JP2010044890A - Method for manufacturing positive electrode active material for lithium secondary battery, positive electrode active material, and lithium secondary battery - Google Patents
Method for manufacturing positive electrode active material for lithium secondary battery, positive electrode active material, and lithium secondary battery Download PDFInfo
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- C01B25/00—Phosphorus; Compounds thereof
- C01B25/16—Oxyacids of phosphorus; Salts thereof
- C01B25/26—Phosphates
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- 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
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- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/624—Electric conductive fillers
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Abstract
Description
本発明は、リチウム二次電池用正極活物質の製造法、正極活物質及びリチウム二次電池に関する。 The present invention relates to a method for producing a positive electrode active material for a lithium secondary battery, a positive electrode active material, and a lithium secondary battery.
従来、正極活物質として、オリビン型リン酸Mリチウム(Mは2価の金属)を用いて作製した正極と、負極活物質として炭素系材料などリチウム金属、リチウム合金或いはリチウムイオンを吸蔵、放出可能な物質を用いた負極とを組み合わせ、電解液として非水電解液を用いたリチウムイオン二次電池(以下、単にリチウム二次電池と称する)は、従来の鉛二次電池やニッケル−カドミウム二次電池などに比し、軽量で放電容量も大きいことから、各種の電子機器に広く用いられている。この場合、2価の金属のうち、特に、産出量が多く安価で安定した鉄を原料として用いて製造したオリビン型リン酸鉄リチウム(LiFePO4)系を正極活物質を用いて製造した正極を具備したリチウム二次電池が好ましく使用されている。また、公知文献には、オリビン型リン酸Mリチウムの製造法及びこれを用いたリチウム二次電池に関する発明、リン酸鉄リチウムの鉄の一部を他の金属元素で置換するなど、複数種の2価の金属元素を多元成分として含む正極材料、即ち、多元系オリビン型リン酸リチウムの製造法及び該正極材料を用いて作製した正極を具備したリチウム二次電池に関する発明などが開示されている。これに関連する特許文献1〜9を以下に例示する。
特許文献1には、アルカリ金属元素と遷移金属元素とリン酸化合物とを焼成してオリビン型リン酸Mリチウムから成る正極活物質を製造することと、これを正極として用いて、放電電圧が高く、充放電特性の優れたリチウム二次電池を提供する発明が開示されている。
特許文献2には、アルカリ金属元素と周期表第IV族〜第VII族の元素とアルカリ金属含有鉄複酸化物を窒素ガス中で或いは鉄が3価の場合は還元雰囲気下で焼成してLiFePO4などオリビン型リン酸Mリチウムを含む正極活物質を製造すること、これを正極として用いて、充放電特性に優れた低コストのリチウム二次電池を提供する発明が開示されている。
特許文献3には、一般式LiFeXPO4で与えられるオリビン型リン酸化合物(但し、Xはリン酸化合物を構成している状態では、リチウム金属の標準電位に対し3〜4Vの電位領域で電気化学的に安定なコバルト、ニッケルなどの金属元素)から成る正極活物質を焼成により製造することと、これを正極として用い、安価で4V以下の電圧で充放電可能なリチウム二次電池が開示されている。
特許文献4には、オリビン型リン酸鉄リチウム系材料粉末上に、導電性で、且つ該リン酸鉄リチウム系材料の正極活物質としての酸化還元電位よりも貴な金属粒子を担持せしめた一般式LiFeXPO4(但し、Xはマグネシウム、コバルト、ニッケル、亜鉛の少なくとも1種)で表される正極活物質を焼成により製造することと、これを正極として用いて安価なリチウム二次電池を提供する発明が開示されている。
特許文献5には、リチウム塩と鉄塩とを含有するリン酸水溶液に水溶性有機還元剤を混合して混合水溶液を調整し、当該混合水溶液にアルカリ溶液を混合してリチウムと鉄との複合リン酸化物の共沈体を生成させ、次いで、該共沈体を焼成することにより、LiFePO4から成る正極活物質を合成する方法とこれを正極として用いて、製造コスト安価で且つ簡便なリチウム二次電池を提供する発明が開示されている。
特許文献6には、LiFePO4の粒子表面を炭素質物質で被覆して成り且つ平均粒径を0.5μmとしたリチウム系鉄リン系複合酸化物炭素複合体から成る正極活物質の製造法とこれを正極として用いて、特に放電容量が高いリチウム二次電池を提供する発明が開示されている。
特許文献7には、LiFe(II)PO4から成る正極活物質を、その成分原料であるLi源、Fe源、P源、C源、O源を含有する溶液、分散液又は懸濁液を高温雰囲気中に噴霧して前駆体とし、この前駆体を還元性雰囲気又は不活性雰囲気中で80〜1000℃で熱処理して製造すること、これを正極として用いて高い充放電容量(特に放電容量)、安定した充放電サイクル性能を有し、高出力のリチウム二次電池を提供する発明が開示されている。
特許文献8には、リン酸又はリン酸を含む溶液中で、鉄、コバルト、マンガン、ニッケル、銅及びバナジウムからなる群より選ばれる金属を含有する1種又は複数種の化合物と、リチウムを含有する1種又は複数種の化合物を反応させ、その後所定の温度に焼成する2次電池用正極材料の製造方法とこの正極材料を用いて電圧効率、電池容量等の電気化学的特性に優れた2次電池を提供する発明で開示されている。
特許文献9には、一般式LiM1-yM′y(XO4)n(茲でMは遷移金属又はその化合物、M′は2価のMg，Ca，Al，Zn元素又はこれらの混合物、XはS,P及びSiから選択されたもの)で表される化合物の合成法と該化合物を正極材料として用いた2次電池に関する発明が開示されている。
In Patent Document 1, an alkali metal element, a transition metal element, and a phosphoric acid compound are baked to produce a positive electrode active material composed of olivine-type lithium M phosphate, and this is used as a positive electrode to increase the discharge voltage. An invention that provides a lithium secondary battery having excellent charge / discharge characteristics is disclosed.
In Patent Document 2, an alkali metal element, an element of Group IV to VII of the periodic table, and an alkali metal-containing iron complex oxide are baked in nitrogen gas or in a reducing atmosphere when iron is trivalent, and LiFePO An invention has been disclosed in which a positive electrode active material containing olivine-type lithium M phosphate such as 4 is produced, and a low-cost lithium secondary battery excellent in charge and discharge characteristics is provided using this as a positive electrode.
Patent Document 3 describes an olivine-type phosphate compound given by the general formula LiFeXPO 4 (where X is a phosphate compound in the state where the electrochemical potential is 3 to 4 V with respect to the standard potential of lithium metal). And a lithium secondary battery that can be charged and discharged at a low voltage of 4 V or less using the positive electrode active material composed of a metal element such as cobalt and nickel) Yes.
In Patent Document 4, a metal particle that is conductive and has noble metal particles that are more precious than the redox potential as the positive electrode active material of the lithium iron phosphate material is supported on the olivine type lithium iron phosphate material powder. Producing a positive electrode active material represented by the formula LiFeXPO 4 (where X is at least one of magnesium, cobalt, nickel, and zinc) by firing, and providing an inexpensive lithium secondary battery using this as a positive electrode The invention is disclosed.
In Patent Document 5, a water-soluble organic reducing agent is mixed with a phosphoric acid aqueous solution containing a lithium salt and an iron salt to prepare a mixed aqueous solution, and an alkaline solution is mixed with the mixed aqueous solution to combine lithium and iron. A method of synthesizing a positive electrode active material comprising LiFePO 4 by forming a coprecipitate of phosphorous oxide and then firing the coprecipitate, and using this as the positive electrode An invention for providing a secondary battery is disclosed.
Patent Document 6 discloses a method for producing a positive electrode active material comprising a lithium-based iron-phosphorus-based composite oxide carbon composite comprising a LiFePO 4 particle surface coated with a carbonaceous material and having an average particle size of 0.5 μm. An invention is disclosed that provides a lithium secondary battery having a particularly high discharge capacity by using as a positive electrode.
Patent Document 7 discloses a positive electrode active material composed of LiFe (II) PO 4 , a solution, dispersion or suspension containing Li source, Fe source, P source, C source, and O source as its component raw materials. Sprayed into a high-temperature atmosphere to make a precursor, and this precursor is heat-treated at 80 to 1000 ° C. in a reducing atmosphere or an inert atmosphere. ), An invention for providing a high-power lithium secondary battery having stable charge / discharge cycle performance is disclosed.
Patent Document 8 contains lithium or one or more compounds containing a metal selected from the group consisting of iron, cobalt, manganese, nickel, copper, and vanadium in phosphoric acid or a solution containing phosphoric acid. A method for producing a positive electrode material for a secondary battery by reacting one or more compounds to be reacted and then firing to a predetermined temperature, and using this positive electrode material, the electrochemical characteristics such as voltage efficiency and battery capacity are excellent. The present invention provides a secondary battery.
Patent Document 9 includes a general formula LiM 1-y M′y (XO 4 ) n (where M is a transition metal or a compound thereof, M ′ is a divalent Mg, Ca, Al, Zn element or a mixture thereof, A method for synthesizing a compound represented by X is selected from S, P and Si) and an invention relating to a secondary battery using the compound as a positive electrode material is disclosed.
しかし乍ら、特許文献1〜3に開示のオリビン型リン酸Mリチウムから成る正極活物質は、従来正極活物質として用いられてきたLiCoO2などのリチウム金属酸化物に比べて電気抵抗が非常に大きいため、充放電を行った場合に抵抗分極が増大し、充分な放電容量が得られない。また、充電受け入れ性が悪いなどの問題がある。特に、大電流の充放電では顕著である。
このような問題を解決する方法として、オリビン型リン酸Mリチウムの粉末粒子を微細化し、反応面積を増やし、リチウムイオン拡散を容易にすること、正極作製に当たり、該正極活物質粉末にカーボンブラックなどの導電剤粉を混合すること、電子がリン酸Mリチウムの粉末粒子内部を流れる距離を短くすることなどが考えられている。
しかし乍ら、オリビン型リン酸Mリチウム系材料の微細な一次粒子は、正極作製時にカーボンブラック等の導電剤粉と混合する際に二次凝集を起こし易い。凝集粒の内部では、充分な集電効果が得られずに電気抵抗が非常に大きくなる。その結果、凝集粒の中央部の活物質は電池の充放電を行っても電子伝導が起こらず、充放電容量が低下する。一方、微細な一次粒子は大きな表面積となるため、正極作製のスラリー調製では必要な分散媒の量が多くなり、集電基材に対し必要な塗工量が得られ難いこと、乾燥時にひび割れが生じ易いこと、充分な圧縮が困難なために高容量の正極が得られない、電解液に正極活物質の金属の溶出が増大し、リチウム二次電池の寿命が短くなる等の長期安定性に問題がある。
また一般に、オリビン型リン酸Mリチウム系材料の粒子表面はバルクと比較して、結晶性が低いためにアモルファス状になっていると考えられている。このために空気中での放置により二価の金属が酸化され、より抵抗の大きな3価のリン酸塩に変化する。これにより、初充電時に大きな分極を発生するので、放置条件が厳しいことや、活性化が煩雑になることや、抵抗成分が残留する問題もある。
このため、特許文献4では、リン酸鉄リチウム系材料の微細粒子上に導電性で酸化還元電位よりも貴な銀、炭素、白金、パラジウム等の微粒子を担持することが提案されているが、酸化還元電位よりも貴な金属粒子は酸化還元を伴う化学的な変性を受け易く、リチウム二次電池として安定性に問題がある。また、粒子同士の接続なので、集電性の問題は充分に解決されていない。
特許文献5では、LiFePO4炭素複合体から成る正極活物質は、リチウム塩と鉄塩とを含有するリン酸水溶液にカーボン源として、カーボンブラックまた他は水溶性有機還元剤を混合した混合水溶液にアルカリ溶液を混合してリチウムと鉄との複合リン酸化物の共沈体を焼成して製造するため、LiFePO4粒子の表面に対するカーボン粒子の分散効果は不充分であり、充分な集電効果が得られない。また、その製造工程が複雑である。
特許文献6では、オリビン系化合物の合成原料であるリチウム化合物、2価の金属化合物及びリン酸化合物へ炭素質前駆体や水溶性有機物を添加し、焼成後に炭素コンポジットを作製するので、特許文献6と同様に製造工程が煩雑となり、また、電池活物質としては高度な粒度制御が必要になるが、上記の製造法では、粒度制御が著しく困難となるなどの問題がある。
特許文献7では、LiFe(II)PO4から成る化合物を主成分とする電極材料粉体の製造は、Li源と、Fe(III)源と、P源と、C(炭素)源とO(酸素)源を含有する液体を高温雰囲気中で噴霧して前駆体とした後、該前駆体を熱処理して製造するので、製造工程に手間がかかりすぎ、製造製が非能率である。
更に、特許文献8及び9では、異種の金属の2種以上を組成成分として含む多元正極材料或いは正極化合物を製造するには、複数種類の金属塩水溶液又は各種の原料粉を混合して前駆体を作製し、次いで、これを焼成して単一の化合物から成る正極材料を製造するため、純粋な化合物を得るために前駆体組成制御が煩雑となり、また、焼成時に部分的にリン酸塩が析出すること、粒度制御が困難であり、更には、特許文献7と同様に製造作業が面倒であり、その生産性が非能率となるなどの問題がある。
本発明は、上記従来の正極活物質の製造法や正極として用いられる正極活物質の微細粒子の上記の課題を解決し、上記の特許文献7のように、オリビン型リン酸Mリチウムの各種成分源を用いたり、特許文献6及び9のように、製造工程における中間物として前駆体を一旦製造したりして、Mが複数種の金属を組成成分として含む化合物から成る正極材料を合成する方法に比し、簡素化した製造工程で高能率に且つ低製造コストで正極材料、即ち、リチウム二次電池用正極活物質を合成することができる正極活物質の製造法を提供すること、更には、該正極活物質をリチウム二次電池の正極として用いて、率放電性能や電池容量維持率が向上した長期安定性を有し、大電流による充放電特性が向上したリチウム二次電池を提供することを目的とする。
However, the positive electrode active material composed of olivine-type M lithium phosphate disclosed in Patent Documents 1 to 3 has a much higher electric resistance than lithium metal oxides such as LiCoO 2 that have been conventionally used as a positive electrode active material. Since it is large, resistance polarization increases when charging and discharging are performed, and a sufficient discharge capacity cannot be obtained. There are also problems such as poor charge acceptance. This is particularly noticeable when charging and discharging with a large current.
As a method for solving such a problem, the powder particles of olivine-type lithium M phosphate are made finer, the reaction area is increased, the lithium ion diffusion is facilitated, and the positive electrode active material powder is carbon black, etc. It is conceivable to mix the conductive agent powder, and to shorten the distance that electrons flow inside the powder particles of lithium M phosphate.
However, the fine primary particles of the olivine-type M lithium phosphate-based material are liable to cause secondary aggregation when mixed with a conductive agent powder such as carbon black during the production of the positive electrode. Inside the agglomerated particles, a sufficient current collecting effect cannot be obtained and the electric resistance becomes very large. As a result, the active material in the central part of the aggregated particles does not cause electron conduction even when the battery is charged / discharged, and the charge / discharge capacity decreases. On the other hand, since the fine primary particles have a large surface area, the amount of the dispersion medium required in the preparation of the slurry for producing the positive electrode is large, and it is difficult to obtain the required coating amount for the current collecting base material, and cracking occurs during drying. Long-term stability, such as being prone to occur, a high-capacity positive electrode cannot be obtained because sufficient compression is difficult, elution of the metal of the positive electrode active material into the electrolyte increases, and the life of the lithium secondary battery is shortened There's a problem.
In general, it is considered that the particle surface of the olivine-type M lithium phosphate-based material is amorphous because of its lower crystallinity than the bulk. For this reason, the divalent metal is oxidized by being left in the air, and converted to a trivalent phosphate having a higher resistance. As a result, a large polarization is generated at the time of initial charge, so that there are problems that the leaving condition is severe, activation becomes complicated, and resistance components remain.
Therefore, in Patent Document 4, it has been proposed to carry fine particles of silver, carbon, platinum, palladium, etc. that are conductive and nobler than the redox potential on the fine particles of the lithium iron phosphate material, Metal particles nobler than the oxidation-reduction potential are susceptible to chemical modification accompanied by oxidation-reduction, and there is a problem in stability as a lithium secondary battery. Moreover, since the particles are connected to each other, the problem of current collection has not been sufficiently solved.
In Patent Document 5, a positive electrode active material composed of a LiFePO 4 carbon composite is mixed into a mixed aqueous solution in which carbon black or other water-soluble organic reducing agent is mixed as a carbon source in a phosphoric acid aqueous solution containing a lithium salt and an iron salt. Since the co-precipitate of lithium and iron composite phosphate is mixed and mixed with an alkaline solution, the dispersion effect of the carbon particles on the surface of the LiFePO 4 particles is insufficient, and a sufficient current collecting effect is obtained. I can't get it. Moreover, the manufacturing process is complicated.
In Patent Document 6, since a carbonaceous precursor and a water-soluble organic substance are added to a lithium compound, a divalent metal compound, and a phosphate compound, which are synthetic raw materials for an olivine compound, and a carbon composite is produced after firing, Patent Document 6 As in the case of the above, the manufacturing process becomes complicated, and the battery active material requires a high degree of particle size control. However, the above manufacturing method has a problem that particle size control becomes extremely difficult.
In Patent Document 7, production of an electrode material powder containing a compound composed of LiFe (II) PO 4 as a main component includes a Li source, an Fe (III) source, a P source, a C (carbon) source, and O ( Since a liquid containing an oxygen) source is sprayed in a high-temperature atmosphere to form a precursor, and then the precursor is heat-treated, the manufacturing process takes too much time, and the production is inefficient.
Furthermore, in Patent Documents 8 and 9, in order to produce a multi-element positive electrode material or a positive electrode compound containing two or more kinds of different metals as composition components, a precursor is prepared by mixing a plurality of types of metal salt aqueous solutions or various raw material powders. Then, this is fired to produce a positive electrode material composed of a single compound, so that the control of the precursor composition becomes complicated in order to obtain a pure compound, and the phosphate is partly at the time of firing. Precipitation, particle size control is difficult, and the manufacturing work is troublesome as in Patent Document 7, and the productivity becomes inefficient.
The present invention solves the above-described problems of the conventional positive electrode active material production method and fine particles of the positive electrode active material used as the positive electrode, and as described in Patent Document 7, various components of olivine-type M lithium phosphate A method of synthesizing a positive electrode material composed of a compound in which M contains a plurality of kinds of metals as a composition component by using a source or once producing a precursor as an intermediate in the production process as in Patent Documents 6 and 9 Providing a method for producing a positive electrode material capable of synthesizing a positive electrode material, that is, a positive electrode active material for a lithium secondary battery, at a high efficiency and at a low production cost by a simplified production process. Using the positive electrode active material as a positive electrode of a lithium secondary battery, to provide a lithium secondary battery having long-term stability with improved rate discharge performance and battery capacity retention rate and improved charge / discharge characteristics with a large current Aimed at
本発明は、オリビン型リン酸Mリチウム(Mは2価の金属元素)から成る化合物のMが異なる複数種類の化合物の粉末を混合し、該混合粉末を不活性雰囲気又は真空中で焼結処理することにより固溶体化を行い、該複数種の金属元素を多元成分として含む単一の化合物から成る正極材料を合成し、次いで、その塊状物を粉砕して平均粒径1ミクロン以上の粉末を得ることを特徴とするリチウム二次電池用正極活物質の製造法に存する。
更に本発明は、請求項2に記載の通り、該2価の金属元素が異なる複数種類のオリビン型リン酸Mリチウムから成る化合物の粉末に少なくとも1種の炭素源を添加、混合し、該混合粉末を不活性雰囲気又は真空中で焼結処理により固溶体化を行い、該複数種の金属を多元成分として含むと共に炭素を含む単一の化合物から成る正極材料を合成し、次いで、これを粉砕して平均粒径1ミクロン以上の粉末を得ることを特徴とするリチウム二次電池用正極活物質の製造法に存する。
更に本発明は、請求項1又は2に記載の製造法により合成した該正極材料の上記の粉末から成るリチウム二次電池用正極活物質。
更に本発明は、請求項1乃至3のいずれか1つに記載の製造法で製造したリチウム二次電池用正極活物質を用いて作製した正極を具備したことを特徴とするリチウム二次電池に存する。
更に本発明は、請求項1乃至3のいずれか1つに記載の製造法により製造した正極活物質粉末と炭素の複合体から成る粒径20ミクロン以下の粉末を用いて作製した正極を具備したことを特徴とするリチウム二次電池に存する。
The present invention mixes powders of a plurality of types of compounds having different M of a compound composed of olivine-type lithium M phosphate (M is a divalent metal element), and the mixed powder is sintered in an inert atmosphere or vacuum To form a solid solution, to synthesize a positive electrode material composed of a single compound containing a plurality of metal elements as a multi-component, and then pulverize the lump to obtain a powder having an average particle size of 1 micron or more The present invention resides in a method for producing a positive electrode active material for a lithium secondary battery.
Further, according to the present invention, as described in claim 2, at least one carbon source is added to and mixed with a powder of a compound composed of a plurality of types of olivine-type M lithium phosphates having different divalent metal elements. The powder is made into a solid solution by sintering in an inert atmosphere or vacuum to synthesize a positive electrode material composed of a single compound containing carbon and a plurality of kinds of metals as a multi-component, and then pulverizing it. The present invention relates to a method for producing a positive electrode active material for a lithium secondary battery, characterized in that a powder having an average particle size of 1 micron or more is obtained.
Furthermore, the present invention provides a positive electrode active material for a lithium secondary battery comprising the above powder of the positive electrode material synthesized by the production method according to claim 1 or 2.
Furthermore, the present invention provides a lithium secondary battery comprising a positive electrode produced using the positive electrode active material for a lithium secondary battery produced by the production method according to any one of claims 1 to 3. Exist.
Furthermore, the present invention includes a positive electrode produced using a powder having a particle size of 20 microns or less composed of a composite of a positive electrode active material powder produced by the production method according to any one of claims 1 to 3 and carbon. It exists in the lithium secondary battery characterized by this.
請求項1に係る発明によれば、Mの2価の遷移金属元素が異なる複数種のオリビン型リン酸Mリチウムから成る化合物の粉末の混合粉末を焼成処理することにより、固溶体化が行われ、夫々の化合物の粒子同士が融合して大きな粒子に成長した無数の固溶体粒子全体が結着した塊状物として得られる。この各固溶体粒子は、後述する該複数種の金属元素を多元成分として含む単一の化合物から成る正極材料、換言すれば、多元素オリビン型リン酸リチウムとでも称する二次電池用正極活物質である。而して、次いでこの正極材料の塊状物を粉砕するときは、平均粒径1ミクロン以上の正極活物質粉末が得られる。このように、従来のような複数種の金属元素を多元成分として含む化合物から成る正極材料を製造に当たり、各種の金属水溶液を反応させたり、各種の成分原料粉を混合し、焼結して前駆体を作製し、更に該前駆体を焼結する工程をとる必要がなく、簡単且つ安価に正極材料を製造することができる。
而も、この正極材料を粉砕することにより、平均粒径1ミクロン以上の粉末が得られるので、この得られた正極活物質粉体を用い正極を作製するときは、導電剤と混合するとき、二次凝集を起こすことがないので、充放電特性の良い正極をもたらす。
請求項2,3に係る発明によれば、炭素を含有した正極材料が得られるので、これを粉砕した正極活物質粉体を用い正極を作製するときは、導電性など電池特性を向上せしめる正極をもたらす。
請求項4に係る発明によれば、容量維持率の向上した長期安定性を有し、更には高率放電性能の向上したリチウム二次電池をもたらす。
請求項5に係る発明によれば、更に電池特性の向上したリチウム二次電池をもたらす。
According to the invention according to claim 1, solid solution is performed by firing a mixed powder of a compound composed of a plurality of olivine-type M lithium phosphates having different divalent transition metal elements of M, It can be obtained as a lump of innumerable solid solution particles, which are formed into large particles by fusing the respective compound particles together. Each of these solid solution particles is a positive electrode material made of a single compound containing a plurality of types of metal elements described later as a multi-component, in other words, a positive electrode active material for a secondary battery, also called multi-element olivine type lithium phosphate. is there. Thus, when the mass of the positive electrode material is then pulverized, a positive electrode active material powder having an average particle diameter of 1 micron or more is obtained. Thus, in manufacturing a positive electrode material composed of a compound containing a plurality of types of metal elements as a multi-component as in the prior art, various precursors of metal aqueous solutions are reacted, or various component raw material powders are mixed and sintered to produce a precursor. The positive electrode material can be manufactured easily and inexpensively without the need to take a step of producing a body and further sintering the precursor.
However, by pulverizing this positive electrode material, a powder having an average particle size of 1 micron or more can be obtained. When producing a positive electrode using the obtained positive electrode active material powder, when mixing with a conductive agent, Since secondary aggregation does not occur, a positive electrode with good charge / discharge characteristics is provided.
According to the inventions according to claims 2 and 3, since a positive electrode material containing carbon is obtained, when producing a positive electrode using a positive electrode active material powder obtained by pulverizing this, a positive electrode that improves battery characteristics such as conductivity Bring.
According to the invention of claim 4, there is provided a lithium secondary battery having long-term stability with improved capacity maintenance rate and further improved high rate discharge performance.
The invention according to claim 5 provides a lithium secondary battery having further improved battery characteristics.
本発明の実施の形態例を以下詳述する。
本発明のリチウム二次電池用正極活物質の製造法は、従来公知の任意の方法である液相反応又は固相反応法を用いて合成したオリビン型リン酸Mリチウムから成る正極活物質の粉体をリチウム二次電池用正極活物質製造法の出発原料として用意する。
茲で、Mは、Co、Ni、Fe、Mn、Cu、Mg、Zn、Ca、Cd、Sr、Baなどの2価の金属の群から選んだ少なくとも1種を表す。特に、オリビン型リン酸Mリチウム合成用金属素材として、3価の遷移金属を用いた場合は、前記の加熱反応時には、水素ガスなどの還元雰囲気下で焼成し、これを2価の金属Mとする。
Embodiments of the present invention will be described in detail below.
The method for producing a positive electrode active material for a lithium secondary battery according to the present invention is a powder of a positive electrode active material comprising olivine-type M lithium phosphate synthesized by a liquid phase reaction or solid phase reaction method which is a conventionally known arbitrary method. The body is prepared as a starting material for a method for producing a positive electrode active material for a lithium secondary battery.
Here, M represents at least one selected from the group of divalent metals such as Co, Ni, Fe, Mn, Cu, Mg, Zn, Ca, Cd, Sr, and Ba. In particular, when a trivalent transition metal is used as the metal material for synthesizing the olivine-type M lithium phosphate, during the heating reaction, it is fired in a reducing atmosphere such as hydrogen gas, and this is referred to as divalent metal M. To do.
本発明によれば、出発原料として用意した各種の上記の合成法によりオリビン型リン酸Mリチウム化合物の中から、Mで表される2価の金属の種類が異なる複数種の、即ち、2種以上のオリビン型リン酸Mリチウムの粉末を混合する。次いで、該混合粉末を不活性雰囲気又は真空中で焼結処理する。不活性ガスとしては、一般に、アルゴンガスを使用する。然るときは、複数種のオリビン型リン酸Mリチウムの化合物粉末の無数の粒子同士は、固溶反応により融合して焼結処理前の上記出発原料粉末の粒子の粒径より大きな固溶体粒子に成長する。無数の固溶体粒子は、後記に明らかにするように、複数種の2価の金属を多元成分として含む単一の化合物から成る正極材料を合成することができる。合成された正極材料は、無数の固溶体粒子全体が結着した塊状物の状態で得られる。従って、次いで、該塊状物を粉砕する。然るときは、平均粒径1ミクロン以上の粒子から成る本発明の正極活物質粉末が得られる。
この正極活物質粉末を用いて好ましい正極を作製するには、後記に明らかにするように、これを篩分して1〜20μmの範囲の粒径を主体とする正極活物質粉末を選択し、これを正極の作製に用いることが好ましい。
According to the present invention, among the olivine-type M lithium phosphate compounds prepared by the various synthesis methods prepared as starting materials, a plurality of types of divalent metals represented by M are different, that is, two types. The above olivine type M lithium phosphate powder is mixed. Next, the mixed powder is sintered in an inert atmosphere or vacuum. Generally, argon gas is used as the inert gas. In such a case, the countless particles of the compound powder of multiple types of olivine type M lithium phosphate are fused together by a solid solution reaction to form solid solution particles larger than the particle size of the starting material powder particles before the sintering treatment. grow up. As will be clarified later, innumerable solid solution particles can synthesize a positive electrode material composed of a single compound containing a plurality of divalent metals as a multi-component. The synthesized positive electrode material is obtained in the form of a lump in which countless solid solution particles are bound together. Therefore, the lump is then pulverized. In such a case, the positive electrode active material powder of the present invention composed of particles having an average particle size of 1 micron or more can be obtained.
In order to produce a preferred positive electrode using this positive electrode active material powder, as will be clarified later, this is sieved to select a positive electrode active material powder mainly having a particle size in the range of 1 to 20 μm, This is preferably used for the production of the positive electrode.
本発明の上記の正極材料から成る正極活物質を合成法に用いられる焼結処理により上記の正極材料を合成するには、出発原料として用いるオリビン型リン酸Mリチウムとしては、一般の従来の製造法で正極作製用正極活物質として平均粒径1ミクロン未満の微細粒子から成るものを用いる。
従って、従来の所望の合成法で合成した該正極活物質粉末の全てが1ミクロン未満の粒子であれば、これをそのまま原料として用い、或いは1ミクロン以上の粒子と混在している場合は、該粉末を篩分けして1ミクロン未満の粉末のみを分取してこれを出発原料として用い、その残余の1ミクロン以上の粒子のものはボールミルなどにより1ミクロン未満の粒子になるまで粉砕して原料とし、該粉末の全てが1ミクロン以上の粒子から成るときは、その全てをミリングして1ミクロン未満の粒子に粉砕して、これを原料とする。また、固相反応法で合成した場合は、通常団塊状で合成されるので、これをボールミルなどで1ミクロン未満になるまで粉砕して出発原料とする。
尚、また、本発明では、該焼結処理における固溶体化に用いる焼結温度は400℃〜900℃の範囲で3〜7時間の範囲、一般に500℃〜800℃の範囲が好ましい。
In order to synthesize the positive electrode material by the sintering treatment used in the synthesis method of the positive electrode active material comprising the positive electrode material of the present invention, the olivine-type M lithium phosphate used as a starting material is a general conventional production. In this method, a positive electrode active material for producing a positive electrode is made of fine particles having an average particle size of less than 1 micron.
Therefore, if all of the positive electrode active material powder synthesized by the conventional desired synthesis method is a particle of less than 1 micron, if it is used as a raw material as it is or mixed with particles of 1 micron or more, The powder is sieved and only the powder of less than 1 micron is collected and used as a starting material. The remaining particles of 1 micron or more are pulverized to a particle of less than 1 micron by a ball mill etc. When all of the powder consists of particles of 1 micron or more, all of the powder is milled and pulverized into particles of less than 1 micron, which is used as a raw material. In addition, when synthesized by a solid phase reaction method, it is usually synthesized in the form of a nodule, so this is pulverized with a ball mill or the like until it becomes less than 1 micron to obtain a starting material.
In the present invention, the sintering temperature used for solid solution formation in the sintering treatment is preferably in the range of 400 ° C to 900 ° C for 3 to 7 hours, and generally in the range of 500 ° C to 800 ° C.
本発明の上記の正極材料の合成法に当たり、上記の混合粉に炭素源として、アセチレンブラック、ケッチェンブラック、グラファイトカーボン、カーボンブラック、気相成長炭素繊維(VGCF)、カーボナノチューブなどの無機質炭素源、ショ糖などの炭水化物、その他の有機質炭素源を混合し、その混合粉を上記と同様に焼結処理するときは、析出した炭素を含む導電性の向上した正極材料から成る正極活物質を製造することができる。 In the synthesis method of the positive electrode material of the present invention, as a carbon source in the mixed powder, inorganic carbon sources such as acetylene black, ketjen black, graphite carbon, carbon black, vapor grown carbon fiber (VGCF), carbon nanotube, etc. When mixed with carbohydrates such as sucrose and other organic carbon sources and sintering the mixed powder in the same manner as described above, a positive electrode active material composed of a positive electrode material with improved conductivity containing precipitated carbon is produced. can do.
Mの2価の金属元素が異なる複数種類のオリビン型リン酸Mリチウムを出発原料として用いる場合、市販のものを用いてもよいことは勿論であるが、以下は、本発明の正極材料から成る正極活物質を製造する出発原料の製造からの実施態様例を説明する。
先ず、2種類のオリビン型リン酸Mリチウムとして、例えば、リン酸鉄リチウムとリン酸コバルトリチウムの2種類のオリビン型リン酸リチウムを従来の合成法により製造し、これらを出発原料として用い、本発明の正極材料から成る正極活物質、即ち、リン酸鉄コバルトリチウム(LiFexCo1-xPO4)を合成する場合につき以下説明する。
When a plurality of types of olivine-type lithium M phosphates having different divalent metal elements of M are used as starting materials, it is of course possible to use commercially available ones, but the following consists of the positive electrode material of the present invention. An embodiment example from the production of the starting material for producing the positive electrode active material will be described.
First, as two types of olivine-type M lithium phosphate, for example, two types of olivine-type lithium phosphates, lithium iron phosphate and lithium cobalt phosphate, are produced by a conventional synthesis method, and these are used as starting materials. The case of synthesizing the positive electrode active material comprising the positive electrode material of the invention, that is, iron cobalt lithium phosphate (LiFe x Co 1-x PO 4 ) will be described below.
オリビン型リン酸MリチウムのMで表される2価の金属の種類を異にする2種類のオリビン型リン酸鉄リチウム及びオリビン型リン酸コバルトリチウムを夫々次のように合成した。
出発原料の作製:
リン酸リチウム486gと2価の鉄化合物として2価の塩化鉄4水和物795gを耐圧容器(オートクレープ)内に蒸留水2000mlと共に入れ、該容器内をアルゴンガスで置換した後に密閉した。該容器を180℃のオイルバス中で、48時間反応させた。次いで、室温まで放冷した後該容器から反応物を取り出し、100℃で乾燥させて粉末試料を得た。得られた粉末はX線回折パターンにより、リン酸鉄リチウム(LiFePO4)の化合物であること及び走査型電子顕微鏡(SEM)観察から、約20nm〜200nmの粒径を有していることが確認された。
一方、リン酸リチウム486gと2価のコバルト化合物として2価の塩化コバルト6水和物952gを、耐圧容器(オートクレープ)内に蒸留水2000mlと共に入れ、該容器内をアルゴンガスで置換した後に密閉した。該容器を180℃のオイルバス中で、48時間反応させた。次いで、室温まで放冷した後該容器から反応物を取り出し、100℃で乾燥させて粉末試料を得た。得られた粉末はX線回折パターンにより、リン酸コバルトリチウム(LiCoPO4)の化合物であること及び走査型電子顕微鏡(SEM)観察から、約20nm〜200nm迄の粒径を有していることが確認された。
Two kinds of olivine-type lithium iron phosphate and olivine-type cobalt lithium phosphate, which are different from the divalent metal represented by M in olivine-type lithium M phosphate, were synthesized as follows.
Starting material preparation:
486 g of lithium phosphate and 795 g of divalent iron chloride tetrahydrate as a divalent iron compound were placed in a pressure vessel (autoclave) together with 2000 ml of distilled water, and the inside of the vessel was replaced with argon gas and sealed. The vessel was reacted in an oil bath at 180 ° C. for 48 hours. Subsequently, after allowing to cool to room temperature, the reaction product was taken out from the container and dried at 100 ° C. to obtain a powder sample. X-ray diffraction pattern confirms that the obtained powder is a compound of lithium iron phosphate (LiFePO 4 ) and has a particle size of about 20 nm to 200 nm from observation with a scanning electron microscope (SEM). It was done.
On the other hand, 486 g of lithium phosphate and 952 g of divalent cobalt chloride hexahydrate as a divalent cobalt compound were placed in a pressure vessel (autoclave) together with 2000 ml of distilled water, and the inside of the vessel was replaced with argon gas and sealed. did. The vessel was reacted in an oil bath at 180 ° C. for 48 hours. Subsequently, after allowing to cool to room temperature, the reaction product was taken out from the container and dried at 100 ° C. to obtain a powder sample. According to the X-ray diffraction pattern, the obtained powder is a compound of lithium cobalt phosphate (LiCoPO 4 ) and has a particle size of about 20 nm to 200 nm from scanning electron microscope (SEM) observation. confirmed.
次に、上記に得られたリン酸鉄リチウム粉末161gとリン酸コバルトリチウム粉末158gを配合した。(即ち、モル比1:1)で配合し、ボールミルで混合して混合粉末を調製し、これをルツボに入れた後、炉内に入れ、窒素ガス、アルゴンガスなどの不活性雰囲気下で、或いは真空下で300℃で5時間、次いで、750℃で5時間焼結処理により固溶体化を行った。室温まで放冷後、該炉からルツボを取り出し、該ルツボ内に得られた塊状の焼結処理物の本発明の試料を得た。次いで、該試料を粉砕した。 Next, 161 g of lithium iron phosphate powder obtained above and 158 g of lithium cobalt phosphate powder were blended. (I.e., a molar ratio of 1: 1), mixed with a ball mill to prepare a mixed powder, put this in a crucible, then put in a furnace, under an inert atmosphere such as nitrogen gas, argon gas, Alternatively, the solid solution was formed by sintering at 300 ° C. for 5 hours and then at 750 ° C. for 5 hours under vacuum. After cooling to room temperature, the crucible was taken out from the furnace to obtain a sample of the present invention of a massive sintered product obtained in the crucible. The sample was then crushed.
図1は、前記の焼結処理前の出発原料の混合粉末と該混合粉末の焼結処理後に得られた上記の塊状物を粉砕した粉末を同倍率(10,000倍)で観察したときの走査電子顕微鏡(SEM)写真を示す。このことは、前記の約20nm〜200nmの微細粒子から成る焼結処理前の出発原料の混合粉末は、焼結処理により複数の粒子毎に融合し、一体化した粒径約0.3ミクロン〜3ミクロンの大きな固溶体粒子に成長したものとなることを示し、同時に、無数の固溶体粒子全体が結着して塊状の焼結処理物現象が見られる。このようにして得られた個々の固溶体粒子は、後記に明らかにするように、FeとCoを組成成分として含むLiFe0.5Co0.5PO4から成る単一の化合物、二元オリビン型リン酸Mリチウムから成る正極材料であることが確認された。従って、該塊状物を粉砕することにより、平均粒径1ミクロン以上の無数の固溶体粒から成る正極活物質粉末として製造することができる。
焼結処理後に得られた上記の成長した固溶体の結晶粒子は、焼結処理前のLiFePO4とLiCoPO4(Fe:Coのモル比1:1)から成る2種類の混合粉末が下記反応式に示すように、固相拡散及び固溶化反応により2モルの単一の化合物LiFe0.5Co0.5PO4から成る正極材料が合成されたものと推定される。
LiFePO4+LiCoPO4→2LiFe0.5Co0.5PO4
FIG. 1 shows scanning electrons when the mixed powder of the starting material before the sintering process and the powder obtained by pulverizing the lump obtained after the sintering process of the mixed powder are observed at the same magnification (10,000 times). A microscope (SEM) photograph is shown. This is because the mixed powder of the starting material before the sintering process composed of fine particles of about 20 nm to 200 nm is fused into a plurality of particles by the sintering process and has an integrated particle size of about 0.3 to 3 microns. The large number of solid solution particles are grown, and at the same time, the whole of the innumerable solid solution particles are bound and a massive sintered product phenomenon is observed. The individual solid solution particles thus obtained are, as will be clarified later, a single compound composed of LiFe 0.5 Co 0.5 PO 4 containing Fe and Co as composition components, a binary olivine-type M lithium phosphate. It was confirmed that the positive electrode material was composed of Therefore, by pulverizing the lump, it can be produced as a positive electrode active material powder composed of countless solid solution particles having an average particle size of 1 micron or more.
The crystal grains of the above-mentioned grown solid solution obtained after the sintering treatment are two types of mixed powders consisting of LiFePO 4 and LiCoPO 4 (Fe: Co molar ratio 1: 1) before the sintering treatment. As shown, it is presumed that a positive electrode material composed of 2 mol of a single compound LiFe 0.5 Co 0.5 PO 4 was synthesized by solid phase diffusion and solid solution reaction.
LiFePO 4 + LiCoPO 4 → 2LiFe 0.5 Co 0.5 PO 4
更に、上記の本発明の化合物から成る正極材料の該結晶粒子につき、結晶断面でのエネルギー分散型X線分析(EDX)を行った。図2にその結果を示す。これにより、結晶の同じ位置にFe、Co、Pが存在することを確認した。
更にまた、上記化合物の元素組成を求めるために、ICPによる分析を行った。その結果、略LiFe0.5Co0.5PO4の組成を持つことを確認した。
Furthermore, energy dispersive X-ray analysis (EDX) in a crystal cross section was performed on the crystal particles of the positive electrode material made of the compound of the present invention. Figure 2 shows the results. This confirmed that Fe, Co, and P were present at the same position of the crystal.
Furthermore, in order to obtain the elemental composition of the above compound, analysis by ICP was performed. As a result, it was confirmed that it had a composition of approximately LiFe 0.5 Co 0.5 PO 4 .
上記と同様の方法で、上記の出発原料であるLiFePO4粉末とLiCoPO4粉末をFe:Coの組成比が0.7:0.3になるように配合混合したものを、上記と同様の方法で焼結処理し、その焼結処理後に得られる固溶体の粉末の結晶粒子につき、エネルギー分散型X線分析を行い、結晶の同じ位置にFe、Co、Pが存在することを確認した。更に、ICPによる分析を行い、該結晶粒子から成る該化合物の元素組成を求め、LiFe0.5Co0.5PO4の組成を持つことを確認した。
尚また、該LiFePO4粉末、LiCoPO4粉末、本発明の上記の焼結処理により得たLiFe0.5Co0.5PO4粉末及びLiFe0.7Co0.3PO4粉末につき、夫々X線回折を行った。その夫々の粉末の回折パターンを図3に示す。いずれの試料も単一の化合物の回折パターンを示し、特に、本発明の焼結処理により、2種類のオリビン型リン酸Mリチウム化合物LiFePO4とLiCoPO4の融合、固溶体化が円滑に行われ、Fe:Coの組成比に夫々対応してFeとCoの二元成分を組成成分として含む二元系オリビン型リン酸Mリチウムから成る正極材料を含む単一化合物が夫々確実に合成されることを確認した。
In the same manner as above, LiFePO 4 powder and LiCoPO 4 powder, which are the above starting materials, are mixed and mixed so that the Fe: Co composition ratio is 0.7: 0.3. Then, energy dispersive X-ray analysis was performed on the crystal particles of the solid solution powder obtained after the sintering treatment, and it was confirmed that Fe, Co, and P were present at the same position of the crystal. Furthermore, analysis by ICP was performed to determine the elemental composition of the compound composed of the crystal particles, and it was confirmed that it had a composition of LiFe 0.5 Co 0.5 PO 4 .
Further, X-ray diffraction was performed on the LiFePO 4 powder, LiCoPO 4 powder, LiFe 0.5 Co 0.5 PO 4 powder and LiFe 0.7 Co 0.3 PO 4 powder obtained by the sintering treatment of the present invention. Fig. 3 shows the diffraction pattern of each powder. Each sample shows a diffraction pattern of a single compound, and in particular, the sintering treatment of the present invention smoothly fused and solidified two kinds of olivine-type M lithium phosphate compounds LiFePO 4 and LiCoPO 4 , Corresponding to the composition ratio of Fe: Co respectively, it is confirmed that a single compound including a positive electrode material composed of binary olivine type M lithium phosphate containing a binary component of Fe and Co as a composition component is surely synthesized. confirmed.
更に、LiFexCo1-xPO4のxの値と(020)面回折角について、詳細に調査したところ、図4に示す関係が得られた。同図に示すように、Co比の増加と共に回折角が略線形的に高角側にシフトすることが認められた。この結果により、本発明の合成法により粒径1ミクロン以上の固溶体粒子から成る正極活物質が形成されることを確認した。 Further, when the value of x and the (020) plane diffraction angle of LiFe x Co 1-x PO 4 were examined in detail, the relationship shown in FIG. 4 was obtained. As shown in the figure, it was recognized that the diffraction angle shifted to the high angle side in a substantially linear manner as the Co ratio increased. From this result, it was confirmed that a positive electrode active material composed of solid solution particles having a particle size of 1 micron or more was formed by the synthesis method of the present invention.
本発明につき、更に詳細な実施例を以下に詳述する。
実施例1
出発原料として、前記の水相法で合成した粒径約20nm〜200nmを有するLiFePO4粉末と粒径約20nm〜200nmを有するLiCoPO4粉末とを前者の粉末と後者の粉末のモル比が0.95:0.05、0.7:0.3及び0.5:0.5となるように夫々混合し、3種類の混合粉末を調製した。混合は、ボール径10mmのボールミルで1時間行った。
次いで、各混合粉末10gを磁性ルツボ内に収容し、これを真空ガス置換炉に入れ、窒素ガスで充分に置換後、真空状態にして、600℃で3時間焼結処理した。次いで、室温まで放冷後に、該炉から各ルツボを取り出し、各ルツボ内の焼結処理物である塊状物を試料として採取した。次いで、夫々の塊状物をコーヒーミルで粉砕し、夫々の粉末を得た。夫々の粉末を篩分し、粒径20ミクロン以下の粒子から成る3種類の試料粉体A,B,Cを得た。夫々の粉体につき、SEMにより粒度分布を測定したところ、焼結処理前の混合粉末の粒子同士が融合し、粒径が成長した粒径約0.7〜3ミクロンの固溶体粒子が大部分を占めていることを確認した。また、X線回折装置で分析した後、単一の化合物であることを確認した。更に、ICPにより、夫々の粉体A,B,Cは、出発原料の夫々の混合粉末の夫々の組成比と同じ、LiFe0.95Co0.05PO4,LiFe0.7Co0.3PO4及びLiFe0.5Co0.5PO4の単一の化合物であることを確認した。
More detailed embodiments of the present invention are described in detail below.
Example 1
As a starting material, a molar ratio of the former powder and the latter powder of LiFePO 4 powder having a particle size of about 20 nm to 200 nm and LiCoPO 4 powder having a particle size of about 20 nm to 200 nm synthesized by the aqueous phase method is 0.95: Three types of mixed powders were prepared by mixing each at 0.05, 0.7: 0.3, and 0.5: 0.5. The mixing was performed for 1 hour with a ball mill having a ball diameter of 10 mm.
Next, 10 g of each mixed powder was placed in a magnetic crucible, placed in a vacuum gas replacement furnace, sufficiently replaced with nitrogen gas, and then evacuated and sintered at 600 ° C. for 3 hours. Subsequently, after cooling to room temperature, each crucible was taken out from the furnace, and a lump which was a sintered product in each crucible was collected as a sample. Then, each lump was pulverized with a coffee mill to obtain each powder. Each powder was sieved to obtain three types of sample powders A, B and C consisting of particles with a particle size of 20 microns or less. When the particle size distribution was measured by SEM for each powder, the particles of the mixed powder before the sintering treatment were fused together, and the solid solution particles with a particle size of about 0.7 to 3 microns grown accounted for the majority. I confirmed. Moreover, after analyzing with the X-ray-diffraction apparatus, it confirmed that it was a single compound. Furthermore, according to ICP, the respective powders A, B, C are the same as the respective composition ratios of the respective mixed powders of the starting materials, LiFe 0.95 Co 0.05 PO 4 , LiFe 0.7 Co 0.3 PO 4 and LiFe 0.5 Co 0.5 PO. It was confirmed to be 4 single compounds.
実施例2
実施例1で使用したと同じ粒径を有するLiFePO4粉末とLiCoPO4粉末とをモル比が0.95:0.05、0.7:0.3及び0.5:0.5となるように夫々混合して3種類の混合粉末を調製した。混合は、ボール径10mmのボールミルで1時間行った。
次いで、各混合粉末10gに炭素源としてショ糖を主成分とし、これに転化糖が少量添加されている市販の砂糖1gを混合し、得られた各混合粉末に蒸留水を10ml投入して、充分混練した後、100℃で2時間乾燥した。
次いで、各混合粉末を磁性ルツボ内に収容し、これを真空ガス置換炉に入れ、窒素ガスで充分に置換後、真空状態にして、300℃で2時間、600℃で3時間焼結処理した。次いで、室温まで放冷後に、該炉から各ルツボを取り出し、各ルツボ内の焼結処理物である塊状物を試料として採取した。次いで、夫々の該塊状物をコーヒーミルで粉砕した夫々の粉末を得た。夫々の粉末を篩分し、粒径20ミクロン以下の粒子から成る3種類の試料粉体D,E,Fを得た。夫々の粉体につき、SEMにより粒度分布を測定したところ、焼結前の混合粉末の粒子同士が融合し粒径が成長した粒径約0.7〜3ミクロンの固溶体粒子が大部分を占めていることを確認した。また、夫々の粉体D,E,Fにつき、X線回折装置で分析した結果、単一の化合物であることを確認した。更に、ICPにより、夫々の粉体D,E,Fは、出発原料の夫々の混合粉末の夫々の組成比と同じ、LiFe0.95Co0.05PO4,LiFe0.7Co0.3PO4,LiFe0.5Co0.5PO4の単一の化合物であることを確認した。また、熱重量分析による含有炭素量を測定した。その結果、夫々の粉体D,E,Fには、1.5%の炭素を含有していることを確認した。
Example 2
Three types of mixed powders were prepared by mixing LiFePO 4 powder and LiCoPO 4 powder having the same particle size as used in Example 1 so that the molar ratios were 0.95: 0.05, 0.7: 0.3, and 0.5: 0.5, respectively. did. The mixing was performed for 1 hour with a ball mill having a ball diameter of 10 mm.
Next, 10 g of each mixed powder is mixed with 1 g of commercially available sugar containing sucrose as a carbon source as a carbon source and a small amount of invert sugar added thereto, and 10 ml of distilled water is added to each of the obtained mixed powders. After sufficiently kneading, it was dried at 100 ° C. for 2 hours.
Next, each mixed powder was placed in a magnetic crucible, placed in a vacuum gas replacement furnace, sufficiently replaced with nitrogen gas, and then vacuumed and sintered at 300 ° C. for 2 hours and 600 ° C. for 3 hours. . Subsequently, after cooling to room temperature, each crucible was taken out from the furnace, and a lump which was a sintered product in each crucible was collected as a sample. Subsequently, each lump was obtained by pulverizing each lump with a coffee mill. Each powder was sieved to obtain three types of sample powders D, E, and F consisting of particles with a particle size of 20 microns or less. When the particle size distribution was measured by SEM for each powder, solid solution particles with a particle size of about 0.7 to 3 microns, in which the particles of the mixed powder before sintering were fused and grown, accounted for the majority. It was confirmed. Each powder D, E, F was analyzed with an X-ray diffractometer, and was confirmed to be a single compound. Furthermore, according to ICP, the respective powders D, E and F have the same composition ratio as the respective mixed powders of the starting materials, LiFe 0.95 Co 0.05 PO 4 , LiFe 0.7 Co 0.3 PO 4 , LiFe 0.5 Co 0.5 PO It was confirmed to be 4 single compounds. Moreover, the carbon content by thermogravimetric analysis was measured. As a result, it was confirmed that each powder D, E, F contained 1.5% carbon.
実施例3
実施例1で使用したと同じ微細な粒径を有するLiFePO4粉末とLiCoPO4粉末とをモル比が0.95:0.05、0.7:0.3及び0.5:0.5となるように夫々混合すると共に、該混合物に、重量比で3.8%のアセチレンブラックを添加混合して3種類の混合粉末を調製した。混合は、ボールミルで1時間行った。
次いで、各混合粉末10gに、更に、炭素源としてショ糖を主成分とし、これに転化糖が少量添加されている市販の砂糖1gを混合し、得られた各混合物に蒸留水を10ml注入して、充分混練後、100℃で2時間乾燥した。
次いで、各混合粉末を磁性ルツボ内に収容し、これを真空ガス置換炉に入れ、窒素ガスで充分に置換後、真空状態にして、300℃で2時間、600℃で3時間焼結処理した。次いで、室温まで放冷後に、該炉から各ルツボを取り出し、各ルツボ内の焼結処理物である塊状物を試料として採取した。次いで、夫々の該塊状物をコーヒーミルで粉砕し、夫々の粉末を得た。次いで、夫々の粉末を篩分し、粒径20ミクロン以下の粒子から成る3種類の試料粉体G,H,Iを得た。夫々の各粉体につき、SEMにより粒度分布を測定したところ、焼結前の混合粉末の粒子同士が融合し粒径が成長した粒径約0.7〜3ミクロンの固溶体粒子が大部分を占めていることを確認した。また、夫々の粉体G,H,Iにつき、X線回折装置で分析した結果、単一の化合物であることを確認した。更に、ICPにより、夫々の粉体G,H,Iは、出発原料の夫々の混合粉末の組成比と同じ、LiFe0.95Co0.05PO4,LiFe0.7Co0.3PO4,LiFe0.5Co0.5PO4であることを確認した。また、熱重量分析による含有炭素量を測定した。その結果、夫々の粉体G,H,Iには、5.0%の炭素を含有していることを確認した。
Example 3
LiFePO 4 powder having the same fine particle size as used in Example 1 and LiCoPO 4 powder were mixed so that the molar ratios were 0.95: 0.05, 0.7: 0.3, and 0.5: 0.5, respectively. Three kinds of mixed powders were prepared by adding and mixing 3.8% by weight of acetylene black. Mixing was performed on a ball mill for 1 hour.
Next, 10 g of each mixed powder is further mixed with 1 g of commercially available sugar containing sucrose as a carbon source as a main component and a small amount of invert sugar added thereto, and 10 ml of distilled water is injected into each resulting mixture. After sufficiently kneading, it was dried at 100 ° C. for 2 hours.
Next, each mixed powder was placed in a magnetic crucible, placed in a vacuum gas replacement furnace, sufficiently replaced with nitrogen gas, and then vacuumed and sintered at 300 ° C. for 2 hours and 600 ° C. for 3 hours. . Subsequently, after cooling to room temperature, each crucible was taken out from the furnace, and a lump which was a sintered product in each crucible was collected as a sample. Then, each lump was pulverized with a coffee mill to obtain each powder. Next, each powder was sieved to obtain three types of sample powders G, H, and I composed of particles having a particle size of 20 microns or less. For each powder, the particle size distribution was measured by SEM. As a result, solid solution particles with a particle size of approximately 0.7 to 3 microns, in which the particles of the mixed powder before sintering were fused and grown, accounted for the majority. It was confirmed. Further, each powder G, H, I was analyzed with an X-ray diffractometer, and was confirmed to be a single compound. Further, according to ICP, the respective powders G, H, and I are LiFe 0.95 Co 0.05 PO 4 , LiFe 0.7 Co 0.3 PO 4 , LiFe 0.5 Co 0.5 PO 4 with the same composition ratio of the respective mixed powders of the starting material. I confirmed that there was. Moreover, the carbon content by thermogravimetric analysis was measured. As a result, it was confirmed that each powder G, H, and I contained 5.0% carbon.
比較例1
従来の固相法により、LiFe0.7Co0.3PO4で表される単一の化合物から成る正極材料粉末を次のように合成した。
即ち、LiFe0.7Co0.3PO4を合成するため、出発原料として、その各組成元素について、化学量論的に秤量したシュウ酸鉄・二水和物、酢酸コバルト(II)・四水和物、リン酸二水素アンモニウム及びフッ化リチウム粉末を配合し、これらをボールミルで3時間混合した。次いで、該混合粉をルツボに収容し、これを電気炉に入れ、アルゴン-水素(92:8 v/v)の雰囲気中で400℃、8時間、焼成処理した。室温まで冷却後、該炉から取り出したルツボ内に前駆体の塊状物を得た。次いで、該塊状物をコーヒーミルで粉砕した後、その粉末を再びルツボ内に収容し、再び該電気炉に入れ、前記と同じ雰囲気中で600℃、24時間焼成処理した。室温まで冷却した後、該炉から取り出したルツボ内の塊状物をコーヒーミルで粉砕し、試料粉体Jを得た。該粉体JをSEMにより粒度分布を測定したところ、大部分が粒径約20〜100nmであることを確認した。また、該粉体JをX線回折装置で分析した結果、単一の化合物であること、更に、ICPにより該化合物は、LiFe0.7Co0.3PO4であることを確認した。
Comparative Example 1
A positive electrode material powder composed of a single compound represented by LiFe 0.7 Co 0.3 PO 4 was synthesized by the conventional solid phase method as follows.
That is, in order to synthesize LiFe 0.7 Co 0.3 PO 4 , as a starting material, for each of its constituent elements, stoichiometrically weighed iron oxalate dihydrate, cobalt acetate (II) tetrahydrate, Ammonium dihydrogen phosphate and lithium fluoride powder were blended and mixed with a ball mill for 3 hours. Next, the mixed powder was placed in a crucible, placed in an electric furnace, and calcined at 400 ° C. for 8 hours in an atmosphere of argon-hydrogen (92: 8 v / v). After cooling to room temperature, a precursor mass was obtained in the crucible removed from the furnace. Subsequently, the lump was pulverized with a coffee mill, and the powder was again placed in a crucible, and again placed in the electric furnace, followed by baking at 600 ° C. for 24 hours in the same atmosphere as described above. After cooling to room temperature, the lump in the crucible taken out from the furnace was pulverized with a coffee mill to obtain sample powder J. When the particle size distribution of the powder J was measured by SEM, it was confirmed that most of the powder J had a particle size of about 20 to 100 nm. Further, as a result of analyzing the powder J with an X-ray diffractometer, it was confirmed that it was a single compound and that the compound was LiFe 0.7 Co 0.3 PO 4 by ICP.
比較例2
従来の液相法により、LiFe0.7Co0.3PO4で表される単一の化合物から成る正極材料粉末を次のように合成した。
出発原料として、CH3COOLiを69.29g、Fe(CH3COO)2を121.77g、Co(CH3COO)2を53.11g、H3PO4(85%)を115.29g秤量し、これらをイオン交換水1000mlに添加、溶解した。ついで、該水溶液を150℃で乾燥した後、得られた乾燥物をルツボに入れた後、これを電気炉に投入し、アルゴン-水素(92:8 v/v)の雰囲気中で400℃、8時間、焼成処理した。室温まで冷却した後、該炉から取り出したルツボ内に前駆体の塊状物を得た。次いで、該塊状物をコーヒーミルで粉砕して、その粉末を再びルツボ内に収容した後、再び該電気炉に入れ、前記と同じ雰囲気中で600℃、24時間焼成処理した。室温まで冷却後、該炉から取り出したルツボ内の塊状物をコーヒーミルで粉砕し、試料粉体Kを得た。該粉体KをSEMにより粒度分布を測定したところ、大部分が粒径約20〜100nmの微細粒子であることを確認した。また、該粉体KをX線回折装置で分析した結果、単一の化合物であること、更に、ICPにより該化合物は、LiFe0.7Co0.3PO4であることを確認した。
Comparative Example 2
A positive electrode material powder composed of a single compound represented by LiFe 0.7 Co 0.3 PO 4 was synthesized by the conventional liquid phase method as follows.
As starting materials, we weighed 69.29 g of CH 3 COOLi, 121.77 g of Fe (CH 3 COO) 2 , 53.11 g of Co (CH 3 COO) 2 and 115.29 g of H 3 PO 4 (85%). It was added and dissolved in 1000 ml of exchange water. Next, after drying the aqueous solution at 150 ° C., the obtained dried product was put in a crucible, and then put in an electric furnace, and the atmosphere was argon-hydrogen (92: 8 v / v) at 400 ° C., Calcination treatment was performed for 8 hours. After cooling to room temperature, a precursor mass was obtained in the crucible removed from the furnace. Subsequently, the lump was pulverized with a coffee mill, and the powder was again placed in the crucible, and then again placed in the electric furnace, followed by baking at 600 ° C. for 24 hours in the same atmosphere as described above. After cooling to room temperature, the lump in the crucible taken out from the furnace was pulverized with a coffee mill to obtain sample powder K. When the particle size distribution of the powder K was measured by SEM, most of the powder K was confirmed to be fine particles having a particle size of about 20 to 100 nm. Further, as a result of analyzing the powder K with an X-ray diffractometer, it was confirmed that it was a single compound and that the compound was LiFe 0.7 Co 0.3 PO 4 by ICP.
上記の本発明の実施例1〜3と従来の比較例1,2の同じFe,Coの組成比をもつ正極材料である二元リン酸Mリチウムを合成する場合、実施例1〜3では、比較例1,2のような前駆体の製造と再焼成、粉砕工程を経ることなく、簡単で低コストで目的とする二元リン酸Mリチウムが合成できる点で有利である効果をもたらし、而も、得られる正極活物質粉体の粒径は焼結処理前の粒径より大きいものに得られるので、その結果、その表面積は低下するので、これを用いてリチウム二次電池の正極の活物質として用いるときは、その組成成分であるFe,Coの電解液への溶出が減少し、以下に明らかにするように、充放電特性の向上、電池寿命の延長などの効果をもたらす。 When synthesizing binary M lithium phosphate, which is a positive electrode material having the same Fe, Co composition ratio as in Examples 1 to 3 of the present invention and the conventional Comparative Examples 1 and 2, in Examples 1 to 3, It produces an advantageous effect in that the target binary M lithium phosphate can be synthesized easily and at low cost without going through the precursor production, re-firing, and pulverization steps as in Comparative Examples 1 and 2. However, since the particle size of the obtained positive electrode active material powder is larger than the particle size before the sintering treatment, the surface area is reduced as a result, and this is used to activate the positive electrode active material of the lithium secondary battery. When used as a substance, the elution of Fe and Co, which are the composition components, into the electrolyte decreases, and as will be clarified below, effects such as improved charge / discharge characteristics and extended battery life are brought about.
正極の作製:
実施例1〜3及び比較例1,2で合成した正極活物質粉体A〜Kの夫々に、導電剤としてアセチレンブラックを添加し、全炭素量として10%となるように混合した。次いで、各混合粉体に結着剤であるポリフッ化ビニリデン(PVdF)を重量比95:5の配合割合で混合し、更に、これにN-メチル-2-ピロリドン(NMP)を加えて充分混練し、正極スラリーを夫々調製した。次いで、各正極スラリーを厚さ15μmのアルミニウム箔から成る集電体に100g/m2の塗工量で塗布し、120℃で30分間乾燥した。その後、ロールプレスで2.0g/ccの密度になるように圧延加工し、2cm2の円盤状に打ち抜いて各正極を作製した。
実施例1〜3で合成した9種類の本発明の正極活物質粉体A,B,C,D,E,F,G,H,Iを用いて作製した9種類の正極を正極A,B,C,D,E,F,G,H,Iと夫々称し、比較例1,2の正極活物質粉体J,Kを用いて作製した夫々の正極J,Kと夫々称する。夫々の正極に対応する粉体の特性を下記表1にまとめて示した。
Production of positive electrode:
Acetylene black was added as a conductive agent to each of the positive electrode active material powders A to K synthesized in Examples 1 to 3 and Comparative Examples 1 and 2, and mixed so that the total carbon amount was 10%. Next, polyvinylidene fluoride (PVdF), which is a binder, is mixed with each mixed powder at a blending ratio of 95: 5 by weight, and further, N-methyl-2-pyrrolidone (NMP) is added thereto and kneaded sufficiently. Then, positive electrode slurries were respectively prepared. Next, each positive electrode slurry was applied to a current collector made of an aluminum foil having a thickness of 15 μm at a coating amount of 100 g / m 2 and dried at 120 ° C. for 30 minutes. Thereafter, it was rolled to a density of 2.0 g / cc with a roll press and punched into a disk shape of 2 cm 2 to produce each positive electrode.
Nine types of positive electrodes prepared using the nine types of positive electrode active material powders A, B, C, D, E, F, G, H, and I of the present invention synthesized in Examples 1 to 3 were positive electrodes A and B. , C, D, E, F, G, H, and I, respectively, and positive electrodes J and K produced using the positive electrode active material powders J and K of Comparative Examples 1 and 2, respectively. The characteristics of the powder corresponding to each positive electrode are summarized in Table 1 below.
尚、上記の夫々の正極の作製において、上記比較例1,2の正極活物質粉体J,Kは、その正極活物質スラリーを集電体に塗布、乾燥後に、その極板表面にひび割れを生じたり、取り扱い時に塗工層が容易に脱落するなどの不都合をしばしば生じたが、これらの不都合を生じないで作製されたものを正極J,Kとした。この不都合が生ずる原因は、粉体の粒径が非常に小さいため、乾燥時の塗工面の結晶が大きくなるからであると推定される。これに対し、上記実施例の正極活物質粉体A〜Iを用いた場合は、その上記正極活物質スラリーにより、上記の不都合を生ずることなく、確実に安定良好な塗工層が得られ、充填密度の向上した正極A〜Iが作製できた。 In the preparation of each of the positive electrodes, the positive electrode active material powders J and K of Comparative Examples 1 and 2 were coated with the positive electrode active material slurry on the current collector, and after drying, cracked on the surface of the electrode plate. There were often inconveniences such as the occurrence of the coating layer and the coating layer easily falling off during handling. The positive electrodes J and K were prepared without causing these inconveniences. The reason why this inconvenience occurs is presumed to be that the particle size of the powder is so small that the crystal on the coated surface during drying becomes large. On the other hand, when the positive electrode active material powders A to I of the above examples are used, the positive electrode active material slurry can surely provide a stable and good coating layer without causing the above disadvantages. Positive electrodes A to I with improved packing density were produced.
正極の電気化学的特性の確認:
上記の化学組成式LiFe0.7Co0.3PO4を有する化合物から成る正極活物質を用いて作製した正極Bの夫々について、サイクリックボルタンメトリーにより電気化学的特性を次のように確認した。即ち、負極及び参照電極については金属リチウムを使用し、電解液にはエチレンカーボネート及びジエチルカーボネートを体積比1:1の割合で混合したものを用いた。電位走査範囲は金属リチウムに対して、2.7V〜5.2Vとし、走査速度は0.5mV/sec.で温度は25℃とした。その結果を図5に示す。同図から明らかなように、充電、放電共に卑側の鉄と貴側のコバルトの電位ピークを示し、クーロン量は略7:3を示すことを確認した。また、正極Bの正極活物質と同じ化学組成式を有する正極活物質を用いて作製した正極E,H,J,Kについても、上記の方法でその電気化学的特性を調べたが、該正極Bと同様に夫々の組成比に相当するクーロン量の比をもつ電気化学的特性が得られた。
また、同じ化学組成式LiFe0.95Co0.05PO4を有する正極活物質を用いて作製した正極A,D及びG及び同じ化学組成式LiFe0.5Co0.5PO4を有する正極活物質を用いて作製された正極C,F及びIについても、その夫々のFeとCoの組成比に相当する夫々のクーロン量を示すことを確認した。
Check the electrochemical properties of the positive electrode:
For each of the positive electrodes B produced using the positive electrode active material composed of the compound having the chemical composition formula LiFe 0.7 Co 0.3 PO 4 , the electrochemical characteristics were confirmed by cyclic voltammetry as follows. That is, metallic lithium was used for the negative electrode and the reference electrode, and an electrolytic solution in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 1: 1 was used. The potential scanning range was 2.7 V to 5.2 V with respect to metallic lithium, the scanning speed was 0.5 mV / sec., And the temperature was 25 ° C. The results are shown in FIG. As is clear from the figure, it was confirmed that both charge and discharge showed potential peaks of iron on the base side and cobalt on the noble side, and the coulomb amount was about 7: 3. Further, the positive electrode E, H, J, K produced using a positive electrode active material having the same chemical composition formula as the positive electrode active material of the positive electrode B was also investigated for its electrochemical characteristics by the above method. Similar to B, electrochemical characteristics with the ratio of Coulomb amount corresponding to each composition ratio were obtained.
Also, produced using positive electrodes A, D and G prepared using a positive active material having the same chemical composition formula LiFe 0.95 Co 0.05 PO 4 and a positive active material having the same chemical composition formula LiFe 0.5 Co 0.5 PO 4 It was confirmed that the positive electrodes C, F, and I also showed their respective coulomb amounts corresponding to the respective Fe and Co composition ratios.
リチウム二次電池の製造:
正極には、上記の正極A〜Kを用いた。負極には、次のように作製したものを用いた。即ち、人造黒鉛(平均粒径5μm、d002=0.337nm、Lc=58nm)及びポリフッ化ビニリデン(PVdF)を重量比95:5の割合で混合し、N-メチル-2-ピロリドン(NMP)を添加し、充分混練して負極ペーストを調製した。次いで、該負極ペーストを厚さ15μmの銅箔集電体上に塗布し、25℃の常温中で自然乾燥後、更に減圧下130℃で12時間乾燥した。その後、ロールプレスで圧延加工し、2cm2の円盤状に打ち抜いて負極とした。
電解液としては、次のように調整したものを用いた。即ち、エチレンカーボネート及びジエチルカーボネートを体積比1:1の割合で混合した混合溶媒に、LiPF6を1Mの濃度で溶解して電解液とした。尚、電解液中の水分量は15ppm未満とした。
また、セパレータとしては、ポリプロピレンなどの高分子多孔フィルムなど、公知のものを用いた。
これらの電池部品を用いてコイン型リチウム二次電池を下記のように製造した。尚、製造時の雰囲気は露点が-50℃以下とした。各正極及び負極は集電体の付いた電槽缶に圧着して用いた。該正極A〜Kの夫々、該負極、上記の電解液及びセパレータを電槽缶内に常法により組み込み収容し、直径25mm、厚さ1.6mmのコイン型リチウム二次電池を夫々製造した。本発明の該正極A〜Iを具備した電池を電池A〜Iとし、比較用正極J,Kを具備した電池を電池J,Kとした。
Production of lithium secondary battery:
The positive electrodes A to K described above were used for the positive electrode. The negative electrode was prepared as follows. That is, artificial graphite (average particle size 5 μm, d 002 = 0.337 nm, Lc = 58 nm) and polyvinylidene fluoride (PVdF) were mixed at a weight ratio of 95: 5, and N-methyl-2-pyrrolidone (NMP) was mixed. The resulting mixture was added and sufficiently kneaded to prepare a negative electrode paste. Next, the negative electrode paste was applied onto a copper foil current collector having a thickness of 15 μm, naturally dried at room temperature of 25 ° C., and further dried at 130 ° C. under reduced pressure for 12 hours. Thereafter, it was rolled with a roll press and punched into a 2 cm 2 disk shape to obtain a negative electrode.
As the electrolytic solution, one prepared as follows was used. That is, LiPF 6 was dissolved at a concentration of 1M in a mixed solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 1: 1 to obtain an electrolytic solution. Note that the amount of water in the electrolyte was less than 15 ppm.
Moreover, as a separator, well-known things, such as polymeric porous films, such as a polypropylene, were used.
Using these battery parts, a coin-type lithium secondary battery was manufactured as follows. Note that the atmosphere during production was a dew point of −50 ° C. or lower. Each positive electrode and negative electrode were used by being pressure-bonded to a battery case with a current collector. Each of the positive electrodes A to K, the negative electrode, the electrolytic solution, and the separator were assembled and housed in a battery case by a conventional method, and coin-type lithium secondary batteries having a diameter of 25 mm and a thickness of 1.6 mm were manufactured. Batteries equipped with the positive electrodes A to I of the present invention were designated as batteries A to I, and batteries equipped with the comparative positive electrodes J and K were designated as batteries J and K.
リチウム二次電池の電池試験:
電池A〜Kの各電池を各々多数個用意した。電池A〜Kの夫々につき、低率での充放電を10サイクル行った。このときの充電条件は、電流0.1CA、電圧4.1Vの定電流定電圧充電とし、放電条件は、電流0.1CA、終止電圧2.0Vの定電流放電とした。温度は全て25℃とした。11サイクル目は5CAの高率放電試験を実施した。試験温度は全て25℃とした。下記表2は、0.1CAの低率放電容量と、5CAの高率放電容量と5c/0.1比の容量を示す。
Battery test of lithium secondary battery:
Many batteries A to K were prepared. For each of the batteries A to K, 10 cycles of charging and discharging at a low rate were performed. The charging conditions at this time were constant current and constant voltage charging with a current of 0.1 CA and a voltage of 4.1 V, and the discharging conditions were constant current discharging with a current of 0.1 CA and a final voltage of 2.0 V. All temperatures were 25 ° C. In the 11th cycle, a 5 CA high rate discharge test was conducted. All test temperatures were 25 ° C. Table 2 below shows a low rate discharge capacity of 0.1 CA, a high rate discharge capacity of 5 CA and a capacity of 5c / 0.1 ratio.
表1及び表2から明らかなように、本発明の電池B、電池E、電池Hは、これら電池と同じ組成を持つ比較電池J及び電池Kと比較すると、本発明の正極活物質粉体B,E,Hが大きな粒径を持つのにも拘らず、5c/0.1C比が大きく、高率放電性能が良いことが分かった。これは、本発明の正極活物質粉体B,E,Hのリン酸塩へのCo固溶状態が異なり導電性が向上したこと、及び比較正極活物質J,Kを用いて電極J,Kを作製するときに生ずるひび割れにより集電体箔との接触が悪化したことによると推定される。 As is clear from Table 1 and Table 2, the battery B, battery E, and battery H of the present invention were compared with the comparative battery J and battery K having the same composition as these batteries, and the positive electrode active material powder B of the present invention. Despite the large particle size of E and H, it was found that the 5c / 0.1C ratio was large and the high rate discharge performance was good. This is because the positive electrode active material powders B, E, H of the present invention are different in the Co solid solution state in the phosphate and the conductivity is improved, and the electrodes J, K using the comparative positive electrode active materials J, K It is presumed that the contact with the current collector foil deteriorated due to the cracks produced when producing the sheet.
リチウム電池の高温フロート充電特性:
次に、電池A〜Kの各電池につき、高温フロート充電特性を次のように試験した。充電設定電圧4.1Vとし、60℃で3ヶ月の試験を実施した。試験後に常温に戻してから0.1CAで放電して残存容量を測定した。10サイクル目容量を基準とした容量維持率を下記表3に示す。
High temperature float charge characteristics of lithium battery:
Next, for each of the batteries A to K, the high temperature float charging characteristics were tested as follows. The test was conducted for 3 months at 60 ° C. with a charge setting voltage of 4.1V. After returning to room temperature after the test, the remaining capacity was measured by discharging at 0.1 CA. Table 3 below shows capacity retention rates based on the 10th cycle capacity.
表3から明らかなように、本発明の電池A〜Iの全ての電池は、比較例の電池J,Kよりも優れた容量維持率を示した。この理由は、本発明の電池A〜Iに夫々用いた本発明の正極活物質粉体A〜Iの粒径は、比較電池J,Kに用いた正極活物質粉体J,Kの粒径より著しく大きな粒径のものが得られ、従って、その表面積の低下により組成金属成分であるFeやCoの電解液による溶出が抑制され、負極への移動量が減少し、SEIの機能阻害を抑制されるからであると推定される。 As is apparent from Table 3, all the batteries A to I of the present invention exhibited capacity retention rates superior to those of the batteries J and K of the comparative example. This is because the particle diameters of the positive electrode active material powders A to I of the present invention used in the batteries A to I of the present invention are the particle diameters of the positive electrode active material powders J and K used in the comparative batteries J and K, respectively. As a result, a material with a significantly larger particle size can be obtained. Therefore, the elution of Fe and Co, which are constituent metal components, by the electrolyte is suppressed by reducing the surface area, and the amount transferred to the negative electrode is reduced. It is estimated that this is because
上記の実施例1〜3では、オリビン型リン酸MリチウムのMの種類、即ち、2価の金属の種類を異にする2種類のオリビン型リン酸Mリチウムを出発原料とした場合を示したが、3種類又はそれ以上のオリビン型リン酸Mリチウムを出発原料としても同様に3種類又はそれ以上の2価の金属を多元成分として含む単一の多元リン酸Mリチウムから成る正極材料、即ち、正極活物質を合成することができる。例えば、LiFePO4,LiCoPO4及びLiMnPO4を用いて上記の実施例と同様の手段でFe、Co、Mnを多元成分として含む単一の化合物から成る正極活物質を合成することができる。 In the above Examples 1 to 3, the type of M of the olivine-type M lithium phosphate, that is, the case where two kinds of olivine-type M lithium phosphates having different divalent metal types were used as starting materials was shown. Is a positive electrode material consisting of a single multi-element M lithium phosphate containing three or more olivine-type M lithium phosphates as starting materials, and similarly containing three or more divalent metals as multi-components, A positive electrode active material can be synthesized. For example, it is possible to synthesize a positive electrode active material composed of a single compound containing Fe, Co, and Mn as multi-components using LiFePO 4 , LiCoPO 4, and LiMnPO 4 by the same means as in the above-described embodiment.
以上から明らかなように、本発明によれば、極めて容易に種類を異にする2価の金属を組成成分とする多元成分系のオリビン型リン酸Mリチウムから成る正極活物質を極めて容易に製造することができ、且つ該正極活物質を用いて長期安定性に優れたリチウム二次電池が得られる。 As is apparent from the above, according to the present invention, it is very easy to produce a positive electrode active material composed of a multi-component olivine-type M lithium phosphate having a divalent metal of different types as a composition component. In addition, a lithium secondary battery excellent in long-term stability can be obtained using the positive electrode active material.
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| JP5314264B2 (en) * | 2007-09-26 | 2013-10-16 | 古河電池株式会社 | Method for producing positive electrode active material for lithium secondary battery, positive electrode active material and lithium secondary battery |
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| JP5121625B2 (en) | 2013-01-16 |
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