Composite negative electrode foil, preparation method thereof and battery

Abstract

The invention relates to the technical field of batteries, and particularly discloses a composite negative electrode foil, a preparation method thereof and a battery. Comprising the following steps: (1) placing a foil in an acid solution for acid pickling; (2) placing the pickled foil in a phosphonic acid solution for surface passivation treatment; and (3) coating a film on the surface of the foil treated in the step (2) to form a lithium-rich alloy layer so as to prepare the composite negative electrode foil. The prepared composite negative electrode foil can effectively reduce the problem of volume expansion of a negative-electrode-free lithium metal battery, can provide good lithium deposition sites, reduce lithium deposition barriers and reduce generation of poor lithium dendrites, lithium-rich alloy can supplement lithium loss and improve cycling stability in the cycling process, and meanwhile, compared with copper, the lithium-rich alloy is lower in density and better in performance. And a conventional negative electrode material such as graphite is not needed, so that the energy density of the whole battery is favorably improved.

Description

Technical Field

[0001] The invention relates to the technical field of batteries, and in particular to a composite negative electrode foil material and a preparation method thereof, and a battery. Background Art

[0002] The negative electrode-free lithium metal battery is an advanced battery technology. It omits the traditional negative electrode material in its design and uses lithium metal to directly deposit between the battery's separator and the negative electrode conductive layer during the charging process to form the negative electrode. It has become an academic hotspot due to its extremely high theoretical capacity, energy density and low cost. Although negative electrode-free lithium metal batteries have many advantages, they still face many challenges. The first is the problem of lithium dendrites: Due to the lithium repellency of copper and the high activity of metallic lithium, the metallic lithium on the negative electrode side is prone to uneven nucleation during deposition, resulting in sharp lithium dendrites, which will not only cause short circuits between the positive and negative electrodes and increase safety hazards, but also aggravate the side reactions between metallic lithium and the electrolyte, causing rapid loss of metallic lithium and resulting in low lithium cycle efficiency. The second is the formation of "dead lithium" on the negative electrode side: when lithium is deposited unevenly, more disordered, loose, and randomly distributed lithium dendrites will be generated. When discharged at a high rate, lithium metal will quickly detach from the negative electrode. The rapid detachment of some lithium will isolate the lithium dendrites on the negative electrode from the connection with the negative electrode, thereby generating "dead lithium". In short, the two factors lead to rapid battery capacity decay and ultimately reduce the electrochemical performance of lithium-free negative electrode batteries. Therefore, how to fundamentally solve the uneven lithium deposition, reduce "dead lithium", and effectively inhibit the growth of lithium dendrites, while increasing specific energy and improving battery safety and cycle stability, is a key scientific and technological problem that negative electrode-free lithium metal batteries urgently need to solve.

[0003] Therefore, in order to address the problem of poor interface stability and low energy density of copper current collectors in the negative electrode of negative electrode-free lithium metal batteries, it is necessary to provide a composite negative electrode foil, a preparation method and a battery, so as to improve the battery cycle stability and the mass energy density of the whole battery by optimizing the structure of the negative electrode side foil. Summary of the invention

[0004] The present invention aims to solve at least one of the technical problems existing in the above-mentioned prior art. To this end, the present invention proposes a composite negative electrode foil and a preparation method and a battery, which improves the battery cycle stability and the mass energy density of the whole battery by optimizing the structure of the negative electrode side foil.

[0005] A first aspect of the present invention provides a method for preparing a composite negative electrode foil.

[0006] Specifically, a method for preparing a composite negative electrode foil comprises the following steps:

[0007] (1) Placing the foil in an acid solution for pickling;

[0008] (2) placing the pickled foil in a phosphonic acid solution for surface passivation treatment;

[0009] (3) coating the surface of the foil after the treatment in step (2) to form a lithium-rich alloy layer, thereby obtaining the composite negative electrode foil.

[0010] Preferably, in step (1), the foil material includes any one of copper foil, stainless steel foil and zinc-clad copper foil.

[0011] More preferably, the copper foil includes at least one of electrolytic copper foil and rolled copper foil.

[0012] More preferably, the copper foil has a thickness of 4 to 15 μm.

[0013] More preferably, the copper foil has a thickness of 6 to 12 μm.

[0014] Preferably, in step (1), the acidic solution includes at least one of hydrochloric acid, sulfuric acid solution, nitric acid solution, phosphoric acid solution, and perchloric acid solution.

[0015] More preferably, the pH of the acidic solvent is 2-6.

[0016] More preferably, the pH of the acidic solvent is 3-4.

[0017] Preferably, in step (1), an oxidant is added to the acidic solvent.

[0018] More preferably, the added amount of the oxidant is 0.5 to 5 wt % of the acidic solvent.

[0019] More preferably, the oxidant comprises any one of hydrogen peroxide, sodium peroxide, potassium peroxide and peracetic acid. Adding an oxidant to an acidic solvent can promote the dissolution of copper.

[0020] Preferably, in step (1), the pickling time is 5 to 30 seconds and the temperature is 25 to 40°C.

[0021] More preferably, the pickling time is 20 to 30 seconds and the temperature is 25 to 30°C.

[0022] Preferably, in step (2), the phosphonic acid solution comprises any one of hydroxyethylidene diphosphonic acid, tetrasodium hydroxyethylidene diphosphonic acid, (2-hydroxyethyl)phosphonic acid, hydroxymethylphosphonic acid, and dichloromethylene diphosphonic acid.

[0023] Preferably, the concentration of the phosphonic acid solution is 0.001-0.1 mol / L.

[0024] Further preferably, the concentration of the phosphonic acid solution is 0.01-0.05 mol / L.

[0025] Preferably, in step (2), the surface passivation treatment time is 20 to 120 seconds.

[0026] More preferably, in step (2), the surface passivation treatment is performed for 30 to 60 seconds.

[0027] Preferably, in step (3), the composition of the lithium-rich alloy layer includes at least one of lithium-magnesium alloy, lithium-aluminum alloy, lithium-silicon alloy and lithium-boron alloy.

[0028] Preferably, the thickness of the lithium-rich alloy layer is 0.01-2 μm.

[0029] More preferably, the thickness of the lithium-rich alloy layer is 0.1-1 μm.

[0030] In step (1), the foil is placed in an acidic solvent for pickling; the oxide layer can be removed, and a concave defect is formed by acid corrosion, which increases the surface roughness of the foil, provides macroscopic pits for subsequent lithium deposition, and reduces the volume expansion problem of the negative electrode-free lithium metal battery.

[0031] In step (2), after the surface passivation treatment, the phosphonic acid and the residual metal ions on the foil surface form a dense complex protective film, which enhances the chemical stability of the foil surface and the adhesion of the coating.

[0032] In step (3), a lithium-rich alloy layer is formed. Compared with the foil, the lithium-rich alloy layer has a better affinity for lithium, can provide a good lithium deposition site, reduce the lithium deposition barrier, and reduce the generation of undesirable lithium dendrites. During the cycle, the lithium-rich alloy can replenish the loss of lithium and improve the cycle stability. At the same time, compared with the foil, the lithium-rich alloy layer has a lower density, which helps to improve the energy density of the whole battery.

[0033] A second aspect of the present invention provides a composite negative electrode foil.

[0034] Specifically, the composite negative electrode foil is prepared by the preparation method provided by the first aspect of the present invention.

[0035] Preferably, the thickness of the composite negative electrode foil is 4-13 μm.

[0036] More preferably, the thickness of the composite negative electrode foil is 4-8 μm.

[0037] A third aspect of the present invention provides a battery.

[0038] Specifically, the battery includes the composite negative electrode foil provided by the second aspect of the present invention.

[0039] Preferably, the battery comprises a button-type lithium battery.

[0040] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0041] The composite negative electrode foil prepared by the present invention can effectively reduce the volume expansion problem of negative electrode-free lithium metal batteries, can provide good lithium deposition sites, reduce lithium deposition barriers, and reduce the generation of undesirable lithium dendrites. During the cycle, the lithium-rich alloy can supplement the loss of lithium and improve the cycle stability. At the same time, compared with copper, the lithium-rich alloy has a lower density and does not require conventional negative electrode materials such as graphite, which helps to improve the energy density of the whole battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 The battery cycle results of the button-type lithium battery assembled with the composite negative electrode foil of Example 1 of the present invention;

[0043] Figure 2 The battery cycle results of the button-type lithium battery assembled with commercial copper foil according to Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0044] In order to make the technical scheme of the present invention more clearly understood by those skilled in the art, the following embodiments are listed for illustration. It should be pointed out that the following embodiments do not limit the protection scope of the present invention.

[0045] Unless otherwise specified, the raw materials, reagents or devices used in the following examples can be obtained from conventional commercial sources or by existing known methods.

[0046] Example 1

[0047] A composite negative electrode foil and a preparation method thereof, comprising the following steps:

[0048] The 6μm copper foil was continuously cleaned in a hydrochloric acid pickling solution at 25°C and pH 3, 1wt% hydrogen peroxide was added to the pickling solution to promote the reaction, the same position of the copper foil stayed in the pickling solution for 10s, and then directly immersed in a 0.02mol / L hydroxyethylidene diphosphonic acid solution for surface passivation, and after staying for 30s, it was taken out and placed in an 80°C oven for drying for 2h. The dried copper foil and single-phase lithium-magnesium alloy (lithium accounts for 80wt%) were placed in a magnetron sputtering ion plating machine for sputtering, the vacuum degree of the vacuum chamber was <0.1Pa, the temperature was 160°C, and after sputtering for 10min, a composite negative electrode copper foil with a lithium-magnesium alloy layer thickness of 0.5μm was obtained.

[0049] Example 2

[0050] A composite negative electrode foil and a preparation method thereof, comprising the following steps:

[0051] The 6μm copper foil was continuously cleaned in a hydrochloric acid pickling solution at 25°C and pH 3, 1wt% sodium peroxide was added to the pickling solution to promote the reaction, the same position of the copper foil stayed in the pickling solution for 20s, and then directly immersed in a 0.02mol / L hydroxyethylidene diphosphonic acid solution for surface passivation, and after staying for 30s, it was taken out and placed in an 80°C oven for drying for 2h. The dried copper foil and single-phase lithium-magnesium alloy (lithium accounts for 80wt%) were placed in a magnetron sputtering ion plating machine for sputtering, the vacuum degree of the vacuum chamber was <0.1Pa, the temperature was 160°C, and after sputtering for 20min, a composite negative electrode copper foil with a lithium-magnesium alloy layer thickness of 1μm was obtained.

[0052] Example 3

[0053] A composite negative electrode foil material and a preparation method thereof.

[0054] The difference from Example 2 is that after sputtering for 1 minute, a composite negative electrode copper foil with a lithium-magnesium alloy layer thickness of 0.06 μm is obtained.

[0055] Example 4

[0056] A composite negative electrode foil and a preparation method thereof, comprising the following steps:

[0057] The 6μm copper foil was placed in a hydrochloric acid pickling solution at 25°C and pH 3 for continuous cleaning. 1wt% sodium peroxide was added to the pickling solution to promote the reaction. The copper foil was kept in the pickling solution for 20s at the same position. Then, it was directly immersed in a 0.02mol / L hydroxyethylidene diphosphonic acid solution for surface passivation. After staying for 30s, it was taken out and placed in an 80°C oven for drying for 2h. The dried copper foil and lithium-boron alloy (lithium accounts for 80wt%) were placed in a magnetron sputtering ion plating machine for sputtering. The vacuum degree of the vacuum chamber was <0.1Pa, the temperature was 160°C, and after sputtering for 15min, a composite negative electrode copper foil with a lithium-boron alloy layer thickness of 0.5μm was obtained.

[0058] Comparative Example 1

[0059] A commercial copper foil.

[0060] The commercial copper foil has a thickness of 6 μm and is not subjected to any treatment.

[0061] Comparative Example 2

[0062] A composite negative electrode foil and a preparation method thereof, comprising the following steps:

[0063] The 6μm copper foil was continuously cleaned in a hydrochloric acid pickling solution at 25°C and pH 3. 1wt% hydrogen peroxide was added to the pickling solution to promote the reaction. The same position of the copper foil stayed in the pickling solution for 10s, and then directly immersed in deionized water for cleaning. After staying for 30s, it was taken out and placed in an 80°C oven for drying for 2h. The dried copper foil and single-phase lithium-magnesium alloy (lithium accounts for 80wt%) were placed in a magnetron sputtering ion plating machine for sputtering. The vacuum degree of the vacuum chamber was <0.1Pa, the temperature was 160°C, and after sputtering for 10min, a composite negative electrode copper foil with a lithium-magnesium alloy layer thickness of 0.5μm was obtained.

[0064] Performance Test:

[0065] Assemble button-type lithium batteries: Assemble button-type lithium batteries with lithium cobalt oxide as the positive electrode active material and a 10 μm thick commercial polypropylene separator with the composite negative electrode foils prepared in Examples 1 to 4 and Comparative Examples 1 to 2. The electrolyte is a non-aqueous electrolyte formed by dissolving 1 mol / L LiPF6 in a mixed solvent of ethylene carbonate (EC) / dimethyl carbonate (DMC) = 1:1. The rate performance and cycle performance of each button-type lithium battery are shown in Table 1.

[0066] Among them, the detection method of rate performance is: charge and discharge test is carried out at 25°C, the battery is first charged and discharged for 3 cycles at a rate of 0.1C to activate the battery and stabilize the interface, and at the same time determine the 0.1C discharge specific capacity, and then adjust the rate to 0.5C for 1 cycle of charge and discharge to determine the 0.5C discharge specific capacity, adjust the rate to 1C for charge and discharge, and determine the 1C discharge specific capacity.

[0067] The method for testing the cycle performance is as follows: after the rate performance test is completed, the battery continues to undergo a 1C charge and discharge test at 25°C to evaluate its cycle performance.

[0068] Table 1 Copper foil thickness and rate performance and cycle performance of each button lithium battery

[0069]

[0070]

[0071] As shown in Table 1, the 0.1C discharge capacity of the button-type lithium battery assembled with the composite negative electrode foil of Example 1 is 159.91 mAh / g, and the capacity retention rate after 30 cycles at 1C is still 98.52%, which has good rate performance and cycle stability.

[0072] In Example 2, compared with Example 1, the thickness of the lithium-magnesium alloy layer is increased to 1 μm, and the 0.1C discharge specific capacity of the battery does not change significantly. The capacity retention rate after 30 cycles at 1C is 99.06%, which is improved to a certain extent.

[0073] In Example 3, compared with Example 1, the thickness of the lithium-magnesium alloy layer is reduced to 0.06 μm. The capacity retention rate of the battery after 30 cycles at 1C is 90.68%, which is significantly reduced.

[0074] Compared with Example 1, after the lithium-rich alloy is changed to lithium-boron alloy, the 0.1C discharge specific capacity of the battery is 149.88 mAh / g, and the capacity retention rate after 30 cycles at 1C is 96.86%, which can also achieve relatively stable cycling.

[0075] Compared with Example 1, the 0.1C discharge specific capacity of the battery in Comparative Example 1 is 147.97 mAh / g, and the capacity retention rate after 30 cycles at 1C is only 40.99%. This may be because the lithium is deposited unevenly directly on the copper foil, resulting in more dead lithium during the charge and discharge cycle.

[0076] Compared with Example 1, the 0.1C discharge specific capacity of the battery in Comparative Example 2 is 151.25 mAh / g, and the capacity retention rate after 30 cycles at 1C is only 82.34%, which may be due to the lack of complex protective film and unstable lithium deposition and release.

[0077] like Figure 1 As shown, the button-type lithium battery assembled with the composite negative electrode foil of Example 1 has a 0.1C charge specific capacity of 175.83 mAh / g, a 0.1C discharge specific capacity of 159.91 mAh / g, an initial efficiency of 92.5%, a 0.5C discharge specific capacity of 150.78 mAh / g, a 1C first-cycle discharge specific capacity of 145.32 mAh / g, and in the subsequent 1C rate cycle, the charge and discharge efficiency of each cycle of the battery is greater than 99.7%, indicating that the deposition and removal of lithium at the positive and negative electrodes in the cycle are relatively stable, the amount of lithium loss in the cycle is small, the negative electrode side is stable and the amount of dead lithium is small, and the overall cycle stability of the battery is good.

[0078] like Figure 2 As shown, the button-type lithium battery assembled with commercial copper foil in Comparative Example 1 has a 0.1C charging capacity of 165.16 mAh / g, a 0.1C discharge capacity of 147.97 mAh / g, an initial efficiency of 88%, a 0.5C discharge capacity of 137.67 mAh / g, and a 1C first-cycle discharge capacity of 132.77 mAh / g. The battery charge and discharge efficiency is less than 98%, and in the subsequent 1C rate cycle, the charge and discharge efficiency is further reduced, and the amount of dead lithium that cannot be stably cycled increases significantly. Compared with Example 1, the stability of the commercial copper foil negative electrode is poor.

[0079] The preferred specific embodiments of the present invention are described in detail above. It should be understood that a person skilled in the art can make many modifications and changes based on the concept of the present invention without creative work. Therefore, any technical solution obtained by any modification, equivalent replacement, improvement, etc. made by a person skilled in the art based on the concept of the present invention through logical analysis, reasoning or limited experiments on the basis of the prior art shall be within the scope of protection determined by the claims.

Claims

1. A method for preparing a composite negative electrode foil, characterized in that: The following steps are involved: (1) Placing the foil in an acid solution for pickling; (2) placing the pickled foil in a phosphonic acid solution for surface passivation treatment; (3) coating the surface of the foil after the treatment in step (2) to form a lithium-rich alloy layer, thereby obtaining the composite negative electrode foil.

2. The preparation method according to claim 1, characterized in that: In step (1), the foil material includes any one of copper foil, stainless steel foil and zinc composite copper foil.

3. The preparation method according to claim 1, characterized in that: In step (1), the acidic solution includes at least one of hydrochloric acid, sulfuric acid solution, nitric acid solution, phosphoric acid solution, and perchloric acid solution.

4. The preparation method according to claim 1, characterized in that: In step (2), the phosphonic acid solution includes any one of hydroxyethylidene diphosphonic acid, tetrasodium hydroxyethylidene diphosphonic acid, (2-hydroxyethyl)phosphonic acid, hydroxymethylphosphonic acid, and dichloromethylene diphosphonic acid.

5. The preparation method according to claim 4, characterized in that: The concentration of the phosphonic acid solution is 0.001-0.1 mol / L.

6. The preparation method according to claim 1, characterized in that: In step (2), the surface passivation treatment time is 20 to 120 seconds.

7. The preparation method according to claim 1, characterized in that: In step (3), the composition of the lithium-rich alloy layer includes at least one of lithium-magnesium alloy, lithium-aluminum alloy, lithium-silicon alloy, and lithium-boron alloy.

8. The preparation method according to claim 7, characterized in that: The thickness of the lithium-rich alloy layer is 0.01-2 μm.

9. A composite negative electrode foil, characterized in that: The composite negative electrode foil is prepared by the preparation method according to any one of claims 1 to 8.

10. A battery, characterized in that: The battery comprises the composite negative electrode foil according to claim 9.

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