JP4292684B2 - Slurry for producing lithium secondary battery electrode and use thereof - Google Patents
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- JP4292684B2 JP4292684B2 JP2000155773A JP2000155773A JP4292684B2 JP 4292684 B2 JP4292684 B2 JP 4292684B2 JP 2000155773 A JP2000155773 A JP 2000155773A JP 2000155773 A JP2000155773 A JP 2000155773A JP 4292684 B2 JP4292684 B2 JP 4292684B2
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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
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Description
【０００１】
【発明の属する技術分野】
本発明は、リチウム二次電池電極製造用スラリー及びその使用に関するものである。詳しくは、小型、軽量の電気機器や電気自動車の電源として好適な、非水系リチウム二次電池電極製造用スラリー及びこれを使用して作成された二次電池用電極シートに関する。
【０００２】
【従来の技術】
近年、ビデオカメラ、携帯電話やポータブルパソコン等の携帯電話の普及に伴い、一次電池に代わって繰り返し使用できる二次電池の需要が高まっている。特に負極活物質に炭素質材料を、正極活物質にＬｉＭＯ2（Ｍ＝Ｃｏ、Ｎｉ等）を用い、電解液に有機溶媒を使った非水系二次電池（特開昭６３−１２１２６０号公報等）が開発され、注目されている。また負極活物質として、例えば、特公平４−２４８３１号公報にはコークス等のソフトカーボン系の材料が、特開平３−２５２０５３号公報にはハードカーボン系の材料が提案されている。これらの正・負極用活物質は粉体状で用いられることが多く、これを電極に加工して用いる方法としては、該粉体を適当な粉体結着剤、及び結着剤を分散或いは溶解させる溶媒と共に混合し、集電体であるアルミ箔や銅箔上に塗布・乾燥する方法が良く用いられる。
【０００３】
【発明が解決しようとする課題】
しかしながら、上述の方法を用いて作成された電極の中には、充放電を繰り返すと大きな容量の低下を招くものも多く見られ、これが、活物質種類の選択の幅を狭めてきた。例えば、活物質が、Ａｇ、Ｚｎ、Ａｌ、Ｇａ、Ｉｎ、Ｓｉ、Ｇｅ、Ｓｎ、Ｓｂ、Ａｓ及びＰｂより選ばれる少なくとも１つの金属元素からなるような負極の場合、充放電サイクルに伴い、容量劣化が大きいことが知られている。これらの要因として、サイクルに伴う活物質自体の劣化の他、電極の構造劣化が主な原因と考えられている。これらを解決するためには、活物質の改良に加え、充放電サイクルに対し、強い電極シートを作成する必要がある。
【０００４】
これまで、リチウム二次電池用電極シートを作成する際に活物質粉体を結着させる結着剤としてはポリフッ化ビニリデンが良く用いられてきた。本品そのものは固体であるので、用いやすくするために、通常は、Ｎ−メチルピロリジノンなどの極性のある有機溶媒に溶解させ、活物質粉体と混合、スラリー化して、集電体となる金属箔上に塗布後、乾燥する方法がとられてきた。しかし、例えば上述のような金属を活物質とする電極に対しては、なおサイクルに伴う容量劣化が大きく、前述の手法は十分なものとは言えない。
【０００５】
【課題を解決するための手段】
本発明者らは、該活物質を結着させる結着剤を分散又は溶解させる有機溶媒を調整する事で上記問題が解決できることを見出し、本発明に到達した。
即ち、本発明は、活物質、結着剤及び分散剤を少くとも含有するリチウム二次電池電極製造用スラリーであって、結着剤がポリフッ化ビニリデン、分散剤が炭化水素化合物から選ばれる一種以上の溶媒であることを特徴とする前記スラリー、及びこれを使用して作成されたリチウム二次電池用電極シート、並びにこの電極シートを有するリチウム二次電池にある。
【０００６】
【発明の実施の形態】
以下に本発明を詳細説明する。
電極の活物質を結着せしめる結着剤にはポリフッ化ビニリデン（ＰＶｄＦ）の粉体を用いる。ＰＶｄＦの平均重合度は特に限定されないが、７００〜２０００、好ましくは、９００〜１５００、更に好ましくは１０００〜１３００のものが用いられる。本品を、分散剤として炭化水素化合物、好ましくは飽和炭化水素化合物から選ばれる一種以上の溶媒に攪拌しつつ分散させる。飽和炭化水素化合物としては、直鎖脂肪族炭化水素化合物（ｎ−アルカン）が好ましい。更にｎ−アルカンの中でも、炭素数６未満の溶媒ではＰＶｄＦの分散性に欠け、１５を越すものは沸点が高くなるので溶媒除去が難しく、炭素数６〜１５のものが更に好ましい。これが、８〜１０であるものは分散性に優れるので最も好ましい。なお、ＰＶｄＦとの攪拌時に上記溶媒を沸点以下で加温して使用しても良い。
【０００７】
電極の活物質としては、従来リチウム二次電池用の活物質として用いられてきたものが限定無く使用できる。中でもリチウムを吸蔵・放出することが可能な金属元素及び炭素質物が好ましい。
リチウムを吸蔵・放出することが可能な金属元素としては、リチウムと合金を作る金属類が挙げられる。具体的には、Ａｇ、Ｚｎ、Ａｌ、Ｇａ、Ｉｎ、Ｓｉ、Ｇｅ、Ｓｎ、Ｓｂ、Ｐｂであり、Ａｇ、Ｚｎ、Ａｌ、Ｓｉ、Ｇｅ、Ｓｎ、Ｐｂ、Ｓｂが好ましく、更に好ましくはＺｎ、Ａｌ、Ｓｉ、Ｇｅ、Ｓｎ、Ｓｂである。これらは、炭素元素、例えば黒鉛のみを用いる電池では、負極材の容量が３７２ｍＡｈ／ｇと限られるために、そのエネルギー密度の向上には限界があるのに対し、これを越える容量を蓄えられる材料として好ましい。しかしながら、金属元素はサイクルに伴う大きな体積変化のため、実用的な電池を作ることが難しかった。即ち、金属は、黒鉛より多くの量のアルカリ金属元素、例えばリチウムを吸蔵できるが、同時に金属内部に捕獲されて使えないリチウム等もまた多い。しかし、本発明の手法を用いると、上述のような材料であっても、より長期のサイクルに亘って可逆的にリチウムの挿入・脱離を行うことができるようになる。
【０００８】
また、上述の様に、その容量に制限はあるものの天然黒鉛、人造黒鉛、これらの黒鉛を核としその表面を比較的結晶性の低い炭素質物で被覆した炭素材料及びこれらの黒鉛と比較的結晶性の低い炭素質物との混合物などのような炭素材料を用いることができ、この場合には、従来よりも更にサイクルの寿命を伸ばすことができる。
これまで、主に負極材料について説明してきたが、本効果はコバルト酸リチウムの様な正極活物質粉体に適用しても同様の効果が十分に期待できる。
この様な従来よりも優れた効果が発現する理由としては、結着剤であるＰＶｄＦの電極乾燥後の結晶状態の違いが考えられる。モデル的な実験として、これまで用いられてきたＮ−メチルピロリジノンなどの良溶媒でＰＶｄＦを溶解させると、ＰＶｄＦポリマー鎖の結晶性ミクロドメインまでほどけ、乾燥し溶媒除去を行った後には、殆どＰＶｄＦは非晶質になるのに対し、本発明に使用する特定の溶媒を用いると、溶媒除去後もＰＶｄＦの結晶性ドメインが残留していることがＸ線回折の結果からわかっている。この残留した結晶性ドメインは、ＰＶｄＦの微細繊維同士の結節を行っており、これが、電極の強度を増していると考えられる。
【０００９】
上記ＰＶｄＦ、炭化水素化合物溶媒、及び活物質を混合する方法については、攪拌子による通常の攪拌方法の他、軸混練機、ニーダー、ハイブリミキサー、自動乳鉢、ペイントシェーカーなど公知の手法を用いることができる。この際の攪拌時間は、用いる炭化水素溶媒の種類によっても異なるが、ＰＶｄＦの高次構造を破壊しない程度が好ましい。本高次構造が保たれているかどうかは、Ｘ線回折によって確認でき、ＰＶｄＦ粉体に基づく結晶ピークが、スラリー乾燥後に再確認できるものが良い。即ち、乾燥後の結着剤の結晶状態が完全に非晶質になっていないものが好ましい。また、上記ＰＶｄＦと飽和炭化水素溶媒を混合する比率については、任意の比率を用いることができるが、飽和炭化水素溶媒１００重量％に対し、ＰＶｄＦは１〜１００重量％が好ましい。３〜５０重量％は更に好ましく、４〜１０重量％は最も好ましい。
【００１０】
上記の様に混合されたものは、粘土状又はスラリー状のものとなる（本発明においては、これらを単にスラリーと呼ぶ）が、これの塗布については、従来公知の方法を限定無く用いることができる。例えば、ドクターブレード、またはダイコーターなどにより、スラリーを銅、アルミニウム、或いはニッケルといった集電体となる金属箔、またはメッシュへ塗布する方法が考えられる。この塗布は、数回に分割して、重ね塗りを行っても良い。
上記の手段によりスラリーを塗布し、その後乾燥を行うが、風乾後、加熱乾燥を行っても良いし、塗布後直ちに加熱乾燥を施しても良い。風乾は、除湿された大気中で行ってもよいが、乾燥窒素中で行うことが好ましい。加熱乾燥する場合には、風乾と同様、乾燥窒素下で２５０℃以下で行うことが好ましく、安全を考慮すると１２０℃以下で１時間以上行うと更に好ましい。
【００１１】
また、上記活物質とＰＶｄＦの比率は、乾燥し飽和炭化水素を除去した後、電極シートとした時に、活物質１００重量％に対し、ＰＶｄＦが２５重量％以下、３重量％以上であることが好ましい。１２重量％以下、６重量％以上であると更に好ましい。ＰＶｄＦの比率が高すぎると、電池にしたときの容量が低くなり、低すぎると結着性に欠ける。
なお、得られた電極シートは、プレス機で適当な厚みに圧延しても良い。
【００１２】
本発明の電極シートを有するリチウム二次電池は、前記電極シートをシート状負極及び／又はシート状正極として電池内に使用しているものであって、その他の構成要素は特に限定されるものではなく、公知のものが使用される。
電解液としては、非水溶媒に電解質を溶解させたものが使用できる。非水溶媒の好ましい例としては、エチレンカーボネート、プロピレンカーボネート、ブチレンカーボネート等の環状カーボネート、ジメチルカーボネート、エチルメチルカーボネート、ジエチルカーボネート等の鎖状カーボネート、γ−ブチロラクトン等の環状エステル、テトラヒドロフラン、メチルテトラヒドロフラン等の環状エーテル等が挙げられる。
電解質としては、ＬｉＰＦ6、ＬｉＢＦ4、等の無機酸リチウムが好ましく、または有機酸リチウムも使用でる。
【００１３】
本発明のリチウム二次電池には、上記の電解液、負極、正極のほかに、電池を構成するための負極用集電体、正極用集電体、セパレータ等を配設することができる。
負極用集電体の材質は、銅、ニッケル、ステンレス等の金属が使用され、中でも銅箔が好ましい。
正極集電体の材質は、アルミニウム、チタン、タンタル等の金属又はその合金が使用され、中でもアルミニウム又はその合金が使用され、中でもアルミニウム又はその合金が、エネルギー密度の点で好ましい。
セパレータとしては、ポリエチレン、ポリプロピレン等のポリオレフィンを原料とする多孔性シート又は不織布等が使用でき、前記電解液を含浸して用いられる。
電池の形状は特に限定されるものではなく、本発明のシート状電極とセパレータをスパイラル状にしたシリンダータイプ等、公知の形状に作製して使用される。
【００１４】
次に本発明によって得られた電極シート、及び測定方法を負極を例にとって示す。
ＰＶｄＦ５重量％に対し、ｎ−デカン１００重量％を加え、室温でスターラーで混合し、均一に分散させた後、負極活物質を加えてスラリー作成した。ＰＶｄＦは乾燥後の重量で、負極活物質１００重量％に対し、８重量％になるように調整した。そして、このペーストを銅箔上に塗布し、６０℃で約１時間窒素気流下で乾燥後、直径１２．５ｍｍに打ち抜いた。これに、７ｔ／ｃｍ2でプレスを施した後、改めて、１００℃窒素気流中で一昼夜真空加熱乾燥を施し、負極体とした。電解液としては、エチレンカーボネート／ジエチルカーボネート（重量比で３／７）にＬｉＰＦ6を１ｍｏｌ／Ｌの濃度に溶解して用いた。
【００１５】
上記負極とセパレータ、電解液、負極カップ、正極缶、ガスケットを用いて、Ｌｉ金属を対極として、Ｌｉ、セパレータ、負極の順で積層し、電解液を注入し、かしめて、ＣＲ２０１６型と同一形状の直径２０×１．６ｍｍ厚さのリチウムイオンコイン型二次電池を作成した。このＬｉ対極電池を用いて、室温にて、対Ｌｉ電位が１００ｍＶに達するまで、０．９ｍＡにて充電を行い、同様にセル電圧が１２００ｍＶに達するまで、放電を０．９ｍＡにて行い、充放電容量を測定した。なお、充放電共に、所定の電位に達した時点で測定を終了した。５０サイクル維持率は、以下の式に従い計算した。
【００１６】
【数１】
【実施例】
以下に、本発明を実施例により更に詳細に説明するが、本発明はその要旨を越えない限り、以下の実施例によって限定されるものではない。
実施例１
ＰＶｄＦ０．１ｇに対し、ｎ−デカン２ｇを加え、室温で自動乳鉢により５分間混合し、均一に分散させた後、負極活物質を加えてスラリーを作成した。負極活物質としてはＴｉｍｃａｌ社製の人造黒鉛ＫＳ４４（平均粒径１９．５μｍ）１．１５ｇを用い、ＫＳ４４ ９２重量％に対し、ＰＶｄＦはｎ−デカン乾燥除去後に８重量％になるように調整した。このペーストを銅箔上に塗布し、電極シートとした後、乾燥し、直径１２．５ｍｍに打ち抜いて負極体とした。この４サイクル時負極容量、及び５０サイクル容量維持率を表１に示す。
【００１８】
実施例２
ＰＶｄＦ０．１ｇに対し、ｎ−ヘキサン２ｇを加え、室温で混合し、均一に分散させた後、負極活物質を加えてスラリーを作成した。負極活物質としてＫＳ４４を用い、これ以外の操作は実施例１と同様に行った。４サイクル時負極容量、及び５０サイクル容量維持率を表１に示す。
【００１９】
実施例３
負極活物質を、ＳＥＭで平均粒径約５００ｎｍと評価した錫−アンチモン合金１．０２５ｇ（８２重量％）と、これに導電剤として平均粒径約５００ｎｍのニッケル０．１２５ｇ（１０重量％）を加えた以外は、実施例１と同様に負極体を作成した。４サイクル時負極容量、及び５０サイクル容量維持率を表１に示す。
【００２０】
比較例１
ＰＶｄＦ０．１ｇに対し、Ｎ−メチルピロリジノン２ｇを加え、室温自動乳鉢により５分間混合し、均一に溶解させた後、負極物質を加えてスラリーを作成した他は、実施例１と同様に評価した。４サイクル時負極容量、及び５０サイクル容量維持率を表１に示す。
【００２１】
比較例２
実施例３の負極活物質並びに導電剤を用いた以外は比較例１と同様にスラリーを作成し、評価した。４サイクル時負極容量、及び５０サイクル容量維持率を表１に示す。
【００２２】
【表１】
【発明の効果】
以上の説明から明らかなように、リチウム二次電池用の電極シートの作成過程で、結着剤としてポリフッ化ビニリデンを用いる場合、Ｎ−メチルピロリジノンのような極性の大きい有機溶媒を用いるよりも、炭化水素化合物溶媒を用いる方が、サイクル特性に優れた電池を作成することができる。即ち、本発明により、長寿命の電池を提供することができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a slurry for producing a lithium secondary battery electrode and use thereof. More specifically, the present invention relates to a slurry for producing a non-aqueous lithium secondary battery electrode suitable as a power source for small and lightweight electric devices and electric vehicles, and an electrode sheet for a secondary battery prepared using the slurry.
[0002]
[Prior art]
In recent years, with the widespread use of mobile phones such as video cameras, mobile phones and portable personal computers, there is an increasing demand for secondary batteries that can be used repeatedly instead of primary batteries. In particular, a non-aqueous secondary battery using a carbonaceous material as a negative electrode active material, LiMO 2 (M = Co, Ni, etc.) as a positive electrode active material, and an organic solvent as an electrolytic solution (Japanese Patent Laid-Open No. 63-121260, etc.) ) Has been developed and attracted attention. As the negative electrode active material, for example, Japanese Patent Publication No. 4-24831 proposes a soft carbon material such as coke, and Japanese Patent Application Laid-Open No. 3-252053 proposes a hard carbon material. These active materials for positive and negative electrodes are often used in the form of powder, and as a method of using this by processing into an electrode, the powder is dispersed in an appropriate powder binder and / or binder. A method of mixing with a solvent to be dissolved, and applying and drying on an aluminum foil or copper foil as a current collector is often used.
[0003]
[Problems to be solved by the invention]
However, among the electrodes prepared by using the above-described method, there are many that cause a large decrease in capacity when charging and discharging are repeated, and this has narrowed the range of selection of the active material type. For example, in the case where the active material is a negative electrode made of at least one metal element selected from Ag, Zn, Al, Ga, In, Si, Ge, Sn, Sb, As, and Pb, the capacity increases with charge / discharge cycles. It is known that deterioration is great. As these factors, it is considered that the deterioration of the active material itself accompanying the cycle and the deterioration of the electrode structure are the main causes. In order to solve these problems, in addition to improving the active material, it is necessary to create an electrode sheet that is strong against charge / discharge cycles.
[0004]
Up to now, polyvinylidene fluoride has been often used as a binder for binding an active material powder when preparing an electrode sheet for a lithium secondary battery. Since this product itself is a solid, for ease of use, it is usually dissolved in a polar organic solvent such as N-methylpyrrolidinone, mixed with the active material powder, and slurried to form a current collector metal. A method of drying after coating on a foil has been taken. However, for example, the above-described method is not sufficient for an electrode using a metal as an active material as described above, because the capacity deterioration due to the cycle is still large.
[0005]
[Means for Solving the Problems]
The present inventors have found that the above problem can be solved by adjusting an organic solvent in which a binder for binding the active material is dispersed or dissolved, and have reached the present invention.
That is, the present invention is a slurry for producing a lithium secondary battery electrode containing at least an active material, a binder and a dispersant, wherein the binder is selected from polyvinylidene fluoride and the dispersant is selected from hydrocarbon compounds. The slurry is the above solvent, the electrode sheet for a lithium secondary battery produced using the slurry, and the lithium secondary battery having the electrode sheet.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
The present invention is described in detail below.
Polyvinylidene fluoride (PVdF) powder is used as the binder for binding the electrode active material. The average degree of polymerization of PVdF is not particularly limited, but 700 to 2000, preferably 900 to 1500, and more preferably 1000 to 1300 is used. This product is dispersed with stirring in one or more solvents selected from hydrocarbon compounds, preferably saturated hydrocarbon compounds, as a dispersant. As the saturated hydrocarbon compound, a linear aliphatic hydrocarbon compound (n-alkane) is preferable. Further, among n-alkanes, solvents with less than 6 carbon atoms lack PVdF dispersibility, and those with more than 15 have a high boiling point, making it difficult to remove the solvent, and those with 6 to 15 carbon atoms are more preferred. This is most preferable because it is excellent in dispersibility. In addition, you may use it, heating the said solvent below a boiling point at the time of stirring with PVdF.
[0007]
As an active material of an electrode, what has been conventionally used as an active material for a lithium secondary battery can be used without limitation. Among these, metal elements and carbonaceous materials that can occlude and release lithium are preferable.
Examples of the metal element capable of inserting and extracting lithium include metals that form an alloy with lithium. Specifically, Ag, Zn, Al, Ga, In, Si, Ge, Sn, Sb, and Pb are preferable, and Ag, Zn, Al, Si, Ge, Sn, Pb, and Sb are preferable, and Zn, Al, Si, Ge, Sn, and Sb. In batteries using only carbon elements, such as graphite, the capacity of the negative electrode material is limited to 372 mAh / g, so that there is a limit in improving the energy density, but a material that can store a capacity exceeding this capacity. As preferred. However, it has been difficult to make a practical battery because the metal element has a large volume change with the cycle. That is, the metal can occlude a larger amount of an alkali metal element, such as lithium, than graphite, but at the same time, there are also many lithium that are trapped inside the metal and cannot be used. However, when the method of the present invention is used, even with the above-described materials, lithium can be reversibly inserted and extracted over a longer cycle.
[0008]
In addition, as described above, natural graphite, artificial graphite, carbon materials whose cores are these graphites and whose surface is coated with a carbonaceous material having relatively low crystallinity, and these graphites and relatively crystalline materials are limited. A carbon material such as a mixture with a carbonaceous material having low properties can be used, and in this case, the cycle life can be further extended as compared with the conventional case.
So far, the negative electrode material has been mainly described, but the same effect can be sufficiently expected even when applied to a positive electrode active material powder such as lithium cobalt oxide.
The reason why such an effect superior to that of the prior art is manifested may be the difference in crystal state after electrode drying of PVdF as a binder. As a model experiment, when PVdF was dissolved in a good solvent such as N-methylpyrrolidinone that has been used so far, the PVdF polymer chain crystalline microdomains were unwound and after drying and solvent removal, PVdF was almost completely removed. From the result of X-ray diffraction, it is known that the crystalline domain of PVdF remains even after removal of the solvent when the specific solvent used in the present invention is used. The remaining crystalline domains are knotted between PVdF fine fibers, which is thought to increase the strength of the electrode.
[0009]
Regarding the method of mixing the PVdF, the hydrocarbon compound solvent, and the active material, a known method such as a shaft kneader, a kneader, a hybrid mixer, an automatic mortar, or a paint shaker may be used in addition to a normal stirring method using a stirrer. it can. The stirring time at this time varies depending on the type of hydrocarbon solvent to be used, but it is preferable that the stirring does not destroy the higher-order structure of PVdF. Whether the higher order structure is maintained can be confirmed by X-ray diffraction, and the crystal peak based on the PVdF powder can be confirmed again after drying the slurry. That is, it is preferable that the binder is not completely amorphous after drying. Moreover, about the ratio which mixes the said PVdF and saturated hydrocarbon solvent, arbitrary ratios can be used, However, 1 to 100 weight% of PVdF is preferable with respect to 100 weight% of saturated hydrocarbon solvents. 3 to 50% by weight is more preferred, and 4 to 10% by weight is most preferred.
[0010]
Those mixed as described above are in the form of clay or slurry (in the present invention, these are simply referred to as slurries), and for this application, a conventionally known method can be used without limitation. it can. For example, a method of applying the slurry to a metal foil or mesh as a current collector such as copper, aluminum, or nickel using a doctor blade or a die coater can be considered. This coating may be divided into several times and overcoated.
The slurry is applied by the above-described means and then dried. However, after air drying, heat drying may be performed, or heat drying may be performed immediately after application. The air drying may be performed in a dehumidified atmosphere, but is preferably performed in dry nitrogen. When drying by heating, as in air drying, it is preferably performed at 250 ° C. or lower under dry nitrogen, and more preferably at 120 ° C. or lower for 1 hour or longer in consideration of safety.
[0011]
The ratio of the active material to PVdF may be 25% by weight or less and 3% by weight or more with respect to 100% by weight of the active material when the electrode sheet is formed after drying and removing saturated hydrocarbons. preferable. More preferably, it is 12 weight% or less and 6 weight% or more. If the PVdF ratio is too high, the capacity of the battery will be low, and if it is too low, the binding will be poor.
In addition, you may roll the obtained electrode sheet to appropriate thickness with a press.
[0012]
The lithium secondary battery having the electrode sheet of the present invention uses the electrode sheet as a sheet-like negative electrode and / or a sheet-like positive electrode in the battery, and other components are not particularly limited. There are no known ones.
As the electrolytic solution, a solution obtained by dissolving an electrolyte in a non-aqueous solvent can be used. Preferred examples of the non-aqueous solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, and butylene carbonate, chain carbonates such as dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate, cyclic esters such as γ-butyrolactone, tetrahydrofuran, methyltetrahydrofuran, and the like. And cyclic ethers.
As the electrolyte, inorganic acid lithium such as LiPF 6 or LiBF 4 is preferable, or organic acid lithium can also be used.
[0013]
In the lithium secondary battery of the present invention, in addition to the electrolyte solution, the negative electrode, and the positive electrode, a negative electrode current collector, a positive electrode current collector, a separator, and the like can be provided.
The negative electrode current collector is made of metal such as copper, nickel, and stainless steel, and copper foil is particularly preferable.
As the material of the positive electrode current collector, a metal such as aluminum, titanium, or tantalum or an alloy thereof is used, and aluminum or an alloy thereof is used, and aluminum or an alloy thereof is particularly preferable in terms of energy density.
As the separator, a porous sheet or a nonwoven fabric made of a polyolefin such as polyethylene and polypropylene can be used, and the separator is used by impregnating the electrolytic solution.
The shape of the battery is not particularly limited, and the battery is manufactured and used in a known shape such as a cylinder type in which the sheet-like electrode and the separator of the present invention are spiral.
[0014]
Next, the electrode sheet obtained by the present invention and the measurement method will be described taking the negative electrode as an example.
After adding 100% by weight of n-decane to 5% by weight of PVdF, mixing with a stirrer at room temperature and dispersing uniformly, a negative electrode active material was added to prepare a slurry. PVdF was adjusted to 8% by weight with respect to 100% by weight of the negative electrode active material after drying. Then, this paste was applied onto a copper foil, dried at 60 ° C. for about 1 hour in a nitrogen stream, and then punched out to a diameter of 12.5 mm. This was pressed at 7 t / cm 2 and then vacuum-heated and dried overnight in a 100 ° C. nitrogen stream to obtain a negative electrode body. As the electrolytic solution, LiPF 6 was dissolved in ethylene carbonate / diethyl carbonate (3/7 by weight) to a concentration of 1 mol / L.
[0015]
Using the above negative electrode and separator, electrolytic solution, negative electrode cup, positive electrode can and gasket, using Li metal as a counter electrode, stacking in the order of Li, separator, negative electrode, injecting the electrolytic solution, caulking, the same shape as CR2016 type A lithium ion coin-type secondary battery having a diameter of 20 × 1.6 mm was prepared. Using this Li counter electrode battery, at room temperature, the battery was charged at 0.9 mA until the potential to Li reaches 100 mV, and similarly discharged at 0.9 mA until the cell voltage reached 1200 mV. The discharge capacity was measured. In addition, measurement was complete | finished when the predetermined electric potential was reached in both charging and discharging. The 50 cycle maintenance rate was calculated according to the following formula.
[0016]
[Expression 1]
【Example】
EXAMPLES The present invention will be described in more detail with reference to the following examples. However, the present invention is not limited to the following examples unless it exceeds the gist.
Example 1
2 g of n-decane was added to 0.1 g of PVdF, mixed for 5 minutes with an automatic mortar at room temperature, and uniformly dispersed, and then a negative electrode active material was added to prepare a slurry. As the negative electrode active material, 1.15 g of artificial graphite KS44 (average particle size 19.5 μm) manufactured by Timcal was used, and PVdF was adjusted to 8 wt% after n-decane dry removal with respect to 92 wt% of KS44. . This paste was applied onto a copper foil to form an electrode sheet, dried, and punched out to a diameter of 12.5 mm to obtain a negative electrode body. Table 1 shows the negative electrode capacity and the 50-cycle capacity retention rate during the 4-cycle.
[0018]
Example 2
2 g of n-hexane was added to 0.1 g of PVdF, mixed at room temperature and uniformly dispersed, and then a negative electrode active material was added to prepare a slurry. KS44 was used as the negative electrode active material, and the other operations were performed in the same manner as in Example 1. Table 1 shows the negative electrode capacity at 4 cycles and the 50 cycle capacity retention rate.
[0019]
Example 3
As the negative electrode active material, 1.025 g (82% by weight) of a tin-antimony alloy evaluated by SEM to have an average particle diameter of about 500 nm, and 0.125 g (10% by weight) of nickel having an average particle diameter of about 500 nm as a conductive agent. A negative electrode body was prepared in the same manner as in Example 1 except for the addition. Table 1 shows the negative electrode capacity at 4 cycles and the 50 cycle capacity retention rate.
[0020]
Comparative Example 1
Evaluation was performed in the same manner as in Example 1 except that 2 g of N-methylpyrrolidinone was added to 0.1 g of PVdF, mixed for 5 minutes in a room temperature automatic mortar and uniformly dissolved, and then a slurry was prepared by adding a negative electrode material. . Table 1 shows the negative electrode capacity at 4 cycles and the 50 cycle capacity retention rate.
[0021]
Comparative Example 2
A slurry was prepared and evaluated in the same manner as in Comparative Example 1 except that the negative electrode active material and the conductive agent of Example 3 were used. Table 1 shows the negative electrode capacity at 4 cycles and the 50 cycle capacity retention rate.
[0022]
[Table 1]
【The invention's effect】
As is clear from the above description, when using polyvinylidene fluoride as a binder in the process of making an electrode sheet for a lithium secondary battery, rather than using a highly polar organic solvent such as N-methylpyrrolidinone. The use of the hydrocarbon compound solvent can produce a battery having excellent cycle characteristics. That is, according to the present invention, a long-life battery can be provided.
Claims (4)
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| JP2000155773A JP4292684B2 (en) | 2000-05-26 | 2000-05-26 | Slurry for producing lithium secondary battery electrode and use thereof |
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| CN107863484A (en) * | 2017-10-17 | 2018-03-30 | 合肥国轩高科动力能源有限公司 | A kind of lithium ion battery slurry-stirring process |
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