LiMn2O4 Batteries Research Articles

Ionic liquid-based electrolyte with dual-functional LiDFOB additive toward high-performance LiMn2O4 batteries

Manganese oxide-based cathodes are one of the most promising lithium-ion battery (LIB) cathode materials due to their cost-effectiveness, high discharge voltage plateau (above 4.0 V vs. Li/Li+), superior rate capability, and environmental benignity. However, these batteries using conventional LiPF6-based electrolytes suffer from Mn dissolution and poor cyclic capability at elevated temperature. In this paper, the ionic liquid (IL)-based electrolytes, consisting of 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfon)imidate (PYR1,4-TFSI), propylene carbonate (PC), lithium bis(trifluoromethanesulfon)imide (LiTFSI), and lithium oxalyldifluoroborate (LiDFOB) additive, were explored for improving the high temperature performance of the LiMn2O4 batteries. It was demonstrated that LiTFSI-ILs/PC electrolyte associated with LiDFOB addition possessed less Mn dissolution and Al corrosion at the elevated temperature in LiMn2O4/Li batteries. Cyclic voltammetry and electrochemical impedance spectroscopy implied that this kind of electrolyte also contributed to the formation of a highly stable solid electrolyte interface (SEI), which was in accordance with the polarization measurement and the Li deposition morphology of the symmetric lithium metal cell, thus beneficial for improving the cycling performance of the LiMn2O4 batteries at the elevated temperature. Cyclic voltammetry and electrochemical impedance spectroscopy implied that the cells using this kind of electrolyte exhibited better interfacial stability, which was further verified by the polarization measurement and the Li deposition morphology of the symmetric lithium metal cell, thus beneficial for improving the cycling performance of the LiMn2O4 batteries at the elevated temperature. These unique characteristics would endow this kind of electrolyte a very promising candidate for the manganese oxide-based batteries.

Lithium carbonate as an electrolyte additive for enhancing the high-temperature performance of lithium manganese oxide spinel cathode

The effect of lithium carbonate (Li2CO3) as an additive on the stability of the electrolyte and cycling performance of lithium manganese oxide spinel (LiMn2O4) batteries at elevated temperature was studied. The addition of Li2CO3 to the electrolyte can suppress the capacity fading of LiMn2O4 batteries. The linear sweep voltammetry (LSV) and the cyclic voltammetry (CV) indicate that Li2CO3 has a lower oxidation potential in the mixed solvents of ethylene carbonate (EC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC), participating in the formation process of the stable cathode electrolyte interface (CEI) film. In addition, the results of electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) demonstrate that the stable CEI film of the cells with Li2CO3 can be formed, which can effectively reduce the dissolution of Mn2+ from LiMn2O4 into the electrolyte at elevated temperature. It is concluded that the addition of Li2CO3 to a solution of 1M LiPF6–EC/EMC/DEC=1/1/1 (weight ratio) may decrease solvent decomposition and change the structure of the passivation film on the LiMn2O4 cathode.

Morphology-control preparation and electrochemical performance of Mn-spinel cathode materials

The disadvantage of the LiMn2O4 batteries is a capacity fade during charge-discharge cycling or high temperature storage. It is well known that this deterioration is mainly caused by Mn dissolution from spinel, especially at elevated temperature (60℃). Extensively studies have been made to explain its degraded cycling performance, but these studies mainly focused on investigating the structural change during lithium intercalation/de-intercalation process. In fact, the recent researches have shown that the surface structure and interface reaction of Mn-spinel greatly affect the Mn dissolution of spinel. In this study, we have successfully synthesized oxygen stoichiometric Mn-spinel cathode with spherical-like morphology. It has a much smaller (111) plane area compared with the single crystal octahedral or polyhedral Mn-spinel products. The decrease of the plane area could reduce the Mn dissolution during cycling process, which made it have better cycling performance than the commercial products. The electrochemical test results showed that 18650 cylinder batteries using this spherical-like Mn-spinel cathode material has an excellent cycle performance with the capacity retention of 80% after 2500 cycles at room temperature. Even at elevated temperature of 60℃, the capacity retention still reached 80% after 400 cycles.

Using probability density function to evaluate the state of health of lithium-ion batteries

A new method, probability density function (PDF), is proposed for evaluating the state of health (SOH) of electric storage batteries by analyzing the charge/discharge (C/D) data. First, a comparison of the PDF method, the cyclic voltammogram (CV), incremental capacity analysis (ICA) and differential voltage analysis (DVA) is provided. The mathematical basis of the four methods are in agreement. Moreover, the PDF method and the ICA/DVA have an equivalence verified by mathematical derivation. Thus the results acquired by the PDF and the ICA/DVA are quite similar. LiFePO4 and LiMn2O4 batteries are tested to demonstrate the PDF method. Coin cells are tested by the PDF and the CV methods. Results show that the PDF curves and the CV curves have similar shapes. In addition, durability tests are conducted on four commercial batteries to analyze the aging regularities using the PDF method. The PDF results show that the height of the peak reduces as the battery capacity fades. Employing the regularity of peak height reduction with battery aging, an algorithm is proposed to evaluate the SOH online. The PDF method extends the application of the ICA/DVA method. The PDF algorithm is promising to be used in the online SOH evaluation of lithium-ion batteries.

Different types of MnO2 recovered from spent LiMn2O4 batteries and their application in electrochemical capacitors

Three types (λ, γ, and β) of MnO2 have been successfully prepared from spent LiMn2O4 electrode materials and utilized as electrode materials for electrochemical capacitors. Experiments show that the obtained λ-MnO2 sample has particle sizes ranging from 0.2 to 3 μm and the as-prepared β-MnO2 and γ-MnO2 samples both exist in nanorods with diameters of about 100 nm. The length of β-MnO2 nanorods varies from 0.2 to 3 μm, while γ-MnO2 nanorods have lengths of 0.2–2 μm. The main results of electrochemical tests indicate that these MnO2 electrodes exhibit good supercapacitive performances which are dependent on their morphology and microstructure. As electrode material, λ-MnO2 sample presents a specific capacitance of 200.55 F g−1, which is higher than those of other two types of MnO2. However, β-MnO2 electrode shows superior long-term cyclic stability and rate performance to other two MnO2 samples. These results indicate that manganese dioxides recycled from spent LiMn2O4 batteries show great potential in application as the active materials for electrochemical capacitors. This study could provide a novel and useful approach to the recovery and reuse of spent LiMn2O4 batteries.

Al2O3 coating for improving thermal stability performance of manganese spinel battery

The synthesis of Al2O3-coated and uncoated LiMn2O4 by solid-state method and fabrication of LiMn2O4/graphite battery were described. The structure and morphology of the powders were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The electrochemical and overcharge performances of Al2O3-coated and uncoated LiMn2O4 batteries were investigated and compared. The uncoated LiMn2O4 battery shows capacity loss of 16.5% after 200 cycles, and the coated LiMn2O4 battery only shows 12.5% after 200 cycles. The uncoated LiMn2O4 battery explodes and creates carbon, MnO, and Li2CO3 after 3C/10 V overcharged test, while the coated LiMn2O4 battery passes the test. The steadier structure, polarization of electrode and modified layer are responsible for the safety performance.