JP5028667B2

JP5028667B2 - Cathode active material for alkaline battery and alkaline battery

Info

Publication number: JP5028667B2
Application number: JP2001274194A
Authority: JP
Inventors: 幸治田上; 義和尾本; 正行仁科; 俊雄上田
Original assignee: Dowa Electronics Materials Co Ltd
Current assignee: Dowa Electronics Materials Co Ltd
Priority date: 2000-09-11
Filing date: 2001-09-10
Publication date: 2012-09-19
Anticipated expiration: 2021-09-10
Also published as: JP2002158006A

Description

【０００１】
【発明の属する技術分野】
本発明は，アルカリ電池用の正極活物質およびそれを用いたアルカリ電池に関する。
【０００２】
【従来の技術】
従来より，時計，計測機器，カメラ等に装着されるアルカリ電池（通称ボタン電池）として酸化銀電池が普及している。酸化銀電池は，正極活物質として酸化銀（Ａｇ₂Ｏおよび／またはＡｇＯ），負極活物質として亜鉛末，電解液としてアルカリ溶液例えばＫＯＨやＮａＯＨの水溶液を用いて構成されるものが一般である。銀は高価な材料であるが，酸化銀は小型でも高容量が要求される場合の不可欠な正極活物質とされており，このためにボタン電池の殆んどは酸化銀電池で構成されていると言っても過言ではない。なお，正極活物質は正極作用物質または陽極作用物質と呼ばれることもあり，同様に負極活物質は負極作用物質または陰極作用物質と呼ばれることもある。
【０００３】
通常，酸化銀電池単価に占める正極活物質（Ａｇ₂Ｏ）の割合は非常に高い。また，Ａｇ₂Ｏは導電性が低く，電池の内部抵抗が高くなって電池の放電容量が低くなるという問題もある。このため，Ａｇ₂ＯにＭｎＯ₂を混合して正極活物質とする場合や，特開昭60-105170 号公報, 特開昭57-849号公報, 特開平10-188975 号公報のように他のＡｇ系化合物例えばＡｇＮｉＯ₂を配合して導電性を改良する案等が提案されている。
【０００４】
同様に，特開昭52-142241 号公報には酸化銀を主体とする陽極に酸化ビスマス (Ｂｉ₂Ｏ₃)を添加するとガス発生が抑制でき且つ放電末期の予知ができると教示している。また米国特許第 5,389,469号明細書, その分割出願である米国特許第5,589,109 号明細書および米国特許第6,001,508 号明細書には，ＡｇＯのコアの周囲にＡｇ₂Ｏの中間層を介して銀とビスマスの外皮 (ＡｇＢｉＯ₂またはＡｇＢｉＯ₃からなる外皮) をもつＡｇＯ系の正極活物質を開示しており，このものは，ＡｇＯ粉とビスマス化合物 (硫化ビスマスなど) とをアルカリ溶液中で還元反応させることによって得られると記載されている。
【０００５】
【発明が解決しようとする課題】
酸化銀電池のコスト高を抑制するには，銀以外の安価な物質を正極活物質に共存させてＡｇ使用量を相対的に低くすることが有利であり, このために, 前記のような各種の提案がなされてきた。しかし，該物質としてＭｎＯ₂を共存させる例では，ＭｎＯ₂は真比重が小さく，また放電電位の平坦性が悪いという性質があるから，電池容量としてはそれほど期待できず放電が進むと放電電位の低下が著しいという問題が付随する。Ｎｉ等との化合物を形成する場合には, これを全て正極活物質とする訳ではなく, 放電後に水酸化物を形成して体積膨張を起こすことから，せいぜい数割の添加しか許容できない。したがって，それほどコスト抑制効果は期待できない。
【０００６】
特開昭52-142241 号公報のように酸化ビスマスを添加する例では，酸化銀との酸化還元電位の差を利用して放電末期に２段の電位を得ることにより，この２段電位発生を検知して電池の消耗時を予知するものであるから，その使用量も自ずと限界があり，正極全量に対して高々３〜１２重量％である。同様に米国特許第 5,389,469号明細書（ほか２件も同様）のように，酸化銀粒子の表面に亜酸化銀とビスマス系化合物の被膜を形成するものでも，Ａｇの含有量として少なくとも７８wt％を必要としており，Ａｇ使用量の低減の意味からは充分ではなく，またコア部が不安定な過酸化銀（ＡｇＯ）であるために，長期的な信頼性に不安があると共に放電態様も多段階になりやすい。
【０００７】
したがって，本発明の課題は前記のような問題を解決して，Ａｇの使用量を低減しても放電特性が悪くならず長期的な信頼性が得られるような安価且つ新規な電池用正極活物質を得ることにある。
【０００８】
【課題を解決するための手段】
前記の課題を解決するため，本発明者らはＡｇ−Ｂｉ−Ｏ系の化合物に着目して種々の試験研究を続けてきたが，湿式法によって銀塩とビスマス塩の中和澱物を得たうえ，これを適正に酸化処理すると正極活物質に適した化合物が得られることを知見した。すなわち本発明によれば，Ａｇ，ＢｉおよびＯの３元素からなる粒子であって，粒子内に化合物の結晶を有し且つ粒子内全域にＢｉが分散している粒子からなる新規な電池用正極活物質を提供する。
【０００９】
より具体的には，銀とビスマスの無機酸塩を水酸化アルカリと水媒体中で反応させて得たＡｇ−Ｂｉ含有中和殿物を酸化剤で酸化してなるＡｇ−Ｂｉ含有酸化生成物からなるアルカリ電池用の正極活物質：更には，銀とビスマスの無機酸塩と水酸化アルカリとを水媒体中で且つ酸化剤の存在下で反応させて得たＡｇ−Ｂｉ−含有酸化生成物からなるアルカリ電池用の正極活物質：を提供する。この正極活物質すなわち該酸化生成物は，銀，ビスマスおよび酸素からなる化合物の結晶を有する粒子であって，粒子表面から中心まで全体にわたってビスマスが存在している粒子からなる。この粒子はＡｇ/ Ｂｉのモル比が１〜７の範囲で酸素含有量が５重量％以上の組成を有し，好ましくは粒径が０.１〜１０μｍである。また，この正極活物質は銀含有量が７０重量％以下で，銀の化合物Ａｇ₂ＯおよびＡｇＯを含まないか，含んだとしてもＡｇ₂ＯおよびＡｇＯを不可避的不純物程度にしか含まない。
【００１０】
【発明の実施の形態】
本発明に従うアルカリ電池用正極活物質は，基本的にはＡｇ，ＢｉおよびＯの３元素からなる粒子であり，この粒子内に化合物結晶を有しており且つ粒子内全域にＢｉが分散しているという特徴がある。
【００１１】
この粒子内の化合物はＡｇ−Ｂｉ−Ｏの三元系化合物であり，好ましくはＡｇ₂ＯまたはＡｇＯの化合物の結晶を粒子内に含まず，含むとしても，不純物程度にしか含まない。
【００１２】
また，この粒子は，Ａｇ／Ｂｉの原子比が１以上７以下，好ましくは２以上５以下で且つ酸素含有量が５重量％以上の組成を有している。Ａｇ含有量は８０重量％以下，好ましくは７０重量％以下，場合によっては６０重量％以下であることもできる。好ましい組成範囲は，Ａｇ：４５〜７５％，Ｂｉ：２０〜４０％，Ｏ（酸素）：５〜２０％，残部：不可避的不純物である。粒子の粒径は０.１〜１５μｍ，好ましくは０.２〜１０μｍである。平均粒径は０.１〜１０μｍの範囲にある。
【００１３】
この粒子を正極活物質の主材として使用した場合，従来の酸化銀電池の場合に比べて銀量が低量であるにも拘わらず同等の放電特性を得ることができることに加え，その導電率は酸化銀に比べると３桁ほど高いので，酸化銀電池では黒鉛等の導電材を要したが，このような導電材が不要となる点でも有利である。
【００１４】
したがって，本発明に従う正極活物質は，前掲の米国特許第 5,389,469号明細書（ほか２件も同様）の粒子と比べた場合にも，粒子内部まで，すなわち粒子内全域にＢｉが分散している点，ＡｇＯやＡｇ₂Ｏの結晶が殆んど存在しない点，更にはＡｇ量が少ない点などで相違しており，このため，各種粉体特性，放電特性，導電特性等についても従来品のものにはない新規な性質を示す。
【００１５】
本発明の正極活物質は，次のような工程を順に経る湿式法によって得ることができる。但し，中和工程と酸化工程は同時に実施してもよい。
(1) 「Ａｇの無機酸塩」および「Ｂｉの無機酸塩」と，「水酸化アルカリ」とを水中で反応させて中和殿物を得る工程（中和工程と言う），
(2) 得られた中和殿物の懸濁液に酸化剤を添加して該澱物を酸化する工程（酸化工程という），
(3) その酸化殿物の懸濁液を固液分離して固体の酸化殿物を回収する工程，
(4) 回収した酸化殿物を水洗乾燥する工程，
(5) 得られた乾燥ケーキを解砕して粉体にする工程。
各工程について順に説明する。
【００１６】
〔中和工程〕
中和工程では，ＡｇとＢｉの無機酸塩と水酸化アルカリとの反応により，ＡｇとＢｉの酸化物と水を生成する中和反応を行わせるものであり，この中和反応では出発物質の金属イオンの価数変化を起こさない。換言すれば，本発明が採用する中和反応は，還元条件下や酸化条件下での反応ではなく，したがって, 金属イオンの価数変化を伴う反応は含まない。
【００１７】
中和反応に用いる水酸化アルカリとしては，水酸化ナトリウム（NaOH）や水酸化カリウム (KOH)を使用することができる。「ＡｇとＢｉの無機酸の塩」としては，これら各金属の硝酸塩，硫酸塩，塩酸塩またはリン酸塩等が使用可能であるが，各金属の硝酸塩または硫酸塩が好ましく，代表的には各金属の硝酸塩を使用することができる。例えば, 硝酸銀（AgNO₃)に対して，所望モル数の硝酸ビスマス[Bi(NO₃)₃]を組み合わせて水酸化アルカリと水中で反応させる。
以下，説明の便宜上，「Ａｇ，Ｂｉの無機酸塩」がこれらの金属の「硝酸塩」である場合を例として説明する。
【００１８】
中和処理は，水酸化アルカリを溶解した水溶液に「Ａｇ，Ｂｉの硝酸塩の粉体」を添加する方法, アルカリ水溶液と「Ａｇ，Ｂｉの硝酸塩を溶解した水溶液」を混合する方法, 「Ａｇ，Ｂｉの硝酸塩を溶解した水溶液」に固体の水酸化アルカリを添加する方法のいずれの方法でもよいが，アルカリ水溶液と「Ａｇ，Ｂｉの硝酸塩の水溶液」を混合する方法が好ましい。
【００１９】
この中和処理にあたってはアルカリ度は高い方がよく，例えば「Ａｇ＋Ｂｉ」に対して, モル比で１０倍程度のアルカリが存在した方が反応が進み易い。反応温度は特に限定されないが室温から１１０℃迄が好ましい。攪拌については，中和反応が均一に進行する程度の攪拌強度が必要である。
【００２０】
反応に供する硝酸銀と硝酸ビスマスのＡｇ／Ｂｉのモル比を変えることによって，最終化合物中のＡｇ／Ｂｉの原子比，ひいては粒子中のＡｇ／Ｂｉの原子比を調節することができる。本発明者らの経験によると, 硝酸銀と硝酸ビスマスのＡｇ／Ｂｉモル比を１以上７以下，好ましくは，２以上５以下の範囲で調節するのがよい。このモル比が小さくなるほど得られる正極活物質の放電容量の低下が大きくなり，逆にこの比があまり大きくなるとＡｇ量が多くなって，その分Ａｇ量低減という本発明の目的が達成できなくなる。
【００２１】
〔酸化工程〕
酸化工程は，中和殿物を酸化剤を用いて酸化処理するものであり，中和殿物中のＡｇ，Ｂｉの価数を上げることを内容とする処理であり，好ましくは中和工程と酸化工程は分離して行う。そして中和工程と酸化工程の間に殿物を含む液を昇温する工程を挿入し，その昇温した液中に酸化剤を供給するのが好ましい。酸化剤としては通常の酸化剤, 例えばKMnO₄, NaOCl, H₂O₂, K₂S₂O₈, Na₂S₂O₈またはオゾン等を使用することができる。
【００２２】
酸化処理中は液温を５０℃以上，好ましくは７０℃以上に維持して攪拌下に酸化剤を添加するのがよいが，あまり温度が高すぎると酸化剤の分解が進むので１１０℃以下が好ましい。前述のように，この酸化処理は中和殿物中のＡｇとＢｉの価数を上げる処理，例えばＡｇ⁺¹をＡｇ⁺²に，Ｂｉ⁺³をＢｉ^+3.5やＢｉ⁺⁵等に酸化する処理であり，この価数変化が充分に行える量の酸化剤を添加することが必要である。具体的には，この価数変化に対して当量以上，好ましくは２倍等量程度の酸化剤を添加するのがよい。酸化量は，中和処理に用いる原料硝酸塩の金属元素の価数のほか，ＡｇとＢｉの相対割合によっても変化し，これに伴って酸化処理後の生成物中のＡｇ−Ｂｉ−Ｏの組成比も変化することになるが，完全酸化を行うことによって，全体としてＡｇ−Ｂｉ−Ｏ系の結晶性の化合物からなる微細な粒子の集合体が生成することになる。後記の実施例に示すように，本発明者らの調査によれば，この結晶性微粒子内はもとより，微粒子の集合体（Ａｇ−Ｂｉ−含有酸化生成物）にはＡｇ₂Ｏ等の低価数の化合物はもとより，ＡｇＯ，独立したＢｉの酸化物，独立したＭの酸化物等が存在する機会も殆んどなくなり，正極活物質に適したＡｇ−Ｂｉ−Ｏ系の結晶性の化合物が得られる。
【００２３】
別法として，このような酸化は中和殿物の生成と同時に行うこともできる。この場合には，前記の中和処理を前記の酸化剤の存在下で行えばよく，アルカリ水溶液に対して，Ａｇ，Ｂｉの無機酸塩と酸化剤を同時に添加する方法や，アルカリ水溶液に酸化剤を予め投入しておき，この液にＡｇ，Ｂｉの無機酸塩を添加する方法を採用すればよい。後記の実施例に示すように，中和工程と酸化工程を同時に行っても，両者を分離して行った場合と実質的に同じ本発明に従うＡｇ−Ｂｉ−含有酸化生成物（酸化殿物）を得ることができる。
【００２４】
〔固液分離・乾燥・解砕工程〕
次いで，酸化殿物の固液分離を処理を行い，水洗し乾燥して黒色のケーキを得る。固液分離を行う前に，酸化殿物を熟成するのがよい。この熟成は，酸化処理後の液をその温度で２０〜９０分程度保持する処理であり，この熟成処理を行うことによって，酸化殿物の均質化を図ることができる。より具体的には，粒子間で組成のばらつきが少なくなり且つ安定したＡｇ−Ｂｉ−Ｏ系化合物の粒子からなる殿物を得ることができる。濾別水洗した殿物の乾燥は５０〜２００℃の温度で行うのがよい。２００℃を超える温度では生成した化合物が分解するおそれがある。得られた乾燥ケーキは，解砕機で解砕することによって，Ａｇ−Ｂｉ含有酸化生成物からなるアルカリ電池用の正極活物質として使用可能な粉体を得ることができる。
【００２５】
このような製法で得られるＡｇ−Ｂｉ−Ｏ系化合物からなる粉末は後記の実施例に示すように，そのＸ線パターン（銅ターゲット使用，波長＝1.5405オングストローム) の主ピーク群はＸ線回折データベース（ＩＣＤＤ）のどの化合物のものとも一致しない。また，この粉末のＸ線回折では，ＡｇＯまたはＡｇ₂Ｏの主ピーク群は現れない。したがって，この粉末中にはＡｇＯまたはＡｇ₂Ｏとしての化合物は存在しないと言える。存在したとしてもそれは不純物としてのものであり，この不純物量はＡｇＯとＡｇ₂Ｏの両者の合計量として高々１重量％以下，好ましくは０.５重量％以下，さらに好ましくはＸ線回折での検量限界以下の量である。したがって，本発明によれば，これまで知られていないＡｇ−Ｂｉ−Ｏ系化合物を提供するものであり，前記の製法におけるこの物質の生成反応も新規な反応であると考えられる。なお，Ａｇ／Ｂｉ比が本発明で規定する範囲で異なっても，図５のようにＸ線回折ではその主ピークがほぼ一致し，従ってほぼ同一の結晶構造を有することになる。このため，本発明に従う正極活物質は，粉末Ｘ線回折法による測定において，好ましくは，面間隔 2.78 ±0.05オングストローム, 面間隔 2.62 ±0.05オングストロームおよび面間隔 2.43 ±0.05オングストロームに主要な回折ピークをもつ化合物からなるとも言い得る。
【００２６】
本発明者らは，本発明に従う化合物を得る反応について，下記のような反応式に基づくものであろうと考えている。ただし，中和反応に使用するＡｇ, Ｂｉの無機酸塩が, 硝酸銀 (AgNO₃)および硝酸ビスマス[Bi(NO₃)₃]であり，水酸化アルカリが水酸化ナトリウム(NaOH)であり，酸化剤はペルオクソ２硫酸ナトリウム(Na₂S₂O₈) であるとする。
【００２７】
中和反応（酸化還元反応は存在しない）の反応式（ 1≦X≦7 )
xAgNO₃＋Bi(NO₃)₃＋(x+3)NaOH
→ Ag_xBiO_(x+3)/2＋(x+3)NaNO₃＋(x+3)/2H₂O
【００２８】
酸化反応の反応式〔 Ag(1)→Ag(1.8) および Bi(3)→Bi(3.5) の酸化反応〕
Ag_xBiO_(x+3)/2＋(0.8x+0.5)/2Na₂S₂O₈＋(0.8x+0.5)NaOH
→Ag_xBiO_(1.8x+3.5)/2＋(0.8x+0.5)Na₂SO₄＋(0.8x+0.5)/2H₂O
【００２９】
以下に本発明者らの行った代表的な試験結果を実施例としてあげ，本発明の正極活物質をさらに説明する。
【００３０】
【実施例】
【００３１】
〔実施例１〕
Ａｇ／Ｂｉのモル比が３となるように硝酸銀 (AgNO₃)と硝酸ビスマス[Bi(NO₃)₃]を秤量した。両者の合計量に対してモル比で１０倍のＮａＯＨを溶解した水溶液（1.5 リットル）に前記の硝酸銀と硝酸ビスマスを添加して攪拌することにより液中に中和殿物を生成させた。得られた中和殿物の懸濁液を９０℃に昇温し，掻き混ぜながら，酸化剤としてペルオクソ２硫酸カリウムK₂S₂O₈を，ＡｇとＢｉの合計量に対してモル比で１倍量で，該懸濁液に攪拌下に添加して酸化処理した。酸化処理終了後，１０４℃の温度に６０分間保持する熟成を行ったあと，殿物を濾別し，水洗し１００℃で乾燥し，その乾燥品を解砕機で解粉した。
【００３２】
得られた粉体の粉体特性は，ＢＥＴ法による比表面積＝1.256 ｍ²/ｇ, タップ密度＝1.72ｇ/cｃ, 圧縮密度＝6.01ｇ/cm³, ヘロス粒度分布計によるＤ50＝6.53μｍであった。なお，ヘロス粒度分布計によるＤ50とは，横軸に粒径Ｄ（μｍ）をとり，縦軸に粒径Ｄμｍ以下の粒子が存在する容積（Ｑ）％をとった累積粒度曲線において，Ｑ＝５０％に対応する粒径Ｄの値 (μｍ) を言う。
【００３３】
得られた粉体の組成を化学分析で調べたところ，Ａｇ＝54.4wt％, Ｂｉ＝34.8wt％, Ｏ＝9.9 wt％であった。また，正極活物質として酸化銀 (Ag₂O) 粉末を測定する場合と同じ方法で，この粉体の導電率を測定したところ，1.53 S/cm ×10^-2であった。ちなみに酸化銀粉体の導電率は 4.8 S/cm ×10^-5程度である。
【００３４】
次に，この粉体の正極活物質とした場合の放電特性を, ほぼ同様の圧縮密度 (6.6 ｇ/cm³) をもつ正極活物質として製品化されている酸化銀(Ag₂O)の粉末と同じ条件で調べた。その結果，初期電位（開回路電圧）＝1.758 V (Ag₂O では1.647 V), 重量エネルギー密度（放電容量）＝205 mAh/g (Ag₂O では204 mAh/g), 体積エネルギー密度＝1232mAh/cm³(Ag₂O では1285mAh/cm³)であった。この粉末の放電曲線を図２に示した。
【００３５】
図１の最上段に，得られた粉体（Ａｇ／Ｂｉの原子比＝３）のＸ線回折チャート（銅ターゲット使用，波長＝1.5405オングストローム，以下同じ) を示した。また，参考のために，Ｂｉ₂Ｏ_3,Ａｇ₂Ｏ_,ＡｇＯのＸ線回折チャートもその下方に対比して示した。図２に見られるように，本例の粉体粒子は多数のピークを有する結晶からなることが明らかであるが，Ｂｉ₂Ｏ₃,Ａｇ₂Ｏ, ＡｇＯのものとは異なっており，Ａｇ，ＢｉおよびＯの３元素からなる化合物としては新規なピークが多い。
【００３６】
〔実施例２〕
Ａｇ／Ｂｉのモル比が４となるように，中和工程で使用した硝酸銀と硝酸ビスマスの配合割合を変えた以外は実施例１を繰り返し，それぞれのＡｇ−Ｂｉ−Ｏ系の粉体を得た。この粉体の圧縮密度，比表面積および開回路電圧を測定した。表１に，それらの測定結果を，実施例１のものと対比して示した。
【００３７】
〔実施例３〕
Ａｇ／Ｂｉのモル比が２となるように，中和工程で使用した硝酸銀と硝酸ビスマスの配合割合を変えた以外は実施例１を繰り返し，それぞれのＡｇ−Ｂｉ−Ｏ系の粉体を得た。この粉体の圧縮密度，比表面積および開回路電圧を測定した。それらの測定結果を同じく表１に示した。
【００３８】
【表１】

【００３９】
〔実施例４〕
本例は，中和と酸化を同時に行って得た本発明の正極活物質の例を示すものである。
Ａｇ／Ｂｉのモル比が３となるように硝酸銀 (AgNO₃)と硝酸ビスマス[Bi(NO₃)₃]を秤量して 0.8リットルの水溶液とした。一方，ペルオクソ二硫化カリウム（k₂S₂O₈）を両硝酸塩の合計量に対してモル比で１倍量秤量し 1.4リットルの水溶液とした。
【００４０】
硝酸塩の合計量に対しモル比で５倍量のＮａＯＨを溶解した溶液 1.6リットルを準備し，このＮａＯＨ溶液に対して，液温を１０４℃に維持しながら，前記の塩類の水溶液とペルオクソ二硫化カリウムの水溶液を３０分間かけて同時に添加した。添加後終了後，１０４℃の温度に３０分間保持する熟成を行ったあと，液から殿物を濾別し，水洗し，１００℃で乾燥し，その乾燥品を解砕機で解粉した。
【００４１】
得られた粉体を正極活物質とした場合の開回路電圧と放電容量（at 1.4Ｖ）を実施例１と同様にして測定したところ，開回路電圧＝1.778 Ｖ，放電容量＝197 (mAh/g) であった。
【００４２】
本例で得られた粉体のＸ線回折結果を図３に示した。図３の結果から，本例で得られた粉体は，実施例１で得られた図１のものに似たＸ線パターンを有しており，中和と酸化を同時に行っても分離して行った場合と同様の結晶構造をもつ粉体が得られることがわかる。
【００４３】
次に本例で得られた粉体から微量の粒子 (平均粒径 0.6μｍ) をサンプリングし，ＥＳＣＡ( electron spectroscopy for chimcal analysis) によって粒子中のＢｉ濃度分布の分析を試みた。測定装置はアルバックファイ株式会社製５８００であり，Ｘ線源はＡｌ陽極線源 (300 V), 粒子表面からの深さエッチング速度は 0.32 ｎｍ/minである。測定結果を図４に示した。図４の横軸は sputter time, 縦軸はＢｉの原子濃度( ％) である。エッチングを約 800分行ったが，これはエッチング速度から換算すると約 0.25 μｍ深さまで, すなわち，粒径 0.6μｍの粒子のほぼ中心にまでエッチングしたことになる。図４の結果は，粒子中のＢｉ濃度は，粒子表面から sputter time 800 分まで殆んど変化せず，ほぼ一定の値を維持している。
【００４４】
〔実施例５〕
Ａｇ／Ｂｉのモル比が７／１，６／１および５／１に変えた以外は，実施例１を繰り返した。そして，得られた各粉末のＸ線回折を行った。その結果を図５に示した。図５には，実施例１〜３の粉末のＸ線回折も併せて示した。図５の結果から，Ａｇ／Ｂｉ比が異なったいずれの粉末でも主ピークはほぼ一致しており，したがって，ほぼ同一の結晶構造を有することがわかる。より具体的は，いずれの粉末も，粉末Ｘ線回折法による測定において面間隔 2.78 ±0.05オングストローム, 面間隔 2.62 ±0.05オングストロームおよび面間隔 2.43 ±0.05オングストロームに特徴的な回折ピークをもつ化合物からなることがわかる。このような主ピーク群はＸ線回折データベース（ＩＣＤＤ）のどの化合物のものとも一致しない。
【００４５】
【発明の効果】
以上説明したように，本発明によれば，アルカリ電池の正極活物質として，従来の代表的なＡｇ₂Ｏ粉末よりＡｇ量が低くても同等以上の放電特性を示すＡｇ−Ｂｉ−Ｏ系の新規な正極活物質が提供され，しかも，この正極活物質は導電率が酸化銀に比べると格段に良好である。したがって，本発明の正極活物質は安価でありながら高導電率で放電特性に優れるから，正極活物質, 負極物質および電解質からなる高性能で且つ安価な電池を構成する上で貢献するところが極めて大である。
【図面の簡単な説明】
【図１】本発明に従う正極活物質のＸ線回折チャートを他の粉体のものと対比して示したものである。
【図２】本発明に従う正極活物質の放電曲線を示したものである。
【図３】本発明に従う他の正極活物質のＸ線回折チャートを示したものである。
【図４】本発明に従う正極活物質の粒子中のＢｉ濃度分布をＥＳＣＡで測定した結果を示す図である。
【図５】本発明に従う正極活物質のＸ線回折チャートを対比して示したものである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a positive electrode active material for an alkaline battery and an alkaline battery using the same .
[0002]
[Prior art]
Conventionally, silver oxide batteries have been widely used as alkaline batteries (commonly called button batteries) attached to watches, measuring instruments, cameras, and the like. Silver oxide batteries are generally constructed using silver oxide (Ag ₂ O and / or AgO) as the positive electrode active material, zinc powder as the negative electrode active material, and an alkaline solution such as an aqueous solution of KOH or NaOH as the electrolyte. . Silver is an expensive material, but silver oxide is considered an indispensable positive electrode active material when high capacity is required even though it is small. For this reason, most button batteries are composed of silver oxide batteries. It is no exaggeration to say. The positive electrode active material is sometimes called a positive electrode active material or an anodic active material. Similarly, the negative electrode active material is sometimes called a negative electrode active material or a cathode active material.
[0003]
Usually, the proportion of the positive electrode active material (Ag ₂ O) in the silver oxide battery unit price is very high. In addition, Ag ₂ O has a problem that the conductivity is low, the internal resistance of the battery is high, and the discharge capacity of the battery is low. Therefore, in the case where Ag ₂ O is mixed with MnO ₂ to obtain a positive electrode active material, there are other cases such as JP-A-60-105170, JP-A57-849, JP-A-10-188975. Proposals have been proposed for improving the conductivity by adding an Ag-based compound such as AgNiO ₂ .
[0004]
Similarly, JP-A-52-142241 teaches that gas generation can be suppressed and the end of discharge can be predicted by adding bismuth oxide (Bi ₂ O ₃ ) to an anode mainly composed of silver oxide. In addition, US Pat. No. 5,389,469, split applications thereof, US Pat. No. 5,589,109 and US Pat. No. 6,001,508 disclose silver and bismuth through an Ag ₂ O intermediate layer around an AgO core. An AgO-based positive electrode active material having an outer shell (a shell made of AgBiO ₂ or AgBiO ₃ ) is disclosed, which is a reduction reaction of AgO powder and a bismuth compound (such as bismuth sulfide) in an alkaline solution. Is obtained.
[0005]
[Problems to be solved by the invention]
In order to suppress the high cost of the silver oxide battery, it is advantageous to make the amount of Ag used relatively low by coexisting an inexpensive material other than silver in the positive electrode active material. Has been proposed. However, in the example in which MnO ₂ coexists as the substance, MnO ₂ has a property that the true specific gravity is small and the flatness of the discharge potential is poor. The problem is that the decline is significant. When a compound such as Ni is formed, not all of this is used as a positive electrode active material, but a hydroxide is formed after discharge to cause volume expansion, so that only a few percent can be added at most. Therefore, the cost control effect cannot be expected so much.
[0006]
In an example in which bismuth oxide is added as in Japanese Patent Laid-Open No. 52-142241, this two-stage potential generation is obtained by obtaining a two-stage potential at the end of discharge using the difference in oxidation-reduction potential with silver oxide. Since it detects and predicts when the battery is depleted, the amount of its use is naturally limited, and it is 3 to 12% by weight based on the total amount of the positive electrode. Similarly, as in US Pat. No. 5,389,469 (the same applies to the other two cases), even if a film of silver suboxide and bismuth compound is formed on the surface of silver oxide particles, the content of Ag should be at least 78 wt%. It is necessary and is not sufficient in terms of reducing the amount of Ag used, and because the core part is unstable silver peroxide (AgO), there are concerns about long-term reliability and the discharge mode is multistage. It is easy to become.
[0007]
Therefore, the object of the present invention is to solve the above-mentioned problems, and to reduce the amount of Ag used and to reduce the discharge characteristics without deteriorating long-term reliability. There is to get the substance.
[0008]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present inventors have continued various studies focusing on Ag-Bi-O compounds, but obtained a neutralized starch of silver salt and bismuth salt by a wet method. In addition, it was found that a compound suitable for the positive electrode active material can be obtained by appropriately oxidizing it. That is, according to the present invention, a novel positive electrode for a battery comprising particles composed of three elements of Ag, Bi and O, wherein the particles have a compound crystal in the particles and Bi is dispersed throughout the particle. Provide active material.
[0009]
More specifically, an Ag-Bi-containing oxidation product obtained by oxidizing an Ag-Bi-containing neutralized precipitate obtained by reacting an inorganic acid salt of silver and bismuth with an alkali hydroxide in an aqueous medium with an oxidizing agent. Cathode active material for alkaline batteries comprising: Ag-Bi-containing oxidation product obtained by reacting an inorganic acid salt of silver and bismuth with an alkali hydroxide in an aqueous medium in the presence of an oxidizing agent A positive electrode active material for an alkaline battery comprising: This positive electrode active material, that is, the oxidation product, is composed of particles having crystals of a compound composed of silver, bismuth and oxygen, and bismuth is present throughout the surface from the particle surface to the center. The particles have a composition in which the molar ratio of Ag / Bi is in the range of 1 to 7 and the oxygen content is 5% by weight or more, and the particle size is preferably 0.1 to 10 μm. Further, this positive electrode active material has a silver content of 70% by weight or less and does not contain silver compounds Ag ₂ O and AgO or even contains Ag ₂ O and AgO only to the extent of inevitable impurities.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
The positive electrode active material for an alkaline battery according to the present invention is basically a particle composed of three elements of Ag, Bi and O, and has a compound crystal in the particle and Bi is dispersed throughout the particle. There is a feature that.
[0011]
The compound in the particle is a ternary compound of Ag-Bi-O, and preferably contains no crystal of Ag ₂ O or AgO compound in the particle, even if it is contained only to the extent of impurities.
[0012]
Further, the particles have a composition in which an atomic ratio of Ag / Bi is 1 or more and 7 or less, preferably 2 or more and 5 or less, and an oxygen content is 5% by weight or more. The Ag content can be 80% by weight or less, preferably 70% by weight or less, and in some cases 60% by weight or less. Preferred composition ranges are Ag: 45 to 75%, Bi: 20 to 40%, O (oxygen): 5 to 20%, and the balance: inevitable impurities. The particle diameter is 0.1 to 15 μm, preferably 0.2 to 10 μm. The average particle size is in the range of 0.1 to 10 μm.
[0013]
When these particles are used as the main material of the positive electrode active material, in addition to being able to obtain the same discharge characteristics in spite of the low amount of silver compared to the case of conventional silver oxide batteries, their conductivity Is about three orders of magnitude higher than silver oxide, so a silver oxide battery requires a conductive material such as graphite, but it is also advantageous in that such a conductive material is unnecessary.
[0014]
Therefore, in the positive electrode active material according to the present invention, Bi is dispersed to the inside of the particle, that is, the entire region within the particle even when compared with the particle of the above-mentioned US Pat. No. 5,389,469 (the same applies to the other two cases). The difference is that there are almost no crystals of AgO or Ag ₂ O, and the amount of Ag is small. Therefore, various powder characteristics, discharge characteristics, conductive characteristics, etc. It shows a new property that is not found in anything.
[0015]
The positive electrode active material of the present invention can be obtained by a wet method through the following steps in order. However, the neutralization step and the oxidation step may be performed simultaneously.
(1) A step of obtaining a neutralized product by reacting “Ag inorganic acid salt” and “Bi inorganic acid salt” with “alkali hydroxide” in water (referred to as neutralization step),
(2) A step of oxidizing the starch by adding an oxidizing agent to the obtained suspension of neutralized precipitate (referred to as an oxidation step),
(3) recovering the solid oxide precipitate by solid-liquid separation of the oxide precipitate suspension;
(4) A process of washing and drying the collected oxide residue,
(5) A step of crushing the obtained dry cake into powder.
Each process will be described in turn.
[0016]
[Neutralization process]
In the neutralization step, a neutralization reaction is performed to produce Ag and Bi oxides and water by a reaction between an inorganic acid salt of Ag and Bi and an alkali hydroxide. Does not cause valence change of metal ions. In other words, the neutralization reaction employed by the present invention is not a reaction under reducing conditions or oxidizing conditions, and therefore does not include reactions involving changes in the valence of metal ions.
[0017]
Sodium hydroxide (NaOH) or potassium hydroxide (KOH) can be used as the alkali hydroxide used for the neutralization reaction. As the “inorganic acid salt of Ag and Bi”, nitrates, sulfates, hydrochlorides or phosphates of these metals can be used, but nitrates or sulfates of each metal are preferable, typically Each metal nitrate can be used. For example, silver nitrate (AgNO ₃ ) is combined with a desired number of moles of bismuth nitrate [Bi (NO ₃ ) ₃ ] and reacted in alkali hydroxide with water.
Hereinafter, for convenience of explanation, the case where “inorganic acid salt of Ag, Bi” is “nitrate” of these metals will be described as an example.
[0018]
Neutralization is performed by adding “Ag, Bi nitrate powder” to an aqueous solution in which alkali hydroxide is dissolved, mixing an alkaline aqueous solution and “aqueous solution in which Ag, Bi nitrate is dissolved”, “Ag, Any method of adding a solid alkali hydroxide to an “aqueous solution in which Bi nitrate is dissolved” may be used, but a method in which an alkaline aqueous solution and an “aqueous solution of Ag and Bi nitrate” are mixed is preferable.
[0019]
In this neutralization treatment, the alkalinity should be high. For example, the reaction proceeds more easily when alkali having a molar ratio of about 10 times that of “Ag + Bi” is present. Although reaction temperature is not specifically limited, Room temperature to 110 degreeC is preferable. About stirring, the stirring intensity | strength of the grade which neutralization reaction advances uniformly is required.
[0020]
By changing the Ag / Bi molar ratio of silver nitrate and bismuth nitrate to be subjected to the reaction, the atomic ratio of Ag / Bi in the final compound, and consequently the atomic ratio of Ag / Bi in the grains can be adjusted. According to the experience of the present inventors, the Ag / Bi molar ratio of silver nitrate and bismuth nitrate should be adjusted in the range of 1 to 7, preferably 2 to 5. As the molar ratio is decreased, the discharge capacity of the obtained positive electrode active material is greatly decreased. Conversely, when the ratio is excessively increased, the amount of Ag is increased, and the object of the present invention, that is, the amount of Ag can be reduced.
[0021]
[Oxidation process]
The oxidation step is a treatment for oxidizing the neutralized precipitate using an oxidizing agent, and is a treatment characterized by increasing the valence of Ag and Bi in the neutralized precipitate. The oxidation step is performed separately. And it is preferable to insert the process which heats up the liquid containing a residue between a neutralization process and an oxidation process, and to supply an oxidizing agent in the heated liquid. As the oxidizing agent, a normal oxidizing agent such as KMnO ₄ , NaOCl, H ₂ O ₂ , K ₂ S ₂ O ₈ , Na ₂ S ₂ O ₈ or ozone can be used.
[0022]
During the oxidation treatment, the liquid temperature should be kept at 50 ° C. or higher, preferably 70 ° C. or higher, and the oxidant should be added with stirring. However, if the temperature is too high, decomposition of the oxidant proceeds, so preferable. As described above, this oxidation treatment increases the valence of Ag and Bi in the neutralized ^precipitate , for example, Ag ⁺¹ is oxidized to Ag ⁺² and Bi ⁺³ is oxidized to Bi ^+3.5 , Bi ^+5, etc. It is necessary to add an oxidizing agent in an amount that can sufficiently change the valence. Specifically, it is preferable to add an oxidizer in an amount equal to or more than this equivalent, preferably about twice the equivalent to this valence change. The amount of oxidation varies depending on the valence of the metal element of the raw material nitrate used for the neutralization treatment, and also the relative proportion of Ag and Bi. Along with this, the composition of Ag-Bi-O in the product after the oxidation treatment Although the ratio also changes, by performing complete oxidation, an aggregate of fine particles made of an Ag—Bi—O-based crystalline compound as a whole is generated. As shown in the examples described later, according to the investigation by the present inventors, the aggregate of fine particles (Ag—Bi—containing oxidation product) as well as the crystalline fine particles has a low price such as Ag ₂ O. There are almost no opportunities for the presence of AgO, independent Bi oxide, independent M oxide, etc., as well as several compounds, and an Ag—Bi—O based crystalline compound suitable for a positive electrode active material can be obtained. can get.
[0023]
Alternatively, such oxidation can occur simultaneously with the formation of neutralized precipitate. In this case, the neutralization treatment may be carried out in the presence of the oxidizing agent, and a method of simultaneously adding an inorganic acid salt of Ag or Bi and an oxidizing agent to the alkaline aqueous solution, or oxidizing the alkaline aqueous solution. A method of adding an agent in advance and adding an inorganic acid salt of Ag or Bi to this solution may be employed. As shown in the examples described later, even when the neutralization step and the oxidation step are performed simultaneously, the Ag-Bi-containing oxidation product (oxidized precipitate) according to the present invention is substantially the same as when the two steps are performed separately. Can be obtained.
[0024]
[Solid-liquid separation, drying, crushing process]
Next, solid oxide separation is processed, washed with water and dried to obtain a black cake. It is recommended to age the oxide before solid-liquid separation. This ripening is a treatment for holding the liquid after the oxidation treatment at that temperature for about 20 to 90 minutes. By carrying out this ripening treatment, the oxide residue can be homogenized. More specifically, it is possible to obtain a product composed of stable Ag—Bi—O-based compound particles with less variation in composition among the particles. It is good to dry the residue washed with water by filtration at a temperature of 50 to 200 ° C. If the temperature exceeds 200 ° C., the produced compound may be decomposed. By crushing the obtained dry cake with a crusher, it is possible to obtain a powder that can be used as a positive electrode active material for an alkaline battery made of an Ag-Bi-containing oxidation product.
[0025]
As shown in the examples below, the powder composed of an Ag—Bi—O compound obtained by such a production method has an X-ray diffraction database of the main peak group of its X-ray pattern (copper target used, wavelength = 1.5405 Å). It does not match that of any compound in (ICDD). Further, in the X-ray diffraction of this powder, the main peak group of AgO or Ag ₂ O does not appear. Therefore, it can be said that there is no compound as AgO or Ag ₂ O in this powder. If present, it is an impurity, and the amount of this impurity is not more than 1 wt%, preferably not more than 0.5 wt%, more preferably X-ray diffraction as the total amount of both AgO and Ag ₂ O. The amount is below the calibration limit. Therefore, according to the present invention, an Ag-Bi-O-based compound that has not been known so far is provided, and the formation reaction of this substance in the above-described production method is also considered a novel reaction. Even if the Ag / Bi ratio is different within the range specified by the present invention, the main peaks in X-ray diffraction are almost the same as shown in FIG. Therefore, the positive electrode active material according to the present invention preferably has a main diffraction peak at an interplanar spacing of 2.78 ± 0.05 angstroms, an interplanar spacing of 2.62 ± 0.05 angstroms and an interplanar spacing of 2.43 ± 0.05 angstroms, as measured by powder X-ray diffraction. It can also be said to consist of compounds.
[0026]
The present inventors consider that the reaction for obtaining the compound according to the present invention will be based on the following reaction formula. However, the inorganic acid salts of Ag and Bi used for the neutralization reaction are silver nitrate (AgNO ₃ ) and bismuth nitrate [Bi (NO ₃ ) ₃ ], the alkali hydroxide is sodium hydroxide (NaOH), and the oxidation The agent is assumed to be sodium peroxodisulfate (Na ₂ S ₂ O ₈ ).
[0027]
Reaction formula for neutralization reaction (no redox reaction) (1 ≦ X ≦ 7)
xAgNO ₃ + Bi (NO ₃ ) ₃ + (x + 3) NaOH
→ Ag _x BiO _{(x + 3) / 2} + (x + 3) NaNO ₃ + (x + 3) / 2H ₂ O
[0028]
Reaction formula of oxidation reaction (Oxidation reaction of Ag (1) → Ag (1.8) and Bi (3) → Bi (3.5))
Ag _x BiO _{(x + 3) / 2} + (0.8x + 0.5) / 2Na ₂ S ₂ O ₈ + (0.8x + 0.5) NaOH
→ Ag _x BiO _{(1.8x + 3.5) / 2} + (0.8x + 0.5) Na ₂ SO ₄ + (0.8x + 0.5) / 2H ₂ O
[0029]
Hereinafter, typical test results conducted by the present inventors will be described as examples, and the positive electrode active material of the present invention will be further described.
[0030]
【Example】
[0031]
[Example 1]
Silver nitrate (AgNO ₃ ) and bismuth nitrate [Bi (NO ₃ ) ₃ ] were weighed so that the Ag / Bi molar ratio was 3. The above-mentioned silver nitrate and bismuth nitrate were added to an aqueous solution (1.5 liters) in which NaOH was dissolved 10 times in molar ratio with respect to the total amount of both, and a neutralized precipitate was produced in the liquid. The obtained neutralized suspension was heated to 90 ° C. and stirred, and potassium peroxodisulfate K ₂ S ₂ O ₈ was used as an oxidizing agent in a molar ratio with respect to the total amount of Ag and Bi. A 1-fold amount was added to the suspension with stirring and oxidized. After completion of the oxidation treatment, aging was carried out at a temperature of 104 ° C. for 60 minutes, and then the residue was filtered, washed with water and dried at 100 ° C., and the dried product was pulverized with a crusher.
[0032]
The powder characteristics of the obtained powder were as follows: specific surface area by BET method = 1.256 m ² / g, tap density = 1.72 g / cc, compression density = 6.01 g / cm ³ , D50 = 6.53 μm by Heros particle size analyzer there were. Note that D50 by the Heros particle size distribution meter is a cumulative particle size curve in which the horizontal axis represents the particle size D (μm) and the vertical axis represents the volume (Q)% in which particles having a particle size of D μm or less exist, Q = The value of particle size D (μm) corresponding to 50%.
[0033]
The composition of the obtained powder was examined by chemical analysis. As a result, Ag = 54.4 wt%, Bi = 34.8 wt%, and O = 9.9 wt%. The electrical conductivity of this powder was measured using the same method used to measure silver oxide (Ag ₂ O) powder as the positive electrode active material, and it was 1.53 S / cm × 10 ^-2 . Incidentally, the conductivity of silver oxide powder is about 4.8 S / cm × 10 ⁻⁵ .
[0034]
Next, the discharge characteristics when this powder is used as the positive electrode active material are silver oxide (Ag ₂ O) powder that has been commercialized as a positive electrode active material having almost the same compression density (6.6 g / cm ³ ). It investigated in the same conditions. As a result, initial potential (open circuit voltage) = 1.758 V (1.647 V for Ag ₂ O), weight energy density (discharge capacity) = 205 mAh / g (204 mAh / g for Ag ₂ O), volumetric energy density = 1232 mAh / cm ³ (1285 mAh / cm ^{3 for} Ag ₂ O). The discharge curve of this powder is shown in FIG.
[0035]
An X-ray diffraction chart (using a copper target, wavelength = 1.5405 Å, the same applies hereinafter) of the obtained powder (Ag / Bi atomic ratio = 3) is shown in the uppermost part of FIG. For reference, an X-ray diffraction chart of Bi ₂ O _3, Ag ₂ O _and AgO is also shown in comparison with the lower part. As can be seen in FIG. 2, the powder particles of this example are clearly composed of crystals having a number of peaks, but are different from those of Bi ₂ O ₃ , Ag ₂ O, and AgO. There are many new peaks as compounds composed of three elements of Bi and O.
[0036]
[Example 2]
Example 1 was repeated except that the mixing ratio of silver nitrate and bismuth nitrate used in the neutralization step was changed so that the Ag / Bi molar ratio was 4, and each Ag-Bi-O-based powder was obtained. It was. The compression density, specific surface area and open circuit voltage of this powder were measured. Table 1 shows the measurement results in comparison with those of Example 1.
[0037]
Example 3
Example 1 was repeated except that the mixing ratio of silver nitrate and bismuth nitrate used in the neutralization step was changed so that the Ag / Bi molar ratio was 2, and each Ag-Bi-O-based powder was obtained. It was. The compression density, specific surface area and open circuit voltage of this powder were measured. The measurement results are also shown in Table 1.
[0038]
[Table 1]

[0039]
Example 4
This example shows an example of the positive electrode active material of the present invention obtained by simultaneously performing neutralization and oxidation.
Silver nitrate (AgNO ₃ ) and bismuth nitrate [Bi (NO ₃ ) ₃ ] were weighed so that the Ag / Bi molar ratio was 3, to obtain a 0.8 liter aqueous solution. On the other hand, potassium peroxodisulfide (k ₂ S ₂ O ₈ ) was weighed in a molar ratio with respect to the total amount of both nitrates to prepare a 1.4 liter aqueous solution.
[0040]
Prepare 1.6 liters of a solution in which 5 times the amount of NaOH is dissolved in a molar ratio with respect to the total amount of nitrate, and maintain the solution temperature at 104 ° C. while maintaining the solution temperature at 104 ° C. An aqueous solution of potassium was added simultaneously over 30 minutes. After completion of the addition, the mixture was aged at a temperature of 104 ° C. for 30 minutes, and the residue was filtered from the liquid, washed with water, dried at 100 ° C., and the dried product was pulverized with a crusher.
[0041]
When the obtained powder was used as a positive electrode active material, the open circuit voltage and the discharge capacity (at 1.4 V) were measured in the same manner as in Example 1. The open circuit voltage = 1.778 V and the discharge capacity = 197 (mAh / g).
[0042]
The X-ray diffraction result of the powder obtained in this example is shown in FIG. From the results of FIG. 3, the powder obtained in this example has an X-ray pattern similar to that of FIG. 1 obtained in Example 1, and is separated even if neutralization and oxidation are performed simultaneously. It can be seen that a powder having a crystal structure similar to that obtained in the above case can be obtained.
[0043]
Next, a small amount of particles (average particle size 0.6 μm) was sampled from the powder obtained in this example, and an analysis of the Bi concentration distribution in the particles was attempted by ESCA (electron spectroscopy for chemical analysis). The measuring device is 5800 manufactured by ULVAC-PHI, the X-ray source is an Al anode source (300 V), and the depth etching rate from the particle surface is 0.32 nm / min. The measurement results are shown in FIG. The horizontal axis of FIG. 4 is sputter time, and the vertical axis is Bi atomic concentration (%). Etching was carried out for about 800 minutes. This is equivalent to about 0.25 μm depth, that is, about the center of a particle with a particle size of 0.6 μm. The results in Fig. 4 show that the Bi concentration in the particle remains almost constant from the particle surface to the sputter time of 800 minutes, with almost no change.
[0044]
Example 5
Example 1 was repeated except that the Ag / Bi molar ratio was changed to 7/1, 6/1 and 5/1. And X-ray diffraction of each obtained powder was performed. The results are shown in FIG. FIG. 5 also shows the X-ray diffraction of the powders of Examples 1 to 3. From the results of FIG. 5, it can be seen that the main peaks of the powders having different Ag / Bi ratios are almost the same, and therefore have almost the same crystal structure. More specifically, each powder is composed of a compound having a diffraction peak characteristic of 2.78 ± 0.05 angstroms, 2.62 ± 0.05 angstroms and 2.43 ± 0.05 angstroms as measured by powder X-ray diffraction. I understand. Such main peak groups do not match those of any compound in the X-ray diffraction database (ICDD).
[0045]
【Effect of the invention】
As described above, according to the present invention, as a positive electrode active material for an alkaline battery, an Ag—Bi—O-based material that exhibits a discharge characteristic equal to or higher than that of a conventional representative Ag ₂ O powder even if the Ag content is lower. A novel positive electrode active material is provided, and this positive electrode active material has a much better conductivity than silver oxide. Therefore, since the positive electrode active material of the present invention is inexpensive and has high conductivity and excellent discharge characteristics, it greatly contributes to the construction of a high-performance and inexpensive battery composed of a positive electrode active material, a negative electrode material and an electrolyte. It is.
[Brief description of the drawings]
FIG. 1 shows an X-ray diffraction chart of a positive electrode active material according to the present invention in comparison with those of other powders.
FIG. 2 shows a discharge curve of a positive electrode active material according to the present invention.
FIG. 3 is an X-ray diffraction chart of another positive electrode active material according to the present invention.
FIG. 4 is a view showing the result of measuring the Bi concentration distribution in the particles of the positive electrode active material according to the present invention by ESCA.
FIG. 5 shows a comparison of X-ray diffraction charts of a positive electrode active material according to the present invention.

Claims

It has a composition with an atomic ratio of Ag / Bi of 2 or more and 7 or less and an oxygen content of 5% by weight or more, and a surface separation of 2.78 ± 0.05 angstrom, a surface separation of 2.62 ± 0.05 angstrom and Positive electrode active material for batteries, consisting of crystals of a compound with a major diffraction peak at an interplanar spacing of 2.43 ± 0.05 angstroms.

In an alkaline battery comprising a negative electrode active material, a positive electrode active material, and an electrolyte, the positive electrode active material has a composition with an Ag / Bi atomic ratio of 2 to 7 and an oxygen content of 5% by weight or more. Alkaline battery consisting of crystals of compounds with major diffraction peaks at 2.78 ± 0.05 angstrom, face spacing 2.62 ± 0.05 angstrom and face spacing 2.43 ± 0.05 angstrom, measured by X-ray diffraction.