Lithium metal negative pole piece, all-solid-state lithium ion battery and preparation method of all-solid-state lithium ion battery

Abstract

The invention relates to the technical field of solid-state batteries, in particular to a lithium metal negative pole piece, an all-solid-state lithium ion battery and a preparation method of the all-solid-state lithium ion battery. Comprising the following steps: S1, preparing a lithium metal negative electrode substrate; s2, preparing reactive material slurry; the reactive material slurry comprises a lithium salt cosolvent, a polymer capable of conducting lithium ions, metal fluoride and an organic solvent; and S3, preparing the reactive lithium metal negative electrode plate. According to the invention, direct contact between the lithium metal negative electrode and the sulfide electrolyte layer is avoided, the influence of an interfacial film on battery impedance is eliminated, and the cycle performance and rate capability of the all-solid-state lithium metal battery are improved.

Description

Technical Field

[0001] This invention relates to the field of solid-state battery technology, and in particular to a lithium metal anode sheet, an all-solid-state lithium-ion battery, and a method for preparing the same. Background Technology

[0002] All-solid-state lithium-ion batteries (ASSBs) use solid-state sulfide electrolytes (SSEs) instead of traditional liquid electrolytes and separators. Their main technological advantages are high energy density, high safety performance, and long cycle life, avoiding the safety issues associated with traditional liquid electrolytes, making them a novel battery type. Currently, solid-state sulfide electrolytes (Li6PS5Cl, LPSCs) are considered one of the most promising solid-state electrolytes due to their ultra-high room-temperature ionic conductivity (>10⁻³ S / cm) and high thermal stability. Lithium metal, with its high theoretical specific energy of 3860 mAh / g and the lowest redox potential, has broad development prospects as a negative electrode material for all-solid-state lithium-ion batteries. However, during charge and discharge, interfacial electrochemical reactions occur between the sulfide electrolyte and the lithium metal negative electrode, forming an interfacial film that reduces ion migration rate and causes high interfacial impedance. Furthermore, during cycling, lithium dendrites are prone to uneven deposition, and their growth and evolution at the negative electrode interface and within the electrolyte can lead to short circuits, severely restricting the practical application of all-solid-state batteries. Therefore, reducing the interfacial electrochemical side reactions between the sulfide electrolyte and the lithium metal anode material, reducing the interfacial film impedance, and improving the lithium dendrite growth at the anode are important goals for all-solid-state lithium metal batteries.

[0003] Currently, mainstream technologies alleviate the above problems through solid electrolyte modification or the introduction of an interface layer. However, in addition, existing technologies also have the following drawbacks: (1) Existing methods for suppressing lithium dendrites often start from the perspective of the solid electrolyte membrane, which will have a certain impact on the ion conductivity of the electrolyte itself, reducing the battery's electrical performance, and the interface modification is relatively simple. (2) Existing methods for suppressing lithium dendrites to reduce the interface membrane impedance do not significantly reduce the interface impedance, and the interface membrane has poor flexibility. Therefore, it is necessary to find a method that can effectively form an interface membrane to improve battery performance. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings and defects of the prior art and to provide a lithium metal anode sheet, an all-solid-state lithium-ion battery and its preparation method.

[0005] To achieve the above objectives, this application adopts the following solution:

[0006] A method for preparing a lithium metal negative electrode sheet includes the following steps:

[0007] S1: Preparation of lithium metal anode substrate;

[0008] S2: Preparation of reactive material slurry; the reactive material slurry includes lithium salt co-solvent, lithium-ion-conducting polymer, metal fluoride, and organic solvent;

[0009] S3: The reactive material slurry prepared in step S2 is drop-coated onto the surface of step S1, or the lithium metal anode substrate obtained in step S1 is immersed in the reactive slurry obtained in step S2, and dried to obtain a reactive lithium metal anode sheet.

[0010] The lithium salt co-solvent is one or more of LiNO3, LiClO4, and LiTFSI;

[0011] Preferably, the lithium-ion-conducting polymer includes one or more of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), and polyvinylidene fluoride-chlorotrifluoroethylene copolymer (PVDF-CTFE).

[0012] Preferably, the metal fluoride includes one or more of InF3, CuF2, SbF3, MgF2, and SnF2;

[0013] Preferably, the organic solvent includes one or more of N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), and dimethyl ether (DME), with NMP being the most preferred.

[0014] The mass fraction of lithium salt co-solvent in reactive material slurry is 2%-6%;

[0015] Preferably, the mass fraction of the lithium-ion-conducting polymer in the reactive material slurry is 2%-5%;

[0016] Preferably, the mass fraction of the metal fluoride in the reactive material slurry is 0.5%-3%.

[0017] The lithium metal anode substrate described in step S1 has a thickness of 50 μm and a diameter of Φ10 mm.

[0018] The specific steps of step S2 are as follows: 1) Disperse the lithium-ion-conducting polymer in an organic solvent, seal it, and stir it at 100-200 rpm for 3-4 hours; 2) Disperse the metal fluoride solution in the organic solvent obtained in step 1) and stir it at 100-200 rpm; 3) Disperse the lithium salt co-solvent in the organic solvent obtained in step 2) and continue stirring for 1-2 hours to obtain a transparent solution.

[0019] The present invention also includes a lithium metal anode sheet, which is obtained by the preparation method described above; the lithium metal anode sheet includes a lithium metal anode substrate and an SEI film and a Li-X alloy phase formed on one or both sides of the lithium metal anode substrate; wherein X is one or more of In, Cu, Sb, Mg and Sn.

[0020] The present invention also includes a method for preparing the all-solid-state lithium metal battery, comprising the following steps: firstly, using a mold battery to press the electrolyte into a disc to obtain a sulfide electrolyte layer, then placing positive electrode powder from above the mold and compacting it to obtain a positive electrode powder layer, placing the lithium metal negative electrode sheet from below the mold and applying pressure, then placing a copper foil, and finally tightening the mold to obtain the all-solid-state lithium metal battery; preferably, the pressure range after tightening is 0.5T-1T, and the holding time is 5-10min.

[0021] The sulfide electrolyte layer is prepared by cold pressing to prepare a dense solid electrolyte disc; preferably, the mold is φ10mm; preferably, the sulfide electrolyte of the sulfide electrolyte layer is LPSC; the mass is 100-150mg, the pressure range is 0.9T-1.2T, and the holding time is 1-2min.

[0022] The positive electrode powder includes a positive electrode active material, a sulfide electrolyte, and a positive electrode conductive agent;

[0023] Preferably, the active material is a ternary NCM;

[0024] The sulfide electrolyte is LPSC;

[0025] The positive electrode conductive agent is VGCF;

[0026] Preferably, the mass ratio of the positive electrode active material, the sulfide electrolyte, and the positive electrode conductive agent is 7:2.7:0.3; preferably, the positive electrode powder is 20mg-30mg, the pressure range is 1.8T-2.2T, and the holding time is 1-2min.

[0027] The present invention also includes an all-solid-state lithium metal battery, characterized in that it is obtained by the preparation method described above.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] The method for preparing lithium metal anode sheets according to this application enables the formation of an organic / inorganic LiF-lithium-ion-conducting polymer mixed electrolyte layer (SEI film) and a Li-X lithiophilic alloy on the surface of a lithium metal anode substrate. This SEI film, composed of an electronically insulating LiF-lithium-ion-conducting polymer and an ion-insulating Li-X alloy phase, constitutes an organic-inorganic composite mixed SEI layer. The LiF-lithium-ion-conducting polymer reduces electron shuttle between the Li anode and the SEI, thus improving the Li-metal anode's conductivity. + Transport medium and interface stabilizer. Li-X alloy phases (such as Li-In and Li-Cu) provide lithiophilic sites, guide uniform lithium deposition, and effectively suppress lithium dendrite growth.

[0030] This invention avoids direct contact between the lithium metal anode and the sulfide electrolyte layer, eliminating the influence of the interface film on battery impedance and further improving the battery's electrochemical performance. Furthermore, the composite SEI layer composed of a lithium-ion-conducting polymer exhibits excellent mechanical flexibility, suppressing lithium deposition volume expansion. Additionally, it simplifies the in-situ interface film preparation method, reducing manufacturing costs and thus improving the cycle performance and rate performance of all-solid-state lithium metal batteries. Therefore, this invention has broad application prospects in the field of all-solid-state lithium metal batteries, injecting new vitality into the innovative development of all-solid-state lithium metal battery technology. Attached Figure Description

[0031] Figure 1 This is a SEM image of the lithium metal negative electrode sheet of Embodiment 1 of the present invention;

[0032] Figure 2 This is a mapping diagram of the lithium metal negative electrode sheet of Embodiment 1 of the present invention;

[0033] Figure 3 This is a mapping diagram of Cu elements in the lithium metal negative electrode sheet of Embodiment 1 of the present invention;

[0034] Figure 4 This is a mapping diagram of the H element in the lithium metal negative electrode sheet of Embodiment 1 of the present invention;

[0035] Figure 5 This is a mapping diagram of the F element in the lithium metal negative electrode sheet of Embodiment 1 of the present invention;

[0036] Figure 6 The image shows the EIS of the all-solid-state lithium metal battery after being fully charged at 0.05C according to an embodiment of the present invention.

[0037] Figure 7 This is a SEM image of the lithium metal negative electrode sheet after cycling in the all-solid-state lithium metal battery of Example 1 of the present invention;

[0038] Figure 8This is a SEM image of the lithium metal anode sheet after cycling in Comparative Example 2 of this invention. Detailed Implementation

[0039] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0040] Example 1:

[0041] This embodiment provides a method for preparing a lithium metal negative electrode sheet, including the following steps:

[0042] S1: Preparation of lithium metal anode sheet: The selected 50um thick lithium sheet is punched with a Φ10mm punching machine to obtain a Φ10mm diameter lithium metal circular sheet as the lithium metal anode substrate.

[0043] S2: Preparation of reactive material slurry includes the following steps: 1) Place 5 ml of organic solution NMP in a small glass bottle, disperse the lithium-ion-conducting polymer PVDF into 5 ml of NMP solvent to a final concentration of 2%, place a magnetic stir bar, seal the bottle, and place it on a magnetic stirrer. Stir at 200 rpm for 4 hours; 2) Disperse the metal fluoride CuF2 solution into the organic solution obtained in step 1), with a final concentration of 3% for the metal fluoride. Stir at 200 rpm; 3) Disperse the lithium salt co-solvent LiNO3 into the organic solvent obtained in step 2), with a final concentration of 4% for the lithium salt co-solvent. Continue stirring for 1 hour to obtain a transparent solution.

[0044] S3: Preparation of reactive lithium metal anode sheet: The lithium metal substrate from step S1 is immersed in the reactive slurry obtained in step S2 using a selected wetting method. The wetting time is 10 s. After drying, a lithium metal anode sheet is obtained. An organic / inorganic LiF-PVDF mixed interface film (SEI film) and a lithiophilic Li-Cu alloy phase are formed on the surface of the lithium metal substrate. The lithium metal after the reaction in Example 1 is observed by SEM. Figure 1 As shown, the mapping image of lithium metal after the reaction is as follows: Figure 2 , Figure 3 , Figure 4 , Figure 5 As shown.

[0045] Example 2:

[0046] The difference between this embodiment and Embodiment 1 is that in step S2, the mass fraction of PVDF is 2.5%, the mass fraction of CuF2 solution is 0.5%, the mass fraction of co-solvent LiNO3 is 2%, and the immersion time in step S3 is 20s.

[0047] Example 3:

[0048] The difference between this embodiment and Embodiment 1 is that in step S2, the mass fraction of PVDF adhesive is 5%, the mass fraction of InF2 solution is 2%, and the wetting time in step S3 is 5s.

[0049] Example 4:

[0050] The difference between this embodiment and Embodiment 1 is that in step S2, the mass fraction of the InF2 solution is 3%, the mass fraction of the co-solvent LiNO3 is 6%, and the immersion time in step S3 is 10s.

[0051] Example 5:

[0052] The difference between this embodiment and Embodiment 1 is that in step S2, the mass fraction of PVDF binder is 0.5%, the mass fraction of InF2 solution is 4%, the mass fraction of co-solvent LiNO3 is 1%, and the wetting time in step S3 is 30s.

[0053] Comparative Example 1:

[0054] This comparative example uses bare lithium metal anode wafers without modification. The procedure is the same as step S1 in Example 1.

[0055] Comparative Example 2:

[0056] This comparative example uses step S1 from Example 1, but differs from step S2 in that it does not add PVDF, a lithium-ion-conducting polymer. Drying yields a reactive lithium metal anode, and a lithiophilic LiF-Cu alloy phase forms on the surface of the lithium metal substrate.

[0057] Comparative Example 3:

[0058] This comparative example uses pure lithium-indium alloy sheets.

[0059] Example 6

[0060] Preparation method of all-solid-state lithium metal battery

[0061] All-solid-state lithium metal batteries were prepared using the lithium metal anode sheets provided in Examples 1-5 and Comparative Examples 1-3, respectively, and the preparation methods are as follows:

[0062] S1: Preparation of sulfide electrolyte layer

[0063] Dense solid electrolyte discs were prepared by cold pressing. 0.15g of LPSC sample was weighed into weighing paper, and the powder sample was placed in a φ10mm mold cavity. The mold was pressurized to a pressure of 2T, and the mold sealing cap was tightened. The pressure holding time was 10min, and dense LPSC discs with a density of more than 95% and a thickness of more than 500μm were produced.

[0064] S2: Preparation of positive electrode powder

[0065] The ternary cathode active material NCM, sulfide electrolyte LPSC, and cathode conductive agent VGCF were mixed and ground for 1 hour at a mass ratio of 7:2.7:0.3.

[0066] S3: Fabrication of all-solid-state lithium metal batteries

[0067] The lithium metal negative electrode sheets provided in Examples 1-5 and Comparative Examples 1-3, the electrolyte layer obtained in step S1, and the positive electrode powder in step S2 were assembled in the following order: First, the LPSC electrolyte in step S1 was pressed into a disc using a mold battery. Then, 20 mg of positive electrode powder was placed from the top of the mold, a pressure of 2T was applied, and the pressure was held for 10 min. Next, a φ10 mm copper foil was placed from the bottom of the mold, the mold was tightened, and a pressure of 1T was applied to press it in place for 5 min.

[0068] Formation process: Perform charge-discharge cycles with a charging voltage range of 1.9-3.7V. First, perform three charge-discharge cycles at 0.05C for standard capacity treatment, with a cutoff current of 0.025C. After full charge, perform EIS testing. The EIS test results are as follows: Figure 6 As shown. Then charge at a rate of 0.1C to 3.7V, with a cutoff current of 0.05C, and discharge at a rate of 0.1C to 1.9V, repeating 100 cycles.

[0069] Performance testing: Initial coulombic efficiency during the formation stage: The initial coulombic efficiency is calculated as follows: Initial coulombic efficiency = discharge capacity of the third cycle / charge capacity of the third cycle during the formation stage of the lithium metal battery manufacturing process.

[0070] Cycle life: The above-mentioned all-solid-state lithium metal battery was charged to 3.7V at a rate of 0.1C, with a cutoff current of 0.05C, and then discharged to 1.9V at a rate of 0.1C. The discharge capacity Q1 at this point was measured. This charge-discharge cycle was repeated, and the discharge capacity Q on the nth cycle was measured. n Capacity retention rate = Q n / Q1×100%, the number of cycles in which the capacity retention rate is less than 80%, is denoted as the cycle life of an all-solid-state lithium metal battery.

[0071] Rate performance: The above-mentioned all-solid-state lithium metal battery was charged to 3.7V at a rate of 0.1C, and discharged to 1.9V at rates of 0.1C, 0.2C, 0.33C, 0.5C, and 1C respectively.

[0072] SEM tests were performed on the lithium metal after cycling of the aforementioned all-solid-state battery to verify whether lithium dendrite formation was suppressed. The results are as follows: Figure 7 , Figure 8 As shown.

[0073] The results of the above performance tests are shown in Table 1 below:

[0074] Table 1

[0075] Group First effect Cycle life Rate performance (1C / 0.1C) Example 1 86.8％ 100 laps @ 92% 78.6％ Example 2 87％ 100 laps @ 94% 77.9％ Example 3 86.9％ 100 laps @ 93% 74.2％ Example 4 86.4％ 100 laps @ 93% 78.3％ Example 5 82.6％ 100 laps @ 88% 68.4％ Comparative Example 1 80.5％ 100 laps @ 81.6% 56.8％ Comparative Example 2 82.5％ 100 laps @ 82.9% 59.2％ Comparative Example 3 82.8％ 100 laps @ 83% 58.6％

[0076] pass Figure 1 It can be seen that an organic / inorganic LiF-PVDF mixed electrolyte layer (SEI film) is formed on the surface of the modified lithium metal sheet, with a thickness of approximately 50 nm. Through... Figures 2-5 The elemental mapping diagram shows that the lithium metal anode sheet does indeed form an organic / inorganic LiF-PVDF mixed electrolyte layer and a Li-X lithiophilic alloy phase mixed interface layer.

[0077] Figure 6 The results show that the electrochemical impedance of Examples 1-5 is much smaller than that of Comparative Examples 2 and 3, indicating that the half-circle of the impedance curve of the lithium metal anode in the examples is significantly reduced, the ohmic impedance is about 0.9Ω, and the interface impedance is about 1.3Ω. This indicates that the pathway constructed by the in-situ generation of organic / inorganic LiF-PVDF mixed electrolyte layer and Li-X lithiophilic alloy plays a role in reducing the electrochemical impedance between the sulfide electrolyte and lithium metal, and its effect is better than that of single interface modification.

[0078] As can be seen from the performance data in Table 1, the all-solid-state lithium metal batteries prepared using the lithium metal anode sheets provided in Examples 1-5 of this invention exhibit high initial efficiency, cycle life, and rate performance. This demonstrates that the synergistic effect of the organic / inorganic LiF-PVDF mixed electrolyte layer and the Li-X lithiophilic alloy effectively regulates lithium-ion transport, achieving rapid and uniform lithium-ion transport, thereby improving the battery's initial efficiency, cycle life, and rate performance.

[0079] from Figure 7 and Figure 8 The SEM images of the all-solid-state battery after cycling show that the in-situ generated organic / inorganic LiF-PVDF mixed electrolyte layer and Li-X lithiophilic alloy effectively suppressed the growth of lithium dendrites.

[0080] In summary, the in-situ generated organic / inorganic LiF-PVDF mixed electrolyte layer and Li-X lithiophilic alloy in this design have significant comprehensive performance advantages, including rate performance, long cycle life, low interfacial impedance, and the ability to suppress lithium dendrites. They have good versatility and will have great application prospects.

[0081] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. It will be apparent to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention.

[0082] Therefore, the embodiments should be regarded as exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of the equivalents of the claims be included within the invention.

[0083] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for preparing a lithium metal negative electrode sheet, characterized in that, Includes the following steps: S1: Preparation of lithium metal anode substrate; S2: Preparation of reactive material slurry; the reactive material slurry includes lithium salt co-solvent, lithium-ion-conducting polymer, metal fluoride, and organic solvent; S3: The reactive material slurry prepared in step S2 is drop-coated onto the surface of step S1, or the lithium metal anode substrate obtained in step S1 is immersed in the reactive slurry obtained in step S2, and dried to obtain a reactive lithium metal anode sheet.

2. The method for preparing the lithium metal negative electrode sheet according to claim 1, characterized in that, The lithium salt co-solvent is one or more of LiNO3, LiClO4, and LiTFSI; Preferably, the lithium-ion-conducting polymer includes one or more of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), and polyvinylidene fluoride-chlorotrifluoroethylene copolymer (PVDF-CTFE). Preferably, the metal fluoride includes one or more of InF3, CuF2, SbF3, MgF2, and SnF2; Preferably, the organic solvent includes one or more of N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), and dimethyl ether (DME), with NMP being the most preferred.

3. The method for preparing the lithium metal negative electrode sheet according to claim 1, characterized in that, The mass fraction of lithium salt co-solvent in reactive material slurry is 2%-6%; Preferably, the mass fraction of the lithium-ion-conducting polymer in the reactive material slurry is 2%-5%; Preferably, the mass fraction of the metal fluoride in the reactive material slurry is 0.5%-3%.

4. The method for preparing the lithium metal negative electrode sheet according to claim 1, characterized in that, The lithium metal anode substrate described in step S1 has a thickness of 50 μm and a diameter of Φ10 mm.

5. The method for preparing a lithium metal negative electrode sheet according to claim 1, characterized in that, The specific steps of step S2 are as follows: 1) Disperse the lithium-ion-conducting polymer in an organic solvent, seal it, and stir it at 100-200 rpm for 3-4 hours; 2) Disperse the metal fluoride solution in the organic solvent obtained in step 1) and stir it at 100-200 rpm; 3) Disperse the lithium salt co-solvent in the organic solvent obtained in step 2) and continue stirring for 1-2 hours to obtain a transparent solution.

6. A lithium metal anode sheet, characterized in that, It is obtained by the preparation method described in any one of claims 1-5.

7. A method for preparing the all-solid-state lithium metal battery, characterized in that, The process includes the following steps: first, using a mold battery, the electrolyte is pressed into a disc to obtain a sulfide electrolyte layer; then, positive electrode powder is placed from above the mold and compacted to obtain a positive electrode powder layer; the lithium metal negative electrode sheet as described in claim 6 is placed from below the mold and pressed; then, a copper foil is placed in; and the mold is tightened to obtain an all-solid-state lithium metal battery. Preferably, the pressure range after tightening is 0.5T-1T, and the holding time is 5-10 minutes.

8. The preparation method according to claim 7, characterized in that, The sulfide electrolyte layer is prepared by cold pressing to prepare a dense solid electrolyte disc; preferably, the mold is φ10mm. Preferably, the sulfide electrolyte in the sulfide electrolyte layer is LPSC; with a mass of 100-150 mg. Preferably, the pressure range is 0.9T-1.2T, and the pressure holding time is 1-2 minutes.

9. The preparation method according to claim 7, characterized in that, The positive electrode powder includes a positive electrode active material, a sulfide electrolyte, and a positive electrode conductive agent; Preferably, the active material is a ternary NCM; Preferably, the sulfide electrolyte is LPSC; Preferably, the positive electrode conductive agent is VGCF; Preferably, the mass ratio of the positive electrode active material, the sulfide electrolyte, and the positive electrode conductive agent is 7:2.7:0.3; Preferably, the positive electrode powder is 20mg-30mg, the pressure range is 1.8T-2.2T, and the holding time is 1-2min.

10. An all-solid-state lithium metal battery, characterized in that, It is obtained by the preparation method according to any one of claims 7-9.

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