A multi-element lithium supplementing agent, a preparation method thereof, and a positive electrode sheet and a lithium ion battery

Abstract

The application provides a multi-element lithium supplementing agent, a preparation method thereof, a positive pole piece and a lithium ion battery. The multi-element lithium supplementing agent comprises a core, a first coating layer and a second coating layer. The core comprises lithium-rich lithium aluminum iron oxide. The first coating layer comprises lithium-rich lithium manganese oxide. The second coating layer comprises lithium-rich lithium nickel oxide. The chemical general formula of the multi-element lithium supplementing agent is Li x Fe a Al b Mn c Ni d O y , 0.1≤d / (a+b)≤0.9, 0.62≤a≤0.96, 0.04≤b≤0.38, 0.005≤c / (a+b)≤0.02, 5a+5b+2c+2d≤x≤5.5a+5.5b+2.1c+2.1d, y=(x+3a+3b+4c+2d) / 2. The application adopts iron and aluminum main elements, simultaneously coats lithium-rich lithium manganese oxide and lithium-rich lithium nickel oxide, can improve the stability of the lithium supplementing agent, reduces gas production, improves ion conductivity and promotes capacity development.

Description

Technical Field

[0001] This invention belongs to the field of battery technology and relates to a multi-element lithium supplement agent and its preparation method, as well as positive electrode sheets and lithium-ion batteries. Background Technology

[0002] In lithium-ion batteries, a complex SEI (solid electrolyte interphase) film forms on the surface of the carbon or silicon carbide anode. The loose structure, large thickness, and unevenness of the SEI film can lead to a decrease in the battery's initial efficiency. Furthermore, during battery use, the SEI film frequently detaches and regenerates, consuming a significant amount of lithium. To compensate for this loss of active lithium and ensure the cathode material can fully utilize its capacity, lithium replenishment is necessary.

[0003] The commonly used lithium replenishing agent is lithium iron ferrite (Li5FeO4) (LFO), which has an extremely high theoretical capacity, with an irreversible lithium replenishment capacity of over 700 mAh / g. However, lithium iron ferrite also suffers from poor ionic and electronic conductivity, resulting in poor capacity utilization, as well as continuous gas generation during charging and subsequent cycling.

[0004] Based on the above research, there is a need to provide a lithium replenishing agent that not only has high lithium replenishment capacity and excellent poor ionic and electronic conductivity, but also low gas production. Summary of the Invention

[0005] The purpose of this invention is to provide a multi-element lithium supplement agent, its preparation method, positive electrode sheet, and lithium-ion battery. The multi-element lithium supplement agent uses iron and aluminum as the main lithium supplement agent elements, and simultaneously coats lithium-rich manganese oxide and lithium-rich nickel oxide, which can improve the stability of traditional lithium-rich lithium iron oxide supplement agents, reduce gas production, improve ionic conductivity, and promote their capacity utilization.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a multi-element lithium supplement agent, the multi-element lithium supplement agent comprising a core, a first coating layer on the surface of the core, and a second coating layer on the surface of the first coating layer away from the core;

[0008] The core includes lithium aluminum iron oxide, the first coating layer includes lithium manganese oxide, and the second coating layer includes lithium nickel oxide.

[0009] The chemical formula of the multi-element lithium supplement is Li. x Fe a Al b Mn c Ni d O y, among them, 0.1≤d / (a+b)≤0.9, 0.62≤a≤0.96, 0.04≤b≤0.38, 0.005≤c / (a+b)≤0.02, 5a+5b+2c+2d≤x≤5.5a+5.5b+2.1c+2.1d, y=(x+3a+3b+4c+2d) / 2.

[0010] This invention employs lithium-rich aluminum iron oxide (LFI) as its core, introducing aluminum as a main element (as confirmed by the chemical formula of the multi-element lithium supplementer). This improves the material's stability and reduces gas generation from residual lithium after supplementation. Then, a layer of lithium-rich manganese oxide (Li₂MnO₃) is first coated onto the surface of the LFI. Compared to incorporating Mn into the core, this coating protects the interface, stabilizes lattice oxygen, and continuously supplements lithium during battery cycling. Finally, lithium-rich nickel oxide (Li₂NiO₂) is coated onto the surface of the manganese oxide, enhancing the material's ionic conductivity, promoting capacity utilization, and further protecting the LFI while mitigating gas generation. Therefore, through the synergistic effect of multiple aspects, this invention provides a multi-element lithium supplementer with high structural stability, high ionic conductivity, high supplementation capacity, and low gas generation.

[0011] The chemical formula of the multi-element lithium supplement is Li. x Fe a Al b Mn c Ni d O y Wherein, 0.1≤d / (a+b)≤0.9, for example, it can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, or 0.9; 0.62≤a≤0.96 (preferably 0.62≤a≤0.80), for example, it can be 0.62, 0.65, 0.70, 0.75, 0.80, 0.90, or 0.96; 0.04≤b≤0.38 (preferably 0.2≤b≤0.38), for example, it can be 0.04, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, or 0.38. 0.005≤c / (a+b)≤0.02, for example, it can be 0.005, 0.01, 0.015 or 0.02; 5a+5b+2c+2d≤x≤5.5a+5.5b+2.1c+2.1d, for example, it can be 5.1a+5.2b+2.05c+2.05d, 5.3a+5.3b+2.05c+2.05d or 5.5a+5.5b+2.1c+2.1d; y=(x+3a+3b+4c+2d) / 2, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0012] The multi-element lithium supplement agent of this invention adopts a specific chemical formula, that is, each element is preferably within a specific range. If the Al element is too small, the material stability will decrease. If the Al element is too large, the Fe element will be relatively reduced, resulting in too high internal resistance and poor conductivity, which will affect the lithium supplement capacity. If the Mn element is too small, the lithium-rich manganese oxide coating layer content will be too small, which will affect its role in stabilizing lattice oxygen. If the Mn element is too large, the lithium manganese oxide coating layer content will be too large, which will affect the capacity of the entire lithium supplement agent system. If the Ni element is too small, the lithium-rich nickel oxide coating layer content will be too small, resulting in uneven coating, limited improvement in conductivity and inability to effectively reduce gas production in the system. If the Ni element is too large, the lithium-rich nickel oxide content will be too large, which will affect the capacity of the entire lithium supplement agent system.

[0013] Preferably, in the core, the iron content gradually decreases from the core to the surface of the core.

[0014] Preferably, in the core, the aluminum content gradually increases from the core to the surface of the core.

[0015] In the core of this invention, iron and aluminum elements are distributed in a gradient. The content of iron gradually decreases and the content of aluminum gradually increases from the core to the surface of the core, which can improve the stability of the surface lattice and improve the air stability of the material.

[0016] In a second aspect, the present invention provides a method for preparing a multi-element lithium supplement as described in the first aspect, the method comprising the following steps:

[0017] (1) The iron-aluminum-manganese oxide precursor material and the first lithium source are mixed and sintered in one step to obtain a sintered material;

[0018] The iron-aluminum-manganese oxide precursor material includes iron-aluminum oxide and manganese oxide coated on the surface of the iron-aluminum oxide.

[0019] (2) The first sintering material, the nickel source and the second lithium source are mixed and sintered twice to obtain the multi-element lithium supplement agent.

[0020] The present invention coats manganese oxide in the precursor stage and then coats lithium-rich nickel oxide in situ after a first sintering. That is, the first coating layer and the second coating layer of the present invention are both obtained in situ. The coating layer is evenly distributed and controllable, and the coating effect is better than that of traditional coating methods.

[0021] Preferably, the method for preparing the iron-aluminum-manganese oxide precursor material in step (1) includes the following steps:

[0022] The iron source solution, aluminum source solution, precipitant solution and complexing agent solution are subjected to a first coprecipitation reaction to obtain iron-aluminum hydroxide;

[0023] A second coprecipitation reaction was carried out with manganese source solution, precipitant solution and complexing agent solution to obtain the hydroxide precursor material;

[0024] The hydroxide precursor material is then heat-treated to obtain the iron-aluminum-manganese oxide precursor material.

[0025] Preferably, the flow rate of the iron source solution gradually decreases.

[0026] Preferably, the flow rate of the aluminum source solution gradually increases.

[0027] Preferably, in the iron-aluminum hydroxide, the molar ratio of iron to aluminum in the core is m:(1-m), and the molar ratio of iron to aluminum on the surface is n:(1-n), wherein 0.96≤m≤1, for example, can be 0.96, 0.97, 0.98, 0.99 or 1, and 0.30≤n≤0.50, for example, can be 0.30, 0.35, 0.4, 0.45 or 0.5, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0028] Preferably, the pH of the first coprecipitation reaction and the second coprecipitation reaction are independently 9.5-11.5, for example, 9.5, 10.0, 10.5, 11.0 or 11.5, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0029] Preferably, in the first coprecipitation reaction system and the second coprecipitation reaction system, the concentration of the complexing agent is 2-4 mol / L, for example, it can be 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L or 4 mol / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0030] Preferably, the temperature of the first coprecipitation reaction is 40-80℃, for example, it can be 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, 75℃ or 80℃, but is not limited to the listed values. Other values ​​not listed within the range are also applicable. The temperature of the second coprecipitation reaction is 30-45℃, for example, it can be 30℃, 35℃, 40℃ or 45℃, but is not limited to the listed values. Other values ​​not listed within the range are also applicable.

[0031] Preferably, the heat treatment temperature is 120-250℃, for example, 120℃, 150℃, 220℃ or 250℃, and the time is 1-2h, for example, 1h, 1.25h, 1.5h, 1.75h or 2h, and the heat treatment is carried out in an air atmosphere or an oxygen atmosphere.

[0032] The present invention mixes the iron, aluminum, and manganese oxide precursor material and the first lithium source according to the formulation amount of the chemical formula of the multi-element lithium supplement.

[0033] Preferably, the first sintering in step (1) includes pre-firing at 400-550℃, for example, 400℃, 450℃, 500℃ or 550℃ for 5-40h, for example, 5h, 10h, 15h, 20h, 25h, 30h, 35h or 40h, and then sintering at 700-850℃, for example, 700℃, 750℃, 800℃ or 850℃ for 5-15h, for example, 5h, 7.5h, 10h, 12.5h or 15h, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0034] The present invention mixes the nickel source and the second lithium source according to the formulation amount of the chemical formula of the multi-element lithium supplement. More preferably, in step (2), the molar ratio of lithium element in the second lithium source and nickel element in the nickel source is (2-2.1):1, for example, it can be 2:1, 2.05:1 or 2.1:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0035] Preferably, the temperature of the secondary sintering in step (2) is 400-650℃, for example, 400℃, 450℃, 500℃, 550℃, 600℃ or 650℃, and the time is 5-15h, for example, 5h, 7.5h, 10h, 12.5h or 15h, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0036] Preferably, the total mass of the nickel source and the second lithium source is 10%-50% of the mass of the first sintering material, for example, it can be 10%, 20%, 30%, 40% or 50%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0037] Thirdly, the present invention provides a positive electrode sheet, the positive electrode sheet comprising the multi-element lithium supplement agent as described in the first aspect.

[0038] Fourthly, the present invention provides a lithium-ion battery, the lithium-ion battery comprising a positive electrode as described in the second aspect.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] This invention uses lithium-rich aluminum ferrite as its core, introducing aluminum as the main element (as confirmed by the chemical formula of the multi-element lithium supplementer), thereby improving material stability and reducing gas production from residues after lithium supplementation. Then, a layer of lithium-rich manganese oxide is first coated onto the surface of the lithium-rich aluminum ferrite. This structure stabilizes the lattice oxygen on the material surface, further improving stability and enabling continuous lithium supplementation. Finally, lithium-rich nickel oxide is coated onto the surface of the lithium-rich manganese oxide, enhancing ionic conductivity, promoting capacity utilization, and further protecting the lithium-rich aluminum ferrite while mitigating gas production. Therefore, through the synergistic effect of multiple aspects, this invention provides a multi-element lithium supplementer with high structural stability, high ionic conductivity, high lithium supplementation capacity, and low gas production. Detailed Implementation

[0041] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention.

[0042] Example 1

[0043] This embodiment provides a multi-element lithium supplement agent, the chemical formula of which is Li. 5.74 Fe 0.8 Al 0.2 Mn 0.01 Ni 0.2 O 4.59 The multi-element lithium supplement includes a core, a first coating layer on the surface of the core, and a second coating layer on the surface of the first coating layer away from the core.

[0044] The core comprises lithium aluminum iron oxide, and the iron content gradually decreases and the aluminum content gradually increases from the core to the surface of the core; the first coating layer comprises lithium manganese oxide, and the second coating layer comprises lithium nickel oxide.

[0045] The preparation method of the multi-element lithium supplement includes the following steps:

[0046] (1) A first coprecipitation reaction was carried out in ferric nitrate solution, aluminum sulfate solution, sodium hydroxide solution and citric acid solution at pH 10.5, temperature 70℃ and system complexing agent concentration of 3 mol / L. The flow rate of the ferric nitrate solution was gradually decreased and the flow rate of the aluminum sulfate solution was gradually increased to obtain an iron-aluminum hydroxide. In the iron-aluminum hydroxide, the molar ratio of iron to aluminum in the core was m:(1-m) and the molar ratio of iron to aluminum on the surface was n:(1-n), where m=0.98 and n=0.38.

[0047] Then, the manganese sulfate solution, sodium hydroxide solution, and citric acid solution were subjected to a second coprecipitation reaction at a pH of 10.5, a temperature of 35°C, and a system complexing agent concentration of 3 mol / L. By controlling the amount of manganese sulfate solution introduced, the molar ratio of Mn / (Fe+Al) was made up to 0.01 to obtain a hydroxide precursor material. The hydroxide precursor material was then heat-treated at 180°C for 2 hours in an oxygen atmosphere to obtain an iron-aluminum-manganese oxide precursor material.

[0048] (2) The iron, aluminum and manganese oxide precursor material and anhydrous lithium hydroxide are mixed according to the formula. After the mixture is completed, the material is pre-calcined at 500°C for 20 hours and then sintered at 800°C for 10 hours to obtain a calcined material.

[0049] (3) Lithium oxide and nickel oxide are mixed in a molar ratio of Li / Ni = 2.05. The mixed material is added to the sintering material in step (1) according to the formula amount, mixed evenly, and then sintered at 550°C for 10 hours in a nitrogen atmosphere to obtain the multi-element lithium supplement.

[0050] Example 2

[0051] This embodiment provides a multi-element lithium supplement agent, the chemical formula of which is Li. 7.04 Fe 0.8 Al 0.2 Mn 0.02 NiO 6.06 The multi-element lithium supplement includes a core, a first coating layer on the surface of the core, and a second coating layer on the surface of the first coating layer away from the core.

[0052] The core comprises lithium aluminum iron oxide, and the iron content gradually decreases and the aluminum content gradually increases from the core to the surface of the core; the first coating layer comprises lithium manganese oxide, and the second coating layer comprises lithium nickel oxide.

[0053] The preparation method of the multi-element lithium supplement includes the following steps:

[0054] (1) Ferric nitrate solution, aluminum sulfate solution, sodium hydroxide solution and citric acid solution are subjected to a first coprecipitation reaction at pH 9.5, temperature 80℃ and system complexing agent concentration of 4 mol / L. The flow rate of the ferric nitrate solution is gradually decreased and the flow rate of the aluminum sulfate solution is gradually increased to obtain an iron-aluminum hydroxide. In the iron-aluminum hydroxide, the molar ratio of iron to aluminum in the core is m:(1-m) and the molar ratio of iron to aluminum on the surface is n:(1-n), where m=0.96 and n=0.36.

[0055] Then, manganese sulfate solution, sodium hydroxide solution, and citric acid solution were subjected to a second coprecipitation reaction at pH 9.5, temperature 30°C, and system complexing agent concentration of 4 mol / L, so that the molar ratio of Mn / (Fe+Al) element = 0.02 to obtain the hydroxide precursor material. The hydroxide precursor material was then heat-treated at 200°C for 2 hours in an oxygen atmosphere to obtain the iron-aluminum-manganese oxide precursor material.

[0056] (2) The iron, aluminum and manganese oxide precursor material and anhydrous lithium hydroxide are mixed according to the formula. After the mixture is completed, the material is pre-calcined at 550°C for 5 hours and then sintered at 850°C for 5 hours to obtain a calcined material.

[0057] (3) Lithium oxide and nickel oxide are mixed in a molar ratio of Li / Ni = 2. The mixed material is added to the sintering material in step (1) according to the formula amount, mixed evenly, and then sintered at 400°C for 15 hours in a nitrogen atmosphere to obtain the multi-element lithium supplement.

[0058] Example 3

[0059] This embodiment provides a multi-element lithium supplement agent, the chemical formula of which is Li. 5.75 Fe 0.62 Al 0.38 Mn 0.005 Ni 0.12 O 4.5 The multi-element lithium supplement includes a core, a first coating layer on the surface of the core, and a second coating layer on the surface of the first coating layer away from the core.

[0060] The core comprises lithium aluminum iron oxide, and the iron content gradually decreases and the aluminum content gradually increases from the core to the surface of the core; the first coating layer comprises lithium manganese oxide, and the second coating layer comprises lithium nickel oxide.

[0061] The preparation method of the multi-element lithium supplement includes the following steps:

[0062] (1) A first coprecipitation reaction was carried out in ferric nitrate solution, aluminum sulfate solution, sodium hydroxide solution and citric acid solution at pH 11.5, temperature 50℃ and system complexing agent concentration of 2 mol / L. The flow rate of the ferric nitrate solution was gradually decreased and the flow rate of the aluminum sulfate solution was gradually increased to obtain an iron-aluminum hydroxide. In the iron-aluminum hydroxide, the molar ratio of iron to aluminum in the core was m:(1-m) and the molar ratio of iron to aluminum on the surface was n:(1-n), where m=0.96 and n=0.72.

[0063] Then, manganese sulfate solution, sodium hydroxide solution and citric acid solution were subjected to a second coprecipitation reaction at pH 11.5, temperature 40℃ and system complexing agent concentration of 2 mol / L, so that the molar ratio of Mn / (Fe+Al) element = 0.005 to obtain hydroxide precursor material. The hydroxide precursor material was then heat-treated at 250℃ for 1 h in an oxygen atmosphere to obtain iron-aluminum-manganese oxide precursor material.

[0064] (2) The iron-aluminum-manganese precursor material and anhydrous lithium hydroxide were mixed according to the formula. After the mixture was completed, the material was pre-calcined at 400°C for 40 hours and then sintered at 700°C for 15 hours to obtain a calcined material.

[0065] (3) Lithium oxide and nickel oxide are mixed in a molar ratio of Li / Ni = 2. The mixed material is added to the sintering material in step (1) according to the formula amount, mixed evenly, and then sintered at 650°C for 5 hours in a nitrogen atmosphere to obtain the multi-element lithium supplement.

[0066] Example 4

[0067] This embodiment provides a multi-element lithium supplement agent, the chemical formula of which is Li. 5.74 Fe 0.9 Al 0.1 Mn 0.01 Ni 0.2 O 4.59 Everything else is the same as in Example 1.

[0068] The preparation method of the multi-element lithium supplement described in this embodiment is the same as that in Example 1, except that the formulation amount is adapted according to the general chemical formula.

[0069] Example 5

[0070] This embodiment provides a multi-element lithium supplement agent, the chemical formula of which is Li. 5.74 Fe 0.95 Al 0.05 Mn 0.01 Ni 0.2 O 4.59 Everything else is the same as in Example 1.

[0071] The preparation method of the multi-element lithium supplement described in this embodiment is the same as that in Example 1, except that the formulation amount is adapted according to the general chemical formula.

[0072] Example 6

[0073] This embodiment provides a multi-element lithium supplement agent. In the multi-element lithium supplement agent, the content of iron and aluminum elements remains unchanged from the core to the surface of the inner core, and all other aspects are the same as in Example 1.

[0074] In the preparation method of the multi-element lithium supplement described in this embodiment, except that the flow rates of the ferric nitrate solution and aluminum sulfate solution in step (1) remain unchanged, and the flow ratio of the ferric nitrate solution and aluminum sulfate solution is always 8:2, and the adaptability of the iron-aluminum hydroxide changes, the rest are the same as in Example 1.

[0075] Comparative Example 1

[0076] This comparative example provides a multi-element lithium supplement agent, the chemical formula of which is Li. 5.74 Fe 0.55 Al 0.45 Mn 0.01 Ni 0.2 O 4.59 Except for the above, everything else is the same as in Example 1.

[0077] The preparation method of the multi-element lithium supplement described in this comparative example is the same as that in Example 1, except that the formulation amount is adapted according to the general chemical formula.

[0078] Comparative Example 2

[0079] This comparative example provides a multi-element lithium supplement agent, the chemical formula of which is Li. 5.74 FeMn 0.01 Ni 0.2 O 4.59 Except for the above, everything else is the same as in Example 1.

[0080] The preparation method of the multi-element lithium supplement described in this comparative example is the same as that in Example 1, except that the formulation amount is adapted according to the general chemical formula.

[0081] Comparative Example 3

[0082] This comparative example provides a multi-element lithium supplement agent, the chemical formula of which is Li. 5.915 Fe 0.7 Al 0.3 Mn 0.1 Ni 0.2 O 4.86 Except for the above, everything else is the same as in Example 1.

[0083] The preparation method of the multi-element lithium supplement described in this comparative example is the same as that in Example 1, except that the formulation amount is adapted according to the general chemical formula.

[0084] Comparative Example 4

[0085] This comparative example provides a multi-element lithium supplement agent, which is the same as that in Example 1 except that it does not contain a first coating layer.

[0086] The preparation method of the multi-element lithium supplement described in this comparative example is the same as that in Example 1, except that the second coprecipitation reaction is not carried out in step (1).

[0087] Comparative Example 5

[0088] This comparative example provides a multi-element lithium supplement agent, which is identical to Example 1 except that it does not contain a second coating layer, thus changing the chemical formula of the multi-element lithium supplement agent.

[0089] The preparation method of the multi-element lithium supplement described in this comparative example is the same as that in Example 1, except that step (3) is not performed.

[0090] The testing methods for the lithium replenishment capacity, gas production and ionic conductivity of the multi-element lithium replenishment agents obtained in the above examples and comparative examples are as follows: (1) Assemble the lithium replenishment agents obtained in the examples and comparative examples into a button cell and perform a charging test to obtain the charging specific capacity, which is the lithium replenishment capacity. The specific button cell preparation method and charging test conditions are as follows: The lithium replenishment agent, SP (conductive carbon black) and PVDF (polyvinylidene fluoride) are homogenized in a mass ratio of 85:10:5 (hoisting in a degassing machine for 5 min), the solid content of the slurry is 50%, and after homogenization, it is coated with a coating surface density of 5 mg / cm. 2 After the electrode sheets are dried, they are punched using a 12mm die for assembly into a coin cell. After the coin cell assembly is completed, a charge-discharge tester is used to perform a charge-discharge test. Specifically, the charge is performed at 25℃ and a 0.05C rate to 4.4V, and then constant voltage charging is performed until the current is ≤0.01C. The charging capacity is recorded, which is the lithium replenishment capacity of the lithium replenishing agent.

[0091] (2) The mass of the fully charged tamper recorded active material was injected into the electrolyte at an injection coefficient of 3.5 g / Ah, sealed in an aluminum-plastic bag, and then stored at 60°C. The gas production was recorded after 7 days of storage.

[0092] (3) The lithium supplements of the examples and comparative examples were subjected to EIS testing to obtain the ionic conductivity of the samples.

[0093] The test results are shown in Table 1:

[0094] Table 1

[0095]

[0096] As can be seen from Table 1:

[0097] As shown in Examples 1-3 and Comparative Examples 1-2, when too much Al is introduced into the core, the Fe content decreases, which affects the lithium replenishment capacity. However, when Al is not present, the stability of the material is affected, as is the gas production. As shown in Examples 1-3 and Comparative Examples 3-4, when the Mn content is too high, the lithium replenishment capacity of the material is also affected. However, when manganese is not present, i.e., when lithium-rich manganese oxide coating is not present, the gas production of the material increases. As shown in Examples 1-3 and Comparative Example 5, when lithium nickel oxide coating is not present, the ionic conductivity of the material decreases. As shown in Examples 1 and 4-5, when Al is added as the main element in the core, when the Al content is too low, the effect of improving material stability decreases, which affects the material performance. As shown in Examples 1 and 6, the present invention preferably uses a gradient change in the content of iron and aluminum, which can further improve the material stability and lithium replenishment capacity, and also reduce gas production.

[0098] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A multi-element lithium supplement, characterized in that, The multi-element lithium supplement includes a core, a first coating layer on the surface of the core, and a second coating layer on the surface of the first coating layer away from the core; The core includes lithium aluminum iron oxide, the first coating layer includes lithium manganese oxide, and the second coating layer includes lithium nickel oxide. The chemical formula of the multi-element lithium supplement is Li. x Fe a Al b Mn c Ni d O y , among them, 0.1≤d / (a+b)≤0.9, 0.62≤a≤0.96, 0.04≤b≤0.38, 0.005≤c / (a+b)≤0.02, 5a+5b+2c+2d≤x≤5.5a+5.5b+2.1c+2.1d, y=(x+3a+3b+4c+2d) / 2; In the core, the iron content gradually decreases from the core to the surface of the core; In the core, the aluminum content gradually increases from the core to the surface of the core.

2. The multi-element lithium supplement agent according to claim 1, characterized in that, 0.62≤a≤0.80, 0.2≤b≤0.

38.

3. A method for preparing a multi-element lithium supplement as described in claim 1 or 2, characterized in that, The preparation method includes the following steps: (1) The iron-aluminum-manganese oxide precursor material and the first lithium source are mixed and sintered in one step to obtain a sintered material; The iron-aluminum-manganese oxide precursor material includes iron-aluminum oxide and manganese oxide coated on the surface of the iron-aluminum oxide. (2) The first sintering material, the nickel source and the second lithium source are mixed and sintered twice to obtain the multi-element lithium supplement agent.

4. The preparation method according to claim 3, characterized in that, The method for preparing the iron-aluminum-manganese oxide precursor material in step (1) includes the following steps: The iron source solution, aluminum source solution, precipitant solution and complexing agent solution are subjected to a first coprecipitation reaction to obtain iron-aluminum hydroxide; A second coprecipitation reaction was carried out with manganese source solution, precipitant solution and complexing agent solution to obtain hydroxide precursor material; The hydroxide precursor material is then heat-treated to obtain the iron-aluminum-manganese oxide precursor material.

5. The preparation method according to claim 4, characterized in that, The flow rate of the iron source solution gradually decreases; And / or, the flow rate of the aluminum source solution gradually increases; And / or, in the iron-aluminum hydroxide, the molar ratio of iron to aluminum in the core is m:(1-m), and the molar ratio of iron to aluminum on the surface is n:(1-n), wherein 0.96≤m≤1 and 0.30≤n≤0.

50.

6. The preparation method according to claim 4 or 5, characterized in that, The pH values ​​for the first and second coprecipitation reactions are independently 9.5-11.5; And / or, in the system of the first coprecipitation reaction and the system of the second coprecipitation reaction, the concentration of the complexing agent is 2-4 mol / L; And / or, the temperature of the first coprecipitation reaction is 40-80℃, and the temperature of the second coprecipitation reaction is 30-45℃; And / or, the heat treatment is performed at a temperature of 120-250°C for 1-2 hours, and the heat treatment is carried out in an air atmosphere or an oxygen atmosphere.

7. The preparation method according to claim 3, characterized in that, The first sintering in step (1) includes pre-firing at 400-550℃ for 5-40h, and then continuing sintering at 700-850℃ for 5-15h.

8. The preparation method according to claim 3, characterized in that, In step (2), the molar ratio of lithium in the second lithium source to nickel in the nickel source is (2-2.1):1; The secondary sintering temperature in step (2) is 400-650℃, and the time is 5-15h.

9. A positive electrode sheet, characterized in that, The positive electrode includes the multi-element lithium supplement agent as described in claim 1 or 2.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes the positive electrode as described in claim 9.

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