Magnesium secondary battery cell and preparation method thereof

Abstract

The invention belongs to the technical field of rechargeable batteries, and particularly relates to a magnesium secondary battery cell and a preparation method thereof. The invention provides a preparation method of a magnesium secondary battery cell, which comprises the following steps: assembling a positive pole piece, an isolating membrane and a magnesium negative pole piece in sequence to obtain a magnesium secondary battery cell to be welded with a tab; welding the magnesium negative pole piece of the magnesium secondary battery cell to be welded with the tab with the tab, and then carrying out solution treatment to obtain the magnesium secondary battery cell; the solid solution temperature of the solid solution treatment is 200-320 DEG C, and the solid solution time is 1-5 hours. Solution treatment is carried out on a welded joint, crystal lattice distortion of solute atoms in a solid solution is promoted, dislocation motion resistance is increased, weld strength is improved, internal stress is eliminated, tensile property is enhanced, crack defects are reduced, and finally the magnesium secondary battery low in internal resistance and high in cycling stability is prepared.

Description

Technical Field

[0001] The present invention belongs to the technical field of rechargeable batteries, and in particular relates to a magnesium secondary battery core and a preparation method thereof. Background Art

[0002] With society's growing demand for green energy, a growing number of researchers are dedicating themselves to the research of various types of metal-ion batteries. Magnesium secondary batteries, among them, have attracted considerable attention due to their high energy density, lack of dendrite formation, and abundant magnesium resources. Tab welding is a critical process in battery production. Poor welding can increase the battery's internal resistance, leading to increased heat generation and decreased cycle life. Existing magnesium secondary batteries use Mg foil / Mg alloy foil for the negative electrode and Ni tabs for the tabs. The significant difference in physical properties during welding increases the risk of defects such as weld cracks, impacting weld quality. Furthermore, the thinnest magnesium-based metal sheet currently available for use as a negative electrode material is 50 μm, far thicker than the copper-based metal sheet used for lithium battery negative electrodes (5-10 μm). This can easily lead to poor welds and other issues, which in turn affect the quality of magnesium secondary batteries.

[0003] Therefore, there is an urgent need for a magnesium secondary battery with good welding between the tab and the magnesium-based negative electrode material, which can improve the mechanical strength of the weld and improve the overcurrent performance of the battery. Summary of the Invention

[0004] The present invention aims to provide a magnesium secondary battery cell and a method for preparing the same. By optimizing the welding process and performing a solution treatment on the weld joint, the present invention promotes lattice distortion of the solute atoms in the solid solution, increases resistance to dislocation movement, improves weld strength, eliminates internal stress, enhances tensile strength, and reduces crack defects, ultimately producing a magnesium secondary battery with low internal resistance and high cycle stability.

[0005] The present invention provides a method for preparing a magnesium secondary battery cell, comprising the following steps: assembling a positive electrode sheet, a separator, and a magnesium negative electrode sheet in sequence to obtain a magnesium secondary battery cell with a tab to be welded; welding the magnesium negative electrode sheet and the tab of the magnesium secondary battery cell with the tab to be welded, and then performing a solid solution treatment to obtain a magnesium secondary battery cell;

[0006] The solution treatment temperature is 200-320° C., and the solution treatment time is 1-5 hours.

[0007] Preferably, the welding is ultrasonic welding; the ultrasonic welding time is 0.2 to 0.5 s, the pressure is 0.15 to 0.25 MPa, and the amplitude is 20 to 40%.

[0008] Preferably, during the welding, the tab is located below the magnesium negative electrode sheet.

[0009] Preferably, the method for preparing the positive electrode sheet comprises: mixing a positive electrode active material, a conductive agent, a binder and a solvent to obtain a positive electrode slurry; and coating the positive electrode slurry on a current collector and then drying the mixture to obtain a positive electrode sheet.

[0010] Preferably, the mass ratio of the positive electrode active material, the conductive agent and the binder is (7-9.8):(0.1-2):(0.1-2); the mass ratio of the positive electrode active material and the solvent is 1:(1-2).

[0011] Preferably, the positive electrode active material comprises one or more of Mo6S8, a polyanion positive electrode and a sulfur positive electrode; the conductive agent comprises one or more of acetylene black, Ketjen black, graphene and carbon nanotubes; the binder comprises one or more of PVDF, PTFE, SBR and CMC; the solvent comprises one or both of NMP and DMF.

[0012] The present invention also provides a magnesium secondary battery cell prepared by the preparation method described in the above technical solution, comprising a magnesium secondary battery cell; the magnesium secondary battery cell comprises a positive electrode sheet, a magnesium negative electrode sheet and a separator arranged between the positive electrode sheet and the magnesium negative electrode sheet; and a tab connected to the magnesium negative electrode sheet of the magnesium secondary battery cell.

[0013] The present invention also provides a magnesium secondary battery, comprising the magnesium secondary battery cell described in the above technical solution.

[0014] Preferably, it further comprises an electrolyte; the electrolyte comprises one or more of an APC electrolyte, a boron-based electrolyte and a MACC electrolyte.

[0015] Preferably, the resistance of the magnesium secondary battery is ≤0.57Ω.

[0016] Beneficial effects:

[0017] The present invention provides a method for preparing a magnesium secondary battery cell, comprising the following steps: assembling a positive electrode sheet, a separator, and a magnesium negative electrode sheet in sequence to obtain a magnesium secondary battery cell with a tab to be welded; welding the magnesium negative electrode sheet and the tab of the magnesium secondary battery cell with the tab to be welded, and then performing a solid solution treatment to obtain the magnesium secondary battery cell; the solid solution treatment temperature is 200-320°C, and the solid solution time is 1-5 hours. The present invention optimizes the welding process, and on the basis of welding the tab and the negative electrode sheet, performs a solid solution treatment on the weld joint, thereby promoting lattice distortion of the solute atoms in the solid solution, increasing the resistance to dislocation movement, thereby improving the strength of the solid solution, effectively eliminating internal stress, increasing the tensile strength of the weld, and reducing crack defects. The magnesium secondary battery cell after the solid solution strengthening treatment of the tab and the negative electrode sheet has excellent current performance, low internal resistance, and high cycle stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments are briefly introduced below.

[0019] Figure 1 This is a comparison chart of the charge and discharge cycle performance of the magnesium secondary battery with a solution-treated welded joint prepared in Example 3 and a magnesium secondary battery with a non-solution-treated welded joint at a current of 1C. DETAILED DESCRIPTION

[0020] The present invention provides a method for preparing a magnesium secondary battery cell, comprising the following steps: assembling a positive electrode sheet, a separator, and a magnesium negative electrode sheet in sequence to obtain a magnesium secondary battery cell with a tab to be welded; welding the magnesium negative electrode sheet and the tab of the magnesium secondary battery cell with the tab to be welded, and then performing a solid solution treatment to obtain a magnesium secondary battery cell;

[0021] The solution treatment temperature is 200-320° C., and the solution treatment time is 1-5 hours.

[0022] In the present invention, unless otherwise specified, all raw material components are commercially available products well known to those skilled in the art.

[0023] The present invention sequentially assembles a positive electrode sheet, a separator, and a magnesium negative electrode sheet to obtain a magnesium secondary battery cell with tabs to be welded. In the present invention, the positive electrode sheet preferably includes a current collector and a positive electrode material layer supported on the current collector. The positive electrode active ingredient in the positive electrode material is preferably one or more of Mo6S8, a polyanion positive electrode, and a sulfur positive electrode. The preparation method of the positive electrode sheet preferably includes: mixing the positive electrode active material, a conductive agent, a binder, and a solvent to obtain a positive electrode slurry; applying the positive electrode slurry to the current collector and then drying it to obtain the positive electrode sheet.

[0024] In the present invention, the mass ratio of the positive electrode active material, the conductive agent, and the binder is preferably (7-9.8):(0.1-2):(0.1-2); the mass ratio of the positive electrode active material and the solvent is preferably 1:(1-2); the conductive agent preferably includes one or more of acetylene black, Ketjen black, graphene, and carbon nanotubes; the binder preferably includes one or more of PVDF, PTFE, SBR, and CMC; the solvent includes one or both of NMP and DMF; the current collector is preferably one or more of nickel foil, copper foil, aluminum foil, and stainless steel foil. In a specific embodiment of the present invention, the conductive agent is preferably acetylene black, the binder is preferably PVDF, and the solvent is preferably NMP; the mass ratio of the positive electrode active material, the conductive agent, and the binder is preferably 8:1:1; and the mass ratio of the positive electrode active material and the solvent is preferably 1:1.5.

[0025] In the present invention, the separator is preferably a glass fiber separator.

[0026] In the present invention, the magnesium negative electrode plate is preferably a Mg metal sheet, and the thickness of the Mg metal sheet is preferably 0.05 mm.

[0027] After obtaining a magnesium secondary battery cell with a tab to be welded, the present invention welds the magnesium negative electrode sheet to the tab of the magnesium secondary battery cell to be welded and then performs a solid solution treatment to obtain the magnesium secondary battery cell. In the present invention, the tab is preferably a nickel metal sheet; the tab is preferably 8 mm wide and 0.1 mm thick.

[0028] In the present invention, the welding is preferably ultrasonic welding; the time of the ultrasonic welding is preferably 0.2 to 0.5 s, specifically 0.3 s, 0.35 s or 0.4 s, the pressure is preferably 0.15 to 0.25 MPa, specifically 0.2 MPa, and the amplitude is preferably 20 to 40%, specifically 30%; the ultrasonic welding is preferably performed using an ultrasonic welding gun; in the present invention, during the welding, the tab is preferably located below the magnesium negative electrode sheet.

[0029] In the present invention, after welding, a weld is formed at the connection between the electrode tab and the magnesium negative electrode sheet.

[0030] In the present invention, the solution temperature of the solution treatment is 200-320°C, specifically 240°C or 280°C, and the solution time is 1-5 hours, specifically 3 hours. In the present invention, if the solution temperature is too low, it will lead to insufficient dissolution, the alloy elements in the solid solution (weld joint) cannot be fully dissolved into the matrix, the amount of precipitated phase is limited, the grain size is large, and it is not conducive to improving the strength of the weld joint; if the solution temperature is too high, it will cause the solid solution to burn, affecting the mechanical properties of the weld joint and reducing its service life and safety.

[0031] The present invention also provides a magnesium secondary battery cell prepared by the preparation method described in the above technical solution, comprising a magnesium secondary battery cell; the magnesium secondary battery cell comprises a positive electrode sheet, a magnesium negative electrode sheet and a separator arranged between the positive electrode sheet and the magnesium negative electrode sheet; and a tab connected to the magnesium negative electrode sheet of the magnesium secondary battery cell.

[0032] The present invention also provides a magnesium secondary battery comprising the magnesium secondary battery cell described in the above technical solution. In the present invention, the magnesium secondary battery preferably further comprises an electrolyte; the electrolyte preferably comprises one or more of an APC electrolyte, a boron-based electrolyte, and a MACC electrolyte. In a specific embodiment of the present invention, the electrolyte is preferably an APC electrolyte.

[0033] In the present invention, the resistance of the magnesium secondary battery is preferably ≤0.57Ω. The present invention achieves a fully reliable connection between the tab and the pole piece by solid solution strengthening treatment of the weld joint, further reducing the charge transfer impedance, which is beneficial to reducing battery resistance and improving cycle performance.

[0034] In a specific embodiment of the present invention, the tab is preferably a Ni metal sheet; the size of the Ni metal sheet is preferably 8mm×0.1mm×61mm; the magnesium negative electrode sheet is preferably a Mg metal sheet; the size of the Mg metal sheet is preferably 8mm×0.05mm×40mm.

[0035] In order to further illustrate the present invention, a magnesium secondary battery cell and a preparation method thereof provided by the present invention are described in detail below with reference to the accompanying drawings and examples, but they should not be construed as limiting the scope of protection of the present invention.

[0036] Comparative Example 1

[0037] The Mg metal sheet was placed on top of the Ni metal sheet, and ultrasonic welding parameters were set. Ultrasonic welding was performed under different welding times, welding pressures, and welding amplitudes.

[0038] A tensile testing machine was used to perform a tensile strength test on the Ni tab-negative electrode sheet after welding and without solution treatment.

[0039] Under the conditions of welding pressure of 0.2MPa and welding amplitude of 30%, different welding times were set to obtain the tensile strength of Ni tab-negative electrode sheet. The test results are shown in Table 1 below:

[0040] Table 1 Tensile strength of Ni tab-negative electrode sheet at different welding times

[0041] Welding time (s) 0.25 0.3 0.35 0.4 0.45 Tensile strength (N) 30 34 40 35 29

[0042] Under the conditions of welding time of 0.35s and welding amplitude of 30%, different welding pressures were set to obtain the tensile strength of Ni tab-negative electrode sheet. The test results are shown in Table 2 below:

[0043] Table 2 Tensile strength of Ni tab-negative electrode sheet under different welding pressures

[0044] Welding pressure (MPa) 0.1 0.15 0.2 0.25 0.3 Tensile strength (N) 18 34 40 37 22

[0045] Under the conditions of welding time of 0.35s and welding pressure of 0.2MPa, different welding amplitudes were set to obtain the tensile strength of Ni tab-negative electrode sheet. The test results are shown in Table 3 below:

[0046] Table 3 Tensile strength of Ni tab-negative electrode sheet at different welding amplitudes

[0047] Welding amplitude (%) 10 20 30 40 50 Tensile strength (N) 26 37 40 34 21

[0048] It can be seen from Tables 1 to 3 that when the welding time is 0.35s, the welding pressure is 0.2MPa, and the welding amplitude is 30%, the tensile strength of the sample is the best, which is 40MPa.

[0049] Example 1

[0050] The Mg metal sheet was placed on top of the Ni metal sheet, and ultrasonic welding parameters were set as welding time 0.35s, welding pressure 0.2MPa, and welding amplitude 30% to form a welded joint; the welded joint was solution treated under different temperature and time conditions.

[0051] The tensile strength of the solution treated samples was tested, and the test results are shown in Table 4. Table 4 shows that under certain conditions, solution treatment can improve the tensile strength of the samples. Under the conditions of solution temperature of 280°C and solution time of 3h, the samples obtain the best mechanical properties.

[0052] Table 4 Tensile strength of Ni tab-negative electrode sheet at different solution temperatures and times (N)

[0053]

[0054] Example 3

[0055] Positive electrode sheet: Mo6S8, acetylene black, and PVDF were mixed in a mass ratio of 8:1:1, and an appropriate amount of NMP solvent (Mo6S8:NMP mass ratio of 1:1.5) was added and stirred to form a positive electrode slurry; the positive electrode slurry was evenly coated on a 50μm thick stainless steel foil and dried and cut to form a positive electrode sheet;

[0056] Magnesium negative electrode sheet: Cut the magnesium foil with a thickness of 50 μm to obtain the magnesium negative electrode sheet;

[0057] Magnesium secondary battery cell: assemble in the order of positive electrode sheet, glass fiber separator, and negative electrode sheet to form a magnesium secondary battery cell with tabs to be welded;

[0058] Welding: Ultrasonic welding of the negative electrode of the magnesium secondary battery cell and the Ni tab: welding time 0.35s, welding pressure 0.2MPa, welding amplitude 30%;

[0059] Solution treatment: The welded joint formed after welding is subjected to solution treatment: the solution temperature is 280°C and the solution time is 3 hours;

[0060] Magnesium secondary battery: The magnesium secondary battery cells after solution treatment and welding are further subjected to packaging, drying, liquid injection (APC electrolyte), chemical formation and other processes to obtain magnesium secondary batteries with solution treatment of welded joints and magnesium secondary batteries with non-solution treatment of welded joints;

[0061] The internal resistance of the magnesium secondary battery obtained by testing is shown in Table 5 below. As can be seen from Table 5, the internal resistance of the battery obtained after solid solution treatment is smaller.

[0062] Table 5 Internal resistance of magnesium secondary battery cells without and after solution treatment

[0063]

[0064] Figure 1 This is a comparison chart of the charge-discharge cycle performance of the magnesium secondary battery with a solution-treated welded joint and a magnesium secondary battery without a solution-treated welded joint at a current of 1C; Figure 1 It can be seen from the figure that the cycle performance of magnesium secondary batteries is better after solid solution treatment of the welded joints.

[0065] Although the above embodiment provides a detailed description of the present invention, it is only a part of the embodiments of the present invention, not all of the embodiments. People can also obtain other embodiments based on this embodiment without creativity, and these embodiments all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a magnesium secondary battery cell, characterized in that: The method comprises the following steps: assembling a positive electrode sheet, a separator and a magnesium negative electrode sheet in sequence to obtain a magnesium secondary battery cell with a tab to be welded; welding the magnesium negative electrode sheet and the tab of the magnesium secondary battery cell with the tab to be welded and then performing a solid solution treatment to obtain a magnesium secondary battery cell; The solution treatment temperature is 200-320° C., and the solution treatment time is 1-5 hours.

2. The preparation method according to claim 1, characterized in that The welding is ultrasonic welding; the ultrasonic welding time is 0.2 to 0.5 s, the pressure is 0.15 to 0.25 MPa, and the amplitude is 20 to 40%.

3. The preparation method according to claim 1, characterized in that During the welding, the tab is located below the magnesium negative electrode sheet.

4. The preparation method according to any one of claims 1 to 3, characterized in that The preparation method of the positive electrode plate comprises: mixing a positive electrode active material, a conductive agent, a binder and a solvent to obtain a positive electrode slurry; applying the positive electrode slurry on a current collector and then drying the mixture to obtain a positive electrode plate.

5. The preparation method according to claim 4, characterized in that The mass ratio of the positive electrode active material, the conductive agent and the binder is (7-9.8):(0.1-2):(0.1-2); the mass ratio of the positive electrode active material and the solvent is 1:(1-2).

6. The preparation method according to claim 4, characterized in that The positive electrode active material includes one or more of Mo6S8, a polyanion positive electrode and a sulfur positive electrode; the conductive agent includes one or more of acetylene black, Ketjen black, graphene and carbon nanotubes; the binder includes one or more of PVDF, PTFE, SBR and CMC; the solvent includes one or both of NMP and DMF.

7. The magnesium secondary battery cell prepared by the preparation method according to any one of claims 1 to 6, characterized in that: The invention comprises a magnesium secondary battery cell; the magnesium secondary battery cell comprises a positive electrode sheet, a magnesium negative electrode sheet and a separator arranged between the positive electrode sheet and the magnesium negative electrode sheet; and a tab connected to the magnesium negative electrode sheet of the magnesium secondary battery cell.

8. A magnesium secondary battery, characterized in that: Including the magnesium secondary battery cell according to claim 7.

9. The magnesium secondary battery according to claim 8, characterized in that It also includes an electrolyte; the electrolyte includes one or more of an APC electrolyte, a boron-based electrolyte and a MACC electrolyte.

10. The magnesium secondary battery according to claim 8 or 9, characterized in that The resistance of the magnesium secondary battery is ≤0.57Ω.

Images