LiMn2O4 Electrode Research Articles

Effects of binder content on manganese dissolution and electrochemical performances of spinel lithium manganese oxide cathodes for lithium ion batteries

In this study, the effects of the polyvinylidene fluoride (PVdF) binder on the Mn dissolution behavior and electrochemical performances of LiMn2O4 (LMO) electrodes are investigated. It is found that increasing the PVdF content (3, 5, 7, and 10 wt.%) leads to reduced Mn dissolution, and thus superior cycle performance at elevated temperature (60 °C). This can be ascribed to increased binder coverage on the LMO surface, as evidenced by X-ray photoelectron spectroscopy measurements, which acts a role as a passivation layer for Mn dissolution. The rate capability of the LMO electrode is hardly deteriorated as the PVdF content increases, despite the increasing surface coverage. Electrochemical impedance measurements reveal that the LMO electrode with higher binder loading exhibits lower electrode impedance, which is suggested to be due to enhanced electronic passage through the composite LMO electrode.

Effect of (Mg, Al) double doping on the thermal decomposition of LiMn2O4 cathodes investigated by time-resolved X-ray diffraction

The performance of undoped and (Mg, Al) doubly doped LiMn2O4 electrodes were compared, with the latter having better cycle retention at room temperature and enhanced cycling performance at elevated temperatures. The effect of double (Mg, Al) doping on the thermal stability of charged and uncharged samples was studied by time-resolved X-ray diffraction, revealing that Mg and Al significantly improve the structural stability of LiMn2O4 during heat treatment.

Synthesis and electrochemical properties of high performance polyhedron sphere like lithium manganese oxide for lithium ion batteries

Polyhedron structured sphere-like lithium manganese oxide (LiMn2O4) is successfully synthesized from β-MnO2 nanorod precursor via a solid state reaction at a temperature of 800°C. For comparison, LiMn2O4 materials with nanorod and octahedron structures are also obtained from β-MnO2 nanorod precursor at temperatures of 700°C and 900°C, respectively. The galvanostatic charge–discharge result shows that the polyhedron sphere-like LiMn2O4 sample exhibits the best electrochemical performance at high rate and high temperature. After 100 cycles at 5C, this electrode is able to maintain 94% of its capacity at 25°C and 81% at 55°C. This is attributed to that the polyhedron sphere-like spinel LiMn2O4 can suppress the dissolution of manganese ions. Based on Brunauer Emmett Teller (BET), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), the polyhedron sphere-like LiMn2O4 sample has the lowest BET surface area, largest diffusion coefficient of Li+ and least charge transfer resistance. This study provides an insight into the capacity fading of LiMn2O4 electrodes and the polyhedron structured sphere-like LiMn2O4 can be a promising material for lithium ion batteries.

Compatibility of LiMn2O4 cathode with electrolyte based on low-viscosity ether-functionalized pyrazolium ionic liquid

One new ether-functionalized ionic liquid (IL) composed of pyrazolium cation with one 2-ethoxyethyl group and bis(trifluoromethylsulfonyl)imide anion was synthesized and characterized. The IL showed the lowest viscosity among all the reported pyrazolium ILs, and the value was 38.9 mPa s at room temperature. The conductivity of the IL was 3.48 mS cm−1 at 25 °C, and its electrochemical window was 4.4 V. Cycling performance of symmetric lithium cell was investigated for the IL electrolyte with 0.6 mol kg−1 of LiTFSI. Li/LiMn2O4 cell using the IL electrolyte owned good cycling and rate performances, and it was found for the first time that LiMn2O4 cathode was compatible with electrolyte based on ether-functionalized IL. By the characterizations of X-ray diffraction and scanning electron microscopy for fresh and cycled LiMn2O4 electrodes, it was inferred that the slow dissolution of LiMn2O4 in the IL electrolyte might happen during the charge–discharge processes.

Probing battery chemistry with liquid cell electron energy loss spectroscopy.

We demonstrate the ability to apply electron energy loss spectroscopy (EELS) to follow the chemistry and oxidation states of LiMn2O4 and Li4Ti5O12 battery electrodes within a battery solvent. This is significant as the use and importance of in situ electrochemical cells coupled with a scanning/transmission electron microscope (S/TEM) has expanded and been applied to follow changes in battery chemistry during electrochemical cycling. We discuss experimental parameters that influence measurement sensitivity and provide a framework to apply this important analytical method to future in situ electrochemical studies.

Evolution of Solid Electrolyte Interphase during Cycling and Its Effect on Electrochemical Properties of LiMn2O4

Thickness variation of the solid electrolyte interphase (SEI) produced during charge-discharge cycling is investigated to analyze the effect of SEI on the electrochemical properties of LiMn2O4. Atomic force microscopy (AFM) is used to measure the SEI thickness and elastic modulus on the LiMn2O4 surface. The SEI shows a broad thickness distribution due to the random nature of the LiMn2O4 electrode surfaces, while the average SEI thickness increases with cycling and stabilizes after the 20th cycle. Formation of a relatively thin SEI on the LiMn2O4 surface accompanies low Coulombic efficiency at early cycling stages. The SEI produced in the early stages of cycling is vulnerable to capacity fading due to inefficient surface protection against possible side reactions. A fully-grown stable SEI after 20 cycles shields the cathode surface from the electrolyte, minimizing capacity fading.

In-Situ Electrochemical Studies of Li-Ion Start-Stop Vehicle Batteries through a Novel Cell Design

Lithium ion batteries are now used extensively for vehicle traction applications. Because of their high specific power and long usage life, lithium ion batteries are very appealing for power assist vehicular applications. Implementation of Li-ion batteries for start-stop systems is one of the pragmatic approaches being considered for reducing vehicle fuel consumption. During start-stop operation, the engine automatically shuts down when the vehicle comes to stop and then quickly restarts when propulsion is desired by the operator. Such start-stop operations of the vehicle can effectively reduce the amount of engine idling time, leading to fuel savings.One of the main challenges for start-stop applications is meeting the cold-cranking power requirements at -30oC. Due to the kinetic limitations, pulse power performance of Li-ion batteries drop dramatically at low temperatures. Given the requirement for starting the engine at low temperature, it is typical that the cold cranking power capability determines the module size needed for start-stop systems; and therefore directly impacts the system weight and cost. It is essential to understand the source of the kinetic limitations (e.g. electrolyte resistance, electrode-electrolyte interfacial resistance, or diffusion resistance) and design a system that can dramatically improve the cold cranking power.In this talk, we demonstrate the implementation of a new cell design to investigate the pulse power performance of LiMn2O4 (LMO) / Li4Ti5O12 (LTO) batteries for start-stop applications. Figure 1 shows the schematic of the cell design; it is composed of four electrodes, with two LTO and two LMO electrodes adjacent to each other. The current collectors are porous, allowing the ions to pass through them. This type of design enables the in-situ investigation of LTO/LTO, LTO/LMO, LMO/LMO cells in a single cell while the neighboring electrodes are used for voltage monitoring. In this report, our focus is to investigate the kinetics of each individual electrode under low temperatures. Using EIS and linear voltage polarization studies, we provide insight on the source of resistance limiting the pulse power capability of the cell at low temperatures (-30oC). We found that electrolyte transport limitations control the cell performance at low temperatures, which directly impacts the cold cranking power.

Effects of polymeric binders on electrochemical performances of spinel lithium manganese oxide cathodes in lithium ion batteries

Effects of polymeric binders on both the dissolution of manganese (Mn) and electrochemical properties of spinel LiMn2O4 (LMO) electrodes are investigated in detail. Three promising polymers, polyvinyl alcohol (PVA), polyacrylic acid (PAA), and polyacrylonitrile (PAN) are chosen as binders for the LMO electrodes and compared to currently popular polyvinylidene fluoride (PVdF). For LMO electrodes fabricated with the selected binders, physicochemical properties including surface coverage, adhesion strength, and electrolyte uptake are examined. Also, electrochemical performance factors such as Mn dissolution behavior, rate capability, cycle performance, and thermal stability are investigated. PAN is revealed to be an outstanding binder for LMO electrodes based on its excellent rate capability, superior cycle performance, and high thermal stability when compared to the other three binders. This can be ascribed to an appropriate amount of electrolyte uptake and low impedance of the PAN despite the relatively large surface coverage of the LMO that leads to lower Mn dissolution.

Carbon covering to improve the storage performance of LiMn2O4 electrode at 60 °C

To improve the storage performance of LiMn2O4 cathode at elevated temperature (60°C), a carbon layer is introduced to directly cover the surface of commercial LiMn2O4-based electrode via room-temperature DC magnetron sputtering. The as-modified cathode (LMO-C) displays enhanced capacity retention after storage at the charge state (4.35V) under 60°C as compared to the bare LiMn2O4 cathode (LMO-N). Specially, after 7, 14 days storage at 60°C, the capacity retention of LMO-N is 89%, 17%, while the capacity retention of LMO-C is 92%, 85%, respectively, with respect to its own capacity before storage. Moreover, the charge–diachage curves and electrochemical impedance spectroscopy results demonstrate that LMO-C has much less increased electrode polarization and electrochemical impedance than LMO-N during the elevated-temperature storage process. SEM and TEM images of both sampes after storage show that LMO-C remains the intial morphology while LMO-N suffers morphological and sturctural degradations.

Surface modification of cathodes with nanosized amorphous MnO2 coating for high-power application in lithium-ion batteries

In this paper, we discuss the surface modification of spinel LiMn2O4 cathodes by MnO2 particles via a simple precipitation method at room temperature, without any heat treatment. Nanosized MnO2 particles with an amorphous structure were formed and distributed evenly on the parent cathode, without severe agglomeration. Electrochemical measurements at ambient temperature revealed that the MnO2-coated LiMn2O4 electrode exhibited superior rate capability as compared to the pristine LiMn2O4 electrode. Based on the capacity at low currents, the surface-modified electrode delivered 62% capacity, whereas the pristine LiMn2O4 electrode maintained 8% capacity during fast discharging for 3min at 20 C-rate. Surface coating with nano-MnO2 enhanced the electrochemical properties such as storage characteristics, particularly at elevated temperatures. X-ray photoelectron spectroscopy data showed that the improved performance of the coated electrode was mainly because of the suppressed side reaction between the cathode and the electrolyte.

High Cycle Stability of Post-Pinel Compound NaMn2O4 as Cathode of Sodium Ion Battery

1. Introduction Room temperature sodium ion batteries (SIB) have been drawing increasing attentions as potential energy storage devices instead of the normally used lithium ion batteries (LIB) due to its advantages of low cost and unlimited sodium resources [1-2]. Design and synthesis of electrode materials for SIB which can meet commercial standard still challenge the materials scientists. Inspired by the material design and development of LIB, popular electrode materials of LIB have been used as SIB electrode by a electrochemical or chemical Li-Na exchange [3]. Manganese-based materials spinel-type LiMn2O4 is widely used in present large-scale LIB because well electrochemical performance and elemental abundance in the Earth. However, the spinel-type NaMn2O4 is a thermodynamically unstable phase and can not be synthesized directly. Electrochemical desertion of Li and followed by an insertion of Na from LiMn2O4 have been investigated in SIB, but a poor cycle performance and structure rearrangement have been reported [4]. Herein, we synthesized a post-spinel structure NaMn2O4 by a high pressure technique and discussed the potential applications as cathode materials for SIB.2. Experiments The NaMn2O4 was synthesized using a high-pressure technique. The mixture of Na2O2 and Mn2O3 (with a 5% excess of Na2O2) were sealed in a Au-capsule and heated at 1223 K under a pressure of 4.5 GPa for 1 hour. The synthesized samples was washed by water and post-heated at 623 K for 5 hours. The structure and morphology have been characterized by XRD, SEM and TEM. Electrodes were fabricated using NaMn2O4, acetylene black and PTFE in a mass ratio of 6:3:1. Coin cells consists by a NaMn2O4 cathode, sodium metal anode and NaPF6 electrolyte. 3. Results and discussionFig.1 XRD pattern (a); SEM images (b); HRTEM (c) and selected charge/discharge profiles at the voltage range of 2.0-4.0 V. The XRD patterns of NaMn2O4 is shown in Fig. 1a. All peaks can be index as the previously known orthorhombic structure with a space group of Pnma. No impurities and secondary phase can be found. It showed a rod-like morphology with a diameter of about 100 nm and a length of 3-5 μm as shown in Fig. 1b. The detailed crystal structure of as prepared NaMn2O4 have also been studied by HRTEM and showed in Fig. 1c. The inner figure of 1c is the structure view of post-spinel NaMn2O4. The 1D tunnels which are surrounded by double rutile chains of Mn2O4 are filled with sodium ions. Sodium ions in the post-spinel structures occupied the sites much larger than that of the Li ions in spine LiMn2O4. Materials with this structure characteristic provide a potentials of reversible sodium ion insertion/desertion with easy ion diffusion and stable framework host. First-principles calculation results showed that this compound is stable at ambient conditions and a high mobility of Na+ in post-spinel phase [5]. Fig. 1d showed the selected charge/discharge profiles at a voltage range of 2.0-4.0 V. It is interesting to note that the superior cycle stability of both charge/discharge capacities and voltages profiles. The stable charge/discharge plateaus at about 3 V (vs. Na+/Na) which can be attributed to the redox reaction of Mn4+/Mn3+. Different from other NaMnxOy compounds, this compound showed that it has a relatively stable structure, sub-plateaus can rarely be founded during charge/discharge processes. As we know, the LiMn2O4 electrode suffered a serious capacity fading when cycled at a temperature higher than 55 °C. The main explanations for this is the Jahn-Teller effects of Mn3+ and dissolution of Mn2+ from the cathode materials. Researchers also endeavored to improve the high temperature performance of Mn-base materials by many ways. We also investigated the cycle performance of this post-spinel NaMn2O4 at 55 °C. A very stable cycle performance at 55 °C have been obtained. The reasons for the superior stability both at room temperature and 55 °C are the large barrier to rearrange Mn ion in this post-spinel structure. The detailed electrochemical performance and relations with structures will be presented at the conference.Reference[1] R. Berthelot, D. Carlier, C. Delmas, Nature Mater. 10 (2011) 74-80[2] V. Palomares, M. Casas-Cabanas, E. Castillo-Martinez, M. H. Han, T. Rojo, Energy Environ. Sci. 6 (2013) 2312-2337[3] H. Pan, Y. Hu, L. Chen, Energy Environ. Sci. 6 (2013) 2338-2360[4] N. Yabuuchi, M. Yano, S. Kuze, S. Komaba, Electrochimica Acta, 82 (2012) 296-301[5] C. Ling, F. Mizuno, Chem. Mater. 25 (2013) 3062-3071

Surface Structure Evolution of LiMn2O4 Cathode Material upon Charge/Discharge

Surface dissolution of manganese is a long-standing issue hindering the practical application of spinel LiMn2O4 cathode material, while few studies concerning the crystal structure evolution at the surface area have been reported. Combining X-ray photoelectron spectroscopy, electron energy loss spectroscopy, scanning transmission electron microscopy, and density functional theory calculations, we investigate the chemical and structural evolutions on the surface of a LiMn2O4 electrode upon cycling. We found that an unexpected Mn3O4 phase was present on the surface of LiMn2O4 via the application of an advanced electron microscopy. Since the Mn3O4 phase contains 1/3 soluble Mn2+ ions, formation of this phase contributes significantly to the Mn2+ dissolution in a LiMn2O4 electrode upon cycling. It is further found that the Mn3O4 appears upon charge and disappears upon discharge, coincident with the valence change of Mn. Our results shed light on the importance of stabilizing the surface structure of cathode m...

Improvement in the Electrochemical Performances of Spinel LiMn2O4 cathodes By MnO2 coating for Lithium Ion Battery Application

Lithium ion batteries (LIBs) are considered as attractive power sources for electric vehicles (EV) and aenergy storage systems (ESS) as well as portable electronic devices due to their high energy density and long cycle life. Importantly, EV and ESS applications require high power density and thermal stability as well as low cost. In this regard, spinel LiMn2O4 is a promising cathode material because of its low cost, good safety, high abundance and environmental harmlessness. However, LiMn2O4 generally exhibits poor capacity retention especially at elevated temperatures mostly owing to the Mn dissolution. Moreover, Jahn Teller effect also causes the structural instability, which can be seen on the surface of LiMn2O4 at high current application. Previous literatures verify that surface-modification by coating plays an important role in electrochemical performances of LiMn2O4. The surface treatment of LiMn2O4 is known to prohibit Mn dissolution from LiMn2O4 electrode. In this study, the MnO2 were prepared on the surface of LiMn2O4 powders. The synthesis procedure includes mixing KMnO4 solution with ethylene glycol through oxidation-reduction reaction under ambient conditions. Electrochemical evaluation as well as storage test at elevated temperatures reveal that the surface-modification with MnO2 enhance the rate capability and improve the storage characteristics at 60oC of spinel LiMn2O4 cathode materials. In-depth analyses such as X-ray Photoelectron Spectroscopy and Electrochemical Impedance Spectroscopy are also performed to elucidate the effect of surface-modification using MnO2.

Electrochemical Characteristics of Li4Ti5O12 - Coated MCMB as an Anode Material for Hybrid Capacitor

In recent years, the over consumption of fossil fuels leads to critical environmental problems and increasing attentions are being paid on energy security issues. The green energy sources, such as solar and wind, are typically periodic or intermittent and therefore requires an electrical energy storage for utilization purposes. Great research effort has been focused on the energy storage systems of capacitors and batteries. The hybrid capacitor incorporates a faradaic lithium ion battery system in combination with a non faradaic electric double layer capacitor system in a unit cell. This combination called hybrid capacitors can be used to obtain better performance in power/energy demands. In this research, we coated Li4Ti5O12 onto meso - carbon micro beads (MCMB) to form a core - shell structure by a sol–gel process followed by calcinations. This MCMB-Li4Ti5O12 of core-shell structure was prepared to improve low electric conductivity of Li4Ti5O12 and cycling behavior. Prepared MCMB-Li4Ti5O12 composite was analyzed by XRD and SEM. The electrochemical performances of hybrid capacitor were investigated using MCMB-Li4Ti5O12 as the negative electrode and LiMn2O4, Active Carbon Fiber (ACF) as the positive electrode. The anodes were prepared by coating slurries containing the active materials (76wt%), Super P (17wt%), and polytetrafluroethylene (PTFE, 7wt%) on Al foil. The cathodes were made by dispersing 85wt% LiMn2O4, 10wt% Super P and 5wt% PTFE binder. The electrolyte consisted of 1M LiPF6in a mixture of ethylene carbonate(EC) / dimethyl carbonate(DMC) / ethyl-methyl carbonate(EMC) with a volume ratio of 1:1:1. The electrochemical behaviors of hybrid capacitor using organic electrolytes were characterized by charge/discharge, cyclic voltammetry, impedence and cycle tests. The hybrid capacitor using MCMB-Li4Ti5O12/LiMn2O4 electrodes had better capacitance than MCMB hybrid systems and was able to deliver a specific energy as high as 67 Wh/kg at a specific power of 781 W/kg. Also, it was found that MCMB-Li4Ti5O12 composite exhibited very good cycle life performance.

Characterization of Surface-Modified LiMn2O4 Electrodes Using Surface-Enhanced Raman Spectroscopy

To date, lithium-ion batteries still represent the most promising electrical energy storage option for many emerging technologies; for instance, the electrification of transportation hinges on the availability of batteries with significantly improved energy and power density, extended lifetime, and reduced cost. In particular, the positive electrode materials used in lithium-ion batteries contribute more than any other component to the overall cell cost and limit the total cell energy density for a given mass because of their substantially lower specific capacities compared to negative electrode material. Thus, many research efforts have been devoted to developing positive electrode materials with low cost, high performance, and improved safety for future lithium-ion systems.One material of interest is LiMn2O4, however capacity fading in the spinel-structured oxide has been reported for many years, limiting its commercial application [1]. The primary mechanism for the observed capacity fading is commonly attributed to a chemical reaction originally proposed by J.C. Hunter in 1981. The Hunter reaction is well accepted in the literature as one of the key features of LiMn2O4 capacity loss in LiPF6 containing carbonate electrolytes, wherein LiPF6 can react with adventitious water in the electrolyte to form highly corrosive HF. Direct observations of the LiMn2O4 electrode after electrochemical cycling have been made which support the Hunter reaction. For example, spontaneous λ-MnO2 formation after storing LiMn2O4 films in an LiPF6 containing carbonate electrolyte at elevated temperatures was observed using ex situ surface-enhanced Raman spectroscopy (SERS) [2]. Applying passivating coatings on the surface of the spinel active material is one approach to limit electrode capacity fading. Specifically, layers of amphoteric oxides, particularly ZrO2, TiO2 and Al2O3, have been shown empirically to be very effective [3].Very little has been reported on the role of ampohteric oxides toward reducing capacity fading of LiMn2O4 positive electrodes, and while it has been suggested that they act as local getters of HF in the electrolyte, their influence on the surface chemistry of modified electrodes has not been specifically investigated. Recently, our group has developed electrochemically stable, SERS-active Ag@SiO2 core-shell nanoparticles via a solution route [4] which dramatically enhanced the sensitivity to surface species and incipient phases on the electrode surface at temperatures up to 450 °C. This presentation will highlight the application of in operando SERS to probing the electrode/electrolyte interfaces of thin-film LiMn2O4 model electrodes with and without a thin layer of amphoteric oxide. Development of advanced surface characterization techniques such as in operandosurface-enhanced Raman spectroscopy will enable us to directly correlate the surface chemistry and structure with electrochemical performance, offering information vital to the rational design of these devices for future high power, long lifetime lithium-ion batteries.[1] G. Amatucci, J.M. Tarascon, J. Electrochem. Soc., 149 (2002) K31-K46.[2] Y. Matsuo, R. Kostecki, F. McLarnon, J. Electrochem. Soc., 148 (2001) A687-A692.[3] J.S. Kim, C.S. Johnson, J.T. Vaughey, S.A. Hackney, K.A. Walz, W.A. Zeltner, M.A. Anderson, M.M. Thackeray, J. Electrochem. Soc., 151 (2004) A1755-A1761.[4] X. Li, J.-P. Lee, K.S. Blinn, D. Chen, S. Yoo, B. Kang, L.A. Bottomley, M.A. El-Sayed, S. Park, M. Liu, Energy Environ. Sci., (2013).

Improvement of the thermal stability of LiMn2O4/graphite cells with methylene methanedisulfonate as electrolyte additive

In order to overcome the severe capacity fading of LiMn2O4/graphite cells cycled at elevated temperature, methylene methanedisulfonate (MMDS) is newly evaluated as an electrolyte additive to improve the thermal stability of LiMn2O4 cathode. The cell using 1.0molL−1LiPF6 -EC/EMC/DMC (1:1:1, weight ratio) with 0.5wt.% MMDS additive keeps 79.2% of initial capacity after100 cycles at 60°C, whereas it is only 52.7% for the cell without additive. After the storage at 85°C for 24h, the cell with 0.5wt.% MMDS additive exhibits higher discharge capacity retention (82.5%) than the cell without additive (71.8%), and the change of thickness, resistance and discharge voltage plateaus decrease. The effects of the additive are characterized by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), transmission electron microscopy (TEM), as well as electrochemical performance tests. These results suggest that MMDS additive can form better electrochemical and thermal stability of surface film on the LiMn2O4 electrode, which reduces both the decomposition of the electrolyte and the dissolution of Mn ion in the electrolyte at elevated temperature, thus leads to the obvious improvement on the thermal stability of LiMn2O4 cathode.

Nanoarchitectured LiMn2O4/Graphene/ZnO Composites as Electrodes for Lithium Ion Batteries

LiMn2O4 nanoparticles are facilely synthesized using a sol–gel processing method. Graphene is added to LiMn2O4 electrode aiming at increasing specific capacity and improving rate capability. In order to further improve cycling stability of LiMn2O4/graphene electrode, atomic layer deposition (ALD) is used to deposit ultrathin ZnO coating composed of six ZnO ALD layers and modify the surface of either LiMn2O4/graphene electrode or individual LiMn2O4 particles to form nanoarchitectured LiMn2O4/graphene/ZnO electrodes. Both ZnO-ALD-modified LiMn2O4/graphene electrodes demonstrate enhanced cycling performance at 1C, retaining the final discharge capacity above 122 mA h g−1 after 100 electrochemical cycles, which is higher than 115 mA h g−1 of pristine LiMn2O4/graphene electrode and 109 mA h g−1 of bare LiMn2O4 electrode. The improved electrochemical performance of nanoarchitectured LiMn2O4/graphene/ZnO electrodes can be attributed to the cooperative effects from high electronic conductivity of graphene sheets to facilitate electron transportation and effective protection of ZnO ALD coating to restrict Mn dissolution and electrolyte decomposition.

Comparison of 4 V and 3 V electrochemical properties of nanocrystalline LiMn2O4 cathode particles in lithium ion batteries prepared by ultrasonic spray pyrolysis

Nanocrystalline LiMn2O4 particles were prepared by an ultrasonic spray pyrolysis method using nitrate salts at 800°C in air atmosphere. Particle properties were characterized by the X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy. In addition, cyclic voltammetry and galvanostatic tests were performed to investigate the effects of structure on electrochemical behavior of both the 4V and 3V potential plateaus. Particle characterization studies show that the nanocrystalline particles have spinel structure of submicron size with spherical morphology. Particles, ranging between 75 and 1250nm, were formed by aggregation of nanoparticles. Discharge capacity of LiMn2O4 particles between 3.0 and 4.5V is 70mAhg−1 and cumulative capacity between 2.2 and 4.5V is 111mAhg−1 at 0.5C rate. Discharge capacity at the 4V potential region reduces to 47% of initial capacity, whereas cumulative capacity fade is 62% after 100 cycles at 0.5C rate. Although nanocrystalline LiMn2O4 cathode particles exhibit good rate capability at the 4V plateau, capacity decreased rapidly by increasing C- rates and cycling between 2.2 and 4.5V. The loss of capacity can be attributed to phase transformation and dissolution of electrode material. Particle characterization of used cathodes showed that nanocrystalline LiMn2O4 electrodes partly dissolve during electrochemical cycling.

Tris (pentafluorophenyl) phosphine: A dual functionality additive for flame-retarding and sacrificial oxidation on LiMn2O4 for lithium ion battery

Tris (pentafluorophenyl) phosphine (TPFPP) additive possesses a dual functionality. The first of which is aimed at decreasing the flammability of the electrolyte, while the second is directed at the inhibition of the oxidative decomposition of electrolyte on cathode materials in lithium-ion batteries. The properties of the electrolyte containing TPFPP and the enhancements of cycling performance of Li/LiMn2O4 cells are investigated via a combination of electrochemical methods, self-extinguishing time (SET), differential scanning calorimeter (DSC), as well as density functional theory (DFT) computations. It is found that the incorporation of TPFPP to 1.0 M LiPF6 in 1:1:1 (v/v/v) ethylene carbonate/dimethyl carbonate/diethyl carbonate improves the thermal stability and decrease the flammability of the electrolyte. In addition, the initial discharge capacity and cycling stability of Li/LiMn2O4 is improved as well. The improved cycling performance with TPFPP added can be ascribed to the participation in surface layer formation process with incorporation of TPFPP. DFT theoretical computations are in good agreement with the modified cyclic voltammetry behavior of electrolyte with and without TPFPP additive on LiMn2O4 and graphite electrodes.

Hetero-epitaxial growth of Li0.17La0.61TiO3 solid electrolyte on LiMn2O4 electrode for all solid-state batteries

A Li0.17La0.61TiO3(111)/LiMn2O4(111) solid electrolyte/electrode hetero-epitaxial system with applications in all solid-state batteries has been synthesized on a SrRuO3(111)/SrTiO3(111) substrate using pulsed laser deposition. XRD patterns provided evidence for the epitaxial growth of Li0.17La0.61TiO3(111) on LiMn2O4 at a low deposition temperature of 750 °C. X-ray reflectivity analysis confirmed that the low temperature deposition resulted in intimate contact between LiMn2O4 and Li0.17La0.61TiO3, although small amounts of oxygen and titanium were found to have diffused between the materials. The Li0.17La0.61TiO3/LiMn2O4 film exhibited reversible electrochemical activity between 3.0 and 4.5 V. No significant structural changes were observed in the cycled film, indicating that the Li0.17La0.61TiO3/LiMn2O4 interface is chemically and electrochemically stable during the battery reaction. The integration of electrode and solid electrolyte oxides in epitaxial multi-layer structures is expected to allow the design of new configurations for all solid-state batteries.