JP4382194B2 - Cathode active material for non-aqueous secondary battery, production method thereof, and non-aqueous secondary battery - Google Patents
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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Description
【０００１】
【発明の属する技術分野】
本発明は、サイクル寿命に優れた、非水系２次電池用正極活物質、その製造方法及び該正極活物質を備えた非水系２次電池に関する。
【０００２】
【従来技術】
近年、軽量且つ高容量の電池として、リチウムイオン２次電池をはじめとする非水電解質の２次電池が注目されている。この２次電池は、リチウム、遷移金属及び酸素を含む複合酸化物を正極活物質として使用するため、充放電を繰り返すことにより、正極活物質の結晶構造が急激に崩壊してしまい、サイクル寿命が低下するという問題が指摘されている。また、この２次電池の電解質としては、プロピレンカーボネート、ジメチルカーボネート等の溶媒に、ＬｉＰＦ6等を溶解した非水系電解質が使用されるため、この非水系電解質が高電位の正極側において、活性な正極活物質表面と反応して分解され、サイクル寿命が低下するという問題も指摘されている。
そこで、このようなサイクル寿命を改善するために種々の提案がなされている。例えば、特開平６−２４３８７１号公報には、正極活物質としての複合酸化物中の酸素の一部を、フッ素で置換することにより、充放電時における正極活物質の結晶崩壊を抑制する技術が提案されている。しかし、この技術では、複合酸化物の結晶格子中にフッ素を導入することによって、複合酸化物の結晶構造の崩壊によるサイクル寿命は改善されるものの、容量が低下するという問題が生じる。
一方、特開平８−２３６１１４号公報には、正極表面に特定の金属酸化物皮膜を形成し、正極の表面活性を制御することにより非水系電解質の分解を抑制する技術が提案されている。しかし、この技術では、正極表面に金属酸化物の皮膜を形成するために、ＣＶＤやスパッタリング等を行なう必要があり、工程が煩雑化すると共に、正極内部での電解液の分解までは抑制できないという問題がある。また、特開平６−３３３５６５号公報には、正極活物質と金属ハロゲン化物とを混合焼成することによって、正極活物質表面の活性を抑制する技術が開示されている。しかし、この技術では、正極活物質表面に安定なリチウム化合物であるハロゲン化リチウムが生成し、容量が低下する等の問題が生じる。
【０００３】
【発明が解決しようとする課題】
従って、本発明の目的は、電池容量の低下を抑制すると共に、正極表面の活性を制御し、サイクル寿命を向上させることができる非水系２次電池用正極活物質及びその製造方法を提供することにある。
本発明の別の目的は、電池容量の低下を抑制すると共に、サイクル寿命に優れた非水系２次電池を提供することにある。
【０００４】
【課題を解決するための手段】
本発明者らは、上記課題を解決するために鋭意検討した結果、非水系２次電池用の正極活物質に、希土類元素のフッ化物及び／又は希土類元素の酸フッ化物を導入することによって、正極活物質表面にフッ化リチウムが生成することに起因する容量の低下を防止すると共に、正極活物質表面の活性度を抑制し、電池のサイクル寿命が向上することを見出し本発明を完成した。希土類元素のフッ化物及び／又は希土類元素の酸フッ化物を導入することによるこのような効果が、いかなる作用によって得られるかは定かではない。例えば、一般的に電解液の分解は、電池の充放電時に電気化学的に活性になった正極表面のある部分に存在する水酸基等と反応して電解液が加水分解することにより起こると考えられている。このため、正極活物質表面に希土類元素のフッ化物等が存在すると、電池の充放電時にその接触部分が選択的に活性になり、他の部分の活性が電解液との加水分解反応に必要なレベルまで活性にならないので、上記効果が得られると考えられる。
【０００５】
【課題を解決するための手段】
本発明によれば、リチウムと、コバルト、マンガン及びニッケルからなる群より選択される１種または２種以上の遷移金属と、酸素とを含む複合酸化物からなる非水系２次電池用の正極活物質であって、該複合酸化物が、スカンジウムを除く希土類元素のフッ化物及び／又はスカンジウムを除く希土類元素の酸フッ化物を含むことを特徴とする非水系２次電池用正極活物質が提供される。
また本発明によれば、リチウムと、コバルト、マンガン及びニッケルからなる群より選択される１種または２種以上の遷移金属と、酸素とを含む複合酸化物の原材料と、平均粒径２０μｍ以下の、希土類元素のフッ化物及び／又は希土類元素の酸フッ化物とを混合し、該混合物を更に粉砕混合することを特徴とする非水系２次電池用正極活物質の製造方法が提供される。
更に本発明によれば、リチウムと、コバルト、マンガン及びニッケルからなる群より選択される１種または２種以上の遷移金属と、酸素とを含む複合酸化物の原材料と、希土類元素の鉱酸塩及び／又は有機酸塩とを混合する工程(Ａ)と、工程(Ａ)で混合した混合物を、フッ素を含むガス中において、該希土類元素の鉱酸塩及び／又は有機酸塩の分解温度以上で保持する工程(Ｂ)とを含むことを特徴とする非水系２次電池用正極活物質の製造方法が提供される。
更にまた本発明によれば、上記正極活物質を含む正極を備えた非水系２次電池が提供される。
【０００６】
【発明の実施の形態】
以下、本発明を更に詳細に説明する。
本発明の非水系２次電池用正極活物質(以下、本発明の正極活物質と略すことがある)は、リチウムと、コバルト、マンガン及びニッケルからなる群より選択される１種又は２種以上の遷移金属と、酸素とを含む複合酸化物が、更に希土類元素のフッ化物及び／又は希土類元素の酸フッ化物を含むことを特徴とする。
本発明において、希土類元素のフッ化物及び／又は希土類元素の酸フッ化物を導入するための上記複合酸化物組成としては、例えば、ＬｉＣｏＯ2、ＬｉＮｉＯ2、ＬｉＭｎＯ 2 、ＬｉＭｎ 2 Ｏ 4 又はこれらの各サイトを他の元素で一部置換した組成等が挙げられる。
【０００７】
本発明の正極活物質における複合酸化物に導入される希土類元素のフッ化物及び／又は希土類元素の酸フッ化物において、希土類元素とは、イットリウム、スカンジウムを含むランタンからルテチウムまでの元素を意味する。
上記希土類元素のフッ化物及び／又は希土類元素の酸フッ化物を導入する場合の量は、複合酸化物全量に対して、０．３〜１０重量％が好ましい。０．３重量％未満では、所望の効果が得られない恐れがあり、１０重量％を超える場合には、活物質の量が減少し、重量あたりの放電容量が低下する恐れがあるので好ましくない。
【０００８】
本発明の正極活物質の製造方法は、上記所望の効果が得られる組成が製造できれば特に限定されないが、簡易な方法としては、以下に示す本発明の第１及び第２の製造方法が好ましい。特に均一な混合物を得た後に複合酸化物化する際の均一混合が容易な点からは第２の製造方法が好ましい。
【０００９】
本発明の第１の製造方法では、リチウムと、コバルト、マンガン及びニッケルからなる群より選択される１種又は２種以上の遷移金属と、酸素とを含む複合酸化物の原材料と、平均粒径２０μｍ以下の、希土類元素のフッ化物及び／又は希土類元素の酸フッ化物とを混合し、該混合物を更に粉砕混合することを特徴とする。
上記リチウム、遷移金属及び酸素を含む複合酸化物の原材料としては、例えば、ＬｉＣｏＯ2、ＬｉＮｉＯ2、ＬｉＭｎＯ 2 、ＬｉＭｎ2Ｏ4又はこれらの各サイトを他の元素で一部置換した組成の材料等が挙げられる。これらの原材料は公知の方法で得ることができる。
上記希土類元素のフッ化物及び／又は希土類元素の酸フッ化物の粒径は、他の材料との接触面積を大きくし複合酸化物化のための反応を円滑に行なうために、平均粒径を２０μｍ以下とする必要があり、特に、１０μｍ以下とすることが好ましい。
混合物を更に粉砕混合するには、通常、大気中において、ボールミル等の粉砕混合機により平均粒径が５μｍ以下になる程度まで粉砕混合することができる。
複合酸化物の原材料と、希土類元素のフッ化物及び／又は希土類元素の酸フッ化物との混合割合は、希土類元素のフッ化物及び／又は希土類元素の酸フッ化物量が混合物全量に対して０．３〜１０重量％の範囲となるように混合することが好ましい。
【００１０】
本発明の第２の製造方法では、上記と同様な、リチウムと、コバルト、マンガン及びニッケルからなる群より選択される１種又は２種以上の遷移金属と、酸素とを含む複合酸化物の原材料と、希土類元素の鉱酸塩及び／又は有機酸塩とを混合する工程(Ａ)と、工程(Ａ)で混合した混合物を、フッ素を含むガス中において、該希土類元素の鉱酸塩及び／又は有機酸塩の分解温度以上で保持する工程(Ｂ)とを含むことを特徴とする。
上記工程(Ａ)において用いる希土類元素の鉱酸塩及び／又は有機酸塩としては、例えば、希土類元素の硝酸塩、塩化物、硫酸塩等の鉱酸塩；希土類元素のシュウ酸塩、酢酸塩等の有機酸塩等が挙げられる。
上記希土類元素の鉱酸塩及び／又は有機酸塩は、固体又は液体で用いても良いし、また水溶液にして用いることもできる。
工程(Ａ)において、リチウム、上記特定の遷移金属及び酸素を含む複合酸化物の原材料と、希土類元素の鉱酸塩及び／又は有機酸塩との混合割合は、複合酸化物の原材料と希土類元素の鉱酸塩及び／又は有機酸塩との合計量に対して、希土類元素の鉱酸塩及び／又は有機酸塩を、０．５〜１．５重量％混合することが好ましい。
【００１１】
工程(Ｂ)において、フッ素を含むガス中は、フッ化水素ガス等の気体を、反応系に直接導入した雰囲気であっても、また、フルオル酢酸等の液体や酸性フッ化アンモニウム等の固体を導入した後、加熱による分解反応を利用して、発生するフッ素を含むガス中であっても良い。
このフッ素を含むガスは、後述する分解温度以上の加熱により、希土類元素の鉱酸塩及び／又は有機酸塩と選択的に且つ優先的に反応し、上記複合酸化物の原材料との反応によるフッ化リチウムの生成は抑制される。
フッ素を含むガスの量は、希土類元素の鉱酸塩及び／又は有機酸塩中の希土類元素をフッ化物とするのに必要量であれば良い。フッ素を含むガスの量が大過剰の場合には、希土類元素の鉱酸塩及び／又は有機酸塩との反応で消費されなかったフッ素を含むガスが、得られる複合酸化物自体と反応してフッ化リチウムを生成する恐れがあるので好ましくない。従って、反応に使用するフッ素を含むガスの量は、希土類元素の鉱酸塩及び／又は有機酸塩をフッ化物とするのに必要なフッ素の当量から１０倍程度、特に、２〜５倍程度が好ましい。
【００１２】
工程(Ｂ)における分解温度とは、希土類元素の鉱酸塩及び／又は有機酸塩が分解し得る温度であれば良く、希土類元素の鉱酸塩及び／又は有機酸塩の種類に応じて適宜選択することができる。保持時間は、含有される希土類元素の鉱酸塩及び／又は有機酸塩の分解が終了するのに必要な時間以上であれば特に限定されない。但し、分解終了後における必要以上の保持は、効率的ではない。
【００１３】
本発明の製造方法では、上記工程(Ｂ)により得られる分解物を冷却することにより所望の非水系２次電池用正極活物質を得ることができる。この正極活物質は、常法により粉砕して正極材料として用いることができる。この正極材料を用いて、例えば、通常の導電助剤や結着剤を用いて集電体に固定することにより非水系２次電池用の正極を得ることができる。
【００１４】
本発明の非水系２次電池は、本発明の正極活物質を含む正極を備えることを特徴とする。従って、他の構成要件、例えば、陰極、電解液及びセパレータ等は特に限定されず、非水系２次電池を構成し得る材料から適宜選択することができ、通常の方法に従って、所望の非水系２次電池を得ることができる。
陰極は、例えば、金属リチウム、リチウム合金、若しくはコークス、黒鉛等のリチウムイオンを吸蔵放出可能な材料から選択することができる。
電解液は、例えば、プロピレンカーボネート、エチレンカーボネート、ビニレンカーボネート等の有機溶媒、若しくは該有機溶媒と、ジメチルカーボネート、ジエチルカーボネート、１，２−ジエトキシエタン、エトキシメトキシエタン等の低沸点溶媒との混合溶媒に、ＬｉＰＦ6、ＬｉＣｌＯ4、ＬｉＣＦ3ＳＯ3等の電解液溶質を溶解した溶液等が挙げられる。
【００１５】
【発明の効果】
本発明の非水系２次電池用正極活物質は、リチウム、特定の遷移金属及び酸素を含む複合酸化物が、希土類元素のフッ化物及び／又は希土類元素の酸フッ化物を含むので、電池容量の低下を抑制すると共に、サイクル寿命を向上させることができ、これを用いた非水系２次電池は、サイクル寿命に優れると共に、高電池容量が維持される。また、本発明の製造方法では、このような正極活物質を容易に得ることができる。
【００１６】
【実施例】
以下、本発明を実施例及び比較例により更に詳細に説明するが、本発明はこれらに限定されるものではない。
実施例１
(正極の作成)
コバルト酸リチウムと、フッ化イットリウムとを、重量比で９８：２の割合で混合した後、ボールミルで平均粒径５μｍになるまで更に粉砕し、正極活物質としての複合酸化物を得た。得られた複合酸化物中のフッ化イットリウム量を、日立製作所社製の吸光光度計(Ｕ−２００１)(フッ素分析)及びセイコーインスツルメンツ社製のＩＣＰ発光分光分析装置(ＳＰＳ−１７００ＨＶＲ)(イットリウム分析)により測定した。また、複合酸化物表面のフッ化リチウムの存在を、ＥＳＣＡ(アルバックファイ社製のＥＳＣＡ５５００ＭＴ)を用いて、６８４．４９ｅＶにおけるピークの有無により確認した。それぞれの結果を表１に示す。
次に、得られた複合酸化物と、導電助剤(電気化学工業社製のアセチレンブラック)と、結着剤(アルドリッチ社製のポリフッ化ビニリデン)とを重量比で、８０：１０：１０の割合で混合して正極合剤を調製し、続いて、ステンレス鋼鈑を集電体として円盤状の正極を作製した。
(負極の作製)
リチウム圧延板を所定寸法に打ち抜いて円盤状のリチウム金属板を得、ステンレス鋼鈑を集電体として負極を作製した。
(電解液の調製)
エチレンカーボネートとジメチルカーボネートとを容量比で１：１の割合で混合した溶液に、６フッ化リン酸リチウムを１ｍｏｌ／リットルの割合で溶解して電解液を調製した。
(電池評価)
上記により得られた、正極、負極及び電解液を用いて、常法によりリチウム２次電池を作製した。得られた電池を、充放電電流密度が０．５ｍＡ／ｃｍ2になる条件で、充電上限電圧を４．１Ｖ、放電下限電圧を２．７５Ｖとして充放電を繰り返し、作製した電池の初期容量と繰り返し充放電による容量維持率を計測器センター社製の電池サイクル寿命特性試験システムにより測定した。結果を表１に示す。
【００１７】
実施例２
コバルト酸リチウムと、硝酸サマリウムと、酸性フッ化アンモニウムとを、重量比で９６：３：１の割合で混合した。次いで、８００℃(硝酸サマリウムの分解温度以上)で５時間保持し、冷却して正極活物質としての複合酸化物を得た。得られた複合酸化物中のフッ化サマリウム量を実施例１と同様に測定した。また、複合酸化物表面におけるフッ化リチウムの存在についても実施例１と同様に測定した。それぞれの結果を表１に示す。
次いで、得られた複合酸化物を用いて、実施例１と同様に、正極を作製し、実施例１と同様に作製又は調製した陰極及び電解液を用いてリチウム２次電池を作製した。得られた電池について、実施例１と同様に容量維持率を測定した。結果を表１に示す。
【００１８】
比較例１
フッ化イットリウムをを用いなかった以外は、実施例１と同様に各材料及び電池を作製し、各測定を行なった。結果を表１に示す。
【００１９】
比較例２
コバルト酸リチウムと、酸性フッ化アンモニウムとを、重量比で９９：１の割合で混合した。次いで、８００℃で５時間保持し、冷却して正極活物質としての複合酸化物を得た。得られた複合酸化物を用いた以外は、実施例２と同様に各材料及び電池を作製し、各測定を行なった。結果を表１に示す。
【００２０】
【表１】
BACKGROUND OF THE INVENTION
The present invention relates to a positive electrode active material for a non-aqueous secondary battery excellent in cycle life, a method for producing the same, and a non-aqueous secondary battery including the positive electrode active material.
[0002]
[Prior art]
In recent years, nonaqueous electrolyte secondary batteries such as lithium ion secondary batteries have attracted attention as lightweight and high-capacity batteries. Since this secondary battery uses a composite oxide containing lithium, a transition metal, and oxygen as a positive electrode active material, the crystal structure of the positive electrode active material rapidly collapses due to repeated charge and discharge, resulting in a cycle life. The problem of decline has been pointed out. Further, as the electrolyte of the secondary battery, a non-aqueous electrolyte in which LiPF 6 or the like is dissolved in a solvent such as propylene carbonate or dimethyl carbonate is used. Therefore, the non-aqueous electrolyte is active on the positive electrode side having a high potential. It has also been pointed out that the cycle life is shortened by reaction with the surface of the positive electrode active material.
Various proposals have been made to improve the cycle life. For example, Japanese Patent Laid-Open No. 6-243871 discloses a technique for suppressing the crystal collapse of the positive electrode active material during charge / discharge by substituting a part of oxygen in the composite oxide as the positive electrode active material with fluorine. Proposed. However, with this technique, by introducing fluorine into the crystal lattice of the composite oxide, the cycle life due to the collapse of the crystal structure of the composite oxide is improved, but the capacity is reduced.
On the other hand, Japanese Patent Laid-Open No. 8-236114 proposes a technique for suppressing decomposition of a non-aqueous electrolyte by forming a specific metal oxide film on the surface of the positive electrode and controlling the surface activity of the positive electrode. However, with this technique, it is necessary to perform CVD, sputtering, etc. to form a metal oxide film on the positive electrode surface, which complicates the process and cannot suppress the decomposition of the electrolyte solution inside the positive electrode. There's a problem. Japanese Patent Laid-Open No. 6-333565 discloses a technique for suppressing the activity of the surface of the positive electrode active material by mixing and baking the positive electrode active material and the metal halide. However, with this technique, there is a problem that lithium halide, which is a stable lithium compound, is generated on the surface of the positive electrode active material, resulting in a decrease in capacity.
[0003]
[Problems to be solved by the invention]
Accordingly, an object of the present invention is to provide a positive electrode active material for a non-aqueous secondary battery and a method for manufacturing the same, which can suppress a decrease in battery capacity, control the activity of the positive electrode surface, and improve cycle life. It is in.
Another object of the present invention is to provide a non-aqueous secondary battery that suppresses a decrease in battery capacity and has an excellent cycle life.
[0004]
[Means for Solving the Problems]
As a result of intensive studies to solve the above problems, the present inventors have introduced a rare earth element fluoride and / or a rare earth element oxyfluoride into a positive electrode active material for a non-aqueous secondary battery, The present invention has been completed by finding that the decrease in capacity caused by the formation of lithium fluoride on the surface of the positive electrode active material is prevented, the activity of the surface of the positive electrode active material is suppressed, and the cycle life of the battery is improved. It is not certain by what kind of action the effect obtained by introducing the rare earth element fluoride and / or the rare earth element acid fluoride is obtained. For example, the decomposition of the electrolytic solution is generally considered to occur when the electrolytic solution hydrolyzes by reacting with a hydroxyl group or the like present on a portion of the positive electrode surface that is electrochemically active during battery charging / discharging. ing. For this reason, when a rare earth element fluoride or the like is present on the surface of the positive electrode active material, the contact portion is selectively activated during charge / discharge of the battery, and the activity of the other portion is necessary for the hydrolysis reaction with the electrolytic solution. Since it does not become active up to the level, it is considered that the above effect can be obtained.
[0005]
[Means for Solving the Problems]
According to the present invention, lithium, cobalt, cathode active for a non-aqueous secondary battery comprising a composite oxide containing one or a two or more transition metals selected from the group consisting of manganese and nickel, and oxygen a substance, said complex oxide, a positive electrode active material for a nonaqueous secondary battery which comprises an acid fluoride of a rare earth element other than fluoride and / or scandium in rare earth element except for scandium is provided The
According to the present invention, lithium, cobalt, one or the two or more transition metals selected from the group consisting of manganese and nickel, and raw materials of the complex oxide containing oxygen, an average particle diameter of 20μm or less of , was mixed with acid fluoride of the fluoride and / or a rare earth element of the rare earth element, method for producing a positive electrode active material for a nonaqueous secondary battery you characterized by further mixing and grinding the mixture are provided.
Further according to the present invention, mineral acid salts of lithium and cobalt, one or the two or more transition metals selected from the group consisting of manganese and nickel, and raw materials of the complex oxide containing oxygen, rare earth elements And / or the organic acid salt mixing step (A) and the mixture mixed in the step (A) in a fluorine-containing gas at a decomposition temperature of the mineral acid salt and / or organic acid salt of the rare earth element in the manufacturing method of the positive electrode active material for a nonaqueous secondary battery you; and a step (B) to hold it is provided.
Furthermore, according to this invention, the non-aqueous secondary battery provided with the positive electrode containing the said positive electrode active material is provided.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in more detail.
The positive electrode active material for non-aqueous secondary batteries of the present invention (hereinafter sometimes abbreviated as the positive electrode active material of the present invention) is one or more selected from the group consisting of lithium , cobalt, manganese and nickel and transition metals, composite oxides containing oxygen, which further comprises an acid fluoride of the fluoride and / or a rare earth element of the rare earth elements.
In the present invention, the composite oxide composition for introducing the rare earth element fluoride and / or the rare earth element acid fluoride may be, for example, LiCoO 2 , LiNiO 2 , LiMnO 2 , LiMn 2 O 4, or each of these. The composition etc. which partially substituted the site with other elements are mentioned.
[0007]
In the rare earth element fluoride and / or rare earth element oxyfluoride introduced into the composite oxide in the positive electrode active material of the present invention, the rare earth element means an element from lanthanum to lutetium including yttrium and scandium.
The amount of the rare earth element fluoride and / or rare earth element oxyfluoride introduced is preferably 0.3 to 10% by weight based on the total amount of the composite oxide. If the amount is less than 0.3% by weight, the desired effect may not be obtained. If the amount exceeds 10% by weight, the amount of the active material decreases, and the discharge capacity per weight may decrease. .
[0008]
Although the manufacturing method of the positive electrode active material of this invention will not be specifically limited if the composition which can obtain the said desired effect can be manufactured, As a simple method, the 1st and 2nd manufacturing method of this invention shown below is preferable. In particular, the second production method is preferable from the viewpoint of easy uniform mixing when obtaining a complex oxide after obtaining a uniform mixture.
[0009]
In the first production method of the present invention, a raw material of a composite oxide containing lithium , one or more transition metals selected from the group consisting of cobalt, manganese and nickel , and oxygen , and an average particle diameter A rare earth element fluoride and / or a rare earth element oxyfluoride of 20 μm or less is mixed, and the mixture is further pulverized and mixed.
The raw material of the complex oxide containing the lithium transition metal and oxygen, if example embodiment, LiCoO 2, LiNiO 2, LiMn O 2, the composition obtained by partly substituting the Li Mn 2 O 4 or the sites of these other elements The material etc. are mentioned. These raw materials can be obtained by a known method.
The particle size of the rare earth element fluoride and / or rare earth element oxyfluoride is 20 μm or less in average particle size in order to increase the contact area with other materials and to facilitate the reaction for forming a composite oxide. In particular, the thickness is preferably 10 μm or less.
In order to further pulverize and mix the mixture, the mixture can usually be pulverized and mixed in the atmosphere to an extent that the average particle size is 5 μm or less by a pulverizing mixer such as a ball mill.
The mixing ratio of the raw material of the composite oxide to the rare earth element fluoride and / or the rare earth element oxyfluoride is such that the rare earth element fluoride and / or the rare earth element oxyfluoride content is 0.000 based on the total amount of the mixture. It is preferable to mix so that it may become the range of 3-10 weight%.
[0010]
In the second production method of the present invention, a raw material for a composite oxide containing lithium , one or more transition metals selected from the group consisting of cobalt, manganese and nickel , and oxygen , as described above And a rare earth element mineral salt and / or an organic acid salt in a step (A) and a mixture of the rare earth element mineral salt and / or organic acid salt in a gas containing fluorine. Or a step (B) of holding at a temperature equal to or higher than the decomposition temperature of the organic acid salt.
Examples of rare earth element mineral salts and / or organic acid salts used in the step (A) include mineral salts such as nitrates, chlorides and sulfates of rare earth elements ; oxalates and acetates of rare earth elements And organic acid salts thereof.
The mineral acid salt and / or organic acid salt of the rare earth element may be used as a solid or liquid, or may be used as an aqueous solution.
In the step (A), the mixing ratio of the raw material of the composite oxide containing lithium, the above-mentioned specific transition metal and oxygen and the mineral acid salt and / or organic acid salt of the rare earth element is as follows. It is preferable to mix 0.5 to 1.5% by weight of the rare earth element mineral salt and / or organic acid salt with respect to the total amount of the mineral acid salt and / or organic acid salt.
[0011]
In the step (B), in the gas containing fluorine, even in an atmosphere in which a gas such as hydrogen fluoride gas is directly introduced into the reaction system, a liquid such as fluoroacetic acid or a solid such as acidic ammonium fluoride is used. After the introduction, it may be in a gas containing fluorine generated by utilizing a decomposition reaction by heating.
This fluorine-containing gas selectively and preferentially reacts with a rare earth element mineral salt and / or organic acid salt by heating at a decomposition temperature or higher, which will be described later, and is a fluorine by reaction with the composite oxide raw material. The formation of lithium fluoride is suppressed.
The amount of the gas containing fluorine may be an amount necessary for making the rare earth element in the mineral acid salt and / or organic acid salt of the rare earth element into a fluoride. When the amount of fluorine-containing gas is excessive, the fluorine-containing gas that has not been consumed in the reaction with the rare earth element mineral salt and / or organic acid salt reacts with the resulting composite oxide itself. This is not preferable because lithium fluoride may be generated. Therefore, the amount of the gas containing fluorine used for the reaction is about 10 times, particularly about 2 to 5 times, from the equivalent of fluorine necessary for converting the rare earth element mineral salt and / or organic acid salt to fluoride. Is preferred.
[0012]
The decomposition temperature in the step (B) may be any temperature at which the mineral acid salt and / or organic acid salt of the rare earth element can be decomposed, and is appropriately selected according to the type of the mineral acid salt and / or organic acid salt of the rare earth element. You can choose. The holding time is not particularly limited as long as it is longer than the time necessary for the decomposition of the mineral acid salt and / or organic acid salt of the rare earth element to be completed. However, holding more than necessary after the completion of decomposition is not efficient.
[0013]
In the production method of the present invention, a desired positive electrode active material for a non-aqueous secondary battery can be obtained by cooling the decomposition product obtained in the step (B). This positive electrode active material can be pulverized by a conventional method and used as a positive electrode material. Using this positive electrode material, for example, a positive electrode for a non-aqueous secondary battery can be obtained by fixing it to a current collector using a normal conductive aid or binder.
[0014]
The non-aqueous secondary battery of the present invention includes a positive electrode including the positive electrode active material of the present invention. Therefore, other constituent elements such as the cathode, the electrolytic solution, and the separator are not particularly limited, and can be appropriately selected from materials that can constitute the non-aqueous secondary battery. A secondary battery can be obtained.
The cathode can be selected from materials capable of occluding and releasing lithium ions such as lithium metal, lithium alloy, coke, and graphite.
The electrolyte is, for example, an organic solvent such as propylene carbonate, ethylene carbonate, vinylene carbonate, or a mixture of the organic solvent and a low boiling point solvent such as dimethyl carbonate, diethyl carbonate, 1,2-diethoxyethane, ethoxymethoxyethane, or the like. Examples of the solvent include solutions in which electrolyte solutes such as LiPF 6 , LiClO 4 , and LiCF 3 SO 3 are dissolved.
[0015]
【The invention's effect】
In the positive electrode active material for a non-aqueous secondary battery of the present invention, the composite oxide containing lithium, a specific transition metal and oxygen contains a rare earth element fluoride and / or a rare earth element oxyfluoride. While suppressing a fall, a cycle life can be improved and the non-aqueous secondary battery using this is excellent in a cycle life, and a high battery capacity is maintained. Moreover, in the manufacturing method of this invention, such a positive electrode active material can be obtained easily.
[0016]
【Example】
EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further in detail, this invention is not limited to these.
Example 1
(Creation of positive electrode)
Lithium cobaltate and yttrium fluoride were mixed at a weight ratio of 98: 2, and then pulverized with a ball mill to an average particle size of 5 μm to obtain a composite oxide as a positive electrode active material. The amount of yttrium fluoride in the obtained composite oxide was measured by using an absorptiometer (U-2001) (fluorine analysis) manufactured by Hitachi, Ltd. and an ICP emission spectrometer (SPS-1700HVR) manufactured by Seiko Instruments Inc. (yttrium analysis). ). The presence of lithium fluoride on the surface of the composite oxide was confirmed by the presence or absence of a peak at 684.49 eV using ESCA (ESCA5500MT manufactured by ULVAC-PHI). The results are shown in Table 1.
Next, the obtained composite oxide, a conductive additive (acetylene black manufactured by Denki Kagaku Kogyo Co., Ltd.), and a binder (polyvinylidene fluoride manufactured by Aldrich Co.) are in a weight ratio of 80:10:10. A positive electrode mixture was prepared by mixing at a ratio, and then a disk-shaped positive electrode was produced using a stainless steel plate as a current collector.
(Preparation of negative electrode)
A lithium rolled plate was punched into a predetermined size to obtain a disc-shaped lithium metal plate, and a negative electrode was produced using a stainless steel plate as a current collector.
(Preparation of electrolyte)
An electrolytic solution was prepared by dissolving lithium hexafluorophosphate in a ratio of 1 mol / liter in a solution in which ethylene carbonate and dimethyl carbonate were mixed at a volume ratio of 1: 1.
(Battery evaluation)
Using the positive electrode, negative electrode, and electrolytic solution obtained as described above, a lithium secondary battery was produced by a conventional method. The obtained battery was repeatedly charged and discharged under the condition that the charge / discharge current density was 0.5 mA / cm 2 and the charge upper limit voltage was 4.1 V and the discharge lower limit voltage was 2.75 V. The capacity retention rate due to repeated charge and discharge was measured by a battery cycle life characteristic test system manufactured by Keiki Center. The results are shown in Table 1.
[0017]
Example 2
Lithium cobaltate, samarium nitrate, and ammonium acid fluoride were mixed at a weight ratio of 96: 3: 1. Subsequently, it was kept at 800 ° C. (above the decomposition temperature of samarium nitrate) for 5 hours and cooled to obtain a composite oxide as a positive electrode active material. The amount of samarium fluoride in the obtained composite oxide was measured in the same manner as in Example 1. The presence of lithium fluoride on the composite oxide surface was also measured in the same manner as in Example 1. The results are shown in Table 1.
Next, using the obtained composite oxide, a positive electrode was produced in the same manner as in Example 1, and a lithium secondary battery was produced using a cathode and an electrolyte prepared or prepared in the same manner as in Example 1. About the obtained battery, the capacity retention rate was measured in the same manner as in Example 1. The results are shown in Table 1.
[0018]
Comparative Example 1
Except that yttrium fluoride was not used, each material and battery were produced in the same manner as in Example 1, and each measurement was performed. The results are shown in Table 1.
[0019]
Comparative Example 2
Lithium cobaltate and acidic ammonium fluoride were mixed at a weight ratio of 99: 1. Subsequently, it hold | maintained at 800 degreeC for 5 hours, it cooled, and the composite oxide as a positive electrode active material was obtained. Except for using the obtained complex oxide, each material and battery were prepared in the same manner as in Example 2, and each measurement was performed. The results are shown in Table 1.
[0020]
[Table 1]
Claims (6)
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| JP5229527B2 (en) * | 2006-08-25 | 2013-07-03 | ソニー株式会社 | Secondary battery electrolyte and secondary battery |
| US9299982B2 (en) | 2011-01-28 | 2016-03-29 | Sanyo Electric Co., Ltd. | Positive electrode active material for nonaqueous electrolyte secondary battery, method for producing the same, positive electrode for nonaqueous electolyte |
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