Method for manufacturing precursors for lithium secondary batteries

Abstract

The present invention relates to a method for producing a precursor for lithium secondary batteries, comprising the steps of: preparing a metal raw material; and forming a reaction solution containing the metal raw material to coprecipitate a metal hydroxide precursor, wherein the reaction solution contains an additional additive, and the additive is a colloidal flocculant.

Description

Technical Field

[0001] The present invention relates to a method for producing a precursor for a lithium secondary battery.

Background Art

[0002] With the increasing development and demand for electric vehicles, the demand for secondary batteries as an energy source has been rapidly increasing. Among such secondary batteries, lithium secondary batteries having a high energy density, voltage, long cycle life, and low self-discharge rate have been commercialized and widely used.

[0003] As the positive electrode active material of a lithium secondary battery, lithium nickel cobalt manganese composite oxide is used. Among these, cobalt has a high operating voltage and affects the rate characteristics.

[0004] However, since the positive electrode active material with a high cobalt composition is expensive, there is a limit to its large-scale use as a power source in fields such as electric vehicles. Also, recently, due to the rapid price increase of cobalt, there is a tendency to gradually reduce the cobalt content, and thus, a solution capable of complementing the rate characteristics and life is required. As one such method, an oriented positive electrode active material has been proposed as an alternative.

[0005] Conventionally, a concentration gradient precursor was mainly utilized to produce a positive electrode active material having an oriented structure. However, the positive electrode active material produced in this way could not have a complete orientation from the inside to the surface of the particles.

[0006] Also, in order to achieve this, complicated processes are used, resulting in poor economic efficiency and difficulty in quality control.

Summary of the Invention

Problems to be Solved by the Invention

[0007] The present invention can provide a uniformly grown precursor using a colloidal flocculant. Such a precursor ensures cost-effectiveness while enabling the production of an oriented cathode active material with high orientation. [Means for solving the problem]

[0008] One embodiment of the present invention provides a method for producing a precursor for a lithium secondary battery, comprising the steps of: preparing a metal raw material; and forming a reaction solution containing the metal raw material to coprecipitate a metal hydroxide precursor, wherein the reaction solution contains additional additives, the additives comprising a colloidal flocculant.

[0009] The precursor obtained by the above manufacturing method may have orientation in which lithium transport pathways are formed radially from the particle center.

[0010] In the stage of preparing the aforementioned metal raw material, the reaction can be carried out using a single metal raw material without separately preparing the metal raw material for the core and the metal raw material for the shell.

[0011] A method for producing a lithium secondary battery precursor is provided, which includes the step of forming a reaction solution containing the aforementioned metal raw material to coprecipitate a metal hydroxide precursor, followed by the step of separating the obtained precursor and waste liquid, and using the separated waste liquid as a substitute for the additive.

[0012] The process includes forming a reaction solution containing the aforementioned metal raw material and coprecipitation of the metal hydroxide precursor, followed by separating the obtained precursor and waste liquid, and the separated waste liquid can be added to the coprecipitation reaction together with the additional additives.

[0013] The waste liquid may contain Na2SO4.

[0014] The colloidal flocculant may contain a 1- to 3-valent inorganic salt.

[0015] The colloidal flocculant may include sodium nitrate, potassium nitrate, ammonium nitrate, sodium sulfate, sodium pyrosulfate, potassium pyrosulfate, ammonium pyrosulfate, potassium sulfate, ammonium sulfate, sodium phosphate, potassium phosphate, ammonium phosphate, sodium pyrophosphate, potassium pyrophosphate, ammonium pyrophosphate, or a combination thereof.

[0016] The colloidal flocculant can reduce the surface charge of nuclei generated during the coprecipitation reaction, thereby causing particle aggregation.

[0017] The manufactured precursor may be a layered precursor containing nickel, manganese, and cobalt. [Effects of the Invention]

[0018] The present invention relates to a lithium secondary battery precursor having an oriented structure and a positive electrode active material produced using the same, and more particularly to a method for producing an oriented lithium secondary battery precursor having long life and high capacity characteristics due to having an oriented structure.

[0019] The lithium secondary battery precursor according to the present invention is a particle with an orientation structure from the inside to the outside of the particle, which reduces the resistance to lithium ion movement and enables the manufacture of secondary batteries with high power output and long lifespan characteristics. [Brief explanation of the drawing]

[0020] [Figure 1] This is a schematic diagram illustrating the principle of controlling the degree of aggregation through zeta potential control in the examples and comparative examples of the present application. [Figure 2] This diagram shows the structure of a conventional reactor for producing core-shell precursors and a schematic diagram of the reactor structure according to the embodiment of the present application. [Figure 3] These are SEM images of the cathode active material precursors produced by the comparative example, Examples 1 and 2. [Figure 4]Evaluation results of the electrochemical properties of the positive electrode active materials produced according to the comparative example, Example 1 and Example 2. [Figure 5] Evaluation results of the electrochemical properties of the positive electrode active materials produced according to the comparative example, Example 1 and Example 2. [Figure 6] Evaluation results of the electrochemical properties of the positive electrode active materials produced according to the comparative example, Example 1 and Example 2. [Figure 7] Evaluation results of the electrochemical properties of the positive electrode active materials produced according to the comparative example, Example 1 and Example 2.

Mode for Carrying Out the Invention

[0021] Hereinafter, embodiments of the present invention will be described in detail. However, this is presented as an example, and the present invention is not limited thereby, and is defined only by the scope of the claims described later.

[0022] Generally, the synthesis of the precursor is carried out in a high-alkali region, and due to the characteristics of transition metals that form coordination bonds well, the additives that can be used are very limited and not known.

[0023] In the present invention, an additive capable of controlling particle aggregation through the control of zeta potential was developed and applied to the method for producing the precursor. As a result, an oriented precursor and an active material can be produced by a method that has not been attempted conventionally.

[0024] Generally, the surface of the precursor has a charge of - due to OH- on the aqueous solution. This is called the zeta potential.

[0025] The compressed stern layer of the precursor moves together with the precursor, but the diffused layer moves with the aqueous solution. The zeta potential plays an absolute role in the dispersion on the aqueous solution.

[0026] To give a concrete example, the larger the surface charge, the greater the repulsive force between particles, causing them to disperse. Conversely, the smaller the surface charge, the less repulsive force between particles, causing them to aggregate.

[0027] Figure 1 is a schematic diagram illustrating the principle of controlling the degree of aggregation through the control of zeta potential in the embodiments and comparative examples of the present application.

[0028] In other words, the present invention can obtain a uniformly grown precursor in which the crystal plane grows uniformly from the inside to the outside of the secondary particle formed from aggregates of primary particles, and this is due to its role as an additive used in the coprecipitation step.

[0029] One embodiment of the present invention provides a method for producing a precursor for a lithium secondary battery, comprising the steps of: preparing a metal raw material; and forming a reaction solution containing the metal raw material to coprecipitate a metal hydroxide precursor, wherein the reaction solution contains additional additives, the additives comprising a colloidal flocculant.

[0030] One embodiment of the present invention provides a method for producing a precursor for a lithium secondary battery, comprising the steps of: preparing a reaction mother liquor; preparing a metal raw material; and adding the metal raw material to the reaction mother liquor to form a reaction solution and coprecipitating a metal hydroxide precursor, wherein the reaction solution includes additional additives, the additives including a colloidal flocculant.

[0031] At this time, the additive may be added to the reaction mother liquor during the stage of preparing the reaction mother liquor.

[0032] As described above, in the method for producing a precursor according to one embodiment of the present invention, an additive containing a colloidal flocculant for reducing the particle surface zeta potential can be used in the coprecipitation reaction. Specifically, this may be an ionic inorganic salt.

[0033] This allows for the formation of a uniform seed through nuclear aggregation in the initial stages of the coprecipitation reaction. A uniformly growing precursor can then be produced based on the formed seed.

[0034] The precursor obtained by the above manufacturing method can have orientation in which lithium migration paths are formed radially from the particle center. This can be interpreted as meaning that the c-axis, which is the lithium migration path, is oriented from the center to the outer corner. This reduces the resistance of lithium migration, thereby improving the output and lifespan characteristics of the battery.

[0035] Furthermore, the precursor obtained by the above manufacturing method may be a secondary particle formed by the aggregation of a plurality of primary particles, and the primary particles may have a plate-like, needle-like, or amorphous particle form, but are not necessarily limited to these.

[0036] In the stage of preparing the aforementioned metal raw material, the reaction can be carried out using a single metal raw material without separately preparing the metal raw material for the core and the metal raw material for the shell.

[0037] Unlike conventional technologies, this allows for orientation even in the bulk form of the precursor.

[0038] Figure 2 is a schematic diagram of the structure of a conventional reactor for producing a core-shell structure precursor and the structure of a reactor according to an embodiment of the present invention.

[0039] Conventionally, in order to achieve orientation, it was necessary to manufacture precursor particles using a technique that differed the metal composition of the core and the metal composition of the shell. However, with the precursor manufacturing method using the additive of the present invention, orientation can be achieved without a metal concentration gradient, making it possible to manufacture precursors in bulk form, thereby ensuring price competitiveness.

[0040] The process includes forming a reaction solution containing the aforementioned metal raw material to coprecipitate the metal hydroxide precursor, followed by separating the obtained precursor and waste liquid, and the separated waste liquid can be used as a substitute for the additive.

[0041] Alternatively, the process may include a step of forming a reaction solution containing the metal raw material and coprecipitation the metal hydroxide precursor, followed by a step of separating the obtained precursor and waste liquid, and the separated waste liquid being added to the coprecipitation reaction together with the additional additives.

[0042] The waste liquid may contain Na2SO4. The colloidal flocculant may contain a 1- to 3-valent inorganic salt.

[0043] More specifically, approximately 10% by weight of sodium sulfate can be present as a by-product in the wastewater after the reaction is complete.

[0044] Recycling such wastewater can have effects similar to those of applying inorganic salt additives, thereby providing a competitive advantage in terms of price.

[0045] More specifically, the colloidal flocculant may be an inorganic salt, but may include, for example, sodium nitrate, potassium nitrate, ammonium nitrate, sodium sulfate, sodium pyrosulfate, potassium pyrosulfate, ammonium pyrosulfate, potassium sulfate, ammonium sulfate, sodium phosphate, potassium phosphate, ammonium phosphate, sodium pyrophosphate, potassium pyrophosphate, ammonium pyrophosphate, or a combination thereof.

[0046] On the other hand, as mentioned above, the colloidal flocculant can be added to the reaction mother liquor by adding it during the stage of preparing the reaction mother liquor before the coprecipitation reaction.

[0047] At this time, the reaction mother liquor may include, but is not limited to, water, distilled water, deionized water, or a combination thereof.

[0048] Furthermore, the colloidal flocculant may be added in an amount of 3 to 15% by weight based on the weight of the reaction mother liquor, and more specifically, in an amount of 4 to 12% by weight based on the weight of the reaction mother liquor. When the amount of colloidal flocculant added falls within the above range, the aforementioned effects of improved precursor orientation and the resulting improvement in battery performance can be more favorably realized. [Examples]

[0049] The following describes preferred embodiments and comparative examples of the present invention. However, the following embodiments are merely preferred embodiments of the present invention, and the present invention is not limited to these embodiments.

[0050] Examples and Comparative Examples

[0051] Example 1: Use of 5% sodium sulfate additive (Preparation of mother liquor) Water was added to a 100L batch reactor to a volume of 15% of the total reactor volume, and sodium sulfate was added to the reactor at a ratio of 5 parts by weight per 100 parts by weight of water. The internal temperature was set to 30-50°C while stirring at a speed of 400 rpm, and nitrogen gas was introduced into the reactor to create an inert atmosphere.

[0052] (Preparation of raw materials) Subsequently, a 2.5M concentration aqueous solution of metal sulfate, in which nickel sulfate, cobalt sulfate, and manganese sulfate were mixed in a molar ratio of 0.88:0.05:0.07, was prepared, along with 25% sodium hydroxide and 28% aqueous ammonia.

[0053] (Formation of reaction solution and coprecipitation reaction) The flow rate of the metal sulfate aqueous solution was adjusted to 3 L / hour, and the flow rate of the ammonia water was adjusted to 0.04 times the flow rate of the metal sulfate aqueous solution. The amount of sodium hydroxide (NaOH) solution added was adjusted so that the hydrogen ion concentration (pH) in the reactor was approximately 10.5 to 11.5 to form the reaction solution and carry out the coprecipitation reaction. At this time, the stirring speed was 400 rpm, the reactants were added so that the average residence time of the entire solution was 20 hours, the reaction temperature was maintained at 30°C to 50°C, and an inert atmosphere was maintained by adding nitrogen gas.

[0054] (Washing and Drying) After the reaction was complete, the solution was washed with water and separated into solid and liquid components using a pressure filter (filter press), and residual moisture was removed using high-pressure fresh air. The solid-liquid separated active material was dried at 100-200°C using a fluidized bed dryer.

[0055] (Castration) The hydroxide particles obtained above were mixed with lithium hydroxide in an equivalent ratio of 1.05 with the hydroxide. Then, the mixture was heated in an oxygen atmosphere at a heating rate of 2.5°C / min, and calcined at 780°C for 9 hours to produce a lithium composite metal oxide having a uniform oriented structure.

[0056] Example 2: Use of 10% sodium sulfate additive The cathode active material precursor and cathode active material were produced in the same manner as in Example 1, except that sodium sulfate was added at a rate of 10 parts by weight per 100 parts by weight of water during the reaction mother liquor preparation stage.

[0057] Comparative example: Non-use of sodium sulfate additive The cathode active material precursor and cathode active material were produced in the same manner as in Example 1, except that sodium sulfate was not added during the reaction mother liquor preparation stage.

[0058] Experimental Example 1: Evaluation of SEM Images Figure 3 is a cross-sectional SEM image of the precursor produced by the method described above.

[0059] SEM analysis revealed that in the comparative example where no additive was applied, the particles were not able to aggregate during the initial stages of the reaction and remained dispersed.

[0060] In the latter half of the reaction, the grown particles merged, resulting in poor sphericity. Cross-sectional analysis confirmed that orientation was not formed.

[0061] In the examples where the additive was applied, aggregated unit seeds were formed in the initial stages of the reaction, resulting in a significant improvement in the sphericity of the final product. Analysis of the particle cross-section confirmed that good orientation was achieved.

[0062] Experimental Example 2: Evaluation of Battery Electrochemical Properties (Manufacturing of Lithium Secondary Batteries) A ​​cathode active material slurry was prepared by mixing the cathode active material, conductive material, and binder in a weight ratio of 96.5:1.5:2 using the cathode active material produced in Examples 1-2 and Comparative Example, SuperC as the conductive material, and PVDF as the binder. The slurry was uniformly applied to a 20 μm thick aluminum foil and vacuum-dried at 130°C to produce a cathode.

[0063] A coin cell was manufactured using the fabricated positive electrode as the working electrode, lithium foil as the counter electrode, and a polypropylene film as the separator, with an electrolyte prepared by dissolving 1.0 M LiPF6 lithium salt in EC / EMC / DMC solvent.

[0064] For lithium secondary batteries manufactured by the above method, the charge-discharge efficiency, initial discharge capacity, and initial discharge capacity at 0.1C, 0.33C, 0.5C, 1C, and 2C were evaluated as the cycle progressed and are shown in Figures 4 to 7.

[0065] Referring to Figures 4 to 7, it was confirmed that in Examples 1 and 2, which were manufactured with an appropriate amount of colloidal flocculant, the charge-discharge efficiency, initial discharge capacity, and high-rate characteristics were all significantly improved compared to the comparative example where no colloidal flocculant was administered. This can be interpreted as an improvement in battery performance due to an improvement in the degree of flocculation and orientation of the active material.

[0066] The present invention is not limited to the embodiments described above, and can be manufactured in a variety of different forms. Those with ordinary skill in the art to which the invention pertains should understand that it can be implemented in other specific forms without altering the technical idea or essential features of the invention. Therefore, it should be understood that the embodiments described above are illustrative in all respects and not limiting.

Claims

1. The step of preparing the metal raw material; and The step includes forming a reaction solution containing the aforementioned metal raw material to coprecipitate a metal hydroxide precursor; The reaction solution contains additional additives, The aforementioned additive is a method for producing a precursor for lithium secondary batteries, comprising a colloidal flocculant.

2. The method for producing a precursor for a lithium secondary battery according to claim 1, wherein the precursor obtained by the above-mentioned manufacturing method has orientation in which lithium transport pathways are formed radially from the particle center.

3. In the step of preparing the aforementioned metal raw material, A method for producing a precursor for a lithium secondary battery according to claim 1, wherein the reaction is carried out using a single metal raw material without separately preparing a metal raw material for the core and a metal raw material for the shell.

4. After the step of forming a reaction solution containing the aforementioned metal raw material and co-precipitating the metal hydroxide precursor, The step includes separating the obtained precursor and waste liquid, A method for producing a lithium secondary battery precursor according to claim 1, wherein the separated waste liquid is used as a substitute for the additive.

5. After the step of forming a reaction solution containing the aforementioned metal raw material and co-precipitating the metal hydroxide precursor, The step includes separating the obtained precursor and waste liquid, A method for producing a lithium secondary battery precursor according to claim 1, wherein the separated waste liquid is added to a coprecipitation reaction together with the additional additive.

6. The aforementioned waste liquid is Na ２ SO ４ A method for producing a lithium secondary battery precursor according to claim 4 or claim 5, including the method described above.

7. The method for producing a precursor for a lithium secondary battery according to claim 1, wherein the colloidal flocculant comprises a monovalent to trivalent inorganic salt.

8. The method for producing a precursor for a lithium secondary battery according to claim 7, wherein the colloidal flocculant comprises sodium nitrate, potassium nitrate, ammonium nitrate, sodium sulfate, sodium pyrosulfate, potassium pyrosulfate, ammonium pyrosulfate, potassium sulfate, ammonium sulfate, sodium phosphate, potassium phosphate, ammonium phosphate, sodium pyrophosphate, potassium pyrophosphate, ammonium pyrophosphate, or a combination thereof.

9. The method for producing a precursor for a lithium secondary battery according to claim 1, wherein the colloidal flocculant reduces the surface charge of nuclei generated during the coprecipitation reaction, causing the particles to aggregate.

10. The method for producing a lithium secondary battery precursor according to claim 1, wherein the produced lithium secondary battery precursor is a layered precursor containing nickel, manganese, and cobalt.

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