Solid-State Electrolyte for Lithium-Ion Battery and a Method of Synthesis thereof

Abstract

Proposed is a method of synthesizing a solid-state electrolyte of Li.sub.3HaIO formula for use in a lithium-ion battery. The method consists of uniformly mixing at least LiOH and LiHaI in a stoichiometric quantities, heating the prepared mixture to a melting temperature and causing a reaction of formula (2LiOH+LiHaI=Li.sub.3HaIO+H.sub.2O) between the at least LiOH and LiHaI in a process free of forming a perovskite structure and at a temperature, at which H.sub.2O that forms at the aforementioned reaction is converted into a bound form, whereby a reaction product is obtained. According to another modification of the method, prior to the stage of melting the mixture, a reinforcement mesh is immersed into the mixture, whereby after mixture is solidified, a solid-state electrolyte reinforced with the mixture embedded into its material is obtained.

Claims

1. A method of synthesizing a solid-state electrolyte of Li.sub.3HaIO formula for use in a lithium-ion battery, the method comprising: uniformly mixing at least LiOH and LiHaI in stoichiometric quantities thus forming a uniform mixture of the at least LiOH and LiHaI; heating the uniform mixture to a mixture melting temperature thus forming a mixture melt; and causing a reaction of formula (2LiOH+LiHaI=Li.sub.3HaIO+H.sub.2O) between the at least LiOH and LiHaI in a process free of forming an anti-perovskite structure and at a temperature, at which H.sub.2O that is formed in the aforementioned reaction is converted into a bound form, whereby a reaction product is obtained; and cooling the reaction product to a solid state, whereby a solid-state electrolyte of Li.sub.3HaIO formula for use in a lithium-ion battery is obtained.

2. The method of claim 1, wherein a HaI is selected at least from Cl, Br, and/or I).

3. The method of claim 2, wherein oxides of Ca, Ba, Mg, and/or Sr are selectively added to the mixture in amounts of 0.001 wt. % to 6 wt. %. to create solid solutions in the obtained solid electrolyte.

4. The method of claim 2, wherein the step of heating is carried out in a stepwise manner with gradual increase of a temperature of the mixture from step to step until the mixture melting temperature is achieved.

5. The method of claim 2, wherein the synthesizing in carried out in solid electrolyte synthesizing tools comprising a container having a container bottom and made of a heat-resistant material, a cuvette having a cuvette bottom placed onto the container bottom, and a pallet having a top surface and placed onto the cuvette bottom and wherein prior to the step of heating the uniform mixture, the solid electrolyte synthesizing tools is preheated to a temperature in the range of 180° C. to 220° C., and the uniform mixture is then loaded onto the top surface of the pallet.

6. The method of claim 3, wherein the synthesizing in carried out in solid electrolyte synthesizing tools comprising a container having a container bottom and made of a heat-resistant material, a cuvette having a cuvette bottom placed onto the container bottom, and a pallet having a top surface and placed onto the cuvette bottom and wherein prior to the step of heating the uniform mixture, the solid electrolyte synthesizing tools is preheated to a temperature in the range of 180° C. to 220° C., and the uniform mixture is then loaded onto the top surface of the pallet.

7. The method of claim 5, wherein the cuvette is made of a metal foil, the pallet is made of metal, and the top surface of the pellet has a polished surface.

8. The method of claim 6, wherein the cuvette is made of a metal foil, the pallet is made of metal, and the top surface of the pellet has a polished surface.

9. The method of claim 1, further comprising a step of placing into the uniform mixture a reinforcement mesh prior to heating and causing the reaction of formula (2LiOH+LiHaI=Li.sub.3HaIO+H.sub.2O) thus embedding the mesh into the solid-state electrolyte.

10. The method of claim 4, further comprising a step of placing into the uniform mixture a reinforcement mesh prior to heating and causing the reaction of formula (2LiOH+LiHaI=Li.sub.3HaIO+H.sub.2O) thus embedding the mesh into the solid-state electrolyte.

11. The method of claim 10, wherein the reinforcement mesh comprises a plate having a thickness in the range of from about 10 microns to several millimeters.

12. The method of claim 11, wherein the reinforcement mesh is made from a material selected from a metal and a dielectric material that possesses heat resistant properties of wetting and chemical neutrality with respect to the mixture.

13. The method of claim 12, wherein the reinforcement mesh has holes to be filled with the mixture melt in the step of forming a mixture melt.

14. The method of claim 12, wherein the dielectric material is mica.

15. The method of claim 13, wherein the dielectric material is mica.

16. A solid-state electrolyte for lithium-ion battery synthesized by the method according to claim 9.

17. A solid-state electrolyte for lithium-ion battery synthesized by the method according to claim 13.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] FIG. 1A is a vertical cross-sectional view of tools for synthesis of a solid Li-ion electrolyte of the present invention.

[0025] FIG. 1B is a diametrical cross-sectional view of the solid Li-ion electrolyte obtained by the method according to one aspect of the invention.

[0026] FIG. 2 is a photograph of a sealed container filled with argon and containing the product shown in FIG. 1B.

[0027] FIG. 3A is a vertical cross-sectional view similar to FIG. 1A that illustrates synthesis of a Li-ion electrolyte that is reinforced by a mesh embedded in the material of the electrolyte, FIG. 3A showing a stage of filling a cuvette with a powdered mixture over the mesh.

[0028] FIG. 3B is a view similar to FIG. 3A showing the Li-ion electrolyte in a solidified state with the reinforcement mesh embedded in the material of the solid electrolyte.

[0029] FIG. 3C is a diametrical cross-sectional view of the reinforced solid Li-ion electrolyte of FIG. 3B, which in a top view has a round shape.

[0030] FIG. 3D is a top view of a solid-state electrolyte in the form of a thin plate having embedded reinforcement mesh with holes.

[0031] FIG. 3E is a diametrical cross-sectional view of the solid-state electrolyte along line IIIE-IIIE of FIG. 3D.

[0032] FIG. 3F is an example of a reinforcement mesh having a square-shape top view.

[0033] FIG. 3G is a top view of the solid-state electrolyte of FIG. 3F with the reinforcement mesh embedded into the material of the solidified mixture.

[0034] FIG. 3H is a cross-sectional view of the solid-state electrolyte along line IIIH-IIIH of FIG. 3G.

[0035] FIG. 4A is a LiCl—LiOH state phase diagram.

[0036] FIG. 4B is a LiBr—LiOH state phase diagram.

[0037] FIG. 4C is a LiI—LiOH state phase diagram.

DETAILED DESCRIPTION OF THE INVENTION

[0038] The present invention relates to the field of electric energy storage devices and, more particularly, to lithium-ion batteries, specifically to solid electrolytes for solid-state lithium-ion batteries.

[0039] The detailed preceding description of the prior art demonstrates complexity, high cost, and time consumption of the known methods used for synthesis of solid-state electrolytes, which are a subject of the present invention. It is important to note that methods discussed in the prior-art section involve a complicated primary step of synthesis of crystalline anti-perovskite structure with subsequent conversion of the obtained structure into an amorphous state. In contrast to this, the method of the present invention suggests direct one-stage synthesis of solid electrolytes of the aforementioned group without resorting to the anti-perovskite phase formation. The method of the invention provides significant decrease in costs and production time along with simplification of the equipment needed for synthesis.

[0040] According to one aspect of the invention, the method of the invention consists of synthesis of a solid Li.sub.3HaIO (where HaI is Cl, Br, I) electrolyte following the well-known reaction (2LiOH+LiHaI=Li.sub.3HaIO+H.sub.2O) directly from starting reagents without preliminary synthesis of anti-perovskites. In other words, all the components are selected in appropriate molar ratios and uniformly mixed. It is allowable to introduce small amounts of Ca, Ba, Mg, or Sr oxides with at least 98% purity to create solid solutions in the structure of the solid electrolyte being produced. The main reagents are LiOH of 98% purity and LiCl of 99.5% purity. The oxides of Ca, Ba, Mg, or Sr are added in amounts of 0.001 wt. % to 6 wt. %. If they are added in amount less than 0.001 wt. %, they do not produce a noticeable effect but if the added amounts exceed the upper limit, they may lead to significant increase in the melting point.

[0041] Solid electrolyte synthesizing tools 20 for synthesis are schematically shown in FIG. 1A in a vertical cross section. The tools 20 consist of a container 22 made of a heat-resistant material, e.g., nickel or stainless steel. Inserted into the container 22 is a cuvette 24 made, e.g., of an aluminum foil having, e.g., 16 mm in diameter. A stainless-steel pellet 26 with a well-polished upper surface 26a is placed onto the bottom 24a of the cuvette 24. The container 22 with the cuvette 24 and the pellet 26 is preheated to a temperature of 200° C. and then filled with an appropriate quantity of the aforementioned mixture 28, which is placed into the cuvette over the pellet 26.

[0042] Next, the temperature is increased in a stepwise manner with 5 min intervals to 220° C., 250° C., 270° C., and 300° C. until complete melting of the mixture is achieved.

[0043] The assembly of the container, cuvette, melt, and pellet is cooled to a temperature at which the melt solidifies to form a solid substance 30 (FIG. 1B) and then is cooled to about 100° C. and is placed into a sealed container 32 filled with argon (FIG. 2). FIG. 2 is a photograph of the sealed container 32, which is filled with argon and contains the obtained product 30.

[0044] In FIG. 1B, the obtained solid Li-ion electrolyte 30, which in this example presumably has a round top view, is shown in a diametrical cross-section.

[0045] According to another aspect of the invention, the method of the invention consists of synthesis of a reinforced solid Li.sub.3HaIO (where HaI is Cl, Br, I) electrolyte. The mixture is prepared in the same way as in the process of the first modification, i.e., the process follows the well-known reaction (2LiOH+LiHaI=Li.sub.3HaIO+H.sub.2O) directly from starting reagents without preliminary synthesis of anti-perovskites. In other words, all the components are selected in appropriate molar ratios. It is allowable to introduce small amounts (in amounts of hundredths of wt. %) of additives such as Ca, Ba, Mg, or Sr oxides having a purity of at least 98% to create solid solutions in the structure of the solid electrolyte being produced. The main reagents are LiOH of 98% purity and LiCl of 99.5% purity.

[0046] Solid electrolyte synthesizing tools 40 for synthesis are schematically shown in FIGS. 3A and 3B in a vertical cross section. The tools 40 are the same as the tools 20 of the first modification but the process is different in that it involves a step of reinforcement of the target product. In other words, the tools consist of a container 22 made of a heat-resistant material, e.g., nickel or stainless steel. Inserted into the container 22 is a cuvette 24 made, e.g., of an aluminum foil having, e.g., 16 mm in diameter. A stainless-steel pellet 26 with a well-polished upper surface 26a is placed onto the bottom 24a of the cuvette 24, and a mesh 42 for reinforcing the product being manufactured is then placed onto a well-polished upper surface 26a.

[0047] Next, the temperature is increased in a stepwise manner with 5 min intervals to 220° C., 250° C., 270° C., and 300° C. until complete melting of the mixture is achieved.

[0048] The assembly of the container, cuvette, mesh, melt, and pellet is cooled to a temperature at which the melt solidifies to form a solid substance 46 (FIG. 3B) and then is cooled to about 100° C. The cuvette 24 is removed from the container 22 and the obtained solid electrolyte 46 is extracted from the cuvette and is placed into a sealed container filled with argon similar to container 32 shown in FIG. 2.

[0049] The obtained reinforced solid Li-ion electrolyte 46, which in this example presumably has a round top view, is shown in a diametrical cross-section in FIG. 3C. The cuvette 24 may be reused or discarded.

[0050] The mesh is made, e.g., from metal or dielectric. It is important that the mesh be made from a heat-resistant material that possesses good properties of wetting and chemical neutrality with respect to the melt of the mixture used in the process. From this point of view, appropriate metallic materials of the mesh are nickel, stainless steel, etc. An example of dielectrics is mica, from which a mesh can be made, e.g., by forming multiple holes in a mica plate. The mica plate may be comprised of a thin film having a thickness of from about 10 microns to several millimeters. The holes may be arranged with regular intervals or at random. An example of a mesh with regular interval of holes or cells embedded into the material of the solid-state electrolyte 46a is shown in FIG. 3D and FIG. 3E, where FIG. 3D is a top view of the solid-state electrolyte 46a in the form of a thin plate having embedded reinforcement mesh 42a with holes 42a1, 42a2, . . . 42an. FIG. 3E is a diametrical cross-section of the solid-state electrolyte 46a along line IIIE-IIIE of FIG. 3D.

[0051] Alternatively, the reinforcement mesh can be woven from a thin, e.g., nickel wire with a wire thickness of about 10 microns or thicker. In that case, the final solid-state electrolyte plate may be as thin as about 25 microns. The thickness of the plate may be further reduced by reducing the thickness of the wire from which the mesh is made.

[0052] The reinforcement net is not necessarily round in its shape and may be square, rectangular or any other shape.

[0053] An example of a reinforcement mesh 42b having a square shape in a top view is shown in FIG. 3F, where reference numerals 42b1, 42b2, . . . 42bn designate cells or holes formed in the mesh. FIG. 3G is a top view of a solid-state electrolyte 46b of a square shape with the reinforcement mesh 42b embedded into the material of the solidified mixture, i.e., in the body of the final product 46b.

[0054] FIG. 3H is a cross-sectional view of the solid-state electrolyte 46b along line IIIH-IIIH of FIG. 3G.

[0055] The cells 42b1, 42b2 . . . 42bn can be formed, e.g., by etching or stamping a thin aluminum or nickel foil as thin as, e.g. 5 microns. In case of aluminum, the surface of the mesh should be passivated.

[0056] According to another aspect of the invention, in the process shown in FIGS. 3A and 3B, instead of covering the mesh 42 with a mixture 44 and subsequent embedding of the mesh 42 in the molten mixture, it is possible to place the mesh 42 onto the stainless-steel pellet 26 by immersing the mesh into. the pre-melted mixture 44.

[0057] As mentioned in the work of Braga et al. that describes the synthesis of solid electrolytes for use in solid Li-ion batteries (see Journal of Materials Chemistry, A., 2014, 2014, pages 1-11), it is possible to create inexpensive solid lithium electrolytes with the Li.sub.3ClO. However, based on the graphs (see FIGS. 1 to 3 of the aforementioned work), it is obvious that the basic Li.sub.3ClO compound, obtained by the authors, has an admixture of water of crystallization in the bound form of hydrates of lithium chlorides such as Li.sub.5(OH).sub.2Cl.sub.3 (see X-ray phase analysis, FIG. 1 of the Braga, et al. publication) as well as in the form (FIG. 2), where, in addition to the temperature determined by the authors as the glass transition temperature of 136° C., one can see a characteristic change in the curve around 70-100° C. indicating the existence of adsorbed water.

[0058] FIG. 4A of the present patent specification is a LiCl—LiOH state diagram (see N. A. Reshetnikov and. G. M. Unzhakov (Journal of Inorganic Chemistry [Russian—Zh. Neorg. Khim. 1958, 3, 1433-1438]). Thermographic and visual polythermal methods were used in studies of LiOH—LiCl and LiOH—NaOH systems. Binary compound forms shown in both systems were not re-examined and are characterized by the presence of only one compound (Li.sub.2OHCl).

[0059] This diagram shows the compositions currently mentioned in the literature. The composition of Li.sub.3(OH).sub.2Cl is eutectic and, as follows from the above, this mixture is the initial one used in the synthesis of anti-perovskite (2LiOH+LiCl). On the other hand, as follows from the reaction, the composition decomposes into water and Li.sub.3OCl, even with simple mixing (see International Patent Publication WO2019129267 issued on 7 Apr. 2019; inventors: B. C. Bogdan, et al.).

[0060] Thus, in reality, only a phase diagram of Li.sub.3ClO—Li.sub.3ClO.2H.sub.2O exists for this composition. After removing the adsorbed water, the composition of Li.sub.3ClO begins to melt at 220° C. When the bound water is removed, further stepwise increase, in temperature (e.g. to 250° C., 270° C., and 300° C.) with subsequent cooling leads to a respective increase in the melting point. Batteries made from the melts of the above-mentioned compositions have a current that decreases with an increase in the melting point, i.e., due to the removal of water. A similar effect is also achieved with the presence in the composition Li.sub.3ClO of additives such as Mg, Ba, Ca, Sr or other elements in the form of solid solutions, which distort the structure of the original composition in such a way that hydroxyl ions with one or another form of water can be incorporated into the structure of the electrolyte and thus increase ionic conductivity of the electrolyte.

[0061] For the LiBr—LIOH compositions, the phase diagram of FIG. 4B [see Data FTsalt—FACT salt databases] shows that at atmospheric pressure the Li.sub.3BrO compound is not observed. However, the properties of the melt of this composition also depend on the amount of water and the size of the impurity ions.

[0062] The state diagram of LiOH—LiI, which is shown in FIG. 4C [see Data FTsalt—FACT salt databases] also does not contain a Li.sub.3IO compound, however, with a general coincidence of the properties of electrolytes, depending on the presence of water, the diagram it is characterized by the expectedly lower melting temperatures of mixtures and compounds.

[0063] It is known that manufacturers try to avoid the presence of water in lithium batteries due to the undesirable reactions of lithium with the release of hydrogen. However, it should be emphasized that in our case we are talking about bound water, which will be released at temperatures above 200° C. On the other hand, it is obvious that we have deal with a special type of ionic conductivity in such batteries, which is fundamentally different from that in traditional batteries. In lithium batteries of a new type, the trace residual water can be redistributed, ultimately resulting in improved battery performance over time.

[0064] Thus, it has been shown the method of the invention for synthesizing a solid-state electrolyte of Li.sub.3HaIO formula for use in a lithium-ion battery consists of uniformly mixing at least LiOH and LiHaI in stoichiometric quantities thus forming a uniform mixture of the at least LiOH and LiHaI, heating the uniform mixture to a mixture melting temperature thus forming a mixture melt, causing a reaction of formula (2LiOH+LiHaI=Li.sub.3HaIO+H.sub.2O) between the at least LiOH and LiHaI in a process free of forming an anti-perovskite structure and at a temperature, at which H.sub.2O that is formed in the aforementioned reaction is converted into a bound form, whereby a reaction product is obtained, and cooling the reaction product to a solid state, whereby a solid-state electrolyte of Li.sub.3HaIO formula for use in a lithium-ion battery is obtained.

[0065] The invention was described in detail with reference to specific examples and drawings. It is understood, however, that these examples and drawings should not be construed as limiting the invention and that any changes and modifications are possible without departure from the scope of the attached claims. For example, the shape of the molded solid-state Li-ion electrolyte may be different from the round and square shapes shown in the drawings. The melting process and its working characteristics may be different from the temperatures and time intervals described in the specification. The mesh may be a commercially available product or produced by different methods. The cells of the mesh may be of any shape, and the cells may be arranged regularly or at random. More than one reinforcement mesh can be used.