JP2018147826A - Negative electrode binder for nonaqueous electrolyte secondary battery, and negative electrode for nonaqueous electrolyte secondary battery - Google Patents
Negative electrode binder for nonaqueous electrolyte secondary battery, and negative electrode for nonaqueous electrolyte secondary battery Download PDFInfo
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- JP2018147826A JP2018147826A JP2017044167A JP2017044167A JP2018147826A JP 2018147826 A JP2018147826 A JP 2018147826A JP 2017044167 A JP2017044167 A JP 2017044167A JP 2017044167 A JP2017044167 A JP 2017044167A JP 2018147826 A JP2018147826 A JP 2018147826A
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- 239000011883 electrode binding agent Substances 0.000 title claims abstract description 15
- 239000011230 binding agent Substances 0.000 claims abstract description 78
- -1 carboxylic acid compound Chemical class 0.000 claims abstract description 58
- 239000011149 active material Substances 0.000 claims abstract description 21
- 229920001577 copolymer Polymers 0.000 claims abstract description 20
- 239000000203 mixture Substances 0.000 claims abstract description 17
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 16
- 125000000217 alkyl group Chemical group 0.000 claims abstract description 12
- 125000003178 carboxy group Chemical group [H]OC(*)=O 0.000 claims abstract description 12
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- 150000001875 compounds Chemical class 0.000 claims abstract description 9
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 8
- 125000003262 carboxylic acid ester group Chemical group [H]C([H])([*:2])OC(=O)C([H])([H])[*:1] 0.000 claims abstract description 3
- 239000000178 monomer Substances 0.000 claims description 9
- 239000000126 substance Substances 0.000 claims description 8
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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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- Battery Electrode And Active Subsutance (AREA)
Abstract
Description
本発明は、非水電解質二次電池用負極バインダに関するものである。より詳細には、寿命特性を向上させうる非水電解質二次電池用負極バインダに関するものである。 The present invention relates to a negative electrode binder for a nonaqueous electrolyte secondary battery. More specifically, the present invention relates to a negative electrode binder for a non-aqueous electrolyte secondary battery that can improve life characteristics.
近年、石油使用量や温室効果ガス削減、エネルギー基盤の更なる多様化や効率化を目指し、繰り返し充放電可能な二次電池として、非水電解質二次電池（例えば、Ｌｉイオン二次電池）に注目が集まっている。特に、電気自動車やハイブリッド電気自動車、燃料電池車への用途展開が見込まれている。電気自動車においては、航続距離の向上が要求され、今後、Ｌｉイオン二次電池の高エネルギー密度化が一層要求されていくことになる。 In recent years, non-aqueous electrolyte secondary batteries (for example, Li-ion secondary batteries) have been used as secondary batteries that can be repeatedly charged and discharged with the aim of reducing oil consumption and greenhouse gas emissions, and further diversifying and improving the energy base. Attention has been gathered. In particular, application to electric vehicles, hybrid electric vehicles, and fuel cell vehicles is expected. In an electric vehicle, an improvement in cruising distance is required, and in the future, higher energy density of Li-ion secondary batteries will be further required.
現状のＬｉイオン二次電池の負極に注目すると、黒鉛電極が一般に用いられている。黒鉛の理論容量は、３７２ｍＡｈ／ｇ（活物質）である。これに対し、黒鉛を上回る容量を示す活物質として、ＳｉやＳｎが近年注目されている。Ｓｉの理論容量は、４２００ｍＡｈ／ｇ（活物質）であり、Ｓｎは、９９０ｍＡｈ／ｇ（活物質）である。しかしながら、ＳｉやＳｎ等の合金系活物質は、Ｌｉ吸蔵や放出に伴う体積変化が大きく、電池特性に様々な悪影響を及ぼす。例えば、Ｓｉは、黒鉛の約１１倍の容量を持っているために、Ｌｉ吸蔵により体積は約３倍増加する。充放電に伴う大きな体積変化は、電解液の還元分解によってもたらされるＳＥＩを安定な皮膜として得ることができず、充放電の繰り返しによる継続的な電解液の還元分解によって、Ｌｉが消費されることによる低いクーロン効率が問題となり、寿命特性の低下をもたらしていた。 When attention is paid to the negative electrode of the current Li ion secondary battery, a graphite electrode is generally used. The theoretical capacity of graphite is 372 mAh / g (active material). On the other hand, Si and Sn have attracted attention in recent years as an active material having a capacity exceeding that of graphite. The theoretical capacity of Si is 4200 mAh / g (active material), and Sn is 990 mAh / g (active material). However, alloy-based active materials such as Si and Sn have a large volume change accompanying Li occlusion and release, and have various adverse effects on battery characteristics. For example, since Si has a capacity about 11 times that of graphite, the volume increases by about 3 times due to Li occlusion. The large volume change accompanying charging / discharging cannot obtain SEI produced by reductive decomposition of the electrolytic solution as a stable film, and Li is consumed by reductive decomposition of the electrolytic solution continuously by repeated charging / discharging. The low Coulomb efficiency caused by the problem became a problem, and the life characteristics were deteriorated.
これに対し、近年、ポリカルボン酸系バインダを適用することにより、クーロン効率の向上と寿命特性の改善が報告されている。非特許文献１では、天然黒鉛電極のバインダとして、ポリアクリル酸を用いて、クーロン効率が改善されることを報告している。また、非特許文献２では、ポリアクリル酸とアクリル酸マレイン酸共重合体をブロック共重合させたバインダを用いることで、Ｓｉ負極の寿命特性を改善できることを報告している。
On the other hand, in recent years, application of a polycarboxylic acid-based binder has been reported to improve coulomb efficiency and lifetime characteristics. Non-Patent
体積変化の小さい天然黒鉛では、ポリカルボン酸によって、天然黒鉛を被覆し、電解液の還元分解によるＬｉ消費を抑制できる。一方で、充放電に伴う大きな体積変化が生じるＳｉでは、ポリアクリル酸とアクリル酸マレイン酸共重合体をブロック共重合させることで、カルボキシル基濃度を減らし、柔軟性を備えたバインダを用いることで、Ｓｉ負極の寿命特性が改善できる。 In natural graphite having a small volume change, natural graphite can be coated with polycarboxylic acid, and Li consumption due to reductive decomposition of the electrolyte can be suppressed. On the other hand, in Si, in which a large volume change occurs due to charge / discharge, block copolymerization of polyacrylic acid and maleic acrylate copolymer reduces the carboxyl group concentration and uses a flexible binder. The life characteristics of the Si negative electrode can be improved.
本発明の課題は、非水電解質二次電池のクーロン効率および寿命特性が改善できる非水電解質二次電池用負極バインダを提供することである。 The subject of this invention is providing the negative electrode binder for nonaqueous electrolyte secondary batteries which can improve the Coulomb efficiency and lifetime characteristic of a nonaqueous electrolyte secondary battery.
上記課題を解決するために、本発明の一態様は、活物質とともに非水電解質二次電池用負極の合剤層を構成するバインダであって、分子量が１００万以上５００万以下であり、繰り返し単位がエチレン性不飽和カルボン酸化合物であるポリマーからなる主バインダと、分子量が１０００以上１万以下のポリマーである補助バインダと、を含み、補助バインダが下記の構成(1)〜(3)の少なくともいずれかからなる非水電解質二次電池用負極バインダを提供する。 In order to solve the above problems, one embodiment of the present invention is a binder that forms a mixture layer of a negative electrode for a nonaqueous electrolyte secondary battery together with an active material, and has a molecular weight of 1,000,000 to 5,000,000. A main binder composed of a polymer whose unit is an ethylenically unsaturated carboxylic acid compound, and an auxiliary binder which is a polymer having a molecular weight of 1000 or more and 10,000 or less, the auxiliary binder having the following constitutions (1) to (3) Provided is a negative electrode binder for a non-aqueous electrolyte secondary battery comprising at least one of them.
(1)エチレン性不飽和カルボン酸化合物(a1)と、アルキル部位(ＣnＨ2n+1−)の炭素数ｎが１以上１０以下であるアルキルカルボン酸エステル基を含む下記の化１に示すエチレン性不飽和化合物(b)と、を繰り返し単位中に含む第一の共重合体。
(2)カルボキシル基のα炭素上に、炭素数ｎが１以上１０以下であるアルキル部位(ＣnＨ2n+1−)を有する、下記の化２に示すエチレン性不飽和カルボン酸化合物(a2)を、繰り返し単位中に含む重合体。
(1) A compound comprising an ethylenically unsaturated carboxylic acid compound (a1) and an alkyl carboxylic acid ester group having an alkyl moiety (C n H 2n + 1 —) having a carbon number n of 1 or more and 10 or less. A first copolymer comprising an ethylenically unsaturated compound (b) in a repeating unit.
(2) An ethylenically unsaturated carboxylic acid compound (a2) represented by the following
(3)前記エチレン性不飽和カルボン酸化合物(a2)以外のエチレン性不飽和カルボン酸化合物(a3)と、前記エチレン性不飽和カルボン酸化合物(a2)と、を繰り返し単位中に含む第二の共重合体。
本発明の一態様によれば、非水電解質二次電池のクーロン効率および寿命特性が改善できる非水電解質二次電池用負極バインダが提供される。 According to one embodiment of the present invention, a negative electrode binder for a non-aqueous electrolyte secondary battery that can improve the Coulomb efficiency and life characteristics of the non-aqueous electrolyte secondary battery is provided.
［本発明者の知見］
本発明者は、Ｓｉ表面を被覆する補助バインダとして、水素結合能を抑えたポリアクリル酸系バインダを用いることで、Ｓｉ表面上に安定な皮膜を形成し、電解液の還元分解によるＬｉ消費を抑え、クーロン効率が改善できることを見出した。
[Inventor's Knowledge]
The present inventor uses a polyacrylic acid binder with reduced hydrogen bonding ability as an auxiliary binder to coat the Si surface, thereby forming a stable film on the Si surface and reducing Li consumption due to reductive decomposition of the electrolyte. We found that the coulomb efficiency can be improved.
［本発明の一態様である非水電解質二次電池用負極バインダの作用］
補助バインダが(1)の場合（第一の共重合の場合）、エチレン性不飽和カルボン酸化合物(a1)のカルボキシル基により、補助バインダが活物質の表面に接着する。また、エチレン性不飽和化合物(b)のアルキル部位(ＣnＨ2n+1−)によって、補助バインダのカルボキシ基による水素結合が阻害されるため、引張負荷が加わった時に分子鎖がすべり易くなり、補助バインダが伸び易くなる。
[Operation of negative electrode binder for non-aqueous electrolyte secondary battery according to one embodiment of the present invention]
When the auxiliary binder is (1) (in the case of the first copolymerization), the auxiliary binder adheres to the surface of the active material by the carboxyl group of the ethylenically unsaturated carboxylic acid compound (a1). Also, ethylenically unsaturated compounds the alkyl moiety of (b) (C n H 2n + 1 -) by the hydrogen bond is hindered by the carboxy group of the auxiliary binder, easily slip the molecular chains when the tensile load is applied The auxiliary binder is easy to extend.
第一の共重合体の単量体配合率は、エチレン性不飽和カルボン酸化合物(a1)が２０モル％以上９０モル％以下、エチレン性不飽和化合物(b)が１０モル％以上８０モル％以下とする。
補助バインダが(2)の場合、エチレン性不飽和カルボン酸化合物(a2)のカルボキシル基により、補助バインダが活物質の表面に接着する。また、エチレン性不飽和カルボン酸化合物(a2)のアルキル部位(ＣnＨ2n+1−)によって、補助バインダのカルボキシ基による水素結合が阻害されるため、引張負荷が加わった時に分子鎖がすべり易くなり、補助バインダが伸び易くなる。
The monomer content of the first copolymer is such that the ethylenically unsaturated carboxylic acid compound (a1) is 20 mol% to 90 mol%, and the ethylenically unsaturated compound (b) is 10 mol% to 80 mol%. The following.
When the auxiliary binder is (2), the auxiliary binder adheres to the surface of the active material by the carboxyl group of the ethylenically unsaturated carboxylic acid compound (a2). In addition, since the hydrogen bond by the carboxy group of the auxiliary binder is inhibited by the alkyl moiety (C n H 2n + 1 −) of the ethylenically unsaturated carboxylic acid compound (a2), the molecular chain slips when a tensile load is applied. It becomes easy and an auxiliary binder becomes easy to extend.
補助バインダが(3)の場合（第二の共重合の場合）、エチレン性不飽和カルボン酸化合物(a3)およびエチレン性不飽和カルボン酸化合物(a2)のカルボキシル基により、補助バインダが活物質の表面に接着する。また、エチレン性不飽和カルボン酸化合物(a2)のアルキル部位(ＣnＨ2n+1−)によって、補助バインダのカルボキシル基による水素結合が阻害されるため、引張負荷が加わった時に分子鎖がすべり易くなり、補助バインダが伸び易くなる。 When the auxiliary binder is (3) (in the case of the second copolymerization), the auxiliary binder is an active material due to the carboxyl group of the ethylenically unsaturated carboxylic acid compound (a3) and the ethylenically unsaturated carboxylic acid compound (a2). Adhere to the surface. In addition, since the alkyl moiety (C n H 2n + 1 −) of the ethylenically unsaturated carboxylic acid compound (a2) inhibits hydrogen bonding by the carboxyl group of the auxiliary binder, the molecular chain slips when a tensile load is applied. It becomes easy and an auxiliary binder becomes easy to extend.
第二の共重合体の単量体配合率は、エチレン性不飽和カルボン酸化合物(a3)が２０モル％以上９０モル％以下、エチレン性不飽和カルボン酸化合物(a2)が１０モル％以上８０モル％以下とする。
よって、補助バインダ(1)〜(3)は、活物質がＳｉを含むものである場合でも、活物質の表面上に安定な皮膜を形成し、電解液の還元分解によるＬｉ消費を抑え、クーロン効率を改善できる。
さらに、主バインダは、カルボキシル基を多く有するとともに、高分子量であることから、高弾性率のバインダであり、Ｓｉの体積変化による合剤層の厚み変化を抑制することができる。
The monomer content of the second copolymer is such that the ethylenically unsaturated carboxylic acid compound (a3) is 20 mol% or more and 90 mol% or less, and the ethylenically unsaturated carboxylic acid compound (a2) is 10 mol% or more and 80 mol% or less. The mol% or less.
Therefore, the auxiliary binders (1) to (3) form a stable film on the surface of the active material even when the active material contains Si, suppress Li consumption due to reductive decomposition of the electrolyte, and improve coulomb efficiency. Can improve.
Furthermore, since the main binder has many carboxyl groups and has a high molecular weight, it is a binder with a high elastic modulus, and can suppress a change in the thickness of the mixture layer due to a change in the volume of Si.
従って、本発明の一態様によれば、体積変化の大きい活物質表面を覆う補助バインダが、活物質表面に安定な皮膜を形成することができるので、繰り返し充放電に伴う継続的なＬｉ消費を抑制することが可能である。これにより、本発明の一態様によれば、寿命特性に優れた非水電解質二次電池用負極バインダを提供することができる。
本発明の一態様の非水電解質二次電池用負極バインダは、主バインダの含有率が６０重量％以上９９重量％以下であり、補助バインダの含有率が１重量％以上４０重量％以下であることが好ましい。このような構成によれば、主バインダによる合剤層の形状保持と、補助バインダによる繰り返し充放電に伴う継続的なＳＥＩの破壊と生成を抑制できる。
Therefore, according to one aspect of the present invention, since the auxiliary binder covering the active material surface with a large volume change can form a stable film on the active material surface, continuous Li consumption associated with repeated charge and discharge is reduced. It is possible to suppress. Thus, according to one embodiment of the present invention, it is possible to provide a negative electrode binder for a non-aqueous electrolyte secondary battery having excellent life characteristics.
The negative electrode binder for a non-aqueous electrolyte secondary battery of one embodiment of the present invention has a main binder content of 60 wt% or more and 99 wt% or less, and an auxiliary binder content of 1 wt% or more and 40 wt% or less. It is preferable. According to such a configuration, it is possible to suppress the shape retention of the mixture layer by the main binder and the continuous destruction and generation of SEI accompanying the repeated charging / discharging by the auxiliary binder.
［実施形態］
以下、本発明の実施形態について図面を参照して説明する。
図１に示すように、実施形態の非水電解質二次電池用負極１は、集電体２上に、合剤層３が積層された構造である。合剤層３は、活物質とともにバインダを含む。バインダは、分子量１００万以上５００万以下（高分子量）のエチレン性不飽和カルボン酸化合物よりなるポリマーからなる主バインダと、分子量１０００以上１万以下（主バインダに比べて低分子量）のポリマーで、前述の(1)〜(3)の少なくともいずれかからなる補助バインダと、を含む。主バインダは、化学結合および金属イオン結合のいずれかまたは両方を含む架橋を有していても良い。補助バインダは、化学結合を含まず、金属イオン結合を含んでいても良い。
[Embodiment]
Embodiments of the present invention will be described below with reference to the drawings.
As shown in FIG. 1, the
このように、本実施形態では、分子量１００万以上５００万以下のエチレン性不飽和カルボン酸化合物、つまり、高分子量かつ分子鎖間相互作用ネットワークを有した主バインダを含むため、合剤全体の機械強度を向上でき、合剤層の厚み変化を抑制できる。また、その結果、導電パスの疎化を抑制でき、寿命特性を良好なものにすることができる。
また、補助バインダは、分子量１０００以上１万以下のポリマーで前述の(1)〜(3)の少なくともいずれかからなるため、前述のように、活物質表面へ付着しやすく、活物質の体積変化にも安定な膜を付与できる。この膜は、カルボキシル基を有するので、Ｌｉイオンを透過でき、ＳＥＩとしての作用とともに、膜への電解液含浸抑制が期待できる。また、水素結合能を抑制する構造を持つ単量体を全構成単量体中に含むため、Ｓｉの体積変化に追随できる安定な皮膜を形成することが期待できる。その結果、繰り返し充放電での継続的なＳＥＩの破壊と生成を抑制し、寿命特性を向上させることができる。
As described above, the present embodiment includes an ethylenically unsaturated carboxylic acid compound having a molecular weight of 1 million or more and 5 million or less, that is, a main binder having a high molecular weight and an interaction network between molecular chains. The strength can be improved, and the thickness change of the mixture layer can be suppressed. As a result, it is possible to suppress the thinning of the conductive path and to improve the life characteristics.
Further, the auxiliary binder is a polymer having a molecular weight of 1000 or more and 10,000 or less, and is composed of at least one of the above (1) to (3). Therefore, as described above, the auxiliary binder easily adheres to the active material surface and changes the volume of the active material. In addition, a stable film can be provided. Since this film has a carboxyl group, it can permeate Li ions, and can be expected to suppress the impregnation of the electrolyte into the film as well as the function as SEI. In addition, since a monomer having a structure that suppresses hydrogen bonding ability is included in all constituent monomers, it can be expected to form a stable film that can follow the volume change of Si. As a result, it is possible to suppress the continuous destruction and generation of SEI by repeated charge and discharge and improve the life characteristics.
また、主バインダに用いられるエチレン性不飽和カルボン酸化合物よりなる高分子としては、例えば、ポリアクリル酸、アクリル酸マレイン酸共重合体、アクリル酸スチレン共重合体、アクリル酸酢酸ビニル重合体等のナトリウム塩、リチウム塩、カリウム塩、マグネシウム塩、カルシウム塩、アンモニウム塩等が望ましい。特に、ポリアクリル酸ナトリウムが望ましい。 Examples of the polymer composed of an ethylenically unsaturated carboxylic acid compound used for the main binder include polyacrylic acid, maleic acrylate copolymer, styrene styrene copolymer, and vinyl acrylate polymer. Sodium salts, lithium salts, potassium salts, magnesium salts, calcium salts, ammonium salts and the like are desirable. In particular, sodium polyacrylate is desirable.
また、主バインダは、架橋処理を行っても良い。架橋は、化学結合または金属イオン結合のいずれか、または、両方を用いても良い。例えば、化学結合は、アジリジン系化合物やカルボジイミド系化合物などを用いることができる。金属イオン結合は、多価カチオンを用いることができ、カルシウムイオンやマグネシウムイオンなどを用いることができる。 The main binder may be subjected to a crosslinking process. Crosslinking may use either chemical bonds or metal ion bonds, or both. For example, an aziridine compound or a carbodiimide compound can be used for chemical bonding. For the metal ion bond, a polyvalent cation can be used, and calcium ion, magnesium ion, or the like can be used.
また、補助バインダを構成するエチレン性不飽和カルボン酸化合物(a1)(a3)としては、例えば、アクリル酸、メタクリル酸、マレイン酸、フマル酸等が望ましい。特に、アクリル酸が望ましい。
活物質としては、Ｌｉを可逆的に吸蔵及び放出できるものであれば、特に制限がなく、公知のものも使用できるがＬｉと合金化する材料を使用することが望ましい。特に、黒鉛よりも容量が大きい材料であれば、本実施形態の効果が顕著に得られる。
As the ethylenically unsaturated carboxylic acid compounds (a1) and (a3) constituting the auxiliary binder, for example, acrylic acid, methacrylic acid, maleic acid, fumaric acid and the like are desirable. Acrylic acid is particularly desirable.
The active material is not particularly limited as long as it can reversibly store and release Li, and a known material can be used, but it is desirable to use a material that is alloyed with Li. In particular, if the material has a capacity larger than that of graphite, the effect of the present embodiment is remarkably obtained.
Ｌｉと合金化する材料としては、Ｓｉ、Ｇｅ、Ｓｎ、Ｐｂ、Ａｌ、Ａｇ、Ｚｎ、Ｈｇ、及びＡｕからなる群から選択された１つ以上の合金を使用できる。好ましくは、ＳｉＯｘであり、より好ましくは、ｘは０以上１．５以下であることが好ましい。ｘが１．５より大きい場合、十分なＬｉの吸蔵及び放出量を確保することができない。また、このような活物質のみならず、黒鉛も活物質として加えてもよい。 As the material to be alloyed with Li, one or more alloys selected from the group consisting of Si, Ge, Sn, Pb, Al, Ag, Zn, Hg, and Au can be used. Preferably, it is SiOx, and more preferably, x is 0 or more and 1.5 or less. When x is larger than 1.5, a sufficient amount of insertion and extraction of Li cannot be ensured. Moreover, not only such an active material but also graphite may be added as an active material.
導電助剤としては、カーボンブラックや天然黒鉛、人造黒鉛、さらには、酸化チタンや酸化ルテニウム等の金属酸化物、金属ファイバー等を使用できる。なかでもストラクチャー構造を呈するカーボンブラックが好ましく、特にその一種であるファーネスブラックやケッチェンブラック、アセチレンブラックが望ましい。なお、カーボンブラックと、その他の導電剤、例えば、気相成長炭素繊維（ＶＧＣＦ）やグラフェン、カーボンナノチューブとの混合系も好ましい。 As the conductive aid, carbon black, natural graphite, artificial graphite, metal oxides such as titanium oxide and ruthenium oxide, metal fibers, and the like can be used. Among these, carbon black having a structure structure is preferable, and furnace black, ketjen black, and acetylene black, which are one of them, are particularly preferable. A mixed system of carbon black and other conductive agent such as vapor grown carbon fiber (VGCF), graphene, or carbon nanotube is also preferable.
非水電解質二次電池に用いる電解液の溶媒としては、ジメチルカーボネート、ジエチルカーボネート等の低粘度の鎖状炭酸エステル、エチレンカーボネート、プロピレンカーボネート、ブチレンカーボネート等の高誘電率の環状炭酸エステル、γ−ブチロラクトン、１，２−ジメトキシエタン、テトラヒドロフラン、２−メチルテトラヒドロフラン、１，３−ジオキソラン、メチルアセテート、メチルプロピオネート、ビニレンカーボネート、ジメチルホルムアミド、スルホラン、及びこれらの混合溶媒等を挙げることができる。 Examples of the solvent of the electrolytic solution used in the nonaqueous electrolyte secondary battery include low-viscosity chain carbonates such as dimethyl carbonate and diethyl carbonate, cyclic carbonates having a high dielectric constant such as ethylene carbonate, propylene carbonate, and butylene carbonate, γ- Examples include butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, methyl acetate, methyl propionate, vinylene carbonate, dimethylformamide, sulfolane, and mixed solvents thereof.
電解液に含まれる電解質としては、特に制限がなく、公知のものも使用できるがＬｉＣｌＯ4、ＬｉＢＦ4、ＬｉＡｓＦ6、ＬｉＰＦ6、ＬｉＣＦ3ＳＯ3、ＬｉＮ（ＣＦ3ＳＯ2）2、ＬｉＩ、ＬｉＡｌＣｌ4等及びそれらの混合物等を使用できる。好ましくは、ＬｉＢＦ4、ＬｉＰＦ6のうちの１種または２種以上を混合したリチウム塩がよい。 The electrolyte contained in the electrolytic solution is not particularly limited, and known ones can be used, but LiClO 4 , LiBF 4 , LiAsF 6 , LiPF 6 , LiCF 3 SO 3 , LiN (CF 3 SO 2 ) 2 , LiI, LiAlCl 4 etc. and mixtures thereof can be used. Preferably, a lithium salt obtained by mixing one or more of LiBF 4 and LiPF 6 is preferable.
以下、本発明の実施例および比較例を記載する。
［主バインダの作製］
水９２．５４ｇに、ポリアクリル酸ナトリウム（日本触媒社製、分子量500万）4.96ｇを加え、攪拌翼としてディスクタービン翼を取り付けたディスパで攪拌した。続いて、この高分子溶液に、アジリジン系化合物（日本触媒社製、ＰＺ−３３）の１０倍希釈水溶液０．１５ｇを加えて、２０分間攪拌した。続いて、塩化カルシウムの１００倍希釈水溶液２．３４ｇを加えてさらに攪拌した。これにより、濃度が５質量％の架橋ポリアクリル酸ナトリウム水溶液を得た。
Examples of the present invention and comparative examples will be described below.
[Preparation of main binder]
To 92.54 g of water, 4.96 g of sodium polyacrylate (manufactured by Nippon Shokubai Co., Ltd., molecular weight 5 million) was added, and the mixture was stirred with a dispaper equipped with a disk turbine blade as a stirring blade. Subsequently, 0.15 g of a 10-fold diluted aqueous solution of an aziridine compound (manufactured by Nippon Shokubai Co., Ltd., PZ-33) was added to this polymer solution, and the mixture was stirred for 20 minutes. Subsequently, 2.34 g of a 100-fold diluted aqueous solution of calcium chloride was added and further stirred. Thereby, a crosslinked sodium polyacrylate aqueous solution having a concentration of 5% by mass was obtained.
［補助バインダ］
実施例１で使用する補助バインダＡとして、ポリ（エチルアクリレート−アクリル酸）を用意した。この補助バインダは、アクリル酸エチルエステルとアクリル酸との共重合体である。すなわち、この補助バインダは、前述の第一の共重合体（補助バインダ(1)）であり、アクリル酸がエチレン性不飽和カルボン酸化合物(a1)に相当し、エチルアクリレートが化１でｎ＝２のエチレン性不飽和化合物(b)に相当する。補助バインダＡ（共重合体）の単量体配合率は、モル比で、アクリル酸：アクリル酸エチルエステル＝５０：５０である。
[Auxiliary binder]
As the auxiliary binder A used in Example 1, poly (ethyl acrylate-acrylic acid) was prepared. This auxiliary binder is a copolymer of acrylic acid ethyl ester and acrylic acid. That is, this auxiliary binder is the above-mentioned first copolymer (auxiliary binder (1)), acrylic acid corresponds to the ethylenically unsaturated carboxylic acid compound (a1), ethyl acrylate is represented by
実施例２で使用する補助バインダＢとして、ポリメタクリル酸を用意した。すなわち、この補助バインダは、前述の補助バインダ(2)であり、単量体であるメタクリル酸が、化２でｎ＝１のエチレン性不飽和カルボン酸化合物(a2)に相当する。
実施例３で使用する補助バインダＣとして、ポリ（アクリル酸−メタクリル酸）を用意した。この補助バインダは、アクリル酸とメタクリル酸との共重合体である。すなわち、この補助バインダは、前述の第二の共重合体（補助バインダ(3)）であり、アクリル酸がエチレン性不飽和カルボン酸化合物(a3)に相当し、メタクリル酸が化２でｎ＝１のエチレン性不飽和カルボン酸化合物(a2)に相当する。補助バインダＢ（共重合体）の単量体配合率は、モル比で、アクリル酸：メタクリル酸＝２０：８０である。
As an auxiliary binder B used in Example 2, polymethacrylic acid was prepared. That is, this auxiliary binder is the above-mentioned auxiliary binder (2), and the monomer methacrylic acid corresponds to the ethylenically unsaturated carboxylic acid compound (a2) in which n = 1 in the
As the auxiliary binder C used in Example 3, poly (acrylic acid-methacrylic acid) was prepared. This auxiliary binder is a copolymer of acrylic acid and methacrylic acid. That is, this auxiliary binder is the above-mentioned second copolymer (auxiliary binder (3)), acrylic acid corresponds to the ethylenically unsaturated carboxylic acid compound (a3), methacrylic acid is embedded image and n = 1 ethylenically unsaturated carboxylic acid compound (a2). The monomer compounding ratio of the auxiliary binder B (copolymer) is acrylic acid: methacrylic acid = 20: 80 in molar ratio.
［負極スラリの作製］
（実施例１）
得られた架橋ポリアクリル酸ナトリウム水溶液（主バインダの水溶液）２６．８２ｇに、水６．４８ｇを加えて、攪拌翼としてディスクタービン翼を取り付けたディスパで攪拌した。続いて、上述の補助バインダＡを０．０７ｇ加えてさらに攪拌した。次に、Ｓｉ粒子（平均粒径２００ｎｍ）４．７１ｇとアセチレンブラック０．９４ｇと気相成長炭素繊維０．９４を加えて攪拌した。続いて、フィルミックスを用いて本分散し、負極スラリを得た。
[Preparation of negative electrode slurry]
Example 1
6.48 g of water was added to 26.82 g of the obtained cross-linked sodium polyacrylate aqueous solution (main binder aqueous solution), and the mixture was stirred with a dispaer equipped with a disk turbine blade as a stirring blade. Subsequently, 0.07 g of the auxiliary binder A described above was added and further stirred. Next, 4.71 g of Si particles (average particle size 200 nm), 0.94 g of acetylene black, and 0.94 of vapor grown carbon fiber were added and stirred. Then, this dispersion was performed using a fill mix to obtain a negative electrode slurry.
（実施例２）
補助バインダＡに代えて上述の補助バインダＢを同じ量だけ用いた。これ以外は実施例１と同じ方法で負極スラリを得た。
（実施例３）
補助バインダＡに代えて上述の補助バインダＣを同じ量だけ用いた。これ以外は実施例１と同じ方法で負極スラリを得た。
(Example 2)
Instead of the auxiliary binder A, the same amount of the above-mentioned auxiliary binder B was used. Except for this, a negative electrode slurry was obtained in the same manner as in Example 1.
(Example 3)
Instead of the auxiliary binder A, the same amount of the above-mentioned auxiliary binder C was used. Except for this, a negative electrode slurry was obtained in the same manner as in Example 1.
（比較例１）
得られた架橋ポリアクリル酸ナトリウム水溶液（主バインダの水溶液）２６．８２ｇに、水６．４５ｇを加えて、攪拌翼としてディスクタービン翼を取り付けたディスパで攪拌した。続いて、５０％アクリル酸マレイン酸共重合体水溶液０．１４ｇを加えてさらに攪拌した。これ以外は実施例１と同じ方法で負極スラリを得た。
(Comparative Example 1)
6.45 g of water was added to 26.82 g of the obtained aqueous crosslinked sodium polyacrylate solution (main binder aqueous solution), and the mixture was stirred with a dispaer equipped with a disk turbine blade as a stirring blade. Subsequently, 0.14 g of a 50% maleic acrylate copolymer aqueous solution was added and further stirred. Except for this, a negative electrode slurry was obtained in the same manner as in Example 1.
［負極の作製］
実施例１、実施例２、実施例３、および比較例１で得られた各負極スラリを、厚さ１２μｍの銅箔からなる各集電体に、１．０ｍｇ／ｃｍ2の目付量になるようにドクターブレードにて塗布した後、８０℃で３０分間予備乾燥した。次に、乾燥した負極スラリ層を有する集電体を直径１５ｍｍの円板状に打ち抜き、１０５℃で５時間減圧乾燥を行った。これにより、負極用電極を得た。
[Production of negative electrode]
Each negative electrode slurry obtained in Example 1, Example 2, Example 3, and Comparative Example 1 has a basis weight of 1.0 mg / cm 2 on each current collector made of 12 μm thick copper foil. After coating with a doctor blade, the sample was pre-dried at 80 ° C. for 30 minutes. Next, the current collector having the dried negative electrode slurry layer was punched into a disk shape having a diameter of 15 mm, and dried under reduced pressure at 105 ° C. for 5 hours. This obtained the electrode for negative electrodes.
［セル作製と充放電評価］
得られた実施例１、実施例２、実施例３、および比較例１の各電極とＬｉ極を用いて、コインセルを作製した。コインセルは２０３２型を使用した。Ｌｉ極は、直径１８ｍｍの円板状である。コインセルの基本構成は、各電極、Ｌｉ極、およびセパレータ（旭化成、ハイポア ＮＤ５２５）とした。電解液は、エチレンカーボネート（ＥＣ）とジエチルカーボネート（ＤＥＣ）とを質量比で３：７に混合した溶液に、ＬｉＰＦ6を１Ｍとなるように加えたものに、さらにフルオロエチレンカーボネート（ＦＥＣ）を１０質量％となるように加えたものを使用した。
[Cell fabrication and charge / discharge evaluation]
A coin cell was manufactured using the obtained electrodes of Example 1, Example 2, Example 3, and Comparative Example 1 and the Li electrode. A 2032 type coin cell was used. The Li pole has a disk shape with a diameter of 18 mm. The basic configuration of the coin cell was each electrode, Li electrode, and separator (Asahi Kasei, Hypore ND525). The electrolyte is a solution in which ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed at a mass ratio of 3: 7, and LiPF 6 is added to 1 M, and further fluoroethylene carbonate (FEC) is added. What was added so that it might become 10 mass% was used.
作製したコインセルを用いて充放電評価を行なった。初回充放電は、充電１６０ｍＡ／ｇ、放電１６０ｍＡ／ｇで、０．０１Ｖ〜１．２Ｖの電圧範囲で充放電を行った。続いて、充電１６００ｍＡ／ｇ、放電１６００ｍＡ／ｇで、０．０３Ｖ〜１．０Ｖの電圧範囲で繰り返し充放電を行った。
繰り返し充放電のセルの容量変化を図２に示す。また、繰り返し充放電の１サイクルから５サイクルまでのクーロン効率を表１に示す。
Charge / discharge evaluation was performed using the produced coin cell. The first charge / discharge was performed by charging at 160 mA / g and discharging at 160 mA / g in a voltage range of 0.01V to 1.2V. Subsequently, charging and discharging were repeatedly performed in a voltage range of 0.03 V to 1.0 V at a charge of 1600 mA / g and a discharge of 1600 mA / g.
FIG. 2 shows changes in the capacity of the repetitive charge / discharge cell. Table 1 shows the Coulomb efficiency from 1 cycle to 5 cycles of repeated charge and discharge.
また、初回クーロン効率は、実施例１では８０％、実施例２では７９％、実施例３では７８％であり、比較例１では７５％であった。これは、補助バインダＡ，Ｂ，Ｃによって安定な皮膜が形成され、Ｌｉ消費が抑えられているためと考えられる。 The initial coulomb efficiency was 80% in Example 1, 79% in Example 2, 78% in Example 3, and 75% in Comparative Example 1. This is presumably because a stable film is formed by the auxiliary binders A, B, and C, and Li consumption is suppressed.
本発明の一態様の非水電解質二次電池用負極バインダを含む合剤層を有する負極は、各種携帯用電子機器の電源、また、高エネルギー密度が求められる電気自動車等の駆動用蓄電池、さらに、ソーラーエネルギーや風力発電等の各種エネルギーの蓄電装置、あるいは家庭用電気器具の蓄電源等の電極に用いられる。 A negative electrode having a mixture layer containing a negative electrode binder for a nonaqueous electrolyte secondary battery of one embodiment of the present invention is a power source for various portable electronic devices, and a storage battery for driving an electric vehicle or the like that requires high energy density, It is used for power storage devices for various types of energy such as solar energy and wind power generation, or electrodes for storage power sources of household electric appliances.
１ 非水電解質二次電池用負極
２ 集電体
３ 合剤層
1 Negative electrode for nonaqueous electrolyte
Claims (4)
分子量が１００万以上５００万以下であり、繰り返し単位がエチレン性不飽和カルボン酸化合物であるポリマーからなる主バインダと、
分子量が１０００以上１万以下のポリマーである補助バインダと、
を含み、
前記補助バインダは、
(1)エチレン性不飽和カルボン酸化合物(a1)と、アルキル部位(ＣnＨ2n+1−)の炭素数ｎが１以上１０以下であるアルキルカルボン酸エステル基を含む下記の化１に示すエチレン性不飽和化合物(b)と、を繰り返し単位中に含む第一の共重合体、
(2)カルボキシル基のα炭素上に、炭素数ｎが１以上１０以下であるアルキル部位(ＣnＨ2n+1−)を有する、下記の化２に示すエチレン性不飽和カルボン酸化合物(a2)を、繰り返し単位中に含む重合体、
および
(3)前記エチレン性不飽和カルボン酸化合物(a2)以外のエチレン性不飽和カルボン酸化合物(a3)と、前記エチレン性不飽和カルボン酸化合物(a2)と、を繰り返し単位中に含む第二の共重合体
の少なくともいずれかからなる非水電解質二次電池用負極バインダ。
A main binder composed of a polymer having a molecular weight of 1,000,000 to 5,000,000 and a repeating unit of an ethylenically unsaturated carboxylic acid compound;
An auxiliary binder which is a polymer having a molecular weight of 1000 or more and 10,000 or less,
Including
The auxiliary binder is
(1) A compound comprising an ethylenically unsaturated carboxylic acid compound (a1) and an alkyl carboxylic acid ester group having an alkyl moiety (C n H 2n + 1 —) having a carbon number n of 1 or more and 10 or less. An ethylenically unsaturated compound (b), and a first copolymer containing in a repeating unit,
(2) An ethylenically unsaturated carboxylic acid compound (a2) represented by the following chemical formula 2 having an alkyl moiety (C n H 2n + 1 —) having a carbon number n of 1 to 10 on the α-carbon of the carboxyl group ) In a repeating unit,
and
(3) a second unit containing, in a repeating unit, an ethylenically unsaturated carboxylic acid compound (a3) other than the ethylenically unsaturated carboxylic acid compound (a2) and the ethylenically unsaturated carboxylic acid compound (a2). A negative electrode binder for a non-aqueous electrolyte secondary battery, comprising at least one of copolymers.
前記第二の共重合体の単量体配合率は、前記エチレン性不飽和カルボン酸化合物(a3)が２０モル％以上９０モル％以下、前記エチレン性不飽和カルボン酸化合物(a2)が１０モル％以上８０モル％以下である請求項１記載の非水電解質二次電池用負極バインダ。 The monomer content of the first copolymer is such that the ethylenically unsaturated carboxylic acid compound (a1) is 20 mol% or more and 90 mol% or less, and the ethylenically unsaturated compound (b) is 10 mol% or more. 80 mol% or less,
The monomer content of the second copolymer is such that the ethylenically unsaturated carboxylic acid compound (a3) is 20 mol% or more and 90 mol% or less, and the ethylenically unsaturated carboxylic acid compound (a2) is 10 mol%. 2. The negative electrode binder for a non-aqueous electrolyte secondary battery according to claim 1, wherein the negative electrode binder is not less than 80% and not more than 80 mol%.
The negative electrode for nonaqueous electrolyte secondary batteries which has a mixture layer containing the negative electrode binder for nonaqueous electrolyte secondary batteries as described in any one of Claims 1-3.
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