Lithium supplement intermediate as well as preparation method and application thereof

Abstract

The invention provides a lithium supplement intermediate as well as a preparation method and application thereof. The chemical formula of the lithium supplement intermediate is Li < 5 + x > FeO < 4-(m / 2). (OH) m, m is more than or equal to 1.95 and less than or equal to 3.27, and x is more than or equal to 0.05 and less than or equal to 0.55. The lithium supplement agent intermediate provided by the invention comprises a proper amount of hydroxide, when the lithium supplement agent is prepared from the hydroxide, the generation of water vapor in the subsequent sintering process can be regulated and controlled, and the uniformity of material reaction can be optimized, so that the lithium supplement agent with uniform materials and high phase purity is obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium - ion batteries, specifically to a lithium supplement agent, and particularly to an intermediate of a lithium supplement agent, a preparation method thereof, and an application thereof. Background Art

[0002] In the application of lithium - ion batteries, during the first charge - discharge process, the electrolyte decomposes on the surface of the negative electrode, and the products deposit on the surface to form a SEI film. This process consumes the active lithium in the positive electrode, resulting in a decrease in the Coulombic efficiency of the first cycle, and further affecting the capacity and energy density of the lithium battery. To solve this problem, lithium compensation technology has emerged. Among them, Li5FeO4 has received wide attention due to its ultra - high theoretical capacity. During the first charging process, Li5FeO4 can theoretically de - intercalate 4 Li + for compensating for lithium loss in the negative electrode, with a corresponding actual capacity of about 700 mAh / g. Due to its advantages of ultra - high lithium - supplementing capacity, low cost, and environmental friendliness, it has become one of the most promising positive - electrode lithium - supplementing materials.

[0003] However, in the existing preparation process of Li5FeO4, lithium oxide and iron oxide are often used for synthesis by high - temperature solid - state method. However, lithium oxide is expensive and easy to absorb water. At the same time, the synthesized lithium - rich lithium ferrate has a high pH, high residual alkali, and low capacity, making large - scale application difficult. If other lithium salts are used for the synthesis of lithium - rich lithium ferrate, there are problems such as harsh process requirements, impure synthesized materials, and uneven element distribution.

[0004] CN116986890A discloses a preparation method of Li5FeO4 material, which simplifies multiple steps such as atomization - precipitation - thermal decomposition into a continuous, fast, and easily controllable process, avoiding the introduction of impurities and the destruction of the crystal structure during the production process. Not only the particle size and morphology of the product are controllable, but also the composition is uniform, the purity is high, and the production cost is low.

[0005] CN117735616A discloses a mixed - coated Li5FeO4 material, where the core is Li5FeO4, the main material of the mixed - coated layer is a mixed carbon - film material, and the filling - coated material is LiF. This mixed - coated layer can isolate water and CO2 in the air, improve the air stability of the material, and inhibit the problem of increasing surface residual alkali during the processes of material storage, transportation, and pulping.

[0006] CN117219761A discloses a composite lithium - supplementing agent Li5FeO4@Li2CO3 and a preparation method thereof. By co - heating a mixed gas containing CO2 and Li5FeO4 in a tube furnace, a Li2CO3 coating layer with good stability is in - situ generated on the surface of Li5FeO4, which can effectively protect Li5FeO4 from the environment, thereby improving the environmental stability of the material.

[0007] In the prior art, only the effects of water or CO2 in the air on the stability of Li5FeO4 have been concerned. Therefore, only by coating Li5FeO4 to isolate impurities in the air, or the preparation process is complex and it is difficult to achieve large-scale production. Moreover, the influence of water vapor released from raw materials during the preparation process on the structure of the lithium supplement agent obtained by preparation has not been concerned. Therefore, it is difficult to prepare a uniform pure-phase lithium supplement agent.

[0008] Therefore, it is of great significance to provide a technical solution with a simple preparation process and a relatively low residual alkali of the prepared lithium supplement agent. Summary of the Invention

[0009] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide an intermediate of a lithium supplement agent, its preparation method and application. The present invention provides an intermediate of a lithium supplement agent containing an appropriate amount of hydroxide. When preparing the lithium supplement agent with this, it can control the generation of water vapor during the subsequent sintering process, optimize the uniformity of the material reaction, so as to obtain a lithium supplement agent with uniform material, high phase purity, low residual alkali content and high capacity.

[0010] To achieve the purpose of this invention, the following technical solutions are adopted in the present invention:

[0011] In the first aspect, the present invention provides an intermediate of a lithium supplement agent, and the chemical formula of the intermediate of the lithium supplement agent is Li 5+ x FeO 4-(m / 2) ·(OH) m , where 1.95 ≤ m ≤ 3.27 and 0.05 ≤ x ≤ 0.55.

[0012] The chemical formula of the intermediate of the lithium supplement agent provided by the present invention is Li 5+x FeO 4-(m / 2) ·(OH) m , which contains an appropriate amount of hydroxide. During the subsequent preparation of the lithium supplement agent, the hydroxide ions in the hydroxide are released in the form of water vapor. By controlling the content of hydroxide in the intermediate, during the subsequent preparation of the lithium supplement agent, the generation of water vapor during the subsequent sintering process can be controlled, and the uniformity of the material reaction can be optimized, so as to obtain a lithium supplement agent with uniform material and high phase purity. Moreover, the uniform material enables the lithium source and the iron source to react fully, and the residual alkali component in the prepared lithium supplement agent is lower and the pH is also lower.

[0013] If the content of hydroxide in the intermediate is too small, the amount of water vapor released during the subsequent preparation of the lithium supplement agent is less, resulting in too violent and uncontrollable reaction between the iron source and the lithium source, thus forming a lithium supplement agent with a large particle size difference, poor product particle size uniformity, and low capacity. If the content of hydroxide in the intermediate is too high, too much water vapor is released during the subsequent preparation of the lithium supplement agent, which will affect the uniformity of the reaction and it is difficult to obtain a lithium supplement agent with a high purity.

[0014] As a preferred technical solution of the present invention, the lithium supplement intermediate further includes a doping element, and the mass of the doping element accounts for 0.3%-1.0% of the total mass of the lithium supplement intermediate; the doping element includes any one or a combination of at least two of Zr, Al, W, Ti, or Mg.

[0015] In a second aspect, the present invention provides a preparation method of the lithium supplement intermediate as described in the first aspect, and the preparation method includes:

[0016] Mixing a lithium source and an iron source, and performing pre-sintering to obtain the lithium supplement intermediate, and the temperature of the pre-sintering is 100°C - 500°C.

[0017] In the present invention, by performing pre-sintering on the mixture of the lithium source and the iron source, part of the crystal water and hydroxide in the mixture are released in the form of water vapor, so as to control the content of hydroxide in the pre-sintered product, and obtain the Li 5+x FeO 4-(m / 2) ·(OH) m intermediate. When preparing the lithium supplement with this intermediate, the generation of water vapor during the subsequent sintering process can be controlled, and the uniformity of the material reaction can be optimized, so as to obtain a lithium supplement with uniform material, high phase purity, and low residual alkali content.

[0018] As a preferred technical solution of the present invention, the time of the pre-sintering is 2h - 10h.

[0019] Preferably, in the lithium source and the iron source, the Li / Fe molar ratio is 5.05 - 5.55.

[0020] Preferably, the pre-sintering is carried out in an inert atmosphere.

[0021] As a preferred technical solution of the present invention, the preparation method further includes adding an additive when mixing the lithium source and the iron source, and the additive includes any one or a combination of at least two of zirconium oxide, aluminum oxide, tungsten oxide, titanium oxide, or magnesium oxide.

[0022] In a third aspect, the present invention provides a lithium supplement, and the lithium supplement is prepared from the lithium supplement intermediate described in the first aspect; the lithium supplement includes a Li5FeO4 matrix, and a metal oxide coating layer and a carbon coating layer sequentially coated on the surface of the Li5FeO4 matrix.

[0023] In a fourth aspect, the present invention provides a preparation method of the lithium supplement as described in the third aspect, and the preparation method includes:

[0024] Perform a first sintering on the lithium supplement intermediate to obtain a first sintered product; mix the first sintered product and a coating agent, and perform a second sintering to obtain a second sintered product; mix the second sintered product and a carbon source, and perform a third sintering to obtain the lithium supplement agent.

[0025] Preferably, the temperature of the first sintering is 700°C - 850°C, and the time of the first sintering is 5h - 10h.

[0026] Preferably, the temperature of the second sintering is 400°C - 700°C, and the time of the second sintering is 4h - 10h.

[0027] Preferably, the temperature of the third sintering is 420°C - 720°C, and the time of the third sintering is 5h - 10h.

[0028] Preferably, before the first sintering, perform a uniformity treatment on the lithium supplement intermediate.

[0029] Preferably, the coating agent includes any one or a combination of at least two of zirconia, alumina, tungsten oxide, titanium oxide, niobium oxide, or magnesium oxide.

[0030] Preferably, the carbon source includes any one or a combination of at least two of conductive carbon black, carbon nanotubes, citric acid, polyethylene glycol, polytetrafluoroethylene, or glucose.

[0031] In a fifth aspect, the present invention provides a lithium-ion battery, which includes the lithium supplement agent as described in the third aspect.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] (1) The chemical formula of the lithium supplement intermediate provided by the present invention is Li 5+x FeO 4-(m / 2) ·(OH) m , which contains an appropriate amount of hydroxide. By controlling the content of hydroxide in the intermediate, during the subsequent preparation of the lithium supplement agent, the generation of water vapor during the subsequent sintering process can be regulated, the uniformity of the material reaction can be optimized, and thus a lithium supplement agent with uniform material, high phase purity, and low residual alkali content can be obtained.

[0034] (2) By pre-sintering the mixture of the lithium source and the iron source, part of the crystal water and hydroxide in the mixture are released in the form of water vapor, thereby regulating the content of hydroxide in the pre-sintered product to obtain the Li 5+x FeO 4-m / 2 ·(OH) mWhen using this intermediate to prepare a lithium supplement agent, it can control the generation of water vapor during the subsequent sintering process and optimize the uniformity of the material reaction, thereby obtaining a lithium supplement agent with uniform material and high phase purity. Description of the Drawings

[0035] Figure 1 It is the XRD pattern of the lithium supplement agents provided in Example 1 and Comparative Example 1. Detailed Embodiments

[0036] The technical solutions of the present invention will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations to the present invention.

[0037] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in this application are intended to cover non-exclusive inclusion.

[0038] In the description of this application, technical terms such as "first" and "second" are only used to distinguish different objects and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity, specific order or primary-secondary relationship of the indicated technical features. In the description of the embodiments of this application, "a plurality" means more than two, unless otherwise clearly and specifically defined.

[0039] For example, it can be, including but not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0040] In the first specific embodiment, the present invention provides a lithium supplement agent intermediate, and the chemical formula of the lithium supplement agent intermediate is Li 5+x FeO 4-(m / 2) ·(OH) m , where 1.95 ≤ m ≤ 3.27 and 0.05 ≤ x ≤ 0.55.

[0041] The chemical formula of the lithium supplement agent intermediate provided by the present invention is Li 5+x FeO 4-(m / 2) ·(OH) m , which contains an appropriate amount of hydroxide. During the subsequent preparation of the lithium supplement agent, the hydroxide radicals in the hydroxide are released in the form of water vapor. By controlling the content of the hydroxide in the intermediate, when preparing the lithium supplement agent subsequently, it can control the generation of water vapor during the subsequent sintering process, optimize the uniformity of the material reaction, and thus obtain a lithium supplement agent with uniform material and high phase purity.

[0042] In some embodiments, the lithium supplement intermediate further includes a doping element, and the doping element includes any one or a combination of at least two of Zr, Al, W, Ti, Nb, or Mg. Typical but non-limiting combinations include the combination of Zr and Al, the combination of W and Ti, the combination of Mg and Zr, the combination of Al and W, or the combination of Ti and Mg.

[0043] In some embodiments, the mass of the doping element accounts for 0.3% - 1.0% of the total mass of the lithium supplement intermediate. For example, it can be 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 1.0%. This includes but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0044] In a second specific embodiment, the present invention provides a method for preparing the lithium supplement intermediate as described in the first embodiment. The preparation method includes:

[0045] Mixing a lithium source and an iron source, and performing pre-sintering to obtain the lithium supplement intermediate. The temperature of the pre-sintering is 100°C - 500°C.

[0046] In the present invention, by performing pre-sintering on the mixture of the lithium source and the iron source, part of the crystal water and hydroxide in the mixture are released in the form of water vapor, thereby regulating the content of hydroxide in the pre-sintered product to obtain the Li 5+x FeO 4-(m / 2) ·(OH) m intermediate. When preparing the lithium supplement using this intermediate, it is possible to regulate the generation of water vapor during the subsequent sintering process, optimize the uniformity of the material reaction, and thus obtain a lithium supplement with uniform material and high phase purity.

[0047] In the present invention, the temperature of the pre-sintering is 100°C - 500°C. For example, it can be 100°C, 150°C, 200°C, 250°C, 300°C, 350°C, 400°C, 450°C, or 500°C. This includes but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0048] In some embodiments, the lithium source includes any one or a combination of at least two of lithium hydroxide, lithium oxide, lithium carbonate, or lithium nitrate. Typical but non-limiting combinations include the combination of lithium hydroxide and lithium oxide, the combination of lithium carbonate and lithium nitrate, the combination of lithium oxide and lithium carbonate, or the combination of lithium nitrate and lithium hydroxide.

[0049] In some embodiments, the iron source includes iron oxide and / or iron hydroxide.

[0050] In some embodiments, the time of pre-sintering is 2h - 10h. For example, it can be 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h or 10h, including but not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0051] In some embodiments, in the lithium source and iron source, the Li / Fe molar ratio is (5.05 - 5.55):1. For example, it can be 5.05:1, 5.10:1, 5.15:1, 5.20:1, 5.25:1, 5.30:1, 5.35:1, 5.40:1, 5.45:1, 5.50:1 or 5.55:1, including but not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0052] In some embodiments, the pre-sintering is carried out in an inert atmosphere, and the inert atmosphere includes nitrogen and / or inert gas.

[0053] In some embodiments, the preparation method further includes adding an additive when mixing the lithium source and the iron source. The additive includes any one or a combination of at least two of zirconia, alumina, tungsten oxide, titanium oxide, niobium oxide or magnesium oxide. Typical but non-limiting combinations include the combination of zirconia and alumina, the combination of tungsten oxide and titanium oxide, the combination of magnesium oxide and zirconia, the combination of alumina and tungsten oxide or the combination of titanium oxide and magnesium oxide.

[0054] In some embodiments, the preparation method further includes mechanically crushing the lithium supplement intermediate to make the material uniform and improve the reaction activity.

[0055] In the third specific embodiment, the present invention provides a lithium supplement. The lithium supplement is prepared from the lithium supplement intermediate described in the first specific embodiment; the lithium supplement includes a Li5FeO4 matrix, and a metal oxide coating layer and a carbon coating layer that are sequentially coated on the surface of the Li5FeO4 matrix.

[0056] In the present invention, a metal oxide coating layer and a carbon coating layer are sequentially provided on the surface of the Li5FeO4 matrix. Among them, the metal oxide coating layer is first provided on the surface of the Li5FeO4 matrix, which can improve its air stability, and then the carbon coating layer is provided, which is beneficial to further improving the material conductivity.

[0057] In some embodiments, the mass of the metal oxide coating layer accounts for 0.05% - 3.00% of the mass of the Li5FeO4 matrix. For example, it can be 0.05%, 0.20%, 0.50%, 0.80%, 1.00%, 1.20%, 1.50%, 2.00%, 2.50% or 3.00%, including but not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0058] In some embodiments, the mass of the carbon coating layer accounts for 0.1% - 1% of the mass of the Li5FeO4 matrix. For example, it can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9% or 1%, including but not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0059] In the fourth specific embodiment, the present invention provides a preparation method of a lithium supplement agent as described in the third specific embodiment. The preparation method includes:

[0060] Performing a first sintering on the lithium supplement agent intermediate to obtain a first sintered product; mixing the first sintered product and a coating agent, and performing a second sintering to obtain a second sintered product; mixing the second sintered product and a carbon source, and performing a third sintering to obtain the lithium supplement agent.

[0061] In some embodiments, the temperature of the first sintering is 700°C - 850°C. For example, it can be 700°C, 720°C, 740°C, 760°C, 780°C, 800°C, 810°C, 830°C or 850°C, including but not limited to the listed values. Other unlisted values within the numerical range are equally applicable. The time of the first sintering is 5h - 10h. For example, it can be 5h, 6h, 7h, 8h, 9h or 10h, including but not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0062] In some embodiments, the temperature of the second sintering is 400°C - 700°C. For example, it can be 400°C, 450°C, 500°C, 550°C, 600°C, 650°C or 700°C, including but not limited to the listed values. Other unlisted values within the numerical range are equally applicable. The time of the second sintering is 4h - 10h. For example, it can be 4h, 5h, 6h, 7h, 8h, 9h or 10h, including but not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0063] In some embodiments, the temperature of the third sintering is 420°C - 720°C. For example, it can be 420°C, 470°C, 520°C, 570°C, 620°C, 670°C, or 720°C, including but not limited to the listed values. Other unlisted values within the numerical range are equally applicable. The time of the third sintering is 5h - 10h. For example, it can be 5h, 6h, 7h, 8h, 9h, or 10h, including but not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0064] In some embodiments, before the first sintering, the lithium - supplementing agent intermediate is subjected to a homogenization treatment. The purpose is to make the components in the intermediate evenly distributed, further optimize the uniformity of the material reaction, and obtain a lithium - supplementing agent with high phase purity. The methods of homogenization treatment include but are not limited to any one of stirring, ball - milling, pulverizing, or vibrating.

[0065] In some embodiments, the first sintering, the second sintering, and the third sintering are each independently carried out in an inert atmosphere, and the inert atmosphere includes nitrogen and / or inert gas.

[0066] In some embodiments, the coating agent includes any one or a combination of at least two of zirconia, alumina, tungsten oxide, titanium oxide, or magnesia. Typical but non - limiting combinations include the combination of zirconia and alumina, the combination of tungsten oxide and titanium oxide, the combination of magnesia and zirconia, the combination of alumina and tungsten oxide, or the combination of titanium oxide and magnesia.

[0067] In some embodiments, the carbon source includes any one or a combination of at least two of conductive carbon black, carbon nanotubes, polytetrafluoroethylene, or glucose. Typical but non - limiting combinations include the combination of conductive carbon black and carbon nanotubes, the combination of polytetrafluoroethylene and glucose, the combination of carbon nanotubes and polytetrafluoroethylene, or the combination of glucose and conductive carbon black.

[0068] In some embodiments, the preparation method further includes, after the first sintering and before the second sintering, successively subjecting the first - sintered product to mechanical pulverization and air - flow pulverization, aiming to control the particle size, homogenize the material, and improve the reaction activity.

[0069] After the air - flow pulverization, it further includes sieving. The mesh number of the sieve is 200 mesh - 400 mesh. For example, it can be 200 mesh, 250 mesh, 300 mesh, 350 mesh, or 400 mesh, including but not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0070] In some embodiments, the preparation method further includes sieving the second sintered product before the third sintering after the second sintering. The mesh number of the sieve is 200 mesh - 400 mesh, for example, it can be 200 mesh, 250 mesh, 300 mesh, 350 mesh or 400 mesh, including but not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0071] In the fifth specific embodiment, the present invention provides a lithium-ion battery, and the lithium-ion battery includes a lithium supplementing agent as described in the third specific embodiment.

[0072] Example 1

[0073] This example provides a lithium supplementing agent intermediate, and the chemical formula of the lithium supplementing agent intermediate is Li 5.2 FeO 2.71 ·(OH) 2.58 , and the lithium supplementing agent intermediate further includes a doping element Zr with a mass ratio of 0.4 wt%. The preparation method of the lithium supplementing agent intermediate includes:

[0074] Mix lithium hydroxide and nano iron oxide according to a Li / Fe molar ratio of 5.2:1, add zirconia additive, heat to 470 °C under a nitrogen atmosphere, sinter for 10 h, and mechanically crush to prepare the lithium supplementing agent intermediate.

[0075] This example also provides a lithium supplementing agent, and the lithium supplementing agent includes a Li5FeO4 matrix with 0.4 wt% doping element Zr, and an alumina coating layer with a mass fraction of 1.5% and a conductive carbon black coating layer with a mass fraction of 0.5% sequentially coated on the surface of the Li5FeO4 matrix. The preparation method of the lithium supplementing agent includes:

[0076] Under a nitrogen atmosphere, perform the first sintering on the Li 5.2 FeO 2.71 ·(OH) 2.58 lithium supplementing agent intermediate at a temperature of 750 °C for 10 h to obtain a first sintered product; mechanically crush the first sintered product, then perform air flow crushing, sieve through a 300-mesh sieve, mix with alumina, and perform the second sintering at a temperature of 600 °C for 6 h to obtain a second sintered product; sieve the second sintered product through a 300-mesh sieve, mix with conductive carbon black, and perform the third sintering at a temperature of 600 °C for 5 h to obtain the lithium supplementing agent.

[0077] Example 2

[0078] This example provides a lithium supplementing agent intermediate, and the chemical formula of the lithium supplementing agent intermediate is Li 5.05 FeO 3.025 ·(OH) 1.95, the lithium supplement intermediate further includes a doping element Mg with a mass ratio of 0.3 wt%. The preparation method of the lithium supplement intermediate includes:

[0079] Mix 72 wt% lithium oxide, 28 wt% lithium hydroxide monohydrate and nano iron oxide according to a Li / Fe molar ratio of 5.05:1, add magnesium oxide additive, and under an argon atmosphere, heat up to 100 °C, sinter for 2 h, and mechanically crush to obtain the lithium supplement intermediate.

[0080] This embodiment also provides a lithium supplement. The lithium supplement includes a Li5FeO4 matrix with 0.3 wt% doping element Mg, and a 1 wt% zirconia coating layer and a 0.8 wt% carbon nanotube coating layer sequentially coated on the surface of the Li5FeO4 matrix. The preparation method of the lithium supplement includes:

[0081] Under an argon atmosphere, for the Li 5.05 FeO 3.025 ·(OH) 1.95 lithium supplement intermediate, perform the first sintering at a temperature of 700 °C for 5 h to obtain a first sintered product; mechanically crush the first sintered product, then perform air flow crushing, pass through a 200-mesh sieve, mix with zirconia, and perform the second sintering at a temperature of 400 °C for 4 h to obtain a second sintered product; pass the second sintered product through a 250-mesh sieve, mix with carbon nanotubes, and perform the third sintering at a temperature of 420 °C for 7 h to obtain the lithium supplement.

[0082] Example 3

[0083] This embodiment provides a lithium supplement intermediate. The chemical formula of the lithium supplement intermediate is Li 5.55 FeO 2.365 ·(OH) 3.27 , the lithium supplement intermediate further includes a doping element Ti with a mass ratio of 0.8 wt%. The preparation method of the lithium supplement intermediate includes:

[0084] Mix lithium hydroxide and nano iron oxide according to a Li / Fe molar ratio of 5.55:1, add titanium oxide additive, and under a nitrogen atmosphere, heat up to 500 °C, sinter for 10 h, and mechanically crush to obtain the lithium supplement intermediate.

[0085] This embodiment also provides a lithium supplement. The lithium supplement includes a Li5FeO4 matrix with 0.8 wt% doping element Mg, and a 0.7 wt% tungsten oxide coating layer and a 0.6 wt% amorphous carbon coating layer sequentially coated on the surface of the Li5FeO4 matrix. The preparation method of the lithium supplement includes:

[0086] Under a nitrogen atmosphere, for the Li5.55 FeO 2.365 ·(OH) 3.27 The lithium supplement intermediate is subjected to a first sintering at a temperature of 850 °C for 10 h to obtain a first sintered product; the first sintered product is mechanically pulverized, then pneumatically pulverized, passed through a 400-mesh sieve, mixed with zirconium tungsten oxide, and subjected to a second sintering at a temperature of 700 °C for 10 h to obtain a second sintered product; after the second sintered product is passed through a 400-mesh sieve, it is mixed with glucose and subjected to a third sintering at a temperature of 720 °C for 10 h to obtain the lithium supplement agent.

[0087] Example 4

[0088] This example provides a lithium supplement agent. Except that the surface of the 0.4 wt% Zr-doped Li5FeO4 matrix only includes a carbon coating layer, the rest are the same as in Example 1. The preparation method of the lithium supplement agent is the same as that in Example 1 except that alumina is not added during the second sintering process.

[0089] Example 5

[0090] This example provides a lithium supplement agent. Except that the surface of the 0.4 wt% Zr-doped Li5FeO4 matrix only includes an alumina coating layer, the rest are the same as in Example 1. The preparation method of the lithium supplement agent is the same as that in Example 1 except that carbon nanotubes are not added during the third sintering process.

[0091] Example 6

[0092] This example provides a lithium supplement agent. Except that the surface of the 0.4 wt% Zr-doped Li5FeO4 matrix sequentially includes a 0.5 wt% conductive carbon black coating layer and a 1.5 wt% alumina coating layer, the rest are the same as in Example 1. The preparation method of the lithium supplement agent is the same as that in Example 1 except that the third sintering is carried out first and then the second sintering.

[0093] Comparative Example 1

[0094] This comparative example provides a lithium supplement agent, including a Li5FeO4 matrix doped with 0.4 wt% doping element Zr, and a 1.5 wt% alumina coating layer and a 0.5 wt% conductive carbon black coating layer sequentially coated on the surface of the Li5FeO4 matrix. The preparation method of the lithium supplement agent includes:

[0095] (1) Prepare Li5FeO4 doped with 0.4 wt% of doping element Zr. According to the Li / Fe molar ratio of 5.1:1, mix lithium nitrate and nano-iron oxide, add titanium oxide additive, and under a nitrogen atmosphere, heat up to 850 °C and sinter for 18 h, then mechanically crush and further perform air-flow pulverization to prepare Li5FeO4 doped with 0.4 wt% of doping element Zr.

[0096] (2) Mix the Zr-doped Li5FeO4 prepared in step (1) with alumina and sinter at 600 °C for 6 h; after screening the sintered product through a 300-mesh sieve, mix it with conductive carbon black and sinter at 600 °C for 5 h to obtain the lithium supplement agent.

[0097] Comparative Example 2

[0098] This comparative example provides an intermediate of the lithium supplement agent. Except that the chemical formula of the intermediate of the lithium supplement agent is Li 5.2 FeO 3.4 ·(OH) 1.2 , the rest are the same as in Example 1; the preparation method of the intermediate of the lithium supplement agent is the same as in Example 1 except that the pre-sintering temperature is 650 °C and the time is 8 h.

[0099] This comparative example also provides a lithium supplement agent, which is the same as in Example 1 except that it is prepared using the intermediate of the lithium supplement agent provided in this comparative example.

[0100] Comparative Example 3

[0101] This comparative example provides an intermediate of the lithium supplement agent. Except that the chemical formula of the intermediate of the lithium supplement agent is Li 5.2 FeO2·(OH)4, the rest are the same as in Example 1; the preparation method of the intermediate of the lithium supplement agent is the same as in Example 1 except that the pre-sintering temperature is 90 °C and the time is 2 h.

[0102] This comparative example also provides a lithium supplement agent, which is the same as in Example 1 except that it is prepared using the intermediate of the lithium supplement agent provided in this comparative example.

[0103] Performance test:

[0104] Test the pH and residual alkali of the lithium supplement agents prepared in all the above examples and comparative examples, and the test results are shown in Table 1.

[0105] Prepare positive electrode sheets by mixing the lithium supplement agents prepared in all the above examples and comparative examples with PVDF and conductive carbon black according to a mass ratio of 85:5:10, use metallic lithium as the negative electrode, and use a solution of 15 wt% LiPF6 in EC:DEC = 1:1 as the electrolyte to assemble button cells, and test the initial charge capacity of the lithium supplement agent under the conditions of 2.5 V - 4.4 V and 0.1 C.

[0106] The XRD of the lithium supplement agents prepared in Example 1 and Comparative Example 1 was tested, and the test results are shown in Figure 1 .

[0107] Table 1

[0108]

[0109] As Figure 1 shown in the XRD patterns of the lithium supplement agents provided by Example 1 and Comparative Example 1, the lithium supplement agent prepared from the lithium supplement agent intermediate containing an appropriate amount of hydroxide provided by the present invention has a higher phase purity, a residual alkali value as low as 0.38%, and a first charge capacity that can be as high as 747 mAh / g.

[0110] According to the test results of Example 1 and Example 4, if the sintering temperature is too high when preparing the lithium supplement agent intermediate, the content of hydroxide in the prepared lithium supplement agent intermediate is too low. When preparing the lithium supplement agent subsequently, the reaction between iron and lithium salt is too violent, and the reaction process is uncontrollable, resulting in too large a difference in the particle size of Li5FeO4 formed and poor particle size uniformity, resulting in a low capacity.

[0111] Similarly, the test results in Example 1 and Comparative Examples 1 to 3 also prove that when the lithium supplement agent provided by the present invention is not used to further prepare the lithium supplement agent, or when the content of hydroxide in the lithium supplement agent intermediate is not within the range of the lithium supplement agent intermediate provided by the present invention, the generation of water vapor during the subsequent sintering process cannot be effectively regulated, and the uniformity of the material reaction cannot be optimized, thereby affecting the uniformity of the obtained material, and a lithium supplement agent with high phase purity, low residual alkali content and high capacity cannot be obtained.

[0112] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by any person skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A lithium supplement intermediate, characterized in that, The chemical formula of the lithium supplement intermediate is Li 5+x FeO 4-(m / 2) ·(OH) m , where 1.95 ≤ m ≤ 3.27 and 0.05 ≤ x ≤ 0.

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2. The lithium supplement intermediate according to claim 1, wherein The lithium supplement intermediate further includes a doping element; The mass of the doping element accounts for 0.3% - 1.0% of the total mass of the lithium supplement intermediate; The doping element includes any one or a combination of at least two of Zr, Al, W, Ti, Nb, or Mg.

3. A method for preparing the lithium supplement intermediate according to claim 1 or 2, characterized in that, The preparation method includes: Mixing a lithium source and an iron source, and performing pre-sintering in an inert atmosphere to prepare the lithium supplement intermediate; The temperature of the pre-sintering is 100°C - 500°C.

4. The preparation method according to claim 3, characterized in that, The time of the pre-sintering is 2h - 10h; And / or, in the lithium source and the iron source, the Li / Fe molar ratio is 5.05 - 5.

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5. The preparation method according to claim 3, characterized in that, The preparation method further includes adding an additive when mixing the lithium source and the iron source, and the additive includes any one or a combination of at least two of zirconia, alumina, tungsten oxide, titanium oxide, or magnesium oxide.

6. A lithium supplement agent, characterized in that, The lithium supplement is prepared from the lithium supplement intermediate described in claim 1 or 2; The lithium supplement includes a Li5FeO4 matrix, and a metal oxide coating layer and a carbon coating layer sequentially coated on the surface of the Li5FeO4 matrix.

7. A method for preparing a lithium supplement agent as described in claim 6, characterized in that, The preparation method includes: Performing first sintering on the lithium supplement intermediate to obtain a first sintered product; mixing the first sintered product and a coating agent, and performing second sintering to obtain a second sintered product; mixing the second sintered product and a carbon source, and performing third sintering to obtain the lithium supplement.

8. The preparation method according to claim 7, characterized in that, The temperature of the first sintering is 700°C - 850°C, and the time of the first sintering is 5h - 10h; And / or, the temperature of the second sintering is 400°C - 700°C, and the time of the second sintering is 4h - 10h; And / or, the temperature of the third sintering is 420°C - 720°C, and the time of the third sintering is 5h - 10h; And / or, before the first sintering, performing a homogenization treatment on the lithium supplement intermediate.

9. The preparation method according to claim 7, characterized in that, The coating agent includes any one or a combination of at least two of zirconia, alumina, tungsten oxide, titanium oxide, niobium oxide, or magnesium oxide; And / or, the carbon source includes any one or a combination of at least two of conductive carbon black, carbon nanotubes, polyethylene glycol, citric acid, polytetrafluoroethylene, or glucose.

10. A lithium-ion battery, characterized in that, The lithium ion battery includes the lithium supplement described in claim 6.

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