LiMn2O4 Cathode Material Research Articles

Effects of Lithium Salt Addition Methods on the High-Temperature Electrochemical Performance of LiMn2O4

The poor high-temperature stability of spinel LiMn2O4 cathode material has become a bottleneck hindering its large-scale application. To enhance its high-temperature electrochemical performance, the effects of two different methods of lithium salt addition on its high-temperature electrochemical performance were studied. Two methods, Li+ infiltration and solid phase mixing, were used to prepare spinel LiMn2O4 cathode material by the same high-temperature solid phase method, respectively. The obtained materials were characterized by X-ray diffraction, scanning electron microscopy, Raman, and particle size analysis. Electrochemical performance tests were carried out on the electrochemical equipment by assembling into a half-battery. The results show that the material obtained by the lithium salt solid phase mixing method presents a loose structure composed of small primary particles to form a spherical secondary particle. However, the material obtained by the Li+ infiltration method presents an octahedral crystal structure, showing a trend toward single crystal. At the same time, its calcination time is greatly shortened (from 26 to 6 h) at the same calcination temperature. The electrochemical performance test results at 55 °C show that the LiMn2O4 prepared by Li+ infiltration has a better high-temperature electrochemical performance.

High electrochemical stability of Al-doped spinel LiMn2O4 cathode material for aqueous lithium-ion batteries

High electrochemical stability of Al-doped spinel LiMn2O4 cathode material for aqueous lithium-ion batteries

Effects of sonication power on electrochemical performance of ZrO2-decorated LiMn2O4 cathode material for LIBs

The LiMn2O4 (LMO) powder is decorated with ZrO2 (denoted as Zr@LMO) particles by using sonication-assisted sol–gel method. Different sonication powers (10, 30 and 50%) are used to disperse ZrO2 and the effects of ZrO2 distribution at LiMn2O4’s electrochemical performance are analysed. Scanning electron microscopy and energy dispersive spectroscopy analyses have been made on laminated samples. For the structural analyses of particles, X-ray diffractometer is used. Electrochemical performances of electrodes are tested with galvanostatic measurements, cyclic voltammograms and electrochemical impedance spectroscopy. The ZrO2 distribution ratio on the particle surfaces is improved by 10% with the increase of sonication power from 10 to 50%. Therefore, at 50% sonication power, lower charge transfer resistance and side reactions (Mn dissolution) are accomplished, which leads to 41 and 9% specific capacity increase compared to pure and the lowest sonication power, respectively. After 100 cycles at 0.1C, 93.2 mAh g–1 specific discharge capacity and 73.4% capacity retention are attained for ZrO2-decorated LMO at 50% sonication power. Furthermore, at 2C rate, the specific discharge capacity of the decorated sample at 50% sonication power is 59% higher than the pure LMO.

Atomic insights into surface orientations and oxygen vacancies in the LiMn2O4 cathode for lithium storage

Abstract Surface anisotropy of spinel LiMn2O4 crystal is of significance for strengthening the lithium storage. In this work, we investigate the evolutions of surface orientations and oxygen vacancies in the LiMn2O4 cathode materials by the spherical aberration-corrected scanning transmission electron microscopy (Cs-STEM) technique. Firstly, the {111} lattice planes appear in the formed LiMn2O4 octahedra, and then the {110} and {001} crystal planes are observed in the subsequent truncated octahedral at a higher temperature or a longer annealing time. The LiMn2O4 crystals with dominated {111} and {110} planes and an appropriate amount of oxygen vacancies exhibits a superior cycling performance and rate performance, suggesting a synergistic effect of surface orientation and concentration of oxygen vacancies achieves an enhanced electrochemical performance. The introduction of oxygen vacancies can accelerate the diffusion of lithium-ions along {110} plane and strengthen the rate performance of LiMn2O4, as elucidated by the combination of Cs-STEM observation, X-ray photoelectronic spectra analysis and property measurements.

Unveiling the role of Mn-interstitial defect and particle size on the Jahn-Teller distortion of the LiMn2O4 cathode material

This work proposes to unveil the underlying effect of Mn-interstitial defect as well as the particle size on the Jahn Teller distortion. Mn-interstitial defects and nanometric particles were characterized by HRTEM, Rietveld fitting and microstrain XRD analysis. The research was conducted by measuring the changes of the Fermi level, entropy, enthalpy and the redox potential due to the JT transition. Other dynamic electrochemical measurements were also carried out. The structural and microstructural measurements led to propose the presence of Mn ions in distorted tetrahedral 48f positions after using irradiation to induce Mn-interstitial defects. By using the proposed methodology it was possible to experimentally observe that this defect vanishes the JT effect and diminishes the shifting of the Fermi level during the phase transition. Subtle correlations between the capacity of the 3V region and the redox potential drop of these materials were revealed and explained. The surface pressure and bonding effects were set as important factors underlying stunning electrochemical and structural changes that characterise nanometric particles below 15 nm.

Facile combustion synthesis of amorphous Al2O3-coated LiMn2O4 cathode materials for high-performance Li-ion batteries

The unique Al2O3-coating layer can suppress the Mn dissolution and resist HF corrosion, hence stabilizing the crystal structure of spinel LiMn2O4 cathode materials.

Optimizing the electrochemical performance of Li2MnO3 cathode materials for Li-ion battery using solution combustion synthesis: Higher temperature and longer syntheses improves performance

Li2MnO3 is the parent compound and a component of the well-studied Li-rich Mn-based layered materials (xLi2MnO3·(1−x)LiMO2) for high capacity Li-ion batteries. Different combinations of citric acid fuel and metal nitrates (C/N) were used to optimize the electrochemical performance of Li2MnO3 nanoparticles by the solution combustion synthesis. Thermodynamic modelling and thermogravimmetric analysis show that the variations of C/N molar ratio affected the combustion process and the Li2MnO3 powder characteristics such as morphology and crystallinity. The fuel-rich composition (C/N = 0.555) with the highest adiabatic flame temperature produced Li2MnO3 cathode materials with the best electrochemical performance. The influence of sintering temperature on the crystallinity of the Li2MnO3 sample was investigated with high-temperature synchrotron XRD. The Li2MnO3 synthesized at a lower temperature (400 °C) had a better initial discharge capacity than the one synthesized at a much higher temperature (800 °C) however, it showed far poorer cycling stability. These differences in their electrochemical performance were explained on the basis of their microstructure and morphology. Furthermore, increasing annealing time at 800 °C (from 2 to 20 h) achieved phase pure materials and improved the electrochemical performance of Li2MnO3 powders. This improvement was due to the well defined, developed and larger particles of the samples annealed at longer times. The results show that apart from increasing synthesis temperature, varying annealing times at optimum temperature could be used to improve the functional performance of ceramic oxides.

Ag-Modified LiMn2O4 Cathode for Lithium-Ion Batteries: Coating Functionalization

In this work, the properties of silver-modified LiMn2O4 cathode materials are revisited. We study the influence of calcination atmosphere on the properties of the Ag-coated LiMn2O4 (Ag/LMO) and highlight the silver oxidation. The effect of the heat treatment in vacuum is compared with that in air by the characterization of the structure, specific surface area, Li transport properties and electrochemical performance of Ag/LMO composites. Surface analyses (XPS and Raman spectroscopy) show that the nature of the coating (~3 wt.%) differs with the calcination atmosphere: Ag/LMO(v) calcined in vacuum displays Ag nanospheres and minor AgO content on its surface (specific surface area of 4.1 m2 g−1), while Ag/LMO(a) treated in air is mainly covered by the AgO insulating phase (specific surface area of 0.6 m2 g−1). Electrochemical experiments emphasize that ~3 wt.% Ag coating is effective to minimize the drawbacks of the spinel LiMn2O4 (Mn dissolution, cycling instability, etc.). The Ag/LMO(v) electrode shows high capacity retention, good cyclability at C/2 rate and capacity fade of 0.06% per cycle (in 60 cycles).

Deep Eutectic Solvent Based on Lithium Bis[(trifluoromethyl)sulfonyl] Imide (LiTFSI) and 2,2,2-Trifluoroacetamide (TFA) as a Promising Electrolyte for a High Voltage Lithium-Ion Battery with a LiMn2O4 Cathode.

To design safe and electrochemically stable electrolytes for lithium-ion batteries, this study describes the synthesis and the utilization of new deep eutectic solvents (DESs) based on the mixture of 2,2,2-trifluoroacetamide (TFA) with a lithium salt (LiTFSI, lithium bis[(trifluoromethane)sulfonyl]imide). These prepared DESs were characterized in terms of thermal properties, ionic conductivity, viscosity, and electrochemical properties. Based on the appearance of the product and DSC measurements, it appears that this system is liquid at room temperature for LiTFSI mole fraction ranging from 0.25 to 0.5. At χLiTFSI = 0.25, DESs exhibited favorable electrolyte properties, such as thermal stability (up to 148 °C), relatively low viscosity (42.2 mPa.s at 30 °C), high ionic conductivity (1.5 mS.cm–1 at 30 °C), and quite large electrochemical stability window up to 4.9–5.3 V. With these interesting properties, selected DES was diluted with slight amount of ethylene carbonate (EC). Different amounts of EC (x = 0–30 %wt) were used to form hybrid electrolytes for battery testing with high voltage LiMn2O4 cathode and Li anode. The addition of the EC solvent into DES expectedly aims at enhancing the battery cycling performance at room temperature due to reducing the viscosity. Preliminary results tests clearly show that LiTFSI-based DES can be successfully introduced as an electrolyte in the lithium-ion batteries cell with a LiMn2O4 cathode material. Among all of the studied electrolytes, DES (LiTFSI: TFA = 4:1 + 10 %wt EC) is the most promising. The EC-based system exhibited a good specific capacity of 102 mAh.g–1 at C/10 with the theoretical capacity of 148 mAh.g–1 and a good cycling behavior maintaining at 84% after 50 cycles.

Self-templated hollow LiMn2O4 nanofibers as extremely long lifespan lithium ion battery cathode

The poor cyclability and inferior capacity retention caused by severe Jahn–Teller effect and dissolution of Mn ions into electrolyte during cycling hinder the commercial application of spinel LiMn2O4 with low cost and non-toxic. Herein, hollow LiMn2O4 nanofibers composed of LiMn2O4 nanograins are proposed, forming 3D network framework with uniform distribution. The slender and firm nanofibers can effectively buffer the irreversible phase transitions triggered by Mn3+ disproportionation and Jahn–Teller distortion and lead to the extremely long cycle life of LiMn2O4 cathode. Meanwhile, the huge specific surface area provided by hollow structure ensures the full contact between the materials and electrolyte, being beneficial to the diffusion of Li ions and transfer of electron to maintain its capacity. It can be observed that the capacity retention is 97.5% after 1000 cycles at 1C. The structure design of the hollow nanofibers modified the LiMn2O4 cathode material at the micro-level, which greatly improves the long-term cycling stability of the material and provides reference for the modification in lithium ion batteries.

Hydrometallurgical Regeneration of LiMn2O4 Cathode Scrap Material and Its Electrochemical Properties

AbstractThe main researches focus on the recovery of metal elements in lithium manganate and not consider regenerating the cathode scrap materials. In this study, first, the polyvinylidene fluoride (PVDF) binder is removed by a combination of solvent dissolution and heat treatment. PVDF is easily separated by dissolving in an N‐methyl‐2‐pyrrolidone solution at a heating temperature of 60 °C, stirring time of 50 min, and solid solution ratio of 80 g⋅L−1. The dissolution rate of the scrap material achieves 86.70 % under optimal conditions. Further, using inductively coupled plasma spectroscopy to define the Li and Mn metal contents, and the LiMn2O4 cathode material is regenerated by a hydrometallurgical method. At the optimum calcination conditions of 500 °C for 12 h, electrochemical performance show that there are obvious charge and discharge platforms in the charge/discharge curves, and high first‐cycle discharge capacity is 123.7 mAh g−1 (3.0–4.3 V and 0.1 C), after 50 cycles, it decrease to 83.2 mAh g−1.

Pyrometallurgically regenerated LiMn2O4 cathode scrap material and its electrochemical properties

Recycling cathode materials from lithium-ion battery scraps can play a significant role in reducing environmental contamination and resource depletion. In this study, we employed pyrometallurgical techniques to regenerate LiMn2O4 cathode materials from recovered cathode scraps. First, the binder was removed under optimal conditions by a heating and stirring method to maximize the dissolution rate of the cathode scrap materials. Next, inductively coupled plasma spectroscopy was used to define the Li and Mn contents, and finally, the LiMn2O4 cathode material was regenerated by a pyrometallurgical method. After calcination under the optimum conditions of 500 °C for 12 h, electrochemical performance testing revealed obvious charge and discharge platforms in the charge/discharge curves; further, a high first-cycle discharge capacity was observed at 136.6 mAh·g-1 (3.0–4.3 V and 0.1 C), which decreased to 93 mAh·g-1 after 50 cycles. This process is low-cost and environmentally friendly, with the potential for recovering other cathode scrap materials.

Efficient process for recovery of waste LiMn2O4 cathode material precipitation thermodynamic analysis and separation experiments

An efficient process is proposed for recovery of waste LiMn2O4 cathode material, which is one of the most commonly used cathode materials in LIBs. This report constitutes the precipitation thermodynamic analysis and separation experiments based on the water-leaching solutions during the processes of low-temperature calcination with (NH4)2SO4 and water-leaching. Precipitation thermodynamic analysis is undertaken to investigate the effects of initial concentration of the target solution, [N]T1, excess precipitant, and addition of (NH4)2SO4 on the manganese precipitation in the Mn2+–Li+–SO42−–NH3–NH4+–CO32−–H2O system. Moreover, the effects of initial concentration of the target solution, [N]T2, and excess precipitant on the lithium precipitation in the Li+–SO42−–NH3–NH4+–CO32−–H2O system are investigated. All these factors clearly influence the manganese and lithium precipitation, particularly the [N]T and the presence of excess precipitant in the system. The precipitation experimental results demonstrate that the optimal conditions are: a precipitation temperature of 35 °C; an excess coefficient of the precipitant of 2.4; the use of NHC-3 to precipitate the ML-3 solution; a maximum precipitation percentage of manganese of 99.96%; and an absence of Li2CO3 precipitation. The double-sulfate salts (Li(NH4)SO4 & (NH4)2SO4) evaporated and crystallised from the Li+/NH4+ solution are mixed with the waste LiMn2O4 cathode material for calcination and water leaching, for which the efficiencies of Li and Mn are 100% and 96.89%, respectively. The double-sulfate salts are calcined at 550 °C for 45 min to obtain the Li2SO4 product. Finally, the complete recovery and separation of Mn and Li in the waste LiMn2O4 cathode material are achieved.

Electronic structure study of Sn-substituted Li2MnO3 cathode material

Li2MnO3, a well known Li-ion battery cathode material, is used against instabilities of other cathode materials despite of its weak performance. To this aim, Sn4+-substitution of Mn could enrich the electronic properties providing during the molecular interactions of valence electrons. Within this work, electronic structure features of Sn-substituted Li2MnO3 material (Li2Mn1−xSnxO3) have been studied by the X-ray absorption fine structure (XAFS) spectroscopy calculations regarding variant x values of 0.00, 0.10, and 0.20. Higher electronegativity of the substituted Sn atom versus the host Mn atom could govern the electronic interactions via the hybridized bonds built between Sn and O atoms. The obtained results indicated that the Sn-substitution could yield better cathode properties for the Li-ion battery devices.

Synthesis, Characterization and Electrochemical Properties of a Fluoride-Substituted Spinel LiMn2O4 Cathode Material

Conventional high-temperature (800 °C) synthesis of fluoride-substituted samples from LiF has been found to encounter the volatilization of fluorine and to limit the fluorine content, as reported in our earlier paper. In the present study, a fluoride-substituted spinel LiMn2O4 material was synthesized by using a solid-state reaction method with (NH4)HF2 as the fluorine source. The structure and the electrochemical properties of the synthesized samples were characterized by using powder X-ray diffraction (XRD), scanning electron microscopy (SEM), surface area analysis, Fourier transform infrared (FT-IR) spectroscopy, cyclic voltammetry (CV) and charge-discharge tests. As indicated by XRD, all samples showed a spinel cubic structure with space group Fd3m. In comparison with the pure LiMn2O4, fluoride substitution leads to an increase in the lattice parameter, as well as the crystal size, and a decrease in the oxidation state of manganese. From N2-sorption, LiMn2O3.85F0.15 was found to have the smallest specific surface area and the largest pore diameter compared to the LiMn2O4 and the LiMn2O3.95F0.05 samples. Additionally, the majority of the pores in all samples were found to be located in the region of mesopores. The results of the electrochemical study showed that a fluoride substitution into LiMn2O4 improved the initial discharge capacity of the materials. Among the synthesized samples, LiMn2O3.85F0.15 can be used as a starting material for producing better performing spinel-type cathode materials.

Efficient process for recovery of waste LiMn2O4 cathode material: Low-temperature (NH4)2SO4 calcination mechanisms and water-leaching characteristics

An efficient process for recycling waste LiMn2O4 cathode material is proposed in this research. This report constitutes low-temperature (NH4)2SO4 calcination mechanisms and water-leaching characteristics of the calcined samples. A calcination temperature range of 420.65–634.12 °C is determined by analysis of the TG-DSC curve under the conditions of heating from 25 to 1000 °C, with a molar ratio of n(2Li + Mn):n(NH4)2SO4 = 1:1 in air atmosphere. The sample calcined at 600 °C for 45 min when the excess coefficient of the (NH4)2SO4 was 1.1 exhibits optimal water-leaching efficiencies of the Li and Mn elements, which are approximately 100% and 96.73%, respectively. The macro-reaction mechanism of the waste LiMn2O4 cathode material calcined with (NH4)2SO4 is determined as the liquid-solid reaction by analysing the apparent morphologies of the calcined samples and their water-leaching residues under different calcination conditions. Moreover, the micro-reaction mechanism is investigated by analysing the phases of the calcined samples and their water-leaching residues under different calcination conditions. The free high-energy H+ released by the decomposition of the NH4+ generated by the molten (NH4)2SO4 play a key role in the entire calcination process. The spinel structure of the LiMn2O4 is broken and Li+ is released owing to the H+ bombarding the MnO bonds. Finally, the LiMn2O4 is converted into soluble sulphate salts, such as Li2Mn2(SO4)3 and MnSO4.

Facile solid-state combustion synthesis of Al–Ni dual-doped LiMn2O4 cathode materials

A series of aluminum and nickel (Al–Ni) co-doped LiAl0.15NixMn1.85−xO4 composites are prepared through a facile solid-state combustion method. All the as-obtained materials show a spinel structure and analogous spherical morphology with uniform particle distribution. Moreover, the synergistic merits of Al and Ni dual substitutions endow the spinel LiMn2O4 with an elevated Mn average valence state of 3.59 and relatively alleviative Jahn–Teller distortion. Among these samples, the LiAl0.15Ni0.03Mn1.82O4 (LANMO-0.03) cathode exhibits an optimal electrochemical performance with the discharge capacities of 103.3 mAh g−1 and 102 mAh g−1 at 1 C and 5 C in the first cycle, and the capacity retentions are 72.0% and 68.6% after 1000 cycles, respectively. Even at 1 C and high temperature of 55 °C, an excellent capacity retention remained to be 76.6% after 200 cycles. Furthermore, the LANMO-0.03 has good Li+ diffusion capability during charge/discharge, the DLi+ value of the LANMO-0.03 (1.65 × 10–11 cm2∙s−1) is higher than that of the LiAl0.15Mn1.85O4 (LAMO) (8.12 × 10–12 cm2∙s−1), and the charge transfer resistances of the LAMO and LANMO-0.03 samples are almost the same at 150 Ω before cycling but decrease to 130 Ω and 95 Ω after 1000 cycles at 1 C, respectively. These results demonstrate that the Al–Ni co-doped strategy can enhance the structural stability and provide stable Li+ diffusion channel during the long cycles even at elevated temperature. Meanwhile, the facile solid-state combustion approach can also be extended to the preparation of other dual cation-doped electrode materials.

A facile synthesis approach of Li2MnO3 cathode material for lithium-ion battery by one-step high-energy mechanical activation method

ABSTRACT In this article, Li2MnO3 was successfully prepared by a facile one-step high-energy mechanical activation method free from sintering. XRD, SEM, and TEM techniques were employed to analyse the materials, meanwhile the electrochemical properties of the obtained material are studied. XRD result shows that the desired material Li2MnO3 can be obtained just by high-energy ball milling without sintering, and the existence of Li2MnO3 was further proved by XPS. The obtained materials by high-energy ball milling are in a nano-scale range from 20 to 100 nm, which was confirmed by TEM and SEM. The electrochemical tests show that the prepared materials can be directly put into use as the cathode of lithium-ion batteries without secondary treatment. Successful preparation of Li2MnO3 by high-energy mechanical activation method provides a breakthrough for the low energy consumption and environmentally friendly industrialisation of new powder materials.

Effect of Al3+ Doping on the Properties of LiMn2O4 Cathode Material

Spinel phase LiAlxMn2-xO4 were prepared by a rheological phase reaction method. The samples were characterized by X-ray diffraction, scanning electron microscopy, AC impedance, and galvanostatic charge/discharge profile measurement. These results showed that the LiAlxMn2-xO4 had better cycling performance than pure LiMn2O4. Among all the doped samples, the LiAlxMn2-xO4 sample showed the best cycling performance, the initial discharge capacitiy is 132 mAh g−1, and the discharge capacity of 115 mAh g−1 at a rate of 1 C after 100 cycles and capacity retention of 87.1% after 100 cycles (1C=148 mA g−1). Rate performance and electrochemical impedance spectroscopy measurements showed that the Al-doped spinels had high rate capability and reversible cycling performance.

A facile strategy for recovering spent LiFePO4 and LiMn2O4 cathode materials to produce high performance LiMnxFe1-xPO4/C cathode materials

To successfully recycle spent LiFePO4 and LiMn2O4 batteries and simultaneously produce high performances nano-LiMnxFe1-xPO4/C powders, a mechanical activation-assisted method was effectively applied in the recycling process. The technique consists of the separation and purification of spent cathode materials, high-energy mechanical mixing of raw materials and a commonly used heat treatment processes. The structural and morphological characterization results indicate that nano-sized LiMnxFe1-xPO4/C composites with uniform amorphous carbon coatings were successfully synthesized from spent LiFePO4 and LiMn2O4 batteries. The electrochemical performance testing results show that the recovered nano-LiMnxFe1-xPO4/C cathodes possess promising Li-ion storage properties. LiMn0.5Fe0.5PO4/C displays high capacities of 143.2, 138.1, and 127.6 mAh g−1 at 0.1, 1, and 2C rates, respectively. The obtained cathodes also show outstanding cycling stabilities of 98.47% and 97.58% for LiMn0.5Fe0.5PO4/C and LiMn0.8Fe0.2PO4/C after 100 cycles, respectively. This work indicates that recycling spent LiFePO4 and LiMn2O4 to produce high-performance LiMnxFe1-xPO4/C is a promising strategy for recycling spent LiFePO4 and LiMn2O4 based lithium ion batteries (LIBs) in an efficient and environmentally friendly manner.