Precursor dispersions and their use

Abstract

The present application relates to a precursor dispersion and its use, the precursor dispersion comprising a lithium source and a phosphorus source dispersed in a non-aqueous solvent, the lithium source having a molar ratio of lithium element to phosphorus element of the phosphorus source of 1.5:1 to 4:1.

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, and in particular to precursor dispersions and their applications. Background Technology

[0002] All-solid-state lithium batteries are considered an important development direction for next-generation energy storage devices due to their high safety and high energy density. Solid-state electrolytes are their core components, among which oxide electrolytes (such as garnet-type structures like LLZO and LLZTO) have attracted much attention due to their good stability to lithium metal and high ionic conductivity.

[0003] However, oxide electrolytes have at least the following two problems: 1. High-Temperature Sintering Issues: The preparation of oxide electrolytes such as LLZO and LLZTO typically requires high-temperature sintering above 1200℃ to obtain high-density ceramic sheets. High-temperature sintering not only consumes a lot of energy but also easily leads to lithium volatilization, forming a lithium-deficient phase, thereby reducing conductivity. Furthermore, since cathode materials (such as lithium cobalt oxide and ternary materials) cannot withstand such high temperatures, oxide electrolytes cannot be co-sintered with cathode materials.

[0004] 2. Interfacial impedance with electrodes: The rigid ceramic electrolyte and the electrode have a solid-solid contact, resulting in high interfacial impedance. Existing technologies use flexible polymer layers or complex interfacial modification layers to improve interfacial impedance, but this increases process complexity and cost. Summary of the Invention

[0005] The purpose of this application is to provide a precursor dispersion, a solid oxide electrolyte, a method for preparing the same, and a solid-state battery, in order to solve the problem that oxide electrolytes in the prior art require high-temperature sintering.

[0006] In a first aspect, embodiments of this application provide a precursor dispersion comprising a lithium source and a phosphorus source dispersed in a non-aqueous solvent. The molar ratio of lithium in the lithium source to phosphorus in the phosphorus source is 1.5:1~4:.

[0007] Secondly, embodiments of this application provide a method for preparing a solid oxide electrolyte, comprising: S1 provides a porous oxide electrolyte framework; S2. The porous oxide electrolyte framework is impregnated with the above-mentioned precursor dispersion to obtain an impregnated porous oxide electrolyte framework. S3. The impregnated porous oxide electrolyte framework is heat-treated at 700~950℃ to obtain the solid oxide electrolyte.

[0008] Thirdly, embodiments of this application provide a solid oxide electrolyte obtained according to the above method.

[0009] Fourthly, embodiments of this application provide a solid oxide electrolyte, including: A porous oxide electrolyte framework comprising interconnected internal channels; An amorphous composite lithium salt, which fills the internal channels to form a continuous ion network, the amorphous composite lithium salt comprising a eutectic structure formed by lithium oxide and phosphorus oxide, wherein the molar ratio of lithium to phosphorus is 1.5:1 to 4:1.

[0010] Fifthly, embodiments of this application provide an integrated electrode sheet, including the aforementioned solid oxide electrolyte and an electrode material layer located on at least one side of the solid oxide electrolyte.

[0011] Sixthly, embodiments of this application provide a method for preparing an integrated electrode, comprising: A positive electrode material is coated on at least one side of the aforementioned solid oxide electrolyte, wherein the positive electrode material includes a positive electrode active material, a conductive agent, and a binder; The solid oxide electrolyte coated with the positive electrode material is subjected to heat treatment at 500~700℃.

[0012] In a seventh aspect, embodiments of this application also provide a solid-state battery, including the aforementioned solid oxide electrolyte or the aforementioned integrated electrode.

[0013] Compared with the prior art, the embodiments of this application have at least the following beneficial effects: The formulation of the precursor dispersion enables it to form an amorphous lithium salt phase with low melting point and high ionic conductivity during subsequent heat treatment. Its eutectic point is below 950℃, which is much lower than the 1200℃ in the prior art.

[0014] During heat treatment, the precursor dispersion decomposes and forms a low-melting-point liquid phase in situ within the pores of the porous oxide electrolyte framework. This liquid-phase sintering mechanism greatly promotes the fusion and densification of ceramic particles, resulting in a bicontinuous phase composite structure with the oxide electrolyte as the main phase and amorphous lithium salt ions as the auxiliary phase. The porous oxide electrolyte framework provides mechanical strength, while the flexible amorphous ionic phase provides densification and interfacial contact; together, they form the bicontinuous phase structure.

[0015] Furthermore, during the heat treatment of the cathode slurry, the precursor dispersion not only forms an ionic / electronic conductive network inside the cathode, but more importantly, it forms chemical bonds at the electrolyte / cathode interface, significantly reducing interfacial impedance. Attached Figure Description

[0016] Figure 1 A flowchart of a method for preparing a solid oxide electrolyte according to an embodiment of this application is shown.

[0017] Figure 2 A flowchart of a method for preparing an integrated electrode according to an embodiment of this application is shown. Detailed Implementation

[0018] The technical solution of this application will be further described below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely for explaining this application and not for limiting it. Furthermore, it should be noted that, for ease of description, only the parts relevant to this application are shown in the accompanying drawings, not all of them.

[0019] This application defines certain directional terms. Unless otherwise stated, the directional terms used, such as "up," "down," "left," "right," "inner," and "outer," are used for ease of understanding and therefore do not constitute a limitation on the scope of protection of this application.

[0020] In this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature being directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature being directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0021] In the description of this application, unless otherwise expressly specified and limited, the terms "connected," "linked," and "fixed" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0022] In a first aspect, embodiments of this application relate to a precursor dispersion comprising a lithium source and a phosphorus source dispersed in a non-aqueous solvent. The molar ratio of lithium in the lithium source to phosphorus in the phosphorus source is 1.5:1 to 4:1, specifically, it can be 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, or any ratio between 1.5:1 and 4:1.

[0023] The total molar concentration of lithium and phosphorus sources is 0.3~0.8 mol / L, specifically, it can be 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, or any value between 0.3 and 0.8 mol / L.

[0024] According to the embodiments of this application, the precursor dispersion forms an amorphous lithium salt phase (e.g., Li2O-P2O5) with a low melting point and high ionic conductivity during heat treatment. Its eutectic point temperature is below 950°C, which is much lower than the sintering temperature of 1200°C for pure oxide electrolytes in the prior art, thereby solving the problem that oxide electrolytes in the prior art require high-temperature sintering.

[0025] In some embodiments, the lithium source is selected from one or more of inorganic lithium salts and organic lithium salts. Inorganic lithium salts may be, for example, one or more of lithium nitrate, lithium chloride, lithium perchlorate, lithium fluoride, lithium bromide, and lithium iodide. Organic lithium salts may be one or more of lithium acetate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium trifluoromethanesulfonate, and lithium bis(oxalatoborate). Preferably, the lithium source is selected from one or both of lithium nitrate and lithium acetate.

[0026] In some embodiments, the phosphorus source can be a phosphate, such as one or more selected from ferrous phosphate, ferric phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, phosphoric acid, and phosphorus pentoxide.

[0027] In some embodiments, the non-aqueous solvent is selected from ethanol, carbonate, carboxylic acid ester, and polymethyl methacrylate sol (PMMA sol).

[0028] In some embodiments, the carbonate is selected from one or more of diethyl carbonate and methyl ethyl carbonate. The carboxylic acid ester may include one or more of ethyl acetate, methyl acetate, methyl propionate, etc.

[0029] Secondly, the embodiments of this application relate to a method for preparing solid oxide electrolytes, which uses the aforementioned precursor dispersion to prepare solid oxide electrolytes.

[0030] Specifically, the method includes: S1 provides a porous oxide electrolyte framework; S2. The porous oxide electrolyte framework is impregnated with the above-mentioned precursor dispersion to obtain the impregnated porous oxide electrolyte framework. S3. The porous oxide electrolyte framework is heat-treated at 700~950℃ to obtain a solid oxide electrolyte.

[0031] During heat treatment, the precursor dispersion decomposes and forms a low-melting-point liquid phase in situ within the pores of the porous oxide electrolyte framework. This liquid-phase sintering mechanism greatly promotes the fusion and densification between ceramic particles, while simultaneously forming a continuous second phase. According to the preparation method described in this application, ultra-high densification of the electrolyte and good interfacial compatibility with the electrode are achieved while significantly reducing the sintering temperature.

[0032] Furthermore, in some embodiments, S1 may include: mixing oxide electrolyte powder, pore-forming agent and binder and then sintering to form a porous oxide electrolyte framework.

[0033] In some embodiments, the porosity of the porous oxide electrolyte framework can be 20-60%, and more specifically, 30-50%. In particular, the porosity can be 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, and any value between 20-60%.

[0034] In some embodiments, the oxide electrolyte powder is selected from one or more of LLZTO and LLZO.

[0035] In some embodiments, the pore-forming agent is selected from one or more of starch, polymethyl methacrylate microspheres (PMMA microspheres).

[0036] In some embodiments, the adhesive is selected from one or more of polyvinyl butyral (PVB), polyvinylidene fluoride (PVDF), and polyvinyl alcohol (PVA).

[0037] In some embodiments, the sintering temperature is 800~1050°C, and further, the sintering temperature is 900-1000°C. Specifically, the sintering temperature is 800°C, 850°C, 900°C, 950°C, 1000°C, 1050°C, and any value between 800~1050°C.

[0038] In some embodiments, sintering can be carried out in an air atmosphere or a nitrogen atmosphere.

[0039] In some embodiments, the sintering time is 1.5 to 2.5 hours. Specifically, the sintering time is 1.5 hours, 1.6 hours, 1.7 hours, 1.8 hours, 1.9 hours, 2 hours, 2.1 hours, 2.2 hours, 2.3 hours, 2.4 hours, 2.5 hours, and any value between 1.5 and 2.5 hours.

[0040] Furthermore, in some embodiments, S2 includes: impregnating the porous oxide electrolyte framework with a precursor dispersion under vacuum. Sufficient impregnation under vacuum ensures that the precursor solution completely fills the pores of the porous oxide electrolyte framework.

[0041] In some embodiments, the impregnation amount of the lithium source and phosphorus source is 20-60%, based on the total weight of the porous oxide electrolyte framework. Within this impregnation range, the pores of the porous oxide electrolyte framework can be loaded with a sufficient amount of lithium source and phosphorus source for the final formation of the amorphous lithium salt phase, so that the final amorphous composite lithium salt can fully fill the internal channels of the porous oxide electrolyte framework to form a continuous ionic network, thereby obtaining a solid oxide electrolyte with high conductivity and low impedance.

[0042] In some implementations, the vacuum level is -0.15 to -0.05 MPa. Specifically, the vacuum level is -0.15 MPa, -0.10 MPa, -0.05 MPa, and any value between -0.15 and -0.05 MPa.

[0043] In some implementations, the vacuum time is 20 to 40 minutes. Specifically, the vacuum time is 20 minutes, 25 minutes, 30 minutes, 35 minutes, 40 minutes, and any value between 20 and 40 minutes.

[0044] Furthermore, in some embodiments, S3 includes: placing the impregnated porous oxide electrolyte skeleton in a sintering apparatus (e.g., a muffle furnace), heating it to 700-950°C at a rate of 1-3°C / min, holding it at that temperature for 3-5 hours, and then cooling it with the sintering apparatus.

[0045] Thirdly, embodiments of this application also relate to solid oxide electrolytes obtained using the above-described method.

[0046] Fourthly, embodiments of this application also relate to solid oxide electrolytes, which include a porous oxide electrolyte framework and an amorphous composite lithium salt. The porous oxide electrolyte framework includes interconnected internal channels, and the amorphous composite lithium salt fills the internal channels to form a continuous ion network. The amorphous composite lithium salt includes a lithium source and a phosphorus source, wherein the molar ratio of lithium in the lithium source to phosphorus in the phosphorus source is 1.5:1 to 4:1.

[0047] According to the solid oxide electrolyte of this application, the precursor dispersion decomposes and forms a low-melting-point liquid phase in situ within the pores of the porous oxide electrolyte framework. This liquid-phase sintering mechanism greatly promotes the fusion and densification between ceramic particles, while simultaneously forming a continuous second phase. The solid oxide electrolyte of this application significantly reduces the sintering temperature while achieving ultra-high densification of the electrolyte and good interfacial compatibility with the electrode.

[0048] The solid oxide electrolyte of this application has an amorphous lithium salt phase (e.g., Li₂O-P₂O₅) with a low melting point and high ionic conductivity, and a low eutectic point temperature, below 950°C. The solid oxide electrolyte of this application with a low eutectic point has the following advantages: 1. Low-temperature sintering: Sintering can be carried out at low sintering temperatures, which can achieve densification, significantly reduce energy consumption, shorten the cycle, and avoid element volatilization, phase transformation, abnormal grain growth caused by high temperatures, thus reducing side reactions. 2. Optimize conductivity: Low eutectic systems are prone to forming continuous, low-resistivity grain boundary phases, which suppress the formation of high-resistivity glass phases or impurity phases and improve the overall ionic conductivity. 3. Improved interface performance: Local liquid phase / grain boundary rheology appears near the sintering temperature of the eutectic component, which can wet and fill the voids between the electrode and the electrolyte, forming a continuous and compact interface and reducing the interface impedance; in addition, low temperature and good wetting can reduce high-temperature interface diffusion and chemical reaction, and improve interface stability and cycle life. 4. Stability: The solid oxide electrolyte of this application still has the characteristics of being non-flammable, leak-proof, and resistant to high temperature, and the low eutectic design does not sacrifice thermal stability.

[0049] Fifthly, embodiments of this application also relate to integrated electrode sheets, which include the aforementioned solid oxide electrolyte and an electrode material layer located on at least one side of the solid oxide electrolyte.

[0050] For example, the electrode material layer includes a positive electrode material layer. That is, a positive electrode slurry can be coated on one side of the solid oxide electrolyte, and then the solid oxide electrolyte coated with the positive electrode material can be heat-treated at 500~700°C.

[0051] Furthermore, the electrode material layer includes a positive electrode active material, a conductive agent, and a binder. The precursor dispersion forms ion-conducting channels inside the positive electrode, achieving integrated solid oxide electrolyte and positive electrode material and interface enhancement.

[0052] According to the embodiments of this application, during the low-temperature heat treatment at 500~700°C, the precursor dispersion not only forms an ionic / electronic conductive network inside the positive electrode, but more importantly, it forms a chemical bond at the electrolyte / positive electrode interface, significantly reducing the interfacial impedance.

[0053] Sixthly, the embodiments of this application also relate to a method for preparing integrated electrodes, including: S10. A positive electrode material is coated on at least one side of the above-mentioned solid oxide electrolyte, wherein the positive electrode material includes a positive electrode active material, a conductive agent, and a binder; in the positive electrode material, the mass ratio of positive electrode active material: conductive agent: binder is (96.6~97.6):(0.6~1.2):(1.8~2.2); S20. Heat treatment is performed on the solid oxide electrolyte coated with positive electrode material at 500~700℃.

[0054] As mentioned above, the integrated electrode obtained by the integrated electrode preparation method according to the embodiments of this application can significantly reduce interface blockage.

[0055] Seventhly, embodiments of this application relate to solid-state batteries, including the aforementioned solid oxide electrolyte or the aforementioned integrated electrode.

[0056] Example 1: Take LLZTO powder (Li6.4La3Zr1.4Ta0.6O) 12 10g of starch was mixed with 2g of starch pore-forming agent and 0.5g of PVB binder, and then pressed into sheets using a mold. The sheets were pre-sintered in air at 950℃ for 2 hours to obtain a porous oxide electrolyte framework (porosity of about 40%).

[0057] Prepare a 0.5M ethanol solution containing LiNO3 and FePO4 (Li:P molar ratio = 1.5:1), and stir magnetically until completely dissolved to obtain the precursor solution.

[0058] The porous oxide electrolyte framework was immersed in the precursor solution and placed in a vacuum drying oven (-0.1 MPa) for 30 minutes. After removal, excess solution was wiped off the surface, and the framework was placed in an alumina crucible.

[0059] The temperature was increased to 900℃ in a muffle furnace at 2℃ / min, held for 4 hours, and then cooled with the furnace to obtain a solid oxide electrolyte.

[0060] The solid oxide electrolyte was polished on both sides to a thickness of 500 μm. NCM811, Super P and PVDF were mixed at a mass ratio of 97.2:1:1.8 to obtain a positive electrode slurry, which was then coated onto one side of the polished solid oxide electrolyte.

[0061] The solid oxide electrolyte coated with positive electrode slurry was heat-treated at 550°C for 2 hours to obtain an integrated electrode.

[0062] Example 2: The difference from Example 1 is that the Li:P molar ratio is 2:1.

[0063] Example 3: The difference from Example 1 is that the Li:P molar ratio is 4:1.

[0064] Example 4: The difference from Implementation 1 is that the total molar concentration of the lithium and phosphorus sources is 0.3 mol / L.

[0065] Example 5: The difference from Implementation 1 is that the total molar concentration of the lithium and phosphorus sources is 0.8 mol / L.

[0066] Example 6: The difference from Embodiment 1 is that the porosity of the porous oxide electrolyte framework is 20%.

[0067] Example 7: The difference from Example 1 is that the porosity of the porous oxide electrolyte framework is 60%.

[0068] Comparative Example 1: The difference from Embodiment 1 is that the precursor dispersion is the sintering aid LiGaO2-Li5GaO4 in the prior art.

[0069] The electrochemical test results of the above embodiments and comparative examples are shown in Table 1.

[0070] Table 1

[0071] Although this application has been described in detail above with general descriptions, specific embodiments, and experiments, some modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of this application fall within the scope of protection claimed in this application.

Claims

1. Precursor dispersions, including lithium and phosphorus sources dispersed in non-aqueous solvents. The molar ratio of lithium in the lithium source to phosphorus in the phosphorus source is 1.5:1 to 4:

1.

2. The precursor dispersion according to claim 1, wherein, The lithium source is selected from one or more of inorganic lithium salts and organic lithium salts; and / or The phosphorus source is selected from one or more of ferrous phosphate, ferric phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, phosphoric acid, and phosphorus pentoxide; and / or The non-aqueous solvent is selected from one of ethanol, carbonate, carboxylic acid ester, and polymethyl methacrylate sol.

3. A method for preparing solid oxide electrolytes, including: S1 provides a porous oxide electrolyte framework; S2. The porous oxide electrolyte framework is impregnated with the precursor dispersion as described in claim 1 or 2 to obtain an impregnated porous oxide electrolyte framework. S3. The impregnated porous oxide electrolyte framework is heat-treated at 700~950℃ to obtain the solid oxide electrolyte.

4. The preparation method according to claim 3, wherein, S1 includes: mixing oxide electrolyte powder, pore-forming agent and binder and then sintering to form the porous oxide electrolyte framework; Preferably, the porosity of the porous oxide electrolyte framework is 20-60%; Preferably, the oxide electrolyte powder is selected from one or more of LLZTO and LLZO; Preferably, the pore-forming agent is selected from one or more of starch and polymethyl methacrylate microspheres; Preferably, the adhesive is selected from one or more of polyvinyl butyral, polyvinylidene fluoride, and polyvinyl alcohol; Preferably, the sintering temperature is 800~1050℃ and the sintering time is 1.5~2.5 hours.

5. The preparation method according to claim 3, wherein, S2 includes: impregnating the porous oxide electrolyte framework with the precursor dispersion in a vacuum environment; Preferably, the vacuum degree is -0.15 to -0.05 MPa; Preferably, the vacuum time is 20 to 40 minutes.

6. The preparation method according to claim 3, wherein, The impregnation amount of the lithium source and phosphorus source is 20-60%, based on the total weight of the porous oxide electrolyte framework.

7. The preparation method according to claim 3, wherein, S3 includes: placing the impregnated porous oxide electrolyte framework in a sintering apparatus, heating it to 700-950°C at a rate of 1-3°C / min, holding it at that temperature for 3-5 hours, and then cooling it along with the sintering apparatus.

8. The solid oxide electrolyte obtained by any one of claims 3-7.

9. Solid oxide electrolytes, including: A porous oxide electrolyte framework comprising interconnected internal channels; An amorphous composite lithium salt, which fills the internal channels to form a continuous ion network, the amorphous composite lithium salt comprising a eutectic structure formed by lithium oxide and phosphorus oxide, wherein the molar ratio of lithium to phosphorus is 1.5:1 to 4:

1.

10. An integrated electrode, comprising a solid oxide electrolyte as described in claim 7 or 8 and an electrode material layer located on at least one side of the solid oxide electrolyte; preferably, the electrode material layer comprises a positive electrode material layer.

11. The method for preparing the integrated electrode of claim 10, comprising: A positive electrode material is coated on at least one side of the solid oxide electrolyte according to claim 7 or 8, wherein the positive electrode material comprises a positive electrode active material, a conductive agent, and a binder; preferably, the positive electrode material is in the following mass ratio: positive electrode active material: conductive agent: binder = (96.6~97.6):(0.6~1.2):(1.8~2.2); The solid oxide electrolyte coated with the positive electrode material is subjected to heat treatment at 500~700℃.

12. A solid-state battery, comprising the solid oxide electrolyte of claim 7 or 8 or the integrated electrode of claim 10 or 11.

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