JP2002158008A - Nonaqueous secondary cell positive electrode activator, and nonaqueous secondary cell using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous secondary cell positive electrode activator with high voltage enabled to restrain a thermal decomposition of an electrolyte (liquid electrolyte). SOLUTION: The nonaqueous secondary cell positive electrode activator composed of a spinel type lithium nickel manganese complex oxide, operating at 4.5 V or more against the Li voltage standard, is expressed by the formula (1); Li(Lix+x'Mez+z'Niy-x-zMn2-y-x'-z')O4. (In the formula, Me represents at least one element chosen from Ti, Cr, Fe, Co, Cu, Zn, Al, and B, and x, x', y, z, z' are 0<=x<=0.10, 0<=x'<=0.10, 0.01<=y<=1.00, 0<=z<=0.10, 0<=z'<=0.10).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positive electrode active material for a non-aqueous secondary battery and a positive electrode for a non-aqueous secondary battery using the same, and more particularly, to a spinel type crystal having an operating voltage of 4.5 V or more. The present invention relates to a positive electrode active material for a non-aqueous secondary battery having a structure, and a positive electrode for a non-aqueous secondary battery having a high energy density and excellent thermal stability using the same.

[0002]

2. Description of the Related Art In recent years, with the development of portable electronic devices such as mobile phones and notebook computers and the practical use of electric vehicles, secondary batteries of small size, light weight and high capacity have been required. Was. At present, a lithium ion secondary battery using LiCoO ₂ for the positive electrode and a carbon-based material as the negative electrode active material has been commercialized as a high-capacity secondary battery that meets this demand.

[0003] The above-mentioned lithium ion secondary battery has an energy
-High density, small size and light weight
Is very promising as a power source for portable electronic devices.
You. And, with the cathode material of this lithium ion secondary battery,
LiCoO used as _TwoIs easy to manufacture
Lithium ion secondary battery
Non-aqueous secondary batteries including secondary batteries, suitable positive electrode active material
It has been heavily used.

[0004] However, LiCoO ₂ is produced from a rare metal, cobalt (Co), as a raw material.
It is expected that resource shortages will become serious in the future. In addition, since the price of cobalt itself is high and the price fluctuates greatly, it is desired to develop a cathode active material that is inexpensive and has a stable supply.

Therefore, a positive electrode active material for a non-aqueous secondary battery and
And LiCoO_TwoHas a spinel-type crystal structure
Lithium manganese oxide-based materials have attracted attention.
The spinel-type lithium manganese oxide has L
i_TwoMn_FourO₉, Li_FourMn _FiveO₁₂, LiMn_TwoO_FourWhat
And among them, LiMn_TwoO_FourIs Li
Charge / discharge in the 4V region with respect to the potential of
Therefore, research has been actively conducted (Japanese Patent Laid-Open No. 6-768).
No. 24, JP-A-7-73883, JP-A-7-83
No. 230802, Japanese Unexamined Patent Publication No. 7-245106.
Etc.)

In order to increase the energy density of a battery, one method is to use a positive electrode active material having a high potential, and a high voltage of 300 V or more is required as a power supply for an electric vehicle. However, when LiCoO ₂ is used as the positive electrode active material, the operating voltage is about 4.2 V, so that the number of connected batteries increases. Therefore, it is necessary to use a positive electrode active material having a higher voltage than LiCoO _2. However, since the operating voltage of the spinel-type lithium manganese oxide as described above is 4 V or less, the capacity is higher than when LiCoO ₂ is used. Is small, and in order to obtain a high voltage of 300 V, the number of connected batteries is even greater than when LiCoO ₂ is used. Further, since it is desirable negative electrode active material is also a high capacity, metal oxides higher capacity can be expected, but may considered to use a metal nitride or a low-temperature sintered carbon material as a negative electrode active material, they LiCoO ₂ In combination with the above, the battery voltage is reduced and the energy density is reduced, and therefore, such metal oxides, metal nitrides, and low-temperature fired carbon materials are also combined with a positive electrode active material that operates at a higher voltage than LiCoO _2. There is a demand for using such a material to exhibit its characteristic of increasing its capacity.

For this reason, higher voltage is being studied for spinel-type lithium manganese oxides. For example, in the case of a composite lithium manganese composite oxide in which manganese sites are replaced with nickel, 4.5 V based on a metal lithium potential is used.
It has been confirmed that the above operating voltage can be obtained (JP-A-09-147867, JP-A-11-73962).
Issue publication).

[0008]

However, by using a nickel-containing lithium manganese oxide having an operating voltage of 4.5 V or more as described above, high energy density can be achieved, but nickel having a high catalytic action can be achieved. , The decomposition of the electrolyte (liquid electrolyte) occurs at a relatively low temperature, gas is generated and the pressure inside the battery rises, and the decomposition reaction of the electrolyte is accelerated, resulting in thermal stability Is reduced.

In order to solve the above problem, it has been proposed to use a nonflammable electrolytic solution or the like, but it has not been sufficiently solved yet. It has also been proposed to use a solid electrolyte such as lithium ion conductive glass, but it has not reached the stage of practical use. Therefore, in order to improve the thermal stability when a high-voltage positive electrode active material is used, it is necessary to make the positive electrode active material itself not to cause thermal decomposition of the electrolytic solution.

The present invention solves the above-mentioned problems in the prior art, and provides a positive electrode active material for a non-aqueous secondary battery which is capable of suppressing thermal decomposition of an electrolyte at a high voltage and a non-aqueous secondary battery. It is intended to provide a positive electrode.

[0011]

According to the present invention, there is provided a compound represented by the general formula (1) Li (Li _{x + x ′} Me _{z + z ′} Ni _yxz Mn _{2-y- x′ -z ′} ) O ₄ (1) Where Me is Ti, Cr, Fe, Co, Cu, Zn,
At least one selected from the group consisting of Al and B, wherein x, x ', y, z, z' are each 0 ≦ x ≦
0.10, 0 ≦ x ′ ≦ 0.10, 0.01 ≦ y ≦ 1.0
0, 0 ≦ z ≦ 0.10, 0 ≦ z ′ ≦ 0.10) and a spinel-type lithium nickel manganese composite oxide having an operating voltage of 4.5 V or more with respect to a Li potential. , The generation of nickel oxide (NiO) can be suppressed,
The inventors have found that thermal decomposition of an electrolytic solution (liquid electrolyte) can be suppressed despite high voltage, and the above-mentioned problem has been solved.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, it is known that an operating voltage of 4.5 V or more can be obtained by substituting a part of the manganese site of LiMn ₂ O ₄ with a transition metal such as nickel. By using such a high-voltage spinel-type lithium manganese oxide as the positive electrode active material, a high energy density can be achieved, but it has been found that gas generation at a high temperature is remarkable.

The inventors of the present invention have examined the reason in detail, and found that LiMn ₂ O ₄ containing about 4 V is charged.
In the presence of a positive electrode (a positive electrode containing LiMn ₂ O ₄ as an active material), the ester organic solvent was found to be 20
Exothermic reaction occurs at 0 ° C. or higher and is thermally stable.
In the coexistence with the nickel-containing lithium manganese composite oxide positive electrode after 1 V charge, it was confirmed by differential calorimetry that an exothermic reaction occurred at about 120 ° C. or higher.

In the decomposition of the electrolytic solution, the positive electrode active material has a noble redox potential in order to increase the voltage,
The presence of nickel oxide (NiO), which is electrochemically inactive but has a strong catalytic action, lowers the activation energy of decomposition of the electrolytic solution. It is considered that the gas increases the internal pressure of the battery and accelerates the decomposition reaction, which is likely to occur.

Therefore, the present invention solves the above problems.
Therefore, Li [Li of the general formula (1) _{x + x '}Me_{z + z '}Ni
_yxzMn_{2-y-x'-z '}O_Four] As represented by lithium
Excessive composition and part of Mn
By substituting with nitrogen, nickel oxide with high catalytic action
Kel generation was suppressed.

The general formula Li [Ni_yMn_2-yO_FourRepresented by
Solid solution reaches the solid solution limit at y = 0.5,
Reports that nickel oxide (NiO) is produced
You. According to the study by the present inventors, it is the solid solution limit.
Li [Ni_0.5Mn_1.5O _FourThe synthesis conditions are slightly
The change easily generates nickel oxide. So
Here, in the present invention, in order to prevent the formation of nickel oxide,
By making the composition excessively high, the content of nickel is reduced.
Phase forms as electrochemically inert lithium nickelate
I expected it to be done. In addition, the solid solubility limit is higher than nickel.
Nickel content by substituting a metal element
Attempt to reduce the production of nickel oxide
Was.

That is, Li [Ni_0.5-aMn_{1.5 + a}]
O_FourIn the state shown by, the solid solution state exists as a stable phase
If it is synthesized with a stoichiometric composition, Li
[Ni _0.5Mn_1.5O_FourIs represented by the following reaction formula 1.
It is considered to proceed as shown in FIG.

[Reaction formula 1] LiOH.H ₂ O + 0.5Ni (OH) ₂ + 1.5Mn
OOH → 1.5 / (1.5 + a) Li [Ni _0.5-a Mn
_{1.5 + a} ] O ₄ + a / (1.5 + a) LiNiO ₂ +0.
5a / (1.5 + a) NiO

Therefore, it was considered that nickel oxide produced by the following reaction can be made into a lithium-containing nickel oxide by making lithium excessive. That is,
As shown in Reaction Formula 2, the production of LiNiO ₂ increases as the excess lithium amount b increases, and the production of nickel oxide is suppressed.

[Reaction formula 2] (1 + b) LiOH.H ₂ O + 0.5Ni (OH) ₂ +
1.5MnOOH → 1.5 / (1.5 + a) Li [Ni
_0.5-a Mn _{1.5 + a} ] O ₄ + [a / (1.5 + a) + b]
LiNiO ₂ + [0.5a / (1.5 + a) -b] Ni
O

By the way, when lithium is insufficient, as shown in the following reaction formula 3, the production of LiNiO ₂ decreases, and the production ratio of nickel oxide increases accordingly.

[Reaction formula 3] (1-b) LiOH.H ₂ O + 0.5Ni (OH) ₂ +
1.5MnOOH → 1.5 / (1.5 + a) Li [Ni
_0.5-a Mn _{1.5 + a} ] O ₄ + [a / (1.5 + a) -b]
LiNiO ₂ + [0.5a / (1.5 + a) -b] Ni
O

Another method for preventing the formation of nickel oxide (NiO) is to simply replace a predetermined amount of nickel with a metal element having a high solid solubility limit with manganese in the spinel skeleton, such as chromium. The purpose is to produce a lithium manganese composite oxide having a phase spinel structure, thereby suppressing the production of nickel oxide. In other words, as shown in Reaction formula 4, the generation of nickel oxide is suppressed by replacing nickel in the spinel skeleton with a metal element.

[Reaction formula 4] LiOH.H ₂ O + (0.5-a) Ni (OH) ₂ + a
CrO ₂ + 1.5MnOOH → Li [Ni _0.5-a Cr _a
Mn _1.5 ] O ₄

L, which is a base material of the positive electrode active material of the present invention,
The theoretical reversible capacity of i [Ni _0.5 Mn _1.5 ] O ₄ correlates with the amount of divalent to tetravalent redox reaction of nickel in the spinel single phase. Therefore, reducing the amount of nickel in the spinel phase by the above method necessarily reduces the reversible capacity. Therefore, in determining the lithium excess amount, the decrease in capacity is determined by Li [Ni _0.5 M
An excess amount of lithium that can be suppressed by 4% or less of n _1.5 ] O ₄ was selected.

In synthesizing the spinel-type lithium nickel manganese composite oxide represented by the general formula (1), for example, powders of lithium hydroxide, manganese dioxide, and nickel hydroxide are used as raw materials. Is weighed in a predetermined amount, mixed with ethanol in a planetary ball mill using ethanol as a solvent, and the mixed powder is dried, formed into pellets, and placed at 750 ° C. in an oxygen stream flowing at a flow rate of 100 ml / min to 500 ml / min. By firing at 850 ° C. for 3 hours to 12 hours and pulverizing the pellet, a spinel-type lithium nickel manganese composite compound represented by the general formula (1) is obtained. As the lithium source, other than the above-described lithium hydroxide, lithium carbonate, lithium nitrate, lithium acetate and the like can be used. As the manganese source, in addition to the above-described electrolytic manganese dioxide, manganite, chemical Synthetic manganese dioxide, manganese carbonate, or the like can be used. However, it is necessary that the obtained lithium nickel manganese composite oxide has a cubic spinel crystal structure.

The general formula Li (Li _{x + x ′} Me _{z + z ′} Ni
_yxz Mn _{2-y- x′ -z ′} ) A positive electrode using a spinel-type lithium nickel manganese composite oxide represented by O ₄ as a positive electrode active material may be, for example, a conductive auxiliary as necessary, Agents, binders and the like are appropriately added and mixed, and the mixture is made into a paste with a solvent (the binder may be dissolved in the solvent in advance and then mixed with the positive electrode active material or the like),
The obtained positive electrode mixture-containing paste is applied to a positive electrode current collector made of aluminum foil or the like, dried to form a positive electrode mixture layer, and subjected to pressure molding as necessary. However, the method for manufacturing the positive electrode is not limited to the above-described example, and may be another method.

In producing the positive electrode, as the conductive additive, for example, graphite (natural graphite, artificial graphite, expanded graphite, etc.), carbon black-based materials such as acetylene black, Ketjen black, and the like can be used. As the binder, for example, polyvinylidene fluoride, polytetrafluoroethylene, ethylene propylene diene rubber, fluoro rubber, styrene butadiene, cellulose resin, polyacrylic acid, and the like can be used.

Examples of the active material of the negative electrode which is a counter electrode to the positive electrode containing the positive electrode active material include lithium, lithium alloys represented by lithium-aluminum, graphite, pyrolytic carbons, cokes, and glassy materials. Carbons, fired bodies of organic polymer compounds, mesocarbon microbeads,
Carbon-based materials such as carbon fibers and activated carbon that can reversibly occlude and release lithium ions, alloys such as Si, Sn, In, and compounds such as oxides and nitrides that can be charged and discharged at a low potential close to Li can also be used as a negative electrode active material. Can be used as

When the negative electrode active material is lithium or a lithium alloy, the negative electrode is used as it is, or is prepared by press-bonding to a current collector, and when the negative electrode active material is a carbon-based material, the negative electrode is optionally used. The same binder as in the case of the positive electrode is added and mixed, and the mixture is made into a paste using a solvent (the binder may be dissolved in a solvent in advance and then mixed with the negative electrode active material). The paste is prepared by applying the agent-containing paste to a negative electrode current collector made of copper foil or the like, drying it to form a negative electrode mixture layer, and, if necessary, performing pressure molding. However, the method of manufacturing the negative electrode is not limited to the above-described example, and another method may be used.

As the electrolyte, any of a non-aqueous liquid electrolyte and a gel polymer electrolyte can be used.
In the present invention, usually, a liquid electrolyte called an electrolyte is frequently used. Therefore, the liquid electrolyte is first described in detail using the expression “electrolyte solution”. The electrolytic solution is prepared, for example, by dissolving an electrolyte salt such as a lithium salt in a non-aqueous solvent containing an organic solvent as a main material.As the solvent, for example, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, A chain ester such as methyl propionate, a chain phosphate triester such as trimethyl phosphate, 1,2-dimethoxyethane, 1,3-dioxolan, tetrahydrofuran, 2-
Methyl-tetrahydrofuran, diethyl ether and the like can be used. In addition, an amine imide organic solvent and a sulfur organic solvent such as sulfolane can also be used.

It is preferable to use an ester having a high dielectric constant (conductivity of 30 or more) as another solvent component from the viewpoint of improving battery characteristics, particularly load characteristics. Specific examples of the ester having a high dielectric constant include: For example, ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, and the like, and sulfur-based esters such as ethylene glycol sulfite can also be used.A cyclic ester is preferable, and particularly, such as ethylene carbonate. Cyclic carbonates are preferred. These solvents can be used alone or in combination of two or more.

In preparing the electrolytic solution, examples of the electrolyte salt such as a lithium salt include LiClO ₄ , LiP
_{F 6, LiBF 4, LiAsF 6} , LiSbF 6, Li
CF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiCF ₃ C
O ₂ , Li ₂ C ₂ F ₄ (SO ₃ ) ₂ , LiN (Rf ₁ S
O ₂ ) (Rf ₂ SO ₂ ) [where Rf ₁ and Rf ₂ are substituents containing a fluoroalkyl group], LiN (Rf
₃ OSO ₂ ) (Rf ₄ OSO ₂ ) [where Rf ₃ , Rf
f ₄ is a fluoroalkyl group], LiC _n F _{2n + 1} S
O ₃ (n ≧ 2), LiC (Rf ₅ SO ₂ ) ₂ , LiN
(Rf ₆ OSO ₂ ) ₂ [where Rf ₅ and Rf ₆ are fluoroalkyl groups], a polymer type imide lithium salt or the like is used alone or in combination of two or more. The concentration of the electrolyte salt in the electrolyte is not particularly limited, but may be 0.1 mol / l or more and 2.0 mol / l or more.
/ L or less.

The gel polymer electrolyte corresponds to a gel obtained by gelling the above-mentioned electrolytic solution with a gelling agent. For the gelation, for example, a linear polymer such as polyvinylidene fluoride, polyethylene oxide, and polyacrylonitrile is used. Or, a polyfunctional monomer (eg, pentaerythritol tetraacrylate, ditrimethylolpropane tetraacrylate, ethoxylated pentaerythritol tetraacrylate, dipentaerythritol hexaacrylate, etc.) which is polymerized by irradiation with an actinic ray such as an ultraviolet ray or an electron beam. For example, tetrafunctional or higher acrylates and tetrafunctional or higher methacrylates similar to the above acrylates) may be used. However, in the case of a monomer, a polymer obtained by polymerizing the above-mentioned monomer acts as a gelling agent, instead of the monomer itself gelling the electrolytic solution.

When the electrolytic solution is gelled using a polyfunctional monomer as described above, if necessary, a polymerization initiator such as benzoyls, benzoin alkyl ethers, benzophenones, benzoylphenylphosphine oxides may be used. , Acetophenones, thioxanthones, anthraquinones, amino esters and the like can also be used.

[0036]

Next, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to only these examples.

Example 1 Li [Ni _0.5 M of Comparative Example 1 having a stoichiometric composition
Composition formula Li [Li] in which a part of nickel is replaced with lithium with respect to n _1.5 ] O ₄ to make lithium 5 atom% excess.
A spinel-type lithium nickel manganese composite oxide represented by _0.05 Ni _0.45 Mn _1.5 ] O ₄ was synthesized. In this synthesis, powders of lithium hydroxide, manganese dioxide, and nickel hydroxide were used as raw materials, weighed in a predetermined amount so as to have the above composition ratio, mixed with ethanol as a solvent in a planetary ball mill, and mixed. After drying the powder, the powder was formed into a pellet and fired at 900 ° C. for 12 hours in an oxygen gas flow at a flow rate of 300 ml / min. After firing, the pellets were pulverized.
In the following examples and comparative examples, the synthesis conditions are almost the same as in the case of the first embodiment.

Example 2 A composition formula Li [Li _0.05 Ni _0.45 Mn _1.5 ] in which a part of manganese was replaced with lithium to make lithium 5 atomic% excess.
A spinel-type lithium nickel manganese composite oxide represented by O ₄ was synthesized.

Example 3 A composition formula of Li _1.05 [Ni
A spinel-type lithium nickel manganese composite oxide represented by _0.5 Mn _1.5 ] O ₄ was synthesized.

Example 4 A composition formula Li [Li _0.03 Ni _0.47 Mn _1.5 ] in which a part of nickel was replaced with lithium to make lithium 3 atomic% excess.
A spinel-type lithium nickel manganese composite oxide represented by O ₄ was synthesized.

Example 5 A composition formula Li [Li _0.03 Ni _0.5 Mn _1.47 ] in which a part of manganese is replaced by lithium to make lithium 3 atomic% excess.
A spinel-type lithium nickel manganese composite oxide represented by O ₄ was synthesized.

Example 6 A composition formula of Li _1.03 [Ni
A spinel-type lithium nickel manganese composite oxide represented by _0.5 Mn _1.5 ] O ₄ was synthesized.

Example 7 A composition formula of Li [Cr in which nickel was replaced by 5 atomic% of chromium
A spinel-type lithium nickel manganese composite oxide represented by _0.05 Ni _0.45 Mn _1.5 ] O ₄ was synthesized.

Example 8 Composition in which nickel and manganese were partially replaced with 5 atomic% of iron
The formula Li [Fe_0.05Ni _0.475Mn_1.475O_FourRepresented by
Spinel-type lithium nickel manganese composite oxide
Done.

Example 9 Nickel and manganese were partially substituted with 5 atomic% of cobalt.
Formula Li [Co_{0. 05}Ni_0.475Mn_1.475O_Fourso
Represented spinel-type lithium nickel manganese composite oxidation
Was synthesized.

Example 10 A composition formula of Li _1.05 [Fe _{1.05 wherein} a part of nickel and manganese was replaced by 5 atom% of iron and lithium was increased by 5 atom%.
A spinel-type lithium nickel manganese composite oxide represented by _0.05 Ni _0.475 Mn _1.475 ] O ₄ was synthesized.

Example 11 A composition formula Li _1.05 in which nickel and manganese were partially substituted with 5 atomic% of cobalt and lithium was increased by 5 atomic%.
A spinel-type lithium nickel manganese composite oxide represented by [Co _0.05 Ni _0.475 Mn _1.475 ] O ₄ was synthesized.

Comparative Example 1 A spinel-type lithium nickel manganese composite oxide represented by a stoichiometric composition formula Li [Ni _0.5 Mn _1.5 ] O ₄ was used as Comparative Example 1.

Comparative Example 2 A composition formula Li [Li _0.1 Ni _0.4 M in which a part of nickel was replaced with lithium to make lithium 10 atomic% excess.
n _1.5 ] O ₄ was synthesized.

Comparative Example 3 A composition formula Li [Li _0.1 Ni _0.5 M in which a part of manganese was replaced with lithium to make lithium 10 atomic% excess.
[n _1.4 ] O ₄ was synthesized.

Comparative Example 4 Composition formula Li _1.1 [Ni
A spinel-type lithium nickel manganese composite oxide represented by _0.5 Mn _1.5 ] O ₄ was synthesized.

Comparative Example 5 A composition formula Li _0.95 [Ni
A spinel-type lithium nickel manganese composite oxide represented by _0.5 Mn _1.5 ] O ₄ was synthesized.

The composition of the spinel-type lithium nickel manganese composite oxide synthesized in Examples 1 to 11 and Comparative Examples 1 to 5 was analyzed by atomic absorption spectrometry, and Li / N
The i ratio was determined. The results are shown in Tables 1 and 2.

The synthesized spinel-type lithium nickel manganese composite oxide was subjected to powder X-ray diffraction measurement. From the results, it was confirmed that the solid solution phase was a single-phase cubic system. Among them, Examples 1 to 3, Example 7,
FIG. 1 shows the measurement results of Comparative Example 1 and Comparative Example 5.

As shown in FIG. 1, the diffraction patterns of Comparative Example 1 and Comparative Example 5 show nickel oxide (NiO) (JCPDS # 4).
7-1049; (2) derived from a cubic crystal, a = 4.117 °)
00) Diffraction lines were observed. On the other hand, in Example 1, Example 2, and Example 3, similar diffraction lines were observed. However, since the diffraction lines were located at a slightly higher angle side, they were not derived from nickel oxide, but lithium nickel oxide (cubic). Crystal, a =
4.094Å). In Example 7, since the diffraction line was not observed, it is considered that a complete solid solution was obtained without producing either nickel oxide or lithium nickel oxide.

Next, the properties of the spinel-type lithium nickel manganese composite oxides of Examples 1 to 11 and Comparative Examples 1 to 5 as positive electrode active materials of lithium secondary batteries were evaluated. First, the positive electrode was composed of 80% by weight of the positive electrode active material composed of the spinel-type lithium nickel manganese composite oxide prepared in the presence of N-methyl-2-pyrrolidone, 15% by weight of graphite, and 5% by weight of polyvinylidene fluoride.
A paste obtained by applying a positive electrode mixture-containing paste containing a percentage by weight (however, a percentage as a solid content) to an aluminum foil and drying was used. And, using metal lithium foil for the negative electrode, using polypropylene non-woven fabric for the separator,
For the electrolyte solution, LiPF ₆ was added to a mixed solvent of ethylene carbonate and ethyl methyl carbonate at a volume ratio of 1: 2.
The coin-shaped non-aqueous secondary battery shown in FIG. 2 was assembled by using 2 mol / l dissolved.

Here, the coin-shaped non-aqueous secondary battery shown in FIG. 2 will be described. Reference numeral 1 denotes a positive electrode, and the positive electrode 1 has the spinel lithium of Examples 1 to 11 and Comparative Examples 1 to 5 as described above. The nickel manganese composite oxide was used as a positive electrode active material, and the positive electrode 1 was different in the positive electrode active material according to Examples 1 to 11 and Comparative Examples 1 to 5. The negative electrode 2 is made of a metallic lithium foil as described above, and is disposed to face the positive electrode 1 via a separator 3 made of a nonwoven polypropylene fabric. The battery case 4 is made of stainless steel, and serves as both a current collector and a terminal on the positive electrode side.
The sealing plate 5 is also made of stainless steel, and serves as both a current collector and a terminal on the negative electrode side. Reference numeral 6 denotes an annular gasket made of polypropylene, into which the above-mentioned electrolyte is injected, though not shown. The negative electrode 2, the separator 3, the battery case 4, the sealing plate 5, the annular gasket 6, and the electrolyte are common to Examples 1 to 11 and Comparative Examples 1 to 5.

The initial discharge characteristics and cycle characteristics of these non-aqueous secondary batteries were examined. The charge / discharge conditions at that time will be described.
Charged at a constant current of A / cm ² and then 0.2 mA / c
Discharge was performed at a constant current of m ² , and 3.5 V was defined as a discharge end voltage. And immediately after the end of the discharge, restart the charge,
That was one cycle.

Tables 1 and 2 show the initial discharge capacity and operating voltage of each battery measured under the above conditions. FIG. 3 shows the initial discharge curves of Example 1, Example 2, Example 3, Example 7, Comparative Example 1 and Comparative Example 5 measured under the above conditions.

As shown in FIG. 3, all of the batteries of Examples 1 to 3, Example 7, Comparative Example 1 and Comparative Example 5 had an operating voltage of 4.6 V to 4.7 V and an initial discharge. The capacity was between 120 mAh / g and 135 mAh / g. In addition,
The operating voltage was a voltage when the discharge capacity was 50%. The results are shown in Tables 1 and 2. As described above, Examples 1 to
3. The spinel-type lithium nickel manganese composite oxide used as the positive electrode active material of Example 7, Comparative Example 1 and Comparative Example 5 has an operating voltage of 4.6 V to 4.7 V and an initial discharge capacity of 120 mAh / g or more. Since they are 135 mAh / g, their median values of 4.65 V and 128 mAh / g
g, the energy density is calculated as 593 mWh / g (4.65 V × 128 mAh / g).
g). On the other hand, the energy density of the 4 V class lithium manganese composite oxide is 466 mWh / g because the operating potential is 4.05 V and the discharge capacity is 115 mAh / g. As is clear from these results, the positive electrode active material used in Example 1 and the like can increase the energy density of the battery by about 30% compared to a 4V-class lithium manganese-based positive electrode active material.

Next, a differential calorimetry was performed in the coexistence of the positive electrode and the electrolyte at the time of charging, and the heat generation starting temperature was examined. This is to confirm that the positive electrode active material of the present invention can reduce the reactivity with the electrolytic solution and improve the thermal stability of the electrolytic solution.

The measurement conditions for the differential calorimetry were as follows: a battery was charged to 5.1 V at 0.2 mA / cm ² , left in a constant temperature bath at 25 ° C. for 48 hours, and disassembled in a glove box under an argon atmosphere. Then, the positive electrode is taken out, washed with ethyl methyl carbonate, and the pressure is reduced to remove the ethyl methyl carbonate. Then, a predetermined size (3.5 mm in diameter) is obtained.
And 0.5 μl of an unused electrolytic solution was added, and molded into a pressure-resistant cell for differential calorimetry.

In the differential calorimetric measurement, the cell was heated from room temperature to 300 ° C. at a rate of 3 ° C./min, and the change in the differential caloric value was examined at that time.
g or more, continuous heat generation occurs as the temperature rises, and 20 m
The temperature at which a change in the amount of heat of W / g · ° C. or more occurred was defined as the heat generation start temperature. The results are shown in Tables 1 and 2.

[0064]

[Table 1]

[0065]

[Table 2]

FIG. 4 shows the changes in the differential calorific values of Examples 1, 2, 3, and 7 and Comparative Examples 1 and 5 among the results of the differential calorimetric measurement. The value obtained by dividing by the total mass of the measured amount of the active material and the added electrolyte solution was used as the amount of heat on the vertical axis of FIG.

As shown in FIG. 4 and Table 2, in Comparative Examples 1 and 5, the initial heat generation started at 120 to 130 ° C., and the electrolyte was thermally unstable. On the other hand, the initial heat generation of the positive electrode active material in which the generation of nickel oxide was suppressed, that is, Examples 1, 2, 3, and 7 started at 200 ° C. or more. This indicates that the thermal stability of the coexisting electrolyte solution is improved by suppressing the formation of nickel oxide in the positive electrode active material.

As shown in Table 2, Li [Ni _0.5 Mn _1.5 ] O ₄ of Comparative Example 1 having a stoichiometric composition had a discharge capacity of 130 mAh / g and a theoretical capacity of 147
About 88% efficiency compared to mAh / g. The reasons may be that the material itself is an imperfect solid solution or that it is an experimentally high potential. The discharge capacity of Comparative Example 2 and Comparative Example 3 was 10% of that of Comparative Example 1.
It was a drop. This is considered to be due to the excessive amount of lithium. The discharge capacity of Comparative Example 5 was 10% lower than that of Comparative Example 1. This is probably because the amount of active spinel-type lithium nickel manganese composite oxide was reduced.

As shown in Table 1, Examples 1 and 2
Example 4 and Example 5 had a discharge capacity of 125 to 128 mAh.
/ G, which is 4% or less of the discharge capacity of Comparative Example 1. Therefore, the lithium excess amount is set to 5% by atom or less, or the substitution amount of the metal element by lithium is set to 5% by atom.
It is considered that the following is necessary in order to maintain high energy density.

When the amount of lithium was increased while the amount of nickel was kept constant as in Examples 3, 6 and Comparative Example 4, there was no significant difference in the discharge capacity.
The capacity was 30 to 138 mAh / g, and the capacity was increased as compared with Li [Ni _0.5 Mn _1.5 ] O ₄ of Comparative Example 1 having a stoichiometric composition. However, as is clear from the comparison between Example 3 and Comparative Example 4, no increase in the discharge capacity was observed even when lithium was excessively increased beyond a predetermined amount.

[0071]

As described above, according to the present invention, a positive electrode active material for a non-aqueous secondary battery and a positive electrode for a non-aqueous secondary battery capable of suppressing thermal decomposition of an electrolytic solution (liquid electrolyte) at a high voltage are provided. Could be provided.

[Brief description of the drawings]

FIG. 1 is a powder X-ray diffraction diagram of Example 1, Example 2, Example 3, Example 7, Comparative Example 1 and Comparative Example 5.

FIG. 2 is a cross-sectional view schematically showing one example of a non-aqueous secondary battery according to the present invention.

FIG. 3 is an initial discharge curve diagram of Example 1, Example 2, Example 3, Example 7, Comparative Example 1 and Comparative Example 5.

FIG. 4 is a view showing a change in differential calorific value of Example 1, Example 2, Example 3, Example 7, Comparative Example 1 and Comparative Example 5.

[Description of Signs] 1 Positive electrode 2 Negative electrode 3 Separator

Claims (4)

[Claims] 1. Formula (1) Li (Li _{x + x ′} Me _{z + z ′} Ni _yxz Mn _{2-y- x′ -z ′} ) O ₄ (1) (where Me is Ti, Cr, Fe, Co, Cu, Zn,
At least one selected from the group consisting of Al and B, wherein x, x ', y, z, z' are each 0 ≦ x ≦
0.10, 0 ≦ x ′ ≦ 0.10, 0.01 ≦ y ≦ 1.0
0, 0 ≦ z ≦ 0.10, 0 ≦ z ′ ≦ 0.10), and is composed of a spinel-type lithium nickel manganese composite oxide having an operating voltage of 4.5 V or more with respect to the Li potential. Cathode active material for non-aqueous secondary batteries. 2. In the general formula (1), x, x ′, y,
z and z ′ are respectively 0 ≦ x ≦ 0.05 and 0 ≦ x ′ ≦
0.05, 0.40 ≦ y ≦ 0.50, 0 ≦ z ≦ 0.0
5. The positive electrode active material for a non-aqueous secondary battery according to claim 1, wherein 0 ≦ z ′ ≦ 0.05. 3. A positive electrode for a non-aqueous secondary battery, comprising the positive electrode active material according to claim 1 or 2, wherein no diffraction line of nickel oxide (NiO) is observed in powder X-ray diffraction. 4. The positive electrode active material according to claim 1 or 2, characterized in that it does not have an exothermic onset temperature of 150 ° C. or less in a charged state in the presence of an organic liquid electrolyte in a differential calorimetric analysis. Positive electrode for non-aqueous secondary batteries.