Method for preparing a composite sulfide electrolyte and use thereof

Abstract

The application discloses a preparation method and application of a composite sulfide electrolyte, belongs to the technical field of lithium batteries, and aims to solve the technical problems of poor interface stability of a traditional sulfide electrolyte and lithium metal electrode and short cycle life of a lithium metal battery. The preparation method comprises the following steps: grinding and uniformly mixing lithium salt A and lithium salt B according to a specific mass ratio, and then grinding and mixing the sulfide electrolyte after ball milling, so as to obtain the composite sulfide electrolyte; wherein the lithium salt A is selected from fluorine-containing lithium salts such as lithium hexafluorophosphate, the lithium salt B is selected from coordination type lithium salts such as lithium nitrate, the two are synergistically compounded, and the total addition amount of the lithium salt is 5-20 wt%. Through the synergistic modification of the double lithium salts, the application in-situ constructs a dense and stable electrode-electrolyte interface, greatly reduces the system bulk impedance, and inhibits the side reaction and lithium dendrite growth; electrochemical tests show that, compared with the single lithium salt modified sample and the pure sulfide electrolyte, the composite electrolyte impedance spectrum is complete, the bulk resistance is significantly reduced, the assembled lithium metal symmetric battery can realize nearly 3000 hours of super-long stable cycle, the overpotential is flat without burrs, and the composite electrolyte has excellent ion conductivity and interface stability. The application has the advantages of simple process, no need of complex sintering equipment, and suitability for industrialized preparation, and provides an efficient modification scheme for long-life all-solid-state lithium metal batteries.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery technology, specifically relating to a method for preparing and applying a composite sulfide electrolyte. Background Technology

[0002] All-solid-state lithium metal batteries combine ultra-high energy density and safety, making them a core direction for next-generation energy storage technology. Sulfide electrolytes, due to their excellent room-temperature ionic conductivity and good machinability, have become the preferred materials in this field, with typical examples being sulfide-silver-germanium compounds such as Li6PS5Cl. However, the poor interfacial stability between sulfide electrolytes and lithium metal electrodes is a core bottleneck restricting their industrialization. The two have inherent chemical incompatibility, easily generating insulating byproducts such as Li2S, leading to a surge in interfacial resistance. Uneven lithium-ion deposition during charging and discharging forms lithium dendrites, easily causing short-circuit risks. Furthermore, the porosity defects at the solid-solid interface require external pressure to maintain contact, increasing the complexity of the battery structure. While existing modification strategies can improve interfacial performance to some extent, they suffer from problems such as complex processes, high costs, or insufficient stability. Adding lithium salts to the electrolyte interface can improve interfacial stability and fill pores, but there is currently no technology to directly composite lithium salts with sulfide electrolytes to solve the aforementioned interfacial problems. Therefore, developing a simple and efficient sulfide electrolyte modification scheme is of great practical value. Summary of the Invention

[0003] The purpose of this invention is to address the shortcomings of the prior art by proposing a method for preparing a composite sulfide electrolyte. The composite sulfide electrolyte prepared by this invention exhibits high stability to lithium metal and extremely low process complexity, effectively solving the interface problems of traditional sulfide electrolytes.

[0004] To achieve the above-mentioned objectives, the present invention is implemented through the following technical solution. A method for preparing a composite sulfide electrolyte, characterized by comprising the following steps: Step 1: Mix and grind lithium salt A and lithium salt B in a certain proportion to obtain a uniformly mixed lithium salt. Step 2: Ball mill the sulfide electrolyte to obtain a low-particle-size sulfide electrolyte; Step 3: Mix the uniformly mixed lithium salt obtained in Step 1 and the low-particle-size sulfide electrolyte obtained in Step 2 in a certain proportion and grind them to obtain a composite sulfide electrolyte.

[0005] Furthermore, the method for preparing the composite sulfide electrolyte is characterized in that, in step 1, the lithium salt A is at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide; the lithium salt B is at least one of lithium bis(oxalateborate), lithium difluorooxalateborate, and lithium nitrate; and the mass ratio of lithium salt A to lithium salt B is 1:(0~1).

[0006] Furthermore, the method for preparing the composite sulfide electrolyte is characterized in that the sulfide electrolyte in step 2 is Li6PS5Cl, Li 5.5 PS 4.5 Cl 1.5 , Li6PS5Br, Li6PS5I, Li6PS5Cl 0.25 Br 0.75 Li 5.3 PS 4.3 ClBr 0.7 Li₂S-P₂S₅, Li 10 GeP2S 12 At least one of the following; the ball milling speed in step 2 is 300~500 rpm, and the ball milling time is 5~20 h; the particle size of the sulfide electrolyte after ball milling is D50=0.5~20 μm.

[0007] Furthermore, the method for preparing the composite sulfide electrolyte is characterized in that, in step 3, the mass ratio of the uniformly mixed lithium salt to the composite sulfide electrolyte is 5~20wt%.

[0008] Another object of the present invention is to provide a composite sulfide electrolyte prepared by the above-described method for preparing composite sulfide electrolyte.

[0009] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention adopts a technical solution of binary compound modified sulfide with dual lithium salts. Through the synergistic effect of binary lithium salts, a solid electrolyte interface phase rich in LiF and LIN can be generated on the electrode surface, and a uniform and dense electrode-electrolyte stable interface can be constructed in situ. This effectively suppresses side reactions on the lithium metal anode surface and blocks the growth of lithium dendrites. It solves the core defects of pure sulfide electrolyte interface instability, many burrs in the cycle curve, and short-term battery failure. It significantly improves the stability and cycle efficiency of lithium metal anode and achieves ultra-long cycle stability of lithium metal symmetric battery.

[0010] 2. The present invention uses direct grinding and mixing to complete the composite preparation. Compared with traditional modification methods such as ball milling and high-temperature sintering, the process complexity is greatly reduced, no complicated equipment is required, the industrial production cost is reduced, and it is easier to achieve large-scale production. Attached Figure Description

[0011] Figure 1 A schematic diagram of the preparation process of a composite sulfide solid electrolyte provided by the present invention; Figure 2 Impedance curves of the composite sulfide electrolytes prepared in Example 1 and the comparative example at room temperature; Figure 3The impedance curve of the composite sulfide electrolyte prepared in Example 2 at room temperature; Figure 4 The graph shows the long-cycle performance of the composite sulfide electrolytes prepared in Example 2 and the comparative example in lithium symmetric batteries. Detailed Implementation

[0012] The technical solutions of the present invention will be further described below with reference to the accompanying drawings, embodiments, and comparative examples.

[0013] Example 1

[0014] This embodiment provides a method for preparing a composite sulfide electrolyte, including the following steps: Step 1: Grind lithium hexafluorophosphate separately to obtain lithium salt with uniform particle size (the addition ratio of lithium salt B is 0, that is, the mass ratio of lithium salt A to lithium salt B is 1:0). Step 2: The sulfide electrolyte is ball-milled at 400 rpm for 10 hours to obtain a low-particle-size sulfide electrolyte with D50≈10μm. Step 3: Mix and grind the uniform lithium salt obtained in Step 1 and the low-particle-size sulfide electrolyte obtained in Step 2 to obtain a composite sulfide electrolyte, wherein the lithium salt accounts for 5 wt% of the composite sulfide electrolyte.

[0015] Example 2

[0016] This embodiment provides a method for preparing a composite sulfide electrolyte, comprising the following steps: Step 1: Mix and grind lithium hexafluorophosphate and lithium nitrate to obtain a uniformly mixed lithium salt, wherein the mass ratio of lithium hexafluorophosphate to lithium nitrate is 1:1; Step 2: The sulfide electrolyte is ball-milled at 400 rpm for 10 hours to obtain a low-particle-size sulfide electrolyte with D50≈10μm. Step 3: Mix and grind the uniformly mixed lithium salt obtained in Step 1 and the low-particle-size sulfide electrolyte obtained in Step 2 to obtain a composite sulfide electrolyte, wherein the mass ratio of the mixed lithium salt to the composite sulfide electrolyte is 10 wt% (lithium hexafluorophosphate and lithium nitrate each account for 5 wt%).

[0017] Comparative Example This comparative example uses the unmodified original sulfide electrolyte. The sulfide electrolyte was ball-milled according to the parameters of step 2 in Example 1 to obtain a low particle size sulfide electrolyte with D50≈10μm, without the addition of any lithium salt.

[0018] The composite sulfide electrolytes prepared in Examples 1, 2, and the comparative example were assembled into steel mold batteries for ionic conductivity performance testing. The ionic conductivity testing method was as follows: 100 mg of composite electrolyte was placed into a 10 mm diameter mold. Two 10 mm diameter steel cylindrical electrodes were pressed onto the upper and lower sides of the composite electrolyte, respectively. A pressure of 300 MPa was applied for 10 minutes to compact the electrolyte, followed by a 5 MPa pressure test. The electrodes were connected to an AC impedance instrument for testing, with a voltage excitation amplitude of 5 mV and a frequency range of 1 MHz to 1 Hz. AC impedance spectra were plotted, and the ionic conductivity was calculated. The formula for calculating ionic conductivity is: Ionic conductivity = electrolyte thickness / (resistance * electrode area).

[0019] Wherein, the unit of ionic conductivity is mS / cm, the unit of electrolyte thickness is cm, the unit of resistance is Ω, and the electrode area is fixed at 0.785cm². 2 .

[0020] Example 1, with only 5% lithium hexafluorophosphate added, showed an impedance spectrum with only incomplete arc segments in the high-frequency region, failing to form a complete impedance semicircle, with an impedance of approximately 175Ω. Example 2, using a composite system of 5% lithium hexafluorophosphate and 5% lithium nitrate, exhibited a complete characteristic arc in its impedance spectrum, clearly distinguishing between the bulk impedance in the high-frequency region and the interfacial impedance in the mid-to-low-frequency region. The bulk impedance was as low as 50Ω, while the interfacial impedance was 150Ω. These results indicate that single-component modification with lithium hexafluorophosphate is insufficient to construct a complete conductive and ion transport network, resulting in poor interparticle contact within the electrolyte. However, the synergistic combination of lithium hexafluorophosphate and lithium nitrate significantly reduces the bulk impedance of the system, optimizes the interfacial contact state, and improves ion transport efficiency and interfacial stability.

[0021] The lithium metal symmetric battery assembled from the sample of Example 2 and the pure sulfide sample was subjected to long-cycle performance testing. The lithium metal symmetric battery assembled from the composite sulfide electrolyte prepared in Example 2 was subjected to constant-current charge-discharge cycling. The assembly method of the lithium metal symmetric battery was as follows: 100 mg of composite electrolyte was placed into a 10 mm diameter mold; two 10 mm diameter steel cylindrical electrodes were pressed onto the upper and lower sides of the composite electrolyte, respectively, and a pressure of 300 MPa was applied for 10 minutes to compact it; two 10 mm diameter lithium metal sheets were then attached to both sides of the electrolyte, and the steel cylindrical electrodes were reinstalled. The test was conducted while maintaining a pressure of 5 MPa, with a current density of 0.1 mA / cm². 2 Surface density 0.1mAh / cm³ 2 .

[0022] The results showed that the initial overpotential of the sample in Example 2 was only 20mV, and after nearly 3000 hours of cycling, the overpotential slowly increased to 40mV. Throughout the cycling process, the voltage curve was stable and regular without significant spikes or fluctuations, demonstrating excellent cycle stability and interfacial compatibility. In contrast, the pure sulfide sample had a low initial overpotential (10mV), but extremely poor cycle stability. After only 400 hours of cycling, the overpotential spiked sharply to over 300mV, leading to rapid battery failure. Furthermore, the voltage curve exhibited frequent spikes and severe fluctuations during cycling. These results fully demonstrate that, compared to the pure sulfide system, the combined modification of lithium hexafluorophosphate and lithium nitrate can effectively regulate the interface state of the lithium metal anode, suppress interfacial side reactions and lithium dendrite growth, construct a stable and durable electrode-electrolyte interface, significantly extend the cycle life of lithium metal batteries, and improve the long-term reliability of the battery.

[0023] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention, and within the spirit and principles of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a composite sulfide electrolyte, characterized in that, Includes the following steps: Step 1: Mix and grind lithium salt A and lithium salt B in a certain proportion to obtain a uniformly mixed lithium salt. Step 2: Ball mill the sulfide electrolyte to obtain a low-particle-size sulfide electrolyte; Step 3: Mix the uniformly mixed lithium salt obtained in Step 1 and the low-particle-size sulfide electrolyte obtained in Step 2 in a certain proportion and grind them to obtain a composite sulfide electrolyte.

2. The method for preparing the composite sulfide electrolyte according to claim 1, characterized in that, In step 1, lithium salt A is at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide; lithium salt B is at least one of lithium bis(oxalateborate), lithium difluorooxalateborate, and lithium nitrate; and the mass ratio of lithium salt A to lithium salt B is 1:(0~1).

3. The method for preparing the composite sulfide electrolyte according to claim 1, characterized in that, The sulfide electrolyte mentioned in step 2 is Li6PS5Cl, Li 5.5 PS 4.5 Cl 1.5 , Li6PS5Br, Li6PS5I, Li6PS5Cl 0.25 Br 0.75 Li 5.3 PS 4.3 ClBr 0.7 Li₂S-P₂S₅, Li 10 GeP2S 12 At least one of the following; the ball milling speed in step 2 is 300~500 rpm, and the ball milling time is 5~20 h; the particle size of the sulfide electrolyte after ball milling is D50=0.5~20 μm.

4. The method for preparing the composite sulfide electrolyte according to claim 1, characterized in that, In step 3, the mass ratio of the uniformly mixed lithium salt to the composite sulfide electrolyte is 5-20 wt%.

5. A composite sulfide electrolyte, characterized in that, It is prepared by the preparation method according to any one of claims 1-4.

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