JP4785341B2 - Negative electrode material for lithium ion secondary battery, negative electrode for lithium ion secondary battery, and lithium ion secondary battery - Google Patents
Negative electrode material for lithium ion secondary battery, negative electrode for lithium ion secondary battery, and lithium ion secondary battery Download PDFInfo
- Publication number
- JP4785341B2 JP4785341B2 JP2003403079A JP2003403079A JP4785341B2 JP 4785341 B2 JP4785341 B2 JP 4785341B2 JP 2003403079 A JP2003403079 A JP 2003403079A JP 2003403079 A JP2003403079 A JP 2003403079A JP 4785341 B2 JP4785341 B2 JP 4785341B2
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- Prior art keywords
- negative electrode
- ion secondary
- lithium ion
- secondary battery
- graphite
- Prior art date
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Description
本発明は、黒鉛質物と金属を含むリチウムイオン二次電池用負極材料、それを用いたリチウムイオン二次電池用負極、およびそれを用いた放電容量やサイクル特性に優れるリチウムイオン二次電池に関する。 The present invention relates to a negative electrode material for a lithium ion secondary battery containing a graphite and a metal, a negative electrode for a lithium ion secondary battery using the same, and a lithium ion secondary battery using the same and having excellent discharge capacity and cycle characteristics.
他の二次電池に比べて、高電圧、高エネルギー密度という優れた特性を有するリチウムイオン二次電池は、電子機器の電源として広く普及している。近年、電子機器の小型化あるいは高性能化が進み、リチウムイオン二次電池のさらなる高エネルギー密度化に対する要望はますます高まっている。
現在、リチウムイオン二次電池は、正極にＬｉＣｏＯ2 、負極に黒鉛を用いたものが一般的である。しかし、黒鉛負極は充放電性に優れるものの、その放電容量はすでに層間化合物ＬｉＣ6 に相当する理論値３７２mAh/g に近い値まで到達しており、さらなる高エネルギー密度化を達成するためには、黒鉛より放電容量の大きい負極材料を開発する必要がある。
Compared to other secondary batteries, lithium ion secondary batteries having excellent characteristics of high voltage and high energy density are widely used as power sources for electronic devices. In recent years, electronic devices have become smaller and have higher performance, and there is an increasing demand for higher energy density of lithium ion secondary batteries.
At present, lithium ion secondary batteries generally use LiCoO 2 for the positive electrode and graphite for the negative electrode. However, although the graphite negative electrode is excellent in charge / discharge characteristics, its discharge capacity has already reached a value close to the theoretical value 372 mAh / g corresponding to the intercalation compound LiC 6 , and in order to achieve further higher energy density, It is necessary to develop a negative electrode material having a larger discharge capacity than graphite.
金属リチウムは、負極材料として最高の放電容量を有するが、充電時にリチウムがデンドライト状に析出して負極が劣化し、充放電サイクルが短くなるという問題がある。また、デントライト状に析出したリチウムがセパレータを貫通して正極に達し、短絡する虞もある。
そのため、金属リチウムに変わる負極材料として、リチウムと合金を形成する金属が検討されてきた。これらの合金負極は、金属リチウムには及ばないものの黒鉛を遥かに凌ぐ放電容量を有する。しかし、合金化に伴う体積膨張により活物質の粉化・剥離が発生し、まだ実用レベルのサイクル特性は得られていない。
Although metallic lithium has the highest discharge capacity as a negative electrode material, there is a problem that lithium is deposited in a dendrite state during charging, the negative electrode is deteriorated, and the charge / discharge cycle is shortened. Moreover, there is a possibility that lithium precipitated in the shape of dentlite penetrates the separator and reaches the positive electrode, causing a short circuit.
Therefore, a metal that forms an alloy with lithium has been studied as a negative electrode material that replaces metallic lithium. These alloy negative electrodes have discharge capacities far surpassing that of graphite, although they do not reach metal lithium. However, the active material is pulverized and peeled off due to volume expansion accompanying alloying, and the practical cycle characteristics have not yet been obtained.
合金負極の例としては、集電体である銅箔に錫を蒸着するもの（特許文献１）、シリコン薄膜を形成するもの（特許文献２、３）などが挙げられる。これらは高い放電容量を有するものの、初期充放電効率が低下する、または、サイクル特性が不足するという課題があった。
前述の合金負極の欠点を改良する技術として、金属と黒鉛質物または炭素質物のどちらか一方または両方との複合化が検討されている。大別すると、（１）金属、黒鉛質物と炭素質物前駆体を混合後、熱処理するもの（特許文献４〜１１）、（２）ＣＶＤ法を用いて金属に炭素質物を被覆するもの（特許文献１２、１３）、（３）黒鉛質物に金属が付着したもの（特許文献１４〜１６）などである。
As an example of an alloy negative electrode, the thing which vapor-deposits tin on the copper foil which is a collector (patent document 1), the thing which forms a silicon thin film (
As a technique for improving the above-described drawbacks of the alloy negative electrode, a composite of a metal and one or both of a graphite material and a carbonaceous material has been studied. Broadly classified, (1) Metal, graphite and carbonaceous material precursors are mixed and then heat-treated (Patent Documents 4 to 11), (2) Metal is coated with carbonaceous material using CVD method (Patent Documents) 12, 13), and (3) those in which a metal adheres to a graphite material (Patent Documents 14 to 16).
しかしながら、（１）、（２）のいずれにおいても、粒状の金属の周囲に黒鉛質物や炭素質物を単に配するだけでは、充放電時の金属の膨張、収縮による活物質の微粉化や剥離、黒鉛質物や炭素質物の破壊といった問題を解決するには至らず、実用レベルのサイクル特性が得られていないのが現状である。具体的には、特許文献６や９の場合、黒鉛、金属化合物（有機ケイ素）および有機物（炭素質物前駆体）を混合し、加熱することによって、黒鉛表面に炭素質物と金属の混合被膜を形成させている。金属は炭素質物の中に粒状で介在しており、充放電時の金属の膨張、収縮に由来して、炭素質物さらには黒鉛の破壊を生じることがある。
However, in both (1) and (2), simply arranging a graphite or carbonaceous material around a granular metal allows the active material to be pulverized or exfoliated due to expansion or contraction of the metal during charge and discharge. At present, the problem of destruction of graphite and carbonaceous materials has not been solved, and a practical level of cycle characteristics has not been obtained. Specifically, in
（３）は実施例から明らかなように、黒鉛質物として一般的な天然黒鉛や人造黒鉛を用い、該黒鉛の表面に金属を担持、付着、被覆している。金属の体積割合が小さい場合には、サイクル特性の低下がある程度抑えられるが高容量化の効果が小さくなる。金属の体積割合を大きくすると、（１）、（２）と同様にサイクル特性の低下を生じることがある。具体的には、特許文献１４の場合、炭素にシリコンなどの金属の酸化物を機械的に混合しており、被覆ではなく付着した状態を呈している。金属酸化物は充電膨張率が比較的小さいとはいえ、金属酸化物が薄膜ではなく粒子を形成し、さらに炭素に対して少なくとも２０％、好ましくは同量となるように金属の混合量を増量するため、金属由来の膨張、収縮の問題が顕在化する。 As is clear from the examples, (3) uses general natural graphite or artificial graphite as a graphite material, and supports, adheres, and coats a metal on the surface of the graphite. When the volume ratio of the metal is small, the deterioration of the cycle characteristics can be suppressed to some extent, but the effect of increasing the capacity is reduced. When the volume ratio of the metal is increased, cycle characteristics may be deteriorated as in (1) and (2). Specifically, in the case of Patent Document 14, an oxide of a metal such as silicon is mechanically mixed with carbon, and it is in a state of adhering rather than coating. Although the metal oxide has a relatively small charge expansion coefficient, the metal oxide forms particles rather than a thin film, and the amount of the mixed metal is increased so that it is at least 20%, preferably the same amount with respect to carbon. Therefore, the problem of expansion and contraction derived from metal becomes obvious.
特許文献１５の場合は、ゲル型高分子電解質と電極活物質の密着性の改良を目的として、炭素粒子の表面にＦｅ、Ｎｉ、Ｃｕを薄膜被覆している。本技術の金属種を高容量のシリコンなどに置換し、その目的を高容量化とした場合、充分な容量を得るためには、金属の厚みが増し、サイクル特性の低下が問題になる。特許文献１６には、黒鉛質物にアルミニウム酸化物を薄膜被覆することによるサイクル特性の向上が示されている。しかし、放電容量は３７０mAh/g と黒鉛の理論容量を超えていない。容量をさらに高めるべく、金属の割合を大きくすると前述の従来技術と同様にサイクル特性の低下を生じる。このように、従来技術では、高放電容量とサイクル特性を始めとする電池の諸特性を高いレベルで両立することができない。 In the case of Patent Document 15, the surface of carbon particles is coated with Fe, Ni, and Cu in a thin film for the purpose of improving the adhesion between the gel polymer electrolyte and the electrode active material. When the metal species of the present technology is replaced with high-capacity silicon or the like and its purpose is to increase the capacity, in order to obtain a sufficient capacity, the thickness of the metal increases and the cycle characteristics deteriorate. Patent Document 16 discloses an improvement in cycle characteristics by coating a graphite material with an aluminum oxide thin film. However, the discharge capacity is 370 mAh / g, which does not exceed the theoretical capacity of graphite. If the metal ratio is increased in order to further increase the capacity, the cycle characteristics are deteriorated as in the above-described conventional technique. Thus, in the prior art, the various characteristics of the battery including high discharge capacity and cycle characteristics cannot be achieved at a high level.
本発明は、上記のような状況を鑑みてなされたものであり、リチウムイオン二次電池用負極材料として用いて、放電容量が高く、優れたサイクル特性と初期充放電効率が得られる負極材料を提供することを目的とする。また、得られた負極材料を用いてなる、放電容量が高く、優れたサイクル特性と初期充放電効率を有するリチウムイオン二次電池用負極および該二次電池用負極を用いたリチウムイオン二次電池を提供することが目的である。 The present invention has been made in view of the above situation, and is used as a negative electrode material for a lithium ion secondary battery. A negative electrode material having a high discharge capacity and excellent cycle characteristics and initial charge / discharge efficiency is obtained. The purpose is to provide. Also, a negative electrode for a lithium ion secondary battery having a high discharge capacity, having excellent cycle characteristics and initial charge / discharge efficiency, and a lithium ion secondary battery using the negative electrode for the secondary battery, comprising the obtained negative electrode material Is the purpose.
本発明は、起毛部を有する粒状黒鉛質物の少なくとも起毛部の外表面の一部に、非晶質シリコンを含む金属が付着し、前記起毛部を有する粒状黒鉛質物が炭素繊維とコールタールピッチとの混練物の黒鉛化物であることを特徴とするリチウムイオン二次電池用負極材料である。
また、本発明のリチウムイオン二次電池用負極材料は、非晶質シリコンを含む金属が膜状に付着していることが好ましい。
In the present invention, a metal containing amorphous silicon is attached to at least a part of the outer surface of a granular graphite material having a raised portion, and the granular graphite material having the raised portion is composed of carbon fiber and coal tar pitch. A negative electrode material for a lithium ion secondary battery, characterized by being a graphitized product of the kneaded product .
In the negative electrode material for a lithium ion secondary battery of the present invention, a metal containing amorphous silicon is preferably attached in a film form.
本発明のリチウムイオン二次電池用負極材料は、前記粒状黒鉛質物のＸ線広角回折による（００２）面の平均格子面間隔ｄ002 が０．３４ｎｍ以下であることが好ましい。 Anode material for a lithium ion secondary battery of the present invention, it is preferable that the particulate graphite pledge of wide-angle X-ray diffraction by the (002) plane average lattice spacing d 002 of less than or equal 0.34 nm.
本発明のリチウムイオン二次電池用負極材料は、前記非晶質シリコンを含む金属の前記リチウムイオン二次電池用負極材料全体に占める体積割合が１〜２０％であることが好ましい。 In the negative electrode material for lithium ion secondary batteries of the present invention, the volume ratio of the metal containing amorphous silicon to the whole negative electrode material for lithium ion secondary batteries is preferably 1 to 20%.
本発明のリチウムイオン二次電池用負極材料は、前記二次電池用負極材料が、リチウムと合金化可能な金属をターゲットとしてスパッタリングを行って前記黒鉛質物に該金属を付着させたものであることが好ましい。 The negative electrode material for a lithium ion secondary battery according to the present invention is such that the negative electrode material for a secondary battery is obtained by performing sputtering using a metal that can be alloyed with lithium as a target and attaching the metal to the graphite. Is preferred.
本発明のリチウムイオン二次電池用負極材料は、前記粒状黒鉛質物の比表面積が１〜１００ｍ2 ／ｇであることが好ましい。 In the negative electrode material for a lithium ion secondary battery according to the present invention, the granular graphite material preferably has a specific surface area of 1 to 100 m 2 / g.
本発明のリチウムイオン二次電池用負極材料は、前記繊維状黒鉛が気相成長炭素繊維またはカーボンナノチューブであることが好ましい。 In the negative electrode material for a lithium ion secondary battery of the present invention, the fibrous graphite is preferably vapor grown carbon fiber or carbon nanotube.
また、本発明は、前記いずれかのリチウムイオン二次電池用負極材料を用いることを特徴とするリチウムイオン二次電池用負極である。 Moreover, this invention uses the said negative electrode material for lithium ion secondary batteries, The negative electrode for lithium ion secondary batteries characterized by the above-mentioned.
また、本発明は、前記のリチウムイオン二次電池用負極を用いることを特徴とするリチウムイオン二次電池である。 The present invention also provides a lithium ion secondary battery using the negative electrode for a lithium ion secondary battery.
本発明のリチウムイオン二次電池用負極材料を用いると、黒鉛の理論容量を超える優れた放電容量が得られ、同時に優れた初期充放電効率とサイクル特性を示すリチウムイオン二次電池を得ることができる。
そのため、本発明の負極材料を用いてなるリチウムイオン二次電池は、近年の電池の高エネルギー密度化に対する要望を満たし、搭載する機器の小型化および高性能化に有効である。
By using the negative electrode material for a lithium ion secondary battery of the present invention, an excellent discharge capacity exceeding the theoretical capacity of graphite can be obtained, and at the same time, a lithium ion secondary battery exhibiting excellent initial charge / discharge efficiency and cycle characteristics can be obtained. it can.
Therefore, the lithium ion secondary battery using the negative electrode material of the present invention satisfies the recent demand for higher energy density of the battery, and is effective in reducing the size and performance of the mounted device.
以下、本発明をより具体的に説明する。
（負極材料）
本発明の負極材料は、起毛部を有する粒状黒鉛質物の少なくとも起毛部の一部に、リチウムと合金化可能な金属が付着した複合型の負極材料である。該負極材料は、起毛し、微細な突起（けば）を有している。起毛部を有すると、起毛部同士が接触することによって負極材料間の導電性が保持され、抵抗が低減されるので、充放電特性やサイクル特性が向上する。また、起毛部により負極材料間に隙間が生じることから、該金属の充放電時の膨張・収縮を緩衝でき、サイクル特性が向上する。さらに、該起毛部の一部に該金属が付着していることから、高い放電容量が得られ、かつ表面に付着していることから、金属の膨張などの影響が低減される。
Hereinafter, the present invention will be described more specifically.
(Negative electrode material)
The negative electrode material of the present invention is a composite negative electrode material in which a metal that can be alloyed with lithium is attached to at least a part of a raised portion of a granular graphite material having a raised portion. The negative electrode material is raised and has fine protrusions (bumps). When the raised portions are included, the raised portions are brought into contact with each other, whereby the conductivity between the negative electrode materials is maintained and the resistance is reduced, so that the charge / discharge characteristics and the cycle characteristics are improved. Moreover, since a gap is generated between the negative electrode materials due to the raised portions, expansion / contraction during charging / discharging of the metal can be buffered, and cycle characteristics are improved. Furthermore, since the metal adheres to a part of the raised portion, a high discharge capacity is obtained, and since the metal adheres to the surface, the influence of metal expansion or the like is reduced.
該黒鉛質物に対する該金属の付着は化学的結合、物理的結合、それらの複合のいずれでもよいが、黒鉛質物と金属の界面は化学的に結合した状態であることが好ましい。例えば、金属がシリコンの場合には、黒鉛質物とシリコンの境界にＳｉＣ層が形成されて両者が結合されていることが好ましい。前記付着形態は膜状、島状、針状などいかなる形態であってもよいが、金属の膨張などの影響が小さいことから膜状であることが好ましい。具体的には、該黒鉛質物の表面を該金属が薄膜状に被覆し、該被覆が黒鉛質物の起毛部の少なくとも一部はもちろん、黒鉛質物の本体の少なくとも一部にも及んでいる場合が好ましい。 The adhesion of the metal to the graphite material may be any of a chemical bond, a physical bond, and a composite thereof, but the interface between the graphite material and the metal is preferably in a chemically bonded state. For example, when the metal is silicon, it is preferable that an SiC layer is formed at the boundary between the graphite and the silicon and the two are bonded. The attachment form may be any form such as a film form, an island form, or a needle form, but is preferably a film form because the influence of metal expansion or the like is small. Specifically, the surface of the graphite material may be coated with the metal in a thin film shape, and the coating may extend to at least a part of the graphite material body as well as at least a part of the raised portion of the graphite material. preferable.
本発明の負極材料の黒鉛質物は起毛しているが、これは、繊維状の黒鉛質物に由来するものである。本発明の負極材料の作用効果は、それを構成する、起毛部を有する粒状黒鉛質物に拠るところが大であり、起毛部を有する粒状黒鉛質物の特性が反映されるので、その点については後述する。 Although the graphite material of the negative electrode material of the present invention is raised, this is derived from the fibrous graphite material. The effect of the negative electrode material of the present invention largely depends on the granular graphite material having a raised portion constituting the negative electrode material, and the characteristics of the granular graphite material having the raised portion are reflected. This will be described later. .
本発明の負極材料全体に占める前記金属の体積割合は１〜２０％、特に３〜１５％であることが好ましい。体積割合が１％未満の場合には、放電容量の向上効果が不足する。一方、体積割合が２０％超の場合には、金属とリチウムの合金化（充放電）に伴う体積膨張、収縮に由来し、粉化、剥離、黒鉛質物の破壊などの問題を生じることがある。
体積割合は公知の元素定量分析やＸ線回折法（ＸＲＤ）などによる金属種の定性分析から換算して得ることができる。
前記金属の付着状態が膜状の場合、該金属の平均厚みは概ね１ｎｍ〜２μｍ、好ましくは１０ｎｍ〜１μｍの範囲である。
平均厚みは負極材料の断面を走査型電子顕微鏡または透過型電子顕微鏡で観察したり、グロー放電発光分析装置（ＧＤＳ）などにより深さ方向の元素濃度を分析することによって測定することができる。
It is preferable that the volume ratio of the said metal to the whole negative electrode material of this invention is 1 to 20%, especially 3 to 15%. When the volume ratio is less than 1%, the effect of improving the discharge capacity is insufficient. On the other hand, when the volume ratio exceeds 20%, it may be caused by volume expansion and contraction associated with alloying (charging / discharging) of metal and lithium, and may cause problems such as powdering, peeling, and destruction of graphite. .
The volume ratio can be obtained by conversion from a qualitative analysis of a metal species by a known elemental quantitative analysis or X-ray diffraction method (XRD).
When the adhesion state of the metal is a film, the average thickness of the metal is generally in the range of 1 nm to 2 μm, preferably 10 nm to 1 μm.
The average thickness can be measured by observing the cross section of the negative electrode material with a scanning electron microscope or a transmission electron microscope, or by analyzing the element concentration in the depth direction with a glow discharge emission spectrometer (GDS) or the like.
前記負極材料は、平均粒子径が１〜５０μｍであることが好ましい。平均粒子径が１μｍ未満の場合は、負極を形成するときの負極合剤ペーストの調整が難しくなるほか、黒鉛質物の活性なエッジが露出しやすくなり、初期充放電効率が低下することがある。平均粒子径が５０μｍ超の場合には、負極の活物質層の厚みを調整することが難しくなる。より好ましい平均粒子径は３〜４０μｍである。
平均粒子径はレーザー回折式粒度分布計によって測定することができる。また、起毛部が黒鉛質物本体に比して大となり、レーザー回折式粒度分布計により測定できない場合には、走査型電子顕微鏡または透過型電子顕微鏡で複数（１００程度）についてそれぞれ、最大径とそれに直交する径を測定し、その平均を粒子径とする。該粒子径の複数の平均値を平均粒子径とする。
The negative electrode material preferably has an average particle size of 1 to 50 μm. When the average particle diameter is less than 1 μm, it is difficult to adjust the negative electrode mixture paste when forming the negative electrode, and active edges of the graphite are likely to be exposed, and the initial charge / discharge efficiency may be reduced. When the average particle diameter exceeds 50 μm, it is difficult to adjust the thickness of the active material layer of the negative electrode. A more preferable average particle diameter is 3 to 40 μm.
The average particle diameter can be measured by a laser diffraction particle size distribution meter. In addition, when the brushed part is larger than the graphite body and cannot be measured by a laser diffraction particle size distribution meter, the maximum diameter and the number of the plurality (about 100) are measured with a scanning electron microscope or a transmission electron microscope. The orthogonal diameter is measured and the average is taken as the particle diameter. A plurality of average values of the particle diameters are defined as average particle diameters.
前記負極材料は、黒鉛質物およびリチウムと合金化可能な金属を必須の構成成分とするが、これに加えて、異種の炭素質物、黒鉛質物、無機質物を含んでいてもよい。具体的には、異種の炭素質物や黒鉛質物との混合物、造粒物、被覆物、積層物であってもよい。また、液相、気相、固相における各種化学的処理、熱処理、酸化処理、物理的処理などを施したものであってもよい。この場合も負極材料全体として平均粒子径が１〜５０μｍであることが好ましい。 The negative electrode material includes a graphite material and a metal that can be alloyed with lithium as essential constituent components, but may further include a different carbonaceous material, a graphite material, and an inorganic material. Specifically, it may be a mixture of a different carbonaceous material or a graphite material, a granulated material, a coating material, or a laminate. Further, it may be subjected to various chemical treatments in the liquid phase, gas phase, and solid phase, heat treatment, oxidation treatment, physical treatment and the like. Also in this case, the average particle diameter of the negative electrode material as a whole is preferably 1 to 50 μm.
本発明の負極材料が、優れたサイクル特性を発現する理由は明らかではないが、金属が表面に付着しているため金属の膨張に伴う割れや粉化などが低減されること、金属が充電によって膨張した場合に、充分な空間が起毛部に確保されていること、金属と電解液との接触が保たれていること、起毛部同士が接触することにより負極内の導電性が保持されることなどが寄与しているものと考えられる。 The reason why the negative electrode material of the present invention exhibits excellent cycle characteristics is not clear, but because the metal adheres to the surface, cracks and powdering associated with metal expansion are reduced, and the metal is charged. When expanded, sufficient space is ensured in the raised portion, the contact between the metal and the electrolyte is maintained, and the conductivity in the negative electrode is maintained by contacting the raised portions. Etc. are considered to be contributing.
（リチウムと合金化可能な金属）
リチウムと合金化可能な金属はＡｌ、Ｐｂ、Ｚｎ、Ｓｎ、Ｂｉ、Ｉｎ、Ｍｇ、Ｇａ、Ｃｄ、Ａｇ、Ｓｉ、Ｂ、Ａｕ、Ｐｔ、Ｐｄ、Ｓｂ、Ｇｅ、Ｎｉなどであり、好ましいのはＳｉ、Ｓｎであり、特に好ましいのはＳｉである。また、金属は該金属の２種以上の合金であってもよい。合金中に、該金属以外の元素が含有されていてもよい。金属は非晶性のものを含むことが好ましい。金属が非晶性であると充電時の膨張が軽減される。非晶性シリコンを含む金属が最適である。
(Metal that can be alloyed with lithium)
Metals that can be alloyed with lithium are Al, Pb, Zn, Sn, Bi, In, Mg, Ga, Cd, Ag, Si, B, Au, Pt, Pd, Sb, Ge, Ni, etc. Si and Sn are preferable, and Si is particularly preferable. The metal may be an alloy of two or more of the metals. Elements other than the metal may be contained in the alloy. The metal preferably includes an amorphous material. If the metal is amorphous, expansion during charging is reduced. Metals containing amorphous silicon are optimal.
（黒鉛質物）
黒鉛質物は負極活物質としてリチウムイオンを吸蔵・放出できるものであればよく、特に限定されない。その一部または全部が黒鉛質で形成されているもの、例えば、天然黒鉛や、タール、ピッチ類を最終的に１５００℃以上で熱処理してなる人造黒鉛が挙げられる。具体的には、易黒鉛化性炭素材料と言われる石油系、石炭系のタール、ピッチ類を原料として重縮合させたメソフェーズ焼成体、メソフェーズ小球体、メソフェーズ炭素繊維、コークス類を１５００℃以上、好ましくは２８００〜３３００℃で黒鉛化処理して得ることができる。さらに、カーボンナノチューブ、カーボンナノホーン、気相成長炭素繊維などの炭素質微細繊維を１５００℃以上、好ましくは２８００〜３３００℃で黒鉛化処理して得ることができる。
(Graphite)
The graphite material is not particularly limited as long as it can absorb and release lithium ions as a negative electrode active material. A part or all of which is made of graphite, for example, natural graphite, and artificial graphite obtained by finally heat treating tar and pitch at 1500 ° C. or higher. Specifically, a mesophase calcined product obtained by polycondensation using petroleum-based and coal-based tars, pitches, and so on, which are called graphitizable carbon materials, mesophase microspheres, mesophase carbon fibers, and cokes at 1500 ° C. or more, Preferably, it can be obtained by graphitizing at 2800-3300 ° C. Further, carbonaceous fine fibers such as carbon nanotubes, carbon nanohorns, and vapor grown carbon fibers can be obtained by graphitization at 1500 ° C. or higher, preferably 2800 to 3300 ° C.
本発明に使用される黒鉛質物は起毛部を有する必要がある。すなわち、その表面に繊維などの突起（けば）を有する必要がある。起毛部（突起）は、外表面に向けて突き出した状態であればよく、その形状や突き出しの方向は限定されない。起毛部は分岐していたり、複数本が収束した状態であってもよい。
本発明における起毛部（突起）の長軸方向の長さ（長軸長）は１〜５００ｎｍであることが好ましく、より好ましくは１０〜２００ｎｍである。該長軸長に直交する短軸方向の長さ（短軸長）は１００ｎｍ〜１０μｍであることが好ましい。また、長軸長と、それに直交する短軸方向の長さ（短軸長）の比（アスペクト比）は３以上であることが好ましい。より好ましいのは３〜５００、さらに好ましいのは１０〜１００である。
起毛部（突起）のアスペクト比は、起毛部を走査型電子顕微鏡または透過型電子顕微鏡で観察し、複数本（１００本程度）の起毛部（突起）の長軸長と短軸長を計測し、算術平均して求めたものである。
The graphite material used in the present invention needs to have a raised portion. That is, it is necessary to have protrusions such as fibers on the surface. The raised portion (protrusion) may be in a state of protruding toward the outer surface, and the shape and the protruding direction are not limited. The raised portion may be branched or a plurality of raised portions may be converged.
The length in the major axis direction (major axis length) of the raised portion (projection) in the present invention is preferably 1 to 500 nm, and more preferably 10 to 200 nm. The length in the minor axis direction (minor axis length) orthogonal to the major axis length is preferably 100 nm to 10 μm. Further, the ratio (aspect ratio) between the major axis length and the length (minor axis length) in the minor axis direction perpendicular to the major axis length is preferably 3 or more. More preferred is 3 to 500, and further preferred is 10 to 100.
The aspect ratio of the raised portions (projections) is determined by observing the raised portions with a scanning electron microscope or a transmission electron microscope, and measuring the major axis length and minor axis length of a plurality of raised portions (projections) (about 100). It is obtained by arithmetic average.
本発明の黒鉛質物は起毛部を有すればよいが、繊維状黒鉛の集合体、または繊維状黒鉛と黒鉛質粒子との複合体であることが好ましい。つまり、該起毛部の形成方法はいかなる方法によってもよく、粒状天然黒鉛や粒状人造黒鉛の表面に微細繊維状黒鉛質物を機械的または結着剤により付着させ、繊維状黒鉛と黒鉛質粒子の複合体とする方法、微細繊維状黒鉛質物を機械的エネルギーまたは結着剤を用いて多数集合（凝集）または造粒し、繊維状黒鉛の集合体とする方法などによって、表面に起毛部を有する黒鉛質物を得ることができる。さらに、具体的には、気相成長繊維などの微細繊維状炭素質物とコールタールピッチを３０００℃近傍で熱処理し、黒鉛化した後、これに機械的エネルギーを付与するか、または結着剤を介して造粒し、表面を起毛させて繊維状黒鉛の集合体とする方法が挙げられる。 The graphite material of the present invention may have a raised portion, but is preferably an aggregate of fibrous graphite or a composite of fibrous graphite and graphite particles. That is, the method for forming the raised portion may be any method, and a fine fibrous graphite is adhered to the surface of granular natural graphite or granular artificial graphite mechanically or by a binder, and a composite of fibrous graphite and graphite particles is obtained. Graphite having a raised portion on the surface by a method of forming a body, a method of collecting (aggregating) or granulating a number of fine fibrous graphite materials using mechanical energy or a binder to form an aggregate of fibrous graphite A quality material can be obtained. More specifically, a fine fibrous carbonaceous material such as a vapor-grown fiber and coal tar pitch are heat-treated at around 3000 ° C. and graphitized, and then mechanical energy is given to this or a binder is added. And a method of raising the surface to form an aggregate of fibrous graphite.
前記黒鉛質物は高い放電容量を得る観点から、結晶性の高いものが好ましい。結晶性の指標としては、Ｘ線広角回折による（００２）面の平均格子面間隔ｄ002 で０．３４ｎｍ以下が好ましく、０．３３７ｎｍ以下が特に好ましい。
なお、格子面間隔の測定は、ＣｕＫα線をＸ線源、高純度シリコンを標準物質に使用して、黒鉛質物の（００２）面の回折ピークを測定し、そのピークの位置よりｄ002 を算出する。算出方法は、学振法（日本学術振興会第１１７委員会が定めた測定法）に従うものであり、具体的には、「炭素繊維」（大谷杉郎著、第７３３〜７４２頁（１９８６年）、近代編集社）などに記載された方法によって測定した値である。
また、該黒鉛質物の比表面積は１〜１００m2/g、特に５〜５０m2/gの範囲であることが好ましい。比表面積が１m2/g未満の場合には、必然的に金属の付着量が多くなり、金属の充電時の割れや粉化を生じることがある。比表面積が１００m2/g超の場合には、金属の付着量が少なくなるものの、黒鉛質物の活性なエッジ面の露出割合が増え、初期充放電効率が低下したり、負極を形成するときの負極合剤ペーストの調整が難しくなる。
比表面積は窒素ガスの吸着によるＢＥＴ法により測定した値である。
From the viewpoint of obtaining a high discharge capacity, the graphite material preferably has high crystallinity. Indicators of crystallinity is preferably not more than 0.34nm at an average lattice spacing d 002 of the X-ray wide angle diffraction (002) plane, and particularly preferably equal to or less than 0.337 nm.
The lattice spacing is measured by measuring the diffraction peak of the (002) plane of the graphite using CuKα ray as the X-ray source and high-purity silicon as the standard substance, and calculating d 002 from the peak position. To do. The calculation method follows the Japan Science and Technology Act (measurement method defined by the 117th Committee of the Japan Society for the Promotion of Science). Specifically, “Carbon Fiber” (Suguro Otani, pp. 733-742 (1986) ), Modern Editing Co.) and the like.
The specific surface area of the graphite material is preferably in the range of 1 to 100 m 2 / g, particularly 5 to 50 m 2 / g. When the specific surface area is less than 1 m 2 / g, the adhesion amount of the metal inevitably increases, and the metal may be cracked or powdered during charging. When the specific surface area is more than 100 m 2 / g, the amount of metal attached decreases, but the exposure rate of the active edge surface of the graphite increases, and the initial charge / discharge efficiency decreases or the negative electrode is formed. It becomes difficult to adjust the negative electrode mixture paste.
The specific surface area is a value measured by the BET method by adsorption of nitrogen gas.
該黒鉛質物は異種の炭素質物や黒鉛質物を含むものであってもよい。この場合、黒鉛質物全体の結晶性の平均値が、Ｘ線広角回折による（００２）面の平均格子面間隔ｄ002 で０．３４ｎｍ以下であることが好ましい。具体的には、異種の炭素質物や黒鉛質物との混合物、造粒物、被覆物、積層物であってもよく、特に炭素質物を被覆したものが好ましい。また、液相、気相、固相における各種化学的処理、熱処理、酸化処理、物理的処理などを施したものであってもよい。 The graphite material may include different types of carbonaceous materials and graphite materials. In this case, the average value of the crystallinity of the entire graphite pledge is preferably at 0.34nm or less at an average lattice spacing d 002 of (002) plane by X-ray wide angle diffraction. Specifically, it may be a mixture of a different carbonaceous material or a graphite material, a granulated material, a coated material, or a laminate, and a carbonaceous material-coated material is particularly preferable. Further, it may be subjected to various chemical treatments in the liquid phase, gas phase, and solid phase, heat treatment, oxidation treatment, physical treatment and the like.
（負極材料の製造方法）
本発明の負極材料の製造方法としては、起毛部を有する黒鉛質物の表面の起毛部の少なくとも一部に、リチウムと合金を形成することが可能な金属が付着した構造が得られる方法であればいかなる方法を用いてもよいが、本発明の効果を最大限に発現する方法を以下に例示する。
金属の付着は、気相または液相で金属または金属の有機化合物を黒鉛質物に付着することができる方法であれば特に限定されないが、気相法が好ましい。気相法としては、真空蒸着法、スパッタリング法、イオンプレーティング法、分子線エピタキシー法などのＰＶＤ（Physical Vapor Deposition)法や、常圧ＣＶＤ(Chemical Vapor Deposition) 法、減圧ＣＶＤ法、プラズマＣＶＤ法、ＭＯ(Magneto-optic）ＣＶＤ法、光ＣＶＤなどのＣＶＤ法が挙げられる。これらの中でも、スパッタリング法が好ましい。スパッタリング法としては、直流スパッタリング法、マグネトロンスパッタリング法、高周波スパッタリング法、反応性スパッタリング法、バイアススパッタリング法、イオンビームスパッタリング法などが例示される。
(Method for producing negative electrode material)
As a method for producing the negative electrode material of the present invention, any method can be used as long as a structure in which a metal capable of forming an alloy with lithium adheres to at least a part of the raised portion of the surface of the graphite material having the raised portion is obtained. Any method may be used, and a method for maximizing the effect of the present invention is exemplified below.
The attachment of the metal is not particularly limited as long as it is a method capable of attaching a metal or an organic compound of a metal to a graphite material in a gas phase or a liquid phase, but a gas phase method is preferable. Vapor deposition methods include PVD (Physical Vapor Deposition) methods such as vacuum deposition, sputtering, ion plating, molecular beam epitaxy, atmospheric pressure CVD (Chemical Vapor Deposition), reduced pressure CVD, and plasma CVD. , MO (Magneto-optic) CVD method, CVD method such as optical CVD. Among these, the sputtering method is preferable. Examples of the sputtering method include a direct current sputtering method, a magnetron sputtering method, a high frequency sputtering method, a reactive sputtering method, a bias sputtering method, and an ion beam sputtering method.
該スパッタリング法は、カソード側に金属のターゲットを設置し、一般に１〜１０-2Ｐａ程度の不活性ガス雰囲気中で電極間にグロー放電を起こし、不活性ガスをイオン化させ、ターゲットの金属を叩き出して、アノード側に設置した黒鉛質物に該金属を被覆する方法である。この場合、黒鉛質物を機械的に攪拌する、または超音波などの振動を与えることによって、黒鉛質物に動きを与え、黒鉛質物の表面に均一に金属を被覆することが有効である。金属は複数の金属を用いてもよい。すなわち、複数の金属をターゲットとして同時にスパッタリングして、合金を合成してもよいし、複数の金属を順に積層してもよい。
得られた負極材料は、目的に応じて、さらに異種の炭素質物、黒鉛質物、無機質物などを混合、被覆、付着させることもできる。例えば、本発明の負極材料にさらにＣＶＤ法によって、炭素質物を薄膜で被覆したり、炭素質物前駆体を液相で付着させ、焼成することもできる。
In the sputtering method, a metal target is set on the cathode side, and generally a glow discharge is generated between the electrodes in an inert gas atmosphere of about 1 to 10 −2 Pa to ionize the inert gas and strike the target metal. In this method, the metal is coated on the graphite material placed on the anode side. In this case, it is effective to mechanically stir the graphite material or apply vibration such as ultrasonic waves to move the graphite material so that the surface of the graphite material is uniformly coated with metal. A plurality of metals may be used as the metal. That is, a plurality of metals may be simultaneously sputtered to synthesize an alloy, or a plurality of metals may be laminated in order.
Depending on the purpose, the obtained negative electrode material can be further mixed, coated and adhered with different carbonaceous materials, graphite materials, inorganic materials and the like. For example, the negative electrode material of the present invention can be further coated with a carbonaceous material by a CVD method, or a carbonaceous material precursor can be attached in a liquid phase and fired.
（負極）
リチウムイオン二次電池の負極を構成する負極材料として、本発明の負極材料以外に公知の負極材料や導電性材料を同時に用いることができる。例えば、天然黒鉛、人造黒鉛、メソフェーズ小球体の黒鉛質物、メソフェーズ炭素繊維の黒鉛質物、メソフェーズ焼成体の黒鉛質物などの各種負極材料や、カーボンブラック、アセチレンブラック、ケッチェンブラック、気相成長炭素繊維などの導電性材料を混合することができる。中でも、本発明の負極材料とメソフェーズ小球体の黒鉛質物を混合して用いると、バランスのとれた電池特性を得ることができ、有効である。
(Negative electrode)
As a negative electrode material constituting the negative electrode of the lithium ion secondary battery, a known negative electrode material or conductive material can be used simultaneously in addition to the negative electrode material of the present invention. For example, various negative electrode materials such as natural graphite, artificial graphite, mesophase globular graphite, mesophase carbon fiber graphite, mesophase calcined graphite, carbon black, acetylene black, ketjen black, vapor grown carbon fiber A conductive material such as can be mixed. Above all, when the negative electrode material of the present invention and the graphite material of mesophase spherules are mixed and used, balanced battery characteristics can be obtained, which is effective.
リチウムイオン二次電池の負極の作製は、通常の負極の成形方法に準じて行うことができるが、化学的、電気化学的に安定な負極を得ることができる成形方法であれば何ら制限されない。
また、負極の作製時には、該負極材料に結合剤を加えた負極合剤を用いることができる。結合剤としては、電解質に対して化学的安定性、電気化学的安定性を有するものを用いるのが好ましく、例えば、ポリフッ化ビニリデン、ポリテトラフルオロエチレンなどのフッ素系樹脂、ポリエチレン、ポリビニルアルコール、スチレンブタジエンゴム、さらにはカルボキシメチルセルローズなどが用いられる。これらを併用することもできる。結合剤は、通常、負極合剤の全量中１〜２０質量％程度の量で用いるのが好ましい。
The production of the negative electrode of the lithium ion secondary battery can be performed according to a normal method of forming a negative electrode, but is not limited as long as it is a molding method capable of obtaining a chemically and electrochemically stable negative electrode.
Moreover, the negative electrode mixture which added the binder to this negative electrode material can be used at the time of preparation of a negative electrode. As the binder, those having chemical stability and electrochemical stability with respect to the electrolyte are preferably used. For example, fluorine resins such as polyvinylidene fluoride and polytetrafluoroethylene, polyethylene, polyvinyl alcohol, and styrene. Butadiene rubber, carboxymethyl cellulose and the like are used. These can also be used together. In general, the binder is preferably used in an amount of about 1 to 20% by mass in the total amount of the negative electrode mixture.
負極の作製の具体例として、前記負極材料の粒子を結合剤と混合することによって負極合剤を調製し、この負極合剤を、通常、集電体の片面または両面に塗布することで負極合剤層を形成する方法が挙げられる。
負極の作製には、負極作製用の通常の溶媒を用いることができる。負極合剤を溶媒中に分散させ、ペースト状にした後、集電体に塗布、乾燥すれば、負極合剤層が均一かつ強固に集電体に接着される。より具体的には、例えば、該負極材料の粒子とポリフッ化ビニリデンなどのフッ素系樹脂粉末またはスチレンブタジエンゴムなどの水分散粘結剤、カルボキシメチルセルロースなどの水溶性粘結剤とを、Ｎ−メチルピロリドン、ジメチルホルムアルデヒドまたは水、アルコールなどの溶媒と混合してスラリーとした後、ニーダーなどで混練し、ペーストを調製する。該ペーストを集電材の片面または両面に塗布し、乾燥すれば、負極合剤層が均一かつ強固に接着した負極が得られる。該負極合剤層の膜厚は１０〜２００μｍ、好ましくは３０〜１００μｍである。
As a specific example of the preparation of the negative electrode, a negative electrode mixture is prepared by mixing the particles of the negative electrode material with a binder, and this negative electrode mixture is usually applied to one or both sides of a current collector to form a negative electrode mixture. The method of forming an agent layer is mentioned.
A normal solvent for preparing a negative electrode can be used for preparing the negative electrode. When the negative electrode mixture is dispersed in a solvent and made into a paste, and then applied to the current collector and dried, the negative electrode mixture layer is uniformly and firmly adhered to the current collector. More specifically, for example, the negative electrode material particles and a fluorine resin powder such as polyvinylidene fluoride or a water-dispersible binder such as styrene butadiene rubber, or a water-soluble binder such as carboxymethylcellulose are mixed with N-methyl. A paste is prepared by mixing with pyrrolidone, dimethylformaldehyde or a solvent such as water or alcohol to form a slurry, and then kneading with a kneader. When the paste is applied to one or both sides of the current collector and dried, a negative electrode in which the negative electrode mixture layer is uniformly and firmly bonded can be obtained. The film thickness of the negative electrode mixture layer is 10 to 200 μm, preferably 30 to 100 μm.
また、前記負極材料の粒子と、結合剤としてのポリエチレン、ポリビニルアルコールなどの樹脂粉末とを乾式混合し、金型内でホットプレス成形して負極を作製することもできる。ただし、乾式混合では、十分な負極の強度を得るために多くの結合剤を必要とし、結合剤が過多の場合は、リチウムイオン二次電池の放電容量や急速充放電効率が低下することがある。
負極合剤層を形成した後、プレス加圧などの圧着を行うと、負極合剤層と集電体との接着強度をさらに高めることができる。
負極に用いる集電体の形状は、特に限定されないが、箔状、またはメッシュ、エキスパンダブルメタルなどの網状のものが挙げられる。集電体の材質としては、銅、ステンレス、ニッケルなどを挙げることができる。集電体の厚みは、箔状の場合、５〜２０μｍ程度であるのが好ましい。
Alternatively, the negative electrode material particles can be dry-mixed with resin powders such as polyethylene and polyvinyl alcohol as a binder, and hot-press molded in a mold to produce a negative electrode. However, dry mixing requires a large amount of binder to obtain sufficient strength of the negative electrode, and if the binder is excessive, the discharge capacity and rapid charge / discharge efficiency of the lithium ion secondary battery may be reduced. .
When the negative electrode mixture layer is formed and then pressure bonding such as pressurization is performed, the adhesive strength between the negative electrode mixture layer and the current collector can be further increased.
The shape of the current collector used for the negative electrode is not particularly limited, and examples thereof include a foil shape or a net shape such as a mesh or an expandable metal. Examples of the material for the current collector include copper, stainless steel, and nickel. In the case of a foil, the thickness of the current collector is preferably about 5 to 20 μm.
また、本発明は、前記リチウムイオン二次電池用負極を用いて形成されるリチウムイオン二次電池でもある。
本発明のリチウムイオン二次電池は、前記負極を用いること以外は特に限定されず、他の電池構成要素については、一般的なリチウムイオン二次電池の要素に準じる。
Moreover, this invention is also a lithium ion secondary battery formed using the said negative electrode for lithium ion secondary batteries.
The lithium ion secondary battery of the present invention is not particularly limited except that the negative electrode is used, and other battery components are in accordance with elements of a general lithium ion secondary battery.
（正極）
本発明のリチウムイオン二次電池に使用される正極材（正極活物質）としては、リチウム化合物が用いられるが、充分量のリチウムを吸蔵／脱離し得るものを選択するのが好ましい。例えば、リチウム含有遷移金属酸化物、遷移金属カルコゲン化物、バナジウム酸化物、およびその他のリチウム含有化合物、一般式ＭX Ｍｏ6 Ｓ8-Y （式中Ｘは０≦Ｘ≦４、Ｙは０≦Ｙ≦１の範囲の数値であり、Ｍは少なくとも一種の遷移金属を表す）で表されるシュブレル相化合物、活性炭、活性炭素繊維などである。バナジウム酸化物はＶ2 Ｏ5 、Ｖ6 Ｏ13、Ｖ2 Ｏ4 、Ｖ3 Ｏ8 で示されるものなどである。
(Positive electrode)
As the positive electrode material (positive electrode active material) used in the lithium ion secondary battery of the present invention, a lithium compound is used, but it is preferable to select a material that can occlude / desorb a sufficient amount of lithium. For example, lithium-containing transition metal oxide, transition metal chalcogenide, vanadium oxide, and other lithium-containing compounds, general formula M X Mo 6 S 8-Y (where X is 0 ≦ X ≦ 4, Y is 0 ≦ Y represents a numerical value in the range of Y ≦ 1, and M represents at least one transition metal), activated carbon, activated carbon fiber, and the like. Examples of the vanadium oxide include those represented by V 2 O 5 , V 6 O 13 , V 2 O 4 , and V 3 O 8 .
リチウム含有遷移金属酸化物はリチウムと遷移金属との複合酸化物であり、リチウムと２種類以上の遷移金属を固溶したものであってもよい。複合酸化物は単独で使用しても、２種類以上を組合わせて使用してもよい。リチウム含有遷移金属酸化物は、具体的には、ＬｉＭ1 1-XＭ2 X Ｏ2 （式中Ｘは０≦Ｘ≦１の範囲の数値であり、Ｍ1 、Ｍ2 は少なくとも一種の遷移金属元素である）またはＬｉＭ1 1-YＭ2 Y Ｏ4 （式中Ｙは０≦Ｙ≦１の範囲の数値であり、Ｍ1 、Ｍ2 は少なくとも一種の遷移金属元素である）で示される。式中Ｍ1 、Ｍ2 で示される遷移金属はＣｏ、Ｎｉ、Ｍｎ、Ｃｒ、Ｔｉ、Ｖ、Ｆｅ、Ｚｎ、Ａｌ、Ｉｎ、Ｓｎなどである。好ましいのはＣｏ、Ｍｎ、Ｃｒ、Ｔｉ、Ｖ、Ｆｅ、Ａｌなどである。具体例はＬｉＣｏＯ2 、ＬｉＮｉＯ2 、ＬｉＭｎＯ2 、ＬｉＮｉ0.9 Ｃｏ0.1 Ｏ2 、 ＬｉＮｉ0.5 Ｃｏ0.5 Ｏ2 などである。 The lithium-containing transition metal oxide is a composite oxide of lithium and a transition metal, and may be a solid solution of lithium and two or more transition metals. The composite oxide may be used alone or in combination of two or more. Specifically, the lithium-containing transition metal oxide is LiM 1 1-X M 2 X O 2 (where X is a numerical value in the range of 0 ≦ X ≦ 1, and M 1 and M 2 are at least one kind of transition. A metal element) or LiM 1 1-Y M 2 Y O 4 (where Y is a numerical value in the range of 0 ≦ Y ≦ 1, and M 1 and M 2 are at least one transition metal element) It is. In the formula, transition metals represented by M 1 and M 2 are Co, Ni, Mn, Cr, Ti, V, Fe, Zn, Al, In, Sn, and the like. Preferred are Co, Mn, Cr, Ti, V, Fe, Al and the like. Specific examples include LiCoO 2 , LiNiO 2 , LiMnO 2 , LiNi 0.9 Co 0.1 O 2 , LiNi 0.5 Co 0.5 O 2 and the like.
また、リチウム含有遷移金属酸化物は、例えば、リチウム、遷移金属の酸化物、塩類などを出発原料とし、これら出発原料を所望の金属酸化物の組成に応じて混合し、酸素雰囲気下６００〜１０００℃の温度で焼成することにより得ることができる。なお、出発原料は酸化物および塩類に限定されず、水酸化物などであってもよい。 The lithium-containing transition metal oxide is, for example, lithium, an oxide of transition metal, salts and the like as starting materials, these starting materials are mixed according to the composition of the desired metal oxide, and 600 to 1000 in an oxygen atmosphere. It can be obtained by firing at a temperature of ° C. The starting materials are not limited to oxides and salts, and may be hydroxides.
本発明のリチウムイオン二次電池においては、正極活物質は前記のリチウム化合物を単独で使用しても、２種類以上併用してもよい。また、正極中に炭酸リチウムなどの炭酸アルカリ塩を添加することもできる。 In the lithium ion secondary battery of the present invention, as the positive electrode active material, the above lithium compounds may be used alone or in combination of two or more. Further, an alkali carbonate such as lithium carbonate can be added to the positive electrode.
正極は、例えば、前記リチウム化合物と結合剤、および正極に導電性を付与するための導電剤よりなる正極合剤を、集電体の片面または両面に塗布して正極合剤層を形成して作製される。結合剤としては、負極の作製に使用されるものと同じものが使用可能である。導電剤としては、黒鉛やカーボンブラックなどの炭素材料が使用される。 The positive electrode is formed by, for example, applying a positive electrode mixture composed of the lithium compound, a binder, and a conductive agent for imparting conductivity to the positive electrode on one or both sides of the current collector to form a positive electrode mixture layer. Produced. As the binder, the same one as that used for producing the negative electrode can be used. As the conductive agent, a carbon material such as graphite or carbon black is used.
正極も負極と同様に、正極合剤を溶剤中に分散させペースト状にし、このペースト状の正極合剤を集電体に塗布、乾燥して正極合剤層を形成してもよく、正極合剤層を形成した後、さらにプレス加圧等の圧着を行ってもよい。これにより正極合剤層が均一且つ強固に集電体に接着される。
集電体の形状は特に限定されないが、箔状またはメッシュ、エキスパンドメタルなどの網状等のものが用いられる。集電体の材質はアルミニウム、ステンレス、ニッケルなどである。その厚さは１０〜４０μｍのものが好適である。
Similarly to the negative electrode, the positive electrode mixture may be formed in a paste by dispersing the positive electrode mixture in a solvent, and the paste-like positive electrode mixture may be applied to a current collector and dried to form a positive electrode mixture layer. After forming the agent layer, pressure bonding such as press pressing may be further performed. As a result, the positive electrode mixture layer is uniformly and firmly bonded to the current collector.
The shape of the current collector is not particularly limited, and a foil shape or a mesh shape such as a mesh or expanded metal is used. The current collector is made of aluminum, stainless steel, nickel, or the like. The thickness is preferably 10 to 40 μm.
（非水電解質）
本発明のリチウムイオン二次電池に用いられる非水電解質としては、通常の非水電解液に使用される電解質塩であり、ＬｉＰＦ6 、ＬｉＢＦ4 、ＬｉＡｓＦ6 、ＬｉＣｌＯ4 、ＬｉＢ（Ｃ6 Ｈ5 ）、ＬｉＣｌ、ＬｉＢｒ、ＬｉＣＦ3 ＳＯ3 、ＬｉＣＨ3 ＳＯ3 、ＬｉＮ（ＣＦ3 ＳＯ2 ）2 、ＬｉＣ（ＣＦ3 ＳＯ2 ）3 、ＬｉＮ（ＣＦ3 ＣＨ2 ＯＳＯ2 ）2 、ＬｉＮ（ＣＦ3 ＣＦ2 ＯＳＯ2 ）2 、ＬｉＮ（ＨＣＦ2 ＣＦ2 ＣＨ2 ＯＳＯ2 ）2 、ＬｉＮ（（ＣＦ3 ）2 ＣＨＯＳＯ2 ）2 、ＬｉＢ［｛Ｃ6 Ｈ3 （ＣＦ3 ）2 ｝］4 、ＬｉＡｌＣｌ4 、ＬｉＳｉＦ6 などのリチウム塩が挙げられる。特に、ＬｉＰＦ6 、ＬｉＢＦ4 が酸化安定性の点から好ましい。
電解液中の電解質塩濃度は０．１〜５mol /lが好ましく、０．５〜３．０mol/l がより好ましい。
(Nonaqueous electrolyte)
The non-aqueous electrolyte used in the lithium ion secondary battery of the present invention, an electrolyte salt used in the
The electrolyte salt concentration in the electrolytic solution is preferably from 0.1 to 5 mol / l, more preferably from 0.5 to 3.0 mol / l.
非水電解質は液状の非水電解質としてもよいし、固体電解質またはゲル電解質などの高分子電解質としてもよい。前者の場合、非水電解質電池は、いわゆるリチウムイオン二次電池として構成され、後者の場合は、非水電解質電池は高分子固体電解質、高分子ゲル電解質電池などの高分子電解質電池として構成される。 The non-aqueous electrolyte may be a liquid non-aqueous electrolyte or a polymer electrolyte such as a solid electrolyte or a gel electrolyte. In the former case, the non-aqueous electrolyte battery is configured as a so-called lithium ion secondary battery, and in the latter case, the non-aqueous electrolyte battery is configured as a polymer electrolyte battery such as a polymer solid electrolyte or a polymer gel electrolyte battery. .
非水電解質液を調製するための溶媒としてエチレンカーボネート、プロピレンカーボネート、ジメチルカーボネート、ジエチルカーボネートなどのカーボネート、１，１−または１，２−ジメトキシエタン、１，２−ジエトキシエタン、テトラヒドロフラン、２−メチルテトラヒドロフラン、γ−ブチロラクトン、１，３−ジオキソラン、４−メチル−1 ，３−ジオキソラン、アニソール、ジエチルエーテルなどのエーテル、スルホラン、メチルスルホランなどのチオエーテル、アセトニトリル、クロロニトリル、プロピオニトリルなどのニトリル、ホウ酸トリメチル、ケイ酸テトラメチル、ニトロメタン、ジメチルホルムアミド、Ｎ−メチルピロリドン、酢酸エチル、トリメチルオルトホルメート、ニトロベンゼン、塩化ベンゾイル、臭化ベンゾイル、テトラヒドロチオフェン、ジメチルスルホキシド、３−メチル−２−オキサゾリドン、エチレングリコール、サルファイト、ジメチルサルファイトなどの非プロトン性有機溶媒を用いることができる。 As a solvent for preparing the non-aqueous electrolyte solution, carbonates such as ethylene carbonate, propylene carbonate, dimethyl carbonate, and diethyl carbonate, 1,1- or 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 2- Methyltetrahydrofuran, γ-butyrolactone, 1,3-dioxolane, 4-methyl-1,3-dioxolane, ethers such as anisole and diethyl ether, thioethers such as sulfolane and methylsulfolane, nitriles such as acetonitrile, chloronitrile and propionitrile , Trimethyl borate, tetramethyl silicate, nitromethane, dimethylformamide, N-methylpyrrolidone, ethyl acetate, trimethylorthoformate, nitrobenzene, benzoyl chloride, benzene Aprotic organic solvents such as nzoyl, tetrahydrothiophene, dimethyl sulfoxide, 3-methyl-2-oxazolidone, ethylene glycol, sulfite, and dimethyl sulfite can be used.
非水電解質を高分子固体電解質または高分子ゲル電解質などの高分子電解質とする場合には、マトリクスとして可塑剤（非水電解液）でゲル化された高分子を用いる。該マトリクスを構成する高分子としては、ポリエチレンオキサイドやその架橋体などのエーテル系高分子化合物、ポリメタクリレート系高分子化合物、ポリアクリレート系高分子化合物、ポリビニリデンフルオライドやビニリデンフルオライド−ヘキサフルオロプロピレン共重合体などのフッ素系高分子化合物などが特に好ましい。 When the nonaqueous electrolyte is a polymer electrolyte such as a polymer solid electrolyte or a polymer gel electrolyte, a polymer gelled with a plasticizer (nonaqueous electrolyte) is used as a matrix. Examples of the polymer constituting the matrix include ether-based polymer compounds such as polyethylene oxide and crosslinked products thereof, polymethacrylate-based polymer compounds, polyacrylate-based polymer compounds, polyvinylidene fluoride, and vinylidene fluoride-hexafluoropropylene. Particularly preferred are fluorine-based polymer compounds such as copolymers.
前記高分子固体電解質または高分子ゲル電解質には、可塑剤が配合されるが、可塑剤としては、前記の電解質塩や非水溶媒が使用可能である。高分子ゲル電解質の場合、可塑剤である非水電解液中の電解質塩濃度は０．１〜５mol /lが好ましく、０．５〜２．０mol /lがより好ましい。 A plasticizer is blended in the polymer solid electrolyte or the polymer gel electrolyte. As the plasticizer, the electrolyte salt and the non-aqueous solvent can be used. In the case of a polymer gel electrolyte, the concentration of the electrolyte salt in the nonaqueous electrolytic solution that is a plasticizer is preferably 0.1 to 5 mol / l, and more preferably 0.5 to 2.0 mol / l.
高分子固体電解質の作製方法は特に限定されないが、例えば、マトリクスを構成する高分子化合物、リチウム塩および非水溶媒（可塑剤）を混合し、加熱して高分子化合物を溶融する方法、有機溶剤に高分子化合物、リチウム塩、および非水溶媒（可塑剤）を溶解させた後、混合用有機溶剤を蒸発させる方法、重合性モノマー、リチウム塩および非水溶媒（可塑剤）を混合し、混合物に紫外線、電子線または分子線などを照射して、重合性モノマーを重合させ、ポリマーを得る方法などを挙げることができる。
前記固体電解質中の非水溶媒（可塑剤）の割合は１０〜９０質量％が好ましく、３０〜８０質量％がより好ましい。１０質量％未満であると導電率が低くなり、９０質量％を超えると機械的強度が弱くなり、成膜しにくくなる。
The method for producing the polymer solid electrolyte is not particularly limited. For example, a method of mixing a polymer compound constituting a matrix, a lithium salt, and a nonaqueous solvent (plasticizer) and heating to melt the polymer compound, an organic solvent A method in which a polymer compound, a lithium salt, and a non-aqueous solvent (plasticizer) are dissolved in, and an organic solvent for mixing is evaporated, a polymerizable monomer, a lithium salt, and a non-aqueous solvent (plasticizer) are mixed, and the mixture is mixed Examples thereof include a method of polymerizing a polymerizable monomer by irradiating an ultraviolet ray, an electron beam, a molecular beam or the like to obtain a polymer.
10-90 mass% is preferable, and, as for the ratio of the nonaqueous solvent (plasticizer) in the said solid electrolyte, 30-80 mass% is more preferable. If it is less than 10% by mass, the electrical conductivity will be low, and if it exceeds 90% by mass, the mechanical strength will be weak and film formation will be difficult.
（セパレータ）
本発明のリチウムイオン二次電池においては、セパレータを使用することもできる。
セパレータの材質は特に限定されるものではないが、例えば織布、不織布、合成樹脂製微多孔膜などが挙げられる。合成樹脂製微多孔膜が好適であるが、なかでもポリオレフィン系微多孔膜が、厚さ、膜強度、膜抵抗の面で好適である。具体的には、ポリエチレンおよびポリプロピレン製微多孔膜、またはこれらを複合した微多孔膜等である。
(Separator)
In the lithium ion secondary battery of the present invention, a separator can also be used.
Although the material of a separator is not specifically limited, For example, a woven fabric, a nonwoven fabric, a synthetic resin microporous film, etc. are mentioned. A synthetic resin microporous membrane is preferred, and among them, a polyolefin microporous membrane is preferred in terms of thickness, membrane strength, and membrane resistance. Specifically, it is a microporous membrane made of polyethylene and polypropylene, or a microporous membrane that combines these.
（リチウムイオン二次電池）
ゲル電解質二次電池は、前記黒鉛質粒子を含有する負極と、正極およびゲル電解質を、例えば、負極、ゲル電解質、正極の順で積層し、電池の外装材内に収容することで構成される。さらには、負極と正極の外側にゲル電解質を配するようにしてもよい。本発明の負極材料を負極に用いるゲル電解質二次電池では、ゲル電解質にプロピレンカーボネートが含有された場合でも、第１サイクルにおける不可逆な容量が小さく抑えられる。
さらに、本発明のリチウムイオン二次電池の構造は特に限定されず、その形状、形態について特に限定されるものではなく、用途、搭載機器、要求される充放電容量などに応じて、円筒型、角型、コイン型、ボタン型などの中から任意に選択することができる。より安全性の高い密閉型非水電解液電池を得るためには、過充電などの異常時に電池内圧上昇を感知して電流を遮断させる手段を備えたものであることが好ましい。高分子固体電解質電池や高分子ゲル電解質電池の場合には、ラミネートフィルムに封入した構造とすることもできる。
(Lithium ion secondary battery)
The gel electrolyte secondary battery is configured by laminating the negative electrode containing the graphite particles, the positive electrode, and the gel electrolyte in the order of, for example, the negative electrode, the gel electrolyte, and the positive electrode, and accommodating them in the battery exterior material. . Furthermore, a gel electrolyte may be disposed outside the negative electrode and the positive electrode. In the gel electrolyte secondary battery using the negative electrode material of the present invention for the negative electrode, the irreversible capacity in the first cycle can be kept small even when propylene carbonate is contained in the gel electrolyte.
Furthermore, the structure of the lithium ion secondary battery of the present invention is not particularly limited, and the shape and form thereof are not particularly limited, and depending on the application, mounted equipment, required charge / discharge capacity, etc., a cylindrical type, A square shape, a coin shape, a button shape, or the like can be arbitrarily selected. In order to obtain a sealed nonaqueous electrolyte battery with higher safety, it is preferable to include a means for detecting an increase in the internal pressure of the battery and shutting off the current when there is an abnormality such as overcharging. In the case of a polymer solid electrolyte battery or a polymer gel electrolyte battery, a structure enclosed in a laminate film can also be used.
高分子ゲル電解質を用いたリチウムイオン二次電池は、本発明の負極材料を用いてなる負極と、正極およびゲル電解質から構成される。例えば、負極、ゲル電解質、正極の順に積層し、電池外装材内に収容することで作製される。なお、これに加えて、さらに、負極と正極の外側にゲル電解質を配するようにしてもよい。本発明の負極材料を用いる高分子ゲル電解質電池においては、ゲル電解質にプロピレンカーボネートを含有させることもできる。 A lithium ion secondary battery using a polymer gel electrolyte is composed of a negative electrode using the negative electrode material of the present invention, a positive electrode and a gel electrolyte. For example, it is produced by laminating a negative electrode, a gel electrolyte, and a positive electrode in this order, and accommodating them in a battery exterior material. In addition, in addition to this, a gel electrolyte may be arranged outside the negative electrode and the positive electrode. In the polymer gel electrolyte battery using the negative electrode material of the present invention, the gel electrolyte can also contain propylene carbonate.
さらに、本発明のリチウムイオン二次電池の構造は任意であり、その形状、形態について特に限定されるものではなく、円筒型、角型、コイン型、ボタン型などの中から任意に選択することができる。より安全性の高い密閉型非水電解液電池を得るためには、過充電などの異常時に電池内圧上昇を感知して電流を遮断させる手段を備えたものであることが好ましい。ゲル電解質を用いた電池の場合には、ラミネートフィルムに封入した構造とすることもできる。 Furthermore, the structure of the lithium ion secondary battery of the present invention is arbitrary, and the shape and form thereof are not particularly limited, and can be arbitrarily selected from a cylindrical shape, a square shape, a coin shape, a button shape, and the like. Can do. In order to obtain a sealed nonaqueous electrolyte battery with higher safety, it is preferable to include a means for detecting an increase in the internal pressure of the battery and shutting off the current when there is an abnormality such as overcharging. In the case of a battery using a gel electrolyte, a structure enclosed in a laminate film can also be used.
次に本発明を実施例により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。また以下の実施例および比較例では、図１に示すように、黒鉛質物を含有する作用電極（負極）２とリチウム箔よりなる対極（正極）４から構成される単極評価用のボタン型二次電池を作製して評価した。実電池は、本発明の概念に基づき、公知の方法に準じて作製することができる。
なお、負極材料の平均粒子径はレーザー回折式粒度分布計により測定し、粒度分布の累積度数が体積百分率で５０％となる粒子径とした。
黒鉛質物粒子の比表面積はＢＥＴ法により測定した。
黒鉛質物粒子のＸ線広角回折による（００２）面の平均格子面間隔は前述したＸ線広角回折法により求めた。
黒鉛質物粒子の起毛部（突起）の長軸長と短軸長およびアスペクト比は２００００倍の走査型電子顕微鏡観察により求めた、任意の１００箇所の長軸長と短軸長の平均値である。アスペクト比は長軸長（平均値）と短軸長（平均値）との比である。
金属シリコン被膜の厚みは透過型電子顕微鏡観察により求めた。
EXAMPLES Next, although an Example demonstrates this invention concretely, this invention is not limited to these Examples. Further, in the following examples and comparative examples, as shown in FIG. 1, a button type two for single electrode evaluation composed of a working electrode (negative electrode) 2 containing a graphite material and a counter electrode (positive electrode) 4 made of lithium foil. Next batteries were fabricated and evaluated. An actual battery can be produced according to a known method based on the concept of the present invention.
The average particle size of the negative electrode material was measured with a laser diffraction particle size distribution meter, and the particle size was such that the cumulative frequency of the particle size distribution was 50% by volume.
The specific surface area of the graphite particles was measured by the BET method.
The average lattice spacing on the (002) plane by X-ray wide angle diffraction of the graphite particles was determined by the X-ray wide angle diffraction method described above.
The major axis length, minor axis length, and aspect ratio of the raised portions (protrusions) of the graphite particles are average values of major axis lengths and minor axis lengths at arbitrary 100 positions obtained by observation with a scanning electron microscope of 20000 times. . The aspect ratio is the ratio of the major axis length (average value) to the minor axis length (average value).
The thickness of the metal silicon coating was determined by observation with a transmission electron microscope.
〔実施例１〕
（黒鉛質物の作製）
高純度酸化第二鉄を固定床流通式反応装置に充填し、常圧、５５０℃で高純度酸化第二鉄１ｇ当たり３００sccmのＣＯおよび１５sccmの水素を流通して、下記式（Ｉ）に示す反応を生じさせ、高純度酸化第二鉄１ｇ当たり３０ｇの気相成長炭素繊維を得た。平均直径は１２０ｎｍ、アスペクト比は３０であった。
２ＣＯ → Ｃ ＋ ＣＯ2 （Ｉ）
該気相成長炭素繊維５０質量部に、コールタールピッチ５０質量部を加え、１５０℃で１時間混練後、不活性ガス雰囲気下６００℃で１０時間熱処理し、冷却後粉砕した。得られた気相成長炭素繊維の集合体を黒鉛坩堝に充填し、該坩堝の周囲にコークスブリーズを充填して３０００℃で５時間加熱し、黒鉛化処理した。得られた黒鉛質物は平均粒子径１０μｍ、Ｘ線広角回折による（００２）面の面間隔ｄ002 が０．３３６６ｎｍであった。走査型電子顕微鏡観察から外観は球状に近い粒子であるが、繊維が絡み合った構造であり、表面が起毛していることが確認された。該黒鉛質物の比表面積は２０m2/gであった。
[Example 1]
(Production of graphite material)
High purity ferric oxide is charged into a fixed bed flow reactor, and 300 sccm of CO and 15 sccm of hydrogen per gram of high purity ferric oxide are circulated at normal pressure and 550 ° C., as shown in the following formula (I) Reaction was caused to obtain 30 g of vapor grown carbon fiber per 1 g of high purity ferric oxide. The average diameter was 120 nm and the aspect ratio was 30.
2CO → C + CO 2 (I)
50 parts by mass of coal tar pitch was added to 50 parts by mass of the vapor-grown carbon fiber, kneaded at 150 ° C. for 1 hour, heat-treated at 600 ° C. for 10 hours in an inert gas atmosphere, cooled and pulverized. The obtained vapor-grown carbon fiber aggregate was filled in a graphite crucible, coke breeze was filled around the crucible, and heated at 3000 ° C. for 5 hours for graphitization. Obtained graphite pledge average particle size 10 [mu] m, surface spacing d 002 of the X-ray wide angle diffraction (002) plane was 0.3366Nm. From the observation with a scanning electron microscope, it was confirmed that the appearance was a nearly spherical particle, but the fiber was intertwined and the surface was raised. The specific surface area of the graphite was 20 m 2 / g.
（金属の被覆）
ＤＣ二極スパッタリング装置のアノード側ステージに前記黒鉛質物を配置し、カソード側に９９．９９９％の単結晶シリコンターゲットを配置して、圧力０．５Ｐａ、電圧６００Ｖ、電流０．５Ａの条件でスパッタリングを２時間行った後、黒鉛質物を攪拌した。再び上記と同じ条件でスパッタリングを２時間行い、攪拌を繰返した。その後、さらに、同様なスパッタリングを２時間行った。
黒鉛質物の表面に付着した金属シリコンについて、Ｘ線回折法による解析から、ほぼ全量が非晶性シリコンであることが確認された。発光分光分析による非晶性シリコンの付着量は１０．３質量％であった。黒鉛質物と非晶性シリコンの密度は、それぞれ２．２５５g/cm3 、２．３２g/cm3 であった。これから非晶性シリコンは１０体積％と換算された。
(Metal coating)
Sputtering under the conditions of pressure 0.5 Pa, voltage 600 V, current 0.5 A by placing the graphite material on the anode side stage of a DC bipolar sputtering apparatus and a 99.999% single crystal silicon target on the cathode side. For 2 hours, and then the graphite material was stirred. Again, sputtering was performed for 2 hours under the same conditions as described above, and stirring was repeated. Thereafter, similar sputtering was further performed for 2 hours.
As for the metal silicon adhering to the surface of the graphite material, it was confirmed from the analysis by the X-ray diffraction method that almost all the amount was amorphous silicon. The amount of amorphous silicon deposited by emission spectroscopic analysis was 10.3% by mass. The density of the graphite pledge and amorphous silicon, respectively 2.255g / cm 3, was 2.32 g / cm 3. From this, amorphous silicon was converted to 10% by volume.
得られた負極材料についての走査型電子顕微鏡による目視観察では、非晶性シリコン付着前の黒鉛質物と外観上の変化は認められず、非晶性シリコンがナノスケールの薄膜状で黒鉛質物の外表面に付着していることが示唆された。また、透過型電子顕微鏡を用いて、負極材料の外表面の一部を観察した結果、黒鉛質物の起毛部に部分的に膜状に非晶性シリコンが被覆している様子が認められた。起毛部における非晶性シリコン被覆の厚みは２０箇所の平均値として５０ｎｍであった。
該負極材料の特性（黒鉛質物の平均粒子径、比表面積、結晶性；起毛部の長軸長、短軸長、アスペクト比；非晶性シリコンの被覆量）を表１に示した。走査型電子顕微鏡写真（倍率１０００倍および１００００倍）を図２および図３に示した。図２および図３において、８は粒状黒鉛質物、９は起毛部を示す。
Visual observation of the obtained negative electrode material with a scanning electron microscope showed no change in appearance from the appearance of the graphite material before adhering to the amorphous silicon, and the amorphous silicon was in the form of a nanoscale thin film and the outside of the graphite material. It was suggested that it adhered to the surface. Further, as a result of observing a part of the outer surface of the negative electrode material using a transmission electron microscope, it was found that the amorphous silicon was partially covered in a film shape on the raised portion of the graphite material. The thickness of the amorphous silicon coating in the raised portion was 50 nm as an average value of 20 locations.
Table 1 shows the characteristics of the negative electrode material (average particle diameter, specific surface area, crystallinity of the graphite material; major axis length, minor axis length, aspect ratio of the brushed portion; covering amount of amorphous silicon). Scanning electron micrographs (magnification 1000 times and 10,000 times) are shown in FIGS. 2 and 3, 8 indicates a granular graphite material, and 9 indicates a raised portion.
(作用電極（負極）の作製）
メソフェーズ小球体の黒鉛質物（球状、平均粒子径２８μｍ、比表面積０．５m2/g、Ｘ線広角回折による（００２）面の面間隔ｄ002 が０．３３６２ｎｍ）と前記の負極材料を同一質量で混合し、これに４質量％の結合剤ポリフッ化ビニリデンを混合し、さらに、溶剤Ｎ−メチルピロリドンを加え、有機溶剤系負極合剤ペーストを作製した。これを銅箔上に均一な厚さに塗布し、さらに真空中９０℃で溶剤を揮発させて乾燥した。次に、この銅箔上に塗布された負極合剤をハンドプレスによって加圧した。さらに直径１５．５ｍｍの円形状に打抜くことで、集電体銅箔（厚み１６μｍ）に密着した負極合剤層（厚み５０μｍ）からなる作用電極（負極）を作製した。
(Production of working electrode (negative electrode))
Mesophase spherulitic graphite (spherical, average particle size 28 μm, specific surface area 0.5 m 2 / g, (002) plane spacing d 002 of 0.3362 nm by X-ray wide angle diffraction) and the above negative electrode material have the same mass The mixture was mixed with 4% by mass of binder polyvinylidene fluoride, and the solvent N-methylpyrrolidone was further added to prepare an organic solvent-based negative electrode mixture paste. This was applied to the copper foil to a uniform thickness, and further the solvent was volatilized at 90 ° C. in a vacuum and dried. Next, the negative electrode mixture applied on the copper foil was pressurized by a hand press. Furthermore, the working electrode (negative electrode) which consists of a negative mix layer (thickness 50 micrometers) closely_contact | adhered to collector copper foil (thickness 16 micrometers) was produced by punching in circular shape of diameter 15.5mm.
(対極（正極）の作製）
リチウム金属箔をニッケルネットに押付け、直径１５．５ｍｍの円形状に打抜いて、ニッケルネットからなる集電体と、該集電体に密着したリチウム金属箔（厚み０．５ｍｍ）からなる対極（正極）を作製した。
(Preparation of counter electrode (positive electrode))
A lithium metal foil is pressed onto a nickel net and punched into a circular shape with a diameter of 15.5 mm, and a current collector made of nickel net and a counter electrode made of a lithium metal foil (thickness 0.5 mm) in close contact with the current collector ( Positive electrode) was prepared.
（電解液、セパレータの作製）
エチレンカーボネート３３mol%−メチルエチルカーボネート６７mol%の混合溶剤に、ＬｉＰＦ6 を１mol/dm3 となる濃度で溶解させ、非水電解液を調製した。得られた非水電解液をポリプロピレン多孔質体（厚み２０μｍ）に含浸させ、電解液が含浸したセパレータを作製した。
(Production of electrolyte and separator)
LiPF 6 was dissolved at a concentration of 1 mol / dm 3 in a mixed solvent of ethylene carbonate 33 mol% -methyl ethyl carbonate 67 mol% to prepare a non-aqueous electrolyte. The obtained nonaqueous electrolytic solution was impregnated into a polypropylene porous body (thickness 20 μm) to produce a separator impregnated with the electrolytic solution.
（評価電池の作製）
評価電池として図１に示すボタン型二次電池を作製した。
外装カップ１と外装缶３は、その周縁部において絶縁ガスケット６を介在させ、両周縁部をかしめて密閉した。その内部に外装缶３の内面から順に、ニッケルネットからなる集電体７ａ、リチウム箔よりなる円筒状の対極（正極）４、電解液が含浸されたセパレータ５、負極合剤からなる円盤状の作用電極（負極）２および銅箔からなる集電体７ｂが積層された電池系である。
評価電池は電解液を含浸させたセパレータ５を集電体７ｂに密着した作用電極２と、集電体７ａに密着した対極４との間に挟んで積層した後、作用電極２を外装カップ１内に、対極４を外装缶３内に収容して、外装カップ１と外装缶３とを合わせ、さらに、外装カップ１と外装缶３との周縁部に絶縁ガスケット６を介在させ、両周縁部をかしめて密閉して作製した。
評価電池は実電池において負極用活物質として使用可能な黒鉛質物粒子を含有する作用電極２と、リチウム金属箔とからなる対極４とから構成される電池である。
(Production of evaluation battery)
A button-type secondary battery shown in FIG. 1 was prepared as an evaluation battery.
The
The evaluation battery was laminated by sandwiching the separator 5 impregnated with the electrolytic solution between the working
The evaluation battery is a battery composed of a working
前記のように作製された評価電池について、２５℃の温度下で下記のような充放電試験を行い、初期充放電効率とサイクル特性を計算した。評価結果（放電容量、初期充放電効率とサイクル特性）を表１に示した。
（初期充放電効率）
回路電圧が０ｍＶに達するまで０．９ｍＡの定電流充電を行った後、回路電圧が０ｍＶに達した時点で定電圧充電に切替え、さらに電流値が２０μＡになるその間の通電量から充電容量を求めた。その後、１２０分間休止した。次に０．９ｍＡの電流値で回路電圧が１．５Ｖに達するまで定電流放電を行い、この間の通電量から放電容量を求めた。これを第１サイクルとした。次式（II）から初期充放電効率を計算した。なおこの試験では、リチウムイオンを負極材料に吸蔵する過程を充電、負極材料からリチウムイオンが脱離する過程を放電とした。
初期充放電効率（％）＝（第１サイクルの放電容量／第１サイクルの充電容量）
×１００ （II）
The evaluation battery produced as described above was subjected to the following charge / discharge test at a temperature of 25 ° C., and the initial charge / discharge efficiency and cycle characteristics were calculated. The evaluation results (discharge capacity, initial charge / discharge efficiency and cycle characteristics) are shown in Table 1.
(Initial charge / discharge efficiency)
After constant current charging of 0.9 mA until the circuit voltage reaches 0 mV, switching to constant voltage charging when the circuit voltage reaches 0 mV, and the charge capacity is obtained from the amount of current during which the current value reaches 20 μA. It was. Then, it rested for 120 minutes. Next, constant current discharge was performed until the circuit voltage reached 1.5 V at a current value of 0.9 mA, and the discharge capacity was determined from the amount of electricity supplied during this period. This was the first cycle. The initial charge / discharge efficiency was calculated from the following formula (II). In this test, the process of occluding lithium ions in the negative electrode material was charged, and the process of detaching lithium ions from the negative electrode material was discharge.
Initial charge / discharge efficiency (%) = (first cycle discharge capacity / first cycle charge capacity)
× 100 (II)
（サイクル特性）
引き続き、回路電圧が０ｍＶに達するまで４．０ｍＡの定電流充電を行った後、回路電圧が０ｍＶに達した時点で定電圧充電に切替え、さらに電流値が２０μＡになるまで充電を続けた後、１２０分間休止した。次に４．０ｍＡの電流値で回路電圧が１．５Ｖに達するまで定電流放電を行った。この充放電を２０回繰返し、得られた放電容量から、次式 (III) を用いてサイクル特性を計算した。
サイクル特性（％）＝（第２０サイクルにおける放電容量／第１サイクルにおける 放電容量）×１００ (III)
(Cycle characteristics)
Subsequently, after performing constant current charging of 4.0 mA until the circuit voltage reaches 0 mV, switching to constant voltage charging when the circuit voltage reaches 0 mV, and further continuing charging until the current value reaches 20 μA, Paused for 120 minutes. Next, constant current discharge was performed until the circuit voltage reached 1.5 V at a current value of 4.0 mA. This charging / discharging was repeated 20 times, and the cycle characteristics were calculated from the obtained discharge capacity using the following formula (III).
Cycle characteristics (%) = (discharge capacity in 20th cycle / discharge capacity in 1st cycle) × 100 (III)
（実施例２〜４）
実施例１において、スパッタリングの回数を変更して非晶性シリコン薄膜の厚み（被覆量）、およびメソフェーズ小球体の混合割合を表１に示すように変える以外は、実施例１と同様に負極合剤の調製、負極の作製、リチウムイオン二次電池の作製および電池の評価を行った。該負極材料の特性と評価結果を表１に示した。
(Examples 2 to 4)
In Example 1, except for changing the number of times of sputtering and changing the thickness (coating amount) of the amorphous silicon thin film and the mixing ratio of the mesophase spherules as shown in Table 1, the negative electrode composition was the same as in Example 1. Preparation of the agent, preparation of the negative electrode, preparation of the lithium ion secondary battery, and evaluation of the battery were performed. The characteristics and evaluation results of the negative electrode material are shown in Table 1.
実施例１〜４から、本発明の負極材料を用いたリチウムイオン二次電池は優れた放電容量、初期充放電効率およびサイクル特性を有していることがわかる。また、負極材料中の非晶性シリコンの割合が多い場合には、初期充放電効率およびサイクル特性が低下し、非晶性シリコンの含有量が少ない場合には、放電容量が低下する傾向にあることがわかる。 Examples 1-4 show that the lithium ion secondary battery using the negative electrode material of the present invention has excellent discharge capacity, initial charge / discharge efficiency, and cycle characteristics. In addition, when the proportion of amorphous silicon in the negative electrode material is large, the initial charge / discharge efficiency and cycle characteristics decrease, and when the content of amorphous silicon is small, the discharge capacity tends to decrease. I understand that.
（比較例１）
実施例１において、気相成長炭素繊維の黒鉛質物をメソフェーズ小球体の黒鉛質物に代え、混合用のメソフェーズ小球体の黒鉛質物を混合せずに、かつスパッタリング時間を１時間に変えて、計３回スパッタリングし、非晶性シリコンを被覆した。前記以外は、実施例１と同様に負極合剤の調製、負極の作製、リチウムイオン二次電池の作製および電池の評価を行った。該負極材料の特性と評価結果を表１に示した。
実施例２と比較例１との対比から、非晶性シリコンの被着体である黒鉛質物が起毛していない比較例１の場合には、初期充放電効率およびサイクル特性が劣ることがわかる。
(Comparative Example 1)
In Example 1, the graphite material of vapor grown carbon fiber was replaced with the graphite material of mesophase spherules, the mixing of the mesophase spheroid graphite material for mixing was not performed, and the sputtering time was changed to 1 hour for a total of 3 Sputtered twice and coated with amorphous silicon. Except for the above, preparation of the negative electrode mixture, preparation of the negative electrode, preparation of the lithium ion secondary battery, and evaluation of the battery were performed in the same manner as in Example 1. The characteristics and evaluation results of the negative electrode material are shown in Table 1.
From the comparison between Example 2 and Comparative Example 1, it can be seen that in the case of Comparative Example 1 in which the graphite material that is the adherend of amorphous silicon is not raised, the initial charge / discharge efficiency and the cycle characteristics are inferior.
（比較例２）
実施例１に用いた混合用のメソフェーズ小球体黒鉛質物と、非晶性シリコン粒子（平均粒子径２μｍ）を体積比で９５：５となるように計量した。これらをボールミルに投入し、剪断加工処理を３時間行い、それぞれの粒子形状を保持したまま、メソフェーズ小球体黒鉛質物の表面に非晶性シリコン粒子が付着した複合粒子を得た。この複合粒子について、実施例１と同様に、負極合剤の調製、負極の作製、リチウムイオン二次電池の作製および電池の評価を行った。該負極材料の特性と評価結果を表１に示した。
実施例２と比較例２との対比から、非晶性シリコンの被着体である黒鉛質物が起毛しておらず、かつ非晶性シリコンが粒子のまま黒鉛質物に付着した負極材料の比較例２の場合には、放電容量、初期充放電効率およびサイクル特性のいずれもが劣ることがわかる。
(Comparative Example 2)
The mesophase small spherical graphite material for mixing used in Example 1 and amorphous silicon particles (
From a comparison between Example 2 and Comparative Example 2, a comparative example of a negative electrode material in which the graphite material which is an adherend of amorphous silicon is not raised and the amorphous silicon is adhered to the graphite material as particles. In the case of 2, it turns out that all of discharge capacity, initial stage charge / discharge efficiency, and cycling characteristics are inferior.
本発明のリチウムイオン二次電池用負極材料は、その特性を活かして、小型から大型までの高性能リチウムイオン二次電池に使用することができる。 The negative electrode material for lithium ion secondary batteries of the present invention can be used for high performance lithium ion secondary batteries ranging from small to large, taking advantage of the characteristics.
１ 外装カップ
２ 作用電極
３ 外装缶
４ 対極
５ 電解質溶液含浸セパレータ
６ 絶縁ガスケット
７ａ，７ｂ 集電体
８ 粒状黒鉛質物
９ 起毛部
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| PCT/JP2004/014301 WO2005031898A1 (en) | 2003-09-26 | 2004-09-22 | Composite particle and, utilizing the same, negative electrode material for lithium ion secondary battery, negative electrode and lithium ion secondary battery |
| KR1020057010514A KR100702980B1 (en) | 2003-09-26 | 2004-09-22 | Composite particle and negative electrode material using the same, negative electrode and lithium ion secondary battery |
| TW093129041A TWI258883B (en) | 2003-09-26 | 2004-09-24 | Composite particle and negative electrode material using the same, negative electrode and lithium ion secondary battery |
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| JP2007165293A (en) * | 2005-11-16 | 2007-06-28 | Jfe Chemical Corp | Lithium-ion secondary battery anode, its manufacturing method, and lithium-ion secondary battery |
| JP5039956B2 (en) * | 2006-09-07 | 2012-10-03 | トヨタ自動車株式会社 | Negative electrode active material, negative electrode and lithium secondary battery |
| US8828481B2 (en) * | 2007-04-23 | 2014-09-09 | Applied Sciences, Inc. | Method of depositing silicon on carbon materials and forming an anode for use in lithium ion batteries |
| HUE054466T2 (en) | 2009-05-19 | 2021-09-28 | Oned Mat Inc | Nanostructured materials for battery applications |
| WO2011041468A1 (en) * | 2009-09-29 | 2011-04-07 | Georgia Tech Research Corporation | Electrodes, lithium-ion batteries, and methods of making and using same |
| US9876221B2 (en) * | 2010-05-14 | 2018-01-23 | Samsung Sdi Co., Ltd. | Negative active material for rechargeable lithium battery and rechargeable lithium battery including same |
| JP5376530B2 (en) * | 2010-11-29 | 2013-12-25 | テックワン株式会社 | Negative electrode active material, negative electrode manufacturing method, negative electrode, and secondary battery |
| JP6106870B2 (en) * | 2013-03-15 | 2017-04-05 | 国立研究開発法人物質・材料研究機構 | Electrode active material for lithium batteries |
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| JP4446415B2 (en) * | 2000-03-16 | 2010-04-07 | 日立マクセル株式会社 | Non-aqueous secondary battery negative electrode, method for producing the same, and non-aqueous secondary battery using the negative electrode |
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