LITHIUM MIXED INORGANIC ELECTROLYTES

Abstract

The present application relates to novel mixed compounds based on oxides and sulfides, and the use thereof as a solid electrolyte, with improved sulfide stability. The application further relates to electrochemical elements and lithium batteries containing such electrolytes.

Claims

1. A compound with formula (I):
((A.sub.(t-v)B.sub.v/2)[(PS.sub.4).sub.(1-x)(OH.sub.zA.sub.UX.sub.1).sub.x]).sub.(1-y)(Li.sub.nX.sub.2).sub.y  (I) Wherein:
A=Li,Na,K;
B=Mg,Ca;
X.sub.1=F,Cl,Br,I;
X.sub.2=N,O,S,F,Cl,Br,I,BH.sub.4,C.sub.iB.sub.jH.sub.j+1; n is such that:
n=3 for X.sub.2=N, or
n=2 for X.sub.2=0,S, or
n=1 for X.sub.2=F,Cl,Br,I,BH.sub.4,C.sub.iB.sub.jH.sub.j+1; where i and j are integers and i=1 or 2 and 8≤j≤11;
0<y<0.40,
0<x<0.7,
0<z<1; u is either positive, negative or zero, and such that u+z=0;
0≤v≤0.3;
2.8≤t≤3.5; Where it is understood that X.sub.2≠X.sub.1.

2. The compound according to claim 1, such as in formula (I):
A=Li; and
X.sub.1=Cl.

3. The compound according to claim 1 such as in formula (I):
Y=0;t=3,y=0,z=0 and u=0.

4. The compound according to am claim 1 wherein the compound with formula (I) is represented by formula (I′):
Li.sub.3(PS.sub.4).sub.1-x(OCl).sub.x  (I′) x being defined according to claim 1.

5. The compound according to claim 4, such that x is preferentially comprised between 0.02 and 0.20.

6. A preparation method for a compound of formula (I) as defined according to claim 1, such that same comprises the step of co-grinding crystalline precursors until an amorphous mixture is obtained.

7. An electrolyte for a battery comprising a compound with formula (I) as defined according to claim 1.

8. An electrochemical element comprising an electrolyte such as defined according to claim 7.

9. An electrochemical module comprising a stack of at least two elements according to claim 8, each element being electrically connected with one or a plurality of other elements.

10. A battery comprising one or a plurality of modules according to claim 9.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0046] FIG. 1 shows the X-ray diffraction spectra of Li.sub.3(PS.sub.4).sub.1-x(OCl).sub.x compounds as a function of x during a 29-hour ball mill grinding; the wavelength used is that of the K lineα of copper (1.5406 angstrom).

[0047] FIG. 2 shows the X-ray diffraction spectrum of the compound Li.sub.3(PS.sub.4).sub.0.884(OCl).sub.0.116 as a function of time for samples ground by a ball mill; the wavelength used is that of the K lineα of copper (1.5406 angstrom).

[0048] FIG. 3 shows the comparison between the H.sub.2S release for a sample of sulfide electrolyte alone (amorphous LPS) and Li.sub.3(PS.sub.4).sub.1-x(OCl).sub.x compounds.

DETAILED DESCRIPTION

Examples

[0049] The following examples illustrate in a representative and non-limiting manner, an embodiment according to the invention.

Example 1: Preparation of a composite in the Li—P—S—O—Cl system, from Li2S-P2S5-Li.SUB.2.O—LiCl

[0050] Selected compositions: [0051] X=0.714 corresponding to a 50% mass % of Li.sub.3OCl [0052] X=0.384 corresponding to a 20% mass % of Li.sub.3OCl [0053] X=0.207 corresponding to a 9.5% mass % of Li.sub.3OCl [0054] X=0.116 corresponding to a 5% mass % of Li.sub.3OCl

[0055] The Li.sub.3(PS.sub.4).sub.1-x(OCl).sub.x compounds were prepared from the precursors Li.sub.2O, LiCl, Li.sub.2S and P.sub.2S.sub.5. Precursor masses are calculated for obtaining the desired stoichiometry.

TABLE-US-00001 TABLE 1 The value of x in the formula Li.sub.3(PS.sub.4).sub.1−x(OCl).sub.x. Li.sub.2S P.sub.2S.sub.5 LiCl Li.sub.2O 0.116 0.7273 g 1.1731 g 0.05866 g  0.0413 g 0.207 0.7283 g 1.1727 g 0.1173 g 0.0827 g 0.384 0.3062 g 0.4938 g 0.1173 g 0.0827 g 0.714 0.3828 g 0.6172 g 0.5865 g 0.4134 g

[0056] Table 1 shows the masses of the different precursors for producing

[0057] Li.sub.3(PS.sub.4).sub.1-x(OCl).sub.x compounds for the different values of x

[0058] The mixtures are carried out by ball milling (Fritsch 7) in 25 ml ZrO.sub.2 bowls with 4 balls with a diameter of 10 mm. The bowls are rotated at 500 rpm for several 30-minute cycles. The powder inside the bowls is detached from the walls every 5 hours so as to homogenize the sample.

[0059] The evolution of the X-ray diffraction graph (DRX) of the compound Li.sub.3(PS.sub.4).sub.0.884(OCl).sub.0.116 as a function of the grinding time is shown in FIG. 2. The three precursors Li.sub.2S, LiCl and Li.sub.2O disappear after 29 h of grinding. It is possible that the precursors have been nanostructured until forming an amorphous compound as is the case for amorphous Li.sub.3PS.sub.4, the amorphous structure being characterized by a lack of medium and long distance order resulting in very wide diffraction lines. The grinding time will thus be taken as a reference for the other mixtures (FIG. 1).

[0060] The DRXs of the other mixtures after 29 h of mechano-synthesis are shown in FIG. 1. Like for the compound with x=0.116, the compound with x=0.207 does not have any very significant peak. For the compounds Li.sub.3(PS.sub.4).sub.0.616(OCl).sub.0.384 and Li.sub.3(PS.sub.4).sub.0.286(OCl).sub.0.714, the precursors are still clearly visible after the 29 h of mechano-synthesis (FIG. 3).

Example 2: Release of H.SUB.2.S

[0061] The release of hydrogen sulfide was measured for a mixed electrolyte according to the invention Li.sub.3PS.sub.4:Li.sub.3OCl according to two compositions with x=0.116 and 0.207. The release was compared with the release from a sample of sulfide-alone electrolyte (amorphous LPS) with similar mass.

[0062] In order to measure the release of H.sub.2S, 25 mg of powder were introduced at the initial time into a 2.5 l container which could be hermetically sealed and wherein an H.sub.2S detector (accuracy of 1 ppm) was placed. In the present example, the container contained ambient air at atmospheric pressure and ambient temperature, so as to assess the risk associated with the release of H.sub.2S under standard conditions in which the materials could be found. The H.sub.2S concentration in the chamber was recorded at regular intervals as soon as the sample was introduced.

[0063] The results are shown in FIG. 3. The curves obtained show that the release from the compound with x=0.116 is lower than the release from the compound with x=0.207, further suggesting a synergistic effect for values of x less than 0.2.

Example 3: Conductivity Measurement

[0064] Since the main function of the electrolyte is the conduction of ions, measurements of ionic conductivity were performed so as to verify the evolution thereof according to the compositions studied. For a given composition, powder coming from the synthesis was introduced into a cell similar to a pelletizing mold, the pistons of which were made of stainless steel and the body was made of insulating material. A pressure of 2t/cm.sup.2 was maintained on the cell during the conductivity measurement. Such measurement was made by impedance (1 MHz to 200 mHz), at a plurality of temperature values from 20° C. to 60° C. The resistance value R from the measurement allowed us to calculate the conductivity value σ via the relation

[00001]$\begin{array}{cc}\sigma =\frac{e}{R.Math.S}& \left[\mathrm{Maths}1\right]\end{array}$

The thickness e of the compressed pellet was measured with a micrometer (accuracy: 1 μm) and the surface area S was the surface area of the cell used.

[0065] The conductivity values obtained at 20 and 60° C. are given in Table 2.

TABLE-US-00002 TABLE 2 Surface Set-point Composition area Thickness temperature σ Li.sub.3(PS.sub.4).sub.1−x(OCl).sub.x (cm.sup.2) (μm) (° C.) (MS/cm) x = 0 0.385 600 20 0.16 60 1.06 x = 0.116 0.385 540 20 0.14 60 0.87 x = 0.207 0.385 480 20 0.16 60 0.90

[0066] Such measurements show that the conductivity does not vary greatly from one sample to another, despite the decrease in the amount of sulfides.

[0067] The reduction in the quantity of H.sub.2S released is thus not to the detriment of the capacity of the material to conduct lithium ions.