O4, exhibits excellent cycling performance and rate capability for lithium-ion batteries. The initial discharge capacities are 127.1, 118.1, 106.3 and 87 mAh·g−1 at 0.2, 1, 5 and 10C, respectively. At 5C the discharge capacity retention rate can be maintained at 95% after 200 cycles. Cyclic voltammetry and electrochemical impedance spectroscopy confirm the excellent electrochemical performances of the synthesized solid sphere spinel LiMn2O4 materials.

Toward high capacity and stable manganese-spinel electrode materials: A case study of Ti-substituted system

LiMn2−xTixO4 (x = 0, 0.5, 1) cathode materials have been synthesized by a conventional solid state method. The capacity of the as-prepared LiMn2O4, LiMn1.5Ti0.5O4 and LiMnTiO4 are 252, 198 and 157 mAh g−1, respectively, when charging/discharging over the voltage range of 2.0–4.8 V at a current density of 40 mA g−1, all of which are consistent with more than 1 Li+ ion insertion into the spinel structure. Compared with the pristine LiMn2O4, Ti-substituted samples exhibit much better cycling stability both at room temperature and 60 °C between 2.0 V and 4.8 V. The underlying mechanism has been investigated by an in situ X-ray diffraction technique. The results demonstrate that Ti4+ ions can suppress the Jahn–Teller distortion associated with Mn3+, and stabilize the spinel structure during the charging/discharging process. Ti–O bond is stronger than Mn–O bond which yields a more stable spinel framework, i.e., [Mn2−xTix]O4. Moreover, Ti substitution helps lower the concentration of Jahn–Teller Mn3+ ions in the spinel structure during discharging process and consequently improves the structural stability. The role of Ti substitution is also confirmed by the ab initio calculations.

Preparation and electrochemical properties of spinel LiMn2O4 prepared by solid-state combustion synthesis

Spinel LiMn2O4 cathode material was rapidly prepared by solid-state combustion synthesis based on a two-stage calcination progress which used lithium carbonate and manganese carbonate as raw materials and citric acid as a fuel. The structure and physicochemical properties of the obtained LiMn2O4 powders were investigated by thermogravimetric analysis (TG) and differential thermal analysis (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM), galvanostatic charge–discharge test, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results show that the successful formation of single-phase LiMn2O4 product is highly dependent on its second-stage calcination temperature. Compared with other conditions, the as-prepared LiMn2O4 powders which experienced the second-stage, and calcined at 700 °C is the most uniform, and the charge transfer resistance (Rct) is the lowest, accompanying the best electrochemical activity and highest discharge capacity. Its initial discharge specific capacity is 119.1 mA h/g.