Galvanostatic Cycling Experiments Research Articles

Electrochemical investigation of LiMn 2O 4 cathodes in gel electrolyte at various temperatures

A composite lithium battery electrode of LiMn 2O 4 in combination with a gel electrolyte (1 M LiBF 4/24 wt% PMMA/1:1 EC:DEC) has been investigated by galvanostatic cycling experiments and electrochemical impedance spectroscopy (EIS) at various temperatures, i.e. −3< T<56 °C. For analysis of EIS data, a mathematical model taking into account local kinetics and potential distribution in the liquid phase within the porous electrode structure was used. Reasonable values of the double-layer capacitance, the exchange-current density and the solid phase diffusion were found as a function of temperature. The apparent activation energy of the charge-transfer (∼65 kJ mol −1), the solid phase transfer (∼45 kJ mol −1) and of the ionic bulk and effective conductance in the gel phase (∼34 kJ mol −1), respectively, were also determined. The kinetic results related to ambient temperature were compared to those obtained in the corresponding liquid electrolyte. The incorporated PMMA was found to reduce the ionic conductivity of the free electrolyte, and it was concluded that the presence of 24 wt% PMMA does not have a significant influence on the kinetic properties of LiMn 2O 4.

Lithium-ion conductors of the system LiCo 1− xFe xO 2: a first electrochemical investigation

LiCo 1− x Fe x O 2 compounds (0≤ x≤ 1) with ordered rock salt structure of α-NaFeO 2 type were prepared by ion exchange reaction in a molten eutectic mixture from the corresponding Na compounds. The Li compounds are investigated by galvanostatic and potentiostatic cycling experiments. The new form, ion-exchanged LiCoO 2 (IE-LiCoO 2), is compared in its electrochemical behaviour with the known high temperature HT-LiCoO 2. A different behaviour at cycling up to 4.8 V versus Li/Li + is evidenced. Galvanostatic and potentiostatic cycling experiments were also carried out on the iron-containing compounds. Charge voltage increases and electrochemical capacity decreases with increasing iron content and reaches a low value for LiFeO 2 with an iron content of x=0.6. Reasons that may account for this behaviour are discussed.

Electrochemical proton insertion in manganese spinel oxides from aqueous borate solution

We report the proton insertion in LiMn 2O 4 and Li 0.32Mn 2O 4 compounds with the spinel structure in borate buffer at pH 9.5. LiMn 2O 4 exhibits a quasi-voltage plateau near −0.2 V and a second one around −0.35 V/Hg/HgO. The charge process results in a single step in the voltage range 0.1/0.8 V. This first cycle leads to new electrochemical features for the subsequent cycles with a reversible behavior and S shaped discharge–charge curves (mean discharge potential=+0.1 V) in the voltage window 0.75/−0.5 V. The proton uptake involved during insertion corresponds to a faradaic yield of 0.45 F/Mn. This new system can be observed from the first cycle when H + insertion directly proceeds in the chemically delithiated oxide Li 0.32Mn 2O 4. In both cases, galvanostatic cycling experiments (C/25 rate) show a stable specific capacity of 100–110 Ah kg −1 is available near 0.1 V over 20 cycles.

Electrochemistry of Chemically Lithiated NaV3 O 8: A Positive Electrode Material for Use in Rechargeable Lithium‐Ion Batteries

Monoclinic was prepared via aqueous precipitation and subsequently chemically lithiated using butyllithium in hexane as lithiation reagent. The topochemical lithiation process leads to materials with variable lithium content depending on the lithiation reaction conditions. Up to could be inserted chemically in the lattice water‐free and result in cleavage of the particles, which leads to highly dispersed materials. In contrast to the chemical insertion method, almost could be electrochemically inserted in , corresponding to a specific charge of about 310 mAh g−1 About could be deinserted potentiodynamically in the potential range from 1.5 to 4.0V vs from a chemically lithiated material with the composition . This corresponds to a specific charge of about 215 mAh g−1 In galvanostatic cycling experiments, a specific charge of more than 200 mAh g−1 could be demonstrated for 100 cycles using this electrode material. The specific charges obtained are independent of the applied specific current up to 50 mA g−1 of the oxide. This behavior indicates that the sodium vanadate host material can support high lithium insertion and deinsertion rates, which make the chemically lithiated form an attractive candidate for lithium‐containing positive electrode materials in high‐power lithium‐ion batteries.

Novel layered chalcogenides as electrode materials for lithium-ion batteries

Misfit layer compounds of general formula (PbS) 1 + δ (TS 2) 2 (T = Ti, Ta) are evaluated as the alternative intercalation electrodes versus lithium metal and in lithium-ion cells versus LiCoO 2 and Li 7Ti 5O 12 electrodes. Galvanostatic cycling experiments of lithium anode cells showed an excellent capacity retention, particularly for the (PbS) 1.14(TaS 2) 2 composition. The potential stability range of the intercalation compounds of the sulfides (1.5–3.5 V) allows the use of these materials as the positive electrode versus Li 7Ti 5O 12 or as the negative electrode versus the 4 V cathode LiCoO 2. The use of titanium oxide anodes requires a previous in situ electrochemical lithiation of Li 4Ti 5O 12 in a three-electrode assembly. Average cell voltages of about 1.0 V were then obtained. The use of LiCoO 2 cathodes allows higher cell voltages (1.3–3.0 V) and capacity retentions during the first 50 cycles up to 80%.

Electrochemical properties of a new non-stoichiometric spinel oxide (Mn 2.5O 4) as Li insertion compound

Preliminary results on electrochemical and structural properties of the cation deficient oxide Mn 2.5O 4 system are discussed in terms of its viability as an electrode for rechargeable lithium batteries. Chronopotentiometric measurements show two well-defined steps in the potential range of 3.5 V-2.0 V and 2.0 V-1.5 V, involving faradaic yields of ≈ 0.6 and ≈ 1.0 F mol −1 respectively. A loss of structural integrity was observed for Li ion contents higher than 0.65 per mol. Galvanostatic cycling experiments were performed in the voltage range 4.0-2.0 V and a specific capacity of 43 mAh g −1 was obtained after the twentieth cycle.

New tin-containing spinel sulfide electrodes for ambient temperature rocking chair cells

Spinel compounds with Cu 2CoSn 2S 8 and CuCoSn 3S 8 stoichiometries were evaluated as the active electrode materials in lithium anode and ‘rocking chair’-type cells. For lithium cells using CuCoSn 3S 8 cathodes, the current-composition curves obtained by step potential electrochemical spectroscopy revealed a first Co 111/Co 11 reduction peak during cell discharge at about 1 F mol −1, which is not observed for the Cu 2CoSn 3S 8 composition. Lithium-ion diffusion coefficients were also larger in this interval. The galvanostatic cycling behaviour in the 2–2.5 V potential window leads to little capacity losses after the first cycle when using CuCoSn 3S 8 electrodes. Three electrodes sulfide/ LiClO 4 (PC)/LiCoO 2 rocking chair cells using lithium auxiliary electrode were examined by galvanostatic cycling experiments. When the cells are cycled in the 1.5–2.5 V interval, cell capacity (15 mAh g −1) remains basically unaffected between the second and tenth cycles. The presence of Sn IV ions in these solids which are suitable for reduction at lower voltages may be of interest as overdischarge protection.

Low temperature molybdenum oxide as host lattice for lithium intercalation

The heat treatment of molybdenum oxide dihydrate resulting from the acidification of Na 2MoO 4 solution leads to various molybdenum trioxides MoO 3. Electrochemical Li insertion into these compounds varies depending on the temperature required for drying the MoO 3 · 2H 2O (250,400 and 500 °C). The lower the temperature of the heat treatment, the better is the electrochemical performance. The lowest temperature 250 °C induced the formation of a long-range disordered oxide characterized by a high surface area exhibiting the best performance both in terms of specific capacity (≈ 2F/MoO 3) and cycling efficiency, which were found to be significantly higher than that usually obtained for the conventional crystalline or amorphous MoO 3 or for the heat-treated form at 500 °C (≈ 1.5F/MoO 3). For example, when galvanostatic cycling experiments are performed at a C/10 discharge-charge rate within cycling limits 3.8/2 V, ∼ 300 Ah kg −1 oxide were still recovered after 10 cycles.

A Semiconductor Model for the Cathodic Passivation of Lead Dioxide

The cathodic passivation of lead dioxide electrode leads to a strong decrease of discharge capacity of the lead acid accumulator with increasing rate of discharge. The same effect is found with electrodes on graphite‐filled polypropylene in lead dissolving electrolytes on the basis of or . Galvanostatic cycling experiments with those electrodes and SEM results strongly suggest the presence of a layer on top of the electrode. The thickness of the layer varies with density and direction of the current and is in the order of 1 μm. A new model is proposed in which a poorly semiconducting layer is contacted with the metal conductor. A Schottky barrier is established upon negative polarization of the contact. The voltage drop in the layer depends strongly on its thickness and on the discharge current density . It was possible to derive Peukert's equationon the basis of this model . The experimental for in lead dissolving electrolytes satisfy this equation. Deviations at low C.D. are due to the anodic oxidation of the graphite base electrode. In the case of the electrode, this effect should be considered in addition to transport kinetics in the pores.