KR102139736B1 - Composite anode active material, a method of preparing the composite anode material, and Lithium secondary battery comprising the composite anode active material - Google Patents

Abstract

Porous carbon structures; A first coating layer disposed on the porous carbon structure and comprising a non-carbon-based material capable of occluding and discharging lithium; And a second coating layer comprising a carbon-based material disposed on the metal layer.

Description

Composite anode active material, a method of preparing the composite anode material, and Lithium secondary battery comprising the composite anode active material}

It relates to a composite cathode active material, and a negative electrode and a lithium battery comprising the same.

Lithium batteries are used for various purposes by having high voltage and high energy density. For example, the field of electric vehicles (HEV, PHEV), etc. can operate at high temperature, and a large amount of electricity must be charged or discharged and used for a long time, so a lithium battery having excellent discharge capacity and life characteristics is required.

The carbon-based material is porous and stable due to little change in volume during charging and discharging. However, in general, the carbon-based material has a low battery capacity due to the porous structure of carbon. For example, the theoretical capacity of graphite with high crystallinity is 372 mAh/g at the LiC ₆ composition. In addition, high rate characteristics are low.

As a negative electrode active material having a higher electric capacity than the carbon-based material, a metal alloyable with lithium may be used. For example, metals alloyable with lithium are Si, Sn, Al, and the like. However, the metals capable of alloying with lithium have a high discharge capacity, but have a large volume change during charging and discharging, so they are easily deteriorated, and thus have low life characteristics.

In order to solve this problem, various studies have been conducted on a silicon-carbon-based composite in which a carbon-based material that contributes to the improvement of electrical conductivity and the role of a matrix of bulk expansion has been conducted.

Existing silicon-carbon-based composites use carbon nanotubes as carbon-based materials to increase the content of silicon, and there are safety problems due to the use of hydrofluoric acid in the manufacturing process. In addition, the existing silicon-carbon-based composite has a problem in that it is difficult to raise the capacity to 800 mAh/g or more due to limited silicon content.

Accordingly, there is a need for a composite cathode active material for a lithium battery and a method for manufacturing the same, which are simple and safe, suppress the volume change of the lithium-alloyable metal without deteriorating the initial efficiency, achieve high capacity, and have improved life characteristics.

One aspect is to provide a novel composite cathode active material.

Another aspect is to provide a method for manufacturing the composite cathode active material.

Another aspect is to provide a lithium secondary battery having a negative electrode containing the composite negative electrode active material.

According to one aspect,

Porous carbon structures;

A first coating layer disposed on the porous carbon structure and comprising a non-carbon-based material capable of occluding and discharging lithium; And

A second coating layer comprising a carbon-based material disposed on the first coating layer

A composite cathode active material is provided.

According to the other aspect,

(a) spray drying a solution containing a carbon source and a pore-forming agent to form a composite structure;

(b) etching the composite structure to form a porous composite structure;

(c) forming a first coating layer on the surface of the porous composite structure by supplying a non-carbon-based material to the porous composite structure; And

(d) forming a second coating layer on the first coating layer on the surface of the porous composite structure by supplying a carbon precursor on the first coating layer;

A method of manufacturing a composite cathode active material is provided.

According to another aspect,

A lithium secondary battery having a negative electrode including the composite negative electrode active material is provided.

According to one aspect, by employing a composite cathode active material comprising a first coating layer containing a non-carbon-based material capable of storing and discharging lithium on the surface of the porous carbon structure and a second coating layer containing a carbon-based material on the first coating layer , A lithium secondary battery having a negative electrode including such a composite negative electrode active material has high capacity, high efficiency, and excellent lifespan characteristics.

1 is a schematic illustration of a porous carbon synthesis method.
2A is an SEM image of porous carbon particles prepared in Preparation Example 1.
2B is an enlarged view of FIG. 2A.
Figure 2c is a SEM image of the cross-section of the porous carbon particles prepared in Preparation Example 1.
3A is an SEM image of the silicon-porous carbon composite prepared in Preparation Example 2-1.
3B is an enlarged view of FIG. 3A.
3C is an SEM image of the silicon-porous carbon composite prepared in Preparation Example 2-1.
3D is an SEM image of the silicon-porous carbon composite prepared in Preparation Example 2-2.
3E is an enlarged view of FIG. 3D.
3f is an SEM image of the silicon-porous carbon composite prepared in Preparation Example 2-3.
3G is an enlarged view of FIG. 3F.
3h is an SEM image of the silicon-porous carbon composite prepared in Preparation Example 2-4.
3i is an enlarged view of FIG. 3h.
Figure 4a is a SEM image of the carbon-silicon-porous carbon composite prepared in Preparation Example 3-1.
4B is an enlarged view of FIG. 4A.
Figure 4c is a SEM image of the carbon-silicon-porous carbon composite prepared in Preparation Example 3-1.
4D and 4E are SEM images of the carbon-silicon-porous carbon composite prepared in Preparation Example 3-2.
4F and 4G are cross-sectional photographs of the carbon-silicon porous carbon composite prepared in Preparation Example 3-2.
4H and 4I are SEM images of the carbon-silicon-porous carbon composite prepared in Preparation Example 3-3.
4J and 4K are cross-sectional photographs of the carbon-silicon porous carbon composite prepared in Preparation Example 3-3.
4L and 4M are SEM images of the carbon-silicon-porous carbon composite prepared in Preparation Example 3-4.
4n and 4o are cross-sectional photographs of the carbon-silicon porous carbon composite prepared in Preparation Example 3-4.
5 is a graph showing a charge/discharge curve of a half cell according to Example 5 and Comparative Example 3.
6 is a graph showing the cycle life of a half cell according to Example 5 and Comparative Example 3.
7 is a graph showing the initial charge and discharge curves of the half cells prepared according to Examples 6 to 8 and Comparative Examples 3 and 4.
8 is a graph showing the cycle life of the half cells prepared according to Examples 6 to 8 and Comparative Examples 3 and 4.
9 is a graph showing the rate characteristics of the half cells prepared according to Examples 6 to 8 and Comparative Examples 3 and 4.
Fig. 10 is a schematic diagram of a lithium battery according to an exemplary embodiment.
<Explanation of reference numerals for main parts of drawings>
1: lithium battery 2: negative electrode
3: anode 4: separator
5: battery case 6: cap assembly

Hereinafter, a composite cathode active material according to exemplary embodiments, a method of manufacturing the same, and a lithium secondary battery having a negative electrode including the same will be described in more detail.

The composite cathode active material according to the embodiment includes a porous carbon structure; A first coating layer disposed on the porous carbon structure and comprising a non-carbon-based material capable of occluding and discharging lithium; And it may include a second coating layer comprising a carbon-based material disposed on the first coating layer.

The porous carbon structure includes a large number of pores, and thus has a larger surface area than the carbon structure having the same volume. Therefore, the first coating layer disposed on the porous carbon structure may include a larger amount of non-carbon-based material without increasing the thickness of the coating layer.

In addition, the porous carbon structure has pores therein, so that it can act as a buffer against expansion of the composite cathode active material during charging and discharging.

The porous carbon structure can provide improved conductivity, and since the pores can accommodate changes in the volume of the non-carbon-based material of the charging/discharging battery, the lithium secondary battery including the composite cathode active material has improved initial efficiency, discharge capacity, and Lifetime characteristics can be obtained.

The average particle diameter (d ₅₀ ) of the porous carbon structure in the composite cathode active material may be 1 to 40 μm. For example, the average particle diameter (d ₅₀ ) of the porous carbon structure may be 1 to 30 μm. For example, the average particle diameter (d ₅₀ ) of the porous carbon structure may be 1 to 20 μm. For example, the average particle diameter (d ₅₀ ) of the porous carbon structure may be 1 to 10 μm. If the average particle diameter of the particles is too small, it may be difficult to prepare an active material slurry and to coat the electrode plate. If the average particle diameter of the particles is too large, the coating layer may be non-uniform or high-rate characteristics may be deteriorated.

In the composite cathode active material, the porous carbon structure may be a spherical or elliptical structure having an aspect ratio of 2 or less. For example, the porous carbon structure may be spherical. When the particles have a spherical shape, it is advantageous for dispersion of the slurry and it is possible to increase the plate strength.

The porous carbon structure in the composite cathode active material may include nanometer-sized pores. For example, the porous carbon structure may include pores having an average pore diameter of 100 nm to 400 nm. For example, the porous carbon structure may include pores having an average pore diameter of 200 nm to 300 nm.

The porous carbon structure may include irregularly shaped pores. That is, the porous carbon structure may include circular and polygonal pores, but is not limited to such a shape.

For example, the cut surface of the particles may include non-spherical pores. The non-spherical pores may be tubular pores having an aspect ratio of 3 or more.

The non-carbon-based material capable of storing and releasing lithium from the composite cathode active material is one or more metals selected from the group consisting of Si, Sn, Al, Ge, Pb, Zn, Ag, and Au, their alloys, their oxides, and their Nitrides, their oxides, or combinations thereof.

According to one embodiment, the non-carbon-based material may be Si. For example, the non-carbon-based material may be amorphous Si, crystalline Si or a mixture thereof. Since the amorphous Si has less structural change stress than crystalline Si, it provides improved charge/discharge characteristics.

In the composite cathode active material, the first coating layer may cover at least a portion of the surface of the porous carbon structure. For example, the first coating layer may cover the entire surface of the porous carbon structure. The surface of the porous carbon structure includes a surface that extends through the pores and into the interior of the porous carbon structure.

According to one embodiment, the first coating layer may uniformly cover the surface of the porous carbon structure. For example, the first coating layer may have a constant thickness from the surface of the porous carbon structure.

The thickness of the first coating layer in the composite cathode active material may be 5 to 100 nm. For example, the thickness of the first coating layer may be 5 to 90 nm. For example, the thickness of the first coating layer may be 5 to 80 nm. For example, the thickness of the first coating layer may be 5 to 70 nm. For example, the thickness of the first coating layer may be 5 to 60 nm. For example, the thickness of the first coating layer may be 5 to 50 nm. For example, the thickness of the first coating layer may be 5 to 40 nm. For example, the thickness of the first coating layer may be 5 to 30 nm. For example, the thickness of the first coating layer may be 5 to 20 nm. For example, the thickness of the first coating layer may be 5 to 10 nm. If the thickness of the first coating layer is too thick, cracking of the active material may occur due to a change in volume of the non-carbon-based material during charging and discharging. If the thickness is too small, a sufficient capacity cannot be obtained.

In general, as the thickness of the first coating layer increases, the content of the non-carbon-based material capable of occluding and discharging lithium increases, and as a result, the capacity of the composite cathode active material may increase. Since there is a disadvantage that cracking of the coating layer may occur due to an increase in the volume change amount, the thickness of the coating layer can be appropriately adjusted to have a maximum capacity in a range that does not degrade life characteristics.

In addition, since the porous carbon structure in the composite cathode active material has a large surface area due to a large number of pores, under the condition that the thickness of the coating layer is the same, compared to the composite cathode active material including a coating layer on a general carbon material, more Since it is possible to form a coating layer containing an amount of non-carbon-based material, there is an advantage that the capacity can be increased without deteriorating the life characteristics.

Alternatively, the composite cathode active material can form a thinner coating layer than the composite cathode active material including a coating layer on a general carbon material under the condition that the content of the non-carbon-based material is the same, thereby reducing the volume change amount I can do it. Therefore, it is possible to significantly improve the life characteristics at the same capacity.

The content of the non-carbon-based material capable of occluding and releasing lithium from the composite cathode active material may be included in an amount of 1 to 80% by weight based on the total weight of the composite cathode active material. For example, the non-carbon-based material may be included in an amount of 1 to 75% by weight based on the total weight of the composite cathode active material. For example, the non-carbon-based material may be included in an amount of 1 to 70% by weight based on the total weight of the composite cathode active material. For example, the non-carbon-based material may be included in an amount of 1 to 65% by weight based on the total weight of the composite cathode active material. For example, the non-carbon-based material may be included in 1 to 60% by weight based on the total weight of the composite cathode active material. For example, the non-carbon-based material may be included in an amount of 1 to 55% by weight based on the total weight of the composite cathode active material. For example, the non-carbon-based material may be included in an amount of 1 to 50% by weight based on the total weight of the composite cathode active material. For example, the non-carbon-based material may be included in an amount of 1 to 45% by weight based on the total weight of the composite cathode active material. For example, the non-carbon-based material may be included in an amount of 1 to 40% by weight based on the total weight of the composite cathode active material. For example, the non-carbon-based material may be included in an amount of 1 to 35% by weight based on the total weight of the composite cathode active material. For example, the non-carbon-based material may be included in an amount of 1 to 30% by weight based on the total weight of the composite cathode active material. For example, the non-carbon-based material may be included in an amount of 1 to 25% by weight based on the total weight of the composite cathode active material. For example, the non-carbon-based material may be included in an amount of 1 to 20% by weight based on the total weight of the composite cathode active material. For example, the non-carbon-based material may be included in 1 to 15% by weight based on the total weight of the composite cathode active material. For example, the non-carbon-based material may be included in 1 to 10% by weight based on the total weight of the composite cathode active material. If the content of the non-carbon-based material capable of occluding and discharging the lithium is too high, cracking of the active material may occur due to a change in volume of the non-carbon-based material during charging and discharging.

In the composite cathode active material, the first coating layer may have a curvature portion. For example, the first coating layer may be formed on some or all of the surface of the porous carbon structure and the surface of the pores extending from the surface of the carbon structure to the inside. For example, the first coating layer may be formed over the periphery of the pores of the porous carbon structure. For example, since the first coating layer is formed of a continuous coating layer on the surface of the pores extending from the surface of the porous carbon structure to the interior of the porous carbon structure, at least a portion of the coating layer may include a curvature portion, 1 By having a curvature portion of the coating layer, it is possible to expand in the radial direction, and thus has an excellent volume expansion buffering effect compared to a flat coating layer that allows volume expansion in one direction.

In the composite cathode active material, the carbon-based material disposed on the first coating layer may include crystalline or amorphous carbon-based material.

In the composite cathode active material, the carbon-based material may be a fired product of a carbon precursor. The carbon precursor may be used in the art, and any carbon-based material obtained by firing may be used.

The carbon precursors are rayon-based carbon fiber, PAN-based carbon fiber, pitch-based carbon fiber, vapor-grown carbon, carbon fiber, graphite, polymer, coal tar pitch, petroleum pitch, meso-phase Pitch, isotropic pitch, coke, low molecular heavy oil, coal-based pitch, phenol resin, naphthalene resin, epoxy resin, vinyl chloride resin, polyimide, polybenzimidazole, polyacrylonitrile, polyethylene glycol, polyvinyl alcohol, polyvinyl chloride, Furfuryl alcohol, furan, cellulose, glucose, sucrose, acetic acid, malic acid, citric acid, organic acids, and derivatives thereof.

For example, the second coating layer is selected from the group comprising rayon carbon fiber, PAN based carbon fiber, pitch based carbon fiber, vapor phase growth carbon, or combinations thereof. It may be formed from a carbon precursor.

In the composite cathode active material, the thickness of the second coating layer may be 0.1 to 100 nm. For example, the thickness of the second coating layer may be 0.1 to 90 nm. For example, the thickness of the second coating layer may be 0.1 to 80 nm. For example, the thickness of the second coating layer may be 0.1 to 70 nm. For example, the thickness of the second coating layer may be 0.1 to 60 nm. For example, the thickness of the second coating layer may be 0.1 to 50 nm. For example, the thickness of the second coating layer may be 0.1 to 40 nm. For example, the thickness of the second coating layer may be 0.1 to 30 nm. For example, the thickness of the second coating layer may be 0.1 to 20 nm. For example, the thickness of the second coating layer may be 0.1 to 100 nm. The second coating layer forms SEI during charging and discharging, and can prevent the porous carbon structure and the non-carbon-based material from contacting an electrolyte or the like due to selective passage of lithium ions. As a result, durability can be improved.

Hereinafter, a method of manufacturing the composite cathode active material will be described.

According to one embodiment, the method of manufacturing the negative electrode active material,

(a) spray drying a solution containing a carbon source and a pore former to obtain a composite structure;

(b) etching the composite structure to form a porous carbon structure;

(c) forming a first coating layer on the surface of the porous carbon structure by supplying a non-carbon-based material to the porous carbon structure; And

(d) forming a second coating layer on the first coating layer on the surface of the porous carbon structure by supplying a carbon precursor on the first coating layer;

It may include.

The carbon source can be easily selected by those skilled in the art from those that can be used in the art as long as it can form a carbon structure by firing.

For example, the carbon source is rayon-based carbon fiber, PAN-based carbon fiber, pitch-based carbon fiber, vapor-grown carbon, carbon fiber, graphite, polymer, coal tar pitch, petroleum pitch, Meso-phase pitch, isotropic pitch, coke, low molecular weight heavy oil, coal-based pitch, phenol resin, naphthalene resin, epoxy resin, vinyl chloride resin, polyimide, polybenzimidazole, polyacrylonitrile, polyethylene glycol, polyvinyl alcohol, poly Vinyl chloride, furfuryl alcohol, furan, cellulose, glucose, sucrose, acetic acid, malic acid, citric acid, organic acid, and derivatives thereof.

The pore forming agent may be silicon oxide.

The carbon source and pore former may be dissolved in tetrahydrofuran (THF). The solution may further include a dispersant so that the pore forming agent is uniformly dispersed.

After the step (a), before the step (b), it may further include a step of sintering under a nitrogen atmosphere.

The sintering process may be performed at 800°C or higher. For example, the sintering process may be performed at 900°C or higher. For example, the sintering process may be performed at 1000°C or higher.

In the step (b), silicon oxide may be etched from the composite structure by immersing the composite structure in a sodium hydroxide (NaOH) solution. As a result, pores may be formed in a position where silicon oxide is removed. Sodium hydroxide is easy to handle and safe, so the process is simpler compared to when hydrofluoric acid is used as an etchant.

In step (c), the non-carbon-based material may be a silane-based gas. The non-carbon-based material can be easily selected by those skilled in the art from those that can be used in the art as long as it can release Si atoms by gasification.

For example, the non-carbon materials include silane (SiH ₄ ), dichlorosilane (SiH ₂ Cl ₂ ), silicon tetrafluoride (SiF ₄ ), and silicon tetratride (Silicon). Tetrachloride, SiCl ₄ ), methylsilane (Methylsilane, CH ₃ SiH ₃ ), disilane (Disilane, Si ₂ H ₆ ), or a combination thereof may be a silicon-based precursor.

In step (d), the carbon precursor is petroleum pitch, coal pitch, polyimide, polybenzimidazole, polyacrylonitrile, mesophase pitch, furfuryl alcohol, furan, cellulose, sucrose, polyvinyl chloride, or Mixtures of these.

Steps (c) and (d) may be performed by chemical vapor deposition (CVD) in an inert gas atmosphere. The inert gas atmosphere is not particularly limited, but may be an argon (Ar) or nitrogen (N ₂ ) atmosphere.

The step (c) may include a process of heat treatment at a temperature of 450°C to 600°C. For example, it may include a process of heat treatment at a temperature of 450 ℃ to 500 ℃. The heat treatment is from 1 minute to 10 hours, for example from 1 minute to 5 hours, for example from 1 minute to 3 hours, for example from 1 minute to 1 hour, for example from 1 minute to It can be performed for 30 minutes.

The step (d) may include a process of heat treatment at a temperature of 700°C to 900°C. For example, it may include a process of heat treatment at a temperature of 750 ℃ to 850 ℃. The heat treatment is from 1 minute to 10 hours, for example from 1 minute to 5 hours, for example from 1 minute to 3 hours, for example from 1 minute to 1 hour, for example from 1 minute to It can be performed for 30 minutes.

A negative electrode for a lithium battery according to another aspect includes a negative electrode current collector; And a negative electrode active material layer disposed on at least one surface of the negative electrode current collector and including the composite negative electrode active material described above.

The negative electrode may include a binder between the negative electrode current collector and the negative electrode active material layer or in the negative electrode active material layer. The binder will be described later.

The negative electrode and the lithium battery including the same may be manufactured as follows.

The negative electrode includes the above-described composite negative electrode active material, for example, by mixing the above-described composite negative electrode active material, a binder and optionally a conductive material in a solvent to prepare a composite negative electrode active material composition, and then molding it into a certain shape, or copper foil (copper foil) can be produced by applying to the current collector.

The binder used in the composite negative electrode active material composition is a component that assists in bonding the composite negative electrode active material and a conductive material to the current collector, and may be included between the negative electrode current collector and the negative electrode active material layer or in the negative electrode active material layer, The composite cathode active material is added in an amount of 1 to 50 parts by weight based on 100 parts by weight. For example, the binder may be added in a range of 1 to 30 parts by weight, 1 to 20 parts by weight, or 1 to 15 parts by weight based on 100 parts by weight of the composite cathode active material. Examples of such binders include polyvinylidene fluoride, polyvinylidene chloride, polybenzimidazole, polyimide, polyvinyl acetate, polyacrylonitrile, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxy Hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polystyrene, polymethylmethacrylate, polyaniline, acrylonitrile butadiene styrene, phenol resin, epoxy resin, polyethylene Terephthalate, polytetrafluoroethylene, polyphenylene sulfide, polyamideimide, polyetherimide, polyethersulfone, polyamide, polyacetal, polyphenylene oxide, polybutylene terephthalate, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluorine rubber, various copolymers, and the like.

The cathode may optionally further include a conductive material to provide a conductive passage to the above-described composite cathode active material to further improve electrical conductivity. As the conductive material, any one generally used for lithium batteries can be used, for example, carbon-based materials such as carbon black, acetylene black, ketjen black, and carbon fibers (eg, vapor-grown carbon fibers); Metal powders such as copper, nickel, aluminum, silver, or metal fibers; Conductive materials containing conductive polymers such as polyphenylene derivatives or mixtures thereof can be used. The content of the conductive material can be suitably adjusted and used. For example, the weight ratio of the composite cathode active material and the conductive material may be added in a range of 99:1 to 90:10.

As the solvent, N-methylpyrrolidone (NMP), acetone, water, or the like can be used. The content of the solvent is 1 to 10 parts by weight based on 100 parts by weight of the composite cathode active material. When the content of the solvent is within the above range, the operation for forming the active material layer is easy.

In addition, the current collector is generally made to a thickness of 3 to 500 μm. The current collector is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surfaces Carbon, nickel, titanium, silver or the like, aluminum-cadmium alloy, or the like may be used. In addition, by forming fine irregularities on the surface, it is also possible to enhance the bonding force of the composite cathode active material, and can be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics.

A negative electrode plate can be obtained by directly coating the prepared composite negative electrode active material composition on a current collector, or by laminating a composite negative electrode active material film cast on a separate support and peeled from the support to a copper foil current collector. The cathode is not limited to the above-listed forms, and may be in a form other than the above-mentioned forms.

The composite cathode active material composition can be used not only for the production of an electrode of a lithium battery, but also for printing a flexible battery printed on a flexible electrode substrate.

Next, a separator is prepared.

The separator can be used as long as it is commonly used in lithium batteries. It is possible to use a low resistance to electrolyte ion migration and an excellent electrolyte-moisturizing ability. For example, glass fiber, polyester, Teflon, polyethylene, polypropylene, polytetrafluoroethylene (PTFE) or a combination thereof, and may be in the form of non-woven or woven fabric. For example, a wound separator such as polyethylene or polypropylene is used for a lithium ion battery, and a separator having excellent organic electrolyte impregnation ability may be used for a lithium ion polymer battery. For example, the separator can be manufactured according to the following method.

A separator composition is prepared by mixing a polymer resin, a filler, and a solvent. The separator composition may be coated and dried directly on the electrode to form a separator. Alternatively, after the separator composition is cast and dried on a support, the separator film peeled from the support may be laminated on the electrode to form a separator.

The polymer resin used in the production of the separator is not particularly limited, and all materials used for the bonding material of the electrode plate can be used. For example, vinylidene fluoride/hexafluoropropylene copolymer, polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, or mixtures thereof may be used.

Next, the electrolyte may be a lithium salt-containing non-aqueous electrolyte.

The lithium salt-containing non-aqueous electrolyte is composed of a non-aqueous electrolyte solution and lithium. Non-aqueous electrolytes, non-aqueous electrolytes, solid electrolytes, inorganic solid electrolytes, and the like are used.

As the non-aqueous electrolyte, for example, N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethylene fluoride carbonate, ethylene methylene carbonate, methyl propyl carbonate, ethyl Propanoate, methyl acetate, ethyl acetate, propyl acetate, dimethyl ester gamma-butylo lactone, 1,2-dimethoxy ethane, tetrahydrofuran, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxo Lan, formamide, dimethylformamide, dioxone, acetonitrile, nitromethane, methyl formate, phosphoric acid triester, trimethoxy methane, dioxolane derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2 -Non-protonic organic solvents such as imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl pyropionate and ethyl propionate can be used.

Examples of the organic solid electrolyte include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate ester polymers, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, and polymers containing ionic dissociative groups. Can be used.

The inorganic solid electrolyte, for example, Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Li ₄ nitrides such as Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₂ S-SiS ₂ , halides, sulfates, and the like can be used.

The lithium salt may be used as long as it is commonly used in lithium batteries, and is a material that is soluble in the non-aqueous electrolyte. For example, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , _{LiPF 6, LiCF 3 SO 3,} LiCF 3 CO 2, LiAsF 6, LiSbF 6, LiAlCl 4, CH 3 SO 3 Li, CF 3 SO 3 Li, (CF 3 SO 2) 2 NLi, lithium chloro borate, lower aliphatic carboxylic One or more substances such as lithium phosphate, 4-phenyl lithium borate, and imide may be used.

Lithium batteries may be classified into lithium ion batteries, lithium ion polymer batteries, and lithium polymer batteries according to the type of separator and electrolyte used, and may be classified into cylindrical, square, coin, and pouch shapes depending on the shape, and size. According to it, it can be divided into bulk type and thin film type. In addition, both lithium primary and lithium secondary batteries are possible.

The lithium battery includes a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode. The above-described positive electrode, negative electrode and separator are wound or folded to be accommodated in a battery container. Subsequently, an electrolyte is injected into the battery container and sealed with an encapsulation member to complete the lithium battery. The battery container may be cylindrical, prismatic, thin film, or the like. The lithium battery may be a lithium ion battery.

The lithium secondary battery has a winding type and a stack type according to an electrode type, and may be classified into a cylindrical shape, a square shape, a coin shape, and a pouch shape according to the type of the exterior material.

Methods for manufacturing these batteries are well known in the art, and detailed descriptions thereof are omitted.

The lithium battery can be used not only for a battery used as a power source for a small device, but also as a unit battery for a medium-to-large-sized device battery module including a plurality of batteries.

Examples of the medium-to-large-sized device include a power tool; XEV including an electric vehicle (EV), a hybrid electric vehicle (HEV) and a plug-in hybrid electric vehicle (PHEV); Electric two-wheeled vehicles including E-bikes and E-scooters; Electric golf cart (Electric golf cart); Electric truck; Electric commercial vehicles; Or power storage systems; And the like, but are not limited to these. In addition, the lithium battery can be used for all other applications requiring high power, high voltage and high temperature driving.

Exemplary embodiments are described in more detail through the following examples and comparative examples. However, the examples are only for illustrating the technical idea, and the scope of the present invention is not limited thereto.

(Preparation of porous carbon composites)

Preparation Example 1

SiO ₂ nanopowders with a pitch and average diameter of 200 nm were dissolved in THF in a weight ratio of 1:4 and stirred to obtain a mixture. After spray drying, the mixture was heat-treated under an atmosphere of 300°C for 3 hours under an oxygen atmosphere, and then heat-treated and carbonized under a nitrogen atmosphere for 900 hours for 1 hour to obtain a carbon-silicon oxide composite of carbon and SiO ₂ . The composite was immersed in a 5M NaOH solution and etched for 24 hours to prepare a porous carbon structure having an average pore diameter of 200 nm.

SEM photographs of the prepared porous carbon are shown in FIGS. 2A-2C.

(Preparation of silicon-porous carbon composites)

Preparation Example 2-1

1 g of the porous carbon structure obtained in Preparation Example 1 was subjected to chemical vapor deposition of SiH ₄ (g) at a rate of 50 sccm for 15 minutes under 475° C. conditions to prepare a silicon-porous carbon composite.

SEM photographs of the prepared silicon-porous carbon composites are shown in FIGS. 3A-3C.

Preparation Example 2-2 (SMM600)

1 g of the porous carbon structure obtained in Preparation Example 1 was subjected to chemical vapor deposition of SiH ₄ (g) at a rate of 50 sccm for 6 minutes at 475° C. to prepare a silicon-porous carbon composite.

SEM photographs of the prepared silicon-porous carbon composites are shown in FIGS. 3D to 3E.

Preparation Example 2-3 (SMM1200)

1 g of the porous carbon structure obtained in Preparation Example 1 was subjected to chemical vapor deposition of SiH ₄ (g) at a rate of 50 sccm for 11 minutes under 475° C. conditions to prepare a silicon-porous carbon composite.

SEM photographs of the prepared silicon-porous carbon composites are shown in FIGS. 3F-3G.

Preparation Example 2-4 (SMM2000)

1 g of the porous carbon structure obtained in Preparation Example 1 was subjected to chemical vapor deposition of SiH ₄ (g) at a rate of 50 sccm for 25 minutes under 475° C. to prepare a silicon-porous carbon composite.

SEM photographs of the prepared silicon-porous carbon composites are shown in FIGS. 3H to 3I.

(Carbon-silicon-porous carbon composite)

Preparation Example 3-1

The pitch of 0.1 g and 0.1 g of the silicon-porous carbon composite obtained in Preparation Example 2-1 were mixed and mixed in a dry mixer. The mixed sample was then heat treated under a nitrogen atmosphere at 900°C for 1 hour to prepare a carbon-silicon-porous carbon composite.

SEM images of the prepared carbon-silicon-porous carbon composites are shown in FIGS. 4A-4C.

Preparation Example 3-2 (CSMM600)

The pitch of 0.1 g and 0.1 g of the silicon-porous carbon composite obtained in Production Example 2-2 was mixed and mixed in a dry mixer. The mixed sample was then heat treated under a nitrogen atmosphere at 900°C for 1 hour to prepare a carbon-silicon-porous carbon composite.

SEM photographs of the prepared carbon-silicon-porous carbon composites are shown in FIGS. 4D and 4E, and cross-sectional photographs and enlarged photographs thereof are shown in FIGS. 4F and 4G.

Preparation Example 3-3 (CSMM1200)

The pitch of 0.1 g and 0.1 g of the silicon-porous carbon composite obtained in Preparation Example 2-3 was mixed and mixed in a dry mixer. The mixed sample was then heat treated under a nitrogen atmosphere at 900°C for 1 hour to prepare a carbon-silicon-porous carbon composite.

SEM photographs of the prepared carbon-silicon-porous carbon composites are shown in FIGS. 4H and 4I, and cross-sectional photographs are shown in FIGS. 4J and 4K.

Preparation Example 3-4 (CSMM2000)

The pitch of 0.1 g and 0.1 g of the silicon-porous carbon composite obtained in Preparation Example 2-3 was mixed and mixed in a dry mixer. The mixed sample was then heat treated under a nitrogen atmosphere at 900°C for 1 hour to prepare a carbon-silicon-porous carbon composite.

SEM photographs of the prepared carbon-silicon-porous carbon composites are shown in FIGS. 4L and 4M, and cross-sectional photographs are shown in FIGS. 4N and 4O.

(Production of cathode)

Example 1

The carbon-silicon-porous carbon composite obtained in Preparation Example 3-1 was used as a negative electrode active material, carbon black as a conductive agent, CMC as a thickener, and SBR as a binder, and the negative electrode active material/conductor/thickener/binder A slurry was prepared at a ratio of 80:10:5:5. The slurry was applied on a copper current collector of 18 μm thickness using a conventional method. The current collector to which the slurry was applied was dried at room temperature, then dried at 120° C. under vacuum, and rolled and punched to prepare a negative electrode to be applied to the cell.

Examples 2 to 4

A negative electrode was prepared in the same manner as in Example 1, except that the carbon-silicon-porous carbon composites obtained in Preparation Examples 3-2 to 3-4 were used as the negative electrode active material.

Comparative Example 1

A negative electrode was prepared in the same manner as in Example 1, except that the porous carbon composite obtained in Preparation Example 1 was used as the negative electrode active material.

Comparative Example 2

A negative electrode was prepared in the same manner as in Example 1, except that silicon nanoparticles were used as the negative electrode active material.

(Production of half cell)

Example 5

A CR2032 coin-type half cell was manufactured by using lithium foil as a negative electrode and a counter electrode prepared in Example 1, placing a separator between the negative electrode and the counter electrode, and injecting a liquid electrolyte.

A porous polyethylene film was used as the separator.

As the liquid electrolyte, 10% by weight of ethylene fluoride carbonate (FEC) was added to a solvent in which ethyl carbonate (EC) and diethyl carbonate (DEC) were mixed in a 3:7 volume ratio, and 1.3M LiPF ₆ was dissolved therein. Was used.

Examples 6 to 8

Coin-type half cells were manufactured in the same manner as in Example 5, except that the cathodes prepared in Examples 2 to 4 were used instead of the anodes prepared in Example 1.

Comparative Example 3

A coin-type half cell was manufactured in the same manner as in Example 5, except that the negative electrode prepared in Comparative Example 1 was used instead of the negative electrode prepared in Example 1.

Comparative Example 4

Coin-type half cells were manufactured in the same manner as in Example 5, except that the negative electrode prepared in Comparative Example 2 was used instead of the negative electrode prepared in Example 1.

Evaluation Example 1: Evaluation of charge/discharge characteristics (1)

The half-cells prepared in Example 5 and Comparative Example 3 start charging at a charging rate of 0.1 C-rate at 25° C., and the voltage is charged to 0.01 V. At this time, the battery is charged to have a constant voltage with a constant current and then to a constant voltage. Charge until constant current or less (0.01C). Then, it was discharged at a constant current until it reached 1.5 V at a discharge rate of 0.1 C-rate. After the two charge and discharge cycles as described above, the voltage section is set to 0.01V to 1.5V at a charge and discharge rate of 0.5C-rate, and 200 charge and discharge cycles are repeated continuously. Some of the results of the charge-discharge test are shown in Table 1 below, and the graphs of the charge-discharge test result and the cycle life graph are shown in FIGS. 5 and 6.

The initial efficiency and capacity retention rate were calculated from Equations 1 to 2 below.

<Equation 1>

The initial efficiency (%) = [discharge capacity / charge capacity at 1 ^st cycle at 1 ^st cycle] ㅧ 100

<Equation 2>

Capacity retention rate [%] = [Discharge capacity of 50 ^th cycle / Discharge capacity of 1 ^st cycle] ㅧ 100

Initial efficiency
[%] Capacity retention rate
[%] Example 5 78 93.2 Comparative Example 3 34 78.3

As can be seen from Table 1, the half-cell comprising the composite cathode active material comprising the carbon-silicon-porous carbon composite of the present invention (Example 5) is a half-cell comprising a negative electrode active material comprising a porous carbon composite ( It can be seen that it has excellent initial efficiency and life characteristics compared to Comparative Example 3).

Evaluation Example 2: Mars voltage profile

Examples 6 to 8, and Comparative Examples 3 and 4 were measured for the weight capacity compared to the voltage due to the initial charge and discharge for the half cells produced, and the results are shown in FIG. 7.

Referring to FIG. 7, the negative electrode active material used in Example 6 has a reversible capacity of about 600 mAh/g, the negative electrode active material used in Example 7 has a reversible capacity of about 1200 mAh/g, and the negative electrode active material used in Example 8 is It can be seen that the reversible capacity is about 2000 mAh/g. On the other hand, the negative electrode active material used in Comparative Example 3 has a reversible capacity of only about 400 mAh/g, and it can be seen that the negative electrode active material used in Examples 6 to 8 of the present invention has excellent capacity. The negative electrode active material used in Comparative Example 4 has a reversible capacity of about 3400 mAh/g, which has a higher capacity than the negative electrode active material used in Examples 6 to 8, but as described later, there is a problem in that the life characteristics are significantly lowered during the charging and discharging process. exist.

Evaluation Example 3: Evaluation of charge/discharge characteristics (2)

Experiments were conducted on the half cells prepared according to Examples 6 to 8 and Comparative Examples 3 and 4 in the same manner as in Evaluation Example 1, and the results are shown in Tables 2 and 8 below.

Initial efficiency
[%] Capacity retention rate
[%] Example 6 73.5 98.6 Example 7 83.3 96.5 Example 8 91.2 74.9 Comparative Example 3 48.6 98.5 Comparative Example 4 78.0 54.7

According to Table 2 and FIG. 8, the half cells according to Examples 6 and 7 showed a capacity retention rate equivalent to that of the half cells according to Comparative Example 3, and the half cells according to Examples 6 to 8 compared to Comparative Example 4 It had a significantly improved capacity retention rate. That is, Examples 6 to 8 employing a carbon-silicon-porous carbon structure as a negative electrode active material achieved an improvement in overall capacity through introduction of silicon, and at the same time, a capacity retention ratio equivalent to that of Comparative Example 3 employing only a carbon structure. Was achieved.

Evaluation Example 4: Evaluation of rate characteristics

Rate characteristics of the half cells produced according to Examples 6 to 8 and Comparative Examples 3 and 4 were evaluated by rate (0.5C, 1C, 2C, 5C, 10C, 20C) while charging and discharging cycles were performed. , The results are shown in FIG. 9. In the graph shown in FIG. 9, the x-axis is the number of cycles, and the y-axis represents the capacity retention rate. The capacity retention rate represents the rate of decrease in capacity compared to the initial reversible capacity.

Referring to Figure 9, it can be seen that the life characteristics of the half cells according to Examples 6 to 8 of the present invention are generally improved compared to the half cells according to Comparative Example 4. In particular, it can be seen that the half-cell according to Example 7 at 20-25 cycles, 10C has a capacity retention rate exceeding 50%, and the half-cell according to Comparative Example 4 is sharply different from the capacity retention rate dropped to about 5%. Contrast. In addition, even at a high rate such as 20C, the half cell according to Example 6 shows a capacity retention rate of about 60%, and it can be seen that it has excellent high rate characteristics.

In the above, a preferred embodiment according to the present invention has been described with reference to the drawings and examples, but this is merely exemplary, and various modifications and equivalent other implementations are possible from those skilled in the art. Will be able to understand. Therefore, the protection scope of the present invention should be defined by the appended claims.

Claims (20)

Porous carbon structures;
A first coating layer disposed on the porous carbon structure and comprising a non-carbon-based material capable of occluding and discharging lithium; And
A second coating layer comprising a carbon-based material disposed on the first coating layer;
Including,
The average diameter of the pores of the porous carbon structure is 200 to 300 nm, composite cathode active material. According to claim 1,
A composite cathode active material having an average particle diameter (d ₅₀ ) of the porous carbon structure of 1 to 40 μm. According to claim 1,
The porous carbon structure is a spherical or elliptical structure having an aspect ratio of 2 or less, a composite cathode active material. delete According to claim 1,
The first coating layer surrounds at least a portion of the surface of the porous carbon structure, composite cathode active material. According to claim 1,
The non-carbon-based material includes one or more metals selected from the group consisting of Si, Sn, Al, Ge, Pb, Zn, Ag and Au, their alloys, their oxides, their nitrides, their nitric oxides or combinations thereof A composite cathode active material. According to claim 1,
The thickness of the first coating layer is 5 to 100nm, composite cathode active material. The method of claim 1
The content of the non-carbon-based material is 1 to 80% by weight based on the total weight of the composite cathode active material, composite cathode active material. According to claim 1,
A composite cathode active material, wherein the first coating layer has a curvature portion. According to claim 1,
The carbon-based material is rayon-based carbon fiber, PAN-based carbon fiber, pitch-based carbon fiber, vapor-grown carbon, carbon fiber, graphite, polymer, coal tar pitch, petroleum pitch, meso- Phase pitch, isotropic pitch, coke, low molecular weight heavy oil, coal-based pitch, phenol resin, naphthalene resin, epoxy resin, vinyl chloride resin, polyimide, polybenzimidazole, polyacrylonitrile, polyethylene glycol, polyvinyl alcohol, polyvinyl chloride , Furfuryl alcohol, furan, cellulose, glucose, sucrose, acetic acid, malic acid, citric acid, organic acids, and those formed from carbon precursors selected from the group comprising derivatives thereof, composite cathode active material. According to claim 1,
A composite cathode active material having a thickness of the second coating layer of 0.1 to 100 nm. (A) spray-drying a solution containing a carbon source and a pore-forming agent to obtain a composite structure;
(b) etching the composite structure to form a porous carbon structure;
(c) forming a first coating layer on the surface of the porous carbon structure by supplying a non-carbon-based material to the porous carbon structure; And
(d) forming a second coating layer on the first coating layer on the surface of the porous carbon structure by supplying a carbon precursor on the first coating layer;
Including,
The average diameter of the pores of the porous carbon structure is 200 to 300 nm, a method for producing a composite cathode active material. The method of claim 12,
The pore forming agent is a silicon oxide, a method for producing a composite cathode active material. The method of claim 12,
After the step (a), before the step (b), further comprising the step of sintering under a nitrogen atmosphere, a method for producing a composite cathode active material. The method of claim 12,
In the step (b), the composite structure is etched with sodium hydroxide (NaOH) solution, a method for producing a composite cathode active material. The method of claim 12,
In the step (c), the non-carbon-based material is a silane-based gas, a method for producing a composite cathode active material. The method of claim 12,
In step (d), the carbon precursor is rayon-based (rayon) carbon fiber, PAN-based (PAN based) carbon fiber, pitch-based carbon fiber, vapor-grown carbon, carbon fiber, graphite, polymer, coal tar pitch , Petroleum pitch, meso-phase pitch, isotropic pitch, coke, low molecular heavy oil, coal-based pitch, phenol resin, naphthalene resin, epoxy resin, vinyl chloride resin, polyimide, polybenzimidazole, polyacrylonitrile, polyethylene glycol, poly Method for producing a composite cathode active material, at least one selected from vinyl alcohol, polyvinyl chloride, furfuryl alcohol, furan, cellulose, glucose, sucrose, acetic acid, malic acid, citric acid, organic acid, and derivatives thereof. The method of claim 12,
The (c) step includes a process of heat treatment at a temperature of 450°C to 600°C, a method of manufacturing a composite cathode active material. The method of claim 12,
The (d) step includes a process of heat treatment at a temperature of 700 °C to 900 °C, a method for producing a composite cathode active material. anode;
Electrolyte; And
Cathode comprising the composite cathode active material according to any one of claims 1 to 3 and 5 to 11;
Lithium secondary battery comprising a.

Images