JP6451071B2 - Carbon silicon negative electrode active material for lithium ion secondary battery and method for producing the same - Google Patents

Carbon silicon negative electrode active material for lithium ion secondary battery and method for producing the same Download PDF

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JP6451071B2
JP6451071B2 JP2014086864A JP2014086864A JP6451071B2 JP 6451071 B2 JP6451071 B2 JP 6451071B2 JP 2014086864 A JP2014086864 A JP 2014086864A JP 2014086864 A JP2014086864 A JP 2014086864A JP 6451071 B2 JP6451071 B2 JP 6451071B2
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向後 雅則
雅則 向後
昌則 阿部
昌則 阿部
高東 修二
修二 高東
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Description

本発明は、リチウムイオン2次電池用の負極活物質およびその製造方法に関するものである。   The present invention relates to a negative electrode active material for a lithium ion secondary battery and a method for producing the same.

スマートフォン、タブレット型端末などモバイル機器の高性能化や、EV、HEV、PHEVなどリチウムイオン2次電池を搭載した車両の普及に伴い、リチウムイオン2次電池の高容量化の要求が高まっている。現在、リチウムイオン2次電池の負極材には主に黒鉛が用いられているが、さらなる高容量化のため、理論容量が高く、リチウムイオンを吸蔵・放出可能な元素であるシリコンやスズ等の金属、もしくは他の元素との合金を用いた負極材の開発が活発化している。   As mobile devices such as smartphones and tablet terminals have higher performance and vehicles equipped with lithium ion secondary batteries such as EV, HEV, and PHEV have spread, there is an increasing demand for higher capacity of lithium ion secondary batteries. At present, graphite is mainly used as the negative electrode material of lithium ion secondary batteries. However, for further increase in capacity, the theoretical capacity is high, and elements such as silicon and tin that can absorb and release lithium ions are used. Development of negative electrode materials using metals or alloys with other elements has been activated.

一方、これらのリチウムイオンを吸蔵・放出可能な金属材料からなる活物質は、充電によってリチウムと合金化した際に、著しく体積膨張することが知られている。そのため、活物質が割れて微細化し、さらにこれらを用いた負極も構造が破壊されて導電性が切断される。従って、これらの金属材料を用いた負極はサイクル経過によって容量が著しく低下することが課題となっている。   On the other hand, it is known that an active material made of a metal material capable of inserting and extracting lithium ions significantly expands when alloyed with lithium by charging. Therefore, the active material is cracked and refined, and the structure of the negative electrode using these is also broken and the conductivity is cut. Therefore, the negative electrode using these metal materials has a problem that the capacity is remarkably lowered with the passage of cycles.

この課題に対し、これらの金属材料を微粒子化し、炭素質物や黒鉛などで複合化する手法が提案されている。このような複合粒子は、これらの金属材料がリチウムと合金化し、微細化しても炭素質物や黒鉛によって導電性が確保されるため、これらの材料を単独で負極材として用いるよりもサイクル特性が著しく向上することが知られている。例えば、特許文献1には、負極の活物質は炭素質物層が表面に形成された微粒子を含み、該微粒子はMg、Al、Si、Ca、SnおよびPbから選ばれる少なくとも一種の元素からなると共に、平均粒径が1〜500nmであり、かつ前記活物質中の微粒子の原子比率は15%以上であることが開示されている。また、特許文献2には、リチウムイオンと化合可能な電池活物質と黒鉛とを混合して混合物を得る混合工程と、該混合物に球形化処理を施し、黒鉛およびリチウムイオンと化合可能な電池活物質を含有する略球状のリチウム二次電池用複合活物質を製造する球形化工程とを有する、リチウム二次電池用複合活物質の製造方法が開示され、前記リチウムイオンと化合可能な電池活物質について、Si、Sn、Al、Sb、Inから選ばれる少なくとも1種の元素、黒鉛として比表面積30m/g以上の膨張黒鉛または薄片状黒鉛が好ましいと記載されている。 In response to this problem, a technique has been proposed in which these metal materials are made into fine particles and combined with carbonaceous material or graphite. Such composite particles have significantly higher cycle characteristics than the use of these materials alone as a negative electrode material, because these metal materials are alloyed with lithium and conductivity is ensured by carbonaceous materials and graphite even when they are miniaturized. It is known to improve. For example, in Patent Document 1, the active material of the negative electrode includes fine particles having a carbonaceous material layer formed on the surface, and the fine particles are composed of at least one element selected from Mg, Al, Si, Ca, Sn, and Pb. In addition, it is disclosed that the average particle diameter is 1 to 500 nm, and the atomic ratio of the fine particles in the active material is 15% or more. Patent Document 2 discloses a mixing step of mixing a battery active material capable of combining with lithium ions and graphite to obtain a mixture, and subjecting the mixture to a spheroidization treatment so that the battery active capable of combining with graphite and lithium ions is obtained. A method for producing a composite active material for a lithium secondary battery comprising a spheroidizing step for producing a substantially spherical composite active material for a lithium secondary battery containing the material, and a battery active material capable of combining with the lithium ion As for, at least one element selected from Si, Sn, Al, Sb, and In, graphite is preferably expanded graphite or flaky graphite having a specific surface area of 30 m 2 / g or more.

このように、膨張黒鉛や薄片状黒鉛によりリチウムイオンと化合可能な電池活物質を包み込むことでサイクル特性の向上が見られるが、まだ必要な特性までは達しておらず、さらなるサイクル寿命の向上が求められていた。   In this way, the cycle characteristics can be improved by encapsulating the battery active material that can be combined with lithium ions by expanded graphite or flake graphite, but the required characteristics have not yet been reached, and the cycle life has been further improved. It was sought after.

特開平10−3920号公報Japanese Patent Laid-Open No. 10-3920 特許第5227483号公報Japanese Patent No. 5227483

本発明は、炭素質物及び黒鉛とSiとを含んでなるリチウムイオン2次電池用負極活物質であり、放電容量が大きく、サイクル寿命が長いリチウムイオン2次電池を与える負極活物質およびその製造方法を提供することにある。   The present invention relates to a negative electrode active material for a lithium ion secondary battery comprising a carbonaceous material, graphite and Si, and a lithium ion secondary battery having a large discharge capacity and a long cycle life, and a method for producing the same Is to provide.

本発明者らは先の課題を解決すべく鋭意検討を重ねた結果、酸処理黒鉛を加熱処理して膨張黒鉛を得る際、1100〜1200℃での熱処理時の130%以下のかさ密度を有する膨張黒鉛からなり、炭素質物と黒鉛の含有量が5〜90重量%含み、複合化している炭素質物と共に0.2μm以下の厚みの黒鉛薄層の間に挟まった構造であり、その構造が積層および/または網目状に広がっており、該黒鉛薄層が活物質粒子の表面付近で湾曲して活物質粒子を覆っていることを特徴とするリチウムイオン2次電池用負極活物質は、放電容量が大きく、サイクル寿命が長いリチウムイオン2次電池が得られることを見出し、本発明を完成するに至った。   As a result of intensive studies to solve the above-mentioned problems, the present inventors have a bulk density of 130% or less during heat treatment at 1100 to 1200 ° C. when heat-treating acid-treated graphite to obtain expanded graphite. It is composed of expanded graphite, containing 5 to 90% by weight of carbonaceous material and graphite, and sandwiched between thin graphite layers with a thickness of 0.2 μm or less together with the composite carbonaceous material. The negative electrode active material for a lithium ion secondary battery is characterized in that the negative electrode active material for a lithium ion secondary battery is spread in a network shape and the graphite thin layer is curved near the surface of the active material particles to cover the active material particles. Has been found that a lithium ion secondary battery having a large cycle life and a long cycle life can be obtained, and the present invention has been completed.

すなわち本発明は、黒鉛と炭素質物、Si化合物とを含んでなるリチウムイオン2次電池用負極活物質において、1100〜1200℃での熱処理時の130%以下のかさ密度を有する膨張黒鉛からなることを特徴とするリチウムイオン2次電池用カーボンシリコン系負極活物質である。   That is, the present invention is a negative electrode active material for a lithium ion secondary battery comprising graphite, a carbonaceous material, and a Si compound, and is composed of expanded graphite having a bulk density of 130% or less during heat treatment at 1100 to 1200 ° C. Is a carbon-silicon-based negative electrode active material for a lithium ion secondary battery.

以下、本発明のリチウムイオン2次電池用カーボンシリコン系負極活物質について詳細に説明する。   Hereinafter, the carbon silicon-based negative electrode active material for a lithium ion secondary battery of the present invention will be described in detail.

本発明でいう黒鉛とは、グラフェン層がc軸に平行な結晶であり、黒鉛を酸処理、酸化処理した後、熱処理することにより膨張させ、黒鉛層間の一部が剥離してアコーディオン状となった膨張黒鉛もしくは膨張黒鉛の粉砕物である。酸処理に使用する酸の種類としては、硫酸、硝酸、過マンガン酸等が挙げられる。膨張黒鉛のかさ密度は、低いことが好ましい。通常、酸処理黒鉛は高温で熱処理すると膨張が大きくなる傾向にあるため、1100〜1200℃の高温で熱処理すれば最大の膨張率が得られ、低かさ密度の膨張黒鉛が得られる。また、これより低い温度で熱処理すると膨張率が低くなり、かさ密度は高くなる傾向となる。本発明の黒鉛は、1100〜1200℃での熱処理時の130%以下のかさ密度を有することが好ましい。さらに好ましい範囲は120%以下である。130%を超えると、膨張率が低いために、後述する黒鉛薄層によるSi表面を覆う機能が低下し、Siと電解液が直接接して、充放電時に反応物が形成され、充放電時の効率低下が激しくなる。これと平行して、かさ密度が高くなると黒鉛の膨張も十分ではなくなることから、比表面積値は低下する傾向となる。この場合、1100〜1200℃での熱処理時の50%以上の比表面積値を有することが好ましい。   Graphite as used in the present invention is a crystal in which the graphene layer is parallel to the c-axis, and the graphite is expanded by heat treatment after acid treatment and oxidation treatment, and part of the graphite layer is peeled off to form an accordion shape. Expanded graphite or a pulverized product of expanded graphite. Examples of the acid used for the acid treatment include sulfuric acid, nitric acid, permanganic acid and the like. The bulk density of expanded graphite is preferably low. Normally, acid-treated graphite tends to expand when heat-treated at a high temperature. Therefore, when heat-treated at a high temperature of 1100 to 1200 ° C., the maximum expansion rate is obtained, and low bulk density expanded graphite is obtained. In addition, when heat treatment is performed at a temperature lower than this, the expansion coefficient tends to be low, and the bulk density tends to be high. The graphite of the present invention preferably has a bulk density of 130% or less during heat treatment at 1100 to 1200 ° C. A more preferable range is 120% or less. If it exceeds 130%, since the expansion coefficient is low, the function of covering the Si surface by the graphite thin layer to be described later is reduced, Si and the electrolytic solution are in direct contact, and a reactant is formed during charge and discharge, and during charge and discharge. The efficiency drop is severe. In parallel with this, when the bulk density increases, the expansion of the graphite is not sufficient, and the specific surface area value tends to decrease. In this case, it is preferable to have a specific surface area value of 50% or more during heat treatment at 1100 to 1200 ° C.

本発明のリチウムイオン2次電池用負極活物質は、炭素質物と黒鉛の含有量として5〜90重量%含むことが好ましく、20〜60重量%がさらに好ましい。炭素質物の含有量が5重量%未満の場合、炭素質物と黒鉛がSi化合物を覆うことができず、導電パスが不十分となって容量劣化が激しく起こりやすく、90重量%より大きい場合、容量が十分に得られない。   The negative electrode active material for a lithium ion secondary battery of the present invention preferably contains 5 to 90% by weight, more preferably 20 to 60% by weight, as the content of carbonaceous material and graphite. When the content of carbonaceous material is less than 5% by weight, the carbonaceous material and graphite cannot cover the Si compound, the conductive path becomes insufficient, and capacity deterioration easily occurs. Is not enough.

本発明でいう炭素質物とは、非晶質もしくは微結晶の炭素物質であり、2000℃を超える熱処理で黒鉛化する易黒鉛化炭素(ソフトカーボン)と、黒鉛化しにくい難黒鉛化炭素(ハードカーボン)がある。   The carbonaceous material referred to in the present invention is an amorphous or microcrystalline carbon material, and easily graphitized carbon (soft carbon) that is graphitized by a heat treatment exceeding 2000 ° C. and non-graphitizable carbon (hard carbon) that is difficult to graphitize. )

また、本発明でいう炭素質物の含有量は、5〜40重量%であることが好ましい。炭素質物の含有量が5重量%未満の場合、炭素質物がSi化合物および黒鉛を覆うことができず、Si化合物と黒鉛との接着が不十分となり、活物質粒子の形成が困難となりやすい。また、40重量%より大きい場合、導電性が炭素質物より高い黒鉛の効果が十分に引き出されない。   Moreover, it is preferable that content of the carbonaceous material said by this invention is 5 to 40 weight%. When the content of the carbonaceous material is less than 5% by weight, the carbonaceous material cannot cover the Si compound and graphite, adhesion between the Si compound and graphite becomes insufficient, and formation of active material particles tends to be difficult. Moreover, when larger than 40 weight%, the effect of the graphite whose electroconductivity is higher than a carbonaceous material is not fully drawn out.

本発明でいうSiとは、純度が98%程度の汎用グレードの金属シリコン、純度が2〜4Nのケミカルグレードの金属シリコン、塩素化して蒸留精製した4Nより高純度のポリシリコン、単結晶成長法による析出工程を経た超高純度の単結晶シリコン、もしくはそれらに周期表13族もしくは15族元素をドーピングして、p型またはn型としたもの、半導体製造プロセスで発生したウエハの研磨や切断の屑、プロセスで不良となった廃棄ウエハなど、汎用グレードの金属シリコン以上の純度であれば特に限定されない。   In the present invention, Si is a general grade metal silicon having a purity of about 98%, a chemical grade metal silicon having a purity of 2 to 4N, a chlorinated and purified by distillation using 4N, a single crystal growth method High-purity single crystal silicon that has undergone a deposition step by the above, or those doped with elements of Group 13 or 15 of the periodic table to be p-type or n-type, and polishing or cutting of wafers generated in the semiconductor manufacturing process There is no particular limitation as long as the purity is higher than that of general-purpose grade metal silicon, such as scraps and waste wafers that have become defective in the process.

本発明のリチウムイオン2次電池用カーボンシリコン系負極活物質において、Siの平均粒径D50は0.01〜0.5μmである。0.01μmより小さいと、表面酸化による容量や初期効率の低下が激しく、0.5μmより大きいと、リチウム挿入による膨張で割れが激しく生じ、サイクル劣化が激しくなる。なお、D50はレーザー回折法又は動的光散乱法で測定した体積平均の粒子径である。また、BET法で測定される比表面積が23〜300m/gである。比表面積が23m/gより小さいと、粒子が大きく、リチウム挿入による膨張で割れが激しく生じ、サイクル劣化が激しくなる。 In the carbon silicon-based negative electrode active material for a lithium ion secondary battery of the present invention, the average particle diameter D50 of Si is 0.01 to 0.5 μm. If it is smaller than 0.01 μm, the capacity and initial efficiency due to surface oxidation are drastically reduced, and if it is larger than 0.5 μm, cracks are severely caused by expansion due to lithium insertion, resulting in severe cycle deterioration. D50 is a volume average particle diameter measured by a laser diffraction method or a dynamic light scattering method. Moreover, the specific surface area measured by BET method is 23-300 m < 2 > / g. When the specific surface area is less than 23 m 2 / g, the particles are large, and cracks are severely caused by expansion due to lithium insertion, resulting in severe cycle deterioration.

Siの含有量は10〜80重量%が好ましく、15〜50重量%がさらに好ましい。Siの含有量が10重量%未満の場合、従来の黒鉛に比べて十分に大きい容量が得られず、80重量%より大きい場合、サイクル劣化が激しくなる。   The content of Si is preferably 10 to 80% by weight, and more preferably 15 to 50% by weight. When the Si content is less than 10% by weight, a sufficiently large capacity cannot be obtained as compared with conventional graphite. When the Si content is more than 80% by weight, cycle deterioration becomes severe.

本発明の負極活物質に含まれる黒鉛の粒子サイズは、負極活物質粒子のサイズより小さければ特に限定されないが、黒鉛粒子の厚みは活物質の平均粒径D50の1/5以下であることが好ましい。黒鉛の添加により活物質粒子の導電性および強度が高まり、充放電のレート特性およびサイクル特性が向上する。黒鉛粒子のX線回折で測定される(002)面の面間隔d002は0.338nm以下であることが好ましく、これは高度に黒鉛化が進んだ黒鉛を意味している。d002がこの値を超える場合、黒鉛による導電性向上効果が小さくなる。   The particle size of the graphite contained in the negative electrode active material of the present invention is not particularly limited as long as it is smaller than the size of the negative electrode active material particles, but the thickness of the graphite particles may be 1/5 or less of the average particle diameter D50 of the active material. preferable. Addition of graphite increases the conductivity and strength of the active material particles, and improves charge / discharge rate characteristics and cycle characteristics. The (002) plane spacing d002 measured by X-ray diffraction of graphite particles is preferably 0.338 nm or less, which means highly graphitized graphite. When d002 exceeds this value, the effect of improving conductivity by graphite becomes small.

本発明のリチウムイオン2次電池用カーボンシリコン系負極活物質において、黒鉛薄層は0.5μm以下が好ましい。0.5μm以下であることで、黒鉛薄層間に挟まれたSi化合物と、炭素質物の層が薄くなって、Si化合物への電子の伝達が良くなり、厚みが0.5μmを超えると黒鉛薄層の電子伝達効果が薄まる。黒鉛薄層を断面で見て線状の場合、その長さは負極活物質粒子のサイズの半分以上あることが電子伝達に好ましく、負極活物質粒子のサイズと同等程度であることがさらに好ましい。黒鉛薄層が網目状の場合、黒鉛薄層の網が負極活物質粒子のサイズの半分以上に渡って繋がっていることが電子伝達に好ましく、負極活物質粒子のサイズと同等程度であることがさらに好ましい。   In the carbon silicon-based negative electrode active material for a lithium ion secondary battery of the present invention, the graphite thin layer is preferably 0.5 μm or less. When the thickness is 0.5 μm or less, the Si compound sandwiched between the graphite thin layers and the carbonaceous material layer are thinned, and the electron transfer to the Si compound is improved. The electron transfer effect of the thin layer is diminished. When the graphite thin layer is linear when viewed in cross section, its length is preferably at least half the size of the negative electrode active material particles for electron transfer, and more preferably about the same as the size of the negative electrode active material particles. When the graphite thin layer is network-like, it is preferable for electron transfer that the graphite thin layer network is connected to more than half of the size of the negative electrode active material particles, and it may be about the same size as the negative electrode active material particles. Further preferred.

本発明のリチウムイオン2次電池用カーボンシリコン系負極活物質では、その構造が積層および/または網目状に広がっており、該黒鉛薄層が活物質粒子の表面付近で湾曲して活物質粒子を覆っていることが好ましい。そのような形状にすることで、黒鉛薄層端面から電解液が侵入して、Si化合物や黒鉛薄層端面と電解液が直接接して、充放電時に反応物が形成され、効率が下がるリスクが低減する。   In the carbon silicon negative electrode active material for a lithium ion secondary battery of the present invention, the structure spreads in a layered and / or network form, and the thin graphite layer is curved near the surface of the active material particles. It is preferable to cover. With such a shape, there is a risk that the electrolyte enters from the end face of the graphite thin layer, the Si compound or the end face of the graphite thin layer is in direct contact with the electrolyte, and a reactant is formed during charge and discharge, resulting in reduced efficiency. To reduce.

本発明でいう黒鉛薄層とは、先に述べた黒鉛を酸処理、酸化処理した後、熱処理することにより膨張させて黒鉛層間の一部が剥離してアコーディオン状となった膨張黒鉛もしくは膨張黒鉛の粉砕物からなる黒鉛薄層である。   In the present invention, the graphite thin layer refers to expanded graphite or expanded graphite in which the above-mentioned graphite is subjected to acid treatment and oxidation treatment and then expanded by heat treatment, and a part of the graphite layer is peeled off to form an accordion shape. It is a graphite thin layer made of a pulverized product.

本発明のリチウムイオン2次電池用カーボンシリコン系負極活物質は、形状が丸みを帯びた平均粒径D50が1〜40μmの複合粒子であり、好ましくは2〜30μmである。D50が1μm未満の場合、かさ高くなって高密度の電極が作製しにくくなり、40μmを超える場合、塗布した電極の凹凸が激しくなって均一な電極が作製しにくくなる。また、前記Siの平均粒径が該負極活物質の平均粒径の1/5以下であることが好ましい。   The carbon silicon-based negative electrode active material for a lithium ion secondary battery of the present invention is a composite particle having a rounded average particle diameter D50 of 1 to 40 μm, preferably 2 to 30 μm. When D50 is less than 1 μm, it becomes bulky and it becomes difficult to produce a high-density electrode, and when it exceeds 40 μm, the unevenness of the applied electrode becomes intense and it becomes difficult to produce a uniform electrode. Moreover, it is preferable that the average particle diameter of Si is 1/5 or less of the average particle diameter of the negative electrode active material.

形状が丸みを帯びた複合粒子とは、粉砕等により生成した粒子の角が取れているもの、球状もしくは回転楕円体形状、円板もしくは小判形状で厚みを有して角が丸いもの、またはそれらが変形したもので角が丸いものなどである。形状が丸みを帯びることにより複合粒子のかさ密度が高まり、負極にした時の充填密度が高まる。   Composite particles with rounded shapes are those in which the corners of particles produced by pulverization, etc. are rounded, spherical or spheroid shapes, discs or oval shapes with thickness and rounded corners, or those Is a deformed one with rounded corners. When the shape is rounded, the bulk density of the composite particles is increased, and the packing density when the negative electrode is formed is increased.

また、本発明のリチウムイオン2次電池用シリコン含有負極活物質においては、前記Si化合物の含有量が10〜60重量%、前記炭素質物の含有量が5〜40重量%、前記黒鉛の含有量が20〜80重量%であることが好ましい。   Moreover, in the silicon-containing negative electrode active material for a lithium ion secondary battery of the present invention, the content of the Si compound is 10 to 60% by weight, the content of the carbonaceous material is 5 to 40% by weight, and the content of the graphite Is preferably 20 to 80% by weight.

本発明のリチウムイオン2次電池用カーボンシリコン系負極活物質では、比表面積が5〜120m/gであることがさらに好ましい。比表面積が5μm未満では、粒子径が大きくなることで、塗布した電極の凹凸が激しくなって均一な電極が作製しにくくなり、120m/gを超えると、表面積が大きいために電解液との反応生成物が多くなり、電池特性にサイクル特性の低下などの影響が発生する。 In the carbon silicon-based negative electrode active material for a lithium ion secondary battery of the present invention, the specific surface area is more preferably 5 to 120 m 2 / g. When the specific surface area is less than 5 μm, the particle diameter becomes large, and the unevenness of the applied electrode becomes intense, making it difficult to produce a uniform electrode. When the specific surface area exceeds 120 m 2 / g, the surface area is large and The amount of reaction products increases, and the battery characteristics are adversely affected such as deterioration of cycle characteristics.

次に、本発明のリチウムイオン2次電池用カーボンシリコン系負極活物質の製造方法について説明する。   Next, the manufacturing method of the carbon silicon type negative electrode active material for lithium ion secondary batteries of this invention is demonstrated.

本発明のリチウムイオン2次電池用カーボンシリコン系負極活物質の製造方法は、膨張黒鉛、炭素前駆体、Siを混合する工程と、造粒・厚密化する工程と、粉砕して複合粒子を形成する工程と、該複合粒子を不活性雰囲気中で焼成する工程を含むものである。   The method for producing a carbon silicon negative electrode active material for a lithium ion secondary battery of the present invention comprises a step of mixing expanded graphite, a carbon precursor and Si, a step of granulating and densifying, and a composite particle by pulverizing A step of forming, and a step of firing the composite particles in an inert atmosphere.

原料である膨張黒鉛は、天然黒鉛、石油や石炭のピッチを黒鉛化した人造黒鉛等で、鱗片状、小判状もしくは球状、円柱状もしくはファイバー状等の形状を有した黒鉛を、酸処理、酸化処理した後、熱処理することにより膨張させて黒鉛層間の一部が剥離してアコーディオン状となった膨張黒鉛もしくは膨張黒鉛の粉砕物を用いる。混合前の粒子サイズとしては5μm〜5mm程度である。膨張黒鉛においては、酸処理を十分に行い、熱処理の温度勾配を大きくすることで大きく膨張させることが可能であり、混合分散を十分に行うことで出来上がった負極活物質の黒鉛薄層の厚みを薄くできるため、良好な電気伝導性、サイクル特性を得ることができる。   Expanded graphite, which is a raw material, is natural graphite, artificial graphite obtained by graphitizing the pitch of petroleum or coal, etc., and graphite having a scaly, oval or spherical, cylindrical or fiber shape is treated with an acid, oxidized After the treatment, expanded graphite or expanded graphite pulverized product that is expanded by heat treatment and peels off part of the graphite layer to form an accordion shape is used. The particle size before mixing is about 5 μm to 5 mm. In expanded graphite, it can be expanded greatly by sufficiently performing acid treatment and increasing the temperature gradient of heat treatment, and the thickness of the graphite thin layer of the negative electrode active material obtained by sufficiently mixing and dispersing can be increased. Since it can be made thin, good electrical conductivity and cycle characteristics can be obtained.

原料の炭素前駆体としては、炭素を主体とする高分子で、不活性ガス雰囲気中での熱処理により炭素質物になるものであれば特に限定されないが、石油系ピッチ、石炭系ピッチ、合成ピッチ、タール類、セルロース、スクロース、ポリ塩化ビニル、ポリビニルアルコール、フェノール樹脂、フラン樹脂、フルフリルアルコール、ポリスチレン、エポキシ樹脂、ポリアクリロニトリル、メラミン樹脂、アクリル樹脂、ポリアミドイミド樹脂、ポリアミド樹脂、ポリイミド樹脂等が使用できる。   The carbon precursor as a raw material is not particularly limited as long as it is a polymer mainly composed of carbon and becomes a carbonaceous material by heat treatment in an inert gas atmosphere, but is not limited to petroleum pitch, coal pitch, synthetic pitch, Tar, cellulose, sucrose, polyvinyl chloride, polyvinyl alcohol, phenol resin, furan resin, furfuryl alcohol, polystyrene, epoxy resin, polyacrylonitrile, melamine resin, acrylic resin, polyamideimide resin, polyamide resin, polyimide resin, etc. it can.

原料であるSiは、平均粒径D50が0.01〜0.5μmであり、BET法で測定される比表面積が23〜300m/gの粉末を使用する。所定の粒子径のSiを得るためには、上述のSiの原料(インゴット、ウエハ、粉末などの状態)を粉砕機で粉砕し、場合によっては分級機を用いる。インゴット、ウエハなどの塊の場合、最初はジョークラッシャー等の粗粉砕機を用いて粉末化することができる。その後、例えば、ボール、ビーズなどの粉砕媒体を運動させ、その運動エネルギーによる衝撃力や摩擦力、圧縮力を利用して被砕物を粉砕するボールミル、媒体撹拌ミルや、ローラによる圧縮力を利用して粉砕を行うローラミルや、被砕物を高速で内張材に衝突もしくは粒子相互に衝突させ、その衝撃による衝撃力によって粉砕を行うジェットミルや、ハンマー、ブレード、ピンなどを固設したローターの回転による衝撃力を利用して被砕物を粉砕するハンマーミル、ピンミル、ディスクミルや、剪断力を利用するコロイドミルや高圧湿式対向衝突式分散機「アルティマイザー」などを用いて粉砕した後、さらに、微粉化を行う。 As the raw material Si, a powder having an average particle diameter D50 of 0.01 to 0.5 μm and a specific surface area of 23 to 300 m 2 / g measured by the BET method is used. In order to obtain Si having a predetermined particle diameter, the above-mentioned Si raw materials (ingot, wafer, powder, etc.) are pulverized by a pulverizer, and a classifier is used in some cases. In the case of a lump such as an ingot or a wafer, it can be first pulverized using a coarse pulverizer such as a jaw crusher. After that, for example, a ball or bead is used to move the grinding medium, and the impact force, frictional force, or compression force of the kinetic energy is used to grind the material to be crushed, the media agitation mill, or the compression force of the roller. Rotation of a roller mill that pulverizes, a jet mill that collides crushed objects with the lining material or collides with each other at high speed, and pulverizes by the impact force of the impact, and a rotor with a fixed hammer, blade, pin, etc. After pulverizing using a hammer mill, pin mill, disk mill that pulverizes the material to be crushed using the impact force of, colloid mill using shear force or high-pressure wet opposed collision disperser `` Ultimizer '', etc., Micronize.

微粉化の方法として例えば、湿式のビーズミルを用い、ビーズの径を段階的に小さくすること等により非常に細かい粒子を得ることができる。ビーズミルに使用するメディアとしては高強度であるジルコニアが好ましい。ビーズの径は、粉砕するSiの粒径により変化させ、例えばSiの平均粒径D50が10〜40μmであれば、0.5〜1mmのビーズを使用し、Siの平均粒径D50が0.5〜10μmでは、0.1〜0.5mmのビーズを使用し、Siの平均粒径D50が0.1〜0.5μmでは、0.03〜0.1mmのビーズを使用することが好ましい。0.1mmよりも小さいビーズを使用する場合、ビーズとスラリーの分離として遠心分離方式を使用することが好ましい。   As a pulverization method, for example, a very fine particle can be obtained by using a wet bead mill and gradually reducing the diameter of the beads. Zirconia, which has high strength, is preferable as the medium used for the bead mill. The diameter of the beads is changed depending on the particle diameter of Si to be crushed. For example, if the average particle diameter D50 of Si is 10 to 40 μm, beads of 0.5 to 1 mm are used, and the average particle diameter D50 of Si is 0.00. When the average particle diameter D50 of Si is 0.1 to 0.5 μm, it is preferable to use 0.03 to 0.1 mm beads. When using beads smaller than 0.1 mm, it is preferable to use a centrifugal separation system for separating the beads and the slurry.

粉砕時の分散剤としては、メタノールやエタノール、イソプロピルアルコール等のアルコールやヘキサン、トルエンなどの炭化水素系溶剤が好ましい。水はSiの酸化が激しくなるので適さない。また、必要に応じてスラリー粘度を下げるためのアニオン系やカチオン系、ノニオン系の分散剤を添加してもよい。スラリーの濃度には特に指定はないが、効率的な粉砕を行うこと、粉砕中の凝集を防ぐこと及びスラリー粘度を低くするための粘度として5〜25%が挙げられ、さらに好ましくは5〜20%が挙げられる。5%よりも濃度が低いと粉砕効率が低くなり、25%よりも高いとスラリー粘度が上昇し、粉砕効率の低下や詰まり等により粉砕ができなくなることがある。   As the dispersing agent during pulverization, alcohols such as methanol, ethanol and isopropyl alcohol, and hydrocarbon solvents such as hexane and toluene are preferable. Water is not suitable because of the intense oxidation of Si. Moreover, you may add the anionic, cationic, and nonionic dispersing agent for lowering | hanging a slurry viscosity as needed. The concentration of the slurry is not particularly specified, but includes 5 to 25% as a viscosity for performing efficient pulverization, preventing aggregation during pulverization and lowering the slurry viscosity, and more preferably 5 to 20%. %. If the concentration is lower than 5%, the pulverization efficiency is lowered, and if it is higher than 25%, the slurry viscosity increases, and pulverization may not be possible due to a decrease in pulverization efficiency or clogging.

粉砕後に粒度分布を整えるため、乾式分級や湿式分級もしくはふるい分け分級を用いることができる。乾式分級は、主として気流を用い、分散、分離(細粒子と粗粒子の分離)、捕集(固体と気体の分離)、排出のプロセスが逐次もしくは同時に行われ、粒子相互間の干渉、粒子の形状、気流の乱れ、速度分布、静電気の影響などで分級効率を低下させないように、分級をする前に前処理(水分、分散性、湿度などの調整)を行うか、使用される気流の水分や酸素濃度を調整して行われる。乾式で分級機が一体となっているタイプでは、一度に粉砕、分級が行われ、所望の粒度分布とすることが可能となる。   In order to adjust the particle size distribution after pulverization, dry classification, wet classification or sieving classification can be used. In the dry classification, the process of dispersion, separation (separation of fine particles and coarse particles), collection (separation of solid and gas), and discharge are performed sequentially or simultaneously, mainly using air flow. Pre-classification (adjustment of moisture, dispersibility, humidity, etc.) before classification, or the moisture in the airflow used so that the classification efficiency is not lowered due to the influence of shape, air flow disturbance, velocity distribution, static electricity, etc. It is done by adjusting the oxygen concentration. In a dry type in which a classifier is integrated, pulverization and classification are performed at a time, and a desired particle size distribution can be obtained.

別の所定の粒子径のSiを得る方法としては、プラズマやレーザー等でSi化合物を加熱して蒸発させ、不活性ガス中で凝固させて得る方法、ガス原料を用いてCVDやプラズマCVD等で得る方法があり、これらの方法は0.1μm以下の超微粒子を得るのに適している。   As another method for obtaining Si having a predetermined particle size, a method of obtaining Si by heating and evaporating a Si compound with plasma or laser and solidifying it in an inert gas, CVD or plasma CVD using a gas raw material, etc. These methods are suitable for obtaining ultrafine particles of 0.1 μm or less.

これらの膨張黒鉛、炭素前駆体、Siとの混合は、炭素前駆体が加熱により軟化、液状化するものである場合は、加熱下で黒鉛、炭素前駆体、Siを混練することによって行うことができる。また、炭素前駆体が溶媒に溶解するものである場合には、溶媒に膨張黒鉛、炭素前駆体、Siを投入し、炭素前駆体が溶解した溶液中で膨張黒鉛、炭素前駆体、Siを分散、混合し、次いで溶媒を除去することで行うことができる。用いる溶媒は、炭素前駆体を溶解できるものであれば特に制限なく使用できる。例えば、炭素前駆体としてピッチ、タール類を用いる場合には、キノリン、ピリジン、トルエン、ベンゼン、テトラヒドロフラン、クレオソート油等が使用でき、ポリ塩化ビニルを用いる場合には、テトラヒドロフラン、シクロヘキサノン、ニトロベンゼン等が使用でき、フェノール樹脂、フラン樹脂を用いる場合には、エタノール、メタノール等が使用できる。   When the carbon precursor is softened or liquefied by heating, mixing with these expanded graphite, carbon precursor, and Si can be performed by kneading graphite, carbon precursor, and Si under heating. it can. If the carbon precursor is dissolved in a solvent, expanded graphite, carbon precursor, and Si are added to the solvent, and the expanded graphite, carbon precursor, and Si are dispersed in the solution in which the carbon precursor is dissolved. , Mixing and then removing the solvent. The solvent to be used can be used without particular limitation as long as it can dissolve the carbon precursor. For example, when pitch or tar is used as the carbon precursor, quinoline, pyridine, toluene, benzene, tetrahydrofuran, creosote oil or the like can be used. When polyvinyl chloride is used, tetrahydrofuran, cyclohexanone, nitrobenzene or the like can be used. When phenol resin or furan resin is used, ethanol, methanol or the like can be used.

混合方法としては、炭素前駆体を加熱軟化させる場合は、混練機(ニーダー)を用いることができる。溶媒を用いる場合は、上述の混練機の他、ナウターミキサー、レーディゲミキサー、ヘンシェルミキサ、ハイスピードミキサー、ホモミキサー等を用いることができる。また、これらの装置でジャケット加熱したり、その後、振動乾燥機、パドルドライヤーなどで溶媒を除去する。   As a mixing method, when the carbon precursor is heat-softened, a kneader (kneader) can be used. In the case of using a solvent, in addition to the above-described kneader, a Nauter mixer, a Roedige mixer, a Henschel mixer, a high speed mixer, a homomixer, or the like can be used. Further, the jacket is heated with these apparatuses, and then the solvent is removed with a vibration dryer, a paddle dryer or the like.

これらの装置で、炭素前駆体を固化、または、溶媒除去の過程における撹拌をある程度の時間続けることで、膨張黒鉛、Si、炭素前駆体の混合物は造粒・圧密化される。また、炭素前駆体を固化、または溶媒除去後の混合物をローラーコンパクタ等の圧縮機によって圧縮し、解砕機で粗粉砕することにより、造粒・圧密化することができる。これらの造粒・圧密化物の大きさは、その後の粉砕工程での取り扱いの容易さから0.1〜5mmが好ましい。   With these apparatuses, the mixture of expanded graphite, Si, and carbon precursor is granulated and consolidated by solidifying the carbon precursor or continuing stirring in the process of removing the solvent for a certain period of time. Further, the carbon precursor is solidified or the mixture after removing the solvent is compressed by a compressor such as a roller compactor and coarsely pulverized by a crusher, whereby granulation and consolidation can be achieved. The size of the granulated / consolidated product is preferably 0.1 to 5 mm in view of ease of handling in the subsequent pulverization step.

造粒・圧密化物の粉砕方法は、圧縮力を利用して被砕物を粉砕するボールミル、媒体撹拌ミルや、ローラによる圧縮力を利用して粉砕を行うローラミルや、被砕物を高速で内張材に衝突もしくは粒子相互に衝突させ、その衝撃による衝撃力によって粉砕を行うジェットミルや、ハンマー、ブレード、ピンなどを固設したローターの回転による衝撃力を利用して被砕物を粉砕するハンマーミル、ピンミル、ディスクミル等の乾式の粉砕方法が好ましい。また、粉砕後に粒度分布を整えるため、風力分級、ふるい分け等の乾式分級が用いられる。粉砕機と分級機が一体となっているタイプでは、一度に粉砕、分級が行われ、所望の粒度分布とすることが可能となる。   The granulated / consolidated material is pulverized by ball mill, medium agitation mill, roller mill for pulverizing using the compressive force of the roller, or lining material to be crushed at high speed. A jet mill that collides with each other or collides with each other and crushes by the impact force of the impact, a hammer mill that crushes the material to be crushed using the impact force of the rotation of a rotor with a fixed hammer, blade, pin, etc. A dry pulverization method such as a pin mill or a disk mill is preferred. In order to adjust the particle size distribution after pulverization, dry classification such as air classification and sieving is used. In the type in which the pulverizer and the classifier are integrated, pulverization and classification are performed at a time, and a desired particle size distribution can be obtained.

粉砕して得られた複合粒子は、アルゴンガスや窒素ガス気流中、もしくは真空など不活性雰囲気中で焼成する。焼成温度は800〜1000℃とすることが好ましい。焼成温度が800℃未満であると、炭素前駆体由来の非晶質炭素の不可逆容量が大きく、またサイクル特性が悪いため、電池の特性が低下する傾向にある。   The composite particles obtained by pulverization are fired in an argon gas or nitrogen gas stream or in an inert atmosphere such as a vacuum. The firing temperature is preferably 800 to 1000 ° C. When the firing temperature is less than 800 ° C., the irreversible capacity of the amorphous carbon derived from the carbon precursor is large, and the cycle characteristics are poor, so that the battery characteristics tend to deteriorate.

本発明のリチウムイオン2次電池用カーボンシリコン系負極活物質の製造方法は、膨張黒鉛、Si、炭素前駆体を、該炭素前駆体が溶解する溶媒に混合分散する工程と、造粒・厚密化する工程と、粉砕および球形化処理して形状が丸みを帯びた複合粒子を形成する工程と、該複合粒子を不活性雰囲気中で焼成する工程を含むことが好ましい。   The method for producing a carbon silicon-based negative electrode active material for a lithium ion secondary battery according to the present invention comprises a step of mixing and dispersing expanded graphite, Si, and a carbon precursor in a solvent in which the carbon precursor is dissolved, and granulation / thickness It is preferable to include a step of forming a composite particle having a round shape by pulverization and spheronization, and a step of firing the composite particle in an inert atmosphere.

造粒・圧密化物を粉砕して球形化処理を施す方法としては、上述の粉砕方法により粉砕して粒度を整えた後、専用の球形化装置を通す方法と、上述のジェットミルやローターの回転による衝撃力を利用して被砕物を粉砕する方法を繰り返す、もしくは処理時間を延長することで球形化する方法がある。専用の球形化装置としては、ホソカワミクロン社のファカルティ(登録商標)、ノビルタ(登録商標)、メカノフュージョン(登録商標)、日本コークス工業社のCOMPOSI、奈良機械製作所社のハイブリダイゼーションシステム、アーステクニカ社のクリプトロンオーブ、クリプトロンエディ等が挙げられる。   As a method of pulverizing the granulated / consolidated product and subjecting it to spheronization, it is pulverized by the above-mentioned pulverization method to adjust the particle size, and then passed through a dedicated spheronization device, and the above-mentioned jet mill or rotor rotation. There is a method of spheroidizing by repeating the method of pulverizing the material to be crushed by using the impact force of or by extending the processing time. Specialized spheroidizing devices include Hosokawa Micron's Faculty (registered trademark), Nobilta (registered trademark), Mechano-Fusion (registered trademark), Nippon Coke Industries' COMPOSI, Nara Machinery Co., Ltd. hybridization system, Earth Technica's Examples include kryptron orb and kryptron eddy.

このようにして得られる本発明のリチウムイオン2次電池用カーボンシリコン系負極活物質は、リチウム二次電池の負極材料として用いることができる。   The carbon silicon-based negative electrode active material for a lithium ion secondary battery of the present invention thus obtained can be used as a negative electrode material for a lithium secondary battery.

本発明の負極活物質は、例えば、有機系結着剤、導電助剤および溶剤と混練して、シート状、ペレット状等の形状に成形するか、または集電体に塗布し、該集電体と一体化してリチウム二次電池用負極とされる。   The negative electrode active material of the present invention is, for example, kneaded with an organic binder, a conductive additive and a solvent, and formed into a sheet shape, a pellet shape or the like, or applied to a current collector, and the current collector A negative electrode for a lithium secondary battery is formed by integrating with the body.

有機系結着剤としては、例えばポリエチレン、ポリプロピレン、エチレンプロピレンポリマー、ブタジエンゴム、スチレンブタジエンゴム、ブチルゴム、イオン導電性の大きな高分子化合物が使用できる。イオン導電率の大きな高分子化合物としては、ポリ弗化ビニリデン、ポリエチレンオキサイド、ポリエピクロロヒドリン、ポリフォスファゼン、ポリアクリロニトリル、ポリイミド等が使用できる。有機系結着剤の含有量は、負極材全体に対して3〜20重量%含有させることが好ましい。また、有機系結着剤の他に粘度調整剤として、カルボキシメチルセルロース、ポリアクリル酸ソーダ、その他のアクリル系ポリマー、または脂肪酸エステル等を添加しても良い。   As the organic binder, for example, polyethylene, polypropylene, ethylene propylene polymer, butadiene rubber, styrene butadiene rubber, butyl rubber, and a polymer compound having a large ion conductivity can be used. Polyvinylidene fluoride, polyethylene oxide, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polyimide and the like can be used as the polymer compound having a high ionic conductivity. The content of the organic binder is preferably 3 to 20% by weight based on the whole negative electrode material. In addition to the organic binder, carboxymethyl cellulose, polysodium acrylate, other acrylic polymers, or fatty acid esters may be added as a viscosity modifier.

導電剤の種類は特に限定されず、構成された電池において、分解や変質を起こさない電子伝導性の材料であれば良く、具体的にはAl,Ti,Fe,Ni,Cu,Zn,Ag,Sn,Si等の金属粉末や金属繊維、または天然黒鉛、人造黒鉛、各種のコークス粉末、メソフェーズ炭素、気相成長炭素繊維、ピッチ系炭素繊維、PAN系炭素繊維、各種の樹脂焼成体等の黒鉛などを用いることができる。導電剤の添加量は、負極材全体中に対して0〜20重量%であり、さらには1〜10重量%が好ましい。導電剤量が少ないと、負極材の導電性に乏しい場合があり、初期抵抗が高くなる傾向がある。一方、導電剤量の増加は電池容量の低下につながるおそれがある。   The type of the conductive agent is not particularly limited, and may be any electron-conductive material that does not cause decomposition or alteration in the configured battery. Specifically, Al, Ti, Fe, Ni, Cu, Zn, Ag, Metal powder and metal fiber such as Sn, Si, or graphite such as natural graphite, artificial graphite, various coke powders, mesophase carbon, vapor-grown carbon fiber, pitch-based carbon fiber, PAN-based carbon fiber, various resin fired bodies, etc. Etc. can be used. The addition amount of the conductive agent is 0 to 20% by weight, more preferably 1 to 10% by weight, based on the whole negative electrode material. When the amount of the conductive agent is small, the conductivity of the negative electrode material may be poor and the initial resistance tends to be high. On the other hand, an increase in the amount of conductive agent may lead to a decrease in battery capacity.

前記溶剤としては特に制限はなく、N−メチル−2−ピロリドン、ジメチルホルムアミド、イソプロパノール、純水等が挙げられ、その量に特に制限はない。集電体としては、例えばニッケル、銅等の箔、メッシュなどが使用できる。一体化は、例えばロール、プレス等の成形法で行うことができる。   There is no restriction | limiting in particular as said solvent, N-methyl- 2-pyrrolidone, a dimethylformamide, isopropanol, a pure water etc. are mentioned, There is no restriction | limiting in particular in the quantity. As the current collector, for example, a foil such as nickel or copper, a mesh, or the like can be used. The integration can be performed by a molding method such as a roll or a press.

このようにして得られた負極は、セパレータを介して正極を対向して配置し、電解液を注入することにより、従来のシリコンを負極材料に用いたリチウム二次電池と比較して、サイクル特性に優れ、高容量、高初期効率という優れた特性を有するリチウム二次電池を作製することができる。   The negative electrode thus obtained has a cycle characteristic compared to a lithium secondary battery using conventional silicon as a negative electrode material by placing the positive electrode opposite to each other through a separator and injecting an electrolytic solution. In addition, a lithium secondary battery having excellent characteristics such as high capacity and high initial efficiency can be manufactured.

正極に用いられる材料については、例えばLiNiO、LiCoO、LiMn、LiNiMnCo1−x−y、LiFePO、Li0.5Ni0.5Mn1.5、LiMnO−LiMO(M=Co,Ni,Mn)、Li箔等を単独または混合して使用することができる。 The material used for the positive electrode, for example LiNiO 2, LiCoO 2, LiMn 2 O 4, LiNi x Mn y Co 1-x-y O 2, LiFePO 4, Li 0.5 Ni 0.5 Mn 1.5 O 4 Li 2 MnO 3 —LiMO 2 (M═Co, Ni, Mn), Li foil and the like can be used alone or in combination.

電解液としては、LiClO、LiPF、LiAsF、LiBF、LiSOCF等のリチウム塩を、例えばエチレンカーボネート、ジエチルカーボネート、ジメトキシエタン、ジメチルカーボネート、テトラヒドロフラン、プロピレンカーボネート等の非水系溶剤に溶解させた、いわゆる有機電解液を使用することができる。さらには、イミダゾリウム、アンモニウム、およびピリジニウム型のカチオンを用いたイオン液体を使用することができる。対アニオンは特に限定されるものではないが、BF 、PF 、(CFSO等が挙げられる。イオン液体は前述の有機電解液溶媒と混合して使用することが可能である。電解液には、ビニレンカーボネートやフロロエチレンカーボネートの様なSEI(固体電解質界面層)形成剤を添加することもできる。 As the electrolytic solution, lithium salts such as LiClO 4 , LiPF 6 , LiAsF 6 , LiBF 4 , LiSO 3 CF 3 are used as non-aqueous solvents such as ethylene carbonate, diethyl carbonate, dimethoxyethane, dimethyl carbonate, tetrahydrofuran, and propylene carbonate. A so-called dissolved organic electrolyte solution can be used. Furthermore, ionic liquids using imidazolium, ammonium, and pyridinium type cations can be used. The counter anion is not particularly limited, and examples thereof include BF 4 , PF 6 , (CF 3 SO 2 ) 2 N − and the like. The ionic liquid can be used by mixing with the organic electrolyte solvent described above. An SEI (solid electrolyte interface layer) forming agent such as vinylene carbonate or fluoroethylene carbonate can also be added to the electrolytic solution.

また、上記塩類をポリエチレンオキサイド、ポリホスファゼン、ポリアジリジン、ポリエチレンスルフィド等やこれらの誘導体、混合物、複合体等に混合された固体電解質を用いることもできる。この場合、固体電解質はセパレータも兼ねることができ、セパレータは不要となる、セパレータとしては、例えばポリエチレン、ポリプロピレン等のポリオレフィンを主成分とした不織布、クロス、微孔フィルムまたはこれらを組み合わせたものを使用することができる。   In addition, a solid electrolyte obtained by mixing the above salts with polyethylene oxide, polyphosphazene, polyaziridine, polyethylene sulfide, or the like, or a derivative, mixture, or complex thereof can also be used. In this case, the solid electrolyte can also serve as a separator, and the separator becomes unnecessary. As the separator, for example, a nonwoven fabric mainly composed of polyolefin such as polyethylene or polypropylene, cloth, microporous film, or a combination thereof is used. can do.

本発明によれば、酸処理黒鉛を1100〜1200℃での熱処理時の130%以下のかさ密度を有する膨張黒鉛を圧縮した黒鉛を使用したことによるSiの包み込んでの導電性の確保により、電解液とシリコンの反応を抑えることによる優れたサイクル特性と、高い初期効率が得られる。また、本発明の製造方法により、高密度の負極形成に適した高いかさ密度の負極活物質を得ることができる。   According to the present invention, the acid-treated graphite is electrolyzed by ensuring conductivity by enclosing Si by using graphite obtained by compressing expanded graphite having a bulk density of 130% or less during heat treatment at 1100 to 1200 ° C. Excellent cycle characteristics by suppressing the reaction between the liquid and silicon, and high initial efficiency can be obtained. In addition, a high bulk density negative electrode active material suitable for forming a high density negative electrode can be obtained by the production method of the present invention.

実施例1で得られた負極活物質粒子断面のFE−SEMによる2次電子像である。2 is a secondary electron image obtained by FE-SEM of a cross section of a negative electrode active material particle obtained in Example 1. FIG.

以下、実施例および比較例により本発明を具体的に説明するが、本発明はこれら実施例に限定されるものではない。   EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention concretely, this invention is not limited to these Examples.

実施例1
粒子径約0.5mm((200)面方向の幅)、厚み約0.02mmの天然黒鉛を、濃硫酸に硝酸ナトリウム1重量%、過マンガン酸カリウム7重量%を添加した液に24時間浸漬し、その後、水洗して乾燥し、酸処理黒鉛を得た。この酸処理黒鉛を振動粉末供給器に入れ、10L/分の流量の窒素ガスに乗せて電気ヒーターで1000℃に加熱した長さ1m、内径11mmの石英管に通し、端面から大気に放出し、亜硫酸等のガスを上部に排気、下部に膨張黒鉛をステンレス容器で捕集した。この膨張黒鉛のかさ密度は2.2g/L、比表面積は60m/gであった。なお、電気ヒーターを1150℃に加熱した同寸法のムライト管に酸処理黒鉛を通して捕集した膨張黒鉛のかさ密度は2.0g/L、比表面積は65m/gであり、この1150℃品に対する膨張率は110%であった。外観はコイル状であり、SEM観察で黒鉛層が剥離し、アコーディオン状であることが確認された。
Example 1
Immerse natural graphite with a particle diameter of about 0.5 mm (width in the (200) plane direction) and a thickness of about 0.02 mm in a solution of concentrated sulfuric acid with 1 wt% sodium nitrate and 7 wt% potassium permanganate added for 24 hours. Then, it was washed with water and dried to obtain acid-treated graphite. This acid-treated graphite was put into a vibrating powder feeder, put on nitrogen gas at a flow rate of 10 L / min, passed through a quartz tube having a length of 1 m and an inner diameter of 11 mm heated to 1000 ° C. with an electric heater, and released from the end face to the atmosphere. A gas such as sulfurous acid was exhausted at the top, and expanded graphite was collected at the bottom in a stainless steel container. The bulk density of this expanded graphite was 2.2 g / L, and the specific surface area was 60 m 2 / g. The bulk density of expanded graphite collected through acid-treated graphite in a mullite tube of the same size heated to 1150 ° C. with an electric heater is 2.0 g / L and the specific surface area is 65 m 2 / g. The expansion coefficient was 110%. The appearance was coiled, and the graphite layer was peeled off by SEM observation, confirming the accordion shape.

平均粒子径D50が7μmのケミカルグレードの金属Si(純度3.5N)をメタノールに20重量%混合し、直径0.3mmのジルコニアビーズを用いた微粉砕湿式ビーズミルを5時間行い、平均粒子径D50が0.30μm、乾燥時のBET表面積が60m/gのSiスラリーを得た。 20% by weight of chemical grade metal Si (purity 3.5N) having an average particle diameter D50 of 7 μm was mixed with methanol, and pulverized wet bead mill using zirconia beads having a diameter of 0.3 mm was performed for 5 hours. Was 0.30 μm, and a Si slurry having a BET surface area of 60 m 2 / g during drying was obtained.

上記膨張黒鉛を24g、上記Siスラリーを60g、レゾール型のフェノール樹脂を10g、エタノール1Lを撹拌容器に入れて、ホモミキサーで1時間混合撹拌した。その後、混合液をロータリーエバポレーターに移し、回転しながら温浴で60℃に加熱し、アスピレータで真空に引き、溶媒を除去した。その後、ドラフト中でバットに広げて排気しながら2時間乾燥し、目開き2mmのメッシュを通し、さらに12時間乾燥して、約40gの混合乾燥物(軽装かさ密度80g/L)を得た。   24 g of the expanded graphite, 60 g of the Si slurry, 10 g of a resol type phenol resin, and 1 L of ethanol were placed in a stirring vessel, and mixed and stirred for 1 hour with a homomixer. Thereafter, the mixed solution was transferred to a rotary evaporator, heated to 60 ° C. with a warm bath while rotating, and evacuated with an aspirator to remove the solvent. Thereafter, it was spread on a bat in a draft and dried for 2 hours while evacuating, passed through a mesh with a mesh opening of 2 mm, and further dried for 12 hours to obtain about 40 g of a dry mixture (light bulk density 80 g / L).

この混合乾燥物を3本ロールミルに2回通し、粒度約2mm、軽装かさ密度385g/Lに造粒・圧密化した。   This mixed dried product was passed through a three-roll mill twice, and granulated and consolidated to a particle size of about 2 mm and a light bulk density of 385 g / L.

次に、この造粒・圧密化物をニューパワーミルに入れて水冷しながら、22000rpmで900秒粉砕し、同時に球形化し、軽装かさ密度650g/Lの球形化粉末を得た。得られた粉末をアルミナボートに入れて、管状炉で窒素ガスを流しながら、最高温度900℃で1時間焼成した。その後、目開き45μmのメッシュを通し、平均粒子径D50が19μm、軽装かさ密度761g/Lの負極活物質を得た。窒素ガスを用いたBET法による比表面積は50m/gであった。 Next, the granulated / consolidated product was placed in a new power mill and pulverized at 22000 rpm for 900 seconds while being cooled with water, and spheroidized at the same time to obtain a spheroidized powder having a light bulk density of 650 g / L. The obtained powder was put into an alumina boat and fired at a maximum temperature of 900 ° C. for 1 hour while flowing nitrogen gas in a tubular furnace. Thereafter, a negative electrode active material having an average particle diameter D50 of 19 μm and a light bulk density of 761 g / L was obtained through a mesh having an opening of 45 μm. The specific surface area by the BET method using nitrogen gas was 50 m 2 / g.

図1に、得られた負極活物質粒子をArイオンビームで切断した断面のFE−SEMによる2次電子像を示す。負極活物質粒子内部は0.05〜0.2μmの長さのSiの微粒子が炭素質物と共に0.02〜0.2μmの厚みの黒鉛薄層(11)の間(12)(隙間は0.05〜1μm)に挟まった構造が網目状に広がり、積層していた。炭素質物はSiの微粒子に密着して覆っていた。また、活物質粒子の表面付近では、黒鉛薄層(11)が湾曲して活物質粒子を覆っていた。   In FIG. 1, the secondary electron image by the FE-SEM of the cross section which cut | disconnected the obtained negative electrode active material particle with Ar ion beam is shown. Inside the negative electrode active material particles, 0.05 to 0.2 μm long Si fine particles and a carbonaceous material (0.02) between the thin graphite layers (11) having a thickness of 0.02 to 0.2 μm (the gap is 0. 0). The structure sandwiched between (05-1 μm) spreads in a mesh pattern and is laminated. The carbonaceous material was in close contact with and covered the Si fine particles. Further, in the vicinity of the surface of the active material particles, the graphite thin layer (11) was curved to cover the active material particles.

得られた負極活物質を用いたリチウムイオン2次電池を以下のようにして作製した。   A lithium ion secondary battery using the obtained negative electrode active material was produced as follows.

「リチウムイオン二次電池用負極の作製」
得られた負極活物質を95.5重量%(固形分全量中の含有量。以下同じ。)に対して、導電助剤としてアセチレンブラック0.5重量%と、バインダとしてCMC1.5重量%とSBR2.5重量%、水とを混合して負極合剤含有スラリーを調製した。
"Preparation of negative electrode for lithium ion secondary battery"
The obtained negative electrode active material was 95.5% by weight (content in the total solid content, the same applies hereinafter), acetylene black 0.5% by weight as a conductive additive, and CMC 1.5% by weight as a binder. A negative electrode mixture-containing slurry was prepared by mixing 2.5% by weight of SBR and water.

得られたスラリーを、アプリケータを用いて固形分塗布量が3mg/cmになるように厚みが15μmの銅箔に塗布し、110℃で定置運転乾燥機にて0.5時間乾燥した。乾燥後、14mmφの円形に打ち抜き、圧力0.6t/cmの条件で一軸プレスし、さらに真空下、110℃で3時間熱処理して、厚みが30μmの負極合剤層を形成したリチウムイオン2次電池用負極を得た。 The obtained slurry was applied to a copper foil having a thickness of 15 μm using an applicator so that the solid content was 3 mg / cm 2 and dried at 110 ° C. in a stationary operation dryer for 0.5 hour. After drying, the lithium ion 2 was punched into a circle of 14 mmφ, uniaxially pressed under conditions of a pressure of 0.6 t / cm 2 , and further heat-treated at 110 ° C. for 3 hours under vacuum to form a negative electrode mixture layer having a thickness of 30 μm. A negative electrode for a secondary battery was obtained.

「評価用セルの作製」
評価用セルは、グローブボックス中でスクリューセルに上記負極、24mmφのポリプロピレン製セパレータ、21mmφのガラスフィルター、18mmφで厚み0.2mmの金属リチウムおよびその基材のステンレス箔を、各々、電解液にディップしたのち、この順に積層し、最後に蓋をねじ込み作製した。電解液はエチレンカーボネートとジエチルカーボネートを体積比1対1の混合溶媒とし、LiPFを1.2mol/Lの濃度になるように溶解させたものを使用した。評価用セルは、さらにシリカゲルを入れた密閉ガラス容器に入れて、シリコンゴムの蓋を通した電極を充放電装置に接続した。
"Production of evaluation cells"
In the glove box, the evaluation cell was prepared by dipping the negative electrode, a 24 mmφ polypropylene separator, a 21 mmφ glass filter, a 18 mmφ 0.2 mm thick metal lithium and a stainless steel foil of the base material into the electrolyte solution in the glove box. After that, the layers were laminated in this order, and finally the lid was screwed in. The electrolytic solution used was a mixture of ethylene carbonate and diethyl carbonate having a volume ratio of 1: 1 and LiPF 6 dissolved to a concentration of 1.2 mol / L. The evaluation cell was further placed in a sealed glass container containing silica gel, and an electrode through a silicon rubber lid was connected to the charge / discharge device.

「評価条件」
評価用セルは25℃の恒温室にて、サイクル試験した。充電は、2mAの定電流で0.01Vまで充電後、0.01Vの定電圧で電流値が0.2mAになるまで行った。また放電は、2mAの定電流で1.5Vの電圧値まで行った。放電容量と初期充放電効率は、初回充放電試験の結果とした。
"Evaluation conditions"
The evaluation cell was cycle tested in a constant temperature room at 25 ° C. Charging was performed after charging to 0.01 V at a constant current of 2 mA until the current value reached 0.2 mA at a constant voltage of 0.01 V. The discharge was performed at a constant current of 2 mA up to a voltage value of 1.5 V. The discharge capacity and the initial charge / discharge efficiency were the results of the initial charge / discharge test.

また、サイクル特性は、前記充放電条件にて30回充放電試験した後の放電容量を初回の放電容量を比較し、その容量維持率として評価した。   In addition, the cycle characteristics were evaluated as the capacity retention rate by comparing the discharge capacity after 30 charge / discharge tests under the charge / discharge conditions with the initial discharge capacity.

比較例1
実施例1と同様の酸処理黒鉛を電気ヒーターで850℃に加熱した長さ1m、内径11mmの石英管に通し、かさ密度2.9g/L、比表面積は34m/g、1150℃品に対する膨張率が145%である以外は実施例1と同様の方法で負極活物質、負極、評価用セルの順に作製し、セル評価した。
Comparative Example 1
The same acid-treated graphite as in Example 1 was heated to 850 ° C. with an electric heater and passed through a quartz tube having a length of 1 m and an inner diameter of 11 mm, a bulk density of 2.9 g / L, a specific surface area of 34 m 2 / g, and a 1150 ° C. product. A negative electrode active material, a negative electrode, and a cell for evaluation were prepared in the same manner as in Example 1 except that the expansion rate was 145%, and cell evaluation was performed.

実施例1の結果と比較例1の結果を表1に示す。   The results of Example 1 and Comparative Example 1 are shown in Table 1.

表1から明らかなように、膨張黒鉛の1150℃品に対するかさ密度が110%である実施例1のリチウムイオン2次電池は、高容量で、初期充放電効率が高く、充放電サイクル特性が良好である。   As is clear from Table 1, the lithium ion secondary battery of Example 1 having a bulk density of 110% with respect to 1150 ° C. expanded graphite has a high capacity, high initial charge / discharge efficiency, and good charge / discharge cycle characteristics. It is.

これに対し、膨張黒鉛の1150℃品に対するかさ密度が145%と高い比較例1のリチウムイオン2次電池は、初期容量、サイクル容量維持率に劣った。   On the other hand, the lithium ion secondary battery of Comparative Example 1 having a high bulk density of 145% with respect to 1150 ° C. expanded graphite was inferior in initial capacity and cycle capacity maintenance rate.

Figure 0006451071
Figure 0006451071

本発明であるリチウムイオン2次電池負極活物質およびその製造方法は、高容量で長寿命が必要とされるリチウムイオン2次電池に利用することができる。   The negative electrode active material for lithium ion secondary battery and the method for producing the same of the present invention can be used for a lithium ion secondary battery that requires a high capacity and a long life.

11 負極活物質内部の黒鉛薄層
12 負極活物質内部のSi微粒子
11 Graphite thin layer inside negative electrode active material 12 Si fine particles inside negative electrode active material

Claims (4)

炭素質物及び黒鉛とSiとを含んでなるリチウムイオン2次電池用負極活物質において、天然黒鉛を、濃硫酸に硝酸ナトリウム1重量%、過マンガン酸カリウム7重量%を添加した液に24時間浸漬し、その後、水洗して乾燥し得た酸処理黒鉛を10L/分の流量の窒素ガス下1100〜1200℃で熱処理した時のかさ密度を基準(100%)として、130%以下のかさ密度を有する膨張黒鉛からなり、炭素質物と黒鉛の含有量が5〜90重量%であり、Siの微粒子が複合化している炭素質物と共に0.5μm以下の厚みの黒鉛薄層の間に挟まった構造であり、その構造が積層および/または網目状に広がっており、該黒鉛薄層が活物質粒子の表面付近で湾曲して活物質粒子を覆っていることを特徴とするリチウムイオン2次電池用負極活物質。 In a negative electrode active material for a lithium ion secondary battery comprising carbonaceous material and graphite and Si, natural graphite is immersed in concentrated sulfuric acid to which 1% by weight of sodium nitrate and 7% by weight of potassium permanganate are added for 24 hours. Thereafter, the acid-treated graphite obtained by washing and drying with water was heat-treated at 1100 to 1200 ° C. under nitrogen gas at a flow rate of 10 L / min. It is composed of expanded graphite having a carbonaceous material and graphite content of 5 to 90% by weight, and sandwiched between thin graphite layers having a thickness of 0.5 μm or less together with carbonaceous material in which Si fine particles are complexed. A negative electrode for a lithium ion secondary battery, characterized in that the structure extends in a laminated and / or network form, and the graphite thin layer is curved near the surface of the active material particles to cover the active material particles. Active material. 前記負極活物質が、形状が丸みを帯び、平均粒径D50が1〜40μm、BET法による比表面積が5〜120m/gの複合粒子であり、炭素質物が、少なくとも活物質表面を覆っていることを特徴とする請求項1に記載のリチウムイオン2次電池用シリコン含有負極活物質。 The negative electrode active material is a composite particle having a round shape, an average particle diameter D50 of 1 to 40 μm, and a specific surface area by a BET method of 5 to 120 m 2 / g, and a carbonaceous material covers at least the active material surface. The silicon-containing negative electrode active material for a lithium ion secondary battery according to claim 1, wherein: 酸処理黒鉛を1100〜1200℃で熱処理した時のかさ密度を基準(100%)として、130%以下のかさ密度を有する膨張黒鉛と、炭素前駆体と、Siを原料とし、これらを混合する工程と、造粒・圧密化する工程と、粉砕および球形化処理して形状が丸みを帯びた複合粒子を形成する工程と、該複合粒子を不活性ガス雰囲気中で焼成する工程とを含むことを特徴とする請求項1に記載のリチウムイオン2次電池用負極活物質の製造方法。 A process of mixing expanded graphite having a bulk density of 130% or less, a carbon precursor, and Si as raw materials based on the bulk density when heat-treating acid-treated graphite at 1100 to 1200 ° C. (100%). And a step of granulating and compacting, a step of forming a composite particle having a rounded shape by pulverization and spheronization, and a step of firing the composite particle in an inert gas atmosphere. The manufacturing method of the negative electrode active material for lithium ion secondary batteries of Claim 1 characterized by the above-mentioned. 前記複合粒子を不活性雰囲気中で焼成する工程の温度が、800〜1000℃であることを特徴とする請求項3に記載のリチウムイオン2次電池用シリコン含有負極活物質の製造方法。 4. The method for producing a silicon-containing negative electrode active material for a lithium ion secondary battery according to claim 3, wherein the temperature of the step of firing the composite particles in an inert atmosphere is 800 to 1000 ° C. 5.
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