JP2004335181A - Discharge method of nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a discharge method enhancing the high temperature cycle life of a nonaqueous electrolyte secondary battery using a 5-volt class positive active material. <P>SOLUTION: In the discharge method of the nonaqueous electrolyte secondary battery comprising a positive electrode containing a positive active material capable of absorbing/releasing lithium ions, a negative electrode, and a nonaqueous electrolyte, the positive active material is represented by general formula Li<SB>X+a</SB>Ni<SB>Y</SB>Mn<SB>2-a-Y</SB>O<SB>4-δ</SB>, (wherein, 0<X≤1.0; 0≤a≤0.1; 0.45≤Y≤0.55; and 0≤δ≤0.4), and the nonaqueous electrolyte secondary battery is discharged in a potential region where Mn<SP>4+</SP>contained in the positive active material does not change to Mn<SP>3+</SP>. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００３７】
＜実施例２＞
正極活物質として組成式ＬｉＮｉ_０．５Ｍｎ_１．５Ｏ_４−δ（ただし、δは約０．２４、Ｍｎの価数は約＋３．６８である）で表されるリチウムニッケルマンガン複合酸化物を用いた。なお、マンガンの価数は、実施例１と同様、酸化還元滴定法によって求めた値である。このリチウムニッケルマンガン複合酸化物を用いた以外は実施例１と同様にして、セルを作製し、充放電試験を行った。
【００３８】
＜比較例２＞
充放電試験において、放電終止電圧を３．５Ｖ ｖｓ．Ｌｉ／Ｌｉ^＋とした他は、実施例２と同様にしてセルを作製し、充放電試験を行った。
実施例２および比較例２の１サイクル目の放電特性を図２に示した。なお、図２において、実施例２では放電終止電圧を４．１Ｖ ｖｓ．Ｌｉ／Ｌｉ^＋とし、比較例２では放電終止電圧を３．５Ｖ ｖｓ．Ｌｉ／Ｌｉ^＋とした。
また、実施例２および比較例２の容量保持率を表２にまとめて示す。
【００３９】
【表２】

【００４０】
＜結果＞
表１から、放電終止電圧を４．１Ｖ ｖｓ．Ｌｉ／Ｌｉ^＋とした実施例１は、容量保持率が８０％であったのに対し、放電終止電圧を３．５Ｖ ｖｓ．Ｌｉ／Ｌｉ^＋とした比較例１は、容量保持率が５９％であった。
【００４１】
また、表２から、放電終止電圧を４．１Ｖ ｖｓ．Ｌｉ／Ｌｉ^＋とした実施例２は、容量保持率が７６％であったのに対し、放電終止電圧を３．５Ｖ ｖｓ．Ｌｉ／Ｌｉ^＋とした比較例２は、容量保持率が４２％であった。
【００４２】
＜他の実施形態＞
本発明は上記記述及び図面によって説明した実施形態に限定されるものではなく、例えば次のような実施形態も本発明の技術的範囲に含まれ、さらに、下記以外にも要旨を逸脱しない範囲内で種々変更して実施することができる。
【００４３】
上記した実施形態では、三極セルとして説明したが、電池構造は特に限定されず、角形、円筒形、袋状、リチウムポリマー電池等としてもよいことは勿論である。
【００４４】
なお、本発明の非水電解質二次電池に用いられる正極活物質としては、一般式Ｌｉ_Ｘ＋ａＮｉ_ＹＭｎ_{２−ａ−Ｙ}Ｏ_４−δで表される化合物において、Ｍｎの一部がさらに他の元素Ｍで置換された一般式Ｌｉ_Ｘ＋ａＮｉ_Ｙ−ｂＭ_ｂＭｎ_{２−ａ−Ｙ}Ｏ_４−δで表される化合物を用いることができる。ここでＭはＡｌ、Ｔｉ、Ｆｅ、Ｎｂ、Ｍｏ、Ｗなどの元素である。
【００４５】
【発明の効果】
本発明によれば、いわゆる５Ｖ級正極活物質を用いた非水電解質二次電池の高温サイクル寿命を向上させることができる。
【図面の簡単な説明】
【図１】実施例１および比較例１の１サイクル目の放電特性を示す図
【図２】実施例２および比較例２の１サイクル目の放電特性を示す図[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for discharging a non-aqueous electrolyte secondary battery.
[0002]
[Prior art]
In recent years, in order to respond to the demand for further miniaturization of portable electronic and communication devices, further higher energy density is required for lithium ion batteries. In order to meet such a demand, a so-called 5V-class positive electrode active material having a discharge potential flat portion of 4.4 V to 5 V has been widely studied (for example, see Patent Document 1).
[0003]
[Patent Document 1]
JP-A-11-73962
[Problems to be solved by the invention]
However, in the case of a non-aqueous electrolyte secondary battery using a 5V-class positive electrode active material as described above, the charge / discharge capacity of the battery may decrease when charge / discharge is repeated at high temperatures, and the so-called high-temperature charge / discharge cycle life decreases. There is a problem that. This is considered to be due to the fact that Mn ³⁺ in the crystal structure dissolves as Mn ^{2+ in the} organic electrolyte.
[0005]
As a result of intensive studies by the inventors, the following findings were obtained. That, 5V-class cathode active material has a discharge potential flat portion near 4.4V~5.0V against Li / Li ^+, in this region, Mn ions in the crystal structure is present as ^{Mn 4+} This Mn ⁴⁺ does not dissolve as Mn ^{2+ in the} organic electrolyte even at high temperatures. On the other hand, the 5V-class positive electrode active material has a discharge potential flat portion near 4.0 V to 4.2 V with respect to Li / Li ⁺ , and in a region lower than the potential flat portion, Mn ions in the crystal structure Was found to change from Mn ⁴⁺ to Mn ³⁺ . Then, if the non-aqueous electrolyte secondary battery is used in a region higher than the potential changing from Mn ⁴⁺ to Mn ³⁺ , the dissolution of Mn ^{2+ in} the non-aqueous electrolyte should be prevented. is there.
[0006]
The present invention has been completed based on the above-described novel findings, and provides a discharge method capable of improving the high-temperature cycle life of a nonaqueous electrolyte secondary battery using a so-called 5V-class positive electrode active material. With the goal.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, a first aspect of the present invention is a method for discharging a non-aqueous electrolyte secondary battery including a positive electrode including a positive electrode active material capable of inserting and extracting lithium ions, a negative electrode, and a non-aqueous electrolyte. In the method, the positive electrode active material has a general formula Li _{X + a} Ni _Y Mn _2-a- YO _4-δ (where 0 <X ≦ 1.0, 0 ≦ a ≦ 0.1, 0.45 ≦ Y ≦ 0.55, 0 ≦ δ ≦ 0.4), wherein the non-aqueous electrolyte secondary battery is discharged in a potential region where Mn ⁴⁺ contained in the positive electrode active material does not change to Mn ³⁺ . I do.
[0008]
Function and effect of the present invention
<Invention of claim 1>
As the positive electrode active material, a general formula Li _{X + a} Ni _Y Mn _2-a- YO _4-δ (where 0 <X ≦ 1.0, 0 ≦ a ≦ 0.1, 0.45 ≦ Y ≦ 0.55, By using the lithium nickel manganese composite oxide represented by (0 ≦ δ ≦ 0.4), a non-aqueous electrolyte secondary battery having a high energy density can be obtained. This is considered for the following reason. In the lithium manganese composite oxide having a spinel structure represented by LiMn ₂ O ₄ , potential flat portions exist near 3 V and 4 V. When LiMn ₂ O ₄ is used as the positive electrode active material, a potential flat portion around 4 V is usually used, and its discharge capacity is about 120 mAh / g. Formula _{Li X + a Ni Y Mn 2} -a-Y O 4-δ lithium-nickel-manganese composite oxide represented by a part obtained by substituting Ni for Mn in the LiMn ₂ O _4, the potential flat portion of the high potential side Is present at a high potential of 4.4 V to 4.7 V. Therefore, when this is used as a positive electrode active material, a non-aqueous electrolyte secondary battery having a high energy density can be obtained.
[0009]
By Mn ions in the crystal lattice of the positive electrode active material to discharge the non-aqueous electrolyte secondary battery in an area that does not change from the ^{Mn 4+} to ^{Mn 3+,} changes ^{Mn 4+} in the crystal lattice to ^{Mn 3+,} the ^{Mn 3+} Can be suppressed from being dissolved as Mn ²⁺ in the non-aqueous electrolyte. As a result, the high-temperature cycle characteristics of the nonaqueous electrolyte secondary battery can be improved.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described.
The positive electrode active material according to the present invention, the general formula _{Li X + a Ni Y Mn 2} -a-Y O 4-δ ( where, 0 <X ≦ 1.0,0 ≦ a ≦ 0.1,0.45 ≦ Y ≦ 0.55, 0 ≦ δ ≦ 0.4) can be used. In general, the lithium nickel manganese composite oxide can be synthesized by, for example, a solid phase method in which a compound serving as a lithium source, a manganese source, and a nickel source are mixed and fired. Further, it can also be synthesized by a sol-gel method as shown in JP-T-2000-515672.
[0011]
Examples of lithium sources include lithium hydroxide monohydrate, lithium nitrate, lithium carbonate, lithium acetate, lithium bromide, lithium chloride, lithium citrate, lithium fluoride, lithium iodide, lithium lactate, and lithium oxalate. , Lithium phosphate, lithium pyruvate, lithium sulfate, lithium oxide and the like. Examples of the manganese source include manganese dioxide, manganese oxide, manganese hydroxide, manganese carbonate, manganese nitrate, manganese sulfate, and manganese oxalate. Of these, manganese dioxide is particularly preferable. Further, examples of the nickel source include nickel nitrate, nickel carbonate, nickel oxide and the like.
[0012]
Further, the positive electrode active material according to the present invention contains two transition metal elements, Ni and Mn, but the positive electrode active material may be made of Al, Ti, Fe, Nb, Mo or W without changing the intention of the invention. Etc. may be included.
[0013]
By replacing the Mn site of LiMn ₂ O ₄ with Ni, it is possible to obtain a positive electrode active material having a high potential of 4.5 V or more, which is a high-potential-side discharge potential flat region. Further, by replacing the Mn site of LiMn ₂ O ₄ with Li, the flat portion of the discharge potential in the 4 V region can be reduced.
[0014]
X indicating the ratio of Li changes by charging and discharging, and becomes 1 when fully charged. On the other hand, when overdischarge occurs, the crystal structure of the lithium nickel manganese composite oxide becomes unstable, so that 0 <X ≦ 1.0 is preferable. a is the ratio of Li substituted for Mn sites as described above. When a part of Mn is replaced with Li, the valence of Mn increases, and the flat portion of the discharge potential in the 4 V region decreases. When a exceeds 0.1, the discharge capacity decreases, which is not preferable. Therefore, 0 ≦ a ≦ 0.1 is preferable. Y is the ratio of Ni substituted for Mn sites as described above. If Y is less than 0.45, the discharge potential flat portion in the 5 V region decreases, which is not preferable. On the other hand, when Y exceeds 0.55, the valence of Ni ions changes from divalent to trivalent, so that the discharge capacity in the 5 V region decreases. Therefore, it is preferable that 0.45 ≦ Y ≦ 0.55. Δ represents oxygen deficiency in the crystal structure. As this δ increases, the valence of Mn decreases, and the potential flat portion in the 4 V region increases. On the other hand, if δ exceeds 0.4, oxygen constituting the frame having the spinel structure becomes insufficient, and the spinel structure may not be maintained. Therefore, it is preferable that 0 ≦ δ ≦ 0.4.
[0015]
The lattice constant and the site occupancy of each atom in the lithium nickel manganese composite oxide can be determined by Rietveld analysis of a diffraction pattern obtained by a powder X-ray diffraction method (for example, “The Rietveld Method,” ed. By R.A. Young, Oxford University Press, Oxford (1993)). The Rietveld analysis is a method of refining parameters related to the crystal structure by fitting a powder diffraction pattern using X-rays and neutrons with a diffraction pattern calculated based on an assumed structural model.
[0016]
The positive electrode active material, a conductive agent, and a binder are mixed to prepare a positive electrode mixture, and the positive electrode mixture is applied to a positive electrode current collector made of a metal foil to produce a positive electrode plate. be able to.
[0017]
There is no particular limitation on the conductive agent, and various materials can be used as appropriate. For example, Ni, Ti, Al, Fe, an alloy of two or more of these, or a carbon material may be used. Among them, it is preferable to use a carbon material. Examples of the carbon material include amorphous carbon such as natural graphite, artificial graphite, vapor grown carbon fiber, acetylene black, Ketjen black, and needle coke.
[0018]
The binder used for the positive electrode is not particularly limited, and various materials can be appropriately used. For example, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, ethylene-propylene-diene terpolymer, styrene-butadiene rubber, acrylonitrile-butadiene rubber, fluorine At least one selected from the group consisting of rubber, polyvinyl acetate, polymethyl methacrylate, polyethylene, nitrocellulose, and derivatives thereof can be used.
[0019]
Examples of the positive electrode current collector include Al, Ta, Nb, Ti, Hf, Zr, Zn, W, Bi, and alloys containing these metals. Since these metals form a passive film on the surface by anodic oxidation in the electrolyte, it is possible to effectively prevent the non-aqueous electrolyte from being oxidized and decomposed at the contact portion between the positive electrode current collector and the electrolyte. it can. As a result, the cycle characteristics of the non-aqueous secondary battery can be effectively improved.
[0020]
There is no particular limitation on the negative electrode active material, and various materials can be used as appropriate. For example, carbon materials such as graphite and amorphous carbon, oxides, nitrides, lithium alloys, and the like can be given. As the lithium alloy, for example, an alloy of lithium and at least one metal selected from the group consisting of aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, and tin can be used. Further, oxides, nitrides, and lithium alloys can be used as a mixture with various carbon materials. In addition, oxides, nitrides, and lithium alloys can be used by being supported on various carbon materials.
[0021]
As the current collector of the negative electrode, iron, copper, stainless steel, or nickel can be used. Examples of the shape include a sheet, a sheet, a mesh, a foam, a sintered porous body, and an expanded lattice. Further, those in which holes are formed in any shape in these current collectors can be used.
[0022]
The method for producing the negative electrode is not particularly limited, and the negative electrode can be produced by the same method as the above-described method for producing the positive electrode.
[0023]
The organic solvent of the electrolyte is not particularly limited, and various solvents can be appropriately used. For example, ethers, ketones, lactones, nitriles, amines, amides, sulfur compounds, halogenated hydrocarbons, esters, carbonates, nitro compounds, phosphate compounds, sulfolane hydrocarbons, etc. Among them, ethers, ketones, esters, lactones, halogenated hydrocarbons, carbonates, and sulfolane hydrocarbons are preferable.
[0024]
Examples of the organic solvent include tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, 1,4-dioxane, anisole, monoglyme, 4-methyl-2-pentanone, methyl acetate, ethyl acetate, methyl propionate, and ethyl propionate. , 1,2-dichloroethane, γ-butyrolactone, γ-valerolactone, dimethoxyethane, diethoxyethane, methylformate, dimethylcarbonate, methylethylcarbonate, diethylcarbonate, dipropylcarbonate, methylpropylcarbonate, ethylenecarbonate, propylenecarbonate , Vinylene carbonate, butylene carbonate, dimethylformamide, dimethylsulfoxide, dimethylthioformamide, sulfolane, 3-methyl-sulfur Examples thereof include holane, trimethyl phosphate, triethyl phosphate, and phosphazene derivatives, and a mixed solvent thereof. Among them, it is preferable to use ethylene carbonate, propylene carbonate, γ-butyrolactone, dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate alone or as a mixture of two or more.
[0025]
The solute of the electrolyte is not particularly limited, and various solutes can be appropriately used. For example, LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiPF ₆ , LiCF (CF ₃ ) ₅ , LiCF ₂ (CF ₃ ) ₄ , LiCF ₃ (CF ₃ ) ₃ , LiCF ₄ (CF ₃ ) ₂ , LiCF ₅ (CF ₃₎ ), LiCF ₃ (C ₂ F ₅ ) ₃ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (C ₂ F ₅ CO) ₂ , LiI, LiAlCl ₄ , LiBC ₄ O _{8 and the} like can be used alone or in combination of two or more. Among them, LiPF ₆ is preferably used. Further, the concentration of these lithium salts is preferably 0.52 to 2.0 mol · dm ⁻³ .
[0026]
In the electrolyte, carbonates such as vinylene carbonate and butylene carbonate, benzenes such as biphenyl and cyclohexylbenzene, sulfurs such as propane sultone, ethylene sulfide, hydrogen fluoride, triazole-based cyclic compounds, fluorine-containing esters, tetraethyl Hydrogen fluoride complex of ammonium fluoride or a derivative thereof, phosphazene and a derivative thereof, an amide group-containing compound, an imino group-containing compound, or at least one selected from the group consisting of nitrogen-containing compounds can also be used. Further, it can be used by containing at least one selected from CO ₂ , NO ₂ , CO, SO _{2 and the} like.
[0027]
As the electrolyte, a solid or gel ion conductive electrolyte can be used alone or in combination. When combining a plurality of ion-conductive electrolytes, the non-aqueous electrolyte battery, for example, a positive electrode, a negative electrode, a separator, an organic or inorganic solid electrolyte, and a non-aqueous electrolyte solution, and, also, a positive electrode, It can also be composed of a negative electrode, an organic or inorganic solid electrolyte membrane as a separator, and a non-aqueous electrolyte. Also, a porous polymer solid electrolyte membrane can be used as the ion conductive electrolyte.
[0028]
Polyethylene oxide as an ion conducting electrolyte, polypropylene oxide, polyacrylonitrile, polyethylene glycol and derivatives _{thereof, LiI, Li 3 N, Li} 1 + x M x Ti 2-x (PO 4) 3 (M = Al, Sc, Y, La), Li _0.5-3x R _{0.5 + x} TiO ₃ (R = La, Pr, Nd, Sm), or thiolysicon represented by Li _4-x Ge _1-x P _x S ₄ can be used. it can. _{Furthermore, LiI-Li 2 O-B} 2 O 5 _system, Li 2 oxide glass such as O-SiO ₂ system or _{LiI-Li 2 S-B 2} S 3 _{type,, LiI-Li 2 S-} SiS 2 system, A sulfide glass such as a Li ₂ S—SiS ₂ —Li ₃ PO ₄ system can be used.
[0029]
The separator is not particularly limited, and various materials can be appropriately used. For example, a woven fabric, a nonwoven fabric, a synthetic resin microporous membrane and the like can be mentioned, and among them, a synthetic resin microporous membrane is preferable. As the material of the synthetic resin microporous membrane, nylon, cellulose acetate, nitrocellulose, polysulfone, polyacrylonitrile, polyvinylidene fluoride, and polyethylene, polypropylene, polyolefins such as polybutene are used, among which polyethylene and polypropylene microporous membrane, Alternatively, a polyolefin-based microporous film in which these are combined is preferable in terms of thickness, film strength, film resistance, and the like.
[0030]
In addition, those obtained by laminating a plurality of microporous films of different materials, those obtained by laminating a plurality of microporous films of the same material having different weight average molecular weights and porosity, It is possible to use a film containing an appropriate amount of additives such as various plasticizers, antioxidants, and flame retardants.
[0031]
Hereinafter, the present invention will be described in detail based on examples. The present invention is not limited by the following examples.
[0032]
Hereinafter, the present invention will be described in detail based on examples. The present invention is not limited by the following examples.
<Example 1>
Lithium nickel manganese composite oxide represented by the composition formula LiNi _0.5 Mn _1.5 O _4-δ (where δ is about 0.03 and Mn valence is about +3.96) as a positive electrode active material Was used. The valence of manganese is a value determined by a redox titration method. This lithium nickel manganese composite oxide, 5% acetylene black as a conductive additive, polyvinylidene fluoride as a binder, and N-methylpyrrolidone as a solvent were mixed to form a paste, which was used as a current collector. And then dried at 80 ° C., and further vacuum-dried at 150 ° C. for 5 hours to manufacture. Metal lithium is used for the counter electrode and the reference electrode, LiPF ₆ having a concentration of 1 mol / l is used as a solute, and ethylene carbonate (EC) and ethyl methyl carbonate (EMC) having a volume ratio of 5: 5 are used as a solvent. The mixture was used.
[0033]
A charge / discharge test was performed using the triode cell manufactured as described above. The charging and discharging conditions were as follows: charging was performed at a constant current of 1.0 mA / cm ² at 4.9 V vs. Li / Li ⁺ up to a discharge of 4.1 V vs. 1.0 mA / cm ² constant current. Up to Li / Li ⁺ , this was regarded as one cycle, and 100 cycles were performed. Then, the ratio of the discharge capacity at the 100th cycle to the discharge capacity at the first cycle was determined, and this was defined as the capacity retention (%).
[0034]
<Comparative Example 1>
In the charge / discharge test, the discharge end voltage was set to 3.5 V vs. 3.5 V. A cell was prepared in the same manner as in Example 1 except that Li / Li ⁺ was used, and a charge / discharge test was performed.
[0035]
FIG. 1 shows the discharge characteristics of the first cycle of Example 1 and Comparative Example 1. In FIG. 1, in Example 1, the discharge end voltage was set to 4.1 V vs. Li / Li ^+, and in Comparative Example 1, the discharge end voltage was 3.5 V vs. Li / Li ⁺ .
Table 1 shows the capacity retention rates of Example 1 and Comparative Example 1.
[0036]
[Table 1]

[0037]
<Example 2>
Lithium nickel manganese composite oxide represented by the composition formula LiNi _0.5 Mn _1.5 O _4-δ (where δ is about 0.24 and Mn valence is about +3.68) as a positive electrode active material Was used. In addition, the valence of manganese is a value obtained by an oxidation-reduction titration method as in Example 1. A cell was prepared and a charge / discharge test was performed in the same manner as in Example 1 except that this lithium nickel manganese composite oxide was used.
[0038]
<Comparative Example 2>
In the charge / discharge test, the discharge end voltage was set to 3.5 V vs. 3.5 V. A cell was prepared in the same manner as in Example 2 except that Li / Li ⁺ was used, and a charge / discharge test was performed.
FIG. 2 shows the discharge characteristics in the first cycle of Example 2 and Comparative Example 2. In FIG. 2, in Example 2, the discharge end voltage was set to 4.1 V vs. Li / Li ⁺ . In Comparative Example 2, the discharge end voltage was 3.5 V vs. Li. Li / Li ⁺ .
Table 2 summarizes the capacity retention rates of Example 2 and Comparative Example 2.
[0039]
[Table 2]

[0040]
<Result>
From Table 1, the discharge end voltage was set to 4.1 V vs. In Example 1 in which Li / Li ⁺ was used, the capacity retention was 80%, whereas the discharge end voltage was 3.5 V vs. 3.5%. Comparative Example 1 in which Li / Li ⁺ was used had a capacity retention of 59%.
[0041]
Also, from Table 2, the discharge end voltage was 4.1 V vs. In Example 2 in which Li / Li ⁺ was used, the capacity retention was 76%, whereas the discharge end voltage was 3.5 V vs. 3.5%. Comparative Example 2 in which Li / Li ⁺ was used had a capacity retention of 42%.
[0042]
<Other embodiments>
The present invention is not limited to the embodiments described with reference to the above description and drawings. For example, the following embodiments are also included in the technical scope of the present invention, and furthermore, besides the following, within the scope not departing from the gist. Can be implemented with various modifications.
[0043]
In the above-described embodiment, a three-electrode cell has been described, but the battery structure is not particularly limited, and may be a square, cylindrical, bag-shaped, lithium polymer battery, or the like.
[0044]
As the positive electrode active material used in the nonaqueous electrolyte secondary battery of the present invention, in the general formula _{Li X + a Ni Y Mn 2} -a-Y O 4-δ compound represented by a portion of Mn is further another can be used substituted with the element M general formula _{Li X + a Ni Y-b} M b Mn 2-a-Y O 4-δ compound represented by. Here, M is an element such as Al, Ti, Fe, Nb, Mo, and W.
[0045]
【The invention's effect】
According to the present invention, the high-temperature cycle life of a nonaqueous electrolyte secondary battery using a so-called 5V-class positive electrode active material can be improved.
[Brief description of the drawings]
FIG. 1 is a diagram showing the first cycle discharge characteristics of Example 1 and Comparative Example 1. FIG. 2 is a diagram showing the first cycle discharge characteristics of Example 2 and Comparative Example 2.

Claims (1)

A positive electrode including a positive electrode active material capable of inserting and extracting lithium ions, a negative electrode, a method for discharging a non-aqueous electrolyte secondary battery including a non-aqueous electrolyte,
The positive electrode active material has a general formula of Li _{X + a} Ni _Y Mn _2-a- YO _4-δ (where 0 <X ≦ 1.0, 0 ≦ a ≦ 0.1, 0.45 ≦ Y ≦ 0.55 , 0 ≦ δ ≦ 0.4), wherein the non-aqueous electrolyte secondary battery is discharged in a potential region where Mn ⁴⁺ contained in the positive electrode active material does not change to Mn ³⁺ . Next battery discharge method.

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