JP3610439B2 - Cathode active material for non-aqueous lithium secondary battery and lithium secondary battery - Google Patents
Cathode active material for non-aqueous lithium secondary battery and lithium secondary battery Download PDFInfo
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- JP3610439B2 JP3610439B2 JP29783694A JP29783694A JP3610439B2 JP 3610439 B2 JP3610439 B2 JP 3610439B2 JP 29783694 A JP29783694 A JP 29783694A JP 29783694 A JP29783694 A JP 29783694A JP 3610439 B2 JP3610439 B2 JP 3610439B2
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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Description
【0001】
【産業上の利用分野】
本発明は、非水リチウム二次電池用正極活物質として有効なLiNiO2 粒子とその製造法および該粒子を主成分とする正極板を用いて充放電の高容量化と負荷特性の向上を達成したリチウム二次電池に関するものである。
【0002】
【従来の技術】
従来、LiNiO2 を製造する代表的な技術においては、リチウム化合物とニッケル化合物との混合物を酸素気流中750℃程度の温度で15時間焼成して所望のLiNiO2 を合成し、Liインターカレーション型の結晶構造を発達させ、リチウムイオンの移動を容易にして電池容量を高めていた。
【0003】
しかしながらこのような従来の技術にあっては、初期の高容量化を達成するための結晶構造を得る条件(例えば出発原料や焼成条件)の検討はなされているが、容量の再現性が低く、また、二次電池の負荷特性が低い等の問題があった。
【0004】
【発明が解決しようとする課題】
上述のように、従来の製造法によって得られた正極活物質には、得られた物質の初期容量の再現性が悪い等の問題があり、LiNiO2 を正極活物質として用いる非水リチウム二次電池において、初期容量の再現性を確保することと、負荷特性の高い新規な正極活物質を開発することが望まれていた。
【0005】
【課題を解決するための手段】
本発明者等は斯かる課題を解決するために鋭意研究した結果、従来公知のLiNiO2 粉末であっても、細孔半径がある特定範囲のものであれば負荷特性が向上することを見いだし、本発明を提供することができた。
【0006】
すなわち、本発明の第1は、平均細孔半径が8〜50nmの範囲内にあるLiNiO2粒子からなることを特徴とする非水リチウム二次電池用正極活物質であり、第2は、平均細孔半径が8〜50nmの範囲内にあり、3回目の放電条件2Cの場合の充放電時の充放電容量比率が69%以上であるLiNiO2粒子からなることを特徴とする非水リチウム二次電池用正極活物質であり、第3は、前記LiNiO2粒子が、水酸化リチウムと水酸化ニッケルとの混合物を乾燥した粒または塊とし、次いで焼成してなるLiNiO2粒子である、第1または2に記載の非水リチウム二次電池用正極活物質であり、第4は、第1〜3のいずれかに記載のLiNiO2粒子を導電剤および結着剤と混練して成形した成形体を正極板として用いてなることを特徴とするリチウム二次電池である。
【0007】
【作用】
電池内のリチウムの移動をモデル的に見ると、非水系の二次電池の場合は、充電時に正極活物質からリチウムが抜け出て電解液または電解質を通って負極に析出する。放電時にはこの逆の変化が生じるが、これらの時、リチウムはイオンあるいは錯体などの化合物の状態で移動すると考えられている。
【0008】
LiNiO2 活物質粉末は一次粒子の集まった二次粒子の構造を有し、その一次粒子は不完全ではあるが1個のLiNiO2 結晶粒子であると考えられており、充放電にともない一次粒子内のリチウムは結晶格子のインターカレーションした層をイオンの状態で固体拡散により移動する。
【0009】
この場合、一次粒子間には多少とも空間があり電解液か電解質が保持されるのでこれらの空間は液を満たした細孔と考えられている。正極は、この活物質、導電剤、結着剤および電解質を含む三次構造から成り立っている。
【0010】
一般に、一次粒子と三次構造内外でのリチウムの移動について特性の良否が検討されているが、二次構造中のリチウムの移動については検討がなされていないのが現状である。しかしながら、一次粒子内の通路の大きさがオングストロームのオーダーであり、一方、三次構造中の通路の大きさがμmのオーダーであるため、特に放電時の二次構造中の通路が重要なことは自明である。
【0011】
充放電時のリチウムイオンの移動は、二次粒子中の空間での液体拡散を伴うが、物質移動の速度は液体拡散のほうが高いことや、流体への抵抗が細孔の径に大きな影響を受けることは容易に推定されることから、単純に考えれば細孔半径が大きくなればなる程物質移動が促進されると期待される。
【0012】
しかしながら、細孔半径がより大きくなると毛管現象による電解液の浸透が抑制されやすく容量が低下するため自ら上限があり、これを踏まえて行った研究の結果、適正な平均細孔半径の範囲は8〜50nmであることを見いだした。
【0013】
通常、細孔はその径の大きさによってミクロ、メゾ、マクロと呼ばれ、その内メゾ細孔は広く1〜100nmの範囲であり、本発明の粒子はメゾ細孔の中心よりも大側にある。これらの範囲の粒子を容積の面から見ると、密度とのバランスから30%以下のものが好ましい。
【0014】
この場合、細孔半径の分布と平均値は、ガス吸着法の吸着・脱離等温線によって求めることが望ましく、また解析はBJH法によれば充分である。
【0015】
これは以下の理由による。すなわち、水銀圧入式では測定時に粉末間の空間も測定されてしまうので粉粒子内の測定と評価が困難である。
【0016】
更に、二次構造内では、リチウムの移動はイオンとしての移動でなく、より大きな形での移動と考えられている。
【0017】
本発明の製造法について、従来法と対比しながら説明する。一般にLiNiO2 の製造において、ニッケル原料成分とリチウム原料成分とを混合し、加熱により反応を行うが、必要によって粉砕も行う。この場合、ニッケル原料としては水酸化物、塩基性炭酸塩、オキシ水酸化物、酸化物が使用可能とされており、リチウム原料としては水酸化物が代表的である。
【0018】
更に焼成時の反応性を高め、結果として得られるLiNiO2 粉末を電池用活物質として良好な結晶相とするため、ニッケルとリチウムの成分が相互に微細かつ均質に分散することが望ましいと考えられている。
【0019】
従って、従来法においては、ニッケル原料とリチウム原料とを有機溶剤中で微粉砕・混合することによって、平均粒径が5μm前後の混合原料を得、これを乾燥した後、500℃程度の温度で仮焼し、圧密成形するが、LiNiO2 の焼成温度を750℃前後とすることが多い。
【0020】
更に、水酸化ニッケルと水酸化リチウムによる公知条件での試作品は、その細孔半径が9nm以下程度であり、その作成ロット毎の容量とサイクル特性を測定すると測定値が安定しない。このようなLiNiO2 粉末は、二次粒子内の移動が困難で負荷特性が劣っている。
【0021】
この対策として、二次粒子径を小さくすることも考えられるが、その結果充填性が低下するので電池としての容量が低下してしまうことから、本発明法は以上の従来法の欠点を制御することにより、活物質としての特性の改善を意図するものである。
【0022】
本発明法において使用するリチウム原料は公知の塩であるが、水酸化リチウムで充分であり、LiNiO2 は焼成によりニッケル原料を母胎として成長する。従ってLiNiO2 粉末の平均径と細孔を制御するには、焼成に至るまでのニッケル原料の形態が重要である。
【0023】
このような場合には、水酸化ニッケルとして比表面積が100m2/g以下の範囲のものを45μm以下の粒径で用いることが反応上は望ましいが、原料の種類によっては、処理条件は若干異なる。
【0024】
焼成条件として750℃付近の温度および10〜20時間の保持時間で、酸化雰囲気、好ましくは酸素気流中にて熱処理することが公知であるが、本発明法においてはこれ以外の条件も使用可能であった。
【0025】
この場合、リチウムは、焼成によりその0.3%程度が揮発するので、必要ならば、前もってこの分を多く計量しておくとよい。焼成後の外観は黒色塊状となるが、正極活物質として使用するにはこの塊を解砕して分級する。
【0026】
一般に電池用の正極活物質粉末としては、その成形方式や条件から、また短絡や保存中の放電を防ぐ理由から、経験的に、その粒径が1μm以上100μm以下の範囲内のものが適切であるとされている。本発明においても30μmの平均径で同様の結果が得られたが、8〜50nmの平均細孔半径を有するものが好ましいことが判明した。尚、上記塊の解砕と分級には一般的な装置を使用できる。
【0027】
リチウム原料とニッケル原料の成分比が、モル比においてLi/Ni=1/1でなくても、Li/Ni=(1±0.05)/1の範囲内であれば、電池特性において同程度の結果が得られ、少量の添加物を用いた場合であっても、その結果が本発明の効果と同様であれば本発明の範囲に含まれる。
【0028】
このようにして得られたLiNiO2 を正極活物質として用い、これに導電剤としてケッチェンブラック、結着剤としてポリテトラフルオロエチレン(PTFE)を重量比で87:8:5の割合で加えて混練し、2ton/cm2 の圧力で直径18mmの円盤状に加圧成形を行った。
【0029】
この加圧成形体を図1に示す試験セル内の正極2として用い、負極4には厚さ0.7mmのリチウム金属を切り抜いたものを用いた。図中のセパレーター3にはポリプロピレンのフィルムを切り抜いたものを使用し、電解液には、プロピレンカーボネート(PC)と1,2−ジメトキシエタン(DME)の体積比1:1の混合液に6フッ化リン酸リチウム(LiPF6 )を1mol/l の濃度に溶解させたものを用いた。この場合、電解液としては他の溶剤を用いてもよい。
【0030】
また、本発明において、繰り返しによる放電容量の低下についても併記し、二次電池としての耐久性を相対評価したが、この場合、2回目までの充放電は再現性が低いので0.2Cで充放電した後に、3回目の充放電で容量を測定し、充電容量に対する放電容量の比率にて良否を比較した。この比率が高いほうが負荷特性が高いものと判定した。尚、実施例1〜5において0.2Cにおける3回目の放電容量が160〜180mAH/g であった。
【0031】
以下、実施例をもって本発明を詳細に説明するが、本発明の範囲はこれらに限定されるものではない。
【0032】
【実施例1】
表1に示すように平均径45μm以下の水酸化リチウム粉末と炭酸リチウムとを用いて、炭酸リチウム/全リチウムの割合が0、5、10、20、40、70となるように調合した粉末と、平均径3μmの水酸化ニッケルとをモル比でLi/Ni=1.01/1となるように秤量し、これらの粉末をエタノールの中で混合し、スプレードライヤーで乾燥・造粒し、ふるい分けを行って平均径約30μmの混合粉末を得た(第1工程)。
【0033】
【表1】
【0034】
次いで、これらの混合粉を酸素気流中765℃で8時間熱処理を行い、焼成物を得た(第2工程)。
【0035】
次いで得られた焼成物を乳鉢内で粉砕することによってLiNiO2 の粉末と成したものを分級したところ、表1に示す細孔半径を有することが判明した(第3工程)。
【0036】
得られた粉末をXRD測定したところ、従来報告されているものと同形のパターンを得ると共に、LiNiO2 以外の相は確認されなかった(図示せず)。
【0037】
このようにして得られたLiNiO2 を正極活物質として用い、これに導電剤としてケッチェンブラック、結着剤としてポリテトラフルオロエチレンを重量比で87:8:5の割合で混練して、2ton/cm2 の圧力で直径18mmの円盤状に加圧成形を行った。
【0038】
この加圧成形体を図1に示す試験セル内の正極2として用い、負極4には厚さ0.7mmのリチウム金属を切り抜いたものを用いた他、セパレーター3には、ポリプロピレンのフィルムを切り抜いたものを、電解液には、プロピレンカーボネート(PC)と1,2−ジメトキシエタン(DME)の体積比1:1の混合液に6フッ化リン酸リチウム(LiPF6 )を0.5mol/l の濃度に溶解させたものを用いた。
【0039】
表1に示すLiNiO2 粉末をそれぞれ個別の正極体として作成して図1の試験セルに組み入れ、充放電試験を行い、その結果を表1に併せて示した。
【0040】
この結果、細孔半径が10〜50nmの範囲に含まれているものを正極として用いたセル(No.2〜No.5)は、4.2V充電放電条件1Cおよび2Cの場合共、69%以上の効率を示していた。
【0041】
【実施例2】
水酸化リチウムとタップ密度2.1で平均径19μmの水酸化ニッケルとをモル比でLi/Ni=1.01/1となるようにそれぞれ秤量した。次いで、これらの粉末に溶剤としてクエン酸を加え、表2に示すように水酸化ニッケルに対するクエン酸の添加量を変え、液中で混合、攪拌しながら60℃で乾固した(第1工程)。
【0042】
次いで、該乾固物を2cm程の塊にし、大気気流中350℃にて3時間仮焼したものを60メッシュパスに粉砕し、該粉末を酸素気流中720℃にて3時間保持し、続いて770℃にて5時間熱処理を行い、実施例1と同様に焼成物を得た(第2工程)。
【0043】
次いで得られた焼成物を乳鉢内で粉砕することによってLiNiO2 の粉末と成したものをふるい分けして150メッシュアンダーの粉末を得、それらの細孔半径を求め表2に示した。
【0044】
このようにして得たLiNiO2 粉末を実施例1に示す手順で正極と成し、試験セルを作製して充放電試験を行い、その結果を表2に併せて示した。実施例1と同様に細孔半径が10〜50nmの範囲にあり、放電条件も1C、2C共69%以上の効率を有している。
【0045】
【表2】
【0046】
【実施例3】
200メッシュパスの水酸化リチウム−水和物(LiOH・H2 O)と水酸化ニッケルを700℃で熱処理して得た平均径20μmの酸化ニッケル(NiO)とをモル比でLi/Ni=0.97/1およびLi/Ni=1.04/1となるようにそれぞれ秤量し、クエン酸をリチウムとニッケルの合量に対して25重量%添加して水中にて90℃、4時間混合した後、冷却した。
【0047】
次いで混合物を攪拌容器から取り出して、乳鉢内で1mm以下に解砕して充分に、乾燥させたものを、直径約2cmの塊にして酸素気流中で750℃にて7時間熱処理を行い、得られた焼成物を実施例1と同様に処理して正極と成し、充放電試験を行い、その結果を表3に併せて示した。
【0048】
【表3】
【0049】
表3の結果から、本実施例によって得られたLiNiO2 粉末も細孔半径が10〜50nmの範囲にあり、充放電効率も73%以上と優れていた。
【0050】
【実施例4】
3%程の炭酸を吸収させた8μmのLiOHと、Ni分をCoで4%置換した平均径が19μmの水酸化ニッケルをモル比でLi/Ni=1/1となるようにそれぞれ秤量したものに、少量の水を加えて混合して塊状体と成した。
【0051】
次いで、該塊状体を350℃大気中で乾燥した後に、10kg/cm2の圧力で加圧成形したものを乳鉢内で解砕して100メッシュパスした粉体の焼成を、酸素気流中760℃において7時間行ったところ、該粉末の平均細孔半径は17nmであり、この粉末を用いて実施例1と同様に正極体として、充放電試験(No.13)を行ったところ、1Cにおける効率は84%、2Cにおける効率は72%であった。
【0052】
【実施例5】
平均径15μmの水酸化リチウムおよびリチウム分の25%に相当する炭酸リチウムとの混合物に、重質の水酸化ニッケルを850℃で焼成したものを粉砕して、表4に示す平均粒径の酸化ニッケルを得、これらの粉末をモル比でLi/Ni=1.005/1となるように秤量して混合し、これを酸素気流中725℃で8時間熱処理を行って焼成物を得た。
【0053】
次いで、該焼成物を乳鉢内で解砕して粉体を得、それぞれの細孔半径を求め、表4に併せて示した。これらの粉末をXRDにて測定したところ、LiNiO2 以外の相は確認されなかった。
【0054】
またこれらの粉末をそれぞれ用いて実施例1と同様な正極体と成して、充放電試験を行いその結果を表4に示したが、これらの結果からも平均細孔半径が8〜50nmの範囲にあるNo.14〜No.16の放電条件は2Cにおいても69%以上を示すのに対して、平均細孔半径が6nmであるNo.17は2Cにおいては58%と効率が悪かった。
【0055】
【表4】
【0056】
【比較例1】
水酸化リチウム−水和物と水酸化ニッケルとをモル比でLi/Ni=1/1となるように秤量し、これらの粉末をアセトン中で24時間粉砕・混合したところ、平均径3.5μmの混合粉末を得た。
【0057】
次いで該混合粉末を0.5ton/cm2 の圧力で成形し、酸素気流中において焼成温度をそれぞれ750℃、720℃、700℃と変化させたものを、それぞれ12時間熱処理を行った後に乳鉢内で解砕し12μmの粉末を得、各温度毎の平均細孔半径を求め、その結果を表5に示した。
【0058】
次いで得られた粉末を用いて実施例1と同様に正極体と成して充放電試験を行い、その結果を表5に併せて示したが、この結果から平均細孔半径が10nm以下であるNo.18〜No.20は共に、放電効率も本発明範囲よりも低いことが判明した。また0.2Cでの充電容量は150mAh/g 前後であった。
【0059】
【表5】
【0060】
【発明の効果】
上述のように、本発明に示す特定範囲のLiNiO2 粒子を用いることにより、負荷特性の高いリチウム二次電池用正極活物質が得られるようになった。
【図面の簡単な説明】
【図1】実施例および比較例において作製した試験セルの断面概略図である。
【符号の説明】
1 正極缶
2 正極
3 セパレーター
4 負極
5 負極缶
6 絶縁パッキン[0001]
[Industrial application fields]
The present invention achieves higher charge / discharge capacity and improved load characteristics by using LiNiO 2 particles effective as a positive electrode active material for non-aqueous lithium secondary batteries, a method for producing the same, and a positive electrode plate mainly composed of the particles. The present invention relates to a lithium secondary battery.
[0002]
[Prior art]
Conventionally, in a typical technique for producing LiNiO 2 , a desired mixture of LiNiO 2 is synthesized by firing a mixture of a lithium compound and a nickel compound in an oxygen stream at a temperature of about 750 ° C. for 15 hours, and a Li intercalation type The crystal structure was developed to facilitate the movement of lithium ions and increase the battery capacity.
[0003]
However, in such a conventional technique, conditions for obtaining a crystal structure for achieving an initial high capacity (for example, starting materials and firing conditions) have been studied, but capacity reproducibility is low, In addition, there are problems such as low load characteristics of the secondary battery.
[0004]
[Problems to be solved by the invention]
As described above, the positive electrode active material obtained by the conventional manufacturing method has problems such as poor reproducibility of the initial capacity of the obtained material, and the nonaqueous lithium secondary using LiNiO 2 as the positive electrode active material. In batteries, it has been desired to ensure reproducibility of initial capacity and to develop a novel positive electrode active material having high load characteristics.
[0005]
[Means for Solving the Problems]
As a result of diligent research to solve such problems, the present inventors have found that even with the conventionally known LiNiO 2 powder, the load characteristics are improved if the pore radius is within a certain range, The present invention could be provided.
[0006]
That is, the first of the present invention is a positive electrode active material for a non-aqueous lithium secondary battery characterized by comprising LiNiO 2 particles having an average pore radius in the range of 8 to 50 nm, and the second is an average The non-aqueous lithium secondary battery is characterized by comprising LiNiO 2 particles having a pore radius in the range of 8 to 50 nm and having a charge / discharge capacity ratio of 69% or more at the time of charge / discharge in the third discharge condition 2C. a positive electrode active material for the next cell, the third, the LiNiO 2 particles, and the mixture dried grains or lumps of lithium hydroxide and nickel hydroxide, and then it is fired formed by LiNiO 2 particles, first Or a positive electrode active material for a non-aqueous lithium secondary battery according to 2, wherein the fourth is a molded article obtained by kneading the LiNiO 2 particles according to any one of the first to third with a conductive agent and a binder. To be used as a positive electrode plate The lithium secondary battery is characterized.
[0007]
[Action]
When the movement of lithium in the battery is viewed as a model, in the case of a non-aqueous secondary battery, lithium escapes from the positive electrode active material during charging and deposits on the negative electrode through the electrolyte or electrolyte. The reverse change occurs during discharge, and at these times, lithium is considered to move in the state of a compound such as an ion or a complex.
[0008]
The LiNiO 2 active material powder has a structure of secondary particles in which primary particles are gathered, and the primary particles are considered to be one LiNiO 2 crystal particle although it is incomplete. The lithium inside moves through the intercalated layer of the crystal lattice in the ionic state by solid diffusion.
[0009]
In this case, since there is some space between the primary particles and the electrolyte or electrolyte is retained, these spaces are considered to be pores filled with the solution. The positive electrode is composed of a tertiary structure including the active material, a conductive agent, a binder, and an electrolyte.
[0010]
In general, the quality of lithium in and out of the primary structure and the tertiary structure has been investigated, but the current situation is that the movement of lithium in the secondary structure has not been studied. However, the size of the passage in the primary particles is on the order of angstroms, while the size of the passage in the tertiary structure is on the order of μm, so that the passage in the secondary structure during discharge is particularly important. It is self-explanatory.
[0011]
The movement of lithium ions during charge / discharge is accompanied by liquid diffusion in the space in the secondary particles, but the mass transfer rate is higher for liquid diffusion and the resistance to fluid has a large effect on the pore diameter. Since it is estimated easily, it is expected that mass transfer will be promoted as the pore radius increases.
[0012]
However, as the pore radius becomes larger, the penetration of the electrolyte due to capillary phenomenon tends to be suppressed and the capacity decreases, so there is an upper limit by itself. As a result of research conducted based on this, the range of an appropriate average pore radius is 8 It was found to be ˜50 nm.
[0013]
Usually, the pores are called micro, meso, or macro depending on the size of the diameter. Among them, the mesopores are widely in the range of 1 to 100 nm, and the particles of the present invention are larger than the center of the mesopores. is there. When particles in these ranges are viewed from the viewpoint of volume, particles having a density of 30% or less are preferable from the balance with density.
[0014]
In this case, it is desirable that the distribution and average value of the pore radii are obtained by the adsorption / desorption isotherm of the gas adsorption method, and the analysis is sufficient according to the BJH method.
[0015]
This is due to the following reason. That is, in the mercury intrusion method, the space between the powders is also measured at the time of measurement, so that it is difficult to measure and evaluate the powder particles.
[0016]
Furthermore, in the secondary structure, the movement of lithium is not a movement as an ion, but a movement in a larger form.
[0017]
The production method of the present invention will be described in comparison with the conventional method. In general, in the production of LiNiO 2 , a nickel raw material component and a lithium raw material component are mixed and reacted by heating, but pulverization is also performed if necessary. In this case, hydroxides, basic carbonates, oxyhydroxides, and oxides can be used as nickel raw materials, and hydroxides are typical as lithium raw materials.
[0018]
Furthermore, in order to increase the reactivity during firing and to make the resulting LiNiO 2 powder a good crystalline phase as an active material for batteries, it is considered desirable to disperse the nickel and lithium components in a fine and homogeneous manner. ing.
[0019]
Therefore, in the conventional method, a nickel raw material and a lithium raw material are finely pulverized and mixed in an organic solvent to obtain a mixed raw material having an average particle size of about 5 μm. After drying this, a temperature of about 500 ° C. is obtained. Although calcined and compacted, the firing temperature of LiNiO 2 is often around 750 ° C.
[0020]
Furthermore, a prototype under known conditions using nickel hydroxide and lithium hydroxide has a pore radius of about 9 nm or less, and the measured value is not stable when the volume and cycle characteristics for each production lot are measured. Such LiNiO 2 powder is difficult to move in the secondary particles and has poor load characteristics.
[0021]
As a countermeasure against this, it is conceivable to reduce the secondary particle diameter, but as a result, the capacity as a battery is lowered because the filling property is lowered, so that the method of the present invention controls the drawbacks of the above conventional methods. This is intended to improve the properties as an active material.
[0022]
The lithium raw material used in the method of the present invention is a known salt, but lithium hydroxide is sufficient, and LiNiO 2 is grown by firing from the nickel raw material as a mother. Therefore, in order to control the average diameter and pores of the LiNiO 2 powder, the form of the nickel raw material up to firing is important.
[0023]
In such a case, nickel hydroxide having a specific surface area in the range of 100 m 2 / g or less is preferably used with a particle size of 45 μm or less, but the processing conditions differ slightly depending on the type of raw material. .
[0024]
It is known that heat treatment is performed in an oxidizing atmosphere, preferably in an oxygen stream, at a temperature around 750 ° C. and a holding time of 10 to 20 hours as firing conditions, but other conditions can be used in the method of the present invention. there were.
[0025]
In this case, since about 0.3% of lithium volatilizes by firing, if necessary, a large amount of this amount should be measured in advance. The appearance after firing becomes a black lump, but this lump is crushed and classified for use as a positive electrode active material.
[0026]
In general, as a positive electrode active material powder for a battery, a powder whose particle size is in the range of 1 μm to 100 μm is empirically suitable for its molding method and conditions, and for the purpose of preventing short circuit and discharge during storage. It is said that there is. In the present invention, similar results were obtained with an average diameter of 30 μm, but it was found that those having an average pore radius of 8 to 50 nm are preferable. In addition, a general apparatus can be used for the crushing and classification of the lump.
[0027]
Even if the component ratio of the lithium raw material and the nickel raw material is not Li / Ni = 1/1 in the molar ratio, if the Li / Ni = (1 ± 0.05) / 1 is in the range, the battery characteristics are comparable. Even when a small amount of additive is used, it is included in the scope of the present invention if the result is similar to the effect of the present invention.
[0028]
LiNiO 2 thus obtained was used as a positive electrode active material, and ketjen black as a conductive agent and polytetrafluoroethylene (PTFE) as a binder were added at a weight ratio of 87: 8: 5. The mixture was kneaded and pressure-formed into a disk shape having a diameter of 18 mm at a pressure of 2 ton / cm 2 .
[0029]
This press-molded body was used as the
[0030]
Further, in the present invention, the decrease in discharge capacity due to repetition was also described, and the durability as a secondary battery was relatively evaluated. In this case, the charge / discharge up to the second time is less reproducible, so charge is performed at 0.2C. After discharging, the capacity was measured by the third charge / discharge, and the quality was compared by the ratio of the discharge capacity to the charge capacity. It was determined that the higher the ratio, the higher the load characteristics. In Examples 1 to 5, the third discharge capacity at 0.2 C was 160 to 180 mAH / g.
[0031]
EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, the scope of the present invention is not limited to these.
[0032]
[Example 1]
As shown in Table 1, using lithium hydroxide powder having an average diameter of 45 μm or less and lithium carbonate, a powder prepared such that the ratio of lithium carbonate / total lithium is 0, 5, 10, 20, 40, 70 Measure nickel hydroxide with an average diameter of 3 μm in a molar ratio of Li / Ni = 1.01 / 1, mix these powders in ethanol, dry and granulate with a spray dryer, and screen. To obtain a mixed powder having an average diameter of about 30 μm (first step).
[0033]
[Table 1]
[0034]
Subsequently, these mixed powders were heat-treated in an oxygen stream at 765 ° C. for 8 hours to obtain a fired product (second step).
[0035]
Next, when the obtained fired product was pulverized in a mortar to classify what was made into a LiNiO 2 powder, it was found to have the pore radius shown in Table 1 (third step).
[0036]
When the obtained powder was subjected to XRD measurement, a pattern having the same shape as that conventionally reported was obtained, and phases other than LiNiO 2 were not confirmed (not shown).
[0037]
LiNiO 2 thus obtained was used as a positive electrode active material, and Ketjen black as a conductive agent and polytetrafluoroethylene as a binder were kneaded at a weight ratio of 87: 8: 5, and 2 ton. Press molding was performed in a disk shape with a diameter of 18 mm at a pressure of / cm 2 .
[0038]
1 was used as the
[0039]
Each LiNiO 2 powder shown in Table 1 was prepared as an individual positive electrode body and incorporated in the test cell of FIG. 1 to perform a charge / discharge test. The results are also shown in Table 1.
[0040]
As a result, the cells (No. 2 to No. 5) in which the pore radius is included in the range of 10 to 50 nm as the positive electrode are 69% in the case of 4.2V charge / discharge conditions 1C and 2C. The above efficiency was demonstrated.
[0041]
[Example 2]
Lithium hydroxide and nickel hydroxide having a tap density of 2.1 and an average diameter of 19 μm were weighed so that the molar ratio was Li / Ni = 1.01 / 1. Next, citric acid was added as a solvent to these powders, and the amount of citric acid added to nickel hydroxide was changed as shown in Table 2, mixed in the liquid and dried at 60 ° C. with stirring (first step). .
[0042]
Next, the dried product is made into a lump of about 2 cm, calcinated in an air stream at 350 ° C. for 3 hours, pulverized to a 60 mesh pass, and the powder is kept in an oxygen stream at 720 ° C. for 3 hours. Then, heat treatment was performed at 770 ° C. for 5 hours to obtain a fired product as in Example 1 (second step).
[0043]
Next, the obtained fired product was pulverized in a mortar, and the powder formed from LiNiO 2 powder was sieved to obtain 150 mesh under powder. The pore radii thereof were determined and shown in Table 2.
[0044]
The LiNiO 2 powder thus obtained was made into a positive electrode by the procedure shown in Example 1, a test cell was prepared and a charge / discharge test was conducted. The results are also shown in Table 2. Like Example 1, the pore radius is in the range of 10 to 50 nm, and the discharge conditions are 69% or higher for both 1C and 2C.
[0045]
[Table 2]
[0046]
[Example 3]
Li / Ni = 0 in a molar ratio of lithium hydroxide-hydrate (LiOH.H 2 O) of 200 mesh pass and nickel oxide (NiO) having an average diameter of 20 μm obtained by heat-treating nickel hydroxide at 700 ° C. .97 / 1 and Li / Ni = 1.04 / 1 were weighed, and citric acid was added in an amount of 25% by weight based on the total amount of lithium and nickel, followed by mixing in water at 90 ° C. for 4 hours. After cooling.
[0047]
Next, the mixture is taken out of the stirring vessel, crushed to a size of 1 mm or less in a mortar and sufficiently dried, and then a heat treatment is performed at 750 ° C. for 7 hours in an oxygen stream in a mass of about 2 cm in diameter. The obtained fired product was treated in the same manner as in Example 1 to form a positive electrode, and a charge / discharge test was conducted. The results are also shown in Table 3.
[0048]
[Table 3]
[0049]
From the results in Table 3, the LiNiO 2 powder obtained by this example also had a pore radius in the range of 10 to 50 nm, and the charge / discharge efficiency was excellent at 73% or more.
[0050]
[Example 4]
What weighed 8 μm LiOH that absorbed about 3% carbonic acid and nickel hydroxide with an average diameter of 19 μm, with Ni content replaced by
[0051]
Next, the mass was dried in the air at 350 ° C., and then pressure-molded at a pressure of 10 kg / cm 2 was crushed in a mortar and baked into a powder that passed 100 meshes at 760 ° C. in an oxygen stream. The powder was found to have an average pore radius of 17 nm, and a charge / discharge test (No. 13) was conducted using this powder as a positive electrode in the same manner as in Example 1. Was 84% and the efficiency at 2C was 72%.
[0052]
[Example 5]
A mixture of lithium hydroxide having an average diameter of 15 μm and lithium carbonate corresponding to 25% of the lithium content was pulverized from calcinated heavy nickel hydroxide at 850 ° C., and oxidized with an average particle diameter shown in Table 4 Nickel was obtained, and these powders were weighed and mixed so that the molar ratio was Li / Ni = 1.005 / 1, and this was heat-treated at 725 ° C. for 8 hours in an oxygen stream to obtain a fired product.
[0053]
Next, the fired product was pulverized in a mortar to obtain powder, and the pore radius of each was determined. When these powders were measured by XRD, phases other than LiNiO 2 were not confirmed.
[0054]
In addition, each of these powders was used to form a positive electrode body similar to that of Example 1, and a charge / discharge test was performed. The results are shown in Table 4, and the average pore radius is 8 to 50 nm from these results. The discharge conditions of No. 14 to No. 16 in the range showed 69% or more even at 2C, whereas No. 17 having an average pore radius of 6 nm was 58% at 2C and the efficiency was poor.
[0055]
[Table 4]
[0056]
[Comparative Example 1]
Lithium hydroxide-hydrate and nickel hydroxide were weighed so that the molar ratio was Li / Ni = 1/1, and these powders were pulverized and mixed in acetone for 24 hours, resulting in an average diameter of 3.5 μm. Of mixed powder was obtained.
[0057]
Next, the mixed powder was molded at a pressure of 0.5 ton / cm 2 , and the calcination temperature was changed to 750 ° C., 720 ° C. and 700 ° C. in an oxygen stream, respectively, and after heat treatment for 12 hours, To obtain a 12 μm powder, the average pore radius for each temperature was determined, and the results are shown in Table 5.
[0058]
Subsequently, the resulting powder was used to form a positive electrode body in the same manner as in Example 1, and a charge / discharge test was performed. The results are also shown in Table 5, and from this result, the average pore radius is 10 nm or less. No. 18-No. In both cases, the discharge efficiency was also lower than the scope of the present invention. The charge capacity at 0.2 C was around 150 mAh / g.
[0059]
[Table 5]
[0060]
【The invention's effect】
As described above, by using LiNiO 2 particles in a specific range shown in the present invention, a positive electrode active material for a lithium secondary battery with high load characteristics can be obtained.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view of test cells prepared in Examples and Comparative Examples.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Positive electrode can 2
Claims (4)
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