JP4297406B2 - Method for producing secondary battery positive electrode material and secondary battery - Google Patents

Description

【０１１９】
実施例４
正極材料ＬｉＦｅＰＯ_４を、以下の手順で合成した。
５．０５３２ｇのＦｅＣ_２Ｏ_４・２Ｈ_２Ｏ（和光純薬工業株式会社製）、３．７０９４ｇの（ＮＨ_４）_２ＨＰＯ_４（和光純薬工業株式会社製）、および１．１７８４ｇのＬｉＯＨ・Ｈ_２Ｏ（和光純薬工業株式会社製）に０．０６１０ｇのアセチレンブラック［電気化学工業株式会社製デンカブラック（登録商標；５０％プレス品）］を加え、めのう製自動乳鉢を用いて粉砕・混合した。この粉砕・混合物をアルミナ製るつぼに入れ、５体積％水素（Ｈ_２）／９５体積％アルゴン（Ａｒ）の混合ガスを２００ｍｌ／分の流量で通気しながら、まず４００℃にて５時間仮焼成した。取出した仮焼成後の原料２．２４３０ｇに０．０５７６ｇの軟化温度２００℃精製石炭ピッチを加え、めのう乳鉢にて粉砕・混合後、さらに同雰囲気で７７５℃にて１０時間本焼成を行った（混合ガスは、昇温開始前から焼成中、さらに放冷後まで流通しつづけた）。これにより合成された正極材料は、粉末Ｘ線回折によりオリビン型結晶構造を有するＬｉＦｅＰＯ_４であると同定された。一方、酸化態不純物であるα−Ｆｅ_２Ｏ_３、ＦｅＰＯ_４の結晶回折ピークは全く認められなかった。
【０１２０】
また、元素分析から、精製石炭ピッチの熱分解により生じた炭素、およびアセチレンブラック由来の炭素が合計３．２７重量％含有されていることが判った。また、結晶子サイズは、７４ｎｍであった。
【０１２１】
この正極材料を用い、実施例１と同様の条件で正極ペレットおよびコイン型リチウム２次電池を作製した。
以上のようにして得た正極材料を組み込んだ２次電池に対して、正極ペレットの見かけ面積当たりの電流密度０.５ｍＡ／ｃｍ^２および１.６ｍＡ／ｃｍ^２にて、３.０Ｖ〜４.０Ｖの作動電圧範囲で充放電を繰り返したところ、１〜２０サイクルの平均初期放電容量は表２に示すとおりであった（初期放電容量は、生成物中の正極活物質量で規格化した）。このように仮焼成前に導電性炭素としてのアセチレンブラックを添加するとともに、仮焼成後に導電性炭素前駆物質としての精製石炭ピッチを添加することによって得られる正極材料は、２次電池の放電容量を大きくし、正極性能を向上させることが示された。
【０１２２】
【表２】

【０１２３】
実施例５
正極材料ＬｉＦｅＰＯ_４を、以下の手順で合成した。
５．０１６１ｇのＦｅ_３（ＰＯ_４）_２・８Ｈ_２Ｏ（添川理化学株式会社製）、１．１５７９ｇのＬｉ_３ＰＯ_４（和光純薬工業株式会社製）に略１．５倍体積のエタノールを加え、２ｍｍ径ジルコニアビーズおよびジルコニアポットを有する遊星ボールミルを用いて粉砕・混合後、減圧下５０℃にて乾燥した。乾燥後の粉砕・混合物をアルミナ製るつぼに入れ、１００体積％アルゴン（Ａｒ）ガスを２００ｍｌ／分の流量で通気しながら、まず４００℃にて５時間仮焼成した。取出した仮焼成後の原料４．１２４８ｇに、０．１９０４ｇの軟化温度２００℃の精製石炭ピッチ［アドケムコ株式会社製ＭＣＰ−２００（商品名）］を加え、めのう乳鉢にて粉砕後、さらに同雰囲気で７００℃にて１０時間本焼成を行った（ガスは、昇温開始前から焼成中、さらに放冷後まで流通しつづけた）。これにより合成された正極材料は、粉末Ｘ線回折によりオリビン型結晶構造を有するＬｉＦｅＰＯ_４であると同定された。一方、酸化態不純物であるα−Ｆｅ_２Ｏ_３、ＦｅＰＯ_４などや、それ以外の不純物の結晶回折ピークは認められなかった。
【０１２４】
また、元素分析から精製石炭ピッチの熱分解により生じた炭素が３．１６重量％含有されていることが判ったものの、Ｘ線回折からは黒鉛結晶の回折ピークは認められなかったことから、非晶質炭素との複合体を形成していると推定された。また、結晶子サイズは、１９４ｎｍであった。
【０１２５】
この正極材料を用い、実施例１と同様の条件で正極ペレットおよびコイン型リチウム２次電池を作製した。
【０１２６】
以上のようにして得た正極材料を組み込んだ２次電池に対して、正極ペレットの見かけ面積当たりの電流密度０.５ｍＡ／ｃｍ^２および１.６ｍＡ／ｃｍ^２にて、３.０Ｖ〜４.０Ｖの作動電圧範囲で充放電を繰り返したところ、１〜２０サイクルの平均初期放電容量は表３に示すとおりであった（初期放電容量は、生成物中の正極活物質量で規格化した）。
【０１２７】
また、このコイン型リチウム２次電池の上記条件における１０サイクル目の充放電特性を図４に示した。
【０１２８】
比較例５
実施例５に対し、軟化温度２００℃の精製石炭ピッチを仮焼成前の原料に加えて仮焼成および本焼成を行った以外は、実施例５と同様の合成方法によって正極材料オリビン型ＬｉＦｅＰＯ_４を得た。
すなわち、実施例５と同量のＦｅ_３（ＰＯ_４）_２・８Ｈ_２Ｏ（添川理化学株式会社製）、およびＬｉ_３ＰＯ_４（和光純薬工業株式会社製）に０．１９４０ｇの軟化温度２００℃の精製石炭ピッチを加え、遊星ボールミルを用いて粉砕・混合、および乾燥後、アルミナ製るつぼ中で同一のアルゴン雰囲気にて４００℃で５時間仮焼成し、粉砕後、さらに同雰囲気で７００℃にて１０時間本焼成した。得られた正極材料は、Ｘ線回折では実施例５とほとんど差異が見られず、また結晶子サイズは１８９ｎｍであり、実施例５とほとんど差がなかった。また、元素分析から、精製石炭ピッチの熱分解により生じた炭素が３．０４重量％含有されており、析出炭素量にも実施例５と大きな差はないことが判明した。
【０１２９】
この正極材料について、実施例５と同様に構成したコイン型リチウム２次電池を作製し、実施例５と同様にして充放電サイクル試験を実施した。この１〜２０サイクルの平均初期放電容量も表３に示した。
【０１３０】
また、このコイン型リチウム２次電池の上記条件における１０サイクル目の充放電特性を図５に示した。
【０１３１】
表３に示すように、仮焼成前の原料に精製石炭ピッチを添加した比較例５についても、比較的大きな初期放電容量を示し、精製石炭ピッチ添加による効果が認められるが、仮焼成後の原料に精製石炭ピッチを添加した実施例５では初期放電容量がさらに大きくなることが判る。
【０１３２】
また、図４と図５を比較すると、仮焼成後に石炭ピッチを加えた実施例５は、仮焼成前に石炭ピッチを加えた比較例５に比べて、より大きな容量値まで充放電電圧の平坦域を有しており、充電電圧と放電電圧の差も少ないことから、充放電特性に優れていることが理解される。
【０１３３】
従って、水素を含まない１００％アルゴンの焼成雰囲気の場合においても、仮焼成後の原料に石炭ピッチを添加することで、より高い正極性能が得られることが判った。
【０１３４】
なお、実施例５のように、デキストリンに比べて溶融時の粘性が比較的低い精製石炭ピッチを用いた場合は、必ずしも水素を焼成雰囲気に添加させなくとも、得られる正極材料が比較的大きな放電容量を示す場合がある。
【０１３５】
【表３】

【０１３６】
【発明の効果】
本発明方法によれば、正極材料の１次粒子の結晶成長を抑制して、得られる正極材料の結晶粒子を細粒化することができる。すなわち、導電性炭素前駆物質および／または導電性炭素を所定のタイミングで添加して、好ましくは水素および／または水分（水または水蒸気）を供給しながら正極材料の原料を焼成することにより、生じる正極材料の１次粒子を効率的に細粒化させ、さらに導電性炭素が均一かつ安定に正極材料中に存在した状態を作り出すことが可能になり、より高い正極性能を得ることができる。
【０１３７】
また、本発明方法によれば、原料の焼成が不十分で最終製品にまで化学変化しなかったり、中間生成物が残留したりする恐れはなく、焼成によって目的の正極材料を原料から確実に合成できる。
【０１３８】
また、水素および／または水分は、強い結晶成長抑制作用および加熱により導電性炭素を析出する物質の正極材料への付着状態を改善する強い作用を持つとともに、取り扱いが容易であり、しかも安価であるため、効率的である。
【０１３９】
また、上記方法によって製造された正極材料を用いた本発明の２次電池は、正極材料の結晶粒子が細粒化されているので、正極材料と電解質との界面においてリチウムイオンを初めとするアルカリ金属イオンの脱ドープ／ドープを伴う電気化学的酸化／還元を該正極材料が受ける際の表面積が大きく、正極材料の粒子内部と電解質との界面でアルカリ金属イオンが容易に出入りできるため、電極反応分極が抑制される。さらに、正極材料に通例混合されるカーボンブラック等の導電性付与材と正極材料との接触が著しく向上するため、導電性が改善されており、正極材料の活物質としての利用率が高く、セル抵抗の小さい、電圧効率と有効電池放電容量が著しく向上した２次電池である。
【図面の簡単な説明】
【図１】２次電池の充放電挙動の説明に供する模式図。
【図２】実施例３で得たコイン型２次電池の充放電特性を示すグラフ図面。
【図３】比較例３で得たコイン型２次電池の充放電特性を示すグラフ図面。
【図４】実施例６で得たコイン型２次電池の充放電特性を示すグラフ図面。
【図５】比較例５で得たコイン型２次電池の充放電特性を示すグラフ図面。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a secondary battery positive electrode material and a secondary battery having the positive electrode material, and more specifically, for example, an alkali metal such as lithium or sodium, or a metal lithium battery using these compounds as active materials. The present invention relates to a method for producing a positive electrode material used for a secondary battery represented by a lithium ion battery, a lithium polymer battery, and the like, and a secondary battery having a positive electrode material produced by the method.
[0002]
[Prior art]
Metal oxides used in secondary batteries such as metal lithium batteries, lithium ion batteries, and lithium polymer batteries, and oxides in which metal atoms are partially substituted, and LiFePO₄, LiCoPO₄Phosphate such as Fe₂(SO₄)₃In a positive electrode material such as sulfate such as lithium, an electrode oxidation-reduction reaction proceeds in a form accompanied by doping / dedoping of alkali metal ions such as lithium during discharge or charging. Such secondary batteries have recently attracted attention as large-capacity batteries. However, in the positive electrode of these batteries, since the rate of alkali metal ions moving inside the electrode material by solid phase diffusion limits the electrode reaction rate, the electrode reaction polarization during charging and discharging is generally large, and a relatively large current It is difficult to charge and discharge at a density. When this polarization is particularly large, charging / discharging does not proceed sufficiently under normal voltage / current density conditions, and only a capacity much smaller than the theoretical capacity can be used. In addition, metal oxides, phosphates, sulfates, metal oxoacid salts, and the like that are often used for these positive electrode materials generally have a low electrical conductivity, which also increases the polarization of the electrode reaction.
[0003]
In order to improve the above problems, it is effective to make the crystal particles of the positive electrode material fine so that alkali metal ions can easily enter and exit the particles. Further, if the crystal grains are made finer, the contact area between the positive electrode material and the conductivity imparting material such as carbon black, which is usually mixed with the positive electrode material, is increased, so that the conductivity is improved. It is possible to improve voltage efficiency and effective battery capacity as well as reducing polarization.
[0004]
For this purpose, in the synthesis of the positive electrode material by firing, in recent years, the cathode temperature is reduced by using a highly reactive raw material and the firing time is restricted to further suppress the crystal growth of the positive electrode material, and the positive electrode material having a small particle size. Attempts have been reported. For example, LiFePO, which is a positive electrode material for lithium secondary batteries₄In the production of LiOH · H, which is highly reactive as a lithium raw material₂By using O, the firing temperature is lowered to 675 ° C., which is lower than usual (usually about 800 to 900 ° C.), and firing is carried out in argon for a relatively short time (about 24 hours). (The 40th Battery Discussion Session Announcement 3C14 (Preliminary Proceedings, p349, 1999); The Electrochemical Society of Japan (Japan)) has been made.
[0005]
Further, although it is not a method for suppressing the crystal growth of the electrode material, Japanese Patent Laid-Open No. 2001-15111 discloses a chemical formula A_aM_mZ_zO_oN_nF_f(In the formula, A is an alkali metal, M is Fe, Mn, V, Ti, Mo, Nb, W or other transition metal, Z is S, Se, P, As, Si, Ge, B, Sn or other non-metal. ) By depositing carbon on the surface of particles of complex oxides (including oxoacid salts such as sulfates, phosphates, silicates, etc.) represented by A method of improving efficiency by homogenizing and stabilizing the composite oxide particles, the current collector (conductivity-imparting) material, and the electric field across the electrolyte interface during the process of electrode redox reaction is disclosed. Has been. In this method, as a method for precipitating carbon on the particle surface of the composite oxide, organic substances (polymer, monomer, low molecule, etc.) that precipitate carbon by thermal decomposition are coexistent, or carbon monoxide is added. Has been proposed (there is coexistence with the raw material of the composite oxide, it is possible to obtain a composite of the composite oxide and surface carbon by reacting at a time under reducing conditions, ). By these means, in Japanese Patent Laid-Open No. 2001-15111, the above-described improvement in the conductivity of the surface of the composite oxide particles is realized.₄When a Li polymer battery is constructed by preparing a composite in which carbon is deposited on the surface of positive electrode material particles such as, a high electrode performance such as a large discharge capacity is obtained.
[0006]
Furthermore, according to JP 2002-110163 A, the general formula LixFePO₄(However, 0 <x ≦ 1) A compound raw material is mixed, milled, and calcined at any point of firing, and the oxygen concentration in the firing atmosphere is 1012 ppm ( A method for producing a positive electrode active material with a volume) or less has been proposed. In the method described in this publication, LiFePO synthesized by firing is used.₄Fe in the carbon composite is oxidized by oxygen in the firing atmosphere, and a trivalent Fe compound (Fe₂O₃) And other impurities are produced and LiFePO₄In order to prevent the single phase synthesis from being hindered, it is also suggested to add a reducing gas such as an inert gas or hydrogen for the purpose of suppressing the oxygen concentration to 1012 ppm (volume).
[0007]
[Problems to be solved by the invention]
When the positive electrode material is synthesized by firing, such as the method of the 40th Battery Conference Presentation 3C14 (ibid. P349, 1999), firing is insufficient when the temperature is lowered or the firing time is shortened. As a result, there is a risk that the final product may not be chemically changed or an intermediate product may remain, so that there is a limit to the method of atomization.
[0008]
Further, the method of Japanese Patent Application Laid-Open No. 2001-15111 is effective for improving the surface conductivity of the electrode material, but there is no description about the suppression of crystal growth during the synthesis of the electrode material. There is no description of a method for more suitably controlling the deposition of carbon on the material in terms of electrode performance.
[0009]
In the method described in Japanese Patent Laid-Open No. 2002-110163, the meaning of the non-oxygen atmosphere is none other than to prevent oxidation of Fe during the firing process as described above. In addition, the carbon material added by the method described in this publication is an amorphous carbon material such as acetylene black, and it can be added to the fired raw material.₄"Carbon composite" is referred to as "LiFePO₄As it is clear from the definition that `` the particle surface has many carbon material particles attached '', the added carbon material adheres between the positive electrode active material particles and improves the electron conductivity. Stop to let. For this reason, in Japanese Patent Laid-Open No. 2002-110163, there is no technical idea that, for example, conductive carbon is uniformly deposited on the positive electrode active material. In addition, no consideration has been given to conditions for allowing the carbon material to exist in a more desirable form in terms of electrode performance, and only a simple temperature raising process is employed for the firing conditions.
[0010]
The object of the present invention is to reliably synthesize the desired positive electrode material from the raw material by firing, and to suppress the crystal growth of the primary particles of the positive electrode material to make it finer and to impart excellent conductivity. It is another object of the present invention to provide a novel method for producing a positive electrode material for a secondary battery, and further, lithium is first introduced between the inside of the positive electrode material particle and the electrolyte by reducing the size of the positive electrode material and optimizing the conductivity. This increases the contact efficiency between the positive electrode material and the conductivity-imparting material, improves the conductivity, and improves the voltage efficiency and the effective battery capacity. The object is to provide a secondary battery.
[0011]
[Means for Solving the Problems]
  To solve the above problem,First aspectThe invention of the manufacturing method of the secondary battery positive electrode material ofGround and mixedRaw materialsIn the absence of oxygen gasBakedContains alkali metals, transition metals and oxygenIn a method for producing a positive electrode material for a secondary battery for producing a positive electrode material, the firing process includes a first stage from room temperature to 300 ° C. to 450 ° C. and a second stage from room temperature to the firing completion temperature, and thermal decomposition A substance capable of generating conductive carbon is added to the raw material after the first stage baking, and then the second stage baking is performed.
[0012]
According to the invention of the manufacturing method of the secondary battery positive electrode material, the substance that can generate conductive carbon by thermal decomposition is added to the raw material after the first stage baking, and the second stage baking is performed. A substance capable of generating conductive carbon by decomposition can be prevented from foaming by a gas generated by decomposition of the raw material during firing. As a result, the substance in the molten state spreads more uniformly on the surface of the positive electrode material in a molten state, and pyrolytic carbon can be deposited more uniformly. For this reason, the surface conductivity of the positive electrode material obtained is further improved, and the contact is firmly stabilized.
[0013]
  Also,Second aspectThe invention of the manufacturing method of the secondary battery positive electrode material ofGround and mixedRaw materialsIn the absence of oxygen gasBakedContains alkali metals, transition metals and oxygenIn the method for manufacturing a positive electrode material for a secondary battery that manufactures a positive electrode material, the firing process includes a first stage from room temperature to 300 ° C. to 450 ° C. and a second stage from room temperature to a firing completion temperature, After adding carbon to the raw material before the first stage baking and adding a substance capable of generating conductive carbon by thermal decomposition to the raw material after the first stage baking, the second stage baking. It is characterized by performing.
[0014]
  According to the invention of the manufacturing method of the secondary battery positive electrode material,The first aspectIn addition to the same action and effect, by adding conductive carbon to the raw material before firing in the first stage and performing firing, the contact time between the heat-reacting raw material and the conductive carbon can be increased. In the meantime, the diffusion of the constituent elements of the positive electrode material caused by the reaction causes the positive electrode material to enter the carbon grain boundaries to form a more uniform and stable carbon-positive electrode material composite. Sintering can be effectively prevented.
[0015]
  Also,Third aspectThe secondary battery positive electrode material manufacturing method according to the present invention is a secondary battery positive electrode material manufacturing method in which a raw material is fired to produce a positive electrode material, wherein the firing step is a first stage from room temperature to 300 ° C. to 450 ° C. And a second stage from normal temperature to a firing completion temperature, and conducting firing by adding conductive carbon to the raw material before firing in the first stage.
[0016]
According to the invention of the method for producing a secondary battery positive electrode material, crystal growth of the primary particles of the positive electrode material can be suppressed, and the crystal particles of the obtained positive electrode material can be refined. That is, by adding conductive carbon to the raw material before firing in the first stage and performing firing, the contact time between the raw material to be heated and the conductive carbon can be increased, and the positive electrode generated by the reaction during that time By diffusion of the constituent elements of the material, the positive electrode material enters the grain boundary of the conductive carbon, and a more uniform and stable carbon-positive electrode material composite can be formed.
[0017]
  Also,Fourth aspectThe invention of the manufacturing method of the secondary battery positive electrode material of the1st aspect or 2nd aspectIn the above, the substance capable of generating conductive carbon by the thermal decomposition is bitumen. Bitumens can produce conductive carbon by thermal decomposition and impart conductivity to the positive electrode material.
[0018]
  Also,Fifth aspectThe invention of the manufacturing method of the secondary battery positive electrode material ofThe fourth aspectIn the above, the bitumens are in the range of softening temperature from 80 ° C to 350 ° C, the weight loss starting temperature by thermal decomposition is in the range of 350 ° C to 450 ° C, and the thermal decomposition / firing is from 500 ° C to 800 ° C. This is a coal pitch capable of depositing conductive carbon.
[0019]
The coal pitch having such properties is very inexpensive and melts during firing and spreads uniformly on the surface of the raw material particles during firing, and after pyrolysis, carbon precipitates exhibiting high conductivity are obtained. It is a substance having excellent properties as a substance capable of producing conductive carbon.
[0020]
  Also,Sixth aspectThe invention of the manufacturing method of the secondary battery positive electrode material ofThe first aspect or the second aspectIn the method, the substance capable of generating conductive carbon by the thermal decomposition is a saccharide. By using saccharides, a more excellent crystal growth suppressing effect and conductivity imparting effect can be obtained at the same time. Saccharide generates conductive carbon by thermal decomposition and imparts conductivity to the positive electrode material. In addition, many hydroxyl groups contained in the saccharide strongly interact with the raw material and the generated positive electrode material particle surface, thereby suppressing crystal growth. It is because it is estimated that it also has an effect | action.
[0021]
  Also,Seventh aspectThe invention of the manufacturing method of the secondary battery positive electrode material ofThe sixth aspectIn the above, the saccharide is decomposed in a temperature range of 250 ° C. or higher and lower than 500 ° C., and at least partially takes a melt state once in the temperature rising process from 150 ° C. to decomposition, and further 500 ° C. or higher and 800 ° C. or lower. It is a saccharide that produces conductive carbon by thermal decomposition until. The saccharide having such specific properties is suitably coated on the surface of the positive electrode material particles during the heating reaction by melting, and deposits conductive carbon well on the surface of the positive electrode material particles generated after the thermal decomposition. In this process, crystal growth is suppressed as described above. For this reason, the saccharide | sugar of the said specific property has the outstanding crystal growth inhibitory effect and electroconductivity provision effect.
[0022]
  Also,Eighth aspectThe invention of the manufacturing method of the secondary battery positive electrode material ofAny one of the first to seventh aspects1 or 2 or more types selected from the group consisting of hydrogen, water and water vapor are added at a temperature of at least 500 ° C. in the second stage firing. According to this feature, it is possible to suppress the crystal growth of the primary particles of the positive electrode material and to refine the crystal particles of the obtained positive electrode material.
[0023]
  That is, in the firing including the first stage from room temperature to 300 ° C. to 450 ° C. and the second stage from room temperature to the firing completion temperature, conductive carbon is generated by thermal decomposition in the raw material after the first stage firing. In the case where hydrogen and / or moisture (water or water vapor) is added at least at a temperature of 500 ° C. or higher after adding the substance to be obtained,The first aspectIn addition to the effects described above, the primary particles of the positive electrode material produced can be efficiently finely divided, and the conductive carbon can be deposited on the positive electrode material particles more uniformly and stably, so that higher positive electrode performance can be obtained. In this process, if hydrogen (including hydrogen generated from moisture) comes into contact with a conductive carbon precursor that melts and pyrolyzes by heating, the melt viscosity of the substance is reduced, presumably through a hydrogenation reaction, which is even better. A carbon deposition state can be realized.
[0024]
  In addition, in the firing including the first stage from room temperature to 300 ° C. to 450 ° C. and the second stage from room temperature to the firing completion temperature, conductive carbon is added to the raw material before firing in the first stage. After firing, a substance capable of generating conductive carbon by thermal decomposition is added to the raw material after the first stage firing, followed by a second stage firing. At least in the temperature range of 500 ° C. or higher, hydrogen and Also when adding moisture (water or water vapor)The second aspectIn addition to the effects described above, primary particles of the positive electrode material produced can be efficiently finely divided, and conductive carbon can be deposited on the positive electrode material particles more uniformly and stably, and higher positive electrode performance can be obtained.
[0025]
  In addition, in the firing including the first stage from room temperature to 300 ° C. to 450 ° C. and the second stage from room temperature to the firing completion temperature, conductive carbon is added to the raw material before firing in the first stage. When firing and adding hydrogen and / or moisture (water or water vapor) at least in the temperature range of 500 ° C. or higher of the second stage firing,The third aspectIn addition to the effects described above, the primary particles of the positive electrode material that are produced can be efficiently finely divided.
[0026]
In addition, according to the method of the present invention, there is no fear that the raw material is insufficiently fired and does not chemically change to the final product, or the intermediate product remains, and the target positive electrode material is reliably synthesized from the raw material by firing. it can.
[0027]
In addition, hydrogen and / or moisture have a strong crystal growth suppressing action and a strong action to improve the adhesion state of substances that deposit conductive carbon by thermal decomposition to the positive electrode material, and are easy to handle and inexpensive. Therefore, it is efficient.
[0028]
Further, the substance capable of generating conductive carbon by the thermal decomposition is bitumen, and in particular, the softening temperature is in the range of 80 ° C. to 350 ° C., and the weight loss starting temperature by the thermal decomposition is in the range of 350 ° C. to 450 ° C. In the case where the coal pitch is capable of producing conductive carbon by pyrolysis / firing at 500 ° C. to 800 ° C., the coal pitch is melted and pyrolyzed by heating during the second stage firing, In a temperature range of at least 500 ° C. or higher, it comes into contact with hydrogen and / or moisture (water or water vapor), so that the conductive carbon deposited on the resulting positive electrode material particles is better in terms of positive electrode performance. Improved to the condition.
[0029]
The substance capable of generating conductive carbon by the thermal decomposition is decomposed in saccharides, particularly in a temperature range of 250 ° C. or higher and lower than 500 ° C., and at least partially once in the temperature rising process from 150 ° C. to decomposition. In the case of a saccharide (for example, dextrin, etc.) that takes a melt state and can generate conductive carbon by thermal decomposition and calcination to 500 ° C. or higher and 800 ° C. or lower, In the process of melting and pyrolysis by heating, it comes into contact with hydrogen and / or moisture (water or water vapor) at least in the temperature range of 500 ° C. or more. The state is improved to a better state in terms of positive electrode performance.
[0030]
  Also,Ninth aspectThe invention of the manufacturing method of the secondary battery positive electrode material ofAny one of the first to eighth aspectsThe cathode material contains an alkali metal, a transition metal and oxygen, and is synthesized by firing the raw material in the absence of oxygen gasBe doneCompound (hereinafter sometimes referred to as "transition metal compound").
[0031]
When the positive electrode material is such a transition metal compound, it can be fired in the absence of oxygen gas when the raw material is added with conductive carbon and / or a substance capable of generating conductive carbon by heating. In addition, the conductive carbon can be favorably deposited on the surface of the positive electrode material of the obtained transition metal compound without burning out. Furthermore, when one or more selected from the group consisting of hydrogen, water and water vapor is added and the raw material is fired in the absence of oxygen gas, the resulting positive electrode material crystal particles are made finer. In particular, the deposition state of a substance capable of producing conductive carbon by thermal decomposition can be well controlled in terms of positive electrode performance. In addition, since hydrogen also has reducibility, it is generated by oxidation with residual oxygen, which is unavoidable even in firing in the absence of oxygen gas, or oxidized impurities (for example, positive electrode material LiFe that originally existed in the raw material).²⁺PO₄Lithium deficient oxidation impurity Fe³⁺PO₄And oxidized oxide Fe₂O₃Etc., which generally leads to a decrease in the discharge capacity of the battery) is reduced by the action of hydrogen having reducibility and changes to the target positive electrode material, so that the oxidation impurities are mixed into the positive electrode material. It can also be prevented. In addition, when water or water vapor (hereinafter referred to as “moisture”) is added, conductive carbon or a substance capable of producing conductive carbon by heating reacts with moisture during firing, so that hydrogen is generated. It produces the same effect as the reaction.
[0032]
Further, depending on the method of selection of the raw material, the transition metal element in the raw material has a higher valence than the transition metal element in the positive electrode material, and only in the process of firing in the absence of oxygen gas, the target In some cases, the transition metal element in the positive electrode material does not have the same valence. Even in such a case, it is possible to reduce the generated positive electrode material as much as necessary by adding hydrogen having a necessary and sufficient reducibility to the raw material (or hydrogen generated secondarily from moisture). The intended positive electrode material can be obtained. Furthermore, the transition metal element in the raw material has a higher valence than the transition metal element in the positive electrode material, and is the same as the transition metal element in the target positive electrode material only by firing in the absence of oxygen gas. Even in the case where the valence is not reached, the target cathode material may be obtained by performing necessary and sufficient reduction by firing in the presence of hydrogen.
[0033]
  Also,Tenth aspectThe invention of the manufacturing method of the secondary battery positive electrode material ofThe ninth stateIn the above, the positive electrode material is M_{(1) a}M_{(2) x}A_yO_z[Where M₍₁₎Represents Li or Na, M₍₂₎Represents Fe (II), Co (II), Mn (II), Ni (II), V (II) or Cu (II), A represents P or S, and a is a number selected from 0 to 3(However, 0 is not included), X represents a number selected from 1 to 2, y represents a number selected from 1 to 3, z represents a number selected from 4 to 12, respectively] or a complex thereof It is characterized by.
[0034]
  Also,Eleventh aspectThe invention of the manufacturing method of the secondary battery positive electrode material ofNinth aspectIn the above, the positive electrode material is Li_qFePO₄, Li_qCoPO₄Or Li_qMnPO₄(Where q is a number selected from 0 to 1)(However, 0 is not included)It is characterized by being a substance represented by the general formula (2) or a complex thereof.
[0035]
  the aboveTenth and eleventh aspectsAs for the positive electrode material described in the above, a compound having a transition element having the same valence as that in the target positive electrode material can be adopted as the raw material, and the target material is calcined from the raw material in an oxygen-free condition (for example, in an inert gas). It is possible to synthesize a positive electrode material. For this reason, even if conductive carbon, a substance that can generate conductive carbon by thermal decomposition, and hydrogen gas having reducibility are added during firing, it can be avoided that it is burned and consumed. In addition, firing can be stably controlled without causing a significant increase in local temperature. In addition, particularly in the case of these positive electrode material systems, when hydrogen or the like is added and baked, the valence of the central metal element [Fe, Co, Mn, Ni, V, Cu, etc.] is further increased by the reducing power. It is difficult for the impurities (for example, a metallic state) to occur in the positive electrode material.
[0036]
  Also,12th aspectThe invention of the secondary battery ofAny one of the first to eleventh aspectsThe positive electrode material manufactured by the method described in 1 is included as a constituent element. In the secondary battery using the positive electrode material manufactured by the method of the present invention, since the crystal particles of the positive electrode material are finely divided, the removal of alkali metal ions such as lithium ions at the interface between the positive electrode material and the electrolyte is eliminated. Electrode oxidation / reduction accompanied by doping / doping has a large surface area when the positive electrode material is subjected to it, and since alkali metal ions can easily enter and exit at the interface between the particles of the positive electrode material and the electrolyte, electrode reaction polarization is suppressed. The Furthermore, since the contact between the positive electrode material and the conductivity imparting material such as carbon black, which is usually mixed with the positive electrode material, is remarkably improved, the conductivity is improved, and the utilization rate of the positive electrode material as the active material is high. It is a secondary battery having a small resistance and a markedly improved voltage efficiency and effective battery discharge capacity.
[0037]
DETAILED DESCRIPTION OF THE INVENTION
The secondary battery positive electrode material manufacturing method of the present invention is a secondary battery positive electrode material manufacturing method in which a raw material is fired to produce a positive electrode material, wherein the firing step is a first stage from room temperature to 300 ° C. to 450 ° C. And a second stage from normal temperature to the completion temperature of firing, and (1) a substance capable of producing conductive carbon by thermal decomposition (hereinafter referred to as “conductive carbon precursor”) after firing in the first stage After the addition to the raw material, the second stage firing is performed, or (2) conductive carbon is added to the raw material before the first stage firing and the firing is performed, or the above (1) and (2) This is done by doing both. In a particularly preferred embodiment, in addition to the above (1) and / or (2), one or more selected from the group consisting of hydrogen, water and water vapor is at least 500 ° C. in the second stage firing. It is better implemented by adding at temperature.
[0038]
In the present invention, “adding” gaseous hydrogen or water vapor includes firing the raw material in the presence of a gas such as hydrogen (ie, in a hydrogen atmosphere).
[0039]
<Positive electrode material>
As the positive electrode material in the present invention, for example, a compound that contains an alkali metal, a transition metal, and oxygen and can be synthesized by firing the raw material in the absence of oxygen gas is preferable. More specifically, as the positive electrode material, for example, M_{( 1 ) A}M_{( 2 ) X}A_yO_z[Where M_{( 1 )}Represents Li or Na, M_{( 2 )}Represents Fe (II), Co (II), Mn (II), Ni (II), V (II) or Cu (II), A represents P or S, and a represents a number selected from 0 to 3. , X represents a number selected from 1 to 2, y represents a number selected from 1 to 3, z represents a number selected from 4 to 12, respectively] or a complex thereof Can do. Here, (II), (III), etc. are transition metal elements M₍₂₎X, y, and z are values satisfying the stoichiometric (electrical) neutral condition of the material. M₍₂₎Includes a plurality of combinations of elements having the same valence among the transition metal elements exemplified above [for example, M₍₂₎This corresponds to the case where is Fe (II) Co (II) or Fe (II) Mn (II). At this time, the total number of moles of Fe (II) and Co (II) or Fe (II) and Mn (II) is x moles per mole of Li (M above)₍₁₎= Li and a = 1)]].
[0040]
These substances can generally be synthesized from the raw material by firing in the absence of oxygen gas (ie, in an inert gas atmosphere such as argon, nitrogen, helium, etc.), and their crystal skeleton structure (spinel type, olivine type) In general, a NASICON type is used, but when it hardly changes due to electrochemical redox, it can be used as a positive electrode material for an alkali metal secondary battery capable of repeated charge and discharge. As the positive electrode material, the state of these substances as they are corresponds to the discharge state, and the alkali metal M is obtained by electrochemical oxidation at the interface with the electrolyte._{( 1 )}Central metal element M with undoping₍₂₎Is oxidized and charged. When subjected to electrochemical reduction from the charged state, alkali metal M₍₁₎Central metal element M with re-doping₍₂₎Is returned to the original discharge state.
[0041]
As a preferable positive electrode material, Li_qFePO₄, Li_qCoPO₄Or Li_qMnPO₄(Where q represents a number selected from 0 to 1), and a substance represented by the general formula or a complex thereof can be exemplified._qFePO₄A substance represented by the general formula (where q has the same meaning as described above) is preferred. These materials can be synthesized from the raw material by firing at a temperature of about 900 ° C. or less in the absence of oxygen gas. For example, the positive electrode of a lithium secondary battery such as a lithium battery, a lithium ion battery, or a lithium polymer battery It can be suitably used as a material.
[0042]
<Raw material>
As a raw material of the positive electrode material, for example, an alkali metal, a compound containing at least the transition metal and oxygen (transition metal compound), or a combination of a plurality of compounds can be used. Usually, the transition metal element in the raw material originally has the same valence as the transition metal element in the positive electrode material, or is fired in the absence of oxygen gas at a predetermined firing temperature and firing time. It is reduced and has the same valence as the transition metal element in the positive electrode material. At this time, when hydrogen or the like is added and the raw material is fired, the crystal particles of the obtained positive electrode material are further refined.
[0043]
More specifically, as a raw material material of the positive electrode material, for example, as a raw material for introducing an alkali metal, a hydroxide such as LiOH or NaOH, Li₂CO₃, Na₂CO₃NaHCO₃Carbonates and bicarbonates such as, halides containing chlorides such as LiCl and NaCl, LiNO₃, NaNO₃In addition, a decomposition volatile compound (for example, an organic acid salt or the like) such as nitrate remaining in the target cathode material only for alkali metal is used. When the target positive electrode material is phosphate, Li₃PO₄, Li₂HPO₄, LiH₂PO₄, Na₃PO₄, Na₂HPO₄, NaH₂PO₄In the case where the target positive electrode material is a sulfate,₂SO₄, LiHSO₄, Na₂SO₄, NaHSO₄Sulfates and hydrogen sulfates such as can also be used.
[0044]
Moreover, as a raw material for introducing transition metals such as Fe, Co, Mn, and V, for example, hydroxides, carbonates, bicarbonates, halides such as chlorides, nitrates, and the like, only the transition metals are intended. Decomposed volatile compounds that remain in the positive electrode material (for example, organic acid salts such as oxalate and acetate, acetylacetone complexes, and organic complexes such as metallocene complexes) are used. In addition, when the target positive electrode material is phosphate, phosphate or hydrogen phosphate, and when the target positive electrode material is sulfate, sulfate or hydrogen sulfate, and these transition metal oxoacid salts and ammonium A double salt with such as can also be used.
[0045]
Further, when the target positive electrode material is phosphate, phosphoric anhydride P₂O₅, Phosphoric acid H₃PO₄, And decomposed volatile phosphates and hydrogen phosphates such as (NH₄)₂HPO₄, NH₄H₂PO₄, (NH₄)₃PO₄In addition, when the target cathode material is sulfate, sulfuric acid H₂SO₄, And decomposition volatile sulfates and hydrogen sulfates (for example, NH₄HSO₄, (NH₄)₂SO₄Etc.) can also be used.
[0046]
When these raw materials contain elements or substances that are not desirable when remaining in the target positive electrode material, it is necessary that these materials decompose and volatilize during firing. Needless to say, when the target product is a phosphate, for example, a non-volatile oxoacid salt other than phosphate ions should not be used as a raw material. In these cases, the hydrate may be used (for example, LiOH.H₂O, Fe₃(PO₄)₂・ 8H₂O and the like, and in the above, all representations as hydrates are omitted.
[0047]
The raw material of the positive electrode material can be subjected to a treatment such as pulverization or mixing and kneading of raw materials (including conductive carbon added in some cases) before firing in the first stage as necessary. . Further, when a conductive carbon precursor (a substance capable of producing conductive carbon by thermal decomposition) is added after the first stage firing, pulverization, mixing, kneading, and the like can also be performed at that time.
[0048]
When the above raw materials are fired in the presence of hydrogen, water, water vapor, etc., there is usually no particular problem, but both of them undergo a rapid reaction at the early stage of firing to obtain the desired positive electrode material. Care must be taken in the selection and combination of the two so that they are not lost or impure.
[0049]
<Conductive carbon>
Examples of the conductive carbon used in the present invention include graphitic carbon and amorphous carbon. Here, graphitic carbon and amorphous carbon include so-called soot, carbon black, and the like.
<Conductive carbon precursor (substance capable of producing conductive carbon by thermal decomposition)>
Examples of conductive carbon precursors include bitumens (so-called asphalt; including pitches obtained from coal and petroleum sludge), sugars, styrene-divinylbenzene copolymers, ABS resins, phenol resins, and other aromatics. And a crosslinked polymer having a group. Among these, bitumens (especially purified so-called coal pitch) and saccharides are preferable. These bitumens and saccharides produce conductive carbon by thermal decomposition and impart conductivity to the positive electrode material. In particular, the refined coal pitch is very inexpensive, melts during firing, spreads uniformly on the surface of the raw material particles being fired, and undergoes a thermal decomposition process at a relatively low temperature (650 ° C. to 800 ° C.). After firing at, carbon precipitates exhibiting high conductivity are obtained. In the case of saccharides, since many hydroxyl groups contained in saccharides interact strongly with the raw material and the surface of the resulting positive electrode material particles, it also has an effect of suppressing crystal growth. This is because a suppressing effect and a conductivity imparting effect can be obtained.
[0050]
Here, as the refined coal pitch, the softening temperature is in the range of 80 ° C to 350 ° C, the weight loss starting temperature by thermal decomposition is in the range of 350 ° C to 450 ° C, and the heating is from 500 ° C to 800 ° C. Those that generate conductive carbon by decomposition and firing are preferably used. In order to further improve the positive electrode performance, a refined coal pitch having a softening temperature in the range of 200 ° C to 300 ° C is more preferable. Needless to say, the impurities contained in the refined coal pitch are preferably those which do not adversely affect the positive electrode performance, but the ash content is preferably 5000 ppm or less.
[0051]
Furthermore, as saccharides, decomposition occurs in a temperature range of 250 ° C. or higher and lower than 500 ° C., and at least partially takes a melt state once in the temperature rising process from 150 ° C. to the temperature range, and further 500 ° C. or higher and 800 ° C. Particularly preferred are saccharides that produce conductive carbon by thermal decomposition and calcination up to ℃ and below. The saccharide having such specific properties is suitably coated on the surface of the positive electrode material particles during the heating reaction by melting, and the conductive carbon is favorably deposited on the surface of the positive electrode material particles generated after the thermal decomposition. This is because crystal growth is suppressed. Here, in order to produce good electrical conductivity, the thermal decomposition temperature can be preferably set to 570 ° C. or higher and 850 ° C. or lower, more preferably 650 ° C. or higher and 800 ° C. or lower, although it depends on the type of positive electrode material. The saccharide should be capable of producing at least 15% by weight, preferably 20% by weight or more of conductive carbon based on the dry weight of the saccharide before baking, by thermal decomposition. This is to facilitate the quantitative management of the conductive carbon produced. Examples of the saccharide having the above properties include high-molecular polysaccharides such as oligosaccharides such as dextrin, soluble starch, and starch with low cross-linking that is easily melted by heating (for example, starch containing 50% or more amylose). It is done.
[0052]
<Addition and firing of conductive carbon precursors>
The conductive carbon, the refined coal pitch, and the conductive carbon precursor represented by saccharide are mixed and added to the raw material (including the intermediate product) at an appropriate timing. At the time of addition, an operation for sufficiently mixing with the raw material, for example, pulverization or kneading can be performed as necessary.
[0053]
Conductive carbon or conductive carbon precursor has a conductive carbon weight concentration of 0.1% to 10%, preferably 0.5% to 7%, more preferably 1% or more in the positive electrode material produced. It can add so that it may become 5% or less.
[0054]
Firing can be carried out by selecting an appropriate temperature range and time in a firing process up to 300 to 900 ° C. as generally employed, although depending on the target positive electrode material. In addition, the firing is preferably performed in the absence of oxygen gas in order to promote the generation of oxidized impurities and the reduction of remaining oxidized impurities.
[0055]
In the method of the present invention, the firing is not carried out by a series of temperature rise and subsequent temperature holding process only once, but a firing process in a lower temperature region of the first stage (usually from normal temperature to 300 to 450 ° C. Temperature range; hereinafter referred to as “temporary firing”), and firing process in a higher temperature range of the second stage (usually normal temperature to firing completion temperature (about 500 ° C. to 800 ° C.); hereinafter, “main firing” This may be divided into two stages. In this case, the performance of the positive electrode material obtained can be further improved by mixing the conductive carbon and the conductive carbon precursor at the following timing.
[0056]
In the pre-baking, the raw material of the positive electrode material reacts to an intermediate state that reaches the final positive electrode material by heating, and in this case, gas generation is often caused by thermal decomposition. The temperature at which the calcining is finished is a temperature at which most of the generated gas has been released and the reaction leading to the positive electrode material of the final product does not proceed completely (that is, during the second stage of the main calcination at a higher temperature range). The temperature that leaves room for re-diffusion / homogenization of the constituent elements in the positive electrode material is selected.
[0057]
In the main firing following the pre-firing, the constituent elements are re-diffusioned and made uniform, the reaction to the positive electrode material is completed, and the temperature is raised and maintained to a temperature range that prevents crystal growth due to sintering as much as possible. Made.
[0058]
When using conductive carbon precursors, especially coal pitch or saccharide that melts by heating, it can be added to the raw material before pre-firing (even in this case, a corresponding positive electrode performance improvement effect can be obtained), In order to obtain a high-performance positive electrode material, it is more preferable to add to the raw material after pre-baking (a state where most of the gas generation from the raw material has already been completed and become an intermediate product) and to perform main baking. That is, a step of adding a conductive carbon precursor to the raw material is provided between the preliminary firing and the main firing in the firing process.
[0059]
This prevents substances such as coal pitch and saccharides that are melted and pyrolyzed by heating from being foamed by the gas generated from the raw material, spread more uniformly in the molten state on the surface of the positive electrode material, and more uniformly pyrolytic carbon. Can be deposited.
[0060]
This is due to the following reason.
That is, most of the gas generated by decomposition of the raw material in the pre-firing is released. As a result, almost no gas is generated in the main firing. By adding the conductive carbon precursor at the timing after the pre-firing, uniform It is possible to deposit conductive carbon. For this reason, the surface conductivity of the positive electrode material obtained is further improved, and the contact is firmly stabilized. On the other hand, when the conductive carbon precursor is added to the raw material before the temporary firing, the conductive carbon precursor that has not been completely thermally decomposed in the molten state by the gas generated vigorously from the raw material during the temporary firing. Foaming prevents uniform precipitation.
[0061]
Addition of carbon that is already conductive and loses weight due to heating, changes in shape and gas generation almost no longer occur (conductive carbon; for example, graphitic carbon such as soot and carbon black, amorphous carbon, etc.) When performing, it is preferable to mix these predetermined amounts with the raw material before temporary baking, and to start a series of baking processes from temporary baking. Thereby, the contact time between the heat-reacting raw material and the conductive carbon can be increased, and the positive electrode material enters the grain boundary of the conductive carbon due to the diffusion of the constituent elements of the positive electrode material generated by the reaction during the reaction. This is because a uniform and stable carbon-positive electrode material composite can be formed and sintering of the positive electrode material particles can be effectively prevented.
[0062]
In addition, it is effective to obtain a positive electrode material having high positive electrode performance by adding both conductive carbon precursors, such as coal pitch and saccharides that are melted and pyrolyzed by heating, and conductive carbon. is there. In this case, it is preferable that conductive carbon is added to the raw material before pre-baking, and substances such as coal pitch and saccharide that are melted and pyrolyzed by heating are added to the raw material after temporary baking.
[0063]
<Supply of hydrogen, etc.>
In a further preferred method of the present invention, the raw material is calcined while continuously supplying a predetermined amount of hydrogen and moisture (water, water vapor, etc.) together with an inert gas into the furnace. For example, over the entire time of the firing process, or particularly at a temperature from 500 ° C. or less to the completion of firing, preferably from 400 ° C. or less to the completion of firing, more preferably from 300 ° C. or less to the firing completion, Hydrogen or moisture can be added.
[0064]
When hydrogen, which is a gas, is used, depending on the target cathode material, a necessary and sufficient amount of hydrogen is selected by selecting an appropriate temperature range and time in a firing process up to 300 to 900 ° C. as generally adopted. It can be supplied and can effectively cause addition or deoxygenation to the oxygen atoms on the surface of the positive electrode material, reduction of the positive electrode material, and the like.
[0065]
In the method of the present invention, hydrogen can be added in a temperature range of at least 500 ° C. during the second stage firing. For example, in the second stage firing, preferably over a temperature range from 500 ° C. or less to the firing completion temperature, more preferably from 400 ° C. or less to the firing completion temperature, desirably from 300 ° C. or less to the firing completion temperature (for example, It can be added over almost the entire firing period). In this range, the crystal growth is effectively suppressed, possibly for the reason described later. In addition, hydrogen can also be added at the time of baking in the first stage.
[0066]
The volume concentration of hydrogen in the atmosphere in the above temperature range can be about 0.1% or more and 20% or less, and preferably 1% or more and 10% or less. Thereby, crystal growth of the positive electrode material made of the transition metal compound is suitably suppressed.
[0067]
In the study by the present inventors, when the raw material of the positive electrode material is baked while supplying hydrogen and / or moisture in the absence of oxygen gas, the crystallinity of the resulting positive electrode material particles is slightly disturbed and produced 1 It was found that the secondary particles were made finer. That is, it has been demonstrated that hydrogen and moisture are effective crystal growth inhibitors. Although this mechanism is not yet clear, on the growth surface of the crystal particles of the cathode material that is synthesized and grown during firing, hydrogen is bonded to surface oxygen atoms to form hydroxyl groups, or water molecules generated from the hydroxyl groups It is considered that the growth of particles is suppressed as a result of disordering and mismatching of the crystal surface structure due to the re-desorption of.
[0068]
Water, like hydrogen, has an effect of suppressing crystal growth. The reason for this is not yet clear, but it is presumed that hydroxyl groups are generated on the surfaces of the raw material and the positive electrode active material as in the case of adding hydrogen gas, which delays crystal growth. Further, water vapor generates hydrogen and carbon monoxide by a so-called water gas reaction by contacting conductive carbon or a substance capable of generating conductive carbon by pyrolysis at a high temperature (about 500 ° C. or more). A crystal growth inhibiting effect and a reducing effect are obtained. In other words, when water is continuously supplied, more hydrogen can be reliably and continuously generated by a water gas reaction even in a high temperature range of 500 ° C. or higher, and crystal growth is suppressed. It is possible to maximize the action and reduction action.
[0069]
As a method for supplying moisture, it is sprayed into a furnace or preferably pre-vaporized and supplied in the form of water vapor. The supply temperature range and supply amount can be the same as in the case of hydrogen. That is, it is preferable to add water in a temperature range in which the firing is completed from at least 500 ° C. or more during the second stage firing. For example, preferably over a temperature range from 500 ° C. or lower to the firing completion temperature in the second stage firing, more preferably from 400 ° C. or less to the firing completion temperature, desirably from about 300 ° C. to the firing completion temperature (for example, It can be added over almost the entire firing period). In this range, it is likely that hydrogen addition to the surface oxygen atoms and hydroxyl group formation of the transition metal compound are likely to occur favorably, so that crystal growth is effectively suppressed. In addition, hydrogen can also be added at the time of baking in the first stage.
[0070]
The volume concentration of water vapor in the atmosphere in the above temperature range can be about 0.1% to 20%, preferably 1% to 10%. Thereby, crystal growth of the positive electrode material is suitably suppressed.
[0071]
Also, when firing with hydrogen added during the main firing, when the added hydrogen (including hydrogen generated from moisture) comes into contact with conductive carbon precursors such as coal pitch and saccharide that melt and pyrolyze by heating In order to reduce the melt viscosity of the substance, a better state can be realized in the aforementioned carbon deposition method. For example, as a conductive carbon precursor, the softening temperature is in the range of 80 ° C. to 350 ° C., the weight loss starting temperature by thermal decomposition is in the range of 350 ° C. to 450 ° C., and the heating is performed from 500 ° C. to 800 ° C. When using refined coal pitch that produces conductive carbon by decomposition, if hydrogen (including hydrogen generated from moisture) acts on the coal pitch that has been melted during the firing process, its viscosity decreases and fluidity improves. Thus, a very uniform and thin coating state can be realized in the obtained positive electrode material.
[0072]
Accordingly, hydrogen (including hydrogen generated from moisture) is at least from 500 ° C. or lower during the main baking to the baking completion temperature, preferably from 400 ° C. or lower to the baking completion temperature, or throughout the main baking. It is good to add. Furthermore, when hydrogen is added even during pre-firing, an effect such as prevention of oxidation of the positive electrode material due to its reducing property can be expected.
[0073]
An example of the outline of the method for producing a positive electrode material according to the present invention is as follows.
First, when the conductive carbon precursor is added after the preliminary calcination in the first stage of the calcination performed in two stages, [a step of performing crushing, mixing, kneading, etc. of raw materials as necessary], [first Stage firing step], [addition of conductive carbon precursor (can be pulverized, mixed, kneaded, etc., if necessary)], [second stage main firing step].
[0074]
In addition, when conductive carbon is added before the first calcination of the first stage of firing performed in two stages and a conductive carbon precursor is added after the first calcination of the first stage, Step of performing addition (can be pulverized, mixed, kneaded, etc., together with the raw material if necessary)], [First-stage calcination step], [Addition of conductive carbon precursor (if necessary, raw material) (Intermediate) can be pulverized, mixed, kneaded, etc.)] and [second stage main firing step].
[0075]
Furthermore, when adding conductive carbon before the pre-firing of the first stage of firing performed in two stages, [step of conducting conductive carbon (if necessary, pulverization, mixing, kneading, etc. with raw materials) Can also be performed)], [first-stage pre-baking step], [step of performing pulverization, mixing, kneading, etc. of the raw material (intermediate if necessary)], [second-stage main baking step] It is carried out in order.
[0076]
In the above, when hydrogen or moisture is added, at least a part of the second-stage firing process, desirably the entire second-stage firing process, more desirably, the first-stage provisional process. It is also added in at least a part of the firing step.
[0077]
<Secondary battery>
Examples of the secondary battery using the positive electrode material of the present invention obtained as described above include a metal lithium battery, a lithium ion battery, a lithium polymer battery, and the like.
[0078]
Hereinafter, the basic configuration of the alkaline ion battery will be described by taking the case where the alkali metal is lithium as an example. Lithium-ion batteries are commonly called rocking chair types or shuttlecock (badminton blades) types.⁺A secondary battery characterized in that ions reciprocate (see FIG. 1). Lithium inside the negative electrode (current systems use carbon such as graphite) during charging⁺Ions are inserted to form an intercalation compound (at this time, the negative carbon is reduced and Li⁺The positive electrode from which the metal is removed is oxidized), and during the discharge, the positive electrode (currently the mainstream is cobalt oxide, but in FIG. 1, an iron (II) / (III) redox system such as lithium iron phosphate is taken as an example. Li) inside⁺Ions are inserted to form an iron compound-lithium complex (at this time, the iron of the positive electrode is reduced and Li⁺The negative electrode that has been removed is oxidized to return to graphite or the like). Li⁺During charge and discharge, ions travel back and forth in the electrolyte and simultaneously carry charge. Examples of the electrolyte include a mixed solution of a cyclic organic solvent such as ethylene carbonate, propylene carbonate, and γ-butyrolactone and a chain organic solvent such as dimethyl carbonate and ethyl methyl carbonate.₆, LiCF₃SO₃LiClO₄A solid electrolyte such as a liquid electrolyte in which an electrolyte salt such as the above is dissolved, a gel electrolyte in which these liquid electrolytes are impregnated in a polymer gel-like substance, or a partly cross-linked polyethylene oxide impregnated with the above electrolyte is used. When a liquid electrolyte is used, a porous diaphragm (separator) made of polyolefin or the like is sandwiched and insulated so that the positive electrode and the negative electrode are not short-circuited in the battery. For the positive and negative electrodes, a predetermined amount of a conductivity imparting agent such as carbon black is added to each of the positive and negative electrode materials. For example, synthetic resins such as polytetrafluoroethylene, poly (vinylidene fluoride) and fluororesin, and synthesis of ethylene propylene rubber, etc. A battery is formed by collecting a binder such as rubber and, if necessary, further adding a polar organic solvent and kneading and thinning it, and collecting the current with a metal foil or a metal net. On the other hand, when metallic lithium is used for the negative electrode, Li (O) / Li is used for the negative electrode.⁺Changes with charge and discharge, and a battery is formed.
[0079]
[Action]
In general, the aforementioned M_{( 1 ) A}M_{( 2 ) X}A_yO_z[Where M_{( 1 )}, M_{( 2 )}, A, a, x, y, and z have the same meanings as described above], etc., when the raw material is synthesized by firing from the raw materials, generation of decomposition gas occurs during the synthesis reaction in the heating temperature rising process. In most cases, more than 80% of the gas is normally generated in the temperature range from room temperature to 350 ° C. to 450 ° C. In one embodiment of the present invention, after adding a conductive carbon precursor (a substance capable of producing conductive carbon by thermal decomposition) to the raw material of the positive electrode material after the first stage baking from room temperature to 350 ° C. to 450 ° C. By carrying out the second stage of baking, the thermal decomposition of the raw material positive electrode material has already progressed halfway, and most of the gas generation has already ended, so the molten conductive carbon precursor is difficult to foam and uniform And is decomposed and pyrolyzed to deposit carbon in a good state.
[0080]
In addition, in the research by the present inventors, when the raw material of the positive electrode material is baked while supplying hydrogen and / or moisture in the absence of oxygen gas, the crystallinity of the resulting positive electrode material particles is slightly disturbed and generated. It was found that the primary particles to be made finer. That is, it has been demonstrated that hydrogen and moisture are effective crystal growth inhibitors. Although this mechanism is not yet clear, on the growth surface of the crystal particles of the positive electrode material synthesized and grown during firing, hydrogen is bonded to surface oxygen atoms, or water molecules are bonded to the surface between metal and oxygen. Particle growth is suppressed as a result of the formation of hydroxyl groups by phenomena such as cleavage and addition, and the re-desorption of water molecules generated from the hydroxyl groups, resulting in disorder and mismatch in the crystal surface structure. Conceivable.
[0081]
In addition, when conducting baking by adding a conductive carbon precursor to the raw material after pre-firing, adding hydrogen (including hydrogen generated by the reaction of moisture with a conductive carbon precursor such as coal pitch or sugar) Thus, it was found that carbon deposition of the obtained positive electrode material was made uniform, and higher positive electrode performance was obtained. Although this mechanism is not yet clear, by adding the conductive carbon precursor to the raw material after pre-calcining, adding to the conductive carbon precursor in a state where hydrogen is melted, the viscosity is lowered, and the positive electrode This is presumably because of the effect of uniformly depositing conductive carbon on the material particles.
[0082]
On the other hand, by adding conductive carbon to the raw material before firing in the first stage and performing firing, the contact time between the raw material to be heated and the conductive carbon can be increased, and the positive electrode generated by the reaction during that time Due to the diffusion of the constituent elements of the material, the positive electrode material enters the grain boundaries of the conductive carbon, and a more uniform and stable carbon-positive electrode material composite can be formed.
[0083]
And by firing at a temperature of 500 ° C. or higher in at least the second stage firing while supplying hydrogen and / or moisture (water or water vapor), the primary particles of the positive electrode material produced are efficiently finely divided, Sintering of the positive electrode material particles can be effectively prevented.
[0084]
【Example】
EXAMPLES Next, although an Example etc. demonstrate this invention further in detail, this invention is not restrict | limited by these.
Example 1
(1) Preparation of positive electrode material:
Cathode material LiFePO₄Was synthesized by the following procedure.
5.0532 g FeC₂O₄・ 2H₂O (made by Wako Pure Chemical Industries, Ltd.), 3.7094 g of (NH₄)₂HPO₄(Wako Pure Chemical Industries, Ltd.), 1.1784 g of LiOH · H₂Approximately 1.5 times the volume of ethanol was added to O (manufactured by Wako Pure Chemical Industries, Ltd.), pulverized and mixed using a planetary ball mill having 2 mm diameter zirconia beads and zirconia pots, and then dried at 50 ° C. under reduced pressure. The dried pulverized mixture is placed in an alumina crucible and 5 volume% hydrogen (H₂) / 95 vol% argon (Ar) mixed gas was first calcined at 400 ° C. for 5 hours while venting at a flow rate of 200 ml / min. 0.1097 g of refined coal pitch [MCP-200 (trade name) manufactured by Adchemco Co., Ltd.] with a softening temperature of 200 ° C. is added to 2.1364 g of the raw material after calcination taken out, and the same atmosphere is further pulverized in an agate mortar. The main calcination was carried out at 775 ° C. for 10 hours (the mixed gas continued to flow from before the start of temperature increase to during the calcination and after being allowed to cool). The synthesized positive electrode material is LiFePO having an olivine type crystal structure by powder X-ray diffraction.₄Was identified. On the other hand, α-Fe which is an oxidation impurity₂O₃, FePO₄No crystal diffraction peaks of other impurities were observed.
[0085]
Although it was found from elemental analysis that carbon produced by pyrolysis of refined coal pitch contained 3.08% by weight, no diffraction peak of graphite crystal was observed from X-ray diffraction. It was presumed to form a complex with crystalline carbon. The crystallite size was 64 nm.
[0086]
(2) Preparation of secondary battery:
This positive electrode material, acetylene black [DENKA BLACK (registered trademark); manufactured by Denki Kagaku Kogyo Co., Ltd., 50% pressed product] as a conductivity imparting material, and unfired PTFE (polytetrafluoroethylene) powder as a binder Are mixed and kneaded so as to have a weight ratio of 70.6 / 24.4 / 5, rolled into a sheet having a thickness of 0.7 mm, and a pellet punched out to a diameter of 1.0 cm is used as a positive electrode. did.
[0087]
Thereafter, a stainless steel coin battery case (model number CR2032) was spot welded with a metal titanium net and a metal nickel net as positive and negative current collectors, respectively, and the positive electrode and the metal lithium foil negative electrode were assembled via a porous polyethylene diaphragm. 1M LiPF as liquid₆A coin-type lithium secondary battery was manufactured by filling a dimethyl carbonate / ethylene carbonate 1/1 mixed solution in which the solution was dissolved. A series of battery assemblies such as positive and negative electrodes, a diaphragm, and an electrolyte solution were performed in a glove box substituted with argon.
[0088]
For the secondary battery incorporating the positive electrode material obtained as described above, the current density per apparent area of the positive electrode pellet is 0.5 mA / cm.²And 1.6 mA / cm²Then, when charging / discharging was repeated in the operating voltage range of 3.0 V to 4.0 V, the average initial discharge capacity of 1 to 20 cycles was as shown in Table 1 (the initial discharge capacity was determined in the product). Standardized by the amount of positive electrode active material).
[0089]
Comparative Example 1
The positive electrode material olivine-type LiFePO was synthesized by the same synthesis method as in Example 1, except that refined coal pitch with a softening temperature of 200 ° C. was added to the raw material before pre-firing to perform pre-firing and main firing.₄Got.
That is, the same amount of FeC as in Example 1.₂O₄・ 2H₂O, (NH₄)₂HPO₄, And LiOH · H₂0.1940 g of refined coal pitch with a softening temperature of 200 ° C. is added to O, pulverized, mixed, and dried using a planetary ball mill, then calcined at 400 ° C. for 5 hours in the same atmosphere in an alumina crucible, after pulverization Further, this baking was performed at 775 ° C. for 10 hours in the same atmosphere. The obtained positive electrode material was hardly different from Example 1 in X-ray diffraction, and the crystallite size was 64 nm, which was not different from Example 1. In addition, elemental analysis revealed that carbon produced by pyrolysis of refined coal pitch contained 3.04% by weight, and the amount of precipitated carbon was not significantly different from that in Example 1.
[0090]
For this positive electrode material, a coin-type lithium secondary battery configured in the same manner as in Example 1 was produced, and a charge / discharge cycle test was performed in the same manner as in Example 1. The average initial discharge capacity for 1 to 20 cycles is also shown in Table 1.
[0091]
As shown in Table 1, with respect to the initial discharge capacity of Comparative Example 1, effects due to the addition of hydrogen and refined coal pitch are recognized and show a considerably large initial discharge capacity. In Example 1, the initial discharge capacity is further increased. It turns out that it becomes.
[0092]
From the above, as shown in Example 1, when the raw material is temporarily fired and main-fired while adding hydrogen, by adding the coal pitch with a softening temperature of 200 ° C. to the raw material after the temporary firing, Cathode material LiFePO₄It can be seen that the initial discharge capacity of the secondary battery using the battery is further increased and the performance is improved.
[0093]
At this time, the precipitated carbon contents in the positive electrode materials of Example 1 and Comparative Example 1 were almost the same, and there was no difference in the crystallite size. Precipitation of carbon generated from the coal pitch on the surface of the positive electrode material particles occurred in a better state than Comparative Example 1, and as a result, higher positive electrode performance was brought about. This is presumed to be due to the following reason.
First, while the refined coal pitch having a softening temperature of 200 ° C. melts well during the temperature increase of the main firing, most of the gas generated by the decomposition of the raw material is released during the preliminary firing, and the main firing Since only a small amount of gas from the raw material is generated, the refined coal pitch melt does not foam. Secondly, since the added hydrogen lowers the viscosity of the coal pitch melt, it spreads more evenly on the surface of the positive electrode material particles to be produced and is thermally decomposed in that state, so that the conductive carbon is very evenly distributed. Precipitates. From the above, it is considered that extremely high positive electrode performance was obtained.
[0094]
Example 2
Cathode material LiFePO₄Was synthesized by the following procedure.
5.0161 g of Fe₃(PO₄)₂・ 8H₂O (manufactured by Soekawa Riken Co., Ltd.), 1.1579 g of Li₃PO₄Approximately 1.5 times volume ethanol was added to (made by Wako Pure Chemical Industries, Ltd.), pulverized and mixed using a planetary ball mill having 2 mm diameter zirconia beads and zirconia pots, and dried at 50 ° C. under reduced pressure. The dried pulverized mixture is placed in an alumina crucible and 5 volume% hydrogen (H₂) / 95 vol% argon (Ar) mixed gas was first calcined at 400 ° C. for 5 hours while venting at a flow rate of 200 ml / min. To 4.0712 g of the raw material after the pre-calcining, 0.1879 g of refined coal pitch [ADCPEMCO Co., Ltd. MCP-200 (trade name)] with a softening temperature of 200 ° C. is added, pulverized in an agate mortar, and the same atmosphere. The main calcination was performed at 725 ° C. for 10 hours (the mixed gas continued to flow from before the start of temperature increase to during the calcination and further after being allowed to cool). The synthesized positive electrode material is LiFePO having an olivine type crystal structure by powder X-ray diffraction.₄Was identified. On the other hand, α-Fe which is an oxidation impurity₂O₃, FePO₄No crystal diffraction peaks of other impurities were observed.
[0095]
Moreover, although it was found from elemental analysis that carbon produced by pyrolysis of refined coal pitch was contained in 2.98% by weight, no diffraction peak of graphite crystals was observed from X-ray diffraction. It was presumed to form a complex with crystalline carbon. The crystallite size was 167 nm.
[0096]
Using this positive electrode material, a positive electrode pellet and a coin-type lithium secondary battery were produced under the same conditions as in Example 1.
[0097]
For the secondary battery incorporating the positive electrode material obtained as described above, the current density per apparent area of the positive electrode pellet is 0.5 mA / cm.²And 1.6 mA / cm²Then, when charging / discharging was repeated in the operating voltage range of 3.0 V to 4.0 V, the average initial discharge capacity of 1 to 20 cycles was as shown in Table 1 (the initial discharge capacity was determined in the product). Standardized by the amount of positive electrode active material).
[0098]
Comparative Example 2
The positive electrode material olivine type LiFePO was synthesized by the same synthesis method as in Example 2, except that refined coal pitch having a softening temperature of 200 ° C. was added to the raw material before pre-firing and calcined and main-fired.₄Got.
That is, the same amount of Fe as in Example 2.₃(PO₄)₂・ 8H₂O (manufactured by Soekawa Riken) and Li₃PO₄0.1940 g of refined coal pitch with a softening temperature of 200 ° C. is added to (made by Wako Pure Chemical Industries, Ltd.), pulverized, mixed and dried using a planetary ball mill at 400 ° C. in the same atmosphere in an alumina crucible. After calcination for 5 hours and pulverization, this was further fired at 725 ° C. for 10 hours in the same atmosphere. The obtained positive electrode material showed almost no difference from Example 2 in X-ray diffraction, and the crystallite size was 162 nm, showing little difference from Example 2. In addition, elemental analysis revealed that carbon produced by pyrolysis of refined coal pitch contained 3.13% by weight, and the amount of precipitated carbon was not significantly different from that in Example 2.
[0099]
For this positive electrode material, a coin-type lithium secondary battery configured in the same manner as in Example 2 was produced, and a charge / discharge cycle test was performed in the same manner as in Example 2. The average initial discharge capacity for 1 to 20 cycles is also shown in Table 1.
[0100]
As shown in Table 1, regarding the initial discharge capacity of Comparative Example 2, the effects of hydrogenation and addition of refined coal pitch are recognized, but in Example 2, it can be seen that the initial discharge capacity is further increased. The reason for this is considered to be the same as in the first embodiment.
[0101]
Example 3
Cathode material LiFePO₄Was synthesized by the following procedure.
Same amount as in Example 2, ie, 5.0161 g of Fe₃(PO₄)₂・ 8H₂O (manufactured by Soekawa Riken) and 1.1579 g of Li₃PO₄Approximately 1.5 times volume ethanol was added to (made by Wako Pure Chemical Industries, Ltd.), pulverized and mixed using a planetary ball mill having 2 mm diameter zirconia beads and zirconia pots, and dried at 50 ° C. under reduced pressure. The dried pulverized mixture is placed in an alumina crucible and 5 volume% hydrogen (H₂) / 95 vol% argon (Ar) mixed gas was first calcined at 400 ° C. for 5 hours while venting at a flow rate of 200 ml / min. 0.5358 g of dextrin (manufactured by Wako Pure Chemical Industries, Ltd.) is added to 4.4762 g of the raw material after pre-baking that has been taken out, pulverized in an agate mortar, and further subjected to main baking at 725 ° C. for 10 hours in the same atmosphere. (The mixed gas continued to flow from before the start of temperature elevation to during firing and after being allowed to cool). The synthesized positive electrode material is LiFePO having an olivine type crystal structure by powder X-ray diffraction.₄Was identified. On the other hand, α-Fe which is an oxidation impurity₂O₃, FePO₄No crystal diffraction peaks of other impurities were observed.
[0102]
In addition, although it was found from elemental analysis that carbon produced by pyrolysis of dextrin was contained by 3.43% by weight, a diffraction peak of graphite crystal was not observed from X-ray diffraction. It was presumed to form a complex with carbon. The crystallite size was 170 nm.
[0103]
Using this positive electrode material, a positive electrode pellet and a coin-type lithium secondary battery were produced under the same conditions as in Example 1.
[0104]
For the secondary battery incorporating the positive electrode material obtained as described above, the current density per apparent area of the positive electrode pellet is 0.5 mA / cm.²And 1.6 mA / cm²Then, when charging / discharging was repeated in the operating voltage range of 3.0 V to 4.0 V, the average initial discharge capacity of 1 to 20 cycles was as shown in Table 1 (the initial discharge capacity was determined in the product). Standardized by the amount of positive electrode active material).
[0105]
In addition, FIG. 2 shows the charge / discharge characteristics of the tenth cycle of the coin-type lithium secondary battery under the above conditions.
[0106]
Comparative Example 3
In contrast to Example 3, the positive electrode material olivine-type LiFePO4 was synthesized by the same synthesis method as Example 3 except that dextrin was added to the raw material before temporary baking and preliminary baking and main baking were performed.₄Got.
That is, the same amount of Fe as in Example 3.₃(PO₄)₂・ 8H₂O (manufactured by Soekawa Riken) and Li₃PO₄0.6600 g of dextrin is added to (Wako Pure Chemical Industries, Ltd.), ground and mixed using a planetary ball mill, and dried, and then calcined at 400 ° C. in the same atmosphere for 5 hours in an alumina crucible. After pulverization, this was further calcined at 725 ° C. for 10 hours in the same atmosphere. The obtained positive electrode material showed almost no difference from Example 3 in X-ray diffraction, and the crystallite size was 165 nm, showing little difference from Example 3. Further, elemental analysis revealed that carbon produced by pyrolysis of dextrin was contained by 3.33% by weight, and the amount of precipitated carbon was not significantly different from that in Example 3.
[0107]
For this positive electrode material, a coin-type lithium secondary battery configured in the same manner as in Example 3 was prepared, and a charge / discharge cycle test was performed in the same manner as in Example 3. The average initial discharge capacity for 1 to 20 cycles is also shown in Table 1. Further, FIG. 3 shows the charge / discharge characteristics of the coin-type lithium secondary battery at the 10th cycle.
[0108]
As shown in Table 1, the effects of hydrogenation and dextrin addition are recognized for the initial discharge capacity of Comparative Example 3, but in Example 3, the initial discharge capacity is further increased. The reason for this is considered to be the same as in the first embodiment.
[0109]
Moreover, when FIG. 2 and FIG. 3 are compared, Example 3 which added dextrin to the raw material after temporary calcination is theoretical capacity (170 mAh / g) compared with Comparative Example 3 which added dextrin to the raw material before temporary calcination. It is understood that the charge / discharge characteristics are excellent because the charge / discharge voltage has a flat region up to a value closer to the value and the difference between the charge voltage and the discharge voltage is sufficiently small.
[0110]
  Reference example 1
  Cathode material LiFePO₄Was synthesized by the following procedure.
  5.0532 g FeC₂O₄・ 2H₂O (manufactured by Wako Pure Chemical Industries, Ltd.), 3.7094 g of (NH₄)₂HPO₄(Manufactured by Wako Pure Chemical Industries, Ltd.) and 1.1784 g of LiOH · H₂0.120 g of acetylene black [Denka Black (registered trademark; 50% press product) manufactured by Denki Kagaku Kogyo Co., Ltd.] was added to O (manufactured by Wako Pure Chemical Industries, Ltd.), and the mixture was pulverized and mixed using an automatic agate mortar. This pulverized mixture is placed in an alumina crucible and 5 volume% hydrogen (H₂) / 95 vol% argon (Ar) mixed gas at a flow rate of 200 ml / min, first calcined at 400 ° C. for 5 hours, taken out and pulverized in an agate mortar, and further at 775 ° C. in the same atmosphere The main calcination was performed for 10 hours (the mixed gas continued to flow from before the start of the temperature rise to during the calcination and after being allowed to cool). The synthesized positive electrode material is LiFePO having an olivine type crystal structure by powder X-ray diffraction.₄Was identified. On the other hand, α-Fe which is an oxidation impurity₂O₃, FePO₄No crystal diffraction peak was observed.
[0111]
Further, elemental analysis revealed that 2.84% by weight of carbon derived from acetylene black was contained. The crystallite size was 111 nm.
[0112]
Using this positive electrode material, a positive electrode pellet and a coin-type lithium secondary battery were produced under the same conditions as in Example 1.
[0113]
For the secondary battery incorporating the positive electrode material obtained as described above, the current density per apparent area of the positive electrode pellet is 0.5 mA / cm.²And 1.6 mA / cm²Then, when charging / discharging was repeated in the operating voltage range of 3.0 V to 4.0 V, the average initial discharge capacity of 1 to 20 cycles was as shown in Table 1 (the initial discharge capacity was determined in the product). Standardized by the amount of positive electrode active material).
[0114]
  Comparative Example 4
  Reference example 1On the other hand, except that the same acetylene black was added to the raw material after the temporary baking and the temporary baking and the main baking were performed,Reference example 1The positive electrode material olivine-type LiFePO by the same synthesis method as₄Got.
  That is,Reference example 1Same amount of FeC₂O₄・ 2H₂O, and (NH₄)₂HPO₄, And 1.1784 g LiOH.H₂Crush and mix using an automatic mortar made of Agate, put this pulverized mixture into an alumina crucible, 5 volume% hydrogen (H₂) / 95 vol% argon (Ar) mixed gas was first calcined at 400 ° C. for 5 hours while venting at a flow rate of 200 ml / min. 0.0707 g of acetylene black (50% pressed product) was added to 2.1856 g of the raw material after pre-baking, which was taken out, pulverized and mixed in an automatic mortar made by agate, and further fired at 775 ° C. for 10 hours in the same atmosphere. (The mixed gas continued to flow from before the start of temperature rise to during firing and after being allowed to cool). The synthesized positive electrode material is LiFePO having an olivine type crystal structure by powder X-ray diffraction.₄Was identified. On the other hand, α-Fe which is an oxidation impurity₂O₃, FePO₄No crystal diffraction peak was observed.
[0115]
  Further, elemental analysis revealed that 2.76% by weight of carbon derived from acetylene black was contained. The crystallite size was 122 nm. Therefore, the carbon content and crystallite size areReference example 1It was not much different.
[0116]
  Using this positive electrode material,Reference example 1A positive electrode pellet and a coin-type lithium secondary battery under the same conditions asReference example 1The charge / discharge cycle test was carried out in the same manner as above. The average initial discharge capacity for 1 to 20 cycles is also shown in Table 1.
[0117]
  As shown in Table 1,Reference example 1The initial discharge capacity is relatively good, and acetylene black as conductive carbon and the effect of hydrogenation are recognized. Also,Reference example 1Then, the initial discharge capacity is larger than that of Comparative Example 4, and when adding acetylene black that is already infusible and carbonized, it is added to the raw material before pre-firing to perform the main firing. However, it turns out that positive electrode performance becomes high.
[0118]
[Table 1]

[0119]
  Example 4
  Cathode material LiFePO₄Was synthesized by the following procedure.
  5.0532 g FeC₂O₄・ 2H₂O (manufactured by Wako Pure Chemical Industries, Ltd.), 3.7094 g of (NH₄)₂HPO₄(Manufactured by Wako Pure Chemical Industries, Ltd.) and 1.1784 g of LiOH · H₂0.0610 g of acetylene black [Denka Black (registered trademark; 50% pressed product) manufactured by Denki Kagaku Kogyo Co., Ltd.] was added to O (Wako Pure Chemical Industries, Ltd.), and pulverized and mixed using an automatic mortar manufactured by Agate. . This pulverized mixture is placed in an alumina crucible and 5 volume% hydrogen (H₂) / 95 vol% argon (Ar) mixed gas was first calcined at 400 ° C. for 5 hours while venting at a flow rate of 200 ml / min. To the extracted post-calcined raw material 2.2430 g, 0.0576 g of a softening temperature 200 ° C. refined coal pitch was added, ground and mixed in an agate mortar, and further subjected to main firing at 775 ° C. for 10 hours in the same atmosphere ( The mixed gas continued to circulate from before the start of temperature rise to during firing and after being allowed to cool). The synthesized positive electrode material is LiFePO having an olivine type crystal structure by powder X-ray diffraction.₄Was identified. On the other hand, α-Fe which is an oxidation impurity₂O₃, FePO₄No crystal diffraction peak was observed.
[0120]
Elemental analysis also revealed that a total of 3.27% by weight of carbon produced by pyrolysis of the refined coal pitch and carbon derived from acetylene black were contained. The crystallite size was 74 nm.
[0121]
Using this positive electrode material, a positive electrode pellet and a coin-type lithium secondary battery were produced under the same conditions as in Example 1.
For the secondary battery incorporating the positive electrode material obtained as described above, the current density per apparent area of the positive electrode pellet is 0.5 mA / cm.²And 1.6 mA / cm²Then, when charging / discharging was repeated in the operating voltage range of 3.0 V to 4.0 V, the average initial discharge capacity of 1 to 20 cycles was as shown in Table 2 (the initial discharge capacity was determined in the product). Standardized by the amount of positive electrode active material). In this way, the positive electrode material obtained by adding acetylene black as conductive carbon before calcination and adding refined coal pitch as conductive carbon precursor after calcination has the discharge capacity of the secondary battery. It was shown that the positive electrode performance was improved by increasing the size.
[0122]
[Table 2]

[0123]
  Example 5
  Cathode material LiFePO₄Was synthesized by the following procedure.
  5.0161g Fe₃(PO₄)₂・ 8H₂O (manufactured by Soekawa Riken), 1.1579 g of Li₃PO₄Approximately 1.5 times volume ethanol was added to (made by Wako Pure Chemical Industries, Ltd.), pulverized and mixed using a planetary ball mill having 2 mm diameter zirconia beads and zirconia pots, and dried at 50 ° C. under reduced pressure. The dried pulverized mixture was placed in an alumina crucible, and first calcined at 400 ° C. for 5 hours while aeration of 100 volume% argon (Ar) gas at a flow rate of 200 ml / min. 0.1904 g of refined coal pitch [ADCPEMCO Co., Ltd. MCP-200 (trade name)] is added to 4.1248 g of the raw material after pre-baking that has been taken out, pulverized in an agate mortar, and the same atmosphere. The main calcination was carried out at 700 ° C. for 10 hours (the gas continued to flow from before the start of the temperature increase to during the calcination and further after the cooling.) The synthesized positive electrode material is LiFePO having an olivine type crystal structure by powder X-ray diffraction.₄Was identified. On the other hand, α-Fe which is an oxidation impurity₂O₃, FePO₄No crystal diffraction peaks of other impurities were observed.
[0124]
Moreover, although it was found from elemental analysis that 3.16% by weight of carbon produced by pyrolysis of refined coal pitch was contained, no diffraction peak of graphite crystals was observed from X-ray diffraction. It was presumed to form a complex with crystalline carbon. The crystallite size was 194 nm.
[0125]
Using this positive electrode material, a positive electrode pellet and a coin-type lithium secondary battery were produced under the same conditions as in Example 1.
[0126]
For the secondary battery incorporating the positive electrode material obtained as described above, the current density per apparent area of the positive electrode pellet is 0.5 mA / cm.²And 1.6 mA / cm²Then, when charging / discharging was repeated in the operating voltage range of 3.0 V to 4.0 V, the average initial discharge capacity of 1 to 20 cycles was as shown in Table 3 (the initial discharge capacity was Standardized by the amount of positive electrode active material).
[0127]
FIG. 4 shows the charge / discharge characteristics at the 10th cycle of the coin-type lithium secondary battery under the above conditions.
[0128]
  Comparative Example 5
  Example 5On the other hand, except that the refined coal pitch with a softening temperature of 200 ° C. was added to the raw material before the temporary firing, and the preliminary firing and the main firing were performedExample 5The positive electrode material olivine type LiFePO₄Got.
  That is,Example 5Same amount of Fe₃(PO₄)₂・ 8H₂O (manufactured by Soekawa Riken) and Li₃PO₄0.1940 g of refined coal pitch with a softening temperature of 200 ° C. is added to (made by Wako Pure Chemical Industries, Ltd.), pulverized, mixed and dried using a planetary ball mill, and then 400 times in the same argon atmosphere in an alumina crucible. After calcining at 5 ° C. for 5 hours, after pulverization, this was further calcined at 700 ° C. for 10 hours in the same atmosphere. The obtained positive electrode material is obtained by X-ray diffraction.Example 5And the crystallite size is 189 nm,Example 5There was almost no difference. In addition, from elemental analysis, it contains 3.04% by weight of carbon produced by thermal decomposition of refined coal pitch.Example 5It turned out that there is no big difference.
[0129]
  About this positive electrode material,Example 5A coin-type lithium secondary battery configured in the same manner asExample 5The charge / discharge cycle test was carried out in the same manner as above. The average initial discharge capacity of 1 to 20 cycles is also shown in Table 3.
[0130]
In addition, FIG. 5 shows the charge / discharge characteristics of the tenth cycle of the coin-type lithium secondary battery under the above conditions.
[0131]
  As shown in Table 3, Comparative Example 5 in which the refined coal pitch was added to the raw material before calcination also showed a relatively large initial discharge capacity, and the effect of adding the refined coal pitch was recognized. Refined coal pitch was added toExample 5It can be seen that the initial discharge capacity is further increased.
[0132]
  Moreover, when FIG. 4 and FIG. 5 are compared, coal pitch was added after temporary baking.Example 5Has a flat area of charge / discharge voltage up to a larger capacity value compared to Comparative Example 5 in which the coal pitch is added before pre-firing, and the difference between the charge voltage and the discharge voltage is small. It is understood that it is excellent.
[0133]
Therefore, it was found that even in the case of a 100% argon firing atmosphere containing no hydrogen, higher positive electrode performance can be obtained by adding coal pitch to the raw material after provisional firing.
[0134]
  In addition,Example 5Thus, when using a refined coal pitch that has a relatively low viscosity when melted compared to dextrin, the resulting positive electrode material may exhibit a relatively large discharge capacity without necessarily adding hydrogen to the firing atmosphere. is there.
[0135]
[Table 3]

[0136]
【The invention's effect】
According to the method of the present invention, the crystal growth of the primary particles of the positive electrode material can be suppressed, and the crystal particles of the obtained positive electrode material can be refined. That is, a positive electrode produced by adding a conductive carbon precursor and / or conductive carbon at a predetermined timing, and preferably firing a raw material of the positive electrode material while supplying hydrogen and / or moisture (water or water vapor) The primary particles of the material can be efficiently finely divided, and a state in which conductive carbon is present in the positive electrode material uniformly and stably can be created, and higher positive electrode performance can be obtained.
[0137]
In addition, according to the method of the present invention, there is no fear that the raw material is insufficiently fired and does not chemically change to the final product, or the intermediate product remains, and the target positive electrode material is reliably synthesized from the raw material by firing. it can.
[0138]
In addition, hydrogen and / or moisture have a strong crystal growth inhibiting action and a strong action to improve the adhesion state of the substance that deposits conductive carbon by heating to the positive electrode material, and are easy to handle and inexpensive. Therefore, it is efficient.
[0139]
Further, in the secondary battery of the present invention using the positive electrode material manufactured by the above method, since the crystal particles of the positive electrode material are finely divided, an alkali such as lithium ion is formed at the interface between the positive electrode material and the electrolyte. Electrode reaction due to the large surface area when the positive electrode material undergoes electrochemical oxidation / reduction accompanied by dedoping / doping of metal ions, and alkali metal ions can easily enter and exit at the interface between the particles inside the positive electrode material and the electrolyte. Polarization is suppressed. Furthermore, since the contact between the positive electrode material and the conductivity imparting material such as carbon black, which is usually mixed with the positive electrode material, is remarkably improved, the conductivity is improved, and the utilization rate of the positive electrode material as the active material is high. It is a secondary battery having a small resistance and a markedly improved voltage efficiency and effective battery discharge capacity.
[Brief description of the drawings]
FIG. 1 is a schematic diagram for explaining charge / discharge behavior of a secondary battery.
2 is a graph showing charge / discharge characteristics of a coin-type secondary battery obtained in Example 3. FIG.
3 is a graph showing charge / discharge characteristics of a coin-type secondary battery obtained in Comparative Example 3. FIG.
4 is a graph showing charge / discharge characteristics of a coin-type secondary battery obtained in Example 6. FIG.
5 is a graph showing charge / discharge characteristics of a coin-type secondary battery obtained in Comparative Example 5. FIG.

Claims (9)

In a method for producing a positive electrode material for a secondary battery, in which a pulverized and mixed raw material is fired in an inert gas atmosphere to produce a positive electrode material containing an alkali metal, a transition metal and oxygen,
The firing process includes a first stage from room temperature to 300 ° C. to 450 ° C. and a second stage from room temperature to a firing completion temperature in the range of 500 ° C. to 800 ° C. ,
A method for producing a positive electrode material for a secondary battery, comprising adding a substance capable of producing conductive carbon by thermal decomposition to a raw material after the first stage baking, and then performing a second stage baking. In a method for producing a positive electrode material for a secondary battery, in which a pulverized and mixed raw material is fired in an inert gas atmosphere to produce a positive electrode material containing an alkali metal, a transition metal and oxygen,
The firing process includes a first stage from room temperature to 300 ° C. to 450 ° C. and a second stage from room temperature to a firing completion temperature in the range of 500 ° C. to 800 ° C. ,
Conductive carbon is added to the raw material before firing in the first stage and fired.
A method for producing a positive electrode material for a secondary battery, comprising adding a substance capable of generating conductive carbon by thermal decomposition to a raw material after the first stage baking, and then performing a second stage baking.   The method for producing a positive electrode material for a secondary battery according to claim 1 or 2, wherein the substance capable of generating conductive carbon by thermal decomposition is bitumen.   4. The bitumen according to claim 3, wherein the bitumen has a softening temperature in the range of 80 ° C. to 350 ° C., a weight loss starting temperature by thermal decomposition in the range of 350 ° C. to 450 ° C., and 500 ° C. to 800 ° C. A method for producing a positive electrode material for a secondary battery, which is a coal pitch capable of depositing conductive carbon by firing.   3. The method for producing a secondary battery positive electrode material according to claim 1, wherein the substance capable of generating conductive carbon by the thermal decomposition is a saccharide.   6. The saccharide according to claim 5, wherein the saccharide undergoes decomposition in a temperature range of 250 ° C. or more and less than 500 ° C., and at least partially takes a melt state once in the temperature rising process from 150 ° C. to decomposition, and further 500 ° C. A method for producing a positive electrode material for a secondary battery, which is a saccharide that generates conductive carbon by thermal decomposition and baking up to 800 ° C or lower. In any one of claims 1 to 6, wherein the positive electrode _{material, M (1) a M (} 2) x A y O z [ _{wherein, M (1)} represents the Li or Na, _{M ( 2)} represents Fe (II), Co (II), Mn (II), Ni (II), V (II) or Cu (II), A represents P or S, and a is selected from 0 to 3 Represented by the general formula: x represents a number selected from 1 to 2, y represents a number selected from 1 to 3, and z represents a number selected from 4 to 12. A method for producing a positive electrode material for a secondary battery, wherein the material is a composite material or a composite thereof. 7. The positive electrode material according to claim 1, wherein the positive electrode material is Li _q FePO ₄ , Li _q CoPO _4, or Li _q MnPO ₄ (where q is a number selected from 0 to 1 (provided that 0 A method for producing a positive electrode material for a secondary battery, which is a substance represented by the general formula A secondary battery comprising a positive electrode made of a positive electrode material produced by the method according to any one of claims 1 to 8 .

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