JP2004079297A - Lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium secondary battery which has a large output and of which degradation of life property, in particular, the input and output property caused by charge and discharge cycle at high temperatures can be suppressed. <P>SOLUTION: Lithium manganate of which the average particle size of the secondary particles, which are made of a particle A having an average particle size 0.5-1 μm and a particle B having an average particle size 2-3 μm, is made 10-30 μm, having spherical shape, is used for the positive electrode active material. The ratio N<SB>A</SB>/ N<SB>B</SB>, the ratio of quantity N<SB>A</SB>of the particle A to the quantity N<SB>B</SB>of the particle B is made to range between 5 and 20. Since lithium manganate having spherical shape of its secondary particles is used, conductive material enters into the active materials and the contact area between the active material and the conductive material is increased. Further, the specific surface area is made large by the particle A and the reaction area of the electrode is increased, and by the particle B, the cohesion between the particles becomes large, thereby, elution of manganese can be suppressed. <P>COPYRIGHT: (C)2004,JPO

Description

【００２７】
（実施例２〜実施例３）
表１に示すように、実施例２〜実施例３では、比Ｎ_Ａ／Ｎ_Ｂを、実施例２では１０、実施例３では２０とし、二次粒子の平均粒子径を、実施例２、実施例３共に１５μｍとした以外は実施例１と同様に電池を作製した。
【００２８】
（実施例４〜実施例５）
表１に示すように、実施例４〜実施例５では、比Ｎ_Ａ／Ｎ_Ｂを、実施例４、実施例５共に１０とし、二次粒子の平均粒子径を、実施例４では１０μｍ、実施例５では３０μｍとした以外は実施例１と同様に電池を作製した。
【００２９】
（実施例６）
表１に示すように、実施例６では、比Ｎ_Ａ／Ｎ_Ｂを５とし、二次粒子の平均粒子径を１５μｍとし、二次粒子の形状が塊状のマンガン酸リチウムを用いて、電池を作製した。
【００３０】
（実施例７〜実施例８）
表１に示すように、実施例７〜実施例８では、比Ｎ_Ａ／Ｎ_Ｂを、実施例７では１０、実施例８では２０とし、二次粒子の平均粒子径を、実施例７、実施例８共に１５μｍとした以外は実施例６と同様に電池を作成した。
【００３１】
（実施例９〜実施例１０）
表１に示すように、実施例９〜実施例１０では、比Ｎ_Ａ／Ｎ_Ｂを、実施例９、実施例１０共に１０とし、二次粒子の平均粒子径を、実施例９では１０μｍ、実施例１０では３０μｍとした以外は実施例６と同様に電池を作成した。
【００３２】
（比較例１）
表１に示すように、比較例１では、比Ｎ_Ａ／Ｎ_Ｂを５０とし、二次粒子の平均粒子径を１５μｍとし、二次粒子の形状が塊状のマンガン酸リチウムを用いた以外は実施例１と同様に電池を作製した。
【００３３】
（比較例２）
表１に示すように、比較例２では、一次粒子を粒子Ａのみとし、二次粒子の平均粒子径を１５μｍとし、二次粒子の形状が塊状のマンガン酸リチウムを用いた以外は実施例１と同様に電池を作製した。
【００３４】
（比較例３）
表１に示すように、比較例３では、一次粒子を粒子Ｂのみとし、二次粒子の平均粒子径を１５μｍとし、二次粒子の形状が塊状のマンガン酸リチウムを用いた以外は実施例１と同様に電池を作製した。
【００３５】
（比較例４〜比較例５）
表１に示すように、比較例４〜比較例５では、比Ｎ_Ａ／Ｎ_Ｂを、実施例４、実施例５共に１０とし、二次粒子の平均粒子径を、実施例４では８μｍ、実施例５では３５μｍとし、二次粒子の形状が塊状のマンガン酸リチウムを用いた以外は実施例１と同様に電池を作製した。
【００３６】
以上のように作製した実施例及び比較例の各（複数個の）電池について充放電試験を実施し、初期及びパルスサイクル試験後の出力並びに容量維持率を測定した。
【００３７】
出力の測定は、２５±２°Ｃの雰囲気において４．１Ｖの満充電状態から１０Ａ、３０Ａ、９０Ａの電流値で各１０秒間放電し、横軸電流に対して、各５秒目の電池電圧を縦軸にプロットし、３点を直線近似した直線が終止電圧である２．７Ｖと交差する点の電流値を読み取り、この電流値と２．７Ｖとの積をその電池の出力とした。
【００３８】
また、５０±３°Ｃの雰囲気において各電池に約５０Ａの高負荷電流を充電方向と放電方向ともに約５秒通電し、休止時間も含め１サイクル約３０秒のパルスサイクル試験を連続して１０万回繰り返した後、上述の方法で出力を測定した。
【００３９】
放電容量の測定は、２５±２°Ｃの雰囲気において充電した後放電し、初期の放電容量を測定した。充電条件は、４．１Ｖ定電圧、制限電流５Ａ、３．５時間とし、放電条件は、１Ａ定電流、終止電圧２．７Ｖとした。上述のパルスサイクル試験後の放電容量を測定し、初期の放電容量に対する維持率を百分率で示した。一連の試験結果を下表２に示す。
【００４０】
【表２】

【００４１】
表２に示すように、比Ｎ_Ａ／Ｎ_Ｂを５〜２０とし、二次粒子の平均粒子径を１５μｍとし、二次粒子の形状を球状とした実施例１〜実施例３の電池では、出力は初期が８５０Ｗ以上、パルスサイクル試験後でも６８０Ｗ以上で、容量維持率も９０％以上であり、高出力で長寿命の優れた電池であった。これに対して、比Ｎ_Ａ／Ｎ_Ｂが２０を超え、二次粒子の形状を塊状とした比較例１の電池及び粒子Ａのみを用いた比較例２の電池では、初期の出力は９００Ｗ以上と優れているものの、パルスサイクル試験後の出力が５５０Ｗ以下、容量維持率が８０％以下であり、十分な性能を確保することができなかった。反対に、比Ｎ_Ａ／Ｎ_Ｂを５未満とした比較例３の電池では、容量維持率は９０％と優れていたものの、初期及びパルスサイクル試験後の出力がそれぞれ６３０Ｗ、５５０Ｗであり、十分な出力を得ることができなかった。
【００４２】
また、比Ｎ_Ａ／Ｎ_Ｂを１０とし、二次粒子の平均粒子径を１０μｍ、３０μｍとし、形状を球状とした実施例４、実施例５の電池は、初期の出力が８６０Ｗ以上、パルスサイクル試験後の出力も６８０Ｗ以上で、容量維持率も９２％以上であり、高出力で長寿命の優れた電池であった。しかしながら、二次粒子の平均粒子径を８μｍ、３５μｍとした比較例４、比較例５の電池は、初期の出力が７３０Ｗ以下、パルスサイクル試験後の出力が５５０Ｗ以下であり、更には容量維持率も８５％以下と大きく劣る結果であった。
【００４３】
更に、比Ｎ_Ａ／Ｎ_Ｂ及び二次粒子の平均粒子径を実施例１〜実施例５と同様とし、形状を塊状とした実施例６〜実施例１０の電池では、出力は初期及びパルスサイクル試験後共に１０％程度低下するものの、パルスサイクル試験後でも６５０Ｗ以上で、容量維持率は９０％以上であり、高出力で長寿命の優れた電池を得ることができた。
【００４４】
以上の試験結果から、比Ｎ_Ａ／Ｎ_Ｂを５〜２０とし、二次粒子の平均粒子径を１０〜３０μｍとしたマンガン酸リチウムを正極活物質に用いた実施例１〜実施例１０の各電池は、出力特性、寿命特性共に大きく向上することが判った。また、二次粒子の形状を球状としたマンガン酸リチウムを正極活物質に用いることにより、寿命特性を維持したまま、更に高出力の電池とすることができた。
【００４５】
上述のように、本実施例の円筒形リチウムイオン電池２０は、マンガン酸リチウムに平均粒子径が０．５〜１μｍの粒子Ａと平均粒子径が２〜３μｍの粒子Ｂとの一次粒子を用い、比表面積増大の効果と粒子間結合力増大の効果を併せ持つようにしたので、高出力、長寿命を実現することができた。また、比Ｎ_Ａ／Ｎ_Ｂを５〜２０とし、粒子Ａによる比表面積の増大と粒子Ｂによる粒子間結合力の増大をバランスよく行ったので、一層高出力で容量維持率の高バランスのよい電池を得ることができた。比Ｎ_Ａ／Ｎ_Ｂが５に満たないと、粒子間結合力が増大して容量維持率の高い電池とすることはできるが、比表面積が減少するため出力が低下し、逆に、比Ｎ_Ａ／Ｎ_Ｂが２０を超えると、比表面積が増大し出力の高い電池とすることはできるが、粒子間結合力が低下し、マンガン酸リチウムからのマンガンの溶出が多くなるため容量が低下した。また、粒子Ａと粒子Ｂを凝集させた二次粒子を用いたので、正極作製時に粉体が飛散することを防止でき、集電体に塗布するためのスラリ化が容易になり、正極作製の作業性を高めることができた。更に、二次粒子の平均粒子径を１０〜３０μｍとしたので、一層粉体の飛散防止やスラリ化が容易となった。二次粒子の平均粒子径が１０μｍに満たないと、粉体の飛散を生じ、３０μｍを超えると、二次粒子中に電解液が均一に浸潤しなくなり充放電を妨げるため出力、容量が低下した。また、正極における導電材の役割は活物質と集電体との導電経路を確保させ電極反応面積を増大させることである。二次粒子の形状を塊状から球状とすることにより、活物質同士の接触面積が減少し反対に活物質と導電材との接触面積が増大されると共に、活物質と集電体との導電経路が確保されるため、電極反応面積が増大するので、更に高出力とすることができた。
【００４６】
なお、本実施形態では、円筒形電池について例示したが、本発明は電池の形状については限定されず、角形、その他の多角形の電池にも適用可能である。また、本発明の適用可能な構造としては、上述した電池容器に電池蓋がカシメによって封口されている構造の電池以外であっても構わない。このような構造の一例として正負外部端子が電池蓋を貫通し、電池容器内で軸芯を介して正負外部端子が押し合っている状態の電池を挙げることができる。更に本発明は、正極及び負極を捲回式の構造とせず、積層式の構造としたリチウム二次電池にも適用可能である。
【００４７】
また、本実施形態以外で用いることのできるリチウム二次電池用正極活物質としては、リチウムイオンを挿入・脱離可能な材料であり、予め十分な量のリチウムイオンを挿入したリチウムマンガン複酸化物であればよく、スピネル構造を有したマンガン酸リチウム（ＬｉＭｎ_２Ｏ_４）のほか、層状岩塩型構造を有するマンガン酸リチウム（ＬｉＭｎＯ_２）、結晶中のリチウムやマンガンの一部をそれら以外の元素、例えば、Ｆｅ、Ｃｏ、Ｎｉ、Ｃｒ、Ａｌ、Ｍｇ等の元素で置換あるいはドープした材料や結晶中の酸素の一部をＳ、Ｐ等で置換あるいはドープした材料を使用するようにしてもよい。また、本実施形態では、正極活物質のマンガン酸リチウムに平均粒子径の異なる２種の一次粒子を用いた例を示したが、これらの一次粒子とは平均粒子径の異なる１種以上の一次粒子を更に補足的に用いるようにしてもよい。
【００４８】
更に、本実施形態では、負極活物質に、晶質の炭素材料を用いた場合と比べて負極集電体への密着性に優れる非晶質炭素を用いた例を示したが、天然黒鉛や、人造の各種黒鉛材、コークスなどの炭素材料等を使用してもよく、その粒子形状についても、鱗片状、球状、繊維状、塊状等、特に制限されるものではない。このような炭素材を負極活物質に用いると、断面渦巻状に捲回して電極群を形成するときの可撓性に優れ、負極からの負極活物質層の剥離離脱を防止することができる。
【００４９】
また、本発明は、本実施形態で例示した導電材、バインダ（結着剤）には限定されず、通常用いられているいずれのものも使用可能である。本実施形態以外で用いることのできるリチウム二次電池用極板活物質結着剤としては、ポリテトラフルオロエチレン（ＰＴＦＥ）、ポリエチレン、ポリスチレン、ポリブタジエン、ブチルゴム、ニトリルゴム、スチレン／ブタジエンゴム、多硫化ゴム、ニトロセルロース、シアノエチルセルロース、各種ラテックス、アクリロニトリル、フッ化ビニル、フッ化ビニリデン、フッ化プロピレン、フッ化クロロプレン等の重合体及びこれらの混合体などがある。
【００５０】
更にまた、本実施形態では、エチレンカーボネート、ジメチルカーボネート、ジエチルカーボネートを体積比１：１：１で混合した混合溶媒にＬｉＰＦ_６を溶解した非水電解液を例示したが、一般的なリチウム塩を電解質とし、これを有機溶媒に溶解した非水電解液を用いてもよく、本発明は用いられるリチウム塩や有機溶媒には特に制限されない。例えば、電解質としては、ＬｉＣｌＯ_４、ＬｉＡｓＦ_６、ＬｉＢＦ_４、ＬｉＢ（Ｃ_６Ｈ_５）_４、ＣＨ_３ＳＯ_３Ｌｉ、ＣＦ_３ＳＯ_３Ｌｉ等やこれらの混合物を用いることができる。また、有機溶媒としては、プロピレンカーボネート、１，２−ジメトキシエタン、１，２−ジエトキシエタン、γ−ブチロラクトン、テトラヒドロフラン、１，３−ジオキソラン、４−メチル−１，３−ジオキソラン、ジエチルエーテル、スルホラン、メチルスルホラン、アセトニトリル、プロピオニトリル等、又はこれらの２種類以上を混合した混合溶媒を用いることができ、更に、混合配合比についても限定されるものではない。このような非水電解液を用いることにより電池容量の向上や寒冷地での使用にも適合させることが可能となる。
【００５１】
【発明の効果】
以上説明したように、本発明によれば、リチウムマンガン複酸化物として平均粒子径の異なる複数種の一次粒子を混在させ集合させて二次粒子を形成させることで、リチウムマンガン複酸化物の比表面積を増大させるため、電極反応面積を増大させて電池の内部抵抗を低減することができると共に、粒子間結合力を増大させてマンガン溶出を抑制することができるので、高出力化と共に、充放電サイクルによる入出力特性の低下を抑制した長寿命のリチウム二次電池を実現することができると共に、正極作製時に粉体が飛散することを防止でき、集電体に塗布するためのスラリ化が容易になるので、正極作製の作業性を高めることができる、という効果を得ることができる。
【図面の簡単な説明】
【図１】本発明が適用可能な円筒形リチウムイオン電池に用いられる、二次粒子の形状が塊状のマンガン酸リチウムの電子顕微鏡写真である。
【図２】本発明が適用可能な円筒形リチウムイオン電池に用いられる、二次粒子の形状が球状のマンガン酸リチウムの電子顕微鏡写真である。
【図３】本発明が適用可能な実施形態の円筒形リチウムイオン電池の断面図である。
【符号の説明】
６　捲回群（電極群）
２０　円筒形リチウムイオン電池（リチウム二次電池）[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a lithium secondary battery, and more particularly to a lithium secondary battery in which an electrode group having a positive electrode using a lithium manganese double oxide as a positive electrode active material and a negative electrode is immersed in an electrolytic solution.
[0002]
[Prior art]
Lithium-ion secondary batteries are mainly used as power supplies for portable devices such as VTR cameras, notebook computers, and mobile phones, taking advantage of their high energy density. The internal structure of this battery is usually of a wound type as shown below. The electrode has a band shape in which an active material is applied to a metal foil for both the positive electrode and the negative electrode. The cross section is spirally wound so that the positive electrode and the negative electrode do not directly contact each other with a separator interposed therebetween, thereby forming a wound group. The wound group is housed in a cylindrical battery can serving as a battery container, and is sealed after the electrolyte is injected.
[0003]
A typical cylindrical lithium ion secondary battery has a diameter of 18 mm and a height of 65 mm, which is called 18650 type, and is widely used as a small consumer lithium ion battery. As the positive electrode active material of the 18650 type lithium ion secondary battery, lithium cobalt oxide characterized by high capacity and long life is mainly used. The battery capacity is approximately 1.3 Ah to 1.7 Ah, and the output is about 10 W. It is about.
[0004]
On the other hand, in the automotive industry, in order to cope with environmental problems, an electric vehicle (EV) having no exhaust gas and a power source entirely using only batteries, and a hybrid (power source using both an internal combustion engine and a battery) ( The development of electric vehicles has been accelerated and some of them are now at the stage of practical use.
[0005]
A battery serving as a power source of an electric vehicle is required to have characteristics capable of obtaining high output and high energy, and a lithium ion battery has attracted attention as a battery that meets these requirements. For the spread of electric vehicles, it is essential to lower the price of batteries, and for that purpose, low-cost battery materials are required.For example, in the case of a positive electrode active material, a resource-rich manganese oxide is used. Particular attention has been paid to improvements aimed at improving the performance of batteries. In addition, batteries for electric vehicles are required to have not only high capacity but also high output that affects acceleration performance and the like, that is, reduction of internal resistance of the battery. This requirement can be met by increasing the specific surface area of the positive electrode active material with the aim of increasing the electrode reaction area.
[0006]
To increase the specific surface area specifically, it is necessary to reduce the particle diameter of the positive electrode active material. However, if the particle diameter is small, adverse effects such as scattering of powder at the time of manufacturing the electrode and difficulty in forming a slurry for coating the current collector are caused. In order to improve this, primary particles having a small particle diameter can be coagulated to form secondary particles.
[0007]
[Problems to be solved by the invention]
However, in the case of a lithium secondary battery using a lithium manganese double oxide as the positive electrode active material, if a lithium manganese double oxide with a small particle diameter and a large specific surface area is used simply for the purpose of high output, the electrolytic solution Since manganese elutes into the remarkable portion and the current becomes difficult to flow, a decrease in capacity due to charge / discharge cycles and storage of the battery increases, and a problem occurs that the life characteristics are impaired.
[0008]
On the other hand, various proposals have been made to improve the life characteristics by replacing a part of the manganese atoms in the lithium manganate crystal with a different metal such as cobalt (Co) or chromium (Cr). Although effective, this is not enough.
[0009]
The present invention has been made in view of the above circumstances, and has as its object to provide a lithium secondary battery capable of suppressing deterioration of input / output characteristics due to charge / discharge cycling at a high temperature while achieving high output.
[0010]
[Means for Solving the Problems]
In order to solve the above problems, the present invention provides a lithium secondary battery in which an electrode group having a positive electrode and a negative electrode using a lithium manganese double oxide as a positive electrode active material is infiltrated in an electrolyte solution, The double oxide includes a plurality of types of primary particles having different average particle diameters, and the primary particles are aggregated to form secondary particles.
[0011]
In the present invention, a lithium manganese double oxide in which a plurality of types of primary particles having different average particle diameters are mixed and aggregated to form secondary particles is used as a positive electrode active material. Primary particles having a small average particle diameter increase the specific surface area for primary particles having a large average particle diameter, and conversely, primary particles having a large average particle diameter are relatively small for primary particles having a small average particle diameter. The bonding force between the primary particles is further increased. By increasing the specific surface area, the electrode reaction area is increased and the internal resistance of the battery is reduced, so that high output can be obtained. Since elution can be suppressed, it is possible to prevent a decrease in capacity, and if a plurality of types of primary particles having different average particle diameters are aggregated to form secondary particles, it is possible to prevent powder from scattering at the time of manufacturing the positive electrode. In addition, the slurry can be easily applied to the current collector, so that the operability of producing the positive electrode can be improved. Therefore, according to the present invention, an increase in specific surface area and an increase in interparticle binding force can be achieved at the same time. Can be realized.
[0012]
In this case, if the primary particles include the particles A having an average particle size of 0.5 μm to 1 μm and the particles B having an average particle size of 2 μm to 3 μm, the specific surface area is increased by the particles A. Can be obtained, and the bonding force between the particles is increased by the particles B, so that manganese elution can be suppressed to prevent a decrease in capacity. Ratio N of the number of particles A to the number of particles B _A / N _B Is less than 5, the ratio of the particles A is small, the specific surface area is reduced, and the output is reduced. Conversely, the ratio N _A / N _B Exceeds 20, the proportion of the particles B is small, the bonding force between the particles is reduced, and the manganese elution is increased, resulting in a decrease in the capacity. _A / N _B Is 5 to 20, a high-output and long-life battery can be obtained. Furthermore, when the average particle diameter of the secondary particles is less than 10 μm, the powder is scattered, and when the average particle diameter exceeds 30 μm, the electrolyte does not uniformly infiltrate into the secondary particles, thereby preventing charge and discharge. Therefore, the output and the capacity are reduced. By setting the average particle diameter of the secondary particles to 10 μm to 30 μm, the scattering of the powder and the formation of a slurry can be further facilitated. Furthermore, when the shape of the secondary particles is a lump, the ratio of contact between the active material and the active material increases, and a conductive path cannot be secured at the contact portion, so that the shape of the secondary particles is spherical. As a result, the porosity between the active materials is increased, and the conductive material can enter the void portions, so that the electrode reaction area increases and high output can be obtained.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment in which the lithium secondary battery of the present invention is applied to a cylindrical lithium ion battery for a hybrid electric vehicle will be described.
[0014]
(Positive electrode)
Lithium manganate as a lithium manganese double oxide is used as the positive electrode active material, and lithium manganate is composed of particles A having an average primary particle diameter of 0.5 to 1 μm and particles B having an average primary particle diameter of 2 to 3 μm. Is the ratio of the number of particles A to the number of particles B, N _A / N _B Was mixed so as to fall within a predetermined range described later, and the average particle diameter of the secondary particles composed of particles A and B was set to 10 to 30 μm. In addition, a secondary particle having a massive or spherical shape was used. To 100 parts by weight of lithium manganate, 10 parts by weight of flaky graphite as a conductive material and 10 parts by weight of polyvinylidene fluoride (PVDF) as a binder are added, and N-methylpyrrolidone (NMP) is used as a dispersion solvent. Was added and kneaded to prepare a positive electrode mixture (slurry). The prepared slurry was applied to both sides of a 20-μm-thick aluminum foil (positive electrode current collector), dried, and then pressed and cut to prepare a positive electrode having a positive-electrode-active-material-applied-portion-thickness of 90 μm without an aluminum foil. The average particle diameter and the ratio N of the particles A and B _A / N _B Was confirmed to be within the above range by observation with an electron microscope. Further, the average particle size and shape of the secondary particles were also confirmed by the same method. In addition, the shape of the secondary particles was determined to be lumpy or spherical with an electron microscope magnifying 2000 times. FIG. 1 shows electron micrographs of the secondary particles determined to be massive, and FIG. 2 shows electron micrographs of the secondary particles determined to be spherical.
[0015]
(Negative electrode)
To 100 parts by weight of amorphous carbon powder as a negative electrode active material, 10 parts by weight of PVDF was added as a binder, NMP was added as a dispersion solvent, and the kneaded slurry was applied to both sides of a 10 μm-thick rolled copper foil. The negative electrode was coated, and then dried, pressed, and cut to produce a negative electrode having a negative electrode active material application portion thickness of 70 μm that did not include a rolled copper foil.
[0016]
(Battery assembly)
As shown in FIG. 3, the positive electrode and the negative electrode produced above were wound together with a polyethylene separator having a width of 90 mm and a thickness of 40 μm so that these two electrodes did not directly contact each other to form a winding group (electrode group) 6. At this time, the positive electrode lead piece and the negative electrode lead piece were respectively positioned on opposite end surfaces of the winding group 6. The length of the positive electrode, the negative electrode, and the separator was adjusted, and the diameter of the winding group 6 was set to 38 ± 0.1 mm.
[0017]
The positive electrode lead pieces are deformed, and all of them are gathered and brought into contact with the vicinity of the flange peripheral surface integrally projecting from the periphery of the positive electrode current collecting ring substantially on the extension of the axis of the winding group 6, and then contacted with the positive electrode. The lead piece and the flange peripheral surface were ultrasonically welded to connect the positive electrode lead piece to the flange peripheral surface. On the other hand, the connection operation between the negative electrode current collector ring and the negative electrode lead piece was also performed in the same manner as the connection operation between the positive electrode current collector ring and the positive electrode lead piece.
[0018]
Thereafter, an insulating coating was applied to the entire peripheral surface of the flange of the positive electrode current collecting ring. For this insulating coating, a pressure-sensitive adhesive tape was used in which the base material was polyimide and one side thereof was coated with a pressure-sensitive adhesive composed of hexamethacrylate. This adhesive tape was wound one or more times from the peripheral surface of the flange to the outer peripheral surface of the winding group 6 to form an insulating coating, and the winding group 6 was inserted into a nickel-plated steel battery container. The outer diameter of the battery container is 40 mm and the inner diameter is 39 mm.
[0019]
A negative electrode lead plate for electrical conduction was previously welded to the negative electrode current collector ring. After inserting the winding group 6 into the battery container, the bottom of the battery container and the negative electrode lead plate were welded.
[0020]
On the other hand, a positive electrode lead formed by laminating a plurality of aluminum ribbons in advance is welded to the positive electrode current collecting ring, and the other end of the positive electrode lead is attached to the lower surface of a battery lid for sealing a battery container. Welded. The battery lid is provided with a cleavage valve of an internal pressure release mechanism that is cleaved according to an increase in the internal pressure of the cylindrical lithium ion battery 20. The cleavage pressure of the cleavage valve is about 9 × 10 ⁵ Pa was set. The battery lid is composed of a lid case, a valve retainer for maintaining airtightness, and a cleavage valve, and these are stacked and assembled by caulking the periphery of the lid case.
[0021]
3. Inject a predetermined amount of non-aqueous electrolyte into the battery container, and then cover the battery container with the battery cover so that the positive electrode lead is folded, and then crimp and seal it via an EPDM resin gasket to design capacity. A 0 Ah cylindrical lithium ion battery 20 was completed.
[0022]
The non-aqueous electrolyte contains lithium hexafluorophosphate (LiPF) in a mixed solution of ethylene carbonate, dimethyl carbonate and diethyl carbonate at a volume ratio of 1: 1: 1. ₆ ) Was dissolved at 1 mol / l.
[0023]
According to this embodiment, by using two types of primary particles having different average particle sizes for lithium manganate, it is possible to have both the effect of increasing the specific surface area and the effect of increasing the bonding force between particles. A battery can be realized. Since the primary particles are particles A having an average particle diameter of 0.5 to 1 μm and particles B having an average particle diameter of 2 to 3 μm, the specific surface area can be increased by the particles A, and the bonding force between the particles can be increased by the particles B. Can be increased. At this time, the ratio N _A / N _B Is 5 to 20, it is possible to increase the specific surface area by the particles A and increase the inter-particle binding force by the particles B in a well-balanced manner, so that a well-balanced battery with high output and long life can be obtained. As mentioned above, the ratio N _A / N _B Is less than 5, the output decreases, and conversely, the ratio N _A / N _B Exceeds 20, the capacity is reduced due to charge / discharge cycles. In addition, since the secondary particles obtained by aggregating the particles A and the particles B are used, the electrode can be easily manufactured as described above. Furthermore, since the average particle diameter of the secondary particles is set to 10 to 30 μm, scattering of the powder can be prevented and the slurry can be easily formed. As described above, when the average particle diameter of the secondary particles is less than 10 μm, the powder is scattered, and when it exceeds 30 μm, the output and the capacity are reduced. In addition, by making the shape of the secondary particles spherical, the porosity between the active materials is increased, and the contact between the active materials and the conductive material that has entered between the active materials is efficiently performed, so that an even higher output is excellent. Battery can be obtained.
[0024]
【Example】
Next, an example of the cylindrical lithium-ion battery 20 manufactured according to the present embodiment will be described. Note that a battery of a comparative example manufactured for comparison is also described.
[0025]
(Example 1)
As shown in Table 1 below, in Example 1, the ratio N _A / N _B Was set to 5, the average particle diameter of the secondary particles was set to 15 μm, and a battery was produced using lithium manganate whose secondary particles had a spherical shape.
[0026]
[Table 1]

[0027]
(Examples 2 and 3)
As shown in Table 1, in Examples 2 and 3, the ratio N _A / N _B Was set to 10 in Example 2 and 20 in Example 3, and a battery was produced in the same manner as in Example 1 except that the average particle diameter of the secondary particles was set to 15 μm in both Examples 2 and 3.
[0028]
(Examples 4 and 5)
As shown in Table 1, in Examples 4 and 5, the ratio N _A / N _B Was set to 10 in both Examples 4 and 5, and a battery was produced in the same manner as in Example 1 except that the average particle diameter of the secondary particles was 10 μm in Example 4 and 30 μm in Example 5.
[0029]
(Example 6)
As shown in Table 1, in Example 6, the ratio N _A / N _B Was set to 5, the average particle diameter of the secondary particles was set to 15 μm, and a battery was produced using lithium manganate in which the shape of the secondary particles was massive.
[0030]
(Examples 7 and 8)
As shown in Table 1, in Examples 7 and 8, the ratio N _A / N _B Was set to 10 in Example 7 and 20 in Example 8, and a battery was prepared in the same manner as in Example 6, except that the average particle diameter of the secondary particles was 15 μm in both Examples 7 and 8.
[0031]
(Examples 9 to 10)
As shown in Table 1, in Examples 9 and 10, the ratio N _A / N _B Was set to 10 in Examples 9 and 10, and the battery was prepared in the same manner as in Example 6, except that the average particle diameter of the secondary particles was 10 μm in Example 9 and 30 μm in Example 10.
[0032]
(Comparative Example 1)
As shown in Table 1, in Comparative Example 1, the ratio N _A / N _B Was set to 50, the average particle diameter of the secondary particles was set to 15 μm, and a lithium secondary battery was used in the same manner as in Example 1 except that lithium manganate was used.
[0033]
(Comparative Example 2)
As shown in Table 1, in Comparative Example 2, the primary particles were only particles A, the average particle diameter of the secondary particles was 15 μm, and the shape of the secondary particles was agglomerated lithium manganate. A battery was produced in the same manner as in the above.
[0034]
(Comparative Example 3)
As shown in Table 1, in Comparative Example 3, the primary particles were only particles B, the average particle diameter of the secondary particles was 15 μm, and the shape of the secondary particles was agglomerated lithium manganate. A battery was produced in the same manner as in the above.
[0035]
(Comparative Example 4 to Comparative Example 5)
As shown in Table 1, in Comparative Examples 4 and 5, the ratio N _A / N _B In each of Examples 4 and 5, the average particle diameter of the secondary particles was set to 8 μm in Example 4, and 35 μm in Example 5, except that lithium manganate in which the shape of the secondary particles was massive was used. Produced a battery in the same manner as in Example 1.
[0036]
A charge / discharge test was performed on each (a plurality of) batteries of the example and the comparative example produced as described above, and the output and the capacity retention rate at the initial stage and after the pulse cycle test were measured.
[0037]
The output was measured at a current of 10 A, 30 A, and 90 A for 10 seconds each from a fully charged state of 4.1 V in an atmosphere of 25 ± 2 ° C., and the battery voltage at each 5 seconds relative to the horizontal axis current Is plotted on the vertical axis, and the current value at the point where a straight line obtained by linearly approximating the three points intersects the final voltage of 2.7 V was read, and the product of this current value and 2.7 V was taken as the output of the battery.
[0038]
In a 50 ± 3 ° C. atmosphere, a high load current of about 50 A is applied to each battery for about 5 seconds in both the charging direction and the discharging direction, and a pulse cycle test of about 30 seconds per cycle including a pause time is continuously performed for 10 seconds. After repeating 10,000 times, the output was measured by the method described above.
[0039]
The discharge capacity was measured by discharging after charging in an atmosphere of 25 ± 2 ° C., and measuring the initial discharge capacity. The charging conditions were a constant voltage of 4.1 V, a limiting current of 5 A, and 3.5 hours, and the discharging conditions were a constant current of 1 A and a final voltage of 2.7 V. The discharge capacity after the above-described pulse cycle test was measured, and the maintenance rate with respect to the initial discharge capacity was shown as a percentage. The results of a series of tests are shown in Table 2 below.
[0040]
[Table 2]

[0041]
As shown in Table 2, the ratio N _A / N _B 5 to 20, the average particle diameter of the secondary particles was 15 μm, and the secondary particles had a spherical shape. In the batteries of Examples 1 to 3, the output was initially 850 W or more, and the output was 680 W even after the pulse cycle test. As described above, the capacity retention ratio was 90% or more, and the battery was excellent in high output and long life. On the other hand, the ratio N _A / N _B Exceeds 20 and the battery of Comparative Example 1 in which the shape of the secondary particles is agglomerated and the battery of Comparative Example 2 using only the particles A have an initial output of as high as 900 W or more. The output was 550 W or less and the capacity retention was 80% or less, and sufficient performance could not be secured. Conversely, the ratio N _A / N _B In the battery of Comparative Example 3 having a value of less than 5, the capacity retention rate was excellent at 90%, but the outputs at the initial stage and after the pulse cycle test were 630 W and 550 W, respectively, and a sufficient output could not be obtained. .
[0042]
Also, the ratio N _A / N _B And the average particle diameter of the secondary particles was 10 μm and 30 μm, and the batteries of Examples 4 and 5 having a spherical shape had an initial output of 860 W or more and an output after the pulse cycle test of 680 W or more. Also, the capacity retention ratio was 92% or more, and the battery was excellent in high output and long life. However, in the batteries of Comparative Examples 4 and 5 in which the average particle diameter of the secondary particles was 8 μm and 35 μm, the initial output was 730 W or less, the output after the pulse cycle test was 550 W or less, and the capacity retention rate was further reduced. Was also inferior to 85% or less.
[0043]
Furthermore, the ratio N _A / N _B In the batteries of Examples 6 to 10 in which the average particle diameter of the secondary particles was the same as in Examples 1 to 5 and the shape was massive, the output decreased by about 10% both in the initial stage and after the pulse cycle test. However, even after the pulse cycle test, the battery was 650 W or more, the capacity retention was 90% or more, and a battery with high output and excellent long life could be obtained.
[0044]
From the above test results, the ratio N _A / N _B And the batteries of Examples 1 to 10 using lithium manganate having a mean particle diameter of secondary particles of 10 to 30 μm as the positive electrode active material have significantly improved output characteristics and life characteristics. It turns out. Further, by using lithium manganate whose secondary particles have a spherical shape as the positive electrode active material, it was possible to obtain a higher output battery while maintaining the life characteristics.
[0045]
As described above, the cylindrical lithium ion battery 20 of the present embodiment uses primary particles of lithium manganate, particles A having an average particle diameter of 0.5 to 1 μm and particles B having an average particle diameter of 2 to 3 μm. Since both the effect of increasing the specific surface area and the effect of increasing the bonding force between particles are achieved, high output and long life can be realized. Also, the ratio N _A / N _B Was set to 5 to 20, and the increase in the specific surface area by the particles A and the increase in the inter-particle binding force by the particles B were performed in a well-balanced manner. Thus, a battery with higher output and a well-balanced capacity retention ratio could be obtained. Ratio N _A / N _B Is less than 5, the binding force between particles increases and a battery with a high capacity retention rate can be obtained, but the output decreases because the specific surface area decreases. _A / N _B Exceeds 20, the battery can have a high specific surface area and a high output. However, the interparticle bonding force decreases, and manganese elutes from lithium manganate. Further, since the secondary particles obtained by aggregating the particles A and the particles B are used, it is possible to prevent the powder from being scattered during the preparation of the positive electrode, to facilitate the slurrying for applying to the current collector, Workability could be improved. Furthermore, since the average particle diameter of the secondary particles was set to 10 to 30 μm, it became easier to prevent the powder from scattering and to make the powder into a slurry. When the average particle diameter of the secondary particles is less than 10 μm, powder scattering occurs. When the average particle diameter exceeds 30 μm, the electrolytic solution does not uniformly infiltrate into the secondary particles and hinders charging / discharging. . The role of the conductive material in the positive electrode is to secure a conductive path between the active material and the current collector and increase the electrode reaction area. By changing the shape of the secondary particles from a lump to a sphere, the contact area between the active materials is reduced, the contact area between the active material and the conductive material is increased, and the conductive path between the active material and the current collector is increased. As a result, the electrode reaction area increases, so that a higher output can be achieved.
[0046]
In the present embodiment, a cylindrical battery has been exemplified, but the present invention is not limited to the shape of the battery, and is applicable to a square battery and other polygon batteries. The structure to which the present invention can be applied may be a battery other than the above-described battery container in which the battery lid is sealed by caulking. An example of such a structure is a battery in which the positive and negative external terminals penetrate the battery lid and the positive and negative external terminals are pressed against each other via the shaft core in the battery container. Further, the present invention is also applicable to a lithium secondary battery having a stacked structure without using a positive electrode and a negative electrode in a wound structure.
[0047]
In addition, the positive electrode active material for a lithium secondary battery that can be used in other than this embodiment is a material capable of inserting and removing lithium ions, and a lithium manganese double oxide in which a sufficient amount of lithium ions have been inserted in advance. Lithium manganate having a spinel structure (LiMn ₂ O ₄ ), And lithium manganate (LiMnO) having a layered rock salt type structure ₂ ), A part of lithium or manganese in the crystal is replaced with an element other than them, for example, an element such as Fe, Co, Ni, Cr, Al, Mg or the like, or a part of oxygen in the crystal is S, A material substituted or doped with P or the like may be used. Further, in the present embodiment, an example in which two kinds of primary particles having different average particle diameters are used for the lithium manganate of the positive electrode active material has been described, but one or more primary particles having different average particle diameters from these primary particles are shown. Particles may be used additionally.
[0048]
Furthermore, in the present embodiment, an example was shown in which amorphous carbon having excellent adhesion to the negative electrode current collector was used as the negative electrode active material as compared with the case where a crystalline carbon material was used. Alternatively, carbon materials such as artificial graphite materials and coke may be used, and the particle shape is not particularly limited, such as flakes, spheres, fibers, and lump. When such a carbon material is used for the negative electrode active material, it is excellent in flexibility when the electrode group is formed by spirally winding the cross section, and peeling and separation of the negative electrode active material layer from the negative electrode can be prevented.
[0049]
Further, the present invention is not limited to the conductive material and the binder (binder) exemplified in the present embodiment, and any commonly used materials can be used. Examples of the electrode active material binder for a lithium secondary battery that can be used in other than this embodiment include polytetrafluoroethylene (PTFE), polyethylene, polystyrene, polybutadiene, butyl rubber, nitrile rubber, styrene / butadiene rubber, and polysulfide. Examples include rubber, nitrocellulose, cyanoethylcellulose, various latexes, polymers such as acrylonitrile, vinyl fluoride, vinylidene fluoride, propylene fluoride, and chloroprene fluoride, and mixtures thereof.
[0050]
Furthermore, in this embodiment, LiPF is added to a mixed solvent obtained by mixing ethylene carbonate, dimethyl carbonate, and diethyl carbonate at a volume ratio of 1: 1: 1. ₆ Although a non-aqueous electrolyte in which is dissolved is exemplified, a general lithium salt may be used as the electrolyte, and a non-aqueous electrolyte in which this is dissolved in an organic solvent may be used. There is no particular limitation. For example, as the electrolyte, LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiB (C ₆ H ₅ ) ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li or a mixture thereof can be used. Examples of the organic solvent include propylene carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 1,3-dioxolan, 4-methyl-1,3-dioxolan, diethyl ether, Sulfolane, methylsulfolane, acetonitrile, propionitrile, and the like, or a mixed solvent obtained by mixing two or more thereof can be used, and the mixing ratio is not limited. By using such a non-aqueous electrolyte, it is possible to improve the battery capacity and adapt the battery to use in cold regions.
[0051]
【The invention's effect】
As described above, according to the present invention, by mixing and assembling a plurality of types of primary particles having different average particle diameters as lithium manganese composite oxides to form secondary particles, the ratio of lithium manganese composite oxides is increased. In order to increase the surface area, it is possible to increase the electrode reaction area to reduce the internal resistance of the battery, and to increase the inter-particle bonding force to suppress the elution of manganese. A long-life lithium secondary battery with reduced deterioration of input / output characteristics due to cycling can be realized, and powder can be prevented from scattering at the time of manufacturing the positive electrode, making it easy to apply a slurry to the current collector. Therefore, it is possible to obtain an effect that the workability of manufacturing the positive electrode can be improved.
[Brief description of the drawings]
FIG. 1 is an electron micrograph of lithium manganate used in a cylindrical lithium ion battery to which the present invention can be applied, in which the shape of secondary particles is massive.
FIG. 2 is an electron micrograph of lithium manganate having a spherical secondary particle shape used in a cylindrical lithium ion battery to which the present invention can be applied.
FIG. 3 is a cross-sectional view of a cylindrical lithium ion battery according to an embodiment to which the present invention can be applied.
[Explanation of symbols]
6 Winding group (electrode group)
20 Cylindrical lithium-ion battery (lithium secondary battery)

Claims (5)

A lithium secondary battery in which an electrode group having a positive electrode and a negative electrode using a lithium manganese composite oxide as a positive electrode active material is infiltrated into an electrolytic solution, wherein the lithium manganese composite oxide has a plurality of types different in average particle diameter. A primary particle, wherein the primary particles are aggregated to form secondary particles. 2. The lithium secondary battery according to claim 1, wherein the primary particles include particles A having an average particle diameter of 0.5 μm to 1 μm and particles B having an average particle diameter of 2 μm to 3 μm. 3. The lithium secondary battery according to claim 2, wherein the ratio N _{A /} N _B quantity of the particles A to the quantity of said particles B is 5 to 20. The lithium secondary battery according to claim 1, wherein the secondary particles have an average particle diameter of 10m to 30m. The lithium secondary battery according to any one of claims 1 to 4, wherein the secondary particles have a spherical shape.

Images