JP5245203B2 - Nonaqueous electrolyte secondary battery - Google Patents
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Description
本発明は非水電解質二次電池に関するものである。 The present invention relates to a non-aqueous electrolyte secondary battery.
民生用の携帯電話、ポータブル機器や携帯情報端末などの急速な小型軽量化・多様化に伴い、その電源である電池に対して、小型で軽量かつ高エネルギー密度で、さらに長期間繰り返し充放電が実現できる二次電池の開発が強く要求されている。なかでも、水溶液系電解液を使用する鉛電池やニッケルカドミウム電池と比較して、これらの欲求を満たす二次電池としてリチウムイオン二次電池などの非水電解質二次電池が最も有望であり、活発な研究がおこなわれている。 Along with the rapid miniaturization and diversification of consumer mobile phones, portable devices and personal digital assistants, etc., the battery that is the power source is small, lightweight, high energy density, and repeatedly charged and discharged for a long time. There is a strong demand for the development of secondary batteries that can be realized. Among them, non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries are the most promising and active as secondary batteries that satisfy these needs compared to lead batteries and nickel cadmium batteries that use aqueous electrolytes. Research has been conducted.
非水電解質二次電池の負極活物質には、金属リチウム、リチウム合金、リチウムの吸蔵・放出が可能な炭素材料などの種々のものが検討されているが、なかでも炭素材料を使用すると、サイクル寿命の長い電池が得られ、かつ安全性が高いという利点がある。 Various negative electrode active materials for non-aqueous electrolyte secondary batteries, such as metallic lithium, lithium alloys, and carbon materials capable of occluding / releasing lithium, have been studied. There is an advantage that a battery having a long life can be obtained and safety is high.
炭素材料の中でも、グラファイトは真密度が高く、粒子が軟質であり、初期不可逆容量が比較的小さいために、高エネルギー密度化の要求が高い民生用の携帯電話、ポータブル機器や携帯情報端末用の電池用負極活物質として、実用化されている。 Among carbon materials, graphite has a high true density, soft particles, and a relatively small initial irreversible capacity. Therefore, there is a high demand for high energy density for consumer mobile phones, portable devices and portable information terminals. It has been put into practical use as a negative electrode active material for batteries.
一方、コークスやハードカーボンに代表される非晶質炭素は、グラファイトに比べて真密度が低く、また、粒子が硬いうえに塊状であり、初期不可逆容量が比較的大きいために、高エネルギー密度化の要求が高い電池には不向きであるが、これらの非晶質炭素の充放電曲線がなだらかであり、電解液との反応性が比較的低いことから、高入出力特性や優れたサイクル寿命特性の要求が高い電池には非常に有望である。 On the other hand, amorphous carbon typified by coke and hard carbon has a lower true density than graphite, and is harder and more agglomerated, and has a relatively large initial irreversible capacity. Although it is not suitable for batteries with high demands, the charge / discharge curves of these amorphous carbons are gentle, and the reactivity with the electrolyte is relatively low, so high input / output characteristics and excellent cycle life characteristics It is very promising for batteries with high demands.
リチウムイオン二次電池において、入出力特性やサイクル寿命特性を向上させるために、正極材料、負極材料、非水電解質の開発が進められており、特に負極活物質に非晶質炭素を用いる方法が近年盛んに研究されている。 In order to improve input / output characteristics and cycle life characteristics in lithium ion secondary batteries, positive electrode materials, negative electrode materials, and non-aqueous electrolytes are being developed. In particular, there is a method using amorphous carbon as the negative electrode active material. It has been actively studied in recent years.
なお「入出力特性」とは、充電時あるいは放電時の電池の直流抵抗のことであり、この値が小さいものが入出力特性に優れていることを示唆している。 The “input / output characteristics” refers to the direct current resistance of the battery during charging or discharging, and a small value indicates that the input / output characteristics are excellent.
例えば特許文献１には、易黒鉛化性炭素と難黒鉛化性炭素との混合物の焼成物を負極に用いることによって放電容量の大きいリチウム二次電池が得られることが例示されている。また、特許文献２には、負極にリチウムがインターカレートした炭素層と金属リチウムの二層が形成されていることで、充電状態の正極の電位を一定にすることができ、サイクル寿命特性が向上することなどが例示されている。 For example, Patent Document 1 exemplifies that a lithium secondary battery having a large discharge capacity can be obtained by using a fired product of a mixture of graphitizable carbon and non-graphitizable carbon for the negative electrode. Further, in Patent Document 2, since the negative electrode is formed with two layers of lithium intercalated carbon layer and metallic lithium, the potential of the positive electrode in a charged state can be made constant, and cycle life characteristics are improved. The improvement is exemplified.
さらに、特許文献３では、炭素材料を負極活物質に用いたリチウムイオン電池において、負極の充放電利用範囲を、２時間率の電流値で充電したときの負極電位の変化が−１ｍＶ／（ｍＡｈ／ｇ）の範囲とすることにより、大電流でのパルス充放電サイクルの寿命特性を改善する技術が開示されている。
近年では、従来から重要視されてきた高エネルギー密度であること以外に、高い入出力性能が長期にわたって持続すること、および長期にわたって高い放電容量を維持する非水電解質二次電池の要求が高まってきている。 In recent years, in addition to the high energy density that has been regarded as important in the past, there has been an increasing demand for non-aqueous electrolyte secondary batteries that maintain high input / output performance over a long period of time and that maintain a high discharge capacity over a long period of time. ing.
特許文献１で開示された技術では、負極活物質に真密度が１．８０ｇ／ｃｍ３以下で、ｃ軸方向の結晶子の大きさＬｃが１００Å以上である炭素材料を用いることにより、放電容量の大きいリチウム二次電池が得られることが記載されているが、充放電サイクル特性については記載がない。 In the technique disclosed in Patent Document 1, the discharge capacity is obtained by using a carbon material having a true density of 1.80 g / cm 3 or less and a c-axis direction crystallite size Lc of 100 mm or more as the negative electrode active material. Although it is described that a lithium secondary battery having a large size can be obtained, there is no description about charge / discharge cycle characteristics.
また、特許文献２で開示された技術は、正極にスピネル系リチウム含有マンガン酸化物を用いた場合の、充放電サイクルに伴う容量劣化を十分に少ないものにするものである。 Moreover, the technique disclosed in Patent Document 2 sufficiently reduces the capacity deterioration associated with the charge / discharge cycle when a spinel-type lithium-containing manganese oxide is used for the positive electrode.
さらに、特許文献３で開示された技術は、負極に炭素材料を用いる場合、充電容量に対する電位変化が滑らかな電位傾斜を有する部分を用いるもので、炭素材料としては「非晶質炭素」が例示されているにすぎない。 Further, the technique disclosed in Patent Document 3 uses a portion having a potential gradient in which the potential change with respect to the charge capacity is smooth when a carbon material is used for the negative electrode. As the carbon material, “amorphous carbon” is exemplified. It has only been done.
充放電サイクルに伴う非水電解質二次電池の放電容量の減少は、電極上での非水電解質の分解反応によって正極と負極の充電レベルのバランスが変化することが主な原因の１つであり、この問題を解決するため負極の観点からも活発な検討がなされてきたが、上記特許文献１〜３に見られるように、いまだにその具体的な手段が見出されていない。 One of the main causes of the decrease in the discharge capacity of the nonaqueous electrolyte secondary battery accompanying the charge / discharge cycle is that the balance between the charge level of the positive electrode and the negative electrode changes due to the decomposition reaction of the nonaqueous electrolyte on the electrode. In order to solve this problem, active studies have been made from the viewpoint of the negative electrode, but no specific means has yet been found as seen in Patent Documents 1 to 3 above.
そこで本発明の目的は、非水電解質二次電池において、特定の性質をもつ炭素材料を負極活物質に使用することにより、長期間の使用において、充放電サイクルに伴う放電容量の低下の小さい非水電解質二次電池を提供することにある。 Accordingly, an object of the present invention is to use a carbon material having specific properties as a negative electrode active material in a non-aqueous electrolyte secondary battery, so that the discharge capacity with a decrease in discharge capacity accompanying a charge / discharge cycle is small in long-term use. The object is to provide a water electrolyte secondary battery.
請求項１の発明は、正極と、炭素材料を含む負極と、非水電解質とを備えた非水電解質二次電池において、電池の充電状態における前記炭素材料の単位重量あたりの充電電気量の変化に対する開回路電位の傾きが、−９．５×１０−４Ｖ／(ｍＡｈ／ｇ)以上であり、かつ前記炭素材料は，コークスを前記炭素材料の総質量に対して１５質量％以上７５質量％以下含有し，真密度が１．５５ｇ／ｃｍ３以上、２．１５ｇ／ｃｍ３以下であることを特徴とする。 The invention according to claim 1 is a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode containing a carbon material, and a non-aqueous electrolyte, and a change in charge amount per unit weight of the carbon material in a charged state of the battery. The slope of the open circuit potential with respect to the carbon material is −9.5 × 10 −4 V / (mAh / g) or more, and the carbon material contains 15% by mass or more and 75 % by mass of coke with respect to the total mass of the carbon material. % Or less, and the true density is 1.55 g / cm 3 or more and 2.15 g / cm 3 or less.
請求項２の発明は、上記の非水電解質二次電池において、電池の放電状態に対する充電状態の負極合材層の膨張率が１．１０以下であることを特徴とする。 The invention according to claim 2 is characterized in that, in the non-aqueous electrolyte secondary battery, an expansion coefficient of the negative electrode mixture layer in a charged state with respect to a discharged state of the battery is 1.10 or less.
請求項１の発明によれば、長期間の使用において放電容量の低下の小さい非水電解質二次電池を得ることができる。この理由は、充放電サイクルにともなう電極上での非水電解質の分解反応によって正極と負極の充電レベルのバランスが変化することに起因するものと考えられ、本発明では、負極の充電レベルのバランスが変化する際の充電時の開回路電位変化が小さいことから、充電時の正極の開回路電位変化を小さくすることが可能となり、このため正極上での電解質の分解反応が抑制できるものであると考えられる。 According to the first aspect of the present invention, a non-aqueous electrolyte secondary battery with a small decrease in discharge capacity can be obtained after long-term use. The reason for this is thought to be due to the change in the balance between the charge level of the positive electrode and the negative electrode due to the decomposition reaction of the nonaqueous electrolyte on the electrode accompanying the charge / discharge cycle. Since the open circuit potential change during charging when the battery changes is small, it becomes possible to reduce the open circuit potential change of the positive electrode during charging, and thus the decomposition reaction of the electrolyte on the positive electrode can be suppressed. it is conceivable that.
請求項２の発明によれば、長期間の使用において放電容量の低下の小さい非水電解質二次電池を得ることができる。これは、負極合材の膨張率が小さいために、充放電サイクルにともなう電解液との反応面積の増加量が少なく、正極と負極の充電レベルのバランスの変化が小さくなることおよび活物質粒子間あるいは活物質と集電体との密着性および導電性の低下が小さくなるものと考えられる。 According to the invention of claim 2, it is possible to obtain a non-aqueous electrolyte secondary battery with a small decrease in discharge capacity after long-term use. This is because the expansion rate of the negative electrode mixture is small, so the increase in the reaction area with the electrolyte accompanying the charge / discharge cycle is small, the change in the balance between the charge level of the positive electrode and the negative electrode is small, and between the active material particles Or it is thought that the fall of the adhesiveness of an active material and an electrical power collector and electroconductivity becomes small.
本発明は、正極と、炭素材料を含む負極と、非水電解質とを備えた非水電解質二次電池において、電池の充電状態における前記炭素材料の単位重量あたりの充電電気量の変化に対する開回路電位の傾きが−９．５×１０−４Ｖ／(ｍＡｈ／ｇ)以上であり、かつ、前記炭素材料の真密度が１．５５ｇ／ｃｍ３以上、２．１５ｇ／ｃｍ３以下であることを特徴とするものである。 The present invention relates to a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode containing a carbon material, and a non-aqueous electrolyte, and an open circuit for a change in the amount of charge per unit weight of the carbon material in a charged state of the battery. The potential gradient is −9.5 × 10 −4 V / (mAh / g) or more, and the true density of the carbon material is 1.55 g / cm 3 or more and 2.15 g / cm 3 or less. It is characterized by.
炭素材料を初充電すると、まず、炭素材料の表面でリチウムと電解液とが反応してＳＥＩ被膜が形成される。このＳＥＩ（Ｓｏｌｉｄ Ｅｌｅｃｔｒｏｌｙｔｅ Ｉｎｔｅｒｐｈａｓｅ）被膜とは、非水電解質中で金属リチウムや炭素材料の初充電をおこなった場合、電解質中の溶媒が還元されて、金属リチウムや炭素材料の表面に形成されるパシベーション膜をさす（芳尾真幸、小沢昭弥編集、「リチウムイオン二次電池−材料と応用」、日刊工業新聞社（１９９６））。そして、金属リチウムや炭素材料の表面に形成されたＳＥＩ被膜が、リチウムイオン伝導性の保護膜として働き、その後の金属リチウムや炭素材料と溶媒との反応が抑制されるものである。 When the carbon material is initially charged, first, lithium and the electrolytic solution react on the surface of the carbon material to form an SEI film. This SEI (Solid Electrolyte Interface) coating is a passivation formed on the surface of metallic lithium or carbon material by reducing the solvent in the electrolyte when the first charging of metallic lithium or carbon material is performed in a non-aqueous electrolyte. Refers to membranes (edited by Masayuki Yoshio and Akiya Ozawa, “Lithium-ion secondary batteries-materials and applications”, Nikkan Kogyo Shimbun (1996)). The SEI film formed on the surface of the metallic lithium or carbon material functions as a lithium ion conductive protective film, and the subsequent reaction between the metallic lithium or carbon material and the solvent is suppressed.
さらに充電を続けると、炭素材料がリチウムを吸蔵し、充電電気量が増えるに従って炭素材料の電位は低下し、炭素材料がリチウムを吸蔵できなくなって、炭素材料の表面にリチウムが析出し始めた時に、電位は０Ｖ（ｖｓ．Ｌｉ／Ｌｉ＋）となる。 When the battery is further charged, the carbon material occludes lithium, the potential of the carbon material decreases as the amount of charged electricity increases, the carbon material cannot occlude lithium, and lithium begins to deposit on the surface of the carbon material. The potential becomes 0 V (vs. Li / Li + ).
つぎに放電を開始すると、炭素材料からリチウムが放出され、放電電気量が増えるに従って炭素材料の電位は上昇するが、初充電で吸蔵されたリチウムの一部は炭素材料中に蓄積されて放出されないため、放電電気量は、初充電時の充電電気量よりも小さくなる。しかし、数サイクル目以後は、充電電気量と放電電気量はほぼ等しくなる。 Next, when discharging is started, lithium is released from the carbon material, and the potential of the carbon material increases as the amount of discharge electricity increases, but a part of the lithium occluded in the initial charge is accumulated in the carbon material and is not released. For this reason, the amount of discharged electricity is smaller than the amount of charged electricity at the time of initial charge. However, after several cycles, the charge electricity amount and the discharge electricity amount are substantially equal.
炭素材料を充放電した場合の、２サイクル目以後の充放電電気量と開回路電位との関係を図１に示す。図１において、横軸は炭素材料単位重量当たりの充放電電気量（ｍＡｈ／ｇ）で、縦軸はリチウム基準電極に対する炭素材料の開回路電位（ｖｓ．Ｌｉ／Ｌｉ＋）である。なお、図１では、充放電容量が約１００ｍＡｈ／ｇより小さい部分は省略した。 FIG. 1 shows the relationship between the amount of charge / discharge electricity after the second cycle and the open circuit potential when the carbon material is charged / discharged. In FIG. 1, the horizontal axis represents the charge / discharge electric quantity (mAh / g) per unit weight of the carbon material, and the vertical axis represents the open circuit potential (vs. Li / Li + ) of the carbon material with respect to the lithium reference electrode. In FIG. 1, portions where the charge / discharge capacity is smaller than about 100 mAh / g are omitted.
炭素材料としては２．０〜０Ｖ（ｖｓ．Ｌｉ／Ｌｉ＋）の範囲で充放電可能であるが、通常の非水電解質二次電池では、図１のＡ点〜Ｂ点の範囲を使用している。図１のＡ点より電位の高い領域では電位変化が大きく、電池電圧が低くなりすぎ、また、Ｂ点〜Ｃ点の範囲では電位が０Ｖ（ｖｓ．Ｌｉ／Ｌｉ＋）に近いため、炭素材料の表面にリチウムが析出しやすい状態にあり、炭素材料の表面にリチウムが析出すると、内部短絡などが起こり易くなる。 The carbon material can be charged / discharged in a range of 2.0 to 0 V (vs. Li / Li + ), but a normal nonaqueous electrolyte secondary battery uses a range of points A to B in FIG. ing. Since the potential change is large in the region where the potential is higher than the point A in FIG. 1, the battery voltage becomes too low, and the potential is close to 0 V (vs. Li / Li + ) in the range from the point B to the point C. When lithium is easily deposited on the surface of the carbon material and lithium is deposited on the surface of the carbon material, an internal short circuit is likely to occur.
図１の曲線において、点Ｂは炭素材料の組成はおよそＬｉ０．７５Ｃ６となっており、この点で充電を終われば、炭素材料の表面にリチウムは析出しない。なお、Ｂ点の電位Ｅ１はリチウム基準電極に対し、やや貴の方向にずれている。本発明においては、Ｅ１＝２０ｍＶとする。 In the curve of FIG. 1, the composition of the carbon material at point B is approximately Li 0.75 C 6, and when charging is finished at this point, lithium does not precipitate on the surface of the carbon material. The potential E 1 at the point B relative to the lithium reference electrode, are shifted slightly directions noble. In the present invention, E 1 = 20 mV.
本発明において「炭素材料における、電池の充電状態における単位重量当たりの充電電気量の変化に対するＬｉ／Ｌｉ＋基準での開回路電位の傾き」とは、図１の点Ｂにおける曲線の接線（図１のＸ）の傾きを意味する。 In the present invention, “the slope of the open circuit potential on the basis of Li / Li + reference with respect to the change in the amount of charged electricity per unit weight in the charged state of the battery in the carbon material” refers to the tangent of the curve at point B in FIG. Means the slope of X).
本発明では、負極活物質として、電池の充電状態における単位重量あたりの充電電気量の変化に対する開回路電位の傾きが、−９．５×１０−４Ｖ／(ｍＡｈ／ｇ)以上である炭素材料を用いる。そのことによって、長期間の使用において放電容量の低下の小さい非水電解質二次電池を得ることができる。 In the present invention, as the negative electrode active material, carbon whose slope of the open circuit potential with respect to the change in the amount of charge per unit weight in the charged state of the battery is −9.5 × 10 −4 V / (mAh / g) or more. Use materials. As a result, a nonaqueous electrolyte secondary battery with a small decrease in discharge capacity can be obtained over a long period of use.
非水電解質二次電池において、充放電サイクルに伴い、電極上で非水電解質が分解し、その結果、正極と負極の充電レベルのバランスが変化する。電池が充電状態における負極の電位は、電池が正常な場合には図１のＢ点のＥ１Ｖ（ｖｓ．Ｌｉ／Ｌｉ＋）にあるが、負極の充電レベルのバランスが変化した場合、充電時の負極の電位は図１のＤ点のＥ２Ｖ（ｖｓ．Ｌｉ／Ｌｉ＋）に移動する。 In the non-aqueous electrolyte secondary battery, the non-aqueous electrolyte is decomposed on the electrode along with the charge / discharge cycle, and as a result, the balance between the charge levels of the positive electrode and the negative electrode changes. When the battery is in a charged state, the potential of the negative electrode is at E 1 V (vs. Li / Li + ) at point B in FIG. 1 when the battery is normal, but the battery is charged when the balance of the charge level of the negative electrode changes. The potential of the negative electrode at that time moves to E 2 V (vs. Li / Li + ) at point D in FIG.
非水電解質二次電池の充電は定電流充電と定電圧充電を組み合わせて行うが、例えば定電圧充電の電圧がＥＶの場合、電池が正常な場合の正極の単極電位は（Ｅ＋Ｅ１）Ｖ（ｖｓ．Ｌｉ／Ｌｉ＋）である。この定電圧充電の電圧ＥＶは、正極の単極電位は（Ｅ＋Ｅ１）Ｖ（ｖｓ．Ｌｉ／Ｌｉ＋）では電解液が分解しない値に設定されている。 The non-aqueous electrolyte secondary battery is charged by combining constant current charging and constant voltage charging. For example, when the voltage of constant voltage charging is EV, the unipolar potential of the positive electrode when the battery is normal is (E + E 1 ) V (Vs. Li / Li + ). The voltage EV of the constant voltage charging is set to a value at which the electrolyte does not decompose when the single electrode potential of the positive electrode is (E + E 1 ) V (vs. Li / Li + ).
ところが、充電時の負極の電位が図１のＤ点に移動した場合、正極の単極電位は（Ｅ＋Ｅ２）Ｖ（ｖｓ．Ｌｉ／Ｌｉ＋）となる。負極の充電レベルのバランスが変化が大きい場合には、Ｅ２の値も大きくなって、正極の単極電位が（Ｅ＋Ｅ２）Ｖ（ｖｓ．Ｌｉ／Ｌｉ＋）では、電解液が分解する。 However, when the potential of the negative electrode during charging moves to point D in FIG. 1, the unipolar potential of the positive electrode becomes (E + E 2 ) V (vs. Li / Li + ). When the change in the balance of the charge level of the negative electrode is large, the value of E 2 also increases. When the single electrode potential of the positive electrode is (E + E 2 ) V (vs. Li / Li + ), the electrolytic solution is decomposed.
本発明では、負極の充電レベルのバランスが変化する際の、充電時のＬｉ／Ｌｉ＋基準での開回路電位の変化、すなわちＥ２の値を小さくすることにより、充電時の正極の単極電位（対基準電極）の変化を小さくし、電解液の分解電位よりも小さくすることが可能となり、正極上での電解質の分解反応が抑制できるものであると考えられる。 In the present invention, when the balance of the charge level of the negative electrode is changed, the change in the open circuit potential at Li / Li + reference during charging, that is, by reducing the value of E 2, unipolar positive electrode during charging It is considered that the change in potential (vs. reference electrode) can be made smaller and smaller than the decomposition potential of the electrolytic solution, and the decomposition reaction of the electrolyte on the positive electrode can be suppressed.
なお、図１においては、炭素材料の開回路電位はリチウム電極（ｖｓ．Ｌｉ／Ｌｉ＋）基準で表示したが、基準電極としては、非水電解質二次電池に用いる非水電解質中で長期間にわたって電位が安定な電極なら、どのような電極でも用いることができる。そして、あらかじめ使用する非水電解質中での金属リチウム電極に対する基準電極の電位を求めておくことにより、基準電極に対する炭素材料の開回路電位を金属リチウム電極に対する電位に換算することができる。 In FIG. 1, the open circuit potential of the carbon material is shown on the basis of a lithium electrode (vs. Li / Li + ), but the reference electrode is used for a long time in a non-aqueous electrolyte used in a non-aqueous electrolyte secondary battery. Any electrode can be used as long as the electrode has a stable potential. And by calculating | requiring the electric potential of the reference electrode with respect to the metal lithium electrode in the nonaqueous electrolyte used previously, the open circuit electric potential of the carbon material with respect to a reference electrode can be converted into the electric potential with respect to a metal lithium electrode.
基準電極としては、金属リチウム電極が適しているが、その他にも、「非水溶液の電気化学」（伊豆津公佑著、１９９５年２月、培風舘発行）の１３７〜１４０ページに記載されている、銀−銀イオン電極、銀−銀クリプテート電極、銀−塩化銀電極、Ｐｔ／Ｉ３ −，Ｉ−電極などを、塩橋と組み合わせて、非水電解質二次電池に用いる非水電解質に応じて適宜選択して用いることができる。 As the reference electrode, a metal lithium electrode is suitable, but in addition, it is described in pages 137 to 140 of “Non-aqueous solution electrochemistry” (published by Izutsu Kosuke, published in February 1995, Baifu Kaoru). are, silver - silver ion electrode, a silver - silver cryptate electrode, a silver - silver chloride electrode, Pt / I 3 -, I - electrodes, etc., in combination with the salt bridge, the non-aqueous electrolyte used in the nonaqueous electrolyte secondary battery It can be appropriately selected and used accordingly.
本発明では、あらかじめ負極活物質の炭素材料の、電池の充電状態における単位重量あたりの充電電気量の変化に対する開回路電位の傾きを測定し、その値が−９．５×１０−４Ｖ／(ｍＡｈ／ｇ)以上である炭素材料を非水電解質二次電池の負極活物質に用いるものである。 In the present invention, the slope of the open circuit potential with respect to the change in the amount of charge per unit weight of the carbon material of the negative electrode active material in the charged state of the battery is measured in advance, and the value is −9.5 × 10 −4 V / A carbon material of (mAh / g) or more is used as a negative electrode active material of a nonaqueous electrolyte secondary battery.
なお、非水電解質二次電池に用いられた負極活物質である炭素材料についての、電池の充電状態における単位重量あたりの充電電気量の変化に対する開回路電位の傾きは、つぎのようにして測定する。なお、以下の操作、測定は、すべて、アルゴン置換グローブボックス中で行うものとする。 The slope of the open circuit potential with respect to the change in the amount of charge per unit weight of the carbon material, which is the negative electrode active material used in the non-aqueous electrolyte secondary battery, was measured as follows. To do. The following operations and measurements are all performed in an argon-substituted glove box.
負極活物質に炭素材料を用いた非水電解質二次電池を解体し、負極板を取り出し、リード端子が接続されている部分を一定の寸法に切り出し、特性測定用負極とした。 A non-aqueous electrolyte secondary battery using a carbon material as a negative electrode active material was disassembled, the negative electrode plate was taken out, and the portion to which the lead terminal was connected was cut out to a certain size to obtain a negative electrode for characteristic measurement.
負極板の他の部分を切り出し、ジメチルカーボネート（ＤＭＣ）で洗浄後、乾燥し、寸法を測定し、負極合材を取り出し、負極の単位面積に含まれる炭素材料の重量を求め、この値から、特性測定用負極に含まれる炭素材料の重量を算出した。 Cut out the other part of the negative electrode plate, washed with dimethyl carbonate (DMC), dried, measured dimensions, taken out the negative electrode mixture, to determine the weight of the carbon material contained in the unit area of the negative electrode, from this value, The weight of the carbon material contained in the characteristic measurement negative electrode was calculated.
つぎに、対極および参照電極に金属リチウム電極、作用電極に特性測定用負極、非水電解液を用いた３極式ガラスセルを作製し、特性測定をおこなった。測定条件は、温度２５℃で、炭素材料１ｇ当たり２５ｍＡの電流密度で、電位範囲０．０Ｖ〜２．０Ｖ（ｖｓ．Ｌｉ／Ｌｉ＋）での充電（リチウム挿入）及び放電（リチウム脱離）を１サイクルとする充放電を３サイクル行い、放電終了後、電流密度２５ｍＡ／ｇで０．０Ｖ（ｖｓ．Ｌｉ／Ｌｉ＋）まで充電した。この充電中に、充電電気量６．２５ｍＡｈ／ｇごとに充電を中断し、端子電圧が一定となった値をＯＣＶとした。 Next, a tripolar glass cell using a metal lithium electrode as a counter electrode and a reference electrode, a negative electrode for characteristic measurement as a working electrode, and a non-aqueous electrolyte was prepared, and characteristic measurement was performed. The measurement conditions are a temperature (25 ° C.), a current density of 25 mA per gram of carbon material, charging (lithium insertion) and discharging (lithium desorption) in a potential range of 0.0 V to 2.0 V (vs. Li / Li + ). 3 cycles of charging and discharging were performed, and after discharging, the battery was charged to 0.0 V (vs. Li / Li + ) at a current density of 25 mA / g. During this charging, charging was interrupted every 6.25 mAh / g of charging electricity, and the value at which the terminal voltage became constant was defined as OCV.
この測定結果から、図１に示したような、充放電電気量と電位の関係を求め、縦軸の電位が２０ｍＶ（ｖｓ．Ｌｉ／Ｌｉ＋）の点での曲線の接線の傾きを求め、その値を「電池の充電状態における単位重量当たりの充電電気量の変化に対する開回路電位の傾き」とした。 From this measurement result, as shown in FIG. 1, the relationship between the charge / discharge electricity amount and the potential is obtained, and the slope of the tangent of the curve at the point where the potential on the vertical axis is 20 mV (vs. Li / Li + ) is obtained. The value was defined as “the slope of the open circuit potential with respect to the change in the amount of charge per unit weight in the charged state of the battery”.
本発明においては、負極活物質に炭素材料を用い、この炭素材料の真密度の範囲を１．５５ｇ／ｃｍ３以上、２．１５ｇ／ｃｍ３以下とする。なお、炭素材料の真密度の測定は、ブタノールを用いたピクノメータ法でおこなった。 In the present invention, a carbon material is used for the negative electrode active material, and the true density range of the carbon material is 1.55 g / cm 3 or more and 2.15 g / cm 3 or less. The true density of the carbon material was measured by a pycnometer method using butanol.
炭素材料の真密度が１．５５ｇ／ｃｍ３より小さい場合には、電池容量を確保するために、所定の負極合材密度を得るのに高いプレス圧力を必要とする。そのため、粒子同士あるいは粒子と集電体間の密着性が大きく低下してしまうので好ましくない。また、炭素材料の真密度が２．１５ｇ／ｃｍ３より大きい場合には、通常、負極の膨張率も大きくなるので好ましくない。 When the true density of the carbon material is smaller than 1.55 g / cm 3 , a high press pressure is required to obtain a predetermined negative electrode mixture density in order to ensure battery capacity. Therefore, the adhesion between particles or between a particle and a current collector is greatly reduced, which is not preferable. Further, when the true density of the carbon material is larger than 2.15 g / cm 3 , the negative electrode usually has a large expansion coefficient, which is not preferable.
なお、請求項１に記載の「真密度」は、つぎの式で定義される「負極平均真密度」とは同じものであり、各種活物質を混合して用いる際に適用するものである。 The “true density” described in claim 1 is the same as the “negative electrode average true density” defined by the following formula, and is applied when various active materials are mixed and used.
負極平均真密度＝１／（（全負極活物質に対する炭素材料Ａの割合（質量％）／１００）／（炭素材料Ａの真密度）＋（全負極活物質に対する炭素材料Ｂの割合（質量％）／１００）／（炭素材料Ｂの真密度）＋（全負極活物質に対する炭素材料Ｃの割合（質量％）／１００）／（炭素材料Ｃの真密度）＋・・・）
本発明においては、請求項１記載の非水電解質二次電池において、電池の放電状態に対する充電状態の負極合材層の膨張率が１．１０以下であることが好ましい。電池の放電状態に対する充電状態の負極合材層の膨張率が１．１０を越える場合には、充放電サイクルに伴う電解液との反応面積の増加量が多く、正極と負極の充電レベルのバランスの変化が大きくなること、および活物質粒子間あるいは活物質と集電体との密着性の低下が大きくなるので好ましくない。
Negative electrode average true density = 1 / ((ratio of carbon material A to the total negative electrode active material (mass%) / 100) / (true density of carbon material A) + (ratio of the carbon material B to the total negative electrode active material (mass%) ) / 100) / (true density of carbon material B) + (ratio of carbon material C to all negative electrode active materials (mass%) / 100) / (true density of carbon material C) +.
In the present invention, in the non-aqueous electrolyte secondary battery according to claim 1, the expansion coefficient of the negative electrode mixture layer in the charged state with respect to the discharged state of the battery is preferably 1.10 or less. When the expansion ratio of the negative electrode mixture layer in the charged state with respect to the discharged state of the battery exceeds 1.10, the amount of increase in the reaction area with the electrolyte accompanying the charge / discharge cycle is large, and the charge level balance between the positive and negative electrodes is large. This is not preferable because the change in the thickness of the active material particles increases and the decrease in the adhesion between the active material particles or between the active material and the current collector increases.
さらに、電池の放電状態に対する充電状態の負極合材層の膨張率は、つぎのように定義される。
膨張率＝（充電状態における負極合材の厚み）／（放電状態における負極合材の厚み）
本発明を適用する非水電解質二次電池の負極活物質としては、本発明を超えない範囲で、以下のような材料を用いることができる。
Furthermore, the expansion coefficient of the negative electrode mixture layer in the charged state with respect to the discharged state of the battery is defined as follows.
Expansion coefficient = (thickness of negative electrode mixture in charged state) / (thickness of negative electrode mixture in discharged state)
As the negative electrode active material of the nonaqueous electrolyte secondary battery to which the present invention is applied, the following materials can be used within the range not exceeding the present invention.
負極活物質の好適な例としては、リチウムを吸蔵・放出可能な炭素材料が挙げられる。この炭素材料の例としては、コークス類（石油コークス、ピッチコークス、石炭コークスなど）、ハードカーボン類、熱分解炭素類、炭素繊維、ガラス状炭素類、天然黒鉛あるいは人造黒鉛等のグラファイト類等が挙げられ、上記各種活物質を混合して用いてもよい。中でも、コークス類あるいはハードカーボン類は、入出力特性やサイクル寿命特性の観点から、特に好ましい。 A suitable example of the negative electrode active material is a carbon material capable of inserting and extracting lithium. Examples of this carbon material include cokes (petroleum coke, pitch coke, coal coke, etc.), hard carbons, pyrolytic carbons, carbon fibers, glassy carbons, graphites such as natural graphite or artificial graphite, etc. The above-mentioned various active materials may be mixed and used. Among these, cokes or hard carbons are particularly preferable from the viewpoint of input / output characteristics and cycle life characteristics.
本発明を適用する非水電解質二次電池の非水電解質としては、電解液または固体電解質のいずれも使用することができる。電解液を用いる場合には、電解液溶媒として、エチレンカーボネート、プロピレンカーボネート、ブチレンカーボネート、トリフルオロプロピレンカーボネート、γ−ブチロラクトン、γ−バレロラクトン、スルホラン、１、２−ジメトキシエタン、１、２−ジエトキシエタン、テトラヒドロフラン、２−メチルテトラヒドロフラン、３−メチル−１、３−ジオキソランやハロゲン化ジオキソラン、トリフルオロエチルメチルエーテル、エチレングリコールジアセテート、プロピレングリコールジアセテート、エチレングリコールジプロピオネート、プロピレングリコールジプロピオネート、酢酸メチル、酢酸エチル、酢酸プロピル、酢酸ブチル、プロピオン酸メチル、プロピオン酸エチル、プロピオン酸プロピル、フルオロ酢酸メチル、フルオロ酢酸エチル、フルオロ酢酸プロピル、ジメチルカーボネート、ジエチルカーボネート、エチルメチルカーボネート、メチルプロピルカーボネート、エチルプロピルカーボネート、ジプロピルカーボネート、メチルイソプロピルカーボネート、エチルイソプロピルカーボネート、ジイソプロピルカーボネート、ジブチルカーボネート、アセトニトリル、フルオロアセトニトリル、エトキシペンタフルオロシクロトリホスファゼン、ジエトキシテトラフルオロシクロトリホスファゼン、フェノキシペンタフルオロシクロトリホスファゼンなどのアルコキシおよびハロゲン置換環状ホスファゼン類および、鎖状ホスファゼン類、リン酸トリエチル、リン酸トリメチル、リン酸トリオクチルなどのリン酸アルキルエステル類、ホウ酸トリエチル、ホウ酸トリブチルなどのホウ酸エステル類、Ｎ−メチルオキサゾリジノン、Ｎ−エチルオキサゾリジノン等の非水溶媒を、単独でまたはこれらの混合溶媒を使用することができる。 As the non-aqueous electrolyte of the non-aqueous electrolyte secondary battery to which the present invention is applied, either an electrolytic solution or a solid electrolyte can be used. In the case of using an electrolytic solution, as an electrolytic solution solvent, ethylene carbonate, propylene carbonate, butylene carbonate, trifluoropropylene carbonate, γ-butyrolactone, γ-valerolactone, sulfolane, 1,2-dimethoxyethane, 1,2-di- Ethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 3-methyl-1,3-dioxolane, halogenated dioxolane, trifluoroethyl methyl ether, ethylene glycol diacetate, propylene glycol diacetate, ethylene glycol dipropionate, propylene glycol dipropio , Methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl fluoroacetate, full Ethyl oloacetate, propyl fluoroacetate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, dipropyl carbonate, methyl isopropyl carbonate, ethyl isopropyl carbonate, diisopropyl carbonate, dibutyl carbonate, acetonitrile, fluoroacetonitrile, ethoxy Alkoxy and halogen-substituted cyclic phosphazenes such as pentafluorocyclotriphosphazene, diethoxytetrafluorocyclotriphosphazene, phenoxypentafluorocyclotriphosphazene and phosphorus such as chain phosphazenes, triethyl phosphate, trimethyl phosphate, trioctyl phosphate Acid alkyl esters, triethyl borate, Boric acid esters such as c acid tributyl, N- methyl oxazolidinone, a non-aqueous solvent such as N- ethyl-oxazolidinones, or in itself can be used a mixture of these solvents.
非水電解質は、これらの非水溶媒に支持塩を溶解して使用する。支持塩としては、ＬｉＣｌＯ４、ＬｉＰＦ６、ＬｉＢＦ４、ＬｉＡｓＦ６、ＬｉＣＦ３ＣＯ２、ＬｉＣＦ３ＳＯ３、ＬｉＣＦ３ＣＦ２ＳＯ３、ＬｉＣＦ３ＣＦ２ＣＦ２ＳＯ３、ＬｉＮ（ＳＯ２ＣＦ３）２、ＬｉＮ（ＳＯ２ＣＦ２ＣＦ３）２、ＬｉＮ（ＣＯＣＦ３）２、ＬｉＮ（ＣＯＣＦ２ＣＦ３）２ＬｉＢＦ２Ｃ２Ｏ４、ＬｉＢＣ４Ｏ８、ＬｉＰＦ２（Ｃ２Ｏ４）２およびＬｉＰＦ３（ＣＦ２ＣＦ３）３などの塩もしくはこれらの混合物を使用することができる。 The nonaqueous electrolyte is used by dissolving the supporting salt in these nonaqueous solvents. Examples of the supporting salt include LiClO 4 , LiPF 6 , LiBF 4 , LiAsF 6 , LiCF 3 CO 2 , LiCF 3 SO 3 , LiCF 3 CF 2 SO 3 , LiCF 3 CF 2 CF 2 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 LiBF 2 C 2 O 4 , LiBC 4 O 8 , LiPF 2 (C 2 O 4 ) 2 and A salt such as LiPF 3 (CF 2 CF 3 ) 3 or a mixture thereof can be used.
また、電池特性向上のために、少量の添加剤を非水電解質中に混合してもよく、ビニレンカーボネート、メチルビニレンカーボネート、エチルビニレンカーボネート、プロピルビニレンカーボネート、フェニルビニレンカーボネート、ビニルエチレンカーボネート、ジビニルエチレンカーボネート、ジメチルビニレンカーボネート、ジエチルビニレンカーボネート、フルオロエチレンカーボネートなどのカーボネート類、酢酸ビニル、プロピオン酸ビニルなどのビニルエステル類、ジアリルスルフィド、アリルフェニルスルフィド、アリルビニルスルフィド、アリルエチルスルフィド、プロピルスルフィド、ジアリルジスルフィド、アリルエチルジスルフィド、アリルプロピルジスルフィド、アリルフェニルジスルフィド等のスルフィド類、１、３−プロパンスルトン、１、４−ブタンスルトン、１、３−プロパ−２−エンスルトン等の環状スルホン酸エステル類、メタンスルホン酸メチル、メタンスルホン酸エチル、メタンスルホン酸プロピル、エタンスルホン酸メチル、エタンスルホン酸エチル、エタンスルホン酸プロピル、ベンゼンスルホン酸メチル、ベンゼンスルホン酸エチル、ベンゼンスルホン酸プロピル、メタンスルホン酸フェニル、エタンスルホン酸フェニル、プロパンスルホン酸フェニル、ベンジルスルホン酸メチル、ベンジルスルホン酸エチル、ベンジルスルホン酸プロピル、メタンスルホン酸ベンジル、エタンスルホン酸ベンジル、プロパンスルホン酸ベンジル、等の鎖状スルホン酸エステル類、ジメチルサルファイト、ジエチルサルファイト、エチルメチルサルファイト、メチルプロピルサルファイト、エチルプロピルサルファイト、ジフェニルサルファイト、メチルフェニルサルファイト、エチルメチルサルファイト、エチレンサルファイト、ビニルエチレンサルファイト、ジビニルエチレンサルファイト、プロピレンサルファイト、ビニルプロピレンサルファイト、ブチレンサルファイト、ビニルブチレンサルファイト、ビニレンサルファイト、フェニルエチレンサルファイト、などの亜硫酸エステル類、ベンゼン、トルエン、キシレン、ビフェニル、シクロヘキシルベンゼン、２−フルオロビフェニル、４−フルオロビフェニル、ジフェニルエーテル、ｔｅｒｔ−ブチルベンゼン、オルトターフェニル、メタターフェニル、ナフタレン、フルオロナフタレン、クメン、フルオロベンゼン、２、４−ジフルオロアニソールなどの芳香族化合物、パーフルオロオクタンなどのハロゲン置換アルカン、ホウ酸トリメチルシリル、ホウ酸トリエチルシリルなど、目的に応じて適宜添加してもよい。 In order to improve battery characteristics, a small amount of additives may be mixed in the non-aqueous electrolyte. Vinylene carbonate, methyl vinylene carbonate, ethyl vinylene carbonate, propyl vinylene carbonate, phenyl vinylene carbonate, vinyl ethylene carbonate, divinyl ethylene Carbonates such as carbonate, dimethyl vinylene carbonate, diethyl vinylene carbonate, fluoroethylene carbonate, vinyl esters such as vinyl acetate and vinyl propionate, diallyl sulfide, allyl phenyl sulfide, allyl vinyl sulfide, allyl ethyl sulfide, propyl sulfide, diallyl disulfide , Sulfides such as allyl ethyl disulfide, allyl propyl disulfide, allyl phenyl disulfide, , Cyclic sulfonic acid esters such as 3-propane sultone, 1,4-butane sultone, 1,3-prop-2-ene sultone, methyl methanesulfonate, ethyl methanesulfonate, propyl methanesulfonate, methyl ethanesulfonate, ethane Ethyl sulfonate, propyl ethane sulfonate, methyl benzene sulfonate, ethyl benzene sulfonate, propyl benzene sulfonate, phenyl methane sulfonate, phenyl ethane sulfonate, phenyl propane sulfonate, methyl benzyl sulfonate, ethyl benzyl sulfonate, benzyl Chain sulfonates such as propyl sulfonate, benzyl methanesulfonate, benzyl ethanesulfonate, benzyl propanesulfonate, dimethyl sulfite, diethyl sulfite, ethyl methyl Rufite, methyl propyl sulfite, ethyl propyl sulfite, diphenyl sulfite, methyl phenyl sulfite, ethyl methyl sulfite, ethylene sulfite, vinyl ethylene sulfite, divinyl ethylene sulfite, propylene sulfite, vinyl propylene sulfite, butylene Sulfites such as sulfite, vinylbutylene sulfite, vinylene sulfite, phenylethylene sulfite, benzene, toluene, xylene, biphenyl, cyclohexylbenzene, 2-fluorobiphenyl, 4-fluorobiphenyl, diphenyl ether, tert-butylbenzene , Orthoterphenyl, metaterphenyl, naphthalene, fluoronaphthalene, cumene, fluorobenzene, 2, Aromatic compounds such as 4-difluoroanisole, halogen-substituted alkanes such as perfluorooctane, trimethylsilyl borate, triethylsilyl borate and the like may be appropriately added depending on the purpose.
固体電解質を用いる場合は、高分子固体電解質として有孔性高分子固体電解質膜を用い、高分子固体電解質にさらに電解液を含有させることで良い。また、ゲル状の高分子固体電解質を用いる場合には、ゲルを構成する電解液と、細孔中等に含有されている電解液とは異なっていてもよい。ただし、高い入出力が要求される電池においては、固体電解質や高分子固体電解質を用いるよりは電解質として非水電解液を単独で用いるほうがより好ましい。 When a solid electrolyte is used, a porous polymer solid electrolyte membrane may be used as the polymer solid electrolyte, and an electrolyte solution may be further contained in the polymer solid electrolyte. Moreover, when using a gel-like polymer solid electrolyte, the electrolyte solution which comprises gel and the electrolyte solution contained in the pore etc. may differ. However, in a battery that requires high input / output, it is more preferable to use a non-aqueous electrolyte alone as the electrolyte than to use a solid electrolyte or a polymer solid electrolyte.
本発明を適用する非水電解質二次電池の正極活物質としては、特に制限はなく、種々の材料を適宜使用できる。例えば、二酸化マンガン、五酸化バナジウムのような遷移金属化合物や、硫化鉄、硫化チタンのような遷移金属カルコゲン化合物、さらにはこれらの遷移金属とリチウムの複合酸化物ＬｉｘＭＯ２−δ（ただし、Ｍは、Ｃｏ、ＮｉまたはＭｎを表し、０．４≦ｘ≦１．２、０≦δ≦０．５である複合酸化物）、またはこれらの複合酸化物にＡｌ、Ｍｎ、Ｆｅ、Ｎｉ、Ｃｏ、Ｃｒ、Ｔｉ、Ｚｎから選ばれる少なくとも一種の元素、または、Ｐ、Ｂなどの非金属元素を含有した化合物を使用することができる。 There is no restriction | limiting in particular as a positive electrode active material of the nonaqueous electrolyte secondary battery to which this invention is applied, A various material can be used suitably. For example, transition metal compounds such as manganese dioxide and vanadium pentoxide, transition metal chalcogen compounds such as iron sulfide and titanium sulfide, and composite oxides of these transition metals and lithium Li x MO 2-δ (however, M represents Co, Ni, or Mn, and is a composite oxide in which 0.4 ≦ x ≦ 1.2 and 0 ≦ δ ≦ 0.5), or these composite oxides may include Al, Mn, Fe, Ni, A compound containing at least one element selected from Co, Cr, Ti, and Zn, or a nonmetallic element such as P and B can be used.
さらに、好ましくはリチウムとマンガンとコバルトとニッケルの複合酸化物、すなわち一般式ＬｉａＭｎｂＣｏｃＮｉｄＯ２（但し、０＜ａ≦１．２、０≦ｂ≦１、０≦ｃ≦１、０≦ｄ≦１）で表される正極活物質を用いることができる。また、有機化合物としては、例えばポリアニリン等の導電性ポリマー等が挙げられる。さらに、無機化合物、有機化合物を問わず、上記各種活物質を混合して用いてもよい。 Further, preferably a composite oxide of lithium, manganese, cobalt, and nickel, that is, the general formula Li a Mn b Co c Ni d O 2 (where 0 <a ≦ 1.2, 0 ≦ b ≦ 1, 0 ≦ c ≦ A positive electrode active material represented by 1, 0 ≦ d ≦ 1) can be used. Examples of the organic compound include conductive polymers such as polyaniline. Furthermore, the above various active materials may be mixed and used regardless of whether they are inorganic compounds or organic compounds.
また、本発明に係る非水電解質電池の隔離体としては、織布、不織布、合成樹脂微多孔膜等を用いることができ、特に、合成樹脂微多孔膜を好適に用いることができる。中でもポリエチレン及びポリプロピレン製微多孔膜、アラミドやポリイミドと複合化させたポリエチレンおよびポリプロピレン製微多孔膜またはこれらを複合した微多孔膜等のポリオレフィン系微多孔膜が、厚さ、膜強度、膜抵抗等の面で好適に用いられる。 Moreover, as a separator of the nonaqueous electrolyte battery according to the present invention, a woven fabric, a non-woven fabric, a synthetic resin microporous membrane, or the like can be used, and a synthetic resin microporous membrane can be particularly preferably used. Among them, polyolefin microporous membranes such as polyethylene and polypropylene microporous membranes, polyethylene and polypropylene microporous membranes combined with aramid and polyimide, or microporous membranes composited with these, thickness, membrane strength, membrane resistance, etc. It is suitably used in terms of
さらに、高分子固体電解質等の固体電解質を用いることで、セパレータを兼ねさせることもできる。さらに、合成樹脂微多孔膜と高分子固体電解質等を組み合わせて使用してもよい。この場合、高分子固体電解質として有孔性高分子固体電解質膜を用い、高分子固体電解質にさらに電解液を含有させることで良い。ただしこの場合、電池出力が低下する原因となるので、好ましくは高分子固体電解質は最小限の量にとどめるほうが好ましい。 Furthermore, a separator can also be used by using a solid electrolyte such as a polymer solid electrolyte. Further, a synthetic resin microporous membrane and a polymer solid electrolyte may be used in combination. In this case, a porous polymer solid electrolyte membrane may be used as the polymer solid electrolyte, and the polymer solid electrolyte may further contain an electrolytic solution. However, in this case, since the battery output is reduced, it is preferable that the amount of the solid polymer electrolyte is kept to a minimum.
また、電池の形状は特に限定されるものではなく、角形、長円筒形、コイン形、ボタン形、シート形、円筒型電池等の様々な形状の非水電解質二次電池に適用可能である。 The shape of the battery is not particularly limited, and can be applied to non-aqueous electrolyte secondary batteries having various shapes such as a rectangular shape, a long cylindrical shape, a coin shape, a button shape, a sheet shape, and a cylindrical battery.
以下、本発明の実施例を図面に基づいて具体的に説明するが、本発明は、本実施例によって何ら限定されるものではなく、その主旨を変更しない範囲において適宜変更して実施することができる。 Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings. However, the present invention is not limited to the embodiments in any way, and may be appropriately modified and implemented without departing from the scope of the present invention. it can.
［負極活物質の調整］
負極活物質である炭素材料をつぎのようにして調整した。平均粒径１５μｍでブタノールを用いたピクノメータ法による真密度が１．９２ｇ／ｃｍ３のコークスを炭素材料Ａとし、平均粒径９μｍでブタノールを用いたピクノメータ法による真密度が１．５２ｇ／ｃｍ３のハードカーボンを炭素材料Ｂとした。
[Adjustment of negative electrode active material]
The carbon material which is a negative electrode active material was adjusted as follows. Coke having an average particle size of 15 μm and a true density of 1.92 g / cm 3 using butanol as the carbon density is carbon material A, and a true density of 1.52 g / cm 3 based on the pycnometer method using butanol having an average particle size of 9 μm. The carbon material B was used as the hard carbon.
炭素材料Ａを負極活物質ａとし、炭素材料Ａ７５質量％と炭素材料Ｂ２５質量％とを混合したものを負極活物質ｂとし、炭素材料Ａ５０質量％と炭素材料Ｂ５０質量％とを混合したものを負極活物質ｃとし、炭素材料Ａ２５質量％と炭素材料Ｂ７５質量％とを混合したものを負極活物質ｄとし、炭素材料Ａ１５質量％と炭素材料Ｂ８５質量％とを混合したものを負極活物質ｅとし、炭素材料Ｂを負極活物質ｆとした。 What mixed carbon material A as negative electrode active material a, mixed carbon material A 75 mass% and carbon material B 25 mass% as negative electrode active material b, mixed carbon material A 50 mass% and carbon material B 50 mass% The negative electrode active material c is a mixture of 25% by mass of carbon material A and 75% by mass of carbon material B. The negative electrode active material d is a mixture of 15% by mass of carbon material A and 85% by mass of carbon material B. And carbon material B was used as negative electrode active material f.
また、真密度が２．２５ｇ／ｃｍ３のグラファイトを炭素材料Ｃとし、これを負極活物質ｇとした。さらに、真密度が２．１７ｇ／ｃｍ３のコークスを炭素材料Ｄとし、これを負極活物質ｈとした。 Further, graphite having a true density of 2.25 g / cm 3 was used as carbon material C, and this was used as negative electrode active material g. Further, coke having a true density of 2.17 g / cm 3 was used as a carbon material D, and this was used as a negative electrode active material h.
負極活物質ａ〜ｈの、電池の充電状態における前記炭素材料の単位重量当たりの充電電気量の変化に対するＬｉ／Ｌｉ＋基準での開回路電位の傾きはつぎのようにして求めた。 The slope of the open circuit potential on the basis of Li / Li + with respect to the change in the amount of charge per unit weight of the carbon material in the charged state of the battery in the negative electrode active materials a to h was determined as follows.
アルゴン置換グローブボックス中で、対極および参照電極に金属リチウム電極を用い、作用電極に特性測定用負極を用い、エチレンカーボネート（ＥＣ）とジエチルカーボネート（ＤＥＣ）との体積比１：１混合溶媒に１ｍｏｌ／ｌのＬｉＰＦ６を溶解させた非水電解液を用いた３極式ガラスセルを作製し、特性測定をおこなった。 In an argon-substituted glove box, a metal lithium electrode is used as a counter electrode and a reference electrode, a negative electrode for characteristic measurement is used as a working electrode, and 1 mol in a 1: 1 mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) is used. A tripolar glass cell using a nonaqueous electrolytic solution in which 1 / L LiPF 6 was dissolved was prepared, and the characteristics were measured.
測定条件は、温度２５℃で、炭素材料１ｇ当たり２５ｍＡの電流密度で、電位範囲０．０Ｖ〜２．０Ｖ（ｖｓ．Ｌｉ／Ｌｉ＋）での充電（リチウム挿入）及び放電（リチウム脱離）を１サイクルとする充放電を１０サイクル行い、放電終了後、電流密度２５ｍＡ／ｇで０．０Ｖ（ｖｓ．Ｌｉ／Ｌｉ＋）まで充電した。この充電中に、充電電気量６．２５ｍＡｈ／ｇごとに充電を中断し、端子電圧が一定となった値をＯＣＶとした。 The measurement conditions are a temperature (25 ° C.), a current density of 25 mA per gram of carbon material, charging (lithium insertion) and discharging (lithium desorption) in a potential range of 0.0 V to 2.0 V (vs. Li / Li + ). 10 cycles of charge and discharge were performed, and after the discharge, the battery was charged to 0.0 V (vs. Li / Li + ) at a current density of 25 mA / g. During this charging, charging was interrupted every 6.25 mAh / g of charging electricity, and the value at which the terminal voltage became constant was defined as OCV.
この測定結果から、図１に示したような関係を求め、縦軸の電位が２０ｍＶ（ｖｓ．Ｌｉ／Ｌｉ＋）の点での曲線の接線の傾きを求め、その値を「電池の充電状態における単位重量当たりの充電電気量の変化に対するＬｉ／Ｌｉ＋基準での開回路電位の傾き」とした。 From this measurement result, the relationship as shown in FIG. 1 is obtained, the slope of the tangent of the curve at the point where the potential on the vertical axis is 20 mV (vs. Li / Li + ) is obtained, and the value is expressed as “battery charge state”. The slope of the open circuit potential on the basis of Li / Li + with respect to the change in the amount of charge per unit weight in
負極平均真密度（＝真密度）は、前述の式から計算で求めた。 The negative electrode average true density (= true density) was calculated from the above formula.
さらに、電池の放電状態に対する充電状態の負極合材層の膨張率は、つぎのようにして測定し、つぎの定義に基づいて計算によって求めた。
膨張率＝（充電状態における負極合材の厚み）／（放電状態における負極合材の厚み）
測定は、対極および参照電極に金属リチウム電極を用い、作用電極に特性測定用負極を用い、ＥＣとＤＥＣ（体積比１：１）混合溶媒に１ｍｏｌ／ｌのＬｉＰＦ６を溶解させた非水電解液を用いた３極式ガラスセルを用い、温度２５℃で、電流密度２５ｍＡ／ｇでＥ１＝２０ｍＶ（ｖｓ．Ｌｉ／Ｌｉ＋）まで定電流にて充電を行い、その後で定電圧にて合計２０時間の充電を行った後、および、０．５Ｖ（ｖｓ．Ｌｉ／Ｌｉ＋）まで放電した後、３極式ガラスセルから取り出した負極板をＤＭＣで洗浄後、２５℃で２時間の真空乾燥をおこない、その電極厚みをマイクロメータで測定し、あらかじめ測定しておいた集電体の厚みを差し引いたものを、その合材厚みとした。
Furthermore, the expansion coefficient of the negative electrode mixture layer in the charged state with respect to the discharged state of the battery was measured as follows, and was obtained by calculation based on the following definition.
Expansion coefficient = (thickness of negative electrode mixture in charged state) / (thickness of negative electrode mixture in discharged state)
Non-aqueous electrolysis in which a metal lithium electrode was used as a counter electrode and a reference electrode, a characteristic measurement negative electrode was used as a working electrode, and 1 mol / l LiPF 6 was dissolved in a mixed solvent of EC and DEC (volume ratio 1: 1). Using a triode glass cell using a liquid, charging is performed at a constant current up to E 1 = 20 mV (vs. Li / Li + ) at a temperature of 25 ° C. and a current density of 25 mA / g, and then at a constant voltage. After charging for a total of 20 hours and after discharging to 0.5 V (vs. Li / Li + ), the negative electrode plate taken out from the tripolar glass cell was washed with DMC, and then at 25 ° C. for 2 hours. It vacuum-dried, the electrode thickness was measured with the micrometer, and what subtracted the thickness of the electrical power collector measured beforehand was made into the compound material thickness.
負極活物質ａ〜ｈの組成を表１にまとめた。 The compositions of the negative electrode active materials a to h are summarized in Table 1.
［実施例１〜４および比較例１〜４］
［実施例１］
図２は本発明に係る非水電解質二次電池の構成例を示す断面図である。図２において、１は非水電解質二次電池（ 以下、電池という）、２は発電要素、３は負極、４は正極、５はセパレータ、６は電池ケース、７は電池蓋、８は安全弁、９は負極端子、１０は負極リードである。発電要素２は、正極４と負極３とをセパレータ５を介して扁平状に巻回したものである。発電要素２は角型の電池ケース６に収納されており、電池ケース６の開口部は、安全弁８及び負極端子９が設けられた電池蓋７をレーザー溶接して密閉している。負極３は負極リード１０を介して負極端子９と接続され、正極４は電池ケース６内面と接続されている。
[Examples 1 to 4 and Comparative Examples 1 to 4 ]
[Example 1]
FIG. 2 is a cross-sectional view showing a configuration example of the nonaqueous electrolyte secondary battery according to the present invention. In FIG. 2, 1 is a non-aqueous electrolyte secondary battery (hereinafter referred to as a battery), 2 is a power generation element, 3 is a negative electrode, 4 is a positive electrode, 5 is a separator, 6 is a battery case, 7 is a battery lid, 8 is a safety valve, 9 is a negative electrode terminal, and 10 is a negative electrode lead. The power generation element 2 is obtained by winding a positive electrode 4 and a negative electrode 3 in a flat shape with a separator 5 interposed therebetween. The power generating element 2 is housed in a rectangular battery case 6, and an opening of the battery case 6 is sealed by laser welding a battery lid 7 provided with a safety valve 8 and a negative electrode terminal 9. The negative electrode 3 is connected to the negative electrode terminal 9 via the negative electrode lead 10, and the positive electrode 4 is connected to the inner surface of the battery case 6.
正極については、活物質として正極活物質ＬｉＣｏ１／３Ｎｉ１／３Ｍｎ１／３Ｏ２８６質量％と、導電助剤としてアセチレンブラック（ＡＢ）６質量％と、結着剤としてポリフッ化ビニリデン（ＰＶＤＦ）８質量％とを混合して正極合剤とし、Ｎ−メチル−２−ピロリドン（ＮＭＰ）に分散させることによりペーストを調製した。このペーストを厚さ２０μmのアルミニウム集電体に均一に塗布して、乾燥させた後、１５０℃で５時間真空乾燥させ、ロールプレスで圧縮成形することにより正極を作製した。 As for the positive electrode, positive electrode active material LiCo 1/3 Ni 1/3 Mn 1/3 O 2 86% by mass as an active material, 6% by mass of acetylene black (AB) as a conductive additive, and polyvinylidene fluoride as a binder A paste was prepared by mixing 8% by mass of (PVDF) to form a positive electrode mixture and dispersing it in N-methyl-2-pyrrolidone (NMP). This paste was uniformly applied to an aluminum current collector with a thickness of 20 μm, dried, then dried in vacuo at 150 ° C. for 5 hours, and compression molded with a roll press to produce a positive electrode.
負極については、負極活物質ｂ ９５質量％と、ポリフッ化ビニリデン５重量％をＮ−メチルピロリドンに加えてペースト状に調製した。このペーストを厚さ１５μｍの銅集電体に均一に塗布し、乾燥させた後、１００℃で５時間真空乾燥させ、ロールプレスで圧縮成形することにより負極を作製した。
The negative electrode was prepared in the form of a paste by adding 95% by mass of the negative electrode active material b and 5% by weight of polyvinylidene fluoride to N-methylpyrrolidone. This paste was uniformly applied to a 15 μm thick copper current collector, dried, then vacuum dried at 100 ° C. for 5 hours, and compression molded with a roll press to produce a negative electrode.
セパレータには、厚さ２０μｍ程度の微多孔性ポリエチレンフィルムを用い、また、電解液には、エチレンカーボネート（ＥＣ）：ジメチルカーボネート（ＤＭＣ）：エチルメチルカーボネート（ＥＭＣ）＝３：２：５（体積比）の混合溶媒に、更にＬｉＰＦ６を調整後に１ｍｏｌ／Ｌとなるように溶解させたものを用いた。 For the separator, a microporous polyethylene film having a thickness of about 20 μm is used. For the electrolyte, ethylene carbonate (EC): dimethyl carbonate (DMC): ethyl methyl carbonate (EMC) = 3: 2: 5 (volume) Ratio) was further dissolved in LiPF 6 to 1 mol / L after adjustment.
以上の構成・手順で実施例１の非水電解質二次電池を３セル作製した。 Three cells of the nonaqueous electrolyte secondary battery of Example 1 were produced by the above-described configuration and procedure.
［実施例２］
負極活物質ｃを用いたこと以外は実施例１ と同様の、実施例２ の非水電解質二次電池を３セル作製した。
[Example 2]
Three cells of the nonaqueous electrolyte secondary battery of Example 2 were produced in the same manner as in Example 1 except that the negative electrode active material c was used.
［実施例３］
負極活物質ｄを用いたこと以外は実施例１と同様の、実施例３の非水電解質二次電池を３セル作製した。
[Example 3]
Three cells of the nonaqueous electrolyte secondary battery of Example 3 were produced in the same manner as in Example 1 except that the negative electrode active material d was used.
［実施例４］
負極活物質ｅを用いたこと以外は実施例１と同様の、実施例４の非水電解質二次電池を３セル作製した。
[Example 4]
Three cells of the non-aqueous electrolyte secondary battery of Example 4 were produced in the same manner as in Example 1 except that the negative electrode active material e was used.
［比較例１］
負極活物質ａを用いたこと以外は実施例１と同様の、比較例１の非水電解質二次電池を３セル作製した。
[Comparative Example 1]
Three cells of the non-aqueous electrolyte secondary battery of Comparative Example 1 were produced in the same manner as in Example 1 except that the negative electrode active material a was used.
［比較例２］
負極活物質ｆを用いたこと以外は実施例１と同様の、比較例２の非水電解質二次電池を３セル作製した。
[Comparative Example 2 ]
Three cells of the nonaqueous electrolyte secondary battery of Comparative Example 2 were produced in the same manner as in Example 1 except that the negative electrode active material f was used.
［比較例３］
負極活物質ｇを用いたこと以外は実施例１と同様の、比較例３の非水電解質二次電池を３セル作製した。
[Comparative Example 3 ]
Three cells of the nonaqueous electrolyte secondary battery of Comparative Example 3 were produced in the same manner as in Example 1 except that the negative electrode active material g was used.
［比較例４］
負極活物質ｈを用いたこと以外は実施例１と同様の、比較例４の非水電解質二次電池を３セル作製した。
[Comparative Example 4 ]
Three cells of the nonaqueous electrolyte secondary battery of Comparative Example 4 were produced in the same manner as in Example 1 except that the negative electrode active material h was used.
［特性測定］
電池の試験条件は、つぎの通りとした。実施例１〜５および比較例１〜３の電池を、充電は５００ｍＡの電流で４．２Ｖまで３時間定電流定電圧充電し、その後５００ｍＡの電流で２．５Ｖまで放電をおこない、初期の放電容量を確認した。その後、同様の充放電サイクルを５００サイクル繰り返し、５００サイクル後の容量保持率（％）を測定した。ここで「容量保持率」とは、初期の放電容量に対する５００サイクル後の放電容量の比率（％）を示すものとする。データは、３セルの平均値とした。
[Characteristic measurement]
The battery test conditions were as follows. The batteries of Examples 1 to 5 and Comparative Examples 1 to 3 were charged at a constant current and a constant voltage for 3 hours up to 4.2 V at a current of 500 mA, and then discharged to 2.5 V at a current of 500 mA. Confirmed the capacity. Thereafter, the same charge / discharge cycle was repeated 500 times, and the capacity retention rate (%) after 500 cycles was measured. Here, the “capacity holding ratio” indicates the ratio (%) of the discharge capacity after 500 cycles to the initial discharge capacity. The data was an average value of 3 cells.
実施例１〜４および比較例１〜４の電池の、負極活物質の性質およびサイクル容量保持率の測定結果を表２にまとめた。
The properties of the negative electrode active material and the measurement results of the cycle capacity retention of the batteries of Examples 1 to 4 and Comparative Examples 1 to 4 are summarized in Table 2.
［実施例６〜１３］
平均粒径１５μｍであり、ブタノールを用いたピクノメータ法による真密度が２．１４ｇ／ｃｍ３のコークスを炭素材料Ｅとする。また、平均粒径１５μｍであり、ブタノールを用いたピクノメータ法による真密度が１．８４ｇ／ｃｍ３のコークスを炭素材料Ｆとする。
[Examples 6 to 13]
Coke having an average particle diameter of 15 μm and a true density of 2.14 g / cm 3 by a pycnometer method using butanol is defined as carbon material E. Further, coke having an average particle size of 15 μm and a true density of 1.84 g / cm 3 by a pycnometer method using butanol is defined as carbon material F.
そして、炭素材料Ｅを負極活物質ｉとし、炭素材料Ｅ７５質量％と炭素材料Ｂ２５質量％とを混合したものを負極活物質ｊとし、炭素材料Ｅ５０質量％と炭素材料Ｂ５０質量％とを混合したものを負極活物質ｋとし、炭素材料Ｅ２５質量％と炭素材料Ｂ７５質量％とを混合したものを負極活物質ｌとした。 And carbon material E was made into negative electrode active material i, what mixed carbon material E75 mass% and carbon material B25 mass% was made into negative electrode active material j, and carbon material E50 mass% and carbon material B50 mass% were mixed. The negative electrode active material k was used as the negative electrode active material k, and a mixture of 25% by mass of the carbon material E and 75% by mass of the carbon material B was used as the negative electrode active material l.
また、炭素材料Ｆを負極活物質ｍとし、炭素材料Ｆ７５質量％と炭素材料Ｂ２５質量％とを混合したものを負極活物質ｎとし、炭素材料Ｆ５０質量％と炭素材料Ｂ５０質量％とを混合したものを負極活物質ｏとし、炭素材料Ｆ２５質量％と炭素材料Ｂ７５質量％とを混合したものを負極活物質ｐとした。 Also, carbon material F was used as negative electrode active material m, and a mixture of carbon material F 75% by mass and carbon material B 25% by mass was used as negative electrode active material n, and carbon material F 50% by mass and carbon material B 50% by mass were mixed. A negative electrode active material o was used, and a mixture of 25% by mass of carbon material F and 75% by mass of carbon material B was used as negative electrode active material p.
負極活物質ｉ〜ｐの組成を表３にまとめた。 The compositions of the negative electrode active materials i to p are summarized in Table 3.
［比較例５］
負極活物質ｉを用いたこと以外は実施例１と同様の、比較例５の非水電解質二次電池を３セル作製した。
[Comparative Example 5]
Three cells of the non-aqueous electrolyte secondary battery of Comparative Example 5 were produced in the same manner as in Example 1 except that the negative electrode active material i was used.
［実施例５］
負極活物質ｊを用いたこと以外は実施例１と同様の、実施例５の非水電解質二次電池を３セル作製した。
[Example 5 ]
Three cells of the nonaqueous electrolyte secondary battery of Example 5 were produced in the same manner as in Example 1 except that the negative electrode active material j was used.
［実施例６］
負極活物質ｋを用いたこと以外は実施例１と同様の、実施例６の非水電解質二次電池を３セル作製した。
[Example 6 ]
Three cells of the nonaqueous electrolyte secondary battery of Example 6 were produced in the same manner as in Example 1 except that the negative electrode active material k was used.
［実施例７］
負極活物質ｌを用いたこと以外は実施例１と同様の、実施例７の非水電解質二次電池を３セル作製した。
[Example 7 ]
Three cells of the nonaqueous electrolyte secondary battery of Example 7 were produced in the same manner as in Example 1 except that the negative electrode active material l was used.
［比較例６］
負極活物質ｍを用いたこと以外は実施例１と同様の、比較例６の非水電解質二次電池を３セル作製した。
[ Comparative Example 6 ]
Three cells of the nonaqueous electrolyte secondary battery of Comparative Example 6 were produced in the same manner as in Example 1 except that the negative electrode active material m was used.
［実施例８］
負極活物質ｎを用いたこと以外は実施例１と同様の、実施例７の非水電解質二次電池を３セル作製した。
[Example 8 ]
Three cells of the nonaqueous electrolyte secondary battery of Example 7 were produced in the same manner as in Example 1 except that the negative electrode active material n was used.
［実施例９］
負極活物質oを用いたこと以外は実施例１と同様の、実施例９の非水電解質二次電池を３セル作製した。
[Example 9 ]
Three cells of the nonaqueous electrolyte secondary battery of Example 9 were produced in the same manner as in Example 1 except that the negative electrode active material o was used.
［実施例１０］
負極活物質ｐを用いたこと以外は実施例１と同様の、実施例１０の非水電解質二次電池を３セル作製した。
[Example 10 ]
Three cells of the nonaqueous electrolyte secondary battery of Example 10 were produced in the same manner as in Example 1 except that the negative electrode active material p was used.
実施例５〜１０および比較例５〜６で作製した電池について、実施例１と同様の条件で、負極膨張率およびサイクル容量保持率を測定した。
With respect to the batteries produced in Examples 5 to 10 and Comparative Examples 5 to 6 , the negative electrode expansion coefficient and cycle capacity retention were measured under the same conditions as in Example 1.
実施例５〜１０および比較例５〜６の電池の、負極活物質の性質およびサイクル容量保持率の測定結果を表４にまとめた。
Table 4 summarizes the measurement results of the properties of the negative electrode active material and the cycle capacity retention of the batteries of Examples 5 to 10 and Comparative Examples 5 to 6 .
実施例１〜１０および比較例１〜６の結果から、開回路電位の傾きが小さいものはサイクル容量保持率が高かった。これは、充放電にともなう電極上での非水電解質の分解反応によって正極と負極の充電レベルのバランスが変化することが主な原因であり、このバランスの変化による負極開回路電位の変化が比較的小さいものは、サイクル経過ごとの負極の開回路電位が貴にシフトしにくくなり、それによって正極の開回路電位が貴にシフトしにくくなることで、正極上での電解液の酸化分解反応がより進行にくくなり、放電容量が低下しにくいと考えられる。
From the results of Examples 1 to 10 and Comparative Examples 1 to 6 , those having a small slope of the open circuit potential had a high cycle capacity retention rate. This is mainly due to the change in the balance between the charge level of the positive electrode and the negative electrode due to the decomposition reaction of the nonaqueous electrolyte on the electrode due to charge and discharge, and the change in the open circuit potential of the negative electrode due to this change in balance is compared. The smaller the open circuit potential of the negative electrode for each cycle, the lower the open circuit potential of the positive electrode is less likely to shift, and the oxidative decomposition reaction of the electrolyte on the positive electrode It is considered that it becomes more difficult to proceed and the discharge capacity is less likely to decrease.
比較例１では、負極活物質として、ハードカーボン単体を用いているが、その真密度が小さく、また不可逆容量が大きいため、実施例１と同等の電池容量が得られるような負極合材密度にして電池を作製した。その結果、負極合材膨張率は１．０２と小さく、また開回路電位の傾きも―２．０×１０−４Ｖ／（ｍＡｈ／ｇ）と大きいにもかかわらず、サイクル容量保持率は、７３．２％と低かった。これは、ハードカーボン粒子が比較的硬質であるために、電池作製の際に所定の負極合材密度を得るのに、高いプレス圧を必要とし、そのため、粒子同士あるいは粒子−集電体間の密着性が大きく低下してしまったことで、サイクル特性が悪くなったものと考えられる。よって、負極真密度は１．５５ｇ／ｃｍ３以上が好ましい。 In Comparative Example 1, hard carbon alone is used as the negative electrode active material. However, since the true density is small and the irreversible capacity is large, the negative electrode composite density is set such that a battery capacity equivalent to that of Example 1 can be obtained. A battery was produced. As a result, although the negative electrode composite material expansion coefficient was as small as 1.02 and the slope of the open circuit potential was as large as −2.0 × 10 −4 V / (mAh / g), the cycle capacity retention ratio was It was as low as 73.2%. This is because the hard carbon particles are relatively hard, and thus a high press pressure is required to obtain a predetermined negative electrode mixture density during battery production. Therefore, between the particles or between the particles and the current collector. It is considered that the cycle characteristics deteriorated due to the significant decrease in adhesion. Therefore, the negative electrode true density is preferably 1.55 g / cm 3 or more.
以上の結果から、充放電にともなう電極上での非水電解質の分解反応によって正極と負極の充電レベルのバランスが変化することが主な原因であり、このバランスの変化による負極開回路電位の変化が比較的小さいものは、サイクル経過ごとの負極の開回路電位が貴にシフトしにくくなり、それによって正極の開回路電位が貴にシフトしにくくなることで、正極上での電解液の酸化分解反応がより進行しにくくなり、放電容量が低下しにくいと考えられる。 From the above results, the main cause is the change in the balance between the charge level of the positive electrode and the negative electrode due to the decomposition reaction of the nonaqueous electrolyte on the electrode due to charge / discharge, and the change in the open circuit potential of the negative electrode due to this change in balance Is relatively small, the open circuit potential of the negative electrode hardly shifts every cycle, and the open circuit potential of the positive electrode becomes difficult to shift preciously, so that the oxidative decomposition of the electrolyte on the positive electrode It is considered that the reaction is less likely to proceed and the discharge capacity is less likely to decrease.
すなわち、開回路電位の傾きを−９．５×１０−４Ｖ／（ｍＡｈ／ｇ）以上とすることで、サイクル寿命特性の大幅な向上を実現できることを示唆している。しかしながら、比較例２では、開回路電位の傾きが−１．４×１０−４Ｖ／（ｍＡｈ／ｇ）と大きいにもかかわらず、サイクル容量保持率は、６２．２％と低かった。これは、充放電にともなう負極上での電解液の還元分解による低下が原因と考えられ、比較例２のように、開回路電位の傾きをより大きくするために、負極の充電深度を高くしすぎると、その分解反応が促進されてしまう。よって、開回路電位の傾きは−１．５×１０−４Ｖ／（ｍＡｈ／ｇ）以下とすることが好ましい。 That is, it is suggested that the cycle life characteristics can be significantly improved by setting the slope of the open circuit potential to −9.5 × 10 −4 V / (mAh / g) or more. However, in Comparative Example 2, the cycle capacity retention was as low as 62.2% despite the large slope of the open circuit potential being −1.4 × 10 −4 V / (mAh / g). This is considered to be caused by a reduction due to reductive decomposition of the electrolyte solution on the negative electrode due to charge / discharge. As in Comparative Example 2, in order to increase the slope of the open circuit potential, the charge depth of the negative electrode was increased. If too much, the decomposition reaction is promoted. Therefore, the slope of the open circuit potential is preferably −1.5 × 10 −4 V / (mAh / g) or less.
［参考例１１、実施例１２、実施例１３および比較例７〜８］
炭素材料Ａ１０質量％と炭素材料Ｃ９０質量％とを混合したものを負極活物質ｑとし、炭素材料Ａ２０質量％と炭素材料Ｃ８０質量％とを混合したものを負極活物質ｒとし、炭素材料Ａ４０質量％と炭素材料Ｃ６０質量％とを混合したものを負極活物質ｓとし、炭素材料Ａ７０質量％と炭素材料Ｃ３０質量％とを混合したものを負極活物質ｔとし、炭素材料Ａ９０質量％と炭素材料Ｃ１０質量％とを混合したものを負極活物質ｕとした。
[ Reference Example 11, Example 12, Example 13 and Comparative Examples 7 to 8 ]
What mixed carbon material A10 mass% and carbon material C90 mass% was made into negative electrode active material q, what mixed carbon material A20 mass% and carbon material C80 mass% was made into negative electrode active material r, and carbon material A40 mass % And carbon material C 60% by mass are used as negative electrode active material s, and carbon material A 70% by mass and carbon material C 30% by mass are used as negative electrode active material t, and carbon material A 90% by mass and carbon material. What mixed C10 mass% was made into the negative electrode active material u.
負極活物質ｑ〜ｕの組成を表５にまとめた。 The compositions of the negative electrode active materials q to u are summarized in Table 5.
［比較例７］
負極活物質ｑを用いたこと以外は実施例１と同様の、比較例７の非水電解質二次電池を３セル作製した。
[Comparative Example 7 ]
Three cells of the nonaqueous electrolyte secondary battery of Comparative Example 7 were produced in the same manner as in Example 1 except that the negative electrode active material q was used.
［比較例８］
負極活物質ｒを用いたこと以外は実施例１と同様の、比較例８の非水電解質二次電池を３セル作製した。
[Comparative Example 8 ]
Three cells of the nonaqueous electrolyte secondary battery of Comparative Example 8 were produced in the same manner as in Example 1 except that the negative electrode active material r was used.
［実施例１２］
負極活物質ｓを用いたこと以外は実施例１と同様の、実施例１２の非水電解質二次電池を３セル作製した。
[ Example 12 ]
Three cells of the nonaqueous electrolyte secondary battery of Example 12 were produced in the same manner as in Example 1 except that the negative electrode active material s was used.
［実施例１３］
負極活物質ｔを用いたこと以外は実施例１と同様の、実施例１３の非水電解質二次電池
を３セル作製した。
[ Example 13 ]
Three cells of the nonaqueous electrolyte secondary battery of Example 13 were produced in the same manner as in Example 1 except that the negative electrode active material t was used.
［参考例１１］
負極活物質ｕを用いたこと以外は実施例１と同様の、参考例１１の非水電解質二次電池を３セル作製した。
[ Reference Example 11 ]
Three cells of the nonaqueous electrolyte secondary battery of Reference Example 11 were produced in the same manner as in Example 1 except that the negative electrode active material u was used.
参考例１１、実施例１２、実施例１３および比較例７〜８で作製した電池について、実施例１と同様の条件で、負極膨張率およびサイクル容量保持率を測定した。 For the batteries produced in Reference Example 11, Example 12, Example 13, and Comparative Examples 7-8 , the negative electrode expansion coefficient and cycle capacity retention were measured under the same conditions as in Example 1.
参考例１１、実施例１２、実施例１３および比較例７〜８の電池の、負極活物質の性質およびサイクル容量保持率の測定結果を表６にまとめた。なお、表６には、比較のため、比較例１および比較例３のデータも示した。 Table 6 summarizes the measurement results of the properties of the negative electrode active material and the cycle capacity retention of the batteries of Reference Example 11, Example 12, Example 13, and Comparative Examples 7-8 . In Table 6, the data of Comparative Examples 1 and 3 are also shown for comparison.
これらの比較から、開回路電位の傾きが、−９．５×１０−４Ｖ／（ｍＡｈ／ｇ）以上−１．５×１０−４Ｖ／（ｍＡｈ／ｇ）以下である負極の中でも、負極合材の膨張率が小さい方がサイクル容量保持率が高い傾向を示した。 From these comparisons, among the negative electrodes whose slope of the open circuit potential is −9.5 × 10 −4 V / (mAh / g) or more and −1.5 × 10 −4 V / (mAh / g) or less, The smaller the negative electrode composite expansion coefficient, the higher the cycle capacity retention rate.
これは、負極合材の膨張率が小さいために、充放電サイクルにともなう電解液との反応面積の増加量が少なく、正極と負極の充電レベルのバランスの変化が小さくなることおよび活物質粒子間あるいは活物質と集電体との密着性および導電性の低下が小さくなることが理由であると考えられる。 This is because the expansion rate of the negative electrode mixture is small, so the increase in the reaction area with the electrolyte accompanying the charge / discharge cycle is small, the change in the balance between the charge level of the positive electrode and the negative electrode is small, and between the active material particles Or it is thought that it is because the fall of the adhesiveness of an active material and an electrical power collector and electroconductivity becomes small.
よって、膨張率は１．１０以下が好ましい。また、真密度が比較的高いものは、負極の膨張率も大きくなる傾向にあることから、負極真密度は２．１５ｇ／ｃｍ３以下が好ましい。 Therefore, the expansion coefficient is preferably 1.10 or less. In addition, since those having a relatively high true density tend to increase the expansion coefficient of the negative electrode, the negative electrode true density is preferably 2.15 g / cm 3 or less.
［比較例１１〜２０］
［比較例１１］
正極活物質としてＬｉ１．１Ｍｎ１．９Ｏ４を用いたこと以外は比較例１と同様の、比較例１１の非水電解質二次電池を３セル作製した。
[ Comparative Examples 11 to 20 ]
[ Comparative Example 11 ]
Three cells of the nonaqueous electrolyte secondary battery of Comparative Example 11 were produced in the same manner as Comparative Example 1 except that Li 1.1 Mn 1.9 O 4 was used as the positive electrode active material.
［比較例１２］
正極活物質としてＬｉＣｏＯ２を用いたこと以外は比較例１と同様の、比較例１２の非水電解質二次電池を３セル作製した。
[ Comparative Example 12 ]
Three cells of the nonaqueous electrolyte secondary battery of Comparative Example 12 were produced in the same manner as Comparative Example 1 except that LiCoO 2 was used as the positive electrode active material.
［比較例１３］
正極活物質としてＬｉＣｏ０．９Ｎｉ０．１Ｏ２を用いたこと以外は比較例１と同様の、比較例１３の非水電解質二次電池を３セル作製した。
[ Comparative Example 13 ]
Three cells of the nonaqueous electrolyte secondary battery of Comparative Example 13 were manufactured in the same manner as Comparative Example 1 except that LiCo 0.9 Ni 0.1 O 2 was used as the positive electrode active material.
［比較例１４］
正極活物質としてＬｉＣｏ０．６Ｎｉ０．４Ｏ２を用いたこと以外は比較例１と同様の、比較例１４の非水電解質二次電池を３セル作製した。
[ Comparative Example 14 ]
Three cells of the nonaqueous electrolyte secondary battery of Comparative Example 14 were produced in the same manner as Comparative Example 1 except that LiCo 0.6 Ni 0.4 O 2 was used as the positive electrode active material.
［比較例１５］
正極活物質としてＬｉＣｏ０．２Ｎｉ０．８Ｏ２を用いたこと以外は比較例１と同様の、比較例１５の非水電解質二次電池を３セル作製した。
[ Comparative Example 15 ]
Three cells of the nonaqueous electrolyte secondary battery of Comparative Example 15 were produced in the same manner as Comparative Example 1 except that LiCo 0.2 Ni 0.8 O 2 was used as the positive electrode active material.
［比較例１６］
正極活物質としてＬｉＮｉＯ２を用いたこと以外は比較例１と同様の、比較例１６の非水電解質二次電池を３セル作製した。
[ Comparative Example 16 ]
Three cells of the nonaqueous electrolyte secondary battery of Comparative Example 16 were produced in the same manner as Comparative Example 1 except that LiNiO 2 was used as the positive electrode active material.
［比較例１７］
正極活物質としてＬｉＣｏ０．９Ｎｉ０．０５Ｍｎ０．０５Ｏ２を用いたこと以外は比較例１と同様の、比較例１７の非水電解質二次電池を３セル作製した。
[ Comparative Example 17 ]
Three cells of the nonaqueous electrolyte secondary battery of Comparative Example 17 were produced in the same manner as Comparative Example 1 except that LiCo 0.9 Ni 0.05 Mn 0.05 O 2 was used as the positive electrode active material.
［比較例１８］
正極活物質としてＬｉＣｏ０．６Ｎｉ０．２Ｍｎ０．２Ｏ２を用いたこと以外は比較例１と同様の、比較例１８の非水電解質二次電池を３セル作製した。
[ Comparative Example 18 ]
Three cells of the nonaqueous electrolyte secondary battery of Comparative Example 18 were produced in the same manner as Comparative Example 1 except that LiCo 0.6 Ni 0.2 Mn 0.2 O 2 was used as the positive electrode active material.
［比較例１９］
正極活物質としてＬｉＣｏ０．２Ｎｉ０．４Ｍｎ０．４Ｏ２を用いたこと以外は比較例１と同様の、比較例１９の非水電解質二次電池を３セル作製した。
[ Comparative Example 19 ]
Three cells of the nonaqueous electrolyte secondary battery of Comparative Example 19 were produced in the same manner as Comparative Example 1 except that LiCo 0.2 Ni 0.4 Mn 0.4 O 2 was used as the positive electrode active material.
［比較例２０］
正極活物質としてＬｉＮｉ０．５Ｍｎ０．５Ｏ２を用いたこと以外は比較例１と同様の、比較例２０の非水電解質二次電池を３セル作製した。
[ Comparative Example 20 ]
Three cells of the nonaqueous electrolyte secondary battery of Comparative Example 20 were manufactured in the same manner as Comparative Example 1 except that LiNi 0.5 Mn 0.5 O 2 was used as the positive electrode active material.
なお、比較例１１〜２０の電池には負極活物質としてａ を用いたため、負極合材の膨張率は１．０７であり、電位の傾きは−８．１×１０−４Ｖ／（ｍＡｈ／ｇ）。
比較例１１〜２０で作製した電池について、比較例１と同様の条件で、負極膨張率およびサイクル容量保持率を測定した。
In addition, since a was used as the negative electrode active material in the batteries of Comparative Examples 11 to 20, the negative electrode composite had an expansion coefficient of 1.07, and the potential gradient was −8.1 × 10 −4 V / (mAh / g) .
The battery fabricated in Comparative Example 11 to 20, under the same conditions as in Comparative Example 1 was measured negative electrode expansion rate and cycle capacity retention rate.
比較例１１〜２０の電池についてのサイクル容量保持率の測定結果を表７にまとめた。なお、表７には、比較のため、比較例１のデータも示した。
Table 7 summarizes the measurement results of the cycle capacity retention rate for the batteries of Comparative Examples 11-20 . Table 7 also shows the data of Comparative Example 1 for comparison.
比較例１および比較例１１〜２０の結果から、正極活物質の種類に係わらず、負極活物質の電位の傾きが−８．１×１０−４Ｖ／（ｍＡｈ／ｇ）の場合には、優れたサイクル容量保持率が得られることがわかった。
From the results of Comparative Example 1 and Comparative Examples 11 to 20, regardless of the type of the positive electrode active material, when the slope of the potential of the negative electrode active material is −8.1 × 10 −4 V / (mAh / g), It was found that excellent cycle capacity retention was obtained.
また、理由は明らかではないが、正極活物質として、リチウムとマンガンとコバルトとニッケルの複合酸化物、すなわち一般式ＬｉａＣｏｂＮｉｃＭｎｄＯ２（但し、０＜ａ≦１．２、０≦ｂ≦１、０≦ｃ≦１、０≦ｄ≦１）で表される活物質を用いた場合、比較的良好な結果を示すことがわかった。 Although the reason is not clear, as the positive electrode active material, composite oxide of lithium and manganese, cobalt and nickel, i.e. the general formula Li a Co b Ni c Mn d O 2 ( where, 0 <a ≦ 1.2, It was found that when an active material represented by 0 ≦ b ≦ 1, 0 ≦ c ≦ 1, 0 ≦ d ≦ 1) was used, relatively good results were shown.
１ 非水電解質二次電池
２ 発電要素
３ 負極
４ 正極
５ セパレータ
６ 電池ケース
７ 電池蓋
DESCRIPTION OF SYMBOLS 1 Nonaqueous electrolyte secondary battery 2 Power generation element 3 Negative electrode 4 Positive electrode 5 Separator 6 Battery case 7 Battery cover
Claims (2)
とする請求項１記載の非水電解質二次電池。 2. The nonaqueous electrolyte secondary battery according to claim 1, wherein an expansion coefficient of the negative electrode mixture layer in a charged state with respect to a discharged state of the battery is 1.10 or less.
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| WO2009022664A1 (en) * | 2007-08-10 | 2009-02-19 | Showa Denko K.K. | Negative electrode for lithium secondary battery, method for producing carbon-based negative electrode active material, lithium secondary battery and use thereof |
| JP5157365B2 (en) * | 2007-10-25 | 2013-03-06 | 株式会社豊田中央研究所 | Lithium ion secondary battery and electric vehicle power source using the same |
| JP5045420B2 (en) * | 2007-12-21 | 2012-10-10 | 宇部興産株式会社 | Electrode evaluation method and evaluation apparatus |
| JP2010092845A (en) * | 2008-09-10 | 2010-04-22 | Sumitomo Chemical Co Ltd | Non-aqueous electrolyte secondary cell |
| JP2013218855A (en) * | 2012-04-06 | 2013-10-24 | Sumitomo Bakelite Co Ltd | Negative electrode carbon material, negative electrode active material, negative electrode and lithium ion secondary battery |
| US20170162874A1 (en) | 2014-03-31 | 2017-06-08 | Kureha Corporation | Carbonaceous material for negative electrode of non-aqueous electrolyte secondary battery, negative electrode for non-aqueous electrolyte secondary battery, non-aqueous electrolyte secondary battery, and vehicle |
| WO2015152092A1 (en) * | 2014-03-31 | 2015-10-08 | 株式会社クレハ | Negative-electrode material for nonaqueous-electrolyte secondary battery, negative-electrode mixture for nonaqueous-electrolyte secondary battery, negative electrode for nonaqueous-electrolyte secondary battery, nonaqueous-electrolyte secondary battery, and vehicle |
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