Preparation method of manganese-rich positive electrode precursor, manganese-rich positive electrode precursor and application

Abstract

The invention provides a preparation method of a manganese-rich positive electrode precursor, the manganese-rich positive electrode precursor and application of the manganese-rich positive electrode precursor. The preparation method comprises the following steps: carrying out at least one time of alkali washing treatment on a manganese-rich positive electrode precursor product obtained after a coprecipitation reaction, and then carrying out at least one time of water washing treatment to obtain the manganese-rich positive electrode precursor, wherein an alkali washing solution for the alkali washing treatment comprises a first reducing agent and an alkaline substance, and a water washing solution for the water washing treatment comprises a second reducing agent and water. According to the preparation method provided by the invention, the reducing agent is added in the washing stage, so that impurities such as Na and S can be effectively removed, the content of the impurities is reduced, precipitation of manganese on the surfaces of the manganese-rich positive electrode precursor particles can be effectively inhibited, the reducing agent is not easy to remain in the precursor particles, and new impurities are not introduced to reduce the quality of a precursor product; and no extra treatment cost is caused, so that the electrochemical performance of the manganese-rich positive electrode material is remarkably improved.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium ion batteries and relates to a method for preparing a manganese-rich positive electrode precursor and the manganese-rich positive electrode precursor and application thereof. Background Art

[0002] In the field of lithium-ion battery material preparation, manganese-rich precursor (binary manganese-rich or ternary manganese-rich precursor containing more than 30wt% manganese) is an important positive electrode material precursor. The positive electrode material prepared with it has the advantages of high energy density, high operating voltage and good capacity retention rate. Therefore, it is widely used in electric vehicles, mobile electronic devices and other fields.

[0003] For example, CN111498908A discloses a method for preparing a quasi-spherical manganese-rich ternary precursor, which comprises the following steps: first, nickel sulfate, cobalt sulfate and manganese sulfate are mixed and dissolved to form a nickel-cobalt-manganese sulfate mixed solution, and then the nickel-cobalt-manganese sulfate mixed solution and the precipitant solution are added to a reactor in parallel, and a complexing agent is added in parallel at the same time, and the pH value is controlled to be 6.8-10.0, the reaction temperature is 40-80°C, and the stirring speed is 200-800r / min. After the solution is added dropwise, the suspension is aged in the reactor for 5-20h; after the aging is completed, the suspension is filtered, washed, and finally vacuum dried at 80°C for 10-20h to obtain a quasi-spherical manganese-rich ternary precursor, which lays a good foundation for the preparation of lithium-rich manganese-based positive electrode materials.

[0004] However, during the preparation and storage of manganese-rich precursors, the oxidation and precipitation of manganese elements becomes an important problem. The precipitated manganese oxide may block the diffusion channel of lithium ions in the positive electrode material, increase the internal resistance of the battery, and thus reduce the battery's charge and discharge performance; the oxidation and precipitation of manganese will also cause structural changes in the material, which may lead to micro-short circuits inside the battery, increase the risk of thermal runaway of the battery, and thus cause safety problems; in addition, the oxidation and precipitation of manganese will also destroy the structural integrity of the positive electrode material and reduce the cycle life of the battery.

[0005] In order to solve this problem, researchers have conducted a lot of research work to try to find an effective method to inhibit manganese oxide precipitation. At present, although some methods have been proposed, such as adding stabilizers, surface coating or chemical doping, the effects of these methods are often affected by multiple factors such as temperature, time, type and concentration of additives, coating or doping process, etc., and it is difficult to achieve the desired effect. At the same time, these methods may also introduce impurities, increase preparation costs, and reduce production efficiency.

[0006] For example, CN110963533A discloses a method for preparing a lithium-rich manganese-based positive electrode material precursor, comprising the following steps: step one, raw material selection; step two, filtering and removing impurities; step three, parallel flow reaction; step four, product treatment; step five, sample quality inspection; in the above step one, metal salt solution, ammonia-alkali mixed solution and protective gas are selected as raw materials, wherein manganese salt, nickel salt and cobalt salt are dissolved in deionized water in a certain stoichiometric ratio, an appropriate amount of reducing agent is added, stirred for a certain period of time, a metal salt solution is obtained, and then a certain concentration of sodium hydroxide and ammonia-alkali mixed solution is prepared. Although a reducing agent is added in this document, this method may also introduce impurities, increase preparation costs, and reduce production efficiency.

[0007] Therefore, developing a method to inhibit the oxidation and precipitation of manganese in manganese-rich positive electrode precursors is still a technical problem that needs to be solved urgently. Summary of the invention

[0008] In view of the deficiencies in the prior art, the object of the present invention is to provide a method for preparing a manganese-rich positive electrode precursor, a manganese-rich positive electrode precursor and its application. The preparation method provided by the present invention adds a reducing agent in the washing stage, which can effectively remove impurities such as Na and S and reduce the content of impurities, and can also effectively inhibit the precipitation of manganese on the surface of the manganese-rich positive electrode precursor particles, improve the particle morphology and stability, and the reducing agent is not easy to remain in the precursor particles, and will not introduce new impurities to reduce the quality of the precursor product, nor will it bring additional processing costs, thereby improving the electrochemical properties of the manganese-rich positive electrode material and enhancing the safety performance of the lithium-ion battery.

[0009] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0010] In a first aspect, the present invention provides a method for preparing a manganese-rich positive electrode precursor, the preparation method comprising the following steps:

[0011] The manganese-rich positive electrode precursor product obtained after the coprecipitation reaction is subjected to at least one alkali washing treatment, and then subjected to at least one water washing treatment to obtain the manganese-rich positive electrode precursor;

[0012] The alkaline washing liquid of the alkaline washing treatment includes a first reducing agent and an alkaline substance, and the water washing liquid of the water washing treatment includes a second reducing agent and water.

[0013] It should be noted that the present invention does not specifically limit the material types of the first reductant and the second reductant. The present invention is applicable to all types of reductants that can be used to inhibit the precipitation of manganese oxides. For example, the first reductant and the second reductant each independently include but are not limited to at least one of glucose, oxalic acid, hydrazine hydrate, sodium sulfite, citric acid, hemic acid or D-isohemic acid.

[0014] The preparation method provided by the present invention adds a reducing agent in the washing stage, and adds the reducing agent in both the alkali washing and water washing processes, which can effectively remove impurities such as Na and S and reduce the content of impurities, and can also effectively inhibit the precipitation of manganese oxides on the surface of manganese-rich positive electrode precursor particles, thereby improving the particle morphology and stability. In addition, the reducing agent is not easy to remain in the precursor particles, and no new impurities will be introduced, and no additional processing costs will be brought about, thereby significantly improving the electrochemical performance of the manganese-rich positive electrode material.

[0015] In the present invention, a reducing agent needs to be added during both the alkali washing and water washing processes during the washing treatment process to achieve the purpose of inhibiting the oxidation precipitation of manganese and improving the crystallinity of the material while avoiding the introduction of more impurities, which can significantly improve the quality of the precursor; if the reducing agent is added during the co-precipitation reaction, it is inevitable that the precursor particles will adsorb a certain amount of reducing agent during the growth process, causing the reducing agent substance to remain in the precursor particles, resulting in the introduction of new impurities and reducing the quality of the precursor product, and bringing additional costs for processing the reducing agent substance.

[0016] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. Through the following preferred technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved and realized.

[0017] Preferably, the chemical formula of the manganese-rich positive electrode precursor product is Mn x M 1-x (A) z , 0.3≤x≤0.95, 1≤z≤2, M includes a transition metal element, and A includes a hydroxide ion or a carbonate ion.

[0018] For example, x can be 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9 or 0.95, etc.; z can be 1, 1.5 or 2, etc.; but it is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0019] In the present invention, Mn x M 1-x (A) z The specific type of the M element in the positive electrode precursor material is specially limited. The M element that can be used in combination with manganese as the positive electrode precursor material is applicable to the present invention, including but not limited to at least one of Ni, Co, Fe, Cu or Al.

[0020] Preferably, the number of alkali washing treatments is ≥ 2 times, for example, 2 times, 3 times, 4 times or 5 times.

[0021] Preferably, the number of water washing treatments is ≥ 2 times, for example, 2 times, 3 times, 4 times or 5 times.

[0022] In the present invention, the number of alkali washing treatments and the number of water washing treatments are both ≥ 2 times, which is more conducive to fully removing a small amount of Na / S impurities wrapped in the coprecipitation reaction process, and fully reducing the trace manganese oxides that have precipitated on the particle surface, thereby improving the quality of the precursor product.

[0023] Preferably, the temperatures of the alkali washing treatment and the water washing treatment are independently 10 to 40°C, such as 10°C, 20°C, 30°C or 40°C.

[0024] Preferably, the mass fraction of the first reducing agent in the alkaline washing solution is 0.1-10wt%, for example, 0.1wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt%, 5wt%, 5.5wt%, 6wt%, 6.5wt%, 7wt%, 7.5wt%, 8wt%, 8.5wt%, 9wt%, 9.5wt% or 10wt%, etc.

[0025] In the present invention, the mass fraction of the first reducing agent in the alkaline washing solution is 0.1-10wt%, which can better achieve the beneficial effects of better inhibiting manganese oxidation precipitation and improving material crystallinity at a lower cost.

[0026] Preferably, the mass fraction of the alkaline substance in the alkaline washing solution is 2 to 20wt%, for example, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt%, 16wt%, 17wt%, 18wt%, 19wt% or 20wt%, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0027] In the present invention, the specific substance types of the alkaline substance are all selected according to conventional techniques, and can be selected from at least one of sodium hydroxide, sodium carbonate, sodium bicarbonate, ammonium carbonate or ammonium bicarbonate.

[0028] Preferably, during each alkaline washing process, the volume ratio of the manganese-rich positive electrode precursor product to the alkaline washing solution is V 产物 :V 碱洗液 =1:(1-5), for example, 1:1, 1:2, 1:3, 1:4 or 1:5, etc.

[0029] Preferably, the washing time of each alkali washing treatment is independently 2 to 8 hours, for example, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours or 8 hours.

[0030] Preferably, the mass fraction of the second reducing agent in the water washing liquid is 0.5-15wt%, for example, 0.5wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, 13wt%, 14wt% or 15wt%, etc.

[0031] Preferably, during each water washing process, the volume ratio of the manganese-rich positive electrode precursor product to the water washing liquid is V 产物 :V 水洗液 =1:(1-5), for example, 1:1, 1:2, 1:3, 1:4 or 1:5, etc.

[0032] Preferably, the washing time of each water washing treatment is independently 2 to 8 hours, for example, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours or 8 hours.

[0033] Preferably, the water washing treatment is followed by a drying treatment.

[0034] Preferably, the D50 of the manganese-rich positive electrode precursor is 2 to 15 μm, for example, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm or 15 μm, etc., preferably 4 to 10 μm.

[0035] As a preferred technical solution, the preparation method comprises the following steps:

[0036] The manganese-rich cathode precursor product Mn x M 1-x (A) z At least two alkaline washing treatments are performed, and during each alkaline washing treatment, the volume ratio of the manganese-rich positive electrode precursor product to the alkaline washing solution is V 产物 :V 碱洗液 =1: (1-5), the washing time of each alkali washing treatment is independently 2-8h;

[0037] Then, the water washing treatment is performed at least twice, and during each water washing treatment, the volume ratio of the manganese-rich positive electrode precursor product to the water washing liquid is V 产物 :V 水洗液 =1: (1-5), the washing time of each water washing treatment is independently 2-8 hours, and after the water washing treatment is completed, a drying treatment is performed to obtain the manganese-rich positive electrode precursor with a D50 of 2-15 μm;

[0038] wherein 0.3≤x≤0.95, 1≤z≤2, M comprises a transition metal element, and A comprises a hydroxide ion or a carbonate ion;

[0039] The alkaline washing solution of the alkaline washing comprises a first reducing agent with a mass fraction of 0.1-10wt% and an alkaline substance with a mass fraction of 2-20wt%, and the water washing solution of the water washing comprises a second reducing agent with a mass fraction of 0.5-15wt% and water.

[0040] It should be noted that the preparation method of the coprecipitation reaction of the manganese-rich positive electrode precursor product in the present invention is a conventional technical scheme, that is, the preparation method of the manganese-rich positive electrode precursor material (or the preparation method of the conventional manganese-based positive electrode material) is applicable to the present invention.

[0041] Exemplarily, the present invention provides a method for preparing a manganese-rich positive electrode precursor product, the preparation method comprising the following steps:

[0042] The manganese-rich mixed salt solution (i.e., according to the chemical formula Mn x M 1-x (A) z A mixed salt solution of Mn and M including a specific material ratio of Mn and M), a precipitant solution and a complexing agent solution are added in parallel to a reactor containing a base liquid, and a coprecipitation reaction is carried out under a protective atmosphere. After reaching a target particle size, the reaction is stopped to obtain a manganese-rich positive electrode precursor product to be washed;

[0043] Optionally, the total metal ion concentration in the manganese-rich mixed salt solution is 1 to 3 mol / L, such as 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L or 3 mol / L, etc. The specific type of the salt solution includes but is not limited to at least one of chloride, nitrate, sulfate or acetate, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable;

[0044] Optionally, the mass fraction of the precipitant solution is 20-40wt%, for example, 20wt%, 25wt%, 30wt%, 35wt% or 40wt%, etc., and the precipitant includes but is not limited to at least one of sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate, potassium carbonate or potassium bicarbonate, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable;

[0045] Optionally, the mass fraction of the complexing agent solution is 10-25wt%, such as 10wt%, 15wt%, 20wt% or 25wt%, etc., and the complexing agent includes but is not limited to at least one of ammonium bicarbonate, ammonia water, oxalic acid or disodium ethylenediaminetetraacetate, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable;

[0046] Optionally, the base solution includes water, a complexing agent and a precipitant, and the pH of the base solution is 11.4 to 12.6, such as 11.4, 11.5, 11.6, 11.8, 12, 12.3, 12.5 or 12.6;

[0047] Optionally, the protective atmosphere includes a nitrogen atmosphere or an inert gas atmosphere (such as an argon atmosphere or a helium atmosphere, etc.);

[0048] Optionally, the reaction temperature of the coprecipitation reaction is 40 to 70° C., such as 40° C., 45° C., 50° C., 55° C., 60° C., 65° C. or 70° C., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable;

[0049] Optionally, the pH value of the coprecipitation reaction is 9.2 to 11.4, such as 9.2, 9.5, 9.8, 10, 10.3, 10.5, 10.8, 11, 11.3 or 11.4, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable;

[0050] Optionally, the target particle size is D50 of the manganese-rich positive electrode precursor.

[0051] It is understandable that those skilled in the art can adaptively select and adjust the preparation parameters in the preparation process of the above coprecipitation reaction according to actual needs.

[0052] In a second aspect, the present invention provides a manganese-rich positive electrode precursor, wherein the manganese-rich positive electrode precursor is prepared by the preparation method described in the first aspect.

[0053] In a third aspect, the present invention provides a positive electrode material, which is obtained by mixing and sintering the manganese-rich positive electrode precursor as described in the second aspect with a lithium source.

[0054] The present invention does not impose any special limitation on the specific preparation process of the positive electrode material, and the present invention is applicable to any conventional preparation process that can be known within a reasonable range by those skilled in the art.

[0055] Exemplarily, the present invention provides a method for preparing a positive electrode material:

[0056] The lithium source and the manganese-rich positive electrode precursor are mixed at a total molar ratio of the lithium element in the lithium source to all metal elements in the manganese-rich positive electrode precursor of (1-1.6):1, and after mixing, they are sintered in an oxygen-containing atmosphere (such as an air atmosphere or an oxygen atmosphere) at a sintering temperature of 800-1200° C. and a sintering time of 8-20 hours to obtain the lithium-rich manganese-based positive electrode material;

[0057] Furthermore, the lithium source includes at least one of LiOH, CH3COOLi or Li2CO3.

[0058] In a fourth aspect, the present invention further provides a lithium-ion battery, wherein the lithium-ion battery comprises the positive electrode material as described in the third aspect.

[0059] It should be noted that due to space limitations and to avoid redundancy, the present invention does not list all applicable point values ​​within the above numerical range one by one, but is not limited to the listed values, and other unlisted values ​​within the above numerical range are also applicable.

[0060] Compared with the prior art, the present invention has the following beneficial effects:

[0061] The preparation method provided by the present invention adds a reducing agent in the washing stage, and adds the reducing agent in both the alkali washing and water washing processes, which can effectively remove impurities such as Na and S and reduce the content of impurities, and can also effectively inhibit the precipitation of manganese oxides on the surface of manganese-rich positive electrode precursor particles, thereby improving the particle morphology and stability. In addition, the reducing agent is not easy to remain in the precursor particles, and no new impurities will be introduced, and no additional processing costs will be brought about, thereby significantly improving the electrochemical performance of the manganese-rich positive electrode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Figure 1 This is an SEM image of the manganese-rich positive electrode precursor provided in Example 1.

[0063] Figure 2 This is the SEM image of the manganese-rich positive electrode precursor provided in Comparative Example 1. DETAILED DESCRIPTION

[0064] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0065] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians 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 inclusions.

[0066] In the description of this application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.

[0067] Example 1

[0068] This embodiment provides a method for preparing a manganese-rich positive electrode precursor, and the preparation method is as follows:

[0069] Step S1, according to the molecular formula Ni 0.35 Mn 0.65 (OH)2 prepares a mixed metal salt solution (sulfate solution containing nickel and manganese) with a total metal ion concentration of 2 mol / L; prepares a sodium hydroxide solution (precipitant solution) with a mass fraction of 32 wt%; prepares an ammonia solution with a mass fraction of 16 wt%;

[0070] A reaction bottom liquid with a pH of 12.2 to 12.4 and an ammonia concentration of 6 to 7 g / L is prepared with liquid alkali, concentrated ammonia water and pure water; under the protection of a nitrogen atmosphere, the prepared mixed metal salt solution, sodium hydroxide solution and ammonia solution are added to a reactor containing the bottom liquid at a flow rate of 4 L / h, 1 L / h and 0.32 L / h, respectively, in a uniform and parallel flow manner to perform a coprecipitation reaction; the reaction temperature of the coprecipitation reaction is controlled to be maintained at 58±1°C, the stirring speed is 400 rpm, the pH in the growth stage is maintained at 10.4 to 10.8, and the ammonia concentration is maintained at 6 to 7 g / L; when the particle size D50 reaches 5 μm, the feeding is stopped to obtain a manganese-rich positive electrode precursor product Ni 0.35 Mn 0.65 (OH)2;

[0071] Step S2, preparing an alkaline cleaning solution A according to a mass ratio of sodium hydroxide: sodium carbonate: ascorbic acid: pure water = 10:3:2:85, and preparing a water cleaning solution B according to a mass ratio of citric acid: ascorbic acid: pure water (deionized water) = 2:3:95, which are used as detergents for alkaline cleaning and water cleaning respectively;

[0072] The manganese-rich positive electrode precursor product obtained in step S1 is allowed to stand, the supernatant is extracted and transferred to a scrubber, and three alkaline washing treatments are performed with alkaline washing solution A (the volume ratio of the object to be washed to the alkaline washing solution A is 1:5), and then three water washing treatments are performed with water washing solution B (the volume ratio of the object to be washed to the water washing solution B is 1:5). After the washing treatment is completed, the solid-liquid separation is performed and then transferred to an oven, and dried at 100°C to obtain the manganese-rich positive electrode precursor product.

[0073] Example 2

[0074] This embodiment provides a method for preparing a manganese-rich positive electrode precursor, and the preparation method is as follows:

[0075] Step S1, according to the molecular formula Ni 0.35 Mn 0.65(OH)2 prepares a mixed metal salt solution (sulfate solution containing nickel and manganese) with a total metal ion concentration of 1 mol / L; prepares a sodium hydroxide solution (precipitant solution) with a mass fraction of 20wt%; prepares an ammonia solution with a mass fraction of 10wt%;

[0076] A reaction bottom liquid with a pH of 12.0 to 12.2 and an ammonia concentration of 6 to 7 g / L was prepared with liquid alkali, concentrated ammonia water and pure water; under the protection of a nitrogen atmosphere, the prepared mixed metal salt solution, sodium hydroxide solution and ammonia solution were added to a reactor containing the bottom liquid at flow rates of 4 L / h, 1 L / h and 0.32 L / h, respectively, in a uniform and parallel flow manner to perform a coprecipitation reaction; the reaction temperature of the coprecipitation reaction was controlled to be maintained at 40° C., the stirring speed was 250 rpm, the pH in the growth stage was maintained at 11.0 to 11.3, and the ammonia concentration was maintained at 6 to 7 g / L; when the particle size D50 reached 10 μm, the feeding was stopped to obtain a manganese-rich positive electrode precursor product Ni 0.35 Mn 0.65 (OH)2;

[0077] Step S2, preparing an alkaline washing solution A according to a mass ratio of sodium hydroxide: sodium carbonate: citric acid: pure water = 15:5:5:80, and preparing a water washing solution B according to a mass ratio of citric acid: oxalic acid: pure water = 1:1:95, and using them as detergents for alkaline washing and water washing respectively;

[0078] The manganese-rich positive electrode precursor product obtained in step S1 is allowed to stand, the supernatant is extracted and transferred to a scrubber, and subjected to two alkaline washing treatments with alkaline washing solution A (the volume ratio of the object to be washed to the alkaline washing solution A is 1:1), and then subjected to two water washing treatments with water washing solution B (the volume ratio of the object to be washed to the water washing solution B is 1:1). After the washing treatment is completed, the solid-liquid separation is performed, and the product is transferred to an oven and dried at 100°C to obtain the manganese-rich positive electrode precursor product.

[0079] Example 3

[0080] This embodiment provides a method for preparing a manganese-rich positive electrode precursor, and the preparation method is as follows:

[0081] Step S1, according to the molecular formula Ni 0.35 Mn 0.65 (OH)2 prepares a mixed metal salt solution (sulfate solution containing nickel and manganese) with a total metal ion concentration of 2 mol / L; prepares a sodium hydroxide solution (precipitant solution) with a mass fraction of 32 wt%; prepares an ammonia solution with a mass fraction of 16 wt%;

[0082] A reaction bottom liquid with a pH of 12.2 to 12.4 and an ammonia concentration of 6 to 7 g / L is prepared with liquid alkali, concentrated ammonia water and pure water; under the protection of a nitrogen atmosphere, the prepared mixed metal salt solution, sodium hydroxide solution and ammonia solution are added to a reactor containing the bottom liquid at a flow rate of 4 L / h, 1 L / h and 0.32 L / h, respectively, in a uniform and parallel flow manner to perform a coprecipitation reaction; the reaction temperature of the coprecipitation reaction is controlled to be maintained at 58±1°C, the stirring speed is 400 rpm, the pH in the growth stage is maintained at 10.4 to 10.8, and the ammonia concentration is maintained at 6 to 7 g / L; when the particle size D50 reaches 5 μm, the feeding is stopped to obtain a manganese-rich positive electrode precursor product Ni 0.35 Mn 0.65 (OH)2;

[0083] Step S2, preparing an alkaline washing solution A according to a mass ratio of sodium hydroxide: sodium carbonate: ascorbic acid: pure water = 5:3:10:82, and preparing a water washing solution B according to a mass ratio of citric acid: ascorbic acid: pure water = 5:5:90, and using them as detergents for alkaline washing and water washing respectively;

[0084] The manganese-rich positive electrode precursor product obtained in step S1 is allowed to stand, the supernatant is extracted and transferred to a scrubber, and three alkaline washing treatments are performed with alkaline washing solution A (the volume ratio of the object to be washed to the alkaline washing solution A is 1:3), and then three water washing treatments are performed with water washing solution B (the volume ratio of the object to be washed to the water washing solution B is 1:3). After the washing treatment is completed, the solid-liquid separation is performed, and then the product is transferred to an oven and dried at 100°C to obtain the manganese-rich positive electrode precursor product.

[0085] Example 4

[0086] The difference between this embodiment and embodiment 1 is that the chemical formula of the manganese-rich positive electrode precursor product in this embodiment is Ni 0.3 Co 0.1 Mn 0.6 (OH)2.

[0087] In the preparation method, according to the molecular formula Ni 0.3 Co 0.1 Mn 0.6 (OH)2 prepares a mixed metal salt solution (sulfate solution containing nickel and manganese).

[0088] The rest of the preparation methods and parameters were the same as those in Example 1.

[0089] Example 5

[0090] The difference between this embodiment and embodiment 1 is that in step S2 of this embodiment, alkaline washing solution A is prepared according to the mass ratio of sodium hydroxide: sodium carbonate: ascorbic acid: pure water = 10:3:15:72, that is, the mass fraction of the reducing agent in the alkaline washing solution is adjusted to 15wt%.

[0091] The rest of the preparation methods and parameters were the same as those in Example 1.

[0092] Example 6

[0093] The difference between this embodiment and embodiment 1 is that in step S2 of this embodiment, water washing liquid B is prepared according to the mass ratio of citric acid: ascorbic acid: pure water = 6:9:85, that is, the mass fraction of the reducing agent in the water washing liquid is adjusted to 15wt%.

[0094] The rest of the preparation methods and parameters were the same as those in Example 1.

[0095] Example 7

[0096] The difference between this embodiment and embodiment 1 is that in step S2 of this embodiment, only one alkali washing treatment and one water washing treatment are performed.

[0097] The rest of the preparation methods and parameters were the same as those in Example 1.

[0098] Comparative Example 1

[0099] The difference between this comparative example and Example 1 is that in step S2 of this comparative example, the alkaline washing solution does not contain a reducing agent (ie, the mass fraction of the alkaline substance remains unchanged, and the amount of water added is adjusted), and the water washing solution does not contain a reducing agent (ie, it is pure water).

[0100] The rest of the preparation methods and parameters were the same as those in Example 1.

[0101] Comparative Example 2

[0102] The difference between this comparative example and Example 1 is that in step S2 of this comparative example, the alkaline washing solution does not contain a reducing agent (ie, the mass fraction of the alkaline substance remains unchanged, and the amount of water added is adjusted).

[0103] The rest of the preparation methods and parameters were the same as those in Example 1.

[0104] Comparative Example 3

[0105] The difference between this comparative example and Example 1 is that in step S2 of this comparative example, the water washing liquid does not contain a reducing agent (ie, pure water).

[0106] The rest of the preparation methods and parameters were the same as those in Example 1.

[0107] Comparative Example 4

[0108] The difference between this comparative example and Example 1 is that in this comparative example, a reducing agent solution is added to the base liquid of the coprecipitation reaction in step S1, and the specific mass fraction of the reducing agent solution (ascorbic acid) is 0.5 mol / L;

[0109] In step S2, the alkaline washing liquid does not contain a reducing agent (ie, the mass fraction of the alkaline substance remains unchanged, and the amount of water added is adjusted), and the water washing liquid does not contain a reducing agent (ie, it is pure water).

[0110] The rest of the preparation methods and parameters were the same as those in Example 1.

[0111] from Figure 1 and Figure 2 It can be seen that the small particles on the surface of the manganese-rich positive electrode precursor obtained in Example 1 of the present invention are basically eliminated, which indicates that the manganese oxidation precipitation is significantly suppressed and the particle morphology is also significantly improved; while in Comparative Example 1, a large number of small particles exist on the surface of the manganese-rich positive electrode precursor obtained without adding a reducing agent in the washing stage, which indicates that the phenomenon of manganese oxide precipitates has not been solved.

[0112] Table 1 shows the impurity contents of Na and S in the lithium-rich manganese-based precursors provided by Examples 1-7 and Comparative Examples 1-4.

[0113] Table 1

[0114] Na(ppm) S(ppm) Example 1 40 476 Example 2 47 493 Example 3 43 483 Example 4 44 481 Example 5 42 480 Example 6 43 483 Example 7 78 734 Comparative Example 1 60 538 Comparative Example 2 53 512 Comparative Example 3 51 515 Comparative Example 4 63 579

[0115] [Preparation of positive electrode materials, preparation of batteries and performance testing]

[0116] Preparation of positive electrode material: The manganese-rich positive electrode precursor obtained in the above Examples 1-7 and Comparative Examples 1-4 was uniformly mixed with lithium hydroxide at a molar ratio of 1:1.5, and sintered at 900° C. in an air atmosphere for 15 h to obtain the corresponding lithium-rich manganese-based positive electrode material;

[0117] Battery preparation: The lithium-rich manganese-based positive electrode materials, conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) prepared in Examples 1-7 and Comparative Examples 1-4 were weighed in a mass ratio of 8:1:1 and dissolved in N-methylpyrrolidone (NMP) and mixed evenly; then, the slurry was applied on aluminum foil with an applicator and dried in a vacuum drying oven at 80°C for 8h; finally, the aluminum foil was punched into 1.13 cm 2 The positive electrode is obtained by a circular shape;

[0118] The obtained electrode sheet was used as the positive electrode, the lithium metal sheet was used as the counter electrode, and a porous polypropylene membrane (Celgard2400) was used as a separator to separate the positive electrode and the counter electrode. The composition of the electrolyte was: a mixture of 1M LiPF6 and EC, DMC and EMC (EC:DMC:EMC volume ratio = 1:1:1); CR2032 button batteries were assembled in an argon glove box.

[0119] The performance test of the batteries provided in Examples 1-7 and Comparative Examples 1-4 was conducted under the following test conditions: the test temperature was 25°C, and the battery was charged to a cut-off voltage of 4.8V at a current of 0.33C using a charge and discharge test system, and then charged to a current of 0.05C at a constant voltage, and after standing for 30 minutes, the battery was discharged to 2.0V at a current of 0.33C, and the capacity obtained in this step was the first cycle discharge capacity; the above steps were repeated to record the battery's 100th cycle discharge capacity; the 100th cycle cycle capacity retention rate = 100th cycle discharge capacity / 1st cycle discharge capacity. The test results are shown in Table 2.

[0120] Table 2

[0121]

[0122]

[0123] from Figure 1-Figure 2 From Table 1, we can get:

[0124] From the data results of Examples 1-4, it can be seen that the manganese-rich positive electrode precursor prepared by the preparation method provided by the present invention has a stable structure, and there is basically no manganese oxide particles precipitated on the particle surface, and the microscopic morphology is significantly improved, thereby improving the electrochemical properties of the manganese-rich positive electrode material and enhancing the safety performance of the lithium-ion battery.

[0125] It can be seen from the data results of Example 1 and Example 5 that if the mass fraction of the first reducing agent in the alkaline washing solution is too large, the material cost of purchasing the reducing agent and the post-processing cost of the reducing agent will increase, and a small amount of reducing agent substance will be easily introduced into the precursor particles, resulting in a lower performance improvement effect of the lithium-rich manganese-based positive electrode material.

[0126] It can be seen from the data results of Example 1 and Example 6 that if the mass fraction of the second reducing agent in the water washing solution is too large, the material cost of purchasing the reducing agent and the post-processing cost of the reducing agent will increase, and a small amount of reducing agent substance will be easily introduced into the precursor particles, resulting in a lower performance improvement effect of the lithium-rich manganese-based positive electrode material.

[0127] It can be seen from the data results of Example 1 and Example 7 that the number of alkaline washing and water washing treatments is too small, resulting in excessive residual Na and S impurities, and the performance improvement effect of the prepared lithium-rich manganese-based positive electrode material is relatively low.

[0128] From the data results of Example 1 and Comparative Examples 1-3, it can be seen that the present invention adds a reducing agent during the washing process, and adds a reducing agent during both the alkaline washing and water washing processes, so that the Na and S impurities can be effectively removed while suppressing the precipitation of manganese oxides on the surface of the manganese-rich positive electrode precursor particles, ultimately improving the particle morphology and stability, thereby simultaneously improving the capacity and cycle performance of the lithium-rich manganese-based positive electrode material.

[0129] It can be seen from the data results of Example 1 and Comparative Example 4 that although adding a reducing agent during the co-precipitation reaction can solve the problem of manganese dissolution to a certain extent, it is easy to cause the reducing agent to remain inside the material, resulting in performance deterioration, and failing to improve the capacity and cycle performance of the lithium-rich manganese-based positive electrode material.

[0130] The preparation method provided by the present invention adds a reducing agent in the washing stage, and adds the reducing agent in both the alkali washing and water washing processes, which can effectively remove impurities such as Na and S and reduce the content of impurities, and can also effectively inhibit the precipitation of manganese on the surface of manganese-rich positive electrode precursor particles, thereby improving the particle morphology and stability. The reducing agent is not easy to remain in the precursor particles, and no new impurities will be introduced. At the same time, it also ensures that the content in the lithium-rich manganese-based precursor material is low, and no additional processing cost will be brought about, thereby improving the electrochemical performance of the manganese-rich positive electrode material and enhancing the safety performance of the lithium-ion battery.

[0131] The applicant declares that the above is only a specific implementation mode 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 those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a manganese-rich positive electrode precursor, characterized in that: The preparation method comprises the following steps: The manganese-rich positive electrode precursor product obtained after the coprecipitation reaction is subjected to at least one alkali washing treatment, and then subjected to at least one water washing treatment to obtain the manganese-rich positive electrode precursor; The alkaline washing liquid of the alkaline washing treatment includes a first reducing agent and an alkaline substance, and the water washing liquid of the water washing treatment includes a second reducing agent and water.

2. The preparation method according to claim 1, characterized in that: The chemical formula of the manganese-rich positive electrode precursor product is Mn x M 1-x (A) z , 0.3≤x≤0.95, 1≤z≤2, M includes a transition metal element, and A includes a hydroxide ion or a carbonate ion.

3. The preparation method according to claim 1 or 2, characterized in that: The number of alkali washing treatments is ≥ 2 times; Preferably, the number of water washing treatments is ≥ 2 times; Preferably, the temperatures of the alkali washing treatment and the water washing treatment are independently 10 to 40°C.

4. The preparation method according to any one of claims 1 to 3, characterized in that The mass fraction of the first reducing agent in the alkaline washing solution is 0.1 to 10 wt %; Preferably, the mass fraction of the alkaline substance in the alkaline washing solution is 2 to 20 wt %; Preferably, during each alkaline washing process, the volume ratio of the manganese-rich positive electrode precursor product to the alkaline washing solution is V 产物 :V 碱洗液 =1:(1~5); Preferably, the washing time of each alkali washing treatment is independently 2 to 8 hours.

5. The preparation method according to any one of claims 1 to 4, characterized in that: The mass fraction of the second reducing agent in the water washing liquid is 0.5 to 15 wt %; Preferably, during each water washing process, the volume ratio of the manganese-rich positive electrode precursor product to the water washing liquid is V 产物 :V 水洗液 =1:(1~5); Preferably, the washing time of each water washing treatment is independently 2 to 8 hours.

6. The preparation method according to any one of claims 1 to 5, characterized in that: After the water washing treatment, a drying treatment is performed; Preferably, the D50 of the manganese-rich positive electrode precursor is 2 to 15 μm, preferably 4 to 10 μm.

7. The preparation method according to claim 1, characterized in that: The preparation method comprises the following steps: The manganese-rich cathode precursor product Mn x M 1-x (A) z At least two alkaline washing treatments are performed, and during each alkaline washing treatment, the volume ratio of the manganese-rich positive electrode precursor product to the alkaline washing solution is V 产物 :V 碱洗液 =1: (1-5), the washing time of each alkali washing treatment is independently 2-8h; Then, the water washing treatment is performed at least twice, and during each water washing treatment, the volume ratio of the manganese-rich positive electrode precursor product to the water washing liquid is V 产物 :V 水洗液 =1: (1-5), the washing time of each water washing treatment is independently 2-8 hours, and after the water washing treatment is completed, a drying treatment is performed to obtain the manganese-rich positive electrode precursor with a D50 of 2-15 μm; wherein 0.3≤x≤0.95, 1≤z≤2, M comprises a transition metal element, and A comprises a hydroxide ion or a carbonate ion; The alkaline washing solution of the alkaline washing comprises a first reducing agent with a mass fraction of 0.1-10wt% and an alkaline substance with a mass fraction of 2-20wt%, and the water washing solution of the water washing comprises a second reducing agent with a mass fraction of 0.5-15wt% and water.

8. A manganese-rich positive electrode precursor, characterized in that The manganese-rich positive electrode precursor is prepared by the preparation method according to any one of claims 1 to 7.

9. A positive electrode material, characterized in that: The positive electrode material is obtained by mixing and sintering the manganese-rich positive electrode precursor as claimed in claim 8 with a lithium source.

10. A lithium ion battery, characterized in that: The lithium-ion battery comprises the positive electrode material as claimed in claim 9.

Images