JP2008004317A - Manufacturing method of iron lithium phosphate for battery and battery using it - Google Patents
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Abstract
Description
本発明は、電池用活物質として用いることのできるリン酸鉄リチウムの製造方法、及び、これを用いた電池に関する。 The present invention relates to a method for producing lithium iron phosphate that can be used as an active material for a battery, and a battery using the same.
近年、携帯電話、ノートパソコン等の携帯機器類用、電気自動車用などの電源としてエネルギー密度が高く、かつ自己放電が少なくてサイクル特性の良い非水二次電池が注目されている。 In recent years, non-aqueous secondary batteries having high energy density, low self-discharge and good cycle characteristics have attracted attention as power sources for portable devices such as mobile phones and notebook computers and electric vehicles.
このような非水二次電池の中で、現在最も広く市場に出回っているのがリチウム二次電池である。リチウム二次電池の主流としては、2Ah未満の携帯電話用を中心とした小型民生用である。現在、リチウム二次電池用の正極活物質としては数多くのものが存在するが、最も一般的に知られているのは、作動電圧が4V付近のリチウムコバルト酸化物(LiCoO2)やリチウムニッケル酸化物(LiNiO2)、又はスピネル構造を持つリチウムマンガン酸化物(LiMn2O4)等を基本構成とするリチウム含有遷移金属酸化物である。中でもリチウムコバルト酸化物は、電池容量2Ahまでの小容量リチウム二次電池では、充放電特性とエネルギー密度に優れることから正極活物質として広く採用されている。 Among such non-aqueous secondary batteries, lithium secondary batteries are currently most widely on the market. The mainstream of lithium secondary batteries is for small-sized consumer use, mainly for mobile phones of less than 2 Ah. Currently, there are many positive electrode active materials for lithium secondary batteries, but the most commonly known positive electrode active materials include lithium cobalt oxide (LiCoO 2 ) and lithium nickel oxide whose operating voltage is around 4V. It is a lithium-containing transition metal oxide having a basic structure of an oxide (LiNiO 2 ) or a lithium manganese oxide (LiMn 2 O 4 ) having a spinel structure. Among them, lithium cobalt oxide is widely adopted as a positive electrode active material in a small-capacity lithium secondary battery up to a battery capacity of 2 Ah because of its excellent charge / discharge characteristics and energy density.
しかしながら、今後の中型・大型、特に大きな需要が見込まれる産業用途への展開を考えた場合、電池の安全性が非常に重要視されるため、現在の小型電池の仕様では要求される安全性を満足することができない。この要因の一つに、4V級正極活物質の熱的不安定性が挙げられ、様々な対策が成されてきたが、未だ十分な電池の安全性は得られていない。また、産業用途では電池が小型民生用では使用されないような高温環境において活用される用途も存在する。このような高温環境では、リチウムイオン二次電池はもとより、ニッケル−カドミ電池や鉛電池も非常に短寿命であり、電池としてユーザーの要求を満足するものは存在しないのが現状である。また、唯一この温度領域で使用できるキャパシターもエネルギー密度が小さく、ユーザーの要求を満足するものではなく、高温長寿命でエネルギー密度の高い電池が求められている。 However, considering the future development of medium-sized and large-sized products, especially industrial applications where large demand is expected, the safety of batteries is very important. I can't be satisfied. One of the factors is the thermal instability of the 4V class positive electrode active material, and various measures have been taken, but sufficient battery safety has not been obtained yet. In industrial applications, there are also applications that are used in high temperature environments where batteries are not used in small consumer applications. In such a high temperature environment, not only lithium ion secondary batteries but also nickel-cadmium batteries and lead batteries have a very short life, and there are currently no batteries that satisfy user requirements. The only capacitor that can be used in this temperature range has a low energy density and does not satisfy the user's requirements, and a battery having a high temperature and a long life and a high energy density is required.
そこで最近、熱安定性が優れるオリビン構造を有するリン酸鉄リチウム(LiFePO4)が注目を集めている。このオリビン構造を有するLiFePO4はリンと酸素が共有結合しているため、高温においても酸素を放出することが無く、電池用活物質として使用することで電池の安全性を飛躍的に高めることができると推察される。さらに、Liイオンの吸蔵・放出が3.4V付近で行われることから、電池の正極に用いた場合に生じる副反応量を抑えることができるため電池の長寿命化が期待できる。 Therefore, recently, lithium iron phosphate (LiFePO 4 ) having an olivine structure with excellent thermal stability has attracted attention. Since LiFePO 4 having this olivine structure is covalently bonded to phosphorus and oxygen, it does not release oxygen even at high temperatures, and it can dramatically improve battery safety when used as a battery active material. It is assumed that it can be done. Furthermore, since the insertion / extraction of Li ions is performed at around 3.4 V, the amount of side reaction that occurs when used for the positive electrode of the battery can be suppressed, so that the life of the battery can be expected to be extended.
オリビン構造を有するリン酸鉄リチウム(LiFePO4)の合成方法としては、溶液中から合成する水熱法もあるが、装置が大がかりなものとなる問題がある。これに対して、原料の粉体を混合して乾式で焼成を行う固相法を採用すれば、極めて簡便な製造装置で合成が可能となる。リン酸鉄リチウムを固相法で構成する方法としては、シュウ酸鉄、酢酸鉄といった2価の鉄原料を用いる方法が一般的である(例えば、特許文献1参照)。しかし、これら2価の鉄原料は、高価なうえ、化学的に不安定であり取り扱いが難しいという問題があった。 As a method of synthesizing lithium iron phosphate (LiFePO 4 ) having an olivine structure, there is a hydrothermal method of synthesizing from a solution, but there is a problem that the apparatus becomes large. On the other hand, if a solid phase method in which raw material powders are mixed and fired dry is used, synthesis can be performed with a very simple manufacturing apparatus. As a method for constituting lithium iron phosphate by a solid phase method, a method using a divalent iron raw material such as iron oxalate or iron acetate is generally used (for example, see Patent Document 1). However, these divalent iron materials are expensive and chemically unstable and difficult to handle.
そこで、鉄原料として金属鉄粉のみを用いて直接リン酸鉄リチウムを合成することができれば、安価な製造方法が提供できると本発明者らは考えた。しかしながら、実際には、鉄粒子の表面は反応に寄与するものの、リン酸源やリチウム源が鉄粒子の内部にまで拡散せず、鉄の融点(鉄の融点は約1530℃である)付近にまで温度を上げない限り、固相反応は殆ど進行しなかった。鉄の融点付近まで焼成炉の温度を上げるにはエネルギーコストが嵩む上、鉄の融点付近まで温度を上げて合成したリン酸鉄リチウムは、大きな塊状となって得られ、そのままでは電極化すら難しく、長時間の粉砕が必要となるといった問題があり、実用化できる方法ではなかった。なお、特許文献2〜5記載の方法は、原料に金属鉄を用いているが、金属鉄を一旦リン酸水溶液に溶解させてリン酸鉄化合物を得た後、特許文献1の場合と同様、これを焼成してリン酸鉄リチウムを合成する方法である。また、非特許文献1には、金属鉄からFe(III)PO4を合成する方法が記載されているが、FePO4の結晶構造はLiFePO4とは全く異なり、非特許文献1記載の方法によって得られたFePO4からLiFePO4を得るためには別途反応工程を設ける必要があった。 Therefore, the present inventors considered that if lithium iron phosphate can be directly synthesized using only metallic iron powder as an iron raw material, an inexpensive production method can be provided. However, in practice, although the surface of the iron particles contributes to the reaction, the phosphoric acid source and the lithium source do not diffuse into the iron particles, and near the melting point of iron (the melting point of iron is about 1530 ° C.). The solid-phase reaction hardly proceeded unless the temperature was raised to. In order to raise the temperature of the firing furnace to near the melting point of iron, energy costs increase, and lithium iron phosphate synthesized by raising the temperature to near the melting point of iron is obtained as a large lump, and as it is, it is difficult to make an electrode However, there is a problem that pulverization for a long time is required, and the method cannot be put into practical use. In addition, although the method of patent documents 2-5 uses metallic iron as a raw material, after dissolving metallic iron in phosphoric acid aqueous solution once and obtaining an iron phosphate compound, as in the case of patent documents 1, This is a method of baking this to synthesize lithium iron phosphate. Non-Patent Document 1 describes a method of synthesizing Fe (III) PO4 from metallic iron. However, the crystal structure of FePO 4 is completely different from LiFePO 4 and is obtained by the method described in Non-Patent Document 1. In order to obtain LiFePO 4 from the obtained FePO 4, it was necessary to provide a separate reaction step.
特許文献6、7には、金属鉄と3価の酸化鉄とリン酸化合物とリチウム化合物を固相法で焼成してテルミット還元法によりリン酸鉄リチウムを得る方法が開示されている。しかしながら、この方法では、原料に起因する3価の鉄成分が生成物中に残存し、電池性能に影響を与える虞があった。本発明者らの検討によれば、この方法において3価の鉄成分を実質含まないものとするには、1000℃近くまでの昇温が必要であった。 Patent Documents 6 and 7 disclose a method in which metallic iron, trivalent iron oxide, a phosphoric acid compound, and a lithium compound are baked by a solid phase method to obtain lithium iron phosphate by a thermite reduction method. However, in this method, the trivalent iron component resulting from the raw material remains in the product, which may affect the battery performance. According to the study by the present inventors, it was necessary to raise the temperature to nearly 1000 ° C. in order to make the method essentially free of a trivalent iron component.
鉄原料として金属鉄のみを原料に用いて、電池用活物質として実用的な性能を有したリン酸鉄リチウムを直接合成する方法が求められていた。
本発明は、かかる問題点に鑑みてなされたものであり、鉄原料として金属鉄のみを用いて、鉄の融解温度まで上昇させることなく、電池用活物質として用いうるリン酸鉄リチウムを直接合成することを目的としている。なお、本発明者らは、微細な粒径の金属鉄粉を用いると合成反応の進行が期待できるとも考えたが、微細な粒径の金属鉄粉はコストが嵩むうえ、大気中での発火の危険性が増大するため取り扱いが難しくなるといった問題があった。 The present invention has been made in view of such problems, and uses only metallic iron as an iron raw material, and directly synthesizes lithium iron phosphate that can be used as an active material for batteries without increasing the melting temperature of iron. The purpose is to do. In addition, although the present inventors thought that the progress of the synthesis reaction can be expected when the metal iron powder having a fine particle size is used, the metal iron powder having a fine particle size is expensive and is ignited in the atmosphere. There has been a problem that handling becomes difficult due to an increase in the risk of the problem.
本発明者らは、見掛け密度の小さい金属鉄粉を用いることにより、上記課題が解決できることを見いだし本発明に至った。本発明の構成は次の通りである。但し、作用機構は推定を含むものであり、その正否は本発明を何ら制限するものではない。
(1)見掛け密度が2g・cm-3以下である鉄粉と、リン酸化合物と、リチウム化合物と、を含む混合物を焼成する工程を含む電池用リン酸鉄リチウムの製造方法。
(2)前記鉄粉は、平均粒径が20μm〜150μmである前記(1)記載の電池用リン酸鉄リチウムの製造方法。
(3)前記(1)又は(2)記載の電池用リン酸鉄リチウムの製造方法によって製造された電池用リン酸鉄リチウムを用いた電池。
The present inventors have found that the above problems can be solved by using metallic iron powder having a small apparent density, and have reached the present invention. The configuration of the present invention is as follows. However, the action mechanism includes estimation, and its correctness does not limit the present invention.
(1) A method for producing lithium iron phosphate for a battery, comprising a step of firing a mixture containing iron powder having an apparent density of 2 g · cm −3 or less, a phosphate compound, and a lithium compound.
(2) The said iron powder is a manufacturing method of the lithium iron phosphate for batteries as described in said (1) whose average particle diameter is 20 micrometers-150 micrometers.
(3) A battery using lithium iron phosphate for batteries produced by the method for producing lithium iron phosphate for batteries according to (1) or (2).
鉄粉の見かけ密度はJIS Z2504によって測定されるものとする。見掛け密度が小さいことは鉄粒子の中に空洞が存在することを示している。この空洞が存在することにより、粒子内部までリン酸源、リチウム源が拡散できるようになり固相反応が進行しやすくなったと推察される。従って、微細粒子の鉄粉を用いる必要がなく、平均粒径が20μm以上の鉄粉を用いて、リン酸鉄リチウムの合成反応の進行を十分なものとすることができる。 The apparent density of iron powder shall be measured according to JIS Z2504. A small apparent density indicates the presence of cavities in the iron particles. It is assumed that the presence of these cavities allowed the phosphoric acid source and the lithium source to diffuse into the interior of the particles and facilitated the solid-phase reaction. Therefore, it is not necessary to use fine iron powder, and the progress of the synthesis reaction of lithium iron phosphate can be made sufficiently by using iron powder having an average particle diameter of 20 μm or more.
但し、平均粒径が150μmを超えると鉄粒子内部への拡散距離が長すぎるため固相反応が進みにくくなってしまうので鉄粉の粒径は150μm以下であることが好ましい。また、平均粒径が150μm以下であっても、その中に存在する150μm以上の粒径のものに関しては殆ど反応が望めないため、150μm以上の粒子は少ない方が好ましく、5%以下であることが好ましい。ここで、鉄粉の平均粒径はレーザー回折(Mie散乱理論)法によって測定されるものとする。 However, if the average particle size exceeds 150 μm, the diffusion distance to the inside of the iron particles is too long, so that the solid phase reaction is difficult to proceed. Therefore, the particle size of the iron powder is preferably 150 μm or less. Also, even if the average particle size is 150 μm or less, almost no reaction can be expected with respect to those having a particle size of 150 μm or more, and therefore it is preferable that the number of particles of 150 μm or more is less, and 5% or less Is preferred. Here, the average particle diameter of the iron powder is measured by a laser diffraction (Mie scattering theory) method.
本発明によれば、鉄原料として金属鉄のみを用いて、鉄の融解温度まで上昇させることなく、電池用リン酸鉄リチウムを製造することができる。 According to the present invention, lithium iron phosphate for batteries can be produced using only metallic iron as an iron raw material without increasing the melting temperature of iron.
鉄粉は、金属材料製造業者から種々の見掛け密度のものが提供されており、比較的嵩密度の低い鉄粉は、現在では使い捨てカイロ用等に用いられているので、所望の見掛け密度を有する鉄粉を入手でき、本発明のリン酸鉄リチウムの製造方法における鉄原料として用いることができる。本発明の製造方法に用いることのできる鉄粉の見掛け密度は小さければ小さいほど反応性が向上するため好ましい。現在の技術で生産可能な最も小さい見掛け密度の鉄粉を用いることができる。 Iron powder is available in various apparent densities from metal material manufacturers, and iron powder with relatively low bulk density is currently used for disposable body warmers, etc., and therefore has a desired apparent density. Iron powder can be obtained and used as an iron raw material in the method for producing lithium iron phosphate of the present invention. The smaller the apparent density of the iron powder that can be used in the production method of the present invention is, the better the reactivity is. The smallest apparent density iron powder that can be produced with current technology can be used.
本発明のリン酸鉄リチウムの製造方法における原料としてのリン酸源としては、リン酸二水素アンモニウム、リン酸水素二アンモニウム等のリン酸水素アンモニウム、あるいはリン酸、リン酸水素リチウム、リン酸鉄等を用いることができる。なかでも、取り扱いの容易なリン酸水素アンモニウム塩が好ましい。 As a phosphoric acid source as a raw material in the method for producing lithium iron phosphate of the present invention, ammonium hydrogen phosphate such as ammonium dihydrogen phosphate and diammonium hydrogen phosphate, or phosphoric acid, lithium hydrogen phosphate, iron phosphate Etc. can be used. Of these, ammonium hydrogen phosphate which is easy to handle is preferable.
本発明のリン酸鉄リチウムの製造方法における原料としてのリチウム源としては、酢酸リチウム、シュウ酸リチウム等のリチウム有機酸塩、炭酸リチウム、水酸化リチウムなどのリチウム無機酸塩が挙げられる。なかでも、吸水性が小さく、取り扱いの容易な炭酸リチウムが好ましい。 Examples of the lithium source as a raw material in the method for producing lithium iron phosphate of the present invention include lithium organic acid salts such as lithium acetate and lithium oxalate, and lithium inorganic acid salts such as lithium carbonate and lithium hydroxide. Of these, lithium carbonate, which has low water absorption and is easy to handle, is preferable.
また、本発明のリン酸鉄リチウムの製造方法における原料として、リン酸水素リチウムやリン酸リチウム等のリン酸源とリチウム源とが共存したリン酸塩も使用可能である。 Further, as a raw material in the method for producing lithium iron phosphate of the present invention, a phosphate in which a phosphate source and a lithium source such as lithium hydrogen phosphate and lithium phosphate coexist can also be used.
焼成温度は、500℃以上1400℃以下が好ましい。500℃以上とすることにより、金属鉄とリン酸源、リチウム源との反応を十分に行わせることができる。また、1400℃以下とすることにより、鉄が溶融することを避けることができる。鉄が融解すると、得られるリン酸鉄リチウムが大きな塊となってしまい、新たに粉砕工程が必要となるため好ましくない。 The firing temperature is preferably 500 ° C. or higher and 1400 ° C. or lower. By making it 500 degreeC or more, reaction with metallic iron, a phosphoric acid source, and a lithium source can fully be performed. Moreover, it can avoid melting iron by setting it as 1400 degrees C or less. When iron melts, the resulting lithium iron phosphate becomes a large lump, which is not preferable because a new pulverization step is required.
焼成時間は金属鉄とリン酸源、リチウム源との反応を十分に進行させるため1時間以上100時間以下で行うことが好ましい。 The firing time is preferably 1 hour or more and 100 hours or less in order to sufficiently advance the reaction between metallic iron, phosphate source and lithium source.
焼成はアルゴン、窒素などの不活性雰囲気下で行うことが好ましい。特に、コストの面から窒素が有効である。 Firing is preferably performed in an inert atmosphere such as argon or nitrogen. In particular, nitrogen is effective in terms of cost.
以下に、本発明の実施の形態を例示するが、本発明は、以下の実施の形態に限定されるものではない。 Embodiments of the present invention will be exemplified below, but the present invention is not limited to the following embodiments.
(実施例1)
(LiFePO4の作製)
金属鉄粉A(JFEスチール社製、品番:JIP KB−90、見掛け密度1.91g・cm-3、平均粒径73.2μm、150μm以上の粒子比率0.3%)とリン酸二水素アンモニウム(NH4H2PO4)と炭酸リチウム(Li2CO3)とをモル比が2:2:1になるように計り取り、混合した。その後、エタノールを溶媒としてボールミルで2時間湿式粉砕混合を行うことで原料混合粉を得た。
(Example 1)
(Production of LiFePO 4 )
Metallic iron powder A (manufactured by JFE Steel, product number: JIP KB-90, apparent density 1.91 g · cm −3 , average particle size 73.2 μm, particle ratio 0.3% of 150 μm or more) and ammonium dihydrogen phosphate (NH 4 H 2 PO 4 ) and lithium carbonate (Li 2 CO 3 ) were weighed out and mixed so that the molar ratio was 2: 2: 1. Then, raw material mixed powder was obtained by performing wet grinding and mixing for 2 hours with a ball mill using ethanol as a solvent.
得られた原料混合粉約22g(未乾燥エタノール含む)をアルミナ製の匣鉢(外形寸法90×90×50mm)に入れ、雰囲気置換式焼成炉(デンケン社製卓上真空ガス置換炉KDF−75)にて窒素雰囲気下で焼成を行った。窒素流量は2リットル/分とした。焼成温度は700℃とし、焼成時間(前記焼成温度を維持する時間)は5時間とした。なお、昇温速度は5℃/分、降温は自然放冷とした。このようにしてリン酸鉄リチウムを作製した。 About 22 g of the obtained raw material mixed powder (including undried ethanol) was placed in an alumina sagger (outside dimension 90 × 90 × 50 mm), and an atmosphere substitution type firing furnace (Denken desktop vacuum gas substitution furnace KDF-75) Was fired in a nitrogen atmosphere. The nitrogen flow rate was 2 liters / minute. The firing temperature was 700 ° C., and the firing time (time for maintaining the firing temperature) was 5 hours. The rate of temperature increase was 5 ° C./minute, and the temperature was naturally cooled. In this way, lithium iron phosphate was produced.
(比較例1)
金属鉄粉Aに代えて、金属鉄粉B(神戸製鋼社製、純鉄粉、品番:300M、見掛け密度3.01g・cm-3、平均粒径85.0μm、150μm以上の粒子比率6.1%)を用いたことを除いては、実施例1と同様にしてリン酸鉄リチウムを作製した。
(Comparative Example 1)
Instead of metal iron powder A, metal iron powder B (manufactured by Kobe Steel, pure iron powder, product number: 300M, apparent density 3.01 g · cm −3 , average particle size 85.0 μm, particle ratio of 150 μm or more 6. 1%) was used, and lithium iron phosphate was produced in the same manner as in Example 1.
上記実施例及び比較例によって得られたリン酸鉄リチウムについて、CuKα線を使用した粉末エックス線回折測定(XRD)を行った。得られたエックス線回折図を図1〜2に示す。 About the lithium iron phosphate obtained by the said Example and comparative example, the powder X-ray-diffraction measurement (XRD) using a CuK alpha ray was performed. The obtained X-ray diffraction patterns are shown in FIGS.
(正極の作製)
上記実施例及び比較例によって得られたリン酸鉄リチウムに、それぞれ、ポリビニルアルコール(分子量約1500)を重量比が1:1になるように乾式混合し、この混合物をアルミナ製の匣鉢に入れ、雰囲気置換式焼成炉にて窒素流通下(2.0l/min)で700℃、2時間熱処理することでLiFePO4に対してカーボンコート処理を行った。これをそれぞれ正極活物質として用い、次の手順で正極を作製した。上記正極活物質、導電剤であるアセチレンブラック及び結着剤であるポリフッ化ビニリデン(PVdF)が質量比80:8:12の割合で混合されたN−メチル−2−ピロリドン(NMP)を溶媒とする正極ペーストを準備した。該正極ペーストを厚さ20μmのアルミニウム箔集電体上の両面に塗布、乾燥した後、プレス加工を行い、正極とした。該正極にはアルミニウム製の正極端子を超音波溶接により接続した。
(Preparation of positive electrode)
Each of the lithium iron phosphates obtained in the above Examples and Comparative Examples was dry-mixed with polyvinyl alcohol (molecular weight of about 1500) so that the weight ratio was 1: 1, and this mixture was placed in an alumina mortar. Then, carbon coating treatment was performed on LiFePO 4 by performing heat treatment at 700 ° C. for 2 hours under a nitrogen flow (2.0 l / min) in an atmosphere substitution type firing furnace. Each of these was used as a positive electrode active material, and a positive electrode was produced by the following procedure. N-methyl-2-pyrrolidone (NMP) in which the positive electrode active material, acetylene black as a conductive agent, and polyvinylidene fluoride (PVdF) as a binder are mixed at a mass ratio of 80: 8: 12 is used as a solvent. A positive electrode paste was prepared. The positive electrode paste was applied on both sides of an aluminum foil current collector having a thickness of 20 μm, dried, and then pressed to obtain a positive electrode. A positive electrode terminal made of aluminum was connected to the positive electrode by ultrasonic welding.
(負極の作製)
負極活物質としてリチウム金属を使用した。厚さ100μmのリチウム金属箔を厚さ10μmのニッケル箔集電体上に貼り付けたものを負極とした。負極にはニッケル製の負極端子を抵抗溶接により接続した。
(Preparation of negative electrode)
Lithium metal was used as the negative electrode active material. A negative electrode was prepared by pasting a lithium metal foil having a thickness of 100 μm onto a nickel foil current collector having a thickness of 10 μm. A negative electrode terminal made of nickel was connected to the negative electrode by resistance welding.
(電解液の調製)
エチレンカーボネート、ジメチルカーボネート及びメチルエチルカーボネートを体積比1:1:1の割合で混合した混合溶媒に、含フッ素系電解質塩であるLiPF6を1mol/lの濃度で溶解させ、非水電解質を作製した。該非水電解質中の水分量は30ppm未満とした。
(Preparation of electrolyte)
A non-aqueous electrolyte is prepared by dissolving LiPF 6 , which is a fluorine-containing electrolyte salt, at a concentration of 1 mol / l in a mixed solvent in which ethylene carbonate, dimethyl carbonate and methyl ethyl carbonate are mixed at a volume ratio of 1: 1: 1. did. The amount of water in the non-aqueous electrolyte was less than 30 ppm.
(電池の作製)
露点温度が−40℃以下の乾燥雰囲気下において非水電解質電池を作製した。正極と負極とを厚さ20μmのポリプロピレン製セパレ−タを介して1枚ずつ対向させた。外装体として、ポリエチレンテレフタレ−ト(15μm)/アルミニウム箔(50μm)/金属接着性ポリプロピレンフィルム(50μm)からなる金属樹脂複合フィルムを用い、この極群を前記正極端子及び負極端子の開放端部が外部露出するように注液孔となる部分を除いて気密封止した。
(Production of battery)
A nonaqueous electrolyte battery was produced in a dry atmosphere with a dew point temperature of −40 ° C. or lower. The positive electrode and the negative electrode were made to face each other via a polypropylene separator having a thickness of 20 μm. A metal resin composite film made of polyethylene terephthalate (15 μm) / aluminum foil (50 μm) / metal adhesive polypropylene film (50 μm) was used as the outer package, and this electrode group was used as the open end of the positive electrode terminal and the negative electrode terminal. Was hermetically sealed except for the portion that would be the liquid injection hole so as to be exposed to the outside.
前記注液孔から一定量の非水電解質を注液後、減圧状態で前記注液孔部分を熱封口し、非水電解質電池を組み立てた。 After injecting a certain amount of nonaqueous electrolyte from the liquid injection hole, the liquid injection hole part was heat sealed in a reduced pressure state to assemble a nonaqueous electrolyte battery.
(電池初期活性化)
次に、3サイクルの充放電を行うことで初期活性化を行った。このときの充電条件は、電流0.05ItmA(20時間率)、電圧3.8V、30時間の定電流定電圧充電とし、放電条件は、電流0.05ItmA(20時間率)、終止電圧2.0Vの定電流放電とした。3サイクル目の放電容量を記録したところ、実施例1のリン酸鉄リチウムを用いた電池においては、2.97mAhの放電容量が得られたが、比較例1のリン酸鉄リチウムを用いた電池においては、放電容量が全く得られなかった。
(Battery initial activation)
Next, initial activation was performed by performing charge and discharge for 3 cycles. The charging conditions at this time were a current of 0.05 ItmA (20 hour rate), a voltage of 3.8 V, and a constant current constant voltage charge of 30 hours, and the discharging conditions were a current of 0.05 ItmA (20 hour rate), a final voltage of 2. The constant current discharge was 0V. When the discharge capacity at the third cycle was recorded, in the battery using lithium iron phosphate of Example 1, a discharge capacity of 2.97 mAh was obtained, but the battery using lithium iron phosphate of Comparative Example 1 was obtained. In, no discharge capacity was obtained.
(見掛け密度の影響)
図1、2から明らかなように、平均粒径としてはそれほど変わらない2種類の金属鉄粉でありながら、見掛け密度の違いによってリン酸鉄リチウムの合成に大きな影響が出ている。見掛け密度の小さい金属鉄粉AではLiFePO4に特徴的なピークが観測されるが、見掛け密度の大きな金属鉄粉BにおいてはLiFePO4に特徴的なピークは小さく、LiFePO4以外の鉄−リン、ポリリン酸、リン酸リチウム等と思われるピークが多数存在している。金属鉄粉Bでは鉄粒子の表面のみLiFePO4生成反応が進み、鉄粒子内部までは原料が拡散できなかったために、余った原料同士で前記のような物質が生成してしまったものと考えられる。電池容量の結果もXRDと同調しており、金属鉄粉Aでは充放電が可能であるが、金属鉄粉Bでは殆ど充放電を行うことができなかった。見掛け密度が2g・cm-3である鉄粉を原料に用いた実施例1において、電池用活物質として実用的な性能を有したリン酸鉄リチウムを直接合成できたことから、鉄粉の見かけ密度が2g・cm-3以下であれば、電池用活物質として実用的な性能を有したリン酸鉄リチウムを直接合成できることがわかった。
(Effect of apparent density)
As can be seen from FIGS. 1 and 2, although there are two types of metallic iron powders whose average particle sizes do not change so much, the difference in the apparent density has a great influence on the synthesis of lithium iron phosphate. Although characteristic peaks in the apparent density of the small metallic iron powder A LiFePO 4 is observed, small peaks characteristic of LiFePO 4 in the large metal iron powder B of apparent density, LiFePO 4 other iron - phosphorus, There are many peaks that are thought to be polyphosphoric acid, lithium phosphate, and the like. In the metal iron powder B, the LiFePO 4 production reaction proceeds only on the surface of the iron particles, and the raw materials could not be diffused to the inside of the iron particles, so it is considered that the above substances were produced between the surplus raw materials. . The result of the battery capacity was also in sync with XRD, and charging / discharging was possible with the metallic iron powder A, but charging / discharging could hardly be performed with the metallic iron powder B. In Example 1 using an iron powder having an apparent density of 2 g · cm −3 as a raw material, lithium iron phosphate having practical performance as an active material for a battery could be directly synthesized. It was found that when the density was 2 g · cm −3 or less, lithium iron phosphate having practical performance as an active material for batteries could be directly synthesized.
上記の実施例では、本発明によって得られたリン酸鉄リチウムを非水電解質電池に用いる例について示したが、他の電池やキャパシター等の電気化学デバイスに用いても良いことはいうまでもない。 In the above-described embodiment, an example in which the lithium iron phosphate obtained by the present invention is used for a non-aqueous electrolyte battery has been described. However, it goes without saying that the battery may be used for other batteries, electrochemical devices such as capacitors. .
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WO2010103821A1 (en) | 2009-03-13 | 2010-09-16 | Jfeケミカル株式会社 | Method for producing iron lithium phosphate |
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