JP2011171012A - Positive electrode for lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a positive electrode for a lithium secondary battery while preventing capacity degradation due to high-potential charge/discharge. <P>SOLUTION: The positive electrode for a lithium secondary battery contains a solid solution compound expressed in a general formula xLi[Li<SB>1/3</SB>M1<SB>2/3</SB>]O<SB>2</SB>(1-x)LiM2O<SB>2</SB>(M1 is at least one kind of metal elements of an average oxide state of 4+, and M2 is at least one kind of transition metal elements and 0<x<1), and a lithium nickel composite oxide having a laminate structure expressed in a general formula LiNi<SB>1-a-b</SB>M3<SB>a</SB>M4<SB>b</SB>O<SB>2</SB>(M3 is Al and/or Mg, M4 is at least one kind of metal elements selected from a group composed of Co, Mn, Fe, Cu and Cr, and 0.3≤a≤0.5, 0≤b≤0.2). <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a positive electrode. Specifically, the present invention relates to a positive electrode for a lithium secondary battery in which capacity deterioration during charging and discharging at a high potential is suppressed.

A lithium secondary battery (typically a lithium ion battery) that is charged and discharged as lithium ions move between the positive electrode and the negative electrode is lightweight and provides high output. The demand for mobile terminals is expected to increase further in the future. In these applications, reduction in size and weight of the battery is required, and increasing the energy density of the battery is an important technical issue. In order to increase the energy density, it is an effective means to increase the operating voltage of the battery. Currently, as a positive electrode active material capable of constituting a 4V class lithium secondary battery, a layered structure lithium cobalt composite oxide (LiCoO ₂ ), a layered structure lithium nickel composite oxide (LiNiO ₂ ), a spinel structure lithium manganese composite oxide (LiMn) ₂ O ₄ ) or the like is considered, but if a positive electrode active material having a higher potential is developed, higher energy can be achieved.

For this purpose, solid solution positive electrode active materials are currently being studied. Among them, Li [Li _1/3 Mn _2/3 ] O ₂ having an electrically inactive layered structure and LiMO ₂ having an electrically active layered structure (where M is Co, Ni, Mn Etc.) is expected as a positive electrode active material having a high capacity and capable of realizing a voltage operating region at a high potential. Patent documents 1 and 2 are mentioned as conventional technology about this kind of solid solution system cathode active material. In addition, Patent Documents 3 and 4 are given as conventional techniques related to the positive electrode active material.

JP 2009-9753 A JP 2008-270201 A International Publication No. 2004/088777 Pamphlet JP 2008-08473 A

However, in a battery using the above-described solid solution of Li [Li _1/3 Mn _2/3 ] O ₂ and LiMO ₂ for the positive electrode, there is a problem that the transition metal is eluted when used at a high charge / discharge potential. . When the transition metal is eluted, the negative electrode active material and the electrolytic solution are deteriorated due to the eluted transition metal, and the battery capacity is reduced. Therefore, when a battery using such a solid solution as a positive electrode is used at a high charge / discharge potential, there is a problem that the capacity deteriorates immediately and the cycle characteristics deteriorate.

  This invention is made | formed in view of this point, The main objective is to provide the positive electrode for lithium secondary batteries by which capacity degradation by charging / discharging by a high potential was suppressed.

In general, when a layered structure lithium nickel composite oxide represented by LiNiO ₂ is used with a high charge / discharge potential, the stability as a compound is lowered and the crystal structure is collapsed. On the other hand, the present inventor substituted a part of the nickel of LiNiO ₂ with aluminum and / or magnesium so that the crystal structure is stabilized, and the compound can exist stably even when used at a high potential. I found.

And it has a layered structure lithium nickel composite oxide stabilized at such a high potential and a solid solution compound represented by xLi [Li _1/3 M1 _2/3 ] O _2. (1-x) LiM ₂ O ₂ Thus, the present inventors have found that the performance deterioration due to the elution of transition metal from the solid solution compound can be suppressed, thereby improving the cycle characteristics in the battery including the positive electrode, and the present invention has been completed.

That is, the positive electrode for a lithium secondary battery provided by the present invention is
The following general formula:
xLi [Li _1/3 M1 _2/3 ] O _2. (1-x) LiM ₂ O ₂ (1)
(Where M1 is at least one metal element having an average oxidation state of 4+, and M2 is at least one transition metal element: 0 <x <1)
A solid solution compound represented by
The following general formula:
LiNi _1-ab M3 _a M4 _b O ₂ (2)
(Here, M3 is Al and / or Mg, and M4 is at least one metal element selected from the group consisting of Co, Mn, Fe, Cu and Cr: 0.3 ≦ a ≦ 0.5 , 0 ≦ b ≦ 0.2)
And a lithium nickel composite oxide having a layered structure represented by

  Here, M3 in the above formula (2) is a metal element of Al and / or Mg. By containing Al and / or Mg, stability as a compound at a high potential can be improved. Preferably, in the above (2), M3 is Al. Al is particularly preferable in that it is inexpensive and easy to synthesize.

  The content ratio of M3 (that is, the value of a in the formula (2)) is 0.3 ≦ a ≦ 0.5. When the proportion of M3 is too small (a <0.3), the structure stabilization effect due to the M3 content may not be sufficiently obtained. On the other hand, when the content ratio of M3 is too large (0.5 <a), unreacted substances may remain or impurities may be generated during synthesis. Accordingly, the content ratio of M3 is suitably about 0.3 or more, usually preferably 0.35 or more, more preferably 0.4 or more, typically 0.4 ≦ It is desirable to contain M3 (Al and / or Mg) at a composition ratio such that a ≦ 0.5.

This compares with a conventional layered structure lithium nickel composite oxide (typically LiNiO ₂ ) that does not contain M3 (Al and / or Mg) or has a M3 content of less than 0.3. Thus, a compound having excellent structural stability at a high potential can be obtained. And it has a layered structure lithium nickel composite oxide stabilized at such a high potential, and a solid solution compound represented by xLi [Li _1/3 M1 _2/3 ] O _2. (1-x) LiM ₂ O ₂ Thus, even when used with a high charge / discharge potential, it is possible to suppress performance degradation due to elution of transition metal from the solid solution compound without causing structural collapse of the layered structure lithium nickel composite oxide. Therefore, if such a positive electrode is used, it is possible to construct a lithium secondary battery with good cycle characteristics in which capacity deterioration during charging and discharging at a high potential is suppressed.

  M4 in the above formula (2) is at least one metal element selected from the group consisting of Co, Mn, Fe, Cu, and Cr. That is, the layered structure lithium nickel composite oxide of the present invention contains a predetermined proportion of Al and / or Mg, but further contains at least one minor addition selected from the group consisting of Co, Mn, Fe, Cu and Cr. Allow the presence of elements (no such minor additive elements may be present). The content ratio of M4 (that is, the value of b in the formula (1)) can be approximately 0 ≦ b ≦ 0.2.

In one embodiment of the positive electrode for a lithium secondary battery disclosed herein, the solid solution compound is a compound represented by the general formula xLi [Li _1/3 M1 _2/3 ] O _2. (1-x) LiM ₂ O ₂ . It is. Here, the value of x may be a value satisfying 0 <x <1. M1 of Li [Li _1/3 M1 _2/3 ] O ₂ is at least one metal element having an average oxidation state of 4+. For example, M1 in the above formula is desirably at least one metal element selected from the group consisting of Mn, Zr, Ti, and Sn. This makes it possible to construct a lithium secondary battery with a high capacity and a high energy density. The M2 of LiM2O _2, a transition metal element of at least one. As M2 in the above formula, at least one transition metal element having an average oxidation state of 3+ can be preferably used. For example, it is desirable to be at least one transition metal element selected from the group consisting of Mn, Co, Ni and Fe. Thereby, a lithium secondary battery having a high capacity and a high energy density can be constructed.

  In a preferred embodiment of the positive electrode for a lithium secondary battery disclosed herein, the content ratio of the layered lithium nickel composite oxide is 1 with respect to the total mass of the layered lithium nickel composite oxide and the solid solution compound. It is mass%-20 mass%. If the content ratio of the layered structure lithium nickel composite oxide is too small (typically less than 1% by mass), the effect of improving the cycle characteristics due to the inclusion of the layered structure lithium nickel composite oxide may not be sufficiently obtained. . On the other hand, if the content of the layered structure lithium nickel composite oxide is too large (typically over 20% by mass), the battery capacity may tend to decrease. Accordingly, the content ratio of the layered structure lithium nickel composite oxide is suitably about 1% by mass to 20% by mass, usually preferably 3% by mass to 20% by mass, for example, 5% by mass to 15% by mass. It is desirable to include the layered structure lithium nickel composite oxide in such a content ratio as to be (for example, approximately 10% by mass).

  In addition, according to the present invention, a lithium secondary battery (typically a lithium ion secondary battery) provided for any of the positive electrodes disclosed herein is provided. Since such a lithium secondary battery is constructed using the positive electrode active material described above as a positive electrode, it can exhibit better battery characteristics. For example, even when used at a high potential, the capacity deterioration is small and the charge / discharge cycle characteristics can be excellent.

  Such a lithium secondary battery has performance suitable as a battery mounted on a vehicle. Therefore, according to the present invention, there is provided a vehicle including the lithium secondary battery disclosed herein (which may be in the form of an assembled battery to which a plurality of lithium secondary batteries are connected). In particular, a vehicle (for example, an automobile) including the lithium secondary battery as a power source (typically, a power source of a hybrid vehicle or an electric vehicle) is provided.

It is a figure which shows typically the lithium secondary battery which concerns on one Embodiment of this invention. It is a figure which shows typically the electrode body of the lithium secondary battery which concerns on one Embodiment of this invention. It is a figure which shows typically the coin cell for a test concerning this test example. It is a side view showing typically a vehicle provided with a lithium secondary battery concerning one embodiment of the present invention.

  Embodiments according to the present invention will be described below with reference to the drawings. In the following drawings, members / parts having the same action are described with the same reference numerals. Note that the dimensional relationship (length, width, thickness, etc.) in each drawing does not reflect the actual dimensional relationship. Further, matters other than the matters specifically mentioned in the present specification and matters necessary for carrying out the present invention (for example, the configuration and manufacturing method of an electrode body including a positive electrode and a negative electrode, the configuration and manufacturing method of a separator and an electrolyte, General techniques relating to the construction of lithium secondary batteries and other batteries, etc.) can be understood as design matters for those skilled in the art based on the prior art in this field.

The positive electrode provided by the present invention includes a solid solution compound represented by a general formula xLi [Li _1/3 M1 _2/3 ] O _2. (1-x) LiM ₂ O ₂ and a general formula LiNi _1-ab M 3 _a M 4. and a lithium nickel composite oxide having a layered structure represented by _{b 2} O ₂ (typically a mixture of both compounds).

<Solid solution compound>
The first positive electrode active material constituting the positive electrode for a lithium secondary battery of the present embodiment has a general formula xLi [Li _1/3 M1 _2/3 ] O _2. (1-x) LiM2O ₂ (where M1 is It is at least one metal element having an average oxidation state of 4+, and M2 is at least one transition metal element: a solid solution compound represented by 0 <x <1). This solid solution compound is a solid solution of Li [Li _1/3 M1 _2/3 ] O ₂ having an electrically inactive layer structure and LiM ₂ O ₂ having an electrically active layer structure. This makes it possible to construct a high-capacity lithium secondary battery.

Here, the value of x may be a value satisfying 0 <x <1. M1 of Li [Li _1/3 M1 _2/3 ] O ₂ is at least one metal element having an average oxidation state of 4+. For example, M1 in the formula is preferably Mn, Zr, Ti, or Sn, or a combination of two or more thereof. Thereby, a lithium secondary battery having a higher capacity and a higher energy density can be constructed. The M2 of LiM2O _2, a transition metal element of at least one. As M2 in the above formula, at least one transition metal element having an average oxidation state of 3+ can be preferably used. For example, Mn, Co, Ni, or Fe is preferable, or a combination of two or more of these may be used. Thereby, a lithium secondary battery having a higher capacity and a higher energy density can be constructed.

The solid solution compound (xLi [Li _1/3 M1 _2/3 ] O _2. (1-x) LiM ₂ O ₂ ) disclosed herein is obtained by a solid phase method or a liquid phase method, as in the case of the same type of complex oxide. Can be synthesized. When using the solid phase method, several kinds of sources (Li source, M1 source, M2 source) appropriately selected according to the constituent elements of the complex oxide are mixed at a predetermined molar ratio, It can be synthesized by firing the mixture by an appropriate means. Typically, a powdered composite oxide having a desired average particle size and particle size distribution can be prepared by pulverization and granulation by an appropriate means after firing. In addition, in various supply sources (M1 supply source, M2 supply source), element diffusion may not occur uniformly during firing, and various supply sources may remain as impurities. For this reason, various sources are dissolved and mixed in an appropriate solution, and then precipitated as complex carbonates, complex hydroxides, complex sulfates, complex nitrates, etc. containing various elements, and the resulting precipitate mixture is used as a raw material. You can also After the addition of the Li supply source, the solid solution compound is obtained by firing by an appropriate means.

For example, lithium compounds such as lithium carbonate and lithium hydroxide can be used as the lithium supply source. Further, as the M1 supply source and the M2 supply source, hydroxides, oxides, various salts (for example, carbonates), halides (for example, fluorides) and the like containing these as constituent elements can be selected. For example, although not particularly limited, when a solid solution of Li [Li _1/3 Mn _2/3 ] O ₂ and LiNi _1/3 Co _1/3 Mn _1/3 O ₂ is synthesized, nickel carbonate is used as a nickel supply source. Nickel oxide, nickel sulfate, nickel nitrate, nickel hydroxide, nickel oxyhydroxide and the like can be used. As the manganese supply source, manganese carbonate, manganese oxide, manganese sulfate, manganese nitrate, manganese hydroxide, manganese oxyhydroxide, or the like can be used. Examples of the cobalt supply source include cobalt carbonate, cobalt oxide, cobalt sulfate, cobalt nitrate, cobalt hydroxide, and cobalt oxyhydroxide.

For example, when a solid solution of Li [Li _1/3 Mn _2/3 ] O ₂ and LiNi _1/3 Co _1/3 Mn _1/3 O ₂ is synthesized, a Li supply source, a Mn supply source, and a Ni supply source A Co source source weighed at a predetermined ratio and mixed may be synthesized by firing for 5 hours at 900 ° C. in the atmosphere or in an atmosphere richer in oxygen than the atmosphere. The solid solution compound obtained by firing as described above is preferably cooled and then pulverized by milling or the like and appropriately classified to obtain a solid solution compound in the form of fine particles having an average particle size of about 1 to 25 μm. .

<Layered structure lithium nickel composite oxide>
The second positive electrode active material constituting the positive electrode for a lithium secondary battery according to the present embodiment has a general formula LiNi _1-ab M3 _a M4 _b O ₂ (where M3 is Al and / or Mg, and M4 Is at least one metal element selected from the group consisting of Co, Fe, Cu and Cr: lithium having a layered structure represented by 0.3 ≦ a ≦ 0.5, 0 ≦ b ≦ 0.2) Nickel composite oxide. This lithium nickel composite oxide is based on LiNiO ₂ , and a part of nickel in the crystal is replaced with aluminum and / or magnesium (M3) for the purpose of stabilizing the crystal structure at a high potential. That is, as M3 in the above formula, any one of Al and Mg can be used alone, or both can be used in combination. By containing M3 (Al and / or Mg), stability as a compound at a high potential can be improved. Particularly preferably, in the above formula, M3 is Al. Al is particularly preferable in that it is inexpensive and easy to synthesize.

  The content ratio of M3 (that is, the value of a in the formula) is 0.3 ≦ a ≦ 0.5. When the content ratio of M3 is too small (a <0.3), the structure stabilization effect due to the M3 content may not be sufficiently obtained. On the other hand, when the content ratio of M3 is too large (0.5 <a), unreacted substances may remain or impurities may be generated during synthesis. Accordingly, the content ratio of M3 is suitably about 0.3 or more, usually preferably 0.35 or more, more preferably 0.4 or more, typically 0.4 ≦ It is desirable to contain M3 (Al and / or Mg) at a composition ratio such that a ≦ 0.5.

As a result, compared with the conventional layered structure lithium nickel composite oxide (typically LiNiO ₂ ) that does not contain M3 or has a M3 content of less than 0.3, It can be set as the compound excellent in structural stability.

  The layered structure lithium nickel composite oxide disclosed here contains Li, Ni, and Al and / or Mg, but allows the presence of other minor additive elements M4. Such M4 is preferably Co, Fe, Cu or Cr, or two or more (typically two or three) metal elements are selected. These additional constituent elements are added at a ratio of 20 atomic% or less, preferably 10 atomic% or less of the total of the additional element, nickel and M3. Alternatively, it may not be added. That is, the content ratio of M4 (that is, the value of b in the formula) can be approximately 0 ≦ b ≦ 0.2.

The layered structure lithium nickel composite oxide (LiNi _1-ab M3 _a M4 _b O ₂ ) disclosed here can be synthesized by a solid phase method or a liquid phase method, as in the case of a conventional composite oxide of the same kind. it can. In the case of using the solid phase method, several kinds of supply sources (Li supply source, Ni supply source, M2 supply source, M1 supply source) appropriately selected according to the constituent elements of the complex oxide are added at a predetermined molar ratio. It can synthesize | combine by mixing and baking the said mixture by a suitable means. Typically, a powdered composite oxide having a desired average particle size and particle size distribution can be prepared by pulverization and granulation by an appropriate means after firing. In addition, various supply sources (Ni supply source, M3 supply source, M4 supply source) may not uniformly diffuse during firing, and various supply sources may remain as impurities. For this reason, various sources are dissolved and mixed in an appropriate solution, and then precipitated as complex carbonates, complex hydroxides, complex sulfates, complex nitrates, etc. containing various elements, and the resulting precipitate mixture is used as a raw material. You can also After the addition of the Li supply source, the layered structure lithium nickel composite oxide is obtained by firing by an appropriate means.

  As the lithium supply source and the nickel supply source, those similar to the solid solution compound described above can be used. For example, lithium compounds such as lithium carbonate and lithium hydroxide can be used as the lithium supply source. Further, hydroxides, oxides, various salts (for example, carbonates), halides (for example, fluorides), and the like containing these as constituent elements can be selected as nickel supply sources and manganese supply sources. In addition, as an aluminum source and a magnesium source, and other metal source compounds (for example, a cobalt compound, an iron compound, a copper compound, and a chromium compound), hydroxides, oxides, and various salts (which include these as constituent elements) For example, carbonates), halides (eg fluorides) and the like can be selected. For example, although not particularly limited, examples of the aluminum supply source include aluminum oxide, aluminum hydroxide, aluminum carbonate, and aluminum acetate. Examples of the magnesium supply source include magnesium oxide, magnesium hydroxide, magnesium carbonate, and magnesium acetate.

For example, when a composite oxide represented by LiNi _0.7 Al _0.3 O ₂ is synthesized, Li source, Ni source, and Al source are Li: Ni: Al = 1: 0.7: 0. .3, which is weighed and mixed so as to be 3 may be synthesized by firing for 10 hours at 750 ° C. in the atmosphere or in an atmosphere richer in oxygen than the atmosphere. The lithium nickel composite oxide obtained by firing as described above is preferably cooled and then pulverized by milling or the like and appropriately classified to thereby form LiNi _{0.7 0.7 in the} form of fine particles having an average particle size of about 1 to 25 μm. Al _0.3 O ₂ can be obtained.

<Mixing of solid solution compound and layered structure lithium nickel composite oxide>
As described above, the positive electrode active material of the present embodiment includes a solid solution compound represented by the general formula xLi [Li _1/3 M1 _2/3 ] O _2. (1-x) LiM ₂ O ₂ obtained by the above method, It is formed by mixing a layered structure lithium nickel composite oxide represented by the general formula LiNi _1-ab M3 _a M4 _b O ₂ . For mixing the compounds, the pulverized and classified materials may be mixed uniformly using a blender device or the like. Alternatively, the mixing may be performed by simultaneously crushing and classifying both composite oxides with a ball mill apparatus or the like.

  In a preferred embodiment of the positive electrode for a lithium secondary battery disclosed herein, the ratio of the layered lithium nickel composite oxide is 1 mass with respect to the total mass of the layered lithium nickel composite oxide and the solid solution compound. % To 20% by mass. If the mixing ratio of the layered structure lithium nickel composite oxide is too small (typically less than 1% by mass), the effect of improving the cycle characteristics by mixing the layered structure lithium nickel composite oxide may not be sufficiently obtained. . On the other hand, if the mixing ratio of the layered structure lithium nickel composite oxide is too large (typically more than 20% by mass), the battery capacity may tend to decrease. Accordingly, the mixing ratio of the layered structure lithium nickel composite oxide is suitably about 1% by mass to 20% by mass, and is usually preferably 3% by mass to 20% by mass, for example, 5% by mass to 15% by mass. It is desirable to contain the layered structure lithium nickel composite oxide in a mixing ratio (for example, approximately 10% by mass).

According to the positive electrode for a lithium secondary battery of the present embodiment, a layered structure lithium nickel composite oxide stabilized at a high potential, and xLi [Li _1/3 M1 _2/3 ] O _2. (1-x) LiM ₂ O _2. 5V-class solid solution compound represented by the above, even when used with a high charge / discharge potential, it is caused by elution of transition metal from the solid solution compound without causing structural collapse of the layered structure lithium nickel composite oxide Performance deterioration (typically, negative electrode active material and electrolytic solution performance deterioration) can be suppressed. Therefore, by using such a positive electrode, it is possible to construct a lithium secondary battery (for example, a lithium ion battery) with excellent cycle characteristics in which capacity deterioration during charging and discharging at a high potential is suppressed.

  In addition, except using the positive electrode active material disclosed here, a lithium secondary battery can be constructed by adopting the same materials and processes as in the past.

  For example, a powder (powder-like positive electrode active material) composed of a mixture of the solid solution compound disclosed herein and a layered structure lithium nickel composite oxide, carbon black such as acetylene black and ketjen black as a conductive material, and others (graphite etc. ) Powdery carbon material can be mixed. In addition to the positive electrode active material and the conductive material, a binder (binder) such as polyvinylidene fluoride (PVDF), styrene butadiene rubber (SBR), polytetrafluoroethylene (PTFE), carboxymethyl cellulose (CMC) is added. be able to. By dispersing these in a suitable dispersion medium and kneading, the composition for forming a positive electrode active material layer (hereinafter referred to as “positive electrode active material layer forming paste”) is in the form of a paste (including slurry or ink. The same shall apply hereinafter). Can be prepared.). An appropriate amount of this paste is preferably applied onto a positive electrode current collector made of aluminum or an alloy containing aluminum as a main component, and further dried and pressed, whereby a positive electrode for a lithium secondary battery can be produced.

  On the other hand, the negative electrode for a lithium secondary battery serving as a counter electrode can be produced by a method similar to the conventional one. For example, the negative electrode active material may be any material that can occlude and release lithium ions. A typical example is a powdery carbon material made of graphite or the like. As in the case of the positive electrode, the powdery material is dispersed in a suitable dispersion medium together with a suitable binder (binder) and kneaded to obtain a paste-like composition for forming a negative electrode active material layer (hereinafter referred to as “negative electrode active material”). May be referred to as “layer forming paste”). An appropriate amount of this paste is preferably applied onto a negative electrode current collector composed of copper, nickel, or an alloy thereof, and further dried and pressed, whereby a negative electrode for a lithium secondary battery can be produced.

  In the lithium secondary battery using the mixture of the solid solution compound of the present invention and the layered lithium nickel composite oxide as the positive electrode active material, a separator similar to the conventional one can be used. For example, a porous sheet (porous film) made of a polyolefin resin can be used.

Further, as the electrolyte, the same electrolyte as a non-aqueous electrolyte (typically, an electrolytic solution) conventionally used for a lithium secondary battery can be used without any particular limitation. Typically, the composition includes a supporting salt in a suitable nonaqueous solvent. Examples of the non-aqueous solvent include one or two selected from the group consisting of propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and the like. More than seeds can be used. Examples of the supporting salt include LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ). ₃ , 1 type, or 2 or more types of lithium compounds (lithium salt) selected from LiI etc. can be used.

In addition, the solid solution compound (xLi [Li _1/3 M1 _2/3 ] O _2. (1-x) LiM ₂ O ₂ ) and the layered structure lithium nickel composite oxide (LiNi _1-ab M 3 _a M ₄ ) disclosed here. _As long as the mixture with _{b 2} O ₂ ) is employed as the positive electrode active material, the shape (outer shape and size) of the lithium secondary battery to be constructed is not particularly limited. The outer package may be a thin sheet type constituted by a laminate film or the like, and the battery outer case may be a cylindrical or cuboid battery, or may be a small button shape.

  Hereinafter, the use mode of the positive electrode disclosed here will be described by taking a lithium secondary battery (here, a lithium ion battery) including a wound electrode body as an example, but the present invention is intended to be limited to such an embodiment. It is not a thing.

  As shown in FIG. 1, in the lithium secondary battery 100 according to the present embodiment, a long positive electrode sheet 10 and a long negative electrode sheet 20 are wound flatly via a long separator 40. The electrode body (winding electrode body) 80 of the form is housed in a container 50 having a shape (flat box shape) capable of housing the wound electrode body 80 together with a non-aqueous electrolyte (not shown).

  The container 50 includes a flat rectangular parallelepiped container body 52 having an open upper end, and a lid body 54 that closes the opening. As a material constituting the container 50, a metal material such as aluminum or steel is preferably used (in this embodiment, aluminum). Or the container 50 formed by shape | molding resin materials, such as polyphenylene sulfide resin (PPS) and a polyimide resin, may be sufficient. On the upper surface of the container 50 (that is, the lid 54), a positive electrode terminal 70 that is electrically connected to the positive electrode of the wound electrode body 80 and a negative electrode terminal 72 that is electrically connected to the negative electrode 20 of the electrode body 80 are provided. Yes. Inside the container 50, a flat wound electrode body 80 is accommodated together with a non-aqueous electrolyte (not shown).

The material and the member itself constituting the wound electrode body 80 having the above-described structure are a solid solution compound (xLi [Li _1/3 M1 _2/3 ] O _2. (1-x) LiM ₂ O ₂ ) and a layered structure lithium as a positive electrode active material. except employing a mixture of nickel composite oxide _{(LiNi 1-a-b M3} a M4 b O 2), it may be the same as the electrode body of the conventional lithium-ion battery is not particularly limited.

  The wound electrode body 80 according to the present embodiment is the same as the wound electrode body of a normal lithium secondary battery, and as shown in FIG. ) Sheet structure.

  The positive electrode sheet 10 has a structure in which a positive electrode active material layer 14 containing a positive electrode active material is held on both surfaces of a long sheet-like foil-shaped positive electrode current collector (hereinafter referred to as “positive electrode current collector foil”) 12. ing. However, the positive electrode active material layer 14 is not attached to one side edge (lower side edge portion in the figure) of the positive electrode sheet 10 in the width direction, and the positive electrode current collector 12 is exposed with a certain width. An active material layer non-formation part is formed.

  The positive electrode active material layer 14 can contain one kind or two or more kinds of materials that can be used as components of the positive electrode active material layer in a general lithium secondary battery, if necessary. An example of such a material is a conductive material. As the conductive material, a carbon material such as carbon powder or carbon fiber is preferably used. Alternatively, conductive metal powder such as nickel powder may be used. In addition, as a material that can be used as a component of the positive electrode active material layer, various polymer materials that can function as a binder (binder) of the above-described constituent materials are exemplified.

  Similarly to the positive electrode sheet 10, the negative electrode sheet 20 holds a negative electrode active material layer 24 containing a negative electrode active material on both sides of a long sheet-like foil-shaped negative electrode current collector (hereinafter referred to as “negative electrode current collector foil”) 22. Has a structured. However, the negative electrode active material layer 24 is not attached to one side edge (the upper side edge portion in the figure) of the negative electrode sheet 20 in the width direction, and the negative electrode active material 22 in which the negative electrode current collector 22 is exposed with a certain width. A material layer non-formation part is formed.

  The negative electrode sheet 20 can be formed by applying a negative electrode active material layer 24 mainly composed of a negative electrode active material for a lithium ion battery on a long negative electrode current collector 22. For the negative electrode current collector 22, a copper foil or other metal foil suitable for the negative electrode is preferably used. As the negative electrode active material, one or more of materials conventionally used in lithium secondary batteries can be used without any particular limitation. Preferable examples include carbon-based materials such as graphite carbon and amorphous carbon, lithium-containing transition metal oxides and transition metal nitrides.

  In producing the wound electrode body 80, the positive electrode sheet 10 and the negative electrode sheet 20 are laminated via the separator sheet 40. At this time, the positive electrode sheet 10 and the negative electrode sheet 20 are formed such that the positive electrode active material layer non-formed portion of the positive electrode sheet 10 and the negative electrode active material layer non-formed portion of the negative electrode sheet 20 protrude from both sides in the width direction of the separator sheet 40. Are overlapped slightly in the width direction. The laminated body thus stacked is wound, and then the obtained wound body is crushed from the side surface direction and ablated, whereby a flat wound electrode body 80 can be produced.

  A wound core portion 82 (that is, the positive electrode active material layer 14 of the positive electrode sheet 10, the negative electrode active material layer 24 of the negative electrode sheet 20, and the separator sheet 40) is densely arranged in the central portion of the wound electrode body 80 in the winding axis direction. Laminated portions) are formed. In addition, the electrode active material layer non-formed portions of the positive electrode sheet 10 and the negative electrode sheet 20 protrude outward from the wound core portion 82 at both ends in the winding axis direction of the wound electrode body 80. A positive electrode lead terminal 74 and a negative electrode lead terminal 76 are respectively provided on the protruding portion 84 (that is, a portion where the positive electrode active material layer 14 is not formed) 84 and the protruding portion 86 (that is, a portion where the negative electrode active material layer 24 is not formed) 86. Attached and electrically connected to the positive terminal 70 and the negative terminal 72 described above.

The wound electrode body 80 having such a configuration is accommodated in the container main body 52, and an appropriate nonaqueous electrolytic solution is disposed (injected) into the container main body 52. Then, the construction (assembly) of the lithium ion battery 100 according to the present embodiment is completed by sealing the opening of the container main body 52 by welding with the lid 54 or the like. In addition, the sealing process of the container main body 52 and the arrangement | positioning (injection) process of electrolyte solution can be performed similarly to the method currently performed by manufacture of the conventional lithium secondary battery. Thereafter, the battery is conditioned (initial charge / discharge). You may perform processes, such as degassing and a quality inspection, as needed. The lithium secondary battery 100 thus constructed includes the above-described solid solution compound (xLi [Li _1/3 M1 _2/3 ] O _2. (1-x) LiM ₂ O ₂ ) and a layered structure lithium nickel composite oxide ( the _{LiNi 1-a-b M3 a} M4 b O 2) a mixture of because it is constructed using as the positive electrode active material, may be indicative of a better cell characteristics. For example, at least one (preferably all) of low capacity deterioration even when used at a high potential (especially excellent cycle characteristics at high temperature), high initial discharge capacity and good high temperature holding characteristics. It can be fulfilled.

  In the following test examples, a lithium secondary battery (sample battery) was constructed using a mixture of the solid solution compound disclosed herein and a layered structure lithium nickel composite oxide as a positive electrode active material, and its performance was evaluated. .

<Preparation of positive electrode active material>
First, a solid solution of 0.6Li [Li _1/3 Mn _2/3 ] O ₂ and 0.4LiNi _1/3 Co _1/3 Mn _1/3 O ₂ was synthesized as a solid solution compound. Specifically, lithium hydroxide as a lithium supply source, nickel hydroxide as a nickel supply source, manganese carbonate as a manganese supply source, and cobalt hydroxide as a cobalt supply source have a predetermined molar ratio. Mix in such quantities. The mixture was fired in the atmosphere at about 900 ° C. for about 5 hours. The solid solution compound shown by 0.6Li [Li _1/3 Mn _2/3 ] O ₂ .0.4LiNi _1/3 Co _1/3 Mn _1/3 O ₂ is obtained by grinding the fired product after the firing process. Powder (average particle size 1 μm) was obtained.

  Moreover, the layered composite oxide shown in Table 1 below was synthesized as the layered structure lithium nickel composite oxide. Specifically, lithium hydroxide as a lithium supply source, nickel hydroxide as a nickel supply source, aluminum oxide as an aluminum supply source, magnesium oxide as a magnesium supply source, and hydroxide as a cobalt supply source Cobalt was mixed in an amount such that a predetermined molar ratio was obtained. The mixture was fired at about 750 ° C. for about 10 hours in the atmosphere. After the firing process, the fired product was pulverized to obtain a powder (average particle size 5 μm) composed of a layered structure lithium nickel composite oxide shown in Table 1 below.

  And the powder (A) of the said solid solution compound and the powder (B) of the said layered structure lithium nickel composite oxide are mixed so that it may become mass ratio (A / B) shown in following Table 1, and a positive electrode active material It was.

<Preparation of positive electrode>
The positive electrode active material powder obtained above (a mixture of a solid solution compound powder and a layered structure lithium nickel composite oxide powder), acetylene black as a conductive material, and polyvinylidene fluoride (PVDF) as a binder, Are weighed so that the mass ratio of the positive electrode active material, acetylene black and PVDF is 85: 10: 5 and uniformly mixed in N-methylpyrrolidone (NMP) to form a paste-like positive electrode active material layer A composition was prepared. The composition for forming a paste-like positive electrode active material layer is applied in a layer on one side of an aluminum foil (positive electrode current collector: thickness 15 μm) and dried, so that the positive electrode active material layer is formed on one side of the positive electrode current collector. The provided positive electrode sheet was obtained.

<Production of negative electrode>
N-methyl is obtained by weighing polyvinylidene fluoride (PVDF) as a binder into graphite powder as the negative electrode active material so that the mass ratio of the negative electrode active material and PVDF is 92.5: 7.5. A paste-like composition for forming a negative electrode active material layer was prepared by uniformly mixing in pyrrolidone (NMP). The paste-like negative electrode active material layer forming composition is applied to one side of a copper foil (negative electrode current collector: thickness 15 μm) in a layered form and dried, so that the negative electrode active material layer is formed on one side of the negative electrode current collector. The provided negative electrode sheet was obtained.

<Production of coin cell>
The obtained positive electrode sheet was punched into a circle having a diameter of 1.6 mm to produce a pellet-shaped positive electrode. Further, the negative electrode sheet was punched into a circle having a diameter of 1.9 mm to produce a pellet-shaped negative electrode. This positive electrode, the negative electrode, and a separator (a three-layer structure (polypropylene (PP) / polyethylene (PE) / polypropylene (PP) porous sheet having a diameter of 22 mm and a thickness of 0.02 mm) was used) The coin cell 60 (half cell for charge / discharge performance evaluation) shown in FIG. 3 having a diameter of 20 mm and a thickness of 3.2 mm (2032 type) was constructed by being incorporated in a stainless steel container together with the water electrolyte. In FIG. 3, reference numeral 61 denotes a positive electrode, reference numeral 62 denotes a negative electrode, reference numeral 63 denotes a separator impregnated with an electrolyte, reference numeral 64 denotes a gasket, reference numeral 65 denotes a container (negative electrode terminal), and reference numeral 66 denotes a lid (positive electrode terminal). ) Respectively. As the non-aqueous electrolyte, LiPF ₆ as a supporting salt was contained in a mixed solvent containing ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 3: 7 at a concentration of about 1 mol / liter. Things were used. In this way, a lithium secondary battery (test coin cell) 60 was produced.

<Charge / discharge cycle test>
The test coin cell obtained as described above was charged to 4.8 V with a constant current of 0.1 C under a temperature condition of 25 ° C., and then discharged to 2.5 V with a constant current of 0.1 C. One charge / discharge cycle was performed.

  Subsequently, the battery after one cycle charge / discharge of 0.1 C was charged at a temperature condition of 25 ° C. with a constant current and constant voltage method with a current of 1 C and a voltage of 4.3 V until the total charge time was 2 hours. Subsequently, a charge / discharge cycle of discharging to 2.5 V with a constant current of 1 C was performed 100 times continuously. Then, from the ratio of the discharge capacity at the first cycle (initial discharge capacity) and the discharge capacity at the 100th cycle, the discharge capacity retention rate after 100 cycles (“discharge capacity at the 100th cycle / discharge capacity at the first cycle ( The initial discharge capacity) ”× 100) was calculated. The results are shown in Table 1.

  As shown in Table 1 above, the test cells (samples 1 to 5) in which the layered structure Al-containing lithium nickel composite oxide was mixed with the solid solution compound were used for the test in which the layered structure Al-containing lithium nickel composite oxide was not mixed. Compared to the cells (Samples 7 and 8), the discharge capacity retention rate at 25 ° C. was clearly improved. Further, a test cell (sample 6) in which a layered structure lithium nickel composite oxide containing Mg in addition to Al was mixed was a test cell (layer 6) mixed with a layered structure lithium nickel composite oxide containing only Al ( It had almost the same performance as Samples 1-5). From this, it was confirmed that the cycle characteristics can be preferably improved by using an Al and / or Mg-containing lithium nickel composite oxide having a layered structure mixed with the solid solution compound.

  In addition, the test cell (sample 5) mixed with the Al-containing layered structure lithium nickel composite oxide containing cobalt obtained in this test example was mixed with the Al-containing layered structure lithium nickel composite oxide not containing cobalt. The test cell (samples 1 to 4) had almost the same performance. Thus, it was confirmed that an additional metal element such as Co could be included at a ratio of 20 atomic% or less (preferably 10 atomic% or less) of the entire other constituent metal elements excluding lithium.

  As mentioned above, although this invention was demonstrated by suitable embodiment, such description is not a limitation matter and of course various modifications are possible.

  Any of the lithium secondary batteries 100 disclosed herein has little charge / discharge cycle deterioration as described above. For this reason, it has the performance suitable as a battery mounted in a vehicle. Therefore, according to the present invention, as shown in FIG. 4, there is provided a vehicle 1 including the lithium secondary battery 100 disclosed herein (which may be in the form of an assembled battery in which a plurality of lithium secondary batteries are connected). The In particular, a vehicle (for example, an automobile) including the lithium secondary battery as a power source (typically, a power source of a hybrid vehicle or an electric vehicle) is provided.

DESCRIPTION OF SYMBOLS 1 Vehicle 10 Positive electrode sheet 12 Positive electrode collector 14 Positive electrode active material layer 20 Negative electrode sheet 22 Negative electrode collector 24 Negative electrode active material layer 40 Separator sheet 50 Container 52 Container body 54 Lid 60 Coin cell 70 Positive electrode terminal 72 Negative electrode terminal 74 Positive electrode lead Terminal 76 Negative electrode lead terminal 80 Winding electrode body 82 Winding core part 100 Lithium secondary battery

Claims (6)

The following general formula:
xLi [Li _1/3 M1 _2/3 ] O _2. (1-x) LiM ₂ O ₂ (1)
(Where M1 is at least one metal element having an average oxidation state of 4+, and M2 is at least one transition metal element: 0 <x <1)
A solid solution compound represented by
The following general formula:
LiNi _1-ab M3 _a M4 _b O ₂ (2)
(Here, M3 is Al and / or Mg, and M4 is at least one metal element selected from the group consisting of Co, Mn, Fe, Cu and Cr: 0.3 ≦ a ≦ 0.5 , 0 ≦ b ≦ 0.2)
And a lithium-nickel composite oxide having a layered structure represented by:   2. The lithium secondary battery according to claim 1, wherein a content ratio of the layered structure lithium nickel composite oxide is 1% by mass to 20% by mass with respect to a total mass of the layered structure lithium nickel composite oxide and the solid solution compound. Positive electrode for secondary battery.   The positive electrode for a lithium secondary battery according to claim 1 or 2, wherein M1 in the formula (1) is at least one metal element selected from the group consisting of Mn, Zr, Ti, and Sn.   The lithium secondary battery according to any one of claims 1 to 3, wherein M2 in the formula (1) is at least one transition metal element selected from the group consisting of Mn, Co, Ni, and Fe. Positive electrode.   A lithium secondary battery constructed using the positive electrode according to any one of claims 1 to 4.   A vehicle comprising the lithium secondary battery according to claim 5.

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