Li-ion Secondary Batteries Research Articles

Electrochemical Properties of Foliated Graphite / Titanate Nanosheets Composites as an Anode Material for Li-ion Secondary Batteries

A novel anode material was prepared by a co-restacking of foliated graphite and titanate nanosheets. Foliated graphite / titanate nanosheets composites with 63wt% of foliated graphite exhibited a charge capacity of 820 mAh/g at the 20th cycle at a current density of 100 mA/g. Even at a high current density of 2000 mA/g, the composites retained 43% of the charge capacity at a current density of 100 mA/g. Foliated graphite / titanate nanosheets composites exhibited both a good cycling durability with a high specific capacity and a high-rate capability.

Characterization and Electrochemical Properties of Li2Cu0.5Ni0.4M0.1O2 Lithium-ion Battery Cathodes

Doped lithium copper-nickel mixed-metal oxides are prepared and studied as cathode materials for secondary Li-ion batteries. The compounds, Li2Cu0.5Ni0.4M0.1O2 (where M = Al, Ga), are made using solid state and micro-emulsion synthesis techniques. All compounds have a body-centered orthorhombic (Immm) crystal structure. The undoped compound has an initial discharge capacity of 270 mAh/g but exhibits poor capacity retention with cycling. The Al- and Ga-doped compounds made by solid-state synthesis have a higher discharge capacity than those made by micro-emulsion. Micro-emulsion processed compounds exhibit better cycleability and capacity retention upon charge/discharge suggesting a more stable crystal structure. Gallium doping improved the structural stability resulting in lowered irreversible capacity loss. Two reversible reaction mechanisms, lithium intercalation/de-intercalation and a displacement reaction are suggested to occur in the Li2Cu0.5Ni0.4M0.1O2 system.

Li diffusion properties of mixed conductingTiO2-Bnanowires

${\text{Li}}_{x}{\text{TiO}}_{2}\text{-B}$ nanowires $(0lx\ensuremath{\le}0.9)$ are considered to act as promising anode materials in secondary Li-ion batteries. Li self-diffusion parameters in mixed conducting nanowires of the composition ${\text{Li}}_{0.3}{\text{TiO}}_{2}$ are directly determined by mixing time $({t}_{m})$-dependent two-time $^{7}\text{L}\text{i}$ spin-alignment echo (SAE) nuclear-magnetic-resonance (NMR) correlation spectroscopy between 330 and 500 K. SAE NMR reveals extremely slow Li self-diffusion processes in ${\text{Li}}_{x}{\text{TiO}}_{2}\text{-B}$. Li jump rates ${\ensuremath{\tau}}^{\ensuremath{-}1}$ range from 5 to $2.5\ifmmode\times\else\texttimes\fi{}{10}^{3}\text{ }{\text{s}}^{\ensuremath{-}1}$. The corresponding hopping correlation functions ${F}_{2}$ can be well parametrized with stretched exponentials, ${F}_{2}\ensuremath{\propto}\text{exp}[\ensuremath{-}{(t/{t}_{m})}^{\ensuremath{\gamma}}]$, with an exponent $\ensuremath{\gamma}=0.35(2)$ being independent of temperature. The influence of spin-diffusion effects on the echo amplitude is elaborated by evolution time-dependent $^{7}\text{L}\text{i}$ SAE-NMR experiments. The results are compared with those obtained by conventional $^{7}\text{L}\text{i}$ NMR spin-lattice relaxation measurements.

Novel low temperature approaches for the eco-efficient synthesis of electrode materials for secondary Li-ion batteries

Abstract Hydrothermal/solvothermal reactions have been widely used over the years for the low temperature synthesis of inorganic compounds. New twists on such synthesis approaches were developed so as to prepare highly performing phosphate or silicate electrode materials at low cost. Herein we review the use of: (1) “Latent bases” to wisely monitor the reaction and (2) ionic liquids rather than water as reaction media to conduct the solvothermal process. The richness and versatility of such approaches towards the elaboration of a wide class of materials having controlled size and shape is highlighted. Ionothermal synthesis is shown to hold great promises for innovative inorganic synthesis.

High rate capability of carbonaceous composites as anode electrodes for lithium-ion secondary battery

Anode materials with high rate capability for Li-ion secondary batteries were investigated by using the mixture of graphite, cokes, and petroleum pitch. Since obvious potential plateaus were obtained at graphite contents above 40 wt.%, which would cause difficulties in perceiving the capacity variations as a function of electrical potential, the graphite content were determined at 20–30 wt.%. The composites with a given content of graphite and remaining content of petroleum pitch/cokes mixtures at 1:4, 1:1, and 4:1 mass ratios were heated at a temperature range of 800–1200 °C. For a given composition of carbonaceous composite, the discharge rate capability improved but the reversible capacity decreased with increasing the heat treatment temperature. Although the reversible capacity increased with increasing content of the petroleum pitch for given graphite content and heat treatment temperature, the discharge rate capability decreased. The carbonaceous composites prepared by the mixture of 30 wt.% graphite and 70 wt.% petroleum pitch/cokes mixture at 1:4 mass ratio with the heat treatment at 800 °C showed relatively high electrochemical properties, of which reversible capacity, initial efficiency, discharge rate capability (retention of discharge capacity in 5 C/0.2 C) and charge capacity at 5 C were 312 mAh/g, 79%, 89% and 78 mAh/g, respectively.

Performance of Li-ion secondary batteries in low power, hybrid power supplies

Small, portable electronic devices need power supplies that have long life, high energy efficiency, high energy density, and can deliver short power bursts. Hybrid power sources that combine a high energy density fuel cell, or an energy scavenging device, with a high power secondary battery are of interest in sensors and wireless devices. However, fuel cells with low self-discharge have low power density and have a poor response to transient loads. A low capacity secondary lithium ion cell can provide short burst power needed in a hybrid fuel cell–battery power supply. This paper describes the polarization, cycling, and self-discharge of commercial lithium ion batteries as they would be used in the small, hybrid power source. The performance of 10 Li-ion variations, including organic electrolytes with Li x V 2O 5 and Li x Mn 2O 4 cathodes and LiPON electrolyte with a LiCoO 2 cathode was evaluated. Electrochemical characterization shows that the vanadium oxide cathode cells perform better than their manganese oxide counterparts in every category. The vanadium oxide cells also show better cycling performance under shallow discharge conditions than LiPON cells at a given current. However, the LiPON cells show significantly lower energy loss due to polarization and self-discharge losses than the vanadium and manganese cells with organic electrolytes.

Power system design of ESMO

The European Student Moon Orbiter (ESMO) spacecraft is a student-built mini satellite being designed for a mission to the Moon. Designing and launching mini satellites are becoming a current trend in the space sector since they provide an economic way to perform innovative scientific experiments and in-flight demonstration of novel space technologies. The generation, storage, control, and distribution of the electrical power in a mini satellite represents unique challenges to the power engineer since the mass and volume restrictions are very stringent. Regardless of these problems, every subsystem and payload equipment must be operated within their specified voltage band whenever they required to be turned on. This paper presents the preliminary design of a lightweight, compact, and reliable power system for ESMO that can generate 720 W. Some of the key components of the EPS include ultra triple-junction (UTJ) GaAs solar cells controlled by maximum power point trackers, and high efficiency Li-ion secondary batteries recharged in parallel.

Combustion synthesis of high-performance Li 4Ti 5O 12 for secondary Li-ion battery

Spinel Li 4Ti 5O 12 was synthesized by a simple glycine-nitrate auto-combustion by applying aqueous medium and constricting the reactions in the pores of cellulose fibers. The products from the auto-combustion and further calcination at various temperatures were characterized by XRD, SEM, BET surface area and TEM examinations. Pure phase and well-crystallized nano-Li 4Ti 5O 12 oxides were obtained at a calcination temperature of 700 °C or higher. The 700 °C calcined one shows the best and high electrochemical performance, which reached a capacity of ∼125 mAh/g at 10 C discharge rate with fairly stable cycling performance even at 40 °C. Electrochemical impedance spectroscopy tests demonstrated that the surface reaction kinetics of Li 4Ti 5O 12 was improved significantly with the increase of its electronic conductivity.

Small polaron transport in Li 7MnN 4 containing isolated MnN 4 tetrahedra

The electrical transport properties related to the Mn 3d-band in Li 7MnN 4, which has been considered as an electrode material of Li ion secondary battery, are studied by combining with the optical absorption and electron paramagnetic resonance (EPR). The optical absorption studies show that the empty Mn 3d-band attributed to isolated MnN 4 tetrahedra in Li 7MnN 4 lies at about 1.15 eV above the top of the valence band. An EPR signal with g -value = 1.9848 is observed at 77 K, suggesting the presence of Mn 5+ in the isolated MnN 4 tetrahedra like that in Li 3MnO 4. The temperature dependence of electrical resistivity shows the hopping conduction with the activation energy of 112 meV at higher temperature above 180 K and the tunneling conduction at lower temperature below 60 K, suggesting the small polaron motion in the Mn-3d band as predicted by Holstein.

Electrochemical Properties of Graphene Sheets / Titanate Nanosheets Composites as an Anode Material for Li-ion Secondary Batteries

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Metallic and semiconducting single-walled carbon nanotubes as the anode material of Li ion secondary battery

In order to elucidate the elctrochemical Li ion storage properties of metallic and semiconducting single-walled carbon nanotubes (SWCNTs), we have attempted several methods to obtain the sufficient amount of the two kinds of SWCNTs for the use of the electrochemical measurements. It was found by the electrochemical charge–discharge measurements that the reversible Li ion storage capacity of the metallic SWCNTs is about 5 times greater than that of the semiconducting SWCNTs.

Electrochemical properties of Si/LiTi2O4 nanocomposite as anode materials for Li-ion secondary batteries

Si/LiTi2O4 nanocomposite film was synthesized by a sol–gel method in combination with a following heat-treatment process. Through this process, the nanosized Si particles were homogeneously distributed in the porous composite. The electrochemically less active LiTi2O4 working as a buffer matrix successfully prevented Si from cracking/crumbling during the charging/discharging process. The Si/LiTi2O4 nanocomposite exhibited a reversible lithium storage capacity of about 1100mAhg−1 with good cyclability, suggesting its promising nature in anode materials for Li ion batteries. A two-parallel diffusion path model fitted well with the impedance data of porous Si/LiTi2O4 composite at different potentials. The impedance in the low-frequency region was directly related to the diffusion of Li ions, and the Li ion diffusivity was on the order of 10−13cm2s−1 based on the semi-infinite diffusion model.

High-rate characteristics of novel anode Li 4Ti 5O 12/polyacene materials for Li-ion secondary batteries

In recent years, spinel lithium titanate (Li 4Ti 5O 12) as a superior anode material for energy storage battery has attracted a great deal of attention because of the excellent Li-ion insertion and extraction reversibility. However, the high-rate characteristics of this material should be improved if it is used as an active material in large batteries. One effective way to achieve this is to prepare electrode materials coated with carbon. A Li 4Ti 5O 12/polyacene (PAS) composite were first prepared via an in situ carbonization of phenol–formaldehyde (PF) resin route to form carbon-based composite. The SEM showed that the Li 4Ti 5O 12 particles in the composite were more rounded and smaller than the pristine one. The PAS was uniformly dispersed between the Li 4Ti 5O 12 particles, which improved the electrical contact between the corresponding Li 4Ti 5O 12 particles, and hence the electronic conductivity of composite material. The electronic conductivity of Li 4Ti 5O 12/PAS composite is 10 −1 S cm −1, which is much higher than 10 −9 S cm −1 of the pristine Li 4Ti 5O 12. High specific capacity, especially better high-rate performance was achieved with this Li 4Ti 5O 12/PAS electrode material. The initial specific capacity of the sample is 144 mAh/g at 3 C, and it is still 126.2 mAh/g after 200 cycles. By increasing the current density, the sample still maintains excellent cycle performance.

Si–Cu/carbon composites with a core–shell structure for Li-ion secondary battery

Si–Cu/carbon composites with a carbon core and a Si–Cu composite shell have been synthesized by two-step mechanical fusion process. Large amount of pores around composite particles as well as the bridging disordered carbon layer between Si–Cu composite and carbon was the structural advantage of Si–Cu/carbon composite, which could prevent the electrochemical degradation induced by enormous volume changes during Li + insertion or extraction. With these structural characteristics, the cyclic property of Si–Cu/carbon composite was greatly improved compared to Si. A phase-controlled shell (Si–Cu composite) acted as another advantage for this Si–Cu/carbon composite, as it rendered not only good ductility for accommodating the volume expansion, but also enhanced kinetics.

Vanadium diphosphides as negative electrodes for secondary Li-ion batteries

We report on the Li electrochemical reactivity of amorphous and crystalline VP 2, synthesized by ball-milling and by 600 °C heat treatment of a ball-milled sample, respectively. The amorphous sample can reversibly react with 3.5 Li per formula unit as compared to solely 2.5 for the crystalline one. However in both cases there is a rapid capacity decay upon cycling that is more pronounced in the case of the crystalline sample. Complementary X-rays, HTREM and NMR tend to show that the Li reactivity mechanism differs from the classical conversion reactions since neither V nanoparticles nor the formation of Li 3P were detected, as opposed to some of the other MP 2 compounds (M = Ni or Cu). Besides structural phase variations within the 3d metal-based binary phosphide series, the possibility of a change in the nature of the redox centre upon lithiation from cation (M) to anion (P) is evoked.

Fabrication of solid thin film electrolyte and LiCoO 2 by aerosol flame pyrolysis deposition

Aerosol flame pyrolysis deposition method was applied to deposit the oxide glass electrolyte film and LiCoO 2 cathode for thin film type Li-ion secondary battery. The thicknesses of as-deposited porous LiCoO 2 and Li 2O–B 2O 3–P 2O 5 electrolyte film were about 6 μm and 15 μm, respectively. The deposited LiCoO 2 was sintered for 2 min at 700 °C to make partially densified cathode layer, and the deposited Li 2O–P 2O 5–B 2O 3 glass film completely densified by the sintering at 700 °C for 1 h. After solid state sintering process the thicknesses were reduced to approximately 4 μm and 6 μm, respectively. The cathode and electrolyte layers were deposited by continuous deposition process and integrated into a layer by co-sintering. It was demonstrated that Aerosol flame deposition is one of the good candidates for the fabrication of thin film battery.

Mesocarbon microbeads heat-treated at low temperature in presence of CoCl 2 as the anode material of a Li-ion battery

Anode materials for Li-ion secondary batteries were prepared by treating mesocarbon microbeads (MCMBs) in presence of CoCl2 at a temperature below 1000℃. They were characterized by Raman spectroscopy and X-ray diffraction. Results indicated that the heat treated samples belonged to low temperature carbons, but micro-crystals on the surface of the treated MCMBs became ordered. The reversible discharge capacity of the MCMBs was significantly improved, the coulombic efficiency was increased from 52.2% to 86.7%, and the cycling performance became better. These improvements were ascribed to the ordered structure on the surface of the treated samples that tended to prevent the electrolyte molecules from penetrating into the inside of the MCMBs, and as a result, reduced the irreversible electrochemical reactions.

Atomic force microscopy study of surface morphology change in spinel LiMn 2O 4: Possibility of direct observation of Jahn–Teller instability

Surface morphology in 3.5 × 3.5 μm 2 area of spinel LiMn 2O 4, which is a typical cathode material for Li ion secondary batteries, is studied using an atomic force microscopy (AFM) with a conductive probe. Negative bias voltage is applied to the probe to attract Li + ions toward LiMn 2O 4 surface during the AFM observation. Before applying the voltage (0 V), the whole LiMn 2O 4 surface is covered with scale-shaped grains. Under the negative voltage of 5.5 V, electric current abruptly increases, indicating Li + ionic conduction. Simultaneously, part of the scale-shaped grains expand and flatten. Jahn–Teller phase transition, which is induced by the repulsive interaction between the Mn-e g and O-2p electrons in Li accumulated layer, is proposed as a possible origin of these results.

Synthesis of Well-Crystallized Manganese Oxide from Precipitation: Effect of Introducing Carbonate Anions

Powdery hausmannite (Mn3O4) is of interest in many industrial and technological applications. It is widely used as reactive catalysts, raw material of humidity sensors, and the cathode oxides of Li-ion secondary batteries. In this study, sub-micron and nano-meter sized Mn3O4 powders are prepared by an efficient method at room temperature. Mn(OH)2 nanocrystalsare commonly precipitated at first and then oxidized in the alkaline solution containing excess OH- anions. However, conventionally prepared Mn3O4 powders by the above process are ill-crystallized. To enhance the crystallinity of fabricated powders, CO3 2- anions are introduced into the process. The modified autoxidation method is practical to fabricate low-cost and high grade powders of Mn3O4. Advantages of the modified method are confirmed by both the electron micrographs and XRD patterns of synthesized powders. It is revealed that particle size of the products is in the sub-micron meter range, and the particle morphology can be adjusted by altering the precipitation sequence.

Effect of bivalent metal element doping on the electronic transport properties of LiCoO2

In order to understand the different effects of Ca and Mg doping on the electronic transport properties of LiCoO2，which is the primary cathode material in Li-ion secondary batteries，the electronic structures of the relevant systems are studied with the ab initio method based on the density-functional theory. It is found that both Ca and Mg partial substitution for Co in LiCoO2 crystal will give rise to partially occupied acceptor band near the Fermi level，but these bands are substantially localized. Moreover，Ca-doped system has a clear energy gap between the acceptor band and the valence band，whereas for the Mg-doped system there isn't such a gap. It's believed that the existence of this gap is the main factor resulting in the non-significant increase of the electronic conductivity in the Ca-doped LiCoO2. In addition，the remarkable distinction in the ionic radii of Ca2+ and Mg2+ can also induce noticeably different effects on the electronic conductivities.