Spinel LiMn Research Articles

Spinel LiMn[sub 2−x]Ti[sub x]O[sub 4] (x=0.5, 0.8) with High Capacity and Enhanced Cycling Stability Synthesized by a Modified Sol-Gel Method

National Natural Science Foundation of China [20873115, 90606015]; National Basic Research Program of China [2007CB209702]

Electrochemical properties of high-power lithium ion batteries made from modified spinel LiMn 2O 4

A prismatic 204056-type high power lithium-ion battery was developed. Modified LiMn 2O 4 and carbonaceous mesophase sphere (CMS) were adopted as the cathode and anode, respectively. The effects of proportion of conductive carbon black in cathode and the rest time after discharge on the electrochemical properties of batteries were investigated. The electrochemical tests show that the proportion of conductive carbon black in cathodes affects the high rate capability and discharge voltage plateau distinctly. The battery with 3.0% of conductive carbon black in cathode shows excellent electrochemical performances when being charged/discharged within 2.5−4.2 V at room temperature. The discharge capacity at 20 C rate is 94.4% of that at 1 C rate, and the capacity retention ratio charged at 1 C and discharged at 5 C is 86.6% after 390 cycles at room temperature. The test result of impulse discharge at 50 C for 5 s shows that the battery has outstanding high rate discharge performance when the battery is in the depth of charge of 90%, 75%, 60%, 45%, 30% and 15%. The battery also shows good charge performance. When the battery is charged at 0.5 C, 1 C, 2 C and 4 C, the ratios of capacity for constant current charge are 98.4%, 96.4%, 91.0% and 72.9% of the whole charge capacity, respectively. In addition, the rest time after discharge affects the cycle performance distinctly when the battery is discharged at high rate.

Effects of synthesis temperature and precursor composition on the crystal structure, morphology, and electrode activity of 1D nanostructured manganese oxides

1D nanostructured manganese oxides are prepared by oxidation reaction of precursor LiMn 2− x Cr x O 4 microcrystals under hydrothermal condition. The crystal structure and morphology of the obtained manganese oxides are strongly dependent on the reaction condition and the chemical composition of the precursors. The α-MnO 2 nanowires are prepared by reaction at 120 °C, and their aspect ratios decrease with the Cr content in the precursor. Treating precursors with persulfate ions at 160–180 °C yields the β-MnO 2 nanorods for the precursors LiMn 2− x Cr x O 4 with lower Cr content and the α-MnO 2 nanowires for the precursors with higher Cr content. The structure dependence of the products on the Cr content in the precursors is related to the high octahedral site stabilization energy of Cr 3+ ions and/or to the increase of Mn valence state upon Cr substitution. The increase of Cr content in the precursors degrades the electrode performance for the manganates prepared at 160 °C but improves electrode activity for those prepared at 180 °C. This observation can be explained by the structural variation and chromium substitution of the hydrothermally treated manganates. We conclude that the use of spinel LiMn 2− x Cr x O 4 as precursors provides an effective way to synthesize 1D nanostructured manganate with tailored crystal structure and morphology.

Synthesis of spinel LiMn 2O 4 with manganese carbonate prepared by micro-emulsion method

Micro-spherical particle of MnCO 3 has been successfully synthesized in CTAB–C 8H 18–C 4H 9OH–H 2O micro-emulsion system. Mn 2O 3 decomposed from the MnCO 3 is mixed with Li 2CO 3 and sintered at 800 °C for 12 h, and the pure spinel LiMn 2O 4 in sub-micrometer size is obtained. The LiMn 2O 4 has initial discharge specific capacity of 124 mAh g −1 at discharge current of 120 mA g −1 between 3 and 4.2 V, and retains 118 mAh g −1 after 110 cycles. High-rate capability test shows that even at a current density of 16 C, capacity about 103 mAh g −1 is delivered, whose power is 57 times of that at 0.2 C. The capacity loss rate at 55 °C is 0.27% per cycle.

Comparison of the microwave-induced combustion and solid-state reaction for the synthesis of LiMn 2O 4 powder and their electrochemical properties

In the current research, we proposed a new method called microwave-induced combustion synthesis to produce LiMn 2O 4 powders. The microwave-induced combustion synthesis entails the dissolution of metal nitrates, and urea in water, and then heating the resulting solution in a microwave oven. Spinel LiMn 2O 4 powders were successfully synthesized by microwave-induced combustion. The microwave-heated LiMn 2O 4 powders annealed at various temperatures in the range of 600–800 °C were determined. The resultant powders were characterized by X-ray diffractometer (XRD), and scanning electron microscopy (SEM). The annealed samples were used as cathode materials for lithium-ion battery, for which their discharge capacity and electrochemical characteristic properties in terms of cycle performance were also investigated. The LiMn 2O 4 cell provides a high initial capacity of 133 mAh/g and excellent reversibility. The excellent capacity and reversibility were attributed to LiMn 2O 4 powders with small and uniform particle size produced by microwave-induced combustion synthesis.

Suppression of Jahn–Teller distortion by chromium and magnesium doping in spinel LiMn 2O 4: A first-principles study using GGA and GGA+U

The effect of doping spinel LiMn 2O 4 with chromium and magnesium has been studied using the first-principles spin density functional theory (DFT) within generalized gradient approximation (GGA ) and GGA+U. We find that GGA and GGA+U give different ground states for pristine LiMn 2O 4 and same ground state for doped systems. For LiMn 2O 4, the body-centered tetragonal phase was found to be the ground-state structure using GGA and face-centered orthorhombic using GGA+U, while for LiM 0.5Mn 1.5O 4 (M Cr or Mg) it was base-centered monoclinic and for LiMMnO 4 (M Cr or Mg) it was body-centered orthorhombic in both GGA and GGA+U. We find that GGA predicts the pristine LiMn 2O 4 to be metallic while GGA+U predicts it to be insulating, which is in accordance with the experimental observations. For doped spinels, GGA predicts the ground state to be half metallic while GGA+U predicts it to be insulating or metallic depending on the doping concentration. GGA+U predicts insulator–metal–insulator transition as a function of doping in case of Cr and in case of Mg the ground state is found to go from insulating to a half metallic state as a function of doping. Analysis of the charge density and the density of states (DOS) suggest a charge transfer from the dopants to the neighboring oxygen atoms and manganese atoms. We have calculated the Jahn–Teller active mode displacement Q 3 for doped compounds using GGA and GGA+U. The bond lengths calculated from GGA+U are found to be in better agreement with experimental bond lengths. Based on the bond lengths of metal and oxygen, we have also estimated the average oxidation states of the dopants.

Hydrothermal synthesis of LiMn 2O 4/C composite as a cathode for rechargeable lithium-ion battery with excellent rate capability

A spinel LiMn 2O 4/C composite was synthesized by hydrothermally treating a precursor of manganese oxide/carbon (MO/C) composite in 0.1 M LiOH solution at 180 °C for 24 h, where the precursor was prepared by reducing potassium permanganate with acetylene black (AB). The AB in the precursor serves as the reducing agent to synthesize the LiMn 2O 4 during the hydrothermal process; the excess of AB remains in the hydrothermal product, forming the LiMn 2O 4/C composite, where the remaining AB helps to improve the electronic conductivity of the composite. The contact between LiMn 2O 4 and C in our composite is better than that in the physically mixed LiMn 2O 4/C material. The electrochemical performance of the LiMn 2O 4/C composite was investigated; the material delivered a high capacity of 83 mAh g −1 and remained 92% of its initial capacity after 200 cycles at a current density of 2 A g −1, indicating its excellent rate capability as well as good cyclic performance.

Effect of LiNi 1/2Mn 1/2O 2 coating on the electrochemical performance of Li–Mn spinel

Lithium nickel manganese oxide (LiNi 1/2Mn 1/2O 2) was coated on spinel lithium manganese oxide (LiMn 2O 4) by a sol–gel process in an attempt to improve the high temperature cycling performance. The ratio of the coating sol to LiMn 2O 4 was adjusted to determine the relationship between the coating thickness and electrochemical performance. The crystal structure and morphology of the samples were examined by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The charge and discharge characteristics, including cyclability and electrochemical properties of the bare and the coated LiMn 2O 4, were measured and compared. The results showed that a LiNi 1/2Mn 1/2O 2 coating on LiMn 2O 4 improves the rate capability at room temperature, and the cyclability at high temperatures.

A literature review and test: Structure and physicochemical properties of spinel LiMn 2O 4 synthesized by different temperatures for lithium ion battery

A series of LiMn 2O 4 spinel was prepared by adipic acid-assisted sol–gel method at different temperatures. The structure and physicochemical properties of spinel LiMn 2O 4 synthesized by different temperatures were investigated by differential thermal analysis (DTA) and thermogravimetery (TG), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron micrographs (SEM), inductively coupled plasma-mass spectroscopy (ICP-MS), galvanostatic charge–discharge test, and cyclic voltammetry (CV), respectively. TG–DTA shows that the weight loss occurs in four temperature regions during the synthesis of LiMn 2O 4. XRD indicates that the sintering temperature affects the formation of spinel phase, and prominent LiMn 2O 4 spinel powder with smaller atom location confusion forms about 800 °C. XPS reveals that the manganese oxidation state in spinel lithium manganese oxide synthesized at different temperatures is between +3 and +4. SEM shows that LiMn 2O 4 spinel synthesized at 800 °C has the uniform, nearly cubic structure morphology with narrow size distribution. ICP-MS indicates that the average chemical valence of Mn element of LiMn 2O 4 synthesized at 800 °C is the most close to 3.5 among the samples synthesized at different temperatures. CV illustrates that the LiMn 2O 4 synthesized at 800 °C has the best electrochemical activity. Charge–discharge test explains that the capacity retention sintered at 350, 700 and 800 °C over the first 50 cycles is 93.6%, 86.1% and 85.2%, respectively, but the discharge capacity at the 50th cycle is 82.2, 104.8 and 110.8 mAh g −1, respectively.

In situ X-ray diffraction studies of mixed LiMn2O4–LiNi1/3Co1/3Mn1/3O2 composite cathode in Li-ion cells during charge–discharge cycling

Abstract The structural changes of the composite cathode made by mixing spinel LiMn 2 O 4 and layered LiNi 1/3 Co 1/3 Mn 1/3 O 2 in 1:1 wt% in both Li-half and Li-ion cells during charge/discharge are studied by in situ XRD. During the first charge up to ∼5.2 V vs. Li/Li + , the in situ XRD spectra for the composite cathode in the Li-half cell track the structural changes of each component. At the early stage of charge, the lithium extraction takes place in the LiNi 1/3 Co 1/3 Mn 1/3 O 2 component only. When the cell voltage reaches at ∼4.0 V vs. Li/Li + , lithium extraction from the spinel LiMn 2 O 4 component starts and becomes the major contributor for the cell capacity due to the higher rate capability of LiMn 2 O 4 . When the voltage passed 4.3 V, the major structural changes are from the LiNi 1/3 Co 1/3 Mn 1/3 O 2 component, while the LiMn 2 O 4 component is almost unchanged. In the Li-ion cell using a MCMB anode and a composite cathode cycled between 2.5 V and 4.2 V, the structural changes are dominated by the spinel LiMn 2 O 4 component, with much less changes in the layered LiNi 1/3 Co 1/3 Mn 1/3 O 2 component, comparing with the Li-half cell results. These results give us valuable information about the structural changes relating to the contributions of each individual component to the cell capacity at certain charge/discharge state, which are helpful in designing and optimizing the composite cathode using spinel- and layered-type materials for Li-ion battery research.

Electrochemical performance of nanostructured spinel LiMn2O4 in different aqueous electrolytes

Abstract A nanostructured spinel LiMn 2 O 4 electrode material was prepared via a room-temperature solid-state grinding reaction route starting with hydrated lithium acetate (LiAc·2H 2 O), manganese acetate (MnAc 2 ·4H 2 O) and citric acid (C 6 H 8 O 7 ·H 2 O) raw materials, followed by calcination of the precursor at 500 °C. The material was characterized by X-ray diffraction (XRD) and transmission electron microscope techniques. The electrochemical performance of the LiMn 2 O 4 electrodes in 2 M Li 2 SO 4 , 1 M LiNO 3 , 5 M LiNO 3 and 9 M LiNO 3 aqueous electrolytes was studied using cyclic voltammetry, ac impedance and galvanostatic charge/discharge methods. The LiMn 2 O 4 electrode in 5 M LiNO 3 electrolyte exhibited good electrochemical performance in terms of specific capacity, rate dischargeability and charge/discharge cyclability, as evidenced by the charge/discharge results.

Suppression of Jahn–Teller distortion of spinel LiMn 2O 4 cathode

Jahn–Teller distortion is one of the most important reasons of capacity fade for spinel LiMn 2O 4 as cathode material for lithium ion batteries. In this work, we proposed an approach to prepare the modified spinel LiMn 2O 4 to suppress this distortion. Transmission electron microscopy (TEM) indicated that the LiNi x Mn 2− x O 4 shell/LiMn 2O 4 core particle was successfully formed. The modified LiMn 2O 4 results in the lattice shrinkage and increases Mn–O bond strength, improving the spinel structural stability. During charge and discharge cycle, the modified LiMn 2O 4 is beneficial to the suppression of Jahn–Teller distortion at the surface of LiMn 2O 4 particles, which is confirmed by differential scanning calorimetry (DSC) and X-ray diffraction (XRD) analysis. This suppression of Jahn–Teller distortion is attributed to the shell of LiNi x Mn 2− x O 4 solid solution formed on the surface of LiMn 2O 4 particles.

Cathode having high rate performance for a secondary Li-ion cell surface-modified by aluminum oxide nanoparticles

In order to enhance the electrochemical properties, the spinel LiMn 2O 4 electrode surface was modified with amorphous Al 2O 3 nanoparticle as heterogeneous phase. LiMn 2O 4 was in preparation based on a conventional solid-state reaction. The LiMn 2O 4 procedure was soaked in aluminum tri 2-propoxide solution. The LiMn 2O 4 whose surface was modified by aluminum oxide was obtained through the heat treatment at 400 °C for 4 h. The Al 2O 3-modified LiMn 2O 4 electrode exhibits a capacity higher than that of the unmodified LiMn 2O 4 electrode. On the other hand, no variation was shown with open circuit potential and apparent chemical diffusion coefficient of Li ion for LiMn 2O 4 before and after the surface modification. The charge-transfer resistance of Al 2O 3-modified LiMn 2O 4 decreased significantly in comparison with the unmodified LiMn 2O 4. The improved charge-transfer kinetics was largely attributed to Al 2O 3 which plays an important role of increasing the chemical potential at the electrode/electrolyte interface.

Effect of Low-Temperature Fluorine Doping on the Properties of Spinel LiMn2 − 2yLiyMyO4 − ηFη (M = Fe , Co, and Zn) Cathodes

Spinel oxy-fluoride compositions (, Co, and Zn) have been synthesized by a selective, low-temperature fluorination with of the corresponding spinel oxides that were synthesized at . With a given cation-substituted composition, the lattice parameter and reversible capacity increase with increasing fluorine content due to a lowering of the Mn oxidation state, confirming the bulk substitution of for in the lattice. The fluorine incorporation with the low melting also provides an added advantage of increased tap density due to a closer particle-particle contact. A correlation of the cyclability of the various compositions to Mn valence reveals that the Mn valence needs to be to impart good capacity retention at 25 and .

Novel approach to preparation of LiMn 2O 4 core/LiNi xMn 2− xO 4 shell composite

Combining two methods, coating and doping, to modify spinel LiMn 2O 4, is a novel approach we used to synthesize active material. First we coated the LiMn 2O 4 particles with the nickel oxide particles by means of homogenous precipitation, and then the nickel oxide-coated LiMn 2O 4 was calcined at 750 °C to form a LiNi x Mn 2− x O 4 shell on the surface of spinel LiMn 2O 4 particles. Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), cyclic voltammetry (CV) and charge–discharge test were performed to characterize the spinel LiMn 2O 4 before and after modification. The experimental results indicated that a spinel LiMn 2O 4 core is surrounded by a LiNi x Mn 2− x O 4 shell. The resulting composite showed excellent electrochemical cycling performance with an average fading rate of 0.014% per cycle. This improved cycle stability is greatly attributed to the suppression of Jahn–Teller distortion on the surface of spinel LiMn 2O 4 particles during cycling.

Advanced electrochemical performance of LiMn 1.4Cr 0.2Ni 0.4O 4 as 5 V cathode material by citric-acid-assisted method

Spinel LiMn 2O 4 and LiMn 1.4Cr 0.2Ni 0.4O 4 cathode materials were successfully synthesized by the citric-acid-assisted sol–gel method with ultrasonic irradiation stirring. The structure and electrochemical performance of the as-prepared powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectrometer, cyclic voltamogram (CV) and the galvanostatic charge–discharge test in detail. XRD shows that all the samples have high phase purity, and the powders are well crystallized. SEM exhibits that LiMn 1.4Cr 0.2Ni 0.4O 4 has more uniform cubic-structure morphology than that of LiMn 2O 4. EDX reveals that a small amount of Mn 3+ still exists in LiMn 1.4Cr 0.2Ni 0.4O 4. The galvanostatic charge–discharge test indicates that the initial discharge capacities for the LiMn 1.4Cr 0.2Ni 0.4O 4 and LiMn 2O 4 at 0.15 C discharge rates are 130.8 and 130.2 mAh g −1, respectively. After 50 cycles, their capacity are 94.1% and 85.1%, respectively. The CV curve implies that Ni and Cr dual substitutions are beneficial to the reversible intercalation and deintercalation of Li +, and suppress Mn 3+ generation at high temperatures and provide improved structural stability.

Enhanced capacity retention of Co and Li doubly doped LiMn 2O 4

Cobalt and lithium doubly doped spinel LiMn 2O 4 have been synthesized by a solid state reaction. The effect of Co and Li doped spinel LiMn 2O 4 was investigated. The undoped and doped spinels were characterised by means of X-ray diffraction (XRD), inductively coupled plasma/atomic emission spectrometer (ICP/AES) and electrochemical test. The results showed that the doped spinel exhibited superior cycling performance than undoped spinel. The capacity retention of graphite/doped spinel full cell was more than 86% after 1000 cycles (2 C rate) at room temperature, which maintained 85% after 100 cycles (1 C rate) at 55 °C. The differential capacity profiles on doped spinel cathode are more fixed than undoped spinel cathode. Compared with undoped spinel, Mn dissolution into electrolyte at 55 °C was reduced by 41%, the lattice parameter difference Δ a was reduced by 82% on doped spinel cathode after cycling. The greatly suppressed structural change and manganese dissolution are responsible for the improved cycling performance on cobalt and lithium doubly doped spinel.

Synthesis and electrochemical characterizations of Nano-SiO 2-coated LiMn 2O 4 cathode materials for rechargeable lithium batteries

LiMn 2O 4 spinel cathode materials were coated with 1.0, 2.0 and 3.0 wt.% of SiO 2 by polymeric process, followed by 850 °C for 6h in air. The surface coated LiMn 2O 4 cathode materials were physically characterized using X-ray diffraction, Scanning electron microscopy, Transmission electron microscopy and X-ray photon spectroscopy. XRD patterns of SiO 2-coated LiMn 2O 4 revealed that the coating did not affect the crystal structure, space group Fd3 m of the cathode materials, compared to the uncoated LiMn 2O 4. The surface morphology and particle agglomeration were investigated using Scanning electron microscopy, and the TEM image showed a compact coating layer on the surface of the core materials that had average thickness of about 50 nm. XPS data illustrated that the SiO 2 was coated over surface on the LiMn 2O 4 core materials. The galvanostatic charge and discharge of the uncoated and SiO 2-coated LiMn 2O 4 cathode materials were carried out 0.1 mA/g in the range of 3.0 and 4.5 V at 30 °C and 60 °C. The discharge capacity of 2.0 wt.% of SiO 2-coated LiMn 2O 4 (120 mAh/g) showed only 4.8% loss of the initial capacity (126 mAh/g) over the 100 cycles at 30 °C and (112 mAh/g) showed only 8.9% of loss of the initial capacity (123 mAh/g) over the 100 cycles at 60 °C. The cycleability improvement of the spinel LiMn 2O 4 coated with 2.0 wt.% of SiO 2 is demonstrated at room temperature and elevated temperature. From the analysis of electrochemical impedance spectroscopy (EIS), the improvement of cycleability may be attributed to the suppression on the formation of the passive film and reduction of Mn dissolution, which results from modifying the surface of the spinel LiMn 2O 4 with SiO 2.

Free Energy for Protonation Reaction in Lithium-Ion Battery Cathode Materials

Calculations are performed of free energies for proton-for-lithium-ion exchange reactions in lithium-ion battery cathode materials. First-principles calculations are employed for the solid phases and tabulated ionization potential and hydration energy data for aqueous ions. Layered structures, spinel LiMn2 O4, and olivine LiFePO4 are considered. Protonation is most favorable energetically in layered systems, such as Li2 MnO3 and LiCoO2. Less favorable are ion-exchange in spinel LiMn2 O4 and LiV3 O8. Unfavorable is the substitution of protons for Li in olivine LiFePO4, because of the large distortion of the Fe and P coordination polyhedra. The reaction free energy scales roughly linearly with the volume change in the reaction.

Preparation, characteristics and electrochemical properties of surface-modified LiMn 2O 4 by doped LiNi 0.05Mn 1.95O 4

The surface-modified spinel LiMn 2O 4 by doped LiNi 0.05Mn 1.95O 4 was prepared by a tartaric acid gel method. Transmission electron microscope (TEM) images indicated that some small particles with 100–200 nm in diameter modified the surface of large particle LiMn 2O 4. Energy dispersive spectrometry (EDS) showed that the particles were LiNi 0.05Mn 1.95O 4. Electrochemical properties of LiNi 0.05Mn 1.95O 4-modified spinel LiMn 2O 4 were intensively investigated by the galvanostatic charge–discharge tests, cyclic voltammetry (CV) and AC impedance measurements. The doped LiNi 0.05Mn 1.95O 4-modified LiMn 2O 4 cathode delivered the same initial discharge capacity as the unmodified LiMn 2O 4, but its cyclic stability was evidently improved, the capacity retention ratio reached 96% after 20 cycles, being higher than 89% of the unmodified LiMn 2O 4. Cyclic voltammograms of the LiNi 0.05Mn 1.95O 4-modified LiMn 2O 4 did not markedly change while the semicircle diameter of AC impedance spectra evidently decreased after 20 cycles, which showed that the surface modification with LiNi 0.05Mn 1.95O 4 improved the electrochemical activity and cycling stability of LiMn 2O 4.