KR20200105236A - An anode active material, an anode comprising the anode active material and a secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a negative electrode active material including a sol-gel reaction product of a monomer represented by formula 1, a negative electrode including the same, and a secondary battery including the negative electrode.

Description

A negative active material, a negative electrode including the negative active material, and a secondary battery including the same (An anode active material, an anode comprising the anode active material and a secondary battery comprising the same}

The present invention relates to a negative active material, a negative electrode including the negative active material, and a secondary battery including the same.

A battery generates electric power by using a material capable of electrochemical reaction for the positive and negative electrodes. A typical example of such a battery is a lithium secondary battery that generates electrical energy by a change in chemical potential when lithium ions are intercalated/deintercalated in the positive electrode and the negative electrode.

Lithium secondary batteries are manufactured by using a material capable of reversible insertion/desorption of lithium ions as a positive electrode and a negative electrode active material, and filling an organic electrolyte or a polymer electrolyte between the positive electrode and the negative electrode.

Lithium composite metal compounds are mainly used as positive electrode active materials for lithium secondary batteries, for example, LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiNi _1-x Co _x O ₂ (0<x<1), LiMnO ₂ etc. Composite metal oxides are being studied.

As a negative active material for lithium secondary batteries, graphite, which can insert/desorb lithium, has been typically used, but since the electrode using such graphite has a low charge capacity of 365mAh/g (theoretical value: 372mAh/g), it has excellent capacity. There was a limit to providing a lithium secondary battery exhibiting characteristics.

As problems such as low reversible capacity and low rate performance emerge, it is difficult to apply various lithium secondary batteries, and thus research on a new negative active material is in progress.

As one of the newly spotlighted materials as negative active materials for lithium secondary batteries, silicon has a significantly higher capacity than existing negative active materials with a theoretical charge capacity of 4200 mAh/g. It has an advantage and is emerging as a material suitable for application of various devices.

Korean Registered Patent Nos. 10-1875950 and 10-0570651 disclose lithium secondary batteries containing silicon as a negative electrode active material, but inorganic negative active materials such as silicon include lithium insertion/desorption, that is, charging of the battery. There is a problem that the capacity gradually decreases as the contact between the current collector and the active material weakens due to a volume change of more than 300% during discharge.In addition, the electrical conductivity of silicon is low, so that the charge transfer reaction that occurs when lithium is inserted/desorbed smoothly occurs. There is a problem of not doing so, and there is a disadvantage of showing a low cycle life characteristic and a capacity retention rate despite the advantage of a high charge capacity.

Korean Patent Registration No. 10-1875950 Korean Patent Registration No. 10-0570651

An object of the present invention is to provide a negative electrode active material capable of increasing the charge/discharge capacity and capacity retention rate of a secondary battery, a negative electrode including the negative electrode active material, and a secondary battery including the negative electrode.

In addition, an object of the present invention is to provide a secondary battery with increased life by suppressing volume expansion of a negative electrode during charging and discharging.

The present invention provides a negative active material comprising a sol-gel reaction product of a monomer represented by the following Formula 1:

[Formula 1]

이고, m 및 n은 각각 독립적으로 0 내지 3의 정수이고, R은 C1 내지 C4의 알킬기이다.In Formula 1, X is a halogen element, -OR, or

And m and n are each independently an integer of 0 to 3, and R is a C1 to C4 alkyl group.

In addition, the present invention provides a negative electrode including the negative active material.

In addition, the present invention is the cathode; anode; Porous separator; It provides a secondary battery comprising; and an electrolyte.

The negative electrode active material according to the present invention is included in the negative electrode of the secondary battery, increases the charge/discharge capacity and life of the secondary battery, and suppresses the volume expansion of the negative electrode during charging and discharging, thereby improving the life of the secondary battery.

1 is a graph showing a change in charge/discharge capacity of a lithium secondary battery (half-cell) according to Examples and Comparative Examples of the present invention.
2 is a capacity curve obtained by separating only the results of Example 1 and Comparative Example 3 in FIG. 1.

Hereinafter, the present invention will be described in detail.

The present invention relates to a negative electrode active material that is included in a negative electrode of a secondary battery and can increase charge/discharge capacity and capacity retention of a secondary battery, and a negative electrode and a secondary battery including the same.

The negative electrode active material of the present invention is produced through a sol-gel reaction and does not require an additional reduction treatment process, and thus has an advantage that the manufacturing process can be shortened. In addition, the negative electrode active material of the present invention has a void in the gel during the process of being generated through the sol-gel reaction, and thus has the effect of suppressing the volume expansion of the negative electrode during charging and discharging of the secondary battery. Can be increased.

Negative active material

The negative active material of the present invention is characterized by including a sol-gel reaction product of a monomer represented by the following formula (1).

[Formula 1]

In Formula 1,

이고, m 및 n은 각각 독립적으로 0 내지 3의 정수이고, R은 C1 내지 C4의 알킬기이다.X is a halogen element, -OR or

And m and n are each independently an integer of 0 to 3, and R is a C1 to C4 alkyl group.

Preferably, m and n in Formula 1 may be 1 or 2 each independently.

For example, the monomer represented by Formula 1 may include a compound represented by Formulas 2 to 4 below.

[Formula 2]

[Formula 3]

[Formula 4]

이고, R은 C1 내지 C4의 알킬기이다.In Formulas 2 to 4, X is a halogen element, -OR, or

And R is a C1 to C4 alkyl group.

For another example, the monomer represented by Formula 1 may include one or more of the compounds represented by Formulas 5 to 8.

[Formula 5]

[Formula 6]

[Formula 7]

[Formula 8]

For example, the sol-gel reaction product of the monomer represented by Formula 1 is characterized by comprising 50 to 99.9% by weight of the monomer represented by Formula 1, and comprising 90 to 99% by weight It is desirable.

The sol-gel reaction of the monomer represented by Formula 1 may be understood as a sol-gel reaction commonly used in the art. For example, after a sol-gel reaction of the monomer represented by Formula 1, When the solvent and the unreacted catalyst are removed through centrifugation and then dried, the negative active material may be prepared.

Since the negative active material prepared through a sol-gel reaction does not require an additional reduction treatment process, the manufacturing process can be shortened.

A negative electrode including the negative active material

The negative electrode includes the negative active material capable of intercalating and deintercalating lithium ions, and accordingly, the charge/discharge capacity and capacity retention rate of the secondary battery including the negative electrode may be increased. The negative electrode including the negative active material has a void in the gel during the process of being generated through a sol-gel reaction, and thus has an effect of suppressing volume expansion during charging and discharging, and thus the life (charge) of the secondary battery. Discharge cycle) can be increased.

According to an embodiment, the negative electrode may include a current collector and the negative active material disposed on at least one surface of the current collector. As the current collector, a copper foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, a copper foam, a polymer substrate coated with a conductive metal, or a combination thereof may be used.

For example, the negative electrode may be prepared by mixing the negative electrode active material, a binder, and a conductive material in a solvent to prepare a negative electrode slurry, and then applying the negative electrode slurry to a current collector, but if necessary, a thickener may be dispersed in a solvent. , It is not limited to the bar described above, and may be manufactured through a method known in the art.

Specifically, the binder is a material that plays a role of a buffering effect on the expansion and contraction of the active material, such as forming a paste of the active material, mutual adhesion of the active material, adhesion to the current collector, and, for example, polyvinylidene fluoride, polyhexafluoro. Low-propylene-polyvinylidene fluoride copolymer (P(VdF/HFP)), poly(vinyl acetate), polyvinyl alcohol, polyethylene oxide, polyvinylpyrrolidone, alkylated polyethylene oxide, polyvinyl ether, poly (Methyl methacrylate), poly(ethyl acrylate), polytetrafluoroethylene, polyvinyl chloride, polyacrylonitrile, polyvinylpyridine, styrene-butadiene rubber, acrylonitrile-butadiene rubber, and the like. The content of the binder is 0.1 to 30% by weight, preferably 1 to 10% by weight, based on the active material. If the content of the binder is too small, the adhesive strength between the active material and the current collector is insufficient. If the content of the binder is too high, the adhesion is improved, but the content of the active material decreases, which is disadvantageous in increasing the battery capacity.

The conductive material is a material that improves electronic conductivity, and at least one selected from the group consisting of a graphite conductive material, a carbon black conductive material, and a metal or metal compound conductive material may be used. Examples of the graphite-based conductive material include artificial graphite and natural graphite, and examples of the carbon black-based conductive material include carbon black, ketjen black, denka black, thermal black, and channel black. channel black), acetylene black, carbon nanotubes, graphene, graphene oxide, fullerene and carbon nanofibers, and examples of metallic or metallic compound-based conductive materials include tin, tin oxide, tin phosphate (SnPO _4). ), titanium oxide, potassium titanate, LaSrCoO ₃ , and perovskite materials such as LaSrMnO ₃ . However, it is not limited to the conductive materials listed above. The content of the conductive material is preferably 1.0 to 20% by weight based on the electrode active material. When the content of the conductive material is less than 1.0% by weight, the electrochemical properties decrease, and when it exceeds 20% by weight, the energy density per weight decreases.

The thickener is not particularly limited as long as it can control the viscosity of the active material slurry. For example, carboxymethyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, and the like may be used.

A non-aqueous solvent or an aqueous solvent is used as the solvent in which the active material, the binder, and the conductive material are dispersed. Examples of the non-aqueous solvent include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, and tetrahydrofuran.

Secondary battery including the negative electrode

The present invention provides a secondary battery including the negative electrode, the positive electrode, a porous separator, and an electrolyte solution including the negative electrode active material.

For example, the secondary battery may be a lithium secondary battery, and it is preferable that the secondary battery has a cylindrical shape or a square shape of a can. In addition, the secondary battery may include a pouch type battery.

The positive electrode includes a positive electrode active material capable of intercalating and desorbing lithium ions, and the positive electrode active material is preferably at least one selected from cobalt, manganese, and nickel, and one or more of a composite oxide of lithium, and a representative example thereof The lithium-containing compounds described below can be preferably used.

Li _x Mn ₁ -yM _y A ₂ (1)

Li _x Mn ₁ -yM _y O ₂ -zX _z (2)

Li _x Mn ₂ O _4-z X _z (3)

Li _x Mn _2-y M _{y M'z} A ₄ (4)

Li _x Co _1-y M _y A ₂ (5)

Li _x Co _1-y M _y O _2-z X _z (6)

Li _x Ni _1-y M _y A ₂ (7)

Li _x Ni _1-y M _y O _2-z X _z (8)

Li _x Ni _1-y Co _y O _2-z X _z (9)

Li _x Ni _1-yz Co _y M _z A _α (10)

Li _x Ni _1-yz Co _y M _z O _2-α X _α (11)

Li _x Ni _1-yz Mn _y M _z A _α (12)

Li _x Ni _1-yz Mn _y M _z O _2-α X _α (13)

In the above formulas (1) to (13), 0.9≤x≤1.1, 0≤y≤0.5, 0≤z≤0.5, 0≤α≤2, M and M'are the same or different, and Mg, Al, It is selected from the group consisting of Co, K, Na, Ca, Si, Ti, Sn, V, Ge, Ga, B, As, Zr, Mn, Cr, Fe, Sr, V and rare earth elements, A is O, F , S and P are selected from the group consisting of, X may be selected from the group consisting of F, S and P.

According to an embodiment, the positive electrode may include a current collector and a positive electrode active material disposed on at least one surface of the current collector. As the current collector, an aluminum foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, an aluminum foam, a polymer substrate coated with a conductive metal, or a combination thereof may be used.

For example, the positive electrode may be prepared by mixing a positive electrode active material, a binder, and a conductive material in a solvent to prepare a positive electrode slurry, and then applying the positive electrode slurry to a current collector, but if necessary, a thickener may be dispersed in a solvent and used. It is not limited to the above, and may be prepared through a method known in the art.

The binder, the conductive material, the solvent, and the thickener may be the same as those used in the negative electrode.

The porous separator separates the negative electrode and the positive electrode and provides a passage for lithium ions, and can be used as long as it is commonly used in a lithium secondary battery, but has low resistance to ion movement of the electrolyte, and has a moisture absorption power for the electrolyte. It is desirable to use a superior one. For example, the porous separator may be selected from glass fiber, polyester, Teflon, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), or a combination thereof, and a polyolefin-based polymer such as polyethylene, polypropylene, etc. It is preferable to use, and a coating containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and may be optionally used in a single layer or multilayer structure.

The electrolyte may include a non-aqueous solvent and a lithium salt.

The non-aqueous solvent serves as a medium through which ions involved in the electrochemical reaction of the secondary battery can move.

For example, as the non-aqueous solvent, a carbonate-based, ester-based, ether-based, ketone-based, alcohol-based, or aprotic solvent may be used. The carbonate-based solvents include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), ethylene carbonate ( EC), propylene carbonate (PC), butylene carbonate (BC), and the like may be used, and as the ester solvent, methyl acetate, ethyl acetate, n-propyl acetate, 1,1-dimethylethyl acetate, methylpropionate , Ethyl propionate, γ-butyrolactone, decanolide, valerolactone, mevalonolactone, caprolactone, and the like may be used. Dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, etc. may be used as the ether solvent, and cyclohexanone may be used as the ketone solvent. have. In addition, ethyl alcohol, isopropyl alcohol, etc. may be used as the alcohol-based solvent, and R-CN (R is a C2 to C20 linear, branched, or cyclic hydrocarbon group, wherein Amides such as nitriles such as dimethylformamide, dioxolanes such as 1,3-dioxolane, sulfolanes such as 1,3-dioxolane, and the like may be used.

The non-aqueous solvent may be used alone or in combination of one or more, and the mixing ratio in the case of using one or more mixtures may be appropriately adjusted according to the desired battery performance.

The lithium salt is dissolved in the non-aqueous solvent, acts as a source of lithium ions in the battery, enables basic operation of a lithium secondary battery, and promotes the movement of lithium ions between the positive electrode and the negative electrode. Representative examples of the lithium salt include LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiC ₄ F ₉ SO ₃ , LiClO ₄ , LiAlO ₂ , LiAlCl ₄ , LiN(C _x F _2x+1 SO ₂ )(C _y F _{2y +1} SO ₂ ) (x and y are natural numbers), LiCl, LiI, LiB(C ₂ O ₄ ) ₂ (lithium bis(oxalato) borate; LiBOB), or a combination thereof.

Hereinafter, the present invention will be described in more detail through examples. However, the following examples are for explaining the present invention more specifically, and the scope of the present invention is not limited by the following examples. The following examples can be appropriately modified and changed by a person skilled in the art within the scope of the present invention. In the following Examples and Comparative Examples, "%" and "parts" indicating the content are based on weight unless otherwise specified.

Examples and Comparative Examples: Preparation of negative electrode active material using sol-gel reaction

Examples 1 to 7

Referring to Table 1 below, after dissolving the precursor of silicon oxide in ethanol, a sol-gel reaction was induced in a 1:7 molar ratio of pure water containing a basic catalyst (NH ₄ OH). After the sol-gel reaction, the remaining solvent and aqueous ammonia were removed by centrifugation. (In one embodiment of the present invention, centrifugation was used, but a vacuum filtration device may be used.) After vacuum drying the material obtained through the reaction at 90° C. for 1 hour at 450° C. in an inert atmosphere to remove residual impurities. An anode active material according to Examples 1 to 7 was prepared by heat treatment, which is a powder-type gel having a porous structure.

Comparative Examples 1 to 3

Referring to Table 1 below, a negative active material of Comparative Example was prepared. The negative active material according to Comparative Example 1 was prepared in the form of silica particles through the same sol-gel reaction as in Examples 1 to 7, and in the case of the negative active material according to Comparative Example 3, the same sol-gel as in Examples 1 to 7 It was prepared by heat-treating the silica particles prepared through the reaction at 1500°C for 5 hours in a reducing atmosphere, and in the case of the negative active material according to Comparative Example 2, a general Si powder (Aldrich, 325 mesh-40 um), not a sol-gel reaction. ) Was used as a negative active material.

Silicon oxide precursor (molar ratio; mol ratio) Example 1

(100)

(100) Example 2

(100) Example 3

(50)

(50) Example 4

(50)

(50) Example 5

(50)

(50) Example 6

(100) Example 7

(100) Comparative Example 1

(100) Comparative Example 2 - Comparative Example 3

(100)

Preparation Example: Preparation of a negative electrode including the negative active material and a lithium secondary battery (coin type half-cell, 2016 R-type)

90% by weight of the negative electrode active material according to Examples 1 to 7 and Comparative Examples 1 to 3, Super-P (carbon black) 5% by weight as a conductive material, SBR (styrene butadiene rubber) 2.5% by weight as a binder, and CMC (carboxy) as a thickener Methylcellulose) 2.5% by weight of pure water was mixed to prepare a negative active material slurry. The negative active material slurry was applied to a copper foil current collector to prepare a negative electrode.

Li metal foil was used as the counter electrode and a porous membrane made of polyethylene was used as the separator. A coin-shaped lithium secondary battery was prepared by injecting an electrolyte containing 5% by weight of FEC (fluoroethylene carbonate) and 1.3M LiPF ₆ EC (ethylene carbonate):DEC (diethyl carbonate) = 3:7 electrolyte.

Experimental Example: Evaluation of capacity and life characteristics of lithium secondary batteries

The lithium secondary battery prepared in Preparation Example above was subjected to a constant current experiment using a charge/discharger capable of constant current/static potential control at 25°C. With a current of C/5 of the capacity each coin battery has, it is charged with a constant current until the voltage reaches 0.01V (vs. Li/Li ⁺ ), and then the voltage reaches 1.2V (vs. Li/Li ⁺ ). Discharged at a constant current of C/5 1 is a charge/discharge capacity change curve when charging/discharging is performed up to 50 times, and FIG. 2 is a capacity curve obtained by separating only the results of Example 1 and Comparative Example 3 in FIG. 1. Compared to the comparative example, it can be seen that the example has excellent life characteristics.

The discharge capacity is the capacity at one cycle, and the capacity retention ratio (%) of the lithium secondary battery was calculated using Equation 1 below, and is shown in Table 2 below.

[Equation 1]

Capacity retention rate [%] = [discharge capacity at the 50th cycle / discharge capacity at the first cycle] × 100

Negative active material Molar ratio of precursor Capacity (mAh/g) Capacity retention rate (%) Need for reduction treatment
(Merit in process: ○/X) Example 1 100 1530 90.2 Not required (○) Example 2 100 1670 85.2 Not required (○) Example 3 50:50 1600 86.2 Not required (○) Example 4 50:50 1030 85.4 Not required (○) Example 5 50:50 1100 84.4 Not required (○) Example 6 100 1490 90.2 Not required (○) Example 7 100 1510 90.1 Not required (○) Comparative Example 1 100 530 35.7 Not required (○) Comparative Example 2 100 3100 8.3 Not required (○) Comparative Example 3 100 980 79.8 Need (X)

As can be seen from Table 2, Figs. 1 and 2, in the case of a secondary battery including a negative electrode manufactured using the negative electrode active material according to the present invention, it shows excellent capacity retention even when repeated charging and discharging 50 times. I can confirm.

On the other hand, in the case of a secondary battery including a negative electrode manufactured using a conventional negative electrode active material other than the negative electrode active material according to the present invention, it can be seen that the discharge capacity is low and the capacity retention rate is very low. In the case of using the negative active material according to Comparative Example 3, in order to suppress a lower discharge capacity and capacity retention rate, a reduction treatment process is additionally required, which complicates the manufacturing process and increases the cost.

Claims (7)

A negative active material comprising a sol-gel reaction product of a monomer represented by the following formula (1):
[Formula 1]

In Formula 1,
X is a halogen element, -OR or

ego,
m and n are each independently an integer of O to 3,
R is a C1 to C4 alkyl group.
The method according to claim 1,
In Formula 1, m and n are each independently 1 or 2, characterized in that the negative active material.
The method according to claim 1,
The monomer represented by Formula 1 includes one or more of the compounds represented by the following Formulas 2 to 4, a negative active material:
[Formula 2]

[Formula 3]

[Formula 4]

In Formulas 2 to 4,
X is a halogen element, -OR or

ego,
R is a C1 to C4 alkyl group.
The method according to claim 1,
The monomer represented by Formula 1 includes a compound represented by Formulas 5 to 8 below:
[Formula 5]

[Formula 6]

[Formula 7]

[Formula 8]

A negative electrode comprising the negative active material of any one of claims 1 to 4.
The method of claim 5,
A negative electrode comprising at least one conductive material selected from the group consisting of graphite, soft carbon, hard carbon, carbon black, carbon nanotube, graphene, graphene oxide, fullerene, and carbon nanofiber.
The cathode of claim 5; anode; Porous separator; And an electrolyte solution.

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