JP2006127911A - Lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive lithium secondary battery having large discharge capacity, and causing little deterioration of charge and discharge capacity even if charge and discharge is repeated. <P>SOLUTION: This lithium secondary battery has a positive electrode, a negative electrode, and a nonaqueous electrolyte, and a positive electrode active material composing the positive electrode comprises lithium copper composite oxide expressed by the general formula Li<SB>2</SB>(Cu<SB>1-x-y</SB>M<SB>x</SB>D<SB>y</SB>)O<SB>2</SB>(in the formula, M expresses one or more elements selected from a group 13 element and a group 14 element in the element periodic table, Fe, Co, and Ni, D expresses one or more elements selected from Ti, V, Y, Zr, Mo, and Pd, and x and y are 0 < x < 0.5, 0 < y < 0.5, x + y < 0.5). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a lithium secondary battery, and more particularly to a positive electrode active material thereof.

Recently, since the amount of CO ₂ gas contained in the atmosphere is increasing, it has been pointed out that global warming may occur due to the greenhouse effect. Thermal power plants convert thermal energy obtained by burning fossil fuels into electrical energy, but burning a large amount of CO ₂ gas makes it difficult to build a new thermal power plant. ing. Therefore, as an effective use of power generated by generators such as thermal power plants, surplus power is stored in secondary batteries installed in ordinary households and used in the daytime when power consumption is high. Level the load. So-called load leveling has been proposed.

In addition, for electric vehicle applications that are characterized by not discharging substances related to air pollution including CO ₂ , NO _x , hydrocarbons, etc., development of secondary batteries with high energy density is expected. Furthermore, in the power supply applications of portable devices such as book-type personal computers, word processors, video cameras, and mobile phones, it is an urgent task to develop a small, lightweight, high-performance lithium secondary battery.

As a positive electrode active material for such a small, lightweight and high-performance lithium secondary battery, lithium-cobalt composite oxide (LiCoO ₂ ) is currently most frequently used. However, since cobalt, which is a raw material for LiCoO ₂ , is expensive, and a secondary battery using this is inevitably expensive, lithium-nickel composite oxide (LiNiO ₂ ) and lithium-manganese composite oxide, which are inexpensive raw materials, are used. Secondary batteries using a material (LiMn ₂ O ₄ ) as a positive electrode active material have been studied. However, since these materials are difficult to synthesize and have a problem that the capacity is greatly deteriorated when charging and discharging are repeated as a secondary battery, researches for improving this problem have been actively conducted. However, sufficient improvement has not been obtained yet.

In Non-Patent Document 1, lithium-copper composite oxide (Li ₂ CuO ₂ ) has been proposed as a positive electrode active material replacing LiCoO ₂ .
Li ₂ CuO ₂ is a relatively inexpensive copper compound as a raw material, and contains about twice as much lithium as LiCoO ₂ and LiNiO ₂ and about 4 times as much as LiMn ₂ O ₄ per unit weight. Therefore, if _two lithiums can be reversibly charged and discharged between the composition formulas Li ₂ CuO ₂ and CuO ₂ , the capacity is about twice that of LiCoO ₂ and LiNiO ₂ and about 4 times that of LiMn ₂ O _4. It is a promising material. However, when Li ₂ CuO ₂ is actually used as the positive electrode material of the secondary battery, only one lithium can contribute to the reversible charge / discharge reaction between Li ₂ CuO ₂ and LiCuO ₂ , The capacity as expected is not obtained. Further, when charging / discharging is repeated, there is a problem that both the charge capacity and the discharge capacity decrease. The reason that only one lithium can contribute to the reversible charge / discharge reaction is that when Li is electrochemically removed from LiCuO ₂ , the structure changes to CuO instead of CuO _2. It is considered that the reason why both the charge capacity and the discharge capacity decrease when the discharge is repeated is due to a structural change between Li ₂ CuO ₂ and LiCuO ₂ . Furthermore, Li ₂ CuO ₂ has a problem that the average discharge potential is lower by about 1 V or more than LiCoO ₂ , LiNiO ₂ , and LiMn ₂ O ₄ .

To improve the above Li ₂ CuO ₂ problems, techniques for mixing different element in Li ₂ CuO ₂ have been filed. For example, the transition metal a part of Cu of Patent Document 1, Li ₂ CuO _2, have material _{Li X Cu 1-y M y} O z which is substituted with a semi-metal element is disclosed, insufficient discharge capacity at this improved In addition, there is no disclosure regarding improvement in reduction in charge / discharge capacity due to repeated charge / discharge.
Japanese Patent Laid-Open No. 9-147861 “Solid State Ionics” Vol 106, p. 45-53, 1998

The present invention suppresses the structural change to CuO and the structural change between Li ₂ CuO ₂ and LiCuO ₂ during charging of the above Li ₂ CuO ₂ , so that the discharge capacity is large and the charge capacity is repeated. The present invention also provides a lithium secondary battery in which the decrease in charge / discharge capacity is small.

That is, the present invention is a lithium secondary battery having a positive electrode, a negative electrode, and a nonaqueous electrolyte, wherein the positive electrode active material constituting the positive electrode is represented by the general formula Li ₂ (Cu _1-xy M _x D _y ) O ₂ (formula M is one or more elements selected from the group consisting of group 13 elements, group 14 elements, Fe, Co, and Ni in the periodic table, and D is composed of Ti, V, Y, Zr, Mo, and Pd. Represents one or more elements selected from the group, x and y are 0 <x <0.5, 0 <y <0.5, and x + y <0.5.) The present invention relates to a lithium secondary battery characterized by comprising a product.

The crystal structure of Li ₂ CuO ₂ is such that, as shown in FIG. 1, planar four-coordinate CuO ₄ shares a ridge to form a linear unit, and lithium is arranged between the CuO ₄ linear units. Has the structure.

The present inventors found that the structure of Li ₂ CuO ₂ having such a crystal structure is changed to CuO instead of CuO ₂ at the time of charging because the copper in the CuO ₄ linear unit is a close atom. This is thought to be due to the fact that the bond strength between the oxygen atom and the oxygen atom is desorbed during charging, and it is assumed that the structural change to CuO can be suppressed by strengthening the bond between oxygen and atoms close to oxygen. In addition, regarding the structural change between Li ₂ CuO ₂ and LiCuO ₂ , it is considered that the arrangement between the CuO ₄ linear units changes with the insertion and extraction of lithium, and the CuO ₄ linear unit It was inferred that the structural change between Li ₂ CuO ₂ and LiCuO ₂ can be suppressed by strengthening the bond between them.

Based on the above inferred, as a result of the avidity and CuO ₄ calculates the bonding strength between the linear unit of the atoms adjacent to oxygen and oxygen in the CuO ₄ linear units, of Li ₂ CuO ₂ copper By substituting a part with the specific element M, the bonding force between the oxygen in the CuO ₄ linear unit and the neighboring element can be strengthened, and by substituting with the specific element D, between the CuO ₄ linear units It was found that the bond strength of can be increased.

The progress of the present invention will be described based on the following calculation.
(Method of calculating binding force)
The calculation of the bonding force between atoms proceeded according to the flow shown in FIG. The calculation is based on the Dv-Xα molecular orbital method described in the document “Phys. Soc. Jpn,” Vol 875, 45 pages (1978) and the Mariken method of “J. Chem. Phys,” Vol 23, pages 1833-1846 (1955). Was used. In step (1), the atomic assembly (cluster) model is cut out from the crystal structure of Li ₂ CuO ₂ in step (1), and the molecular orbitals in the model are analyzed using the Dv-Xα molecular orbital method in steps (2) to (5). The electron density is calculated, and the bonding force between atoms is calculated from the molecular orbital calculated in step (6) and the electron density using the Mariken method. Each step will be described in detail below.

Step (1) (Atom Assembly Model)
The atomic assembly model used for the calculation is obtained by cutting out a part of the Li ₂ CuO ₂ crystal and replacing the central copper atom with other atoms (substitution elements M and D) as shown in FIG.
Then, the state of the crystal was approximated by arranging about 1,000 charges around the model and considering the electrostatic potential.

Steps (2) to (5) (Calculation of molecular orbitals and electron density)
In steps (2) to (5), molecular orbitals and electron density in the model were calculated using the Dv-Xα molecular orbital method. In the Dv-Xα molecular orbital method, the atomic orbital of each atom in the model is calculated in step (2) assuming the initial value of the electron density distribution in the model, and in step (3) the calculation is performed in step (2). By solving the secular equation with the atomic orbitals as basis functions, the molecular orbitals and eigenenergy in the model are calculated. In step (4), the electron density distribution (output value) is obtained from the molecular orbitals calculated in step (3). In 5), the output value of the electron density distribution is compared with the initial value. If the output value and the initial value are the same, the output value is set as the final value of the electron density. The calculation is performed again as the initial value, and steps (2) to (5) are repeated until the output value and the initial value are the same. Steps (2) to (5) will be described in detail below.

Step (2) (Calculation of atomic orbitals)
The initial value of the electron density in the model is located

In the function

The position of the isolated atom ν

Orbit for the i-th electron

And its intrinsic energy ε _i is the Hamiltonian of equation (1)

And the Schrödinger equation (2).

Z _v is the nuclear charge,

Is the position of the nucleus, and α is a coefficient of 0.7. The first term on the right side of equation (1) is the kinetic energy of the electrons, the second term is the potential received from the nucleus, the third term is the potential of the electron system, and the fourth term is the exchange potential.

Step (3) (Calculation of molecular orbitals)
The molecular orbitals in the model are expressed by linear combinations of the atomic orbitals calculated in step (2). That is, the position of the lth electron

The molecular orbital in, as shown in equation (3)

It expresses. Here, C _il is a constant. The value of C _il (0 ≦ C _il ≦ 1) makes it possible to investigate which atomic orbitals are greatly involved in molecular orbitals. Using this relationship, molecular orbitals

And its specific energy ε _l . To that end, the following formula (4) Hamiltonian

And the Schrodinger equation (5).

  Here, the first term on the right side of equation (4) is the kinetic energy of the electrons, the second term is the potential received from all the nuclei, the third term is the potential of the electron system, and the fourth term is the exchange potential. is there.

Substituting the Schrödinger equation (5) into the molecular orbital equation (3) yields the equation (6) or (9). In practice, the component display (6) or matrix display (9) Eigenenergy ε _l and its molecular orbitals by solving the secular equation

Ask for.

H _ij is an overlap integral, and S _ij is a Coulomb integral (i = j) and a resonance integral (i ≠ j), which are expressed by Equations (7) and (8).

  In addition, the component display of Equation (7) is arranged and expressed in matrix form as Equation (9).

The ∧ above the symbol indicates that it is a matrix.
Step (4) (Calculation of electron density)
Electron density

Is the molecular orbital obtained in step (3)

Is obtained by the following equation (10).

Step (5) (Comparison of initial value of electron density and output value)
Next, a difference Z between the electron density calculation initial value and the output value is obtained from the equation (11).

  When the difference in electron density Z ≠ 0, the initial value when the output value of the electron density is first input again, that is,

Return to step (2).
Final electron density when Z = 0

As the molecular orbital at that time

とその固有エネルギーε_l を得る。

And its intrinsic energy ε _l .

Step (6) (Calculation of binding force)
The bonding force between atoms is calculated using the molecular orbitals calculated above and the electron density. The calculation used the method of Mariken. The bond strength here represents the strength of the covalent bond. In the Mariken method, the strength of the bonding force between atom A and atom B is expressed by the following equation.

Here, f _l is the occupation number of electrons occupying the molecular orbital l. Moreover, the sum about i and j means performing only about what belongs to A atom and B atom. The strength of the binding force is evaluated based on the magnitude of Q _AB .

Using the method of the Mulliken was calculated avidity and CuO ₄ binding force between the linear unit of the atoms adjacent to oxygen and oxygen in the CuO ₄ linear unit. The bond strength between oxygen and the atoms close to oxygen in the CuO ₄ linear unit was expressed as the sum of the bond strength between oxygen and a substitution element and oxygen and a copper atom. The bond strength between the CuO ₄ linear units is determined by the atomic 4-plane coordination of oxygen centered on the substitution element (the atoms in the dotted line in FIG. 3) and the 4-plane oxygen coordination centered on copper. The bond strength with the atomic group in the middle (the atom in the solid line in FIG. 3) is expressed as a sum of the binding forces.

FIG. 4 shows the bonding force between oxygen and adjacent atoms in a CuO ₄ linear unit when a part of the copper of Li ₂ CuO ₂ calculated by the above method is replaced with another element M. It is shown by the rate of change with respect to the bonding force of Li ₂ CuO ₂ that has not been formed. As is clear from FIG. 4, the substitution elements that strengthen the bonding force between oxygen and adjacent atoms in the CuO ₄ linear unit are group 13 elements, group 14 elements in the periodic table of elements such as Al and Si, It was found that Fe, Co, Ni, and more preferably Al, Si.

FIG. 5 shows the bonding force between the CuO ₄ linear units when a part of copper of Li ₂ CuO ₂ is substituted with another element D, with respect to the bonding force in the case of Li ₂ CuO _{2 in} which no element is substituted. The rate of change is shown. As is clear from FIG. 5, it was found that the substitution elements that strengthen the binding force between the CuO ₄ linear units are Ti, V, Y, Zr, Mo, and Pd.

As a result of experiments based on the above calculation, the present inventors have found that the general formula is Li ₂ (Cu _1-xy M _x D _y ) O ₂ (0 <x <0.5, 0 <y <0.5, In the lithium-copper composite oxide represented by x + y <0.5), an element periodic table that is an element that can strengthen the bonding force between oxygen in a CuO ₄ linear unit and adjacent atoms as an M element. Using one or more elements selected from the group consisting of group 13 elements, group 14 elements, Fe, Co, and Ni, more preferably one or more elements selected from the group consisting of Al and Si; By using one or more elements selected from the group consisting of Ti, V, Y, Zr, Mo, and Pd, which are elements capable of strengthening the bonding force between CuO ₄ linear units, The discharge capacity is larger than that of lithium copper composite oxide, and charging and discharging are repeated. It has been found that a positive electrode active material with a small decrease in discharge capacity can be obtained.

According to the present invention, the general formula is represented by Li ₂ (Cu _1-xy M _x D _y ) O ₂ (0 <x <0.5, 0 <y <0.5, x + y <0.5), and M The element is one or more elements selected from the group consisting of Group 13 elements, Group 14 elements, Fe, Co, and Ni in the Periodic Table of Elements, and Group D is a group consisting of Ti, V, Y, Zr, Mo, and Pd by using the lithium-copper mixed oxide is one or more elements selected from the positive electrode active material, Li ₂ CuO ₂ during structural changes and the charge and discharge of the CuO during charging of Li ₂ CuO ₂ and LiCuO ₂ It is possible to provide a lithium secondary battery that can suppress the structural change between them, is inexpensive, has a large discharge capacity, and has a small decrease in charge / discharge capacity due to repeated charge / discharge.

Hereinafter, the present invention will be described in detail.
The lithium secondary battery of the present invention is a lithium secondary battery having a positive electrode, a negative electrode, and a nonaqueous electrolyte, and the positive electrode active material constituting the positive electrode is represented by the general formula Li ₂ (Cu _1-xy M _x D _y ) O. _It consists of lithium copper complex oxide represented by ₂ .

[Positive electrode active material]
The positive electrode active material according to the present invention is a lithium copper composite oxide represented by Li ₂ (Cu _{1 -xy} M _x D _y ) O ₂ having an orthorhombic Li ₂ CuO ₂ type structure.

The positive electrode active material preferably has an orthorhombic Li ₂ CuO ₂ type structure and a structure belonging to the space group Imm.
The substitution element M is an element that can strengthen the bonding force between oxygen and adjacent atoms in the CuO ₄ linear unit, and is composed of a group 13 element, a group 14 element, Fe, Co, and Ni in the periodic table of elements. One or more elements selected from the group, more preferably one or more elements selected from the group consisting of Al and Si.

The substitution element D is an element that can strengthen the bonding force between the CuO ₄ linear units, and is one or more elements selected from the group consisting of Ti, V, Y, Zr, Mo, and Pd. .

The range of x and y is 0 <x <0.5 and 0 <y <0.5, and two kinds of substitution elements M and D are necessarily included. This is the case of substituting only element M capable of strongly bonding force between oxygen and the proximity atom in CuO ₄ linear unit, weak binding force between CuO ₄ linear unit, charge This is because the change in arrangement between the CuO ₄ linear units at the time of discharge cannot be sufficiently suppressed. When only the element D is substituted, it is possible to strengthen the binding force between the CuO ₄ linear units. However, this is because the bonding force between oxygen and neighboring atoms in the CuO ₄ linear unit becomes weak, and desorption of oxygen occurs remarkably during charging, and the structure changes to CuO. That is, by appropriately substituting the two types of substitution elements M and D, both the change in arrangement between the CuO ₄ linear units and the desorption of oxygen during charging and discharging can be suppressed, and the discharge capacity is high. A positive electrode active material with a small decrease in capacity can be obtained even when charging and discharging are repeated. Further, it is more preferable that x ≧ y has a relationship of x ≧ y. This is because if the substitution element D is larger than the substitution element M, the bonding force between oxygen and neighboring atoms in the CuO ₄ linear unit may be weakened.

The range of x + y is x + y <0.5. This is because when x + y is 0.5 or more, the orthorhombic Li ₂ CuO ₂ type structure cannot be maintained or the structure becomes unstable, causing a reduction in discharge capacity.

(Method for producing positive electrode active material)
As an example of a method for producing a positive electrode active material, each raw material of a lithium compound, a copper compound, and a substitution element compound is weighed to a predetermined composition and then mixed by a predetermined mixing method, and a temperature range of 400 to 1000 ° C. is fired. A desired positive electrode active material is obtained by heating and baking within 72 hours.

(Lithium and copper raw materials)
Examples of the raw materials for lithium and copper include, but are not limited to, metal and metal salts and oxides, hydroxides, nitrides, sulfides, halides, and organometallic compounds of the above elements.

(Lithium and copper salts)
Representative examples of lithium and copper salts include carbonates, nitrates, sulfates, sulfamates, acetates, oxalates, citrates, tartrates, formates, ammonium salts, etc. Is not to be done.

(Raw material for M and D substitution elements)
As the transition metal raw materials (Ti, V, Fe, Co, Ni, Y, Zr, Mo, Pd), the transition metal element metal and transition metal salts, oxides, hydroxides, nitrides, sulfides , Halides, organic transition metal compounds, and the like are used, but not limited thereto. Aluminum, silicon metal and aluminum, silicon salts, oxides, hydroxides, nitrides, sulfides, halides, organometallic compounds, etc. are used as raw materials for Al and Si, but are not limited thereto. .

(M and D element salts)
Typical examples of M and D element salts include carbonate, nitrate, sulfate, sulfamate, acetate, oxalate, citrate, tartrate, formate, and ammonium salt. It is not limited.

(Method of mixing raw materials)
The raw material mixing method is a method in which a powdery raw material is weighed to a desired composition and then mixed in a dry manner, and after a powdery raw material is weighed to a desired composition, the raw material is dissolved in an aqueous solution or an organic solvent. Alternatively, after dispersion, water or an organic solvent is dispersed to obtain a dried and uniform mixture. After the powdery raw material is weighed to a desired composition, the raw material is dissolved in an acidic solution, and then an alkaline solution is dropped. Although the method of obtaining a deposit, etc. are mentioned, it is not limited to these.

(Dry mixing method)
Examples of the dry mixing method include, but are not limited to, a mechanical mixing method using a ball mill or the like.

(Wet mixing method)
Using a wet mixing method, weigh the powdery raw material to the desired composition, dissolve or disperse the raw material in an aqueous solution in which citric acid is dissolved at a predetermined concentration, and then use a spray dryer. A method for obtaining a uniform dried precursor by dispersing moisture, more preferably, when the moisture of an aqueous solution in which raw materials and citric acid are dissolved is splashed with a spray dryer, at a high temperature of 400 ° C. or higher and 1000 ° C. or lower. Although the method of obtaining a target object directly by applying heat instantaneously is mentioned, it is not limited to these.

[Production method of electrode structure]
(Electrode structure)
FIG. 6 is a conceptual diagram schematically showing a cross section of one embodiment of the electrode structure 602 made of the positive electrode active material powder in the present invention. FIG. 6A shows an electrode structure 602 in which an electrode material layer 601 made of a positive electrode active material powder 603 is provided on a current collector 600. In FIG. 6B, the electrode structure 602 is provided with an electrode material layer 601 including a positive electrode active material powder 603, a conductive auxiliary material 604, and a binder 605. Although the electrode material layer 601 is provided on only one surface of the current collector 600 in FIG. 10, it can be provided on both surfaces of the current collector 600 depending on the form of the battery.

(Preparation of electrode structure 602)
The positive electrode active material powder 603 according to the present invention is mixed with the binder 605 and the conductive auxiliary material 604 and formed together with the current collector 600. Specifically, the binder 605 and the conductive auxiliary material 604 are mixed with the positive electrode active material powder 603, the viscosity is adjusted by appropriately adding a solvent, the paste is applied onto the current collector 600, and dried. An electrode structure 602 is formed. Although the method of forming by adjusting thickness with a roll press etc. as needed is mentioned, it is not limited to these. The formation step is preferably performed in dry air from which moisture has been sufficiently removed, and more preferably performed in an inert gas atmosphere. Further, after the electrode structure 602 is formed, it may be dehydrated by microwave heating and dehydrated with a vacuum dryer. The mixing ratio of the binder to the positive electrode active material is preferably 0.1 or less.

(Conductive auxiliary material 604)
The role of the conductive auxiliary material is to assist electronic conduction and facilitate current collection because the positive electrode active material has low electronic conductivity. As the conductor powder, various carbon materials such as acetylene black, ketjen black and graphite powder, and metal materials such as nickel, titanium, copper and stainless steel can be used. The mixing weight ratio of the conductor powder to the positive electrode active material is preferably 1 or less.

(Binder 605)
The binder has a role of adhering the positive electrode active material powders and preventing a crack from being generated in the charge / discharge cycle and falling off from the current collector. As the binder material, one or more kinds of resins selected from fluororesins, polyvinylidene fluoride, styrene-butadiene rubber, polyethylene, polypropylene, silicone resins, and polyvinyl alcohol, which are stable in organic solvents, can be used. .

(Positive electrode current collector 600)
The positive electrode current collector is inactive to the battery reaction, and fiber, porous or mesh-like aluminum, titanium, nickel, stainless steel, platinum, or the like is used.

[Configuration of secondary battery]
FIG. 7 is a conceptual diagram schematically showing a cross section of one embodiment of the secondary battery (lithium secondary battery) of the present invention. The positive electrode 703 and the negative electrode 701 which are the electrode structures of the present invention are ion conductors ( Electrolyte) 702 faces each other and is accommodated in a battery housing (case) 706, and the negative electrode 701 and the positive electrode 703 are connected to the negative electrode terminal 704 and the positive electrode terminal 705, respectively.

(Positive electrode 703)
The above-described electrode structure 602 of the present invention is used for the positive electrode 703 of the lithium secondary battery of the present invention described above.

(Negative electrode 701)
The negative electrode 701 serving as a counter electrode of a lithium secondary battery using the above-described electrode structure of the present invention as a positive electrode is composed of at least a negative electrode material serving as a lithium ion host material, and preferably from a negative electrode material serving as a lithium ion host material. It consists of a formed layer and a current collector. Further, the layer formed from the negative electrode material is preferably made of a negative electrode material that becomes a lithium ion host material and a binder, and in some cases, a material obtained by adding a conductive auxiliary material thereto.

(Negative electrode material)
Examples of the negative electrode material used as a lithium ion host material for the lithium secondary battery of the present invention include carbon materials such as graphite, metal materials that are electrically alloyed with lithium, lithium metals, transition metal oxides, and transition metal sulfides. A transition metal nitride, a lithium-transition metal oxide, a lithium-transition metal sulfide, and a lithium-transition metal nitride. As a metal material that is electrically alloyed with lithium, a metal material containing one or more elements selected from silicon, tin, lithium, magnesium, aluminum, potassium, sodium, calcium, zinc, and lead is suitable. Used for. The transition metal elements of transition metal oxides, transition metal sulfides, and transition metal nitrides are elements partially having a d-shell or f-shell, such as Sc, Y, lanthanoids, actinoids, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Wn, Tc, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, and Au are preferably used. In order to obtain a battery having a high energy density, it is preferable to use lithium metal for the negative electrode active material.

(Negative electrode current collector)
As the current collector material used for the negative electrode, fibrous, porous or mesh-like carbon, stainless steel, titanium, nickel, copper, platinum, gold, or the like is used.

(Ion conductor 702)
The ionic conductor of the lithium secondary battery of the present invention includes a separator holding an electrolytic solution (an electrolytic solution prepared by dissolving an electrolyte in a solvent), a solid electrolyte, and a solid obtained by gelling the electrolytic solution with a polymer gel. Lithium ion conductors such as fluorinated electrolytes can be used.

The ion conductor of the lithium secondary battery of the present invention is preferably as high as possible, and the conductivity at 25 ° C. is preferably 1 × 10 ⁻³ S / cm or more, and preferably 5 × 10 ⁻³ S / cm. More preferably, it is cm or more.

(Electrolytes)
The electrolytes include lithium ions (Li +) and Lewis acid ions (BF ₄ ⁻ , PF ₆ ⁻ , AsF ₆ ⁻ , ClO ₄ ⁻ , PF ₆ ⁻ , CF ₃ SO ₃ ⁻ , (CF ₃ SO ₂ ) ₃ C ⁻ , ( CF ₃ SO ₂ ) ₂ N ⁻ , B (C ₆ H ₅ ) ₄ ⁻ , C ₄ F ₉ SO ₃ ⁻ ), and mixed salts thereof are used. In addition to the supporting electrolyte, a salt of a cation such as sodium ion, potassium ion, tetraalkylammonium ion and Lewis acid ion can be used. It is desirable that the salt be sufficiently dehydrated and deoxygenated by heating under reduced pressure. In order to prevent leakage of the electrolytic solution, gelation is preferable. As the gelling agent, it is desirable to use a polymer that swells by absorbing the solvent of the electrolytic solution, and polymers such as polyethylene oxide, polyvinyl alcohol, polyacrylonitrile, and polyvinylidene fluoride are used.

(Electrolyte solvent)
Solvents for the electrolyte include acetonitrile: CH ₃ CN, benzonitrile: C ₆ H ₅ CN, propylene carbonate: PC, ethylene carbonate: EC, dimethylformamide: DMF, tetrahydrofuran: THF,
Nitrobenzene: C ₆ H ₅ NO ₂ , dichloroethane, diethoxyethane, chlorobenzene, γ-butyrolactone, dioxolane, sulfolane, nitromethane, dimethyl sulfide, dimethylsulfoxide, dimethoxyethane, methyl formate, 3-methyl-2-oxazolidinone, 2- Methyltetrahydrofuran, sulfur dioxide, phosphoryl chloride, thionyl chloride, sulfuryl chloride, and the like, and mixtures thereof can be used.

  The solvent may be dehydrated with activated alumina, molecular sieve, phosphorus pentoxide, calcium chloride or the like, or depending on the solvent, it may be distilled in an inert gas in the presence of an alkali metal to remove impurities and dehydrate.

  In order to prevent leakage of the electrolytic solution, it is preferable to use a solid electrolyte or a solidified electrolyte. Examples of the solid electrolyte include glass such as an oxide made of lithium element, silicon element, oxygen element, phosphorus element or sulfur element, and a polymer complex of an organic polymer having an ether structure. As the solidified electrolyte, a solution obtained by gelling the electrolytic solution with a gelling agent and solidifying it is preferable. As the gelling agent, it is desirable to use a polymer that swells by absorbing the solvent of the electrolytic solution. As such a polymer, polyethylene oxide, polyvinyl alcohol, polyacrylamide, polymers of various vinyl monomers, and the like are used.

(Separator)
The separator has a role of preventing a short circuit between the negative electrode 701 and the positive electrode 703 in the secondary battery. Moreover, it may have a role of holding the electrolytic solution.

  The separator must have pores through which lithium ions can move and must be insoluble and stable in the electrolyte solution. Therefore, the separator is made of a non-woven fabric such as glass, polypropylene, polyethylene, or a non-woven material such as a fluororesin, or a micropore structure. Those are preferred. Moreover, the metal oxide film which has a micropore, or the resin film which compounded the metal oxide can also be used.

[Battery shape and structure]
Specific examples of the secondary battery of the present invention include a flat shape, a cylindrical shape, a rectangular parallelepiped shape, and a sheet shape. In addition, examples of the battery structure include a single layer type, a multilayer type, and a spiral type. Among them, the spiral cylindrical battery is characterized in that the electrode area can be increased by winding a separator between the positive electrode and the negative electrode, and a large current can be passed during charging and discharging. Moreover, a rectangular parallelepiped type or sheet type battery has a feature that a storage space of a device configured by storing a plurality of batteries can be used effectively.

  8 and 9, 801 and 903 are negative electrodes, 803 and 906 are positive electrodes, 804 and 908 are negative terminals (negative electrode cap or negative electrode can), 805 and 909 are positive terminals (positive electrode can or positive electrode cap), Reference numerals 802 and 907 are ion conductors, 806 and 910 are gaskets, 901 is a negative electrode current collector, 907 is a positive electrode current collector, 911 is an insulating plate, 912 is a negative electrode lead, 913 is a positive electrode lead, and 914 is a safety valve.

(Flat)
In the single-layer flat type (coin-type) secondary battery shown in FIG. 8, a positive electrode 803 including a positive electrode material layer and a negative electrode 801 including a negative electrode material layer are formed of, for example, a separator holding at least an electrolyte solution. The stacked body is stacked in a positive electrode can 805 as a positive electrode terminal from the positive electrode side, and the negative electrode side is covered with a negative electrode cap 804 as a negative electrode terminal. And the gasket 806 is arrange | positioned in the other part in a positive electrode can.

(Spiral cylindrical)
In the spiral cylindrical secondary battery shown in FIG. 9, a positive electrode 906 having a positive electrode (material) layer 905 formed on the positive electrode current collector 904 and a negative electrode (material) formed on the negative electrode current collector 901. A negative electrode 903 having a layer 902 is opposed to, for example, an ionic conductor 907 formed of a separator holding at least an electrolytic solution, and forms a multilayer structure having a cylindrical structure wound in multiple layers. The laminated body having the cylindrical structure is accommodated in a negative electrode can 908 serving as a negative electrode terminal. Further, a positive electrode cap 909 as a positive electrode terminal is provided on the opening side of the negative electrode can 908, and a gasket 910 is disposed in another part of the negative electrode can. The electrode stack having a cylindrical structure is separated from the positive electrode cap side by an insulating plate 911. The positive electrode 906 is connected to the positive electrode cap 909 via the positive electrode lead 913. The negative electrode 903 is connected to the negative electrode can 908 via the negative electrode lead 912. A safety valve 914 for adjusting the internal pressure inside the battery is provided on the positive electrode cap side.
As described above, the layer made of the above-described positive electrode material powder of the present invention is used for the active material layer of the positive electrode 803 and the active material layer 905 of the positive electrode 906.

(Battery assembly)
Below, an example of the assembly method of the battery shown in FIG. 8, FIG. 9 is demonstrated.
(1) The separator (801, 907) is sandwiched between the negative electrode (801, 903) and the formed positive electrode (803, 906), and is assembled into the positive electrode can (805) or the negative electrode can (908).
(2) After injecting the electrolytic solution, the negative electrode cap (804) or the positive electrode cap (909) and the gasket (806, 910) are assembled.
(3) The battery is completed by caulking (2) above.

It is desirable that the above-described lithium battery material preparation and battery assembly be performed in dry air from which moisture has been sufficiently removed or in a dry inert gas.
The member which comprises the above secondary batteries is demonstrated.

(gasket)
As a material for the gasket (806, 910), for example, fluororesin, polyamide resin, polysulfone resin, and various rubbers can be used. As a battery sealing method, a glass sealing tube, an adhesive, welding, soldering, or the like is used in addition to “caulking” using a gasket as shown in FIGS. Further, as the material of the insulating plate (911) in FIG. 9, various organic resin materials and ceramics are used.

(Outside can)
As an outer can of the battery, a positive electrode can or negative electrode can (805, 908) and a negative electrode cap or positive electrode cap (804, 909) are formed. As the material of the outer can, stainless steel or aluminum alloy is preferably used. In particular, a titanium clad stainless plate, a copper clad stainless plate, a nickel plated steel plate, etc. are frequently used.

  In FIG. 8, since the positive electrode can (805) is used in FIG. 9 and the negative electrode can (908) is also used as a battery housing (case) and a terminal, the above stainless steel is preferable. However, when the positive electrode can or negative electrode can does not serve as the battery housing and terminal, the battery case is made of metal such as zinc, plastic such as polypropylene, or metal or glass fiber and plastic in addition to stainless steel. The composite material can be used.

(safety valve)
A lithium secondary battery is provided with a safety valve as a safety measure when the internal pressure of the battery increases. As the safety valve, for example, rubber, a spring, a metal ball, a rupture foil, or the like can be used.

Hereinafter, the present invention will be described more specifically with reference to examples.
Example 1
(Production of Li ₂ Cu _0.8 Al _0.1 Zr _0.1 O ₂ )
Lithium hydroxide, copper oxide, aluminum nitrate and zirconium nitrate are weighed and mixed well in a ball mill so that the atomic ratio of Li, Cu, Al, and Zr is 2: 0.8: 0.1: 0.1 And calcination at 750 ° C. for 12 hours in an oxygen atmosphere (10 L / min), so that in general formula Li ₂ (Cu _1-xy M _x D _y ) O ₂ , M is Al, D is Zr, x = A positive electrode active material with y = 0.1 was obtained.

(XRD analysis)
From the powder X-ray diffraction peak of the produced positive electrode active material, it was confirmed that it was a single crystal structure having an orthorhombic Li ₂ CuO ₂ type structure.

(Production of battery)
(Positive electrode 703)
A coin-type lithium secondary battery was produced using this positive electrode active material as follows. A positive electrode active material, graphite powder as a conductive auxiliary material and poly (vinylidene fluoride) powder as a binder were mixed at a weight ratio of 70: 25: 5, and n-methyl-2-pyrrolidone was added and kneaded sufficiently to prepare a slurry. . This slurry was uniformly applied to one side of a 30 μm-thick aluminum foil as a positive electrode current collector, dried, and then pressure-molded with a roll press to obtain a sheet-like electrode. This electrode was punched into a disk shape having a diameter of 5 mm to form a positive electrode active material layer, which was dried in a vacuum dryer at a temperature of 80 ° C. for 3 hours to produce a positive electrode 703.

(Negative electrode 701)
As the negative electrode 701, a metal lithium foil having a thickness of 0.5 mm was pressed onto a rolled copper foil having a thickness of 30 μm, which is a negative electrode current collector, and punched into a disk shape having a diameter of 5 mm, thereby producing the negative electrode 701.

(Ion conductor 702)
As the ion conductor 702, a separator holding an electrolytic solution (an electrolyte solution prepared by dissolving an electrolyte in a solvent) was used. A liquid medium in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 3: 7 was used as the electrolytic solution, and 1 M (mol / l) of lithium tetrafluoroborate was used as the electrolyte. The separator used was a polypropylene nonwoven fabric sandwiched with polypropylene microporous separators.

(Battery assembly)
In battery assembly, an ion conductor 702 is sandwiched between a negative electrode 701 and a positive electrode 703, inserted into a titanium clad stainless steel positive electrode can 805, injected with an electrolyte, and then a titanium clad stainless steel negative electrode cap 804 and A lithium secondary battery was produced by sealing with a fluoro rubber gasket 806.

(Battery evaluation)
Battery evaluation performed charging / discharging in the range of voltage 1.5-4.0V by current density 0.2mA / cm < ² >. For the evaluation of the discharge capacity, the value of the fifth cycle in which the charge / discharge reaction was relatively stable was adopted, and the decrease in capacity when the charge / discharge was repeated was determined as the capacity maintenance ratio of the 15th cycle [capacity maintenance ratio (%) = { 15th cycle discharge capacity / 5th cycle discharge capacity} × 100].

Example 2
(Production of Li ₂ Cu _0.7 Al _0.1 Zr _0.2 O ₂ )
Lithium hydroxide, copper oxide, aluminum nitrate and zirconium nitrate are weighed and mixed well in a ball mill so that the atomic ratio of Li, Cu, Al, and Zr is 2: 0.7: 0.1: 0.2 And calcination at 750 ° C. for 12 hours in an oxygen atmosphere (10 L / min), so that in general formula Li ₂ (Cu _1-xy M _x D _y ) O ₂ , M is Al, D is Zr, x = A positive electrode active material of 0.1, y = 0.2 was obtained. Thereafter, the battery fabrication and charge / discharge test are the same as in Example 1.

Example 3
(Production of Li ₂ Cu _0.7 Al _0.2 Zr _0.1 O ₂ )
Lithium hydroxide, copper oxide, aluminum nitrate and zirconium nitrate are weighed and mixed well in a ball mill so that the atomic ratio of Li, Cu, Al, and Zr is 2: 0.7: 0.2: 0.1 And calcination at 750 ° C. for 12 hours in an oxygen atmosphere (10 L / min), so that in general formula Li ₂ (Cu _1-xy M _x D _y ) O ₂ , M is Al, D is Zr, x = A positive electrode active material of 0.2 and y = 0.1 was obtained. Thereafter, the battery fabrication and charge / discharge test are the same as in Example 1.

Example 4
(Preparation of Li ₂ Cu _0.6 Al _0.2 Zr _0.2 O ₂ )
Lithium hydroxide, copper oxide, aluminum nitrate and zirconium nitrate are weighed and mixed well in a ball mill so that the atomic ratio of Li, Cu, Al, and Zr is 2: 0.6: 0.2: 0.2 And calcination at 750 ° C. for 12 hours in an oxygen atmosphere (10 L / min), so that in general formula Li ₂ (Cu _1-xy M _x D _y ) O ₂ , M is Al, D is Zr, x = A positive electrode active material of 0.2 and y = 0.2 was obtained. Thereafter, the battery fabrication and charge / discharge test are the same as in Example 1.

Comparative Example 1
(Production of Li ₂ CuO ₂ )
Lithium hydroxide and copper oxide are weighed so that the atomic ratio of Li and Cu is 2: 1, and then thoroughly mixed in a ball mill and fired in an oxygen atmosphere (10 L / min) at 750 ° C. for 12 hours. Thus, Li ₂ CuO ₂ was synthesized to obtain a positive electrode active material. Thereafter, the battery fabrication and charge / discharge test are the same as in Example 1.

Comparative Example 2
(Production of Li ₂ Cu _0.9 Al _0.1 O ₂ )
Lithium hydroxide, copper oxide, and aluminum nitrate were weighed so that the atomic ratio of Li, Cu, and Al was 2: 0.9: 0.1, and then thoroughly mixed in a ball mill, 750 ° C., 12 hours, By firing in an oxygen atmosphere (10 L / min), in the general formula Li ₂ (Cu _1-xy M _x D _y ) O ₂ , M is Al and D is not included, x = 0.1, y = 0 positive electrode active material was obtained. Thereafter, the battery fabrication and charge / discharge test are the same as in Example 1.

Comparative Example 3
(Production of Li ₂ Cu _0.8 Al _0.2 O ₂ )
Lithium hydroxide, copper oxide, and aluminum nitrate were weighed so that the atomic ratio of Li, Cu, and Al was 2: 0.8: 0.2, and then thoroughly mixed in a ball mill, 750 ° C., 12 hours, By firing in an oxygen atmosphere (10 L / min), in the general formula Li ₂ (Cu _1-xy M _x D _y ) O ₂ , M is Al and D is not included, x = 0.2, y = 0 positive electrode active material was obtained. Thereafter, the battery fabrication and charge / discharge test are the same as in Example 1.

Comparative Example 4
(Production of Li ₂ Cu _0.9 Zr _0.1 O ₂ )
Lithium hydroxide, copper oxide, and zirconium nitrate were weighed so that the atomic ratio of Li, Cu, and Zr was 2: 0.9: 0.1, and then thoroughly mixed in a ball mill, and 750 ° C., 12 hours, oxygen By firing in an atmosphere (10 L / min), in the general formula Li ₂ (Cu _1-xy M _x D _y ) O ₂ , M is not contained, D is Zr, x = 0, y = 0.1 The positive electrode active material was obtained. Thereafter, the battery fabrication and charge / discharge test are the same as in Example 1.

Comparative Example 5
(Production of Li ₂ Cu _0.8 Zr _0.2 O ₂ )
Lithium hydroxide, copper oxide, and zirconium nitrate were weighed so that the atomic ratio of Li, Cu, and Zr was 2: 0.8: 0.2, and then thoroughly mixed in a ball mill, at 750 ° C. for 12 hours, oxygen By firing in an atmosphere (10 L / min), in the general formula Li ₂ (Cu _1-xy M _x D _y ) O ₂ , M is not contained, D is Zr, x = 0, y = 0.2 The positive electrode active material was obtained. Thereafter, the battery fabrication and charge / discharge test are the same as in Example 1.

  The results of the battery tests of the examples and comparative examples are summarized in Table 1.

As is apparent from Table 1, the discharge capacity and capacity retention rate are improved by partially replacing the copper of Li ₂ CuO ₂ with both Al and Zr. In addition, it is understood that when only Al is replaced, the discharge capacity is improved, but the capacity retention ratio is decreased, and when only Zr is replaced, the capacity retention ratio is improved but the discharge capacity is decreased. .

The lithium secondary battery of the present invention uses a lithium copper composite oxide represented by the general formula Li ₂ (Cu _1-xy M _x D _y ) O ₂ as a positive electrode active material, thereby charging Li ₂ CuO ₂ . The structure change to CuO at the time and the structure change between Li ₂ CuO ₂ and LiCuO ₂ at the time of charge / discharge can be suppressed, the discharge capacity is low, the discharge capacity is large, and the decrease in the charge / discharge capacity due to repeated charge / discharge is small A lithium secondary battery can be provided. The lithium secondary battery of the present invention has an operating voltage equivalent to that of a conventional primary battery such as an alkaline dry battery or a manganese dry battery, and is stable in that the voltage drop during discharge is smaller than that of a conventional primary battery. Further, the discharge capacity is larger than that of the conventional primary battery, and the deterioration of the charge / discharge capacity due to repeated charge / discharge is small. Therefore, it can be used for a digital camera, a portable information device, etc. as an alternative to the conventional primary battery.

Is a diagram showing the crystal structure of Li ₂ CuO _2. It is a float chart of the calculation method of bond strength used for the present invention. It is a figure which shows the atomic assembly model used for calculation of the binding force of this invention. CuO ₄ is a graph showing calculation results of change in the bonding force between oxygen and adjacent atoms of oxygen in the linear unit. CuO ₄ is a graph showing calculation results of change in the bonding force between the linear unit. It is sectional drawing which shows typically an example of the cross-section of the electrode structure in this invention. It is sectional drawing which shows an example of the lithium secondary battery of this invention. It is sectional drawing which shows the structure of a single layer type flat battery. It is a schematic sectional drawing which shows the structure of a spiral type cylindrical battery.

Explanation of symbols

600 Current collector 601 Electrode material layer 602 Electrode structure layer 603 Positive electrode active material 604 Conductive auxiliary material 605 Binder 701, 801, 903 Negative electrode 702, 802, 907 Ion conductor 703, 803, 906 Positive electrode 704 Negative electrode terminal 705 Positive electrode terminal 706 Battery case (housing)
804 Negative electrode cap 805 Positive electrode can 806, 910 Gasket 901 Negative electrode current collector 902 Negative electrode active material layer 904 Positive electrode current collector 905 Positive electrode active material layer 908 Negative electrode can (negative electrode terminal)
909 Positive Cap (Positive Terminal)
911 Insulating plate 912 Negative electrode lead 913 Positive electrode lead 914 Safety valve

Claims (6)

A lithium secondary battery having a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode active material constituting the positive electrode is a general formula Li ₂ (Cu _1-xy M _x D _y ) O ₂ (where M is an element period) In the table, one or more elements selected from the group consisting of group 13 elements, group 14 elements, Fe, Co, Ni, D is selected from the group consisting of Ti, V, Y, Zr, Mo, Pd 1 And x and y are 0 <x <0.5, 0 <y <0.5, and x + y <0.5)). Lithium secondary battery.   2. The lithium secondary battery according to claim 1, wherein x and y are 0 <x <0.5, 0 <y <0.5, x + y <0.5, and x ≧ y. The lithium secondary battery according to claim 1, wherein the positive electrode active material has an orthorhombic Li ₂ CuO ₂ type structure.   The lithium secondary battery according to claim 1, wherein the positive electrode active material has a structure belonging to a space group Imm.   M is one or more elements selected from the group consisting of Al, Si, Fe, Co, and Ni, and D is one or more elements selected from the group consisting of Ti, V, Y, Zr, Mo, and Pd. The lithium secondary battery according to claim 1, wherein:   The M is one or more elements selected from the group consisting of Al and Si, and the element D is one or more elements selected from the group consisting of Ti, V, Y, Zr, Mo, and Pd. The lithium secondary battery according to claim 1.

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