JP2004111076A - Positive electrode active material and nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a positive electrode activve material by which a nonaqueous electrolyte lithium ion secondary battery with high capacity and excellent cycle property can be manufactured, and to provide a nonaqueous electrolyte lithium ion secondary battery using the same. <P>SOLUTION: The positive electrode active material contains a lithium compound oxide having electron conductivity σ satisfying the relation; 10<SP>-4</SP>≤σ≤10<SP>-1</SP>S/cm, expressed by general formula; Li<SB>x</SB>Ni<SB>(1-Y-Z)</SB>Co<SB>Y</SB>Mn<SB>Z</SB>A<SB>a</SB>O<SB>2</SB>(1) (in the formula, A represents an element like Fe, V, Cr, Mn, Ti, Mg, Al, B, or Ca, and X, Y, Z satisfy the relations 0.05≤X≤1.10, 0.10≤Y+Z≤0.70, 0.05≤Z≤0.40, 0≤a≤0.1 respectively). The nonaqueous electrolyte lithium ion secondary battery comprises a positive electrode and a negative electrode containing positive electrode active material and negative electrode active material respectively which can dope and dedope lithium ions and a nonaqueous electrolyte with an electrolyte dispersed in a nouaqueous medium, of which, the positive electrode active material contains the lithium compound oxide. <P>COPYRIGHT: (C)2004,JPO

Description

【００４４】
表１に示した実施例１〜５及び比較例１〜７の評価結果より、
一般式Ｌｉ_ｘＮｉ_{（１−ｙ−ｚ）}Ｃｏ_ｙＭｎ_ｚＡ_ａＯ_２…▲１▼で表されるリチウム複合酸化物のニッケル、コバルト、マンガン組成比を０．１≦ｙ＋ｚ≦０．７、０．０５≦ｚ≦０．４０の範囲で規定することで高容量を有し、高温サイクル特性に優れた非水電解液二次電池を作製することができることが分かった。
実施例５で示したように、添加元素としてＡｌを組成比で０．０５添加すると、高温でのサイクル特性が著しく向上する。他にも添加元素としてＦｅ、Ｖ、Ｃｒ、Ｍｇ、Ｔｉ、Ａｌ、Ｂ又はＣａ及びこれらの任意の混合物を加えることで同様の効果が期待できる。
【００４５】
比較例１〜３の評価結果から分かるように、上記で示した組成の範囲外で活物質を作製すると、初期放電容量が著しく低下したり、高温サイクル特性が悪化してしまう。
なお、上記の条件だけでは、比較例６及び比較例７のように、初期放電容量と高温サイクル特性には優れるものの、電子伝導度が高いために高温での電解液との反応性が高くなってしまい、容量回復率は満足した結果を得ることが難しい。そこで、実施例１及び実施例５で示すように、導電剤量を減少することで、電子伝導度を低下させ、高温での電解液との反応を抑制して高温フロート充電での容量回復率を向上することができた。
【００４６】
以上の結果から、上述の一般式▲１▼で表されるリチウム複合酸化物を正極活物質とする正極と、リチウムを吸蔵・放出可能な負極活物質と、非水電解液とを組み合わせることで、高容量を有しサイクル特性とフロート特性に優れた非水電解液二次電池を作製できることが明らかとなった。
【００４７】
【発明の効果】
以上説明してきたように、本発明によれば、所定組成を有するリチウム複合酸化物を用いることとしたため、高容量を有しサイクル特性に優れるリチウムイオン非水電解質二次電池を実現できる正極活物質、及びこの正極活物質を用いたリチウムイオン非水電解質二次電池を提供することができる。
【図面の簡単な説明】
【図１】本発明のリチウムイオン非水電解質二次電池の一例を示す断面図である。
【図２】帯状正極の構造を示す斜視図である。
【図３】図１のＡ−Ａ線で切断した巻回電極体を示す断面図である。
【図４】巻回電極体の他の例を示す断面図である。
【図５】巻回電極体の他の例を示す断面図である。
【図６】巻回電極体の更に他の例を示す断面図である。
【図７】巻回電極体の他の例を示す断面図である。
【符号の説明】
１　　電池缶
２　　絶縁板
４　　電池蓋
５　　安全弁
５ａ　ディスク板
６　　感熱抵抗素子
７　　ガスケット
１０　　巻回電極体
１１　　正極
１１ａ　正極集電体
１１ｂ　正極合剤層（外側）
１１ｃ　正極合剤層（内側）
１２　　負極
１２ａ　負極集電体
１２ｂ　負極合剤層（外側）
１２ｃ　負極合剤層（内側）
１３　　セパレータ
１４　　センターピン
１５　　正極リード
１６　　負極リード[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery. More specifically, a positive electrode active material containing a lithium composite oxide having a specific composition and capable of realizing a lithium ion nonaqueous electrolyte secondary battery having high capacity and excellent cycle characteristics, and a lithium ion nonaqueous electrolyte secondary using the same It relates to a battery.
[0002]
[Prior art]
2. Description of the Related Art In recent years, with the development of electronic devices and the miniaturization thereof accompanying the progress of semiconductor integrated technology, demands for batteries serving as power sources of portable electronic devices have been increasing. The characteristics required for such a battery are that it is compact, lightweight, durable, and capable of charging and discharging. Examples of the small secondary battery having these characteristics include a nickel hydride battery, a nickel cadmium battery, and a lithium ion secondary battery. Among them, a lithium ion secondary battery having a high voltage of 4V class and a high energy density has a large size. There is a growing demand for portable electronic devices and the like that have power consumption and cannot be fully accommodated by primary batteries.
[0003]
The feature of the above-mentioned lithium ion secondary battery is that, by combining a positive electrode having a high oxidation-reduction potential and a negative electrode having a low oxidation-reduction potential as compared with other batteries, a battery having a large capacity, that is, a battery having a large energy density is used. It can be manufactured.
However, an actual battery is often used not only in a normal temperature environment but also in an electronic device used in a wide environment from a low temperature to a high temperature. When the discharge is performed, the amount of electricity that can be taken out decreases, and the voltage decreases due to the internal resistance. It is also known that, even though the battery exhibits excellent cycle characteristics when used at room temperature, battery capacity and cycle characteristics are easily damaged by use or storage under a high temperature environment.
[0004]
In order to further improve the battery characteristics, LiCoO 2 ₂ To form a solid solution with Al _x Co _(1-y) Al _y O ₂ Japanese Patent Laid-Open No. 11-7958 discloses that an active material satisfying 0.05 ≦ x ≦ 1.10 and 0.01 ≦ y ≦ 0.10 is produced to improve cycle characteristics under a high-temperature environment. It is proposed in the gazette.
Further, Japanese Patent Application Laid-Open No. 7-192721 discloses a method for improving the high-temperature holding characteristics by using Li _x Ni ( _1-y) M _y O _z (Where 0 <x <1.3, 0 ≦ y ≦ 1, 1.8 <z <2.2, and M is cobalt or two or more transition metals containing cobalt) One of a salt or a hydroxide of a metal selected from the group consisting of Na, Mg, Al, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn for the positive electrode active material. Or two or more are added in a total amount of 0.1 to 20 mol%.
[0005]
[Problems to be solved by the invention]
However, even if such a conventional positive electrode active material is used, the resulting lithium ion secondary battery does not always have sufficient high capacity and cycle characteristics, and there is room for further improvement.
The present invention has been made in view of such problems of the related art, and an object of the present invention is to provide a positive electrode active material capable of realizing a lithium ion nonaqueous electrolyte secondary battery having high capacity and excellent cycle characteristics. An object of the present invention is to provide a material and a lithium ion nonaqueous electrolyte secondary battery using the positive electrode active material.
[0006]
[Means for Solving the Problems]
The present inventors have conducted intensive studies to solve the above problems, and as a result, have found that the above problems can be solved by using a lithium composite oxide having a predetermined composition, and have completed the present invention. .
[0007]
That is, the positive electrode active material of the present invention is used for a lithium ion nonaqueous electrolyte secondary battery, and has the following general formula:
Li _x Ni _(1-yz) Co _y Mn _z A _a O ₂ … ▲ 1 ▼
(A in the formula is Fe (iron), V (vanadium), Cr (chromium), Mn (manganese), Ti (titanium), Mg (magnesium), Al (aluminum), B (boron) and Ca (calcium) Represents at least one element selected from the group consisting of: x, y and z are respectively 0.05 ≦ x ≦ 1.10, 0.10 ≦ y + z ≦ 0.70, 0.05 ≦ z ≦ 0. 40, a satisfies 0 ≦ a ≦ 0.1), and has an electron conductivity σ of 10 ^-4 ≦ σ ≦ 10 ^-1 It is composed of or contains a lithium composite oxide of S / cm.
[0008]
Further, the lithium ion nonaqueous electrolyte secondary battery of the present invention has a positive electrode using a material capable of doping and undoping lithium ions as a positive electrode active material and a negative electrode active material using a material capable of doping and undoping lithium ions. A secondary battery comprising a negative electrode and a non-aqueous electrolyte obtained by dispersing an electrolyte in a non-aqueous medium,
The positive electrode active material is represented by the above formula (1) and has an electron conductivity σ of 10 ^-4 ≦ σ ≦ 10 ^-1 It consists of or contains a lithium composite oxide of S / cm.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the positive electrode active material of the present invention will be described in detail. In addition, in this specification, "%" indicates a mass percentage unless otherwise specified.
As described above, the positive electrode active material of the present invention is used for a lithium ion nonaqueous electrolyte secondary battery, and has the following general formula (1)
Li _x Ni _(1-yz) Co _y Mn _z A _a O ₂ … ▲ 1 ▼
(A in the formula represents an element relating to Fe, V, Cr, Mn, Ti, Mg, Al, B or Ca and any combination thereof, and x, y and z are each 0.05 ≦ x ≦ 1. 10, 0.10 ≦ y + z ≦ 0.70, 0.05 ≦ z ≦ 0.40, a satisfies 0 ≦ a ≦ 0.1) or a composite oxide of the same. Containing material.
[0010]
Such a lithium composite oxide has a crystal structure belonging to a hexagonal system and forming a layered structure, and the composition ratio x of Li needs to be in the range of 0.05 ≦ x ≦ 1.10.
If x is less than 0.05, the crystal structure becomes unstable, so that when exposed to thermal stress, such as during high-temperature storage, the crystal structure is broken and lithium storage / release cannot be performed normally. On the other hand, when x exceeds 1.10, the charge / discharge capacity decreases due to an increase in the amount of residual lithium not involved in the battery reaction.
As for the composition ratio y of Co, the larger the ratio, the higher the charge / discharge efficiency of the obtained secondary battery, but the lower the composition ratio of Ni, the lower the capacity. In actual use, since the discharge voltage tends to increase when a large amount of Co is added, the value may be appropriately changed within the range of 0.00 ≦ y ≦ 0.50 according to the required battery characteristics. It is possible to continue.
[0011]
Further, in the formula (1), the composition ratio z of Mn needs to be in the range of 0.05 ≦ z ≦ 0.40.
If z is less than 0.05, the crystal structure becomes unstable in the charged state in which Li is undoped. Therefore, if thermal stress is applied during a charge / discharge cycle in which the state is repeated or during high-temperature storage, the crystal structure is broken and lithium is not normally absorbed and released, and the performance as a positive electrode active material is reduced. Significantly impaired. Conversely, if the ratio exceeds 0.40, the high temperature characteristics and the cycle characteristics are improved, but the charge / discharge capacity is drastically reduced.
[0012]
The composition ratio a of the element A such as Fe, V, and Cr needs to be in the range of 0 ≦ a ≦ 0.1.
If a is less than 0.01, the crystal structure is likely to collapse during charge / discharge cycles or high-temperature storage, and if it exceeds 0.1, the charge / discharge capacity is reduced.
As the element A, Al, B, Mg, and Ti among the above-mentioned elements can be suitably used.
[0013]
Further, in the present invention, the lithium composite oxide represented by the above formula (1) has an electron conductivity σ of 10 ^-4 ≦ σ ≦ 10 ^-1 It needs to be in the range of S / cm. This is required from the viewpoint of the cycle characteristics of the battery. ^-4 If it is less than S / cm, it is difficult to secure conduction between particles, and the cycle characteristics are significantly reduced. Conversely 10 ^-1 If it exceeds S / cm, the reaction between the active material and the electrolyte in a high temperature environment deteriorates the high temperature cycle characteristics.
[0014]
In addition, as the lithium composite oxide as described above, it is preferable that the 50% particle size, that is, the lithium composite oxide having a frequency of 50% in the particle size distribution curve, have a particle size of 5 to 20 μm. .
When the particle size is less than 5 μm, the specific surface area becomes large and the reaction with the electrolytic solution easily occurs, and the formation and the formation of decomposition products on the surface of the positive electrode active material may hinder the absorption and release of lithium, If it exceeds 20 μm, the reaction area between the positive electrode active material and the electrolytic solution becomes small, so that occlusion and release of lithium ions hardly occur, and battery characteristics may deteriorate.
In addition, such a measurement of the particle size can be performed by a dynamic light scattering method.
Furthermore, the specific surface area of such a lithium composite oxide is 0.1 to 1.5 m. ² / G is preferred.
0.1m specific surface area ² / G, the reaction area between the powder and the electrolyte required for inserting and extracting lithium ions is small, so that the battery characteristics may be deteriorated. ² If it exceeds / g, the reaction area with the electrolyte increases due to an increase in the reaction area with the electrolyte, and the absorption and release of lithium are hindered by the decomposition of the electrolyte and generation on the powder surface. There is.
[0015]
Next, a method for producing the above-described lithium composite oxide will be described.
Such a lithium transition metal composite oxide is prepared by mixing and mixing hydroxides such as Ni, Co, and Mn as transition metal sources according to the respective compositions, and mixing LiOH as a lithium source with the mixture. It can be obtained by firing at １1100 ° C.
In this case, the starting materials of the transition metal source that can be used are not limited to those described above, and transition metal carbonates, nitrates, sulfates, and the like can also be used. Further, a complex transition metal hydroxide or carbonate containing a plurality of types of transition metals can also be used.
On the other hand, as a starting material of the lithium source, in addition to hydroxide, Li ₂ O, Li ₂ O ₃ And LiNiO ₃ Can be used.
[0016]
Next, the lithium ion nonaqueous electrolyte secondary battery of the present invention will be described.
As described above, this non-aqueous electrolyte secondary battery includes a positive electrode using the lithium composite oxide as a positive electrode active material, a negative electrode using a material capable of absorbing and releasing lithium as a negative electrode active material, and a non-aqueous electrolyte. Prepare.
[0017]
Here, as the negative electrode active material, any material capable of electrochemically inserting and extracting (doping and undoping) lithium at a potential lower than that of lithium metal or lithium may be used. No, but pyrolytic carbons, cokes (pitch coke, needle coke, petroleum coke), graphites (natural graphite, artificial graphite, graphite), glassy carbons, organic polymer compound fired bodies (phenolic resin, furan) Resin or the like fired at an appropriate temperature), carbon fiber, activated carbon, and the like can be used.
In addition, other materials that form lithium alloys of lithium and aluminum, lead, copper, indium, and the like, metal oxides such as iron oxide, titanium oxide, and tin oxide, and intermetallic compounds; Releasable polymers such as polyacetylene and polypyrrole can also be used.
[0018]
The above-described doping of lithium into the carbonaceous material or alloy material may be performed electrochemically in the battery after the battery is manufactured, or may be a positive electrode or a lithium source other than the positive electrode after or before the battery is manufactured. And may be electrochemically doped. Further, it may be synthesized as a lithium-containing material at the time of material synthesis, and may be contained in the negative electrode active material at the time of manufacturing a battery.
[0019]
In the nonaqueous electrolyte secondary battery of the present invention, the positive electrode or the negative electrode is typically a positive electrode mixture or a negative electrode containing the above-mentioned active material and a binder on both surfaces of a band-shaped or rectangular current collector. It is produced by forming a positive electrode mixture layer or a negative electrode mixture layer coated with the mixture. Here, the current collector is not particularly limited as long as it has a current collecting function, and in terms of shape, a net-like material such as a foil, a mesh, and an expanded metal may be used. As the material, aluminum, stainless steel, nickel, or the like is used for the positive electrode current collector, and a copper foil, stainless steel, and nickel foil that do not form an alloy with lithium is used for the negative electrode current collector.
Further, the positive electrode mixture or the negative electrode mixture is obtained by mixing a known binder such as polyvinylpyrrolidone and a known additive such as a conductive agent such as graphite, if necessary, in addition to the above active material.
The formation of the positive electrode mixture layer or the negative electrode mixture layer is typically performed by applying the positive electrode mixture or the negative electrode mixture on both surfaces of the current collector and drying the mixture.
[0020]
Further, in the present invention, from the demand for higher capacity and the like, typically, the positive electrode and the negative electrode as described above, the separator is typically formed in a band shape or a rectangular shape, and such a positive electrode sheet and a negative electrode sheet are formed. A laminate sheet is formed with a separator inserted between the laminate sheets, and a battery is formed using a wound electrode produced by winding the laminate sheet.
The mode of winding is not particularly limited, and may be spiral or spiral. Usually, winding is performed many times to produce a wound electrode.
[0021]
It is sufficient for the separator to have a function of separating the positive electrode and the negative electrode and preventing a short circuit due to physical contact between the two, and examples thereof include a woven fabric, a nonwoven fabric, and a microporous synthetic resin membrane. Specifically, it is preferable to use a microporous polyethylene or polypropylene film.Since such a microporous film softens at a high temperature, closes the micropores and suppresses the outflow of lithium ions, it is used as a measure against overcurrent. Can also be suitably used.
Note that, from the relationship between lithium ion conductivity and energy density, it is preferable that the thickness of the separator be as small as possible, and typically, it is desirable that the thickness be 50 μm or less.
[0022]
Next, as for "non-aqueous electrolyte", in the present specification, a non-aqueous electrolyte in which an electrolyte is dispersed or dissolved in a non-aqueous medium, and a solid electrolyte, in which the electrolyte is dissolved in a non-aqueous solvent such as propylene carbonate, In addition, a solid electrolyte having lithium ion conductivity and a solution obtained by dissolving an electrolyte in a non-aqueous dispersion medium (a polymer such as polyvinylidene fluoride) in a gel state are used.
Such non-aqueous electrolytes can be broadly classified into non-aqueous electrolyte solutions in which the electrolyte is dissolved in a non-aqueous solvent, gel electrolytes in which the electrolyte is dissolved in a gel-like non-aqueous dispersion medium, and solid electrolytes.
[0023]
Here, examples of the electrolyte dissolved in a non-aqueous solvent or dispersed in a gel non-aqueous dispersion medium include various lithium salts such as LiCl, LiBr, and LiClO. ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiCH ₃ SO ₃ , LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ Or LiB (C ₆ H ₅ ) ₄ And mixtures thereof, among which LiPF ₆ And LiBF ₄ It is preferred to use
[0024]
Further, as the non-aqueous solvent, aprotic solvents like the conventional non-aqueous lithium battery, for example, propylene carbonate, ethylene carbonate, butylene carbonate, vinylene carbonate, γ-butyl lactone, γ-butyrolactan, sulfolane, methyl sulfolane, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolan, 4-methyl-1,3-dioxolan, methyl propionate, methyl butyrate, dimethyl carbonate, diethyl carbonate , Dipropyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, propionitrile, acetonitrile, anisole, diethyl ether, acetate, butyrate and propionate And the like.
In particular, from the viewpoint of voltage stability, it is preferable to use cyclic carbonates such as propylene carbonate and vinylene carbonate, and chain carbonates such as dimethyl carbonate, diethyl carbonate and dipropyl carbonate. In addition, such a non-aqueous solvent may be used alone or as a mixture of two or more.
[0025]
On the other hand, examples of the gel-like non-aqueous dispersion medium include polymers such as polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyethylene oxide, and polysiloxane. The molecular weight of these polymers is suitably about 300,000 to 800,000.
The dispersion of the electrolyte in the polymer can be typically carried out by dissolving a polymer such as polyvinylidene fluoride in a non-aqueous electrolyte in which the electrolyte is dissolved in a non-aqueous solvent, and forming a sol.
[0026]
Further, as the solid electrolyte, a crystalline solid electrolyte such as LiI or LiI.Li ₂ SP ₂ S ₆ Glass and LiI.Li ₂ SB ₂ S ₆ The material is not particularly limited as long as it is an amorphous solid electrolyte represented by a lithium ion conductive glass such as a system glass.
[0027]
The non-aqueous electrolyte secondary battery of the present invention is typically formed by housing the above-mentioned wound electrode together with the non-aqueous electrolyte in a metal or plastic case, etc., from the viewpoint of lightness and thinness. Is preferably housed in a film-shaped outer case, and the material of the laminate film forming the film-shaped outer case is polyethylene terephthalate (PET), molten polypropylene (PP), unstretched polypropylene (CPP), polyethylene Plastic materials such as (PE), low-density polyethylene (LDPE), high-density polyethylene (HDPE), linear low-density polyethylene (LLDPE), and polyamide-based synthetic polymer materials (trade name: nylon: Ny); Aluminum (Al) is used as a moisture-permeable barrier film.
[0028]
The most common configuration of the above-mentioned laminated film can be exemplified by the case where the exterior layer / metal film (barrier film) / sealant layer is PET / Al / PE. Further, not limited to this combination, in the configuration of the outer layer / metal film / sealant layer, Ny / Al / CPP, PET / Al / CPP, PET / Al / PET / CPP, PET / Ny / Al / CPP, PET / Adopts combinations of Ny / Al / Ny / CPP, PET / Ny / Al / Ny / PE, Ny / PE / Al / LLDPE, PET / PE / Al / PET / LDPE, PET / Ny / Al / LDPE / CPP, etc. You can also. Of course, a metal other than Al can be used for the metal film.
[0029]
As described above, the lithium ion nonaqueous electrolyte secondary battery of the present invention has a positive electrode, a negative electrode, and a nonaqueous electrolyte containing the positive electrode active material of the present invention as essential components, but the battery shape is not particularly limited. However, various battery shapes such as a cylindrical type, a square type, a coin type, and a button type can be adopted.
Further, in order to obtain a sealed non-aqueous electrolyte secondary battery with higher safety, it is desirable to provide a means such as a safety valve which operates due to an increase in battery internal pressure and shuts off current in the event of an abnormality such as overcharging. .
Since the non-aqueous electrolyte secondary battery of the present invention is configured using the above-described various materials, particularly the specific positive electrode active material, the capacity retention rate accompanying the charge / discharge cycle at a high capacity is high. .
[0030]
Next, some embodiments of the above-described lithium ion nonaqueous electrolyte secondary battery will be specifically described with reference to the drawings.
FIG. 1 is a sectional view showing an example of the lithium ion nonaqueous electrolyte secondary battery of the present invention. As shown in the figure, this non-aqueous electrolyte secondary battery is obtained by laminating a strip-shaped positive electrode 11 and a negative electrode 12 with a separator 13 interposed therebetween, and further winding a wound electrode body 10 above and below the wound electrode body 10. It is housed in the battery can 1 with the plate 2 attached.
Further, a battery cover 4 is caulked to the battery can 1 via a gasket 7, and the battery cover 4 is electrically connected to the positive electrode 11 via a positive electrode lead 15, and functions as a positive electrode of the battery. On the other hand, the negative electrode 12 is electrically connected to the bottom of the battery can 1 via the negative electrode lead 16, and the battery can 1 is configured to function as a negative electrode of the battery.
[0031]
In this battery, a center pin 14 is provided at the center of the wound electrode body 10 to perform a function of interrupting current, and the safety valve 5 having the disk plate 5a is provided with a positive electrode lead 15 when the pressure inside the battery increases. This is a safety device that deforms a portion electrically connected to the device and releases the electrical connection.
The thermal resistance element 6 disposed between the safety valve 5 and the battery lid 4 serves as an element in the battery that cuts off current when the battery is charged or discharged in excess of the maximum rated current value or when the battery is exposed to high temperatures. Function.
[0032]
FIG. 2 shows the structure of the above-described belt-shaped positive electrode 11. As shown in the figure, the strip-shaped positive electrode 11 is formed by coating both sides (front and back) of a strip-shaped positive electrode current collector 12a with positive electrode mixture layers 12b and 12c.
In the nonaqueous electrolyte secondary battery of the present invention, as shown, the ends of the positive electrode mixture layers 12b and 12c are arranged irregularly in the longitudinal direction at both or one end of the band-shaped positive electrode 11, As described below, it is preferable to reduce the amount of active material not involved in the battery reaction to effectively utilize the inside of the battery and to improve the energy density of the obtained nonaqueous electrolyte secondary battery.
Further, the strip-shaped negative electrode 12 has the same structure as the strip-shaped positive electrode 11, and similarly to the case of the positive electrode, the ends of the negative electrode mixture layer coated on the front and back surfaces of the current collector are flush with each other when viewed from the side. The same effect as described above can be obtained by arranging them so as not to be disturbed, but the negative electrode structure is not shown.
The above-described effect can be obtained by performing the above-described mixture layer edge treatment on at least one of the positive electrode and the negative electrode. However, the mixture layer edge treatment may be performed on both the positive electrode and the negative electrode.
[0033]
FIG. 3 is a cross-sectional view of the non-aqueous electrolyte secondary battery shown in FIG. 1 taken along line AA, and shows a wound electrode body 10.
In FIG. 1, a spirally wound electrode body 10 is formed by spirally winding a laminated body in which four layers of a band-shaped negative electrode 12, a separator 13 (not shown), a band-shaped positive electrode 11, and a separator 13 (not shown) are laminated in this order. The strip-shaped negative electrode 12 is disposed so as to be inside (at the center) of the electrode body 10. And about the strip | belt-shaped positive electrode 11 and the strip | belt-shaped negative electrode, each mixture layer 11c and 12c are arrange | positioned so that the mixture layer 11b and 12b may exist outside (center side) of the spirally wound electrode body 10 (outside). (See FIG. 2).
In general, in such a wound electrode body, in order to prevent deposition of lithium during charging and an internal short circuit, a negative electrode 12 existing in parallel with the positive electrode 11 via a separator 13 (not shown) is provided. The width (height in FIG. 1) and length (winding length), that is, the reaction area, are formed to be larger than the width and length (reaction area) of the positive electrode 11.
The spirally wound electrode body shown in this figure is of a general spiral wound type, in which the ends of the mixture layers of the strip-shaped positive electrode 11 and the strip-shaped negative electrode 12 are not treated, and the cathode mixture layer is not treated. The ends of 11b and 11c and the ends of negative electrode mixture layers 12b and 12c are flush with each other when viewed from the side.
[0034]
FIG. 4 shows a wound electrode body formed by another winding method.
In the spirally wound electrode body shown in the figure, a negative electrode mixture layer is formed on one side only at one end of the strip-shaped negative electrode 12, that is, at the end that constitutes the outermost periphery of the wound electrode body. In other words, on the outermost periphery of the wound electrode body, only the inner mixture layer 12c of the negative electrode is formed, and the outer mixture layer 12b is not formed. Note that no treatment is applied to both ends of the strip-shaped positive electrode 11, and the inner mixture layer 11c and the outer mixture layer 11b are flush with each other at both ends.
By adopting such a winding type, only the positive electrode mixture layer portion and the negative electrode mixture layer portion that actually participate in the battery reaction can be present inside the battery, so that the inside of the battery can be effectively utilized. And the energy density of the obtained non-aqueous electrolyte secondary battery can be improved.
[0035]
FIG. 5 shows a spirally wound electrode body employing another spirally wound type. In the other end (the innermost end) of the strip-shaped negative electrode 12, only the outer mixture layer 12b is formed. As for the positive electrode 11, only the inner mixture layer 11c is formed at one end (the outermost end). At one end (the outermost end) of the strip-shaped negative electrode 12 and the other end (the innermost end) of the strip-shaped positive electrode, the mixture layer is formed flush.
Even by adopting such a winding type, the inside of the battery is effectively used as described above, and the energy density of the obtained battery can be improved.
[0036]
FIG. 6 shows another winding type in which only the inner mixture layer 11c is formed at one end (outermost end) of the strip-shaped positive electrode 11, and the other end (innermost end). Part), the positive electrode mixture layers are flush with each other. In addition, about the strip | belt-shaped negative electrode 12, the negative electrode mixture layer is flush at both ends.
FIG. 7 shows another winding type, in which the other end (innermost end) of the strip-shaped positive electrode 11 has an outer mixture layer 11b and the other end (outermost end) has an inner mixture layer. Only 11c is formed. As for the strip-shaped negative electrode 12, the negative electrode mixture layers are flush at both ends.
6 and 7, the inside of the battery can be effectively used as described above, and the energy density of the obtained battery can be improved.
[0037]
【Example】
Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.
[0038]
(Examples 1 to 5, Comparative Examples 1 to 7)
As shown in Table 1 below, commercially available lithium hydroxide, nickel hydroxide, cobalt hydroxide and manganese hydroxide were used, and in Examples 1 to 5, the molar ratio was 0.05 ≦ x ≦ 1.10. In the range of 1 ≦ y + z ≦ 0.7, 0.05 ≦ z ≦ 0.4, Comparative Examples 1 to 3 are prepared and mixed so as to be out of this range, fired in an oxygen stream, Li _x Ni _(1-yz) Co _y Mn _z A _a O ₂ ... A lithium composite oxide represented by (1) was produced.
When the obtained powder samples of each example were analyzed by X-ray diffraction, LiNiO ₂ The substance was identified as having a structure similar to that of. The confirmed peak is LiNiO ₂ Nothing other than the origin was present, indicating that this sample was a single-layer material with cobalt and aluminum forming a solid solution at nickel sites.
[0039]
90% of the active material of each example prepared as above was mixed with 7% of graphite as a conductive agent and 3% of polyvinylidene fluoride (PVdF) as a binder, and mixed with N-methyl-2-pyrrolidone (NMP). This was dispersed to obtain a positive electrode mixture slurry. After drying and re-grinding, a coin-type compact was pressed by a hydraulic press so that the surface density was constant.
Each of the obtained green compact samples was sandwiched between stainless steel electrodes, and the volume density was 3.3 g / cm. ³ A constant voltage (V) was applied to the green compact while maintaining a constant pressure from both ends such that At the moment when a voltage is applied, Li ions and the like in addition to electrons also carry charge transfer, so that the current value becomes larger than the actual value. However, polarization occurs immediately, so that the current value decreases and settles to a constant value. The DC resistance value (R) was estimated from the current value (I) and Ohm's law (V = IR) at this time.
This measurement was performed at 23 ° C. The thickness of the green compact is d, and the contact area with the electrode is S (1.8 cm in this measurement). ² ) Can be calculated by σ = d / (RS). After the measurement, the thickness d of the green compact was measured, and the electron conductivity was estimated. The results obtained are also shown in Table 1.
[0040]
At the same time, a positive electrode mixture slurry prepared with the same composition as above was uniformly applied to both sides of a 25 μm-thick strip-shaped aluminum foil, dried, and then compressed by a rotor press to obtain a strip-shaped positive electrode.
On the other hand, 90% of powdered artificial graphite as a negative electrode active material was mixed with 10% of PVdF, and further dispersed in NMP to obtain a negative electrode mixture slurry. This negative electrode mixture slurry was uniformly applied to both surfaces of a copper foil having a thickness of 15 μm, dried, and then compressed by a roller press to obtain a strip-shaped negative electrode.
[0041]
The strip-shaped positive electrode and the strip-shaped negative electrode manufactured as described above were wound many times via the porous polyolefin, thereby manufacturing a spiral electrode body as shown in FIG.
The electrode body was housed in a nickel-plated iron battery can, and insulating plates were arranged on both upper and lower surfaces of the electrode body. Next, the aluminum positive electrode lead was led out from the current collector, and was welded to the projection of the safety valve, which was electrically connected to the battery lid, and the nickel negative electrode lead was led out from the negative electrode current collector to form a battery can. Welded to the bottom.
On the other hand, LiPF was added to a mixed solution having a deposition mixing ratio of ethylene carbonate and methyl ethyl carbonate of 1: 1 as an electrolytic solution. ₆ To 1 mol / dm ³ To obtain a non-aqueous electrolyte solution.
Thereafter, the electrolyte solution is injected into the battery can into which the above-described electrode body is incorporated, and the battery can is caulked through an insulating sealing gasket to fix the safety valve, the PTC element, and the battery lid. Each cylindrical battery of 18 mm in height and 65 mm in height was produced.
[0042]
[Performance evaluation]
The non-aqueous electrolyte secondary batteries of the respective examples prepared as described above were charged under the conditions of an environmental temperature of 25 ° C., a charging pressure of 4.20 V, a charging current of 1000 mA, a charging time of 2.5 hours, and then discharging. Discharge was performed at a current of 750 mA and a final voltage of 3.0 V, and the initial capacity was determined. Further, charge and discharge were repeated at an environmental temperature of 50 ° C., and the discharge capacity at the 100th cycle was measured to determine the maintenance ratio with respect to the initial capacity.
After applying a constant voltage of 4.2 V to each of the produced batteries and continuing to charge them at an environmental temperature of 60 ° C. for one month, the batteries were discharged under the same conditions as above, and the capacity retention was calculated from the discharge capacity and the initial capacity. Calculated. The results obtained are also shown in Table 1.
[0043]
[Table 1]

[0044]
From the evaluation results of Examples 1 to 5 and Comparative Examples 1 to 7 shown in Table 1,
General formula Li _x Ni _(1-yz) Co _y Mn _z A _a O ₂ ... The nickel, cobalt, and manganese composition ratios of the lithium composite oxide represented by (1) are defined in the range of 0.1 ≦ y + z ≦ 0.7 and 0.05 ≦ z ≦ 0.40 to achieve high capacity. It has been found that a non-aqueous electrolyte secondary battery having excellent high-temperature cycle characteristics can be manufactured.
As shown in Example 5, when Al is added as an additive element at a composition ratio of 0.05, the cycle characteristics at high temperatures are significantly improved. Similar effects can be expected by adding Fe, V, Cr, Mg, Ti, Al, B or Ca as an additional element and any mixture thereof.
[0045]
As can be seen from the evaluation results of Comparative Examples 1 to 3, when an active material is produced outside the above composition range, the initial discharge capacity is significantly reduced and the high-temperature cycle characteristics are deteriorated.
Under the above conditions alone, as in Comparative Examples 6 and 7, although the initial discharge capacity and the high-temperature cycle characteristics are excellent, the reactivity with the electrolytic solution at a high temperature is increased due to the high electron conductivity. As a result, it is difficult to obtain a satisfactory result in the capacity recovery rate. Therefore, as shown in Example 1 and Example 5, by reducing the amount of the conductive agent, the electron conductivity is reduced, the reaction with the electrolytic solution at high temperature is suppressed, and the capacity recovery rate at high temperature float charging is reduced. Could be improved.
[0046]
From the above results, the combination of a positive electrode using the lithium composite oxide represented by the above general formula (1) as a positive electrode active material, a negative electrode active material capable of inserting and extracting lithium, and a nonaqueous electrolyte solution It was clarified that a non-aqueous electrolyte secondary battery having a high capacity and excellent cycle characteristics and float characteristics could be manufactured.
[0047]
【The invention's effect】
As described above, according to the present invention, since a lithium composite oxide having a predetermined composition is used, a positive electrode active material capable of realizing a lithium ion nonaqueous electrolyte secondary battery having a high capacity and excellent cycle characteristics And a lithium ion nonaqueous electrolyte secondary battery using the positive electrode active material.
[Brief description of the drawings]
FIG. 1 is a sectional view showing an example of a lithium ion nonaqueous electrolyte secondary battery of the present invention.
FIG. 2 is a perspective view showing a structure of a belt-shaped positive electrode.
FIG. 3 is a cross-sectional view showing the wound electrode body taken along line AA in FIG.
FIG. 4 is a cross-sectional view showing another example of a wound electrode body.
FIG. 5 is a cross-sectional view showing another example of a wound electrode body.
FIG. 6 is a sectional view showing still another example of a wound electrode body.
FIG. 7 is a cross-sectional view showing another example of a wound electrode body.
[Explanation of symbols]
1 Battery can
2 Insulating plate
4 Battery cover
5 Safety valve
5a disk board
6 Thermal resistance element
7 Gasket
10-wound electrode body
11 Positive electrode
11a positive electrode current collector
11b Positive electrode mixture layer (outside)
11c Positive electrode mixture layer (inside)
12 Negative electrode
12a negative electrode current collector
12b Negative electrode mixture layer (outside)
12c Negative electrode mixture layer (inside)
13 Separator
14 Center pin
15 Positive electrode lead
16 Negative electrode lead

Claims (6)

Following general formula _{Li x Ni (1-y-} z) Co y Mn z A a O 2 ... ▲ 1 ▼
(A in the formula represents at least one element selected from the group consisting of Fe, V, Cr, Mn, Ti, Mg, Al, B and Ca, and x, y and z each represent 0.05 ≦ x ≤ 1.10, 0.10 ≤ y + z ≤ 0.70, 0.05 ≤ z ≤ 0.40, a satisfies 0 ≤ a ≤ 0.1), and has an electron conductivity σ of 10 ⁻ A positive electrode active material for a lithium ion nonaqueous electrolyte secondary battery, comprising a lithium composite oxide satisfying ⁴ ≦ σ ≦ 10 ⁻¹ S / cm. The positive electrode active material according to claim 1, wherein the particle diameter distribution curve of the lithium composite oxide has a particle diameter of 5 to 20 m at a frequency of 50%. The cathode active material according to claim 1, specific surface area of the lithium composite oxide is characterized by a 0.1~1.5m 2 / ^g. Positive and negative electrodes using a material capable of doping and undoping lithium ions as a positive electrode active material or a negative electrode active material,
In a lithium ion non-aqueous electrolyte secondary battery comprising a non-aqueous electrolyte obtained by dispersing the electrolyte in a non-aqueous medium,
The positive electrode active material has the following general formula: Li _x Ni _(1-yz) Co _{y M} n _{M z} A _a O ₂ .
(A in the formula represents at least one element selected from the group consisting of Fe, V, Cr, Mn, Ti, Mg, Al, B and Ca, and x, y and z each represent 0.05 ≦ x ≤ 1.10, 0.10 ≤ y + z ≤ 0.70, 0.05 ≤ z ≤ 0.40, a satisfies 0 ≤ a ≤ 0.1), and has an electron conductivity σ of 10 ⁻ A lithium ion nonaqueous electrolyte secondary battery comprising a lithium composite oxide satisfying ⁴ ≦ σ ≦ 10 ⁻¹ S / cm. The lithium ion nonaqueous electrolyte secondary battery according to claim 4, wherein a 50% particle size of the lithium composite oxide is 5 to 20 m. The non-aqueous electrolyte secondary battery according to claim 5 in which the specific surface area of the lithium composite oxide is characterized by a 0.1~1.5m 2 / ^g.

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