JPH10270019A - Nonaqueous electrolyte secondary battery - Google Patents
Nonaqueous electrolyte secondary batteryInfo
- Publication number
- JPH10270019A JPH10270019A JP9074049A JP7404997A JPH10270019A JP H10270019 A JPH10270019 A JP H10270019A JP 9074049 A JP9074049 A JP 9074049A JP 7404997 A JP7404997 A JP 7404997A JP H10270019 A JPH10270019 A JP H10270019A
- Authority
- JP
- Japan
- Prior art keywords
- graphite
- negative electrode
- carbon material
- active material
- electrode active
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Pending
Links
Classifications
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Abstract
Description
【０００１】[0001]
【発明の属する技術分野】本発明は、炭素材料を負極活
物質として用いた非水電解液二次電池に関するものであ
る。The present invention relates to a nonaqueous electrolyte secondary battery using a carbon material as a negative electrode active material.
【０００２】[0002]
【従来の技術】従来、非水電解液二次電池には、負極活
物質として金属リチウムあるいはリチウム合金が用いら
れていた。このような構成の電池では、充電時に、リチ
ウムがデンドライト状に負極に析出、成長して内部短絡
を起こしたり、金属リチウムの化学的活性度が高いため
に安全性が低下するという問題があった。そこで、負極
活物質として金属リチウムではなく、充電、放電に伴
い、リチウムを吸蔵、放出することができる炭素材料が
用いられるようになった。炭素材料として結晶性が高い
黒鉛（またはそれに類するものを含む）や、結晶性の低
い非晶質炭素を用いた非水電解液二次電池が既に商品化
されている。2. Description of the Related Art Conventionally, in a non-aqueous electrolyte secondary battery, lithium metal or a lithium alloy has been used as a negative electrode active material. In the battery having such a configuration, during charging, lithium precipitates and grows on the negative electrode in the form of dendrite, causing an internal short circuit, or having a problem in that safety is reduced due to high chemical activity of metallic lithium. . Therefore, instead of metallic lithium, a carbon material capable of inserting and extracting lithium with charge and discharge has been used as the negative electrode active material. Non-aqueous electrolyte secondary batteries using graphite with high crystallinity (or the like) as a carbon material or amorphous carbon with low crystallinity have already been commercialized.
【０００３】黒鉛を負極活物質として用いた負極板は、
黒鉛の真密度が高いこととあいまって、負極板成形工程
のひとつである活物質のプレス充填工程後の負極板密度
が高くなる。また、リチウムの吸蔵、放出電位、すなわ
ち充電、放電電位の経時変化が平坦で、しかもリチウム
の酸化還元電位に極めて近い。さらに、初回充放電のク
ーロン効率が高い。従って、黒鉛を負極活物質として用
いた電池はエネルギ密度が高いという長所がある。一
方、結晶性の低い非晶質炭素を負極活物質として用いた
負極板は、非晶質炭素の真密度が低いこととあいまっ
て、負極板成形工程のひとつである活物質のプレス充填
工程後の負極板密度があまり高くならない。また、リチ
ウムの吸蔵、放出電位、すなわち充電、放電電位の経時
変化が黒鉛のように平坦ではなく傾斜を持っている。リ
チウムの吸蔵量が少ない状態での負極電位は、リチウム
の酸化還元電位よりもずっと高く、リチウムの吸蔵量が
増えるに従いリチウムの酸化還元電位に近づく。さら
に、初回充放電のクーロン効率が黒鉛を負極活物質とし
て用いた場合のようには高くない。従って、非晶質炭素
を負極活物質として用いた電池はエネルギ密度が低いと
いう短所がある。このような炭素材料の種類による特性
の違いから、負極活物質には黒鉛が用いられるようにな
ってきている。A negative electrode plate using graphite as a negative electrode active material is:
In combination with the high true density of graphite, the negative electrode plate density after the active material press-filling step, which is one of the negative electrode plate forming steps, is increased. In addition, the change over time of the lithium absorption and desorption potentials, that is, the charging and discharging potentials, is flat and extremely close to the oxidation-reduction potential of lithium. Furthermore, the coulomb efficiency of the first charge / discharge is high. Therefore, a battery using graphite as a negative electrode active material has an advantage of high energy density. On the other hand, the negative electrode plate using amorphous carbon having low crystallinity as the negative electrode active material, combined with the low true density of the amorphous carbon, has a negative electrode plate after the active material press filling step, which is one of the negative electrode plate forming steps. Of the negative electrode plate does not increase so much. In addition, the temporal change in the potentials for absorbing and releasing lithium, that is, the charging and discharging potentials, is not flat like graphite, but has a slope. The negative electrode potential in a state where the amount of stored lithium is small is much higher than the oxidation-reduction potential of lithium, and approaches the oxidation-reduction potential of lithium as the amount of stored lithium increases. Furthermore, the coulomb efficiency of the initial charge and discharge is not as high as when graphite is used as the negative electrode active material. Therefore, a battery using amorphous carbon as a negative electrode active material has a disadvantage of low energy density. Due to such a difference in characteristics depending on the type of carbon material, graphite has been used as a negative electrode active material.
【０００４】しかし、黒鉛を負極活物質として用いた非
水電解液二次電池は、上記のような長所がある反面、以
下のような短所もある。すなわち、リチウムの吸蔵、放
出に伴う黒鉛の体積膨張、収縮が非晶質炭素よりも大き
いために負極構造が崩壊しやすい。黒鉛が高密度充填さ
れた負極板構造では、非水電解液が保持されるべき空間
が少なく、充放電反応時のリチウムの拡散が阻まれ過電
圧が増大し、負極電位がリチウムの酸化還元電位よりも
卑となり、黒鉛や負極集電体表面で充放電可逆性に乏し
いリチウムが析出することが原因で、充放電の繰り返し
に伴う容量低下が大きい。However, a non-aqueous electrolyte secondary battery using graphite as a negative electrode active material has the above advantages, but also has the following disadvantages. That is, since the volume expansion and shrinkage of graphite due to occlusion and release of lithium is larger than that of amorphous carbon, the negative electrode structure is easily broken. In the negative electrode plate structure filled with graphite at a high density, the space for holding the non-aqueous electrolyte is small, diffusion of lithium during charge / discharge reaction is prevented, overvoltage increases, and the negative electrode potential is higher than the oxidation-reduction potential of lithium. In addition, the poor charge / discharge reversibility of lithium deposited on the surface of graphite or the negative electrode current collector causes a large decrease in capacity due to repeated charge / discharge.
【０００５】そこで、負極活物質として黒鉛と非黒鉛炭
素材料の混合体を用いる提案がなされている（特開平７
−１９２７２４公報）。この技術は、炭素材料を高密度
充填した負極板構造を目指すと共に、充放電に際してリ
チウムイオンの拡散速度を速くすることを目指してい
る。さらに、充電終止時の電位（負極単体の電位）が卑
な負極が得られるとしており、エネルギ密度、サイクル
特性、信頼性に優れた非水電解液二次電池を目指してい
る。Therefore, a proposal has been made to use a mixture of graphite and a non-graphitic carbon material as a negative electrode active material (Japanese Patent Application Laid-Open No.
-192724). This technique aims at a negative electrode plate structure filled with a carbon material at a high density, and at the same time, at a high charge / discharge rate of lithium ions. Furthermore, it is stated that a negative electrode having a low potential at the end of charging (potential of the negative electrode alone) can be obtained, and a nonaqueous electrolyte secondary battery excellent in energy density, cycle characteristics, and reliability is aimed at.
【０００６】しかし、上記公開公報が開示する技術は、
黒鉛と非黒鉛炭素材料の混合割合と黒鉛と非黒鉛炭素材
料の粒子径比について、混合割合と粒子径比の最適な組
合せを具体的に示していない。本発明者が確認したとこ
ろでは、黒鉛と非黒鉛炭素材料を単に混合して負極に用
いただけでは、充放電サイクル特性が不十分であった。
充放電サイクルの繰り返しに伴う容量低下の状況を調査
した結果、次のことが明らかとなった。 （１）放電はできるが充電ができないという充電量不
足、すなわち、放電電気量をすべて充電できないという
状況になっている。 （２）しかし、充電した電気量は次の放電で放電できる
という状態で充放電サイクルが繰り返されており、しか
も、電池の内部抵抗、特に負極の抵抗増加を伴ってい
る。このような現象は、次のメカニズムで起こると推測
される。すなわち、黒鉛と非黒鉛炭素材料の混合割合と
黒鉛と非黒鉛炭素材料の粒子径比について、混合割合と
粒子径比の最適な組合せを採用しない限り、黒鉛や非黒
鉛炭素材料粉末の粒子同士のつながりによって形成され
る電子伝導のネットワークがあまり発達しない。特に、
黒鉛が収縮している放電後においては、上記粒子同士の
つながりが切れた箇所が現れ、電子伝導のネットワーク
が部分的に切断される。電子伝導のネットワークが切断
された粒子は、電気的に孤立し、もはや次の充電で反応
に関与しない。その結果、負極の充電利用率が低下し充
電量不足の状態になる。充放電サイクルでこのような状
態がが繰り返されると、負極抵抗の増大と、充電量不足
による容量低下を引き起こす。However, the technology disclosed in the above publication is
With respect to the mixing ratio of graphite and non-graphitic carbon material and the particle size ratio of graphite and non-graphitic carbon material, the optimum combination of the mixing ratio and the particle size ratio is not specifically shown. According to the findings of the present inventors, charge / discharge cycle characteristics were insufficient when a graphite and a non-graphite carbon material were simply mixed and used for a negative electrode.
As a result of investigating the state of capacity reduction due to the repetition of the charge / discharge cycle, the following became clear. (1) There is a shortage of charge amount that discharge is possible but charge is not possible, that is, it is not possible to charge all discharge electricity amounts. (2) However, the charge / discharge cycle is repeated in such a state that the charged amount of electricity can be discharged by the next discharge, and the internal resistance of the battery, particularly, the resistance of the negative electrode is increased. Such a phenomenon is assumed to occur by the following mechanism. That is, regarding the mixing ratio of graphite and non-graphite carbon material and the particle size ratio of graphite and non-graphite carbon material, unless the optimal combination of the mixing ratio and the particle size ratio is adopted, the particles of graphite or non-graphite carbon material powder The electronic conduction network formed by the connection does not develop much. Especially,
After the discharge in which the graphite contracts, a portion where the connection between the particles is broken appears, and the electron conduction network is partially cut. Particles whose electronic conduction network is broken are electrically isolated and no longer participate in the reaction at the next charge. As a result, the charge utilization rate of the negative electrode is reduced, resulting in a state of insufficient charge. When such a state is repeated in the charge / discharge cycle, an increase in the negative electrode resistance and a decrease in the capacity due to an insufficient charge amount are caused.
【０００７】一方、炭素質材料からなる粉末にそれより
粒子径の小さい導電性粉末を混合した負極を用いること
により、サイクル特性の改善を目指した非水溶媒系二次
電池が提案されている（特開平８−３０６３５４公
報）。具体的には、前記公開公報に開示された技術は、
炭素質材料からなる粉末として平均粒径６μｍの非晶質
炭素粉末と粒子径の小さい導電性粉末として平均粒径
０．０４μｍのアセチレンブラックの組合せを示してい
る。この技術においては、炭素質材料からなる粉末粒子
間の空隙を埋める導電剤としての役割を、粒子径の小さ
い導電性粉末に期待している。しかし、粒子径の小さい
導電性粉末を単に炭素質材料粉末に混合するというだけ
では、粒子径の小さい導電性粉末が炭素質材料粉末の粒
子間の空隙（この空隙は電解液が入り込む空隙でもあ
る）を埋め過ぎてしまい、電解液中のリチウムイオンの
拡散を阻害することになる。その結果、拡散過電圧の増
大を伴って容量低下を引き起こすという不都合が生じ
る。このような不都合を避けるために、粒子径の小さい
導電性粉末の混合割合を減らすと、導電剤としての作用
を十分に発揮できないことになる。特に、炭素質材料と
して黒鉛を用いた場合には、粒子径の小さい導電性粉末
が充電・放電時のリチウムの吸蔵・放出に伴う黒鉛の層
間の膨張・収縮に十分追随できない。黒鉛の層間が収縮
している放電後においては、黒鉛粒子や粒子径の小さい
導電性粉末の粒子の間のつながりが切れた箇所が現れ、
電子伝導のネットワークが部分的に切断される。電子伝
導のネットワークが切断された粒子は、電気的に孤立
し、もはや次の充電で反応に関与しない。その結果、負
極の充電利用率が低下し充電量不足の状態になる。充放
電サイクルでこのような状態が繰り返されると、負極抵
抗の増大と、充電量不足による容量低下を引き起こす。
特開平８−３０６３５４号公報に開示された技術の範囲
では、充放電サイクル特性改善が十分達されているとは
いえない。On the other hand, a non-aqueous solvent secondary battery aimed at improving cycle characteristics has been proposed by using a negative electrode in which a conductive powder having a smaller particle diameter is mixed with a powder made of a carbonaceous material (see, for example, Japanese Patent Application Laid-Open No. H10-157,027). JP-A-8-306354). Specifically, the technology disclosed in the above publication is
A combination of an amorphous carbon powder having an average particle diameter of 6 μm as a powder made of a carbonaceous material and acetylene black having an average particle diameter of 0.04 μm as a conductive powder having a small particle diameter is shown. In this technology, a conductive powder having a small particle diameter is expected to play a role as a conductive agent for filling voids between powder particles made of a carbonaceous material. However, simply mixing the conductive powder having a small particle diameter with the carbonaceous material powder causes the conductive powder having a small particle diameter to have a gap between the particles of the carbonaceous material powder (this gap is also a gap into which the electrolytic solution enters). ) Is overfilled, which hinders diffusion of lithium ions in the electrolyte. As a result, there is a disadvantage that the capacity is reduced with an increase in the diffusion overvoltage. If the mixing ratio of the conductive powder having a small particle diameter is reduced in order to avoid such inconvenience, the effect as the conductive agent cannot be sufficiently exhibited. In particular, when graphite is used as the carbonaceous material, the conductive powder having a small particle size cannot sufficiently follow the expansion and contraction between layers of graphite caused by the occlusion and release of lithium during charging and discharging. After the discharge in which the layers of graphite are contracting, a portion where the connection between the graphite particles and the particles of the conductive powder having a small particle size is broken,
The electronic conduction network is partially broken. Particles whose electronic conduction network is broken are electrically isolated and no longer participate in the reaction at the next charge. As a result, the charge utilization rate of the negative electrode is reduced, resulting in a state of insufficient charge. When such a state is repeated in the charge / discharge cycle, an increase in the negative electrode resistance and a decrease in the capacity due to an insufficient charge amount are caused.
In the range of the technology disclosed in JP-A-8-306354, it cannot be said that the charge-discharge cycle characteristics have been sufficiently improved.
【０００８】[0008]
【発明が解決しようとする課題】本発明が解決しようと
する課題は、電子伝導のネットワークが切断されるとい
う負極構造の崩壊と充放電の繰り返しに伴う容量低下を
抑えて、高容量で充放電サイクル特性に優れた非水電解
液二次電池とすることである。SUMMARY OF THE INVENTION An object of the present invention is to provide a high-capacity charge / discharge system which suppresses the collapse of the negative electrode structure, in which the electron conduction network is cut off, and the reduction in capacity due to the repetition of charge / discharge. A non-aqueous electrolyte secondary battery having excellent cycle characteristics is provided.
【０００９】[0009]
【課題を解決するための手段】そこで、本発明に係る非
水電解液二次電池は、リチウムを含む遷移金属複合酸化
物を正極活物質とする正極と、非水電解液と、炭素材料
を負極活物質とする負極を具備した構成において、前記
炭素材料を黒鉛と第一の非黒鉛炭素材料と第二の非黒鉛
炭素材料の混合体とする。前記第一の非黒鉛炭素材料
は、前記黒鉛と第一の非黒鉛炭素材料の合計重量のうち
の４〜４０％を占めるようにし、その平均粒子径は黒鉛
の平均粒子径の０．３〜３倍とする。かつ、前記第二の
非黒鉛炭素材料は、前記黒鉛と第一の非黒鉛炭素材料の
合計重量に対して２０％以下の重量の混合割合とし、そ
の平均粒子径を、前記黒鉛と第一の非黒鉛炭素材料のい
ずれの粒子径よりも小さく、０．１μｍ以下にする。第
二の非黒鉛炭素材料の混合割合は、上記黒鉛と第一の非
黒鉛炭素材料の合計重量に対して０．５％以上の重量と
するのが好ましい。これらの特徴により非水電解液二次
電池の上記課題を達成できる。Accordingly, a nonaqueous electrolyte secondary battery according to the present invention comprises a positive electrode using a transition metal composite oxide containing lithium as a positive electrode active material, a nonaqueous electrolyte, and a carbon material. In a configuration including a negative electrode serving as a negative electrode active material, the carbon material is a mixture of graphite, a first non-graphite carbon material, and a second non-graphite carbon material. The first non-graphite carbon material accounts for 4 to 40% of the total weight of the graphite and the first non-graphite carbon material, and the average particle size is 0.3 to 0.3% of the average particle size of graphite. 3 times. The second non-graphitic carbon material has a mixing ratio of 20% or less by weight to the total weight of the graphite and the first non-graphite carbon material, and the average particle size thereof is equal to the graphite and the first non-graphite carbon material. It is smaller than any particle diameter of the non-graphite carbon material, and is set to 0.1 μm or less. The mixing ratio of the second non-graphite carbon material is preferably 0.5% or more based on the total weight of the graphite and the first non-graphite carbon material. With these features, the above-described problem of the nonaqueous electrolyte secondary battery can be achieved.
【００１０】負極に用いる炭素材料を黒鉛と非黒鉛炭素
材料の混合体とするのは、非黒鉛炭素材料（特に非晶質
炭素）を用いた場合の負極板密度があまり高くならない
という短所を逆に有効利用して、負極板の密度をあまり
高くせずに、電解液が保持される空隙を確保する作用を
発揮させるためである。また、リチウムの吸蔵・放出に
よる体積膨張・収縮が黒鉛よりも小さい第一の非黒鉛炭
素材料を混合することで、負極板全体としての体積膨張
・収縮を低減し、負極構造の崩壊をくい止める作用を発
揮させるためである。The use of a mixture of graphite and a non-graphite carbon material as the carbon material for the negative electrode is contrary to the disadvantage that the non-graphite carbon material (especially amorphous carbon) does not significantly increase the negative electrode plate density. This is because the effect of securing the voids for holding the electrolyte solution is exhibited without increasing the density of the negative electrode plate so much that it is used effectively. In addition, by mixing the first non-graphitic carbon material, whose volume expansion and contraction due to insertion and extraction of lithium is smaller than that of graphite, the volume expansion and contraction of the negative electrode plate as a whole is reduced and the collapse of the negative electrode structure is prevented. It is to exhibit.
【００１１】上記作用を発揮させるためには、黒鉛と第
一の非黒鉛炭素材料の混合体に占める第一の非黒鉛炭素
材料の割合が４重量％以上４０重量％以下でなければな
らない。４重量％未満であれば、負極板密度は黒鉛を活
物質として用いた負極板と同等に高くなる。一方、４０
重量％を越えると、非黒鉛炭素材料は初回充放電のクー
ロン効率が低いという面が顕在化し、十分な電池容量が
得られないという不都合が生じるため好ましくない。さ
らに、第一の非黒鉛炭素材料の平均粒子径が黒鉛の平均
粒子径の０．３倍未満であると、第一の非黒鉛炭素材料
が黒鉛粒子間に詰め込まれて負極板密度が高くなり、電
解液が保持される空間を確保することができなくなる。
一方、３倍を越えると逆に負極板密度が低下しすぎ、負
極活物質の充填量が低下するために電池容量が低下す
る。In order to exert the above-mentioned effects, the proportion of the first non-graphite carbon material in the mixture of graphite and the first non-graphite carbon material must be 4% by weight or more and 40% by weight or less. If it is less than 4% by weight, the density of the negative electrode plate is as high as that of a negative electrode plate using graphite as an active material. On the other hand, 40
If the content is more than 10% by weight, the non-graphite carbon material is not preferable because the coulomb efficiency of the initial charge / discharge becomes low and a problem that a sufficient battery capacity cannot be obtained occurs. Further, when the average particle diameter of the first non-graphite carbon material is less than 0.3 times the average particle diameter of graphite, the first non-graphite carbon material is packed between the graphite particles and the density of the negative electrode plate increases. In addition, a space for holding the electrolyte cannot be secured.
On the other hand, if it exceeds three times, the density of the negative electrode plate will be too low, and the capacity of the negative electrode active material will be low.
【００１２】尚、黒鉛に非黒鉛炭素材料を混合せずに、
負極板成形工程でプレス条件を工夫することにより負極
板密度が高くならないようにすることもできるが、この
ようにして作製した負極板では、黒鉛粒子同士のつなが
りによって形成される電子伝導のネットワークがあまり
発達していないために、特に黒鉛が収縮している放電後
においては、黒鉛粒子同士のつながりが切れた箇所が現
れ、電子伝導のネットワークが部分的に切断される。電
子伝導のネットワークが切断された黒鉛はもはや次の充
電で反応に関与せず、負極板の充電利用率が低下する。
充放電サイクルによりこのような現象が繰り返される
と、負極抵抗の増大と、充電量不足による容量低下をひ
き起こすこととなり所望の効果は得られない。Incidentally, without mixing non-graphite carbon material with graphite,
By devising the pressing conditions in the negative electrode plate forming process, it is possible to prevent the negative electrode plate density from increasing, but in the negative electrode plate manufactured in this way, the electron conduction network formed by the connection of the graphite particles has Since the graphite particles have not developed much, particularly after the discharge in which the graphite is contracted, a portion where the connection between the graphite particles is broken appears, and the electron conduction network is partially cut. The graphite whose electron conduction network has been cut is no longer involved in the reaction in the next charge, and the charge utilization rate of the negative electrode plate is reduced.
When such a phenomenon is repeated by the charge / discharge cycle, an increase in the negative electrode resistance and a decrease in the capacity due to a shortage of the charge amount are caused, and the desired effect cannot be obtained.
【００１３】さらに、平均粒子径が黒鉛と第一の非黒鉛
炭素材料のいずれの粒子径よりも小さく０．１μｍ以下
である第二の非黒鉛炭素材料をも混合するのは、その導
電性と非常に細かい粒子特性を生かし、第二の非黒鉛炭
素材料を黒鉛等の粒子間に適当に回り込ませるためであ
る。第二の非黒鉛炭素材料は、第一の非黒鉛炭素材料と
共に充放電に伴う黒鉛の膨張・収縮に追随する。すなわ
ち、第二の非黒鉛炭素材料の混合によって、黒鉛の膨張
・収縮の緩衝材的作用を付与し、いかなる状態において
も黒鉛や第一の非黒鉛炭素材料の粒子間に電解液が入り
込む隙間を確保しつつ、電子伝導のネットワークを保持
させることができる。第二の非黒鉛炭素材料の混合割合
を黒鉛と第一の非黒鉛炭素材料の合計重量に対して２０
％以下の重量としたのは、２０％を越えると、第二の非
黒鉛炭素材料の非常に細かい粒子特性のために結着性が
急激に低下し、電極に成形できなかったり、集電体に塗
着できなかったり、また、仮に塗着できたとしても、す
ぐに集電体から活物質が剥離してしまうといった物理的
不都合を生じるからである。配合するバインダ（結着
剤）の増量でこのような不都合を回避することはできる
が、バインダには一般に絶縁性の有機物が用いられるた
め、電極の電気抵抗が増大するし、バインダ配合量が増
えた分、活物質比率が減ることになる。バインダ配合量
の増加は、電池容量、エネルギ密度の低下等、デメリッ
トの方が多いので実用的とはいえない。第二の非黒鉛炭
素材料の混合割合を黒鉛と第一の非黒鉛炭素材料の合計
重量に対して０．５％以上の重量にすると、黒鉛や第一
の非黒鉛炭素材料の粒子間に電子伝導のネットワークを
構築する作用、黒鉛の膨張・収縮の緩衝材的作用、電解
液保持材的作用を十二分に発揮させることができる。Furthermore, the mixing of the second non-graphitic carbon material having an average particle size smaller than 0.1 μm or less than the particle size of either graphite or the first non-graphite carbon material is due to its conductivity and This is because the second non-graphite carbon material can be appropriately wrapped between particles of graphite or the like by utilizing the very fine particle characteristics. The second non-graphite carbon material follows the expansion and contraction of graphite accompanying charge and discharge together with the first non-graphite carbon material. That is, by mixing the second non-graphitic carbon material, a buffering effect of the expansion and contraction of graphite is given, and in any state, a gap where the electrolyte enters between the particles of the graphite or the first non-graphite carbon material is formed. The network of electron conduction can be maintained while securing. The mixing ratio of the second non-graphite carbon material is set to 20 with respect to the total weight of graphite and the first non-graphite carbon material.
When the weight exceeds 20%, the binding property sharply decreases due to the very fine particle characteristics of the second non-graphitic carbon material, so that the second non-graphite carbon material cannot be formed into an electrode or has a current collector. This is because physical inconvenience is caused such that the active material cannot be applied to the current collector, or even if the active material can be applied, the active material is immediately separated from the current collector. Such inconvenience can be avoided by increasing the amount of the binder (binder) to be compounded, but since an insulating organic material is generally used for the binder, the electric resistance of the electrode increases, and the amount of the binder increases. Accordingly, the active material ratio is reduced. Increasing the amount of the binder is not practical because there are many disadvantages such as a decrease in battery capacity and energy density. When the mixing ratio of the second non-graphite carbon material is 0.5% or more of the total weight of the graphite and the first non-graphite carbon material, the electron between the particles of the graphite and the first non-graphite carbon material The function of constructing a conduction network, the function of a buffering material for expansion and contraction of graphite, and the function of a material for holding an electrolyte can be sufficiently exhibited.
【００１４】本発明に係る非水電解液二次電池は上記の
ように絶大なる効果が得られるにもかかわらず、負極製
造工程は、従来の非水電解液二次電池の負極製造工程を
大幅に変更することがなく、簡単で安全であることか
ら、工業的利用価値は極めて大きいといえる。Although the non-aqueous electrolyte secondary battery according to the present invention has the above-mentioned great effect, the negative electrode manufacturing process is substantially the same as the conventional non-aqueous electrolyte secondary battery negative electrode manufacturing process. Since it is simple and safe without any change, the value of industrial use is extremely large.
【００１５】[0015]
【発明の実施の形態】正極活物質となるリチウムを含む
遷移金属複合酸化物としてLiCoO2を用い、LiCoO2粉末と
黒鉛粉末（導電剤）とポリフッ化ビニリデン（PVDF，バ
インダ）の混合物にＮ−メチル−２−ピロリドン（分散
媒）を加え、混練混合してスラリを調製する。このスラ
リを正極集電体となるアルミニウム箔に塗着、乾燥、プ
レスの工程後、裁断し帯状の正極板とする。負極活物質
となる炭素材料として黒鉛と第一の非黒鉛炭素材料であ
る非晶質炭素と第二の非黒鉛炭素材料であるカーボンブ
ラックを用い、黒鉛と非晶質炭素とカーボンブラックと
PVDFの混合物にＮ−メチル−２−ピロリドンを加え、混
練混合してスラリを調製する。このスラリを負極集電体
となる銅箔に塗着、乾燥、プレス、裁断し帯状の負極板
とする。カーボンブラックは、一般に吸油量の大きい炭
素材として知られており、負極の電解液保持材としての
働きもあるので、リチウムイオンの拡散性の向上に有利
である。カーボンブラックは、アセチレンブラックやケ
ッチェンブラック等である。BEST MODE FOR CARRYING OUT THE INVENTION LiCoO 2 is used as a transition metal composite oxide containing lithium as a positive electrode active material, and a mixture of LiCoO 2 powder, graphite powder (conductive agent) and polyvinylidene fluoride (PVDF, binder) is mixed with N- A slurry is prepared by adding methyl-2-pyrrolidone (dispersion medium), kneading and mixing. The slurry is applied to an aluminum foil serving as a positive electrode current collector, dried and pressed, and then cut to obtain a belt-shaped positive electrode plate. Graphite, amorphous carbon, which is a first non-graphite carbon material, and carbon black, which is a second non-graphite carbon material, are used as a carbon material to be a negative electrode active material.
N-methyl-2-pyrrolidone is added to the PVDF mixture, and the mixture is kneaded and mixed to prepare a slurry. The slurry is applied to a copper foil serving as a negative electrode current collector, dried, pressed, and cut into a strip-shaped negative electrode plate. Carbon black is generally known as a carbon material having a large oil absorption, and also has a function as a material for holding an electrolytic solution of a negative electrode, and thus is advantageous in improving the diffusibility of lithium ions. The carbon black is acetylene black, Ketjen black, or the like.
【００１６】得られた帯状の正極板と負極板を、帯状の
セパレータを介して重ね、捲回する。できあがった捲回
電極体は円筒状の電池缶に入れ、電解液注入後、上蓋を
取付け、封口して本発明に係る電池が得られる。電解液
は、炭酸エチレンと炭酸ジメチルと炭酸ジエチルの混合
溶媒にLiPF6を１ｍｏｌ／ｌ溶解したものであり、前記
各溶媒の混合比は体積にして３０：５０：２０である。
組立てた電池は充電、放電を繰り返し、所期のサイクル
容量低下のないことを確認する。The obtained strip-shaped positive and negative plates are stacked and wound with a strip-shaped separator interposed therebetween. The completed wound electrode body is placed in a cylindrical battery can, and after injecting the electrolytic solution, the upper lid is attached and sealed to obtain the battery according to the present invention. The electrolytic solution is obtained by dissolving 1 mol / l of LiPF 6 in a mixed solvent of ethylene carbonate, dimethyl carbonate and diethyl carbonate, and the mixing ratio of the above solvents is 30:50:20 by volume.
The assembled battery is repeatedly charged and discharged to confirm that the expected cycle capacity does not decrease.
【００１７】[0017]
比較例ａ、実施例ａ〜ｅ、比較例ｂ 図１は、本発明を実施した円筒形リチウム二次電池の断
面図である。１は正極集電体で、厚さ２０μｍのアルミ
ニウム箔である。平面サイズは５０mm×４５０mmであ
る。２は正極集電体１に保持させた正極活物質層で、リ
チウムイオンを電極反応種とし充電・放電に伴いリチウ
ムイオンを放出・吸蔵する正極活物質LiCoO2と黒鉛（導
電助剤）とPVDF（バインダ）と電解液とから構成され
る。正極活物質層２の詳細な作製方法を記す。LiCoO
2(平均粒径約１〜２μｍ）と黒鉛（平均粒径約０．５μ
ｍ）とPVDFを重量比で８０：１０：１０に十分混合し、
そこへＮ−メチル−２−ピロリドンを適量加え、十分に
混練混合しスラリにする。このスラリをロールtoロール
の転写により正極集電体１の両面に同じ厚さで塗着、乾
燥した後、プレスにより所定の極板厚さになるまで圧縮
し、正極活物質層２を得る（但し、この段階では電解液
は入っていない）。正極活物質層２の厚さは正極集電体
１の両面共各々７４〜８４μｍである。Comparative Example a, Examples a to e, and Comparative Example b FIG. 1 is a cross-sectional view of a cylindrical lithium secondary battery embodying the present invention. Reference numeral 1 denotes a positive electrode current collector, which is an aluminum foil having a thickness of 20 μm. The plane size is 50 mm × 450 mm. Reference numeral 2 denotes a positive electrode active material layer held on the positive electrode current collector 1, a positive electrode active material LiCoO 2 that uses lithium ions as an electrode reactive species to release and occlude lithium ions during charge and discharge, graphite (a conductive auxiliary), and PVDF. (Binder) and an electrolytic solution. A detailed manufacturing method of the positive electrode active material layer 2 will be described. LiCoO
2 (average particle size of about 1 to 2 μm) and graphite (average particle size of about 0.5 μm)
m) and PVDF are sufficiently mixed in a weight ratio of 80:10:10,
An appropriate amount of N-methyl-2-pyrrolidone is added thereto, and the mixture is sufficiently kneaded and mixed to form a slurry. This slurry is applied to both surfaces of the positive electrode current collector 1 with the same thickness by roll-to-roll transfer, dried, and then compressed by pressing to a predetermined electrode plate thickness to obtain the positive electrode active material layer 2 ( However, no electrolyte is contained at this stage). The thickness of the positive electrode active material layer 2 is 74 to 84 μm on both sides of the positive electrode current collector 1.
【００１８】３は負極集電体で、厚さ１０μｍの銅箔で
ある。平面サイズは５０mm×４９０mmである。４は負極
集電体３に保持させた負極活物質層で、リチウムイオン
を電極反応種とし充電・放電に伴いリチウムイオンを吸
蔵・放出する負極活物（黒鉛と第一の非黒鉛炭素材料で
ある非晶質炭素と第二の非黒鉛炭素材料であるアセチレ
ンブラックの混合体）とPVDF（バインダ）と電解液とか
ら構成される。負極活物質層４の詳細な作製方法を記
す。平均粒径１５μｍの黒鉛と平均粒径２３μｍの非晶
質炭素（平均粒径は黒鉛の１．５倍）と平均粒径４０nm
のアセチレンブラック（電気化学工業製「デンカブラッ
ク」粉状品）を、表１に示すように混合する。すなわ
ち、黒鉛と第一の非黒鉛炭素材料である非晶質炭素（表
中では「第一」と表示）は、重量比で９８：２〜５０：
５０の範囲で混合する。第二の非黒鉛炭素材料であるア
セチレンブラック（表中では「第二」と表示）は、黒鉛
と非晶質炭素の合計重量に対し５％混合する。さらに、
前記混合体とPVDFを重量比で９０：１０となるように混
合し、そこへＮ−メチル−２−ピロリドンを適量加え、
十分に混練混合しスラリにする。このスラリをロールto
ロールの転写により負極集電体３の両面に同じ厚さで塗
着、乾燥した後、プレスにより所定の極板厚さになるま
で圧縮し、負極活物質層４を得る（但し、この段階では
電解液は入っていない）。負極活物質層４の厚さは負極
集電体３の両面共各々７６〜８６μｍである。このとき
の負極活物質層の密度は、表１に示すように、約１．３
〜１．４５ｇ／cm3である。Reference numeral 3 denotes a negative electrode current collector, which is a copper foil having a thickness of 10 μm. The plane size is 50 mm × 490 mm. Reference numeral 4 denotes a negative electrode active material layer held on the negative electrode current collector 3. The negative electrode active material (a graphite and a first non-graphitic carbon material, which uses lithium ions as an electrode reactive species and stores and releases lithium ions during charge and discharge. A mixture of certain amorphous carbon and acetylene black as a second non-graphite carbon material), PVDF (binder), and electrolyte. A detailed method for forming the negative electrode active material layer 4 will be described. Graphite having an average particle size of 15 μm, amorphous carbon having an average particle size of 23 μm (the average particle size is 1.5 times that of graphite), and an average particle size of 40 nm
Of acetylene black ("Denka Black" powder product manufactured by Denki Kagaku Kogyo) is mixed as shown in Table 1. That is, graphite and amorphous carbon (indicated as “first” in the table) as the first non-graphite carbon material are in a weight ratio of 98: 2 to 50:
Mix in the range of 50. Acetylene black (designated as "second" in the table), which is a second non-graphite carbon material, is mixed at 5% with respect to the total weight of graphite and amorphous carbon. further,
The mixture and PVDF were mixed at a weight ratio of 90:10, and an appropriate amount of N-methyl-2-pyrrolidone was added thereto.
Mix well and make a slurry. Roll this slurry to
After applying the same thickness to both surfaces of the negative electrode current collector 3 by transfer of a roll and drying, the resultant is compressed to a predetermined electrode plate thickness by pressing to obtain the negative electrode active material layer 4 (however, at this stage, There is no electrolyte). The thickness of the negative electrode active material layer 4 is 76 to 86 μm on both sides of the negative electrode current collector 3. At this time, the density of the negative electrode active material layer was about 1.3 as shown in Table 1.
１1.45 g / cm 3 .
【００１９】５は帯状のセパレータで、厚さ２５μｍの
微多孔性のポリエチレンフィルムである。帯状の正極板
と負極板を、セパレータ５を介し重ね、捲回する。でき
あがった捲回電極体を円筒状の電池缶６に挿入する。そ
して、負極集電体に予め溶接しておいたタブ端子を電池
缶６の底部に溶接する。Reference numeral 5 denotes a strip-shaped separator, which is a microporous polyethylene film having a thickness of 25 μm. A strip-shaped positive electrode plate and a negative electrode plate are stacked with a separator 5 interposed therebetween and wound. The completed wound electrode body is inserted into a cylindrical battery can 6. Then, the tab terminal welded in advance to the negative electrode current collector is welded to the bottom of the battery can 6.
【００２０】正極活物質層と負極活物質層の厚さの和は
３２０μｍとした。３２０μｍを越えると、捲回電極体
の直径が電池缶６の内径よりも大きくなって、捲回電極
体を電池缶６に挿入できない。３２０μｍ未満であれ
ば、逆に捲回電極体の直径が電池缶６の内径よりも小さ
くなって、電池としての容量が十分得られないからであ
る。また、正極活物質の初回充電容量を１４５ｍAh／
ｇ、負極活物質の初回充電容量を黒鉛、非晶質炭素共に
３６０ｍAh／ｇとして、初回充電容量が同じになるよう
に正極、負極活物質量を決定した。このバランスが崩
れ、例えば正極活物質量よりも負極活物質量が多けれ
ば、負極での不可逆容量が大きくなって、容量が低くな
るし、逆に負極活物質量よりも正極活物質量が多けれ
ば、負極活物質のリチウム吸蔵能力以上のリチウムが正
極活物質から供給されるため、初回の充電で、負極活物
質や負極集電体表面でリチウムが析出するという問題が
生じる。The sum of the thicknesses of the positive electrode active material layer and the negative electrode active material layer was 320 μm. If it exceeds 320 μm, the diameter of the wound electrode body becomes larger than the inner diameter of the battery can 6, and the wound electrode body cannot be inserted into the battery can 6. If the diameter is less than 320 μm, the diameter of the wound electrode body is smaller than the inner diameter of the battery can 6, and a sufficient capacity as a battery cannot be obtained. Also, the initial charge capacity of the positive electrode active material was 145 mAh /
g, the initial charge capacity of the negative electrode active material was set to 360 mAh / g for both graphite and amorphous carbon, and the amounts of the positive electrode and the negative electrode active material were determined so that the initial charge capacity was the same. If this balance is lost, for example, if the amount of the negative electrode active material is larger than the amount of the positive electrode active material, the irreversible capacity at the negative electrode becomes larger, the capacity becomes lower, and conversely, the amount of the positive electrode active material becomes larger than the amount of the negative electrode active material. For example, since lithium more than the lithium storage capacity of the negative electrode active material is supplied from the positive electrode active material, there is a problem that lithium is deposited on the surface of the negative electrode active material or the negative electrode current collector during the first charging.
【００２１】７は正極キャップで、８は正極タブ端子で
ある。正極タブ端子８は予め正極集電体１に溶接してお
き、正極キャップ７に溶接する。次に、電解液５mlを電
池缶６内に注入する。電解液は、炭酸エチレンと炭酸ジ
メチルと炭酸ジエチルの混合溶媒にLiPF6を１ｍｏｌ／
ｌ溶解したものであり、前記各溶媒の混合比は体積にし
て３０：５０：２０である。９は絶縁性のガスケットで
ある。正極キャップ７を電池缶上部に配置し、ガスケッ
ト９を介して電池缶上部をかしめ、電池を密閉する。Reference numeral 7 denotes a positive electrode cap, and 8 denotes a positive electrode tab terminal. The positive electrode tab terminal 8 is welded to the positive electrode current collector 1 in advance, and then welded to the positive electrode cap 7. Next, 5 ml of the electrolytic solution is injected into the battery can 6. The electrolytic solution was a mixture of ethylene carbonate, dimethyl carbonate, and diethyl carbonate in which LiPF 6 was 1 mol / mol.
1 dissolved, and the mixing ratio of each solvent is 30:50:20 by volume. 9 is an insulating gasket. The positive electrode cap 7 is arranged on the upper part of the battery can, and the upper part of the battery can is caulked via the gasket 9 to seal the battery.
【００２２】ここで、正極キャップ７内には、電池内圧
の上昇に応じて作動する電流遮断機構（圧力スイッチ）
と前記電流遮断機構が作動する圧力よりも高い圧力に応
じて開放作動する弁機構が組み込まれている。このよう
にして、電池を完成した。Here, in the positive electrode cap 7, a current cut-off mechanism (pressure switch) that operates in response to an increase in battery internal pressure.
And a valve mechanism that opens in response to a pressure higher than the pressure at which the current cutoff mechanism operates. Thus, the battery was completed.
【００２３】[0023]
【表１】 [Table 1]
【００２４】比較例ｃ、実施例ｆ〜ｋ、比較例ｄ 負極活物質となる黒鉛と非晶質炭素とを重量比で８０：
２０、アセチレンブラックを黒鉛と非晶質炭素の合計重
量に対し５％となるように混合し、上記実施例ｃと同様
に電極、電池を作製した。各例で黒鉛の平均粒径を１５
μｍとし、非晶質炭素の平均粒径を各例で３〜６０μｍ
の範囲から選択して、表２に示すように、非晶質炭素
（表中では「第一」と表示）の平均粒径を黒鉛の０．２
〜４倍の範囲で変化させた。このときの負極活物質密度
は、表２に示すように、約１．３４〜１．４４ｇ／cm3
である。尚、アセチレンブラックは、表中では「第二」
と表示した。Comparative Example c, Examples f to k, and Comparative Example d A weight ratio of graphite and amorphous carbon as the negative electrode active material was 80:
20, acetylene black was mixed at 5% with respect to the total weight of graphite and amorphous carbon, and an electrode and a battery were produced in the same manner as in Example c. In each case, the average particle size of graphite was 15
μm, and the average particle size of the amorphous carbon is 3 to 60 μm in each example.
And the average particle size of the amorphous carbon (indicated as “first” in the table) is 0.2% as shown in Table 2.
It was changed in a range of ４4 times. As shown in Table 2, the negative electrode active material density at this time was about 1.34 to 1.44 g / cm 3.
It is. In addition, acetylene black is "second" in the table.
Displayed.
【００２５】[0025]
【表２】 [Table 2]
【００２６】実施例ｍ〜ｒ、比較例ｅ 負極活物質となる黒鉛と非晶質炭素とを重量比で８０：
２０、アセチレンブラックを黒鉛と非晶質炭素の合計重
量に対し０．１〜２５％の範囲から選択して混合し、上
記実施例ｃと同様に電極、電池を作製した。負極と正極
の仕様を表３に示す。表中では、非晶質炭素を「第
一」、アセチレンブラックを「第二」と表示した。Examples m to r, Comparative Example e Graphite as the negative electrode active material and amorphous carbon were mixed in a weight ratio of 80:
20, acetylene black was selected and mixed in the range of 0.1 to 25% based on the total weight of graphite and amorphous carbon, and an electrode and a battery were produced in the same manner as in Example c. Table 3 shows the specifications of the negative electrode and the positive electrode. In the table, amorphous carbon is indicated as "first" and acetylene black is indicated as "second".
【００２７】[0027]
【表３】 [Table 3]
【００２８】従来例１〜４ 従来例１として、負極活物質に黒鉛を用い、非晶質炭素
とアセチレンブラックは混合しない負極板とし、他は上
記実施例と同様に電池を作製した。従来例１の負極活物
質層の密度は１．５ｇ／cm3である。また、従来例２と
して負極活物質層の密度を１．４ｇ／cm3とした以外は
前記従来例１と同様に電池を作製した。従来例３，４と
して、負極活物質に黒鉛とアセチレンブラックを用い、
非晶質炭素は混合しない負極板とし、他は上記実施例と
同様に電池を作製した。従来例３の負極活物質層の密度
は１．４６ｇ／cm3である。また、従来例４の負極活物
質層の密度は１．４４ｇ／cm3である。各従来例の負極
と正極の仕様を表４に示す。Conventional Examples 1 to 4 As Conventional Example 1, a battery was produced in the same manner as in the above Examples, except that graphite was used as the negative electrode active material and amorphous carbon and acetylene black were not mixed. The density of the negative electrode active material layer of Conventional Example 1 is 1.5 g / cm 3 . A battery was fabricated in the same manner as in Conventional Example 1 except that the density of the negative electrode active material layer was changed to 1.4 g / cm 3 . As Conventional Examples 3 and 4, graphite and acetylene black were used for the negative electrode active material,
A battery was produced in the same manner as in the above example except that a negative electrode plate containing no amorphous carbon was used. The density of the negative electrode active material layer of Conventional Example 3 is 1.46 g / cm 3 . Further, the density of the negative electrode active material layer of Conventional Example 4 was 1.44 g / cm 3 . Table 4 shows the specifications of the negative electrode and the positive electrode of each conventional example.
【００２９】[0029]
【表４】 [Table 4]
【００３０】実施例ａ〜ｒ、比較例ａ〜ｅにおいて負極
活物質層の密度は、プレスによって可能な最大値であ
る。各例で負極活物質層の密度が異なるのは、炭素材混
合体中の非晶質炭素の混合割合の違い、アセチレンブラ
ックの混合割合の違い、黒鉛と非晶質炭素の粒径比の違
いによって、プレスで可能な最大値が異なるためであ
る。これ以上プレスすると負極活物質層の密度は大きく
なることなく、負極板が負極集電体と共に圧延されるだ
けで、負極板の幅、長さ共に大きくなるといった寸法変
化が生じてしまう。実施例ａ〜ｒ、比較例ａ〜ｅにおい
て負極活物質層の厚さ、正極活物質層の厚さが異なるの
は、正極活物質の初回充電容量を１４５ｍAh／ｇ、負極
活物質の初回充電容量を黒鉛、非晶質炭素共に３６０ｍ
Ah／ｇとして、初回充電容量が同じになるように正極、
負極活物質量を決定したからである。実施例ａ〜ｒ、比
較例ａ〜ｅにおいて正極活物質層の密度３．５ｇ／cm3
は、プレスによって可能な最大値である。これ以上プレ
スすると正極活物質層の密度は大きくなることなく、正
極板が正極集電体と共に圧延されるだけで、正極板の
幅、長さ共に大きくなるといった寸法変化が生じてしま
う。比較例ｅでは、負極を形成することができなかっ
た。これは、アセチレンブラックの非常に微細な粒子特
性（平均粒径０．１μｍ以下）のために、アセチレンブ
ラックの混合割合が多くなると負極活物質層の粘着性が
急激に低下したことに起因している。In Examples a to r and Comparative examples a to e, the density of the negative electrode active material layer is the maximum value possible by pressing. The difference in the density of the negative electrode active material layer in each example is due to the difference in the mixing ratio of amorphous carbon in the carbon material mixture, the difference in the mixing ratio of acetylene black, and the difference in the particle size ratio of graphite and amorphous carbon. This is because the maximum value possible in the press differs depending on the type of press. If the pressing is carried out further, the dimensional change such that both the width and the length of the negative electrode plate are increased only by rolling the negative electrode plate together with the negative electrode current collector without increasing the density of the negative electrode active material layer. The difference in the thickness of the negative electrode active material layer and the thickness of the positive electrode active material layer in Examples a to r and Comparative examples a to e is that the initial charge capacity of the positive electrode active material is 145 mAh / g, and the first charge of the negative electrode active material is The capacity is 360m for both graphite and amorphous carbon.
Ah / g, positive electrode so that initial charge capacity is the same,
This is because the amount of the negative electrode active material was determined. In Examples a to r and Comparative examples a to e, the density of the positive electrode active material layer was 3.5 g / cm 3.
Is the maximum value possible with the press. If the pressing is carried out further, the density of the positive electrode active material layer does not increase, and only the positive electrode plate is rolled together with the positive electrode current collector, and a dimensional change occurs such that both the width and the length of the positive electrode plate increase. In Comparative Example e, a negative electrode could not be formed. This is because, due to the very fine particle characteristics (average particle size of 0.1 μm or less) of acetylene black, when the mixing ratio of acetylene black increases, the adhesiveness of the negative electrode active material layer sharply decreases. I have.
【００３１】上記各例の電池を充放電し、容量確認と充
放電サイクルの進行に伴う容量保持率を調べた。充放電
条件は以下の通りである。 充電：４．１５Ｖ定電圧，制限電流１Ａ，３時間，２５
℃ 放電：１Ａ定電流，終止電圧２．５Ｖ，２５℃ 図２に、比較例ａ、実施例ａ〜ｅ、比較例ｂの電池およ
び従来例１、従来例２の電池について、黒鉛と非晶質炭
素（第一の非黒鉛炭素材料）の合計重量に対する非晶質
炭素の混合量と初回放電容量の関係を示す。比較例ａ、
実施例ａ〜ｅ、比較例ｂの電池では、非晶質炭素混合量
が増えるに従って初回放電容量が直線的に低下してい
る。これは、非晶質炭素の混合量が増えると負極活物質
層の密度が低下することに起因している。非晶質炭素混
合量が４０重量％を越えると、この直線からずれ、初回
放電容量の低下が大きくなる。これは、非晶質炭素混合
量が４０重量％を越えると、負極活物質層の密度が大き
く低下することに起因している。非晶質炭素を混合しな
い従来例１の電池では初回の放電容量は１４２７ｍAhと
大きな値を示したのに対し、従来例２の電池では１３８
０ｍAhと低くなった。これは、従来例１の電池では負極
活物質層の上限密度が１．５ｇ／cm3であったために負
極活物質の充填量が多く、一方、従来例２の電池では負
極活物質層の密度を意図的に１．４ｇ／cm3としたので
負極活物質の充填量が少ないためである。The batteries of each of the above examples were charged and discharged, and the capacity was confirmed and the capacity retention with the progress of the charge and discharge cycle was examined. The charge and discharge conditions are as follows. Charge: 4.15V constant voltage, limited current 1A, 3 hours, 25
2 C. Discharge: 1 A constant current, cut-off voltage 2.5 V, 25 ° C. FIG. 2 shows graphite and amorphous materials for the batteries of Comparative Example a, Examples a to e, Comparative Example b and Conventional Examples 1 and 2. 4 shows the relationship between the mixed amount of amorphous carbon and the initial discharge capacity with respect to the total weight of porous carbon (first non-graphite carbon material). Comparative Example a,
In the batteries of Examples a to e and Comparative example b, the initial discharge capacity decreases linearly as the amount of mixed amorphous carbon increases. This is because the density of the negative electrode active material layer decreases as the amount of mixed amorphous carbon increases. If the amount of the amorphous carbon exceeds 40% by weight, it deviates from this straight line, and the initial discharge capacity is greatly reduced. This is because the density of the negative electrode active material layer is significantly reduced when the amount of the amorphous carbon exceeds 40% by weight. In the battery of Conventional Example 1 in which amorphous carbon was not mixed, the initial discharge capacity showed a large value of 1,427 mAh, whereas in the battery of Conventional Example 2, it was 138.
It became as low as 0 mAh. This is because the battery of Conventional Example 1 had a large amount of the negative electrode active material because the upper limit density of the negative electrode active material layer was 1.5 g / cm 3 , while the battery of Conventional Example 2 had a high density of the negative electrode active material layer. Is intentionally set to 1.4 g / cm 3 , so that the filling amount of the negative electrode active material is small.
【００３２】図３に、比較例ａ、実施例ａ〜ｅ、比較例
ｂの電池および従来例１、従来例２の電池について、充
放電サイクルを繰り返した時の放電容量の推移を示す。
比較例ａおよび従来例１、従来例２の電池では充放電サ
イクルの繰り返しに伴う放電容量低下が大きいのに対し
て、実施例ａ〜ｅ、比較例ｂの電池では良好なサイクル
特性を示している。比較例ａおよび従来例１の電池にお
いて放電容量低下が大きいのは、電池の負極活物質層の
密度が高いために、高密度充填された負極板構造では非
水電解液が保持されるべき空間が少なく、充放電反応時
のリチウムの拡散が阻まれ、過電圧が増大、負極電位が
リチウムの酸化還元電位よりも卑となり、黒鉛や負極集
電体表面で充放電可逆性に乏しいリチウムが析出するこ
とが原因と考えられる。従来例２の電池において負極活
物質層の密度を１．４ｇ／cm3と意図的に低く抑えてあ
るにもかかわらず放電容量低下が大きいのは、次のよう
な現象が起こっているからと考えられる。すなわち、意
図的に負極活物質層の密度を低く抑えたことによって、
黒鉛粒子同士のつながりによって形成される電子伝導の
ネットワークがあまり発達していないために、特に黒鉛
が収縮している放電後においては、黒鉛粒子同士のつな
がりが切れた箇所が現れ、電子伝導のネットワークが部
分的に切断される。電子伝導のネットワークが切断され
た黒鉛はもはや次の充電で反応に関与せず、負極の充電
利用率が低下し、充放電サイクルによりこのような現象
が繰り返されると、負極抵抗の増大を伴って容量低下を
ひき起こす。FIG. 3 shows the transition of the discharge capacity when the charge / discharge cycle is repeated for the batteries of Comparative Example a, Examples a to e, Comparative Example b, and the batteries of Conventional Example 1 and Conventional Example 2.
The batteries of Comparative Example a, Conventional Example 1, and Conventional Example 2 showed a large decrease in discharge capacity due to repetition of the charge / discharge cycle, whereas the batteries of Examples a to e and Comparative Example b showed good cycle characteristics. I have. The large decrease in the discharge capacity in the batteries of Comparative Example a and Conventional Example 1 is due to the high density of the negative electrode active material layer of the battery, and the space in which the nonaqueous electrolyte should be held in the densely packed negative electrode plate structure And diffusion of lithium during charge / discharge reaction is prevented, overvoltage increases, the negative electrode potential becomes lower than the oxidation-reduction potential of lithium, and lithium with poor charge / discharge reversibility precipitates on the graphite or negative electrode current collector surface This is probably the cause. Although the density of the negative electrode active material layer in the battery of Conventional Example 2 was intentionally kept low at 1.4 g / cm 3 , the decrease in discharge capacity was large because the following phenomenon occurred. Conceivable. That is, by intentionally keeping the density of the negative electrode active material layer low,
Since the electron conduction network formed by the connection between the graphite particles has not developed much, especially after the discharge in which the graphite is contracted, a portion where the connection between the graphite particles is broken appears, and the electron conduction network appears. Is partially cut. The graphite whose electron conduction network has been cut is no longer involved in the reaction at the next charge, the charge utilization of the negative electrode decreases, and when such a phenomenon is repeated by the charge and discharge cycle, the negative electrode resistance is increased. Causes capacity reduction.
【００３３】以上の実施例、比較例、従来例の結果か
ら、負極板の黒鉛と非晶質炭素（第一の非黒鉛炭素材
料）の合計重量に対する非晶質炭素の混合割合は、４重
量％以上４０重量％以下でなければならないことが理解
できる。４重量％未満であれば、第一の非黒鉛炭素材料
（特に非晶質炭素）を用いた場合に負極板密度があまり
高くならないという短所を逆に有効利用することができ
なくなり、負極板密度は黒鉛だけを活物質として用いた
場合と同等に高くなる。すなわち、電解液が保持される
空隙を確保しにくくなる。第一の非黒鉛炭素材料が４０
重量％を越えると、初回充放電のクーロン効率が低いこ
とと負極抵抗の増大が原因で、十分な電池容量が得られ
ないという不都合が生じるため好ましくないことが明ら
かとなった。From the results of the above Examples, Comparative Examples and Conventional Examples, the mixing ratio of amorphous carbon to the total weight of graphite and amorphous carbon (first non-graphite carbon material) of the negative electrode plate was 4% by weight. It should be understood that it must be not less than 40% by weight and not more than 40% by weight. If the amount is less than 4% by weight, the disadvantage that the negative electrode plate density does not increase so much when the first non-graphitic carbon material (especially amorphous carbon) is used cannot be effectively utilized. Is as high as when only graphite is used as the active material. That is, it is difficult to secure a space for holding the electrolytic solution. The first non-graphitic carbon material is 40
When the amount exceeds 10% by weight, it becomes clear that the disadvantage is that a sufficient battery capacity cannot be obtained due to a low Coulomb efficiency of the initial charge and discharge and an increase in the negative electrode resistance.
【００３４】図４に、比較例ｃ、実施例ｆ〜ｋ、比較例
ｄの電池について、黒鉛の平均粒子径に対する非晶質炭
素（第一の非黒鉛炭素材料）の平均粒子径の比（粒径
比）と初回放電容量の関係を示す。粒径比が大きくなる
につれて緩やかな下に凸の形状を示しながら初回放電容
量が低下していく。ところが、粒径比が３を越えると初
回放電容量の低下が大きくなる。これは、粒径比が３を
越えると、すなわち、黒鉛に対して非晶質炭素の平均粒
径が大きすぎると負極活物質層の密度の低下も大きくな
り、負極活物質の充填量が少なくなったためである。FIG. 4 shows the ratio of the average particle diameter of amorphous carbon (first non-graphite carbon material) to the average particle diameter of graphite (b) for the batteries of Comparative Example c, Examples f to k, and Comparative Example d. The relationship between the particle size ratio) and the initial discharge capacity is shown. As the particle size ratio increases, the initial discharge capacity decreases while showing a gentle downward convex shape. However, when the particle size ratio exceeds 3, the initial discharge capacity is greatly reduced. This is because when the particle size ratio exceeds 3, that is, when the average particle size of the amorphous carbon is too large with respect to graphite, the density of the negative electrode active material layer is greatly reduced, and the filling amount of the negative electrode active material is small. Because it became.
【００３５】図５に、比較例ｃ、実施例ｆ〜ｋ、比較例
ｄの電池について、充放電サイクルを繰り返した時の放
電容量推移を示す。比較例ｃの電池では充放電サイクル
を繰り返しに伴う放電容量低下が大きいのに対して、実
施例ｆ〜ｋ、比較例ｄの電池では良好なサイクル特性を
示している。比較例ｃの電池において放電容量低下が大
きいのは、負極活物質層の密度が高いために、高密度充
填された負極板構造では非水電解液が保持されるべき空
間が少なく、充放電反応時のリチウムの拡散が阻まれ、
過電圧が増大、負極電位がリチウムの酸化還元電位より
も卑となり、黒鉛や負極集電体表面で充放電可逆性に乏
しいリチウムが析出することが原因と考えられる。FIG. 5 shows a change in the discharge capacity of the batteries of Comparative Example c, Examples f to k, and Comparative Example d when the charge / discharge cycle was repeated. The battery of Comparative Example c shows a large decrease in discharge capacity due to repeated charge / discharge cycles, whereas the batteries of Examples f to k and Comparative Example d show good cycle characteristics. The large decrease in the discharge capacity of the battery of Comparative Example c is because the density of the negative electrode active material layer is high, and the negative electrode plate structure densely packed has a small space for holding the nonaqueous electrolyte, and the charge / discharge reaction The diffusion of lithium at the time is prevented,
It is considered that the overvoltage is increased, the negative electrode potential becomes lower than the oxidation-reduction potential of lithium, and lithium having poor charge / discharge reversibility is deposited on graphite or on the surface of the negative electrode current collector.
【００３６】以上の実施例、比較例の結果から、非黒鉛
炭素材料（第一の非黒鉛炭素材料）の平均粒子径は黒鉛
の平均粒子径の０．３〜３倍であることが好ましいこと
が判る。非黒鉛炭素材料（第一の非黒鉛炭素材料）の平
均粒子径が黒鉛の平均粒子径の０．３倍未満であると、
非黒鉛炭素材（第一の非黒鉛炭素材料）粒子が黒鉛粒子
間に詰め込まれ、負極板密度が高くなり、電解液が保持
される空隙を確保することができず、課題を達成できな
いし、３倍を越えると逆に負極板密度が低下しすぎ、負
極活物質の充填量が低下するために電池容量が低下する
ことが明らかとなった。From the results of the above Examples and Comparative Examples, it is preferable that the average particle size of the non-graphite carbon material (first non-graphite carbon material) is 0.3 to 3 times the average particle size of graphite. I understand. When the average particle size of the non-graphite carbon material (first non-graphite carbon material) is less than 0.3 times the average particle size of graphite,
Non-graphite carbon material (first non-graphite carbon material) particles are packed between the graphite particles, the density of the negative electrode plate increases, it is not possible to secure a space for holding the electrolyte, and the problem cannot be achieved. On the other hand, when the ratio is more than three times, the density of the negative electrode plate is too low, and it is clear that the capacity of the negative electrode active material is low and the battery capacity is low.
【００３７】図６に、実施例ｍ〜ｒ、従来例３、従来例
４の電池について、充放電サイクルを繰り返した時の放
電容量推移を示す。従来例３、従来例４の電池では、充
放電サイクルの繰り返しに伴う放電容量の低下が大きい
のに対し、実施例ｍ〜ｒの電池では、良好な充放電サイ
クル特性を示している。就中、アセチレンブラック（第
二の非黒鉛炭素材料）の混合割合を黒鉛と非晶質炭素
（第一の非黒鉛炭素材料）の合計重量に対して０．５％
以上とした実施例ｎ〜ｒの電池では、極めて良好な充放
電サイクル特性を示している。導電性と非常に細かい粒
子特性を生かして、黒鉛等の粒子間に適当に回り込ませ
たアセチレンブラック（第二の非黒鉛炭素材料）が、充
放電に伴う黒鉛の膨張・収縮に追随して黒鉛の膨張・収
縮の緩衝材的な作用をし、また、いかなる状態において
も黒鉛や第一の非黒鉛炭素材料の粒子間に電解液が入り
込む間隙を確保しつつ、電子伝導のネットワークを保持
する作用をしている。以上の実施結果から、アセチレン
ブラック（第二の非黒鉛炭素材料）の混合割合は、黒鉛
と第一の非黒鉛炭素材料の合計重量に対して２０％以下
であり、好ましくは０．５％以上である。従来例３にお
いて放電容量低下が大きいのは、負極活物質層の炭素材
中に非晶質炭素（第一の非黒鉛炭素材料）が混合されて
おらず、微細なアセチレンブラック（第二の非黒鉛炭素
材料）の少量混合だけでは、充放電による黒鉛の膨張・
収縮に追随できないからである。特に、黒鉛が収縮して
いる放電後においては、黒鉛粒子や、アセチレンブラッ
ク同士のつながりが切れた箇所が現れ、電子伝導のネッ
トワークが部分的に切断される。電子伝導のネットワー
クが切断された粒子は電気的に孤立し、もはや次の充電
で反応に関与せず、負極の充電利用率が低下する。充放
電サイクルによりこのような現象が繰り返されると、負
極抵抗の増大と、充電量不足による容量低下をひき起こ
す。従来例４において放電容量の低下が大きいのは、負
極活物質の炭素材中に非晶質炭素（第一の非黒鉛炭素材
料）が混合されておらず、微細なアセチレンブラック
（第二の非黒鉛炭素材料）だけが相当量混合されてお
り、負極活物質層の密度が高くなっているからである。
そして、このように炭素材が高密度充填された負極板構
造では、非水電解液が保持されるべき空隙が少なく、充
放電反応時のリチウムの拡散が阻まれ、過電圧が増大
し、負極電位がリチウムの酸化還元電位よりも卑とな
り、黒鉛や負極集電体表面で充放電可逆性に乏しいリチ
ウムが析出する。FIG. 6 shows the transition of the discharge capacity of the batteries of Examples m to r, Conventional Example 3 and Conventional Example 4 when the charge / discharge cycle was repeated. The batteries of Conventional Examples 3 and 4 show a large decrease in the discharge capacity due to the repetition of the charge / discharge cycle, whereas the batteries of Examples m to r show good charge / discharge cycle characteristics. Particularly, the mixing ratio of acetylene black (second non-graphite carbon material) is 0.5% based on the total weight of graphite and amorphous carbon (first non-graphite carbon material).
The batteries of Examples n to r described above exhibit extremely good charge / discharge cycle characteristics. Acetylene black (second non-graphitic carbon material), which is appropriately wrapped between particles such as graphite, taking advantage of its electrical conductivity and very fine particle characteristics, is capable of following the expansion and contraction of graphite during charging and discharging. Acts as a buffer material for the expansion and contraction of the particles, and in any state, maintains a gap between the particles of graphite and the first non-graphitic carbon material where the electrolyte enters, while maintaining an electron conduction network. You are. From the above results, the mixing ratio of acetylene black (second non-graphite carbon material) is 20% or less, preferably 0.5% or more, based on the total weight of graphite and the first non-graphite carbon material. It is. The large decrease in the discharge capacity in Conventional Example 3 is because amorphous carbon (first non-graphite carbon material) is not mixed in the carbon material of the negative electrode active material layer, and fine acetylene black (second non-graphite carbon material) is used. If only a small amount of graphite (carbon material) is mixed,
This is because it cannot follow contraction. In particular, after the discharge in which the graphite is contracted, a portion where the connection between the graphite particles and the acetylene black is broken appears, and the electron conduction network is partially cut. The particles whose electron conduction network has been cut off are electrically isolated and no longer participate in the reaction in the next charge, and the charge utilization of the negative electrode decreases. When such a phenomenon is repeated by the charge / discharge cycle, an increase in the negative electrode resistance and a decrease in the capacity due to a shortage of the charge amount are caused. The large decrease in the discharge capacity in Conventional Example 4 is because amorphous carbon (first non-graphite carbon material) is not mixed in the carbon material of the negative electrode active material and fine acetylene black (second non-graphite carbon material) is used. This is because only the graphite carbon material) is mixed in a considerable amount, and the density of the negative electrode active material layer is increased.
In the negative electrode plate structure in which the carbon material is densely filled in this way, there are few voids in which the nonaqueous electrolyte is to be retained, diffusion of lithium during the charge / discharge reaction is prevented, overvoltage increases, and the negative electrode potential increases. Is lower than the oxidation-reduction potential of lithium, and lithium having poor charge / discharge reversibility is deposited on the surface of graphite or the negative electrode current collector.
【００３８】[0038]
【発明の効果】本発明に係る実施例で説明したように、
黒鉛を負極活物質として用いる場合には、第一の非黒鉛
炭素材料と第二の非黒鉛炭素材料を負極活物質層に適量
共存させることが有効であるある。第一の非黒鉛炭素材
料の役割は、負極活物質層の密度を高め過ぎず、電解液
が入り込める間隙を確保することである。また、第二の
非黒鉛炭素材料の役割は、黒鉛の膨張・収縮の緩衝作用
と、いかなる充電状態、放電状態においても負極活物質
層の電子伝導のネットワークを維持すること、電解液を
保持することである。これらの作用により、本発明に係
る非水電解液二次電池は、高容量でかつ充放電サイクル
特性にこの上なく優れたものとなる。As described in the embodiment according to the present invention,
When graphite is used as the negative electrode active material, it is effective to make the first non-graphite carbon material and the second non-graphite carbon material coexist in an appropriate amount in the negative electrode active material layer. The role of the first non-graphite carbon material is to secure a gap in which the electrolyte can enter without increasing the density of the negative electrode active material layer too much. In addition, the role of the second non-graphite carbon material is to buffer the expansion and contraction of graphite, to maintain the electronic conduction network of the negative electrode active material layer in any state of charge and discharge, and to hold the electrolyte. That is. Due to these effects, the nonaqueous electrolyte secondary battery according to the present invention has a high capacity and excellent charge / discharge cycle characteristics.
【図１】本発明に係る実施例の非水電解液二次電池の断
面図である。FIG. 1 is a sectional view of a non-aqueous electrolyte secondary battery according to an embodiment of the present invention.
【図２】比較例ａ、実施例ａ〜ｅ、比較例ｂの電池およ
び従来例１、従来例２の電池について、非晶質炭素（第
一の非黒鉛炭素材料）混合量と初回放電容量の関係を示
す図である。FIG. 2 shows the amounts of mixed amorphous carbon (first non-graphite carbon material) and the initial discharge capacity of the batteries of Comparative Example a, Examples a to e, Comparative Example b and the batteries of Conventional Example 1 and Conventional Example 2. FIG.
【図３】比較例ａ、実施例ａ〜ｅ、比較例ｂの電池およ
び従来例１、従来例２の電池について、充放電サイクル
を繰り返した時の放電容量推移を示す図である。FIG. 3 is a diagram showing a change in discharge capacity when a charge / discharge cycle is repeated for the batteries of Comparative Example a, Examples a to e, and Comparative Example b, and the batteries of Conventional Example 1 and Conventional Example 2.
【図４】比較例ｃ、実施例ｆ〜ｋ、比較例ｄの電池につ
いて、黒鉛の平均粒子径に対する非晶質炭素の平均粒子
径の比（粒径比）と初回放電容量の関係を示す図であ
る。FIG. 4 shows the relationship between the ratio of the average particle size of amorphous carbon to the average particle size of graphite (particle size ratio) and the initial discharge capacity for the batteries of Comparative Example c, Examples f to k, and Comparative Example d. FIG.
【図５】比較例ｃ、実施例ｆ〜ｋ、比較例ｄの電池につ
いて、充放電サイクルを繰り返した時の放電容量推移を
示す図である。FIG. 5 is a diagram showing a change in discharge capacity when a charge and discharge cycle is repeated for the batteries of Comparative Example c, Examples f to k, and Comparative Example d.
【図６】実施例ｍ〜ｒ、比較例ｅ、従来例３、従来例４
の電池について、充放電サイクルを繰り返した時の放電
容量推移を示す図である。FIG. 6 shows examples m to r, comparative example e, conventional example 3, and conventional example 4.
FIG. 5 is a diagram showing a change in discharge capacity when a charge / discharge cycle is repeated for the battery of FIG.
１は正極集電体 ２は正極活物質層 ３は負極集電体 ４は負極活物質層 ５はセパレータ ６は電池缶 ７は正極キャップ ８は正極タブ端子 ９はガスケット 1 is a positive electrode current collector 2 is a positive electrode active material layer 3 is a negative electrode current collector 4 is a negative electrode active material layer 5 is a separator 6 is a battery can 7 is a positive electrode cap 8 is a positive electrode tab terminal 9 is a gasket
Claims (2)
活物質とする正極と、非水電解液と、炭素材料を負極活
物質とする負極を具備してなる非水電解液二次電池にお
いて、 前記炭素材料が黒鉛と第一の非黒鉛炭素材料と第二の非
黒鉛炭素材料の混合体であり、 上記第一の非黒鉛炭素材料は、上記黒鉛と第一の非黒鉛
炭素材料の合計重量のうちの４〜４０％を占め、その平
均粒子径が黒鉛の平均粒子径の０．３〜３倍であり、 上記第二の非黒鉛炭素材料は、上記黒鉛と第一の非黒鉛
炭素材料の合計重量に対して２０％以下の重量の混合割
合であり、その平均粒子径は、上記黒鉛と第一の非黒鉛
炭素材料のいずれの粒子径よりも小さく、０．１μｍ以
下であることを特徴とする非水電解液二次電池。1. A non-aqueous electrolyte secondary battery comprising a positive electrode using a transition metal composite oxide containing lithium as a positive electrode active material, a non-aqueous electrolyte, and a negative electrode using a carbon material as a negative electrode active material. Wherein the carbon material is a mixture of graphite, a first non-graphite carbon material, and a second non-graphite carbon material, and the first non-graphite carbon material is a total of the graphite and the first non-graphite carbon material The second non-graphite carbon material occupies 4 to 40% of the weight, and has an average particle size of 0.3 to 3 times the average particle size of graphite; The mixing ratio is 20% or less of the total weight of the material, and the average particle size is smaller than any of the graphite and the first non-graphite carbon material, and is 0.1 μm or less. Non-aqueous electrolyte secondary battery characterized by the above-mentioned.
黒鉛炭素材料の合計重量に対して０．５％以上の重量の
混合割合である請求項１記載の非水電解液二次電池。2. The non-aqueous electrolyte according to claim 1, wherein the second non-graphite carbon material has a mixing ratio of 0.5% or more to the total weight of graphite and the first non-graphite carbon material. Rechargeable battery.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP9074049A JPH10270019A (en) | 1997-03-26 | 1997-03-26 | Nonaqueous electrolyte secondary battery |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP9074049A JPH10270019A (en) | 1997-03-26 | 1997-03-26 | Nonaqueous electrolyte secondary battery |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| JPH10270019A true JPH10270019A (en) | 1998-10-09 |
Family
ID=13535948
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP9074049A Pending JPH10270019A (en) | 1997-03-26 | 1997-03-26 | Nonaqueous electrolyte secondary battery |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPH10270019A (en) |
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