JP2021103664A - Negative electrode resin composition, negative electrode, and secondary battery - Google Patents
Negative electrode resin composition, negative electrode, and secondary battery Download PDFInfo
- Publication number
- JP2021103664A JP2021103664A JP2019234949A JP2019234949A JP2021103664A JP 2021103664 A JP2021103664 A JP 2021103664A JP 2019234949 A JP2019234949 A JP 2019234949A JP 2019234949 A JP2019234949 A JP 2019234949A JP 2021103664 A JP2021103664 A JP 2021103664A
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- Prior art keywords
- negative electrode
- resin composition
- mass
- conductive material
- dispersant
- Prior art date
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- 230000000717 retained effect Effects 0.000 description 1
- 239000004576 sand Substances 0.000 description 1
- 238000007789 sealing Methods 0.000 description 1
- 238000007086 side reaction Methods 0.000 description 1
- 150000003377 silicon compounds Chemical class 0.000 description 1
- QDRKDTQENPPHOJ-UHFFFAOYSA-N sodium ethoxide Chemical compound [Na+].CC[O-] QDRKDTQENPPHOJ-UHFFFAOYSA-N 0.000 description 1
- MWNQXXOSWHCCOZ-UHFFFAOYSA-L sodium;oxido carbonate Chemical class [Na+].[O-]OC([O-])=O MWNQXXOSWHCCOZ-UHFFFAOYSA-L 0.000 description 1
- 238000001179 sorption measurement Methods 0.000 description 1
- 229920003066 styrene-(meth)acrylic acid ester copolymer Polymers 0.000 description 1
- 238000010557 suspension polymerization reaction Methods 0.000 description 1
- 229910052715 tantalum Inorganic materials 0.000 description 1
- GUVRBAGPIYLISA-UHFFFAOYSA-N tantalum atom Chemical compound [Ta] GUVRBAGPIYLISA-UHFFFAOYSA-N 0.000 description 1
- 239000011135 tin Substances 0.000 description 1
- 238000006276 transfer reaction Methods 0.000 description 1
- WFKWXMTUELFFGS-UHFFFAOYSA-N tungsten Chemical compound [W] WFKWXMTUELFFGS-UHFFFAOYSA-N 0.000 description 1
- 229910052721 tungsten Inorganic materials 0.000 description 1
- 239000010937 tungsten Substances 0.000 description 1
- 229910052720 vanadium Inorganic materials 0.000 description 1
- GPPXJZIENCGNKB-UHFFFAOYSA-N vanadium Chemical compound [V]#[V] GPPXJZIENCGNKB-UHFFFAOYSA-N 0.000 description 1
- 229920002554 vinyl polymer Polymers 0.000 description 1
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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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- Compositions Of Macromolecular Compounds (AREA)
- Battery Electrode And Active Subsutance (AREA)
Abstract
Description
本発明は、負極樹脂組成物、負極及び二次電池に関する。 The present invention relates to a negative electrode resin composition, a negative electrode and a secondary battery.
環境・エネルギー問題の高まりから、化石燃料への依存度を減らす低炭素社会の実現に向けた技術の開発が盛んに行われている。このような技術開発の例としては、ハイブリッド電気自動車や電気自動車等の低公害車の開発、太陽光発電や風力発電等の自然エネルギー発電・蓄電システムの開発、電力を効率よく供給し、送電ロスを減らす次世代送電網の開発等があり、多岐に渡っている。
これらの技術に共通して必要となるキーデバイスの一つが電池であり、このような電池に対しては、システムを小型化するための高いエネルギー密度が求められる。また、使用環境温度に左右されずに安定した電力の供給を可能にするための高い出力特性が求められる。さらに、長期間の使用に耐えうる良好なサイクル特性等も求められている。そのため、従来の鉛蓄電池、ニッケル−カドミウム電池、ニッケル−水素電池から、より高いエネルギー密度、出力特性およびサイクル特性を有するリチウムイオン二次電池への置き換えが急速に進んでいる。
Due to growing environmental and energy problems, technologies for the realization of a low-carbon society that reduces dependence on fossil fuels are being actively developed. Examples of such technological development include the development of low-emission vehicles such as hybrid electric vehicles and electric vehicles, the development of renewable energy power generation and power storage systems such as solar power generation and wind power generation, the efficient supply of power, and transmission loss. There is a wide range of activities such as the development of next-generation power grids that reduce the number of electricity.
One of the key devices commonly required for these technologies is a battery, and such a battery is required to have a high energy density for miniaturizing the system. In addition, high output characteristics are required to enable stable power supply regardless of the operating environment temperature. Further, good cycle characteristics and the like that can withstand long-term use are also required. Therefore, the replacement of conventional lead-acid batteries, nickel-cadmium batteries, and nickel-hydrogen batteries with lithium-ion secondary batteries having higher energy density, output characteristics, and cycle characteristics is rapidly progressing.
従来、リチウムイオン二次電池の負極は、負極活物質及び結着材（バインダー）を含有する電極ペーストを、集電体に塗工することにより製造されている。負極活物質としては、天然黒鉛、人造黒鉛、難黒鉛化炭素、易黒鉛化炭素、ケイ素化合物、チタン酸リチウム等が用いられてきた。最近では、リチウムイオンの受入れ性を向上させて、充放電時間を短縮するためや、充放電時に負極活物質が繰り返し膨張収縮して導電性が損なわれるのを防止するために、アグリゲート（一次粒子が複数融着した構造：一次凝集体）が発達したカーボンブラックや、円筒状で結晶が発達したカーボンナノチューブ等の導電材を添加することが検討されている。 Conventionally, a negative electrode of a lithium ion secondary battery is manufactured by applying an electrode paste containing a negative electrode active material and a binder to a current collector. As the negative electrode active material, natural graphite, artificial graphite, non-graphitized carbon, easily graphitized carbon, silicon compound, lithium titanate and the like have been used. Recently, in order to improve the acceptability of lithium ions and shorten the charge / discharge time, and to prevent the negative electrode active material from repeatedly expanding and contracting during charging / discharging and impairing conductivity, aggregates (primary). It is being studied to add a conductive material such as carbon black in which a structure in which a plurality of particles are fused: a primary agglomerate) or carbon nanotubes in which a cylindrical shape and crystals are developed.
負極での導電材の基本的な役割は二つある。一つ目は、負極活物質間に均一な導電経路を形成することであり、充放電時に負極活物質が繰り返し膨張収縮して導電性が損なわれるのを防止する。二つ目は、リチウムイオンが溶解した電解液を保液して、全ての負極活物質に十分なリチウムイオンを供給することであり、充放電時にリチウムイオンの供給が不足して、電池性能が損なわれるのを防止する。そのため、負極作製において、導電材として使用されるカーボンブラックは、平均一次粒子径と比表面積の大きさがある範囲内に制御されていることが重要である。制御が十分でない場合や負極活物質間での分散が悪い場合には、負極活物質とカーボンブラックの接触が十分得られず、導電経路が確保できなくなると共に、一部の活物質にしか十分なリチウムイオンの供給ができなくなる。結果として、電極内に導電性や電解液の保液性が劣る部分が局所的に現れ、負極活物質が有効に利用されずに放電容量が低下したり、電池の寿命が短くなったりする原因となっている。 There are two basic roles of the conductive material in the negative electrode. The first is to form a uniform conductive path between the negative electrode active materials, thereby preventing the negative electrode active materials from repeatedly expanding and contracting during charging and discharging to impair conductivity. The second is to retain the electrolytic solution in which lithium ions are dissolved and supply sufficient lithium ions to all the negative electrode active materials, and the supply of lithium ions is insufficient during charging and discharging, resulting in poor battery performance. Prevent damage. Therefore, in the fabrication of the negative electrode, it is important that the carbon black used as the conductive material is controlled within a certain range of the average primary particle size and the specific surface area. If the control is not sufficient or the dispersion between the negative electrode active materials is poor, sufficient contact between the negative electrode active material and carbon black cannot be obtained, a conductive path cannot be secured, and only some active materials are sufficient. Lithium ion cannot be supplied. As a result, a portion having inferior conductivity and electrolyte retention property appears locally in the electrode, which causes the negative electrode active material to not be effectively used, the discharge capacity to be reduced, and the battery life to be shortened. It has become.
そこで、特許文献１には、負極活物質、導電材、ビニルアルコールとエチレン性不飽和カルボン酸アルカリ金属中和物との共重合体からなる結着材、及び分散助剤を用いたリチウムイオン二次電池電極用合剤についての技術が開示されている。特許文献１によれば、このような構成とすることで、リチウムイオン二次電池電極用合剤の保存安定性が増し、その合剤により作製した負極を用いた電池は、５０サイクル後の保持率が良好になることが記されている。 Therefore, Patent Document 1 describes a negative electrode active material, a conductive material, a binder made of a copolymer of vinyl alcohol and an ethylenically unsaturated carboxylic acid alkali metal neutralizer, and a lithium ion II using a dispersion aid. A technique for a mixture for a secondary battery electrode is disclosed. According to Patent Document 1, such a configuration increases the storage stability of the mixture for the lithium ion secondary battery electrode, and the battery using the negative electrode produced by the mixture can be retained after 50 cycles. It is noted that the rate will be good.
また特許文献２には、負極活物質、導電材及び鹸化度が８７〜９９．９モル％のポリビニルアルコール樹脂である結着材を電極合剤層に用いた非水電解質二次電池用負極についての技術が開示されている。特許文献２によれば、この負極を用いた電池は、１００サイクル後の容量維持率が良好になることが記載されている。 Further, Patent Document 2 describes a negative electrode for a non-aqueous electrolyte secondary battery using a negative electrode active material, a conductive material, and a binder which is a polyvinyl alcohol resin having a saponification degree of 87 to 99.9 mol% as an electrode mixture layer. Technology is disclosed. According to Patent Document 2, a battery using this negative electrode has a good capacity retention rate after 100 cycles.
このように、リチウムイオン二次電池の負極の結着材として、ポリビニルアルコールやその共重合体を用いる技術が従来提案されてきたが、未だ実用上十分な分散性と電池性能を両立する技術はなかった。例えば特許文献１に開示された技術によれば、導電材の分散性が向上するものの、この技術を用いた負極をリチウムイオン二次電池に用いると、高い電流負荷での放電時に放電容量が低下してしまう問題があった。しかし、現在のリチウムイオン二次電池市場では、高い電流負荷での充電・放電でも容量が低下しない性能が望まれており、分散性と電池性能を両立した負極樹脂組成物が必要不可欠である。 As described above, a technique using polyvinyl alcohol or a copolymer thereof as a binder for the negative electrode of a lithium ion secondary battery has been conventionally proposed, but there is still a technique for achieving both practically sufficient dispersibility and battery performance. There wasn't. For example, according to the technique disclosed in Patent Document 1, the dispersibility of the conductive material is improved, but when the negative electrode using this technique is used for a lithium ion secondary battery, the discharge capacity is reduced when discharging under a high current load. There was a problem of doing it. However, in the current lithium-ion secondary battery market, performance is desired in which the capacity does not decrease even when charging / discharging under a high current load, and a negative electrode resin composition having both dispersibility and battery performance is indispensable.
本発明は、上記問題と実情に鑑み、分散性と電池性能に優れた負極樹脂組成物を提供することを目的の一つとする。加えて、本発明は、この負極樹脂組成物を用いて製造される極板抵抗が低い負極、更にこの負極を用いて製造される放電レート特性及びサイクル特性に優れた二次電池を提供することを別の目的とする。 One object of the present invention is to provide a negative electrode resin composition having excellent dispersibility and battery performance in view of the above problems and circumstances. In addition, the present invention provides a negative electrode having a low electrode plate resistance manufactured by using this negative electrode resin composition, and further providing a secondary battery manufactured by using this negative electrode and having excellent discharge rate characteristics and cycle characteristics. For another purpose.
本発明者等は、上記目的を達成するために鋭意研究した結果、特定の鹸化度を有するポリビニルアルコールを分散剤として含有し、且つ、特定の平均一次粒子径を有するカーボンブラックを導電材として含有する負極樹脂組成物を用いることにより、上記課題が解決できることを見出した。
具体的には、本発明者は、導電材としてカーボンブラック、結着材、及び分散剤として特定の鹸化度を有するポリビニルアルコールを含有する負極樹脂組成物を用いて製造した負極は、極板抵抗が低く、加えて、この負極を用いて製造した二次電池は、放電レート特性及びサイクル特性に優れることを見出した。本発明は当該知見に基づき、完成されたものである。
As a result of diligent research to achieve the above object, the present inventors have contained polyvinyl alcohol having a specific degree of saponification as a dispersant and carbon black having a specific average primary particle size as a conductive material. It has been found that the above-mentioned problems can be solved by using the negative electrode resin composition.
Specifically, the present inventor has prepared a negative electrode using a negative electrode resin composition containing carbon black as a conductive material, a binder, and polyvinyl alcohol having a specific degree of saponification as a dispersant. In addition, it was found that the secondary battery manufactured using this negative electrode is excellent in discharge rate characteristics and cycle characteristics. The present invention has been completed based on this finding.
すなわち、上記課題を解決する本発明は、下記に例示される。
［１］
導電材、結着材及び分散剤を含有する負極樹脂組成物であって、前記分散剤が少なくともポリビニルアルコールを含み、前記導電材が少なくともカーボンブラックを含み、前記ポリビニルアルコールの鹸化度が８５．５〜９６．５モル％であり、前記カーボンブラックの平均一次粒子径が１６〜５０ｎｍである負極樹脂組成物。
［２］
前記ポリビニルアルコールの平均重合度が２５０〜１８００である［１］に記載の負極樹脂組成物。
［３］
前記カーボンブラックの比表面積が３５〜４００ｍ2／ｇである［１］又は［２］に記載の負極樹脂組成物。
［４］
前記分散剤と導電材の固形分で比べたときの質量比｛分散剤の質量／導電材の質量｝が０．０３〜０．１５である［１］〜［３］のいずれか１項に記載の負極樹脂組成物。
［５］
前記結着材がスチレン−ブタジエン共重合体である［１］〜［４］のいずれか１項に記載の負極樹脂組成物。
［６］
［１］〜［５］のいずれか１項に記載の負極樹脂組成物を含む負極。
［７］
［６］に記載の負極を備えた二次電池。
なお、本明細書において、特にことわりがない限り、「〜」という記号は両端の値「以上」および「以下」の範囲を意味する。例えば、「Ａ〜Ｂ」というのは、Ａ以上、Ｂ以下であるという意味である。
That is, the present invention that solves the above problems is exemplified below.
[1]
A negative electrode resin composition containing a conductive material, a binder and a dispersant, wherein the dispersant contains at least polyvinyl alcohol, the conductive material contains at least carbon black, and the degree of saponification of the polyvinyl alcohol is 85.5. A negative electrode resin composition having an average primary particle size of ~ 96.5 mol% and an average primary particle size of 16 to 50 nm of the carbon black.
[2]
The negative electrode resin composition according to [1], wherein the polyvinyl alcohol has an average degree of polymerization of 250 to 1800.
[3]
The negative electrode resin composition according to [1] or [2], wherein the specific surface area of the carbon black is 35 to 400 m 2 / g.
[4]
In any one of [1] to [3], the mass ratio {mass of the dispersant / mass of the conductive material} when the solid content of the dispersant and the conductive material is compared is 0.03 to 0.15. The negative electrode resin composition according to the above.
[5]
The negative electrode resin composition according to any one of [1] to [4], wherein the binder is a styrene-butadiene copolymer.
[6]
A negative electrode containing the negative electrode resin composition according to any one of [1] to [5].
[7]
A secondary battery provided with the negative electrode according to [6].
In the present specification, unless otherwise specified, the symbol "~" means a range of values "greater than or equal to" and "less than or equal to" at both ends. For example, "A to B" means that it is A or more and B or less.
本発明の一実施形態によれば、分散性及び電池性能に優れた負極樹脂組成物を提供することができる。
本発明の一実施形態によれば、極板抵抗が低い負極を提供することができる。
本発明の一実施形態によれば、放電レート特性及びサイクル特性に優れた二次電池を提供することができる。
また、本発明の好適な実施態様によれば、エネルギー密度が高く、放電レート特性、サイクル特性に優れた二次電池を簡便に得ることができる負極を提供することができる。
According to one embodiment of the present invention, it is possible to provide a negative electrode resin composition having excellent dispersibility and battery performance.
According to one embodiment of the present invention, it is possible to provide a negative electrode having a low electrode plate resistance.
According to one embodiment of the present invention, it is possible to provide a secondary battery having excellent discharge rate characteristics and cycle characteristics.
Further, according to a preferred embodiment of the present invention, it is possible to provide a negative electrode capable of easily obtaining a secondary battery having a high energy density and excellent discharge rate characteristics and cycle characteristics.
以下、本発明を詳細に説明する。なお、本発明は、以下に説明する実施形態に限定されるものではない。 Hereinafter, the present invention will be described in detail. The present invention is not limited to the embodiments described below.
以下、本発明の構成材料について詳細に説明する。 Hereinafter, the constituent materials of the present invention will be described in detail.
＜導電材＞
本発明における導電材は、少なくともカーボンブラックを含有する。導電材中のカーボンブラックの含有濃度は例えば５０質量％以上とすることができ、好ましくは７０質量％以上とすることができ、より好ましくは９０質量％以上とすることができる。導電材としてカーボンブラックのみを使用することもできる。カーボンブラックは、一般の電池用導電材としてのカーボンブラック同様、アセチレンブラック、ファーネスブラック、チャンネルブラックなどの中から選ばれるものである。中でも、結晶性及び純度に優れるアセチレンブラックが好ましい。
<Conductive material>
The conductive material in the present invention contains at least carbon black. The content concentration of carbon black in the conductive material can be, for example, 50% by mass or more, preferably 70% by mass or more, and more preferably 90% by mass or more. It is also possible to use only carbon black as the conductive material. Carbon black is selected from acetylene black, furnace black, channel black, and the like, like carbon black as a general conductive material for batteries. Of these, acetylene black, which has excellent crystallinity and purity, is preferable.
本発明におけるカーボンブラックの平均一次粒子径は１６〜５０ｎｍであることが好ましい。平均一次粒子径を好ましくは５０ｎｍ以下、より好ましくは４０ｎｍ以下とすることで、負極活物質及び集電体との接点が多くなり、良好な導電性付与効果と保液性が得られる。平均一次粒子径を１６ｎｍ以上、より好ましくは１８ｎｍ以上とすることで、粒子間の相互作用が抑制されるため、負極活物質の間に均一に分散され、良好な導電経路と保液性が得られる。この観点から、カーボンブラックの平均一次粒子径は１８〜４０ｎｍであることがより好ましい。なお、本発明において、カーボンブラックの平均一次粒子径は、透過型電子顕微鏡などで撮影した写真をもとに測定した粒子径を平均した値である。具体的には、透過電子顕微鏡ＪＥＭ−２０００ＦＸ（日本電子社製）を用いて１０万倍の画像５枚を撮影し、無作為に抽出した２００個以上の１次粒子について画像解析により粒子径を求め、それらの個数平均を算出することによって測定した。なお、粒子径とは、一次粒子の円相当径のことである。 The average primary particle size of carbon black in the present invention is preferably 16 to 50 nm. By setting the average primary particle size to preferably 50 nm or less, more preferably 40 nm or less, the number of contacts with the negative electrode active material and the current collector is increased, and a good conductivity-imparting effect and liquid retention property can be obtained. By setting the average primary particle size to 16 nm or more, more preferably 18 nm or more, the interaction between the particles is suppressed, so that the particles are uniformly dispersed between the negative electrode active materials, and a good conductive path and liquid retention property are obtained. Be done. From this point of view, the average primary particle size of carbon black is more preferably 18 to 40 nm. In the present invention, the average primary particle size of carbon black is a value obtained by averaging the particle size measured based on a photograph taken with a transmission electron microscope or the like. Specifically, five images of 100,000 times were taken using a transmission electron microscope JEM-2000FX (manufactured by JEOL Ltd.), and the particle size of 200 or more primary particles randomly selected was determined by image analysis. It was calculated and measured by calculating the average of the number of them. The particle size is the equivalent circle diameter of the primary particles.
本発明におけるカーボンブラックの比表面積は３５〜４００ｍ2／ｇであることが好ましい。比表面積を４００ｍ2／ｇ以下とすることで、粒子間の相互作用が抑制されるため、負極活物質の間に均一に分散され、良好な導電経路と保液性が得られ易くなる。また、３５ｍ2／ｇ以上、より好ましくは４０ｍ2／ｇ以上とすることで、負極活物質及び集電体との接点が多くなり、良好な導電性付与効果と保液性が得られ易くなる。なお、本発明において、比表面積は、ＪＩＳ Ｋ６２１７−２：２０１７に準拠して測定した単点法窒素吸着比表面積を指す。 The specific surface area of carbon black in the present invention is preferably 35 to 400 m 2 / g. By setting the specific surface area to 400 m 2 / g or less, the interaction between the particles is suppressed, so that the particles are uniformly dispersed between the negative electrode active materials, and a good conductive path and liquid retention property can be easily obtained. Further, when it is 35 m 2 / g or more, more preferably 40 m 2 / g or more, the number of contacts with the negative electrode active material and the current collector is increased, and it becomes easy to obtain a good conductivity-imparting effect and liquid retention property. .. In the present invention, the specific surface area refers to the single point method nitrogen adsorption specific surface area measured in accordance with JIS K6217-2: 2017.
本発明におけるカーボンブラックの体積抵抗率はとくに限定されるものではないが、導電性の観点から低いほど好ましい。具体的には、７．５ＭＰａ圧縮下で測定した体積抵抗率は０．３０Ω・ｃｍ以下が好ましく、０．２５Ω・ｃｍ以下がより好ましい。 The volume resistivity of carbon black in the present invention is not particularly limited, but the lower the volume resistivity is, the more preferable it is from the viewpoint of conductivity. Specifically, the volume resistivity measured under 7.5 MPa compression is preferably 0.30 Ω · cm or less, more preferably 0.25 Ω · cm or less.
本発明におけるカーボンブラックの灰分及び水分は特に限定されるものではないが、副反応の抑制の観点から、どちらも少ないほど好ましい。具体的には、灰分は０．０４質量％以下が好ましく、水分は０．１０質量％以下が好ましい。 The ash content and water content of carbon black in the present invention are not particularly limited, but from the viewpoint of suppressing side reactions, the smaller the amount, the more preferable. Specifically, the ash content is preferably 0.04% by mass or less, and the water content is preferably 0.10% by mass or less.
＜結着材＞
本発明で用いる結着材としては、例えば、ポリフッ化ビニリデン、ポリテトラフルオロエチレン、スチレン−ブタジエン共重合体、（メタ）アクリル酸エステル共重合体が挙げられる。結着材としてのポリマーの構造には制約がなく、ランダム共重合体、交互共重合体、グラフト共重合体、ブロック共重合体なども使用できる。これらの中では、電池性能の点でスチレン−ブタジエン共重合体が好ましい。
<Bundling material>
Examples of the binder used in the present invention include polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene copolymer, and (meth) acrylic acid ester copolymer. There are no restrictions on the structure of the polymer as a binder, and random copolymers, alternating copolymers, graft copolymers, block copolymers, and the like can also be used. Among these, a styrene-butadiene copolymer is preferable in terms of battery performance.
＜分散剤＞
本発明で用いる分散剤は、少なくともポリビニルアルコール（以下、ＰＶＡと略すことがある。）を含有する。分散剤中のＰＶＡの含有濃度は例えば５０質量％以上とすることができ、好ましくは７０質量％以上とすることができ、より好ましくは９０質量％以上とすることができる。分散剤としてＰＶＡのみを使用することもできる。ＰＶＡはそれ自体既知の重合方法、例えば、酢酸ビニルに代表される脂肪酸ビニルエステルを重合し、加水分解することにより得ることができる。
<Dispersant>
The dispersant used in the present invention contains at least polyvinyl alcohol (hereinafter, may be abbreviated as PVA). The concentration of PVA in the dispersant can be, for example, 50% by mass or more, preferably 70% by mass or more, and more preferably 90% by mass or more. It is also possible to use only PVA as the dispersant. PVA can be obtained by a polymerization method known per se, for example, by polymerizing and hydrolyzing a fatty acid vinyl ester typified by vinyl acetate.
上記脂肪酸ビニルエステルとしては、例えば、ギ酸ビニル、酢酸ビニル、プロピオン酸ビニル、酪酸ビニル、カプリン酸ビニル、ラウリン酸ビニル、パルミチン酸ビニル、ステアリン酸ビニルおよびその他の直鎖または分岐状の飽和脂肪酸ビニルエステルが挙げられる。なかでも酢酸ビニルが好ましい。 Examples of the fatty acid vinyl ester include vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl caprate, vinyl laurate, vinyl palmitate, vinyl stearate and other linear or branched saturated fatty acid vinyl esters. Can be mentioned. Of these, vinyl acetate is preferable.
上記ポリビニルアルコールは、脂肪酸ビニルエステル以外の重合性不飽和モノマーと共重合して得ることもできる。脂肪酸ビニルエステルと共重合可能な重合性不飽和モノマーとしては、例えば、エチレン、プロピレンなどのオレフィン類；アルキル（メタ）アクリレート、２−ヒドロキシエチル（メタ）アクリレート、グリシジル（メタ）アクリレートなどの（メタ）アクリロイル基含有モノマー；アリルグリシジルエーテルなどのアリルエーテル；塩化ビニル、塩化ビニリデン、フッ化ビニルなどのハロゲン化ビニル系化合物；アルキルビニルエーテル、４−ヒドロキシビニルエーテルなどのビニルエーテルなどが挙げられる。これらは１種を単独で又は２種以上を併用して用いることができる。 The polyvinyl alcohol can also be obtained by copolymerizing with a polymerizable unsaturated monomer other than the fatty acid vinyl ester. Examples of the polymerizable unsaturated monomer copolymerizable with the fatty acid vinyl ester include olefins such as ethylene and propylene; (meth) such as alkyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, and glycidyl (meth) acrylate. ) Acryloyl group-containing monomer; allyl ether such as allyl glycidyl ether; vinyl halide compound such as vinyl chloride, vinylidene chloride and vinyl fluoride; vinyl ether such as alkyl vinyl ether and 4-hydroxy vinyl ether. These can be used alone or in combination of two or more.
ポリビニルアルコールの重合方法は、それ自体既知の重合方法、例えば、酢酸ビニルをアルコール系有機溶媒中で溶液重合してポリ酢酸ビニルを製造し、これを鹸化する等の方法により製造することができるが、これに限られるものではなく、例えば、バルク重合や乳化重合や懸濁重合等でもよい。溶液重合を行う場合には、連続重合でもよいしバッチ重合でもよく、単量体は一括して仕込んでもよいし、分割して仕込んでもよく、あるいは連続的又は断続的に添加してもよい。 The method for polymerizing polyvinyl alcohol can be produced by a polymerization method known per se, for example, by solution-polymerizing vinyl acetate in an alcohol-based organic solvent to produce polyvinyl acetate, and then saponifying the polyvinyl acetate. However, the present invention is not limited to this, and for example, bulk polymerization, emulsion polymerization, suspension polymerization and the like may be used. When solution polymerization is carried out, continuous polymerization or batch polymerization may be performed, the monomers may be charged all at once, may be charged separately, or may be added continuously or intermittently.
溶液重合において使用する重合開始剤は、特に限定するものではないが、アゾビスイソブチロニトリル、アゾビス−２，４−ジメチルバレロニトリル、アゾビス（４−メトキシ−２，４−ジメチルバレロニトリル）等のアゾ化合物；アセチルパーオキサイド、ベンゾイルパーオキサイド、ラウロイルパーオキサイド、アセチルシクロヘキシルスルホニルパーオキシド、２，４，４−トリメチルペンチル−２−パーオキシフェノキシアセテート等の過酸化物；ジイソプロピルパーオキシジカーボネート、ジ−２−エチルヘキシルパーオキシジカーボネート、ジエトキシエチルパーオキシジカーボネート等のパーカーボネート化合物；ｔ−ブチルパーオキシネオデカネート、α−クミルパーオキシネオデカネート、ｔ−ブチルパーオキシネオデカネート等のパーエステル化合物；アゾビスジメチルバレロニトリル、アゾビスメトキシバレロニトリル等の公知のラジカル重合開始剤を使用することができる。 The polymerization initiator used in solution polymerization is not particularly limited, but is azobisisobutyronitrile, azobis-2,4-dimethylvaleronitrile, azobis (4-methoxy-2,4-dimethylvaleronitrile), etc. Azo compounds; peroxides such as acetyl peroxide, benzoyl peroxide, lauroyl peroxide, acetylcyclohexylsulfonyl peroxide, 2,4,4-trimethylpentyl-2-peroxyphenoxyacetate; diisopropylperoxydicarbonate, diisopropylperoxydicarbonate. Percarbonate compounds such as -2-ethylhexyl peroxydicarbonate and diethoxyethyl peroxydicarbonate; such as t-butylperoxyneodecanate, α-cumylperoxyneodecanate and t-butylperoxyneodecanate. Perester compound; known radical polymerization initiators such as azobisdimethylvaleronitrile and azobismethoxyvaleronitrile can be used.
重合反応温度は、特に限定するものではないが、通常３０〜１５０℃程度の範囲で設定することができる。 The polymerization reaction temperature is not particularly limited, but can usually be set in the range of about 30 to 150 ° C.
ポリビニルアルコールを製造する際の鹸化条件は特に限定されず、公知の方法で鹸化することができる。一般的には、メタノール等のアルコール溶液中において、アルカリ触媒又は酸触媒の存在下で、分子中のエステル部を加水分解することで行うことができる。アルカリ触媒としては、例えば、水酸化ナトリウム、水酸化カリウム、ナトリウムメチラート、ナトリウムエチラート、カリウムメチラート等のアルカリ金属の水酸化物や、アルコラート等を用いることができる。酸触媒としては、例えば、塩酸、硫酸等の無機酸水溶液、ｐ−トルエンスルホン酸等の有機酸を用いることができるが、水酸化ナトリウムを用いることが望ましい。鹸化反応の温度は、特に限定されないが、好ましくは１０〜７０℃、より好ましくは３０〜４０℃の範囲であることが望ましい。反応時間は、特に限定されないが、３０分〜３時間の範囲で行なうことが望ましい。 The saponification conditions for producing polyvinyl alcohol are not particularly limited, and saponification can be performed by a known method. Generally, it can be carried out by hydrolyzing the ester portion in the molecule in the presence of an alkali catalyst or an acid catalyst in an alcohol solution such as methanol. As the alkali catalyst, for example, hydroxides of alkali metals such as sodium hydroxide, potassium hydroxide, sodium methylate, sodium ethylate, potassium methylate and the like, alcoholates and the like can be used. As the acid catalyst, for example, an aqueous inorganic acid solution such as hydrochloric acid or sulfuric acid or an organic acid such as p-toluenesulfonic acid can be used, but it is desirable to use sodium hydroxide. The temperature of the saponification reaction is not particularly limited, but is preferably in the range of 10 to 70 ° C, more preferably 30 to 40 ° C. The reaction time is not particularly limited, but it is desirable to carry out the reaction in the range of 30 minutes to 3 hours.
本発明におけるポリビニルアルコールの鹸化度は８５．５〜９６．５モル％であることが好ましい。鹸化度を９６．５モル％以下とすることで、Ｎ−メチル−２−ピロリドン等の溶媒への溶解性が高まるため、導電材の分散性が向上し、均一で低粘度の負極樹脂組成物を含むスラリーが得られ易くなる。鹸化度を８５．５モル％以上とすることで、高い耐電圧性を得られ易くなる。尚、ここでいうポリビニルアルコールの鹸化度は、ＪＩＳ Ｋ ６７２６：１９９４に準ずる方法で測定される値である。 The degree of saponification of polyvinyl alcohol in the present invention is preferably 85.5 to 96.5 mol%. By setting the saponification degree to 96.5 mol% or less, the solubility in a solvent such as N-methyl-2-pyrrolidone is improved, so that the dispersibility of the conductive material is improved, and a uniform and low viscosity negative electrode resin composition is prepared. It becomes easy to obtain a slurry containing. By setting the saponification degree to 85.5 mol% or more, it becomes easy to obtain high withstand voltage resistance. The degree of saponification of polyvinyl alcohol referred to here is a value measured by a method according to JIS K 6726: 1994.
本発明におけるポリビニルアルコールの平均重合度は２５０〜１８００であることが好ましい。平均重合度を好ましくは１８００以下、より好ましくは１３００以下とすることで、Ｎ−メチル−２−ピロリドン等の溶媒への溶解性が高まるため、導電材の分散性が向上し、均一で低粘度の負極樹脂組成物を含むスラリーが得られ易くなる。平均重合度を２５０以上、より好ましくは５００以上とすることで、負極活物質及び導電材の分散性が高まり、良好な導電経路が得られ易くなる。尚、ここでいう平均重合度は、ＪＩＳ Ｋ ６７２６：１９９４に準ずる方法で測定される値である。 The average degree of polymerization of polyvinyl alcohol in the present invention is preferably 250 to 1800. By setting the average degree of polymerization to preferably 1800 or less, more preferably 1300 or less, the solubility in a solvent such as N-methyl-2-pyrrolidone is increased, so that the dispersibility of the conductive material is improved, and the uniform and low viscosity is improved. It becomes easy to obtain a slurry containing the negative electrode resin composition of. By setting the average degree of polymerization to 250 or more, more preferably 500 or more, the dispersibility of the negative electrode active material and the conductive material is enhanced, and a good conductive path can be easily obtained. The average degree of polymerization referred to here is a value measured by a method according to JIS K 6726: 1994.
＜負極活物質＞
負極活物質としては、天然黒鉛や人造黒鉛等の黒鉛や難黒鉛化炭素、易黒鉛化炭素ポリアセン等の炭素材料、ケイ素原子含有物質、スズ原子含有物質及びチタン酸リチウム等が挙げられる。これらは単独で使用しても、２種以上を併用してもよい。これらの中では、炭素材料、及びケイ素原子含有物質から選択される少なくとも１種以上が好ましく、黒鉛、及びケイ素原子含有物質から選択される少なくとも１種以上がより好ましい。
<Negative electrode active material>
Examples of the negative electrode active material include graphite such as natural graphite and artificial graphite, carbon-resistant carbon, carbon materials such as easily graphitized carbon polyacene, silicon atom-containing substances, tin atom-containing substances, and lithium titanate. These may be used alone or in combination of two or more. Among these, at least one selected from a carbon material and a silicon atom-containing substance is preferable, and at least one selected from graphite and a silicon atom-containing substance is more preferable.
ケイ素原子含有物質としては、例えば、（ｉ）シリコン微粒子、（ii）マグネシウム、カルシウム、リチウム、スズ、ニッケル、銅、鉄、コバルト、モリブデン、マンガン、亜鉛、インジウム、銀、チタン、ゲルマニウム、タンタル、ビスマス、バナジウム、タングステン、ニオブ、アンチモン又はクロムと、珪素との合金又は化合物、（iii）ホウ素、窒素、酸素又は炭素と珪素との化合物等が挙げられる。珪素の合金あるいは化合物の一例としては、ＳｉＢ4、ＳｉＢ6、Ｍｇ2Ｓｉ、Ｎｉ2Ｓｉ、ＴｉＳｉ2、ＭｏＳｉ2、ＣｏＳｉ2、ＮｉＳｉ2、ＣａＳｉ2、ＣｒＳｉ2、Ｃｕ5Ｓｉ、ＦｅＳｉ2、ＭｎＳｉ2、ＮｂＳｉ2、ＴａＳｉ2、ＶＳｉ2、ＷＳｉ2、ＺｎＳｉ2、ＳｉＣ、Ｓｉ3Ｎ4、Ｓｉ2Ｎ2Ｏ、ＳｉＯx（０＜ｘ≦２）あるいはＬｉＳｉＯ等が挙げられる。
スズ原子含有物質としては、例えば、（ｉ）珪素、ニッケル、銅、鉄、コバルト、マンガン、亜鉛、インジウム、銀、チタン、ゲルマニウム、ビスマス、アンチモン又はクロムと、スズとの合金又は化合物、（ｉｉ）酸素又は炭素とスズとの化合物等が挙げられる。
Examples of silicon atom-containing substances include (i) silicon fine particles, (ii) magnesium, calcium, lithium, tin, nickel, copper, iron, cobalt, molybdenum, manganese, zinc, indium, silver, titanium, germanium, and tantalum. Examples thereof include alloys or compounds of bismuth, vanadium, tungsten, niobium, antimony or chromium and silicon, and (iii) boron, nitrogen, oxygen or compounds of carbon and silicon. Examples of silicon alloys or compounds include SiB 4 , SiB 6 , Mg 2 Si, Ni 2 Si, TiSi 2 , MoSi 2 , CoSi 2 , NiSi 2 , CaSi 2 , CrSi 2 , Cu 5 Si, FeSi 2 , MnSi. 2 , NbSi 2 , TaSi 2 , VSi 2 , WSi 2 , ZnSi 2 , SiC, Si 3 N 4 , Si 2 N 2 O, SiO x (0 <x ≦ 2), LiSiO, and the like can be mentioned.
Examples of the tin atom-containing substance include (i) an alloy or compound of silicon, nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony or chromium and tin, (ii). ) Examples thereof include oxygen or a compound of carbon and tin.
＜増粘剤＞
負極樹脂組成物の粘度調整のために増粘剤を適宜添加することが可能である。後述する分散媒が水である場合、増粘剤は、ポリエチレングリコール、セルロース、ポリアクリルアミド、ポリ（Ｎ−ビニルアミド）、ポリ（Ｎ−ビニルピロリドン）及びこれらの誘導体等が挙げられる。それらの中でも、増粘剤は、ポリエチレングリコール、セルロース及びこれらの誘導体が好ましく、カルボキシメチルセルロース（ＣＭＣ）がさらに好ましい。
<Thickener>
A thickener can be appropriately added to adjust the viscosity of the negative electrode resin composition. When the dispersion medium described later is water, examples of the thickener include polyethylene glycol, cellulose, polyacrylamide, poly (N-vinylamide), poly (N-vinylpyrrolidone), and derivatives thereof. Among them, the thickener is preferably polyethylene glycol, cellulose and derivatives thereof, and more preferably carboxymethyl cellulose (CMC).
＜負極樹脂組成物＞
本発明に用いる負極樹脂組成物の製造には公知の方法を用いることができる。例えば、負極活物質、導電材、結着材及び分散剤の溶媒分散溶液をボールミル、サンドミル、二軸混練機、自転公転式攪拌機、プラネタリーミキサー、ディスパーミキサー等により混合することで得られ、一般的には、スラリーにして用いられる。負極樹脂組成物には増粘剤等の慣用成分を添加することも可能である。前記の負極活物質、導電材、結着材及び分散剤としては、既述したものを用いれば良い。負極樹脂組成物を含むスラリーの分散媒としては、水、Ｎ−メチル−２−ピロリドン、シクロヘキサン、メチルエチルケトン、メチルイソブチルケトン等が挙げられる。高分子結着材としてスチレン−ブタジエン共重合体を使用する際は水が好ましく、ポリフッ化ビニリデンを使用する際は、溶解性の点でＮ−メチル−２−ピロリドンが好ましい。
<Negative electrode resin composition>
A known method can be used for producing the negative electrode resin composition used in the present invention. For example, it can be obtained by mixing a solvent dispersion solution of a negative electrode active material, a conductive material, a binder and a dispersant with a ball mill, a sand mill, a twin-screw kneader, a rotating / revolving stirrer, a planetary mixer, a disper mixer, etc. Specifically, it is used as a slurry. It is also possible to add a conventional component such as a thickener to the negative electrode resin composition. As the negative electrode active material, the conductive material, the binder, and the dispersant, those described above may be used. Examples of the dispersion medium of the slurry containing the negative electrode resin composition include water, N-methyl-2-pyrrolidone, cyclohexane, methyl ethyl ketone, methyl isobutyl ketone and the like. When a styrene-butadiene copolymer is used as the polymer binder, water is preferable, and when polyvinylidene fluoride is used, N-methyl-2-pyrrolidone is preferable in terms of solubility.
本発明に用いる負極樹脂組成物中の分散剤と導電材の固形分で比べたときの質量比｛分散剤の質量／導電材の質量｝は０．０３〜０．１５であることが好ましく、０．０４〜０．１２がより好ましく、０．０５〜０．１が最も好ましい。負極樹脂組成物中の分散剤と導電材の質量比を０．０３〜０．１５にすることで分散剤が導電材に吸着し、より高い分散効果が得られ易くなり、０．０５〜０．１にすることでより高い分散効果に加えて、過剰な分散剤が導電材表面を被覆し電荷移動反応を妨害する効果を抑えるので、電池の高抵抗化を抑制できる。 The mass ratio {mass of the dispersant / mass of the conductive material} when comparing the solid content of the dispersant and the conductive material in the negative electrode resin composition used in the present invention is preferably 0.03 to 0.15. 0.04 to 0.12 is more preferable, and 0.05 to 0.1 is most preferable. By setting the mass ratio of the dispersant to the conductive material in the negative electrode resin composition to 0.03 to 0.15, the dispersant is adsorbed on the conductive material, and a higher dispersion effect can be easily obtained, which is 0.05 to 0. By setting it to 1.1, in addition to the higher dispersion effect, the effect of the excess dispersant covering the surface of the conductive material and interfering with the charge transfer reaction is suppressed, so that the increase in resistance of the battery can be suppressed.
＜負極＞
本発明に用いる負極は以下の手順で作製可能である。まず、上記の負極樹脂組成物を含むスラリーを銅箔等の集電体上に塗布した後、加熱によりスラリーに含まれる溶媒を除去し、負極活物質が結着材を介して集電体表面に結着された多孔質体である負極合材層を形成する。次いで、集電体と負極合材層をロールプレス等により加圧して密着させることにより、目的とする負極を得ることができる。
<Negative electrode>
The negative electrode used in the present invention can be produced by the following procedure. First, the slurry containing the above negative electrode resin composition is applied onto a current collector such as a copper foil, and then the solvent contained in the slurry is removed by heating, and the negative electrode active material is applied to the surface of the current collector via the binder. A negative electrode mixture layer, which is a porous body bound to the above, is formed. Next, the target negative electrode can be obtained by pressing the current collector and the negative electrode mixture layer with a roll press or the like to bring them into close contact with each other.
＜リチウムイオン二次電池＞
本発明に用いられるリチウムイオン二次電池の作製方法には、特に制限は無く、従来公知の電池の作製方法を用いて行えば良いが、例えば、図１に模式的に示した構成で、以下の方法により作製することもできる。すなわち、正極１にアルミ製タブ５を溶接し、前記の負極を用いた負極２にニッケル製タブ６を溶接した後、正極１と負極２の間に絶縁層となるポリオレフィン製微多孔膜３を配し、正極１、負極２およびポリオレフィン製微多孔膜３の空隙部分に非水電解液が十分に染込むまで注液し、外装４で封止することで作製することができる。
<Lithium-ion secondary battery>
The method for producing the lithium ion secondary battery used in the present invention is not particularly limited, and a conventionally known method for producing a battery may be used. For example, the configuration schematically shown in FIG. 1 is as follows. It can also be produced by the method of. That is, after welding the
本発明のリチウムイオン二次電池の用途は、特に限定されないが、例えば、デジタルカメラ、ビデオカメラ、ポータブルオーディオプレイヤー、携帯液晶テレビ等の携帯ＡＶ機器、ノート型パソコン、スマートフォン、モバイルＰＣ等の携帯情報端末、その他、携帯ゲーム機器、電動工具、電動式自転車、ハイブリッド自動車、電気自動車、電力貯蔵システム等の幅広い分野において使用することができる。 The application of the lithium ion secondary battery of the present invention is not particularly limited, but for example, mobile information such as a digital camera, a video camera, a portable audio player, a portable AV device such as a portable LCD TV, a notebook computer, a smartphone, and a mobile PC. It can be used in a wide range of fields such as terminals, other portable game devices, electric tools, electric bicycles, hybrid vehicles, electric vehicles, and power storage systems.
以下、実施例および比較例を挙げて本発明をより具体的に説明するが、本発明は、その趣旨を損なわない限り、以下に示す実施例に限定されるものではない。また、実施例および比較例ともに使用した負極は、吸着した水分を揮発させるために１００℃で４時間真空乾燥を行った。 Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the Examples shown below as long as the gist thereof is not impaired. The negative electrode used in both Examples and Comparative Examples was vacuum dried at 100 ° C. for 4 hours in order to volatilize the adsorbed water.
＜実施例１＞
（負極樹脂組成物を含むスラリーの調製）
溶媒として純水（関東化学社製）、導電材としてカーボンブラック（デンカ社製、「Ｌｉ−４３５」、以下、Ｌｉ−４３５と記載）、分散剤としてポリビニルアルコール（ポリビニルアルコールＡと記載）、結着材としてスチレン−ブタジエン共重合体（以下、ＳＢＲと記載）、増粘剤としてカルボキシメチルセルロース（以下、ＣＭＣと記載）、活物質として人造黒鉛（Ｓｈｅｎｚｈｅｎ ＢＴＲ社製、「ＡＧＰ−２Ａ」）をそれぞれ用意した。Ｌｉ−４３５が固形分で１質量％、ポリビニルアルコールＡが固形分で０．１質量％（分散剤の質量／導電材の質量＝０．１）、ＣＭＣが固形分で１質量％、人造黒鉛が固形分で９６質量％となるように秤量して混合し、この混合物に純水を添加し、自転公転式混合機（シンキー社製、「あわとり練太郎ＡＲＶ−３１０」）を用いて、均一になるまで混合した。さらに、ＳＢＲが固形分で１．９質量％となるように秤量し、上記混合物に添加し、自転公転式混合機（シンキー社製、「あわとり練太郎ＡＲＶ−３１０」）を用いて、均一になるまで混合し、固形分濃度５０質量％の負極樹脂組成物を含むスラリーを得た。
<Example 1>
(Preparation of slurry containing negative electrode resin composition)
Pure water (manufactured by Kanto Chemical Co., Inc.) as a solvent, carbon black (manufactured by Denka, "Li-435", hereinafter referred to as Li-435) as a conductive material, polyvinyl alcohol (described as polyvinyl alcohol A) as a dispersant, and a conclusion. Styrene-butadiene copolymer (hereinafter referred to as SBR) as a coating material, carboxymethyl cellulose (hereinafter referred to as CMC) as a thickener, and artificial graphite (manufactured by Shenzhen BTR, "AGP-2A") as an active material, respectively. I prepared it. Li-435 has a solid content of 1% by mass, polyvinyl alcohol A has a solid content of 0.1% by mass (mass of dispersant / mass of conductive material = 0.1), CMC has a solid content of 1% by mass, and artificial graphite. Weighed and mixed so that the solid content was 96% by mass, pure water was added to this mixture, and a rotating and revolving mixer (manufactured by Shinky Co., Ltd., "Awatori Rentaro ARV-310") was used. Mix until uniform. Further, the SBR is weighed so as to have a solid content of 1.9% by mass, added to the above mixture, and homogenized using a rotation / revolution type mixer (manufactured by Shinky Co., Ltd., "Awatori Rentaro ARV-310"). The mixture was mixed until a solid content concentration of 50% by mass was obtained to obtain a slurry containing a negative electrode resin composition.
［分散性の評価（負極樹脂組成物を含むスラリーの粘度）］
負極樹脂組成物を含むスラリーの分散性をＪＩＳ Ｋ７２４４−１０に記載される回転型レオメータを用いた方法で粘度を評価した。具体的には、回転型レオメータ（アントンパール社製、「ＭＣＲ３００」）を用いて、固形分含有量が５０質量％の負極樹脂組成物を含むスラリー１ｇをディスク上に塗布し、せん断速度を１００ｓ-1から０．０１ｓ-1まで変化させて測定を行い、せん断速度１ｓ-1の粘度を評価した。粘度の数値が低い程、良好な分散性を意味する。本実施例の粘度は、３．５Ｐａ・ｓであった。
[Evaluation of dispersibility (viscosity of slurry containing negative electrode resin composition)]
The dispersibility of the slurry containing the negative electrode resin composition was evaluated by the method using a rotary rheometer described in JIS K7244-10. Specifically, using a rotary rheometer (manufactured by Anton Pearl Co., Ltd., "MCR300"), 1 g of a slurry containing a negative electrode resin composition having a solid content of 50% by mass is applied onto a disk, and a shear rate is set to 100 s. The measurement was carried out by changing from -1 to 0.01s -1 , and the viscosity at a shear rate of 1s -1 was evaluated. The lower the viscosity value, the better the dispersibility. The viscosity of this example was 3.5 Pa · s.
（負極の作製）
負極樹脂組成物を含むスラリーを、厚さ１０μｍの銅箔（ＵＡＣＪ社製）上にアプリケータにて成膜し、乾燥機内に静置して６０℃、一時間で予備乾燥させた。次に、ロールプレス機にて１００ｋｇ／ｃｍの線圧でプレスし、厚さ１０μｍの銅箔を含んだ塗膜の厚さが５０μｍになるように調製した。残留水分を完全に除去するため、１２０℃で３時間真空乾燥して負極を得た。
(Preparation of negative electrode)
A slurry containing the negative electrode resin composition was formed on a copper foil (manufactured by UACJ Corporation) having a thickness of 10 μm with an applicator, allowed to stand in a dryer, and pre-dried at 60 ° C. for 1 hour. Next, it was pressed with a roll press machine at a linear pressure of 100 kg / cm to prepare a coating film containing a copper foil having a thickness of 10 μm so that the thickness of the coating film was 50 μm. In order to completely remove the residual water, vacuum drying was performed at 120 ° C. for 3 hours to obtain a negative electrode.
［負極の極板抵抗評価］
作製した負極を直径１４ｍｍの円盤状に切り抜き、表裏をＳＵＳ３０４製平板電極によって挟んだ状態で、電気化学測定システム（ソーラトロン社製、「ファンクションジェネレーター１２６０」および「ポテンショガルバノスタット１２８７」）を用いて、振幅電圧１０ｍＶ、周波数範囲１Ｈｚ〜１００ｋＨｚにて交流インピーダンスを測定した。得られた抵抗成分値に、切り抜いた円盤状の面積を掛けた抵抗値を極板抵抗とした。本実施例の負極の極板抵抗は１．２Ω・ｃｍ2であった。
[Evaluation of electrode plate resistance of negative electrode]
The prepared negative electrode was cut out into a disk shape with a diameter of 14 mm, and the front and back surfaces were sandwiched between SUS304 flat plates, and an electrochemical measurement system (Solartron, "Function Generator 1260" and "Potensho Galvanostat 1287") was used. The AC impedance was measured at an amplitude voltage of 10 mV and a frequency range of 1 Hz to 100 kHz. The resistance value obtained by multiplying the obtained resistance component value by the cut-out disk-shaped area was defined as the electrode plate resistance. The electrode plate resistance of the negative electrode of this example was 1.2 Ω · cm 2 .
（正極の作製）
溶媒としてＮ−メチル−２−ピロリドン（関東化学株式会社製、以下、ＮＭＰと記載）、結着材としてポリフッ化ビニリデン（アルケマ社製、「ＨＳＶ９００」、以下、ＰＶｄＦと記載）、導電材としてカーボンブラック（デンカ社製、「Ｌｉ−４３５」、以下、Ｌｉ−４３５と記載）、分散剤としてポリビニルアルコール（ポリビニルアルコールＡと記載）、活物質としてＬｉＮｉ0.5Ｍｎ0.3Ｃｏ0.2Ｏ2（ユミコア社製、「ＴＸ１０」平均一次粒子径（Ｄ５０）１０μｍ、以下、「ＮＭＣ５３２」と記載）をそれぞれ用意した。ＰＶｄＦが固形分で１．９質量％、Ｌｉ−４３５が固形分で１質量％、ポリビニルアルコールＡが固形分で０．１質量％（分散剤の質量／導電材の質量＝０．１）、ＮＭＣ５３２が固形分で９７質量％となるように秤量して混合し、この混合物に固形分含有量が６８質量％になるようにＮＭＰを添加し、自転公転式混合機（シンキー社製、「あわとり練太郎ＡＲＶ−３１０」）を用いて、均一になるまで混合し正極樹脂組成物を含むスラリーを得た。調製した正極樹脂組成物を含むスラリーを、厚さ１５μｍのアルミニウム箔（ＵＡＣＪ社製）の片面上に、アプリケータにて成膜し、乾燥機内に静置して１０５℃、一時間で予備乾燥させ、ＮＭＰ溶媒を完全に除去した。次に、ロールプレス機にて２００ｋｇ／ｃｍの線圧でプレスし、厚さ１５μｍのアルミニウム箔を含んだ塗膜の厚さが８０μｍになるように調製した。次いで、残留水分を完全に除去するため、１７０℃で３時間真空乾燥して正極を得た。
(Preparation of positive electrode)
N-methyl-2-pyrrolidone (manufactured by Kanto Chemical Co., Inc., hereinafter referred to as NMP) as a solvent, polyvinylidene fluoride (manufactured by Alchema, hereinafter referred to as PVdF) as a binder, and carbon as a conductive material. Black (manufactured by Denka, "Li-435", hereinafter referred to as Li-435), polyvinyl alcohol as a dispersant (described as polyvinyl alcohol A), LiNi 0.5 Mn 0.3 Co 0.2 O 2 (manufactured by Yumicore) “TX10” average primary particle diameter (D50) of 10 μm, hereinafter referred to as “NMC532”) was prepared. PVdF is 1.9% by mass in solid content, Li-435 is 1% by mass in solid content, polyvinyl alcohol A is 0.1% by mass in solid content (mass of dispersant / mass of conductive material = 0.1), NMC532 is weighed and mixed so that the solid content is 97% by mass, NMP is added to this mixture so that the solid content is 68% by mass, and a rotating and revolving mixer (manufactured by Shinky Co., Ltd., "Awa" Using Tori-Kentaro ARV-310 ”), the mixture was mixed until uniform to obtain a slurry containing a positive resin composition. A slurry containing the prepared positive electrode resin composition was formed on one side of a 15 μm-thick aluminum foil (manufactured by UACJ Corporation) with an applicator, allowed to stand in a dryer, and pre-dried at 105 ° C. for 1 hour. The NMP solvent was completely removed. Next, it was pressed with a roll press machine at a linear pressure of 200 kg / cm, and the thickness of the coating film containing the aluminum foil having a thickness of 15 μm was adjusted to 80 μm. Then, in order to completely remove the residual water, vacuum drying was performed at 170 ° C. for 3 hours to obtain a positive electrode.
（リチウムイオン二次電池の作製）
露点−５０℃以下に制御したドライルーム内で、上記正極を４０ｍｍ×４０ｍｍに加工し、負極を４４ｍｍ×４４ｍｍに加工した後、正極にアルミ製タブ、負極にニッケル製タブを溶接した。正極と負極それぞれの合材塗工面が中央で対向するようにし、さらに正極と負極間に４５ｍｍ×４５ｍｍに加工したポリオレフィン製微多孔質膜を配置した。次に７０ｍｍ×１４０ｍｍ角に切断・加工したシート状の外装を長辺の中央部で二つ折りにした。次いで、正極用アルミ製タブと負極用ニッケル製タブが外装の外部に露出するように外装を配置しながら、二つ折りにした外装によって正極−ポリオレフィン製微多孔質膜−負極の積層体を挟んだ。次にヒートシーラーを用いて、外装の正極用アルミ製タブと負極用ニッケル製タブが露出した辺を含む２辺を加熱融着した後、加熱融着していない一辺から、２ｇの電解液（キシダ化学製、エチレンカーボネート／ジエチルカーボネート＝１／２（体積比）＋１Ｍ ＬｉＰＦ6溶液、以下、電解液と記載）を注液し、正極、負極およびポリオレフィン製微多孔膜に十分に染み込ませてから、真空ヒートシーラーにより、電池の内部を減圧しながら、外装の残り１辺を加熱融着してリチウムイオン二次電池を得た。
(Manufacturing of lithium ion secondary battery)
In a dry room controlled to have a dew point of −50 ° C. or lower, the positive electrode was processed to 40 mm × 40 mm, the negative electrode was processed to 44 mm × 44 mm, and then an aluminum tab was welded to the positive electrode and a nickel tab was welded to the negative electrode. The coated surfaces of the mixture of the positive electrode and the negative electrode were opposed to each other in the center, and a microporous polyolefin film processed to 45 mm × 45 mm was arranged between the positive electrode and the negative electrode. Next, the sheet-like exterior cut and processed into a 70 mm × 140 mm square was folded in half at the center of the long side. Next, while arranging the exterior so that the aluminum tab for the positive electrode and the nickel tab for the negative electrode are exposed to the outside of the exterior, the laminated body of the positive electrode-polyolefin microporous film-negative electrode was sandwiched between the two-folded exterior. .. Next, using a heat sealer, two sides including the exposed side of the aluminum tab for the positive electrode and the nickel tab for the negative electrode of the exterior are heat-sealed, and then 2 g of the electrolytic solution (2 g of the electrolytic solution) is applied from one side that is not heat-sealed. Kishida Chemical Co., Ltd., ethylene carbonate / diethyl carbonate = 1/2 (volume ratio) + 1M LiPF 6 solution, hereinafter referred to as electrolyte solution) is injected and sufficiently soaked into the positive electrode, negative electrode and polyolefin microporous film. A lithium ion secondary battery was obtained by heating and fusing the remaining one side of the exterior while depressurizing the inside of the battery with a vacuum heat sealer.
作製したリチウムイオン二次電池について、以下の方法により電池性能を評価した。 The battery performance of the produced lithium ion secondary battery was evaluated by the following method.
（リチウムイオン二次電池の評価）
［放電レート特性（３Ｃ放電時の放電容量維持率）］
作製したリチウムイオン二次電池を、２５℃において、４．３Ｖ、０．２Ｃ制限の定電流定電圧充電をした後、０．２Ｃの定電流で３．０Ｖまで放電した。次いで、再度４．３Ｖ、０．２Ｃ制限の定電流定電圧で回復充電した後、放電電流を０．２Ｃとして３．０Ｖまで放電させ、このときの放電容量を測定した。引き続き、前記の回復充電の条件は毎回保って充電し、一方で放電電流は０．５Ｃ、１Ｃ、２Ｃ、３Ｃと段階的に変化させながら、回復充電と放電とを繰り返し、各放電電流に対する放電容量を測定した。電池の放電レート特性の指標として、０．２Ｃ放電時に対する３Ｃ放電時の放電容量維持率を算出した。本実施例のリチウムイオン二次電池の３Ｃ放電時の放電容量維持率は８３．５％であった。
(Evaluation of lithium-ion secondary battery)
[Discharge rate characteristics (discharge capacity retention rate during 3C discharge)]
The prepared lithium ion secondary battery was charged at 25 ° C. with a constant current and constant voltage limited to 4.3 V and 0.2 C, and then discharged to 3.0 V with a constant current of 0.2 C. Then, after recovering and charging again at a constant current constant voltage limited to 4.3 V and 0.2 C, the discharge current was set to 0.2 C and the battery was discharged to 3.0 V, and the discharge capacity at this time was measured. Subsequently, the recovery charging conditions are maintained and charged each time, while the recovery charging and discharging are repeated while the discharge current is gradually changed to 0.5C, 1C, 2C, and 3C, and the discharge for each discharge current is performed. The capacity was measured. As an index of the discharge rate characteristic of the battery, the discharge capacity retention rate at the time of 3C discharge with respect to the time of 0.2C discharge was calculated. The discharge capacity retention rate of the lithium ion secondary battery of this example during 3C discharge was 83.5%.
［サイクル特性（サイクル後の放電容量維持率）］
作製したリチウムイオン二次電池を、２５℃において、４．３Ｖ、１Ｃ制限の定電流定電圧充電をした後、１Ｃの定電流で３．０Ｖまで放電した。上記充放電を５００サイクル繰り返し、各サイクルにおける放電容量を測定した。電池のサイクル特性の指標として、特に１サイクル後に対する５００サイクル後の放電容量維持率を算出した。本実施例のリチウムイオン二次電池のサイクル後の放電容量維持率は９１％であった。
[Cycle characteristics (discharge capacity retention rate after cycle)]
The produced lithium ion secondary battery was charged at a constant current constant voltage of 4.3 V and 1 C limit at 25 ° C., and then discharged to 3.0 V at a constant current of 1 C. The above charge and discharge were repeated for 500 cycles, and the discharge capacity in each cycle was measured. As an index of the cycle characteristics of the battery, the discharge capacity retention rate after 500 cycles with respect to one cycle was calculated. The discharge capacity retention rate after the cycle of the lithium ion secondary battery of this example was 91%.
実施例１〜９、比較例１〜４で使用したポリビニルアルコールの鹸化度及び平均重合度を表１に示す。また、実施例１〜９、比較例１〜６で使用したカーボンブラックの平均一次粒子径及び比表面積を表２に示す。 Table 1 shows the saponification degree and the average degree of polymerization of the polyvinyl alcohols used in Examples 1 to 9 and Comparative Examples 1 to 4. Table 2 shows the average primary particle size and specific surface area of carbon black used in Examples 1 to 9 and Comparative Examples 1 to 6.
＜実施例２＞
実施例１の負極用分散剤を、ポリビニルアルコールＢへ変更した以外は、実施例１と同様な方法で負極、正極及びリチウムイオン二次電池を作製し、各評価を実施した。結果を表３に示す。
<Example 2>
A negative electrode, a positive electrode, and a lithium ion secondary battery were prepared in the same manner as in Example 1 except that the dispersant for the negative electrode of Example 1 was changed to polyvinyl alcohol B, and each evaluation was carried out. The results are shown in Table 3.
＜実施例３＞
実施例１の負極用分散剤を、ポリビニルアルコールＣへ変更した以外は、実施例１と同様な方法で負極、正極及びリチウムイオン二次電池を作製し、各評価を実施した。結果を表３に示す。
<Example 3>
A negative electrode, a positive electrode, and a lithium ion secondary battery were prepared in the same manner as in Example 1 except that the dispersant for the negative electrode of Example 1 was changed to polyvinyl alcohol C, and each evaluation was carried out. The results are shown in Table 3.
＜実施例４＞
実施例１の負極用分散剤を、ポリビニルアルコールＤへ変更した以外は、実施例１と同様な方法で負極、正極及びリチウムイオン二次電池を作製し、各評価を実施した。結果を表３に示す。
<Example 4>
A negative electrode, a positive electrode, and a lithium ion secondary battery were prepared in the same manner as in Example 1 except that the dispersant for the negative electrode of Example 1 was changed to polyvinyl alcohol D, and each evaluation was carried out. The results are shown in Table 3.
＜実施例５＞
実施例１の負極用導電材を、ＳＡＢ（デンカ社製）へ変更した以外は、実施例１と同様な方法で負極、正極及びリチウムイオン二次電池を作製し、各評価を実施した。結果を表３に示す。
<Example 5>
A negative electrode, a positive electrode, and a lithium ion secondary battery were produced in the same manner as in Example 1 except that the conductive material for the negative electrode of Example 1 was changed to SAB (manufactured by Denka), and each evaluation was carried out. The results are shown in Table 3.
＜実施例６＞
実施例１の負極用導電材を、Ｌｉ−２５０（デンカ社製）へ変更し、負極樹脂組成物の固形分組成を、Ｌｉ−２５０が固形分で１質量％、ポリビニルアルコールＡが固形分で０．０５質量％（分散剤の質量／導電材の質量＝０．０５）、ＣＭＣが固形分で１質量％、人造黒鉛が固形分で９６質量％、ＳＢＲが固形分で１．９５質量％となるように変更した以外は、実施例１と同様な方法で負極、正極及びリチウムイオン電池を作製し、各評価を実施した。結果を表３に示す。
<Example 6>
The conductive material for the negative electrode of Example 1 was changed to Li-250 (manufactured by Denka Co., Ltd.), and the solid content composition of the negative electrode resin composition was such that Li-250 had a solid content of 1% by mass and polyvinyl alcohol A had a solid content. 0.05% by mass (mass of dispersant / mass of conductive material = 0.05), CMC is 1% by mass in solid content, artificial graphite is 96% by mass in solid content, and SBR is 1.95% by mass in solid content. A negative electrode, a positive electrode, and a lithium ion battery were produced in the same manner as in Example 1 except that the values were changed to the above, and each evaluation was performed. The results are shown in Table 3.
＜実施例７＞
実施例１の負極用導電材を、Ｌｉ−４００（デンカ社製）へ変更した以外は、実施例１と同様な方法で負極、正極及びリチウムイオン電池を作製し、各評価を実施した。結果を表３に示す。
<Example 7>
A negative electrode, a positive electrode, and a lithium ion battery were produced in the same manner as in Example 1 except that the conductive material for the negative electrode of Example 1 was changed to Li-400 (manufactured by Denka Co., Ltd.), and each evaluation was carried out. The results are shown in Table 3.
＜実施例８＞
実施例１の導電材を、ＥＣＰ（ライオン社製）へ変更し、負極樹脂組成物の固形分組成を、ＥＣＰが固形分で１質量％、ポリビニルアルコールＡが固形分で０．１６質量％（分散剤の質量／導電材の質量＝０．１６）、ＣＭＣが固形分で１質量％、人造黒鉛が固形分で９６質量％、ＳＢＲが固形分で１．８４質量％となるように変更した以外は、実施例１と同様な方法で負極、正極及びリチウムイオン電池を作製し、各評価を実施した。結果を表３に示す。
<Example 8>
The conductive material of Example 1 was changed to ECP (manufactured by Lion), and the solid content composition of the negative electrode resin composition was 1% by mass for ECP and 0.16% by mass for polyvinyl alcohol A. Dispersant mass / conductive material mass = 0.16), CMC was changed to 1% by mass in solid content, artificial graphite was changed to 96% by mass in solid content, and SBR was changed to 1.84% by mass in solid content. A negative electrode, a positive electrode, and a lithium ion battery were produced in the same manner as in Example 1 except for the above, and each evaluation was carried out. The results are shown in Table 3.
＜実施例９＞
実施例１の負極用導電材を、Ｌｉ−２５０（デンカ社製）へ変更し、負極樹脂組成物の固形分組成を、Ｌｉ−２５０が固形分で１質量％、ポリビニルアルコールＡが固形分で０．０２質量％（分散剤の質量／導電材の質量＝０．０２）、ＣＭＣが固形分で１質量％、人造黒鉛が固形分で９６質量％、ＳＢＲが固形分で１．９８質量％となるように変更した以外は、実施例１と同様な方法で負極、正極及びリチウムイオン電池を作製し、各評価を実施した。結果を表３に示す。
<Example 9>
The conductive material for the negative electrode of Example 1 was changed to Li-250 (manufactured by Denka Co., Ltd.), and the solid content composition of the negative electrode resin composition was such that Li-250 had a solid content of 1% by mass and polyvinyl alcohol A had a solid content. 0.02% by mass (mass of dispersant / mass of conductive material = 0.02), CMC is 1% by mass in solid content, artificial graphite is 96% by mass in solid content, and SBR is 1.98% by mass in solid content. A negative electrode, a positive electrode, and a lithium ion battery were produced in the same manner as in Example 1 except that the values were changed to the above, and each evaluation was carried out. The results are shown in Table 3.
＜比較例１＞
実施例１の分散剤を、ポリビニルアルコールＥへ変更した以外は、実施例１と同様な方法で負極、正極及びリチウムイオン電池を作製し、各評価を実施した。結果を表３に示す。
<Comparative example 1>
A negative electrode, a positive electrode, and a lithium ion battery were prepared in the same manner as in Example 1 except that the dispersant of Example 1 was changed to polyvinyl alcohol E, and each evaluation was carried out. The results are shown in Table 3.
＜比較例２＞
実施例１の分散剤を、ポリビニルアルコールＦへ変更した以外は、実施例１と同様な方法で負極、正極及びリチウムイオン電池を作製し、各評価を実施した。結果を表３に示す。
<Comparative example 2>
A negative electrode, a positive electrode, and a lithium ion battery were prepared in the same manner as in Example 1 except that the dispersant of Example 1 was changed to polyvinyl alcohol F, and each evaluation was carried out. The results are shown in Table 3.
＜比較例３＞
実施例１の導電材を、＃３０３０Ｂ（三菱化学社製）へ変更し、負極樹脂組成物の固形分組成を、＃３０３０Ｂが固形分で１質量％、ポリビニルアルコールＡが固形分で０．０３質量％（分散剤の質量／導電材の質量＝０．０３）、ＣＭＣが固形分で１質量％、人造黒鉛が固形分で９６質量％、ＳＢＲが固形分で１．９７質量％となるように変更した以外は、実施例１と同様な方法で負極、正極及びリチウムイオン電池を作製し、各評価を実施した。結果を表３に示す。
<Comparative example 3>
The conductive material of Example 1 was changed to # 3030B (manufactured by Mitsubishi Chemical Corporation), and the solid content composition of the negative electrode resin composition was such that # 3030B had a solid content of 1% by mass and polyvinyl alcohol A had a solid content of 0.03. Mass% (mass of dispersant / mass of conductive material = 0.03), CMC is 1% by mass in solid content, artificial graphite is 96% by mass in solid content, and SBR is 1.97% by mass in solid content. A negative electrode, a positive electrode, and a lithium ion battery were produced in the same manner as in Example 1 except that the results were changed to, and each evaluation was carried out. The results are shown in Table 3.
＜比較例４＞
実施例１の導電材を、ＢｌａｃｋＰｅａｒｌｓ２０００（キャボット社製）へ変更し、負極樹脂組成物の固形分組成を、ＢｌａｃｋＰｅａｒｌｓ２０００が固形分で１質量％、ポリビニルアルコールＡが固形分で０．１５質量％（分散剤の質量／導電材の質量＝０．１５）、ＣＭＣが固形分で１質量％、人造黒鉛が固形分で９６質量％、ＳＢＲが固形分で１．８５質量％となるように変更した以外は、実施例１と同様な方法で負極、正極及びリチウムイオン電池を作製し、各評価を実施した。結果を表３に示す。
<Comparative example 4>
The conductive material of Example 1 was changed to BlackPearls2000 (manufactured by Cabot), and the solid content composition of the negative electrode resin composition was 1% by mass for BlackPearls2000 and 0.15% by mass for polyvinyl alcohol A (solid content). Dispersant mass / conductive material mass = 0.15), CMC was changed to 1% by mass in solid content, artificial graphite was changed to 96% by mass in solid content, and SBR was changed to 1.85% by mass in solid content. A negative electrode, a positive electrode, and a lithium ion battery were produced in the same manner as in Example 1 except for the above, and each evaluation was carried out. The results are shown in Table 3.
＜比較例５＞
実施例１の導電材を、ポリビニルピロリドン（日本触媒社製、「Ｋ−９０」）へ変更した以外は、実施例１と同様な方法で負極、正極及びリチウムイオン電池を作製し、各評価を実施した。結果を表３に示す。
<Comparative example 5>
A negative electrode, a positive electrode, and a lithium ion battery were produced in the same manner as in Example 1 except that the conductive material of Example 1 was changed to polyvinylpyrrolidone (manufactured by Nippon Shokubai Co., Ltd., “K-90”), and each evaluation was performed. Carried out. The results are shown in Table 3.
＜比較例６＞
実施例１の分散剤を添加せずに、負極樹脂組成物の固形分組成を、Ｌｉ−４３５が固形分で１質量％、ＣＭＣが固形分で１質量％、人造黒鉛が固形分で９６質量％、ＳＢＲが固形分で２質量％となるように変更した以外は、実施例１と同様な方法で負極、正極及びリチウムイオン電池を作製し、各評価を実施した。結果を表３に示す。
<Comparative Example 6>
Without adding the dispersant of Example 1, the solid content composition of the negative electrode resin composition was such that Li-435 had a solid content of 1% by mass, CMC had a solid content of 1% by mass, and artificial graphite had a solid content of 96% by mass. A negative electrode, a positive electrode, and a lithium ion battery were prepared in the same manner as in Example 1 except that% and SBR were changed to 2% by mass in terms of solid content, and each evaluation was carried out. The results are shown in Table 3.
実施例１〜９の負極樹脂組成物は、比較例１〜６の負極樹脂組成物に比べて分散性が高いことが明らかになった。これにより本発明の実施例の負極は極板抵抗が低くなり、放電時の電圧降下を抑えられることが分かった。 It was clarified that the negative electrode resin compositions of Examples 1 to 9 had higher dispersibility than the negative electrode resin compositions of Comparative Examples 1 to 6. As a result, it was found that the negative electrode of the embodiment of the present invention has a low electrode plate resistance and can suppress the voltage drop during discharging.
さらに、実施例１〜９のリチウムイオン二次電池は、比較例１〜６のリチウムイオン二次電池に比べて放電レート特性が高く、サイクル特性も高いことが明らかになった。これにより本発明の負極樹脂組成物を用いたリチウムイオン二次電池は放電電流の増加に伴う放電レート特性の低下を抑えられ、高い寿命も兼ね備えていることが分かった。 Further, it was revealed that the lithium ion secondary batteries of Examples 1 to 9 have higher discharge rate characteristics and higher cycle characteristics than the lithium ion secondary batteries of Comparative Examples 1 to 6. As a result, it was found that the lithium ion secondary battery using the negative electrode resin composition of the present invention can suppress the deterioration of the discharge rate characteristic due to the increase in the discharge current and also has a long life.
１ リチウムイオン二次電池正極
２ リチウムイオン二次電池負極
３ ポリオレフィン製微多孔膜
４ 外装
５ アルミ製タブ
６ ニッケル製タブ
1 Lithium-ion secondary battery Positive electrode 2 Lithium-ion secondary battery Negative electrode 3 Polyolefin microporous film 4
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