JP2017212236A - Sintered body - Google Patents
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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
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Abstract
Description
本発明は、焼結体に係り、特にリチウムイオン電池等の負極材料に用いるのに好適な、安価で長寿命のリチウムイオン電池を高能率で製造することが可能な焼結体に関する。 The present invention relates to a sintered body, and more particularly, to a sintered body capable of efficiently producing an inexpensive and long-life lithium ion battery suitable for use in a negative electrode material such as a lithium ion battery.
携帯電子機器や電気自動車の普及により、リチウムイオン電池の需要が高まっている。現在、リチウムイオン電池の負極には炭素材料が用いられているが、エネルギー密度に制限がある。そこで、シリコン材料からなる負極（シリコン負極と称する）が注目されている。シリコン負極のエネルギー密度は炭素負極の５倍以上であり、電池の高容量化が可能である。 With the spread of portable electronic devices and electric vehicles, the demand for lithium ion batteries is increasing. Currently, a carbon material is used for the negative electrode of a lithium ion battery, but the energy density is limited. Therefore, a negative electrode made of a silicon material (referred to as a silicon negative electrode) has attracted attention. The energy density of the silicon negative electrode is 5 times or more that of the carbon negative electrode, and the capacity of the battery can be increased.
一般に、シリコン負極は、銅基板にシリコン薄膜を化学気相蒸着（ＣＶＤ）や物理蒸着（ＰＶＤ）するシリコン薄膜技術によって製造されている。このように形成されたシリコン薄膜の膜厚は５００ｎｍ以下であるが、シリコンの理論容量を十分に発揮して十分な導電性を得るためには、少なくとも厚さ５μｍ以上の膜厚が必要である。この導電性の問題を解決するために、金や銅等の異種金属との積層蒸着膜を作成すれば、金属が融解してシリコン蒸着膜内等に拡散し、電極特性が大幅に向上することが明らかになっている（非特許文献１）。一方で、異種金属を挟むことにより、膜厚が大きくなるにつれて膜に応力が生じ、集電体からの剥離が懸念されている。 In general, a silicon negative electrode is manufactured by a silicon thin film technology in which a silicon thin film is formed on a copper substrate by chemical vapor deposition (CVD) or physical vapor deposition (PVD). The thickness of the silicon thin film formed in this way is 500 nm or less, but in order to fully exhibit the theoretical capacity of silicon and obtain sufficient conductivity, a film thickness of at least 5 μm is required. . In order to solve this conductivity problem, if a laminated vapor deposition film with different metals such as gold and copper is created, the metal melts and diffuses into the silicon vapor deposition film, and the electrode characteristics are greatly improved. (Non-patent Document 1). On the other hand, with the dissimilar metal being sandwiched, stress is generated in the film as the film thickness increases, and there is a concern about peeling from the current collector.
また、容量の増加に伴う体積膨張の対策に多孔質シリコンを用いる技術として、多孔質のシリコン粉末を用いた高容量のシリコン負極が開発されている（非特許文献２）。この手法は、シリコンウエハをエッチングして多孔質化し、スポンジ状のシリコン膜を作成する方法であり、多孔質化によって表面積を大きくすることで、膨張を吸収する隙間を多く持たせている。多孔質シリコンの製造方法は、特許文献１に、シリコンの表面に形成した酸化膜をフッ化水素酸により除去する技術が記載されている。 In addition, as a technique for using porous silicon as a countermeasure for volume expansion accompanying an increase in capacity, a high-capacity silicon negative electrode using porous silicon powder has been developed (Non-patent Document 2). This method is a method of creating a sponge-like silicon film by etching a silicon wafer to make a porous silicon film. By increasing the surface area by making the silicon wafer porous, there are many gaps for absorbing expansion. As a method for producing porous silicon, Patent Document 1 describes a technique for removing an oxide film formed on the surface of silicon with hydrofluoric acid.
また、シリコンナノワイヤーを用いた技術として、非特許文献３には、酸化珪素の薄膜をシリコンナノチューブにコーティングすることによって、ナノチューブの外壁が膨張から保護され、ダメージを受けないようにすることが記載されている。シリコンは内側の中空部に向かって膨らむため、膨張による負極への影響がなく、又、内側の中空部は十分小さいため、電解質の分子が内部に入り込んでくることもない。 In addition, as a technique using silicon nanowires, Non-Patent Document 3 describes that by coating a silicon nanotube with a silicon oxide thin film, the outer wall of the nanotube is protected from expansion and is not damaged. Has been. Since silicon swells toward the inner hollow portion, there is no influence on the negative electrode due to expansion, and since the inner hollow portion is sufficiently small, electrolyte molecules do not enter the inside.
また、高速噴射成形成膜技術として、特許文献２には、固体微粒子を気体の噴流に乗せてノズルから噴射し、音速未満の速度で基材に衝突させて付着させ、常温且つ常圧の環境下で基材上に固体材料の膜を形成する成膜方法が記載されている。同様の技術は、特許文献３にも記載されている。 Further, as a high-speed injection molding film forming technique, Patent Document 2 discloses that a solid fine particle is put on a gas jet and ejected from a nozzle, and is made to collide with and adhere to a substrate at a speed lower than the speed of sound. A film forming method for forming a film of a solid material on a substrate is described below. A similar technique is also described in Patent Document 3.
しかしながら、現在のシリコン系リチウムイオン電池の製造工程では、シリコンナノ粒子やナノワイヤが大量に必要になり、生産コストが高く、生産能率が低いという問題点を有する。また、シリコン負極の場合は、炭素電極に比べて電気伝導性が低いだけでなく、リチウムイオン吸蔵量の増加に伴い体積がおよそ３〜４倍（炭素電極はおよそ１．１倍）に膨張し、充放電の繰り返しにより粒子脱落やクラックが発生しやすいため、寿命が短くなるという問題点も有する。 However, the current production process of silicon-based lithium ion batteries requires a large amount of silicon nanoparticles and nanowires, resulting in high production costs and low production efficiency. In addition, in the case of a silicon negative electrode, not only is the electrical conductivity lower than that of the carbon electrode, but the volume expands to about 3 to 4 times (the carbon electrode is about 1.1 times) as the lithium ion storage amount increases. In addition, particle dropping and cracking are likely to occur due to repeated charging / discharging, and thus there is a problem that the life is shortened.
一方、半導体デバイスや太陽電池に使用されるシリコンウエハの製造工程では、単結晶シリコンインゴットからウエハを切り出すときにウエハの体積とほぼ同量のシリコン切屑が発生する。シリコンウエハが薄くなり、ウエハの枚数が多くなるに伴い、シリコン切屑の発生量も増加する。このシリコン切屑には、ワイヤーソーの砥粒材料である高硬度の炭化珪素粉末やダイヤモンド粒子が混在しているので、溶融してシリコンインゴット生産へ再利用するにはこの炭化珪素やダイヤモンドを除去する必要がある。しかし、特に炭化珪素はシリコンと性質が似ているので、シリコン切屑から炭化珪素を完全に除去するのは極めて困難とされている。このような状況において、シリコン切屑の再利用がほとんど行われておらず、産業廃棄物として処理されているのが現状である。一方、シリコンウエハの出荷数量は、日本が世界シェアの６割強を占めている。もし大量に発生するシリコン切屑を回収して有効に再利用することができれば、産業上の利点が非常に大きいと考えられる。 On the other hand, in the manufacturing process of a silicon wafer used for a semiconductor device or a solar battery, silicon chips are generated in an amount substantially equal to the volume of the wafer when the wafer is cut out from the single crystal silicon ingot. As silicon wafers become thinner and the number of wafers increases, the amount of silicon chips generated also increases. The silicon chips contain high-hardness silicon carbide powder and diamond particles, which are abrasive materials for wire saws, so the silicon carbide and diamond must be removed for melting and reuse for silicon ingot production. There is a need. However, since silicon carbide has similar properties to silicon, it is extremely difficult to completely remove silicon carbide from silicon chips. Under such circumstances, silicon chips are hardly reused and are currently treated as industrial waste. On the other hand, Japan accounts for more than 60% of the world's share of silicon wafer shipments. If a large amount of generated silicon chips can be recovered and reused effectively, the industrial advantage is considered to be very large.
近年、シリコン切屑再利用のための濾過洗浄および不純物除去技術について多くの研究が行われているが、満足できる成果が得られていないのが現状である。一方、違う視点から考えて、シリコン切屑のインゴット生産への再利用ではなく、炭化珪素セラミックス生産への応用が注目されている。炭化珪素は従来から研磨材や耐火材として広く利用されており、近年は高純度化および高緻密化によってファインセラミックス原料として用途が広がっている。この炭化珪素の工業的に確立された製造方法としては、アチソン法とシリカの直接還元法が知られている。もし、シリコン切屑から炭化珪素セラミックスの効率的な生産が可能となれば、画期的な材料生産プロセスになると考えられる。最近、シリコン切屑に対してカーボン粉を当量以上混合し、この混合粉を非酸化性雰囲気下、１０００℃〜１４００℃で、６時間〜２４時間加熱してシリコン切屑とカーボン粉を反応させてブロック状の炭化珪素を製造するプロセスが提案されている。しかし、必要な処理時間が長く、雰囲気制御の焼結装置も高価であるため、実用化が困難とされている。また、製作された高硬度の炭化珪素ブロックの機械加工も難関となっている。 In recent years, much research has been conducted on filtration cleaning and impurity removal technology for silicon chip recycling, but at present, satisfactory results have not been obtained. On the other hand, from a different viewpoint, attention is focused on the application to the production of silicon carbide ceramics rather than the reuse of silicon chips for the production of ingots. Silicon carbide has been widely used as a polishing material and a refractory material, and has recently been used as a fine ceramic material due to high purity and high densification. As industrially established methods for producing silicon carbide, the Atchison method and the direct reduction method of silica are known. If silicon carbide ceramics can be efficiently produced from silicon chips, it will be a revolutionary material production process. Recently, an equivalent amount or more of carbon powder is mixed with silicon chips, and the mixed powder is heated at 1000 ° C. to 1400 ° C. for 6 hours to 24 hours in a non-oxidizing atmosphere to cause the silicon chips and carbon powder to react and block. A process for producing a shaped silicon carbide has been proposed. However, since the necessary processing time is long and the sintering apparatus for controlling the atmosphere is expensive, it is difficult to put it into practical use. In addition, machining of the manufactured high-hardness silicon carbide block is also difficult.
本発明は、前記従来の問題点を解決するべくなされたもので、シリコン負極に導電性を付与すると共に、機械的特性を向上した、安価で長寿命のリチウムイオン電池を高能率で製造することが可能な技術を提供することを課題とする。 The present invention has been made to solve the above-mentioned conventional problems, and provides a low-cost and long-life lithium-ion battery with high efficiency, imparting conductivity to the silicon negative electrode and improving mechanical properties. It is an object to provide a technology that can be used.
本願の第１の発明は、不純物除去が行われていない、炭酸珪素粉末及びダイヤモンド粒子の少なくとも一方が混在するシリコン切屑で構成されるシリコン粒子と、その周囲のポーラス構造を有する銅からなり、前記銅が導電性ネットワークを形成していることを特徴とする焼結体により、前記課題を解決したものである。 1st invention of this application consists of the silicon particle which the silicon carbonate powder in which at least one of the silicon carbonate powder and the diamond particle were mixed, and the porous structure of the circumference | surroundings which the impurities removal is not performed, and the surrounding porous structure, The above problem is solved by a sintered body characterized in that copper forms a conductive network.
ここで、前記銅はバインダーとして存在することができる。 Here, the copper may be present as a binder.
本願の第２の発明は、不純物除去が行われていない、炭酸珪素粉末及びダイヤモンド粒子の少なくとも一方が混在するシリコン切屑で構成されるシリコン粒子と、その周囲の炭素系膜からなり、該炭素系膜が気孔を持つポーラス構造で導電性ネットワークを形成していることを特徴とする焼結体により、前記課題を解決したものである。 The second invention of the present application comprises silicon particles composed of silicon chips in which at least one of silicon carbonate powder and diamond particles is mixed and impurities are not removed, and a carbon-based film around the silicon particles. The above-mentioned problem is solved by a sintered body characterized in that a conductive network is formed with a porous structure in which the film has pores.
本発明によれば、産業廃棄物とされているシリコン粉末をリチウムイオン電池材料へ活用できる。また、第１の発明の場合は銅の含有率やプレス力、赤外線強度、第２の発明の場合はカーボンナノファイバー、カーボンナノチューブ、カーボンフラーレン又は炭素系微粒子の含有率やプレス力、レーザ出力等を変化させることによって、焼結体の密度やポーラス率、機械的特性ならびに導電性等を自由に制御することができるため、安価で長寿命のシリコン負極のリチウムイオン電池の製造が実現できる。特に、第１の発明で赤外線を用いた場合には、シリコン粒子を溶融することなく焼結するため、従来の焼結法より大幅なエネルギー削減が可能である。一方、第２の発明のレーザ焼結では、シリコン粒子の表面だけを溶融するため、最小限の焼結エネルギーにより成膜が可能であり、シリコン粒子の結晶性制御も可能である。 According to the present invention, silicon powder, which is regarded as industrial waste, can be used as a lithium ion battery material. In the case of the first invention, the copper content, pressing force and infrared intensity, and in the case of the second invention, the content of carbon nanofibers, carbon nanotubes, carbon fullerene or carbon-based fine particles, pressing force, laser output, etc. By changing the density, it is possible to freely control the density, the porous rate, the mechanical characteristics, the conductivity, and the like of the sintered body, so that it is possible to manufacture a lithium ion battery with a silicon negative electrode that is inexpensive and has a long life. In particular, when infrared rays are used in the first invention, since the silicon particles are sintered without melting, energy can be significantly reduced compared to the conventional sintering method. On the other hand, in the laser sintering of the second invention, since only the surface of the silicon particles is melted, the film can be formed with the minimum sintering energy, and the crystallinity of the silicon particles can be controlled.
また、短時間の赤外線照射又は極めて短時間のレーザ照射によって高速焼結が行われるため、材料の酸化や変質が抑制され、特殊雰囲気が不要であり、大気中での処理が可能である。 In addition, since high-speed sintering is performed by short-time infrared irradiation or extremely short-time laser irradiation, oxidation and alteration of the material are suppressed, a special atmosphere is unnecessary, and processing in the air is possible.
更に、様々な形状の複合材料膜を生成することが可能であり、機械要素や電子部品、センサ、ＭＥＭＳ等の多分野への波及効果が期待される。 Furthermore, composite material films having various shapes can be generated, and a ripple effect is expected in various fields such as mechanical elements, electronic components, sensors, and MEMS.
以下、図面を参照して、本発明の実施形態について詳細に説明する。 Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
まず、第１の発明に係る第１実施形態について説明する。 First, a first embodiment according to the first invention will be described.
本実施形態では、シリコン負極に強度と導電性を付加するために、バインダーとしてシリコン粉末に銅粉末を混合し、赤外線を照射することにより複合膜を焼結させる。 In this embodiment, in order to add strength and conductivity to the silicon negative electrode, copper powder is mixed with silicon powder as a binder, and the composite film is sintered by irradiating with infrared rays.
具体的には、図１（ａ）に示す如く、サブミクロン粒径の銅粒子１２の粉末を所定の比率でシリコン粒子１０の粉末に混合し、銅板（図示省略）上に塗布した後、図２に示す如く赤外線ランプ２２により赤外線２３を照射して高速加熱しながら、一体型のプレス機２０により所定の圧力を加えながらプレスする。図２において、１４は混合粉末、１６はシリコンウエハ、２４は温度測定用の熱電対である。 Specifically, as shown in FIG. 1 (a), a powder of submicron-sized copper particles 12 is mixed with a powder of silicon particles 10 at a predetermined ratio and coated on a copper plate (not shown). As shown in FIG. 2, pressing is performed while applying a predetermined pressure by an integrated press 20 while irradiating infrared rays 23 from an infrared lamp 22 and heating at high speed. In FIG. 2, 14 is a mixed powder, 16 is a silicon wafer, and 24 is a thermocouple for temperature measurement.
図３に示す如く、シリコンは赤外線をほぼ完全に透過するため、シリコン粒子１０には熱的ダメージがほとんど発生しない。一方、銅は赤外線を効率よく吸収するので、銅粒子１２のみを効率良く加熱することができる。その結果、銅粒子１２が瞬間的に溶融し、その後、再凝固する。これにより、図１（ｃ）に示す如く、シリコン粒子１０の周囲に銅粒子１２が融解されて銅バインダー１３となる。また、焼結時にプレス圧力を制御することで、体積膨張緩和のための気孔１５を持つポーラス構造の導電性ネットワークが形成される。なお、気孔１５を残すため、焼結前に超音波振動プレス条件を制御することも可能である。 As shown in FIG. 3, since silicon transmits infrared light almost completely, the silicon particles 10 hardly undergo thermal damage. On the other hand, since copper absorbs infrared rays efficiently, only the copper particles 12 can be efficiently heated. As a result, the copper particles 12 are instantaneously melted and then re-solidified. Thereby, as shown in FIG. 1C, the copper particles 12 are melted around the silicon particles 10 to form the copper binder 13. Further, by controlling the pressing pressure during sintering, a porous structure conductive network having pores 15 for volume expansion relaxation is formed. In order to leave the pores 15, it is also possible to control the ultrasonic vibration press conditions before sintering.
図４に示す如く、複合膜にＳｉＣ砥粒１８やダイヤモンド粒子が混在しているが、極微量であるため、複合膜の電気的特性への影響はないと考えられる。 As shown in FIG. 4, although SiC abrasive grains 18 and diamond particles are mixed in the composite film, it is considered that there is no influence on the electrical characteristics of the composite film because it is extremely small.
シリコン粉末（融点１４００℃、密度２．３３ｇ／ｃｍ3、平均粒径３μｍ）と銅粉末（融点１０８３℃、密度８．９６ｇ／ｃｍ3、平均粒径０．２μｍ）を用いて、質量比で、１：３、１：１、１：３の割合の混合粉末を作製した。膜の形成を観察するため、図２に示したように、混合粉末１４との反応性の少ないシリコンウエハ１６（１ｃｍ角）で混合粉末１４を挟んで焼結を行い、又、ウエハと粉末の間に銅基板を入れて実験することにより、負極の集電体である銅基板への成膜を行った。超精密プレス成形装置を用いて、温度７８０℃、圧力１０〜１００ＭＰａ、保持時間０．５〜１７分間の範囲の条件で加圧焼結を行った。一例として、測定温度（実際の温度より低い）７８０℃、圧力５０ＭＰａ、保持時間１７分間で実験した温度・圧力変化を図５に示す。 Using silicon powder (melting point 1400 ° C., density 2.33 g / cm 3 , average particle size 3 μm) and copper powder (melting point 1083 ° C., density 8.96 g / cm 3 , average particle size 0.2 μm), by mass ratio 1: 3, 1: 1, 1: 3 mixed powders were prepared. In order to observe the formation of the film, as shown in FIG. 2, sintering is performed by sandwiching the mixed powder 14 with a silicon wafer 16 (1 cm square) that is less reactive with the mixed powder 14, and the wafer and the powder. By conducting an experiment with a copper substrate in between, a film was formed on the copper substrate which is the current collector of the negative electrode. Using an ultra-precise press molding apparatus, pressure sintering was performed under the conditions of a temperature of 780 ° C., a pressure of 10 to 100 MPa, and a holding time of 0.5 to 17 minutes. As an example, FIG. 5 shows changes in temperature and pressure that were measured at a measurement temperature (lower than the actual temperature) of 780 ° C., a pressure of 50 MPa, and a holding time of 17 minutes.
焼結した膜（厚さ２００〜５００μｍ）を垂直に切断し、研磨した断面を走査型電子顕微鏡（ＳＥＭ）で観察した。次に、断面の強度評価として、ナノインデンターを用いて、シリコンと銅の割合が異なる場所の境界付近を１０μｍ間隔で圧痕をマッピングし、硬さと弾性の測定を行った。 The sintered film (thickness 200 to 500 μm) was cut vertically, and the polished cross section was observed with a scanning electron microscope (SEM). Next, as a strength evaluation of the cross section, using a nanoindenter, indentations were mapped at intervals of 10 μm in the vicinity of the boundary where the ratio of silicon and copper was different, and the hardness and elasticity were measured.
銅粒子が多いため、シリコンとの結合が見やすい、シリコン：銅＝１：３の割合で図５の条件での焼結実験を行った時の、焼結体の断面のＳＥＭ写真とエネルギー分散型Ｘ線分析（ＥＤＸ）によるシリコンと銅の分布を図６に示す。図６からシリコンと銅が均一に混合されている部分があり、図１のように緻密化し、焼結されている様子が見受けられた。しかし、体積膨張緩和のための気孔１５の生成が見られないため、プレス力や保持時間が過剰であると考えられた。 Since there are many copper particles, the bonding with silicon is easy to see, and the SEM photograph and energy dispersion type of the cross section of the sintered body when the sintering experiment was performed at the ratio of silicon: copper = 1: 3 under the conditions of FIG. The distribution of silicon and copper by X-ray analysis (EDX) is shown in FIG. From FIG. 6, there was a portion where silicon and copper were uniformly mixed, and it was observed that the silicon was densified and sintered as shown in FIG. However, since the formation of pores 15 for relaxing the volume expansion was not observed, it was considered that the pressing force and holding time were excessive.
以上の考察から、圧力を５０ＭＰａ以下、保持時間１分以内で加圧焼結実験を行うと同時に銅板への成膜を行った結果を表１に示す。 From the above consideration, Table 1 shows the results of film forming on a copper plate at the same time as performing a pressure sintering experiment with a pressure of 50 MPa or less and a holding time of 1 minute or less.
この結果は、膜に触れた際に崩れた試料を×としたが、圧力又は保持時間を大きくするにつれて、銅板への付着度が増した。 As a result, although the sample collapsed when touching the film was marked with x, the degree of adhesion to the copper plate increased as the pressure or holding time was increased.
図７に成膜が行われたと判断した（ａ）保持時間６０秒、圧力３０ＭＰａと、（ｂ）保持時間３０秒、圧力５０ＭＰａの断面のＳＥＭ写真を示す。（ａ）と（ｂ）を比べると、（ａ）の方がクラックの発生箇所が多く、銅板への成膜ができたが、膜としての強度が乏しいように思われる。更に、（ｂ）の膜の拡大図を図８に示す。図８から焼結の様子が見られ、気孔も形成されていることがわかる。 FIG. 7 shows an SEM photograph of a cross section of (a) a holding time of 60 seconds and a pressure of 30 MPa, and (b) a cross section of a holding time of 30 seconds and a pressure of 50 MPa, in which it was determined that film formation was performed. When (a) and (b) are compared, in (a), the number of cracks generated is larger, and the film can be formed on the copper plate, but it seems that the strength as a film is poor. Furthermore, the enlarged view of the film | membrane of (b) is shown in FIG. It can be seen from FIG. 8 that sintering is observed and pores are also formed.
図９に、シリコンと銅の割合の変化領域付近で左図の各格子点上に圧痕を形成し、圧痕のその場所毎の弾性率をグラフで示す。このグラフから全体としての弾性率の平均値が２００ｋＮ／ｍｍ2であることが読み取れ、黄銅等の銅合金の縦弾性率が１００ｋＮ／ｍｍ2程度であるので、約２倍の弾性率及び硬さを持つ焼結体が形成されることが確認できた。 In FIG. 9, indentations are formed on each lattice point in the left diagram in the vicinity of the change region of the ratio of silicon and copper, and the elastic modulus at each location of the indentations is shown in a graph. From this graph, it can be seen that the average value of the elastic modulus as a whole is 200 kN / mm 2 , and the longitudinal elastic modulus of a copper alloy such as brass is about 100 kN / mm 2 , so that the elastic modulus and hardness are approximately doubled. It was confirmed that a sintered body having a thickness was formed.
このように、第１実施形態によれば、シリコンと銅の混合粉末から、銅合金の約２倍の弾性率及び硬さを持つ焼結体を生成することができた。また、圧力や保持時間によって、負極の集電体として用いられる銅板への成膜も可能であり、気孔の形成も確認できた。なお、加熱は赤外線に限定されない。 Thus, according to the first embodiment, a sintered body having an elastic modulus and hardness about twice that of a copper alloy could be generated from a mixed powder of silicon and copper. Moreover, it was possible to form a film on a copper plate used as a negative electrode current collector depending on the pressure and holding time, and it was confirmed that pores were formed. In addition, heating is not limited to infrared rays.
しかも、シリコン粒子として、シリコンウエハ生産時の廃棄物であるシリコン粉末を再利用できるので、リチウムイオン電池を低コストで生産することが可能となる。第１実施形態により、太陽電池廃材からリチウムイオン電池を製造する様子を図１０に示す。 In addition, since silicon powder, which is a waste product during the production of silicon wafers, can be reused as silicon particles, a lithium ion battery can be produced at low cost. FIG. 10 shows a state in which a lithium ion battery is manufactured from solar cell waste according to the first embodiment.
次に、第２の発明に係る第２実施形態について説明する。 Next, a second embodiment according to the second invention will be described.
第２の発明によるシリコンとカーボンナノファイバー焼結時のモデルを図１１に示す。 FIG. 11 shows a model for sintering silicon and carbon nanofibers according to the second invention.
本実施形態では、図１２に示す如く、バインダーとしてカーボンナノファイバー（ＣＮＦ）３２をシリコン粒子１０の粉末に混合し、レーザ４２を照射することにより複合膜４４を焼結させる。具体的には、直径１μｍ以下のＣＮＦ３２を一定の比率でシリコン粒子１０の粉末に混合し、銅基板３４上に塗布した後、レーザ４２の照射により高速加熱しながら成膜する。これによりシリコン粉末表面の瞬間的溶融・再凝固によって、ＣＮＦ３２との高強度結合が形成され、Ｓｉ／Ｃ複合膜４４が形成される。また、焼結時にプレス圧力を制御することによって、体積膨張緩和のために気孔を有するポーラス構造を形成させる。 In this embodiment, as shown in FIG. 12, carbon nanofibers (CNF) 32 as a binder are mixed with the powder of silicon particles 10, and the composite film 44 is sintered by irradiating a laser 42. Specifically, CNF 32 having a diameter of 1 μm or less is mixed with a powder of silicon particles 10 at a certain ratio, applied onto the copper substrate 34, and then deposited while being heated at high speed by irradiation with a laser 42. As a result, a high-strength bond with the CNF 32 is formed by instantaneous melting and re-solidification of the silicon powder surface, and the Si / C composite film 44 is formed. Further, by controlling the pressing pressure during sintering, a porous structure having pores is formed for relaxation of volume expansion.
実施例２では、高出力パルスレーザ４０とリニアステージ５０を用いた。シリコンとＣＮＦの混合粉末をガラス、銅の基板上に塗布し、レーザ４２を照射した。レーザ照射条件を表２に示す。 In the second embodiment, the high output pulse laser 40 and the linear stage 50 are used. A mixed powder of silicon and CNF was applied on a glass / copper substrate and irradiated with a laser 42. Table 2 shows the laser irradiation conditions.
その後、形成された膜をＳＥＭ及びラマン分光装置により評価をした。また、有限要素法ベース汎用物理シミュレーションソフトを用いて、レーザ照射時のシリコン粉末及び基板での熱伝導について解析を行った。図１３にＦＥＭ解析モデルを示す。熱源を与える際、表面から深さｚでの放射強度Ｉ(ｚ)として次式を用いた。
Ｉ(ｚ)＝Ｉ0ｅｘｐ(−αｚ) ・・・（１）
ここで、Ｉ0、αは、それぞれ材料表面での強度及び材料の吸収係数である。
Thereafter, the formed film was evaluated by SEM and Raman spectroscopy. In addition, the heat conduction in the silicon powder and the substrate during laser irradiation was analyzed using finite element method-based general-purpose physical simulation software. FIG. 13 shows an FEM analysis model. When applying a heat source, the following equation was used as the radiation intensity I (z) at a depth z from the surface.
I (z) = I 0 exp (−αz) (1)
Here, I 0 and α are the strength on the surface of the material and the absorption coefficient of the material, respectively.
図１２のようにリニアステージ５０を移動させ、レーザ４２を連続で照射し、粉末飛散防止のためガラス板３６と銅基板３４により混合粉末３８を挟んで成膜を試みた。混合粉末３８の混合割合はＳｉ：ＣＮＦ＝３：１（質量比）とした。ステージ移動速度１ｍｍ／秒で３ｍｍ四方にレーザ（周波数３ｋＨｚ，平均出力約１．６Ｗ）を照射したところ、下部の銅基板３４上に成膜が行われず、上部のガラス板３６へ膜が形成された（図１４（ａ））。この成膜方法は、レーザ光を透過するガラス板３６等にしか適用できず、実際のリチウムイオン電池負極に集電体として用いられる銅等には適用できないため、粉末をガラス板でカバーせずに同様のレーザ出力条件で銅板への成膜を試みた。しかし、粉末自体の焼結は行われたものの、基板への付着は確認できなかった。そこで、平均出力を約３Ｗとし、ステージ移動速度を０．５ｍｍ／秒とし、成膜を試みたところ、図１４（ｂ）に示すように銅基板３４への付着が確認された。また、膜厚をレーザプローブ形状測定装置により測定した結果を図１５に示す。 As shown in FIG. 12, the linear stage 50 was moved, the laser 42 was continuously irradiated, and a mixed powder 38 was sandwiched between the glass plate 36 and the copper substrate 34 in order to prevent powder scattering. The mixing ratio of the mixed powder 38 was Si: CNF = 3: 1 (mass ratio). When a laser (frequency 3 kHz, average output about 1.6 W) was irradiated on a 3 mm square at a stage moving speed of 1 mm / second, no film was formed on the lower copper substrate 34, and a film was formed on the upper glass plate 36. (FIG. 14A). This film forming method can be applied only to the glass plate 36 and the like that transmit laser light, and cannot be applied to copper or the like used as a current collector in an actual lithium ion battery negative electrode, so the powder is not covered with the glass plate. In addition, an attempt was made to form a film on a copper plate under the same laser output conditions. However, although the powder itself was sintered, adhesion to the substrate could not be confirmed. Therefore, when the average output was set to about 3 W, the stage moving speed was set to 0.5 mm / second, and deposition was attempted, adhesion to the copper substrate 34 was confirmed as shown in FIG. Moreover, the result of having measured the film thickness with the laser probe shape measuring apparatus is shown in FIG.
高速度カメラによるレーザ照射時の画像を図１６に示す。レーザ照射により火花放電が発生していることから、プラズマが発生している可能性が考えられる。即ち、上部ガラス板３６への膜の形成は、図１７のようにレーザを照射した部分が溶融し、気体もしくはプラズマ４６となり、上部ガラス板３６に膜として付着すると考えられる。一方、銅基板３４への成膜は、レーザの平均出力及びステージ移動速度を予測したことにより、混合粉末と基板の境界付近までレーザのエネルギーによる熱が伝わり、粉末が溶融し焼結したと考えられる。 An image at the time of laser irradiation by a high-speed camera is shown in FIG. Since spark discharge is generated by laser irradiation, it is possible that plasma is generated. That is, the formation of the film on the upper glass plate 36 is considered that the portion irradiated with the laser melts as shown in FIG. 17 to become gas or plasma 46 and adheres to the upper glass plate 36 as a film. On the other hand, in the film formation on the copper substrate 34, the average power of the laser and the stage moving speed were predicted, so that heat by the laser energy was transmitted to the vicinity of the boundary between the mixed powder and the substrate, and the powder was considered to be melted and sintered. It is done.
図１８のＳＥＭ写真により、ＣＮＦ３２又はＳｉにより結合している部分やポーラス構造が見られた。ＣＮＦ３２が複雑に絡み合うことにより、リチウムイオン電池負極として導電性の向上が見込める他、ポーラス構造となることで、膨張・収縮が緩和され、電池耐久性の向上性も見込める。 The SEM photograph of FIG. 18 shows a portion bonded with CNF32 or Si and a porous structure. Intricately entangled with CNF32, an improvement in conductivity as a lithium ion battery negative electrode can be expected. In addition, since a porous structure is obtained, expansion / contraction is alleviated and battery durability can be improved.
異なる条件で焼結した試料をラマン分光装置で測定したところ、図１９に示す如く、単結晶シリコンのラマンシフト５２０ｃｍ-1と比較してピーク位置が低波数側へシフトしている点と、ピークが広がっている点から、単結晶シリコンが多結晶化している可能性が見られた。リチウムイオン電池負極として充放電を繰り返すことで、シリコンが膨張・収縮するため耐久性が懸念されるが、シリコンを多結晶化することで、膨張・収縮の均一化により耐久性の向上が見込める。 When the samples sintered under different conditions were measured with a Raman spectroscope, as shown in FIG. 19, the peak position was shifted to the lower wavenumber side compared to the Raman shift of 520 cm −1 of single crystal silicon, and the peak The possibility that single crystal silicon is polycrystallized was seen from the point that the By repeating charge and discharge as a lithium ion battery negative electrode, the silicon expands and contracts, so there is concern about durability. However, by polycrystallizing silicon, it is possible to improve the durability by making the expansion and contraction uniform.
また、レーザの各出力とピークの半値幅をプロットとしたものを図２０に示す。図２０から、レーザの出力と半値幅は概ね比例している傾向が見られた。このことから、レーザの出力等の条件を変えることによって結晶性の制御ができる可能性がある。 FIG. 20 shows a plot of the laser output and the half width of the peak. From FIG. 20, there was a tendency that the laser output and the full width at half maximum were proportional. Therefore, there is a possibility that the crystallinity can be controlled by changing conditions such as the output of the laser.
表面からの各深さにおける温度と時刻の関係を図２１に示す。図２１から、表面に近い部分の温度上昇が大きいことがわかる。これは、（１）式にあるように材料内部で光の強度あるいはエネルギーが指数関数的に減衰することによるものである。そして、表面付近の温度は９０００Ｋ程度まで上昇しており、シリコンの溶融及び沸点以上の温度となっており、溶融もしくはプラズマとなるのに十分な温度となっていることがわかる。 FIG. 21 shows the relationship between temperature and time at each depth from the surface. FIG. 21 shows that the temperature rise near the surface is large. This is because the intensity or energy of light attenuates exponentially inside the material as shown in equation (1). The temperature in the vicinity of the surface rises to about 9000 K, and it can be seen that the temperature is higher than the melting and boiling point of silicon, which is sufficient to melt or become plasma.
以上のように、第２実施形態においても、（１）レーザの平均出力及びステージ移動速度を制御することで、レーザ焼結によるガラス基板や銅板上へのシリコン・ＣＮＦ複合膜の成膜ができる。（２）焼結された複合膜において、シリコンとＣＮＦの結合及びポーラス構造が形成され、リチウムイオン電池負極の性能の向上が可能である。（３）レーザ照射により単結晶シリコン粒子の微細化が見られることが確認できた。 As described above, also in the second embodiment, (1) a silicon / CNF composite film can be formed on a glass substrate or a copper plate by laser sintering by controlling the average output of the laser and the stage moving speed. . (2) In the sintered composite film, a bond between silicon and CNF and a porous structure are formed, and the performance of the lithium ion battery negative electrode can be improved. (3) It was confirmed that the single crystal silicon particles were refined by laser irradiation.
この第２実施形態においても、第１実施形態と同様に、シリコン粒子として、シリコンウエハ生産時の廃棄物であるシリコン粉末を再利用できるので、リチウムイオン電池を低コストで生産することが可能となる。 Also in the second embodiment, as in the first embodiment, since silicon powder, which is a waste product during the production of silicon wafers, can be reused as silicon particles, it is possible to produce a lithium ion battery at low cost. Become.
なお、第２実施形態においては、カーボンナノファイバーを用いていたが、代わりにカーボンナノチューブ、カーボンフラーレンやその誘導体、グラファイト又は炭素系微粒子を用いることも可能である。 In the second embodiment, carbon nanofibers are used. However, carbon nanotubes, carbon fullerenes and derivatives thereof, graphite, or carbon-based fine particles may be used instead.
１０…シリコン粒子
１２…銅粒子
１３…銅バインダー
１４、３８…混合粉末
１５…気孔
１６…シリコンウエハ
２０…プレス機
２２…赤外線ランプ
２３…赤外線
３２…カーボンナノファイバー（ＣＮＦ）
３４…銅基板
３６…ガラス板
４０…高出力パルスレーザ
４２…レーザ
４４…複合膜
５０…リニアステージ
DESCRIPTION OF SYMBOLS 10 ... Silicon particle 12 ... Copper particle 13 ... Copper binder 14, 38 ... Mixed powder 15 ... Pore 16 ... Silicon wafer 20 ... Press machine 22 ... Infrared lamp 23 ... Infrared ray 32 ... Carbon nanofiber (CNF)
34 ... Copper substrate 36 ... Glass plate 40 ... High power pulse laser 42 ... Laser 44 ... Composite film 50 ... Linear stage
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| WO2021237199A1 (en) * | 2020-05-22 | 2021-11-25 | Fastcap Systems Corporation | Si-containing composite anode for energy storage devices |
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