SOLID ELECTROLYTE FOR SOLID STATE BATTERIES

TECHNICAL FIELD

[0001] The present disclosure is related to solid state batteries, and more particularly to all-solid state batteries comprising solid electrolyte comprising sulfur having the following formula XM ₂ (PS4)3, where X is Li, Na, Ag or Mg ₀ ,s and M is Ti, Zr, Ge, Si, Sn or (X+AI).

BACKGROUND

[0002] Solid state batteries offer the possibility of having a battery pack with high energy density.

[0003] Different materials are studied for solid electrolyte for solid state batteries. Of particular interest are materials comprising sulfur and exhibiting peaks in positions of 2Q = 15,08° (±0,50°), 15,28° (±0,50°), 15,92° (±0,50°), 17,5° (±0,50°), 18,24° (±0,50°), 20,30° (±0,50°), 23,44° (±0,50°), 24,48° (±0,50°), and 26,66° (±0,50°) in a X-ray diffraction measurement using CuKa line. These materials generally exhibit good lithium ionic conductivity.

[0004] However, increase of the lithium ionic conductivity of such materials is still required for application as solid electrolyte. Indeed, such increase in ionic conductivity of the lithium allows for increase of the electronic conductivity of the solid electrolyte.

SUMMARY

[0005] Therefore, according to embodiments of the present disclosure, a method for producing a solid electrolyte material for a solid state battery is provided. The solid electrolyte material has the following chemical formula XM ₂ (PS ₄ ) ₃ , where P is phosphorus, S is sulfur and X is lithium (Li), sodium (Na), silver (Ag) or magnesium (Mg ₀ s) and M is titanium (Ti), zirconium (Zr), germanium (Ge), silicon (Si), tin (Sn) or a mixture of X and aluminium (X + Al) and the method comprises:

- mixing powders so as to obtain a powder mixture; and

- sintering the powder mixture for a period of time equal to or greater than 75 hours and equal to or smaller than 500 hours at a sintering plateau temperature so as to obtain the solid electrolyte material;

wherein the solid electrolyte material exhibits peaks in positions of 2Q = 13,64° (±1°), 16,48° (±1°) and 22,18° (±1°) in a X-ray diffraction measurement using CuKa line, where is the intensity in arbitrary units of the peak at 13,64°(±1°) and IB is the intensity in arbitrary units of a peak at 23,34°

[0006] The solid electrolyte material having the above chemical formula and exhibiting the cited peak in a X-ray diffraction measurement using CuKa line have a crystallographic structure allowing for an increase of the X ionic conductivity of such solid electrolyte material.

[0007] This increase in ionic conductivity of the X species allows for fast charging of the battery, especially at low temperature, for example at temperature below 0°C (degree Celsius).

[0008] The solid electrolyte material is crystalized in an orthorhombic crystal system (space group Fddd (70)). The crystal structure is made of PS ₄ tetrahedra and MS ₆ octahedra. A three dimensional (3D) framework structure is formed by edge sharing of PS ₄ and MS ₆ and X species are located at the interstitial site of the 3D framework structure.

[0009] According to embodiments, the solid electrolyte material exhibits peaks in positions of 2Q = 13,64° (±1°), 13,76° (±1°), 14,72° (±1°), 15,36° (±1°), 15,90° (±1°), 16,48° (±1°), 17,42° (±1°), 17,56° (±1°), 18,58° (±1°), and 22,18° (±1°) in a X-ray diffraction measurement using CuKa line.

[0010] According to embodiments, the component is placed in a container and sealed under Argon at a pressure equal to or smaller than 100 Pa, preferably equal to or smaller than 50 Pa.

[0011] According to embodiments, the method comprises a step of amorphasizing the powder mixture so as to obtain an amorphasized powder mixture. [0012] According to embodiments, the sintering plateau temperature is equal to or smaller than 500°C, preferably equal to or smaller than 400°C.

[0013] The powder mixture being amorphasized, the powder mixture is more reactive and sintering of the powder mixture may be obtained at temperature equal to or smaller than 500°C.

[0014] According to embodiments, the sintering plateau time is equal to or greater than 100 hours, preferably equal to or greater than 150 hours and equal to or smaller than 400 hours, preferably equal to or smaller than 300 hours.

[0015] According to embodiments, the powder mixture is pressed at a pressure equal to or greater than 25 MPa, preferably equal to or greater than 50 MPa, more preferably equal to or greater than 75 MPa, and equal to or smaller than 500 MPa, preferably equal to or smaller than 400 MPa, more preferably equal to or smaller than 300 MPa.

[0016] According to embodiments, X is lithium.

[0017] According to embodiments, M is titanium.

[0018] According to embodiments, M is (X + Al).

[0019] M being a mixture of X and aluminium, the content of X is increased and the electrochemical stability of the solid electrolyte material is increased thanks to aluminium.

[0020] According to embodiments, X is lithium and M is titanium.

[0021] According to embodiments, X is lithium and M is a mixture of lithium and aluminium (Li + Al).

[0022] According to embodiments, when X is lithium, the diffusion coefficient of lithium in the solid electrolyte material at -20°C is greater than or equal to 3,0.10 ¹² m ² /s (meter square per second).

[0023] The diffusion coefficient is obtained from the Stejskal-Tanner equation:

/ = /„ exp (- y ² g ² d ² (D - 0 ) (1)

where I is the signal intensity with the gradient, Io is the signal intensity without the diffusion weighting, g is the proton gyromagnetic ratio, g is the strength of the gradient pulse, 6 is the duration of the pulse, D is the time between the leading edges of two gradient pulses and D is the diffusion coefficient.

[0024] The diffusion coefficient of lithium in the solid electrolyte material is measured by ⁷ Li pulse field gradient (PFG) nuclear magnetic resonance (NMR). The measurement is performed at 155,6 MHz using Avance III HD spectrometer (Bruker Biospin) with a Diff60 diffusion probe. The diffusion coefficient D is measured with D varying from 6 ms (millisecond) to 500 ms in a temperature range between 253,15 K (Kelvin) (-20°C) and 353,15 K (80°C) by varying the gradient strength g from 0 to 25 Tm ¹ (Tesla per meter) and the duration d of the pulse field gradient g from 1 ms to 2,5 ms.

[0025] The present disclosure also provides a method for producing a solid electrolyte for a solid state battery, the method comprising the steps of producing a solid electrolyte material as defined above.

[0026] According to embodiments, the powder mixture is formed in a shape of the solid electrolyte.

[0027] The present disclosure also provides a solid electrolyte material for a solid state battery having the following chemical formula XM ₂ (PS ₄ )3, where P is phosphorus, S is sulfur and X is lithium (Li), sodium (Na), silver (Ag) or magnesium (Mg ₀ ,s) and M is titanium (Ti), zirconium (Zr), germanium (Ge), silicon (Si), tin (Sn) or a mixture of X and aluminium (X + Al) and exhibiting peaks in positions of 2Q = 13,64° (±1°), 16,48° (±1°) and 22,18° (±1°) in a X- ray diffraction measurement using CuKa line, where I _A is the intensity in arbitrary units of the peak at 13,64°(±1°) and IB is the intensity in arbitrary units of a peak at 23,34° (±1°), (IA - IB)/(IA + IB) > 0.

[0028] The solid electrolyte material having the above chemical formula and exhibiting the cited peak in a X-ray diffraction measurement using CuKa line have a crystallographic structure allowing for an increase of the X ionic conductivity of such solid electrolyte material.

[0029] This increase in ionic conductivity of the X species allows for fast charging of the battery especially at low temperature, for example at temperature below 0°C.

[0030] According to embodiments, the solid electrolyte material exhibits peaks in positions of 2Q = 13,64° (±1°), 13,76° (±1°), 14,72° (±1°), 15,36° (±1°), 15,90° (±1°), 16,48° (±1°), 17,42° (±1°), 17,56° (±1°), 18,58° (±1°), and 22,18° (±1°) in a X-ray diffraction measurement using CuKa line.

[0031] According to embodiments, X is lithium.

[0032] According to embodiments, M is titanium.

[0033] According to embodiments, M is (X + Al).

[0034] M being a mixture of X and aluminium, the content of X is increased and the electrochemical stability of the solid electrolyte material is increased thanks to aluminium.

[0035] According to embodiments, X is lithium and M is titanium.

[0036] According to embodiments, X is lithium and M is a mixture of lithium and aluminium (Li + Al).

[0037] According to embodiments, when X is lithium, the diffusion coefficient of lithium in the solid electrolyte material at -20°C (degree Celsius) is greater than or equal to 3,0.10 ¹² m ² /s (meter square per second),

[0038] The present disclosure also provides a solid electrolyte comprising such a solid electrolyte material.

[0039] The present disclosure also provides a solid state battery comprising such a solid electrolyte.

[0040] It is intended that combinations of the above-described elements and those within the specification may be made, except where otherwise contradictory.

[0041] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the disclosure, as claimed.

[0042] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the disclosure and together with the description, serve to explain the principles thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Fig. 1 shows a schematic cross-sectional view of an exemplary solid state battery according to embodiments of the present disclosure. [0044] Figs. 2A-2C show X-ray diffraction spectrums of solid electrolyte materials according to embodiments of the present disclosure;

[0045] Fig. 3A-3B show X-ray diffraction spectrums of comparative sample;

[0046] Fig. 4. Fig. 4 shows a flow chart of a method for producing a solid electrolyte material according to embodiments of the present disclosure;

[0047] Fig. 5 shows a graph of (IA - IB)/(IA + IB) as a function of the sintering plateau time expressed in hours.

DETAILED DESCRIPTION

[0048] Reference will now be made in detail to exemplary embodiments of the disclosure, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.

[0049] Fig. 1 shows a schematic cross-sectional view of an exemplary solid state battery 10 according to embodiments of the present disclosure. In Fig. 1, the solid state battery 10 comprises a first cell 20A and a second cell 20B, adjacent to the fist cell 20A. The first cell 20A and the second cell 20B form a stack of cells 22. Each cell 20A, 20B comprises a positive electrode 12 and a negative electrode 14. The cell 10 also comprises a solid electrolyte 16 disposed between the positive electrode 12 and the negative electrode 14, the positive electrode 12, the solid electrolyte 16 and the negative electrode 14 being disposed between two current collectors 18. The solid electrolyte 16 is as previously defined.

[0050] The current collectors 18 may be made of stainless steel, gold (Au), platinum (Pt), nickel (Ni), aluminum (Al) or copper (Cu) or alloys comprising these materials. This list is not limitative. The two current collectors 18 may be made of the same material or the two current collectors may be made of different materials. For example, the current collector on the positive electrode side may be made of Al and the current collector on the negative electrode side may be made of Cu.

[0051] The solid state battery 10 comprises a container 24 enclosing the stack of cells 22. In Fig. 1, the stack of cells 22 comprises a first cell 20A and a second cell 20B, the two adjacent cells 10 share a current collector 18. The stack of cells 22 may comprise more cells 10. The elements of the solid state battery 10 that are not requested for the comprehension of the present disclosure have been omitted and will not be describe in this disclosure.

[0052] The solid state battery 10 of Fig. 1 is schematic. It is understood that an solid state battery 10 may comprise a large number of adjacent cells 20A, 20B.

[0053] Fig. 2A-2C show X-ray diffraction spectrum of respectively Sample 1- Sample 3, which are solid electrolyte 16 according to embodiments of the present disclosure. The intensity of the peak is in arbitrary units and is given as a function of 2Q values expressed in degrees.

[0054] As may be seen on Fig. 2A-2C, Samples 1 to 3 exhibit the peaks in positions of 2Q = 13, 64° (±1°), 13,76° (±1°), 14,72° (±1°), 15,36° (±1°), 15,90° (±1°), 16,48° (±1°), 17,42° (±1°), 17,56° (±1°), 18,58° (±1°), and 22,18° (±1°) in a X-ray diffraction measurement using CuKa line.

[0055] Fig. 3A-3C show X-ray diffraction spectrum of respectively Sample 4 and Sample 5, which are comparative sample.

[0056] Samples 1 to 5 are LiThiPS^ solid electrolyte.

[0057] I _A is the intensity in arbitrary units of the peak at 13,64°(±1°) (see Figs. 2A-2C) and I _B is the intensity in arbitrary units of a peak at 23,34° (±1°) (see Figs. 2C, 3A-3B).

[0058] A method 100 for producing a solid electrolyte material and/or a solid electrolyte 16 according to embodiments of the present disclosure will be described in reference to Fig. 4, taking Sample 1.

[0059] In step 102, 0,0396 g (gram) of Li ₂ S, 0,5745 g of P2S5 and 0,3859 g of TiS ₂ are mixed together so as to obtain a powder mixture. U ₂ S (99%, lithium sulphide, Sigma-Aldrich®), P2S5 (98%, phosphorous pentasulfide, Sigma- Aldrich®) and TiS ₂ (99,9%, titanium disulphide, Sigma-Aldrich®) are powders having a degree of purity equal to or greater than 99 mass%.

[0060] In step 104, which is not a mandatory step, the powder mixture is amorphasized in a planetary milling equipment (Fritsch, P7). The powder mixture was disposed in a zirconium pot of 45 mL (millilitre) content with 18 zirconium balls having a diameter of 10 mm (millimetre) under Argon. The powder mixture was amorphasized for 40 hours at 370 rpm (round per minute) so as to obtain amorphasized powder mixture.

[0061] In step 106, which is not a mandatory step, the amorphasized powder mixture is pressed at a pressure equal to or greater than 25 MPa, preferably equal to or greater than 50 MPa, more preferably equal to or greater than 75 MPa, and equal to or smaller than 500 MPa, preferably equal to or smaller than 400 MPa, more preferably equal to or smaller than 300 MPa.

[0062] For example 100 mg of the amorphasized powder mixture is pressed at 200 MPa.

[0063] In step 108, the pressed amorphasized powder mixture is sintered in a closed glass tube.

[0064] For example, the 100 mg pressed amorphasized powder mixture is put into a glass tube and the glass tube is sealed under Argon under very low pressure, for example 30 Pa. The pressed amorphasized powder mixture is sintered at a sintering plateau temperature of 400°C (degree Celsius) for a sintering plateau time of 300 hours so as to obtain the solid electrolyte material and/or the solid electrolyte 16 of Sample 1.

[0065] The method may further include a step of shaping the powder mixture into a desired shape of the solid electrolyte 16. For example, the shaping step may be included in step 106. Shaping of powder into a component such as the solid electrolyte 16 is known.

[0066] The method for producing Sample 2 to Sample 5 is similar to the method for producing Sample 1, except that, in step 108, the sintering plateau time of the pressed amorphasized powder was respectively 200 hours, 100 hours, 72 hours and 8 hours.

[0067] As shown on Figs. 2A and 5, (I _A - IB)/(IA + IB) = 1 for Sample 1.

[0068] As shown on Figs. 2B and 5, (I _A - IB)/(IA + IB) = 1 for Sample 2.

[0069] As shown on Figs. 2C and 5, (I _A - IB)/(I _A + IB) = 0.104 for Sample 3.

[0070] As shown on Figs. 3A and 5, (I _A - I _B )/(I _A + IB) = -1 for Sample 4.

[0071] As shown on Figs. 3B and 5, (I _A - I _B )/(I _A + IB) = -1 for Sample 5.

[0072] The diffusion coefficient of lithium in the solid electrolyte material was measured for Sample 1 and Sample 5 at -20°C. [0073] The diffusion coefficient is obtained from the Stejskal-Tanner equation:

where I is the signal intensity with the gradient, I ₀ is the signal intensity without the diffusion weighting, g is the proton gyromagnetic ratio, g is the strength of the gradient pulse, d is the duration of the pulse, D is the time between the leading edges of two gradient pulses and D is the diffusion coefficient.

[0074] The diffusion coefficient of lithium in the solid electrolyte material is measured by ⁷ U pulse field gradient (PFG) nuclear magnetic resonance (NMR). The measurement is performed at 155,6 MHz using Avance III HD spectrometer (Bruker Biospin) with a Diff60 diffusion probe. The diffusion coefficient D is measured with D varying from 6 ms (millisecond) to 500 ms in a temperature range between 253,15 K (Kelvin) (-20°C) and 353,15 K (80°C) by varying the gradient strength g from 0 to 25 Tm ¹ (Tesla per meter) and the duration d of the pulse field gradient g from 1 ms to 2,5 ms.

[0075] The diffusion coefficient D of lithium in the solid electrolyte material is equal to 3,2.10 ¹² m ² /s for Sample 1 and to 2,8.10 ¹² m ² /s for Sample 5.

[0076] Throughout the description, including the claims, the term "comprising a" should be understood as being synonymous with "comprising at least one" unless otherwise stated. In addition, any range set forth in the description, including the claims should be understood as including its end value(s) unless otherwise stated. Specific values for described elements should be understood to be within accepted manufacturing or industry tolerances known to one of skill in the art, and any use of the terms "substantially" and/or "approximately" and/or "generally" should be understood to mean falling within such accepted tolerances.

[0077] Where any standards of national, international, or other standards body are referenced (e.g., ISO, etc.), such references are intended to refer to the standard as defined by the national or international standards body as of the priority date of the present specification. Any subsequent substantive changes to such standards are not intended to modify the scope and/or definitions of the present disclosure and/or claims. [0078] Although the present disclosure herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present disclosure.

[0079] It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims.