A kind of Li 5 FeO 4 @rGO@C composite lithium supplement additive and its preparation and application in lithium-ion batteries

Abstract

The present invention belongs to the technical field of lithium-ion batteries, and specifically relates to a Li5FeO4@rGO@C composite lithium supplement additive, which is characterized by having a double carbon-coated core-shell structure, which includes a Li5FeO4 core, a graphene layer coated on the surface of the core, and an amorphous carbon layer coated on the surface of the graphene layer. The present invention also relates to a preparation method and application of the material. The double carbon coating of the required structure has a significant effect on reducing the size of Li5FeO 4‑ The grain size and the improvement of the air stability of Li5FeO4 have good synergy, which helps to improve the air stability and prompt it to preferentially participate in the construction of the SEI film of the negative electrode, thereby improving the first charge and discharge coulomb efficiency.

Description

Technical Field

[0001] The present invention belongs to the field of energy storage devices, and in particular relates to a lithium supplement and a preparation method of a lithium ion battery and a lithium ion battery. Background Art

[0002] Lithium ion battery (LIB) is currently the most promising and fastest-growing high-efficiency secondary battery, with many advantages such as high specific energy, low self-discharge, good cycle performance, and no memory effect.

[0003] Lithium in lithium-ion batteries + All of them come from the positive electrode material, and the negative electrode generally uses graphite material. When the battery is charged for the first time, the negative electrode surface of the lithium-ion battery consumes Li + The formation of a layer of SEI film causes the initial charge and discharge capacity loss problem (Initial Capacity Loss, ICL). The ICL of lithium-ion batteries with graphite negative electrodes is about 7% to 10%. High-capacity silicon negative electrode materials are gradually being used in lithium-ion batteries, but the ICL of silicon negative electrodes is as high as 50% to 70%. Therefore, it is extremely important to develop a simple and efficient lithium replenishment technology.

[0004] The current lithium replenishment scheme is mainly negative electrode lithium replenishment, which can be subdivided into primary battery lithium replenishment technology and auxiliary anode lithium replenishment technology. However, research results show that the existing lithium replenishment technology has the following problems: the lithium insertion current of the primary battery lithium replenishment is uncontrollable, the production process is extremely demanding and there are safety hazards; the auxiliary anode lithium replenishment is difficult to produce continuously and is prone to safety hazards. In recent years, domestic and foreign researchers have gradually turned their attention to positive electrode lithium replenishment. Positive electrode lithium replenishment is to select a positive electrode material with a high lithium content in addition to the traditional positive electrode material, mix it with the traditional positive electrode material in a certain proportion and use it as a new positive electrode material for battery assembly. During the first charge and discharge process, the excess Li released by the high-lithium-containing positive electrode material as an additive + It will fill the irreversible Li + loss, thereby reducing the ICL of the entire battery. Compared with negative electrode lithium replenishment technology, positive electrode lithium replenishment is safer and easier to industrialize. It does not require changes to existing factory equipment and processes and is a very promising lithium replenishment technology. However, the high-lithium positive electrode material required for positive electrode lithium replenishment still requires further research. In other words, the core of positive electrode lithium replenishment technology lies in finding a positive electrode material with a high lithium content, which can release lithium to the maximum extent under the charge and discharge conditions of existing batteries, and is low-cost and easy to prepare.

[0005] Li5FeO4 is a lithium-rich transition metal oxide with an inverse fluorite structure. It has a very high specific capacity of up to 867mAh / g. Its initial charge and discharge efficiency is very low. It can remove lithium to the maximum extent and replenish the ICL on the negative electrode. Therefore, Li5FeO4 has great application potential in solving the ICL problem of lithium-ion batteries. However, the sintering process conditions for the preparation of traditional Li5FeO4 reported so far are harsh, the air stability is extremely poor, the synthesized Li5FeO4 has a large particle size, and the electronic conductivity is low, which affects the electrochemical performance and application of Li5FeO4. Summary of the invention

[0006] In order to solve the shortcomings and defects of the prior art, the first purpose of the present invention is to provide a Li5FeO4@rGO@C lithium supplement agent, aiming to improve air stability and improve lithium supplement effect.

[0007] The second object of the present invention is to provide a method for preparing Li5FeO4@rGO@C, aiming to improve the air stability of the prepared material and improve its lithium supplementation effect.

[0008] The third object of the present invention is to provide the use of the lithium supplement additive in lithium ion batteries and the obtained positive electrode and battery.

[0009] A Li5FeO4@rGO@C composite lithium supplement additive having a double carbon-coated core-shell structure, comprising a Li5FeO4 core, a graphene layer coated on the surface of the core, and an amorphous carbon layer coated on the surface of the graphene layer;

[0010] The present invention provides a material with a double carbon coating structure, which uses Li5FeO4 as a core, and the core is pre-coated with a graphene layer, and then coated with an amorphous carbon source. Studies have found that through the combined control of the components and the special double carbon structure, synergy can be generated, which can effectively improve the air stability of the material and improve its electrochemical performance.

[0011] The inventors have innovatively discovered that the double carbon coating of the required structure is effective in reducing the size of Li5FeO 4- The grain size and the improvement of the air stability of Li5FeO4 have good synergy, which helps to improve the air stability and prompt it to preferentially participate in the construction of the SEI film of the negative electrode, thereby improving the first charge and discharge coulomb efficiency.

[0012] Preferably, the Li5FeO4@rGO@C composite lithium supplement additive has a particle size of less than or equal to 5 μm and a specific surface area of ​​200 to 800 m 2 ·g -1 .

[0013] The present invention also provides a method for preparing the Li5FeO4@rGO@C composite lithium supplement additive, comprising the following steps:

[0014] Step (1):

[0015] The iron source and graphene are dispersed in liquid phase to assemble an iron source@rGO precursor; the iron source is iron oxide; the weight ratio of the iron source to the graphene is 1:0.01-0.1;

[0016] Step (2):

[0017] The iron source @rGO precursor, the lithium source, and the amorphous precursor carbon source are ball-milled and activated, and then sintered under a protective atmosphere to obtain the Li5FeO4@rGO@C lithium supplement additive;

[0018] The roasting process is divided into a first roasting and a second roasting which are performed in sequence, wherein the temperature of the first roasting is 500-700°C; and the temperature of the second roasting is 800-900°C.

[0019] The present invention has found that by combining graphene pre-coating and subsequent lithium roasting-simultaneous carbonization, and further coordinating the control of process conditions such as iron source, iron source / graphene ratio, and lithium sintering mechanism, synergy can be achieved, which can effectively control the crystal phase purity and unit cell size of Li5FeO4, improve air stability, improve ion-electron conductivity, and improve its lithium supplementation performance. The study found that the material prepared by this preparation method can preferentially participate in the construction of the negative electrode SEI film, which can effectively improve the initial charge and discharge capacity and improve the electrochemical performance.

[0020] In the present invention, graphene pre-coating of the iron source, lithium carbonization calcination and joint control of various conditions are the key to improving the air stability and lithium replenishment performance of the material.

[0021] In the present invention, the graphene pre-coating process is carried out under liquid phase conditions.

[0022] Preferably, in the liquid phase dispersion stage, the iron source is in a non-dissolved state;

[0023] Preferably, the solvent in the liquid dispersion stage is water;

[0024] Preferably, the iron source is at least one of Fe2O3 and Fe3O4.

[0025] Preferably, the weight ratio of the iron source to the graphene is 1:0.04-0.08; more preferably, it is 1:0.04-0.06.

[0026] In the present invention, the lithium source is not pre-coated with graphene, but is calcined with lithium in the carbonization stage after graphene coating. This can unexpectedly further improve the air stability of the prepared lithium supplement, and also help to improve the lithium supplement performance and the electrochemical performance of the material after lithium supplementation.

[0027] Preferably, the lithium source is at least one of Li2O, Li2CO3, LiF, Li3PO4, and Li2C2O4; more preferably, it is at least one of Li2CO3, LiF, and Li2C2O4.

[0028] Preferably, the molar ratio of Li:Fe in the lithium source and the iron source is 4.5 to 9.5:1; more preferably 5 to 6:1.

[0029] The amorphous precursor carbon source is at least one of citric acid, glucose, sucrose, acetic acid, and p123;

[0030] Preferably, the weight ratio of the amorphous precursor carbon source to the iron source is 0.05-0.3:1; more preferably 0.1-0.2:1.

[0031] In the present invention, each material is ball-milled for activation, and then dried and subsequently carbonized with lithium.

[0032] The ball milling step is preferably wet ball milling, and the solvent used is, for example, at least one of water, C1-C4 units or polyols.

[0033] The ball milling speed is 200-400r / min.

[0034] Preferably, the ball milling time is 1 to 9 hours; more preferably, it is 4 to 6 hours.

[0035] After ball milling, the solid and liquid are separated, and the solid is dried to obtain a precursor which is then carbonized with lithium.

[0036] Preferably, the temperature of the first calcination is 500-600°C; more preferably, 550-600°C.

[0037] Preferably, the temperature of the second calcination is 800-850° C. At this preferred sintering temperature, the electrochemical properties of the obtained material can be further improved.

[0038] Preferably, the first calcination time is 5 to 20 hours, preferably 10 to 15 hours; the second calcination time is 1 to 10 hours, more preferably 1 to 6 hours.

[0039] A more preferred method for preparing Li5FeO4@rGO@C lithium supplement comprises the following steps:

[0040] (1) Weigh a certain proportion of Fe2O3 and graphene and disperse them in deionized water. After ultrasonic treatment for 1 to 2 hours, mechanical stirring is performed for 4 to 6 hours, and the reaction product is placed in an oven for drying to obtain Fe2O3@rGO.

[0041] (2) The Fe2O3@rGO and Li2O obtained in step (1) are dispersed with glucose by ethanol and ball-milled for 1 to 9 hours. The dried ball-milled mixture is kept at 500 to 700°C for 10 to 15 hours and at 800 to 900°C for 2 to 6 hours under an Ar atmosphere to obtain Li5FeO4@rGO@C; the Li / Fe element molar ratio of the Fe2O3 and Li2O is 5 to 6:1.

[0042] In the present invention, GO sheets are innovatively anchored on the Fe2O3 surface through electrostatic adsorption, which not only ensures that Li5FeO4 is evenly distributed on the GO sheet surface after sintering, but also limits the agglomeration of Li5FeO4 during sintering, which is beneficial to the uniformity of the carbon coating layer. Further combined with the subsequent lithium addition and simultaneous carbonization, Li5FeO4@rGO@C with small particle size, uniform coating, and stable existence in the air can be obtained.

[0043] The present invention also includes the Li5FeO4@rGO@C composite lithium supplement additive prepared by the preparation method. The material has the physical and chemical properties imparted by the preparation method, and has better air stability and lithium supplement effect.

[0044] The initial charging capacity of the Li5FeO4@rGO@C is 450-750 mAh·g -1 The initial charge and discharge efficiency is 1-10%, the particle size is less than or equal to 2μm, and the specific surface area is 200-800m 2 ·g -1 .

[0045] The present invention also provides the application of the Li5FeO4@rGO@C composite lithium supplement additive as an additive for preparing lithium ion batteries;

[0046] Preferably, it is used to prepare the positive electrode of a lithium ion battery;

[0047] Preferably, it is used to prepare positive electrode materials for lithium-ion batteries.

[0048] In the present invention, based on existing materials, equipment and principles, the Li5FeO4@rGO@C composite lithium supplement additive can be used to prepare lithium-ion batteries and their associated components and materials.

[0049] The present invention also provides a lithium-ion battery lithium-supplementing positive electrode material, comprising a positive electrode active material and the Li5FeO4@rGO@C composite lithium-supplementing additive.

[0050] The positive electrode active material may be an existing conventional positive electrode active material.

[0051] Preferably, the positive electrode active material is at least one of LiCoO2, LiFePO4, and NCM ternary materials;

[0052] Preferably, the weight percentage of the Li5FeO4@rGO@C composite lithium supplement additive is 2-15%; preferably 5-10%; research has found that controlling the Li5FeO4@rGO@C composite lithium supplement additive within the said range can further exert the performance of the additive, further improve the electrical performance, and improve the first charge and discharge coulomb efficiency.

[0053] In the present invention, the lithium-supplementing positive electrode material, in addition to the lithium-supplementing additive and the positive electrode active material, also contains other components allowed to be added to the positive electrode material, such as a conductive agent, a binder, etc.

[0054] The conductive agent can be a material with conductive properties that can be used for the positive electrode and is known in the industry; for example, at least one of acetylene black and Ketjen black. The weight percentage of the conductive agent is 1 to 15%, preferably 5 to 10%.

[0055] The binder can be a material known in the industry that can be used to bond the positive electrode components to each other; for example, it can be at least one of PVDF and PTFE. The weight percentage of the binder is 1 to 15%, preferably 5 to 10%.

[0056] In the present invention, the balance is the positive electrode active material.

[0057] In the present invention, the preparation method of the lithium-supplementing positive electrode material comprises slurrying the lithium-supplementing additive, positive electrode active material, conductive agent, binder and solvent to obtain positive electrode slurry, coating the positive electrode slurry on the surface of the positive electrode collector, curing, and compounding on the surface of the positive electrode collector to obtain the lithium-supplementing positive electrode material.

[0058] The present invention also provides a lithium-ion battery, which includes the Li5FeO4@rGO@C composite lithium-supplementing additive; preferably, includes the lithium-supplementing positive electrode material.

[0059] In the present invention, the lithium-ion battery, except for the positive electrode containing the Li5FeO4@rGO@C composite lithium supplement additive of the present invention, other components and materials can be known. For example, the negative electrode active material is one or more of graphite, hard carbon, and silicon-carbon materials.

[0060] The lithium-replenishing positive electrode material is used to replenish lithium in the assembled lithium-ion battery. Preferably, the lithium-replenishing treatment is a charge-discharge cycle. The first charge is charged with a constant current or constant voltage of 0.02-0.1C, and the cut-off voltage is 4.0-4.5V. The first discharge is discharged with a constant current of 0.02-0.1C, and the cut-off voltage is 1.5-2.0V. A small current is used during charging to completely remove the lithium in the material, and a large current is used during discharge to destroy the material structure and prevent the lithium from returning.

[0061] As a general technical concept, the present invention also provides a lithium-ion battery assembled from the lithium-supplementing positive electrode material. The initial charge and discharge coulomb efficiency of the lithium-ion battery is 90-99%.

[0062] Compared with the prior art, the advantages of the present invention are:

[0063] 1. The present invention provides a Li5FeO4@rGO@C material with an amorphous-graphene double carbon coating structure. Studies have shown that the material has good structural stability, excellent air stability, good ion-electron conductivity, and excellent lithium replenishment performance. Studies have shown that using it to replenish lithium in the negative electrode of a lithium battery can effectively reduce the capacity loss of the battery during the first charge and discharge process, and improve the energy density and cycle performance of the entire battery.

[0064] 2. The present invention innovatively provides a graphene pre-coating-lithium carbonization combined process, which can effectively control the grain and crystal phase purity, improve coating uniformity and density, improve stability, help improve its ion-electron conductivity, and improve its lithium supplementation performance;

[0065] The process of the present invention can effectively solve the problems of extremely poor air stability and low electronic conductivity of Li5FeO4, and the synthesized Li5FeO4@rGO@C has loose environmental requirements and can be coated together with existing positive electrode materials. The process is simple, easy to control and low cost.

[0066] 3. Li5FeO4@rGO@C material has a smaller particle size and a higher specific surface area. The higher specific surface area can provide more active sites for the action of active ions, which is beneficial for Li5FeO4 to release more lithium ions. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] Figure 1 SEM image of Li5FeO4@rGO@C

[0068] Figure 2 The cycle diagram of the material prepared in Example 1 at 0.1C

[0069] Figure 3The cycle diagram of the material prepared in Example 2 at 0.1C

[0070] Figure 4 The cycle diagram of the material prepared in Example 3 at 0.1C

[0071] Figure 5 The cycle diagram of the material prepared in Example 4 at 0.1C

[0072] Figure 6 The cycle diagram of the material prepared in Example 5 at 0.1C

[0073] Figure 7 The cycle diagram of the material prepared in Example 6 at 0.1C DETAILED DESCRIPTION

[0074] In order to facilitate the understanding of the present invention, the present invention will be described more comprehensively and carefully in combination with preferred embodiments below, but the protection scope of the present invention is not limited to the following specific embodiments.

[0075] Unless otherwise defined, all the professional terms used below have the same meanings as those generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0076] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0077] Example 1

[0078] A method for preparing a lithium-ion battery using a Li5FeO4@rGO@C lithium supplement comprises the following steps:

[0079] 1. Preparation of lithium supplement materials

[0080] (1) Fe2O3 and graphene in a mass ratio of 10:0.5 were weighed and dispersed in deionized water. After ultrasonic treatment for 1 h, mechanical stirring was performed for 4 h, and the reaction product was placed in an oven at 80 °C to dry, thereby obtaining Fe2O3@rGO;

[0081] (2) The Fe2O3@rGO and Li2O (Li / Fe molar ratio of 5.5:1) obtained in step (1) and glucose (mass ratio of glucose:Fe2O3 of 1:10) were placed in ethanol (weight ratio of ethanol to glucose of 40:1), and ball-milled at 400 r / min for 4 h. The dried ball-milled mixture was kept at 600 °C (first stage sintering) for 10 h and 800 °C (second stage sintering) for 2 h in an Ar atmosphere to obtain Li5FeO4@rGO@C. The particle size of the Li5FeO4@rGO@C composite lithium supplement additive was 3 μm and the specific surface area was 400 m 2 ·g -1 .

[0082] 2. Preparation of positive electrode

[0083] NCM811 (positive electrode active material, 75wt%), Li5FeO4@rGO@C (5wt%), Super P (10wt%) and PVDF (10wt%) were mixed evenly, and then the positive electrode sheet was obtained by slurry preparation, coating, drying and rolling.

[0084] 3. Negative electrode preparation

[0085] After graphite (90wt%), SuperP (5wt%) and PVDF (5wt%) are uniformly mixed, the negative electrode sheet is obtained by slurry preparation, coating, drying and rolling.

[0086] 4. After assembling the positive and negative electrode sheets, a lithium-ion battery is obtained, and lithium replenishment of the negative electrode material is achieved in the first charge and discharge cycle.

[0087] Example 2

[0088] Compared with Example 1, the only difference is that the iron source is Fe3O4.

[0089] Example 3

[0090] Compared with Example 1, the only difference is that Li / Fe=5:1.

[0091] Example 4

[0092] Compared with Example 1, the only difference is that Li / Fe=6:1.

[0093] Example 5

[0094] Compared with Example 1, the only difference is that the sintering temperature of the first stage is 500° C. and the sintering time is 15 h; the sintering temperature of the second stage is 900° C. and the sintering time is 1 h.

[0095] Example 6

[0096] Compared with Example 1, the only difference is that the positive electrode active material is LiFePO4.

[0097] Example 7

[0098] Compared with Example 1, the only difference is that in step (1), the mass ratio of Fe2O3 to graphene is 10:0.4.

[0099] Example 8

[0100] Compared with Example 1, the only difference is that in step (1), the mass ratio of Fe2O3 to glucose is 10:2.

[0101] Example 9

[0102] Compared with Example 1, the only difference is that in 2, the content of Li5FeO4@rGO@C composite lithium supplement additive is 10wt%; the balance is NCM811 (positive electrode active material, 70wt%).

[0103] Example 10

[0104] Compared with Example 1, the only difference is that in 2, the content of Li5FeO4@rGO@C composite lithium supplement additive is 2wt%; the balance is NCM811 (positive electrode active material, 78wt%).

[0105] Comparative Example 1

[0106] Compared with Example 1, the only difference is that step (1) does not contain graphene.

[0107] Comparative Example 2

[0108] Compared with Example 1, the only difference is that in step (1), the mass ratio of Fe2O3 to graphene is 10:2.

[0109] Comparative Example 3

[0110] Compared with Example 1, the only difference is that the iron source used in step (1) is FeC2O4.

[0111] Comparative Example 4

[0112] Compared with Example 1, the only difference is that the lithium source in step (2) is added in step (1): for example, Fe2O3 is pre-mixed with Li2O and then mixed with the graphene liquid phase.

[0113] Comparative Example 5

[0114] Compared with Example 1, the only difference is that no glucose is added in step (2).

[0115] Comparative Example 6

[0116] Compared with Example 1, the only difference is that a one-stage sintering process is adopted, for example, the temperature is directly raised to 800° C. and kept for 12 hours during the sintering process.

[0117] Comparative Example 7

[0118] Compared with Example 1, the only difference is that two-stage sintering is adopted, but the sintering temperature of the first stage is 400°C.

[0119] Comparative Example 8

[0120] Compared with Example 1, the only difference is that graphene is not pre-coated and then amorphous carbon is coated. Instead, graphene, iron source, carbon source, lithium source and glucose are mixed and ball-milled in ethanol, dried and then sintered according to the two-stage sintering mechanism.

[0121] Comparative Example 9

[0122] Compared with Example 1, the only difference is that in step (1), the iron source, lithium source and carbon source are pyrolyzed to first form amorphous carbon, and then the above materials are mixed and dispersed with graphene to assemble; Li5FeO4@C@rGO is constructed.

[0123] Performance data:

[0124] 1. Air stability test

[0125] The cyclic stability data of the lithium supplement additives prepared in each case after being stored in an air atmosphere at a temperature of 30°C and a humidity of 30% for different periods of time are shown in Table 1:

[0126] Table 1

[0127]

[0128]

[0129] 2. Full battery cycle data:

[0130] The test results are shown in Table 2:

[0131] Table 2

[0132]

[0133]

[0134] It can be seen from the embodiments and comparative examples that the technical solution of the present invention can effectively improve stability and improve its cyclic stability under air resistance.

Claims

1. A Li5FeO4@rGO@C composite lithium supplement additive, characterized in that: A double carbon-coated core-shell structure comprising a Li5FeO4 core, a graphene layer coated on the surface of the core, and an amorphous carbon layer coated on the surface of the graphene layer; The Li5FeO4@rGO@C composite lithium supplement additive is prepared by the following steps: Step (1): The iron source and graphene are dispersed in liquid phase to assemble an iron source@rGO precursor; the iron source is iron oxide; the weight ratio of the iron source to the graphene is 1:0.01~0.1; Step (2): The iron source @rGO precursor, the lithium source, and the amorphous precursor carbon source are ball-milled and activated, and then sintered under a protective atmosphere to obtain the Li5FeO4@rGO@C lithium supplement additive; The roasting process is divided into a first roasting and a second roasting which are performed sequentially, wherein the temperature of the first roasting is 500-700°C; and the temperature of the second roasting is 800-900°C.

2. The Li5FeO4@rGO@C composite lithium supplement additive according to claim 1, characterized in that: The particle size of the Li5FeO4@rGO@C composite lithium supplement additive is less than or equal to 5 μm, and the specific surface area is 200-800 m 2 ·g -1 .

3. A method for preparing the Li5FeO4@rGO@C composite lithium supplement additive according to claim 1 or 2, characterized in that: The following steps are involved: Step (1): The iron source and graphene are dispersed in liquid phase to assemble an iron source@rGO precursor; the iron source is iron oxide; the weight ratio of the iron source to the graphene is 1:0.01~0.1; Step (2): The iron source @rGO precursor, the lithium source, and the amorphous precursor carbon source are ball-milled and activated, and then sintered under a protective atmosphere to obtain the Li5FeO4@rGO@C lithium supplement additive; The roasting process is divided into a first roasting and a second roasting which are performed sequentially, wherein the temperature of the first roasting is 500-700°C; and the temperature of the second roasting is 800-900°C.

4. The method for preparing the Li5FeO4@rGO@C composite lithium supplement additive according to claim 3, characterized in that: The iron source is at least one of Fe2O3 and Fe3O4.

5. The method for preparing the Li5FeO4@rGO@C composite lithium supplement additive according to claim 3, characterized in that: The weight ratio of the iron source to graphene is 1:0.04~0.

08.

6. The method for preparing the Li5FeO4@rGO@C composite lithium supplement additive according to claim 3, characterized in that: The weight ratio of the iron source to graphene is 1:0.04~0.

06.

7. The method for preparing the Li5FeO4@rGO@C composite lithium supplement additive according to claim 3, characterized in that: The lithium source is at least one of Li2O, Li2CO3, LiF, Li3PO4, and Li2C2O4.

8. The method for preparing the Li5FeO4@rGO@C composite lithium supplement additive according to claim 3, characterized in that: The molar ratio of Li:Fe in the lithium source and the iron source is 4.5~9.5:

1.

9. The method for preparing the Li5FeO4@rGO@C composite lithium supplement additive according to claim 3, characterized in that: The amorphous precursor carbon source is at least one of citric acid, glucose, sucrose, acetic acid and p123.

10. The method for preparing the Li5FeO4@rGO@C composite lithium supplement additive according to claim 3, characterized in that: The weight ratio of the amorphous precursor carbon source to the iron source is 0.05~0.3:

1.

11. The method for preparing the Li5FeO4@rGO@C composite lithium supplement additive according to claim 3, characterized in that: The weight ratio of the amorphous precursor carbon source to the iron source is 0.1-0.2:

1.

12. The method for preparing the Li5FeO4@rGO@C composite lithium supplement additive according to claim 3, characterized in that: The ball milling speed is 200~400r / min; The ball milling time is 1~9h.

13. The method for preparing the Li5FeO4@rGO@C composite lithium supplement additive according to claim 3, characterized in that: The first roasting time is 5 to 20 hours; the second roasting time is 1 to 10 hours.

14. An application of the Li5FeO4@rGO@C composite lithium supplement additive according to any one of claims 1 to 2 or the Li5FeO4@rGO@C composite lithium supplement additive prepared by the preparation method according to any one of claims 3 to 13, characterized in that: It is used to prepare lithium-ion batteries.

15. The use according to claim 14, characterized in that It is used to prepare the positive electrode of lithium-ion batteries.

16. The use according to claim 15, characterized in that It is used to prepare positive electrode materials for lithium-ion batteries.

17. A lithium-ion battery lithium-supplementing positive electrode material, characterized in that: It comprises a positive electrode active material and the Li5FeO4@rGO@C composite lithium supplement additive described in any one of claims 1 to 2 or the Li5FeO4@rGO@C composite lithium supplement additive prepared by the preparation method of any one of claims 3 to 13.

18. The lithium-ion battery lithium-supplementing positive electrode material according to claim 17, characterized in that: The positive electrode active material is at least one of LiCoO2, LiFePO4 and NCM ternary materials.

19. The lithium-ion battery lithium-supplementing positive electrode material according to claim 17, characterized in that: Also includes a conductive agent and a binder; Wherein, the weight percentage of the Li5FeO4@rGO@C composite lithium supplement additive is 2-15%; The weight percentage of the conductive agent is 1-15%; The weight percentage of the binder is 1-15%; the remainder is the positive electrode active material.

20. A lithium ion battery, characterized in that: It comprises the Li5FeO4@rGO@C composite lithium supplement additive described in any one of claims 1 to 2 or the Li5FeO4@rGO@C composite lithium supplement additive prepared by the preparation method of any one of claims 3 to 13.

21. The lithium ion battery according to claim 20, characterized in that Contains the lithium-supplementing positive electrode material according to any one of claims 17 to 19.

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