KR20240061740A - Negative active material for lithium secondary battery, preparing method for the same and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a negative electrode active material for a lithium secondary battery comprising a core and a shell layer formed outside the core, wherein the core contains metal, the shell layer contains carbon, and a plurality of pores are formed between the core and the shell layer. It relates to a negative active material for a lithium secondary battery, including a layer, and having an angle formed between a line connecting the center of the core and the center of the void and the long axis of the void being 60° or more and 90° or less.

Description

Negative active material for lithium secondary battery, manufacturing method thereof, and lithium secondary battery comprising the same {Negative active material for lithium secondary battery, preparing method for the same and lithium secondary battery comprising the same}

The present invention relates to a negative electrode active material for lithium secondary batteries, a manufacturing method thereof, and a lithium secondary battery using the same.

A ‘battery’ is a device that converts chemical energy into electrical energy. 'Secondary battery' refers to a battery that, unlike primary batteries, can be recharged and used after being discharged. Among them, 'lithium secondary batteries' produce electricity through a chemical reaction in which lithium ions move from the cathode to the anode when discharging.

Recently, market demand for lithium secondary batteries has been rapidly increasing. Accordingly, as its applications diversify, the required performance is also being adjusted upward, and there is a demand for higher capacity and longer lifespan of lithium secondary batteries. The currently widely used anode active material is graphite. However, its theoretical capacity is 372 mAh/g, which is insufficient performance in terms of high capacity required in the market. In order to increase the capacity of batteries, silicon (Si) or its compounds are emerging as new materials representing negative electrode active materials.

However, there are limits to the immediate and comprehensive application of silicon as a negative electrode active material. Specifically, during the charging/discharging process, the structure of the active material collapses due to volume expansion of 300-400%, which causes an electrical short circuit in the particles within the electrode plate, increasing resistance, or direct contact with the electrolyte through the damaged part. It causes an oxidation reaction of silicon, drastically reducing the lifespan of the battery.

Methods for making up for the shortcomings of these silicon materials have been known. For example, this is a method of suppressing expansion by crushing primary silicon particles to the nanometer (nm) level or forming a coating layer on the outer surface of the silicon particles. However, these methods also have problems in that as the size of the silicon particles decreases, the capacity and efficiency of the battery decreases, the process cost increases, or the structure of the outer coating layer collapses due to silicon expansion.

In order to solve the above problems, the present invention allows volume expansion into the void layer previously secured between the silicon and the carbon layer when charging/discharging the active material made of silicon particles. In particular, the purpose is to provide a negative active material for a lithium secondary battery that shows optimal battery activity by adjusting the porosity and pore angle and improves electrical conductivity by physically connecting the silicon and carbon layers in the pore layer.

However, the problems to be solved by the present invention are not limited to those mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the description below.

According to one embodiment of the present invention, in the negative active material for a lithium secondary battery including a core and a shell layer formed outside the core,

The core contains metal,

The shell layer contains carbon,

A negative electrode active material for a lithium secondary battery comprising a void layer in which a plurality of voids are formed between the core and the shell layer, and the angle formed between the line connecting the center of the core and the center of the void and the long axis of the void is 60° or more and 90° or less. to provide.

According to one side, a lithium secondary battery including the negative electrode active material for a lithium secondary battery is provided.

The anode active material for a lithium secondary battery of the present invention contains silicon in the core, has excellent lithium ion capacity, and prevents structural collapse of the active material by expanding the volume of silicon particles into the void layer during charging/discharging. At this time, the structure of the active material is maintained stably by adjusting the porosity and pore angle of the pore layer, and direct contact between the electrolyte and silicon is prevented, thereby improving the lifespan of the battery. Additionally, the core and shell layers are physically connected to improve electrical conductivity and enable high-rate charging and discharging.

The effects of the present invention are not limited to the effects described above, and should be understood to include all effects that can be inferred from the configuration of the invention described in the detailed description or claims of the present invention.

1 is a cross-sectional view of a negative electrode active material for a lithium secondary battery before and after charging/discharging according to an embodiment of the present invention.
Figure 2 is a diagram showing the pore angle of a negative electrode active material for a lithium secondary battery according to an embodiment of the present invention.
Figure 3 is a diagram showing the structural change according to the pore angle change of the negative electrode active material for a lithium secondary battery according to an embodiment of the present invention.
Figure 4 shows the capacity retention results of a lithium secondary battery according to another embodiment of the present invention.

Hereinafter, embodiments will be described in detail with reference to the attached drawings. However, since various changes can be made to the embodiments, the scope of the patent application is not limited or limited by these embodiments. It should be understood that all changes, equivalents, or substitutes for the embodiments are included in the scope of rights.

The terms used in the examples are for descriptive purposes only and should not be construed as limiting. Singular expressions include plural expressions unless the context clearly dictates otherwise. In this specification, terms such as “comprise” or “have” are intended to designate the presence of features, numbers, steps, operations, components, parts, or combinations thereof described in the specification, but are not intended to indicate the presence of one or more other features. It should be understood that this does not exclude in advance the possibility of the existence or addition of elements, numbers, steps, operations, components, parts, or combinations thereof.

Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as generally understood by a person of ordinary skill in the technical field to which the embodiments belong. Terms defined in commonly used dictionaries should be interpreted as having meanings consistent with the meanings they have in the context of the related technology, and unless clearly defined in the present application, should not be interpreted in an ideal or excessively formal sense. No.

In addition, when describing with reference to the accompanying drawings, identical components will be assigned the same reference numerals regardless of the reference numerals, and overlapping descriptions thereof will be omitted. In describing the embodiments, if it is determined that detailed descriptions of related known technologies may unnecessarily obscure the gist of the embodiments, the detailed descriptions are omitted.

Additionally, in describing the components of the embodiment, terms such as first, second, A, B, (a), and (b) may be used. These terms are only used to distinguish the component from other components, and the nature, sequence, or order of the component is not limited by the term.

Components included in one embodiment and components including common functions will be described using the same names in other embodiments. Unless stated to the contrary, the description given in one embodiment may be applied to other embodiments, and detailed description will be omitted to the extent of overlap.

Throughout the specification, when a part “includes” a certain component, this does not mean excluding other components, but rather means that it can further include other components.

Throughout the specification, 'pore angle' refers to the angle formed by the line connecting the center of the core of the active material and the center of the pore in the active material (a) and the long axis of the pore (b) (Figure 2). The pore angle may have a value between 0° and 90°.

According to one embodiment of the present invention, it is possible to provide a negative electrode active material for a lithium secondary battery including a core and a shell layer formed outside the core. The core may contain metal and the shell layer may contain carbon. At this time, a void layer in which a plurality of voids are formed may be included between the core and shell layers.

At this time, the pore angle may be 60° or more and 90° or less. When the pore angle is smaller than 60°, the long axis of the pores is directed toward the shell layer, so when the volume of the active material core expands, there is a high possibility that the structure of the shell layer containing carbon will collapse (FIG. 3).

In the negative active material for a lithium secondary battery according to an embodiment of the present invention, the porosity of the void layer may be 5 to 40%, preferably 30 to 40%. If the porosity is less than 5%, the structural collapse of the shell layer may occur when the active material expands in volume, which may deteriorate the lifespan characteristics of the secondary battery containing it. If the porosity exceeds 40%, electrical conductivity decreases and initial efficiency decreases. There may be problems that arise.

Meanwhile, the pore angle and porosity can be adjusted during the manufacturing process of the negative electrode active material for lithium secondary batteries. A method of manufacturing a negative electrode active material for a lithium secondary battery may include combining silicon precursor powder, an amorphous carbon precursor, and crystalline carbon. When manufacturing a negative electrode active material for a lithium secondary battery according to an embodiment of the present invention, the weight ratio of the silicon precursor powder and the crystalline carbon may be, for example, 1:0.1 to 1:0.7, and the weight ratio of the silicon precursor powder and the amorphous carbon precursor may be 1:0.1 to 1:0.7. For example, it may be 1:0.6 to 1:1.1. Additionally, as an example, the rotation speed of the composite device may be 400 to 1500 rpm, and the rotation time may be, for example, 10 minutes to 180 minutes.

In the anode active material for a lithium secondary battery according to an embodiment of the present invention, the thickness of the void layer may be 10 nm to 2 μm. If the thickness of the void layer is less than 10 nm, there is a problem that the volume expansion capacity due to charge and discharge is reduced, and if the thickness of the void layer exceeds 2 μm, the contact route of the carbon connection connecting the core and shell layer is reduced. There may be a problem of decreased electrical conductivity.

In the anode active material for a lithium secondary battery according to an embodiment of the present invention, the void layer may include a carbon connection portion connecting the core and the shell layer. Because the core and the shell layer are physically connected by the carbon connector, electrons can easily move to the core, which can be advantageous for high rate charging and discharging of the lithium secondary battery.

The carbon linkage may include one or more selected from the group consisting of crystalline and amorphous carbon. As an example, crystalline carbon may include graphitic carbon. Graphite-based carbon may be natural graphite produced and mined in nature, or artificial graphite (artificial, synthetic, pyrolytic graphite) manufactured by heat-treating coal-based or petroleum-based pitch. Amorphous carbon is, for example, sucrose, phenol, naphthalene, polyvinyl alcohol resin, furfuryl alcohol resin, polyacrylonitrile resin, styrene ( stylene resin, polyimide resin, epoxy, vinyl chloride resin, petroleum pitch, coal-based pitch, polyvinyl chloride, mesophase pitch and tar. You can. However, it is not limited to this.

In the anode active material for a lithium secondary battery according to an embodiment of the present invention, the metal is silicon, magnesium, aluminum, calcium, iron, manganese, cobalt, nickel, zinc, germanium, tin, lead, oxides thereof, and It contains at least one selected from the group consisting of alloys, and may preferably be flaky silicon. Silicon has the advantage of having an energy density about 10 times higher than that of graphite and a faster charge/discharge speed.

The diameter of the metal may be 20 nm to 120 nm. For example, when the metal has a major axis and a minor axis, such as a flaky structure, the major axis and minor axis may be 80 nm to 120 nm and 20 nm to 60 nm, respectively. However, it is not limited to this.

In the anode active material for a lithium secondary battery according to an embodiment of the present invention, the shell layer may include at least one selected from the group consisting of crystalline and amorphous carbon. Examples of crystalline and amorphous carbon are the same as those described previously.

According to another embodiment of the present invention, a lithium secondary battery including the negative electrode active material for a lithium secondary battery can be provided.

A lithium secondary battery may include a positive electrode, a negative electrode, an electrolyte, and a separator.

The positive electrode is a source of lithium ions, and the positive electrode may include a substrate, a positive electrode active material, a conductive material, and a binder, and a compound such as lithium oxide may be used as the positive electrode active material.

Meanwhile, the negative electrode may include a substrate, a negative electrode active material, a conductive material, and a binder, and the negative electrode active material stores or releases lithium ions from the positive electrode to allow current to flow.

The separator functions to block physical contact between the anode and the cathode, and contains micropores through which lithium ions can pass. The electrolyte is a medium that enables the movement of lithium ions, and is a non-aqueous electrolyte solution or solid electrolyte. etc. can be used.

Hereinafter, embodiments will be described in detail with reference to the attached drawings. However, since various changes can be made to the examples, the scope of rights of the patent application is not limited or limited by these examples. It should be understood that all changes, equivalents or substitutions to the embodiments are included in the scope of rights.

Experimental Example 1: Preparation of negative electrode active material for lithium secondary battery

Example 1

Through the method below, a negative electrode active material for a lithium secondary battery with a porosity of 37.8% and a pore angle of 80° was prepared.

A mixture containing silicon, alcohol, and additives was added to a bead mill to prepare a solution ground to a median particle size (Dv50) of 90 nm, and then the solution was sprayed at 50°C to 60°C based on the discharge temperature. Silicon precursor powder with a median particle size of 4 μm was prepared by drying (GEA, Mobile minor). Thereafter, the silicon precursor powder, graphite (purity of 99.9% or more, particle size of 200 mesh or more) and petroleum pitch were mixed in xylene solvent at a weight ratio of 1:0.3:0.9, stirred for 4 hours, and vacuumed at 120°C. It was dried in the oven for 3 hours. The dried mixture was put into the coating equipment and coating was performed at 1300 rpm for 30 minutes. The coated mixture was heat-treated in a nitrogen atmosphere furnace at 920°C, and classified through a 325 mesh sieve to obtain a negative electrode active material for a lithium secondary battery.

Example 2

Silicon precursor powder, graphite, and pitch were mixed at a weight ratio of 1:0.4:0.8, and the coating equipment was rotated at 1000 rpm, in the same manner as Example 1, which resulted in a porosity of 34.9% and a pore angle of 34.9%. A negative electrode active material for a lithium secondary battery with a temperature of 78° was manufactured.

Example 3

Silicon precursor powder, graphite, and pitch were mixed in a tetrahydrofuran solvent at a weight ratio of 1:0.5:0.8, and the coating equipment was rotated at 1200 rpm. The same method as Example 1 was performed, Through this, a negative active material for a lithium secondary battery with a porosity of 30.5% and a pore angle of 76° was manufactured.

Example 4

Silicon precursor powder, graphite, and pitch were mixed at a weight ratio of 1:0.5:0.7, and the coating equipment was rotated for 60 minutes, except that the method was carried out in the same manner as Example 1, resulting in a porosity of 25.4% and a pore angle of 25.4%. A negative electrode active material for a lithium secondary battery with a temperature of 78° was manufactured.

Comparative Example 1

Silicon precursor powder, graphite, and pitch were mixed at a weight ratio of 1:0.7:0.6, and the coating equipment was rotated for 90 minutes, in the same manner as Example 1, and through this, lithium secondary with a porosity of 3.0% was obtained. A negative electrode active material for a battery was prepared. Meanwhile, the pore angle could not be measured due to the porosity being too low.

Comparative Example 2

Silicon precursor powder, graphite, and pitch were mixed at a weight ratio of 1:0.1:1.1, and the coating equipment was rotated at 800 rpm for 90 minutes, except that the same method as Example 1 was performed, resulting in a porosity of 56.6%. And a negative electrode active material for a lithium secondary battery with a pore angle of 78° was prepared.

Comparative Example 3

Silicon precursor powder, graphite, and pitch were mixed in xylene solvent at a weight ratio of 1:0.4:0.9, stirred for 1 hour, and then dried in a vacuum oven at 150°C for 20 hours. The dried mixture was pulverized using dry grinding equipment, then put into coating equipment and coating was performed at 400 rpm for 3 hours. Other than this, it was manufactured in the same manner as Example 1. Through this, a negative electrode active material for a lithium secondary battery with a porosity of 35.0% and a pore angle of 44° was manufactured.

Experimental Example 2: Porosity and pore angle of negative electrode active material for lithium secondary battery

The porosity of the pore layer of Examples 1 to 4 and Comparative Examples 1 to 3 was measured using a specific surface area measuring device using nitrogen adsorption. Porosity was calculated using the following formula. The true density was set at 2.33 g/cc.

The results are shown in Table 1 below.

Additionally, the pore angles of the pore layers of Examples 1 to 4 and Comparative Examples 1 to 3 are shown in Table 2 below.

Compared to Examples 1 to 4, the porosity of Comparative Example 1 is low, and the porosity of Comparative Example 2 is high. Meanwhile, the pore angle of Comparative Example 3 was less than 60°.

Experimental Example 3: Manufacturing of lithium secondary battery

Experimental Example 3-1: Cathode production

An anode active material slurry was prepared by uniformly mixing the anode active materials for lithium secondary batteries of Examples 1 to 4 and Comparative Examples 1 to 3, a conductive material (Super P), and a binder (SBR-CMC) at a weight ratio of 93:2:5. . A negative electrode was manufactured by coating this slurry on a Cu foil current collector, drying it, and rolling it to a mixture density of 1.55 g/cc.

Experimental Example 3-2: Production of coin half cell

When evaluating the half cell, a CR2032 type coin half cell was manufactured. Lithium metal was used as a counter electrode of the cathode, polyethylene was used as a separator, and ethylene carbonate: diethyl carbonate: dimethyl carbonate was used as the electrolyte. A solution (1.0 M) of LiPF ₆ dissolved in a mixed solvent with a volume ratio of 3:5:2 was used.

Experimental Example 3-3: Coin full cell production

Evaluation was performed using a CR2032 battery. When evaluating a full cell, the NCM active material positive electrode was used as a counter electrode to create a full cell with a N/P ratio of 1:1 with the manufactured negative electrode. As the electrolyte, the volume ratio of ethylene carbonate:diethyl carbonate is 3:7, and LiPF ₆ is dissolved in a solvent containing 7% by weight of fluoroethylene carbonate based on the total weight of the solvent. solution (1.0 M) was used.

The anode was manufactured as follows. A positive electrode active material slurry was prepared by uniformly mixing NCM (LiNiMnCoO ₂ ) positive electrode active material: acetylene black conductive material: polyvinylidene fluoride binder in N-methyl pyrrolidone solvent at a weight ratio of 96:2:2. This slurry was coated on an aluminum foil current collector and dried to prepare a positive electrode.

Experimental Example 4: Evaluation of electrochemical properties of lithium secondary battery

Lifespan, output characteristics, and plate expansion rate were evaluated using a full cell.

Experimental Example 4-1: Lifespan

First, charge the coin full cell twice at 0.1 C (charge at CC/CV 4.2 V and discharge at CC 2.75 V), then charge at 1 C 100 times (charge at CC/CV 4.2 V and discharge at CC 2.75 V). /Discharge capacity after discharge was measured. Life is the percentage ratio of the 100th discharge capacity of 1 C to the first discharge capacity of 1 C.

The results are shown in Figure 4 and Table 3 below.

Experimental Example 4-2: Output characteristics

Charge/discharge a coin full cell twice at 0.1 C (charge to CC/CV 4.2 V and discharge to CC 2.75 V), charge/discharge to 1 C five times (charge to CC/CV 4.2 V and discharge to CC 2.75 V). The discharge capacity after discharging was measured. The output characteristic is the percentage ratio of the fifth discharge capacity of 1 C to the second discharge capacity of 0.1 C. The results are shown in Table 4 below.

Experimental Example 4-3: Electrode plate expansion rate

After charging/discharging the coin full cell 100 times at 1 C, the cell was disassembled and the thickness of the cathode was measured. The expansion rate is the percentage ratio of the cathode thickness after charging/discharging 100 times compared to the cathode thickness before charging/discharging.

The results are shown in Table 5 below.

In light of the above experimental example, it can be seen that when the negative electrode active material for a lithium secondary battery according to the present invention has the porosity and pore angle described in the claims, a lithium secondary battery with excellent output and lifespan characteristics can be provided.

Although the embodiments have been described with limited drawings as described above, those skilled in the art can apply various technical modifications and variations based on the above. For example, the described techniques are performed in a different order than the described method, and/or components of the described system, structure, device, circuit, etc. are combined or combined in a different form than the described method, or other components are used. Alternatively, appropriate results may be achieved even if substituted or substituted by an equivalent.

Therefore, other implementations, other embodiments, and equivalents of the claims also fall within the scope of the following claims.

100: core
110: Lithium-containing core
200: shell layer
300: void layer

Claims (13)

In the negative active material for a lithium secondary battery comprising a core and a shell layer formed outside the core,
The core contains metal,
The shell layer contains carbon,
A negative electrode active material for a lithium secondary battery, comprising a void layer in which a plurality of voids are formed between the core and the shell layer, and the angle formed between the line connecting the center of the core and the center of the void and the long axis of the void is 60° or more and 90° or less.
According to paragraph 1,
A negative electrode active material for a lithium secondary battery, wherein the void layer has a porosity of 5 to 40%.
According to paragraph 1,
A negative electrode active material for a lithium secondary battery, wherein the void layer has a porosity of 30 to 40%.
According to paragraph 1,
A negative electrode active material for a lithium secondary battery, wherein the thickness of the void layer is 10 nm to 2 μm.
According to paragraph 1,
The void layer is a negative electrode active material for a lithium secondary battery including a carbon connection portion connecting the core and the shell layer.
According to clause 5,
The carbon connector is a negative electrode active material for a lithium secondary battery comprising at least one selected from the group consisting of crystalline and amorphous carbon.
According to clause 6,
The crystalline carbon is a negative electrode active material for a lithium secondary battery including graphite-based carbon.
According to clause 6,
The amorphous carbon is sucrose, phenol, naphthalene, polyvinyl alcohol resin, furfuryl alcohol resin, polyacrylonitrile resin, and styrene resin. , polyimide resin, epoxy, vinyl chloride resin, petroleum pitch, coal-based pitch, polyvinyl chloride, mesophase pitch, and one or more selected from the group consisting of tar. Manufactured negative electrode active material for lithium secondary battery.
According to paragraph 1,
The metal includes at least one selected from the group consisting of silicon, magnesium, aluminum, calcium, iron, manganese, cobalt, nickel, zinc, germanium, tin, lead, oxides thereof, and alloys thereof, for a lithium secondary battery. Cathode active material.
According to paragraph 1,
The metal is a negative electrode active material for a lithium secondary battery containing flaky silicon.
According to paragraph 1,
A negative electrode active material for a lithium secondary battery, wherein the metal has a diameter of 20 nm to 120 nm.
According to paragraph 1,
The shell layer is a negative electrode active material for a lithium secondary battery comprising at least one selected from the group consisting of crystalline and amorphous carbon.
A lithium secondary battery comprising the negative electrode active material for a lithium secondary battery according to any one of claims 1 to 12.