KR100589511B1 - SnO2-impregnated anode material for a lithium secondary battery, its processing method, and lithium secondary batteries by using it - Google Patents

Abstract

The present invention relates to a negative electrode material of a lithium secondary battery, a manufacturing method of the negative electrode material, and a lithium secondary battery comprising a negative electrode made of the negative electrode material. The negative electrode material of the lithium secondary battery according to the present invention is prepared by uniformly inserting a small amount of tin oxide (SnO ₂ ) as a second phase additive into a carbon powder used as a negative electrode material of a conventional lithium secondary battery using a charge titration method. . As such, the lithium secondary battery of the present invention including a negative electrode made of carbon powder surface-modified by tin oxide insertion exhibits a higher initial discharge capacity and a charging capacity than a lithium secondary battery including a negative electrode made of conventional carbon powder. In addition, it exhibits high reversibility and better cycleability.

Lithium secondary battery, negative electrode material, carbon electrode, tin oxide

Description

Lithium secondary battery negative electrode material containing tin oxide, a method of manufacturing the same and a lithium secondary battery comprising the negative electrode material {SnO2-impregnated anode material for a lithium secondary battery, its processing method, and lithium secondary batteries by using it}

1 is a process flow diagram for a process of inserting tin oxide into MCMB powder.

Figure 2 is an EDS analysis of the MCMB powder reacted with a 2.25 × 10 ^-3 mol SnCl ₄ · 5H ₂ O aqueous solution.

3 is a graph showing a comparison of the first charge and discharge curves of MCMB powder without tin oxide and MCMB powder with tin oxide inserted.

4 is a graph comparing the reversible capacity and the irreversible capacity of MCMB powder without tin oxide and MCMB powder with tin oxide inserted.

5 is a graph showing discharge capacities according to the number of charge / discharge cycles of MCMB powder without tin oxide and MCMB powder with tin oxide inserted.

6 is a graph showing a comparison of the charging capacity according to the number of times of charging and discharging the MCMB powder is not inserted into the tin oxide and MCMB powder is inserted into the tin oxide.

The present invention relates to a negative electrode material of a lithium secondary battery, a manufacturing method of the negative electrode material, and a lithium secondary battery comprising a negative electrode made of the negative electrode material. More specifically, the present invention provides a lithium secondary battery prepared by uniformly inserting a small amount of tin oxide (SnO ₂ ) as a second phase additive into a carbon powder used as a negative electrode material of a conventional lithium secondary battery using a charge titration method. The present invention relates to a lithium secondary battery comprising a negative electrode material, a method for producing the negative electrode material, and a negative electrode made of the negative electrode material.

As portable electronic devices such as video cameras, cordless phones, mobile phones, and notebook computers are rapidly spreading in daily life, the demand for secondary batteries used as a power source has increased greatly. Among them, lithium secondary batteries have high capacity and high energy density. Due to the battery characteristics, active research and development has been carried out at home and abroad, and is currently the most widely used secondary battery.

A lithium secondary battery basically consists of a positive electrode, a negative electrode, and an electrolyte. Therefore, the research and development of a lithium secondary battery can be largely divided into a study on a cathode, an anode material, and an electrolyte. Among them, the carbon material used as a negative electrode material of a lithium secondary battery has Li atoms entering between the carbon layers during the reduction process (charging), or nano-scale clusters are formed on the carbon surface and the micropore. As a result, no dendrite is formed in the Li-metal. In addition, the chargeability (rechargeability) is relatively excellent, safe and high energy density can be obtained, as well as has the advantage that can be manufactured in a normal atmosphere atmosphere. However, since the energy density per weight (3.9 Ah / g) of the Li metal is somewhat lowered, there is a problem in that a limitation on the capacity follows.

Carbon electrode materials have a wide variety of crystal structures depending on the raw materials, organic precursors, and pyrolysis processes to be produced. Li-intercalation varies considerably according to the type, and thus shows various capacities and reversible characteristics. . In general, when one kind of carbon material has excellent characteristics as a negative electrode material, it has been shown to have a relatively inferior property in other fields. For example, in the case of a cathode using carbon treated at low temperatures such as mesocarbon microbeads (MCMB) and poly-p-phenylene (PPP) obtained from phenolic resin, It has been reported to have a capacity of 2.5 times higher than a battery using LiC ₆ graphite. However, the carbon heat-treated at low temperature showed a large loss of irreversible capacity due to charging and discharging.

In general, since the electrode material is in contact with the electrolyte, some electrolyte decomposition may occur on the electrode surface to reduce the charge and discharge characteristics. Similarly, in the case of the carbon electrode, a solid-electrolyte interface (SEI) film is formed by side reaction with the electrolyte, and the initial irreversible capacity is large due to the severe volume change during charging and discharging, and causes cycle life deterioration. . This problem is to minimize the irreversible capacity by modulating the carbon surface crystal structure by the method of modifying the surface of the electrode material, it is possible to improve the performance of the lithium ion battery through the prevention of cycle life degradation. Recently, studies have been actively conducted to minimize the irreversible capacity by modulating the carbon surface crystal structure by surface modification methods such as surface coating and surface oxidation by heat treatment, or by adsorbing gases such as HF and CO ₂ on the surface.

   An object of the present invention is to insert a small amount of tin oxide as a second phase additive into a carbon powder used as a negative electrode material of a lithium secondary battery, thereby modifying the surface of the carbon powder to exhibit excellent charge / discharge capacity and cycle characteristics. It is to provide a negative electrode material of the battery.

Another object of the present invention is to provide a method for producing a negative electrode material of a lithium secondary battery, characterized in that a small amount of tin oxide as a second phase additive is uniformly inserted into the carbon powder used as a negative electrode material of the lithium secondary battery. It is.

Still another object of the present invention is to provide a lithium secondary battery including a negative electrode of the negative electrode material.

The negative electrode material of the lithium secondary battery according to the present invention is characterized in that it is made by inserting 3 to 13% by weight of tin oxide as a second phase additive to the carbon powder used as a negative electrode material of a conventional lithium secondary battery.

Carbon powder used in the present invention can be used without limitation conventionally used in lithium secondary batteries, for example, it is possible to use a powder of various kinds of artificial carbon materials such as graphite, mesocarbon microbeads (MCMB) Can be.

In the present invention, the content of tin oxide to be inserted into the carbon powder is preferably 3 to 13% by weight. When the amount of tin oxide is less than 3% by weight, the increase in charge and discharge capacity is less than that of the carbon powder to which tin oxide is not inserted. If the content exceeds 13% by weight, the irreversible capacity increase rate is greatly increased, which is undesirable.

The method for manufacturing a negative electrode material of a lithium secondary battery according to the present invention is characterized in that 3 to 13% by weight of tin oxide is inserted into the carbon powder used as a negative electrode material of a conventional lithium secondary battery as a charge titration method. do.

Specifically, the tin chloride aqueous solution and the carbon powder were mixed, and then NaOH aqueous solution was added to adjust the pH to 7-12 to precipitate the carbon powder containing tin, and the precipitate was filtered and dried, followed by heat treatment. The oxidized tin is oxidized to obtain a carbon powder containing tin oxide.

In the method of the present invention, the mixed weight ratio of the tin chloride aqueous solution and the carbon powder is preferably in the range of 30: 1 to 80: 1. When the mixed weight ratio is less than 30: 1, the amount of tin to be inserted may be lower than the target value, 80 If: 1 is exceeded, the insertion amount of tin may be higher than the target value.

In the method of the present invention, the pH is adjusted to 7 to 12 by adding an NaOH aqueous solution to the mixed solution of the tin chloride aqueous solution and the carbon powder to cause deposition of tin.

In the method of the present invention, the method of drying and heat-treating the carbon powder precipitate in which tin is inserted is not limited, and the drying temperature is appropriately 100-120 ° C., and the heat treatment is suitably 30 minutes-2 hours at 230-300 ° C. . The drying temperature is a temperature set for the evaporation of water, the heat treatment temperature and time to ensure the oxidation rate and the oxidation amount of the tin, while preventing the burning phenomenon of carbon partially occurs, the SnO ₂ phase is stable It is a range to be formed.

The lithium secondary battery of the present invention is characterized in that it comprises a negative electrode material of the lithium secondary battery prepared as described above, that is, a negative electrode made of carbon powder in which tin oxide is inserted.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples.

EXAMPLE

Comparative example

MCMB powder supplied from Osaka Gas Ltd. was used as the negative electrode material used for the electrochemical characteristic experiment. Add about 3% by weight of Vulcan XC-72R as conductive agent to MCMB powder for electrode preparation, and then mix well with binder solution made by dissolving polyvinylidene fluoride (PVDF) in N-methylpyrrolidone (NMP). To make a viscous slurry. Then, the slurry was applied to the copper foil in a thickness of about 0.2 to 0.3 mm, and then dried at 100 ° C. for about 6 hours with a constant temperature vacuum dryer to prepare a carbon electrode.

Example

  A charge titration method, which is a wet process, was used to impregnate Sn on the surface of MCMB powder supplied from Osaka Gas Ltd.

MCMB powder was mixed with four kinds of SnCl ₄ ㆍ 5H ₂ O solutions having different molar ratios of 8.55 × 10 ^-4 mol, 2.25 × 10 ^-3 mol, 2.97 × 10 ^-3 mol, and 7.13 × 10 ^-3 mol, respectively. Thereafter, the mixture was stirred while adding 0.1 mol of an aqueous NaOH solution as a precipitant at a temperature of 60 ° C. until the pH reached 9. The precipitated MCMB powder was washed several times with ethanol, filtered through a filter paper, and dried at 110 ° C. for 24 hours. Sn-inserted MCMB powder was heat-treated at 250 ° C. for 1 hour to oxidize the impregnated Sn to tin oxide (SnO ₂ is the main phase). The surface modification process of MCMB powder by tin oxide insertion is shown schematically in FIG. 1.

Prepared by mixing MCMB powder with 8.55 × 10 ^-4 mol, 2.25 × 10 ^-3 mol, 2.97 × 10 ^-3 mol, and 7.13 × 10 ^-3 mol of SnCl ₄ ㆍ 5H ₂ O aqueous solution, respectively, as described above. In the MCMB powder containing tin oxide, quantitative analysis was performed through energy dispersive x-ray spectroscopy (EDS) analysis to determine the amount of impregnated Sn. FIG. 2 is an EDS analysis result of MCMB powder reacted in an aqueous solution in which 2.25 × 10 ⁻³ mol of SnCl ₄ · 5H ₂ O was dissolved. FIG. As described above, in the case of Sn-inserted MCMB powder oxidized and heat-treated at 250 ° C using the results of analyzing the Sn component by EDS, the tin oxide composition ratio was calculated by assuming that all Sn was oxidized to SnO ₂ . It was found that%, 7.5%, 9.3%, and 12.8% by weight SnO ₂ was incorporated into the MCMB powder.

Each carbon electrode was manufactured in the same manner as in the comparative example by using four kinds of MCMB powders in which tin oxide was inserted as described above.

Battery cell test

A half cell was configured to perform a cell test, and the working electrode used each carbon electrode manufactured in Comparative Examples and Examples, and the counter electrode used lithium metal. Li and Li ⁺ were used as reference electrodes. Celgard 2400 microporous sheet (Hoechst Celanese Co.) was used as a separator to prevent contact between electrodes. The electrolyte was used by dissolving 1.1 M LiPF ₆ in a 50:50 mixture of ethylene carbonate (EC) and diethylene carbonate (DEC). The charge / discharge test was performed using Potentiostat / Galvanostat (EG & G 263), and the charge / discharge potential was performed at 2.0 V to 0.0 mA (vs. Li / Li ⁺ ).

Figure 3 shows a cell prepared using a carbon electrode as a negative electrode of Comparative Example prepared using MCMB powder (hereinafter referred to as "raw MCMB") without tin oxide, and Example prepared using SnO ₂ -inserted MCMB powder. The graph shows a comparison of the first charge / discharge curve of a battery using a carbon electrode as a negative electrode. As the amount of inserted tin oxide increased, the initial discharge capacity gradually increased, resulting in an increase of about 59% of the discharge capacity of the 12.8% by weight SnO ₂ -inserted MCMB compared to the raw MCMB. In the case of the filling capacity, the amount of tin oxide also increased, and the increase of 12.8% by weight SnO ₂ -inserted MCMB showed an increase of about 35% compared to the raw MCMB. However, it can be seen that as the amount of inserted tin oxide increases, the loss of initial charge / discharge capacity (non-reversible capacity) increases.

Comparing the first discharge curve, the raw MCMB reacts with the electrolyte at the electrode surface in the process of intercalation of lithium ions into the MCMB around 0.7V, and a thin passivation film is formed on the electrode surface. An extra plateau can be seen, whereas for SnO ₂ -inserted MCMB it was observed that this extra plateo appeared near the higher potential of about 1.2V. In general, the passivation film formed on the electrode surface of the cathode using lithium and carbon materials is known to mainly produce lithium alkyl carbonate and lithium carbonate, and is known to be produced at a potential lower than 0.9V based on lithium. In contrast, the passivation film generated on the electrode surface of the cathode using lithium and tin oxide is known to produce lithium oxide, which is generated at a potential slightly higher than 0.9V. In this experiment, it was observed that such extra plato appeared around 1.2V.

4 is a graph comparing reversible specific charge capacity and irreversible specific charge capacity of raw MCMB and SnO ₂ -inserted MCMB. Here, the reversible capacity is represented by the average value of the discharge capacity of the first cycle (cycle) and the discharge capacity of the second cycle, the irreversible capacity is represented by the difference between the discharge capacity and the charging capacity of the first cycle. The reversible capacity of the raw MCMB was 214 mAh / g, and in the case of SnO ₂ -inserted MCMB, the reversible capacity gradually increased as the amount of tin oxide was increased. In the case of 12.8 wt% SnO ₂ -inserted MCMB, the raw MCMB was 282 mAh / g. The reversible capacity was about 32% higher. As the amount of inserted tin oxide increases, the irreversible capacity also increases gradually. The irreversible capacity of the 12.8 wt% SnO ₂ -inserted MCMB is 194 mAh / g, which is about 120% higher than the raw MCMB of 87 mAh / g. Showed capacity.

5 and 6, the discharge capacity and the charge capacity of the raw MCMB and the SnO ₂ -inserted MCMB according to the number of charge and discharge cycles were compared, respectively. It can be seen that as the amount of inserted tin oxide increases, the overall charge / discharge capacity increases.

   In general, a lithium ion secondary battery using tin oxide as a negative electrode has a very high initial discharge capacity compared to a carbon electrode, while the loss of initial discharge capacity is also very large and the reversible characteristics are low, and the cycle performance is known to be low. In this experiment, the first charge and discharge characteristics showed high charge capacity and high capacity loss, and showed similar charge and discharge characteristics as the tin oxide anode, but after the second cycle, the high reversibility and excellent cycle characteristics were observed. It was found that the charge and discharge characteristics and reversible characteristics of the inserted and surface modified MCMB were excellent.

The MCMB powder surface-modified by tin oxide insertion, which is a negative electrode material of the lithium secondary battery according to the present invention, exhibited higher initial discharge capacity and higher initial charge capacity than conventional MCMB powder. And, as the amount of the tin oxide inserted increased, the reversible capacity was high, and the irreversible capacity was also high. The lithium secondary battery including the negative electrode made of the negative electrode material of the lithium secondary battery of the present invention exhibits a higher charge and discharge capacity than the conventional lithium secondary battery, and exhibits high reversible characteristics and excellent cycle characteristics.

Claims (8)

delete delete After mixing the carbon powder in the tin chloride aqueous solution, the aqueous solution of NaOH was added to adjust the pH to 7-12, to precipitate the carbon powder containing tin, and the precipitate was filtered and dried, followed by heat treatment to oxidize the inserted tin. To obtain a carbon powder containing tin oxide, thereby producing a negative electrode material of a lithium secondary battery. According to claim 3, wherein the mixed weight ratio of the tin chloride aqueous solution and the carbon powder is 30: 1 to 80: 1, the drying temperature is 100 ~ 120 ℃, heat treatment is carried out for 30 minutes to 2 hours at 230 ~ 300 ℃ Method for producing a negative electrode material of a lithium secondary battery. delete A lithium secondary battery prepared by the method for preparing a negative electrode material of a lithium secondary battery according to claim 3 or 4, wherein tin oxide of 3 to 13% by weight is inserted into the carbon powder as a second phase additive. Cathode material. The negative electrode material of a lithium secondary battery according to claim 6, wherein the carbon powder is graphite powder or mesocarbon microbead powder. A lithium secondary battery comprising a negative electrode made of a negative electrode material of the lithium secondary battery of claim 6.

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