JP2014067625A - Nonaqueous electrolytic secondary battery - Google Patents

Nonaqueous electrolytic secondary battery Download PDF

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JP2014067625A
JP2014067625A JP2012212841A JP2012212841A JP2014067625A JP 2014067625 A JP2014067625 A JP 2014067625A JP 2012212841 A JP2012212841 A JP 2012212841A JP 2012212841 A JP2012212841 A JP 2012212841A JP 2014067625 A JP2014067625 A JP 2014067625A
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graphite
secondary battery
negative electrode
electrolyte secondary
active material
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Akira Kinoshita
晃 木下
Takuya Shinomiya
拓也 四宮
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Sanyo Electric Co Ltd
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    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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    • Y02E60/10—Energy storage using batteries

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Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolytic secondary battery in which battery swelling and reduction in capacity-keeping rate are suppressed while the battery is charged and stored.SOLUTION: A nonaqueous electrolytic secondary battery of the invention comprises: a positive electrode having a positive electrode active material capable of absorbing and releasing lithium ions; a negative electrode having a negative electrode active material capable of absorbing and releasing lithium ions; a nonaqueous electrolyte; and a separator. The negative electrode active material includes at least two kinds of graphite which are coated with amorphous carbon differing from each other in coating amount. In the negative electrode active material, the coating amounts of the amorphous carbon coating the graphite are preferably 0.5 to less than 1 mass%, and 1 mass% or larger.

Description

本発明は、負極活物質として少なくとも２種類の、非晶質炭素で被覆された黒鉛を用いた非水電解質二次電池に関する。   The present invention relates to a non-aqueous electrolyte secondary battery using graphite coated with amorphous carbon as at least two types of negative electrode active materials.

従来、非水電解質二次電池の負極活物質としては、黒鉛、人造黒鉛等の黒鉛材料が多く用いられている。これは、黒鉛材料が、リチウム金属やリチウム合金に匹敵する充放電電位を有しながらも、デンドライトが成長することがないために安全性が高く、さらに初期効率に優れ、電位平坦性も良好であり、また、密度も高いという優れた性質を有しているためである。   Conventionally, graphite materials such as graphite and artificial graphite are often used as negative electrode active materials for non-aqueous electrolyte secondary batteries. This is because the graphite material has a charge / discharge potential comparable to that of lithium metal or lithium alloy, but the dendrite does not grow, so the safety is high, the initial efficiency is excellent, and the potential flatness is also good. This is because it has excellent properties such as high density.

しかしながら、負極活物質として特に黒鉛を用いると、初期の充電過程において電極表面で有機溶媒が還元分解され、ガスの発生によって電池の膨れが生じるとともに、副反応生成物の堆積等により負極インピーダンスが増大し、充放電効率の低下、充放電サイクル特性の劣化等を引き起すという問題点が存在していた。そこで、黒鉛材料の表面を非晶質炭素で被覆することにより、比表面積を下げて初期充電時の副反応を低減し、これにより初期の放電容量の低下を抑制することが行われていた。   However, especially when graphite is used as the negative electrode active material, the organic solvent is reduced and decomposed on the electrode surface during the initial charging process, and the battery is swollen due to the generation of gas, and the negative electrode impedance is increased due to deposition of side reaction products. However, there existed a problem of causing a decrease in charge / discharge efficiency, deterioration of charge / discharge cycle characteristics, and the like. Therefore, the surface of the graphite material is coated with amorphous carbon to reduce the specific surface area and reduce the side reaction during the initial charge, thereby suppressing the decrease in the initial discharge capacity.

たとえば、下記特許文献１には、非晶質炭素で表面被覆された黒鉛に対して非晶質黒鉛で表面被覆を行っていない黒鉛を特定範囲で混合させた負極材料を用いた非水電解液二次電池の発明が開示されている。また、下記特許文献２には、Ｘ線広角回折法による（００２）面の面間隔（ｄ００２）が０．３４ｎｍ（３．４Å）未満である黒鉛系粒子の表面を面間隔０．３４ｎｍ（３．４Å）以上の非晶質炭素層で被覆した二重構造黒鉛粒子と黒鉛化メソカーボンマイクロビーズとからなる混合物を負極活物質とした非水系二次電池の発明が開示されている。さらに、下記特許文献３には、負極活物質として、芯材となる第１の黒鉛材料の表面の一部又は全部をこの第１の黒鉛材料より結晶性の低い第２の炭素材料で被覆させた低結晶性炭素被覆黒鉛を用いた非水電解質二次電池の発明が開示されている。   For example, the following Patent Document 1 discloses a non-aqueous electrolyte solution using a negative electrode material in which graphite not surface-coated with amorphous graphite is mixed with graphite not surface-coated with amorphous carbon within a specific range. An invention of a secondary battery is disclosed. Further, in Patent Document 2 below, the surface of a graphite-based particle having a (002) plane spacing (d002) of less than 0.34 nm (3.4 mm) by an X-ray wide angle diffraction method is defined as a plane spacing of 0.34 nm (3 (4)) The invention of a non-aqueous secondary battery using a mixture of double-structured graphite particles coated with the above amorphous carbon layer and graphitized mesocarbon microbeads as a negative electrode active material is disclosed. Further, in Patent Document 3 below, as a negative electrode active material, a part or all of the surface of the first graphite material serving as a core material is coated with a second carbon material having lower crystallinity than the first graphite material. An invention of a non-aqueous electrolyte secondary battery using low-crystalline carbon-coated graphite is disclosed.

特開２００１−１８５１４７号公報JP 2001-185147 A 特開２００３−０３１２６２号公報JP 2003-031262 A 特開２００４−１３４２４５号公報JP 2004-134245 A

上記特許文献１に開示されている発明によれば、高容量と良好な室温及び低温での容量維持率を兼ね備えた非水電解質二次電池が得られるようになる。また、上記特許文献２に開示された発明によれば、高容量でサイクル寿命及び安全性に優れた非水系二次電池が得られるようになる。さらに、上記特許文献３に開示された発明によれば、充放電サイクル後における容量低下や高率放電特性等が低下するのが抑制された非水電解質二次電池が得られるようになる。   According to the invention disclosed in Patent Document 1, a non-aqueous electrolyte secondary battery having both high capacity and good capacity retention at room temperature and low temperature can be obtained. Moreover, according to the invention disclosed in Patent Document 2, a non-aqueous secondary battery having a high capacity and excellent cycle life and safety can be obtained. Furthermore, according to the invention disclosed in Patent Document 3, it is possible to obtain a nonaqueous electrolyte secondary battery in which a decrease in capacity, high-rate discharge characteristics, and the like after a charge / discharge cycle are suppressed.

しかしながら、発明者らの実験結果によると、黒鉛を被覆する非晶質炭素の被覆量の増加に伴って、充電保存時の電池の膨れは抑制されるが、充電保存後に電池容量の低下が生じることが見出された。   However, according to the results of experiments by the inventors, as the amount of amorphous carbon covering graphite is increased, the swelling of the battery during charge storage is suppressed, but the battery capacity is reduced after charge storage. It was found.

本発明は、上述のような従来技術の有する問題点を解決すべくなされたものであり、充電保存時の電池の膨れを抑制するとともに、電池の容量維持率の低下をも抑制した非水電解質二次電池を提供することを目的とする。   The present invention has been made to solve the above-described problems of the prior art, and suppresses the swelling of the battery during charge storage, and also suppresses the decrease in the capacity retention rate of the battery. An object is to provide a secondary battery.

上記課題を解決するために、本発明の非水電解質二次電池は、リチウムイオンを吸蔵・放出する正極活物質を有する正極と、リチウムイオンを吸蔵・放出する負極活物質を有する負極と、
非水電解質と、セパレータとを有し、前記負極活物質は、互いに異なる被覆量で非晶質炭素により被覆された少なくとも２種類の黒鉛を含有することを特徴とする。 In order to solve the above problems, a nonaqueous electrolyte secondary battery of the present invention includes a positive electrode having a positive electrode active material that absorbs and releases lithium ions, a negative electrode having a negative electrode active material that absorbs and releases lithium ions, and
It has a non-aqueous electrolyte and a separator, and the negative electrode active material contains at least two types of graphite coated with amorphous carbon at different coating amounts.

黒鉛を被覆する非晶質炭素の層は、充電保存時に正極と電解液との反応で発生する二酸化炭素（ＣＯ２）ガスを吸収するため、電池が膨れることが抑制される。一方、ＣＯ２ガスを吸収した非晶質炭素の層は、リチウムイオンの移動を阻害するため、充電保存時の容量維持率の低下につながる。これに対し、互いに異なる被覆量で非晶質炭素により被覆された少なくとも２種類の黒鉛を含有することで、ＣＯ２ガスの吸収とリチウムイオンの移動の確保とが両立される。このため、本発明の非水電解質二次電池によれば、充電保存時の電池の膨れを抑制することができるとともに、容量維持率の低下をも抑制することができるようになる。 Since the amorphous carbon layer covering the graphite absorbs carbon dioxide (CO 2 ) gas generated by the reaction between the positive electrode and the electrolyte during charge storage, the battery is prevented from being swollen. On the other hand, the amorphous carbon layer that has absorbed the CO 2 gas inhibits the movement of lithium ions, leading to a decrease in capacity retention rate during charge storage. On the other hand, by containing at least two types of graphite coated with amorphous carbon with different coating amounts, both absorption of CO 2 gas and securing of migration of lithium ions can be achieved. For this reason, according to the nonaqueous electrolyte secondary battery of the present invention, it is possible to suppress the swelling of the battery during charge storage and to suppress the decrease in the capacity maintenance rate.

なお、黒鉛に非晶質炭素を被覆する方法としては、黒鉛粒子と固体の非晶質炭素との間に圧縮剪断応力を加えて被覆するメカノフュージョン法や、スパッタリング法等により被覆する固相法や、非晶質炭素をトルエン等の溶剤に溶解させて黒鉛を浸漬したのち熱処理する液相法等を採用し得る。   As a method of coating amorphous carbon on graphite, a mechanofusion method in which a compression shear stress is applied between graphite particles and solid amorphous carbon, or a solid phase method in which coating is performed by a sputtering method or the like. Alternatively, a liquid phase method in which amorphous carbon is dissolved in a solvent such as toluene and graphite is immersed and then heat treated can be employed.

また、本発明に係る非水電解質二次電池においては、前記負極活物質は、前記黒鉛に対する非晶質炭素の被覆量が０．５質量％以上１質量％未満のもの及び１質量％以上のものを含有することが好ましい。かかる態様においては、前記負極活物質は、前記黒鉛に対する非晶質炭素の被覆量が１質量％以上２質量％以下のものを含有することがより好ましい。さらに、かかる態様においては、前記負極活物質は、前記非晶質炭素の被覆量がそれぞれ異なる２種の黒鉛からなり、両者の質量比が１０：９０〜９０：１０となるようにすることが好ましい。   Moreover, in the nonaqueous electrolyte secondary battery according to the present invention, the negative electrode active material has an amorphous carbon coating amount of 0.5% by mass or more to less than 1% by mass and 1% by mass or more of the graphite. It is preferable to contain a thing. In such an embodiment, the negative electrode active material more preferably contains an amorphous carbon covering amount of 1% by mass to 2% by mass with respect to the graphite. Furthermore, in this embodiment, the negative electrode active material is made of two types of graphite each having a different coating amount of the amorphous carbon, and the mass ratio between the two is 10:90 to 90:10. preferable.

この様な構成を備えていると、ＣＯ２ガスの吸収とリチウムイオンの移動の確保とがより効果的に両立され、電池の膨れの抑制と容量維持率の低下の抑制とをより効果的に両立することができるようになる。 With such a configuration, absorption of CO 2 gas and securing of migration of lithium ions are more effectively achieved, and more effective suppression of battery swelling and reduction of capacity retention rate It becomes possible to achieve both.

また、本発明に係る非水電解質二次電池においては、前記非晶質炭素はピッチであることが好ましい。非晶質炭素としては、活性炭のような固体のもの及びピッチのような液体となるものが周知である。しかしながら、ピッチは、安価で、容易に入手できる上、溶剤に容易に溶解するため、液相法によって容易に黒鉛粒子の表面を被覆することができる。そのため、非晶質炭素としてピッチを使用すると、上記効果を奏することができる非水電解質二次電池を安価にかつ容易に製造することができるようになる。   In the nonaqueous electrolyte secondary battery according to the present invention, the amorphous carbon is preferably a pitch. As the amorphous carbon, a solid carbon such as activated carbon and a liquid such as pitch are well known. However, since pitch is inexpensive and easily available, and easily dissolved in a solvent, the surface of graphite particles can be easily coated by a liquid phase method. Therefore, when pitch is used as amorphous carbon, a non-aqueous electrolyte secondary battery capable of producing the above effects can be manufactured at low cost and easily.

なお、本発明に係る非水電解質二次電池においては、正極活物質としてリチウムイオンを可逆的に吸蔵・放出することが可能な化合物であれば適宜選択して使用できる。これらのリチウム遷移金属酸化物としては、ＬｉＭＯ２（但し、ＭはＣｏ、Ｎｉ、Ｍｎの少なくとも１種である）で表されるリチウム遷移金属複合酸化物、すなわち、ＬｉＣｏＯ２、ＬｉＮｉＯ２、ＬｉＮｉｙＣｏ１−ｙＯ２（ｙ＝０．０１〜０．９９）、ＬｉＭｎＯ２、ＬｉＣｏｘＭｎｙＮｉｚＯ２（ｘ＋ｙ＋ｚ＝１）や、ＬｉＭｎ２Ｏ４又はＬｉＦｅＰＯ４などを一種単独もしくは複数種を混合して用いることができる。さらには、リチウム遷移金属複合酸化物にジルコニウムやマグネシウム、アルミニウム等の異種金属元素を添加したものも使用し得る。 In the non-aqueous electrolyte secondary battery according to the present invention, any compound that can reversibly occlude and release lithium ions as the positive electrode active material can be appropriately selected and used. Examples of these lithium transition metal oxides include lithium transition metal composite oxides represented by LiMO 2 (where M is at least one of Co, Ni, and Mn), that is, LiCoO 2 , LiNiO 2 , LiNi y. Co 1-y O 2 (y = 0.01 to 0.99), LiMnO 2 , LiCo x Mn y Ni z O 2 (x + y + z = 1), LiMn 2 O 4, LiFePO 4, etc. Can be mixed and used. Furthermore, a lithium transition metal composite oxide obtained by adding a different metal element such as zirconium, magnesium, or aluminum can be used.

また、本発明に係る非水電解質二次電池においては、電極体の形状に限定されることなく電池の膨れの抑制と容量維持率の低下の抑制を両立することができため、円筒形、偏平形ないし角形のいずれの形状の電極体も採用することができる。しかしながら、本発明に係る構成を偏平形ないし角形形状の電極体の場合に適用すると、電池の膨れの抑制効果がより顕著に現れる。   Further, in the non-aqueous electrolyte secondary battery according to the present invention, it is possible to achieve both suppression of battery swelling and reduction in capacity maintenance rate without being limited to the shape of the electrode body. An electrode body having a shape or a square shape may be employed. However, when the structure according to the present invention is applied to a flat or rectangular electrode body, the effect of suppressing the swelling of the battery appears more remarkably.

また、本発明の非水電解質二次電池において使用し得る非水溶媒としては、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（ＢＣ）などの環状炭酸エステル、フッ素化された環状炭酸エステル、γ−ブチロラクトン（ＢＬ）、γ−バレロラクトン（ＶＬ）などの環状カルボン酸エステル、ジメチルカーボネート（ＤＭＣ）、エチルメチルカーボネート（ＥＭＣ）、ジエチルカーボネート（ＤＥＣ）、メチルプロピルカーボネート（ＭＰＣ）、ジブチルカーボネート（ＤＢＣ）などの鎖状炭酸エステル、フッ素化された鎖状炭酸エステル、ピバリン酸メチル、ピバリン酸エチル、メチルイソブチレート、メチルプロピオネートなどの鎖状カルボン酸エステル、Ｎ、Ｎ'−ジメチルホルムアミド、Ｎ−メチルオキサゾリジノンなどのアミド化合物、スルホランなどの硫黄化合物、テトラフルオロ硼酸１−エチル−３−メチルイミダゾリウムなどの常温溶融塩などが例示できる。これらは２種以上混合して用いることが望ましい。これらの中では、特に誘電率が大きく、非水電解液のイオン伝導度が大きい環状炭酸エステル及び鎖状炭酸エステルが好ましい。   Nonaqueous solvents that can be used in the nonaqueous electrolyte secondary battery of the present invention include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC), and fluorinated cyclic carbonates. Esters, cyclic carboxylic acid esters such as γ-butyrolactone (BL) and γ-valerolactone (VL), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate (MPC), dibutyl Chain carbonates such as carbonate (DBC), fluorinated chain carbonates, chain carboxylates such as methyl pivalate, ethyl pivalate, methyl isobutyrate, methyl propionate, N, N′— Dimethylformamide, N-me Amide compounds such as oxazolidinone, sulfur compounds such as sulfolane, etc. ambient temperature molten salt such as tetrafluoroboric acid 1-ethyl-3-methylimidazolium can be exemplified. It is desirable to use a mixture of two or more of these. Among these, cyclic carbonates and chain carbonates having a particularly high dielectric constant and a high ionic conductivity of the nonaqueous electrolytic solution are preferable.

なお、本発明の非水電解質二次電池で使用する非水電解質中には、電極の安定化用化合物として、さらに、ビニレンカーボネート（ＶＣ）、ビニルエチレンカーボネート（ＶＥＣ）、無水コハク酸（ＳＵＣＡＨ）、無水マレイン酸（ＭＡＡＨ）、グリコール酸無水物、エチレンサルファイト（ＥＳ）、ジビニルスルホン（ＶＳ）、ビニルアセテート（ＶＡ）、ビニルピバレート（ＶＰ）、カテコールカーボネートなどを添加してもよい。これらの化合物は、２種以上を適宜に混合して用いることもできる。   In the non-aqueous electrolyte used in the non-aqueous electrolyte secondary battery of the present invention, vinylene carbonate (VC), vinyl ethylene carbonate (VEC), and succinic anhydride (SUCAH) are further used as compounds for stabilizing the electrode. , Maleic anhydride (MAAH), glycolic anhydride, ethylene sulfite (ES), divinyl sulfone (VS), vinyl acetate (VA), vinyl pivalate (VP), catechol carbonate and the like may be added. Two or more of these compounds can be appropriately mixed and used.

また、本発明の非水電解質二次電池で使用する非水溶媒中に溶解させる電解質塩としては、非水電解質二次電池において一般に電解質塩として用いられるリチウム塩を用いることができる。このようなリチウム塩としては、ＬｉＰＦ６、ＬｉＢＦ４、ＬｉＣＦ３ＳＯ３、ＬｉＮ（ＣＦ３ＳＯ２）２、ＬｉＮ（Ｃ２Ｆ５ＳＯ２）２、ＬｉＮ（ＣＦ３ＳＯ２）（Ｃ４Ｆ９ＳＯ２）、ＬｉＣ（ＣＦ３ＳＯ２）３、ＬｉＣ（Ｃ２Ｆ５ＳＯ２）３、ＬｉＡｓＦ６、ＬｉＣｌＯ４、Ｌｉ２Ｂ１０Ｃｌ１０、Ｌｉ２Ｂ１２Ｃｌ１２など及びそれらの混合物が例示される。これらの中でも、ＬｉＰＦ６（ヘキサフルオロリン酸リチウム）が特に好ましい。前記非水溶媒に対する電解質塩の溶解量は、０．８〜２．０ｍｏｌ／Ｌとするのが好ましい。 In addition, as the electrolyte salt dissolved in the non-aqueous solvent used in the non-aqueous electrolyte secondary battery of the present invention, a lithium salt generally used as an electrolyte salt in the non-aqueous electrolyte secondary battery can be used. Such lithium salts include LiPF 6 , LiBF 4 , LiCF 3 SO 3 , LiN (CF 3 SO 2 ) 2 , LiN (C 2 F 5 SO 2 ) 2 , LiN (CF 3 SO 2 ) (C 4 F 9 SO 2 ), LiC (CF 3 SO 2 ) 3 , LiC (C 2 F 5 SO 2 ) 3 , LiAsF 6 , LiClO 4 , Li 2 B 10 Cl 10 , Li 2 B 12 Cl 12 , and mixtures thereof Illustrated. Among these, LiPF 6 (lithium hexafluorophosphate) is particularly preferable. The amount of electrolyte salt dissolved in the non-aqueous solvent is preferably 0.8 to 2.0 mol / L.

以下、本発明を実施するための形態の詳細について説明する。ただし、以下に示す形態は本発明の技術思想を具体化するためのものであり、本発明は、特許請求の範囲に示した技術思想を逸脱することなく種々の変更を行ったものにも適用し得る。   Hereinafter, the detail of the form for implementing this invention is demonstrated. However, the embodiments shown below are for embodying the technical idea of the present invention, and the present invention is also applicable to those in which various modifications are made without departing from the technical idea shown in the claims. Can do.

［実施例１］
最初に、実施例１に係る非水電解質二次電池の具体的作製方法について説明する。
（負極極板の作製）
平均粒径１５μｍの天然黒鉛に、固相法を用いて０．５５質量％となるようにピッチを被覆させ、黒鉛Ａ１を調製した。次に、平均粒径１５μｍの天然黒鉛に、固相法を用いて１．２１質量％となるようにピッチを被覆させ、黒鉛Ｂ１を調製した。そして、黒鉛Ａ１と黒鉛Ｂ１とを質量比で５０：５０となるように混合し、実施例１の非水電解質二次電池用の負極活物質を調製した。 [Example 1]
First, a specific method for producing the nonaqueous electrolyte secondary battery according to Example 1 will be described.
(Preparation of negative electrode plate)
A natural graphite having an average particle size of 15 μm was coated with a pitch so as to be 0.55 mass% using a solid phase method to prepare graphite A1. Next, natural graphite having an average particle size of 15 μm was coated with a pitch so as to be 1.21% by mass using a solid phase method, thereby preparing graphite B1. And graphite A1 and graphite B1 were mixed so that it might be set to 50:50 by mass ratio, and the negative electrode active material for nonaqueous electrolyte secondary batteries of Example 1 was prepared.

上述のように作製した負極活物質と、増粘剤としてのカルボシキメチルセルロース（ＣＭＣ）と、結着剤としてのスチレンブタジエンゴム（ＳＢＲ）とを、それぞれ質量比で９７：１．５：１．５となるように秤量し、これらを水に分散させて負極合剤スラリーを調製した。この負極合剤スラリーを厚さ８μｍの銅箔からなる集電体の両面にドクターブレード法により塗布することにより、負極合剤層を形成した。その後、乾燥して水分を除去し、圧延ローラーを用いて所定の厚さまで圧延し、所定のサイズに裁断して負極極板を作製した。   The negative electrode active material produced as described above, carboxymethyl cellulose (CMC) as a thickener, and styrene butadiene rubber (SBR) as a binder were each in a mass ratio of 97: 1.5: 1. 5 were weighed and dispersed in water to prepare a negative electrode mixture slurry. The negative electrode mixture slurry was applied to both surfaces of a current collector made of a copper foil having a thickness of 8 μm by a doctor blade method to form a negative electrode mixture layer. Then, it dried and removed the water | moisture content, it rolled to the predetermined thickness using the rolling roller, and it cut | judged to the predetermined size, and produced the negative electrode plate.

（正極極板の作製）
正極活物質としてのコバルト酸リチウム（ＬｉＣｏＯ２）粉末と、導電剤としての炭素粉末と、結着剤としてのポリフッ化ビニリデン（ＰＶｄＦ）粉末とを、それぞれ質量比で９５：２．５：２．５となるように秤量し、これらをＮ―メチルピロリドン（ＮＭＰ）に分散して正極合剤スラリーを調製した。この正極合剤スラリーを、厚さ１５μｍのアルミニウム箔からなる集電体の両面にドクターブレード法により塗布することにより、集電体の両面に正極合剤層を形成した。その後、乾燥してＮＭＰを除去し、圧延ローラーを用いて所定の厚さまで圧延し、所定のサイズに裁断して正極極板を作製した。 (Preparation of positive electrode plate)
The lithium cobaltate (LiCoO 2 ) powder as the positive electrode active material, the carbon powder as the conductive agent, and the polyvinylidene fluoride (PVdF) powder as the binder are 95: 2.5: 2. 5, and these were dispersed in N-methylpyrrolidone (NMP) to prepare a positive electrode mixture slurry. The positive electrode mixture slurry was applied to both surfaces of a current collector made of an aluminum foil having a thickness of 15 μm by a doctor blade method to form a positive electrode mixture layer on both surfaces of the current collector. Then, it dried and removed NMP, it rolled to the predetermined thickness using the rolling roller, and cut | judged to the predetermined size, and produced the positive electrode plate.

（非水電解液の調製）
エチレンカーボネート（ＥＣ）と、エチルメチルカーボネート（ＥＭＣ）と、ジエチルカーボネート（ＤＥＣ）とを、１気圧、２５℃において、それぞれ体積比で３０：６０：１０の割合で混合した溶媒に、ヘキサフルオロリン酸リチウム（ＬｉＰＦ６）を１．０ｍｏｌ／Ｌとなるように溶解させた。さらに、この溶液に、ビニレンカーボネート（ＶＣ）を非水電解液全量に対して２．０質量％となるように添加して溶解させ、非水電解液を作製した。 (Preparation of non-aqueous electrolyte)
To a solvent in which ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed at a volume ratio of 30:60:10 at 1 atm and 25 ° C., hexafluorophosphorus was added. Lithium acid (LiPF 6 ) was dissolved so as to be 1.0 mol / L. Furthermore, vinylene carbonate (VC) was added and dissolved in this solution so that it might become 2.0 mass% with respect to the nonaqueous electrolyte whole quantity, and the nonaqueous electrolyte was produced.

（非水電解質二次電池の作製）
上述のようにして作製した負極極板及び正極極板を、ポリエチレン製微多孔膜からなるセパレータを介して巻回してプレスし、偏平状渦巻電極体を作製した。この偏平状渦巻電極体をアルミニウム合金製の角形外装缶に挿入し、注液口を備える封口体によりこの角形外装缶を封止した。そして、注液口から上述のようにして調製した非水電解液を注入した後、注液口を封止した。このようにして、高さ５０ｍｍ、幅３４ｍｍ、定格厚み５．５ｍｍの実施例１に係る非水電解質二次電池を作製した。なお、作製された非水電解質二次電池の定格放電容量は１２００ｍＡｈである。 (Preparation of non-aqueous electrolyte secondary battery)
The negative electrode plate and the positive electrode plate produced as described above were wound and pressed through a separator made of a polyethylene microporous film, to produce a flat spiral electrode body. The flat spiral electrode body was inserted into a rectangular outer can made of aluminum alloy, and the rectangular outer can was sealed with a sealing body having a liquid inlet. And after pouring the non-aqueous electrolyte prepared as mentioned above from the injection hole, the injection hole was sealed. Thus, a nonaqueous electrolyte secondary battery according to Example 1 having a height of 50 mm, a width of 34 mm, and a rated thickness of 5.5 mm was produced. The rated discharge capacity of the produced nonaqueous electrolyte secondary battery is 1200 mAh.

なお、正極極板の正極合剤層及び負極極板の負極合剤層のそれぞれの塗布量は、正極極板と負極極板とが対向する部分における充電容量比（負極充電容量／正極充電容量）が、電池を４．２Ｖまで充電した際に１．１となるように設定した。   The coating amount of the positive electrode mixture layer of the positive electrode plate and the negative electrode mixture layer of the negative electrode plate is the charge capacity ratio (negative electrode charge capacity / positive electrode charge capacity) at the portion where the positive electrode plate and the negative electrode plate face each other. ) Was set to 1.1 when the battery was charged to 4.2V.

［実施例２］
実施例２に係る非水電解質二次電池は次のようにして作製した。実施例１における負極活物質を調製する工程において、平均粒径１５μｍの天然黒鉛に固相法を用いて１．８２質量％となるようにピッチを被覆させ、黒鉛Ｂ２を調製した。そして、上述した黒鉛Ａ１とこの黒鉛Ｂ２とを質量比で５０：５０となるように混合し、実施例２の非水電解質二次電池用の負極活物質を調製した。これ以外は実施例１の場合と同様にして、実施例２に係る非水電解質二次電池を作製した。 [Example 2]
The nonaqueous electrolyte secondary battery according to Example 2 was manufactured as follows. In the step of preparing the negative electrode active material in Example 1, natural graphite having an average particle diameter of 15 μm was coated with a pitch so as to be 1.82% by mass using a solid phase method to prepare graphite B2. And the graphite A1 mentioned above and this graphite B2 were mixed so that it might become 50:50 by mass ratio, and the negative electrode active material for nonaqueous electrolyte secondary batteries of Example 2 was prepared. A nonaqueous electrolyte secondary battery according to Example 2 was made in the same manner as in Example 1 except for the above.

［実施例３］
実施例３に係る非水電解質二次電池は次のようにして作製した。実施例１における負極活物質を調製する工程において、平均粒径１５μｍの天然黒鉛に固相法を用いて０．９１質量％となるようにピッチを被覆させ、黒鉛Ａ２を調製した。そして、上述した黒鉛Ｂ１とこの黒鉛Ａ２とを質量比で５０：５０となるように混合し、実施例３の非水電解質二次電池用の負極活物質を調製した。これ以外は実施例１の場合と同様にして、実施例３に係る非水電解質二次電池を作製した。 [Example 3]
The nonaqueous electrolyte secondary battery according to Example 3 was produced as follows. In the step of preparing the negative electrode active material in Example 1, natural graphite having an average particle diameter of 15 μm was coated with a pitch so as to be 0.91% by mass using a solid phase method to prepare graphite A2. And the graphite B1 mentioned above and this graphite A2 were mixed so that it might be set to 50:50 by mass ratio, and the negative electrode active material for nonaqueous electrolyte secondary batteries of Example 3 was prepared. A nonaqueous electrolyte secondary battery according to Example 3 was made in the same manner as in Example 1 except for the above.

［実施例４］
実施例４に係る非水電解質二次電池は次のようにして作製した。実施例１における負極活物質を調製する工程において、上述した黒鉛Ａ２と黒鉛Ｂ２とを質量比で５０：５０となるように混合し、実施例４の非水電解質二次電池用の負極活物質を調製した。これ以外は実施例１の場合と同様にして、実施例４に係る非水電解質二次電池を作製した。 [Example 4]
The nonaqueous electrolyte secondary battery according to Example 4 was produced as follows. In the step of preparing the negative electrode active material in Example 1, the above-described graphite A2 and graphite B2 were mixed at a mass ratio of 50:50, and the negative electrode active material for the nonaqueous electrolyte secondary battery of Example 4 was mixed. Was prepared. A nonaqueous electrolyte secondary battery according to Example 4 was made in the same manner as in Example 1 except for the above.

［実施例５］
実施例５に係る非水電解質二次電池は次のようにして作製した。実施例１における負極活物質を調製する工程において、平均粒径１５μｍの天然黒鉛に固相法を用いて２．８３質量％となるようにピッチを被覆させ、黒鉛Ｂ３を調製した。そして、上述した黒鉛Ａ１とこの黒鉛Ｂ３とを質量比で５０：５０となるように混合し、実施例５の非水電解質二次電池用の負極活物質を調製した。これ以外は実施例１の場合と同様にして、実施例５に係る非水電解質二次電池を作製した。 [Example 5]
The nonaqueous electrolyte secondary battery according to Example 5 was produced as follows. In the step of preparing the negative electrode active material in Example 1, natural graphite having an average particle diameter of 15 μm was coated with a pitch so as to be 2.83% by mass using a solid phase method to prepare graphite B3. And the graphite A1 mentioned above and this graphite B3 were mixed so that it might become 50:50 by mass ratio, and the negative electrode active material for nonaqueous electrolyte secondary batteries of Example 5 was prepared. A nonaqueous electrolyte secondary battery according to Example 5 was made in the same manner as in Example 1 except for the above.

［実施例６］
実施例６に係る非水電解質二次電池は次のようにして作製した。実施例１における負極活物質を調製する工程において、平均粒径１５μｍの天然黒鉛に固相法を用いて４．５７質量％となるようにピッチを被覆させ、黒鉛Ｂ４を調製した。そして、上述した黒鉛Ａ１とこの黒鉛Ｂ４とを質量比で５０：５０となるように混合し、実施例６の非水電解質二次電池用の負極活物質を調製した。これ以外は実施例１の場合と同様にして、実施例６に係る非水電解質二次電池を作製した。 [Example 6]
The nonaqueous electrolyte secondary battery according to Example 6 was produced as follows. In the step of preparing the negative electrode active material in Example 1, natural graphite having an average particle diameter of 15 μm was coated with a pitch so as to be 4.57% by mass using a solid phase method to prepare graphite B4. And graphite A1 mentioned above and this graphite B4 were mixed so that it might be set to 50:50 by mass ratio, and the negative electrode active material for nonaqueous electrolyte secondary batteries of Example 6 was prepared. A nonaqueous electrolyte secondary battery according to Example 6 was made in the same manner as in Example 1 except for the above.

［実施例７］
実施例７に係る非水電解質二次電池は次のようにして作製した。実施例１における負極活物質を調製する工程において、平均粒径１５μｍの天然黒鉛に固相法を用いて６．５５質量％となるようにピッチを被覆させ、黒鉛Ｂ５を調製した。そして、上述した黒鉛Ａ１とこの黒鉛Ｂ５とを質量比で５０：５０となるように混合し、実施例７の非水電解質二次電池用の負極活物質を調製した。これ以外は実施例１の場合と同様にして、実施例７に係る非水電解質二次電池を作製した。 [Example 7]
The nonaqueous electrolyte secondary battery according to Example 7 was produced as follows. In the step of preparing the negative electrode active material in Example 1, natural graphite having an average particle size of 15 μm was coated with a pitch so as to be 6.55% by mass using a solid phase method to prepare graphite B5. And the graphite A1 mentioned above and this graphite B5 were mixed so that it might be set to 50:50 by mass ratio, and the negative electrode active material for nonaqueous electrolyte secondary batteries of Example 7 was prepared. A nonaqueous electrolyte secondary battery according to Example 7 was made in the same manner as in Example 1 except for the above.

［比較例１］
比較例１に係る非水電解質二次電池は次のようにして作製した。実施例１における負極活物質を調製する工程において、平均粒径１５μｍの天然黒鉛に非晶質炭素を被覆していないものを黒鉛Ｘとし、上述した黒鉛Ａ１とこの黒鉛Ｘとを質量比で５０：５０となるように混合し、比較例１の非水電解質二次電池用の負極活物質を調製した。これ以外は実施例１の場合と同様にして、比較例１に係る非水電解質二次電池を作製した。 [Comparative Example 1]
The nonaqueous electrolyte secondary battery according to Comparative Example 1 was produced as follows. In the step of preparing the negative electrode active material in Example 1, natural graphite having an average particle size of 15 μm and not coated with amorphous carbon is defined as graphite X, and the above-described graphite A1 and graphite X are 50 by mass. The negative electrode active material for the non-aqueous electrolyte secondary battery of Comparative Example 1 was prepared. Except for this, a nonaqueous electrolyte secondary battery according to Comparative Example 1 was produced in the same manner as in Example 1.

［比較例２］
比較例２に係る非水電解質二次電池は次のようにして作製した。実施例１における負極活物質を調製する工程において、上述した黒鉛Ｂ１と黒鉛Ｘとを質量比で５０：５０となるように混合し、比較例２の非水電解質二次電池用の負極活物質を調製した。これ以外は実施例１の場合と同様にして、比較例２に係る非水電解質二次電池を作製した。 [Comparative Example 2]
The nonaqueous electrolyte secondary battery according to Comparative Example 2 was produced as follows. In the step of preparing the negative electrode active material in Example 1, the above-described graphite B1 and graphite X were mixed at a mass ratio of 50:50, and the negative electrode active material for the nonaqueous electrolyte secondary battery of Comparative Example 2 was mixed. Was prepared. Except for this, a nonaqueous electrolyte secondary battery according to Comparative Example 2 was produced in the same manner as in Example 1.

［比較例３］
比較例３に係る非水電解質二次電池は次のようにして作製した。実施例１における負極活物質を調製する工程において、上述した黒鉛Ａ１を単独で用いて、比較例３の非水電解質二次電池用の負極活物質を調製した。これ以外は実施例１の場合と同様にして、比較例３に係る非水電解質二次電池を作製した。 [Comparative Example 3]
The nonaqueous electrolyte secondary battery according to Comparative Example 3 was produced as follows. In the step of preparing the negative electrode active material in Example 1, the negative electrode active material for the nonaqueous electrolyte secondary battery of Comparative Example 3 was prepared using the above-described graphite A1 alone. A nonaqueous electrolyte secondary battery according to Comparative Example 3 was fabricated in the same manner as in Example 1 except for the above.

［比較例４］
比較例４に係る非水電解質二次電池は次のようにして作製した。実施例１における負極活物質を調製する工程において、上述した黒鉛Ｂ１を単独で用いて、比較例４の非水電解質二次電池用の負極活物質を調製した。これ以外は実施例１の場合と同様にして、比較例４に係る非水電解質二次電池を作製した。 [Comparative Example 4]
The nonaqueous electrolyte secondary battery according to Comparative Example 4 was produced as follows. In the step of preparing the negative electrode active material in Example 1, the negative electrode active material for the nonaqueous electrolyte secondary battery of Comparative Example 4 was prepared using the above-described graphite B1 alone. A nonaqueous electrolyte secondary battery according to Comparative Example 4 was produced in the same manner as in Example 1 except for this.

［比較例５］
比較例５に係る非水電解質二次電池は次のようにして作製した。実施例１における負極活物質を調製する工程において、上述した黒鉛Ｘを単独で用いて、比較例５の非水電解質二次電池用の負極活物質を調製した。これ以外は実施例１の場合と同様にして、比較例５に係る非水電解質二次電池を作製した。 [Comparative Example 5]
The nonaqueous electrolyte secondary battery according to Comparative Example 5 was produced as follows. In the step of preparing the negative electrode active material in Example 1, the above-described graphite X was used alone to prepare the negative electrode active material for the nonaqueous electrolyte secondary battery of Comparative Example 5. A nonaqueous electrolyte secondary battery according to Comparative Example 5 was produced in the same manner as in Example 1 except for the above.

［充電保存特性の測定］
実施例１〜７及び比較例１〜５に係る非水電解質二次電池を用い、それぞれの電池について、以下のようにして充電保存特性としての電池膨れ率及び容量維持率を求めた。 [Measurement of charge storage characteristics]
Using the nonaqueous electrolyte secondary batteries according to Examples 1 to 7 and Comparative Examples 1 to 5, the battery swelling ratio and capacity retention ratio as charge storage characteristics were determined for each battery as follows.

（電池膨れ率の測定）
実施例１〜７及び比較例１〜５に係る非水電解質二次電池のそれぞれを、２５℃において、１Ｉｔ＝１２００ｍＡの定電流で電池電圧が４．２Ｖに達するまで充電し、電池電圧が４．２Ｖに達した後は４．２Ｖの定電圧で電流が２４ｍＡに収束するまで充電した。そして、充電後の非水電解質二次電池を１Ｉｔ＝１２００ｍＡの定電流で電池電圧が２．７５Ｖに達するまで放電させ、このときに流れた電気量から実施例１〜７及び比較例１〜５に係る非水電解質二次電池の「保存前放電容量」を測定した。 (Measurement of battery expansion rate)
Each of the nonaqueous electrolyte secondary batteries according to Examples 1 to 7 and Comparative Examples 1 to 5 was charged at 25 ° C. with a constant current of 1 It = 1200 mA until the battery voltage reached 4.2 V, and the battery voltage was 4 After reaching 0.2 V, the battery was charged with a constant voltage of 4.2 V until the current converged to 24 mA. Then, the non-aqueous electrolyte secondary battery after charging was discharged at a constant current of 1 It = 1200 mA until the battery voltage reached 2.75 V, and Examples 1 to 7 and Comparative Examples 1 to 5 were calculated from the amount of electricity flowing at this time. The “discharge capacity before storage” of the nonaqueous electrolyte secondary battery according to the present invention was measured.

そして、実施例１〜７及び比較例１〜５に係る非水電解質二次電池のそれぞれを、再度、２５℃において、１Ｉｔ＝１２００ｍＡの定電流で電池電圧が４．２Ｖに達するまで充電し、電池電圧が４．２Ｖに達した後は４．２Ｖの定電圧で電流が２４ｍＡに収束するまで充電し、電池の厚みを測定した。このときの電池の厚みを「保存前厚み」として求めた。   And each of the nonaqueous electrolyte secondary batteries according to Examples 1 to 7 and Comparative Examples 1 to 5 is charged again at 25 ° C. with a constant current of 1 It = 1200 mA until the battery voltage reaches 4.2 V, After the battery voltage reached 4.2 V, the battery was charged at a constant voltage of 4.2 V until the current converged to 24 mA, and the thickness of the battery was measured. The thickness of the battery at this time was determined as “thickness before storage”.

続いて、「保存前厚み」を測定した実施例１〜７及び比較例１〜５に係る非水電解質二次電池のそれぞれを、６０℃に設定した恒温槽内で２０日間保存した。その後、それぞれの非水電解質二次電池を恒温槽から取り出し、２５℃において１時間放置し、電池の厚みを測定した。このときの電池の厚みを「保存後厚み」として求めた。   Subsequently, each of the non-aqueous electrolyte secondary batteries according to Examples 1 to 7 and Comparative Examples 1 to 5 whose “thickness before storage” was measured was stored in a thermostat set at 60 ° C. for 20 days. Then, each nonaqueous electrolyte secondary battery was taken out from the thermostat, left at 25 ° C. for 1 hour, and the thickness of the battery was measured. The thickness of the battery at this time was determined as “thickness after storage”.

６０℃で２０日間充電保存した後の実施例１〜７及び比較例１〜５に係る非水電解質二次電池のそれぞれに対して、２５℃において、１Ｉｔ＝１２００ｍＡの定電流で電池電圧が２．７５Ｖに達するまで放電させ、このときに流れた電気量から実施例１〜７及び比較例１〜５に係る非水電解質二次電池の「保存後放電容量」を測定した。   For each of the nonaqueous electrolyte secondary batteries according to Examples 1 to 7 and Comparative Examples 1 to 5 after being charged and stored at 60 ° C. for 20 days, the battery voltage was 2 at a constant current of 1 It = 1200 mA at 25 ° C. The battery was discharged until it reached .75 V, and the “discharge capacity after storage” of the nonaqueous electrolyte secondary batteries according to Examples 1 to 7 and Comparative Examples 1 to 5 was measured from the amount of electricity flowing at this time.

そして、実施例１〜７及び比較例１〜５に係る非水電解質二次電池のそれぞれについて、「電池膨れ率」及び「容量維持率」を下記計算式によって算出した。
電池膨れ率（％）＝（（保存後厚み−保存前厚み）／保存前厚み）×１００
容量維持率（％）＝（保存後放電容量／保存前放電容量）×１００ And about each of the nonaqueous electrolyte secondary battery which concerns on Examples 1-7 and Comparative Examples 1-5, "battery swelling rate" and "capacity maintenance factor" were computed with the following formula.
Battery swelling ratio (%) = ((thickness after storage−thickness before storage) / thickness before storage) × 100
Capacity retention rate (%) = (discharge capacity after storage / discharge capacity before storage) × 100

黒鉛Ａ１、黒鉛Ａ２、黒鉛Ｂ１〜黒鉛Ｂ５、黒鉛Ｘのそれぞれについての非晶質炭素の被覆量をまとめたものを表１に示した。また、実施例１〜７及び比較例１〜５の「電池膨れ率」及び「容量維持率」の測定結果を表２に示した。   Table 1 shows a summary of the amorphous carbon coverage for each of graphite A1, graphite A2, graphite B1 to graphite B5, and graphite X. In addition, Table 2 shows the measurement results of “battery expansion ratio” and “capacity maintenance ratio” of Examples 1 to 7 and Comparative Examples 1 to 5.

なお、判定結果は、電池膨れ率が５％以下かつ容量維持率が８５％以上であるものを「◎」、電池膨れ率が５％以下かつ容量維持率が８０％以上８５％未満であるものを「○」、電池膨れ率が５％よりも大きい又は容量維持率が８０％未満であるものを「×」とした。   The determination result is “結果” when the battery expansion rate is 5% or less and the capacity maintenance rate is 85% or more, and the battery expansion rate is 5% or less and the capacity maintenance rate is 80% or more and less than 85%. Was marked with “◯”, and the battery swelling rate was greater than 5% or the capacity retention rate was less than 80%.

Figure 2014067625
Figure 2014067625

Figure 2014067625
Figure 2014067625

表２に示した結果から以下のことが分かる。すなわち、実施例１〜７のように、互いに異なる被覆量で非晶質炭素により被覆された２種類の黒鉛を含有する非水電解質二次電池においては、電池の膨れが抑制されるとともに高い容量維持率が得られた。より具体的には、実施例１〜７のように、非晶質炭素の被覆量が０．５質量％以上１質量％未満のものと、１質量％以上のものとを含有する非水電解質二次電池においては、電池の膨れの抑制と高い容量維持率とが両立されていた。また、実施例１〜４のように、非晶質炭素の被覆量が０．５質量％以上１質量％未満のものと、１質量％以上２質量％以下のものとを含有する非水電解質二次電池は、この数値範囲から外れる実施例５〜７のものと比較して、より良好な結果が得られた。   From the results shown in Table 2, the following can be understood. That is, as in Examples 1 to 7, in the nonaqueous electrolyte secondary battery containing two types of graphite coated with amorphous carbon at different coating amounts, the swelling of the battery is suppressed and the capacity is high. A retention rate was obtained. More specifically, as in Examples 1 to 7, a non-aqueous electrolyte containing amorphous carbon having a coating amount of 0.5% by mass or more and less than 1% by mass and 1% by mass or more In secondary batteries, suppression of battery swelling and a high capacity retention ratio are compatible. Further, as in Examples 1 to 4, the non-aqueous electrolyte contains amorphous carbon having a coating amount of 0.5% by mass or more and less than 1% by mass and 1% by mass or more and 2% by mass or less. The secondary battery obtained better results as compared with those of Examples 5 to 7 out of this numerical range.

これに対し、比較例１〜５のように、互いに異なる被覆量で非晶質炭素により被覆された複数種類の黒鉛を含有しない非水電解質二次電池においては、実施例１〜７と比較して容量維持率が低い値となった。また、比較例１、２のように、負極活性物質として２種の黒鉛を含有する場合であっても、そのうちの１種が非晶質炭素により被覆されていない黒鉛（黒鉛Ｘ）であるときは、高い容量維持率は得られなかった。なお、比較例３〜５の結果を比較すると、電池膨れ率は比較例４、比較例３、比較例５の順に小さくなった。このことから、黒鉛の表面を非晶質炭素で被覆することにより、さらにはその被覆量が増加するほど、電池の膨れが抑制されることが分かる。   On the other hand, as in Comparative Examples 1 to 5, non-aqueous electrolyte secondary batteries not containing a plurality of types of graphite coated with amorphous carbon at different coating amounts are compared with Examples 1 to 7. As a result, the capacity retention rate was low. Further, even when two types of graphite are contained as the negative electrode active material as in Comparative Examples 1 and 2, when one of them is graphite (graphite X) not coated with amorphous carbon However, a high capacity retention rate was not obtained. In addition, when the results of Comparative Examples 3 to 5 were compared, the battery swelling ratio decreased in the order of Comparative Example 4, Comparative Example 3, and Comparative Example 5. From this, it can be seen that by covering the surface of graphite with amorphous carbon, the swelling of the battery is further suppressed as the coating amount is further increased.

これらの現象は、黒鉛を被覆する非晶質炭素の層が充電保存時に正極と電解液との反応で発生する二酸化炭素（ＣＯ２）ガスを吸収することにより電池の膨れが抑制される一方、この非晶質炭素が過剰になると、ＣＯ２ガスを吸収した非晶質炭素の層がリチウムイオンの移動を阻害して反応抵抗が上昇して容量維持率が低下することに起因するものと推測される。また、比較例３及び比較例４の結果から明らかなように、１種の被覆量で被覆した黒鉛を単独で用いた場合には、電池の膨れの抑制と高い容量維持率とが両立できなかった。 These phenomena are caused by the fact that the amorphous carbon layer covering graphite suppresses the swelling of the battery by absorbing carbon dioxide (CO 2 ) gas generated by the reaction between the positive electrode and the electrolyte during charge storage, When this amorphous carbon is excessive, it is assumed that the amorphous carbon layer that has absorbed the CO 2 gas inhibits the migration of lithium ions, increases the reaction resistance, and decreases the capacity retention rate. Is done. Further, as apparent from the results of Comparative Examples 3 and 4, when graphite coated with one coating amount is used alone, it is impossible to achieve both suppression of battery swelling and high capacity retention rate. It was.

このように、本発明の非水電解質二次電池においては、互いに非晶質炭素の被覆量の異なる２種類の黒鉛を混合して用いることにより、電池の膨れの抑制と高い容量維持率とを両立することができることが確認された。   As described above, in the non-aqueous electrolyte secondary battery of the present invention, the use of a mixture of two types of graphite having different amorphous carbon coating amounts reduces the swelling of the battery and provides a high capacity retention rate. It was confirmed that both can be achieved.

［実施例８］
実施例８に係る非水電解質二次電池は次のようにして作製した。実施例１における負極活物質を調製する工程において、上述した黒鉛Ａ１と黒鉛Ｂ１とを質量比で９５：５となるように混合し、実施例８の非水電解質二次電池用の負極活物質を調製した。これ以外は実施例１の場合と同様にして、実施例８に係る非水電解質二次電池を作製した。 [Example 8]
The nonaqueous electrolyte secondary battery according to Example 8 was produced as follows. In the step of preparing the negative electrode active material in Example 1, the above-mentioned graphite A1 and graphite B1 were mixed at a mass ratio of 95: 5, and the negative electrode active material for the nonaqueous electrolyte secondary battery of Example 8 was mixed. Was prepared. A nonaqueous electrolyte secondary battery according to Example 8 was made in the same manner as in Example 1 except for the above.

［実施例９］
実施例９に係る非水電解質二次電池は次のようにして作製した。実施例１における負極活物質を調製する工程において、上述した黒鉛Ａ１と黒鉛Ｂ１とを質量比で９０：１０となるように混合し、実施例９の非水電解質二次電池用の負極活物質を調製した。これ以外は実施例１の場合と同様にして、実施例９に係る非水電解質二次電池を作製した。 [Example 9]
The nonaqueous electrolyte secondary battery according to Example 9 was produced as follows. In the step of preparing the negative electrode active material in Example 1, the above-described graphite A1 and graphite B1 were mixed at a mass ratio of 90:10, and the negative electrode active material for the nonaqueous electrolyte secondary battery of Example 9 was mixed. Was prepared. A nonaqueous electrolyte secondary battery according to Example 9 was made in the same manner as in Example 1 except for the above.

［実施例１０］
実施例１０に係る非水電解質二次電池は次のようにして作製した。実施例１における負極活物質を調製する工程において、上述した黒鉛Ａ１と黒鉛Ｂ１とを質量比で１０：９０となるように混合し、負極活物質を作製した。これ以外は実施例１と同様にして、実施例１０に係る非水電解質二次電池を作製した。 [Example 10]
The nonaqueous electrolyte secondary battery according to Example 10 was produced as follows. In the step of preparing the negative electrode active material in Example 1, the above-described graphite A1 and graphite B1 were mixed at a mass ratio of 10:90 to prepare a negative electrode active material. A nonaqueous electrolyte secondary battery according to Example 10 was made in the same manner as Example 1 except for the above.

［実施例１１］
実施例１１に係る非水電解質二次電池は次のようにして作製した。実施例１における負極活物質を調製する工程において、上述した黒鉛Ａ１と黒鉛Ｂ１とを質量比で５：９５となるように混合し、実施例１１の非水電解質二次電池用の負極活物質を調製した。これ以外は実施例１の場合と同様にして、実施例１１に係る非水電解質二次電池を作製した。 [Example 11]
The nonaqueous electrolyte secondary battery according to Example 11 was produced as follows. In the step of preparing the negative electrode active material in Example 1, the above-described graphite A1 and graphite B1 were mixed at a mass ratio of 5:95, and the negative electrode active material for the nonaqueous electrolyte secondary battery of Example 11 was mixed. Was prepared. A nonaqueous electrolyte secondary battery according to Example 11 was made in the same manner as in Example 1 except for the above.

上述のようにして得られた実施例８〜１１のそれぞれの非水電解質二次電池を用い、実施例１の非水電解質二次電池の場合と同様にして、「電池膨れ率」及び「容量維持率」を測定した。そして、実施例８〜１１のそれぞれの測定結果を、実施例１、比較例３及び４のそれぞれの測定結果とともに表２にまとめて示した。なお、判定結果は、表２について示したのと同様である。   Using each of the nonaqueous electrolyte secondary batteries of Examples 8 to 11 obtained as described above, similarly to the case of the nonaqueous electrolyte secondary battery of Example 1, “battery swelling rate” and “capacity” "Retention rate" was measured. And each measurement result of Examples 8-11 was put together in Table 2 with each measurement result of Example 1, and Comparative Examples 3 and 4, and was shown. The determination result is the same as that shown for Table 2.

Figure 2014067625
Figure 2014067625

表３に示した結果から以下のことが分かる。すなわち、実施例１、８〜１１のように、互いに異なる被覆量で非晶質炭素により被覆された２種類の黒鉛を含有する非水電解質二次電池においては、電池の膨れが抑制されるとともに高い容量維持率となった。より具体的には、実施例１、８〜１１のように、黒鉛Ａ１と黒鉛Ｂ１との質量比が９５：５〜５：９５となるように混合されている非水電解質二次電池においては、電池の膨れと高い容量維持率とが両立された。また、実施例１、９、１０のように、一方の被覆量のもの黒鉛Ａ１と他方の被覆量のもの黒鉛Ｂ１との質量比が、１０：９０〜９０：１０であれば、この数値範囲から外れる実施例１及び１１の場合と比較して、より良好な結果となった。   From the results shown in Table 3, the following can be understood. That is, as in Examples 1 and 8 to 11, in the nonaqueous electrolyte secondary battery containing two types of graphite coated with amorphous carbon at different coating amounts, the swelling of the battery is suppressed. High capacity retention rate. More specifically, in the nonaqueous electrolyte secondary battery in which the mass ratio of graphite A1 and graphite B1 is 95: 5 to 5:95 as in Examples 1 and 8 to 11, Both battery swelling and high capacity retention were achieved. In addition, as in Examples 1, 9, and 10, if the mass ratio of graphite A1 with one coating amount and graphite B1 with the other coating amount is 10:90 to 90:10, this numerical range Compared with the case of Example 1 and 11 which remove | deviate from, it became a better result.

したがって、本発明の非水電解質二次電池においては、負極活物質として非晶質炭素の被覆量がそれぞれ異なる２種の黒鉛からなるものを用いた場合には、両者の質量比が１０：９０〜９０：１０であれば、より良好な電池の膨れの抑制効果と高い容量維持率とが達成されることが確認された。   Therefore, in the nonaqueous electrolyte secondary battery of the present invention, when two types of graphite having different coating amounts of amorphous carbon are used as the negative electrode active material, the mass ratio between the two is 10:90. It was confirmed that if it was ˜90: 10, a better battery swelling suppression effect and a high capacity retention rate were achieved.

なお、上記各実施例においては、負極活物質として非晶質炭素の被覆量がそれぞれ異なる２種の黒鉛からなるものを用いた例を示したが、本発明の非水電解質二次電池においては、これに限らず、負極活物質としてそれぞれ非晶質炭素の被覆量が相違する３種以上の黒鉛を含有するものを用いても同様の作用効果を奏することができることは明白である。   In each of the above-described examples, an example in which the anode active material is composed of two types of graphite having different coating amounts of amorphous carbon is shown. However, in the nonaqueous electrolyte secondary battery of the present invention, However, the present invention is not limited to this, and it is obvious that the same effect can be obtained even when a negative electrode active material containing three or more kinds of graphites each having a different coating amount of amorphous carbon is used.

Claims (5)

リチウムイオンを吸蔵・放出する正極活物質を有する正極と、
リチウムイオンを吸蔵・放出する負極活物質を有する負極と、
非水電解質と、セパレータと、
を有し、
前記負極活物質は、互いに異なる被覆量で非晶質炭素により被覆された少なくとも２種類の黒鉛を含有することを特徴とする非水電解質二次電池。 A positive electrode having a positive electrode active material that absorbs and releases lithium ions;
A negative electrode having a negative electrode active material that absorbs and releases lithium ions;
A non-aqueous electrolyte, a separator,
Have
The non-aqueous electrolyte secondary battery, wherein the negative electrode active material contains at least two types of graphite coated with amorphous carbon in different coating amounts. 前記負極活物質は、前記黒鉛に対する非晶質炭素の被覆量が０．５質量％以上１質量％未満のもの及び１質量％以上のものを含有することを特徴とする請求項１記載の非水電解質二次電池。   2. The non-active material according to claim 1, wherein the negative electrode active material contains amorphous carbon with respect to the graphite having a coating amount of 0.5% by mass to less than 1% by mass and 1% by mass or more. Water electrolyte secondary battery. 前記負極活物質は、前記黒鉛に対する非晶質炭素の被覆量が１質量％以上２質量％以下のものを含有することを特徴とする請求項２記載の非水電解質二次電池。   3. The nonaqueous electrolyte secondary battery according to claim 2, wherein the negative electrode active material contains an amorphous carbon covering amount of 1% by mass to 2% by mass with respect to the graphite. 前記負極活物質は、前記非晶質炭素の被覆量がそれぞれ異なる２種の黒鉛からなり、両者の質量比が１０：９０〜９０：１０であることを特徴とする請求項１〜３いずれか記載の非水電解質二次電池。   The said negative electrode active material consists of two types of graphite from which the coating amount of the said amorphous carbon differs, respectively, and mass ratio of both is 10: 90-90: 10, The any one of Claims 1-3 characterized by the above-mentioned. The nonaqueous electrolyte secondary battery as described. 前記非晶質炭素は、ピッチであることを特徴とする請求項１〜４いずれか記載の非水電解質二次電池。   The non-aqueous electrolyte secondary battery according to claim 1, wherein the amorphous carbon is a pitch.
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