Preparation method of composite lithium-rich and lithium-supplementing additive

Abstract

The invention discloses a preparation method of a composite lithium-rich and lithium-supplement additive, which comprises the following steps: taking lithium ferrite as a core, preparing NiO (at) lithium salt by adopting an ALD atomic deposition method, fully and uniformly mixing carbon-coated lithium ferrite and the NiO (at) lithium salt, and sintering to prepare the composite lithium-rich and lithium-supplement additive. According to the invention, the advantages of high lithium supplement capacity of lithium ferrite, less gas production of lithium nickelate and good environmental adaptability are fully exerted, and the lithium supplement agent with high capacity and good stability is obtained; the nanometer nickel protoxide is in full contact with a lithium salt coating layer prepared by an ALD method, subsequent sintering is facilitated, preparation can be performed at a lower temperature, cost reduction is facilitated, meanwhile, the nickel protoxide and the peripheral lithium salt coating layer are subjected to a solid solution reaction, and residual lithium on the surface of lithium ferrite of a nuclear body can be obtained. The'two-channel lithium acquisition mode 'can reduce the overall residual alkali amount of the material, and is beneficial to improving the processing performance of subsequent battery slurry.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and particularly relates to a preparation method of a composite lithium-rich lithium supplement additive. Background Art

[0002] During the first charge and discharge process of a lithium-ion battery, a solid electrolyte interface (SEI) film is formed on the surface of the negative electrode, which causes the active lithium in the positive electrode sheet to be consumed, resulting in the loss of the first specific capacity of the lithium-ion battery. At present, the irreversible capacity loss of the graphite negative electrode widely used in mass production lines can reach 10%, and the irreversible specific capacity of the silicon-based and tin-based negative electrodes with high specific capacity is even as high as more than 30%, which greatly reduces the energy density of the lithium-ion battery. Therefore, a lithium supplement method is usually adopted to make up for the irreversible capacity loss of the lithium-ion battery, restore the capacity of the positive electrode sheet, and improve the energy density of the lithium-ion battery.

[0003] At present, the commonly used lithium supplement methods include positive electrode lithium supplement, negative electrode lithium supplement, and electrochemical lithium supplement. Among them, lithium powder and lithium foil are often used for negative electrode lithium supplement. However, since metallic lithium reacts violently with water, the environmental requirements are very high, so that a large amount of funds need to be invested in the mass production line and lithium supplement equipment for modification and procurement. However, due to its high safety and operability, positive electrode lithium supplement has the most promising industrial production prospects. Commonly used positive electrode lithium supplement additives mainly include Li5FeO4, Li2NiO2, Li6CoO4, Li6MnO4, Li5ReO6, etc. Among them, Li5FeO4 can theoretically release 5 Li + / mol and the theoretical specific capacity is as high as more than 850 mAh / g. Therefore, it is regarded as a very ideal lithium supplement additive for positive electrode materials. By adding a certain amount of Li5FeO4 to the traditional positive electrode materials, the first efficiency and energy density of the lithium-ion battery can be significantly improved. However, the conductivity of pure Li5FeO4 is poor, and it is also difficult to ensure the electrical performance of the lithium-ion battery.

[0004] In order to improve the lithium compensation effect, conductivity and other properties of lithium compensation agents, researchers have currently developed various lithium compensation materials. Among them, the mainstream lithium compensation materials include preparing various coating layers on the surface of common lithium compensation agents. Patent CN112490415 A discloses a lithium compensation additive for lithium-ion cathode materials. By sequentially coating a carbon layer and a transition metal oxide layer on the surface of the Li5FeO4 matrix, the electron and ion conductivity of Li5FeO4 is significantly improved, the lithium compensation performance and electrochemical performance of the material are enhanced, and the service life of lithium-ion batteries is extended. However, the charging specific capacity of the battery assembled with the lithium compensation agent prepared by this method is relatively low, and the charging efficiency is poor. Patent CN 114497514 B discloses a cathode lithium compensation agent. By using Li2NiO2 to coat Li5FeO4, the energy density and stability of the battery are effectively improved, and the lithium compensation effect and the conductivity of the lithium compensation agent are improved. However, the process of combining Li2NiO2 and Li5FeO4 is difficult, and the stability of the lithium compensation agent still needs to be improved.

[0005] Therefore, it is particularly important to prepare a conductive lithium compensation additive with excellent lithium compensation performance, conductivity and stability. Summary of the Invention

[0006] Aiming at the above existing problems, the purpose of the present invention is to provide a preparation method of a composite lithium-rich lithium compensation additive. By mixing and sintering carbon-coated lithium-rich compound Li5FeO4 with NiO@lithium salt prepared by ALD technology, a lithium ferrite composite lithium compensation additive with a carbon coating layer coated with lithium nickelate is prepared. The composite lithium-rich lithium compensation agent Li5FeO4@C@Li2NiO2 proposed by the present invention gives full play to the advantages of both lithium nickelate and lithium ferrite materials, and lithium nickelate with good environmental adaptability is used as the shell, which is used as a protective layer for lithium ferrite to a certain extent. In addition, the lithium-rich lithium compensation additive of the present invention reduces the overall residual alkali amount of the material and improves the subsequent battery slurry processing performance.

[0007] Aiming at the above purpose, the present invention first provides a preparation method of a composite lithium-rich lithium compensation additive, including the following steps:

[0008] (1) Mix iron oxide powder and lithium source powder evenly to obtain a blended powder;

[0009] (2) Sinter the blended powder obtained in step (1) in an inert gas atmosphere, cool, crush and screen to obtain a lithium compensation additive substrate A with the chemical formula Li5FeO4;

[0010] (3) Put the substrate A obtained in step (2) into a CVD device, introduce a carbon source and a protective gas, and react to obtain carbon-coated lithium ferrite Li5FeO4@C;

[0011] (4) The nano nickel oxide is modified by the atomic layer deposition (ALD) method, and a lithium salt is coated on the surface of the nano nickel oxide to obtain a precursor of the shell material, NiO@lithium salt;

[0012] (5) After Li5FeO4@C and NiO@lithium salt are fully mixed and homogenized, they are sintered at a high temperature under the protection of nitrogen to obtain a composite lithium-rich lithium supplement agent, Li5FeO4@C@Li2NiO2.

[0013] In an embodiment of the present invention, the particle size range of the iron oxide powder in step (1) is 50 nm to 20 μm.

[0014] In an embodiment of the present invention, the lithium source powder in step (1) is at least one of Li2O, LiOH, LiOH·H2O, and Li2CO3.

[0015] In an embodiment of the present invention, in step (1), the molar ratio of the Fe element of the iron oxide powder to the Li element of the lithium source powder is 1:(5 - 5.5).

[0016] In an embodiment of the present invention, in step (2), the inert gas includes nitrogen and / or argon.

[0017] In an embodiment of the present invention, in step (2), the sintering means pre-sintering at 500 - 600 °C for 5 - 15 h, then high-temperature sintering at 700 - 1000 °C for 10 - 24 h, the heating rate is 2 - 5 °C / min, and cooling is carried out at room temperature after sintering.

[0018] In an embodiment of the present invention, in step (2), the sieving is through a 300-mesh sieve.

[0019] In an embodiment of the present invention, in step (3), the carbon source includes at least one of acetylene, carbon monoxide, ethylene, and propylene, and the protective gas is nitrogen and / or argon.

[0020] In an embodiment of the present invention, in step (3), the flow rate of the carbon source is 200 - 300 mL / min, and the flow rate of the protective gas is 200 - 1000 mL / min.

[0021] In an embodiment of the present invention, in step (3), the reaction temperature is 600 - 650 °C, the reaction time is 2 - 3 h, and the heating rate is 6 °C / min.

[0022] In an embodiment of the present invention, in step (3), the carbon coating amount is 0.5 - 5%.

[0023] In one embodiment of the present invention, in step (4), the preparation method of the NiO@lithium salt comprises the following steps: putting the nano nickelous oxide matrix material into the reaction chamber of the ALD device, first introducing a mixed gas of a lithium source precursor and a carrier gas, adsorbing the lithium source on the matrix material under the action of a lithium source pulse, then purging with the carrier gas for 10 s, then introducing a mixed gas of an oxygen source precursor and a carrier gas, reacting the oxygen source with the lithium source precursor under the action of an oxygen source pulse, then using the carrier gas to purge for 10 s, then successively introducing a mixed gas of a lithium source precursor and a carrier gas, purging with the carrier gas for 10 s, introducing a mixed gas of an oxygen source precursor and a carrier gas, purging with the carrier gas for 10 s, repeating 3 - 5 times to obtain the NiO@lithium salt composite coating material.

[0024] In one embodiment of the present invention, in step (4), the coating thickness of the lithium layer is 20 - 50 nm, and the molar ratio of Li / Ni is 2.0 ± 0.05.

[0025] In one embodiment of the present invention, in step (4), the lithium source precursor is lithium tert - butoxide (C4H9LiO), the oxygen source precursor is ozone (O3), and the carrier is nitrogen or argon.

[0026] In one embodiment of the present invention, in step (4), in the mixed gas of the lithium source precursor and the carrier gas, the volume ratio of the lithium source precursor to the carrier gas is 1:1 to 1:5, and the flow rate of the mixed gas of the lithium source precursor and the carrier gas is 200 - 400 mL / min.

[0027] In one embodiment of the present invention, in step (4), the temperature during the lithium source pulse is 100 - 150 °C, and the pulse time is 1.6 - 2.5 s.

[0028] In one embodiment of the present invention, in step (4), in the mixed gas of the oxygen source precursor and the carrier gas, the volume ratio of the oxygen source precursor to the carrier gas is 1:1 to 1:5, and the flow rate of the mixed gas of the oxygen source precursor and the carrier gas is 200 - 400 mL / min.

[0029] In one embodiment of the present invention, in step (4), the temperature during the oxygen source pulse is 100 - 150 °C, and the pulse time is 4 - 5 s.

[0030] In one embodiment of the present invention, in step (4), the flow rate of the carrier gas during the carrier gas purge is 100 - 250 cm 3 / min.

[0031] In one embodiment of the present invention, in step (s), the molar ratio of the Li5FeO4@C to the NiO@lithium salt is (99 - 98):(1 - 2).

[0032] In one embodiment of the present invention, the sintering temperature in step (5) is 500-700° C., preferably 550-650° C., and the holding time is 5-20 h.

[0033] The invention also discloses a composite lithium-rich lithium-supplementing additive prepared by the method.

[0034] The present invention also discloses an application of the composite lithium-rich lithium-supplementing additive in the field of lithium-ion batteries.

[0035] In one embodiment of the present invention, the application includes adding a lithium supplement agent to a lithium battery positive electrode material to form a slurry to prepare a positive electrode sheet, and forming a lithium battery by using a positive electrode sheet, a negative electrode sheet, a separator, an electrolyte, a positive and negative electrode collector and a shell, or forming a button battery by using a positive electrode sheet, a negative electrode sheet, a separator, an electrolyte and a positive / negative electrode shell.

[0036] Beneficial effects:

[0037] (1) Lithium ferrite lithium supplement has the advantage of high lithium supplement capacity, generally 800mAh / g, but because of its inherent high lithium content, it leads to high residual alkali content, high requirements for the use environment, and large gas production during the lithium supplement process. Although lithium nickelate lithium supplement is superior to lithium ferrite in processability and gas production, its own lithium supplement capacity is relatively low, less than 300mAh / g; the composite lithium-rich lithium supplement Li5FeO4@C@Li2NiO2 prepared by the present invention fully utilizes the advantages of both materials, and uses lithium nickelate with good environmental adaptability as a shell, which to a certain extent serves as a protective layer for lithium ferrite.

[0038] (2) The contact between nano nickel oxide and the lithium salt coating prepared by the ALD method is fully conducive to subsequent sintering and can be prepared at a lower temperature, which is conducive to cost reduction. At the same time, nickel oxide can obtain residual lithium on the surface of the core lithium ferrite in addition to the solid solution reaction with the outer lithium salt coating. Its "dual-channel lithium acquisition mode" can reduce the overall residual alkali content of the material, which is conducive to improving the subsequent battery slurry processing performance.

[0039] (3) The button battery prepared using Li5FeO4@C@Li2NiO2 prepared by the method of the present invention as a lithium supplement has a high charge capacity. The stability of the lithium supplement is also very good. After two days of storage, the charge capacity retention rate of the prepared battery can be as high as 75.96%. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is a structural diagram of the composite lithium-rich lithium-supplementing additive prepared in an embodiment of the present invention, where the right figure is a partial enlarged view.

[0041] Figure 2 This is the charge and discharge curve of Example 3 at a rate of 0.1C. DETAILED DESCRIPTION

[0042] The present invention will be further introduced and described below through specific examples, comparative examples and the accompanying drawings.

[0043] The argon gas used in the present invention is high-purity argon gas with a purity of 99.999%.

[0044] Test method for charge specific capacity:

[0045] Take the composite lithium-rich lithium-supplementing additive material, conductive carbon black and polyvinylidene fluoride and mix them in a mass ratio of 92:4:4, add N-methylpyrrolidone to prepare an electrode sheet, use a lithium sheet as the counter electrode to form a CR2032 button battery, and perform charge and discharge tests at a rate of 0.1C.

[0046] Example 1

[0047] A preparation method of a composite lithium-rich lithium-supplementing additive, comprising the following steps:

[0048] (1) Mix 20 g of iron oxide powder evenly with 55.03 g of lithium source powder (LiOH·H2O) to obtain a blended powder;

[0049] (2) Pre-sinter the blended powder obtained in step (i) in a nitrogen atmosphere at 580 °C for 12 h, then perform high-temperature sintering at 850 °C for 20 h, with a heating rate of 3 °C / min, naturally cool to room temperature at room temperature, pulverize, and screen through a 300-mesh sieve to obtain a lithium-supplementing additive substrate A with the chemical formula Li5FeO4;

[0050] (3) Put the prepared substrate A into a CVD device, use acetylene as the carbon source and nitrogen as the protective gas, with an acetylene flow rate of

[0051] (4) Put the nano nickel oxide matrix material into the reaction chamber of the ALD device. First, introduce a mixed gas of lithium tert-butoxide and argon (1:4, 250 mL / min), and under the action of 135 °C and a lithium source pulse (2 s), adsorb the lithium source on the matrix material. Subsequently, purge with argon for 10 s, then introduce a mixed gas of O3 and argon (1:4, 250 mL / min), and under the action of an oxygen source pulse (4.6 s), react O3 with lithium tert-butoxide. Then use argon to purge for 10 s, and then successively introduce a mixed gas of lithium tert-butoxide and argon, purge with argon for 10 s, introduce a mixed gas of O3 and argon, and purge with argon for 10 s. Repeat 5 times to prepare a NiO@lithium salt composite coating material. During the whole process, the flow rate of argon during purging is 200 mL / min. Finally, the Li / Ni in the prepared NiO@lithium salt is 2.04, and the thickness of the coated lithium layer is 36 nm;​

[0052] (5) After thoroughly mixing 80 g of Li5FeO4@C and 20 g of NiO@lithium salt evenly, sinter them at 650 °C for 15 h with nitrogen as the protective gas and a heating rate of 2 °C / min, and then cool them naturally to room temperature to obtain the composite lithium-rich lithium supplement Li5FeO4@C@Li2NiO2.

[0053] Example 2

[0054] The difference between Example 2 and Example 1 is that the carbon coating amount in step (3) is changed to 2.0%.

[0055] Change the flow rate of acetylene in step (3) to 250 mL / min, the flow rate of nitrogen to 800 mL / min, the heating rate to 6 °C / min, heat up to 650 °C, keep the temperature for 2 h, and cool it to room temperature in the natural environment to obtain Li5FeO4@C;

[0056] Example 3

[0057] The difference between Example 3 and Example 1 is that the carbon coating amount in step (3) is changed to 2.5%.

[0058] Change step (3) to perform CVD carbon coating on the prepared substrate A, use acetylene as the carbon source, nitrogen as the protective gas, the acetylene flow rate is 300 mL / min, the nitrogen flow rate is 800 mL / min, the heating rate is 6 °C / min, heat up to 650 °C, keep the temperature for 2 h, and cool it to room temperature in the natural environment to obtain Li5FeO4@C.

[0059] Example 4

[0060] The difference between Example 4 and Example 3 is that the carbon source in step (3) is changed.

[0061] Change the carbon source in step (3) to propylene, nitrogen as the protective gas, the propylene flow rate is 300 mL / min, the nitrogen flow rate is 800 mL / min, the heating rate is 6 °C / min, heat up to 700 °C, keep the temperature for 2 h, and cool it to room temperature in the natural environment to obtain Li5FeO4@C.

[0062] Example 5

[0063] The difference between Example 5 and Example 1 is that the dosage ratio of Li5FeO4@C to NiO@lithium salt in step (5) is changed.

[0064] Change the mass of Li5FeO4@C in step (5) to 70 g, mix it evenly with 30 g of NiO@lithium salt and then sinter it to obtain the composite lithium-rich lithium supplement Li5FeO4@C@Li2NiO2.

[0065] Example 6

[0066] Example 6 is different from Example 1 in that the dosage ratio of Li5FeO4@C to NiO@lithium salt in step (5) is changed.

[0067] Change the mass of Li5FeO4@C in step (5) to 90 g, mix it evenly with 10 g of NiO@lithium salt, and then sinter it to obtain the composite lithium-rich lithium supplement agent Li5FeO4@C@Li2NiO2.

[0068] Comparative Example 1

[0069] Comparative Example 1 is different from Example 1 in that in Example 1, the step of carbon coating is omitted, and the Li5FeO4 prepared in step (2) is directly mixed and sintered with the NiO@lithium salt prepared in step (4).

[0070] Comparative Example 2

[0071] Comparative Example 2 is different from Example 1 in that the amount of carbon coating in step (3) is changed to exceed 5%.

[0072] Step (3) is changed to perform CVD carbon coating on the prepared substrate A. Acetylene is used as the carbon source, nitrogen is used as the protective gas, the flow rate of acetylene is 400 mL / min (carbon coating amount 5.5%), the flow rate of nitrogen is 800 mL / min, the heating rate is 6 °C / min, the temperature is raised to 650 °C, held for 3 h, and naturally cooled to room temperature in the natural environment to obtain Li5FeO4@C.

[0073] Comparative Example 3

[0074] Comparative Example 3 is different from Example 1 in that commercially purchased Li2NiO2 is used for co-sintering with Li5FeO4@C obtained in step (3).

[0075] Comparative Example 4

[0076] A preparation method of a lithium supplement agent Li5FeO4@C:

[0077] (1) Mix 20 g of iron oxide powder evenly with 55.03 g of lithium source powder (LiOH·H2O) to obtain a blended powder;

[0078] (2) Pre-sinter the blended powder obtained in step (1) at 580 °C for 12 h in a nitrogen atmosphere, then perform high-temperature sintering at 850 °C for 20 h, with a heating rate of 3 °C / min, and naturally cool to room temperature at room temperature, crush it, and screen it through a 300-mesh sieve to obtain the lithium supplement additive substrate A with the chemical formula Li5FeO^4;

[0079] (3) Place the substrate A prepared in step (2) in a CVD device. Use acetylene as the carbon source and nitrogen as the protective gas. The flow rate of acetylene is 200 mL / min, the flow rate of nitrogen is 800 mL / min, the heating rate is 6 °C / min, heat up to 650 °C, keep the temperature for 3 h, and cool to room temperature in the natural environment to obtain Li5FeO4@C.

[0080] Comparative Example 5

[0081] A preparation method of a lithium supplement agent Li2NiO2:

[0082] (1) Put the nano nickel oxide matrix material into the reaction chamber of the ALD device. First, introduce a mixed gas of lithium tert-butoxide and argon (1:4, 250 mL / min). Under the action of 135 °C and the lithium source pulse (2 s), adsorb the lithium source on the matrix material. Then purge with argon for 10 s. Then introduce a mixed gas of O3 and argon (1:4, 250 mL / min). Under the action of the oxygen source pulse (4.6 s), react O3 with lithium tert-butoxide. Then use argon to purge for 10 s. Then successively introduce a mixed gas of lithium tert-butoxide and argon, purge with argon for 10 s, introduce a mixed gas of O3 and argon, purge with argon for 10 s, and repeat 5 times to prepare the NiO@lithium salt composite coating material. During the whole process, the flow rate during argon purging is 130 cm 3 / min. The Li / Ni molar ratio in the finally prepared NiO@lithium salt is 2.04, and the thickness of the lithium coating layer is 36 nm;

[0083] (2) Sinter the NiO@lithium salt obtained in step (1) at 650 °C for 15 h with nitrogen as the protective gas and a heating rate of 2 °C / min, and cool down to room temperature naturally to obtain Li2NiO2.

[0084] Assemble the lithium supplement agents in Examples 1-6 and Comparative Examples 1-5 and the lithium supplement agents after being placed for different days into button cells respectively, and test their charging specific capacities at a rate of 0.1C. The results are shown in Table 1. It can be seen from the data in Table 1 that the battery with Li5FeO4@C as the lithium supplement agent has a relatively high charging specific capacity, up to 806 mAh / g, but the stability of the lithium supplement agent is poor. After only one day of placement, the charging specific capacity of the prepared battery decreased by about 74%. Although the stability of the lithium supplement agent Li2NiO2 is acceptable, its charging specific capacity is very low, only 404 mAh / g, far from meeting the requirements of lithium-ion batteries. In the present invention, by combining the above two lithium supplement agents, a lithium supplement agent with a high charging specific capacity and good stability is prepared. In addition, by using the ALD deposition method to prepare NiO@lithium salt and then mixing and sintering NiO@lithium salt with Li5FeO4@C, the charging specific capacity and stability can be improved to a greater extent.

[0085] Table 1 Charge specific capacity and stability data of the lithium supplement agents prepared in Examples 1-6 and Comparative Examples 1-5

[0086]

[0087] The examples provided above are not intended to limit the scope covered by the present invention, nor are the described steps intended to limit the order of their execution. Obvious improvements made by those skilled in the art in combination with the existing well-known common knowledge also fall within the protection scope defined by the claims of the present invention.

Claims

1. A preparation method of a composite lithium-rich lithium supplement additive, characterized in that, It includes the following steps: (1) Mix iron oxide powder and lithium source powder evenly to obtain a blended powder; (2) Sinter the blended powder obtained in step (1) in an inert gas atmosphere, cool, crush, and screen it to obtain a lithium supplement additive substrate A with the chemical formula Li5FeO4; (3) Place the substrate A obtained in step (2) into a CVD device, introduce a carbon source and a protective gas, and obtain carbon-coated lithium ferrite Li5FeO4@C after the reaction; (4) Place the nano nickel oxide matrix material into the reaction chamber of an ALD device. First, introduce a mixed gas of a lithium source precursor and a carrier gas. Under the action of the lithium source pulse, the lithium source is adsorbed on the matrix material. Subsequently, purge with the carrier gas for 10 s. Then, introduce a mixed gas of an oxygen source precursor and a carrier gas. Under the action of the oxygen source pulse, the oxygen source reacts with the lithium source precursor. After that, use the carrier gas to purge for 10 s. Then, successively introduce a mixed gas of a lithium source precursor and a carrier gas, purge with the carrier gas for 10 s, introduce a mixed gas of an oxygen source precursor and a carrier gas, purge with the carrier gas for 10 s, and repeat 3 - 5 times to obtain a shell material precursor NiO@lithium salt; (5) After fully mixing the Li5FeO4@C obtained in step (3) and the NiO@lithium salt obtained in step (4) evenly, sinter them at a high temperature under the protection of nitrogen to obtain a composite lithium-rich lithium supplement agent Li5FeO4@C@Li2NiO2.

2. The preparation method according to claim 1, wherein In step (1), the particle size range of the iron oxide powder is 50 nm to 20 μm, the lithium source powder is at least one of Li2O, LiOH, LiOH·H2O, and Li2CO3, and the molar ratio of the Fe element of the iron oxide powder to the Li element of the lithium source powder is 1:(5 - 5.5).

3. The preparation method according to claim 1, characterized in that, In step (2), the inert gas includes nitrogen and / or argon. The sintering means pre-sintering at 500 - 600 °C for 5 - 15 h, then high-temperature sintering at 700 - 1000 °C for 10 - 24 h, with a heating rate of 2 - 5 °C / min, and cooling to room temperature after sintering. The screening is through a 300-mesh sieve.

4. The preparation method according to claim 1, characterized in that, In step (3), the carbon source includes at least one of acetylene, carbon monoxide, ethylene, and propylene, the protective gas is nitrogen and / or argon, the flow rate of the carbon source is 200 - 300 mL / min, the flow rate of the protective gas is 200 - 1000 mL / min, the reaction temperature is 600 - 650 °C, the reaction time is 2 - 3 h, and the heating rate is 6 °C / min.

5. The preparation method according to claim 1, characterized in that, In step (4), the lithium source precursor is lithium tert-butoxide, the oxygen source precursor is ozone, and the carrier is nitrogen or argon.

6. The preparation method according to claim 1, wherein, In step (4), in the mixed gas of the lithium source precursor and the carrier gas, the volume ratio of the lithium source precursor to the carrier gas is 1:1 - 1:5, the flow rate of the mixed gas of the lithium source precursor and the carrier gas is 200 - 400 mL / min, the temperature during the lithium source pulse is 100 - 150 °C, and the pulse time is 1.6 - 2.5 s.

7. The preparation method according to claim 1, characterized in that, In step (4), in the mixed gas of the oxygen source precursor and the carrier gas, the volume ratio of the lithium oxygen source precursor to the carrier gas is 1:1 to 1:5, the flow rate of the mixed gas of the oxygen source precursor and the carrier gas is 200 - 400 mL / min, the temperature during the oxygen source pulse is 100 - 150 °C, the pulse time is 4 - 5 s, and the flow rate of the carrier gas during the carrier gas purge is 100 - 250 cm 3 / min.

8. The preparation method according to claim 1, characterized in that, In step (5), the molar ratio of Li5FeO4@C to NiO@lithium salt is (99 - 98):(1 - 2), the sintering temperature is 500 - 700 °C, and the heat preservation time is 5 - 20 h.

9. The composite lithium-rich lithium supplement additive prepared according to any one of claims 1 to 8.

10. The application of the composite lithium-rich lithium supplement additive according to claim 9 in the field of lithium-ion batteries.

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