Lithium gallium germanate modified PEO-based composite solid electrolyte and preparation method thereof, solid-state battery

Abstract

The present invention belongs to the technical field of solid electrolytes, and specifically discloses a lithium gallium germanate modified PEO-based composite solid electrolyte, a preparation method thereof, and a solid-state battery. The components of the solid electrolyte include: lithium gallium germanate, PEO, and a lithium-based electrolyte, wherein: the structural formula of lithium gallium germanate is LiGaGe2O6. The lithium gallium germanate in the lithium gallium germanate modified PEO-based composite solid electrolyte prepared by the present invention has the molecular formula LiGaGe2O6, which has high-temperature stability, excellent conductivity, and a wide electrochemical stability window. Using it to modify the PEO-based solid-state battery electrolyte can endow the PEO-based solid electrolyte with higher conductivity and lithium-ion transport performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of solid electrolytes, and in particular relates to a lithium gallium germanate modified PEO-based composite solid electrolyte and a preparation method thereof, and a solid-state battery. Background Art

[0002] Lithium-ion batteries have safety issues such as easy leakage, volatility, flammability, explosion, and poor thermal stability, which limit their development. Solid-state lithium batteries use solid electrolytes and do not contain liquid organic electrolytes. They perfectly overcome a series of safety and process problems brought by organic electrolytes, greatly improve the mechanical properties and stability of the battery, and significantly improve the safety of the battery.

[0003] At present, solid electrolytes can be divided into two types: inorganic solid electrolytes and polymer solid electrolytes. Inorganic solid electrolytes such as sulfide solid electrolytes have a rigid interface and large interface resistance that is difficult to overcome. In addition, their preparation process is complex, the cost is high, and their application is difficult. Polymer solid electrolytes have inherent advantages in interface contact, good film forming properties and flexibility, and show good application prospects in flexible wearable electronic devices. At present, the commonly used polymer matrices of polymer solid electrolytes are polyethylene oxide (PEO), polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), polyvinyl pyrrolidone (PVP) and polymethyl methacrylate (PMMA). Among the many polymer-based solid electrolytes, PEO (polyethylene oxide)-based polymer solid electrolytes have the highest conductivity, and at the same time have the advantages of high safety, mechanical flexibility, viscoelasticity and easy film formation. They are considered to be one of the most promising solid electrolytes. The working mechanism of PEO solid electrolytes is mainly that lithium ions continuously undergo a complexation-decomplexation process with the ether oxygen bonds in the PEO long chain, and lithium ion migration is achieved by the movement of PEO chain segments. Therefore, the mobility of PEO segments largely determines the ionic conductivity of PEO-based solid electrolytes. However, pure PEO has high crystallinity at room temperature, low solubility of lithium salts in the amorphous phase, and low carrier concentration, resulting in a small number of lithium ion migration. Therefore, how to further improve the crystallinity of PEO and enhance the ion transport capacity of solid electrolytes is an urgent problem to be solved. Summary of the invention

[0004] The purpose of the present invention is to provide a lithium gallium germanate modified PEO-based composite solid electrolyte with good ion transmission capability, a preparation method thereof, and a solid-state battery.

[0005] In the first aspect, the present invention provides a lithium gallium germanate modified PEO-based composite solid electrolyte, which adopts the following technical scheme:

[0006] A lithium gallium germanate modified PEO-based composite solid electrolyte comprises components of lithium gallium germanate, PEO and a lithium-based electrolyte, wherein the structural formula of the lithium gallium germanate is LiGaGe2O6.

[0007] Preferably, the lithium-based electrolyte is one or more of LiPF6, LiTFSI, LiFSI, and LiBF4.

[0008] Preferably, the ratio of the mass of the lithium gallium germanate to the total mass of PEO and the lithium-based electrolyte is (5-15):100.

[0009] Preferably, the ratio of the molar number of repeating units in PEO to the molar number of lithium-based electrolyte is (15-20):1.

[0010] The structural formula of PEO is ; The repeating unit is OCH2CH2.

[0011] In a second aspect, the present invention provides a method for preparing a lithium gallium germanate modified PEO-based composite solid electrolyte, comprising the following steps:

[0012] Lithium gallium germanate, PEO and lithium-based electrolyte are mixed to obtain mixed powder; a solvent is dripped into the mixed powder, and a slurry is obtained after grinding; the slurry is coated on a bottom plate, and after drying, a lithium gallium germanate modified PEO-based composite solid electrolyte is obtained.

[0013] Preferably, the preparation method of lithium gallium germanate comprises the following steps: dispersing a germanium source, a gallium source and a lithium source in deionized water to form a mixed slurry, and spray pyrolyzing the mixed slurry to obtain lithium gallium germanate LiGaGe2O6.

[0014] Preferably, the germanium source is one or both of germanium dioxide and germanium monoxide; the gallium source is one or both of gallium trioxide and gallium nitrate; and the lithium source is one or more of lithium oxide, lithium carbonate, lithium hydroxide and lithium acetate.

[0015] The present invention adopts spray pyrolysis to synthesize LiGaGe2O6, which can reduce the volatilization of lithium and gallium caused by direct high-temperature reaction, thereby avoiding lattice defects.

[0016] Preferably, the germanium source, gallium source and lithium source are added in a molar ratio of Ge:Ga:Li of 2:1:(1.04-1.06).

[0017] Preferably, the spray pyrolysis temperature is 700-1000° C., and the pyrolysis time is 4-8 s.

[0018] Preferably, the solvent is acetonitrile, tetrahydrofuran and N,N-One or more of dimethylformamide; the mass volume ratio of PEO to solvent is 1g:(10~30)mL.

[0019] Preferably, the drying is vacuum drying, the vacuum drying temperature is 70-90° C., and the vacuum drying time is 6-12 h.

[0020] In a third aspect, the present invention provides a solid-state battery, the electrolyte of which adopts the aforementioned lithium gallium germanate modified PEO-based composite solid-state electrolyte.

[0021] The above one or more technical solutions of the present invention can achieve at least one of the following beneficial effects:

[0022] (1) The lithium gallium germanate in the lithium gallium germanate modified PEO-based composite solid electrolyte prepared by the present invention has a molecular formula of LiGaGe2O6, which has high temperature stability, excellent electrical conductivity and a wide electrochemical stability window. By using it to modify the PEO-based solid-state battery material, the PEO-based solid-state electrolyte can have higher electrical conductivity and lithium ion transport performance.

[0023] (2) The present invention first synthesizes the lithium gallium germanate material by ball milling-sintering method, and then composites it with the solid electrolyte main component PEO and lithium-based electrolyte, and finally forms a lithium gallium germanate modified PEO-based composite solid electrolyte. The preparation process of the present invention is simple, the process is short, the raw materials are easy to obtain, no toxic and harmful substances are generated in the preparation process, and it is easy to achieve large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The graph is a cycle performance diagram of a solid-state battery assembled with the modified PEO-based composite solid electrolyte in Examples 1 to 5 and Comparative Examples 1 to 3. DETAILED DESCRIPTION

[0025] In order to facilitate the understanding of the present invention, the present invention will be described more comprehensively and meticulously below in conjunction with the accompanying drawings and preferred embodiments of the present invention, but the protection scope of the present invention is not limited to the following specific embodiments.

[0026] Unless otherwise defined, all the professional terms used below have the same meanings as those generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0027] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0028] The molecular weight range of PEO used in the embodiments of the present invention is 2,000,000-5,000,000.

[0029] Example 1

[0030] In the solid electrolyte of this embodiment: the structural formula of lithium gallium germanate is LiGaGe2O6; the lithium-based electrolyte is LiFSI; and the molecular weight of PEO is 3000000.

[0031] The specific preparation method is as follows:

[0032] (1) Add 10.5 g GeO2, 9.35 g Ga2O3 and 1.57 g Li2O into 50 mL water and disperse them evenly to obtain a slurry. Add the slurry into a spray pyrolysis furnace and spray pyrolyze at 850 °C for 6 seconds to obtain lithium gallium germanate LiGaGe2O6.

[0033] (2) 10 g of LiGaGe2O6 prepared in step (1), 80.9 g of PEO and 19.1 g of LiFSI were ball-milled and mixed to obtain a mixture; wherein the ratio of the molar number of repeating units in PEO to the molar number of LiFSI was 18:1. 2 L of acetonitrile was dripped into the mixture, and the mixture was continuously ground to be evenly dispersed to obtain a slurry. The slurry was evenly coated on a polytetrafluoroethylene plate (coating thickness was 0.22 mm), and after vacuum drying at 80°C for 8 h, a lithium gallium germanate modified PEO-based composite solid electrolyte membrane was obtained.

[0034] Comparative Example 1

[0035] 80.9g PEO and 19.1g LiFSI were ball-milled and mixed to obtain a mixture, wherein the molar ratio of PEO to LiFSI was 18:1. 2L acetonitrile was dripped into the mixture, and the mixture was continuously ground to be evenly dispersed to obtain a slurry. The slurry was evenly coated on a polytetrafluoroethylene plate (coating thickness was 0.22mm), and after vacuum drying at 80°C for 8h, a PEO-based composite solid electrolyte membrane was obtained.

[0036] Comparative Example 2

[0037] (1) Add 10.5 g GeO2 and 3.2 g Li2O into 50 mL water and disperse them evenly to obtain a slurry. Add the slurry into a spray pyrolysis furnace and spray pyrolyze at 850 °C for 6 seconds to obtain lithium germanate Li2GeO3.

[0038] (2) 10 g of Li2GeO3 prepared in step (1), 80.9 g of PEO and 19.1 g of LiFSI were ball-milled and mixed to obtain a mixture; wherein the ratio of the molar number of repeating units in PEO to the molar number of LiFSI was 18:1. 2 L of acetonitrile was dripped into the mixture, and the mixture was continuously ground to be evenly dispersed to obtain a slurry. The slurry was evenly coated on a polytetrafluoroethylene plate (coating thickness was 0.22 mm), and after vacuum drying at 80°C for 8 h, a lithium germanate-modified PEO-based composite solid electrolyte membrane was obtained.

[0039] Comparative Example 3

[0040] (1) Add 18.7 g of Ga2O3 and 3.2 g of Li2O into 50 mL of water and disperse them evenly to obtain a slurry; add the slurry into a spray pyrolysis furnace and spray pyrolyze at 850°C for 6 seconds to obtain lithium gallate LiGaO2.

[0041] (2) 10 g of LiGaO2 prepared in step (1), 80.9 g of PEO and 19.1 g of LiFSI were ball-milled and mixed to obtain a mixture; wherein the ratio of the molar number of repeating units in PEO to the molar number of LiFSI was 18:1. 2 L of acetonitrile was dripped into the mixture and continuously ground until it was evenly dispersed to obtain a slurry. The slurry was evenly coated on a polytetrafluoroethylene plate (coating thickness was 0.22 mm), and after vacuum drying at 80 ° C for 8 h, a lithium gallate-modified PEO-based composite solid electrolyte membrane was obtained.

[0042] Example 2

[0043] The method is basically the same as Example 1, except that in step (2), the amount of lithium gallium germanate added is 5 g.

[0044] Example 3

[0045] The method is basically the same as Example 1, except that in step (2), the amount of lithium gallium germanate added is 15 g.

[0046] Example 4

[0047] In the solid electrolyte of this embodiment: the structural formula of lithium gallium germanate is LiGaGe2O6; the lithium-based electrolyte is LiTFSI; and the molecular weight of PEO is 2000000.

[0048] The specific preparation method is as follows:

[0049] (1) Add 10.5 g GeO2, 9.35 g Ga2O3, and 1.59 g Li2O into 60 mL water and disperse them evenly to obtain a slurry; add the slurry into a spray pyrolysis furnace and spray pyrolyze at 700 °C for 8 seconds to obtain lithium gallium germanate LiGaGe2O6.

[0050] (1) Ball milling is performed at a rotation speed of 200 r / min for 30 hours to obtain a mixed powder; the mixed powder is transferred to a tube furnace and vacuum sintered at 900° C. for 30 hours to obtain lithium gallium germanate LiGaGe2O6.

[0051] (2) 10 g of LiGaGe2O6 prepared in step (1), 69.7 g of PEO and 30.3 g of LiTFSI were ball-milled and mixed to obtain a mixture; wherein the ratio of the molar number of repeating units in PEO to the molar number of LiTFSI was 15:1. 2 L of acetonitrile was dripped into the mixture and continuously ground until it was evenly dispersed to obtain a slurry. The slurry was evenly coated on a polytetrafluoroethylene plate (coating thickness was 0.23 mm), and after vacuum drying at 70°C for 12 h, a lithium gallium germanate modified PEO-based composite solid electrolyte was obtained.

[0052] Example 5

[0053] In the solid electrolyte of this embodiment: the structural formula of lithium gallium germanate is LiGaGe2O6; the lithium-based electrolyte is LiBF4; and the molecular weight of PEO is 5000000.

[0054] The specific preparation method is as follows:

[0055] (1) Add 10.5 g GeO2, 12.83 g Ga(NO3)3, and 3.85 g Li2CO3 into 60 mL water and disperse them evenly to obtain a slurry; add the slurry into a spray pyrolysis furnace and spray pyrolyze at 1000°C for 4 seconds to obtain lithium gallium germanate LiGaGe2O6.

[0056] (2) 10 g of LiGaGe2O6 prepared in step (1), 90.37 g of PEO and 9.63 g of LiBF4 were ball-milled and mixed to obtain a mixture; wherein the ratio of the molar number of repeating units in PEO to the molar number of LiBF4 was 20:1. 2 L of acetonitrile was dripped into the mixture and the mixture was continuously ground until uniformly dispersed to obtain a slurry. The slurry was evenly coated on a polytetrafluoroethylene plate (coating thickness was 0.21 mm), and after vacuum drying at 90°C for 6 h, a lithium gallium germanate modified PEO-based composite solid electrolyte was obtained.

[0057] Solid-state battery assembly is accomplished by:

[0058] The modified PEO-based composite solid electrolyte membrane prepared in Examples 1 to 5 and Comparative Examples 1 to 3 was cut into 18 mm diameter discs as electrolyte membranes, lithium sheets were used as negative electrodes, and LiFePO4 was used as positive electrode materials to prepare positive electrode sheets; the positive electrode sheets, electrolyte membrane sheets and lithium sheets were assembled into CR2032 button batteries in a glove box. Wherein: the method for preparing LiFePO4 as a positive electrode material into a positive electrode sheet is: mixing LiFePO4: acetylene black: PVDF in a mass ratio of 8:1:1, using N-methylpyrrolidone (NMP) as a solvent, placing the mixture in a small beaker at a speed of 800 r / min and stirring the mixture for 2 hours to obtain a slurry; using an automatic coating machine to coat the slurry on a current collector aluminum foil, placing it flat on a tempered glass and transferring it to a vacuum drying oven at 85°C for drying for 4 hours, punching the sheet into a positive electrode sheet with a diameter of 12 mm, and drying it in a vacuum drying oven at 105°C for 4 hours.

[0059] After the battery is assembled and aged for 12 hours, the charge and discharge test is carried out. The battery is activated at a voltage of 2.5~4.3V for 3 cycles at a current density of 0.1C, and then cycled for 100 cycles at a current density of 1C. The test results show that Figure 1 and Table 1 (the initial specific capacity in Table 1 is the specific capacity of the first cycle at a current density of 0.1C; the capacity retention rate is calculated based on the specific capacity of the first cycle at a current density of 1C (the 4th cycle in the figure) as the initial specific capacity).

[0060] Table 1

[0061]

[0062] from Figure 1 It can be seen from the data in Table 1 that the solid-state battery assembled with the PEO-based composite solid electrolyte modified with lithium gallium germanate in Example 1 has good specific capacity and cycle performance. The specific capacity and cycle performance of the solid-state battery assembled with the unmodified PEO-based composite solid electrolyte in Comparative Example 1 are significantly lower than those in Example 1. In Comparative Examples 2 and 3, Li2GeO3 and LiGaO2 are used to modify the PEO-based solid electrolyte, respectively, and the specific capacity and cycle performance of the corresponding assembled solid-state batteries are improved compared with Comparative Example 1, and decreased compared with Example 1.

[0063] In Examples 1 to 3, the addition amount of lithium gallium germanate is different, and the specific capacity and cycle performance of the corresponding assembled solid-state batteries fluctuate to a certain extent, but all have good electrochemical properties.

[0064] In Examples 4 and 5, there are certain changes in the preparation process of the lithium gallium germanate modified PEO-based composite solid electrolyte, and the specific capacity and cycle stability of the corresponding assembled solid-state batteries fluctuate to a certain extent.

[0065] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A lithium gallium germanate modified PEO-based composite solid electrolyte, characterized in that: The components include: lithium gallium germanate, PEO and lithium-based electrolyte, wherein: the structural formula of lithium gallium germanate is LiGaGe2O6; the ratio of the mass of lithium gallium germanate to the total mass of PEO and lithium-based electrolyte is (5-15):

100.

2. The lithium gallium germanate modified PEO-based composite solid electrolyte according to claim 1, characterized in that: The lithium-based electrolyte is one or more of LiPF6, LiTFSI, LiFSI, and LiBF4.

3. The lithium gallium germanate modified PEO-based composite solid electrolyte according to claim 1 or 2, characterized in that: The ratio of the molar number of repeating units in PEO to the molar number of lithium-based electrolyte is (15~20):

1.

4. A method for preparing a lithium gallium germanate modified PEO-based composite solid electrolyte according to any one of claims 1 to 3, characterized in that: The following steps are involved: Lithium gallium germanate, PEO and lithium-based electrolyte are mixed to obtain mixed powder; a solvent is dripped into the mixed powder, and a slurry is obtained after grinding; the slurry is coated on a bottom plate, and after drying, a lithium gallium germanate modified PEO-based composite solid electrolyte is obtained.

5. The method for preparing the lithium gallium germanate modified PEO-based composite solid electrolyte according to claim 4, characterized in that: The preparation method of lithium gallium germanate comprises the following steps: dispersing a germanium source, a gallium source and a lithium source in water to form a mixed slurry, and spraying and pyrolyzing the mixed slurry to obtain lithium gallium germanate LiGaGe2O6.

6. The method for preparing the lithium gallium germanate modified PEO-based composite solid electrolyte according to claim 5, characterized in that: The germanium source is one or both of germanium dioxide and germanium monoxide; the gallium source is one or both of gallium trioxide and gallium nitrate; the lithium source is one or more of lithium oxide, lithium carbonate, lithium hydroxide and lithium acetate; the germanium source, gallium source and lithium source are added in a molar ratio of Ge, Ga and Li of 2:1:(1.04-1.06).

7. The method for preparing the lithium gallium germanate modified PEO-based composite solid electrolyte according to claim 5, characterized in that: The spray pyrolysis temperature is 700~1000℃, and the pyrolysis time is 4~8s.

8. The method for preparing the lithium gallium germanate modified PEO-based composite solid electrolyte according to claim 4, characterized in that: The solvent is acetonitrile, tetrahydrofuran and N,N- One or more of dimethylformamide; the mass volume ratio of PEO to solvent is 1g:(10~30)mL.

9. The method for preparing the lithium gallium germanate modified PEO-based composite solid electrolyte according to claim 4, characterized in that: The drying is vacuum drying, the vacuum drying temperature is 70-90° C., and the vacuum drying time is 6-12 hours.

10. A solid-state battery, characterized in that: The electrolyte is a lithium gallium germanate modified PEO-based composite solid electrolyte as described in any one of claims 1 to 3.

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