JP3813001B2 - Non-aqueous secondary battery - Google Patents

Description

【００２９】
【発明の効果】
以上述べたように、本発明は次の一般式Ｌｉ_X Ｍｎ_(2-Y-Z) Ｍ_Y Ｃｒ_Z Ｏ_(4+P) （ただし、ＭはＮｉまたはＣｏを示し、X 、Y 、Z 、P は各々１．００≦ X ≦１．１５、０．２≦ Y ≦０．４、０．４≦ Z ＜０．８でかつ２Y ＋Z ≦X 、０≦P である）で表わされ、Ｌｉ／Ｌｉ⁺ に対して４．５Ｖ以上の電位を有するスピネル系のリチウムマンガン複合酸化物を正極活物質に用いることにより、高電圧、高容量でサイクル性に優れ、さらに高温での保存およびサイクル性にも優れた非水系二次電池を得ることができ、より高エネルギー密度の電池を提供できることからその工業的価値は非常に大きい。
【図面の簡単な説明】
【図１】 （イ）実施例１のＬｉＭｎ_1.4 Ｃｒ_0.4 Ｎｉ_0.2 Ｏ₄ の放電曲線を示す図である。
（ロ）比較例１のＬｉＭｎ_1.6 Ｎｉ_0.4 Ｏ₄ の放電曲線を示す図である。
（ハ）比較例２のＬｉＭｎ_1.2 Ｃｒ_0.8 Ｏ₄ の放電曲線を示す図である。
【図２】 実施例１及び比較例１〜２の電池のサイクル性（１グラム当たりの放電容量）を示す図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a non-aqueous secondary battery using a lithium manganese composite oxide as a positive electrode.
[0002]
[Prior art]
In recent years, electronic devices have become increasingly smaller, thinner and lighter, and as a result, batteries for power supplies can be reduced in size, thickness, weight and energy density regardless of whether they are for driving or backup. The demand is growing. Since it is possible to reduce the size and weight of devices, lithium ion secondary batteries have recently been widely used in mobile devices such as mobile phones and notebook personal computers.
[0003]
In lithium ion secondary batteries that are currently commercially available, lithium cobaltate is used as the positive electrode active material, and carbon is used as the negative electrode active material. However, lithium cobaltate, which is a positive electrode active material, may be insufficient in the future because cobalt is expensive and its reserves are small. On the other hand, recently, a cathode active material that is cheap, rich in reserves, and capable of occluding and releasing lithium at a high voltage equivalent to lithium nickelate or lithium cobaltate, which has a larger capacity per weight than lithium cobaltate. As a spinel lithium-containing manganese oxide, much research has been conducted. However, if a higher voltage positive electrode active material is developed, a higher energy density can be achieved. Furthermore, a metal oxide that has a high capacity but has a high potential, resulting in a low energy density in combination with a lithium cobaltate positive electrode,
A low-temperature fired carbon material can also be used for the negative electrode.
For this purpose, replacement of a part of manganese of spinel type lithium manganate with nickel has been examined (Journal of Electrochemical Society 1994, Vol. 141, p. 2279). 4.6-4.7V is not necessarily sufficient.
[0004]
[Problems to be solved by the invention]
An object of the present invention is to provide a nonaqueous secondary battery having high voltage, high capacity, excellent cycleability, and excellent storage at high temperatures and cycleability.
[0005]
[Means for Solving the Problems]
As a result of intensive studies by the present inventors, nickel, chromium-containing lithium manganate in which a part of the spinel-type lithium manganese composite oxide is replaced with chromium and nickel or cobalt, or cobalt and chromium-containing lithium manganate are converted into metal lithium. On the other hand, the present invention was completed by finding that it has a high voltage of about 4.8 V and excellent cycle characteristics.
[0006]
That is, the present invention includes a negative electrode active material capable of occluding and releasing lithium ions, a positive electrode active material comprising a lithium-containing composite oxide capable of occluding and releasing lithium ions, and a lithium ion conductive non-aqueous electrolyte. in the nonaqueous secondary battery, the lithium-containing composite oxide of the general formula _{Li X Mn (2-YZ)} M Y Cr Z O (4 + P) ( however, M represents Ni or Co, X, Y , Z and P are 1.00 ≦ X ≦ 1.15, 0.2 ≦ Y ≦ 0.4, 0.4 ≦ Z <0.8 , and 2Y + Z ≦ X and 0 ≦ P, respectively. It is a non-aqueous secondary battery characterized by being a spinel-type lithium manganese composite oxide having a potential of 4.5 V or more with respect to Li / Li ⁺ .
[0007]
The present invention will be described in detail below.
The present invention is a lithium-containing composite oxide as a cathode active material, the general formula _{Li X Mn (2-YZ)} M Y Cr Z O (4 + P) ( however, M represents Ni or Co, X Y, Z and P are 1.00 ≦ X ≦ 1.15, 0.2 ≦ Y ≦ 0.4, 0.4 ≦ Z <0.8 and 2Y + Z ≦ X and 0 ≦ P), respectively. This is a non-aqueous secondary battery characterized by being a spinel-type lithium manganese composite oxide having a potential of 4.5 V or more with respect to Li / Li ⁺ .
The discharge potential of the spinel-structure lithium manganese composite oxide represented by LiMn ₂ O ₄ appears in the vicinity of 3V and 4V. Usually, the 4V region is used as the positive electrode of the non-aqueous secondary battery, and its capacity is about 120 mAh / g. It is.
[0008]
On the other hand, in LiMn _1.6 Ni _0.4 O ₄ in which a part of manganese of LiMn ₂ O ₄ is replaced with nickel, a high potential plateau appears at 4.4 to 4.7 V, the cycle characteristics are good, but the discharge potential is still It is insufficient. In addition, LiMn _1.2 Cr _0.8 O _{4 in} which a part of manganese is substituted with chromium has a high potential plateau of 4.9 V to 4.5 V, which can further increase the voltage, but has poor cycle characteristics.
Therefore, the present inventors have found that a positive electrode material having a high potential and excellent cycle characteristics can be obtained by replacing a part of manganese with both nickel and chromium. Furthermore, it has been found that the same effect can be obtained by substituting with both cobalt and chromium .
[0009]
The reason why such an effect can be obtained by substituting a part of manganese with another metal element is not clear, but the oxidation and reduction of the substitution element at a voltage of 4.5 V or more is stably performed. (Ni, Co 2+ to 4+, Cr 3+ to 4+) and stabilization of the crystal structure are considered.
The spinel-type lithium manganese composite oxide of the present invention preferably has X, Y and Z values in the following ranges.
1.00 ≦ X ≦ 1.15
0.2 ≦ Y ≦ 0.4
0.4 ≦ Z <0.8
[0010]
As the manganese compound for synthesizing the above spinel-type lithium manganese composite oxide of the present invention, electrolytic manganese dioxide, chemically synthesized manganese dioxide, γ-MnOOH, manganese carbonate, manganese nitrate, and the like are used. Lithium carbonate, lithium hydroxide, lithium nitrate, lithium acetate and the like are used, and as the nickel, cobalt and chromium compounds, respective oxides, chlorides, nitrates, carbonates and the like can be used.
[0011]
The heat treatment temperature at that time is preferably 650 ° C. to 900 ° C., more preferably 750 ° C. to 900 ° C., and the heating atmosphere is preferably in air, an oxygen atmosphere, or a nitrogen atmosphere.
The method of synthesizing the spinel-based lithium manganese composite oxide of the present invention includes a lithium compound in an amount such that the number of Li atoms is X mol, a manganese compound in which the number of manganese atoms is (2-YZ) mol, and A nickel compound with an amount of nickel atoms of Y mol, or a cobalt compound with an amount of cobalt atoms of Y mol and a chromium compound with an amount of chromium atoms of Z mol, are mixed at the above temperature and atmosphere. Consisting of heating.
[0012]
As the negative electrode active material used in combination with the positive electrode active material composed of the spinel-based lithium manganese composite oxide of the present invention, any material usually used for this type of non-aqueous electrolyte secondary battery can be used. , Lithium alloys, TiO ₂ , SnSiO ₃ and other metal oxides, LiCoN _{2 and} other metal nitrides, carbon materials, and the like can be used. As the carbon material, coke, natural graphite, artificial graphite, non-graphitizable carbon, or the like can be used. Moreover, although it has a high capacity as the negative electrode active material, a metal oxide or a low-temperature fired carbon material whose energy density becomes low when combined with the current lithium cobaltate positive electrode due to its high potential can be used without any problem. .
[0013]
As the electrolytic solution, a lithium salt as an electrolyte and dissolved in a non-aqueous solvent can be used. As the electrolyte, LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃
Li (CF ₃ SO ₂ ) ₂ N can be used alone or in combination of two or more.
Examples of the organic solvent include, but are not limited to, carbonates, lactones, ethers, and the like. For example, ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, 1,2-dimethoxyethane, 1,2 -Solvents such as diethoxyethane, tetrahydrofuran, 1,3-dioxolane, and γ-butyrolactone can be used alone or in admixture of two or more. The concentration of the electrolyte dissolved in these solvents can be 0.5 to 2.0 mol / liter.
[0014]
In addition to the above, a solid or viscous material in which the above electrolyte is uniformly dispersed in a polymer matrix, or a material in which a nonaqueous solvent is impregnated with these can be used. As the polymer matrix, for example, polyethylene oxide, polypropylene oxide, polyacrylonitrile, polyvinylidene fluoride, or the like can be used.
Moreover, as a separator for preventing a short circuit between the positive electrode and the negative electrode, a porous sheet made of a material such as polyethylene, polypropylene, or cellulose, a nonwoven fabric, or the like is used.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail.
【Example】
Example 1
The positive electrode active material was synthesized by the following procedure. Manganese nitrate, nickel nitrate, and chromium nitrate are weighed and mixed in such a ratio that the number of Mn, Ni, and Cr atoms is (2-YZ) = 1.4 mol, Y = 0.2 mol, and Z = 0.4 mol, respectively. Water was added to make an aqueous nitric acid solution. Next, lithium hydroxide in an amount such that the number of Li atoms (X) was 1.0 mol and a sufficient amount of aqueous ammonia were added and mixed to form a precipitate. The precipitate was heated at 100 ° C. and then heated at 150 ° C. and further at 450 ° C. to remove ammonium nitrate.
[0016]
Finally, a heat treatment was performed in air at 750 ° C. for 12 hours to obtain a lithium-containing composite oxide. The obtained product was LiMn _1.4 Ni _0.2 Cr _0.4 O ₄ having a spinel structure by X-ray diffraction and chemical analysis.
After mixing 3 parts by weight of acetylene black and 3 parts by weight of flaky graphite as a conductive agent with respect to 100 parts by weight of this lithium manganese composite oxide, N-methylpyrrolidone (NMP) was added at a ratio of 3 parts by weight with respect to the total weight. It was added and wet-mixed to obtain a paste. Next, the paste was uniformly applied to both surfaces of a 20 μm-thick aluminum foil as a positive electrode current collector and dried, followed by pressure molding with a roller press machine heated to 150 ° C. to obtain a belt-like positive electrode.
[0017]
Ethylene carbonate (EC) in which 1.0 m / liter of LiPF ₆ is dissolved with metallic lithium as a positive electrode and a negative electrode facing each other through a separator of a 25 μm thick polyethylene microporous membrane, assembled in a tripolar glass cell, and A mixed solution of dimethyl carbonate (DMC) (capacity ratio 1: 2) was injected to measure charge / discharge capacity and cycleability.
Next, a mixture of 95 parts by weight of graphitized mesocarbon fiber and 5 parts by weight of flaky graphite was added with 1 part by weight of carboxymethyl cellulose, 2 parts by weight of styrene butadiene rubber, and purified water as a solvent to perform wet mixing to obtain a paste. This paste was uniformly applied to both sides of a 12 μm thick copper foil as a negative electrode current collector, dried and then pressure-molded to produce a strip-shaped negative electrode.
[0018]
A 25 μm-thick polyethylene microporous film was sandwiched between the belt-like positive electrode and the belt-like negative electrode as a separator and wound into a roll to obtain a wound body.
An insulating film was inserted into the bottom of the iron square can, and the wound body was crushed and inserted. Next, the negative electrode tab taken out from the wound body was welded to the closing lid body, and the positive electrode tab was welded to the positive electrode pin of the closing lid body. After pouring an electrolytic solution in which LiPF ₆ was dissolved in a 1: 2 mixed solvent of ethylene carbonate and dimethyl carbonate into a battery can at a concentration of 1 mol / liter, the closure lid was welded to a thickness of 8.6 mm. A square battery having a width of 34 mm and a height of 48 mm was produced and subjected to a high temperature characteristic test.
[0019]
(Example 2)
LiMn _1.25 Ni _0.25 Cr _0.5 O ₄ was synthesized in the same manner as in Example 1. A battery was produced in the same manner as in Example 1 using the obtained lithium manganese composite oxide .
[0020]
(Example 3 )
Electrolytic manganese dioxide as a manganese compound, LiOH as a lithium compound, cobalt nitrate as a cobalt compound, chromium nitrate as a chromium compound, and the number of atoms of Mn, Li, Co, and Cr are (2-YZ) = 1.4 mol, X = 1.0 , Y = 0.2 mol and Z = 0.4 mol were weighed and mixed, and this was heat-treated in air at 850 ° C. for 24 hours to obtain LiMn _1.4 Co _0.2 Cr _0.4 O ₄ .
A battery was produced in the same manner as in Example 1 using the obtained lithium manganese composite oxide.
[0021]
[0022]
Example 1 except that the obtained lithium manganese composite oxide was used in which an electrolyte was prepared by dissolving LiBF ₄ at a concentration of 1 mol / liter in a 1: 2 mixed solvent of ethylene carbonate and dimethyl carbonate. A battery was produced in the same manner.
(Comparative Example 1)
LiMn _1.6 Ni _0.4 O ₄ was synthesized in the same manner as in Example 1. A battery was produced in the same manner as in Example 1 using the obtained lithium manganese composite oxide.
[0023]
(Comparative Example 2)
LiMn _1.2 Cr _0.8 O ₄ was synthesized in the same manner as in Example 1.
A battery was produced in the same manner as in Example 1 using the obtained lithium manganese composite oxide.
(Comparative Example 3)
LiMn _1.5 Cr _0.5 O ₄ was synthesized by heat treatment in air at 900 ° C. for 24 hours using electrolytic manganese dioxide, Li ₂ CO ₃ and chromium nitrate.
A battery was produced in the same manner as in Example 1 using the obtained lithium manganese composite oxide.
[0024]
(Comparative Example 4)
Li _1.0 Mn _1.90 Co _0.1 0 ₄ was synthesized in the same manner as in Example 1. Example 1 except that the obtained lithium manganese composite oxide was used in which an electrolyte was prepared by dissolving LiBF ₄ at a concentration of 1 mol / liter in a 1: 2 mixed solvent of ethylene carbonate and dimethyl carbonate. A battery was produced in the same manner.
(Test results)
The batteries produced in the examples and comparative examples were evaluated as follows.
After charging for 5 hours at a charging voltage of 5.2 V, the battery was discharged to 3.5 V with a current at a discharge rate of 0.3 C, and the capacity per gram was determined. Further, a cycle test was performed at room temperature (25 ° C.) under the above charge / discharge conditions.
[0025]
The discharge curves and cycle characteristics (25 ° C.) of Example 1 and Comparative Examples 1 and 2 are shown in FIGS. 1A to 1C (the upward curve is a charging curve, and the downward curve is a discharging curve.) And shown in FIG.
As shown in FIGS. 1-2, a nonaqueous secondary battery of the present invention have the general formula _{Li X Mn (2-YZ)} M Y Cr Z O (4 + P) ( however, M a is Ni or Co X, Y, Z, and P are 1.00 ≦ X ≦ 1.15, 0.2 ≦ Y ≦ 0.4, 0.4 ≦ Z <0.8 , and 2Y + Z ≦ X, 0 ≦ P, respectively. And a spinel-type lithium manganese composite oxide having a potential of 4.5 V or more with respect to Li / Li ⁺ is used as the positive electrode active material, thereby providing high voltage, high capacity, and excellent cycleability. You can see that
[0026]
(Test results)
Furthermore, after charging the battery for high temperature characteristic evaluation with the charging voltage 5.2V for 5 hours, it discharged to 3.5V with the discharge rate 0.5C, and calculated | required battery capacity. Subsequently, this charge / discharge cycle was repeated 5 cycles, and then stored in a charged state of 5.2 V at 85 ° C. for 120 hours, followed by cooling to room temperature and discharging. The self-discharge rate was determined by {1- (discharge amount at the sixth cycle / discharge amount at the fifth cycle)} × 100. In addition, using another cell produced at the same time, after charging for 5 hours at a charging voltage of 5.2 V, a cycle of discharging to 3.5 V at a discharge rate of 0.5 C was performed at 60 ° C. for 100 cycles, and 1 cycle. The ratio of the discharge capacity at the 100th cycle to the discharge capacity at the eye was determined and used as the cycle retention rate at 60 ° C.
[0027]
The results of this high temperature storage and cycling test are shown in Table 1.
As shown in Table 1, it can be seen that the nonaqueous secondary battery of the present invention is excellent in storage and cycleability at high temperatures.
[0028]
[Table 1]

[0029]
【The invention's effect】
As described above, the present invention is the general formula _{Li X Mn (2-YZ)} M Y Cr Z O (4 + P) ( however, M represents Ni or Co, X, Y, Z, P is 1.00 ≦ X ≦ 1.15, 0.2 ≦ Y ≦ 0.4, 0.4 ≦ Z <0.8 and 2Y + Z ≦ X, 0 ≦ P, respectively), Li / By using a spinel-type lithium manganese composite oxide having a potential of 4.5 V or higher with respect to Li ⁺ as a positive electrode active material, high voltage, high capacity, excellent cycleability, and high temperature storage and cycleability In addition, an excellent non-aqueous secondary battery can be obtained, and a battery having a higher energy density can be provided. Therefore, its industrial value is very large.
[Brief description of the drawings]
1A is a diagram showing a discharge curve of LiMn _1.4 Cr _0.4 Ni _0.2 O ₄ of Example 1. FIG.
(B) is a diagram showing discharge curves of LiMn _1.6 Ni _0.4 O ₄ of Comparative Example 1.
(C) is a diagram showing discharge curves of LiMn _1.2 Cr _0.8 O ₄ of Comparative Example 2.
FIG. 2 is a diagram showing the cycle characteristics (discharge capacity per gram) of the batteries of Example 1 and Comparative Examples 1 and 2;

Claims (1)

A non-aqueous secondary battery comprising a negative electrode active material capable of occluding and releasing lithium ions, a positive electrode active material comprising a lithium-containing composite oxide capable of occluding and releasing lithium ions, and a lithium ion conductive non-aqueous electrolyte The lithium-containing composite oxide has the following general formula: Li _X Mn _(2-YZ) M _Y Cr _Z O _{(4 + P)} (where M represents Ni or Co, and X, Y, Z and P are 1.00 ≦ X ≦ 1.15, 0.2 ≦ Y ≦ 0.4, 0.4 ≦ Z <0.8 and 2Y + Z ≦ X, 0 ≦ P, respectively), Li / A non-aqueous secondary battery, which is a spinel lithium manganese composite oxide having a potential of 4.5 V or more with respect to Li ⁺ . "

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