JP2002352801A - Lithium secondary cell, negative electrode material for it, and improving method therefor - Google Patents
Lithium secondary cell, negative electrode material for it, and improving method thereforInfo
- Publication number
- JP2002352801A JP2002352801A JP2001157860A JP2001157860A JP2002352801A JP 2002352801 A JP2002352801 A JP 2002352801A JP 2001157860 A JP2001157860 A JP 2001157860A JP 2001157860 A JP2001157860 A JP 2001157860A JP 2002352801 A JP2002352801 A JP 2002352801A
- Authority
- JP
- Japan
- Prior art keywords
- negative electrode
- lithium secondary
- electrode material
- secondary battery
- thin film
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Landscapes
- Battery Electrode And Active Subsutance (AREA)
- Secondary Cells (AREA)
Abstract
Description
【0001】[0001]
【発明の属する技術分野】本発明は新規なリチウム二次
電池用負極材料とその改良方法および得られるリチウム
二次電池に関する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel negative electrode material for a lithium secondary battery, a method for improving the same, and a resulting lithium secondary battery.
【0002】[0002]
【従来の技術】リチウム二次電池は、コバルト酸リチウ
ムLiCoO2などのリチウムを放出できる陽極材料と、炭素
などのリチウムを挿入脱離できる負極材料と、過塩素酸
リチウムなどの電解液を組み合わせて作成されるもの
で、高いエネルギー密度を有するという特徴を有する。 2. Description of the Related Art A lithium secondary battery combines an anode material capable of releasing lithium such as lithium cobaltate LiCoO 2 , a negative electrode material capable of inserting and removing lithium such as carbon, and an electrolyte such as lithium perchlorate. It is made and has the feature of having a high energy density.
【0003】現在、リチウム二次電池用負極としては黒
鉛あるいは難黒鉛性炭素が実用されている。しかし、炭
素層間のリチウムの拡散がスムーズでなく、出力特性が
上がらず、またエネルギー容量も汎用されている天然黒
鉛の場合300mAh/g程度の値しか得られていないので、従
来技術において各種の工夫が提案されているが(特開平
2001-23638号公報、同2000-357506号公報、同2000-2646
14号公報、同2000-90928号公報、同10-214615号公報、
同11-40158号公報、同2000-260428号公報など)、十分
ではなく、これらの特性をさらに改良することが望まれ
ている。At present, graphite or non-graphitizable carbon is in practical use as a negative electrode for a lithium secondary battery. However, the diffusion of lithium between carbon layers is not smooth, the output characteristics are not improved, and the energy capacity is only about 300 mAh / g for natural graphite, which is widely used. Has been proposed (see
JP 2001-23638, JP 2000-357506, JP 2000-2646
No. 14, No. 2000-90928, No. 10-214615,
Nos. 11-40158 and 2000-260428), which are not sufficient, and it is desired to further improve these characteristics.
【0004】[0004]
【発明が解決しようとする課題】そこで、本発明は、リ
チウム二次電池用負極として用いられている材料のエネ
ルギー容量を増加させ、また出力特性と充放電サイクル
特性を向上させることを目的とする。SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to increase the energy capacity of a material used as a negative electrode for a lithium secondary battery and to improve output characteristics and charge / discharge cycle characteristics. .
【0005】[0005]
【課題を解決するための手段】本発明は、上記目的を達
成するために鋭意検討し、下記によって上記目的を達成
することができること見出したものである。 (1)リチウム二次電池用負極材料の表面に金属化合物
薄膜を被覆してなることを特徴とするリチウム二次電池
用負極材料。Means for Solving the Problems The present invention has been studied diligently to achieve the above object, and has found that the above object can be achieved by the following. (1) A negative electrode material for a lithium secondary battery, wherein the surface of the negative electrode material for a lithium secondary battery is coated with a metal compound thin film.
【0006】(2)前記金属化合物薄膜の膜厚が2〜5
00nmの範囲内である(1)に記載のリチウム二次電
池用負極材料。 (3)前記金属化合物薄膜がアルミニウム酸化物薄膜で
ある(1)(2)に記載のリチウム二次電池用負極材
料。 (4)前記リチウム二次電池用負極材料がグラファイト
またはバナジウム系酸化物である(1)〜(3)に記載
のリチウム二次電池用負極材料。(2) The metal compound thin film has a thickness of 2 to 5
The negative electrode material for a lithium secondary battery according to (1), wherein the thickness is within a range of 00 nm. (3) The negative electrode material for a lithium secondary battery according to (1) or (2), wherein the metal compound thin film is an aluminum oxide thin film. (4) The negative electrode material for a lithium secondary battery according to any one of (1) to (3), wherein the negative electrode material for a lithium secondary battery is graphite or a vanadium-based oxide.
【0007】(5)リチウム二次電池用負極材料の表面
を金属化合物薄膜で被覆することを特徴とするリチウム
二次電池用負極材料の改良方法。 (6)前記金属化合物薄膜を金属アルコキシド処理法、
ゾルゲル法、CVD法、PVD法、めっき法から選ばれ
る方法で形成する(5)に記載のリチウム二次電池用負
極材料の改良方法。(5) A method for improving a negative electrode material for a lithium secondary battery, which comprises coating the surface of the negative electrode material for a lithium secondary battery with a metal compound thin film. (6) a metal alkoxide treatment method for the metal compound thin film,
(5) The method for improving a negative electrode material for a lithium secondary battery according to (5), which is formed by a method selected from a sol-gel method, a CVD method, a PVD method, and a plating method.
【0008】(7)リチウム二次電池用負極材料の表面
に金属アルコキシドを付着させ、しかる後加熱分解して
リチウム二次電池用負極材料の表面を金属酸化物薄膜で
被覆する(5)(6)に記載のリチウム二次電池用負極
材料の改良方法。 (8)(1)〜(4)に記載のリチウム二次電池用負極
材料を用いたことを特徴とするリチウム二次電池。(7) A metal alkoxide is adhered to the surface of the negative electrode material for a lithium secondary battery, and then is thermally decomposed to cover the surface of the negative electrode material for a lithium secondary battery with a metal oxide thin film. A method for improving a negative electrode material for a lithium secondary battery according to the above item. (8) A lithium secondary battery using the negative electrode material for a lithium secondary battery according to any one of (1) to (4).
【0009】[0009]
【発明の実施の形態】本発明のリチウム二次電池用負極
材料は、リチウムイオンを挿入脱離することができる材
料であればよく、典型的にはグラファイト、難黒鉛性炭
素その他の炭素材料が用いられるが、それに限定され
ず、バナジウム系酸化物、例えば、MnV2O6などでも
よい。MnV2O6は本発明者らリチウム二次電池用負極
材料として好適であることを見出したものであるが、そ
の物質および製法自体は公知である。MnV2O6は、炭
素とくらべて、エネルギー容量が600〜700mAh/gと高
く、さらに炭素より密度が大きいので体積当たりのエネ
ルギー容量密度はより高いという特徴とともに、酸化物
であるので炭素と比べて有機電解質との反応性が低く、
温度上昇、爆発などの危険性が少ない特徴を有するもの
である。BEST MODE FOR CARRYING OUT THE INVENTION The negative electrode material for a lithium secondary battery of the present invention may be any material capable of inserting and removing lithium ions, and typically, graphite, non-graphitizable carbon and other carbon materials are used. It is used, but not limited thereto, and may be a vanadium-based oxide such as MnV 2 O 6 . The present inventors have found that MnV 2 O 6 is suitable as a negative electrode material for a lithium secondary battery, but its substance and its production method are known. MnV 2 O 6 has a higher energy capacity of 600 to 700 mAh / g than carbon, and has a higher energy capacity density per volume because of its higher density than carbon. Low reactivity with organic electrolytes
It has the characteristic that there is little danger such as temperature rise and explosion.
【0010】これらのリチウム二次電池用負極材料は、
本発明により金属化合物薄膜で被覆すると、サイクル特
性が向上すること、あるいはエネルギー容量と出力特性
の向上する効果があることが見出された。特に天然黒鉛
では、従来のエネルギー容量は300mAh/g程度であるが、
本発明により金属化合物薄膜で被覆すると理論容量であ
る372mAh/gにほぼ等しい値(例えば370mAh/g)を示すと
共に、従来の炭素材料では0.2C以上の出力密度(1Cは
容量を1時間で放出する電流密度)では安定したサイク
ル特性を確保することが困難であったが、本発明により
金属化合物薄膜で被覆すると0.5Cの出力密度においても
極めて安定したサイクル特性を示すことができた。また
MnV2O6などのバナジウム系酸化物においては、今ま
でに実用化されている炭素材料と比べて2倍以上のエネ
ルギー容量を示しているが(図4参照)、他の酸化物系
負極と同様に初回の不可逆容量に問題があった。本発明
によれば、バナジウム系酸化物を金属化合物薄膜で被覆
することにより、初回の不可逆容量が大きく抑制するこ
とができ、また2回目以降の可逆エネルギー容量の損失
も、サイクル特性の劣化も観察されなくなる効果が得ら
れた。[0010] These negative electrode materials for lithium secondary batteries include:
It has been found that when coated with a metal compound thin film according to the present invention, cycle characteristics are improved, or energy capacity and output characteristics are improved. Especially in natural graphite, the conventional energy capacity is about 300 mAh / g,
When coated with a metal compound thin film according to the present invention, it shows a value almost equal to the theoretical capacity of 372 mAh / g (for example, 370 mAh / g), and the conventional carbon material has an output density of 0.2 C or more (1 C discharges capacity in one hour). However, it was difficult to secure stable cycle characteristics at a current density of 0.5 C. However, when coated with a metal compound thin film according to the present invention, extremely stable cycle characteristics could be exhibited even at an output density of 0.5 C. Vanadium-based oxides such as MnV 2 O 6 have twice or more the energy capacity of carbon materials that have been put to practical use (see FIG. 4). There was a problem with the irreversible capacity of the first time as well. According to the present invention, by coating a vanadium-based oxide with a metal compound thin film, the irreversible capacity at the first time can be largely suppressed, and the loss of reversible energy capacity and the deterioration of cycle characteristics after the second time are observed. The effect of not being obtained was obtained.
【0011】電池の充放電に伴うリチウム挿入脱離が繰
返されると、負極材料の構造破壊が進行することが、サ
イクル特性の劣化の原因であると考えられるが、本発明
により負極材料の表面を金属化合物薄膜で被覆すると、
負極材料の表面の薄膜がリチウム挿入脱離の繰返しに伴
う構造破壊を抑制するためにサイクル特性が向上すると
考えられる。また、負極材料の表面を金属化合物薄膜で
被覆すると、負極材料の表面に金属または金属化合物が
作用してリチウム挿入脱離口が拡大し、リチウム挿入脱
離が容易になり、エネルギー容量と出力特性の向上に寄
与するものと考えられる。また、酸化物系負極材料では
不働態被膜が形成されて初回不可逆容量が大きいことが
問題であるが、酸化物系負極材料の表面を金属化合物薄
膜で被覆すると、不働態被膜の形成が抑制されて初回不
可逆容量の大部分を抑制することができると考えられ
る。従って、本発明の金属化合物薄膜で被覆はリチウム
二次電池用負極材料一般に適用できるものである。[0011] When the insertion and detachment of lithium due to the charge and discharge of the battery are repeated, the progress of structural destruction of the negative electrode material is considered to be the cause of the deterioration of the cycle characteristics. When coated with a metal compound thin film,
It is considered that the cycle characteristics are improved because the thin film on the surface of the negative electrode material suppresses structural destruction due to repeated insertion and extraction of lithium. In addition, when the surface of the negative electrode material is coated with a metal compound thin film, the metal or metal compound acts on the surface of the negative electrode material, thereby expanding the lithium insertion / desorption opening, facilitating lithium insertion / desorption, and improving energy capacity and output characteristics. It is thought to contribute to the improvement of Also, in the oxide-based negative electrode material, a passivation film is formed and the first irreversible capacity is large, which is a problem. However, when the surface of the oxide-based negative electrode material is coated with a metal compound thin film, the formation of the passive film is suppressed. Therefore, it is considered that most of the initial irreversible capacity can be suppressed. Therefore, the coating with the metal compound thin film of the present invention can be generally applied to negative electrode materials for lithium secondary batteries.
【0012】薄膜を形成する金属化合物としては、アル
ミニウム、チタン、亜鉛、鉄、珪素などの金属の化合物
が広く適用できる。金属化合物としてはリチウム二次電
池の使用条件で安定な化合物であればよく、例えば、酸
化物、窒化物、酸窒化物、炭化物、酸炭化物、酸窒炭化
物などが好適である。用いる金属あるいは金属化合物の
種類は負極材料に応じて適宜選択すればよい。As a metal compound for forming a thin film, a compound of a metal such as aluminum, titanium, zinc, iron and silicon can be widely applied. Any metal compound may be used as long as it is a compound that is stable under the conditions of use of the lithium secondary battery. The type of metal or metal compound to be used may be appropriately selected according to the negative electrode material.
【0013】本発明の金属化合物薄膜はその膜厚が2〜
500nmの範囲内であることが好ましく、より好まし
くは2〜100nm、さらには5〜50nm、特に5〜
20nmの範囲内が好適である。金属化合物薄膜は負極
材料の表面を完全に覆う必要はない。金属化合物薄膜の
膜厚が2nmより薄いと、薄膜として形成することが困
難であり、負極材料の特性の向上の効果が小さく、一方
金属化合物薄膜の膜厚が500nmより厚いと負極材料
の特性を阻害する恐れが高くなるので好ましくない。The metal compound thin film of the present invention has a thickness of 2 to 2.
It is preferably within a range of 500 nm, more preferably 2 to 100 nm, furthermore 5 to 50 nm, especially 5 to 5 nm.
A range of 20 nm is preferred. The metal compound thin film does not need to completely cover the surface of the negative electrode material. If the thickness of the metal compound thin film is less than 2 nm, it is difficult to form the thin film as a thin film, and the effect of improving the characteristics of the negative electrode material is small. It is not preferable because the possibility of inhibition increases.
【0014】用いるリチウム二次電池用負極材料は、通
常、粉末状で用いられるが、その粒径は従来と同様でよ
い。限定するわけではないが、典型的には、0.1〜5
0μm、特に0.5〜30μmの範囲内である。リチウ
ム二次電池用負極材料を金属酸化物薄膜で被覆する方法
は、特に限定されず、金属アルコキシド処理法、ゾルゲ
ル法、CVD法、PVD法(スパッタリングその他)、
めっき法などでもよい。The negative electrode material for a lithium secondary battery to be used is usually used in the form of a powder, and the particle size may be the same as that of the conventional one. Typically, but not limited to, 0.1-5
0 μm, especially in the range of 0.5 to 30 μm. The method of coating the negative electrode material for a lithium secondary battery with a metal oxide thin film is not particularly limited, and includes a metal alkoxide treatment method, a sol-gel method, a CVD method, a PVD method (sputtering and others),
A plating method or the like may be used.
【0015】金属アルコキシド処理では、リチウム二次
電池用負極材料を金属アルコキシド溶液に浸漬し、引き
上げてリチウム二次電池用負極材料の表面に金属アルコ
キシド(溶液)を付着させた後、熱処理(熱分解)して
金属アルコキシドの有機分を除去することが効果的であ
る。金属アルコキシドとしてはアルミニウム、チタン、
亜鉛、鉄、珪素などの金属のアルコキシド、例えば、エ
トキシド、メタキシド、プロポキシド、ブトキシドなど
から適当に選択して用いることができる。金属アルコキ
シドは熱処理されると金属化合物、特に空気中で加熱す
ると金属酸化物の膜になると考えられるが、金属酸化物
は一般的に絶縁体であるにもかかわらず、金属アルコキ
シド処理したリチウム二次電池用負極材料では導電性の
向上さえ観察されたので、明確ではないが上記の如くリ
チウム挿入脱離口が拡大したものと考えられる一方、金
属酸化物などの金属化合物膜はその膜厚が薄いので問題
にならないものと考えられる。In the metal alkoxide treatment, a negative electrode material for a lithium secondary battery is immersed in a metal alkoxide solution, pulled up, and a metal alkoxide (solution) is attached to the surface of the negative electrode material for a lithium secondary battery. ) To remove the organic components of the metal alkoxide. Aluminum, titanium,
An alkoxide of a metal such as zinc, iron, silicon or the like, for example, ethoxide, metaoxide, propoxide, butoxide and the like can be appropriately selected and used. It is believed that metal alkoxides are heat-treated to form metal compounds, especially metal oxide films when heated in air. Despite the fact that metal oxides are generally insulators, metal alkoxide-treated lithium secondary Although the improvement in conductivity was observed even in the negative electrode material for batteries, although it is not clear, it is considered that the lithium insertion / desorption opening was expanded as described above, while the thickness of the metal compound film such as a metal oxide is thin. So it is not considered a problem.
【0016】実験によれば金属アルコキシド溶液の濃度
はあまり関係しなかった。これは負極材料を金属アルコ
キシド溶液に浸漬し引き上げた後、負極材料に付着した
金属アルコキシドの濃度にあまり差がないためと思われ
る。複数回の処理を行えば別であるが通常の1回の処理
であれば溶液の濃度はあまり重要ではない。限定はされ
ないが、一般的には2〜30重量%濃度の溶液を用いれ
ばよい。用いる溶媒は限定されず、メチルピロリドンな
どの代表的な溶媒を用いることができるが、例えば、エ
タノール、プロパノール、ブタノールなどのアルコール
を簡便に用いることができる。水と混合して用いてもよ
い。Experiments have shown that the concentration of the metal alkoxide solution is less relevant. This is presumably because the concentration of the metal alkoxide adhering to the negative electrode material was not so different after the negative electrode material was immersed in the metal alkoxide solution and pulled up. Unless the processing is performed a plurality of times, the concentration of the solution is not so important in the usual one processing. Although not limited, a solution having a concentration of 2 to 30% by weight may be generally used. The solvent to be used is not limited, and a typical solvent such as methylpyrrolidone can be used. For example, an alcohol such as ethanol, propanol and butanol can be easily used. It may be used by mixing with water.
【0017】熱処理の温度は金属アルコキシドを熱分解
して有機分を完全に除去できる温度が好ましく、熱分解
温度は金属アルコキシドの種類にも依存するが、例え
ば、アルミニウムアルコキシドでは、200℃以上、一
般的には200〜500℃、より好ましくは200〜3
00℃の範囲内が好ましいが、200℃未満の加熱でも
一定の効果を得ることは可能である。熱処理は空気中で
行えば十分であるが、理論的にはその他の酸化性ガスや
不活性ガスでも可能である。The temperature of the heat treatment is preferably a temperature at which organic components can be completely removed by thermal decomposition of the metal alkoxide. The thermal decomposition temperature also depends on the type of the metal alkoxide. 200 to 500 ° C., more preferably 200 to 3
The temperature is preferably in the range of 00 ° C., but it is possible to obtain a certain effect even by heating at less than 200 ° C. It is sufficient to perform the heat treatment in air, but theoretically, other oxidizing gas or inert gas can be used.
【0018】金属アルコキシド処理法以外の金属化合物
薄膜の形成方法は公知である。従って、公知の方法を利
用して、負極材料に応じて金属化合物の種類、薄膜の厚
さを適当に選択して、金属化合物薄膜を形成すればよ
い。本発明により金属化合物薄膜を被覆して得られたリ
チウム二次電池用負極材料は、定法に従って、リチウム
二次電池用負極を製造するために使用することができ
る。一般的には、金属化合物薄膜被覆して得られた負極
材料(活物質)をバインダー(例えば、ポリビニリデン
フルオリド、ポリテトラフルオロエチレンなど)、さら
には導電剤(例えば、アセチレンブラック)と混合し、
電極基材(例えば、銅板)上に成形して負極を作成す
る。A method for forming a metal compound thin film other than the metal alkoxide treatment method is known. Therefore, the metal compound thin film may be formed using a known method by appropriately selecting the type of the metal compound and the thickness of the thin film according to the negative electrode material. The negative electrode material for a lithium secondary battery obtained by coating the metal compound thin film according to the present invention can be used for producing a negative electrode for a lithium secondary battery according to a conventional method. In general, a negative electrode material (active material) obtained by coating a metal compound thin film is mixed with a binder (for example, polyvinylidene fluoride, polytetrafluoroethylene, etc.) and a conductive agent (for example, acetylene black). ,
The negative electrode is formed by molding on an electrode substrate (for example, a copper plate).
【0019】この負極を用いてリチウム二次電池を作成
する方法も従来と同様でよい。負極、陽極、電解液、隔
膜など適当な材料を選択してリチウム二次電池を作成す
ることができる。リチウム二次電池の種類も限定されな
い。The method for producing a lithium secondary battery using this negative electrode may be the same as the conventional method. A lithium secondary battery can be manufactured by selecting appropriate materials such as a negative electrode, an anode, an electrolytic solution, and a diaphragm. The type of the lithium secondary battery is not limited.
【0020】[0020]
【実施例】(実施例1)平均粒径2μmの天然黒鉛(NG
2:関西熱化学(株))とアルミニウムトリエトキシド(A
l(OC2H5)3)を重量比で9:1にしたものをエタノール
溶液に浸漬し、超音波照射下で3時間攪拌した後、ろ過
し空気中 200℃以上で加熱乾燥した。これを新たな負極
活物質とした。EXAMPLES (Example 1) Natural graphite (NG) having an average particle size of 2 μm
2: Kansai Thermal Chemical Co., Ltd.) and aluminum triethoxide (A
A mixture of l (OC 2 H 5 ) 3 ) in a weight ratio of 9: 1 was immersed in an ethanol solution, stirred for 3 hours under ultrasonic irradiation, filtered, and dried by heating at 200 ° C. or higher in air. This was used as a new negative electrode active material.
【0021】図1に通常の未処理のNG2 とアルミニウム
トリエトキシドで表面処理した新たな天然黒鉛のラマン
スペクトルを示す。表面処理した天然黒鉛のG−バンド
(1580cm-1)は未処理のものに比べ高波数側にシフト
し、強度も上がっている。表面処理した天然黒鉛の結合
強度は未処理のものに比べ増加していると思われる。一
方Algの振動モードに由来する1360cm-1付近の黒鉛結晶
の無秩序さに相当するD−バンドは両者で殆ど変化して
いない。またEDX (エネルギー分散X線分析法)による
分析の結果、表面処理した天然黒鉛では明らかにアルミ
ニウムが存在していた。このことから、アルミニウムは
黒鉛表面上に薄い酸化物被膜として存在していると推察
できる。FIG. 1 shows the Raman spectrum of ordinary untreated NG2 and new natural graphite surface-treated with aluminum triethoxide. The G-band (1580 cm -1 ) of the surface-treated natural graphite is shifted to a higher wavenumber side and the strength is increased as compared with the untreated one. It is considered that the bond strength of the surface-treated natural graphite is increased as compared with the untreated one. On the other hand corresponds to the randomness of the graphite crystal in the vicinity of 1360 cm -1 derived from the vibration mode of A lg D-band hardly changed in both. Analysis by EDX (energy dispersive X-ray analysis) revealed that aluminum was clearly present in the surface-treated natural graphite. From this, it can be inferred that aluminum exists as a thin oxide film on the graphite surface.
【0022】次に酸化物被膜処理した天然黒鉛と未処理
の天然黒鉛の負極活物質は定電流法によりそれらの電気
化学特性を比較検討した。電極は、活物質80wt%、導電
材アセチレンブラック10wt%、結着材(ポリビニリデン
フルオリドPVdF)10wt%を溶媒(1−メチルー2−ピロ
リドンNMP)に溶解混合後銅箔上に伸ばして 120℃で乾
燥させ負極とした。電気化学的測定は、対極に金属リチ
ウム、電解液には(エチレンカーボネートEC)/(ジエ
チルカーボネートDEC)(体積比1:1)に過塩素酸リチ
ウムLiClO4を1 mol/lの濃度で溶解したものを用い、
アルゴン循環型グローブボックス内でCR2032型セルに組
み常温で行った。Next, the electrochemical properties of the negative electrode active materials of the natural graphite treated with the oxide film and the untreated natural graphite were compared and studied by a constant current method. The electrode was prepared by dissolving and mixing 80% by weight of active material, 10% by weight of conductive material acetylene black, and 10% by weight of binder (polyvinylidene fluoride PVdF) in a solvent (1-methyl-2-pyrrolidone NMP) and then stretching it on copper foil. To obtain a negative electrode. In the electrochemical measurement, lithium perchlorate LiClO 4 was dissolved at a concentration of 1 mol / l in a counter electrode of metallic lithium and an electrolytic solution of (ethylene carbonate EC) / (diethyl carbonate DEC) (volume ratio 1: 1). Using
The test was carried out at room temperature in a CR2032 type cell in an argon circulation type glove box.
【0023】リチウムの化学拡散係数は電流パルス緩和
法により算出した。未処理の天然黒鉛と 240℃でアルミ
ニウムエトキシドを熱分解し、酸化物被膜による表面処
理をした天然黒鉛を負極として電流密度をそれぞれ 0.2
C(70mA/g)、 0.5C(175mA/g)、 1.0C(350mA/
g)としたときの初回および50サイクル目の充放電曲線
を図2に示す。アルムニウム酸化物被膜処理したものは
未処理のものに比較し、明らかにエネルギー容量が約2
割増加し、初回容量はほぼ理論容量に近い370mAh/gを
示した。また、サイクル特性も向上している。The chemical diffusion coefficient of lithium was calculated by a current pulse relaxation method. Untreated natural graphite and aluminum ethoxide were thermally decomposed at 240 ° C, and the current density was 0.2
C (70mA / g), 0.5C (175mA / g), 1.0C (350mA / g)
FIG. 2 shows the charge / discharge curves of the first and 50th cycles when g) was used. The treated aluminum oxide film has an apparent energy capacity of about 2 compared to the untreated aluminum oxide film.
The initial capacity was 370 mAh / g, which was close to the theoretical capacity. Also, the cycle characteristics have been improved.
【0024】図3に未処理の天然黒鉛およびアルミニウ
ム酸化物被膜処理した天然黒鉛の 0.2C、 0.5C、 1.0
Cの電流密度での放電容量とサイクル数の関係を示す。
アルミニウム処理によりサイクル特性、出力特性とも格
段に向上している。アルミニウム酸化物被膜処理した天
然黒鉛のリチウムの化学拡散係数は約 10-8cm2/sとな
り未処理の天然黒鉛に比し約 100倍大きな値を示し、図
3の結果を裏づけている。FIG. 3 shows 0.2C, 0.5C, 1.0 of untreated natural graphite and natural graphite treated with aluminum oxide film.
The relationship between the discharge capacity and the number of cycles at the current density of C is shown.
The cycle characteristics and output characteristics have been significantly improved by the aluminum treatment. The chemical diffusion coefficient of lithium in the natural graphite treated with the aluminum oxide film was about 10 −8 cm 2 / s, which is about 100 times larger than that of the untreated natural graphite, confirming the results of FIG.
【0025】(実施例2)Mn(CH3COO)24H2O(純度99.9%)
とV2O5(純度99.9%)を化学量論的量比で別々に水に溶解
し、混合攪拌して透明溶液とした後、混合を均一にする
目的で適当量(金属の2.5倍量)のPVA(分子量1500
〜1800のポリビニルアルコール)溶液を混合した。溶液
は着色したが、緩やかに攪拌しながら約80℃で加熱
し、水分を蒸発させ、褐色粘性ゲル化させた。この間ず
っと緩やかに攪拌して均一性を維持した。次いで空気中
約300℃で2時間加熱して、酸化分解させて粉末前駆
体を生成した。これを粉砕した後、450℃で24時間
仮焼して、目的のMnV2O6を得た。この物質がMnV2O6であ
ることはX線回折法その他で確認した。[0025] (Example 2) Mn (CH 3 COO) 2 4H 2 O ( 99.9%)
And V 2 O 5 (purity 99.9%) were separately dissolved in water in a stoichiometric ratio, mixed and stirred to form a clear solution, and then mixed with an appropriate amount (2.5% of metal) for uniform mixing. PVA (molecular weight 1500)
~ 1800 polyvinyl alcohol) solution. Although the solution was colored, it was heated at about 80 ° C. with gentle stirring to evaporate the water and turn into a brown viscous gel. During this time, the mixture was gently stirred to maintain uniformity. Then, the mixture was heated at about 300 ° C. for 2 hours in the air to be oxidatively decomposed to produce a powder precursor. After pulverized, it was calcined at 450 ° C. for 24 hours to obtain the target MnV 2 O 6 . It was confirmed by X-ray diffraction and the like that this substance was MnV 2 O 6 .
【0026】このようにしてポリマーで均一混合してゾ
ル−ゲル法により合成したバナジウム系酸化物MnV2O6と
アルミニウムトリエトキシド(Al(C2H5O)3)を重量比
9:1にしたものをエタノール溶液に浸漬し、超音波照
射下で3時間攪拌した後濾過し空気中 200℃以上で加熱
乾燥する。これを新たな負極活物質とした。このMnV2O6
を負極活物質としたリチウムの挿入脱離特性を調べた結
果を図4の実線に示す。エネルギー容量が600〜70
0mAh/gと大きいことが認められる。The vanadium-based oxide MnV 2 O 6 and aluminum triethoxide (Al (C 2 H 5 O) 3 ), which were homogeneously mixed with the polymer and synthesized by the sol-gel method, had a weight ratio of 9: 1. The resultant is immersed in an ethanol solution, stirred for 3 hours under ultrasonic irradiation, filtered, and dried by heating at 200 ° C. or more in air. This was used as a new negative electrode active material. This MnV 2 O 6
The results obtained by examining the insertion / desorption characteristics of lithium using as a negative electrode active material are shown by the solid lines in FIG. Energy capacity 600-70
It is recognized as large as 0 mAh / g.
【0027】なお、初回の充放電における不可逆容量
は、不動態皮膜の形成のために余分にLiが消費されるか
らである。不動態皮膜は、活物質表面で電解液が分解す
ることで生成することが知られているが、はっきりした
ことは分かっていない。しかし、不動態皮膜の生成時に
磁気特性を含めたバルク構造に変化がないと考えて良
く、磁気特性についての検討を行った。XANES(X線吸
収近端部構造) 測定から、Mnは+2価、Vは+5であるこ
とが分かった。磁化率測定によるボーア磁子数は5.86で
あり、Mn2+の理論値5.92とよく一致しており磁化率測定
の結果は信頼できるものである。Liを挿入する際の電荷
保障はMnの価数がこれ以上減らないことからVによって
なされている。この際、Vの価数は+5から+4、+3、+2へ
と変化し、それに伴い磁化率も変化するのに対して、不
動態皮膜の生成では磁化率が変化しない。磁化率測定に
よって、不動態皮膜の生成と、Li挿入反応とを区別する
ことができる。磁化率測定から 1.0〜0.7 V付近のプラ
トーにおいて不動態皮膜が生成していることがわかる。
このように、不可逆容量を制御するには、不動態皮膜の
生成を抑制する必要があり、表面処理が数多くなされて
いる。The irreversible capacity in the first charge / discharge is because Li is consumed extra for the formation of the passivation film. It is known that the passivation film is formed by the decomposition of the electrolytic solution on the surface of the active material, but it is not known clearly. However, it can be considered that there is no change in the bulk structure including the magnetic properties when the passivation film is formed, and the magnetic properties were examined. XANES (X-ray absorption near-end structure) Measurement showed that Mn was +2 and V was +5. The Bohr magneton number measured by magnetic susceptibility is 5.86, which is in good agreement with the theoretical value 5.92 of Mn 2+ , and the result of magnetic susceptibility measurement is reliable. The charge guarantee when inserting Li is made by V since the valence of Mn does not decrease any more. At this time, the valence of V changes from +5 to +4, +3, and +2, and the magnetic susceptibility also changes accordingly. However, the magnetic susceptibility does not change when the passive film is formed. Magnetic susceptibility measurements can distinguish between the formation of a passive film and the Li insertion reaction. From the measurement of the magnetic susceptibility, it can be seen that a passivation film is formed at a plateau near 1.0 to 0.7 V.
As described above, in order to control the irreversible capacity, it is necessary to suppress the formation of a passive film, and many surface treatments have been performed.
【0028】図4を参照すると、表面処理により充放電
曲線(破線)の1〜0.7 V付近のプラトーが減少してお
り、不動態皮膜の生成が抑制されたことを意味してい
る。すなわち、不可逆容量が減少したことになる。その
要因を調べるために、界面での反応の様子を見るのに有
効なインピーダンスの測定を行った。結果を図5に示
す。1〜100 HZの周波数帯の半円は電荷移動抵抗を表す
ことが知られている。図5を参照すると、この半円が小
さくなっていることから、電荷移動抵抗が減少したとい
える。また高周波数側の半円はバルク抵抗を表してお
り、半円が小さくなっていることから、同様に抵抗が減
少したといえる。低周波数側ではバルク内の拡散を示す
直線に変化が見られ、表面処理によりバルク内の拡散に
も影響があったといえる。Referring to FIG. 4, the surface treatment reduced the plateau around 1-0.7 V of the charge / discharge curve (broken line), which means that the formation of the passive film was suppressed. That is, the irreversible capacity has decreased. In order to investigate the cause, we measured the effective impedance to see the reaction at the interface. FIG. 5 shows the results. It is known that a semicircle in the frequency band of 1-100 HZ represents charge transfer resistance. Referring to FIG. 5, since this semicircle is smaller, it can be said that the charge transfer resistance has been reduced. Also, the semicircle on the high frequency side represents the bulk resistance, and since the semicircle is smaller, it can be said that the resistance similarly decreased. On the low frequency side, there is a change in the straight line indicating the diffusion in the bulk, and it can be said that the surface treatment also affected the diffusion in the bulk.
【0029】表面処理により不動態であるアルミナが活
物質表面の一部を覆い、そこでの不動態皮膜の生成を妨
げ、電荷移動抵抗を減少させている。それにより、不可
逆容量が減少した。The surface treatment causes the passivated alumina to cover a part of the surface of the active material, prevent the formation of a passivated film there, and reduce the charge transfer resistance. Thereby, the irreversible capacity was reduced.
【0030】[0030]
【発明の効果】従来の炭素材料をリチウム二次電池の負
極活物質として用いたとき、対極のリチウムに対し作動
電位が低くクーロン効率が高い利点があるが、炭素層間
上でのリチウムの拡散が容易でなく、高エネルギー密度
で放電すると、サイクル劣化につながる構造破壊がある
ことが指摘されており、炭素負極の高エネルギー密度充
放電出力特性向上、エネルギー容量増大、サイクル性向
上等が求められていた。本発明では炭素材料の表面に薄
い金属酸化物被膜を形成することで、炭素層端面の一部
をより大きく開口し充放電によるリチウムの挿入脱離を
容易にし、 0.5Cの充放電でも従来の炭素での 0.1Cの
ものと同等の出力特性を保持し約五倍に向上した。ま
た、充放電サイクル時の層間の膨張収縮による構造破壊
を抑制し、 100回目のサイクルでも初期容量の95%を保
持した。さらに天然黒鉛を本法で表面処理した場合、従
来では初回の放電容量が300mAh/g程度であるのに対
し、理論エネルギー容量の372mAh/gに近い370mAh/g
を示した。このように金属アルコキシドによる炭素の表
面処理は電気化学特性を著しく向上させる事ができるこ
とが明らかになった。When a conventional carbon material is used as a negative electrode active material of a lithium secondary battery, there is an advantage that the operating potential is low and the Coulomb efficiency is high with respect to lithium of the counter electrode, but lithium diffusion between carbon layers is difficult. It has been pointed out that when discharged at a high energy density, it is not easy to cause structural destruction leading to cycle degradation.Therefore, it is required to improve the high energy density charge / discharge output characteristics, the energy capacity, and the cycleability of the carbon anode. Was. In the present invention, by forming a thin metal oxide film on the surface of the carbon material, a part of the end face of the carbon layer is opened more to facilitate the insertion / desorption of lithium by charging / discharging. The output characteristics were equivalent to those of 0.1C in carbon and improved about 5 times. In addition, structural destruction due to expansion and contraction between layers during charge / discharge cycles was suppressed, and 95% of the initial capacity was maintained even in the 100th cycle. Furthermore, when natural graphite is surface-treated by this method, the initial discharge capacity is about 300 mAh / g in the prior art, whereas 370 mAh / g, which is close to the theoretical energy capacity of 372 mAh / g.
showed that. Thus, it became clear that the surface treatment of carbon with a metal alkoxide can significantly improve the electrochemical properties.
【0031】また、一般的に酸化物負極は大きいエネル
ギー容量を可能にするが、初回の充放電で不可逆容量が
大きいという問題を有している。図4の未処理およびア
ルミニウム処理したMnV2O6の充放電曲線を参照すると、
1.0〜0.7V付近において不動態皮膜が生成してい
ることが認められる。このような不可逆容量を抑制する
には不動態皮膜の生成を抑制する必要がある。本発明に
よれば、図4に見られるように、金属酸化物被膜を形成
することにより1.0〜0.7V付近のプラトーが減少
しており、不動態皮膜の生成が抑制されていること、即
ち、不可逆容量が減少したことが認められる。その要因
を調べるために、界面での反応の様子を見るのに有効な
インピーダンスの測定を行った。図5を参照すると、1
〜100Hzの周波数帯の半円は電荷移動抵抗を表すこ
とが知られているが、この半円が小さくなっていること
から電荷移動抵抗が減少したことがわかる。また高周波
数側の半円はバルク抵抗を表しており、その半円が小さ
くなっていることから同様にバルク抵抗も減少したこと
がわかる。低周波数側ではバルク内の拡散を示す直線に
変化が見られ、表面処理によりバルク内の拡散にも影響
があったことが窺える。即ち、本発明の表面処理により
不動態である金属酸化物が活性物質表面の一部を覆い、
そこでの不動態皮膜の生成を妨げて電荷移動抵抗を減少
させることにより、不可逆容量が減少したことが認めら
れる。In general, an oxide negative electrode enables a large energy capacity, but has a problem that the irreversible capacity is large in the first charge / discharge. Referring to the charge and discharge curves of untreated and aluminized MnV 2 O 6 in FIG.
It is recognized that a passivation film was formed at around 1.0 to 0.7 V. In order to suppress such irreversible capacity, it is necessary to suppress generation of a passive film. According to the present invention, as shown in FIG. 4, the plateau around 1.0 to 0.7 V is reduced by forming the metal oxide film, and the formation of the passive film is suppressed. That is, it is recognized that the irreversible capacity has decreased. In order to investigate the cause, we measured the effective impedance to see the reaction at the interface. Referring to FIG.
It is known that the semicircle in the frequency band of 100100 Hz represents the charge transfer resistance, but it can be seen that the charge transfer resistance has decreased because the semicircle has become smaller. Further, the semicircle on the high frequency side represents the bulk resistance, and since the semicircle is smaller, it can be seen that the bulk resistance has also been reduced. On the low frequency side, a change was seen in the straight line indicating the diffusion in the bulk, indicating that the surface treatment also affected the diffusion in the bulk. That is, the passivation metal oxide covers a part of the active material surface by the surface treatment of the present invention,
It is recognized that the irreversible capacity was reduced by reducing the charge transfer resistance by preventing the formation of the passivation film there.
【0032】このように、本発明によりリチウム二次電
池用負極材料の表面に金属化合物薄膜を形成すること
は、リチウム二次電池用負極材料のエネルギー容量、出
力特性、サイクル特性などの特性の改良、さらには初回
の不可逆容量の減少などに有効な方法である。As described above, forming the metal compound thin film on the surface of the negative electrode material for a lithium secondary battery according to the present invention can improve the characteristics such as the energy capacity, output characteristics, and cycle characteristics of the negative electrode material for a lithium secondary battery. This is an effective method for reducing the irreversible capacity for the first time.
【図1】通常の未処理の天然黒鉛 とアルミニウムトリ
エトキシドで表面処理した天然黒鉛のラマンスペクトル
を示す。FIG. 1 shows Raman spectra of ordinary untreated natural graphite and natural graphite surface-treated with aluminum triethoxide.
【図2】未処理の天然黒鉛と アルミニウムエトキシド
処理をした天然黒鉛を負極として電流密度をそれぞれ
0.2C(70mA/g)、 0.5C(175mA/g)、 1.0C(350mA
/g)としたときの初回および50サイクル目の充放電曲
線を示す。Fig. 2 Current densities of untreated natural graphite and aluminum ethoxide-treated natural graphite as negative electrodes
0.2C (70mA / g), 0.5C (175mA / g), 1.0C (350mA
/ G) shows the charge and discharge curves at the first and 50th cycles.
【図3】未処理の天然黒鉛およびアルミニウム酸化物被
膜処理した天然黒鉛の 0.2C、0.5C、 1.0Cの電流密
度での放電容量とサイクル数の関係を示す。FIG. 3 shows the relationship between the discharge capacity and the number of cycles at current densities of 0.2 C, 0.5 C, and 1.0 C for untreated natural graphite and natural graphite treated with an aluminum oxide coating.
【図4】MnV2O6とアルミニウム処理したMnV2O6試料につ
いてのリチウム充放電サイクルの比較を示す。FIG. 4 shows a comparison of lithium charge / discharge cycles for MnV 2 O 6 and aluminized MnV 2 O 6 samples.
【図5】MnV2O6とアルミニウム処理したMnV2O6試料につ
いてのインピーダンスの比較を示す。FIG. 5 shows a comparison of impedance for MnV 2 O 6 and aluminized MnV 2 O 6 samples.
───────────────────────────────────────────────────── フロントページの続き (72)発明者 門磨 義浩 東京都目黒区大岡山2−12−1 東京工業 大学内 Fターム(参考) 5H029 AJ03 AJ05 AL02 AL03 AL07 AM03 AM05 AM07 CJ24 DJ12 EJ05 HJ04 5H050 AA07 AA08 BA17 CB02 CB03 CB08 DA09 EA12 EA24 FA12 FA18 GA22 GA24 HA04 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Yoshihiro Kaduma 2-12-1, Ookayama, Meguro-ku, Tokyo F-term inside Tokyo Institute of Technology 5H029 AJ03 AJ05 AL02 AL03 AL07 AM03 AM05 AM07 CJ24 DJ12 EJ05 HJ04 5H050 AA07 AA08 BA17 CB02 CB03 CB08 DA09 EA12 EA24 FA12 FA18 GA22 GA24 HA04
Claims (8)
属化合物薄膜を被覆してなることを特徴とするリチウム
二次電池用負極材料。1. A negative electrode material for a lithium secondary battery, comprising a metal compound thin film coated on the surface of a negative electrode material for a lithium secondary battery.
nmの範囲内である請求項1記載のリチウム二次電池用
負極材料。2. The metal compound thin film having a thickness of 2 to 500.
The negative electrode material for a lithium secondary battery according to claim 1, wherein the thickness is in the range of nm.
物薄膜である請求項1または2に記載のリチウム二次電
池用負極材料。3. The negative electrode material for a lithium secondary battery according to claim 1, wherein the metal compound thin film is an aluminum oxide thin film.
ファイトまたはバナジウム系酸化物である請求項1、2
または3記載のリチウム二次電池用負極材料。4. The negative electrode material for a lithium secondary battery is graphite or a vanadium-based oxide.
Or the negative electrode material for lithium secondary batteries according to 3.
属化合物薄膜で被覆することを特徴とするリチウム二次
電池用負極材料の改良方法。5. A method for improving a negative electrode material for a lithium secondary battery, wherein the surface of the negative electrode material for a lithium secondary battery is coated with a metal compound thin film.
処理法、ゾルゲル法、CVD法、PVD法、めっき法か
ら選ばれる方法で形成する請求項5に記載のリチウム二
次電池用負極材料の改良方法。6. The method for improving a negative electrode material for a lithium secondary battery according to claim 5, wherein the metal compound thin film is formed by a method selected from a metal alkoxide treatment method, a sol-gel method, a CVD method, a PVD method, and a plating method.
属アルコキシドを付着させ、しかる後加熱分解してリチ
ウム二次電池用負極材料の表面を金属酸化物薄膜で被覆
する請求項5または6に記載のリチウム二次電池用負極
材料の改良方法。7. The negative electrode material for a lithium secondary battery according to claim 5 or 6, wherein a metal alkoxide is adhered to the surface of the negative electrode material for a lithium secondary battery, and then thermally decomposed to cover the surface of the negative electrode material for a lithium secondary battery with a metal oxide thin film. The method for improving a negative electrode material for a lithium secondary battery according to the above.
チウム二次電池用負極材料を用いたことを特徴とするリ
チウム二次電池。8. A lithium secondary battery using the negative electrode material for a lithium secondary battery according to claim 1. Description:
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