Positive electrode lithium supplement agent, positive electrode lithium supplement agent preparation method, battery positive electrode and battery

Abstract

The invention relates to the technical field of batteries, in particular to a positive electrode lithium supplementing agent, a preparation method of the positive electrode lithium supplementing agent, a battery positive electrode and a battery, the positive electrode lithium supplementing agent comprises a lithium oxide, a coating is arranged on the outer side of the lithium oxide, the structural formula of the coating is FexSy, and the morphology of the coating is of a hollow tubular structure. Comprising the following steps: weighing FeCl3. 6H2O and 1, 4 phthalic acid, and dissolving the FeCl3. 6H2O and the 1, 4 phthalic acid in a first solvent; adding a NaOH solution, transferring into a high-pressure reaction kettle, and heating; taking out the product, washing the product with N, N-dimethylformamide, and drying the product to obtain a product F-MIL; the preparation method comprises the following steps: weighing F-MIL, powdered sulfur and carbon disulfide, putting the F-MIL, powdered sulfur and carbon disulfide into a quartz porcelain boat, carrying out sealed heating, washing with formaldehyde to obtain a FeS2atC nanorod called FS-MOF, weighing FS-MOF and lithium ferrite, carrying out vacuum ball milling, uniformly mixing, heating, cooling and grinding to obtain a lithium supplement agent A. The lithium oxide has a coating on the outer layer, and is good in conductivity, good in battery cycle performance and high in battery capacity.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and specifically refers to a cathode lithium supplement agent, a preparation method thereof, a battery cathode, and a battery. Background Art

[0002] In existing lithium iron phosphate battery electrode materials, there is a problem of excessive lithium loss during the first charge-discharge cycle, that is, lithium in the positive electrode undergoes an irreversible side reaction on the surface of the negative electrode to form a solid electrolyte interface layer, which cannot return to the positive electrode during subsequent discharge processes, resulting in an irreversible reduction in battery capacity, a shortened cycle life, and a reduced first-week efficiency. Currently, commonly used lithium supplement agents such as lithium ferrite (Li 5 FeO 4 ), due to reaction process problems, generate a large amount of lithium carbon oxide impurities, resulting in poor conductivity of lithium ferrite as a lithium supplement agent, which is not conducive to direct use in the positive electrode. When applied to batteries subsequently, it will lead to low battery capacity and short battery life. Summary of the Invention

[0003] The purpose of the present invention is to solve the deficiencies of the existing technology and provide a cathode lithium supplement material with a clever structure, a coating on the outer layer of lithium oxide, good conductivity, good battery cycling performance, and high battery capacity, as well as a preparation method thereof, a battery cathode plate, and a battery.

[0004] To achieve the above purpose, the technical solution adopted by the present invention is: A cathode lithium supplement agent includes lithium oxide, and is characterized in that: a coating is provided outside the lithium oxide, the coating covers the outer surface of the lithium oxide, and the structural formula of the coating is Fe x S y , where 1 ≤ x ≤ 2 and 2 ≤ y ≤ 3, so as to improve the conductivity and battery life of the lithium supplement agent by coating a sulfide outside the lithium oxide.

[0005] The coating of the present invention has a hollow tubular structure, with a diameter of 0.5 - 1 μm, a length of 5 - 10 μm, and a specific surface area of 600 - 650 m 2 / g, so as to improve the battery cycling performance and reduce the battery internal resistance as a lithium ion transmission channel during the charge and discharge process of the battery.

[0006] The lithium oxide of the present invention includes a compound with the general formula Li x MO y , M is a transition metal, and the lithium oxide is Li 5 FeO 4 or Li 2 NiO 2 or Li 2 C 2 O 4 or Li2 MnO 3 -LiMO 2 。

[0007] A preparation method of a cathode lithium supplement agent, comprising the following steps: First step: Weigh FeCl 3 ·6H 2 O and 1,4-benzenedicarboxylic acid and dissolve them in the first solvent by ultrasonic dispersion and stirring; Second step: Add the NaOH solution to the mixture obtained in the first step and stir to dissolve; Third step: Transfer the solution obtained in the second step to a high-pressure reactor, and place the high-pressure reactor in an oven for heating; Fourth step: Wash the product obtained in the third step with N,N-dimethylformamide, collect the product, and dry the product to obtain the product F-MIL; Fifth step: Weigh F-MIL, sulfur powder, and carbon disulfide, put them into a quartz boat, seal and heat, and collect the reaction product; Sixth step: Wash the product obtained in the fifth step with formaldehyde to obtain FeS2@C nanorods, called the coating FS-MOF.

[0008] Seventh step: Weigh the coating FS-MOF and lithium ferrite, mix them evenly by vacuum ball milling, transfer the obtained solid mixture to a tube furnace for heating, cool and grind to obtain FS@LFO, named cathode lithium supplement agent A.

[0009] The morphology of the coating described in the present invention is a hollow tubular structure, with a diameter of 0.5-1 μm, a length of 5-10 μm, and a specific surface area of 600-650 m 2 / g, to be used as a lithium ion transport channel during the charge and discharge process of the battery to improve the battery cycle performance and reduce the battery internal resistance.

[0010] The mass ratio of FeCl 3 ·6H 2 O and 1,4-benzenedicarboxylic acid in the present invention is (0.1-0.2):(0.1-0.2).

[0011] The first solvent described in the present invention is N,N-dimethylformamide or dimethyl sulfoxide or absolute ethanol, and the addition amount of the first solvent is 30 ml.

[0012] The oven heating temperature in the third step of the present invention is 80-120 °C, and the heating time is 12 hours.

[0013] The concentration of the NaOH solution described in the present invention is 0.4 mol / L, and the addition amount of the NaOH solution is 3 ml.

[0014] In the fifth step of the present invention, the mass ratio of F-MIL, sulfur powder, and carbon disulfide is (0.5-1):(0.5-1):0.1.

[0015] In the fifth step of the present invention, the heating condition is a nitrogen atmosphere, the heating rate is 2 °C / min, the temperature is raised to 500 °C, and maintained for 2 hours.

[0016] In the seventh step of the present invention, the mass ratio of FS-MOF and lithium ferrite is (0.1-1):(0.8-1).

[0017] In the seventh step of the present invention, the heating condition is a closed space, a nitrogen atmosphere, the heating rate is 1 °C / min, the temperature is raised to 700 °C, and maintained for 2 hours.

[0018] A battery positive electrode includes a current collector, and a positive electrode material layer is provided on the current collector. It is characterized in that: the positive electrode material layer includes the positive electrode lithium supplement agent described above or the positive electrode lithium supplement agent prepared by the preparation method described above, as well as a positive electrode material, a binder, and a conductive agent.

[0019] The addition amount of the positive electrode lithium supplement agent of the present invention is 1%-5% of the weight of the positive electrode material.

[0020] A battery is characterized by including a battery negative electrode and the battery positive electrode described above.

[0021] Due to the adoption of the above structure, the present invention has the advantages of ingenious structure, a coating on the outer layer of lithium oxide, good conductivity, good battery cycle performance, high battery capacity, etc. Description of the Drawings

[0022] Figure 1 is a topographical map of F-MIL-1 to F-MIL-9 in Synthesis Examples 1-9 of the present invention under an electron scanning microscope.

[0023] Figure 2 In the present invention, the topographical map of FS-MOF-1 in Synthesis Example 1 and FS-MOF-10 to FS-MOF-12 in Synthesis Examples 10-12 under an electron scanning microscope. Detailed Embodiments

[0024] The following combines the drawings to further describe in detail the specific embodiments of the present invention.

[0025] A positive electrode lithium supplement agent includes lithium oxide. It is characterized in that: a coating is provided on the outside of the lithium oxide, the coating covers the outer surface of the lithium oxide, and the structural formula of the coating is Fe x S y , where 1≤x≤2 and 2≤y≤3.

[0026] The morphology of the coating of the present invention is a tubular hollow structure.

[0027] The lithium oxide described in the present invention includes a compound with the general formula Li x MO y , where M is a transition metal, and Li 5 FeO 4 , Li 2 NiO 2 , Li 2 C 2 O 4 , Li 2 MnO 3 -LiMO 2 is one of them.

[0028] Synthesis Example 1 of the Preparation Method of the Cathode Lithium Supplement A preparation method of a cathode lithium supplement includes the following steps: First step: Weigh 0.1 moL of FeCl 3 ·6H 2 O and 0.1 moL of 1,4-benzenedicarboxylic acid, and dissolve them in 30 mL of N,N-dimethylformamide by ultrasonic dispersion and stirring; Second step: Add 3 ml of 0.4 mol / L NaOH solution to the mixture obtained in the first step, and stir to dissolve; Third step: Transfer the solution obtained in the third step to a high-pressure reaction kettle, place the high-pressure reaction kettle in an oven, and heat it at 100°C for 12 hours; Fourth step: Wash the product obtained in the third step three times with N,N-dimethylformamide, collect the product, and perform a drying treatment on the product. The drying temperature is 60°C and the time is 12 hours to obtain a product called F-MIL-1; Fifth step: Weigh F-MIL-1, sulfur powder, and carbon disulfide in a mass ratio of 1:1:0.1, put them into a quartz porcelain boat and seal it. In a nitrogen atmosphere, the heating rate is 2°C / min, heat up to 500°C, and keep it for 2 hours, and collect the reaction product; Sixth step: Wash the product obtained in the fifth step with formaldehyde to obtain FeS2@C nanorods, called the coating FS-MOF-1.

[0029] Seventh step: Weigh the coating FS-MOF-1 and lithium ferrite powder in a mass ratio of 0.8:1, mix them evenly by vacuum ball milling, transfer the obtained solid mixture to a tube furnace for heating. In a closed space and nitrogen atmosphere, the heating rate is 1°C / min, heat up to 700°C, keep it for 2 hours, and cool it naturally. After grinding, FS@LFO is obtained, named as the lithium supplement A-1.

[0030] Synthesis Example 2 of the Preparation Method of the Cathode Lithium Supplement The difference between Synthesis Example 2 and Synthesis Example 1 is that the amount of 1,4-benzenedicarboxylic acid in the first step is changed from 0.1 moL to 0.2 moL, and the other steps are the same as those in Synthesis Example 1. The product obtained in the fourth step is called F-MIL-2, the product obtained in the sixth step is called the coated FS-MOF-2, and the product obtained in the seventh step is named the lithium supplement agent A-2.

[0031] Synthesis Example 3 for the Preparation Method of the Cathode Lithium Supplement Agent The difference between Synthesis Example 3 and Synthesis Example 1 is that the amount of FeCl 3 ·6H 2 O is changed from 0.1 moL to 0.2 moL, and the other steps are the same as those in Synthesis Example 1. The product obtained in the fourth step is called F-MIL-3, the product obtained in the sixth step is called the coated FS-MOF-3, and the product obtained in the seventh step is named the lithium supplement agent A-3.

[0032] Synthesis Example 4 for the Preparation Method of the Cathode Lithium Supplement Agent The difference between Synthesis Example 4 and Synthesis Example 1 is that the amount of FeCl 3 ·6H 2 O is changed from 0.1 moL to 0.15 moL, and the other steps are the same as those in Synthesis Example 1. The product obtained in the fourth step is called F-MIL-4, the product obtained in the sixth step is called the coated FS-MOF-4, and the product obtained in the seventh step is named the lithium supplement agent A-4.

[0033] Synthesis Example 5 for the Preparation Method of the Cathode Lithium Supplement Agent The difference between Synthesis Example 5 and Synthesis Example 1 is that the amount of FeCl 3 ·6H 2 O is changed from 0.1 moL to 0.2 moL, and the amount of 1,4-benzenedicarboxylic acid is changed from 0.1 moL to 0.2 moL, and the other steps are the same as those in Synthesis Example 1. The product obtained in the fourth step is called F-MIL-5, the product obtained in the sixth step is called the coated FS-MOF-5, and the product obtained in the seventh step is named the lithium supplement agent A-5.

[0034] Synthesis Example 6 for the Preparation Method of the Cathode Lithium Supplement Agent The difference between Synthesis Example 6 and Synthesis Example 1 is that N,N-dimethylformamide in the first step is changed to dimethyl sulfoxide, and the other steps are the same as those in Synthesis Example 1. The product obtained in the fourth step is called F-MIL-6, the product obtained in the sixth step is called the coated FS-MOF-6, and the product obtained in the seventh step is named the lithium supplement agent A-6.

[0035] Synthesis Example 7 for the Preparation Method of the Cathode Lithium Supplement Agent The difference between Synthesis Example 7 and Synthesis Example 1 is that N,N-dimethylformamide in the first step is changed to absolute ethanol, and the other steps are the same as those in Synthesis Example 1. The product obtained in the fourth step is called F-MIL-7, the product obtained in the sixth step is called the coated product FS-MOF-7, and the product obtained in the seventh step is named the lithium supplement agent A-7.

[0036] Synthesis Example 8 for the preparation method of the positive electrode lithium supplement agent The difference between Synthesis Example 8 and Synthesis Example 1 is that the heating temperature of the oven in the third step is changed from 100 °C to 80 °C, and the other steps are the same as those in Synthesis Example 1. The product obtained in the fourth step is called F-MIL-8, the product obtained in the sixth step is called the coated product FS-MOF-8, and the product obtained in the seventh step is named the lithium supplement agent A-8.

[0037] Synthesis Example 9 for the preparation method of the positive electrode lithium supplement agent The difference between Synthesis Example 9 and Synthesis Example 1 is that the heating temperature of the oven in the third step is changed from 100 °C to 120 °C, and the other steps are the same as those in Synthesis Example 1. The product obtained in the fourth step is called F-MIL-9, the product obtained in the sixth step is called the coated product FS-MOF-9, and the product obtained in the seventh step is named the lithium supplement agent A-9.

[0038] Synthesis Example 10 for the preparation method of the positive electrode lithium supplement agent The difference between Synthesis Example 10 and Synthesis Example 1 is that in the fifth step, the mass ratio of F-MIL-1, sulfur powder, and carbon disulfide is changed from 1:1:0.1 to 0.5:1:0.1, and the other steps are the same as those in Synthesis Example 1. The product obtained in the sixth step is called the coated product FS-MOF-10, and the product obtained in the seventh step is named the lithium supplement agent A-10.

[0039] Synthesis Example 11 for the preparation method of the positive electrode lithium supplement agent The difference between Synthesis Example 11 and Synthesis Example 1 is that in the fifth step, the mass ratio of F-MIL-1, sulfur powder, and carbon disulfide is changed from 1:1:0.1 to 0.75:1:0.1, and the other steps are the same as those in Synthesis Example 1. The product obtained in the sixth step is called the coated product FS-MOF-11, and the product obtained in the seventh step is named the lithium supplement agent A-11.

[0040] Synthesis Example 12 for the preparation method of the positive electrode lithium supplement agent The difference between Synthesis Example 12 and Synthesis Example 1 is that in the fifth step, the mass ratio of F-MIL-1, sulfur powder, and carbon disulfide is changed from 1:1:0.1 to 1:0.5:0.1, and the other steps are the same as those in Synthesis Example 1. The product obtained in the sixth step is called the coated product FS-MOF-12, and the product obtained in the seventh step is named the lithium supplement agent A-12.

[0041] Synthesis Example 13 for the preparation method of the positive electrode lithium supplement agent The difference between Synthesis Example 13 and Synthesis Example 1 is that in the seventh step, the mass ratio of FS-MOF-1 to lithium ferrite is changed from 0.8:1 to 0.8:0.8, and the other steps are the same as those in Synthesis Example 1. The product obtained in the seventh step is named lithium supplement agent A-13.

[0042] Synthesis Example 14 for the preparation method of the cathode lithium supplement agent The difference between Synthesis Example 14 and Synthesis Example 1 is that in the seventh step, the mass ratio of FS-MOF-1 to lithium ferrite is changed from 0.8:1 to 0.1:1, and the other steps are the same as those in Synthesis Example 1. The product obtained in the seventh step is named lithium supplement agent A-14.

[0043] Synthesis Example 15 for the preparation method of the cathode lithium supplement agent The difference between Synthesis Example 15 and Synthesis Example 1 is that in the seventh step, the mass ratio of FS-MOF-1 to lithium ferrite is changed from 0.8:1 to 0.5:1, and the other steps are the same as those in Synthesis Example 1. The product obtained in the seventh step is named lithium supplement agent A-15.

[0044] Synthesis Comparative Example 1 for the preparation method of the cathode lithium supplement agent A preparation method of a cathode lithium supplement agent includes the following steps: The first step: Weigh S powder and lithium ferrite powder with a mass ratio of 1:1, mix them evenly by vacuum ball milling, transfer the obtained solid mixture to a tube furnace for heating, seal the space, in a nitrogen atmosphere, with a heating rate of 1 °C / min, heat up to 700 °C, hold for 2 hours, and cool naturally. After grinding, FS@LFO is obtained, which is called lithium supplement agent A-16.

[0045] X-ray diffraction analysis and scanning electron microscope analysis were respectively carried out on F-MIL-1 to F-MIL-9 in Synthesis Examples 1 - 9, FS-MOF-1 in Synthesis Example 1, and FS-MOF-10 to FS-MOF-12 in Synthesis Examples 10 - 12 of the preparation method of the cathode lithium supplement agent. Table 1 shows the data obtained from the X-ray diffraction analysis of FS-MOF-1 to FS-MOF-9: Table 1 X-ray diffraction data of F-MIL-1 to F-MIL-9 Appendix Figure 1 In a-i in the appendix correspond to the morphology diagrams of F-MIL-1 to F-MIL-9 in Synthesis Examples 1 - 9 taken under an electron scanning microscope. Combining the X-ray diffraction data of F-MIL-1 to F-MIL-9, it can be seen that the morphology of F-MIL-1 in Synthesis Example 1 is a hexagonal tubular hollow structure with the largest specific surface area. Comparing Synthesis Examples 1 - 5, it can be seen that by changing FeCl 3 ·6H 2The feeding ratio of the two reactants, O and 1,4-benzenedicarboxylic acid, will affect the morphology of the product. F-MIL-1 has the largest specific surface area. Comparing Synthesis Example 1 with Synthesis Examples 6 and 7, it can be seen that when N,N-dimethylformamide is changed to dimethyl sulfoxide or absolute ethanol, the morphology of F-MIL-6 and F-MIL-7 changes from hollow tubular to solid spherical and amorphous, and the specific surface area is greatly reduced. Comparing Synthesis Example 1 with Synthesis Example 8, it can be seen that reducing the heating temperature of the oven will cause F-MIL to change from hollow tubular to solid rod-shaped. Comparing Synthesis Example 1 with Synthesis Example 9, it can be seen that increasing the heating temperature of the oven will cause the length of the hollow tube to decrease. Appendix Figure 2 Figure J in the appendix is the morphology diagram of FS-MOF-1 in Synthesis Example 1 taken under an electron scanning microscope. Appendix Figure 2 Figures K - M in the appendix correspond to the morphology diagrams of FS-MOF-10 to FS-MOF-12 in Synthesis Examples 10 - 12 taken under an electron scanning microscope. It can be seen that the specific surface area of FS-MOF-1 in Synthesis Example 1 is smaller than that of F-MIL-1 in Synthesis Example 1. That is, after the reaction of F-MIL-1 in Synthesis Example 1 with sulfur powder and carbon disulfide, due to the addition of sulfur element, the specific surface area of FS-MOF-1 in Synthesis Example 1 becomes smaller. The difference between Synthesis Examples 10 - 12 and Synthesis Example 1 is that the mass ratios of F-MIL-1, sulfur powder, and carbon disulfide in the fifth step are 0.5:1:0.1, 0.75:1:0.1, and 1:0.5:0.1 respectively. It can be seen that in FS-MOF-10 to FS-MOF-11 in Synthesis Examples 10 - 11, the content of F-MIL-1 first decreases and then increases, and the morphology of FS-MOF changes from hollow tubular FS-MOF-1 to solid tubular FS-MOF-10 and FS-MOF-11, and the specific surface area gradually decreases. Comparing Synthesis Example 1 and Synthesis Example 12, it can be seen that both FS-MOF-1 in Synthesis Example 1 and FS-MOF-12 in Synthesis Example 12 are hollow tubular structures. The reduction of the proportion of sulfur powder results in the specific surface area of FS-MOF-12 being smaller than that of FS-MOF-1. It can be seen that F-MIL-1 needs to maintain an appropriate ratio with sulfur powder to ensure the hollow tubular structure and a relatively large specific surface area.

[0046] A battery positive electrode includes a current collector, and a positive electrode material layer is provided on the current collector. It is characterized in that: the positive electrode material layer includes the above-mentioned positive electrode lithium supplement agent or the positive electrode lithium supplement agent prepared by the above-mentioned preparation method, as well as a positive electrode material, a binder, and a conductive agent.

[0047] The addition amount of the positive electrode lithium supplement agent of the present invention is 1% - 5% of the weight of the positive electrode material.

[0048] A battery, characterized in that it includes a battery negative electrode and the above-mentioned battery positive electrode.

[0049] The following gives the performance tests of batteries and related batteries made using the lithium supplement agents A-1 to A-16 in the above Synthesis Examples 1-15 and Synthesis Comparative Example 1.

[0050] Example 1 of the battery preparation method Battery positive electrode: Mix the ternary cathode material lithium iron phosphate (LFP), conductive carbon black (SP), binder polyvinylidene fluoride (PVDF), and solvent N-methylpyrrolidone (NMP) in a mass ratio of 95:3:2, and then add the lithium supplement agent A-1 after ball milling and passing through a 200-mesh sieve to obtain the positive electrode slurry. The addition amount of the lithium supplement agent A-1 is 1% of the weight of LFP, and the addition amount of NMP is 60% of the weight of the positive electrode slurry; coat the positive electrode slurry onto aluminum foil to obtain the positive electrode, and the compaction density of the electrode sheet is 2.4 g / cm 3 .

[0051] Battery negative electrode: Use an existing graphite electrode, mix graphite, CMC, conductive agent, and binder in a ratio of 94:1:3:2 to obtain a negative electrode sheet, and the compaction density of the electrode sheet is 1.7 g / cm3; Make a soft-pack battery by roll pressing, assembling, and injecting electrolyte for the positive and negative electrodes, and then perform formation and grading to obtain the battery for cycle testing.

[0052] Example 2 of the battery preparation method The difference between Example 2 and Example 1 is that the addition ratio of the lithium supplement agent A-1 is changed from 1% to 3%, and the other operating steps of the battery positive electrode are the same, the negative electrode sheet remains unchanged, and the battery test conditions are the same.

[0053] Example 3 of the battery preparation method The difference between Example 3 and Example 1 is that the addition ratio of the lithium supplement agent A-1 is changed from 1% to 5%, and the other operating steps of the battery positive electrode are the same, the negative electrode sheet remains unchanged, and the battery test conditions are the same.

[0054] Example 4 of the battery preparation method The difference between Example 4 and Example 2 is that the lithium supplement agent A-1 is changed to the lithium supplement agent A-2, and the other operating steps of the battery positive electrode are the same, the negative electrode sheet remains unchanged, and the battery test conditions are the same.

[0055] Example 5 of the battery preparation method The difference between Example 5 and Example 2 is that the lithium supplement agent A-1 is changed to the lithium supplement agent A-3, and the other operating steps of the battery positive electrode are the same, the negative electrode sheet remains unchanged, and the battery test conditions are the same.

[0056] Example 6 of the battery preparation method The difference between Example 6 and Example 2 is that the lithium supplement agent A-1 is changed to lithium supplement agent A-4, and the other battery positive electrode operation steps are the same. The negative electrode sheet remains unchanged, and the battery test conditions are the same.

[0057] Example 7 of the battery preparation method The difference between Example 7 and Example 2 is that the lithium supplement agent A-1 is changed to lithium supplement agent A-5, and the other battery positive electrode operation steps are the same. The negative electrode sheet remains unchanged, and the battery test conditions are the same.

[0058] Example 8 of the battery preparation method The difference between Example 8 and Example 2 is that the lithium supplement agent A-1 is changed to lithium supplement agent A-6, and the other battery positive electrode operation steps are the same. The negative electrode sheet remains unchanged, and the battery test conditions are the same.

[0059] Example 9 of the battery preparation method The difference between Example 9 and Example 2 is that the lithium supplement agent A-1 is changed to lithium supplement agent A-7, and the other battery positive electrode operation steps are the same. The negative electrode sheet remains unchanged, and the battery test conditions are the same.

[0060] Example 10 of the battery preparation method The difference between Example 10 and Example 2 is that the lithium supplement agent A-1 is changed to lithium supplement agent A-8, and the other battery positive electrode operation steps are the same. The negative electrode sheet remains unchanged, and the battery test conditions are the same.

[0061] Example 11 of the battery preparation method The difference between Example 11 and Example 2 is that the lithium supplement agent A-1 is changed to lithium supplement agent A-9, and the other battery positive electrode operation steps are the same. The negative electrode sheet remains unchanged, and the battery test conditions are the same.

[0062] Example 12 of the battery preparation method The difference between Example 12 and Example 2 is that the lithium supplement agent A-1 is changed to lithium supplement agent A-10, and the other battery positive electrode operation steps are the same. The negative electrode sheet remains unchanged, and the battery test conditions are the same.

[0063] Example 13 of the battery preparation method The difference between Example 13 and Example 2 is that the lithium supplement agent A-1 is changed to lithium supplement agent A-11, and the other battery positive electrode operation steps are the same. The negative electrode sheet remains unchanged, and the battery test conditions are the same.

[0064] Example 14 of the battery preparation method The difference between Example 14 and Example 2 is that the lithium supplement agent A-1 is changed to lithium supplement agent A-12, and the other battery positive electrode operation steps are the same. The negative electrode sheet remains unchanged, and the battery test conditions are the same.

[0065] Example 15 of Battery Preparation Method The difference between Example 15 and Example 2 is that the lithium supplement agent A-1 is changed to lithium supplement agent A-13, and the remaining battery positive electrode operation steps are the same. The negative electrode sheet remains unchanged, and the battery test conditions are the same.

[0066] Example 16 of Battery Preparation Method The difference between Example 16 and Example 2 is that the lithium supplement agent A-1 is changed to lithium supplement agent A-14, and the remaining battery positive electrode operation steps are the same. The negative electrode sheet remains unchanged, and the battery test conditions are the same.

[0067] Example 17 of Battery Preparation Method The difference between Example 17 and Example 2 is that the lithium supplement agent A-1 is changed to lithium supplement agent A-15, and the remaining battery positive electrode operation steps are the same. The negative electrode sheet remains unchanged, and the battery test conditions are the same.

[0068] Comparative Example 1 of Battery Preparation Method Battery positive electrode: The ternary cathode material lithium iron phosphate (LFP), conductive carbon black (SP), binder polyvinylidene fluoride (PVDF) and solvent N-methylpyrrolidone (NMP) with a mass ratio of 95:3:2 are mixed evenly to obtain the positive electrode slurry. The addition amount of NMP is 60% of the weight of the positive electrode slurry; the positive electrode slurry is coated on the aluminum foil to obtain the positive electrode, and the compaction density of the electrode sheet is 2.4 g / cm 3 .

[0069] Battery negative electrode: An existing graphite electrode is used. Graphite, CMC, conductive agent, and binder are mixed evenly in a ratio of 94:1:3:2 to prepare the negative electrode sheet, and the compaction density of the electrode sheet is 1.7 g / cm3; The positive electrode and the negative electrode are made into a soft-pack battery through roll pressing, assembly, and liquid injection, and then formation and grading are carried out to obtain the battery for cycle testing, That is, compared with Example 2 of the battery preparation method, the positive electrode lithium supplement agent prepared by the present invention is not added in Comparative Example 1, the negative electrode sheet remains unchanged, and the battery test conditions are the same.

[0070] Comparative Example 2 of Battery Preparation Method The difference between Comparative Example 2 and Example 2 is that the lithium supplement agent A-1 is changed to the existing lithium ferrite as the lithium supplement agent, and the remaining battery positive electrode operation steps are the same. The negative electrode sheet remains unchanged, and the battery test conditions are the same.

[0071] Comparative Example 3 of Battery Preparation Method The difference between Comparative Example 3 and Example 2 is that the lithium supplement agent A-1 is changed to FeS 2 , and the remaining battery positive electrode operation steps are the same. The negative electrode sheet remains unchanged, and the battery test conditions are the same.

[0072] Comparative Example 4 of Battery Preparation Method The difference between Comparative Example 4 and Example 2 is that the lithium supplement agent A-1 is changed to A-16, and the remaining battery cathode operation steps are the same. The anode sheet remains unchanged, and the battery test conditions are the same.

[0073] For ease of description, the differences between Examples 1-17 and Comparative Examples 1-4 are presented in Table 2 below.

[0074] Table 2 Types and Dosages of Lithium Supplement Agents Added in Examples 1-17 and Comparative Examples 1-4 Then, performance tests were conducted on the batteries of Examples 1-17 and Comparative Examples 1-4 respectively. The specific test methods are as follows: After soft-pack injection, with a rated capacity of 2.5 Ah and an injection coefficient of 6 g / Ah, formation, aging, grading, and static settling were carried out after injection. Then, three soft packs with similar capacities were selected to calculate the initial efficiency, test the internal resistance, and open-circuit voltage. Then, they were transferred to a constant-temperature test chamber, with a fixture, a voltage range of 2.5-3.65 V, and a 1 C cycle test for 500 weeks.

[0075] The battery was formed according to the following steps: constant-current charging at 0.1 C to 3.0 V, then constant-current charging at 0.2 C to 3.3 V. After formation, the battery was aged first, then evacuated and sealed. The battery was graded according to the following steps: constant-current discharging at 0.5 C to 2.5 V, constant-current constant-voltage charging to 3.65 V at 0.5 C, constant-current discharging to 2.5 V, constant-current charging to 3.3 V. Initial efficiency = (total constant-current discharging capacity / constant-current constant-voltage charging capacity + formation charging capacity) * 100%.

[0076] Cycle performance test: The battery was left to stand at 25°C for 30 min, charged at a constant current of 0.5 C to 3.65 V, then charged at a constant voltage to 0.05 C, and then discharged at a constant current of 0.5 C to 2.5 V. The discharge capacity at this time was recorded as the discharge capacity of the first cycle. After standing for 10 min, the capacity of the lithium-ion battery after 1000 cycles was recorded. The capacity retention rate at the 1000th cycle = discharge capacity at the 1000th cycle / discharge capacity of the first cycle. Table 3 presents the initial efficiency, capacity, internal resistance, and capacity retention rate of the 1000th cycle at 1 C for each group of batteries in Examples 1-17 and Comparative Examples 1-4: Table 3 Initial Efficiency, Capacity, Internal Resistance, and Capacity Retention Rate of the 1000th Cycle at 1 C for Each Group of Batteries in Examples 1-17 and Comparative Examples 1-4 Combined with Table 3, it can be seen from the comparison of Examples 1-4 that at an addition ratio of 3%, the lithium supplement agent A-1 has the highest initial efficiency and capacity retention rate, that is, the battery has the highest efficiency during the first charge and discharge process and the longest battery life.

[0077] As can be seen from the comparison between Example 2 and Examples 4 - 14, in Synthesis Example 1 corresponding to Example 2, for the hollow tubular morphology of F-MIL-1 and FS-MOF-1, the specific surface area of F-MIL-1 in Example 2 is the largest compared to that in Examples 4 - 11, and the specific surface area of FS-MOF-1 in Example 2 is the largest relative to that in Examples 12 - 14. According to the morphology diagrams of F-MIL-1 and FS-MOF-1 in Synthesis Example 1 and the X-ray diffraction analysis results, the hollow tubular structure and surface flaky structure of the lithium supplement agent A-1 can serve as a lithium ion transport channel during the charge and discharge process of the battery, improving the battery cycle performance, reducing the battery internal resistance, and enhancing the battery conductivity. In addition, sulfur powder and carbon disulfide are added to the positive electrode lithium supplement agent in the present invention. The addition of sulfide participates in the formation of the SEI film. The larger the specific surface area, the higher the degree of sulfide participating in the formation of the SEI film, so the impedance is lower and the cycle life is longer.

[0078] As can be seen from the comparison between Example 2 and Examples 4 - 7, Example 2 adds lithium supplement agent A-1, and Examples 4 - 7 add lithium supplement agents A-2 to A-5. The morphology diagrams and X-ray diffraction analysis data of A-1 to A-5 show that the specific surface area of F-MIL-1 in lithium supplement agent A-1 is the largest. Combining Table 3, it can be seen that a large specific surface area of the material results in a short lithium ion transport path, showing the advantages of lower internal resistance and long cycle life in the battery cycle test.

[0079] As can be seen from the comparison between Example 2 and Examples 8 - 9, the initial efficiency of the battery in Example 2 is significantly greater than that of the batteries in Examples 8 and 9. Examples 8 - 9 add lithium supplement agents A-6 and A-7. It can be seen that the first solvent causes a change in the morphology of F-MIL. Neither F-MIL-6 nor F-MIL-7 in lithium supplement agents A-6 and A-7 has a hollow structure, resulting in a significant decrease in the initial efficiency and a decline in battery performance after adding the lithium supplement agents A-6 and A-7 to the battery.

[0080] As can be seen from the comparison between Example 2 and Examples 10 and 11, the battery performance of Example 2 is the best and the battery has good cycle performance, that is, the synthesis temperature of the lithium supplement agent in Example 2 is relatively appropriate. A decrease or increase in the synthesis temperature will lead to a decline in battery performance.

[0081] As can be seen from the comparison between Example 2 and Examples 12 - 14, by changing the mass ratio of F-MIL-1, sulfur powder, and carbon disulfide and increasing the proportion of F-MIL-1, the degree of sulfidation is relatively low, finally resulting in insufficient encapsulation of FS-MOF. Although the specific surface area gradually increases, with the decrease in the content of sulfide, it will affect the membrane impedance and battery cycle life of the battery. It can be seen that the mass ratio of F-MIL-1, sulfur powder, and carbon disulfide in the lithium supplement agent in Example 1 is superior to that in Examples 12 - 14.

[0082] From the comparison between Example 2 and Examples 15 - 17, it can be seen that adjusting the mass ratio of FS - MOF - 1 and lithium ferrite will affect the capacity performance of the final battery. From Example 16, Example 17 to Example 2, the proportion of FS - MOF - 1 gradually increases. In Examples 16, 17 and Example 2, the initial efficiency of the battery first decreases and then increases, the capacity gradually increases, the internal resistance gradually decreases, and the capacity retention rate first decreases and then increases. Generally speaking, the mass ratio of FS - MOF - 1 and lithium ferrite in Example 2 is the best.

[0083] By comparing the data of Example 2 with that of Comparative Examples 1, 2, 3 and 4, we can find that the lithium supplement agent A - 1, compared with the uncoated blank lithium supplement agent, pure FeS 2 , and the addition of the directly sulfided lithium supplement agent, has significantly improved the impedance, initial efficiency and cycle life, indicating that the lithium supplement agent A - 1 has significantly improved the performance of the polymer solid - state battery.

[0084] In the present invention, a coating is coated on the outer side of the existing lithium ferrite lithium supplement agent. This coating is preferably a hollow tubular structure with a large specific surface area. In the homogenization stage, because the coating is coated on the surface of lithium ferrite, it reduces the contact between lithium ferrite and PVDF, reduces the influence of residual alkali on the slurry, reduces the probability of slurry gelation, replaces the lithium oxide with poor conductivity on the surface of the lithium ferrite lithium supplement agent, and makes part of the lithium oxide react into lithium sulfide. In the charge - discharge stage of the battery, the high - specific - surface - area structure improves the conductivity of the positive - electrode lithium supplement agent of the present invention, improves the initial efficiency, capacity and cycle retention rate of the battery, and reduces the internal resistance of the battery.

[0085] Due to the adoption of the above - mentioned structure, the present invention has the advantages of ingenious structure, a coating on the outer layer of lithium oxide, good conductivity, good battery cycle performance, high battery capacity, etc.

Claims

1. A positive electrode lithium supplement, comprising lithium oxide, characterized in that: The lithium oxide is provided with a coating on the outside, and the coating is coated on the outer surface of the lithium oxide. The structural formula of the coating is Fe x S y , where 1≤x≤2, 2≤y≤3.

2. A positive electrode lithium supplement according to claim 1, characterized in that: The coating has a hollow tubular structure with a diameter of 0.5-1 μm, a length of 5-10 μm, and a specific surface area of ​​600-650 m 2 / g.

3. A method for preparing a positive electrode lithium supplement comprises the following steps: Step 1: weigh FeCl3·6H2O and 1,4-phthalic acid and dissolve them in the first solvent by ultrasonic dispersion and stirring; Step 2: Add NaOH solution to the mixture obtained in step 1 and stir to dissolve; Step 3: The solution obtained in step 2 is transferred into a high pressure reactor, and the high pressure reactor is placed in an oven for heating; Step 4: washing the product obtained in the third step with N,N-dimethylformamide, collecting the product, and drying the product to obtain the product F-MIL; Step 5: Weigh F-MIL, sulfur powder and carbon disulfide, place them in a quartz boat, seal and heat, and collect the reaction products; Step 6: washing the product obtained in step 5 with formaldehyde to obtain a coated material; Step 7: Weigh the coating and lithium ferrite, mix them evenly by vacuum ball milling, transfer the obtained solid mixture to a tube furnace for heating, and obtain the positive electrode lithium supplement after cooling and grinding.

4. The method for preparing a positive electrode lithium supplement according to claim 3, characterized in that: The mass ratio of the FeCl3·6H2O to 1,4-phthalic acid is (0.1-0.2): (0.1-0.2).

5. The method for preparing a positive electrode lithium supplement according to claim 3, characterized in that: The first solvent is N,N-dimethylformamide or dimethyl sulfoxide or anhydrous ethanol, the amount of the first solvent added is 30 ml, and the oven heating temperature in the third step is 80-120° C., and the heating time is 12 hours.

6. The method for preparing a positive electrode lithium supplement according to claim 3, characterized in that: The concentration of the NaOH solution is 0.4 mol / L, and the amount of the NaOH solution added is 3 ml.

7. The method for preparing a positive electrode lithium supplement according to claim 3, characterized in that: The mass ratio of F-MIL, sulfur powder and carbon disulfide in the fifth step is (0.5-1): (0.5-1): 0.1, the heating conditions in the fifth step are nitrogen atmosphere, the heating rate is 2°C / min, the temperature is increased to 500°C, and it is maintained for 2 hours. The mass ratio of FS-MOF and lithium ferrite in the seventh step is (0.1-1): (0.8-1), and the heating conditions in the seventh step are closed space, nitrogen atmosphere, the heating rate is 1°C / min, the temperature is increased to 700°C, and it is maintained for 2 hours.

8. A positive electrode of a battery, comprising a current collector, on which a positive electrode material layer is provided, characterized in that: The positive electrode material layer comprises the positive electrode lithium replenisher according to claim 1 or 2 or the positive electrode lithium replenisher prepared by the preparation method according to any one of claims 3 to 7, as well as a positive electrode material, a binder and a conductive agent.

9. A battery positive electrode according to claim 8, characterized in that: The added amount of the positive electrode lithium supplement is 1%-5% of the weight of the positive electrode material.

10. A battery, characterized in that It comprises a battery negative electrode and a battery positive electrode as claimed in claim 8 or 9.

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