Electrochemical study on LiCo1/6Mn11/6O4 as cathode material for lithium ion batteries at elevated temperature

A novel process via sintering of a precursor from the solution of metal acetates by spray-drying technology was used to synthesize Co-substituted LiCo_1/6Mn_11/6O₄ material for lithium ion batteries. The as-prepared particles were identified as single-phase spinel structure without any impurities in the XRD pattern. The SEM image showed that the particles had good cubic shapes and uniform size distribution with sizes of about 100–200 nm. An ex situ XRD technique was used to characterize the first charge process of the LiCo_1/6Mn_11/6O₄ electrode. The result suggested that the material configuration maintained invariability. The electrochemical properties of the synthesized cathode material were investigated using Li-ion model cells at room and elevated temperature, respectively. In the charge/discharge potential of 3.5–4.4 V at 1/10 C rate, the LiCo_1/6Mn_11/6O₄ electrode delivered high initial capacities of 123 and 127 mAh g⁻¹ at 25 and 55 °C, respectively. Electrochemical cycling tests revealed that the capacity fading occurred mainly in the high-voltage region of 4.08–4.40 V, and the fading rate was 0.107% and 0.302% per cycle at 25 and 55 °C, respectively. The excellent cycling stability and low material cost make it an attractive cathode for high-temperature lithium ion batteries.     

Improvement of cycle behaviour of SiO/C anode composite by thermochemically generated Li4SiO4 inert phase for lithium batteries

A new anode composite material is prepared by thermal treatment of a blend made of silicon monoxide (SiO) and lithium hydroxide (LiOH) at 550 °C followed by ball milling with graphite. X-ray diffraction pattern confirms the presence of Li₄SiO₄ in the thermally treated (SiO + LiOH) material. The electrode appears to be smooth and glassy as evident from observation with a scanning electron microscope (SEM), possibly due to the presence of nano-silicon and Li₄SiO₄ particles, and exhibits superior performance with a charge capacity of ∼333 mAh g⁻¹ at the 100th cycle with a low-capacity fade on cycling. Cyclic voltammograms of the electrode predict high power capability. On the other hand, the electrode comprising of only SiO and C prepared through ball milling, devoid of Li₄SiO_4, shows hard crust particulates in the electrode exhibiting low charge–discharge capacities with cycling.     

Lithium iron phosphate with high-rate capability synthesized through hydrothermal reaction in glucose solution

Carbon-coated lithium iron phosphate (LiFePO₄/C) was hydrothermally synthesized from commercial LiOH, FeSO₄ and H₃PO₄ as raw materials and glucose as carbon precursor in aqueous solution at 180 °C for 6 h followed by being fired at 750 °C for 6 h. The samples were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and constant current charge–discharge cycling test. The results show that the synthesized powders are in situ coated with carbon precursor produced from glucose. At ambient temperature (25 ± 2 °C), the specific discharge capacities are 154 mAh g⁻¹ at 0.2 C and 136 mAh g⁻¹ at 5 C rate, and the cycling capacity retention rate reaches 98% over 90 cycles. The excellent electrochemical performance can be correlated with the in situ formation of carbon precursor/carbon, thus leading to the even distribution of carbon and the enhancement of conductibility of individual grains.     

Effects of the addition of ZnO and Y2O3 on the electrochemical characteristics of a Ni(OH)2 electrode in nickel–metal hydride secondary batteries

This study examined the effects of the addition of ZnO and Y₂O₃ on the electrochemical characteristics of a Ni(OH)₂ electrode in nickel–metal hydride (Ni–MH) secondary batteries. The discharge capacity of the electrode was less affected by the addition of ZnO and Y₂O₃ at a 0.2 C-rate and 25 °C. However, the addition of Y₂O₃ deteriorated the discharge capacity and the cycle life of the electrode by increasing the charge transfer resistance of the electrode at an increased C-rate of 1 C and 25 °C. Under severer conditions at 1 C-rate and 60 °C, the electrode materials were separated from the current collector and, accordingly, the discharge capacity was abruptly degraded with cycling for the electrodes comprising only 4 wt% ZnO or 4 wt% Y₂O₃. In contrast, the electrodes containing both 2 wt% ZnO and 2 wt% Y₂O₃ exhibited stable discharge capacity with cycling and excellent cycle life due to the high overvoltage for oxygen evolution. The present results indicate that the addition of ZnO and Y₂O₃ with an optimum composition suppresses oxygen evolution in the interfaces between active materials and the current collector and improves the cycle life of the electrode.     

New manganese dioxides for lithium batteries

Lithium/manganese dioxide primary batteries use heat treated manganese dioxide (HEMD), a defect pyrolusite structure material as the cathode active material. Ion exchange of the structural protons in electrolytic manganese dioxide (EMD) with lithium before heating results in formation of a lithium containing γ-MnO₂. Increased lithium hydroxide concentration and increased temperature lead to increased lithium levels. At 80 °C with a combination of LiOH and LiBr, almost all of the structural protons in MnO₂ are replaced by lithium resulting in a γ-MnO₂ phase substantially free of protons and containing about 1.8% Li. This highly substituted lithium containing MnO₂ is reduced at between 3.5 and 1.8 V and has a capacity of 250 mAh g⁻¹. There are two reduction processes, one at 3.25 and the other at 2.9 V. TGA studies reveal two processes during heat treatment. Heating the lithium substituted MnO₂ to 350–400 °C results in a partially ordered HEMD-like MnO₂ (LiMD) phase with higher running voltage and superior discharge kinetics. Continued heating of the lithiated manganese dioxide to 450–480 °C under oxygen partial pressure can result in formation of a mixed phase containing both HEMD and a new, ordered MnO₂ phase (OMD). The intimately mixed HEMD/OMD composition has a discharge voltage near 2.9 V with a capacity about 220 mAh g⁻¹. Heating exhaustively lithiated MnO₂ to 350–400 °C results in formation of the partially ordered LiMD MnO₂ phase as with the previous partially lithium substituted MnO₂. Additional heating of the highly lithium substituted MnO₂ to 450–480 °C under oxygen results in formation of the new OMD phase in substantially pure form. Discharge of the new OMD phase shows it has a discharge capacity near 200 mAh g⁻¹ between 3.4 and 2.4 V versus lithium in a single, well-defined discharge process. OMD demonstrated good cycling against Li with no indication of formation of LiMn₂O₄ spinel after 80 deep discharge cycles.     

In situ high-resolution transmission electron microscopy synthesis observation of nanostructured carbon coated LiFePO4

In situ high-resolution transmission electron microscopy (HRTEM) studies of the structural transformations that occur during the synthesis of carbon-coated LiFePO₄ (C-LiFePO₄) and heat treatment to elevated temperatures were conducted in two different electron microscopes. Both microscopes have sample holders that are capable of heating up to 1500 °C, with one working under high vacuum and the other capable of operating with the sample surrounded by a low gaseous environment. The C-LiFePO₄ samples were prepared using three different compositions of precursor materials with Fe(0), Fe(II) or Fe(III), a Li-containing salt and a polyethylene-block-poly(ethylene glycol)-50% ethylene oxide or lactose. The in situ TEM studies suggest that low-cost Fe(0) and a low-cost carbon-containing compound such as lactose are very attractive precursors for mass production of C-LiFePO₄, and that 700 °C is the optimum synthesis temperature. At temperatures higher than 800 °C, LiFePO₄ has a tendency to decompose. The same in situ measurements have been made on particles without carbon coat. The results show that the homogeneous deposit of the carbon deposit at 700 °C is the result of the annealing that cures the disorder of the surface layer of bare LiFePO₄. Electrochemical tests supported the conclusion that the C-LiFePO₄ derived from Fe(0) is the most attractive for mass production.     

MoO2 synthesized by reduction of MoO3 with ethanol vapor as an anode material with good rate capability for the lithium ion battery

MoO₂ synthesized through reduction of MoO₃ with ethanol vapor at 400 °C was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Its electrochemical performance as an anode material for lithium ion battery was tested by cyclic voltammetry (CV) and capacity measurements. During the reduction process, the starting material (MoO₃) collapsed into nanoparticles (∼100 nm), on the nanoparticles remains a carbon layer from ethanol decomposition. Rate capacity and cycling performance of the as-prepared product is very satisfactory. It displays 318 mAh g⁻¹ in the initial charge process with capacity retention of 100% after 20 cycles in the range of 0.01–3.00 V vs. lithium metal at a current density of 5.0 mA cm⁻², and around 85% of the retrievable capacity is in the range of 1.00–2.00 V. This suggests the application of this type of MoO₂ as anode material in lithium ion batteries.     

Preparation of C-LiFePO4/polypyrrole lithium rechargeable cathode by consecutive potential steps electrodeposition

In this work carbon coated lithium iron phosphate (C-LiFePO₄)/polypyrrole (PPy) composite preparation has been carried out using electrochemical techniques. This composite has been deposited on a stainless steel mesh in order to use it as a cathode in a lithium-ion battery. When an oxidation potential is applied to the working electrode, the pyrrole monomer is polymerized and the C-LiFePO₄ particles are incorporated into the polymer matrix and bound to the polymer and mesh. An experimental procedure was performed in order to understand how the composite formation is carried out and what the oxidation state of the composite material is during the charge-discharge process. As the electrochemical method of synthesis has a big influence in the electrochemical properties of the polymer, the use of consecutive potential steps has been studied in order to improve the charge-storage capacity of the composite material. The influence on the final composite properties of the oxidation-deposition time and potential and the effect of the number of cycles has been analyzed. An improvement of about 20% has been achieved using short oxidation times (3 s) at 0.9 V vs. Ag/AgCl. The reasons for this improvement are discussed and analyzed using different experimental techniques.     

Electrochemical activity of Li2FeTiO4 and Li2MnTiO4 as potential active materials for Li ion batteries: A comparison with Li2NiTiO4

We demonstrate, for the first time, a considerable electrochemical activity of two members of lithium transition element titanates: Li₂FeTiO₄ and Li₂MnTiO₄. Both materials consist of 10–20 nm particles embedded in a conductive carbon coating. We show that not the coating but the small particle size is decisive for materials’ activity. Li₂FeTiO₄ shows a stable reversible capacity of up to 123 mA hg⁻¹ at C/20 and 60 °C which is 83% of the theoretical value for exchange of 1 electron (148 mA hg⁻¹). Li₂MnTiO₄ could only be prepared in a nanosized form that contained about 30% of impurities. The capacity of the whole material (including impurities) is comparable to that of Li₂FeTiO₄ but the cycling stability is much poorer. In contrast to the Fe and Mn analogues, the third member of the titanate family, Li₂NiTiO₄, shows a good electrochemistry even when the particle size is much larger (about 100 nm). During initial cycles at C/10 and 60 °C, exchange of more than 1 electron per compound formula has been observed. The cycling stability at high temperatures, however, is poor.     

Cycling and rate performance of Li-LiFePO4 cells in mixed FSI-TFSI room temperature ionic liquids

A study is conducted of the performance of lithium iron(II) phosphate, LiFePO₄, as a cathode material in a lithium secondary battery that features an ionic liquid electrolyte solution and a metallic lithium anode. The electrolyte solution comprises an ionic liquid of a N-methyl-N-alkyl-pyrrolidinium (alkyl = n-propyl or n-butyl) cation and either the bis(fluorosulfonyl)imide [(FSO₂)₂N⁻] or bis(trifluoromethanesulfonyl)imide [(F₃CSO₂)₂N⁻] anion, together with 0.5 mol kg⁻¹ of lithium bis(trifluoromethanesulfonyl)imide salt. For N-methyl-N-propyl-pyrrolidinium bis(fluorosulfonyl)imide, coin cells discharging at rates of C/10 and 4C yield specific capacities of 153 and 110 mAh g⁻¹, respectively, at an average coulombic efficiency of 99.8%. This performance is maintained for over 400 cycles at 50 °C and therefore indicates that these electrolyte solutions support long-term cycling of both LiFePO₄ and metallic lithium while, due to the negligible volatility of ionic liquids, surrounding the lithium in an inherently safe, non-flammable medium.     

New composite polymer electrolyte comprising mesoporous lithium aluminate nanosheets and PEO/LiClO4

Mesoporous materials, due to its potential for advanced applications in catalysis and nanoscience, have attracted much attention in the past decade. In this work, mesoporous lithium aluminate (next called MLA) nanosheets with high specific surface area were prepared by a hydrothermal method using hex-adecyltrimethyl ammonium bromide (CTAB) as the template. A novel PEO-based composite polymer electrolyte has been developed by using MLA powders as the filler. The electrochemical impedance showed that the conductivity was improved simultaneously. A high conductivity of 2.24 × 10⁻⁵ S cm⁻¹ at 25 °C was obtained. The lithium polymer battery using this novel composite polymer electrolyte and with lithium metal and LiFePO₄ employed as anode and cathode, respectively, showed high discharge capacity (more than 140 mAh g⁻¹ at 60 °C) and excellent cycling stability as revealed by galvanostastically charge/discharge cycling tests. The excellent electrochemical performances at low temperature of the cells were obtained, which was attributed to the high surface area and channels structure of the filler. The excellent properties of the solid-state lithium battery suggested that, PEO₁₆–LiClO₄–MLA composite polymer electrolyte can be used as a candidate material for lithium polymer batteries.     

High temperature solid oxide electrolysis cell employing porous structured (La0.75Sr0.25)0.95MnO3 with enhanced oxygen electrode performance

An efficient steam electrolysis process for hydrogen production via a solid oxide electrolysis cell using porous network-like strontium doped lanthanum manganite (LSM)-yttria stabilized zirconia (YSZ) as the oxygen electrode material has been demonstrated. The porous network-like LSM powder was prepared by a nitrate–glycine combustion method. Impedance spectra and voltage-current density curves were measured as a function of cell current density and absolute humidity at 800 °C and 900 °C to characterize the cell performance. The cell area specific resistance (ASR) was 0.26 Ω cm² at 900 °C with 0.5 A/cm² current density and 50% absolute humidity (AH). The hydrogen production rate calculated from the Faraday's law was 362 ml/cm² h at 900 °C with 80 vol.% AH. The cell performance results indicate that the porous network-like LSM–YSZ is a promising oxygen electrode for high temperature electrolysis cells.     

Novel electrospun poly(vinylidene fluoride-co-hexafluoropropylene)–in situ SiO2 composite membrane-based polymer electrolyte for lithium batteries

Composite membranes of poly(vinylidene fluoride-co-hexafluoropropylene) {P(VdF-HFP)} and different composition of silica have been prepared by electrospinning polymer solution containing in situ generated silica. These membranes are made up of fibers of 1–2 μm diameters. These fibers are stacked in layers to produce fully interconnected pores that results in high porosity. Polymer electrolytes were prepared by immobilizing 1 M LiPF₆ in ethylene carbonate (EC)/dimethyl carbonate (DMC) in the membranes. The composite membranes exhibit a high electrolyte uptake of 550–600%. The optimum electrochemical properties have been observed for the polymer electrolyte containing 6% in situ silica to show ionic conductivity of 8.06 mS cm⁻¹ at 20 °C, electrolyte retention ratio of 0.85, anodic stability up to 4.6 V versus Li/Li⁺, and a good compatibility with lithium metal resulting in low interfacial resistance. A first cycle specific capacity of 170 mAh g⁻¹ was obtained when the polymer electrolyte was evaluated in a Li/lithium iron phosphate (LiFePO₄) cell at 0.1 C-rate at 25 °C, corresponding to 100% utilization of the cathode material. The properties of composite membrane prepared with in situ silica were observed to be comparatively better than the one prepared by direct addition of silica.     

Synthesis and characterization of three-dimensional carbon foams-LiFePO4 composites

The characterization of three-dimensional (3D) carbon foams coated with olivine structured lithium iron phosphate is reported for the first time. The LiFePO₄ as cathode material for lithium ion batteries was prepared by a Pechini-assisted reversed polyol process. The coating has been successfully performed on commercially available 3D-carbon foams by soaking in aqueous solution containing lithium, iron salts and phosphates at 70 °C for 2-4 h. After drying-out, the composites were annealed at different temperatures in the range 600-700 °C for 15-20 min under nitrogen. The formation of the olivine-like structured LiFePO₄ was confirmed by X-ray diffraction analysis performed on the powder prepared under similar conditions. The surface investigation of the prepared composites showed the formation of a homogeneous coating by LiFePO₄ on the foams. The cyclic voltammetry curves of the composites show an enhancement of electrode reaction reversibility by decreasing the annealing temperature. The electrochemical measurements on the composites showed good performances delivering a discharge specific capacity of 85 mAh g⁻¹ at a discharging rate of C/25 at room temperature.     

Surface modification of LiNi0.5Mn1.5O4 by ZrP2O7 and ZrO2 for lithium-ion batteries

The spinel LiNi_0.5Mn_1.5O₄ has been surface modified separately with 1.0 wt.% ZrO₂ and ZrP₂O₇ for the purpose of improving its cycle performance as a cathode in a 5-V lithium-ion cell. Although the modifications did not change the crystallographic structure of the surface-modified samples, they exhibited better cyclability at elevated temperature (55 °C) compared with pristine LiNi_0.5Mn_1.5O₄. The material that was surface modified with ZrO₂ gave the best cycling performance, only 4% loss of capacity after 150 cycles at 55 °C. Electrochemical impedance spectroscopy demonstrated that the improved performance of the ZrO₂-surface-modified LiNi_0.5Mn_1.5O₄ is due to a small decrease in the charge transfer resistance, indicating limited surface reactivity during cycling. Differential scanning calorimetry showed that the ZrO₂-modified LiNi_0.5Mn_1.5O₄ exhibits lower heat generation and higher onset reaction temperature compared to the pristine material. The excellent cycling and safety performance of the ZrO₂-modified LiNi_0.5Mn_1.5O₄ electrode was found to be due to the protective effect of homogeneous ZrO₂ nano-particles that form on the LiNi_0.5Mn_1.5O₄, as shown by transmission electron microscopy.     

Chromium doping as a new approach to improve the cycling performance at high temperature of 5 V LiNi0.5Mn1.5O4-based positive electrode

LiCr_2YNi_0.5−YMn_1.5−YO₄ (0 < Y ≤ 0.2) spinels have been synthesized by a sucrose-aided combustion method. Two sets of Cr-doped samples have been obtained by heating the “as-prepared” samples at 700 and 900 °C for 1 h. X-ray diffraction and thermogravimetric data show that pure and single phase spinels with similar lattice parameter have been synthesized. The homogeneity and the sub-micrometric particle size of the spinels have been shown by SEM and TEM. The main effect of the temperature is to increase the particle size from ≈50 to ≈500 nm, on heating from 700 to 900 °C. The study of the influence of Cr-dopant content and thermal treatment on the electrochemical properties at 25 °C and at 55 °C has been carried out by galvanostatic cycling in Li-cells. The discharge capacity (≈130 mAh g⁻¹) does not noticeably change with the synthesis conditions; but the cycling performances are strongly modified. Key factors that control the cycling performances have been determined. The most highlighted result is that spinels heated at 900 °C with Y ≤ 0.1 have very high capacity retention at 55 °C (>96% after 40 cycles, cyclability >99.9% by cycle) indicating that metal doping is a new approach to prepare 5 V LiNi_0.5Mn_1.5O₅-based cathodes with excellent cycling performances at high temperature.     

Effects of TiO2 coating on high-temperature cycle performance of LiFePO4-based lithium-ion batteries

LiFePO₄ particles were coated with TiO₂ (molar ratio = 3%) via a sol–gel process, and the effects of the coating on cycle performance of LiFePO₄ cathode at 55 °C against either a Li or a C (mesocarbon microbead) anode were investigated. It was found that, while the coating reduces capacity fading of the LiFePO₄/Li cell, it imposes a deteriorating effect on the LiFePO₄/C cell. Analyses on cell impedance and electrode surface morphology and composition showed that the oxide coating reduced Fe dissolution from the LiFePO₄ cathode and hence alleviated the impedance increase associated with the erosion process. This leads to reduced capacity fading as observed for the LiFePO₄/Li cell. However, the oxide coating itself was eroded upon cycling, and the dissolved Ti ions were subsequently reduced at the anode surface. Ti deposit on the C anode was found to be more active than Fe in catalyzing the formation of the solid-electrolyte interphase (SEI) layer, causing accelerated capacity decay for the LiFePO₄/C cell. The results point out the importance of evaluating the effect of cathode coating material on the anode side, which has generally been overlooked in the past studies.     

Low-temperature study of lithium-ion cells using a LiySn micro-reference electrode

Lithium-ion batteries are considered to be the next battery system for hybrid electric vehicles (HEVs) due to their high power density. However, their power is severely limited at −30 °C and the concern exists that lithium metal could plate on the negative electrode during regen (charge) pulses. The goal of this work is to determine the reason for this poor low-temperature performance using an in situ Li_ySn micro reference electrode (RE) over a wide temperature range of 30 °C to −30 °C. A variety of negative and positive electrode materials with unique morphologies was used in this work to help elucidate the dominant low-temperature mechanism. In this work, it was observed that the potential of graphite negative electrodes does dip below lithium potentials not only during charge pulses, but also under normal charging if the cell cutoff voltage is not reduced from its room-temperature setting of 4.1 V, whereas hard carbon electrodes do not because they operate further from lithium potential. The most surprising finding from this work was that a second impedance mechanism dominates below 0 °C that affects the positive and negative electrodes almost equally. This suggests that the responsible phenomenon is independent of the active material and is most likely a pure electrolyte-interface effect.     

Enhanced high rate performance of LiMn2O4 spinel nanoparticles synthesized by a hard-template route

A nanosized LiMn₂O₄ (nano-LiMn₂O₄) spinel was prepared by a novel route using a porous silica gel as a sacrificial hard template. This material was found to be made up of 8–20 nm nanoparticles with a mean crystallite size of 15 nm. The electrochemical properties of nano-LiMn₂O₄ were tested in lithium cells at different cycling rates and compared to those of microsized LiMn₂O₄ (micro-LiMn₂O₄) obtained by the classical solid state route. Microsized LiMn₂O₄ is formed by 3–20 μm agglomerates, the size of each individual particle being approximately 0.20 μm. The behaviour of nano-LiMn₂O₄ as a positive electrode improves with increasing current densities (from C/20 to 2C). Moreover, it was found to exhibit a noticeably better performance at high rates (2C), with higher initial capacity values and very good retention (only 2% loss after 30 cycles), with respect to micro-LiMn₂O₄, almost certainly due to enhanced lithium diffusion in the small particles.     

Removal of NOx by microwave reactor with ammonium bicarbonate and Ga-A zeolites at low temperature

Microwave reactor with the mixture of ammonium bicarbonate (NH₄HCO₃) and Ga-A zeolites was set up to study the removal of nitrogen oxides (NO_x) from waste gas with excess oxygen concentration (14–19%) at low temperature (80–120 °C). The results showed that the microwave reactor filled with NH₄HCO₃ and Ga-A zeolites could reduce NO_x to nitrogen with the best purifying efficiency of 95.45% and the best denitrification amount of 89.28 mg h⁻¹. The optimal microwave power and residence time (RT) on denitrification was 259–280 W and 0.259 s, respectively. Microwave denitrification effect of the experiment using ammonium bicarbonate and Ga-A zeolites was much higher than that using ammonium bicarbonate or Ga-A zeolites only. The mechanism for microwave-induced NO_x reduction can be explained as the microwave-induced catalytic reaction between NO_x and ammonium bicarbonate with Ga-A zeolites being the catalyst and microwave absorbent.