JP2013093259A - Negative electrode active material for lithium ion secondary battery and production method therefor and lithium ion secondary battery - Google Patents
Negative electrode active material for lithium ion secondary battery and production method therefor and lithium ion secondary battery Download PDFInfo
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本発明はスズを含みリチウムイオン二次電池に用いられる負極活物質およびその製造方法ならびにこの負極活物質を用いたリチウムイオン二次電池に関する。 The present invention relates to a negative electrode active material containing tin and used for a lithium ion secondary battery, a method for producing the same, and a lithium ion secondary battery using the negative electrode active material.
リチウムイオン二次電池は、小型で大容量であるため、携帯電話やノートパソコン等の二次電池として広く用いられている。近年では、電気自動車やハイブリッド自動車等のバッテリとしての用途も提案されている。 Lithium ion secondary batteries are small and have a large capacity, and are therefore widely used as secondary batteries for mobile phones and notebook computers. In recent years, applications as batteries for electric vehicles and hybrid vehicles have also been proposed.
リチウムイオン二次電池は、リチウム（Ｌｉ）を挿入および脱離できる活物質を正極と負極とに持つ。リチウムイオン二次電池は、リチウムイオンの両極間の移動によって動作する。 A lithium ion secondary battery has an active material capable of inserting and removing lithium (Li) in a positive electrode and a negative electrode. A lithium ion secondary battery operates by movement between both electrodes of lithium ions.
近年、リチウムイオン二次電池の初期容量を高めるために、負極活物質としてスズ（Ｓｎ）を含むものを用いることが提案されている。ＳｎはＬｉと合金可能な元素であり、炭素材料に比べて理論容量が大きいため、リチウムイオン二次電池用の負極活物質として有用であると考えられている。すなわち、Ｓｎを含む負極活物質を用いることにより、炭素材料等を用いるよりも高容量のリチウムイオン二次電池を得ることができる。 In recent years, in order to increase the initial capacity of a lithium ion secondary battery, it has been proposed to use a material containing tin (Sn) as a negative electrode active material. Sn is an element that can be alloyed with Li and has a larger theoretical capacity than a carbon material, and is considered useful as a negative electrode active material for a lithium ion secondary battery. That is, by using a negative electrode active material containing Sn, a lithium ion secondary battery having a higher capacity than that using a carbon material or the like can be obtained.
Ｓｎを含む一般的な負極活物質として、ＳｎＯが挙げられる。しかし近年、Ｌｉとのコンバージョン反応を生じ得るＳｎＯ2を負極活物質として用いる場合に、Ｌｉとの合金化反応を生じ得るＳｎを負極活物質として用いる場合に比べて、リチウムイオン二次電池をさらに高容量化できると考えられている（例えば、非特許文献１参照）。 SnO is mentioned as a general negative electrode active material containing Sn. However, in recent years, when SnO 2 capable of generating a conversion reaction with Li is used as the negative electrode active material, the lithium ion secondary battery has been further compared with the case where Sn capable of causing an alloying reaction with Li is used as the negative electrode active material. It is considered that the capacity can be increased (for example, see Non-Patent Document 1).
しかし、コンバージョン反応は一般に反応速度が遅いとされている。つまり、ＳｎＯ2を負極活物質とし、コンバージョン反応を生じさせるためには、充放電速度を非常に遅くする必要があった。このためこのような負極活物質は、一般的な用途のリチウムイオン二次電池に適用し難い問題があった。 However, the conversion reaction is generally considered to be slow. That is, in order to use SnO 2 as a negative electrode active material and cause a conversion reaction, it was necessary to make the charge / discharge rate very slow. Therefore, such a negative electrode active material has a problem that it is difficult to apply it to a lithium ion secondary battery for general use.
本発明は上記の事情に鑑みてなされたものであり、Ｓｎを含み充放電容量が大きくかつ一般的な用途のリチウムイオン二次電池に適用可能な負極活物質、およびこの負極活物質の製造方法、ならびに負極活物質としてＳｎを含み充放電容量が大きくかつ一般的な用途に利用できるリチウムイオン二次電池を提供することを、解決すべき課題とする。 The present invention has been made in view of the above circumstances, and has a negative electrode active material that includes Sn and has a large charge / discharge capacity and can be applied to a lithium ion secondary battery for general use, and a method for producing the negative electrode active material An object to be solved is to provide a lithium ion secondary battery that contains Sn as a negative electrode active material, has a large charge / discharge capacity, and can be used for general purposes.
上記課題を解決する本発明の負極活物質の製造方法は、スズ（Ｓｎ）を含むリチウムイオン二次電池用負極活物質を製造する方法であって、
ＳｎＯを主成分とするスズ原料をメカニカルミリング処理する第１工程と、該メカニカルミリング処理されたスズ原料を酸化処理する第２工程と、を含むことを特徴とする。
The negative electrode active material manufacturing method of the present invention that solves the above problems is a method of manufacturing a negative electrode active material for a lithium ion secondary battery containing tin (Sn),
The method includes a first step of mechanically milling a tin raw material containing SnO as a main component and a second step of oxidizing the tin raw material that has been mechanically milled.
上記課題を解決する本発明の負極活物質は、スズ（Ｓｎ）を含むリチウムイオン二次電池用負極活物質であって、
ＳｎとＳｎＯ2とを含み、
該ＳｎＯ2に含まれるＳｎ原子の量は、該負極活物質に含まれるＳｎ原子全体を１００原子％としたときに、５０原子％を超えるＳｎ原子をＳｎＯ2として含むことを特徴とする。
The negative electrode active material of the present invention for solving the above problems is a negative electrode active material for a lithium ion secondary battery containing tin (Sn),
Including Sn and SnO 2 ,
The amount of Sn atoms contained in the SnO 2 is an overall Sn atoms contained in the negative electrode active material is 100 atomic%, characterized in that it comprises a Sn atom more than 50 atomic% as SnO 2.
また、上記課題を解決する本発明のリチウムイオン二次電池は、本発明の負極活物質を負極に含むことを特徴とする。 Moreover, the lithium ion secondary battery of this invention which solves the said subject contains the negative electrode active material of this invention in a negative electrode, It is characterized by the above-mentioned.
以下、特に説明のない場合、本発明のリチウムイオン二次電池用負極活物質を本発明の負極活物質と略する。また、本発明のリチウムイオン二次電池用負極活物質の製造方法を本発明の製造方法と略する。 Hereinafter, unless otherwise specified, the negative electrode active material for lithium ion secondary batteries of the present invention is abbreviated as the negative electrode active material of the present invention. Moreover, the manufacturing method of the negative electrode active material for lithium ion secondary batteries of this invention is abbreviated as the manufacturing method of this invention.
本発明の製造方法によると、一般的な速度で充放電した場合にもリチウムイオン二次電池の充放電容量を増大できる負極活物質を製造できる。これは、メカニカルミリング処理により酸化第１スズすなわちＳｎＯを微細化かつ不均化（２ＳｎＯ→Ｓｎ＋ＳｎＯ2）させ、さらにメカニカルミリング処理後のスズ原料に含まれるＳｎ、および、メカニカルミリング処理で処理しきれていないＳｎＯ（換言すると、残存するＳｎＯ）を酸化処理により酸化してＳｎＯ2を生成させることで、ＳｎＯからＳｎおよびＳｎＯ2の２相を生成できたことによると考えられる。ここで生成したＳｎおよびＳｎＯ2は、それぞれ別々にリチウムイオン二次電池用負極活物質として機能すると考えられる。また、ＳｎおよびＳｎＯ2はＬｉと可逆的に反応すると考えられる。このため、このような負極活物質を用いれば、負極活物資としてＳｎＯを用いる場合やＳｎのみを用いる場合に比べて、リチウムイオン二次電池を高容量化でき、かつ、反応速度もさほど低下しないと考えられる。よって、本発明の製造方法によると、Ｓｎを含み充放電容量が大きくかつ一般的な用途のリチウムイオン二次電池に適用可能な負極活物質を製造できる。 According to the production method of the present invention, a negative electrode active material capable of increasing the charge / discharge capacity of a lithium ion secondary battery even when charged / discharged at a general rate can be produced. This is because the stannous oxide, that is, SnO is refined and disproportionated (2SnO → Sn + SnO 2 ) by mechanical milling treatment, and Sn contained in the tin raw material after mechanical milling treatment and mechanical milling treatment can be used. This is considered to be because SnO 2 (in other words, remaining SnO) was oxidized by oxidation treatment to produce SnO 2 to produce two phases of Sn and SnO 2 . Here resulting Sn and SnO 2 is thought to function as a negative electrode active material for a separately lithium ion secondary battery. Sn and SnO 2 are considered to react reversibly with Li. For this reason, when such a negative electrode active material is used, the capacity of the lithium ion secondary battery can be increased and the reaction rate does not decrease much compared to the case where SnO is used as the negative electrode active material or when only Sn is used. it is conceivable that. Therefore, according to the manufacturing method of the present invention, it is possible to manufacture a negative electrode active material that includes Sn and has a large charge / discharge capacity and can be applied to a lithium ion secondary battery for general use.
また、本発明の負極活物質は、上述したように、Ｓｎを含み充放電容量が大きくかつ一般的な用途のリチウムイオン二次電池に適用可能である。以下、必要に応じてメカニカルミリング処理をＭＭ処理と略する。 In addition, as described above, the negative electrode active material of the present invention is applicable to lithium ion secondary batteries having a large charge / discharge capacity and containing Sn. Hereinafter, the mechanical milling process is abbreviated as MM process as necessary.
本発明の製造方法は第１工程と第２工程とを備える。 The manufacturing method of the present invention includes a first step and a second step.
第１工程は、ＳｎＯを主成分とするスズ原料をメカニカルミリング処理する工程である。ここで、メカニカルミリングとは、遊星ボールミル等を用いて機械的な力を加えることで、物質に化学反応を起こさせる（または化学反応を起こしやすくする）処理を指す。物質を微粒子状にでき、かつ、不均化反応による物質の表面改質等を生じさせ得る。 The first step is a step of mechanically milling a tin raw material containing SnO as a main component. Here, mechanical milling refers to a process of causing a chemical reaction (or facilitating a chemical reaction) to a substance by applying a mechanical force using a planetary ball mill or the like. The substance can be made into fine particles, and the surface of the substance can be modified by a disproportionation reaction.
上述したように、第１工程でスズ原料（ＳｎＯ）をメカニカルミリング処理することで、２ＳｎＯ→Ｓｎ＋ＳｎＯ2の不均化反応が生じ、Ｓｎ相と、ＳｎＯ2相とが生成すると考えられる。このＳｎ相はメカニカルミリング処理されたスズ原料（負極活物質前駆体）における芯部を構成すると考えられ、ＳｎＯ2相は芯部を覆う被覆部を構成すると考えられる。スズ原料は、ＳｎＯのみからなっても良いし、ＳｎやＳｎＯ2等のスズ含有物質を含んでも良いし、その他の不可避不純物を含んでも良い。 As described above, it is considered that a disproportionation reaction of 2SnO → Sn + SnO 2 occurs by mechanically milling the tin raw material (SnO) in the first step, and a Sn phase and a SnO 2 phase are generated. This Sn phase is considered to constitute a core part in a tin raw material (negative electrode active material precursor) subjected to mechanical milling, and the SnO 2 phase is considered to constitute a covering part covering the core part. The tin raw material may be composed only of SnO, may contain a tin-containing substance such as Sn or SnO 2, or may contain other inevitable impurities.
第２工程は、上述した負極活物質前駆体を酸化処理する工程である。酸化処理は、既知の種々の方法を用いることができる。例えば、負極活物質前駆体に、酸素ガスやオゾンガス等の酸素元素含有ガスを高濃度で接触させても良い。或いは、負極活物質前駆体を、酸素元素存在下（例えば空気等の酸素元素含有雰囲気下）で加熱しても良い。負極活物質前駆体を酸素元素存在下で加熱する場合には、負極活物質前駆体を効率よくかつ安価に酸化できる利点がある。 The second step is a step of oxidizing the negative electrode active material precursor described above. Various known methods can be used for the oxidation treatment. For example, an oxygen element-containing gas such as oxygen gas or ozone gas may be brought into contact with the negative electrode active material precursor at a high concentration. Alternatively, the negative electrode active material precursor may be heated in the presence of an oxygen element (for example, in an oxygen element-containing atmosphere such as air). When the negative electrode active material precursor is heated in the presence of oxygen element, there is an advantage that the negative electrode active material precursor can be oxidized efficiently and inexpensively.
上述したように、負極活物質前駆体は芯部と被覆部とを持つ多層構造をなすと考えられる。第２工程においては、負極活物質前駆体を酸化することで、負極活物質前駆体の被覆部にＳｎＯ2を生成させる。メカニカルミリング処理で得られた被覆部には、ＳｎＯ2（および、場合によっては未処理のＳｎＯ）が存在すると考えられる。第２工程においては、芯部に含まれるＳｎが酸化されてＳｎＯ2が生成する。または、被覆部に含まれるＳｎＯが酸化してＳｎＯ2が生成する。このような反応によって、ＳｎとＳｎＯ2とを含む負極活物質が得られる。なお、第２工程は、第１工程後に行っても良いし、第１工程と同時に行っても良い。何れの場合にも、メカニカルミリング処理されたスズ原料をさらに酸化することで、ＳｎとＳｎＯ2とを含む負極活物質におけるＳｎＯ2含量を多くできる。 As described above, the negative electrode active material precursor is considered to have a multilayer structure having a core portion and a covering portion. In the second step, the negative electrode active material precursor is oxidized to produce SnO 2 in the coating portion of the negative electrode active material precursor. It is considered that SnO 2 (and untreated SnO in some cases) is present in the coating portion obtained by the mechanical milling treatment. In the second step, Sn contained in the core is oxidized to produce SnO 2 . Alternatively, SnO contained in the covering portion is oxidized to produce SnO 2 . By such a reaction, a negative electrode active material containing Sn and SnO 2 is obtained. The second step may be performed after the first step or may be performed simultaneously with the first step. In any case, the SnO 2 content in the negative electrode active material containing Sn and SnO 2 can be increased by further oxidizing the mechanically milled tin raw material.
ところで、ＳｎＯからなる従来の負極活物質において、ＳｎＯとＬｉとの反応は以下のように進行すると考えられている。 By the way, in the conventional negative electrode active material which consists of SnO, it is thought that reaction of SnO and Li advances as follows.
ＳｎＯ＋２Ｌｉ＋２ｅ→Ｌｉ2Ｏ＋Ｓｎ・・・（１）
Ｓｎ＋４．４Ｌｉ＋４．４ｅ←→Ｌｉ4.4Ｓｎ・・・（２）
上記反応（１）は不可逆反応であり、反応（２）は可逆反応であるため、（１）で消費されたＬｉ（Ｌｉ2Ｏに含まれるＬｉ）はリチウムイオン二次電池の充放電に関与しない。このためＳｎＯを負極活物質とするリチウムイオン二次電池においては不可逆容量が生じる問題があった。なお、反応（２）は可逆反応であり、この反応によってリチウムイオン二次電池の充放電が可能になる。反応（２）は合金化反応と呼ばれる反応である。
SnO + 2Li + 2e → Li 2 O + Sn (1)
Sn + 4.4Li + 4.4e ← → Li 4.4 Sn (2)
Since the above reaction (1) is an irreversible reaction and the reaction (2) is a reversible reaction, Li consumed in (1) (Li contained in Li 2 O) is involved in charge / discharge of the lithium ion secondary battery. do not do. For this reason, in the lithium ion secondary battery which uses SnO as a negative electrode active material, there existed a problem which an irreversible capacity | capacitance produced. In addition, reaction (2) is a reversible reaction, and charging / discharging of a lithium ion secondary battery is attained by this reaction. Reaction (2) is a reaction called alloying reaction.
本発明の負極活物質は、上述したように、ＳｎとＳｎＯ2とを含む。ＳｎＯ2とＬｉとの反応は以下のように進行すると考えられている。 As described above, the negative electrode active material of the present invention contains Sn and SnO 2 . It is considered that the reaction between SnO 2 and Li proceeds as follows.
ＳｎＯ2＋４Ｌｉ＋４ｅ←→Ｓｎ＋２Ｌｉ2Ｏ・・・（３）
Ｓｎ＋４．４Ｌｉ＋４．４ｅ←→Ｌｉ4.4Ｓｎ・・・（２）
上式のように、ＳｎＯ2とＬｉとの反応には、不可逆反応がなく、可逆反応のみである。上式（３）の反応はコンバージョン反応と呼ばれる反応であり、上式（２）はＳｎＯとＬｉとの反応と同様の合金化反応である。本発明の負極活物質においては、コンバージョン反応を利用することで、容量を大幅に増大させ得る。
SnO 2 + 4Li + 4e ← → Sn + 2Li 2 O (3)
Sn + 4.4Li + 4.4e ← → Li 4.4 Sn (2)
As in the above formula, the reaction between SnO 2 and Li has no irreversible reaction and is only a reversible reaction. The reaction of the above formula (3) is a reaction called a conversion reaction, and the above formula (2) is an alloying reaction similar to the reaction of SnO and Li. In the negative electrode active material of the present invention, the capacity can be greatly increased by utilizing the conversion reaction.
さらに、本発明の製造方法で得られた負極活物質にはＳｎＯ2だけでなくＳｎが含まれるが、このＳｎもまた上式（２）のようにＬｉと可逆的に反応するため、負極活物質として利用できる。つまり、本発明の製造方法で得られた負極活物質はＳｎ元素を含む２種類の物質（つまり、ＳｎおよびＳｎＯ2）を別々に負極活物質として利用でき、かつ、不可逆容量を生じないため、リチウムイオン二次電池を大容量にできる利点がある。参考までに、ＳｎＯからなる負極活物質の理論容量は８７５ｍＡｈ／ｇであり、ＳｎＯ2からなる負極活物質の理論容量は１４９４ｍＡｈ／ｇである。 Further, the negative electrode active material obtained by the production method of the present invention contains not only SnO 2 but also Sn. This Sn also reacts reversibly with Li as shown in the above formula (2). It can be used as a substance. That is, since the negative electrode active material obtained by the production method of the present invention can use two kinds of materials containing Sn element (that is, Sn and SnO 2 ) separately as the negative electrode active material and does not cause irreversible capacity, There is an advantage that the capacity of the lithium ion secondary battery can be increased. For reference, the theoretical capacity of the negative electrode active material made of SnO is 875 mAh / g, and the theoretical capacity of the negative electrode active material made of SnO 2 is 1494 mAh / g.
なお、上述したように、コンバージョン反応は反応速度が遅いとされている。しかし、本発明の負極活物質においては、充放電の際にコンバージョン反応と合金化反応との２つの反応を用いているため、一般的なリチウムイオン二次電池の充放電速度と同様の速度で充放電しても、合金化反応のみの場合に比べて充放電容量を大きくできる。 As described above, the conversion reaction has a slow reaction rate. However, since the negative electrode active material of the present invention uses two reactions of a conversion reaction and an alloying reaction at the time of charge / discharge, the charge / discharge rate of a general lithium ion secondary battery is the same. Even if charging / discharging is performed, the charge / discharge capacity can be increased as compared with the case of only the alloying reaction.
ＳｎとＳｎＯ2とを含む負極活物質の形状は特に問わないが、粒子状であるのが好ましい。この粒子は一次粒子であっても良いし二次粒子であっても良いが、小径であるのが好ましい。例えば負極活物質粒子は平均粒径０．２μｍ〜５μｍの範囲にあることが望ましい。平均粒径が５μｍより大きいと、この負極活物質を用いたリチウムイオン二次電池の充放電特性が低下する場合がある。また、平均粒径が０．２μｍより小さいと凝集して粗大な粒子となる場合があるため、同様に、この負極活物質を用いたリチウムイオン二次電池の充放電特性が低下する場合がある。なお、ここでいう平均粒径とは、レーザー光回折法による粒度分布測定における質量平均粒子径を指す。本発明の製造方法におけるスズ原料（ＳｎＯ）の粒径もまた特に限定しないが、上記した粒径の負極活物質を製造するためには平均粒径１０〜２０μｍ程度であるのが好ましい。 The shape of the negative electrode active material containing Sn and SnO 2 is not particularly limited, but is preferably particulate. The particles may be primary particles or secondary particles, but preferably have a small diameter. For example, the negative electrode active material particles desirably have an average particle size in the range of 0.2 μm to 5 μm. When the average particle size is larger than 5 μm, the charge / discharge characteristics of the lithium ion secondary battery using the negative electrode active material may be deteriorated. In addition, if the average particle size is smaller than 0.2 μm, the particles may agglomerate and become coarse particles. Similarly, the charge / discharge characteristics of a lithium ion secondary battery using this negative electrode active material may deteriorate. . In addition, the average particle diameter here refers to the mass average particle diameter in the particle size distribution measurement by a laser beam diffraction method. The particle diameter of the tin raw material (SnO) in the production method of the present invention is not particularly limited, but in order to produce the negative electrode active material having the above-mentioned particle diameter, the average particle diameter is preferably about 10 to 20 μm.
本発明の負極活物質はＬｉを含まないか、またはＬｉを多く含まない。このため、本発明の負極活物質を用いたリチウムイオン二次電池においては、正極活物質としてＬｉを含む材料を用いたり、負極活物質にＬｉをプリドープしたりする必要がある。負極活物質にＬｉをプリドープする場合、Ｌｉを一般的な方法でＳｎ、ＳｎＯおよびＳｎＯ2の少なくとも一種にプリドープすれば良く、その方法は特に限定しない。例えば、Ｌｉのプリドープにあたって、Ｓｎ、ＳｎＯおよびＳｎＯ2の少なくとも一種をＬｉと接触させればよい。このとき、上記したＳｎ、ＳｎＯおよびＳｎＯ2の少なくとも一種とＬｉとは、イオン、固体、液体、ガスの何れの状態で接触させても良い。さらにこのときＬｉは酸化物、塩化物等のＬｉ含有化合物であっても良い。 The negative electrode active material of the present invention does not contain Li or does not contain much Li. For this reason, in the lithium ion secondary battery using the negative electrode active material of the present invention, it is necessary to use a material containing Li as the positive electrode active material or to pre-doped Li to the negative electrode active material. When Li is predoped in the negative electrode active material, Li may be predoped into at least one of Sn, SnO, and SnO 2 by a general method, and the method is not particularly limited. For example, when Li is pre-doped, at least one of Sn, SnO, and SnO 2 may be brought into contact with Li. At this time, at least one of Sn, SnO, and SnO 2 described above and Li may be brought into contact in any state of ions, solids, liquids, and gases. Further, at this time, Li may be a Li-containing compound such as an oxide or a chloride.
本発明の負極活物質を負極に含むリチウムイオン二次電池の構成を以下に説明する。負極は、上述した本発明の負極活物質以外の材料を含み得る。例えば、バインダー樹脂、導電助剤等の負極材料を構成する既知の材料を含み得る。 A configuration of a lithium ion secondary battery including the negative electrode active material of the present invention in the negative electrode will be described below. The negative electrode can include materials other than the negative electrode active material of the present invention described above. For example, a known material constituting the negative electrode material such as a binder resin or a conductive aid may be included.
バインダー樹脂は、負極活物質及び導電助剤を集電体に結着するための結着剤として用いられる。バインダー樹脂には、なるべく少ない量で負極活物質等を結着させることが求められる。バインダー樹脂の配合量は、負極活物質、導電助剤、及びバインダー樹脂の合計量を１００質量％としたときに、０．５〜５０質量％であるのが好ましい。バインダー樹脂量が０．５質量％未満では電極の成形性が低下し、５０質量％を超えると電極のエネルギー密度が低くなる。バインダー樹脂の種類は限定的ではないが、ポリフッ化ビニリデン（ＰＶＤＦ）、ポリテトラフルオロエチレン（ＰＴＦＥ）等のフッ素系ポリマー、スチレンブタジエンゴム（ＳＢＲ）等のゴム、ポリイミド等のイミド系ポリマー、アルコキシルシリル基含有樹脂、ポリアクリル酸、ポリメタクリル酸、ポリイタコン酸などが例示される。 The binder resin is used as a binder for binding the negative electrode active material and the conductive additive to the current collector. The binder resin is required to bind the negative electrode active material and the like in as small an amount as possible. The blending amount of the binder resin is preferably 0.5 to 50% by mass when the total amount of the negative electrode active material, the conductive assistant and the binder resin is 100% by mass. When the amount of the binder resin is less than 0.5% by mass, the moldability of the electrode is lowered, and when it exceeds 50% by mass, the energy density of the electrode is lowered. The type of binder resin is not limited, but fluorine polymers such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), rubbers such as styrene butadiene rubber (SBR), imide polymers such as polyimide, and alkoxy silyl Examples thereof include group-containing resins, polyacrylic acid, polymethacrylic acid, and polyitaconic acid.
導電助剤は、電極の導電性を高めるために添加される。導電助剤として、炭素質微粒子であるカーボンブラック、黒鉛、アセチレンブラック（ＡＢ）、ケッチェンブラック（ＫＢ）、気相法炭素繊維（Ｖａｐｏｒ Ｇｒｏｗｎ Ｃａｒｂｏｎ Ｆｉｂｅｒ：ＶＧＣＦ）等を単独でまたは二種以上組み合わせて添加することが出来る。導電助剤の使用量については、特に限定的ではないが、負極活物質１００質量部に対して、１〜１０質量部程度とすることができる。また、充放電に伴うＳｎの体積変化を考慮すると、Ｓｎの体積変化を緩衝し得る黒鉛を導電助剤として配合しても良い。負極は、これらの材料に有機溶剤を加えて混合しスラリーにしたものを、ロールコート法、ディップコート法、ドクターブレード法、スプレーコート法、カーテンコート法などの方法で集電体に塗布（積層）し、バインダー樹脂を硬化させることによって作製することができる。 The conductive assistant is added to increase the conductivity of the electrode. Carbon black, graphite, acetylene black (AB), ketjen black (KB), vapor grown carbon fiber (Vapor Carbon Carbon Fiber: VGCF), etc., which are carbonaceous fine particles, are used alone or in combination of two or more as conductive aids. Can be added. The amount of the conductive aid used is not particularly limited, but can be about 1 to 10 parts by mass with respect to 100 parts by mass of the negative electrode active material. Further, in consideration of Sn volume change accompanying charging / discharging, graphite capable of buffering Sn volume change may be blended as a conductive aid. The negative electrode is prepared by adding an organic solvent to these materials and mixing them into a slurry, and applying (lamination) to the current collector by methods such as roll coating, dip coating, doctor blade, spray coating, and curtain coating. And the binder resin can be cured.
集電体としては、箔、板、メッシュ等の形状を採用することが出来るが、目的に応じた形状であれば特に限定されない。集電体として、例えば銅箔やアルミニウム箔等を好適に用いることができる。 As the current collector, a shape such as a foil, a plate, or a mesh can be adopted, but is not particularly limited as long as it has a shape according to the purpose. For example, a copper foil or an aluminum foil can be suitably used as the current collector.
上記した負極を用いるリチウムイオン二次電池の負極以外の構成要素としては、特に限定されない公知の正極、電解液、セパレータを用いることが出来る。正極は、リチウムイオン二次電池で使用可能なものであれば良い。正極は、集電体と、集電体上に結着された正極活物質層とを有する。正極活物質層は、正極活物質と、バインダーとを含み、さらには導電助剤を含んでも良い。正極活物質、導電助材およびバインダーは、特に限定はなく、リチウムイオン二次電池で使用可能なものであれば良い。 As a component other than the negative electrode of the lithium ion secondary battery using the negative electrode described above, a known positive electrode, electrolyte, and separator that are not particularly limited can be used. The positive electrode may be anything that can be used in a lithium ion secondary battery. The positive electrode has a current collector and a positive electrode active material layer bound on the current collector. The positive electrode active material layer includes a positive electrode active material and a binder, and may further include a conductive additive. The positive electrode active material, the conductive additive, and the binder are not particularly limited as long as they can be used in the lithium ion secondary battery.
正極活物質としては、金属リチウム、ＬｉＣｏＯ2、ＬｉＮｉ1/3Ｃｏ1/3Ｍｎ1/3Ｏ2、Ｌｉ2ＭｎＯ2、Ｓなどが挙げられる。集電体は、アルミニウム、ニッケル、ステンレス鋼など、リチウムイオン二次電池の正極に一般的に使用されるものであれば良い。導電助剤は上記の負極で記載したものと同様のものを使用できる。 Examples of the positive electrode active material include lithium metal, LiCoO 2 , LiNi 1/3 Co 1/3 Mn 1/3 O 2 , Li 2 MnO 2 , and S. The current collector may be any material generally used for the positive electrode of a lithium ion secondary battery, such as aluminum, nickel, and stainless steel. As the conductive auxiliary agent, the same ones as described in the above negative electrode can be used.
電解液は、有機溶媒に電解質であるＬｉ金属塩を溶解させたものである。電解液は、特に限定されない。有機溶媒として、非プロトン性有機溶媒、たとえばプロピレンカーボネート（ＰＣ）、エチレンカーボネート（ＥＣ）、ジメチルカーボネート（ＤＭＣ）、ジエチルカーボネート（ＤＥＣ）、エチルメチルカーボネート（ＥＭＣ）等から選ばれる一種以上を用いることができる。また、溶解させる電解質としては、ＬｉＰＦ6、ＬｉＢＦ4、ＬｉＡｓＦ6、ＬｉＩ、ＬｉＣｌＯ4、ＬｉＣＦ3ＳＯ3等の有機溶媒に可溶なＬｉ金属塩を用いることができる。 The electrolytic solution is obtained by dissolving an Li metal salt as an electrolyte in an organic solvent. The electrolytic solution is not particularly limited. As the organic solvent, an aprotic organic solvent such as propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC) or the like is used. Can do. As the electrolyte to be dissolved, a Li metal salt soluble in an organic solvent such as LiPF 6 , LiBF 4 , LiAsF 6 , LiI, LiClO 4 , LiCF 3 SO 3 can be used.
例えば、エチレンカーボネート、ジメチルカーボネート、プロピレンカーボネート、ジメチルカーボネートなどの有機溶媒にＬｉＣｌＯ4、ＬｉＰＦ6、ＬｉＢＦ4、ＬｉＣＦ3ＳＯ3等のＬｉ金属塩を０．５ｍｏｌ／Ｌ〜１．７ｍｏｌ／Ｌ程度の濃度で溶解させた溶液を使用することが出来る。 For example, an Li metal salt such as LiClO 4 , LiPF 6 , LiBF 4 , and LiCF 3 SO 3 in an organic solvent such as ethylene carbonate, dimethyl carbonate, propylene carbonate, and dimethyl carbonate is about 0.5 mol / L to 1.7 mol / L. A solution dissolved at a concentration can be used.
セパレータは、リチウムイオン二次電池に使用されることが出来るものであれば特に限定されない。セパレータは、正極と負極とを分離し電解液を保持するものであり、ポリエチレン、ポリプロピレン等の薄い微多孔膜を用いることができる。 A separator will not be specifically limited if it can be used for a lithium ion secondary battery. The separator separates the positive electrode and the negative electrode and holds the electrolytic solution, and a thin microporous film such as polyethylene or polypropylene can be used.
本発明の負極活物質を用いたリチウムイオン二次電池の形状には特に限定はなく、円筒型、積層型、コイン型等、種々の形状を採用することができる。いずれの形状を採る場合であっても、正極および負極にセパレータを挟装させ電極体とし、正極集電体および負極集電体から外部に通ずる正極端子および負極端子までの間を、集電用リード等を用いて接続した後、この電極体を電解液とともに電池ケースに密閉して電池となる。 The shape of the lithium ion secondary battery using the negative electrode active material of the present invention is not particularly limited, and various shapes such as a cylindrical shape, a stacked shape, and a coin shape can be employed. Regardless of the shape, a separator is sandwiched between the positive electrode and the negative electrode to form an electrode body, and the space between the positive electrode current collector and the negative electrode current collector to the positive electrode terminal and the negative electrode terminal is used for current collection. After connecting using a lead or the like, the electrode body is sealed in a battery case together with an electrolyte to form a battery.
以下、実施例により本発明の製造方法および本発明の負極活物質を具体的に説明する。 Hereinafter, the production method of the present invention and the negative electrode active material of the present invention will be specifically described by way of examples.
（実施例）
＜負極活物質の製造方法＞
スズ原料として、ＳｎＯ粉末（株式会社高純度研究所社製）を準備した。このスズ原料をボールミル装置（ドイツ・フリッチュ社製、Ｐ−７）に投入し、空気中、室温、回転数４５０ｒｐｍで２０時間メカニカルミリング処理した。
(Example)
<Method for producing negative electrode active material>
As a tin raw material, SnO powder (manufactured by Kojundo Laboratories Inc.) was prepared. This tin raw material was put into a ball mill apparatus (P-7, manufactured by Fritsch, Germany), and subjected to mechanical milling treatment in air at room temperature at a rotation speed of 450 rpm for 20 hours.
次いで、メカニカルミリング処理後のスズ原料を、加熱炉にて空気中、４００℃で３時間加熱した。このときの昇温速度は１０℃／分であった。 Subsequently, the tin raw material after the mechanical milling process was heated in air at 400 ° C. for 3 hours in a heating furnace. The temperature rising rate at this time was 10 ° C./min.
３時間加熱した後、熱処理したスズ原料を自然冷却して実施例の負極活物質を得た。 After heating for 3 hours, the heat-treated tin raw material was naturally cooled to obtain a negative electrode active material of an example.
＜負極＞
得られた負極活物質と、導電助剤としてのアセチレンブラック（ＡＢ）と、バインダー樹脂としてのポリアミック酸溶液（ポリイミド前駆体）とを混合し、スラリーを調製した。スラリー中の各成分の組成比は固形分として、負極活物質：ＡＢ：ポリイミドバインダー＝８５：５：１０である。このスラリーを、厚さ２０μｍの電解銅箔（集電体）の表面にドクターブレードを用いて塗布し、銅箔上に負極活物質層を形成した。
<Negative electrode>
The obtained negative electrode active material, acetylene black (AB) as a conductive additive, and a polyamic acid solution (polyimide precursor) as a binder resin were mixed to prepare a slurry. The composition ratio of each component in the slurry is, as solid content, negative electrode active material: AB: polyimide binder = 85: 5: 10. This slurry was applied to the surface of an electrolytic copper foil (current collector) having a thickness of 20 μm using a doctor blade to form a negative electrode active material layer on the copper foil.
その後、８０℃で２０分間乾燥し、次いで２００℃で２０時間真空乾燥した。この工程により、負極活物質層から有機溶媒を揮発させて除去した。その後、直径１５ｍｍの円板状に打ち抜き、プレス機により、集電体と負極活物質層を強固に密着接合させた。これを２００℃で２０時間加熱硬化させて、活物質層の厚さが１５μｍ程度の電極を形成した。 Thereafter, it was dried at 80 ° C. for 20 minutes, and then vacuum dried at 200 ° C. for 20 hours. Through this step, the organic solvent was volatilized and removed from the negative electrode active material layer. Thereafter, it was punched into a disk shape having a diameter of 15 mm, and the current collector and the negative electrode active material layer were firmly bonded to each other with a press. This was heat-cured at 200 ° C. for 20 hours to form an electrode having an active material layer thickness of about 15 μm.
＜正極＞
正極としては、直径１５．５ｍｍの円板状、厚さ５００μｍの金属Ｌｉ箔を用いた。
<Positive electrode>
As the positive electrode, a disk-shaped metal having a diameter of 15.5 mm and a metal Li foil having a thickness of 500 μm was used.
＜電解液＞
エチレンカーボネートと、エチルメチルカーボネートとを３：７（体積比）で混合し、混合溶媒を調製した。この混合溶媒に、ＬｉＰＦ6を１Ｍの濃度となるように溶解することで、非水電解液を調製した。
<Electrolyte>
Ethylene carbonate and ethyl methyl carbonate were mixed at 3: 7 (volume ratio) to prepare a mixed solvent. A non-aqueous electrolyte was prepared by dissolving LiPF 6 in this mixed solvent to a concentration of 1M.
＜リチウムイオン二次電池＞
上記の負極、正極および電解液を用いてコイン電池を製作した。詳しくは、ドライルーム内で、厚さ２５μｍのポリプロピレン微孔質膜からなるセパレータ（Ｃｅｌｇａｒｄ２４００）と、厚さ５００μｍのガラス不織布フィルタと、を正極と負極との間に挟装して、電極体電池とした。この電極体電池を、ステンレス容器からなる電池ケース（ＣＲ２０３２型コイン電池用部材、宝泉株式会社製）に収容した。電池ケースには上記の電解液を注入した。電池ケースをカシメ機で密閉して、実施例のリチウムイオン二次電池を得た。
<Lithium ion secondary battery>
A coin battery was manufactured using the above negative electrode, positive electrode, and electrolytic solution. Specifically, in a dry room, a separator (Celgard 2400) made of a polypropylene microporous membrane with a thickness of 25 μm and a glass nonwoven fabric filter with a thickness of 500 μm are sandwiched between a positive electrode and a negative electrode, and an electrode body battery It was. This electrode body battery was accommodated in a battery case (CR2032-type coin battery member, manufactured by Hosen Co., Ltd.) made of a stainless steel container. The above electrolyte was injected into the battery case. The battery case was sealed with a caulking machine to obtain the lithium ion secondary battery of the example.
（比較例１）
比較例１の負極活物質はＳｎである。このＳｎを負極活物質とし、実施例１と同じ方法で比較例１のリチウムイオン二次電池を製造した。
(Comparative Example 1)
The negative electrode active material of Comparative Example 1 is Sn. Using this Sn as the negative electrode active material, a lithium ion secondary battery of Comparative Example 1 was produced in the same manner as in Example 1.
（比較例２）
比較例２の負極活物質の製造方法は、スズ原料すなわちＳｎＯにメカニカルミリング処理のみを施し加熱処理を施さなかったこと以外は実施例１の負極活物質の製造方法と同じである。比較例２の負極活物質は、メカニカルミリング処理されたスズ原料（すなわち負極活物質前駆体）である。比較例２の負極活物質を用い、実施例１と同じ方法で比較例２のリチウムイオン二次電池を製造した。
(Comparative Example 2)
The method for producing the negative electrode active material of Comparative Example 2 is the same as the method for producing the negative electrode active material of Example 1 except that only the mechanical milling treatment is performed on the tin raw material, that is, SnO, and the heat treatment is not performed. The negative electrode active material of Comparative Example 2 is a tin raw material (that is, a negative electrode active material precursor) that has been mechanically milled. Using the negative electrode active material of Comparative Example 2, a lithium ion secondary battery of Comparative Example 2 was produced in the same manner as in Example 1.
＜試験＞
（ＳＥＭによる硫黄系正極活物質の分析）
スズ原料、実施例の負極活物質および比較例２の負極活物質を、走査型電子顕微鏡（ＳＥＭ；Ｓｃａｎｎｉｎｇ Ｅｌｅｃｔｒｏｎ Ｍｉｃｒｏｓｃｏｐｅ）により表面観察した。このときの加速電圧は２０ｋＶであり倍率は５００倍と２０００倍であった。スズ原料のＳＥＭ像を図１に示し、比較例２の負極活物質のＳＥＭ像を図２に示し、実施例の負極活物質のＳＥＭ像を図３に示す。
<Test>
(SEM analysis of sulfur-based positive electrode active materials)
The surface of the tin raw material, the negative electrode active material of Example and the negative electrode active material of Comparative Example 2 was observed with a scanning electron microscope (SEM). The acceleration voltage at this time was 20 kV, and the magnifications were 500 times and 2000 times. FIG. 1 shows an SEM image of the tin raw material, FIG. 2 shows an SEM image of the negative electrode active material of Comparative Example 2, and FIG. 3 shows an SEM image of the negative electrode active material of the example.
図１〜図３に示すように、メカニカルミリング処理後の負極活物質つまり比較例２および実施例の負極活物質は、メカニカルミリング処理前の負極活物質つまりスズ原料に比べて小径である。具体的には、比較例２の負極活物質の平均粒径は１μｍ程度であり、実施例の負極活物質の平均粒径は２μｍ程度である。これに対して、スズ原料の平均粒径は１５μｍ程度である。これは、スズ原料すなわちＳｎＯがメカニカルミリング処理により微粉化されたためと考えられる。つまり、負極活物質の粒径により、スズ原料（ＳｎＯ）がメカニカルミリング処理されているか否かを推測できる。スズ原料を原料とする負極活物質の平均粒径は０．２〜５μｍ程度であるのが好ましく、０．５〜２μｍ程度であるのがより好ましいと考えられる。平均粒径がこれらの範囲内にあれば、ＳｎＯが充分にメカニカルミリング処理されていると判断できる。なお、実施例の負極活物質の平均粒径が比較例２の負極活物質の平均粒径よりも大きいのは、メカニカルミリング処理後の加熱処理により、負極活物質が凝集したためだと考えられる。参考までに、本明細書においては、ＳＥＭ像を基に１０〜２０個の負極活物質の粒子径を測定し、測定した粒子径の平均値を算出した。この平均値を負極活物質の平均粒径とした。 As shown in FIGS. 1 to 3, the negative electrode active material after the mechanical milling treatment, that is, the negative electrode active materials of Comparative Example 2 and Examples, has a smaller diameter than the negative electrode active material before the mechanical milling treatment, that is, the tin raw material. Specifically, the average particle size of the negative electrode active material of Comparative Example 2 is about 1 μm, and the average particle size of the negative electrode active material of Example is about 2 μm. On the other hand, the average particle diameter of the tin raw material is about 15 μm. This is considered because the tin raw material, that is, SnO was pulverized by the mechanical milling process. That is, it can be estimated whether the tin raw material (SnO) is mechanically milled by the particle size of the negative electrode active material. The average particle diameter of the negative electrode active material made from a tin raw material is preferably about 0.2 to 5 μm, and more preferably about 0.5 to 2 μm. If the average particle diameter is within these ranges, it can be determined that SnO is sufficiently mechanically milled. In addition, it is thought that the average particle diameter of the negative electrode active material of an Example is larger than the average particle diameter of the negative electrode active material of the comparative example 2 because the negative electrode active material aggregated by the heat processing after a mechanical milling process. For reference, in this specification, the particle diameters of 10 to 20 negative electrode active materials were measured based on the SEM images, and the average value of the measured particle diameters was calculated. This average value was defined as the average particle size of the negative electrode active material.
（Ｘ線回折による硫黄系正極活物質の分析）
実施例の負極活物質および比較例２の負極活物質について、Ｘ線回折分析を行った。装置として粉末Ｘ線回折装置（リガク社製、ＭｉｎｉＦｌｅｘ）を用いた。測定条件は、ＣｕＫα線、電圧：３０ｋＶ、電流：２０ｍＡ、スキャン速度：２°／分、サンプリング：０．０１°、積算回数：１回、回折角（２θ）：５°〜８０°であった。Ｘ線回折で得られた回折パターンを図４に示す。図４に示すように、実施例の負極活物質および比較例２の負極活物質には、Ｓｎのピーク（図中▲）、ＳｎＯのピーク（図中×）およびＳｎＯ2のピーク（図中○）が確認された。また、実施例の負極活物質において確認されたＳｎのピークは、比較例２の負極活物質で検出されたＳｎのピークに比べて、強度が低く数も少なかった。このことから、ＳｎＯをメカニカルミリング処理することでＳｎが生成することがわかる。また、実施例（酸化処理後）の負極活物質におけるＳｎのピークが、ＳｎＯ2のピークに比べて相対的に小さくなっていることから、酸化処理によりＳｎの表面の酸化被膜が成長したことがわかる。つまりこの結果から、実施例の負極活物質はＳｎからなる芯部と芯部を覆う被覆部とで構成され、被覆部にはＳｎＯ2が含まれていることがわかる。
(Analysis of sulfur-based positive electrode active materials by X-ray diffraction)
The negative electrode active material of the example and the negative electrode active material of Comparative Example 2 were subjected to X-ray diffraction analysis. A powder X-ray diffractometer (manufactured by Rigaku Corporation, MiniFlex) was used as the apparatus. The measurement conditions were CuKα line, voltage: 30 kV, current: 20 mA, scan speed: 2 ° / min, sampling: 0.01 °, integration number: 1, diffraction angle (2θ): 5 ° -80 °. . A diffraction pattern obtained by X-ray diffraction is shown in FIG. As shown in FIG. 4, the negative electrode active material of Example and the negative electrode active material of Comparative Example 2 were Sn peak (▲ in the figure), SnO peak (x in the figure) and SnO 2 peak (○ in the figure). ) Was confirmed. In addition, the Sn peak confirmed in the negative electrode active material of the example was lower in intensity and less in number than the Sn peak detected in the negative electrode active material of Comparative Example 2. From this, it can be seen that Sn is generated by mechanically milling SnO. In addition, since the Sn peak in the negative electrode active material of the example (after the oxidation treatment) was relatively smaller than the SnO 2 peak, the oxide film on the surface of Sn grew due to the oxidation treatment. Recognize. That is, from this result, it can be seen that the negative electrode active material of the example is composed of a core portion made of Sn and a covering portion covering the core portion, and the covering portion contains SnO 2 .
（熱質量分析による硫黄系正極活物質の分析）
比較例１の負極活物質および比較例２の負極活物質の熱質量変化（ＴＧ）を測定した。測定装置としてはリガク製熱分析装置（Ｔｈｅｒｍｏ Ｐｌｕｓ ＴＧ８１２０）を用いた。詳しくは、空気を３００ｍｌ／分の流量で供給しつつ、各試料を室温から４００℃まで１０℃／分の昇温速度で加熱し、温度と質量変化との関係を測定することによって、熱質量−示差熱分析を行った。分析結果を図５に示す。図５に示すように、比較例２の負極活物質（つまり、ＳｎＯのメカニカルミリング処理品）は、比較例１の負極活物質（つまり単体Ｓｎ）に比べて質量変化が大きい。具体的には、比較例２の負極活物質の質量は、加熱前には２３ｍｇであり、室温から１００℃まで加熱すると０．１１ｍｇ減少し、その後、４００℃まで加熱すると０．６３６ｍｇ増加した。つまり、ＳｎＯのメカニカルミリング処理品を加熱すると、１００℃までの加熱で吸着水０．１１ｍｇが蒸発し、その後、０．６３６−（−０．１１）＝０．７４６ｍｇ質量増加した。
(Analysis of sulfur-based positive electrode active materials by thermal mass spectrometry)
The thermal mass change (TG) of the negative electrode active material of Comparative Example 1 and the negative electrode active material of Comparative Example 2 was measured. A Rigaku thermal analyzer (Thermo Plus TG8120) was used as the measuring device. Specifically, while supplying air at a flow rate of 300 ml / min, each sample was heated from room temperature to 400 ° C. at a heating rate of 10 ° C./min, and the thermal mass was measured by measuring the relationship between temperature and mass change. -Differential thermal analysis was performed. The analysis results are shown in FIG. As shown in FIG. 5, the negative electrode active material of Comparative Example 2 (that is, a SnO mechanically milled product) has a larger mass change than the negative electrode active material of Comparative Example 1 (that is, simple substance Sn). Specifically, the mass of the negative electrode active material of Comparative Example 2 was 23 mg before heating, decreased by 0.11 mg when heated from room temperature to 100 ° C., and then increased by 0.636 mg when heated to 400 ° C. That is, when the SnO mechanical milled product was heated, 0.11 mg of adsorbed water was evaporated by heating up to 100 ° C., and then 0.636 − (− 0.11) = 0.746 mg increased in mass.
Ｓｎ１モルは１１８．６９ｇであり、ＳｎＯ2１モルは１５０．６９ｇである。メカニカルミリング処理によるＳｎＯの不均化反応は、２ＳｎＯ→Ｓｎ＋ＳｎＯ2であると考えられる。このためＳｎＯのメカニカルミリング処理品（加熱前）に含まれるＳｎの質量は、｛１１８．６９／（１１８．６９＋１５０．６９）｝×２３≒１０．１３４（ｍｇ）であると考えられる。 1 mol of Sn is 118.69 g and 1 mol of SnO 2 is 150.69 g. The disproportionation reaction of SnO by the mechanical milling process is considered to be 2SnO → Sn + SnO 2 . Therefore, the mass of Sn contained in the SnO mechanically milled product (before heating) is considered to be {118.69 / (118.69 + 150.69)} × 23≈10.134 (mg).
ＳｎＯのメカニカルミリング処理品に含まれるＳｎ全てがＳｎＯ2にまで酸化されたと仮定し、そのときに増加した質量をｘとすると、Ｏ2／Ｓｎ＝３２／１１８．６９＝ｘ／１０．１３４であるため、ｘ＝２．７３２（ｍｇ）となる。上述した加熱で増加した質量全てがＳｎの酸化によると仮定すると、実際に生じた質量増加は０．７４６ｍｇであったため、ＳｎがＳｎＯ2に変化した割合は（０．７４６／２．７）×１００＝２７．６％であった。 Assuming that all Sn contained in the SnO mechanically milled product is oxidized to SnO 2 , and assuming that the mass increased at that time is x, O 2 /Sn=32/118.69=x/10.134 Therefore, x = 2.732 (mg). Assuming that all the mass increased by the heating described above is due to the oxidation of Sn, the actual mass increase was 0.746 mg, so the rate at which Sn changed to SnO 2 was (0.746 / 2.7) × 100 = 27.6%.
上述したように、理論上、ＳｎＯに含まれるＳｎ原子の５０％がメカニカルミリング処理でＳｎＯ2になると考えられる。また、ＳｎＯのメカニカルミリング処理品に含まれるＳｎの２７．６％が酸化処理によりＳｎＯ2に変化すると考えられる。このため、メカニカルミリング処理および加熱処理後の実施例の負極活物質にＳｎＯ2として含まれているＳｎ原子は、この負極活物質全体に含まれているＳｎ原子を１００原子％とすると、（メカニカルミリング処理で生じた５０原子％）＋（酸化処理で生じた２７．６原子％）＝７７．６原子％であると考えられる。 As described above, theoretically, 50% of Sn atoms contained in SnO are considered to be SnO 2 by mechanical milling. Further, it is considered that 27.6% of Sn contained in the SnO mechanical milling product is changed to SnO 2 by the oxidation treatment. For this reason, Sn atoms contained as SnO 2 in the negative electrode active materials of the examples after the mechanical milling treatment and the heat treatment are expressed as (mechanical) when the Sn atoms contained in the whole negative electrode active material is 100 atomic%. It is considered that 50 atomic% generated in the milling process) + (27.6 atomic% generated in the oxidation process) = 77.6 atomic%.
なお、ＳｎＯのメカニカルミリング処理品は、酸化処理前の段階で、５０原子％のＳｎＯ2を含むと考えられる。したがって、本発明の負極活物質は、負極活物質全体に含まれているＳｎ原子を１００原子％としたときに、５０原子％を超えるＳｎ原子をＳｎＯ2として含めば良い。なお、本発明の負極活物質は、負極活物質全体に含まれているＳｎ原子を１００原子％としたときに６５原子％を超えるＳｎ原子をＳｎＯ2として含むのが好ましく、７０原子％を超えるＳｎ原子をＳｎＯ2として含むのがより好ましく、７５原子％を超えるＳｎ原子をＳｎＯ2として含むのがさらに好ましい。本発明の負極活物質において、ＳｎＯ2の大部分は、Ｓｎの表面に配置されると考えられる。つまり、本発明の負極活物質は、Ｓｎからなる芯部と、この芯部を覆いＳｎＯ2を含む被覆部と、を持つと考えられる。芯部はメカニカルミリング処理時に生成すると考えられ、被覆部の一部もまたメカニカルミリング処理時に生成すると考えられる。さらに、被覆部の他の一部は、芯部の一部が酸化処理によって酸化され、生成したＳｎＯ2で構成されると考えられる。 Incidentally, SnO mechanical milling products, at the stage of pre-oxidation treatment, is believed to contain 50 atomic% of SnO 2. Therefore, the negative electrode active material of the present invention may contain Sn atoms exceeding 50 atomic% as SnO 2 when Sn atoms contained in the whole negative electrode active material are 100 atomic%. In addition, the negative electrode active material of the present invention preferably contains Sn atoms exceeding 65 atomic% as SnO 2 when Sn atoms contained in the whole negative electrode active material are 100 atomic%, and exceeds 70 atomic%. It is more preferable to include Sn atoms as SnO 2 , and it is more preferable to include Sn atoms exceeding 75 atomic% as SnO 2 . In the negative electrode active material of the present invention, it is considered that most of SnO 2 is disposed on the surface of Sn. That is, the negative electrode active material of the present invention is considered to have a core portion made of Sn and a covering portion that covers the core portion and contains SnO 2 . The core part is considered to be generated during the mechanical milling process, and part of the covering part is also considered to be generated during the mechanical milling process. Furthermore, the other part of the covering part is considered to be composed of SnO 2 produced by oxidizing a part of the core part by oxidation treatment.
ところで、Ｓｎを加熱酸化する場合、加熱温度が２７０℃以下であればＳｎＯが生じ、２８０℃以上３９０℃未満であればＳｎＯとＳｎＯ2との両方が生じ、３９０℃以上であればほぼＳｎＯ2のみが生じることが知られている（例えば、「金属酸化物と複合酸化物」、田部浩三 他 編、講談社、１９７８年、ｐ１３４参照）。したがって、Ｓｎを充分に酸化させＳｎＯ2を生成させるためには、酸化工程における加熱温度は２８０℃以上であるのが好ましく、３９０℃以上であるのがより好ましいといえる。 Incidentally, when heating oxidizing Sn, SnO occurs if the heating temperature is 270 ° C. or less, occur both SnO and SnO 2 is less than 280 ° C. or higher 390 ° C., approximately SnO 2 if 390 ° C. or higher (See, for example, “Metal oxides and composite oxides”, Kozo Tabe et al., Kodansha, 1978, p. 134). Therefore, in order to sufficiently oxidize Sn to produce SnO 2 , the heating temperature in the oxidation step is preferably 280 ° C. or higher, and more preferably 390 ° C. or higher.
（電池特性の評価）
実施例および比較例１、２のリチウムイオン二次電池の充放電容量を測定した。詳しくは、各リチウムイオン二次電池に、負極活物質１ｃｍ2あたり０．２ｍＡとなる電流密度、放電終止電圧０Ｖ、充電終止電圧３．０Ｖ、０．１Ｃで１サイクル目の充放電を行った。２サイクル目以降は、負極活物質１ｃｍ2あたり０．５ｍＡとなる電流密度で充放電をおこなった。なお、２サイクル目以降の放電終止電圧、充電終止電圧およびＣレートは１サイクル目と同じである。充放電は１０サイクル繰り返した。評価試験（１サイクル目）の結果を表１に示す。実施例および比較例１、２のリチウムイオン二次電池の１サイクル目の充放電曲線を図６に示す。実施例および比較例１、２のリチウムイオン二次電池のサイクル試験の結果を図７および図８に示す。なお、図７はサイクル経過に伴う放電容量の変化を表すグラフであり、図８はサイクル経過に伴うクーロン効率の変化を表すグラフである。
(Evaluation of battery characteristics)
The charge / discharge capacities of the lithium ion secondary batteries of Examples and Comparative Examples 1 and 2 were measured. Specifically, each lithium ion secondary battery was charged and discharged in the first cycle at a current density of 0.2 mA per 1 cm 2 of the negative electrode active material, a final discharge voltage of 0 V, a final charge voltage of 3.0 V, and 0.1 C. . After the second cycle, charging / discharging was performed at a current density of 0.5 mA per 1 cm 2 of the negative electrode active material. The discharge end voltage, the charge end voltage, and the C rate after the second cycle are the same as in the first cycle. Charging / discharging was repeated 10 cycles. The results of the evaluation test (first cycle) are shown in Table 1. The charge / discharge curves of the first cycle of the lithium ion secondary batteries of Examples and Comparative Examples 1 and 2 are shown in FIG. The results of the cycle test of the lithium ion secondary batteries of Examples and Comparative Examples 1 and 2 are shown in FIGS. FIG. 7 is a graph showing a change in discharge capacity over the course of a cycle, and FIG. 8 is a graph showing a change in coulomb efficiency over the course of a cycle.
表１および図６に示すように、実施例のリチウムイオン二次電池は、比較例１、２のリチウムイオン二次電池に比べて充放電容量が大きい。実施例のリチウムイオン二次電池の容量はＳｎＯの理論容量８７５を超えている。このため、実施例の負極活物質においては比較例１、２では生じていないコンバージョン反応が生じていると考えられる。また、この充放電容量は０．１Ｃという一般的なＣレートで充放電した場合の容量である。このため、実施例のリチウムイオン二次電池は、通常の速度で充放電する場合にも充分に大きな容量を示すといえる。つまり、ＳｎＯにメカニカルミリング処理と酸化処理とを施す実施例の製造方法によると、充放電容量が大きくかつ一般的な用途のリチウムイオン二次電池に適用可能な負極活物質を製造できる。 As shown in Table 1 and FIG. 6, the lithium ion secondary batteries of the examples have larger charge / discharge capacities than the lithium ion secondary batteries of Comparative Examples 1 and 2. The capacity of the lithium ion secondary battery of the example exceeds the theoretical capacity 875 of SnO. For this reason, in the negative electrode active material of an Example, it is thought that the conversion reaction which has not arisen in Comparative Examples 1 and 2 has arisen. The charge / discharge capacity is a capacity when charge / discharge is performed at a general C rate of 0.1C. For this reason, it can be said that the lithium ion secondary battery of an Example shows a sufficiently large capacity even when charging and discharging at a normal rate. That is, according to the manufacturing method of the embodiment in which SnO is subjected to mechanical milling treatment and oxidation treatment, a negative electrode active material having a large charge / discharge capacity and applicable to a general-purpose lithium ion secondary battery can be produced.
また、図７に示すように、実施例のリチウムイオン二次電池は比較例１、２のリチウムイオン二次電池に比べてサイクル経過後にも充放電容量が大きかった。つまり実施例のリチウムイオン二次電池は比較例１、２のリチウムイオン二次電池に比べてサイクル特性に優れる。これは、実施例のリチウムイオン二次電池はＳｎおよびＳｎＯ以外にＳｎＯ2を含むために体積変化が緩和されたこと、および、コンバージョン反応する活物質量（割合）が増加したことに由来すると考えられる。なお、図８に示すように、実施例および比較例２のリチウムイオン二次電池における２回目充放電時のクーロン効率は、初回充放電時のクーロン効率に比べて上昇している。これは、活物質の不可逆容量が低減したためと考えられる。このクーロン効率の上昇は、実施例のリチウムイオン二次電池においてより顕著である。このため、実施例のリチウムイオン二次電池はサイクル特性に優れているといえる。さらに、比較例１のリチウムイオン二次電池における２回目充放電時のクーロン効率は、初回充放電時のクーロン効率に比べて大幅に減少している。これは比較例１の負極活物質において不可逆容量が生じていること、つまり、比較例１の負極活物質では合金化反応が生じコンバージョン反応が生じていないことを示している。 Further, as shown in FIG. 7, the lithium ion secondary battery of the example had a larger charge / discharge capacity after the cycle than the lithium ion secondary batteries of Comparative Examples 1 and 2. That is, the lithium ion secondary battery of the example is superior in cycle characteristics as compared with the lithium ion secondary batteries of Comparative Examples 1 and 2. This is thought to be because the lithium ion secondary battery of the example contained SnO 2 in addition to Sn and SnO, so that the volume change was alleviated, and the amount (ratio) of the active material for conversion reaction increased. It is done. In addition, as shown in FIG. 8, the Coulomb efficiency at the time of the 2nd charge / discharge in the lithium ion secondary battery of an Example and the comparative example 2 is rising compared with the Coulomb efficiency at the time of first charge / discharge. This is considered because the irreversible capacity of the active material was reduced. This increase in coulomb efficiency is more remarkable in the lithium ion secondary battery of the example. For this reason, it can be said that the lithium ion secondary battery of an Example is excellent in cycling characteristics. Furthermore, the Coulomb efficiency at the second charge / discharge in the lithium ion secondary battery of Comparative Example 1 is significantly reduced compared to the Coulomb efficiency at the first charge / discharge. This indicates that an irreversible capacity is generated in the negative electrode active material of Comparative Example 1, that is, in the negative electrode active material of Comparative Example 1, an alloying reaction occurs and no conversion reaction occurs.
Claims (12)
ＳｎＯを主成分とするスズ原料をメカニカルミリング処理する第１工程と、該メカニカルミリング処理されたスズ原料を酸化処理する第２工程と、を含むことを特徴とするリチウムイオン二次電池用負極活物質の製造方法。 A method for producing a negative electrode active material for a lithium ion secondary battery containing tin (Sn), comprising:
A negative electrode active for a lithium ion secondary battery, comprising: a first step of mechanically milling a tin raw material containing SnO as a main component; and a second step of oxidizing the tin raw material that has been mechanically milled. A method for producing a substance.
前記第２工程において、該負極活物質前駆体の該被覆部にＳｎＯ2を生成させる請求項５〜請求項７の何れか一つに記載のリチウムイオン二次電池用負極活物質の製造方法。 In the first step, a negative electrode active material precursor having a core portion made of Sn and a covering portion containing SnO 2 and covering the core portion is generated,
The method for producing a negative electrode active material for a lithium ion secondary battery according to any one of claims 5 to 7, wherein in the second step, SnO 2 is generated in the covering portion of the negative electrode active material precursor.
ＳｎとＳｎＯ2とを含み、
該ＳｎＯ2に含まれるＳｎ原子の量は、該負極活物質に含まれるＳｎ原子全体を１００原子％としたときに、５０原子％を超えることを特徴とするリチウムイオン二次電池用負極活物質。 A negative electrode active material for a lithium ion secondary battery containing tin (Sn),
Including Sn and SnO 2 ,
The amount of Sn atoms contained in the SnO 2 exceeds 50 atomic% when the total Sn atoms contained in the negative electrode active material is 100 atomic%, and the negative electrode active material for a lithium ion secondary battery, .
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| KR101836311B1 (en) * | 2015-06-11 | 2018-03-08 | 금오공과대학교 산학협력단 | Methods for manufacturing disproprotionated SnO/C, anode material for composites disproprotionated SnO/C, and rechargeable battery comprising the same |
| WO2019163895A1 (en) * | 2018-02-22 | 2019-08-29 | 日産自動車株式会社 | Pre-doping method for negative electrode active material, production method for negative electrode, and production method for power storage device |
| WO2023202202A1 (en) * | 2022-04-22 | 2023-10-26 | 广东邦普循环科技有限公司 | Preparation method for cobaltosic oxide doped and coated with tin and use thereof |
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| JP2005235439A (en) * | 2004-02-17 | 2005-09-02 | Japan Storage Battery Co Ltd | Manufacturing method of active material and nonaqueous electrolyte electrochemical cell equipped with it |
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| JPH07288123A (en) * | 1994-02-28 | 1995-10-31 | Fuji Photo Film Co Ltd | Nonaqueous secondary battery |
| JPH11292535A (en) * | 1998-04-03 | 1999-10-26 | Tokuyama Corp | Production of multiple tin oxide powder |
| JP2005235439A (en) * | 2004-02-17 | 2005-09-02 | Japan Storage Battery Co Ltd | Manufacturing method of active material and nonaqueous electrolyte electrochemical cell equipped with it |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
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| KR101836311B1 (en) * | 2015-06-11 | 2018-03-08 | 금오공과대학교 산학협력단 | Methods for manufacturing disproprotionated SnO/C, anode material for composites disproprotionated SnO/C, and rechargeable battery comprising the same |
| WO2019163895A1 (en) * | 2018-02-22 | 2019-08-29 | 日産自動車株式会社 | Pre-doping method for negative electrode active material, production method for negative electrode, and production method for power storage device |
| US11456447B2 (en) | 2018-02-22 | 2022-09-27 | Nissan Motor Co., Ltd. | Predoping method for negative electrode active material, manufacturing method for negative electrode, and manufacturing method for power storage device |
| WO2023202202A1 (en) * | 2022-04-22 | 2023-10-26 | 广东邦普循环科技有限公司 | Preparation method for cobaltosic oxide doped and coated with tin and use thereof |
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