KR101105354B1 - Negative active material for rechargeable lithium battery, method of preparing the same, and rechargeable lithium battery including the same - Google Patents

Abstract

It provides a negative electrode active material for a lithium secondary battery comprising a disk containing a phosphate of tin (Sn), the disk provides a negative electrode active material for a lithium secondary battery containing pores.

Description

A negative active material for a lithium secondary battery, a method of manufacturing the same, and a lithium secondary battery including the same.

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

Cells generate electricity by using materials that can electrochemically react to the positive and negative electrodes. A typical example of such a battery is a lithium secondary battery that generates electric energy by a change in chemical potential when lithium ions are intercalated / deintercalated at a positive electrode and a negative electrode.

The lithium secondary battery is prepared by using a material capable of reversible intercalation / deintercalation of lithium ions as a positive electrode active material and a negative electrode active material, and filling an organic electrolyte or a polymer electrolyte between the positive electrode and the negative electrode.

As a cathode active material of a lithium secondary battery, a lithium composite metal compound is used. Examples thereof include a composite of LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiNi _{1- x} Co _x O ₂ (0 <x <1), and LiMnO ₂ . Metal oxides are being studied.

As a negative electrode active material of a lithium secondary battery, various types of carbon-based materials including artificial graphite, natural graphite, and hard carbon capable of inserting / desorbing lithium have been applied. The graphite of the carbon series has a low discharge voltage of -0.2 V compared to lithium, and the battery using the negative electrode active material exhibits a high discharge voltage of 3.6 V, providing an advantage in terms of energy density of the lithium battery and excellent reversibility in lithium secondary. It is most widely used to ensure the long life of the battery. However, the graphite active material has a problem that the capacity of graphite is low in terms of energy density per unit volume of the electrode plate because the density of graphite is about 1.6 g / cc.

Recently, research has been made on a high capacity negative electrode active material to replace the graphite active material.

One aspect of the present invention is to provide a negative active material for a lithium secondary battery having excellent coulombic efficiency, rate-specific characteristics, and cycle life characteristics.

Another aspect of the present invention is to provide a method of manufacturing the negative active material for the lithium secondary battery.

Another aspect of the present invention to provide a lithium secondary battery comprising the negative electrode active material for the lithium secondary battery.

According to an aspect of the invention, there is provided a negative electrode active material for a lithium secondary battery comprising a disk containing a phosphate of tin (Sn). The disk includes pores.

The phosphate salt of tin may comprise at least about 80% by weight of the amorphous phase.

The phosphates of tin are, for example, Sn ₂ P ₂ O ₇ , Sn _x P ₂ O _{7 -y} (where x is 1.8 ≦ x <2 and y is 0 ≦ y ≦ 0.2) or a combination thereof. It may include.

The disk may be polygonal or cylindrical, may have a thickness of about 5 nm to about 50 nm, and may have a diameter of about 10 nm to about 300 nm.

The porosity of the disk may be about 20% to about 80%.

The negative active material for the lithium secondary battery may have a surface area of Brunauer-Emmett-Teller (BET) of about 5 m ² / g to about 60 m ² / g.

According to another aspect of the present invention, preparing a phosphate precursor of tin by mixing a precursor of tin (Sn), a precursor of phosphorus (P) and water (H ₂ O); Leaving the tin phosphate precursor at a high temperature; And after leaving at the high temperature, it provides a method for producing a negative electrode active material for a lithium secondary battery comprising the step of quenching (quenching).

The precursor of tin may include SnCl ₄ , SnF _4, or a combination thereof, and the precursor of phosphorus may include H ₃ PO ₄ , (NH ₄ ) ₂ HPO ₅ , P ₂ O _5, or a combination thereof. .

The phosphate precursor of tin may include (SnHPO ₄ ) ₂ .H ₂ O, SnHPO _4, or a combination thereof.

The phosphate precursor of tin may be crystalline, and the crystal particles of the phosphate precursor of tin may have a diameter of about 10 nm to about 300 nm.

The step of leaving at the high temperature may be performed by leaving at a temperature of about 100 ℃ to about 200 ℃.

The quenching may be performed at a temperature of about 600 ° C. to about 800 ° C., and maintained at 0.1 hour to 1 hour, followed by rapid cooling to room temperature. It can be / hour.

According to another aspect of the present invention, there is provided a lithium secondary battery including a negative electrode including the negative electrode active material, a positive electrode including a positive electrode active material, and an electrolyte.

The negative active material for a lithium secondary battery according to an aspect of the present invention is excellent in coulombic efficiency, rate-specific characteristics, and cycle life characteristics.

1 illustrates a form before a cycle of a negative active material for a rechargeable lithium battery according to one embodiment of the present invention.
Figure 2 shows the form after one cycle of the negative electrode active material for a lithium secondary battery according to an embodiment of the present invention.
3 shows a form after a large number of cycles of the negative electrode active material for a rechargeable lithium battery according to one embodiment of the present invention.
4 is an X-ray diffraction graph of the negative active material for a lithium secondary battery prepared in Example 1 above.
5 is an X-ray diffraction analysis graph of the negative electrode prepared in Example 2 measured while charging and discharging up to 220 times.
6A is a SEM photograph of a phosphate precursor having a structure in which a plurality of disks prepared in Example 1 are stacked.
FIG. 6B is an enlarged view of a portion A of FIG. 6A.
6C is a SEM photograph of the negative electrode active material for a lithium secondary battery prepared in Example 1;
FIG. 6D is an enlarged view of a portion B of FIG. 6C.
7A is a TEM photograph of the negative active material for a lithium secondary battery prepared in Example 1;
FIG. 7B is an enlarged photograph of FIG. 7A.
8 is a TEM photograph of a negative electrode active material for a lithium secondary battery prepared in Comparative Example 1;
9 is a TEM photograph of the negative electrode active material for a lithium secondary battery prepared in Comparative Example 3.
10A and 10B are TEM photographs and HRTEM photographs after one time charge and discharge of the negative electrode active material for a lithium secondary battery prepared in Example 1 above.
10C is a TEM photograph after 50 charging and discharging operations of the negative active material for a lithium secondary battery prepared in Example 1 above.
10D is a TEM photograph after 100 charging and discharging of the negative electrode active material for a lithium secondary battery prepared in Example 1 above.
10E and 10F are TEM photographs and HRTEM photographs after 220 charge / discharge runs of the negative active material for a lithium secondary battery prepared in Example 1 above.
11A and 11B are TEM photographs and HRTEM photographs after 20 charge / discharge cycles of the negative electrode active material for a lithium secondary battery prepared in Comparative Example 1 above.
11C and 11D are TEM photographs and HRTEM photographs after 100 charge / discharge runs of the negative active material for a lithium secondary battery prepared in Comparative Example 1 above.
12 is a TEM photograph after 100 charging and discharging of the negative electrode active material for a lithium secondary battery prepared in Comparative Example 3 above.
FIG. 13 is a graph showing the discharge capacity versus the number of cycles of the half cells prepared in Example 2 and Comparative Example 2. FIG.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. However, this is presented as an example, by which the present invention is not limited and the present invention is defined only by the scope of the claims to be described later.

In the drawings, the thickness of layers, films, panels, regions, etc., are exaggerated for clarity. Like parts are designated by like reference numerals throughout the specification.

Whenever a portion of a layer, film, region, plate, or the like is referred to as being "on" another portion, it includes not only the case where it is "directly on" another portion, but also the case where there is another portion in between. On the contrary, when a part is "just above" another part, there is no other part in the middle.

According to one embodiment of the invention provides a negative electrode active material for a lithium secondary battery comprising a disk containing a phosphate of tin (Sn). The disk includes pores. In other words, the disk is a porous disk.

When the negative electrode active material for a lithium secondary battery includes a disk shape, the diffusion rate of lithium ions is increased, thereby The negative active material for a rechargeable lithium battery according to one embodiment of the present invention may improve lifespan characteristics, coulombic efficiency, and rate-specific characteristics.

In addition, when the disk contains pores, the pores play a buffer role, whereby a cycle proceeds, whereby Li _x PO _y (where x is 1 ≦ x ≦ 3 and y is 1 ≦ y ≦ 4). Formed, and even though the volume expands as tin particles are formed, tin particles are not pulverized in the Li _x PO _y (where x is 1 ≦ x ≦ 3 and y is 1 ≦ y ≦ 4) matrix. You can grow without. In addition, since the electrolyte can enter the pores, the doping and dedoping of lithium ions can be easily performed. For this reason, the negative active material for a rechargeable lithium battery according to one embodiment of the present invention may improve lifespan characteristics, coulombic efficiency, and rate-specific characteristics.

The phosphate of tin in the disk may be at least about 80% by weight in the amorphous phase. The growth of tin particles when the phosphate of tin is in the above range can be effectively suppressed. Specifically, about 30% to about 80% by weight of the phosphate salt of tin may be in an amorphous phase.

In addition, the phosphate salt of tin is, for example, Sn ₂ P ₂ O ₇ , Sn _x P ₂ O _7-y (where x is 1.8 ≦ x <2, y is 0 ≦ y ≦ 0.2, and specifically, 0 <y ≦ 0.2.) Or a combination thereof.

Hereinafter, the case in which the phosphate of tin is Sn ₂ P ₂ O ₇ will be described as an example, but the phosphate of tin is not limited thereto, and various tin phosphates may be used.

For example, when the phosphate of tin included in the disk including the pores is Sn ₂ P ₂ O ₇ , the reaction as in Scheme 1 is performed by insertion and desorption of lithium.

Scheme 1

_{12.8Li + Sn 2 P 2 O 7} → 2Li 4 .4 Sn + Li 3 PO 4 + LiPO 3 ↔ 8.8Li + 2Sn + Li 3 PO 4 + LiPO 3

As shown in Scheme 1, when Sn ₂ P ₂ O ₇ initially reacts with Li, a matrix of Li _4.4 Sn and Li ₃ PO ₄ and LiPO ₃ is formed. Subsequently, continuous insertion and desorption of Li takes place in Li _4.4 Sn dispersed in a matrix of Li ₃ PO ₄ and LiPO ₃ .

Li ₃ PO ₄ and LiPO ₃ included in the matrix of Li ₃ PO ₄ and LiPO ₃ may be amorphous.

The matrix of Li ₃ PO ₄ and LiPO ₃ serves as an adhesive to fix the tin particles to the matrix. The matrix of Li ₃ PO ₄ and LiPO ₃ can effectively fix the tin particles to the matrix even if lithium is repeatedly inserted and desorbed on the tin particles to change the volume of the tin particles.

In addition, the tin particles formed after the first cycle may be amorphous.

As described above, the Li ₃ PO ₄ and LiPO ₃ matrices formed by the reaction of Sn ₂ P ₂ O ₇ and Li do not easily react with the electrolyte. Therefore, the lithium secondary battery using the negative electrode active material for the lithium secondary battery according to the embodiment of the present invention may exhibit excellent capacity retention and may have excellent cycle life characteristics.

The negative electrode active material for a rechargeable lithium battery according to one embodiment of the present invention changes its shape as the reaction is performed as in Scheme 1. 1 to 3 show changes in form of the cycle of the negative electrode active material for a lithium secondary battery.

1 illustrates a form before a cycle of a negative active material for a rechargeable lithium battery according to one embodiment of the present invention.

As shown in FIG. 1, a negative electrode active material 10 for a rechargeable lithium battery according to one embodiment of the present invention is in the form of stacking a plurality of disks including pores 1.

Figure 2 shows the form after one cycle of the negative electrode active material for a lithium secondary battery according to an embodiment of the present invention.

FIG once a negative active material 10 in accordance with one embodiment of the invention after the cycle, as shown in 2, the pores disappear, Li _x PO _y (where, x is 1≤x≤3, y is 1? Y? 4. The matrix 5, specifically, a matrix of Li ₃ PO ₄ and LiPO ₃ is formed, and tin 3 is dispersed in the matrix. In addition, the size of the tin particles does not change significantly before and after the cycle.

In the Li _x PO _y (where x is 1 ≦ x ≦ 3 and y is 1 ≦ y ≦ 4) matrix, the tin particles are dispersed far apart from each other. Since the Li _x PO _y (where x is 1 ≦ x ≦ 3 and y is 1 ≦ y ≦ 4) matrix has poor lithium ion conductivity, lithium ions readily diffuse from one tin atom to a neighboring tin atom Can't be. In such a case, tin atoms dispersed in the matrix after one cycle may have limited lithium ion conductivity and limited electron conductivity. As a result, the initial discharge capacity and the coulomb efficiency may not be excellent.

3 shows a form after a large number of cycles of the negative electrode active material for a rechargeable lithium battery according to one embodiment of the present invention.

As shown in FIG. 3, when the negative electrode active material 10 for a rechargeable lithium battery according to one embodiment of the present invention undergoes a large number of cycles, the size of the matrix 5 does not change significantly, but the size of the tin particles 3 is increased. The size is larger than the tin particle size after one cycle. In addition, tin particles, which were initially amorphous, are changed to crystalline as the cycle progresses. However, the tin particles are still dispersed in the matrix. In this case, the distance between the tin particles becomes short, and lithium ions can easily diffuse from one tin atom to a neighboring tin atom. This allows tin atoms dispersed in the matrix after a large number of cycles to have good lithium ion conductivity and electronic conductivity, and can improve discharge capacity and capacity retention.

The disk may have a polygonal columnar shape or a cylindrical shape, and specifically, the disk may be an octagonal column.

The disk may have a thickness of about 5 nm to about 50 nm. If the thickness of the disk is within the above range, tin particles can grow in the matrix of Li _x PO _y (where x is 1 ≦ x ≦ 3 and y is 1 ≦ y ≦ 4). Specifically, the disk may have a thickness of about 10 nm to about 20 nm.

The disk may have a diameter of about 10 nm to about 300 nm. If the diameter of the disk is within the above range, the reaction area with the electrolyte may be increased to facilitate the insertion and desorption of lithium ions.

The porosity of the disk can be from about 20% to about 80%. If the porosity of the disk is within the above range, the volume change of tin can be alleviated at the time of insertion and removal of lithium. Specifically, the porosity of the disk may be about 30% to about 60%.

The negative active material for the lithium secondary battery may have a BET surface area of about 5 m ² / g to about 60 m ² / g. When the BET surface area of the negative electrode active material for the lithium secondary battery is within the above range, it may have an effect of increasing the reactivity with lithium ions. Specifically, the negative active material for the lithium secondary battery may have a BET surface area of about 30 m ² / g to about 50 m ² / g.

According to another embodiment of the present invention, preparing a phosphate precursor of tin by mixing a precursor of tin (Sn), a precursor of phosphorus (P) and water (H ₂ O); Leaving the tin phosphate precursor at a high temperature; After leaving at the high temperature, it provides a method for producing a negative electrode active material for a lithium secondary battery comprising the step of quenching (quenching).

The precursor of tin may include SnCl ₄ , SnF _4, or a combination thereof, and the precursor of phosphorus may include H ₃ PO ₄ , (NH ₄ ) ₂ HPO ₅ , P ₂ O _5, or a combination thereof. .

First, the precursor of tin and the precursor of phosphorus are mixed with water to react to form a phosphate precursor of tin. For example, the formed phosphate precursor of tin may be formed in a form in which a plurality of polygonal pillars or cylinders, specifically octagonal disks are stacked. The disk may have a thickness of about 5 nm to about 50 nm and may have a diameter of about 10 nm to about 300 nm. The phosphate precursor of tin can then be converted to phosphate through quenching, in which case the shape of the disk can be maintained.

The phosphate precursor of tin may include (SnHPO ₄ ) ₂ .H ₂ O, SnHPO _4, or a combination thereof.

For example, (SnHPO ₄ ) ₂ .H ₂ O is quenched to form a reaction such as Scheme 2 below to form Sn ₂ P ₂ O ₇ , which is a phosphate tin.

Scheme 2

_{(SnHPO 4) 2 · H 2} O → Sn 2 P 2 O 7 + 2H 2 O

The phosphate precursor of tin may be crystalline. Since the phosphate precursor of tin includes crystal grains as crystalline, the disk containing the phosphate precursor of tin can have pores. For this reason, the phosphate of tin obtained by quenching the phosphate precursor of tin may also have pores. The pores included in the phosphate salt of tin may serve as a buffer during insertion and removal of lithium.

Subsequently, the phosphate precursor of tin is placed in a solvent and stirred. However, the present invention is not limited thereto, and the step of adding the phosphate precursor of tin into a solvent and stirring may be omitted. The solvent is water; Organic solvents such as methanol and ethanol; Or combinations thereof.

The phosphate precursor of tin is then left at high temperature. When the phosphate precursor of tin is left at high temperature, disk-shaped particles including pores are formed.

Leaving the tin phosphate precursor at a high temperature may be performed by leaving it at a temperature of about 100 ℃ to about 200 ℃. When the phosphate precursor of tin is left in the above temperature range, disk-shaped particles including pores can be effectively formed. In addition, the step of leaving the phosphate precursor of tin at a high temperature may be performed by leaving for about 10 hours to about 30 hours within the temperature range.

The phosphate precursor is then centrifuged. However, the present invention is not limited thereto, and the centrifugation step may be omitted.

The phosphate precursor is then washed and dried. However, the present invention is not limited thereto, and the washing and drying steps may be omitted. The washing with water; Organic solvents such as methanol and ethanol; Or a combination thereof, and the drying may be performed in vacuo.

The phosphate precursor is then quenched. Quenching is the step of raising the temperature to a high temperature and maintaining it for a predetermined time, and then rapidly cooling it to room temperature, specifically about 25 ° C. By performing the quenching, the phosphate precursor is changed to phosphate, and the phosphate salt may be in an amorphous phase. Even if the phosphate precursor is changed to phosphate, its form remains the same.

The quenching may be performed by increasing the temperature at a rate of about 300 ° C. to about 800 ° C. per hour, maintaining the temperature at about 600 ° C. to about 800 ° C. for 0.1 hour to 1 hour, and then rapidly cooling to room temperature. If the conditions of quenching are within the above range, it is possible to form the amorphous phase phosphate more effectively.

According to the above process can be prepared a negative electrode active material for a lithium secondary battery according to an aspect of the present invention.

The negative electrode active material for a lithium secondary battery may be usefully used for the negative electrode of an electrochemical cell such as a lithium secondary battery. The lithium secondary battery includes a cathode and an electrolyte including a cathode active material together with the anode.

The negative electrode may be prepared by mixing the negative electrode active material for a lithium secondary battery, a conductive material, a binder, and a solvent to prepare a negative electrode active material composition, and then directly coating and drying the copper current collector. Alternatively, the negative electrode active material composition may be cast on a separate support, and then the film obtained by peeling from the support may be manufactured by laminating on an aluminum current collector.

The conductive material is carbon black, graphite, metal powder, the binder is vinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polytetrafluoro Rhoethylene and mixtures thereof may be used, but are not limited thereto. The solvent may be N-methylpyrrolidone, acetone, tetrahydrofuran, decane and the like, but is not limited thereto. In this case, the amounts of the negative electrode active material, the conductive material, the binder, and the solvent may be used at levels commonly used in a lithium secondary battery.

Like the negative electrode, the positive electrode is mixed with a positive electrode active material, a binder, and a solvent to prepare an anode active material composition, which is directly coated on an aluminum current collector or cast on a separate support and peeled from the support to a copper current collector. It can be prepared by lamination. At this time, the positive electrode active material composition may further contain a conductive material if necessary.

As the cathode active material, a material capable of intercalating / deintercalating lithium may be used, and as the cathode active material, a metal oxide, a lithium composite metal oxide, a lithium composite metal sulfide, and a lithium composite metal nitride may be used. It is not limited to this.

The separator may be used as long as it is commonly used in lithium secondary batteries, and specific examples thereof may include polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more thereof, and a polyethylene / polypropylene two-layer separator. Of course, a mixed multilayer film such as polyethylene / polypropylene / polyethylene three-layer separator, polypropylene / polyethylene / polypropylene three-layer separator, and the like may be used.

As the electrolyte charged in the lithium secondary battery, a non-aqueous electrolyte or a known solid electrolyte may be used, and a lithium salt may be used.

Examples of the solvent for the non-aqueous electrolyte include cyclic carbonates such as ethylene carbonate, diethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, chain carbonates such as dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate, methyl acetate, and ethyl acetate. , Esters such as propyl acetate, methyl propionate, ethyl propionate and γ-butyrolactone, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 1,2-dioxane , Ethers such as 2-methyltetrahydrofuran, nitriles such as acetonitrile, amides such as dimethylformamide, and the like can be used, but are not limited thereto. These can be used individually or in combination of two or more. In particular, a mixed solvent of cyclic carbonate and chain carbonate can be used.

The electrolyte may be a gel polymer electrolyte in which an electrolyte solution is impregnated with a polymer electrolyte such as polyethylene oxide or polyacrylonitrile, or an inorganic solid electrolyte such as LiI or Li ₃ N, but is not limited thereto.

In this case, LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiSbF ₆ , LiAlO ₄ , LiAlO ₂ , LiAlCl ₄ may be selected from the group consisting of LiCl and LiI, but is not limited thereto.

Hereinafter, the Example and comparative example of this description are described. However, the following examples are merely examples of the present disclosure, and the present disclosure is not limited to the following examples.

Example

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

Phosphate precursor of tin was synthesized by mixing 8.8 g of SnCl ₄ H ₅ O and 7.5 g of H ₃ PO ₄ aqueous solution (85% concentration). The phosphate precursor of tin was then dissolved in 120 ml of ethanol and stirred at 40 ° C. for 1 hour. It was then placed in an autoclave and left at 180 ° C. for 24 hours. After cooling to room temperature, the precipitate was centrifuged and then washed repeatedly with distilled water and dried at 100 ° C. in vacuo for 10 hours. This produced a phosphate precursor of tin having a structure in which a plurality of disks were stacked.

The phosphate precursor of tin having a structure in which a plurality of disks were stacked was heated to 600 ° C. at a temperature increase rate of 300 ° C./hour, maintained for 10 minutes, and quenched by rapidly cooling to room temperature. This produced the negative electrode active material for lithium secondary batteries in which the disk containing tin phosphate plurally laminated. Phosphate of tin contained in the negative electrode active material for a lithium secondary battery was Sn ₂ P ₂ O ₇ .

The thickness of each of the disks included in the prepared negative active material for a lithium secondary battery was about 20 nm, and the diameter was about 200 nm. In addition, the porosity of the prepared negative electrode active material for lithium secondary batteries was 20%.

Example 2: Preparation of Half Cells

A negative active material slurry was prepared by mixing a negative active material, a super P carbon black, and a poly (vinylidene fluoride) binder prepared in Example 1 in an N-methyl pyrrolidone solvent at a ratio of 80:10:10 by weight. It was. The prepared negative electrode active material slurry was coated on a 50 μm thick copper foil, dried at 150 ° C. for 20 minutes, and then roll-pressed to prepare a negative electrode.

A coin-type half cell (2016 R-type half cell) was prepared in a helium-filled glove box using the negative electrode, a lithium counter electrode, a microporous polyethylene separator, and an electrolyte. As the electrolyte, 1 M LiPF ₆ was dissolved in a solvent in which ethylene carbonate, diethylene carbonate, and ethyl methyl carbonate were mixed in a volume ratio of 30:30:40.

Comparative Example 1: Preparation of Anode Active Material for Lithium Secondary Battery

8.8 g of SnCl ₄ 5H ₂ O was dissolved in 120 ml of ethanol and stirred at 40 ° C. for 1 hour. It was then placed in a sterilizer and left at 180 ° C. for 24 hours. Then, after cooling to room temperature, the precipitate was centrifuged. Then, the mixture was washed repeatedly with distilled water and dried at 100 ° C. in vacuo for 10 hours. Thus, a negative active material containing SnO ₂ were prepared. The particle diameter of the prepared negative active material for a lithium secondary battery was about 10 nm.

Comparative example  2: Preparation of Half Cells

A coin type half cell was manufactured in the same manner as in Example 2, except that the negative active material for the lithium secondary battery prepared according to Comparative Example 1 was used.

Comparative example  3: Manufacture of negative electrode active material for lithium secondary battery

Phosphate precursor of tin was synthesized by mixing 8.8 g of SnCl ₄ H ₅ O and 7.5 g of H ₃ PO ₄ aqueous solution (85% concentration). The phosphate precursor of tin was then dissolved in 120 ml of ethanol and stirred at 40 ° C. for 1 hour. It was then placed in a sterilizer and left at 180 ° C. for 24 hours. After cooling to room temperature, the precipitate was centrifuged and then washed repeatedly with distilled water and dried at 100 ° C. in vacuo for 10 hours. Subsequently, it heated to 600 degreeC at the temperature increase rate of 300 degree-C / hour, hold | maintained for 10 hours, and cooled slowly at the rate of 200 degree-C / hour. Thus, to prepare a negative active material comprising a bulk amorphous Sn ₂ P ₂ O ₇ particles. The particle diameter of the prepared negative electrode active material for a lithium secondary battery was about 5 μm.

Comparative example  4: Preparation of Half Cells

A coin type half cell was manufactured in the same manner as in Example 2, except that the negative active material for the lithium secondary battery manufactured according to Comparative Example 3 was used.

Test Example

Test Example  1: X-ray diffraction (X- ray diffraction , XRD ) Measure

An X-ray diffraction analysis of a negative electrode active material for a lithium secondary battery in which a plurality of disks including a phosphate precursor having a structure in which a plurality of disks were laminated in Example 1 and a phosphate salt of tin was stacked was performed. The results thereof are shown in FIG. 4.

Further, X-ray diffraction analysis of the negative electrode prepared in Example 2 was conducted while charging and discharging up to 220 times. The results after charging, discharging once, 50 times, 100 times, 150 times, and 220 times are shown in FIG. 5.

Cu-Kα ray was used as the light source in the X-ray diffraction analysis.

As shown in FIG. 4, it can be seen that the phosphate precursor having a structure in which the plurality of disks are stacked includes (SnHPO ₄ ) ₂ · H ₂ O. In addition, it can be seen that the negative electrode active material for a lithium secondary battery in which a plurality of discs containing tin phosphate formed by quenching is stacked is an amorphous phase and contains Sn ₂ P ₂ O ₇ .

As shown in FIG. 5, it can be seen that a peak indicating a Sn phase is not observed in the cathode. This means that even if charging and discharging are repeated, the Sn particles formed in the negative electrode active material for the lithium secondary battery are well held in the Li ₃ PO ₄ and LiPO ₃ matrices.

Test Example  2: Inductively Coupled Plasma Mass spectrometry inductively coupled plasma - mass  spectroscopy, ICP - MS )

Inductively coupled plasma-mass spectrometry was performed to determine the composition of the negative electrode active material for a lithium secondary battery prepared in Example 1. As a result, a negative active material prepared in Example 1 is shown to include Sn _{1 .99} P ₂ O ₇ phase. This may be regarded as Sn ₂ P ₂ O ₇ formed according to Scheme 2, considering the error of the device.

Test Example  3: scanning electron microscope scanning electron microscope , SEM ) Picture

SEM photographs were taken of a negative electrode active material for a lithium secondary battery, in which a plurality of disks including a phosphate precursor having a structure in which a plurality of disks were prepared in Example 1 and a disk containing tin phosphate were stacked. The results are shown in Figs. 6A and 6C, respectively. An enlarged view of portion A in FIG. 6A is shown in FIG. 6B, and an enlarged view of portion B in FIG. 6C is shown in FIG. 6D.

As shown in FIG. 6A, the phosphate precursor having a structure in which the plurality of disks are stacked has a structure in which octagonal disks are stacked, and each disk has a thickness of about 20 nm and a diameter of about 200 nm. Can be confirmed. It can also be seen that each disk has a thickness of about 20 nm, as indicated by the arrows in FIG. 6B.

In addition, as shown in Figure 6c, it can be seen that the original octagonal shape of the disk is maintained even after quenching. That is, it can be seen that the negative electrode active material for the lithium secondary battery manufactured in Example 1 has a structure in which octagonal disks are stacked. As indicated by the arrows in FIG. 6D, it can be seen that each of the disks has a thickness of about 20 nm.

Test Example  4: transmission electron microscope ( transmission electron microscope , TEM Photo and high resolution transmission electron microscope high resolution transmission electron microscope , HRTEM) Photo

Samples were prepared by depositing negative electrode active materials for lithium secondary batteries prepared according to Example 1, Comparative Example 1 and Comparative Example 3 on a carbon coated copper grid, and taken a TEM photograph of the cross section.

7A and 7B show TEM photographs of the negative electrode active material for a lithium secondary battery prepared in Example 1 above. FIG. 7B is an enlarged photograph of FIG. 7A 100 times.

The TEM photograph which photographed the negative electrode active material for lithium secondary batteries manufactured by the comparative example 1 is shown in FIG. 8, and the TEM photograph which photographed the negative electrode active material for lithium secondary batteries manufactured by the comparative example 3 is shown in FIG.

As shown in FIGS. 7A and 7B, it can be observed that the negative active material for the lithium secondary battery manufactured in Example 1 has randomly distributed pores C having a diameter of about 4 nm or less in an amorphous matrix. On the other hand, lattice fringes indicated by circles indicated by D indicate that the negative active material for the lithium secondary battery may include a crystalline phase.

As shown in FIG. 8, in Comparative Example 1, it was confirmed that a negative active material for a lithium secondary battery including SnO ₂ having a particle diameter of about 10 nm was prepared.

As shown in FIG. 9, in Comparative Example 3, it was confirmed that a negative active material for a lithium secondary battery including bulk amorphous Sn ₂ P ₂ O ₇ particles having a size of about 5 μm was prepared.

In addition, the half cell prepared in Example 2 was charged and discharged once at 0.5 C (350 mA / g) at 0 V to 1.2 V, and then charged and discharged 50 times, and then charged and discharged 100 times. After 220 charge and discharge cycles, a negative electrode active material for a lithium secondary battery was extracted, and a TEM photograph and an HRTEM photograph were taken in the same manner as described above. The results are shown in Figs. 10A to 10F, respectively.

10A and 10B are TEM photographs and HRTEM photographs of a negative electrode active material for a lithium secondary battery after a single charge and discharge. 10A and 10B, after one charge and discharge, pores in the disc collapsed, and tin particles having a size of about 2 nm were embedded in a rod-shaped amorphous matrix. Can be. The tin particles may be amorphous. The amorphous matrix is one comprising Li ₃ PO ₄ and LiPO ₃ .

10C is a TEM photograph of a negative electrode active material for a lithium secondary battery after 50 charge and discharge cycles. As shown in FIG. 10C, after 50 charge and discharge cycles, the tin particles were grown to about 5 nm.

10D is a TEM photograph of a negative electrode active material for a lithium secondary battery after 100 charge and discharge cycles. As shown in FIG. 10D, after 100 charge and discharge cycles, the size of the matrix did not change, and the number of tin particles increased to cover the matrix.

10E and 10F are TEM photographs and HRTEM photographs of a negative electrode active material for a lithium secondary battery after 220 charge and discharge cycles. As shown in FIGS. 10E and 10F, even after 220 charge and discharge cycles, some tin particles grew to 10 nm, but most tin particles grew to 5 nm. In addition, the rod shape was maintained and the tin particles covered the matrix without being micronized.

After charging and discharging the half cell prepared in Comparative Example 2 at 0 V to 1.2 V at 0.5 C (350 mA / g) 20 times, and performing 100 times charging and discharging, the negative electrode active material for a lithium secondary battery was extracted and , TEM pictures were taken in the same manner as above, and HRTEM pictures were also taken. The taken TEM photographs are shown in Figs. 11A and 11C, respectively, and HRTEM photographs are shown in Figs. 11B and 11D.

As shown in FIG. 11A, after 20 charge / discharge cycles, SnO ₂ particles having a particle diameter of about 10 nm included in the negative active material for a lithium secondary battery prepared in Comparative Example 1 may be confirmed to be micronized.

As shown in FIG. 11B, it can be confirmed that an amorphous layer is formed on the tin particles after 20 charge / discharge cycles, and the amorphous layer is considered to be a Li ₂ O matrix. However, no tin particles dispersed in the Li ₂ O matrix could be found. This means that the Li ₂ O matrix collapsed during the cycle from 0 V to 1.2 V.

It is known that the stability of the Li ₂ O matrix formed when SnO ₂ is used as a negative electrode active material for a lithium secondary battery is sensitive to cut-off voltages, and rapidly increases when the cut-off voltage increases to 1.3 V. It is known that capacity fading is observed.

11C and 11D, after 100 charge / discharge cycles, it can be seen that the tin particles were severely micronized. The particle diameter of the tin was about 5 nm.

In addition, after charging and discharging the half cell prepared in Comparative Example 4 at 0.5 C (350 mA / g) at 0 V to 1.2 V for 50 times, the negative active material for a lithium secondary battery was extracted, and the TEM was prepared in the same manner as described above. Photo was taken. The taken TEM photograph is shown in FIG.

As shown in FIG. 12, after 100 charge / discharge cycles, it can be confirmed that the original particles having a size of about 5 μm were completely micronized into particles having a size of about 10 nm.

Test Example  5: BET  Surface area

In order to determine the surface area of the negative electrode active material for the lithium secondary battery prepared in Example 1 and Comparative Example 1, a nitrogen isothermal adsorption experiment was performed with a Micrometrics ASAP 2020 system. As a result and the specific surface area of the negative electrode active material for a lithium secondary battery prepared in Example 1 calculated using the Brunauer-Emmett-Teller (BET) formula was 38 m 2 / g, the negative electrode for a lithium secondary battery prepared in Comparative Example 2 The specific surface area of the active material was 43 m 2 / g.

Test Example  6: discharge capacity and coulomb  efficiency

The half cells prepared in Example 2, Comparative Example 2 and Comparative Example 4 were charged and discharged at 0.5 C (350 mA / g) once at 0 V to 1.2 V to measure reversible capacity and coulombic efficiency.

The half cell prepared in Example 2 had a reversible capacity of 600 mAh / g and a coulombic efficiency of 68%.

The half cell prepared in Comparative Example 2 had a reversible capacity of 650 mAh / g, a coulombic efficiency of 45%, and the half cell prepared in Comparative Example 4 had a reversible capacity of 500 mAh / g, and a coulombic efficiency of 70%. It was.

Although the negative electrode active material for the lithium secondary battery prepared in Example 1 has a similar BET surface area to the negative electrode active material for the lithium secondary battery prepared in Comparative Example 1, the Coulomb efficiency of the negative electrode active material for the lithium secondary battery prepared in Example 1 is The Coulomb efficiency of the lithium secondary battery negative electrode active material prepared in Comparative Example 1 was improved by about 23%. This is because the amorphous Li ₃ PO ₄ and LiPO ₃ matrixes formed using the negative electrode active material for lithium secondary batteries of Example 1 are more reactive with electrolyte than the Li ₂ O matrix formed using the negative electrode active materials for lithium secondary batteries of Comparative Example 1. This means less.

In addition, the negative electrode active material for the lithium secondary battery prepared in Example 1 was similar in coulombic efficiency to the negative electrode active material for the lithium secondary battery prepared in Comparative Example 3, but the reversible capacity was larger than that of the lithium secondary battery negative electrode active material prepared in Comparative Example 3. .

Test Example  7: cycle life characteristics

The change in the discharge capacity was measured while charging and discharging the half cells prepared in Example 2 and Comparative Example 2 at 0.5 C (350 mA / g) at 0 V to 1.2 V. The result is shown in FIG.

As shown in FIG. 13, in the case of using the negative electrode active material for the lithium secondary battery of Example 1, the discharge capacity gradually increased as the number of cycles increased, reached the highest value at 620 mAh / g after 20 cycles, and 547 after 220 cycles. You can see that it slowly decreased to mAh / g. In addition, it can be seen that the capacity retention rate of 93%.

This is because the tin particles formed during the first charge / discharge of the negative active material for a lithium secondary battery manufactured in Example 1 are far from each other, and as the charge and discharge are repeated, the size of the tin particles increases, so that the distance between the tin particles is closer. This is because the conductivity and electron conductivity of lithium ions between neighboring tin particles are improved. In addition, Li ₃ PO ₄ in the negative active material for the lithium secondary battery And LiPO ₃ This is because the matrix was maintained without collapse and held the tin particles stably.

On the other hand, the half cell prepared in Comparative Example 2 had a capacity retention ratio of about 20% after initial cycle of 20 C at 0.5 C (350 mA / g) at 0 V to 1.2 V, and discharge capacity after about 40 cycles. 80 mAh / g, the capacity retention rate was about 10% relative to the initial dose. As such, when charging and discharging at 0.5 C, the charge capacity is continuously decreased for 200 cycles, which indicates that the negative active material for the lithium secondary battery prepared in Comparative Example 1 is gradually being micronized.

The present invention is not limited to the above embodiments, but may be manufactured in various different forms, and a person having ordinary knowledge in the art to which the present invention pertains does not change the technical spirit or essential features of the present invention. It will be appreciated that the present invention may be practiced as. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive.

1: pore, 3: tin (Sn),
5: Li _x PO _y matrix, 10: negative electrode active material for lithium secondary battery

Claims (18)

It is a negative electrode active material for lithium secondary batteries containing the disk containing the phosphate of tin (Sn),
The disk is a negative electrode active material for a lithium secondary battery containing pores.
The method of claim 1,
The tin phosphate is a negative active material for a lithium secondary battery containing at least 80% by weight of the amorphous phase.
The method of claim 1,
The phosphate salt of tin includes Sn ₂ P ₂ O ₇ , Sn _x P ₂ O _{7 -y} (where x is 1.8 ≦ x <2 and y is 0 ≦ y ≦ 0.2) or a combination thereof. Anode active material for phosphorus lithium secondary battery.
The method of claim 1,
The disk is a negative electrode active material for a lithium secondary battery that is polygonal or cylindrical.
The method of claim 1,
The disk is a negative active material for a lithium secondary battery having a thickness of 5 nm to 50 nm.
The method of claim 1,
The disk is a negative active material for a lithium secondary battery having a diameter of 10 nm to 300 nm.
The method of claim 1,
The disk is a negative active material for a lithium secondary battery having a porosity of 20% to 80%.
The method of claim 1,
The negative active material for a lithium secondary battery is a negative electrode active material for a lithium secondary battery having a BET (Brunauer-Emmett-Teller) surface area of 5 m ² / g to 60 m ² / g.
Preparing a phosphate precursor of tin by mixing a precursor of tin (Sn), a precursor of phosphorus (P), and water (H ₂ O);
Leaving the tin phosphate precursor at a high temperature;
After standing at the high temperature, quenching
Including,
The step of leaving at a high temperature is a method for producing a negative electrode active material for a lithium secondary battery that is performed by leaving at a temperature of 100 ℃ to 200 ℃.
10. The method of claim 9,
The precursor of the tin is a method of producing a negative electrode active material for a lithium secondary battery containing SnCl ₄ , SnF ₄ or a combination thereof.
10. The method of claim 9,
The precursor of phosphorus is H ₃ PO ₄ , (NH ₄ ) ₂ HPO ₅ , P ₂ O ₅ or a combination thereof will be prepared a method for producing a negative electrode active material for a lithium secondary battery.
10. The method of claim 9,
The phosphate precursor of the tin is (SnHPO ₄ ) ₂ H ₂ O, SnHPO ₄ or a combination thereof, a method for producing a negative electrode active material for a lithium secondary battery.
10. The method of claim 9,
The tin phosphate precursor is a crystalline method of producing a negative electrode active material for a lithium secondary battery.
The method of claim 13,
The crystal particles of the phosphate precursor of tin has a diameter of 10 nm to 300 nm manufacturing method of a negative electrode active material for a lithium secondary battery.
delete 10. The method of claim 9,
The quenching is a method of manufacturing a negative electrode active material for a lithium secondary battery that is carried out by heating to 600 ℃ to 800 ℃ and maintained for 0.1 hour to 1 hour, followed by rapid cooling to room temperature.
The method of claim 16,
The temperature increase is a method for producing a negative electrode active material for a lithium secondary battery that the temperature increase at a temperature increase rate of 300 ℃ / hour to 800 ℃ / hour.
A negative electrode comprising a negative electrode active material;
A positive electrode including a positive electrode active material; And
Contains an electrolyte,
The negative electrode active material is a lithium secondary battery which is the negative electrode active material for a lithium secondary battery according to any one of claims 1 to 8.

Images