Negative electrode interface composite buffer layer, preparation method and solid-state lithium metal battery

Abstract

The invention discloses a negative electrode interface composite buffer layer, a preparation method and a solid-state lithium metal battery. The negative electrode interface composite buffer layer is composed of ceramic particles, a polymer matrix and a lithium salt. The solid-state lithium metal battery comprises a positive electrode, a polymer solid electrolyte, a negative electrode interface composite buffer layer and a negative electrode. The main polymer component of the polymer solid electrolyte is polyoxyethylene; the polymer solid electrolyte contains a butanedinitrile plasticizer; and the main component of the negative electrode is lithium metal. The negative electrode interface composite buffer layer provided by the invention can inhibit the growth of lithium dendrites and isolate the corrosion of succinonitrile in an electrolyte to lithium metal, and can form alloy components and a stable lithium compound at the same time, thereby improving the stability of an electrolyte / lithium interface and prolonging the cycle life of a solid-state lithium metal battery.

Description

Technical Field

[0001] This invention belongs to the field of solid-state battery technology, specifically relating to a negative electrode interface composite buffer layer and its preparation method, and a solid-state lithium metal battery. Background Technology

[0002] Lithium metal boasts an extremely high theoretical capacity (3860 mA hg). -1 ) and a low redox potential (−3.04 V) vs. The standard hydrogen electrode (HME) gives lithium metal batteries a promising future. However, in traditional liquid lithium metal battery systems, uneven lithium deposition and continuous growth of lithium dendrites can easily cause internal short circuits, posing safety hazards such as combustion and explosion, which severely restricts their practical application in electrochemical energy storage. Polymer solid electrolytes, due to their excellent flexibility, processability, scalability, and high safety, are considered one of the most promising electrolyte systems for all-solid-state lithium metal batteries.

[0003] However, polymer solid electrolytes, represented by polyethylene oxide (PEO), exhibit poor chain segment mobility at room temperature, resulting in low ionic conductivity. They typically require operation above 50°C, significantly limiting their application range. Numerous studies have shown that introducing plasticizers (such as succinic anionylene, SN) into polymer solid electrolytes can significantly improve their ionic conductivity. However, the addition of plasticizers often brings a series of serious interface problems, primarily due to their high reactivity with the lithium metal anode, easily triggering continuous interfacial corrosion reactions, causing electrolyte / lithium interface failure, and thus significantly shortening battery life. Furthermore, the electrolyte-lithium anode interface faces other challenges, such as uneven lithium deposition. During repeated charge-discharge cycles, lithium dendrites and interfacial voids easily form on the lithium metal anode surface. These voids increase local current density, further exacerbating dendrite growth and severely impacting the cycle life of solid-state lithium metal batteries. Therefore, developing an interface optimization strategy that can both suppress the chemical corrosion of the lithium metal anode by electrolyte components and promote uniform lithium deposition is crucial for advancing the development and application of polymer-based all-solid-state lithium metal batteries capable of stable operation at room temperature. Summary of the Invention

[0004] To address the problems existing in the above-mentioned background art, the first aspect of the present invention is to provide a negative electrode interface composite buffer layer, which is composed of ceramic particles, a polymer matrix and a lithium salt.

[0005] Furthermore, the thickness of the negative electrode interface composite buffer layer is 2-10 μm.

[0006] Furthermore, the ceramic particles are one or a combination of more than one of aluminum nitride, magnesium nitride, gallium fluoride, and magnesium fluoride.

[0007] Furthermore, the polymer matrix is ​​one or more of polyethylene oxide, polyvinylidene fluoride, and polyvinylidene fluoride-hexafluoropropylene copolymer.

[0008] Furthermore, the lithium salt is one or a combination of more than one of lithium bis(trifluoromethanesulfonyl)imide, lithium perchlorate, and lithium bis(fluorosulfonyl)imide.

[0009] The second aspect of this invention is to provide a method for preparing a negative electrode interface composite buffer layer, comprising the following steps: 1) Add 1-2 parts by weight of lithium salt to 30-60 parts by weight of solvent and stir for the first time. Then add 1-2 parts by weight of polymer matrix and stir for the second time under heating conditions. After the polymer matrix is ​​completely dissolved, add 4-12 parts by weight of ceramic particles and stir for the third time to obtain the negative electrode interface composite precursor solution. 2) Drop the negative electrode interface composite precursor solution onto a substrate coated with polytetrafluoroethylene, set the spin coating parameters, and spin coat to obtain a substrate coated with the precursor solution. 3) The substrate coated with the precursor solution is dried under an inert atmosphere to obtain a negative electrode interface composite buffer layer attached to the substrate. 4) Attach the polymer solid electrolyte to the negative electrode interface composite buffer layer on the dried substrate, and transfer the buffer layer to the surface of the polymer solid electrolyte membrane by pressing or rolling.

[0010] Further, in step 1), the solvent is one or more of acetonitrile, N-methylpyrrolidone, and N,N-dimethylformamide; the heating temperature during the second stirring is 50-80℃, and the heating and stirring time is 3-9h; the spin coating parameters in step 2) are: rotation speed 1000-2000 rpm, spin coating time 5-15 s; in step 3), the inert atmosphere is argon or nitrogen, and the drying parameters are: temperature 40-80℃, time 10-30 min.

[0011] The third invention relates to providing a solid-state lithium metal battery with a negative electrode interface composite buffer layer, comprising a positive electrode, a polymer solid electrolyte, a negative electrode interface composite buffer layer, and a negative electrode. The negative electrode interface composite buffer layer is fabricated by spin-coating-transfer printing and is disposed at the interface between the polymer solid electrolyte and the lithium metal negative electrode. This negative electrode interface composite buffer layer can both inhibit lithium dendrite growth to prevent electrolyte puncture and induce the formation of a more stable interface component, promoting the formation of Li... + Rapid migration and regulation of lithium nucleation and uniform deposition enhance the electrochemical performance of solid-state lithium metal batteries and extend battery life.

[0012] Furthermore, the positive electrode is an electrode sheet containing one or more positive electrode active materials selected from lithium iron phosphate, nickel cobalt manganese ternary materials; the main polymer component of the polymer solid electrolyte is polyethylene oxide; the polymer solid electrolyte contains succinic acid plasticizer; and the main component of the negative electrode is lithium metal.

[0013] Compared with the prior art, the present invention has the following beneficial effects: 1) The negative electrode interface composite buffer layer in this invention has a dense structure, in which uniformly distributed rigid ceramic particles can effectively block and suppress the puncture growth of lithium dendrites, thereby improving the safety of the battery. 2) The ceramic particles in the buffer layer can react in situ with lithium metal to generate lithium-aluminum alloys, lithium-magnesium alloys, etc. These alloy phases can significantly reduce the nucleation overpotential of lithium and guide the uniform nucleation and deposition of lithium. At the same time, lithium compounds such as LiF and Li3N with high ionic conductivity and high mechanical modulus are generated, which together construct a stable interface layer with both high ionic conductivity and excellent mechanical strength. 3) The negative electrode interface composite buffer layer in this invention can also serve as an effective physical barrier layer to prevent active plasticizer molecules such as succinate (SN) in the polymer solid electrolyte from directly contacting and corroding the lithium metal negative electrode, thereby avoiding the increase in impedance and capacity decay caused by continuous interface side reactions. 4) The spin-coating-transfer printing method used in this invention is simple, low-cost, and easy to scale up. Moreover, the buffer layer has good compatibility and adhesion with mainstream PEO-based solid electrolytes and lithium anodes, and can form a tight solid-solid contact, effectively reducing interface impedance. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the negative electrode interface composite buffer layer prepared in Example 1 of the present invention bonded to a polymer solid electrolyte. Figure 2 This is a scanning electron microscope (SEM) image of the cross-section of the composite buffer layer at the negative electrode interface in Example 1. Figure 3 The X-ray diffraction (XRD) pattern of the composite buffer layer at the negative electrode interface in Example 1; Figure 4 The lithium-symmetric battery assembled using the buffer layer of Example 1 at 0.1 mA cm⁻¹ -2 Long-cycle performance at current density; Figure 5 The graph shows the cycle performance of the solid-state lithium metal full cell assembled using the buffer layer of Example 1 at 30°C. Figure 6 This is an SEM image of the surface of the composite buffer layer at the negative electrode interface in Example 2; Figure 7The cycling performance diagram shows the lithium symmetric battery assembled using the buffer layer of Example 2. Figure 8 This is an SEM image of the surface of the composite buffer layer at the negative electrode interface in Example 3; Figure 9 The cycling performance diagram shows the lithium symmetric battery assembled using the buffer layer of Example 3. Figure 10 The graph shows the cycle performance of the lithium symmetric battery in Comparative Example 1 (without a buffer layer). Figure 11 The full-cell cycle performance diagram is for Comparative Example 1 (without buffer layer). Figure 1 In this composition, 1-a polymer matrix and lithium salt are combined, 2-ceramic particles are formed, and 3-a polymer solid electrolyte is formed. Detailed Implementation

[0015] The present invention will be further described below with reference to the accompanying drawings and specific embodiments in order to better understand the present technical solution.

[0016] Example 1: A solid-state lithium metal battery with a negative electrode interface composite buffer layer The specific preparation steps are as follows: S1. Preparation of the precursor solution for the negative electrode interface composite buffer layer: Add 0.15 g of LiTFSI to 6 g of anhydrous acetonitrile and stir at 400 rpm for 5 min at room temperature. Then add 0.2 g of polyethylene oxide (PEO) and heat and stir at 50°C and 400 rpm for 7 h. After the PEO is completely dissolved, add 0.8 g of aluminum nitride (AlN) ceramic particles and continue to heat and stir at 40°C and 500 rpm for 3 h to obtain the negative electrode interface composite precursor solution.

[0017] S2. Preparation of polymer solid electrolyte: 0.2 g of LiTFSI was added to 8 g of anhydrous acetonitrile and stirred at 400 rpm for 5 min at room temperature. Then, 0.6 g of PEO powder was added and heated and stirred at 60℃ and 400 rpm for 9 h. After stirring evenly, the resulting solution was poured into a 4 cm × 8 cm silicone mold and dried at room temperature for 12 h in an environment with humidity <20%, and then dried at 50℃ for 12 h.

[0018] S3. Drop the negative electrode interface composite buffer layer precursor solution obtained in S1 onto a circular glass plate coated with polytetrafluoroethylene (PTFE). Set the spin coating speed to 1000 rpm and the spin coating time to 15 s. Turn on the vacuum pump to tighten the circular glass plate and start spin coating.

[0019] S4. The substrate coated with the precursor solution of the negative electrode interface composite buffer layer obtained in S2 is heated at 40°C for 30 min in a glove box under an argon atmosphere to obtain the negative electrode interface composite buffer layer.

[0020] S5. Attach the PEO-based polymer solid electrolyte obtained in S2 to the negative electrode interface composite buffer layer that has been dried and coated on the substrate in S4, and press or roll it, then peel it off. This will make the negative electrode interface composite buffer layer tightly adhere to the PEO-based polymer solid electrolyte.

[0021] The structure of the negative electrode interface composite buffer layer bonded to the surface of the PEO-based polymer solid electrolyte obtained in this embodiment is as follows: Figure 1 As shown; its cross-sectional scanning electron microscope image is as follows. Figure 2 As shown, the thickness of the negative electrode interface composite buffer layer is approximately 4 μm; the XRD image of the negative electrode interface composite buffer layer in this embodiment is shown below. Figure 3 As shown, the characteristic peaks of AlN are obvious; a lithium-ion symmetric battery was assembled by attaching a composite buffer layer at the negative electrode interface prepared in Example 1 to both sides of the PEO-based polymer solid electrolyte, and tested at 30°C with a current of 0.1 mA cm⁻¹. -2 and 0.1 mAh cm -2 Under these conditions, repeated lithium plating / stripping is performed, and the cycle curve is as follows: Figure 4 As shown, it can cycle stably for 2000 hours without short circuit; a solid-state lithium metal battery is assembled by attaching the negative electrode interface composite buffer layer prepared in Example 1 to only one side, wherein the positive electrode is lithium iron phosphate, and its cycling performance at 30°C is as follows. Figure 5 As shown, the initial discharge specific capacity is 162 mAh g. -1 The discharge specific capacity after 600 cycles is 121 mAh g. -1 .

[0022] Example 2: A solid-state lithium metal battery with a negative electrode interface composite buffer layer The specific preparation steps are as follows: S1. Preparation of the precursor solution for the negative electrode interface composite buffer layer: Add 0.3 g of LiFSI to 7 g of N-methylpyrrolidone (NMP) and stir at 300 rpm for 10 min at room temperature. Then add 0.3 g of polyvinylidene fluoride (PVDF) and heat and stir at 80℃ and 300 rpm for 3 h. After the PVDF is completely dissolved, add 0.6 g of magnesium nitride (Mg3N2) ceramic particles and continue to heat and stir at 80℃ and 300 rpm for 6 h to obtain the negative electrode interface composite precursor solution.

[0023] S2. Preparation of polymer solid electrolyte: 0.2 g of LiTFSI was added to 8 g of anhydrous acetonitrile and stirred at 500 rpm for 5 min at room temperature. Then, 0.6 g of PEO powder was added and heated and stirred at 60℃ and 500 rpm for 5 h. After stirring evenly, the resulting solution was poured into a 4 cm × 8 cm silicone mold and dried at room temperature for 12 h in an environment with humidity <20%, and then dried at 50℃ for 12 h.

[0024] S3. Drop the negative electrode interface composite buffer layer precursor solution obtained in S1 onto a circular glass plate coated with polytetrafluoroethylene (PTFE). Set the spin coating speed to 1500 rpm and the spin coating time to 10 s. Turn on the vacuum pump to tighten the circular glass plate and start spin coating.

[0025] S4. The substrate coated with the precursor solution of the negative electrode interface composite buffer layer obtained in S2 is heated at 70°C for 10 min in a glove box under nitrogen atmosphere to obtain the negative electrode interface composite buffer layer.

[0026] S5. Attach the PEO-based polymer solid electrolyte obtained in S2 to the negative electrode interface composite buffer layer that has been dried and coated on the substrate in S4, and press or roll it, then peel it off. This will make the negative electrode interface composite buffer layer tightly adhere to the PEO-based polymer solid electrolyte.

[0027] The scanning electron microscope image of the negative electrode interface composite buffer layer bonded to the surface of the PEO-based polymer solid electrolyte obtained in this embodiment is as follows: Figure 6 As shown, Mg3N2 particles are uniformly distributed and embedded in the PVDF polymer matrix; a lithium-ion symmetric battery is assembled by attaching the negative electrode interface composite buffer layer prepared in this embodiment to both sides of the PEO-based polymer solid electrolyte. The battery is tested at 30°C with a current of 0.1 mA cm⁻¹. -2 and 0.1 mAh cm -2 Under these conditions, repeated lithium plating / stripping is performed, and the cycle curve is as follows: Figure 7 As shown, it can stably cycle for 800 hours without short circuit; a solid-state lithium metal battery is assembled by attaching the negative electrode interface composite buffer layer prepared in this embodiment to only one side, wherein the positive electrode is lithium iron phosphate, and its initial discharge specific capacity at 30°C is 156 mAh g. -1 The discharge specific capacity after 300 cycles is 143 mAh g. -1 .

[0028] Example 3: A solid-state lithium metal battery with a negative electrode interface composite buffer layer The specific preparation steps are as follows: S1. Preparation of the precursor solution for the negative electrode interface composite buffer layer: Add 0.15 g of LiClO4 to 9 g of N,N-dimethylformamide (DMF) and stir at 400 rpm for 5 min at room temperature. Then add 0.2 g of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) and heat and stir at 70℃ and 550 rpm for 9 h. After PVDF-HFP is completely dissolved, add 1.8 g of gallium fluoride (GaF3) ceramic particles and continue to heat and stir at 70℃ and 500 rpm for 5 h to obtain the negative electrode interface composite precursor solution.

[0029] S2. Preparation of polymer solid electrolyte: 0.2 g of LiTFSI was added to 8 g of anhydrous acetonitrile and stirred at 400 rpm for 5 min at room temperature. Then, 0.6 g of PEO powder was added and heated and stirred at 60℃ and 400 rpm for 9 h. After stirring evenly, the resulting solution was poured into a 4 cm × 8 cm silicone mold and dried at room temperature for 12 h in an environment with humidity <20%, and then dried at 50℃ for 12 h.

[0030] S3. Drop the negative electrode interface composite buffer layer precursor solution obtained in S1 onto a circular glass plate coated with polytetrafluoroethylene (PTFE). Set the spin coating speed to 2000 rpm and the spin coating time to 5 s. Turn on the vacuum pump to tighten the circular glass plate and start spin coating.

[0031] S4. The substrate coated with the precursor solution of the negative electrode interface composite buffer layer obtained in S2 is heated at 80°C for 20 min in a glove box under an argon atmosphere to obtain the negative electrode interface composite buffer layer.

[0032] S5. Attach the PEO-based polymer solid electrolyte obtained in S2 to the negative electrode interface composite buffer layer that has been dried and coated on the substrate in S4, and press or roll it, then peel it off. This will make the negative electrode interface composite buffer layer tightly adhere to the PEO-based polymer solid electrolyte.

[0033] The scanning electron microscope image of the negative electrode interface composite buffer layer bonded to the surface of the PEO-based polymer solid electrolyte obtained in this embodiment is as follows: Figure 8 As shown, CaF2 particles are uniformly distributed and embedded in the PVDF-HFP polymer matrix; a lithium-ion symmetric battery is assembled by attaching a composite buffer layer at the negative electrode interface prepared in Example 3 to both sides of the PEO-based polymer solid electrolyte. The battery is tested at 30°C with a current of 0.1 mA cm⁻¹. -2 and 0.1 mAh cm -2 Under these conditions, repeated lithium plating / stripping is performed, and the cycle curve is as follows: Figure 9As shown, it can cycle stably for 1700 h without short circuit; a solid-state lithium metal battery is assembled by attaching the negative electrode interface composite buffer layer prepared in this embodiment to only one side, wherein the positive electrode is lithium iron phosphate, and its initial discharge specific capacity at 30°C is 151 mAh g. -1 The discharge specific capacity after 400 cycles is 139 mAh g. -1 .

[0034] Example 4: A solid-state lithium metal battery with a negative electrode interface composite buffer layer The specific preparation steps are as follows: S1. Preparation of the precursor solution for the negative electrode interface composite buffer layer: Add 0.15 g of LiTFSI to 7 g of anhydrous acetonitrile and stir at 400 rpm for 5 min at room temperature. Then add 0.15 g of polyethylene oxide (PEO) and heat and stir at 50℃ and 550 rpm for 6 h. After the PEO is completely dissolved, add 1.2 g of magnesium fluoride (MgF2) ceramic particles and continue to heat and stir at 50℃ and 500 rpm for 4 h to obtain the negative electrode interface composite precursor solution.

[0035] S2. Preparation of polymer solid electrolyte: 0.2 g of LiTFSI was added to 8 g of anhydrous acetonitrile and stirred at 400 rpm for 5 min at room temperature. Then, 0.6 g of PEO powder was added and heated and stirred at 60℃ and 400 rpm for 9 h. After stirring evenly, the resulting solution was poured into a 4 cm × 8 cm silicone mold and dried at room temperature for 12 h in an environment with humidity <20%, and then dried at 50℃ for 12 h.

[0036] S3. Drop the negative electrode interface composite buffer layer precursor solution obtained in S1 onto a circular glass plate coated with polytetrafluoroethylene (PTFE). Set the spin coating speed to 1200 rpm and the spin coating time to 8 s. Turn on the vacuum pump to tighten the circular glass plate and start spin coating.

[0037] S4. The substrate coated with the precursor solution of the negative electrode interface composite buffer layer obtained in S2 is heated at 40°C for 30 min in a glove box under an argon atmosphere to obtain the negative electrode interface composite buffer layer.

[0038] S5. Attach the PEO-based polymer solid electrolyte obtained in S2 to the negative electrode interface composite buffer layer that has been dried and coated on the substrate in S4, and press or roll it, then peel it off. This will make the negative electrode interface composite buffer layer tightly adhere to the PEO-based polymer solid electrolyte.

[0039] A lithium-ion symmetric battery was assembled by attaching a composite buffer layer at the negative electrode interface prepared in this embodiment to both sides of a PEO-based polymer solid electrolyte. The battery was then tested at 30°C with a current of 0.1 mA cm⁻¹. -2 and 0.1 mAh cm -2 Under these conditions, repeated lithium plating / stripping was performed, and the battery could cycle stably for 1200 h without short circuit. A solid-state lithium metal battery was assembled by attaching the negative electrode interface composite buffer layer prepared in Example 4 to only one side, with the positive electrode being lithium iron phosphate. Its initial discharge specific capacity at 30°C was 154 mAhg. -1 The discharge specific capacity after 200 cycles is 142 mAh g. -1 .

[0040] Comparative Example 1 To highlight the superior performance of the product obtained by this invention, a lithium-symmetric battery was assembled using the same PEO-based polymer solid electrolyte as in Examples 1-4, and tested at 30°C with a current of 0.1 mA cm⁻¹. -2 and 0.1 mAh cm -2 Repeated lithium plating / stripping under certain conditions, such as Figure 10 As shown, the battery short-circuited after only 320 hours; a solid-state lithium metal battery was assembled using the same PEO-based polymer solid electrolyte as in Examples 1-4, with lithium iron phosphate as the positive electrode, and its cycle curve is shown below. Figure 11 As shown, the initial discharge specific capacity at 30°C is 159 mAh g. -1 The discharge specific capacity after 200 cycles is 62 mAh g. -1 .

Claims

1. A negative electrode interface composite buffer layer, characterized in that, The negative electrode interface composite buffer layer is composed of ceramic particles, polymer matrix and lithium salt.

2. The negative electrode interface composite buffer layer as described in claim 1, characterized in that, The thickness of the negative electrode interface composite buffer layer is 2-10 μm.

3. The negative electrode interface composite buffer layer as described in claim 1, characterized in that, The ceramic particles are one or a combination of one or more of aluminum nitride, magnesium nitride, gallium fluoride, and magnesium fluoride.

4. The negative electrode interface composite buffer layer as described in claim 1, characterized in that, The polymer matrix is ​​one or a combination of more than one of polyethylene oxide, polyvinylidene fluoride, and polyvinylidene fluoride-hexafluoropropylene copolymer.

5. The negative electrode interface composite buffer layer as described in claim 1, characterized in that, The lithium salt is one or a combination of more than one of lithium bis(trifluoromethanesulfonyl)imide, lithium perchlorate, and lithium bis(fluorosulfonyl)imide.

6. The method for preparing the negative electrode interface composite buffer layer according to any one of claims 1-5, characterized in that, The method includes the following steps: 1) Add 1-2 parts by weight of lithium salt to 30-60 parts by weight of solvent and stir for the first time. Then add 1-2 parts by weight of polymer matrix and stir for the second time under heating conditions. After the polymer matrix is ​​completely dissolved, add 4-12 parts by weight of ceramic particles and stir for the third time to obtain the negative electrode interface composite precursor solution. 2) Drop the negative electrode interface composite precursor solution onto a substrate coated with polytetrafluoroethylene, set the spin coating parameters, and spin coat to obtain a substrate coated with the precursor solution. 3) The substrate coated with the precursor solution is dried under an inert atmosphere to obtain a negative electrode interface composite buffer layer attached to the substrate. 4) Attach the polymer solid electrolyte to the negative electrode interface composite buffer layer on the dried substrate, and transfer the buffer layer to the surface of the polymer solid electrolyte membrane by pressing or rolling.

7. The method for preparing the negative electrode interface composite buffer layer as described in claim 6, characterized in that, The solvent in step 1) is one or more of acetonitrile, N-methylpyrrolidone, and N,N-dimethylformamide; the heating temperature during the second stirring is 50-80℃, and the heating and stirring time is 3-9h; the spin coating parameters in step 2) are: rotation speed 1000-2000 rpm, spin coating time 5-15 s; the inert atmosphere in step 3) is argon or nitrogen, and the drying parameters are: temperature 40-80℃, time 10-30min.

8. A solid-state lithium metal battery having any one of the negative electrode interface composite buffer layers according to claims 1-7, characterized in that, The solid-state lithium metal battery includes a positive electrode, a polymer solid electrolyte, a negative electrode interface composite buffer layer, and a negative electrode.

9. A solid-state lithium metal battery as described in claim 8, characterized in that, The positive electrode is an electrode containing one or more of the following ternary materials: lithium iron phosphate, nickel cobalt manganese, etc.; the main polymer component of the polymer solid electrolyte is polyethylene oxide; the polymer solid electrolyte contains succinic acid plasticizer; and the main component of the negative electrode is lithium metal.

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