Dominique Guyomard

Positive electrode materials with high operating voltage for lithium batteries: LiCryMn2 − yO4 (0 ≤ y ≤ 1)

Reversible lithium deintercalation of chromium-substituted spinel manganese oxides LiCryMn2 − yO4 (0 ≤ y ≤ 1) in the voltage range 3.4–5.4 V versus Li, occurs in two main steps for 0 < y < 1: one at about 4.9 V and the other at about 4 V. The 4.9 V process capacity increases with the chromium content while the 4 V process capacity decreases at the same time. Excellent cyclability was observed for y ≤ 0.5 while materials with y ≥ 0.75 were loosing capacity rapidly upon cycling. Changing the chromium composition of these materials enables the control of the average intercalation voltage in the range 4.05–4.5 V versus Li, a voltage range where no material was known before. A low manganese to chromium substitution rate in LiMn2O4 was found to be beneficial to the specific capacity and energy and to the cyclability of the spinel materials. Due to the selected electrolyte composition with high stability against oxidation, extra capacity due to electrolyte oxidation at each cycle remained very low even though the charge voltage was highly oxidative.

Silicon Composite Electrode with High Capacity and Long Cycle Life

A nanosilicon-based composite electrode that can achieve more than 700 cycles at a high capacity of 960 mAh/g of electrode was prepared using aqueous processing in an acidic medium. The buffering of the aqueous solution is mandatory to promote covalent bonding between Si particles and the carboxymethyl cellulose (CMC) binder. The latter is claimed to allow the formation of mechanically stronger contacts within the composite electrode in addition to the CMC bridging of the Si and carbon black particles.

LiMBO3 (M=Mn, Fe, Co):: synthesis, crystal structure and lithium deinsertion/insertion properties

Abstract The LiMBO3 (M=Mn, Fe, Co) compounds were synthesized by a solid state reaction. LiFeBO3 and h-LiMnBO3 crystal structures were determined from single crystal data. LiFeBO3 exhibits the same structure as that of other already described LiMBO3 compounds (M=Mg, Mn, Co, Zn). The structure of h-LiMnBO3 is isotypic with the hexagonal form of LiCdBO3. The electrochemical study shows that a very small amount of lithium (less than 0.04 Li per formula unit) can be deinserted reversibly from the three compounds. According to the thermodynamic study performed in the case of LiFeBO3, the Fe3+/Fe2+ redox couple lies between 3.1 and 2.9 V/Li, demonstrating an important inductive effect of the BO3 group.

New electrolyte compositions stable over the 0 to 5 V voltage range and compatible with the Li1+xMn2O4/carbon Li-ion cells

Safe use of the emerging Li1+xMn2O4/C Li-ion batteries requires an electrolyte that is resistant to oxidation up to 5 V both at room temperature and at 55°C. Permutations of different solvents and lithium-based salt mixtures were tested for their resistance to oxidation at high voltages on Li1+xMn2O4 electrodes and for their ability to maintain high ionic conductivity over a wide temperature range. This survey allowed us to select new electrolyte compositions that are highly stable against oxidation which consist of mixtures of ethylene carbonate (EC), dimethyl carbonate (DMC) and lithium hexafluorophosphate (LiPF6). This new electrolyte composition can be used in practical Li1+xMn2O4/carbon Li-ion batteries, and shows enhanced safety characteristics and performance in terms of cycle life and self-discharge. The electrochemical stability of this new electrolyte composition against oxidation in contact with other highly oxidizing materials, such as LiCoO2 or LiNiO2 has also been verified.

Electrochemically synthesized vanadium oxides as lithium insertion hosts

The electrochemical oxidation of vanadyl cations in aqueous solution leads to a solid deposit on the working electrode, called electrolytic vanadium oxide (e-V2O5). The electrodeposition reaction occurs in two steps including an oxidation into soluble species followed by a precipitation. Electrodeposited compounds are mixed valence, hydrated vanadic acids. Their chemical formula can be written H0.4V2O5.2−δ·nH2O with 0.04<δ<0.2 and 0<n<1.8. These two latter parameters depend on the current density applied during electrodeposition, the duration and the temperature of a subsequent mild thermal treatment in air. e-V2O5 materials are porous, poorly crystallized layered compounds. At 260°C, they become completely anhydrous and undergo a phase transformation into α-V2O5. The electrochemical intercalation of lithium into these compounds shows two main single phase phenomena near 2.6 and 3.1 V/Li. This reduction induces a lengthening of the average vanadium oxygen bond, and a decrease of the lithium diffusion coefficient. e-V2O5 compounds reversibly intercalate 1.4≅Li per formula unit at an average voltage of 2.8≅V/Li, at a rate of C/50 in the 4–2 V range, and this capacity is maintained during several tens of discharge/charge cycles. The electrochemical behavior is slightly dependent on the VIV content and the crystallization state of the compounds.

A low-cost and high performance ball-milled Si-based negative electrode for high-energy Li-ion batteries

A Si-based anode with improved performance can be achieved using high-energy ball-milling as a cheap and easy process to produce Si powders prepared from a coarse-grained material. Ball-milled powders present all the advantages of nanometric Si powders, but not the drawbacks. Milled powders are nanostructured with micrometric agglomerates (median size ∼10 μm), made of submicrometric cold-welded particles with a crystallite size of ∼10 nm. The micrometric particle size provides handling and non-toxicity advantages compared to nanometric powders, as well as four times higher tap density. The nanostructuration is assumed to provide a shortened Li+ diffusion path, a fast Li+ diffusion path along grain boundaries and a smoother phase transition upon cycling. Compared to non-milled 1–5 μm powders, the improved performance of nanostructured milled Si powders is linked to a strong lowering of particle disconnection at each charge, while the irreversibility due to SEI formation remains unchanged. An electrode prepared in acidic conditions with the CMC binder achieves 600 cycles at more than 1170 mA h per gram of the milled Si-based electrode, in an electrolyte containing FEC/VC SEI-forming additives, with a coulombic efficiency above 99%, compared to less than 100 cycles at the same capacity for an electrode containing nanometric Si powder.

Ionic vs Electronic Power Limitations and Analysis of the Fraction of Wired Grains in LiFePO4 Composite Electrodes

This study, realized within the framework of the optimization of aqueous LiFePO 4 composite electrodes, relies on Prosinis approach [J. Electrochem. Soc. 152, A1925 (2005)] that characterizes the LiFeP0 4 /Li discharge behavior through simple equations. Two key parameters extracted from the LiFeP0 4 discharge curves are analyzed to determine the optimal electrode engineering and to interpret the origins of the electrode performance limitations. In particular, the calendaring step plays a critical role. Low packing results in electronic limitation, while the ionic contribution dominates for dense electrodes. The best compromise is achieved for an optimal porosity in the 30-35% volume range. A simple equation is proposed to predict the ionic limitations of rate performance from the electrode thickness and porosity, and the liquid electrolyte diffusion constant.

Low temperature LiMn2O4 spinel films for secondary lithium batteries

Low temperature thin film spinel, with , are fabricated for use in secondary batteries. The spinel crystal structure is obtained by in situ postdeposition annealing of the films at temperatures as low as 400°C. Such temperatures are compatible with semiconductor processing, permitting future integration of the batteries with electronics. 1–3 μm thin films are tested in arrangements. They intercalate nearly one Li+ ion at an average potential of 4.1 V and show very good intercalation kinetics, so that a 10 C discharge rate produces an energy density of 500 W‐h per kilogram of active cathode material. These films show very promising cycle life, even at 55°C. Films cycled more than 220 times maintain more than 70% of their original capacity.

Design of Aqueous Processed Thick LiFePO4 Composite Electrodes for High-Energy Lithium Battery

Small-amplitude oscillatory rheology is used to probe the microstructure present in aqueous composite electrode slurries for lithium batteries. The materials prepared with carboxymethyl cellulose as the thickener displays a solidlike behavior due to the buildup of a three-dimensional network of colloidal carbon black (CB) particles bridged by the polymeric chains. This network is able to support and inhibit the settling of the larger LiFePO 4 particles. Thus, a homogeneous morphology is achieved in the dried composite electrode and good electrochemical performance is displayed both at low and high rates. Contrarily, hydroxypropylmethyl cellulose is observed to create weaker bonds between the CB particles and the materials prepared with this thickener display a liquidlike behavior. Then, the settling of the LiFePO 4 particles results in a concentration gradient, and thus poor electronic wiring and electrochemical performance, unless drying is accelerated by heating.

The Li1+xMn2O4C system Materials and electrochemical aspects

Abstract The importance of the synthesis conditions of Li 1+ x Mn 2 O 4 on its electrochemical performance, namely, capacity fading and initial capacity is discussed. By using a well-defined thermal treatment and a particular nominal composition, x =0.05, one can overcome the problem of capacity fading that was previously experienced with LiMn 4 while, at the same time, enhancing the usable capacity. The importance of the thermal treatment in terms of oxygen stoichiometry effects and how cyclic voltammetry can be used to optimize Li 1 + x Mn 2 O 4 powders have been discussed.