JP5182498B2 - Anode material for non-aqueous electrolyte secondary battery, method for producing the same, lithium ion secondary battery, and electrochemical capacitor - Google Patents
Anode material for non-aqueous electrolyte secondary battery, method for producing the same, lithium ion secondary battery, and electrochemical capacitor Download PDFInfo
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Abstract
Description
本発明は、非水電解質二次電池、特にリチウムイオン二次電池用負極活物質として用いた際に、優れた初回充放電効率、サイクル特性を有する非水電解質二次電池用負極材及びその製造方法、ならびにリチウムイオン二次電池及び電気化学キャパシタに関するものである。 The present invention relates to a negative electrode material for a nonaqueous electrolyte secondary battery having excellent initial charge and discharge efficiency and cycle characteristics when used as a negative electrode active material for a nonaqueous electrolyte secondary battery, particularly a lithium ion secondary battery, and its production. The present invention relates to a method, and a lithium ion secondary battery and an electrochemical capacitor.
近年、携帯型の電子機器、通信機器等の著しい発展に伴い、経済性と機器の小型化、軽量化の観点から、高エネルギー密度の二次電池が強く要望されている。従来、この種の二次電池の高容量化策として、例えば、負極材料にＶ、Ｓｉ、Ｂ、Ｚｒ、Ｓｎ等の酸化物及びそれらの複合酸化物を用いる方法（例えば、特許文献１：特開平５−１７４８１８号公報、特許文献２：特開平６−６０８６７号公報参照）、溶融急冷した金属酸化物を負極材として適用する方法（例えば、特許文献３：特開平１０−２９４１１２号公報参照）、負極材料に酸化珪素を用いる方法（例えば、特許文献４：特許第２９９７７４１号公報参照）、負極材料にＳｉ2Ｎ2Ｏ及びＧｅ2Ｎ2Ｏを用いる方法（例えば、特許文献５：特開平１１−１０２７０５号公報参照）等が知られている。また、負極材に導電性を付与する目的として、ＳｉＯを黒鉛とメカニカルアロイング後、炭化処理する方法（例えば、特許文献６：特開２０００−２４３３９６号公報参照）、珪素粒子表面に化学蒸着法により炭素層を被覆する方法（例えば、特許文献７：特開２０００−２１５８８７号公報参照）、酸化珪素粒子表面に化学蒸着法により炭素層を被覆する方法（例えば、特許文献８：特開２００２−４２８０６号公報参照）等が挙げられる。 In recent years, with the remarkable development of portable electronic devices, communication devices, etc., secondary batteries with high energy density are strongly demanded from the viewpoints of economy and downsizing and weight reduction of devices. Conventionally, as a measure for increasing the capacity of this type of secondary battery, for example, a method of using an oxide such as V, Si, B, Zr, or Sn and a composite oxide thereof as a negative electrode material (for example, Patent Document 1: Kaihei 5-174818, Patent Document 2: Japanese Patent Laid-Open No. 6-60867, and a method of applying a melt-quenched metal oxide as a negative electrode material (for example, see Patent Document 3: Japanese Patent Laid-Open No. 10-294112) , A method using silicon oxide as a negative electrode material (for example, see Patent Document 4: Japanese Patent No. 2999741), a method using Si 2 N 2 O and Ge 2 N 2 O as a negative electrode material (for example, Patent Document 5: 11-102705) and the like are known. In addition, for the purpose of imparting conductivity to the negative electrode material, a method of carbonizing SiO with graphite and then carbonizing (see, for example, Patent Document 6: JP 2000-243396 A), a chemical vapor deposition method on the surface of silicon particles (For example, see Patent Document 7: Japanese Patent Laid-Open No. 2000-215887), and a method for coating a carbon layer on the surface of silicon oxide particles by chemical vapor deposition (for example, Patent Document 8: Japanese Patent Laid-Open No. 2002-2002). 42806) and the like.
しかしながら、上記従来の方法では、充放電容量が上がり、エネルギー密度が高くなるものの、サイクル性が不十分であったり、市場の要求特性には未だ不十分であったりし、必ずしも満足でき得るものではなく、更なるエネルギー密度の向上が望まれていた。 However, in the above conventional method, although the charge / discharge capacity is increased and the energy density is increased, the cycleability is insufficient, or the required characteristics of the market are still insufficient, and are not always satisfactory. However, further improvement in energy density has been desired.
特に、特許第２９９７７４１号公報（特許文献４）では、酸化珪素をリチウムイオン二次電池負極材として用い、高容量の電極を得ているが、本発明者らが見る限りにおいては、未だ初回充放電時における不可逆容量が大きかったり、サイクル性が実用レベルに達しておらず、改良する余地がある。また、負極材に導電性を付与した技術についても、特開２０００−２４３３９６号公報（特許文献６）では、固体と固体の融着であるため、均一な炭素皮膜が形成されず、導電性が不十分であるといった問題がある。また、特開２０００−２１５８８７号公報（特許文献７）の方法においては、均一な炭素皮膜の形成が可能となるものの、Ｓｉを負極材として用いているため、リチウムイオンの吸脱着時の膨張・収縮があまりにも大きすぎて、結果として実用に耐えられず、サイクル性が低下するためにこれを防止するべく充電量の制限を設けなくてはならず、特開２００２−４２８０６号公報（特許文献８）の方法においては、微細な珪素結晶の析出、炭素被覆の構造及び基材との融合が不十分であることより、サイクル性の向上は確認されるも、充放電のサイクル数を重ねると徐々に容量が低下し、一定回数後に急激に低下するという現象があり、二次電池用としてはまだ不十分であるといった問題があった。 In particular, in Japanese Patent No. 2997741 (Patent Document 4), silicon oxide is used as a negative electrode material for a lithium ion secondary battery to obtain a high-capacity electrode. There is room for improvement because the irreversible capacity at the time of discharge is large and the cycle performance has not reached the practical level. In addition, regarding the technique for imparting conductivity to the negative electrode material, in Japanese Patent Application Laid-Open No. 2000-243396 (Patent Document 6), since it is a solid-solid fusion, a uniform carbon film is not formed, and conductivity is improved. There is a problem that it is insufficient. Further, in the method disclosed in Japanese Patent Application Laid-Open No. 2000-215887 (Patent Document 7), although a uniform carbon film can be formed, since Si is used as a negative electrode material, expansion / desorption during lithium ion adsorption / desorption is performed. The contraction is too large, and as a result, it cannot be put into practical use, and the cycle performance is lowered. Therefore, a charge amount limit must be provided in order to prevent this, and Japanese Patent Application Laid-Open No. 2002-42806 (Patent Document) In the method of 8), although the improvement of cycleability is confirmed from the fact that the precipitation of fine silicon crystals, the carbon coating structure and the fusion with the base material are insufficient, the cycle number of charge / discharge is repeated. There is a phenomenon in which the capacity gradually decreases and rapidly decreases after a certain number of times, and there is a problem that it is still insufficient for a secondary battery.
本発明は、上記事情に鑑みなされたもので、良好な初回充放電効率、サイクル特性を有する、特にリチウムイオン二次電池用として有効な非水電解質二次電池用負極材及びその製造方法、ならびにリチウムイオン二次電池及び電気化学キャパシタを提供することを目的とする。 The present invention has been made in view of the above circumstances, and has good initial charge / discharge efficiency and cycle characteristics, and in particular, a negative electrode material for a non-aqueous electrolyte secondary battery effective as a lithium ion secondary battery, and a method for producing the same, and An object is to provide a lithium ion secondary battery and an electrochemical capacitor.
本発明者らは、上記目的を達成するため種々検討を行った結果、酸化珪素粒子又は珪素の微結晶が珪素系化合物に分散した構造を有する粒子の表面に、ウィスカーが形成されたウィスカー酸化珪素粒子を負極材として用いることで、充放電サイクルを重ねてもウィスカーにより集電性が損なわれず、著しい電池特性の向上が見られることを知見した。 As a result of various studies to achieve the above object, the present inventors have found that whisker silicon oxide in which whiskers are formed on the surface of silicon oxide particles or particles having a structure in which silicon microcrystals are dispersed in a silicon-based compound. It has been found that by using the particles as the negative electrode material, even if the charge and discharge cycles are repeated, the current collecting property is not impaired by the whisker, and the battery characteristics are remarkably improved.
即ち、本発明者らは検討過程において、種々の条件にて得られた粒子の電池特性評価を行った結果、各材料によって特性の相違があることを確認した。そこで、得られた各種材料の分析を行った結果、粒子にウィスカーを有する材料を負極材とすることで、特性の良好な非水電解質二次電池用負極材が得られること及びこれら負極材の製造方法を知見した。 That is, as a result of evaluating battery characteristics of particles obtained under various conditions during the examination process, the present inventors confirmed that there are differences in characteristics depending on the materials. Therefore, as a result of analysis of the obtained various materials, it is possible to obtain a negative electrode material for a nonaqueous electrolyte secondary battery with good characteristics by using a material having whiskers in particles as a negative electrode material, and The manufacturing method was discovered.
従って、本発明は、下記の非水電解質二次電池用負極材及びその製造方法、ならびにリチウムイオン二次電池及び電気化学キャパシタを提供する。
［１］．一般式ＳｉＯx（０．５≦ｘ＜１．６）で表される酸化珪素粒子、珪素の微結晶が珪素系化合物に分散した構造を有する粒子、又はこれらの混合粒子の表面に、酸化珪素、珪素の微結晶が珪素系化合物に分散した構造、又はこれらの混合物からなるウィスカーが形成されたウィスカー含有粒子からなることを特徴とする非水電解質二次電池用負極材。
［２］．ウィスカー含有粒子が、その表面がカーボン皮膜で被覆された粒子である［１］記載の非水電解質二次電池用負極材。
［３］．一般式ＳｉＯx（０．５≦ｘ＜１．６）で表される酸化珪素粒子、珪素の微結晶が珪素系化合物に分散した構造を有する粒子、又はこれらの混合粒子を、３００００Ｐａ以下の減圧下、９００〜１３００℃で熱処理することを特徴とする［１］記載の非水電解質二次電池用負極材の製造方法。
［４］．一般式ＳｉＯ x （０．５≦ｘ＜１．６）で表される酸化珪素粒子、珪素の微結晶が珪素系化合物に分散した構造を有する粒子、又はこれらの混合粒子を、３００００Ｐａ以下の減圧下、９００〜１３００℃の熱処理温度で熱分解してカーボンを生成する有機物のガス中で、９００〜１３００℃で熱処理することを特徴とする請求項２記載の非水電解質二次電池用負極材の製造方法。
［５］．［１］又は［２］記載の非水電解質二次電池用負極材を含むことを特徴とするリチウムイオン二次電池。
［６］．［１］又は［２］記載の非水電解質二次電池用負極材を含むことを特徴とする電気化学キャパシタ。
Accordingly, the present invention provides the following negative electrode material for a non-aqueous electrolyte secondary battery, a method for producing the same, a lithium ion secondary battery, and an electrochemical capacitor.
[1]. Silicon oxide particles represented by the general formula SiO x (0.5 ≦ x <1.6), particles having a structure in which silicon microcrystals are dispersed in a silicon-based compound, or a mixture of these particles are formed on the surface of silicon oxide. A negative electrode material for a non-aqueous electrolyte secondary battery comprising a structure in which fine crystals of silicon are dispersed in a silicon-based compound, or whisker-containing particles in which whiskers made of a mixture thereof are formed.
[2]. The negative electrode material for a nonaqueous electrolyte secondary battery according to [1], wherein the whisker-containing particles are particles whose surfaces are coated with a carbon film.
[3]. Silicon oxide particles represented by the general formula SiO x (0.5 ≦ x <1.6), particles having a structure in which silicon microcrystals are dispersed in a silicon-based compound, or mixed particles thereof are reduced in pressure to 30000 Pa or less. The method for producing a negative electrode material for a nonaqueous electrolyte secondary battery according to [1], wherein the heat treatment is performed at 900 to 1300 ° C.
[4]. Silicon oxide particles represented by the general formula SiO x (0.5 ≦ x <1.6), particles having a structure in which silicon microcrystals are dispersed in a silicon-based compound, or mixed particles thereof are reduced in pressure to 30000 Pa or less. The negative electrode material for a non-aqueous electrolyte secondary battery according to claim 2, wherein the heat treatment is performed at 900 to 1300 ° C in an organic gas that is thermally decomposed at a heat treatment temperature of 900 to 1300 ° C to generate carbon. Manufacturing method.
[5]. A lithium ion secondary battery comprising the negative electrode material for a nonaqueous electrolyte secondary battery according to [1] or [2] .
[6]. An electrochemical capacitor comprising the negative electrode material for a non-aqueous electrolyte secondary battery according to [1] or [2] .
本発明で得られた負極材を非水電解質二次電池の負極材として用いることで、高い初回充放電効率を有し、サイクル性に優れた非水電解質二次電池を得ることができる。 By using the negative electrode material obtained in the present invention as a negative electrode material for a non-aqueous electrolyte secondary battery, a non-aqueous electrolyte secondary battery having high initial charge / discharge efficiency and excellent cycleability can be obtained.
本発明の非水電解質二次電池用負極材は、一般式ＳｉＯx（０．５≦ｘ＜１．６）で表される酸化珪素粒子、珪素の微結晶が珪素系化合物に分散した構造を有する粒子、又はこれらの混合粒子の表面に、ウィスカーが形成されたウィスカー含有粒子からなるものである。 The negative electrode material for a non-aqueous electrolyte secondary battery of the present invention has a structure in which silicon oxide particles represented by the general formula SiO x (0.5 ≦ x <1.6) and silicon microcrystals are dispersed in a silicon compound. It is made of whisker-containing particles in which whiskers are formed on the surface of the particles having the above or mixed particles thereof.
［酸化珪素粒子］
本発明において酸化珪素とは、二酸化珪素と金属珪素との混合物を加熱して生成した一酸化珪素ガスを冷却・析出して得られた非晶質の珪素酸化物の総称であり、本発明においては、一般式ＳｉＯx（０．５≦ｘ＜１．６）で表されるものをいう。ｘは０．８≦ｘ＜１．６が好ましく、０．８≦ｘ＜１．３がより好ましい。
[Silicon oxide particles]
In the present invention, silicon oxide is a general term for amorphous silicon oxides obtained by cooling and precipitating silicon monoxide gas generated by heating a mixture of silicon dioxide and metal silicon. Means a material represented by the general formula SiO x (0.5 ≦ x <1.6). x is preferably 0.8 ≦ x <1.6, and more preferably 0.8 ≦ x <1.3.
酸化珪素はさらに粉砕して酸化珪素粒子とする。酸化珪素粒子の物性については特に限定されるものではないが、平均粒子径はレーザー回折散乱式粒度分布測定法による体積平均値Ｄ50（即ち、累積体積が５０％となる時の粒子径（メジアン径）が、０．０１〜５０μｍが好ましく、０．１〜１０μｍがより好ましい。Ｄ50が０．０１μｍより小さいと表面酸化の影響で純度が低下し、非水電解質二次電池用負極材として用いた場合、充放電容量が低下したり、嵩密度が低下し、単位体積あたりの充放電容量が低下するおそれがある。一方、５０μｍより大きいと負極膜を貫通してショートする原因となるおそれがある。また、ＢＥＴ比表面積は０．１ｍ2／ｇ以上が好ましく、より好ましくは０．２ｍ2／ｇ以上で、上限として３０ｍ2／ｇ以下が好ましく、より好ましくは２０ｍ2／ｇ以下である。 The silicon oxide is further pulverized into silicon oxide particles. The physical properties of the silicon oxide particles are not particularly limited, but the average particle size is a volume average value D 50 according to the laser diffraction scattering type particle size distribution measurement method (that is, the particle size (median when the cumulative volume becomes 50%) (Diameter) is preferably from 0.01 to 50 μm, more preferably from 0.1 to 10 μm, and if D 50 is smaller than 0.01 μm, purity decreases due to the effect of surface oxidation, and the negative electrode material for a non-aqueous electrolyte secondary battery is used. If used, the charge / discharge capacity may decrease, the bulk density may decrease, and the charge / discharge capacity per unit volume may decrease, whereas if it exceeds 50 μm, it may cause a short circuit through the negative electrode film. there are. Further, BET specific surface area is preferably not less than 0.1 m 2 / g, more preferably 0.2 m 2 / g or more, preferably 30 m 2 / g or less as the upper limit, more preferably 20 m 2 / g or more It is.
［珪素の微結晶が珪素系化合物に分散した構造を有する粒子］
珪素の微結晶が珪素系化合物に分散した構造を有する粒子（珪素複合体粉末）における、珪素系化合物としては、不活性なものが好ましく、二酸化珪素、窒化珪素、炭化珪素、酸窒化珪素が好ましい。
[Particles having a structure in which silicon microcrystals are dispersed in a silicon compound]
In the particles having a structure in which silicon microcrystals are dispersed in a silicon compound (silicon composite powder), the silicon compound is preferably inactive, and silicon dioxide, silicon nitride, silicon carbide, and silicon oxynitride are preferable. .
珪素の微結晶が珪素系化合物に分散した構造を有する粒子は、下記性状を有してことが好ましい。
ｉ．銅を対陰極としたＸ線回折（Ｃｕ−Ｋα）において、２θ＝２８．４°付近を中心としたＳｉ（１１１）に帰属される回折ピークが観察され、その回折線の広がりをもとに、シェーラーの式によって求めた珪素の結晶の粒子径が好ましくは１〜５００ｎｍ、より好ましくは２〜２００ｎｍ、さらに好ましくは２〜２０ｎｍである。珪素の微粒子の大きさが１ｎｍより小さいと、充放電容量が小さくなる場合があるし、逆に５００ｎｍより大きいと充放電時の膨張収縮が大きくなり、サイクル性が低下するおそれがある。なお、珪素の微粒子の大きさは透過電子顕微鏡写真により測定することができる。
ｉｉ．固体ＮＭＲ（29Ｓｉ−ＤＤＭＡＳ）測定において、そのスペクトルが−１１０ｐｐｍ付近を中心とするブロードな二酸化珪素のピークとともに−８４ｐｐｍ付近にＳｉのダイヤモンド結晶の特徴であるピークが存在する。なお、このスペクトルは、通常の酸化珪素（ＳｉＯx：ｘ＝１．０＋α）とは全く異なるもので、構造そのものが明らかに異なっているものである。また、透過電子顕微鏡によって、シリコンの結晶が無定形の二酸化珪素に分散していることが確認される。
The particles having a structure in which silicon microcrystals are dispersed in a silicon-based compound preferably have the following properties.
i. In X-ray diffraction (Cu-Kα) using copper as the counter-cathode, a diffraction peak attributed to Si (111) centered around 2θ = 28.4 ° is observed, and based on the broadening of the diffraction line The particle diameter of the silicon crystal determined by the Scherrer equation is preferably 1 to 500 nm, more preferably 2 to 200 nm, and still more preferably 2 to 20 nm. If the size of the silicon fine particles is smaller than 1 nm, the charge / discharge capacity may be reduced. Conversely, if the silicon fine particle is larger than 500 nm, the expansion / contraction during charge / discharge increases, and the cycle performance may decrease. The size of the silicon fine particles can be measured by a transmission electron micrograph.
ii. In solid-state NMR ( 29 Si-DDMAS) measurement, there is a peak characteristic of Si diamond crystals in the vicinity of −84 ppm, along with a broad silicon dioxide peak whose spectrum is centered around −110 ppm. This spectrum is completely different from ordinary silicon oxide (SiO x : x = 1.0 + α), and the structure itself is clearly different. Further, it is confirmed by transmission electron microscope that silicon crystals are dispersed in amorphous silicon dioxide.
珪素の微結晶が珪素系化合物に分散した構造を有する粒子中における、珪素微結晶（Ｓｉ）の分散量は２〜３６質量％が好ましく、１０〜３０質量％が好ましい。この分散珪素量が２質量％未満では、充放電容量が小さくなる場合があり、逆に３６質量％を超えるとサイクル性が低下する場合がある。 The amount of silicon microcrystals (Si) dispersed in particles having a structure in which silicon microcrystals are dispersed in a silicon-based compound is preferably 2 to 36% by mass, and more preferably 10 to 30% by mass. If the amount of dispersed silicon is less than 2% by mass, the charge / discharge capacity may be reduced, and conversely if it exceeds 36% by mass, the cycle performance may be reduced.
珪素の微結晶が珪素系化合物に分散した構造を有する粒子は、平均粒子径はレーザー回折散乱式粒度分布測定法による体積平均値Ｄ50（即ち、累積体積が５０％となる時の粒子径（メジアン径）が、０．０１〜５０μｍを有するものであれば、その製造方法は特に限定されるものではないが、例えば、一般式ＳｉＯx（０．５≦ｘ＜１．６）で表される酸化珪素粉末を不活性ガス雰囲気下９００〜１４００℃の温度域で熱処理を施して不均化する方法により得ることができる。 Particles having a structure in which silicon microcrystals are dispersed in a silicon-based compound have an average particle diameter of a volume average value D 50 (that is, a particle diameter at a cumulative volume of 50% (according to a laser diffraction scattering particle size distribution measurement method) The production method is not particularly limited as long as the median diameter is 0.01 to 50 μm. For example, it is represented by the general formula SiO x (0.5 ≦ x <1.6). The silicon oxide powder can be obtained by subjecting it to a disproportionation by subjecting it to a heat treatment in the temperature range of 900 to 1400 ° C. in an inert gas atmosphere.
酸化珪素粉末の平均粒子径（体積平均値Ｄ50）は０．０１μｍ以上が好ましく、０．１μｍ以上がより好ましく、０．５μｍ以上がさらに好ましい。上限は特に限定されないが、５０μｍ以下が好ましく、３０μｍ以下がより好ましい。ＢＥＴ比表面積は０．１ｍ2／ｇ以上が好ましく、０．２ｍ2／ｇ以上が好ましく、上限としては特に限定されないが、３０ｍ2／ｇ以下が好ましく、２０ｍ2／ｇ以下がより好ましい。ｘの範囲は０．５≦ｘ＜１．６であり、０．８≦ｘ＜１．３が好ましく、０．８≦ｘ≦１．２がより好ましい。酸化珪素粉末の平均粒子径及びＢＥＴ比表面積が上記範囲外では所望の平均粒子径及びＢＥＴ比表面積を有する珪素の微結晶が珪素系化合物に分散した構造を有する粒子が得られないおそれがあり、ｘの値が０．５より小さいＳｉＯx粉末の製造は困難であるし、ｘの値が１．６以上のものは、熱処理を行い、不均化反応を行なった際に、不活性なＳｉＯ2の割合が大きく、リチウムイオン二次電池として使用した場合、充放電容量が低下するおそれがある。 The average particle diameter (volume average value D 50 ) of the silicon oxide powder is preferably 0.01 μm or more, more preferably 0.1 μm or more, and further preferably 0.5 μm or more. Although an upper limit is not specifically limited, 50 micrometers or less are preferable and 30 micrometers or less are more preferable. BET specific surface area is preferably not less than 0.1 m 2 / g, preferably at least 0.2 m 2 / g, is not particularly limited but preferably is 30 m 2 / g or less, 20 m 2 / g or less is more preferable. The range of x is 0.5 ≦ x <1.6, preferably 0.8 ≦ x <1.3, and more preferably 0.8 ≦ x ≦ 1.2. If the average particle diameter and the BET specific surface area of the silicon oxide powder are outside the above ranges, particles having a structure in which silicon microcrystals having a desired average particle diameter and a BET specific surface area are dispersed in a silicon-based compound may not be obtained. It is difficult to produce a SiO x powder having an x value of less than 0.5, and those having an x value of 1.6 or more are treated with heat treatment and subjected to a disproportionation reaction. The ratio of 2 is large, and when used as a lithium ion secondary battery, the charge / discharge capacity may be reduced.
一方、酸化珪素の不均化において、熱処理温度が９００℃より低いと、不均化が全く進行しないかシリコンの微細なセル（珪素の微結晶）の形成に極めて長時間を要し、効率的でなく、逆に１４００℃より高いと、二酸化珪素部の構造化が進み、リチウムイオンの往来が阻害されるので、リチウムイオン二次電池としての機能が低下するおそれがある。熱処理温度は１０００〜１３００℃が好ましく、１１００〜１２５０℃がより好ましい。なお、処理時間（不均化時間）は不均化処理温度に応じて１０分〜２０時間、特に３０分〜１２時間程度の範囲で適宜選定することができるが、例えば１１００℃の処理温度においては５時間程度で所望の物性を有する、珪素の微結晶が珪素系化合物に分散した構造を有する粒子（珪素複合体粉末）が得られる。 On the other hand, in disproportionation of silicon oxide, if the heat treatment temperature is lower than 900 ° C., disproportionation does not proceed at all or it takes an extremely long time to form fine silicon cells (silicon microcrystals), which is efficient. On the other hand, if the temperature is higher than 1400 ° C., the structure of the silicon dioxide portion is advanced and the lithium ion traffic is hindered, so that the function as the lithium ion secondary battery may be deteriorated. 1000-1300 degreeC is preferable and the heat processing temperature has more preferable 1100-1250 degreeC. The treatment time (disproportionation time) can be appropriately selected in the range of 10 minutes to 20 hours, particularly 30 minutes to 12 hours, depending on the disproportionation treatment temperature. For example, at a treatment temperature of 1100 ° C. Gives particles (silicon composite powder) having a desired physical property and having a structure in which silicon microcrystals are dispersed in a silicon-based compound in about 5 hours.
上記不均化処理は、不活性ガス雰囲気において、加熱機構を有する反応装置を用いればよく、特に限定されず、連続法、回分法での処理が可能で、具体的には流動層反応炉、回転炉、竪型移動層反応炉、トンネル炉、バッチ炉、ロータリーキルン等をその目的に応じ適宜選択することができる。この場合、（処理）ガスとしては、Ａｒ、Ｈｅ、Ｈ2、Ｎ2等の上記処理温度にて不活性なガス単独もしくはそれらの混合ガスを用いることができる。 The disproportionation treatment may be performed using a reaction apparatus having a heating mechanism in an inert gas atmosphere, and is not particularly limited, and can be performed by a continuous process or a batch process. Specifically, a fluidized bed reactor, A rotary furnace, a vertical moving bed reactor, a tunnel furnace, a batch furnace, a rotary kiln, or the like can be appropriately selected according to the purpose. In this case, as the (treatment) gas, an inert gas alone or a mixed gas thereof such as Ar, He, H 2 , N 2 or the like can be used.
［ウィスカー含有粒子］
本発明のウィスカー含有粒子は、一般式ＳｉＯx（０．５≦ｘ＜１．６）で表される酸化珪素粒子、珪素の微結晶が珪素系化合物に分散した構造を有する粒子、又はこれらの混合粒子の表面に、ウィスカーが形成されたものである。
[Whisker-containing particles]
The whisker-containing particles of the present invention include silicon oxide particles represented by the general formula SiO x (0.5 ≦ x <1.6), particles having a structure in which silicon microcrystals are dispersed in a silicon-based compound, or these Whisker is formed on the surface of the mixed particles.
なお、本出願人は、先に特許３９５２１８０号において、
「Ｘ線回折において、Ｓｉ（１１１）に帰属される回折ピークが観察され、その回折線の半価幅をもとにシェーラー法により求めた珪素の結晶の大きさが１〜５００ｎｍである、珪素の微結晶が珪素系化合物に分散した構造を有する粒子の表面を炭素でコーティングしてなることを特徴とする非水電解質二次電池負極材用導電性珪素複合体。」
を提案しているが、これは通常、酸化珪素を９００〜１４００℃の温度で、しかも常圧（大気圧）下で、有機物ガス及び／又は蒸気で不均化することにより製造するものであって、本発明のウィスカーが形成されないものであるから、本発明のウィスカー含有粒子と相違する。
In addition, the applicant of the present invention in Patent No. 3952180,
“In X-ray diffraction, a diffraction peak attributed to Si (111) is observed, and the silicon crystal size determined by the Scherrer method based on the half width of the diffraction line is 1 to 500 nm. A conductive silicon composite for a negative electrode material for a non-aqueous electrolyte secondary battery, wherein the surface of particles having a structure in which microcrystals of the above are dispersed in a silicon compound is coated with carbon. "
This is usually produced by disproportionating silicon oxide with organic gas and / or steam at a temperature of 900 to 1400 ° C. and under normal pressure (atmospheric pressure). Thus, since the whisker of the present invention is not formed, it is different from the whisker-containing particle of the present invention.
ウィスカーは、酸化珪素、珪素の微結晶が珪素系化合物に分散した構造、又はこれらの混合物からなるものであり、その長さは０．０１〜３０μｍが好ましく、０．１〜１０μｍがより好ましい。０．０１μｍより短いと集電性向上への寄与が不十分となるおそれがあり、３０μｍより長いと電極作製時に折れてしまうおそれがある。また、ウィスカーの太さは０．００１〜１μｍが好ましく、０．０１〜０．１μｍがより好ましい。０．００１μｍより細いと強度が不十分となる場合があり、１μｍより太いとウィスカーとしての効力を発揮できないおそれがある。酸化珪素粒子に対するウィスカーの存在割合は、０．００１〜１０質量％が好ましく、０．０１〜５質量％がより好ましく、０．１〜１質量％がさらに好ましい。０．００１質量％より少ないと存在効果が不十分となるおそれがあり、１０質量％より多いと電極作製が困難となるおそれがある。 The whisker is composed of silicon oxide, a structure in which microcrystals of silicon are dispersed in a silicon-based compound, or a mixture thereof, and the length is preferably 0.01 to 30 μm, and more preferably 0.1 to 10 μm. If it is shorter than 0.01 μm, the contribution to improving the current collecting property may be insufficient, and if it is longer than 30 μm, it may be broken during electrode production. The thickness of the whisker is preferably 0.001 to 1 μm, and more preferably 0.01 to 0.1 μm. If it is thinner than 0.001 μm, the strength may be insufficient, and if it is thicker than 1 μm, the effect as a whisker may not be exhibited. 0.001-10 mass% is preferable, the presence ratio of the whisker with respect to a silicon oxide particle is more preferable, 0.01-5 mass% is more preferable, and 0.1-1 mass% is further more preferable. If the amount is less than 0.001% by mass, the existence effect may be insufficient. If the amount is more than 10% by mass, electrode preparation may be difficult.
ウィスカー含有粒子は、粒子、ウィスカー又は両者の表面を、カーボン皮膜で被覆して導電性を付与することが好ましい。カーボン被覆量は特に限定されるものではないが、酸化珪素粒子に対して０．３〜４０質量％が好ましく、０．５〜３０質量％がより好ましい。カーボン被覆量が０．３質量％より少ないと、導電性を維持できなくなるおそれがあり、結果として非水電解質二次電池用負極材とした場合にサイクル性が低下するおそれがある。逆にカーボン被覆量が４０質量％より多くても、効果の向上が見られないばかりか、負極材料に占めるカーボンの割合が多くなり、非水電解質二次電池用負極材として用いた場合、充放電容量が低下するおそれがある。 The whisker-containing particles are preferably provided with conductivity by coating the surfaces of the particles, whiskers, or both with a carbon film. The carbon coating amount is not particularly limited, but is preferably 0.3 to 40% by mass, and more preferably 0.5 to 30% by mass with respect to the silicon oxide particles. If the carbon coating amount is less than 0.3% by mass, the conductivity may not be maintained, and as a result, when the negative electrode material for a non-aqueous electrolyte secondary battery is used, the cycle performance may be reduced. Conversely, even if the carbon coating amount is more than 40% by mass, not only the improvement of the effect is seen, but also the proportion of carbon in the negative electrode material increases, and when used as a negative electrode material for a non-aqueous electrolyte secondary battery, The discharge capacity may be reduced.
ウィスカー含有粒子の平均粒子径は、レーザー回折散乱式粒度分布測定法による体積平均値Ｄ50において、０．０１〜５０μｍが好ましく、０．１〜１０μｍがより好ましい。 The average particle diameter of the whisker-containing particles is preferably 0.01 to 50 μm, and more preferably 0.1 to 10 μm, in the volume average value D 50 by the laser diffraction / scattering particle size distribution measurement method.
本発明のウィスカー含有粒子を得る方法としては、例えば、一般式ＳｉＯx（０．５≦ｘ＜１．６）で表される酸化珪素粒子、珪素の微結晶が珪素系化合物に分散した構造を有する粒子、又はこれらの混合粒子を、３００００Ｐａ以下、好ましくは１〜２００００Ｐａの減圧下、９００〜１３００℃、好ましくは９５０〜１１００℃で熱処理する方法が挙げられる。上記圧力が３００００Ｐａより大きいと、ウィスカーの生成が困難となり、処理温度が９００℃より低いとウィスカー生成量が少なくなり、１３００℃より高いと、二酸化珪素部の構造化が進み、リチウムイオンの往来が阻害されるので、リチウムイオン二次電池用負極材としての機能が低下するおそれがある。なお、処理時間は目的とするウィスカー生成量、処理温度、処理圧力等によって適宜選定されるが、通常、１〜１０時間、特に２〜５時間程度が経済的にも効率的である。この製造方法は簡便であり、工業的規模の生産にも十分耐え得るものである。なお、一般式ＳｉＯx（０．５≦ｘ＜１．６）で表される酸化珪素粒子を、３００００Ｐａ以下、９００〜１３００℃で熱処理する場合に、珪素の微結晶が珪素系化合物に分散した構造を有する粒子形成する場合がある。 Examples of the method for obtaining the whisker-containing particles of the present invention include a structure in which silicon oxide particles represented by the general formula SiO x (0.5 ≦ x <1.6) and silicon microcrystals are dispersed in a silicon compound. The method which heat-processes the particle | grains which have or these mixed particles at 900-1300 degreeC under the reduced pressure of 30000 Pa or less, Preferably 1-20000 Pa, Preferably it is 950-1100 degreeC. When the pressure is higher than 30000 Pa, it becomes difficult to generate whiskers. When the processing temperature is lower than 900 ° C., the amount of whisker generated is reduced. When the processing temperature is higher than 1300 ° C., the structuring of the silicon dioxide portion progresses and lithium ions come and go. Since it will be inhibited, the function as a negative electrode material for lithium ion secondary batteries may be reduced. The treatment time is appropriately selected depending on the desired whisker production amount, treatment temperature, treatment pressure, etc. Usually, about 1 to 10 hours, particularly about 2 to 5 hours is economically efficient. This manufacturing method is simple and can sufficiently withstand industrial scale production. When silicon oxide particles represented by the general formula SiO x (0.5 ≦ x <1.6) are heat-treated at 30000 Pa or less and 900 to 1300 ° C., silicon microcrystals are dispersed in the silicon-based compound. Particles having a structure may be formed.
ウィスカー含有粒子の表面をカーボン皮膜で被覆する場合は、化学蒸着による方法が好ましく、上記ウィスカーを形成する熱処理時に、反応器内に有機物ガスを導入することで効率よく行うことも可能である。 When the surface of the whisker-containing particles is coated with a carbon film, a chemical vapor deposition method is preferable, and it is also possible to efficiently carry out by introducing an organic gas into the reactor during the heat treatment for forming the whisker.
本発明における有機物ガスを発生する原料として用いられる有機物としては、特に非酸性雰囲気下において、上記熱処理温度で熱分解してカーボン（黒鉛）を生成し得るものが選択され、例えば、メタン、エタン、エチレン、アセチレン、プロパン、ブタン、ブテン、ペンタン、イソブタン、ヘキサン等の炭化水素の単独又は混合物、ベンゼン、トルエン、キシレン、スチレン、エチルベンゼン、ジフェニルメタン、ナフタレン、フェノール、クレゾール、ニトロベンゼン、クロルベンゼン、インデン、クマロン、ピリジン、アントラセン、フェナントレン等の１環〜３環の芳香族炭化水素又はこれらの混合物が挙げられる。また、タール蒸留工程で得られるガス軽油、クレオソート油、アントラセン油、ナフサ分解タール油も単独又は混合物を用いることができる。 As an organic substance used as a raw material for generating an organic gas in the present invention, a substance that can be pyrolyzed at the above heat treatment temperature to generate carbon (graphite) is selected, particularly in a non-acidic atmosphere. For example, methane, ethane, A single or mixture of hydrocarbons such as ethylene, acetylene, propane, butane, butene, pentane, isobutane, hexane, benzene, toluene, xylene, styrene, ethylbenzene, diphenylmethane, naphthalene, phenol, cresol, nitrobenzene, chlorobenzene, indene, coumarone , Pyridine, anthracene, phenanthrene, and the like, and monocyclic to tricyclic aromatic hydrocarbons or a mixture thereof. In addition, gas gas oil, creosote oil, anthracene oil, and naphtha cracked tar oil obtained in the tar distillation step can be used alone or as a mixture.
［非水電解質二次電池用負極材］
本発明は、上記ウィスカー含有粒子を非水電解質二次電池用負極材に用いるものであり、ウィスカー含有粒子からなる非水電解質二次電池用負極材である。この本発明で得られた非水電解質二次電池負極材を用いて、負極を作製し、リチウムイオン二次電池を製造することができる。
[Negative electrode material for non-aqueous electrolyte secondary battery]
This invention uses the said whisker containing particle | grain for the negative electrode material for nonaqueous electrolyte secondary batteries, and is a negative electrode material for nonaqueous electrolyte secondary batteries which consists of whisker containing particles. Using the nonaqueous electrolyte secondary battery negative electrode material obtained in the present invention, a negative electrode can be produced to produce a lithium ion secondary battery.
なお、上記非水電解質二次電池用負極材を用いて負極を作製する場合、カーボン、黒鉛等の導電剤を添加することができる。この場合においても導電剤の種類は特に限定されず、構成された電池において、分解や変質を起こさない電子伝導性の材料であればよく、具体的にはＡｌ，Ｔｉ，Ｆｅ，Ｎｉ，Ｃｕ，Ｚｎ，Ａｇ，Ｓｎ，Ｓｉ等の金属粉末や金属繊維又は天然黒鉛、人造黒鉛、各種のコークス粉末、メソフェーズ炭素、気相成長炭素繊維、ピッチ系炭素繊維、ＰＡＮ系炭素繊維、各種の樹脂焼成体等の黒鉛を用いることができる。 In addition, when producing a negative electrode using the said negative electrode material for nonaqueous electrolyte secondary batteries, electrically conductive agents, such as carbon and graphite, can be added. Also in this case, the kind of the conductive agent is not particularly limited, and any electronic conductive material that does not cause decomposition or alteration in the constituted battery may be used. Specifically, Al, Ti, Fe, Ni, Cu, Metal powder such as Zn, Ag, Sn, Si, metal fiber or natural graphite, artificial graphite, various coke powders, mesophase carbon, vapor grown carbon fiber, pitch carbon fiber, PAN carbon fiber, various resin fired bodies Such graphite can be used.
負極（成型体）の調製方法としては下記の方法が挙げられる。上記ウィスカー含有粒子と、必要に応じて導電剤と、結着剤等の他の添加剤とに、Ｎ−メチルピロリドン又は水等の溶剤を混練してペースト状の合剤とし、この合剤を集電体のシートに塗布する。この場合、集電体としては、銅箔、ニッケル箔等、通常、負極の集電体として使用されている材料であれば、特に厚さ、表面処理の制限なく使用することができる。なお、合剤をシート状に成形する成形方法は特に限定されず、公知の方法を用いることができる。 Examples of the method for preparing the negative electrode (molded body) include the following methods. A paste-like mixture is prepared by kneading the whisker-containing particles, if necessary, a conductive agent and other additives such as a binder with a solvent such as N-methylpyrrolidone or water. Apply to current collector sheet. In this case, as the current collector, any material that is usually used as a negative electrode current collector, such as a copper foil or a nickel foil, can be used without any particular limitation on thickness and surface treatment. In addition, the shaping | molding method which shape | molds a mixture into a sheet form is not specifically limited, A well-known method can be used.
［リチウムイオン二次電池］
リチウムイオン二次電池は、上記負極材を用いる点に特徴を有し、その他の正極、負極、電解質、セパレータ等の材料及び電池形状等は公知のものを使用することができ、特に限定されない。例えば、正極活物質としてはＬｉＣｏＯ2、ＬｉＮｉＯ2、ＬｉＭｎ2Ｏ4、Ｖ2Ｏ5、ＭｎＯ2、ＴｉＳ2、ＭｏＳ2等の遷移金属の酸化物、リチウム、及びカルコゲン化合物等が用いられる。電解質としては、例えば、六フッ化リン酸リチウム、過塩素酸リチウム等のリチウム塩を含む非水溶液が用いられ、非水溶媒としてはプロピレンカーボネート、エチレンカーボネート、ジエチルカーボネート、ジメトキシエタン、γ−ブチロラクトン、２−メチルテトラヒドロフラン等の１種又は２種類以上を組み合わせて用いられる。また、それ以外の種々の非水系電解質や固体電解質も使用できる。
[Lithium ion secondary battery]
The lithium ion secondary battery is characterized in that the negative electrode material is used, and other materials such as the positive electrode, the negative electrode, the electrolyte, and the separator, and the battery shape and the like can be known, and are not particularly limited. For example, as the positive electrode active material, LiCoO 2 , LiNiO 2 , LiMn 2 O 4 , V 2 O 5 , MnO 2 , TiS 2 , MoS 2 and other transition metal oxides, lithium, chalcogen compounds, and the like are used. As the electrolyte, for example, a non-aqueous solution containing a lithium salt such as lithium hexafluorophosphate and lithium perchlorate is used. Examples of the non-aqueous solvent include propylene carbonate, ethylene carbonate, diethyl carbonate, dimethoxyethane, γ-butyrolactone, One type or a combination of two or more types such as 2-methyltetrahydrofuran is used. Various other non-aqueous electrolytes and solid electrolytes can also be used.
［電気化学キャパシタ］
また、電気化学キャパシタを得る場合は、電気化学キャパシタは、上記負極材を用いる点に特徴を有し、その他の電解質、セパレータ等の材料及びキャパシタ形状等は限定されない。例えば、電解質として六フッ化リン酸リチウム、過塩素リチウム、ホウフッ化リチウム、六フッ化砒素酸リチウム等のリチウム塩を含む非水溶液が用いられ、非水溶媒としてはプロピレンカーボネート、エチレンカーボネート、ジメチルカーボネート、ジエチルカーボネート、ジメトキシエタン、γ−ブチロラクトン、２−メチルテトラヒドロフラン等の１種又は２種類以上を組み合わせて用いられる。また、それ以外の種々の非水系電解質や固体電解質も使用できる。
[Electrochemical capacitor]
In the case of obtaining an electrochemical capacitor, the electrochemical capacitor is characterized in that the negative electrode material is used, and other materials such as an electrolyte and a separator and a capacitor shape are not limited. For example, non-aqueous solutions containing lithium salts such as lithium hexafluorophosphate, lithium perchlorate, lithium borofluoride, lithium hexafluoroarsenate, etc. are used as the electrolyte, and propylene carbonate, ethylene carbonate, dimethyl carbonate are used as the non-aqueous solvent. , Diethyl carbonate, dimethoxyethane, γ-butyrolactone, 2-methyltetrahydrofuran and the like. Various other non-aqueous electrolytes and solid electrolytes can also be used.
以下、実施例と比較例を示し、本発明を具体的に説明するが、本発明は下記の実施例に限定されるものではない。 EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated concretely, this invention is not limited to the following Example.
［実施例１］
平均粒子径５．０μｍの一般式ＳｉＯx（ｘ＝１．０２）で表される酸化珪素粉末２００ｇをバッチ式加熱炉内に仕込んだ。その後、油回転式真空ポンプで１００Ｐａ以下まで減圧しつつ、３００℃／ｈｒの昇温速度で１１００℃まで昇温、５時間保持したのち室温まで自然冷却した。得られた粉末は平均粒子径＝５．３μｍであった。ＴＥＭで確認したところ、珪素の微結晶が珪素系化合物に分散した構造を有する粒子であり、走査型電子顕微鏡（ＳＥＭ）で確認したところ、視野全体にウィスカーが確認された（図１参照）。ウィスカーの長さは０．５〜５μｍであり、ウィスカーの太さは０．０５〜０．３μｍであり、酸化珪素粒子に対するウィスカーの存在割合は、０．１〜０．３質量％であった。
[Example 1]
200 g of silicon oxide powder represented by the general formula SiO x (x = 1.02) having an average particle diameter of 5.0 μm was charged into a batch type heating furnace. Thereafter, while reducing the pressure to 100 Pa or less with an oil rotary vacuum pump, the temperature was raised to 1100 ° C. at a temperature rising rate of 300 ° C./hr, held for 5 hours, and then naturally cooled to room temperature. The obtained powder had an average particle size = 5.3 μm. When confirmed by TEM, it was a particle having a structure in which silicon microcrystals were dispersed in a silicon-based compound. When confirmed by a scanning electron microscope (SEM), whiskers were confirmed over the entire field of view (see FIG. 1). The length of the whisker was 0.5 to 5 μm, the thickness of the whisker was 0.05 to 0.3 μm, and the ratio of the whisker to the silicon oxide particles was 0.1 to 0.3% by mass. .
＜電池特性＞
負極材の有用性を確認するため、下記方法で電池特性を評価した。
得られた粉末８５質量部と電気化学工業製デンカブラック（カーボン）５質量部、ポリイミド１０質量部を混合し、さらにＮ−メチルピロリドンを加えてスラリーとし、このスラリーを厚さ２０μｍの銅箔に塗布し、８０℃で１時間乾燥後、ローラープレスにより電極を加圧成形し、この電極を３５０℃で１時間真空乾燥した後、２ｃｍ2に打ち抜き負極とした。
<Battery characteristics>
In order to confirm the usefulness of the negative electrode material, the battery characteristics were evaluated by the following method.
85 parts by mass of the obtained powder, 5 parts by mass of Denka Black (carbon) manufactured by Denki Kagaku Kogyo, and 10 parts by mass of polyimide were mixed, and further N-methylpyrrolidone was added to form a slurry. This slurry was formed into a copper foil having a thickness of 20 μm. After coating and drying at 80 ° C. for 1 hour, the electrode was pressure-molded by a roller press, and this electrode was vacuum-dried at 350 ° C. for 1 hour, and then punched out to 2 cm 2 to obtain a negative electrode.
ここで、得られた負極の充放電特性を評価するために、対極にリチウム箔を使用し、非水電解質として六フッ化リンリチウムをエチレンカーボネートとジエチルカーボネートの１／１（体積比）混合液に１モル／Ｌの濃度で溶解した非水電解質溶液を用い、セパレータに厚さ３０μｍのポリエチレン製微多孔質フィルムを用いた評価用リチウムイオン二次電池を作製した。 Here, in order to evaluate the charge / discharge characteristics of the obtained negative electrode, a lithium foil was used as a counter electrode, and lithium hexafluoride was mixed with 1/1 (volume ratio) of ethylene carbonate and diethyl carbonate as a non-aqueous electrolyte. A lithium ion secondary battery for evaluation using a non-aqueous electrolyte solution dissolved at a concentration of 1 mol / L and a polyethylene microporous film having a thickness of 30 μm as a separator was prepared.
作製したリチウムイオン二次電池は、一晩室温で放置した後、二次電池充放電試験装置（（株）ナガノ製）を用い、テストセルの電圧が０Ｖに達するまで０．５ｍＡ／ｃｍ2の定電流で充電を行い、０Ｖに達した後は、セル電圧を０Ｖに保つように電流を減少させて充電を行った。そして、電流値が４０μＡ／ｃｍ2を下回った時点で充電を終了した。放電は０．５ｍＡ／ｃｍ2の定電流で行い、セル電圧が２．０Ｖを上回った時点で放電を終了し、放電容量を求めた。 The prepared lithium ion secondary battery was allowed to stand at room temperature overnight, and then charged with a secondary battery charge / discharge tester (manufactured by Nagano Co., Ltd.) until the test cell voltage reached 0 V at 0.5 mA / cm 2 . Charging was performed at a constant current, and after reaching 0V, charging was performed by decreasing the current so as to keep the cell voltage at 0V. Then, charging was terminated when the current value fell below 40 μA / cm 2 . Discharging was performed at a constant current of 0.5 mA / cm 2 , and discharging was terminated when the cell voltage exceeded 2.0 V, and the discharge capacity was determined.
以上の充放電試験を繰り返し、評価用リチウムイオン二次電池の５０サイクル後の充放電試験を行った。その結果、初回充電容量１８４４ｍＡｈ／ｇ、初回放電容量１４７５ｍＡｈ／ｇ、初回充放電効率８０％、５０サイクル目の放電容量１３４２ｍＡｈ／ｇ、５０サイクル後のサイクル保持率９１％の高容量であり、かつ初回充放電効率及びサイクル性に優れたリチウムイオン二次電池であることが確認された。 The above charge / discharge test was repeated, and a charge / discharge test after 50 cycles of the lithium ion secondary battery for evaluation was performed. As a result, the initial charge capacity is 1844 mAh / g, the initial discharge capacity is 1475 mAh / g, the initial charge / discharge efficiency is 80%, the discharge capacity at the 50th cycle is 1342 mAh / g, the cycle retention after 50 cycles is 91%, and the high capacity. It was confirmed that the lithium ion secondary battery was excellent in initial charge / discharge efficiency and cycleability.
［比較例１］
実施例１で用いた一般式ＳｉＯx（ｘ＝１．０２）で示される酸化珪素粉末を熱処理せずそのまま使用した他は、実施例１と同様に粉末を得て、電池を作製した。粉末を走査型電子顕微鏡（ＳＥＭ）で確認したところ、ウィスカーは確認されなかった（図２参照）。
[Comparative Example 1]
A battery was prepared by obtaining a powder in the same manner as in Example 1 except that the silicon oxide powder represented by the general formula SiO x (x = 1.02) used in Example 1 was used as it was without heat treatment. When the powder was confirmed with a scanning electron microscope (SEM), whiskers were not confirmed (see FIG. 2).
この電池に対しても同様な評価を行った結果、初回充放電容量１８４６ｍＡｈ／ｇ、初回放電容量１４０３ｍＡｈ／ｇ、初回充放電効率７６％、５０サイクル目の放電容量１２２１ｍＡｈ／ｇ、５０サイクル後のサイクル保持率８７％であり、実施例１に比べ初回充放電効率、サイクル性の劣るリチウムイオン二次電池であった。 As a result of the same evaluation for this battery, the initial charge / discharge capacity was 1846 mAh / g, the initial discharge capacity was 1403 mAh / g, the initial charge / discharge efficiency was 76%, the 50th cycle discharge capacity was 1221 mAh / g, and after 50 cycles. It was a lithium ion secondary battery having a cycle retention of 87% and inferior initial charge / discharge efficiency and cycleability compared to Example 1.
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