Composite solid electrolyte modified by grain boundary modification and preparation method thereof, solid-state battery

Abstract

This invention belongs to the field of solid-state battery technology, specifically relating to a grain boundary modified composite solid-state electrolyte, its preparation method, and a solid-state battery. The composite solid-state electrolyte comprises a crystalline sulfide electrolyte, wherein grain boundaries exist between the grains of the crystalline sulfide electrolyte, and these grain boundaries are filled with a polymer solid-state electrolyte; wherein the ionic conductivity of the polymer solid-state electrolyte is greater than 1×10⁻⁶. ‑6 S / cm, electronic conductivity less than 1×10 ‑9 S / cm. This composite solid electrolyte can significantly improve the ability of sulfide electrolytes to suppress lithium dendrites, extend the cycle life of sulfide solid lithium metal batteries, and at the same time, reduce the self-discharge effect of sulfide solid batteries and improve the coulombic efficiency of the battery.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of solid-state batteries, and particularly relates to a grain boundary modified composite solid-state electrolyte and a preparation method thereof and a solid-state battery. BACKGROUND

[0002] Full-solid-state lithium batteries use high-ionic-conductivity solid-state electrolytes to match metal lithium negative electrodes, and have high energy density and high safety, which will provide great help for the full popularization of new energy vehicles and the realization of the "double carbon" goal. As a core component of solid-state batteries, solid-state electrolytes directly determine the comprehensive electrochemical performance of solid-state batteries. Therefore, it is of great significance to develop high-performance solid-state electrolytes. Among various solid-state electrolyte systems, sulfide electrolytes have high ionic conductivity and interface compatibility with electrodes, and are considered to be one of the most promising solid-state electrolyte systems for room-temperature full-solid-state batteries.

[0003] Although sulfide electrolytes have unique advantages in ionic conductivity and interface compatibility with electrodes, uncontrollable lithium dendrite growth limits the development of sulfide solid-state lithium metal batteries to a great extent. In addition, the high electronic conductivity of sulfides can cause free transmission of electrons in the battery, resulting in serious self-discharge and reduced battery coulomb efficiency. These problems limit the development of sulfide solid-state lithium metal batteries to a great extent. SUMMARY

[0004] The purpose of the present application is to provide a grain boundary modified composite solid-state electrolyte and a preparation method thereof and a solid-state battery. The composite solid-state electrolyte effectively inhibits lithium dendrite growth along the grain boundary and inhibits self-discharge in the solid-state battery by realizing electron shielding at the grain boundary of the sulfide solid-state electrolyte, which is conducive to the development of long-life, high-safety and low-self-discharge-rate full-solid-state sulfide lithium metal batteries.

[0005] Specifically, the present application first provides a grain boundary modified composite solid-state electrolyte, which comprises a crystalline sulfide electrolyte, the crystalline sulfide electrolyte has grain boundaries between the crystal grains, and the grain boundaries between the crystal grains are filled with a polymer solid-state electrolyte.

[0006] The ionic conductivity of the polymer solid-state electrolyte is greater than 1x10 -6 S / cm, and the electronic conductivity is less than 1x10 -9 S / cm.

[0007] The present application researches and finds that the polymer electrolyte with high ion conductivity and low electron conductivity is used for interface modification of sulfide electrolyte, which can realize electron shielding at the grain boundary, thereby inhibiting the deposition and growth of lithium dendrites at the grain boundary by hindering the reduction of lithium ions by electrons at the grain boundary, and effectively improving the cycle performance of the solid-state lithium metal battery. At the same time, since the polymer electrolyte used has high ion conductivity, the rapid transmission of lithium ions at the grain boundary can be ensured, which will not cause a substantial decrease in ion conductivity of the sulfide electrolyte and a sharp increase in polarization of the solid-state battery. In addition, the electron shielding effect at the grain boundary can hinder the conduction of electrons inside the sulfide electrolyte, thereby greatly reducing the self-discharge effect of the solid-state battery (see Figure 1 ).

[0008] As preferred, the ion conductivity of the polymer solid-state electrolyte is 1x10 -6 S / cm~1x10 -2 S / cm; and the electron conductivity is 1x10 -14 S / cm~1x10 -9 S / cm.

[0009] As preferred, the polymer solid-state electrolyte comprises lithium salt and high molecular polymer in a mass ratio of 4 / 1~1 / 20.

[0010] Further preferably, the lithium salt is one or two or more of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(trifluoromethylsulfonyl)amide (LiFSI), lithium (nonafluorobutanesulfonyl)fluorosulfonylimide (LiFNFSI), lithium (trifluoromethylsulfonyl)fluorosulfonylimide (LiFTFSI), lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium difluoro(oxalato)borate (LiDFOB), lithium bis(oxalato)borate (LiBOB).

[0011] And / or, the high molecular polymer is one or two or more of polyethylene oxide (PEO), polyethylene glycol (PEG), polyethylene glycol dimethyl ether (PEGDME), polytetrahydrofuran (PTHF), poly(1,3-dioxolane) (PDOL).

[0012] Further preferably, the polymer solid-state electrolyte further comprises a plasticizer in a mass percentage, and the amount of the plasticizer is 50% or less based on the mass of the polymer solid-state electrolyte; most preferably, the plasticizer is one or two or more of butanedinitrile, urea, tetraethylene glycol dimethyl ether (TEGDME). The present application finds that the introduction of the above-mentioned plasticizer into the polymer electrolyte can significantly improve the ion conductivity of the polymer electrolyte and reduce the coating difficulty.

[0013] As preferred, the crystalline sulfide electrolyte is one or two or more of Li3PS4, Li7P3S 11 , Li6PS5Cl, Li6PS5Br, Li6PS5I, Li 5.5 PS 4.5 Br 1.5 , Li 5.5 PS 4.5 Cl 1.5 .

[0014] The application also provides a preparation method of the above-mentioned grain boundary modified composite solid electrolyte, comprising the following steps:

[0015] (1) adding raw materials comprising the high molecular polymer and lithium salt into a ball mill tank for ball milling to obtain a polymer solid electrolyte;

[0016] (2) ball milling the polymer solid electrolyte and the crystalline sulfide electrolyte in a ball mill tank to obtain a sulfide-polymer mixed powder;

[0017] (3) placing the sulfide-polymer mixed powder in a pressure mold for tabletting, to obtain the grain boundary modified composite solid electrolyte.

[0018] As preferred, in the above-mentioned step (1), the raw materials further comprise the plasticizer.

[0019] As preferred, in the above-mentioned step (1), the rotation speed of the ball milling is 50-300 rpm, and the ball milling time is 0.5-5 h. The application adopts reasonable raw material formula and suitable process conditions to obtain a polymer solid electrolyte with high ionic conductivity and low electronic conductivity, thereby better meeting the preparation requirements of the composite solid electrolyte.

[0020] As preferred, in the above-mentioned step (2), the mass fraction of the crystalline sulfide electrolyte is 70%-99.5% based on the total mass of the polymer solid electrolyte and the crystalline sulfide electrolyte. The application finds that too much polymer solid electrolyte will reduce the comprehensive electrochemical performance of the obtained composite solid electrolyte, especially the ionic conductivity, and too little polymer solid electrolyte will not effectively modify the grain boundary, and cannot effectively inhibit the growth of lithium dendrites along the grain boundary and the self-discharge effect in the solid-state battery.

[0021] As preferred, in the above-mentioned step (2), the rotation speed of the ball milling is 50-300 rpm, and the ball milling time is 0.5-5 h. The application finds that the rotation speed of the ball milling in step (2) should not be too high, and the ball milling time should not be too long, otherwise the particle size of the sulfide electrolyte will be too small, and the ionic conductivity will be reduced, and the sulfide electrolyte that is too small will increase the difficulty of the modification of the grain boundary by the polymer.

[0022] Preferably, in step (3) above, the pressure for tableting is 3t to 10t. In a preferred embodiment, the sulfide-polymer mixed powder is placed in a pressure mold with a diameter of 10mm and tableted.

[0023] The present invention also provides a solid-state battery, comprising a positive electrode, a negative electrode and an electrolyte, wherein the electrolyte is a composite solid-state electrolyte modified by grain boundary modification as described above or a composite solid-state electrolyte modified by grain boundary modification prepared by the above preparation method.

[0024] The beneficial effects of this invention are as follows:

[0025] 1) The grain boundary modified composite solid electrolyte provided by the present invention achieves grain boundary electron shielding of sulfide solid electrolyte by introducing a polymer electrolyte with high ionic conductivity and low electronic conductivity to modify the grain boundary. The method is simple, the grain boundary electronic conductivity is adjustable, and it is easy to scale up.

[0026] 2) The grain boundary modified composite solid electrolyte provided by the present invention can significantly improve the ability of sulfide electrolyte to suppress lithium dendrites and extend the cycle life of sulfide solid lithium metal battery.

[0027] 3) The grain boundary modified composite solid electrolyte provided by the present invention can reduce the self-discharge effect of sulfide solid batteries and improve the coulombic efficiency of the batteries. Attached Figure Description

[0028] Figure 1 A comparison of the advantages and disadvantages of electron shielding before and after the sulfide electrolyte interface.

[0029] Figure 2 The room temperature ionic conductivity of PVDF, PEGDME, and PEDOT:PSS electrolytes is given.

[0030] Figure 3 The electronic conductivity of PVDF, PEGDME, and PEDOT:PSS electrolytes.

[0031] Figure 4 The room temperature ionic conductivity and electronic conductivity of Li6PS5Cl electrolyte are shown.

[0032] Figure 5 To compare the lithium symmetric batteries assembled with those in Examples 1-3 at 0.5 mA cm⁻¹ -2 1mA cm -2 Cyclic performance testing under test conditions.

[0033] Figure 6 For the comparative example and the Li-LiCoO2 full cell assembled in Example 2, at 0.1 mA cm⁻¹ -2 Cyclic performance test (a) and self-discharge test (b).

[0034] Figure 7 The Li-LiCoO2full cell assembled for Example 2 was cycled at 0.5 mA cm -2 under the test conditions.

[0035] Figure 8 The Li-LiCoO2full cell assembled for Comparative Example was cycled at 0.5 mA cm -2 under the test conditions. DETAILED DESCRIPTION

[0036] The following examples are intended to illustrate the present application but not to limit the scope of the present application. Modifications or substitutions of the methods, steps or conditions of the present application, which do not depart from the spirit and essence of the present application, are intended to fall within the scope of the present application.

[0037] Unless otherwise specified, the techniques or conditions in the examples were carried out according to the techniques or conditions described in the literature or according to the product instructions. Unless otherwise specified, all reagents or instruments were conventional products available through regular channels.

[0038] Preparation of PVDF, PEGDME and PEDOT:PSS electrolytes:

[0039] 2 g of PVDF polymer (Mn = 180000) and 1 g of LiTFSI were ball-milled at 200 rpm for 0.5 h to obtain the PVDF electrolyte. The PVDF polymer refers to polyvinylidene fluoride, which was used in Example 1.

[0040] 2 g of PEGDME polymer (Mn = 2000) and 1 g of LiTFSI were ball-milled at 200 rpm for 0.5 h to obtain the PEGDME electrolyte, which was used in Example 2.

[0041] 1.4 g of PEDOT:PSS polymer from Beli Technology (Chongqing) Co., Ltd., 0.6 g of succinonitrile and 1 g of LiTFSI were ball-milled at 200 rpm for 0.5 h to obtain the PEDOT:PSS electrolyte. The PEDOT:PSS polymer is poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid), which was used in Example 3.

[0042] The electronic conductivities of the PVDF, PEGDME and PEDOT:PSS electrolytes are shown in Table 1. Figure 3 The electronic conductivities of the PVDF, PEGDME and PEDOT:PSS electrolytes are shown in Table 1. -11 S cm -1 and 6.5 x 10 -11 S cm -1, which is much lower than 5.7 x 10 -8 S cm -1 ( Figure 4 ). The low electronic conductivity of PEGDME and PVDF electrolytes is used to modify the Li6PS5Cl electrolyte grain boundary, which can achieve the electron shielding of Li6PS5Cl grain boundary, reduce the transmission speed of electrons at the grain boundary, and hinder the combination of electrons and lithium ions at the grain boundary to form lithium dendrites. On the contrary, the electronic conductivity of PEDOT: PSS electrolyte can reach 0.7 S cm -1 , which can accelerate the conduction of electrons at the grain boundary, causing more serious lithium dendrite growth.

[0043] In addition to electronic conduction, ion conduction at the grain boundary is also crucial for the performance of the battery. The ion conductivities of PVDF, PEGDME and PEDOT: PSS electrolytes are shown in Figure 2 . Li + + in PEGDME electrolyte can conduct along the PEGDME ether chain, making the room temperature ion conductivity of PEGDME reach 5.0 x 10 -6 S cm -1 , which is much higher than 2.1 x 10 -9 S cm -1 . When butanedinitrile plasticizer is introduced into the PEDOT: PSS electrolyte, its room temperature ion conductivity can reach 1.1 x 10 -4 S cm -1 . The high ion conductivity of PEGDME and PEDOT: PSS electrolytes can ensure the free transmission of lithium ions at the Li6PS5Cl grain boundary. The low ion conductivity of PVDF makes it difficult for lithium ions to pass through the Li6PS5Cl grain boundary, resulting in increased polarization of the assembled battery.

[0044] 2 g of PEGDME polymer (Mn = 2000), 0.4 g of tetraethylene glycol dimethyl ether (TEGDME) (plasticizer) and 1 g of LiTFSI were ball milled at 200 rpm for 0.5 h to obtain a plasticizer-added PEGDME electrolyte, which was used in Example 4.

[0045] Comparative Example 1

[0046] 2 g of Li6PS5Cl was placed in a ball mill jar and ball milled at 200 rpm for 4 h to obtain a comparative sample.

[0047] The lithium symmetric battery was assembled from the comparative sample as follows: 100 mg of the comparative sample was placed in a pressure die with a diameter of 10 mm and pressed to 4 t, and after constant voltage for 1 min, one lithium sheet was placed on each side of the electrolyte sheet, and then pressed to 0.5 t, and constant voltage for 1 min. The assembled die battery was cycled at 0.5 mA cm -2Current density and 1 mAh cm -2 The cycling performance test was performed at a capacity of 1 mAh cm x The coated LiCoO2(coating thickness of 5 nm) and 0.3 g of the comparative sample were hand-mixed for 10 min and added to one side of the electrolyte sheet, pressed to 4 t, and held for 1 min. Then, one lithium sheet was added to the other side of the electrolyte sheet, pressed to 0.5 t, and held for 1 min. The assembled coin cell was tested at a constant current density of 0.1 mA cm -2 and 0.5 mA cm -2 The test was performed at a constant current density. The test voltage range was 2.5-4.2 V, and the test temperature was room temperature. The self-discharge test was performed as follows: the assembled Li-LiCoO2was discharged at a constant current density of 0.1 mA cm -2 After 3 cycles at a constant current density, the cell was charged to 4.2 V, and then left to stand for 1 week (168 h). Then, the cell was discharged, and the coulombic efficiency was calculated to evaluate the self-discharge rate.

[0048] Example 1

[0049] Example 1 was obtained by placing 1.9 g of Li6PS5Cl and 0.1 g of PVDF electrolyte in a ball mill jar and ball-milling at 200 rpm for 4 h. Lithium symmetric cells were assembled from Example 1, and the evaluation process and method were the same as those of Comparative Example 1.

[0050] Example 2

[0051] Example 2 was obtained by placing 1.9 g of Li6PS5Cl and 0.1 g of PEGDME electrolyte in a ball mill jar and ball-milling at 200 rpm for 4 h. Lithium symmetric cells, full cell cycling performance, and self-discharge rate evaluation processes and methods were the same as those of Comparative Example 1.

[0052] Example 3

[0053] Example 3 was obtained by placing 1.9 g of Li6PS5Cl and 0.1 g of PEDOT:PSS electrolyte in a ball mill jar and ball-milling at 200 rpm for 4 h. Lithium symmetric cells were assembled from Example 3, and the evaluation process and method were the same as those of Comparative Example 1.

[0054] Example 4

[0055] Example 4 was obtained by placing 1.9 g of Li6PS5Cl and 0.1 g of PEGDME electrolyte with an additive plasticizer in a ball mill jar and ball-milling at 200 rpm for 4 h. Lithium symmetric cells, full cell cycling performance, and self-discharge rate evaluation processes and methods were the same as those of Comparative Example 1.

[0056] Test case

[0057] Li-Li symmetric cells assembled with Li6PS5Cl, Li6PS5Cl modified with PVDF electrolyte (Example 1), Li6PS5Cl modified with PEGDME electrolyte (Example 2), and Li6PS5Cl modified with PEDOT:PSS electrolyte (Example 3) were tested at 0.5 mA / cm². -2 Current density, 1mAh cm -2 Cyclic performance at capacity, such as Figure 5 As shown, when the grain boundaries of Li6PS5Cl electrolyte are modified with PVDF, which has low lithium-ion and low electronic conductivity, the overpotential of the assembled Li-Li symmetric cell is 0.35V, which is 8.7 times that of the comparative example, due to the obstruction of ion transport at the grain boundaries. This results in a short circuit under prolonged cycling at a higher bias voltage. However, thanks to the electronic shielding effect of the grain boundaries, the cycle life of the Li-Li symmetric cell (250h) is significantly improved compared to the comparative example (30h). When the grain boundaries of Li6PS5Cl electrolyte are modified with PEDOT:PSS electrolyte, which has high electronic and high ion conductivity, the grain boundaries exhibit rapid ion and electron conduction. Electrons and lithium ions combine more easily at the grain boundaries, leading to more severe dendrite growth and a short circuit after 12h. However, when the grain boundaries of Li6PS5Cl electrolyte are modified with PEGDME electrolyte, which has high ion conductivity and low electronic conductivity, lithium ions can freely transport at the grain boundaries, while electrons have difficulty transporting there, achieving electronic shielding at the grain boundaries. At this point, only ion conduction occurs in the bulk electrolyte, and lithium tends to nucleate and grow at the electrolyte / lithium interface, thus inhibiting the growth of lithium dendrites in the bulk phase. The Li-Li symmetric battery assembled in Example 2 can operate stably for 1000 hours without any short circuit. In summary, among the comparative examples (Examples 1-3), the lithium symmetric battery assembled in Example 2, which uses PEGDME with high ionic conductivity and low electronic conductivity to modify the Li6PS5Cl grain boundaries, exhibits better cycle performance and less polarization. Therefore, modifying sulfide grain boundaries with high ionic conductivity and low electronic conductivity materials is key to achieving grain boundary electronic shielding.

[0058] The Li-LiCoO2 full cells assembled in Comparative Example 1 and Example 2 were tested at 0.1 mA / cm². -2 Cyclic performance and self-discharge rate tests at current density, such as Figure 6As shown, after being fully charged and left to rest for one week, the coulombic efficiency of the Li-LiCoO2 full cell assembled in the comparative example was 88.1%, while the coulombic efficiency of the Li-LiCoO2 full cell assembled in Example 2 was as high as 96.1%, which is 8% higher than that of the Li-LiCoO2 full cell assembled in the comparative example. This result indicates that the grain boundary electron shielding of Li6PS5Cl can effectively suppress the self-discharge effect caused by the free conduction of electrons inside the battery. In addition, during the cycle performance test, the average coulombic efficiency of the Li-LiCoO2 full cell assembled in Example 2 after stabilization was 99.7%, which was also higher than the 98.6% of the Li-LiCoO2 full cell assembled in the comparative example, further verifying the effect of the grain boundary electron shielding strategy on the suppression of self-discharge.

[0059] The Li-LiCoO2 full cells assembled in Comparative Example 1 and Example 2 were tested at a high current density of 0.5 mA / cm². -2 Cyclic performance at current density, such as Figure 7 and Figure 8 As shown. The results indicate that the Li-LiCoO2 full cell assembled in Example 2 can achieve a speed of 0.5 mA / cm². -2 The battery remained stable for 2600 cycles at the specified current density without any short circuit. However, the Li-LiCoO2 full cell assembled in comparison showed a sudden drop in coulombic efficiency to around 0 after only 7 cycles, indicating a short circuit. The difference in cycling performance of the Li-LiCoO2 full cell under high-rate conditions further validates the effect of the grain boundary electron shielding strategy on suppressing lithium dendrite growth, consistent with the results of lithium symmetric batteries. In conclusion, the grain boundary electron shielding strategy can effectively suppress lithium dendrite growth along grain boundaries and suppress self-discharge effects in solid-state batteries, which is of great significance for developing high-safety, high-energy-density, and long-life sulfide solid-state lithium metal batteries.

[0060] The Li-NCM (8-series) full cells assembled in Comparative Example 1 and Examples 2 and 4 were tested at 0.1 mA cm⁻¹. -2 After 500 cycles at the specified current densities, the capacity retention rates were 85%, 89%, and 92%, respectively. After one week of rest at 45°C in a fully charged state, the coulombic efficiency of the full cell assembled in the comparative example was 85.4%, while the coulombic efficiency of the full cell assembled in Example 2 reached 90.2%, and the coulombic efficiency of the full cell assembled in Example 4 reached 94.1%. This result indicates that the grain boundary electron shielding of Li6PS5Cl can effectively suppress the free conduction of electrons within the battery. Furthermore, during the cycle performance test, the average coulombic efficiency of the full cell assembled in Example 2 after stabilization was 99.5%, and the average coulombic efficiency of the full cell assembled in Example 4 after stabilization was 99.8%, both higher than the 98.3% of the full cell assembled in the comparative example, further verifying the effectiveness of the grain boundary electron shielding strategy in suppressing self-discharge.

[0061] The above embodiments are merely intended to describe the preferred embodiments of the present application, but not to limit the scope of the present application. Various alternations and modifications of the technical solutions of the present application made by those ordinarily skilled in the art without departing from the spirit of the present application shall fall into the scope of protection of the present application as defined by the claims.

Claims

1. A grain boundary modified composite solid state electrolyte, characterized by, The composite solid electrolyte comprises a crystalline sulfide electrolyte, and a grain boundary between the crystalline sulfide electrolyte is filled with a polymer solid electrolyte. The polymer solid-state electrolyte has an ionic conductivity greater than 1 x 10 -6 S / cm and an electronic conductivity less than 1 x 10 - 9 S / cm. The polymer solid electrolyte comprises a lithium salt and a polymer in a mass ratio of 4 / 1 to 1 / 20.

2. The grain boundary modified composite solid state electrolyte of claim 1, wherein, The polymer solid electrolyte has an ionic conductivity of 1 x 10 -6 S / cm to 1 x 10 -2 S / cm; and an electronic conductivity of 1 x 10 -14 S / cm to 1 x 10 - 9 S / cm.

3. The grain boundary modified composite solid state electrolyte of claim 2, wherein, The lithium salt is one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(trifluoromethylsulfonyl)amide, lithium (nonafluorobutanesulfonyl)fluorosulfonylimide, lithium (trifluoromethylsulfonyl)fluorosulfonylimide, lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium difluoro(oxalato)borate, and lithium bis(oxalato)borate. The polymer is one or more of poly(ethylene oxide), poly(ethylene glycol), poly(ethylene glycol) dimethyl ether, poly(tetrahydrofuran), and poly(1,3-dioxolane).

4. The grain boundary modified composite solid state electrolyte of claim 3, wherein, The polymer solid electrolyte further comprises a plasticizer, and the amount of the plasticizer is 50% or less based on the mass of the polymer solid electrolyte.

5. The grain boundary modified composite solid state electrolyte of claim 4, wherein, The plasticizer is one or more of butanedinitrile, urea, and tetraglyme.

6. The grain boundary modified composite solid state electrolyte of any one of claims 1-5, wherein the composite solid state electrolyte is a lithium ion conducting composite solid state electrolyte. Li3PS4, Li7P3S 11 , Li6PS5Cl, Li6PS5Br, Li6PS5I, Li 5.5 PS 4.5 Br 1.5 , Li 5.5 PS 4.5 Cl 1.5 ​ 7. A method of preparing the grain boundary modified composite solid state electrolyte of any one of claims 1-6, characterized in that, The method comprises the following steps: (1) adding raw materials comprising the polymer and the lithium salt into a ball mill tank to perform ball milling to obtain a polymer solid electrolyte; (2) ball milling the polymer solid electrolyte and a crystalline sulfide electrolyte in a ball mill tank to obtain a sulfide-polymer mixed powder; (3) placing the sulfide-polymer mixed powder in a pressure mold to perform tabletting to obtain the grain boundary modified composite solid electrolyte.

8. The preparation method according to claim 7, characterized in that, In the step (1), the raw materials further comprise the plasticizer. In the step (1), the ball milling is performed at a speed of 50-300 rpm for 0.5-5 h. In the step (2), the mass fraction of the crystalline sulfide electrolyte is 70%-99.5% based on the total mass of the polymer solid electrolyte and the crystalline sulfide electrolyte. In the step (2), the ball milling is performed at a speed of 50-300 rpm for 0.5-5 h. In the step (3), the tabletting is performed at a pressure of 3-10 t.

9. A solid-state battery comprising a positive electrode, a negative electrode, and an electrolyte, characterized by, The electrolyte is the grain boundary modified composite solid electrolyte according to any one of claims 1-6 or prepared by the method according to claim 7 or 8.

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