Matériaux d'électrode positive à charpente polyanionique pour batteries au lithium (approches cristallochimiques et électrochimiques)

AMIENS-BU Sciences (800212103) / SudocSudocFranceF

Lithium insertion chemistry of some iron vanadates

Lithium insertion into various iron vanadates has been investigated. Fe2V4O13 and Fe4(V2O7)3 · 3H2O have discharge capacities approaching 200 mAh g−1 above 2.0 V vs. Li+/Li. Although the potential profiles change significantly between the first and subsequent discharges, capacity retention is unexpectedly good. Other phases, structurally related to FeVO4, containing copper and/or sodium ions were also studied. One of these, β-Cu3Fe4(VO4)6, reversibly consumes almost 10 moles of electrons per formula unit (ca. 240 mAh g−1) between 3.6 and 2.0 V vs. Li+/Li, in a non-classical insertion process. It is proposed that both copper and vanadium are electrochemically active, whereas iron(III) reacts to form LiFeIIIO2. The capacity of the Cu3Fe4(VO4)6/Li system is nearly independent of cycling rate, stabilizing after a few cycles at 120–140 mAh g−1. Iron vanadates exhibit better capacities than their phosphate analogues, whereas the latter display more constant discharge potentials. Keywords: Lithium batteries, Iron vanadates, Insertion compounds, GIT

New insights into the limiting parameters of the Li/S rechargeable cell

International audienceThe lithium/sulfur (Li/S) battery is a promising electrochemical system that has high theoretical capacity of 1675 mAh g−1. However, the system suffers from several drawbacks: poor active material conductivity, active material dissolution, and use of the highly reactive lithium metal electrode. This study was aimed at understanding the most important limiting parameters of a Li/S cell. Different sulfur material pre-treatments were experimented to increase the practical capacity, and various morphologies were obtained. But none of these treatments led to improvements in electrochemical performance. Electrolyte additives were also used to increase cell discharge capacity, but again without success. Finally, it was concluded that the cell capacity limitation may be linked to dissolution of sulfur material and to passivation of the positive electrode. As the final discharge products are insulating and poorly soluble, they precipitate and induce passivation of the positive electrode surface, leading to incomplete active material utilization. EIS measurements confirmed this passivation problem

High voltage spinel oxides for Li-ion batteries: From the material research to the application

International audienceLi-ion batteries are already used in many nomad applications, but improvement of this technology is still necessary to be durably introduced on new markets such as electric vehicles (EVs), hybrid electric vehicles (HEVs) or eventually photovoltaic solar cells. Modification of the nature of the active materials of electrodes is the most challenging and innovative aspect. High voltage spinel oxides for Li-ion batteries, with general composition LiMn2−xMxO4 (M a transition metal element), may be used to face increasing power source demand. It should be possible to obtain up to 240 Wh kg−1 at cell level when combining a nickel manganese spinel oxide with graphite (even more with silicon/carbon nanocomposites at the anode). Specific composition and material processing have to be selected with care, as discussed in this paper. It is demonstrated that ‘LiNi0.5Mn1.5O4' and LiNi0.4Mn1.6O4 have remarkable properties such as high potential, high energy density, good cycle life and high rate capability. Choice of the electrolyte is also of primary importance in order to prevent its degradation at high voltage in contact with active surfaces. We showed that a few percents of additive in the electrolyte were suitable for protecting the positive electrode/electrolyte interface, and reducing the self-discharge. High voltage materials are also possibly interesting to be used in safe and high power Li-ion cells. In this case, the negative electrode may be made of Li4Ti5O12 or TiO2 to give a ‘3 V' system

High voltage nickel manganese spinel oxides for Li-ion batteries

International audienceHigh voltage spinel oxides with composition LiMn2 − xMxO4 (M, a transition metal element) have remarkable properties such as high potential, high energy density and high rate capability. We believe that these positive electrode materials could replace the widespread commercial layered nickel cobalt oxides in some applications. The present assessment highlights electrochemical performance of optimized LiNi0.5Mn1.5O4 and substituted counterparts, all having a spinel structure (cubic close-packed oxygen array) similar to the relative LiMn2O4. To fully emphasize the benefit from high potential spinel oxides, tests have been performed versus lithium metal, Li4Ti5O12 and graphite, using various electrode loadings (0.3-4.5 mAh cm−2) and cycling rates (from C/20 to 60C rate). Steady capacity retention (130-140 mAh g−1 for nearly 500 cycles) and flat voltage (4.7 V vs. Li+/Li) have been obtained at C/5 rate at room temperature. Effect of cycling at high temperature has been shown to be less critical than for LiMn2O4. High voltage spinel oxides still sustain 100 mAh g−1 and over after 400 cycles at 55 °C at 1C rate. Rate capability is also excellent, with only 4% loss of capacity when comparing C/8 and 8C rates (thin electrodes)

Lithium/Sulfur Cell Discharge Mechanism: An Original Approach for Intermediate Species Identification

International audienc

Novel positive electrode architecture for rechargeable lithium/sulfur batteries

International audienceThe lithium/sulfur battery is a very promising technology for high energy applications. Among other advantages, this electrochemical system has a high theoretical specific capacity of 1675 mAh g−1, but suffers from several drawbacks: poor elemental sulfur conductivity, active material dissolution and use of the highly reactive lithium metal electrode. More particularly, the discharge capacity is known to be dictated by the short lithium polysulfide precipitation. These poorly soluble and highly insulating species are produced at the end of discharge, and are responsible for the positive electrode passivation and the early end of discharge. Nevertheless, the discharge capacity can be improved by working on the positive electrode specific surface area and morphology, as well as on the electrolyte composition. In this paper, we focused on the positive electrode issue. To this purpose, various current collector structures have been tested in order to achieve a high positive electrode surface area and a stable morphology during cycling. We demonstrated that the discharge capacity could be increased up to 1400 mAh g−1 thanks to the use of carbon foam. As well, the capacity fading could be dramatically decreased in comparison with the one obtained for conventional sulfur composite electrodes