JP3552210B2 - Lithium ion secondary battery, cathode active material and sheath for synthesis of lithium-containing composite oxide for cathode active material - Google Patents

Description

【０１１０】
表１から明らかなように、原料粉末を、ＭｇＯ及びＭｇＡｌ_２Ｏ_４スピネルよりなる群から選択される少なくとも１種類からなる化合物成分を含む鞘に収納した状態で焼成することにより得られるリチウム含有複合酸化物を含む実施例１〜４の二次電池は、アルミナ（Ａｌ_２Ｏ_３）製の鞘を用いて合成された正極活物質を含む比較例１、２の二次電池に比べて、初期容量が高くかつ容量バラツキが少なく、サイクル寿命が長く、釘刺し試験の際の温度上昇率が低く、釘刺し試験による破裂および発火が皆無であることがわかる。
【０１１１】
（実施例５）
出発原料としてＬｉＯＨ・Ｈ_２Ｏと、Ｎｉ（ＯＨ）_２と、元素Ｍｅ１（Ｃｏ）の酸化物、炭酸化物、硝酸化物と、ＮａＯＨと、ＫＯＨと、Ｃａ（ＯＨ）_２と、硫化化合物として硫化ナトリウム（Ｎａ_２Ｓ・９Ｈ_２Ｏ）及び硫酸化合物（ＮｉＳＯ_４・６Ｈ_２Ｏ）と、Ｓｉの酸化物、硫化物、アルコキサイドと、Ｆｅの酸化物、硫化物、アルコキサイドとを用意し、これらの化合物粉末から組成Ｌｉ_１．１Ｎｉ_０．７８Ｃｏ_０．２２Ｏ_１．９５Ｆ_０．０５＋ｃＣ）になるように選択し、調合後、ヘンシェルミキサで３０分混合することにより混合粉（原料粉末）を作製した。この混合粉を前述した実施例１で説明したのと同様な角鞘に収容し、このような角鞘４つを前述した図２に示すように電気炉にセットし、焼成を行った。焼成は５リットル／分の酸素をフローさせながら４８０℃で１０時間保持した後、７００℃で１５時間行い、リチウム含有複合酸化物粉末を得た。なお、リチウム含有複合酸化物の組成式における元素Ｃの種類と、酸化物中の元素Ｃの含有量ｃ（ｐｐｍ）は、下記表２に示した。
【０１１２】
得られたリチウム含有複合酸化物粉末をレーザー回折粒度分布測定装置で測定した結果、粒度分布において最大比率を占める粒径Ｄは５．０μｍであった。一方、半値幅Ｓは３．５μｍで、０．７Ｄに相当する値であった。よって、リチウム含有複合酸化物粉末の粒度分布は、前述した（Ｉ）式の関係を満足するものであった。
【０１１３】
なお、正極活物質の組成分析は、グロー放電型質量分析法（ＧＤＭＳ：Ｇｌｏｗ Ｄｉｓｃｈａｒｇｅ Ｍａｓｓ Ｓｐｅｃｔｒｏｍｅｔｒｙ）を用いて行う。ここで、ＧＤＭＳとは１Ｔｏｒｒ程度のＡｒ雰囲気下で、一方の電極を試料として数ｋＶの電圧をかけ、形成したグロー放電により試料表面をスパッタして、生成した試料イオンを電極にあるアパーチャから引き出して加速し、質量分析する方法である。このグロー放電型質量分析により複合酸化物を構成する各元素の含有量が求められ、元素Ｃ以外の各元素の含有量をモル％に換算することにより、求める化学式を得る。以下の実施例により得られる正極活物質についても、組成分析は、グロー放電型質量分析法で行われる。
【０１１４】
このような正極活物質を用いること以外は、前述した実施例１で説明したのと同様にして円筒形リチウムイオン二次電池を製造した。
【０１１５】
（実施例６〜８）
リチウム含有複合酸化物の組成における元素Ｃの種類及び酸化物中の元素Ｃの含有量ｃ（ｐｐｍ）を下記表２に示すように変更すること以外は、前述した実施例５で説明したのと同様にしてリチウム含有複合酸化物粉末を得た。
【０１１６】
このような正極活物質を用いること以外は、前述した実施例１で説明したのと同様にして円筒形リチウムイオン二次電池を製造した。
【０１１７】
（実施例９）
出発原料としてＬｉＯＨ・Ｈ_２Ｏと、Ｎｉ（ＯＨ）_２と、元素Ｍｅ１（Ｃｏ）の酸化物、炭酸化物、硝酸化物と、ＮａＯＨと、ＫＯＨと、Ｃａ（ＯＨ）_２と、硫化化合物として硫化ナトリウム（Ｎａ_２Ｓ・９Ｈ_２Ｏ）及び硫酸化合物（ＮｉＳＯ_４・６Ｈ_２Ｏ）と、Ｓｉの酸化物、硫化物、アルコキサイドと、Ｆｅの酸化物、硫化物、アルコキサイドとを用意し、これらの化合物粉末から組成Ｌｉ_１．１Ｎｉ_０．７８Ｃｏ_０．２２Ｏ_１．９５Ｆ_０．０５＋ｃＣ）になるように選択し、調合後、ヘンシェルミキサで３０分混合することにより混合粉（原料粉末）を作製した。この混合粉を前述した実施例４で説明したのと同様な角鞘に収容し、このような角鞘４つを前述した図２に示すように電気炉にセットし、焼成を行った。焼成は５リットル／分の酸素をフローさせながら４８０℃で１０時間保持した後、７００℃で１５時間行い、リチウム含有複合酸化物粉末を得た。なお、リチウム含有複合酸化物の組成式における元素Ｃの種類と、酸化物中の元素Ｃの含有量ｃ（ｐｐｍ）は、下記表２に示した。
【０１１８】
得られたリチウム含有複合酸化物粉末をレーザー回折粒度分布測定装置で測定した結果、粒度分布において最大比率を占める粒径Ｄは６．５μｍであった。一方、半値幅Ｓは３．３μｍで、０．５Ｄに相当する値であった。よって、リチウム含有複合酸化物粉末の粒度分布は、前述した（Ｉ）式の関係を満足するものであった。
【０１１９】
このような正極活物質を用いること以外は、前述した実施例１で説明したのと同様にして円筒形リチウムイオン二次電池を製造した。
【０１２０】
（実施例１０〜１２）
リチウム含有複合酸化物の組成における元素Ｃの種類及び酸化物中の元素Ｃの含有量ｃ（ｐｐｍ）を下記表２に示すように変更すること以外は、前述した実施例９で説明したのと同様にしてリチウム含有複合酸化物粉末を得た。
【０１２１】
このような正極活物質を用いること以外は、前述した実施例１で説明したのと同様にして円筒形リチウムイオン二次電池を製造した。
【０１２２】
得られた実施例５〜１２の二次電池について、初期容量、５００サイクル後の放電容量平均低下率、釘刺し試験による電池温度、釘刺し試験時の破裂と発火の有無を、前述した実施例１で説明したのと同様にして測定し、その結果を下記表２に示す。なお、表２には、前述した比較例１，２の結果を併記する。
【０１２３】
【表２】

【０１２４】
表２から明らかなように、実施例５〜１２の二次電池は、比較例１，２の二次電池に比べて、初期容量のばらつきが少なく、５００サイクル後の放電容量低下率が小さく、釘刺し試験時の温度上昇が抑制されて破裂と発火が皆無であることがわかる。
【０１２５】
なお、角鞘の成分をＭｇＯ成分の量が９９．０％で、Ａｌ成分量が５２０ｐｐｍで、Ｓｉ成分量が３５０ｐｐｍで、Ｃａ成分量が２０００ｐｐｍで、Ｙ成分量が１６０ｐｐｍで、Ｚｒ成分量が１６００ｐｐｍであるものに変更すること以外は、前述した実施例１で説明したのと同様にしてリチウムイオン二次電池を製造したところ、前述した実施例１と同様な優れた電池特性と安全性を得ることができた。
【０１２６】
また、角鞘の成分をＭｇＡｌ_２Ｏ_４スピネル成分の量が９９．０％で、Ｓｉ成分量が２１０ｐｐｍで、Ｃａ成分量が６００ｐｐｍで、Ｙ成分量が３２０ｐｐｍで、Ｚｒ成分量が２０００ｐｐｍで、Ｈｆ成分量が１６０ｐｐｍであるものに変更すること以外は、前述した実施例４で説明したのと同様にしてリチウムイオン二次電池を製造したところ、前述した実施例４と同様な優れた電池特性と安全性を得ることができた。
【０１２７】
（実施例１３）
＜正極の作製＞
前述した実施例１で説明したのと同様な組成のリチウム含有複合酸化物粉末９１重量％をアセチレンブラック２．５重量％、グラファイト３重量％、ポリフッ化ビニリデン（ＰＶｄＦ）４重量％と、Ｎ−メチルピロリドン（ＮＭＰ）溶液を加えて混合し、厚さ１５μｍのアルミニウム箔の集電体に塗布し、乾燥後、プレスすることにより電極密度３．０ｇ／ｃｍ^３の帯状の正極を作製した。
【０１２８】
＜負極の作製＞
３０００℃で熱処理したメソフェーズピッチ系炭素繊維（平均粒径２５μｍ、平均繊維長３０μｍ）の粉末９４重量％と、ポリフッ化ビニリデン（ＰＶｄＦ）６重量％と、Ｎ−メチルピロリドン（ＮＭＰ）溶液を加えて混合し、厚さ１２μｍの銅箔に塗布し、乾燥後、プレスすることにより電極密度１．４ｇ／ｃｍ^３の帯状の負極を作製した。
【０１２９】
＜電極群の作製＞
前記正極、厚さ１６μｍで、多孔度５０％で、空気透過率２００秒／１００ｃｍ^３のポリエチレン製多孔質フィルムからなるセパレータ、前記負極、前記セパレータの順序に積層した後、渦巻き状に捲回した。これを９０℃で加熱プレスすることにより、幅３０ｍｍで、厚さ３．０ｍｍの偏平状電極群を作製した。得られた電極群を、厚さが４０μｍのアルミニウム箔と、前記アルミニウム箔の両面に形成されたポリプロピレン層とから構成された厚さが０．１ｍｍのラミネートフィルムパックに収納し、８０℃で２４時間真空乾燥を施した。
【０１３０】
＜非水電解液（液状非水電解質）の調製＞
エチレンカーボネート（ＥＣ）、γ−ブチロラクトン（ＢＬ）及びビニレンカーボネート（ＶＣ）の混合溶媒（体積比率２４：７５：１）に電解質としての四フッ化ホウ酸リチウム（ＬｉＢＦ_４）を１．５ｍｏｌ／Ｌ溶解することにより非水電解液を調製した。
【０１３１】
前記電極群が収納されたラミネートフィルムパック内に前記非水電解液を注入した後、前記ラミネートフィルムパックをヒートシールにより完全密閉し、前述した図６，７に示す構造を有し、幅３５ｍｍ、厚さ３．２ｍｍ、高さ６５ｍｍの薄型リチウムイオン二次電池を製造した。
【０１３２】
（実施例１４）
前述した実施例４で説明したのと同様な組成のリチウム含有複合酸化物を正極活物質として用いること以外は、前述した実施例１３で説明したのと同様にして薄型リチウムイオン二次電池を製造した。
【０１３３】
（実施例１５）
前述した実施例５で説明したのと同様な組成のリチウム含有複合酸化物を正極活物質として用いること以外は、前述した実施例１３で説明したのと同様にして薄型リチウムイオン二次電池を製造した。
【０１３４】
（実施例１６）
前述した実施例９で説明したのと同様な組成のリチウム含有複合酸化物を正極活物質として用いること以外は、前述した実施例１３で説明したのと同様にして薄型リチウムイオン二次電池を製造した。
【０１３５】
得られた実施例１３〜１６の二次電池について、５００サイクル後の放電容量平均低下率、釘刺し試験による電池温度、釘刺し試験時の破裂と発火の有無を、前述した実施例１で説明したのと同様にして測定し、その結果を下記表３に示す。
【０１３６】
【表３】

【０１３７】
表３から明らかなように、二次電池の形態を円筒形から薄型に変更しても、本発明に係る正極活物質を用いる限り、優れたサイクル特性と高い安全性を得られることがわかる。
【０１３８】
【発明の効果】
以上詳述したように本発明によれば、放電容量のバラツキが少なく、サイクル寿命が長く、かつ安全性が向上されたリチウムイオン二次電池を提供することができる。また、本発明によれば、放電容量のバラツキが少なく、サイクル寿命が長く、かつ安全性が向上された電池を実現することが可能な正極活物質およびリチウム含有複合酸化物合成用鞘を提供することができる。
【図面の簡単な説明】
【図１】本発明に係る正極活物質を合成する際に使用される鞘の一例を示す斜視図。
【図２】本発明に係る正極活物質を合成するための焼成工程の一例を示す概略斜視図。
【図３】本発明に係る正極活物質を合成するための焼成工程のさらに別な例を示す概略斜視図。
【図４】リチウム含有複合酸化物粉末の粒度分布の一例を示す特性図。
【図５】本発明に係るリチウムイオン二次電池の一例である円筒形リチウムイオン二次電池を示す部分切欠斜視図。
【図６】本発明に係るリチウムイオン二次電池の一例である薄型リチウムイオン二次電池を示す断面図。
【図７】図６のＡ部を示す断面図。
【図８】実施例１及び比較例１における正極活物質の粒度分布を示す特性図。
【符号の説明】
４１…底胴一体型の角鞘、
４２…底胴一体型の丸鞘、
４３、４５…胴部、
４４、４６…底板、
４７…原料粉末。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a sheath used for synthesizing a lithium-containing composite oxide, a positive electrode active material containing a lithium-containing composite oxide, and a lithium ion secondary battery including a positive electrode active material containing a lithium-containing nickel oxide. It is.
[0002]
[Prior art]
In recent years, as portable personal computers, mobile phones, and the like have become smaller and lighter, there has been a demand for smaller and lighter secondary batteries as power supplies for these electronic devices.
[0003]
As such a secondary battery, a lithium ion secondary battery using a material capable of occluding and releasing lithium ions, such as a carbon material, as a negative electrode material has been developed and has been put to practical use as a power source for small electronic devices. The demand for this secondary battery is increasing because it is smaller and lighter than conventional lead storage batteries and nickel-cadmium batteries and has a high energy density.
[0004]
As a positive electrode active material of this lithium ion secondary battery, a lithium-containing cobalt oxide (LiCoO) having a high discharge potential and a high energy density can be obtained.₂) Has been put to practical use. However, cobalt, which is a raw material of this composite oxide, is scarce in resources and is ubiquitous in countries where commercially available deposits are few, so it is expensive, has large price fluctuations, and will be used in the future. It is accompanied by supply anxiety.
[0005]
Therefore, research on positive electrode active materials other than lithium-containing cobalt oxide has been actively conducted in recent years. As an example, numerous compounds have been reported for a composite oxide of lithium and manganese synthesized from various manganese raw materials and lithium raw materials. Specifically, LiMn having a spinel type crystal structure₂O₄The lithium-manganese composite oxide represented by represents a potential of 3 V with respect to lithium by electrochemical oxidation, and has a theoretical charge / discharge capacity of 148 mAh / g.
[0006]
However, a lithium ion secondary battery using a manganese oxide or a lithium manganese composite oxide as a positive electrode active material has a disadvantage that the capacity is significantly deteriorated when used in an environment at room temperature or higher. This is because manganese oxide and lithium manganese composite oxide are destabilized by high temperature, and Mn is eluted in the non-aqueous electrolyte. In particular, in recent years, large-sized lithium ion secondary batteries for electric vehicles or road leveling have been developed in various fields. With this large-sized lithium ion secondary battery, the heat generation during use cannot be ignored as the size of the battery increases, and the inside of the battery tends to become relatively high even when the ambient environmental temperature is around room temperature. In addition, even a relatively small battery used for a small portable device or the like may be used in a high-temperature environment such as a cabin of a car in the middle of summer, and the temperature inside the battery may be relatively high. is there. Due to these problems, it is very difficult to put a positive electrode active material using manganese as a raw material into practical use.
[0007]
Meanwhile, nickel composite oxides have been actively studied as post-cobalt composite oxides. For example, LiNiO₂Is a complex capacity of 180 to 200 mAh / g and LiCoO₂Active material and LiMn₂O₄This is a very promising positive electrode active material because it is larger than a system active material and has an optimum discharge potential of about 3.6 V on average. However, LiNiO₂The problem is that the initial discharge capacity in the charge / discharge cycle test is greatly reduced with the number of charge / discharges due to the unstable crystal structure of LiNiO.₂In a nail penetration test of a lithium-ion secondary battery manufactured using a battery, there is a problem in safety leading to rupture and ignition.
[0008]
As a method for synthesizing these lithium-containing composite oxides, a starting material powder is prepared by adding alumina (Al₂O₃) Or mullite (3Al₂O₃・ 2SiO₂) Is generally put into a sheath and fired.
[0009]
However, when a sheath containing alumina or mullite as a main component is used, the sheath and the starting material powder easily react with each other, and a by-product generated by this reaction is mixed into the lithium-containing composite oxide. Not only does the charge / discharge cycle characteristic deteriorate, but also the risk of rupture or ignition in the event of a short circuit as in a nail penetration test increases. In addition, lithium-containing composite oxide powder synthesized using a sheath containing alumina or mullite as a main component is a broad powder containing a wide variety of particles ranging from small particles having a submicron diameter to aggregated particles having a particle diameter of about 100 microns. With a good particle size distribution. With such a particle size distribution, the charge / discharge cycle characteristics and safety may not only be further deteriorated, but also the active material filling density of the positive electrode may be reduced. It is desirable to make the distribution uniform. However, since the variation in the particle size distribution is inherently large, sieving for uniforming the particle size distribution must be repeated many times, which causes a problem that not only the yield of the positive electrode active material is reduced but also the manufacturing process becomes complicated.
[0010]
[Problems to be solved by the invention]
An object of the present invention is to provide a lithium ion secondary battery that can easily make the particle size distribution of the positive electrode active material uniform, has no bursting and ignition in a nail penetration test, has high safety, and has a long life. It is.
[0011]
Further, an object of the present invention is to provide a positive electrode active material which is easy to make the particle size distribution uniform, has no burst ignition in a nail penetration test, has high safety, and can realize a long-life battery. It is assumed that.
[0012]
Furthermore, an object of the present invention is to provide a lithium-containing composite oxide that can easily achieve a particle size distribution, has no rupture and ignition in a nail penetration test, has high safety, and can realize a long-life battery. An object of the present invention is to provide a sheath for synthesizing a lithium-containing composite oxide used in the synthesis.
[0013]
[Means for Solving the Problems]
The lithium ion secondary battery according to the present invention is a positive electrode containing an active material, a negative electrode, a lithium ion secondary battery including a non-aqueous electrolyte,
The active material of the positive electrode is a raw material powder.sheathContaining lithium-containing composite oxides obtained by firingSee
The sheath is a material containing at least one component selected from the group consisting of Al, Si, Ca, Y and Zr and MgO, or is selected from the group consisting of Si, Ca, Y, Zr and Hf. At least one component and MgAl _Two O _Four Made of spinel-containing materialA lithium ion secondary battery characterized in that:
[0016]
In the lithium ion secondary battery according to the present invention, it is preferable that the lithium-containing composite oxide has a particle size distribution defined by the following formula (I).
[0017]
S ≦ 2D (I)
Here, S is the half width of the particle size distribution of the lithium-containing composite oxide, and D is the particle size showing the maximum peak in the particle size distribution of the lithium-containing composite oxide.
[0018]
The positive electrode active material according to the present invention is a raw material powdersheathIncluding lithium-containing composite oxide obtained by firing in a state stored inA positive electrode active material,
The sheath is a material containing at least one component selected from the group consisting of Al, Si, Ca, Y and Zr and MgO, or is selected from the group consisting of Si, Ca, Y, Zr and Hf. At least one component and MgAl _Two O _Four Made of spinel-containing materialIt is a positive electrode active material characterized by the above.
[0019]
According to the present inventionFor positive electrode active materialLithium-containing composite oxideofThe synthetic sheath isA material containing at least one component selected from the group consisting of Al, Si, Ca, Y and Zr and MgO, or at least one type selected from the group consisting of Si, Ca, Y, Zr and Hf Components and MgAl _Two O _Four Made of spinel-containing materialIt is characterized by the following.
[0020]
According to the present invention, the raw material powder is made of MgO and MgAl.₂O₄A process for synthesizing a lithium-containing composite oxide by baking in a state of being housed in a sheath containing at least one compound component selected from the group consisting of spinels. Can be provided.
[0021]
BEST MODE FOR CARRYING OUT THE INVENTION
First, the positive electrode active material according to the present invention will be described.
[0022]
This positive electrode active material is obtained by mixing raw material powder with MgO and MgAl₂O₄It includes a lithium-containing composite oxide obtained by firing in a state of being housed in a sheath containing at least one compound component selected from the group consisting of spinels.
[0023]
The sheath is also called a firing tray, and its shape is not particularly limited as long as the intended lithium-containing composite oxide can be obtained, but an example is shown in FIG. FIG. 1 (a) shows a bottom sheath-integrated square sheath 41, and FIG. 1 (b) shows a bottom trunk-integrated round sheath 42. On the other hand, FIG. 1 (c) shows a bottom-body-separated type square sheath having a rectangular tubular body 43 and a rectangular bottom plate 44, and FIG. 1 (d). , A bottom-body-separated round sheath having a cylindrical body portion 45 and a circular bottom plate 46 is shown. The powder stored in each sheath is the raw material powder 47. In particular, according to the bottom-body-separated type sheath, oxygen gas is supplied from above the sheath at the time of firing, and is also supplied from the gap between the body and the bottom plate, so that the oxygen gas is uniformly supplied to the raw material powder. And a firing reaction can be uniformly generated.
[0024]
FIG. 2 shows a state in which four bottom-body-separated square sheaths each containing a raw material powder 47 are set in an electric furnace 48. The atmosphere (firing atmosphere) in the furnace 48 is oxygen gas (O 2₂) Atmosphere or oxygen gas (O₂) Is preferable. Further, the number of sheaths housed in the electric furnace is not limited to four, and can be set to any number. For example, as shown in FIG. 3, the sheath may be housed in the electric furnace 48 in two stages. Furthermore, a tunnel pot may be used as an electric furnace in order to enhance mass productivity.
[0025]
When a sheath containing MgO is used as the sheath, it is preferable that MgO is a main component of the sheath. Here, the main component means a component having the highest abundance ratio among components constituting the sheath. The MgO content of the sheath is preferably in the range of 99% to 100%. If the MgO content of the sheath is less than 99%, components other than MgO contained in the sheath may react with the raw material powder, making it difficult to obtain high safety and charge / discharge characteristics. Among them, a sheath having a MgO content of 99% or more and containing at least one element selected from the group consisting of Al, Si, Ca, Y and Zr is preferable. Since such a sheath can improve thermal shock resistance, it is difficult to crack when the sheath is forcibly taken out of the furnace at a high temperature to room temperature, and the sheath can be taken out of the furnace immediately after firing. , Can improve productivity. In addition, since the sheath is expensive, if it is difficult to break, the production cost of the positive electrode active material can be reduced. Regarding the content of each element in the sheath, the Al content is preferably 30 ppm or more and 2000 ppm or less, the Si content is preferably 30 ppm or more and 10000 ppm or less, and the Ca content is 30 ppm or more and 10000 ppm or less. The Y content is preferably 30 ppm or more and 2000 ppm or less, and the Zr content is preferably 30 ppm or more and 30000 ppm or less. When the content of each element in the sheath is in the above range, it is possible to improve the thermal shock resistance of the sheath while improving the characteristics of the positive electrode active material.
[0026]
MgAl as sheath₂O₄When using a material containing spinel, MgAl₂O₄Spinel is preferably the main component of the sheath. Here, the main component means a component having the highest abundance ratio among components constituting the sheath. Sheath MgAl₂O₄The spinel content is preferably in the range of 95% to 100%. Sheath MgAl₂O₄If the content is less than 95%, MgAl contained in the sheath₂O₄This is because components other than the above and the raw material powder may react with each other to make it difficult to obtain high safety and charge / discharge characteristics. Among them, MgAl₂O₄A sheath having a spinel content of 95% or more and containing at least one element selected from the group consisting of Si, Ca, Y, Zr, and Hf is preferable. Since such a sheath can improve thermal shock resistance, it is difficult to crack when the sheath is forcibly taken out of the furnace at a high temperature to room temperature, and the sheath can be taken out of the furnace immediately after firing. , Can improve productivity. In addition, since the sheath is expensive, if it is difficult to break, the production cost of the positive electrode active material can be reduced. Regarding the content of each element in the sheath, the Si content is preferably 30 ppm or more and 10000 ppm or less, the Ca content is preferably 30 ppm or more and 10000 ppm or less, and the Y content is 30 ppm or more and 2000 ppm or less. The Zr content is preferably 30 ppm or more and 30000 ppm or less, and the Hf content is preferably 30 ppm or more and 2000 ppm or less. When the content of each element in the sheath is in the above range, it is possible to improve the thermal shock resistance of the sheath while improving the characteristics of the positive electrode active material.
[0027]
The components of the sheath are MgO and MgAl₂O₄Both spinels may be contained.
[0028]
The firing is desirably performed in a two-stage firing in which firing is performed at a temperature of 450 to 550 ° C for 2 to 20 hours, and then at 630 to 730 ° C for 2 to 50 hours.
[0029]
The present invention can be applied to lithium-containing composite oxides having various compositions. Among them, the composition of the lithium-containing composite oxide is LiCoO 2₂A composite oxide containing Li and Co such as LiMnO₂And LiMn₂O₄A composite oxide containing Li and Mn such as LiNiO₂It is preferable to use a composite oxide containing Li and Ni as described above. In particular, the composition of the lithium-containing composite oxide may be a composite oxide containing Li and Ni, a lithium-containing composite oxide in which some of the oxygen atoms are replaced by fluorine atoms, a hydroxyl group (OH) or H₂This is effective when a raw material powder containing a starting compound containing O molecules is used.
[0030]
The composition of the composite oxide containing Li and Ni can be, for example, a composition represented by the following formulas (1) to (4).
[0031]
Li_{1 + x}Ni_1-xO_u-yF_y      (1)
However, the molar ratios x, y and u indicate {(y + 0.05) / 2} ≦ x <{(y + 1) / 3}, y> 0, 1.9 ≦ u ≦ 2.1.
[0032]
Li_{1 + x}Ni_1-xO_u-yF_y+ CC (2)
However, the molar ratios x, y and u indicate {(y + 0.05) / 2} ≦ x <{(y + 1) / 3}, y> 0, 1.9 ≦ u ≦ 2.1. C is at least one element selected from the group consisting of Na, K, Ca, S, Si and Fe, and the content c of the element C in the composite oxide is in the range of 20 to 3000 ppm.
[0033]
Li_x(Ni_1-yMe1_y) (O_2-zX_z(3)
Here, Me1 is B, Mg, Al, Sc, Ti, V, Cr, Mn, Co, Cu, Zn, Ga, Y, Zr, Nb, Mo, Tc, Ru, Sn, La, Hf, Ta, W , Re, Pb, and Bi, at least one element selected from the group consisting of F, Cl, Br, and I, and at least one halogen element selected from the group consisting of F, Cl, Br, and I; z indicates 0.02 ≦ x ≦ 1.3, 0.005 ≦ y ≦ 0.5, and 0.01 ≦ z ≦ 0.5, respectively.
[0034]
Li_x(Ni_1-yMe1_y) (O_2-zX_z) + CC (4)
Here, Me1 is B, Mg, Al, Sc, Ti, V, Cr, Mn, Co, Cu, Zn, Ga, Y, Zr, Nb, Mo, Tc, Ru, Sn, La, Hf, Ta, W , Re, Pb, and Bi, at least one element selected from the group consisting of F, Cl, Br, and I, and at least one halogen element selected from the group consisting of F, Cl, Br, and I; z represents 0.02 ≦ x ≦ 1.3, 0.005 ≦ y ≦ 0.5, 0.01 ≦ z ≦ 0.5, respectively, wherein C is Na, K, Ca, S, Si and At least one element selected from the group consisting of Fe, and the content c of the element C in the composite oxide is in the range of 20 to 3000 ppm.
[0035]
The reason for defining the molar ratios x, y and z in the composition formulas (3) and (4) within the above ranges will be described below.
[0036]
The molar ratio x of lithium will be described. If the molar ratio x is less than 0.02, the crystal structure of the composite oxide becomes extremely unstable, and the cycle characteristics and safety of the secondary battery may be insufficient. On the other hand, when the molar ratio x exceeds 1.3, the discharge capacity and safety of the secondary battery may be insufficient. A more preferable range of the molar ratio x is 0.05 ≦ x ≦ 1.2.
[0037]
The molar ratio y of the element Me1 will be described. If the molar ratio y is less than 0.005, the safety of the secondary battery may be insufficient. On the other hand, if the molar ratio y exceeds 0.5, a high discharge capacity may not be obtained. A more preferable range of the molar ratio y is 0.01 ≦ y ≦ 0.35. Further, among the elements Me1, Al, Ti, Mn, Nb, and Ta are preferable.
[0038]
The molar ratio z of the halogen element X will be described. If the molar ratio z is less than 0.01, the cycle characteristics and safety of the secondary battery may be insufficient. On the other hand, when the molar ratio z exceeds 0.5, a high discharge capacity may not be obtained. A more preferable range of the molar ratio z is 0.02 ≦ z ≦ 0.3. Further, the halogen element X is preferably F.
[0039]
The element C contained in the composite oxide having the composition represented by (2) or (4) will be described. By including element C in the composite oxide, it is possible to suppress a rapid rise in battery temperature when a large current flows through the secondary battery due to a short circuit or the like, thereby improving the safety of the secondary battery. can do. If the content c of the element C in the composite oxide is less than 20 ppm, it may be difficult to sufficiently suppress rapid heat generation of the battery when a large current flows. On the other hand, when the content c of the element C in the composite oxide exceeds 3000 ppm, the charge / discharge cycle characteristics may be significantly deteriorated.
[0040]
Further, the optimum content c of the element C in the composite oxide tends to vary depending on the type of the element C, and is desirably set as described below.
[0041]
When the element C is at least one selected from the group consisting of Na, K and S, the content c of the element C is preferably in the range of 20 to 3000 ppm. The more preferable range of the content c is 20 ppm ≦ c ≦ 1500 ppm, and the more preferable range is 20 ppm ≦ c ≦ 1000 ppm. Further, the lower limit of the content c is more preferably set to 50 ppm.
[0042]
On the other hand, when Ca is used as the element C, the content c of the element C is preferably in the range of 20 to 500 ppm. A more preferable range of the content c is 20 ppm ≦ c ≦ 300 ppm.
[0043]
When at least one element selected from the group consisting of Si and Fe is used as the element C, the content c of the element C is preferably in the range of 20 to 500 ppm. A more preferable range of the content c of the element C is 20 ppm ≦ c ≦ 250 ppm.
[0044]
Of the above-described composition formulas (1) to (4), (2) to (4) are preferable because the safety and cycle characteristics of the secondary battery can be further improved. Most preferred is a lithium-containing composite oxide represented by the composition formula (4), which can dramatically improve safety and cycle characteristics.
[0045]
The lithium-containing composite oxide powder preferably has a particle size distribution defined by the following formula (I).
[0046]
S ≦ 2D (I)
Here, S is the half width of the particle size distribution of the lithium-containing composite oxide powder, and D is the particle size showing the maximum peak in the particle size distribution of the lithium-containing composite oxide powder.
[0047]
FIG. 4 shows an example of the particle size distribution of the lithium-containing composite oxide powder. The particle size D having the maximum peak in this particle size distribution is, for example, 10 μm. On the other hand, the half width S of the particle size distribution is, for example, 5 μm, and thus corresponds to a value 0.5 times the particle diameter D. Therefore, this particle size distribution satisfies the relationship of the above-mentioned formula (I).
[0048]
If the half-value width S exceeds the value obtained by doubling the particle diameter D, the dispersion of the particle size distribution becomes large, so that the dispersion of discharge capacity and the cycle deterioration may occur, and the safety may be impaired. The particle size distribution preferably satisfies S ≦ 1.5D, and more preferably satisfies S ≦ D. If the half width S is smaller than 0.01D, a high discharge capacity may not be obtained. Therefore, the minimum value of the half width S is preferably 0.01D.
[0049]
Raw material powder is MgO and MgAl₂O₄When fired in a state of being housed in a sheath containing at least one compound component selected from the group consisting of spinel, a lithium-containing composite oxide powder having a uniform particle size distribution is easily obtained. However, a lithium-containing composite oxide having a particle size distribution satisfying the above-mentioned formula (I) can be obtained. In the case where the particle size distribution after firing is out of the above-mentioned formula (I), classification is performed after firing or after crushing to classify a particle size satisfying the above-mentioned formula (I). It is good to set to distribution. ADVANTAGE OF THE INVENTION According to this invention, since agglomeration of particles hardly occurs at the time of baking and the particle size distribution after baking is relatively uniform, the number of times of classification can be reduced and the particle size sorting can be easily performed.
[0050]
Next, a lithium ion secondary battery using the positive electrode active material according to the present invention will be described.
[0051]
A lithium ion secondary battery according to the present invention includes a positive electrode including the above-described positive electrode active material, a negative electrode, and a non-aqueous electrolyte.
[0052]
Examples of the non-aqueous electrolyte include a liquid non-aqueous electrolyte (non-aqueous electrolyte) prepared by dissolving an electrolyte in a non-aqueous solvent, and a polymer gel in which a polymer material holds a non-aqueous solvent and an electrolyte. A non-aqueous electrolyte, a polymer solid electrolyte containing an electrolyte as a main component, and an inorganic solid non-aqueous electrolyte having lithium ion conductivity. As the non-aqueous solvent and the electrolyte contained in each non-aqueous electrolyte, those described in the liquid non-aqueous electrolyte described later can be used.
[0053]
Examples of the polymer material contained in the gelled nonaqueous electrolyte include polyacrylonitrile, polyacrylate, polyvinylidene fluoride (PVdF), polyethylene oxide (PEO), or acrylonitrile, acrylate, vinylidene fluoride or ethylene oxide as a monomer. And the like. Examples of the polymer material contained in the polymer solid electrolyte include polyacrylonitrile, polyvinylidene fluoride (PVdF), polyethylene oxide (PEO), and polymers containing acrylonitrile, vinylidene fluoride, or ethylene oxide as a monomer. And the like. On the other hand, examples of the inorganic solid nonaqueous electrolyte include a ceramic material containing lithium. Specifically, Li₃N, Li₃PO₄−Li₂S-SiS glass etc. can be mentioned.
[0054]
Hereinafter, an example of the lithium ion secondary battery according to the present invention will be described.
[0055]
This lithium ion secondary battery includes a positive electrode containing the positive electrode active material according to the present invention, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and at least a liquid non-aqueous electrolyte impregnated in the separator. Have.
[0056]
The positive electrode, separator, negative electrode and liquid non-aqueous electrolyte will be described in detail.
[0057]
1) Positive electrode
The positive electrode is prepared, for example, by mixing a positive electrode active material according to the present invention, an electric conduction auxiliary agent and a binder, and pressing the current collector, or the positive electrode active material, an electric conduction auxiliary agent and It is prepared by suspending a binder in a suitable solvent, applying the suspension to a current collector, and drying.
[0058]
Examples of the electric conduction aid include acetylene black, carbon black, graphite and the like.
[0059]
Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), ethylene-propylene-diene copolymer (EPDM), and styrene-butadiene rubber (SBR).
[0060]
The mixing ratio of the positive electrode active material, the electric conduction aid and the binder is in the range of 80 to 95% by weight of the positive electrode active material, 3 to 20% by weight of the electric conduction aid, and 2 to 7% by weight of the binder. Is preferred. As the current collector, a conductive substrate having a porous structure or a non-porous conductive substrate can be used. Examples of a material constituting the current collector include aluminum, stainless steel, and nickel.
[0061]
2) Separator
As the separator, for example, a synthetic resin nonwoven fabric, a polyethylene porous film, a polypropylene porous film, or the like can be used.
[0062]
3) Negative electrode
This negative electrode contains a material capable of inserting (doping) and releasing (dedoping) lithium.
[0063]
Such materials include, for example, lithium metal, a Li-containing alloy capable of occluding and releasing lithium, a metal oxide capable of occluding and releasing lithium, and a metal sulfide capable of occluding and releasing lithium. Materials, metal nitrides capable of storing and releasing lithium, chalcogen compounds capable of storing and releasing lithium, and carbon materials capable of storing and releasing lithium ions. In particular, a negative electrode containing the chalcogen compound or the carbon material is preferable because it has high safety and can improve the cycle life of the secondary battery.
[0064]
Examples of the carbon material that occludes and releases lithium ions include coke, carbon fiber, pyrolytic gas-phase carbonaceous material, graphite, fired resin, mesophase pitch-based carbon fiber, mesophase pitch spherical carbon, and the like. The above-mentioned types of carbon materials are desirable because they can increase the electrode capacity.
[0065]
Examples of the chalcogen compound include titanium disulfide, molybdenum disulfide, niobium selenide, tin oxide and the like. When such a chalcogen compound is used for a negative electrode, the capacity of the negative electrode is increased although the battery voltage is reduced, so that the capacity of the secondary battery is improved.
[0066]
The negative electrode containing the carbon material is produced, for example, by kneading the carbon material and a binder in the presence of a solvent, applying the obtained suspension to a current collector, and drying the resultant.
[0067]
In this case, as the binder, for example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), ethylene-propylene-diene copolymer (EPDM), styrene-butadiene rubber (SBR) and the like can be used. . Further, the mixing ratio of the carbon material and the binder is preferably in the range of 90 to 98% by weight of the carbon material and 2 to 10% by weight of the binder. Further, as the current collector, for example, a conductive substrate of aluminum, stainless steel, nickel, or the like can be used. The current collector may have a porous structure or a non-porous structure.
[0068]
4) Liquid non-aqueous electrolyte (non-aqueous electrolyte)
This liquid non-aqueous electrolyte is prepared by dissolving the electrolyte in a non-aqueous solvent.
[0069]
Examples of the non-aqueous solvent include cyclic carbonates and chain carbonates (eg, ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, etc.), cyclic ethers and chain ethers (eg, 1,2- Dimethoxyethane, 2-methyltetrahydrofuran, etc.), cyclic ester or chain ester (for example, γ-butyrolactone, γ-valerolactone, σ-valerolactone, methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, methyl propionate, propion) Ethylate, propyl propionate, etc.). As the non-aqueous solvent, one kind or a mixed solvent of 2 to 5 kinds selected from the above-mentioned kinds can be used, but it is not necessarily limited to these.
[0070]
As the electrolyte, for example, lithium perchlorate (LiClO₄), Lithium hexafluorophosphate (LiPF₆), Lithium borofluoride (LiBF₄), Lithium arsenic hexafluoride (LiAsF)₆), Lithium trifluoromethylsulfonylimide (LiCF₃SO₃), Lithium bistrifluoromethylsulfonylimide [LiN (CF₃SO₂)₂] And other lithium salts. As such an electrolyte, one or two or three lithium salts selected therefrom can be used, but the electrolyte is not limited thereto.
[0071]
The amount of the electrolyte dissolved in the non-aqueous solvent is desirably in the range of 0.5 to 2 mol / L.
[0072]
One example of the lithium ion secondary battery according to the present invention is shown in FIGS.
[0073]
FIG. 5 is a partially cutaway perspective view showing a cylindrical lithium ion secondary battery which is an example of the lithium ion secondary battery according to the present invention, and FIG. 6 is a thin type which is an example of the lithium ion secondary battery according to the present invention. FIG. 7 is a cross-sectional view showing a lithium ion secondary battery, and FIG.
[0074]
As shown in FIG. 5, a cylindrical container 1 with a bottom made of, for example, stainless steel has an insulator 2 disposed at the bottom. The electrode group 3 is housed in the container 1. The electrode group 3 has a structure in which a band formed by laminating a positive electrode 4, a separator 5 and a negative electrode 6 in this order is spirally wound.
[0075]
A non-aqueous electrolyte is contained in the container 1. A PTC element 7 having a hole opened in the center, a safety valve 8 disposed on the PTC element 7, and a hat-shaped positive terminal 9 disposed on the safety valve 8 are provided with an insulating gasket 10 in an upper opening of the container 1. The crimped through is fixed. The positive electrode terminal 9 has a built-in safety mechanism serving as a gas vent hole (not shown). One end of the positive electrode lead 11 is connected to the positive electrode 4, and the other end is connected to the PTC element 7. The negative electrode 6 is connected to the container 1 serving as a negative terminal via a negative lead (not shown).
[0076]
As shown in FIG. 6, an electrode group 22 is housed in a housing 21 made of, for example, a film material. Examples of the film material include a metal film, a resin sheet such as a thermoplastic resin, and a sheet in which one or both surfaces of a metal layer are covered with a resin layer such as a thermoplastic resin. The electrode group 22 has a structure in which a laminate including a positive electrode, a separator, and a negative electrode is wound into a flat shape. The laminated body includes a separator 23, a positive electrode layer 24, a positive electrode current collector 25, and a positive electrode 26 including a positive electrode layer 24, a separator 23, a negative electrode layer 27, a negative electrode current collector 28, and a negative electrode layer 27 from the lower side in FIG. , A separator 23, a positive electrode layer 24, a positive electrode current collector 25, a positive electrode 26 having a positive electrode layer 24, a separator 23, a negative electrode 29 having a negative electrode layer 27 and a negative electrode current collector 28 are laminated in this order. It has the structure which was done. On the outermost periphery of the electrode group 22, a negative electrode current collector 28 is located. One end of the strip-shaped positive electrode lead 30 is connected to the positive electrode current collector 25 of the electrode group 22, and the other end is extended from the storage container 21. On the other hand, the strip-shaped negative electrode lead 31 has one end connected to the negative electrode current collector 28 of the electrode group 22 and the other end extended from the storage container 21.
[0077]
The positive electrode active material according to the present invention described above uses raw material powders of MgO and MgAl₂O₄It includes a lithium-containing composite oxide obtained by firing in a state of being housed in a sheath containing at least one compound component selected from the group consisting of spinels. According to such a positive electrode active material, the reaction between the raw material powder and the sheath during firing can be suppressed, so that the amount of impurities in the positive electrode active material can be reduced. Further, the particle size distribution of the lithium-containing composite oxide can be made sharper. Therefore, the lithium ion secondary battery including the positive electrode including the positive electrode active material can reduce variation in discharge capacity, improve charge / discharge cycle characteristics, and have a short-circuit state as in a nail penetration test. As a result, when a large current flows, rapid heat generation can be suppressed, and rupture and ignition can be prevented.
[0078]
By ensuring that the particle size distribution of the lithium-containing composite oxide satisfies the relational expression (I) described above, it is possible to further reduce the variation in discharge capacity while securing a high positive electrode active material filling density, The cycle characteristics can be improved, and the battery temperature when a large current flows due to a short circuit state as in a nail penetration test can be further reduced.
[0079]
Further, in the present invention, a sheath having an MgO content of 99% or more and further containing at least one component selected from the group consisting of Al, Si, Ca, Y and Zr, or MgAl₂O₄By using a sheath having a spinel content of 95% or more and further containing at least one component selected from the group consisting of Si, Ca, Y, Zr and Hf, the discharge capacity, the charge / discharge cycle characteristics and A positive electrode active material capable of realizing a secondary battery having excellent safety can be manufactured with high productivity.
[0080]
【Example】
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.
[0081]
(Example 1)
A detachable bottom sheath having the shape shown in FIG. 1C was prepared. This square sheath has an MgO content of 99.5%, an Al content of 160 ppm, a Si content of 140 ppm, a Ca content of 1000 ppm, a Y content of 140 ppm and a Zr content of 2000 ppm. there were. The analysis of the elements constituting the sheath was performed by the method described below.
[0082]
The components (subcomponents) other than MgO contained in the sheath were analyzed by glow discharge mass spectrometry (GDMS: Glow Discharge Mass Spectrometry). The purity of MgO as the main component was calculated by subtracting the concentration of the subcomponent from 100% with all the constituent components of the sheath being 100%.
[0083]
LiOH, Ni as starting materials_0.78Co_0.22(OH)₂・ H₂The composition is Li using O and LiF._1.1Ni_0.78Co_0.22O_1.95F_0.05After mixing, a mixed powder (raw material powder) was prepared by mixing with a Henschel mixer for 30 minutes. This mixed powder was accommodated in a square sheath, and four such square sheaths were set in an electric furnace as shown in FIG. 2 described above and fired. The firing was maintained at 480 ° C. for 15 hours while flowing oxygen at 5 L / min, and then performed at 700 ° C. for 20 hours to obtain a lithium-containing composite oxide powder.
[0084]
As a result of measuring the obtained lithium-containing composite oxide powder with a laser diffraction particle size distribution analyzer, as shown in FIG. 8, the particle diameter D that accounts for the maximum ratio in the particle size distribution was 5 μm. On the other hand, the half width S was 3 μm, a value corresponding to 0.6D. Therefore, the particle size distribution of the lithium-containing composite oxide powder satisfied the relationship of the above-described formula (I).
[0085]
<Preparation of positive electrode>
To a solution of polyvinylidene fluoride dissolved in N-methyl-2-pyrrolidone, lithium-containing composite oxide powder as a positive electrode active material, acetylene black and artificial graphite as conductive agents were added and mixed with stirring. A positive electrode mixture comprising 0.2% by weight, 1.8% by weight of acetylene black, 2.2% by weight of artificial graphite, and 3.8% by weight of polyvinylidene fluoride was prepared. This positive electrode mixture was applied to both surfaces of an aluminum foil (thickness: 20 μm), dried, and then pressure-formed using a roller press to prepare a positive electrode.
[0086]
<Preparation of negative electrode>
After carbonizing mesophase pitch carbon fiber from mesophase pitch as a raw material at 1000 ° C. in an argon atmosphere, the average fiber length is 30 μm, the average fiber diameter is 11 μm, and the particle size is 1 to 80 μm so that 90% by volume is present and the particle size is After appropriately pulverizing so that particles having a particle size of 0.5 μm or less were reduced (5% or less), the resultant was graphitized at 3000 ° C. in an argon atmosphere to produce a carbonaceous material.
[0087]
The carbonaceous material and artificial graphite were added to a solution in which polyvinylidene fluoride was dissolved in N-methyl-2-pyrrolidone, and the mixture was stirred and mixed. The mixture composition was 86.5% by weight of carbonaceous material, 9.5% by weight of artificial graphite, A negative electrode mixture comprising 4% by weight of polyvinylidene fluoride was prepared. This was applied to both surfaces of a copper foil (thickness: 15 μm), dried, and then pressed by a roller press to produce a negative electrode. At this time, the packing density and the electrode length were adjusted so that the ratio (capacity balance) of the designed capacity of the negative electrode to the designed capacity of the positive electrode after molding was 1.03 or more and 1.1 or less.
[0088]
<Preparation of non-aqueous electrolyte (liquid non-aqueous electrolyte)>
Lithium hexafluorophosphate (LiPF) was added to a non-aqueous solvent in which ethylene carbonate (EC) and methyl ethyl carbonate (MEC) were mixed at a volume ratio of 1: 2.₆) Was dissolved at 1 M to prepare a non-aqueous electrolyte.
[0089]
<Assembly of battery>
After welding a positive electrode lead made of aluminum and a negative electrode lead made of nickel to the positive electrode and the negative electrode, respectively, the positive electrode, a separator made of a polyethylene porous film and the negative electrode are laminated in this order, and the negative electrode is formed. The electrode group was produced by spirally winding it so as to be located on the outside.
[0090]
The electrode group was housed in a cylindrical container with a bottom, and the negative electrode lead was welded to a bottom of the cylindrical container with a bottom, and the positive electrode lead was welded to a safety valve arranged at an opening of the cylindrical container with a bottom. Subsequently, 4 mL of a non-aqueous electrolyte was injected into the bottomed cylindrical container, and the electrode group was sufficiently impregnated with the non-aqueous electrolyte. Then, after the positive electrode terminal was arranged on the safety valve, it was fixed by caulking. As described above, a cylindrical lithium ion secondary battery (18650 size) having a designed rated capacity of 1600 mAh was assembled.
[0091]
(Example 2)
Except that the baking conditions in the synthesis of the positive electrode active material were changed to 720 ° C. for 25 hours after maintaining at 480 ° C. for 15 hours while flowing oxygen at 5 liter / min, lithium-containing was carried out in the same manner as in Example 1 described above. A composite oxide powder was obtained.
[0092]
As a result of measuring the obtained lithium-containing composite oxide powder with a laser diffraction particle size distribution analyzer, a relational expression of S = 1.2D is established between the particle size D and the half width S that occupy the largest ratio in the particle size distribution. Was.
[0093]
A cylindrical lithium ion secondary battery was manufactured in the same manner as described in Example 1 except that such a positive electrode active material was used.
[0094]
(Example 3)
Except that the firing conditions in the synthesis of the positive electrode active material were changed to 730 ° C. for 30 hours after holding at 480 ° C. for 15 hours while flowing oxygen at 5 liters / minute, lithium-containing was carried out in the same manner as in Example 1 described above. A composite oxide powder was obtained.
[0095]
As a result of measuring the obtained lithium-containing composite oxide powder with a laser diffraction particle size distribution measuring device, a relational expression of S = 1.7D is established between the particle size D and the half width S which occupy the maximum ratio in the particle size distribution. Was.
[0096]
A cylindrical lithium ion secondary battery was manufactured in the same manner as described in Example 1 except that such a positive electrode active material was used.
[0097]
(Example 4)
A detachable bottom sheath having the shape shown in FIG. 1C was prepared. This square sheath is made of MgAl₂O₄The content of the spinel component was 98.0%, the content of the Si component was 410 ppm, the content of the Ca component was 1100 ppm, the content of the Y component was 500 ppm, the content of the Zr component was 8100 ppm, and the content of the Hf component was 210 ppm. The analysis of the elements constituting the sheath was performed by the method described below.
[0098]
MgAl contained in sheath₂O₄The components (subcomponents) other than the spinel were analyzed by glow discharge mass spectrometry (GDMS: Glow Discharge Mass Spectrometry). MgAl as main component₂O₄The purity of the spinel was calculated by setting the total constituent components of the sheath to 100% and subtracting the concentration of the subcomponent from 100%.
[0099]
Explained in Example 1 described above, except that such a square sheath was used, and the firing conditions were changed to 700 ° C. for 15 hours after holding at 480 ° C. for 10 hours while flowing oxygen at 5 L / min. In the same manner as described above, a lithium-containing composite oxide powder was synthesized.
[0100]
As a result of measuring the obtained lithium-containing composite oxide powder with a laser diffraction particle size distribution analyzer, the particle diameter D that accounts for the maximum ratio in the particle size distribution was 6 μm. On the other hand, the half width S was 3 μm, a value corresponding to 0.5D. Therefore, the particle size distribution of the lithium-containing composite oxide powder satisfied the relationship of the above-described formula (I).
[0101]
A cylindrical lithium ion secondary battery was manufactured in the same manner as described in Example 1 except that such a positive electrode active material was used.
[0102]
(Comparative Example 1)
The bottom-body separated type having the shape shown in FIG.₂O₃) Was prepared. A lithium-containing composite oxide powder was synthesized in the same manner as described in Example 1 except that such a square sheath was used.
[0103]
As a result of measuring the obtained lithium-containing composite oxide powder with a laser diffraction particle size distribution analyzer, as shown in FIG. 8, the particle size showed a broad particle size distribution ranging from submicron to several hundred μm, and the particle size was Giant particles of about 100 μm were also present. In addition, the particle diameter D occupying the largest ratio in the particle size distribution was 4.5 μm. On the other hand, the half width S was 13.5 μm, which was a value corresponding to 3D. Therefore, the particle size distribution of the lithium-containing composite oxide powder deviated from the relationship of the above-described formula (I).
[0104]
A cylindrical lithium ion secondary battery was manufactured in the same manner as described in Example 1 except that such a positive electrode active material was used.
[0105]
(Comparative Example 2)
Fine particles and coarse particles of the lithium-containing composite oxide synthesized in Comparative Example 1 were classified to make the particle size distribution the same as in Example 1 described above. A cylindrical lithium ion secondary battery was manufactured in the same manner as described in Example 1 except that such a positive electrode active material was used.
[0106]
For each of the obtained secondary batteries of Examples 1 to 4 and Comparative Examples 1 and 2, 20 batteries were prepared, and the initial capacity at 20 ° C. was measured. The results are shown in Table 1 below. The charging was performed at a current value corresponding to the designed rated capacity of 0.2 C up to 4.2 V, and then maintained at a constant voltage of 4.2 V for a total of 8 hours. The discharge was performed up to 2.7 V at the same current value.
[0107]
In addition, for each of the secondary batteries of Examples 1 to 4 and Comparative Examples 1 and 2, three batteries were prepared, a charge / discharge cycle test was performed at room temperature, and the average reduction rate of the discharge capacity after 500 cycles was obtained. The results are shown in Table 1 below. The charge / discharge cycle test was performed at a current value corresponding to the designed rated capacity of 0.5 C up to 4.2 V, and then maintained at a constant voltage of 4.2 V for a total of 5 hours. The discharge was performed up to 2.7 V at the same current value. There was a 30-minute pause between charging and discharging.
[0108]
Further, three batteries were prepared for each of Examples 1 to 4 and Comparative Examples 1 and 2, and after charging at 4.2 V, safety was examined by a nail penetration test. The nail used for the test had a diameter of 2 mm and a nail speed of 135 mm / s. The temperature rise of the battery in the nail penetration test was measured using a thermocouple attached to the outer surface of the battery. Table 1 below shows the presence or absence of rupture / ignition in the nail penetration test and the battery temperature in the nail penetration test.
[0109]
[Table 1]

[0110]
As is clear from Table 1, the raw material powder was made of MgO and MgAl₂O₄The secondary batteries of Examples 1 to 4 each containing a lithium-containing composite oxide obtained by firing in a state of being housed in a sheath containing at least one compound component selected from the group consisting of spinel, were prepared using alumina (Al₂O₃), The initial capacity is higher, the capacity variation is shorter, the cycle life is longer, and the temperature at the time of the nail penetration test is higher than those of the secondary batteries of Comparative Examples 1 and 2 including the positive electrode active material synthesized using the sheath made of It can be seen that the rate of rise was low and there was no rupture or ignition in the nail penetration test.
[0111]
(Example 5)
LiOH · H as starting material₂O and Ni (OH)₂And oxides, carbonates and nitrates of the element Me1 (Co), NaOH, KOH and Ca (OH)₂And sodium sulfide (Na₂S ・ 9H₂O) and a sulfuric acid compound (NiSO₄・ 6H₂O), oxides, sulfides, and alkoxides of Si, and oxides, sulfides, and alkoxides of Fe, and a composition Li from these compound powders._1.1Ni_0.78Co_0.22O_1.95F_0.05+ CC), and after mixing, mixed with a Henschel mixer for 30 minutes to prepare a mixed powder (raw material powder). This mixed powder was accommodated in a square sheath similar to that described in Example 1 described above, and four such square sheaths were set in an electric furnace as shown in FIG. 2 described above and fired. The firing was maintained at 480 ° C. for 10 hours while flowing oxygen at 5 L / min, and then performed at 700 ° C. for 15 hours to obtain a lithium-containing composite oxide powder. The type of the element C in the composition formula of the lithium-containing composite oxide and the content c (ppm) of the element C in the oxide are shown in Table 2 below.
[0112]
As a result of measuring the obtained lithium-containing composite oxide powder with a laser diffraction particle size distribution analyzer, the particle size D that accounts for the maximum ratio in the particle size distribution was 5.0 μm. On the other hand, the half width S was 3.5 μm, which was a value corresponding to 0.7D. Therefore, the particle size distribution of the lithium-containing composite oxide powder satisfied the relationship of the above-described formula (I).
[0113]
Note that the composition analysis of the positive electrode active material is performed using glow discharge mass spectrometry (GDMS: Glow Discharge Mass Spectrometry). Here, GDMS is a method in which a voltage of several kV is applied to one electrode as a sample in an Ar atmosphere of about 1 Torr, the sample surface is sputtered by the formed glow discharge, and generated sample ions are extracted from an aperture in the electrode. This is a method of mass spectrometry. The content of each element constituting the composite oxide is obtained by the glow discharge mass spectrometry, and the content of each element other than the element C is converted into mol% to obtain a desired chemical formula. The composition analysis of the positive electrode active material obtained in the following examples is also performed by glow discharge mass spectrometry.
[0114]
A cylindrical lithium ion secondary battery was manufactured in the same manner as described in Example 1 except that such a positive electrode active material was used.
[0115]
(Examples 6 to 8)
Except that the type of the element C in the composition of the lithium-containing composite oxide and the content c (ppm) of the element C in the oxide were changed as shown in Table 2 below, the same as described in Example 5 described above was used. Similarly, a lithium-containing composite oxide powder was obtained.
[0116]
A cylindrical lithium ion secondary battery was manufactured in the same manner as described in Example 1 except that such a positive electrode active material was used.
[0117]
(Example 9)
LiOH · H as starting material₂O and Ni (OH)₂And oxides, carbonates and nitrates of the element Me1 (Co), NaOH, KOH and Ca (OH)₂And sodium sulfide (Na₂S ・ 9H₂O) and a sulfuric acid compound (NiSO₄・ 6H₂O), oxides, sulfides, and alkoxides of Si, and oxides, sulfides, and alkoxides of Fe, and a composition Li from these compound powders._1.1Ni_0.78Co_0.22O_1.95F_0.05+ CC), and after mixing, mixed with a Henschel mixer for 30 minutes to prepare a mixed powder (raw material powder). This mixed powder was accommodated in the same square sheath as described in Example 4 described above, and four such square sheaths were set in an electric furnace as shown in FIG. 2 described above and fired. The firing was maintained at 480 ° C. for 10 hours while flowing oxygen at 5 L / min, and then performed at 700 ° C. for 15 hours to obtain a lithium-containing composite oxide powder. The type of the element C in the composition formula of the lithium-containing composite oxide and the content c (ppm) of the element C in the oxide are shown in Table 2 below.
[0118]
As a result of measuring the obtained lithium-containing composite oxide powder with a laser diffraction particle size distribution analyzer, the particle diameter D occupying the largest ratio in the particle size distribution was 6.5 μm. On the other hand, the half width S was 3.3 μm, a value corresponding to 0.5D. Therefore, the particle size distribution of the lithium-containing composite oxide powder satisfied the relationship of the above-described formula (I).
[0119]
A cylindrical lithium ion secondary battery was manufactured in the same manner as described in Example 1 except that such a positive electrode active material was used.
[0120]
(Examples 10 to 12)
Except that the type of the element C in the composition of the lithium-containing composite oxide and the content c (ppm) of the element C in the oxide were changed as shown in Table 2 below, the same as described in Example 9 described above was used. Similarly, a lithium-containing composite oxide powder was obtained.
[0121]
A cylindrical lithium ion secondary battery was manufactured in the same manner as described in Example 1 except that such a positive electrode active material was used.
[0122]
For the obtained secondary batteries of Examples 5 to 12, the initial capacity, the average reduction rate of the discharge capacity after 500 cycles, the battery temperature by the nail penetration test, the presence or absence of rupture and ignition during the nail penetration test, and the above-described Example The measurement was performed in the same manner as described in Example 1, and the results are shown in Table 2 below. Table 2 also shows the results of Comparative Examples 1 and 2 described above.
[0123]
[Table 2]

[0124]
As is clear from Table 2, the secondary batteries of Examples 5 to 12 have smaller initial capacity variations than the secondary batteries of Comparative Examples 1 and 2, a smaller discharge capacity reduction rate after 500 cycles, It can be seen that the temperature rise during the nail penetration test is suppressed and there is no rupture or ignition.
[0125]
The components of the horn sheath were 99.0% of the MgO component, 520 ppm of the Al component, 350 ppm of the Si component, 2000 ppm of the Ca component, 160 ppm of the Y component, and 160 ppm of the Zr component. Except for changing to 1600 ppm, a lithium ion secondary battery was manufactured in the same manner as described in Example 1 above, and the same excellent battery characteristics and safety as in Example 1 described above were obtained. I got it.
[0126]
In addition, the component of the horn sheath is MgAl₂O₄The amount of the spinel component is 99.0%, the content of the Si component is 210 ppm, the content of the Ca component is 600 ppm, the content of the Y component is 320 ppm, the content of the Zr component is 2,000 ppm, and the content of the Hf component is 160 ppm. Except for this, when a lithium ion secondary battery was manufactured in the same manner as described in Example 4 above, excellent battery characteristics and safety similar to those in Example 4 described above could be obtained.
[0127]
(Example 13)
<Preparation of positive electrode>
91% by weight of the lithium-containing composite oxide powder having the same composition as that described in Example 1 described above was prepared by mixing 2.5% by weight of acetylene black, 3% by weight of graphite, 4% by weight of polyvinylidene fluoride (PVdF), and N- A methylpyrrolidone (NMP) solution was added and mixed, applied to a 15 μm-thick aluminum foil current collector, dried, and pressed to obtain an electrode density of 3.0 g / cm.³Was produced.
[0128]
<Preparation of negative electrode>
94% by weight of powder of mesophase pitch-based carbon fiber (average particle size 25 μm, average fiber length 30 μm) heat-treated at 3000 ° C., 6% by weight of polyvinylidene fluoride (PVdF), and N-methylpyrrolidone (NMP) solution were added. After mixing, applying to a copper foil having a thickness of 12 μm, drying and pressing, the electrode density was 1.4 g / cm.³Was produced.
[0129]
<Preparation of electrode group>
The positive electrode has a thickness of 16 μm, a porosity of 50%, and an air permeability of 200 seconds / 100 cm.³After laminating in order of the separator made of a polyethylene porous film, the negative electrode, and the separator, the resultant was spirally wound. This was hot-pressed at 90 ° C. to produce a flat electrode group having a width of 30 mm and a thickness of 3.0 mm. The obtained electrode group was housed in a 0.1 mm-thick laminated film pack composed of an aluminum foil having a thickness of 40 μm and polypropylene layers formed on both sides of the aluminum foil. Vacuum drying was performed for hours.
[0130]
<Preparation of non-aqueous electrolyte (liquid non-aqueous electrolyte)>
Lithium tetrafluoroborate (LiBF) as an electrolyte in a mixed solvent (volume ratio 24: 75: 1) of ethylene carbonate (EC), γ-butyrolactone (BL) and vinylene carbonate (VC)₄) Was dissolved at 1.5 mol / L to prepare a non-aqueous electrolyte.
[0131]
After injecting the non-aqueous electrolyte into the laminated film pack in which the electrode group is stored, the laminated film pack is completely sealed by heat sealing, and has the structure shown in FIGS. A thin lithium ion secondary battery having a thickness of 3.2 mm and a height of 65 mm was manufactured.
[0132]
(Example 14)
A thin lithium ion secondary battery was manufactured in the same manner as described in Example 13 except that a lithium-containing composite oxide having the same composition as that described in Example 4 was used as the positive electrode active material. did.
[0133]
(Example 15)
A thin lithium ion secondary battery was manufactured in the same manner as described in Example 13 except that a lithium-containing composite oxide having the same composition as that described in Example 5 was used as the positive electrode active material. did.
[0134]
(Example 16)
A thin lithium ion secondary battery was manufactured in the same manner as described in Example 13 except that a lithium-containing composite oxide having the same composition as that described in Example 9 was used as the positive electrode active material. did.
[0135]
Regarding the obtained secondary batteries of Examples 13 to 16, the average discharge capacity reduction rate after 500 cycles, the battery temperature by the nail penetration test, and the presence or absence of rupture and ignition at the time of the nail penetration test are described in Example 1 described above. The measurement was performed in the same manner as described above, and the results are shown in Table 3 below.
[0136]
[Table 3]

[0137]
As is clear from Table 3, even if the form of the secondary battery is changed from cylindrical to thin, as long as the positive electrode active material according to the present invention is used, excellent cycle characteristics and high safety can be obtained.
[0138]
【The invention's effect】
As described in detail above, according to the present invention, it is possible to provide a lithium ion secondary battery with reduced variation in discharge capacity, a long cycle life, and improved safety. Further, according to the present invention, there is provided a cathode active material and a sheath for synthesizing a lithium-containing composite oxide capable of realizing a battery with less variation in discharge capacity, a long cycle life, and improved safety. be able to.
[Brief description of the drawings]
FIG. 1 is a perspective view showing an example of a sheath used when synthesizing a positive electrode active material according to the present invention.
FIG. 2 is a schematic perspective view showing an example of a firing step for synthesizing a positive electrode active material according to the present invention.
FIG. 3 is a schematic perspective view showing still another example of a firing step for synthesizing a positive electrode active material according to the present invention.
FIG. 4 is a characteristic diagram showing an example of a particle size distribution of a lithium-containing composite oxide powder.
FIG. 5 is a partially cutaway perspective view showing a cylindrical lithium ion secondary battery as an example of the lithium ion secondary battery according to the present invention.
FIG. 6 is a cross-sectional view showing a thin lithium ion secondary battery which is an example of the lithium ion secondary battery according to the present invention.
FIG. 7 is a sectional view showing a portion A in FIG. 6;
FIG. 8 is a characteristic diagram showing a particle size distribution of a positive electrode active material in Example 1 and Comparative Example 1.
[Explanation of symbols]
41 ... square body integral with the bottom body,
42 ... bottom shell integrated type round sheath,
43, 45 ... trunk,
44, 46 ... bottom plate,
47: Raw material powder.

Claims (5)

In a positive electrode including an active material, a negative electrode, and a lithium ion secondary battery including a nonaqueous electrolyte,
The active material of positive electrode, viewed contains a lithium-containing composite oxide obtained by calcining raw material powders in a state of being housed in the sheath,
The sheath is a material containing at least one component selected from the group consisting of Al, Si, Ca, Y and Zr and MgO, or is selected from the group consisting of Si, Ca, Y, Zr and Hf. A lithium ion secondary battery formed of a material containing at least one kind of component and MgAl ₂ O ₄ spinel . The Al content and the Y content in the MgO-containing material are each 30 to 2000 ppm, the Si content and the Ca content are each 30 to 10000 ppm, and the Zr content is 30 to 30000 ppm,
The Si content and the Ca content in the MgAl ₂ O ₄ spinel-containing material are respectively 30 to 10000 ppm, the Y content and the Hf content are 30 to 2000 ppm, respectively, and the Zr content is 30 to 30000 ppm. The lithium-ion secondary battery according to claim 1, wherein: 3. The lithium ion secondary battery according to claim 1, wherein the powder of the lithium-containing composite oxide has a particle size distribution represented by the following formula (I) .
S ≦ 2D (I)
Here, S is the half width of the particle size distribution of the lithium-containing composite oxide powder, and D is the particle size showing the maximum peak in the particle size distribution. A positive electrode active material containing a lithium-containing composite oxide obtained by firing the raw material powder stored in a sheath ,
The sheath is a material containing at least one component selected from the group consisting of Al, Si, Ca, Y and Zr and MgO, or is selected from the group consisting of Si, Ca, Y, Zr and Hf. A cathode active material formed of a material containing at least one kind of component and MgAl ₂ O ₄ spinel . A material containing at least one component selected from the group consisting of Al, Si, Ca, Y and Zr and MgO, or at least one type selected from the group consisting of Si, Ca, Y, Zr and Hf synthesis sheath component and MgAl ₂ O ₄ positive electrode active material for a lithium-containing composite oxide is characterized by being formed of a material containing a spinel.

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