JP5395350B2 - Sheet-like negative electrode for lithium ion secondary battery and lithium ion secondary battery using the same - Google Patents
Sheet-like negative electrode for lithium ion secondary battery and lithium ion secondary battery using the same Download PDFInfo
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Description
本発明は、リチウムイオン二次電池用シート状負極に関する。 The present invention relates to a sheet-like negative electrode for a lithium ion secondary battery.
近年、環境影響への配慮から、風力発電や潮流発電、太陽光発電のような自然力を利用した発電方式への関心が高まっている。このような自然力を利用した発電方式は、発電量が一定しない。例えば、風力発電では電力消費量が少ない夜間に発電量が大きくなる傾向があり、太陽光発電では夜間には全く発電されない。 In recent years, due to consideration for environmental impact, interest in power generation methods using natural power such as wind power generation, tidal current power generation, and solar power generation has increased. In such a power generation method using natural force, the power generation amount is not constant. For example, wind power generation tends to increase power generation at night when power consumption is low, and solar power generation does not generate power at all at night.
このため、自然力を利用した発電方式の活用には、電力消費の少ない時間帯に発電した電気を蓄電し、電力消費の大きい時間帯に蓄電した電気エネルギーを放出する技術が不可欠である。リチウムイオン二次電池は、エネルギー密度が高く高容量であるので、自然力を利用した発電方式の上記欠点を補うための蓄電池として最適である。 For this reason, in order to utilize a power generation method using natural power, a technique for storing electricity generated in a time zone with low power consumption and discharging the electrical energy stored in a time zone with high power consumption is indispensable. A lithium ion secondary battery has a high energy density and a high capacity, and is therefore optimal as a storage battery to compensate for the above-described drawbacks of the power generation method using natural force.
このようなリチウムイオン二次電池には、炭素負極が用いられており、炭素負極は、活物質である炭素質粒子と、結着剤と、溶剤と、を混合してスラリーとなし、銅箔に塗布し、乾燥、プレスする方法により製造されているが、近年、銅価格が高騰し負極製造コストが上昇している。このため、銅箔を用いない負極が望まれている。また、大規模蓄電には大量のリチウムイオン二次電池が必要であるため、大規模蓄電向きの安価なリチウムイオン二次電池に対する要望が高まっている。 In such a lithium ion secondary battery, a carbon negative electrode is used. The carbon negative electrode is a slurry obtained by mixing carbonaceous particles as an active material, a binder, and a solvent, and a copper foil. However, in recent years, the price of copper has risen and the negative electrode manufacturing cost has increased. For this reason, the negative electrode which does not use copper foil is desired. Moreover, since a large amount of lithium ion secondary batteries are required for large-scale power storage, there is an increasing demand for inexpensive lithium-ion secondary batteries suitable for large-scale power storage.
銅箔を用いない負極に関する技術としては、下記特許文献１がある。 As a technique regarding the negative electrode which does not use copper foil, there is the following Patent Document 1.
特許文献１は、膨張黒鉛シートを負極に用いる技術である。しかし、膨張黒鉛シートの価格が高いため、電池の低コスト化を図れないという問題がある。 Patent document 1 is a technique using an expanded graphite sheet for a negative electrode. However, since the expanded graphite sheet is expensive, there is a problem that the cost of the battery cannot be reduced.
本発明は、上記に鑑みなされたものであって、高性能な炭素負極を低コストで提供することを目的とする。 This invention is made | formed in view of the above, Comprising: It aims at providing a high performance carbon negative electrode at low cost.
上記課題を解決するための本発明は、次のように構成されている。
リチウムイオンを吸蔵脱離する炭素質粒子と、繊維状炭素質物と、前記炭素質粒子及び前記繊維状炭素質物を結着する、熱可塑性樹脂からなる結着剤と、を有し、負極集電体を有しないリチウムイオン二次電池用シート状負極であって、０．０５〜１００μｍの範囲の気孔の気孔体積が質量当たり０．０７〜１．０ｃｃ／ｇであり、前記結着剤は、その融点以上に加熱しつつ加圧されて、前記炭素質粒子及び前記繊維状炭素質物を結着していることを特徴とするリチウムイオン二次電池用シート状負極。
The present invention for solving the above problems is configured as follows.
A carbonaceous particle that occludes and desorbs lithium ions, a fibrous carbonaceous material, and a binder made of a thermoplastic resin that binds the carbonaceous particle and the fibrous carbonaceous material , and a negative electrode current collector a lithium ion secondary battery for a sheet-like negative electrode having no body, Ri 0.07~1.0cc / g der per pore volume mass of the pores in the range of 0.05～100Myuemu, the binder A sheet-like negative electrode for a lithium ion secondary battery, wherein the carbonaceous particles and the fibrous carbonaceous material are bound by being heated while being heated to the melting point or higher .
この構成では、負極が炭素質物と結着剤とから構成され、シート状であるため、銅などの集電体を用いなくともよい。よって、コストの低減を図れる。 In this configuration, since the negative electrode is composed of a carbonaceous material and a binder and is in the form of a sheet, a current collector such as copper may not be used. Therefore, cost can be reduced.
また、マクロ孔と呼ばれる気孔径（直径）０．０５〜１００μｍの範囲の気孔は、電解液を浸透させやすく、且つリチウムイオンの伝導性がよい。上記構成では、このマクロ孔が質量当たり０．０７〜１．０ｃｃ／ｇである。このため、負極活物質である炭素質物の周囲に十分な量の電解液が供給され、リチウムイオンの吸蔵・脱離がスムースに進行するので、充放電反応がスムースに進行し、十分な充放電効率が得られる。なお、マクロ孔が１．０ｃｃ／ｇを超えると、実質的に気孔量が多くなりすぎて体積当たりの容量の低下を招くことになるので好ましくない。
また、炭素質粒子を結着する結着剤は、通常、導電性が低いため、シート状負極の導電性を高めるために繊維状炭素質物を加えることが好ましい。また、良好な結着性能を得るためには、結着剤として熱可塑性樹脂を用いることが好ましい。
In addition, pores having a pore diameter (diameter) in the range of 0.05 to 100 μm called macropores are easy to permeate the electrolyte and have good lithium ion conductivity. In the said structure, this macropore is 0.07-1.0 cc / g per mass. For this reason, a sufficient amount of electrolyte is supplied around the carbonaceous material, which is the negative electrode active material, and the lithium ion insertion / desorption proceeds smoothly, so that the charge / discharge reaction proceeds smoothly and sufficient charge / discharge occurs. Efficiency is obtained. In addition, it is not preferable that the macropores exceed 1.0 cc / g because the amount of pores substantially increases and the capacity per volume is reduced.
Moreover, since the binder for binding the carbonaceous particles usually has low conductivity, it is preferable to add a fibrous carbonaceous material in order to increase the conductivity of the sheet-like negative electrode. In order to obtain good binding performance, it is preferable to use a thermoplastic resin as the binder.
ここで、繊維状炭素質物とは、炭素繊維、カーボンナノファイバー、気相成長炭素繊維、カーボンナノチューブ等の、繊維形態をとる炭素質物全てを含む概念である。 Here, the fibrous carbonaceous material is a concept including all carbonaceous materials in the form of fibers, such as carbon fibers, carbon nanofibers, vapor-grown carbon fibers, and carbon nanotubes.
なお、異なる粒径の炭素質粒子を混合して用い、粒径の小さい炭素質粒子を導電剤としてもよい。 Note that carbonaceous particles having different particle diameters may be mixed and used, and carbonaceous particles having a small particle diameter may be used as the conductive agent.
上記第１の発明において、前記結着剤が、熱可塑性樹脂である、とする構成とすることができる。 In the first invention, the binder may be a thermoplastic resin.
良好な結着性能を得るためには、結着剤として熱可塑性樹脂を用いることが好ましい。 In order to obtain good binding performance, it is preferable to use a thermoplastic resin as the binder.
上記課題を解決するための本発明に係るリチウムイオン二次電池用シート状負極を製造する方法は、次のように構成されていることが好ましい。
リチウムイオンを吸蔵脱離する炭素質粒子と、不溶性結着剤と、可溶性気孔形成剤と、を含む負極合剤を加圧し、シート状負極前駆体を作製するシート状負極前駆体作製工程と、溶剤を用いて、前記シート状負極前駆体溶剤から前記可溶性気孔形成剤を除去する除去工程と、前記除去工程の後、前記溶剤を乾燥除去する乾燥工程と、を備えるリチウムイオン二次電池用シート状負極の製造方法。
The method for producing a sheet-like negative electrode for a lithium ion secondary battery according to the present invention for solving the above-mentioned problems is preferably configured as follows.
A negative electrode mixture containing carbonaceous particles that occlude and desorb lithium ions, an insoluble binder, and a soluble pore-forming agent, and pressurize a negative electrode mixture to produce a negative electrode precursor sheet, A lithium ion secondary battery sheet comprising: a removal step of removing the soluble pore-forming agent from the sheet-like negative electrode precursor solvent using a solvent; and a drying step of drying and removing the solvent after the removal step. Of manufacturing negative electrode.
この構成によると、シート状負極前駆体作製工程により炭素質粒子と、不溶性結着剤と、可溶性気孔形成剤が強固に結合されたシート状負極前駆体が得られる。この後、溶剤を用いて可溶性気孔形成剤を除去することにより、シート状負極に電解液の浸透できる気孔（気孔）が形成される。よって、円滑に電気化学的反応が進行する高性能なリチウムイオン二次電池用シート状負極を得ることができる。 According to this configuration, a sheet-like negative electrode precursor in which the carbonaceous particles, the insoluble binder, and the soluble pore-forming agent are firmly bonded is obtained by the sheet-like negative electrode precursor preparation step. Thereafter, the soluble pore-forming agent is removed using a solvent to form pores (pores) through which the electrolytic solution can permeate the sheet-like negative electrode. Therefore, a high-performance sheet-like negative electrode for a lithium ion secondary battery in which an electrochemical reaction proceeds smoothly can be obtained.
上記製造方法において、前記負極合剤は、さらに繊維状炭素質物を含む構成とすることができる。 In the manufacturing method , the negative electrode mixture may further include a fibrous carbonaceous material.
不溶性結着剤は、通常、導電性が低いため、不溶性結着剤によりシート状負極全体としての導電性が低下する。このため、負極導電性を高めることのできる繊維状炭素質物を加えることが好ましい。 Since the insoluble binder usually has low conductivity, the conductivity of the whole sheet-like negative electrode is lowered by the insoluble binder. For this reason, it is preferable to add a fibrous carbonaceous material that can increase negative electrode conductivity.
上記製造方法において、前記可溶性気孔形成剤は、水溶性であり、前記溶剤が水である構成とすることができる。 In the above production method , the soluble pore forming agent may be water-soluble, and the solvent may be water.
コスト、環境への影響の観点から、水溶性の気孔形成剤を用いると共に、溶剤として水を用いることが好ましい。 From the viewpoint of cost and environmental impact, it is preferable to use a water-soluble pore-forming agent and water as a solvent.
水溶性気孔形成剤としては、水溶性セルロース類、砂糖、食塩が例示できる。 Examples of the water-soluble pore forming agent include water-soluble celluloses, sugars and salt.
上記製造方法において、前記負極合剤全質量に占める前記可溶性気孔形成剤の質量割合が、１〜１０質量％である構成とすることができる。 The said manufacturing method WHEREIN: The mass ratio of the said soluble pore formation agent which occupies for the said negative electrode mixture total mass can be set as the structure which is 1-10 mass%.
負極合剤全質量に占める気孔形成剤の質量割合が低すぎると、十分な量の気孔が形成できないおそれがある。他方、気孔形成剤の質量割合が高すぎると、放電容量の低下を招くおそれがある。よって、上記範囲内に規制することが好ましい。 If the mass proportion of the pore forming agent in the total mass of the negative electrode mixture is too low, there is a possibility that a sufficient amount of pores cannot be formed. On the other hand, if the mass ratio of the pore forming agent is too high, the discharge capacity may be reduced. Therefore, it is preferable to regulate within the above range.
上記製造方法において、前記不溶性結着剤が、熱可塑性樹脂である構成とすることができる。 In the above production method , the insoluble binder may be a thermoplastic resin.
気孔形成剤を除去する除去工程などにより結着力が低下しないようにするために、結着剤として熱可塑性樹脂を用いることが好ましい。この場合においては、炭素材料粉末を結着させるために、シート状負極前駆体作製工程において、負極合剤を熱可塑性樹脂の融点以上に加熱しつつ加圧する。 It is preferable to use a thermoplastic resin as the binder in order to prevent the binding force from being lowered due to the removal step of removing the pore forming agent. In this case, in order to bind the carbon material powder, in the sheet-like negative electrode precursor preparation step, the negative electrode mixture is pressurized while being heated to the melting point or higher of the thermoplastic resin.
上記製造方法において、前記負極合剤全質量に占める前記結着剤の質量割合が、３〜１５質量％である構成とすることができる。 The said manufacturing method WHEREIN: The mass ratio of the said binder to the said negative electrode mixture total mass can be set as the structure which is 3-15 mass%.
負極合剤全質量に占める結着剤の質量割合が低すぎると、強度が低くなり、除去工程においてシート状負極がばらけてしまうおそれがある。他方、結着剤の質量割合が高すぎると、シート状負極の導電性が低くなり、放電容量の低下を招くおそれがある。よって、上記範囲内に規制することが好ましい。 If the mass ratio of the binder to the total mass of the negative electrode mixture is too low, the strength becomes low, and the sheet-like negative electrode may be scattered in the removing step. On the other hand, if the mass ratio of the binder is too high, the conductivity of the sheet-like negative electrode is lowered, and the discharge capacity may be reduced. Therefore, it is preferable to regulate within the above range.
上記で説明したように、本発明によると、電気化学的反応が円滑になされる高性能なリチウムイオン二次電池用シート状負極を低コストで提供することができる。 As described above, according to the present invention, a high-performance sheet-like negative electrode for a lithium ion secondary battery in which an electrochemical reaction is smoothly performed can be provided at a low cost.
本発明を実施するための最良の形態を、図面を通じて、詳細に説明する。なお、本発明は下記の形態に限定されるものではなく、その要旨を変更しない範囲において適宜変更して実施することができる。 The best mode for carrying out the present invention will be described in detail with reference to the drawings. In addition, this invention is not limited to the following form, In the range which does not change the summary, it can change suitably and can implement.
（実施の形態）
図４は、本発明にかかる負極活物質を用いた負極を示す図であり、図５は、本発明にかかる負極活物質を用いた負極を有する電池の基本構造を示す図であり、図６は、従来技術にかかる負極を示す図である。
(Embodiment)
4 is a diagram showing a negative electrode using the negative electrode active material according to the present invention, and FIG. 5 is a diagram showing a basic structure of a battery having a negative electrode using the negative electrode active material according to the present invention. These are figures which show the negative electrode concerning a prior art.
図６に示すように、従来技術にかかる負極は、銅箔からなる集電体１０に炭素を主体と刷る負極活物質層１１が設けられ、集電体１０の負極活物質層１１が設けられていない部分に、例えば銅からなる集電タブ１２が取り付けられている。これに対し、本発明にかかる負極活物質を用いた負極は、図４に示すように、集電体を有さず、炭素を主体とする負極活物質１に直接、例えば銅からなる集電タブ２が取り付けられている。充放電に関与しない銅からなる集電体を有さないため、本発明にかかる負極は、従来技術に比べ、コスト安であり、且つエネルギー密度が高い。 As shown in FIG. 6, the negative electrode according to the conventional technique is provided with a negative electrode active material layer 11 that mainly prints carbon on a current collector 10 made of copper foil, and a negative electrode active material layer 11 of the current collector 10. A current collecting tab 12 made of, for example, copper is attached to the portion that is not. On the other hand, the negative electrode using the negative electrode active material according to the present invention does not have a current collector as shown in FIG. Tab 2 is attached. Since it does not have a current collector made of copper that does not participate in charging / discharging, the negative electrode according to the present invention is cheaper and has a higher energy density than the prior art.
図５に、本発明にかかる負極活物質を用いた電池の基本構造を示す。炭素を主体とする負極１００と、アルミニウム箔からなる集電体にコバルト酸リチウムを主体とする正極活物質層が設けられた正極３００とが、オレフィン樹脂製等のセパレータ２００を介して対向配置されており、負極１００には負極タブ１１０が取り付けられ、正極３００には正極タブ３１０が取り付けられている。なお、この図は電池の基本構造を示す図であって、負極−セパレータ−正極−セパレータからなる電池基本単位を複数積層した構造を備えていてもよい。 FIG. 5 shows a basic structure of a battery using the negative electrode active material according to the present invention. A negative electrode 100 mainly composed of carbon and a positive electrode 300 in which a current collector made of aluminum foil is provided with a positive electrode active material layer mainly composed of lithium cobaltate are disposed to face each other with a separator 200 made of olefin resin or the like interposed therebetween. A negative electrode tab 110 is attached to the negative electrode 100, and a positive electrode tab 310 is attached to the positive electrode 300. In addition, this figure is a figure which shows the basic structure of a battery, Comprising: You may have the structure which laminated | stacked the battery basic unit which consists of a negative electrode-separator-positive electrode-separator.
また、この電池の基本構造は外装体内に非水電解質とともに収容され、外装体の開口が封止されることにより、リチウムイオン二次電池が完成する。 Moreover, the basic structure of this battery is accommodated in the exterior body together with the nonaqueous electrolyte, and the opening of the exterior body is sealed, thereby completing the lithium ion secondary battery.
正極活物質としては、公知の材料を用いることができ、例えば、ＬｉＣｏＯ2、ＬｉＮｉＯ2、ＬｉＮｉxＣｏ1-xＯ2、ＬｉＭｎＯ2、ＬｉＭｎ2Ｏ4、ＬｉＦｅＯ2が挙げられる。 As the positive electrode active material can be used a known material, for example, LiCoO 2, LiNiO 2, LiNi x Co 1-x O 2, LiMnO 2, LiMn 2 O 4, LiFeO 2 and the like.
電解液に用いる有機溶媒としては、エチレンカーボネート、プロピレンカーボネート、ジエチルカーボネート、ジメチルカーボネート、エチルメチルカーボネート、γ−ブチロラクトン、１，２−ジメトキシエタン、１，２−ジエトキシエタン、エトキシメトキシエタン等の一種または二種以上の混合物を用いることができる。また、電解質塩としては、ＬｉＰＦ6、ＬｉＢＦ4、ＬｉＣｌＯ4、ＬｉＣＦ3ＳＯ3等の一種または二種以上の混合物を用いることができる。電解質塩の濃度は、０．５〜２．０Ｍ（モル／リットル）とすることが好ましい。 Examples of the organic solvent used in the electrolytic solution include ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, and the like. Alternatively, a mixture of two or more kinds can be used. As the electrolyte salt, one kind or a mixture of two or more kinds such as LiPF 6 , LiBF 4 , LiClO 4 , LiCF 3 SO 3 can be used. The concentration of the electrolyte salt is preferably 0.5 to 2.0 M (mol / liter).
また、他の構成要素（例えば、セパレータ、外装体、封口体等）は、公知の材料を用いればよく、負極の製造方法以外については、公知の製造方法を採用できる。 Moreover, what is necessary is just to use a well-known material for other structural elements (for example, a separator, an exterior body, a sealing body etc.), and can employ | adopt a well-known manufacturing method except the manufacturing method of a negative electrode.
次に、実施例を用いて本発明をさらに詳細に説明する。 Next, the present invention will be described in more detail using examples.
（実施例１）
〈シート状負極の作製〉
（材料の混合）
人造黒鉛（製鋼用電極を粉砕したもの、平均粒径１７μｍ）７４質量部と、気相成長炭素繊維（昭和電工株式会社製）１０質量部と、気孔形成剤（メチルセルロース、キシダ化学株式会社製 ３５０〜５５０ｍP・ｓ）６質量％と、熱可塑性樹脂バインダとしてのポリプロピレン樹脂粉末平均粒径５μｍ）１０質量部とを、高速流動型混合機を用いてせん断混合し、負極合剤を得た。
Example 1
<Production of sheet negative electrode>
(Mixing of materials)
Artificial graphite (pulverized steelmaking electrode, average particle diameter 17 μm) 74 parts by mass, vapor grown carbon fiber (manufactured by Showa Denko KK) 10 parts by mass, pore forming agent (methylcellulose, manufactured by Kishida Chemical Co., Ltd. 350 ˜550 mP · s) 6% by mass and 10 parts by mass of polypropylene resin powder having an average particle size of 5 μm) as a thermoplastic resin binder were shear mixed using a high-speed fluid mixer to obtain a negative electrode mixture.
（シート状負極前駆体作製工程）
内径φ５５ｍｍの金型に上記負極合剤を入れ、１９０℃に設定した油圧式の熱圧プレスにセットし、５００ｋｇ／ｃｍ2の圧力をかけて２分間保持した。その後、冷却し、シート状負極前駆体を得た。金型に入れる混合粉体の量は、シート状負極前駆体の厚みがおよそ０．４ｍｍになるようにした。この加熱により、ポリプロピレンが溶融して、負極合剤が結着される。
(Sheet-like negative electrode precursor production process)
The negative electrode mixture was placed in a metal mold having an inner diameter of 55 mm, set in a hydraulic hot press set at 190 ° C., and held at pressure of 500 kg / cm 2 for 2 minutes. Then, it cooled and obtained the sheet-like negative electrode precursor. The amount of the mixed powder put into the mold was set so that the thickness of the sheet-like negative electrode precursor was about 0.4 mm. By this heating, the polypropylene melts and the negative electrode mixture is bound.
（除去工程）
上記シート状負極前駆体を水に４時間浸漬し、その後乾燥して、負極シートを得た。この浸漬により、メチルセルロースが水中に溶解して気孔が形成される。
(Removal process)
The sheet-like negative electrode precursor was immersed in water for 4 hours and then dried to obtain a negative electrode sheet. By this immersion, methylcellulose is dissolved in water to form pores.
上記負極シートを、φ１６ｍｍに打ち抜いて、実施例１にかかるシート状負極を作製した。このシート状負極のかさ密度は、１．３１ｇ／ｃｍ3であった。 The negative electrode sheet was punched into φ16 mm to produce a sheet-like negative electrode according to Example 1. The bulk density of this sheet-like negative electrode was 1.31 g / cm 3 .
（比較例１）
浸漬工程を行っていないシート状負極前駆体を負極シートとして用いたこと以外は、上記実施例１と同様にして、比較例１にかかるシート状負極を作製した。このシート状負極のかさ密度は、１．５７ｇ／ｃｍ3であった。
(Comparative Example 1)
A sheet-like negative electrode according to Comparative Example 1 was produced in the same manner as in Example 1 except that a sheet-like negative electrode precursor that was not subjected to the dipping process was used as the negative electrode sheet. The bulk density of this sheet-like negative electrode was 1.57 g / cm 3 .
（比較例２）
（材料の混合）
人造黒鉛（製鋼用電極を粉砕したもの、平均粒径１７μｍ）６９質量部と、気相成長炭素繊維（昭和電工株式会社製）８質量部と、気孔形成剤（メチルセルロース、キシダ化学株式会社製 ３５０〜５５０ｍP・ｓ）３質量％と、熱可塑性樹脂バインダとしてのポリプロピレン樹脂粉末平均粒径５μｍ）２０質量部とを、高速流動型混合機を用いてせん断混合し、負極合剤を得た。
(Comparative Example 2)
(Mixing of materials)
Artificial graphite (pulverized steelmaking electrode, average particle size 17 μm) 69 parts by mass, vapor grown carbon fiber (manufactured by Showa Denko KK) 8 parts by mass, pore forming agent (methylcellulose, manufactured by Kishida Chemical Co., Ltd. 350 ˜550 mP · s) 3% by mass and 20 parts by mass of polypropylene resin powder having an average particle diameter of 5 μm as a thermoplastic resin binder were shear mixed using a high-speed fluid mixer to obtain a negative electrode mixture.
（シート状負極前駆体作製工程）
内径φ５５ｍｍの金型に上記負極合剤を入れ、１９０℃に設定した油圧式の熱圧プレスにセットし、５００ｋｇ／ｃｍ2の圧力をかけて２分間保持した。その後、冷却し、シート状負極前駆体を得た。金型に入れる混合粉体の量は、シート状負極前駆体の厚みがおよそ０．４ｍｍになるようにした。この加熱により、ポリプロピレンが溶融して、負極合剤が結着された負極シートを得た。
(Sheet-like negative electrode precursor production process)
The negative electrode mixture was placed in a metal mold having an inner diameter of 55 mm, set in a hydraulic hot press set at 190 ° C., and held at pressure of 500 kg / cm 2 for 2 minutes. Then, it cooled and obtained the sheet-like negative electrode precursor. The amount of the mixed powder put into the mold was set so that the thickness of the sheet-like negative electrode precursor was about 0.4 mm. By this heating, the polypropylene melted and a negative electrode sheet with the negative electrode mixture bound thereto was obtained.
上記負極シートを、φ１６ｍｍに打ち抜いて、実施例１にかかるシート状負極を作製した。このシート状負極のかさ密度は、１．５４ｇ／ｃｍ3であった。 The negative electrode sheet was punched into φ16 mm to produce a sheet-like negative electrode according to Example 1. The bulk density of this sheet-like negative electrode was 1.54 g / cm 3 .
（電極セルの組み立て）
アルゴンガス雰囲気のグローブボックス内で、電極セルの組み立てを行った。
エチレンカーボネート（ＥＣ）とエチルメチルカーボネート（ＥＭＣ）とを体積比１：２（２５℃）で混合した混合溶媒に、ＬｉＰＦ6を１Ｍ（モル／リットル）に溶解した非水電解液を用意した。
(Assembly of electrode cell)
The electrode cell was assembled in a glove box in an argon gas atmosphere.
A nonaqueous electrolytic solution in which LiPF 6 was dissolved in 1 M (mol / liter) in a mixed solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 1: 2 (25 ° C.) was prepared.
上記非水電解液に、上記シート状負極、リチウム対極、リファレンス極を浸漬し、電極セルを完成させた。 The sheet-like negative electrode, lithium counter electrode, and reference electrode were immersed in the non-aqueous electrolyte solution to complete an electrode cell.
（電池特性の測定）
上記電極セルをグローブボックスから２５℃の恒温槽内に移し、リチウム対極、シート状負極、及びリファレンス極端子に充放電装置接続コードを繋いで、充放電容量及び抵抗率を測定した。
充電条件：電流密度０．５ｍＡ／ｃｍ2の定電流で電圧が１０ｍＶとなるまで充電し、その後定電圧１０ｍＶで４０時間充電。
放電条件：０．５ｍＡ／ｃｍ2の定電流で電圧が１．２Ｖとなるまで放電した。
また、三菱化学製 Loresta−GP MCP-T600を用いて、抵抗率を測定した。
この結果を下記表１に示す。
(Measurement of battery characteristics)
The electrode cell was transferred from the glove box into a constant temperature bath at 25 ° C., and a charge / discharge device connection cord was connected to a lithium counter electrode, a sheet-like negative electrode, and a reference electrode terminal, and charge / discharge capacity and resistivity were measured.
Charging conditions: Charge at a constant current of 0.5 mA / cm 2 until the voltage reaches 10 mV, and then charge at a constant voltage of 10 mV for 40 hours.
Discharge conditions: Discharge was performed at a constant current of 0.5 mA / cm 2 until the voltage reached 1.2V.
Moreover, resistivity was measured using Mitsubishi Chemical Loresta-GP MCP-T600.
The results are shown in Table 1 below.
（気孔分布の測定）
Thermo Electron Corporation製 Pascal 440を用い、水銀圧入法により、気孔分布及び気孔率を測定した。この結果を図１〜３及び下記表１に示す。
(Measurement of pore distribution)
Using Pascal 440 manufactured by Thermo Electron Corporation, pore distribution and porosity were measured by mercury porosimetry. The results are shown in FIGS.
上記表１から、気孔形成剤を含む負極合剤を用いたシート状負極前駆体を水に浸漬して作製した実施例１にかかるシート状負極は、充電容量が２１１ｍＡｈ／ｇ、放電容量が８４ｍＡｈ／ｇと、浸漬を行っていない比較例１、比較例２の充電容量１００ｍＡｈ／ｇ，５３ｍＡｈ／ｇ、放電容量６２ｍＡｈ／ｇ，０．２ｍＡｈ／ｇよりも優れていることがわかる。 From Table 1 above, the sheet-like negative electrode according to Example 1 prepared by immersing a sheet-like negative electrode precursor using a negative electrode mixture containing a pore-forming agent in water has a charge capacity of 211 mAh / g and a discharge capacity of 84 mAh. It can be seen that it is superior to the charge capacity of 100 mAh / g, 53 mAh / g, discharge capacity of 62 mAh / g, and 0.2 mAh / g of Comparative Example 1 and Comparative Example 2 where no soaking is performed.
このことは、次のように考えられる。気孔形成剤を含む負極合剤を用いたシート状負極前駆体を水に浸漬すると、気孔形成剤が溶解除去され、空隙が生じる。このため、表１に示すように、実施例１にかかるシート状負極は、比較例１、２よりも気孔率が大きい。また、この除去による空隙は、マクロ孔と呼ばれる気孔径（直径）０．０５〜１００μｍの範囲に現れ（実施例１：０．４９８ｃｃ／ｇ、比較例１：０．０５０ｃｃ／ｇ、比較例２：０．０２１ｃｃ／ｇ、図１〜３参照）、このマクロ孔は電解液の浸透性が極めて大きい。このため、負極活物質周囲に十分な量の電解液が供給され、充放電反応がスムースに進行する。このため、充電容量及び放電容量が大きくなる。このため、０．０５〜１００μｍの範囲の気孔の気孔体積が質量当たり０．０５ｃｃ／ｇより大きいことが好ましく、０．０７ｃｃ／ｇ以上であることがより好ましく、０．４０ｃｃ／ｇ以上であることがさらに好ましい。 This is considered as follows. When a sheet-like negative electrode precursor using a negative electrode mixture containing a pore forming agent is immersed in water, the pore forming agent is dissolved and removed, and voids are generated. For this reason, as shown in Table 1, the sheet-like negative electrode according to Example 1 has a higher porosity than Comparative Examples 1 and 2. In addition, voids resulting from this removal appear in a pore diameter (diameter) of 0.05 to 100 μm called macropores (Example 1: 0.498 cc / g, Comparative Example 1: 0.050 cc / g, Comparative Example 2). : 0.021 cc / g, see FIGS. 1 to 3), the macropores have extremely high electrolyte permeability. For this reason, a sufficient amount of electrolyte solution is supplied around the negative electrode active material, and the charge / discharge reaction proceeds smoothly. For this reason, the charge capacity and the discharge capacity are increased. For this reason, the pore volume of pores in the range of 0.05 to 100 μm is preferably larger than 0.05 cc / g, more preferably 0.07 cc / g or more, and 0.40 cc / g or more. More preferably.
また、実施例１の抵抗率は１６．５ｍΩ・ｃｍと、十分に低いことがわかる。 Moreover, it turns out that the resistivity of Example 1 is sufficiently low as 16.5 mΩ · cm.
好ましくは、黒鉛粉末（炭素質粒子）を７０〜８８質量％、不溶性結着剤を７〜１０質量％、導電剤を３〜１５質量％、可溶性気孔形成剤を２〜１０質量％とする。 Preferably, the graphite powder (carbonaceous particles) is 70 to 88% by mass, the insoluble binder is 7 to 10% by mass, the conductive agent is 3 to 15% by mass, and the soluble pore forming agent is 2 to 10% by mass.
以上に説明したように、本発明によれば、銅からなる集電体を用いずに高性能なシート状負極を得ることが可能であり、負極の製造コストを飛躍的に低下させることができる。よって、産業上の利用可能性は大きい。 As described above, according to the present invention, a high-performance sheet-like negative electrode can be obtained without using a current collector made of copper, and the production cost of the negative electrode can be drastically reduced. . Therefore, industrial applicability is great.
Claims (2)
繊維状炭素質物と、
前記炭素質粒子及び前記繊維状炭素質物を結着する、熱可塑性樹脂からなる結着剤と、を有し、負極集電体を有しないリチウムイオン二次電池用シート状負極であって、
０．０５〜１００μｍの範囲の気孔の気孔体積が質量当たり０．０７〜１．０ｃｃ／ｇであり、
前記結着剤は、その融点以上に加熱しつつ加圧されて、前記炭素質粒子及び前記繊維状炭素質物を結着している、
ことを特徴とするリチウムイオン二次電池用シート状負極。 Carbonaceous particles that occlude and desorb lithium ions;
Fibrous carbonaceous matter,
A binder composed of a thermoplastic resin that binds the carbonaceous particles and the fibrous carbonaceous material , and a sheet-like negative electrode for a lithium ion secondary battery having no negative electrode current collector,
Pore volume per mass 0.07~1.0cc / g Der pores ranging 0.05~100μm is,
The binder is pressurized while being heated above its melting point to bind the carbonaceous particles and the fibrous carbonaceous material,
A sheet-like negative electrode for a lithium ion secondary battery .
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