JP3550783B2 - Lithium-containing transition metal composite oxide, method for producing the same, and use thereof - Google Patents

Description

【００６６】
層状構造の発達程度を表すＸ線回折ピークの強度比、｛Ｉ（００６）＋Ｉ（１０２）｝／Ｉ（１０１）の値が０．５以下であることから、Ｌｉ面へのＮｉ、Ｃｏ及びＭｎの進入が殆どないことが分った。
【００６７】
［電池の構成］
得られた層状構造のＬｉ_１．０ Ｍｎ_０．２ Ｃｏ_０．３ Ｎｉ_０．５ Ｏ_２ と、導電剤のポリテトラフルオロエチレンとアセチレンブラックの混合物（商品名：ＴＡＢ−２）を、重量比で２：１の割合で混合した。混合物７５ｍｇを１ｔｏｎ／ｃｍ^２の圧力で、２０ｍｍφのメッシュ（ＳＵＳ ３１６）上にペレット状に成型した後、２００℃で５時間、減圧乾燥処理を行った。これを図１の３の正極に用いて、図１の５の負極にはリチウム箔（厚さ０．２ｍｍ）から切り抜いたリチウム片を用いて、電解液には六フッ化リン酸リチウムを１ｍｏｌ／ｄｍ^３の濃度で溶解したプロピレンカーボネートとジエチルカーボネートの体積比１：４の混合溶媒に溶解したものを図１の４のセパレーターに含浸させて、断面積２．５ｃｍ^２の図１に示した電池を構成した。
【００６８】
［電池特性の評価］
上記方法で作成した電池を用いて、０．４ｍＡ／ｃｍ^２の一定電流で、電池電圧が４．３Ｖから３．０Ｖの間で充放電を繰り返した。結果を表２に示した。
【００６９】
【表２】

【００７０】
２５サイクル目の放電容量は１５０ｍＡｈ／ｇを示し、１サイクル目の放電容量に対して９６％の容量を維持していた。
【００７１】
実施例２
［Ｌｉ_１．１ Ｍｎ_０．２ Ｃｏ_０．０５Ｎｉ_０．７５Ｏ_２ ］
実施例２として、水酸化リチウム一水和物（試薬特級）とγ−ＭｎＯＯＨ（東ソー株式会社製）と四三酸化コバルト（試薬特級）と水酸化ニッケル（試薬特級）とをモル比でＬｉ：Ｍｎ：Ｃｏ：Ｎｉが１．１：０．２：０．０５：０．７５になるように混合した以外は、実施例１と同様にして、リチウム含有遷移金属複合酸化物を製造した。
【００７２】
得られた化合物のＸ線回折及び化学分析の結果から、この化合物は層状構造を持つ、Ｌｉ_１．１ Ｍｎ_０．２ Ｃｏ_０．０５Ｎｉ_０．７５Ｏ_２ であることが分った。
【００７３】
図２にＸ線回折図、表１に化学分析結果を示した。
【００７４】
層状構造の発達程度を表すＸ線回折ピークの強度比、｛Ｉ（００６）＋Ｉ（１０２）｝／Ｉ（１０１）の値は０．５以下であり、Ｌｉ面へのＮｉ、Ｃｏ及びＭｎの進入が殆どないことが分った。
【００７５】
次に、このＬｉ_１．１ Ｍｎ_０．２ Ｃｏ_０．０５Ｎｉ_０．７５Ｏ_２ を正極に使用する以外は、実施例１と同様に電池を構成して評価し、その結果を表２に示した。
【００７６】
２５サイクル目の放電容量を１６１ｍＡｈ／ｇを示し、１サイクル目の放電容量の９６％を維持していた。
【００９６】
比較例１
比較例１として、Ｌｉ_１．０ Ｍｎ_０．２ Ｎｉ_０．８ Ｏ_２ を以下の方法により製造した。
【００９７】
水酸化リチウム一水和物（試薬特級）と水酸化ニッケル（試薬特級）と二酸化マンガン（国際標準サンプル、ＩＣ−１７）をモル比でＬｉ：Ｍｎ：Ｎｉが１．０：０．２：０．８になるように混合した後、錠剤に成型し、酸素雰囲気下４５０℃の温度で１０時間、第１の熱処理を施した。次にこれを室温まで降温した後、乳鉢で粉砕、混合し、再度錠剤に成型し、酸素雰囲気下７５０℃の温度で２４時間、第２の熱処理を施した。
【００９８】
得られた化合物のＸ線回折の結果から、この化合物は、Ｌｉ_２ＭｎＯ_３とＬｉＮｉＯ_２型の層状構造を持つ化合物の複合体であることが分った。図２にＸ線回折図、表１に化学分析結果を示した。
【００９９】
層状構造の発達程度を表すＸ線回折ピークの強度比、｛Ｉ（００６）＋Ｉ（１０２）｝／Ｉ（１０１）の値は、０．５９３であり、０．５以上であることから、Ｌｉ面へ一部Ｎｉ及びＭｎが挿入していることが分った。
【０１００】
次に、これを図１の３の正極に用いた以外は、実施例１と同様な電池を構成し、評価した。結果を図３に示した。
【０１０１】
２５サイクル目の放電容量は１３０ｍＡｈ／ｇを示し、１サイクル目の放電容量に対して８５％の容量しか維持していなかった。
【０１０２】
比較例２
比較例２として、層状構造のＬｉＮｉＯ_２を以下の方法により作成した。
【０１０３】
水酸化リチウム一水和物（試薬特級）と水酸化ニッケル（試薬特級）をモル比でＬｉ：Ｎｉが１．０：１．０になるように混合した後、錠剤に成型し、酸素中で７５０℃の温度で１６時間、第１の熱処理を施した。次にこれを室温まで降温した後、乳鉢で粉砕、混合し、再度錠剤に成型し、酸素雰囲気下７５０℃の温度で２４時間、第２の熱処理を施した。得られた化合物のＸ線回折及び化学分析の結果から、この化合物は層状構造を持つ、ＬｉＮｉＯ_２であることが分った。図２にＸ線回折図を、表１に化学分析結果を示した。
【０１０４】
層状構造の発達程度を表すＸ線回折ピークの強度比、｛Ｉ（００６）＋Ｉ（１０２）｝／Ｉ（１０１）の値が０．３７９で、Ｌｉ面へのＮｉ及びＭｎの進入が殆どないことが分った。
【０１０５】
次に、これを図１の３の正極に用いた以外は、実施例１と同様な電池を構成し、評価した。結果を図３に示した。
【０１０６】
２５サイクル目の放電容量は１２０ｍＡｈ／ｇを示し、１サイクル目の放電容量に対して７０％の容量しか維持していなかった。
【０１０７】
【発明の効果】
以上述べてきたとおり、本発明によってリチウム含有遷移金属複合酸化物を再現良く製造することが可能となる。
【０１０８】
さらに、これを正極に用いることで、安定した充放電サイクル特性を示し、従来にはない高容量で高エネルギー密度の高性能なリチウム二次電池が構成可能になる。
【図面の簡単な説明】
【図１】実施例１〜２及び比較例１〜２で構成した電池の実施態様を示す断面図である。
【符号の説明】
１ 正極リード線
２ 正極集電用メッシュ
３ 正極
４ セパレータ
５ 負極
６ 負極集電用メッシュ
７ 負極用リード線
８ 容器
【図２】実施例１〜２及び比較例１〜２で作成した化合物のＸ線回折図を示す。[0001]
[Industrial applications]
The present invention relates to a novel method for producing a lithium-containing transition metal composite oxide and a lithium secondary battery using the same, and more specifically, a lithium compound, a nickel compound,Contains trivalent manganeseA manganese compound and a cobalt compound are heat-treated to give Li_xMn_yCo_zNi_{1- (y + z)}O_Two(Where x is 0.9 <x ≦ 1.2, and y and z are respectively 0.0 <y <0.5 and 0.0<z <0.5 and 0.0 <y + z ≦ 0.5. The present invention relates to a method for producing a lithium nickel manganese composite oxide having a layered structure, and a lithium secondary battery using the same for a positive electrode.
[0002]
A lithium-containing transition metal oxide having a layered structure is a material that is expected to function as a lithium host compound because it has a migration path and an accommodation site for lithium ions in a crystal structure. Further, lithium in the crystal structure can be electrochemically contained and released from the redox ability of the transition metal, and is attracting attention as an active material of a lithium secondary battery.
[0003]
A lithium secondary battery is a new type of secondary battery that is expected to be put to practical use as a high energy density battery.
[0004]
[Prior art]
LiMO with a rock salt type structure and a layered structure in which lithium and transition metals are regularly arranged on the (111) plane index₂Type oxides (M is a transition metal) have attracted attention as a positive electrode active material for lithium secondary batteries.
[0005]
Among them, lithium cobalt oxide (LiCoO)₂) And lithium nickel oxide (LiNiO)₂) Shows a high discharge voltage of 4V class when used as a positive electrode active material of a lithium secondary battery, and a wide range of researches from basics to practical use of these two compounds have been actively conducted. I have.
[0006]
Already, ion-type lithium secondary batteries using lithium cobalt oxide for the positive electrode active material and carbon material for the negative electrode have been put into practical use. However, due to resource constraints and cost of the cobalt raw material, lithium nickel oxide Attention is focused on the practical use of things.
[0007]
Lithium nickel oxide is a cathode active material that can be expected to have a discharge capacity higher than that of lithium cobalt oxide in the 4V class. However, there are significant differences in discharge performance depending on the manufacturing method, and materials that exhibit constant charge and discharge characteristics with good reproducibility. In order to manufacture, it is necessary to set extremely strict manufacturing conditions, and even with the obtained material, the charge / discharge characteristics are significantly deteriorated with the increase in the number of charge / discharge cycles. Therefore, it has not been put to practical use until now.
[0008]
The cause is considered as follows.
[0009]
Generally, for nickel compounds, Ni²⁺Is stable, and when various nickel compounds are heat-treated, NiO having a rock salt type structure is easily generated.
[0010]
When the molar ratio of the nickel compound and the lithium compound is not completely stoichiometric, it is easy to take a structure in which Ni is mixed on the Li surface, and the LiNiO layer having a layered structure is developed.₂Difficult to generate.
[0011]
It has long been known that the generation of NiO and the irregular arrangement of Ni on the Li surface significantly reduce the charge / discharge characteristics. Therefore, it is originally required to produce a material exhibiting constant charge / discharge characteristics with good reproducibility. Have difficulty. As a solution, for example, Ni³⁺From Ni²⁺In order to prevent the reduction reaction to oxidization, it is necessary to perform heat treatment in an oxidizing atmosphere.
[0012]
Further, even when lithium nickel oxide having a layered structure can be synthesized by the above method, there are the following essential problems with respect to the charge / discharge reaction.
[0013]
Ni in layered lithium nickel oxide³⁺The ions have a low spin type electron configuration (3d⁷: T_2g ⁶・ E_g ¹)have. Ni by charging³⁺One electron of ion is removed and Ni⁴⁺Is generated. At this time, two energetically different orbits forming a 3d orbit (t_2g ⁶And e_g ¹) Of the upper e_g ¹Since one electron is removed from the orbit, the crystal field changes, causing a change in the crystal structure.
[0014]
Ohzuku et al. Have confirmed that the crystal structure change of lithium nickel oxide due to charging changes from hexagonal to monoclinic to hexagonal by X-ray diffraction (J. Electrochem. Soc., Vol. 140, pp-1862 (1993)).
[0015]
According to Arai et al., The charge eventually changes into two hexagonal crystals whose C-axis lengths are greatly increased, causing an irreversible decomposition reaction of a part of the crystal structure, and reinsertion of lithium. It is considered that the discharge capacity is reduced due to the impossibility of the above (34th Battery Symposium, Lecture No .: 2A09, Abstracts of Publications, p. 49 (1993)).
As described above, it is considered that it is difficult to promote a reversible charge / discharge reaction due to an irreversible change in crystal structure based on the intrinsic properties of nickel accompanying the charge / discharge reaction.
[0016]
As described above, lithium nickel oxide is a positive electrode active material that can be expected to have a discharge capacity higher than that of lithium cobalt oxide in the 4V class, but has not yet been put to practical use.
[0017]
For this reason, for practical use, in order to solve problems relating to production and electrochemical characteristics due to the intrinsic physical properties of nickel, studies are being made on changes in basic physical properties due to complexation with other transition metals.
[0018]
Japanese Patent Application Laid-Open No. 5-283076 proposes a method of improving charge / discharge cycle characteristics by complexing with another transition metal.
[0019]
This is because the energy level of the 3d orbit is changed to Ni by the complexation of nickel and another transition metal.³⁺By changing the energy level of the 3d orbit so as to suppress the change of the crystal field during charge and discharge, thereby improving the reproducibility of synthesis and improving the charge and discharge cycle characteristics. This is a proposal for improvement.
[0020]
However, according to our study, under the manufacturing conditions in which the heat treatment is performed in a single step at a high temperature of 700 ° C. to 900 ° C. as proposed in this proposal, the reduction reaction of nickel itself is likely to occur together with the complexation with the transition metal, As a result, a part of NiO having a rock salt type structure is generated, so that it is difficult to produce a compound having sufficient charge / discharge cycle characteristics.
[0021]
On the other hand, Japanese Patent Application Laid-Open No. 6-96768 proposes a method for producing a material exhibiting constant charge / discharge characteristics with good reproducibility by performing heat treatment in oxygen in two steps using manganese dioxide as a transition metal to be complexed. are doing.
[0022]
This proposal proposes a layered structure of lithium nickel manganese oxide with stable charge-discharge cycle characteristics through an intermediate composed of lithium, manganese, and nickel, which can be easily converted to a layered structure by heating. It is intended to propose a method of combining.
[0023]
However, according to our study, when a mixture of a lithium compound, a nickel compound and manganese dioxide is subjected to a heat treatment as described in this patent, a rock salt structure but an insulator and an electrochemically inactive layered structure are obtained. Li₂MnO₃Are easily generated, and it is difficult to obtain a positive electrode material having sufficient charge / discharge characteristics.
[0024]
As described above, various studies have been made on the change in basic physical properties due to complexing with other transition metals for the purpose of solving the problems related to production and electrochemical properties, but the physical properties inherent in nickel have been studied. Due to the cause considered to be caused by the above, it has not yet been put to practical use.
[0025]
On the other hand, with the recent spread of portable devices for personal use, there is a strong demand for the development of a small, lightweight, and high energy density secondary battery.
[0026]
As a secondary battery that can meet this demand, a lithium secondary battery using lithium or a substance capable of inserting and extracting lithium as a negative electrode has been proposed.
[0027]
Until now, ion-type lithium secondary batteries using lithium cobalt oxide as the positive electrode active material have been put into practical use. Attention has been focused on the practical use of nickel oxide and even lithium manganese oxide.
[0028]
[Problems to be solved by the invention]
An object of the present invention relates to improvement of a lithium-containing transition metal composite oxide, and more specifically, proposes a new method for producing a lithium-containing transition metal composite oxide having a novel layered structure with good reproducibility, and further uses this compound as a positive electrode. It is an object of the present invention to provide a 4V-class lithium secondary battery having an unprecedented high output and high energy density.
[0029]
[Means for Solving the Problems]
The present inventors have conducted intensive studies in order to solve the above problems, and as a result, heat-treated a lithium compound and a transition metal compound to obtain a novel Li compound._xMn_yCo_zNi_{1- (y + z)}O₂(Where x is 0.9 <x ≦ 1.2, and y and z are 0.0 <y <0.5 and 0.0 ≦ z <0.5 and 0.0 <y + z ≦ 0.5)). A lithium-containing transition metal composite oxide having a layered structure of 0.5) can be produced with good reproducibility. Further, when this is used for a positive electrode, stable charge / discharge cycle characteristics are exhibited, which has not been achieved conventionally. The present inventors have found that a lithium secondary battery having a high capacity and a high energy density can be constructed, and have completed the present invention.
[0030]
[Action]
Hereinafter, the present invention will be described specifically.
[0031]
Of the present invention,Synthesized using a compound containing trivalent manganese as a manganese raw materialLi_xMn_yCo_zNi_{1- (y + z)}O_Two(Where x is 0.9 <x ≦ 1.2, and y and z are respectively 0.0 <y <0.5 and 0.0<z <0.5 and 0.0 <y + z ≦ 0.5. The layered lithium-containing transition metal composite oxide according to (1) is a layered structure LiNiO._TwoHas the same space group R-3m structure as More specifically, it is a compound having a layered structure in which a surface containing nickel and manganese in a predetermined molar ratio with a lithium surface is regularly arranged along a plane index (111) plane of a rock salt type structure. As a manganese compound used for the synthesis of this compound, it is essential to use a manganese compound containing manganese of +3 valence.
[0032]
Although the details are unknown, when a manganese compound consisting of +4 manganese is used, the reaction between +4 manganese and lithium tends to occur in the early stage of the reaction, and although it has a rock salt structure, it is an insulator and has conductivity. Bad layered structure Li₂MnO₃Is likely to be generated. Conversely, when a manganese compound composed of +2 manganese is used, the oxidation reaction of manganese itself occurs partially in the heat treatment process, which is a factor that promotes the reduction reaction of nickel, thereby producing NiO having poor conductivity. Is likely to occur.
[0033]
On the other hand, when a manganese compound containing +3 manganese is used, the progress of the above complex reaction is suppressed, the average valence of the transition metal is +3, the electrochemical capacity is large, and a layered structure having good crystallinity is obtained. A lithium-containing transition metal composite oxide having a developed structure can be produced with good reproducibility.
[0034]
The manganese compound containing +3 manganese is not particularly limited.₂O₃, MnOOH, Mn₃O₄However, when γ-MnOOH is used, the effect of suppressing the progress of the side reaction is high, which is more preferable.
[0035]
The lithium compound used in the present invention is not particularly limited, and examples thereof include lithium hydroxide, lithium oxide, lithium carbonate, lithium nitrate, lithium chloride, lithium sulfate, lithium acetate, lithium iodide, lithium peroxide, and alkyl lithium. Illustrated.
[0036]
Although the nickel compound used in the present invention is not particularly limited, for example, nickel hydroxide, nickel oxide (NiO, Ni₂O₃Etc.), nickel carbonate, nickel nitrate, nickel chloride, nickel sulfate, nickel acetate, nickel oxyhydroxide (NiOOH) and the like.
[0037]
Although the cobalt compound used in the present invention is not particularly limited, for example, cobalt hydroxide, cobalt oxide (CoO, Co₂O₃, Co₃O₄Etc.), cobalt carbonate, cobalt nitrate, cobalt chloride, cobalt sulfate, cobalt acetate, cobalt oxyhydroxide (CoOOH).
[0038]
When the reaction system was made basic, the lithium compound and the nickel compound produced Ni Ni.³⁺Ni²⁺It is more preferable to use each of the hydroxides, since the reduction reaction to is suppressed.
[0039]
Further, there is no particular problem even if hydrate or anhydride is used for the lithium compound and the nickel compound, respectively.
[0040]
Of the present invention,Synthesized using a compound containing trivalent manganese as a manganese raw materialLi_xMn_yCo_zNi_{1- (y + z)}O_Two(Where x is 0.9 <x ≦ 1.2, and y and z are respectively 0.0 <y <0.5 and 0.0<z <0.5 and 0.0 <y + z ≦ 0.5. In the method for producing a lithium-containing transition metal composite oxide having a layered structure, the heat treatment of the lithium compound and the transition metal compound is preferably performed in the range of 450 ° C to 900 ° C.
[0041]
This is because when the heat treatment temperature is lower than 450 ° C., the Li salt having a rock salt structure but an insulator and an electrochemically inert layer structure is formed.₂MnO₃Is easily generated, and it is difficult to finally obtain a positive electrode material exhibiting sufficient charge / discharge characteristics. Further, when the heat treatment temperature exceeds 900 ° C., release of lithium to the outside of the reaction system is liable to occur. Since the +3 valence of Ni is reduced to +2 and the generation of electrochemically inactive NiO is likely to occur, and the reduction reaction of the composite manganese to +2 is likely to occur. This is because it becomes difficult to obtain an array of high-performance compounds.
[0042]
Of the present invention,Synthesized using a compound containing trivalent manganese as a manganese raw materialLi_xMn_yCo_zNi_{1- (y + z)}O_Two(Where x is 0.9 <x ≦ 1.2, and y and z are respectively 0.0 <y <0.5 and 0.0<z <0.5 and 0.0 <y + z ≦ 0.5. In the production of the lithium-containing transition metal composite oxide having the layered structure of the above), it is preferable to perform heat treatment in two or more stages. Further, it is particularly preferable to perform two or more heat treatments at successively higher temperatures.
[0043]
Because, in the one-step heat treatment, a heat treatment at a high temperature exceeding 700 ° C. is required in order to produce a lithium nickel manganese composite oxide having a layered structure, and the complex of a lithium compound and a transition metal compound is required. This is because the reduction reaction of nickel itself is likely to occur with the progress of the conversion reaction, and the rock salt type NiO becomes a partially generated compound, and the electrochemical capacity decreases.
[0044]
On the other hand, in a state where the reduction reaction of nickel itself is suppressed by heat treatment at two or more stages, that is, a low-temperature heat treatment, a composite reaction of lithium and a transition metal is advanced, and then a layered structure is developed.LetWhen the heat treatment is performed at a high temperature, it is possible to reduce the non-uniformity of the reaction due to the slight temperature distribution generated inside the solid phase and to reduce the occurrence of side reactions due to local deviation of the raw material composition. Li, in which the progress of so-called side reactions is suppressed, the average valence of the transition metal is +3, the electrochemical capacity is high, and a layered structure with good crystallinity is developed._xMn_yCo_zNi_{1- (y + z)}O_Two(Where x is 0.9 <x ≦ 1.2, and y and z are respectively 0.0 <y <0.5 and 0.0<z <0.5 and 0.0 <y + z ≦ 0.5. The lithium-containing transition metal composite oxide having the layered structure of (a) can be produced with good reproducibility.
[0045]
Of the present invention,Synthesized using a compound containing trivalent manganese as a manganese raw materialLi_xMn_yCo_zNi_{1- (y + z)}O_Two(Where x is 0.9 <x ≦ 1.2, and y and z are respectively 0.0 <y <0.5 and 0.0<z <0.5 and 0.0 <y + z ≦ 0.5. In the production of the layer-structured lithium-containing transition metal composite oxide according to (1), it is desirable to provide a temperature lowering step during the heat treatment step, and pulverize and mix the reactants during the temperature lowering step.
[0046]
Because, during the heat treatment, a temperature lowering process is provided, and during this temperature lowering process, the reactants are crushed and mixed, thereby causing a non-uniform reaction due to a slight temperature distribution inside the solid phase, which occurs during the heat treatment, This is because it is possible to suppress the occurrence of a side reaction due to local deviation of the raw material composition.
[0047]
Although there are no particular restrictions on the temperature lowering conditions, it is desirable to lower the temperature in the atmosphere to a temperature at which moisture does not adsorb to the surface or the like.
[0048]
Of the present invention,Synthesized using a compound containing trivalent manganese as a manganese raw materialLi_xMn_yCo_zNi_{1- (y + z)}O_Two(Where x is 0.9 <x ≦ 1.2, and y and z are respectively 0.0 <y <0.5 and 0.0<z <0.5 and 0.0 <y + z ≦ 0.5. In the case of using a solid compound as a starting material in the production of the lithium-containing transition metal composite oxide having the layered structure of the above-mentioned), it is preferable that the mixed raw material is formed into a molded body and heat-treated.
[0049]
The reason for this is that by forming a molded body, the contact between the raw materials becomes good, and the above-mentioned non-uniformity of the reaction can be eliminated.
[0050]
The shape and molding conditions of the molded body are not particularly limited, but it is desirable that the contact between the raw materials is sufficiently maintained.
[0051]
Of the present invention,Synthesized using a compound containing trivalent manganese as a manganese raw materialLi_xMn_yCo_zNi_{1- (y + z)}O_Two(Where x is 0.9 <x ≦ 1.2, and y and z are respectively 0.0 <y <0.5 and 0.0<z <0.5 and 0.0 <y + z ≦ 0.5. In the production of the layer-structured lithium-containing transition metal composite oxide according to (2), the atmosphere for the heat treatment is preferably an oxidizing atmosphere.
[0052]
This is because the reduction reaction of nickel and manganese can be made less likely to occur by using an oxidizing atmosphere. In particular, it is desirable to use oxygen for the oxidizing atmosphere. By performing the heat treatment in the oxygen atmosphere, the reduction reaction of nickel and manganese can be made more difficult to occur.
[0053]
For the positive electrode of the lithium secondary battery of the present invention, it is essential to use the lithium-containing transition metal composite oxide having a layered structure obtained by the method for producing a lithium-containing transition metal composite oxide of the present invention.
[0054]
By using the above compound for the positive electrode, a secondary battery having a high capacity and a high energy density can be configured.
[0055]
In addition, a secondary battery having excellent cycle characteristics is obtained as compared with the case where a layered lithium nickel oxide or lithium manganese nickel composite oxide is used.
[0056]
As the negative electrode used in the lithium secondary battery of the present invention, lithium metal, a lithium alloy, or a compound capable of inserting and extracting lithium can be used. Examples of the lithium alloy include a lithium / aluminum alloy, a lithium / tin alloy, and a lithium / lead alloy. Compounds capable of inserting and extracting lithium include carbonaceous materials such as graphite and graphite, FeO, Fe₂O₃, Fe₃O₄Such as iron oxide, CoO, Co₂O₃, Co₃O₄And metal oxides such as cobalt oxide.
[0057]
The electrolyte used in the lithium secondary battery of the present invention is not particularly limited, for example, propylene carbonate, carbonates such as diethyl carbonate, sulfolane, sulfolane such as dimethoxyethane, lactones such as γ-butyrolactone, In an organic solvent of at least one kind of ether such as dimethoxyethane, at least one kind of lithium salt such as lithium perchlorate, lithium tetrafluoroborate, lithium hexafluorophosphate, lithium trifluoromethanesulfonate, etc. Or an inorganic or organic lithium ion conductive solid electrolyte can be used.
[0058]
Li prepared by heat-treating a lithium compound, a nickel compound, and a manganese compound composed of +3 manganese according to the present invention._xMn_yCo_zNi_{1- (y + z)}O_Two(Where x is 0.9 <x ≦ 1.2, and y and z are respectively 0.0 <y <00.5 and 0.0<z <0.5 and 0.0 <y + z ≦ 0.5. The battery shown in FIG. 1 was constructed using the lithium-containing transition metal composite oxide having the layered structure of the above) as the positive electrode active material.
[0059]
In the figure, 1: positive electrode lead wire, 2: positive electrode current collecting mesh, 3: positive electrode, 4: separator, 5: negative electrode, 6: negative electrode current collecting mesh, 7: negative electrode lead wire, 8: container, Is shown.
[0060]
Examples are shown below as specific examples of the present invention, but the present invention is not limited to these examples.
[0061]
【Example】
Example 1
[Li_1.0Mn_0.2Co_0.3Ni_0.5O₂]
As Example 1, Li_1.0Mn_0.2Co_0.3Ni_0.5O₂Was produced by the following method.
[0062]
Li: Mn: Co: Ni by molar ratio of lithium hydroxide monohydrate (special grade reagent), γ-MnOOH (manufactured by Tosoh Corporation), cobalt trioxide (special grade reagent), and nickel hydroxide (special grade reagent) Was mixed so as to be 1.0: 0.2: 0.3: 0.5, then molded into tablets, and subjected to a first heat treatment at 600 ° C. for 24 hours in an oxygen atmosphere. Next, after the temperature was lowered to room temperature, it was pulverized and mixed in a mortar, molded again into tablets, and subjected to a second heat treatment at a temperature of 850 ° C. for 20 hours in an oxygen atmosphere.
[0063]
From the results of X-ray diffraction and chemical analysis of the obtained compound, this compound has a layered structure._1.0Mn_0.2Co_0.3Ni_0.5O₂It turned out to be.
[0064]
FIG. 2 shows the X-ray diffraction pattern, and Table 1 shows the results of the chemical analysis.
[0065]
[Table 1]

[0066]
Since the value of the intensity ratio of the X-ray diffraction peak, {I (006) + I (102)} / I (101), which indicates the degree of development of the layer structure, is 0.5 or less, Ni, Co, and It was found that there was almost no ingress of Mn.
[0067]
[Battery configuration]
Li of layered structure obtained_1.0Mn_0.2Co_0.3Ni_0.5O₂And a mixture of a conductive agent, polytetrafluoroethylene and acetylene black (trade name: TAB-2) were mixed at a weight ratio of 2: 1. 75 mg of the mixture is 1 ton / cm²After being formed into a pellet on a 20 mmφ mesh (SUS 316) at a pressure of, a vacuum drying treatment was performed at 200 ° C. for 5 hours. This was used for the positive electrode 3 in FIG. 1, the negative electrode 5 in FIG. 1 was a piece of lithium cut out from a lithium foil (thickness 0.2 mm), and the electrolyte was 1 mol of lithium hexafluorophosphate. / Dm³1 was dissolved in a mixed solvent of propylene carbonate and diethyl carbonate at a concentration of 1: 4 in a volume ratio of 1: 4, and impregnated into the separator of FIG.²The battery shown in FIG.
[0068]
[Evaluation of battery characteristics]
0.4 mA / cm using the battery prepared by the above method.²The charging / discharging was repeated at a constant current of 4.3 V and a battery voltage of 4.3 V to 3.0 V. The results are shown in Table 2.
[0069]
[Table 2]

[0070]
The discharge capacity at the 25th cycle was 150 mAh / g, and was 96% of the discharge capacity at the 1st cycle.
[0071]
Example 2
[Li_1.1Mn_0.2Co_0.05Ni_0.75O₂]
In Example 2, lithium hydroxide monohydrate (special grade reagent), γ-MnOOH (manufactured by Tosoh Corporation), cobalt trioxide (special grade reagent), and nickel hydroxide (special grade reagent) were used in a molar ratio of Li: A lithium-containing transition metal composite oxide was produced in the same manner as in Example 1 except that Mn: Co: Ni was mixed so as to be 1.1: 0.2: 0.05: 0.75.
[0072]
From the results of X-ray diffraction and chemical analysis of the obtained compound, this compound has a layered structure._1.1Mn_0.2Co_0.05Ni_0.75O₂It turned out to be.
[0073]
FIG. 2 shows the X-ray diffraction pattern, and Table 1 shows the results of the chemical analysis.
[0074]
The value of the intensity ratio of the X-ray diffraction peak, {I (006) + I (102)} / I (101), which indicates the degree of development of the layered structure, is 0.5 or less, and Ni, Co and Mn on the Li surface It turned out that there was almost no approach.
[0075]
Next, this Li_1.1Mn_0.2Co_0.05Ni_0.75O₂A battery was constructed and evaluated in the same manner as in Example 1, except that was used for the positive electrode. The results are shown in Table 2.
[0076]
The discharge capacity at the 25th cycle was 161 mAh / g, and 96% of the discharge capacity at the first cycle was maintained.
[0096]
Comparative Example 1
As Comparative Example 1, Li_1.0Mn_0.2Ni_0.8O₂Was produced by the following method.
[0097]
Li: Mn: Ni is 1.0: 0.2: 0 in a molar ratio of lithium hydroxide monohydrate (reagent grade), nickel hydroxide (reagent grade) and manganese dioxide (international standard sample, IC-17). After that, the mixture was molded into tablets, and subjected to a first heat treatment at 450 ° C. for 10 hours in an oxygen atmosphere. Next, after the temperature was lowered to room temperature, it was pulverized and mixed in a mortar, molded again into tablets, and subjected to a second heat treatment at 750 ° C. for 24 hours in an oxygen atmosphere.
[0098]
From the result of X-ray diffraction of the obtained compound, this compound was found to be Li₂MnO₃And LiNiO₂It was found to be a complex of compounds having a layered structure of the type. FIG. 2 shows the X-ray diffraction pattern, and Table 1 shows the results of the chemical analysis.
[0099]
The value of the intensity ratio of the X-ray diffraction peak, {I (006) + I (102)} / I (101), which indicates the degree of development of the layered structure, is 0.593, which is 0.5 or more. It was found that Ni and Mn were partially inserted into the surface.
[0100]
Next, a battery similar to that of Example 1 was constructed and evaluated except that this was used for the positive electrode of 3 in FIG. The results are shown in FIG.
[0101]
The discharge capacity at the 25th cycle was 130 mAh / g, and only 85% of the discharge capacity at the first cycle was maintained.
[0102]
Comparative Example 2
As Comparative Example 2, LiNiO having a layered structure was used.₂Was prepared by the following method.
[0103]
Lithium hydroxide monohydrate (special grade reagent) and nickel hydroxide (special grade reagent) are mixed at a molar ratio of Li: Ni of 1.0: 1.0, then molded into tablets, and then mixed with oxygen. The first heat treatment was performed at a temperature of 750 ° C. for 16 hours. Next, after the temperature was lowered to room temperature, it was pulverized and mixed in a mortar, molded again into tablets, and subjected to a second heat treatment at 750 ° C. for 24 hours in an oxygen atmosphere. From the results of X-ray diffraction and chemical analysis of the obtained compound, this compound has a layered structure.₂It turned out to be. FIG. 2 shows an X-ray diffraction pattern, and Table 1 shows the results of chemical analysis.
[0104]
The intensity ratio of the X-ray diffraction peak representing the degree of development of the layered structure, {I (006) + I (102)} / I (101), is 0.379, and there is almost no penetration of Ni and Mn into the Li surface. I understood that.
[0105]
Next, a battery similar to that of Example 1 was constructed and evaluated except that this was used for the positive electrode of 3 in FIG. The results are shown in FIG.
[0106]
The discharge capacity at the 25th cycle was 120 mAh / g, and only 70% of the discharge capacity at the first cycle was maintained.
[0107]
【The invention's effect】
As described above, the present invention makes it possible to produce a lithium-containing transition metal composite oxide with good reproducibility.
[0108]
Furthermore, by using this as the positive electrode, a stable high-capacity, high-energy-density, high-performance lithium secondary battery exhibiting stable charge / discharge cycle characteristics can be constructed.
[Brief description of the drawings]
FIG. 1 Example 12FIG. 3 is a cross-sectional view illustrating an embodiment of the battery configured in Comparative Examples 1 and 2.
[Explanation of symbols]
1 Positive lead wire
2 Mesh for positive electrode current collection
3 Positive electrode
4 separator
5 Negative electrode
6 Negative electrode current collector mesh
7 Lead wire for negative electrode
8 containers
FIG. 2 Example 12And X-ray diffraction diagrams of the compounds prepared in Comparative Examples 1 and 2.

Claims (3)

_{Li x Mn y Co z Ni 1-} (y + z) O 2 ( wherein x, which is synthesized using a compound containing a trivalent manganese as manganese starting material, at 0.9 <x ≦ 1.2, y and z are 0.0 <y <0.5 and 0.0 < z <0.5 and 0.0 <y + z ≦ 0.5, respectively.) Metal composite oxide. The process according to claim as a manganese compound consisting of trivalent manganese according to 1, lithium-containing transition metal composite oxide of a layered structure of claim 1, wherein the use of gamma-MnOOH. A lithium secondary battery using the lithium-containing transition metal composite oxide according to claim 1 for a positive electrode.

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