Nickel-manganese binary precursor material with multilayer core-shell structure as well as preparation method and application of nickel-manganese binary precursor material

Abstract

The invention discloses a nickel-manganese binary precursor material with a multilayer core-shell structure as well as a preparation method and application of the nickel-manganese binary precursor material. The core-shell structure of the precursor material comprises an inner core, shell layers, middle layers and an outermost layer from inside to outside, the shell layers and the middle layers are alternately distributed, and the secondary outer layer is the shell layer; wherein the inner core structure is loose, and the shell structure is compact; the middle layer and the outermost layer are the same in structure and are both loose and porous needle-shaped structures. According to the invention, a coprecipitation method is used, and a multi-layer core-shell structure with alternated density and density is formed by different processes in stages during synthesis. The material can effectively solve the problem that a common core-shell structure material is prone to structural stripping and collapse under the high-voltage condition, the stability of the material is improved, the ion transmission efficiency is improved, and the battery capacity and the service life are guaranteed.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion battery positive electrode materials, and in particular to a multi-layer core-shell structured nickel-manganese binary precursor material and a preparation method and application thereof. Background Art

[0002] As a clean and efficient energy storage device, lithium-ion batteries have been widely used in various portable electronic devices and large equipment such as electric vehicles (EVs). As the core of lithium-ion batteries, the positive electrode material determines the capacity and energy density of the battery. Lithium nickel manganese oxide materials can provide higher discharge voltage and energy density, which is crucial to improving the overall performance and endurance of the battery. The core-shell structure of nickel-manganese binary materials can effectively inhibit lattice distortion during cycling and improve lattice oxygen stability, thereby effectively inhibiting the anisotropic strain generated by the continuous lithium insertion and extraction process, improving the reversibility of structural changes, and further improving its rate performance on this basis.

[0003] However, the interface between the primary particles of the ordinary core-shell structure is very prone to microcracks or pulverization under high voltage, which increases the interface resistance and polarization, resulting in many pores inside the secondary spherical particles, large contact area, increased side reactions, and serious gas production. In addition, the conventional core-shell structure has different primary particles from the core and the shell. The primary particles of the core are small and loosely agglomerated. They will migrate outward during sintering, and eventually leave voids inside the positive electrode material. The traditional preparation method of controlling the looseness inside and outside the precursor cannot guarantee the shrinkage rate of the core, resulting in uneven pore size in the end, affecting the power performance of the material. In addition, the internal pores of the hollow material will cause the secondary agglomerated spheres to be unpressure-resistant, and under high voltage or large current charge and discharge conditions, it is easy to peel off and collapse from the grain boundaries, causing the battery capacity to decay significantly during high-temperature cycling.

[0004] Therefore, how to solve the above-mentioned deficiencies in the prior art has become a subject to be studied and solved by the present invention. Summary of the invention

[0005] The purpose of the present invention is to provide a multi-layer core-shell structured nickel-manganese binary precursor material and a preparation method and application thereof.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A multi-layer core-shell structured nickel-manganese binary precursor material has a core-shell structure, which includes a core, a shell, an intermediate layer and an outermost layer from the inside to the outside, and the shell layer and the intermediate layer are alternately distributed, and the second outermost layer is the shell layer; wherein the core structure is loose, and the shell structure is dense; the intermediate layer and the outermost layer have the same structure, both of which are loose and porous needle-like structures.

[0008] According to a further technical solution, the number of the shell layers is greater than or equal to two, and the number of the intermediate layers is greater than or equal to one.

[0009] A further technical solution, the chemical formula of which is Ni x Mn (1-x) (OH)2, wherein 0.2≤x≤0.8; the particle size D50 is 7 to 15 μm; the particle size D50 of the inner core is 1 to 5 μm.

[0010] Furthermore, the present invention also discloses a method for preparing a multilayer core-shell structured nickel-manganese binary precursor material, comprising:

[0011] Step 1, preparing a mixed metal salt solution of nickel and manganese, wherein the sum of the concentrations of nickel ions and manganese ions in the mixed metal salt solution is 1.0 to 2.5 mol / L;

[0012] Prepare sodium hydroxide or potassium hydroxide with a molar ratio concentration of 10 mol / L as a precipitant;

[0013] Prepare ammonia water or ammonium sulfate with a molar concentration of 2 to 2.6 mol / L as a complexing agent;

[0014] Step 2: adding pure water, the complexing agent and the precipitant into the reaction kettle to prepare a bottom liquid, introducing nitrogen or an inert gas into the kettle as protection, wherein the pH value of the bottom liquid is 10.5-12.5, the ammonia concentration in the bottom liquid is 0.05-0.3 mol / L, and the temperature of the bottom liquid is 40-70° C.;

[0015] Step 3, adding the mixed metal salt solution, precipitant and complexing agent described in step 1 into the reaction kettle in parallel, and introducing an oxidant to perform a co-precipitation reaction to prepare the core;

[0016] When the inner core reaches a first particle size, the introduction of the oxidant is stopped to prepare the shell layer;

[0017] When the slurry particle size reaches the second particle size, introducing an oxidant again for micro-oxidation to prepare the intermediate layer;

[0018] When the slurry particle size reaches the third particle size, the introduction of the oxidant is stopped to prepare the second shell layer;

[0019] When the slurry particle size reaches the fourth particle size, an oxidant is introduced to prepare the outermost layer, and finally a nickel-manganese binary precursor material with a multi-layer core-shell structure is obtained.

[0020] In step 3, the flow rate of the oxidant introduced three times is the same.

[0021] According to a further technical solution, in step 2, the inert gas is at least one of helium and argon;

[0022] In step 3, the oxidant is at least one of compressed air, hydrogen peroxide, oxygen, peracetic acid, sodium hypochlorite, and sodium permanganate; and when the oxidant is compressed air, the flow ratio of compressed air to mixed metal salt solution is 1-3:1; when the oxidant is oxygen, the flow ratio of oxygen to mixed metal salt solution is 0.2-0.6:1; when the oxidant is hydrogen peroxide and peracetic acid, the molar ratio of the oxidant to the mixed metal salt solution is 0.1-0.5:1; when the oxidant is sodium hypochlorite, the molar ratio of the oxidant to the mixed metal salt solution is 0.2-0.1; when the oxidant is sodium permanganate, the molar ratio of the oxidant to the mixed metal salt solution is 0.05-0.25.

[0023] According to a further technical solution, in step three, the first particle size is 1-5 μm, the second particle size is 3-7 μm, the third particle size is 6-10 μm, the fourth particle size is 8-12 μm, and the first particle size is less than the second particle size and less than the third particle size and less than the fourth particle size.

[0024] In a further technical solution, in step 3, the coprecipitation reaction temperature is 50-70°C;

[0025] During the preparation of the inner core, the pH value of the reaction process is 12.0 to 12.5; during the preparation of the shell layer and the intermediate layer, the pH value of the reaction process is 10.5 to 12.0.

[0026] A further technical solution is that in step 3, during the preparation stage of the shell layer, the slurry density is controlled to be greater than the slurry density during the preparation stage of the intermediate layer and the core layer;

[0027] In the shell layer preparation stage, the flow rate of the mixed metal salt solution is a first flow rate; in the intermediate layer and the core preparation stage, the flow rate of the mixed metal salt solution is a second flow rate, and the first flow rate is greater than the second flow rate;

[0028] The ammonia concentration in the shell preparation stage is 0.1-0.3 mol / L; the ammonia concentration in the intermediate layer and the core preparation stage is 0.05-0.2 mol / L;

[0029] During the preparation of the inner core, the slurry density is controlled between 0.15 and 0.2 g / ml; during the preparation of the middle layer, the slurry density is controlled between 0.2 and 0.25 g / ml; during the preparation of the shell layer and the outermost layer, the slurry density is controlled between 0.25 and 0.3 g / ml.

[0030] According to a further technical solution, the first flow rate is 15 to 30 L / h, and the second flow rate is 10 to 20 L / h.

[0031] Furthermore, the present invention also discloses a positive electrode material, which is prepared by the multi-layer core-shell structure nickel-manganese binary precursor material, and is used as a multi-layer core-shell structure nickel-manganese binary precursor material.

[0032] The terms “first”, “second”, etc. used in this document do not specifically refer to an order or sequence, nor are they used to limit the present case. They are only used to distinguish components or operations described with the same technical terms.

[0033] The terms “include,” “including,” “have,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0034] The terms used herein generally have the ordinary meanings of each term used in the art, in the context of the present invention, and in the specific context, unless otherwise noted. Certain terms used to describe the present invention will be discussed below or elsewhere in this specification to provide additional guidance to those skilled in the art regarding the description of the present invention.

[0035] The working principle and advantages of the present invention are as follows:

[0036] The present invention has a multi-layer core-shell structure, the core of which is loose and porous, has good rate performance, and can provide high capacity. Its multiple tightly structured shell layers and loose and porous middle layers are alternately distributed to form a multi-layer core-shell structure with alternating density, which can greatly reduce the structural instability during sintering of ordinary core-shell structure materials and the problem of easy collapse during charging and discharging under high voltage and high current conditions. While ensuring the battery capacity and improving the ion transmission efficiency, the battery life can also be extended. In addition, the preparation method described in the present invention does not require additional additives, and the process flow is basically the same as the conventional precursor preparation process. There is no need to add or modify the existing production line, and it is easy to scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Attached Figure 1 This is an electron microscope image of a multilayer core-shell structured nickel-manganese binary precursor prepared in Example 1 of the present invention;

[0038] Attached Figure 2 This is a cross-sectional view of a multi-layer core-shell structured nickel-manganese binary precursor prepared in Example 1 of the present invention;

[0039] Attached Figure 3 It is a cross-sectional view of a conventional non-core-shell structured nickel-manganese binary precursor of Comparative Example 1;

[0040] Attached Figure 4 This is a cross-sectional view of the single-layer core-shell structured nickel-manganese binary precursor of Comparative Example 2. DETAILED DESCRIPTION

[0041] The present invention will be further described below in conjunction with the accompanying drawings and embodiments:

[0042] The present invention will be clearly described below with drawings and detailed descriptions. After understanding the embodiments of the present invention, any person skilled in the art can make changes and modifications based on the techniques taught by the present invention without departing from the spirit and scope of the present invention.

[0043] The terms used herein are only for describing specific embodiments and are not intended to be limiting of the present invention. Singular forms such as "a", "this", "here", "this" and "the" as used herein also include plural forms.

[0044] Example 1

[0045] This embodiment provides a multi-layer core-shell structured nickel-manganese binary precursor material, the multi-layer core-shell precursor material comprising a loose and porous core, an intermediate layer and an outermost layer, and multiple dense shell layers. The preparation method of the multi-layer core-shell structure precursor comprises the following steps:

[0046] S1, the preparation ratio is Ni 0.35 Mn 0.65 The mixed metal salt solution of (OH)2 has a total ion molar concentration of 2 mol / L, sodium hydroxide with a molar concentration of 10 mol / L, and an ammonia solution with a molar concentration of 2.5 mol / L.

[0047] S2. Add 250L of pure water to a 500L reactor, add the sodium hydroxide solution and ammonia solution prepared in step S1, adjust the pH of the bottom solution to 12.0-12.5, and the ammonia concentration to 0.15mol / L. Maintain the temperature at 55±1°C and the stirring speed at 600rpm.

[0048] S3, add the prepared mixed metal salt solution, sodium hydroxide solution, and ammonia solution into the reactor in parallel, with flow rates of 15L / h, 7.5L / h, and 1.5L / h, respectively. At the same time, introduce compressed air for micro-oxidation, with a flow rate of 0.02m 3 / h, and the inner core preparation is completed when the slurry particle size D50 reaches 2.5μm.

[0049] S4. Stop passing compressed air, and introduce nitrogen into the kettle as a protective gas. Adjust the flow rates of sodium hydroxide and ammonia water to control the pH value within the range of 11.6 to 12.0 and the ammonia concentration within the range of 0.2 to 0.3 mol / L. React until the particle size D50 reaches 3.5 μm to complete the preparation of the first shell layer.

[0050] S5. Stop nitrogen flow, introduce compressed air into the reactor, adjust the ammonia concentration to 0.1-0.2 mol / L, and react until the particle size D50 reaches 6 μm to complete the preparation of the intermediate layer.

[0051] S6. Repeat step S4 to react until the slurry particle size D50 reaches 8 μm, thereby completing the preparation of the second shell layer.

[0052] S7, repeat step S5, react until the slurry particle size D50 reaches 10 μm, and stop feeding.

[0053] S8. Centrifuge, wash, dry and sieve the slurry prepared in step S7 to obtain a nickel-manganese binary precursor material with a multi-layer core-shell structure.

[0054] Example 2

[0055] The difference from Example 1 is that the inner core preparation is completed when the particle size of the inner core reaches 4 μm in step S3, the preparation is completed when the particle size of the slurry of the first shell layer reaches 6 μm in step S4, the preparation is completed when the particle size of the intermediate layer slurry reaches 8.5 μm in step S5, the preparation is completed when the particle size of the second shell layer slurry reaches 10.5 μm in step S6, and the particle size of the reaction stopping slurry in step S7 is 12 μm.

[0056] Comparative Example 1

[0057] This comparative example provides a method for preparing a conventional non-core-shell structured nickel-manganese binary precursor material. The method for preparing the nickel-manganese binary precursor comprises the following steps:

[0058] S1, the preparation ratio is Ni 0.35 Mn 0.65 The mixed metal salt solution of (OH)2 has a total ion molar concentration of 2 mol / L, sodium hydroxide with a molar concentration of 10 mol / L, and an ammonia solution with a molar concentration of 2.5 mol / L.

[0059] S2. Add 250L of pure water to a 500L reactor, add the sodium hydroxide solution and ammonia solution prepared in step S1, adjust the pH of the bottom solution to 12.0-12.5, and the ammonia concentration to 0.3mol / L. Maintain the temperature at 55±1°C and the stirring speed at 600rpm.

[0060] S3, add the prepared mixed metal salt solution, sodium hydroxide solution, and ammonia solution into the reactor in parallel, with flow rates of 20 L / h, 8 L / h, and 2 L / h, respectively. At the same time, introduce nitrogen for protection, and complete the first stage of synthesis when the slurry particle size D50 reaches 3.5 μm.

[0061] S4. Adjust the flow rate of sodium hydroxide and ammonia water, control the pH value in the range of 11.4-11.8, and the ammonia concentration in the range of 0.15-0.25 mol / L. React until the particle size D50 reaches 8 μm and then stop the synthesis.

[0062] S5. Centrifuge, wash, dry and sieve the slurry prepared in step S4 to obtain a conventional non-core-shell structured nickel-manganese binary precursor material.

[0063] Comparative Example 2

[0064] This comparative example provides a single core-shell structured nickel-manganese binary precursor material. The preparation method of the core-shell structure precursor comprises the following steps:

[0065] S1, the preparation ratio is Ni 0.35 Mn 0.65 The mixed metal salt solution of (OH)2 has a total ion molar concentration of 2 mol / L, sodium hydroxide with a molar concentration of 10 mol / L, and an ammonia solution with a molar concentration of 2.5 mol / L.

[0066] S2. Add 250L of pure water to a 500L reactor, add the sodium hydroxide solution and ammonia solution prepared in step S1, adjust the pH of the bottom solution to 12.0-12.5, and the ammonia concentration to 0.15mol / L. Maintain the temperature at 55±1°C and the stirring speed at 600rpm.

[0067] S3, add the prepared mixed metal salt solution, sodium hydroxide solution, and ammonia solution into the reactor in parallel, with flow rates of 250ml / min, 125ml / min, and 25ml / min respectively. At the same time, introduce compressed air for micro-oxidation, with a flow rate of 0.02m 3 / h, the slurry particle size D50 reaches 4μm to complete the core preparation.

[0068] S4. Stop passing compressed air, and introduce nitrogen into the kettle as a protective gas. Adjust the flow rates of sodium hydroxide and ammonia water to control the pH value within the range of 11.6 to 12.0, and the ammonia concentration within the range of 0.2 to 0.3 mol / L. React until the particle size D50 reaches 8.5 μm to complete the shell preparation.

[0069] S5. Centrifuge, wash, dry and sieve the slurry prepared in step S4 to obtain a nickel-manganese binary precursor material with a single-layer core-shell structure.

[0070] The precursor materials prepared in the above-mentioned Example 1, Example 2, Comparative Example 1 and Comparative Example 2 were characterized and tested, and the results are shown in Table 1.

[0071] Table 1

[0072] sample Particle size D50(μm) <![CDATA[Bulk density (g / cm 3 )]]> <![CDATA[Specific gravity (m 2 / g)]]> Example 1 10 1.95 21.24 Example 2 12 1.93 20.01 Comparative Example 1 8.0 1.91 13.12 Comparative Example 2 8.5 1.89 15.68

[0073] The core-shell nickel-manganese binary precursor material prepared in the above examples and comparative examples was mixed with lithium hydroxide and sintered to obtain a positive electrode material, which was prepared into a pole piece, and a metal lithium sheet was used as a negative electrode to form a lithium-ion battery. A charge and discharge test was performed for 100 cycles at a voltage range of 2.0 to 4.8 V and a current density of 1C, and the sintering yield was calculated. The test results are shown in Table 2

[0074] Table 2

[0075] sample Sintering yield rate (%) First discharge specific capacity (mAh) Cycle stability (%) Example 1 95.8 270.2 91.3 Example 2 96.1 273.1 90.6 Comparative Example 1 95.2 261.9 90.8 Comparative Example 2 85.3 270.1 85.4

[0076] According to Table 2, the multilayer core-shell structure precursors prepared in Examples 1 and 2 have a higher sintering yield, the problem of sintering collapse of the core-shell structure precursor is improved, and the cycle stability is higher, which can extend the battery life. Since Comparative Example 1 does not have a core-shell structure, the internal and external structures of the particles are relatively consistent, and the internal structure is dense, resulting in a small internal ion transmission distance of the prepared nickel-manganese binary precursor material, and relatively low capacity and rate performance. Since Comparative Example 2 only has a single-layer core-shell structure, the probability of structural collapse during sintering is higher than that of the embodiment, and the sintering yield is reduced.

[0077] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A multilayer core-shell structured nickel-manganese binary precursor material, characterized in that: It has a core-shell structure, which includes a core, a shell, an intermediate layer and an outermost layer from the inside to the outside, and the shell layer and the intermediate layer are alternately distributed, and the second outermost layer is the shell layer; wherein the core structure is loose, and the shell structure is dense; the intermediate layer and the outermost layer have the same structure, both of which are loose and porous needle-like structures.

2. The multilayer core-shell structured nickel-manganese binary precursor material according to claim 1, characterized in that: The number of the shell layers is greater than or equal to two, and the number of the intermediate layers is greater than or equal to one.

3. A multi-layer core-shell structured nickel-manganese binary precursor material according to claim 1 or 2, characterized in that: Its chemical formula is Ni x Mn (1-x) (OH)2, wherein 0.2≤x≤0.8; the particle size D50 is 7~15μm; the particle size D50 of the inner core is 1~5μm.

4. A method for preparing a multilayer core-shell structured nickel-manganese binary precursor material, characterized in that: Used to prepare a multi-layer core-shell structured nickel-manganese binary precursor material as described in any one of claims 1 to 3, the preparation method comprising: Step 1, preparing a mixed metal salt solution of nickel and manganese, wherein the sum of the concentrations of nickel ions and manganese ions in the mixed metal salt solution is 1.0-2.5 mol / L; Prepare sodium hydroxide or potassium hydroxide with a molar concentration of 10 mol / L as a precipitant; Prepare ammonia water or ammonium sulfate with a molar concentration of 2-2.6 mol / L as a complexing agent; Step 2: adding pure water, the complexing agent and the precipitant into the reaction kettle to prepare a bottom liquid, introducing nitrogen or inert gas into the kettle as protection, wherein the pH value of the bottom liquid is 10.5-12.5, the ammonia concentration in the bottom liquid is 0.05-0.3 mol / L, and the temperature of the bottom liquid is 40-70°C; Step 3, adding the mixed metal salt solution, precipitant and complexing agent described in step 1 into the reaction kettle in parallel, and introducing an oxidant to perform a co-precipitation reaction to prepare the core; When the inner core reaches a first particle size, the introduction of the oxidant is stopped to prepare the shell layer; When the slurry particle size reaches the second particle size, introducing an oxidant again for micro-oxidation to prepare the intermediate layer; When the slurry particle size reaches the third particle size, the introduction of the oxidant is stopped to prepare the second shell layer; When the slurry particle size reaches the fourth particle size, an oxidant is introduced to prepare the outermost layer, and finally a nickel-manganese binary precursor material with a multi-layer core-shell structure is obtained.

5. The method for preparing a multi-layer core-shell structured nickel-manganese binary precursor material according to claim 4, characterized in that: In step 2, the inert gas is at least one of helium and argon; In step 3, the oxidant is at least one of compressed air, hydrogen peroxide, oxygen, peracetic acid, sodium hypochlorite, and sodium permanganate; and when the oxidant is compressed air, the flow ratio of compressed air to mixed metal salt solution is 1-3:1; when the oxidant is oxygen, the flow ratio of oxygen to mixed metal salt solution is 0.2-0.6:1; when the oxidant is hydrogen peroxide and peracetic acid, the molar ratio of the oxidant to the mixed metal salt solution is 0.1-0.5:1; when the oxidant is sodium hypochlorite, the molar ratio of the oxidant to the mixed metal salt solution is 0.2-0.1; when the oxidant is sodium permanganate, the molar ratio of the oxidant to the mixed metal salt solution is 0.05-0.

25.

6. The method for preparing a multi-layer core-shell structured nickel-manganese binary precursor material according to claim 4, characterized in that: In step three, the first particle size is 1-5 μm, the second particle size is 3-7 μm, the third particle size is 6-10 μm, the fourth particle size is 8-12 μm, and the first particle size is less than the second particle size and less than the third particle size and less than the fourth particle size.

7. The method for preparing a multi-layer core-shell structured nickel-manganese binary precursor material according to claim 4, characterized in that: In step 3, the coprecipitation reaction temperature is 50-70° C.; During the preparation of the inner core, the pH value of the reaction process is 12.0-12.5; during the preparation of the shell layer and the intermediate layer, the pH value of the reaction process is 10.5-12.

0.

8. The method for preparing a multi-layer core-shell structured nickel-manganese binary precursor material according to claim 4, characterized in that: In step 3, during the preparation of the shell layer, the slurry density is controlled to be greater than the slurry density during the preparation of the middle layer and the core layer; In the shell preparation stage, the flow rate of the mixed metal salt solution is a first flow rate; During the preparation of the intermediate layer and the inner core, the flow rate of the mixed metal salt solution is a second flow rate, and the first flow rate is greater than the second flow rate; The ammonia concentration in the shell preparation stage is 0.1-0.3 mol / L; the ammonia concentration in the intermediate layer and the core preparation stage is 0.05-0.2 mol / L; During the preparation of the inner core, the slurry density is controlled between 0.15 and 0.2 g / ml; during the preparation of the intermediate layer, the slurry density is controlled between 0.2 and 0.25 g / ml; during the preparation of the shell layer and the outermost layer, the slurry density is controlled between 0.25 and 0.3 g / ml.

9. The method for preparing a multi-layer core-shell structured nickel-manganese binary precursor material according to claim 8, characterized in that: The first flow rate is 15-30 L / h, and the second flow rate is 10-20 L / h.

10. A positive electrode material, characterized in that: The method is prepared by using a multi-layer core-shell structured nickel-manganese binary precursor material as described in any one of claims 1 to 4.

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