Lithium supplement additive, preparation method thereof, and secondary battery

Abstract

The present application provides a lithium-replenishing additive, a preparation method thereof, and a secondary battery. The lithium-replenishing additive comprises a lithium-rich material core and a coating disposed on the lithium-rich material core. The coating comprises an organophosphorus compound, the organophosphorus compound comprising an organophosphate or an organophosphate salt, and / or the organophosphorus compound comprising an organophosphorus acid or an organophosphorus acid salt. The substituents in the organophosphate or the organophosphate salt, the organophosphorus acid or the organophosphorus acid salt are independently selected from substituted or unsubstituted alkyl groups or silicon-containing groups, and the substituents of the alkyl groups comprise fluorine atoms, hydroxyl groups, carboxyl groups, amino groups, and amide groups. The lithium-replenishing additive not only effectively replenishes lithium in lithium secondary batteries and improves the initial efficiency of the battery, but also has good stability and is not easily reacted in air, which facilitates the production, storage, and transportation of the lithium-replenishing additive.

Description

Technical Field

[0001] The present application relates to the field of secondary batteries, and in particular to a lithium supplement additive, a preparation method thereof, and a secondary battery. Background Art

[0002] During the first charging process of the battery, a surface solid electrolyte film (SEI film) will form on the surface of the positive and negative electrodes. The formation of the SEI film will consume the lithium in the battery and convert the lithium into inactive lithium-containing compounds, thereby causing reversible lithium loss, reducing the first efficiency and reducing the battery discharge capacity.

[0003] In order to compensate for the lithium loss caused by the formation of the SEI film during the first charge, the existing method is to add lithium supplement additives to the positive or negative electrode. However, due to the high activity of existing lithium supplement additives, they easily react with water in the air, resulting in a high residual alkali content on the surface of the lithium supplement additive, reducing the lithium supplement effect and causing battery capacity loss. In addition, the deterioration of the lithium supplement material will also lead to an increase in battery gas production, which is not conducive to the safety performance of the battery. In order to ensure effective lithium supplementation, the existing lithium supplement additives have extremely stringent environmental requirements during use and storage; and in the preparation process, the lithium supplement additives are easily oxidized, making them difficult to synthesize in large quantities, which is not conducive to industrial production. Therefore, it is necessary to provide a new lithium supplement additive and its preparation method to solve the problems of poor stability, poor lithium supplement effect and difficulty in industrial production of existing lithium supplement additives. Summary of the Invention

[0004] In light of this, the present application provides a lithium-supplementing additive that not only effectively replenishes lithium in lithium secondary batteries and improves the initial efficiency of the batteries, but also exhibits excellent stability and is less susceptible to air-induced reactions, facilitating the production, storage, and transportation of the lithium-supplementing additive. The present application also provides a method for preparing the lithium-supplementing additive.

[0005] In a first aspect, the present application provides a lithium-supplementing additive, comprising a lithium-rich material core and a coating layer disposed on the lithium-rich material core, wherein the coating layer comprises an organic phosphorus compound, wherein the organic phosphorus compound comprises an organic phosphoric acid or an organic phosphate thereof having a structural formula as shown in formula (1-1), and / or the organic phosphorus compound comprises an organic hypophosphorous acid or an organic hypophosphite thereof having a structural formula as shown in formula (2-1);

[0006]

[0007] In formula (1-1) and formula (2-1), R1, R2, and R3 are independently selected from substituted or unsubstituted alkyl groups or silicon-containing groups, and the substituents of the substituted alkyl groups include fluorine atoms, hydroxyl groups, carboxyl groups, amino groups, and amide groups.

[0008] In the lithium-supplementing additive of the present application, the lithium-rich material core can make up for the capacity loss of the lithium secondary battery during the first charge and discharge, thereby improving the first charge and discharge efficiency; the organic phosphorus compound in the coating layer can form lattice oxygen through the strong interaction between PO, thereby reducing the loss of lattice oxygen on the surface of the lithium-rich material core and improving the structural stability of the lithium-supplementing additive; and the organic phosphorus compound has good hydrophobic properties, which can reduce the contact between the lithium-rich material core and moisture and effectively isolate the air, thereby inhibiting the lithium-supplementing additive from generating residual alkali, allowing the lithium-supplementing additive to exist stably in the air, which is beneficial to the production, storage and use of the lithium-supplementing additive.

[0009] Optionally, the substituted or unsubstituted alkyl group has 3 to 20 carbon atoms.

[0010] Optionally, the organic phosphorus compound includes one or more of the organic hypophosphorous acid and the organic hypophosphite, and the mass percentage of the organic hypophosphorous acid and / or the organic hypophosphite in the coating layer is greater than or equal to 50%.

[0011] Optionally, the cations in the organic phosphate or the organic hypophosphite include metal ions, ions, ammonium ions or one or more thereof.

[0012] Optionally, the melting point of the organophosphorus compound is greater than or equal to 50°C.

[0013] Optionally, the organophosphorus compound includes one or more of n-hexyl phosphoric acid and its salts, n-dodecyl phosphoric acid and its salts, 1-tetradecyl phosphoric acid and its salts, n-hexadecyl phosphoric acid and its salts, n-octadecyl phosphoric acid and its salts, 11-carboxyundecyl phosphoric acid and its salts, 11-hydroxyundecyl phosphoric acid and its salts, diethyl hypophosphorous acid and its salts, triethyltetradecylphosphine bis(2,4,4-trimethylpentyl) hypophosphorous acid and its salts.

[0014] Optionally, the coating layer includes a first coating layer close to the lithium-rich material core and a second coating layer away from the lithium-rich material core, the first coating layer includes one or more of organic lithium phosphate and organic lithium hypophosphite, the structural formula of the organic lithium phosphate is shown in Formula (3-1) or Formula (3-2), and the structural formula of the organic lithium hypophosphite is shown in Formula (3-3); the second coating layer includes one or more of the organic phosphoric acid, the organic hypophosphorous acid, or the organic phosphate shown in Formula (1-2);

[0015]

[0016] Optionally, the average thickness of the coating layer is 2 nm to 150 nm.

[0017] Optionally, the D of the lithium-rich material core 50The particle size is 0.5μm~30μm.

[0018] Optionally, the mass ratio of the lithium-rich material core to the coating layer is 1:(0.01-0.15).

[0019] Optionally, the lithium-rich material core comprises an average chemical formula of Li x M y O z A lithium supplement material, wherein 0.1<x<10, 0<y<5, 2≤z<10; and the M includes one or more of Mn, Fe, Cr, Co, Ni, Cu, Zn, Mg, Ti, Si, Sn, Ce or Zr.

[0020] Optionally, the lithium-rich material core includes one or more of primary particles of lithium-supplementing material and secondary particles of lithium-supplementing material.

[0021] Optionally, the total residual alkali content of the lithium supplement additive is less than or equal to 1%.

[0022] The lithium-supplementing additive provided in the first aspect of the present application can effectively replenish the loss of lithium ions during the initial charge and discharge process of a lithium secondary battery, thereby improving the initial charge and discharge efficiency of the lithium-ion battery and increasing the battery energy density. In addition, the lithium-supplementing additive has good stability, can exist stably in the air, and has a low amount of residual alkali on the surface, which is conducive to adding it to a lithium secondary battery to achieve lithium replenishment.

[0023] The second aspect of the present application provides a method for preparing a lithium supplement additive, comprising:

[0024] Provides the average chemical formula Li x M y O z A lithium-supplementing material, wherein 0.1<x<10, 0<y<5, 2≤z<10; the M comprises one or more of Mn, Fe, Cr, Co, Ni, Cu, Zn, Mg, Ti, Si, Sn, Ce or Zr; the lithium-supplementing material is mixed with an organic phosphorus compound and then heat-treated to obtain a lithium-supplementing additive; the organic phosphorus compound comprises an organic phosphoric acid or an organic phosphate thereof having a structural formula as shown in formula (1-1), and / or the organic phosphorus compound comprises an organic hypophosphorous acid or an organic hypophosphite thereof having a structural formula as shown in formula (2-1);

[0025]

[0026] In formula (1-1) and formula (2-1), R1, R2, and R3 are independently selected from substituted or unsubstituted alkyl groups or silicon-containing groups, and the substituents of the substituted alkyl groups include fluorine atoms, hydroxyl groups, carboxyl groups, amino groups, and amide groups.

[0027] Optionally, the heat treatment temperature is 50° C. to 300° C., and the heat treatment time is 1 hour to 5 hours.

[0028] Optionally, the mixing of the lithium-supplementing material and the organic phosphorus compound includes one or more of solid-phase mixing and liquid-phase mixing.

[0029] Optionally, the solid phase mixing includes one or more of ball milling and stirring.

[0030] Optionally, the liquid phase mixing includes: mixing the lithium supplementing material, the organophosphorus compound and an organic solvent to form a mixed liquid, and the solvent includes one or more of ethanol, n-hexane, cyclohexane, dichloromethane, ethyl acetate, tetrahydrofuran, and N-methylpyrrolidone.

[0031] Optionally, the mass concentration of the mixed solution is 0.5% to 20%.

[0032] Optionally, the preparation method of the lithium-supplementing material includes: mixing a lithium source and a doping source and sintering them to obtain a lithium-supplementing material, wherein the lithium source includes one or more of lithium hydroxide, lithium carbonate, lithium oxide, lithium acetate, and lithium oxalate; the doping source includes a doping metal element M, and the doping source can be one or more of oxides, hydroxides or salts of the doping metal element M, and the doping metal element M includes one or more of Mn, Fe, Cr, Co, Ni, Cu, Zn, Mg, Ti, Si, Sn, Ce or Zr.

[0033] A third aspect of the present application provides a positive electrode plate, which includes a current collector and an active material layer disposed on the current collector, wherein the active material layer includes the lithium supplement additive as described in the first aspect.

[0034] A fourth aspect of the present application provides a secondary battery comprising the lithium supplement additive as described in the third aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 A schematic structural diagram of a lithium supplement additive provided in one embodiment of the present application;

[0036] Figure 2 A schematic structural diagram of a lithium supplement additive provided in one embodiment of the present application;

[0037] Figure 3 This is a schematic structural diagram of a lithium supplement additive provided in one embodiment of the present application. DETAILED DESCRIPTION

[0038] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0039] The present application embodiment provides a lithium supplement additive for supplementing lithium to the positive electrode of a lithium secondary battery. Figure 1 , Figure 1 This is a schematic structural diagram of a lithium supplement additive provided in one embodiment of the present application. The lithium supplement additive 100 includes a lithium-rich material core 10 and a coating layer 20 disposed on the lithium-rich material core 10, wherein the coating layer includes an organic phosphorus compound.

[0040] In the embodiment of the present application, the lithium-rich material core includes an average chemical formula of Li x M y O z The lithium-rich material comprises one or more of a primary particle of a lithium-rich material and a secondary particle of a lithium-rich material. In some embodiments, the lithium-rich material core is a primary particle of a lithium-rich material, and its structural diagram is as follows: Figure 1 See Figure 2 , Figure 2 This is a schematic structural diagram of a lithium supplement additive provided in one embodiment of the present application. Figure 2 In some embodiments of the present application, the lithium-rich material core is a secondary particle formed by stacking multiple lithium-supplementing materials, and the coating layer is coated on the surface of the secondary particle of the lithium-supplementing material. 50 The particle size is 0.5μm to 30μm, and can further be 0.5μm to 12μm. The D 50 The particle size may be, but is not limited to, 0.5 μm, 1 μm, 3 μm, 5 μm, 8 μm, 10 μm or 12 μm.

[0041] In the present application, the coating layer on the surface of the lithium-rich material core includes an organic phosphorus compound, which includes one or more of organic phosphoric acid, organic phosphate, organic hypophosphorous acid, and organic hypophosphite. Among them, the structural formula of the organic phosphoric acid is shown in formula (1-1), the structural formula of the organic phosphate is shown in formula (1-2) or formula (1-3), the structural formula of the organic hypophosphorous acid is shown in formula (2-1), and the structural formula of the organic hypophosphite is shown in formula (2-2):

[0042]

[0043] In formula (1-1), formula (1-2), formula (1-3), formula (2-1) and formula (2-2), R1, R2, and R3 are independently selected from substituted or unsubstituted alkyl groups or silicon-containing groups, and the substituents of the substituted alkyl groups include fluorine atoms, hydroxyl groups, carboxyl groups, amino groups, and amide groups. M1 + Including metal ions, ions, ammonium ions, and metal ions, for example, lithium ions, sodium ions, aluminum ions, and magnesium ions. In some embodiments, the substituted or unsubstituted alkyl group has 3 to 20 carbon atoms. Controlling the alkyl group's carbon number to 3 to 20 ensures that the organophosphorus compound has good hydrophobicity. The substituted or unsubstituted alkyl group has, but is not limited to, 3, 5, 8, 10, 12, 15, 17, or 20 carbon atoms.

[0044] In the lithium-supplementing additive of the present application, the organophosphorus compound in the coating layer contains hydrophobic functional groups such as alkyl groups and silicon-containing groups. The organophosphorus compound with this structure can improve the moisture resistance of the lithium-supplementing additive and inhibit the penetration of moisture. In addition, the coating layer can also isolate the lithium-rich material core from the outside world, thereby improving the stability of the lithium-supplementing additive in the air, so that the lithium-supplementing additive has an excellent lithium-supplementing effect and reduces the production and storage costs of the lithium-supplementing additive. In addition, the organophosphorus compound can form lattice oxygen through the strong action of PO, reduce the loss of lattice oxygen on the surface of the lithium-supplementing core particles, and prevent the oxygen vacancies formed on the surface from diffusing into the interior of the particles and causing the particle structure to collapse, thereby improving the structural stability of the lithium-supplementing material.

[0045] In some embodiments of the present application, the substituted alkyl group includes one or more of hydroxyl, carboxyl, or amino groups. The hydroxyl, carboxyl, or amino groups in the organophosphorus compound help enhance the interaction between the coating layer and the lithium-rich core, improving the coating effect. In some embodiments of the present application, the substituted alkyl group includes fluorine atoms. The fluorine atoms in the organophosphorus compound can make the coating layer hydrophobic, inhibiting the penetration of water into the lithium-supplementing additive.

[0046] In some embodiments of the present application, the melting point of the organophosphorus compound is greater than or equal to 50°C, and the decomposition temperature of the organophosphorus compound is greater than or equal to 100°C. The organophosphorus compound in the lithium-supplementing additive coating layer of the present application is solid at room temperature, thereby forming a structurally stable solid-phase coating layer with improved storage stability and processing performance.

[0047] In the embodiment of the present application, the organophosphorus compound can also react with the residual alkali on the surface of the lithium-rich material core to reduce the amount of residual alkali, thereby ensuring that the lithium-supplementing additive has a good lithium-supplementing effect. In some embodiments, the organophosphorus compound includes one or more of organophosphoric acid, organophosphorous acid, and an organophosphate having a structural formula as shown in formula (1-2). The organophosphorus compound of the above structure can also form a salt with the residual alkali on the surface of the lithium-rich material core to reduce the amount of residual alkali, so that the lithium-supplementing additive has a good lithium-supplementing effect. Please refer to Figure 3 , Figure 3 This is a schematic structural diagram of a lithium supplement additive provided in one embodiment of the present application. The coating layer 20 on the surface of the lithium-rich material core includes a first coating layer 21 and a second coating layer 22, wherein the first coating layer includes one or more of organic lithium phosphate and organic lithium hypophosphite. The structural formula of the organic lithium phosphate is shown in Formula (3-1) or Formula (3-2), and the structural formula of the organic lithium hypophosphite is shown in Formula (3-3):

[0048]

[0049] The second coating layer includes one or more of an organic phosphoric acid, an organic hypophosphorous acid, and an organic phosphate as shown in formula (1-2). The organic lithium phosphate or the organic hypophosphite in the first coating layer is obtained by reacting the organic phosphoric acid, the organic hypophosphorous acid, and the organic phosphate having the structural formula shown in formula (1-2) with the residual alkali (lithium oxide, lithium hydroxide) on the surface of the lithium-rich material core. The lithium-supplementing material with this structure has a low residual alkali content on the surface, which is beneficial for reducing side reactions between the lithium-supplementing material and the electrolyte and improving battery performance. In some embodiments of the present application, the total residual alkali content of the lithium-supplementing additive is less than or equal to 1%, and further, the total residual alkali content of the lithium-supplementing additive is less than or equal to 0.3%.

[0050] In some embodiments of the present application, the organophosphorus compound includes one or more of organophosphorous acid and organophosphite salts. These organic hypophosphorous acid and organophosphite salts are reducing and can absorb reactive oxygen species generated by the lithium supplement during charging and discharging, inhibiting gassing reactions triggered by the reactive oxygen species and effectively improving battery safety. In some embodiments of the present application, the weight percentage of the organic hypophosphorous acid and / or organophosphite salt in the coating layer is 50% to 100%. Specifically, the weight percentage of the organic hypophosphorous acid and / or organophosphite salt in the coating layer can be, but is not limited to, 50%, 60%, 70%, 80%, 90%, or 100%. That is, when the organophosphorus compound includes organophosphorous acid, the mass percentage of organophosphorous acid in the coating layer is 50% to 100%; when the organophosphorus compound includes organophosphite, the mass percentage of organophosphite in the coating layer is 50% to 100%; when the organophosphorus compound includes organophosphorous acid and organophosphite, the mass percentage of organophosphorous acid and organophosphite in the coating layer is 50% to 100%.

[0051] In some embodiments of the present application, the organophosphorus compound includes one or more of n-hexyl phosphate and its salts, n-dodecyl phosphate and its salts, 1-tetradecyl phosphate and its salts, n-hexadecyl phosphate and its salts, n-octadecyl phosphate and its salts, 11-carboxy undecyl phosphate and its salts, 11-hydroxy undecyl phosphate and its salts, diethyl hypophosphorous acid and its salts, triethyl tetradecyl phosphine bis (2,4,4-trimethylpentyl) hypophosphorous acid and its salts. In some embodiments, the organophosphorus compound includes one or more of diethyl aluminum hypophosphite and triethyl tetradecyl phosphine bis (2,4,4-trimethylpentyl) hypophosphite. The organophosphorus compound in the present application has good stability. When it is used in a battery, the coating layer can also inhibit the side reaction between the electrolyte and the lithium-rich material, thereby ensuring the lithium replenishment performance of the lithium replenishment material.

[0052] In some embodiments of the present application, the average thickness of the coating layer is 2nm to 150nm, and the average thickness of the coating layer can be, but is not limited to, 2nm, 5nm, 10nm, 30nm or 40nm. In some embodiments, the average thickness of the coating layer is 2nm to 40nm. When the coating layer is within the above-mentioned thickness range, it can achieve effective protection of the lithium-rich material core without affecting the kinetic transport of ions and electrons, thereby achieving effective lithium replenishment of the battery. In some embodiments of the present application, the mass ratio of the lithium-rich material core to the coating layer is 1:(0.01 to 0.15), further 1:(0.01 to 0.1), and the mass ratio of the lithium-rich material core to the coating layer can be, but is not limited to, 1:0.01, 1:0.02, 1:0.04, 1:0.06, 1:0.08 or 1:0.1. Controlling the mass ratio of the lithium-rich material core to the coating layer can adjust the thickness of the protective layer, thereby achieving effective protection of the lithium-rich material core by the coating layer; and the lithium ions in the lithium-rich material core have a moderate escape rate, thereby enabling effective lithium replenishment; in addition, the lower mass proportion of the coating layer can also ensure that the lithium replenishment additive has a high lithium replenishment capacity.

[0053] In the lithium-supplement additive provided in the present application, the lithium-rich material core can replenish the lithium ions consumed by the formation of the SEI film during the initial charge and discharge process of the battery, thereby improving the initial charge capacity of the battery. The coating layer can enhance the surface stability of the lithium-supplement material and increase the storage life of the lithium-supplement material. In addition, the coating layer accounts for a low weight proportion in the lithium-supplement material, which enables the lithium-supplement additive to have a higher specific capacity. The surface interface of the lithium-supplement material has hydrophobic and stable properties, and its production and storage do not require a harsh operating environment, which is conducive to large-scale production.

[0054] The present application also provides a method for preparing a lithium supplement additive, comprising the following steps:

[0055] Provides the average chemical formula Lix M y O z A lithium-supplementing material, wherein 0.1<x<10, 0<y<5, 2≤z<10; M comprises one or more of Mn, Fe, Cr, Co, Ni, Cu, Zn, Mg, Ti, Si, Sn, Ce, or Zr; the lithium-supplementing material is mixed with an organic phosphorus compound and then heat-treated to obtain a lithium-supplementing additive. The organic phosphorus compound comprises one or more of organic phosphoric acid, organic phosphate, organic hypophosphorous acid, and organic hypophosphite. The structural formula of the organic phosphoric acid is shown in formula (1-1), the structural formula of the organic phosphate is shown in formula (1-2) or formula (1-3), the structural formula of the organic hypophosphorous acid is shown in formula (2-1), and the structural formula of the organic hypophosphite is shown in formula (2-2):

[0056]

[0057] In formula (1-1), formula (1-2), formula (1-3), formula (2-1) and formula (2-2), R1, R2, and R3 are independently selected from substituted or unsubstituted alkyl groups or silicon-containing groups, and the substituents of the substituted alkyl groups include fluorine atoms, hydroxyl groups, carboxyl groups, amino groups, and amide groups. M1 + Including metal ions, The metal ion may be any of lithium ion, sodium ion, aluminum ion, and magnesium ion.

[0058] In the embodiments of the present application, the mixing of the lithium-replenishing material and the organophosphorus compound can be solid-phase mixing or liquid-phase mixing. During the mixing, the mass ratio of the lithium-replenishing material to the organophosphorus compound is 1:(0.01 to 0.15). In some embodiments of the present application, the solid-phase mixing includes one or more of ball milling and stirring. In some embodiments of the present application, the liquid-phase mixing is to mix the lithium-replenishing material, the organophosphorus compound and the solvent to form a mixed liquid, wherein the solvent is a non-aqueous solvent that does not react with the lithium-replenishing material and can dissolve the organophosphorus compound, and the mass concentration of the mixed liquid is 0.5% to 20%. In some embodiments, the solvent for the liquid-phase mixing includes one or more of ethanol, n-hexane, cyclohexane, dichloromethane, ethyl acetate, tetrahydrofuran, and N-methylpyrrolidone.

[0059] In the preparation method of the lithium supplement additive of the present application, the organophosphorus compound melts at a certain temperature during the heat treatment process and then coats the surface of the lithium supplement material to form a uniform and dense coating layer. In some embodiments of the present application, the heat treatment temperature is 50°C to 300°C, and the heat treatment time is 1h to 5h, wherein the heat treatment temperature can be, but is not limited to, 50°C, 80°C, 100°C, 150°C, 200°C, 250°C or 300°C, and the heat treatment time can be, but is not limited to, 1h, 2h, 3h, 4h or 5h. It should be noted that in the present application, the heat treatment temperature is lower than the decomposition temperature of the organophosphorus compound. For example, when the decomposition temperature of the organophosphorus compound is 250°C, the heat treatment temperature can be 200°C; when the decomposition temperature of the organophosphorus compound is 150°C, the heat treatment temperature can be 100°C.

[0060] In some embodiments of the present application, when the organophosphorus compound is any one of organophosphoric acid, organophosphorous acid, and an organophosphate having a structural formula as shown in formula (1-2), during the heat treatment process, the organophosphorus compound reacts with the residual alkali on the surface of the lithium supplementing material, such as lithium oxide or lithium hydroxide, to generate the corresponding organophosphate or organophosphorous acid lithium, thereby reducing the amount of residual alkali and forming the following: Figure 3 The lithium supplement additive having a first coating layer and a second coating layer structure, wherein the structural formula of the organic lithium phosphate is as shown in formula (3-1) or formula (3-2), and the structural formula of the organic lithium hypophosphite is as shown in formula (3-3):

[0061]

[0062] The residual alkali content on the surface of the lithium-supplementing material with this structure is low, which is beneficial to reducing the side reaction between the lithium-supplementing material and the electrolyte and improving the battery performance.

[0063] In some embodiments of the present application, the preparation of the lithium-supplementing material includes: mixing a lithium source and a doping source and sintering them to obtain a lithium-supplementing material. In an embodiment of the present application, the sintering is carried out in a non-oxidizing atmosphere, and the non-oxidizing atmosphere includes one or more of nitrogen, helium, and argon. In some embodiments of the present application, after the lithium source and the doping source are mixed according to a molar ratio, they are sintered at 250°C-500°C for 4h to 10h, then heated to 700-900°C and sintered for 6h to 24h, and the lithium-supplementing material is obtained after cooling in the furnace. In an embodiment of the present application, the sintering equipment can be any one of a rotary furnace, a rotary furnace, a box furnace, a tubular furnace, a roller kiln, a push plate kiln or a fluidized bed. In some embodiments of the present application, after the sintering is completed, the product is further granulated to obtain secondary particles of the lithium-supplementing material. In some embodiments of the present application, the lithium source includes one or more of lithium hydroxide, lithium carbonate, lithium oxide, lithium acetate, and lithium oxalate, and the doping source includes a doping metal element M. The doping source can be one or more of oxides, hydroxides or salts of the doping metal element M, and the doping metal element M includes one or more of Mn, Fe, Cr, Co, Ni, Cu, Zn, Mg, Ti, Si, Sn, Ce or Zr.

[0064] The preparation method of the lithium supplement additive provided in the present application has a simple process and is convenient to operate. The obtained lithium supplement additive has good stability and is suitable for large-scale production.

[0065] The present application also provides a positive electrode plate, which includes a current collector and an active material layer disposed on the current collector, the active material layer including the lithium supplement additive of the present application. In some embodiments of the present application, the current collector includes any one of copper foil and aluminum foil. In some embodiments, the active material layer includes an electrode active material, a lithium supplement additive, a binder, and a conductive agent. In an embodiment of the present application, 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. In an embodiment of the present application, the conductive agent includes one or more of graphite, carbon black, acetylene black, graphene, carbon fiber, C60, and carbon nanotubes. In an embodiment of the present application, the electrode active material includes one or more of lithium cobaltate, lithium manganate, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadium oxyphosphate, lithium vanadium phosphate fluorophosphate, lithium titanate, lithium nickel cobalt manganate, and lithium nickel cobalt aluminum oxide. In some embodiments of the present application, the preparation process of the positive electrode sheet is: mixing the 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 sheet through steps such as drying, rolling, and die cutting.

[0066] The present application also provides a secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the positive electrode comprises the positive electrode sheet provided herein. The secondary battery provided herein, due to the use of the lithium supplement additive provided herein, exhibits excellent cycle performance and safety, facilitating the application of secondary batteries in various fields.

[0067] The following is a further description of the implementation of this application with reference to a number of examples.

[0068] Example 1

[0069] A lithium-supplementing additive comprises a lithium-rich material core and a coating layer on the surface of the lithium-rich material core, wherein the lithium-rich material core comprises a lithium-supplementing material with an average chemical formula of Li6MnO4, the coating layer comprises tetradecylphosphoric acid, and the mass percentage of the organic phosphorus compound in the lithium-supplementing additive is 4%.

[0070] 1) Preparation of lithium supplement materials

[0071] According to the molar ratio of Li:Mn=6.0:1, a certain amount of lithium oxide and manganese carbonate were weighed and mixed evenly. The mixture was first sintered at 250°C for 5 hours under a nitrogen atmosphere, and then sintered at 750°C for 7 hours under a nitrogen atmosphere. After the tube furnace was cooled naturally, the material was taken out to obtain Li6MnO4 lithium-supplementing material.

[0072] 2) Preparation of lithium supplement additives

[0073] Take 3 g of the lithium supplement material prepared in step 1, add 0.12 g of tetradecyl phosphoric acid, mix well, and heat treat at 250° C. for 2 h under a nitrogen atmosphere to obtain a lithium supplement additive.

[0074] 3) Preparation of lithium secondary batteries

[0075] N-methylpyrrolidone, lithium iron phosphate, lithium supplement additive, Super P and polyvinylidene fluoride were mixed in a mass ratio of 100:93:2:2:3, and ball milled to obtain a positive electrode slurry. The ball milling time was 60 minutes and the speed was set to 30Hz. After homogenization, coating, drying and cutting, the slurry was baked in a vacuum oven at 100°C to remove trace water to obtain a positive electrode sheet.

[0076] The negative electrode slurry is prepared by mixing graphite, a conductive agent Super P, a thickener carboxymethyl cellulose (CMC), and a binder styrene-butadiene rubber (SBR) in deionized water. The mass ratio of graphite, Super P, CMC, and SBR is 95:2:0.5:2.5. The negative electrode slurry is coated on the current collector copper foil and then dried, rolled, and dried again to obtain the negative electrode sheet.

[0077] EC (ethylene carbonate) and DEC (diethyl carbonate) were mixed in a volume ratio of 3:7, and LiPF6 was added to form an electrolyte solution with a LiPF6 concentration of 1 mol / L. The positive electrode sheet, negative electrode sheet, polyethylene (PE) separator, and electrolyte solution were assembled to obtain a lithium secondary battery.

[0078] Example 2

[0079] A lithium-supplementing additive comprises a lithium-rich material core and a coating layer on the surface of the lithium-rich material core, wherein the lithium-rich material core comprises a lithium-supplementing material with an average chemical formula of Li6MnO4, the coating layer comprises sodium tetradecyl phosphate, and the mass percentage of an organic phosphorus compound in the lithium-supplementing additive is 4%.

[0080] The lithium supplement material was prepared by the same method as in Example 1. The preparation method of the lithium supplement additive is as follows:

[0081] Take 3 g of the lithium supplement material prepared in step 1, add 0.12 g of sodium tetradecyl phosphate, mix well, and heat treat at 250° C. for 2 h under a nitrogen atmosphere to obtain a lithium supplement additive.

[0082] A lithium secondary battery was prepared using the same method as in Example 1.

[0083] Example 3

[0084] A lithium-supplementing additive comprises a lithium-rich material core and a coating layer on the surface of the lithium-rich material core, wherein the lithium-rich material core comprises a lithium-supplementing material with an average chemical formula of Li6MnO4, the coating layer comprises diethyl hypophosphorous acid, and the mass percentage of the organic phosphorus compound in the lithium-supplementing additive is 4%.

[0085] The lithium supplement material was prepared by the same method as in Example 1. The preparation method of the lithium supplement additive is as follows:

[0086] Take 3 g of the lithium supplement material prepared in step 1, add 0.12 g of diethyl hypophosphorous acid, mix well, and heat treat at 200° C. for 2 h under a nitrogen atmosphere to obtain a lithium supplement additive.

[0087] A lithium secondary battery was prepared using the same method as in Example 1.

[0088] Example 4

[0089] A lithium-supplementing additive comprises a lithium-rich material core and a coating layer on the surface of the lithium-rich material core, wherein the lithium-rich material core comprises a lithium-supplementing material with an average chemical formula of Li6MnO4, the coating layer comprises diethylaluminum hypophosphite, and the mass percentage of an organic phosphorus compound in the lithium-supplementing additive is 4%.

[0090] The lithium supplement material was prepared by the same method as in Example 1. The preparation method of the lithium supplement additive is as follows:

[0091] Take 3 g of the lithium supplement material prepared in step 1, add 0.12 g of diethylaluminum hypophosphite, mix well, and heat treat at 200° C. for 2 h under a nitrogen atmosphere to obtain a lithium supplement additive.

[0092] A lithium secondary battery was prepared using the same method as in Example 1.

[0093] Example 5

[0094] A lithium-supplementing additive comprises a lithium-rich material core and a coating layer on the surface of the lithium-rich material core, wherein the lithium-rich material core comprises a lithium-supplementing material with an average chemical formula of Li6MnO4, the coating layer comprises tetradecylphosphoric acid and diethyl hypophosphorous acid, and the mass percentage of the organic phosphorus compound in the lithium-supplementing additive is 4%.

[0095] The lithium supplement material was prepared by the same method as in Example 1. The preparation method of the lithium supplement additive is as follows:

[0096] Take 3 g of the lithium supplement material prepared in step 1, add 0.04 g of tetradecyl phosphoric acid and 0.08 g of diethyl hypophosphorous acid, mix well, and heat treat at 220° C. for 2 h under a nitrogen atmosphere to obtain a lithium supplement additive.

[0097] A lithium secondary battery was prepared using the same method as in Example 1.

[0098] Example 6

[0099] A lithium-supplementing additive comprises a lithium-rich material core and a coating layer on the surface of the lithium-rich material core, wherein the lithium-rich material core comprises a lithium-supplementing material with an average chemical formula of Li6MnO4, the coating layer comprises tetradecylphosphoric acid, and the mass percentage of the organic phosphorus compound in the lithium-supplementing additive is 0.5%.

[0100] The lithium supplement material was prepared by the same method as in Example 1. The preparation method of the lithium supplement additive is as follows:

[0101] Take 3 g of the lithium supplement material prepared in step 1, add 0.015 g of tetradecyl phosphoric acid, mix well, and heat treat at 250° C. for 2 h under a nitrogen atmosphere to obtain a lithium supplement additive.

[0102] A lithium secondary battery was prepared using the same method as in Example 1.

[0103] Example 7

[0104] A lithium-supplementing additive comprises a lithium-rich material core and a coating layer on the surface of the lithium-rich material core, wherein the lithium-rich material core comprises a lithium-supplementing material with an average chemical formula of Li6MnO4, the coating layer comprises tetradecylphosphoric acid, and the mass percentage of the organic phosphorus compound in the lithium-supplementing additive is 20%.

[0105] The lithium supplement material was prepared by the same method as in Example 1. The preparation method of the lithium supplement additive is as follows:

[0106] Take 3 g of the lithium supplement material prepared in step 1, add 0.60 of tetradecylphosphoric acid, mix well, and heat treat at 250° C. for 2 h under a nitrogen atmosphere to obtain a lithium supplement additive.

[0107] A lithium secondary battery was prepared using the same method as in Example 1.

[0108] Example 8

[0109] A lithium-supplementing additive comprises a lithium-rich material core and a coating layer on the surface of the lithium-rich material core, wherein the lithium-rich material core comprises a lithium-supplementing material with an average chemical formula of Li6MnO4, the coating layer comprises tetradecylphosphoric acid, and the mass percentage of the organic phosphorus compound in the lithium-supplementing additive is 4%.

[0110] The lithium supplement material was prepared by the same method as in Example 1. The preparation method of the lithium supplement additive is as follows:

[0111] 3 g of the lithium supplement material prepared in step 1 was added with 0.12 g of tetradecylphosphoric acid, mixed evenly, and then heat-treated at 40° C. for 1 h under a nitrogen atmosphere to obtain a lithium supplement additive.

[0112] A lithium secondary battery was prepared using the same method as in Example 1.

[0113] In order to demonstrate the beneficial effects of the embodiments of the present application, the following comparative examples are set up.

[0114] Comparative Example 1

[0115] The difference between Comparative Example 1 and Example 1 is that the Li6MnO4 lithium supplement material is directly added to the battery as a lithium supplement additive, and the battery is prepared using the same method as Example 1.

[0116] Effect embodiment

[0117] 1) The particle size and morphology of the lithium supplement additives of Examples 1-8 were measured using a laser particle size analyzer and a transmission electron microscope to obtain the structural parameters of the lithium supplement additives in Examples 1-8. The specific parameters are shown in Table 1.

[0118] Table 1 Structural parameters of lithium supplement additives in Examples 1-8

[0119] Experimental group <![CDATA[D of the core of the lithium-rich material 50 Particle size (μm)]]> Average thickness of coating layer (nm) Example 1 14.94 9.2 Example 2 13.98 9.5 Example 3 15.32 9.1 Example 4 15.82 8.9 Example 5 14.69 9.1 Example 6 15.05 1.3 Example 7 14.42 44.1 Example 8 15.51 4.2

[0120] As can be seen from Table 1, the thickness of the surface coating layer of the lithium-replenishing additives of Examples 1-5 is moderate, which is conducive to the effective protection of the lithium-rich material core by the coating layer; in the lithium-replenishing additive of Example 6, the content of the organophosphorus compound is too low, resulting in a thin coating layer; in the lithium-replenishing additive of Example 7, the content of the organophosphorus compound is too high, resulting in a thick coating layer; in the preparation process of the lithium-replenishing additive of Example 8, the heat treatment temperature is low, the adhesion performance of the organophosphorus compound to the lithium-rich material core is poor, the uniformity of the formed coating layer is poor, and the average thickness of the coating layer is thin.

[0121] 2) The residual alkali content of the lithium supplement additives of Examples 1-8 and Comparative Example 1 was tested. The specific testing method is as follows: 5 g of the lithium supplement additives of Examples 1-8 and Comparative Example 1 were weighed respectively, and 50 mL of ultrapure water freed of carbon dioxide was added to dissolve in a beaker. The sample was ultrasonically oscillated at an ultrasonic frequency of 5 KHz and a power of 50 W for 5 minutes, and stirred every 1 minute; the mixed solution was filtered into a 100 ml volumetric flask with quantitative paper and the volume was fixed. The above sample solution was taken and potentiometrically titrated with a standard hydrochloric acid solution. The volumes V1 and V2 of the consumed standard hydrochloric acid solution were recorded, where V1 is the volume of the standard HCl solution consumed by titration to the first hop point; and V2 is the volume of the standard HCl solution consumed from the first hop point to the second hop point. Calculate OH according to the following formula - and CO3 2- Residual alkali content:

[0122]

[0123] Total residual alkali content = w(OH - )+w(CO3 2- )

[0124] Wherein, m is the actual mass of the sample, c is the concentration of the HCl standard solution, V3 is the volume of the filtrate, and V4 is the volume of the filtrate after constant volume to 100 mL. Please refer to Table 2 for the test results of the total residual alkali content of the lithium supplement additives of Examples 1-8 and Comparative Example 1.

[0125] Table 2 Summary of the total residual alkali content of lithium supplement additives in Examples 1-8 and Comparative Example 1

[0126] Experimental group Total residual alkali content (%) Example 1 0.259 Example 2 0.424 Example 3 0.274 Example 4 0.391 Example 5 0.269 Example 6 0.833 Example 7 0.082 Example 8 0.293 Comparative Example 1 1.211

[0127] As can be seen from Table 2, the total residual alkali content of the positive electrode lithium replenishing additive containing an organophosphorus compound (Examples 1-8) is significantly lower than that of Comparative Example 1, indicating that the organophosphorus compound coating can effectively reduce the residual alkali of the lithium replenishing additive. For each example, the coating layer of Example 1 includes tetradecyl phosphoric acid, that is, the coating layer includes organophosphoric acid, and the coating layer of Example 2 includes sodium tetradecyl phosphate, that is, the coating layer includes organophosphate. From the comparison of Example 1 and Example 2, it can be seen that compared with the organophosphate coating layer, the use of the organophosphate coating layer can effectively reduce the residual alkali content of the lithium replenishing additive. This is because the organophosphoric acid can also react with the residual alkali on the surface of the lithium-rich material core to reduce the residual alkali content; the coating layer of Example 3 includes diethyl hypophosphorous acid, that is, the coating layer includes organophosphorous acid, and the coating layer of Example 4 includes diethyl aluminum hypophosphite, that is, the coating layer includes organophosphorous acid. From the comparison of Example 1 and Example 2, it can be seen that the use of organic hypophosphorous acid as the coating layer can effectively reduce the residual alkali content of the lithium replenishing additive compared with the organic hypophosphorous acid.

[0128] 3) The electrochemical properties of the lithium secondary batteries of Examples 1-8 and Comparative Example 1 were tested. The test conditions were: the batteries were placed in an environment of 25°C and subjected to charge and discharge cycles using a 0.1C current in the charge and discharge voltage range of 3.0 to 4.4 V. The gas production was measured using a differential electrochemical mass spectrometer under the same conditions. Please refer to Table 3 for the test results.

[0129] Table 3 Performance parameters of batteries of Examples 1-8 and Comparative Example 1

[0130]

[0131] As can be seen from Table 3, the lithium-ion batteries of Examples 1-8 of the present application have excellent electrochemical properties relative to the lithium-ion battery of Comparative Example 1, and the first charge specific capacity, first discharge specific capacity, and first efficiency are significantly higher than those of the lithium-ion battery of Comparative Example 1, indicating that the positive electrode lithium replenishing additive provided by the present application has a more excellent lithium replenishing effect; in addition, it can also be seen from the gas production test results that the lithium-ion batteries of Examples 1-8 of the present application produce less gas, which fully demonstrates that the organic phosphorus compound coating can effectively reduce the loss of lattice oxygen on the surface of the lithium-rich material core, inhibit the gas production caused by the release of active oxygen, and improve the structural stability and safety of the lithium replenishing additive.

[0132] For each embodiment, Examples 3-5 use organic hypophosphorous acid or organic hypophosphite with reducing properties as the coating layer, which is more conducive to absorbing the active oxygen generated by the lithium replenishing additive during the charging and discharging process, and inhibiting the gas production reaction caused by the active oxygen; in Example 6, the content of the organic phosphorus compound is low, and the residual alkali content on the surface of the lithium replenishing additive is high, which reduces the lithium replenishment effect, reduces the first efficiency of the battery, and produces more gas; in Example 7, the content of the organic phosphorus compound is too high. Although it can effectively protect the lithium-rich material core to reduce gas production, the lithium replenishment capacity of the lithium replenishing additive is reduced due to the low mass proportion of the lithium-rich material core; in the preparation process of the lithium replenishing additive in Example 8, the heat treatment temperature is low, the coating layer has poor uniformity and low density, which weakens the protective effect on the lithium-rich material core, the first efficiency of the battery is low, and the gas production is more.

[0133] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A lithium supplement additive, characterized in that: The lithium-supplementing additive includes a lithium-rich material core and a coating layer disposed on the lithium-rich material core, the coating layer includes an organic phosphorus compound, the organic phosphorus compound includes one or more of organic hypophosphorous acid and organic hypophosphite, and the mass percentage of the organic hypophosphorous acid and / or the organic hypophosphite in the coating layer is greater than or equal to 50%; the coating layer includes a first coating layer close to the lithium-rich material core and a second coating layer away from the lithium-rich material core, the first coating layer includes one or more of an organic lithium phosphate as shown in formula (3-1) or formula (3-2) and an organic lithium hypophosphite as shown in formula (3-3); the second coating layer includes one or more of an organic phosphoric acid as shown in formula (1-1), an organic hypophosphorous acid as shown in formula (2-1), and an organic phosphate as shown in formula (1-2); （3-1）， （3-2）， （3-3）， （1-1）， （2-1）， （1-2）， Wherein, R1, R2, and R3 are independently selected from substituted or unsubstituted alkyl groups or silicon-containing groups, and the substituents of the substituted alkyl groups include one or more of fluorine atoms, hydroxyl groups, carboxyl groups, amino groups, and amide groups.

2. The lithium supplement additive according to claim 1, wherein The melting point of the organic phosphorus compound is greater than or equal to 50°C.

3. The lithium supplement additive according to claim 1, wherein The average thickness of the coating layer is 2nm~150nm.

4. The lithium supplement additive according to claim 1, wherein The mass ratio of the lithium-rich material core to the coating layer is 1:(0.01~0.15).

5. The lithium supplement additive according to claim 1, wherein The total residual alkali content of the lithium supplement additive is less than or equal to 1%.

6. The lithium supplement additive according to claim 1, wherein The lithium-rich material core includes an average chemical formula of Li x M y O z A lithium supplement material, wherein 0.1<x<10, 0<y<5, 2≤z<10; and the M includes one or more of Mn, Fe, Cr, Co, Ni, Cu, Zn, Mg, Ti, Si, Sn, Ce or Zr.

7. A method for preparing a lithium supplement additive, characterized in that: include: Provides the average chemical formula Li x M y O z A lithium-supplementing material, wherein 0.1<x<10, 0<y<5, 2≤z<10; the M comprises one or more of Mn, Fe, Cr, Co, Ni, Cu, Zn, Mg, Ti, Si, Sn, Ce or Zr; the lithium-supplementing material is mixed with an organic phosphorus compound and then heat-treated to obtain a lithium-supplementing additive; the lithium-supplementing additive comprises a lithium-rich material core and a coating layer provided on the lithium-rich material core, the coating layer comprises an organic phosphorus compound, the organic phosphorus compound comprises one or more of organic hypophosphorous acid and organic hypophosphite, the organic hypophosphite The mass percentage of phosphoric acid and / or the organic hypophosphite in the coating layer is greater than or equal to 50%; the coating layer includes a first coating layer close to the lithium-rich material core and a second coating layer away from the lithium-rich material core, the first coating layer includes one or more of an organic lithium phosphate as shown in formula (3-1) or formula (3-2) and an organic lithium hypophosphite as shown in formula (3-3); the second coating layer includes one or more of an organic phosphoric acid as shown in formula (1-1), an organic hypophosphorous acid as shown in formula (2-1), and an organic phosphate as shown in formula (1-2); （3-1）， （3-2）， （3-3）， （1-1）， （2-1）， （1-2）， Wherein, R1, R2, and R3 are independently selected from substituted or unsubstituted alkyl groups or silicon-containing groups, and the substituents of the substituted alkyl groups include one or more of fluorine atoms, hydroxyl groups, carboxyl groups, amino groups, and amide groups.

8. A positive electrode plate, characterized in that: The positive electrode sheet includes a current collector and an active material layer disposed on the current collector, and the active material layer includes the lithium supplement additive according to any one of claims 1 to 6.

9. A secondary battery, characterized in that: Comprising the positive electrode sheet as claimed in claim 8.

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