JP2004259485A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery using metal or its oxide as a negative electrode activator of which the short circuit generated at charging and discharging is reduced. <P>SOLUTION: The square-shaped nonaqueous electrolyte secondary battery 1 uses metal or its oxide as a negative electrode activator, and houses an electricity generating element 2 wound in a cylindrical swirl shape having an elongated circle-shaped lateral cross section in a flat box-shaped battery case 6. A ratio of an inside length D1 of the battery case 6 to a corresponding short diameter D1 of the electricity generating element 2 is made 98% or more and 115% or less. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【００８３】
発電要素の短径Ｄ１に対する電池容器の内側の寸法Ｄ２の割合（Ｄ２／Ｄ１比率）が９８％以上、１１５％未満である実施例１〜５に対して、Ｄ２／Ｄ１比率が９５％である比較例１の電池は初期放電容量が小さくなり、また、３００サイクル目の放電容量保持率も実施例１〜５の電池に対して小さくなった。
【００８４】
これは、発電要素内で負極板の圧迫が不十分になって、充放電サイクルに伴う、負極板の膨張収縮による集電製の低下が進行し、負極板の分極が増大し充放電反応が阻害されたことや、充電状態のまま電子伝導性を失った活物質の容量ロスによるものと考えられる。
【００８５】
また、Ｄ２／Ｄ１比率が１２０％の比較例２の電池も、比較例１と同様に、初期放電容量が小さくなり、３００サイクル目の容量保持率も小さくなった。さらに比較例２の電池は内部短絡不良も５０セル中２セル発生した。
これは、充電時に膨張した負極板によって、発電要素のコーナーに過度の圧力がかかったために、その部分のセパレータの空孔が閉塞し充放電が出来なかったことや、セパレータの空孔が閉塞していない箇所に電流が集中し負極板表面に不可逆な金属リチウムが析出したことが原因であると考えられる。
【００８６】
また、充放電サイクル試験では、発電要素が充電時に過度に圧迫されることによって、その箇所のセパレータの細孔が閉塞してイオンの移動を妨げられて充放電が出来ない状態になったり、発電要素内に存在していた電解液が発電要素外に押し出されて、発電要素内の電解液が枯渇してしまったことが原因であると考えられる。なお、短絡不良が発生した電池を解体したところ、最も圧迫を受けている発電要素のコーナー部で短絡した痕が確認された。
【００８７】
以上のことから、満充電状態の発電要素の、発電要素の短径Ｄ１に対する電池容器の内側の寸法Ｄ２の割合（Ｄ２／Ｄ１比率）を９８％以上１１５％以下とすることによって金属酸化物を負極活物質として用いた角型電池の初期容量を増大し、充放電サイクル性能を向上し、かつ内部短絡を低減することができた。
【００８８】
＜円筒型電池＞
次に、表２に示す実施例６〜１０、比較例３および比較例４の円筒型電池の結果について検討する。
【００８９】
【表２】

【００９０】
円筒形電池についても角型電池と同様に、実施例６〜１０の電池は、満充電状態の発電要素の、Ｄ２／Ｄ１比率を９８％以上１１５％以下とすることによって金属酸化物を負極活物質として用いた角型電池の初期容量を増大し、充放電サイクル性能を向上し、かつ内部短絡を低減することができた。なお、内部短絡した箇所を確認したところ、角型電池が発電要素のコーナー部であったのに対して、円筒型電池は内周部であった。
【００９１】
＜角型：スピネル構造を有するマンガン酸リチウムを正極活物質に用いた場合＞
次に、正極活物質としてコバルト酸リチウムの代わりにスピネル構造を有するマンガン酸リチウムを用いた以外は実施例６〜１０、比較例３および比較例４と同様にして、実施例１１〜１５、比較例５および比較例６の電池を作製し、正極活物質にスピネル構造を有するマンガン酸リチウムを用いた角型電池の結果について検討した。結果を表３にまとめた。
【００９２】
【表３】

コバルト酸リチウムを正極活物質に用いた角型電池と同様に、実施例の１１〜１５の電池は、満充電状態の発電要素のＤ２／Ｄ１比率を９８％以上１１５％以下とすることによって金属酸化物を負極活物質として用いた角型電池の初期容量を増大し、充放電サイクル性能を向上した。
【００９３】
また、正極活物質にスピネル構造を有するマンガン酸リチウムを用いた比較例６の電池は、正極活物質にコバルト酸リチウムを用いた比較例４の電池とくらべて内部短絡不良が低減した。その理由は、スピネル構造を有するマンガン酸リチウムは脱リチウム時（＝充電時）に粒子の体積が減少する傾向にあるため、それを用いた正極は充電時には体積が減少する傾向にあるために、充電時の負極の体積膨張を相殺し、充電時にセパレータにかかる過度の圧力を抑制した為であると考えられる。
【００９４】
これらの結果から、内部短絡不良の低減のためには、充電時に体積膨張がない、もしくは低減する正極活物質を用いることが効果的であることがわかった。なお、今回はＬｉＭｎ_２Ｏ_４を正極活物質に用いたが、状況に応じて、コバルト酸リチウムと混合したり、またＬｉＮｉ_１−ｘＭｎ_ｘＯ_２のようなスピネル構造を有する正極活物質も適宜選択することができる。
【００９５】
（実施例１６〜１９）
負極活物質に用いる金属または金属酸化物の種類を変更した以外は実施例２と同様にして、Ｄ２／Ｄ１＝１００％である、実施例１６〜１９の角型電池を作製した。そして、各電池について、２５℃における初期放電容量と３００サイクル後の容量維持率を求めた。
作製した電池を、７００ｍＡ定電流で４．２Ｖまで充電し、さらに４．２Ｖ定電圧で、合計５時間充電した後に、７００ｍＡの定電流で２．７５Ｖまで放電し、初期放電容量を確認した。そして、初期容量確認試験後の電池を、７００ｍＡ定電流で４．２Ｖまで充電し、さらに４．２Ｖ定電圧で、合計５時間充電した後に、７００ｍＡの定電流で２．７５Ｖまでの放電を１サイクルとして、３００サイクル充放電をおこない、初期容量確認試験時の放電容量と３００サイクル目の放電容量の比較をおこない、初期放電容量に対する３００サイクル目の放電容量の比率を容量維持率（％）とした。
【００９６】
作製した電池の負極活物質と、試験結果を表４に示した。なお、表４における初期放電容量および容量維持率は、各電池とも１０セルの平均値を示した。また、表４には、比較のため、実施例２のデータも示した。
【００９７】
【表４】

【００９８】
表４から、負極活物質として各種金属またはその酸化物を使用した場合、初期放電容量および容量維持率はほぼ同じような優れた値を示すことがわかった。
【００９９】
（実施例２０〜２４）
負極活物質にＳｉＯとグラファイトとの複合粒子を使用し、ＳｉＯとグラファイトの混合比を変更した以外は実施例２と同様にして、Ｄ２／Ｄ１＝１００％である、実施例２０〜２４の角型電池を作製した。そして、各電池について、実施例１６と同様の条件で、２５℃における初期放電容量と３００サイクル後の容量維持率を求めた。
作製した電池のＳｉＯとグラファイトの混合比と、試験結果を表５に示した。なお、表５における初期放電容量および容量維持率は、各電池とも１０セルの平均値を示した。
【０１００】
【表５】

【０１０１】
表５から、複合粒子中のグラファイトの含有量が５重量部より少ない実施例２０の場合には、負極での導電経路の維持が困難となるため、容量維持率がやや小さくなり、また、グラファイトの含有量が８０重量部を超えると、負極の充放電容量が小さくなるため、初期放電容量がやや小さくなった。
【０１０２】
（実施例２５〜２９）
負極活物質として、ＳｉＯ９０重量部とグラファイト１０重量部の複合粒子の表面を炭素で被覆し、ＳｉＯとグラファイトの合計重量に対する被覆炭素の重量比を変えた以外は、実施例２と同様にして、Ｄ２／Ｄ１＝１００％である、実施例２５〜２９の角型電池を作製した。
【０１０３】
そして、各電池について、実施例１６と同様の条件で、２５℃における初期放電容量と３００サイクル後の容量維持率を求めた。
作製した電池のＳｉＯとグラファイトの合計重量に対する被覆炭素の重量比と、試験結果を表６に示した。なお、表６における初期放電容量および容量維持率は、各電池とも１０セルの平均値を示した。
【０１０４】
【表６】

【０１０５】
表６から、ＳｉＯとグラファイトからなる複合粒子の表面を炭素で被覆することにより、容量維持率は向上するが、炭素被覆量が０．５重量部よりも小さい場合には、その効果はほとんどなく、また、炭素被覆量が２０重量部よりも大きくなると、被覆炭素上で電解液の還元分解が促進され、初期の不可逆容量が大きくなるために、初期放電容量がやや減少することがわかった。
【０１０６】
【発明の効果】
本発明によれば、金属酸化物および金属を負極活物質として用いた非水電解質二次電池の内部短絡不良を抑制し、かつ充放電サイクル寿命を向上させることができる。
【図面の簡単な説明】
【図１】本発明の第１実施形態にかかる角型電池の分解斜視図
【図２】本発明の第２実施形態にかかる円筒形電池の分解斜視図
【図３】発電要素の短径、長径、電極幅を示す図
【符号の説明】
１…角型非水電解質二次電池
２…発電要素
６…電池容器
Ｄ１…発電要素の短径
Ｄ２…発電要素の短径に対応する電池容器の内側の寸法[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a non-aqueous electrolyte secondary battery.
[0002]
[Prior art]
In a non-aqueous electrolyte secondary battery using a carbonaceous material as a negative electrode active material, a separator such as a microporous film is generally used from the viewpoint of safety.
[0003]
However, in a non-aqueous electrolyte secondary battery having a wound power generating element, the separator is compressed and broken when the power generating element is manufactured, and as a result, the positive electrode and the negative electrode come into direct contact with each other, causing a short circuit. Battery failure occurred.
[0004]
Accordingly, a technique has been disclosed in which the molecular weight of the separator is set to a predetermined value or more to improve the strength of the separator and reduce the initial failure of the battery (for example, see Patent Document 1).
[0005]
[Patent Document 1]
Japanese Patent No. 3108142
[0006]
[Problems to be solved by the invention]
However, even when the strength of the separator is improved, when a metal oxide such as silicon monoxide (SiO) is used as the negative electrode active material, the charge and discharge are repeated and the active material expands and contracts due to the charge and discharge. There is a problem that a short circuit occurs due to a large change in electrode thickness.
[0007]
The present invention has been completed on the basis of the above circumstances, and suppresses internal short circuit failure of a nonaqueous electrolyte secondary battery using a metal or an oxide thereof as a negative electrode active material, and has a charge / discharge cycle life. The purpose is to improve.
[0008]
[Means for Solving the Problems]
The present inventors have intensively studied to solve such a problem. As a result, in a non-aqueous electrolyte secondary battery using a metal oxide as a negative electrode active material, in order to reduce short-circuits due to charge and discharge, rather than the physical properties of the separator, It has been found that the ratio of the dimensions inside the battery container to be used is very important.
[0009]
The reason why the ratio of the inner dimensions of the battery container to the outer dimensions of the power generating element is important is assumed as follows.
A negative electrode active material containing a metal oxide has a feature that the volume increase due to occlusion of lithium ions during charging is extremely large as compared with a carbon material. When a carbon material is used as the negative electrode active material, expansion during charging is small, and since the material itself has conductivity, the electron conductivity between the active materials or between the current collector and the active material during charging is also low. When the negative electrode active material is made of a metal or metal oxide with large expansion of the active material due to charging and low conductivity, the electronic conduction between the active materials or between the current collector and the active material does not decrease. The deterioration of the property becomes remarkably large.
[0010]
As a result, the polarization at the time of charge / discharge becomes large, and the charge reaction is hindered. Therefore, a battery using a metal and a metal oxide as a negative electrode active material has a problem that a decrease in battery capacity during a charge / discharge cycle test is greater than a battery using a carbon material as a negative electrode active material. .
As one of the methods for suppressing the decrease in the current collecting property of the negative electrode due to the charge / discharge cycle, there is a method in which an appropriate pressure is applied to the power generating element to press the electrode plate. If the electrode plate is moderately compressed, even if the active material expands during charging, the electrical contact between the active materials, the conductive auxiliary material and the active material, and the current collector and the active material layer are maintained. This is because a decrease in the conductivity of the active material is suppressed. Therefore, in the case of a battery using a negative electrode containing a metal or a metal oxide as an active material, it is desirable that the negative electrode plate be appropriately compressed.
However, a battery having a power generating element manufactured by winding a negative electrode containing a metal or a metal oxide, a separator, and a positive electrode has a problem that, if the pressure is excessively applied, the charge / discharge cycle characteristics deteriorate or an internal short circuit easily occurs. .
[0011]
In the wound power generation element, there are always places where the electrode plates are not uniformly pressed. Particularly strong pressure is applied to the corners of the wound power generating element having an oval power generating element and to the inner peripheral portion of the wound power generating element having the oval power generating element.
In these places, in addition to being squeezed, the electrode plate is further squeezed with the progress of charging, so that the conductivity is maintained, and the charging tends to progress further. As a result, the thickness of the electrode becomes extremely large, the separator may be broken, and an internal short circuit may occur between the electrode plates. In addition, negative active materials such as metals and metal oxides are alloys that have grown in dendrite shape during charging, or alloys that have become finer due to charging and discharging. Easy to cause.
[0012]
Furthermore, when only a specific portion of the power generating element expands, the shape of the power generating element is distorted, and the power generating element comes into contact with the case to easily cause an internal short circuit. In particular, when a thin polyolefin separator having low mechanical strength is used, an internal short circuit tends to occur.
In addition to the internal short circuit, when the separator is excessively compressed, the pores of the separator at that location are blocked and the movement of ions is hindered, so that charging and discharging cannot be performed, or the separator is present in the power generating element. There is also a problem that the electrolytic solution that has been pushed out of the power generating element is depleted of the electrolytic solution inside the power generating element.
[0013]
Therefore, in order to maintain the conductivity of the electrodes during charge and discharge cycles, to suppress the occurrence of internal short circuits due to excessive compression, and to improve the charge and discharge cycle characteristics, it is necessary that the power generation elements are appropriately compressed. Therefore, it is important to adjust the ratio of the inner dimensions of the battery container to the outer dimensions of the power generating element so that an appropriate pressure is always applied to the power generating element.
[0014]
From the above assumption, it is considered that even if the initial failure is reduced as in the related art, the short circuit during charging and discharging is not reduced.
[0015]
The present inventors have studied in more detail, and found that the internal short-circuit can be significantly reduced by determining the inner size of the battery container based on the outer size of the power generating element in a fully charged state.
Here, the fully charged state refers to a state in which the nonaqueous electrolyte secondary battery is charged to a predetermined voltage at a constant current of 1 C and further charged at a constant voltage of a predetermined voltage for a total of 5 hours. The predetermined voltage is a voltage determined by the positive and negative electrode active materials and the electrolyte of the non-aqueous electrolyte secondary battery, and is usually slightly lower than the maximum chargeable voltage of the battery system in view of safety. .
[0016]
When charging a battery, the inner dimensions of the battery container are constant and the outer dimensions of the power generating element are considered to be maximum in a fully charged state, so the pressure applied to the separator will not be greater than in the fully charged state. Conceivable. Therefore, it is considered that by determining the inside dimensions of the battery container based on the outside dimensions of the power generating element in the fully charged state, the short circuit due to the breakage of the separator can be significantly reduced.
The present invention has been made based on the above findings.
[0017]
That is, the invention of claim 1 is a power generating element in which a positive electrode containing a positive electrode active material and a negative electrode containing a negative electrode active material are wound via a separator into a cylindrical spiral shape having an oblong cross section, In a nonaqueous electrolyte secondary battery housed in a flat battery container, the negative electrode active material is at least one metal selected from Si, Sn, Zn, Ge, Al, Pb, and Sb, or an oxide thereof. And the inside dimension of the battery case corresponding to the short diameter of the power generating element when the power generating element is accommodated is 98% or more and 115% or less of the short diameter of the power generating element in a fully charged state. Thus, a non-aqueous electrolyte secondary battery was obtained.
[0018]
Further, the invention of claim 2 is that a cylindrical spiral power generating element in which a positive electrode containing a positive electrode active material and a negative electrode containing a negative electrode active material are wound via a separator is accommodated in a cylindrical battery container. In the non-aqueous electrolyte secondary battery, the negative electrode active material contains at least one metal selected from Si, Sn, Zn, Ge, Al, Pb, and Sb or an oxide thereof, and the battery container Has an inner diameter of 98% or more and 115% or less of the outer diameter of the power generating element in a fully charged state.
[0019]
The invention of claim 3 provides a nonaqueous electrolyte secondary battery, wherein the positive electrode active material is a lithium manganese composite oxide having a spinel structure.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described.
<First embodiment>
FIG. 1 is an exploded perspective view of a prismatic nonaqueous electrolyte secondary battery 1 (hereinafter, abbreviated as “square battery 1”) according to a first embodiment of the present invention. The prismatic battery 1 is configured such that a power generating element 2 is accommodated in a flat box-shaped battery container 6 formed of an aluminum plate or the like together with a non-aqueous electrolyte (not shown), and is sealed with a battery lid 7. The power generating element 2 is configured by winding a positive electrode 3 and a negative electrode 4 through a separator 5 in a flat spiral shape having an oblong cross section.
[0021]
The battery lid 7 is provided with a negative electrode terminal 9 and a safety valve 8. The positive electrode 3 is electrically connected to the battery lid 7 by the positive electrode lead 10, and the negative electrode terminal 9 is electrically insulated from the battery lid 7 and is also electrically connected to the negative electrode 4 via the negative electrode lead 11.
[0022]
The positive electrode 3 includes a positive electrode mixture layer formed by applying a positive electrode mixture on both surfaces of a positive electrode current collector formed of aluminum foil or the like, drying and pressing. The positive electrode mixture contains a positive electrode active material.
[0023]
As the positive electrode active material, a material capable of inserting and extracting lithium can be used. For example, LiCoO 2 ₂ , LiNiO ₂ , LiNi _1/2 Mn _1/2 O ₂ , LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , LiCo _x Ni _1-x O ₂ , LiMn ₂ O ₄ , Li ₂ Mn ₂ O ₄ , NiO ₂ , MnO ₂ , FeO ₂ , V ₂ O ₅ , V ₆ O _Thirteen , TiO ₂ Or TiS ₂ Etc. can be used. Among these, in particular, those whose volume decreases with charging can be preferably used as the positive electrode active material, and it is preferable to contain a lithium manganese composite oxide having a spinel structure.
[0024]
In addition to the above-described positive electrode active material, a conductive agent, a binder, and the like can be added to the positive electrode mixture. As the conductive agent, an inorganic compound such as graphite or carbon black, or an organic compound such as polyaniline can be used.As the binder, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, or the like can be used. it can.
[0025]
The negative electrode 4 includes a negative electrode mixture layer formed by applying a negative electrode mixture on both surfaces of a negative electrode current collector formed of a copper foil or the like, drying and pressing. The negative electrode mixture contains a negative electrode active material.
[0026]
As the negative electrode active material, a metal capable of inserting and extracting lithium or an oxide thereof is used. These metals or their oxides contain at least one metal element selected from Si, Sn, Zn, Ge, Al, Pb, and Sb. As the metal oxide, for example, SiO, SiO ₂ , Li _x SiO, SnO, SnO ₂ At least one kind of compound selected from such as can be used. In addition to the negative electrode active material, a conductive agent, a binder, and the like can be added to the negative electrode mixture in the same manner as the positive electrode mixture.
[0027]
Further, as the negative electrode active material, composite particles composed of the above metal or metal oxide and a carbon material (hereinafter, the carbon material constituting the composite particles is referred to as “carbon material A”) can be used. When such composite particles are used, the carbon material functions as a conductive auxiliary and also functions as a negative electrode active material.
In the composite particles, the mixing ratio of the metal or metal oxide to the carbon material A is not particularly limited, but the content of the carbon material A in the composite particles may be 5 parts by weight or more and 80 parts by weight or more. preferable. When the content of the carbon material A in the composite particles is less than 5 parts by weight, it is difficult to maintain the conductive path in the negative electrode, and when the content of the carbon material A in the composite particles exceeds 80 parts by weight. This is because the charge / discharge capacity of the negative electrode is reduced.
[0028]
Further, the cycle is performed by coating the surface of the composite particles comprising the metal or metal oxide and the carbon material A with a carbon material (hereinafter, the carbon material covering the surface of the composite particles is referred to as “carbon material B”). A non-aqueous electrolyte secondary battery with improved characteristics can be obtained.
The reason is considered as follows. Metals or oxide particles thereof exposed on the surfaces of the composite particles may have reduced cycle characteristics due to the fine powder generated by repeated charge and discharge falling off the composite particles. By coating the composite particles with the carbon material B, the metal or oxide particles exposed on the surface of the composite particles can also maintain a conductive path, so that the cycle characteristics are considered to be improved. .
[0029]
In addition, when the surface of the composite particles is not coated with a carbon material, there is a portion on the metal or its oxide particles that has higher reactivity with lithium ions than others, and the occlusion and release reactions of lithium ions are as follows. A so-called reaction unevenness, in which the reaction proceeds intensively in this highly reactive portion, may occur. Then, in a highly reactive portion, the volume of the negative electrode active material expands due to occlusion of lithium ions, whereas in a low reactivity portion, the volume expansion of the negative electrode active material becomes small. When such unevenness in volume fluctuation occurs, the shape of the metal or oxide particles thereof is broken and a portion isolated from the surroundings is generated, and the conductive path may be disconnected.
[0030]
By coating the surface of the composite particles with the carbon material B, the above-described reaction unevenness is reduced, and the metal or its oxide particle and the lithium ion react uniformly. As a result, the metal or oxide particles thereof are uniformly expanded in volume, so that isolation is prevented and the conductive path is maintained. As a result, a nonaqueous electrolyte secondary battery having excellent cycle characteristics can be obtained.
When the surface of the composite particles comprising the metal or metal oxide and the carbon material A is coated with the carbon material B, the ratio of the carbon material B to the composite particles is preferably 0.5 parts by weight or more and 20 parts by weight or less. . When the ratio of the carbon material B to the composite particles is less than 0.5 parts by weight, the surface of the composite particles cannot be sufficiently coated, so that the cycle characteristics are reduced, and the ratio of the carbon material B to the composite particles is reduced. If the content exceeds 20 parts by weight, the content ratio of the metal or the oxide particles thereof decreases, and the discharge capacity decreases.
[0031]
As the separator 5, a woven fabric, a nonwoven fabric, a microporous film, or the like can be used. In particular, a synthetic resin microporous film can be suitably used. Above all, a polyolefin-based microporous film formed of polyethylene, polypropylene, or the like, or a microporous film obtained by combining these can be suitably used in terms of thickness, film strength, film resistance, and the like.
[0032]
The thickness of the separator 5 is preferably 8 μm or more and 25 μm or less, more preferably 16 μm or more and 23 μm or less. When the thickness of the separator 5 is 25 μm or less, the power generation element 6 can be made smaller, and the volume energy density of the battery can be made larger. This is preferable. preferable.
[0033]
As the non-aqueous electrolyte, a non-aqueous electrolyte or a solid electrolyte can be used, and a non-aqueous electrolyte and a solid electrolyte may be used in combination. As the solid electrolyte, a known solid electrolyte can be used, and for example, an inorganic solid electrolyte and a polymer solid electrolyte can be used. Further, the solid electrolyte can also serve as a separator. In addition, when a gel-like polymer solid electrolyte is used as the polymer solid electrolyte, even if the electrolyte constituting the gel and the electrolyte contained in the pores of the active material of the electrode plate are different from each other. Good. Further, a synthetic resin microporous membrane and a solid polymer electrolyte may be used in combination.
[0034]
As the non-aqueous electrolyte, either an electrolytic solution or a solid electrolyte can be used. When an electrolytic solution is used, examples of the electrolytic solution solvent include ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, gamma-butyrolactone, sulfolane, dimethyl sulfoxide, acetonitrile, dimethylformamide, dimethylacetamide, and 1,2- A polar solvent such as dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dioxolan, methyl acetate, or a mixture thereof may be used.
[0035]
The non-aqueous electrolyte negative electrode film forming agent may contain, as a compound to be added, vinyl ethylene carbonate, vinylene carbonate, cyclic sulfonic acid or cyclic sulfate, cyclic acid anhydride, or cyclic sulfonic acid.
Examples of the cyclic sulfonic acid include 1,3-propane sultone, 1,4-butane sultone, 1,3-butane sultone, and 1,3-propene sultone. Examples of the cyclic sulfate include glycol sulfate and propyl glycol sulfate. Further, the cyclic acid anhydride is succinic anhydride, glunic anhydride, maleic anhydride, citraconic anhydride, diglycolic anhydride, cyclohexanedicarboxylic anhydride, 4-cyclohexene-1,2-dicarboxylic anhydride, 3, Examples thereof include 4,5,6-tetrahydrophthalic anhydride, 5-norbrunene-2,3-dicarboxylic anhydride, phenylsuccinic anhydride, and 2-phenylgrunuric anhydride.
[0036]
In the present invention, it is preferable to use a lithium salt as the salt of the light metal dissolved in the organic solvent. As a lithium salt, LiPF ₆ , LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiCF (CF ₃ ) ₅ , LiCF ₂ (CF ₃ ) ₄ , LiCF ₃ (CF ₃ ) ₃ , LiCF ₄ (CF ₃ ) ₂ , LiCF ₅ (CF ₃ ), LiCF ₃ (C ₂ F ₅ ) ₃ , LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ CF ₂ CF ₃ ) ₂ , LiN (COCF ₃ ) ₂ , LiN (COCF ₂ CF ₃ ) ₂ , LiC ₄ BO ₈ Or a mixture thereof. Among them, since the cycle characteristics are improved, LiPF is used as the lithium salt. ₆ It is preferable to use Further, the concentration of these lithium salts is preferably 0.5 to 2.0M.
The non-aqueous solvent, the film-forming additive, and the electrolyte salt are not particularly limited, and may be used in an appropriate combination according to the intended use.
[0037]
Here, the power generation element 2 in the fully charged state in the prismatic battery 1 was set at 7792 N / m in the short diameter direction. ² Let D1 be the length compressed by (see FIG. 1). When the power generation element 2 is accommodated in the battery container 6, the inside dimension of the battery container 6 corresponding to the short diameter D1 of the power generation element 2 is defined as D2. In addition, the minor axis refers to a length (minor axis) corresponding to a short diameter in an oval cut surface obtained by cutting a flat wound power generating element along a plane perpendicular to a center axis of the winding.
[0038]
The ratio of the dimension D2 inside the battery container 6 to the short diameter D1 of the power generation element 2 in the fully charged state needs to be 98% or more and 115% or less, and preferably 100% or more and 110% or less. More preferably, it is 100% or more and 105% or less. Thereby, a short circuit between the positive electrode 3 and the negative electrode 4 during charging and discharging can be reduced.
[0039]
Hereinafter, the operation of the present embodiment will be described.
In the negative electrode 4 of the prismatic battery 1 in the present embodiment, a metal oxide such as SiO is contained in the negative electrode mixture layer as a negative electrode active material. Since the volume of the metal oxide increases due to occlusion of lithium ions during charging, the volume of the negative electrode mixture layer increases by charging. At this time, the power generation element 2 is compressed by the increase in the volume of the negative electrode mixture layer itself inside the battery container 6, and the separator 5 located between the positive electrode 3 and the negative electrode 4 of the power generation element 2 is compressed. Then, it is considered that the volume of the power generation element 2 becomes maximum in the fully charged state.
[0040]
In the present embodiment, the ratio of the dimension D2 inside the battery container 6 to the short diameter D1 of the power generating element 2 in the fully charged state is 98% or more. Therefore, even if the power generation element 2 is stored in the battery container 6 and charged, the separator 5 is not compressed to the extent that the separator 5 is broken, so that a short circuit can be prevented.
[0041]
On the other hand, since the dimension D2 inside the battery case 6 is set to 115% or less of the short diameter D1 of the power generation element 2 in a fully charged state, a high volume energy density can be secured.
[0042]
In addition, when the positive electrode mixture layer of the positive electrode 3 contains a lithium manganese composite oxide having a spinel structure as a positive electrode active material, a short circuit of the prismatic battery 1 can be further reduced. Since the volume of the lithium manganese composite oxide having a spinel structure is reduced by charging, even if the volume of the negative electrode active material increases due to charging, the increase in the volume of the power generation element 2 can be moderated. Therefore, since the pressure applied to the separator 5 is reduced, the separator 5 is less likely to be broken, and short circuits can be reduced.
[0043]
<Second embodiment>
FIG. 2 is an exploded perspective view of a cylindrical non-aqueous electrolyte secondary battery 21 (hereinafter, abbreviated as “cylindrical battery 21”) according to a second embodiment of the present invention. This cylindrical battery 21 is different from the prismatic battery 1 according to the first embodiment in the shapes of the power generation element 22 and the battery container 26. For the same configuration as the above-described embodiment, a duplicate description of the structure, operation, and effect will be omitted.
[0044]
The cylindrical battery 21 includes a power generation element 22 wound in a tubular spiral shape and a non-aqueous electrolyte (not shown) housed in a battery container 26 formed in a cylindrical shape with a bottom. The battery case 26 is formed of, for example, a nickel-plated iron plate or the like, and the opening of the battery case 26 is caulked together with the sealing gasket 33 by the positive electrode cap 27 to hermetically seal. The battery case 26 also serving as the negative electrode terminal is electrically connected to the negative electrode via the negative electrode lead 31, and the positive electrode cap 27 is electrically connected to the positive electrode 3 via the positive electrode lead 30.
[0045]
In the present embodiment, when the outer diameter of the cylindrical power generating element 22 is D3 and the inner diameter of the battery container 26 is D4, the ratio of D4 to D3 needs to be 98% or more and 115% or less, and is preferably. It is 100% or more and 110% or less, more preferably 100% or more and 105% or less.
[0046]
Thereby, similarly to the first embodiment, it is possible to reduce a short circuit during charging and discharging of the cylindrical battery 21 using the metal oxide as the negative electrode active material.
[0047]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples.
[Production of Battery]
(Example 1)
The battery of Example 1 was manufactured by the following method.
[0048]
<Production method of negative electrode>
In producing the negative electrode, a negative electrode active material was first synthesized.
SiO is microcrystalline Si and amorphous SiO ₂ And SiO powder that had been phase-separated. In the X-ray diffraction pattern of the CuKα ray, the SiO powder shows a diffraction peak in the range of 46 ° to 49 ° from the Si peak, and the half value width of the main diffraction peak appearing in the above range is represented by B B <3 ° (2θ).
[0049]
Carbon was supported on the surface of the SiO particles by a method (CVD) of thermally decomposing benzene gas at 1000 ° C. in an argon atmosphere. The amount of carbon carried was 20% by weight based on the total weight of the negative electrode active material. The number average particle size of the active material after supporting carbon was 6 μm.
[0050]
A negative electrode was manufactured using this negative electrode active material. First, a mixture of 10% by weight of the obtained negative electrode active material, 40% by weight of mesocarbon microbeads, 30% by weight of natural graphite, and 20% by weight of artificial graphite was used as a carbon material, and 97% by weight of the mixed active material was used. A paste was prepared by dispersing styrene-butadiene rubber (SBR) 2% by weight and carboxymethylcellulose (CMC) 1% by weight in water.
[0051]
This paste was applied to a copper foil having a thickness of 12 μm at 1.15 mg · cm. ^-2 Then, water was evaporated by drying at 150 ° C. This operation was performed on both surfaces of the copper foil, and both surfaces were compression-molded by a roll press. In this way, a negative electrode plate having negative electrode mixture layers on both surfaces was manufactured.
[0052]
<Method of manufacturing positive electrode>
A paste was prepared by dispersing 90% by weight of lithium cobaltate, 5% by weight of acetylene black, and 5% by weight of polyvinylidene fluoride (PVdF) in NMP. This paste was coated on a 15 μm-thick aluminum foil by 2.5 mg · cm. ^-2 Then, NMP was evaporated by drying at 150 ° C. The above operation was performed on both sides of the aluminum foil, and both sides were compression-molded by a roll press. Thus, a positive electrode plate provided with the positive electrode material mixture layers on both surfaces was manufactured.
[0053]
<Preparation of battery>
The positive electrode plate and the negative electrode plate prepared in this manner are superposed and wound around a polyethylene separator which is a communicating porous body having a thickness of 20 μm and a porosity of 40% to form a power generating element having a thickness of 3.5 mm. It was inserted into an aluminum case having a thickness of 48 mm, a width of 30 mm and a thickness of 4.2 mm and a thickness of 0.2 mm. The internal dimension D2 of the battery was adjusted by inserting an aluminum spacer.
[0054]
FIG. 3 shows the minor axis, major axis, and electrode width of the power generating element. In FIG. 3, reference numeral 2 denotes a flat wound power generating element, and reference numeral 40 denotes a winding center axis. In the flat wound power generating element, 7792 N / m in the direction of the arrow in FIG. ² , X indicates the minor axis, Y indicates the major axis, and Z indicates the electrode width. In an oval cut surface obtained by cutting the flat wound power generating element at a plane perpendicular to the winding center axis 40, a length (short axis) corresponding to a short diameter is defined as a short diameter X, and a length corresponding to a long diameter. The length (long axis) is defined as the major axis Y. The length of the power generating element 2 in the direction along the winding center axis 40 of the flat wound power generating element 2 is defined as an electrode width Z.
[0055]
In the non-aqueous electrolyte, 1.2 mol / L of LiPF was mixed in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) at a volume ratio of 4: 6. ₆ Was used.
Finally, 50 cells of the battery of Example 1 having a rated capacity of 700 mAh were manufactured by injecting the non-aqueous electrolyte.
[0056]
<Test method>
The prepared battery of Example 1 was charged at a constant current of 700 mA to 4.2 V, further charged at a constant voltage of 4.2 V for a total of 5 hours, and then discharged to 2.75 V at a constant current of 700 mA, and the initial discharge capacity was increased. It was confirmed. The battery after the initial discharge capacity confirmation test was left for one week, and the battery having a battery voltage of 2 V or less was defined as an internal short-circuit failure battery.
The battery after the initial capacity confirmation test was charged at a constant current of 700 mA to 4.2 V, and further charged at a constant voltage of 4.2 V for a total of 5 hours. The battery was disassembled, the power generating element was taken out, and the thickness of D1 was measured. , D2 / D1 = 98%.
[0057]
Further, the battery after the initial capacity confirmation test was charged to 4.2 V at a constant current of 700 mA, further charged at a constant voltage of 4.2 V for a total of 5 hours, and then discharged to 2.75 V at a constant current of 700 mA for 1 hour. As a cycle, charge and discharge were performed for 300 cycles, and the discharge capacity at the time of the initial capacity confirmation test and the discharge capacity at the 300th cycle were compared.
[0058]
(Example 2)
Except that an aluminum spacer was inserted into the battery and the D2 / D1 ratio was adjusted to be 100%, 50 cells of the battery of Example 2 were produced and tested in exactly the same manner as in Example 1. .
[0059]
(Example 3)
Except that an aluminum spacer was inserted into the battery and the D2 / D1 ratio was adjusted to be 105%, 50 cells of the battery of Example 3 were produced and tested in exactly the same manner as in Example 1. .
[0060]
(Example 4)
Except that an aluminum spacer was inserted into the battery and the D2 / D1 ratio was adjusted to be 110%, 50 cells of the battery of Example 4 were manufactured and tested in exactly the same manner as in Example 1. .
[0061]
(Example 5)
Except that an aluminum spacer was inserted into the battery and the D2 / D1 ratio was adjusted to 115%, exactly 50 cells of the battery of Example 5 were produced and tested in exactly the same manner as in Example 1. .
[0062]
(Comparative Example 1)
Except that an aluminum spacer was inserted into the battery and the D2 / D1 ratio was adjusted to be 95%, 50 cells of the battery of Comparative Example 1 were produced and tested in exactly the same manner as in Example 1. .
[0063]
(Comparative Example 2)
Except that an aluminum spacer was inserted into the battery and the D2 / D1 ratio was adjusted to be 120%, 50 cells of the battery of Comparative Example 2 were produced and tested in exactly the same manner as in Example 1. .
[0064]
<Preparation of cylindrical battery>
(Example 6)
The battery case is made of stainless steel with a thickness of 0.3 mm, a cylindrical shape with a bottom having a height of 64.8 mm and an outer diameter of 18 mm (D2 = 17.4). A stainless steel foil is used for adjusting the internal dimensions of the battery. Except for the above, 50 cells of the cylindrical battery of Example 6 having a rated capacity of 1800 mAh were produced using exactly the same method for producing the positive electrode and the negative electrode, the separator, and the electrolytic solution as in Example 1.
[0065]
The prepared battery of Example 6 was charged to 4.2 V at a constant current of 1800 mA, further charged at a constant voltage of 4.2 V for a total of 5 hours, and then discharged to 2.75 V at a constant current of 1800 mA to obtain an initial discharge capacity. It was confirmed. The battery after the initial discharge capacity confirmation test was left for one week, and the battery having a battery voltage of 2 V or less was defined as an internal short-circuit failure battery.
The battery after the initial capacity confirmation test was charged to 4.2 V at a constant current of 1800 mA, and further charged at a constant voltage of 4.2 V for a total of 5 hours. The battery was disassembled, the power generating element was taken out, and the thickness of D2 was measured. , D2 / D1 = 98%.
[0066]
The battery after the initial capacity confirmation test was charged to 4.2 V at a constant current of 1800 mA, further charged at a constant voltage of 4.2 V for a total of 5 hours, and then discharged to 2.75 V at a constant current of 1800 mA for 1 hour. As a cycle, charge and discharge were performed for 300 cycles, and a comparison was made between the discharge capacity at the initial capacity confirmation test and the discharge capacity at the 3000th cycle.
[0067]
(Example 7)
Except that the D2 / D1 ratio was adjusted to 100%, 50 cells of the battery of Example 7 were produced and tested in exactly the same manner as in Example 6.
[0068]
(Example 8)
Except that the D2 / D1 ratio was adjusted to be 105%, 50 cells of the battery of Example 8 were manufactured and tested in exactly the same manner as in Example 6.
[0069]
(Example 9)
Except that the D2 / D1 ratio was adjusted to 110%, 50 cells of the battery of Example 9 were produced and tested in exactly the same manner as in Example 6.
[0070]
(Example 10)
Except that the D2 / D1 ratio was adjusted to 115%, 50 cells of the battery of Example 10 were produced and tested in exactly the same manner as in Example 6.
[0071]
(Comparative Example 3)
Except that the D2 / D1 ratio was adjusted to 95%, 50 cells of the battery of Comparative Example 3 were produced and tested in exactly the same manner as in Example 6.
[0072]
(Comparative Example 4)
Except that the D2 / D1 ratio was adjusted to be 120%, 50 cells of the battery of Comparative Example 4 were produced and tested in exactly the same manner as in Example 6.
[0073]
<When lithium manganese composite oxide having spinel structure is used as positive electrode active material>
(Example 11)
LiMn having a spinel structure as the positive electrode active material ₂ O ₄ Except for using, the same battery as in Example 1 was used to produce 50 rectangular batteries of Example 11 having a rated capacity of 600 mAh.
The prepared battery of Example 11 was charged to 4.2 V at a constant current of 600 mA, further charged at a constant voltage of 4.2 V for a total of 5 hours, and then discharged to 2.75 V at a constant current of 600 mA, thereby obtaining an initial discharge capacity. It was confirmed. The battery after the initial discharge capacity confirmation test was left for one week, and the battery having a battery voltage of 2 V or less was defined as an internal short-circuit failure battery.
[0074]
The battery after the initial capacity confirmation test was charged to 4.2 V at a constant current of 600 mA, and further charged at a constant voltage of 4.2 V for a total of 5 hours. The battery was disassembled, the power generating element was taken out, and the thickness of D1 was measured. , D2 / D1 = 98%.
After the initial capacity confirmation test, the battery was charged to 4.2 V at a constant current of 600 mA, further charged at a constant voltage of 4.2 V for a total of 5 hours, and then discharged to 2.75 V at a constant current of 600 mA. As a cycle, charge and discharge were performed for 300 cycles, and the discharge capacity at the time of the initial capacity confirmation test and the discharge capacity at the 300th cycle were compared.
[0075]
(Example 12)
A battery of Example 12 was produced and tested in exactly the same manner as in Example 6, except that the D2 / D1 ratio was adjusted to 100%.
[0076]
(Example 13)
Except that the D2 / D1 ratio was adjusted to 105%, 50 cells of the battery of Example 13 were manufactured and tested in exactly the same manner as in Example 6.
[0077]
(Example 14)
Except that the D2 / D1 ratio was adjusted to 110%, 50 cells of the battery of Example 14 were produced and tested in exactly the same manner as in Example 6.
[0078]
(Example 15)
Except that the D2 / D1 ratio was adjusted to 115%, 50 cells of the battery of Example 15 were produced and tested in exactly the same manner as in Example 6.
[0079]
(Comparative Example 5)
Except that the D2 / D1 ratio was adjusted to 95%, 50 cells of the battery of Comparative Example 5 were produced and tested in exactly the same manner as in Example 6.
[0080]
(Comparative Example 6)
Except that the D2 / D1 ratio was adjusted to be 120%, 50 cells of a battery of Comparative Example 6 were produced and tested in exactly the same manner as in Example 6.
[0081]
<Result>
<Square battery>
First, the results of the prismatic batteries of Examples 1 to 5 and Comparative Examples 1 and 2 shown in Table 1 will be examined.
[0082]
[Table 1]

[0083]
The ratio D2 / D1 is 95% with respect to Examples 1 to 5 in which the ratio of the dimension D2 inside the battery container to the minor diameter D1 of the power generating element (D2 / D1 ratio) is 98% or more and less than 115%. The battery of Comparative Example 1 had a smaller initial discharge capacity, and the discharge capacity retention at the 300th cycle was smaller than the batteries of Examples 1 to 5.
[0084]
This is because the pressure of the negative electrode plate in the power generating element becomes insufficient, the reduction in current collection due to the expansion and contraction of the negative electrode plate accompanying the charge / discharge cycle progresses, the polarization of the negative electrode plate increases, and the charge / discharge reaction occurs. It is considered to be caused by the inhibition and the capacity loss of the active material that has lost the electron conductivity in the charged state.
[0085]
Also, in the battery of Comparative Example 2 having a D2 / D1 ratio of 120%, similarly to Comparative Example 1, the initial discharge capacity was small, and the capacity retention at the 300th cycle was also small. Further, in the battery of Comparative Example 2, internal short-circuit failure also occurred in 2 cells out of 50 cells.
This is because excessive pressure was applied to the corners of the power generating element due to the negative electrode plate that expanded during charging, and the pores of the separator in that part were blocked and charging / discharging could not be performed, or the pores of the separator were blocked. It is considered that the cause was that the current was concentrated on the non-existing portions and irreversible metallic lithium was deposited on the surface of the negative electrode plate.
[0086]
In addition, in the charge / discharge cycle test, when the power generating element is excessively pressed during charging, pores of the separator at that location are blocked and the movement of ions is hindered, so that charging / discharging becomes impossible. It is considered that the cause is that the electrolyte present in the element was pushed out of the power generation element, and the electrolyte in the power generation element was depleted. In addition, when the battery in which the short-circuit failure occurred was disassembled, traces of a short-circuit were confirmed at the corner of the power generating element that was most pressed.
[0087]
From the above, the metal oxide can be reduced by setting the ratio (D2 / D1 ratio) of the dimension D2 inside the battery container to the short diameter D1 of the power generating element of the fully charged power generating element to be 98% or more and 115% or less. The initial capacity of the prismatic battery used as the negative electrode active material was increased, the charge / discharge cycle performance was improved, and the internal short circuit was reduced.
[0088]
<Cylindrical battery>
Next, the results of the cylindrical batteries of Examples 6 to 10 and Comparative Examples 3 and 4 shown in Table 2 will be examined.
[0089]
[Table 2]

[0090]
Similarly to the prismatic batteries, the batteries of Examples 6 to 10 of the cylindrical batteries have the D2 / D1 ratio of 98% or more and 115% or less in the fully charged power generation element, so that the metal oxide can be used as the negative electrode. The initial capacity of the prismatic battery used as the material was increased, the charge / discharge cycle performance was improved, and the internal short circuit was reduced. In addition, when the location where the internal short-circuit occurred, it was confirmed that the rectangular battery was the corner portion of the power generating element, whereas the cylindrical battery was the inner peripheral portion.
[0091]
<Square: When lithium manganate having a spinel structure is used as the positive electrode active material>
Next, in the same manner as in Examples 6 to 10, Comparative Examples 3 and 4, except that lithium manganate having a spinel structure was used instead of lithium cobaltate as the positive electrode active material, Examples 11 to 15, The batteries of Example 5 and Comparative Example 6 were produced, and the results of the prismatic batteries using lithium manganate having a spinel structure as the positive electrode active material were examined. The results are summarized in Table 3.
[0092]
[Table 3]

Similarly to the prismatic batteries using lithium cobalt oxide as the positive electrode active material, the batteries of Examples 11 to 15 were prepared by setting the D2 / D1 ratio of the fully charged power generating element to 98% or more and 115% or less. The initial capacity of the prismatic battery using the oxide as the negative electrode active material was increased, and the charge / discharge cycle performance was improved.
[0093]
In addition, the battery of Comparative Example 6 using lithium manganate having a spinel structure as the positive electrode active material had a reduced internal short circuit as compared with the battery of Comparative Example 4 using lithium cobalt oxide as the positive electrode active material. The reason is that lithium manganate having a spinel structure tends to decrease the volume of particles at the time of delithiation (= at the time of charging), and the positive electrode using the same tends to decrease at the time of charging. This is considered to be because the volume expansion of the negative electrode at the time of charging was offset, and excessive pressure applied to the separator during charging was suppressed.
[0094]
From these results, it has been found that it is effective to use a positive electrode active material that does not have or reduces volume expansion during charging in order to reduce internal short circuit failure. This time, LiMn ₂ O ₄ Was used as the positive electrode active material, but depending on the situation, it could be mixed with lithium cobalt oxide, or LiNi. _1-x Mn _x O ₂ Such a positive electrode active material having a spinel structure can be appropriately selected.
[0095]
(Examples 16 to 19)
Except having changed the kind of metal or metal oxide used for a negative electrode active material, it carried out similarly to Example 2, and produced D / D1 = 100%. Then, the initial discharge capacity at 25 ° C. and the capacity retention rate after 300 cycles were obtained for each battery.
The produced battery was charged to 4.2 V at a constant current of 700 mA, further charged at a constant voltage of 4.2 V for a total of 5 hours, and then discharged to 2.75 V at a constant current of 700 mA to confirm the initial discharge capacity. After the initial capacity confirmation test, the battery was charged at a constant current of 700 mA to 4.2 V, further charged at a constant voltage of 4.2 V for a total of 5 hours, and then discharged to 2.75 V at a constant current of 700 mA for 1 hour. As a cycle, charge / discharge was performed for 300 cycles, the discharge capacity at the initial capacity confirmation test was compared with the discharge capacity at the 300th cycle, and the ratio of the discharge capacity at the 300th cycle to the initial discharge capacity was defined as a capacity retention ratio (%). did.
[0096]
Table 4 shows the negative electrode active materials of the manufactured batteries and the test results. In addition, the initial discharge capacity and the capacity retention rate in Table 4 showed the average value of 10 cells for each battery. Table 4 also shows the data of Example 2 for comparison.
[0097]
[Table 4]

[0098]
Table 4 shows that when various metals or oxides thereof were used as the negative electrode active material, the initial discharge capacity and the capacity retention ratio exhibited almost the same excellent values.
[0099]
(Examples 20 to 24)
In the same manner as in Example 2 except that the composite particles of SiO and graphite were used as the negative electrode active material and the mixing ratio of SiO and graphite was changed, D2 / D1 = 100%. A type battery was manufactured. Then, the initial discharge capacity at 25 ° C. and the capacity retention after 300 cycles were obtained under the same conditions as in Example 16 for each battery.
Table 5 shows the mixing ratio of SiO and graphite of the manufactured battery and the test results. In addition, the initial discharge capacity and the capacity retention rate in Table 5 showed the average value of 10 cells for each battery.
[0100]
[Table 5]

[0101]
From Table 5, it can be seen that in the case of Example 20 in which the content of graphite in the composite particles is less than 5 parts by weight, it is difficult to maintain the conductive path in the negative electrode, so that the capacity retention ratio is slightly reduced. When the content exceeds 80 parts by weight, the charge / discharge capacity of the negative electrode was reduced, and the initial discharge capacity was slightly reduced.
[0102]
(Examples 25 to 29)
As the negative electrode active material, the surface of the composite particles of 90 parts by weight of SiO 2 and 10 parts by weight of graphite was coated with carbon, and the weight ratio of the coated carbon to the total weight of SiO and graphite was changed in the same manner as in Example 2, The square batteries of Examples 25 to 29 in which D2 / D1 = 100% were produced.
[0103]
Then, the initial discharge capacity at 25 ° C. and the capacity retention after 300 cycles were obtained under the same conditions as in Example 16 for each battery.
Table 6 shows the weight ratio of the coated carbon to the total weight of SiO and graphite of the fabricated battery and the test results. In addition, the initial discharge capacity and the capacity retention rate in Table 6 showed the average value of 10 cells for each battery.
[0104]
[Table 6]

[0105]
From Table 6, it can be seen that by coating the surface of the composite particles composed of SiO and graphite with carbon, the capacity retention ratio is improved, but when the carbon coating amount is smaller than 0.5 part by weight, the effect is almost negligible. Also, it was found that when the carbon coating amount was larger than 20 parts by weight, the reductive decomposition of the electrolytic solution was promoted on the coated carbon, and the initial irreversible capacity was increased, so that the initial discharge capacity was slightly reduced.
[0106]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the internal short circuit defect of a nonaqueous electrolyte secondary battery using a metal oxide and a metal as a negative electrode active material can be suppressed, and the charge / discharge cycle life can be improved.
[Brief description of the drawings]
FIG. 1 is an exploded perspective view of a prismatic battery according to a first embodiment of the present invention.
FIG. 2 is an exploded perspective view of a cylindrical battery according to a second embodiment of the present invention.
FIG. 3 is a diagram showing a short diameter, a long diameter, and an electrode width of a power generating element.
[Explanation of symbols]
1: Square non-aqueous electrolyte secondary battery
2. Power generation elements
6. Battery case
D1: short diameter of the power generating element
D2: Dimension of the inside of the battery container corresponding to the minor diameter of the power generation element

Claims (3)

A power generating element in which a positive electrode containing a positive electrode active material and a negative electrode containing a negative electrode active material are wound into a cylindrical spiral shape having an elliptical cross section via a separator is housed in a flat battery container. In non-aqueous electrolyte secondary batteries,
The negative electrode active material contains at least one metal selected from Si, Sn, Zn, Ge, Al, Pb, and Sb or an oxide thereof, and when the power generation element is accommodated, A non-aqueous electrolyte secondary battery, wherein an inner dimension of the battery container corresponding to a minor diameter is 98% or more and 115% or less of a minor diameter of the power generating element in a fully charged state. In a non-aqueous electrolyte secondary battery in which a cylindrical spiral power generating element in which a positive electrode containing a positive electrode active material and a negative electrode containing a negative electrode active material are wound via a separator is housed in a cylindrical battery container,
The negative electrode active material contains at least one metal selected from Si, Sn, Zn, Ge, Al, Pb, and Sb or an oxide thereof, and the inner diameter of the battery container is in a fully charged state. A non-aqueous electrolyte secondary battery characterized by being 98% or more and 115% or less of the outer diameter of the power generating element. The non-aqueous electrolyte secondary battery according to claim 1, wherein the positive electrode active material is a lithium manganese composite oxide having a spinel structure.

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