Solid electrolyte materials, their manufacturing process and uses

Abstract

A manufacturing process for a lithium titanium phosphate-based solid electrolyte material is disclosed, the process comprising the steps of: (i) providing a solution containing a Li source material, a Ti source material, a P source material, and optionally a Si source material and / or a source material of a metal M, where M is selected from the group of Al, Ga, Ge, In, Sc, V, Cr, Mn, Co, Fe, Y, a lanthanide, or a combination thereof; (ii) generating an aerosol from the solution; (iii) subjecting the generated aerosol to flame pyrolysis to form a granular precursor material therefrom; and (iv) subjecting the granular precursor material to electric field assisted sintering to form a lithium titanium phosphate-based solid electrolyte material. Further disclosed are solid electrolyte materials obtainable by said manufacturing process and articles comprising the same.

Description

[Technical Field]

[0001] The present invention relates to a solid electrolyte material and a method for its manufacture. More particularly, the present invention is directed to a process for the manufacture of a lithium titanium phosphate-based solid electrolyte material, which involves producing a granular precursor material by flame pyrolysis, followed by a subsequent electric field-assisted sintering step. The present invention further relates to articles comprising such formed solid electrolyte material, and their use as, for example, electrolytic membranes in processes for separating lithium from spent lithium batteries. [Background technology]

[0002] Lithium plays an important role in today's rechargeable energy storage devices, with many applications including electric vehicles, portable devices, and intermittent energy storage facilities for storing energy from renewable sources such as solar and wind energy. Given the greatly increased use of lithium-based energy storage devices and the limited lithium resource, recycling such devices at their end of life is of both commercial and environmental interest. A process for separating lithium from spent battery materials can involve, for example, subjecting the material obtained from shredding spent batteries to a leaching process, which dissolves metals, particularly lithium, contained therein. In a subsequent step, such lithium can be recovered from the mixture via an electrolysis process. The electrolysis process is based on a current-driven redox reaction and is carried out by applying an appropriate voltage difference to two electrodes, i.e., an anode and a cathode, in contact with a metal-containing solution and typically separated by a membrane of a solid electrolyte material. The solid electrolyte material exhibits selective conductivity for ions, such as lithium ions, thus facilitating ion exchange between the anode and cathode half-cells. Industrial electrolysis processes impose high requirements on the electrolyte membranes used, such as electrical properties, reliability, and resistance to mechanical breakdown. When such materials are used as electrode materials or electrolytes for all-solid-state lithium-based energy storage devices, similarly demanding characteristics are also required. Therefore, there is a need to provide solid electrolyte materials that combine high lithium-ion conductivity with robustness and high reliability against mechanical breakdown.

[0003] A typical material used to fabricate the electrolytic membrane or solid electrolyte is, for example, lithium titanium phosphate (LTP for short). LTP is known as a material with excellent conductivity of lithium ions due to its so-called NASICON-type crystal structure. NASICON is an acronym for sodium ("Na") superionic conductor, typically with the chemical formula Na 1+x Zr2Si x P 3-x O 12Refers to a group of solids having x where 0 < x < 3. In a broader sense, it is also used for similar compounds in which Na, Zr, and / or Si are replaced by equivalent elements such as Na by Li. Due to the mobility of sodium or lithium ions within the crystal structure, NASICON-type compounds are characterized by an ionic conductivity of about 10 -5 ~10 -3 S / cm at room temperature. Thereby, sodium or lithium ions are located at two types of interstitial positions within a covalent network consisting of ZrO6 / TiO6 octahedra and SiO4 / PO4 tetrahedra sharing common corners. When moving between these two interlattice sites, sodium or lithium ions must pass through a bottleneck, the size of which accordingly affects the ionic conductivity of the NASICON-type material. By changing the chemical composition of the NASICON-type material, the size of the bottleneck can be varied. Thus, the ionic conductivity depends especially on the specific chemical composition of the material and can be positively influenced by doping with other elements. For example, in LTP materials, Ti 4+ ions can be partially substituted with M 3+ cations such as Al 3+ , V 3+ or Sc 3+ , which may result in positive charge defects that can be compensated by additional Na + / Li + ions, and thus it is known that the ionic conductivity increases due to an increase in the number of charge carriers. Alternatively or additionally, substitution of SiO4 groups for PO4 may also potentially increase the ionic conductivity of the resulting NASICON-type electrolyte material.

[0004] Different methods for manufacturing LTP solid electrolytes are known in the literature, and these typically involve the preparation of a granular precursor material that is subsequently subjected to a sintering process.

[0005] One of the most frequently used methods for preparing granular precursor materials is sol-gel synthesis, as described, for example, in EP 3 189 008. However, the gel thus obtained must be extensively dried and ground before the sintering process, which is both costly and time-consuming. Furthermore, the method according to EP 3 189 008 requires a pre-sintering step at 600 °C to remove organic compounds contained in the resulting gel, which is necessary to ensure the sinterability of the granular precursor material subjected to the sintering step.

[0006] Another method conventionally applied in this regard is the rapid cooling of a melt containing the individual components, as described, for example, for lithium aluminum phosphate titanate (abbreviated as LATP) by Waetzig et al. in Journal of Alloys and Compounds 818 (2020) 153237. However, this method requires, on the one hand, a large amount of energy to melt the additive material, and, on the other hand, one or more grinding steps to obtain a sinterable granular precursor material from the sintered frit.

[0007] Conventional sintering processes typically involve preparing a cast film from a suspension containing granular precursor materials and subjecting it to sintering temperatures in a furnace, as described, for example, by Yi et al. in Journal of Power Sources 269 (2014) 577-588. Thus, the heating rates typically achieved in furnaces are on the order of a few degrees per minute, which is known to produce fairly large grain sizes within the sintered microstructure. Large grain sizes typically contribute to the formation of microcracks, which can increase the likelihood of mechanical failure of the resulting ceramic material.

[0008] It is therefore an object of the present invention to provide a method for producing a lithium titanium phosphate-based solid electrolyte that overcomes or mitigates at least some of the above-mentioned drawbacks and limitations of the prior art. In particular, it is an object to provide a process that does not require steps such as drying, grinding, or pre-sintering, and that results in a solid electrolyte that exhibits both favorable mechanical and ionic conductivity properties in an efficient and economical manner, e.g., for electrolysis and energy storage applications. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] European Patent No. 3189008 [Non-patent literature]

[0010] [Non-Patent Document 1] Waetzig et al., Journal of Alloys and Compounds 818(2020)153237 [Non-patent document 2] Yi et al., Journal of Power Sources 269(2014)577-588 Summary of the Invention

[0011] This object and the additional advantages described herein have been unexpectedly achieved by providing a process as defined in the attached independent claim 1.

[0012] That is, the present invention provides a process for producing a lithium titanium phosphate-based solid electrolyte material, i) providing a solution comprising a Li source material, a Ti source material, a P source material, and optionally a Si source material and / or a source material of a metal M, wherein M is selected from the group consisting of Al, Ga, Ge, In, Sc, V, Cr, Mn, Co, Fe, Y, a lanthanide, or a combination thereof; ii) generating an aerosol from the solution; and iii) subjecting the generated aerosol to flame pyrolysis to form a particulate precursor material therefrom; iv) subjecting the particulate precursor material to electric field assisted sintering to form a lithium titanium phosphate based solid electrolyte material; The present invention relates to a process including:

[0013] The present invention is also directed to solid electrolyte materials obtainable by the process disclosed herein. The solid electrolyte materials are in particular those of the formula Li n·(1+x+y+z) M n’·x Ti n’’·(2-x) (PO4) (n’’’)·(3-y) (SiO4) (n’’’’)·y wherein M is a metal selected from the group of Al, Ga, Ge, In, Sc, V, Cr, Mn, Co, Fe, Y, a lanthanide, or a combination thereof; 0≦x≦1, 0≦y≦1, 0≦z≦0.8; and n, n', n'', n''n''', and n'''' are each independently a number in the range of 0.8 to 1.2.

[0014] The present invention further relates to an article comprising the solid electrolyte material according to the present invention, such as a solid electrolyte, an electrode, a separator, or a membrane. For example, the present invention relates to a membrane comprising the solid electrolyte material according to the present disclosure for use in a process for separating and recycling lithium from spent lithium-containing batteries.

[0015] Also within the scope of the present invention are energy storage devices, in particular lithium batteries, comprising a solid electrolyte, electrodes and / or separators comprising the solid electrolyte material according to the present invention.

[0016] The process of the present invention, based on flame pyrolysis for the production of granular precursor materials and subsequent electric-field-assisted sintering of the resulting granular precursor materials, offers several benefits and advantages. Thus, flame pyrolysis readily produces sinterable particles with narrow size distributions and relatively small particle sizes, e.g., on the order of 100 nm or less. This allows for the elimination of further processing steps such as drying, grinding, or pre-sintering. Flame pyrolysis also enables continuous, large-scale synthesis of granular precursor materials with flexible control of the material stoichiometry by varying the amount of precursor material in the solution subjected to flame pyrolysis. Subsequent electric-field-assisted sintering of the as-obtained precursor materials facilitates the formation of corresponding solid electrolyte materials with small particle sizes and, therefore, with high heating rates and short holding times that are believed to be less prone to microcrack formation. Unexpectedly, the solid electrolytes obtained by the process of the present invention exhibit improved mechanical properties, such as a very high elastic modulus E, while simultaneously exhibiting competitive Li-ion conductivity. This makes the solid electrolytes disclosed herein attractive for use in membranes for lithium batteries or industrial electrolysis processes, among others. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 shows the pressure and temperature profiles over time and the path of the stamp during electric-field-assisted sintering of the granular precursor material according to Example 1. [Figure 2] FIG. 1 shows the volume-based particle size distribution of particulate precursor material produced according to Example 1, as measured by laser diffraction. [Figure 3] FIG. 1 shows the volume-based particle size distribution of a conventional commercially available granular precursor material used according to Comparative Example 1, as measured by laser diffraction. [Figure 4] FIG. 1 shows the volume-based particle size distribution of particulate precursor material produced according to Example 3, as measured by laser diffraction. DETAILED DESCRIPTION OF THE INVENTION

[0018] As used herein, the term "comprising" is understood to be open-ended and not to exclude the presence of additional, undescribed or unenumerated elements, materials, components, method steps, etc. "Including," "containing," and similar terms are understood to be synonymous with "comprising." As used herein, the term "consisting of" is understood to exclude the presence of any unspecified elements, components, method steps, etc.

[0019] As used herein, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise.

[0020] Unless indicated to the contrary, the numerical parameters and ranges set forth in the following specification and appended claims are approximations. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values ​​set forth in the specific examples are reported as precisely as possible. However, any numerical value contains errors necessarily resulting from the standard deviation in their respective measurements.

[0021] It is also to be understood that any numerical range recited herein is intended to include all subranges subsumed therein. For example, a range of "1 to 10" is intended to include any and all subranges between and including the recited minimum value of 1 and the recited maximum value of 10, i.e., all subranges beginning with a minimum value of 1 or greater and ending with a maximum value of 10 or less, and all subranges therebetween, for example, 1 to 6.3, or 5.5 to 10, or 2.7 to 6.1.

[0022] All parts, amounts, concentrations, etc. referred to herein are by weight unless otherwise specified.

[0023] As described above, the present invention provides a process for producing a lithium titanium phosphate-based solid electrolyte material, comprising: i) providing a solution comprising a Li source material, a Ti source material, a P source material, and optionally a Si source material and / or a source material of a metal M, wherein M is selected from the group consisting of Al, Ga, Ge, In, Sc, V, Cr, Mn, Co, Fe, Y, a lanthanide, or a combination thereof; ii) generating an aerosol from the solution; and iii) subjecting the generated aerosol to flame pyrolysis to form a particulate precursor material therefrom; iv) subjecting the particulate precursor material to electric field assisted sintering to form a lithium titanium phosphate based solid electrolyte material; The present invention relates to a process including:

[0024] Thus, the present invention provides a process for producing a lithium titanium phosphate-based solid electrolyte material. As used herein, a solid lithium titanium phosphate-based solid electrolyte material refers to a solid-phase material that contains lithium titanium phosphate or a derivative thereof and exhibits ionic conductivity. Derivatives of lithium titanium phosphate include lithium titanium phosphate (LiTi2PO 12 ), in which some of the constituent atoms are replaced with other elements, such as some P atoms replaced with Si and / or some Ti atoms replaced with a metal M, where M can be selected from the group consisting of Al, Ga, Ge, In, Sc, V, Cr, Mn, Co, Fe, Y, a lanthanide, or a combination thereof, and such substitutions can be offset, for example, by lithium content, resulting in overall electroneutrality. Alternatively or additionally, there can be a deficiency or excess of one or more constituent elements of the lithium titanium phosphate, such as an excess due to, for example, the occupation of interstitial lattice sites, e.g., a lithium excess, or a deficiency due to vacancies in the lattice, e.g., oxygen vacancies. The lithium titanium phosphate-based solid electrolyte material can particularly include one or more phases of unsubstituted or substituted lithium titanium phosphate in a NASICON-type crystal structure that exhibits ionic conductivity, particularly for lithium ions.

[0025] The process for producing a lithium titanium phosphate-based solid electrolyte material according to the present invention includes providing a solution containing a Li source material, a Ti source material, a P source material, and optionally a Si source material and / or a source material for a metal M, where M is selected from the group consisting of Al, Ga, Ge, In, Sc, V, Cr, Mn, Co, Fe, Y, a lanthanide, or a combination thereof. As used herein, the term "solution" refers to a solution in the general sense, i.e., a liquid containing materials (such as the source materials described above) dissolved in a liquid carrier medium. Thus, the solution may be substantially or completely free of any undissolved solid or gel-like components or precipitates. The solution is preferably stable over time, i.e., no phase separation or precipitation occurs.

[0026] The solution can be provided by adding a Li source material, a Ti source material, a P source material, and optionally, a Si source material and / or a source material for the metal M, if used, to a suitable solvent and dissolving the source materials in the solvent. It is also possible to prepare solutions of one or more source materials, combine such solutions, and optionally add additional source materials or optional components to form a solution containing a Li source material, a Ti source material, a P source material, and optionally, a Si source material and / or a source material for the metal M. Preparing the solution can involve mixing the individual source materials (which, as described above, can be provided, for example, in neat form or as a mixture or solution), the solvent, and, if present, any additional optional components, at room temperature or elevated temperature in a suitable mixing device, such as a beaker or any container suitable for preparing solutions. Mixing is typically carried out for a period of time sufficient to dissolve all solid components so as to obtain a clear, homogeneous solution.

[0027] The source material of element X refers to a material that contains the specified element X and serves as a source of this element in the manufacturing process of a lithium titanium phosphate-based solid electrolyte material. In general, any Li source material, Ti source material, P source material, and optionally, Si source material and / or metal M source material can be used as long as the respective solutions can be prepared.

[0028] Therefore, in principle, any soluble Li-containing material can be used as the Li source material according to the present invention. Typically, lithium salts, complexes, or organometallic compounds can be used as the Li source material. Non-limiting examples of inorganic lithium salts include lithium chloride, lithium hydroxide, lithium carbonate, lithium nitrate, lithium bromide, lithium phosphate, and lithium sulfate. Non-limiting examples of organic lithium salts include lithium carboxylates, e.g., C1-C 20 Examples of suitable lithium salts include lithium salts of carboxylic acids, such as lithium acetate, lithium oxalate, or lithium neodecanoate; and lithium alkoxides, such as lithium ethoxide or lithium naphthenate. Organic lithium compounds include alkyllithium and aryllithium compounds, such as butyllithium or phenyllithium. Organic complexes of lithium can be exemplified by lithium β-diketonato compounds, such as 2,4-pentanedionato-lithium. It may be preferable to use a Li source material containing an organic moiety other than lithium that can be removed in the flame pyrolysis step, so that undesired residues from the Li source material are substantially absent in the resulting granular precursor material. Thus, the Li source material may be selected from, for example, organic salts, organic complexes, or organometallic compounds of lithium. Preferably, an organic lithium salt, such as any one of the organic salts described above, can be used as the Li-containing material in the process according to the present invention.

[0029] Any soluble Ti-containing material can be used as the Ti source material in the present invention. Typically, titanium salts, complexes, or compounds can be utilized as the Ti source material. Non-limiting examples include halides such as titanium tetrachloride, titanium bromide, titanium fluoride, titanium oxysulfate, titanium alkoxides such as titanium methoxide, titanium ethoxide, titanium propoxide, titanium tetraisopropoxide, and titanium butoxide, as well as acetylacetonate compounds. It may also be preferable to use a Ti source material containing an organic moiety other than titanium that can be removed in the flame pyrolysis step so that undesired residues from the Ti source material are substantially absent in the resulting granular precursor material. Thus, the Ti source material may be selected from, for example, organic titanium salts, organic complexes, or organometallic compounds. Preferably, a compound such as an organic titanium salt or any one of the above organic salts and compounds can be used as the Ti source material in the process according to the present invention.

[0030] In the practice of the present invention, any soluble phosphorus-containing material can be used as the P source material. For example, inorganic or organic phosphorus-containing compounds can be used as the P source material. Non-limiting examples of such phosphorus-containing compounds include phosphorus halides and phosphorus oxoacids, such as phosphonic acid, orthophosphoric acid, metaphosphoric acid, and pyrophosphoric acid, as well as their salts and esters. Non-limiting examples of such salts and esters include phosphates or pyrophosphates, such as ammonium phosphate or sodium phosphate, or trialkyl phosphates, such as triethyl phosphate, or hydrogen phosphates and dihydrogen phosphates with various counterions, such as ammonium or alkali metals. It may be preferable to use a P source material that contains an organic moiety other than phosphorus that can be removed in the flame pyrolysis step so that the resulting granular precursor material is substantially free of undesirable residues from the P source material. Therefore, the P source material may preferably include an organic phosphorus-containing compound, such as an organic phosphate or pyrophosphate, e.g., a trialkyl phosphate compound, such as triethyl phosphate.

[0031] As described above, a source material for metal M is optionally used. The source of metal M can be any soluble material containing metal M, where M is selected from the group consisting of Al, Ga, Ge, In, Sc, V, Cr, Mn, Co, Fe, Y, a lanthanide, or a combination thereof. Typically, a salt, complex, or compound of metal M can be utilized as the source of metal M. It may also be preferable to use a source material for metal M that includes an organic moiety other than metal M that can be removed in the flame pyrolysis step so that substantially no undesired residue from the metal source material remains in the resulting particulate precursor material. Thus, the source material for metal M may be selected from, for example, organic salts, organic complexes, or organometallic compounds of Al, Ga, Ge, In, Sc, V, Cr, Mn, Co, Fe, Y, a lanthanide, or a combination thereof. Metal M may preferably include Al. Exemplary Al source materials include inorganic and organic aluminum compounds such as aluminum chloride, aluminum tri-sec-butoxide, and aluminum ethylacetoacetate.

[0032] As described above, a Si source material is optionally used. In principle, any soluble Si-containing material can be used as the Si source material in the practice of the present invention. For example, silicates or esters or other derivatives of silicic acid can be used as the Si source material. Exemplary Si-containing compounds include, for example, silicates and / or organosilicon compounds, such as silanols, siloxanes, and silyl ethers. It may be preferable to use a Si source material that contains an organic moiety other than silicon that can be removed in the flame pyrolysis step so that undesirable residues from the Si source material are substantially absent from the resulting granular precursor material.

[0033] It should be understood that a single source material, or a combination or mixture of two or more source materials as described above, can be used for either the Li source material, the Ti source material, the P source material, and the optional Si source material and optional source material for metal M, respectively. It is also possible for the source material used to function as a source for two or more of the elements mentioned. For example, lithium phosphate represents a Li source material and a P source material. However, typically, individual source materials are used for the Li source material, the Ti source material, the P source material, and the optional Si source material and / or the source material for metal M.

[0034] In principle, inorganic source materials such as those described above are suitable, although it is preferred if some or preferably all of the source materials used contain only organic moieties in addition to their respective source elements (Li, Ti, P, Si, metal M). The organic moieties can be removed in the flame pyrolysis step, for example by combustion, so that undesirable residues from the source materials that could adversely affect, for example, the sinterability and / or properties of the final lithium titanium phosphate-based solid electrolyte material are substantially absent from the resulting granular precursor material. For example, the Li source material, Ti source material, and metal M source material, if used, may each be individually selected from organic salts, organic complexes, or organometallic compounds of the respective metals, or combinations thereof; and / or the P source material comprises an ester or salt of a phosphorus oxoacid, preferably an organic phosphate; and / or the Si source material, if used, comprises a silicate and / or an organosilicon compound.

[0035] The source materials provide elements along with oxygen added in the flame pyrolysis step to form the granular precursor material, and ultimately the lithium titanium phosphate-based solid electrolyte material in subsequent steps of the process according to the present invention. Thus, by varying the relative amounts of the Li source material, Ti source material, P source material, and optional Si source material and / or optional source material of metal M, if used, the composition of the granular precursor material in the solution and ultimately the lithium titanium phosphate-based solid electrolyte material produced therefrom can be flexibly controlled. Thus, a solid electrolyte material having a predefined stoichiometric ratio can be obtained by preparing a solution having the respective ratios of Li, Ti, P, and optionally Si and / or M. For example, the source materials can be prepared according to the formula Li (1+x+y+z) M x Ti (2-x) (PO4) (3-y) (SiO4) y (wherein M is a metal selected from the group consisting of Al, Ga, Ge, In, Sc, V, Cr, Mn, Co, Fe, Y, a lanthanide, or a combination thereof, where 0≦x≦1, 0≦y≦1, and 0≦z≦0.8; the solid electrolyte material may have a NASICON-type crystal structure and exhibit Li-ion conductivity) can be used in relative amounts to form a solid electrolyte material having a composition according to or close to the formula: (wherein M is a metal selected from the group consisting of Al, Ga, Ge, In, Sc, V, Cr, Mn, Co, Fe, Y, a lanthanide, or a combination thereof, where 0≦x≦1, 0≦y≦1, and 0≦z≦0.8; the solid electrolyte material may have a NASICON-type crystal structure and exhibit Li-ion conductivity. For example, the provided solution can contain a Li source material, a Ti source material, a P source material, and optionally a Si source material and / or a metal M source material in amounts corresponding to an equivalent ratio Li:(Ti, M):(P, Si) of (0.5-2):(1.5-2.5):3, preferably (1.3-2):(1.8-2.2):3. The equivalent ratio of M:Ti in the solution can be, for example, in the range of 0-1:2, e.g., 0-1:3 or 0-1:4. In one variation, the M:Ti equivalent ratio is 0, i.e., no metal M source material is used. The Si:P equivalent ratio in the solution can be 0-1:2, e.g., 0-1:3, or 0-1:4, or 0-1:5, or 0-1:10. In one variation, the Si:P equivalent ratio is 0, i.e., no Si source material is used.

[0036] As described above, a solvent is further used to prepare a solution containing the Li, Ti, and P source materials, and optionally, the Si and / or M metal source materials, if used. Any solvent or mixture of solvents useful for dissolving the Li, Ti, and P source materials, and the optional Si and / or M metal source materials, if used, can be used. The type and concentration of the one or more solvents can be selected to obtain a homogeneous and stable solution, preferably free of any undissolved components or precipitates. Possible solvents include inorganic solvents such as water, acids or bases such as hydrochloric acid, sulfuric acid, phosphoric acid, or alkali hydroxides, as well as various organic solvents and mixtures or combinations thereof. In a preferred implementation of the present invention, the solution contains one or more organic solvents. Organic solvents are generally flammable and therefore provide additional heat during the flame pyrolysis step of the present invention. Furthermore, due to their combustion, they typically do not leave any undesirable residues in the granular precursor material obtained by flame pyrolysis. Any type of common organic solvent can be used in accordance with the present invention, including, but not limited to, alcohols, ketones, aldehydes, esters, ethers, carboxylic acids, hydrocarbons, or mixtures or combinations thereof. Non-limiting examples of suitable organic solvents or components of solvent mixtures or combinations include, for example, C1-C 15 Alcohols such as ethanol, n-propanol, isopropanol, n-butanol, tert-butanol, methanol, diols such as ethanediol, pentanediol, and 2-methyl-2,4-pentanediol, C1-C 12Examples of suitable solvents include carboxylic acids such as acetic acid, propionic acid, butanoic acid, hexanoic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, octanoic acid, 2-ethylhexanoic acid, valeric acid, capric acid, and lauric acid, 2-methoxyethonal, ethers such as diethyl ether and diisopropyl ether, ketones such as acetone or ethyl methyl ketone, esters such as n-butyl acetate or ethyl acetate, hydrocarbons such as alkanes like n-hexane or n-pentane, aromatics such as benzene or toluene, naphtha, gasoline, mineral spirits, or heterocycles such as cyclohexane, 1,4-dioxane, tetrahydrofuran, or pyridine, or acetonitrile. In one example, the solvent comprises a mixture of an alcohol, such as ethanol, and a carboxylic acid, such as ethylhexanoic acid. Preferably, the solution is organic solvent-based. For example, the solvent may comprise more than 50 wt. % of organic solvent, such as 60 wt. % or more, or 70 wt. % or more, or 80 wt. % or more, or 90 wt. % or more, or 95 wt. % or more, or 99 wt. % or more, e.g., 100 wt. %, based on the total weight of the solvent of the solution comprising the Li source material, the Ti source material, the P source material, and optionally the Si source material and / or the source material of the metal M. In a preferred practice of the present invention, only organic solvent is utilized as the solvent in the solutions of the different source materials.

[0037] Optionally, one or more additional components can be used in the solution containing the Li source material, Ti source material, P source material, and optionally the Si source material and / or the metal M source material. Non-limiting examples of such additional components include common adjuvants such as rheology modifiers, complexing agents, stabilizers, etc. For example, one or more complexing agents, preferably organic complexing agents such as ethylenediaminetetraacetic acid, can be used to promote dissolution of one or more source materials. Such optional additional components, if used, are used in effective amounts according to conventional practice. For example, such optional additional components, if used, can be used in an amount ranging from 0.001 to 10 wt %, based on the total weight of the solution.

[0038] The solutions according to the invention can be characterized by the concentration of dissolution source materials Li, Ti, P, and, if present, Si and M. The solutions according to the invention can have a total concentration of dissolution source materials in the range of, for example, 0.5 wt. % to 40 wt. %, e.g., 1 wt. % to 30 wt. %, or 2 wt. % to 20 wt. %, or 3 wt. % to 10 wt. %, based on the total weight of the solution.

[0039] According to the process of the present invention, the solution thus prepared allows for the synthesis of dimensionally and compositionally uniform granular precursor materials by flame pyrolysis, for which purpose an aerosol is generated from the solution and subjected to flame pyrolysis to form the granular precursor material therefrom.

[0040] Flame pyrolysis generally refers to the chemical transformation of chemicals at high temperatures, whereby the high temperatures are provided by a flame. Typically, these temperatures are on the order of several hundred degrees Celsius. Flame pyrolysis and reactors for carrying it out are known in the art and are described, for example, in WO 2015 / 173114. The reactor typically comprises a reaction chamber containing an ignition source, a means for generating an aerosol from a solution, a means for cooling the particle-gas mixture effluent from the ignition source, and a means for collecting the formed particulate material. The walls of the reaction chamber are typically formed from a suitable heat-resistant material, such as a ceramic or glass material like quartz, and may be at least partially equipped with external cooling means. Ignition sources include, for example, a gas torch, a laser beam, or an electric arc.

[0041] In the process according to the present invention, an aerosol is generated from a solution containing a Li source material, a Ti source material, a P source material, and optionally a Si source material and / or a metal M source material, typically by the aerosol generating means of the flame pyrolysis reactor described above. Aerosol, as understood herein, refers to a gas having fine droplets dispersed therein. The average diameter of the aerosol droplets may be, for example, 1 μm to 150 μm, e.g., 30 μm to 100 μm. Generation of the aerosol from the solution can be achieved by feeding the solution into a nozzle, such as a one-component or two-component nozzle, as known in the art of aerosol generation. Before feeding the solution into the nozzle, the solution may be heated to increase its vapor pressure and reduce its viscosity. The nozzle is generally made of a material capable of withstanding the temperatures present in the respective proximity of a flame. Generating the aerosol from the solution may, inter alia, involve atomizing the solution through a nozzle using an atomizing gas. In one preferred implementation of the present invention, the solution is atomized together with the atomizing gas through individual outlets of a two-component nozzle to obtain the aerosol. A two-component nozzle may be preferred for high solution throughput and a stable flame. The atomizing gas may be selected from, for example, air, oxygen, nitrogen, or mixtures thereof.

[0042] The aerosol thus produced is then subjected to flame pyrolysis in a process according to the present invention to form a particulate precursor material therefrom. This typically involves contacting the aerosol with a flame, for example, in a flame pyrolysis reactor as described above. In one implementation of the present invention, the aerosol is fed into a stable flame of a gas torch. The flame can be produced by burning a combustible gas with an oxidizer. The combustible gas can include, for example, hydrogen, methane, ethane, propane, butane, natural gas, and mixtures thereof. The oxidizer can include oxygen or an oxygen-containing gas mixture, such as air. For example, the combustible gas can include hydrogen, and the oxidizer can include air. The amount of oxygen is typically selected so that the combustible gas and the combustible or oxidizable components in the aerosolized solution introduced into the flame are completely combusted or oxidized, respectively. The flame temperature reached during the flame pyrolysis step of the present invention can be from about 400°C to about 2000°C, preferably from about 800°C to about 1400°C. Thus, combustible components contained in the aerosol, such as flammable gases, and solvents or organic portions of the source materials used in the provided initial solution, may be combusted and converted into gaseous reaction products, such as carbon dioxide and / or water molecules, while the Li, Ti, P, and, if used, metal M and / or Si components contained in the aerosolized solution are oxidized in the flame pyrolysis step to form the granular precursor material.

[0043] The gas-particle mixture effluent obtained from the flame may then be cooled. Thus, the flame spray pyrolysis reactor may comprise means for cooling the gas-particle mixture effluent from the flame. Such means may comprise, for example, one or more cooling tubes which may be cooled with a cooling liquid such as water or oil.

[0044] The formed particulate precursor material may then be separated from the gas stream. Accordingly, flame spray pyrolysis reactors typically include means for collecting the formed particulate precursor material. Suitable means for collecting the particulate precursor material include, for example, high temperature membrane filters, cyclone separators, bag filters, electrostatic precipitators, and / or thermophoretic surface collectors.

[0045] The granular precursor material thus formed generally contains oxides derived from the source materials used. It therefore represents a granular lithium titanium phosphate-based material. The exact composition depends on the type and relative amounts of the different source materials used. The granular precursor material formed is particularly a material of the formula Li n·(1+x+y+z) M n’·x Ti n’’·(2-x) (PO4) (n’’’)·(3-y) (SiO4) (n’’’’)·y where M is a metal selected from the group consisting of Al, Ga, Ge, In, Sc, V, Cr, Mn, Co, Fe, Y, a lanthanide, or a combination thereof, where 0≦x≦1, 0≦y≦1, 0≦z≦0.8, and n, n', n'', n'', n''', and n'''' are each independently a number in the range of 0.8 to 1.2. For example, x can be in the range of 0.2 to 0.7, e.g., 0.3 to 0.6. Additionally or alternatively, y can be in the range of 0 to 0.8, e.g., 0 to 0.6. In certain variations, y is 0 and / or M is Al. Furthermore, the parameters n, n', n'', n''n''', and n'''' can each independently be a number in the range of 0.8 to 1.2, e.g., 0.9 to 1.1 or 0.95 to 1.05, e.g., about 1 or equal to 1.

[0046] The resulting granular precursor material may contain multiple phases that may differ in their crystallinity and / or elemental composition. Such phases may include, for example, AlPO, TiO, LiPO, LiTiPO, and LiOH. For example, an ion-conducting lithium titanium phosphate phase of a NASICON-type crystal structure may or may not be present in significant amounts in the granular precursor material. Typically, such ion-conducting phases are largely formed during the subsequent electric-field-assisted sintering step.

[0047] The granular precursor material according to the present invention can be characterized by its particle size distribution. The particle size can affect the properties of the solid electrolyte material obtainable from the granular precursor material. Smaller particles tend to provide a smaller particle size, which can reduce the risk of microcrack formation. The granular precursor material obtained by flame pyrolysis according to the present invention is typically characterized by a small particle size and a narrow particle size distribution. Thus, the granular precursor material has a D of less than 200 nm, or less than 150 nm, or preferably less than 100 nm. 50 particle size, and / or span (D) of less than 1.5, preferably less than 1.0, or less than 0.8 90 -D 10 ) / D 50 The particle size distribution may be based on a volume having a particle size distribution of D 50 The particle size indicates the median particle size, and D 50 Below or above which 50% of the population, i.e. 50% of the volume of all particles, is present. Therefore, D 90 The particle size is D 90 This refers to the particle size below which 90% of the population, i.e., 90% of the volume of all particles, exists. D 10 The particle size is D 10 This refers to the particle size below which 10% of the population, i.e., 10% of the volume of all particles, exists. (D 90 -D 10 ) / D 50 The span, calculated as , is a measure of the width of the particle size distribution. The particle size distribution of the particulate precursor material according to the present invention is typically unimodal. The particle size distribution can be measured by laser diffraction using a Horiba LA-950 laser particle size analyzer according to the procedure described in the Examples section.

[0048] The granular precursor material formed by the flame pyrolysis step can optionally be subjected to further treatments before subjecting it to electric-field-assisted sintering in the process according to the present invention. For example, the granular precursor material can, in principle, be subjected to a drying or grinding process or a calcination treatment. Calcination can be carried out at temperatures between 630°C and 770°C. Calcination times can range from 4.5 to 5.5 hours. The atmosphere during calcination is not critical: it can be either inert or in the presence of oxygen. Calcination can be carried out in dedicated calcination equipment, such as a muffle furnace. Alternatively, calcination can be carried out using sintering equipment before the actual sintering process begins. In all cases, the purpose of the calcination treatment is to convert the amorphous powder structure into a crystalline powder structure. If crystallization during calcination leads to an inappropriate increase in particle size, a deagglomeration step can be carried out between the calcination and sintering steps.

[0049] In contrast to particles obtained by sol-gel or melt quenching processes, the granular precursor material obtained by flame pyrolysis can be used directly for sintering and does not require any processing prior to the sintering process, which is an advantage of the present invention. In particular, due to the high flame temperature, organic and other components that reduce the sinterability of the granular precursor material are substantially removed. Therefore, the granular precursor material according to the present invention is preferably subjected to electric field-assisted sintering without any further processing steps, such as drying, grinding, or calcination. If a calcination step is required to crystallize the amorphous powder obtained by flame pyrolysis, the calcination step may be carried out using the same equipment as that used for the subsequent sintering step.

[0050] The method according to the present invention further includes subjecting the granular precursor material to electric-field-assisted sintering to form a lithium titanium phosphate-based solid electrolyte material. Generally, electric-field-assisted sintering, as understood herein, refers to a sintering process also known as spark plasma sintering (SPS), in which heat generated by an electric field and pressure is applied to sinter the granular material to form a solid, compacted workpiece. Electric-field-assisted sintering according to the present invention can be performed using conventional electric-field-assisted sintering systems, such as those commercially available from Dr. Fritsch GmbH & Co. KG (Felbach, Germany), FCT Systeme GmbH (Efelder-Lauenstein, Germany), and Sumitomo Coal Mining Co. Ltd. (Tokyo, Japan). Such electric-field-assisted sintering systems include a mold in which the granular precursor material can be loaded and placed under a controlled atmosphere, and a mechanical loading system that operates simultaneously with a high-power electrical circuit. Thus, during electric-field-assisted sintering, the granular precursor material can be simultaneously subjected to high sintering temperatures and pressures on the order of tens of MPa. Electric-field-assisted sintering typically offers several advantages over conventional sintering processes, such as tape casting. Therefore, EAS can provide a sintered microstructure with a relatively small grain size, which positively impacts both the ionic conductivity and mechanical properties of the resulting solid electrolyte material. One important factor determining grain size can be seen in the relatively high heating rate and short hold and process times achievable with EAS compared to conventional furnace sintering processes. Short hold and process times can significantly reduce energy costs compared to conventional furnace heating. In contrast to conventional external heating, for example, via an oven, samples can be heated directly in EAS based on the ohmic resistance of the granular material within the mold. Compared to cold pressing prior to the sintering process, the application of pressure during heating to the sintering temperature can provide a solid electrolyte with a reduced or virtually nonexistent amount of pores and increased density. This can result in a solid electrolyte material with both high ionic conductivity and high mechanical reliability.

[0051] Thus, electric-field-assisted sintering according to the present invention may include providing a granular precursor material in a mold between a pair of electrodes, applying pressure to the granular precursor material, and passing a current through the mold and / or the granular precursor material via the electrodes. The granular precursor material may optionally be mixed with one or more additional substances prior to electric-field-assisted sintering. However, preferably, no additional substances are intentionally added to the granular precursor material subjected to electric-field-assisted sintering. Thus, electric-field-assisted sintering may include subjecting the granular precursor material to a predetermined temperature and pressure program. Precise temperature control of the material in the mold may be achieved by applying a predetermined voltage difference to two opposing electrodes in electrical contact with the material in the mold in combination with a temperature measurement and regulation system. The current resulting from the applied voltage difference may be alternating or direct current. Optionally, the current may be pulsed. For example, such pulses may have a frequency of 1 Hz to 20 kHz and a duration of 50 μs to 999 ms. Depending on the electrical conductivity of the material, an electrically insulating mold can be utilized, thus allowing current to flow through the material in the mold, resulting in efficient internal heating of the material. An additional heat source, such as an induction heat source, can optionally be utilized to heat the material in the mold. Electric-field-assisted sintering according to the present invention can include heating the granular precursor material in the mold to a sintering temperature of 700°C or higher, e.g., 750°C or higher, or 800°C or higher, or 850°C or higher, or 900°C or higher, or 950°C or higher. For example, the granular precursor material can be heated to a sintering temperature of 1500°C or lower, e.g., 1300°C or lower, e.g., 1100°C or lower, or 1000°C or lower, or 950°C or lower, or 900°C or lower. Electric-field-assisted sintering can include heating the granular precursor material to a sintering temperature ranging between any of the above values, e.g., 700°C to 1100°C, e.g., 800°C to 1000°C. Preferably, the sintering temperature is 850°C to 950°C. Temperatures above 1000°C may be less preferred as they may enhance grain growth.The temperature can be increased to the sintering temperature linearly, i.e., at a constant heating rate, or nonlinearly, e.g., stepwise (with hold periods at certain or intermediate temperatures), or at a steady but time-variable heating rate. Heating rates of up to 1000 K / min can be applied. However, typically, such heating rates of 10 K / min or more are used, such as 25 K / min or more, or 50 K / min or more, or 60 K / min or more. The heating rate can be, for example, 200 K / min or less, such as 100 K / min or less, or 80 K / min or less. Heating rates within any of the above-mentioned ranges can be applied, e.g., 10 to 200 K / min or 20 K / min to 100 K / min. The heating rate can be calculated from the difference between the sintering temperature and the starting temperature and the heating time required to reach the sintering temperature. The sintering temperature, as used herein, refers to the maximum temperature to which the granular precursor material is heated in the electric-field-assisted sintering step.

[0052] The electric field-assisted sintering method according to the present invention further includes applying pressure to the granular precursor material. Optionally, the material in the mold can be pre-densified before being loaded into the electric field-assisted sintering apparatus or before the temperature is increased to the sintering temperature. The pressure during electric field-assisted sintering can be generated by applying a force to the material in the mold using a mechanical loading system (e.g., a press) of the electric field-assisted sintering apparatus. For example, one of the opposing electrodes can be movable and configured to tightly close the surface of the mold. The application of force by the electrode toward and along the mold exerts pressure on the material in the mold, which is determined by the surface area of ​​the electrode's contact area with the material and the force applied by the movable electrode toward the sample. For example, the mold can have the form of a hollow cylinder, whereby one end of the cylinder is closed, i.e., the base of the mold is closed, and the opposite end is open. In this case, the movable electrode has a circular contact area with a diameter corresponding to the inner diameter of the cylinder. This electrode is co-aligned with the open side of the cylindrical mold so that the material filled within the mold can be compressed by pressing against the other opposing electrode.

[0053] The pressure applied to the sample during electric-field-assisted sintering typically varies over time. For example, the pressure can be increased at a constant rate or at varying rates from 0 to a maximum pressure. The pressure can be applied before the temperature of the sample is elevated above room temperature, or after heating has begun or the maximum temperature has been reached. For example, a pre-pressure, such as a pressure in the range of 5 to 15 MPa, can be applied before the temperature of the sample is elevated above room temperature. The pressure on the sample can then be increased at a constant or variable rate to the sintering pressure while the temperature is increased to the sintering temperature. Electric-field sintering according to the present invention can include subjecting the granular precursor material to a sintering pressure of 20 MPa or more, e.g., 30 MPa or more, or 40 MPa or more, or 50 MPa or more, or 60 MPa or more. Electric-field sintering can also include subjecting the granular precursor material to a sintering pressure of 70 MPa or less, e.g., 60 MPa or less, or 50 MPa or less, or 40 MPa or less. Electric-field-assisted sintering can involve subjecting the granular precursor material to a sintering pressure ranging between any of the values ​​listed above, e.g., 20 to 70 MPa, e.g., 30 to 50 MPa. The pressure can be increased to the sintering pressure linearly, i.e., at a constant rate, or nonlinearly, e.g., stepwise (with hold periods at a pressure or intermediate pressures), or at a steady but time-variable pressure increase rate. The pressure can be increased at a constant rate of 0.5 MPa / min or greater, e.g., 1 MPa / min or greater, or 2 MPa / min or greater, or 3 MPa / min or greater. The pressure can be increased at a rate of 10 MPa / min or less, or 5 MPa / min or less, or 3 MPa / min or less. The pressure can be increased at a rate ranging between any of the values ​​listed above, e.g., 0.5 MPa / min to 10 MPa / min or 1 MPa / min to 5 MPa / min. The rate of pressure increase can be calculated from the difference between the sintering pressure and the starting pressure and the time required to reach the sintering pressure. Sintering pressure, as used herein, refers to the maximum pressure applied to the granular precursor material in the electric field-assisted sintering step. Typically, pressure is applied while the sample is heated to the sintering temperature. In other words, the temperature and pressure may preferably be increased simultaneously during part of the temperature and pressure program.

[0054] The electric field-assisted sintering process according to the present invention can further include maintaining the granular precursor material at the sintering temperature and sintering pressure for a holding time. The holding time at the sintering temperature and sintering pressure can be, for example, 1 minute or more, e.g., 2 minutes or more, or 3 minutes or more, or 4 minutes or more, or 5 minutes or more. It can be, for example, 10 minutes or less, e.g., 8 minutes or less, or 6 minutes or less. The holding time can be between any of the indicated values, such as 1 minute to 10 minutes, e.g., 2 minutes to 8 minutes, or 3 minutes to 6 minutes. Although not preferred, it is also possible to apply a temperature and pressure program in which there is no temporal overlap between the sintering temperature and the applied sintering pressure.

[0055] The electric field-assisted sintering according to the present invention can further include decreasing the temperature from the sintering temperature at a constant or variable rate. The temperature of the material in the mold can be decreased by reducing or turning off the current applied to the electrodes and optional additional heat sources. Furthermore, the electrodes of the sintering apparatus can be actively cooled, for example, by a cooling liquid such as water, which can increase the cooling rate of the mold. The pressure can be decreased before, simultaneously with, and / or after the temperature is decreased from the sintering temperature. The pressure can be decreased from the sintering pressure at a constant or variable rate. This can be achieved by reducing or removing the applied mechanical force.

[0056] The electric field-assisted sintering of the particulate precursor material can be carried out under vacuum and / or a protective gas atmosphere, which can comprise, for example, nitrogen, argon or any other gas or gas mixture that is essentially inert at the temperatures reached during the electric field-assisted sintering process.

[0057] By the above process, a solid electrolyte material can thus be obtained. The solid electrolyte material formed is a lithium titanium phosphate-based material. The exact composition depends on the type and relative amounts of the different source materials used. The granular precursor material formed is in particular a material of the formula Li n·(1+x+y+z) M n’·xTi n’’·(2-x) (PO4) (n’’’)·(3-y) (SiO4) (n’’’’)·y where M is a metal selected from the group of Al, Ga, Ge, In, Sc, V, Cr, Mn, Co, Fe, Y, a lanthanide, or a combination thereof, and 0≦x≦1, 0≦y≦1, and 0≦z≦0.8. The parameters n, n′, n″, n″n′″, and n′″ can each independently be a number in the range of 0.8 to 1.2, e.g., 0.9 to 1.1, or 0.95 to 1.05, e.g., about 1 or a range equal thereto. Li optionally can have a composition according to the above formula Li (1+x+y) M x Ti (2-x) (PO4) 3-y Lithium can be provided in excess compared to the stoichiometry with (SiO4). This is reflected in the parameter z in the above composition formula. The parameter z can be 0≦z≦0.6, or 0≦z≦0.5, 0≦z≦0.3, or 0≦z≦0.2, or 0≦z≦0.1, or 0≦z≦0.8. If no excess lithium is used, z is 0.

[0058] The solid lithium titanium phosphate-based electrolyte material can include one or more solid phases. Thus, the solid electrolyte material of the present invention can include, for example, multiple phases with different crystallinity and / or elemental composition. The solid lithium titanium phosphate-based electrolyte material can be particularly represented by the formula Li (1+x+y) M x Ti (2-x) (PO4) 3-y (SiO4) y wherein M is a metal selected from the group consisting of Al, Ga, Ge, In, Sc, V, Cr, Mn, Co, Fe, Y, a lanthanide, or a combination thereof, and 0≦x≦1 and 0≦y≦1. Illustrative, non-limiting examples of such phases include Li, ... (1+x) Al x Ti (2-x) (PO4)3, e.g., Li 1.3 Al 0.3 Ti 1.7 (PO4)3, or Li 1.5 Al 0.3 Ti1.7 (PO4) 2.8 (SiO4) 0.2 , Li 1.8 Al 0.4 Ti 1.6 (PO4) 2.6 (SiO4) 0.4 , Li 2.0 Al 0.4 Ti 1.6 (PO4) 2.4 (SiO4) 0.6 , or Li 1.75 Al 0.6 Ti 1.4 (PO4) 2.85 (SiO4) 0.15 Such phases can crystallize in a NASICON-type crystal structure and provide Li-ion conductivity to the solid electrolyte material. Optionally, in addition to one or more phases, a phase of the formula Li (1+x+y) M x Ti (2-x) (PO4) 3-y (SiO4) y For example, the solid electrolyte material formed according to the present invention may comprise a further phase having a composition represented by the formula Li in a total amount of at least 70 wt.%, preferably at least 80 wt.% or at least 90 wt.%, based on the total weight of the solid electrolyte material. (1+x+y) M x Ti (2-x) (PO4) 3-y (SiO4) y The solid electrolyte material may include one or more phases having a composition represented by the formula: The type and amount of phases present in the solid electrolyte material can be determined by X-ray diffraction (XRD) analysis.

[0059] The parameter x in the above formula for possible compositions of solid electrolytes and specific phases therein is generally 0≦x≦1. In particular, in the composition of solid electrolyte materials, x can be 0.05 or greater, or 0.10 or greater, or 0.15 or greater, or 0.20 or greater, or 0.25 or greater, or 0.30 or greater, or 0.35 or greater, or 0.40 or greater, or 0.45 or greater, or 0.50 or greater, or 0.55 or greater, or 0.60 or greater. The parameter x can be 0.95 or less, or 0.90 or less, or 0.85 or less, or 0.80 or less, or 0.75 or less, or 0.70 or less, or 0.65 or less, or 0.60 or less, or 0.55 or less, or 0.50 or less, or 0.45 or less, or 0.40 or less. The parameter x can range between any of the listed values, for example, between 0.05 and 0.95, or between 0.10 and 0.90, or between 0.20 and 0.70, or between 0.30 and 0.60, or between 0.40 and 0.60.

[0060] The parameter y in the above formula for possible compositions of solid electrolytes and specific phases therein generally ranges from 0 to 1. In particular, in the composition of solid electrolyte materials, y can be 0.05 or greater, or 0.10 or greater, or 0.15 or greater, or 0.20 or greater, or 0.25 or greater, or 0.30 or greater, or 0.35 or greater, or 0.40 or greater, or 0.45 or greater, or 0.50 or greater. The parameter y can be, for example, 0.80 or less, or 0.70 or less, or 0.60 or less, or 0.50 or less, or 0.40 or less, or 0.30 or less, or 0.20 or less, or 0.10 or less, or 0.05 or less. The parameter y can be within any of the recited values, such as from 0 to 1, or from 0 to 0.80, or from 0.05 to 0.60, or from 0.10 to 0.60. In certain variations, the parameter y can be 0.

[0061] When the solid electrolyte material includes a metal M, the metal M can be selected from the group consisting of Al, Ga, Ge, In, Sc, V, Cr, Mn, Co, Fe, Y, a lanthanide, or a combination thereof. The metal M, when used, can specifically include or be aluminum. In one embodiment of the present invention, M is a combination of Al and Ge. The solid electrolyte material of this embodiment is named LAGTP. Examples of LAGTPs include Li 1.45 Al 0.45 Ge 0.2 Ti 1.35 It is P3O1.

[0062] The solid electrolyte material of the present invention can be characterized by its elastic modulus E, also known as Young's modulus. The elastic modulus E represents the stress-strain relationship of a material in the elastic region and can be determined, for example, by nanoindentation, as described in the Experimental Section. Surprisingly, it has been found that the solid electrolyte material of the present invention can have a very high elastic modulus E. The elastic modulus E of the solid electrolyte material can be, for example, 200 GPa or more, such as 300 GPa or more, for example 350 GPa or more, or 400 GPa or more, or 500 GPa or more, or 600 GPa or more, or 700 GPa or more, or 750 GPa or more, or 800 GPa or more. The solid electrolyte material can have, for example, an elastic modulus of up to 1,000 GPa, or up to 900 GPa. Preferably, the solid electrolyte material of the present invention has an elastic modulus E of 700 GPa or more, for example, between 700 and 1,000 GPa.

[0063] The solid electrolyte material of the present invention can be further characterized by its specific ionic conductivity, which can be determined by impedance spectroscopy according to the method described in the experimental section. The solid electrolyte material of the present invention can have a specific ionic conductivity of, for example, 1·10 -5 S / cm or more, e.g., 2·10 -5 S / cm or more, or 5·10 -5 The solid electrolyte material of the present invention can have a specific ionic conductivity of, for example, 0.5 to 10 S / cm or more. -5 S / cm or more, e.g., 0.5 10-5 S / cm~1·10 -3 The specific ionic conductivity may be in the range of 1000 S / cm. Specific ionic conductivity refers to the specific ionic conductivity at room temperature (20° C.) unless otherwise indicated herein.

[0064] Typically, the solid lithium titanium phosphate-based electrolyte material obtained by the process disclosed herein is in the form of a coherent body. Thus, electric field-assisted sintering according to the present invention provides a solid lithium titanium phosphate-based electrolyte material in the form of a coherent macroscopic body having predetermined external dimensions, which can optionally be tailored, for example, by cutting or grinding. The solid electrolyte may also be pulverized to form a powder, depending on the respective intended application.

[0065] The solid electrolyte material of the present invention can have a high density. Therefore, the solid electrolyte material of the present invention can have a density of 95% or more, for example, 97% or more, based on the theoretical density of the material. The density can be determined by Archimedes' principle.

[0066] The solid lithium titanium phosphate-based electrolyte material obtained by the present invention can generally be used in any application in which solid ion-conducting materials, particularly lithium ion-conducting materials, are conventionally used or useful. The solid lithium titanium phosphate-based electrolyte material of the present disclosure can be used, for example, as or be included in a Li-ion conductor, solid electrolyte, electrode, or separator for, for example, an all-solid-state or hybrid Li-ion battery. The solid lithium titanium phosphate-based electrolyte material can also find use in saltwater batteries and osmotic processes.

[0067] Accordingly, the present invention also relates to an article comprising the solid electrolyte material disclosed herein. The article can be, for example, a solid electrolyte, an electrode, a separator, or a membrane.

[0068] Due to its very high elastic modulus, the solid electrolyte material according to the present invention is particularly suitable for industrial applications such as industrial electrolysis processes. Accordingly, the present invention is also directed to membranes, such as ceramic membranes, comprising or consisting of the solid titanium phosphate-based electrolyte material disclosed herein for use in processes for the separation and recycling of lithium from spent lithium-containing devices, such as lithium-containing batteries.

[0069] The present disclosure also relates to energy storage devices, particularly lithium batteries, that include solid electrolytes, electrodes and / or separators that include the solid electrolyte material provided by the present invention.

[0070] Having generally described the invention above, a further understanding can be obtained by reference to the following specific examples, which are provided herein for illustrative purposes only and are not intended to limit the invention, which rather is to be accorded the full scope of the appended claims, including any equivalents thereof. [Example]

[0071] Example 1 Preparation of source material solutions 8.26 kg of a solution containing 1949 g of a commercial solution having 2 wt % Li in the form of lithium neodecanoate (Borchers® DecaLithium 2 from Borchers GmbH, Langenfeld, Germany), 558 g of a commercial solution having 4.5 wt % Al in the form of aluminum ethylacetoacetate (TIB KAT 851 from TIB Chemicals AG, Mannheim, Germany), 1529 g of a commercial solution having 16.5 wt % Ti in the form of tetrapropyl orthotitanate (TIB KAT 530 from TIB Chemicals AG, Mannheim, Germany), 1729 g of a commercial solution having 16.66 wt % P in the form of triethyl phosphate (4001 from Alfa Aesar, Heysham, UK) were combined and mixed at room temperature with 2500 g of a solution containing 50 wt % ethylhexanoic acid and 50 wt % ethanol. The result was a clear solution with no visible precipitate.

[0072] flame pyrolysis The resulting solution was subsequently used to prepare a granular precursor material by flame pyrolysis. For this purpose, a 15 Nm 2 nozzle was used to form the granular precursor material. 3 The aerosol was formed by spraying the solution into a flame in a tubular reaction chamber at a throughput of 2.5 kg / h with 8.0 Nm / h of air. 3 / h hydrogen was supplied at a rate of 75 Nm 3 The flame was generated by burning with air supplied at a rate of 25 Nm / h. 3 / h of secondary air was introduced into the tubular reaction chamber. The reaction gas containing the particulate precursor material leaving the tubular reaction chamber was cooled, and then the particulate precursor material was separated from the reaction gas by filtration. The particulate precursor material thus obtained was Li, determined by the relative amounts of Li, Ti, P, and Aluminum source materials in the solution subjected to flame pyrolysis 1.82 Al 0.3 Ti 1.7 P3O 12 It had a composition corresponding to The particle size distribution of the resulting granular precursor material was determined by laser diffraction analysis using a Horiba LA-950-V2 laser particle size analyzer manufactured by HORIBA Europe GmbH (Oberrussell, Germany) with software version 8.3 (P2001793B). For this purpose, a water dispersion medium to which five droplets of Dolapix CE64 (Zschimmer & Schwarz Chemie GmbH (Lahnstein, Germany) had been added was provided to the fluidic system of the instrument. The dispersion medium was stirred (speed setting 6) and circulated using a pump through an in-line ultrasonic probe (30 W) and flow cell. The tip of a spatula of the granular precursor material to be analyzed was then added to the stirred dispersion medium. Particle size measurement was initiated 5 min after sample addition under constant ultrasonic application. The volumetric particle size distribution was determined by the instrument software using Mie theory based on the measured data and refractive indices of 1.333 for the solvent and 1.590–0.000i for the particles, respectively. The measured particle size distribution is shown in Figure 2, and the derived D 10 , D 50 and D 90 The values ​​are reported in Table 1 below.

[0073] Firing treatment The granular precursor material obtained from the flame pyrolysis process was then subjected to an additional calcination treatment at 700° C. under an inert atmosphere to obtain a calcined precursor material.

[0074] Electric field assisted sintering The calcined precursor material obtained from the above calcination process was then subjected to electric field-assisted sintering to form a lithium titanium phosphate-based solid electrolyte material. Electric field-assisted sintering was performed using a DSP515-725 from Dr. Fritsch GmbH & Co. KG (Felbach, Germany). For this purpose, 5 g of the precursor material was loaded into a cylindrical graphite mold with a circular opening at one end. The mold opening was tightly closed with a circular stamp. The mold thus prepared was transferred to the furnace chamber of an electric field-assisted sintering apparatus. The furnace chamber was set under a nitrogen atmosphere. Then, increasing pressure was applied to the sample contained in the mold by the stamp, and an alternating current was applied to the sample contained in the mold via a pair of electrodes of the electric field-assisted sintering apparatus. Heating of the sample was achieved solely by the current supplied by the electrodes. The time-resolved pressure and heating program applied to the sample, along with the stamp path, is shown in Figure 1. Thus, at the start of the program, the sample was heated from room temperature to a sintering temperature of approximately 900 °C at a heating rate of approximately 50 K / min. The initial pressure was set at 10 MPa and then increased at a rate of approximately 3 MPa / min to a maximum pressure of approximately 40 MPa. The maximum temperature of approximately 900 °C was reached after approximately 17 minutes, and the maximum pressure was reached after approximately 13 minutes. When both the maximum temperature and pressure were reached, the temperature and pressure were held constant for a holding time of approximately 5 minutes. The voltage applied to the electrodes was then turned off, and the sample was depressurized while the electrodes were water-cooled, and cooled to room temperature within 20 minutes. After cooling, the solid electrolyte material formed in the form of a coherent body was separated from the graphite mold.

[0075] Example 2 A granular precursor material was prepared as described above for Example 1, except that the granular precursor material was not subjected to an additional calcination treatment. The granular precursor thus obtained by flame pyrolysis was subjected to electric field-assisted sintering according to the procedure described above for Example 1 to form a lithium titanium phosphate-based solid electrolyte material therefrom.

[0076] Comparative Example 1 Commercially available LATP granular precursor material was obtained from Toshima Manufacturing Co., Ltd. (Saitama, Japan) (Lot 00081034). 1.3 Al 0.3 Ti 1.7 P3O 12 The particle size distribution of this particulate precursor material was determined by laser diffraction analysis according to the procedure described above for Example 1, except using a particle refractive index of 1.980 to 0.100i. The measured particle size distribution is shown in Figure 3, and the derived D 10 , D 50 and D 90 The values ​​are reported in Table 1 below. From this precursor material, a solid electrolyte material was prepared by field-assisted sintering carried out according to the procedure described above in connection with Example 1.

[0077] The mechanical and electrical properties of the solid electrolyte materials obtained in Examples 1, 2 and Comparative Example 1 were analyzed as follows:

[0078] Analysis of mechanical properties by nanoindentation The mechanical properties of the solid electrolyte materials were analyzed using nanoindentation measurements. For nanoindentation measurements, samples of the solid electrolyte materials were used as obtained from electric field-assisted sintering without polishing. Nanoindentation measurements were performed using a standard Picodentor HM500 (Helmut Fischer GmbH, Sindelfingen, Germany) equipped with a Vickers diamond tip (a pyramidal indenter with opposing faces at a half angle of θ = 68°, thus forming an angle β = 22° with the flat specimen surface). All samples were indented in force-controlled mode with maximum loads of 10 mN, 50 mN, 100 mN, and 500 mN. Individual indentations were performed by applying a trapezoidal loading function defined by a 20-second loading time, a 5-second hold time at maximum load, and a 20-second unloading time. For each load, a 100 × 100 μm area was measured. 2 A 2x2 indentation with an area of ​​was recorded. Thermal drift was measured and corrected for each indentation.

[0079] The force-displacement curves were analyzed using software based on the Oliver-Pharr method described in Journal of Materials Research, Volume 7, Issue 6, June 1992, pp. 1564-1583, doi: https: / / doi.org / 10.1557 / JMR.1992.1564. First, the curve was shifted to the first contact point. 0 displacement was defined as the onset of the repulsive force during approach / loading. The reduced elastic modulus, E r is the expression TIFF2024541848000001.tif26133 where S is the initial unloading stiffness and A is the projected contact area at peak load. For this purpose, a linear fit was applied to the experimentally measured unloading curve of the recorded force-displacement curve, TIFF2024541848000002.tif26133 S was determined by using the equation, where dP is the applied force difference and dh is the displacement difference. The upper and lower fitting ranges were set to 95-60% of the unloading curve. A is TIFF2024541848000003.tif26133 (ideal Vickers indenter), and thus h c teeth TIFF2024541848000004.tif26133 is given by h max and P max are the maximum displacement and maximum applied load, respectively. The elastic modulus E of the sample is TIFF2024541848000005.tif33133 (In the formula, E i and v i are the elastic modulus and Poisson's ratio of the indenter, respectively). i is 1140 GPa, and Poisson's ratio v i was 0.07. v is the Poisson's ratio of the sample, which was defined as 0.3 for the samples analyzed here. Calculate the yield strength σ as TIFF2024541848000006.tif33133 y of The elastic modulus, yield strength, and hardness determined in this way for the multiple indentations performed for each sample were then averaged (arithmetic mean). Table 1 reports the determined average elastic modulus, yield strength, and hardness values ​​and standard deviations for the investigated solid electrolyte materials.

[0080] Impedance spectroscopy Electrochemical impedance spectroscopy of the obtained solid electrolyte material was carried out as follows:

[0081] The measurement arrangement consisted of two cylindrical electrodes between which the sample was placed. A weight was placed on top of the sample to ensure optimal contact with the electrodes and reproducible contraction pressure. A potentiostat (ZAHNER-elektrik I. Zahner-Schiller GmbH & Co. KG, Kronach-Gundelsdorf, Germany) was connected to the electrodes and controlled by Thales software (ZAHNER). Measurements were performed in the frequency range of 1 Hz to 4 MHz using an amplitude of 5 mV on polished samples sputtered with a thin conductive layer of Au.

[0082] The measurement results were plotted in the form of a Nyquist diagram and analyzed using the software Analysis (ZAHNER). The electrical resistance was read at the maximum value of the curve of the Nyquist diagram. The specific conductivity σ [mS / cm] was then calculated using the formula Calculations were based on TIFF2024541848000008.tif42101, where h is the plate height in mm, R is the measured electrical resistance in Ω, and d is the diameter in mm. The determined specific conductivities σ are reported in Table 1 for the investigated solid electrolyte materials.

[0083] Table 1 TIFF2024541848000009.tif126163

[0084] As is evident from the results shown in Table 1, the combination of flame pyrolysis and electric-field-assisted sintering in the process according to the present invention provides solid electrolyte materials with improved mechanical properties compared to reference materials based on conventional, commercially available granular precursor materials. In particular, the solid electrolyte materials of Examples 1 and 2 are characterized by significantly higher elastic moduli compared to the comparative examples. Without intending to be bound by any theory, it is believed that one reason for this may be the significantly smaller particle size and narrower particle size distribution of the granular precursor material obtained by flame pyrolysis disclosed herein compared to the conventional granular material of Comparative Example 1 (see Table 1 and Figures 2 and 3). It is believed that smaller particles reduce the grain size of the solid electrolyte material, which may reduce the probability of microcrack formation and therefore improve its reliability against mechanical fracture. A comparison of the elastic modulus E, hardness, and yield strength of Examples 1 and 2 further demonstrates that calcination treatment of the granular precursor material prior to electric-field-assisted sintering does not further improve the mechanical properties of the resulting solid electrolyte material. Thus, the granular precursor material obtained from flame pyrolysis can be subjected to electric field-assisted sintering without any intermediate processing steps and still provide a solid electrolyte material with beneficial mechanical properties, in particular a very high elastic modulus. Furthermore, the specific conductivity of the solid electrolyte material produced by the process according to the invention is typically 10 -5 ~10 -3 This is comparable in magnitude to conventional solid electrolyte materials of similar composition that exhibit specific conductivities on the order of 500 S / cm. Thus, the process of the present invention provides solid electrolyte materials that exhibit improved mechanical properties, including very high elastic modulus, while at the same time having competitive conductivity.

[0085] Furthermore, the solid electrolyte materials obtained in Example 1 and Comparative Example 1 were analyzed for their crystal structures by X-ray diffraction at a wavelength of 1.5406 nm. The results of the semi-quantitative analysis are shown in Table 2.

[0086] Table 2 TIFF2024541848000010.tif47159

[0087] In Table 2, the compound LiTi2P3O 12 LATP and LiTi2P3O 12 Since the crystal structure of these two materials is identical, it represents the ion-conducting LATP (lithium-aluminum-titanium-phosphate).

[0088] Example 3 A 6.62 kg solution containing 1336 g of a commercial solution containing 2 wt. % lithium in the form of lithium neodecanoate (Borchers® Deca Lithium 2), 699 g of a commercial solution containing 4.5 wt. % Al in the form of aluminum-ethylacetoacetate (TIB KAT 851), 1014 g of a commercial solution containing 16.5 wt. % Ti in the form of tetrapropyl orthotitanate (TIB KAT 530), 131 g of a solution containing 28.7 wt. % Ge in the form of tetraethoxide, and 1444 g of a commercial solution containing 16.66 wt. % phosphite in the form of triethyl phosphate (Alfa Aesar) was mixed with 2000 g of a solution containing 50 wt. % ethylhexanoic acid and 50 wt. % ethanol to obtain a clear solution. This solution contained Li 1.45 Al 0.45 Ge 0.2 Ti 1.35 Corresponding to the composition of P3O1(LAGTP).

[0089] An aerosol of 2.5 kg / h of this solution and 15 Nm3 / h of air was formed through a two-component nozzle and sprayed onto the tubular reactor using a combustion flame. The combustion gases of the flame consisted of 8.0 Nm3 / h of hydrogen and 75 Nm3 / h of air. In addition, 25 Nm3 / h of secondary air was used. After the reactor, the reaction gases were cooled and filtered.

[0090] The LAGTP precursor material obtained in Example 3 was subjected to particle size distribution analysis by laser scattering using the same Horiba LA-950 laser particle size analyzer as described above. The results are shown in Figure 4. The average particle size of the LAGTP precursor was d 50 = 90 nm. The particle size distribution is unimodal.

[0091] Example 4 The precursor powder obtained in Example 3 is amorphous. For better sintering results, the amorphous powder is crystallized by an additional temperature treatment at 700 °C for 5 hours. This is followed by a deagglomeration step. The resulting nanopowder is then spark plasma sintered. During sintering, the powder is subjected to high temperature and pressure. A pressure of 45 MPa is applied. The temperature regime includes several segments. In the first segment, the temperature is increased to 300 °C at a heating rate of 60 K / min. In the second segment, the temperature is increased to a sintering temperature of 650 to 950 °C at a heating rate varying from 40 to 50 K / min. After a dwell time of 1 to 30 minutes, the pressure is released and the cooling phase begins.

[0092] The LAGTP type sintered material obtained in Example 4 was subjected to measurement of particle size distribution, mechanical properties and specific conductivity using the same methods and equipment as in Examples 1 and 2 and Comparative Example 1. The results are shown in Table 3.

[0093] Table 3 TIFF2024541848000011.tif115159

Claims

1. A process for producing a lithium titanium phosphate-based solid electrolyte material, comprising: i) providing a solution comprising a Li source material, a Ti source material, a P source material, and optionally a Si source material and / or a source material of a metal M, wherein M is selected from the group of Al, Ga, Ge, In, Sc, V, Cr, Mn, Co, Fe, Y, a lanthanide, or a combination thereof; ii) generating an aerosol from the solution; and iii) subjecting the generated aerosol to flame pyrolysis to form a particulate precursor material therefrom; iv) subjecting the particulate precursor material to electric field assisted sintering to form the lithium titanium phosphate based solid electrolyte material; The process includes:

2. 2. The process of claim 1, wherein the Li source material, the Ti source material, and the source material of the metal M are each individually selected from organic salts, organic complexes, or organometallic compounds of the respective metals, or combinations thereof; and / or the P source material comprises an ester or salt of an oxoacid of phosphorus; and / or the Si source material comprises a silicate and / or an organosilicon compound.

3. 2. The process of claim 1, wherein the solution comprises the Li source material, the Ti source material, the P source material, and optionally the Si source material and / or the metal M source material in amounts corresponding to an equivalent ratio of Li:(Ti,M):(P,Si) of (0.5-2):(1.5-2.5):

3.

4. 4. The process of claim 3, wherein the equivalent ratio of M:Ti in the solution is in the range of 0 to 1:2 and / or the equivalent ratio of Si:P in the solution is 0 to 1:

2.

5. The process of claim 1 , wherein the solution comprises at least one organic solvent.

6. 10. The process of claim 1, wherein generating an aerosol from the solution comprises spraying the solution through a nozzle using an atomizing gas.

7. 10. The process of claim 1, wherein subjecting the aerosol to flame pyrolysis comprises contacting the aerosol with a flame.

8. The formed particulate precursor material has the formula Li ｎ・（１＋ｘ＋ｙ＋ｚ） M ｎ’・ｘ Ti ｎ’’・（２－ｘ） (P.O. ４ ) （ｎ’’’）・（３－ｙ） (SiO ４ ) （ｎ’’’’）・ｙ 10. The process of claim 1, wherein M is a metal selected from the group of Al, Ga, Ge, In, Sc, V, Cr, Mn, Co, Fe, Y, a lanthanide, or a combination thereof; 0≦x≦1, 0≦y≦1, 0≦z≦0.8; and n, n', n'', n''n''', and n'''' are each independently a number in the range of 0.8 to 1.

2.

9. The formed particulate precursor material has a D of less than 200 nm as measured by laser diffraction using a Horiba LA-950 laser particle size analyzer. ５０ particle size, and / or a span (D ９０ -D １０ ) / D ５０ 10. The process of claim 1, wherein the particle size distribution is based on volume and has the following formula:

10. 2. The process of claim 1 , wherein the electric-field-assisted sintering comprises providing the granular precursor material in a mold between a pair of electrodes, applying pressure to the granular precursor material, and passing an electric current through the mold and / or the granular precursor material by the electrodes.

11. The process of claim 1 , wherein the electric field-assisted sintering comprises heating the particulate precursor material to a sintering temperature of 700° C. or greater and / or applying a sintering pressure of 20 MPa or greater.

12. 12. The process of claim 11, wherein the particulate precursor material is heated to the sintering temperature at a rate of 10 K / min or greater and / or the pressure is increased to the sintering pressure at a rate of 0.5 MPa / min or greater.

13. 12. The process of claim 11, wherein the electric field assisted sintering comprises maintaining the particulate precursor material at the sintering temperature and sintering pressure for a hold time of 10 minutes or less.

14. A solid electrolyte material obtainable by the process according to claim 1.

15. Formula Li ｎ・（１＋ｘ＋ｙ＋ｚ） M ｎ’・ｘ Ti ｎ’’・（２－ｘ） (P.O. ４ ) （ｎ’’’）・（３－ｙ） (SiO ４ ) （ｎ’’’’）・ｙ 15. The solid electrolyte material of claim 14 having a composition according to the formula: wherein M is a metal selected from the group of Al, Ga, Ge, In, Sc, V, Cr, Mn, Co, Fe, Y, a lanthanide, or a combination thereof; 0≦x≦1, 0≦y≦1, 0≦z≦0.8; and n, n', n'', n''n''', and n'''' are each independently a number in the range of 0.8 to 1.

2.

16. Formula Li （１＋ｘ＋ｙ） M ｘ Ti （２－ｘ） (P.O. ４ ) ３－ｙ (SiO ４ ) ｙ 15. The solid electrolyte material of claim 14, comprising one or more phases having a composition represented by the formula: wherein M is a metal selected from the group of Al, Ga, Ge, In, Sc, V, Cr, Mn, Co, Fe, Y, a lanthanide, or a combination thereof, and 0≦x≦1 and 0≦y≦1.

17. The solid electrolyte material according to claim 15, wherein x is in the range of 0.2 to 0.7 and / or y is in the range of 0 to 0.

8.

18. The solid electrolyte material according to claim 17, wherein y is 0.

19. The solid electrolyte material according to claim 15, wherein M is Al.

20. The solid electrolyte material has an elastic modulus of 200 GPa or more, and / or the solid electrolyte material has an elastic modulus of 1.10 －５ 15. The solid electrolyte material according to claim 14, having a specific ionic conductivity of 100 S / cm or more.

21. An article comprising the solid electrolyte material of claim 13.

22. 22. The article of claim 21, wherein the article is a solid electrolyte, an electrode, a separator, or a membrane.

23. 14. An energy storage device, in particular a lithium battery, comprising a solid electrolyte, an electrode and / or a separator comprising the solid electrolyte material according to claim 13.

24. The process of claim 1 , wherein the particulate precursor material is subjected to a calcination treatment prior to subjecting the particulate precursor material to electric field-assisted sintering.

25. 25. The process of claim 24, wherein the calcination is carried out at a temperature of from 630°C to 770°C.

26. 25. The process of claim 24, wherein the calcination is carried out for 4.5 to 5 hours.

27. 25. The process of claim 24, wherein the calcination is carried out in a dedicated calcination facility.

28. 28. The process of claim 27, wherein the calcined particulate precursor material is subjected to a deagglomeration step before subjecting the particulate precursor material to electric field assisted sintering.

29. The subject matter of claim 1 , wherein M is a combination of Al and Ge.

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