Michel Broussely

Lithium insertion into host materials: the key to success for Li ion batteries

The aim of this paper is to summarise the present situation in Li ion batteries, from a short historical perspective of the concepts and materials, to the present trends. It aims also at giving the scientists working in this field some picture of the impact of the insertion material properties on the final cell characteristics. The market and applications of lithium ion batteries, present and future, are also briefly discussed.

On safety of lithium-ion cells

Abstract Safety of lithium-ion cells is mainly related to thermal reactivity of the components. Active materials play a major role: carbon materials because they directly influence the kinetics of reactions at the negative electrode, positive materials because of their relation with their respective delithiation state. Adequately substituted nickel based materials appear as the most stable positive materials. Electrolyte is mainly concerned through its reactivity with lithium of LixC6 and with O2 generated by the positive materials decomposition. Moreover, non-active materials, in particular binders, also clearly influence thermal stability and consequently safety behaviour of lithium-ion cells.

Crystal chemistry of electrochemically inserted LixV2O5

Abstract The capacity of Li/V2O5 batteries is improved by the extension of the usual cycling domain from 0 ⩽ x ⩽ 1 to 0 ⩽ x ⩽ 1.8. Such behavior is attributed to the formation of a γ-LiV2O5 bronze for x ⩾ 1. Reversible deintercalation of lithium from the γ-phase leads to a new form of V2O5 that explains the enhancement of cell potential.

On the behavior of the LixNiO2 system: an electrochemical and structural overview

Lithium nickel oxide exhibits a departure from stoichiometry (Li1 − zNi1 + zO2) consisting in the presence of extra-nickel ions within the lithium sites. Using optimized experimental synthesis conditions, compositions very close to the ideal stoichiometry (z = 0.02) can be obtained. By using the sensitivity of the lithium site isotropic temperature factor to the stoichiometry, the amount of extra-nickel ions can be determined in a very precise way. The loss of reversibility at the first cycle is mainly related to the change in the oxidation state of the extra-nickel ions, which induces a local collapse of the structure and makes difficult the lithium re-intercalation. A systematic structural study of LixNiO2 phases has been performed by extended X-ray absorption fine structure (EXAFS) as well as X-ray and electron diffraction. In the case of the starting Li0.98Ni1.02O2 phase, a local distortion of the NiO6 octahedra, resulting from a dynamic Jahn-Teller effect of low spin trivalent nickel ions has been evidenced from the EXAFS study. For the partially de-intercalated materials (0.50 < x < 0.75) which crystallize in the monoclinic system, the EXAFS study shows that the NiO6 octahedra are only slightly distorted due to the occurrence of a hopping phenomenon between NiIV and NiIII. Electron diffraction experiments show the existence of a superstructure due to a peculiar lithium-ion ordering. Systematic electrochemical studies have shown that this ordering is strongly sensititve to the presence of extra-nickel ions.

LixNiO2, a promising cathode for rechargeable lithium batteries

Abstract Lithiated nickel oxide has been prepared and studied with the aim of using it as the positive active reversible material in rechargeable lithium batteries. This paper describes the particular features of this material, and discusses the results that demonstrate its interest as cathode in practical cells, using carbon as the negative electrode. Specific energy and energy density of more than 130 Wh/kg and 320 Wh/l were obtained in prototypes, and a cycleability of over 1000 cycles was demonstrated.

The relationship between the composition of lithium nickel oxide and the loss of reversibility during the first cycle

Abstract A quantitative relationship between the reversibility of the intercalation/de-intercalation process and the amount z of extra-nickel ions within the lithium layers has been demonstrated by specific electrochemical studies of Li1 − zNi1 + zO2 cells. The oxidation of extra-nickel ions from divalent to trivalent state during the first electrochemical charge, leads to an irreversible shrinkage of the interslab space, and as a consequence, to a loss of reversibility in the first cycle. The re-intercalation composition limit is thus directly related to the concentration of extra-nickel ions. However, the overall reversibility can be recovered by a forced discharge up to the starting composition.

On the δ → γ irreversible transformation in Li//V2O5 secondary batteries

Discharging LixV2O5 electrodes beyond x = 1 leads to an irreversible transformation of the δ-phase into a γ-phase. The achievement of this transformation is governed by the number of cycles, the depth of discharge as well as by grain size and morphology of the active material. The study of the OCV versus time curves, at various stages of discharge, reveals a rather complex behavior resulting from diffusional and phase transition phenomena.

Li/LixNiO2 and Li/LixCoO2 rechargeable systems: comparative study and performance of practical cells

Lithiated cobalt and nickel oxides have been prepared using an original synthesis process, based on thermal treatment with LiOH. Their properties as reversible cathodic material for lithium rechargeable cell were studied, showing different behavior in electrochemical mechanisms. Excellent energy densities were obtained from the two compounds. At high working potential from 4 to 3 V, up to 300 W h/l and 174 W h/kg were obtained in ‘C’-size cells. The kinetics of cathode reactions are fairly rapid, which allows high rate of discharge (> ‘C’). Cycle life was demonstrated over more than 100 cycles. Storage capability was tested at 45 °C at the charged state. Better results were obtained with LixNiO2 than with LixCoO2.

Lithium-ion batteries for electric vehicles: performances of 100 Ah cells

Among the new electrochemical systems, lithium ion using a liquid electrolyte appears to be one of the most promising technologies for the mid-term requirements of electric vehicles (EVs). Thanks to a dedicated research program over the past five years, SAFT is developing a complete EV battery system, including thermal management and electronic control system. Electrochemical cells of about 100 Ah, using LiNiO2 and graphite, have been built and tested. They show performances of 125 Wh/kg and 265 Wh/l at the 1-h rate, at the beginning of life. Specific power obtained along the complete discharge fulfill the requirements for EV application. A 20 kWh 220 V assembly was built, including the associated electronic control equipment and air thermal regulation.

Electrochemical behavior of orthorhombic LiMnO2: influence of the grain size and cationic disorder

Abstract Stoichiometric orthorhombic O-LiMnO 2 , prepared at high temperature from a mixture of Mn 2 O 3 and LiOH.H 2 O, is electrochemically active in a lithium deintercalation/intercalation process. The samples with the smallest grains ( O μ m), and corresponding to the phases prepared with some lithium hydroxide deficiency developed the higher weight capacities. These could reach up to 160 mAh/g under a C/15 regime following a forming that spanned over about thirty cycles. The cells capacity remained constant after forming, showing the very good cyclability of the system. It has not been clearly demonstrated whether the Li/Mn substitution in the O-LiMnO 2 samples played an important role in the electrochemical characteristics of the Li/Li x MnO 2 cells, although the group with small grains also showed, on average, a higher cationic disorder. A phase transition took place upon the first oxidation of O-LiMnO 2 . The new phase presented an electrochemical behavior resembling that of spinel LiMn 2 O 4 . A modeling of the discharge curves showed a progressive forming of the materials during a few cycles.