JP2004063386A - Method of manufacturing positive electrode material for secondary battery, and secondary battery - Google Patents

Abstract

A secondary material capable of reliably synthesizing a target positive electrode material from raw materials by baking, imparting excellent conductivity, and suppressing the crystal growth of primary particles of the positive electrode material to make it finer. To provide a novel method for producing a positive electrode material for a battery.
In a method of manufacturing a positive electrode material for a secondary battery, in which a raw material is fired to manufacture a positive electrode material, a firing process includes a first stage from normal temperature to 300 ° C. to 450 ° C., and a first step from normal temperature to a firing completion temperature. (1) adding a substance capable of producing conductive carbon by thermal decomposition to the raw material after the first firing, and then performing the second firing, or (2) conducting carbon Is added to the raw material before firing in the first stage, and firing is performed, or both of the above (1) and (2) are performed, and one or more selected from the group consisting of hydrogen, water and steam are more preferable. The seed or more is added at a temperature of at least 500 ° C. or more in the second stage firing.
[Selection diagram] None

Description

【０１１９】
実施例５
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６
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６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６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６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６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６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６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６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６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６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６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６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]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing a positive electrode material for a secondary battery and a secondary battery having the positive electrode material. More specifically, for example, a metal lithium battery using an alkali metal such as lithium and sodium or a compound thereof as an active material The present invention relates to a method for manufacturing a positive electrode material used for a secondary battery typified by a lithium ion battery, a lithium polymer battery, and the like, and a secondary battery having the positive electrode material manufactured by the method.
[0002]
[Prior art]
Metal oxides used for secondary batteries such as metal lithium batteries, lithium ion batteries and lithium polymer batteries, and oxides in which metal atoms are partially substituted, and LiFePO4₄, LiCoPO₄Phosphates such as Fe₂(SO₄)₃In a positive electrode material such as a sulfate, etc., an electrode oxidation-reduction reaction proceeds in a process of discharging or charging with doping / dedoping of an alkali metal ion such as lithium. In recent years, such secondary batteries have been spotlighted as large capacity batteries. However, in the positive electrodes of these batteries, the speed of the alkali metal ions moving inside the electrode material due to solid-phase diffusion limits the electrode reaction speed. It is difficult to charge and discharge at a high density. When the polarization is particularly large, charging and discharging do not proceed sufficiently under normal voltage and 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, which are often used for these positive electrode materials, generally have low electrical conductivity, and this also causes an increase in the polarization of the electrode reaction.
[0003]
In order to solve the above problems, it is effective to make the crystal particles of the positive electrode material finer so that alkali metal ions can easily enter and exit inside the particles. In addition, when the crystal grains are refined, the contact area between the conductivity-imparting material such as carbon black, which is usually mixed with the cathode material, and the cathode material is increased, so that the conductivity is improved. The voltage efficiency and the effective battery capacity can be improved while the polarization is reduced.
[0004]
For this purpose, when synthesizing the positive electrode material by firing, in recent years, the firing temperature has been reduced by using a highly reactive raw material, and further, the firing time has been restricted to suppress the crystal growth of the positive electrode material, and the positive electrode material having a small particle size has been suppressed. Attempts to obtain have been reported. For example, LiFePO, which is a positive electrode material for a lithium secondary battery,₄Of LiOH.H₂By using O, the firing temperature is lowered to 675 ° C., which is lower than the conventional value (usually about 800 to 900 ° C.), and firing is performed in argon for a relatively short time (about 24 hours), thereby sintering (particles) the positive electrode material powder. (40th {Battery Symposium} Announcement 3C14 (Preliminary Proceedings, p349, 1999); The Institute of Electrical Chemistry of Japan (Japan)) has been reported.
[0005]
Although this is not a method of suppressing the crystal growth of the electrode material, JP-A-2001-15111 discloses a chemical formula A_aM_mZ_zO_oN_nF_f(Where A is an alkali metal, M is Fe, Mn, V, Ti, Mo, Nb, W and other transition metals, Z is S, Se, P, As, Si, Ge, B, Sn and other nonmetals )), By depositing carbon on the surface of the particles of the complex oxides (including oxo acid salts such as sulfates, phosphates, silicates, etc.) to increase the surface conductivity, these composites can be used in batteries and the like. Discloses a method of improving the efficiency by homogenizing and stabilizing the electric field around the interface of the composite oxide particles, the current collecting (conductivity-imparting) material and the electrolyte in the course of the electrode oxidation-reduction reaction. Have been. There, as a method of depositing carbon on the surface of the composite oxide particles, an organic substance (polymer, monomer, low molecule, etc.) that deposits carbon by thermal decomposition is used, or carbon monoxide is added thereto. A method of thermally decomposing (these can coexist in the raw material of the composite oxide and thermally react at a time under reducing conditions to obtain a composite of the composite oxide and surface carbon, And it is). By these means, Japanese Patent Application Laid-Open No. 2001-15111 realizes an improvement in the electrical conductivity of the surface of the composite oxide particles as described above.₄For example, when a composite is prepared by depositing carbon on the surface of positive electrode material particles to form a Li polymer battery, high electrode performance such as a large discharge capacity is obtained.
[0006]
Further, according to JP-A-2002-110163, according to the general formula LixFePO₄(However, a raw material of the compound represented by 0 <x ≦ 1) is mixed, milled, and calcined at any point of time, and a carbon material is added at any time, and the oxygen concentration in the calcining atmosphere is 1012 ppm ( A method for producing a positive electrode active material having a volume (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 the trivalent Fe compound (Fe₂O₃) Is generated, and LiFePO₄It has also been suggested to add an inert gas or a reducing gas such as hydrogen for the purpose of suppressing the oxygen concentration to the above-mentioned 1012 ppm (volume) in order to prevent the single-phase synthesis from being hindered.
[0007]
[Problems to be solved by the invention]
In the synthesis of the positive electrode material by sintering, the method of lowering the temperature or shortening the sintering time, as in the method of the 40th Battery Symposium Announcement 3C14 (P349, 1999), is insufficient in sintering. As a result, there is a possibility that no chemical change occurs in the final product or an intermediate product remains, so that there is a limit as a method of grain refinement.
[0008]
Although the method disclosed in Japanese Patent Application Laid-Open No. 2001-15111 is effective for improving the surface conductivity of an electrode material, there is no description about suppression of crystal growth during synthesis of the electrode material. There is also no description of a method for more appropriately controlling the deposition of carbon on a material in terms of electrode performance.
[0009]
In the method described in Japanese Patent Application Laid-Open No. 2002-110163, a non-oxygen atmosphere has no other meaning than to prevent oxidation of Fe in the firing process as described above. Further, the carbon material added by the method described in this publication is an amorphous carbon material such as acetylene black, and can be added to the raw material after firing.₄The carbon composite is replaced by “LiFePO₄The carbon material added is attached between the positive electrode active material particles to improve electron conductivity, as defined by the definition of `` a material in which a large number of carbon material particles adhere to the surface of the particles. '' Stop it. For this reason, in JP-A-2002-110163, there is no technical idea that, for example, conductive carbon is uniformly deposited on the positive electrode active material. In addition, there is no study on the conditions for allowing the carbon material to exist in a more desirable form in terms of electrode performance, and the firing conditions simply employ a simple heating process.
[0010]
An object of the present invention is to reliably synthesize a desired positive electrode material from raw materials by firing, and to suppress the crystal growth of primary particles of the positive electrode material to make it finer and to impart excellent conductivity. To provide a novel method for producing a positive electrode material for a secondary battery, and furthermore, by reducing the size of the positive electrode material and optimizing the provision of conductivity, lithium is initially interposed between the inside of the positive electrode material particles and the electrolyte. Promotes entry and exit of alkali metal ions, suppresses electrode reaction polarization, increases the contact area between the cathode material and the conductivity-imparting material, improves conductivity, improves voltage efficiency and effective battery capacity. An object of the present invention is to provide a high performance secondary battery.
[0011]
[Means for Solving the Problems]
In order to solve the above problems, the invention of a method for manufacturing a positive electrode material for a secondary battery according to claim 1 is a method for manufacturing a positive electrode material for a secondary battery, in which a raw material is fired to manufacture a positive electrode material. And a second stage from room temperature to a firing completion temperature, wherein a substance capable of generating conductive carbon by thermal decomposition is added to the raw material after the first stage firing. After that, the second stage baking is performed.
[0012]
According to the invention of this method for producing a positive electrode material for a secondary battery, a substance capable of producing conductive carbon by thermal decomposition is added to the raw material after the first firing step, and the second firing step is performed. A substance that can generate conductive carbon by decomposition can be prevented from being foamed 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 the molten state, and the pyrolytic carbon can be more uniformly deposited. For this reason, the surface conductivity of the obtained positive electrode material is further improved, and the contact is firmly stabilized.
[0013]
According to a second aspect of the present invention, there is provided a method for manufacturing a positive electrode material for a secondary battery, in which a raw material is fired to manufacture a positive electrode material. ° C, and a second stage from room temperature to a firing completion temperature. Conductive carbon is added to the raw material before firing in the first stage, and firing is performed. The method is characterized in that a substance capable of forming carbon is added to the raw material after the first-stage firing, and then the second-stage firing is performed.
[0014]
According to the invention of this method for producing a positive electrode material for a secondary battery, in addition to the same function and effect as in claim 1, by further adding conductive carbon to the raw material before firing in the first stage and firing it, The contact time between the raw material to be heated and the conductive carbon and the conductive carbon can be made longer, and during that time, the diffusion of the constituent elements of the positive electrode material caused by the reaction causes the positive electrode material to enter grain boundaries of the carbon, resulting in a more uniform material. A stable carbon-cathode material composite can be formed, and sintering of the cathode material particles can be effectively prevented.
[0015]
According to a third aspect of the present invention, there is provided a method for manufacturing a positive electrode material for a secondary battery in which a raw material is fired to manufacture a positive electrode material. C. and a second stage from a room temperature to a sintering completion temperature, wherein the sintering is performed by adding conductive carbon to the raw material before the sintering in the first stage.
[0016]
According to the invention of the method for manufacturing a positive electrode material for a secondary battery, it is possible to suppress the crystal growth of primary particles of the positive electrode material and to reduce the crystal particles of the obtained positive electrode material. 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 reacted 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 cathode material enters the grain boundaries of the conductive carbon, and a more uniform and stable carbon-cathode material composite can be formed.
[0017]
In a fourth aspect of the present invention, the substance capable of producing conductive carbon by thermal decomposition is bitumen. Bitumens can impart conductivity to the positive electrode material by generating conductive carbon by thermal decomposition.
[0018]
Further, in the invention of the method for manufacturing a positive electrode material for a secondary battery according to claim 5, in claim 4, the bitumen has a softening temperature in the range of 80 ° C to 350 ° C, and a temperature at which weight loss due to thermal decomposition starts. The coal pitch is in the range of 350 ° C. to 450 ° C. and is capable of depositing conductive carbon by thermal decomposition and firing at 500 ° C. to 800 ° C.
[0019]
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 thermal decomposition, becomes carbon deposits that exhibit high conductivity. It is a substance having excellent properties as a substance that can generate conductive carbon.
[0020]
According to a sixth aspect of the present invention, there is provided a method of manufacturing a positive electrode material for a secondary battery according to the first or second aspect, wherein the substance capable of generating conductive carbon by thermal decomposition is a saccharide. . By using a saccharide, a more excellent crystal growth suppressing effect and a conductivity imparting effect can be simultaneously obtained. The saccharides not only give rise to conductive carbon by thermal decomposition and give conductivity to the cathode material, but also suppress the crystal growth by the strong interaction of many hydroxyl groups contained in the saccharide with the raw material and the surface of the produced cathode material particles. This is because it is presumed that they also have an effect.
[0021]
Further, in the invention of the method for manufacturing a positive electrode material for a secondary battery according to claim 7, in claim 6, the saccharide decomposes in a temperature range of 250 ° C. or more and less than 500 ° C. and from 150 ° C. to decomposition. It is a saccharide that at least partially attains a molten state at least once in the temperature-raising process, and further generates conductive carbon by thermal decomposition from 500 ° C to 800 ° C. The saccharide having such specific properties is suitably coated on the surfaces of the positive electrode material particles undergoing the heating reaction by melting, and satisfactorily precipitates conductive carbon on the surfaces of the positive electrode material particles generated after thermal decomposition. In this process, the crystal growth is suppressed as described above. For this reason, the saccharides having the above specific properties exhibit particularly excellent crystal growth suppressing effects and conductivity imparting effects.
[0022]
Further, the invention of a method for manufacturing a cathode material for a secondary battery according to claim 8 is the method according to any one of claims 1 to 7, wherein one or two kinds selected from the group consisting of hydrogen, water and water vapor are provided. It is characterized in that the above is added at least at a temperature of 500 ° C. or more in the second stage firing. According to this feature, 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 made finer.
[0023]
That is, at the time of baking including the first stage from room temperature to 300 ° C. to 450 ° C. and the second stage from room temperature to the baking completion temperature, conductive carbon is generated by thermal decomposition of the raw material after the first baking. After the addition of the substance to be obtained, the second stage baking is performed, and when hydrogen and / or moisture (water or steam) is added at least at a temperature of 500 ° C. or more, the effect described in claim 1 is added. In addition, the primary particles of the resulting positive electrode material can be efficiently refined, and conductive carbon can be more uniformly and stably deposited on the positive electrode material particles, whereby higher positive electrode performance can be obtained. In this process, when hydrogen (including hydrogen generated from moisture) comes into contact with the conductive carbon precursor that melts and thermally decomposes by heating, the melt viscosity of the substance is reduced, possibly due to a hydrogen addition reaction, so Carbon deposition state can be realized.
[0024]
Further, at the time of 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 the first stage firing. While performing the firing, a substance capable of generating conductive carbon by thermal decomposition is added to the raw material after the first firing, and then the second firing is performed, and at least in the temperature range of 500 ° C. or higher, hydrogen and Also in the case of adding water (water or steam), in addition to the effect described in claim 2, the primary particles of the generated positive electrode material are efficiently finely divided, and the conductive carbon is more uniformly and stably formed. It can be deposited on the cathode material particles to obtain higher cathode performance.
[0025]
Further, at the time of 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 the first stage firing. When hydrogen and / or moisture (water or steam) are added at least in a temperature range of 500 ° C. or more in the second stage of firing, the firing of the positive electrode material is performed in addition to the effect described in claim 3. The primary particles can be efficiently refined.
[0026]
Further, according to the method of the present invention, there is no possibility that the raw material is insufficiently calcined to cause a chemical change to the final product or an intermediate product remains, and the desired positive electrode material is reliably synthesized from the raw material by the calcining. it can.
[0027]
Hydrogen and / or water have a strong crystal growth suppressing effect and a strong effect of improving the state of attachment of a substance that precipitates conductive carbon by thermal decomposition to the cathode material, and are easy to handle and inexpensive. Therefore, it is efficient.
[0028]
Further, the substance capable of producing conductive carbon by the thermal decomposition is a bitumen, among which, especially, the softening temperature is in the range of 80 ° C to 350 ° C, and the temperature at which weight loss due to thermal decomposition is started is in the range of 350 ° C to 450 ° C. In the case where there is a coal pitch capable of producing conductive carbon by thermal decomposition and firing at 500 ° C. to 800 ° C., in the process of melting and thermally decomposing such coal pitch by heating during the second stage firing, In a temperature range of at least 500 ° C. or more, the conductive material comes into contact with hydrogen and / or moisture (water or water vapor). The condition is improved.
[0029]
Further, the substance capable of producing conductive carbon by the thermal decomposition may cause decomposition of saccharides, particularly, in a temperature range of 250 ° C. or more and less than 500 ° C., and at least partially at least once in a temperature rising process from 150 ° C. to decomposition. In the case of a saccharide (for example, dextrin or the like) that can generate conductive carbon by being thermally decomposed and fired at a temperature of 500 ° C. or more and 800 ° C. or less, such a saccharide remains In the process of melting and pyrolyzing by heating, it comes into contact with hydrogen and / or moisture (water or steam) at least in a temperature range of 500 ° C. or more, so that conductive carbon deposited on the obtained cathode material particles is deposited. The state is improved to a better state in terms of positive electrode performance.
[0030]
In a ninth aspect of the present invention, there is provided a method of manufacturing a positive electrode material for a secondary battery according to any one of the first to eighth aspects, wherein the positive electrode material contains an alkali metal, a transition metal and oxygen, A compound that can be synthesized by baking the raw material in the absence of gas (hereinafter, may be referred to as “transition metal compound”).
[0031]
When the positive electrode material is such a transition metal compound, when the raw material is added with conductive carbon and / or a substance capable of generating conductive carbon by heating and then fired, firing can be performed in the absence of oxygen gas. In addition, the conductive carbon can be satisfactorily deposited on the surface of the obtained transition metal compound positive electrode material without being burned out. Further, in the case where one or more kinds selected from the group consisting of hydrogen, water and water vapor are added in the absence of oxygen gas and the raw material is fired, the crystal particles of the obtained positive electrode material are finer. In particular, the deposition state of a substance that can generate conductive carbon by thermal decomposition can be favorably controlled in terms of positive electrode performance. In addition, since hydrogen also has a reducing property, it is generated by oxidation due to unavoidable residual oxygen even in firing in the absence of oxygen gas, or oxidized impurities originally present in the raw material (for example, the positive electrode material LiFe²⁺PO₄Deficient oxidized impurity Fe in the atmosphere³⁺PO₄Or oxidized oxide Fe₂O₃Etc .; the mixture of these generally causes a decrease in the discharge capacity of the battery), which is reduced by the action of hydrogen having a reducing property and changes into the desired cathode material, so that the oxidized impurities are mixed into the cathode material. It can also be prevented. When water or water vapor (hereinafter, referred to as “moisture”) is added, conductive carbon or a substance capable of generating conductive carbon by heating reacts with moisture to generate hydrogen, so that a so-called water gas is used. It produces the same effect as the reaction.
[0032]
Further, depending on the method of selecting 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. In some cases, the transition metal element in the positive electrode material may not have the same valence. Even in such a case, it is possible to reduce the necessary and sufficient amount of the generated positive electrode material by adding hydrogen (or hydrogen generated secondarily from moisture) having a necessary and sufficient reducing property to the raw material. Thus, a desired 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 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 it does not have a valency, firing may be performed in the presence of hydrogen to reduce the necessary and sufficient amount to obtain a desired cathode material.
[0033]
Further, according to the invention of the method for producing a cathode material for a secondary battery according to claim 10, the method according to claim 9, wherein the cathode material is M_{( 1 ) A}M_{( 2 ) X}A_yO_z[Where M_{( 1 )}Represents Li or Na;_{( 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, and z represents a number selected from 4 to 12, respectively] or a complex thereof. It is characterized.
[0034]
Further, the invention of the method for producing a cathode material for a secondary battery according to claim 11 is the method according to claim 9, wherein the cathode material is Li_qFePO₄, Li_qCoPO₄Or Li_qMnPO₄(Where q represents a number selected from 0 to 1) or a complex thereof.
[0035]
For the positive electrode material according to the tenth and eleventh aspects, a compound having a transition element having the same valence as that of the target positive electrode material can be used as a raw material. It is possible to synthesize the desired cathode material by firing in gas). Therefore, even if conductive carbon or a substance capable of generating conductive carbon by thermal decomposition and hydrogen gas having a reducing property are added during firing, it can be prevented from being burned and consumed, Further, the firing can be stably controlled without causing a significant rise in local temperature. In addition, particularly in the case of these positive electrode material systems, when hydrogen or the like is added and calcined, the valence of the central metal element [Fe, Co, Mn, Ni, V, Cu, etc.] is further increased by the reducing power. It is also unlikely that the positive electrode material lowers to produce impurities (for example, a metal state) in the positive electrode material.
[0036]
The invention of a secondary battery according to a twelfth aspect has, as a constituent element, a positive electrode material produced by the method according to any one of the first to eleventh aspects. In the secondary battery using the cathode material manufactured by the method of the present invention, since the crystal particles of the cathode material are finely divided, removal of alkali metal ions such as lithium ions at the interface between the cathode material and the electrolyte is performed. The positive electrode material has a large surface area when subjected to electrochemical oxidation / reduction involving doping / doping, and alkali metal ions can easily enter and exit at the interface between the inside of the particles of the positive electrode material and the electrolyte, so that electrode reaction polarization is suppressed. You. Furthermore, since the contact between the conductivity-imparting material such as carbon black, which is usually mixed with the cathode material, and the cathode material is remarkably improved, the conductivity is improved, the utilization rate of the cathode material as an active material is high, and the cell This is a secondary battery having a small resistance and having significantly improved voltage efficiency and effective battery discharge capacity.
[0037]
BEST MODE FOR CARRYING OUT THE INVENTION
The method for manufacturing a positive electrode material for a secondary battery according to the present invention is a method for manufacturing a positive electrode material for a secondary battery, in which a raw material is fired to manufacture a positive electrode material. , A second step from normal temperature to a firing completion temperature, and (1) a substance capable of generating conductive carbon by thermal decomposition (hereinafter, referred to as a “conductive carbon precursor”) after the first step of firing. After the addition to the raw material of the first step, or (2) the conductive carbon is added to the raw material before the first step of the firing, and the firing is performed. It is implemented by doing both. In a further particularly preferred embodiment, in addition to the above (1) and / or (2), one or more kinds selected from the group consisting of hydrogen, water and steam are used at least at 500 ° C. or more in the second stage firing. It is better carried out 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 (that is, in a hydrogen atmosphere or the like).
[0039]
<Positive electrode material>
As the positive electrode material in the present invention, for example, a compound containing an alkali metal, a transition metal, and oxygen, which 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;_{( 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, and z represents a number selected from 4 to 12.], or a complex thereof. Can be. Here, (II), (III), etc. are transition metal elements M₍₂₎And x, y, and z take values that satisfy the stoichiometric (electrical) neutral condition of the material. Also, M₍₂₎Includes a plurality of combinations of the same valence among the transition metal elements exemplified above [for example, M₍₂₎Is Fe (II) Co (II) or Fe (II) Mn (II). At this time, the total content mole number of Fe (II) and Co (II) or Fe (II) and Mn (II) has a ratio of x mole to Li 1 mole (M₍₁₎= Li and a = 1)]].
[0040]
These substances can be generally synthesized from the raw materials by calcination in the absence of oxygen gas (ie, in an atmosphere of an inert gas such as argon, nitrogen, helium, etc.), and have a crystal skeleton structure (spinel type, olivine type). , Nasicon type, etc.) are hardly changed by electrochemical oxidation-reduction, and can be used as a positive electrode material for an alkali metal secondary battery that can be repeatedly charged and discharged. As a positive electrode material, the state of these substances as they are corresponds to the discharge state, and the electrochemical oxidation at the interface with the electrolyte causes the alkali metal M_{( 1 )}Central metal element M₍₂₎Is oxidized and becomes charged. When subjected to electrochemical reduction from the charged state, alkali metal M₍₁₎Central metal element M with re-doping of₍₂₎Is reduced and returns to the original discharge state.
[0041]
Preferred cathode materials include Li_qFePO₄, Li_qCoPO₄Or Li_qMnPO₄(Where q represents a number selected from 0 to 1) or a complex thereof, and in particular, Li_qFePO₄(Where q has the same meaning as described above) is preferred. These substances can be synthesized from the raw materials by firing at a temperature of about 900 ° C. or less in the absence of oxygen gas. For example, the positive electrodes of lithium-based secondary batteries such as lithium batteries, lithium-ion batteries, and lithium polymer batteries It can be suitably used as a material.
[0042]
<Raw materials>
As the 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 to have the same valence as the transition metal element in the positive electrode material. At this time, when the raw material is fired by adding hydrogen or the like, the crystal particles of the obtained positive electrode material are further refined.
[0043]
More specifically, as a raw material of the positive electrode material, for example, as a raw material for introducing an alkali metal, a hydroxide such as LiOH, NaOH,₂CO₃, Na₂CO₃, NaHCO₃And chlorides such as LiCl and NaCl, LiNO and the like.₃, NaNO₃In addition, a decomposition volatile compound (for example, an organic acid salt or the like) in which only an alkali metal remains in the intended positive electrode material, such as a nitrate, etc., is used. When the target cathode material is phosphate, Li₃PO₄, Li₂HPO₄, LiH₂PO₄, Na₃PO₄, Na₂HPO₄, NaH₂PO₄And the like, and when the target cathode material is a sulfate, Li₂SO₄, LiHSO₄, Na₂SO₄, NaHSO₄And the like, such as sulfates and hydrogen sulfates.
[0044]
Examples of raw materials for introducing transition metals such as Fe, Co, Mn, and V include hydroxides, carbonates, bicarbonates, halides such as chlorides, nitrates, and the like. Decomposition volatile compounds that remain in the positive electrode material (for example, organic acid salts such as oxalates and acetates, acetylacetone complexes, and organic complexes such as metallocene complexes) are used. When the target cathode material is phosphate, phosphate or hydrogen phosphate, and when the target cathode material is sulfate, sulfate or hydrogen sulfate, or a transition metal oxo acid salt and ammonium salt, And the like can also be used.
[0045]
When the intended cathode material is a phosphate, phosphoric anhydride P₂O₅, Phosphoric acid H₃PO₄, And decomposed volatile phosphates or hydrogen phosphates (for example, (NH₄)₂HPO₄, NH₄H₂PO₄, (NH₄)₃PO₄Ammonium salt, etc.), and when the intended cathode material is a sulfate, sulfuric acid H₂SO₄, And decomposition volatile volatile sulfate or hydrogen sulfate (for example, NH 4) such that only sulfate ions remain in the target cathode material.₄HSO₄, (NH₄)₂SO₄Etc.) can also be used.
[0046]
If these raw materials contain undesired elements or substances when remaining in the target positive electrode material, it is necessary that these be decomposed and volatilized during firing. Further, when the target product is, for example, a phosphate, it is needless to say that a non-volatile oxo acid salt other than the phosphate ion should not be used as a raw material. In these cases, the hydrate may be used (for example, LiOH.H₂O, Fe₃(PO₄)₂・ 8H₂O, etc.), and in the above description, hydrates are all omitted.
[0047]
The raw material of the positive electrode material can be subjected to a process of pulverizing or mixing and kneading the raw materials (including the conductive carbon optionally added) before firing in the first step, if necessary. . When a conductive carbon precursor (a substance that can generate conductive carbon by thermal decomposition) is added after the first-stage firing, treatments such as pulverization, mixing, and kneading can be performed at that time.
[0048]
When sintering the above raw materials in the presence of hydrogen, water, steam, etc., there is usually no particular problem, but the two react rapidly in the early stage of sintering to obtain the desired cathode material. Care must be taken in the selection and combination of the two so that they are not lost or impurities do not occur.
[0049]
<Conductive carbon>
Examples of the conductive carbon used in the present invention include graphitic carbon and amorphous carbon. Here, the graphitic carbon and the amorphous carbon include so-called soot and carbon black.
<Conductive carbon precursor (a substance that can generate conductive carbon by thermal decomposition)>
Examples of the conductive carbon precursor include bitumens (so-called asphalt; including pitches obtained from coal and petroleum sludge), sugars, styrene-divinylbenzene copolymer, ABS resin, phenol resin, and other aromatic materials. And a crosslinked polymer having a group. Among them, bitumens (especially, refined, so-called coal pitch) and sugars are preferred. These bitumens and saccharides generate conductive carbon by thermal decomposition and impart conductivity to the positive electrode material. In particular, refined coal pitch is very inexpensive, melts during firing, spreads uniformly on the surface of the raw material particles during firing, and has a relatively low temperature (650 ° C. to 800 ° C.) through a pyrolysis process. After firing in, carbon deposits exhibiting high conductivity are obtained. In the case of saccharides, since many hydroxyl groups contained in the saccharide strongly interact with the raw material and the surface of the generated positive electrode material particles, they also have a crystal growth suppressing effect. This is because a suppression 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 temperature at which weight loss due to thermal decomposition starts is in the range of 350 ° C to 450 ° C, and heating to 500 ° C or more and 800 ° C or less. Those that generate conductive carbon by decomposition and firing are preferably used. In order to further enhance the positive electrode performance, a refined coal pitch having a softening temperature in the range of 200 ° C to 300 ° C is more preferable. It is needless to say that the impurities contained in the refined coal pitch do not adversely affect the positive electrode performance, but it is particularly preferable that the ash content is 5000 ppm or less.
[0051]
Further, the saccharides are decomposed in a temperature range of 250 ° C. or more and less than 500 ° C., and at least partially at least once in a melted state in a temperature rising process from 150 ° C. to the temperature range, and further have a temperature of 500 ° C. to 800 ° C. Saccharides that generate conductive carbon by heating and decomposing and firing at a temperature of not more than ° C are particularly preferred. The saccharide having such a specific property is suitably coated on the surface of the positive electrode material particles undergoing 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 as described above. Here, in order to generate good conductivity, the thermal decomposition temperature can be set to preferably 570 ° C to 850 ° C, more preferably 650 ° C to 800 ° C, although it depends on the type of the positive electrode material. The saccharide is preferably one that can generate at least 15% by weight or more, preferably 20% by weight or more, of conductive carbon based on the dry weight of the saccharide before calcination by thermal decomposition. This is for facilitating quantitative management of the generated conductive carbon. Examples of the saccharides having the above-mentioned properties include oligosaccharides such as dextrin, and high-molecular polysaccharides such as soluble starch and low-crosslinking starch that is easily melted by heating (for example, starch containing 50% or more amylose). Can be
[0052]
<Addition and firing of conductive carbon precursor etc.>
The conductive carbon, the conductive carbon precursor typified by the refined coal pitch, and the 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 materials, for example, pulverization or kneading can be performed as necessary.
[0053]
The conductive carbon or the conductive carbon precursor has a weight concentration of the conductive carbon of 0.1% or more and 10% or less, preferably 0.5% or more and 7% or less, more preferably 1% or more in the resulting positive electrode material. It can be added so as to be 5% or less.
[0054]
The baking can be carried out by selecting an appropriate temperature range and time in a baking process of 300 to 900 ° C., which is generally adopted, depending on a target cathode material. The firing is preferably performed in the absence of oxygen gas to prevent generation of oxidized impurities and promote reduction of remaining oxidized impurities.
[0055]
In the method of the present invention, the calcination is not carried out by a single series of heating and a subsequent temperature holding step, but a calcination step in the first stage at a lower temperature range (usually from room temperature to 300 to 450 ° C.). Temperature range; hereinafter, sometimes referred to as “temporary firing”), and a firing process in the second stage in a higher temperature range [usually from normal temperature to firing completion temperature (about 500 ° C. to 800 ° C.); May be described as two steps]. In this case, the performance of the obtained positive electrode material can be further improved by mixing the conductive carbon and the conductive carbon precursor at the following timing.
[0056]
In the calcination, the raw material of the positive electrode material reacts by heating to an intermediate state leading to the final positive electrode material, and at this time, gas generation is often accompanied by thermal decomposition. The pre-firing end temperature is a temperature at which most of the evolved gas has been released and the reaction to the final product cathode material does not proceed completely (that is, during the second-stage main firing at a higher temperature range). (A temperature that leaves room for re-diffusion and homogenization of the constituent elements in the positive electrode material).
[0057]
In the main firing following the preliminary firing, re-diffusion and homogenization of the constituent elements occur, the reaction to the positive electrode material is completed, and the temperature is raised and the temperature is maintained to a temperature range that minimizes crystal growth due to sintering and the like. Done.
[0058]
When using a conductive carbon precursor, particularly coal pitch or saccharides that melts by heating, it can be added to the raw material before calcination (in this case, a corresponding positive electrode performance improving effect is obtained). In order to obtain a high-performance positive electrode material, it is more preferable to add it to the raw material after the preliminary firing (the state in which most of the gas generation from the raw material has already been completed and become an intermediate product) and then perform the main firing. That is, a step of adding the 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 sugars that are melted and thermally decomposed by heating from foaming by the gas generated from the raw material, spreads more uniformly on the surface of the positive electrode material in a molten state, and more uniformly spreads pyrolytic carbon. Can be precipitated.
[0060]
This is for the following reason.
That is, most of the gas generated by the decomposition of the raw material in the preliminary firing is released, so that almost no gas is generated in the final firing, and by adding the conductive carbon precursor at the timing after the preliminary firing, uniformity is obtained. It becomes possible to deposit conductive carbon. For this reason, the surface conductivity of the obtained positive electrode material 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 calcination, the gas generated vigorously from the raw material during calcination causes the conductive carbon precursor that has not yet been completely thermally decomposed in a molten state. It foams and prevents uniform precipitation.
[0061]
In addition, carbon (conductive carbon; for example, graphitic carbon such as soot and carbon black, amorphous carbon, etc.), which is already conductive and hardly causes weight loss, morphological change or gas generation by heating, is added. In this case, it is preferable that a predetermined amount of these materials be mixed with the raw material before the preliminary firing, and a series of firing processes be started from the preliminary firing. This makes it possible to increase the contact time between the raw material to be heated and reacted and the conductive carbon, and during the diffusion of the constituent elements of the positive electrode material generated by the reaction, the positive electrode material enters the grain boundaries of the conductive carbon. This is because a uniform and stable carbon-cathode material composite can be formed, and sintering of the cathode material particles can be effectively prevented.
[0062]
Also, adding both a conductive carbon precursor, for example, a substance such as coal pitch or saccharides that melts and thermally decomposes upon heating, and conductive carbon is effective in obtaining a positive electrode material having high positive electrode performance. is there. In this case, it is preferable that the conductive carbon be added to the raw material before calcining, and that substances such as coal pitch and saccharides that are melted and thermally decomposed by heating be added to the raw material after calcining.
[0063]
<Supply of hydrogen etc.>
In a further preferred method of the present invention, the raw material is fired while continuously supplying a predetermined amount of hydrogen or moisture (water, steam, etc.) together with an inert gas into the furnace. For example, over the entire time of the firing process, or especially at a temperature from 500 ° C or lower to the completion of firing, preferably at a temperature of 400 ° C or lower to the completion of firing, more preferably at a firing temperature of 300 ° C or lower to the completion of firing, Hydrogen or moisture can be added.
[0064]
In the case of using gaseous hydrogen, 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 generally employed at 300 to 900 ° C. It can be supplied, and can effectively cause addition and deoxygenation to 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. or more during the firing in the second stage. For example, during the second stage firing, preferably over a temperature range from 500 ° C. or lower to the firing completion temperature, more preferably from 400 ° C. or lower to the firing completion temperature, preferably from 300 ° C. or lower to the firing completion temperature (for example, It can be added over almost the entire firing period). In this range, suppression of crystal growth occurs effectively, probably for the reason described later. Note that hydrogen can be added during the first stage firing.
[0066]
The volume concentration of hydrogen in the atmosphere in the above temperature range can be about 0.1% to 20%, and preferably 1% to 10%. Thereby, the crystal growth of the positive electrode material composed of the transition metal compound is suitably suppressed.
[0067]
In a study by the present inventors, when a raw material of a positive electrode material is calcined in the absence of oxygen gas while supplying hydrogen and / or moisture, a slight disorder occurs in the crystallinity of particles of the positive electrode material, and the generated 1 The secondary particles were found to be more refined. That is, it was proved that hydrogen and moisture are effective crystal growth inhibitors. Although the mechanism is not yet clear, hydrogen bonds to surface oxygen atoms to form hydroxyl groups on the growth surface of crystal particles of the cathode material that is synthesized and grown during firing, and water molecules generated from the hydroxyl groups. It is considered that, due to elimination of or the like, as a result of disorder or mismatch in the crystal surface structure, grain growth is suppressed.
[0068]
Water has a crystal growth suppressing effect similarly to hydrogen. Although the reason is not clear yet, 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, and this may be to delay crystal growth. In addition, water vapor generates hydrogen and carbon monoxide by a so-called water gas reaction when it comes into contact with conductive carbon or a substance capable of generating conductive carbon by thermal decomposition at a high temperature (about 500 ° C. or higher). A crystal growth suppressing effect and a reducing effect can be obtained. In other words, when the water is continuously supplied, more hydrogen can be surely and continuously generated by the water gas reaction even in a high temperature range of 500 ° C. or more, and the crystal growth can be suppressed. The action and the reducing action can be maximized.
[0069]
As a method for supplying the water, the water is sprayed into the furnace or preferably pre-vaporized and supplied in the form of steam. The supply temperature range and the supply amount can be the same as in the case of hydrogen. That is, it is preferable that the water is added in a temperature range of at least 500 ° C. or higher and at which the firing is completed during the firing in the second stage. For example, preferably, the temperature ranges from 500 ° C. or lower to the firing completion temperature during the firing in the second stage, more preferably from 400 ° C. or lower to the firing completion temperature, and more preferably from about 300 ° C. to the firing completion temperature (for example, Over substantially the entire firing period). In this range, it is supposed that the addition of hydrogen to the surface oxygen atom of the transition metal compound and the formation of a hydroxyl group are likely to occur satisfactorily, so that the crystal growth is effectively suppressed. Note that hydrogen can be added during the first stage firing.
[0070]
The volume concentration of water vapor in the atmosphere in the above temperature range can be about 0.1% to 20%, and preferably 1% to 10%. Thereby, the crystal growth of the positive electrode material is suitably suppressed.
[0071]
In addition, in the case of firing by adding hydrogen during the main firing, when the added hydrogen (including hydrogen generated from moisture) comes into contact with a conductive carbon precursor such as coal pitch or saccharide which is melted and thermally decomposed by heating. Perhaps, in order to reduce the melt viscosity of the substance, a better condition can be realized in the above-mentioned carbon deposition method. For example, as the conductive carbon precursor, the softening temperature is in the range of 80 ° C. to 350 ° C., the temperature at which the weight loss due to thermal decomposition starts is in the range of 350 ° C. to 450 ° C., and heating to 500 ° C. or more and 800 ° C. or less. When using refined coal pitch that generates conductive carbon by decomposition, when hydrogen (including hydrogen generated from moisture) acts on the coal pitch that has become molten during the firing process, its viscosity decreases and its fluidity improves. A very uniform and thin coating thickness can be realized in the positive electrode material obtained as described above.
[0072]
Therefore, hydrogen (including hydrogen generated from moisture) is at least between 500 ° C. or lower and the firing completion temperature during the main firing, preferably from 400 ° C. or lower to the firing completion temperature, or over the entire area during the main firing. It is good to add. Further, when hydrogen is added even during the pre-baking, effects such as prevention of oxidation of the positive electrode material due to its reducibility 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 pulverization, mixing, kneading, and the like of the raw materials as necessary, Stage baking step], [addition of conductive carbon precursor (pulverization, mixing, kneading and the like can be performed if necessary)], and [second stage main baking step].
[0074]
In addition, when the conductive carbon is added before the preliminary firing in the first stage of the firing performed in two stages, and when the conductive carbon precursor is added after the temporary firing in the first stage, [ Addition step (pulverization, mixing, kneading, etc. can be performed together with the raw material if necessary)], [First-stage calcination step], [Addition of conductive carbon precursor (if necessary, raw material (Pulverization, mixing, kneading, and the like can be performed together with the (intermediate).)] And [Second-stage main firing step].
[0075]
Further, in the case where conductive carbon is added before the preliminary firing in the first stage of the firing performed in two stages, the step of adding conductive carbon (pulverizing, mixing, kneading, etc. together with the raw material as necessary) Can be performed)], [the first-stage calcination step], [the step of performing the pulverization, mixing, kneading, etc. of the raw material (intermediate) as necessary], and [the second-stage main calcination step] It is performed in order.
[0076]
In the above, when hydrogen or moisture is added, at least a part of the main firing step of the second step, desirably in the entire area of the main firing step of the second step, more preferably, in addition to the temporary firing step of the first step, 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, and a lithium polymer battery.
[0078]
Hereinafter, the basic configuration of an alkaline ion battery will be described using an example in which the alkali metal is lithium. Lithium-ion batteries are commonly referred to as rocking-chair type or shuttlecock (badminton blade) type.⁺A secondary battery is characterized in that ions reciprocate (see FIG. 1). At the time of charging, Li is placed inside the negative electrode (the current system uses carbon such as graphite).⁺The ions are inserted to form an intercalation compound (at this time, the anode carbon is reduced and Li⁺During discharge, the positive electrode (currently the mainstream is a cobalt oxide type, but in FIG. 1, an iron (II) / (III) redox system such as lithium iron phosphate is taken as an example. Li) inside⁺The ions are inserted to form an iron compound-lithium complex (at this time, iron of the positive electrode is reduced and Li⁺The oxidized negative electrode returns to graphite or the like). Li⁺Ions reciprocate through the electrolyte during charge and discharge, 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, LiCF₃SO₃, LiClO₄For example, a liquid electrolyte in which electrolyte salts such as those described above are dissolved, a gel electrolyte in which these liquid electrolytes are impregnated in a polymer gel substance, and a solid polymer electrolyte in which partially cross-linked polyethylene oxide is impregnated with the above electrolytes are used. When a liquid electrolyte is used, a porous diaphragm (separator) made of polyolefin or the like is interposed between them so that the positive electrode and the negative electrode are not short-circuited in the battery. For the positive electrode and the negative electrode, a predetermined amount of a conductivity-imparting agent such as carbon black is added to each of the positive electrode material and the negative electrode material. For example, synthetic resins such as polytetrafluoroethylene, polyvinylidene fluoride, and fluororesin; A binder is formed by adding a binder such as rubber and, if necessary, a polar organic solvent and kneading the mixture to form a thin film. On the other hand, when metal lithium is used for the negative electrode, Li (O) / Li⁺Change occurs with charging and discharging, and a battery is formed.
[0079]
[Action]
In general, 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), however, when a positive electrode material is synthesized from the raw material by firing, a decomposition gas is generated during the synthesis reaction in the heating and heating process. In most cases, more than 80% of the gas is generated in the temperature range from room temperature to 350 ° C. to 450 ° C. In one embodiment of the present invention, after a conductive carbon precursor (a substance capable of generating conductive carbon by thermal decomposition) is added to the raw material of the positive electrode material after the first stage of firing from room temperature to 350 ° C. to 450 ° C. By performing the second-stage baking, the thermal decomposition of the raw material positive electrode material has already progressed halfway, and since most of the gas generation has already ended, the molten conductive carbon precursor is less likely to foam and is uniform. And is thermally decomposed and fired to deposit carbon in a good condition.
[0080]
In addition, in the study by the present inventors, when the raw material of the positive electrode material is calcined in the absence of oxygen gas while supplying hydrogen and / or moisture, the crystallinity of the resulting positive electrode material particles is slightly disturbed, and It has been found that the primary particles are further refined. That is, it was proved that hydrogen and moisture are effective crystal growth inhibitors. Although the mechanism is not clear yet, on the growth surface of the crystal particles of the cathode material synthesized and grown from the raw material during firing, hydrogen bonds to surface oxygen atoms, or water molecules form a bond between metal and oxygen on the surface. Hydroxyl groups are generated by phenomena such as cutting and addition, and water molecules generated from the hydroxyl groups are desorbed again, resulting in disorder and inconsistency in the crystal surface structure, thereby suppressing the growth of particles. Conceivable.
[0081]
In the case where the conductive carbon precursor is added to the pre-baked raw material and firing is performed, hydrogen (including hydrogen generated by a reaction between water and a conductive carbon precursor such as coal pitch or sugar) is added. As a result, it was found that carbon deposition of the obtained cathode material was uniform, and higher cathode performance was obtained. The mechanism is not yet clear, but by adding the conductive carbon precursor to the calcined raw material, hydrogen is added to the molten conductive carbon precursor to lower its viscosity, This is presumed to be due to 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 lengthened, and the positive electrode generated by the reaction during that time Due to the diffusion of the constituent elements of the material, the cathode material enters the grain boundaries of the conductive carbon, and a more uniform and stable carbon-cathode material composite can be formed.
[0083]
By sintering while supplying hydrogen and / or moisture (water or steam) at least at a temperature of 500 ° C. or more in the sintering of the second stage, the primary particles of the positive electrode material generated are efficiently refined, Sintering of the positive electrode material particles can be effectively prevented.
[0084]
【Example】
Next, the present invention will be described in more detail with reference to Examples and the like, but the present invention is not limited by these.
Example 1
(1) Preparation of positive electrode material:
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.), 1.1784 g of LiOH.H₂O (manufactured by Wako Pure Chemical Industries, Ltd.) was added with approximately 1.5 times the volume of ethanol, and the mixture was ground and mixed using a planetary ball mill having 2 mm zirconia beads and a zirconia pot, and then dried at 50 ° C. under reduced pressure. The dried crushed mixture is placed in an alumina crucible, and 5% by volume hydrogen (H₂) / 95% by volume argon (Ar) gas was first calcined at 400 ° C. for 5 hours while passing the gas at a flow rate of 200 ml / min. 0.12.17 g of a purified coal pitch having a softening temperature of 200 ° C. [MCP-200 (trade name) manufactured by Adchemco Co., Ltd.] was added to 2.1364 g of the raw material after calcining taken out, pulverized in an agate mortar, and then the same atmosphere. At 775 ° C. for 10 hours (the mixed gas continued to flow from before the start of the temperature increase to during the firing, and further after being allowed to cool). The positive electrode material synthesized in this manner has LiFePO 4 having an olivine type crystal structure by powder X-ray diffraction.₄Was identified. On the other hand, the oxidation impurities α-Fe₂O₃, FePO₄And no crystal diffraction peaks of other impurities were observed at all.
[0085]
Although elemental analysis revealed that 3.08% by weight of carbon produced by the thermal decomposition of the refined coal pitch was contained, the diffraction peak of graphite crystals was not recognized by X-ray diffraction. It was presumed that a complex with crystalline carbon was formed. The crystallite size was 64 nm.
[0086]
(2) Preparation of secondary battery:
This positive electrode material, acetylene black [Denka Black (registered trademark); 50% pressed product manufactured by Denki Kagaku Kogyo Co., Ltd.] as a conductivity-imparting material, and unfired PTFE (polytetrafluoroethylene) powder as a binder Are mixed and kneaded so that the weight ratio becomes 70.6 / 24.4 / 5, and the resultant is rolled into a sheet having a thickness of 0.7 mm. did.
[0087]
Thereafter, a metal titanium net and a metal nickel net are spot-welded to a stainless steel coin battery case (model number CR2032) as positive and negative electrode current collectors, and the positive electrode and the metal lithium foil negative electrode are assembled via a porous polyethylene diaphragm, and electrolytically separated. 1M LiPF as liquid₆Was filled and sealed with a 1/1 mixed solution of dimethyl carbonate / ethylene carbonate in which was dissolved to prepare a coin-type lithium secondary battery. A series of battery assembly including the positive and negative electrodes, the diaphragm, and the electrolyte was performed in a glove box replaced with argon.
[0088]
For the secondary battery incorporating the cathode material obtained as described above, the current density per apparent area of the cathode pellet was 0.5 mA / cm.²And 1.6 mA / cm²When charge and discharge were 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 by It was standardized by the amount of the positive electrode active material).
[0089]
Comparative Example 1
Positive electrode material olivine type LiFePO 4 was prepared by the same synthesis method as in Example 1 except that purified coal pitch having a softening temperature of 200 ° C. was added to the raw material before pre-firing and pre-firing and main firing were performed.₄Got.
That is, the same amount of FeC as in Example 1 was used.₂O₄・ 2H₂O, (NH₄)₂HPO₄, And LiOH.H₂After adding 0.1940 g of refined coal pitch having a softening temperature of 200 ° C. to O, pulverizing / mixing and drying using a planetary ball mill, calcining at 400 ° C. for 5 hours in the same atmosphere in an alumina crucible, and pulverizing Then, main firing was performed at 775 ° C. for 10 hours in the same atmosphere. The obtained positive electrode material showed almost no difference from Example 1 in X-ray diffraction, and had a crystallite size of 64 nm, which was not different from Example 1. From elemental analysis, it was found that 3.04% by weight of carbon produced by the thermal decomposition of the refined coal pitch was contained, and the amount of precipitated carbon was not significantly different from that of Example 1.
[0090]
Using this positive electrode material, a coin-type lithium secondary battery configured in the same manner as in Example 1 was manufactured, and a charge / discharge cycle test was performed in the same manner as in Example 1. Table 1 also shows the average initial discharge capacity for the 1 to 20 cycles.
[0091]
As shown in Table 1, with respect to the initial discharge capacity of Comparative Example 1, the effects of the addition of hydrogen and the addition of the refined coal pitch were recognized, and the initial discharge capacity was considerably large. It turns out to be.
[0092]
From the above, as shown in Example 1, when pre-firing and main-firing the raw material while adding hydrogen, by adding a coal pitch having a softening temperature of 200 ° C to the raw material after the pre-firing, and performing main firing, Cathode material LiFePO₄It can be seen that the initial discharge capacity of the secondary battery using the Pb further increased, and the performance was improved.
[0093]
At this time, the precipitated carbon content in the positive electrode materials of Example 1 and Comparative Example 1 was almost the same, and there was no difference in crystallite size. Precipitation of carbon from the coal pitch on the surface of the positive electrode material particles occurred in a better state than in Comparative Example 1, resulting in higher positive electrode performance. This is presumed to be due to the following reasons.
First, while the refined coal pitch having a softening temperature of 200 ° C. is well melted during the heating in the main firing, most of the gas generated by decomposition of the raw materials is released in the pre-firing process, and Since only a small amount of gas from the raw material is generated inside, the melt of the refined coal pitch does not foam. Second, since the added hydrogen reduces the viscosity of the melt of coal pitch, it spreads more evenly on the surface of the generated positive electrode material particles, and is thermally decomposed in that state, so that the conductive carbon becomes very uniform. 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 Soegawa Riken Co., Ltd.), 1.1579 g of Li₃PO₄After adding approximately 1.5 times the volume of ethanol to Wako Pure Chemical Industries, Ltd., the mixture was ground and mixed using a planetary ball mill having 2 mm zirconia beads and a zirconia pot, and dried at 50 ° C. under reduced pressure. The dried crushed mixture is placed in an alumina crucible, and 5% by volume hydrogen (H₂) / 95% by volume argon (Ar) gas was first calcined at 400 ° C. for 5 hours while passing the gas at a flow rate of 200 ml / min. 0.1879 g of refined coal pitch having a softening temperature of 200 ° C. [MCP-200 (trade name) manufactured by Adchemco Co., Ltd.] was added to 4.0712 g of the taken out calcined raw material, and the mixture was pulverized in an agate mortar and then the same atmosphere. At 725 ° C. for 10 hours (the mixed gas continued to flow from before the start of the temperature increase to during the firing and further after being allowed to cool). The positive electrode material synthesized in this way has LiFePO 4 having an olivine type crystal structure by powder X-ray diffraction₄Was identified. On the other hand, the oxidation impurities α-Fe₂O₃, FePO₄And no crystal diffraction peaks of other impurities were observed.
[0095]
Although elemental analysis revealed that carbon produced by the thermal decomposition of the refined coal pitch was contained at 2.98% by weight, no diffraction peak of graphite crystal was observed from X-ray diffraction. It was presumed that a complex with crystalline carbon was formed. 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 cathode material obtained as described above, the current density per apparent area of the cathode pellet was 0.5 mA / cm.²And 1.6 mA / cm²When charge and discharge were 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 by It was standardized by the amount of the positive electrode active material).
[0098]
Comparative Example 2
A positive electrode material olivine type LiFePO 4 was prepared by the same synthesis method as in Example 2, except that purified coal pitch having a softening temperature of 200 ° C. was added to the raw material before pre-firing and pre-firing and main firing were performed.₄Got.
That is, the same amount of Fe as in Example 2₃(PO₄)₂・ 8H₂O (manufactured by Soekawa Riken Co., Ltd.) and Li₃PO₄0.1940 g of refined coal pitch having a softening temperature of 200 ° C. was added to (Wako Pure Chemical Industries, Ltd.), pulverized and mixed using a planetary ball mill, and dried, and then dried at 400 ° C. in the same atmosphere in an alumina crucible. After calcination for 5 hours and pulverization, calcination was further performed 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 had a crystallite size of 162 nm, which was almost no difference from Example 2. Further, from elemental analysis, it was found that carbon produced by thermal decomposition of the refined coal pitch was contained at 3.13% by weight, and the amount of precipitated carbon was not significantly different from that of Example 2.
[0099]
Using this positive electrode material, a coin-type lithium secondary battery configured in the same manner as in Example 2 was manufactured, and a charge / discharge cycle test was performed in the same manner as in Example 2. Table 1 also shows the average initial discharge capacity for the 1 to 20 cycles.
[0100]
As shown in Table 1, with respect to the initial discharge capacity of Comparative Example 2, the effects of hydrogenation and the addition of refined coal pitch are recognized, but in Example 2, the initial discharge capacity is further increased. The reason is considered to be the same as in the first embodiment.
[0101]
Example 3
Cathode material LiFePO₄Was synthesized by the following procedure.
The same amount as in Example 2, that is, 5.0161 g of Fe₃(PO₄)₂・ 8H₂O (manufactured by Soekawa Rikagaku Co., Ltd.) and 1.1579 g of Li₃PO₄After adding approximately 1.5 times the volume of ethanol to Wako Pure Chemical Industries, Ltd., the mixture was ground and mixed using a planetary ball mill having 2 mm zirconia beads and a zirconia pot, and dried at 50 ° C. under reduced pressure. The dried crushed mixture is placed in an alumina crucible, and 5% by volume hydrogen (H₂) / 95% by volume argon (Ar) gas was first calcined at 400 ° C. for 5 hours while passing the gas at a flow rate of 200 ml / min. 0.5358 g of dextrin (manufactured by Wako Pure Chemical Industries, Ltd.) was added to 4.4762 g of the raw material that had been taken out and calcined, and the mixture was pulverized in an agate mortar, followed by main firing at 725 ° C. for 10 hours in the same atmosphere. (The mixed gas continued to flow from before the start of the temperature increase to during the firing and further after the cooling.). The positive electrode material synthesized in this way has LiFePO 4 having an olivine type crystal structure by powder X-ray diffraction₄Was identified. On the other hand, the oxidation impurities α-Fe₂O₃, FePO₄And no crystal diffraction peaks of other impurities were observed.
[0102]
In addition, although elemental analysis revealed that 3.43% by weight of carbon generated by the thermal decomposition of dextrin was contained, no diffraction peak of graphite crystal was 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 cathode material obtained as described above, the current density per apparent area of the cathode pellet was 0.5 mA / cm.²And 1.6 mA / cm²When charge and discharge were 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 by It was standardized by the amount of the positive electrode active material).
[0105]
FIG. 2 shows the charge / discharge characteristics of the coin-type lithium secondary battery at the tenth cycle under the above conditions.
[0106]
Comparative Example 3
A positive electrode material olivine type LiFePO 4 was prepared by the same synthesis method as in Example 3 except that dextrin was added to the raw material before pre-calcination and pre-firing and main firing were performed.₄Got.
That is, the same amount of Fe as in Example 3₃(PO₄)₂・ 8H₂O (manufactured by Soekawa Riken Co., Ltd.) and Li₃PO₄0.6600 g of dextrin was added to the product (manufactured by Wako Pure Chemical Industries, Ltd.), crushed and mixed using a planetary ball mill, dried, and calcined at 400 ° C. for 5 hours in the same atmosphere in an alumina crucible. After the pulverization, firing was further performed in the same atmosphere at 725 ° C. for 10 hours. The obtained positive electrode material showed almost no difference from Example 3 in X-ray diffraction, and had a crystallite size of 165 nm, which was almost no difference from Example 3. From elemental analysis, it was found that carbon produced by thermal decomposition of dextrin was contained at 3.33% by weight, and the amount of deposited carbon was not much different from that of Example 3.
[0107]
Using this positive electrode material, a coin-type lithium secondary battery configured in the same manner as in Example 3 was produced, and a charge / discharge cycle test was performed in the same manner as in Example 3. Table 1 also shows the average initial discharge capacity for the 1 to 20 cycles. FIG. 3 shows the charge / discharge characteristics at the 10th cycle of the coin-type lithium secondary battery.
[0108]
As shown in Table 1, with respect to the initial discharge capacity of Comparative Example 3, the effects of hydrogenation and dextrin addition are recognized, but it is found that in Example 3, the initial discharge capacity is further increased. The reason is considered to be the same as in the first embodiment.
[0109]
Further, comparing FIG. 2 and FIG. 3, the theoretical capacity (170 mAh / g) of Example 3 in which dextrin was added to the raw material after calcination was higher than that of Comparative Example 3 in which dextrin was added to the raw material before calcination. It has a flat region of the charge / discharge voltage up to a value closer to the above, and the difference between the charge voltage and the discharge voltage is sufficiently small, so it is understood that the charge / discharge characteristics are excellent.
[0110]
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.H₂To O (manufactured by Wako Pure Chemical Industries, Ltd.), 0.1220 g of acetylene black [Denka Black (registered trademark; 50% pressed product) manufactured by Denki Kagaku Kogyo Co., Ltd.] was added, and ground and mixed using an automatic mortar made of agate. This crushed mixture is placed in an alumina crucible, and 5% by volume hydrogen (H₂) / 95% by volume argon (Ar) gas was passed through at a flow rate of 200 ml / min, temporarily calcined at 400 ° C. for 5 hours, taken out and ground in an agate mortar, and further heated to 775 ° C. in the same atmosphere. For 10 hours (the mixed gas continued to flow from before the start of the temperature increase to during the firing and further after being allowed to cool). The positive electrode material synthesized in this way has LiFePO 4 having an olivine type crystal structure by powder X-ray diffraction₄Was identified. On the other hand, the oxidation impurities α-Fe₂O₃, FePO₄No crystal diffraction peak was observed.
[0111]
In addition, elemental analysis revealed that carbon derived from acetylene black was contained at 2.84% by weight. 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 cathode material obtained as described above, the current density per apparent area of the cathode pellet was 0.5 mA / cm.²And 1.6 mA / cm²When charge and discharge were 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 by It was standardized by the amount of the positive electrode active material).
[0114]
Comparative Example 4
A positive electrode material olivine type LiFePO 4 was prepared in the same manner as in Example 4 except that the same acetylene black was added to the raw material after the preliminary firing and the preliminary firing and the final firing were performed.₄Got.
That is, the same amount of FeC as in Example 4.₂O₄・ 2H₂O, and (NH₄)₂HPO₄, And 1.1784 g of LiOH.H₂O is crushed and mixed using an agate mortar, and the crushed and mixed mixture is placed in an alumina crucible and 5% by volume hydrogen (H₂) / 95% by volume argon (Ar) gas was first calcined at 400 ° C. for 5 hours while passing the gas 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 pre-baked raw material thus taken out, pulverized and mixed in an automatic mortar made of agate, and further baked at 775 ° C. for 10 hours in the same atmosphere. (The mixed gas continued to flow from before the start of the temperature rise to during the baking and further after being allowed to cool). The positive electrode material synthesized in this way has LiFePO 4 having an olivine type crystal structure by powder X-ray diffraction₄Was identified. On the other hand, the oxidation impurities α-Fe₂O₃, FePO₄No crystal diffraction peak was observed.
[0115]
In addition, elemental analysis revealed that carbon derived from acetylene black was contained at 2.76% by weight. The crystallite size was 122 nm. Therefore, the carbon content and the crystallite size were not much different from those in Example 4.
[0116]
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 4, and a charge / discharge cycle test was performed in the same manner as in Example 4. Table 1 also shows the average initial discharge capacity for the 1 to 20 cycles.
[0117]
As shown in Table 1, the initial discharge capacity of Example 4 was relatively good, and the effects of acetylene black as conductive carbon and hydrogenation were observed. Further, in Example 4, the initial discharge capacity was larger than that in Comparative Example 4, and when acetylene black which was already in an infusible state and was carbonized was added, it was added to the raw material before calcining. It can be seen that the performance of the positive electrode is higher when the firing is performed.
[0118]
[Table 1]

[0119]
Example 5
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.H₂O (manufactured by Wako Pure Chemical Industries, Ltd.) was mixed with 0.0610 g of acetylene black [DENKA BLACK (registered trademark; 50% pressed product manufactured by Denki Kagaku Kogyo Co., Ltd.)] and ground and mixed using an automatic mortar made of agate. . This crushed mixture is placed in an alumina crucible, and 5% by volume hydrogen (H₂) / 95% by volume argon (Ar) gas was first calcined at 400 ° C. for 5 hours while passing the gas at a flow rate of 200 ml / min. To 2.2430 g of the raw material that had been taken out and calcined, 0.0576 g of a refined coal pitch having a softening temperature of 200 ° C. was added, pulverized 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 flow from before the start of the temperature increase to during the firing and further after the cooling. The positive electrode material synthesized in this way has LiFePO 4 having an olivine type crystal structure by powder X-ray diffraction₄Was identified. On the other hand, the oxidation impurities α-Fe₂O₃, FePO₄No crystal diffraction peak was observed.
[0120]
In addition, elemental analysis revealed that carbon generated by thermal decomposition of the refined coal pitch and carbon derived from acetylene black were contained in a total amount of 3.27% by weight. 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 cathode material obtained as described above, the current density per apparent area of the cathode pellet was 0.5 mA / cm.²And 1.6 mA / cm²When charge and discharge were repeated in an 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 by It was standardized by the amount of the positive electrode active material). Thus, the positive electrode material obtained by adding acetylene black as conductive carbon before calcination and adding purified coal pitch as a conductive carbon precursor after calcination can reduce the discharge capacity of the secondary battery. It was shown to increase the size and improve the positive electrode performance.
[0122]
[Table 2]

[0123]
Example 6
Cathode material LiFePO₄Was synthesized by the following procedure.
5.0161 g of Fe₃(PO₄)₂・ 8H₂O (manufactured by Soegawa Riken Co., Ltd.), 1.1579 g of Li₃PO₄After adding approximately 1.5 times the volume of ethanol to Wako Pure Chemical Industries, Ltd., the mixture was ground and mixed using a planetary ball mill having 2 mm zirconia beads and a zirconia pot, and dried at 50 ° C. under reduced pressure. The dried and ground mixture was placed in an alumina crucible and calcined at 400 ° C. for 5 hours while passing 100% by volume argon (Ar) gas at a flow rate of 200 ml / min. To 4.1248 g of the taken out raw material after calcining, 0.1904 g of a refined coal pitch [MCP-200 (trade name) manufactured by Adchemco Co., Ltd.] having a softening temperature of 200 ° C. was added, followed by pulverization in an agate mortar, followed by the same atmosphere. At 700 ° C. for 10 hours (the gas continued to flow from before the start of the temperature increase, during the firing, and after cooling). The positive electrode material synthesized in this way has LiFePO 4 having an olivine type crystal structure by powder X-ray diffraction₄Was identified. On the other hand, the oxidation impurities α-Fe₂O₃, FePO₄And no crystal diffraction peaks of other impurities were observed.
[0124]
In addition, although elemental analysis revealed that 3.16% by weight of carbon produced by the thermal decomposition of the refined coal pitch was contained, the diffraction peak of graphite crystals was not recognized by 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 cathode material obtained as described above, the current density per apparent area of the cathode pellet was 0.5 mA / cm.²And 1.6 mA / cm²When charge and discharge were 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 determined by It was standardized by the amount of the positive electrode active material).
[0127]
FIG. 4 shows the charge / discharge characteristics of the coin-type lithium secondary battery at the tenth cycle under the above conditions.
[0128]
Comparative Example 5
A positive electrode material olivine type LiFePO 4 was prepared in the same manner as in Example 6 except that purified coal pitch having a softening temperature of 200 ° C. was added to the raw material before pre-firing and pre-firing and main firing were performed.₄Got.
That is, the same amount of Fe as in Example 6₃(PO₄)₂・ 8H₂O (manufactured by Soekawa Riken Co., Ltd.) and Li₃PO₄0.1940 g of refined coal pitch having a softening temperature of 200 ° C. was added to (Wako Pure Chemical Industries, Ltd.), pulverized and mixed using a planetary ball mill, and dried, and then dried in an alumina crucible under the same argon atmosphere. Temporarily baked at 5 ° C. for 5 hours, crushed, and further baked at 700 ° C. for 10 hours in the same atmosphere. The obtained positive electrode material showed almost no difference from Example 6 in X-ray diffraction, and had a crystallite size of 189 nm, which was almost no difference from Example 6. Further, elemental analysis revealed that carbon produced by the thermal decomposition of the refined coal pitch was contained at 3.04% by weight, and the amount of precipitated carbon was not significantly different from that of Example 6.
[0129]
Using this positive electrode material, a coin-type lithium secondary battery configured in the same manner as in Example 6 was manufactured, and a charge / discharge cycle test was performed in the same manner as in Example 6. Table 3 also shows the average initial discharge capacity for the 1 to 20 cycles.
[0130]
FIG. 5 shows charge / discharge characteristics of the coin-type lithium secondary battery at the 10th cycle under the above conditions.
[0131]
As shown in Table 3, Comparative Example 5 in which refined coal pitch was added to the raw material before calcining also exhibited a relatively large initial discharge capacity, and the effect of adding refined coal pitch was recognized. It can be seen that in Example 6 in which refined coal pitch was added, the initial discharge capacity was further increased.
[0132]
In addition, comparing FIG. 4 with FIG. 5, Example 6 in which the coal pitch was added after the preliminary firing had a flat charge-discharge voltage up to a larger capacity value than Comparative Example 5 in which the coal pitch was added before the preliminary firing. Since it has a range and the difference between the charging voltage and the discharging voltage is small, it is understood that the charging and discharging characteristics are excellent.
[0133]
Therefore, even in a firing atmosphere of 100% argon containing no hydrogen, it was found that higher positive electrode performance can be obtained by adding coal pitch to the raw material after the preliminary firing.
[0134]
When a purified coal pitch having a relatively low viscosity at the time of melting as compared with dextrin is used as in Example 6, even if hydrogen is not necessarily added to the firing atmosphere, the obtained positive electrode material has a relatively large discharge. May indicate capacity.
[0135]
[Table 3]

[0136]
【The invention's effect】
According to the method of the present invention, the crystal growth of primary particles of the positive electrode material can be suppressed, and the crystal particles of the obtained positive electrode material can be made finer. That is, a positive electrode produced by adding a conductive carbon precursor and / or conductive carbon at a predetermined timing and firing the raw material of the positive electrode material while preferably supplying hydrogen and / or moisture (water or steam) is provided. Primary particles of the material can be efficiently refined, and a state in which conductive carbon is uniformly and stably present in the positive electrode material can be created, so that higher positive electrode performance can be obtained.
[0137]
Further, according to the method of the present invention, there is no possibility that the raw material is insufficiently calcined to cause a chemical change to the final product or an intermediate product remains, and the desired positive electrode material is reliably synthesized from the raw material by the calcining. it can.
[0138]
In addition, hydrogen and / or moisture have a strong crystal growth suppressing action and a strong action of improving the state of adhesion of a substance that precipitates conductive carbon by heating to a 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, the lithium ion and other alkalis are present at the interface between the positive electrode material and the electrolyte. The positive electrode material has a large surface area when subjected to electrochemical oxidation / reduction accompanied by undoping / doping of metal ions, and alkali metal ions can easily enter and exit at the interface between the inside of the particles of the positive electrode material and the electrolyte, so that the electrode reaction Polarization is suppressed. Furthermore, since the contact between the conductivity-imparting material such as carbon black, which is usually mixed with the cathode material, and the cathode material is remarkably improved, the conductivity is improved, the utilization rate of the cathode material as an active material is high, and the cell This is a secondary battery having a small resistance and having significantly improved voltage efficiency and effective battery discharge capacity.
[Brief description of the drawings]
FIG. 1 is a schematic diagram for explaining the charge and discharge behavior of a secondary battery.
FIG. 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.

Claims (12)

In a method for producing a positive electrode material for a secondary battery in which a raw material is fired to produce 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.
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 a first-stage firing, and then performing a second-stage firing. In a method for producing a positive electrode material for a secondary battery in which a raw material is fired to produce 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.
Conductive carbon is added to the raw material before firing in the first stage and firing is performed,
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 a first-stage firing, and then performing a second-stage firing. In a method for producing a positive electrode material for a secondary battery in which a raw material is fired to produce 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.
A method for producing a positive electrode material for a secondary battery, characterized in that conductive carbon is added to a raw material before firing in the first stage and firing is performed. 3. The method according to claim 1, wherein the substance capable of generating conductive carbon by thermal decomposition is bitumen. The bitumen according to claim 4, wherein the bitumen has a softening temperature of 80 ° C to 350 ° C, a weight loss onset temperature by thermal decomposition of 350 ° C to 450 ° C, and a thermal decomposition temperature of 500 ° C to 800 ° C. A method for producing a positive electrode material for a secondary battery, comprising a coal pitch capable of depositing conductive carbon by firing. 3. The method according to claim 1, wherein the substance capable of generating conductive carbon by thermal decomposition is a saccharide. 7. The method according to claim 6, wherein the saccharide decomposes in a temperature range of 250 ° C. or more and less than 500 ° C., and at least partially at least once in a molten state in a temperature rising process from 150 ° C. to 500 ° C. A method for producing a positive electrode material for a secondary battery, wherein the saccharide is a saccharide that generates conductive carbon by heating and decomposing and firing to 800 ° C. or lower. The method according to any one of claims 1 to 7, wherein one or more kinds selected from the group consisting of hydrogen, water, and steam are added at least at a temperature of 500 ° C or more in the firing in the second stage. A method for producing a positive electrode material for a secondary battery. 9. The positive electrode material according to claim 1, wherein the positive electrode material is a compound containing an alkali metal, a transition metal, and oxygen and capable of being synthesized by firing the raw material in the absence of oxygen gas. A method for producing a positive electrode material for a secondary battery. According to claim 9, 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)} is Fe (II), Co (II), Mn (II), Ni (II), V (II) or Cu (II), A represents P or S, a is a number selected from 0 to 3, x is from 1 to 2 A selected number, y represents a number selected from 1 to 3, and z represents a number selected from 4 to 12], or a complex thereof. A method for producing a battery positive electrode material. According to claim 9, wherein the positive electrode _{material, Li q FePO 4, Li q} CoPO 4 or _Li q MnPO ₄ (here, q is a number selected from 0 to 1) material or of the general formula of A method for producing a positive electrode material for a secondary battery, which is a composite. A secondary battery comprising, as a constituent element, a positive electrode material produced by the method according to claim 1.

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