JP2003257426A - Electrode material for lithium secondary battery and manufacturing method thereof - Google Patents
Electrode material for lithium secondary battery and manufacturing method thereofInfo
- Publication number
- JP2003257426A JP2003257426A JP2002055883A JP2002055883A JP2003257426A JP 2003257426 A JP2003257426 A JP 2003257426A JP 2002055883 A JP2002055883 A JP 2002055883A JP 2002055883 A JP2002055883 A JP 2002055883A JP 2003257426 A JP2003257426 A JP 2003257426A
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- Japan
- Prior art keywords
- secondary battery
- lithium
- electrode material
- feooh
- lithium secondary
- Prior art date
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Classifications
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- 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
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- Compounds Of Iron (AREA)
- Secondary Cells (AREA)
- Battery Electrode And Active Subsutance (AREA)
Abstract
Description
【０００１】[0001]
【産業上の利用分野】本発明は、Ｌｉイオン二次電池，
金属Ｌｉ二次電池等のリチウム二次電池に使用される正
極、負極等の電極材料及びその製造方法に関する。The present invention relates to a Li-ion secondary battery,
The present invention relates to an electrode material such as a positive electrode and a negative electrode used in a lithium secondary battery such as a metal Li secondary battery and a method for manufacturing the same.
【０００２】[0002]
【従来技術及び問題点】リチウム電池は起電力が高く、
適切な電極材料の選択により高エネルギー密度発電が可
能な電源である。電極材料には、Ｌｉイオン二次電池で
はＬｉＣｏＯ2，ＬｉＮｉＯ2，ＬｉＭｎ2Ｏ4等のリチウ
ム複合酸化物，小型の金属Ｌｉ二次電池ではＶ2Ｏ5等の
遷移金属酸化物が使用されている。従来の電極材料は何
れも高価な材料であり、リチウム二次電池のコストを上
昇させる原因になっている。比較的毒性の強い金属元素
を使用することもあり、廃電池の処理に負担がかかる。
これらの欠陥を解消する電極材料として、資源が豊富で
毒性が低い安価な鉄が有望視されている。４Ｖ域で充放
電特性を示す鉄系の酸化物も知られており、種々の方法
で合成されている。2. Description of the Related Art Lithium batteries have high electromotive force,
This is a power source capable of high energy density power generation by selecting an appropriate electrode material. As the electrode material, lithium composite oxides such as LiCoO 2 , LiNiO 2 and LiMn 2 O 4 are used in Li-ion secondary batteries, and transition metal oxides such as V 2 O 5 are used in small metal Li secondary batteries. There is. All of the conventional electrode materials are expensive materials, which causes the cost of the lithium secondary battery to increase. Since a metal element having a relatively high toxicity is used, the processing of the waste battery is burdened.
As an electrode material that eliminates these defects, inexpensive iron, which has abundant resources and low toxicity, is considered promising. Iron-based oxides exhibiting charge / discharge characteristics in the 4V range are also known and have been synthesized by various methods.
【０００３】たとえば、沈殿合成法の例として、J. Kim
及びA. Manthiramは、J. Electrochem. Soc., 146, 437
1 (1999)で、過酸化リチウムを酸化剤に使用して水酸化
リチウム水溶液中でＦｅ(II)を酸化沈殿させることによ
り、電極材料として有用な鉄系酸化物を合成する方法を
報告している。合成された鉄系酸化物を電極材料に使用
して充放電を繰り返すと、安定した充放電が可能である
ものの、最大でも１４０ｍＡｈ／ｇと電気容量が十分で
ない。For example, as an example of the precipitation synthesis method, J. Kim
And A. Manthiram, J. Electrochem. Soc., 146, 437.
1 (1999) reported a method of synthesizing an iron-based oxide useful as an electrode material by oxidizing and precipitating Fe (II) in a lithium hydroxide aqueous solution using lithium peroxide as an oxidant. There is. When the synthesized iron-based oxide is used as an electrode material and charging and discharging are repeated, stable charging and discharging is possible, but the electric capacity is 140 mAh / g at the maximum, which is not sufficient.
【０００４】[0004]
【課題を解決するための手段】本発明は、低温で沈殿合
成したα-ＦｅＯＯＨの超微粒子を低温焼成するとα-Ｆ
ｅ2Ｏ3に構造変化し，表面積が大きく活性度の高い電極
材料になることを見出し、当該知見をベースに完成され
たものであり、充放電の可逆性が高く長期充放電サイク
ル特性に優れたリチウム二次電池を提供することを目的
とする。According to the present invention, when ultrafine particles of α-FeOOH precipitated and synthesized at low temperature are fired at low temperature, α-F
It has been completed based on this finding that it has been found to become an electrode material with a large surface area and high activity by changing its structure to e 2 O 3 and has excellent charge / discharge reversibility and excellent long-term charge / discharge cycle characteristics. It is intended to provide a lithium secondary battery.
【０００５】本発明は、鉄塩水溶液へのアルカリ添加に
よって沈殿したＦｅＯＯＨを低温焼成することによって
合成されたα-Ｆｅ2Ｏ3の超微粒子をリチウム二次電池
の電極材料に使用している。α-Ｆｅ2Ｏ3の超微粒子
は、必要に応じて可溶性リチウム化合物を添加した鉄塩
水溶液をアルカリと混合して鉄塩をＦｅＯＯＨとして沈
殿させ、該ＦｅＯＯＨを１００〜４００℃の温度域で加
熱処理することにより合成される。In the present invention, ultrafine particles of α-Fe 2 O 3 synthesized by firing FeOOH precipitated by adding an alkali to an aqueous solution of iron salt at low temperature are used as an electrode material for a lithium secondary battery. The ultrafine particles of α-Fe 2 O 3 are mixed with an aqueous solution of an iron salt to which a soluble lithium compound is added, if necessary, to precipitate the iron salt as FeOOH, and heat the FeOOH in a temperature range of 100 to 400 ° C. It is synthesized by processing.
【０００６】[0006]
【作用】Ｆｅ2Ｏ3等の鉄系酸化物は、通常、充放電の可
逆性が低く、二次電池への適用が困難な物質である。他
方、沈殿合成した鉄系酸化物は、比表面積が大きな微粒
子であって正極，負極等の電極材料としての展開が期待
できる。そこで、本発明者等は、沈殿合成条件が合成さ
れた鉄系酸化物に及ぼす影響を種々調査・研究した結
果、硝酸鉄，水酸化リチウム，過酸化リチウムから沈殿
するＦｅＯＯＨが非常に微細な粒子であることを見出し
た。沈殿したＦｅＯＯＨ微粒子は、２００℃程度の低温
焼成によって容易に脱水し、α-Ｆｅ2Ｏ3の超微粒子に
なる。OPERATION Iron-based oxides such as Fe 2 O 3 are usually low in reversibility of charge and discharge and are difficult to apply to secondary batteries. On the other hand, the precipitation-synthesized iron-based oxide is a fine particle having a large specific surface area and can be expected to be developed as an electrode material such as a positive electrode and a negative electrode. Therefore, the present inventors have conducted various investigations and studies on the influence of the precipitation synthesis condition on the synthesized iron-based oxide, and as a result, FeOOH particles that precipitate from iron nitrate, lithium hydroxide, and lithium peroxide are very fine particles. I found that. The precipitated FeOOH fine particles are easily dehydrated by baking at a low temperature of about 200 ° C., and become α-Fe 2 O 3 ultrafine particles.
【０００７】合成されたα-Ｆｅ2Ｏ3超微粒子は、比表
面積が非常に大きく、リチウム二次電池の電極材料に使
用すると充放電の可逆性が高く、２Ｖ域で放電する特性
を呈する。α-Ｆｅ2Ｏ3超微粒子は、充放電の前後で結
晶の母構造が変化しないため、長期充放電サイクルにも
適している。更に、２Ｖ域での放電が可能なことから、
ＩＣメモリバックアップ用等における半導体駆動電圧の
低下に対応する２Ｖ程度の小型二次電池としての要求特
性を満足する。The synthesized α-Fe 2 O 3 ultrafine particles have a very large specific surface area, and when used as an electrode material of a lithium secondary battery, they have high reversibility of charge and discharge and exhibit a characteristic of discharging in the 2V range. The α-Fe 2 O 3 ultrafine particles are suitable for long-term charge / discharge cycles because the crystal mother structure does not change before and after charge / discharge. Furthermore, since it is possible to discharge in the 2V range,
Satisfies the required characteristics as a small secondary battery of about 2 V, which corresponds to a decrease in semiconductor driving voltage for IC memory backup and the like.
【０００８】[0008]
【実施の形態】ＦｅＯＯＨ沈殿合成用の鉄塩としては、
硫酸鉄，硝酸鉄，塩化鉄等、Ｆｅ(II)やＦｅ(III)の化
合物の１種又は２種以上が使用される。水酸化リチウ
ム，水酸化ナトリウム，水酸化カリウム等の水溶性アル
カリ（沈殿生成剤）と鉄塩を混合し、空気攪拌によって
ＦｅＯＯＨが沈殿合成される。沈殿生成に必要な溶液の
濃度には特段の制約が加わるものではないが、最適な粒
子サイズの沈殿物を得る上で高濃度の溶液ほど有利であ
る。BEST MODE FOR CARRYING OUT THE INVENTION As an iron salt for FeOOH precipitation synthesis,
One or more of Fe (II) and Fe (III) compounds such as iron sulfate, iron nitrate, and iron chloride are used. A water-soluble alkali (precipitating agent) such as lithium hydroxide, sodium hydroxide or potassium hydroxide is mixed with an iron salt, and FeOOH is precipitated and synthesized by stirring with air. There is no particular restriction on the concentration of the solution required for the formation of the precipitate, but the higher the concentration of the solution is, the more advantageous it is to obtain the precipitate having the optimum particle size.
【０００９】リチウム電池材料としてリチウムを含む材
料が適していることを考慮すると、塩基性の可溶性化合
物としてリチウム塩を添加することが好ましい。沈殿反
応には水酸化物イオンが直接関与するが、反応系にＬｉ
イオン，硝酸，硫酸等の陰イオンが共存すると、沈殿物
に微量の陰イオンが取り込まれる。沈殿物が同じ結晶構
造であっても、取り込まれた陰イオンによって電池特性
が向上する。塩基性のリチウム化合物としては、水酸化
リチウム，酸化リチウム，過酸化リチウム，炭酸リチウ
ム，ギ酸リチウム，リン酸リチウム等、水溶液が塩基性
を示す塩が使用される。Considering that a material containing lithium is suitable as a lithium battery material, it is preferable to add a lithium salt as a basic soluble compound. The hydroxide ion is directly involved in the precipitation reaction, but Li
When ions, nitric acid, sulfuric acid, and other anions coexist, a trace amount of anions is incorporated in the precipitate. Even if the precipitate has the same crystal structure, the incorporated anions improve the battery characteristics. As the basic lithium compound, salts such as lithium hydroxide, lithium oxide, lithium peroxide, lithium carbonate, lithium formate and lithium phosphate whose aqueous solution is basic are used.
【００１０】目的生成物は酸化状態がＦｅ(III)である
ことから、二価のＦｅ（塩化第一鉄）を鉄塩に使用する
場合、鉄塩水溶液に酸化剤を添加する。酸化剤には、酸
素，過酸化水素，過酸化アルカリ，次亜塩素酸等、酸化
剤として一般に知られている化合物が使用される。三価
のＦｅ（塩化第二鉄）を鉄塩に使用する場合でも、Ｆｅ
(III)を安定化させるため同様な酸化剤の添加が好まし
い。酸化剤に過酸化リチウム，次亜塩素酸リチウム等の
リチウム化合物を使用すると、沈殿物に微量のＬｉイオ
ンが取り込まれ電池特性が向上する。Since the target product has an oxidation state of Fe (III), when divalent Fe (ferrous chloride) is used as the iron salt, an oxidizing agent is added to the iron salt aqueous solution. As the oxidizing agent, compounds generally known as oxidizing agents such as oxygen, hydrogen peroxide, alkali peroxide, hypochlorous acid and the like are used. Even when trivalent Fe (ferric chloride) is used in the iron salt, Fe
It is preferable to add a similar oxidizing agent to stabilize (III). When a lithium compound such as lithium peroxide or lithium hypochlorite is used as the oxidant, a minute amount of Li ions is incorporated in the precipitate, and the battery characteristics are improved.
【００１１】ＦｅＯＯＨの生成は、鉄塩，塩基性化合
物，酸化剤の濃度及び液量に応じて変化するが、少なく
とも鉄塩の量に対して十分な量の塩基性化合物，酸化剤
を添加する必要がある。沈殿反応では、沈殿粒子の核生
成及び核成長によって粒子サイズが決まると考えられて
いる。そこで、多量の沈殿核が迅速に生成し、その後の
核成長が抑制される条件下で沈殿反応させると、目的に
叶った超微粒子の生成が予想される。このような条件を
満たすためには、各成分の混合比，沈殿温度が重要であ
り、特に０℃近傍の低温度で沈殿反応を継続させること
が効果的である。The formation of FeOOH changes depending on the concentration and liquid amount of the iron salt, basic compound and oxidizing agent, but at least a sufficient amount of basic compound and oxidizing agent is added to the amount of iron salt. There is a need. In the precipitation reaction, it is believed that the particle size is determined by the nucleation and growth of the precipitated particles. Therefore, when a large amount of precipitation nuclei are rapidly generated and the precipitation reaction is performed under the condition that the subsequent nuclei growth is suppressed, it is expected that ultrafine particles suitable for the purpose will be generated. In order to satisfy such conditions, the mixing ratio of each component and the precipitation temperature are important, and it is particularly effective to continue the precipitation reaction at a low temperature near 0 ° C.
【００１２】沈殿合成されたＦｅＯＯＨは５０℃近傍の
温度から脱水反応を開始するが、加熱処理を１００〜４
００℃の温度域で実施することが好ましい。加熱処理雰
囲気には空気，酸素，窒素，アルゴン，真空等を採用で
き、脱水反応の完了までＦｅＯＯＨが１時間以上加熱さ
れる。加熱処理で得られたα-Ｆｅ2Ｏ3は、粒径が数ｎ
ｍ，比表面積が１００ｍ2／ｇ以上の超微粒子である。
添加剤としてリチウム塩を用いて沈殿合成したＦｅＯＯ
Ｈから得られた超微粒子を元素分析すると、微量のリチ
ウムが取り込まれた生成物になっていることが確認され
る。The FeOOH synthesized by precipitation starts the dehydration reaction at a temperature near 50 ° C., but the heat treatment is performed at 100 to 4 ° C.
It is preferably carried out in the temperature range of 00 ° C. Air, oxygen, nitrogen, argon, vacuum or the like can be adopted as the heat treatment atmosphere, and FeOOH is heated for 1 hour or more until the dehydration reaction is completed. Α-Fe 2 O 3 obtained by heat treatment has a particle size of several n
Ultrafine particles having m and a specific surface area of 100 m 2 / g or more.
FeOO precipitated and synthesized using a lithium salt as an additive
Elemental analysis of the ultrafine particles obtained from H confirms that it is a product in which a trace amount of lithium is incorporated.
【００１３】合成されたα-Ｆｅ2Ｏ3超微粒子を導電
剤，結着剤と混合し、圧着成形することにより電極が作
製される。α-Ｆｅ2Ｏ3超微粒子の電気化学特性は、リ
チウム電池に通常使用されている電解液に当該電極を接
触させることにより評価される。α-Ｆｅ2Ｏ3は、比表
面積の大きな超微粒子であるため，電解液との接触面積
が大きく反応効率に優れ，充放電容量が２００ｍＡｈ／
ｇ以上で安定した充放電サイクル特性を呈する。通常の
α-Ｆｅ2Ｏ3の放電反応では不可逆な構造変化が起こ
り、安定した長期充放電が望めないと考えられている
〔M.M. Thackeray et al., Mat. Res. Bull., 17, 785-
793 (1982)〕。他方、本発明で合成されたα-Ｆｅ2Ｏ3
超微粒子又は微量のリチウムを含むα-Ｆｅ2Ｏ3超微粒
子は、結晶サイズ及び微量添加物によって構造の安定性
が大幅に改善されている。実際、充放電を繰り返したα
-Ｆｅ2Ｏ3超微粒子をＸＲＤ測定しても、不可逆的な構
造変化が検出されない。したがって、安定した充放電サ
イクル特性をもつ大容量の電極材料として使用される。An electrode is manufactured by mixing the synthesized α-Fe 2 O 3 ultrafine particles with a conductive agent and a binder and press-bonding them. The electrochemical characteristics of the α-Fe 2 O 3 ultrafine particles are evaluated by bringing the electrode into contact with an electrolytic solution that is usually used in lithium batteries. Since α-Fe 2 O 3 is an ultrafine particle with a large specific surface area, it has a large contact area with the electrolytic solution, excellent reaction efficiency, and a charge / discharge capacity of 200 mAh /
Stable charge / discharge cycle characteristics are exhibited when g or more. It is considered that irreversible structural changes occur in the usual α-Fe 2 O 3 discharge reaction and stable long-term charge / discharge cannot be expected [MM Thackeray et al., Mat. Res. Bull., 17, 785-
793 (1982)]. On the other hand, α-Fe 2 O 3 synthesized by the present invention
Ultra-fine particles or α-Fe 2 O 3 ultra-fine particles containing a trace amount of lithium have their structure stability greatly improved by the crystal size and trace additives. Actually, repeated charging and discharging α
No irreversible structural change was detected by XRD measurement of -Fe 2 O 3 ultrafine particles. Therefore, it is used as a large capacity electrode material having stable charge / discharge cycle characteristics.
【００１４】α-Ｆｅ2Ｏ3超微粒子は、優れた電極特
性、特にリチウム基準で２〜３Ｖの充放電電圧であるこ
とから、正極，負極の相溶に適用できる。具体的には、
α-Ｆｅ2Ｏ3超微粒子を正極，金属リチウム又はＬｉ−
Ａｌ合金を負極とする組合せで２〜３Ｖのリチウム二次
電池として使用できる。α-Ｆｅ2Ｏ3超微粒子を負極と
する場合、ＬｉＣｏＯ2，ＬｉＮｉＯ2，ＬｉＭｎ2Ｏ4，
ＬｉＭｎＯ2等のリチウム基準で４Ｖの正極と組み合わ
せることにより、１〜２ＶのＬｉイオン二次電池として
使用できる。このようなα-Ｆｅ2Ｏ3超微粒子を使用し
た電池は、従来の電池材料に比較して原料が低コストで
あるばかりでなく、廃棄された場合の毒性も低い。更
に、安定な酸化物であることから有機電解液との反応に
起因した発火等の危険も抑制される。Since the α-Fe 2 O 3 ultrafine particles have excellent electrode characteristics, particularly a charging / discharging voltage of 2 to 3 V based on lithium, they can be applied to the compatibility of the positive electrode and the negative electrode. In particular,
α-Fe 2 O 3 ultrafine particles are used as a positive electrode, metallic lithium or Li-
It can be used as a lithium secondary battery of 2 to 3 V by combining Al alloy as a negative electrode. When α-Fe 2 O 3 ultrafine particles are used as the negative electrode, LiCoO 2 , LiNiO 2 , LiMn 2 O 4 ,
By combining with a 4 V positive electrode based on lithium such as LiMnO 2, it can be used as a 1 to 2 V Li-ion secondary battery. Batteries using such α-Fe 2 O 3 ultrafine particles are low in cost as raw materials as compared with conventional battery materials, and have low toxicity when discarded. Furthermore, since it is a stable oxide, the risk of ignition etc. due to the reaction with the organic electrolyte is suppressed.
【００１５】[0015]
【実施例】濃度２モル／ｄｍ3の硝酸第二鉄水溶液〔Ｆ
ｅ(ＮＯ3)3・９Ｈ2Ｏ〕１０ｃｍ3に濃度２モル／ｄｍ3の
水酸化リチウム〔ＬｉＯＨ・Ｈ2Ｏ〕２０ｃｍ3を添加し
２０分攪拌した後、攪拌しながら濃度０.２５モル／ｄ
ｍ3の過酸化リチウム（Ｌｉ2Ｏ2：酸化剤）３００ｃｍ3
を滴下し、ＦｅＯＯＨを沈殿させた。ＦｅＯＯＨの沈殿
は０℃という低温で良好に進行し、高温になるほど粒子
サイズが大きくなりながら構造変化を起こし、電池特性
に悪影響を及ぼした。[Example] A ferric nitrate aqueous solution [F having a concentration of 2 mol / dm 3
e (NO 3) 3 · 9H 2 O ] 10 cm 3 After stirring concentration of 2 mol / dm 3 of added lithium hydroxide [LiOH · H 2 O] 20 cm 3 20 minutes, stirring concentration of 0.25 mol / D
m 3 of lithium peroxide (Li 2 O 2 : oxidizer) 300 cm 3
Was dropped to precipitate FeOOH. The precipitation of FeOOH proceeded well at a low temperature of 0 ° C., and the higher the temperature, the larger the particle size and the structural change occurred, which adversely affected the battery characteristics.
【００１６】沈殿したＦｅＯＯＨを吸引濾過によって水
溶液から分離した後、乾燥し、次いで２００〜５００℃
の温度域で加熱処理した。加熱処理で得られた合成物を
Ｘ線回折によって測定し、加熱温度が合成物に及ぼす影
響を調査した。図１の調査結果にみられるように、２０
０℃以上の加熱処理でＦｅＯＯＨのピークが消え、α-
Ｆｅ2Ｏ3の強いピークが検出された。３００℃，４００
℃の高温で加熱処理したものをＸ線回折した測定結果で
は、加熱処理温度の上昇に応じて結晶性が強くなってい
た。しかし、５００℃で加熱処理すると、α-Ｆｅ2Ｏ3
の他にγ-Ｆｅ2Ｏ3のピークも検出された。この結果か
ら、好ましくは２００〜３００℃の比較的低温で加熱処
理することにより、目標とするα-Ｆｅ2Ｏ3の合成が確
認できる。また、α-Ｆｅ2Ｏ3の(104)ピークの半値幅
は、加熱温度の上昇に応じて小さくなっていた。半値幅
の減少は、シェラー式に従った結晶サイズの増大に起因
している。The precipitated FeOOH is separated from the aqueous solution by suction filtration, dried and then 200-500 ° C.
It heat-processed in the temperature range of. The composition obtained by the heat treatment was measured by X-ray diffraction, and the influence of the heating temperature on the composition was investigated. As can be seen in the survey results in Figure 1, 20
The peak of FeOOH disappeared by heat treatment at 0 ° C or higher, and α-
A strong peak of Fe 2 O 3 was detected. 300 ° C, 400
According to the measurement result of the X-ray diffraction of the one heat-treated at a high temperature of ° C, the crystallinity became stronger as the heat-treatment temperature increased. However, when heat-treated at 500 ° C, α-Fe 2 O 3
Besides, a peak of γ-Fe 2 O 3 was also detected. From this result, it is possible to confirm the target synthesis of α-Fe 2 O 3 by heat treatment at a relatively low temperature of preferably 200 to 300 ° C. Further, the full width at half maximum of the (104) peak of α-Fe 2 O 3 became smaller as the heating temperature increased. The decrease in full width at half maximum is due to the increase in crystal size according to the Scherrer equation.
【００１７】合成されたα-Ｆｅ2Ｏ3は、何れも粒径が
ナノメータオーダの超微粒子であった。因みに、２００
℃の加熱処理で合成されたα-Ｆｅ2Ｏ3のＴＥＭ観察し
たところ針状のＦｅＯＯＨが消失した超微細結晶が検出
され（図２）、ＢＥＴ法で測定した比表面積も１２５ｍ
2／ｇと非常に大きな値であった。合成されたα-Ｆｅ2
Ｏ3を電極材料に用い、ＬｉＣｌＯ4／プロピレンカーボ
ネート溶液／超微粒子α-Ｆｅ2Ｏ3のリチウム二次電池
を作製した。当該リチウム二次電池を電流密度０.１ｍ
Ａ／ｃｍ2，電位範囲４.０〜１.５Ｖの充放電サイクル
試験に供したところ、加熱処理温度に応じて充放電サイ
クル特性が異なっていた（図３）。All of the synthesized α-Fe 2 O 3 were ultrafine particles having a particle size on the order of nanometers. By the way, 200
TEM observation of α-Fe 2 O 3 synthesized by heat treatment at ℃ detected ultrafine crystals in which needle-like FeOOH disappeared (Fig. 2), and the specific surface area measured by BET method was 125 m.
It was a very large value of 2 / g. Synthesized α-Fe 2
A lithium secondary battery of LiClO 4 / propylene carbonate solution / ultrafine particle α-Fe 2 O 3 was prepared by using O 3 as an electrode material. Current density of the lithium secondary battery is 0.1 m
When subjected to a charge / discharge cycle test with A / cm 2 and a potential range of 4.0 to 1.5 V, the charge / discharge cycle characteristics were different depending on the heat treatment temperature (FIG. 3).
【００１８】未加熱処理のα-ＦｅＯＯＨ・ｎＨ2Ｏを電
極材料に用いたリチウム二次電池では１３０〜１５０ｍ
Ａｈ／ｇの放電容量であったが、２００℃で合成された
α-Ｆｅ2Ｏ3を電極材料に用いたリチウム二次電池では
２Ｖ域で２００ｍＡｈ／ｇ以上の高い放電容量を示し
た。放電容量は、加熱処理温度が高くなるに従って低下
していたが、市販のＦｅ2Ｏ3や従来報告されているＦｅ
2Ｏ3とは全く異なる放電特性であった。市販Ｆｅ2Ｏ3に
みられない放電特性は、低温合成でα-Ｆｅ2Ｏ3が超微
粒子になることに由来すると考えられる。A lithium secondary battery using unheated α-FeOOH.nH 2 O as an electrode material is 130 to 150 m
The discharge capacity was Ah / g, but the lithium secondary battery using α-Fe 2 O 3 synthesized at 200 ° C. as an electrode material showed a high discharge capacity of 200 mAh / g or more in the 2V region. The discharge capacity decreased as the heat treatment temperature increased, but the commercially available Fe 2 O 3 and previously reported Fe were used.
The discharge characteristic was completely different from that of 2 O 3 . The discharge characteristics not found in commercially available Fe 2 O 3 are considered to be derived from α-Fe 2 O 3 becoming ultrafine particles in low temperature synthesis.
【００１９】充放電サイクル数の増加に応じて放電容量
が低下したが、２００℃で合成したα-Ｆｅ2Ｏ3を電極
材料に用いたリチウム二次電池では、１〜５サイクルま
では１９０ｍＡｈ／ｇ以上の大きな放電容量が安定して
得られた（図４）。しかし、２００℃を超える温度で合
成したα-Ｆｅ2Ｏ3を電極材料に使用すると初期放電容
量が低下し、放電容量は２回目以降の放電で容量が１０
０ｍＡ／ｇ以下と更に低下した。このような挙動は、本
発明に従って合成されたα-Ｆｅ2Ｏ3超微粒子を正極，
負極の何れに使用する場合でも、組み合わせる電極材料
の選択によって定電圧のリチウム二次電池が実現される
ことを示している。しかも、安定なＦｅ2Ｏ3を電極材料
に使用していることから、廃電池の処理にかかる負担も
軽減され、発火等のトラブルも防止される。The discharge capacity decreased as the number of charge / discharge cycles increased, but in a lithium secondary battery using α-Fe 2 O 3 synthesized at 200 ° C. as an electrode material, 190 mAh / A large discharge capacity of g or more was stably obtained (FIG. 4). However, when α-Fe 2 O 3 synthesized at a temperature higher than 200 ° C. is used as an electrode material, the initial discharge capacity decreases, and the discharge capacity is 10% in the second and subsequent discharges.
It was further reduced to 0 mA / g or less. This behavior is obtained by using the α-Fe 2 O 3 ultrafine particles synthesized according to the present invention as a positive electrode,
It is shown that a lithium secondary battery of constant voltage can be realized by selecting an electrode material to be combined regardless of whether it is used for the negative electrode. Moreover, since stable Fe 2 O 3 is used as the electrode material, the burden of treating the waste battery is reduced, and troubles such as ignition are prevented.
【００２０】[0020]
【発明の効果】以上に説明したように、鉄塩水溶液中で
の沈殿反応によって生成したＦｅＯＯＨを低温焼成焼成
すると、α-Ｆｅ2Ｏ3の超微粒子が合成される。得られ
た超微粒子は電気化学的な活性度が高く比表面積も大き
なため、リチウム二次電池の正極又は負極材料に使用す
ると、放電容量が大きく優れた充放電サイクル特性を呈
するリチウム二次電池を製造できる。このリチウム二次
電池は、可逆容量が大きく、安全性の高い駆動電圧が低
下する傾向にあるＩＣメモリバックアップ用等に適した
二次電池として使用される。As described above, when FeOOH produced by the precipitation reaction in the iron salt aqueous solution is calcined at a low temperature, ultrafine particles of α-Fe 2 O 3 are synthesized. Since the obtained ultrafine particles have high electrochemical activity and a large specific surface area, when used as a positive electrode or a negative electrode material of a lithium secondary battery, a lithium secondary battery having a large discharge capacity and excellent charge / discharge cycle characteristics can be obtained. Can be manufactured. This lithium secondary battery has a large reversible capacity and is used as a secondary battery suitable for IC memory backup, which has a high safety and tends to lower the driving voltage.
【図１】 ＦｅＯＯＨを種々の温度で加熱処理して得ら
れた合成物のＸ線回折結果を示すグラフFIG. 1 is a graph showing the X-ray diffraction results of a compound obtained by heat treating FeOOH at various temperatures.
【図２】 ２００℃で合成されたα-Ｆｅ2Ｏ3のＴＥＭ
写真FIG. 2 TEM of α-Fe 2 O 3 synthesized at 200 ° C.
Photo
【図３】 未加熱処理のＦｅＯＯＨ及び種々の温度で加
熱処理された合成物を電極材料に使用したリチウム二次
電池の充放電サイクル特性を示すグラフFIG. 3 is a graph showing charge-discharge cycle characteristics of a lithium secondary battery using an unheated FeOOH and a compound heat-treated at various temperatures as an electrode material.
【図４】 充放電サイクル数に応じた放電容量の変化を
示すグラフFIG. 4 is a graph showing changes in discharge capacity according to the number of charge / discharge cycles.
───────────────────────────────────────────────────── フロントページの続き Ｆターム(参考） 4G002 AA03 AB04 AD04 AE05 5H029 AJ03 AJ05 AK02 AK03 AL02 AL12 AM03 AM07 CJ02 CJ08 CJ12 DJ16 HJ02 HJ05 HJ14 5H050 AA07 AA08 BA16 BA17 CA02 CA07 CB02 CB12 FA17 GA02 GA10 GA12 HA02 HA05 HA14 ─────────────────────────────────────────────────── ─── Continued front page F-term (reference) 4G002 AA03 AB04 AD04 AE05 5H029 AJ03 AJ05 AK02 AK03 AL02 AL12 AM03 AM07 CJ02 CJ08 CJ12 DJ16 HJ02 HJ05 HJ14 5H050 AA07 AA08 BA16 BA17 CA02 CA07 CB02 CB12 FA17 GA02 GA10 GA12 HA02 HA05 HA14
Claims (3)
殿したＦｅＯＯＨの低温焼成で合成されたα-Ｆｅ2Ｏ3
の超微粒子からなることを特徴とするリチウム二次電池
用電極材料。1. α-Fe 2 O 3 synthesized by low-temperature calcination of FeOOH precipitated by adding an alkali to an aqueous solution of iron salt.
An electrode material for a lithium secondary battery, comprising the ultrafine particles of
ＦｅＯＯＨとして沈殿させ、該ＦｅＯＯＨを１００〜４
００℃の温度域で加熱処理して超微粒子状のα-Ｆｅ2Ｏ
3を合成することを特徴とするリチウム二次電池用電極
材料の製造方法。2. An iron salt aqueous solution is added with an alkali to precipitate the iron salt as FeOOH, and the FeOOH is added in an amount of 100-4.
Heat-treated in the temperature range of 00 ° C to obtain ultra-fine particles of α-Fe 2 O
A method for producing an electrode material for a lithium secondary battery, which comprises synthesizing 3 .
む請求項２記載の製造方法。3. The method according to claim 2, wherein the iron salt aqueous solution contains a soluble lithium compound.
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