LiMn2O4 Film Research Articles

Construction of nitrogen-doped carbon cladding LiMn2O4 film electrode with enhanced stability for electrochemically selective extraction of lithium ions

Construction of nitrogen-doped carbon cladding LiMn2O4 film electrode with enhanced stability for electrochemically selective extraction of lithium ions

Preparation of a novel hollow porous LiMn2O4 film electrode (H-LMOE) and its improved performance for lithium extraction

Lithium extraction from the solution in low Li+ concentration by an energy-saving and high-efficiency method is still a challenge. Herein, a novel hollow porous LiMn2O4 (H-LMO) with highly active site was proposed to enhance the extraction performance of Li+. Based on the established hollow porous structure, the H-LMO film electrode (H-LMOE) exhibits excellent lithium electrosorption performance and stability. Under the current density of 0.5 C, the electrosorption capacity of Li+ could reach 31.52 mg/g, the separation coefficient of Li+/Mg2+ was 581.67, and the energy consumption was as low as 0.49 Wh/mol Li. This unique structural strengthening mechanism made H-LMOE maintain a good Li+ extraction performance even in a solution of low Li+ concentration. The Li+ electrosorption capacity of H-LMOE was 2.13 times that of T-LMOE in a 60 mg/L Li+ solution, while the specific energy consumption of the H-LMOE was 15.78% lower than that of the traditional-LiMn2O4 film electrode (T-LMOE). Even in a 10 mg/L Li+ solution, the electrosorption capacity of H-LMOE was 21.48 mg/g, which was 10.0% higher than that of T-LMOE. Moreover, after 50 recycling processes, the final electrosorption capacity of the H-LMOE was about 25.0% higher than that of the T-LMOE.

First-principles calculation of Co doped LiMn2O4 and analysis of film transparency

Based on the pseudo-potential plane wave method of density functional theory, the feasibility of LiMn2O4 thin films in transparent devices was investigated. Co doped LiMn2O4 was used to calculate and analyze the electronic structure before and after doping. After doping, the energy density and cycle performance of LiMn2O4 film were effectively improved, and the optical properties of LiMn2O4 film were calculated and analyzed to study the transparency of the film. The results show that the cell volume of LiMn2O4 is reduced, the band gap is narrowed, the bonding between Mn-O is strengthened, and the electrocyclic performance of LiMn2O4 is improved after Co doping. As for the established thin film system, the (100)- LiMn2O4 monolayer film is a low dielectric material and has good absorption performance in the ultraviolet region. The static refractive index of the system decreases after Co doping, and the absorption coefficient is close to 0 when the photon energy is 37–43 eV and 64 eV. To some extent, the (100)- LiMn2O4 material is transparent in this region. The computational results of this work contribute to the in-depth study of the properties of LiMn2O4 materials and provide some ideas for the design of corresponding innovative experiments, in order to seek more valuable discoveries in the field of battery and optical transparency applications.

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.

Preparation of a Novel Hollow Porous Limn2o4 Film Electrode (H-Lmoe) and its Improved Performance for Lithium Recovery at Low Concentration

Preparation of a Novel Hollow Porous Limn2o4 Film Electrode (H-Lmoe) and its Improved Performance for Lithium Recovery at Low Concentration

Combined Role of Biaxial Strain and Nonstoichiometry for the Electronic, Magnetic, and Redox Properties of Lithiated Metal-Oxide Films: The LiMn2O4 Case.

Understanding the interplay between strain and nonstoichiometry for the electronic, magnetic, and redox properties of LiMn2O4 films is essential for their development as Li-ion battery (LIB) cathodes, photoelectrodes, and systems for sustainable spintronics applications as well as for emerging applications that combine these technologies. Here, density functional theory (DFT) simulations suggest that compressive strain increases the reduction drive of (111) LiMn2O4 films by inducing >1 eV upshift of the valence band edge. The DFT results indicate that, regardless of the crystallographic orientation for the LiMn2O4 film, biaxial expansion increases the magnetic moments of the Mn atoms. Conversely, biaxial compression reduces them. For ferromagnetic films, these changes can be substantial and as large as over 4 Bohr magnetons per unit cell over the simulated range of strain (from -6 to +3%). The DFT simulations also uncover a compensation mechanism whereby strain induces opposite changes in the magnetic moment of the Mn and O atoms, leading to an overall constant magnetic moment for the ferromagnetic films. The calculated strain-induced changes in atomic magnetic moments reflect modifications in the local electronic hybridization of both the Mn and O atoms, which in turn suggests strain-tunable, local chemical, and electrochemical reactivity. Several energy-favored (110) and (111) ferromagnetic surfaces turn out to be half-metallic with minority-spin band gaps as large as 3.2 eV and compatible with spin-dependent electron-transport and possible spin-dependent electrochemical and electrocatalytic properties. The resilience of the ferromagnetic, half-metallic states to surface nonstoichiometry and compositional changes invites exploration of the potential of LiMn2O4 thin films for sustainable spintronic applications beyond state-of-the-art, rare-earth metal-based, ferromagnetic half-metallic oxides.

Establishment of PPy-derived carbon encapsulated LiMn2O4 film electrode and its performance for efficient Li+ electrosorption

Improving the cycle stability and Li+ electrosorption rate of the LiMn2O4 (LMO) film electrode in the selective Li+ electrosorption process is still a considerable challenge. In this work, a novel polypyrrole (PPy) - derived carbon encapsulated material LiMn2O4@Carbon/Nitrogen-4 (LMO@CN-4) was prepared by the three-dimensional in-situ polymerization and high-temperature annealing of PPy on the LMO surface. The LMO@CN-4 film electrode showed a faster Li+ electrosorption rate, higher lithium-ion selectivity, and higher stability than the LMO film electrode. The maximum capacity of the LMO@CN-4 film electrode for Li+ could reach 34.57 mg/g within 40 min in 0.05 mol/L LiCl solution. Even in the simulated concentrated seawater with a low Li+ concentration (0.17 g/L), it could quickly reach adsorption equilibrium and maintain the high selectivity of Li+. The adsorption capacity was about 37.14 mg/g and the separation coefficient of α (Li+/Mg2+), α (Li+/Na+), and α (Li+/Ca2+) was about 228.25, 2110.64, and 1381.89. The carbon encapsulation served as a conductive layer to enhance charge and ion transport. It also provided a buffer layer to prevent the volume collapse of the crystal and the dissolution of Mn. Therefore, the charge and discharge capacity of the LMO@CN-4 film electrode could be maintained at about 80% after 50 cycles at the 1C (148 mAh/g) rate, which was 20% higher than that of the bare LMO. What’s more, the high cycle stability and Li+ electrosorption rate of the modified film electrode also suggested its potential for lithium electrosorption from concentration seawater.

Plasma diagnostic in LiMn2O4 thin film process for Li-ion battery application

This work reports an advanced plasma-material process comprising the process design, plasma characterization, and surface engineering of LiMn2O4 films deposited by dual RF magnetron sputtering (MS). Several plasma diagnostic techniques integrated with the MS system were carefully utilized for the in-situ process monitoring to control the plasma parameters. Glancing angle deposition is used to create uniform plasma, which assists excellent film uniformity in the central region. Various standard techniques such as XRD, Raman, TEM, and AFM were used to study the characteristic properties of the deposited films. High plasma density that assists high ion energy flux (IF) and high energy tails in the EEPF, deposition of total energy-in-flux (EF) on the substrate, and high optical emission intensities characterized by the excited species of Mn, O, Li, and Ar, respectively, measured by the radio frequency compensated Langmuir probe (LP), energy flux probe, and optical emission spectroscopy (OES) methods at pressures of 0.93 Pa and 1.33 Pa produced LiMn2O4 films with superior crystallinity and smooth microstructure. This work also reports the collective effect of plasma parameters and thermal energy on the growth and properties of LiMn2O4 film intended for Li-ion battery application.

(Invited) Novel Method for Conformal LiMn2O4 thin Films Fabrication on Planar and 3D Microstuctured Substrates

In this work we report for the first time on a novel LiMn2O4 (LMO) thin film fabrication method. Using this fabrication method crystalline LMO thin films were prepared on both planar and 3D microstructured Si pillar substrates. The process is based on a solid state reaction between an electrolytic manganese dioxide (EMD) and Li2CO3 stacked-layers upon thermal annealing. The main advantage of using the electrochemical deposition technique to prepare the MnO2 layer is its capability of providing a conformal film deposition on high aspect ratio substrates. Moreover the electrolytic manganese dioxide film shows a high porosity (~50%) which will help later to release the mechanical strain during the Li-ion insertion and extraction process. The Li2CO3 deposition was done either by chemical solution deposition (CSD) or atomic layer deposition (ALD). The temperature dependence of the EMD conversion was investigated. The annealing time was adjusted based on the film thicknesses. Further, different current collector materials such as the noble Pt, Ni and MnO2seed layer on TiN were evaluated for the EMD conversion. The phase and morphology of the prepared LiMn2O4 films were investigated using X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The XRD patterns show the characteristic LMO diffraction peaks confirming the formation of the crystalline phase. SEM images display a continuous and conformal film on both planar and 3D microstructured substrates. The stoichiometry of the fabricated LMO films was evaluated by X-ray photoelectron spectroscopy (surface spectra and depth profile analyses) and elastic recoil detection (ERD) analyses. The results indicate that the fabricated film has a stoichiometry close to the theoretical stoichiometry of LiMn2O4with a homogeneous elements distribution through the layer. In addition, in-situ XRD measurements were performed in order to investigate the conversion mechanism evolution upon annealing and its kinetics. The electrochemical performance of the fabricated films was examined using cyclic voltammetry and charge and discharge measurements. The cyclic voltammogram reveals sharp redox peaks centered around 3 and 4V (vs. Li+/Li) corresponding to Li+ ion insertion/extraction in/from the spinel LiMn2O4. Figure 1.b shows that the converted EMD film shows a similar electrochemical performance to a LiMn2O4 film prepared by RF-sputtering. Also, the lithiation and delithiation curves show the typical LMO potential plateaus. About 100% of the maximum theoretical capacity was reached at 0.1 C. Furthermore, a study of the electrochemical performance of the prepared film based on its annealing time and temperature was done. The LiMn2O4 coated Si Pillar array showed 19 times higher capacity than the film prepared with the same conditions on planar substrate. The relevance of this technique for the fabrication of high rate and high capacity 3D thin-film Li-ion batteries will be discussed. Figure 1

In Situ Studies of Oxide-Electrolyte Interface Reactivity in Lithium-Ion Batteries

Li-ion batteries (LIBs) have been widely used in the past 2 decades, due to their higher energy density and cycling ability, typically using carbon as an anode and layered LiCoO2 as a cathode. The spinel, LiMn2O4 (LMO) is cheaper, safer, and more environmental friendly compared with widely-used LiCoO2 cathodes. However, LMO is known to lose capacity during cycling, ultimately due to disproportionation reactions of Mn3+ transforming to Mn2+ and Mn4+, and the subsequent dissolution of Mn2+ into the electrolyte. Yet our understanding of this process remains rudimentary, and we expect that it can be effectively addressed through interfacial modification (e.g., coatings). This work specifically focuses on developing and using a well-defined model system to observe these interfacial instabilities, and to develop suitable approaches to prevent it.Recently, we have successfully grown high quality epitaxial LMO film on multiple substrates by pulsed laser deposition (PLD). Since LMO film itself is a poor electrical conductor, we have designed systems with built-in current collectors that maintains the LMO-substrate epitaxy. Multiple approaches have been investigated to make the whole system conductive and suitable for cycling: using conductive substrates, a conductive buffer layer, or a conductive surface coating. Conductive substrate is the most straightforward method. High quality epitaxial LMO film has been grown on Nb:STO. For the conductive buffer layer approach, we have tried many possible material including TiN, Al:ZnO, ITO, SrRuO3. It turns out that ITO and SrRuO3 are robust and enable oriented LMO deposition. Graphene was adopted as conductive surface coating. We have successfully transferred graphene onto the surface of LMO film using an anhydrous method.We focus on the in situ real-time surface X-ray studies of well orientated LMO films in the standard lithium ion battery electrolytes (e.g., LiPF6 in EC/DMC). Using the high quality model films grown by PLD, we have probed the mobility of ions and interfacial atomic- and molecular- structures across the electrolyte/electrode interface, including the surface/interface structure changes and reconstruction (using XRR and CTR), individual processes of cation adsorption (resonant XRR/CTR), insertion/extraction.

Synthesis and Characterization of Ba and Ta Substituted Garnet-Type Li7La3Zr2O12 Solid Electrolyte for All-Solid-State Lithium Battery

All-solid-state lithium-ion battery (LiB) is expected as one of the next generation energy storage devices because of their high energy density, high safety and excellent cycle stability. Although oxide-based solid electrolyte materials have rather lower conductivity and poor deformability than sulfide-based one, they have other advantages such as their chemical stability and easiness for handling. Among the various oxide-based solid electrolytes, cubic garnet-type oxide with the formula of Li7La3Zr2O12 (LLZ) have been widely studied because of their high conductivity above 10-4 Scm-1 at room temperature, excellent thermal performance and stability against Li metal anode. Li7La3Zr2O12 (LLZ) have been widely studied because of their high conductivity above 10-4 Scm-1 at room temperature, excellent thermal performance and stability against Li metal anode. LLZ has two different crystal phases, one is cubic phase and another is tetragonal one, but high conductivity above 10-4 Scm-1 at room temperature is mostly confirmed in cubic phase sintered at high temperature. The concentration of Li+ in a garnet framework has crucial importance to stabilize cubic phaseIn this study, we present our recent progress for the development of garnet-type solid electrolytes with high conductivity by simultaneous substitution of Ta5+ into Zr4+ site and Ba2+ into La3+ site in LLZ. Li+ concentration was fixed to 6.5 per chemical formulae, so that the formulae of our Li garnet-type oxide is expressed as Li6.5La3-xBaxZr1.5-xTa0.5+xO12 (LLBZT) and Ba contents x are changed from 0 to 0.3. We don’t use Al2O3 crucible for sample synthesis because Al3+ contamination from the crucible into the LLBZT lattice during high temperature sintering may influence on Li+ concentration and the contamination level is very difficult to control. As results, all LLBZT samples have cubic garnet structure without containing any secondary phases. The lattice constants of LLBZT decrease with increasing Ba2+ contents x from 0 to 0.1 while increase with x from 0.1 to 0.3, possibly due to the simultaneous change of Ba2+ and Ta5+substitution levels. Relative densities of LLBZT are in the range between 89% and 93% and not influenced so much by the compositions. From AC impedance spectroscopy measurements, the total (bulk + grain) conductivity at 27ºC of LLBZT has its maximum value of 0.83 mS/cm at x = 0.10, which is slightly higher than the conductivity (= 0.80 mS/cm) of the sample without substituting Ba (x = 0). Activation energy for the conductivity is lowered with increasing Ba substitution levels but excess Ba substitution degrades the conductivity in LLBZT. LLBZT is electrochemically stable at the potential range from 0 to 6.0 V vs. Li+/Li. Moreover, Li+ insertion and extraction reactions of LiMn2O4 (LMO) or TiNb2O7(TNO) film electrode formed on LLBZT by aerosol deposition were confirmed successfully. Particularly, TNO film electrode in all solid state cell with LLBZT showed initial capacities of 220 mAh/g for Li+ insertion and 170 mAh/g for Li+ extraction at 60ºC and 5 mA/g-TNO. These results indicate that cubic garnet-type LLBZT can potentially be used as a solid electrolyte in all-solid-state batteries. Figure 1

Microstructural Characterization of Oriented Cathodic Thin Films for Lithium Ion Batteries Prepared By Chemical Solution Deposition

Rechargeable Li-ion secondary batteries are being developed for use in high power applications, such as fully electric vehicles and hybrid electric vehicles, because of their high energy density and high power density compared to other battery technologies. Future application of multilayer lithium ion secondary batteries requires a thorough understanding of the influence of microstructure on battery performance. In particular, cathode-substrate and cathode-electrolyte interfaces are known to affect charge/discharge rates, cyclability and battery lifetime. In this study, oriented LiMn2O4 and LiCoPO4 cathodic thin films were successfully fabricated on Au/Al2O3 substrates from precursor solutions. The films were analyzed by X-ray diffraction and Cs-corrected scanning transmission electron microscopy (STEM) using high-angle annular dark-field (HAADF) and annular bright-field (ABF) detectors. It was found that the film/substrate lattice misfit affects the degree of epitaxy of the thin films. Direct observation of atom columns showed that epitaxial LiMn2O4 film forms an atomically flat and coherent heterointerface with the substrate, but that the crystal lattice is distorted with a compositional gradient in the film near the interface. Using ABF-STEM, Li-ion columns in the LiCoPO4 cathode film could be viewed directly and antisite defects were identified in the surface regions.

Deposition of Li4Ti5O12 and LiMn2O4 films on the lithium-ion conductor of Li1.3Al0.3Ti1.7(PO4)3 sintered pellet

LiMn2O4 and Li4Ti5O12 films were deposited on the lithium-ion conductor of Li1.3Al0.3Ti1.7(PO4)3 sintered pellet by spray technique. The effect of annealing temperature, annealing time, Li:Ti and Li:Mn molar ratio on the phase and crystallization of the films were investigated with X-ray diffraction. The LiMn2O4/Li1.3Al0.3Ti1.7(PO4)3/Li4Ti5O12 thin-film lithium-ion battery using Li1.3Al0.3Ti1.7(PO4)3 sintered pellet as both electrolyte and substrate was also studied. The results show that the effect of annealing temperature, annealing time, Li:Ti and Li:Mn molar ratio has great effect on the phase and crystallization of Li4Ti5O12 and LiMn2O4 films deposited on the Li1.3Al0.3Ti1.7(PO4)3 sintered pellet. The optimal Li:Ti and Li:Mn molar ratio for the deposition of Li4Ti5O12 and LiMn2O4 films on Li1.3Al0.3Ti1.7(PO4)3 sintered pellet are 7.2:5 and 1.05:2, respectively. The optimal annealing temperature and time for the deposition of LiMn2O4 film on Li1.3Al0.3Ti1.7(PO4)3 sintered pellet are 650°C and 10min. While those for Li4Ti5O12 film are 700°C and 10min. The LiMn2O4/Li1.3Al0.3Ti1.7(PO4)3/Li4Ti5O12 thin-film battery offers a working voltage about 2.25V and can be easily cycled.

Electrochemical Properties of LiMn2O4-Li7La3Zr2O12 Composite Film Electrode Fabricated By Aerosol Deposition Method

LiMn2O4 (LMO)-Li7La3Zr2O12(LLZO) composite film electrode was successfully fabricated without any heat treatments by using aerosol deposition (AD) method. Mixture of 75wt%-LMO and 25wt%-LLZO powders with the averaged particle sizes around 1 μm was directly used as raw material. The mixed LMO and LLZO powders were sprayed onto a stainless steel substrate in deposition chamber evacuated to a low vacuum state below 10 Pa with N2 carrier gas for several 10 minutes. Mass flow of N2 carrier gas was set to be 20 L min-1 to form LMO-LLZ composite film via room temperature impact consolidation (RTIC). From both SEM observation and XRD measurement, it was found that as-deposited film has very dense structure without pores and is consisted from fractured LMO and LLZO crystalline particles with the sizes of several 10-100 nm. The thickness of composite film is 4 μm and LLZO content in the film was estimated to be around 21wt%. LMO-LLZO composite film electrode showed good electrochemical property in liquid electrolyte and higher discharge capacity than LMO film without including LLZO. The discharge capacities reduced by the weight of LMO-LLZO composite film electrode was 70 mAh g-1, 62 mAh g-1 and 55 mAh g-1 at different discharge current rates of 0.07C, 0.7C and 3C (1C = 0.11 mA cm-2). They are corresponding to the specific capacity per LMO in the film of 90 mAh g-1, 80 mAh g-1 and 71 mAh g-1, respectively. In addition, the LMO-LLZO composite film electrode showed good capacity retention during cycle testing, which is attributed to strong adhesion between the composite film and substrate by AD. The present results suggest that AD method can potentially be used for electrode layer composed of active material and solid electrolyte for all-solid state lithium-ion battery.

Spray deposition of LiMn2O4 nanoparticle-decorated multiwalled carbon nanotube films as cathode material for lithium-ion batteries

We prepared LiMn2O4 nanoparticle-decorated multiwalled carbon nanotube (MWCNT) films as a cathode electrode for lithium-ion batteries using a spray-deposition method. The surface morphologies and structures of the films were characterized using scanning electron microscopy and X-ray diffraction analysis. The results revealed that fairly homogeneous spinel LiMn2O4 nanopowder-based films with the grain size of 20–50nm were successfully formed on the surface of the MWCNTs. Cyclic voltammetry confirmed the presence of typical spinel LiMn2O4 structure on the MWCNTs with showing stronger oxidative peaks of better reversibility as compared to a pure LiMn2O4 electrode. The spray-deposited LiMn2O4-decorated MWCNT film was also found to have a higher discharge capacity (97.2 mAh/g) than the as-deposited LiMn2O4 film (75.2 mAh/g) as well as excellent cycling stability. These characteristics are due to the fact that MWCNTs provide the cathode with multiple electron tunneling pathways and a mechanically strong framework.

Superior electrochemical properties of porous Mn2O3-coated LiMn2O4 thin-film cathodes for Li-ion microbatteries

Thin-film LiMn2O4 cathodes coated with Mn2O3 overlayer were prepared by a sol–gel method for Li-ion microbattery tests. The double-layered structure was fabricated on Pt(111) substrate through spin-coating the precursor solution for LiMn2O4 followed by that for Mn2O3. The Mn2O3 overlayer exhibited granular morphology with significant volume of pores while the LiMn2O4 film consisted of compacted grains. The electrochemical properties of the porous Mn2O3-coated LiMn2O4 (Mn2O3/LiMn2O4) cathodes characterized by charge–discharge (C–D) cycling performance, cyclic voltammetry, and rate capability were compared with those of the pristine LiMn2O4 cathodes. The Mn2O3/LiMn2O4 cathodes exhibited good cycle-life, only 0.007% capacity loss per cycle at 25°C, thereby achieved discharge capacity retention of 80% after 3000 cycles, while the pristine LiMn2O4 cathodes retained only 35% of the initial capacity under the same C–D condition. The Mn2O3/LiMn2O4 cathodes also exhibited better rate capabilities compared to the pristine LiMn2O4 cathodes. The improved electrochemical performance is ascribed to the porous Mn2O3 overlayer that not only protects the underlying LiMn2O4 film from direct exposure to the electrolyte but also provides efficient Li+ diffusion path during the C–D cycling.

Preparation of a spinel LiMn2O4 single crystal film from a MnO wafer

Spinel LiMn2O4 is a very promising material for positive electrodes in a wide range of Li-ion battery applications due to its lower cost and more environmental friendliness than any other electrode materials. Although the bulk properties of LiMn2O4 have been studied intensively, there have been few reports about the structure and properties of LiMn2O4 surfaces in spite of the importance of solid/electrolyte interfaces. This is caused by the difficulty in preparing LiMn2O4 samples with accessible flat surfaces suitable for atomistic observations. To address this, we have successfully prepared a single crystalline LiMn2O4 film with an atomically flat surface by solid-state reaction from a MnO wafer with LiOH.H2O powder. X-ray diffraction (XRD) reveals the single crystalline growth of LiMn2O4 films depending on the orientation of a MnO wafer. Atomic force microscopy observations revealed that a LiMn2O4 (111) film has an atomically flat surface with steps of a {111} interlayer height. Electron energy-loss spectroscopy (EELS) study of the (111) film revealed that the sample consists of Li, Mn3+ and Mn4+ with a composition similar to LiMn2O4. The (111) film sample is also investigated by cyclic voltammetry and galvanostatic experiments, revealing that a crushed powder sample from the film has electrochemical activity as usual positive electrode material.

Effect of crystallization route on the properties of LiMn2O4 thin films prepared by spin coating

LiMn2O4 thin films were prepared by spin coating through intermediate amorphous layer route (IALR) and intermediate crystallized layer route (ICLR). The phase identification, surface morphology, and electrochemical properties of the films prepared by different crystallization routes were studied by X-ray diffraction, scanning electron microscopy, and galvanostatic charge–discharge experiments. The results show that both films prepared by different crystallization routes are homogeneous and crack free. Compared with the film prepared by IALR, the film prepared by ICLR shows smaller grain size and is smoother and denser. The LiMn2O4 film prepared by ICLR delivers the specific capacity of 39.8 μAh cm−2 μm−1, which is higher than 35.6 μAh cm−2 μm−1 for the one prepared by IALR. The capacity loss of the film prepared by ICLR after being cycled 100 times is 3.4 %, which is smaller than that of 5.5 % for the film prepared by IALR. The film prepared by ICLR shows higher specific capacity and better cycling behavior than the one prepared by IALR.

Influence of annealing temperature on microstructural and electrochemical properties of rf-sputtered LiMn2O4 film cathodes

The microstructural and electrochemical properties of rf-sputtered LiMn2O4 films were investigated as a function of post-deposition process. The degree of crystallization in the films gradually increased with the increase of annealing temperature (Ta). The films annealed at Ta = 973 K exhibited characteristic peaks with predominant (111) orientation representing the cubic spinel structure of Fd3m symmetry. The estimated Mn–Mn and Mn–O distances obtained from the X-ray diffraction data were observed to be increased slightly with Ta. Characteristic changes in surface morphological features were observed as a function of Ta as evidenced from scanning electron microscopy. The estimated root mean square (RMS) roughness of the films increased from 97 to 161 nm with augmentation of Ta. The electrochemical studies, viz. cyclic voltammetry (CV), specific discharge capacity and Li ion diffusion coefficient were carried out for annealed LiMn2O4 films in saturated aqueous electrolyte (Li2SO4) in the potential window of 0–1.2 V and correlated with surface morphology and grain size. The LiMn2O4 films annealed at Ta = 973 K exhibited better electrochemical performance and demonstrated a discharge capacity of about 53.5 μA h cm−2 μm−1 with diffusion coefficient of 1.2 × 10−13 cm2 s−1.

Characteristics of SnO<sub>x</sub>-Coated Lithium Manganese Oxide Thin Film for MEMS Power System

We prepared spinel-phase LiMn2O4 layer by using rf magnetron sputtering system. LiMn2O4 films were deposited at room temperature and then annealed at 750°C for crystallization to spinel type. In order to reduce the interface reaction such as Mn dissolution phenomenon during operation, we introduced SnOx (coating-layer) thin film. The SnOx films were deposited on LiMn2O4 films by rf magnetron sputtering system. A SnOx-coated LiMn2O4 film was more stable during the chargingdischarging reaction and maintained good cycle behavior at high temperature conditions of 55°C.