Surface coating modified halide solid electrolyte as well as preparation method and application thereof

Abstract

The invention relates to the technical field of lithium ion batteries, and provides a surface coating modified halide solid electrolyte as well as a preparation method and application thereof. The method comprises the following steps: preparing a halide solid electrolyte, mixing the halide solid electrolyte with a lithium salt, and carrying out ball milling to obtain the surface coated and modified halide solid electrolyte. The coating layer is directly constructed on the surface of the halide solid electrolyte by adopting a mechanochemical ball milling method, traditional high-energy-consumption processes such as vapor deposition and high-temperature sintering are abandoned, and in-situ modification of the surface of the halide electrolyte is realized. After the lithium salt is used for coating, the side reaction between the halide solid-state electrolyte and lithium metal and the growth of lithium dendrites can be effectively reduced, so that the lithium stability of the halide solid-state electrolyte is improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a surface-coated modified halide solid electrolyte, its preparation method, and its application. Background Technology

[0002] All-solid-state lithium batteries have attracted much attention due to their high safety and energy density. A key driving factor is the solid-state electrolyte. Halide solid-state electrolytes, with their high ionic conductivity, good compatibility with high-voltage cathodes, and excellent mechanical deformability, can overcome the disadvantages of oxide electrolytes (poor interfacial contact) and sulfide electrolytes (narrow electrochemical window), making them a research hotspot in the all-solid-state battery field. Currently, LZC is one of the most promising electrolyte materials because it retains the ideal properties of halide solid-state electrolytes while also offering significant cost-effectiveness. Most all-solid-state lithium-ion batteries assembled using halide as the solid electrolyte use lithium alloys instead of lithium metal. For example, the negative electrode used in Li3YCl6 and Li3YBr6 all-solid-state batteries is a Li-In alloy, and Li7P3S is inserted between the solid electrolyte and lithium metal during cyclic voltammetry testing. 11 However, Li-In alloys, when used as a negative electrode, significantly reduce the voltage of all-solid-state batteries.

[0003] Lithium metal is an ideal anode for all-solid-state batteries, but current reports indicate that halide solid electrolytes are not stable with lithium. When halide electrolytes come into contact with metallic lithium, they spontaneously decompose, forming a mixed ion-electron conductive interface layer. This layer gradually increases the battery's internal resistance during cycling, ultimately leading to rapid battery failure. Furthermore, at high current densities, lithium dendrites easily grow along surface defects and bulk gaps in the halide solid electrolyte, causing short circuits and affecting the operating capacity and lifespan of the all-solid-state battery.

[0004] Studies have shown that surface coatings on electrode or electrolyte materials can meet the requirements for battery interface stability and moisture resistance. For example, Li metal coatings on lithium metal surfaces... x SiS y The coating not only improves the air stability of lithium metal but also effectively prevents the reduction of solid electrolytes; Li 10 GeP2S 12 Hydrophobic coatings on electrolyte surfaces can enhance the stability of electrolytes against humid air and lithium metal. Generally, coatings primarily act as physical barriers, preventing direct contact between the two reactants. The main shortcomings of existing coatings are their inability to effectively and persistently isolate electron transfer, insufficient mechanical properties to cope with lithium volume changes, and potential chemical stability issues. Summary of the Invention

[0005] To address the problems mentioned above, the present invention aims to provide a surface-coated modified halide solid electrolyte, its preparation method, and its applications. The lithium salt coated on the surface of the halide solid electrolyte can suppress side reactions between the halide solid electrolyte and lithium metal, as well as the growth of lithium dendrites, effectively improving the cycle performance of all-solid-state batteries. The present invention provides the following technical solution:

[0006] The first aspect of this invention provides a method for preparing a surface-coated modified halide solid electrolyte, comprising the following steps:

[0007] S1. Preparation of halide solid electrolytes;

[0008] S2. The halide solid electrolyte is mixed with lithium salt and ball milled to obtain a surface-coated modified halide solid electrolyte.

[0009] This invention employs a mechanochemical ball milling method to directly construct a coating layer on the surface of a halide solid electrolyte, eliminating the need for energy-intensive processes such as traditional vapor deposition and high-temperature sintering, thus achieving in-situ modification of the halide electrolyte surface. Applying a coating to the halide electrolyte surface enhances its compatibility with lithium metal and reduces interfacial side reactions. After coating with lithium salts, side reactions between the halide solid electrolyte and lithium metal and the growth of lithium dendrites can be effectively reduced, thereby improving the lithium stability of the halide solid electrolyte.

[0010] Preferably, in step S1, the raw materials for the halide solid electrolyte are LiCl and ZrCl4.

[0011] Preferably, the molar ratio of LiCl to ZrCl4 is 2:1.

[0012] Preferably, step S1 involves preparing a halide solid electrolyte via a two-step ball milling process. The first step aims to uniformly mix the precursor materials, while the second step provides activation energy for the chemical reaction. Electrolytes synthesized through this process typically exhibit superior overall performance compared to products obtained via a one-step method.

[0013] Preferably, in the two-step ball milling method, the ball milling conditions for the first step are: a ball-to-material mass ratio of (5-15):1, a rotation speed of 300-800 rpm, and a ball milling time of 6-24 h; the ball milling conditions for the second step are: a ball-to-material mass ratio of (40-120):1, a rotation speed of 300-800 rpm, and a ball milling time of 24-48 h.

[0014] Preferably, the ball milling in steps S1 and S2 is carried out under a protective atmosphere.

[0015] Preferably, the protective atmosphere is at least one of nitrogen, argon, and helium.

[0016] Preferably, in step S2, the lithium salt is lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The core purpose of selecting LiTFSI as the coating is to leverage the experience of its spontaneous reaction with lithium metal to form stable SEIs of LiF and Li3N, thereby constructing an interface layer rich in LiF and other components in situ on the lithium metal surface. LiF possesses low electronic conductivity, high interfacial energy, and significant thermodynamic stability, which can enhance the stability of halide electrolytes for lithium metal and inhibit the nucleation and growth of lithium dendrites, reducing interfacial side reactions with lithium metal; the highly ionicly conductive Li3N facilitates the cross-interfacial transport of lithium ions. This interface layer not only has excellent electronic insulation (preventing further reduction and decomposition of the electrolyte) but also good Li... + The combination of ionic conductivity (maintaining battery performance), certain mechanical flexibility (adapting to volume changes and suppressing dendrites), and a relatively simple preparation process comprehensively solves the stability and dendrite problems at the interface between halide solid electrolytes and lithium metal.

[0017] Preferably, in step S2, the mass ratio of the halide solid electrolyte to the lithium salt is 90-99.5:10-0.5.

[0018] Preferably, in step S2, the ball milling speed is 100-600 rpm and the time is 1-20 h.

[0019] Preferably, in step S2, the grinding balls used in the ball mill are at least one of zirconium oxide balls, alumina balls, and silicon nitride balls.

[0020] Preferably, in step S2, the diameter of the grinding balls used in the ball mill is 1-7 mm.

[0021] Preferably, in step S2, the mass ratio of balls to material in the ball mill is 5-15:1.

[0022] A second aspect of the present invention is to provide a surface-coated modified halide solid electrolyte, which is prepared by any of the above preparation methods.

[0023] A third aspect of the present invention is to provide an application of a surface-coated modified halide solid electrolyte in lithium metal secondary batteries.

[0024] The electrolyte of this lithium metal secondary battery is the surface-coated modified halide solid electrolyte.

[0025] Compared with the prior art, the present invention can achieve the following beneficial effects:

[0026] (1) This invention employs a mechanochemical ball milling method to directly construct the coating layer, abandoning the high-energy-consuming processes of traditional vapor deposition and high-temperature sintering, and achieving in-situ modification of the halide electrolyte surface. Compared with processes such as calcination and wet coating, this invention can achieve uniform coating of halide solid electrolytes using simple ball milling. This not only effectively reduces energy consumption but also avoids the problem of incompatibility between halide solid electrolytes and solvents in wet coating processes.

[0027] (2) Applying a coating to the surface of the halide electrolyte can enhance its compatibility with lithium metal and reduce interfacial side reactions with lithium metal. After coating with lithium salt, the side reactions between the halide solid electrolyte and lithium metal and the growth of lithium dendrites can be effectively reduced, thereby improving the lithium stability of the halide solid electrolyte and effectively improving the cycle performance of the all-solid-state battery.

[0028] (3) Due to the narrow electrochemical window of halide solid electrolytes, they are prone to side reactions with lithium metal, generating substances with poor ionic conductivity, which is detrimental to the cross-interface transport of lithium ions and increases the internal resistance of the battery. This invention uses fluorine- and nitrogen-rich lithium salts to coat and modify the halide solid electrolyte. The lithium salts preferentially react with lithium metal to generate an SEI layer rich in LiF and Li3N, reducing the side reactions between the halide solid electrolyte and lithium metal. The generated highly ionicly conductive Li3N is beneficial for the cross-interface transport of lithium ions, while LiF can inhibit the growth of lithium dendrites, significantly improving the stability of the halide solid electrolyte to lithium metal.

[0029] (4) The coating layer thickness of the modified halide solid electrolyte used in this invention can be adjusted by the ratio of precursor materials, thereby reducing the impact on the ionic conductivity of the halide solid electrolyte.

[0030] (5) The operation method of the present invention is simple, low cost, and easy to scale up production. Attached Figure Description

[0031] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0032] Figure 1 The XRD patterns of LiTFSI-coated Li₂ZrCl₆ prepared in Examples 1-3 of this invention are shown below.

[0033] Figure 2 SEM and EDS images of LiTFSI-coated Li₂ZrCl₆ prepared in Example 2 of this invention;

[0034] Figure 3The lithium deposition / stripping curves are for the symmetric cells of LiTFSI-coated Li2ZrCl6 prepared in Examples 1-3 of this invention and the Li2ZrCl6 prepared in Comparative Example 1. Detailed Implementation

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0037] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0038] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0039] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0040] A preferred embodiment of the present invention provides a method for preparing a surface-coated modified halide solid electrolyte, comprising the following steps:

[0041] S1. LiCl and ZrCl4 raw materials are mixed in a molar ratio of 2:1. Under a protective atmosphere, a halide solid electrolyte is prepared by a two-step ball milling method. The first step ball milling conditions are: ball-to-material mass ratio of (5-15):1, rotation speed of 300-800 rpm, and milling time of 6-24 h. The second step ball milling conditions are: ball-to-material mass ratio of (40-80):1, rotation speed of 300-800 rpm, and milling time of 24-48 h. The resulting halide solid electrolyte material is Li2ZrCl6.

[0042] S2. A halide solid electrolyte with a mass ratio of 90-99.5:10-0.5 is mixed with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and ball-milled under an argon atmosphere at a speed of 100-600 rpm for 1-20 hours. The grinding balls have a diameter of 1-7 mm and are made of at least one of zirconium oxide, alumina, or silicon nitride. The ball-to-material mass ratio is 5-15:1. This yields a surface-modified halide solid electrolyte, denoted as Li₂ZrCl₆-x%LTFSI, where x represents the mass percentage of LTFSI in the overall surface-modified halide solid electrolyte.

[0043] The resulting surface-coated modified halide solid electrolyte can be used in lithium metal secondary batteries as an electrolyte.

[0044] The following are some specific embodiments.

[0045] Example 1

[0046] Inside the glove box, weigh out 0.2668g LiCl and 0.7332g ZrCl4, mix them thoroughly, add them to a zirconium oxide ball mill jar, and seal. The ball-to-material mass ratio is 10:1. Place the ball mill jar in a ball mill and mill at 600 rpm. -1 The first step of ball milling was performed after 12 hours; then the ball-to-material mass ratio was increased to 80:1, and the milling was carried out at 500 rpm. -1 The second step of ball milling was performed by high-energy ball milling for 36 hours to obtain a halide solid electrolyte material with the chemical formula Li2ZrCl6.

[0047] Under an argon atmosphere, 970 mg of Li₂ZrCl₆ and 30 mg of LiTFSI were prepared at a mass ratio of 97:3, resulting in a total precursor material weight of 1 g. The mixture was ball-milled using 3 mm diameter zirconia balls at 300 rpm for 8 hours, with a ball-to-material mass ratio of 10:1. This product is denoted as Li₂ZrCl₆-3%LTFSI.

[0048] Example 2

[0049] Inside the glove box, weigh out 0.2668g LiCl and 0.7332g ZrCl4, mix them thoroughly, add them to a zirconium oxide ball mill jar, and seal. The ball-to-material mass ratio is 10:1. Place the ball mill jar in a ball mill and mill at 600 rpm. -1 The first step of ball milling was performed after 12 hours; then the ball-to-material mass ratio was increased to 80:1, and the milling was carried out at 500 rpm. -1 The second step of ball milling was performed by high-energy ball milling for 36 hours to obtain a halide solid electrolyte material with the chemical formula Li2ZrCl6.

[0050] Under an argon atmosphere, 950 mg of Li₂ZrCl₆ and 50 mg of LiTFSI were prepared at a mass ratio of 95:5, resulting in a total precursor material weight of 1 g. The mixture was ball-milled using 3 mm diameter zirconia balls at 300 rpm for 8 hours, with a ball-to-material mass ratio of 10:1. This product is denoted as Li₂ZrCl₆-5%LTFSI.

[0051] Example 3

[0052] Inside the glove box, weigh out 0.2668g LiCl and 0.7332g ZrCl4, mix them thoroughly, add them to a zirconium oxide ball mill jar, and seal. The ball-to-material mass ratio is 10:1. Place the ball mill jar in a ball mill and mill at 600 rpm. -1 The first step of ball milling was performed after 12 hours; then the ball-to-material mass ratio was increased to 80:1, and the milling was carried out at 500 rpm. -1 The second step of ball milling was performed by high-energy ball milling for 36 hours to obtain a halide solid electrolyte material with the chemical formula Li2ZrCl6.

[0053] Under an argon atmosphere, 900 mg of Li₂ZrCl₆ and 100 mg of LiTFSI were prepared at a mass ratio of 90:10, resulting in a total precursor material weight of 1 g. The mixture was ball-milled using 3 mm diameter zirconia balls at 300 rpm for 8 hours, with a ball-to-material mass ratio of 10:1. This mixture is denoted as Li₂ZrCl₆-10%LTFSI.

[0054] Example 4

[0055] Inside the glove box, weigh out 0.2668g LiCl and 0.7332g ZrCl4, mix them thoroughly, add them to a zirconium oxide ball mill jar, and seal. The ball-to-material mass ratio is 7:1. Place the ball mill jar in a ball mill and mill at 400 rpm. -1The first ball milling step was performed after 18 hours; then the ball-to-material mass ratio was increased to 40:1, and the milling was carried out at 700 rpm. -1 The second step of ball milling was performed by high-energy ball milling for 30 hours to obtain a halide solid electrolyte material with the chemical formula Li2ZrCl6.

[0056] Under an argon atmosphere, 990 mg of Li₂ZrCl₆ and 10 mg of LiTFSI were prepared at a mass ratio of 99:1, resulting in a total precursor material weight of 1 g. The mixture was ball-milled using 3 mm diameter zirconia balls at 200 rpm for 12 hours, with a ball-to-material mass ratio of 12:1. This product is denoted as Li₂ZrCl₆-1%LTFSI.

[0057] Example 5

[0058] Inside the glove box, weigh out 0.2668g LiCl and 0.7332g ZrCl4, mix them thoroughly, add them to a zirconium oxide ball mill jar, and seal. The ball-to-material mass ratio is 12:1. Place the ball mill jar in a ball mill and mill at 700 rpm. -1 The first step of ball milling is performed in the ball mill for 8 hours; then the ball-to-material mass ratio is increased to 100:1, and the milling is carried out at 400 rpm for 1 minute. -1 The second step of ball milling was performed by high-energy ball milling for 42 hours to obtain a halide solid electrolyte material with the chemical formula Li2ZrCl6.

[0059] Under an argon atmosphere, 930 mg of Li₂ZrCl₆ and 70 mg of LiTFSI were prepared at a mass ratio of 93:7, resulting in a total precursor material weight of 1 g. The mixture was ball-milled using 3 mm diameter zirconia balls at a speed of 500 rpm for 4 hours, with a ball-to-material mass ratio of 7:1. This product is denoted as Li₂ZrCl₆-7%LTFSI.

[0060] Comparative Example 1

[0061] This comparative example is a halide solid electrolyte obtained without coating material. The specific preparation method is as follows:

[0062] Inside the glove box, weigh out 0.2668g LiCl and 0.7332g ZrCl4, mix them thoroughly, add them to a zirconium oxide ball mill jar, and seal. The ball-to-material mass ratio is 10:1. Place the ball mill jar in a ball mill and mill at 600 rpm. -1 The first step of ball milling was performed after 12 hours; then the ball-to-material mass ratio was increased to 80:1, and the milling was carried out at 500 rpm. -1The second step of ball milling was performed by high-energy ball milling for 36 hours to obtain a halide solid electrolyte material with the chemical formula Li2ZrCl6.

[0063] The ionic conductivity of the surface-coated modified halide solid electrolytes obtained in Examples 1-3 and the halide solid electrolyte obtained in Comparative Example 1 was obtained by AC impedance spectroscopy. The test frequency range was 1MHz-1Hz, and the test temperature was 25℃. The test method was as follows: 80mg of electrolyte powder was weighed in a glove box, poured into a measuring mold, and a pressure of 380MPa was applied to obtain a cylindrical electrolyte sheet. Its thickness was measured and recorded as L, and its diameter was measured as d. Then, a symmetrical blocked battery of carbon-coated aluminum foil / electrolyte sheet / carbon-coated aluminum foil was assembled in the mold. The AC impedance of the battery under open-circuit conditions was tested, and the obtained impedance value was recorded as R. The impedance was calculated using the formula σ = 4L / πd. 2 R is obtained as the ionic conductivity σ. The test results are shown in Table 1:

[0064] Table 1

[0065] Components <![CDATA[Ionic conductivity (mS cm -1 )]]> Example 1 <![CDATA[Li2ZrCl6-3%LTFSI]]> 0.36 Example 2 <![CDATA[Li2ZrCl6-5%LTFSI]]> 0.31 Example 3 <![CDATA[Li2ZrCl6-10%LTFSI]]> 0.24 Example 4 <![CDATA[Li2ZrCl6-1%LTFSI]]> 0.38 Example 5 <![CDATA[Li2ZrCl6-7%LTFSI]]> 0.29 Comparative Example 1 <![CDATA[Li2ZrCl6]]> 0.42

[0066] As shown in Table 1, with the increase of LTFSI coating (0-10%), the ionic conductivity of Li₂ZrCl₆ electrolyte gradually decreases (from 0.42 mS / cm⁻¹ in Li₂ZrCl₆). -1 The concentration of Li₂ZrCl₆-10%LTFSI decreased to 0.24 mS / cm. -1 This is attributed to the insufficient ionic conductivity of LTFSI itself.

[0067] The following are the characterization analysis and current cycling tests.

[0068] XRD tests were performed on the surface-coated modified halide solid electrolytes obtained in Examples 1-3 and the halide solid electrolyte obtained in Comparative Example 1. Figure 1 It was found that all four samples belonged to the trigonal crystal system with space group P3_1c. Among them, the broad peak at 13-23° was the peak of PI tape.

[0069] Compared to Li₂ZrCl₆, the Li₂ZrCl₆-x%LTFSI (x = 3, 5, 10) samples showed no impurity peaks, indicating good chemical stability between LTFSI and Li₂ZrCl₆. No obvious LTFSI characteristic peaks were observed in the Li₂ZrCl₆-x%LTFSI (x = 3, 5, 10) samples. It is speculated that the higher peak intensity of Li₂ZrCl₆ makes the characteristic peaks of LTFSI difficult to detect. Overall, XRD analysis confirms the successful synthesis of LTFSI and Li₂ZrCl₆ and their good chemical compatibility.

[0070] SEM analysis of the coating effect, combined with energy-dispersive X-ray spectroscopy results and referencing the inherent Zr and Cl signals of Li₂ZrCl₆, revealed a uniform F signal distribution on the Li₂ZrCl₆ surface. This indicates that LiTFSI is uniformly distributed on the Li₂ZrCl₆ surface. Figure 2 ).

[0071] Inside an argon-filled glove box, to verify the compatibility of the electrolytes prepared in the above embodiments or comparative examples with the lithium metal anode, a lithium / electrolyte / lithium symmetric battery was assembled and subjected to a step-current cycling test. First, 80 mg of electrolyte was pressed into a circular sheet of a certain thickness using a 10 mm inner diameter PEEK insulating outer cylinder at a pressure of 380 MPa. Then, two lithium metal sheets, each 10 mm in diameter and 100 μm thick, were adhered to both sides of the electrolyte. The current density was 0.1 mA cm⁻¹. -2 .

[0072] To investigate the effect of LTFSI coating on lithium dendrite formation, at 0.1 mA cm⁻¹... -2 At a current density of [value missing], the cycle performance of lithium-lithium symmetric batteries containing the Li₂ZrCl₆-x%LTFSI electrolyte prepared in Examples 1-3 was tested. Figure 3 The results showed that 3-10% LTFSI coatings improved the cycling performance of lithium-lithium symmetric batteries containing Li2ZrCl6 electrolyte compared to pure Li2ZrCl6. Specifically, after 60 hours of cycling, the lithium-lithium symmetric battery containing Li2ZrCl6-5% LTFSI electrolyte exhibited less voltage polarization, and the interfacial stability between the Li2ZrCl6-5% LTFSI electrolyte and lithium metal was significantly improved. This stability may be attributed to the formation of an interfacial phase with high ionic conductivity after the reaction of Li2ZrCl6-5% LTFSI electrolyte with lithium metal. Furthermore, the low ionic conductivity of LTFSI on the particle surface and between particles hinders the flow of electrons into the electrolyte, effectively preventing the growth of lithium dendrites into the electrolyte. In contrast, the symmetric battery containing pure Li2ZrCl6 electrolyte reached the upper limit of the instrument range (5V) after approximately 60 hours of cycling. The high voltage polarization of the symmetric battery containing pure Li2ZrCl6 electrolyte is attributed to the formation of byproducts with low ionic conductivity and the increase in interfacial impedance.

[0073] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a surface-coated modified halide solid electrolyte, characterized in that, Includes the following steps: S1. Preparation of halide solid electrolytes; S2. The halide solid electrolyte is mixed with lithium salt and ball milled to obtain a surface-coated modified halide solid electrolyte.

2. The method for preparing a surface-coated modified halide solid electrolyte according to claim 1, characterized in that, In step S1, the raw materials for the halide solid electrolyte are LiCl and ZrCl4.

3. The method for preparing a surface-coated modified halide solid electrolyte according to claim 1, characterized in that, In step S1, a halide solid electrolyte is prepared by a two-step ball milling method.

4. The method for preparing a surface-coated modified halide solid electrolyte according to claim 3, characterized in that, In the two-step ball milling method, the ball milling conditions for the first step are: a ball-to-material mass ratio of (5-15):1, a rotation speed of 300-800 rpm, and a ball milling time of 6-24 h; the ball milling conditions for the second step are: a ball-to-material mass ratio of (40-120):1, a rotation speed of 300-800 rpm, and a ball milling time of 24-48 h.

5. The method for preparing a surface-coated modified halide solid electrolyte according to claim 3, characterized in that, In both steps S1 and S2, the ball milling is carried out under a protective atmosphere.

6. The method for preparing a surface-coated modified halide solid electrolyte according to claim 1, characterized in that, In step S2, the lithium salt is lithium bis(trifluoromethanesulfonylimide)LiTFSI.

7. The method for preparing a surface-coated modified halide solid electrolyte according to claim 1, characterized in that, In step S2, the mass ratio of the halide solid electrolyte to the lithium salt is 90-99.5:10-0.

5.

8. The method for preparing a surface-coated modified halide solid electrolyte according to claim 1, characterized in that, In step S2, the ball milling speed is 100-600 rpm and the time is 1-20 h; and / or the ball-to-material mass ratio is 5-15:

1.

9. A surface-coated modified halide solid electrolyte, characterized in that, Prepared by the method according to any one of claims 1-8.

10. The application of a surface-coated modified halide solid electrolyte according to claim 9 in lithium metal secondary batteries.

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