KR100853888B1 - Anode material of secondary battery and secondary battery using the same - Google Patents

Abstract

An anode material for a secondary battery is provided to protect decomposition of an electrolyte, thereby improving the efficiency and cycle characteristics of a secondary battery. An anode material for a secondary battery is obtained by coating low crystalline carbon onto a core carbon material, followed by baking. The anode has a porosity of 0.0025 or less as calculated by the following mathematical formula: P = Rpm/[Rp*10^-IDeltaEcorr/betaaI]. In the formula, P is the total porosity, Rpm is the polarization resistance of the electrode; Rp is the polarization resistance of the electrode coated with the mixture of the core carbon material and low crystalline carbon; delta Ecorr is a difference in potential between the electrode and the mixture of the core carbon material and low crystalline carbon; betaa is the Tafel constant of the cathode.

Description

Anode material of secondary battery and secondary battery using the same}

The present invention relates to a negative electrode material for a secondary battery and a secondary battery including the same as a negative electrode. More specifically, a secondary battery capable of improving the efficiency and cycle capacity of a secondary battery by improving protection against electrolyte decomposition reactions. It relates to a battery negative electrode material and a secondary battery comprising the same as a negative electrode.

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 high 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, research and development of a lithium secondary battery can be largely divided into studies on a cathode, an anode material, and an electrolyte.

Among these, natural graphite, which is used as a negative electrode material for lithium secondary batteries, has excellent initial capacity but poor efficiency and cycle capacity. This is known to be due to the electrolyte decomposition reaction in the highly crystalline natural graphite edge portion.

In order to overcome this characteristic, the initial capacity is reduced by surface treatment (coating) of low-crystalline carbon on natural graphite and heat-treated at 1,000 ° C or higher to coat low crystalline carbide on the surface of natural graphite. An anode active material with improved characteristics was obtained. In order to use the negative electrode active material as an electrode, the coated carbide is broken in the process of coating and compressing the electrode current collector such as a copper coil, and through this portion, the highly crystalline natural graphite edge portion reacts with the electrolyte again, and actually carbides The coating effect is reduced.

Japanese Patent Application Laid-Open No. 11-111296 discloses a method for producing a carbon negative electrode material for a secondary battery and a micropore distribution amount. However, the patent does not present data on the pores of the electrode, the carbon material and the pitch mixture.

Accordingly, efforts to solve the above-mentioned problems of the prior art have been continued in the related art, and the present invention has been devised under such a technical background.

The technical problem to be achieved by the present invention is to improve the protection function against the electrolyte decomposition reaction to improve the efficiency and cycle capacity of the secondary battery, including the negative electrode material for a secondary battery and the negative electrode capable of achieving such a technical problem It is an object of the present invention to provide a secondary battery.

In order to achieve the technical problem to be achieved by the present invention, the secondary battery negative electrode material is a secondary battery negative electrode material manufactured by coating a low crystalline carbon on a core carbon material and firing the porosity of the negative electrode material according to Equation 1 below. Is 0.0025 or less.

[Equation 1]

In Equation 1, P is the total porosity, R _pm is the polarization resistance of the electrode, R _p is the polarization resistance of the electrode coated with a mixture of core carbon material and low crystalline carbon, ΔEcorr is the electrode and core carbon The potential difference between the material and the low crystalline carbon mixture, βa represents the positive electrode Tafel constant of the electrode.

The negative electrode material for a secondary battery for achieving the technical problem to be achieved by the present invention is a secondary battery negative electrode material prepared by coating a low crystalline carbon on the core carbon material and calcined, the electrolyte solution decomposition reaction according to It is characterized in that the protection rate of the negative electrode material against.

[Equation 2]

In Equation 2, Pi is a protection rate against electrolyte decomposition reaction, i _corr is the current density of the electrode coated with a core carbon material and a low crystalline carbon mixture, i _0corr is the current density of the electrode.

In the negative electrode material for the secondary battery, it is preferable that the peak intensity ratio in the vicinity of 1360 cm ⁻¹ and the peak intensity in the vicinity of 1580 cm ^{−1 be} 0.45 or less in an argon laser Raman spectroscopic measurement having a wavelength of 514.5 nm.

It is preferable that the peak half width of the said negative electrode material for secondary batteries is 16-35 in the vicinity of 1580 cm <^-1> .

It is preferable that the tap density of the said negative electrode material for secondary batteries is 0.7 g / cm <3> or more.

It is preferable that the specific surface area of the said negative electrode material for secondary batteries is 4 m <2> / g or less.

A secondary battery for achieving the technical problem to be achieved by the present invention is characterized by including the negative electrode material as a negative electrode.

Hereinafter, preferred embodiments of the present invention will be described in detail. Prior to this, terms or words used in the specification and claims should not be construed as having a conventional or dictionary meaning, and the inventors should properly explain the concept of terms in order to best explain their own invention. Based on the principle that can be defined, it should be interpreted as meaning and concept corresponding to the technical idea of the present invention. Therefore, the exemplary embodiments described herein are only exemplary embodiments of the present invention and do not represent all of the technical ideas of the present invention, and various equivalents and modifications that may substitute them at the time of the present application may be used. It should be understood that there may be.

The negative electrode material for secondary batteries of the present invention is characterized in that its porosity is 0.0025 or less. Moreover, the negative electrode material for secondary batteries of this invention is characterized by 90% or more of protection rate against electrolyte solution decomposition reaction.

The negative electrode material for the secondary battery may be prepared by coating a low crystalline carbon on the core carbon material and baking according to a conventional method performed in the art.

The core carbon material may be natural graphite, artificial graphite, a mixture thereof, and in particular, natural graphite may be used.

It is preferable that the core carbon material has a spherical shape, and in particular, the spheroidization of the core carbon material is preferably 15 or more, more preferably about 15 to 60 in the case of powder type. In addition, the core carbon material is preferably used having an average particle diameter of 10 to 20 ㎛ to improve the tap density.

As the low crystalline carbon, pitch, tar, phenol resin, furan resin, or furfuryl alcohol may be used as the carbon.

It is preferable that the mixing weight ratio of the core carbon material and the low crystalline carbon is 85 to 95: -15, and when the mixing weight ratio is within the above range, the capacity and the charge / discharge efficiency are increased.

The negative electrode material for the secondary battery of the present invention is mixed with the low crystalline carbon and the core carbon material as described above, wet stirred at normal pressure for 2 hours or more, dried, fired at a temperature of 150 to 200 ° C. for 1 to 4 hours, and classified. It can manufacture by removing fine powder. The surface-coated core carbon material may be covered by some or all of the edge portions of the core carbon material by low crystalline carbon.

The porosity of the negative electrode material for the secondary battery is a porosity of the negative electrode material for the secondary battery manufactured by coating the core carbon material with low crystalline carbon, and the porosity is preferably 0.0025 or less, and more preferably the porosity. Lower is preferable. In the above porosity range, when the lower limit is less than the lower limit, an electrolyte decomposition decomposition reaction occurs between the electrode and the carbon interface, which is not preferable.

In addition, the protective efficiency of the secondary battery negative electrode material for the electrolyte decomposition reaction (protective efficiency) is preferably at least 90%, more preferably at least 95%. In the protection rate range with respect to the said electrolyte solution decomposition reaction, when below the said lower limit, the battery characteristic by electrolyte solution decomposition reaction falls and it is unpreferable.

Raman spectra generally contribute to the microstructure of the carbon that forms the surface layer. Therefore, in the negative electrode material for secondary batteries of the present invention having the porosity as described above, it is preferable that the peak intensity ratio near 1360 cm ⁻¹ and the peak intensity ratio near 1580 cm ⁻¹ are 0.45 or less in argon laser Raman spectroscopic measurement of wavelength 514.5 nm. More preferably, it is 0.01-0.45. In the Raman strength ratio range, when the lower limit is less than or exceeds the upper limit, the charge / discharge efficiency is lowered, which is not preferable.

The half width of the peak is narrower as the high-dimensional structure of carbon is uniform, and this half width is one of the configurations that define the characteristics of carbon, and the peak half width at around 1580 cm ⁻¹ in the negative electrode material for secondary batteries of the present invention. Is preferably from 16 to 35. In the peak half-width range, when less than the said lower limit or exceeds the upper limit, charge / discharge efficiency falls and it is unpreferable.

In addition, the tap density of the carbon material is related to the diameter, shape, surface shape, etc. of the powder, and appears different depending on the particle size distribution even if the average particle diameter of the particles is the same. In general, the tap density is increased by the coating, and therefore, the tap density does not increase when there are many particles of barbed or fine powder.

Therefore, in the present invention, a carbon material having an average particle diameter of 10 to 20 µm is used as the core carbon material, and the penetration of the electrolyte solution is not prevented by maintaining the tap density of the negative electrode material for the secondary battery manufactured using the same as 0.7 g / cm 3 or more. The packing density can be improved.

The tap density of the negative electrode material for the secondary battery is preferably 0.7 g / cm 3 or more, and more preferably 1.0 to 1.3 g / cm 3. In the range of the tap density, when the lower limit is less than the upper limit or exceeds the upper limit, penetration of the electrolyte is hindered and the packing density is lowered, which is not preferable.

In addition, when natural graphite or the like is used as the core carbon material, it has a high specific surface area, and pores of the core carbon material are blocked by adhesion or coating of carbon derived from low crystalline carbon.

Therefore, it is preferable that the specific surface area of the said negative electrode material for secondary batteries is 4 m <2> / g or less, More preferably, it is 2 m <2> / g or less. In the said specific surface area range, when exceeding the said upper limit, battery property falls and it is unpreferable.

Porosity (0.0025 or less) or protection rate (90% or more), Raman strength ratio (0.45 or less), peak half width (16 to 35) at around 1580 cm ^-1 , tap density (0.7 g / cm 3 or more) ) And the negative electrode material for a secondary battery of the present invention having a specific surface area (4 m 2 / g or less) may optionally be added with a small amount of a conductive agent or a binder to prepare a slurry for producing a plate.

The use amount of the conductive agent or binder can be appropriately adjusted and used to the extent commonly used in the art, the range does not affect the present invention.

The conductive agent may be used as long as it is an electron conductive material that does not cause chemical change in the battery configured. For example, carbon black such as acetylene black, ketjen black, farnes black, thermal black, and the like, natural graphite, artificial graphite, or conductive fibrous fibers, and the like, and in particular, carbon black, graphite powder, or carbon fiber is preferably used. Do.

As the binder, a thermoplastic resin, a thermosetting resin, or a mixture thereof may be used, and in particular, polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE) is preferably used, and more preferably polyvinyl fluoride. It is to use Leeden.

As described above, the slurry for preparing a cathode plate including the negative electrode material and optionally at least one of a conductive agent and a binder is then applied to an electrode current collector and then dried to remove a solvent or a dispersion medium, thereby binding the active material to the current collector. It binds between active materials.

The electrode current collector is not particularly limited as long as it is made of a conductive material, and it is particularly preferable to use a foil made of copper, gold, nickel, a copper alloy, or a combination thereof.

In addition, the present invention is characterized in that in the secondary battery comprising a separator and an electrolyte interposed between the positive electrode, the negative electrode, both electrodes, the negative electrode material prepared by the above-described manufacturing method as a negative electrode.

The secondary battery of the present invention can be prepared by inserting a porous separator between the positive electrode and the negative electrode in a conventional manner known in the art.

The electrolyte is a non-aqueous electrolyte containing a lithium salt and an electrolyte compound, wherein the lithium salt is selected from the group consisting of LiClO ₄ , LiCF ₃ SO ₃ , LiPF ₆ , LiBF ₄ , LiAsF ₆ and LiN (CF ₃ SO ₂ ) ₂ . Preference is given to compounds of species or more. In addition, the electrolyte solution is ethylene carbonate (EC), propylene carbonate (PC), gamma butyrolactone (GBL), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC) and methyl propyl carbonate (MPC). It is preferable that it is 1 or more types chosen from the group which consists of.

In manufacturing the battery of the present invention, it is preferable to use a porous separator as a separator, and non-limiting examples include a polypropylene-based, polyethylene-based or polyolefin-based porous separator.

The secondary battery of the present invention is not limited in appearance, but may be cylindrical, square, pouch type, or coin type using a can.

As described above, the secondary battery of the present invention preferably has a charge / discharge efficiency of 90% or more and a discharge capacity of 340 mAh / g or more.

Hereinafter, in order to help the understanding of the present invention will be described in more detail through preferred examples and comparative examples.

Example 1

The pitch dissolved with tetrahydrofuran in a natural graphite carbon material having a spherical degree of 15 to 60 was mixed by wet stirring at atmospheric pressure for 2 hours at a weight ratio of 9: 1. The mixture was calcined first and second at 1,100 ° C. and 1,500 ° C. for 1 hour, and classified to remove fine powder to prepare a negative electrode material.

100 g of the prepared negative electrode material was placed in a 500 ml reactor, a small amount of N-methylpyrrolidone (NMP) and polyvinylidene fluoride (PVDF) were added as a binder, and kneaded using a mixer to prepare a plate. Slurry was prepared. Then, the prepared electrode plate slurry was pressed and dried on a rolled mesh to be used as an electrode.

Example 2

The weight ratio of the spherical natural graphite carbon material used in Example 1 and the pitch dissolved in tetrahydrofuran was changed to 9.5: 0.5 in the same manner as in Example 1.

Comparative Example 1

In the same manner as in Example 1 except that the spheroidizing degree of natural graphite carbon material was used instead of the negative electrode material used in Example 1.

Comparative Example 2

The same procedure as in Example 1 was carried out except that the spheroidizing degree of natural graphite carbon material having a spherical degree of 10 was used in place of the spheroidizing degree of natural graphite carbon material of 15 to 60.

Samgeuk the cell using LiCoO ₂ electrode in the example 1 or 2 and Comparative Example 1, or to evaluate the peeling area to the electrolyte of the electrode produced understood dipole, a reference electrode 2 was produced from. A mixed solution of ethylene carbonate and diethyl carbonate (1: 1 by volume) in which 1 mol / l of LiPF ₆ was dissolved was used as an electrolyte solution. The resistance was measured.

In addition, the specific surface area, tap density, aspect ratio, Raman strength ratio, half width, porosity, protection rate and charge / discharge efficiency of the negative electrode materials prepared in Examples 1 or 2 and Comparative Examples 1 or 2 are as follows. It measured by the method and the results are shown in Table 1 below.

end. Specific surface area-Kinetic surface area was measured using an ASAP2400 / nitrogen adsorption BET specific surface area measuring apparatus manufactured by MICROMERITEX.

I. Tap density-It measured in the following procedure based on JIS-K5101. First, Hosokawa Micro Co., Ltd. 'Powder Tester PT-R' was used, and a sieve having a graduation interval of 200 μm was used as a sieve through which the sample passed. After the graphite powder was dropped into the tapping cell of 20 mm 3 and the cell was filled with a full amount, tapping with a stroke length of 18 mm was performed 3,000 times at one time / second, and the tap density at this time was measured.

All. Aspect ratio-The image of 3000 times the magnification of the graphite particle (powder) was obtained using the scanning electron microscope (S-2500) by Hitachi Corporation. Among them, 50 graphite particles were randomly selected, and the ratio of (long diameter) / (short diameter) was measured, and the average value was calculated.

la. Raman-From the two peaks observed by Raman spectroscopic measurement using an argon laser of 514.5 nm, the R value was obtained as a peak intensity type of 1360 cm ^-1 / 1580 cm ^-1 , and a peak fit program Half width was measured using.

hemp. Porosity-Measured using PAR 273A Potentiostat, an electrochemical analysis equipment of EG & G. At this time, the porosity was derived according to Equation 1 by measuring the polarization resistance of the electrode and the polarization resistance of the electrode coated with a mixture of the core carbon material and the low crystalline carbon.

bar. Protection rate-Measured using PAR 273A Potentiostat, EG & G's electrochemical analysis equipment. The current density of the electrode, the core carbon material, and the electrode coated with low crystalline carbon was measured to derive a protection rate according to Equation 2 above.

four. Charging / discharging characteristics-Charge the electric potential within the range of 0 to 1.5 V until the charging current is 0.5 V / cm 2 until it becomes 0.01 V, maintain the voltage of 0.01 V and until the charging current reaches 0.02 mA / cm 2 Charging continued. The discharge current was discharged up to 1.5 V at 0.5 mA / cm 2. In Table 1, the charge / discharge efficiency shows the ratio of the discharged capacity to the charged capacity.

The discharge capacity of 340 mAh / g or more and the charge / discharge efficiency of 90% or more are the standards in terms of high capacity and high efficiency of battery performance.

division Example 1 Example 2 Comparative Example 1 Comparative Example 2 Specific surface area (㎡ / g) 1.6 1.8 7.5 8.7 Tap density (g / cm 3) 1.1 1.05 0.92 0.76 Aspect ratio 1.432 1.497 1.728 1.998 Raman intensity ratio 0.41 0.40 0.09 0.08 Half width 32.6 31.2 14.2 14.1 Porosity 0.00154 0.00234 0.00413 0.00939 Protection rate (%) 93 91 85 74 Discharge Capacity (mAh / g) 348.2 342.5 330.4 321.7 efficiency (%) 92.2 92.7 81.2 77.4

As shown in Table 1, in the case of Example 1 and Example 2 using the negative electrode material having a porosity of 0.0025 or less or 90% or more protection against electrolyte decomposition reaction according to the present invention compared to Comparative Examples 1 and 2 It was confirmed that the discharge capacity is excellent at 340 mAh / g or more, the efficiency is also excellent in more than 90%.

As described above, although the present invention has been described by means of a limited embodiment, the present invention is not limited thereto and will be described below by the person skilled in the art and the technical spirit of the present invention. Of course, various modifications and variations are possible within the scope of the claims.

According to the present invention, it is possible to improve the protection function against the electrolyte decomposition reaction to improve the efficiency and cycle capacity of the secondary battery.

Claims (13)

A negative electrode material for a secondary battery prepared by coating a core carbon material with low crystalline carbon and firing, wherein the negative electrode material according to Equation 1 below has a porosity of 0.0025 or less. [Equation 1]

In Equation 1, P is the total porosity, R _pm is the polarization resistance of the electrode, R _p is the polarization resistance of the electrode coated with a mixture of core carbon material and low crystalline carbon, ΔEcorr is the electrode and core carbon The potential difference between the material and the low crystalline carbon mixture, βa represents the positive electrode Tafel constant of the electrode. In the negative electrode material for a secondary battery prepared by coating a low crystalline carbon on the core carbon material and calcining, the negative electrode for secondary battery, characterized in that the protection rate of the negative electrode material to the electrolyte decomposition reaction according to the following equation (2) is 90% or more ashes. [Equation 2]

In Equation 2, Pi is a protection rate against electrolyte decomposition reaction, i _corr is the current density of the electrode coated with a core carbon material and a low crystalline carbon mixture, i _0corr is the current density of the electrode. The method of claim 1, In the negative electrode material for secondary batteries, the ratio of the peak intensity I ₁₃₆₀ near 1360 cm ⁻¹ and the peak intensity I ₁₅₈₀ near 1580 cm ⁻¹ in an argon laser Raman spectroscopic measurement having a wavelength of 514.5 nm is as follows. Battery anode material.

The method according to claim 1 or 2, Said negative electrode material for secondary batteries has a peak half width in the vicinity of 1580 cm ^-1 of 16 to 35, wherein the negative electrode material for secondary batteries. The method according to claim 1 or 2, The negative electrode material for the secondary battery has a tap density of 0.7 g / cm 3 to 1.3 g / cm 3. The method according to claim 1 or 2, Said negative electrode material for secondary batteries has a specific surface area of 4 m <2> / g or less, The negative electrode material for secondary batteries characterized by the above-mentioned. The method according to claim 1 or 2, The core carbon material is a negative electrode material for a secondary battery, characterized in that a single substance or a mixture of two or more selected from the group consisting of natural graphite and artificial graphite. The method according to claim 1 or 2, The core material carbon material is a spherical degree of 15 to 60, the negative electrode material for a secondary battery, characterized in that. The method according to claim 1 or 2, The core material carbon material is a negative electrode material for a secondary battery, characterized in that the average particle diameter is 10 to 20 ㎛. The method according to claim 1 or 2, The low crystalline carbon is a negative electrode material for a secondary battery, characterized in that a single substance or a mixture of two or more selected from the group consisting of pitch, tar (tar), phenol resin, furan resin, and furfuryl alcohol. The method according to claim 1 or 2, The core carbon material and the low crystalline carbon are mixed in a weight ratio of 85 to 95: 5 to 15, characterized in that the secondary battery negative electrode material. A secondary battery comprising the negative electrode material according to claim 1 or 2 as a negative electrode. The method of claim 12, The secondary battery has a charge / discharge efficiency of 90% or more and a discharge capacity of 340 mAh / g or more.