JP2004299975A - Method of producing hetero element-containing cobalt hydroxide, method of producing positive electrode material and nonaqueous electrolyte secondary battery - Google Patents
Method of producing hetero element-containing cobalt hydroxide, method of producing positive electrode material and nonaqueous electrolyte secondary battery Download PDFInfo
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Abstract
Description
【0001】
【発明が属する技術分野】
この発明は、非水電解質二次電池の正極材料製造用原料として有用な異種元素含有水酸化コバルトの製造方法、及びこの製造方法で作製された異種元素含有水酸化コバルトを用いた異種元素含有コバルト酸リチウム(LiCoO2)からなる非水電解質二次電池用正極材料の製造方法、及びこの製造方法で作製された異種元素含有コバルト酸リチウムからなる正極材料を用いた非水電解質二次電池に関する。
【0002】
【従来の技術】
携帯型の電子機器の急速な普及に伴い、それに使用される電池への要求仕様は、年々厳しくなり、特に小型・薄型化、高容量でサイクル特性が優れ、性能の安定したものが要求されている。そして、二次電池分野では他の電池に比べて高エネルギー密度であるリチウム非水電解質二次電池が注目され、このリチウム非水電解質二次電池の占める割合は二次電池市場において大きな伸びを示している。
【0003】
このリチウム非水電解質二次電池は、細長いシート状の銅箔等からなる負極芯体(集電体)の両面にリチウムイオンを吸蔵放出する負極活物質を含む負極合剤を塗布した負極と、細長いシート状のアルミニウム箔等からなる正極芯体の両面にリチウムイオンを吸蔵・放出する正極活物質を含む正極合剤を塗布した正極との間に、微多孔性ポリプロピレンフィルム等からなるセパレータを配置し、負極及び正極をセパレータにより互いに絶縁した状態で円柱状又は楕円形状に巻回した後、負極及び正極の各所定部分にそれぞれ負極タブ及び正極タブを接続し、その外側を外装で被覆することにより製造されている。
【0004】
そして、正極材料として、従来から主としてコバルト酸リチウム(LiCoO2)が、リチウムに対し4V以上の電位を示し、高エネルギー密度を有する二次電池が実現できることから使用されているが、現状の電池性能は市場の要求に答えるには不充分であり、さらなる高性能化及び高寿命化、特に負荷特性、サイクル特性の向上が望まれている.
【0005】
一方、コバルト酸リチウムを正極活物質として用いたリチウム非水電解質二次電池の特性向上方法として、コバルト酸リチウムへ異種元素を添加する方法が知られている。例えば、下記特許文献1には正極活物質であるコバルト酸リチウムにジルコニウムを添加することで、高電圧を発生し、かつ優れた充放電特性と保存特性を示す非水電解質二次電池が開示されている。
【0006】
このジルコニウムを添加したコバルト酸リチウムは、LiCoO2粒子の表面が酸化ジルコニウムZrO2もしくはリチウムとジルコニウムとの複合酸化物Li2ZrO3により覆われることによって安定化され、その結果、高い電位においても電解液の分解反応や結晶破壊を起こすことなく、優れたサイクル特性、保存特性を示す正極活物質が得られることによるものであって、この効果は、単に焼成後のLiCoO2にジルコニウムもしくはジルコニウムの化合物を混合するだけでは得られず、リチウム塩とコバルト化合物とを混合したものにジルコニウムを添加して焼成することにより得られるものである。この特許文献1に開示されている異種元素含有コバルト酸リチウムは、Li2CO3とCoCO3とをLiとCoの原子比が1:1になるように混合したものに、酸化ジルコニウム(ZrO2)を添加し、空気中において900℃で5時間焼成して作製されている。
【0007】
【特許文献1】
特開平4−319260号公報(特許請求の範囲、段落[0006]、[0008]〜[0011])
【0008】
【発明が解決しようとする課題】
本発明者等は、ジルコニウム(Zr)以外に、チタン(Ti)及びフッ素(F)を使用しても同様に効果を奏することを見出しているが、異種元素としてZr、Ti及びFのいずれを使用した場合においても、これらの元素は電池反応に寄与しないので、添加量が増大すると電池容量が低下することになる。したがって、異種元素添加は極力少ない添加量で、より大きな効果を得ることが好ましい。しかし、特許文献1に開示されている方法では、電池容量を維持するために異種元素添加量を減少させると、異種元素添加により得られるはずの電池特性改善効果が得られなくなった。本発明者等は、この現象の原因を特許文献1に開示されているものは固体原料を混合して焼成するといった固相反応に基づくものであり、異種元素がコバルト酸リチウム内に不均質に存在しているためであると考え、まず、コバルト酸リチウムの製造における出発物質であるコバルト化合物内に均一に異種元素を存在させることによって、リチウム源と該コバルト化合物を反応させて合成されたコバルト酸リチウム内の異種元素を均一に存在させることを検討した。
【0009】
通常、コバルト塩水溶液と異種元素塩水溶液を混合した酸性水溶液をアルカリ水溶液により中和して作製した水酸化コバルトは異種元素が均一に存在していると考えられているから、まず、このようにして作製した異種元素含有水酸化コバルトと炭酸リチウムを混合し、焼成して異種元素含有コバルト酸リチウムを得たが、これを用いても電池特性改善効果は不充分であった。
【0010】
本発明者等はこの原因について種々検討した結果、コバルト塩水溶液と異種元素塩水溶液を混合した酸性水溶液のアルカリ水溶液による中和反応は、非常に反応速度が速いため、一部の異種元素が水酸化コバルトと固溶せずに遊離した状態となっており、均一度は高いとは言い難いこと、及び、水酸化コバルトは製造中或は保存中に酸化を受けやすいことから、一部が三価の水酸化コバルトとなっていることを知見した。
【0011】
そこで、本発明者等は更に実験を重ねた結果、中和反応液のpHをコントロールして遊離した異種元素の存在を極力低減させると共に酸化防止剤を共存させることによって中和反応と並行して生じると考えられる水酸化コバルトの酸化を抑制し、より反応条件を安定にコントロールすれば均質な異種元素含有水酸化コバルトが得られること、及び、このようにして得られた水酸化コバルトを出発物質として合成されたコバルト酸リチウムを正極に使用すると特性の優れたリチウムイオン電池を得ることができることを見出し、本発明を完成するに至ったのである。
【0012】
すなわち、本発明は異種元素が均質に分散された非水電解質二次電池の正極材料製造用原料として有用な異種元素含有水酸化コバルトの製造方法、及びこの製造方法で作製された異種元素含有水酸化コバルトを用いた異種元素含有コバルト酸リチウム(LiCoO2)からなる非水電解質二次電池用正極材料の製造方法、及びこの製造方法で作製された異種元素含有コバルト酸リチウムからなる正極材料を用いた非水電解質二次電池を提供することを目的とする。
【0013】
【課題を解決するための手段】
本発明の上記目的は以下の構成により達成することができる。すなわち、本発明の第1の態様によれば、コバルト塩とコバルト以外の異種元素を含有する塩との混合水溶液を、酸化防止剤を含有し、アルカリ水溶液によりpHが9〜14の間の所定の一定値に保たれた反応液中に滴下し、異種元素を含む水酸化コバルトを得ることからなる異種元素含有水酸化コバルトの製造方法が提供される。
【0014】
係る製造方法によれば、反応時のpHが一定に保たれているため、反応条件が安定化しており、しかも、コバルト塩とコバルト以外の異種元素を含有する塩との混合水溶液を反応液中に滴下して反応させているから、反応液中には未反応の異種元素含有塩は実質的に存在せず、前記混合水溶液の中和反応は徐々に一定の条件下で進行し、加えて反応液中には酸化防止剤が添加されているため、二価の水酸化コバルトが酸化して三価の水酸化コバルトとなるのを防止することができるので、より均質な異種元素含有水酸化コバルトを製造することができるようになる。
【0015】
係る態様においては、前記酸化防止剤が、ギ酸、シュウ酸、2価の鉄イオンから選択される少なくとも1種であることが好ましい。この種の酸化防止剤を使用すれば有効に二価の水酸化コバルトが酸化して三価の水酸化コバルトとなるのを防止することができるので、より均質な異種元素含有水酸化コバルトを製造することができるようになる。
【0016】
さらに、係る態様においては、前記異種元素含有塩が、ジルコニウム塩、チタン塩、フッ化物塩から選択された少なくとも1種であることが好ましい。これらの化合物を使用すれば、得られた異種元素含有水酸化コバルトを用いて作製された異種元素含有コバルト酸リチウムは優れた非水電解質二次電池用正極原料となる。
【0017】
また、本発明の別の態様では、上述の製造方法により製造された異種元素含有水酸化コバルトとリチウム塩とを混合した後、焼成することによる異種元素含有コバルト酸リチウムからなる非水電解質二次電池用正極材料の製造方法が提供される。係る態様によれば、均質に異種元素が添加された非水電解質二次電池用正極材料が得られるので、この正極材料を用いて製造された非水電解質二次電池の特性が向上する。
【0018】
さらに本発明の別の態様によれば、上述の製造方法により製造された正極材料を用いてなる非水電解質二次電池が提供される。係る態様によれば、均質に異種元素が添加された非水電解質二次電池用正極材料を用いるので、非水電解質二次電池の特性が向上する。
【0019】
【発明の実施の形態】
以下、本発明の具体例を実施例及び比較例を用いて詳細に説明する。
【0020】
(実施例)
(異種元素を添加した水酸化コバルトの作製)
硫酸コバルト水溶液(1mol%)と硫酸ジルコニウム水溶液(1mol%)を1000:1で混合した混合溶液と、水酸化ナトリウム水溶液(1mol%)とを用意し、酸化防止剤としてのギ酸を含む反応溶液中に前記混合溶液を徐々に滴下し、それと同時に前記水酸化ナトリウム水溶液も滴下することにより反応溶液のpHを10に制御して、ジルコニウム含有水酸化コバルト粒子を析出させた後、水洗、乾燥してジルコニウム含有水酸化コバルト粉末を作製した。
【0021】
(コバルト酸リチウムの作製)
上記ジルコニウム含有水酸化コバルト粉末と炭酸リチウムをモル比で1:1となるように混合して、空気中で900℃×6時間焼成してジルコニウム含有コバルト酸リチウムを作製した。
【0022】
(正極板の作製)
上記ジルコニウム含有コバルト酸リチウム粉末と、正極導電剤としての人造黒鉛粉末を、質量比9:1で混合して正極合剤を調製した。この正極合剤とポリフッ化ビニリデンをN−メチル2−ピロリドン(NMP)に5質量%溶解した結着剤溶液とを固形分質量比95:5で混棟して、正極板作製用スラリーを調製した。このスラリーを正極集電体であるアルミニウム箔(箔厚み:15μm)に塗布、乾燥し、その後極板を電池幅に合うようにスリットし、110℃で2時間で真空乾燥して電池用正極板を作製した。
【0023】
(負極板の作製)
リン片状天然黒鉛(d002値:3.356Å、Lc値:1000Å、平均粒径=20μm)と、スチレン−ブタジエンゴム(SBR)のディスパージョン(固形分:50%)を水に分散させて、増粘剤であるカルボキシメチルセルロース(CMC)を添加し、この負極の乾燥後の固形分質量組成比が、黒鉛:SBR:CMC=100:3:2となるようにスラリーを調製した。このスラリーを負極集電体である銅箔(箔厚み:8μm)の両面に乾燥後質量で200g/m2(片面塗布100g/m2、集電体除く)となるよう塗布した後、乾燥してその極板を圧縮し、活物質の充填密度1.5g/ccの負極板を作製した。その後極板を電池幅に合うようにスリットし、110℃で2時間で真空乾燥して電池用負極種板を得た。
【0024】
(電解質とセパレータ)
非水電解質として、エチレンガーボネート(EC)とジエチルカーボネート(DEC)との体積比50:50の混合溶媒に、LiPF6を1mol/l溶解した溶液を使用した。また、セパレ一夕としては、ポリエチレン製の微多孔膜を使用した。
【0025】
(電池の作製)
以上のようにして得られた正極、負極およびセパレータを捲回し、同様に上記のように作製した電解質を用いて、円筒型(AAサイズ、放電容量:600mAh)のリチウムイオン電池を作製した。
【0026】
(電池特性試験)
各電池において、25℃中1It(1C)で4.2Vまで充電した後、4.2Vで定電圧充電(10mAカット)し、1Itあるいは2Itで2.75Vまで放電させ、このときの放電容量および放電容量比を比較した。なお、1Itは600mAに設定した。測定結果を表1に示した。
【0027】
(比較例1)
水酸化コバルト粉末を作製する際に反応液中にギ酸を添加しない以外は実施例同様の方法で作製したジルコニウム添加コバルト酸リチウムを使用して比較例1の電池を作製し、実施例1と同じ条件で電池特性試験を行った。結果をまとめて表1に示した。
【0028】
(比較例2)
水酸化コバルトを作製する際に反応液中にギ酸を添加せず、また、反応溶液のpHを制御しない以外は実施例と同様の方法で作製したジルコニウム添加コバルト酸リチウムを使用して比較例2の電池を作製し、実施例1と同じ条件で電池特性試験を行った。結果をまとめて表1に示した。
【0029】
【表1】
【0030】
表1の結果から、本発明のリチウム非水電解質二次電池は、1It放電容量と2It放電容量との差が小さいが、比較例1及び比較例2のものは、1It放電容量は実施例のものと差異はないが、2It放電容量は大幅に小さくなっている。したがって、本発明のリチウム非水電解質二次電池は優れた放電性能を有することがわかる。
【0031】
なお、本実施例ではpH=10で実施したが、本発明においては中和反応時のpHが一定に保たれておれば均質な異種元素含有水酸化コバルトが得られるから、少なくとも水酸化コバルトの沈殿が生じる範囲である9以上に保てばよい。pHを14以上となしてもアルカリ濃度が濃すぎるので実用的ではない。
【0032】
また、本実施例では硫酸コバルト水溶液と硫酸ジルコニウム水溶液を使用したが、本発明で生起する反応は本質的にはコバルトイオンの中和反応であるから、硫酸塩だけでなく、硝酸塩やハロゲン化物塩等水溶性塩であれば等しく使用し得る。さらに、本発明では異種金属としてジルコニウムを使用したが、チタン及びフッ素をも含めた3種類のうち少なくとも1種を使用すればよく、フッ素としてはLiF等のフッ化物塩の形で添加すればよい。
【0033】
また、酸化防止剤としては、ギ酸の他にシュウ酸や2価のFe塩(FeSO4)等を用いても良いてもよい。さらに、反応液中には硫酸アンモニウム等のアンモニウム塩を添加しておくこともできる。アンモニウム塩が存在していると、コバルトイオンはアンモニウム錯体を形成するから、反応液中のコバルトイオン濃度が低下するので、コバルトイオンの中和反応は徐々に進行し、より均質な異種元素含有水酸化コバルトを得ることができる。
【0034】
【発明の効果】
以上述べたように、本発明によれば異種元素が均一に分散した二価の水酸化コバルトを得ることができ、放電効率に優れた非水電解質二次電池を製造することができる。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention provides a method for producing a hetero element-containing cobalt hydroxide useful as a raw material for producing a positive electrode material of a nonaqueous electrolyte secondary battery, and a hetero element-containing cobalt using the hetero element-containing cobalt hydroxide produced by the production method. The present invention relates to a method for producing a positive electrode material for a non-aqueous electrolyte secondary battery made of lithium oxide (LiCoO 2 ), and a non-aqueous electrolyte secondary battery using a positive electrode material made of a different element-containing lithium cobalt oxide produced by this production method.
[0002]
[Prior art]
With the rapid spread of portable electronic devices, the required specifications for batteries used in them have become stricter year by year. Particularly, small and thin type, high capacity, excellent cycle characteristics, and stable performance are required. I have. In the field of secondary batteries, lithium non-aqueous electrolyte secondary batteries, which have a higher energy density than other batteries, are attracting attention, and the proportion of lithium non-aqueous electrolyte secondary batteries has shown a significant growth in the secondary battery market. ing.
[0003]
The lithium non-aqueous electrolyte secondary battery includes a negative electrode in which a negative electrode mixture containing a negative electrode active material that inserts and desorbs lithium ions is applied to both surfaces of a negative electrode core (current collector) formed of a long and thin sheet-like copper foil, A separator made of a microporous polypropylene film or the like is placed between a positive electrode coated with a positive electrode mixture containing a positive electrode active material that absorbs and releases lithium ions on both sides of a positive electrode core made of an elongated sheet-like aluminum foil etc. Then, after the negative electrode and the positive electrode are wound in a columnar or elliptical shape while being insulated from each other by a separator, the negative electrode tab and the positive electrode tab are respectively connected to predetermined portions of the negative electrode and the positive electrode, and the outside thereof is covered with an exterior. It is manufactured by.
[0004]
As a positive electrode material, lithium cobalt oxide (LiCoO 2 ) has been used mainly since it exhibits a potential of 4 V or more with respect to lithium and can realize a secondary battery having a high energy density. Is not enough to respond to market demands, and further improvement in performance and service life, especially improvement in load characteristics and cycle characteristics, is desired.
[0005]
On the other hand, as a method for improving characteristics of a lithium nonaqueous electrolyte secondary battery using lithium cobaltate as a positive electrode active material, a method of adding a different element to lithium cobaltate is known. For example, Patent Literature 1 below discloses a nonaqueous electrolyte secondary battery that generates a high voltage by adding zirconium to lithium cobalt oxide, which is a positive electrode active material, and exhibits excellent charge / discharge characteristics and storage characteristics. ing.
[0006]
This zirconium-added lithium cobalt oxide is stabilized by covering the surface of the LiCoO 2 particles with zirconium oxide ZrO 2 or a composite oxide of lithium and zirconium Li 2 ZrO 3 , and as a result, even at a high electric potential, This is because a positive electrode active material exhibiting excellent cycle characteristics and storage characteristics can be obtained without causing a decomposition reaction or crystal destruction of the liquid, and this effect is obtained by simply adding a zirconium or zirconium compound to LiCoO 2 after firing. Can be obtained only by mixing zirconium into a mixture of a lithium salt and a cobalt compound, followed by firing. The different element-containing lithium cobalt oxide disclosed in Patent Document 1 is obtained by mixing Li 2 CO 3 and CoCO 3 in such a manner that the atomic ratio of Li to Co is 1: 1 and adding zirconium oxide (ZrO 2). ) Is added and calcined in the air at 900 ° C. for 5 hours.
[0007]
[Patent Document 1]
JP-A-4-319260 (claims, paragraphs [0006], [0008] to [0011])
[0008]
[Problems to be solved by the invention]
The present inventors have found that the same effect can be obtained by using titanium (Ti) and fluorine (F) in addition to zirconium (Zr). However, any of Zr, Ti and F is used as a different element. Even when used, these elements do not contribute to the battery reaction, so that an increase in the amount of addition decreases the battery capacity. Therefore, it is preferable to obtain a greater effect with the addition of different elements as little as possible. However, in the method disclosed in Patent Literature 1, when the amount of addition of a different element is reduced in order to maintain the battery capacity, the effect of improving the battery characteristics that can be obtained by adding the different element cannot be obtained. The inventors of the present invention disclose that the cause of this phenomenon is disclosed in Patent Document 1 based on a solid phase reaction of mixing and firing a solid raw material, and heterogeneous elements are heterogeneously mixed in lithium cobalt oxide. First, the cobalt compound synthesized by reacting the lithium compound with the cobalt compound by causing a heterogeneous element to be uniformly present in the cobalt compound as a starting material in the production of lithium cobalt oxide. We studied the existence of different elements uniformly in lithium oxide.
[0009]
Usually, cobalt hydroxide produced by mixing an aqueous solution of a cobalt salt and an aqueous solution of a different element salt and neutralizing it with an aqueous alkali solution is considered to contain the different elements uniformly. The different element-containing cobalt hydroxide and lithium carbonate prepared as described above were mixed and calcined to obtain a different element-containing lithium cobalt oxide, but the effect of improving the battery characteristics was insufficient even with this.
[0010]
As a result of various studies on the cause, the present inventors have found that the neutralization reaction of an acidic aqueous solution obtained by mixing an aqueous solution of a cobalt salt and an aqueous solution of a different element salt with an aqueous alkali solution has a very high reaction rate. It is in a state of being liberated without solid solution with cobalt oxide, and it is difficult to say that the degree of uniformity is high. Also, cobalt hydroxide is easily oxidized during production or storage, so that a part thereof is It was found that it was a cobalt hydroxide having a valency.
[0011]
Therefore, the present inventors conducted further experiments, and as a result, by controlling the pH of the neutralization reaction solution to minimize the presence of the released heterogeneous element as much as possible and to coexist with the antioxidant in parallel with the neutralization reaction. Suppressing the oxidation of cobalt hydroxide, which is considered to occur, and obtaining a homogeneous hetero element-containing cobalt hydroxide by controlling the reaction conditions more stably, and using the cobalt hydroxide thus obtained as a starting material. It has been found that using lithium cobaltate synthesized as above as a positive electrode makes it possible to obtain a lithium ion battery having excellent characteristics, and has completed the present invention.
[0012]
That is, the present invention provides a method for producing a heterogeneous element-containing cobalt hydroxide useful as a raw material for producing a positive electrode material of a nonaqueous electrolyte secondary battery in which a heterogeneous element is homogeneously dispersed, and a heterogeneous element-containing water produced by this production method. A method for producing a positive electrode material for a non-aqueous electrolyte secondary battery comprising lithium cobaltate containing a different element using cobalt oxide (LiCoO 2 ), and a positive electrode material comprising lithium cobaltate containing a different element prepared by this method It is an object of the present invention to provide a non-aqueous electrolyte secondary battery.
[0013]
[Means for Solving the Problems]
The above object of the present invention can be achieved by the following configurations. That is, according to the first aspect of the present invention, a mixed aqueous solution of a cobalt salt and a salt containing a heterogeneous element other than cobalt contains an antioxidant and has a predetermined pH between 9 and 14 with an alkaline aqueous solution. And a method for producing a cobalt hydroxide containing a different element, which is obtained by dropping the mixture into a reaction solution maintained at a constant value.
[0014]
According to such a production method, since the pH during the reaction is kept constant, the reaction conditions are stabilized, and a mixed aqueous solution of a cobalt salt and a salt containing a different element other than cobalt is added to the reaction solution. Since there is substantially no unreacted hetero element-containing salt in the reaction solution, the neutralization reaction of the mixed aqueous solution gradually proceeds under certain conditions, and Since an antioxidant is added to the reaction solution, it is possible to prevent divalent cobalt hydroxide from being oxidized to trivalent cobalt hydroxide, so that a more homogeneous hetero element-containing hydroxide can be obtained. Cobalt can be manufactured.
[0015]
In such an embodiment, the antioxidant is preferably at least one selected from formic acid, oxalic acid and divalent iron ions. The use of this type of antioxidant effectively prevents the oxidation of divalent cobalt hydroxide to become trivalent cobalt hydroxide, thereby producing a more homogeneous heteroelement-containing cobalt hydroxide. Will be able to
[0016]
Further, in such an embodiment, the different element-containing salt is preferably at least one selected from a zirconium salt, a titanium salt, and a fluoride salt. When these compounds are used, the different element-containing lithium cobalt oxide produced using the obtained different element-containing cobalt hydroxide becomes an excellent positive electrode material for a non-aqueous electrolyte secondary battery.
[0017]
In another aspect of the present invention, a non-aqueous electrolyte secondary material comprising a hetero element-containing lithium cobalt oxide obtained by mixing the hetero element-containing cobalt hydroxide and the lithium salt produced by the above-described production method and then firing the mixture. A method for producing a positive electrode material for a battery is provided. According to this aspect, a positive electrode material for a non-aqueous electrolyte secondary battery to which a different element is uniformly added is obtained, so that the characteristics of the non-aqueous electrolyte secondary battery manufactured using this positive electrode material are improved.
[0018]
According to still another aspect of the present invention, there is provided a non-aqueous electrolyte secondary battery using the positive electrode material manufactured by the above-described manufacturing method. According to this aspect, the characteristics of the non-aqueous electrolyte secondary battery are improved because the positive electrode material for a non-aqueous electrolyte secondary battery to which a different element is uniformly added is used.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, specific examples of the present invention will be described in detail using examples and comparative examples.
[0020]
(Example)
(Preparation of cobalt hydroxide with addition of different elements)
A mixed solution in which an aqueous solution of cobalt sulfate (1 mol%) and an aqueous solution of zirconium sulfate (1 mol%) were mixed at a ratio of 1000: 1 and an aqueous solution of sodium hydroxide (1 mol%) were prepared, and a reaction solution containing formic acid as an antioxidant was prepared. The mixed solution was gradually dropped, and simultaneously with the sodium hydroxide aqueous solution, the pH of the reaction solution was controlled at 10 to precipitate zirconium-containing cobalt hydroxide particles, followed by washing with water and drying. A zirconium-containing cobalt hydroxide powder was produced.
[0021]
(Production of lithium cobaltate)
The zirconium-containing cobalt hydroxide powder and lithium carbonate were mixed at a molar ratio of 1: 1 and calcined in air at 900 ° C. for 6 hours to prepare zirconium-containing lithium cobalt oxide.
[0022]
(Production of positive electrode plate)
The positive electrode mixture was prepared by mixing the zirconium-containing lithium cobaltate powder and artificial graphite powder as a positive electrode conductive agent at a mass ratio of 9: 1. This positive electrode mixture and a binder solution obtained by dissolving 5% by mass of polyvinylidene fluoride in N-methyl 2-pyrrolidone (NMP) were mixed at a solid content mass ratio of 95: 5 to prepare a slurry for preparing a positive electrode plate. did. This slurry is applied to an aluminum foil (foil thickness: 15 μm) as a positive electrode current collector, dried, and then the electrode plate is slit to fit the width of the battery, and dried at 110 ° C. for 2 hours under vacuum to dry the positive electrode plate for a battery. Was prepared.
[0023]
(Production of negative electrode plate)
A flaky natural graphite (d 002 value: 3.356 °, Lc value: 1000 °, average particle size = 20 μm) and a dispersion of styrene-butadiene rubber (SBR) (solid content: 50%) are dispersed in water. Then, carboxymethylcellulose (CMC) as a thickener was added, and a slurry was prepared such that the solid content mass ratio of the negative electrode after drying was graphite: SBR: CMC = 100: 3: 2. This slurry was dried on both surfaces of a copper foil (foil thickness: 8 μm) as a negative electrode current collector so as to have a mass of 200 g / m 2 (100 g / m 2 on one side, excluding the current collector) and then dried. The electrode plate was compressed to prepare a negative electrode plate having a packing density of 1.5 g / cc of the active material. Thereafter, the electrode plate was slit to fit the width of the battery, and vacuum dried at 110 ° C. for 2 hours to obtain a negative electrode seed plate for a battery.
[0024]
(Electrolyte and separator)
As the non-aqueous electrolyte, a solution obtained by dissolving 1 mol / l of LiPF 6 in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) at a volume ratio of 50:50 was used. In addition, a polyethylene microporous membrane was used for separation.
[0025]
(Production of battery)
The positive electrode, the negative electrode, and the separator obtained as described above were wound, and a cylindrical (AA size, discharge capacity: 600 mAh) lithium-ion battery was manufactured using the electrolyte similarly manufactured as described above.
[0026]
(Battery characteristics test)
Each battery was charged to 4.2 V at 1 It (1 C) in 25 ° C., then charged at 4.2 V at a constant voltage (10 mA cut), discharged to 2.75 V at 1 It or 2 It, and discharged capacity and The discharge capacity ratio was compared. In addition, 1 It was set to 600 mA. Table 1 shows the measurement results.
[0027]
(Comparative Example 1)
A battery of Comparative Example 1 was prepared using a zirconium-doped lithium cobalt oxide prepared in the same manner as in the Example except that formic acid was not added to the reaction solution when preparing the cobalt hydroxide powder, and the same as in Example 1. A battery characteristic test was performed under the conditions. The results are summarized in Table 1.
[0028]
(Comparative Example 2)
Comparative Example 2 using a zirconium-doped lithium cobaltate prepared in the same manner as in the example except that formic acid was not added to the reaction solution when preparing cobalt hydroxide and the pH of the reaction solution was not controlled. And a battery characteristic test was performed under the same conditions as in Example 1. The results are summarized in Table 1.
[0029]
[Table 1]
[0030]
From the results shown in Table 1, although the difference between the 1It discharge capacity and the 2It discharge capacity of the lithium nonaqueous electrolyte secondary battery of the present invention is small, the ones of Comparative Examples 1 and 2 have the 1It discharge capacity of the embodiment. Although there is no difference from the above, the 2It discharge capacity is significantly reduced. Therefore, it is understood that the lithium nonaqueous electrolyte secondary battery of the present invention has excellent discharge performance.
[0031]
In this example, the reaction was carried out at pH = 10, but in the present invention, if the pH during the neutralization reaction is kept constant, a homogeneous heteroelement-containing cobalt hydroxide can be obtained. What is necessary is just to keep it at 9 or more in the range where precipitation occurs. Even if the pH is 14 or more, it is not practical because the alkali concentration is too high.
[0032]
In this example, an aqueous solution of cobalt sulfate and an aqueous solution of zirconium sulfate were used. However, since the reaction occurring in the present invention is essentially a neutralization reaction of cobalt ions, not only sulfate but also nitrate and halide salts are used. Equally water-soluble salts can equally be used. Further, in the present invention, zirconium is used as the dissimilar metal, but at least one of three types including titanium and fluorine may be used, and the fluorine may be added in the form of a fluoride salt such as LiF. .
[0033]
Further, as the antioxidant, oxalic acid, a divalent Fe salt (FeSO 4 ), or the like may be used in addition to formic acid. Further, an ammonium salt such as ammonium sulfate can be added to the reaction solution. If an ammonium salt is present, cobalt ions form an ammonium complex, and the concentration of cobalt ions in the reaction solution decreases. Cobalt oxide can be obtained.
[0034]
【The invention's effect】
As described above, according to the present invention, divalent cobalt hydroxide in which different elements are uniformly dispersed can be obtained, and a nonaqueous electrolyte secondary battery having excellent discharge efficiency can be manufactured.
Claims (5)
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JP2005085635A (en) * | 2003-09-09 | 2005-03-31 | Sanyo Electric Co Ltd | Nonaqueous electrolyte secondary battery |
US8338030B2 (en) | 2005-02-24 | 2012-12-25 | Sanyo Electric Co., Ltd. | Non-aqueous electrolyte secondary battery |
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US8338030B2 (en) | 2005-02-24 | 2012-12-25 | Sanyo Electric Co., Ltd. | Non-aqueous electrolyte secondary battery |
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