All-solid-state composite positive electrode and preparation method and application thereof

Abstract

The invention relates to the technical field of solid-state lithium batteries, and provides an all-solid-state composite positive electrode and a preparation method and application thereof.The preparation method of the all-solid-state composite positive electrode comprises the steps that nickel nitrate hexahydrate (Ni (NO3) 2.6 H2O), manganese chloride tetrahydrate (MnCl2. 4H2O) and an amino-containing organic ligand are dissolved in ethyl alcohol, and NiMn-MOF-NH2 is synthesized through a hydrothermal method; the preparation method comprises the following steps: respectively dissolving NiMn-MOF-NH2, a positive electrode active material, a conductive agent, a polymer and a lithium salt in an organic solvent, uniformly stirring to obtain all-solid-state composite positive electrode slurry, blade-coating an aluminum foil with the all-solid-state composite positive electrode slurry, and heating to remove the solvent to obtain the all-solid-state composite positive electrode. Amino groups in NiMn-MOF-NH2 can form coordination with the polymer, and the crystallinity of the polymer is reduced, so that the lithium ion transmission capacity of the all-solid-state composite positive electrode is improved. Amino groups in NiMn-MOF-NH2 have strong interaction with the polymer, so that the interface stability of the electrode is further improved, and the all-solid-state battery assembled by the NiMn-MOF-NH2 has relatively high charge-discharge efficiency, rate capability and service life.

Description

Technical Field

[0001] The present invention relates to the technical field of solid-state lithium batteries, and in particular to an all-solid-state composite positive electrode and a preparation method and application thereof. Background Art

[0002] Solid-state electrolytes are widely considered to be an important component of next-generation high-performance batteries due to their excellent safety and potential high energy density. Compared with traditional liquid electrolytes, solid-state electrolytes can effectively suppress the growth of lithium dendrites and support the application of high-voltage cathode materials. However, despite certain progress in material design and ionic conductivity of solid-state electrolytes, the interface problem between the cathode and solid-state electrolyte remains one of the key challenges restricting their practical application.

[0003] The interface problems between solid electrolytes and positive electrode materials are mainly manifested in poor interface contact, interface side reactions, high interface impedance and insufficient electrochemical stability. First, since both the solid electrolyte and the positive electrode material are solid, it is difficult to form a close interface contact between the two, and there may be micron-scale or even nano-scale gaps at the interface. These gaps reduce the transmission efficiency of lithium ions and increase the interface impedance, resulting in a decrease in the battery's rate performance. In addition, the positive electrode material is usually accompanied by a large volume change during the charge and discharge process, which further aggravates the interface stress, causing the interface to gradually crack and peel, seriously affecting the battery's cycle stability. Secondly, irreversible interface side reactions may occur between the solid electrolyte and the high-voltage positive electrode material. For example, polymer solid electrolytes have poor antioxidant capacity and are easily decomposed under high voltage, affecting battery life.

[0004] Therefore, it is necessary to study a high-performance all-solid-state composite positive electrode to improve the interface stability problem in solid-state batteries. Summary of the Invention

[0005] In order to solve the problem of interface stability between the positive electrode and the solid electrolyte in the prior art, the present invention provides an all-solid-state composite positive electrode and a preparation method and application thereof.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A method for preparing an all-solid-state composite positive electrode comprises the following steps:

[0008] S1: Synthesis of NiMn-MOF-NH2: Nickel nitrate hexahydrate (Ni(NO3)2·6H2O), manganese chloride tetrahydrate (MnCl2·4H2O), and an amino-containing organic ligand were dissolved in ethanol and synthesized by a hydrothermal method to obtain NiMn-MOF-NH2;

[0009] S2: Preparation of an all-solid-state composite positive electrode: Dissolve the NiMn-MOF-NH2, positive electrode active material, conductive agent, polymer and lithium salt in an organic solvent respectively, stir evenly to obtain an all-solid-state composite positive electrode slurry, and then scrape the all-solid-state composite positive electrode slurry on aluminum foil and heat to remove the solvent to obtain an all-solid-state composite positive electrode.

[0010] The present invention provides a method for preparing an all-solid-state composite positive electrode. NiMn-MOF-NH2 incorporated into the positive electrode forms coordination with a polymer via amino groups, reducing the polymer's crystallinity and thereby improving the electrode's lithium-ion transport capacity. Furthermore, the amino groups in the NiMn-MOF-NH2, due to their strong interaction with the polymer, further enhance the electrode's interfacial stability.

[0011] As a preferred embodiment of the present invention, in step 1, the molar ratio of the nickel nitrate hexahydrate (Ni(NO3)2·6H2O), manganese chloride tetrahydrate (MnCl2·4H2O), and amino-containing organic ligand added is 2:1:(0.5-2.5).

[0012] As a preferred embodiment of the present invention, in step 1, the material of the amino-containing organic ligand comprises a combination of one or more of 2-aminoterephthalic acid, 3-aminotriphenol, 5-(5-aminotetrazolyl)-1,3-benzenedicarboxylic acid, 5-aminotetrazolyl, 3-amino-4-(pyridin-4-yl)benzoic acid, 5-amino-1H-imidazole-4-carbonitrile, 2-aminobenzimidazole, adenine and 2-amino-1,3,5-benzenetricarboxylic acid.

[0013] As a preferred embodiment of the present invention, in step 2, the positive electrode active material comprises a combination of one or more of lithium cobalt oxide (LiCoO2), lithium iron phosphate (LiFePO4), and nickel-cobalt-manganese ternary electrode material (NCM).

[0014] As a preferred embodiment of the present invention, in step 2, the polymer material comprises one or more combinations of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), and polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE).

[0015] As a preferred embodiment of the present invention, in step 2, the lithium salt material includes one or more combinations of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(oxalatoborate) (LiBOB), lithium difluorooxalatoborate (LiDFOB) and lithium hexafluorophosphate (LiPF6).

[0016] As a preferred embodiment of the present invention, in step 2, the added mass ratio of the NiMn-MOF-NH2, the positive electrode active material, the conductive agent, the polymer and the lithium salt is: (0.5-15): (40-95): (1-10): (5-50): (1-15).

[0017] The present invention also provides an all-solid-state composite positive electrode, which is prepared by the above-mentioned preparation method of the all-solid-state composite positive electrode.

[0018] The present invention adopts an all-solid-state composite positive electrode, in which the lone pair electrons in the amino group form a dynamic hydrogen bond network with the polymer, reducing the crystallinity, significantly increasing the free volume of the amorphous region, and reducing the energy barrier for lithium ion migration; the periodic pores of the MOF and the decrystallized polymer form a through-type ion transmission path, thereby improving the lithium ion transmission capacity.

[0019] As a preferred embodiment of the present invention, the thickness of the all-solid-state composite positive electrode is 1 μm to 150 μm.

[0020] The present invention also provides an all-solid-state battery, comprising applying the all-solid-state composite positive electrode as described above in the all-solid-state battery.

[0021] The present invention adopts an all-solid-state battery, and the all-solid-state composite positive electrode used has high ionic conductivity and low interface impedance. The amino coordination effect of NiMn-MOF-NH2 can inhibit the degradation of the electrode structure. The all-solid-state battery assembled with the all-solid-state composite positive electrode provided by the present invention has high charge and discharge efficiency, rate performance and life.

[0022] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0023] 1. A method for preparing an all-solid-state composite cathode. NiMn-MOF-NH2 incorporated into the cathode forms coordination with a polymer via amino groups, reducing the polymer's crystallinity and thereby improving the lithium-ion transport capacity of the all-solid-state composite cathode. Furthermore, the amino groups in the NiMn-MOF-NH2, due to their strong interaction with the polymer, further enhance the electrode's interfacial stability.

[0024] 2. An all-solid-state composite positive electrode, in which the lone pair electrons in the amino group form a dynamic hydrogen bond network with the polymer, reducing the crystallinity, significantly increasing the free volume of the amorphous region, and reducing the energy barrier for lithium ion migration; the periodic pores of MOF and the decrystallized polymer form a through-type ion transmission path, improving the lithium ion transmission capacity.

[0025] 3. An all-solid-state battery, wherein the all-solid-state composite positive electrode used has high ionic conductivity and low interfacial impedance, and the amino coordination effect of NiMn-MOF-NH2 can inhibit the degradation of the electrode structure. The all-solid-state battery assembled with the all-solid-state composite positive electrode provided by the present invention has high charge and discharge efficiency, rate performance and life. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The figure is a comparison of the rate performance of battery A, battery B and battery C at room temperature of 25°C;

[0027] Figure 2 The cycling performance test of battery A and battery C at room temperature 25°C and 0.2C. DETAILED DESCRIPTION

[0028] The present invention will be described in detail below with reference to the accompanying drawings.

[0029] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0030] Example 1

[0031] The present invention provides a method for preparing an all-solid-state composite positive electrode, comprising the following steps:

[0032] S1: Synthesis of NiMn-MOF-NH2: Nickel nitrate hexahydrate (Ni(NO3)2·6H2O), manganese chloride tetrahydrate (MnCl2·4H2O), and an amino-containing organic ligand were dissolved in ethanol and synthesized by a hydrothermal method to obtain NiMn-MOF-NH2;

[0033] S2: Preparation of an all-solid-state composite positive electrode: Dissolve the NiMn-MOF-NH2, positive electrode active material, conductive agent, polymer and lithium salt in an organic solvent respectively, stir evenly to obtain an all-solid-state composite positive electrode slurry, and then scrape the all-solid-state composite positive electrode slurry on aluminum foil and heat to remove the solvent to obtain an all-solid-state composite positive electrode.

[0034] Furthermore, in step 1, the molar ratio of the added amounts of nickel nitrate hexahydrate (Ni(NO3)2·6H2O), manganese chloride tetrahydrate (MnCl2·4H2O), and amino-containing organic ligand is 2:1:(0.5-2.5).

[0035] Furthermore, in step 1, the material of the amino-containing organic ligand comprises a combination of one or more of 2-aminoterephthalic acid, 3-aminotriphenol, 5-(5-aminotetrazolyl)-1,3-benzenedicarboxylic acid, 5-aminotetrazolyl, 3-amino-4-(pyridin-4-yl)benzoic acid, 5-amino-1H-imidazole-4-carbonitrile, 2-aminobenzimidazole, adenine and 2-amino-1,3,5-benzenetricarboxylic acid.

[0036] Furthermore, in step 2, the positive electrode active material comprises a combination of one or more of lithium cobalt oxide (LiCoO2), lithium iron phosphate (LiFePO4), and nickel-cobalt-manganese ternary electrode material (NCM).

[0037] Furthermore, in step 2, the polymer material includes one or more combinations of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), and polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE).

[0038] Furthermore, in step 2, the lithium salt material includes one or more combinations of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(oxalatoborate) (LiBOB), lithium difluorooxalatoborate (LiDFOB) and lithium hexafluorophosphate (LiPF6).

[0039] Furthermore, in step 2, the added mass ratio of the NiMn-MOF-NH2, the positive electrode active material, the conductive agent, the polymer and the lithium salt is: (0.5-15): (40-95): (1-10): (5-50): (1-15).

[0040] The NiMn-MOF-NH2 incorporated into the cathode forms coordination with the polymer through amino groups, reducing the polymer's crystallinity and thus improving the lithium-ion transport capacity of the all-solid-state composite cathode. Furthermore, the amino groups in the NiMn-MOF-NH2, due to their strong interaction with the polymer, can further improve the electrode's interfacial stability.

[0041] In this embodiment, the preparation method of the all-solid-state composite positive electrode is as follows:

[0042] Synthesis of NiMn-MOF-NH2: 0.58 g of nickel nitrate hexahydrate (Ni(NO3)2·6H2O), 0.396 g of manganese chloride tetrahydrate (MnCl2·4H2O), and 0.724 g of 2-aminoterephthalic acid were dissolved in ethanol and heated at 150°C for 15 h to obtain NiMn-MOF-NH2 by a hydrothermal method.

[0043] Preparation of all-solid-state composite cathode slurry: In this embodiment, conductive carbon black (Super-P) is used as the conductive agent; NiMn-MOF-NH2, lithium iron phosphate, conductive carbon black (Super-P), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) are added to NMP solvent in a mass ratio of 5:60:10:13:8, and the slurry solid solution ratio is 1 g:1.5 mL;

[0044] The all-solid-state composite cathode slurry was stirred at a speed of 3000 rpm for 10 h, and then the stirred slurry was filtered and allowed to stand under vacuum for 30 min to remove bubbles.

[0045] The all-solid composite positive electrode slurry was poured onto an aluminum foil with a thickness of 15 μm. The thickness of the scraper was set to 120 μm. The positive electrode material was uniformly coated by the coating machine, and then pre-dried at 90 ° C for 0.5 h. The electrode was rolled with a compression of 10% and cut into 5×6 cm 2 , and further dried in a vacuum drying oven at 80°C for 9 hours to prepare an all-solid-state composite cathode;

[0046] Example 2

[0047] The present invention provides an all-solid-state composite positive electrode, which is prepared by the preparation method of the all-solid-state composite positive electrode described in Example 1.

[0048] Furthermore, the thickness of the all-solid-state composite positive electrode is 1 μm to 150 μm.

[0049] The lone pair electrons in the amino group form a dynamic hydrogen bond network with the polymer, reducing the crystallinity, significantly increasing the free volume of the amorphous region, and reducing the energy barrier for lithium ion migration; the periodic pores of MOF and the decrystallized polymer form a through-type ion transmission path, which improves the lithium ion transmission capacity.

[0050] Example 3

[0051] The present invention provides an all-solid-state battery, comprising applying an all-solid-state composite positive electrode as described in Example 2 in the all-solid-state battery.

[0052] The all-solid-state composite positive electrode used has high ionic conductivity and low interfacial impedance. The amino coordination effect of NiMn-MOF-NH2 can inhibit the degradation of the electrode structure. The all-solid-state battery assembled with the all-solid-state composite positive electrode provided by the present invention has high charge and discharge efficiency, rate performance and life.

[0053] In this embodiment, the specific preparation method of the all-solid-state battery is as follows:

[0054] 1. Preparation of all-solid-state composite cathode

[0055] The all-solid-state composite positive electrode was prepared by the preparation method of Example 1, and had a thickness of 30 μm.

[0056] 2. Preparation of solid electrolyte membrane

[0057] The solid electrolyte separator is composed of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) in a mass ratio of 1:1, and the thickness of the separator is 150 μm.

[0058] 3. Assembly of all-solid-state batteries

[0059] The all-solid-state composite positive electrode and lithium metal negative electrode plates are welded with aluminum tabs and nickel tabs respectively, and then stacked in the order of all-solid-state composite positive electrode / solid-state electrolyte membrane / lithium metal negative electrode plates. The stacked battery cells are left with the tabs and vacuum-sealed in an aluminum-plastic film. The battery is then statically pressed at 6 MPa for 20 minutes to obtain an all-solid-state battery, which is recorded as Battery A.

[0060] Example 4

[0061] The present invention provides an all-solid-state battery, which is basically the same as Example 3, except that: when preparing the all-solid-state composite positive electrode slurry in the preparation method of the all-solid-state composite positive electrode, the addition ratio of NiMn-MOF-NH2, lithium iron phosphate, conductive carbon black (Super-P), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) is 15:60:10:13:8, and the obtained all-solid-state battery is recorded as Battery B.

[0062] Comparative Example 1

[0063] This embodiment provides an all-solid-state battery, and the preparation method is basically the same as the method for preparing the all-solid-state battery in Example 3, except that: in the preparation method of the all-solid-state composite positive electrode, when preparing the all-solid-state composite positive electrode slurry, no NiMn-MOF-NH2 is added, and lithium iron phosphate, conductive carbon black (Super-P), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), and lithium bis(trifluoromethanesulfonyl imide) (LiTFSI) are added to NMP solvent in a mass ratio of 60:10:13:8, and the slurry solid solution ratio is 1 g:1.5 mL. The obtained all-solid-state battery is recorded as Battery C;

[0064] The battery A, battery B and battery C prepared in Examples 3 to 4 and Comparative Example 1 were subjected to rate performance tests and cycle performance tests at room temperature of 25° C. The test results are as follows.

[0065] (1) Rate performance test: Figure 1The figure shows the rate performance of battery A, battery B and battery C at rates of 0.1C, 0.2C, 0.5C, 0.8C and 1C at room temperature of 25°C. Both battery A and battery B show better rate performance than battery C, and battery A has better rate performance than battery B. Therefore, the all-solid-state battery assembled with an all-solid-state composite positive electrode has excellent rate performance, and the addition ratio of NiMn-MOF-NH2, lithium iron phosphate, Super-P, PVDF-HFP and LiTFSI is 5:60:10:13:8, which has more excellent performance. Battery A and battery C were subjected to cycle performance tests and analyzed.

[0066] (2) Cyclic performance test: Figure 2 The following graph shows the cycle life of batteries A and C. Tested at room temperature, 25°C, and a rate of 0.2C, battery A was able to cycle stably for 100 cycles, maintaining 93% of its initial capacity and an average coulombic efficiency of 99.9%. Battery C began to experience a significant performance decline after 18 cycles at room temperature, 25°C, and a rate of 0.2C. By the 100th cycle, the performance had dropped to 6.5%. Therefore, the all-solid-state battery assembled with the NiMn-MOF-NH2 all-solid-state composite cathode exhibits excellent charge-discharge efficiency and cycling performance.

[0067] Based on the above test results, the all-solid-state battery assembled with the all-solid-state composite positive electrode containing NiMn-MOF-NH2 has better rate performance, charge and discharge efficiency, cycle performance and longer service life than the all-solid-state battery assembled with the general all-solid-state composite positive electrode.

[0068] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing an all-solid-state composite positive electrode, characterized in that: The following steps are involved: S1: Synthesis of NiMn-MOF-NH2: Nickel nitrate hexahydrate (Ni(NO3)2·6H2O), manganese chloride tetrahydrate (MnCl2·4H2O), and an amino-containing organic ligand were dissolved in ethanol and synthesized by a hydrothermal method to obtain NiMn-MOF-NH2; S2: Preparation of an all-solid-state composite positive electrode: Dissolve the NiMn-MOF-NH2, positive electrode active material, conductive agent, polymer and lithium salt in an organic solvent respectively, stir evenly to obtain an all-solid-state composite positive electrode slurry, and then scrape the all-solid-state composite positive electrode slurry on aluminum foil and heat to remove the solvent to obtain an all-solid-state composite positive electrode.

2. The method for preparing an all-solid-state composite positive electrode according to claim 1, wherein: In step 1, the molar ratio of nickel nitrate hexahydrate (Ni(NO3)2·6H2O), manganese chloride tetrahydrate (MnCl2·4H2O), and amino-containing organic ligand is 2:1:(0.5-2.5).

3. The method for preparing an all-solid-state composite positive electrode according to claim 2, wherein: In step 1, the material of the amino-containing organic ligand includes one or more combinations of 2-aminoterephthalic acid, 3-aminotriphenol, 5-(5-aminotetrazolyl)-1,3-benzenedicarboxylic acid, 5-aminotetrazolyl, 3-amino-4-(pyridin-4-yl)benzoic acid, 5-amino-1H-imidazole-4-carbonitrile, 2-aminobenzimidazole, adenine and 2-amino-1,3,5-benzenetricarboxylic acid.

4. The method for preparing an all-solid-state composite positive electrode according to claim 1, wherein: In step 2, the positive electrode active material includes one or more combinations of lithium cobalt oxide (LiCoO2), lithium iron phosphate (LiFePO4), and nickel cobalt manganese ternary electrode material (NCM).

5. The method for preparing an all-solid-state composite positive electrode according to claim 1, wherein: In step 2, the polymer material includes one or more combinations of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), and polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE).

6. The method for preparing an all-solid-state composite positive electrode according to claim 1, characterized in that: In step 2, the lithium salt material includes one or more combinations of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(oxalatoborate) (LiBOB), lithium difluorooxalatoborate (LiDFOB) and lithium hexafluorophosphate (LiPF6).

7. The method for preparing an all-solid-state composite cathode according to any one of claims 1 to 6, characterized in that: In step 2, the addition mass ratio of the NiMn-MOF-NH2, the positive electrode active material, the conductive agent, the polymer and the lithium salt is: (0.5-15): (40-95): (1～10):(5～50):(1～15)。 8. An all-solid-state composite positive electrode, characterized in that: The invention is prepared by the preparation method of an all-solid-state composite positive electrode according to any one of claims 1 to 7.

9. The all-solid-state composite cathode according to claim 8, characterized in that: The thickness of the all-solid-state composite positive electrode is 1 μm to 150 μm.

10. An all-solid-state battery, characterized in that: The method comprises applying an all-solid-state composite positive electrode as described in any one of claims 8 to 9 in an all-solid-state battery.

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