JP3655737B2 - Method for producing positive electrode active material for non-aqueous electrolyte secondary battery - Google Patents
Method for producing positive electrode active material for non-aqueous electrolyte secondary battery Download PDFInfo
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- JP3655737B2 JP3655737B2 JP22711297A JP22711297A JP3655737B2 JP 3655737 B2 JP3655737 B2 JP 3655737B2 JP 22711297 A JP22711297 A JP 22711297A JP 22711297 A JP22711297 A JP 22711297A JP 3655737 B2 JP3655737 B2 JP 3655737B2
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- XZGVWXIFQDZYFE-UHFFFAOYSA-N CCCCCCCCC1C(CC(C)CCC)CCCC1 Chemical compound CCCCCCCCC1C(CC(C)CCC)CCCC1 XZGVWXIFQDZYFE-UHFFFAOYSA-N 0.000 description 1
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- Y02E60/10—Energy storage using batteries
Description
【0001】
【発明の属する技術分野】
本発明は、非水電解液二次電池の正極活物質の製造方法に関するものであり、さらに詳しくは、組成が均一であり、微細で比表面積の高い正極材料として有用なリチウムマンガナイトを製造する方法に関する。
【0002】
【従来の技術】
近年、ラップトップ型コンピューターや携帯電話、カムコーダ等に代表されるポータブル機器の需要の増加に伴い、電源となる二次電池の開発が進んでいる。リチウム二次電池は、これまでの二次電池に比べて高電圧、高エネルギー密度を得ることができるため小型軽量化が期待されている。
この二次電池の正極に用いる材料として、LiCoO2 、LiNiO2 、LiMn2 O4 等の層状構造あるいはトンネル構造を有する材料が研究されている。これらの正極材料においては、リチウムイオンが結晶格子中の空サイトヘインターカレートとデインターカレートすることにより、電気化学反応が進行する。この中で、LiMn2 O4 については、いくつかの合成法が知られており、Mn硝酸塩や酢酸塩などを出発物質として水溶液中で析出させる方法(P.Barboux,J.M.Tarascon,and F.K.Shokoohi,J.Soid State Chem.,94,185−196,1991)、あるいは炭酸リチウムと二酸化マンガンを混合して固相法により合成する方法(J.M.Tarascon,W.R.McKinnon,F.Coowar,T.N.Bowmer,G.Amatucci,and D.Guymard,J.Electrochem.Soc.141,1421−1431)等が用いられている。
しかし、従来の方法では、低温において、微細な比表面積の高い正極材料を得ることは困難であった。
【0003】
【発明が解決しようとする課題】
このような状況の中で、本発明者らは、微細で比表面積の高い正極材料を簡便な操作で作製する方法を開発することを目標として鋭意研究を積み重ねた結果、安定な前駆体溶液を用いて合成したリチウムマンガン化合物を、酸素雰囲気中で200〜750℃で加熱処理することにより所期の目的を達成し得ることを見出し、本発明を完成するに至った。
即ち、本発明は、非水電解液を用いた二次電池の正極の活物質材料に用いるのに有用な、微細で歪みの少ない粒子からなるリチウムマンガン酸化物を製造する方法を提供することを目的とする。
また、本発明は、低温において微細な比表面積の高い正極材料を提供することを目的とする。
さらに、本発明は、上記正極材料を用いて、放電容量が大きく、サイクル特性に優れた二次電池を提供することをも目的としている。
【0004】
【課題を解決するための手段】
上記課題を達成する本発明は、一般式Li1-x Mn2-y O4 (0≦x<1.0、0≦y<0.5)で示されるスピネル型構造の複合酸化物の製造方法において、出発物質であるリチウム前駆体とマンガン前駆体を溶媒に溶解させ配位子置換することにより安定な前駆体溶液を調製し、この溶媒を留去あるいは濃縮することにより得られる前駆体を加熱処理させ正極材料を製造することを特徴とする二次電池の正極活物質の製造方法、である。
【0005】
【発明の実施の形態】
次に、本発明についてさらに詳述する。
非水電解液二次電池において大きな放電容量を得るための課題は、組成が均一であり、微細で比表面積の高いリチウムマンガナイトを得ることにある。上記目的を達成するために、本発明の非水電解液二次電池の正極活物質の製造方法では、一般式Li1-x Mn2-y O4 (0≦x<1.0、0≦y<0.5)で表されるスピネル型構造の複合酸化物の製造方法において、出発物質であるリチウム前駆体とマンガン前駆体を溶媒に溶解させ配位子置換することにより安定な前駆体溶液を調製し、この溶媒を留去あるいは濃縮することにより得られる前駆体を加熱処理させ、正極材料を製造する方法が採られる。
本発明は、前駆体としてLi(O−A)、Mn(O−B)z(z=2,3)とLi、Mnの配位子を変化させた原料を用いることを特徴とし、リチウムアルコキシドおよびリチウム塩、マンガンアルコキシドおよびマンガン錯塩などLi(O−A)、Mn(O−B)zとLi、Mnの配位子を変化させた原料を用いて適正な溶媒を用いることにより配位子を置換させ、安定な前駆体を形成させ正極材料を製造する方法を提供する。この方法によれば、固体混合法、水溶液からの沈澱法等、通常の正極材料の製造に使用される方法によるよりも、さらに低温において微細な比表面積の高い正極材料の提供が可能となる。
【0006】
本発明は、非水二次電池の正極材料チリウムマンガナイトの特殊な製造方法として前駆体法を提起しているが、この前駆体法の場合のリチウムマンガナイトの原料については、リチウム源としては、リチウムアルコキシドおよびリチウム塩が好ましい。望ましくはリチウムメトキサイド、リチウムエトキサイド、リチウムプロポキサイド、酢酸リチウムなどが好ましい。また、マンガン源としては、マンガンアルコキシドおよびマンガン錯塩が好ましい。アルコキシドとしては、メトキシド、エトキシド、およびイソプロポキシド等の炭素数1〜3のアルコキシド類が、また、マンガン錯塩としては、マンガンアセチルアセトナート(Mn=2価、3価)が好ましい。
それぞれの原料を溶解する溶媒については、エチレングリコールモノエチルエーテル、エチレングリコールモノメチルエーテルなどが好ましい。
【0007】
アルゴン雰囲気下、例えば、上記のリチウムアルコキシドあるいはリチウム塩とマンガンアルコキシドあるいはマンガン錯塩をリチウムとマンガンの原子比がLi/Mn(モル比)=0.5となるよう不活性ガス雰囲気中で秤量した後、それぞれ溶媒に溶解し、約125℃から140℃の温度で、3時間以上窒素あるいは酸素雰囲気中で還流し配位子置換を行う。得られた2溶液の溶媒を濃縮あるいは留去後さらに溶媒を加える。このリチウムおよびマンガン前駆体溶液を混合し常温で1時間以上攪拌しても良いし、さらに還流を3時間以上続けても良い。次いで、例えば、この前駆体溶液を80℃で減圧乾燥し、溶媒を留去し前駆体粉末を得る。合成した前駆体は150℃〜200℃で酸素雰囲気中3時間加熱することが好ましい。加熱処理の温度は出発原料により適宜設定されるが温度は200〜750℃が好ましい。加熱処理の温度が100℃未満では結晶化は進行しない。100℃以上200℃以下でも結晶化は進行するが長時間を要するので好ましくない。
焼成雰囲気については、空気雰囲気または空気よりも高濃度の酸素を含む雰囲気で合成を行う方が好ましい。さらに好ましくは、純酸素雰囲気中で加熱処理を行うことが好ましい。
【0008】
【作用】
本発明の非水電解液二次電池の正極材料の製造方法により、均質で、微細なLiMn2 O4 粉末の合成ができるのは、安定な前駆体溶液を調製できた効果による。即ち、本発明の出発物質であるリチウム前駆体とマンガン前駆体を溶媒に溶解させ配位子置換することにより、沈澱しない安定な前駆体溶液を調製できる。この溶媒を混合し攪拌あるいは還流することにより得られた前駆体溶液の溶媒を留去することにより得られる前駆体粉末を加熱処理することにより、配位子置換リチウムと配位子置換マンガンからほぼ同時に配位子の離脱が開始され、これに伴う前駆体由来のリチウムマンガナイトの結晶化が進行し、微細な結晶核が形成されたと考えられる。
【0009】
【実施例】
以下、実施例を挙げて本発明をさらに詳細に説明するが、本発明は、当該実施例によって何ら限定されるものではない。
実施例1
窒素雰囲気下、市販のリチウムエトキサイドとマンガンイソプロポキサイドをリチウムとマンガンの原子比がLi/Mn(モル比)=0.5となるよう秤量した後、それぞれエチレングリコールモノエチルエーテルに溶解し、135℃で3時間還流し配位子置換を行った。得られた2溶液の溶媒を濃縮後エチレングリコールモノエチルエーテルを加えた。この2溶液を混合し常温で1時間攪拌した後、得られた溶液を80℃で減圧乾燥し、前駆体粉末を得た。合成した前駆体粉末を200℃で酸素雰囲気中3時間加熱後250℃で酸素中3時間熱処理しリチウムマンガナイトを得た。得られたリチウムマンガナイトを粉末X線回折による分析(CuKα)を行った。その結果を図1に示す。図1から明らかなようにLiMn2 O4 に対応するピークが同定され250℃という低温でLiMn2 O4 が生成されたことが確認できた。電子顕微鏡観察結果より、得られた粉末の平均一次粒子径は20nmであった。
【0010】
実施例2
実施例1と同様に合成した前駆体粉末を、200℃で酸素雰囲気中3時間仮焼後500℃で酸素中3時間焼成してリチウムマンガナイトを得た。得られたリチウムマンガナイトを粉末X線回折による分析(CuKα)を行った。その結果を図1に示す。図1から明らかなように500℃での焼成においてもLiMn2 O4 の生成が確認された。電子顕微鏡観察結果より、得られた粉末の平均一次粒子径は20nmであった。
【0011】
実施例3
実施例1と同様に合成した前駆体粉末を、200℃で酸素雰囲気中3時間仮焼後700℃で酸素中3時間焼成してリチウムマンガナイトを得た。得られたリチウムマンガナイトを粉末X線回折による分析(CuKα)を行った。その結果を図1に示す。図1から明らかなように700℃の焼成によりLiMn2 O4 に対応するピークが同定されLiMn2 O4 の生成が確認された。電子顕微鏡観察結果より、得られた粉末の平均一次粒子径は22nmであった。
【0012】
比較例1
窒素雰囲気下、リチウムエトキサイドとマンガンイソプロポキサイドをリチウムとマンガンの原子比がLi/Mn(モル比)=0.5となるよう秤量した後、それぞれエチレングリコールモノエチルエーテルに溶解し、135℃で3時間還流し配位子置換を行った。得られた2溶液を溶媒留去後エチレングリコールモノエチルエーテルを加えた。この2溶液を混合し常温で1時間攪拌した後、得られた溶液を80℃で減圧乾燥し、前駆体粉末を得た。粉末X線回折(CuKα)の結果より、得られた粉末はアモルファス相であった。
【0013】
実施例4
実施例1から実施例3で合成した前駆体の熱分解挙動をTG−DTAにより調べた結果を図2に示す。測定に供した前駆体粉末は5.6gであり、昇温速度は5℃/minで酸素雰囲気中で評価した。200℃には燃焼によるLi/Mnの配位子の結合の開裂に伴う発熱ピークが見られた。発熱ピークが一つであることからリチウムアルコキシドとマンガンアルコキシドがほぼ同時に配位子の離脱が開始され、これに伴う前駆体由来のリチウムマンガナイトの結晶化が進行し、LiMn2 O4 単相が得られたことが分かる。
【0014】
実施例5
酢酸リチウムを溶解させたエチレングリコールモノメチルエーテルに等量のアセチルアセトンを加え、これを混合し酸素気流中で3時間還流した。また、マンガンとアセチルアセトナートを溶解させたエチレングリコールモノメチルエーテルに等量の2−アミノエタノールを加え、これを混合し酸素気流中で3時間還流した。ここでLi/Mnは0.5とした。得られた溶液をそれぞれ溶媒留去し、これにエチレングリコールモノメチルエーテルを加え、窒素中で還流を行った後に溶液を溶媒留去し、前駆体粉末を得た。得られた粉末を酸素中200℃で加熱し配位子部分を解裂させたのち、700℃で3時間焼成を行った。得られたリチウムマンガナイトについて粉末X線回折(CuKα)を行った。その結果を図3に示す。図3にみられるようにLiMn2 O4 に対応するピークが得られLiMn2 O4 単相の粉末であることが確認できた。電子顕微鏡観察結果より、得られた粉末の平均一次粒子径は30nmであった。本実施例により配位子を制御することで安定な前駆体が得られ、これを焼成して微細なLiMn2 O4 を生成することが可能となった。
【0015】
試験例1
図1のX線回折結果から得られた回折ピークの回折角度と、半価幅をHallの式に代入すると結晶子径と歪みの関係が得られる。250℃から700℃の全域にわたって、結晶子径はほぼ20nmであった。また700℃で焼成した試料の歪みは0.02%であった。
この700℃で製造した正極活物質の初期容量を評価するために試料電極を作製した。試料電極の構成は、正極活物質とアセチレンブラックとふっ素樹脂系結着剤が重量比で5:4:1となるように混合した正極合剤とし、対極Li、参照極を別のLi、電解液をプロピレンカーボネート、ジメトキシエタンの混合溶液にLiClO4 を溶かした液を用いて電池を組み立て、電池性能を評価したところ初期容量は126mAh/gが得られ、放電容量の大きく、かつサイクル特性の優れた電池となることが分かった。
【0016】
【発明の効果】
本発明によれば、前駆体法を用いて、従来技術では達成されなかった微細な、歪みの少ない粒子からなる正極材料が得られる。即ち、本発明の範囲外である比較例においては、結晶化していないアモルファス相、あるいは第二相の不純物が存在している。これに対し、本発明の範囲内である実施例においては、20〜35nmの微細なリチウムマンガナイト単相からなる粉末を得ることができる。したがって、本発明の正極活物質製造方法によれば、比表面積の高いリチウムマンガナイトが得られる。さらには、放電容量が大きく、サイクル特性に優れた電池を得ることができる。
【図面の簡単な説明】
【図1】本発明の実施例1、2、3において得られたLiMn2 O4 の粉末X線回折図である。
【図2】本発明の実施例4において得られた材料のTG−DTA曲線である。
【図3】本発明の実施例5において得られたLiMn2 O4 の粉末X線回折図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery. More specifically, the present invention produces lithium manganite having a uniform composition, a fine and high specific surface area, and useful as a positive electrode material. Regarding the method.
[0002]
[Prior art]
In recent years, with the increase in demand for portable devices such as laptop computers, mobile phones, camcorders, etc., development of secondary batteries that serve as power sources is progressing. Lithium secondary batteries are expected to be smaller and lighter because they can obtain higher voltage and higher energy density than conventional secondary batteries.
As a material used for the positive electrode of the secondary battery, materials having a layered structure or a tunnel structure such as LiCoO 2 , LiNiO 2 , LiMn 2 O 4 have been studied. In these positive electrode materials, the lithium ions intercalate with empty sites in the crystal lattice, whereby an electrochemical reaction proceeds. Among them, several synthesis methods are known for LiMn 2 O 4 , and a method of precipitation in an aqueous solution using Mn nitrate or acetate as a starting material (P. Barboux, JM Tarascon, and F. K. Shokohi, J. Soid State Chem., 94, 185-196, 1991), or a method in which lithium carbonate and manganese dioxide are mixed and synthesized by a solid phase method (JM Tarascon, WR McKinnon, F. Coower, TN Bowmer, G. Amatocci, and D. Guymard, J. Electrochem. Soc. 141, 1421-1431) are used.
However, in the conventional method, it is difficult to obtain a fine positive electrode material having a high specific surface area at a low temperature.
[0003]
[Problems to be solved by the invention]
Under such circumstances, the present inventors have conducted intensive research aimed at developing a method for producing a fine cathode material having a high specific surface area by a simple operation, and as a result, a stable precursor solution was obtained. It has been found that the intended purpose can be achieved by heat-treating the lithium manganese compound synthesized by use at 200 to 750 ° C. in an oxygen atmosphere, and the present invention has been completed.
That is, the present invention provides a method for producing a lithium manganese oxide composed of fine and less distorted particles, which is useful for use as an active material for a positive electrode of a secondary battery using a non-aqueous electrolyte. Objective.
Another object of the present invention is to provide a fine positive electrode material having a high specific surface area at low temperatures.
Another object of the present invention is to provide a secondary battery having a large discharge capacity and excellent cycle characteristics, using the positive electrode material.
[0004]
[Means for Solving the Problems]
The present invention for achieving the above object is to produce a composite oxide having a spinel structure represented by the general formula Li 1-x Mn 2-y O 4 (0 ≦ x <1.0, 0 ≦ y <0.5). In the method, a stable precursor solution is prepared by dissolving a lithium precursor and a manganese precursor as starting materials in a solvent and replacing the ligand, and a precursor obtained by distilling or concentrating the solvent is prepared. A method for producing a positive electrode active material for a secondary battery, wherein the positive electrode material is produced by heat treatment.
[0005]
DETAILED DESCRIPTION OF THE INVENTION
Next, the present invention will be described in further detail.
The problem for obtaining a large discharge capacity in a non-aqueous electrolyte secondary battery is to obtain lithium manganite having a uniform composition, fineness and high specific surface area. In order to achieve the above object, in the method for producing a positive electrode active material of a non-aqueous electrolyte secondary battery of the present invention, a general formula Li 1-x Mn 2-y O 4 (0 ≦ x <1.0, 0 ≦ In the method for producing a composite oxide having a spinel structure represented by y <0.5), a stable precursor solution is obtained by dissolving a lithium precursor and a manganese precursor as starting materials in a solvent and replacing the ligand. And a precursor obtained by distilling or concentrating the solvent is heat-treated to produce a positive electrode material.
The present invention is characterized in that Li (OA), Mn (OB) z (z = 2, 3) and a raw material in which Li and Mn ligands are changed are used as a precursor, and lithium alkoxide is used. Lithium salts, manganese alkoxides and manganese complex salts such as Li (OA), Mn (OB) z and Li, by using a suitable solvent using raw materials in which Li and Mn ligands are changed Is provided to form a stable precursor and to produce a positive electrode material. According to this method, it is possible to provide a fine positive electrode material having a high specific surface area at a lower temperature than by a method used for producing a normal positive electrode material, such as a solid mixing method or a precipitation method from an aqueous solution.
[0006]
The present invention proposes a precursor method as a special method for producing the positive electrode material thyllium manganite of the non-aqueous secondary battery. The lithium manganite raw material in this precursor method is used as a lithium source. Are preferably lithium alkoxides and lithium salts. Desirably, lithium methoxide, lithium ethoxide, lithium propoxide, lithium acetate and the like are preferable. Further, as the manganese source, manganese alkoxide and manganese complex salt are preferable. As the alkoxide, alkoxides having 1 to 3 carbon atoms such as methoxide, ethoxide and isopropoxide are preferable, and as the manganese complex salt, manganese acetylacetonate (Mn = 2 valent, trivalent) is preferable.
As the solvent for dissolving each raw material, ethylene glycol monoethyl ether, ethylene glycol monomethyl ether, and the like are preferable.
[0007]
After weighing, for example, the above lithium alkoxide or lithium salt and manganese alkoxide or manganese complex salt in an inert gas atmosphere so that the atomic ratio of lithium and manganese is Li / Mn (molar ratio) = 0.5 in an argon atmosphere. Each of them is dissolved in a solvent and refluxed in a nitrogen or oxygen atmosphere at a temperature of about 125 ° C. to 140 ° C. for 3 hours or more to perform ligand substitution. The solvent of the obtained two solutions is concentrated or distilled off, and then the solvent is added. The lithium and manganese precursor solutions may be mixed and stirred at room temperature for 1 hour or longer, and reflux may be continued for 3 hours or longer. Next, for example, the precursor solution is dried under reduced pressure at 80 ° C., and the solvent is distilled off to obtain a precursor powder. The synthesized precursor is preferably heated at 150 to 200 ° C. in an oxygen atmosphere for 3 hours. The temperature of the heat treatment is appropriately set depending on the starting material, but the temperature is preferably 200 to 750 ° C. When the temperature of the heat treatment is less than 100 ° C., crystallization does not proceed. Although crystallization proceeds even at 100 ° C. or more and 200 ° C. or less, it takes a long time, which is not preferable.
As for the firing atmosphere, it is preferable to perform the synthesis in an air atmosphere or an atmosphere containing oxygen at a higher concentration than air. More preferably, heat treatment is performed in a pure oxygen atmosphere.
[0008]
[Action]
The homogeneous and fine LiMn 2 O 4 powder can be synthesized by the method for producing the positive electrode material of the non-aqueous electrolyte secondary battery of the present invention because of the effect of preparing a stable precursor solution. That is, a stable precursor solution that does not precipitate can be prepared by dissolving the lithium precursor and manganese precursor, which are the starting materials of the present invention, in a solvent and replacing the ligand. By heating the precursor powder obtained by distilling off the solvent of the precursor solution obtained by mixing and stirring or refluxing this solvent, almost from the ligand-substituted lithium and the ligand-substituted manganese. At the same time, the detachment of the ligand was initiated, and the accompanying crystallization of lithium manganite derived from the precursor progressed, and it was considered that fine crystal nuclei were formed.
[0009]
【Example】
EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further in detail, this invention is not limited at all by the said Example.
Example 1
Under a nitrogen atmosphere, commercially available lithium ethoxide and manganese isopropoxide were weighed so that the atomic ratio of lithium and manganese was Li / Mn (molar ratio) = 0.5, and then dissolved in ethylene glycol monoethyl ether. The mixture was refluxed at 135 ° C. for 3 hours to perform ligand substitution. After concentrating the solvent of the obtained two solutions, ethylene glycol monoethyl ether was added. The two solutions were mixed and stirred at room temperature for 1 hour, and then the obtained solution was dried under reduced pressure at 80 ° C. to obtain a precursor powder. The synthesized precursor powder was heated at 200 ° C. in an oxygen atmosphere for 3 hours and then heat treated at 250 ° C. in oxygen for 3 hours to obtain lithium manganite. The obtained lithium manganite was analyzed by powder X-ray diffraction (CuKα). The result is shown in FIG. As is clear from FIG. 1, a peak corresponding to LiMn 2 O 4 was identified, and it was confirmed that LiMn 2 O 4 was produced at a low temperature of 250 ° C. From the result of observation with an electron microscope, the average primary particle size of the obtained powder was 20 nm.
[0010]
Example 2
The precursor powder synthesized in the same manner as in Example 1 was calcined at 200 ° C. for 3 hours in an oxygen atmosphere and then calcined at 500 ° C. for 3 hours in oxygen to obtain lithium manganite. The obtained lithium manganite was analyzed by powder X-ray diffraction (CuKα). The result is shown in FIG. As is apparent from FIG. 1, the formation of LiMn 2 O 4 was confirmed even in the firing at 500 ° C. From the result of observation with an electron microscope, the average primary particle size of the obtained powder was 20 nm.
[0011]
Example 3
The precursor powder synthesized in the same manner as in Example 1 was calcined at 200 ° C. for 3 hours in an oxygen atmosphere and then calcined at 700 ° C. for 3 hours in oxygen to obtain lithium manganite. The obtained lithium manganite was analyzed by powder X-ray diffraction (CuKα). The result is shown in FIG. As is clear from FIG. 1, a peak corresponding to LiMn 2 O 4 was identified by firing at 700 ° C., and the production of LiMn 2 O 4 was confirmed. From the result of observation with an electron microscope, the average primary particle diameter of the obtained powder was 22 nm.
[0012]
Comparative Example 1
In a nitrogen atmosphere, lithium ethoxide and manganese isopropoxide were weighed so that the atomic ratio of lithium and manganese was Li / Mn (molar ratio) = 0.5, and then dissolved in ethylene glycol monoethyl ether, respectively. The mixture was refluxed for 3 hours to perform ligand substitution. The obtained two solutions were evaporated, and then ethylene glycol monoethyl ether was added. The two solutions were mixed and stirred at room temperature for 1 hour, and then the obtained solution was dried under reduced pressure at 80 ° C. to obtain a precursor powder. From the result of powder X-ray diffraction (CuKα), the obtained powder was in an amorphous phase.
[0013]
Example 4
The results of examining the thermal decomposition behavior of the precursors synthesized in Examples 1 to 3 by TG-DTA are shown in FIG. The precursor powder used for the measurement was 5.6 g, and the temperature elevation rate was 5 ° C./min. At 200 ° C., an exothermic peak was observed accompanying the cleavage of the Li / Mn ligand bond by combustion. Since the exothermic peak is one, lithium alkoxide and manganese alkoxide start to detach from the ligand almost simultaneously, the accompanying crystallization of lithium manganite derived from the precursor proceeds, and the LiMn 2 O 4 single phase becomes You can see that it was obtained.
[0014]
Example 5
An equal amount of acetylacetone was added to ethylene glycol monomethyl ether in which lithium acetate was dissolved, and this was mixed and refluxed in an oxygen stream for 3 hours. Further, an equal amount of 2-aminoethanol was added to ethylene glycol monomethyl ether in which manganese and acetylacetonate were dissolved, and this was mixed and refluxed in an oxygen stream for 3 hours. Here, Li / Mn was set to 0.5. Each of the obtained solutions was distilled off, ethylene glycol monomethyl ether was added thereto, refluxed in nitrogen, and then the solution was distilled off to obtain a precursor powder. The obtained powder was heated in oxygen at 200 ° C. to cleave the ligand portion, and then calcined at 700 ° C. for 3 hours. The obtained lithium manganite was subjected to powder X-ray diffraction (CuKα). The result is shown in FIG. It was confirmed peak corresponding to LiMn 2 O 4 as seen in FIG. 3 is a powder of LiMn 2 O 4 single phase obtained. From the electron microscope observation results, the average primary particle size of the obtained powder was 30 nm. By controlling the ligand according to this example, a stable precursor was obtained, and this could be fired to produce fine LiMn 2 O 4 .
[0015]
Test example 1
By substituting the diffraction angle of the diffraction peak obtained from the X-ray diffraction result of FIG. 1 and the half-value width into the Hall equation, the relationship between the crystallite diameter and the strain can be obtained. The crystallite diameter was approximately 20 nm over the entire region from 250 ° C to 700 ° C. The distortion of the sample fired at 700 ° C. was 0.02%.
In order to evaluate the initial capacity of the positive electrode active material produced at 700 ° C., a sample electrode was prepared. The sample electrode is composed of a positive electrode mixture in which a positive electrode active material, acetylene black, and a fluororesin binder are mixed at a weight ratio of 5: 4: 1. The battery was assembled using a solution obtained by dissolving LiClO 4 in a mixed solution of propylene carbonate and dimethoxyethane, and the battery performance was evaluated. As a result, the initial capacity was 126 mAh / g, the discharge capacity was large, and the cycle characteristics were excellent. It turned out to be a battery.
[0016]
【The invention's effect】
According to the present invention, the precursor method is used to obtain a positive electrode material composed of fine, low-distortion particles that could not be achieved by the prior art. That is, in the comparative example that is outside the scope of the present invention, there is an amorphous phase that is not crystallized or impurities in the second phase. On the other hand, in the Example which is in the scope of the present invention, a powder composed of a fine lithium manganite single phase of 20 to 35 nm can be obtained. Therefore, according to the positive electrode active material manufacturing method of the present invention, lithium manganite having a high specific surface area can be obtained. Furthermore, a battery having a large discharge capacity and excellent cycle characteristics can be obtained.
[Brief description of the drawings]
FIG. 1 is a powder X-ray diffraction pattern of LiMn 2 O 4 obtained in Examples 1, 2, and 3 of the present invention.
FIG. 2 is a TG-DTA curve of the material obtained in Example 4 of the present invention.
FIG. 3 is a powder X-ray diffraction pattern of LiMn 2 O 4 obtained in Example 5 of the present invention.
Claims (7)
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