A lithium garnet type electrolyte sintering embedding powder and a method for preparing a lithium garnet type electrolyte using the embedding powder

Abstract

The present invention provides a lithium garnet electrolyte sintering embedding powder, a method for preparing a lithium garnet electrolyte using the embedding powder, a lithium garnet electrolyte prepared by the preparation method, and a lithium ion battery including the lithium garnet electrolyte. The lithium garnet electrolyte sintering embedding powder comprises a embedding powder main phase and an embedding powder additive. The sintering embedding powder of the present invention can provide a reversibly controlled sintering atmosphere for LLZO sintering, thereby obtaining a lithium ion battery having a relative density exceeding 96% and an ionic conductivity exceeding 0.4 mS·cm. ‑1 LLZO, high density and ionic conductivity; the buried powder for sintering the lithium garnet type electrolyte of the present invention solves the problems of low electrolyte density caused by insufficient Li2O atmosphere in the sintering atmosphere and abnormal growth of electrolyte grains caused by excessive Li2O atmosphere.

Description

Technical Field

[0001] The present invention belongs to the technical field of solid-state lithium-ion batteries, and in particular relates to an embedding powder for sintering a lithium garnet-type electrolyte, a method for preparing a lithium garnet-type electrolyte using the embedding powder, a lithium garnet-type electrolyte prepared by the preparation method, and a lithium-ion battery comprising the lithium garnet-type electrolyte. Background Art

[0002] Lithium-ion batteries, as highly promising electrochemical energy storage devices, play a vital role in the development of portable electronic devices, electric vehicles, and grid energy storage. However, they remain limited by issues such as energy density, power density, and safety. This poses challenges to their large-scale application in electrical devices. Solid-state lithium batteries offer exceptional safety and can combine high-voltage cathodes with lithium metal, resulting in high energy density. Therefore, highly safe and energy-dense solid-state lithium metal batteries are a key area of future lithium battery development.

[0003] As a key component of solid-state lithium metal batteries, garnet-type electrolyte Li7La3Zr2O 12 (LLZO) has been widely studied. Generally, this type of electrolyte has high strength, high electrochemical window, high thermal stability, easy to handle and use, and the corresponding conductivity is generally 10 -4 ~10 -3 S cm -1 LLZO usually needs to be prepared by high-temperature sintering, and the most common and low-cost method is atmospheric pressure sintering. The green blank is placed in a crucible (corundum, zirconia, magnesium oxide, platinum, etc.), placed in an ordinary muffle furnace, heated to the set temperature and sintered. During the atmospheric pressure sintering process, LLZO has problems such as volatilization of alkali metal elements (such as Li2O) and low density (Solid State Ionics 2017, 311, 69-74; Int. J. Appl. Ceram. Technol. 2017, 14; J. Power Sources 2010, 9, 195). In this regard, researchers have reported some solutions. For example, using a large amount of materials with similar components as embedding powder to embed the LLZO green blank to compensate for Li2O volatilization and improve electrolyte density and lithium ion conductivity (J. Energy Chem. 2019, 39, 8-16). However, the embedding powder cannot be reused, resulting in material waste. The buried powder contains a large amount of La and Ta elements, which will undoubtedly increase the preparation cost of LLZO. x MO y (M=Al, Ti, Si and Zr) compounds provide atmosphere for sintering of LLZO (Journal of Materiomics 2019, 5, 221-228).x MO y As buried powder (compensate for lithium loss), it decomposes unidirectionally at the sintering temperature to produce Li2O, which provides atmosphere for the sintering of LLZO. The obtained LLZO electrolyte has a density of 95% and a lithium ion conductivity of 5.7×10 -4 S cm -1 , which shows similar performance to LLZTO ceramics sintered from LLZO mother powder. It is worth noting that the amount of buried powder used usually needs to be precisely controlled to ensure the provision of a suitable Li2O atmosphere, otherwise it is easy to cause low electrolyte, low density, the presence of internal pores and defects, or abnormal grain growth (Energy Storage Mater. 2019, 22, 207-217). Lithium dendrites will form in pores and defects and infiltrate and grow inside LLZO, causing battery short circuits (Chem. Eng. J. 2021, 411, 128508).

[0004] Therefore, since the sintering atmosphere is difficult to control, it is easy to cause poor sintering consistency of LLZO, which brings huge challenges to the application of solid-state lithium batteries. Summary of the Invention

[0005] In response to the above-mentioned problems, the present invention aims to provide a lithium garnet electrolyte sintering embedding powder, a method for preparing a lithium garnet electrolyte using the embedding powder, a lithium garnet electrolyte prepared by the preparation method, and a lithium-ion battery including the lithium garnet electrolyte. The lithium garnet electrolyte obtained by sintering the embedding powder of the present invention avoids abnormal grain growth, promotes densification of the lithium garnet electrolyte, improves sintering consistency, reversibly controls the sintering atmosphere, and eliminates the need for precise control of the amount of sintering embedding powder used.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides an embedding powder for sintering a lithium garnet-type electrolyte, the embedding powder comprising:

[0008] (a) a powder-embedded main phase, the powder-embedded main phase comprising at least one of the following:

[0009] Lithium garnet composite powder, the lithium garnet composite powder comprising at least one of the following:

[0010] (i)Li 7-3a La3Zr2L a O 12 , where L = Al, Ga or Fe, and 0 <a<0.33;

[0011] (ii)Li7La 3-b ZlUT b O12 , where M=Bi or Y, and 0 <b<1;

[0012] (iii)Li 7-c La3(Zr 2-c ,N c )O 12 , wherein N=In, Si, Ge, Sn, Sb, Sc, Ti, Hf, V, W, Te, Nb, Ta, Al, Ga, Fe, Bi, Y, Mg, Ca or a combination thereof, and 0 <c<1;

[0013] LiOH·H2O;

[0014] LiOH;

[0015] CH3COOLi;

[0016] Li2C2O4;

[0017] LiNO3;

[0018] Li2CO3;

[0019] Li2O;

[0020] Li2O2;

[0021] (b) a powder embedding additive, wherein the powder embedding additive comprises at least one of the following:

[0022] Lithium tungstate x WO (x+6) / 2 , where 1 / 3≤x≤6;

[0023] Lithium zirconate x ZrO (x+4) / 2 , where 2≤x≤10;

[0024] Lithium titanate x TiO (x+4) / 2 , where 0.66≤x≤4;

[0025] Lithium stannate x SnO (x+4) / 2 , where 2≤x≤8;

[0026] Lithium lead acid x PbO (x+4) / 2 , where 2≤x≤8;

[0027] Lithium-niobium-oxide Li x NbO (x+5) / 2 , where 1≤x≤7;

[0028] Lithium silicate x SiO (x+4) / 2, where 2≤x≤8;

[0029] Lithium aluminate x AlO (x+3) / 2 , where 1 / 5≤x≤5;

[0030] Lithium-tantalum oxide Li x TaO (x+5) / 2 , where 1 / 3≤x≤7;

[0031] Lithium gallate x GaO (x+3) / 2 , where 1 / 5≤x≤5.

[0032] Preferably, the lithium content in the lithium garnet composite powder is 1-30 mol%.

[0033] Preferably, the embedding powder additive accounts for 0-49 wt.% of the total mass of the embedding powder for sintering the lithium garnet type electrolyte.

[0034] Preferably, the embedding powder additive accounts for 3-25 wt.% of the total mass of the embedding powder for sintering the lithium garnet type electrolyte, preferably 4-15 wt.%.

[0035] In a second aspect, the present invention also provides a method for preparing a lithium garnet-type electrolyte, which comprises sintering a lithium garnet-type electrolyte blank at a high temperature, wherein the sintering process uses the lithium garnet-type electrolyte sintering buried powder as described above to provide a reversibly controlled sintering atmosphere.

[0036] Preferably, the sintering temperature is 700-1300°C.

[0037] In a third aspect, the present invention also provides a lithium garnet-type electrolyte prepared by the preparation method described above.

[0038] Preferably, the lithium garnet electrolyte LLZO is preferably selected from (i) Li 7-3a La3Zr2L a O 12 , L=Al, Ga, or Fe, and 0<a<0.33; (ii) Li7La 3-b ZlUT b O 12 , wherein M=Bi, or Y, and 0<b<1; (iii) Li 7-c La3(Zr 2-c ,N c )O 12 , where N = one or more of In, Si, Ge, Sn, Sb, Sc, Ti, Hf, V, W, Te, Nb, Ta, Al, Ga, Fe, Bi, Y, Mg or Ca, and 0<c<1.

[0039] Preferably, the lithium garnet electrolyte has a relative density greater than 96% and a relative density greater than 0.4 mS·cm -1 ionic conductivity.

[0040] In a fourth aspect, the present invention further provides a solid-state lithium-ion battery comprising the lithium garnet-type electrolyte described above.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] (1) The sintering buried powder of the present invention can provide a reversibly controlled sintering atmosphere for LLZO sintering, and obtain a sintered product with a relative density exceeding 96% and an ionic conductivity exceeding 0.4 mS·cm -1 LLZO, high density and ionic conductivity;

[0043] (2) The preparation method of the embedded powder main phase and embedded powder additives in the embedded powder is simple and efficient, does not require the use of complex equipment, and is low in cost;

[0044] (3) The lithium garnet-type electrolyte sintering powder of the present invention solves the problems of low electrolyte density caused by insufficient Li2O atmosphere in the sintering atmosphere and abnormal growth of electrolyte grains caused by excessive Li2O atmosphere;

[0045] (4) The embedding powder for sintering the lithium garnet type electrolyte of the present invention can be selected to have the same elements as the lithium garnet type electrolyte, so as to avoid contamination of the lithium garnet type electrolyte by the embedding powder. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 This is a schematic diagram of the sintering and powder embedding process for preparing a lithium garnet-type electrolyte according to the present invention;

[0047] Figure 2 The scanning electron microscope (SEM) cross-sectional morphology of LLZO prepared by the buried powder main phase in comparative samples 1 and 2 of the present invention;

[0048] Figure 3 This is the SEM cross-sectional morphology of LLZO prepared by sintering buried powder in sample 1 of the present invention;

[0049] Figure 4 The SEM cross-sectional morphology of LLZO prepared by sintering different amounts of buried powder in samples 2-6 of the present invention;

[0050] Figure 5 This is the SEM cross-sectional morphology of LLZO prepared by sintering buried powder in sample 7 of the present invention;

[0051] Figure 6X-ray diffraction (XRD) patterns of LLZO prepared with different usage amounts of sintered buried powder in samples 2-6 of the present invention;

[0052] Figure 7 This is the XRD pattern of the reaction between the powder embedding additive Li2ZrO3 and the powder embedding main phase LiOH·H2O of the present invention;

[0053] Figure 8 Cycling results of the lithium metal symmetric battery assembled for sample 4 of the present invention;

[0054] Figure 9 The charge and discharge cycle diagram and discharge curve of the lithium metal full battery assembled by sample 4 of the present invention. DETAILED DESCRIPTION

[0055] The present invention is further described below through the following embodiments. It should be understood that the following embodiments are only used to illustrate the present invention, rather than to limit the present invention.

[0056] The present invention provides a sintering powder for a lithium garnet-type electrolyte, a method for preparing a lithium garnet-type electrolyte using the sintering powder, a lithium garnet-type electrolyte prepared by the preparation method, and a lithium-ion battery comprising the lithium garnet-type electrolyte. High sintering temperatures (e.g., 1100-1300°C) are essential for preparing dense lithium-ion electrolytes. However, at such high temperatures, severe lithium loss is likely to occur. Garnet-type sintering powder containing an excess of lithium source material can be used to compensate for lithium loss in LLZO garnet samples during the sintering process. Adding garnet-type sintering powder also helps to obtain high-density LLZO.

[0057] In the present invention, the embedding powder for sintering the lithium garnet type electrolyte includes an embedding powder main phase and an embedding powder additive.

[0058] Specifically, the buried powder main phase includes but is not limited to at least one of the following:

[0059] (1) A lithium garnet composite powder, wherein the lithium garnet composite powder comprises at least one of the following:

[0060] (i)Li 7-3a La3Zr2L a O 12 , where L = Al, Ga or Fe, and 0 <a<0.33;

[0061] (ii)Li7La 3-b ZlUT b O 12 , where M=Bi or Y, and 0 <b<1;

[0062] (iii)Li 7-c La3(Zr 2-c,N c )O 12 , where N=In, Si, Ge, Sn, Sb, Sc, Ti, Hf, V, W,

[0063] Te, Nb, Ta, Al, Ga, Fe, Bi, Y, Mg, Ca or a combination thereof, and 0 <c<1;

[0064] (2) LiOH·H2O;

[0065] (3) LiOH;

[0066] (4) CH3COOLi;

[0067] (5)Li2C2O4;

[0068] (6)LiNO3;

[0069] (7)Li2CO3;

[0070] (8)Li2O;

[0071] (9)Li2O2.

[0072] The powder embedding additives include but are not limited to at least one of the following:

[0073] Lithium tungstate x WO (x+6) / 2 , where 1 / 3≤x≤6;

[0074] Lithium zirconate x ZrO (x+4) / 2 , where 2≤x≤10;

[0075] Lithium titanate x TiO (x+4) / 2 , where 0.66≤x≤4;

[0076] Lithium stannate x SnO (x+4) / 2 , where 2≤x≤8;

[0077] Lithium lead acid x PbO (x+4) / 2 , where 2≤x≤8;

[0078] Lithium-niobium-oxide Li x NbO (x+5) / 2 , where 1≤x≤7;

[0079] Lithium silicate x SiO (x+4) / 2 , where 2≤x≤8;

[0080] Lithium aluminate xAlO (x+3) / 2 , where 1 / 5≤x≤5;

[0081] Lithium-tantalum oxide Li x TaO (x+5) / 2 , where 1 / 3≤x≤7;

[0082] Lithium gallate x GaO (x+3) / 2 , where 1 / 5≤x≤5.

[0083] <Preparation of embedding powder additive powder>

[0084] Step 1: First Mixing

[0085] In the first mixing step, an inorganic raw material and an additive material are mixed and refined by grinding in a stoichiometric ratio. The inorganic raw material can be a lithium source compound and at least one transition metal compound (e.g., a Zr-based compound) in the form of a carbonate, nitrate, hydroxide, oxide, or other compound containing the constituent elements, or any combination thereof.

[0086] Step 2: First calcination

[0087] The first calcination step is after the first mixing step, wherein the inorganic raw material mixture is calcined at a predetermined temperature, for example, at 400°C to 1100°C (for example, 950°C), including any value in the intermediate value and range. The predetermined temperature depends on the type of buried powder additive. The calcination time is selected, for example, from 1 min to 48 h (for example, 30 min to 36 h, or 1 h to 24 h, for example 24 h), or any value in the intermediate value or range disclosed therein. The calcination time also depends on the sintering activity of the selected inorganic starting material. In some examples, the predetermined temperature is selected independently of the calcination time, for example, 950°C for 24 hours.

[0088] The powder embedding additive is lithium zirconate Li x ZrO (x+4) / 2 (where 2≤x≤10, such as Li2ZrO3), the inorganic raw materials are precursor powders LiOH·H2O(AR) and ZrO2(AR), weighed at a molar ratio of x (2≤x≤10) (e.g. x=2). Yttrium-stabilized zirconia (YSZ) balls are used as grinding media, isopropyl alcohol is used as solvent, and the grinding speed is 250 rpm min. -1 The mixture was wet ball milled at a speed of 1000 nm for 24 hours. After drying, the mixture powder was calcined in an alumina crucible at 950°C for 24 hours to obtain a Li2ZrO3 buried powder additive.

[0089] <Preparation of buried main phase powder>

[0090] The preparation of buried powder main phase powder is similar to the preparation process of buried powder additive in steps 1 and 2, except that the buried powder main phase powder is, for example, lithium garnet type composite powder (such as Li 6.75 La3Zr 1.75 Nb 0.25 O 12 , LLZNO), the lithium excess is, for example, 15%. The inorganic raw materials are precursor powders LiOH·H2O, La2O3, ZrO2, Nb2O5, using yttrium-stabilized zirconia (YSZ) balls as grinding media and isopropyl alcohol as solvent at 250 rpm min -1 The mixture was wet ball milled for 12 h (step 1), and then the dried mixed powder was calcined at 950 ° C for 6 h (step 2) to obtain LLZNO buried powder main phase powder.

[0091] <Preparation of buried powder for sintering lithium garnet-type electrolyte>

[0092] Step 3: Second Mixing

[0093] The embedding powder additive powder and the lithium garnet embedding powder are mixed in a certain proportion to obtain the embedding powder for sintering the lithium garnet type electrolyte, so that the total content of the embedding powder additive in the embedding powder for sintering the lithium garnet type electrolyte is in the range of 0-49wt.%, for example, 1-25wt.%, or 1-10wt.%, or 4-15wt.% (for example, 9.1wt.%, 6.3wt.%, 4.2wt.%), or any value within the disclosed intermediate value or range.

[0094] The second mixing step can be a dry mixing process (e.g., tubular mixing first, dry ball milling later, or dry ball milling first, tubular mixing later), a dry milling process or a wet milling process using a suitable liquid that does not dissolve the inorganic raw material as a solvent. The mixing time can be adjusted according to the scale or degree of the materials and the observed mixing effect, for example, from a few minutes to a few hours (e.g., 1 min to 48 h, or 30 min to 36 h, or 1 h to 24 h, or any value in the disclosed range, such as 12 h). Grinding can be achieved by, for example, manual grinding, planetary grinder, attritor, ball mill mixing, tubular mixing or similar mixing or grinding equipment.

[0095] <Preparation of lithium garnet electrolyte powder for lithium garnet type electrolyte>

[0096] Step 4: Third Mixing

[0097] In the mixing step of step 4, the inorganic raw materials in the stoichiometric ratio of the lithium garnet electrolyte molecular formula are mixed and refined by grinding. The lithium garnet LLZO is preferably selected from (i) Li 7-3a La3Zr2L a O12 , L=Al, Ga, or Fe, and 0<a<0.33; (ii) Li7La 3-b ZlUT b O 12 , wherein M=Bi, or Y, and 0<b<1; (iii) Li 7-c La3(Zr 2-c ,N c )O 12 , wherein N=In, Si, Ge, Sn, Sb, Sc, Ti, Hf, V, W, Te, Nb, Ta, Al, Ga, Fe, Bi, Y, Mg or Ca one or more, 0<c<1. The inorganic materials in the stoichiometric ratio of the garnet oxide molecular formula are mixed and refined by grinding. The inorganic raw materials can be a lithium source compound and at least one transition metal compound (for example, Li-based, La-based and Zr-based compounds) of carbonate, sulfate, nitrate, oxalate, hydroxide, oxide or other compound containing constituent elements, one of which or a combination thereof. In some embodiments, the inorganic material compound chemical formula can also include at least one of In, Si, Ge, Sn, Sb, Sc, Ti, Hf, V, W, Te, Nb, Ta, Al, Ga, Fe, Bi, Y, Mg and Ca or a combination thereof.

[0098] In some embodiments, it may be necessary to add excess lithium source material (e.g., 2% lithium excess) to the mixed feedstock to compensate for high temperature lithium loss during the 800°C to 1300°C (e.g., 1100°C to 1200°C) calcination / electrolyte sintering step.

[0099] The third mixing step can be a dry mixing process (e.g., tubular mixing first, dry ball milling later, or dry ball milling first, tubular mixing later), a dry milling process, or a wet milling process using a suitable liquid that does not dissolve the inorganic raw material as a solvent. The mixing time can be adjusted according to the scale or degree of the materials and the observed mixing effect, for example, from a few minutes to a few hours (e.g., 1 min to 48 h, or 30 min to 36 h, or 1 h to 24 h, or any value or any value within the disclosed range, such as 12 h). Grinding can be achieved by, for example, manual grinding, planetary grinder, attritor, ball mill mixing, tubular mixing, or similar mixing or grinding equipment.

[0100] Step 5: Second calcination

[0101] The second calcination step is to calcine the mixture of inorganic materials at a predetermined temperature (e.g., a temperature between 800°C and 1200°C, including intermediate values (e.g., 950°C)) after the third mixing step to react and form the target lithium garnet electrolyte powder (or garnet oxide). The predetermined temperature depends on the type of lithium garnet electrolyte. The calcination time may generally be 1 h to 48 h (e.g., 2 h to 36 h, or 3 h to 24 h, or 4 h to 12 h, such as 6 h), or any value or any value within the range disclosed therein, depending on the relative reactivity of the selected inorganic raw material or billet. In some embodiments, the premixed inorganic ingredients may be ground and then calcined or sintered as needed. For example, after the second calcination, the calcined mixture of inorganic materials may be optionally calcined at a higher predetermined temperature, for example, between 1000°C and 1300°C (e.g., 1200°C), including any value within the intermediate value and range. The predetermined temperature for calcination depends on the type of lithium garnet. The calcination time is, for example, from 1 hour to 48 hours (e.g., 2 hours to 36 hours, or 3 hours to 24 hours, or 4 hours to 12 hours, such as 5 hours), or any value or range disclosed therein. In some embodiments, the calcinations after the second calcination can be combined into a single calcination step with two holding stages.

[0102] Here, steps 4 and 5 can be implemented, wherein the precursor powders LiOH·H2O (AR, lithium excess 2%), La2O3 (99.99%, calcined at 900°C for 12h), ZrO2 (AR) and Ta2O5 (99.99%) are prepared according to Li 6.5 La3Zr 1.5 Ta 0.5 O 12 Yttrium stabilized zirconia (YSZ) balls were used as grinding media and isopropyl alcohol was used as solvent at 250 rpm min -1 The mixed powder was wet ball milled at a speed of 1000 nm for 12 h. After drying, the mixed powder was calcined in an alumina crucible at 950° C. for 6 h to obtain a pure cubic lithium garnet electrolyte powder. Preferably, the solid electrolyte according to the chemical formula defined above is referred to as a lithium garnet ceramic electrolyte LLZO.

[0103] <Preparation of lithium garnet-type electrolyte>

[0104] Step 6: Refinement

[0105] The refinement step is similar to the refinement in step 4 above, and is used to refine the lithium garnet electrolyte powder obtained in step 5 and to refine the lithium garnet electrolyte powder at 250 rpm min. -1 Wet grinding for 12 hours.

[0106] Step 7: Sieve

[0107] The mixture obtained in step 6 is dried at 70° C. for 12 h, and then the mixture is passed through a 200 mesh sieve. Further, the mixture is compacted into a green billet having a diameter range of 0.1 mm to 100 mm (or 1 mm to 50 mm, or 10 mm to 25 mm (e.g., 18 mm)) by uniaxial pressing under a pressure of, for example, 100 MPa. The weight of the green billet can be in the range of 0.01 g to 50 g, or 0.1 g to 25 g, or 1 g to 10 g (e.g., 1.25 g). The green billet can be of any geometric shape and any thickness (film, sheet, block or tubular, etc.). When formed into any shape, the green billet can have at least one dimension ranging from 0.1 to 100 mm, and the thickness can have at least one dimension ranging from 0.01 to 100 mm.

[0108] Step 8: Sintering the green billet

[0109] During the sintering process, the green billet is placed in a crucible with a lid (e.g., a Pt, ZrO2, Al2O3, and MgO crucible) and the lithium garnet-type electrolyte sintering buried powder obtained in step 3 is used to compensate for the lithium loss during the LLZO sintering process (e.g., 0.5, 1, 2, 4, 6 g of lithium garnet-type electrolyte sintering buried powder is used for every 5 g of LLZO green billet). Two types of sintering methods can be used: conventional sintering and rapid sintering. In conventional sintering, the heating rate is in the range of 100°C / h to 600°C / h (e.g., in an air environment, argon (Ar) or nitrogen (N2) atmosphere). In rapid sintering, the heating rate is in the range of 100°C / min to 1000°C / min (e.g., in an air environment).

[0110] Step 8 can be sintered at a temperature in the range of 750°C to 1500°C, or 900°C to 1400°C, or 1000°C to 1250°C (e.g., 1220°C), or any value or range of temperature disclosed therein, and the holding time is 1 minute to 300 minutes, or 5 minutes to 100 minutes, or 10 minutes to 50 minutes (e.g., 30 minutes), or any value or range of time disclosed therein to form a lithium garnet-type ceramic electrolyte. The heating and cooling rates during sintering are both 5°C / min. The obtained lithium garnet-type ceramic electrolyte can be further cut, thinned or polished into different shapes and thicknesses (films, sheets, blocks or tubes, etc.). The thickness can have at least one dimension ranging from 0.01-100 mm (e.g., 800 μm).

[0111] <Assembly of solid-state lithium-ion batteries Li / LLZO / Li symmetric cells and Li / LLZO / NCM full cells>

[0112] All electrolyte sheets were polished with 400- and 1200-grit SiC sandpaper, and then a layer of Au was sputtered on both sides for 5 minutes. After being transferred to an argon-filled glove box, a lithium metal sheet was attached to the center of the LLZO sheet and heated to 250-300°C on a heater. The molten lithium spread over the surface of the electrolyte sheet. The sample was flipped, and the same treatment was applied to the other surface of the LLZO sample. Lithium metal was attached and heated to obtain a Li / LLZO / Li symmetric cell. The Li / LLZO / Li symmetric cell was then sealed in a CR2032 coin cell for performance characterization and research.

[0113] A lithium metal sheet was attached to the center of the LLZO sheet and placed on a heater. When heated to 250-300°C, the molten lithium spread across the surface of the electrolyte sheet. A trace amount of electrolyte was added to the other side to wet the positive electrode interface, and the NCM positive electrode sheet was attached to create a Li / LLZO / NCM full cell. The Li / LLZO / NCM full cell was then sealed in a CR2032 coin cell for performance characterization and research.

[0114] <Characterization of Battery Performance>

[0115] Morphology and phase analysis:

[0116] Scanning electron microscopy (SEM) images and elemental mapping analysis were performed by scanning electron microscopy (Hitachi, S-3400N). X-ray powder diffraction (Rigaku, Ultima IV, nickel-filtered Cu-Kα radiation, ) to obtain X-ray powder diffraction (XRD) patterns. The density of the ceramic samples was measured using the Archimedean method with ethanol as the immersion medium. All tests were performed at room temperature (e.g., 25°C).

[0117] Electrochemical impedance spectroscopy (EIS) analysis:

[0118] EIS was measured by AC impedance analysis (Autolab, model PGSTAT302 N) in the frequency range of 0.1 Hz to 1 MHz.

[0119] Electrochemical performance analysis:

[0120] All Li symmetric cells and full cells were tested on a Neware battery test system (NEWARE CT-4008, Shenzhen, China). -2 The cycle test was carried out at a current density of 1000 nm. The charge and discharge duration was set to 30 min. The Li / LLZO / NCM full battery was cycled at a rate of 0.2C. The theoretical specific capacity of NCM is 180 mAh g-1 All battery tests were performed at 25°C.

[0121] The following examples are further given to illustrate the present invention in detail. It should also be understood that the following examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention all fall within the scope of protection of the present invention. The specific process parameters and the like in the following examples are only examples within a suitable range, that is, those skilled in the art can make selections within a suitable range through the description herein, and are not limited to the specific numerical values exemplified below.

[0122] Example 1: Preparation of Sample 1

[0123] The buried powder additive Li2ZrO3 was weighed by precursor powder LiOH·H2O(AR) and ZrO2(AR) with a molar ratio of 2. YSZ balls were used as grinding media and isopropyl alcohol was used as solvent at 250 rpm min -1 The mixture was wet ball milled at a speed of 24 hours. After drying, the mixture powder was calcined in an alumina crucible at 950℃ for 24 hours. The main phase of the buried powder was composed of LiOH·H2O (AR, excess 2%), La2O3 (99.99%, calcined at 900℃ for 12 hours), ZrO2 (AR) and Nb2O5 (99.99%) according to Li 6.75 La3Zr 1.75 Nb 0.25 O 12 The stoichiometric ratio was weighed, wherein the lithium was in excess of 15%. Yttrium stabilized zirconia (YSZ) balls were used as the grinding media and isopropyl alcohol was used as the solvent at 250 rpm min -1 The mixed powder was wet ball milled at a speed of 12h. After drying, the mixed powder was calcined in an alumina crucible at 950℃ for 6h to obtain the buried powder main phase. The buried powder additive Li2ZrO3 and the buried powder main phase were uniformly mixed according to the buried powder additive content of 9.1wt.%. The lithium garnet ceramic electrolyte was prepared by precursor powders LiOH·H2O (AR, excess 2%), La2O3 (99.99%, calcined at 900℃ for 12h), ZrO2 (AR) and Ta2O5 (99.99%) according to Li 6.5 La3Zr 1.5 Ta 0.5 O 12 Yttrium stabilized zirconia (YSZ) balls were used as grinding media and isopropyl alcohol was used as solvent at 250 rpm min -1The mixture was wet ball milled at a speed of 100°C for 12 hours. After drying, the mixed powder was calcined at 950°C in an alumina crucible for 6 hours to obtain pure cubic lithium garnet electrolyte powder LLZO. The obtained LLZO was refined, passed through a 200-mesh sieve, and pressed into a green billet (1.25g) with a diameter of 18mm. The green billet was placed in a platinum crucible and sintered at 1220°C for 30 minutes. Every 5g of LLZO green billet was sintered with 2g of garnet-type sintering buried powder. The heating and cooling rates during sintering were both 5°C / min.

[0124] Example 2: Preparation of Sample 2

[0125] The preparation process is the same as that of sample 1, except that the buried powder additive Li2ZrO3 and the buried powder main phase are uniformly mixed according to the buried powder additive content of 6.3wt.% during the sintering process of the lithium garnet-type electrolyte LLZO; and 0.5g of garnet-type sintering buried powder is used for every 5g of LLZO green body.

[0126] Example 3: Preparation of Sample 3

[0127] The preparation process is the same as that of sample 2, except that 1 g of garnet-type sintering buried powder is used for every 5 g of LLZO green body during the sintering process of the lithium garnet-type electrolyte LLZO.

[0128] Example 4: Preparation of Sample 4

[0129] The preparation process is the same as that of sample 2, except that 2 g of garnet-type sintering buried powder is used for every 5 g of LLZO green body during the sintering process of the lithium garnet-type electrolyte LLZO.

[0130] Example 5: Preparation of Sample 5

[0131] The preparation process is the same as that of sample 2, except that 4 g of garnet-type sintering buried powder is used for every 5 g of LLZO green body during the sintering process of the lithium garnet-type electrolyte LLZO.

[0132] Example 6: Preparation of Sample 6

[0133] The preparation process is the same as that of sample 2, except that 6 g of garnet-type sintering buried powder is used for every 5 g of LLZO green body during the sintering process of the lithium garnet-type electrolyte LLZO.

[0134] Example 7: Preparation of Sample 7

[0135] The preparation process is the same as that of sample 1, except that the embedded powder additive Li2ZrO3 and the embedded powder main phase are uniformly mixed according to the embedded powder additive content of 4.2 wt.% during the sintering process of the lithium garnet electrolyte LLZO.

[0136] Comparative Example 1: Preparation of Comparative Sample 1

[0137] The preparation process is the same as that of sample 1, except that only the buried powder main phase is used in the sintering process of the lithium garnet electrolyte LLZO, and no buried powder additives are used; and 0.5 g of the buried powder main phase is sintered for every 5 g of LLZO green billet.

[0138] Comparative Example 2: Preparation of Comparative Sample 2

[0139] The preparation process is the same as that of sample 1, except that only the buried powder main phase is used and no buried powder additive is used during the sintering process of the lithium garnet electrolyte LLZO.

[0140] Sample analysis:

[0141] Figure 1 Schematic diagram of the sintering buried powder effect when preparing a lithium garnet-type electrolyte according to the present invention. Burying powder for sintering a lithium garnet-type electrolyte is used to provide a sintering atmosphere (e.g., Li2O) for sintering LLZO. Excessive sintering buried powder can be used to avoid the low sintering atmosphere (Li2O) level that causes LLZO to show low density. By reacting the buried powder additive (e.g., Li2ZrO3) with the excess reversible Li2O in the buried powder main phase, high sintering atmosphere (Li2O) levels and abnormal grain growth (AGG) during the sintering process are avoided. The reversible reaction of the buried powder additive with Li2O is utilized to provide a suitable sintering atmosphere (Li2O) level for LLZO sintering, thereby obtaining a high-density, high-ionic-conductivity electrolyte.

[0142] Figure 2 The scanning electron microscope (SEM) cross-sectional morphology of LLZO prepared by embedding powder main phase in comparative samples 1 and 2 of the present invention. Figure 2 As can be seen in Comparative Sample 1, under the appropriate sintering atmosphere (Li2O), LLZO has smooth crystal faces, clear grain outlines, well-grown and tightly bound grains, showing a dense structure. The grain size is mostly between 3-8μm. However, as the sintering atmosphere increases, that is, the use of 0.5g buried powder main phase for every 5g LLZO green billet increases to 2g buried powder main phase to provide sintering atmosphere (Comparative Sample 2, Figure 2 B) LLZO exhibits abnormal grain growth, with large grains of 100-300μm observed. This deteriorates LLZO's mechanical properties and easily leads to lithium dendrite growth along grain boundaries, causing battery short circuits. This indicates that using only the buried powder main phase to provide the sintering atmosphere for LLZO is unacceptable for excessive buried powder and the sintering atmosphere (Li2O) cannot be tolerated during LLZO sintering.

[0143] Figure 3-5The SEM cross-sectional morphology of LLZO prepared by sintering buried powder in samples 1-7 of the present invention, wherein the content of the buried powder additive Li2ZrO3 in the sintered buried powder is 9.1wt.%, 6.3wt.% and 4.2wt.%, respectively. As can be seen from the figure, when the amount of sintered buried powder used is 2g per 5g of LLZO green body, sample 1 (9.1wt.%, Figure 3 ), sample 4 (6.3wt.%, Figure 4 C, D) and sample 7 (4.2 wt.%, Figure 5 ) all have smooth crystal faces, clear grain outlines, well-grown and tightly bound grains, showing a dense structure. This indicates that the use of the embedding powder additive can absorb the excess sintering atmosphere (Li2O) in the embedding powder main phase and avoid the occurrence of AGG. When the embedding powder additive Li2ZrO3 content in the sintering embedding powder is 6.3wt.%, the sintering embedding powder usage is 0.2g, 1g, 2g, 4g, and 6g (samples 2-6, Figure 4 ), all samples have a dense structure and well-grown grains, maintaining a uniform grain size distribution and no obvious AGG. This shows that the embedded powder additive Li2ZrO3 does not affect the sintering atmosphere provided by the embedded powder main phase (sample 2). At the same time, AGG does not occur even when the embedded powder is sintered at 12 times the amount of embedded powder used in the main phase (sample 6). At the same time, the obtained LLZO relative density exceeds 96%, and the ionic conductivity exceeds 0.7mS cm -1 (See Table 1).

[0144] Table 1 below lists the preparation parameters and performance test results of samples 1-7 and comparative sample 1.

[0145] Table 1

[0146]

[0147] Figure 6 X-ray diffraction (XRD) patterns of LLZO were obtained for different amounts of sintered embedded powder used in Samples 2-6 of the present invention. The XRD results show that the obtained XRD peaks match well with the standard card for cubic lithium garnet electrolyte (PDF#45-0109). This indicates that the embedded powder additive Li2ZrO3 does not affect the cubic phase structure of LLZO, which maintains its structural integrity.

[0148] In order to further illustrate the role of reversible atmosphere control of buried powder additives, the buried powder additive Li2ZrO3 was uniformly mixed with the buried powder main phase LiOH·H2O and calcined at the LLZO sintering temperature of 1220℃ for 30 minutes. Figure 7This is the XRD pattern of the reaction between the embedded powder additive Li2ZrO3 and the embedded powder main phase LiOH·H2O. To illustrate the mechanism of the embedded powder addition, the embedded powder additive Li2ZrO3 and the embedded powder main phase LiOH·H2O were uniformly mixed in molar ratios of 1:1 and 1:2 and calcined at the LLZO sintering temperature of 1220°C for 30 minutes. XRD characterization of the resulting powder revealed that as the proportion of the embedded powder main phase LiOH·H2O increased, the reaction product transformed from a mixed phase of Li2ZrO3 and Li6Zr2O7 to a pure Li6Zr2O7 phase. At the sintering temperature, excess Li2O is absorbed and stored by the Li2ZrO3, forming Li6Zr2O7. This demonstrates that the embedded powder addition, through the reaction of Li2ZrO3 with excess sintering atmosphere (Li2O), maintains an appropriate sintering atmosphere (Li2O) partial pressure in the crucible, and prevents the occurrence of AGG. Furthermore, when the sintering atmosphere is insufficient for Li₂O₃, Li₆Zr₂O₃ begins to decompose at 1170°C (Chemical Engineering Journal 2021, 411, 128508). This suggests that embedding additives can reversibly control the Li₂O atmosphere during LLZO sintering. Combined with these results, it can be concluded that Li₂ZrO₃ can be used as an embedding additive, without requiring precise control of the sintering embedding additive dosage.

[0149] Figure 8 The cycling results of the lithium metal symmetric battery assembled with sample 4 of the present invention. The Li / LLZO / Li symmetric battery was cycled at 0.3 mA cm -2 Stable cycling for 1000 hours demonstrates LLZO's excellent resistance to lithium dendrites. The inherent properties of LLZO are a factor in determining its ability to suppress lithium dendrites. Due to the pores and defects in LLZO, lithium dendrites may form in these pores and defects and propagate and grow within the LLZO, posing a significant challenge to the application of solid electrolytes in solid-state lithium metal batteries. High-density LLZO results in closer grain contact and reduced porosity, which can effectively improve the electrolyte's resistance to lithium dendrites.

[0150] Figure 9 The charge and discharge cycle diagram and discharge curve of the Li / LLZO / NCM lithium metal full battery assembled with sample 4 of the present invention. The full battery was subjected to constant current charge and discharge test at 25°C, and the charge and discharge cut-off voltage was 2.8~4.5V. The results are as follows Figure 9 As shown, the first three cycles were at a rate of 0.1C and the initial discharge capacity was 175.9 mAh g -1 Then, the fourth discharge capacity was 165.3 mAh g at 0.2 C constant current cycle. -1During the cycle, the discharge capacity of the battery remains stable and the efficiency is always close to 100%. After 100 cycles, the discharge capacity is 157.4 mAh g -1 , and still maintains a capacity retention rate of about 95.2%.

[0151] The invention discloses an embedding powder for sintering a lithium garnet type electrolyte, a method for preparing a lithium garnet type electrolyte using the embedding powder, a lithium garnet type electrolyte prepared by the preparation method, and a lithium ion battery comprising the lithium garnet type electrolyte.

[0152] Specifically, the present invention discloses the preparation of a lithium garnet cubic phase (e.g., LLZO, as defined above), and a buried powder main phase and buried powder additives for sintering lithium garnet-type electrolytes. In some examples, the buried powder main phase LLZO can be doped with one or a combination of In, Si, Ge, Sn, Sb, Sc, Ti, Hf, V, W, Te, Nb, Ta, Al, Ga, Fe, Bi, Y, Mg and Ca. By using sintering buried powder in the sintering process of LLZO (doped or not doped with various elements), sintering control is simplified. The buried powder main phase can provide a sintering atmosphere (Li2O) for LLZO sintering, and the buried powder additive can reversibly react with Li2O to ensure a suitable sintering atmosphere (Li2O). In some examples, the main phase of the buried powder can be a lithium garnet-type composite powder containing excess lithium and a lithium-rich material, such as LiOH·H2O; LiOH; Li2C2O4; CH3COOLi; LiNO3; Li2CO3; Li2O; Li2O2, etc. The buried powder additive is a lithium metal oxide with different lithium contents, such as lithium oxides of W, Zr, Ti, Nb, Si, Al, Ta, and Ga. Therefore, the sintered buried powder can react with the excess sintering atmosphere (Li2O), improving the performance of the lithium garnet-type electrolyte, avoiding abnormal grain growth, improving sintering consistency, and eliminating the need for precise control of the sintered buried powder usage.

[0153] Compared with the prior art, the present invention has the following beneficial effects:

[0154] (1) The sintering buried powder of the present invention can provide a reversibly controlled sintering atmosphere for LLZO sintering, and obtain a sintered product with a relative density exceeding 96% and an ionic conductivity exceeding 0.4 mS·cm -1 LLZO, high density and ionic conductivity;

[0155] (2) The preparation method of the buried powder main phase and the buried powder additive in the buried powder is simple and efficient, does not require the use of complex equipment, and is low in cost;

[0156] (3) The lithium garnet-type electrolyte sintering powder of the present invention solves the problems of low electrolyte density caused by insufficient Li2O atmosphere in the sintering atmosphere and abnormal growth of electrolyte grains caused by excessive Li2O atmosphere;

[0157] (4) The embedding powder for sintering the lithium garnet type electrolyte of the present invention can be selected to have the same elements as the lithium garnet type electrolyte, so as to avoid contamination of the lithium garnet type electrolyte by the embedding powder.

[0158] Finally, it is necessary to explain here that the above embodiments are only used to further illustrate the technical solution of the present invention in detail and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by technicians in this field based on the above content of the present invention all fall within the scope of protection of the present invention.

Claims

1. A lithium garnet type electrolyte sintering powder, characterized in that: The buried powder comprises: (a) a powder-embedded main phase, the powder-embedded main phase comprising at least one of the following: Lithium garnet composite powder, the lithium garnet composite powder comprising at least one of the following: (i) Li 7-3a La3Zr2L a O 12 , where L = Al, Ga or Fe, and 0 <a<0.33; (ii) Li7La 3-b ZlUT b O 12 , where M=Bi or Y, and 0 <b<1; (iii) Li 7-c La3(Zr 2-c ,N c )O 12 , wherein N=In, Si, Ge, Sn, Sb, Sc, Ti, Hf, V, W, Te, Nb, Ta, Al, Ga, Fe, Bi, Y, Mg, Ca or a combination thereof, and 0 <c<1; LiOH·H2O; LiOH; CH3COOLi; Li2C2O4; LiNO3; Li2CO3; Li2O; Li2O2; (b) a powder embedding additive, wherein the powder embedding additive is Li2ZrO3.

2. The lithium garnet type electrolyte sintering embedding powder according to claim 1, characterized in that: The lithium content in the lithium garnet composite powder is 1-30 mol%.

3. The lithium garnet type electrolyte sintering embedding powder according to claim 1 or 2, characterized in that: The embedding powder additive accounts for 3-25 wt.% of the total mass of the embedding powder for sintering the lithium garnet-type electrolyte.

4. The lithium garnet type electrolyte sintering embedding powder according to claim 3, characterized in that: The embedding powder additive accounts for 4-15 wt.% of the total mass of the embedding powder for sintering the lithium garnet-type electrolyte.

5. A method for preparing a lithium garnet-type electrolyte, characterized in that: The preparation method comprises sintering a lithium garnet type electrolyte green body at a high temperature, wherein the sintering process uses the lithium garnet type electrolyte sintering embedding powder according to any one of claims 1 to 4 to provide a reversibly controlled sintering atmosphere.

6. The preparation method according to claim 5, characterized in that The sintering temperature is 700-1300°C.

7. A lithium garnet electrolyte prepared by the preparation method according to claim 5 or 6.

8. The lithium garnet electrolyte according to claim 7, characterized in that The lithium garnet electrolyte is selected from (i) Li 7-3a La3Zr2L a O 12 , L = Al, Ga, or Fe, and 0<a<0.33; (ii) Li7La 3-b ZlUT b O 12 , where M = Bi, or Y, and 0<b<1; (iii) Li 7-c La3(Zr 2-c ,N c )O 12 , where N=one or more of In, Si, Ge, Sn, Sb, Sc, Ti, Hf, V, W, Te, Nb, Ta, Al, Ga, Fe, Bi, Y, Mg or Ca, and 0<c<1.

9. The lithium garnet-type electrolyte according to claim 7 or 8, characterized in that The lithium garnet electrolyte has a relative density greater than 96% and a relative density greater than 0.4 mS·cm -1 ionic conductivity.

10. A lithium ion battery, characterized in that: The method comprises the lithium garnet-type electrolyte according to any one of claims 7 to 9.

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