JP4467317B2 - Negative electrode and non-aqueous electrolyte secondary battery - Google Patents
Negative electrode and non-aqueous electrolyte secondary battery Download PDFInfo
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- 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
Description
本発明は、負極およびそれを備えた非水電解質二次電池に関する。 The present invention relates to a negative electrode and a nonaqueous electrolyte secondary battery including the negative electrode.
近年、携帯機器の発達に伴い、軽量および高エネルギー密度を特徴とするリチウムニ次電池が多く用いられるようになった。最近では、リチウムニ次電池の動力用電源としての用途が期待され、高容量および高出カを有し、温度特性、サイクル特性に優れたリチウムニ次電池が要求されている。 In recent years, with the development of portable devices, lithium secondary batteries characterized by light weight and high energy density have come to be used frequently. Recently, the lithium secondary battery is expected to be used as a power source for power, and a lithium secondary battery having high capacity and high output and excellent temperature characteristics and cycle characteristics is required.
リチウムニ次電池の負極材料としては、リチウムイオンの吸蔵および放出が可能な黒鉛、コークス、有機焼成体等の炭素材料が使用されている。特に、天然黒鉛および人造黒鉛は、高容量でかつ電位平坦性に優れ、単位体積当りのエネルギー密度が高いことから、最も多く用いられている。 As a negative electrode material of a lithium secondary battery, carbon materials such as graphite, coke, and organic fired body capable of inserting and extracting lithium ions are used. In particular, natural graphite and artificial graphite are most frequently used because of their high capacity, excellent potential flatness, and high energy density per unit volume.
ところが、負極材料として黒鉛を用いた非水電解質二次電池において、電解液としてプロピレンカーボネート（ＰＣ）を用いた場合、充電時に電極表面において電解液が分解し、リチウムのインターカレーション反応を進行させることができないことが知られている。 However, in a non-aqueous electrolyte secondary battery using graphite as a negative electrode material, when propylene carbonate (PC) is used as an electrolytic solution, the electrolytic solution is decomposed on the surface of the electrode during charging, and the lithium intercalation reaction proceeds. It is known that it cannot.
このため、エチレンカーボネート（ＥＣ）を用いた電解液が多く用いられているが、活性な黒鉛からなる電極表面において電解液が分解することにより可逆容量が低下するとともにサイクル特性が低下する。 For this reason, an electrolytic solution using ethylene carbonate (EC) is often used. However, when the electrolytic solution is decomposed on the surface of the electrode made of active graphite, the reversible capacity is lowered and the cycle characteristics are also lowered.
そこで、天然黒鉛または人造黒鉛の表面を、黒鉛よりも結晶性の低い炭素系材料で被覆することにより、プロピレンカーボネートを用いた電解液中でも安定な充電反応を可能にする方法が数多く提案されている（特許文献１参照）。 Therefore, many methods have been proposed that enable a stable charging reaction even in an electrolytic solution using propylene carbonate by coating the surface of natural graphite or artificial graphite with a carbon-based material having lower crystallinity than graphite. (See Patent Document 1).
また、黒鉛は電解液に対する分解活性が高いという問題を有することから、黒鉛よりも結晶性が低く電解液に対して分解活性の低い非黒鉛炭素材料を負極材料として用いる技術も提案されている（特許文献２参照）。 Further, since graphite has a problem of high decomposition activity with respect to an electrolytic solution, a technique using a non-graphite carbon material having a lower crystallinity and lower decomposition activity with respect to an electrolytic solution as a negative electrode material has been proposed ( Patent Document 2).
しかしながら、この非黒鉛炭素材料は、充放電効率が低く、密度が低いことから、電池としてのエネルギー密度が低くなるため、要求されるリチウム二次電池の特性を満足することができない。そこで、黒鉛に非黒鉛炭素材料（難黒鉛化性炭素または易黒鉛化性炭素）を混合した複合炭素材料を用いる技術が提案されている（特許文献３参照）。
しかし、黒鉛は、非黒鉛炭素材料に比べ硬度が低いので、極板の圧延形成時において必要とされるエネルギー密度を得る充填密度まで加圧すると、黒鉛粒子が潰れ、粒子間の空隙率が大きく低下する。そのため、負極活物質の黒鉛への電解液の含浸が充分に行われない。その結果、黒鉛を負極活物質として用いた非水電解質二次電池は、負荷特性が悪く、低温において充分な電気化学的特性を得ることができない。 However, graphite has a lower hardness than non-graphitic carbon materials, so when pressed to a packing density that obtains the energy density required for rolling the electrode plate, the graphite particles are crushed and the porosity between the particles is large. descend. Therefore, the negative electrode active material is not sufficiently impregnated with the electrolyte in the graphite. As a result, the nonaqueous electrolyte secondary battery using graphite as a negative electrode active material has poor load characteristics and cannot obtain sufficient electrochemical characteristics at low temperatures.
特に、低結晶性炭素で被覆された黒鉛では、極板を加圧形成する際の粒子の潰れにより低結晶性炭素が崩壊し、黒鉛部分の露出により低温における電気化学的特性が劣化する。 In particular, in graphite coated with low crystalline carbon, the low crystalline carbon collapses due to particle collapse when the electrode plate is formed under pressure, and the electrochemical properties at low temperatures deteriorate due to the exposure of the graphite portion.
このような電気化学特性を向上させるには、極板の加圧形成時における黒鉛の粒子の潰れを防ぎ、黒鉛粒子間の空隙率を増加させ、負極活物質への電解液の含浸性を向上させることが重要である。 In order to improve such electrochemical properties, the graphite particles are prevented from being crushed during pressure forming of the electrode plate, the porosity between the graphite particles is increased, and the impregnation of the electrolyte into the negative electrode active material is improved. It is important to let
本発明の目的は、エネルギー密度が高くかつ負荷特性および低温特性に優れた負極およびそれを用いた非水電解質二次電池を提供することである。 An object of the present invention is to provide a negative electrode having high energy density and excellent load characteristics and low-temperature characteristics, and a nonaqueous electrolyte secondary battery using the negative electrode.
本発明に係る非水電解質二次電池は、正極および負極を備えた非水電解質二次電池であって、負極は、低結晶性炭素被覆黒鉛および難黒鉛化性炭素の混合物を含み、低結晶性炭素被覆黒鉛は、黒鉛からなる第１の炭素材料と、第１の炭素材料の表面の一部または全部を被覆する第２の炭素材料とから構成され、第２の炭素材料は、第１の炭素材料よりも結晶性が低く、難黒鉛化性炭素は、第１の炭素材料よりも結晶性が低く、前記低結晶性炭素被覆黒鉛に対する前記難黒鉛化炭素の割合が０よりも大きく１０重量％以下であり、前記難黒鉛化性炭素の平均粒径は、前記低結晶性炭素被覆黒鉛の平均粒径以上である。
A non-aqueous electrolyte secondary battery according to the present invention is a non-aqueous electrolyte secondary battery including a positive electrode and a negative electrode, the negative electrode including a mixture of low crystalline carbon-coated graphite and non-graphitizable carbon, and low crystal The carbon-coated graphite is composed of a first carbon material made of graphite and a second carbon material that covers a part or all of the surface of the first carbon material. crystallinity is lower than the carbon material, non-graphitizable carbon, crystalline than the first carbon material is rather low, greater than the percentage of the flame graphitized carbon for the low crystalline
本発明に係る非水電解質二次電池においては、低結晶性炭素被覆黒鉛中の第１の炭素材料が高い充放電効率および高い密度を有する黒鉛からなるので、十分に高いエネルギー密度が得られる。また、黒鉛からなる第１の炭素材料が低結晶性炭素からなる第２の炭素材料で被覆されているので、非水電解質の分解が起こらず、安定な充放電が可能となる。 In the non-aqueous electrolyte secondary battery according to the present invention, since the first carbon material in the low crystalline carbon-coated graphite is made of graphite having high charge / discharge efficiency and high density, a sufficiently high energy density can be obtained. In addition, since the first carbon material made of graphite is coated with the second carbon material made of low crystalline carbon, the nonaqueous electrolyte is not decomposed and stable charge / discharge is possible.
さらに、負極の圧延形成時には、低結晶性炭素被覆黒鉛および難黒鉛化性炭素の混合物が加圧される。この場合、難黒鉛化性炭素が低結晶性炭素被覆黒鉛と比較して高い硬度を有するので、難黒鉛化性炭素および低結晶性炭素被覆黒鉛の粒子の潰れが抑制され、粒子間の空隙率の低下が防止される。その結果、負極への非水電解質の含浸性が高くなり、二次電池の負荷特性および低温特性が向上する。 Furthermore, a mixture of low crystalline carbon-coated graphite and non-graphitizable carbon is pressurized during the rolling of the negative electrode. In this case, since the non-graphitizable carbon has a higher hardness than the low-crystalline carbon-coated graphite, crushing of the particles of the non-graphitizable carbon and the low-crystalline carbon-coated graphite is suppressed, and the porosity between the particles Is prevented. As a result, the impregnation property of the nonaqueous electrolyte into the negative electrode is increased, and the load characteristics and low temperature characteristics of the secondary battery are improved.
また、低結晶性炭素からなる第２の炭素材料および難黒鉛化性炭素は黒鉛からなる第１の炭素材料と比べて結晶性が低く、結晶面がランダムな方向を向いている。それにより、非水電解質中のイオンがあらゆる方向から低結晶性炭素からなる第２の炭素材料および難黒鉛化性炭素の粒子内に浸入することができるので、粒子間の電荷移動抵抗が小さくなる。その結果、二次電池の負荷特性および低温特性がより向上する。 In addition, the second carbon material made of low crystalline carbon and the non-graphitizable carbon are lower in crystallinity than the first carbon material made of graphite, and the crystal plane faces a random direction. As a result, ions in the non-aqueous electrolyte can enter the second carbon material made of low crystalline carbon and the non-graphitizable carbon particles from all directions, so that the charge transfer resistance between the particles is reduced. . As a result, the load characteristics and low temperature characteristics of the secondary battery are further improved.
第１の炭素材料は、天然黒鉛または人造黒鉛であることが好ましい。それにより、十分に高いエネルギー密度が得られる。 The first carbon material is preferably natural graphite or artificial graphite. Thereby, a sufficiently high energy density is obtained.
低結晶性炭素被膜黒鉛に対する難黒鉛化性炭素材料の混合割合が０よりも大きく１０重量％以下であることが好ましい。
The mixing ratio of the non-graphitizable carbon material to the low crystalline carbon-coated graphite is preferably greater than 0 and 10% by weight or less .
難黒鉛化性炭素の混合割合が０よりも大きいことにより低結晶性炭素被覆黒鉛の粒子の潰れが抑制される。また、難黒鉛化性炭素の混合割合が１０重量％以下にすることにより負極中の黒鉛の量を十分に確保することができる。それにより、十分なエネルギー密度を得ることができる。
When the mixing ratio of the non-graphitizable carbon is larger than 0, the collapse of the particles of the low crystalline carbon-coated graphite is suppressed. Moreover, when the mixing ratio of the non-graphitizable carbon is 10% by weight or less, the amount of graphite in the negative electrode can be sufficiently ensured. Thereby, sufficient energy density can be obtained.
難黒鉛化性炭素の平均粒径は、低結晶性炭素被覆黒鉛の平均粒径以上であることが好ましい。それより、負極の加圧形成時に低結晶性炭素被覆黒鉛の粒子が潰れることを十分に防止することができる。 The average particle size of the non-graphitizable carbon is preferably equal to or greater than the average particle size of the low crystalline carbon-coated graphite. Thereby, it is possible to sufficiently prevent the particles of the low crystalline carbon-coated graphite from being crushed during the pressure forming of the negative electrode.
本発明に係る負極は、非水電解質二次電池に用いられる負極であって、低結晶性炭素被膜黒鉛および難黒鉛化性炭素の混合物を含み、低結晶性炭素被膜黒鉛は、黒鉛からなる第１の炭素材料と、第１の炭素材料の表面の一部または全部を被覆する第２の炭素材料とから構成され、第２の炭素材料は、第１の炭素材料よりも結晶性が低く、難黒鉛化炭素は、第１の炭素材料よりも結晶性が低く、前記低結晶性炭素被覆黒鉛に対する前記難黒鉛化炭素の割合が０よりも大きく１０重量％以下であり、前記難黒鉛化性炭素の平均粒径は、前記低結晶性炭素被覆黒鉛の平均粒径以上であることを特徴とする。
The negative electrode according to the present invention is a negative electrode used for a non-aqueous electrolyte secondary battery, and includes a mixture of low crystalline carbon-coated graphite and non-graphitizable carbon, and the low crystalline carbon-coated graphite is composed of graphite. 1 carbon material and a second carbon material covering a part or all of the surface of the first carbon material, the second carbon material has lower crystallinity than the first carbon material, non-graphitizable carbon, crystalline than the first carbon material is rather low, the proportion of the flame-graphitizable carbon for the low crystalline carbon-coated graphite is not more than 10 wt% greater than 0, the flame-graphitizable The average particle size of the crystalline carbon is not less than the average particle size of the low crystalline carbon-coated graphite.
本発明に係る負極においては、低結晶性炭素被覆黒鉛中の第１の炭素材料が高い充放電効率および高い密度を有する黒鉛からなるので、十分に高いエネルギー密度が得られる。また、黒鉛からなる第１の炭素材料が低結晶性炭素からなる第２の炭素材料で被覆されているので、非水電解質の分解が起こらず、安定な充放電が可能となる。さらに、難黒鉛化性炭素が低結晶性炭素からなる第２の炭素材料に比べて高い密度を有するので、エネルギー密度の低下が生じない。 In the negative electrode according to the present invention, since the first carbon material in the low crystalline carbon-coated graphite is made of graphite having high charge / discharge efficiency and high density, a sufficiently high energy density can be obtained. In addition, since the first carbon material made of graphite is coated with the second carbon material made of low crystalline carbon, the nonaqueous electrolyte is not decomposed and stable charge / discharge is possible. Furthermore, since the non-graphitizable carbon has a higher density than the second carbon material made of low crystalline carbon, the energy density does not decrease.
さらに、負極の圧延形成時には、低結晶性炭素被覆黒鉛および難黒鉛化性炭素の混合物が加圧される。この場合、難黒鉛化性炭素が低結晶性炭素被覆黒鉛と比較して高い硬度を有するので、難黒鉛化性炭素および低結晶性炭素被覆黒鉛の粒子の潰れが抑制され、粒子間の空隙率の低下が防止される。その結果、負極への非水電解質の含浸性が高くなり、二次電池の負荷特性および低温特性が向上する。 Furthermore, a mixture of low crystalline carbon-coated graphite and non-graphitizable carbon is pressurized during the rolling of the negative electrode. In this case, since the non-graphitizable carbon has a higher hardness than the low-crystalline carbon-coated graphite, crushing of the particles of the non-graphitizable carbon and the low-crystalline carbon-coated graphite is suppressed, and the porosity between the particles Is prevented. As a result, the impregnation property of the nonaqueous electrolyte into the negative electrode is increased, and the load characteristics and low temperature characteristics of the secondary battery are improved.
また、低結晶性炭素からなる第２の炭素材料および難黒鉛化性炭素は黒鉛からなる第１の炭素材料と比べて結晶性が低く、結晶面がランダムな方向を向いている。それにより、非水電解質中のイオンがあらゆる方向から低結晶性炭素からなる第２の炭素材料および難黒鉛化性炭素の粒子内に侵入することができるので、粒子間の電荷移動抵抗が小さくなる。その結果、二次電池の負荷特性および低温特性がより向上する。
更に、低結晶性炭素被覆黒鉛に対する難黒鉛化性炭素の混合割合が０よりも大きく１０重量％以下であることが好ましい。
難黒鉛化性炭素の混合割合が０よりも大きいことにより低結晶性炭素被覆黒鉛の粒子の潰れが抑制される。また、難黒鉛化性炭素の混合割合が１０重量％以下にすることにより負極中の黒鉛の量を十分に確保することができる。それにより、十分なエネルギー密度を得ることができる。
難黒鉛化性炭素の平均粒径は、低結晶性炭素被覆黒鉛の平均粒径以上であることが好ましい。それより、負極の加圧形成時に低結晶性炭素被覆黒鉛の粒子が潰れることを十分に防止することができる。
In addition, the second carbon material made of low crystalline carbon and the non-graphitizable carbon are lower in crystallinity than the first carbon material made of graphite, and the crystal plane faces a random direction. As a result, ions in the non-aqueous electrolyte can enter the second carbon material made of low crystalline carbon and particles of non-graphitizable carbon from all directions, so that the charge transfer resistance between the particles is reduced. . As a result, the load characteristics and low temperature characteristics of the secondary battery are further improved.
Furthermore, it is preferable that the mixing ratio of the non-graphitizable carbon to the low crystalline carbon-coated graphite is greater than 0 and 10% by weight or less.
When the mixing ratio of the non-graphitizable carbon is larger than 0, the collapse of the particles of the low crystalline carbon-coated graphite is suppressed. Moreover, when the mixing ratio of the non-graphitizable carbon is 10% by weight or less, the amount of graphite in the negative electrode can be sufficiently ensured. Thereby, sufficient energy density can be obtained.
The average particle size of the non-graphitizable carbon is preferably equal to or greater than the average particle size of the low crystalline carbon-coated graphite. Thereby, it is possible to sufficiently prevent the particles of the low crystalline carbon-coated graphite from being crushed during the pressure forming of the negative electrode.
本発明に係る負極および非水電解質二次電池によれば、エネルギー密度が高く、負荷特性および低温特性が向上する。 According to the negative electrode and the nonaqueous electrolyte secondary battery according to the present invention, the energy density is high, and the load characteristics and the low temperature characteristics are improved.
以下、本発明の実施の形態に係る非水電解質二次電池について説明する。本発明は以下に示す実施の形態に限定されるものではなく、その要旨を変更しない範囲において適宜変更して実施できるものである。 Hereinafter, the nonaqueous electrolyte secondary battery according to the embodiment of the present invention will be described. The present invention is not limited to the embodiments described below, and can be implemented with appropriate modifications within a scope not changing the gist thereof.
本実施の形態に係る非水電解質二次電池は、負極、正極および非水電解質により構成される。 The nonaqueous electrolyte secondary battery according to the present embodiment includes a negative electrode, a positive electrode, and a nonaqueous electrolyte.
負極活物質は、低結晶性炭素被覆黒鉛と難黒鉛化性炭素との混合物からなる。以下、低結晶性炭素被覆黒鉛と難黒鉛化性炭素との混合物を複合炭素材料と呼ぶ。 The negative electrode active material is composed of a mixture of low crystalline carbon-coated graphite and non-graphitizable carbon. Hereinafter, a mixture of low crystalline carbon-coated graphite and non-graphitizable carbon is referred to as a composite carbon material.
図１は本実施の形態に係る非水電解質二次電池における負極活物質の構成を示す模式図である。 FIG. 1 is a schematic diagram showing the configuration of the negative electrode active material in the nonaqueous electrolyte secondary battery according to the present embodiment.
図１において、複合炭素材料１００は、低結晶性炭素被覆黒鉛１０および難黒鉛化性炭素２０の混合物により構成される。低結晶性炭素被覆黒鉛１０は、芯材となる黒鉛１１の表面が低結晶性炭素１２で被覆された構造を有する。黒鉛１１としては、天然黒鉛または人造黒鉛が用いられる。低結晶性炭素１２としては、非晶質炭素等が用いられる。難黒鉛化性炭素２０は、フェノール樹脂、フラン樹脂、セルロース樹脂、キシレノール樹脂、塩化ビニル樹脂、ポリビニルアルコール樹脂、エポキシ樹脂、ポリスチレン樹脂等を炭化することにより得られる。
In FIG. 1, the
なお、黒鉛１１の表面の全てが低結晶性炭素１２で被覆されていることが好ましいが、黒鉛１１の表面の一部が低結晶性炭素１２で被覆されていてもよい。
Although it is preferable that the entire surface of the
低結晶性炭素１２は、黒鉛１１に比べて配向性が低く、エッジ面が多い。すなわち、低結晶性炭素１２の結晶性は黒鉛１１の結晶性よりも低い。また、難黒鉛化性炭素２０は、黒鉛１１に比べて配向性が低く、エッジ面が多い。すなわち、難黒鉛化性炭素２０の結晶性は黒鉛１１の結晶性よりも低い。
The low
また、難黒鉛化性炭素２０の硬度は、黒鉛１１および低結晶性炭素１２の硬度よりも高い。難黒鉛化性炭素２０の密度は、低結晶性炭素被覆黒鉛２０の密度よりも大きい。
Further, the hardness of the
正極活物質としては、コバルト酸リチウム（ＬｉＣｏＯ2 ）、マンガン酸リチウム（ＬｉＭｎＯ2 ）、ニッケル酸リチウム（ＬｉＮｉＯ2 ）等のリチウム遷移金属複合酸化物が用いられる。あるいは、正極活物質として、上記のリチウム遷移金属複合酸化物の遷移金属の一部を他の金属（置換金属）で置換することにより得られる置換体を用いてもよい。置換金属としては、コバルト（Ｃｏ）、ニッケル（Ｎｉ）、バナジウム（Ｖ）、マンガン（Ｍｎ）、ジルコニウム（Ｚｒ）、チタン（Ｔｉ）、亜鉛（Ｚｎ）、アルミニウム（Ａｌ）、鉄（Ｆｅ）等のうち一種類または二種類以上を用いることができる。 As the positive electrode active material, lithium transition metal composite oxides such as lithium cobaltate (LiCoO 2 ), lithium manganate (LiMnO 2 ), and lithium nickelate (LiNiO 2 ) are used. Or you may use the substituted body obtained by substituting a part of transition metal of said lithium transition metal complex oxide with another metal (substitution metal) as a positive electrode active material. Examples of substitution metals include cobalt (Co), nickel (Ni), vanadium (V), manganese (Mn), zirconium (Zr), titanium (Ti), zinc (Zn), aluminum (Al), iron (Fe), etc. 1 type or 2 types or more can be used.
非水電解質としては、特に限定されず、一般の非水電解質二次電池に用いられる非水電解質を用いることができる。非水電解質の非水溶媒としては、エチレンカーボネート（ＥＣ）、ジエチルカーボネート（ＤＥＣ）、ジメチルカーボネート（ＤＭＣ）等のうち１種類または２種類以上を用いることができる。電解質塩としては、ＬｉＰＦ6 等を用いることができる。 It does not specifically limit as a nonaqueous electrolyte, The nonaqueous electrolyte used for a general nonaqueous electrolyte secondary battery can be used. As the nonaqueous solvent for the nonaqueous electrolyte, one or more of ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and the like can be used. As the electrolyte salt, LiPF 6 or the like can be used.
本実施の形態に係る非水電解質二次電池においては、複合炭素材料１００を構成する低結晶性炭素被覆黒鉛１０中の黒鉛１１が高い充放電効率および高い密度を有するので、十分に高いエネルギー密度が得られる。また、黒鉛１１が低結晶性炭素１２で被覆されているので、非水電解質の分解が起こらず、安定な充放電が可能となる。
In the nonaqueous electrolyte secondary battery according to the present embodiment, the
さらに、負極極板の圧延形成時には、負極活物質である複合炭素材料１００が加圧される。この場合、難黒鉛化性炭素２０が低結晶性炭素被覆黒鉛１０と比較して高い硬度を有するので、難黒鉛化性炭素２０および低結晶性炭素被覆黒鉛１０の粒子の潰れが抑制され、粒子間の空隙率の低下が防止される。その結果、負極活物質への非水電解質の含浸性が高くなり、二次電池の負荷特性および低温特性が向上する。
Furthermore, the
また、低結晶性炭素１０および難黒鉛化性炭素２０は黒鉛１１と比べて結晶性が低く、結晶面がランダムな方向を向いている。それにより、非水電解質中のイオンがあらゆる方向から低結晶性炭素１０および難黒鉛化性炭素２０の粒子内に浸入することができるので、粒子間の電荷移動抵抗が小さくなる。その結果、二次電池の負荷特性および低温特性がより向上する。
Further, the low
低結晶性炭素被覆黒鉛１０に対する難黒鉛化性炭素２０の混合割合をｘ［重量％］とすると、混合割合ｘは次式を満足することが好ましい。
When the mixing ratio of the
０＜ｘ＜１０
難黒鉛化性炭素２０の混合割合ｘが０よりも大きいことにより複合炭素材料１００の粒子の潰れが抑制される。また、難黒鉛化性炭素２０の混合割合ｘが１０重量％よりも小さいことにより負極活物質中の黒鉛１１の量を十分に確保することができる。それにより、十分なエネルギー密度を得ることができる。
0 <x <10
When the mixing ratio x of the
難黒鉛化性炭素２０の平均粒径は、低結晶性炭素被覆黒鉛１０の平均粒径以上であることが好ましい。それより、負極極板の加圧形成時に低結晶性炭素被覆黒鉛１０の粒子が潰れることを十分に防止することができる。
The average particle size of the
レーザーラマン分光法による難黒鉛化性炭素２０のラマンスベクトルにおいて、１３５０／ｃｍ付近の強度Ｉ1350と１５８０／ｃｍ付近の強度Ｉ1580との比Ｉ1350／Ｉ1580が０．５〜１．５の範囲にあることが好ましい。比Ｉ1350／Ｉ1580が０．５以上であることにより、難黒鉛化性炭素２０の結晶性が黒鉛１１に比べて十分に低くなり、粒子間の電荷移動抵抗が十分に低減される。また、比Ｉ1350／Ｉ1580が１．５以下であることにより、クーロン効率の極端な低下が防止される。
The ratio I 1350 / I 1580 between the intensity I 1350 near 1350 / cm and the intensity I 1580 near 1580 / cm is 0.5 to 1.5 in the Raman vector of
以下に説明する実施例および比較例では、３極式電池を作製し、負極活物質の評価を行った。 In the examples and comparative examples described below, tripolar batteries were prepared and the negative electrode active material was evaluated.
（実施例１〜３）
（作用極の作製）
平均粒径１１．４μｍの低結晶性炭素で被覆された黒鉛（低結晶性炭素被覆黒鉛）と、平均粒径２２μｍの難黒鉛化性炭素とを混合し、負極活物質を作製した。以下、低結晶性炭素被覆黒鉛と難黒鉛化性炭素との混合物を複合炭素材料と呼ぶ。実施例１、実施例２および実施例３では、低結晶性炭素被覆黒鉛に対する難黒鉛化性炭素の割合をそれぞれ２重量％、５重量％および１０重量％とした。
(Examples 1-3)
(Production of working electrode)
Graphite coated with low crystalline carbon having an average particle size of 11.4 μm (low crystalline carbon-coated graphite) and non-graphitizable carbon having an average particle size of 22 μm were mixed to prepare a negative electrode active material. Hereinafter, a mixture of low crystalline carbon-coated graphite and non-graphitizable carbon is referred to as a composite carbon material. In Example 1, Example 2, and Example 3, the ratio of the non-graphitizable carbon to the low crystalline carbon-coated graphite was 2% by weight, 5% by weight, and 10% by weight, respectively.
結着剤としてポリイミドＮＭＰ（Ｎ−メチル−２−ピロリドン）溶液を用い、上記負極活物質と結着剤とを混合し、スラリーを調製した。このスラリーを銅箔の表面にドクターブレード法により塗布し、３５０℃の温度で２時間熱処理することによりイミド化および乾燥して作用極（負極）を作製した。 Using a polyimide NMP (N-methyl-2-pyrrolidone) solution as a binder, the negative electrode active material and the binder were mixed to prepare a slurry. This slurry was applied to the surface of the copper foil by a doctor blade method, and heat treated at a temperature of 350 ° C. for 2 hours to imidize and dry to produce a working electrode (negative electrode).
負極活物質の難黒鉛化性炭素のレーザーラマン分光法におけるラマンスぺクトルを測定した。ラマンスぺクトルの１３５０／ｃｍ付近の強度Ｉ1350は２７．６ｃｐｓであり、１５８０／ｃｍ付近の強度Ｉ1580は２８．４ｃｐｓであり、強度比Ｉ1350／Ｉ1580は０．９７であった。 The Raman spectrum in laser Raman spectroscopy of the non-graphitizable carbon of the negative electrode active material was measured. The intensity I 1350 near 1350 / cm of the Raman spectrum was 27.6 cps, the intensity I 1580 near 1580 / cm was 28.4 cps, and the intensity ratio I 1350 / I 1580 was 0.97.
（対極の作製）
対極としてはリチウム金属箔を用いた。
(Production of counter electrode)
Lithium metal foil was used as the counter electrode.
（非水電解質の調製）
エチレンカーボネート（ＥＣ）とジエチルカーボネート（ＤＥＣ）とジメチルカーボネート（ＤＭＣ）との混合溶媒に１Ｍ（モル／リットル）のＬｉＰＦ6 を溶解させて非水電解質を調製した。
(Preparation of non-aqueous electrolyte)
A nonaqueous electrolyte was prepared by dissolving 1 M (mol / liter) LiPF 6 in a mixed solvent of ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC).
（電池の作製）
図２は実施例１〜３および比較例において作製した電池の構成を示す模式図である。
(Production of battery)
FIG. 2 is a schematic diagram showing the configuration of the batteries produced in Examples 1 to 3 and the comparative example.
作用極１、対極２およびセパレータ（ポリプロピレン製微多孔膜）を用い、アルゴン雰囲気中にて発電要素となる巻き取り電極体を作製した。ガラス製の３極式ビーカーセル５に巻き取り電極体およびリチウム金属からなる参照極３を配置し、非水電解質４を注液した。このようにして、実施例１、実施例２および実施例３の３極式電池を作製した。なお、図２においては、作用極１、対極２および参照極３が模式的に表されている。
Using the working
（比較例）
比較例では、低結晶性炭素で被覆された黒鉛（低結晶性炭素被覆黒鉛）を負極活物質として用いたこと以外は、実施例１〜３と同様の構成を有する電池を作製した。
(Comparative example)
In the comparative example, a battery having the same configuration as in Examples 1 to 3 was produced except that graphite coated with low crystalline carbon (low crystalline carbon coated graphite) was used as the negative electrode active material.
表１に実施例１〜３および比較例の電池における負極活物質の構成要素を示す。 Table 1 shows the components of the negative electrode active material in the batteries of Examples 1 to 3 and the comparative example.
（評価）
（ＳＥＭ観察）
低結晶性炭素被覆黒鉛からなる極板（比較例の電池の作用極）、難黒鉛化性炭素からなる極板、および低結晶性炭素被覆黒鉛と難黒鉛化性炭素との混合物（複合炭素材料）からなる極板を作製し、５ｋＮ／ｃｍ2 で加圧した。それらの極板の断面を走査型電子顕微鏡（ＳＥＭ）で観察した。
(Evaluation)
(SEM observation)
Electrode plate made of low crystalline carbon-coated graphite (working electrode of comparative battery), non-graphitizable carbon plate, and mixture of low crystalline carbon-coated graphite and non-graphitizable carbon (composite carbon material) ) Was prepared and pressed at 5 kN / cm 2 . The cross sections of the electrode plates were observed with a scanning electron microscope (SEM).
なお、上記の複合炭素材料における低結晶性炭素被覆黒鉛および難黒鉛化性炭素の割合はそれぞれ９１重量％および９重量％である。この複合炭素材料は、実施例３の電池の作用極における複合炭素材料に近い混合割合を有する。 The proportions of low crystalline carbon-coated graphite and non-graphitizable carbon in the composite carbon material are 91% by weight and 9% by weight, respectively. This composite carbon material has a mixing ratio close to that of the composite carbon material in the working electrode of the battery of Example 3.
図３は未加圧の低結晶性炭素被覆黒鉛からなる極板のＳＥＭによる観察結果を示し、図４は加圧後の低結晶性炭素被覆黒鉛からなる極板のＳＥＭによる観察結果を示し、図５は加圧後の難黒鉛化性炭素からなる極板のＳＥＭによる観察結果を示し、図６は加圧後の複合炭素材料からなる極板のＳＥＭによる観察結果を示す。 FIG. 3 shows the SEM observation results of the electrode plate made of unpressurized low crystalline carbon-coated graphite, and FIG. 4 shows the SEM observation results of the electrode plate made of low crystalline carbon-coated graphite after pressing. FIG. 5 shows the result of SEM observation of the electrode plate made of non-graphitizable carbon after pressing, and FIG. 6 shows the result of SEM observation of the electrode plate made of composite carbon material after pressing.
（ＳＥＭ観察結果）
図３に示すように、未加圧の低結晶性炭素被覆黒鉛からなる極板では、１０μｍ程度の二次粒径が見られる。図４に示すように、加圧後の低結晶性炭素被覆黒鉛からなる極板では、粒子が潰れ、粒子間の空隙率が減少している。
(SEM observation results)
As shown in FIG. 3, in the electrode plate made of unpressurized low crystalline carbon-coated graphite, a secondary particle size of about 10 μm is observed. As shown in FIG. 4, in the electrode plate made of low crystalline carbon-coated graphite after pressurization, the particles are crushed and the porosity between the particles is reduced.
図５に示すように、加圧後の難黒鉛化性炭素からなる極板では、２２μｍの二次粒径の難黒鉛化性炭素の粒子の潰れは見られなかった。これは、難黒鉛化性炭素の硬度が高いためである。 As shown in FIG. 5, in the electrode plate made of non-graphitizable carbon after pressurization, no collapse of the non-graphitizable carbon particles having a secondary particle diameter of 22 μm was observed. This is because the non-graphitizable carbon has a high hardness.
図６に示すように、加圧後の複合炭素材料からなる極板では、低結晶性炭素被覆黒鉛粒子の潰れが見られず、空隙率の減少が抑制された。この結果から、黒鉛よりも硬度の高い難黒鉛化性炭素を低結晶性炭素被覆黒鉛に混合すると、低結晶性炭素被覆黒鉛粒子の潰れが抑制され、極板の空隙が維持されることがわかる。 As shown in FIG. 6, in the electrode plate made of the composite carbon material after pressurization, the low crystalline carbon-coated graphite particles were not crushed, and the decrease in porosity was suppressed. From this result, it can be seen that when non-graphitizable carbon having a hardness higher than that of graphite is mixed with low crystalline carbon-coated graphite, the collapse of the low crystalline carbon-coated graphite particles is suppressed and the voids of the electrode plate are maintained. .
（負荷特性評価）
実施例１〜３および比較例の電池の負荷特性を次のように評価した。なお、定格容量が１時間で完全に放電されるときの電流値を定格電流と呼び、１．０Ｃで表記される。
(Load characteristic evaluation)
The load characteristics of the batteries of Examples 1 to 3 and the comparative example were evaluated as follows. The current value when the rated capacity is completely discharged in 1 hour is called the rated current, and is represented by 1.0C.
実施例１〜３および比較例の電池を温度２５℃で０．５Ｃの電流値で０Ｖまで放電した後、電圧１Ｖまで充電し、再び１Ｃの電流値で放電した。また、電圧１Ｖまで充電し、再び２Ｃの電流値で放電した。 The batteries of Examples 1 to 3 and the comparative example were discharged to 0 V at a current value of 0.5 C at a temperature of 25 ° C., charged to a voltage of 1 V, and discharged again at a current value of 1 C. Further, the battery was charged to a voltage of 1 V and discharged again at a current value of 2C.
負荷率として、０．５Ｃの電流値での放電容量に対する１Ｃの電流値での放電容量の比率（１Ｃ／０．５Ｃ負荷率と呼ぶ）、および０．５Ｃの電流値での放電容量に対する２Ｃの電流値での放電容量の比率（２Ｃ／０．５Ｃ負荷率と呼ぶ）を算出した。 As a load factor, the ratio of the discharge capacity at a current value of 1C to the discharge capacity at a current value of 0.5C (referred to as 1C / 0.5C load factor) and 2C with respect to the discharge capacity at a current value of 0.5C The ratio of the discharge capacity at the current value (referred to as the 2C / 0.5C load factor) was calculated.
（負荷特性評価結果）
表２に実施例１〜３および比較例の電池における負荷率の算出結果を示す。また、図７は複合炭素材料における難黒鉛化性炭素の混合割合と負荷率との関係を示す図である。
(Load characteristic evaluation results)
Table 2 shows the calculation results of the load factor in the batteries of Examples 1 to 3 and the comparative example. FIG. 7 is a graph showing the relationship between the mixing ratio of non-graphitizable carbon in the composite carbon material and the load factor.
表２および図７に示すように、低結晶性炭素被覆黒鉛からなる負極活物質を用いた比較例の電池では、１Ｃ／０．５Ｃ負荷率は３０％程度であった。これに対して、複合炭素材料からなる負極活物質を用いた実施例１、実施例２および実施例３の電池では、１Ｃ／０．５Ｃ負荷率がそれぞれ４７．３％、４８．９％および４３．０％と比較例に比べて高くなった。すなわち、難黒鉛化性炭素の混合割合が５重量％付近になると１Ｃ／０．５Ｃ負荷率が約５０％と極大になり、難黒鉛化性炭素の混合割合がそれ以上になると、１Ｃ／０．５Ｃ負荷率はやや減少を示した。 As shown in Table 2 and FIG. 7, in the battery of the comparative example using the negative electrode active material made of low crystalline carbon-coated graphite, the 1C / 0.5C load factor was about 30%. On the other hand, in the batteries of Example 1, Example 2 and Example 3 using the negative electrode active material made of the composite carbon material, the 1C / 0.5C load factors were 47.3%, 48.9% and It was 43.0%, which was higher than the comparative example. That is, when the mixing ratio of the non-graphitizable carbon is close to 5% by weight, the 1C / 0.5C loading ratio becomes a maximum of about 50%, and when the mixing ratio of the non-graphitizable carbon is more than 1%, .5C load factor showed a slight decrease.
この結果は、次の理由によるものと考えられる。難黒鉛化性炭素の混合割合が５重量％付近までは、難黒鉛化性炭素の混合により形成される空隙により電解液が負極活物質に効率よく含浸することにより負荷率が向上するが、５重量％以上になると、空隙が増加し、複合炭素材料の粒子間における接触がややとれにくくなるためであると考えられる。すなわち、難黒鉛化性炭素の混合割合が５重量％付近で複合炭素材料中の空隙率および複合炭素材料の粒子間の接触の両方が適切な程度となると考えられる。 This result is considered to be due to the following reason. When the mixing ratio of the non-graphitizable carbon is close to about 5% by weight, the load factor is improved by efficiently impregnating the negative electrode active material with the electrolyte by the voids formed by mixing the non-graphitizable carbon. It is considered that when the amount is not less than% by weight, voids increase and it becomes difficult to make contact between the particles of the composite carbon material. That is, it is considered that both the porosity in the composite carbon material and the contact between the particles of the composite carbon material become appropriate when the mixing ratio of the non-graphitizable carbon is around 5% by weight.
２Ｃ／０．５Ｃ負荷率についても、複合炭素材料からなる負極活物質を用いた実施例１、実施例２および実施例３の電池では、低結晶性炭素被覆黒鉛からなる負極活物質を用いた比較例の電池に比べて高くなったが、低負荷においてこの負荷率の向上が顕著であった。 As for the 2C / 0.5C load factor, the negative electrode active material made of low crystalline carbon-coated graphite was used in the batteries of Example 1, Example 2 and Example 3 using the negative electrode active material made of the composite carbon material. Although it was higher than the battery of the comparative example, the improvement in the load factor was remarkable at low load.
上記の結果から、複合炭素材料中の難黒鉛化性炭素の混合割合が０よりも大きく１０重量％よりも小さい場合に、負荷特性が向上することがわかる。 From the above results, it is understood that the load characteristics are improved when the mixing ratio of the non-graphitizable carbon in the composite carbon material is larger than 0 and smaller than 10% by weight.
（低温特性の評価）
実施例１〜３および比較例の電池の低温特性を次のように評価した。実施例１〜３および比較例の電池を温度２５℃および放電電流０．５１ｍＡ／ｃｍ2 で放電終止電圧０Ｖまで放電した後、１０分間の休止後、再び放電電流０．２５ｍＡ／ｃｍ2 で放電終止電圧０Ｖまで放電し、１０分間の休止後、さらに放電電流０．１ｍＡ／ｃｍ2 で放電終止電圧０Ｖまで放電した後、３０分間の休止後、充電終止電圧１．０Ｖまで充電する工程を１サイクルとし、３サイクルの試験を行った。
(Evaluation of low temperature characteristics)
The low temperature characteristics of the batteries of Examples 1 to 3 and the comparative example were evaluated as follows. After discharging the batteries of Examples 1-3 and Comparative Examples to a discharge end voltage 0V at temperature 25 ° C. and the discharge current 0.51mA / cm 2, after 10 minutes of resting, discharging again the discharge current 0.25 mA /
また、実施例１〜３および比較例の電池を−１０℃まで十分冷却した後、上記の放電試験を同様に行った。 In addition, after the batteries of Examples 1 to 3 and the comparative example were sufficiently cooled to −10 ° C., the above discharge test was similarly performed.
温度２５℃での放電容量および温度−１０℃での放電容量を求め、温度２５℃での放電容量に対する温度−１０℃での放電容量の比（低温における容量比）を算出した。 The discharge capacity at a temperature of 25 ° C. and the discharge capacity at a temperature of −10 ° C. were determined, and the ratio of the discharge capacity at a temperature of −10 ° C. to the discharge capacity at a temperature of 25 ° C. (capacity ratio at a low temperature) was calculated.
（低温特性の評価結果）
表３に実施例１〜３および比較例の電池の低温における容量比の算出結果を示す。また、図８は複合炭素材料における難黒鉛化性炭素の混合割合と低温における容量比との関係を示す図である。
(Evaluation results of low temperature characteristics)
Table 3 shows the calculation results of the capacity ratio at low temperatures of the batteries of Examples 1 to 3 and the comparative example. FIG. 8 is a graph showing the relationship between the mixing ratio of non-graphitizable carbon in the composite carbon material and the capacity ratio at low temperature.
表３および図８に示すように、低結晶性炭素被覆黒鉛からなる負極活物質を用いた比較例の電池では、低温における容量比は３９％程度であった。これに対して、複合炭素材料からなる負極活物質を用いた実施例１、実施例２および実施例３の電池では、低温における容量比がそれぞれ４８．１％、４９．２％および４６．０％と比較例に比べて高くなった。すなわち、難黒鉛化性炭素の混合割合が５重量％付近になると低温における容量比が約５０％と極大になり、難黒鉛化性炭素の混合割合がそれ以上になると、低温における容量比はやや減少を示した。 As shown in Table 3 and FIG. 8, in the battery of the comparative example using the negative electrode active material made of low crystalline carbon-coated graphite, the capacity ratio at low temperature was about 39%. On the other hand, in the batteries of Example 1, Example 2 and Example 3 using the negative electrode active material made of the composite carbon material, the capacity ratios at low temperature were 48.1%, 49.2% and 46.0, respectively. % And higher than the comparative example. That is, when the mixing ratio of non-graphitizable carbon is close to 5% by weight, the capacity ratio at low temperature becomes a maximum of about 50%, and when the mixing ratio of non-graphitizable carbon is more than that, the capacity ratio at low temperature is slightly higher. Showed a decrease.
このように、低温における容量比との関係は負荷率と類似した傾向となった。これは、低温における容量比についても、負荷率の場合と同様に、難黒鉛化性炭素の混合割合が５重量％付近が複合炭素材料中の空隙率および複合炭素材料の粒子間の接触の両方が適切な程度となるためであると考えられる。 Thus, the relationship with the capacity ratio at low temperature tended to be similar to the load factor. As for the capacity ratio at low temperature, as in the case of the load factor, the mixture ratio of non-graphitizable carbon is around 5% by weight both in the porosity in the composite carbon material and in the contact between the particles of the composite carbon material. Is considered to be an appropriate level.
上記の結果から、複合炭素材料中の難黒鉛化性炭素の混合割合が０よりも大きく１０重量％よりも小さい場合に、低温特性が向上することがわかる。 From the above results, it is understood that the low temperature characteristics are improved when the mixing ratio of the non-graphitizable carbon in the composite carbon material is larger than 0 and smaller than 10% by weight.
本発明に係る非水電解質二次電池は、携帯用電源、自動車用電源等の種々の電源として利用することができる。 The nonaqueous electrolyte secondary battery according to the present invention can be used as various power sources such as a portable power source and an automobile power source.
１ 作用極
２ 対極
３ 参照極
４ 非水電解質
５ ３極式ビーカーセル
１０ 低結晶性炭素被覆黒鉛
１１ 黒鉛
１２ 低結晶性炭素
２０ 難黒鉛化性炭素
１００ 複合炭素材料
DESCRIPTION OF
Claims (4)
前記負極は、低結晶性炭素被覆黒鉛および難黒鉛化性炭素の混合物を含み、
前記低結晶性炭素被覆黒鉛は、黒鉛からなる第１の炭素材料と、前記第１の炭素材料の表面の一部または全部を被覆する第２の炭素材料とから構成され、前記第２の炭素材料は、前記第１の炭素材料よりも結晶性が低く、
前記難黒鉛化性炭素は、前記第１の炭素材料よりも結晶性が低く、
前記低結晶性炭素被覆黒鉛に対する前記難黒鉛化炭素の割合が０よりも大きく１０重量％以下であり、
前記難黒鉛化性炭素の平均粒径は、前記低結晶性炭素被覆黒鉛の平均粒径以上であることを特徴とする非水電解質二次電池。 A non-aqueous electrolyte secondary battery comprising a positive electrode and a negative electrode,
The negative electrode includes a mixture of low crystalline carbon-coated graphite and non-graphitizable carbon,
The low crystalline carbon-coated graphite is composed of a first carbon material made of graphite and a second carbon material that covers a part or all of the surface of the first carbon material, and the second carbon The material is less crystalline than the first carbon material,
The flame-graphitizable carbon, the crystalline than the first carbon material is rather low,
The ratio of the non-graphitizable carbon to the low crystalline carbon-coated graphite is greater than 0 and 10% by weight or less,
The non-aqueous electrolyte secondary battery , wherein an average particle diameter of the non-graphitizable carbon is equal to or greater than an average particle diameter of the low crystalline carbon-coated graphite .
低結晶性炭素被覆黒鉛および難黒鉛化性炭素の混合物を含み、 Comprising a mixture of low crystalline carbon-coated graphite and non-graphitizable carbon;
前記低結晶性炭素被覆黒鉛は、黒鉛からなる第１の炭素材料と、前記第１の炭素材料の表面の一部または全部を被覆する第２の炭素材料とから構成され、前記第２の炭素材料は、前記第１の炭素材料よりも結晶性が低く、 The low crystalline carbon-coated graphite is composed of a first carbon material made of graphite and a second carbon material that covers a part or all of the surface of the first carbon material, and the second carbon The material is less crystalline than the first carbon material,
前記難黒鉛化性炭素は、前記第１の炭素材料よりも結晶性が低く、前記低結晶性炭素被覆黒鉛に対する前記難黒鉛化炭素の割合が０よりも大きく１０重量％以下であり、前記難黒鉛化性炭素の平均粒径は、前記低結晶性炭素被覆黒鉛の平均粒径以上であることを特徴とする負極。 The non-graphitizable carbon has lower crystallinity than the first carbon material, and the ratio of the non-graphitizable carbon to the low crystalline carbon-coated graphite is greater than 0 and 10% by weight or less. An average particle diameter of graphitizable carbon is equal to or greater than an average particle diameter of the low crystalline carbon-coated graphite.
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| JP4187347B2 (en) * | 1998-04-02 | 2008-11-26 | 三星エスディアイ株式会社 | Method for producing negative electrode active material for lithium ion battery |
| JP4446510B2 (en) * | 1998-05-21 | 2010-04-07 | 三星エスディアイ株式会社 | Negative electrode active material for lithium secondary battery and lithium secondary battery |
| JP4245219B2 (en) * | 1999-03-09 | 2009-03-25 | 三洋電機株式会社 | Lithium secondary battery |
| JP3654790B2 (en) * | 1999-04-22 | 2005-06-02 | 三菱化学株式会社 | Graphite material for electrode and lithium ion secondary battery using the same |
| JP3691714B2 (en) * | 2000-03-06 | 2005-09-07 | 三洋電機株式会社 | Lithium secondary battery |
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2004
- 2004-01-26 JP JP2004017592A patent/JP4467317B2/en not_active Expired - Lifetime
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