JP3892957B2 - Method for producing graphite particles - Google Patents
Method for producing graphite particles Download PDFInfo
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- JP3892957B2 JP3892957B2 JP33100697A JP33100697A JP3892957B2 JP 3892957 B2 JP3892957 B2 JP 3892957B2 JP 33100697 A JP33100697 A JP 33100697A JP 33100697 A JP33100697 A JP 33100697A JP 3892957 B2 JP3892957 B2 JP 3892957B2
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- graphite particles
- graphite
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- secondary battery
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- 239000002245 particle Substances 0.000 title claims description 149
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 title claims description 123
- 229910002804 graphite Inorganic materials 0.000 title claims description 114
- 239000010439 graphite Substances 0.000 title claims description 114
- 238000004519 manufacturing process Methods 0.000 title claims description 8
- 239000011230 binding agent Substances 0.000 claims description 23
- 238000005087 graphitization Methods 0.000 claims description 14
- 239000003054 catalyst Substances 0.000 claims description 10
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 claims description 8
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 6
- 239000012299 nitrogen atmosphere Substances 0.000 claims description 6
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 claims description 4
- 229910052759 nickel Inorganic materials 0.000 claims description 4
- 239000010703 silicon Substances 0.000 claims description 4
- 229910052710 silicon Inorganic materials 0.000 claims description 4
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims description 3
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 claims description 3
- 229910052742 iron Inorganic materials 0.000 claims description 3
- 239000010936 titanium Substances 0.000 claims description 3
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- 239000007789 gas Substances 0.000 claims description 2
- 150000001247 metal acetylides Chemical class 0.000 claims description 2
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 37
- 229910052744 lithium Inorganic materials 0.000 description 37
- 239000000203 mixture Substances 0.000 description 15
- 239000013078 crystal Substances 0.000 description 13
- -1 boron carbides Chemical class 0.000 description 10
- 238000000034 method Methods 0.000 description 9
- 238000001878 scanning electron micrograph Methods 0.000 description 8
- 239000002904 solvent Substances 0.000 description 8
- SECXISVLQFMRJM-UHFFFAOYSA-N N-Methylpyrrolidone Chemical compound CN1CCCC1=O SECXISVLQFMRJM-UHFFFAOYSA-N 0.000 description 6
- 239000002033 PVDF binder Substances 0.000 description 5
- 229910052796 boron Inorganic materials 0.000 description 5
- 239000000463 material Substances 0.000 description 5
- 238000002156 mixing Methods 0.000 description 5
- 229920002981 polyvinylidene fluoride Polymers 0.000 description 5
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 description 4
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 4
- 239000004698 Polyethylene Substances 0.000 description 4
- 229910021383 artificial graphite Inorganic materials 0.000 description 4
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- 238000010298 pulverizing process Methods 0.000 description 4
- ZMXDDKWLCZADIW-UHFFFAOYSA-N N,N-Dimethylformamide Chemical compound CN(C)C=O ZMXDDKWLCZADIW-UHFFFAOYSA-N 0.000 description 3
- 239000011280 coal tar Substances 0.000 description 3
- 150000001875 compounds Chemical class 0.000 description 3
- 239000011889 copper foil Substances 0.000 description 3
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- 239000011269 tar Substances 0.000 description 3
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- 238000012360 testing method Methods 0.000 description 3
- KMTRUDSVKNLOMY-UHFFFAOYSA-N Ethylene carbonate Chemical compound O=C1OCCO1 KMTRUDSVKNLOMY-UHFFFAOYSA-N 0.000 description 2
- UQSXHKLRYXJYBZ-UHFFFAOYSA-N Iron oxide Chemical compound [Fe]=O UQSXHKLRYXJYBZ-UHFFFAOYSA-N 0.000 description 2
- KFZMGEQAYNKOFK-UHFFFAOYSA-N Isopropanol Chemical compound CC(C)O KFZMGEQAYNKOFK-UHFFFAOYSA-N 0.000 description 2
- 229910012851 LiCoO 2 Inorganic materials 0.000 description 2
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 description 2
- WYURNTSHIVDZCO-UHFFFAOYSA-N Tetrahydrofuran Chemical compound C1CCOC1 WYURNTSHIVDZCO-UHFFFAOYSA-N 0.000 description 2
- 229910052782 aluminium Inorganic materials 0.000 description 2
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 2
- 229910052810 boron oxide Inorganic materials 0.000 description 2
- 239000011248 coating agent Substances 0.000 description 2
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- JKWMSGQKBLHBQQ-UHFFFAOYSA-N diboron trioxide Chemical compound O=BOB=O JKWMSGQKBLHBQQ-UHFFFAOYSA-N 0.000 description 2
- IEJIGPNLZYLLBP-UHFFFAOYSA-N dimethyl carbonate Chemical compound COC(=O)OC IEJIGPNLZYLLBP-UHFFFAOYSA-N 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
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- 229910001416 lithium ion Inorganic materials 0.000 description 2
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- OEPOKWHJYJXUGD-UHFFFAOYSA-N 2-(3-phenylmethoxyphenyl)-1,3-thiazole-4-carbaldehyde Chemical compound O=CC1=CSC(C=2C=C(OCC=3C=CC=CC=3)C=CC=2)=N1 OEPOKWHJYJXUGD-UHFFFAOYSA-N 0.000 description 1
- 229910052582 BN Inorganic materials 0.000 description 1
- PZNSFCLAULLKQX-UHFFFAOYSA-N Boron nitride Chemical compound N#B PZNSFCLAULLKQX-UHFFFAOYSA-N 0.000 description 1
- OIFBSDVPJOWBCH-UHFFFAOYSA-N Diethyl carbonate Chemical compound CCOC(=O)OCC OIFBSDVPJOWBCH-UHFFFAOYSA-N 0.000 description 1
- XTHFKEDIFFGKHM-UHFFFAOYSA-N Dimethoxyethane Chemical compound COCCOC XTHFKEDIFFGKHM-UHFFFAOYSA-N 0.000 description 1
- 229910015015 LiAsF 6 Inorganic materials 0.000 description 1
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Images
Classifications
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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
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- Carbon And Carbon Compounds (AREA)
- Catalysts (AREA)
- Secondary Cells (AREA)
- Battery Electrode And Active Subsutance (AREA)
Description
【0001】
【発明の属する技術分野】
本発明は、新規な黒鉛粒子、黒鉛粒子の製造法、黒鉛粒子を用いた黒鉛ペースト、リチウム二次電池用負極及びリチウム二次電池に関する。さらに詳しくは、ポータブル機器、電気自動車、電力貯蔵等に用いるのに好適な、急速充放電特性、サイクル特性等に優れたリチウム二次電池とそれを得るための黒鉛粒子及びその製造法、黒鉛粒子を用いた黒鉛ペースト、リチウム二次電池用負極並びにリチウム二次電池に関する。
【0002】
【従来の技術】
従来の黒鉛粒子としては、例えば天然黒鉛粒子、コークスを黒鉛化した人造黒鉛粒子、有機系高分子材料、ピッチ等を黒鉛化した人造黒鉛粒子、これらを粉砕した黒鉛粒子などがある。これらの黒鉛粒子は、有機系結着剤及び有機溶剤と混合して黒鉛ペーストとし、この黒鉛ペーストを銅箔の表面に塗布し、溶剤を乾燥させてリチウム二次電池用負極として使用されている。例えば、特公昭62−23433号公報に示されるように、負極に黒鉛を使用することでリチウムのデンドライトによる内部短絡の問題を解消し、サイクル特性の改良を図っている。
【0003】
しかしながら、黒鉛結晶が発達している天然黒鉛粒子及びコークスを黒鉛化した人造黒鉛粒子は、c軸方向の結晶の層間の結合力が、結晶の面方向の結合に比べて弱いため、粉砕により黒鉛層間の結合が切れ、アスペクト比が大きい、いわゆる鱗状の黒鉛粒子となる。この鱗状の黒鉛粒子は、アスペクト比が大きいために、バインダと混練して集電体に塗布して電極を作製したときに、鱗状の黒鉛粒子が集電体の面方向に配向し、その結果、黒鉛結晶へのリチウムの吸蔵・放出の繰り返しによって発生するc軸方向の歪みにより電極内部の破壊が生じ、サイクル特性が低下する問題があるばかりでなく、急速充放電特性が悪くなる傾向にある。
【0004】
また、従来のような面方向の結晶子の大きさが大きい黒鉛粒子は、リチウムの吸蔵・放出に時間を要する。さらに、従来のようなアスペクト比が大きい鱗状の黒鉛粒子は、比表面積が大きいため場合によっては得られるリチウム二次電池の第一サイクル目の不可逆容量が大きいばかりでなく、集電体との密着性が悪く、多くのバインダが必要となる問題点がある。集電体との密着性が悪いと、集電効果が低下し、放電容量、急速充放電特性、サイクル特性等が低下する問題がある。そこで、リチウム二次電池の急速充放電特性及びサイクル特性又は第一サイクル目の不可逆容量が小さく、サイクル特性若しくは第一サイクル目の不可逆容量が小さく、急速充放電特性及びサイクル特性が向上できる黒鉛粒子が要求されている。
【0005】
【発明が解決しようとする課題】
請求項1に記載の発明は、高容量で急速充放電特性に優れた、リチウム二次電池に好適な黒鉛粒子の製造法を提供するものである。
【0006】
【発明を解決するための手段】
本発明は、黒鉛粒子のX線広角回折における結晶のc軸方向(厚み方向)の結晶子の大きさが1000〜100000Å及び面方向の結晶子の大きさが800〜50Åである黒鉛粒子(黒鉛粒子中にホウ素、B 4 C、BN又はホウ素酸化物を含有するものを除く)に関する。また本発明は、前記黒鉛粒子が扁平状の粒子を複数配向面が非平行となるように集合又は結合させてなる黒鉛粒子に関する。また本発明は、前記黒鉛粒子のアスペクト比が5以下である黒鉛粒子に関する。
【0007】
また本発明は、黒鉛化可能な骨材又は黒鉛と黒鉛化可能なバインダに平均粒径が150μm以下である黒鉛化触媒を1〜50重量%添加して混合し、焼成した後粉砕することを特徴とする黒鉛粒子の製造法に関する。また本発明は、前記黒鉛化触媒が、鉄、ニッケル、チタン、ケイ素、硼素、これらの炭化物、窒化物のいずれかである黒鉛粒子の製造法に関する。また本発明は、前記黒鉛粒子に有機系結着剤及び溶剤を添加し、混合してなる黒鉛ペーストに関する。また本発明は、前記の黒鉛ペーストを集電体に塗布、一体化してなるリチウム二次電池用負極に関する。さらに本発明は、前記リチウム二次電池用負極と正極とを有してなるリチウム二次電池に関する。
【0008】
【発明の実施の形態】
本発明の黒鉛粒子は、黒鉛粒子のX線広角回折における結晶のc軸方向(厚み方向)の結晶子の大きさLc(002)が1000〜100000Å(但しX線広角回折によるLc(002)は3000Å以上は明確に測定することは困難である)及び面方向の結晶子の大きさLa(110)が800〜50Åである黒鉛粒子(黒鉛粒子中にホウ素、B 4 C、BN又はホウ素酸化物を含有するものを除く)である。該黒鉛粒子を負極に使用すると、得られるリチウム二次電池の急速充放電特性及びサイクル特性を向上させることができる。c軸方向の結晶子の大きさLc(002)又はLa(110)が上記範囲外であると、放電容量が小さくなるという問題点がある。また、この黒鉛粒子において、黒鉛粒子のX線広角回折における結晶の層間距離d(002)は3.38Å以下が好ましく、3.37〜3.35Åの範囲がより好ましい。結晶の層間距離d(002)が3.38Åを超えると放電容量が小さくなる傾向がある。
【0009】
また、本発明の黒鉛粒子は、扁平状の粒子を複数、配向面が非平行となるように集合又は結合させたものが好ましい。
本発明において、扁平状の粒子とは、長軸と短軸を有する形状の粒子のことであり、完全な球状でないものをいう。例えば鱗状、鱗片状、一部の塊状等の形状のものがこれに含まれる。
黒鉛粒子において、複数の扁平状の粒子の配向面が非平行とは、それぞれの粒子の形状において有する扁平した面、換言すれば最も平らに近い面を配向面として、複数の扁平状の粒子がそれぞれの配向面を一定の方向にそろうことなく集合している状態をいう。
【0010】
この黒鉛粒子において扁平状の粒子は集合又は結合しているが、結合とは互いの粒子が、タール、ピッチ等のバインダーを炭素化した炭素質を介して、化学的に結合している状態をいい、集合とは互いの粒子が化学的に結合してはないが、その形状等に起因して、その集合体としての形状を保っている状態をいう。機械的な強度の面から、結合しているものが好ましい。
1つの黒鉛粒子において、扁平状の粒子の集合又は結合する数としては、3個以上であることが好ましい。個々の扁平状の粒子の大きさとしては、粒径で1〜100μmであることが好ましく、これらが集合又は結合した黒鉛粒子の平均粒径の2/3以下であることが好ましい。
【0011】
該黒鉛粒子を負極に使用すると、集電体上に黒鉛粒子が配向し難く、負極黒鉛にリチウムを吸蔵・放出し易くなるため、得られるリチウム二次電池の急速充放電特性及びサイクル特性を向上させることができる。
なお、図1に本発明で用いる黒鉛粒子の一例の粒子構造の走査型電子顕微鏡写真を示す。図1において、(a)は本発明になる黒鉛粒子の外表面の走査型電子顕微鏡写真、(b)は黒鉛粒子の断面の走査型電子顕微鏡写真である。(a)においては、細かな鱗片状の黒鉛粒子が数多く、それらの粒子の配向面を非平行にして結合し、黒鉛粒子を形成している様子が観察できる。
【0012】
またアスペクト比が5以下である黒鉛粒子は、集電体上で粒子が配向し難い傾向があり、上記と同様にリチウムを吸蔵・放出し易くなるので好ましい。
アスペクト比は1.2〜5であることがより好ましい。アスペクト比が1.2未満では、粒子間の接触面積が減ることにより、導電性が低下する傾向にある。
同様の理由で、さらに好ましい範囲の下限は1.3以上である。また、さらに好ましい範囲の上限は、3以下であり、アスペクト比がこれより大きくなると、急速充放電特性が低下し易くなる傾向がある。従って、特に好ましいアスペクト比は1.3〜3である。
【0013】
なお、アスペクト比は、黒鉛粒子の長軸方向の長さをA、短軸方向の長さをBとしたとき、A/Bで表される。本発明におけるアスペクト比は、顕微鏡で黒鉛粒子を拡大し、任意に100個の黒鉛粒子を選択し、A/Bを測定し、その平均値をとったものである。
また、アスペクト比が5以下である黒鉛粒子の構造としては、より小さい黒鉛粒子の集合体又は結合体であることが好ましく、前記の、扁平状の粒子を複数、配向面が非平行となるように集合又は結合させた黒鉛粒子を用いることがより好ましい。
【0014】
本発明の黒鉛粒子の製造法に特に制限はないが、黒鉛化可能な骨材又は黒鉛と黒鉛化可能なバインダに黒鉛化触媒を1〜50重量%添加して混合し、焼成した後粉砕することによりまず黒鉛粒子を得ることが好ましい。
ついで、該黒鉛粒子に有機系結着剤及び溶剤を添加して混合し、粘度を調製した後、該混合物を集電体に塗布し、乾燥して溶剤を除去した後、加圧して一体化してリチウム二次電池用負極とすることができる。
【0015】
黒鉛化可能な骨材としては、例えば、コークス粉末、樹脂の炭化物等が使用できるが、黒鉛化できる粉末材料であれば特に制限はない。中でも、ニードルコークス等の黒鉛化しやすいコークス粉末が好ましい。
また黒鉛としては、例えば天然黒鉛粉末、人造黒鉛粉末等が使用できるが粉末状であれば特に制限はない。黒鉛化可能な骨材又は黒鉛の粒径は、本発明で作製する黒鉛粒子の粒径より小さいことが好ましい。
【0016】
さらに黒鉛化触媒としては、例えば鉄、ニッケル、チタン、ケイ素、硼素等の金属、これらの炭化物、酸化物などの黒鉛化触媒が使用できる。これらの中で、ケイ素または硼素の炭化物または酸化物が好ましい。
これらの黒鉛化触媒の添加量は、得られる黒鉛粒子に対して好ましくは1〜50重量%、より好ましくは5〜40重量%の範囲、さらに好ましくは5〜30重量%の範囲とされ、1重量%未満であると黒鉛粒子のアスペクト比及び比表面積が大きくなり黒鉛の結晶の発達が悪くなる傾向にあり、一方50重量%を超えると均一に混合することが困難で作業性が悪くなる傾向にある。
【0017】
また黒鉛化触媒の平均粒径は150μm以下であり、100μm以下であることが好ましく、50μm以下であることがさらに好ましい。平均粒径が150μmを超えるものを使用すると黒鉛粒子間の空隙が大きくなり、粒子が脆弱化するため、粉砕の際に空隙を破壊して微細化され易くなり、急速充放電性に劣る。
【0018】
バインダとしては、例えば、タール、ピッチの他、熱硬化性樹脂、熱可塑性樹脂等の有機系材料が好ましい。バインダの配合量は、扁平状の黒鉛化可能な骨材又は黒鉛に対し、5〜80重量%添加することが好ましく、10〜80重量%添加することがより好ましく、15〜80重量%添加することがさらに好ましい。バインダの量が多すぎたり少なすぎると、作製する黒鉛粒子のアスペクト比及び比表面積が大きくなり易いという傾向がある。
黒鉛化可能な骨材又は黒鉛とバインダの混合方法は、特に制限はなく、ニーダー等を用いて行われるが、バインダの軟化点以上の温度で混合することが好ましい。具体的にはバインダがピッチ、タール等の際には、50〜300℃が好ましく、熱硬化性樹脂の場合には、20〜100℃が好ましい。
【0019】
次に上記の混合物を焼成し、黒鉛化処理を行う。なお、この処理の前に上記混合物を所定形状に成形しても良い。さらに、成形後、黒鉛化前に粉砕し、粒径を調整した後、黒鉛化を行っても良い。焼成は前記混合物が酸化し難い条件で焼成することが好ましく、例えば窒素雰囲気中、アルゴンガス雰囲気中、真空中で焼成する方法が挙げられる。黒鉛化の温度は、2000℃以上が好ましく、2500℃以上であることがより好ましく、2800℃〜3200℃であることがさらに好ましい。
黒鉛化の温度が低いと、黒鉛の結晶の発達が悪く、放電容量が低くなる傾向があると共に添加した黒鉛化触媒が作製する黒鉛粒子に残存し易くなる傾向がある。黒鉛化触媒が、作製する黒鉛粒子中に残存すると、放電容量が低下する。黒鉛化の温度が高すぎると、黒鉛が昇華することがある。
【0020】
次に、得られた黒鉛化物を粉砕することが好ましい。黒鉛化物の粉砕方法は、特に制限はないが、例えばジェットミル、振動ミル、ピンミル、ハンマーミル等の既知の方法をとることができる。粉砕後の粒径は、平均粒径が1〜100μmが好ましく、10〜50μmであることがより好ましい。平均粒径が大きくなりすぎる場合は作製する電極の表面に凹凸ができ易くなる傾向がある。なお、本発明において平均粒径は、レーザー回折粒度分布計により測定することができる。
【0021】
以上に示す工程を経ることにより、本発明の黒鉛粒子を得ることができる。
得られた前記黒鉛粒子は、有機系結着剤及び溶剤を含む材料を混合して、シート状、ペレット状等の形状に成形される。
有機系結着剤としては、例えば、ポリエチレン、ポリプロピレン、エチレンプロピレンターポリマー、ブタジエンゴム、スチレンブタジエンゴム、ブチルゴム、イオン伝導率の大きな高分子化合物等が使用できる。
本発明においてイオン伝導率の大きな高分子化合物としては、ポリフッ化ビニリデン、ポリエチレンオキサイド、ポリエピクロルヒドリン、ポリフォスファゼン、ポリアクリロニトリル等が使用できる。
これらの中では、イオン伝導率の大きな高分子化合物が好ましく、ポリフッ化ビニリデンが特に好ましい。
【0022】
黒鉛粒子と有機系結着剤との混合比率は、黒鉛粒子100重量部に対して、有機系結着剤を3〜10重量部用いることが好ましい。
溶剤としては特に制限はなく、N−メチル2−ピロリドン、ジメチルホルムアミド、イソプロパノール等が用いられる。
溶剤の量に特に制限はなく、所望の粘度に調整できればよいが、混合物に対して、30〜70重量%用いられることが好ましい。
【0023】
集電体としては、例えばニッケル、銅等の箔、メッシュなどの金属集電体が使用できる。
なお一体化は、例えばロール、プレス等の成形法で行うことができ、またこれらを組み合わせて一体化してもよい。
このようにして得られた負極はリチウムイオン二次電池やリチウムポリマ二次電池等の二次電池の負極として用いられる。例えば、リチウムイオン二次電池においては、セパレータを介して正極を対向して配置し、かつ電解液を注入する。本発明によれば、従来の炭素材料を負極に使用したリチウム二次電池に比較して、急速充放電特性及びサイクル特性に優れ、かつ不可逆容量が小さいリチウム二次電池を作製することができる。
【0024】
本発明におけるリチウム二次電池の正極に用いられる材料については特に制限はなく、LiNiO2、LiCoO2、LiMn2O4等を単独又は混合して使用することができる。
電解液としては、LiClO4、LiPF6、LiAsF6、LiBF4、LiSO3CF3等のリチウム塩を例えばエチレンカーボネート、ジエチルカーボネート、ジメトキシエタン、ジメチルカーボネート、テトラヒドロフラン、プロピレンカーボネート等の非水系溶剤、ポリフッ化ビニリデン等の高分子固体電解質に溶解又は含有させたいわゆる有機電解液を使用することができる。
【0025】
液体の電解液を使用する場合に用いられるセパレータとしては、例えばポリエチレン、ポリプロピレン等のポリオレフィンを主成分とした不織布、クロス、微孔フィルム又はこれらを組み合わせたものを使用することができる。
なお、図2に円筒型リチウム二次電池の一例の一部断面正面図を示す。図2に示す円筒型リチウム二次電池は、薄板状に加工された正極1と、同様に加工された負極2が、ポリエチレン製微孔膜等のセパレータ3を介して重ね合わせたものを捲回し、これを金属製等の電池缶7に挿入し、密閉化されている。正極1は正極タブ4を介して正極蓋6に接合され、負極2は負極タブ5を介して電池底部へ接合されている。正極蓋6はガスケット8にて電池缶7へ固定されている。
【0026】
【実施例】
以下、本発明の実施例を図面を引用し説明する。
実施例1
(1)黒鉛粒子の調整
平均粒径が10μmのコークス粉末50重量部、タールピッチ20重量部、平均粒径が65μmの酸化鉄12重量部及びコールタール18重量部を混合し、200℃で1時間撹拌した。次いで、窒素雰囲気中で800℃で焼成し、さらに2800℃で焼成したのち粉砕し、平均粒径が20μmの黒鉛粒子を得た。得られた黒鉛粒子の走査型電子顕微鏡写真(SEM写真)によれば、この黒鉛粒子は、扁平状の粒子が複数配向面が非平行となるように集合又は結合した構造をしていた。得られた黒鉛粒子を100個任意に選び出し、アスペクト比の平均値を測定した結果、1.7であった。また得られた黒鉛粒子のX線広角回折による結晶の層間距離d(002)は3.360Å、面方向の結晶子の大きさLa(110)は720Å及びc軸方向の結晶子の大きさLc(002)は1800Åであった。
【0027】
(2)リチウム二次電池の作製
図2に示すリチウム二次電池は以下のようにして作製した。正極活物質としてLiCoO2を88重量%、導電剤として平均粒径が1μmの鱗片状天然黒鉛を7重量%及び結着剤としてポリフッ化ビニリデン(PVDF)を5重量%添加して、これにN−メチル−2−ピロリドンを加え混合して正極合剤のペーストを調整した。同様に負極活物質として(1)で得た黒鉛粉末90重量%及び結着剤としてPVDFを10重量%添加して、これにN−メチル−2−ピロリドンを加え混合して負極合剤のペーストを得た。
【0028】
次に正極合剤のペーストを厚みが25μmのアルミニウム箔の両面に塗布し、その後120℃で1時間真空乾燥した。真空乾燥後、ローラープレスによって電極を加圧成形して厚みを190μmとした。単位面積当りの正極合剤塗布量は49mg/cm2であり、幅が40mmで長さが285mmの大きさに切り出して正極1を作製した。但し、正極1の両端の長さ10mmの部分は正極合剤が塗布されておらずアルミニウム箔が露出しており、この一方に正極タブ4を超音波接合によって圧着している。
【0029】
一方、負極合剤のペーストを厚みが10μmの銅箔の両面に塗布し、その後120℃で1時間真空乾燥した。真空乾燥後、ローラープレスによって電極を加圧成形して厚みを175μmとした。単位面積当りの負極合剤塗布量は20mg/cm2であり、幅が40mmで長さが290mmの大きさに切り出して負極2を作製した。これを正極1と同様に、負極2の両端の長さ10mmの部分は負極合剤が塗布されておらず銅箔が露出しており、この一方に負極タブ5を超音波接合によって圧着した。
【0030】
セパレータ3は、厚みが25μmで幅が44mmのポリエチレン製の微孔膜を用いた。次いで図2に示すように正極1、セパレータ3、負極2及びセパレータ3の順で重ね合わせ、これを捲回して電極群とした。これを単三サイズの電池缶7に挿入して、負極タブ5を缶底溶接し、正極蓋6をかしめるための絞り部を設けた。この後体積比で1:1のエチレンカーボネートとジメチルカーボネートの混合溶媒に六フッ化リン酸リチウムを1モル/リットル溶解させた電解液(図示せず)を電池缶7に注入した後、正極タブ4を正極蓋6に溶接した後、正極蓋6をかしめてリチウム二次電池を得た。
得られたリチウム二次電池を用いて、充放電電流300mA、充電終止電圧を4.15V及び放電終止電圧2.8Vで充放電を繰り返した。また、充放電電流を300mAから600mAの範囲で変化させ、急速充放電も行った。このときの1サイクル目の黒鉛粒子の単位重量当たりの放電容量及び100サイクル目の黒鉛粒子の単位重量当たりの放電容量の維持率を測定した。その結果を表1に示す。
【0031】
実施例2
平均粒径が10μmのコークス粉末55重量部、タールピッチ22重量部、平均粒径が25μmの窒化硼素8重量部及びコールタール15重量部を混合し、200℃で1時間撹拌した。次いで、窒素雰囲気中で800℃で焼成し、さらに2800℃で焼成したのち粉砕し、平均粒径が20μmの黒鉛粒子を得た。得られた黒鉛粒子の走査型電子顕微鏡写真(SEM写真)によれば、この黒鉛粒子は、扁平状の粒子が複数配向面が非平行となるように集合又は結合した構造をしていた。得られた黒鉛粒子を100個任意に選び出し、アスペクト比の平均値を測定した結果、1.5であった。また得られた黒鉛粒子のX線広角回折による結晶の層間距離d(002)は3.363Å、面方向の結晶子の大きさLa(110)は560Å及びc軸方向の結晶子の大きさLc(002)は1760Åであった。
得られた黒鉛粒子を実施例1と同様の工程を経てリチウム二次電池を作製し、実施例1と同様の電池特性試験を行った。その結果を表1に示す。
【0032】
比較例1
平均粒径が15μmのコークス粉末57重量部、タールピッチ23重量部及びコールタール20重量部を混合し、200℃で1時間撹拌した。次いで、窒素雰囲気中で800℃で焼成し、さらに窒素雰囲気中で2600℃で焼成したのち粉砕し、平均粒径が20μmの黒鉛粒子を得た。得られた黒鉛粒子の走査型電子顕微鏡写真(SEM写真)によれば、この黒鉛粒子は、扁平状の粒子が複数、配向面が非平行となるように集合又は結合した構造をしていた。得られた黒鉛粒子を100個任意に選び出し、アスペクト比の平均値を測定した結果、2.0であった。また得られた黒鉛粒子のX線広角回折による結晶の層間距離d(002)は3.390Å、面方向の結晶子の大きさLa(110)は460Å及びc軸方向の結晶子の大きさLc(002)は300Åであった。
得られた黒鉛粒子を比較例1と同様の工程を経てリチウム二次電池を作製し、実施例1と同様の電池特性試験を行った。その結果を表1に示す。
【0033】
比較例2
焼成を3000℃で行った以外は、比較例1と同様の工程を経て、平均粒径が20μmの黒鉛粒子を得た。得られた黒鉛粒子の走査型電子顕微鏡写真(SEM写真)によれば、この黒鉛粒子は、扁平状の粒子が複数配向面が非平行となるように集合又は結合した構造をしていた。得られた黒鉛粒子を100個任意に選び出し、アスペクト比の平均値を測定した結果、2.2であった。また得られた黒鉛粒子のX線広角回折による結晶の層間距離d(002)は3.357Å、面方向の結晶子の大きさLa(110)は1730Å及びc軸方向の結晶子の大きさLc(002)は2050Åであった。
得られた黒鉛粒子を実施例1と同様の工程を経てリチウム二次電池を作製し、実施例1と同様の電池特性試験を行った。その結果を表1に示す。
【0034】
【表1】
【0035】
表1に示されるように、本発明の黒鉛粒子を用いたリチウム二次電池は、充放電電流が300mAにおける放電容量において高容量であることが示され、また充放電電流を600mAに上げても放電容量は90%以上維持し、急速充放電特性に優れることが明らかである。
【0036】
【発明の効果】
請求項1に記載の製造法によれば、高容量で急速充放電特性に優れた、リチウム二次電池に好適な黒鉛粒子が得られる。
【図面の簡単な説明】
【図1】本発明に用いる黒鉛粒子の走査型電子顕微鏡写真であり、(a)は粒子の外表面の写真、(b)は粒子の断面の写真である。
【図2】円筒型リチウム二次電池の一部断面正面図である。
【符号の説明】
1 正極
2 負極
3 セパレータ
4 正極タブ
5 負極タブ
6 正極蓋
7 電池缶
8 ガスケット[0001]
BACKGROUND OF THE INVENTION
The present invention relates to novel graphite particle, method for producing graphite particles, graphite paste using the graphite particle, about negative Goku及beauty Lithium secondary battery for a lithium secondary battery. More specifically, a lithium secondary battery excellent in rapid charge / discharge characteristics, cycle characteristics, etc., suitable for use in portable equipment, electric vehicles, power storage, etc., and graphite particles for obtaining the same, and a method for producing the same, graphite particles The present invention relates to a graphite paste using lithium, a negative electrode for a lithium secondary battery, and a lithium secondary battery.
[0002]
[Prior art]
Examples of conventional graphite particles include natural graphite particles, artificial graphite particles obtained by graphitizing coke, organic polymer materials, artificial graphite particles obtained by graphitizing pitch and the like, and graphite particles obtained by pulverizing these. These graphite particles are mixed with an organic binder and an organic solvent to form a graphite paste. The graphite paste is applied to the surface of a copper foil, and the solvent is dried to be used as a negative electrode for a lithium secondary battery. . For example, as disclosed in Japanese Examined Patent Publication No. 62-23433, the use of graphite for the negative electrode eliminates the problem of internal short circuit due to lithium dendrite and improves the cycle characteristics.
[0003]
However, natural graphite particles in which graphite crystals are developed and artificial graphite particles graphitized from coke have a weaker bonding force between crystals in the c-axis direction than in the crystal plane direction. Bonds between layers are broken and so-called scaly graphite particles having a large aspect ratio are obtained. Since the scaly graphite particles have a large aspect ratio, when the electrodes are produced by kneading with a binder and applying to the current collector, the scaly graphite particles are oriented in the surface direction of the current collector, and as a result In addition, the c-axis direction strain generated by repeated insertion and extraction of lithium into and from the graphite crystal causes breakdown inside the electrode, resulting in a problem that cycle characteristics deteriorate, and rapid charge / discharge characteristics tend to deteriorate. .
[0004]
Further, conventional graphite particles having a large crystallite size in the plane direction require time for occlusion / release of lithium. Furthermore, the conventional scaly graphite particles with a large aspect ratio have a large specific surface area, so that in some cases, not only the irreversible capacity of the first cycle of the obtained lithium secondary battery is large, but also the close contact with the current collector. There is a problem that a lot of binders are required. If the adhesiveness with the current collector is poor, there is a problem that the current collecting effect is lowered and the discharge capacity, rapid charge / discharge characteristics, cycle characteristics, etc. are lowered. Therefore, graphite particles that can improve the rapid charge / discharge characteristics and cycle characteristics of the lithium secondary battery with low rapid charge / discharge characteristics and cycle characteristics or small irreversible capacity of the first cycle and low cycle characteristics or irreversible capacity of the first cycle. Is required.
[0005]
[Problems to be solved by the invention]
The invention described in 請 Motomeko 1 was excellent in rapid charge-discharge characteristics at high capacity, there is provided a process for the preparation of suitable graphite particles in the lithium secondary battery.
[0006]
[Means for Solving the Invention]
The present invention relates to graphite particles (graphite having a crystallite size in the c-axis direction (thickness direction) of 1000 to 100000 の and a crystallite size in the plane direction of 800 to 50Å in X-ray wide-angle diffraction of graphite particles. Except those containing boron, B 4 C, BN or boron oxide in the particles) . Or the invention relates to graphite particles, wherein the graphite particles are allowed to set or combined to a plurality orientation plane of flat particles are non-parallel. The present invention also relates to a graphite particle having an aspect ratio of 5 or less.
[0007]
Further, the present invention is to add 1 to 50 wt% of a graphitization catalyst having an average particle size of 150 μm or less to a graphitizable aggregate or graphite and a graphitizable binder, mix, calcinate, and pulverize. a process for producing the black lead particles you characterized. The present invention also relates to a method for producing graphite particles, wherein the graphitization catalyst is any one of iron, nickel, titanium, silicon, boron, carbides thereof, and nitrides thereof . Or the present invention comprises adding an organic binder and a solvent to the graphite particles child relates graphite paste made by mixing. The present invention also relates to a negative electrode for a lithium secondary battery obtained by applying and integrating the above graphite paste to a current collector. Furthermore, this invention relates to the lithium secondary battery which has the said negative electrode for lithium secondary batteries, and a positive electrode.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
The graphite particles of the present invention have a crystallite size Lc (002) in the c-axis direction (thickness direction) of the crystal in the X-ray wide-angle diffraction of the graphite particles of 1000 to 100,000 (however, Lc (002) by the X-ray wide-angle diffraction is 3,000 and above are difficult to measure clearly) and graphite particles whose plane direction crystallite size La (110) is 800 to 50 Å (boron, B 4 C, BN or boron oxide in the graphite particles ) Is excluded) . When the graphite particles are used for the negative electrode, the rapid charge / discharge characteristics and cycle characteristics of the obtained lithium secondary battery can be improved . If the crystallite size Lc (002) or La (110) in the c- axis direction is outside the above range, there is a problem that the discharge capacity becomes small. Further, in this graphite particle, the crystal interlayer distance d (002) in the X-ray wide angle diffraction of the graphite particle is preferably 3.38 mm or less, and more preferably in the range of 3.37 to 3.35 mm. When the crystal interlayer distance d (002) exceeds 3.38 mm, the discharge capacity tends to be small.
[0009]
Moreover, the graphite particles of the present invention are preferably those in which a plurality of flat particles are aggregated or bonded so that the orientation planes are non-parallel.
In the present invention, flat particles are particles having a major axis and a minor axis, and are not completely spherical. This includes, for example, those having a shape such as a scale shape, a scale shape, and a partial lump shape.
In graphite particles, the orientation planes of a plurality of flat particles are non-parallel. The flat surfaces in the shape of each particle, in other words, the plane that is closest to the plane is the orientation plane, and the plurality of flat particles are A state in which the orientation planes are gathered together in a certain direction.
[0010]
In this graphite particle, the flat particles are aggregated or bonded, but the bond is a state in which the particles are chemically bonded through carbonaceous carbonized binder such as tar and pitch. The term “aggregate” refers to a state in which the particles are not chemically bonded, but the shape of the aggregate is maintained due to the shape and the like. From the viewpoint of mechanical strength, those bonded are preferable.
In one graphite particle, the number of flat particles aggregated or bonded is preferably 3 or more. The size of the individual flat particles is preferably 1 to 100 μm in particle size, and preferably 2/3 or less of the average particle size of the aggregated or bonded graphite particles.
[0011]
When the graphite particles are used for the negative electrode, the graphite particles are difficult to orient on the current collector, and it becomes easier to occlude and release lithium into the negative electrode graphite, improving the rapid charge / discharge characteristics and cycle characteristics of the resulting lithium secondary battery. Can be made.
FIG. 1 shows a scanning electron micrograph of the particle structure of an example of the graphite particles used in the present invention. In FIG. 1, (a) is a scanning electron micrograph of the outer surface of the graphite particles according to the present invention, and (b) is a scanning electron micrograph of the cross section of the graphite particles. In (a), it can be observed that there are many fine scaly graphite particles that are bonded with the orientation planes of these particles non-parallel to form graphite particles.
[0012]
Further, graphite particles having an aspect ratio of 5 or less are preferred because the particles tend not to be oriented on the current collector, and lithium can be easily inserted and extracted as described above.
The aspect ratio is more preferably 1.2-5. If the aspect ratio is less than 1.2, the contact area between particles tends to decrease, and the conductivity tends to decrease.
For the same reason, the lower limit of the more preferable range is 1.3 or more. Further, the upper limit of the more preferable range is 3 or less, and when the aspect ratio is larger than this, the rapid charge / discharge characteristics tend to be deteriorated. Therefore, a particularly preferable aspect ratio is 1.3 to 3.
[0013]
The aspect ratio is represented by A / B, where A is the length in the major axis direction of the graphite particles and B is the length in the minor axis direction. The aspect ratio in the present invention is obtained by enlarging graphite particles with a microscope, arbitrarily selecting 100 graphite particles, measuring A / B, and taking the average value.
Further, the structure of the graphite particles having an aspect ratio of 5 or less is preferably an aggregate or a combination of smaller graphite particles, and a plurality of the above-mentioned flat particles and the orientation planes are non-parallel. It is more preferable to use graphite particles aggregated or bonded to each other.
[0014]
The method for producing the graphite particles of the present invention is not particularly limited, but 1 to 50% by weight of a graphitization catalyst is added to a graphitizable aggregate or graphite and a graphitizable binder, mixed, fired and then pulverized. It is preferable to obtain graphite particles first.
Next, an organic binder and a solvent are added to the graphite particles and mixed to adjust the viscosity. Then, the mixture is applied to a current collector, dried to remove the solvent, and then pressurized to be integrated. Thus, a negative electrode for a lithium secondary battery can be obtained.
[0015]
Examples of the aggregate that can be graphitized include coke powder and resin carbide, but there is no particular limitation as long as it is a powder material that can be graphitized. Among these, coke powder that is easily graphitized such as needle coke is preferable.
Moreover, as graphite, natural graphite powder, artificial graphite powder, etc. can be used, for example, but there is no restriction | limiting in particular if it is a powder form. The particle size of the graphitizable aggregate or graphite is preferably smaller than the particle size of the graphite particles produced in the present invention.
[0016]
Further, as the graphitization catalyst, for example, a graphitization catalyst such as a metal such as iron, nickel, titanium, silicon, or boron, or a carbide or oxide thereof can be used. Of these, silicon or boron carbides or oxides are preferred.
The addition amount of these graphitization catalysts is preferably 1 to 50% by weight, more preferably 5 to 40% by weight, and further preferably 5 to 30% by weight with respect to the obtained graphite particles. If it is less than% by weight, the aspect ratio and specific surface area of the graphite particles tend to increase and the development of graphite crystals tends to deteriorate. On the other hand, if it exceeds 50% by weight, it is difficult to mix uniformly and workability tends to deteriorate. It is in.
[0017]
The average particle diameter of the graphitizing catalyst Ri der below 150 [mu] m, it is good Mashiku is 100μm or less, more preferably 50μm or less. Average particle diameter becomes large gaps between the graphite particles by using the in excess of 150 [mu] m, since the particles are fragile, easily be miniaturized by destroying the voids during the milling, Ru inferior in rapid charging and discharging property.
[0018]
As the binder, for example, an organic material such as a thermosetting resin and a thermoplastic resin is preferable in addition to tar and pitch. The blending amount of the binder is preferably 5 to 80% by weight, more preferably 10 to 80% by weight, and more preferably 15 to 80% by weight based on the flat graphitizable aggregate or graphite. More preferably. If the amount of the binder is too large or too small, the aspect ratio and specific surface area of the graphite particles to be produced tend to increase.
The method for mixing the graphitizable aggregate or graphite and the binder is not particularly limited and is performed using a kneader or the like, but it is preferable to mix at a temperature equal to or higher than the softening point of the binder. Specifically, when the binder is pitch, tar or the like, 50 to 300 ° C is preferable, and when the binder is a thermosetting resin, 20 to 100 ° C is preferable.
[0019]
Next, the above mixture is fired and graphitized. In addition, you may shape | mold the said mixture in a predetermined shape before this process. Furthermore, after forming and pulverizing before graphitization to adjust the particle size, graphitization may be performed. Firing is preferably performed under conditions where the mixture is not easily oxidized, and examples thereof include a method of baking in a nitrogen atmosphere, an argon gas atmosphere, and in a vacuum. The graphitization temperature is preferably 2000 ° C. or higher, more preferably 2500 ° C. or higher, and further preferably 2800 ° C. to 3200 ° C.
When the graphitization temperature is low, the development of graphite crystals tends to be poor, the discharge capacity tends to be low, and the added graphitization catalyst tends to remain in the graphite particles produced. When the graphitization catalyst remains in the graphite particles to be produced, the discharge capacity decreases. If the graphitization temperature is too high, the graphite may sublime.
[0020]
Next, it is preferable to grind the obtained graphitized material. The method for pulverizing the graphitized material is not particularly limited, and known methods such as a jet mill, a vibration mill, a pin mill, a hammer mill and the like can be used. As for the particle size after pulverization, the average particle size is preferably 1 to 100 μm, and more preferably 10 to 50 μm. If the average particle size becomes too large, the surface of the electrode to be produced tends to be uneven. In the present invention, the average particle diameter can be measured with a laser diffraction particle size distribution meter.
[0021]
By passing through the process shown above, the graphite particle of this invention can be obtained.
The obtained graphite particles are formed into a sheet shape, a pellet shape or the like by mixing a material containing an organic binder and a solvent.
As the organic binder, for example, polyethylene, polypropylene, ethylene propylene terpolymer, butadiene rubber, styrene butadiene rubber, butyl rubber, a high molecular compound having high ionic conductivity, and the like can be used.
In the present invention, polyvinylidene fluoride, polyethylene oxide, polyepichlorohydrin, polyphosphazene, polyacrylonitrile and the like can be used as the polymer compound having a high ionic conductivity.
Among these, a polymer compound having a high ionic conductivity is preferable, and polyvinylidene fluoride is particularly preferable.
[0022]
The mixing ratio of the graphite particles and the organic binder is preferably 3 to 10 parts by weight of the organic binder with respect to 100 parts by weight of the graphite particles.
There is no restriction | limiting in particular as a solvent, N-methyl 2-pyrrolidone, a dimethylformamide, isopropanol etc. are used.
There is no restriction | limiting in particular in the quantity of a solvent, Although it should just be able to adjust to a desired viscosity, It is preferable to use 30 to 70 weight% with respect to a mixture.
[0023]
As the current collector, for example, a metal current collector such as a foil or mesh of nickel, copper or the like can be used.
The integration can be performed by a molding method such as a roll or a press, or these may be combined and integrated.
The negative electrode thus obtained is used as a negative electrode for secondary batteries such as lithium ion secondary batteries and lithium polymer secondary batteries. For example, in a lithium ion secondary battery, a positive electrode is disposed opposite to a separator, and an electrolytic solution is injected. According to the present invention, it is possible to produce a lithium secondary battery that is excellent in rapid charge / discharge characteristics and cycle characteristics and has a small irreversible capacity as compared with a lithium secondary battery that uses a conventional carbon material as a negative electrode.
[0024]
There is no particular limitation on the material used for a cathode of a lithium secondary battery of the present invention may be used alone or as a mixture of LiNiO 2, LiCoO 2, LiMn 2
Examples of the electrolyte include lithium salts such as LiClO 4 , LiPF 6 , LiAsF 6 , LiBF 4 , and LiSO 3 CF 3, for example, nonaqueous solvents such as ethylene carbonate, diethyl carbonate, dimethoxyethane, dimethyl carbonate, tetrahydrofuran, and propylene carbonate; A so-called organic electrolytic solution dissolved or contained in a polymer solid electrolyte such as vinylidene chloride can be used.
[0025]
As a separator used when using a liquid electrolytic solution, for example, a nonwoven fabric, a cloth, a microporous film, or a combination thereof, which is mainly composed of a polyolefin such as polyethylene or polypropylene, can be used.
FIG. 2 shows a partial cross-sectional front view of an example of a cylindrical lithium secondary battery. The cylindrical lithium secondary battery shown in FIG. 2 is formed by winding a thin plate-like positive electrode 1 and a similarly processed negative electrode 2 with a
[0026]
【Example】
Embodiments of the present invention will be described below with reference to the drawings.
Example 1
(1) Adjustment of graphite particles 50 parts by weight of coke powder having an average particle diameter of 10 μm, 20 parts by weight of tar pitch, 12 parts by weight of iron oxide having an average particle diameter of 65 μm, and 18 parts by weight of coal tar are mixed at 200 ° C. Stir for hours. Subsequently, it was fired at 800 ° C. in a nitrogen atmosphere, and further fired at 2800 ° C. and then pulverized to obtain graphite particles having an average particle diameter of 20 μm. According to the scanning electron micrograph (SEM photograph) of the obtained graphite particles, the graphite particles had a structure in which flat particles were assembled or bonded so that a plurality of orientation planes were non-parallel. As a result of arbitrarily selecting 100 obtained graphite particles and measuring the average value of the aspect ratio, it was 1.7. Further, the obtained graphite particles have an inter-crystal distance d (002) of 3.360 mm, a crystallite size La (110) in the plane direction of 720 mm, and a crystallite size Lc in the c-axis direction by X-ray wide angle diffraction. (002) was 1800cm.
[0027]
(2) Production of Lithium Secondary Battery The lithium secondary battery shown in FIG. 2 was produced as follows. 88% by weight of LiCoO 2 as a positive electrode active material, 7% by weight of scaly natural graphite having an average particle diameter of 1 μm as a conductive agent, and 5% by weight of polyvinylidene fluoride (PVDF) as a binder are added to the N -Methyl-2-pyrrolidone was added and mixed to prepare a paste of the positive electrode mixture. Similarly, 90% by weight of the graphite powder obtained in (1) as a negative electrode active material and 10% by weight of PVDF as a binder are added, and N-methyl-2-pyrrolidone is added thereto and mixed to paste a negative electrode mixture. Got.
[0028]
Next, the paste of the positive electrode mixture was applied to both surfaces of an aluminum foil having a thickness of 25 μm, and then vacuum-dried at 120 ° C. for 1 hour. After vacuum drying, the electrode was pressure-formed by a roller press to a thickness of 190 μm. The coating amount of the positive electrode mixture per unit area was 49 mg / cm 2 , cut into a size of 40 mm in width and 285 mm in length to produce the positive electrode 1. However, the positive electrode mixture is not applied to the 10 mm long portions at both ends of the positive electrode 1 and the aluminum foil is exposed, and the
[0029]
On the other hand, the paste of the negative electrode mixture was applied to both surfaces of a copper foil having a thickness of 10 μm, and then vacuum-dried at 120 ° C. for 1 hour. After vacuum drying, the electrode was pressure-formed by a roller press to a thickness of 175 μm. The coating amount of the negative electrode mixture per unit area was 20 mg / cm 2 , and the negative electrode 2 was produced by cutting it into a size of 40 mm in width and 290 mm in length. Similarly to the positive electrode 1, the negative electrode mixture was not applied to the 10 mm long portions at both ends of the negative electrode 2, and the copper foil was exposed, and the negative electrode tab 5 was pressure bonded to this one by ultrasonic bonding.
[0030]
As the
Using the obtained lithium secondary battery, charge / discharge was repeated at a charge / discharge current of 300 mA, a charge end voltage of 4.15 V, and a discharge end voltage of 2.8 V. Moreover, the charge / discharge current was changed in the range of 300 mA to 600 mA, and rapid charge / discharge was also performed. At this time, the discharge capacity per unit weight of the graphite particles in the first cycle and the maintenance ratio of the discharge capacity per unit weight of the graphite particles in the 100th cycle were measured. The results are shown in Table 1.
[0031]
Example 2
55 parts by weight of coke powder having an average particle diameter of 10 μm, 22 parts by weight of tar pitch, 8 parts by weight of boron nitride having an average particle diameter of 25 μm, and 15 parts by weight of coal tar were mixed and stirred at 200 ° C. for 1 hour. Subsequently, it was fired at 800 ° C. in a nitrogen atmosphere, and further fired at 2800 ° C. and then pulverized to obtain graphite particles having an average particle diameter of 20 μm. According to the scanning electron micrograph (SEM photograph) of the obtained graphite particles, the graphite particles had a structure in which flat particles were assembled or bonded so that a plurality of orientation planes were non-parallel. As a result of arbitrarily selecting 100 obtained graphite particles and measuring the average value of the aspect ratio, it was 1.5. Further, the obtained graphite particles were measured by X-ray wide-angle diffraction, the crystal interlayer distance d (002) was 3.363 Å, the crystallite size La (110) in the plane direction was 560 Å, and the crystallite size Lc in the c-axis direction. (002) was 1760cm.
A lithium secondary battery was produced from the obtained graphite particles through the same steps as in Example 1, and a battery characteristic test similar to that in Example 1 was performed. The results are shown in Table 1.
[0032]
Comparative Example 1
57 parts by weight of coke powder having an average particle size of 15 μm, 23 parts by weight of tar pitch and 20 parts by weight of coal tar were mixed and stirred at 200 ° C. for 1 hour. Subsequently, it was fired at 800 ° C. in a nitrogen atmosphere, and further fired at 2600 ° C. in a nitrogen atmosphere and then pulverized to obtain graphite particles having an average particle diameter of 20 μm. According to the scanning electron micrograph (SEM photograph) of the obtained graphite particles, the graphite particles had a structure in which a plurality of flat particles were assembled or combined so that the orientation planes were non-parallel. As a result of arbitrarily selecting 100 obtained graphite particles and measuring the average value of the aspect ratio, it was 2.0. In addition, the obtained graphite particles have a crystal interlayer distance d (002) by X-ray wide angle diffraction of 3.390 mm, a crystallite size La (110) in the plane direction of 460 mm, and a crystallite size Lc in the c-axis direction. (002) was 300 kg.
A lithium secondary battery was produced from the obtained graphite particles through the same steps as in Comparative Example 1, and the same battery characteristic test as in Example 1 was performed. The results are shown in Table 1.
[0033]
Comparative Example 2
Except for firing at 3000 ° C., graphite particles having an average particle size of 20 μm were obtained through the same steps as in Comparative Example 1. According to the scanning electron micrograph (SEM photograph) of the obtained graphite particles, the graphite particles had a structure in which flat particles were assembled or bonded so that a plurality of orientation planes were non-parallel. As a result of arbitrarily selecting 100 obtained graphite particles and measuring the average value of the aspect ratio, it was 2.2. Further, the obtained graphite particles have an inter-crystal distance d (002) of 3.357 mm, a crystallite size La (110) in the plane direction of 1730 mm and a crystallite size Lc in the c-axis direction by X-ray wide angle diffraction. (002) was 2050 kg.
A lithium secondary battery was produced from the obtained graphite particles through the same steps as in Example 1, and a battery characteristic test similar to that in Example 1 was performed. The results are shown in Table 1.
[0034]
[Table 1]
[0035]
As shown in Table 1, the lithium secondary battery using the graphite particles of the present invention is shown to have a high charge / discharge current at a discharge capacity of 300 mA, and even when the charge / discharge current is increased to 600 mA. It is clear that the discharge capacity is maintained at 90% or more and the rapid charge / discharge characteristics are excellent.
[0036]
【The invention's effect】
According to the production method described in 請 Motomeko 1, excellent rapid charge-discharge characteristics at high capacity, suitable graphite particles are obtained in the lithium secondary battery.
[Brief description of the drawings]
FIG. 1 is a scanning electron micrograph of graphite particles used in the present invention, (a) is a photograph of the outer surface of the particles, and (b) is a photograph of a cross section of the particles.
FIG. 2 is a partial cross-sectional front view of a cylindrical lithium secondary battery.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Positive electrode 2
Claims (1)
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JP4547504B2 (en) * | 1999-10-04 | 2010-09-22 | 中央電気工業株式会社 | Graphite material suitable for negative electrode of lithium ion secondary battery and method for producing the same |
WO2005069410A1 (en) * | 2004-01-16 | 2005-07-28 | Hitachi Chemical Co., Ltd. | Negative electrode for lithium secondary battery and lithium secondary battery |
WO2006022100A1 (en) * | 2004-08-27 | 2006-03-02 | Jfe Chemical Corporation | Graphite material, method for producing same, negative electrode material for lithium ion secondary battery, negative electrode for lithium ion secondary battery, and lithium ion secondary battery |
JP4707570B2 (en) * | 2006-01-20 | 2011-06-22 | Jfeケミカル株式会社 | Method for producing fine graphite particles |
JP5118877B2 (en) | 2007-04-27 | 2013-01-16 | トヨタ自動車株式会社 | Secondary battery |
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