JP2006066298A - Lithium secondary battery - Google Patents
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Abstract
Description
本発明は、リチウム二次電池用負極材料および電解液、ならびにそれらを備えたリチウム二次電池に関する。 The present invention relates to a negative electrode material for lithium secondary batteries, an electrolytic solution, and a lithium secondary battery including the same.
リチウム二次電池は、リチウムイオンを吸蔵・放出し得る材料（活物質）を有する正極と負極を備え、該二極間の電解質（典型的には非水電解液）をリチウムイオンが行き来することにより充放電する二次電池であり、車両搭載バッテリー、或いはパソコン及び携帯端末用電源として重要性が高まっている。
かかるリチウム二次電池に求められる性能の一つとして、低温特性に優れることが挙げられる。ここで低温特性とは、低温条件下（例えば０℃）における充放電性能をいう。従って、低温特性に優れるとは、典型的には低温条件下において所望する容量（又は出力）の放電が安定的に実現されることを包含する。
このような低温特性に優れるリチウム二次電池を得る一つの手段として、γ−ブチロラクトン等のラクトン類を溶媒の主体とする非水電解液の使用が挙げられる。γ−ブチロラクトンは融点が低く（約−４５℃）、氷点下（例えば−２０℃）での使用であっても、非水電解液として求められる性能を高いレベルで維持することができる。例えば、下記特許文献１には、γ−ブチロラクトンを含む非水電解液を使用したリチウム二次電池が記載されている。
A lithium secondary battery includes a positive electrode and a negative electrode having a material (active material) capable of inserting and extracting lithium ions, and lithium ions travel back and forth between the electrolyte (typically a non-aqueous electrolyte) between the two electrodes. It is a secondary battery that is charged and discharged by the above, and has become increasingly important as a vehicle-mounted battery or a power source for personal computers and portable terminals.
One of the performances required for such a lithium secondary battery is excellent low temperature characteristics. Here, the low temperature characteristic refers to charge / discharge performance under low temperature conditions (for example, 0 ° C.). Therefore, excellent low temperature characteristics typically include the stable realization of a desired capacity (or output) discharge under low temperature conditions.
One means for obtaining such a lithium secondary battery having excellent low temperature characteristics is the use of a non-aqueous electrolyte mainly composed of a lactone such as γ-butyrolactone. γ-Butyrolactone has a low melting point (about −45 ° C.) and can maintain the performance required as a non-aqueous electrolyte at a high level even when used below freezing point (for example, −20 ° C.). For example, Patent Document 1 below describes a lithium secondary battery using a non-aqueous electrolyte containing γ-butyrolactone.
ところで、低融点のラクトン類を非水電解液成分として用いるリチウム二次電池において改善すべき点として、負極活物質に黒鉛等の炭素材料を用いた場合のサイクル特性の向上が挙げられる。ここでサイクル特性とは、二次電池の耐久性（寿命）に関する指標であり、充放電を繰り返した際の電池の充放電性能をいう。従って、サイクル特性に優れるとは、典型的には充放電の繰り返しに拘わらず所望する容量（又は出力）の放電が安定的に実現されることを包含する。サイクル特性を向上させることによって、高耐久性（長寿命）を実現したリチウム二次電池を提供することができる。
本発明は、かかる従来の課題を解決すべく開発されたものであり、炭素材料を負極活物質の主成分として使用した負極とラクトン含有非水電解液とを備えるリチウム二次電池であって、低温特性とサイクル特性に優れるリチウム二次電池の提供を目的とする。
By the way, as a point to be improved in a lithium secondary battery using a low melting point lactone as a non-aqueous electrolyte component, there is an improvement in cycle characteristics when a carbon material such as graphite is used as the negative electrode active material. Here, the cycle characteristic is an index relating to the durability (life) of the secondary battery, and refers to the charge / discharge performance of the battery when charge / discharge is repeated. Therefore, excellent cycle characteristics typically include that a desired capacity (or output) discharge can be stably realized regardless of repeated charge and discharge. By improving the cycle characteristics, a lithium secondary battery realizing high durability (long life) can be provided.
The present invention has been developed to solve such conventional problems, and is a lithium secondary battery including a negative electrode using a carbon material as a main component of a negative electrode active material and a lactone-containing non-aqueous electrolyte, An object of the present invention is to provide a lithium secondary battery excellent in low temperature characteristics and cycle characteristics.
本発明によって提供されるリチウム二次電池は、正極（典型的にはリチウム遷移金属複合酸化物）、負極、ならびに融点０℃以下のラクトンを少なくとも一種類含む非水電解液（以下「ラクトン含有非水電解液」と略称する。）を備えたリチウム二次電池であり、負極活物質としてリチウムイオンの吸蔵及び放出が可能な炭素材料とチタン酸リチウムとを含む。
そして、ここで開示される好適なリチウム二次電池は、負極活物質の総量に対する前記炭素材料の含有率が８０〜９９質量％であり、チタン酸リチウムの含有率が１〜２０質量％である。負極活物質の総量に対する炭素材料の含有率が９０〜９５質量％であり、チタン酸リチウムの含有率が５〜１０質量％であることが特に好ましい。
The lithium secondary battery provided by the present invention includes a positive electrode (typically a lithium transition metal composite oxide), a negative electrode, and a non-aqueous electrolyte solution (hereinafter referred to as “lactone-containing non-aqueous electrolyte) containing at least one lactone having a melting point of 0 ° C. Lithium secondary battery provided with an abbreviated “water electrolyte”), which includes a carbon material capable of inserting and extracting lithium ions and lithium titanate as a negative electrode active material.
And the suitable lithium secondary battery disclosed here has a content of the carbon material of 80 to 99% by mass and a content of lithium titanate of 1 to 20% by mass with respect to the total amount of the negative electrode active material. . It is particularly preferable that the content of the carbon material with respect to the total amount of the negative electrode active material is 90 to 95% by mass, and the content of lithium titanate is 5 to 10% by mass.
本発明者は、ラクトン含有非水電解液とともに負極活物質として黒鉛等の炭素材料を採用した電池では、負極活物質表面に形成されるパシベーション被膜、即ちＳＥＩ（Solid Electrolyte Interface：電解液等の還元的分解によって生成する界面被膜）の負極活物質表面への密着性が乏しく、それ故に放電末期の負極電位の急激な上昇時に当該被膜が破壊・剥離し得、更なる電解液の還元的分解が放電末期毎に生じ得ることを見出した。かかる電解液の過剰な還元的分解の進行は、サイクル特性の低下に繋がる為、好ましくない。
そして、本発明者は、黒鉛等の炭素材料に所定の割合でチタン酸リチウムを添加することによって、放電末期の負極電位の上昇の度合いを緩やかにし得、結果、ＳＥＩの破壊・剥離を抑えて延いては電解液の過剰な還元的分解を防止し得ることを見出し、本発明を完成するに至った。
本発明のリチウム二次電池では、ラクトン含有非水電解液と、所定の割合でチタン酸リチウムを含む炭素材料を主体とする負極活物質の採用によって、優れた低温特性とサイクル特性とを共に実現することができる。
In the battery employing a lactone-containing non-aqueous electrolyte and a carbon material such as graphite as a negative electrode active material, the present inventor has found that a passivation film formed on the surface of the negative electrode active material, that is, SEI (Solid Electrolyte Interface) The adhesion of the interfacial coating produced by the thermal decomposition) to the surface of the negative electrode active material is poor, and therefore the coating can be destroyed and peeled off when the negative electrode potential suddenly rises at the end of discharge, and further reductive decomposition of the electrolyte solution occurs. It has been found that this can occur at the end of each discharge. Such excessive reductive decomposition of the electrolytic solution is not preferable because it leads to deterioration of cycle characteristics.
The present inventor can moderate the degree of increase in the negative electrode potential at the end of discharge by adding lithium titanate to a carbon material such as graphite at a predetermined ratio. As a result, it has been found that excessive reductive decomposition of the electrolytic solution can be prevented, and the present invention has been completed.
The lithium secondary battery of the present invention achieves both excellent low temperature characteristics and cycle characteristics by adopting a lactone-containing non-aqueous electrolyte and a negative electrode active material mainly composed of a carbon material containing lithium titanate at a predetermined ratio. can do.
ここで開示される好ましい一つのリチウム二次電池は、非水電解液を構成する溶媒中の前記ラクトンの含有率が５５〜８５体積％であることを特徴とする。
かかる構成のラクトン含有非水電解液を使用することによって、優れた低温特性とサイクル特性を維持しつつ、より高い出力を得ることができる。前記ラクトンとしてγ−ブチロラクトンを含むものが好ましい。
One preferable lithium secondary battery disclosed herein is characterized in that the content of the lactone in the solvent constituting the non-aqueous electrolyte is 55 to 85% by volume.
By using the lactone-containing non-aqueous electrolyte having such a configuration, a higher output can be obtained while maintaining excellent low-temperature characteristics and cycle characteristics. Those containing γ-butyrolactone as the lactone are preferred.
また本発明は、上記課題を解決する他の一側面として、リチウム二次電池に用いられ得る負極活物質（組成物）であって炭素材料の含有率が８０〜９９質量％（好ましくは９０〜９５質量％）でありチタン酸リチウムの含有率が１〜２０質量％（好ましくは５〜１０質量％）であることを特徴とする負極活物質を提供する。また、かかる組成の負極活物質とラクトン含有非水電解液とを使用することを特徴とするリチウム二次電池の製造方法を提供する。 Moreover, this invention is another negative aspect which solves the said subject, It is a negative electrode active material (composition) which can be used for a lithium secondary battery, Comprising: The content rate of a carbon material is 80-99 mass% (preferably 90- 95% by mass) and the content of lithium titanate is 1 to 20% by mass (preferably 5 to 10% by mass). Moreover, the manufacturing method of the lithium secondary battery characterized by using the negative electrode active material of this composition and a lactone containing non-aqueous electrolyte is provided.
さらに本発明は、上記課題を解決する他の一側面として、正極（典型的にはリチウム遷移金属複合酸化物）と、炭素材料を主体とする負極とラクトン含有非水電解液を備えるリチウム二次電池のサイクル特性を向上させる方法を提供する。
ここで開示されるリチウム二次電池のサイクル特性向上方法は、負極活物質である炭素材料にチタン酸リチウムを添加することを特徴とする。典型的には、負極活物質の総量に対するチタン酸リチウムの含有率が１〜２０質量％（好ましくは５〜１０質量％）となるように該化合物を添加する。典型的には負極活物質の総量に対する炭素材料の含有率は８０〜９９質量％（好ましくは９０〜９５質量％）であり得る。
Furthermore, the present invention provides, as another aspect to solve the above problems, a lithium secondary comprising a positive electrode (typically a lithium transition metal composite oxide), a negative electrode mainly composed of a carbon material, and a lactone-containing non-aqueous electrolyte. A method for improving the cycle characteristics of a battery is provided.
The method for improving the cycle characteristics of a lithium secondary battery disclosed herein is characterized in that lithium titanate is added to a carbon material that is a negative electrode active material. Typically, the compound is added so that the content of lithium titanate with respect to the total amount of the negative electrode active material is 1 to 20% by mass (preferably 5 to 10% by mass). Typically, the content of the carbon material with respect to the total amount of the negative electrode active material may be 80 to 99% by mass (preferably 90 to 95% by mass).
以下、本発明の好適な実施形態について詳細に説明する。なお、本明細書において特に言及している事項（例えば負極活物質の組成や非水電解液の組成）以外の技術的事項であって本発明の実施に必要な事項（例えば種々の形状のリチウム二次電池の一般的な製造技法）は、従来技術に基づく当業者の設計事項として把握され得る。本発明は、本明細書に開示される技術内容と当該分野における技術常識とに基づいて実施することができる。 Hereinafter, preferred embodiments of the present invention will be described in detail. It should be noted that the technical matters other than the matters specifically mentioned in the present specification (for example, the composition of the negative electrode active material and the composition of the non-aqueous electrolyte) and the matters necessary for the practice of the present invention (for example, lithium having various shapes) The general manufacturing technique of the secondary battery can be understood as a design matter of a person skilled in the art based on the prior art. The present invention can be implemented based on the technical contents disclosed in the present specification and the common general technical knowledge in the field.
ここで開示されるリチウム二次電池の負極に備えられる負極活物質は、炭素材料を主体とする。リチウムイオンの吸蔵及び放出が可能な炭素質物質を使用し得るが、容量が高く電圧の平坦性にも優れることから、高結晶性の天然黒鉛、人造黒鉛等の黒鉛系材料が好適である。
一方、ここで開示される負極活物質を調製するために炭素材料に添加されるチタン酸リチウムの組成比（原子比）は限定されず、活物質として機能し得る種々の組成比のものを使用することができる。例えば、一般式：ＬｉｘＴｉｙＯ４（ここでｘは典型的には０．８≦ｘ≦１．４を満たす実数であり、ｙは典型的には１．６≦ｙ≦２．２を満たす実数である。）で表され得る種々の組成比（原子比）のチタン酸リチウムを用いることができる。
The negative electrode active material provided in the negative electrode of the lithium secondary battery disclosed here is mainly composed of a carbon material. A carbonaceous material capable of occluding and releasing lithium ions can be used, but graphite materials such as highly crystalline natural graphite and artificial graphite are suitable because of their high capacity and excellent voltage flatness.
On the other hand, the composition ratio (atomic ratio) of lithium titanate added to the carbon material in order to prepare the negative electrode active material disclosed herein is not limited, and those having various composition ratios that can function as the active material are used. can do. For example, the general formula: Li x Ti y O 4 (where x is a real number that typically satisfies 0.8 ≦ x ≦ 1.4, and y is typically 1.6 ≦ y ≦ 2.2). Lithium titanate having various composition ratios (atomic ratios) that can be represented by the following formula:
チタン酸リチウムの添加量は、目的とするリチウム二次電池の放電末期の負極電位の上昇の度合いを緩やかにし得る量であれば特に限定されない。負極活物質の総量に対するチタン酸リチウムの含有率は概ね１〜２０質量％が適当であり、３〜１５質量％程度が好ましく、５〜１０質量％程度が特に好ましい。他方、炭素材料の負極活物質総量に対する含有率は概ね８０〜９９質量％が適当であり、８５〜９７質量％程度が好ましく、９０〜９５質量％程度が特に好ましい。
なお、放電末期において負極電位を過度に上昇させない限りにおいて、負極活物質として炭素材料及びチタン酸リチウム以外の物質を添加してもよい。
The amount of lithium titanate added is not particularly limited as long as the amount of increase in the negative electrode potential at the end of discharge of the target lithium secondary battery can be moderated. The content of lithium titanate with respect to the total amount of the negative electrode active material is generally 1 to 20% by mass, preferably about 3 to 15% by mass, and particularly preferably about 5 to 10% by mass. On the other hand, the content of the carbon material with respect to the total amount of the negative electrode active material is suitably about 80 to 99% by mass, preferably about 85 to 97% by mass, and particularly preferably about 90 to 95% by mass.
As long as the negative electrode potential is not increased excessively at the end of discharge, a substance other than the carbon material and lithium titanate may be added as the negative electrode active material.
リチウム二次電池の負極は、上述した本発明に係る負極活物質を使用して構築すればよく、そのために用いられる負極活物質以外の材料、或いは構築方法に特に制限はない。
典型的には、負極活物質と、結着材と、必要に応じて適宜用いられる導電材とを適当な溶媒に混合・分散させることによってペースト（スラリー）状の負極活物質層形成用組成物（以下「負極用合材」という。）を調製する。使用する負極活物質（炭素材料及びチタン酸リチウムを含む）、結着材及び導電材は、いずれも粉末状であることが好ましい。
溶媒（分散媒）としては 水系溶媒（典型的には水）または非水系溶媒（有機溶剤）を使用することができる。非水系溶媒としては、例えば、Ｎ−メチル−２−ピロリドン（ＮＭＰ）、メチルエチルケトン、トルエン等が挙げられる。ＮＭＰの使用が好ましい。
導電材としては、カーボンブラック（アセチレンブラック等）のような炭素（カーボン）粉末或いはニッケル粉末等の導電性金属粉末等を用いることができる。なお、ここで開示される負極活物質は炭素材料を主体に構成されるため、導電材の添加は必須ではない。
The negative electrode of the lithium secondary battery may be constructed using the above-described negative electrode active material according to the present invention, and there are no particular limitations on the materials or construction methods other than the negative electrode active material used for that purpose.
Typically, a composition for forming a negative electrode active material layer in the form of a paste (slurry) is prepared by mixing and dispersing a negative electrode active material, a binder, and a conductive material used as necessary in an appropriate solvent. (Hereinafter referred to as “a negative electrode composite”). It is preferable that the negative electrode active material (including the carbon material and lithium titanate), the binder, and the conductive material to be used are in powder form.
As the solvent (dispersion medium), an aqueous solvent (typically water) or a non-aqueous solvent (organic solvent) can be used. Examples of the non-aqueous solvent include N-methyl-2-pyrrolidone (NMP), methyl ethyl ketone, toluene and the like. The use of NMP is preferred.
As the conductive material, carbon powder such as carbon black (acetylene black or the like), conductive metal powder such as nickel powder, or the like can be used. In addition, since the negative electrode active material disclosed here is mainly composed of a carbon material, the addition of a conductive material is not essential.
結着材としては、非水系溶媒を使用する場合には、有機溶剤に可溶性であるポリマーを好ましく用いることができる。好適例として、ポリフッ化ビニリデン（ＰＶＤＦ）、ポリ塩化ビニリデン（ＰＶＤＣ）、ポリエチレンオキサイド（ＰＥＯ）、ポリプロピレンオキサイド（ＰＰＯ）、ポリエチレンオキサイド−プロピレンオキサイド共重合体（ＰＥＯ−ＰＰＯ）等が挙げられる。ＰＶＤＦ、ＰＶＤＣ等が好ましい。或いは、水系溶媒を使用する場合には 水に溶解する親水性ポリマー及び／又は水に分散するポリマーを好ましく用いることができる。かかる親水性ポリマーの好適例として、カルボキシメチルセルロース（ＣＭＣ）、メチルセルロース（ＭＣ）、酢酸フタル酸セルロース（ＣＡＰ）、ヒドロキシプロピルメチルセルロース（ＨＰＭＣ）、ヒドロキシプロピルメチルセルロースフタレート（ＨＰＭＣＰ）等、種々のセルロース誘導体が挙げられる。ＣＭＣの使用が好ましい。また、好適な水分散ポリマーとしては、ポリテトラフルオロエチレン（ＰＴＦＥ）、テトラフルオロエチレン−パーフルオロアルキルビニルエーテル共重含体（ＰＦＡ）、テトラフルオロエチレン−ヘキサフルオロプロピレン共重合体（ＦＥＰ）、エチレン−テトラフルオロエチレン共重合体（ＥＴＦＥ）等のフッ素系樹脂、酢酸ビニル共重合体、スチレンブタジエンブロック共重合体（ＳＢＲ）、アクリル酸変性ＳＢＲ樹脂（ＳＢＲ系ラテックス）、アラビアゴム等のゴム類が挙げられる。ＰＴＦＥ等のフッ素系樹脂が特に好ましい。 As the binder, when a non-aqueous solvent is used, a polymer that is soluble in an organic solvent can be preferably used. Preferable examples include polyvinylidene fluoride (PVDF), polyvinylidene chloride (PVDC), polyethylene oxide (PEO), polypropylene oxide (PPO), polyethylene oxide-propylene oxide copolymer (PEO-PPO), and the like. PVDF, PVDC and the like are preferable. Alternatively, when an aqueous solvent is used, a hydrophilic polymer that dissolves in water and / or a polymer that disperses in water can be preferably used. Preferable examples of such hydrophilic polymer include various cellulose derivatives such as carboxymethyl cellulose (CMC), methyl cellulose (MC), cellulose acetate phthalate (CAP), hydroxypropyl methylcellulose (HPMC), hydroxypropyl methylcellulose phthalate (HPMCP) and the like. It is done. The use of CMC is preferred. Suitable water-dispersed polymers include polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), ethylene- Fluorine resins such as tetrafluoroethylene copolymer (ETFE), vinyl acetate copolymer, styrene butadiene block copolymer (SBR), acrylic acid-modified SBR resin (SBR latex), rubbers such as gum arabic It is done. A fluorine resin such as PTFE is particularly preferable.
而して上述したような材料を適宜混和して得られた負極用合材を適当な集電体の表面に適当な塗布装置を用いて塗布することによって、負極活物質層を備えた負極を構築することができる。集電体の形状は、電池の形状に応じて異なり得るため特に制限はなく、棒状、板状、シート状若しくは箔状等の種々の形態であり得る。例えば銅箔、ニッケル箔等の金属箔の表面に負極用合材を塗布することによって、シート状負極を構築することができる。 Thus, a negative electrode having a negative electrode active material layer is obtained by applying a negative electrode mixture obtained by appropriately mixing the materials as described above to the surface of an appropriate current collector using an appropriate application device. Can be built. The shape of the current collector can be different depending on the shape of the battery, and is not particularly limited. For example, a sheet-like negative electrode can be constructed by applying a negative electrode mixture on the surface of a metal foil such as copper foil or nickel foil.
リチウム二次電池の正極は、従来使用されている正極活物質を適宜選択・使用して構築すればよく、使用する材料、或いは構築方法に特に制限はない。
負極の場合と同様、典型的には、正極活物質と、結着材と、導電材とを適当な溶媒に混合・分散させることによってペースト（スラリー）状の正極活物質層形成用組成物（以下「正極用合材」という。）を調製する。使用する正極活物質、結着材及び導電材は、いずれも粉末状であることが好ましい。
例えば、正極活物質としては、一般的なリチウム二次電池に用いられる層状構造の酸化物系正極活物質、或いはスピネル構造の酸化物系正極活物質等を好ましく用いることができる。種々のリチウム遷移金属複合酸化物（リチウム含有遷移金属酸化物ともいう。）の使用が好ましい。例えば、リチウムコバルト系複合酸化物（典型的にはＬｉＣｏＯ２）、リチウムニッケル系複合酸化物（典型的にはＬｉＮｉＯ２）、リチウムマンガン系複合酸化物（ＬｉＭｎ２Ｏ４）、等を主成分とする正極活物質を用いることができる。遷移金属元素が２種以上含まれる複合酸化物（例えば一般式：ＬｉＮｉｘＣｏ１−ｘＯ２で示される複合酸化物、ここでｘは０＜ｘ＜１を満足する正の実数）であってもよい。ＬｉＮｉＯ２の使用が特に好ましい。導電材としては、カーボンブラック（アセチレンブラック等）のような炭素（カーボン）粉末或いはニッケル粉末等の導電性金属粉末等を用いることができる。
溶媒（分散媒）としては 上述した負極用合材と同様の有機溶剤（非水系溶媒）或いは水系溶媒（典型的には水）を用いることができる。また、溶媒の性質（水系又は非水系）に応じて適当な結着材を採用するとよい。非水系溶媒を使用する場合には有機溶剤に可溶性であるポリマーを好ましく用いることができる。好適例は、負極用合材と同様である。或いは、水系溶媒を使用する場合には 水に溶解する親水性ポリマー及び／又は水に分散するポリマーの使用が好ましい。好適例は、負極用合材と同様である。
The positive electrode of the lithium secondary battery may be constructed by appropriately selecting and using a conventionally used positive electrode active material, and the material used or the construction method is not particularly limited.
As in the case of the negative electrode, a composition for forming a positive electrode active material layer in the form of a paste (slurry) is typically obtained by mixing and dispersing a positive electrode active material, a binder, and a conductive material in an appropriate solvent ( Hereinafter, it is referred to as “a positive electrode composite”). The positive electrode active material, the binder, and the conductive material to be used are preferably in the form of powder.
For example, as the positive electrode active material, an oxide-based positive electrode active material having a layered structure used for a general lithium secondary battery, an oxide-based positive electrode active material having a spinel structure, or the like can be preferably used. It is preferable to use various lithium transition metal composite oxides (also referred to as lithium-containing transition metal oxides). For example, a lithium cobalt complex oxide (typically LiCoO 2 ), a lithium nickel complex oxide (typically LiNiO 2 ), a lithium manganese complex oxide (LiMn 2 O 4 ), etc. A positive electrode active material can be used. A composite oxide containing two or more transition metal elements (for example, a composite oxide represented by the general formula: LiNi x Co 1-x O 2 , where x is a positive real number satisfying 0 <x <1). May be. The use of LiNiO 2 is particularly preferred. As the conductive material, carbon powder such as carbon black (acetylene black or the like), conductive metal powder such as nickel powder, or the like can be used.
As the solvent (dispersion medium), the same organic solvent (non-aqueous solvent) or aqueous solvent (typically water) as the above-described negative electrode mixture can be used. In addition, an appropriate binder may be employed depending on the nature of the solvent (aqueous or non-aqueous). When a non-aqueous solvent is used, a polymer that is soluble in an organic solvent can be preferably used. A suitable example is the same as that of the negative electrode mixture. Alternatively, when an aqueous solvent is used, it is preferable to use a hydrophilic polymer that dissolves in water and / or a polymer that disperses in water. A suitable example is the same as that of the negative electrode mixture.
而して上述したような材料を適宜混和して得られた正極用合材を適当な集電体の表面に適当な塗布装置を用いて塗布することによって、正極活物質層を備えた正極を構築することができる。導電性の良好な金属から成る導電性部材が正極集電体として好ましい。例えばアルミニウム製のものが好ましい。集電体の形状は、電池の形状に応じて異なり得るため特に制限はなく、棒状、板状、シート状若しくは箔状等の種々の形態であり得る。例えばアルミニウム箔等の金属箔の表面に正極用合材を塗布することによって、シート状正極を構築することができる。 Thus, a positive electrode having a positive electrode active material layer can be obtained by applying a positive electrode mixture obtained by appropriately mixing the materials described above to the surface of an appropriate current collector using an appropriate application device. Can be built. A conductive member made of a metal with good conductivity is preferred as the positive electrode current collector. For example, those made of aluminum are preferable. The shape of the current collector can be different depending on the shape of the battery, and is not particularly limited. For example, a sheet-like positive electrode can be constructed by applying a positive electrode mixture on the surface of a metal foil such as an aluminum foil.
ここで開示されるリチウム二次電池に用いられる非水電解液は、γ−ブチロラクトン（Ｃ４Ｈ６Ｏ２：以下「γ−ＢＬ」と略称する。）、γ−バレルラクトン（Ｃ５Ｈ８Ｏ２）、δ−バレルラクトン（Ｃ５Ｈ８Ｏ２）等の融点０℃以下のラクトンを少なくとも一種類含むことで特徴付けられる非水電解液（有機電解液）である。好ましくはγ−ＢＬを含む。典型的には、高出力化のための好適なイオン伝導性を確保するという観点から、ラクトン以外の好ましくは高誘電率及び／又は低粘性である非プロトン性溶媒を配合する。リチウム二次電池の電解液を構成する溶媒として使用され得る従来公知の一種又は二種以上のエステル系、エーテル系その他の溶媒を使用することができる。例えば、環状カーボネート類、鎖状カーボネート類、エステル類、環状エーテル類、鎖状エーテル類、ニトリル類、スルホン類等の非プロトン性の溶媒を用いることができる。具体例として、エチレンカーボネート（ＥＣ）、プロピレンカーボネート（ＰＣ）、ブチレンカーボネート、ジエチルカーボネート、ジメチルカーボネート、エチルメチルカーボネート（ＥＭＣ）、１，２−ジメトキシエタン、１，２−ジエトキシエタン、テトラヒドロフラン、２−メチルテトラヒドロフラン、ジオキサン、１，３−ジオキソラン、ジエチレングリコールジメチルエーテル、エチレングリコールジメチルエーテル、アセトニトリル、プロピオニトリル、ニトロメタン、Ｎ，Ｎ−ジメチルホルムアミド、ジメチルスルホキシド、スルホラン等が挙げられる。エチレンカーボネート（ＥＣ）、プロピレンカーボネート（ＰＣ）、ブチレンカーボネート等の環状カーボネートが好適である。 Non-aqueous electrolytes used in the lithium secondary battery disclosed herein are γ-butyrolactone (C 4 H 6 O 2 : hereinafter abbreviated as “γ-BL”), γ-barrel lactone (C 5 H 8 ). It is a nonaqueous electrolytic solution (organic electrolytic solution) characterized by containing at least one lactone having a melting point of 0 ° C. or lower, such as O 2 ) and δ-barrel lactone (C 5 H 8 O 2 ). Preferably γ-BL is included. Typically, from the viewpoint of ensuring suitable ionic conductivity for high output, an aprotic solvent preferably having a high dielectric constant and / or low viscosity other than a lactone is blended. One or more conventionally known ester-based, ether-based and other solvents that can be used as a solvent constituting the electrolyte solution of the lithium secondary battery can be used. For example, aprotic solvents such as cyclic carbonates, chain carbonates, esters, cyclic ethers, chain ethers, nitriles, and sulfones can be used. Specific examples include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate (EMC), 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 2 -Methyltetrahydrofuran, dioxane, 1,3-dioxolane, diethylene glycol dimethyl ether, ethylene glycol dimethyl ether, acetonitrile, propionitrile, nitromethane, N, N-dimethylformamide, dimethyl sulfoxide, sulfolane and the like. Cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC) and butylene carbonate are preferred.
ラクトン含有非水電解液を調製するにあたり、ラクトンと他の非プロトン性溶媒との配合比は特に限定されず、使用する溶媒の種類に応じて電池の低温特性と高出力特性とを勘案して適当に設定するとよい。例えば、γ−ＢＬ等のラクトンとＥＣ等の環状カーボネートとを配合する場合、非水電解液中のラクトン含有率が５５〜８５体積％であることが好ましく、６０〜８０体積％であることが特に好ましい。 In preparing the lactone-containing non-aqueous electrolyte, the mixing ratio of the lactone and the other aprotic solvent is not particularly limited, considering the low temperature characteristics and high output characteristics of the battery depending on the type of solvent used. Set it appropriately. For example, when a lactone such as γ-BL and a cyclic carbonate such as EC are blended, the lactone content in the non-aqueous electrolyte is preferably 55 to 85% by volume, and preferably 60 to 80% by volume. Particularly preferred.
非水電解液の支持塩としては、従来公知の種々のリチウム塩を使用することができる。例えば、ＬｉＰＦ６、ＬｉＢＦ４、ＬｉＣｌＯ４、ＬｉＡｓＦ６、ＬｉＣＦ３ＳＯ３、ＬｉＣ４Ｆ９ＳＯ３、ＬｉＮ（ＣＦ３ＳＯ２）２、ＬｉＣ（ＣＦ３ＳＯ２）３、ＬｉＩ等から選択される一種または二種以上のリチウム化合物（リチウム塩）を用いることができる。特にＬｉＰＦ６及び／又はＬｉＢＦ４の使用が好ましい。なお、非水電解液における支持塩の濃度は、従来のリチウム二次電池で使用される電解液と同様でよく、特に制限はない。適当なリチウム化合物を０．１〜５ｍｏｌ／Ｌ（好ましくは０．２〜３ｍｏｌ／Ｌ、より好ましくは０．５〜２ｍｏｌ／Ｌ）程度の濃度で含有する電解液（初期電解液）を使用することができる。 Various known lithium salts can be used as the supporting salt for the non-aqueous electrolyte. For example, selected from LiPF 6, LiBF 4, LiClO 4 , LiAsF 6, LiCF 3 SO 3, LiC 4 F 9 SO 3, LiN (CF 3 SO 2) 2, LiC (CF 3 SO 2) 3, LiI , etc. One or more lithium compounds (lithium salts) can be used. In particular, the use of LiPF 6 and / or LiBF 4 is preferred. In addition, the density | concentration of the support salt in a nonaqueous electrolyte solution may be the same as that of the electrolyte solution used with the conventional lithium secondary battery, and there is no restriction | limiting in particular. An electrolytic solution (initial electrolytic solution) containing an appropriate lithium compound at a concentration of about 0.1 to 5 mol / L (preferably 0.2 to 3 mol / L, more preferably 0.5 to 2 mol / L) is used. be able to.
電池を製造するにあたって使用されるセパレータとしては、従来公知のものでよく特に限定はない。織布、不織布、合成樹脂製の多孔質膜等を用いることができる。特に合成樹脂製多孔質膜としては、ポリエチレン、ポリプロピレン等のポリオレフィン系多孔質膜が好ましく使用される。 The separator used in manufacturing the battery may be a conventionally known separator and is not particularly limited. A woven fabric, a nonwoven fabric, a porous film made of a synthetic resin, or the like can be used. In particular, as the synthetic resin porous membrane, a polyolefin-based porous membrane such as polyethylene and polypropylene is preferably used.
以上に説明したような材料を用いて、従来同様のプロセスによって種々の形状・用途（容量）のリチウム二次電池を製造することができる。
即ち、ここで開示されるリチウム二次電池は、リチウムイオンの吸蔵及び放出が可能な炭素材料とチタン酸リチウムとを含む組成物（負極活物質）を負極に有し、γ−ブチロラクトン等の融点０℃以下のラクトンを少なくとも一種類含む非水電解液（即ちラクトン含有非水電解液）を使用することによって製造・提供され得るリチウム二次電池（リチウムイオン二次電池）であり、他の構成要素、或いは電池自体の構造や形状（外形）等に特に制限はない。本発明のリチウム二次電池は、ここで言及されるいずれかの負極活物質と非水電解液を使用する他は、従来の構成要素（正極活物質、電極端子、セパレータ、ラミネートフィルムその他のケーシング部材、等）を適宜組み合わせて使用し、従来のリチウム二次電池と同様の製法に基づいて所望する形状（例えばコイン型、円筒型、角型）に製造することができる。
Using the materials as described above, lithium secondary batteries of various shapes and applications (capacities) can be manufactured by the same process as before.
That is, the lithium secondary battery disclosed herein has a composition (negative electrode active material) containing a carbon material capable of occluding and releasing lithium ions and lithium titanate at the negative electrode, and has a melting point such as γ-butyrolactone. A lithium secondary battery (lithium ion secondary battery) that can be manufactured and provided by using a non-aqueous electrolyte solution containing at least one lactone at 0 ° C. or lower (that is, a lactone-containing non-aqueous electrolyte solution), and other configurations There are no particular restrictions on the structure or shape (outer shape) of the element or the battery itself. The lithium secondary battery of the present invention uses conventional negative electrode active materials, electrode terminals, separators, laminate films and other casings, except that any of the negative electrode active materials and non-aqueous electrolytes mentioned here are used. And a desired shape (for example, a coin shape, a cylindrical shape, and a square shape) based on a manufacturing method similar to that of a conventional lithium secondary battery.
以下、本発明を実施例に基づき詳細に説明する。なお、本発明は下記実施例によりなんら限定されるものではなく、例えば電解質のリチウム塩、正極材料、セパレータ等を変更することも可能である。 Hereinafter, the present invention will be described in detail based on examples. In addition, this invention is not limited at all by the following Example, For example, lithium salt of electrolyte, positive electrode material, a separator, etc. can also be changed.
＜実施例１：リチウム二次電池の製造（１）＞
以下のようにして円筒形標準タイプである１８６５０型のリチウム二次電池を製造した。
黒鉛粉末とチタン酸リチウムの粉末とを質量比９５：５の割合で混合して本実施例に係る負極活物質を調製した。得られた負極活物質と結着材であるＳＢＲ及びＣＭＣをイオン交換水と混合して本実施例に係るスラリー状の負極用合材を調製した。この負極用合材に含まれる各材料（水以外）の凡その質量比は、負極活物質が９８質量％、ＳＢＲが１質量％、ＣＭＣが１質量％である。
この負極用合材（スラリー）を、負極集電体としての厚み約１５μｍの長尺状銅箔の両面に塗布（付着）して乾燥させ、銅箔集電体両面に厚み１２０μｍの負極活物質層を形成した。次いで全体の厚みが８５μｍとなるようにプレスした。このようにして負極シートを作製した。
<Example 1: Production of lithium secondary battery (1)>
A cylindrical standard type 18650 type lithium secondary battery was manufactured as follows.
A negative electrode active material according to this example was prepared by mixing graphite powder and lithium titanate powder at a mass ratio of 95: 5. The obtained negative electrode active material and the binder SBR and CMC were mixed with ion-exchanged water to prepare a slurry-like negative electrode mixture according to this example. The approximate mass ratio of each material (other than water) contained in this negative electrode composite is 98% by mass for the negative electrode active material, 1% by mass for SBR, and 1% by mass for CMC.
This negative electrode mixture (slurry) was applied (attached) to both sides of a long copper foil having a thickness of about 15 μm as a negative electrode current collector and dried, and a negative electrode active material having a thickness of 120 μm on both sides of the copper foil current collector. A layer was formed. Subsequently, it pressed so that the whole thickness might be set to 85 micrometers. In this way, a negative electrode sheet was produced.
他方、正極活物質であるニッケル酸リチウム（ＬｉＮｉＯ２）粉末、導電材であるアセチレンブラック粉末、並びに、結着材であるＰＴＦＥ及びＣＭＣをイオン交換水と混合して本実施例に係るスラリー状の正極用合材を調製した。この正極用合材に含まれる各材料（水以外）の凡その質量比は、ニッケル酸リチウムが９０質量％、アセチレンブラックが７質量％、ＰＴＦＥが２質量％、ＣＭＣが１質量％である。
この正極用合材（スラリー）を、正極集電体としての厚み約１５μｍの長尺状アルミニウム箔の両面に塗布（付着）して乾燥させ、アルミニウム箔集電体両面に厚み１２０μｍの正極活物質層を形成した。次いで全体の厚みが８５μｍとなるようにプレスした。このようにして正極シートを作製した。
On the other hand, lithium nickelate (LiNiO 2 ) powder as a positive electrode active material, acetylene black powder as a conductive material, and PTFE and CMC as binders are mixed with ion-exchanged water to form a slurry according to this example. A positive electrode mixture was prepared. The approximate mass ratio of each material (other than water) contained in the positive electrode composite is 90% by mass of lithium nickelate, 7% by mass of acetylene black, 2% by mass of PTFE, and 1% by mass of CMC.
This positive electrode mixture (slurry) is applied (attached) to both sides of a long aluminum foil having a thickness of about 15 μm as a positive electrode current collector and dried, and a positive electrode active material having a thickness of 120 μm on both sides of the aluminum foil current collector. A layer was formed. Subsequently, it pressed so that the whole thickness might be set to 85 micrometers. In this way, a positive electrode sheet was produced.
エチレンカーボネート（ＥＣ）とγ−ブチロラクトン（γ−ＢＬ）とを体積比３０：７０の割合で混合し、この混合溶媒に濃度が１．５ｍｏｌ／ＬとなるようにＬｉＢＦ４を溶解し、本実施例に係る非水電解液を調製した。
そして、上記作製した正極シート及び負極シートにそれぞれ集電タブを付けた後、これらシートを２枚のセパレータ（ここでは多孔質ポリプロピレンシートを用いた。）とともに積層し、この積層シートを捲回して捲回型電極構造体を作製した。この電極構造体を所定の電池容器（ケーシング）に収容し、集電タブとケーシングを溶接した。次いで、ケーシング内に上記ラクトン含有非水電解液を注入し、該ケーシング内を減圧することで該ケーシング内に配置されている上記捲回型電極構造体に非水電解液を含浸させた。以上により、直径１８ｍｍ、高さ６５ｍｍ（即ち１８６５０型）の円筒型リチウム二次電池を製造した。
Ethylene carbonate (EC) and γ-butyrolactone (γ-BL) were mixed at a volume ratio of 30:70, and LiBF 4 was dissolved in this mixed solvent to a concentration of 1.5 mol / L. A non-aqueous electrolyte solution according to an example was prepared.
And after attaching a current collection tab to the produced positive electrode sheet and negative electrode sheet, these sheets were laminated together with two separators (here, a porous polypropylene sheet was used), and this laminated sheet was wound. A wound electrode structure was produced. The electrode structure was accommodated in a predetermined battery container (casing), and the current collecting tab and the casing were welded. Next, the lactone-containing nonaqueous electrolytic solution was poured into the casing, and the inside of the casing was decompressed to impregnate the wound electrode structure disposed in the casing with the nonaqueous electrolytic solution. Thus, a cylindrical lithium secondary battery having a diameter of 18 mm and a height of 65 mm (that is, 18650 type) was manufactured.
＜実施例２：リチウム二次電池の製造（２）＞
黒鉛粉末とチタン酸リチウム粉末との質量比が９０：１０である負極活物質を調製・使用したことを除いて実施例１と同様の材料・プロセスによって、同形状のリチウム二次電池を製造した。
<Example 2: Production of lithium secondary battery (2)>
A lithium secondary battery having the same shape was manufactured by the same material and process as in Example 1 except that a negative electrode active material having a mass ratio of graphite powder to lithium titanate powder of 90:10 was prepared and used. .
＜実施例３：リチウム二次電池の製造（３）＞
黒鉛粉末とチタン酸リチウム粉末との質量比が８０：２０である負極活物質を調製・使用したことを除いて実施例１と同様の材料・プロセスによって、同形状のリチウム二次電池を製造した。
<Example 3: Production of lithium secondary battery (3)>
A lithium secondary battery having the same shape was manufactured by the same material and process as in Example 1 except that a negative electrode active material having a mass ratio of graphite powder to lithium titanate powder of 80:20 was prepared and used. .
＜実施例４：リチウム二次電池の製造（４）＞
黒鉛粉末とチタン酸リチウム粉末との質量比が９９：１である負極活物質を調製・使用したことを除いて実施例１と同様の材料・プロセスによって、同形状のリチウム二次電池を製造した。
<Example 4: Production of lithium secondary battery (4)>
A lithium secondary battery having the same shape was manufactured by the same material and process as in Example 1 except that a negative electrode active material having a mass ratio of graphite powder to lithium titanate powder of 99: 1 was prepared and used. .
＜実施例５：リチウム二次電池の製造（５）＞
ＥＣとγ−ＢＬとの体積比が４０：６０である混合溶媒を用いて調製した非水電解液（リチウム塩の種類及び濃度に変更はない。）を使用したことを除いて実施例１と同様の材料・プロセスによって、同形状のリチウム二次電池を製造した。
<Example 5: Production of lithium secondary battery (5)>
Example 1 except that a non-aqueous electrolyte prepared using a mixed solvent having a volume ratio of EC to γ-BL of 40:60 (the type and concentration of the lithium salt is not changed) was used. A lithium secondary battery having the same shape was manufactured by the same material and process.
＜実施例６：リチウム二次電池の製造（６）＞
ＥＣとγ−ＢＬとの体積比が２０：８０である混合溶媒を用いて調製した非水電解液（リチウム塩の種類及び濃度に変更はない。）を使用したことを除いて実施例１と同様の材料・プロセスによって、同形状のリチウム二次電池を製造した。
<Example 6: Production of lithium secondary battery (6)>
Example 1 except that a non-aqueous electrolyte prepared using a mixed solvent in which the volume ratio of EC to γ-BL is 20:80 (the type and concentration of the lithium salt are not changed) was used. A lithium secondary battery having the same shape was manufactured by the same material and process.
＜実施例７：リチウム二次電池の製造（７）＞
ＥＣとγ−ＢＬとの体積比が５０：５０である混合溶媒を用いて調製した非水電解液（リチウム塩の種類及び濃度に変更はない。）を使用したことを除いて実施例１と同様の材料・プロセスによって、同形状のリチウム二次電池を製造した。
<Example 7: Production of lithium secondary battery (7)>
Example 1 except that a non-aqueous electrolyte prepared using a mixed solvent having a volume ratio of EC to γ-BL of 50:50 (the type and concentration of the lithium salt is not changed) is used. A lithium secondary battery having the same shape was manufactured by the same material and process.
＜実施例８：リチウム二次電池の製造（８）＞
ＥＣとγ−ＢＬとの体積比が１０：９０である混合溶媒を用いて調製した非水電解液（リチウム塩の種類及び濃度に変更はない。）を使用したことを除いて実施例１と同様の材料・プロセスによって、同形状のリチウム二次電池を製造した。
<Example 8: Production of lithium secondary battery (8)>
Example 1 except that a non-aqueous electrolyte prepared using a mixed solvent having a volume ratio of EC and γ-BL of 10:90 (the type and concentration of the lithium salt is not changed) was used. A lithium secondary battery having the same shape was manufactured by the same material and process.
＜比較例１：リチウム二次電池の製造（９）＞
負極活物質として黒鉛粉末のみ（即ちチタン酸リチウムを使用しない。）を使用し、且つ、非水電解液としてＥＣとエチルメチルカーボネート（ＥＭＣ）との体積比が３０：７０であって支持塩としてＬｉＢＦ４に代えてＬｉＰＦ６を採用すると共にその濃度が１．０ｍｏｌ／Ｌであるもの（即ちラクトン類を含有していない非水電解液）を調製・使用したことを除いて実施例１と同様の材料・プロセスによって、同形状のリチウム二次電池を製造した。
<Comparative Example 1: Production of lithium secondary battery (9)>
Only graphite powder (that is, lithium titanate is not used) is used as the negative electrode active material, and the volume ratio of EC and ethyl methyl carbonate (EMC) is 30:70 as the non-aqueous electrolyte, and as the supporting salt. The same as Example 1 except that LiPF 6 was used instead of LiBF 4 and the concentration thereof was 1.0 mol / L (that is, a non-aqueous electrolyte not containing lactones) was prepared and used. The lithium secondary battery of the same shape was manufactured by using the materials and processes.
＜比較例２：リチウム二次電池の製造（１０）＞
比較例１と同様に負極活物質として黒鉛粉末のみ（即ちチタン酸リチウムを使用しない。）を使用したことを除いて実施例１と同様の材料・プロセスによって、同形状のリチウム二次電池を製造した。
<Comparative Example 2: Production of lithium secondary battery (10)>
A lithium secondary battery having the same shape is manufactured by the same material and process as in Example 1 except that only graphite powder (that is, lithium titanate is not used) is used as the negative electrode active material as in Comparative Example 1. did.
＜比較例３：リチウム二次電池の製造（１１）＞
負極活物質として黒鉛粉末とハードカーボン（難黒鉛化炭素）粉末との質量比が９５：５である混合炭素材料（即ちチタン酸リチウムを使用しない。）を調製・使用したことを除いて実施例１と同様の材料・プロセスによって、同形状のリチウム二次電池を製造した。
以上、実施例１〜８並びに比較例１〜３においてそれぞれ使用した電解液用混合溶媒の組成（体積比）と負極活物質の組成（質量比）を表１にまとめて示す。
<Comparative Example 3: Production of Lithium Secondary Battery (11)>
Example except that a mixed carbon material (that is, lithium titanate is not used) having a mass ratio of graphite powder to hard carbon (non-graphitizable carbon) powder of 95: 5 was prepared and used as the negative electrode active material. A lithium secondary battery having the same shape was manufactured by the same material and process as in No. 1.
The composition (volume ratio) of the mixed solvent for electrolytic solution and the composition (mass ratio) of the negative electrode active material used in Examples 1 to 8 and Comparative Examples 1 to 3 are summarized in Table 1, respectively.
＜試験例１：２５℃初期出力の測定＞
各実施例及び比較例に係るリチウム二次電池の２５℃初期出力を以下のプロセスで測定した。
即ち、各実施例及び比較例で製造したリチウム二次電池の各々について、先ず、８００ｍＡの定電流で４．１Ｖに達するまで充電を行い、その後、８００ｍＡの定電流で３Ｖまで放電した。次いで、各電池を２５℃の恒温槽に入れて３時間放置した後、８００ｍＡの定電流で３．７Ｖまで充電した。その後、３Ｖを下限電圧として適宜電流を変化させ、１０秒間のパルス放電・充電を行った。こうして得られた電流電圧曲線に基づいて２５℃初期出力（Ｗ）を算出した。結果を表２に示す。
<Test Example 1: Measurement of initial output at 25 ° C.>
The initial output at 25 ° C. of the lithium secondary batteries according to the examples and comparative examples was measured by the following process.
That is, each of the lithium secondary batteries manufactured in each of the examples and comparative examples was first charged to reach 4.1 V at a constant current of 800 mA, and then discharged to 3 V at a constant current of 800 mA. Next, each battery was placed in a thermostat at 25 ° C. and left for 3 hours, and then charged to 3.7 V at a constant current of 800 mA. Thereafter, the current was appropriately changed with 3 V as the lower limit voltage, and pulse discharge / charge was performed for 10 seconds. Based on the current-voltage curve thus obtained, an initial output (W) at 25 ° C. was calculated. The results are shown in Table 2.
＜試験例２：５００サイクル容量維持率の測定＞
各実施例及び比較例に係るリチウム二次電池の５００サイクル容量維持率を以下のプロセスで測定した。
即ち、各実施例及び比較例で製造したリチウム二次電池の各々について、先ず、８００ｍＡの定電流で４．１Ｖに達するまで充電を行い、その後、８００ｍＡの定電流で３Ｖまで放電した。次いで、各電池を６０℃の恒温槽に入れて３時間放置した後、３Ｖから４．１Ｖの電圧範囲で１６００ｍＡの定電流で充放電を行った。これを１サイクルとし、計５００サイクル繰り返して充放電を実施した。そして、５００サイクル目の放電容量を１サイクル目の放電容量で割り１００をかけることで、５００サイクル容量維持率（％）を算出した。結果を表２に示す。
<Test Example 2: Measurement of 500 cycle capacity retention ratio>
The 500 cycle capacity retention rate of the lithium secondary batteries according to the examples and comparative examples was measured by the following process.
That is, each of the lithium secondary batteries manufactured in each of the examples and comparative examples was first charged to reach 4.1 V at a constant current of 800 mA, and then discharged to 3 V at a constant current of 800 mA. Next, each battery was placed in a thermostat at 60 ° C. and left for 3 hours, and then charged and discharged at a constant current of 1600 mA in a voltage range of 3V to 4.1V. This was made into 1 cycle, and charging / discharging was implemented by repeating a total of 500 cycles. The 500 cycle capacity retention rate (%) was calculated by dividing the discharge capacity at the 500th cycle by the discharge capacity at the first cycle and multiplying by 100. The results are shown in Table 2.
＜試験例３：放電容量に対する負極電位（放電カーブ）の測定＞
実施例１、比較例２及び比較例３のリチウム二次電池について放電容量に対する負極電位の変化の度合い（即ち放電カーブ）を測定した。本試験では、実施例１、比較例２及び比較例３の負極を作用極、電解液を使用し、リチウム金属を対極と参照極として単極セルを作製した。参照極基準で０Ｖ〜１．５Ｖの電位範囲で０．２Ｃの充電レートで定電流充放電を行い、負極質量別の容量（ｍＡｈ／ｇ）に対する負極電位（Ｖ）の推移を測定したものである。結果を図１に示す。図中の点線は実施例１に係る負極電位、実線は比較例２に係る負極電位、一点鎖線は比較例３に係る負極電位についての放電カーブを示している。
図示した放電カーブから明らかなように、比較例２に係る電池の負極電位は、放電末期に急激に上昇した。また、比較例３に係る電池の負極電位は、３２０ｍＡｈ／ｇ付近で一時的に上昇した後、放電末期に再び急激に上昇した。これら比較例に対して、実施例１に係る電池の負極電位は、３２０ｍＡｈ／ｇ付近から放電末期にかけて緩やかな上昇を示した。
<Test Example 3: Measurement of negative electrode potential (discharge curve) with respect to discharge capacity>
For the lithium secondary batteries of Example 1, Comparative Example 2, and Comparative Example 3, the degree of change in the negative electrode potential with respect to the discharge capacity (that is, the discharge curve) was measured. In this test, a negative electrode of Example 1, Comparative Example 2 and Comparative Example 3 was used as a working electrode and an electrolytic solution, and a single electrode cell was produced using lithium metal as a counter electrode and a reference electrode. A constant current charge / discharge is performed at a charge rate of 0.2 C in the potential range of 0 V to 1.5 V on the basis of the reference electrode, and the transition of the negative electrode potential (V) with respect to the capacity (mAh / g) by negative electrode mass is measured. is there. The results are shown in FIG. The dotted line in the figure indicates the discharge curve for the negative electrode potential according to Example 1, the solid line indicates the negative electrode potential according to Comparative Example 2, and the alternate long and short dash line indicates the discharge curve for the negative electrode potential according to Comparative Example 3.
As is apparent from the illustrated discharge curve, the negative electrode potential of the battery according to Comparative Example 2 rapidly increased at the end of discharge. Further, the negative electrode potential of the battery according to Comparative Example 3 temporarily increased around 320 mAh / g, and then rapidly increased again at the end of discharge. In contrast to these comparative examples, the negative electrode potential of the battery according to Example 1 showed a gradual increase from around 320 mAh / g to the end of discharge.
上記試験例１〜３の結果を示した表２及び図１から明らかなように、本発明によって提供されるリチウム二次電池はサイクル特性に優れ、且つ、高い出力を実現することができる。
また、具体的なデータは示していないが、ラクトン含有非水電解液を使用しているために低温特性にも優れている。
本発明で提供されるリチウム二次電池では、放電末期の負極電位の上昇が緩やかであるため、負極表面に形成されているＳＥＩ被膜の破壊が生じ難く、充放電を繰り返しても電解液の過剰な分解が抑制され、結果、サイクル特性が向上するものと推測される。
また、表２から明らかなように、ハードカーボンを添加した負極活物質を用いた比較例３に係る電池よりも、本発明に係るリチウム二次電池は、明らかにサイクル特性が向上している。更に実施例１、２、５及び６に係る電池においては、優れたサイクル特性を示すとともに１５Ｗ以上の高い２５℃初期出力が得られた。
As is clear from Table 2 showing the results of Test Examples 1 to 3 and FIG. 1, the lithium secondary battery provided by the present invention is excellent in cycle characteristics and can realize high output.
Moreover, although specific data are not shown, since the lactone containing non-aqueous electrolyte is used, it is excellent also in the low temperature characteristic.
In the lithium secondary battery provided by the present invention, the negative electrode potential rises slowly at the end of discharge, so that the SEI film formed on the negative electrode surface hardly breaks down, and an excessive amount of electrolyte remains even after repeated charge and discharge. Therefore, it is estimated that the cycle characteristics are improved.
Further, as apparent from Table 2, the cycle characteristics of the lithium secondary battery according to the present invention are clearly improved as compared with the battery according to Comparative Example 3 using the negative electrode active material added with hard carbon. Furthermore, the batteries according to Examples 1, 2, 5 and 6 exhibited excellent cycle characteristics and a high initial output of 25 ° C. of 15 W or more.
以上、本発明の具体例を詳細に説明したが、これらは例示にすぎず、特許請求の範囲を限定するものではない。特許請求の範囲に記載の技術には、以上に例示した具体例を様々に変形、変更したものが含まれる。
また、本明細書に説明した技術要素は、単独であるいは各種の組み合わせによって技術的有用性を発揮するものであり、出願時請求項記載の組み合わせに限定されるものではない。また、本明細書に例示した技術は複数目的を同時に達成するものであり、そのうちの一つの目的を達成すること自体で技術的有用性を持つものである。
Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.
Further, the technical elements described in the present specification exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology exemplified in the present specification achieves a plurality of objects at the same time, and has technical utility by achieving one of the objects.
Claims (4)
負極活物質として、リチウムイオンの吸蔵及び放出が可能な炭素材料とチタン酸リチウムとを含み、
負極活物質の総量に対する前記炭素材料の含有率が８０〜９９質量％であり、チタン酸リチウムの含有率が１〜２０質量％である、リチウム二次電池。 A lithium secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte containing at least one lactone having a melting point of 0 ° C. or lower,
As a negative electrode active material, including a carbon material capable of occluding and releasing lithium ions and lithium titanate,
The lithium secondary battery whose content rate of the said carbon material with respect to the total amount of a negative electrode active material is 80-99 mass%, and whose content rate of lithium titanate is 1-20 mass%.
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