Patent Grant
8323532
The invention relates to a lamellar-type oxide, in particular used as active material of a positive electrode for a lithium battery and to a method for synthesizing such an oxide.
Lithium batteries are progressively replacing nickel-cadmium (Ni—Cd) or metallic nickel-hydride (Ni-MH) batteries as autonomous power source, in particular in portable equipment. This tendency can be explained by the continuous improvement of the performances of lithium batteries giving them substantially higher mass and volume energy densities than those of Ni—Cd and Ni-MH batteries. Thus, whereas the first Li-ion type lithium batteries had a mass energy density of about 85 Wh/kg, a mass energy density of about 200 Wh/kg can be obtained at present. For comparison purposes, Ni—MH batteries and Ni—Cd batteries respectively have a mass energy density of 100 Wh/kg and 50 Wh/kg.
However, to efficiently meet the requirements of new applications which present ever-increasing power demands, lithium batteries have to be further improved. Improving the performances of Li-Ion batteries and in particular increasing their capacity are closely related to the search for new active electrode materials.
At present, the active materials generally used for negative electrodes in commercial lithium batteries are carbon (graphite, coke, . . . ), a spinel oxide of Li4Ti5O12 type or a metal forming an alloy with lithium such as Sn or Si.
In general, the active materials used for positive electrodes in commercial lithium batteries are compounds of lamellar-type structure, such as LiCoO2 and LiNiO2 oxides, or compounds of spine structure such as LiMn2O4 and derivatives thereof.
It is however well known that the active material of the positive electrode of Li-Ion batteries is currently the limiting factor for obtaining an increase of the mass energy density.
One path for improvement consists in increasing the redox potential of the active material of the positive electrode. Active materials for positive electrodes presenting a high-voltage electrochemical activity, of more than 4.2 V with respect to the redox potential of the LOU pair (also noted 4.2 V vs Li+/Li), have thus been developed over the past few years in order to increase the energy density of Li-Ion batteries. Among these promising new compounds, the following are noteworthy:
However, to be able to use such compounds in commercial batteries, these compounds have to be further improved and the electrode/electrolyte interface has to be stabilized at high voltage as the lifetime is about a few tens of cycles and is therefore low. These compounds furthermore have low theoretical specific capacities generally comprised between 145 and 170 mAh/g.
Another possible path for improvement consists in finding active materials for the positive electrodes of lithium batteries having higher specific capacities than the active materials used at present.
Lamellar-type oxides of LiMO2 type, where M represents a transition element such as cobalt, do however enable theoretical capacities that are among the highest to be obtained. The theoretical capacities are in fact comprised between about 270 to 300 mAh/g, according to the molar mass of the transition element. In practice however, the capacity obtained is generally about 150 mAh/g, due to the obligation of preserving the structural coherence of such oxides.
Alternative compounds have thus been proposed to replace lamellar oxides of LiMO2 type. It has for example been proposed to use several transition metals in lamellar-type oxides. For example the LiNi0.8Co0.15Al0.05O2 and LiNi1/3Co1/3Mn1/3O2 compounds, also of lamellar-type structure, enable similar or substantially higher electrochemical performances to be obtained than oxides of LiMO2 type for lower or equal cost and an improved chemical stability in particular in charged state.
Among the active materials proposed recently in the literature, oxides of xLi2M′O3.(1−x)LiMO2 type, where:
In particular, the article by Jeom-Soo Kim et al. (“Electrochemical and Structural Properties of xLi2M′O3.(1−x)LiMn0.5Ni0.5O2 Electrodes for Lithium Batteries (M′=Ti, Mn, Zr; 0≦x≦0.3)”, Chem Mater. 2004, 16, 1996-2006) studies the structural and electrochemical properties of electrodes comprising an active material of xLi2M′O3.(1−x)LiMn0.5Ni0.5O2 type, with M′=Ti, Mn, Zr and 0≦x≦0.3 compared with a metallic lithium reference electrode. Such oxides have the particularity of presenting multiple electrochemical phenomena associated with the changes of oxidation degrees of the different transition elements. This enables high specific capacities to be obtained in certain cases, paving the way for development of particularly attractive active materials. However, it is not sure that the specific capacity can be maintained with such materials when cycling takes place. A decrease of the specific capacity can in fact be observed in the course of the charging/discharging cycles. A great deal of progress therefore still remains to be made in order to propose active materials for positive electrodes enabling a high and stabilized specific capacity to be obtained, therefore providing Lithium-Ion batteries with improved performances.
International Patent application WO-A-2004107480 proposes using lamellar oxides of formula LixMnyM1-yO2, where x≦0.20. Mn is in a +4 oxidation state and M is at least a transition metal or another metal cation having an ionic radius able to be inserted in the structure without breaking the latter unduly.
In Patent application US2005/0136329, the electrochemical performances of materials having the general formula Li{Li(1-2x)/3Mn(2-x)/3Nix}O2 is improved by doping said materials with a divalent cation chosen from Ca, Cu, Mg and Zn.
The object of the invention is to propose active materials for the positive electrode remedying the shortcomings of materials according to the prior art and in particular, in the field of lithium batteries, enabling a stabilized in cycling and high specific capacity to be obtained, advantageously at all the cycling temperatures usually used and in the usual range of potentials.
According to the invention, this object is achieved by the appended claims.
In particular, this object is achieved by a new family of lamellar-type oxides of following general formula:
xLi2MnO3.(1−x)LiM1aM2bM3cO2
According to a development of the invention, the lamellar-type oxide is represented by the following formula:
0.75Li2MnO3.0.25LiNi0.9Mn0.05Mg0.05O2.
According to another development of the invention, it is represented by the following formula:
0.75Li2MnO3.0.25LiNi0.6Mn0.2Mg0.2O2.
Other advantages and features will become more clearly apparent from the following description of particular embodiments of the invention, given as non-restrictive examples only and represented in the accompanying drawings in which:
Lamellar-type oxides of the following general formula:
xLi2MnO3.(1−x)LiM1aM2bM3cO2 (1)
where:
In particular, it has been found that such oxides are capable of delivering a high specific capacity over a large number of charging/discharging cycles while at the same time enabling the specific capacity on cycling to be stabilized.
Compared with xLi2M′O3.(1−x)LiMO2 oxides and in particular with the xLi2M′O3.(1−x)LiMn0.5Ni0.5O2 oxides reported in the above-mentioned article by Jeom-Soo Kim, oxides of the general formula (1) comprise at least one electrochemically inactive chemical element (M3), also called chemical element devoid of electrochemical activity.
What is meant by electrochemically inactive chemical element is a chemical element that does not oxidize or that is not reduced during charging or discharging of a lithium battery, in the usual range of potentials. M3 is more particularly at least a chemical element chosen from the group formed by Mg, Zn, Al, Na, Ca, Li, K, Sc, B, C, Si, P and S. M3 can thus also be formed by several of the chemical elements of the above-mentioned group. M3 thereby enables the specific capacity on cycling to be indirectly stabilized.
M3 is further associated:
Advantageously, in the general formula (1), M1 is nickel, M2 is manganese and M3 is magnesium. b is moreover preferably equal to c.
The positive electrode of a lithium battery can thus comprise a majority quantity of an oxide of the general formula (1) as active material. The positive electrode advantageously comprises minority quantities of an organic binder such as a polyether, a polyester, a polymer with a base of methyl methacrylate, acrylonitrile, or vinylidene fluoride and an electron-conducting additive such carbon.
The lithium battery also comprises a negative electrode the active material of which can be of any known type. For example, the active material of the negative electrode can be lithium in metal form or it can be a material able to insert and de-insert Li+ ions, such as carbon in general in graphite form, an oxide such as Li4Ti5O12 or a compound forming an alloy with lithium such as silicon or tin.
Finally, the electrolyte of the lithium battery in general comprises a lithium salt for example chosen from LiClO4, LiAsF6, LiPF6, LiBF4, LiRFSO3, LiCH3SO3, LiN(RFSO2)2, LiC(RFSO2)3, lithium bis(trifluoromethanesulphonyl)imide (also noted LiTFSI), lithium bis(oxalato)borate (also noted LiBOB), lithium bis(perfluoroethylsulfonyl)imide (also noted LiBETI), or lithium fluoroalkylphosphate (LiFAP). RF is a radical chosen from a fluorine atom and a perfluoroalkyl group containing between one and eight carbon atoms. The lithium salt is further preferably dissolved in an aprotic polar solvent. The salt is for example supported by a separating element arranged between the two electrodes of the battery, the separating element then being imbibed with electrolyte. In the case of a lithium battery comprising a polymer electrolyte, the lithium salt is not dissolved in an organic solvent, but in a solid polymer composite such as polyethylene oxide (PEO), poly(acrylonitrile) (PAN), poly(methyl methacrylate) (PMMA), poly(vinylidene fluoride (PVdF), polyvinyl chloride (PVC) or a derivative thereof.
Moreover, to achieve high specific capacities, the voltage cycling boundary limits of the battery have to be from about 2 to 3V vs. Li+/Li for the lower limit and from about 4.6 to 4.8 V vs. Li+/Li for the upper limit. The mean operating voltage is generally about 3.4 to 3.8 V vs. Li+/Li on discharge.
According to a first example embodiment (hereafter noted Example no 1), the 0.75Li2MnO3.0.25LiNi0.6Mn0.2Mg0.2O2 compound was synthesized and then tested in a lithium battery of “buttoncell” format.
The 0.75Li2MnO3.0.25LiNi0.6Mn0.2Mg0.2O2 compound is in particular obtained by intimately mixing 2 g of a previously synthesized precursor A and 1.502 g of lithium hydroxide LiON.H2O, by heating the mixture at 900° C. for 24 hours and then cooling it very quickly to ambient temperature (quenching). In particular, the precursor A was previously synthesized from:
Characterization of the product obtained after the quenching operation confirms synthesis of the 0.75Li2MnO3.0.25LiNi.,6Mn.,2Mg0.2O2 compound and its lamellar-type structure.
A “buttoncell” format lithium battery is then achieved with:
The variation of the specific capacity versus the number of cycles corresponding to this lithium battery is represented by plot A in
According to a second example embodiment (hereafter noted Example no2), the 0.75Li2MnO3.0.25LiNi0.9Mn0.05Mg0.05O2 compound was synthesized and then tested in a “buttoncell” format lithium battery similar to the one produced in example no1.
The 0.75Li2MnO3.0.25LiNi0.9Mn0.05Mg0.05O2 compound is in particular synthesized by intimately mixing 1.50 g of a previously synthesized precursor A′ and 1.11 g of lithium hydroxide LiOH.H2O, and by then heating the mixture at 1000° C. for 24 hours before cooling it very quickly to ambient temperature (quenching). In particular precursor A′ was previously synthesized from:
These two aqueous solutions are added simultaneously to a third aqueous solution of 0.25 L containing 10.070 g of lithium hydroxide LiOH.H2O and maintained under mechanical stirring. A precipitate forms, before being filtered, washed several times with distilled water and then dried for 60 hours at 100° C. to obtain precursor A′. Precursor A′ is represented by the general formula Mn0.7625Ni0.225Mg0.0125(OH)2.
The 0.75Li2MnO3.0.25LiNi0.9Mn0.05Mg0.055O2 compound thus synthesized was characterized by X-ray diffraction (
Such a compound was further used as active material of a positive electrode in a “buttoncell” format lithium battery similar to the battery produced in example no1. Only the active material of the positive electrode was replaced in the lithium battery according to example no1.
Furthermore,
Plot F of
The mass energy is very high in comparison with that obtained with active materials used in currently marketed batteries (generally about 600 Wh/kg), all the more so as it is obtained after a large number of cycles.
Thus, as illustrated by
As illustrated by examples no1 and 2, the oxides according to the invention are advantageously prepared by thermally treating a powder obtained by mixing a precursor forming a source of elements M1, M2 and M3 in predetermined proportions with lithium hydroxide LiOH.H2O, at a temperature at least equal to 800° C. and more often of about 900° C. to 1000° C. The precursor is in particular represented by the general formula MnxM1a(1-x)M2b(1-x)M3c(1-x)(OH)2. Once the heat treatment has been completed, the powder is cooled very quickly, by performing quenching for example.
Furthermore, once synthesized, the oxide can be subjected to post-treatment in a slightly acid aqueous solution to improve its electrochemical properties and therefore the specific capacity of the lithium battery.
Thus, according to a third example embodiment (hereafter noted Example no3), 10 g of the 0.75Li2MnO3.0.25LiNi0.9Mn0.05Mg0.05O2 compound obtained according to example no2 are mixed with 250 mL of an aqueous solution having a pH equal to 5.5. The aqueous solution is for example water in which an acid such as H2SO4 or HNO3 is added to adjust the pH. The mixture is then stirred for 30 minutes, and is then placed in an ultrasonic tank for 10 minutes. The mixture finally placed under magnetic stirring for 24 hours. A centrifugation operation consisting in three washings with water enables a powder to be recovered, which powder is then dried at 50° C. for 24 hours. Finally the powder is subjected to heat treatment at a temperature of 350° C., for 3 hours in air.
The compound treated in this way is then tested as active material for the positive electrode in a “buttoncell” format battery respectively with cycling temperatures at 20° C. and at 55° C. The battery is similar to the batteries produced according to examples no1 and 2. It thus comprises the same constituents as the batteries produced according to examples no1 and 2, with the exception of the active material of the positive electrode.
The electrochemical characteristics corresponding to example no3 are reported in
As illustrated in
| Number | Date | Country | Kind |
|---|---|---|---|
| 08 03139 | Jun 2008 | FR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/FR2009/000625 | 5/28/2009 | WO | 00 | 12/20/2010 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2009/147315 | 12/10/2009 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 5443929 | Yamamoto et al. | Aug 1995 | A |
| 6677082 | Thackeray et al. | Jan 2004 | B2 |
| 6680143 | Thackeray et al. | Jan 2004 | B2 |
| 20050136329 | Howard, Jr. et al. | Jun 2005 | A1 |
| Number | Date | Country |
|---|---|---|
| 1 837 937 | Sep 2007 | EP |
| WO 2004107480 | Sep 2004 | WO |
| WO 2008086041 | Jul 2008 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 20110089369 A1 | Apr 2011 | US |
