CN115000362B

CN115000362B - Li5FexMyO4@C composite material, preparation method thereof and application thereof in lithium ion battery

Info

Publication number: CN115000362B
Application number: CN202210467630.4A
Authority: CN
Inventors: 张治安; 朱斌; 赖延清; 温奶峰; 洪波; 张凯; 李劼
Original assignee: Central South University
Current assignee: Central South University
Priority date: 2022-04-29
Filing date: 2022-04-29
Publication date: 2024-06-11
Anticipated expiration: 2042-04-29
Also published as: CN115000362A

Abstract

The invention belongs to the field of lithium battery materials, and particularly relates to a Li ₅Fe_xM_yO₄ @C composite material which comprises a core and a carbon shell encapsulated on the surface of the core; the core is Li ₅Fe_xM_yO₄, wherein x is 0.8-0.9, and 3x+Ay=3; m is a transition metal element; a is the valence state of M. The invention also provides a preparation method of the composite material and application of the composite material in lithium ion battery lithium supplement. In the invention, the combined control of the lattice hybridization and the core-shell structure of M is the key to synergistically improve the air and crystal stability, ICL and electrochemical performance. Further research of the invention finds that the core structure and the carbon shell substance are further controlled, which is helpful for further improving the synergy of the components and the structure and is helpful for further synergistically improving the stability, ICL and electrochemical performance of the composite material.

Description

Li 5FexMyO4 @C composite material, preparation method thereof and application thereof in lithium ion battery

Technical Field

The invention belongs to the technical field of lithium ion batteries, and particularly relates to the field of lithium ion lithium supplementing materials.

Background

The lithium ion battery (Lithium Ion Battery, LIB) has the most promising and fastest-growing high-efficiency secondary battery at present and has the advantages of higher specific energy, low self-discharge, good cycle performance, no memory effect and the like.

Li+ in lithium ion batteries is derived entirely from the positive electrode material, and the negative electrode is typically a graphite material. When the battery is charged for the first time, li+ is consumed on the surface of the negative electrode of the lithium ion battery to form a layer of SEI film, so that the problem of Loss of the first charge and discharge capacity (INITIAL CAPACITY Loss, ICL) is caused, and the ICL of the lithium ion battery of the graphite negative electrode is about 7% -10%. High capacity silicon negative electrode materials are gradually applied to lithium ion batteries, but ICL of the silicon negative electrode is as high as 50% -70%. Therefore, the development of a simple and efficient lithium supplementing technology has extremely important significance.

The current lithium supplementing scheme is mainly negative electrode lithium supplementing, wherein the lithium supplementing scheme can be subdivided into a primary battery lithium supplementing technology and an auxiliary anode lithium supplementing technology. However, the research results show that the existing lithium supplementing technology has the following problems: the lithium supplementing and inserting current of the primary battery is uncontrollable, the requirement on the production process is extremely high, and potential safety hazards exist; the auxiliary anode lithium supplementing is difficult to continuously produce and has potential safety hazard easily. In recent years, researchers at home and abroad gradually put the line of sight on the positive electrode lithium supplement. The positive electrode lithium supplementing is to select a positive electrode material with high lithium content outside the traditional positive electrode material, mix the positive electrode material with the traditional positive electrode material according to a certain proportion and use the positive electrode material as a brand new positive electrode material for the assembly of the battery. In the first charge and discharge process, the excessive Li+ released by the positive electrode material with high lithium content as an additive fills the irreversible Li+ loss generated at the cathode, thereby reducing ICL of the whole battery. Compared with the cathode lithium supplementing technology, the cathode lithium supplementing technology is safer and easy to industrialize, does not need to change the existing equipment and flow of a factory, and is a very promising lithium supplementing technology. However, the high-lithium cathode material required by the cathode lithium supplement still needs further research, namely the core of the cathode lithium supplement technology is to find a cathode material which has high lithium content, can release lithium to the maximum degree under the charge and discharge conditions of the existing battery, and has low cost and simple preparation.

Li ₅FeO₄ is a lithium-rich transition metal oxide with an inverse fluorite structure, has very high specific capacity which can reach 867mAh/g, has very low first charge and discharge efficiency, and can maximally remove lithium and supplement ICL on a cathode, so that Li ₅FeO₄ has great application potential in the field of solving ICL problems of lithium ion batteries. However, the sintering process conditions for preparing the traditional Li ₅FeO₄ reported at present are harsh, the air stability is extremely poor, the particle size of the synthesized Li ₅FeO₄ is large, the electron conductivity is low, the electrochemical performance and the application of Li ₅FeO₄ are affected, and in addition, the subsequent rate performance of the battery is greatly affected due to the poor electron conductivity of the product obtained after Li ₅FeO₄ is delithiated.

Disclosure of Invention

Aiming at the problems of poor air stability, ICL and non-ideal electrochemical performance of the Li ₅FeO₄ positive electrode lithium supplementing material, the first aim of the invention is to provide a Li ₅Fe_xM_yO₄ @C composite material, aiming at improving the air and structural stability and improving the ICL and the electrochemical performance of the Li ₅Fe_xM_yO₄ @C composite material.

The second purpose of the invention is to provide a preparation method of the Li ₅Fe_xM_yO₄ @C composite material, which aims to solve the problem of hetero-phase in the carbon coating process and improve the stability, ICL and electrochemical performance of the prepared material.

The third object of the invention is to provide the application of the Li ₅Fe_xM_yO₄ @C composite material as a lithium supplementing material.

The fourth object of the invention is to provide a lithium ion battery containing the Li ₅Fe_xM_yO₄ @C composite material, and a lithium supplementing positive electrode material and a positive electrode thereof.

The Li ₅FeO₄ has poor air stability, the crystal structure is easy to collapse, the lithium supplementing performance is not ideal, and aiming at the problem, the invention provides a Li ₅Fe_xM_yO₄ @C composite material which comprises a core and a carbon shell encapsulated on the surface of the core;

The core is Li ₅Fe_xM_yO₄, wherein x is 0.8-0.9, and 3x+Ay=3; m is a transition metal element; a is the valence state of M.

According to the invention, through the combination of M lattice hybridization and carbon coating and the combination control of the parameters, synergy can be realized, the lattice stability of the material can be effectively improved, the air tolerance is improved, and ICL and electrochemical properties, particularly electrochemical properties after air exposure, are effectively improved.

The research of the invention finds that the combined control of the lattice hybridization and the core-shell structure of M is the key to synergistically improve the air and crystal stability, ICL and electrochemical performance. Further research of the invention finds that the further control of the core structure and the carbon shell substance is helpful for further improving the synergy of the components and the structure and further synergistically improving the stability of the composite material, the ICL and the electrochemical performance after air exposure.

Preferably, M is at least one of divalent, trivalent, tetravalent transition metals (i.e., a is 2, 3, or 4), and more preferably Zr, mn, cu, ni, ti;

Preferably, the core is Li ₅Fe_xM^a _y1M^b _y2O₄ and the M ^a is Zr; and M ^b is Ti. Wherein y1+y2=y. According to the research of the invention, the Li ₅Fe_xM^a _y1M^b _y2O₄ can be further cooperated with the carbon shell, so that better air-structure stability can be obtained, and better ICL and electrochemical performance can be obtained. Said y1: the ratio of y2 is not particularly limited, for example, y1: y2 is 0.5-1.5:1.

Preferably, the core is spherical; preferably, the particle size of the D50 is 300-800 nm;

Preferably, the thickness of the carbon shell is 5-10 nm.

Li ₅FeO₄ has poor air stability, and carbon coating is helpful to improve the air stability, however, li ₅FeO₄ has poor tolerance to the traditional carbonization process, is easy to transform and form unfavorable impurity phases in the carbonization stage, and has the problem that the conductivity of a carbon layer, a coating structure and the purity of a nuclear phase are difficult to be compatible. Aiming at the problems of non-ideal carbon coating form, easy occurrence of mixed phase, ICL, non-ideal electrochemical performance and the like in the Li ₅FeO₄ carbon coating process, the invention provides the following preparation method:

A preparation method of Li ₅Fe_xM_yO₄ @ C composite material comprises slurrying an iron source, a lithium source and an M metal source to obtain slurry, and then carrying out spray drying-roasting treatment or spray pyrolysis treatment to obtain a core;

and (3) carrying out heat treatment on the core in the atmosphere of gasified organic matters at the temperature of 200-350 ℃ to obtain the Li ₅Fe_xM_yO₄ @C composite material.

According to the invention, the M auxiliary spray-roasting (spray pyrolysis) treatment is adopted, and the subsequent combined control of the internal heat treatment and the temperature of the gasified organic matter atmosphere is further matched, so that the synergy can be realized unexpectedly, the transformation hetero-phase stability in the preparation process can be solved, the hetero-phase related to the ferrous iron of the core can be effectively avoided under the mild condition, the phase purity of the core and the crystal structure and the grain size are improved, the uniform compounding of the carbon layer structure modified by special functional groups on the surface of the core is facilitated, the synergy can be realized unexpectedly, and the phase, ICL and electrochemical properties of the material can be improved synergistically.

In the invention, the iron source is at least one of iron oxide, carbonate, organic acid salt, nitrate and hydroxide; for example, at least one of ferrous oxalate, ferric oxide and ferric oxide may be used.

Preferably, the M source is at least one of an oxide, a carbonate, an organic acid salt, a nitrate, and a hydroxide of M metal.

Preferably, the lithium source is at least one of lithium oxide, nitrate, carbonate, hydroxide and organic acid salt; for example, at least one of lithium carbonate, lithium bicarbonate, lithium acetate, and lithium oxide may be used.

Preferably, the solvent in the slurry comprises water; other water-soluble organic solvents are also permissible; the solvent is preferably water in view of the cost of treatment.

In the invention, li: the molar ratio of M is 5-6: x: y; preferably, li in the raw materials is Fe: and M is mixed according to the stoichiometric ratio.

The granularity D50 of solid particles in the slurry is less than or equal to 300nm;

preferably, the solids content in the slurry is 30 to 60wt.%;

preferably, the slurry is obtained by pulping the raw materials and then performing ball milling and sand milling. For example, the slurry particle size after ball milling is d50.ltoreq.2μm, and the ball milling medium is preferably zirconia balls. The grain size of the ground slurry is D50 less than or equal to 300nm, and the rotating speed of the grinding machine is preferably 1500-2400 rpm.

In the present invention, the core may be produced by spray-drying the raw material slurry and then calcining the slurry, or directly spray-pyrolyzing the slurry.

Preferably, the inlet temperature of the spray drying process is 150-300 ℃; the spraying rate is preferably 20 to 40ml/min.

Preferably, the roasting atmosphere is a protective atmosphere;

preferably, the roasting temperature is 500-700 ℃, and preferably, the heat preservation time is 4-16 h;

Preferably, the spray pyrolysis temperature is 500-700 ℃; the spraying rate is preferably 20 to 40ml/min.

In the invention, the core is innovatively subjected to heat treatment in the atmosphere of the gasified organic matters, and the combined control of the temperature is further matched, so that ferrous iron and doping related impurity phases in the carbon compounding process can be effectively avoided, the stability of phases and structures is maintained, the defect is filled, the carbon layer with a special structure is uniformly compounded on the surface of the core, and the ICL and electrochemical performance of the composite material are synergistically improved.

The gasified organic matter is an organic matter which is in a gaseous state at the temperature of 200-350 ℃;

Preferably, the gasified organic matter is at least one of C1-C6 alkane, C2-C6 alkene, C2-C6 alkyne, C1-C6 alcohol and C4-C8 ether; further preferred is a source of a combination of C2-C6 olefins and C2-C6 alkynes. It was found that better performance can be obtained in a preferred atmosphere.

In the present invention, the heat treatment may be performed under a pure gasified organic atmosphere or under a mixed gas diluted with a diluent.

Preferably, the diluent gas is at least one of nitrogen and inert gas;

preferably, in the atmosphere containing the gasified organic matter, the volume content of the gasified organic matter is 5% or more, and further may be 10 to 30%.

In the present invention, the total time of the heat treatment is, for example, 2 to 5 hours.

Preferably, the heat treatment process comprises a first-stage heat treatment process and a second-stage heat treatment process, wherein the temperature (T1) of the first-stage heat treatment process is 200-250 ℃; the time is 0.5 to 1.5 hours; the temperature (T2) of the second stage heat treatment process is 250-350 ℃ and the time is 1.5-3 h. It was found that better performance can be achieved with the preferred gradient heat treatment. Further preferably, the temperature difference between T2 and T1 is preferably 50 to 100 ℃.

The invention also provides application of the Li ₅Fe_xM_yO₄ @C composite material in preparing a lithium ion battery.

Preferably, the lithium ion battery is used as a lithium supplementing material for preparing a lithium supplementing positive electrode of the lithium ion battery;

Preferably, the composite material is used as a lithium supplementing material and is compounded with a positive electrode composite material to prepare the lithium supplementing positive electrode of the lithium ion battery.

In the application of the invention, the Li ₅Fe_xM_yO₄ @C composite material can be used as a lithium supplementing material, and the positive electrode and the lithium ion battery are prepared based on the existing means and materials.

The invention also provides a lithium supplementing positive electrode material, which comprises a positive electrode active material and the Li ₅Fe_xM_yO₄ @C composite material.

According to the research of the invention, the Li ₅Fe_xM_yO₄ @C composite material has better discharge activity compared with the positive electrode active material in the first turn, and can show better ICL performance and electrochemical performance.

Preferably, the positive electrode active material is at least one of NCM and LiCoO ₂; the NCM is a nickel-cobalt-manganese ternary material, and the proportion of elements can be adjusted according to the requirements, for example, the ratio can be 8:1:1 or 5:2:3.

Preferably, the weight ratio of the Li ₅Fe_xM_yO₄ @C composite material to the positive electrode active material is 3-5: 95-97.

Preferably, the lithium-supplementing positive electrode material further comprises at least one of a binder and a conductive agent;

In the invention, the binder can be a component which is known in the industry and has binding property and allows the addition in lithium battery, such as at least one of PVDF and CMCC;

Preferably, in the lithium-supplementing positive electrode material, the weight content of the binder is 5-15 wt%;

preferably, the conductive agent can be a component which is known in the industry to have conductivity and is allowed to be added in lithium electricity, such as at least one of carbon black and SP;

preferably, in the lithium-supplementing positive electrode material, the weight content of the conductive agent is 5-15 wt%.

The invention also provides a lithium supplementing anode, which comprises an anode current collector and the lithium supplementing anode material compounded on the surface of the anode current collector.

The positive electrode current collector can be a positive electrode current collector known in the industry, for example, at least one of metal foil and carbon material current collector Cu/Al, preferably Cu;

in the invention, the compounding amount of the positive electrode material in the lithium supplementing positive electrode can be adjusted according to the well-known principle of industry.

The invention also provides a lithium ion battery, which comprises the lithium supplementing anode.

The lithium ion battery of the invention can be provided with other components, component structures and materials except the lithium supplementing positive electrode of the invention, which are all well known in the industry.

The beneficial effects are that:

(1) The invention provides a brand new Li ₅Fe_xM_yO₄ @C composite material, which can realize synergy through M hybridization and control of a core-shell structure constructed by a carbon layer, and can improve air and phase stability of the material and ICL and electrochemical performance.

(2) Aiming at the problems of impurity phase, structural collapse and the like which are easy to occur in the lithium ferrate doping and carbon coating process, the invention innovatively discovers that under the condition of adopting the M auxiliary spray-roasting (spray pyrolysis), the subsequent combined control of carbon gas source heat treatment and temperature is further matched, the synergy can be realized accidentally, the problems of impurity phase such as ferrous iron and structural collapse and the like which are easy to occur in the preparation process and are caused by doping can be solved, in addition, uniform graphitized carbon shells with few defects can be formed on the surface, so that the air and structural stability of the prepared material can be improved synergistically, and ICL and electrochemical performance can be improved.

The method has the advantages of low cost, large-scale production, environmental friendliness, simple operation and excellent industrial application prospect.

Drawings

FIG. 1 is a graph of the first-turn capacity voltage curve of example 1;

Detailed Description

Example 1

1. Preparation of Li ₅Fe0.9Zr0.075O₄ @ C:

(1) Lithium oxide, ferric oxide and zirconium ethoxide (M metal source) are mixed according to the mole ratio of Li to Fe to Zr of 5:0.9:0.075 mixing and dispersing in deionized water, ball milling and sand milling to obtain slurry with solid content of 40% (solid particle size D50 in slurry is less than or equal to 300 nm);

(2) Spray drying the slurry obtained in the step (1) at 200 ℃ to obtain a uniformly mixed precursor, wherein the feeding speed is 30ml/min;

(3) And (3) placing the precursor obtained in the step (2) in an argon atmosphere and sintering at 600 ℃ for 10 hours. After cooling, uniform Li ₅Fe0.9Zr0.075O₄ was obtained.

(4) On the basis of the step (3), ball milling, crushing, and then conducting heat treatment on methane-N ₂ mixed gas (volatile organic gas source) with the volume ratio of 1:9, wherein the temperature of the first heat treatment process is 250 ℃ (T1); the time is 1h; the temperature of the second stage heat treatment process is 300 ℃ (T2) for 2 hours, and then the uniform carbon-coated transition metal doped Li ₅Fe0.9Zr0.075O₄ @C with the D50 of 400nm is obtained through crushing and screening.

Example 2

Compared to example 1, the only difference is that Li: fe: the molar ratio of Zr is 5.5:0.8:0.15.

Example 3

The difference compared with example 1 is that in the step (3), the baking temperature is 700 ℃ and the holding time is 4 hours. In the step (4), the atmosphere content and the temperature of T1 are 250 ℃; t2 has a temperature of 350 ℃.

Example 4

The difference compared with example 1 is that in the step (3), the baking temperature is 500℃and the holding time is 16 hours. In the step (4), the atmosphere content and the temperature of T1 are 200 ℃; t2 has a temperature of 250 ℃.

Example 5

Compared with example 1, the difference is that TiO ₂ is adopted to replace Zr as an M metal source, and the element proportion is the same as that of example 1; other conditions were the same as in example 1.

Example 6

The only difference compared to example 1 is that CuO is used as the M source; li: fe: other conditions were the same as in example 1, except that the molar ratio of Cu was 5:0.9:0.15.

Example 7

The difference compared to example 1 is only that the molar amount of Ti: zr is 1: tiO ₂ and zirconium ethoxide of example 1 are used as M metal sources, and the total molar amount of the M sources is the same as that of example 1, and the other conditions are the same as that of example 1.

Example 8

The difference compared to example 1 is that (2) is spray pyrolysis and its temperature is 600 ℃, the flow rate is the same as example 1, and the other conditions are the same as example 1.

Example 9

The only difference compared to example 1 is that the volatile organic gas source in (4) is replaced by acetylene in a volume ratio of 3:7: nitrogen composite gas under the same conditions as in example 1

Example 10

The only difference compared to example 1 is that the volatile organic gas source in (4) is replaced by propylene in a volume ratio of 3:7: nitrogen composite gas under the same conditions as in example 1

Example 11

The only difference compared with example 1 is that the volatile organic gas source in (4) is replaced by a volume ratio of 1:2: acetylene of 7: propylene: the nitrogen compound gas and other conditions were the same as in example 1.

Example 12

The difference compared to example 1 is that the stepwise heat treatment is not performed under the gasified organic matter, for example, in the difference (4), the heat treatment temperature is 300 degrees celsius, the treatment time is 3 hours, and the other conditions are the same as in example 1.

Comparative example 1

The only difference compared to example 1 is that step (1) does not contain a source of transition metal M.

Comparative example 2

The only difference compared to example 1 is that in step (2) no spray treatment is performed, but the solution is dried to constant weight in a vacuum oven.

Comparative example 3

The difference from example 1 is only that in step (4), the gaseous carbon source is replaced by glucose, and that in step (4): dispersing the Li ₅Fe0.9Zr0.075O₄ prepared in the step (3) in an aqueous solution of glucose (Li ₅Fe0.9Zr0.075O₄ and glucose in a weight ratio of 8:1), ball-milling and mixing, evaporating the solvent and performing subsequent two-stage heat treatment (same as in example 1).

Comparative example 4

The difference compared with example 1 is that in step (4), the heat treatment atmosphere is nitrogen and no methane is contained.

Comparative example 5

The difference compared to example 1 is only that in step (4), the temperature of T2 during the heat treatment is 400 ℃.

The lithium supplementing performance of each example and comparative example was measured, and the main steps of the test were:

The final material prepared in each case is taken as a lithium supplementing active material, and is made into a 2025 type battery by slurrying the lithium supplementing active material, conductive carbon (acetylene black) and a binder (PVDF) (the mass ratio of the active material to the conductive carbon to the binder is 7:2:1) with NMP, coating and drying the positive electrode, taking metallic lithium as a negative electrode and taking 1.0M LiPF6 in EC:DMC:EMC =1:1:1 (volume ratio) as electrolyte. The cell was measured at 0.1C and the results are shown in table 1:

TABLE 1

Case (B)	First circle capacity (mAh/g)
		Example 1	740
Example 2	689
		Example 3	703
Example 4	709
		Example 5	685
Example 6	689
		Example 7	754
Example 8	715
		Example 9	688
Example 10	712
		Example 11	762
Example 12	710
		Comparative example 1	560
Comparative example 2	546
		Comparative example 3	557
Comparative example 4	472
		Comparative example 5	389

Air exposure electrochemical performance measurement:

Example 13:

And (3) slurrying the lithium-supplementing positive electrode active material, conductive carbon (acetylene black) and a binder (PVDF) (the mass ratio of the active material to the conductive carbon to the binder is 8:1:1) with NMP, coating, drying to obtain a positive electrode, and assembling by taking metal lithium as a negative electrode and 1.0M LiPF6 in EC:DMC:EMC =1:1:1 (volume ratio) as electrolyte to obtain the 2025 type battery. The lithium-supplementing positive electrode active material is Li ₅Fe_0.9Zr_0.075O₄ @C (lithium-supplementing additive which is exposed in advance in air at room temperature (25-35 ℃) and humidity of 30% for 3 hours) and NCM811, wherein the mass ratio of the Li ₅Fe_0.9Zr_0.075O₄ @C is 5:95, and the lithium-supplementing positive electrode active material is prepared in example 1. The cell was measured at 0.1C. The results were: the capacity of the battery is 220mAh g ^-1; the capacity retention was 80% at 0.5C for 300 cycles.

Example 14

The difference compared to example 13 is only that the material prepared in example 7 is used instead of the material of example 1 as a lithium supplement additive (exposure treatment using the same process). The performance was determined by the same method, and the results were: the cell was measured at 0.1C. The results were: the capacity of the battery is 235mAh g ^-1; the capacity retention was 86% at 0.5C for 300 cycles.

Example 15

The difference compared to example 13 is only that the material prepared in example 11 is used instead of the material of example 1 as a lithium supplement additive (exposure treatment is performed using the same process). The performance was determined by the same method, and the results were: the cell was measured at 0.1C. The results were: the capacity of the battery is 237mAh g ^-1; the capacity retention was 85% at 0.5C for 300 cycles.

Comparative example 6

The difference compared with example 13 is that the lithium supplement additive of example 13 was replaced with the material prepared in comparative example 1 (previously exposed to air at room temperature (25 to 35 ℃ C.) and humidity of 30% for 3 hours), and the capacity thereof was determined to be 180mAh g ^-1; the capacity retention rate was 51% at 0.5C for 300 cycles.

Comparative example 7

The difference compared with example 13 is that the lithium supplement additive of example 13 was replaced with the material prepared in comparative example 4 (previously exposed to air at room temperature (25 to 35 ℃ C.) and humidity of 30% for 3 hours), and the capacity thereof was measured to be 200mAh g ^-1; the capacity retention was 65% at 0.5C for 300 cycles.

Comparative example 8

The difference compared with example 13 is that the lithium supplement additive of example 13 was replaced with the material prepared in comparative example 5 (previously exposed to air at room temperature (25 to 35 ℃ C.) and humidity of 30% for 3 hours), and the capacity thereof was measured to be 191mAh g ^-1; the capacity retention was 68% at 0.5C for 300 cycles.

Claims

1. A Li ₅Fe_xM_yO₄ @ C composite comprising a core and a carbon shell encapsulated on the surface thereof;

the core is Li ₅Fe_xM_yO₄, wherein x is 0.8-0.9, and 3x+Ay=3; m is at least one of Zr, mn, cu, ni, ti; a is the valence state of M;

The particle size of the core D50 is 300-800 nm; the thickness of the carbon shell is 5-10 nm;

The preparation method of the Li ₅Fe_xM_yO₄ @C composite material comprises the following steps: slurrying an iron source, a lithium source and an M metal source to obtain slurry, and then carrying out spray drying-roasting treatment or spray pyrolysis treatment to obtain a core;

And carrying out heat treatment on the core in the atmosphere of gasified organic matters at the temperature of 200-350 ℃ to obtain the Li ₅Fe_xM_yO₄ @C composite material.

2. The Li ₅Fe_xM_yO₄ @ C composite of claim 1 wherein said core is Li ₅Fe_xM^a _y1M^b _y2O₄ and said M ^a is Zr; m ^b is Ti; wherein y1+y2=y.

3. The Li ₅Fe_xM_yO₄ @ C composite of claim 1, wherein the core is spherical.

4. A method for preparing the Li ₅Fe_xM_yO₄ @ C composite material according to any one of claims 1 to 3, wherein an iron source, a lithium source and an M metal source are slurried to obtain a slurry, and then subjected to spray drying-roasting treatment, or spray pyrolysis treatment, to obtain a core;

5. The method for preparing a Li ₅Fe_xM_yO₄ @ C composite material according to claim 4, wherein the iron source is at least one of an oxide, carbonate, organic acid salt, nitrate, and hydroxide of iron.

6. The method for preparing a Li ₅Fe_xM_yO₄ @ C composite material according to claim 4, wherein the M source is at least one of an oxide, a carbonate, an organic acid salt, a nitrate, and a hydroxide of M metal.

7. The method for preparing a Li ₅Fe_xM_yO₄ @ C composite material according to claim 4, wherein the lithium source is at least one of lithium oxide, nitrate, carbonate, hydroxide, and organic acid salt.

8. The method for producing a Li ₅Fe_xM_yO₄ @ C composite material according to claim 4, wherein the solid particle size d50 in the slurry is not more than 300 nm.

9. The method for preparing a Li ₅Fe_xM_yO₄ @ C composite material according to claim 4, wherein the solid content in the slurry is 30 to 60wt.%.

10. The method for preparing the Li ₅Fe_xM_yO₄ @C composite material according to claim 4, wherein the slurry is obtained by pulping the raw materials, ball milling and sand milling.

11. The method for preparing a Li ₅Fe_xM_yO₄ @ C composite material according to claim 4, wherein the inlet temperature of the spray drying process is 150-300 ℃; the spraying rate is 20-40 ml/min.

12. The method for producing a Li ₅Fe_xM_yO₄ @ C composite material according to claim 4, wherein the firing atmosphere is a protective atmosphere.

13. The method for preparing a Li ₅Fe_xM_yO₄ @ C composite material according to claim 4, wherein the baking temperature is 500-700 ℃.

14. The method for preparing the Li ₅Fe_xM_yO₄ @C composite material according to claim 13, wherein the baking heat preservation time is 4-16 hours.

15. The method for preparing the Li ₅Fe_xM_yO₄ @C composite material according to claim 4, wherein the spray pyrolysis temperature is 500-700 ℃.

16. The method for preparing the Li ₅Fe_xM_yO₄ @C composite material according to claim 15, wherein the spray rate of spray pyrolysis is 20-40 ml/min.

17. The method for preparing a Li ₅Fe_xM_yO₄ @ C composite material as claimed in claim 4, wherein,

The gasified organic matter is an organic matter which is in a gaseous state at the temperature of 200-350 ℃.

18. The method for preparing a Li ₅Fe_xM_yO₄ @ C composite material according to claim 17, wherein the gasified organic substance is at least one of C1-C6 alkane, C2-C6 alkene, C2-C6 alkyne, C1-C6 alcohol, and C4-C8 ether.

19. The method for preparing a Li ₅Fe_xM_yO₄ @ C composite material according to claim 18, wherein the vaporized organic material is a composite gas source of C2 to C6 olefins and C2 to C6 alkynes.

20. The method for preparing a Li ₅Fe_xM_yO₄ @ C composite material according to claim 18, wherein the atmosphere of vaporized organic material further contains a diluent gas.

21. The method for preparing a Li ₅Fe_xM_yO₄ @ C composite material according to claim 20, wherein the diluent gas is at least one of nitrogen and inert gas.

22. The method for producing a Li ₅Fe_xM_yO₄ @ C composite material according to claim 4, wherein the volume content of the gasified organic matter in the atmosphere containing the gasified organic matter is 5% or more.

23. The method for preparing the Li ₅Fe_xM_yO₄ @C composite material according to claim 4, wherein the heat treatment process comprises a first heat treatment process and a second heat treatment process, and the temperature of the first heat treatment process is 200-250 ℃; the time is 0.5-1.5 h; the temperature of the second heat treatment process is 250-350 ℃ and the time is 1.5-3 h.

24. The use of a Li ₅Fe_xM_yO₄ @ C composite material as defined in any one of claims 1 to 3 or a Li ₅Fe_xM_yO₄ @ C composite material as defined in any one of claims 4 to 23 for the preparation of a lithium ion battery.

25. Use according to claim 24 as lithium-supplementing material for the preparation of lithium-supplementing positive electrodes of lithium-ion batteries.

26. The use of claim 25 as a lithium-supplementing material, in combination with a positive electrode composite material, to produce a lithium-supplementing positive electrode for a lithium-ion battery.

27. A lithium-supplementing positive electrode material, characterized by comprising a positive electrode active material and the Li ₅Fe_xM_yO₄ @ C composite material according to any one of claims 1 to 3 or the Li ₅Fe_xM_yO₄ @ C composite material produced by the production method according to any one of claims 4 to 23.

28. The lithium-compensating positive electrode material of claim 27, wherein the positive electrode active material is at least one of NCM and LiCoO ₂.

29. The lithium-compensating positive electrode material according to claim 27, wherein the weight ratio of the Li ₅Fe_xM_yO₄ @ C composite material to the positive electrode active material is 3 to 5: 95-97%.

30. The lithium-compensating cathode material of claim 27, further comprising at least one of a binder and a conductive agent.

31. The lithium-compensating anode material of claim 30, wherein the binder is at least one of PVDF and CMCC.

32. The lithium-compensating positive electrode material of claim 30, wherein the binder is present in an amount of 5 to 10wt.% of the lithium-compensating positive electrode material.

33. The lithium-compensating anode material of claim 30, wherein the conductive agent is at least one of carbon black and super P.

34. The lithium-compensating positive electrode material of claim 30, wherein the weight content of the conductive agent in the lithium-compensating positive electrode material is 5-20 wt.%.

35. A lithium-supplementing positive electrode, comprising a positive electrode current collector, and the lithium-supplementing positive electrode material according to any one of claims 27 to 34 composited on the surface of the positive electrode current collector.

36. A lithium ion battery comprising the lithium-supplemented positive electrode of claim 35.