Spinel LiMn2O4 Cathode Material Research Articles

Study on the performance of LiMn2O4 using spent Zn–Mn batteries as manganese source

Recycling spent Zn–Mn batteries by synthesizing the products with high added value is very active internationally. In this work, we have successfully synthesized the spinel LiMn2O4 cathode materials for rechargeable lithium-ion batteries by simple sol–gel method using the manganese source that is recovered from spent Zn–Mn batteries through hydrometallurgy recycling technology. The influence of sintering temperature on the structure, the morphological properties, and the electrochemical properties of the product is investigated. The results show that spinel LiMn2O4 prepared at 700 °C has the best comprehensive performance. Moreover, the electrochemical performance of spinel LiMn2O4 has been further optimized by Co-ion doping.

Performance improvement of spinel LiMn2O4 cathode material by LaF3 surface modification

Abstract LiMn 2 O 4 cathode material synthesized by a sol–gel method was modified by LaF 3 via wet coating strategy. The phase structures, components and morphologies of pristine and LaF 3 -coated LiMn 2 O 4 are investigated by X-ray diffraction (XRD), Raman spectroscopy, field emission scanning electron microscopy (FESEM) and electron diffraction spectroscopy (EDS). The electrochemical performances are investigated and compared at room temperature (25 °C) and elevated temperature (55 °C) for pristine and LaF 3 -coated LiMn 2 O 4 . The investigation on their cycling performance demonstrates that 3 wt.% LaF 3 -coated LiMn 2 O 4 exhibits the best cycling performance, with the capacity losses of only 15.9% after 200 cycles at 25 °C and 19.7% after 100 cycles at 55 °C, much better than those of pristine materials, 60% and 59.8%. Rate performance was improved after LaF 3 surface modification. Chronoamperometry experiments indicate that phase transformation is the rate determining step in 4.0–3.5 V region. Cyclic voltammetry (CV) results confirm that LaF 3 surface coating improves structure stability of LiMn 2 O 4 during cycling. Electrochemical impedance spectroscopy (EIS) data further demonstrate that modification layer suppresses the undesirable growth of resistance of surface (R sf ) film. Differential scanning calorimetry (DSC) tests show that LaF 3 coating layer helps to improve the thermal stability of pristine electrode.

Effect of β-Cyclodextrin on Electrochemical Properties of LiMn<sub>2</sub>O<sub>4</sub> Synthesized by Solid-State Combustion Synthesis

Spinel LiMn2O4 cathode material was rapidly prepared by solid-state combustion synthesis which used lithium carbonate and manganese carbonate as raw materials and β-cyclodextrin as a fuel. The effects of amount of β-cyclodextrin and calcination temperature on their structure and electrochemical properties were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), galvanostatic charge-discharge test and cyclic voltammetry (CV). The optimal synthesis conditions were found to be 5 wt% β-cyclodextrin. Under these conditions, high-purity spinel LiMn2O4 was obtained, and its discharge specific capacity was 110.5 mAh/g in the first cycle and still retained at 99.9 mAh/g after 40 cycles.

Improvement of capacity and cycling performance of spinel LiMn2O4 cathode materials with TiO2-B nanobelts

The spinel LiMn2O4 was modified with TiO2-B nanobelts to improve its specific capacity and cycling performance. TiO2-B/LiMn2O4 composites were fabricated by a facile liquid phase mixing method. The morphology and structure of the samples were characterized by means of X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The results show that TiO2-B nanobelts are uniformly distributed in LiMn2O4 particle. Compared with bare LiMn2O4, TiO2-B/LiMn2O4 composite cathode material shows enhanced specific capacity of 129mAhg−1 and improved cycling stability. After 50 cycles, the 0, 0.5, 1.0, 2.0 and 3.0wt.% TiO2-B nanobelts modified LiMn2O4 exhibited the capacity retention of 86.1, 92.6, 93.7, 94.5 and 92.8%, respectively. The improvement of the electrochemical performance is attributed to suppression of Mn2+ dissolution, higher structural stability of the composite and rapid Li+ diffusion resulting from the open lattice channels and unique one-dimensional structure of TiO2-B nanobelts.

Structure and electrochemical performance of surface modified LaPO4 coated LiMn2O4 cathode materials for rechargeable lithium batteries

LiMn2O4 spinel cathode materials were coated with 1.0, 2.0 and 3.0 wt% of LaPO4 by the polymeric process, followed by calcinations at 800 °C for 6 h in air. The structure and electrochemical properties of the surface modified LiMn2O4 materials were characterized by XRD, SEM, XPS, cyclic voltammetry and charge–discharge techniques. XRD patterns of LaPO4 coated LiMn2O4 revealed that the coating did not affect the crystal structure and space group Fd3m of the powder materials, compared to the uncoated LiMn2O4. XPS data illustrate that the LaPO4 was completely coated over the surface of the LiMn2O4 core materials. 2 wt% of LaPO4 coated LiMn2O4 cathode material exhibits specific capacity of 103 mAh/g (versus lithium metal) and excellent capacity retention (82% of its initial capacity) between 4.5 and 3 V after 100 cycles at elevated temperature (50 °C). LiMn2O4 coated with 0.0–3.0 wt% of LaPO4 has slightly decreased the initial capacity, but the cycling stability increased remarkably over 3–4.5 V. This result indicates that the surface treatment should be an effective way to improve the overall properties of the cathode materials for lithium ion batteries. Among them, 2 wt% of LaPO4 coated spinel LiMn2O4 cathode material has improved the structural stability, high reversible capacity at elevated temperature and excellent electrochemical performances of the rechargeable lithium batteries.

Surface modification of spinel LiMn2O4 with FeF3 for lithium ion batteries

Cycling performance and thermal stability of spinel LiMn2O4 cathode material synthesized by a sol–gel method are improved by surface modification with FeF3 through chemical deposition method. The phase structures, components and morphologies of pristine and FeF3-coated LiMn2O4 are investigated by X-ray diffraction (XRD), Raman spectroscopy and field emission scanning electron microscopy (FESEM). The cycling performances are thoroughly investigated and compared at room and high temperatures. The FeF3-coated LiMn2O4 electrodes display enhanced cycling stabilities compared with that of pristine LiMn2O4. Especially, the 5wt.% FeF3-coated LiMn2O4 demonstrates the best cycling performance, with the capacity retentions of 68.2% after 200 cycles at room temperature (25°C) and 61.5% after 100 cycles at elevated temperature (55°C), much better than those of the pristine materials, 49.8 and 40.2%. Cyclic voltammetry (CV) confirms that FeF3 modification layer improves the structure stability of LiMn2O4. Electrochemical impedance spectroscopy (EIS) data illustrate that FeF3 coating can suppress the fast growth of undesirable solid electrolyte interfacial (SEI) film. Differential scanning calorimetry (DSC) tests show that the existence of FeF3 helps to enhance the thermal stability of LiMn2O4 cathode.

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.

Preparation and electrochemical properties of x Li2MnO3·(1-x)LiMn2O4 composites

Li2MnO3-doped spinel LiMn2O4 composites were synthesized by sol-gel method to improve the electrochemical performance of LiMn2O4. The microstructures, morphologies and electrochemical performance of the obtained xLi2MnO3·(1-x)LiMn2O4 composites were characterized by X-ray diffraction(XRD), scan electron microscopy(SEM) and a galvanostatic charge-discharge process. It was found that both Li2MnO3 and LiMn2O4 components exist in xLi2MnO3·(1-x)LiMn2O4(0<x<1) composites. The 0.3Li2MnO3·0.7LiMn2O4 composite shows the optimized electrochemical performance, including discharge capacity and cycle stability. It was demonstrated that Li2MnO3-doped spinel LiMn2O4 cathode material can work at wide potential window with quite good capacity retention and considerably larger reversible capacity compared to single-phase LiMn2O4 component.

Using graphene nanosheets as a conductive additive to enhance the rate performance of spinel LiMn2O4 cathode material

Graphene nanosheets (GNs) were directly used as a type of novel but powerful planar conductive additive in spinel LiMn2O4 (LMO)-based electrodes, to improve the low electronic conductivity of LMO. It was found that the specific capacity and cycling performance of LMO were obviously enhanced when GNs co-existed with acetylene black (AB), a conventional carbon-based conductive agent, at an appropriate weight ratio in the LMO-based electrode (GNs and AB were 5 wt% and 10 wt% of the total weight, respectively). The unusual phenomenon was attributed to the following two reasons: (i) the planar GNs could bridge LMO particles more effectively via a "plane-to-point" conducting mode; (ii) AB particles might serve as the fillings in the electrode and connect the isolated LMO particles to GNs through a "filling effect", thereby constructing a novel and more effective conducting network. In this way, the synergy effect between the "plane-to-point" conducting mode (due to GNs) and the "filling" mode (due to AB) significantly decreased the charge-transfer resistance of the LMO-based electrode. With the much faster charge-transfer process, the rate performance of LMO was greatly enhanced. In contrast, when GNs were in excess, the effective conducting network was weakened by the agglomeration of GNs and the absence of AB, so the conductivity and the rate performance of LMO were not improved and even decreased.

Solid-state combustion synthesis of spinel LiMn2O4 using glucose as a fuel

Spinel LiMn2O4 cathode material was rapidly synthesized in 1 h by solid-state combustion synthesis using metal carbonates as metal ion sources and glucose as a fuel. The effect of different amounts of glucose on the structure and electrochemical performance of as-prepared LiMn2O4 was investigated by X-ray diffraction (XRD), scanning electron micrographs (SEM), galvanostatic charge–discharge test, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). LiMn2O4 spinel was identified as the main crystalline phase with the presence of minor Mn3O4. The amount of glucose greatly affected the formation of Mn3O4. The optimal content of glucose was found to be 10 wt%. Under this condition, the Mn3O4 peaks almost disappeared, and high-purity spinel LiMn2O4 was obtained. Its initial discharge specific capacity of was 125.9 mAh/g, and discharge specific capacity retained at 105.2 mAh/g after 40 cycles. The detail influence of glucose on the electrochemical activity, reversibility and cycling performance of LiMn2O4 was discussed.

Influence of particle sizes and morphologies on the electrochemical performances of spinel LiMn2O4 cathode materials

Monodispersed and uniform cubic LiMn2O4 with side length of 5.0 μm denoted as CB and spherical LiMn2O4 with different diameters (2.0, 3.5, 8.0 μm) denoted as SS, MS, BS respectively are prepared through a controllable precipitation of precursors MnCO3 and a followed melt-impregnation process. Studies show that the electrochemical performance of LiMn2O4 samples with spherical morphology are better than those of the cubic one. Moreover, the spherical LiMn2O4 (MS) with middle size (3.5 μm in diameter) has the best electrochemical performance among three spherical samples instead of the smallest spherical LiMn2O4. The determined apparent lithium ion diffusion coefficients of prepared samples decrease in the order of MS > SS > BS > CB and their values are in the range of 10−9.5–10−11.5 cm2 s−1 and 10−8.0–10−10.5 cm2 s−1 from PITT and CITT respectively. This trend matched well with the electrochemical performances of the four cathode materials. This observation can be addressed to the fact that the middle size spherical particles balance the contradictory of diffusion length in solid phase and particle agglomeration, which lead to perfect contacts with the conductive additive, considerable apparent Li-ion diffusion rate and the best performance of MS LiMn2O4.

Effect of MgF2 coating on the electrochemical performance of LiMn2O4 cathode materials

Spinel LiMn2O4 cathode materials were coated with 1.0, 3.0 and 5.0 wt.% of MgF2 by precipitation, followed by heat treatment at 400 °C for 5 h in air. The effects of MgF2 coating on the structural and electrochemical properties of LiMn2O4 cathodes were investigated using XRD, SEM, and electrochemical tests. XRD and SEM results show that no significant bulk structural differences are observed between the coated and pristine LiMn2O4. The charge–discharge tests show that the discharge capacity of LiMn2O4 decreases slightly, but the cyclability of LiMn2O4 is clearly improved when the amount of the MgF2 coated was increased to 3.0 wt.%. The 3.0 wt.% MgF2-coated LiMn2O4 exhibits capacity retention of 80.1 and 76.7 % after 100 cycles at room temperature (25 °C) and elevated temperature (55 °C) at a rate of 1 C, respectively, much higher than those of the bare LiMn2O4 (70.1 and 61.6 %). The improvement of electrochemical performance is attributed to the suppression of Mn dissolution into the electrolyte via the MgF2 coating layer.

Structure and electrochemical performance of single-crystal Li1.05Ni0.1Mn1.9O3.98F0.02 coated by Li–La–Ti–O solid electrolyte

The composite cathode materials consisting of spinel-structure Li1.05Ni0.1Mn1.9O3.98F0.02 and nano-sized solid electrolyte Li–La–Ti–O (LLTO) coating were synthesized by the molten salt method and sol–gel coating process. Our results showed that Ni–F co-doping, recrystallization and LLTO coating can significantly improve the electrochemical performance of spinel LiMn2O4 cathode materials at elevated temperature and large rates. The doping and recrystallization can improve the stability of spinel grain structure and solid electrolyte LLTO coating can effectively suppresses HF-induced Mn2+ dissolution and maintains the structural integrity during cycling. At room temperature and low rates, the doping and recrystallization play dominant roles, at elevated temperature and large rates, the protective role of solid electrolyte coating is prominent.

Significant Improved Electrochemical Performance of Spinel LiMn2O4 Promoted by FePO4 Incorporation

Electrochemically-active FePO4 was introduced for surface modification of spinel LiMn2O4 cathode material to improve the electrochemical performance. Optimal technique for the LiMn2O4/FePO4 composites was specified. With proper content of FePO4 and annealing temperature, significant improvement in capacity and cyclability was obtained at room temperature and 60 °C. As compared with the LiMn2O4 coated with other oxides such as Al2O3, SiO2 and ZrO2, the FePO4 incorporated LiMn2O4 shows both enhanced initial capacity and cyclability. Examined by impedance measurement, the FePO4 incorporation in LiMn2O4 significantly suppresses the increase of charge-transfer impedance.

Preliminary studies of biominerals-coated spinel LiMn2O4 as a cathode material on electrochemical performances for Li-ion rechargeable batteries

Lithium manganese oxide (LiMn2O4) is an inexpensive and pollution-free cathode material for Li-ion rechargeable batteries. In this study, spinel LiMn2O4 cathode material was coated with biomineral powders by the mechano-chemical method. In the course of the material synthesis, citric acid and acryl amide were added to serve as a complexing agent and a gelling agent, respectively, followed by a calcination process at 700 °C for 6 h in a high-purity argon atmosphere. The spinel LiMn2O4 and biominerals-coated spinel LiMn2O4 cathode materials were, from diverse viewpoints, characterized by x-ray diffraction, field emission-scanning electron microscopy, Fourier transform infrared spectroscopy and the electrochemical cycling method to understand the mechanism of improvements in electrochemical performances. We suggest that the biominerals-coated spinel LiMn2O4 is a good candidate as a low cost and environmentally friendly cathode material showing the enlarged capacity characteristic of Li-ion rechargeable batteries.

SnO2 Modification of Spherical Spinel LiMn2O4 Cathode Materials for Li-ion Batteries

SnO2 Modification of Spherical Spinel LiMn2O4 Cathode Materials for Li-ion Batteries

Synthesis and Characterization of Scdoped Li1+xScyMn2-yO4Spinel Cathode Material for Li ion Batteries

A series of Sc3+-doped spinel lithium manganese oxides Li1+xScyMn2-yO4（y=0.01, 0.02, 0.06, and 0.10）were synthesized by solid state reaction using LiOH·H2O, MnO2, and Sc2O3 as starting materials. The results of powder X-ray diffraction indicated that the doped Li1+xScyMn2-yO4 maintain the cubic structure of spinel phase Fd3m. The electrochemical properties were characterized by electrochemical methods. The initial discharge capacity reached 135 mAh/g and the capacity fading rate was less than 2% after 40 cycles. The spinel phase was well preserved after 40 cycles. The doping of Sc3+ effectively improved the cycleability of spinels, and was a promising way for the improvement of spinel LiMn2O4 cathode materials.

Combustion synthesis of spinel LiMn2O4 cathode materials for lithium secondary batteries

Combustion synthesis of spinel LiMn2O4 cathode materials for lithium secondary batteries