JP3670864B2 - Lithium secondary battery - Google Patents

Description

【００２７】
表１に示すように、本発明電池Ａ１〜Ａ４は、比較電池Ｂ１〜Ｂ６に比べて放電容量が大きい。
【００２８】
〈実験２〉
リチウム塩（電解質塩）の種類と放電容量の関係を調べた。
【００２９】
非水電解液の調製において、リチウム塩として、ＬｉＢＦ₄ １モル／リットルに代えてＬｉＰＦ₆ 、ＬｉＮ（ＣＦ₃ ＳＯ₂ ）₂ 、ＬｉＮ（ＣＦ₃ ＳＯ₂ ）（Ｃ₂ Ｆ₅ ＳＯ₂ ）、ＬｉＮ（ＣＦ₃ ＳＯ₂ ）（Ｃ₃ Ｆ₇ ＳＯ₂ ）、ＬｉＮ（ＣＦ₃ ＳＯ₂ ）（Ｃ₄ Ｆ₉ ＳＯ₂ ）、ＬｉＮ（Ｃ₂ Ｆ₅ ＳＯ₂ ）₂ 、ＬｉＮ（Ｃ₂ Ｆ₅ ＳＯ₂ ）（Ｃ₄ Ｆ₉ ＳＯ₂ ）又はＬｉＮ（Ｃ₃ Ｆ₇ ＳＯ₂ ）₂ １モル／リットルを使用したこと以外は、実施例１と同様にして、本発明電池Ａ７〜Ａ１４を作製した。次いで、各電池について、実験１と同じ条件の充放電試験を行い、それぞれの正極材料１ｇ当たりの放電容量（ｍＡｈ／ｇ）を求めた。各電池の放電容量を表２に示す。表２には、本発明電池Ａ１の放電容量も表１より転記して示してある。
【００３０】
【表２】

【００３１】
表２に示すように、本発明電池Ａ７〜Ａ１４は、本発明電池Ａ１に比べて、放電容量が大きい。この結果から、リチウム塩としては、ＬｉＰＦ₆ 又は式：ＬｉＮ（Ｃ_m Ｆ_2m+1ＳＯ₂ ）（Ｃ_n Ｆ_2n+1ＳＯ₂ ）（但し、１≦ｍ≦４、１≦ｎ≦４）で表されるイミド塩が好ましいことが分かる。この実験では、正極材料としてＬｉＭｎ_1.9 Ｎｉ_0.1 Ｏ₄ を使用したが、本発明で規定する範囲内の他の組成の正極材料を使用した場合においても、ＬｉＰＦ₆ 又は式：ＬｉＮ（Ｃ_m Ｆ_2m+1ＳＯ₂ ）（Ｃ_n Ｆ_2n+1ＳＯ₂ ）（但し、１≦ｍ≦４、１≦ｎ≦４）で表されるイミド塩が好ましいことを、確認した。
【００３２】
叙上の実施例では、扁平型のリチウム二次電池を例に挙げて説明したが、本発明は、電池形状に特に制限はなく、種々の形状のリチウム二次電池に適用可能である。
【００３３】
【発明の効果】
放電電圧が高く、しかも放電容量が大きいリチウム二次電池が提供される。
【図面の簡単な説明】
【図１】実施例で作製した各正極材料の（ｙ，ａ）をプロットして示したグラフである。
【図２】実施例で作製した扁平形のリチウム二次電池の断面図である。
【符号の説明】
Ａ リチウム二次電池
１ 正極
２ 負極
３ セパレータ
４ 正極缶
５ 負極缶
６ 正極集電体
７ 負極集電体
８ 絶縁パッキング[0001]
[Technical field to which the invention belongs]
The present invention is a composition _{formula: Li x Ni y Mn 2-} y O 4 ( where, 0.02 ≦ x ≦ 1.10, 0.1 ≦ y ≦ 0.4, and x varies with charge and discharge.) Lithium secondary comprising a positive electrode that is a composite oxide represented by the following formula, a positive electrode that exhibits a discharge potential of 4.5 V or more on the basis of Li, a negative electrode, and a nonaqueous electrolyte solution obtained by dissolving a lithium salt in a nonaqueous solvent More particularly, the present invention relates to an improvement in a positive electrode material for the purpose of providing a lithium secondary battery having a high discharge voltage and a large discharge capacity.
[0002]
[Prior art and problems to be solved by the invention]
Conventionally, LiCoO ₂ and LiNiO ₂ are well known as positive electrode materials (positive electrode active materials) for lithium secondary batteries, but these positive electrode materials are expensive and have a problem in terms of raw material costs.
[0003]
Accordingly, lithium-containing manganese oxides such as spinel-type lithium-containing manganese oxide (LiMn ₂ O ₄ ) and orthorhombic lithium-containing manganese oxide (LiMnO ₂ ) have been proposed. Lithium-containing manganese oxide is one of the promising materials as a positive electrode material for lithium secondary batteries because manganese as a raw material exists in abundant resources and is inexpensive.
[0004]
However, the lithium-containing manganese oxide has an average discharge potential as low as 4.2 V or less on the basis of lithium (Li / Li ⁺ ), and thus has a small discharge capacity.
[0005]
As a positive electrode material with a high discharge potential having a flat portion (plateau) of discharge potential near 4.7 V with respect to lithium, a part of manganese of the spinel type lithium-containing manganese oxide is made of other transition elements M such as nickel and chromium. Replaced by the formula: Li _{x + y} M z Mn _2-yz A lithium-containing manganese oxide represented by O ₄ (0 ≦ x <1, 0 ≦ y <0.33, 0 <z <1) has been proposed (see JP-A-9-147867).
[0006]
However, although the above lithium-containing manganese oxide has a high discharge potential, the discharge capacity is almost the same as that of the conventional lithium-containing manganese oxide and is small.
[0007]
The present invention has been made in view of the above circumstances, and an object thereof is to provide a lithium secondary battery using a lithium-containing manganese oxide as a positive electrode material having a high discharge voltage and a large discharge capacity. . This object is achieved by using a specific lithium-containing manganese oxide as the positive electrode material, as described below.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, a lithium secondary battery (present invention battery) according to the present invention has a composition formula: Li _x Ni _y Mn _{2 -y} O ₄ (where 0.02 ≦ x ≦ 1.10 . 1 ≦ y ≦ 0.4 , and x varies depending on charge and discharge.) The cathode is a composite oxide represented by the following formula: a positive electrode showing a discharge potential of 4.5 V or more on the basis of Li, a negative electrode, and a lithium salt In the lithium secondary battery including a non-aqueous electrolyte solution obtained by dissolving a non-aqueous solvent in a non-aqueous solvent, the complex oxide has a lattice constant a (nm) when the lithium content is x = 1.00, the formula: a + 0. It is a composite oxide satisfying 0098y ≦ 0.821.
[0010]
Examples of the negative electrode material include lithium alloys such as lithium metal, lithium-aluminum alloy, lithium-lead alloy, and lithium-tin alloy, carbon materials such as graphite, coke, and organic fired bodies, and SnO whose potential is lower than that of the positive electrode material. ₂ , metal oxides such as SnO, TiO ₂ and Nb ₂ O ₃ are exemplified.
[0011]
The lithium salt (electrolyte _{salt), LiClO 4, LiCF 3 SO} 3, LiPF 6, LiN (CF 3 SO 2) 2, LiN (C 2 F 5 SO 2) 2, LiBF 4, LiSbF 6 and LiAsF ₆ are illustrative Is done. LiPF ₆ or an imide salt represented by the formula: LiN (C _m F _{2m + 1} SO ₂ ) (C _n F _{2n + 1} SO ₂ ) (where 1 ≦ m ≦ 4, 1 ≦ n ≦ 4) is discharged. It is preferable for obtaining a lithium secondary battery having a large capacity.
[0012]
Non-aqueous solvents include cyclic carbonates such as ethylene carbonate, propylene carbonate, vinylene carbonate, butylene carbonate, cyclic carbonates, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, 1,2-dimethoxyethane, 1,2-dicarbonate. Examples thereof include mixed solvents with low-boiling solvents such as ethoxyethane and ethoxymethoxyethane.
[0013]
The positive electrode material of the battery of the present invention has a high discharge potential of 4.5 V or more on the basis of Li, and the lattice constant a (nm) when the lithium content is x = 1.00 is the formula: a + 0.0098y ≦ 0.821 Therefore, the lattice constant a (nm) when the lithium content is x = 1.0 does not satisfy the formula: a + 0.0098y ≦ 0.821: Li _{x + y} Compared to _{M z Mn 2-yz O 4} (0 ≦ x <1,0 ≦ y <0.33,0 <z <1) lithium-containing manganese oxide represented by, a large discharge capacity. Therefore, according to the present invention, a lithium secondary battery having a high discharge voltage and a large discharge capacity is provided.
[0014]
【Example】
Hereinafter, the present invention will be described in more detail on the basis of examples. However, the present invention is not limited to the following examples, and can be implemented with appropriate modifications without departing from the scope of the present invention. It is.
[0015]
<Experiment 1>
A battery of the present invention and a comparative battery were produced, and the discharge capacities of both were compared.
[0016]
( Examples 1-4 and Reference Examples 1 and 2 )
[Production of positive electrode]
Manganese acetate (Mn (CH ₃ COO) ₂ ) and nickel nitrate (Ni (NO ₃ ) ₂ ) in a molar ratio of 1.9: 0.1, 1.8: 0.2, 1.7: 0.3, 1.6: 0.4, 1.5: 0.5 or 1.4: 0.6 are mixed to form a mixture. Each mixture is placed in a 50% by volume ethyl alcohol aqueous solution and stirred vigorously, and then 30 volumes. % Ammonia water was added to obtain a precipitate. This precipitate and lithium nitrate (LiNO ₃ ) were mixed at a molar ratio of 2.0: 1.0 to form a mixture. This mixture was calcined in an oxygen stream at 700 ° C. for 20 hours, and then pulverized by a jet mill. Then, LiMn _1.9 Ni _0.1 O ₄ , LiMn _1.8 Ni _0.2 O ₄ , LiMn _1.7 Ni _0.3 O ₄ , LiMn _1.6 Ni _0.4 O ₄ , LiMn _1.5 Ni _0.5 O _4, and LiMn _1.4 Ni as the positive electrode material in order. _0.6 O ₄ was produced. When the lattice constant a of each positive electrode material was determined by powder X-ray diffraction, 0.82002 (nm), 0.81884 (nm), 0.81776 (nm), 0.81674 (nm), and 0.81587 were sequentially obtained. (Nm) and 0.81512 (nm). All were single phase spinel type compounds.
[0017]
FIG. 1 is a graph showing the value of the lattice constant a of each positive electrode material on the vertical axis and the value of _{y in the} composition formula: LiNi _y Mn _{2 -y} O ₄ on the horizontal axis. It is. As shown in FIG. 2, all the plots (y, a) (indicated by ◯ in FIG. 1) of each positive electrode material were in the region of a + 0.0098y ≦ 0.821.
[0018]
Each positive electrode material, acetylene black as a conductive agent, and polyvinylidene fluoride as a binder are kneaded at a weight ratio of 90: 6: 4 to prepare a positive electrode mixture. After being pressure-molded into a disk shape having a diameter of 20 mm at a pressure of ton / cm ² , the obtained molded product was heat-treated at 250 ° C. for 2 hours in a vacuum to produce six types of positive electrodes.
[0019]
(Production of negative electrode)
A rolled plate of lithium-aluminum alloy was punched into a disk shape having a diameter of 20 mm to produce a negative electrode.
[0020]
(Preparation of non-aqueous electrolyte)
A non-aqueous electrolyte was prepared by dissolving 1 mol / liter of LiBF ₄ in a mixed solvent of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a volume ratio of 1: 2: 1.
[0021]
[Production of lithium secondary battery]
A flat lithium secondary battery ( present invention batteries A1 to A4 and reference batteries C1 and C2 ) was prepared by a conventional method using each of the positive electrode, the negative electrode, and the nonaqueous electrolytic solution. The capacity ratio between the positive electrode and the negative electrode was 1: 1.1. As the separator, a polypropylene film having ion permeability was used. In the following batteries, the capacity ratio of the positive electrode to the negative electrode was all set to 1: 1.1. FIG. 2 is a cross-sectional view of the manufactured lithium secondary battery A. The battery A shown in FIG. 2 includes a positive electrode 1, a negative electrode 2, a separator 3 that separates them, a positive electrode can 4, a negative electrode can 5, and a positive electrode current collector. 6, a negative electrode current collector 7, an insulating packing 8, and the like. The positive electrode 1 and the negative electrode 2 are accommodated in a battery can formed by the positive electrode can 4 and the negative electrode can 5 so as to face each other with a separator 3 therebetween. The positive electrode 1 is connected to the positive electrode can 4 via a positive electrode current collector 6. The negative electrode 2 is connected to the negative electrode can 5 via a negative electrode current collector 7 so that chemical energy generated inside the battery can be taken out as electric energy.
[0022]
(Comparative Examples 1-6)
Manganese carbonate (MnCO ₃ ), nickel nitrate and lithium carbonate (Li ₂ CO ₃ ) in molar ratios of 1.9: 0.1: 0.5, 1.8: 0.2: 0.5, 1.7: 0.3: 0.5, 1.6: 0.4: 0.5, 1.5: 0.5: 0.5 or 1.4: 0.6: 0.5 Each mixture was fired in the atmosphere at 700 ° C. for 20 hours, and then pulverized by a jet mill, and in order, LiMn _1.9 Ni _0.1 O ₄ , LiMn _1.8 Ni _0.2 O ₄ , LiMn _1.7 Ni with a median diameter of 6 μm as a positive electrode material. _0.3 O ₄ , LiMn _1.6 Ni _0.4 O ₄ , LiMn _1.5 Ni _0.5 O ₄ and LiMn _1.4 Ni _0.6 O ₄ were prepared. When the lattice constant a of each positive electrode material was determined by powder X-ray diffraction, 0.82028 (nm), 0.81934 (nm), 0.81842 (nm), 0.81745 (nm), 0.81640 were sequentially obtained. (Nm) and 0.81538 (nm). All were single phase spinel type compounds.
[0023]
FIG. 1 plots (y, a) of each positive electrode material. As shown in FIG. 1, all the plots (y, a) (indicated by ▲ in FIG. 1) of each positive electrode material were in the region of a + 0.0098y> 0.821.
[0024]
Comparative batteries B1 to B6 were produced in the same manner as in Examples 1 to 4 , except that the above positive electrode materials were used for the positive electrode.
[0025]
[Discharge capacity of each battery]
Each battery was charged at 0.15 mA / cm ² up to 4.9 V, and discharged at 0.15 mA / cm ² up to 3.0 V, respectively determined discharge capacity per positive electrode material 1g of (mAh / g) It was. Table 1 shows the discharge capacity of each battery.
[0026]
[Table 1]

[0027]
As shown in Table 1, the batteries A1 to A4 of the present invention have a larger discharge capacity than the comparative batteries B1 to B6 .
[0028]
<Experiment 2>
The relationship between the type of lithium salt (electrolyte salt) and the discharge capacity was investigated.
[0029]
In the preparation of the non-aqueous electrolyte, LiPF ₆ , LiN (CF ₃ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₂ F ₅ SO ₂ ), LiN are used as lithium salts instead of LiBF ₄ 1 mol / liter. (CF ₃ SO ₂ ) (C ₃ F ₇ SO ₂ ), LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂₎ ) (C ₄ F ₉ SO ₂ ) or LiN (C ₃ F ₇ SO ₂ ) ₂ 1 mol / liter was used, and the inventive batteries A7 to A14 were produced in the same manner as in Example 1. Each battery was then subjected to a charge / discharge test under the same conditions as in Experiment 1 to determine the discharge capacity (mAh / g) per gram of each positive electrode material. Table 2 shows the discharge capacity of each battery. In Table 2, the discharge capacity of the battery A1 of the present invention is also transferred from Table 1.
[0030]
[Table 2]

[0031]
As shown in Table 2, the batteries A7 to A14 of the present invention have a larger discharge capacity than the battery A1 of the present invention. From this result, as the lithium salt, LiPF ₆ or the formula: LiN (C _m F _{2m + 1} SO ₂ ) (C _n F _{2n + 1} SO ₂ ) (where 1 ≦ m ≦ 4, 1 ≦ n ≦ 4) It can be seen that the imide salt represented by In this experiment, LiMn _1.9 Ni _0.1 O ₄ was used as the positive electrode material, but LiPF ₆ or the formula: LiN (C _m F _2m is also used when a positive electrode material having another composition within the range specified in the present invention is used. It was confirmed that an imide salt represented by ₊₁ SO ₂ ) (C _n F _{2n + 1} SO ₂ ) (where 1 ≦ m ≦ 4, 1 ≦ n ≦ 4) is preferable.
[0032]
In the above embodiment, a flat lithium secondary battery has been described as an example, but the present invention is not particularly limited in battery shape, and can be applied to lithium secondary batteries having various shapes.
[0033]
【The invention's effect】
A lithium secondary battery having a high discharge voltage and a large discharge capacity is provided.
[Brief description of the drawings]
FIG. 1 is a graph plotting (y, a) of each positive electrode material produced in an example.
FIG. 2 is a cross-sectional view of a flat lithium secondary battery manufactured in an example.
[Explanation of symbols]
A Lithium secondary battery 1 Positive electrode 2 Negative electrode 3 Separator 4 Positive electrode can 5 Negative electrode can 6 Positive electrode current collector 7 Negative electrode current collector 8 Insulation packing

Claims (2)

Composition formula: Li _x Ni _y Mn _2-y O ₄ (where 0.02 ≦ x ≦ 1.10, 0.1 ≦ y ≦ 0.4 , and x varies depending on charge / discharge) In a lithium secondary battery comprising a composite oxide as a positive electrode material, a positive electrode exhibiting a discharge potential of 4.5 V or more on the basis of Li, a negative electrode, and a nonaqueous electrolyte obtained by dissolving a lithium salt in a nonaqueous solvent, The composite oxide is a composite oxide in which the lattice constant a (nm) when the lithium content is x = 1.00 satisfies the formula: a + 0.0098y ≦ 0.821 . The lithium salt is LiPF ₆ Or the formula: LiN (C _m F _{2m + 1} SO ₂ ) (C _n F _{2n + 1} SO ₂ The lithium secondary battery according to claim 1, wherein the lithium secondary battery is an imide salt represented by 1 ≦ m ≦ 4 and 1 ≦ n ≦ 4.

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