Positive electrode lithium supplementing material, preparation method thereof and lithium ion battery

Abstract

The invention provides an anode lithium supplementing material, a preparation method thereof and a lithium ion battery. The positive electrode lithium supplementing material comprises an inner core and a carbon coating layer arranged on the surface of the inner core, the inner core has a general formula of Li5Fe1-xBxO4, and x is greater than or equal to 0.01 and less than or equal to 0.1. The carbon coating layer can improve the air stability of the positive electrode lithium supplementing material, so that the capacity loss of the positive electrode lithium supplementing material is reduced. The boron element doped in the inner core can occupy tetrahedral gaps in lithium ferrite and form a B-O bond with oxygen in crystal lattices, so that the structural stability of the positive electrode lithium supplementing material is improved, the structure of the positive electrode lithium supplementing material can be prevented from being damaged in the charging and discharging process, and the loss of active lithium is reduced. Compared with other ranges, the range of x in the general formula Li5Fe1-xBxO4 is limited in the specific range of the invention, so that the structural stability of the positive electrode lithium supplementing material can be improved. When the anode lithium supplementing material is applied to the lithium ion battery, the electrochemical performance and the cycling stability of the lithium ion battery can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a positive electrode lithium supplement material, a preparation method thereof and a lithium ion battery. Background Art

[0002] As the secondary battery with the most extensive application prospects, lithium-ion batteries have been applied to portable products, energy storage systems, electric vehicles and other fields. Among them, high energy density is the key to the application of lithium-ion batteries in these systems. Currently, the most widely used negative electrode material in commercial batteries, graphite, has a limited theoretical capacity. Therefore, silicon-carbon negative electrodes and silicon-oxygen negative electrodes with high theoretical capacity are gradually being applied to lithium-ion batteries. However, these high-capacity negative electrodes face large capacity losses during the first discharge process, resulting in low initial efficiency and capacity of the battery.

[0003] The capacity loss during the first charge and discharge process can be compensated by pre-lithiation, thereby achieving the purpose of improving the initial efficiency and capacity. At present, the pre-lithiation methods are mainly divided into several types: (1) pre-lithiation of negative electrode materials, using metal lithium powder or lithium foil as a pre-lithiation agent, and directly pre-reserving it on the negative electrode by evaporation or mechanical rolling. This type of pre-lithiation technology has high requirements for the operating environment and equipment; (2) pre-lithiation of positive electrode materials, adding a pre-lithiation agent during the positive electrode slurry process. This type of pre-lithiation agent is mainly a high-capacity lithium-rich material. The high capacity of the lithium-rich material is used to achieve the pre-lithiation effect. Compared with the negative electrode lithium replenishment technology, the positive electrode lithium replenishment is safer and easier to industrialize. It does not require changes to the existing equipment and processes of the factory. It is a very promising lithium replenishment technology. However, the existing lithium replenishment materials have poor air stability and unstable material structure, which makes their processing and application difficult and difficult to exert high lithium replenishment capacity.

[0004] Therefore, researching and developing a lithium-supplementing material with stable structure and high lithium-supplementing capacity is of great significance for improving the electrochemical performance and cycle stability of lithium-ion batteries. Summary of the invention

[0005] The main purpose of the present invention is to provide a positive electrode lithium supplement material, a preparation method thereof and a lithium ion battery, so as to solve the problem that the lithium supplement material in the prior art has poor air stability and structural stability, which makes its processing and application difficult and makes it difficult to exert its lithium supplement capacity.

[0006] In order to achieve the above-mentioned object, the present invention provides a positive electrode lithium supplement material, which comprises a core and a carbon coating layer arranged on the surface of the core, and the core has a general formula: Li5Fe 1-x B x O4, where 0.01≤x≤0.1.

[0007] The outer carbon coating layer in the positive electrode lithium supplement material provided by the present application can effectively separate the inner core from the air, inhibiting its side reactions with the air, thereby improving the air stability of the positive electrode lithium supplement material, and further reducing the capacity loss of the positive electrode lithium supplement material. The boron element doped in the inner core can occupy the tetrahedral gap position in the lithium ferrite and form a BO bond with the oxygen in the lattice, thereby improving the structural stability of the positive electrode lithium supplement material, and can inhibit the structure from being destroyed during the charge and discharge process, reducing the loss of active lithium. Compared with other ranges, the general formula Li5Fe 1-x B x The range of x in O4 is limited to the specific range of the present application, which can improve the structural stability of the positive electrode lithium supplement material.

[0008] In summary, applying the above-mentioned positive electrode lithium supplement material provided in the present application to lithium-ion batteries can improve the electrochemical performance and cycle stability of lithium-ion batteries.

[0009] Further, x is selected from 0.01 to 0.05.

[0010] The value of x includes but is not limited to the above range. Limiting it to the above range is beneficial to making the structure of the positive electrode lithium supplement material more stable.

[0011] Furthermore, the D50 of the inner core is ≤12 μm.

[0012] Compared with other ranges, the D50 of the core within this range is conducive to better exerting the electrochemical capacity of the core.

[0013] Furthermore, the thickness of the carbon coating layer is 100-500 nm.

[0014] Compared with other ranges, limiting the thickness of the carbon coating layer within this range is beneficial to further suppress the side reaction between the core and the air, thereby further improving the air stability of the positive electrode lithium supplement material.

[0015] Furthermore, based on the total weight of the positive electrode lithium supplement material, the coating amount of the carbon coating layer is 1 to 8 wt %.

[0016] Compared with other ranges, limiting the coating amount of the carbon coating layer within the above range is beneficial to separating the core from the air, inhibiting the side reactions between the core and the air, and further beneficial to improving the air stability of the positive electrode lithium supplement material.

[0017] In order to achieve the above-mentioned purpose, another aspect of the present invention provides a method for preparing the above-mentioned positive electrode lithium replenishing material provided in the present application, and the preparation method includes: step S1, mixing a lithium source, an iron source, a boron source, a carbon source and a solvent to obtain a mixed system containing a precursor; wherein the molar ratio of the lithium element in the lithium source, the iron element in the iron source and the boron element in the boron source is 5:(1-x):x; step S2, heat-treating the precursor in a protective atmosphere to obtain a positive electrode lithium replenishing material.

[0018] A lithium source, an iron source, a boron source, and a carbon source are mixed with a solvent, wherein the lithium source, the iron source, and the boron source are aggregated to form a crystal nucleus, and as the crystal nucleus gradually grows, the carbon source gradually adheres to the surface of the crystal nucleus to form a precursor, thereby obtaining a mixed system containing the precursor; the above-mentioned precursor is heat-treated in a protective atmosphere, and the carbon source undergoes a thermal decomposition reaction in the process to obtain a carbon coating layer and is coated on the surface of the inner core, thereby obtaining a positive electrode lithium supplement material. The carbon coating layer can effectively separate the inner core from the air, inhibiting its side reaction with the air, thereby improving the air stability of the positive electrode lithium supplement material, and then reducing the capacity loss of the positive electrode lithium supplement material. The doping of the boron element can occupy the tetrahedral interstitial position in lithium ferrite and form a BO bond with oxygen in the lattice, thereby improving the structural stability of the positive electrode lithium supplement material. The application of the above-mentioned positive electrode lithium supplement material provided in the present application to lithium ion batteries can improve the electrochemical performance and cycle stability of lithium ion batteries.

[0019] Compared with other ranges, the general formula Li5Fe 1-x B x The range of x in O4 is limited to the specific range of the present application, which can improve the structural stability of the positive electrode lithium supplement material.

[0020] In addition, the above-mentioned preparation method of the present application has a simple process flow and is suitable for large-scale industrial production of materials.

[0021] Furthermore, the ratio of the total molar amount of lithium in the lithium source, iron in the iron source and boron in the boron source to the molar amount of carbon in the carbon source is 6:(0.01-0.08).

[0022] Compared with other ranges, limiting the molar ratio of the two within the above range is conducive to the formation of the carbon coating layer. The carbon coating layer can effectively separate the core and the air, inhibiting its side reactions with the air, thereby improving the air stability of the positive electrode lithium replenishing material and reducing the capacity loss of the positive electrode lithium replenishing material.

[0023] Furthermore, the ratio of the total molar amount of lithium in the lithium source, iron in the iron source, and boron in the boron source to the volume of the solvent is (0.03-1):(200-400).

[0024] Compared with other ranges, limiting the ratio of the total molar amount of lithium in the lithium source, iron in the iron source, and boron in the boron source to the volume of the solvent within the above range can more effectively form a carbon coating layer and improve the air stability of the positive electrode lithium supplement material.

[0025] Furthermore, in step S1, stirring is performed during the mixing process.

[0026] Stirring helps to improve mixing uniformity.

[0027] Furthermore, the stirring speed is 200 to 2000 rpm, and the stirring time is 30 to 180 min.

[0028] Stirring at the above rotation speed and time makes the mixing more uniform, which is beneficial to the formation of the carbon coating layer and core of the positive electrode lithium supplement material, thereby being beneficial to the air and structural stability of the positive electrode lithium supplement material.

[0029] Furthermore, in step S1, the temperature of the mixing process is 25-80°C.

[0030] Compared with other ranges, limiting the temperature of the mixing process to the above range is beneficial to making the mixing more uniform.

[0031] Furthermore, the lithium source is selected from one or more of lithium carbonate, lithium hydroxide and lithium oxalate.

[0032] The present application has no particular limitation on the type of lithium source, and commonly used types in the art may be used.

[0033] Furthermore, the iron source is selected from one or more of iron oxide, iron hydroxide, iron sulfate and iron oxalate.

[0034] Compared with other types, the above-mentioned types of iron sources are widely available and of low cost.

[0035] Further, the boron source is boric acid and / or boron oxide.

[0036] Compared with other types, there are no by-products after the reaction using the above-mentioned types of boron sources.

[0037] Furthermore, the carbon source is polyvinyl alcohol and / or citric acid.

[0038] Compared with other types, the above-mentioned carbon sources have no by-products after the reaction and are low in price.

[0039] Furthermore, the solvent is water and / or ethanol.

[0040] The combination of specific types of lithium sources, iron sources, boron sources, carbon sources and solvents is beneficial to reducing costs and simplifying the preparation process on the one hand, and on the other hand, it is beneficial to improving the stability and electrochemical capacity of the positive electrode lithium supplement material, thereby improving the electrochemical performance and cycle stability of lithium-ion batteries.

[0041] Furthermore, when the carbon source is polyvinyl alcohol, the weight average molecular weight of the polyvinyl alcohol is 10,000 to 100,000.

[0042] The use of polyvinyl alcohol is conducive to the formation of a carbon coating layer, which effectively separates the core from the air and inhibits side reactions with the air, thereby improving the air stability of the positive electrode lithium supplement material.

[0043] Furthermore, between step S1 and step S2, a process of drying the mixed system is also included to obtain a precursor.

[0044] The above drying process is beneficial to remove the solvent in the mixed system, inhibit the splashing of the solvent during the subsequent heat treatment, facilitate the subsequent heat treatment, thereby improving the effect of the heat treatment and further improving the stability of the positive electrode lithium supplement material.

[0045] Furthermore, the drying temperature is 80 to 130° C., and the drying time is 12 to 48 hours.

[0046] Compared with other ranges, limiting the drying temperature and time within the above range is beneficial to further remove the solvent in the mixed system and inhibit the splashing of the solvent during the subsequent heat treatment, thereby further improving the effect of the heat treatment.

[0047] Further, the heat treatment in step S2 includes a first calcination process and a second calcination process.

[0048] Furthermore, the first calcination process includes calcining at 400-600°C for 3-8 hours at a heating rate of 3-10°C / min to obtain a first calcined product; the second calcination process includes: calcining at 600-1000°C for 8-20 hours at a heating rate of 3-10°C / min to obtain a positive electrode lithium supplement material.

[0049] Compared with other heat treatment methods, the above-mentioned staged calcination process and limiting the process parameters of each stage within the above-mentioned range is beneficial to improving the purity of the positive electrode lithium supplement material crystal form, improving the bonding force between the inner core and the carbon coating, thereby improving the structural stability of the carbon coating, improving the stability of the positive electrode lithium supplement material, and further improving the electrochemical performance and cycle stability of lithium-ion batteries.

[0050] Furthermore, the protective atmosphere is selected from nitrogen and / or argon.

[0051] Compared with other protective atmospheres, the above-mentioned types of protective atmospheres are easy to obtain and relatively safe to use.

[0052] Another aspect of the present invention provides a lithium-ion battery, comprising a positive electrode, a negative electrode, an electrolyte and a separator arranged between the positive electrode and the negative electrode, wherein the positive electrode comprises the positive electrode lithium supplement material provided in the present application.

[0053] The above-mentioned positive electrode lithium supplement material provided in the present application has excellent air stability and structural stability. Applying it to lithium-ion batteries can significantly improve the electrochemical performance (such as the initial charge and discharge efficiency) and cycle stability of lithium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0055] Figure 1 The XRD pattern of the core prepared in Example 1 of the present application is shown;

[0056] Figure 2 The SEM image of the positive electrode lithium supplement material prepared in Example 1 of the present application is shown. DETAILED DESCRIPTION

[0057] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0058] The present application is further described in detail below in conjunction with specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in the present application.

[0059] As described in the background technology section of this application, the existing lithium supplement materials have poor air stability and structural stability, which makes their processing and application difficult and difficult to fully utilize their lithium supplement capacity. In order to solve the above problems, the first aspect of this application provides a positive electrode lithium supplement material, wherein the positive electrode lithium supplement material includes a core and a carbon coating layer arranged on the surface of the core, and the core has a general formula: Li5Fe 1-x B x O4, where 0.01≤x≤0.1.

[0060] The outer carbon coating layer in the positive electrode lithium supplement material provided by the present application can effectively separate the inner core from the air, inhibiting its side reactions with the air, thereby improving the air stability of the positive electrode lithium supplement material, and further reducing the capacity loss of the positive electrode lithium supplement material. The boron element doped in the inner core can occupy the tetrahedral gap position in the lithium ferrite and form a BO bond with the oxygen in the lattice, thereby improving the structural stability of the positive electrode lithium supplement material, and can inhibit the structure from being destroyed during the charge and discharge process, reducing the loss of active lithium. Compared with other ranges, the general formula Li5Fe 1-x B x The range of x in O4 is limited to the specific range of the present application, which can improve the structural stability of the positive electrode lithium supplement material.

[0061] In summary, applying the above-mentioned positive electrode lithium supplement material provided in the present application to lithium-ion batteries can improve the electrochemical performance and cycle stability of lithium-ion batteries.

[0062] In a preferred embodiment, x includes but is not limited to 0.01 to 0.05. The value of x includes but is not limited to the above range, and limiting it to the above range is conducive to making the structure of the positive electrode lithium supplement material more stable.

[0063] In a preferred embodiment, the D50 of the core is ≤12 μm. Compared with other ranges, the D50 of the core within this range is conducive to better exerting the electrochemical capacity of the core.

[0064] In a preferred embodiment, the thickness of the carbon coating layer is 100-500 nm. Compared with other ranges, limiting the thickness of the carbon coating layer within this range is beneficial to further inhibit the side reaction between the core and the air, thereby further improving the air stability of the positive electrode lithium supplement material.

[0065] In a preferred embodiment, the coating amount of the carbon coating layer is 1 to 8 wt % based on the total weight of the positive electrode lithium supplement material. Compared with other ranges, limiting the coating amount of the carbon coating layer to the above range is beneficial to isolating the core from the air, inhibiting the side reaction between the core and the air, and thus is beneficial to improving the air stability of the positive electrode lithium supplement material.

[0066] The second aspect of the present application also provides a method for preparing the above-mentioned positive electrode lithium replenishing material provided by the present application, and the preparation method includes: step S1, mixing a lithium source, an iron source, a boron source, a carbon source and a solvent to obtain a mixed system containing a precursor; the molar ratio of the lithium element in the lithium source, the iron element in the iron source and the boron element in the boron source is 5:(1-x):x; step S2, heat treating the precursor in a protective atmosphere to obtain a positive electrode lithium replenishing material.

[0067] A lithium source, an iron source, a boron source, and a carbon source are mixed with a solvent, wherein the lithium source, the iron source, and the boron source are aggregated to form a crystal nucleus, and as the crystal nucleus gradually grows, the carbon source gradually adheres to the surface of the crystal nucleus to form a precursor, thereby obtaining a mixed system containing the precursor; the above-mentioned precursor is heat-treated in a protective atmosphere, and the carbon source undergoes a thermal decomposition reaction in the process to obtain a carbon coating layer and is coated on the surface of the inner core, thereby obtaining a positive electrode lithium supplement material. The carbon coating layer can effectively separate the inner core from the air, inhibiting its side reaction with the air, thereby improving the air stability of the positive electrode lithium supplement material, and then reducing the capacity loss of the positive electrode lithium supplement material. The doping of the boron element can occupy the tetrahedral interstitial position in lithium ferrite and form a BO bond with oxygen in the lattice, thereby improving the structural stability of the positive electrode lithium supplement material. The application of the above-mentioned positive electrode lithium supplement material provided in the present application to lithium ion batteries can improve the electrochemical performance and cycle stability of lithium ion batteries.

[0068] Compared with other ranges, the general formula Li5Fe 1-x B x The range of x in O4 is limited to the specific range of the present application, which can improve the structural stability of the positive electrode lithium supplement material.

[0069] In addition, the above-mentioned preparation method of the present application has a simple process flow and is suitable for large-scale industrial production of materials.

[0070] In a preferred embodiment, the total molar amount ratio of lithium in the lithium source, iron in the iron source, and boron in the boron source to the molar amount of carbon in the carbon source is 6:(0.01-0.08). Compared with other ranges, limiting the molar amount ratio of the two within the above range is conducive to the formation of the carbon coating layer, which can effectively separate the core from the air and inhibit its side reaction with the air, thereby improving the air stability of the positive electrode lithium supplement material, and further reducing the capacity loss of the positive electrode lithium supplement material.

[0071] In order to more effectively form the carbon coating layer and improve the air stability of the positive electrode lithium supplement material, preferably, the ratio of the total molar amount of lithium in the lithium source, iron in the iron source, and boron in the boron source to the volume of the solvent is (0.03~1):(200~400).

[0072] In a preferred embodiment, in step S1, stirring is performed during the mixing process. Stirring is beneficial to improving the mixing uniformity.

[0073] In a preferred embodiment, the stirring speed is 200-2000 rpm and the time is 30-180 min. Stirring at the above speed and time makes the mixing more uniform, which is beneficial to the formation of the carbon coating layer and the core of the positive electrode lithium supplement material, thereby facilitating the air and structural stability of the positive electrode lithium supplement material.

[0074] In order to make the mixing more uniform, preferably, in step S1, the temperature of the mixing process is 25-80°C.

[0075] The present application has no particular limitation on the type of lithium source, and commonly used types in the art may be used. In a preferred embodiment, the lithium source includes but is not limited to one or more of lithium carbonate, lithium hydroxide and lithium oxalate.

[0076] In a preferred embodiment, the iron source includes, but is not limited to, one or more of iron oxide, iron hydroxide, iron sulfate, and iron oxalate. Compared with other types, the above-mentioned iron sources have a wide range of sources and low costs.

[0077] In a preferred embodiment, the boron source includes but is not limited to boric acid and / or boron oxide. Compared with other types, the boron source of the above types has no by-products after the reaction.

[0078] In a preferred embodiment, the carbon source includes but is not limited to polyvinyl alcohol and / or citric acid. Compared with other types, the carbon source of the above types has no by-products after the reaction and is low in price.

[0079] In a preferred embodiment, the solvent is water and / or ethanol.

[0080] The combination of specific types of lithium sources, iron sources, boron sources, carbon sources and solvents is beneficial to reducing costs and simplifying the preparation process on the one hand, and on the other hand, it is beneficial to improving the stability and electrochemical capacity of the positive electrode lithium supplement material, thereby improving the electrochemical performance and cycle stability of lithium-ion batteries.

[0081] In a preferred embodiment, when the carbon source is polyvinyl alcohol, the weight average molecular weight of the polyvinyl alcohol is 10000 to 100000. The use of polyvinyl alcohol is conducive to the formation of the carbon coating layer, effectively separating the core from the air, inhibiting its side reaction with the air, thereby improving the air stability of the positive electrode lithium supplement material.

[0082] In a preferred embodiment, between step S1 and step S2, a process of drying the mixed system is also included to obtain a precursor. The above drying process is conducive to removing the solvent in the mixed system, inhibiting the splashing of the solvent during the subsequent heat treatment, facilitating the subsequent heat treatment, thereby improving the effect of the heat treatment, and further improving the stability of the positive electrode lithium supplement material.

[0083] In order to further remove the solvent in the mixed system and suppress the splashing of the solvent during the subsequent heat treatment, thereby further improving the effect of the heat treatment, preferably, the drying temperature is 80 to 130° C. and the drying time is 12 to 48 hours.

[0084] In a preferred embodiment, the heat treatment in step S2 includes a first calcination process and a second calcination process; preferably, the first calcination process includes calcining at 400-600°C for 3-8h at a heating rate of 3-10°C / min to obtain a first calcined product; the second calcination process includes: calcining at 600-1000°C for 8-20h at a heating rate of 3-10°C / min to obtain a positive electrode lithium supplement material. Compared with other heat treatment methods, the use of the above-mentioned staged calcination process and limiting the process parameters of each stage within the above-mentioned range is conducive to improving the purity of the positive electrode lithium supplement material crystal form, improving the bonding force between the core and the carbon coating, thereby improving the structural stability of the carbon coating, improving the stability of the positive electrode lithium supplement material, and then improving the electrochemical performance and cycle stability of the lithium ion battery.

[0085] In a preferred embodiment, the protective atmosphere includes but is not limited to nitrogen and / or argon. Compared with other protective atmospheres, the protective atmospheres of the above types are easy to obtain and relatively safe to use.

[0086] The third aspect of the present application provides a lithium-ion battery, comprising a positive electrode, a negative electrode, an electrolyte, and a separator disposed between the positive electrode and the negative electrode, wherein the positive electrode comprises the positive electrode lithium supplement material provided in the present application. The positive electrode lithium supplement material provided in the present application has excellent air stability and structural stability, and its application in lithium-ion batteries can significantly improve the electrochemical performance (such as initial charge and discharge efficiency) and cycle stability of lithium-ion batteries.

[0087] The beneficial effects of the present invention will be further described below in conjunction with examples. The reagents, equipment, etc. used in the following examples and comparative examples can be purchased on the market or prepared by existing methods.

[0088] Example 1

[0089] A method for preparing a positive electrode lithium supplement material, comprising:

[0090] (1) lithium hydroxide, iron oxide, boric acid, and citric acid were weighed and set aside according to a molar ratio of lithium element, iron element, boron element, and carbon element of 5:0.99:0.01:0.01, wherein the weight of lithium hydroxide was 6.0 g, and the lithium hydroxide, iron oxide, boric acid, citric acid, and 300 mL of water were mixed under constant temperature stirring at 45° C. to obtain a mixed system containing a precursor, wherein the stirring speed was 600 rpm, and the precursor was dried at 110° C. for 30 h to obtain a precursor;

[0091] (2) The precursor prepared above was transferred to a tubular furnace, and in a nitrogen atmosphere, the temperature was increased to 450°C at a heating rate of 5°C / min and calcined for 5 h, and then the temperature was increased to 600°C at a heating rate of 5°C / min and calcined for 12 h to obtain a positive electrode lithium supplement material.

[0092] The positive electrode lithium supplement material comprises a core and a carbon coating layer arranged on the surface of the core. Figure 1 It can be seen that the core obtained in Example 1 is Li5Fe 0.99 B 0.01 O4, which corresponds to the Li5FeO4 standard card, indicating that the crystal structure has not changed after doping with element B. Figure 2 It can be seen that the positive electrode lithium supplement material is granular, and the D50 of the core in the positive electrode lithium supplement material is 10.1 μm, the thickness of the carbon coating layer is 201 nm, and the coating amount of the carbon coating layer is 1 wt% based on the total weight of the positive electrode lithium supplement material.

[0093] Example 2

[0094] The difference from Example 1 is that the amount of citric acid is changed so that the molar ratio of the lithium element, iron element, boron element and carbon element is 5:0.99:0.01:0.02, and the remaining steps are the same as those in Example 1 to obtain a positive electrode lithium supplement material. The coating amount of the carbon coating layer is 2wt% based on the total weight of the positive electrode lithium supplement material.

[0095] Example 3

[0096] The difference from Example 1 is that the amount of citric acid is changed so that the molar ratio of the lithium element, iron element, boron element and carbon element is 5:0.99:0.01:0.03, and the remaining steps are the same as those in Example 1 to obtain a positive electrode lithium supplement material. The coating amount of the carbon coating layer is 3wt% based on the total weight of the positive electrode lithium supplement material.

[0097] Example 4

[0098] The difference from Example 1 is that the amount of citric acid is changed so that the molar ratio of the lithium element, iron element, boron element and carbon element is 5:0.99:0.01:0.05, and the remaining steps are the same as those in Example 1 to obtain a positive electrode lithium supplement material. The coating amount of the carbon coating layer is 4wt% based on the total weight of the positive electrode lithium supplement material.

[0099] Example 5

[0100] The difference from Example 1 is that the amount of citric acid is changed so that the molar ratio of the lithium element, iron element, boron element and carbon element is 5:0.99:0.01:0.08, and the remaining steps are the same as those in Example 1 to obtain a positive electrode lithium supplement material. The coating amount of the carbon coating layer is 5wt% based on the total weight of the positive electrode lithium supplement material.

[0101] Example 6

[0102] The difference from Example 1 is that the amount of boric acid is changed so that the molar ratio of the lithium element, iron element, boron element and carbon element is 5:0.9:0.1:0.01. The remaining steps are the same as those in Example 1 to obtain a positive electrode lithium supplement material. The core of the positive electrode lithium supplement material is Li5Fe 0.9 B 0.1 O4.

[0103] Example 7

[0104] The difference from Example 1 is that the amount of boric acid is changed so that the molar ratio of the lithium element, iron element, boron element and carbon element is 5:0.95:0.05:0.01. The remaining steps are the same as those in Example 1 to obtain a positive electrode lithium supplement material. The core of the positive electrode lithium supplement material is Li5Fe 0.95 B 0.05 O4.

[0105] Example 8

[0106] The difference from Example 1 is that polyvinyl alcohol is used instead of citric acid, wherein the weight average molecular weight of the polyvinyl alcohol is 10,000, to obtain a positive electrode lithium supplement material.

[0107] Example 9

[0108] The difference from Example 1 is that polyvinyl alcohol is used instead of citric acid, wherein the weight average molecular weight of the polyvinyl alcohol is 100,000, to obtain a positive electrode lithium supplement material.

[0109] Example 10

[0110] The difference from Example 1 is that polyvinyl alcohol is used instead of citric acid, wherein the weight average molecular weight of the polyvinyl alcohol is 150,000, to obtain a positive electrode lithium supplement material.

[0111] Embodiment 11

[0112] The difference from Example 1 is that the temperature is raised to 600°C at a heating rate of 3°C / min and calcined for 3 hours, and then the temperature is raised to 1000°C at a heating rate of 3°C / min and calcined for 8 hours. The remaining steps are the same as Example 1 to obtain a positive electrode lithium supplement material.

[0113] Example 12

[0114] The difference from Example 1 is that the temperature is raised to 400°C at a heating rate of 10°C / min and calcined for 8 hours, and then the temperature is raised to 800°C at a heating rate of 10°C / min and calcined for 20 hours. The remaining steps are the same as Example 1 to obtain a positive electrode lithium supplement material.

[0115] Embodiment 13

[0116] The difference from Example 1 is that the temperature is raised to 500°C at a heating rate of 12°C / min and calcined for 5 hours, and then the temperature is raised to 800°C at a heating rate of 12°C / min and calcined for 15 hours. The remaining steps are the same as Example 1 to obtain a positive electrode lithium supplement material.

[0117] Comparative Example 1

[0118] The difference from Example 1 is that citric acid is not used, and the remaining steps are the same as those of Example 1 to obtain a positive electrode lithium replenishing material, which does not include a carbon coating layer.

[0119] Comparative Example 2

[0120] The difference from Example 1 is that boric acid is not used, and the remaining steps are the same as those of Example 1 to obtain the positive electrode lithium supplement material Li5FeO4.

[0121] Comparative Example 3

[0122] The difference from Example 1 is that the amount of boric acid is changed so that the molar ratio of the lithium element, iron element, boron element and carbon element is 5:0.85:0.15:0.01, and the remaining steps are the same as Example 1 to obtain a positive electrode lithium supplement material.

[0123] Performance Testing:

[0124] (1) Air stability test: The positive electrode lithium replenishing materials prepared in the above-mentioned embodiments and comparative examples of the present application were exposed to air with a relative humidity of 30% for 12 hours to observe whether the color of the positive electrode lithium replenishing materials changed significantly.

[0125] (2) Electrochemical performance and cycle performance test: lithium iron phosphate, the positive electrode lithium supplement material prepared in the embodiment and the comparative example, conductive carbon black and PVDF were weighed in a mass ratio of 93:3:2:2, and the above lithium iron phosphate, positive electrode lithium supplement material, conductive carbon black and PVDF were mixed with NMP evenly, and the positive electrode was obtained after coating and rolling; graphite, conductive carbon black, SBR and CMC were weighed in a mass ratio of 95:2:2:1, and the above graphite, conductive carbon black, SBR and CMC were mixed with deionized water evenly, and the negative electrode was obtained after coating and rolling; the above positive and negative electrodes were assembled into a lithium ion battery and the electrochemical performance and cycle performance test were tested, wherein the electrolyte used 1 mol / L LiPF6 (the solvent was EC:DMC:EMC=1:1:1), and PE was used as the separator; wherein the test conditions are shown in Table 1:

[0126] Table 1

[0127] cycle Starting voltage Cut-off voltage Testing Mechanism First charge OCV 4.3V Constant current charging (1C) First discharge 4.3V 2.0V Constant current discharge (1C)

[0128] First charge and discharge efficiency = first discharge capacity / first charge capacity × 100%;

[0129] Capacity retention rate after 1000 cycles (%) = (discharge capacity after 1000th cycle - discharge capacity at first cycle) / discharge capacity at first cycle × 100%.

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

[0131] Table 2

[0132]

[0133] From the above description, it can be seen that the above-mentioned embodiments of the present invention achieve the following technical effects: the outer carbon coating layer in the positive electrode lithium supplement material provided by the present application can effectively separate the inner core from the air, inhibiting its side reactions with the air, thereby improving the air stability of the positive electrode lithium supplement material, and further reducing the capacity loss of the positive electrode lithium supplement material. The boron element doped in the inner core can occupy the tetrahedral gap position in the lithium ferrite and form a BO bond with the oxygen in the lattice, thereby improving the structural stability of the positive electrode lithium supplement material, and can inhibit the destruction of the structure during the charge and discharge process, reducing the loss of active lithium. Compared with other ranges, the general formula Li5Fe 1-x B x The range of x in O4 is limited to the specific range of the present application, which can improve the structural stability of the positive electrode lithium supplement material.

[0134] In summary, applying the above-mentioned positive electrode lithium supplement material provided in the present application to lithium-ion batteries can improve the electrochemical performance and cycle stability of lithium-ion batteries.

[0135] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A positive electrode lithium supplement material, characterized in that: The positive electrode lithium supplement material comprises a core and a carbon coating layer arranged on the surface of the core, and the core has a general formula: Li5Fe 1-x B x O4, where 0.01≤x≤0.

1.

2. The positive electrode lithium supplement material according to claim 1, characterized in that: The x is selected from 0.01 to 0.

05.

3. The positive electrode lithium supplement material according to claim 1 or 2, characterized in that: The D50 of the inner core is ≤12 μm; and / or the thickness of the carbon coating layer is 100-500 nm.

4. The positive electrode lithium supplement material according to any one of claims 1 to 3, characterized in that: The coating amount of the carbon coating layer is 1 to 8 wt % based on the total weight of the positive electrode lithium supplement material.

5. A method for preparing a positive electrode lithium supplement material according to any one of claims 1 to 4, characterized in that: The preparation method comprises: Step S1, mixing a lithium source, an iron source, a boron source, a carbon source and a solvent to obtain a mixed system containing a precursor; wherein the molar ratio of the lithium element in the lithium source, the iron element in the iron source and the boron element in the boron source is 5:(1-x):x; Step S2, heat-treating the precursor in a protective atmosphere to obtain the positive electrode lithium supplement material.

6. The preparation method according to claim 5, characterized in that: The ratio of the total molar amount of the lithium element in the lithium source, the iron element in the iron source and the boron element in the boron source to the molar amount of the carbon element in the carbon source is 6:(0.01-0.08); and / or, the ratio of the total molar amount of the lithium element in the lithium source, the iron element in the iron source and the boron element in the boron source to the volume of the solvent is (0.03-1):(200-400); Preferably, in step S1, stirring is performed during the mixing process, and more preferably, the stirring speed is 200 to 2000 rpm and the stirring time is 30 to 180 min; Preferably, in step S1, the temperature of the mixing process is 25-80°C.

7. The preparation method according to claim 5 or 6, characterized in that: The lithium source is selected from one or more of lithium carbonate, lithium hydroxide, and lithium oxalate; and / or, the iron source is selected from one or more of iron oxide, iron hydroxide, iron sulfate, and iron oxalate; and / or, the boron source is boric acid and / or boron oxide; and / or, the carbon source is polyvinyl alcohol and / or citric acid; and / or, the solvent is water and / or ethanol; Preferably, when the carbon source is polyvinyl alcohol, the weight average molecular weight of the polyvinyl alcohol is 10,000 to 100,000.

8. The preparation method according to any one of claims 5 to 7, characterized in that: The step between step S1 and step S2 also includes a process of drying the mixed system to obtain the precursor; Preferably, the drying temperature is 80-130° C. and the drying time is 12-48 hours.

9. The preparation method according to any one of claims 5 to 7, characterized in that: The heat treatment in step S2 includes a first calcination process and a second calcination process; preferably, the first calcination process includes calcining at 400-600°C for 3-8h at a heating rate of 3-10°C / min to obtain a first calcined product; The second calcination process comprises: calcining at 600-1000° C. for 8-20 hours at a heating rate of 3-10° C. / min to obtain the positive electrode lithium supplement material; Preferably, the protective atmosphere is selected from nitrogen and / or argon.

10. A lithium ion battery comprising a positive electrode, a negative electrode, an electrolyte and a separator arranged between the positive electrode and the negative electrode, characterized in that: The positive electrode comprises the positive electrode lithium supplement material according to any one of claims 1 to 4.

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