KR20070091938A - Lithium secondary battery - Google Patents

Abstract

A lithium secondary battery is provided to secure excellent capacity and life characteristics by using a negative electrode active material including a graphite and a metal oxide of Li_xM_yV_zO_(2+d). A lithium secondary battery(3) comprises: a negative electrode(6) including a negative electrode active material consisting of a graphite and a metal oxide represented by the following formula 1 of Li_xM_yV_zO_(2+d), wherein 0.1<=x<=2.5, 0<=y<=0.5, 0.5<=z<=1.5, 0<=d<=0.5, and M is at least one metal selected from the group consisting of Al, Cr, Mo, Ti, W, and Zr; a positive electrode(5) including a positive electrode active material capable of intercalating and de-intercalating lithium ions; and an electrolyte including a non-aqueous organic solvent, a lithium salt and an additive. The lithium secondary battery is charged with 0.01 to 5C and has a charge voltage of 4.3V or more.

Description

Lithium secondary battery {LITHIUM SECONDARY BATTERY}

1 is a schematic cross-sectional view of a lithium secondary battery according to an embodiment of the present invention.

[Industrial use]

The present invention relates to a lithium secondary battery, and more particularly, to a lithium secondary battery having excellent capacity and life characteristics.

[Prior art]

Lithium secondary batteries, which are in the spotlight as power sources of recent portable small electronic devices, exhibit high energy density by showing a discharge voltage that is twice as high as that of a battery using an alkaline aqueous solution using an organic electrolyte solution.

Examples of the positive electrode active material of a lithium secondary battery include lithium and a transition metal having a structure capable of intercalating lithium, such as LiCoO ₂ , LiMn ₂ O ₄ , and LiNi _{1- x} Co _x O ₂ (0 <x <1). Oxides were mainly used.

As the negative electrode active material, various types of carbon-based materials including artificial graphite, natural graphite, and hard carbon capable of inserting and desorbing lithium have been used. The graphite in the carbon series has a low discharge voltage of -0.2V compared to lithium, and the battery using graphite as a negative electrode active material exhibits a high discharge voltage of 3.6V, providing an advantage in terms of energy density of the lithium battery and providing excellent reversibility. It is the most widely used to ensure the long life of the lithium secondary battery. However, in the case of manufacturing the electrode plate with graphite as an active material, the electrode plate density is lowered, so there is a problem in that the capacity is low in terms of energy density per unit volume of the electrode plate. Further, at high discharge voltages, side reactions with organic electrolytes in which graphite is used easily occur, and there is a risk of ignition or explosion due to battery malfunction and overcharge.

In order to solve this problem, an oxide-based negative electrode active material has been recently developed. For example, the amorphous tin oxide researched and developed by Fujifilm has a high capacity of 800 mAh / g per weight, but has a fatal problem of having an initial irreversible capacity of about 50%. In addition, incidental problems such as reduction of some tin oxides from oxides to tin metals due to charging and discharging are also seriously occurring, making it more difficult to use them in batteries.

In addition, Japanese Patent Laid-Open No. 2002-216753 describes Li _a Mg _b VO _c (0.05 ≦ a ≦ 3, 0.12 ≦ _b ≦ 2, 2 ≦ 2c-a-2b ≦ 5) as an oxide cathode. Further, in the Japanese Battery discussion yojijip number 3B05 2002 years been published for a lithium secondary battery negative electrode characteristics of the _{Li 1 .1 V 0 .9 O 2} .

However, the oxide negative electrode does not yet exhibit satisfactory battery performance, and research on it is ongoing.

The present invention is to solve the above problems, an object of the present invention to provide a lithium secondary battery having excellent capacity and life characteristics.

In order to achieve the above object, the present invention is a negative electrode comprising a negative electrode active material comprising a metal oxide and graphite of the formula (1), a positive electrode comprising a positive electrode active material that can intercalate and deintercalate lithium ions, and It provides a lithium secondary battery comprising a non-aqueous organic solvent, an electrolyte containing a lithium salt and an additive, and prepared by charging at 0.01 to 5C. In this case, the lithium secondary battery may have a charging voltage of 4.3 V or more, and more preferably 4.3 to 4.5 V.

[Formula 1]

Li _x M _y V _z O _{2 + d}

Wherein 0.1 ≦ x ≦ 2.5, 0 ≦ y ≦ 0.5, 0.5 ≦ z ≦ 1.5, 0 ≦ d ≦ 0.5, and M is 1 selected from the group consisting of Al, Cr, Mo, Ti, W, and Zr It is a metal of more than one species.)

In addition, the lithium secondary battery exhibits an average discharge voltage of 3.5 V or more when discharged at 0.5 to 1 C, more preferably at 0.2 to 1 C, and an average discharge voltage of 3.5 to 3.7 V when discharged at 0.5 to 2 C.

Hereinafter, the present invention will be described in more detail.

Conventional lithium secondary batteries using a metal oxide as a negative electrode have been difficult to implement at 4.3V or more. In addition, even when implemented at 4.3V or more, the average discharge voltage was lowered to obtain excellent capacity characteristics and lifetime characteristics.

In the present invention, on the other hand, a lithium secondary battery having excellent capacity and lifespan characteristics can be obtained by mixing metal oxide and graphite as a negative electrode and filling them with an optimal C-rate.

1 is a view showing the structure of a lithium secondary battery of the present invention.

Referring to Figure 1 describes the manufacturing process of the lithium secondary battery of the present invention, the lithium secondary battery 3 is present between the positive electrode 5, the negative electrode 6 and the positive electrode 5 and the negative electrode 6 The electrode assembly 4 including the separator 7 may be manufactured by placing the electrode assembly 4 into the case 8, injecting an electrolyte into the upper part of the case 8, and sealing the cap plate 11 and the gasket 12. have.

The negative electrode 6 includes a negative electrode active material.

The negative electrode active material may be prepared by mixing the metal oxide and graphite represented by the following formula (1).

[Formula 1]

Li _x M _y V _z O _{2 + d}

Wherein 0.1 ≦ x ≦ 2.5, 0 ≦ y ≦ 0.5, 0.5 ≦ z ≦ 1.5, 0 ≦ d ≦ 0.5, and M is 1 selected from the group consisting of Al, Cr, Mo, Ti, W, and Zr It is a metal of more than one species.)

The metal oxide may be synthesized by substituting Co in the LiCoO ₂ structure with another transition metal element V and another second metal element Al, Mo, W, Ti, Cr, Zr, or a combination thereof, and graphite. Shows similar discharge potential and lifetime characteristics. In particular, when the compound represented by Formula 1 is used as the negative electrode active material, a capacity per unit volume of 1000 mAh / cc or more can be obtained. Among the metal elements represented by M in Formula 1, Mo and W are preferable.

When x, y, z and d in the above formula 1 is out of the above-described range, since the average discharge potential is 1.0V or higher compared to lithium metal, the discharge voltage of the battery is increased. There is a problem that is too low. Specifically, a negative electrode active material of a metal vanadium oxide that does not contain Li (ie, x = 0; Solid State Ionics, 139, 57-65, 2001 and Journal of Power Source, 81-82, 651-655, 1999) ) Is different from the crystal structure of the active material of the present invention, the average discharge potential is also 1.0V or more there is a problem to use as a negative electrode.

The metal oxide in the negative electrode active material has a theoretical energy density of 4.2 g / cc per unit volume, and when manufactured with an actual electrode plate, an electrode plate density of approximately 3.0 g / cc can be obtained. If the capacity per unit weight is 300 mAh / g, the theoretical capacity per unit volume is theoretically 1200 mAh / cc or more, and an energy density of 900 mAh / cc or more can be obtained. When only graphite, which is a conventional anode active material, is used, the theoretical energy density per unit volume is 2.0 g / cc, the actual energy density is 1.6 g / cc, and the capacity per unit weight is 360 mAh / g, and the actual capacity per unit volume is 570 mAh / cc. Compared to the energy density can be improved by more than twice.

The graphite serves to improve the conductivity of the metal oxide, and may use natural graphite or artificial graphite in the form of a plate, sphere or fiber.

The metal oxide and graphite may be included in a weight ratio of 20:80 to 80:20, and more preferably 40:70 to 70:40. When the content of graphite to the metal oxide is too small, it is difficult to secure sufficient conductivity, and when too much, it is difficult to implement a high capacity cathode.

That is, the negative electrode active material is a mixture of a metal oxide and graphite having an excellent energy density per unit volume, overcomes the low capacity and efficiency of the graphite and low conductivity of the metal oxide, and maintains a high density by high density, high capacity lithium A secondary battery can be provided.

The negative electrode may be prepared by mixing the negative electrode active material, a binder, and optionally a conductive material to prepare a composition for forming a negative electrode active material layer, and then applying the composition to a negative electrode current collector such as copper. As the binder, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropylene cellulose, diacetylene cellulose, polyvinyl chloride, polyvinylpyrrolidone, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene or polypropylene may be used. It may be, but is not limited thereto. In addition, as the conductive material, any battery can be used as long as it is an electronic conductive material without causing chemical change, and examples thereof include natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, copper, Metal powders, such as nickel, aluminum, silver, metal fiber, etc. can be used, and 1 type (s) or 1 or more types can be mixed and used for conductive materials, such as a polyphenylene derivative.

The positive electrode 5 includes a positive electrode active material.

As the cathode active material, a compound (lithiated intercalation compound) capable of reversible intercalation and deintercalation of lithium may be used. Specifically, at least one selected from cobalt, manganese, nickel and at least one of complex oxides with lithium may be used, and more preferably, a compound represented by one of the following Chemical Formulas 2 to 19 may be used:

[Formula 2]

LiNiO ₂

[Formula 3]

LiCoO ₂

[Formula 4]

LiMnO ₂

[Formula 5]

LiMn ₂ O ₄

[Formula 6]

Li _a Ni _b B _c M _d O ₂

(Wherein 0.90 ≦ a ≦ 1.1, 0 ≦ b ≦ 0.9, 0 ≦ c ≦ 0.5, and 0.001 ≦ d ≦ 0.1.)

[Formula 7]

Li _a Ni _b Co _c Mn _d M _e O ₂

(Wherein 0.90 ≦ a ≦ 1.1, 0 ≦ b ≦ 0.9, 0 ≦ c ≦ 0.5, 0 ≦ d ≦ 0.5, and 0.001 ≦ e ≦ 0.1).

[Formula 8]

Li _a NiM _b O ₂

(Wherein 0.90 ≦ a ≦ 1.1 and 0.001 ≦ b ≦ 0.1)

[Formula 9]

Li _a CoM _b O ₂

(Wherein 0.90 ≦ a ≦ 1.1 and 0.001 ≦ b ≦ 0.1)

[Formula 10]

Li _a MnM _b O ₂

(Wherein 0.90 ≦ a ≦ 1.1 and 0.001 ≦ b ≦ 0.1)

[Formula 11]

Li _a Mn ₂ M _b O ₄

(Wherein 0.90 ≦ a ≦ 1.1 and 0.001 ≦ b ≦ 0.1)

[Formula 12]

DS ₂

[Formula 13]

LiDS ₂

[Formula 14]

V ₂ O ₅

[Formula 15]

LiV ₂ O ₅

[Formula 16]

LiEO ₂

[Formula 17]

LiNiVO ₄

[Formula 18]

Li _(3-x) F ₂ (PO ₄ ) ₃ (0 ≤ x ≤ 3)

[Formula 19]

Li _(3-x) Fe ₂ (PO ₄ ) ₃ (0 ≤ x ≤ 2)

In Chemical Formulas 2 to 19, B is Co or Mn; D is Ti or Mo; E is selected from the group consisting of Cr, V, Fe, Sc, and Y; F is selected from the group consisting of V, Cr, Mn, Co, Ni, and Cu; And M is at least one transition metal or lanthanide element selected from the group consisting of Al, Cr, Mn, Fe, Mg, La, Ce, Sr, and V.

In addition, inorganic sulfur (S ₈ , elemental sulfur) and sulfur compounds may be used in addition to the above, and the sulfur compounds include Li ₂ S _n (n ≧ 1) and Li ₂ S _n (n dissolved in catholyte). ≧ 1), an organic sulfur compound or a carbon-sulfur polymer ((C ₂ S _x ) _n : x = 2.5 to 50, n ≧ 2) and the like.

Like the negative electrode, the positive electrode may also be prepared by mixing the positive electrode active material, a binder, and optionally a conductive material to prepare a composition for forming a positive electrode active material layer, and then applying the composition to a positive electrode current collector such as aluminum.

The electrolyte charged in the lithium secondary battery includes a lithium salt, a non-aqueous organic solvent and an additive.

The lithium salt acts as a source of lithium ions in the battery to enable operation of the basic lithium secondary battery. Examples of the lithium salt include LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiAlO ₄ , LiAlCl ₄ , At least one selected from the group consisting of LiN (C _p F _{2p + 1} SO ₂ ) (C _q F _{2q + 1} SO ₂ ), wherein p and q are natural numbers, and LiSO ₃ CF ₃ Can be used. It is preferable to contain at least LiBF ₄ in the lithium salt, and most preferably, LiPF ₆ and LiBF ₄ are mixed and used.

The concentration of the lithium salt can be used in the range of 0.6 to 2.0 M, more preferably in the range of 0.7 to 1.6 M. If the concentration of the lithium salt is less than 0.6 M, the conductivity of the electrolyte is lowered and the performance of the electrolyte is lowered. If the concentration of the lithium salt is more than 2.0 M, the viscosity of the electrolyte is increased, thereby reducing the mobility of lithium ions.

The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move. As the non-aqueous organic solvent, a carbonate, ester, ether or ketone solvent may be used. As the carbonate solvent, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), ethylmethyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. may be used. Examples of the ester solvent include n-methyl acetate, n-ethyl acetate, n-propyl acetate, and the like. Can be used.

In addition, in the case of the carbonate solvent, it is preferable to use a mixture of cyclic carbonate and chain carbonate. In this case, it is preferable to use the cyclic carbonate and the chain carbonate by mixing in a volume ratio of 1: 1 to 1: 9. The performance of the electrolytic solution is desirable when mixed in the above volume ratio.

The non-aqueous organic solvent of the present invention may further include an aromatic hydrocarbon organic solvent in the carbonate solvent. In this case, the carbonate solvent and the aromatic hydrocarbon organic solvent are preferably mixed in a volume ratio of 1: 1 to 30: 1.

As the aromatic hydrocarbon-based organic solvent, an aromatic hydrocarbon compound of Formula 20 may be used.

[Formula 20]

(In Formula 20, R is selected from halogen, an alkyl group having 1 to 10 carbon atoms, haloalkyl, and a combination thereof, and n is an integer of 0 to 6).

Preferably, the aromatic hydrocarbon organic solvent is at least one solvent selected from the group consisting of benzene, fluorobenzene, toluene, fluorotoluene, trifluorotoluene, and xylene.

The electrolyte of the present invention also includes additives such as overcharge inhibitors.

Examples of the overcharge inhibitor include a carbonate compound having a substituent selected from the group consisting of halogen, cyano group (CN) and nitro group (NO ₂ ); Vinylene carbonate; Divinyl sulfone; Ethylene sulfite; Thioacetic acid phenyl ester compounds, such as a thioacetic acid S-phenyl ester or a thioacetic acid O-phenyl ester; Chroman-based compounds such as 6-Fluoro-chroman; And succinonitrile (succinonitrile [(CH ₂ CN) ₂ ]) may be used. Among the additives, carbonate additives are preferable, and as the carbonate additive, ethylene carbonate derivatives represented by the following general formula (21) are preferred, and fluoroethylene carbonate is most preferred.

[Formula 21]

(In Formula 21, X1 is selected from the group consisting of halogen, cyano group (CN) and nitro group (NO ₂ ).)

The overcharge inhibitor may provide a battery having excellent electrochemical characteristics such as high temperature swelling characteristics, capacity, lifespan, and low temperature characteristics by exhibiting an excellent effect on securing safety at high temperature.

The content of the overcharge inhibitor is preferably 0.1 to 5% by weight, more preferably 3 to 5% by weight based on the total weight of the electrolyte. When the content of the overcharge inhibitor is less than 0.1% by weight, the addition effect is insignificant, and when it exceeds 5% by weight, it is not preferable because there is a problem of charge and discharge life.

The separator may exist between the positive electrode and the negative electrode according to the type of the lithium secondary battery. As the separator, polyethylene, polypropylene, polyvinylidene fluoride or two or more multilayer films thereof may be used, and polyethylene / polypropylene two-layer separator, polyethylene / polypropylene / polyethylene three-layer separator, polypropylene / polyethylene / It goes without saying that a mixed multilayer film such as a polypropylene three-layer separator can be used.

Lithium secondary battery according to an embodiment of the present invention having the configuration as described above has a charge voltage of 4.3V or more, more preferably has a charge voltage of 4.3 to 4.5V. If the charge voltage of the lithium secondary battery is less than 4.3V it is difficult to implement a high capacity battery.

In addition, the lithium secondary battery exhibits an average discharge voltage of 3.5 V or more when discharged at 0.5 to 1 C, more preferably at 0.2 to 1 C, and an average discharge voltage of 3.5 to 3.7 V when discharged at 0.5 to 2 C.

As described above, the lithium secondary battery of the present invention exhibits excellent capacity and lifetime characteristics and can be used as a power source for various electronic products. For example, the present invention may be used in a portable telephone, a mobile phone, a game machine, a portable television, a notebook computer, a calculator, and the like, but is not limited thereto.

Hereinafter, preferred examples and comparative examples of the present invention are described. However, the following embodiments are only preferred embodiments of the present invention, and the present invention is not limited to the following embodiments.

(Example 1)

Li ₂ CO ₃ , V ₂ O ₃ , and MoO ₃ are mixed in a solid phase so that the ratio of Li: V: Mo is 1.08: 0.9: 0.02, heat-treated at nitrogen atmosphere for 10 hours at 1,000 ° C., and then cooled to room temperature to provide metal oxides. Was prepared. 150g of natural graphite was finely ground and then mixed with 150g of the prepared metal oxide in a planetary mixer to prepare a negative electrode active material.

The negative electrode active material was mixed with polyvinylidene fluoride in N-methylpyrrolidone in a ratio of 90:10 to prepare a negative electrode slurry. The negative electrode slurry was coated on a copper foil (Cu-foil) to a thickness of 70 μm to form a thin electrode plate, dried at 135 ° C. for at least 3 hours, and then pressed to prepare a negative electrode.

LiCoO ₂ as a positive electrode active material, polyvinylidene fluoride (PVDF) as a binder and carbon as a conductive agent were mixed in a weight ratio of 92: 4: 4, and then dispersed in N-methyl-2-pyrrolidone to prepare a positive electrode slurry. It was. The positive electrode slurry was coated on aluminum foil with a thickness of 70 μm to form a thin electrode plate, dried at 135 ° C. for at least 3 hours, and then pressed to prepare a positive electrode.

To the mixed solvent of propylene carbonate (PC), diethyl carbonate (DEC) and ethylene carbonate (EC) (PC: DEC: EC = 1: 1: 1), 2% by weight of fatigue carbonate was added, followed by LiPF ₆ as a lithium salt. Was added to prepare an electrolytic solution having a LiPF ₆ concentration of 1.15 M.

The prepared electrodes were wound and compressed using a separator made of a porous polypropylene film, placed in a battery case, and then injected with the electrolyte to prepare a lithium secondary battery. At this time, the amount of electrolyte used was 2.7 g.

 (Comparative Example 1)

100 g of natural graphite was finely ground and then mixed with 100 g of SnO in a planetary mixer to prepare a negative electrode active material.

A lithium secondary battery was manufactured by the same method as Example 1, except that the prepared negative active material was used.

Electrical characteristics of the batteries prepared in Example 1 and Comparative Example 1 were evaluated.

Charge was 0.2C and discharge was 0.5C. The results are shown in Table 1 below.

Discharge capacity once (mAh / cc) 10 times discharge capacity (mAh / cc) 10 times life (%) Charge voltage (V) Average discharge voltage (V) Example 1 800 750 93 4.3 3.6 Comparative Example 1 720 250 35 4.3 3.3

As shown in Table 1, the lithium secondary battery of Example 1 exhibited a charge voltage of 4.3V and an average discharge voltage of 3.6V, and had excellent capacity characteristics and life characteristics compared to the lithium secondary battery of Comparative Example 1. I could confirm it.

The lithium secondary battery according to the present invention exhibits excellent capacity characteristics and lifespan characteristics.

Claims (11)

A negative electrode including a negative electrode active material including a metal oxide of the formula (1) and graphite; A positive electrode comprising a positive electrode active material capable of intercalating and deintercalating lithium ions; And An electrolyte comprising a non-aqueous organic solvent, a lithium salt and an additive, It is prepared by filling in 0.01 to 5C, Lithium secondary battery having a charge voltage of 4.3V or more. [Formula 1] Li _x M _y V _z O _{2 + d} Wherein 0.1 ≦ x ≦ 2.5, 0 ≦ y ≦ 0.5, 0.5 ≦ z ≦ 1.5, 0 ≦ d ≦ 0.5, and M is 1 selected from the group consisting of Al, Cr, Mo, Ti, W, and Zr It is a metal of more than one species.) The method of claim 1, The lithium secondary battery is a lithium secondary battery having a charging voltage of 4.3 to 4.5V. The method of claim 1, The lithium secondary battery is a lithium secondary battery that exhibits an average discharge voltage of 3.5V or more when discharged at 0.5 to 1C. The method of claim 1, The lithium secondary battery is charged at 0.2 to 1C, and exhibits an average discharge voltage of 3.5 to 3.7V when discharged at 0.5 to 2C. The method of claim 1, Wherein M is Mo or W negative electrode active material. The method of claim 1, The metal oxide and graphite are included in the weight ratio of 20:80 to 80:20. The method of claim 1, The positive electrode active material is at least one selected from cobalt, manganese, nickel and at least one of a composite oxide of lithium. The method of claim 1, The lithium salt is LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiAlO ₄ , LiAlCl ₄ , At least one lithium secondary battery selected from the group consisting of LiN (C _p F _{2p +1} SO ₂ ) (C _q F _{2q +1} SO ₂ ), wherein p and q are natural water) and LiSO ₃ CF ₃ . The method of claim 1, The non-aqueous organic solvent is at least one lithium secondary battery selected from the group consisting of carbonate, ester, ether and ketone solvents. The method of claim 1, The additive may include a carbonate compound having a substituent selected from the group consisting of halogen, cyano group (CN) and nitro group (NO ₂ ); Vinylene carbonate; Divinyl sulfone; Ethylene sulfite; Thioacetic acid phenyl ester compound; Chroman based compounds; And succinonitrile is a lithium secondary battery that is at least one anti-charge agent selected from the group consisting of. The method of claim 10, The overcharge inhibitor is a lithium secondary battery that is contained in 0.1 to 5% by weight based on the total weight of the electrolyte.

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