JP4069784B2

JP4069784B2 - Non-aqueous electrolyte secondary battery and its negative electrode material

Info

Publication number: JP4069784B2
Application number: JP2003097558A
Authority: JP
Inventors: 一重河野; 寿一新井
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 2003-04-01
Filing date: 2003-04-01
Publication date: 2008-04-02
Anticipated expiration: 2023-04-01
Also published as: JP2004303674A

Description

【０００１】
【発明の属する技術分野】
本発明は、ポータブル電子機器等に用いるのに好適な新規な非水系電解液二次電池とその負極材料に関する。
【０００２】
【従来の技術】
従来、非水系電解液二次電池の負極には黒鉛質材料を用いられている（例えば、天然黒鉛材料，コークス等を黒鉛化した人造黒鉛等）。しかしながら、黒鉛結晶が発達している天然黒鉛及びコークスを黒鉛化した人造黒鉛は、放電末期において負極側の分極による電圧変化が大きく、過放電を抑制する為に終止電圧を高く設定し、負極材料が有する容量を充分に活用することが困難であった。例えば、電池の放電終止電圧を２.７Ｖと設定した場合、放電終止時の正極の電位を約３.０Ｖと推定すると、負極の電位としては約０.３Ｖに達するまでの放電容量が、実質的な電池容量となる。そこで、黒鉛質材料よりリチウムイオンの拡散が早い、非黒鉛質材料との混合負極を用い、放電末期の分極を抑制する手法が提案されている。
【０００３】
特許文献１では黒鉛質材料とＸ線回折で求めた００２面の間隔が０.３４３〜０.３９ｎｍ、結晶子の大きさを示すＬｃが０.９〜９.９ｎｍを示す炭素質材料を混合する手法が提案されている。また、特許文献２では黒鉛質材料と黒鉛質材料の重量あたりの容量８０％以上を有する非黒鉛炭素材料と混合し、負極の分極を抑制する手法などが提案されている。
【０００４】
【特許文献１】
特開平６−３６７６０号公報
【特許文献２】
特開平７−１９２７２４号公報
【０００５】
【発明が解決しようとする課題】
しかし、特許文献１に記載の材料を電池に用いた際には、混合する炭素質材料が黒鉛質材料より、重量あたりの放電容量が低い物質であり、混合して形成された負極を用いた電池では、重量あたりの放電容量が低くなってしまう危険性があった。また、炭素質材料の混合量が３０体積％を超えると、分極が大きくなり電池の放電電位が低くなってしまう問題があった。
【０００６】
また、特許文献２に記載の材料を電池に用いた際に充電終止時の負極側の電位は、黒鉛質材料と比較して卑になる。しかし、混合する炭素質材料に黒鉛質材料と比較して、重量あたりの放電容量が８０％〜９０％程度の材料を用いた際に、重量あたりの放電容量が低い電池になってしまう危険性があった。
【０００７】
本発明の目的は、放電末期に両極間の電圧低下を緩やかにし、放電容量の優れた非水系電解液二次電池とその負極材料を提供することにある。
【０００８】
【課題を解決するための手段】
本発明は、負極活物質に黒鉛質材料と該黒鉛質材料より高い放電容量を有する非黒鉛質材料の混合材料を用いる（但しここで述べる放電容量は、対極を金属リチウムとして、ある電流密度で端子間電圧が０Ｖに成るまでリチウムをドープし、その後１.５Ｖまでリチウムを脱ドープした際の負極材料単位重量あたりの放電量を指す）。それにより、放電末期に両極間の電圧低下を緩やかにし、放電可能な電池容量が向上される。また、非黒鉛質材料の混合量は１０体積％より大きく９０体積％未満とする。また、非黒鉛質材料は参照極及び対極に金属リチウムを用いて作成したモデル電池評価において、Ｌｉ基準電位で０Ｖまで充電後、
１.５Ｖまで放電した際の初回充放電効率（但しここで述べる初回充放電効率は、対極を金属リチウムとして、一定電流密度で端子間電圧が０Ｖに成るまでリチウムをドープした負極材料単位重量あたりの充電量Ｃと、その後１.５Ｖまでリチウムを脱ドープした際の負極材料単位重量あたりの放電量Ｄとの百分率比＝（Ｄ／Ｃ）×１００を指す）が８５％より高い値を示す材料を用いる。
【０００９】
具体的用いる非黒鉛質材料物性としては、Ｘ線回折結果より算出される結晶子の厚みを示すＬｃ値が０ . ７０以上２ . ２０ｎｍ未満で、且つラマン分光スペクトルで測定される１３００〜１４００cm^-1範囲の非結晶質乱層構造に由来する振動モードを示すピークの高さ（Ｉ_D）と１５８０〜１６２０cm^-1の範囲の黒鉛結晶質構造に由来する振動モードを示すピークの高さ（Ｉ_G）の比から求められる黒鉛化度Ｒ値（Ｉ_D／Ｉ_G）が０ . ９０以上１ . ２０未満、窒素吸着比表面積が２ｍ ² ／ｇ未満であるものを用いることが望ましい。この、物性値を外れると、放電容量が低く成ったりする危険性がある。また、Ｌｉ基準電位で０Ｖまで充電後、１.５Ｖまで放電した際の初回充放電効率８５％以下である場合、不可逆容量が大きくなり、電池として過剰な活物質が必要となり重量あたりのエネルギー密度が低下したり、コストが高くなってしまう問題が生じる。
【００１０】
本発明により、放電末期に両極間の電圧低下を緩やかにすることが可能になり、０Ｖまで充電し、例えば０.３Ｖまで放電可能な容量が、黒鉛質材料単体及び非黒鉛質材料単体における評価容量から推算される、予想値以上に優れた特性を示す負極材料を見出した。
【００１１】
即ち、本発明は、リチウムの吸蔵放出が可能な正極活物質が集電体箔の両面に形成された正極と、リチウムの吸蔵放出が可能な負極活物質が集電体箔の両面に形成された負極と、リチウム塩を含む非水電解液とを有し、前記正極及び負極がセパレータを介して巻回または積層された非水系電解液二次電池において、前記負極活物質が黒鉛質材料と該黒鉛質材料より高い放電容量を有する非黒鉛質材料の混合材料からなることを特徴とする。
【００１２】
従来の黒鉛質材料と非黒鉛質材料の混合負極の評価では、結晶内にリチウムイオンを可逆的にドープ／脱ドープする為の指標として用いられていた００２面の面間隔ｄ（００２）及び結晶子サイズＬｃを適正化していた。それに対して本発明の非黒鉛質材料はＬｃ値を最適化し、且つ、リチウムイオンの可逆的にドープ／脱ドープするためのサイトとなる材料表面の黒鉛化度Ｒ値が結晶質な性質と炭素質な性質の両面を持ち合わせる適正値にし、更に非黒鉛質材料の比表面積及び充放電効率を適正化することにより、電解液の分解等の副反応を抑制し、活物質界面でのイオンのドープ／脱ドープに伴う電荷移動などに起因する反応分極を抑制し、従来黒鉛質材料と非黒鉛質材料の混合負極と比較して、放電末期に両極間の電圧低下を緩やかにすることが可能になり、０Ｖまで充電後、例えば負極電位で０.３Ｖまで放電可能な容量が、黒鉛質材料単体及び非黒鉛質材料単体における評価容量から推算される、予想値以上の優れた特性が得られるものである。
【００１３】
負極材料を集電体と密着させるために用いるバインダーは、ポリフッ化ビニリデン−６フッ化プロピレン共重合体，エチレン−プロピレン−ジエン共重合体等が好ましい。また非水溶媒としては、プロピレンカーボネート，ジメチルカーボネート１，２−ジメトキシエタン，テトラヒドロフラン等の単体または混合物が好ましい。
【００１４】
電解質は、過塩素酸リチウム，六フッ化リン酸リチウム，ホウフッ化リチウム，ビストリフルオロメチルスルホニイミドリチウムなどを用いることが好ましい。
【００１５】
本発明の負極材料と組み合わせて使用する正極材料としては、化学式がLiCoO₂，ＬｉＮｉＯ_2,ＬｉＭｎ_xＮｉ_1-xＯ₂，ＬｉＭｎ₂Ｏ₄，ＬｉＭｎＯ₂（但しｘは
０.００１≦ｘ≦０.５の範囲）等が上げられる。
【００１６】
【発明の実施の形態】
本実施例で示すバインダー，非水系溶媒，集電体，電解質等は一例であり、本発明は本実施例に示すものには限定されない。
【００１７】
（実施例１）
本実施例の非水系電解液二次電池用負極材料の調製方法を以下に示す。実施形態１〜４において非黒鉛質材料としては、セルロース系の先駆体を焼成したものを用いた。焼成方法の一例を以下に示す。まず、前記先駆体を５℃／分の昇温速度で３００℃まで加熱し１時間保持後（大気中）、冷却後粉砕する。その後、分級することで７０ミクロン以上の粗粒を除去した。分級した粉末を１０^-2Torrの真空下で７００℃まで昇温（５℃／分）して１時間保持後、更に１２００℃まで昇温（５℃／分）し２時間保持して調製した。このようにして調製した非黒鉛材料の物性値は、Ｘ線回折結果より算出される結晶子の厚みを示すＬｃ値が１ｎｍで、且つラマン分光スペクトルで測定される非結晶質乱層構造に由来するピークの高さ（Ｉ_D ）と黒鉛結晶質構造に由来するピークの高さ（Ｉ_G ）の比から求められる黒鉛化度Ｒ値（Ｉ_D／Ｉ_G）が０.９８、窒素吸着による比表面積は１ｍ²／ｇであった。また、用いた黒鉛質材料としては、放電容量が３６０ｍＡｈ／ｇで初回の充放電効率が９０％である人造黒鉛を用いた。また比較例１〜４は非黒鉛材料として前述の実施形態１と同じ物を用い混合割合を変化させたものである。また、比較例５〜７は原料として前述の実施形態１と同じ物を用い、７００℃での保持をなくしＡｒ雰囲気下で焼成したもの、最高到達温度１５００℃で１０時間保持したもの、最高到達温度９００℃としたものをそれぞれ用いた。その他の焼成の詳細条件は実施形態１に準じた。このようにして調整した非黒鉛質材料の物性値，混合割合を表１に示す。
【００１８】
【表１】

【００１９】
以下にこれらの負極材料を用いて、電極を作成し負極材料特性を評価する手法を示す。まず電極の作成方法を以下に示す。任意の割合で秤量した負極材料にポリフッ化ビニリデン（クレハ製＃１１２０）１０重量部と成るように添加して、溶媒として１−メチル−２−ピロリドンを、固形分濃度が４５重量部となるように添加して混練する。そうして得たスラリーを集電体である銅箔上に塗布し、
１２０℃で３時間恒温槽内において乾燥させた。その後、直径１５mmに打ち抜き電極とした。
【００２０】
以下にテストセルを作製し、負極材料特性を評価する方法を示す。負極材料特性評価に用いたテストセルは、直径が１５mmでセパレータとしてはポリプロピレン製多孔質膜を介して対極となるリチウム金属箔（１mm厚）と対向させて配置し、その間に、非水系電解液を充填させた。本実施例で用いた電解液はエチレンカーボネートとメチルエチルカーボネートとの混合溶媒（容量比１：１）に電解質として六フッ化リン酸リチウムを１Ｍ溶解させたものを用いた。このようにして調製したテストセルの充放電条件は、以下に示す条件で行った。充電は定電流充電０.５ｍＡ（０.２８４ｍＡ／cm² ），定電圧充電０Ｖ，０.０５ｍＡで実施し、放電は電流０.５ｍＡでカット電圧０.３Ｖとした。表１に示す放電容量及び初回充放電効率は、別途作成したテストセルで、前述の充放電条件と同一電流密度とし、放電カット電圧を１.５Ｖとし評価した値である。
【００２１】
上記の条件で充放電を行った後に、混合物負極材料単位量あたりの放電容量を算出した。その結果を図１に示す。図１より本発明である混合負極は、黒鉛質材料単独負極及び非黒鉛質材料単独負極の特性評価から推算される値より高い放電量を示し、優れた負極材料であることが確認された。
【００２２】
（実施例２）
本発明の非水系電解液二次電池用負極材料を用いたリチウム二次電池の性能評価方法を示す。本実施例で用いた電極及び電池の調製方法を以下に示す。正極は材料としてＬｉＭｎ₂Ｏ₄を用いた。正極活物質８７重量部に導電助剤となる人造黒鉛８.７重量部，１−メチル−２−ピロリドンに溶解させたポリフッ化ビニリデン（クレハ製＃１１２０）を固形分で４.３重量部と成るように混合し、ペーストを作成して集電体であるアルミ箔に両面塗布し、８０℃で３時間乾燥させた。その後、プレスして約２.７ｇ／cm³程度の密度とし、１２０℃で３時間真空乾燥して正極を得た。
【００２３】
負極は実施形態１に示す非黒鉛材料に任意の割合で黒鉛材料を混合した材料にポリフッ化ビニリデン（クレハ製＃１１２０）１０重量部と成るように添加して、溶媒として１−メチル−２−ピロリドンを、固形分濃度が４５重量部となるように添加して混練する。そうして得たスラリーを集電体である銅箔に両面の塗布し、８０℃で３時間乾燥させた。その後、プレスして約１.０ｇ／cm³程度の密度とし、１２０℃で３時間真空乾燥して得た。
【００２４】
実施形態５〜８の電池は実施形態１〜４に示す負極材料を用い、また、比較例９〜１４の電池は比較例１〜７の負極材料を用いて、前述と同様の手法で電極を作成した。得られた正極及び負極は、ポリエチレン製多孔質膜セパレータ（厚み：０.０２５mm ）と組み合わせて捲回し、外寸法が直径１８mm，長さ６５mmの電池缶に収納した。用いた電解液は、エチレンカーボネートとメチルエチルカーボネートとの混合溶媒（容量比１：１）に電解質として六フッ化リン酸リチウムを１Ｍ溶解させたものを用いた。図２に本試験に用いた電池の一例の一部断面正面図を示す。
【００２５】
図２に示す円筒型リチウム二次電池は、薄板状に加工された正極１と同様に加工された負極２がポリエチレン製多孔膜等のセパレータ３を介して重ね合わせたものを捲回し、これを金属製等の電池缶７に挿入し、密閉化されている。正極には正極タブ４を介して正極蓋６に接合され、負極２は負極タブ５を介して電池底部へ接合されている。正極蓋６はガスケット８にて電池缶７へ固定されている。
【００２６】
上記のようにして調製した電池の充放電条件は、以下に示す条件で行った。電流５００ｍＡ一定で、充電停止電圧４.２Ｖ，放電停止電圧２.７Ｖとして性能評価を実施した。表２に電池の充放電効率評価結果を示す。本実施例においても実施形態１〜４と同様の傾向を有し、黒鉛質材料単独負極を用いた際の電池の放電容量と、非黒鉛質材料単独負極を用いた際の電池の放電容量から推算される容量より、優れた放電容量を示す二次電池を製造できることが確認された。
【００２７】
【表２】

【００２８】
【発明の効果】
本発明の負極材料を用いることにより、放電容量特性が優れた非水系電解液二次電池を製造することが可能となり、ポータブル電子機器、等の小型化に寄与できる。
【図面の簡単な説明】
【図１】本発明の負極材料の単極容量特性を示す線図。
【図２】本発明に係る円筒型リチウム二次電池の断面図。
【符号の説明】
１…正極、２…負極、３…セパレータ、４…正極タブ、５…負極タブ、６…正極蓋、７…電池缶、８…ガスケット。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a novel non-aqueous electrolyte secondary battery suitable for use in portable electronic devices and the like, and a negative electrode material thereof.
[0002]
[Prior art]
Conventionally, a graphite material has been used for a negative electrode of a non-aqueous electrolyte secondary battery (for example, artificial graphite obtained by graphitizing natural graphite material, coke or the like). However, natural graphite with developed graphite crystals and artificial graphite graphitized coke has a large voltage change due to the polarization on the negative electrode side at the end of discharge, and the end voltage is set high to suppress overdischarge. It has been difficult to fully utilize the capacity of the. For example, if the end-of-discharge voltage of the battery is set to 2.7 V, and the potential of the positive electrode at the end of the discharge is estimated to be about 3.0 V, the discharge capacity until the potential of the negative electrode reaches about 0.3 V is substantially Battery capacity. In view of this, a method has been proposed in which polarization at the end of discharge is suppressed by using a mixed negative electrode with a non-graphitic material that diffuses lithium ions faster than a graphite material.
[0003]
In Patent Document 1, a graphite material is mixed with a carbonaceous material in which the distance between the 002 planes determined by X-ray diffraction is 0.343 to 0.39 nm and the crystallite size Lc is 0.9 to 9.9 nm. A technique has been proposed. Patent Document 2 proposes a technique in which the graphite material and a non-graphitic carbon material having a capacity of 80% or more per weight of the graphite material are mixed to suppress the polarization of the negative electrode.
[0004]
[Patent Document 1]
JP-A-6-36760 [Patent Document 2]
Japanese Patent Laid-Open No. 7-192724
[Problems to be solved by the invention]
However, when the material described in Patent Document 1 is used for a battery, the carbonaceous material to be mixed is a substance having a lower discharge capacity per weight than the graphite material, and a negative electrode formed by mixing was used. In the battery, there was a risk that the discharge capacity per weight would be low. Further, when the mixing amount of the carbonaceous material exceeds 30% by volume, there is a problem that the polarization becomes large and the discharge potential of the battery becomes low.
[0006]
Further, when the material described in Patent Document 2 is used for a battery, the potential on the negative electrode side at the end of charging is lower than that of the graphite material. However, when a material having a discharge capacity per unit weight of about 80% to 90% is used for the carbonaceous material to be mixed as compared with the graphite material, there is a risk that the battery will have a low discharge capacity per unit weight. was there.
[0007]
An object of the present invention is to provide a non-aqueous electrolyte secondary battery having a good discharge capacity and a negative electrode material thereof, in which a voltage drop between both electrodes is moderated at the end of discharge.
[0008]
[Means for Solving the Problems]
The present invention uses a mixed material of a graphite material and a non-graphitic material having a discharge capacity higher than that of the graphite material as the negative electrode active material (however, the discharge capacity described here is a current density with the counter electrode being metallic lithium). This refers to the amount of discharge per unit weight of the negative electrode material when lithium is doped until the terminal voltage reaches 0 V, and then lithium is dedoped to 1.5 V). Thereby, the voltage drop between both electrodes is moderated at the end of discharge, and the battery capacity that can be discharged is improved. The mixing amount of the non-graphitic material is greater than 10% by volume and less than 90% by volume. In addition, the non-graphitic material is a model battery evaluated using metallic lithium as a reference electrode and a counter electrode, and after charging to 0 V at the Li reference potential,
Initial charge / discharge efficiency when discharged to 1.5V (however, the initial charge / discharge efficiency described here is per unit weight of negative electrode material doped with lithium until the counter electrode is metal lithium and the terminal voltage is 0V at a constant current density) The percentage ratio of the charge amount C of the battery and the discharge amount D per unit weight of the negative electrode material when lithium is dedope up to 1.5 V = (D / C) × 100) is higher than 85%. Use materials.
[0009]
1300~1400cm Non graphitic material properties to be used specifically in the Lc value indicating the thickness of a crystallite calculated from the X-ray diffraction results 0 70 2 or more than 20 nm, that is and measured by Raman spectroscopy.. ^- Peak height (I _D ) indicating vibration modes derived from ^one range of amorphous turbostratic structure and peak height (I _D ) indicating vibration modes derived from graphite crystalline structure in the range of 1580 to 1620 cm ⁻¹ degree of graphitization R value calculated from the ratio of _{_{_{G) (I D / I G}}} ) is zero. 90 or more 1. less than 20, the nitrogen adsorption specific surface area it is desirable to use a less than 2m ² / g. If this physical property value is deviated, there is a risk that the discharge capacity becomes low. In addition, if the initial charge / discharge efficiency is 85% or less after charging to 0 V at the Li reference potential and then discharging to 1.5 V, the irreversible capacity increases, and an excessive active material is required as a battery, resulting in an energy density per weight. This causes problems such as a decrease in cost and an increase in cost.
[0010]
According to the present invention, the voltage drop between the two electrodes can be moderated at the end of discharge, and the capacity that can be charged to 0V, for example, discharged to 0.3V, is evaluated in the graphite material alone and the non-graphitic material alone. The present inventors have found a negative electrode material that exhibits characteristics superior to expected values estimated from capacity.
[0011]
That is, according to the present invention, a positive electrode active material capable of occluding and releasing lithium is formed on both surfaces of the current collector foil, and a negative electrode active material capable of occluding and releasing lithium is formed on both surfaces of the current collector foil. A non-aqueous electrolyte secondary battery having a negative electrode and a non-aqueous electrolyte containing a lithium salt, wherein the positive electrode and the negative electrode are wound or laminated with a separator interposed therebetween. It is characterized by comprising a mixed material of non-graphitic materials having a higher discharge capacity than the graphite materials.
[0012]
In the evaluation of a conventional mixed negative electrode of a graphite material and a non-graphitic material, the interplanar spacing d (002) and the crystal used as an index for reversibly doping / dedoping lithium ions in the crystal The child size Lc was optimized. On the other hand, the non-graphitic material of the present invention optimizes the Lc value, and the graphitization degree R value on the surface of the material that becomes a site for reversibly doping / dedoping lithium ions has a crystalline property and carbon. By adjusting the specific surface area and charge / discharge efficiency of the non-graphitic material to an appropriate value that has both sides of a high quality property, side reactions such as decomposition of the electrolyte are suppressed, and ions are doped at the active material interface. / Suppresses reaction polarization caused by charge transfer associated with de-doping, etc., and makes it possible to moderate the voltage drop between both electrodes at the end of discharge compared to conventional mixed negative electrode of graphite material and non-graphite material After charging to 0 V, for example, the capacity that can be discharged to 0.3 V at the negative electrode potential is estimated from the evaluation capacities of the graphite material alone and the non-graphite material alone, and excellent characteristics more than expected can be obtained. It is.
[0013]
The binder used for adhering the negative electrode material to the current collector is preferably a polyvinylidene fluoride-6-fluoropropylene copolymer, an ethylene-propylene-diene copolymer, or the like. The nonaqueous solvent is preferably a simple substance or a mixture of propylene carbonate, dimethyl carbonate 1,2-dimethoxyethane, tetrahydrofuran and the like.
[0014]
As the electrolyte, lithium perchlorate, lithium hexafluorophosphate, lithium borofluoride, lithium bistrifluoromethylsulfonimide, or the like is preferably used.
[0015]
As the positive electrode material used in combination with the negative electrode material of the present invention, the chemical formula is LiCoO ₂ , LiNiO _2, LiMn _x Ni _1-x O ₂ , LiMn ₂ O ₄ , LiMnO ₂ (where x is 0.001 ≦ x ≦ 0. .5 range) etc.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
The binder, non-aqueous solvent, current collector, electrolyte, and the like shown in this embodiment are examples, and the present invention is not limited to those shown in this embodiment.
[0017]
Example 1
A method for preparing the negative electrode material for a non-aqueous electrolyte secondary battery of this example is shown below. In Embodiments 1 to 4, as the non-graphitic material, a material obtained by firing a cellulose precursor was used. An example of the firing method is shown below. First, the precursor is heated to 300 ° C. at a heating rate of 5 ° C./min, held for 1 hour (in the atmosphere), cooled and then pulverized. Then, coarse particles of 70 microns or more were removed by classification. The classified powder was heated to 700 ° C. under a vacuum of 10 ⁻² Torr (5 ° C./min) and held for 1 hour, and further heated to 1200 ° C. (5 ° C./min) and held for 2 hours. . The physical property values of the non-graphite material thus prepared are derived from an amorphous disordered layer structure having an Lc value indicating the thickness of the crystallite calculated from the X-ray diffraction result of 1 nm and measured by Raman spectroscopy. The graphitization degree R value (I _D / I _G ) obtained from the ratio of the peak height (I _D ) to the peak height (I _G ) derived from the graphite crystalline structure is 0.98, and is due to nitrogen adsorption The specific surface area was 1 m ² / g. As the graphite material used, artificial graphite having a discharge capacity of 360 mAh / g and an initial charge / discharge efficiency of 90% was used. Moreover, Comparative Examples 1-4 uses the same thing as above-mentioned Embodiment 1 as a non-graphite material, and changes the mixing ratio. In Comparative Examples 5 to 7, the same materials as those of the first embodiment described above were used as raw materials, and the material was fired in an Ar atmosphere without holding at 700 ° C., held at 1500 ° C. for 10 hours, and reached the maximum. Each having a temperature of 900 ° C. was used. Other detailed firing conditions were the same as in the first embodiment. Table 1 shows the physical property values and mixing ratios of the non-graphitic materials thus adjusted.
[0018]
[Table 1]

[0019]
A method for producing an electrode using these negative electrode materials and evaluating the negative electrode material characteristics will be described below. First, a method for producing an electrode is shown below. The negative electrode material weighed at an arbitrary ratio is added so as to be 10 parts by weight of polyvinylidene fluoride (Kureha # 1120), 1-methyl-2-pyrrolidone is used as a solvent, and the solid content concentration is 45 parts by weight. And kneaded. The slurry thus obtained was applied onto a copper foil as a current collector,
It was dried in a constant temperature bath at 120 ° C. for 3 hours. Thereafter, a punched electrode having a diameter of 15 mm was obtained.
[0020]
A method for preparing a test cell and evaluating the negative electrode material characteristics will be described below. The test cell used for the negative electrode material characteristic evaluation is 15 mm in diameter and is placed as a separator facing a lithium metal foil (1 mm thickness) as a counter electrode through a polypropylene porous membrane, and a non-aqueous electrolyte solution therebetween. Was filled. The electrolytic solution used in this example was prepared by dissolving 1M lithium hexafluorophosphate as an electrolyte in a mixed solvent of ethylene carbonate and methyl ethyl carbonate (capacity ratio 1: 1). The charge / discharge conditions of the test cell thus prepared were as follows. Charging was performed with constant current charging of 0.5 mA (0.284 mA / cm ² ), constant voltage charging of 0 V and 0.05 mA, and discharging was performed with a current of 0.5 mA and a cut voltage of 0.3 V. The discharge capacities and initial charge / discharge efficiencies shown in Table 1 are values obtained by evaluating separately the test cells prepared at the same current density as the charge / discharge conditions described above and the discharge cut voltage of 1.5V.
[0021]
After charging / discharging on said conditions, the discharge capacity per unit amount of mixture negative electrode materials was computed. The result is shown in FIG. From FIG. 1, the mixed negative electrode according to the present invention showed a discharge amount higher than the value estimated from the characteristic evaluation of the graphite material single negative electrode and the non-graphitic material single negative electrode, and was confirmed to be an excellent negative electrode material.
[0022]
(Example 2)
The performance evaluation method of the lithium secondary battery using the negative electrode material for nonaqueous electrolyte secondary batteries of this invention is shown. The electrode and battery preparation method used in this example is shown below. LiMn ₂ O ₄ was used as a material for the positive electrode. 8.7 parts by weight of artificial graphite serving as a conductive assistant in 87 parts by weight of the positive electrode active material, 4.3 parts by weight of solid content of polyvinylidene fluoride (# 1120 manufactured by Kureha) dissolved in 1-methyl-2-pyrrolidone A paste was prepared and applied on both sides to an aluminum foil as a current collector, and dried at 80 ° C. for 3 hours. Then, it pressed to a density of about 2.7 g / cm ³ and vacuum dried at 120 ° C. for 3 hours to obtain a positive electrode.
[0023]
A negative electrode is added to a material obtained by mixing a graphite material in an arbitrary ratio with the non-graphite material shown in Embodiment 1 so as to be 10 parts by weight of polyvinylidene fluoride (# 1120 manufactured by Kureha), and as a solvent, 1-methyl-2- Pyrrolidone is added and kneaded so that the solid content concentration is 45 parts by weight. The slurry thus obtained was applied to both sides of a copper foil as a current collector and dried at 80 ° C. for 3 hours. Then, it was pressed to obtain a density of about 1.0 g / cm ³ and obtained by vacuum drying at 120 ° C. for 3 hours.
[0024]
The batteries of Embodiments 5 to 8 use the negative electrode materials shown in Embodiments 1 to 4, and the batteries of Comparative Examples 9 to 14 use the negative electrode materials of Comparative Examples 1 to 7, and electrodes are formed in the same manner as described above. Created. The obtained positive electrode and negative electrode were wound in combination with a polyethylene porous membrane separator (thickness: 0.025 mm) and stored in a battery can having an outer dimension of 18 mm in diameter and 65 mm in length. The electrolytic solution used was a solution of 1M lithium hexafluorophosphate dissolved in a mixed solvent of ethylene carbonate and methyl ethyl carbonate (capacity ratio 1: 1) as an electrolyte. FIG. 2 shows a partial cross-sectional front view of an example of the battery used in this test.
[0025]
The cylindrical lithium secondary battery shown in FIG. 2 is obtained by winding a negative electrode 2 processed in the same manner as a thin plate-like positive electrode 1 via a separator 3 such as a polyethylene porous membrane. It is inserted into a battery can 7 made of metal or the like and sealed. The positive electrode is bonded to the positive electrode lid 6 via the positive electrode tab 4, and the negative electrode 2 is bonded to the battery bottom via the negative electrode tab 5. The positive electrode lid 6 is fixed to the battery can 7 with a gasket 8.
[0026]
The charging / discharging conditions of the battery prepared as described above were performed under the following conditions. The performance was evaluated with a constant current of 500 mA, a charge stop voltage of 4.2 V, and a discharge stop voltage of 2.7 V. Table 2 shows the results of evaluating the charge / discharge efficiency of the battery. This example also has the same tendency as in Embodiments 1 to 4, from the discharge capacity of the battery when using a single graphite material negative electrode and the discharge capacity of the battery when using a non-graphitic material single negative electrode It was confirmed that a secondary battery exhibiting an excellent discharge capacity can be produced from the estimated capacity.
[0027]
[Table 2]

[0028]
【The invention's effect】
By using the negative electrode material of the present invention, a non-aqueous electrolyte secondary battery having excellent discharge capacity characteristics can be manufactured, which can contribute to miniaturization of portable electronic devices and the like.
[Brief description of the drawings]
FIG. 1 is a diagram showing single electrode capacity characteristics of a negative electrode material of the present invention.
FIG. 2 is a cross-sectional view of a cylindrical lithium secondary battery according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Positive electrode, 2 ... Negative electrode, 3 ... Separator, 4 ... Positive electrode tab, 5 ... Negative electrode tab, 6 ... Positive electrode cover, 7 ... Battery can, 8 ... Gasket.

Claims

黒鉛質材料と非黒鉛質材料との混合物からなる負極材料において、前記非黒鉛質材料の混合量が１０体積％より大きく９０体積％未満であって、前記非黒鉛材料の（Ｉ _D ／Ｉ _G ）が０ . ９０以上１ . ２０未満であり、Ｌｃ値が０ . ７０ｎｍ以上２ . ２０ｎｍ未満であり、比表面積が２ . ０ｍ ² ／ｇ未満であり、前記非黒鉛材料は、セルロース系の前駆体を真空中で焼成したものであって、前記黒鉛質材料より高い放電容量を有し、且つ、前記非黒鉛質材料は参照極及び対極に金属リチウムを用いて作成したモデル電池評価において、Ｌｉ基準電位で０Ｖまで充電後、１.５Ｖまで放電した際の初回充放電効率が８５％より高い値を示す材料であることを特徴とする非水系電解液二次電池用負極材料。In a negative electrode material made of a mixture of a graphite material and a non-graphitic material, the amount of the non-graphitic material mixed is more than 10% by volume and less than 90% by volume, and the non-graphite material has a (I _D / I _G ) 0. 90 or more 1. less than 20, Lc value is 2. less than 20 nm 0. 70 nm or more, a specific surface area of less than 2. 0 m ² / g, the non-graphite material, a precursor of cellulosic The body was fired in a vacuum and had a higher discharge capacity than the graphite material, and the non-graphitic material was produced by using a lithium metal as a reference electrode and a counter electrode. A negative electrode material for a non-aqueous electrolyte secondary battery, characterized in that the initial charge / discharge efficiency is a value higher than 85% when charged to 0 V at a reference potential and then discharged to 1.5 V.

リチウムの吸蔵放出が可能な正極活物質が集電体箔の両面に形成された正極と、リチウムの吸蔵放出が可能な負極活物質が集電体箔の両面に形成された負極と、リチウム塩を含む非水電解液とを有し、前記負極活物質が黒鉛質材料と非黒鉛質材料の混合材料であり、前記非黒鉛材料の（Ｉ _D ／Ｉ _G ）が０ . ９０以上１ . ２０未満であり、Ｌｃ値が０ . ７０ｎｍ以上２ . ２０ｎｍ未満であり、比表面積が２ . ０ｍ ² ／ｇ未満であり、前記非黒鉛材料は、セルロース系の前駆体を真空中で焼成したものであって、前記黒鉛質材料より高い放電容量を有し、前記正極及び負極がセパレータを介して巻回または積層された非水系電解液二次電池において、前記非黒鉛質材料の混合量が１０体積％より大きく９０体積％未満であり、また、前記非黒鉛質材料は０Ｖまで充電後、１.５Ｖまで放電した際の初回充放電効率が８５％より高い値を示す材料であることを特徴とする非水系電解液二次電池。A positive electrode in which a positive electrode active material capable of occluding and releasing lithium is formed on both sides of the current collector foil, a negative electrode in which a negative electrode active material capable of occluding and releasing lithium is formed on both sides of the current collector foil, and a lithium salt and a nonaqueous electrolyte containing the negative electrode active material is a mixed material of graphitic material and a non-graphitic material, wherein the non-graphitic material (I _D / I _G) to zero. 90 or more 1.20 less than, Lc value is 2. less than 20 nm 0. 70 nm or more, a ratio less than surface area 2. 0 m ² / g, the non-graphite material is obtained by sintering in vacuum precursor cellulose In the non-aqueous electrolyte secondary battery having a higher discharge capacity than the graphite material, and the positive electrode and the negative electrode are wound or laminated via a separator, the mixing amount of the non-graphitic material is 10 volumes. % And less than 90% by volume, and the non-graphitic Fee after charging up to 0V, the non-aqueous electrolytic solution secondary battery initial charge and discharge efficiency when the discharge is characterized in that the material exhibiting a higher than 85% the value to 1.5V.