JP2012129102A - Lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium secondary battery containing a LiM1O-LiM2Osolid solution as a positive electrode active material and having a high capacity and excellent rate characteristics.SOLUTION: The lithium secondary battery contains a solid solution represented by the formula: xLiM1O-(1-x)LiM2O, as a positive electrode active material, wherein M1 represents at least one kind of metal element forming tetravalent cations, M2 represents at least one kind of metal element forming trivalent cations, and x represents a real number satisfying 0<x<1. A portion of M1 and/or M2 in the solid solution is substituted by at least one kind of metal element M3 selected from the group consisting of Fe, Al, and Cr.

Description

  The present invention relates to a lithium secondary battery having a positive electrode active material.

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, Li ₂ MnO ₃ —LiMO ₂ (M = Ni, Co, Mn, etc.) solid solution positive electrode materials are currently being studied. It is known that the Li ₂ MnO ₃ -LiMO ₂ solid solution positive electrode material is desorbed of oxygen when charged at 4.5 V or higher, and the electrochemical activity is improved. Further, since this solid solution positive electrode material has a high discharge potential and a high energy density can be expected, it is expected as a promising positive electrode material. Include Patent Document 1 as a prior art relating to this kind of _{Li 2 MnO} 3 -LiMO 2 solid solution positive electrode material. In addition, Patent Document 2 is given as a conventional technique related to the positive electrode active material.

JP 2010-103086 A JP 2005-197004 A

However, since the Li ₂ MnO ₃ -LiMO ₂ solid solution positive electrode material described above takes in lithium by the reduction reaction of Mn Mn ⁴⁺ → Mn ³⁺ at the time of discharge, the crystal structure is large due to the Mn ³⁺ Yarn Teller effect that takes octahedral coordination. Distortion occurs. Therefore, there has been a problem that the reduction reaction of Mn ⁴⁺ → Mn ³⁺ does not proceed easily, and the rate characteristics are insufficient (the voltage drop when a large current is passed is fast).

The present invention has been made in view of the above points, and its main purpose is a lithium secondary battery using a Li ₂ M1O ₃ -LiM2O ₂ solid solution as a positive electrode active material, and has high capacity and excellent rate characteristics. It is to provide a lithium secondary battery.

The lithium secondary battery provided by the present invention has the following general formula as a positive electrode active material:
_{xLi 2 M1O 3 - (1-} x) LiM2O 2 (1)
(Here, M1 is at least one metal element constituting a tetravalent cation, M2 is at least one metal element constituting a trivalent cation, and x is a real number satisfying 0 <x <1. is there);
The solid solution represented by these is contained.
A part of M1 and / or M2 in the solid solution is substituted with at least one metal element M3 selected from the group consisting of Fe, Al and Cr.

According to the configuration of the present invention, a part of M1 and / or M2 of the Li ₂ M1O ₃ -LiM2O ₂ solid solution is substituted with at least one metal element M3 selected from the group consisting of Fe, Al, and Cr. Therefore, compared with the conventional Li ₂ M1O ₃ -LiM2O ₂ solid solution not substituted with M3, the distortion of the crystal structure that can occur due to the insertion and removal of lithium ions is reduced, and the stable crystal structure even at high output Become. Therefore, the rate characteristic of the lithium secondary battery using this Li ₂ M1O ₃ -LiM2O ₂ solid solution as the positive electrode active material is preferably improved.

Here, M3 contained in the Li ₂ M1O ₃ -LiM2O ₂ solid solution is one or more metal elements of Fe, Al, and Cr. Among these, Fe or Al, or two types of combinations of Fe and Al are preferable, and a composition having a high content of such elements is preferable. In particular, it is preferable that M3 is Fe or that the Fe content is high (for example, M3 contains 50 mol% or more of Fe). The higher the Fe content, the better the rate characteristics of a lithium secondary battery using this solid solution as the positive electrode active material.

The M3 content in the Li ₂ M1O ₃ -LiM2O ₂ solid solution is not particularly limited. For example, the overall composition of the positive electrode active material is expressed by the following abbreviation:
LiM1M2M3 _y O ₂ (2)
It is appropriate that the value of y indicating the content of M3 is 0 <y ≦ 0.015. In the above formula (2), if the value of y is larger than 0.015, unreacted substances remain or impurities are generated during synthesis, which affects the rate characteristics. It is preferable to regulate to 0.015 or less. The lower limit value of the M3 content is not particularly limited, but if the M3 content is too small, the effect of improving the rate characteristics by M3 substitution may not be sufficiently obtained. In order to obtain the rate characteristic improving effect with certainty, the range that y can take is generally 0.001 ≦ y, preferably 0.003 ≦ y, and particularly preferably 0.005 ≦ y. is there. This reduces the distortion of the crystal structure that may occur due to the insertion and removal of lithium ions, compared to the conventional Li ₂ M1O ₃ -LiM2O ₂ solid solution not substituted with M3, and a stable crystal structure even at high output It becomes. Therefore, the rate characteristic of the lithium secondary battery using this Li ₂ M1O ₃ -LiM2O ₂ solid solution as the positive electrode active material is preferably improved.

  In a preferred embodiment of the lithium secondary battery disclosed herein, M1 in the above formula (1) contains at least one metal element selected from the group consisting of Mn, Ti, Zr and Sn. Of these, Mn or Ti, or two combinations of Mn and Ti are preferable, and a composition having a high content of such a metal element is preferable. In particular, it is preferable that M1 is Mn or that the Mn content is high (for example, M1 contains 50 mol% or more in M1). Those containing mainly Mn are particularly useful to apply the present invention because the crystal structure is greatly distorted when lithium ions are taken in and out.

In a preferred embodiment of the lithium secondary battery disclosed herein, M2 in the above formula (1) contains at least one metal element selected from the group consisting of Mn, Co and Ni. Any combination of two or more of these is preferred. In particular, it is preferable that all of Mn, Co and Ni are contained in M2, and it is more preferable that M2 is Ni _1/3 Co _1/3 Mn _1/3 . Those containing one or more metal elements of Mn, Co, and Ni are preferable in that a higher potential of the Li ₂ M1O ₃ -LiM2O ₂ solid solution can be realized. Preferably, the overall composition of the positive electrode active material is Li _1.2 Mn _(0.4-y Co _0.13 Ni _0.13) M3 _y O ₂ (where y is a real number satisfying 0 <y <1). Is).

Moreover, according to this invention, the positive electrode used for any lithium secondary battery disclosed here is provided. This positive electrode has the following general formula as a positive electrode active material:
_{xLi 2 M1O 3 - (1-} x) LiM2O 2 (1)
(Here, M1 is at least one metal element constituting a tetravalent cation, M2 is at least one metal element constituting a trivalent cation, and x is a real number satisfying 0 <x <1. is there);
Containing a solid solution represented by
Here, a part of M1 and / or M2 in the solid solution is substituted with at least one metal element M3 selected from the group consisting of Fe, Al, and Cr.

Preferably, the overall composition of the positive electrode active material has the following abbreviation:
LiM1M2M3 _y O ₂ (2)
In this case, the value of y indicating the content of M3 is 0 <y ≦ 0.015.
Also preferably, M1 in the above formula (1) contains at least one metal element selected from the group consisting of Mn, Ti, Zr and Sn.
More preferably, M2 in the above formula (1) contains at least one metal element selected from the group consisting of Mn, Co and Ni.

In addition, according to the present invention, a positive electrode active material used for any of the lithium secondary batteries disclosed herein is provided. This positive electrode active material is
The following general formula:
_{xLi 2 M1O 3 - (1-} x) LiM2O 2 (1)
(Here, M1 is at least one metal element constituting a tetravalent cation, M2 is at least one metal element constituting a trivalent cation, and x is a real number satisfying 0 <x <1. is there);
Containing a solid solution represented by
Here, a part of M1 and / or M2 in the solid solution is substituted with at least one metal element M3 selected from the group consisting of Fe, Al, and Cr.

Preferably, the overall composition of the positive electrode active material has the following abbreviation:
LiM1M2M3 _y O ₂ (2)
In this case, the value of y indicating the content of M3 is 0 <y ≦ 0.015.
Also preferably, M1 in the above formula (1) contains at least one metal element selected from the group consisting of Mn, Ti, Zr and Sn.
More preferably, M2 in the above formula (1) contains at least one metal element selected from the group consisting of Mn, Co and Ni.

A lithium secondary battery (typically a lithium ion battery) having a positive electrode active material containing any one of the Li ₂ M1O ₃ -LiM2O ₂ -based solid solutions disclosed herein as a positive electrode has a high capacity and a high power cycle. Since it is less deteriorated, it has performance suitable for 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 nonaqueous electrolyte secondary battery which concerns on one Embodiment of this invention. It is a figure which shows typically the wound electrode body which concerns on one Embodiment of this invention. 3 is a diagram showing an X-ray diffraction pattern according to Example 1. FIG. 6 is a diagram showing an X-ray diffraction pattern according to Example 2. FIG. 6 is a diagram showing an X-ray diffraction pattern according to Example 3. FIG. It is a figure which shows the X-ray-diffraction pattern which concerns on Example 4. FIG. It is a figure which shows the X-ray-diffraction pattern which concerns on a comparative example. It is a figure which shows typically the coin cell for a test. It is a graph which shows the relationship between Fe content and 1C discharge capacity. It is a graph which shows the relationship between Fe content and a 20C / 1C capacity | capacitance ratio. 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 lithium secondary battery of the present embodiment has the following general formula as a positive electrode active material:
_{xLi 2 M1O 3 - (1-} x) LiM2O 2 (1)
(Here, M1 is at least one metal element constituting a tetravalent cation, M2 is at least one metal element constituting a trivalent cation, and x is a real number satisfying 0 <x <1. is there);
The solid solution represented by these is contained.
A part of M1 and / or M2 in the solid solution is substituted with at least one metal element M3 selected from the group consisting of Fe, Al and Cr.

<Li ₂ M1O ₃ >
_Li 2 M1O ₃ constituting one end component of _{Li 2 M1O} 3 -LiM2O 2 based solid solution used in the lithium secondary battery of the present embodiment is an oxide having a low layered structure with an electrochemically active. M1 in the above formula (1) is at least one metal element that can form a tetravalent cation, preferably among manganese (Mn), titanium (Ti), zirconium (Zr), and tin (Sn). Or one or more metal elements. Of these, Mn or Ti, or two combinations of Mn and Ti are preferable, and a composition having a high content of such a metal element is preferable. In particular, it is preferable that M1 is Mn or that the Mn content is high (for example, M1 contains 50 mol% or more in M1). It is particularly useful to apply this configuration to those mainly containing Mn because the distortion of the crystal structure accompanying the taking in and out of lithium ions is large.

<LiM2O _2>
LiM2O ₂ constituting the other end component of _{Li 2 M1O} 3 -LiM2O 2 based solid solution used in the lithium secondary battery of the present embodiment is an oxide having an electrochemically more active layered structure. M2 in the formula (1) is at least one metal element that can form a trivalent cation, and preferably one or two of manganese (Mn), cobalt (Co), and nickel (Ni) These are the above metal elements. Any combination of two or more of these is preferred. In particular, it is preferable that Mn, Co, and Ni are all contained in M2, and it is particularly preferable that M2 is Ni _1/3 Co _1/3 Mn _1/3 . Those containing one or more metal elements of Mn, Co, and Ni are preferable in that a higher potential of the Li ₂ M1O ₃ -LiM2O ₂ solid solution can be realized.

In _{Li 2 M1O} 3 -LiM2O 2 based solid solution used in the lithium secondary battery of the present _embodiment, the ratio for solid solution and Li 2 M1O ₃ and LiM2O _{2 is,} Li 2 M1O ₃ and LiM2O ₂ and the composition of the inseparable As long as an object can be formed, any real number may be taken as long as it is within the range of 0 <x <1. That is, the proportion of Li ₂ M1O ₃ and LiM ₂ O ₂ in solid solution is appropriately selected according to the purpose of this configuration, but preferably 0.3 ≦ x ≦ 0.8, more preferably 0.4 ≦ x ≦ 0.7, more preferably 0.45 ≦ x ≦ 0.55 (particularly preferably 0.5). If the value of x is too small, it is not preferable because the effect of increasing the potential by dissolving Li ₂ M ₁ O ₃ in LiM ₂ O ₂ becomes insufficient. On the other hand, if the value of x is larger than 0.8, the characteristics of Li ₂ M1O ₃ are lost and the discharge capacity is lowered, which is not preferable.

In the Li ₂ M1O ₃ -LiM2O ₂ solid solution used in the lithium secondary battery of the present embodiment, a part of M1 and / or M2 in the solid solution is one or more of Fe, Al, and Cr. The metal element is substituted. Here, M3 contained in the Li ₂ M1O ₃ -LiM2O ₂ solid solution is one or more metal elements of Fe, Al, and Cr. Among these, Fe or Al, or two types of combinations of Fe and Al are preferable, and a composition having a high content of such elements is preferable. In particular, it is preferable that M3 is Fe or that the Fe content is high (for example, M3 contains 50 mol% or more of Fe).

Thus, by replacing a part of M1 and / or M2 in the Li ₂ M1O ₃ -LiM2O ₂ solid solution with at least one metal element M3 selected from the group consisting of Fe, Al and Cr, M3 Compared with a conventional Li ₂ M1O ₃ -LiM2O ₂ solid solution not substituted with, the distortion of the crystal structure that can be caused by the insertion and removal of lithium ions is reduced, and a stable crystal structure is obtained even at high output. Therefore, the rate characteristic of the lithium secondary battery using this Li ₂ M1O ₃ -LiM2O ₂ solid solution as the positive electrode active material is preferably improved.

The M3 content in the Li ₂ M1O ₃ -LiM2O ₂ solid solution used in the lithium secondary battery of the present embodiment is not particularly limited. For example, the overall composition of the positive electrode active material is represented by the following abbreviation:
LiM1M2M3 _y O ₂ (2)
It is appropriate that the value of y indicating the content of M3 is 0 <y ≦ 0.015. In the above formula (2), if the value of y is too larger than 0.015, unreacted substances remain or impurities are generated during synthesis, which affects the rate characteristics. For this reason, the value of y is preferably regulated to 0.015 or less. The lower limit value of the M3 content is not particularly limited, but if the M3 content is too small, the effect of improving the rate characteristics by M3 substitution may not be sufficiently obtained. In order to obtain the rate characteristic improving effect with certainty, the range that y can take is generally 0.001 ≦ y, preferably 0.003 ≦ y, and particularly preferably 0.005 ≦ y. is there. This reduces the distortion of the crystal structure that can occur due to the insertion and removal of lithium ions, compared to Li ₂ M1O ₃ -LiM2O ₂ solid solutions that are not substituted with M3 or have a M3 content greater than 0.015. However, a stable crystal structure is obtained even at high output. Therefore, the rate characteristic of the lithium secondary battery using this Li ₂ M1O ₃ -LiM2O ₂ solid solution as the positive electrode active material is preferably improved.

Incidentally, _{Li 2 M1O} 3 -LiM2O 2 based solid solution used in the lithium secondary battery of the present embodiment is preferably a granular shape, the average particle diameter, in 0.1Myuemu～50myuemu (particularly 1 m to 10 m) Preferably there is. Here, the average particle diameter is a volume-based median (D50) diameter. If the average particle size is too small or too large, it may be difficult to produce the positive electrode. Further, BET specific surface area of the _{Li 2 M1O} 3 -LiM2O 2 based solid solution used in the lithium secondary battery of this ^embodiment, in 1m ² / g~20m 2 / g (especially ^{2m 2} / ^g~10m 2 / g) Preferably there is. If the BET specific surface area is too small or too large, it may be difficult to produce the positive electrode.

The Li ₂ M1O ₃ -LiM2O ₂ solid solution used in the lithium secondary battery of this embodiment can be synthesized by a solid phase method or a liquid phase method. Specifically, when the solid solution is synthesized by a liquid phase method, the solid solution can be manufactured through a raw material mixed slurry preparation step, a heating step, and a firing step. Hereinafter, each process will be described in detail.

<Raw material mixed slurry preparation process>
In the raw material mixed slurry preparation step, raw materials (Li supply source, M1 supply source, M2 supply source, M3 supply source) for configuring a solid solution appropriately selected according to the constituent elements of the Li ₂ M1O ₃ -LiM2O ₂ -based solid solution ) Is mixed with a predetermined solvent to prepare a raw material mixed slurry.

As the raw material, one or more compounds including at least a Li supply source, an M1 supply source, an M2 supply source, and an M3 supply source can be appropriately selected and used. The Li supply source, the M1 supply source, the M2 supply source, and the M3 supply source are not particularly limited as long as the target Li ₂ M1O ₃ -LiM2O ₂ solid solution can be formed by final firing. For example, various salts (for example, acetate), hydroxides, oxides, and the like containing these as constituent elements can be selected. These may be used alone or in combination of two or more.

  Particularly preferred examples include lithium acetate, lithium carbonate, lithium hydroxide, etc. as a Li supply source, manganese acetate, manganese carbonate, manganese oxide, manganese nitrate, manganese hydroxide, manganese oxyhydroxide, etc. as a Mn supply source, Co supply Cobalt acetate, cobalt carbonate, cobalt oxide, cobalt sulfate, cobalt nitrate, cobalt hydroxide, cobalt oxyhydroxide, etc. as sources, nickel acetate, nickel carbonate, nickel oxide, nickel nitrate, nickel hydroxide, oxy as sources of Ni And nickel hydroxide.

  In addition, titanium acetate, titanium oxide, titanium hydroxide, titanium ethoxide, titanium chloride, etc. as Ti supply source, zirconium acetate, zirconium oxide, zirconium hydroxide, etc. as Zr supply source, tin acetate, oxidation as Sn supply source Tin, tin hydroxide, etc., iron acetate, iron carbonate, iron oxide, etc. as Fe supply source, aluminum acetate, aluminum carbonate, aluminum oxide, etc. as Al supply source, chromium acetate, chromium carbonate, chromium oxide as Cr supply source Etc. may be selected.

  The solvent used for the raw material mixed slurry may be any solvent that can uniformly dissolve or disperse the raw material. For example, water or a mixed solvent mainly composed of water is preferably used. As a solvent component other than water constituting such a mixed solvent, one or more organic solvents (lower alcohol, lower ketone, etc.) that can be uniformly mixed with water can be appropriately selected and used. For example, it is preferable to use an aqueous solvent in which 80% by mass or more (more preferably 90% by mass or more, more preferably 95% by mass or more) of the aqueous solvent is water. A particularly preferred example is an aqueous solvent substantially consisting of water. Since the boiling point of water is about 100 ° C., it is possible to easily heat the raw material mixture slurry to a predetermined temperature range while suppressing the evaporation of excess solvent.

  A starting material mixture slurry is prepared by weighing starting materials to a predetermined composition ratio and mixing them in the solvent. When preparing the raw material mixed slurry, stirring may be performed as necessary. The stirring operation can be performed using an appropriate stirring means such as a magnetic stirrer. By this stirring, the raw material mixed slurry can be prepared in a short time. In the raw material mixed slurry, the raw material may be completely dissolved, or a part or all of the raw material may be dispersed in an undissolved state. Moreover, additives, such as glycolic acid and carboxylic acid, can also be used as needed. These additives act as particle growth inhibitors.

<Heating process>
In the heating step, the precursor is obtained by heating the prepared raw material mixed slurry to volatilize the solvent. The means for heating the raw material mixed slurry is not particularly limited, and any means such as an oil bath can be adopted. Although heating temperature changes also with the solvent to be used, when using water as a solvent, for example, it is necessary to heat at the temperature which volatilization of water fully advances, and usually 70 degreeC or more (for example, 70-90 degreeC, The temperature is preferably about 75 ° C to 85 ° C, particularly preferably about 80 ° C. The upper limit of the heating temperature may be a temperature lower than the boiling point of the solvent used. The heating time may be a time until the starting material sufficiently diffuses or permeates through the liquid phase and the production of the precursor sufficiently proceeds, and is usually about 5 to 48 hours, preferably 10 to 10 hours. About 24 hours.

<Baking process>
In the firing step, the obtained precursor is fired at 600 ° C to 1000 ° C. By this firing, the target Li ₂ M1O ₃ -LiM2O ₂ solid solution can be synthesized from the precursor. The firing temperature is not particularly limited as long as it is a temperature capable of synthesizing the solid solution. However, in order to sufficiently advance the reaction, the firing temperature is required to be 600 ° C. or higher. If the temperature exceeds 1000 ° C., the particles grow and the particle size becomes too large, which is not preferable. The firing temperature is usually suitably 600 to 1000 ° C, preferably 700 to 950 ° C, more preferably 800 to 900 ° C. The firing time may be a time until each component constituting the precursor reacts uniformly, and is usually 2 to 24 hours. The firing means is not particularly limited, and any means such as an electric heating furnace can be adopted. The firing atmosphere is not particularly limited, and may be, for example, the air or an oxygen gas atmosphere richer in oxygen than the air. Alternatively, it can be fired in an inert gas atmosphere such as Ar gas as necessary. Preferably, it is in the atmosphere or an oxygen gas atmosphere richer in oxygen than the atmosphere.

If necessary, the firing can be performed in a plurality of times. That is, in performing the above-mentioned firing, first, pre-baking in a relatively low temperature range (for example, less than 600 ° C., for example, 400 ° C. or more and less than 600 ° C.) The main baking is performed in a region (for example, 600 ° C. to 1000 ° C.). As described above, when the precursor is fired in a higher temperature range (for example, 600 ° C. to 1000 ° C.) from the beginning by performing preliminary firing in a higher temperature range after first performing preliminary firing in a lower temperature range. In comparison, the homogeneity of the finally obtained Li ₂ M1O ₃ -LiM2O ₂ solid solution can be enhanced. The operation of crushing the calcined product and firing it again may be repeated before the main firing.

The Li ₂ M1O ₃ -LiM2O ₂ solid solution obtained by firing as described above is preferably cooled, pulverized by milling or the like, and appropriately classified to obtain an average particle size of 0.1 μm to 50 μm (particularly 1 μm). A solid solution in the form of fine particles of about 10 μm to 10 μm can be obtained.

The Li ₂ M1O ₃ —LiM2O ₂ solid solution powder thus obtained can be used as it is as the positive electrode active material. For example, the Li ₂ M1O ₃ -LiM2O ₂ solid solution powder can be preferably used as a constituent element of a lithium secondary battery of various forms or a constituent element (positive electrode active material) of an electrode incorporated in the lithium secondary battery. . In this case, a lithium secondary battery can be constructed by adopting a process similar to the conventional one except that the Li ₂ M1O ₃ -LiM2O ₂ solid solution powder disclosed herein is used as the positive electrode active material.

For example, a positive electrode active material containing the Li ₂ M1O ₃ -LiM2O ₂ solid solution powder disclosed here is mixed with carbon black such as acetylene black and ketjen black and other (graphite etc.) powdered carbon materials as a conductive material can do. 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), or 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 applied onto a positive electrode current collector preferably made of aluminum or an aluminum-based alloy, and then dried and pressed to produce a positive electrode for a nonaqueous electrolyte secondary battery. it can.

  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. 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 Li ₂ M1O ₃ -LiM2O ₂ -based solid solution powder disclosed here as the positive electrode active material, the same separator as 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, a non-aqueous electrolyte (typically, an electrolytic solution) can be used. 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.

Furthermore, the extent employed a Li ₂ M1O ₃ -LiM2O ₂ solid solution powder disclosed herein as a positive electrode active material, there is no particular restriction on the shape of the lithium secondary battery to be constructed (outer and size). 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, although the usage mode of the positive electrode disclosed here will be described using a lithium secondary battery including a wound electrode body as an example, it is not intended to limit the present invention to such an embodiment.

  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 configuration are the same as the electrode body of the conventional lithium secondary battery except that the Li ₂ M1O ₃ -LiM2O ₂ solid solution disclosed here is adopted as the positive electrode active material. The same may be applied and there is no particular limitation. As shown in FIG. 2, the wound electrode body 80 according to the present embodiment has a long (strip-shaped) sheet structure in a stage before assembling the wound electrode body 80.

  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 12. However, the positive electrode active material layer 14 is not attached to one side edge (the upper side edge portion in the figure) of the positive electrode sheet 10 in the width direction, and the positive electrode active material 12 in which the positive electrode current collector 12 is exposed with a certain width. A material layer non-formation part is formed. Similarly to the positive electrode sheet 10, the negative electrode sheet 20 has a structure in which a negative electrode active material layer 24 containing a negative electrode active material is held on both surfaces of a long sheet-like foil-shaped negative electrode current collector 22. However, the negative electrode active material layer 24 is not attached to one side edge (the lower side edge portion in the figure) of the negative electrode sheet 20 in the width direction, and the negative electrode current collector 22 is exposed with a certain width. An active material layer non-formation part is formed.

  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. The construction (assembly) of the lithium secondary battery 100 according to this embodiment is completed by sealing the opening of the container body 52 by welding or the like with the lid 54. 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.

In the following test examples, a lithium secondary battery (sample battery) was constructed using the Li ₂ M1O ₃ -LiM2O ₂ solid solution powder disclosed herein as a positive electrode active material, and its performance was evaluated.

[Synthesis of Li ₂ M1O ₃ -LiM2O ₂ solid solution]
In this performance evaluation test, a solid solution represented by 0.5Li ₂ M1O ₃ -0.5LiM2O ₂ was synthesized by substituting a part of the transition metal in the solid solution with M3. Specifically, the overall composition is Li _1.2 [Mn _0.54-y M3 _y Co _0.13 Ni _0.13 ] O ₂ (M3 = Fe, Ar, Cr, y = 0, 0.005, 0 .01, 0.015, 0.02) were synthesized.

<Example 1>
In this example, a solid solution sample whose total composition is represented by Li _1.2 [Mn _0.535 Fe _0.005 Co _0.13 Ni _0.13 ] O ₂ (M3 = Fe, y = 0.005) was synthesized. did. Specifically, lithium acetate, manganese acetate, cobalt acetate, nickel acetate, and iron acetate are weighed to achieve the above composition ratio, dissolved and mixed in water, and an appropriate amount of glycolic acid is added to prepare a raw material mixed slurry. did. This raw material mixed slurry was heated at about 80 ° C. for 24 hours to evaporate water to obtain a precursor. The precursor was calcined at 500 ° C. in the atmosphere, and this was once pulverized by a ball mill, and further calcined at 900 ° C. The fired body was pulverized to a suitable particle size with a ball mill to obtain a Li _1.2 [Mn _0.535 Fe _0.005 Co _0.13 Ni _0.13 ] O ₂ solid solution powder. When the obtained solid solution powder was analyzed by X-ray diffraction measurement, as shown in FIG. 3, it had a crystal structure belonging to the space group R-3m and a superlattice structure in the vicinity of 2θ = 20 to 23 °. It was confirmed that there was a peculiar peak in the Li ₂ M1O ₃ -LiM2O ₂ solid solution.

<Example 2>
In this example, a solid solution sample whose total composition is Li _1.2 [Mn _0.53 Fe _0.01 Co _0.13 Ni _0.13 ] O ₂ (M3 = Fe, y = 0.01) was synthesized. did. The synthesis conditions were the same as in Example 1 except that the blending ratio of each raw material was changed so as to achieve the above composition ratio. When the obtained solid solution powder was analyzed by X-ray diffraction measurement, as shown in FIG. 4, it had a crystal structure belonging to the space group R-3m and a superlattice structure in the vicinity of 2θ = 20 to 23 °. It was confirmed that there was a peculiar peak in the Li ₂ M1O ₃ -LiM2O ₂ solid solution.

<Example 3>
In this example, a solid solution sample whose total composition is represented by Li _1.2 [Mn _0.525 Fe _0.015 Co _0.13 Ni _0.13 ] O ₂ (M3 = Fe, y = 0.015) was synthesized. did. The synthesis conditions were the same as in Example 1 except that the blending ratio of each raw material was changed so as to achieve the above composition ratio. When the obtained solid solution powder was analyzed by X-ray diffraction measurement, as shown in FIG. 5, it had a crystal structure belonging to the space group R-3m and a superlattice structure in the vicinity of 2θ = 20 to 23 °. It was confirmed that there was a peculiar peak in the Li ₂ M1O ₃ -LiM2O ₂ solid solution.

<Example 4>
In this example, a solid solution sample whose total composition is represented by Li _1.2 [Mn _0.52 Fe _0.02 Co _0.13 Ni _0.13 ] O ₂ (M3 = Fe, y = 0.02) was synthesized. did. The synthesis conditions were the same as in Example 1 except that the blending ratio of each raw material was changed so as to achieve the above composition ratio. When the obtained solid solution powder was analyzed by X-ray diffraction measurement, as shown in FIG. 6, it had a crystal structure belonging to the space group R-3m and a superlattice structure in the vicinity of 2θ = 20-23 °. It was confirmed that there was a peculiar peak in the Li ₂ M1O ₃ -LiM2O ₂ solid solution.

<Example 5>
In this example, a solid solution sample whose total composition is represented by Li _1.2 [Mn _0.535 Al _0.005 Co _0.13 Ni _0.13 ] O ₂ (M3 = Al, x = 0.005) was synthesized. did. The synthesis conditions were the same as in Example 1 except that aluminum acetate (Al supply source) was used instead of iron acetate, and the blending ratio of each raw material was adjusted to the above composition ratio. The obtained solid solution powder was analyzed by X-ray diffraction measurement. As a result, Li ₂ M1O ₃ -LiM2O ₂ having a crystal structure belonging to the space group R-3m and showing a superlattice structure in the vicinity of 2θ = 20 to 23 °. It was confirmed that there was a peak peculiar to the system solid solution.

<Example 6>
In this example, a solid solution sample is synthesized whose overall composition is represented by Li _1.2 [Mn _0.535 Cr _0.005 Co _0.13 Ni _0.13 ] O ₂ (M3 = Cr, x = 0.005). did. The synthesis conditions were the same as in Example 1 except that chromium acetate (Cr supply source) was used instead of iron acetate, and the blending ratio of each raw material was adjusted to the above composition ratio. The obtained solid solution powder was analyzed by X-ray diffraction measurement. As a result, Li ₂ M1O ₃ -LiM2O ₂ having a crystal structure belonging to the space group R-3m and showing a superlattice structure in the vicinity of 2θ = 20 to 23 °. It was confirmed that there was a peak peculiar to the system solid solution.

<Comparative example>
In this example, for comparison, a solid solution sample not synthesized with M3 (Fe, Al, and Cr) was synthesized. Specifically, a solid solution sample whose total composition was represented by Li _1.2 [Mn _0.54 Co _0.13 Ni _0.13 ] O ₂ (x = 0) was synthesized. The synthesis conditions were the same as in Example 1 except that the blending ratio of each raw material was changed so as to achieve the above composition ratio. When the obtained solid solution powder was analyzed by X-ray diffraction measurement, as shown in FIG. 7, it had a crystal structure belonging to the space group R-3m and a superlattice structure in the vicinity of 2θ = 20 to 23 °. It was confirmed that there was a peculiar peak in the Li ₂ M1O ₃ -LiM2O ₂ solid solution.

[Preparation of positive electrode sheet]
In each of the Li ₂ M1O ₃ -LiM2O ₂ solid solution powders of Examples 1 to 6 and Comparative Example obtained above, acetylene black as a conductive material and polyvinylidene fluoride (PVDF) as a binder, Were weighed so that the mass ratio was 85: 10: 5 and mixed uniformly in N-methylpyrrolidone (NMP) to prepare a paste-like composition for forming a positive electrode active material layer. 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.

[Preparation of negative electrode sheet]
A composition for forming a paste-like negative electrode active material layer is prepared by weighing SBR as a binder to natural graphite powder as a negative electrode active material so that the mass ratio thereof is 98: 2 and uniformly mixing in water. A product was prepared. The paste-like negative electrode active material layer forming composition is applied in a layer form on one side of a copper foil (negative electrode current collector: thickness 10 μm) 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 16 mm to produce a pellet-shaped positive electrode. This positive electrode (working electrode), metallic lithium (a metal Li foil having a diameter of 19 mm and a thickness of 0.02 mm) as a negative electrode (counter electrode), and a separator (a three-layer structure having a diameter of 19 mm and a thickness of 0.02 mm) (Polypropylene (PP) / polyethylene (PE) / polypropylene (PP) porous sheet) was incorporated into a stainless steel container together with a non-aqueous electrolyte, and the diameter was 20 mm and the thickness was 3.2 mm (2032). The coin cell 60 (half cell for charge / discharge performance evaluation) shown in FIG. In FIG. 8, 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. In addition, as a non-aqueous electrolyte, LiPF ₆ as a supporting salt is approximately mixed with a mixed solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 3: 4: 4. The one contained at a concentration of 1 mol / liter was used. In this way, a lithium secondary battery (test coin cell) 60 was produced.

[Charge / discharge test]
Each test coin cell obtained as described above was charged at a constant current of 1/3 C (50 mA / g) under a temperature condition of 25 ° C. until the voltage between terminals reached 4.8V. The battery after the CC charge was discharged at a constant current of 1/3 C until the voltage between the terminals became 2.5V, and the first cycle (first time) charge / discharge was performed. Next, each battery after charge and discharge in the first cycle was charged with a constant current of 1/3 C under a temperature condition of 25 ° C. until the voltage between terminals reached 4.3 V. The battery after the CC charge was discharged at a constant current of 1/3 C until the voltage between the terminals became 2.5 V, and the second cycle charge / discharge was performed. And the discharge capacity at that time was measured. Further, the charge rate and discharge rate in the second cycle were changed to 1C and 20C, respectively, and the discharge capacity at each rate was measured. Then, from the ratio of the discharge capacity at the discharge rate 1C and the discharge capacity at the discharge rate 20C, the 20C / 1C capacity ratio = [discharge capacity at the discharge rate 20C / discharge capacity at the discharge rate 1C]. X100 was calculated. The results are shown in Table 1, FIG. 9 and FIG. FIG. 9 is a graph showing the relationship between Fe content and 1C discharge capacity (mAh / g), and FIG. 10 is a graph showing the relationship between Fe content and 20C / 1C capacity ratio.

  As is clear from FIGS. 9 and 10 and Table 1, the battery according to the comparative example had a lower 1C discharge capacity than the batteries according to Examples 1 to 3. Further, the potential drop when a large current was passed was no longer so that the 20C / 1C capacity ratio remained at a low value. On the other hand, since the batteries according to Examples 1 to 3 partially substituted Mn with Fe, the 1C discharge capacity was higher than that of the battery according to the comparative example, and the discharge rate was increased to 20C. The 20C / 1C capacity ratio at that time was also good, showing an extremely high value of 64% or more.

  In the case of the battery used here, by setting the Fe content to 0 <y ≦ 0.015, a high 20C / 1C capacity ratio of 64.3% or more can be realized. In particular, the Fe content is set to 0.01. By doing so, an extremely high 20C / 1C capacity ratio of 64.6% or more was realized. From the viewpoint of improving rate characteristics, the Fe content is suitably 0 <y ≦ 0.015, preferably 0.005 ≦ y ≦ 0.015, and more preferably 0.008 ≦ y ≦ 0. .012, particularly preferably y = 0.01. In addition, in the case of the battery tested here, by setting the Fe content to 0.015 or less, a high 1C discharge capacity of 157 mAh / g or more can be realized, and in particular by making the Fe content 0.005 or less. 1C discharge capacity of 163 mAh / g or more was achieved. From the viewpoint of increasing the capacity, the Fe content is suitably 0 <y ≦ 0.015, preferably 0 <y ≦ 0.01, and particularly preferably 0 <y ≦ 0.005.

  In addition, the batteries according to Examples 5 and 6 substituted with Al or Cr instead of Fe had substantially the same performance as the batteries according to Examples 1 to 3 substituted with Fe. From this, it was confirmed that the same effect as the substitution with Fe can be obtained by substituting with Al or Cr. In the case of the battery tested here, the batteries according to Examples 5 and 6 substituted with Al or Cr had a higher 1C discharge capacity than the battery according to Example 1 substituted with Fe. From the viewpoint of increasing the capacity, M3 contained in the solid solution is preferably Al or Cr, and particularly preferably M3 is Al. In addition, the batteries according to Examples 1 and 5 replaced with Fe or Al had a higher 20C / 1C capacity ratio than the battery according to Example 6 replaced with Cr. From the viewpoint of improving the rate characteristics, M3 contained in the solid solution is preferably Fe or Al, and particularly preferably M3 is Fe. Furthermore, from the viewpoint of achieving both rate characteristics and high capacity, M3 contained in the solid solution is preferably Fe or Al, and particularly preferably M3 is Al.

From the above results, according to the present example, a part of M1 and / or M2 in the Li ₂ M1O ₃ -LiM2O ₂ solid solution is at least one metal element M3 selected from the group consisting of Fe, Al, and Cr. Thus, a lithium secondary battery having a high 1C discharge capacity and a high 20C / 1C capacity ratio could be constructed. Therefore, according to this configuration, it is possible to provide a lithium secondary battery having high capacity and excellent rate characteristics.

  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.

  Since any of the lithium secondary batteries 100 disclosed herein has a high capacity and a small capacity drop at the time of high output as described above, the lithium secondary battery 100 has performance suitable as a battery mounted on a vehicle. Therefore, according to the present invention, as shown in FIG. 11, there is provided a vehicle 1 including the lithium secondary battery 100 disclosed herein (which may be in the form of an assembled battery to 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 (9)

A lithium secondary battery,
As a positive electrode active material, the following general formula:
_{xLi 2 M1O 3 - (1-} x) LiM2O 2 (1)
(Here, M1 is at least one metal element constituting a tetravalent cation, M2 is at least one metal element constituting a trivalent cation, and x is a real number satisfying 0 <x <1. is there);
Containing a solid solution represented by
Here, a part of M1 and / or M2 in the solid solution is substituted with at least one metal element M3 selected from the group consisting of Fe, Al, and Cr. . The overall composition of the positive electrode active material is represented by the following abbreviations:
LiM1M2M3 _y O ₂ (2)
The lithium secondary battery according to claim 1, wherein a value of y indicating a content of M3 is represented by 0 <y ≦ 0.015.   The lithium secondary battery according to claim 2, wherein a value of y in the formula (2) is 0.005 ≦ y.   The lithium secondary battery according to claim 2 or 3, wherein a value of y in the formula (2) is y≤0.01.   The lithium secondary battery according to any one of claims 1 to 4, wherein M1 in the formula (1) includes at least one metal element selected from the group consisting of Mn, Ti, Zr, and Sn.   The lithium secondary battery according to any one of claims 1 to 5, wherein M2 in the formula (1) includes at least one metal element selected from the group consisting of Mn, Co, and Ni. The overall composition of the positive electrode active material is Li _1.2 Mn _(0.4-y) Co _0.13 Ni _0.13 M3 _y O ₂ (where y is a real number satisfying 0 <y <1). The lithium secondary battery as described in any one of Claims 1-6 shown. A positive electrode for a lithium secondary battery,
As a positive electrode active material, the following general formula:
_{xLi 2 M1O 3 - (1-} x) LiM2O 2 (1)
(Here, M1 is at least one metal element constituting a tetravalent cation, M2 is at least one metal element constituting a trivalent cation, and x is a real number satisfying 0 <x <1. is there);
Containing a solid solution represented by
Here, a part of M1 and / or M2 in the solid solution is substituted with at least one metal element M3 selected from the group consisting of Fe, Al, and Cr. Positive electrode. The following general formula:
_{xLi 2 M1O 3 - (1-} x) LiM2O 2 (1)
(Here, M1 is at least one metal element constituting a tetravalent cation, M2 is at least one metal element constituting a trivalent cation, and x is a real number satisfying 0 <x <1. is there);
Containing a solid solution represented by
Here, a part of M1 and / or M2 in the solid solution is substituted with at least one metal element M3 selected from the group consisting of Fe, Al, and Cr. Positive electrode active material.

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