JP2004362999A

JP2004362999A - Lead-acid battery

Info

Publication number: JP2004362999A
Application number: JP2003161499A
Authority: JP
Inventors: Hidetoshi Abe; 英俊阿部; Ryoji Komiyama; 亮二小宮山; Masaru Miura; 優三浦; Daisuke Kikuchi; 大介菊地; Hiromasa Noguchi; 博正野口; Tooru Mangahara; 徹萬ヶ原
Original assignee: Furukawa Battery Co Ltd
Current assignee: Furukawa Battery Co Ltd
Priority date: 2003-06-06
Filing date: 2003-06-06
Publication date: 2004-12-24
Anticipated expiration: 2023-06-06
Also published as: JP4390481B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lead-acid battery for highly maintaining utilization rate of a positive electrode active material from a chemical formation process up to float charge. <P>SOLUTION: The battery has the active material with a plural kinds of graphite powder different in content of sulfuric added thereto. The battery has the active material with graphite powder not containing the sulfuric and graphite powder containing the sulfuric added thereto. An electrolytic solution is well supplied to an electrode, since the graphite powder containing the sulfuric in large quantity generates clacks in the active material in the formation process, and the graphite powder containing the sulfuric in small quantity or the graphite not containing the sulfuric generates clacks in the active material during the float discharging. Therefor, the utilization rate of the active material is highly maintained from the formation process up to the float discharging. The graphite powder containing the sulfuric can be easily obtained by treating natural graphite powder by a treating solution containing the sulfuric and an oxidant. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、利用率の高い正極活物質を備えた鉛蓄電池に関する。
【０００２】
【従来の技術】
鉛蓄電池は、正極活物質の利用率（エネルギー密度）が低いため小型軽量化が困難とされてきた。前記正極活物質の利用率が低い主な原因は、放電中に生成する難溶性の硫酸鉛結晶が活物質バルク中の細孔を閉塞して、電解液が正極板に供給されなくなり正負両極板間の放電反応が継続できなくなるためである。
【０００３】
この他、電解液中の硫酸も活物質として作用するが、前記細孔の閉塞により正負両極板間の硫酸イオンが正極に拡散しなくなることも前記利用率の低い原因の１つで、特に０．２Ｃ以上の高率放電時においては、活物質バルク中の硫酸を使い果たすと新たな硫酸が供給されないため利用率が急激に低下する。この現象は電解液の少ない制御弁式鉛蓄電池において起き易い。
【０００４】
このようなことから活物質の気孔率を増加させる方法が提案されている。
具体的には（１）ペースト混練時の水量を増やして活物質の密度を減少させる方法、（２）未化成活物質中の硫酸鉛量を増加させて化成後に気孔率を高める方法、（３）活物質に異方性の大きい黒鉛を添加する方法（例えば特許文献１）、（４）膨張化黒鉛を添加し化成後に酸化消失させる方法（例えば特許文献２）などである。
【０００５】
しかし、これらの方法は、正極活物質の軟化現象が起き易くなるため、充放電サイクルを繰り返す（フロート充電）用途では電池寿命が極端に悪くなる。
そのうえ（１）の方法ではペースト粘度が低いため充填性が悪化して正極板の製造歩留りが悪化する、また（２）の方法ではペースト混練時の硫酸量が増加してＰＨが低下し、通常の熟成方法では金属鉛量が５％未満に減少せず、化成が十分に行えなくなる、といった問題がある。
【０００６】
また正極活物質の利用率を高めるため、極板を薄くして極板の枚数を増やす方法はコスト高になり、また薄板の正極格子は腐食により早期に破断し電池寿命が低下するという問題がある。
【０００７】
この他、正極活物質に、硫酸処理した（硫酸を含有させた）黒鉛粉を添加する方法（例えば特許文献３）が提案されている。この方法によれば、黒鉛粉が化成工程で陽極酸化してＣ軸方向に膨張するため活物質バルクにクラックが生じ、このクラックを通って電解液が正極活物質の中央部にまで浸入するため活物質の利用率が高まる。しかし、前記硫酸処理した黒鉛粉はフロート充電初期において酸化消耗してしまうため長期にわたるフロート充電中に、前記黒鉛粉による群圧保持効果が得られなくなるという問題があった。
【０００８】
一方、硫酸処理をしない黒鉛粉を添加したのでは、化成工程での黒鉛粉の効果（膨張して電解液を活物質バルク中央部にまで浸入させるという効果）が十分に得られない。
【０００９】
【特許文献１】特公昭６３−０５７９１３号公報
【特許文献２】特開昭５６−１５９０６３号公報
【特許文献３】特開昭５６−１５９０６２号公報
【００１０】
【発明が解決しようとする課題】
本発明の目的は、正極活物質の利用率が、化成工程からフロート充電まで高度に維持される鉛蓄電池を提供することにある。
【００１１】
【課題を解決するための手段】
請求項１発明は、正極活物質に、硫酸の含有量が異なる複数種の黒鉛粉が添加されていることを特徴とする鉛蓄電池である。
【００１２】
請求項２発明は、正極活物質に、硫酸を含有させてない黒鉛粉と、硫酸を含有させた黒鉛粉とが添加されていることを特徴とする鉛蓄電池である。
【００１３】
請求項３発明は、前記硫酸を含有させた黒鉛粉が、天然黒鉛粉を硫酸と酸化剤を含む処理液により処理したものであることを特徴とする請求項１または２記載の鉛蓄電池である。
【００１４】
【発明の実施の形態】
請求項１発明において、硫酸の含有量が異なる複数種の黒鉛粉とは、例えば硫酸を多量に含有させた黒鉛粉と少量含有させた黒鉛粉であり、前記硫酸を多量に含有させた黒鉛粉は、化成工程で電解酸化してＣ軸方向に膨張し、活物質バルクにクラックを生じさせ、硫酸を正極活物質中央部にまで浸入させる作用を果たす。また硫酸を少量含有させた黒鉛粉は、フロート充電中に徐々にＣ軸方向に膨張して活物質バルクにクラックを生じさせるとともに、群圧保持効果に寄与する。
【００１５】
請求項２発明は、前記硫酸を少量含有させた黒鉛粉に代えて、硫酸を含有させてない黒鉛粉を添加したもので、請求項１発明と同様の作用効果が得られる。
【００１６】
このように、本発明では、硫酸の含有量が異なる複数種の黒鉛粉のうち、例えば、硫酸を多量に含有させた黒鉛粉が化成工程で活物質にクラックを生じさせ、硫酸を少量含有させた黒鉛粉或いは硫酸を含有させてない黒鉛粉がフロート充電中に活物質にクラックを生じさせるので電極に電解液が良好に供給され、活物質の利用率が化成工程からフロート充電まで高度に維持される。
【００１７】
本発明において、黒鉛粉には、異方性が高くかつ層状構造で硫酸が含有され易い天然黒鉛粉が適している。前記天然黒鉛粉は、天然黒鉛塊を粉砕し分級して得られる。前記黒鉛粉の平均粒径は３００μｍ程度がその効果が良好に発現され望ましい。
【００１８】
本発明において、前記硫酸を含有させた黒鉛粉は、前記天然黒鉛粉を硫酸と酸化剤を含む処理液により処理することで容易かつ迅速に得られる。前記酸化剤は、黒鉛粉に硫酸が含有されるのを促進する役目を果たす。
【００１９】
黒鉛粉に含有される硫酸量は、前記酸化剤の種類、量、処理温度、処理時間などにより制御できる。前記酸化剤には過酸化水素、過塩素酸類、オゾンなどが適用できる。
【００２０】
本発明において、硫酸を含有させた黒鉛粉とは硫酸処理をした黒鉛粉であり、硫酸を含有させてない黒鉛粉とは硫酸処理をしていない黒鉛粉である。また前記硫酸の含有量が多量とは黒鉛粉が化成工程でＣ軸方向に十分膨張する量であり、少量とは黒鉛粉がフロート充電初期に酸化消耗してしまわない量である。
【００２１】
本発明において、硫酸を少量含有させた黒鉛粉或いは硫酸を含有させてない黒鉛粉と、硫酸を多量に含有させた黒鉛粉の添加量はほぼ同程度とするのが、活物質の利用率を化成工程からフロート充電まで高度に維持することができて望ましい。
【００２２】
黒鉛粉の総添加量は、正極活物質量に対する質量比率で０．２〜１．０％が望ましい。酸化剤には過酸化水素、過塩素酸類、オゾンなどが適用できる。
【００２３】
【実施例】
以下に、本発明を実施例により詳細に説明する。
（実施例１）
中国産の天然黒鉛塊を粉砕機により粉砕し分級して平均粒径が３００μｍの黒鉛粉を得た。次いでこれを１Ｎの希硫酸水溶液中に投入し、浮遊選鉱法によりシリカ、アルミナ、金属不純物（例えば鉄、ニッケル）などを除去した。なお、前記金属不純物は水素過電圧を過大に低減させて電池の減液性能を悪化させる。
【００２４】
次に、前記浮遊選鉱後の黒鉛粉を８０℃に保持した濃硫酸と過酸化水素の混酸中に０．５時間または１．０時間保持して硫酸を含有させ（硫酸処理）、その後、水洗および乾燥を行った。なお、硫酸濃度や温度等他の条件が同じなら処理時間が長いほど硫酸の含有量は増加する。
【００２５】
次に、ボールミルにより粉砕した鉛粉２００ｇに、黒鉛粉Ａ（硫酸処理してない黒鉛粉）と前記硫酸処理を０．５時間保持した黒鉛粉Ｂまたは１．０時間保持した黒鉛粉Ｃをそれぞれ所定量添加し、これにポリエステル製のカットファイバーを適量添加し、次いで水を２５ｃｃ加えてボールミルで混合し、この混合体に比重１．４０の希硫酸を１８ｃｃ加えて混練してペースト状の正極用活物質を作製した。
【００２６】
次に、前記正極用活物質３４ｇを、厚さ３．８ｍｍのＰｂ−Ｓｎ−Ｃａ系合金の正極用鋳造格子に充填し、これを温度４０℃湿度９５％で４０時間熟成して厚さ４．２ｍｍの正極板を得た。次いで前記正極板１枚と常法により作製した負極板２枚とで極板群を形成し、これを各ＡＢＳ樹脂製電槽に１個ずつ挿入した。正極板の厚さが均一だったため極板群の挿入圧に差は見られなかった。
【００２７】
次に、前記電槽に種々電池部品を組付けたのち、前記電槽の各セルに比重１．２０の希硫酸を２０ｃｃずつ注入したのち、電解液温度を２５℃に制御して電槽化成を行い、定格容量２Ａｈの制御弁式鉛蓄電池を製造した。前記電槽化成での電気量は正極理論容量の２００％とした。
【００２８】
（実施例２）
鉛粉２００ｇに、硫酸処理時間を０．１ｈｒとして硫酸を少量含有させた黒鉛粉Ａ’と処理時間を１．０ｈｒとして硫酸を多量に含有させた黒鉛粉Ｃとを添加した他は、実施例１と同じ方法により制御弁式鉛蓄電池を製造した。
【００２９】
（比較例１）
鉛粉２００ｇに、硫酸処理を行わない黒鉛粉Ａのみを添加した他は、実施例１と同じ方法により制御弁式鉛蓄電池を製造した。
【００３０】
（比較例２）
鉛粉２００ｇに、処理時間を１．０ｈｒとして硫酸を多量に含有させた黒鉛粉Ｃのみを添加した他は、実施例１と同じ方法により制御弁式鉛蓄電池を製造した。
【００３１】
（比較例３）
鉛粉２００ｇに、黒鉛粉を添加しなかった他は、実施例１と同じ方法により制御弁式鉛蓄電池を製造した。
【００３２】
得られた各々の制御弁式鉛蓄電池について、温度２５℃、設定電圧２．２７５Ｖ／セル、最大電流１Ａ、放電容量０．２５ＣＡの条件で初期容量を測定した。引続き温度６５℃で連続フロート充電試験を２ヵ月間行ったのち、残存容量を前記初期容量の場合と同じ条件で測定した。
測定結果を表１に示す。表１には各種黒鉛粉の添加量を併記した。
【００３３】
【表１】

【００３４】
表１から明らかなように、本発明に係る実施例１（Ｎｏ．１〜４）および実施例２（Ｎｏ．５）はいずれも初期容量および残存容量が大きく、化成工程からフロート充電まで正極活物質の利用率が高度に維持された。
【００３５】
これに対し、比較例１（Ｎｏ．６）は硫酸処理を行わない黒鉛粉Ａのみを添加したため初期容量が低下した。比較例２（Ｎｏ．７）は硫酸を多量に含有させた黒鉛粉Ｃのみを添加したため黒鉛粉Ｃがフロート充電初期に酸化消耗してしまい群圧保持効果が持続しなくなり残存容量が低下した。比較例３（Ｎｏ．８）は黒鉛粉を添加しなかったため初期容量および残存容量が共に低下した。
【００３６】
【発明の効果】
以上に説明したように、本発明は、正極活物質に、硫酸を多量に含有させた黒鉛粉と、硫酸を少量含有させた黒鉛粉或いは硫酸を含有させてない黒鉛粉などの複数種の黒鉛粉を添加するので、化成工程では、前者がＣ軸方向に膨張して活物質バルクにクラックを生じさせて硫酸（電解液）を良好に供給し、フロート充電時には、後者がＣ軸方向に膨張して活物質バルクにクラックを生じさせて硫酸を良好に供給し、同時に群圧保持効果にも寄与する。従って、正極活物質は化成工程からフロート充電まで利用率が高度に維持され、鉛蓄電池の小型軽量化などが実現する。前記硫酸を含有させた黒鉛粉は黒鉛粉を硫酸と酸化剤を含む処理液により処理することで容易に得られる。依って、工業上顕著な効果を奏する。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a lead-acid battery provided with a highly active cathode active material.
[0002]
[Prior art]
Lead storage batteries have been considered difficult to reduce in size and weight because of a low utilization rate (energy density) of the positive electrode active material. The main cause of the low utilization rate of the positive electrode active material is that the poorly soluble lead sulfate crystals generated during discharge block the pores in the bulk of the active material, and the electrolyte is not supplied to the positive electrode plate. This is because it becomes impossible to continue the discharge reaction during the period.
[0003]
In addition, sulfuric acid in the electrolytic solution also acts as an active material, but the fact that sulfate ions between the positive and negative electrode plates are not diffused to the positive electrode due to the blockage of the pores is also one of the causes of the low utilization rate. At the time of high-rate discharge of 0.2 C or more, when the sulfuric acid in the bulk of the active material is used up, no new sulfuric acid is supplied, so that the utilization rate sharply decreases. This phenomenon is likely to occur in a control valve type lead storage battery with a small amount of electrolyte.
[0004]
For this reason, methods for increasing the porosity of the active material have been proposed.
Specifically, (1) a method of decreasing the density of the active material by increasing the amount of water at the time of kneading the paste, (2) a method of increasing the porosity after chemical formation by increasing the amount of lead sulfate in the unformed active material, (3) ) A method of adding graphite having a large anisotropy to an active material (for example, Patent Document 1), and (4) A method of adding expanded graphite and causing it to disappear by oxidation after formation (for example, Patent Document 2).
[0005]
However, in these methods, since the softening phenomenon of the positive electrode active material is apt to occur, the battery life is extremely deteriorated in applications where charge / discharge cycles are repeated (float charging).
In addition, in the method (1), the paste viscosity is low, so that the filling property deteriorates, and the production yield of the positive electrode plate deteriorates. In the method (2), the amount of sulfuric acid during the kneading of the paste increases to lower the PH. In the aging method, there is a problem that the amount of metallic lead does not decrease to less than 5%, and the chemical conversion cannot be performed sufficiently.
[0006]
Also, in order to increase the utilization rate of the positive electrode active material, it is costly to increase the number of the electrode plates by thinning the electrode plates, and the positive electrode grid of the thin plate is ruptured early due to corrosion and the battery life is shortened. is there.
[0007]
In addition, there has been proposed a method of adding sulfuric acid-treated (containing sulfuric acid) graphite powder to a positive electrode active material (for example, Patent Document 3). According to this method, the graphite powder is anodically oxidized in the chemical conversion step and expands in the C-axis direction, so that a crack occurs in the active material bulk, and the electrolytic solution penetrates into the central portion of the positive electrode active material through the crack. The utilization rate of the active material increases. However, the graphite powder subjected to the sulfuric acid treatment is oxidized and consumed in the initial stage of float charging, so that there is a problem that the group pressure holding effect of the graphite powder cannot be obtained during the long-term float charging.
[0008]
On the other hand, if graphite powder not subjected to sulfuric acid treatment is added, the effect of the graphite powder in the chemical conversion step (the effect of expanding and causing the electrolyte to penetrate into the center of the active material bulk) cannot be sufficiently obtained.
[0009]
[Patent Document 1] JP-B-63-0557913 [Patent Document 2] JP-A-56-159063 [Patent Document 3] JP-A-56-159062 [0010]
[Problems to be solved by the invention]
An object of the present invention is to provide a lead storage battery in which the utilization rate of a positive electrode active material is maintained at a high level from a chemical conversion step to float charging.
[0011]
[Means for Solving the Problems]
A first aspect of the present invention is a lead storage battery, wherein a plurality of types of graphite powders having different sulfuric acid contents are added to the positive electrode active material.
[0012]
According to a second aspect of the present invention, there is provided a lead-acid battery, wherein graphite powder not containing sulfuric acid and graphite powder containing sulfuric acid are added to the positive electrode active material.
[0013]
The invention according to claim 3 is the lead-acid battery according to claim 1 or 2, wherein the graphite powder containing sulfuric acid is obtained by treating natural graphite powder with a treatment solution containing sulfuric acid and an oxidizing agent. .
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
In claim 1, the plurality of types of graphite powder having different sulfuric acid contents are, for example, a graphite powder containing a large amount of sulfuric acid and a graphite powder containing a small amount of the sulfuric acid, and the graphite powder containing a large amount of the sulfuric acid. Performs an action of electrolytic oxidation in a chemical conversion step, expanding in the C-axis direction, causing cracks in the active material bulk, and allowing sulfuric acid to penetrate into the center of the positive electrode active material. The graphite powder containing a small amount of sulfuric acid gradually expands in the C-axis direction during float charging, causing cracks in the active material bulk and contributing to the group pressure holding effect.
[0015]
According to a second aspect of the invention, graphite powder not containing sulfuric acid is added in place of the graphite powder containing a small amount of sulfuric acid, and the same operation and effect as the first aspect of the invention can be obtained.
[0016]
As described above, in the present invention, among a plurality of types of graphite powders having different sulfuric acid contents, for example, graphite powder containing a large amount of sulfuric acid causes a crack in an active material in a chemical conversion step, and contains a small amount of sulfuric acid. The graphite powder without sulfuric acid or graphite powder containing no sulfuric acid causes cracks in the active material during float charging, so the electrolyte is supplied to the electrodes well, and the utilization rate of the active material is maintained at a high level from the formation process to the float charging. Is done.
[0017]
In the present invention, natural graphite powder having high anisotropy and having a layered structure and easily containing sulfuric acid is suitable for the graphite powder. The natural graphite powder is obtained by crushing and classifying a natural graphite lump. The average particle size of the graphite powder is desirably about 300 μm because the effect is well exhibited.
[0018]
In the present invention, the graphite powder containing sulfuric acid can be easily and quickly obtained by treating the natural graphite powder with a treatment solution containing sulfuric acid and an oxidizing agent. The oxidizing agent serves to promote the sulfuric acid contained in the graphite powder.
[0019]
The amount of sulfuric acid contained in the graphite powder can be controlled by the type and amount of the oxidizing agent, the processing temperature, the processing time, and the like. Hydrogen peroxide, perchloric acids, ozone and the like can be applied to the oxidizing agent.
[0020]
In the present invention, the graphite powder containing sulfuric acid is a graphite powder treated with sulfuric acid, and the graphite powder not containing sulfuric acid is a graphite powder not treated with sulfuric acid. The large amount of the sulfuric acid is the amount of the graphite powder that expands sufficiently in the C-axis direction in the chemical conversion step, and the small amount is the amount that the graphite powder is not oxidized and consumed in the initial stage of float charging.
[0021]
In the present invention, the addition amount of the graphite powder containing a small amount of sulfuric acid or the graphite powder containing no sulfuric acid and the addition amount of the graphite powder containing a large amount of sulfuric acid are substantially the same. It is desirable because it can be maintained at a high level from the chemical conversion process to the float charging.
[0022]
The total addition amount of the graphite powder is desirably 0.2 to 1.0% by mass ratio to the positive electrode active material amount. Hydrogen peroxide, perchloric acids, ozone, and the like can be used as the oxidizing agent.
[0023]
【Example】
Hereinafter, the present invention will be described in detail with reference to Examples.
(Example 1)
A natural graphite mass produced in China was pulverized by a pulverizer and classified to obtain a graphite powder having an average particle size of 300 μm. Next, this was poured into a 1N diluted sulfuric acid aqueous solution, and silica, alumina, metal impurities (for example, iron and nickel) and the like were removed by a flotation method. In addition, the metal impurities excessively reduce the hydrogen overvoltage and deteriorate the liquid reduction performance of the battery.
[0024]
Next, the graphite powder after the flotation is kept in a mixed acid of concentrated sulfuric acid and hydrogen peroxide kept at 80 ° C. for 0.5 hours or 1.0 hour to contain sulfuric acid (sulfuric acid treatment), and then washed with water And drying. If other conditions such as sulfuric acid concentration and temperature are the same, the longer the treatment time, the higher the sulfuric acid content.
[0025]
Next, graphite powder A (graphite powder not subjected to sulfuric acid treatment) and graphite powder B holding the sulfuric acid treatment for 0.5 hour or graphite powder C holding 1.0 hour were added to 200 g of lead powder pulverized by a ball mill, respectively. A predetermined amount is added, and an appropriate amount of a cut fiber made of polyester is added thereto. Then, 25 cc of water is added and mixed by a ball mill. An active material was prepared.
[0026]
Next, 34 g of the positive electrode active material was filled in a 3.8 mm thick Pb-Sn-Ca-based alloy casting grid for a positive electrode, which was aged at a temperature of 40 ° C and a humidity of 95% for 40 hours to obtain a thickness of 4 g. A positive electrode plate of 0.2 mm was obtained. Next, an electrode plate group was formed by one positive electrode plate and two negative electrode plates produced by a conventional method, and this was inserted into each ABS resin container one by one. Since the thickness of the positive electrode plate was uniform, there was no difference in the insertion pressure of the electrode plate group.
[0027]
Next, after assembling various battery parts in the battery case, 20 cc of diluted sulfuric acid having a specific gravity of 1.20 was injected into each cell of the battery case, and the temperature of the electrolytic solution was controlled at 25 ° C. to form a battery case. Was performed to produce a control valve type lead-acid battery having a rated capacity of 2 Ah. The quantity of electricity in the battery case formation was 200% of the theoretical capacity of the positive electrode.
[0028]
(Example 2)
Except that 200 g of lead powder was added with a graphite powder A ′ containing a small amount of sulfuric acid at a sulfuric acid treatment time of 0.1 hr and a graphite powder C containing a large amount of sulfuric acid at a treatment time of 1.0 hr. A control valve type lead storage battery was manufactured in the same manner as in Example 1.
[0029]
(Comparative Example 1)
A control valve type lead-acid battery was manufactured in the same manner as in Example 1 except that only graphite powder A not subjected to sulfuric acid treatment was added to 200 g of lead powder.
[0030]
(Comparative Example 2)
A control valve type lead storage battery was manufactured in the same manner as in Example 1 except that only graphite powder C containing a large amount of sulfuric acid with a treatment time of 1.0 hr was added to 200 g of lead powder.
[0031]
(Comparative Example 3)
A control valve type lead-acid battery was manufactured in the same manner as in Example 1 except that graphite powder was not added to 200 g of lead powder.
[0032]
The initial capacity of each of the obtained control valve type lead-acid batteries was measured under the conditions of a temperature of 25 ° C., a set voltage of 2.275 V / cell, a maximum current of 1 A, and a discharge capacity of 0.25 CA. Subsequently, after a continuous float charge test was conducted for 2 months at a temperature of 65 ° C., the remaining capacity was measured under the same conditions as in the case of the initial capacity.
Table 1 shows the measurement results. Table 1 also shows the amounts of various graphite powders added.
[0033]
[Table 1]

[0034]
As is evident from Table 1, both of Example 1 (Nos. 1 to 4) and Example 2 (No. 5) according to the present invention have a large initial capacity and a large residual capacity. Material utilization was highly maintained.
[0035]
On the other hand, in Comparative Example 1 (No. 6), only the graphite powder A without the sulfuric acid treatment was added, so that the initial capacity was reduced. In Comparative Example 2 (No. 7), only graphite powder C containing a large amount of sulfuric acid was added, so graphite powder C was oxidized and consumed in the early stage of float charging, and the group pressure holding effect was not maintained, resulting in a decrease in the remaining capacity. In Comparative Example 3 (No. 8), both the initial capacity and the remaining capacity decreased because no graphite powder was added.
[0036]
【The invention's effect】
As described above, the present invention relates to a positive electrode active material, a graphite powder containing a large amount of sulfuric acid, a plurality of types of graphite such as a graphite powder containing a small amount of sulfuric acid or a graphite powder containing no sulfuric acid. Since the powder is added, in the chemical conversion step, the former expands in the C-axis direction to cause cracks in the active material bulk to supply sulfuric acid (electrolyte solution) well, and the latter expands in the C-axis direction during float charging. As a result, cracks are generated in the bulk of the active material to supply sulfuric acid well, and at the same time contribute to the group pressure maintaining effect. Therefore, the utilization rate of the positive electrode active material is maintained at a high level from the chemical conversion step to the float charging, and the lead storage battery can be reduced in size and weight. The graphite powder containing sulfuric acid can be easily obtained by treating the graphite powder with a treatment solution containing sulfuric acid and an oxidizing agent. Therefore, a remarkable industrial effect is achieved.

Claims

A lead-acid battery, wherein a plurality of types of graphite powders having different sulfuric acid contents are added to a positive electrode active material.

A lead-acid battery, wherein a graphite powder containing no sulfuric acid and a graphite powder containing sulfuric acid are added to a positive electrode active material.

The lead-acid battery according to claim 1, wherein the graphite powder containing sulfuric acid is obtained by treating natural graphite powder with a treatment liquid containing sulfuric acid and an oxidizing agent.