WO2013018757A1 - Method for producing iron lithium phosphate, electrode active substance, and secondary battery - Google Patents

Method for producing iron lithium phosphate, electrode active substance, and secondary battery Download PDF

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WO2013018757A1
WO2013018757A1 PCT/JP2012/069317 JP2012069317W WO2013018757A1 WO 2013018757 A1 WO2013018757 A1 WO 2013018757A1 JP 2012069317 W JP2012069317 W JP 2012069317W WO 2013018757 A1 WO2013018757 A1 WO 2013018757A1
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iron
phosphate
electrode active
active material
lifepo
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金高　祐仁
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株式会社 村田製作所
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B25/00—Phosphorus; Compounds thereof
    • C01B25/16—Oxyacids of phosphorus; Salts thereof
    • C01B25/26—Phosphates
    • C01B25/45—Phosphates containing plural metal, or metal and ammonium
    • 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

Definitions

  • the FePO 4 .nH 2 O and the LiOH ⁇ H 2 O are weighed so that the molar ratio of the FePO 4 ⁇ nH 2 O and the LiOH ⁇ H 2 O is 1: 1.
  • the weighed product is put into a ball mill together with pure water and a polymer dispersant such as polycarboxylic acid, mixed and pulverized, and LiFePO 4 powder can be obtained.
  • LiFePO 4 has high purity without forming a heterogeneous phase, and can be suitably used as an electrode active material for a secondary battery.
  • the amount of carbon was measured with a CS meter, and the specific surface area was determined by the BET method.
  • This secondary battery has a voltage range of 2.0 to 4.2 V in a thermostat at 25 ° C. and a charge / discharge rate of 0.2 C (1 C is the amount of current until charging or discharging is completed in one hour) As a charge and discharge. That is, the battery was charged until the voltage reached 4.2 V at a charge rate of 0.2 C, and then discharged to 2.0 V at a discharge rate of 0.2 C.

Abstract

In the present invention, a mixed aqueous solution is prepared by blending prescribed proportions of a P source such as H3PO4, a divalent iron compound such as FeSO4·7H2O and an oxidizing agent such as H2O2. Next, this mixed aqueous solution is added dropwise to a buffer solution having a pH of 1.5 to 9 so as to generate a FePO4·nH2O co-precipitated powder. LiOH·nH2O is dissolved in pure water so as to obtain a strongly alkaline aqueous solution having a pH of 12 to 13, the FePO4·nH2O is added to the strongly alkaline aqueous solution so as to cause a reaction between the FePO4·nH2O and the LiOH·nH2O and produce a LiFePO4 co-precipitated powder, and this LiFePO4 co-precipitated powder is then fired so as to obtain a LiFePO4 fired powder. In this way, it is possible to easily produce a finely particulate, high purity iron lithium phosphate, which is suitable for use as an electrode active substance for a secondary battery, using a simple production process.

Description

リン酸鉄リチウムの製造方法、電極活物質、及び二次電池Lithium iron phosphate manufacturing method, electrode active material, and secondary battery
　本発明は、リン酸鉄リチウムの製造方法、電極活物質、及び二次電池に関し、より詳しくは二次電池用電極活物質に適したリン酸鉄リチウムの製造方法、このリン酸鉄リチウムを使用した電極活物質、及び該電極活物質を正極に含む二次電池に関する。 The present invention relates to a method for producing lithium iron phosphate, an electrode active material, and a secondary battery, and more specifically, a method for producing lithium iron phosphate suitable for an electrode active material for a secondary battery, and using the lithium iron phosphate The present invention relates to an electrode active material and a secondary battery including the electrode active material in a positive electrode.
　携帯電話、ノートパソコン、デジタルカメラ等の携帯用電子機器の市場拡大に伴い、これら電子機器のコードレス電源としてエネルギー密度が大きく長寿命の二次電池が待望されている。 With the expansion of the market for portable electronic devices such as mobile phones, notebook computers, and digital cameras, secondary batteries with high energy density and long life are expected as cordless power sources for these electronic devices.
　そして、このような要求に応えるべく、リチウムイオン等のアルカリ金属イオンを荷電担体とし、その電荷授受に伴う電気化学反応を利用した二次電池が開発されている。特に、エネルギー密度の大きなリチウムイオン二次電池は、現在では広く普及している。 In order to meet such demands, secondary batteries using an alkali metal ion such as lithium ion as a charge carrier and utilizing an electrochemical reaction accompanying the charge transfer have been developed. In particular, lithium ion secondary batteries having a high energy density are now widely used.
　二次電池の構成要素のうち電極活物質は、充電反応、放電反応という電池電極反応に直接寄与する物質であり、二次電池の中心的役割を有する。すなわち、電池電極反応は、電解質中に配された電極と電気的に接続された電極活物質に対し電圧を印加することにより、電子の授受を伴って生じる反応であり、電池の充放電時に進行する。したがって、上述したように電極活物質は、システム的には、二次電池の中心的役割を有する。 Among the constituent elements of the secondary battery, the electrode active material is a substance that directly contributes to the battery electrode reaction such as the charge reaction and the discharge reaction, and has the central role of the secondary battery. That is, the battery electrode reaction is a reaction that occurs with the transfer of electrons by applying a voltage to an electrode active material that is electrically connected to an electrode disposed in the electrolyte, and proceeds during charging and discharging of the battery. To do. Therefore, as described above, the electrode active material has a central role of the secondary battery in terms of system.
　そして、上記リチウムイオン二次電池では、正極活物質としてリチウム含有遷移金属酸化物を使用し、負極活物質として炭素材料を使用し、これらの電極活物質に対するリチウムイオンの挿入反応、及び脱離反応を利用して充放電を行っている。 In the lithium ion secondary battery, a lithium-containing transition metal oxide is used as a positive electrode active material, a carbon material is used as a negative electrode active material, and lithium ion insertion reaction and desorption reaction with respect to these electrode active materials. Charging and discharging is performed using
　正極活物質に使用されるリチウム含有遷移金属酸化物としては、従来より、ＬｉＣｏＯ２（リチウム酸コバルト）、ＬｉＮｉＯ２（ニッケル酸リチウム）、ＬｉＭｎ２Ｏ４（マンガン酸リチウム）等が知られている。この中でも、ＬｉＣｏＯ２は、ＬｉＭｎ２Ｏ４等に比べ、充放電特性やエネルギー密度が良好であることから広く採用されている。 Conventionally, LiCoO 2 (cobalt lithium), LiNiO 2 (lithium nickelate), LiMn 2 O 4 (lithium manganate), and the like are known as lithium-containing transition metal oxides used for the positive electrode active material. . Among these, LiCoO 2 is widely adopted because it has better charge / discharge characteristics and energy density than LiMn 2 O 4 and the like.
　しかしながら、ＬｉＣｏＯ２は、資源的制約が大きく高価な上に毒性の強いＣｏを含んでいるという問題がある。また、ＬｉＣｏＯ２は、１８０℃程度の温度で大量の酸素を放出するため、可燃性の有機電解質を使用するリチウムイオン電池では、安全性の面でも問題がある。このため、ＬｉＣｏＯ２を電極活物質に使用した場合は、小容量二次電池には適しているが、高出力・大容量の二次電池に使用するには多くの解決すべき課題がある。 However, LiCoO 2 has a problem that it has high resource constraints and is expensive and contains highly toxic Co. Moreover, since LiCoO 2 releases a large amount of oxygen at a temperature of about 180 ° C., there is a problem in terms of safety in a lithium ion battery using a flammable organic electrolyte. For this reason, when LiCoO 2 is used as the electrode active material, it is suitable for a small capacity secondary battery, but there are many problems to be solved when it is used for a high output and large capacity secondary battery.
　そこで、近年では、リチウムイオン二次電池用の電極活物質として、オリビン型結晶構造を有するＬｉＦｅＰＯ４（リン酸鉄リチウム）が注目されている。このＬｉＦｅＰＯ４は、リン（Ｐ）を構成元素に含み、全ての酸素がリンと強固に共有結合している。このため、高温になっても酸素を放出することがなく、熱安定性に優れており、高出力・大容量の二次電池用電極活物質への応用に適していると考えられている。 Therefore, in recent years, LiFePO 4 (lithium iron phosphate) having an olivine crystal structure has attracted attention as an electrode active material for lithium ion secondary batteries. This LiFePO 4 contains phosphorus (P) as a constituent element, and all oxygen is strongly covalently bonded to phosphorus. For this reason, it does not release oxygen even at a high temperature, is excellent in thermal stability, and is considered suitable for application to an electrode active material for secondary batteries with high output and large capacity.
　このＬｉＦｅＰＯ４の合成法としては、従来より、固相法、水熱合成法、共沈法、ゾルーゲル法等が知られており、特に、共沈法は０．１μｍ程度の微粒子を工業的に合成することが可能である。 As a method for synthesizing this LiFePO 4 , conventionally, a solid phase method, a hydrothermal synthesis method, a coprecipitation method, a sol-gel method, and the like are known. It is possible to synthesize.
　そして、特許文献１には、２価の鉄塩と２価のマンガン塩及びリン酸を溶解した水溶液にアルカリを添加し、鉄、マンガン及びリンを含む共沈体を得る第１工程、前記共沈体、リン酸リチウム及び導電性炭素材料を混合する第２工程、得られた混合物を乾式で粉砕処理して比容積が１．５ｍＬ／ｇ以下の反応前駆体を得る第３工程、該反応前駆体を５００～７００℃で焼成する第４工程を含むＭｎ原子を含有するリチウム鉄リン系複合酸化物炭素複合体の製造方法が提案されている。 Patent Document 1 discloses a first step in which an alkali is added to an aqueous solution in which a divalent iron salt, a divalent manganese salt, and phosphoric acid are dissolved to obtain a coprecipitate containing iron, manganese, and phosphorus. A second step of mixing the precipitate, lithium phosphate and the conductive carbon material, a third step of obtaining a reaction precursor having a specific volume of 1.5 mL / g or less by dry-grinding the resulting mixture, and the reaction A method for producing a lithium iron-phosphorus composite oxide-carbon composite containing Mn atoms, which includes a fourth step of firing the precursor at 500 to 700 ° C., has been proposed.
　この特許文献１では、ＦｅＳＯ４・７Ｈ２Ｏ等の２価のＦｅ塩、ＭｎＳＯ４・Ｈ２Ｏ等の２価のＭｎ塩、及Ｈ３ＰＯ４を溶解させた水溶液に水酸化ナトリウム等のアルカリを添加して（Ｆｅ，Ｍｎ)３(ＰＯ４)２・ｎＨ２Ｏの共沈粉を合成し、この共沈体にＬｉ３ＰＯ４及びカーボンブラック等の導電性炭素材料を混合し、１．５ｍＬ／ｇ以下に粉砕した後、５００～７００℃の温度で焼成し、これによりＬｉ－Ｆｅ－Ｐ系複合酸化物炭素複合体を得ている。 In Patent Document 1, a divalent Fe salt such as FeSO 4 · 7H 2 O, a divalent Mn salt such as MnSO 4 · H 2 O, and an aqueous solution in which H 3 PO 4 is dissolved, such as sodium hydroxide (Fe, Mn) 3 (PO 4 ) 2 .nH 2 O coprecipitated powder is synthesized by adding alkali, and the coprecipitate is mixed with a conductive carbon material such as Li 3 PO 4 and carbon black, After being pulverized to 1.5 mL / g or less, it is fired at a temperature of 500 to 700 ° C., thereby obtaining a Li—Fe—P-based composite oxide carbon composite.
　また、非特許文献１には、共沈法で作製された高タップ密度を有するＬｉＦｅＰＯ４－炭素複合体の電気化学的挙動における形態特性の効果が報告されている。 Non-Patent Document 1 reports the effect of morphological characteristics on the electrochemical behavior of a LiFePO 4 -carbon composite having a high tap density produced by a coprecipitation method.
　この非特許文献１では、３価のＦｅ塩であるＦｅ（ＮＯ）３・９Ｈ２ＯとＨ３ＰＯ４とを出発原料とし、共沈法を使用してＦｅＰＯ４・ｎＨ２Ｏを合成し、これをアルゴン雰囲気下、５５０℃の温度で１０時間熱処理し、水和水を脱離させてＦｅＰＯ４無水物を作製し、この後、このＦｅＰＯ４無水物をＬｉ源となるＬｉ２ＣＯ３及びＣ塗布源となるスクロースと混合し、Ａｒ－Ｈ２雰囲気中、６５０～８５０℃の焼成温度で１５時間焼成し、これによりＬｉＦｅＰＯ４－炭素複合体を得ている。 In the non-patent document 1, the trivalent and Fe (NO) 3 · 9H 2 O and H 3 PO 4 is Fe salt as the starting material, synthesis was FePO 4 · nH 2 O by using a co-precipitation method This was heat-treated at a temperature of 550 ° C. for 10 hours under an argon atmosphere, and hydrated water was desorbed to produce FePO 4 anhydride. Thereafter, this FePO 4 anhydride was used as Li 2 CO 3 as a Li source. And sucrose as a C coating source and baked in an Ar—H 2 atmosphere at a calcination temperature of 650 to 850 ° C. for 15 hours, thereby obtaining a LiFePO 4 -carbon composite.
　すなわち、この非特許文献１では、ＦｅＰＯ４・ｎＨ２ＯをＬｉ２ＣＯ３と直接混合して焼成した場合、焼成中に水和水がＦｅＰＯ４を酸化させるおそれがあるとし、焼成前にＦｅＰＯ４・ｎＨ２Ｏを熱処理し、水和水を脱離させている。 That is, in Non-Patent Document 1, when FePO 4 .nH 2 O is directly mixed with Li 2 CO 3 and baked, it is assumed that hydrated water may oxidize FePO 4 during calcination. 4 · nH 2 O is heat-treated to dehydrate the water of hydration.
特開２００５－０４７７５１号公報（請求項１）Japanese Patent Laying-Open No. 2005-047751 (Claim 1)
　しかしながら、特許文献１は、共沈粉である（Ｆｅ，Ｍｎ)３(ＰＯ４)２・ｎＨ２Ｏ中のＦｅが２価であることから、大気中で不安定であり、３価のＦｅに酸化されやすいという問題点があった。 However, in Patent Document 1, since Fe in (Fe, Mn) 3 (PO 4 ) 2 .nH 2 O, which is a coprecipitated powder, is divalent, it is unstable in the atmosphere, and trivalent Fe There was a problem that it was easily oxidized.
　また、非特許文献１については、本発明者の実験結果でも、ＦｅＰＯ４・ｎＨ２Ｏを熱処理せずに直接Ｌｉ２ＣＯ３と混合し、焼成した場合は、ＬｉＦｅＰＯ４を単一相として得ることはできなかった。 As for non-patent document 1, even in the experiment results of the present inventors, when FePO 4 .nH 2 O is directly mixed with Li 2 CO 3 without heat treatment and baked, LiFePO 4 is obtained as a single phase. I couldn't.
　そして、ＦｅＰＯ４・ｎＨ２ＯとＬｉ２ＣＯ３とを混合する前に、ＦｅＰＯ４・ｎＨ２Ｏを熱処理することにより、単一相のＬｉＦｅＰＯ４を合成できることも確認した。 It was also confirmed that single-phase LiFePO 4 can be synthesized by heat-treating FePO 4 .nH 2 O before mixing FePO 4 .nH 2 O and Li 2 CO 3 .
　ただし、前記熱処理が必要である理由としては、非特許文献１に記載されているようなＦｅＰＯ４・ｎＨ２Ｏ共沈粉の水和水の酸化作用だけが原因ではなく、Ｌｉ２ＣＯ３にも原因があると思われる。すなわち、焼成前に前記共沈粉を熱処理しない場合は、ＦｅＰＯ４・ｎＨ２Ｏの水和水が焼成中に酸化剤として作用するが、Ｌｉ２ＣＯ３から発生するＣＯ２も酸化剤として作用する。そしてその結果、Ｆｅの３価から２価への還元が抑制されることから、３価のＦｅ化合物が異相として残存し、単一相の高純度なＬｉＦｅＰＯ４を得ることができなかったものと思われる。 However, the reason why the heat treatment is necessary is not only due to the oxidizing action of hydrated water of FePO 4 · nH 2 O co-precipitated powder as described in Non-Patent Document 1, but to Li 2 CO 3 . There seems to be a cause. That is, when the coprecipitated powder is not heat-treated before firing, the hydrated water of FePO 4 · nH 2 O acts as an oxidizing agent during firing, but CO 2 generated from Li 2 CO 3 also acts as an oxidizing agent. To do. As a result, since the reduction of Fe from trivalent to divalent is suppressed, the trivalent Fe compound remains as a different phase, and a single-phase high-purity LiFePO 4 could not be obtained. Seem.
　つまり、非特許文献１のようにＦｅＰＯ４・ｎＨ２ＯとＬｉ２ＣＯ３とを混合させる場合、焼成前に熱処理を行なってＦｅＰＯ４・ｎＨ２Ｏの水和水を脱離させ、これにより酸化源を減少させた後、焼成処理を行なうことにより、単一相のＬｉＦｅＰＯ４を合成することができると考えられる。 That is, when FePO 4 .nH 2 O and Li 2 CO 3 are mixed as in Non-Patent Document 1, heat treatment is performed before firing to desorb the hydrated water of FePO 4 .nH 2 O, thereby It is considered that single-phase LiFePO 4 can be synthesized by performing a baking treatment after reducing the oxidation source.
　いずれにしても非特許文献１のようにＦｅＰＯ４・ｎＨ２ＯとＬｉ２ＣＯ３とを反応させてＬｉＦｅＰＯ４を作製するためには、ＦｅＰＯ４・ｎＨ２Ｏの共沈粉を熱処理した後、Ｌｉ２ＣＯ３と混合し、その後、焼成処理を行なう必要がある。 In any case, in order to produce LiFePO 4 by reacting FePO 4 · nH 2 O and Li 2 CO 3 as in Non-Patent Document 1, after co-precipitated FePO 4 · nH 2 O is heat-treated It is necessary to mix with Li 2 CO 3 and then perform a baking treatment.
　すなわち、非特許文献１の方法では、少なくとも２回の熱処理を行なわなければならず、製造工程が煩雑化し、しかも焼成粉中に異相が混在するため、高純度のＬｉＦｅＰＯ４を得るのは困難であるという問題点があった。 That is, in the method of Non-Patent Document 1, at least two heat treatments must be performed, the manufacturing process becomes complicated, and foreign phases are mixed in the calcined powder, so it is difficult to obtain high purity LiFePO 4. There was a problem that there was.
　本発明はこのような事情に鑑みなされたものであって、簡素な製造工程で二次電池用電極活物質に適した微粒で高純度のリン酸鉄リチウムを容易に製造することができるリン酸鉄リチウムの製造方法、及びこの製造方法を使用して得られたリン酸鉄リチウムを主体とする電極活物質、及び該電極活物質を正極に含む二次電池を提供することを目的とする。 The present invention has been made in view of such circumstances, and phosphoric acid capable of easily producing fine, high-purity lithium iron phosphate suitable for an electrode active material for a secondary battery by a simple production process. An object of the present invention is to provide a method for producing iron lithium, an electrode active material mainly composed of lithium iron phosphate obtained by using this production method, and a secondary battery including the electrode active material in a positive electrode.
　本発明者は、上記目的を達成するために鋭意研究を行ったところ、３価の鉄を含有したリン酸鉄（III）とリチウム水酸化物を湿式で混合することで前記リン酸鉄（III）の粒子が微細化して、より微粒のリン酸鉄リチウムを得ることができるという知見を得た。 The present inventor conducted intensive research to achieve the above object, and mixed the iron phosphate (III) containing trivalent iron and lithium hydroxide by wet mixing. ) Was refined to obtain a finer lithium iron phosphate.
　本発明はこのような知見に基づきなされたものであって、本発明に係るリン酸鉄リチウムの製造方法は、リン酸鉄（III）とリチウム水酸化物とを湿式で混合した後、焼成処理を行ってリン酸鉄リチウムの粉末を合成することを特徴としている。 The present invention has been made on the basis of such knowledge, and the method for producing lithium iron phosphate according to the present invention is a method in which iron (III) phosphate and lithium hydroxide are mixed by a wet process followed by a firing treatment. To synthesize lithium iron phosphate powder.
　また、本発明のリン酸鉄リチウムの製造方法は、前記リチウム水酸化物が強アルカリ性となるような水溶液下で、前記リチウム水酸化物と前記リン酸鉄(III)と混合するのが好ましい。 Further, in the method for producing lithium iron phosphate of the present invention, it is preferable to mix the lithium hydroxide and the iron (III) phosphate in an aqueous solution in which the lithium hydroxide becomes strongly alkaline.
　これによりリン酸鉄は強アルカリ下、分解してリチウムと反応することから、リン酸鉄が微細化し、焼成後には比表面積の大きな電極活物質材料に適した微粒のリン酸鉄リチウムを製造することができる。 As a result, iron phosphate decomposes and reacts with lithium in a strong alkali, so that iron phosphate is refined and, after firing, produces fine lithium iron phosphate suitable for electrode active material with a large specific surface area. be able to.
　さらに、本発明者が鋭意研究を重ねたところ、リン酸鉄（III）が水和水を含有した非晶質のものであっても、リチウム塩にリチウム水酸化物を用いることにより、二次電池の電極活物質に適した微粒で高純度のリン酸鉄リチウム（ＬｉＦｅＰＯ４）を容易に製造することができるということが分かった。 Furthermore, as a result of extensive research by the present inventor, even if the iron (III) phosphate is an amorphous one containing hydrated water, the secondary salt can be obtained by using lithium hydroxide as the lithium salt. It was found that fine and high-purity lithium iron phosphate (LiFePO 4 ) suitable for an electrode active material of a battery can be easily produced.
　すなわち、本発明のリン酸鉄リチウムの製造方法は、前記リン酸鉄（III）は、水和水を含有しているのが好ましい。 That is, in the method for producing lithium iron phosphate of the present invention, the iron (III) phosphate preferably contains hydration water.
　また、リン酸鉄（III）は、リン源と３価の鉄を含有した鉄化合物とを反応させて合成することができ、より好ましくはリン源と前記鉄化合物を溶解させた水溶液を、ｐＨが１．５～９に調製された緩衝溶液に滴下して接触させることにより、鉄とリンの元素分布に分散ムラが生じることもなく、鉄とリンが均一乃至略均一に分散した高純度のリン酸鉄を高効率で製造することができる。 Further, iron (III) phosphate can be synthesized by reacting a phosphorus source with an iron compound containing trivalent iron. More preferably, an aqueous solution in which the phosphorus source and the iron compound are dissolved is adjusted to pH. Is dripped into a buffer solution prepared in a range of 1.5 to 9, and the dispersion of the elemental distribution of iron and phosphorus is not unevenly distributed, and iron and phosphorus are uniformly and substantially uniformly dispersed. Iron phosphate can be produced with high efficiency.
　すなわち、本発明のリン酸鉄リチウムの製造方法は、前記リン酸鉄（III）はリン源と３価の鉄を含有した鉄化合物とを反応させて合成するのが好ましい。 That is, in the method for producing lithium iron phosphate of the present invention, the iron (III) phosphate is preferably synthesized by reacting a phosphorus source with an iron compound containing trivalent iron.
　また、本発明のリン酸鉄リチウムの製造方法は、前記リン酸鉄（III）は、リン源と前記鉄化合物とを溶解させた混合水溶液をｐＨが１．５～９の緩衝溶液に接触させて生成するのがより好ましい。 In the method for producing lithium iron phosphate of the present invention, the iron (III) phosphate is brought into contact with a buffer solution having a pH of 1.5 to 9 by mixing a mixed aqueous solution in which a phosphorus source and the iron compound are dissolved. It is more preferable to produce them.
　これによりＦｅ（ＯＨ）３のような副生物が生成されることもなく、ＦｅとＰの元素分布が均一乃至略均一に分散した高純度のリン酸鉄を高効率で得ることができる。しかも、緩衝溶液の緩衝作用により粉末生成時のｐＨの変動も小さく、微粒で粒径の揃ったリン酸鉄の粉末を得ることができる。 Thereby, by-products such as Fe (OH) 3 are not generated, and high-purity iron phosphate in which the element distribution of Fe and P is uniformly or substantially uniformly dispersed can be obtained with high efficiency. In addition, due to the buffering action of the buffer solution, fluctuations in pH during the production of the powder are small, and it is possible to obtain iron phosphate powder with fine particles and uniform particle size.
　また、本発明に係る電極活物質は、電池電極反応によって充放電を繰り返す二次電池の活物質として使用される電極活物質であって、上記いずれかに記載の方法で製造されたリン酸鉄リチウムを主体としていることを特徴としている。 Moreover, the electrode active material according to the present invention is an electrode active material used as an active material of a secondary battery that repeats charging and discharging by a battery electrode reaction, and is manufactured by any of the above methods. The main feature is lithium.
　また、本発明に係る二次電池は、正極、負極、及び電解質を有し、前記正極が、上記電極活物質を含むことを特徴としている。 The secondary battery according to the present invention includes a positive electrode, a negative electrode, and an electrolyte, and the positive electrode includes the electrode active material.
　上記リン酸鉄リチウムの製造方法によれば、リン酸鉄（III）又は水和水を含有したリン酸鉄（III）とリチウム水酸化物とを湿式で混合した後、焼成処理を行ってリン酸鉄リチウムの粉末を合成するので、安定した３価の鉄を含有したリン酸鉄から１回の熱処理で容易に高純度のリン酸鉄リチウムを製造することが可能となる。 According to the above-mentioned method for producing lithium iron phosphate, iron (III) phosphate or iron (III) phosphate containing hydrated water and lithium hydroxide are mixed in a wet process, and then subjected to a firing treatment to obtain phosphorus. Since the powder of lithium iron oxide is synthesized, it is possible to easily produce high purity lithium iron phosphate from iron phosphate containing stable trivalent iron by one heat treatment.
　また、本発明の電極活物質によれば、電池電極反応によって充放電を繰り返す二次電池の活物質として使用される電極活物質が、上記リン酸鉄リチウムを主体としているので、安全で高エネルギー密度を有する電極活物質を得ることができる。 Further, according to the electrode active material of the present invention, the electrode active material used as the active material of the secondary battery that repeats charging and discharging by the battery electrode reaction is mainly composed of the lithium iron phosphate, so that it is safe and high energy. An electrode active material having a density can be obtained.
　また、本発明の二次電池によれば、正極、負極、及び電解質を有し、前記正極が、上記電極活物質を含むので、安全面に優れた大容量・高出力の二次電池を得ることができる。 In addition, according to the secondary battery of the present invention, it has a positive electrode, a negative electrode, and an electrolyte, and since the positive electrode contains the electrode active material, a high-capacity and high-output secondary battery excellent in safety is obtained. be able to.
本発明に係る二次電池としてのコイン型電池の一実施の形態を示す断面図である。It is sectional drawing which shows one Embodiment of the coin-type battery as a secondary battery which concerns on this invention. 実施例のＸ線回折スペクトルを比較例と共に示した図である。It is the figure which showed the X-ray-diffraction spectrum of the Example with the comparative example. 実施例に使用したＦｅＰＯ４・２Ｈ２ＯのＳＥＭ像である。Is an SEM image of FePO 4 · 2H 2 O used in Example. 実施例試料の乾燥後のＳＥＭ像である。It is a SEM image after drying of an example sample. 実施例試料の焼成後のＳＥＭ像である。It is a SEM image after baking of an Example sample. 実施例で得られた二次電池の充放電曲線である。It is a charging / discharging curve of the secondary battery obtained in the Example.
　次に、本発明を実施するための形態を詳説する。 Next, an embodiment for carrying out the present invention will be described in detail.
　本発明に係るリン酸鉄リチウムの製造方法は、Ｐ源と３価のＦｅを含有したＦｅ化合物とを反応させてＦｅＰＯ４・ｎＨ２Ｏ（リン酸鉄（III））の粉末（共沈粉）を生成し、この共沈粉とＬｉＯＨ・Ｈ２Ｏ（水酸化リチウム）とを湿式で混合し、焼成処理を行なってＬｉＦｅＰＯ４（リン酸鉄リチウム）の粉末（焼成粉）を生成している。 In the method for producing lithium iron phosphate according to the present invention, a P source and a Fe compound containing trivalent Fe are reacted to obtain a powder (coprecipitated powder) of FePO 4 .nH 2 O (iron phosphate (III)) ), And the coprecipitated powder and LiOH.H 2 O (lithium hydroxide) are mixed in a wet manner, followed by firing to produce LiFePO 4 (lithium iron phosphate) powder (fired powder). Yes.
　そしてこれにより、製造工程の煩雑化を招くこともなく、１回の焼成処理でＦｅＰＯ４・ｎＨ２ＯからＬｉＦｅＰＯ４を容易に製造することができる。しかも、ＦｅＰＯ４・ｎＨ２Ｏは３価のＦｅを含有していることから、大気中でも安定しており、合成反応が安定的に進行し、異相を形成することもなく高純度のＬｉＦｅＰＯ４を得ることができる。特に、ＦｅＰＯ４・ｎＨ２Ｏを強アルカリ性に調製されたＬｉＯＨ・ｎＨ２Ｏと湿式混合させることにより、ＦｅＰＯ４・ｎＨ２Ｏは分解しながらＬｉと反応する。したがって、湿式混合で得られた反応物は微細となり、焼成処理により比表面積が大きく、微粒のＬｉＦｅＰＯ４粉末を得ることができる。 And thereby, without incurring the complication of the manufacturing process, it is possible to easily produce LiFePO 4 from FePO 4 · nH 2 O in a single firing process. Moreover, since FePO 4 .nH 2 O contains trivalent Fe, it is stable in the air, the synthesis reaction proceeds stably, and high-purity LiFePO 4 is not formed without forming a heterogeneous phase. Obtainable. In particular, when FePO 4 · nH 2 O is wet mixed with LiOH · nH 2 O prepared to be strongly alkaline, FePO 4 · nH 2 O reacts with Li while being decomposed. Therefore, the reaction product obtained by the wet mixing becomes fine, and the specific surface area is increased by the baking treatment, so that a fine LiFePO 4 powder can be obtained.
　以下、上記ＬｉＦｅＰＯ４の製造方法を具体的に説明する。 Hereinafter, the manufacturing method of the LiFePO 4 will be specifically described.
　まず、Ｐ源と３価のＦｅを含有したＦｅ化合物とを反応させてＦｅＰＯ４・ｎＨ２Ｏの粉末を生成する。 First, a P source and a Fe compound containing trivalent Fe are reacted to produce FePO 4 .nH 2 O powder.
　このＦｅＰＯ４・ｎＨ２Ｏを生成するための具体的な方法は、特に限定されるものではないが、Ｐ源とＦｅ化合物とを溶解させた混合水溶液をｐＨが１．５～９の緩衝溶液に接触させて反応させ、ＦｅＰＯ４・ｎＨ２Ｏを生成するのが好ましい。 A specific method for producing this FePO 4 .nH 2 O is not particularly limited, but a buffer solution having a pH of 1.5 to 9 is prepared by mixing a mixed aqueous solution in which a P source and an Fe compound are dissolved. It is preferable that FePO 4 .nH 2 O is produced by contacting with the reaction.
　すなわち、Ｐ源と３価のＦｅ化合物とを溶解させた混合水溶液を、ｐＨが９以下に調製された緩衝溶液に滴下して接触させると、Ｆｅ（ＯＨ）３等の副生物が生成されることもなく、ＦｅＰＯ４・ｎＨ２Ｏを生成することができる。そして、これによりＦｅとＰの元素分布が均一乃至略均一で、微粒かつ高純度のＦｅＰＯ４・ｎＨ２Ｏを高効率で生成することが可能となる。しかも、緩衝溶液の緩衝作用により、ｐＨの変動が抑制されるので、ＦｅＰＯ４・ｎＨ２Ｏの粉末生成時のｐＨの変動も小さく、粒径の揃った球形状のＦｅＰＯ４・ｎＨ２Ｏ粉末を得ることができる。 That is, when a mixed aqueous solution in which a P source and a trivalent Fe compound are dissolved is dropped and brought into contact with a buffer solution having a pH of 9 or less, a by-product such as Fe (OH) 3 is generated. Without being able to produce FePO 4 .nH 2 O. As a result, it is possible to produce FePO 4 .nH 2 O having a uniform and substantially uniform elemental distribution of Fe and P and having a fine particle and high purity with high efficiency. Moreover, the buffering action of the buffer solution, the variation of the pH is inhibited, less variation in pH during FePO 4 · nH 2 O powder product, a uniform particle size spherical FePO 4 · nH 2 O powder Can be obtained.
　尚、緩衝溶液のｐＨが１．５未満になると、沈殿せずに溶出してしまうＦｅとＰの量が増加し、粉末生成の収率が低下するおそれがあることから好ましくない。 In addition, it is not preferable that the pH of the buffer solution is less than 1.5 because the amount of Fe and P that are eluted without precipitation increases and the yield of powder production may decrease.
　次に、この緩衝溶液を使用したＦｅＰＯ４・ｎＨ２Ｏの作製方法を詳述する。 Next, a method for producing FePO 4 .nH 2 O using this buffer solution will be described in detail.
　まず、ＦｅＳＯ４・７Ｈ２ＯやＦｅＣｌ２・４Ｈ２Ｏ等の２価のＦｅを含有したＦｅ化合物、Ｈ３ＰＯ４、（ＮＨ４）Ｈ２ＰＯ４、（ＮＨ４）２ＨＰＯ４等のＰ源、及びＨ２Ｏ２等の酸化剤を用意し、これらが所定割合となるように混合し、混合水溶液を作製する。ここで、２価のＦｅ化合物とＰ源とは、モル比率で等量乃至略等量となるように混合し、酸化剤は、２価のＦｅが３価にＦｅに完全に酸化されるように２価のＦｅ化合物に対し過剰（例えば、モル比で１．５倍程度）に添加する。 First, Fe compounds containing divalent Fe such as FeSO 4 .7H 2 O and FeCl 2 .4H 2 O, H 3 PO 4 , (NH 4 ) H 2 PO 4 , (NH 4 ) 2 HPO 4 and the like A P source and an oxidizing agent such as H 2 O 2 are prepared and mixed so that these are in a predetermined ratio to prepare a mixed aqueous solution. Here, the divalent Fe compound and the P source are mixed so that the molar ratio is equal to or substantially equal, and the oxidizing agent is such that the divalent Fe is completely oxidized to Fe in the trivalent state. In excess of the divalent Fe compound (for example, about 1.5 times in molar ratio).
　次いで、ｐＨが９以下、好ましくは１．５～９に調製された緩衝溶液を作製する。 Next, a buffer solution having a pH of 9 or less, preferably 1.5 to 9 is prepared.
　ここで、緩衝溶液の作製方法は特に限定されるものではなく、例えば、酢酸－酢酸アンモニウム、乳酸－乳酸ナトリウム、グリコール酸－グリコール酸ナトリウム、マレイン酸－マレイン酸二ナトリウム等の弱酸－共役塩基を混合させて緩衝溶液を作製する方法が広く知られており、これら弱酸－共役塩基の混合割合を適宜調整して作製することができる。また、緩衝溶液の構成物質の組み合わせも弱酸－共役塩基に限定されるものではなく、その他の組み合わせ、例えば弱酸－強塩基等であってもよい。 Here, the method for preparing the buffer solution is not particularly limited. For example, a weak acid-conjugate base such as acetic acid-ammonium acetate, lactic acid-sodium lactate, glycolic acid-sodium glycolate, maleic acid-disodium maleate is used. A method of preparing a buffer solution by mixing is widely known, and can be prepared by appropriately adjusting the mixing ratio of these weak acid-conjugated bases. In addition, the combination of constituents of the buffer solution is not limited to the weak acid-conjugated base, and other combinations such as a weak acid-strong base may be used.
　次いで、この緩衝溶液を常温で撹拌し、緩衝溶液のｐＨを監視しながら前記混合水溶液を緩衝溶液に滴下して接触させ、これにより褐色のＦｅＰＯ４・ｎＨ２Ｏの共沈粉が得られる。 Next, the buffer solution is stirred at room temperature, and the mixed aqueous solution is dropped into contact with the buffer solution while monitoring the pH of the buffer solution, whereby a brown FePO 4 .nH 2 O coprecipitated powder is obtained.
　尚、混合水溶液の滴下量が増加するに伴い、緩衝溶液のｐＨは低下するが、混合水溶液の滴下はｐＨが１．５に到達する前に終了するのが好ましい。ｐＨが１．５以下になった後も混合水溶液の滴下を継続すると、上述したように沈殿したＦｅＰＯ４・ｎＨ２Ｏが溶解し始めて、ＦｅやＰが溶出し、このため沈殿粉末の収率低下を招くおそれがある。 In addition, as the dropping amount of the mixed aqueous solution increases, the pH of the buffer solution decreases, but the dropping of the mixed aqueous solution is preferably terminated before the pH reaches 1.5. If dropping of the mixed aqueous solution is continued even after the pH becomes 1.5 or less, the precipitated FePO 4 .nH 2 O starts to dissolve as described above, and Fe and P are eluted, and thus the yield of the precipitated powder There is a risk of lowering.
　また、上記緩衝溶液を使用せずにアンモニア水やＮａＯＨ等のアルカリ溶液を混合水溶液に滴下した場合は、滴下周辺のｐＨが一時的に大きくなってＦｅ（ＯＨ）３が優先的に生成されることから好ましくない。すなわち、この場合、混合水溶液を撹拌することにより、滴下周辺のｐＨは低下し、ＦｅＰＯ４が生成されていくが、一旦生成されたＦｅ（ＯＨ）３は、ＦｅＰＯ４に変化しにくい。このため、得られた共沈粉はＦｅＰＯ４とＦｅ（ＯＨ）３との混合物となり、ＦｅとＰが均一に分散せずに分散ムラが生じ、粒度分布もバラツキが大きく、形状も不揃いになり、好ましくない。 Further, when an alkaline solution such as aqueous ammonia or NaOH is dropped into the mixed aqueous solution without using the buffer solution, the pH around the dropping is temporarily increased, and Fe (OH) 3 is preferentially generated. That is not preferable. That is, in this case, by stirring the mixed aqueous solution, the pH around the dropping is lowered and FePO 4 is generated, but once generated Fe (OH) 3 is hardly changed to FePO 4 . For this reason, the obtained coprecipitated powder becomes a mixture of FePO 4 and Fe (OH) 3, and Fe and P are not uniformly dispersed, resulting in dispersion unevenness, large variation in particle size distribution, and uneven shape. It is not preferable.
　次いで、このＦｅＰＯ４・ｎＨ２ＯをＬｉＯＨ・Ｈ２Ｏと湿式混合して反応させ、これによりＬｉＦｅＰＯ４を生成する。 Next, this FePO 4 · nH 2 O is wet mixed with LiOH · H 2 O and reacted to produce LiFePO 4 .
　すなわち、ＬｉＯＨ・Ｈ２Ｏは白色固体であるが水溶性を有しており、例えば、溶媒としての純水に溶解させると、スラリーはｐＨが１２～１３の強アルカリ性になる。そして、このような強アルカリ性の下、ＦｅＰＯ４・ｎＨ２ＯとＬｉＯＨ・Ｈ２Ｏとを湿式混合させると、ＦｅＰＯ４・ｎＨ２Ｏが分解してＬｉと反応し、微細化する。したがって、このスラリーを乾燥、造粒することにより、微粒で比表面積の大きなＬｉＦｅＰＯ４の粉末を得ることができる。 That is, LiOH.H 2 O is a white solid but water-soluble. For example, when dissolved in pure water as a solvent, the slurry becomes strongly alkaline with a pH of 12 to 13. Under such strong alkalinity, when FePO 4 · nH 2 O and LiOH · H 2 O are wet-mixed, FePO 4 · nH 2 O decomposes and reacts with Li to be refined. Therefore, by drying and granulating this slurry, it is possible to obtain a fine LiFePO 4 powder having a large specific surface area.
　具体的には、上記ＦｅＰＯ４・ｎＨ２ＯとＬｉＯＨ・Ｈ２Ｏとが、モル比率で１：１となるように、これらＦｅＰＯ４・ｎＨ２Ｏ及びＬｉＯＨ・Ｈ２Ｏを秤量し、この秤量物を純水及びポリカルボン酸等の高分子分散剤と共にボールミルに投入し、混合粉砕し、ＬｉＦｅＰＯ４の粉末を得ることができる。 Specifically, the FePO 4 .nH 2 O and the LiOH · H 2 O are weighed so that the molar ratio of the FePO 4 · nH 2 O and the LiOH · H 2 O is 1: 1. The weighed product is put into a ball mill together with pure water and a polymer dispersant such as polycarboxylic acid, mixed and pulverized, and LiFePO 4 powder can be obtained.
　尚、電子伝導性を確保する観点からは、ＦｅＰＯ４・ｎＨ２Ｏにスクロース等のカーボン源を添加し、ＬｉＦｅＰＯ４の表面をカーボンで被覆するのが好ましい。また、ＬｉＦｅＰＯ４を微細化して比表面積を増大させるためにもカーボンを添加するのが好ましい。すなわち、ＬｉＦｅＰＯ４の表面をカーボンで被覆することにより、焼成時にＬｉＦｅＰＯ４の粒成長が阻害され、大きな比表面積を確保することができる。 From the viewpoint of ensuring electron conductivity, it is preferable to add a carbon source such as sucrose to FePO 4 .nH 2 O and coat the surface of LiFePO 4 with carbon. Moreover, it is preferable to add carbon in order to refine LiFePO 4 and increase the specific surface area. That is, by covering the surface of LiFePO 4 with carbon, the grain growth of LiFePO 4 is inhibited during firing, and a large specific surface area can be secured.
　次いで、この混合粉末を乾燥し、造粒した後、所定の還元雰囲気下、所定温度（例えば、５００～７００℃）で５時間程度熱処理を行う。そしてこれにより３価のＦｅが２価に還元され、微粒で比表面積の大きなＬｉＦｅＰＯ４の焼成粉が得られる。 Next, the mixed powder is dried and granulated, and then heat-treated at a predetermined temperature (for example, 500 to 700 ° C.) for about 5 hours in a predetermined reducing atmosphere. As a result, trivalent Fe is reduced to divalent, and a sintered powder of LiFePO 4 having fine particles and a large specific surface area is obtained.
　このようにして得られたＬｉＦｅＰＯ４は、異相が形成されることもなく、高純度であり、二次電池用の電極活物質に好適に使用することができる。 Thus obtained LiFePO 4 has high purity without forming a heterogeneous phase, and can be suitably used as an electrode active material for a secondary battery.
　また、上記ＬｉＦｅＰＯ４は、微粒で比表面積が大きいことから、反応表面積が増大し、電子導電性が向上し、このＬｉＦｅＰＯ４を電極活物質に使用することにより、より一層良好な電池特性を得ることが可能となる。 Moreover, since the LiFePO 4 is fine and has a large specific surface area, the reaction surface area is increased and the electronic conductivity is improved. By using this LiFePO 4 as an electrode active material, even better battery characteristics can be obtained. It becomes possible.
　しかも、本発明のＬｉＦｅＰＯ４を主体とした電極活物質は、原材料がＣｏのような資源的制約もなく、安価で入手容易であり、しかも安全性にも優れた大容量・高出力の二次電池を低コストで実現することが可能となる。 Moreover, the electrode active material mainly composed of LiFePO 4 of the present invention is a secondary material having a large capacity and a high output that is inexpensive and easily available, and is excellent in safety without being limited by resources such as Co. The battery can be realized at low cost.
　次に、前記電極活物質を使用した二次電池について詳述する。 Next, a secondary battery using the electrode active material will be described in detail.
　図１は、本発明に係る二次電池の一実施の形態としてのコイン型二次電池を示す断面図であって、本実施の形態では、ＬｉＦｅＰＯ４を主体とした電極活物質を正極活物質に使用している。 FIG. 1 is a cross-sectional view showing a coin-type secondary battery as an embodiment of a secondary battery according to the present invention. In this embodiment, an electrode active material mainly composed of LiFePO 4 is used as a positive electrode active material. It is used for.
　電池缶１は、正極ケース２と負極ケース３とを有し、該正極ケース２及び負極ケース３は、いずれも円盤状の薄板形状に形成されている。また、正極集電体を構成する正極ケース２の底部中央には、電極活物質をシート状に形成した正極４が配されている。また、正極４上にはポリプロピレン等の多孔質フィルムで形成されたセパレータ５が積層され、さらにセパレータ５には負極６が積層されている。負極６としては、例えば、Ｃｕにリチウムの金属箔を重ね合わせたものや、黒鉛やハードカーボン等のリチウム吸蔵材料を前記金属箔に塗布したものを使用することができる。そして、負極６にはＣｕ等で形成された負極集電体７が積層されると共に、該負極集電体７には金属製ばね８が載置されている。また、電解質９が内部空間に充填されると共に、負極ケース３は金属製ばね８の付勢力に抗して正極ケース２に固着され、ガスケット１０を介して封止されている。 The battery can 1 has a positive electrode case 2 and a negative electrode case 3, and both the positive electrode case 2 and the negative electrode case 3 are formed in a disk-like thin plate shape. Moreover, the positive electrode 4 which formed the electrode active material in the sheet form is distribute | arranged to the center of the bottom part of the positive electrode case 2 which comprises a positive electrode electrical power collector. A separator 5 formed of a porous film such as polypropylene is laminated on the positive electrode 4, and a negative electrode 6 is further laminated on the separator 5. As the negative electrode 6, for example, one obtained by superimposing a lithium metal foil on Cu or one obtained by applying a lithium storage material such as graphite or hard carbon to the metal foil can be used. A negative electrode current collector 7 made of Cu or the like is laminated on the negative electrode 6, and a metal spring 8 is placed on the negative electrode current collector 7. Further, the electrolyte 9 is filled in the internal space, and the negative electrode case 3 is fixed to the positive electrode case 2 against the urging force of the metal spring 8 and is sealed through the gasket 10.
　次に、上記二次電池の製造方法の一例を詳述する。 Next, an example of a method for manufacturing the secondary battery will be described in detail.
　まず、電極活物質の主体となるＬｉＦｅＰＯ４を電極形状に形成する。例えば、ＬｉＦｅＰＯ４を導電補助剤、及び結着剤と共に混合し、溶媒を加えてスラリーとし、該スラリーを正極集電体上に任意の塗工方法で塗工し、乾燥することにより正極４を形成する。 First, LiFePO 4 as a main component of the electrode active material is formed into an electrode shape. For example, LiFePO 4 is mixed with a conductive additive and a binder, a solvent is added to form a slurry, the slurry is applied on the positive electrode current collector by an arbitrary coating method, and dried to form the positive electrode 4. Form.
　ここで、導電補助剤としては、特に限定されるものでなく、例えば、グラファイト、カーボンブラック、アセチレンブラック等の炭素質微粒子、気相成長炭素繊維、カーボンナノチューブ、カーボンナノホーン等の炭素繊維、ポリアニリン、ポリピロール、ポリチオフェン、ポリアセチレン、ポリアセン等の導電性高分子などを使用することができる。また、導電補助剤を２種類以上混合して用いることもできる。尚、導電補助剤の正極４中の含有率は１０～８０重量％が好ましい。 Here, the conductive auxiliary agent is not particularly limited, for example, carbonaceous fine particles such as graphite, carbon black, and acetylene black, vapor grown carbon fibers, carbon nanotubes, carbon fibers such as carbon nanohorns, polyaniline, Conductive polymers such as polypyrrole, polythiophene, polyacetylene, and polyacene can be used. Further, two or more kinds of conductive assistants can be mixed and used. The content of the conductive auxiliary agent in the positive electrode 4 is preferably 10 to 80% by weight.
　また、結着剤も特に限定されるものではなく、ポリエチレン、ポリフッ化ビニリデン、ポリヘキサフルオロプロピレン、ポリテトラフルオロエチレン、ポリエチレンオキサイド、カルボキシメチルセルロース等の各種樹脂を使用することができる。 Also, the binder is not particularly limited, and various resins such as polyethylene, polyvinylidene fluoride, polyhexafluoropropylene, polytetrafluoroethylene, polyethylene oxide, carboxymethylcellulose, and the like can be used.
　さらに、溶媒についても、特に限定されるものではなく、例えば、ジメチルスルホキシド、ジメチルホルムアミド、Ｎ－メチル－２－ピロリドン、プロピレンカーボネート、ジエチルカーボネート、ジメチルカーボネート、γ－ブチロラクトン等の塩基性溶媒、アセトニトリル、テトラヒドロフラン、ニトロベンゼン、アセトン等の非水溶媒、メタノール、エタノール等のプロトン性溶媒等を使用することができる。 Further, the solvent is not particularly limited, and examples thereof include basic solvents such as dimethyl sulfoxide, dimethylformamide, N-methyl-2-pyrrolidone, propylene carbonate, diethyl carbonate, dimethyl carbonate, and γ-butyrolactone, acetonitrile, Nonaqueous solvents such as tetrahydrofuran, nitrobenzene, and acetone, and protic solvents such as methanol and ethanol can be used.
　また、溶媒の種類、有機化合物と溶媒との配合比、添加剤の種類とその添加量等は、二次電池の要求特性や生産性等を考慮し、任意に設定することができる。 Also, the type of solvent, the compounding ratio between the organic compound and the solvent, the type of additive and the amount of the additive, etc. can be arbitrarily set in consideration of the required characteristics and productivity of the secondary battery.
　次いで、この正極４を電解質９に含浸させて該正極４に前記電解質９を染み込ませ、その後、正極ケース２の底部中央の正極集電体上に正極４を載置する。次いで、前記電解質９を含浸させたセパレータ５を正極４上に積層し、さらに負極６及び負極集電体７を順次積層し、その後内部空間に電解質９を注入する。そして、負極集電体７上に金属製ばね８を載置すると共に、ガスケット１０を周縁に配し、かしめ機等で負極ケース３を正極ケース２に固着して外装封止し、これによりコイン型二次電池が作製される。 Next, the positive electrode 4 is impregnated in the electrolyte 9 so that the positive electrode 4 is impregnated with the electrolyte 9, and then the positive electrode 4 is placed on the positive electrode current collector at the bottom center of the positive electrode case 2. Next, the separator 5 impregnated with the electrolyte 9 is laminated on the positive electrode 4, the negative electrode 6 and the negative electrode current collector 7 are sequentially laminated, and then the electrolyte 9 is injected into the internal space. Then, a metal spring 8 is placed on the negative electrode current collector 7, and a gasket 10 is arranged on the periphery, and the negative electrode case 3 is fixed to the positive electrode case 2 with a caulking machine or the like, and the outer casing is sealed. A type secondary battery is produced.
　尚、上記電解質９は、正極４と対向電極である負極６との間に介在して両電極間の荷電担体輸送を行うが、このような電解質９としては、室温で１０-5～１０-1Ｓ/ｃｍの電気伝導度を有するものを使用することができ、例えば、電解質塩を有機溶剤に溶解させた電解液を使用することができる。 The electrolyte 9 is interposed between the positive electrode 4 and the negative electrode 6 which is a counter electrode, and transports charge carriers between the two electrodes. Such an electrolyte 9 has 10 −5 to 10 − at room temperature. Those having an electrical conductivity of 1 S / cm can be used. For example, an electrolytic solution in which an electrolyte salt is dissolved in an organic solvent can be used.
　ここで、電解質塩としては、例えば、ＬｉＰＦ６、ＬｉＣｌＯ４、ＬｉＢＦ４、ＬｉＣＦ３ＳＯ３、Ｌｉ（ＣＦ３ＳＯ２）２、Ｌｉ（Ｃ２Ｆ５ＳＯ２）２Ｎ、Ｌｉ（ＣＦ３ＳＯ２）３Ｃ、Ｌｉ（Ｃ２Ｆ５ＳＯ２）３Ｃ等を使用することができる。 Here, as the electrolyte salt, for example, LiPF 6 , LiClO 4 , LiBF 4 , LiCF 3 SO 3 , Li (CF 3 SO 2 ) 2 , Li (C 2 F 5 SO 2 ) 2 N, Li (CF 3 SO 2 ) 3 C, Li (C 2 F 5 SO 2 ) 3 C, or the like can be used.
　また、有機溶剤としては、エチレンカーボネート、プロピレンカーボネート、ジメチルカーボネート、ジエチルカーボネート、メチルエチルカーボネート、γ－ブチロラクトン、テトラヒドロフラン、ジオキソラン、スルホラン、ジメチルホルムアミド、ジメチルアセトアミド、Ｎ－メチル－２－ピロリドン等を使用することができる。 As the organic solvent, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, γ-butyrolactone, tetrahydrofuran, dioxolane, sulfolane, dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone, etc. are used. be able to.
　このように本実施の形態によれば、上述した微粒で高純度のＬｉＦｅＰＯ４を正極活物質の主体として使用しているので、大容量・高出力で安全性にも優れた二次電池を低コストで実現することが可能となる。 As described above, according to the present embodiment, the above-described fine and high-purity LiFePO 4 is used as the main component of the positive electrode active material, so that the secondary battery having a large capacity, high output, and excellent safety can be reduced. It can be realized at a cost.
　尚、本発明は上記実施の形態に限定されるものではない。例えば、上記実施の形態では、リチウム水酸化物は、ＬｉＯＨ・Ｈ２Ｏで表される水和物を例示して説明したが、無水物であってもよい。 The present invention is not limited to the above embodiment. For example, in the above-described embodiment, the lithium hydroxide is exemplified by a hydrate represented by LiOH.H 2 O, but may be an anhydride.
　また、上記実施の形態では、ＬｉＯＨ・Ｈ２Ｏを純水に溶解させて強アルカリ性にしているが、強アルカリ性の水溶液に調製できるのであれば、純水以外の溶媒を使用してもよい。 In the above embodiment, LiOH · H 2 O is dissolved in pure water to make it strongly alkaline. However, a solvent other than pure water may be used as long as it can be prepared into a strongly alkaline aqueous solution.
　また、上記実施の形態では、ＦｅＰＯ４の製造過程において、２価のＦｅ化合物と酸化剤とを混合させることにより、２価のＦｅを３価のＦｅも酸化させて３価のＦｅ化合物を得ているが、当初から３価のＦｅ化合物を使用し、緩衝溶液に滴下して接触させてもよく、この場合のＦｅ化合物としては、例えばＦｅＣｌ３・６Ｈ２Ｏ等を使用することができる。 In the above embodiment, in the production process of FePO 4 , a divalent Fe compound and an oxidizing agent are mixed to oxidize divalent Fe to trivalent Fe to obtain a trivalent Fe compound. However, a trivalent Fe compound may be used from the beginning and dropped into the buffer solution to be brought into contact. For example, FeCl 3 .6H 2 O can be used as the Fe compound in this case.
　また、上記実施の形態では、コイン型二次電池について説明したが、電池形状は特に限定されるものでないのはいうまでもなく、円筒型、角型、シート型等にも適用できる。また、外装方法も特に限定されず、金属ケースや、モールド樹脂、アルミラミネートフイルム等を使用してもよい。 In the above embodiment, the coin-type secondary battery has been described. However, it is needless to say that the battery shape is not particularly limited, and can be applied to a cylindrical type, a square type, a sheet type, and the like. Also, the exterior method is not particularly limited, and a metal case, mold resin, aluminum laminate film, or the like may be used.
　次に、本発明の実施例を具体的に説明する。 Next, specific examples of the present invention will be described.
〔試料の作製〕
　ＦｅＳＯ４・７Ｈ２Ｏを純水に溶解させ、これにＰ源としてのＨ３ＰＯ４（８５％水溶液）と酸化剤としてのＨ２Ｏ２（３０％水溶液）を加えた混合水溶液を作製した。ここで、ＦｅＳＯ４・７Ｈ２Ｏ、Ｈ３ＰＯ４、及びＨ２Ｏ２はモル比率で１:１：１．５となるように調合した。 [Sample preparation]
FeSO 4 · 7H 2 O was dissolved in pure water, and a mixed aqueous solution was prepared by adding H 3 PO 4 (85% aqueous solution) as a P source and H 2 O 2 (30% aqueous solution) as an oxidizing agent. . Here, FeSO 4 · 7H 2 O, H 3 PO 4 , and H 2 O 2 were prepared so as to have a molar ratio of 1: 1: 1.5.
　次に、酢酸に純水を加え、これに酢酸アンモニウムを溶かすことで緩衝溶液を作製した。尚、酢酸と酢酸アンモニウムのモル比は１:１であり、酢酸及び酢酸アンモニウムの濃度は、いずれも０．５mol／Ｌとした。この緩衝溶液のｐＨを測定したところ、４．６であった。 Next, pure water was added to acetic acid, and ammonium acetate was dissolved therein to prepare a buffer solution. The molar ratio of acetic acid to ammonium acetate was 1: 1, and the concentrations of acetic acid and ammonium acetate were both 0.5 mol / L. The pH of this buffer solution was measured and found to be 4.6.
　次いで、この緩衝溶液を常温で撹拌しながら、前記混合水溶液を緩衝溶液に滴下し、沈殿粉末を作製した。尚、混合水溶液の滴下量が増加するに伴い、緩衝溶液のｐＨは低下し、ｐＨが２．０になった時点で混合水溶液の緩衝溶液への滴下を終了した。 Next, the mixed aqueous solution was dropped into the buffer solution while stirring the buffer solution at room temperature to prepare a precipitated powder. As the amount of the mixed aqueous solution dropped, the pH of the buffer solution decreased, and when the pH reached 2.0, the dropping of the mixed aqueous solution into the buffer solution was terminated.
　次いで、得られた沈殿粉末をろ過し、大量の純水で洗浄した後、１２０℃の温度に加熱し、乾燥させ、褐色のＦｅＰＯ４・２Ｈ２Ｏの粉末を作製した。 Then filtered and the precipitate powder obtained was washed with a large amount of pure water, and heated to a temperature of 120 ° C., dried to prepare a powder of the FePO 4 · 2H 2 O brown.
　次に、このＦｅＰＯ４・２Ｈ２Ｏの粉末とＬｉＯＨ・Ｈ２Ｏ（水酸化リチウム・一水和物）とをモル比で１：１となるように調合し、さらに焼成後のＬｉＦｅＰＯ４：１００重量部に対して７重量部となるように、カーボン源としてのスクロースを秤量し、これらに純水とポリカルボン酸系高分子分散剤とを添加し、ボールミルを使用して混合粉砕し、スラリーを得た。次いで得られたスラリーをスプレードライヤで乾燥した後、造粒し、Ｈ２－Ｈ２Ｏの混合ガスを使用して酸素分圧が１０-20ＭＰａの還元雰囲気に調整し、６００℃の温度で５時間、熱処理し、実施例試料を作製した。 Next, this FePO 4 .2H 2 O powder and LiOH.H 2 O (lithium hydroxide monohydrate) were mixed at a molar ratio of 1: 1, and further calcined LiFePO 4 : Weigh sucrose as a carbon source so that it becomes 7 parts by weight with respect to 100 parts by weight, add pure water and a polycarboxylic acid polymer dispersant to these, mix and grind using a ball mill, A slurry was obtained. Next, the obtained slurry was dried with a spray dryer, granulated, adjusted to a reducing atmosphere having an oxygen partial pressure of 10 −20 MPa using a mixed gas of H 2 —H 2 O, and at a temperature of 600 ° C. A heat treatment was performed for 5 hours to prepare an example sample.
　また、Ｌｉ源として、ＬｉＯＨ・Ｈ２Ｏの代わりにＬｉ２ＣＯ３を使用した以外は、実施例試料と同様の方法・手順で比較例試料を作製した。 Further, as the Li source, except for using Li 2 CO 3 in place of LiOH · H 2 O, was prepared Comparative Sample in a similar manner and procedure as example samples.
〔試料の評価〕
　実施例及び比較例の各試料について、Ｘ線回折装置を使用してＸ線回折スペクトルを測定し、構成相を同定した。 (Sample evaluation)
About each sample of an Example and a comparative example, the X-ray-diffraction spectrum was measured using the X-ray-diffraction apparatus, and the constituent phase was identified.
　図２はその測定結果を示す。横軸が回折角２θ（°）、縦軸はＸ線強度（a.u.）である。図中、○印がＬｉＦｅＰＯ４の発生点を示し、△印はＦｅ２Ｏ３の発生点を示し、×印はＬｉ３ＰＯ４の発生点を示している。 FIG. 2 shows the measurement results. The horizontal axis is the diffraction angle 2θ (°), and the vertical axis is the X-ray intensity (au). In the figure, a circle mark indicates the generation point of LiFePO 4 , a triangle mark indicates the generation point of Fe 2 O 3 , and a cross mark indicates the generation point of Li 3 PO 4 .
　この図２から明らかなように、比較例試料は、ＬｉＦｅＰＯ４の他、Ｆｅ２Ｏ３やＬｉ３ＰＯ４のような異相が形成されているのに対し、実施例試料は、これらの異相が形成されず、ＬｉＦｅＰＯ４の単相粉末となっており、高純度のＬｉＦｅＰＯ４が得られることが分かった。 As apparent from FIG. 2, the comparative example sample has different phases such as Fe 2 O 3 and Li 3 PO 4 in addition to LiFePO 4 , whereas the example sample has these different phases. not formed, has a single-phase powder of LiFePO 4, it was found that the high purity LiFePO 4 can be obtained.
　次いで、実施例試料について、ＣＳ計でカーボン量を測定し、さらにＢＥＴ法で比表面積を求めた。 Next, for the example samples, the amount of carbon was measured with a CS meter, and the specific surface area was determined by the BET method.
　表１は、実施例及び比較例の各試料のＬｉ源、構成相、カーボン量、及び比表面積を示している。 Table 1 shows the Li source, constituent phase, carbon amount, and specific surface area of each sample of the examples and comparative examples.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
　この表１から明らかなように、実施例試料の比表面積は３２．１５ｍ２／ｇと大きく、微細なＬｉＦｅＰＯ４が得られることが分かった。 As apparent from Table 1, the specific surface area of the example sample was as large as 32.15 m 2 / g, and it was found that fine LiFePO 4 was obtained.
　図３は原料に使用したＦｅＰＯ４・２Ｈ２ＯのＳＥＭ像、図４は実施例試料の乾燥後のＳＥＭ像、図５は実施例試料の焼成後のＳＥＭ像であり、いずれも同一倍率で撮像している。 3 is an SEM image of FePO 4 · 2H 2 O used as a raw material, FIG. 4 is an SEM image after drying of the example sample, and FIG. 5 is an SEM image after firing of the example sample, both at the same magnification. I'm shooting.
　図３及び図４の対比から明らかなように、原料段階に比べ、乾燥後には粒子が極めて微粒化していることが分かる。 As is clear from the comparison between FIG. 3 and FIG. 4, it can be seen that the particles are extremely fine after drying compared to the raw material stage.
　そして、図４及び図５から明らかなように、実施例試料は、焼成前の乾燥時点で既に粒径が５０ｎｍ程度の微細な粒子が形成され、焼成後も微粒状態を維持することが分かった。 As can be seen from FIGS. 4 and 5, it was found that in the example sample, fine particles having a particle size of about 50 nm were already formed at the time of drying before firing, and the fine particle state was maintained after firing. .
〔二次電池の作製〕
　実施例試料を使用して二次電池を作製した。 [Production of secondary battery]
A secondary battery was fabricated using the example sample.
　まず、ＬｉＦｅＰＯ４、導電補助剤としてのアセチレンブラック、結着剤としてのポリフッ化ビニリデンを用意し、これらＬｉＦｅＰＯ４、アセチレンブラック、及びポリフッ化ビニリデンが、重量比で８８：６：６となるように秤量して混合し、これを溶媒としてのＮ-メチル-２-ピロリドン中に分散させてスラリーを作製し、これを厚さ２０μｍのアルミ箔上に６ｍｇ／ｃｍ２となるように塗布し、１４０℃の温度で乾燥した後、９８ＭＰａの圧力でプレスし、これにより電極シートを作製し、さらに直径１２ｍｍに打ち抜き、ＬｉＦｅＰＯ４を主体とする正極活物質を有する正極を作製した。 First, LiFePO 4 , acetylene black as a conductive auxiliary agent, and polyvinylidene fluoride as a binder are prepared. The weight ratio of these LiFePO 4 , acetylene black, and polyvinylidene fluoride is 88: 6: 6. Weigh and mix, and disperse this in N-methyl-2-pyrrolidone as a solvent to prepare a slurry, which is applied onto an aluminum foil having a thickness of 20 μm so as to be 6 mg / cm 2. After drying at a temperature of ° C., pressing was performed at a pressure of 98 MPa, thereby producing an electrode sheet, and punching out to a diameter of 12 mm to produce a positive electrode having a positive electrode active material mainly composed of LiFePO 4 .
　次に、この正極を電解液に含浸し、該正極中の空隙に電解液を染み込ませた。電解液としては、モル濃度が１．０mol／ＬのＬｉＰＦ６（電解質塩）を含有した有機溶剤であるエチレンカーボネート／ジエチルカーボネート混合溶液を使用した。尚、エチレンカーボネートとジエチルカーボネートの混合比率は体積％でエチレンカーボネート：ジエチルカーボネート＝３：７とした。 Next, the positive electrode was impregnated with an electrolytic solution, and the electrolytic solution was infiltrated into voids in the positive electrode. As the electrolytic solution, an ethylene carbonate / diethyl carbonate mixed solution, which is an organic solvent containing LiPF 6 (electrolyte salt) having a molar concentration of 1.0 mol / L, was used. In addition, the mixing ratio of ethylene carbonate and diethyl carbonate was ethylene carbonate: diethyl carbonate = 3: 7 by volume%.
　次に、この正極を正極集電体上に載置し、さらに前記電解液を含浸させたポリプロピレン多孔質フイルムからなる厚さ２０μｍのセパレータを前記正極上に積層し、さらに銅箔の両面にリチウムを貼布した負極をセパレータ上に積層した。そして、負極上にＣｕ製の負極集電体を積層した後、内部空間に電解液を注入し、その後負極集電体上に金属製ばねを載置すると共に、周縁にガスケットを配置した状態で負極ケースを正極ケースに接合し、かしめ機によって外装封止し、これにより、正極活物質としてＬｉＦＰＯ４、負極活物質として金属リチウムを有する直径２０ｍｍ、厚さ３．２ｍｍの二次電池を作製した。 Next, this positive electrode was placed on a positive electrode current collector, and a separator having a thickness of 20 μm made of a polypropylene porous film impregnated with the electrolytic solution was laminated on the positive electrode. The negative electrode to which was attached was laminated on the separator. And after laminating | stacking the negative electrode collector made from Cu on a negative electrode, inject | pouring electrolyte solution into interior space, and mounting a metal spring on a negative electrode collector after that, and having arrange | positioned the gasket to the periphery The negative electrode case was joined to the positive electrode case and sealed with a caulking machine, thereby producing a secondary battery having a diameter of 20 mm and a thickness of 3.2 mm having LiFPO 4 as the positive electrode active material and metallic lithium as the negative electrode active material. .
〔二次電池の動作確認〕
　この二次電池を、２５℃の恒温槽内で、電圧範囲を２．０～４．２Ｖとし、充放電レートを０．２Ｃ(１Ｃは１時間で充電又は放電が終了するまでの電流量)として充放電させた。すなわち、充電レート０．２Ｃで電圧が４．２Ｖになるまで充電し、その後、放電レート０．２Ｃで２．０Ｖまで放電した。 [Confirmation of secondary battery operation]
This secondary battery has a voltage range of 2.0 to 4.2 V in a thermostat at 25 ° C. and a charge / discharge rate of 0.2 C (1 C is the amount of current until charging or discharging is completed in one hour) As a charge and discharge. That is, the battery was charged until the voltage reached 4.2 V at a charge rate of 0.2 C, and then discharged to 2.0 V at a discharge rate of 0.2 C.
　図６はその測定結果を示し、横軸が容量密度（ｍＡｈ／ｇ）、縦軸は電圧（Ｖ）である。 FIG. 6 shows the measurement results, with the horizontal axis representing capacity density (mAh / g) and the vertical axis representing voltage (V).
　この図６に示すように、充放電電圧が約３．４Ｖで電圧平坦部を有する二次電池であることが確認された。 As shown in FIG. 6, it was confirmed that the secondary battery had a voltage flat portion with a charge / discharge voltage of about 3.4V.
　そして、放電容量から電極活物質当たりの容量密度を算出したところ、１５４ｍＡｈ／ｇの高容量が得られることが分かった。 And when the capacity density per electrode active material was calculated from the discharge capacity, it was found that a high capacity of 154 mAh / g was obtained.
　簡素な製造工程で二次電池用電極活物質に適した微粒で高純度のリン酸鉄リチウムを容易に製造できる。 It is possible to easily produce fine and high-purity lithium iron phosphate suitable for an electrode active material for a secondary battery with a simple manufacturing process.
４　正極
６　負極
９　電解質 4 Positive electrode 6 Negative electrode 9 Electrolyte

Claims (7)

  1. 　リン酸鉄（III）とリチウム水酸化物とを湿式で混合した後、焼成処理を行ってリン酸鉄リチウムの粉末を合成することを特徴とするリン酸鉄リチウムの製造方法。 A method for producing lithium iron phosphate, comprising mixing iron (III) phosphate and lithium hydroxide in a wet manner and then performing a baking treatment to synthesize a powder of lithium iron phosphate.
  2. 　前記リチウム水酸化物が強アルカリ性を有するような水溶液下で、前記リチウム水酸化物と前記リン酸鉄（III）とを混合させることを特徴とする請求項１記載のリン酸鉄リチウムの製造方法。 The method for producing lithium iron phosphate according to claim 1, wherein the lithium hydroxide and the iron (III) phosphate are mixed in an aqueous solution in which the lithium hydroxide has strong alkalinity. .
  3. 　前記リン酸鉄（III）は水和水を含有していることを特徴とする請求項１又は請求項２記載のリン酸鉄リチウムの製造方法。 3. The method for producing lithium iron phosphate according to claim 1, wherein the iron (III) phosphate contains hydration water.
  4. 　前記リン酸鉄（III）は、リン源と３価の鉄を含有した鉄化合物とを反応させて合成することを特徴とする請求項１乃至請求項３のいずれかに記載のリン酸鉄リチウムの製造方法。 4. The lithium iron phosphate according to claim 1, wherein the iron (III) phosphate is synthesized by reacting a phosphorus source with an iron compound containing trivalent iron. 5. Manufacturing method.
  5. 　前記リン酸鉄は、リン源と前記鉄化合物とを溶解させた混合水溶液をｐＨが１．５～９の緩衝溶液に接触させて生成することを特徴とする請求項４記載のリン酸鉄リチウムの製造方法。 5. The lithium iron phosphate according to claim 4, wherein the iron phosphate is produced by bringing a mixed aqueous solution in which a phosphorus source and the iron compound are dissolved into contact with a buffer solution having a pH of 1.5 to 9. Manufacturing method.
  6. 　電池電極反応によって充放電を繰り返す二次電池の活物質として使用される電極活物質であって、
    　請求項１乃至請求項５のいずれかに記載の方法で製造されたリン酸鉄リチウムを主体としていることを特徴とする電極活物質。     An electrode active material used as an active material of a secondary battery that repeats charging and discharging by a battery electrode reaction,
    An electrode active material mainly comprising lithium iron phosphate produced by the method according to any one of claims 1 to 5.
  7. 　正極、負極、及び電解質を有し、前記正極が、請求項６記載の電極活物質を含むことを特徴とする二次電池。 A secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode includes the electrode active material according to claim 6.
PCT/JP2012/069317 2011-08-03 2012-07-30 Method for producing iron lithium phosphate, electrode active substance, and secondary battery WO2013018757A1 (en)

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