JP2004006247A - Lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve life property of a lithium secondary battery using lithium manganese double oxide as a positive electrode active material. <P>SOLUTION: A raw material of electrolyzed manganese dioxide containing sulphur content S of 2 % or less, and iron content F of 80 ppm or less is sorted out, and lithium manganate having a spinel type crystal structure is fabricated, and by using this lithium manganate as the positive electrode active material, a battery is fabricated fulfilling that the sulphur content S (%), the iron content F (ppm), and the thickness T of a separator (μm) have a relationship of 20 (μm/%) ≤ T (μm)/S (%) ≤ 40 (μm/%) and 0.5 (μm/ppm) ≤ T (μm)/F (ppm). A minute short-circuit by dendrite precipitation due to Fe ion is prevented. <P>COPYRIGHT: (C)2004,JPO

Description

【００１２】
また、鉄の含有量をＦ（ｐｐｍ）、セパレータの厚さをＴ（μｍ）としたときに、式（２）を満たすようにすることで、微少短絡を更に減少させることができる。また、リチウムマンガン複酸化物に、層状結晶構造を有するマンガン酸リチウムを用いるようにしてもよい。
【００１３】
【数４】

【００１４】
【発明の実施の形態】
以下、本発明を１８６５０型リチウムイオン二次電池に適用した実施の形態について説明する。
【００１５】
（正極）
正極活物質にリチウムマンガン複酸化物としてのスピネル型結晶構造を有するマンガン酸リチウム（ＬｉＭｎ_２Ｏ_４）を使用した。このマンガン酸リチウムは、電解二酸化マンガンと、例えば、炭酸リチウム等のリチウム塩と、を混合して焼成することにより合成したものである。このとき、マンガンに対するリチウムの比（以下、Ｌｉ／Ｍｎ比という。）を、電解二酸化マンガンとリチウム塩との比率を調整して、焼成後０．５５≦Ｌｉ／Ｍｎ≦０．６０の範囲に入るようにした。Ｌｉ／Ｍｎ比は合成後、分析により確認することができる。また、電解二酸化マンガンに含まれる硫黄量と鉄量とを予め検査してＬｉＭｎ_２Ｏ_４に含まれる硫黄の含有量（以下、硫黄含有量Ｓ、という。）が２％以下、かつ、鉄の含有量（以下、鉄の含有量Ｆ、という。）が８０ｐｐｍ以下となるように、電解二酸化マンガンを選別して使用した。
【００１６】
次に、合成したＬｉＭｎ_２Ｏ_４粉末８６ｗｔ％と、導電剤として炭素粉末９ｗｔ％と、ポリフッ化ビニリデン（ＰＶＤＦ、バインダ）をＮ−メチル−２−ピロリドン（以下、ＮＭＰと略称する。）で溶解した液を固形分濃度で５ｗｔ％として、これらを混練してスラリを得る。このとき使用されるＬｉＭｎ_２Ｏ_４は、原料である電解二酸化マンガンを選別してＬｉＭｎ_２Ｏ_４に含まれる硫黄含有量Ｓが所定％（２％以下）、かつ、鉄の含有量Ｆが所定％（８０ｐｐｍ以下）であることを確認して使用した。得られた合剤溶液を、コンマロールを用いてアルミニウム箔に塗布、乾燥させ活物質層とした。この活物質層を、８０°Ｃ〜１２０°Ｃに加熱したロールを有するロールプレス機にて、プレス圧（線圧）０．２〜０．７ｋｇ／ｃｍで、合剤かさ密度が２．８ｇ／ｍ^３となるまで圧縮して、５０ｍｍ×４５０ｍｍの帯状に裁断して正極とした。
【００１７】
（負極）
負極にリチウムイオンを挿入、脱挿入可能な炭素粉末を用い、炭素粉末９０ｗｔ％とＰＶＤＦ１０ｗｔ％との混合物に、ＮＭＰを加え、混練してスラリを得た。このスラリを負極集電体となる銅箔に塗布、乾燥させた。この活物質層を、８０°Ｃ〜１２０°Ｃに加熱したロールを有するロールプレス機にて、プレス圧０．２〜０．７ｋｇ／ｃｍで、かさ密度が１．０４ｇ／ｍ^３となるまで圧縮して、プレスの工程後、５０ｍｍ×４８０ｍｍの帯状に裁断して負極とした。
【００１８】
（電池の作製）
得られた帯状の正極と負極とを、下記条件を満たす帯状のポリエチレン製セパレータを介して重ねて、捲回し捲回電極体を作製した。
【００１９】
セパレータの厚さをＴ（μｍ）としたときに、マンガン酸リチウム中の硫黄含有量Ｓ（％）に対するセパレータの厚さＴ（μｍ）の比Ｔ／Ｓ（μｍ／％）が式（１）を満たすようにした。
【００２０】
【数５】

【００２１】
又は、マンガン酸リチウム中の鉄の含有量Ｆ（ｐｐｍ）に対するセパレータの厚さＴ（μｍ）の比Ｔ／Ｆ（μｍ／ｐｐｍ）が式（２）を満たすようにした。
【００２２】
【数６】

【００２３】
次に、捲回電極体を円筒状の電池缶に入れ、エチレンカーボネート（ＥＣ）とジメチルカーボネート（ＤＭＣ）とを体積比で１：１に混合した溶液に６フッ化リン酸リチウム（ＬｉＰＦ_６）を１モル／リットルの濃度で溶解した非水電解液を５ｍ注入後、上蓋を取り付け、封口して１８６５０型リチウムイオン二次電池を得た。
【００２４】
なお、本実施形態では、スピネル構造を有するマンガン酸リチウムをリチウムマンガン複酸化物として使用した例を示したが、本発明による効果はリチウムマンガン複酸化物の結晶構造を、層状岩塩型構造を含む層状構造を有するように変えても同様な効果が得られる。また、マンガン酸リチウムのほかにＬｉ、Ｖ、Ｃｒ、Ｆｅ、Ｃｏ、Ｎｉ、Ｍｏ、Ｗ、Ｚｎ、Ｂ、Ｍｇから選ばれる少なくとも一種類以上の金属でマンガンサイト又はリチウムサイトを置換したリチウムマンガン複合酸化物を用いるようにしてもよい。また、本実施形態では、プレス工程で加熱処理を行う処理方法についてロールを用いて加熱する例を示したが、活物質のバインダを溶融固化することができれば他の方法により加熱するようにしてもよい。
【００２５】
更に、本実施形態では、電解液にＥＣとＤＭＣとを混合した溶液にＬｉＰＦ_６で溶解したものを例示したが、他に、電解液の有機溶媒としては、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、ジエタルカーボネート、γ−ブチルラクトン、テトラヒドロフラン、ジエチルエーテル、スルホラン、アセトニトリル等の単独もしくはこれらのうち二種類以上の混合溶媒を使用することができ、電解質も、ＬｉＣｌＯ_４、ＬｉＢＦ_４、ＬｉＣｌ、ＬｉＢｒ、ＣＨ_３ＳＯ_３Ｌｉ、ＬｉＡｓＦ_６等を使用することができる。
【００２６】
また、炭素材料としては、ピッチコークス、石油コークス、黒鉛、炭素繊維、活性炭等や又はこれらの混合物を使用してもよい。更に、バインダとしては、他にイソブチルアクリルレート、オクチルアクリレート、ノニルアクリレート、ブチルメタクリレート及び２−エチルヘキシルメタクリレート等のアクリル酸及び／又はメタクリル酸のＣ４〜Ｃ１２アルキルエステルとメタクリル酸、イタコン酸、マレイン酸、フマル酸やアクリルアミド及びメタクリルアミド等のポリアクリル酸等のカルホギシル基又はアミド基の官能基を有する不飽和単量体との共重合体やポリアミドやポリアミドイミドやポリアミドビスマレイミドやポリブチレンテレフタレート、ポリエチレンテレフタレート等のポリエステルなどを挙げることができ、これら単独のほか併用して使用することができる。
【００２７】
【実施例】
以下、上記実施形態に従って、ＬｉＭｎ_２Ｏ_４のＬｉ／Ｍｎ比を０．５５とし、硫黄含有量Ｓ及び鉄の含有量Ｆを変更して作製した実施例の電池について説明する。なお、比較のために作製した比較例の電池についても併記する。
【００２８】
（実施例１）
下表１に示すように、実施例１では、セパレータの厚さＴ（μｍ）を４０μｍとし、ＬｉＭｎ_２Ｏ_４中に含まれる硫黄含有量Ｓを原料の電解二酸化マンガンを選別して１％とし、セパレータの厚さＴ／硫黄含有量Ｓが４０（μｍ／％）の電池を作製した。
【００２９】
【表１】

【００３０】
（実施例２）
表１に示すように、実施例２では、ＬｉＭｎ_２Ｏ_４中に含まれる硫黄含有量Ｓを原料の電解二酸化マンガンを選別して２％とし、セパレータの厚さＴ／硫黄含有量Ｓを２０（μｍ／％）とした以外は実施例１と同様に電池を作製した。
【００３１】
（実施例３）
表１に示すように、実施例３では、ＬｉＭｎ_２Ｏ_４中に含まれる鉄の含有量Ｆを原料の電解二酸化マンガンを選別して２０ｐｐｍとし、セパレータの厚さＴ／鉄の含有量Ｆが２（μｍ／ｐｐｍ）の電池を作製した。
【００３２】
（実施例４）
表１に示すように、実施例４では、ＬｉＭｎ_２Ｏ_４中に含まれる鉄の含有量Ｆを原料の電解二酸化マンガンを選別して８０ｐｐｍとし、セパレータの厚さＴ／鉄の含有量Ｆが０．５（μｍ／ｐｐｍ）の電池を作製した。
【００３３】
（比較例１）
表１に示すように、比較例１では、ＬｉＭｎ_２Ｏ_４中に含まれる硫黄含有量Ｓを原料の電解二酸化マンガンを選別して３％とし、セパレータの厚さＴ／硫黄含有量Ｓを１３．３（μｍ／％）とした以外は実施例１と同様に電池を作製した。
【００３４】
（比較例２）
表１に示すように、比較例２では、セパレータの厚さＴ（μｍ）を３０μｍとし、ＬｉＭｎ_２Ｏ_４中に含まれる硫黄含有量Ｓを原料の電解二酸化マンガンを選別して２％とし、セパレータの厚さＴ／硫黄含有量Ｓを１５（μｍ／％）とした以外は実施例１と同様に電池を作製した。
【００３５】
（比較例３）
表１に示すように、比較例３では、ＬｉＭｎ_２Ｏ_４中に含まれる鉄の含有量Ｆを原料の電解二酸化マンガンを選別して１００ｐｐｍとし、セパレータの厚さＴ／鉄の含有量Ｆが０．５（μｍ／ｐｐｍ）の電池を作製した。
【００３６】
（試験）
次に、以上のように作製した実施例及び比較例の各電池について、高温（５０°Ｃ）雰囲気下で充放電サイクル試験を実施した。充放電サイクル試験の内容は以下の通りである。
１）充電条件：定電圧充電４．２Ｖ、制限電流１０００ｍＡ、３ｈ、５０°Ｃ２）放電条件：定電流放電１０００ｍＡ、２４分、５０°Ｃ
３）休止条件：充電、放電の間に、休止時間を１０分間設けた。
４）放電容量の確認：２５サイクル毎に５０°Ｃの雰囲気で充電は電流１０００ｍＡ、４．２Ｖの定電圧で３時間とし、放電は電流１０００ｍＡ、放電終止電圧２．７Ｖとして放電容量を確認した。
５）容量維持率の算出：２００サイクル目の放電容量（以下、２００サイクル目容量という。）を測定し、初期の放電容量に対する２００サイクル目容量を容量維持率として算出した。
【００３７】
充放電サイクル試験の試験結果を下表２に示す。
【００３８】
【表２】

【００３９】
表２から明らかなように、Ｌｉ／Ｍｎ比が０．５５のスピネル型結晶構造のＬｉＭｎ_２Ｏ_４を使用し、硫黄含有量Ｓに対するセパレータの厚さＴの比Ｔ／Ｓが式１の範囲内にある実施例１及び実施例２の電池では、容量維持率に大きな変化はないが、２０（μｍ／％）を下回る比較例１及び比較例２の電池では、２００サイクル目容量維持率が低下することが判明した。
【００４０】
この原因は、ＬｉＭｎ_２Ｏ_４の原料である電解二酸化マンガンに残存している硫酸イオンＳＯ_４ ⁻がＬｉＭｎ_２Ｏ_４に残留することにより充放電又は放置（休止）中に溶解し、これが電解液中のわずかな水分を酸性にし電極を劣化させることにあると推測される。
【００４１】
また、鉄の含有量Ｆの充放電サイクル試験の試験結果から明らかなように、セパレータの厚さＴに対する鉄の含有量Ｆの比が式（２）の０．５（μｍ／ｐｐｍ）以上の範囲にある実施例３及び実施例４の電池では、鉄の影響はほとんどなく、０．５（μｍ／ｐｐｍ）を下回る比較例３の電池では、容量維持率、すなわち、寿命特性に影響してくるものと考えられる。
【００４２】
鉄の含有量Ｆが多くなるとＬｉＭｎ_２Ｏ_４中にも多くのＦｅ分が残留し、初期の充放電やサイクル中にＦｅイオンが溶解析出を繰り返し、デンドライトとなって析出し電池内部で微小短絡を起こし容量減少を起こしているものと考えられる。これより、セパレータの厚さＴに対する鉄の含有量Ｆの比が０．５（μｍ／ｐｐｍ）を下回ると寿命特性に影響すると考えられる。
【００４３】
【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中の硫黄含有量を２％以下、かつ、金属含有量を８０ｐｐｍ以下としたので、硫黄や金属成分がリチウムマンガン複酸化物中に含まれていても、電極劣化を助長することなく、寿命特性に優れたリチウム二次電池を実現することができる、という効果を得ることができる。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a lithium secondary battery, in particular, a positive electrode using a lithium manganese double oxide capable of inserting and extracting lithium by discharging and charging a positive electrode active material, and a negative electrode using a carbon material as a negative electrode active material The present invention relates to a lithium secondary battery infiltrated with an electrolyte through a separator.
[0002]
[Prior art]
Lithium-ion secondary batteries, which are representative of lithium secondary batteries, have been used for power sources of portable devices such as VTR cameras, notebook computers, mobile phones, and automobiles, taking advantage of their high energy density. The internal structure of such a lithium ion secondary battery is usually a wound structure as shown below. Each of the electrodes has a band shape in which the active material is coated on 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 come into direct contact with each other with a separator interposed therebetween, and a wound group is formed. . The wound group is housed in a cylindrical battery can serving as a battery container, and is sealed after the electrolyte is injected.
[0003]
The outer diameter of a general cylindrical lithium ion secondary battery is 18650 type, which has a diameter of 18 mm and a height of 65 mm, and is widely used as a small consumer lithium ion secondary battery. In recent years, studies on lithium ion secondary batteries using a lithium-manganese oxide or other composite oxide containing manganese rich and inexpensive as a positive electrode active material have been actively conducted. Technology for secondary batteries has also been developed.
[0004]
However, in lithium manganate, the crystal expands and contracts as lithium ions are inserted and desorbed by charging and discharging, and when charging and discharging with expansion and contraction are repeated, the electron conductivity as a positive electrode decreases and the discharge capacity decreases. Is reduced. In addition, the positive electrode using lithium manganate as the active material dissolves the manganese component in the electrolytic solution regardless of the discharged or charged state, and the dissolution of the manganese component decreases the charge / discharge cycle life characteristics and the storage characteristics. This is a major cause of the decrease in the number.
[0005]
In order to address these problems, technologies for producing highly crystalline lithium manganate by improving the conditions for synthesizing lithium manganate and additives, and technology for doping different elements in the crystal structure of lithium manganate have been developed. It is disclosed (for example, see Patent Documents 1 and 2).
[0006]
[Patent Document 1]
JP-A-10-182160 (paragraph numbers "0011" and "0021")
[Patent Document 2]
JP-A-10-182157 (paragraph numbers "0011" and "0020")
[0007]
[Problems to be solved by the invention]
However, at the present time, even with the techniques disclosed in these publications, sufficient charge / discharge cycle life characteristics have not been obtained. An object of the present invention is to improve the life characteristics of a lithium secondary battery using a lithium manganese double oxide as a positive electrode active material in view of the above proposal.
[0008]
[Means for Solving the Problems]
In order to solve the above problems, the present invention provides a positive electrode using a lithium manganese double oxide capable of inserting and extracting lithium by discharging and charging a positive electrode active material, and a negative electrode using a carbon material as a negative electrode active material. In a lithium secondary battery impregnated with an electrolyte through a separator, the lithium content of the lithium manganese double oxide is 2% or less and the metal content is 80 ppm or less.
[0009]
In the present invention, a lithium manganese double oxide capable of inserting and extracting lithium by discharging and charging the positive electrode active material, a carbon material is used for the negative electrode active material, and the positive and negative electrodes coated with these active materials are interposed through a separator. Is soaked in the electrolyte. Manganese dioxide is used as part of the material to make a lithium manganese double oxide, but sulphate and metals remain during manganese dioxide production, and manganese dioxide contains some sulfur and metal components As a result, as a result, the lithium manganese double oxide contains sulfur and metal components. When the lithium manganese double oxide containing a certain amount or more of sulfur and a metal component is infiltrated into the electrolytic solution, it affects the electrolytic solution and promotes deterioration of the electrode. Therefore, if the content of sulfur or metal in the lithium manganese double oxide is limited to a certain amount or less, deterioration of the electrode due to sulfur or metal component can be suppressed. According to the present invention, since the sulfur content in the lithium manganese composite oxide is 2% or less and the metal content is 80 ppm or less, even if sulfur or a metal component is contained in the lithium manganese composite oxide. In addition, a lithium secondary battery having excellent life characteristics can be realized without promoting electrode deterioration.
[0010]
In this case, if the ratio Li / Mn of lithium to manganese in the lithium-manganese composite oxide is set to be in the range of 0.55 ≦ Li / Mn ≦ 0.60, the lithium secondary having excellent initial capacity and capacity retention rate is obtained. It can be a battery. Further, if lithium manganate having a spinel-type crystal structure is used as the lithium-manganese double oxide, the spinel-type has high thermal stability, so that the safety of the lithium secondary battery can be improved. Furthermore, if iron is contained in the lithium manganese double oxide, Fe ions repeatedly dissolve and precipitate during the initial charge / discharge or charge / discharge cycle, precipitate as dendrites and cause a micro short circuit inside the battery, It is more preferable that the content of iron in the lithium manganese double oxide be 80 ppm or less. Further, when the sulfur content in the lithium manganese double oxide is S (%) and the thickness of the separator is T (μm), by satisfying the expression (1), micro short circuit is further reduced. be able to.
[0011]
[Equation 3]

[0012]
Further, when the content of iron is F (ppm) and the thickness of the separator is T (μm), by satisfying the expression (2), it is possible to further reduce the minute short circuit. Further, lithium manganate having a layered crystal structure may be used as the lithium manganese double oxide.
[0013]
(Equation 4)

[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment in which the present invention is applied to a 18650 type lithium ion secondary battery will be described.
[0015]
(Positive electrode)
As the positive electrode active material, lithium manganate (LiMn ₂ O ₄ ) having a spinel-type crystal structure as a lithium manganese double oxide was used. This lithium manganate is synthesized by mixing electrolytic manganese dioxide and a lithium salt such as lithium carbonate and baking the mixture. At this time, the ratio of lithium to manganese (hereinafter referred to as Li / Mn ratio) is adjusted to a range of 0.55 ≦ Li / Mn ≦ 0.60 after firing by adjusting the ratio of electrolytic manganese dioxide and lithium salt. I tried to enter. After synthesis, the Li / Mn ratio can be confirmed by analysis. In addition, the amount of sulfur and the amount of iron contained in the electrolytic manganese dioxide are inspected in advance, and the content of sulfur contained in LiMn ₂ O ₄ (hereinafter, referred to as sulfur content S) is 2% or less, and Electrolytic manganese dioxide was selected and used so that the content (hereinafter, referred to as iron content F) was 80 ppm or less.
[0016]
Next, 86 wt% of the synthesized LiMn ₂ O ₄ powder, 9 wt% of carbon powder as a conductive agent, and polyvinylidene fluoride (PVDF, binder) are dissolved in N-methyl-2-pyrrolidone (hereinafter abbreviated as NMP). The obtained liquid is adjusted to a solid concentration of 5 wt%, and these are kneaded to obtain a slurry. The LiMn ₂ O ₄ used at this time is selected from electrolytic manganese dioxide as a raw material, and the sulfur content S contained in the LiMn ₂ O ₄ is a predetermined percentage (2% or less) and the iron content F is a predetermined percentage. % (80 ppm or less) before use. The obtained mixture solution was applied to an aluminum foil using a comma roll and dried to form an active material layer. The active material layer was pressed by a roll press having a roll heated to 80 ° C. to 120 ° C. at a pressing pressure (linear pressure) of 0.2 to 0.7 kg / cm and a mixture bulk density of 2.8 g. and compressed to a / ^{m 3,} and by cutting a strip of 50 mm × 450 mm and the positive electrode.
[0017]
(Negative electrode)
NMP was added to a mixture of 90% by weight of carbon powder and 10% by weight of PVDF, and a kneaded mixture was obtained by using carbon powder capable of inserting and removing lithium ions in the negative electrode. This slurry was applied to a copper foil serving as a negative electrode current collector and dried. This active material layer is rolled with a roll press having a roll heated to 80 ° C. to 120 ° C. under a pressing pressure of 0.2 to 0.7 kg / cm until the bulk density becomes 1.04 g / m ^3. After compressing and pressing, it was cut into a 50 mm x 480 mm strip to obtain a negative electrode.
[0018]
(Production of battery)
The obtained strip-shaped positive electrode and the obtained strip-shaped negative electrode were overlapped with each other via a strip-shaped polyethylene separator satisfying the following conditions, and wound to produce a wound electrode body.
[0019]
Assuming that the thickness of the separator is T (μm), the ratio T / S (μm /%) of the thickness T (μm) of the separator to the sulfur content S (%) in lithium manganate is represented by the formula (1). To meet.
[0020]
(Equation 5)

[0021]
Alternatively, the ratio T / F (μm / ppm) of the separator thickness T (μm) to the iron content F (ppm) in lithium manganate was set to satisfy the expression (2).
[0022]
(Equation 6)

[0023]
Next, the wound electrode body is placed in a cylindrical battery can, and a solution of ethylene carbonate (EC) and dimethyl carbonate (DMC) mixed at a volume ratio of 1: 1 is prepared by adding lithium hexafluorophosphate (LiPF ₆ ). Was dissolved at a concentration of 1 mol / liter, 5 m of the non-aqueous electrolyte was injected, the upper lid was attached, and the container was sealed to obtain a 18650 type lithium ion secondary battery.
[0024]
In the present embodiment, an example in which lithium manganate having a spinel structure is used as the lithium manganese double oxide has been described, but the effects of the present invention include the crystal structure of the lithium manganese double oxide, including the layered rock salt type structure. The same effect can be obtained even if the structure is changed to have a layered structure. Further, in addition to lithium manganate, a lithium manganese composite in which a manganese site or a lithium site is substituted with at least one or more metals selected from Li, V, Cr, Fe, Co, Ni, Mo, W, Zn, B, and Mg. An oxide may be used. Further, in the present embodiment, an example in which heating is performed using a roll for the processing method of performing the heat treatment in the pressing step has been described. However, if the binder of the active material can be melted and solidified, heating may be performed by another method. Good.
[0025]
Furthermore, in the present embodiment, an example in which LiPF ₆ is dissolved in a solution in which EC and DMC are mixed in an electrolytic solution is exemplified. However, propylene carbonate, 1,2-dimethoxyethane is also used as an organic solvent in the electrolytic solution. , 1,2-diethoxyethane, diethal carbonate, γ-butyl lactone, tetrahydrofuran, diethyl ether, sulfolane, acetonitrile, etc., or a mixed solvent of two or more of these can be used. ₄ , LiBF ₄ , LiCl, LiBr, CH ₃ SO ₃ Li, LiAsF _{6 and the} like can be used.
[0026]
As the carbon material, pitch coke, petroleum coke, graphite, carbon fiber, activated carbon, or a mixture thereof may be used. Further, as the binder, C4-C12 alkyl esters of acrylic acid and / or methacrylic acid such as isobutyl acrylate, octyl acrylate, nonyl acrylate, butyl methacrylate and 2-ethylhexyl methacrylate, and methacrylic acid, itaconic acid, maleic acid, Copolymers with unsaturated monomers having a functional group of carphogicyl group or amide group such as polyacrylic acid such as fumaric acid, acrylamide and methacrylamide, polyamide, polyamideimide, polyamidebismaleimide, polybutylene terephthalate, polyethylene terephthalate And the like, and these can be used alone or in combination.
[0027]
【Example】
Hereinafter, a description will be given of a battery of an example manufactured by changing the Li / Mn ratio of LiMn ₂ O ₄ to 0.55 and changing the sulfur content S and the iron content F according to the above embodiment. Note that a battery of a comparative example manufactured for comparison is also described.
[0028]
(Example 1)
As shown in Table 1 below, in Example 1, the thickness T (μm) of the separator was set to 40 μm, and the sulfur content S contained in LiMn ₂ O ₄ was set to 1% by selecting electrolytic manganese dioxide as a raw material. A battery having a separator thickness T / sulfur content S of 40 (μm /%) was produced.
[0029]
[Table 1]

[0030]
(Example 2)
As shown in Table 1, in Example 2, the sulfur content S contained in LiMn ₂ O ₄ was selected to be 2% by selecting the raw material electrolytic manganese dioxide, and the separator thickness T / sulfur content S was 20%. (Μm /%), and a battery was fabricated in the same manner as in Example 1.
[0031]
(Example 3)
As shown in Table 1, in Example 3, the content F of iron contained in LiMn ₂ O ₄ was set to 20 ppm by selecting electrolytic manganese dioxide as a raw material, and the thickness T of the separator / the content F of iron was 2 (μm / ppm) batteries were produced.
[0032]
(Example 4)
As shown in Table 1, in Example 4, the content F of iron contained in LiMn ₂ O ₄ was adjusted to 80 ppm by selecting electrolytic manganese dioxide as a raw material, and the thickness T of the separator / the content F of iron was A battery of 0.5 (μm / ppm) was produced.
[0033]
(Comparative Example 1)
As shown in Table 1, in Comparative Example 1, the sulfur content S contained in LiMn ₂ O ₄ was 3% by selecting electrolytic manganese dioxide as a raw material, and the separator thickness T / sulfur content S was 13%. A battery was fabricated in the same manner as in Example 1, except that the battery was changed to 0.3 (μm /%).
[0034]
(Comparative Example 2)
As shown in Table 1, in Comparative Example 2, the thickness T (μm) of the separator was 30 μm, the sulfur content S contained in LiMn ₂ O ₄ was 2% by selecting the raw material electrolytic manganese dioxide, A battery was fabricated in the same manner as in Example 1, except that the thickness T / sulfur content S of the separator was 15 (μm /%).
[0035]
(Comparative Example 3)
As shown in Table 1, in Comparative Example 3, the content F of iron contained in LiMn ₂ O ₄ was set to 100 ppm by selecting electrolytic manganese dioxide as a raw material, and the thickness T / iron content F of the separator was 100 ppm. A battery of 0.5 (μm / ppm) was produced.
[0036]
(test)
Next, a charge / discharge cycle test was performed in a high-temperature (50 ° C.) atmosphere for each of the batteries of Examples and Comparative Examples manufactured as described above. The contents of the charge / discharge cycle test are as follows.
1) Charge condition: constant voltage charge 4.2V, limited current 1000mA, 3h, 50 ° C 2) Discharge condition: constant current discharge 1000mA, 24 minutes, 50 ° C
3) Pause condition: A pause time of 10 minutes was provided between charging and discharging.
4) Confirmation of discharge capacity: charge was performed at a constant current of 1000 mA and 4.2 V for 3 hours in an atmosphere of 50 ° C. every 25 cycles, and discharge capacity was confirmed at a current of 1000 mA and a discharge end voltage of 2.7 V. .
5) Calculation of capacity retention ratio: The discharge capacity at the 200th cycle (hereinafter referred to as the 200th cycle capacity) was measured, and the capacity at the 200th cycle with respect to the initial discharge capacity was calculated as the capacity retention rate.
[0037]
The test results of the charge / discharge cycle test are shown in Table 2 below.
[0038]
[Table 2]

[0039]
As is clear from Table 2, LiMn ₂ O ₄ having a spinel crystal structure with a Li / Mn ratio of 0.55 was used, and the ratio T / S of the separator thickness T to the sulfur content S was in the range of the formula 1. In the batteries of Example 1 and Example 2 which are within the above, there is no significant change in the capacity retention ratio, but in the batteries of Comparative Example 1 and Comparative Example 2 below 20 (μm /%), the capacity retention ratio at the 200th cycle is lower. It was found to be lower.
[0040]
This cause, LiMn ₂ O ₄ of sulfate ions is a starting material remaining in the electrolytic manganese dioxide SO ₄ ^- are dissolved by remaining in LiMn ₂ O ₄ during charging and discharging or left (pause), which electrolyte It is presumed that the slight moisture in the inside is acidified to deteriorate the electrode.
[0041]
Further, as is clear from the test results of the charge / discharge cycle test of the iron content F, the ratio of the iron content F to the separator thickness T is 0.5 (μm / ppm) or more in the formula (2). In the batteries of Example 3 and Example 4 in the range, the influence of iron was almost negligible, and in the battery of Comparative Example 3 less than 0.5 (μm / ppm), the capacity retention rate, that is, the life characteristic was affected. It is thought to come.
[0042]
When the iron content F increases, a large amount of Fe remains in LiMn ₂ O ₄ , and Fe ions repeatedly dissolve and precipitate during the initial charge / discharge or cycle, and precipitate as a dendrite to cause a short circuit inside the battery. It is considered that the capacity was reduced and the capacity was reduced. From this, it is considered that when the ratio of the iron content F to the separator thickness T is less than 0.5 (μm / ppm), the life characteristics are affected.
[0043]
【The invention's effect】
As described above, according to the present invention, since the sulfur content in the lithium manganese composite oxide is 2% or less and the metal content is 80 ppm or less, the sulfur and the metal component are contained in the lithium manganese composite oxide. , It is possible to obtain an effect that a lithium secondary battery having excellent life characteristics can be realized without promoting electrode deterioration.

Claims (7)

A lithium secondary battery in which a positive electrode using a lithium manganese double oxide capable of occluding and releasing lithium by discharging and charging a positive electrode active material and a negative electrode using a carbon material as a negative electrode active material is infiltrated into an electrolyte through a separator. In a secondary battery, the lithium secondary battery has a sulfur content of 2% or less in the lithium manganese double oxide and a metal content of 80 ppm or less. 2. The lithium secondary battery according to claim 1, wherein a ratio Li / Mn of lithium to manganese in the lithium-manganese double oxide is in a range of 0.55 ≦ Li / Mn ≦ 0.60. 3. The lithium secondary battery according to claim 1, wherein the lithium-manganese double oxide is lithium manganate having a spinel-type crystal structure. 4. The lithium secondary battery according to claim 1, wherein the metal is iron. 5. The lithium secondary battery according to claim 4, wherein the following formula (1) is satisfied when the sulfur content is S (%) and the thickness of the separator is T (μm).

The lithium secondary battery according to claim 4, wherein the following formula (2) is satisfied when the content of the iron is F (ppm) and the thickness of the separator is T (μm).

The lithium secondary battery according to claim 1, wherein the lithium manganese double oxide is lithium manganate having a layered crystal structure.