JP2004273377A

JP2004273377A - CHARGEABLE/DISCHARGEABLE INORGANIC COMPOUND, ITS MANUFACTURInG METHOD, AND NONAQUEOUS ELECTROLYTE SECONDARY BATTERY USING IT

Info

Publication number: JP2004273377A
Application number: JP2003065965A
Authority: JP
Inventors: Shuhin Cho; 守斌張; Yusuke Watarai; 祐介渡会; Kanji Hisayoshi; 完治久芳
Original assignee: Mitsubishi Materials Corp
Current assignee: Mitsubishi Materials Corp
Priority date: 2003-03-12
Filing date: 2003-03-12
Publication date: 2004-09-30

Abstract

<P>PROBLEM TO BE SOLVED: To enhance charge and discharge cycle characteristics and heavy current charge and discharge characteristics, by reducing a volume change when occluding and discharging an alkali metal ion such as a lithium ion. <P>SOLUTION: This chargeable/dischargeable inorganic compound has silicon, carbon and oxygen as main components, and comprises a particle with an average particle diameter of 0.3-100 μm, which is expressed by formula A<SB>x</SB>Si<SB>y</SB>C<SB>1-y</SB>O<SB>z</SB>by inserting an alkali metal. It also has a slender hole with an average hole diameter of 0.3-50 nm. In addition, the chargeable/dischargeable inorganic compound has 1-30% porosity, and contains 50-5 wt.% silicon. The chargeable/dischargeable inorganic compound also has an X-ray diffraction pattern analogous to amorphous silicon dioxide. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、リチウム二次電池等の非水電解液二次電池の負極活物質に含有される充放電可能な無機化合物と、この充放電可能な無機化合物の製造方法と、この充放電可能な無機化合物を負極活物質に含む非水二次電池に関するものである。
【０００２】
【従来の技術】
従来、負極活物質として、黒鉛やコークス等の炭素系化合物を用いたリチウム二次電池が知られている。
しかし、上記炭素系化合物を用いたリチウム二次電池の充放電容量は小さく、例えば純粋な炭素では理論充放電容量が３７２ｍＡｈ／ｇと小さな値しか示さない問題点があった。
この点を解消するために、ケイ素を含む負極活物質を用いたリチウム二次電池が知られており、このリチウム二次電池の充放電容量は大きく、純粋なケイ素では理論充放電容量が４０１７ｍＡｈ／ｇと極めて大きな値を示す。
しかし、上記ケイ素を含む負極活物質を用いたリチウム二次電池では、この電池の充放電時に、即ちリチウムイオンの吸蔵及び放出の繰返し時に、ケイ素を含む負極活物質が初期状態と比べて３００〜４００％と大きく体積変化し、この負極活物質の内部に亀裂が発生して負極活物質粒子が微細化してしまう問題点があった。更に負極活物質の膨張及び収縮の繰返しにより負極活物質と集電体の間や負極活物質と導電助剤の間に隙間が発生してこれらが接触しなくなり、二次電池の充放電サイクル特性が低下する問題点があった。
【０００３】
この点を解消するために、式Ａ_ｘＳｉ_ｙＣ_１−ｙＯ_ｚで表される炭素質挿入化合物であって、無定形ＳｉＯ_２に類似したＸ線回折パターンを有する炭素質挿入化合物が開示されている（例えば、特許文献１参照）。ここで、式Ａ_ｘＳｉ_ｙＣ_１−ｙＯ_ｚ中のＡは挿入されたアルカリ金属であり、ｘ＞０であり、０＜ｙ＜１であり、更に０＜ｚ／ｙ＜４である。
このように構成された炭素質挿入化合物は可逆的容量が大きいので、この炭素質挿入化合物をリチウム二次電池の負極活物質として用いると、高容量のリチウム二次電池が得られるようになっている。
【０００４】
【特許文献１】
特開平８−２５９２１３号公報
【０００５】
【発明が解決しようとする課題】
しかし、上記特許文献１に示された炭素質挿入化合物では、この炭素質挿入化合物をリチウム二次電池の負極活物質として用いた場合、上記従来のケイ素をリチウム二次電池の負極活物質として用いた場合より、充放電時の体積変化が小さくなるけれども、未だその体積変化が大きいため、充放電サイクル特性を向上できず実用化が困難であった。
また、上記特許文献１に示された炭素質挿入化合物では、この炭素質挿入化合物をリチウム二次電池の負極活物質として用いた場合、ケイ素と酸素が結合しかつケイ素と炭素が結合してしまうため、リチウムイオン及び電子の伝導度が低下し、大電流充放電特性が上記従来の炭素系化合物をリチウム二次電池の負極活物質として用いた場合より低くなる問題点もあった。
【０００６】
本発明の目的は、リチウムイオン等のアルカリ金属イオンの吸蔵及び放出時における体積変化を低減できる、充放電可能な無機化合物及びその製造方法並びにこれを用いた非水電解液二次電池を提供することにある。
本発明の別の目的は、充放電サイクル特性及び大電流充放電特性を向上できる、充放電可能な無機化合物及びその製造方法並びにこれを用いた非水電解液二次電池を提供することにある。
【０００７】
【課題を解決するための手段】
請求項１に係る発明は、ケイ素、炭素及び酸素を主成分とするとともにアルカリ金属を挿入して次式（１）で表されかつ平均粒径が０．３μｍ〜１００μｍである粒子からなり、更に平均孔径が０．３ｎｍ〜５０ｎｍである細孔を有する充放電可能な無機化合物である。
Ａ_ｘＳｉ_ｙＣ_１−ｙＯ_ｚ ……（１）
上記式（１）において、Ａがアルカリ金属であり、ｘ＞０であり、１＞ｙ＞０であり、４＞ｚ／ｙ＞０である。
請求項２に係る発明は、請求項１に係る発明であって、更に気孔率が１〜３０％であることを特徴とする。
【０００８】
この請求項１又は２に記載された充放電可能な無機化合物では、リチウムイオン等のアルカリ金属イオンの吸蔵及び放出時、即ち充放電時における体積変化を低減できるとともに、粒子の比表面積を増やすことにより、充放電時の粒子の反応性が向上するので、大電流充放電特性を向上できる。
【０００９】
請求項３に係る発明は、請求項１に係る発明であって、更にケイ素を５０〜５重量％含有することを特徴とする。
この請求項３に記載された充放電可能な無機化合物では、アルカリイオンを吸蔵するサイトが増大するため、充放電容量が向上し、充放電時の体積変化を抑制できる。
また充放電可能な無機化合物は、無定形二酸化ケイ素に類似するＸ線回折パターンを有することが好ましい。
【００１０】
請求項５に係る発明は、Ｓｉ−Ｃ結合を有する有機化合物を前駆体としこの有機化合物を加水分解及び脱水重縮合反応によりゲル化する工程と、このゲル化した有機化合物を非酸化雰囲気中で熱処理することにより合成する工程とを含む充放電可能な無機化合物の製造方法である。
この請求項５に記載された充放電可能な無機化合物の製造方法では、請求項１ないし４いずれか１項に記載の無機化合物を安定的でかつ高効率で合成できる。また上記無機化合物の合成段階でのプロセスの最適化により、無機化合物の構造を上記請求項１ないし４いずれか１項に記載の特徴を有するように作製できる。
【００１１】
またＳｉ−Ｃ結合を有する有機化合物が次式（２）で表されるシランであることが好ましい。
Ｒ_ｍ−Ｓｉ−（ＯＲ’）_ｎ ……（２）
上記式（２）において、Ｒはアルキル基であり、Ｒ’はアリール基であり、（ｍ＋ｎ）＜４である。
更にゲル化した有機化合物を非酸化雰囲気中で熱処理するときの温度が８００〜１６００℃であることが好ましい。
【００１２】
請求項８に係る発明は、請求項１ないし４いずれか１項に記載の充放電可能な無機化合物を負極活物質に含む非水電解液二次電池である。
請求項９に係る発明は、請求項５ないし７いずれか１項に記載の方法で製造された充放電可能な無機化合物を用いた負極活物質に含む非水電解液二次電池である。
この請求項８又は９に記載された非水電解液二次電池では、リチウムイオン等のアルカリ金属イオンの吸蔵及び放出時における体積変化を低減できるとともに、充放電サイクル特性及び大電流充放電特性を向上できる。
【００１３】
【発明の実施の形態】
次に本発明の実施の形態を説明する。
本発明の充放電可能な無機化合物は、ケイ素、炭素及び酸素を主成分とするとともにアルカリ金属を挿入して次式（１）で表されかつ平均粒径が０．３μｍ〜１００μｍ、好ましくは１μｍ〜５０μｍである粒子からなる。
Ａ_ｘＳｉ_ｙＣ_１−ｙＯ_ｚ ……（１）
上記式（１）において、Ａがアルカリ金属であり、ｘ＞０であり、１＞ｙ＞０であり、４＞ｚ／ｙ＞０である。
また上記充放電可能な無機化合物の粒子は平均孔径が０．３ｎｍ〜５０ｎｍ、好ましくは０．８ｎｍ〜１０ｎｍである細孔を有する。上記アルカリ金属としては、リチウム、ナトリウム等が挙げられるが、リチウムが好適である。
【００１４】
ここで、上記無機化合物の粒子の平均粒径を０．３μｍ〜１００μｍの範囲に限定したのは、０．３μｍ未満では粒子が小さすぎて取扱い難く、１００μｍを越えると無機化合物の粒子に混合される負極合剤を均一に調製し難く、この混合物を塗布した負極集電体の表面が粗くなり二次電池の特性が低下してしまうからである。また上記無機化合物粒子の平均粒径の好ましい範囲を１μｍ〜５０μｍに限定したのは、無機化合物粒子に負極合剤を混合した混合物（活物質）を負極集電体に塗布する際にこの混合物（活物質）の充填密度を向上するためである。更に上記無機化合物の粒子の細孔の平均孔径を０．３ｎｍ〜５０ｎｍの範囲に限定したのは、０．３ｎｍ未満では細孔による体積変化の緩和効果が不顕著となり、５０ｎｍを越えると体積変化の緩和効果の改善が低下するとともに、細孔の孔径の増大により粒子の密度及び機械的強度が低下するからである。なお、リチウム二次電池では、非水電解液（例えばプロピレンカーボネート）中のリチウムイオンの溶媒和イオンの直径が０．８２ｎｍであるため、０．８２ｎｍ以上の細孔であれば、上記溶媒和イオンの通過が可能となる。このため、０．８２ｎｍ以上の細孔は粒子の体積変化を緩和できるとともに、充放電反応の反応表面積を増やし、負極活物質の反応性を向上できる。上記細孔の孔径の分布はＮ_２吸着法により求められる。
【００１５】
更に無機化合物の粒子の気孔率は１〜３０％、好ましくは２〜２０％であり、無機化合物の粒子はケイ素を５０〜５重量％、好ましくは４０〜１０重量％含有する。ここで、無機化合物の粒子の気孔率を１〜３０％の範囲に限定したのは、１％未満では細孔による体積変化の緩和効果が不顕著となり、３０％を越えると粒子の機械的強度が著しく低下するとともに粒子の体積充放電容量が低下するからである。また無機化合物の粒子の含有するケイ素を５０〜５重量％の範囲に限定したのは、５０重量％を越えると充放電容量は増大するけれども、充放電時の無機化合物の粒子の膨張及び収縮が著しく大きくなり、５重量％未満ではアルカリ金属イオンを吸蔵できるサイトが少なく、無機化合物の粒子の充放電容量が低下するからである。
【００１６】
なお、上記無機化合物は無定形二酸化ケイ素に類似するＸ線回折パターンを有することが好ましい。無機化合物が無定形二酸化ケイ素に類似するＸ線回折パターンを有すると、充放電の繰返しに伴う膨張及び収縮の繰返しにより上記無機化合物の構造上の微細化を最小限に抑えることができるという利点があるからである。
【００１７】
このように構成された充放電可能な無機化合物の製造方法を説明する。
先ずＳｉ−Ｃ結合を有する有機化合物を前駆体とし、この有機化合物に有機溶媒を添加し、１０〜３０分間攪拌して第１溶液を調製する。上記Ｓｉ−Ｃ結合を有する有機化合物は次式（２）で表されるシランであることが好ましい。
Ｒ_ｍ−Ｓｉ−（ＯＲ’）_ｎ ……（２）
上記式（２）において、Ｒはアルキル基であり、Ｒ’はアリール基であり、（ｍ＋ｎ）＜４である。具体的には、Ｓｉ−Ｃ結合を有する有機化合物としては、表１に示すシラン系化合物が挙げられる。また有機溶媒としては、１−プロパノール、エタノール、アセトン、ブタノール等が挙げられる。なお、表１に示すシラン系化合物のうちフェニルトリメトキシシランとフェニルトリエトキシシランから作成したＳｉ−Ｏ−Ｃが比較的高い充放電容量を有する。
【００１８】
【表１】

【００１９】
一方、加水分解用純水に有機溶媒と触媒とを添加し、１０〜３０分間攪拌して第２溶液を調製する。上記有機溶媒としては、１−プロパノール、アセトン、ブタノール等が挙げられる。また触媒としては、１Ｍ（１モル濃度）のＨＣｌ水溶液、１Ｍ（１モル濃度）のアンモニア水溶液、１Ｍ（１モル濃度）の酢酸水溶液等が挙げられる。
【００２０】
次いで第１溶液を攪拌しながら、第２溶液をゆっくり第１溶液に滴下し、シラン化合物の加水分解反応及び脱水重縮合反応を起こさせる。第２溶液の滴下の終了後、上記均一透明になった溶液（ゾル液）を５０〜１００℃で０．５〜２時間攪拌すると、加水分解反応及び脱水重縮合反応が進行してゲル化が開始する。次にこのゲル化が開始したゾル液を３０〜８０℃の空気中に２〜１５日間放置すると、加水分解反応及び脱水重縮合反応により更にゲル化が進行して透明なバルクゲルとなる。
【００２１】
更にこのバルクゲルを非酸化雰囲気中で８００〜１６００℃、好ましくは１０００〜１４００℃に０．３〜２時間、好ましくは０．５〜１時間保持して焼成し硬いバルクを作製した後に、この硬いバルクを平均粒径０．３μｍ〜１００μｍ、好ましくは１μｍ〜５０μｍの粒子になるまで粉砕して、充放電可能な無機化合物の粉末を得る。上記非酸化雰囲気は、０〜３０体積％の水素ガスと１００〜７０体積％の不活性ガスの混合ガス雰囲気であることが好ましく、不活性ガスとしては、アルゴンガス、窒素ガス等が挙げられる。またバルクゲルの焼成温度を８００〜１６００℃の範囲に限定したのは、８００℃未満ではゲル中に含まれるＯＨ基や有機分子を除去できず、かつバルクの３次元網目構造を十分に形成できず、１６００℃を越えるとバルクの緻密化が進み、細孔の平均孔径及び気孔率を上記範囲内に形成できず、Ｓｉ−Ｃ結合が多数形成されてアルカリ金属イオンを吸蔵できるサイトが減少してしまうからである。バルクゲルの焼成時間を０．３〜２時間の範囲に限定したのは、０．３時間未満ではＯＨ基や有機分子を除去できずバルクの３次元網目構造を十分に形成できず、２時間を越えるとバルクの構造変化が殆どなくなり材料の特性に有益な影響を与えないからである。
【００２２】
このように製造された充放電可能な無機化合物では、リチウムイオン等のアルカリ金属イオンの吸蔵及び放出時、即ち充放電時における体積変化を低減できるとともに、粒子の比表面積を増やすことにより、充放電時の粒子の反応性が向上するので、大電流充放電特性を向上できる。
また上記充放電可能な無機化合物を負極活物質に含む非水電解液二次電池では、リチウムイオン等のアルカリ金属イオンの吸蔵及び放出時における体積変化を低減できるとともに、充放電サイクル特性及び大電流充放電特性を向上できる。
【００２３】
【実施例】
次に本発明の実施例を比較例とともに詳しく説明する。
＜実施例１＞
先ずＳｉ−Ｃ結合を有する有機化合物のフェニルメトキシシランを前駆体とし、このフェニルメトキシシラン１０ｇに１−プロパノール７ｇを添加し、スターラで３０分間攪拌して第１溶液を調製した。一方、加水分解用純水３．６ｇに１−プロパノール７ｇと触媒の１Ｍ（１モル濃度）のＨＣｌ水溶液０．１ｇとを添加し、スターラで３０分間攪拌して第２溶液を調製した。次いで第１溶液を攪拌しながら、第２溶液をゆっくり第１溶液に滴下し、フェニルトリメトキシシランの加水分解反応及び脱水重縮合反応を起こさせた。第２溶液の滴下の終了後、上記均一透明になった溶液（ゾル液）を６０℃で１時間攪拌したところ、加水分解反応及び脱水重縮合反応が進行してゲル化が開始した。ここで、フェニルトリメトキシシランの加水分解反応は次の化学反応式（３）で表され、脱水重縮合反応は次の化学反応式（４）で表される。
【００２４】
【化１】

【００２５】
【化２】

【００２６】
次にこのゲル化が開始したゾル液を９０℃の空気中に１４日間放置したところ、加水分解反応及び脱水重縮合反応により更にゲル化が進行して透明なバルクゲルとなった。更にこのバルクゲルを水素ガス１０体積％及びアルゴンガス９０体積％の混合ガスからなる非酸化雰囲気中で１０００℃に１時間保持して焼成し硬いバルクを作製した後に、この硬いバルクをボールミルを用いて平均粒径が１０μｍになるまで粉砕して、充放電可能な無機化合物の粒子であるシリコンオキシカーバイド粒子を得た。この粒子を実施例１とした。
【００２７】
＜実施例２＞
先ずＳｉ−Ｃ結合を有する有機化合物のフェニルエトキシシランを前駆体とし、このフェニルエトキシシラン１０ｇに１−プロパノール５ｇを添加し、スターラで３０分間攪拌して第１溶液を調製した。一方、加水分解用純水３ｇに１−プロパノール５ｇと触媒の１Ｍ（１モル濃度）のＨＣｌ水溶液０．１ｇとを添加し、スターラで３０分間攪拌して第２溶液を調製した。次いで第１溶液を攪拌しながら、第２溶液をゆっくり第１溶液に滴下し、フェニルトリメトキシシランの加水分解反応及び脱水重縮合反応を起こさせた。第２溶液の滴下の終了後、上記均一透明になった溶液（ゾル液）を６０℃で１時間攪拌したところ、加水分解反応及び脱水重縮合反応が進行してゲル化が開始した。
【００２８】
次にこのゲル化が開始したゾル液を９０℃の空気中に１４日間放置したところ、加水分解反応及び脱水重縮合反応により更にゲル化が進行して透明なバルクゲルとなった。更にこのバルクゲルを水素ガス１０体積％及びアルゴンガス９０体積％の混合ガスからなる非酸化雰囲気中で１０００℃に１時間保持して焼成し硬いバルクを作製した後に、この硬いバルクを平均粒径が１０μｍになるまで粉砕して、充放電可能な無機化合物の粒子であるシリコンオキシカーバイド粒子を得た。この粒子を実施例２とした。
【００２９】
＜実施例３＞
触媒として、１Ｍ（１モル濃度）のＨＣｌ水溶液０．１ｇに代えて、１Ｍ（１モル濃度）のアンモニア水１ｇを用いたことを除いて、実施例１と同様にしてシリコンオキシカーバイド粒子を得た。この粒子を実施例３とした。
＜実施例４＞
触媒として、１Ｍ（１モル濃度）のＨＣｌ水溶液０．１ｇに代えて、１Ｍ（１モル濃度）のアンモニア水１ｇを用い、第１及び第２溶液に添加するアルコールとして、１−プロパノール７ｇに代えてエタノール７ｇを用いたことを除いて、実施例１と同様にしてシリコンオキシカーバイド粒子を得た。この粒子を実施例４とした。
【００３０】
＜比較例１＞
先ずフェニルトリメトキシシラン１０ｇとエポキシノボラック（ＤＥＮ４３８：ダウ・ケミカル社製）１０ｇとを加熱しながら均一に混合した。次にこの混合体に４−アミノ安息香酸４ｇを添加し、９０℃で１時間保持した後に１７０℃まで昇温し、この状態に３時間保持して混合体を完全に固化させた。更にこの固化体をアルゴンガス雰囲気中で１０００℃に１時間保持して焼成した後に、この焼成した固化体を平均粒径が１０μｍになるまで粉砕して、充放電可能な無機化合物の粒子を得た。この粒子を比較例１とした。
【００３１】
＜比較例２＞
先ずＳｉ−Ｃ結合を有する有機化合物のフェニルメトキシシランを前駆体とし、このフェニルメトキシシラン１０ｇにメタノール７ｇを添加し、スターラで３０分間攪拌して第１溶液を調製した。一方、加水分解用純水３．６ｇにメタノール７ｇを添加し、スターラで３０分間攪拌して第２溶液を調製した。次いで第１溶液を攪拌しながら、第２溶液をゆっくり第１溶液に滴下し、フェニルトリメトキシシランの加水分解反応及び脱水重縮合反応を起こさせた。第２溶液の滴下の終了後、上記均一透明になった溶液（ゾル液）を６０℃で１時間攪拌したところ、加水分解反応及び脱水重縮合反応が進行してゲル化が開始した。
【００３２】
次にこのゲル化が開始したゾル液を９０℃の空気中に１４日間放置したところ、加水分解反応及び脱水重縮合反応により更にゲル化が進行して透明なバルクゲルとなった。更にこのバルクゲルを水素ガス１０体積％及びアルゴンガス９０体積％の混合ガスからなる非酸化雰囲気中で１０００℃に１時間保持して焼成し硬いバルクを作製した後に、この硬いバルクを平均粒径が１０μｍになるまで粉砕して、充放電可能な無機化合物の粒子であるシリコンオキシカーバイド粒子を得た。この粒子を比較例２とした。
【００３３】
＜比較試験１及び評価＞
実施例１〜４、比較例１及び比較例２の各粒子に形成された細孔の平均孔径をＮ_２吸着法により測定し、各粒子の気孔率を気相置換法により測定した。その結果を各粒子のケイ素含有量とともに表２に示す。なお、Ｎ_２吸着法とは、液体窒素温度下で物理吸着する窒素ガス吸着量と圧力の関係から、吸着等温線を求め、Ｗｈｅｅｌｅｒ法やＢ．Ｊ．Ｈ法などにより細孔分布を算出する方法をいう。また気相置換法とは、ピークのメータ法とも呼ばれ、アルキメデスの原理に基づき置換媒体としてガスを用いて固体・粉体の真密度を測定する方法をいう。
【００３４】
＜比較試験２及び評価＞
実施例１〜４、比較例１及び比較例２の粒子を含む負極活物質を用いて負電極を作製した。具体的には、上記粒子１８ｇとポリフッ化ビニリデン（ＰＶＤＦ）２ｇとｎ−メチルピロリドン１８ｇとを混練してスラリーを調製し、このスラリーをドクタブレード法により負極集電体である銅メッシュ板上に引き伸ばして圧着した後に乾燥・圧延して負電極を作製した。
【００３５】
これらの負電極を図１に示すように、充放電サイクル試験装置２１に取付けた。この装置２１は容器２２に電解液２３（１Ｍ（１モル濃度）のＬｉＰＦ_６を支持塩とするエチレンカーボネート及びジエチルカーボネートの溶液）が貯留され、上記負電極１２が正電極１４（金属リチウム）及び参照極２４（金属リチウム）とともに電解液２３に浸され、更に負電極１２、正電極１４及び参照極２４がポテンシオスタット２５（ポテンショメータ）にそれぞれ電気的に接続された構成となっている。この装置を用いて充放電サイクル試験を行い、各負電極の初期放電容量と減少率を測定した。なお、各負電極の放電容量は、負電極に対して７０ｍＡ／ｇの充放電電量で測定し、測定電圧範囲は０〜３．０Ｖとした。また減少率とは、１０サイクル充放電を行った後の放電容量の初期放電容量に対する容量低下率を％表した値をいう。上記負電極の初期放電容量と１０サイクル目の放電容量と減少率とを表２に示す。
【００３６】
【表２】

【００３７】
表２から明らかなように、比較例１及び２では減少率が８７．１％及び８１．５％と大きかったのに対し、実施例１〜４では減少率が１９．７％〜４２．１％と小さかった。この結果、実施例１〜４の粒子を負極活物質に含む負電極は、比較例１及び２の粒子を負極活物質に含む負電極と比較して、充放電を繰返しても充放電容量の低下する割合が小さい、即ち充放電サイクル特性が向上することが判った。なお、比較例１において減少率が８７．１％と大きくなったのは、粒子の細孔の平均孔径が１００ｎｍと大きくかつ粒子の気孔率が６５％大きかったためであり、比較例２において減少率が８１．５％と大きくなったのは、粒子の気孔率が１５％と小さいけれども、粒子の細孔の平均孔径が１００ｎｍと大きかったためである。
【００３８】
＜比較試験３及び評価＞
実施例１〜４及び平均粒径１０μｍの無定形二酸化ケイ素の各粒子のＸ線回折パターン（銅のＫα線を用いて測定した結果）を図２に示す。
図２から明らかなように、実施例１〜４の各粒子のＸ線回折パターンは無定形二酸化ケイ素の粒子のＸ線回折パターンと略同一であった。
【００３９】
【発明の効果】
以上述べたように、本発明によれば、充放電可能な無機化合物が、ケイ素、炭素及び酸素を主成分とし、アルカリ金属を挿入して式Ａ_ｘＳｉ_ｙＣ_１−ｙＯ_ｚで表されかつ平均粒径が０．３μｍ〜１００μｍである粒子からなり、更に平均孔径が０．３ｎｍ〜５０ｎｍである細孔を有するので、リチウムイオン等のアルカリ金属イオンの吸蔵及び放出時、即ち充放電時における体積変化を低減できるとともに、粒子の比表面積を増やすことにより、充放電時の粒子の反応性が向上し、大電流充放電特性を向上できる。
【００４０】
また上記充放電可能な無機化合物の気孔率が１〜３０％であれば、充放電時における体積変化を更に低減でき、大電流充放電特性を更に向上できる。
また上記充放電可能な無機化合物がケイ素を５０〜５重量％含有すれば、アルカリイオンを吸蔵するサイトが増大するため、充放電容量が向上し、充放電時の体積変化を抑制できる。
【００４１】
またＳｉ−Ｃ結合を有する有機化合物を前駆体としこの有機化合物を加水分解及び脱水重縮合反応によりゲル化した後に、このゲル化した有機化合物を非酸化雰囲気中で熱処理することにより合成すれば、上記無機化合物を安定的でかつ高効率で合成できるとともに、上記無機化合物の合成段階でのプロセスの最適化により、無機化合物の構造を上記記載の特徴を有するように作製できる。
更に上記充放電可能な無機化合物を負極活物質に含む非水電解液二次電池を製造すれば、リチウムイオン等のアルカリ金属イオンの吸蔵及び放出時における体積変化を低減できるとともに、充放電サイクル特性及び大電流充放電特性を向上できる。
【図面の簡単な説明】
【図１】実施例１〜４、比較例１及び比較例２の非水電解液二次電池用負極活物質の充放電サイクル試験に用いられる装置。
【図２】実施例１〜４の粒子及び無定形二酸化ケイ素の粒子のＸ線回折パターンを示す図。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention provides a chargeable / dischargeable inorganic compound contained in a negative electrode active material of a nonaqueous electrolyte secondary battery such as a lithium secondary battery, a method for producing the chargeable / dischargeable inorganic compound, and a chargeable / dischargeable inorganic compound. The present invention relates to a non-aqueous secondary battery including an inorganic compound in a negative electrode active material.
[0002]
[Prior art]
Conventionally, a lithium secondary battery using a carbon-based compound such as graphite or coke as a negative electrode active material has been known.
However, the charge / discharge capacity of a lithium secondary battery using the above-described carbon-based compound is small. For example, pure carbon has a problem in that the theoretical charge / discharge capacity shows only a small value of 372 mAh / g.
In order to solve this problem, a lithium secondary battery using a negative electrode active material containing silicon is known. The lithium secondary battery has a large charge / discharge capacity, and pure silicon has a theoretical charge / discharge capacity of 4017 mAh /. g and an extremely large value.
However, in the lithium secondary battery using the negative electrode active material containing silicon, when charging and discharging the battery, that is, at the time of repeating occlusion and release of lithium ions, the negative electrode active material containing silicon is 300 to 300 compared to the initial state. There is a problem that the volume changes as large as 400%, cracks are generated inside the negative electrode active material, and the negative electrode active material particles are miniaturized. Furthermore, due to the repeated expansion and contraction of the negative electrode active material, gaps are generated between the negative electrode active material and the current collector and between the negative electrode active material and the conductive auxiliary agent so that they are not in contact with each other. However, there was a problem that the temperature was reduced.
[0003]
To solve this problem, a carbonaceous insertion compound of the formula _{_{_{A x Si y C 1-y}}} O z, carbonaceous insertion compounds having similar X-ray diffraction pattern for amorphous SiO ₂ is disclosed (For example, see Patent Document 1). Here, A in the formula A _x Si _y C _1-y O _z is an inserted alkali metal, x> 0, 0 <y <1, and 0 <z / y <4. .
Since the carbonaceous insertion compound thus configured has a large reversible capacity, when this carbonaceous insertion compound is used as a negative electrode active material of a lithium secondary battery, a high capacity lithium secondary battery can be obtained. I have.
[0004]
[Patent Document 1]
JP-A-8-259213 [0005]
[Problems to be solved by the invention]
However, in the carbonaceous insertion compound disclosed in Patent Document 1, when this carbonaceous insertion compound is used as a negative electrode active material of a lithium secondary battery, the conventional silicon is used as a negative electrode active material of a lithium secondary battery. Although the change in volume during charge / discharge is smaller than that in the case, the charge / discharge cycle characteristics could not be improved because the change in volume was still large, and practical application was difficult.
In addition, in the carbonaceous insertion compound disclosed in Patent Document 1, when this carbonaceous insertion compound is used as a negative electrode active material of a lithium secondary battery, silicon and oxygen are bonded and silicon and carbon are bonded. For this reason, the conductivity of lithium ions and electrons is reduced, and the large current charge / discharge characteristics are also lower than when the above-described conventional carbon-based compound is used as a negative electrode active material of a lithium secondary battery.
[0006]
An object of the present invention is to provide a chargeable / dischargeable inorganic compound capable of reducing a volume change at the time of occlusion and release of an alkali metal ion such as lithium ion, a method for producing the same, and a nonaqueous electrolyte secondary battery using the same. It is in.
Another object of the present invention is to provide a chargeable / dischargeable inorganic compound capable of improving charge / discharge cycle characteristics and large current charge / discharge characteristics, a method for producing the same, and a nonaqueous electrolyte secondary battery using the same. .
[0007]
[Means for Solving the Problems]
The invention according to claim 1 comprises particles having silicon, carbon and oxygen as main components and having an alkali metal inserted therein and represented by the following formula (1) and having an average particle size of 0.3 μm to 100 μm. It is a chargeable / dischargeable inorganic compound having pores having an average pore diameter of 0.3 nm to 50 nm.
_{_{_{_{A x Si y C 1-y}}}} O z ...... (1)
In the above formula (1), A is an alkali metal, x> 0, 1>y> 0, and 4> z / y> 0.
The invention according to claim 2 is the invention according to claim 1, wherein the porosity is 1 to 30%.
[0008]
The chargeable / dischargeable inorganic compound according to claim 1 or 2 can reduce the volume change during occlusion and release of alkali metal ions such as lithium ions, that is, during charge / discharge, and increase the specific surface area of the particles. Thereby, the reactivity of the particles at the time of charge and discharge is improved, so that the large current charge and discharge characteristics can be improved.
[0009]
The invention according to a third aspect is the invention according to the first aspect, further comprising 50 to 5% by weight of silicon.
In the chargeable / dischargeable inorganic compound according to the third aspect, the number of sites that occlude alkali ions is increased, so that the charge / discharge capacity is improved and the volume change during charge / discharge can be suppressed.
The chargeable / dischargeable inorganic compound preferably has an X-ray diffraction pattern similar to that of amorphous silicon dioxide.
[0010]
The invention according to claim 5 is a step of using an organic compound having a Si—C bond as a precursor to gel the organic compound by hydrolysis and dehydration polycondensation, and subjecting the gelled organic compound to a non-oxidizing atmosphere. And a step of synthesizing by heat treatment.
In the method for producing a chargeable / dischargeable inorganic compound according to the fifth aspect, the inorganic compound according to any one of the first to fourth aspects can be synthesized stably and with high efficiency. In addition, by optimizing the process in the step of synthesizing the inorganic compound, the structure of the inorganic compound can be manufactured so as to have the features described in any one of the above-mentioned claims 1 to 4.
[0011]
The organic compound having a Si—C bond is preferably silane represented by the following formula (2).
R _m -Si- (OR ') _n ... (2)
In the above formula (2), R is an alkyl group, R ′ is an aryl group, and (m + n) <4.
Further, the temperature at which the gelled organic compound is heat-treated in a non-oxidizing atmosphere is preferably 800 to 1600 ° C.
[0012]
The invention according to claim 8 is a non-aqueous electrolyte secondary battery including the chargeable / dischargeable inorganic compound according to any one of claims 1 to 4 as a negative electrode active material.
A ninth aspect of the present invention is a nonaqueous electrolyte secondary battery including a negative electrode active material using a chargeable / dischargeable inorganic compound produced by the method according to any one of the fifth to seventh aspects.
In the non-aqueous electrolyte secondary battery according to claim 8 or 9, the volume change at the time of occlusion and release of alkali metal ions such as lithium ions can be reduced, and the charge / discharge cycle characteristics and the large current charge / discharge characteristics are improved. Can be improved.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, an embodiment of the present invention will be described.
The chargeable / dischargeable inorganic compound of the present invention contains silicon, carbon, and oxygen as main components and is expressed by the following formula (1) by inserting an alkali metal, and has an average particle size of 0.3 μm to 100 μm, preferably 1 μm. Consists of particles that are ５０50 μm.
_{_{_{_{A x Si y C 1-y}}}} O z ...... (1)
In the above formula (1), A is an alkali metal, x> 0, 1>y> 0, and 4> z / y> 0.
The chargeable / dischargeable inorganic compound particles have pores having an average pore diameter of 0.3 nm to 50 nm, preferably 0.8 nm to 10 nm. Examples of the alkali metal include lithium and sodium, and lithium is preferable.
[0014]
Here, the average particle diameter of the particles of the inorganic compound is limited to the range of 0.3 μm to 100 μm. If the particle diameter is less than 0.3 μm, the particles are too small to handle easily, and if it exceeds 100 μm, the particles are mixed with the particles of the inorganic compound. This is because it is difficult to uniformly prepare such a negative electrode mixture, and the surface of the negative electrode current collector coated with this mixture becomes rough, and the characteristics of the secondary battery deteriorate. Further, the preferable range of the average particle diameter of the inorganic compound particles is limited to 1 μm to 50 μm because the mixture (active material) obtained by mixing the inorganic compound particles with the negative electrode mixture is applied to the negative electrode current collector. This is for improving the packing density of the active material). Further, the average pore diameter of the pores of the inorganic compound particles is limited to the range of 0.3 nm to 50 nm. When the average pore diameter is less than 0.3 nm, the effect of reducing the volume change due to the pores becomes inconspicuous. This is because the improvement of the relaxation effect of the particles decreases, and the density and mechanical strength of the particles decrease due to the increase in the pore diameter of the pores. In a lithium secondary battery, the diameter of the solvated ion of lithium ion in a nonaqueous electrolyte (for example, propylene carbonate) is 0.82 nm. Is possible. Therefore, the pores having a diameter of 0.82 nm or more can reduce the volume change of the particles, increase the reaction surface area of the charge / discharge reaction, and improve the reactivity of the negative electrode active material. Distribution of pore diameter of the pores is determined by the N ₂ adsorption method.
[0015]
Further, the porosity of the particles of the inorganic compound is 1 to 30%, preferably 2 to 20%, and the particles of the inorganic compound contain 50 to 5% by weight, preferably 40 to 10% by weight of silicon. Here, the porosity of the particles of the inorganic compound is limited to the range of 1 to 30%. When the porosity is less than 1%, the effect of reducing the volume change due to the pores becomes inconspicuous, and when it exceeds 30%, the mechanical strength of the particles is increased. Is significantly reduced and the volume charge / discharge capacity of the particles is reduced. Further, the reason why the content of silicon in the particles of the inorganic compound is limited to the range of 50 to 5% by weight is that when the content exceeds 50% by weight, the charge and discharge capacity increases, but the expansion and contraction of the particles of the inorganic compound at the time of charge and discharge are limited. This is because the content is extremely large, and if the content is less than 5% by weight, the number of sites capable of occluding the alkali metal ions is small, and the charge / discharge capacity of the inorganic compound particles is reduced.
[0016]
Preferably, the inorganic compound has an X-ray diffraction pattern similar to that of amorphous silicon dioxide. When the inorganic compound has an X-ray diffraction pattern similar to that of amorphous silicon dioxide, there is an advantage that the structural refinement of the inorganic compound can be minimized due to repeated expansion and contraction accompanying repeated charge and discharge. Because there is.
[0017]
A method for producing the chargeable / dischargeable inorganic compound thus configured will be described.
First, an organic compound having a Si—C bond is used as a precursor, an organic solvent is added to the organic compound, and the mixture is stirred for 10 to 30 minutes to prepare a first solution. The organic compound having the Si—C bond is preferably a silane represented by the following formula (2).
R _m -Si- (OR ') _n ... (2)
In the above formula (2), R is an alkyl group, R ′ is an aryl group, and (m + n) <4. Specifically, examples of the organic compound having a Si—C bond include silane compounds shown in Table 1. Examples of the organic solvent include 1-propanol, ethanol, acetone, butanol and the like. Note that among the silane compounds shown in Table 1, Si-OC formed from phenyltrimethoxysilane and phenyltriethoxysilane has a relatively high charge / discharge capacity.
[0018]
[Table 1]

[0019]
On the other hand, an organic solvent and a catalyst are added to pure water for hydrolysis, and the mixture is stirred for 10 to 30 minutes to prepare a second solution. Examples of the organic solvent include 1-propanol, acetone, butanol and the like. Examples of the catalyst include a 1 M (1 molar concentration) aqueous HCl solution, a 1 M (1 molar concentration) aqueous ammonia solution, a 1 M (1 molar concentration) aqueous acetic acid solution, and the like.
[0020]
Next, while stirring the first solution, the second solution is slowly dropped into the first solution to cause a hydrolysis reaction and a dehydration polycondensation reaction of the silane compound. After completion of the dropping of the second solution, the uniformly transparent solution (sol solution) is stirred at 50 to 100 ° C. for 0.5 to 2 hours. Start. Next, when the sol liquid in which the gelation has started is left in the air at 30 to 80 ° C. for 2 to 15 days, the gelation further proceeds by a hydrolysis reaction and a dehydration polycondensation reaction to form a transparent bulk gel.
[0021]
Further, the bulk gel is kept at 800 to 1600 ° C., preferably 1000 to 1400 ° C. in a non-oxidizing atmosphere for 0.3 to 2 hours, preferably 0.5 to 1 hour, and fired to produce a hard bulk. The bulk is pulverized to particles having an average particle diameter of 0.3 μm to 100 μm, preferably 1 μm to 50 μm to obtain a chargeable / dischargeable inorganic compound powder. The non-oxidizing atmosphere is preferably a mixed gas atmosphere of 0 to 30% by volume of hydrogen gas and 100 to 70% by volume of an inert gas, and examples of the inert gas include an argon gas and a nitrogen gas. The reason why the firing temperature of the bulk gel is limited to the range of 800 to 1600 ° C. is that if the temperature is lower than 800 ° C., the OH groups and organic molecules contained in the gel cannot be removed, and the bulk three-dimensional network structure cannot be formed sufficiently. If the temperature exceeds 1600 ° C., the densification of the bulk proceeds, the average pore diameter and porosity of the pores cannot be formed within the above ranges, and a large number of Si—C bonds are formed, and the number of sites capable of occluding alkali metal ions decreases. It is because. The reason why the firing time of the bulk gel is limited to the range of 0.3 to 2 hours is that if the time is less than 0.3 hour, the OH group and organic molecules cannot be removed, the bulk three-dimensional network structure cannot be sufficiently formed, and the time required for 2 hours is 2 hours. If it exceeds, the structural change of the bulk hardly occurs, and the properties of the material are not beneficially affected.
[0022]
The chargeable / dischargeable inorganic compound manufactured in this manner can reduce the volume change during occlusion and release of alkali metal ions such as lithium ions, that is, during charge / discharge, and increase the specific surface area of the particles, thereby increasing the charge / discharge rate. Since the reactivity of the particles at the time is improved, the large current charge / discharge characteristics can be improved.
Further, in the non-aqueous electrolyte secondary battery containing the chargeable / dischargeable inorganic compound in the negative electrode active material, the volume change at the time of occlusion and release of alkali metal ions such as lithium ions can be reduced, and the charge / discharge cycle characteristics and high current The charge / discharge characteristics can be improved.
[0023]
【Example】
Next, examples of the present invention will be described in detail together with comparative examples.
<Example 1>
First, 1 g of 1-propanol was added to 10 g of this phenylmethoxysilane as a precursor using phenylmethoxysilane, an organic compound having a Si-C bond, and stirred with a stirrer for 30 minutes to prepare a first solution. On the other hand, to 3.6 g of pure water for hydrolysis, 7 g of 1-propanol and 0.1 g of a 1M (1 molar concentration) aqueous HCl solution of a catalyst were added, and the mixture was stirred with a stirrer for 30 minutes to prepare a second solution. Next, while stirring the first solution, the second solution was slowly dropped into the first solution to cause a hydrolysis reaction and a dehydration polycondensation reaction of phenyltrimethoxysilane. After the completion of the dropwise addition of the second solution, when the uniformly transparent solution (sol solution) was stirred at 60 ° C. for 1 hour, the hydrolysis reaction and the dehydration polycondensation reaction proceeded, and gelation started. Here, the hydrolysis reaction of phenyl trimetoquinol shish run is represented by the following chemical equation (3), the polycondensation reaction is dehydration represented by the following chemical equation (4).
[0024]
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[0025]
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[0026]
Next, when the gelled sol solution was left in the air at 90 ° C. for 14 days, the gelation further proceeded by a hydrolysis reaction and a dehydration polycondensation reaction to form a transparent bulk gel. Further, the bulk gel is held at 1000 ° C. for 1 hour in a non-oxidizing atmosphere composed of a mixed gas of 10% by volume of hydrogen gas and 90% by volume of argon gas to form a hard bulk, and then the hard bulk is formed using a ball mill. Pulverization was performed until the average particle diameter became 10 μm, thereby obtaining silicon oxycarbide particles that were chargeable and dischargeable inorganic compound particles. These particles were used as Example 1.
[0027]
<Example 2>
First, phenylethoxysilane, an organic compound having a Si-C bond, was used as a precursor, and 5 g of 1-propanol was added to 10 g of this phenylethoxysilane, followed by stirring with a stirrer for 30 minutes to prepare a first solution. On the other hand, 5 g of 1-propanol and 0.1 g of a 1M (1 molar concentration) aqueous HCl solution of a catalyst were added to 3 g of pure water for hydrolysis, followed by stirring with a stirrer for 30 minutes to prepare a second solution. Next, while stirring the first solution, the second solution was slowly dropped into the first solution to cause a hydrolysis reaction and a dehydration polycondensation reaction of phenyltrimethoxysilane. After the completion of the dropwise addition of the second solution, when the uniformly transparent solution (sol solution) was stirred at 60 ° C. for 1 hour, the hydrolysis reaction and the dehydration polycondensation reaction proceeded, and gelation started.
[0028]
Next, when the gelled sol solution was left in the air at 90 ° C. for 14 days, the gelation further proceeded by a hydrolysis reaction and a dehydration polycondensation reaction to form a transparent bulk gel. Further, the bulk gel is kept at 1000 ° C. for 1 hour in a non-oxidizing atmosphere composed of a mixed gas of 10% by volume of hydrogen gas and 90% by volume of argon gas to be baked to produce a hard bulk. It was pulverized to 10 μm to obtain silicon oxycarbide particles which are inorganic compound particles capable of being charged and discharged. The particles were designated as Example 2.
[0029]
<Example 3>
Silicon oxycarbide particles were obtained in the same manner as in Example 1 except that 1 g of 1 M (1 molar) aqueous ammonia was used instead of 0.1 g of 1 M (1 molar) aqueous HCl as a catalyst. Was. The particles were designated as Example 3.
<Example 4>
As a catalyst, 1 g of 1 M (1 molar) aqueous ammonia was used in place of 0.1 g of a 1 M (1 molar) aqueous HCl solution, and 1 g of 1-propanol was used as an alcohol to be added to the first and second solutions. Silicon oxycarbide particles were obtained in the same manner as in Example 1, except that 7 g of ethanol was used. The particles were designated as Example 4.
[0030]
<Comparative Example 1>
First, 10 g of phenyltrimethoxysilane and 10 g of epoxy novolak (DEN438: manufactured by Dow Chemical Company) were uniformly mixed while heating. Next, 4 g of 4-aminobenzoic acid was added to the mixture, and the mixture was maintained at 90 ° C. for 1 hour, heated to 170 ° C., and maintained in this state for 3 hours to completely solidify the mixture. Further, the solidified product is fired while being kept at 1000 ° C. for 1 hour in an argon gas atmosphere, and then the fired solidified product is pulverized to an average particle size of 10 μm to obtain particles of a chargeable / dischargeable inorganic compound. Was. These particles were used as Comparative Example 1.
[0031]
<Comparative Example 2>
First, phenylmethoxysilane, an organic compound having a Si-C bond, was used as a precursor, and 7 g of methanol was added to 10 g of the phenylmethoxysilane, followed by stirring with a stirrer for 30 minutes to prepare a first solution. On the other hand, 7 g of methanol was added to 3.6 g of pure water for hydrolysis, and the mixture was stirred with a stirrer for 30 minutes to prepare a second solution. Next, while stirring the first solution, the second solution was slowly dropped into the first solution to cause a hydrolysis reaction and a dehydration polycondensation reaction of phenyltrimethoxysilane. After the completion of the dropwise addition of the second solution, when the uniformly transparent solution (sol solution) was stirred at 60 ° C. for 1 hour, the hydrolysis reaction and the dehydration polycondensation reaction proceeded, and gelation started.
[0032]
Next, when the gelled sol solution was left in the air at 90 ° C. for 14 days, the gelation further proceeded by a hydrolysis reaction and a dehydration polycondensation reaction to form a transparent bulk gel. Further, the bulk gel is kept at 1000 ° C. for 1 hour in a non-oxidizing atmosphere composed of a mixed gas of 10% by volume of hydrogen gas and 90% by volume of argon gas to be baked to produce a hard bulk. It was pulverized to 10 μm to obtain silicon oxycarbide particles which are inorganic compound particles capable of being charged and discharged. These particles were used as Comparative Example 2.
[0033]
<Comparative test 1 and evaluation>
Examples 1 to 4, an average pore diameter of the pores formed in each particle of Comparative Example 1 and Comparative Example 2 were measured by N ₂ adsorption method, the porosity of the particles was determined by vapor phase substitution method. The results are shown in Table 2 together with the silicon content of each particle. Incidentally, N and the ₂ adsorption method, the relationship between the nitrogen gas adsorption and pressure physisorbed under liquid nitrogen temperature, determine the adsorption isotherm, Wheeler method and B. J. A method of calculating the pore distribution by the H method or the like. The gas phase replacement method is also called a peak meter method and refers to a method of measuring the true density of a solid or powder using a gas as a replacement medium based on the Archimedes principle.
[0034]
<Comparative test 2 and evaluation>
Negative electrodes were produced using the negative electrode active materials containing the particles of Examples 1 to 4, Comparative Example 1 and Comparative Example 2. Specifically, a slurry is prepared by kneading 18 g of the particles, 2 g of polyvinylidene fluoride (PVDF) and 18 g of n-methylpyrrolidone, and the slurry is placed on a copper mesh plate as a negative electrode current collector by a doctor blade method. After stretching and pressing, drying and rolling were performed to produce a negative electrode.
[0035]
These negative electrodes were attached to a charge / discharge cycle test apparatus 21 as shown in FIG. In this apparatus 21, an electrolyte solution 23 (a solution of ethylene carbonate and diethyl carbonate using 1M (1 molar concentration) of LiPF ₆ as a supporting salt) is stored in a container 22, and the negative electrode 12 is connected to the positive electrode 14 (metal lithium) and The electrode is immersed in an electrolytic solution 23 together with a reference electrode 24 (metal lithium), and the negative electrode 12, the positive electrode 14 and the reference electrode 24 are electrically connected to a potentiostat 25 (potentiometer). Using this apparatus, a charge / discharge cycle test was performed, and the initial discharge capacity and reduction rate of each negative electrode were measured. The discharge capacity of each negative electrode was measured at a charge / discharge capacity of 70 mA / g with respect to the negative electrode, and the measured voltage range was 0 to 3.0 V. Further, the reduction rate is a value expressing the capacity reduction rate of the discharge capacity after 10 cycles of charge / discharge to the initial discharge capacity as a percentage. Table 2 shows the initial discharge capacity of the negative electrode, the discharge capacity at the 10th cycle, and the decrease rate.
[0036]
[Table 2]

[0037]
As is clear from Table 2, the reduction rates in Comparative Examples 1 and 2 were as large as 87.1% and 81.5%, whereas in Examples 1 to 4, the reduction rates were 19.7% to 42.1. % Was small. As a result, the negative electrode including the particles of Examples 1 to 4 in the negative electrode active material has a higher charge / discharge capacity even when charge / discharge is repeated than the negative electrodes including the particles of Comparative Examples 1 and 2 in the negative electrode active material. It was found that the rate of decrease was small, that is, the charge / discharge cycle characteristics were improved. The reason why the reduction rate was increased to 87.1% in Comparative Example 1 was that the average pore diameter of the pores of the particles was as large as 100 nm and the porosity of the particles was 65%. Increased to 81.5% because the average porosity of the pores of the particles was as large as 100 nm, although the porosity of the particles was as small as 15%.
[0038]
<Comparative test 3 and evaluation>
FIG. 2 shows an X-ray diffraction pattern (measured using Kα ray of copper) of each of Examples 1 to 4 and amorphous silicon dioxide particles having an average particle diameter of 10 μm.
As is clear from FIG. 2, the X-ray diffraction patterns of the particles of Examples 1 to 4 were substantially the same as the X-ray diffraction patterns of the particles of amorphous silicon dioxide.
[0039]
【The invention's effect】
As described above, according to the present invention, the chargeable / dischargeable inorganic compound is represented by the formula A _x Si _y C _1-y O _z containing silicon, carbon and oxygen as main components and inserting an alkali metal. In addition, since it is composed of particles having an average particle diameter of 0.3 μm to 100 μm and further has pores having an average pore diameter of 0.3 nm to 50 nm, at the time of occlusion and release of alkali metal ions such as lithium ions, that is, at the time of charge and discharge By increasing the specific surface area of the particles, the reactivity of the particles during charging and discharging can be improved, and the large current charging and discharging characteristics can be improved.
[0040]
When the porosity of the chargeable / dischargeable inorganic compound is 1 to 30%, the volume change during charge / discharge can be further reduced, and the large current charge / discharge characteristics can be further improved.
If the chargeable / dischargeable inorganic compound contains 50 to 5% by weight of silicon, sites for occluding alkali ions increase, so that the charge / discharge capacity is improved and the volume change during charge / discharge can be suppressed.
[0041]
Further, if an organic compound having a Si-C bond is used as a precursor and the organic compound is gelated by hydrolysis and dehydration polycondensation reaction, and then synthesized by heat-treating the gelled organic compound in a non-oxidizing atmosphere, The inorganic compound can be synthesized stably and with high efficiency, and the structure of the inorganic compound can be manufactured to have the above-described features by optimizing the process in the synthesis step of the inorganic compound.
Further, by manufacturing a non-aqueous electrolyte secondary battery containing the chargeable / dischargeable inorganic compound in the negative electrode active material, it is possible to reduce the volume change at the time of occlusion and release of alkali metal ions such as lithium ions, as well as the charge / discharge cycle characteristics. In addition, the large current charge / discharge characteristics can be improved.
[Brief description of the drawings]
FIG. 1 shows an apparatus used for a charge / discharge cycle test of the negative electrode active materials for nonaqueous electrolyte secondary batteries of Examples 1 to 4, Comparative Examples 1 and 2.
FIG. 2 is a view showing X-ray diffraction patterns of particles of Examples 1 to 4 and particles of amorphous silicon dioxide.

Claims

It consists of particles having silicon, carbon and oxygen as main components and having an alkali metal inserted therein and represented by the following formula (1) and having an average particle diameter of 0.3 μm to 100 μm, and further having an average pore diameter of 0.3 nm to 50 nm. Chargeable / dischargeable inorganic compound having fine pores.
_{_{_{_{A x Si y C 1-y}}}} O z ...... (1)
In the above formula (1), A is an alkali metal, x> 0, 1>y> 0, and 4> z / y> 0.

The chargeable / dischargeable inorganic compound according to claim 1, having a porosity of 1 to 30%.

The chargeable / dischargeable inorganic compound according to claim 1, which contains 50 to 5% by weight of silicon.

The chargeable / dischargeable inorganic compound according to claim 1, which has an X-ray diffraction pattern similar to that of amorphous silicon dioxide.

A step of using an organic compound having a Si-C bond as a precursor and gelling the organic compound by hydrolysis and dehydration polycondensation,
Synthesizing the gelled organic compound by heat treatment in a non-oxidizing atmosphere to produce a chargeable / dischargeable inorganic compound.

The method for producing a chargeable / dischargeable inorganic compound according to claim 5, wherein the organic compound having a Si-C bond is a silane represented by the following formula (2).
R _m -Si- (OR ') _n ... (2)
In the above formula (2), R is an alkyl group, R ′ is an aryl group, and (m + n) <4.

The method for producing a chargeable / dischargeable inorganic compound according to claim 5, wherein the temperature at which the gelled organic compound is heat-treated in a non-oxidizing atmosphere is 800 to 1600C.

A nonaqueous electrolyte secondary battery comprising the chargeable / dischargeable inorganic compound according to claim 1 in a negative electrode active material.

A non-aqueous electrolyte secondary battery comprising a negative electrode active material using a chargeable / dischargeable inorganic compound produced by the method according to claim 5.