Lithium-rich iron composite material and preparation method and application thereof

Abstract

The present invention discloses a lithium-rich iron-based composite material, a preparation method thereof, and an application thereof. The lithium-rich iron-based composite material is characterized in that it comprises a lithium-rich iron-based material, and the molecular formula of the lithium-rich iron-based material is aLiFeO2·bLi2O·cM x O y , wherein a, b, and c in the molecular formula are molar amounts, and 0 ≤ c / (a + b + c) ≤ 0.02, 1.8 ≤ b / a ≤ 2.1; M is a doping element; 1 ≤ y / x ≤ 2.5. The lithium-rich iron-based composite material can provide abundant lithium, and the lithium-rich iron-based material has high purity, low residual alkali content on the surface layer, high capacity and lithium supplement effect, as well as good storage stability and processing stability. The preparation method can ensure the stability of the structure and electrochemical performance of the prepared lithium-rich iron-based composite material and save production costs. The lithium-rich iron-based composite material is applied in a cathode lithium supplement additive, a cathode material, a cathode, and a lithium ion battery.

Description

Technical Field

[0001] The present invention belongs to the field of lithium-ion batteries, and in particular relates to a lithium-rich iron composite material and a preparation method and application thereof. Background Art

[0002] The oil energy crisis in the 1960s and 1970s forced people to look for new alternative energy sources. Lithium-ion batteries are considered to be one of the most promising energy sources because of their high operating voltage and energy density, relatively small self-discharge level, no memory effect, no heavy metal pollution such as lead and cadmium, and ultra-long cycle life.

[0003] During the first charging process of lithium-ion batteries, the negative electrode surface is usually accompanied by the formation of a solid electrolyte membrane SEI film, which consumes a large amount of Li + , which means that Li released from the positive electrode material + Part of it is irreversibly consumed, and the reversible specific capacity of the corresponding battery cell is reduced. The negative electrode material, especially the silicon-based negative electrode material, will further consume Li + , resulting in the first time low Coulomb efficiency.

[0004] In order to improve the low coulombic efficiency problem caused by irreversible loss of the negative electrode, in addition to pre-lithiation of the negative electrode material and the pole piece, lithium supplementation of the positive electrode can also achieve the requirements of high energy density. The theoretical capacity of lithium-rich iron-based materials is as high as 867mAh / g, the operating voltage window is consistent with that of conventional lithium-ion batteries, and it basically does not participate in the electrochemical process in the later stage. It is a lithium supplement additive with broad prospects.

[0005] There are public reports on positive electrode lithium replenishing materials. For example, in a public positive electrode lithium replenishing material, the lithium ion positive electrode lithium replenishing material Li5FeO4 is prepared by the sol-gel method. This material is used as a positive electrode lithium replenishing material for lithium ion batteries and has the characteristics of large charging capacity and small discharge capacity. However, this material has harsh environmental adaptability, large residual alkali on the surface, and is difficult to process.

[0006] In another disclosed positive electrode lithium supplement material, it is a lithium supplement material formed by Co-doped or Co-doped lithium ferrate and carbon material and a sol-gel preparation method. However, during the in-situ coating process of the carbon source at high temperature, the conventional sol-gel is prone to react with the lithium source to partially form non-electrochemically active lithium carbonate, which affects the proportion of the active main body.

[0007] In another disclosed positive electrode lithium supplement material, it is a carbon-coated lithium ferrite material and its preparation method, which is to isolate the external environment by gas phase coating with a carbon source to avoid contact between lithium ferrite and water or carbon dioxide in the air, thereby improving the stability of the material. However, the control of the Li2O component of the material is not explained.

[0008] Research on the relevant positive electrode replenishing materials disclosed found that although the currently disclosed positive electrode replenishing materials can play a role in replenishing lithium, the existing publicly reported positive electrode replenishing materials still have shortcomings, which are specifically manifested in low purity and a large amount of residual alkali remaining on the surface. The material interface lacks the protection of the passivation layer and is very easy to react with moisture in the environment to re-form Li2O. It is precisely because of the low purity and unstable interface that the large amount of residual alkali remaining on the surface leads to the existing positive electrode replenishing materials. The storage stability and processing stability are not ideal, the lithium replenishing effect is not ideal, the capacity needs to be improved, and it is not easy to mass produce. Summary of the invention

[0009] The purpose of the present invention is to overcome the above-mentioned shortcomings of the prior art and provide a lithium-rich iron-based composite material and a preparation method and application thereof, so as to solve the technical problems that the existing positive electrode lithium replenishing additives have low purity and a large amount of residual alkali remaining on the surface, resulting in the difficulty of existing lithium replenishing processing and low capacity.

[0010] In order to achieve the above-mentioned purpose, the present invention provides a lithium-rich iron composite material in one aspect. The lithium-rich iron composite material of the present invention comprises a lithium-rich iron material, wherein the molecular formula of the lithium-rich iron material is aLiFeO2·bLi2O·cM x O y , wherein a, b, c in the molecular formula are molar numbers, and 0≤c / (a+b+c)≤0.02, 1.8≤b / a≤2.1; M is a doping element; 1≤y / x≤2.5.

[0011] Furthermore, the lithium-rich iron-based material is in a particle morphology, and a carbon coating layer is also coated on the surface of the lithium-rich iron-based material.

[0012] Another aspect of the present invention provides a method for preparing a lithium-rich iron composite material. The method for preparing a lithium-rich iron composite material of the present invention comprises the following steps:

[0013] According to the molecular formula aLiFeO2·bLi2O·cM x O y An iron source, a lithium source, and a doping element source are mixed in a stoichiometric ratio to form a precursor;

[0014] The precursor is subjected to a first sintering treatment to generate a LiFeO2·bLi2O·cM x O y Lithium-rich iron-based materials;

[0015] Wherein, a, b, c in the molecular formula are molar numbers, and 0≤c / (a+b+c)≤0.02, 1.8≤b / a≤2.1; M is a doping element; 1≤y / x≤2.5.

[0016] In another aspect of the present invention, a positive electrode lithium supplement additive is provided. The positive electrode lithium supplement additive of the present invention comprises the lithium-rich iron composite material of the present invention or the lithium-rich iron composite material prepared by the lithium-rich iron composite material preparation method of the present invention.

[0017] Another aspect of the present invention provides a positive electrode material, which includes the lithium-rich iron composite material of the present invention, or the lithium-rich iron composite material prepared by the method for preparing the lithium-rich iron composite material of the present invention, or the positive electrode lithium supplement additive of the present invention.

[0018] In another aspect of the present invention, a positive electrode is provided. The positive electrode of the present invention comprises a current collector and a positive electrode active layer bonded to the surface of the current collector, wherein the positive electrode active layer comprises a positive electrode active material, a lithium supplement additive, a binder and a conductive agent; wherein the lithium supplement additive is the lithium-rich iron composite material of the present invention or the lithium-rich iron composite material prepared by the method for preparing the lithium-rich iron composite material of the present invention or the positive electrode lithium supplement additive of the present invention.

[0019] In another aspect of the present invention, a lithium ion battery is provided. The lithium ion battery of the present invention comprises a positive electrode, and the positive electrode is the positive electrode of the present invention.

[0020] Compared with the prior art, the present invention has the following technical effects:

[0021] The lithium-rich iron-based material contained in the lithium-rich iron-based composite material of the present invention is rich in lithium and can provide abundant lithium, so that in the first cycle charging process, as a "sacrificial agent", all lithium ions are released at once as much as possible to supplement the irreversible lithium ions consumed by the negative electrode to form the SEI film, thereby maintaining the abundance of lithium ions in the battery system and improving the first efficiency and overall electrochemical performance of the battery. In addition, the lithium-rich iron-based material has high purity and low residual alkali content on the surface, giving the lithium-rich iron-based composite material high capacity and lithium supplementation effect as well as good storage stability and processing stability.

[0022] Furthermore, coating the carbon coating layer on the surface of the lithium-rich iron-based material can effectively reduce the residual alkali content remaining in the surface layer of the lithium-rich iron-based material, effectively ensuring and improving the storage stability and processing stability of the lithium-rich iron-based composite material; at the same time, it effectively improves the electrical conductivity of the lithium-rich iron-based material, endows the lithium-rich iron-based composite material with high electrical conductivity, stimulates the specific capacity of the lithium-rich iron-based composite material, and realizes truly efficient lithium replenishment.

[0023] The preparation method of the lithium-rich iron composite material of the present invention directly follows the method of aLiFeO2·bLi2O·cM x O yThe lithium-rich iron-based material is prepared by mixing the corresponding source compounds in the stoichiometric ratio of the elements and sintering them, which can effectively ensure that the prepared lithium-rich iron-based material is rich in lithium, has high purity, and has a low residual alkali content on the surface, giving the prepared lithium-rich iron-based composite material a high capacity and lithium replenishment effect as well as good storage stability and processing stability. In addition, the preparation method of the lithium-rich iron-based composite material can ensure that the structure and electrochemical properties of the prepared lithium-rich iron-based composite material are stable, and the efficiency is high, saving production costs.

[0024] Since the positive electrode lithium replenishing additive and positive electrode material of the present invention contain the lithium-rich iron-based composite material of the present invention, the positive electrode lithium replenishing additive and positive electrode material can be used as a lithium source and a "sacrificial agent" in the first cycle of charging during charging and discharging to replenish the irreversible lithium ions consumed by the formation of the SEI film at the negative electrode, thereby maintaining the abundance of lithium ions in the battery system and improving the first efficiency and overall electrochemical performance of the battery.

[0025] Since the lithium-ion battery of the present invention contains the lithium-rich iron composite material of the present invention, the positive electrode has good cycle performance and low internal resistance, thereby giving the lithium-ion battery of the present invention excellent first coulomb efficiency and battery capacity and cycle performance, long life and stable electrochemical performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0027] Figure 1 This is a schematic structural diagram of a lithium-rich iron composite material according to an embodiment of the present invention;

[0028] Figure 2 Schematic diagram of the process of preparing the lithium-rich iron composite material according to an embodiment of the present invention;

[0029] Figure 3 This is a scanning electron microscope image of the lithium-rich iron composite material provided in Example 11;

[0030] Figure 4 This is a scanning electron microscope image of the lithium-rich iron composite material provided in Example 14;

[0031] Figure 5 This is a scanning electron microscope image of the lithium-rich iron composite material provided in Comparative Example 11;

[0032] Figure 6 The X-ray diffraction pattern of the lithium-rich iron composite material provided in Example 11;

[0033] Figure 7 This is the X-ray diffraction pattern of the lithium-rich iron-based composite material provided in Example 15. DETAILED DESCRIPTION

[0034] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application more clearly understood, the present application is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0035] In this application, the term "and / or" describes the association relationship of associated objects, indicating that there may be three relationships. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. A and B can be singular or plural. The character " / " generally indicates that the associated objects are in an "or" relationship.

[0036] In this application, "at least one" means one or more, and "plurality" means two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can all mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0037] It should be understood that in the various embodiments of the present application, the size of the serial numbers of the above-mentioned processes does not mean the order of execution, some or all of the steps can be executed in parallel or sequentially, and the execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0038] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms "a", "said" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings.

[0039] The weight of the relevant components mentioned in the embodiment description of the present application can not only refer to the specific content of each component, but also indicate the proportional relationship between the weights of the components. Therefore, as long as the content of the relevant components is proportionally enlarged or reduced according to the embodiment description of the present application, it is within the scope disclosed in the embodiment description of the present application. Specifically, the mass described in the embodiment description of the present application can be a mass unit known in the chemical industry such as µg, mg, g, kg, etc.

[0040] The terms "first" and "second" are used only for descriptive purposes to distinguish objects such as substances from each other, and should not be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. For example, without departing from the scope of the embodiments of the present application, the first XX may also be referred to as the second XX, and similarly, the second XX may also be referred to as the first XX. Thus, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features.

[0041] In one aspect, an embodiment of the present invention provides a lithium-rich iron composite material. The lithium-rich iron composite material of the embodiment of the present invention comprises a lithium-rich iron material. The molecular formula of the lithium-rich iron material is aLiFeO2·bLi2O·cM x O y , wherein a, b, c in the molecular formula are molar numbers, and 0≤c / (a+b+c)≤0.02, 1.8≤b / a≤2.1; M is a doping element; 1≤y / x≤2.5.

[0042] Since the lithium-rich iron-based composite material of the embodiment of the present invention contains the above-mentioned molecular formula aLiFeO2·bLi2O·cM x O y The lithium-rich iron-based materials enable the lithium-rich iron-based composite materials of the embodiments of the present invention to provide abundant lithium, so that in the first cycle of charging, as a "sacrificial agent", all lithium ions are released at once as much as possible to replenish the irreversible lithium ions consumed by the formation of the SEI film at the negative electrode, thereby maintaining the abundance of lithium ions in the battery system and improving the first efficiency and overall electrochemical performance of the battery. In addition, the lithium-rich iron-based materials are of high purity and low residual alkali content on the surface, giving the lithium-rich iron-based composite materials high capacity and lithium replenishment effect as well as good storage stability and processing stability.

[0043] Among them, the molecular formula is aLiFeO2·bLi2O·cM x O y The doping element M contained in the lithium-rich iron-based material can combine with the Li2O contained in the lithium-rich iron-based material to give the lithium-rich iron-based material a capacity to play, thereby giving the lithium-rich iron-based composite material a high capacity, and improving the kinetic release of lithium ions and improving the interface and structural stability of the lithium-rich iron-based composite material. In an embodiment, the doping element includes at least one of Ni, Co, Mn, Ti, Al, Cu, V, and Zr. These metal doping elements can further improve the Li2O combination to improve the capacity of the lithium-rich iron-based material to further improve the high capacity of the lithium-rich iron-based composite material, and relative to the anti-fluorite structure of the Fe system, these metal doping elements are more conducive to the kinetic release of lithium ions and improve the interface and structural stability of the lithium-rich iron-based composite material.

[0044] The morphology of the lithium-rich iron-based material can be controlled as needed, such as particles or other morphologies. In an embodiment of the present invention, the particle morphology is relatively preferred. In addition, when the lithium-rich iron-based material is in the form of particles, it can be a primary particle or a secondary particle. In an embodiment, when the morphology of the lithium-rich iron-based material is particles, its particle size is 1μm≤D50≤15μm, D10 / D50≥0.3, and D90 / D50≤2.

[0045] In the embodiment, when the lithium-rich iron-based material is in particle morphology, a carbon coating layer is also coated on the surface of the lithium-rich iron-based material, specifically as follows Figure 1 As shown, the surface of the lithium-rich iron-based material 10 is coated with a carbon coating layer 20. Coating the carbon coating layer 20 on the surface of the lithium-rich iron-based material 10 can effectively reduce the residual alkali content remaining on the surface of the lithium-rich iron-based material 10, effectively ensure and improve the storage stability and processing stability of the lithium-rich iron-based composite material; at the same time, it effectively improves the electrical conductivity of the lithium-rich iron-based material 10, endows the lithium-rich iron-based composite material with high electrical conductivity, stimulates the specific capacity of the lithium-rich iron-based composite material, and realizes efficient lithium supplementation in a true sense.

[0046] In a further embodiment, the thickness of the carbon coating layer 20 is 1-200 nm. In other embodiments, the carbon coating layer 20 accounts for 1 wt%-5wt% of the total mass of the lithium-rich iron-based composite material. Controlling the thickness and content of the carbon coating layer 20 within this range can improve the residual alkali content remaining on the surface of the lithium-rich iron-based material 10 to further improve the storage stability and processing stability of the lithium-rich iron-based composite material; at the same time, improve the conductivity of the lithium-rich iron-based material 10.

[0047] The lithium-rich iron-based composite material in the above-mentioned embodiments may be in the form of particles, or other forms. In the embodiments, when the lithium-rich iron-based composite material is in the form of particles, the particle size of the lithium-rich iron-based composite material is: 1μm≤D50≤15μm, D10 / D50≥0.3, and D90 / D50≤2. The inventors found in their research that when the D50 of the lithium-rich iron-based composite material is less than 1μm, the particles of the lithium-rich iron-based composite material are relatively small, the specific surface area is too large, and the high activity is prone to performance failure and degradation. When the D50 of the lithium-rich iron-based composite material is greater than 15um, the particles are too large, and the lithium ion migration path is too long, causing kinetic polarization problems and insufficient capacity. Therefore, in the embodiments, the specific surface area of ​​the lithium-rich iron-based composite material is 0.5≤BET≤20 m 2 The lithium-rich iron composite material within this particle size range and specific surface area enables the lithium-rich iron composite material to fully exert its aforementioned functions such as lithium supplementation and high capacity, and improve its dispersibility.

[0048] After testing, in the above embodiments, the lithium-rich iron composite material is particularly Figure 1The resistivity of the lithium-rich iron-based composite material containing the carbon coating layer 20 in the lithium-rich iron-based material 10 is 1.0-1000 Ω / cm. It has low resistance and good electrical conductivity, and can effectively stimulate the specific capacity of the lithium-rich iron-based composite material.

[0049] X-ray crystal phase analysis of the lithium-rich iron-based composite materials of the above-mentioned embodiments shows that the peaks in the range of 2θ=16.7±0.5° and 33.7±0.5° in the X-ray diffraction spectra of the lithium-rich iron-based composite materials of the above-mentioned embodiments are from the (111) and (222) crystal planes of LiFeO2·2Li2O, and the intensities of the peaks in the range of 2θ=16.7±0.5° and 33.7±0.5° are respectively recorded as I a ,I b In the embodiment, when I a ,I b Satisfaction: I a / I b When ≥0.26, the lithium-rich iron-based composite material having the specific crystal phase characteristics has abundant lithium sources contributing to the capacity and endows the lithium-rich iron-based composite material with high capacity.

[0050] Further analysis shows that the X-ray diffraction spectrum of the lithium-rich iron composite material corresponds to the crystal plane (220) of LiFeO2 in the range of 2θ=43.5±0.5°, and its intensity is recorded as I c In the embodiment, in I a ,I b On the basis of satisfying the above relationship, when I a ,I c Satisfy I a / I c When the relationship is ≥0.5, the lithium source content contributing to the capacity can be further increased, thereby increasing the capacity of the lithium-rich iron composite material.

[0051] The inventors further discovered that if the I in the crystal phase of the lithium-rich iron composite material a ,I b ,I c When the above relationship is deviated, the lithium replenishment effect is not ideal and the capacity is reduced, thereby resulting in a decrease in the electrochemical properties of the battery such as charging capacity and gram capacity.

[0052] The X-ray diffraction spectrum may be but is not limited to CuKα rays.

[0053] The Raman spectrum analysis of the lithium-rich iron composite materials in the above embodiments shows that in the Raman spectrum of the lithium-rich iron composite materials, the wavelength of 1330 cm -1 With 1580cm -1 There is a scattering peak at a wavelength of 1330cm -1 With 1580cm -1The intensities of the scattering peaks at D ,I G In the embodiment, when I D ,I G Satisfaction: I D / I G When <4.0, it can be further D / I G <3.0, the lithium-rich iron composite material has excellent conductivity, more and appropriate surface pores, and is not easy to absorb water during storage, thereby giving the lithium-rich iron composite material stable performance. The inventors further found that I D / I G When it increases, such as when it is greater than 4.0, the lithium-rich iron composite material shows a decrease in conductivity. When its surface contains a carbon coating layer, the carbon source coking value is low, the carbon coating layer has more pores, the material is not easy to preserve, and it is easy to absorb water in a normal environment, resulting in a decrease in performance.

[0054] Accordingly, the present invention also provides a method for preparing the lithium-rich iron composite material as described above. The process flow of the method for preparing the lithium-rich iron composite material is as follows: Figure 2 As shown, the preparation method thereof comprises the following steps:

[0055] Step S01: According to the molecular formula aLiFeO2·bLi2O·cM x O y An iron source, a lithium source, and a doping element source are mixed in a stoichiometric ratio to form a precursor;

[0056] Step S02: subjecting the precursor to a first sintering treatment to generate a LiFeO2·bLi2O·cM x O y Lithium-rich iron materials.

[0057] The preparation method of the lithium-rich iron-based composite material sinters a precursor to prepare a lithium-rich iron-based material that is rich in lithium, has high purity, and has a low residual alkali content on the surface, so that the prepared lithium-rich iron-based composite material has high capacity and lithium replenishment effect as well as good storage stability and processing stability.

[0058] Wherein, in the molecular formula in step S01, aLiFeO2·bLi2O·cM x O ya, b, c are molar numbers, and 0≤c / (a+b+c)≤0.02, 1.8≤b / a≤2.1; M is the doping element; 1≤y / x≤2.5. Therefore, the stoichiometric ratio of the elements in step S01 can be a molar ratio, or a mass ratio converted according to the molar ratio. In the embodiment, the iron source includes at least one of iron oxide, iron nitrate, iron chloride, iron hydroxide, iron acetate, iron hydroxide, and iron oxalate; the lithium source includes at least one of lithium hydroxide, lithium carbonate, lithium nitrate, lithium acetate, lithium oxide, and lithium oxalate; and the doping element source includes at least one of Cu, Co, Al, Ti, Fe, V, and Zr sources. These iron sources, lithium sources, and doping element sources can be effectively mixed and uniformly after being mixed in proportion, and these raw materials have low costs, which effectively reduces the cost of lithium-rich iron-based materials. In addition, the doping element source can be selected and the type can be adjusted as needed. In a specific embodiment, the Cu source can be at least one of copper oxide, copper nitrate, copper chloride, copper hydroxide, copper acetate, copper hydroxide, and copper carbonate, the Co source can be at least one of cobalt oxide, cobalt nitrate, cobalt chloride, cobalt hydroxide, cobalt acetate, cobalt hydroxide, and cobalt carbonate, the Al source can be at least one of aluminum oxide, aluminum nitrate, aluminum chloride, aluminum hydroxide, aluminum acetate, and aluminum hydroxide, the Ti source can be at least one of titanium dioxide and titanium chloride, the Ni source can be at least one of nickel oxide, nickel nitrate, nickel chloride, nickel hydroxide, nickel acetate, and nickel hydroxide, the V source can be at least one of vanadium pentoxide and vanadium nitrate, and the Zr source can be at least one of zirconium oxide, zirconium nitrate, zirconium chloride, zirconium hydroxide, zirconium acetate, zirconium hydroxide, and zirconium carbonate.

[0059] The purpose of the mixing treatment is to make the source materials mix evenly. Therefore, the mixing treatment can be a conventional mixing treatment, and ideally a grinding treatment. On the premise of achieving uniform mixing of the source materials, the particle size of each source compound is refined to further improve the mixing uniformity of the source materials, thereby improving the stability of the structure and electrochemical properties of the prepared lithium-rich iron-based materials.

[0060] In a further embodiment, a carbon source is also added during the mixing of the iron source, the lithium source, and the doping element source in step S01. By directly adding the carbon source to the precursor, the sintering conditions in step S02 can be controlled, such as controlling the sintering process in a non-oxygen environment, so that the carbon source is in-situ coated on the surface of the lithium-rich iron-based material particles formed by sintering, and a carbon coating layer is formed on the surface of the lithium-rich iron-based material particles. The carbon coating layer generated at this time is the carbon coating layer contained in the lithium-rich iron-based composite material mentioned above, that is, Figure 1In the embodiment, the total mass of the carbon source and the reactants is 5wt%-50wt%. In a specific embodiment, the carbon source includes at least one of citric acid, succinic acid, glucose, lactose, sucrose, starch, and polyethylene glycol. The amount of carbon coating and the quality of the carbon coating layer formed are controlled by selecting the amount and type of the carbon source.

[0061] In step S02, the precursor is subjected to a first sintering treatment to form aLiFeO2·bLi2O·cM x O y Lithium-rich iron-based materials. In an embodiment, the temperature of the first sintering treatment is 600-1000°C, and the time is 4-48h. In a further embodiment, the first sintering treatment is heated to the first sintering treatment temperature at a heating rate of 10-500°C / h. By controlling and optimizing the sintering temperature and heating rate, the purity of the lithium-rich iron-based material formed by sintering can be improved, the residual alkali content remaining on its surface can be reduced, and the lithium-rich iron-based composite material has a high capacity and lithium replenishment effect as well as good storage stability and processing stability.

[0062] After the first sintering step, the method further includes the following second sintering step:

[0063] The product obtained through the first sintering treatment is crushed and then heated to 600-1000° C. at 0-500° C. / h for heat treatment for 1-20 hours.

[0064] The second sintering treatment can be used to sinter the reactants that did not participate in the reaction into the expected target products, improve the overall electrical properties of the composite material and reduce the residual alkali. In principle, the more sintering times, the higher the purity. Therefore, without considering the cost, the second sintering treatment can be multiple times, that is, more than twice.

[0065] The lithium-rich iron-based material generated after the first sintering treatment or the further second sintering treatment may be a primary particle or a secondary particle.

[0066] In a further embodiment, after step S02, specifically after the first sintering treatment or the second sintering treatment, the following is further included: Figure 2 Step S03 described in:

[0067] A carbon coating is formed on the surface of the lithium-rich iron material, that is, a carbon coating is formed. Figure 1 The carbon coating layer 20 in.

[0068] A carbon coating layer is formed on the surface of the lithium-rich iron-based material to achieve surface modification of the lithium-rich iron-based material, which can effectively reduce the residual alkali content remaining on the surface of the lithium-rich iron-based material, effectively ensure and improve the storage stability and processing stability of the lithium-rich iron-based composite material; at the same time, it effectively improves the electrical conductivity of the lithium-rich iron-based material, endows the lithium-rich iron-based composite material with high electrical conductivity, stimulates the gram capacity of the lithium-rich iron-based composite material, and realizes truly efficient lithium replenishment.

[0069] Method for forming a carbon coating layer: Step S03 can be a conventional carbon coating method, such as preparing a carbon source into a solution and dispersing the lithium-rich iron-based material prepared in the previous step in the carbon source solution to form a carbon source film layer on the surface of the lithium-rich iron-based material, and then carbonizing it after drying to form a carbon coating layer.

[0070] Alternatively, the carbon source may be melted and the lithium-rich iron-based material may be dispersed in the molten carbon source to form a carbon source film on the surface of the lithium-rich iron-based material, which may be cooled and crushed and then carbonized or carbonized and then cooled and crushed to form a carbon coating.

[0071] Alternatively, a deposition method such as chemical deposition may be used to directly grow a carbon coating layer in situ on the surface of the lithium-rich iron-based material.

[0072] In addition, when the precursor in the above step S01 contains a carbon source, and the first sintering treatment or the further second sintering treatment in step S02 is performed in a non-oxygen environment, then the above step S03 can be omitted, or the carbon coating treatment in step S03 can still be performed.

[0073] When the precursor in the above step S01 contains a carbon source, and the first sintering treatment or the further second sintering treatment in step S02 is performed in an oxygen environment, then the above step S03 is preferably performed to perform carbon coating on the surface of the lithium-rich iron-based material.

[0074] When the precursor in the above step S01 does not contain a carbon source, after the first sintering treatment in step S02 or the further second sintering treatment, the above step S03 is preferably performed to perform a carbon coating treatment on the surface of the lithium-rich iron-based material.

[0075] By controlling the content of the carbon source in step S01 or further controlling the amount of carbon coating in step S03, the thickness of the carbon coating layer is controlled within the thickness range described above, or the carbon coating layer is further controlled to account for 1 wt%-5wt% of the total mass of the lithium-rich iron-based composite material, thereby giving full play to the above-mentioned role of the carbon coating layer.

[0076] Therefore, the preparation method of the lithium-rich iron composite material can effectively ensure that the prepared lithium-rich iron material is rich in lithium, has high purity, and has low residual alkali content on the surface, giving the prepared lithium-rich iron composite material a high capacity and lithium replenishment effect as well as good storage stability and processing stability. In addition, the preparation method of the lithium-rich iron composite material can ensure that the structure and electrochemical properties of the prepared lithium-rich iron composite material are stable, and the efficiency is high, saving production costs.

[0077] On the other hand, an embodiment of the present invention provides a positive electrode lithium replenishing additive. The positive electrode lithium replenishing additive of the embodiment of the present invention includes the lithium-rich iron-based composite material of the embodiment of the present invention described above. The positive electrode lithium replenishing additive can be the lithium-rich iron-based composite material of the embodiment of the present invention described above, and of course can further include other additives suitable for the positive electrode, or auxiliary additives that are conducive to giving full play to the lithium-rich iron-based composite material of the embodiment of the present invention described above to play the role of lithium replenishing. When other additives are contained, the ratio between the lithium-rich iron-based composite material and the additive can be adjusted according to the needs of actual application. Since the positive electrode lithium replenishing additive contains the lithium-rich iron-based composite material of the embodiment of the present invention described above, the positive electrode lithium replenishing additive can be used as a lithium source during the charging and discharging process and as a "sacrificial agent" during the first cycle of charging to replenish the irreversible lithium ions consumed by the formation of the SEI film at the negative electrode, thereby maintaining the abundance of lithium ions in the battery system and improving the battery's first efficiency and overall electrochemical performance.

[0078] On the other hand, an embodiment of the present invention provides a positive electrode material. The positive electrode material of the embodiment of the present invention includes a lithium supplement additive. Among them, the lithium supplement additive is the lithium-rich iron-based composite material of the embodiment of the present invention above or the positive electrode lithium supplement additive of the embodiment of the present invention above. Of course, the positive electrode material can also include positive electrode materials in the field of lithium-ion batteries. Since the positive electrode material of the embodiment of the present invention contains the lithium-rich iron-based composite material of the embodiment of the present invention above. Therefore, the lithium-rich iron-based composite material contained in the positive electrode material can be used as a lithium source during the charging and discharging process and as a "sacrificial agent" during the first cycle of charging to supplement the irreversible lithium ions consumed by the formation of the SEI film at the negative electrode, thereby maintaining the abundance of lithium ions in the battery system and improving the battery's first efficiency and overall electrochemical performance.

[0079] In the embodiment, the content of the lithium-rich iron composite material in the positive electrode material of the embodiment of the present invention is 0.5 wt%-10wt%. By controlling and optimizing the content of the lithium-rich iron composite material in the positive electrode material, the lithium-rich iron composite material can be improved to fully exert its above functions.

[0080] At the same time, based on the positive electrode material of the embodiment of the present invention, the embodiment of the present invention also provides a positive electrode and a lithium ion battery containing the positive electrode of the embodiment of the present invention.

[0081] The active material contained in the positive electrode is the positive electrode material of the embodiment of the present invention. The positive electrode can be a conventional positive electrode of a lithium ion battery, such as a positive electrode active layer including a current collector and a current collector.

[0082] The positive electrode current collector includes but is not limited to any one of copper foil and aluminum foil.

[0083] The positive electrode active layer contains the positive electrode material of the embodiment of the present invention, that is, contains a lithium supplement additive, specifically contains the lithium-rich iron composite material of the embodiment of the present invention or the positive electrode lithium supplement additive of the embodiment of the present invention. In the embodiment, the mass content of the lithium supplement additive, that is, the lithium-rich iron composite material of the embodiment of the present invention or the positive electrode lithium supplement additive of the embodiment of the present invention in the positive electrode active layer is 0.5 wt%-10wt%; specifically, it can be 0.5 wt%, 1 wt%, 2 wt%, 3wt%, 4wt%, 5 wt%, 6wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, etc., preferably 1wt%~6wt%, and more preferably 3 wt%-6wt%.

[0084] The positive electrode active layer includes a positive electrode active material, a binder and a conductive agent in addition to the lithium replenishing additive.

[0085] In an embodiment, the positive electrode active material includes at least one of lithium cobalt oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium manganese oxide, lithium nickel cobalt manganese oxide, and lithium nickel manganese oxide.

[0086] In the embodiment, the content of the binder in the positive electrode active layer is 0.5 wt%-3wt%. In a specific embodiment, the binder includes one or more of polyvinylidene chloride, soluble polytetrafluoroethylene, styrene-butadiene rubber, hydroxypropyl methylcellulose, methylcellulose, carboxymethyl cellulose, polyvinyl alcohol, acrylonitrile copolymer, sodium alginate, chitosan and chitosan derivatives.

[0087] In an embodiment, the content of the conductive agent in the positive electrode active layer is 0.2 wt%-5 wt%. In a specific embodiment, the conductive agent includes one or more of graphite, carbon black, acetylene black, graphene, carbon fiber, C60 and carbon nanotubes.

[0088] In the embodiment, the preparation process of the positive electrode is: mixing the positive electrode active material, lithium supplement additive, conductive agent and binder to obtain electrode slurry, coating the electrode slurry on the current collector, and preparing the positive electrode plate through the steps of drying, rolling, die cutting, etc.

[0089] At this time, the lithium ion battery of the embodiment of the present invention contains the positive electrode. Of course, the lithium ion battery of the embodiment of the present invention also has the necessary components such as the negative electrode, the separator and the electrolyte required by the lithium ion battery.

[0090] Since the positive electrode contains the lithium-rich iron composite material or the positive electrode lithium replenishing additive of the embodiment of the present invention, during the first cycle of charging of the lithium ion battery of the embodiment of the present invention, the positive electrode contains the lithium replenishing additive of the embodiment of the present invention as a "sacrificial agent" to release all lithium ions at one time as much as possible to replenish the irreversible lithium ions consumed by the formation of the SEI film of the negative electrode, thereby maintaining the abundance of lithium ions in the lithium ion battery system of the embodiment of the present invention and improving the overall electrochemical properties of the lithium ion battery of the embodiment of the present invention, such as the first efficiency, capacity and cycle performance.

[0091] The lithium-rich iron-based composite material and its preparation method and application according to the present invention are described below by means of a number of specific embodiments.

[0092] 1. Lithium-rich iron composite material and preparation method thereof:

[0093] Embodiment 11

[0094] This embodiment provides a lithium-rich iron composite material and a preparation method thereof. The structure of the lithium-rich iron composite material is as follows: Figure 1 As shown, it includes LiFeO2·1.99Li2O lithium-rich iron-based material and a carbon coating layer coating the lithium-rich iron-based material.

[0095] The preparation method of the lithium-rich iron composite material of this embodiment comprises the following steps:

[0096] S1. Fe(NO3)3·9H2O and LiNO3 were added into 15wt% citric acid aqueous solution in a molar ratio of 1:4.98, mixed well, spray dried at 280°C and crushed to obtain a precursor;

[0097] S2. In a nitrogen atmosphere, the precursor was heated to 850°C at a rate of 300°C / h and kept at this temperature for 15 h. After cooling, the product was mechanically crushed and classified to obtain in-situ carbon-coated LiFeO2·1.99Li2O powder.

[0098] The results show that the average particle size of the in-situ carbon-coated LiFeO2·1.99Li2O powder is 12.3 μm, the thickness of the carbon coating is 17 nm, and the BET is 9.4 m. 2 / g.

[0099] Example 12

[0100] This embodiment provides a lithium-rich iron composite material and a preparation method thereof. The structure of the lithium-rich iron composite material is as follows: Figure 1 As shown, it includes LiFeO2·2.05Li2O·0.015CoO lithium-rich iron-based material and a carbon coating layer coating the lithium-rich iron-based material.

[0101] The preparation method of the lithium-rich iron composite material of this embodiment comprises the following steps:

[0102] S1. Fe(NO3)3·9H2O, LiOH and Co(NO3)3 were added into a 15wt% citric acid aqueous solution at a molar ratio of 1:5.1:0.015, mixed well, spray dried at 280°C and crushed to obtain a precursor;

[0103] S2. In a nitrogen atmosphere, the precursor was heated to 800°C at a rate of 300°C / h and kept at this temperature for 20 h. After cooling, the product was mechanically crushed and graded to obtain in-situ carbon-coated LiFeO2·2.05Li2O·0.015CoO powder.

[0104] The results show that the average particle size of the in-situ carbon-coated LiFeO2·2.05Li2O·0.015CoO powder is 7.8 μm, the thickness of the carbon coating layer is 35 nm, and the BET is 16 m. 2 / g.

[0105] Embodiment 13

[0106] This embodiment provides a lithium-rich iron composite material and a preparation method thereof. The structure of the lithium-rich iron composite material is as follows: Figure 1 As shown, it includes LiFeO2·2.05Li2O·0.015ZrO2 lithium-rich iron-based material and a carbon coating layer coating the lithium-rich iron-based material.

[0107] The preparation method of the lithium-rich iron composite material of this embodiment comprises the following steps:

[0108] S1. FeCl3, Li2CO3, and ZrCl4 were added into a 15wt% citric acid aqueous solution in a molar ratio of 1:2.55:0.015, mixed well, spray dried at 280°C, and crushed to obtain a precursor;

[0109] S2. In a nitrogen atmosphere, the precursor was heated to 800°C at a rate of 300°C / h and kept at this temperature for 20 h. After cooling, the product was mechanically crushed and graded to obtain in-situ carbon-coated LiFeO2·2.05Li2O·0.015ZrO2 powder.

[0110] The results show that the average particle size of the in-situ carbon-coated LiFeO2·2.05Li2O·0.015ZrO2 powder is 7.3 μm, the thickness of the carbon coating is 19 nm, and the BET is 6.2 m. 2 / g.

[0111] Embodiment 14

[0112] This embodiment provides a lithium-rich iron composite material and a preparation method thereof. The structure of the lithium-rich iron composite material is as follows: Figure 1 As shown, it includes LiFeO2·1.99Li2O·0.005Al2O3 lithium-rich iron-based material and a carbon coating layer coating the lithium-rich iron-based material.

[0113] The preparation method of the lithium-rich iron composite material of this embodiment comprises the following steps:

[0114] S1. Fe(NO3)3·9H2O, LiNO3, and Al(NO3)3 were added into a 15wt% citric acid solution in a molar ratio of 1:4.98:0.01, mixed well, spray dried at 280°C, and crushed to obtain a precursor;

[0115] S2. In a nitrogen atmosphere, the precursor was heated to 850°C at a rate of 300°C / h and kept at this temperature for 15 h. After cooling, the product was mechanically crushed and graded to obtain in-situ carbon-coated LiFeO2·1.99Li2O·0.005Al2O3 powder.

[0116] The results show that the average particle size of the in-situ carbon-coated LiFeO2·1.99Li2O·0.005Al2O3 powder is 9 μm, the thickness of the carbon coating layer is 40 nm, and the BET is 5.2 m 2 / g.

[0117] Embodiment 15

[0118] This embodiment provides a lithium-rich iron composite material and a preparation method thereof. The structure of the lithium-rich iron composite material is as follows: Figure 1 As shown, it includes LiFeO2·1.99Li2O·0.01CuO lithium-rich iron-based material and a carbon coating layer coating the lithium-rich iron-based material.

[0119] The preparation method of the lithium-rich iron composite material of this embodiment comprises the following steps:

[0120] S1. Fe2O3, LiOH and CuO are mixed uniformly in a molar ratio of 1:10.1:0.01 to obtain a precursor;

[0121] S2. In a nitrogen atmosphere, the precursor was heated to 900°C at a rate of 300°C / h and kept at this temperature for 20h. After cooling, the product was mechanically crushed and classified to obtain LiFeO2·1.99Li2O·0.01CuO powder;

[0122] S3. The crushed powder was protected by nitrogen in a rotary furnace, and the temperature was raised to 900°C at a heating rate of 200°C / h. 1L / min acetylene and 20L / min nitrogen were passed through the furnace for 0.5h, and the temperature was reduced to obtain carbon-coated LiFeO2·1.99Li2O·0.01CuO powder.

[0123] The results show that the average particle size of the in-situ carbon-coated LiFeO2·1.99Li2O·0.01CuO powder is 6 μm, the thickness of the carbon coating layer is 32 nm, and the BET is 4.5 m. 2 / g.

[0124] Example 16

[0125] This embodiment provides a lithium-rich iron composite material and a preparation method thereof. The structure of the lithium-rich iron composite material is as follows: Figure 1 As shown, it includes LiFeO2·1.99Li2O·0.01MnO2 lithium-rich iron-based material and a carbon coating layer coating the lithium-rich iron-based material.

[0126] The preparation method of the lithium-rich iron composite material of this embodiment comprises the following steps:

[0127] S1. Fe2O3, LiOH and MnO2 are mixed uniformly in a molar ratio of 1:10.1:0.01 to obtain a precursor;

[0128] S2. In a nitrogen atmosphere, the precursor was heated to 900°C at a rate of 300°C / h and kept at this temperature for 20h. After cooling, the product was mechanically crushed and classified to obtain LiFeO2·1.99Li2O·0.01MnO2 powder;

[0129] S3. The crushed powder was placed in a rotary kiln with nitrogen protection, heated to 700°C at a heating rate of 200°C / h, and kept warm for 5 hours with 1L / min ethanol and 20L / min nitrogen. The furnace was then cooled to obtain carbon-coated LiFeO2·1.99Li2O·0.01MnO2 powder.

[0130] The results show that the average particle size of the in-situ carbon-coated LiFeO2·1.99Li2O·0.01MnO2 powder is 2.3 μm, the thickness of the carbon coating layer is 17 nm, and the BET is 18 m 2 / g.

[0131] Embodiment 17

[0132] This embodiment provides a lithium-rich iron composite material and a preparation method thereof. The structure of the lithium-rich iron composite material is as follows: Figure 1As shown, it includes LiFeO2·1.99Li2O·0.005Al2O3 lithium-rich iron-based material and a carbon coating layer coating the lithium-rich iron-based material.

[0133] The preparation method of the lithium-rich iron composite material of this embodiment comprises the following steps:

[0134] S1. Fe(NO3)3·9H2O, LiNO3, and Al(NO3)3 were added into a 15wt% citric acid solution in a molar ratio of 1:4.98:0.01, mixed well, spray dried at 280°C, and crushed to obtain a precursor;

[0135] S2. In a nitrogen atmosphere, the precursor was heated to 850°C at a rate of 300°C / h and kept at this temperature for 15h. After cooling, the product was mechanically crushed and classified to obtain in-situ carbon-coated LiFeO2·1.99Li2O·0.005Al2O3 powder;

[0136] S3. The crushed powder was placed in a rotary furnace with nitrogen protection, heated to 900°C at a heating rate of 200°C / h, and kept warm for 10 hours with 1L / min acetylene and 20L / min nitrogen. The furnace was then cooled to obtain carbon-coated LiFeO2·1.99Li2O·0.005Al2O3 powder.

[0137] The results show that the average particle size of the in-situ carbon-coated LiFeO2·1.99Li2O·0.005Al2O3 powder is 11.4 μm, the thickness of the carbon coating layer is 130 nm, and the BET is 21 m 2 / g.

[0138] Embodiment 18

[0139] This embodiment provides a lithium-rich iron composite material and a preparation method thereof. The structure of the lithium-rich iron composite material is as follows: Figure 1 As shown, it includes LiFeO2·1.99Li2O·0.005Al2O3 lithium-rich iron-based material and a carbon coating layer coating the lithium-rich iron-based material.

[0140] The preparation method of the lithium-rich iron composite material of this embodiment comprises the following steps:

[0141] S1. Fe(NO3)3·9H2O, LiNO3, and Al(NO3)3 were added into a 40wt% citric acid aqueous solution at a molar ratio of 1:4.98:0.01, mixed well, spray dried at 280°C, and crushed to obtain a precursor;

[0142] S2. In a nitrogen atmosphere, the precursor was heated to 850°C at a rate of 300°C / h and kept at this temperature for 15h. After cooling, the product was mechanically crushed and classified to obtain in-situ carbon-coated LiFeO2·1.99Li2O·0.005Al2O3 powder.

[0143] The results show that the average particle size of the in-situ carbon-coated LiFeO2·1.99Li2O·0.005Al2O3 powder is 11.3 μm, the thickness of the carbon coating layer is 110 nm, and the BET is 15 m 2 / g.

[0144] Embodiment 19

[0145] This embodiment provides a lithium-rich iron composite material and a preparation method thereof. The structure of the lithium-rich iron composite material is as follows: Figure 1 As shown, it includes LiFeO2·1.99Li2O·0.005Al2O3 lithium-rich iron-based material and a carbon coating layer coating the lithium-rich iron-based material.

[0146] The preparation method of the lithium-rich iron composite material of this embodiment comprises the following steps:

[0147] S1. Fe(NO3)3·9H2O, LiNO3, and Al(NO3)3 were added into a 15wt% citric acid solution in a molar ratio of 1:4.98:0.01, mixed well, spray dried at 280°C, and crushed to obtain a precursor;

[0148] S2. In an air atmosphere, the temperature was raised to 850°C at a rate of 300°C / h and kept at that temperature for 15h. After cooling, the product was mechanically crushed and classified to obtain LiFeO2·1.49Li2O·0.005Al2O3 powder;

[0149] S3. The crushed powder was placed in a rotary furnace with nitrogen protection, heated to 700°C at a heating rate of 200°C / h, and kept warm for 10 hours with 1L / min acetylene and 20L / min nitrogen. The furnace was then cooled to obtain carbon-coated LiFeO2·1.99Li2O·0.005Al2O3 powder.

[0150] Embodiment 20

[0151] This embodiment provides a lithium-rich iron composite material and a preparation method thereof. The structure of the lithium-rich iron composite material is as follows: Figure 1 As shown, it includes LiFeO2·1.99Li2O lithium-rich iron-based material and a carbon coating layer coating the lithium-rich iron-based material.

[0152] The preparation method of the lithium-rich iron composite material of this embodiment comprises the following steps:

[0153] S1. Fe(NO3)3·9H2O and LiNO3 were mixed uniformly at a molar ratio of 1:4.98, spray-dried at 280°C, and crushed to obtain a precursor;

[0154] S2. In a nitrogen atmosphere, the temperature was raised to 850°C at a rate of 300°C / h and kept at this temperature for 15h. After cooling, the product was mechanically crushed and classified to obtain LiFeO2·1.99Li2O powder;

[0155] S3. The crushed powder was placed in a rotary furnace with nitrogen protection, heated to 900°C at a heating rate of 200°C / h, and kept warm for 1h with 1L / min acetylene and 20L / min nitrogen, and then cooled to obtain carbon-coated LiFeO2·1.99Li2O powder.

[0156] Embodiment 21

[0157] This embodiment provides a lithium-rich iron composite material and a preparation method thereof. The structure of the lithium-rich iron composite material is as follows: Figure 1 As shown, it includes LiFeO2·1.99Li2O·0.005Al2O3 lithium-rich iron-based material and a carbon coating layer coating the lithium-rich iron-based material.

[0158] The preparation method of the lithium-rich iron composite material of this embodiment comprises the following steps:

[0159] S1. Fe(NO3)3·9H2O and LiNO3 were mixed uniformly in a molar ratio of 1:4.98:0.01, spray-dried at 280°C, and crushed to obtain a precursor;

[0160] S2. In an air atmosphere, the temperature was raised to 850°C at a rate of 300°C / h and kept at that temperature for 15h. After cooling, the product was mechanically crushed and classified to obtain LiFeO2·1.99Li2O·0.005Al2O3 powder;

[0161] S3. The crushed powder was placed in a rotary furnace with nitrogen protection, heated to 600°C at a heating rate of 200°C / h, and kept warm for 1h with 1L / min acetylene and 20L / min nitrogen. The furnace was then cooled to obtain carbon-coated LiFeO2·1.99Li2O·0.005Al2O3 powder.

[0162] Embodiment 22

[0163] This embodiment provides a lithium-rich iron composite material and a preparation method thereof. The structure of the lithium-rich iron composite material is as follows: Figure 1 As shown, it includes LiFeO2·2.05Li2O·0.015CoO lithium-rich iron-based material and a carbon coating layer coating the lithium-rich iron-based material.

[0164] The preparation method of the lithium-rich iron composite material of this embodiment comprises the following steps:

[0165] S1. Fe(NO3)3·9H2O, LiOH and Co(NO3)3 were mixed uniformly in a molar ratio of 1:5.1:0.015, spray dried at 280°C and crushed to obtain a precursor;

[0166] S2. In an air atmosphere, the temperature was raised to 800°C at a rate of 300°C / h and kept at that temperature for 20h. After cooling, the product was mechanically crushed and classified to obtain LiFeO2·2.05Li2O·0.015CoO powder;

[0167] S3. The crushed powder was placed in a rotary furnace with nitrogen protection, heated to 700°C at a heating rate of 200°C / h, and kept warm for 1h with 1L / min acetone and 20L / min nitrogen. The furnace was then cooled to obtain carbon-coated LiFeO2·2.05Li2O·0.015CoO powder.

[0168] Embodiment 23

[0169] This embodiment provides a lithium-rich iron composite material and a preparation method thereof. The structure of the lithium-rich iron composite material is as follows: Figure 1 As shown, it includes LiFeO2·1.99Li2O·0.01CuO lithium-rich iron-based material and a carbon coating layer coating the lithium-rich iron-based material.

[0170] The preparation method of the lithium-rich iron composite material of this embodiment comprises the following steps:

[0171] S1. Fe2O3, LiOH and CuO are mixed uniformly in a molar ratio of 1:10.1:0.01 to obtain a precursor;

[0172] S2. In a nitrogen atmosphere, the precursor was heated to 900°C at a rate of 300°C / h and kept at this temperature for 20h. After cooling, the product was mechanically crushed and classified to obtain LiFeO2·1.99Li2O·0.01CuO powder;

[0173] S3. The crushed powder was placed in a rotary furnace with nitrogen protection, heated to 900°C at a heating rate of 200°C / h, and kept warm for 2h with 1L / min methanol and 20L / min nitrogen. The furnace was cooled to obtain carbon-coated LiFeO2·1.99Li2O·0.01CuO powder.

[0174] Comparative Example 11

[0175] This comparative example provides a lithium-rich iron material and a preparation method thereof. The lithium-rich iron material is LiFeO2·1.99Li2O.

[0176] The preparation method of lithium-rich iron-based materials comprises the following steps:

[0177] Fe(NO3)3·9H2O and LiNO3 were added to a 15wt% citric acid aqueous solution at a molar ratio of 1:4.98 and mixed thoroughly, then spray dried at 280°C and crushed. In an air atmosphere, the temperature was raised to 850°C at a rate of 300°C / h and kept for 15h. After cooling, the product was mechanically crushed and classified to obtain LiFeO2·1.99Li2O powder.

[0178] Comparative Example 12

[0179] Direct access to existing LCO materials.

[0180] Comparative Example 13

[0181] This comparative example provides a lithium-rich iron composite material and a preparation method thereof. The structure of the lithium-rich iron composite material is as follows Figure 1 As shown, it includes LiFeO2·1.49Li2O·0.005Al2O3 lithium-rich iron-based material and a carbon coating layer coating the lithium-rich iron-based material.

[0182] The preparation method of the lithium-rich iron composite material of this comparative example comprises the following steps:

[0183] S1. Fe(NO3)3·9H2O, LiNO3, and Al(NO3)3 were added into a 15wt% citric acid solution in a molar ratio of 1:3.98:0.01, mixed well, spray dried at 280°C, and crushed to obtain a precursor;

[0184] S2. In an air atmosphere, the temperature was raised to 850°C at a rate of 300°C / h and kept at that temperature for 15h. After cooling, the product was mechanically crushed and classified to obtain LiFeO2·1.49Li2O·0.005Al2O3 powder;

[0185] S3. The crushed powder was placed in a rotary furnace with nitrogen protection, heated to 900°C at a heating rate of 200°C / h, and kept warm for 10 hours with 1L / min acetylene and 20L / min nitrogen. The furnace was then cooled to obtain carbon-coated LiFeO2·1.49Li2O·0.005Al2O3 powder.

[0186] Comparative Example 14

[0187] This comparative example provides a lithium-rich iron composite material and a preparation method thereof. The structure of the lithium-rich iron composite material is as follows Figure 1 As shown, it includes LiFeO2·1.6Li2O·0.005Al2O3 lithium-rich iron-based material and a carbon coating layer coating the lithium-rich iron-based material.

[0188] The preparation method of the lithium-rich iron composite material of this comparative example comprises the following steps:

[0189] S1. Fe(NO3)3·9H2O, LiNO3, and Al(NO3)3 were added into a 15wt% citric acid solution in a molar ratio of 1:4.22:0.01, mixed well, spray dried at 280°C, and crushed to obtain a precursor;

[0190] S2. In an air atmosphere, the temperature was raised to 850°C at a rate of 300°C / h and kept at that temperature for 15h. After cooling, the product was mechanically crushed and classified to obtain LiFeO2·1.6Li2O·0.005Al2O3 powder;

[0191] S3. The crushed powder was placed in a rotary furnace with nitrogen protection, heated to 900°C at a heating rate of 200°C / h, and kept warm for 10 hours with 1L / min acetylene and 20L / min nitrogen. The furnace was then cooled to obtain carbon-coated LiFeO2·1.6Li2O·0.005Al2O3 powder.

[0192] Comparative Example 15

[0193] This comparative example provides a lithium-rich iron composite material and a preparation method thereof. The structure of the lithium-rich iron composite material is as follows Figure 1 As shown, it includes LiFeO2·1.49Li2O·0.005Al2O3 lithium-rich iron-based material and a carbon coating layer coating the lithium-rich iron-based material.

[0194] The preparation method of the lithium-rich iron composite material of this comparative example comprises the following steps:

[0195] S1. Add Fe(NO3)3·9H2O, LiNO3, Al(NO3)3 in a molar ratio of 1:3.98:0.01 into 15wt% grape carbon solution and mix well;

[0196] S2. In a nitrogen atmosphere, the precursor was heated to 850°C at a rate of 300°C / h and kept at this temperature for 15 h. After cooling, the product was mechanically crushed and graded to obtain carbon-coated LiFeO2·1.49Li2O·0.005Al2O3 powder.

[0197] 2. Lithium-ion battery example:

[0198] The lithium-rich iron-based composite materials provided in Examples 11 to 23 and the lithium-rich iron-based materials provided in Comparative Examples 11 to 15 were respectively prepared into positive electrodes and assembled into lithium-ion batteries according to the following methods:

[0199] Positive electrode: a lithium supplement additive and lithium cobalt oxide are mixed in a mass ratio of 5:95 to obtain a mixture, the mixture is mixed with polyvinylidene fluoride and SP-Li in a mass ratio of 93:3:4 by ball milling and stirring to obtain a positive electrode slurry, the positive electrode slurry is coated on the surface of aluminum foil, rolled, and vacuum dried at 110° C. overnight to obtain a positive electrode sheet;

[0200] Negative electrode: lithium metal sheet;

[0201] Electrolyte: Ethylene carbonate and ethyl methyl carbonate were mixed in a volume ratio of 3:7, and LiPF6 was added to form an electrolyte, the concentration of LiPF6 was 1 mol / L;

[0202] Diaphragm: Polypropylene microporous separator.

[0203] Lithium-ion battery assembly: Lithium-ion batteries are assembled in an inert atmosphere glove box in the order of lithium metal sheet-diaphragm-electrolyte-positive electrode sheet.

[0204] Related characteristics test

[0205] 1. Characterization of Li-rich Iron Composite Materials:

[0206] 1.1 The morphology of the lithium-rich iron composite materials of Example 11, Example 14 and Comparative Example 11 was characterized by scanning electron microscopy. Figure 3 , Figure 4 and Figure 5 ,in, Figure 3 This is a scanning electron microscope image of the lithium-rich iron composite material provided in Example 11 of the present application. Figure 4 This is a scanning electron microscope image of the lithium-rich iron composite material provided in Example 14 of the present application, Figure 5 This is a scanning electron microscope image of the lithium-rich iron composite material provided in Comparative Example 11 of the present application. Figure 3 It can be seen that the in-situ carbon-coated lithium-rich iron composite material of Example 11 has a large number of irregular particles and a relatively rough interface. Figure 4 It can be seen that the surface of the lithium-rich iron-based composite material of Example 14 is relatively smooth. Figure 5 It was found that the interface of the uncoated lithium-rich iron-based composite material was also relatively rough.

[0207] 1.2 X-ray diffraction characterization of the lithium-rich iron composite materials of Example 11 and Example 14 is performed. Figure 6 and Figure 7 ,in, Figure 6 This is the X-ray diffraction pattern of the lithium-rich iron composite material provided in Example 11 of the present application, Figure 7 This is the X-ray diffraction pattern of the lithium-rich iron composite material provided in Example 14 of the present application. Figure 6It can be seen that the lithium-rich iron composite material has a diffraction peak of Li5FeO4 in addition to the main peak, and also has a partial diffraction peak of LiFeO2. Figure 7 It can be seen that the lithium-rich iron composite material is mainly Li5FeO4, with less LiFeO2.

[0208] 1.3 The content of the doping element M contained in the lithium-rich iron-based composite materials of Examples 11 to 18 and the lithium-rich iron-based materials of Comparative Examples 11 to 12 was analyzed by inductively coupled plasma (ICP) emission spectroscopy. Please refer to Table 1 for the test results. The y value of the doping element M in Table 1 is the content of the doping element M in the lithium-rich iron-based composite materials.

[0209] 2. Electrochemical performance of lithium-ion batteries:

[0210] The electrochemical performance of lithium secondary batteries containing the lithium-rich iron composite materials of Examples 11 to 23 and the lithium-rich iron materials of Comparative Examples 11 to 12 was tested, and the test conditions were: the assembled battery was placed at room temperature for 24 hours and then charged and discharged, and the charge and discharge voltage was 2.7V-4.3V. Among them, the electrochemical performance of lithium secondary batteries containing the lithium-rich iron composite materials of Examples 11 to 18 and the lithium-rich iron materials of Comparative Examples 11 to 12 is shown in Table 1.

[0211] Table 1

[0212]

[0213] As can be seen from Table 1, the positive electrode slurry prepared with the lithium-rich iron-based composite materials in Examples 11 to 18 of the present application does not show jelly phenomenon and is easy to coat. When it is added to a lithium secondary battery, the positive electrode can have a higher initial gram capacity and a lower initial efficiency, thereby compensating for the reduced energy density caused by the irreversible lithium loss of the first negative electrode.

[0214] It can be seen from the comparative example experiments that the lithium-rich iron-based material of comparative example 11 is not coated, and absorbs water during the preparation of the positive electrode slurry to form jelly, which is not conducive to the coating of the positive electrode slurry.

[0215] It can be seen from Example 17, Example 14 and Example 18 that when the carbon coating content of the lithium-rich iron-based composite materials of Example 17 and Example 18 increases, the main electrochemical activity ratio of the lithium-ion battery decreases and the capacity is also reduced. Therefore, in the embodiments of the present invention, the thickness of the carbon coating layer of the lithium-rich iron-based composite material should not be too thick or the content should not be too high, which will reduce the lithium replenishment effect of the lithium-rich iron-based composite material.

[0216] 3. XRD analysis and capacity test of lithium-rich iron composite materials:

[0217] The lithium-rich iron composite materials of Examples 11 to 23, Comparative Example 11, Comparative Example 13 and Comparative Example 14 were subjected to XRD analysis, and the lithium-ion batteries containing the lithium-rich iron composite materials of Examples 11 to 23, Comparative Example 11, Comparative Example 13 and Comparative Example 14 were subjected to the following charging capacity analysis in Table 2. Among them, the lithium-rich iron composite materials of Examples 11, 12, 15, 19 and Comparative Example 11, Comparative Example 13 and Comparative Example 14 were selected, and the peak intensities of 2θ=16.7±0.5°, 33.7±0.5° and 43.5±0.5° in the X-ray diffraction spectrum obtained by CuKα rays were 1 a ,I b ,I c The relationships among the three and the corresponding charging capacities of lithium-ion batteries are shown in Table 2 below:

[0218] Table 2 Capacity of lithium-rich iron composite materials corresponding to different peak intensity ratios

[0219]

[0220] It can be seen from Table 2 that after the lithium-rich iron-based composite materials in Examples 11, 12, 15, and 19 of the present application are coated with carbon, a / I b Above 0.26, I a / I c When it is above 0.5, it means that the proportion of Li5FeO4 that can release lithium ions is higher, and the prepared lithium-ion battery has a higher first-charge gram capacity. Compounding it into existing positive electrode material systems such as LFP / NCM / LCO / LMO can compensate for the reduction in energy density caused by the irreversible lithium loss of the negative electrode in the first charge.

[0221] It can be seen from Comparative Examples 13 and 14 that the lithium-rich iron composite material aLiFeO2·bLi2O·cM x O y In the case where b / a is less than 1.8, the lithium source available for capacity contribution is limited, the peak intensity of LiFeO2 is high, the ratio of Ia / Ic is low, and the charging capacity is low. Since the lithium-rich iron composite material of Comparative Example 11 is not coated, the material easily absorbs water in a normal environment, resulting in I a / I b and I a / I c The peak shape ratio changes, which ultimately manifests as a decrease in the material's first electrical capacity.

[0222] 4. Raman analysis, resistivity and capacity testing of lithium-rich iron composite materials:

[0223] The lithium-rich iron composite materials of Examples 11 to 23, Comparative Example 11, and Comparative Example 15 were subjected to XRD analysis, and the lithium-ion batteries containing the lithium-rich iron composite materials of Examples 11 to 23, Comparative Example 11, and Comparative Example 15 were subjected to charging capacity analysis as shown in Table 3. Among them, the lithium-rich iron composite materials of Examples 20 to 23, Comparative Example 11, and Comparative Example 15 were selected to be subjected to Raman spectroscopy analysis, resistivity, and the charging capacity of the corresponding lithium-ion batteries, respectively, as shown in Table 3:

[0224] Table 3 Capacity utilization of lithium-rich iron composite materials corresponding to different Raman D / G peak intensity ratios

[0225]

[0226] It can be seen from Table 3 that after the lithium-rich iron-based composite materials of Examples 20 to 23 of the present application are coated with CVD chemical vapor phase carbon, D / I G Below 4.0, the powder resistivity is within 1000Ω·cm, which means that the carbon layer deposited by chemical vapor carbon deposition has better conductivity and good density. The prepared lithium-ion battery has a higher first charge gram capacity. Compounding it into existing positive electrode material systems such as LFP / NCM / LCO / LMO can compensate for the reduction in energy density caused by the irreversible lithium loss of the negative electrode in the first charge.

[0227] As can be seen from the test results of Comparative Examples 11 and 15, the carbon layer is highly disordered when the lithium-rich iron composite material is coated using the in-situ carbon thermal reduction coating technology. D / I G The larger the carbon source coking value, the lower the conductivity. After carbonization, there are more pores, and under the premise that a / b≤1.8 in the molecular formula of lithium-rich iron-based materials, lithium-rich iron-based composite materials are not easy to preserve and are easy to absorb water in ordinary environments, resulting in performance degradation.

[0228] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A lithium-rich iron composite material, characterized in that: The lithium-rich iron material comprises a LiFeO2·bLi2O·cM x O y , wherein a, b, and c in the molecular formula are molar numbers, and 0≤c / (a+b+c)≤0.02, 1.8≤b / a≤2.1; M is a doping element; 1≤y / x≤2.5; The peaks in the range of 2θ=16.7±0.5° and 33.7±0.5° in the X-ray diffraction spectrum of the lithium-rich iron composite material are derived from the (111) and (222) crystal planes of LiFeO2·2Li2O. The intensities of the peaks in the range of 2θ=16.7±0.5° and 33.7±0.5° are respectively recorded as I a ,I b ; and I a ,I b Satisfaction: I a / I b ≥0.26; The doping element includes at least one of Ni, Co, Mn, Ti, Al, Cu, V, and Zr.

2. The lithium-rich iron composite material according to claim 1, characterized in that: The lithium-rich iron-based material has a particulate morphology, and its particle size satisfies 1 μm ≤ D50 ≤ 15 μm, D10 / D50 ≥ 0.3, and D90 / D50 ≤ 2; and / or The lithium-rich iron-based material has a particulate morphology, and a carbon coating layer is further coated on the surface of the lithium-rich iron-based material.

3. The lithium-rich iron composite material according to claim 2, characterized in that: The thickness of the carbon coating layer is 1-200 nm; and / or The carbon coating layer accounts for 1 wt%-5 wt% of the total mass of the lithium-rich iron-based composite material.

4. The lithium-rich iron-based composite material according to any one of claims 1 to 3, characterized in that: The lithium-rich iron-based composite material has a particulate morphology, and the particle size of the lithium-rich iron-based composite material is: 1 μm ≤ D50 ≤ 10 μm, D10 / D50 ≥ 0.3, and D90 / D50 ≤ 2; and / or The specific surface area of ​​the lithium-rich iron composite material is 0.5-20 m 2 / g; and / or The resistivity of the lithium-rich iron-based composite material is 1.0-1000 Ω / cm.

5. The lithium-rich iron-based composite material according to any one of claims 1 to 3, characterized in that: The range of 2θ = 43.5 ± 0.5° corresponds to the crystal plane (220) of LiFeO2, and its intensity is recorded as I c , and I a ,I c Satisfaction: I a / I c ≥0.

5.

6. The lithium-rich iron composite material according to any one of claims 1 to 3, characterized in that: In the Raman spectrum of the lithium-rich iron composite material, at a wavelength of 1330 cm -1 With 1580cm -1 There is a scattering peak at a wavelength of 1330cm -1 With 1580cm -1 The intensities of the scattering peaks at D ,I G , and I D ,I G Satisfaction: I D / I G <4.

0.

7. A method for preparing a lithium-rich iron-based composite material, comprising the following steps: According to the molecular formula aLiFeO2·bLi2O·cM x O y An iron source, a lithium source, and a doping element source are mixed in a stoichiometric ratio to form a precursor; The precursor is subjected to a first sintering treatment to generate a LiFeO2·bLi2O·cM x O y Lithium-rich iron-based materials; in, In the molecular formula, a, b, and c are the number of moles, and 0 < c / (a + b + c) ≤ 0.02, 1.8 ≤ b / a ≤ 2.1; M is a doping element; 1 ≤ y / x ≤ 2.5; The peaks in the range of 2θ=16.7±0.5° and 33.7±0.5° in the X-ray diffraction spectrum of the lithium-rich iron composite material are derived from the (111) and (222) crystal planes of LiFeO2·2Li2O. The intensities of the peaks in the range of 2θ=16.7±0.5° and 33.7±0.5° are respectively recorded as I a ,I b ; and I a ,I b Satisfaction: I a / I b ≥0.26; The doping element includes at least one of Ni, Co, Mn, Ti, Al, Cu, V, and Zr.

8. The preparation method according to claim 7, characterized in that: The iron source includes at least one of iron oxide, iron nitrate, iron chloride, iron hydroxide, iron oxalate, and iron acetate; and / or The lithium source includes at least one of lithium hydroxide, lithium carbonate, lithium nitrate, lithium acetate, lithium oxide, and lithium oxalate; and / or The doping element source includes at least one of Cu, Co, Al, Ti, Fe, V, and Zr sources; and / or The temperature of the first sintering treatment is 600-1000 °C, and the time is 4-48 h; and / or The first sintering treatment is heated to the first sintering treatment temperature at a heating rate of 10-500 °C / h; and / or After the step of the first sintering treatment, the following second sintering treatment step is further included: The product obtained by the first sintering treatment is crushed and then heated to 600-1000 °C at 0-500 °C / h for heat treatment for 1-20 h.

9. The preparation method according to claim 7 or 8, characterized in that: In the step of mixing the iron source, the lithium source, and the doping element source, a carbon source is further added; the total mass of the carbon source and the reactants is 5 wt%-50 wt%; Or After the step of the first sintering treatment or the second sintering treatment, a step of forming a carbon coating layer on the surface of the lithium-rich iron-based material is further included.

10. A positive electrode lithium supplement additive, characterized in that: Including the lithium-rich iron-based composite material according to any one of claims 1-6 or the lithium-rich iron-based composite material prepared by the preparation method according to any one of claims 7-9.

11. A positive electrode material, characterized in that: Including the lithium-rich iron-based composite material according to any one of claims 1-6 or the lithium-rich iron-based composite material prepared by the preparation method according to any one of claims 7-9 or the cathode lithium supplement additive according to claim 10.

12. A positive electrode, characterized in that: It comprises a current collector and a positive electrode active layer bonded to the surface of the current collector, wherein the positive electrode active layer comprises a positive electrode active material, a lithium supplement additive, a binder and a conductive agent; wherein the lithium supplement additive is the lithium-rich iron-based composite material described in any one of claims 1 to 6, or the lithium-rich iron-based composite material prepared by the preparation method described in any one of claims 7 to 9, or the positive electrode lithium supplement additive described in claim 10.

13. The positive electrode according to claim 12, characterized in that: The content of the lithium supplement additive in the positive electrode active layer is 0.5 wt%-10wt%; and / or The content of the conductive agent in the positive electrode active layer is 0.2 wt%-5wt%; and / or The content of the binder in the positive electrode active layer is 0.5 wt%-3wt%.

14. A lithium ion battery comprising a positive electrode, characterized in that: The positive electrode is the positive electrode according to any one of claims 12 to 13.

15. The lithium ion battery according to claim 14, characterized in that: The lithium-ion battery is a lithium-ion half-cell, and the first coulombic efficiency is 75%-99%.

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