JP6709991B2 - Lithium ion secondary battery - Google Patents
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- JP6709991B2 JP6709991B2 JP2016152387A JP2016152387A JP6709991B2 JP 6709991 B2 JP6709991 B2 JP 6709991B2 JP 2016152387 A JP2016152387 A JP 2016152387A JP 2016152387 A JP2016152387 A JP 2016152387A JP 6709991 B2 JP6709991 B2 JP 6709991B2
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Description
本発明は、負極集電体と負極合剤層とからなる負極板、および正極板を含んで構成されるリチウムイオン二次電池に関するものである。 TECHNICAL FIELD The present invention relates to a negative electrode plate composed of a negative electrode current collector and a negative electrode mixture layer, and a lithium ion secondary battery including a positive electrode plate.
近年、リチウムイオン二次電池は高い作動電圧と高エネルギー密度を有する二次電池として携帯電話やノート型パソコン、携帯電話などのモバイル電子機器の駆動用電源として実用化されている。また、リチウムイオン二次電池は急速な成長を遂げ、小型二次電池をリードする電池系として生産量は増え続けている。 In recent years, lithium-ion secondary batteries have been put into practical use as secondary batteries having a high operating voltage and a high energy density, as a power source for driving mobile electronic devices such as mobile phones, notebook computers, and mobile phones. In addition, lithium-ion secondary batteries have achieved rapid growth, and the production volume continues to increase as a battery system that leads small secondary batteries.
リチウムイオン二次電池は、最近では、これら小型民生用途のみならず、車載用電池への需要が高まっており、高エネルギー密度のリチウムイオン二次電池の開発が加速されている。さらに、リチウムイオン二次電池の正極材料の高容量化に伴い、負極材料の高容量化が重要視されている。高容量の負極活物質としては、従来のリチウムイオン二次電池に採用されている黒鉛などの炭素質材料に代えて、シリコン（Ｓｉ）、スズ（Ｓｎ）など、より多くのリチウムイオンを吸蔵・放出可能な材料が注目されている。とりわけ、シリコンの微粒子がＳｉＯ２中に分散した構造を持つＳｉＯｘは、負荷特性に優れるなどの特徴も併せ持つことが報告されている。 In recent years, lithium-ion secondary batteries have been in demand not only for these small consumer applications but also for in-vehicle batteries, and the development of high-energy-density lithium-ion secondary batteries has been accelerated. Further, as the capacity of the positive electrode material of the lithium-ion secondary battery is increased, it is important to increase the capacity of the negative electrode material. As a high-capacity negative electrode active material, instead of a carbonaceous material such as graphite used in a conventional lithium ion secondary battery, more lithium ions such as silicon (Si) and tin (Sn) can be stored. Releasable materials are receiving attention. In particular, it has been reported that SiO x having a structure in which fine particles of silicon are dispersed in SiO 2 also has characteristics such as excellent load characteristics.
ところが、前記ＳｉＯｘは、充放電反応に伴う体積膨張収縮が大きいため、電池の充放電サイクル毎にシリコン粒子が粉砕され、負極の表面に析出したＳｉが非水電解液溶媒と反応して不可逆な負極の容量の増大が生じたり、この反応によって電池内でガスが発生して電池缶が膨れたりするなどの問題が生じることも知られている。 However, since the SiO x has a large volume expansion/contraction associated with charge/discharge reaction, silicon particles are crushed at each charge/discharge cycle of the battery, and Si deposited on the surface of the negative electrode reacts with the non-aqueous electrolyte solvent to cause irreversible It is also known that problems such as an increase in the capacity of the negative electrode occur and gas is generated in the battery due to this reaction to swell the battery can.
従来このような問題に対しては、ＳｉＯｘの含有率や正極活物質と負極活物質との質量比を制限して充放電反応に伴う体積膨張収縮を抑制したり、ＳｉＯｘの表面に炭素などの導電質材料と被覆して負荷特性を改善したり、ハロゲン置換された環状カーボネートなどを添加した非水電解液を用いることで、充放電サイクル特性を向上したりする技術が提案されている（例えば、特許文献１参照）。 Conventionally, in order to solve such a problem, the content ratio of SiO x and the mass ratio of the positive electrode active material and the negative electrode active material are limited to suppress the volume expansion and contraction due to the charge/discharge reaction, or the carbon on the surface of SiO x. Techniques have been proposed to improve the load characteristics by coating with a conductive material such as, or to improve the charge/discharge cycle characteristics by using a non-aqueous electrolyte solution added with a halogen-substituted cyclic carbonate or the like. (For example, refer to Patent Document 1).
しかしながら、前記従来の構成では、負極活物質にＳｉＯｘを使用しており、一部のＳｉＯ２がリチウムイオンと反応し、リチウムシリケートが形成されるため、不可逆容量が多くなり初回充放電効率が低いという課題がある。また車載用電池への需要が高まっている中で更なる高寿命化が求められており、充放電サイクル特性を向上させる必要がある。 However, in the above-mentioned conventional configuration, since SiO x is used as the negative electrode active material and a part of SiO 2 reacts with lithium ions to form lithium silicate, irreversible capacity is increased and initial charge/discharge efficiency is increased. There is a problem of being low. Further, as the demand for in-vehicle batteries is increasing, further extension of life is required, and it is necessary to improve charge/discharge cycle characteristics.
本発明は、前記従来の課題を解決するもので、充放電サイクル特性の向上を図ることを目的とする。 The present invention solves the above-mentioned conventional problems, and an object thereof is to improve charge/discharge cycle characteristics.
上記目的を達成するために、本発明のリチウムイオン二次電池は、正極集電体と前記正極集電体の表面に接して設けられる正極合剤層とからなる正極板と、負極集電体と前記負極集電体の表面に接して設けられる負極合剤層とからなる負極板と、前記正極板と前記負極板との間に設けられるセパレータとが電解液とともにケースに収納されるリチウムイオン二次電池であって、前記負極合剤層は、少なくとも第１の負極活物質と、前記第１の負極活物質を前記負極集電体の表面に固定化するバインダとを含み、前記第１の負極活物質は、少なくとも無機化合物にシリコン微粒子が分散された構造を有し、前記第１の負極活物質の少なくとも一部は表面に平坦面を有し、前記負極合剤層は第２の負極活物質をさらに含み、前記平坦面は前記第１の負極活物質にのみ設けられ、前記負極合剤層は、前記第１の負極活物質より前記第２の負極活物質を多く含み、前記第１の負極活物質と前記第２の負極活物質との比率が、０．０１≦前記第１の負極活物質／前記第２の負極活物質＜１．０であり、前記負極合剤層は黒鉛の炭素材料を有し、前記第１の負極活物質と前記第２の負極活物質とを併せた粒子と黒鉛の炭素材料との比率が２．０以上９９．０以下であり、前記第１の負極活物質の平坦面は直線形体となっており、その直線部の長さと真直度の比が０．０７未満であり、前記第１の負極活物質は空隙を有し、前記平坦面の近傍における前記空隙の空隙率が他の領域における前記空隙の空隙率より低く、その空隙率差が１１％以上３８％以下であることを特徴とする。 To achieve the above object, the lithium ion secondary batteries of the present invention includes a positive electrode plate comprising a positive electrode mixture layer provided in contact with the surface of the positive electrode current collector a positive electrode current collector, the anode current collector A negative electrode plate comprising a body and a negative electrode mixture layer provided in contact with the surface of the negative electrode current collector, and a separator provided between the positive electrode plate and the negative electrode plate are stored in a case together with an electrolytic solution in lithium. In the ion secondary battery, the negative electrode mixture layer includes at least a first negative electrode active material and a binder that fixes the first negative electrode active material on the surface of the negative electrode current collector, negative electrode active material 1 has at least silicon microparticles inorganic compound dispersed structure, at least a portion of the first negative electrode active material have a flat surface on the surface, the negative electrode mixture layer and the second Of the negative electrode active material, the flat surface is provided only on the first negative electrode active material, the negative electrode mixture layer contains more of the second negative electrode active material than the first negative electrode active material, The ratio of the first negative electrode active material and the second negative electrode active material is 0.01≦the first negative electrode active material/the second negative electrode active material<1.0, and the negative electrode mixture. The layer has a graphite carbon material, and the ratio of the particles of the first negative electrode active material and the second negative electrode active material combined to the graphite carbon material is 2.0 or more and 99.0 or less, The flat surface of the first negative electrode active material is a linear body, the ratio of the length of the linear portion to the straightness is less than 0.07, the first negative electrode active material has voids, The porosity of the voids in the vicinity of the flat surface is lower than the porosity of the voids in other regions, and the difference in the void ratio is 11% or more and 38% or less.
本構成によって、優れた充放電サイクル特性のリチウムイオン二次電池を提供することができる。 With this configuration, it is possible to provide a lithium ion secondary battery having excellent charge/discharge cycle characteristics.
以上のように、負極合剤層の構成物質である負極活物質に平坦面を形成することにより、充放電サイクル特性を向上することができる。 As described above, the charge/discharge cycle characteristics can be improved by forming a flat surface on the negative electrode active material that is a constituent material of the negative electrode mixture layer.
以下、本発明の実施の形態について、図面を参照しながら説明する。図１はリチウムイオン二次電池の構成を例示する断面図である。
図１に示すように、本発明のリチウムイオン二次電池１０は、例えば、正極板１１と負極板１２とセパレータ１３からなる電極体と、非水電解液１４と、それらを収納するケース１５とから構成される。
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a sectional view illustrating the configuration of a lithium ion secondary battery.
As shown in FIG. 1, the lithium-ion secondary battery 10 of the present invention includes, for example, an electrode body including a positive electrode plate 11, a negative electrode plate 12, and a separator 13, a non-aqueous electrolyte solution 14, and a case 15 for housing them. Composed of.
本発明のリチウムイオン二次電池１０は、上記の正極板１１、セパレータ１３、非水電解液１４、およびケース１５は特に限定されるものではないが、例えば、以下に記載するものを用いることができる。 In the lithium ion secondary battery 10 of the present invention, the positive electrode plate 11, the separator 13, the non-aqueous electrolyte solution 14, and the case 15 are not particularly limited, but, for example, those described below may be used. it can.
正極板１１は、導電性を有するフィルムからなる正極集電体と、前記正極集電体の少なくとも一つの表面に設けられた正極合剤層とからなる。正極集電体は、例えば、アルミニウム、アルミニウム合金、チタン、銅、ニッケルなどの金属箔やエキスパンドメタルや、ＰＥＴなどの高分子フィルムの表面に金属を蒸着した積層体、導電性高分子フィルムなど従来と同様のものを用いることができ、特に限定されるものではない。正極合剤層は、少なくとも正極活物質と導電助材とバインダとからなる。正極活物質は、例えば、リチウムニッケル酸化物、リチウムコバルト酸化物、リチウムマンガン酸化物（これらは、通常、ＬｉＮｉＯ２、ＬｉＣｏＯ２、ＬｉＭｎ２Ｏ４で表されるが、ＬｉとＮｉの比、ＬｉとＣｏの比、ＬｉとＭｎの比は化学量論組成からずれている場合が多い）などのリチウム含有複合金属酸化物を用いることができる。また、これらのリチウム含有複合金属酸化物は単独でまたは２種以上の混合物として、あるいはそれらの固溶体として用いることができるが、特に限定されるものではない。導電助材は、例えば、ケッチェンブラック、アセチレンブラック等のカーボンブラック、ファイバー状カーボン、燐片状黒鉛を用いることができるが、特に限定されるものではない。バインダは、例えば、熱可塑性樹脂、ゴム弾性を有するポリマーおよび多糖類の単独、あるいは混合物を用いることができる。具体的には、バインダは、ポリテトラフルオロエチレン、ポリフッ化ビニリデンや、ヘキサフルオロプロペンとの共重合体、ポリエチレン、ポリプロピレン、エチレン−プロピレン−ジエン共重合体、スチレン−ブタジエンゴム、ポリブタジエン、フッ素ゴム、ポリエチレンオキシド、ポリビニルピロリドン、ポリエステル樹脂、アクリル樹脂、フェノール樹脂、エポキシ、ポリビニルアルコール、ヒドロキシプロピルセルロース、カルボキシメチルセルロースなどのセルロース樹脂などを用いることができるが、特に限定されるものではない。 The positive electrode plate 11 includes a positive electrode current collector made of a conductive film and a positive electrode mixture layer provided on at least one surface of the positive electrode current collector. The positive electrode current collector is, for example, a metal foil such as aluminum, an aluminum alloy, titanium, copper, or nickel, an expanded metal, a laminate in which a metal is vapor-deposited on the surface of a polymer film such as PET, or a conductive polymer film. The same as can be used and is not particularly limited. The positive electrode mixture layer is composed of at least a positive electrode active material, a conductive auxiliary material, and a binder. Examples of the positive electrode active material include lithium nickel oxide, lithium cobalt oxide, and lithium manganese oxide (these are usually represented by LiNiO 2 , LiCoO 2 , and LiMn 2 O 4 , but the ratio of Li to Ni, Li The ratio of Li to Mn and the ratio of Li to Mn are often deviated from the stoichiometric composition). Further, these lithium-containing mixed metal oxides can be used alone or as a mixture of two or more kinds, or as a solid solution thereof, but are not particularly limited. As the conductive auxiliary material, for example, carbon black such as Ketjen black or acetylene black, fibrous carbon, or flake graphite can be used, but it is not particularly limited. As the binder, for example, a thermoplastic resin, a polymer having rubber elasticity, and a polysaccharide can be used alone or in a mixture. Specifically, the binder, polytetrafluoroethylene, polyvinylidene fluoride or a copolymer with hexafluoropropene, polyethylene, polypropylene, ethylene-propylene-diene copolymer, styrene-butadiene rubber, polybutadiene, fluororubber, Cellulose resins such as polyethylene oxide, polyvinylpyrrolidone, polyester resins, acrylic resins, phenol resins, epoxies, polyvinyl alcohol, hydroxypropyl cellulose, carboxymethyl cellulose and the like can be used, but are not particularly limited.
また、セパレータ１３は、正極板１１と負極板１２とを絶縁し、かつその内部（セパレータ１３を構成する材料内またはセパレータ１３内に形成された空孔内）をリチウムイオンが移動できるものであり、かつリチウムイオン二次電池１０の使用時に安定な素材であれば特に限定されず、例えば、ポリエチレンやポリプロピレンからなる絶縁性の高分子多孔フィルムや、セルロースからなる絶縁性の不織布である。また、セパレータ１３は、アルミナ、シリカ、酸化マグネシウム、酸化チタン、ジルコニア、炭化ケイ素、窒化ケイ素などの無機物粒子や、ポリエチレン、ポリプロピレン、ポリスチレン、ポリアクリロニトリル、ポリメチルメタクリレート、ポリフッ化ビニリデン、ポリテトラフルオロエチレン、ポリイミドなどの有機物粒子、前記無機物粒子と有機物粒子との混合物、結着材、溶媒、各種添加剤などを混合したものを、塗布し、乾燥させ、圧延することにより形成することもできる。セパレータ１３の厚みは、特に限定されないが、例えば１０μｍ以上５０μｍ以下である。 Further, the separator 13 insulates the positive electrode plate 11 and the negative electrode plate 12 and allows lithium ions to move inside thereof (in the material forming the separator 13 or in the holes formed in the separator 13). The material is not particularly limited as long as it is a stable material when the lithium ion secondary battery 10 is used, and examples thereof include an insulating polymer porous film made of polyethylene or polypropylene and an insulating nonwoven fabric made of cellulose. The separator 13 includes inorganic particles such as alumina, silica, magnesium oxide, titanium oxide, zirconia, silicon carbide and silicon nitride, polyethylene, polypropylene, polystyrene, polyacrylonitrile, polymethylmethacrylate, polyvinylidene fluoride, polytetrafluoroethylene. Alternatively, organic particles such as polyimide, a mixture of the inorganic particles and organic particles, a mixture of a binder, a solvent, various additives, and the like may be applied, dried, and rolled. The thickness of the separator 13 is not particularly limited, but is, for example, 10 μm or more and 50 μm or less.
非水電解液１４は、非水溶媒と電解質とからなる。非水溶媒は、特に限定されないが、例えば、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、ジメチルカーボネート、メチルエチルカーボネート、ジエチルカーボネート、γ−ブチロラクトン、スルホラン、アセトニトリル、１，２−ジメトキシエタン、１，３−ジメトキシプロパン、ジエチルエーテル、テトラヒドロフラン、２−メチルテトラヒドロフラン、γ−ブチロラクトンなどである。これらの非水溶媒は、単独で使用されてもよいし、２種以上を混合して使用されてもよい。また、正極板１１および負極板１２上に良好な皮膜を形成するため、または過充電時の安定性を確保するために、非水溶媒として、ビニレンカーボネート（ＶＣ）、またはシクロヘキシルベンゼン（ＣＨＢ）およびその変性体を用いることも好ましい。また、前記非水溶媒は、前記した材料に限らず、一定の電解液を用いることも可能である。また、非水電解液１４の電解質は、特に限定されないが、例えば、過塩素酸リチウム（ＬｉＣｌＯ４）、六フッ化リン酸リチウム（ＬｉＰＦ６）、ホウフッ化リチウム（ＬｉＢＦ４）、六フッ化砒素リチウム（ＬｉＡｓＦ６）、トリフルオロメタスルホン酸リチウム（ＬｉＣＦ３ＳＯ３）、ビストリフルオロメチルスルホニルイミドリチウム［ＬｉＮ（ＣＦ３ＳＯ２）２］などのリチウム塩などである。 The non-aqueous electrolyte solution 14 comprises a non-aqueous solvent and an electrolyte. Non-aqueous solvent is not particularly limited, for example, ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, γ-butyrolactone, sulfolane, acetonitrile, 1,2-dimethoxyethane, 1,3- Examples include dimethoxypropane, diethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone and the like. These non-aqueous solvents may be used alone or in combination of two or more. Further, in order to form a good film on the positive electrode plate 11 and the negative electrode plate 12 or to ensure stability during overcharge, vinylene carbonate (VC) or cyclohexylbenzene (CHB) and It is also preferable to use the modified product. Further, the non-aqueous solvent is not limited to the above-mentioned materials, and it is possible to use a certain electrolytic solution. Further, the electrolyte of the non-aqueous electrolyte solution 14 is not particularly limited, and examples thereof include lithium perchlorate (LiClO 4 ), lithium hexafluorophosphate (LiPF 6 ), lithium borofluoride (LiBF 4 ), and arsenic hexafluoride. Lithium salts such as lithium (LiAsF 6 ), lithium trifluorometasulfonate (LiCF 3 SO 3 ), and bistrifluoromethylsulfonylimide lithium [LiN(CF 3 SO 2 ) 2 ] are included.
ケース１５は、例えば、アルミニウム、鉄、ステンレスなどの金属を成形したものや、アルミニウムなどの金属層と高分子層とを積層したフィルムなどを用いることができるが、特に限定されるものではない。 The case 15 may be formed of a metal such as aluminum, iron, or stainless, or a film obtained by laminating a metal layer such as aluminum and a polymer layer, but is not particularly limited.
次に、本発明において、特徴的な負極板について、図２〜図１０を参照して、以下に詳細に説明する。図２は本発明の一実施形態における負極板の構成を例示する概略図であり、円で囲んだ部分の拡大図を合わせて表示する。図３，図４は本発明の一実施形態における好ましい負極活物質の構成を例示する概略図、図５は不適切な負極活物質の構成を例示する概略図、図６は本発明の一実施形態における負極合剤層の形成過程を順に例示する模式図、図７は本発明の一実施形態における負極活物質の充放電時の構成変化を例示する断面模式図、図８は本発明の一実施形態における負極活物質の構成を例示する概略図、図９，図１０は不適切な負極合剤層の構成を例示する概略図である。 Next, in the present invention, the characteristic negative electrode plate will be described in detail below with reference to FIGS. FIG. 2 is a schematic view illustrating the configuration of the negative electrode plate according to the embodiment of the present invention, and an enlarged view of a portion surrounded by a circle is also displayed. 3 and 4 are schematic views illustrating the configuration of a preferable negative electrode active material in one embodiment of the present invention, FIG. 5 is a schematic view illustrating the configuration of an inappropriate negative electrode active material, and FIG. 6 is one implementation of the present invention. 7A to 7C are schematic views sequentially illustrating the formation process of the negative electrode mixture layer in the embodiment, FIG. 7 is a schematic cross-sectional view illustrating the configuration change of the negative electrode active material during charging and discharging in one embodiment of the present invention, and FIG. Schematic diagrams illustrating the configuration of the negative electrode active material in the embodiment, and FIGS. 9 and 10 are schematic diagrams illustrating the configuration of an inappropriate negative electrode mixture layer.
負極板１２は、図２に示すような、導電性を有するフィルムからなる負極集電体１と、前記負極集電体１の少なくとも一つの表面に設けられた負極合剤層２とからなる。図２では、負極集電体１を負極合剤層２で挟み込む構成を示し、負極集電体１の表裏２つの表面に負極合剤層２が設けられている場合を図示した。 As shown in FIG. 2, the negative electrode plate 12 includes a negative electrode current collector 1 made of a conductive film and a negative electrode mixture layer 2 provided on at least one surface of the negative electrode current collector 1. FIG. 2 shows a structure in which the negative electrode current collector 1 is sandwiched between the negative electrode current collector layers 2 and the case where the negative electrode current collector layer 2 is provided on two front and back surfaces of the negative electrode current collector 1 is illustrated.
負極集電体１は、例えば、銅、アルミニウム、アルミニウム合金、チタン、ニッケルなどの金属箔やエキスパンドメタルや、ＰＥＴなどの高分子フィルムの表面に金属を蒸着した積層体、導電性高分子フィルムなど従来と同様のものを用いることができるが、特に限定されるものではない。 The negative electrode current collector 1 is, for example, a metal foil or expanded metal such as copper, aluminum, aluminum alloy, titanium, or nickel, a laminated body in which a metal is vapor-deposited on the surface of a polymer film such as PET, a conductive polymer film, or the like. The same material as the conventional one can be used, but it is not particularly limited.
負極合剤層２は、少なくとも負極活物質（第１の負極活物質）３ａを備え、さらに、負極活物質３ｂ、３ｃを備えても良い。また、負極合剤層２は、負極活物質３ａ、３ｂ、３ｃを負極集電体１の表面に固定化するためのバインダ４を備える。バインダ４は、正極板１１（図１参照）と同様のものを用いることができ、例えば、熱可塑性樹脂、ゴム弾性を有するポリマーおよび多糖類の単独、あるいは混合物を用いることができる。具体的には、バインダ４は、ポリテトラフルオロエチレン、ポリフッ化ビニリデンや、ヘキサフルオロプロペンとの共重合体、ポリエチレン、ポリプロピレン、エチレン−プロピレン−ジエン共重合体、スチレン−ブタジエンゴム、ポリブタジエン、フッ素ゴム、ポリエチレンオキシド、ポリビニルピロリドン、ポリエステル樹脂、アクリル樹脂、フェノール樹脂、エポキシ、ポリビニルアルコール、ヒドロキシプロピルセルロース、カルボキシメチルセルロースなどのセルロース樹脂などを用いることができるが、特に限定されるものではない。 The negative electrode mixture layer 2 includes at least a negative electrode active material (first negative electrode active material) 3a, and may further include negative electrode active materials 3b and 3c. Further, the negative electrode mixture layer 2 includes a binder 4 for fixing the negative electrode active materials 3a, 3b, 3c on the surface of the negative electrode current collector 1. The binder 4 may be the same as that used for the positive electrode plate 11 (see FIG. 1), and may be, for example, a thermoplastic resin, a polymer having rubber elasticity, or a polysaccharide, or a mixture thereof. Specifically, the binder 4 is polytetrafluoroethylene, polyvinylidene fluoride, a copolymer with hexafluoropropene, polyethylene, polypropylene, ethylene-propylene-diene copolymer, styrene-butadiene rubber, polybutadiene, fluororubber. Polyethylene oxide, polyvinylpyrrolidone, polyester resin, acrylic resin, phenol resin, epoxy, polyvinyl alcohol, hydroxypropyl cellulose, carboxymethyl cellulose, and other cellulose resins can be used, but not limited thereto.
負極活物質３ａは、図３〜図４に示すように、無機化合物６にシリコン微粒子５が分散された構造である。
シリコン微粒子５のサイズは５ｎｍより大きく１０００ｎｍ未満が好ましく、より好ましくは５ｎｍより大きく２００ｎｍ未満が好ましい。シリコン微粒子５を２００ｎｍ未満の微粒子にすることにより、充放電時のシリコン微粒子５の膨張収縮の体積変化を小さくすることができる。さらにシリコン微粒子５を無機化合物６が覆う構造とすることにより、シリコン微粒子５の膨張収縮を抑制することができる。これに対してシリコン微粒子５が２００ｎｍ以上の場合、充放電時のシリコン微粒子５の膨張収縮による体積変化が大きいため、無機化合物６が覆っている構造においても割れ等の問題を生じやすい。ただし、２００ｎｍ未満のシリコン微粒子を形成するために製造時間が長くなるため、高コスト化に繋がる。シリコン微粒子５が１０００ｎｍ未満の粒子サイズであれば、膨張収縮による体積変化が大きくなるため２００ｎｍより前記問題は生じやすいが、製造コストは抑えることが出来るため、シリコン微粒子５は１０００ｎｍ未満であることが好ましい。
As shown in FIGS. 3 to 4, the negative electrode active material 3 a has a structure in which the silicon fine particles 5 are dispersed in the inorganic compound 6.
The size of the silicon fine particles 5 is preferably larger than 5 nm and smaller than 1000 nm, more preferably larger than 5 nm and smaller than 200 nm. By making the silicon fine particles 5 smaller than 200 nm, it is possible to reduce the volume change of expansion and contraction of the silicon fine particles 5 during charging and discharging. Further, by having a structure in which the silicon fine particles 5 are covered with the inorganic compound 6, expansion and contraction of the silicon fine particles 5 can be suppressed. On the other hand, when the silicon fine particles 5 have a thickness of 200 nm or more, the volume change due to the expansion and contraction of the silicon fine particles 5 during charging/discharging is large, so that problems such as cracking are likely to occur even in the structure covered with the inorganic compound 6. However, since the manufacturing time becomes long because the silicon fine particles having a size of less than 200 nm are formed, the cost is increased. If the silicon fine particles 5 have a particle size of less than 1000 nm, the volume change due to expansion and contraction becomes large, and thus the above-mentioned problem is more likely to occur than 200 nm, but since the manufacturing cost can be suppressed, the silicon fine particles 5 may be less than 1000 nm. preferable.
この構成と同時に、あるいはこの構成とは別に、無機化合物６内に空隙７を有しても良い。そして、負極活物質３ａは部分的に平坦な平坦面８を有する。
平坦面８は任意の立体形状の負極活物質３ａの表面の一部が平面となっている面である。負極活物質３ａの断面形状を観察した場合、平坦な面である平坦面８は直線形体となっている。その直線部の長さαと真直度βの比（β／α）は、０．０７未満が好ましい。また、直線部の長さαと負極活物質３ａの粒径Ｒの比（α／Ｒ）は、０．３より大きいことが好ましい。バインダ４により負極活物質３ａが負極集電体１の表面に固定され、負極合剤層２が形成される。前記直線部の長さαと真直度βの比（β／α）が０．０７未満、かつ、直線部の長さαと負極活物質３ａの粒径Ｒの比（α／Ｒ）が０．３より大きい平坦面８を有する負極活物質３ａ（図３、図４）を含むことにより、負極活物質３ａと負極集電体１との接点の面積が増えるため負極合剤層２と負極集電体１との密着性が向上する。図５では、直線部の長さαと真直度βの比（β／α）は、０．０７未満、かつ、直線部の長さαと負極活物質３ａの粒径Ｒの比（α／Ｒ）は、０．３以下になる構成として、直線部の長さαと負極活物質３ａの粒径Ｒの比（α／Ｒ）が０．２５となる構成を例示している。
At the same time as this configuration, or separately from this configuration, voids 7 may be provided in the inorganic compound 6. The negative electrode active material 3a has a partially flat flat surface 8.
The flat surface 8 is a surface in which a part of the surface of the negative electrode active material 3a having an arbitrary three-dimensional shape is a flat surface. When the cross-sectional shape of the negative electrode active material 3a is observed, the flat surface 8 which is a flat surface is a linear body. The ratio (β/α) between the length α of the straight line portion and the straightness β is preferably less than 0.07. Further, the ratio (α/R) of the length α of the straight line portion and the particle diameter R of the negative electrode active material 3a is preferably larger than 0.3. The binder 4 fixes the negative electrode active material 3a on the surface of the negative electrode current collector 1, and the negative electrode mixture layer 2 is formed. The ratio (β/α) between the straight line length α and the straightness β is less than 0.07, and the ratio between the straight line length α and the particle size R of the negative electrode active material 3a (α/R) is 0. The inclusion of the negative electrode active material 3a (FIGS. 3 and 4) having the flat surface 8 larger than 3 increases the contact area between the negative electrode active material 3a and the negative electrode current collector 1, and thus the negative electrode mixture layer 2 and the negative electrode. The adhesion with the current collector 1 is improved. In FIG. 5, the ratio (β/α) between the straight line length α and the straightness β is less than 0.07, and the ratio between the straight line length α and the particle size R of the negative electrode active material 3a (α/ R) is 0.3 or less, and the ratio (α/R) of the length α of the linear portion and the particle diameter R of the negative electrode active material 3a is 0.25.
図６に示すように、負極合剤層２を形成する際、例えばダイなどの塗布装置を用いて負極集電体１上に負極活物質３ａ、３ｂ、３ｃ、バインダ４、溶媒９を含む溶液を塗布する（図６の（ａ）塗布直後）。その後、溶媒９を乾燥させる過程（図６の（ｂ）乾燥中）において、乾燥時生じる対流により負極活物質３ａ、３ｂ、３ｃは移動しながら負極合剤層２を形成する。直線部の長さαと真直度βの比（β／α）が０．０７未満、かつ、直線部の長さαと負極活物質３ａの粒径Ｒの比（α／Ｒ）が０．３より大きい平坦面８を有することにより、溶媒９中を対流により負極活物質３ａ、３ｂ、３ｃは移動しながら、平坦面８を有する負極活物質３ａは負極集電体１と強い付着力が働き、平坦面８が負極集電体１に接触する状態で溶媒が乾燥し、負極活物質３ａの平坦面８が負極集電体１の接点となるように負極合剤層２を形成することができる（図６の（ｃ）乾燥後）。したがって、負極集電体１と負極活物質３ａとの間での接点が増え、負極集電体１と負極合剤層２との密着性を向上することができる。これにより、負極集電体１から負極合剤層２の剥がれ等による集電性の劣化を抑制できるため、充放電サイクル特性に優れたリチウムイオン二次電池１０が実現できる。しかし、前記直線部の長さαと真直度βの比（β／α）が０．０７未満、かつ、直線部の長さαと負極活物質３ａの粒径Ｒの比（α／Ｒ）が０．３以下の平坦な面を有する負極活物質３ａ（図５）を用いる場合は、平坦面を有する効果が低く、負極集電体１と負極合剤層２との密着性を向上する効果が得られない。また、前記直線部の長さαと真直度βの比（β／α）が０．０７以上で平坦な面を有さない粒子を用いる場合は、負極集電体との密着性が低下し、充放電サイクル特性の低下の要因となる。そのため、シリコン微粒子５の平坦面８は直線部の長さαと真直度βの比（β／α）が０．０７未満、かつ、直線部の長さαと負極活物質３ａの粒径Ｒの比（α／Ｒ）が０．３より大きいことが好ましい。 As shown in FIG. 6, when forming the negative electrode mixture layer 2, a solution containing the negative electrode active materials 3a, 3b, 3c, the binder 4, and the solvent 9 on the negative electrode current collector 1 using a coating device such as a die. (Immediately after (a) application in FIG. 6). After that, in the process of drying the solvent 9 (during drying in FIG. 6(b)), the negative electrode active materials 3a, 3b, and 3c move to form the negative electrode mixture layer 2 due to convection that occurs during drying. The ratio (β/α) between the straight line length α and the straightness β is less than 0.07, and the ratio between the straight line length α and the particle size R of the negative electrode active material 3a (α/R) is 0. By having the flat surface 8 larger than 3, the negative electrode active materials 3a, 3b, and 3c move by convection in the solvent 9 while the negative electrode active material 3a having the flat surface 8 has a strong adhesive force with the negative electrode current collector 1. Forming the negative electrode mixture layer 2 so that the solvent dries while the flat surface 8 is in contact with the negative electrode current collector 1 and the flat surface 8 of the negative electrode active material 3a serves as a contact point of the negative electrode current collector 1. Can be formed (after drying in FIG. 6(c)). Therefore, the number of contacts between the negative electrode current collector 1 and the negative electrode active material 3a is increased, and the adhesion between the negative electrode current collector 1 and the negative electrode mixture layer 2 can be improved. As a result, it is possible to suppress deterioration of the current collecting property due to peeling of the negative electrode mixture layer 2 from the negative electrode current collector 1, and thus it is possible to realize the lithium ion secondary battery 10 having excellent charge/discharge cycle characteristics. However, the ratio (β/α) between the straight line length α and the straightness β is less than 0.07, and the ratio between the straight line length α and the particle size R of the negative electrode active material 3a (α/R). When the negative electrode active material 3a (FIG. 5) having a flat surface of 0.3 or less is used, the effect of having the flat surface is low, and the adhesion between the negative electrode current collector 1 and the negative electrode mixture layer 2 is improved. No effect. Further, when particles having a ratio (β/α) of the straight line length α to the straightness β of 0.07 or more and having no flat surface are used, the adhesion to the negative electrode current collector decreases. , Which causes deterioration of charge/discharge cycle characteristics. Therefore, in the flat surface 8 of the silicon fine particles 5, the ratio (β/α) of the length α of the straight line portion to the straightness β is less than 0.07, and the length α of the straight line portion and the particle size R of the negative electrode active material 3a. It is preferable that the ratio (α/R) of is larger than 0.3.
なおこの負極活物質３ａに平坦な面を形成させるには、例えば、２枚の金属板間に試料であるシリコン微粒子５を分散した無機化合物６を挟み、例えば５０から５０００ＭＰａの圧力をかけながら、２００℃以上８００℃以下で焼成し、所定の粒径に粉砕したものを用いることができるが、特に限定されるものではない。 In order to form a flat surface on the negative electrode active material 3a, for example, an inorganic compound 6 in which silicon fine particles 5 as a sample are dispersed is sandwiched between two metal plates, and a pressure of 50 to 5000 MPa is applied, for example. It is possible to use the one that is fired at 200° C. or more and 800° C. or less and pulverized to a predetermined particle size, but it is not particularly limited.
また本発明において、負極活物質３ａの形状以外に、負極活物質３ａの母材となる無機化合物６も重要である。無機化合物６は、リチウムイオン伝導性を有する化合物であれば、特に限定させるものではない。例えば、ＳｉＯ２、Ｂ２Ｏ３、Ｐ２Ｏ５などの酸素を含む化合物、Ｌｉ２Ｓ−Ｐ２Ｓ５、Ｌｉ３Ｎ、Ｌｉ１０ＧｅＰ２Ｓ１２、Ｌｉ３．２５Ｇｅ０．２５Ｐ０．７５Ｓ４、Ｌｉ２Ｓ−Ｂ２Ｓ５−ＬｉＩ、Ｌｉ２Ｓ−ＧｅＳ２などのリチウムを含む化合物、Ｌｉ３ＢＯ３、Ｌｉ３ＰＯ４、Ｌｉ２Ｓｉ２Ｏ５、Ｌｉ２ＳｉＯ３、Ｌｉ４ＳｉＯ４、Ｌａ０．５１Ｌｉ０．３４ＴｉＯ２．９４、Ｌｉ１．５Ａｌ０．３Ｔｉ１．７（ＰＯ４）３、Ｌｉ７Ｌａ３Ｚｒ２Ｏ１２、Ｌｉ１．０７Ａｌ０．６９Ｔｉ１．４６（ＰＯ４）３、Ｌｉ１．５Ａｌ０．５Ｇｅ１．５（ＰＯ４）３などの酸素とリチウムを含む化合物などを用いることができる。 In addition to the shape of the negative electrode active material 3a, the inorganic compound 6 that is the base material of the negative electrode active material 3a is also important in the present invention. The inorganic compound 6 is not particularly limited as long as it is a compound having lithium ion conductivity. For example, oxygen-containing compounds such as SiO 2 , B 2 O 3 , and P 2 O 5 , Li 2 S-P 2 S 5 , Li 3 N, Li 10 GeP 2 S 12 , and Li 3.25 Ge 0.25 P. 0.75 S 4, Li 2 S- B 2 S 5 -LiI, compounds containing lithium, such as Li 2 S-GeS 2, Li 3 BO 3, Li 3 PO 4, Li 2 Si 2 O 5, Li 2 SiO 3 , Li 4 SiO 4 , La 0.51 Li 0.34 TiO 2.94 , Li 1.5 Al 0.3 Ti 1.7 (PO 4 ) 3 , Li 7 La 3 Zr 2 O 12 , Li 1. A compound containing oxygen and lithium such as 07 Al 0.69 Ti 1.46 (PO 4 ) 3 and Li 1.5 Al 0.5 Ge 1.5 (PO 4 ) 3 can be used.
また前記無機化合物６は、融点がシリコンより低いことがより好ましい。シリコンより低い融点の無機化合物６を用いることにより、シリコンの結晶状態やシリコンの粒子サイズを変化させることなく、無機化合物のみを焼結することが可能となる。 It is more preferable that the melting point of the inorganic compound 6 is lower than that of silicon. By using the inorganic compound 6 having a melting point lower than that of silicon, it is possible to sinter only the inorganic compound without changing the crystalline state of silicon or the particle size of silicon.
また、負極活物質３ａは粒子内に空隙７を含む構造であることが好ましい。図７に示すように、負極活物質３ａの粒子内部に空隙７を含むことにより、充電時におけるリチウムイオンの吸蔵によりシリコン微粒子５の体積が膨張し（図７の（ａ）の状態）、放電時におけるリチウムイオンの放出によりシリコン微粒子５の体積が収縮する（図７の（ｂ）の状態）。このシリコン微粒子５の体積変化を負極活物質３ａ内に空隙７を含むことにより吸収できるため、シリコン微粒子５の体積変化による割れ等を防ぐことができ、初回充放電効率および充放電サイクル特性が改善される。なお、シリコン微粒子５の体積変化により負極活物質３ａが割れると、シリコン微粒子５の比表面積が大きくなるため、非水電解液１４との副反応が加速され、初回充放電効率および充放電サイクル特性が低下する要因となるが、空隙７を設けることにより、初回充放電効率および充放電サイクル特性が低下を抑制することができる。 Further, the negative electrode active material 3a preferably has a structure including voids 7 in the particles. As shown in FIG. 7, by including the voids 7 inside the particles of the negative electrode active material 3a, the volume of the silicon fine particles 5 expands due to the absorption of lithium ions during charging (state (a) of FIG. 7), and discharge occurs. At this time, the volume of the silicon fine particles 5 is contracted by the release of lithium ions (state (b) of FIG. 7). Since the volume change of the silicon fine particles 5 can be absorbed by including the voids 7 in the negative electrode active material 3a, cracks and the like due to the volume change of the silicon fine particles 5 can be prevented, and the initial charge/discharge efficiency and charge/discharge cycle characteristics are improved. To be done. When the negative electrode active material 3a is cracked due to the volume change of the silicon fine particles 5, the specific surface area of the silicon fine particles 5 is increased, so that the side reaction with the non-aqueous electrolyte solution 14 is accelerated, and the initial charge/discharge efficiency and charge/discharge cycle characteristics are increased. However, the provision of the voids 7 can suppress the deterioration of the initial charge/discharge efficiency and charge/discharge cycle characteristics.
前記空隙７は、負極活物質３ａにおいて、平坦面８近傍の領域以外の領域の無機化合物６中の空隙率に比べて平坦面８近傍の空隙率が低くなっていることが好ましい。前述したように、平坦面８において負極集電体１との密着性や負極活物質３ａ間の密着性を向上させるため、平坦面８近傍において空隙率が低いことにより、その密着性を確保することができ、平坦面８以外の部分の空隙７で充放電時のシリコン微粒子５の体積変化を吸収することができる。これにより、充放電サイクル特性を向上することができる。 It is preferable that the voids 7 in the negative electrode active material 3a have a lower void ratio in the vicinity of the flat surface 8 than in the region other than the region near the flat surface 8 in the inorganic compound 6. As described above, in order to improve the adhesion between the negative electrode current collector 1 and the negative electrode active material 3a on the flat surface 8, the adhesion is secured by the low porosity in the vicinity of the flat surface 8. It is possible to absorb the volume change of the silicon fine particles 5 at the time of charging/discharging by the voids 7 other than the flat surface 8. As a result, the charge/discharge cycle characteristics can be improved.
負極活物質（第２の負極活物質）３ｂとしては、図８に示すように、無機化合物６にシリコン微粒子５が分散された構造であり、かつ、その粒子内に空隙７を有する。また、負極活物質３ｂは、負極活物質３ａと異なり、平坦な面を有しない。 As shown in FIG. 8, the negative electrode active material (second negative electrode active material) 3b has a structure in which silicon fine particles 5 are dispersed in an inorganic compound 6, and has voids 7 in the particles. Further, the negative electrode active material 3b does not have a flat surface, unlike the negative electrode active material 3a.
負極合剤層２は、負極活物質３ａのみを含む構成としても良いが、負極活物質３ａと負極活物質３ｂとを含むことが好ましい。また、負極活物質３ａと負極活物質３ｂとの比率（負極活物質３ａ／負極活物質３ｂ）は、０．０１より大きく１．０より小さいことが好ましい。図９に示すように、負極活物質３ａと負極活物質３ｂとの比率が１．０以上であると表面粗さの小さい平坦面８の割合が増えるため、シリコン微粒子５を含む負極活物質３ａ、３ｂの比表面積が小さくなり、負極活物質３ａ、３ｂと非水電解液１４との接触面が低下する。負極活物質３ａ、３ｂと非水電解液１４との接触面が低下することにより、リチウムイオンの吸蔵および放出量が低下するため、出入力特性が低下する。また、図１０に示すように、負極活物質３ａと負極活物質３ｂとの比率が０．０１以下であると、平坦面８が少なくなるため、負極活物質３ａ、３ｂと前述した負極集電体１との密着性や負極活物質３ａ、３ｂ間の密着性の効果が得られず、充放電サイクル特性の低下する要因となる。 The negative electrode mixture layer 2 may have a configuration including only the negative electrode active material 3a, but preferably includes the negative electrode active material 3a and the negative electrode active material 3b. Further, the ratio of the negative electrode active material 3a and the negative electrode active material 3b (negative electrode active material 3a/negative electrode active material 3b) is preferably larger than 0.01 and smaller than 1.0. As shown in FIG. 9, when the ratio of the negative electrode active material 3a and the negative electrode active material 3b is 1.0 or more, the ratio of the flat surface 8 having a small surface roughness increases, so that the negative electrode active material 3a containing the silicon fine particles 5 is included. The specific surface area of 3b is reduced, and the contact surface between the negative electrode active materials 3a and 3b and the non-aqueous electrolyte solution 14 is reduced. Since the contact surface between the negative electrode active materials 3a and 3b and the non-aqueous electrolyte solution 14 is reduced, the amount of occlusion and release of lithium ions is reduced, and thus the input/output characteristics are reduced. Further, as shown in FIG. 10, when the ratio of the negative electrode active material 3a and the negative electrode active material 3b is 0.01 or less, the number of the flat surfaces 8 is small, so that the negative electrode active materials 3a and 3b and the above-described negative electrode current collector are collected. The effect of the adhesiveness with the body 1 and the adhesiveness between the negative electrode active materials 3a and 3b cannot be obtained, which causes a decrease in charge/discharge cycle characteristics.
負極合剤層２は、負極活物質３ａまたは、負極活物質３ａおよび負極活物質３ｂに加えて負極活物質（第３の負極活物質）３ｃを含むことができる。負極活物質３ｃとしては、黒鉛などの炭素材料を用いることができるが、特に限定されるものではない。 The negative electrode mixture layer 2 can include a negative electrode active material 3a or a negative electrode active material (third negative electrode active material) 3c in addition to the negative electrode active material 3a and the negative electrode active material 3b. As the negative electrode active material 3c, a carbon material such as graphite can be used, but it is not particularly limited.
負極合剤層２中に黒鉛などの炭素材料を用いる場合は、負極活物質３ａと負極活物質３ｂとを併せた粒子と黒鉛などの炭素材料との比率（黒鉛粒子／（負極活物質３ａと負極活物質３ｂとの総量））は、２．０以上９９．０以下であることが好ましい。比率が前記範囲内であれば、高容量化とサイクル特性向上の両立が可能となる。負極活物質３ａと負極活物質３ｂとを併せた粒子と炭素材料との比率が９９．０より大きいと、高容量化に寄与するシリコン微粒子５の割合が低下するため高容量化の効果が小さくなる。また、２．０より小さいと電子伝導に寄与する黒鉛粒子の割合が低下するため電子伝導性が低下する。 When a carbon material such as graphite is used in the negative electrode mixture layer 2, the ratio of particles obtained by combining the negative electrode active material 3a and the negative electrode active material 3b and the carbon material such as graphite (graphite particles/(negative electrode active material 3a and The total amount of the negative electrode active material 3b)) is preferably 2.0 or more and 99.0 or less. When the ratio is within the above range, both high capacity and improved cycle characteristics can be achieved. If the ratio of the particles including the negative electrode active material 3a and the negative electrode active material 3b to the carbon material is larger than 99.0, the ratio of the silicon fine particles 5 contributing to the high capacity decreases, and the effect of increasing the capacity is small. Become. On the other hand, if it is less than 2.0, the proportion of graphite particles contributing to electron conduction is lowered, so that the electron conductivity is lowered.
以下、本発明の一実施の形態における実施例および比較例を示すが、本発明はこれらに限定されるものではない。図１１は実施例１から９および比較例１から６の電池性能を測定した結果を示す図である。 Hereinafter, examples and comparative examples in one embodiment of the present invention will be shown, but the present invention is not limited thereto. FIG. 11 is a diagram showing the results of measuring the battery performance of Examples 1 to 9 and Comparative Examples 1 to 6.
以下実施例１から９および比較例１から６において、正極板１１、セパレータ１３、非水電解液１４、ケース１５はいずれの場合においても同じものを用いた。
正極板１１は、正極集電体として、厚み１５μｍのアルミニウム箔を用い、その両表面に設けた正極合剤層は、活物質としてのコバルト酸リチウム１００重量部、導電助材としてのアセチレンブラック５重量部、バインダとしてのポリフッ化ビニリデン５重量部からなり、片面厚み３０μｍとしたものである。
In the following Examples 1 to 9 and Comparative Examples 1 to 6, the same positive electrode plate 11, separator 13, non-aqueous electrolyte solution 14, and case 15 were used.
The positive electrode plate 11 uses an aluminum foil having a thickness of 15 μm as a positive electrode current collector, and the positive electrode material mixture layers provided on both surfaces thereof have 100 parts by weight of lithium cobalt oxide as an active material and acetylene black 5 as a conductive additive. It is composed of 5 parts by weight of polyvinylidene fluoride as a binder and has a thickness of 30 μm on one side.
セパレータ１３は、厚み２７μｍのポリプロピレン製の微多孔膜を用い、非水電解液１４としては、エチレンカーボネートとジメチルカーボネートとエチルメチルカーボネートを１：１：１の重量比率で混合した溶媒に、溶質として１モル／Ｌの六フッ化リン酸リチウムを溶解したものを用いた。また、ケース１５としては、直径２６ｍｍ、高さ６５ｍｍの円筒型のものを用いた。 As the separator 13, a polypropylene microporous film having a thickness of 27 μm is used, and as the non-aqueous electrolyte solution 14, a solvent obtained by mixing ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a weight ratio of 1:1:1 is used as a solute. What melt|dissolved 1 mol/L lithium hexafluorophosphate was used. As the case 15, a cylindrical case having a diameter of 26 mm and a height of 65 mm was used.
負極板１２は、厚み１０μｍの電解銅箔からなる負極集電体１と、負極集電体１の両表面に設けた負極合剤層２とから構成される。負極合剤層２は、負極活物質３ａ、負極活物質３ｂ、負極活物質３ｃおよびバインダ４を備え、厚み５０μｍである。負極活物質３ａ、負極活物質３ｂはシリコン微粒子５を含む無機化合物６から構成される。負極活物質３ｃは活物質として黒鉛を用いた。負極合剤層２は、活物質として黒鉛とシリコン微粒子を含む無機化合物との混合粉末１００重量部、バインダ４としてのカルボキシルメチルセルロース１重量部、スチレン−ブタジエンゴム２重量部を用いた。以上の構成は、実施例、比較例の各場合において同じとし、本発明の特徴的な条件である、負極活物質３ａと負極活物質３ｂとの比率、負極活物質３ａと負極活物質３ｂとを併せた粒子量と黒鉛との比率、負極活物質３ａの平坦面８の直線部の長さαと真直度βの比（β／α）、平坦面８近傍とそれ以外の領域での負極活物質３ａ内の空隙率差、については、実施例および比較例の各場合で用いた条件を図１１にまとめた。 The negative electrode plate 12 is composed of a negative electrode current collector 1 made of an electrolytic copper foil having a thickness of 10 μm, and a negative electrode mixture layer 2 provided on both surfaces of the negative electrode current collector 1. The negative electrode mixture layer 2 includes the negative electrode active material 3a, the negative electrode active material 3b, the negative electrode active material 3c, and the binder 4, and has a thickness of 50 μm. The negative electrode active material 3a and the negative electrode active material 3b are composed of an inorganic compound 6 containing silicon fine particles 5. As the negative electrode active material 3c, graphite was used as the active material. The negative electrode mixture layer 2 used 100 parts by weight of a mixed powder of graphite and an inorganic compound containing silicon fine particles as an active material, 1 part by weight of carboxymethyl cellulose as a binder 4, and 2 parts by weight of styrene-butadiene rubber. The above configuration is the same in each of the examples and comparative examples, and the characteristic conditions of the present invention are the ratio of the negative electrode active material 3a and the negative electrode active material 3b, the negative electrode active material 3a and the negative electrode active material 3b. The ratio of the particle amount to graphite, the ratio of the straight line length α of the flat surface 8 of the negative electrode active material 3a to the straightness β (β/α), and the negative electrode in the vicinity of the flat surface 8 and other regions. Regarding the difference in porosity in the active material 3a, the conditions used in each of the examples and comparative examples are summarized in FIG.
なお、負極活物質３ａ内の空隙率差は粒子断面ＳＥＭ画像より、負極活物質３ａ内を５分割し、画像処理により平坦面８近傍とそれ以外の領域の空隙率を測定し、最大値から最小値の差を算出した。 The difference in porosity in the negative electrode active material 3a was determined by dividing the negative electrode active material 3a into 5 parts from the particle cross-section SEM image, and measuring the porosity in the vicinity of the flat surface 8 and other regions by image processing. The minimum difference was calculated.
上述の正極板１１と負極板１２を、セパレータ１３を介して重ねて捲回した集電体を、非水電解液１４とともにケース１５内に収納して、実施例１から９、および比較例１から６のリチウムイオン二次電池を作製した。 A current collector obtained by stacking the positive electrode plate 11 and the negative electrode plate 12 with the separator 13 in between and winding them together is housed in a case 15 together with the non-aqueous electrolyte solution 14, and Examples 1 to 9 and Comparative Example 1 6 to 6 were produced.
以上の各電池の充放電を、２５℃環境下において、４００ｍＡの定電流で、充電上限電圧４．２Ｖ、放電下限電圧２．５Ｖの条件下で行い、充電容量（ｍＡｈ）および放電容量（ｍＡｈ）を測定した。また、この充電および放電の一連の操作を５００サイクル繰り返し、５００サイクル目の充電容量および放電容量を測定した。この測定結果から初回充放電効率と容量維持率を算出した。なお、初回充放電効率は、「（１サイクル目放電容量／１サイクル目の充電容量）×１００％」により算出され、容量維持率は、「（５００サイクル目放電容量／１サイクル目放電容量）×１００％」により算出される。算出した結果も、図１１に併せて記載した。 Charging/discharging of each of the above batteries was performed under a condition of a constant current of 400 mA and a charge upper limit voltage of 4.2 V and a discharge lower limit voltage of 2.5 V under an environment of 25° C. to obtain a charge capacity (mAh) and a discharge capacity (mAh). ) Was measured. Further, this series of charging and discharging operations was repeated for 500 cycles, and the charging capacity and discharging capacity at the 500th cycle were measured. The initial charge/discharge efficiency and capacity retention rate were calculated from the measurement results. The initial charge/discharge efficiency is calculated by “(first cycle discharge capacity/first cycle charge capacity)×100%”, and the capacity retention rate is “(500th cycle discharge capacity/first cycle discharge capacity). X 100%". The calculated results are also shown in FIG.
図１１に示す結果から明らかなように、本発明の実施例１から９の電池のいずれにおいても、高い容量維持比率を実現し、車載用途などで求められる優れた充放電サイクル特性を実現可能である。これに対し、本発明の範囲外となる比較例１から６の電池のいずれにおいても、容量維持率が実施例１から９に比べて低く、車載用途などで求められる充放電サイクル特性を満足できるものではない。 As is clear from the results shown in FIG. 11, in any of the batteries of Examples 1 to 9 of the present invention, a high capacity maintenance ratio can be realized, and excellent charge/discharge cycle characteristics required for in-vehicle applications can be realized. is there. On the other hand, in any of the batteries of Comparative Examples 1 to 6 which are out of the range of the present invention, the capacity retention ratio is lower than that of Examples 1 to 9, and the charge/discharge cycle characteristics required for vehicle applications can be satisfied. Not a thing.
本発明は、充放電サイクル特性の向上を図ることができ、負極集電体と負極合剤層とからなる負極板、および正極板を備えるリチウムイオン二次電池等に有用である。 INDUSTRIAL APPLICABILITY The present invention can improve charge/discharge cycle characteristics and is useful for a negative electrode plate including a negative electrode current collector and a negative electrode mixture layer, a lithium ion secondary battery including a positive electrode plate, and the like.
１ 負極集電体
２ 負極合剤層
３ａ 負極活物質（第１の負極活物質）
３ｂ 負極活物質（第２の負極活物質）
３ｃ 負極活物質（第３の負極活物質）
４ バインダ
５ シリコン微粒子
６ 無機化合物
７ 空隙
８ 平坦面
９ 溶媒
１０ リチウムイオン二次電池
１１ 正極板
１２ 負極板
１３ セパレータ
１４ 非水電解液
１５ ケース
1 Negative electrode current collector 2 Negative electrode mixture layer 3a Negative electrode active material (first negative electrode active material)
3b Negative electrode active material (second negative electrode active material)
3c Negative electrode active material (third negative electrode active material)
4 Binder 5 Silicon Fine Particle 6 Inorganic Compound 7 Void 8 Flat Surface 9 Solvent 10 Lithium Ion Secondary Battery 11 Positive Electrode Plate 12 Negative Electrode Plate 13 Separator 14 Non-Aqueous Electrolyte 15 Case
Claims (4)
前記負極合剤層は、少なくとも第１の負極活物質と、前記第１の負極活物質を前記負極集電体の表面に固定化するバインダとを含み、
前記第１の負極活物質は、少なくとも無機化合物にシリコン微粒子が分散された構造を有し、前記第１の負極活物質の少なくとも一部は表面に平坦面を有し、
前記負極合剤層は第２の負極活物質をさらに含み、前記平坦面は前記第１の負極活物質にのみ設けられ、
前記負極合剤層は、前記第１の負極活物質より前記第２の負極活物質を多く含み、
前記第１の負極活物質と前記第２の負極活物質との比率が、０．０１≦前記第１の負極活物質／前記第２の負極活物質＜１．０であり、
前記負極合剤層は黒鉛の炭素材料を有し、前記第１の負極活物質と前記第２の負極活物質とを併せた粒子と黒鉛の炭素材料との比率が２．０以上９９．０以下であり、
前記第１の負極活物質の平坦面は直線形体となっており、その直線部の長さと真直度の比が０．０７未満であり、
前記第１の負極活物質は空隙を有し、前記平坦面の近傍における前記空隙の空隙率が他の領域における前記空隙の空隙率より低く、その空隙率差が１１％以上３８％以下であることを特徴とするリチウムイオン二次電池。 A positive electrode plate comprising a positive electrode current collector and a positive electrode mixture layer provided in contact with the surface of the positive electrode current collector, a negative electrode current collector and a negative electrode mixture layer provided in contact with the surface of the negative electrode current collector A lithium ion secondary battery in which a negative electrode plate made of, and a separator provided between the positive electrode plate and the negative electrode plate are housed in a case together with an electrolytic solution,
The negative electrode mixture layer includes at least a first negative electrode active material and a binder that fixes the first negative electrode active material on the surface of the negative electrode current collector,
The first negative electrode active material has a structure in which fine silicon particles are dispersed in at least an inorganic compound, and at least a part of the first negative electrode active material has a flat surface.
The negative electrode mixture layer further includes a second negative electrode active material, and the flat surface is provided only on the first negative electrode active material,
The negative electrode mixture layer contains more of the second negative electrode active material than the first negative electrode active material,
The ratio of the first negative electrode active material and the second negative electrode active material is 0.01≦the first negative electrode active material/the second negative electrode active material<1.0,
The negative electrode mixture layer contains a graphite carbon material, and the ratio of the particles of the first negative electrode active material and the second negative electrode active material to the graphite carbon material is 2.0 or more and 99.0. Is less than
The flat surface of the first negative electrode active material is a linear body, and the ratio of the length and straightness of the linear portion is less than 0.07,
The first negative electrode active material has voids, the void ratio of the voids in the vicinity of the flat surface is lower than the void ratios of the voids in other regions, and the void ratio difference is 11% or more and 38% or less. A lithium-ion secondary battery characterized in that
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