A composite negative electrode and a battery

Abstract

The present invention relates to the field of battery manufacturing, in particular to a composite negative electrode and a battery. The composite negative electrode includes a current collector, an alloy layer, and an organic layer. The alloy layer is disposed on the current collector, and the organic layer is disposed on the surface of the alloy layer; the alloy layer is a mixture of lithium metal and lithiumophilic metal, and the organic layer is a polymer weak acid; the battery includes a positive electrode, a separator, and the above-mentioned composite negative electrode. The present invention provides a composite negative electrode; wherein, the surface of the lithiumophilic metal in the alloy layer has a lower lithium nucleation overpotential, which can induce uniform deposition of lithium metal on its surface; the polylactic acid of the organic layer can react in-situ with the lithium metal in the alloy layer, and then generate lithium polylactate as the SEI film of the negative electrode; lithium polylactate has excellent lithium ion conduction ability and mechanical properties, and the lithium polylactate with lithium-phobicity can inhibit the longitudinal growth of lithium dendrites; thereby improving the capacity retention rate of the battery.

Description

Technical Field

[0001] The present invention relates to the field of battery manufacturing, and particularly to a composite negative electrode and a battery. Background Art

[0002] New energy alkali metal element batteries have many advantages such as being clean, having a high specific energy, fast charge and discharge speeds, and no memory effect, and are widely used in many fields of life. Currently, the capacity of the existing composite negative electrode material graphite is 360 mAh / g, which is very close to its theoretical capacity of 372 mAh / g, and the compaction development of graphite has also approached the limit. Therefore, the effect of improving the energy density through the composite negative electrode is very limited.

[0003] With the pursuit of high energy density by people, new composite negative electrode materials are constantly being developed. However, the currently existing high-capacity silicon-based composite negative electrodes still face serious problems such as severe particle swelling and fragmentation, and the existing lithium metal composite negative electrodes have serious problems such as uneven deposition-dissolution and low capacity retention rate. Summary of the Invention

[0004] The purpose of the present invention is to overcome the deficiencies of the prior art, and provide a composite negative electrode, which ingeniously solves the problems of serious uneven deposition-dissolution and low capacity retention rate existing in the existing lithium metal composite electrodes.

[0005] To achieve the above purpose, the present invention adopts the following technical solutions:

[0006] The present invention provides a composite negative electrode, which includes a current collector, an alloy layer, and an organic layer. The alloy layer is disposed on the current collector, and the organic layer is disposed on the surface of the alloy layer; the alloy layer is a mixture of lithium metal and a lithiumophilic metal, and the organic layer is a polymer weak acid.

[0007] Optionally, the lithiumophilic metal is at least one of Sn, Be, Ge, Bi, Ga, Zr, Nb, Mo, In, Pt, Ag, Au, Zn.

[0008] Optionally, the molar ratio of lithium metal in the alloy layer is 10% - 90%.

[0009] Optionally, the lithiumophilic metals are mixed in any ratio.

[0010] Optionally, the organic layer is polylactic acid.

[0011] Optionally, the current collector is copper metal or copper alloy.

[0012] Optionally, the thickness of the alloy layer is 5 - 500 nm.

[0013] Optionally, the alloy layer is obtained by at least one of magnetron sputtering, atomic layer deposition, thermal evaporation, and pulsed laser deposition.

[0014] Optionally, the thickness of the organic layer is 0.5 to 100 μm.

[0015] The present invention also provides a battery, which includes a positive electrode, a separator, and the above-mentioned composite negative electrode.

[0016] The beneficial effects of the present invention are as follows. Compared with the prior art, the present invention provides a composite negative electrode. Among them, the surface of the lithiumophilic metal in the alloy layer has a low lithium nucleation overpotential, which can induce uniform deposition of lithium metal on its surface. The polylactic acid in the organic layer can react in-situ with the lithium metal in the alloy layer to generate lithium polylactate as the SEI film of the negative electrode. Lithium polylactate has excellent lithium ion conduction ability and mechanical properties, and the lithium polylactate with lithium-phobicity can inhibit the longitudinal growth of lithium dendrites. Thus, the current collector / alloy layer / organic layer composite negative electrode can effectively resist the influence of high-temperature storage and the frequent rupture and recombination of the SEI film caused by lithium deposition, thereby reducing the effective lithium loss, and then improving the capacity retention rate of the battery. Description of the Drawings

[0017] The present invention will be further described below in conjunction with the drawings and embodiments. In the drawings:

[0018] Figure 1 is a schematic structural diagram of a composite negative electrode provided by the present invention.

[0019] In the figure: 110, current collector; 120, alloy layer; 121, lithium metal; 122, lithiumophilic metal; 130, organic layer. Detailed Embodiments

[0020] One of the main reasons for the reduction of the lithium-ion battery capacity is the irreversible loss of lithium elements (compounds and ions), that is, the formation of irreversible lithium compounds or lithium metal. The irreversible lithium compounds are one of the main components for forming the SEI film, and the irreversible lithium metal mainly forms dendritic lithium and dead lithium.

[0021] The initial nucleation and growth process of lithium dendrites can be divided into 3 stages.

[0022] In the first stage, after the battery is assembled, due to the high activity of lithium metal, it can undergo an instantaneous reaction when contacting components such as organic solvents in the electrolyte to form an SEI film, that is, the formation of the SEI film precedes the generation of dendrites. The dense SEI film can prevent further reaction between the electrolyte and lithium metal, and it is a good ion conductor but an electronic insulator. Li + can pass through this SEI film and deposit on the electrode surface, but due to the characteristics of lithium, electrolyte, SEI film itself and charge-discharge conditions, its deposition distribution is uneven.

[0023] In the second stage, the nucleation stage, i.e., the continuous accumulation of inhomogeneous precipitation, causes bulges in some places until the original SEI film is broken through.

[0024] Finally, it enters the growth stage. After piercing the original SEI film, it continues to grow in the length direction and becomes visible dendrites. At the same time, the SEI film also continuously reacts and proliferates as the lithium metal dendrites grow, but always coats the surface of the lithium metal.

[0025] It can be seen that the reduction of the lithium-ion battery capacity is closely related to the inhomogeneous deposition of lithium ions on the negative electrode.

[0026] In order to further improve the negative electrode capacity, inhibit the side reaction between the negative electrode active material and the electrolyte, improve the lithium ion deposition-dissolution efficiency on the negative electrode, and slow down the dendrite growth; the present invention provides a novel composite negative electrode. The composite negative electrode provided by the present invention has a lithium-philic layer and a lithium-phobic layer. By uniformly depositing an alloy of lithium metal and lithium-philic metal on the negative electrode current collector; then uniformly coating polylactic acid on the surface of the alloy, polylactic acid in-situ generates lithium polylactate as the SEI film with the lithium metal in the alloy layer, the lithium-philic metal serves as the lithium-philic layer, and lithium polylactate serves as the lithium-phobic layer, and the two jointly promote the uniform deposition-dissolution of lithium on the negative electrode.

[0027] Lithium polylactate has excellent lithium ion conduction ability and mechanical properties. Lithium polylactate with lithium-phobicity can inhibit the longitudinal growth of lithium dendrites; thus enabling the current collector / alloy layer / organic layer composite negative electrode to effectively resist the influence of frequent rupture and recombination of the SEI film caused by high-temperature storage and lithium deposition, thereby reducing the effective lithium loss, and then being able to improve the capacity retention rate of the battery.

[0028] Now, in combination with the attached drawings, the technical solutions and embodiments of the present invention will be described in detail.

[0029] The technical solution adopted by the present invention is as follows:

[0030] The present invention provides a composite negative electrode, which includes a current collector 110, an alloy layer 120, and an organic layer 130. The alloy layer 120 is disposed on the current collector 110, and the organic layer 130 is disposed on the surface of the alloy layer 120; the alloy layer 120 is a mixture of a lithium metal 121 and a lithium-philic metal 122, and the organic layer 130 is a polymer weak acid.

[0031] Furthermore, the lithium-philic metal 122 is at least one of Sn, Be, Ge, Bi, Ga, Zr, Nb, Mo, In, Pt, Ag, Au, Zn. In the embodiments of the present application, Sn, Zn, Mo, and Bi are preferably selected and mixed with the lithium metal 121 as the lithium-philic metal 122.

[0032] Specifically, the molar ratio of the lithium metal 121 in the alloy layer 120 is 10% - 90%.

[0033] Specifically, the lithiophilic metal 122 is mixed in any proportion.

[0034] Preferably, the organic layer 130 is polylactic acid, and its structural formula is as follows:

[0035]

[0036] Lithium metal in the alloy layer and polylactic acid will in-situ generate lithium polylactate as the SEI film. The lithiophilic metal serves as the lithiophilic layer, and lithium polylactate serves as the lithium-phobic layer. The two jointly promote the uniform deposition and dissolution of lithium at the negative electrode.

[0037] Polylactic acid itself has a certain adhesive force. Therefore, no additional oil-soluble binder needs to be added during the coating process of the organic layer. The oil-soluble binder will generate toxic and harmful gases during the processing, making the product more environmentally friendly.

[0038] Preferably, the current collector 110 is copper metal or copper alloy; copper metal has excellent electrical conductivity, good ductility, and low cost; during the charge and discharge process of the battery, metallic copper has only a very small lithium intercalation capacity and can maintain the stability of the material structure and electrochemical performance.

[0039] Specifically, the thickness of the alloy layer 120 is 5 - 500 nm.

[0040] Furthermore, the alloy layer 120 is obtained by at least one of magnetron sputtering, atomic layer deposition, thermal evaporation, and pulsed laser deposition.

[0041] Specifically, the thickness of the organic layer 130 is 0.5 - 100 μm.

[0042] The present invention also provides a battery, which includes a positive electrode, a separator, and the above-mentioned composite negative electrode.

[0043] The preparation method of a composite negative electrode and a battery provided by the present invention is as follows:

[0044] (1) According to the ratio of the molar number of lithium metal 121: the molar number of lithiophilic metal 122 = (10% - 90%):(10% - 90%), the lithium metal 121 and the lithiophilic metal 122 are melt-mixed to prepare a mixed metal block;

[0045] Optionally, the lithiophilic metal 122 can be at least one of Sn, Be, Ge, Bi, Ga, Zr, Nb, Mo, In, Pt, Ag, Au, Zn. In the embodiments of the present application, Sn, Zn, Mo, and Bi are preferably used and mixed with the lithium metal 121 as the lithiophilic metal 122.

[0046] (2) Perform corresponding treatment on the mixed metal block and deposit it on the surface of the current collector 110 of the negative electrode by methods such as magnetron sputtering, atomic layer deposition, thermal evaporation plating, pulsed laser deposition, etc., with a thickness of 5 - 500 nm, to obtain the composite negative electrode 1 for use.

[0047] Optionally, the current collector 110 can be copper metal or copper alloy. In the embodiments of the present application, copper foil is preferably used as the current collector 110.

[0048] (3) Add polylactic acid to NMP (N-methylpyrrolidone), stir evenly, and adjust to an appropriate viscosity.

[0049] (4) Coat the polylactic acid slurry on the surface of the composite negative electrode 1 by a coater, with a coating thickness of 0.5 - 100 μm, and obtain the composite negative electrode 2 after drying, that is, the current collector 110 / alloy layer 120 / polylactic acid composite negative electrode as shown. Figure 1 shown.

[0050] (5) Prepare the positive electrode sheet. The main material in the positive electrode sheet can be at least one of positive electrode materials such as lithium cobaltate, lithium manganate, lithium iron phosphate, and ternary positive electrode materials, with a proportion of 50.0% - 99.5%; in the embodiments of the present application, the preparation materials of the positive electrode sheet are not specifically limited.

[0051] (6) The separator can be selected from various forms and materials of separators such as PP / PE separators, solid-state separators, and gel separators. In the embodiments of the present application, the form and material of the separator are not specifically limited.

[0052] (7) Assemble into a battery in the form of composite negative electrode 2 / separator / positive electrode.

[0053] Optionally, the lithiophilic metal 122 can be at least one of Sn, Be, Ge, Bi, Ga, Zr, Nb, Mo, In, Pt, Ag, Au, Zn. In the embodiments of the present application, Sn, Zn, Mo, Bi are preferably used as the lithiophilic metal 122 to be mixed with the lithium metal 121.

[0054] Polylactic acid in-situ generates lithium polylactate with the lithium metal 121 in the alloy layer 120, and its structural formula is as follows:

[0055]

[0056] Use lithium polylactate as the SEI film. Among them, the lithiophilic metal 122 serves as the lithiophilic layer, and lithium polylactate serves as the lithium-phobic layer, making the deposition of lithium ions on the negative electrode more uniform, thereby alleviating the growth of lithium dendrites, and further improving the capacity retention rate of the battery to obtain better battery performance.

[0057] Polylactic acid is granular and insoluble in water, so NMP is required as a solvent for the preparation of the polylactic acid slurry needed for coating. Polylactic acid itself has a certain adhesive force, so no additional oil-soluble binder needs to be added during the preparation of the polylactic acid slurry. Oil-soluble binders generate high-temperature organic waste gas during the coating process, which not only causes serious environmental pollution but also harms the health of operators. The polylactic acid slurry composed of polylactic acid and NMP reduces production costs and pollutant emissions in the production process, and is more environmentally friendly.

[0058] Preferably, during the production of the composite negative electrode, the air humidity in the environment needs to be controlled below 5%. Lithium metal 121 is the metal with the strongest known activity. Too high humidity will cause the lithium metal 121 in the negative electrode to undergo a hydrogen evolution reaction, and the hydrogen evolution reaction will release heat, which will then damage the composite negative electrode and cause unnecessary lithium loss.

[0059] The embodiments of the present invention will be described in detail below. The embodiments are exemplary and are intended to explain the present invention and should not be construed as limiting the present invention.

[0060] The present invention will be described in detail through specific embodiments as follows:

[0061] Example 1

[0062] Example 1 provides a composite negative electrode and a battery, and its preparation method includes the following steps:

[0063] 1. Preparation of the composite negative electrode

[0064] (1) By means of thermal evaporation, a lithium-tin mixed metal layer with a lithium molar ratio: tin molar ratio of 10%:90% is evaporated onto a 6μm copper foil of the negative electrode current collector, and the evaporation thickness is about 50 - 100nm, and the air humidity needs to be controlled below 5%;

[0065] (2) The polylactic acid slurry is coated on the surface of the lithium-tin metal layer, and the coating thickness is about 10μm, and then dried to obtain the composite negative electrode.

[0066] 2. Assembly of the battery

[0067] (1) The positive electrode uses lithium cobaltate, and the single-sided surface density of the positive electrode is 120g / m 2 , and the aluminum foil is 9μm;

[0068] (2) The separator uses a 5μm base film and is coated in the way of 1μm PVDF + 2μm Al2O3 + 1μm PVDF;

[0069] (3) The electrolyte uses a carbonate-based electrolyte, the solute is 1mol / L LiPF6, and the solvent is EC, DMC, and DEC with a volume ratio of 1:1:1;

[0070] (4) Assemble the above composite negative electrode, positive electrode, separator and electrolyte into a battery according to the specifications of a button cell CR2025.

[0071] Example 2

[0072] Example 2 provides a composite negative electrode and a battery, and its preparation method includes the following steps:

[0073] 1. Preparation of the composite negative electrode

[0074] (1) By thermal evaporation method, deposit a lithium-zinc alloy layer with a lithium molar ratio: zinc molar ratio of 10%:90% onto a 6μm copper foil of the negative electrode current collector, with a deposition thickness of about 50 - 100nm, and the air humidity needs to be controlled below 5%;

[0075] (2) Coat the surface of the lithium-zinc alloy layer with a polylactic acid slurry, with a coating thickness of about 10μm, and then dry it to obtain the composite negative electrode.

[0076] 2. Assembly of the battery

[0077] (1) The positive electrode uses lithium cobaltate, and the single-sided surface density of the positive electrode is 120g / m 2 , and the aluminum foil is 9μm;

[0078] (2) The separator uses a 5μm base film and is coated in the way of 1μm PVDF + 2μm Al2O3 + 1μm PVDF;

[0079] (3) The electrolyte uses a carbonate-based electrolyte, the solute is 1mol / L LiPF6, and the solvent is EC, DMC and DEC with a volume ratio of 1:1:1;

[0080] (4) Assemble the above composite negative electrode, positive electrode, separator and electrolyte into a battery according to the specifications of a button cell CR2025.

[0081] Example 3

[0082] Example 3 provides a composite negative electrode and a battery, and its preparation method includes the following steps:

[0083] 1. Preparation of the composite negative electrode

[0084] (1) By magnetron sputtering method, sputter a lithium-bismuth alloy layer with a lithium molar ratio: bismuth molar ratio of 10%:90% onto a 6μm copper foil of the negative electrode current collector, with a deposition thickness of about 50 - 100nm, and the air humidity needs to be controlled below 5%;

[0085] (2) Coat the surface of the lithium-bismuth alloy layer with a polylactic acid slurry, with a coating thickness of about 10μm, and then dry it to obtain the composite negative electrode.

[0086] 2. Assembly of the battery

[0087] (1) The positive electrode uses lithium cobaltate, and the single-sided surface density of the positive electrode is 120 g / m 2 , and the aluminum foil is 9 μm;

[0088] (2) The separator uses a 5-μm base film and is coated with 1-μm PVDF + 2-μm Al2O3 + 1-μm PVDF;

[0089] (3) The electrolyte uses a carbonate-based electrolyte, the solute is 1 mol / L LiPF6, and the solvent is EC, DMC, and DEC with a volume ratio of 1:1:1;

[0090] (4) Assemble the above composite negative electrode, positive electrode, separator, and electrolyte into a battery according to the specifications of a button cell CR2025.

[0091] Example 4

[0092] Example 4 provides a composite negative electrode and a battery, and its preparation method includes the following steps:

[0093] 1. Preparation of the composite negative electrode

[0094] (1) By magnetron sputtering method, a lithium molybdenum alloy layer with a lithium molar ratio: molybdenum molar ratio of 10%:90% is sputtered onto a 6-μm copper foil of the negative electrode current collector, and the evaporation thickness is about 50 - 100 nm, and the air humidity needs to be controlled below 5%;

[0095] (2) Coat the surface of the lithium tin alloy layer with a polylactic acid slurry, and the coating thickness is about 10 μm, and then dry it to obtain the composite negative electrode.

[0096] 2. Assemble the battery

[0097] (1) The positive electrode uses lithium cobaltate, and the single-sided surface density of the positive electrode is 120 g / m 2 , and the aluminum foil is 9 μm;

[0098] (2) The separator uses a 5-μm base film and is coated with 1-μm PVDF + 2-μm Al2O3 + 1-μm PVDF;

[0099] (3) The electrolyte uses a carbonate-based electrolyte, the solute is 1 mol / L LiPF6, and the solvent is EC, DMC, and DEC with a volume ratio of 1:1:1;

[0100] (4) Assemble the above composite negative electrode, positive electrode, separator, and electrolyte into a battery according to the specifications of a button cell CR2025.

[0101] Comparative Example 1

[0102] Comparative Example 1 provides a battery, and its preparation method includes the following steps:

[0103] (1) The negative electrode uses a lithium sheet;

[0104] (1) The positive electrode uses lithium cobalt oxide, and the single-sided surface density of the positive electrode is 120 g / m 2 , and the aluminum foil is 9 μm;

[0105] (2) The separator uses a 5-μm base film and is coated in the way of 1-μm PVDF + 2-μm Al2O3 + 1-μm PVDF;

[0106] (3) The electrolyte uses a carbonate-based electrolyte, the solute is 1 mol / L LiPF6, and the solvent is EC, DMC, and DEC with a volume ratio of 1:1:1;

[0107] (4) Assemble the above-mentioned negative electrode, positive electrode, separator, and electrolyte into a battery according to the specifications of a button cell CR2025.

[0108] Comparative Example 2

[0109] Comparative Example 2 provides a composite negative electrode and a battery, and its preparation method includes the following steps:

[0110] 1. Preparation of the composite negative electrode

[0111] (1) Coat a polylactic acid slurry on the surface of a 6-μm copper foil with a thickness of about 10 μm, and then dry it to obtain a composite electrode.

[0112] 2. Assemble the battery

[0113] (1) The positive electrode uses lithium cobalt oxide, and the single-sided surface density of the positive electrode is 120 g / m 2 , and the aluminum foil is 9 μm;

[0114] (2) The separator uses a 5-μm base film and is coated in the way of 1-μm PVDF + 2-μm Al2O3 + 1-μm PVDF;

[0115] (3) The electrolyte uses a carbonate-based electrolyte, the solute is 1 mol / L LiPF6, and the solvent is EC, DMC, and DEC with a volume ratio of 1:1:1;

[0116] (4) Assemble the above-mentioned composite negative electrode, positive electrode, separator, and electrolyte into a battery according to the specifications of a button cell CR2025.

[0117] The following method is used to test the electrochemical cycling performance:

[0118] Assemble into a CR2025 button cell according to the conventional production process, and perform constant current charge and discharge at a 1C rate, and the charge and discharge voltage range is 3.0 - 4.45 V.

[0119] The summary of the electrochemical test results of the batteries prepared in Examples 1 to 4 and Comparative Examples 1 and 2 is shown in Table 1 as follows:

[0120] Table 1

[0121] Item Capacity retention rate at 500 cycles Average Coulombic efficiency Example 1 93.1％ 97.5％ Example 2 94.0％ 97.3％ Example 3 94.9％ 98.1％ Example 4 95.3％ 98.4％ Comparative Example 1 84.3％ 87.5％ Comparative Example 2 90.5％ 94.8％

[0122] The test results show that, compared with the batteries in Comparative Examples 1 and 2, the batteries in Examples 1 to 4 have improved 500-week cycle retention rate and average Coulombic efficiency; among them, when metallic bismuth and metallic molybdenum are used as the main components of the lithiumophilic layer alloy, the 500-week cycle retention rate and average Coulombic efficiency of the batteries in Examples 3 and 4 are better.

[0123] The above-described are only the preferred embodiments of the present invention, and the above specific embodiments do not limit the present invention. Various deformations and modifications can occur within the scope of the technical idea of the present invention. Any retouching, modification or equivalent replacement made by those of ordinary skill in the art according to the above description shall fall within the scope protected by the present invention.

Claims

1. A composite negative electrode, characterized in that, It includes a current collector, an alloy layer, and an organic layer. The alloy layer is disposed on the current collector, and the organic layer is disposed on the surface of the alloy layer; the alloy layer is a mixture of lithium metal and lithiumophilic metal; The organic layer is polylactic acid. The polylactic acid in-situ generates lithium polylactate as the SEI film with the lithium metal in the alloy layer, the lithiumophilic metal serves as the lithiumophilic layer, and the lithium polylactate serves as the lithium-phobic layer.

2. The composite negative electrode according to claim 1, wherein The lithiumophilic metal is at least one of Sn, Be, Ge, Bi, Ga, Zr, Nb, Mo, In, Pt, Ag, Au, Zn.

3. The composite negative electrode according to claim 2, wherein The molar ratio of the lithium metal in the alloy layer is 10% - 90%.

4. The composite negative electrode according to claim 3, characterized in that, The lithiumophilic metals are mixed in any proportion.

5. The composite negative electrode according to claim 1, wherein The current collector is metal copper or copper alloy.

6. The composite negative electrode according to claim 1, characterized in that, The thickness of the alloy layer is 5 - 500 nm.

7. The composite negative electrode according to claim 6, characterized in that, The alloy layer is obtained by at least one of magnetron sputtering, atomic layer deposition, thermal evaporation, and pulsed laser deposition.

8. The composite negative electrode according to claim 4, wherein The thickness of the organic layer is 0.5 - 100 μm.

9. A battery, characterized in that, It includes a positive electrode, a separator, and the composite negative electrode according to any one of claims 1 - 8.

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