JP2019140054A - Positive electrode and non-aqueous electrolyte secondary battery - Google Patents
Positive electrode and non-aqueous electrolyte secondary battery Download PDFInfo
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- JP2019140054A JP2019140054A JP2018024834A JP2018024834A JP2019140054A JP 2019140054 A JP2019140054 A JP 2019140054A JP 2018024834 A JP2018024834 A JP 2018024834A JP 2018024834 A JP2018024834 A JP 2018024834A JP 2019140054 A JP2019140054 A JP 2019140054A
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Classifications
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Landscapes
- Cell Electrode Carriers And Collectors (AREA)
- Secondary Cells (AREA)
- Battery Electrode And Active Subsutance (AREA)
Abstract
Description
本発明は、正極及び非水電解液二次電池に関する。 The present invention relates to a positive electrode and a non-aqueous electrolyte secondary battery.
非水電解液二次電池は、携帯電話、ノートパソコン等のモバイル機器やハイブリットカー等の動力源としても広く用いられている。これらの分野の発展と共に、非水電解液二次電池の様々な性能を高めることが求められている。 Nonaqueous electrolyte secondary batteries are also widely used as power sources for mobile devices such as mobile phones and notebook computers, and hybrid cars. With the development of these fields, it is required to improve various performances of nonaqueous electrolyte secondary batteries.
その性能の一つが、非水電解液二次電池の高エネルギー密度化である。非水電解液二次電池のエネルギー密度は、非水電解液二次電池の正極によって大きな影響を受ける。エネルギー密度に優れた正極を得るために、活物質粒子の材料開発、表面処理等の種々の検討が行われている（例えば、特許文献１）。 One of the performances is to increase the energy density of the non-aqueous electrolyte secondary battery. The energy density of the nonaqueous electrolyte secondary battery is greatly influenced by the positive electrode of the nonaqueous electrolyte secondary battery. In order to obtain a positive electrode excellent in energy density, various studies such as material development and surface treatment of active material particles have been performed (for example, Patent Document 1).
しかしながら、設計された活物質粒子を利用しても、想定される特性を十分発揮できない場合があり、特にサイクル特性が低下する場合があった。 However, even if the designed active material particles are used, the expected characteristics may not be sufficiently exhibited, and in particular, the cycle characteristics may be deteriorated.
本発明は上記問題に鑑みてなされたものであり、サイクル特性に優れた非水電解液二次電池に用いられる正極を提供することを目的とする。 This invention is made | formed in view of the said problem, and it aims at providing the positive electrode used for the nonaqueous electrolyte secondary battery excellent in cycling characteristics.
本発明者らは、鋭意検討の結果、非水電解液二次電池のサイクル特性の低下は、正極活物質層をプレスする際に活物質粒子が割れてしまうことに起因するということを見出した。高エネルギー密度化を実現する為には、正極活物質層を高密度にする必要があり、製造時に正極活物質層をプレスする。プレス時に活物質粒子が割れると、設計して作製された活物質粒子が割れてしまう。活物質粒子の割れは不可逆容量の原因となり、非水電解液二次電池のサイクル特性を低下させる原因となる。
すなわち、上記課題を解決するため、以下の手段を提供する。
As a result of intensive studies, the present inventors have found that the deterioration of the cycle characteristics of the nonaqueous electrolyte secondary battery is caused by the active material particles being cracked when the positive electrode active material layer is pressed. . In order to realize high energy density, the positive electrode active material layer needs to have a high density, and the positive electrode active material layer is pressed during production. If the active material particles are broken during pressing, the active material particles designed and produced are broken. Cracking of the active material particles causes irreversible capacity, and causes deterioration in cycle characteristics of the nonaqueous electrolyte secondary battery.
That is, in order to solve the above problems, the following means are provided.
（１）第１の態様にかかる正極は、正極集電体と、前記正極集電体の少なくとも一面に塗布され、活物質粒子を有する正極活物質層と、を備え、前記正極活物質層において、前記正極活物質層を積層方向と直交する切断面で１０等分した際に、前記活物質粒子の割れ率が最も低い切断面における前記活物質粒子の割れ率が１．５％未満であり、前記割れ率は、前記切断面における画像を、前記活物質粒子の階調の中央値が２２５以下、かつ、前記活物質粒子の階調の中央値と前記活物質粒子以外の部分の階調の中央値との差が３０以上１１０以下となるようにコントラスト調整した２５６諧調のグレースケール画像から前記活物質粒子を抽出し直した第２グレースケール画像において、計測頻度が最大頻度の２０％以下となる所定の閾値階調以上の階調を示す割れ部の面積を、前記画像の全体面積で割って求められる。 (1) A positive electrode according to a first aspect includes a positive electrode current collector and a positive electrode active material layer having active material particles coated on at least one surface of the positive electrode current collector, When the positive electrode active material layer is divided into 10 equal parts by a cut surface orthogonal to the stacking direction, the active material particle has a crack rate of less than 1.5% at the cut surface with the lowest crack rate of the active material particles. The crack rate is determined based on the image on the cut surface, the median gradation of the active material particles is 225 or less, and the gradation of the portion other than the active material particles and the median gradation of the active material particles In the second grayscale image obtained by re-extracting the active material particles from the 256-tone grayscale image, the contrast of which is adjusted so that the difference from the median of 30 to 110 is less than 20% of the maximum frequency. A predetermined threshold gradation The area of the crack part showing a gradation of the upper, obtained by dividing the entire area of the image.
（２）上記態様にかかる正極は、前記活物質粒子の割れ率が最も高い切断面における前記活物質粒子の割れ率が１０％以下であってもよい。 (2) In the positive electrode according to the above aspect, the active material particles may have a cracking rate of 10% or less at a cut surface where the active material particles have the highest cracking rate.
（３）上記態様にかかる正極において、前記活物質粒子の割れ率が最も低い切断面は、前記正極活物質層の積層方向の中央部に位置してもよい。 (3) In the positive electrode according to the above aspect, the cut surface with the lowest cracking rate of the active material particles may be located at the center of the positive electrode active material layer in the stacking direction.
（４）上記態様にかかる正極において、前記活物質粒子がリチウム複合酸化物であり、前記リチウム複合酸化物は、一般式ＬｉｘＭ１ｙＭ２１−ｙＯ２で表記され、前記一般式において、Ｍ１はＮｉ、Ｃｏ及びＭｎからなる群から選択される少なくとも１種の金属元素であり、Ｍ２はＡｌ、Ｆｅ、Ｔｉ、Ｃｒ、Ｍｇ、Ｃｕ、Ｇａ、Ｚｎ、Ｓｎ、Ｂ、Ｖ、Ｃａ及びＳｒからなる群から選択される少なくとも１種の金属元素であり、ｘは０．０５≦ｘ≦１．２を満たし、ｙは０．３≦ｙ≦１．０を満たしてもよい。 (4) In the positive electrode according to the above aspect, the active material particles are a lithium composite oxide, and the lithium composite oxide is represented by a general formula Li x M1 y M2 1-y O 2 , M1 is at least one metal element selected from the group consisting of Ni, Co, and Mn, and M2 is Al, Fe, Ti, Cr, Mg, Cu, Ga, Zn, Sn, B, V, Ca, and Sr. At least one metal element selected from the group consisting of: x may satisfy 0.05 ≦ x ≦ 1.2, and y may satisfy 0.3 ≦ y ≦ 1.0.
（５）上記態様にかかる正極において、前記活物質粒子は、中央部と外周部とで構成する元素の組成又は組成比が異なっていてもよい。 (5) In the positive electrode according to the aspect described above, the active material particles may have different compositions or composition ratios of elements composed of a central portion and an outer peripheral portion.
（６）上記態様にかかる正極において、前記活物質粒子は、表面にコーティング層を備えてもよい。 (6) In the positive electrode according to the above aspect, the active material particles may include a coating layer on the surface.
（７）上記態様にかかる正極は、前記正極集電体と前記正極活物質層との間に、アンダーコート層をさらに備えてもよい。 (7) The positive electrode according to the above aspect may further include an undercoat layer between the positive electrode current collector and the positive electrode active material layer.
（８）第２の態様にかかる非水電解液二次電池は、上記態様にかかる正極と、前記正極と対向する負極と、前記正極と前記負極との間に配設されたセパレータと、備える。 (8) A non-aqueous electrolyte secondary battery according to a second aspect includes a positive electrode according to the above aspect, a negative electrode facing the positive electrode, and a separator disposed between the positive electrode and the negative electrode. .
上記態様に係る正極を非水電解液二次電池に用いると、サイクル特性に優れた非水電解液二次電池を得ることができる。 If the positive electrode which concerns on the said aspect is used for a nonaqueous electrolyte secondary battery, the nonaqueous electrolyte secondary battery excellent in cycling characteristics can be obtained.
以下、本実施形態について、図を適宜参照しながら詳細に説明する。以下の説明で用いる図面は、本発明の特徴をわかりやすくするために便宜上特徴となる部分を拡大して示している場合があり、各構成要素の寸法比率等は実際とは異なっていることがある。以下の説明において例示される材料、寸法等は一例であって、本発明はそれらに限定されるものではなく、その要旨を変更しない範囲で適宜変更して実施することが可能である。 Hereinafter, the present embodiment will be described in detail with appropriate reference to the drawings. In the drawings used in the following description, in order to make the characteristics of the present invention easier to understand, there are cases where the characteristic parts are enlarged for the sake of convenience, and the dimensional ratios and the like of each component are different from actual ones. is there. The materials, dimensions, and the like exemplified in the following description are examples, and the present invention is not limited to them, and can be appropriately modified and implemented without departing from the scope of the invention.
「非水電解液二次電池」
図１は、本実施形態にかかる非水電解液二次電池の模式図である。図１に示す非水電解液二次電池１００は、発電素子４０と外装体５０とを備える。外装体５０は、発電素子４０の周囲を被覆する。発電素子４０は、接続された一対の端子６０、６２によって外部と接続される。また図示されていないが、発電素子４０とともに電解液が、外装体５０内に収容されている。
"Nonaqueous electrolyte secondary battery"
FIG. 1 is a schematic diagram of a non-aqueous electrolyte secondary battery according to this embodiment. A nonaqueous electrolyte secondary battery 100 shown in FIG. 1 includes a power generation element 40 and an exterior body 50. The exterior body 50 covers the periphery of the power generation element 40. The power generating element 40 is connected to the outside by a pair of connected terminals 60 and 62. Although not shown, the electrolytic solution is housed in the exterior body 50 together with the power generation element 40.
（発電素子）
発電素子４０は、正極２０と負極３０とセパレータ１０とを備える。セパレータ１０は、正極２０と負極３０との間に配設される。
(Power generation element)
The power generating element 40 includes a positive electrode 20, a negative electrode 30, and a separator 10. The separator 10 is disposed between the positive electrode 20 and the negative electrode 30.
＜セパレータ＞
セパレータ１０は、電気絶縁性の多孔質構造から形成されていればよく、例えば、ポリエチレン又はポリプロピレン等のポリオレフィンからなるフィルムの単層体、積層体や上記樹脂の混合物の延伸膜、或いはセルロース、ポリエステル、ポリアクリロニトリル、ポリアミド、ポリエチレン及びポリプロピレンからなる群より選択される少なくとも１種の構成材料からなる繊維不織布が挙げられる。
<Separator>
The separator 10 only needs to be formed of an electrically insulating porous structure. For example, a monolayer of a film made of polyolefin such as polyethylene or polypropylene, a stretched film of a laminate or a mixture of the above resins, or cellulose or polyester , A fiber nonwoven fabric made of at least one constituent material selected from the group consisting of polyacrylonitrile, polyamide, polyethylene and polypropylene.
セパレータ１０は、電気絶縁性の多孔質構造から形成されたものの代わりに、固体電解質であってもよい。 The separator 10 may be a solid electrolyte, instead of being formed from an electrically insulating porous structure.
固体電解質は、公知のものを用いることができる。例えば、ポリエチレンオキサイド系高分子にアルカリ金属塩を溶解させた高分子固体電解質や、Ｌｉ１．３Ａｌ０．３Ｔｉ１．７（ＰＯ４）３（ナシコン型）、Ｌｉ１．０７Ａｌ０．６９Ｔｉ１．４６（ＰＯ４）３（ガラスセラミックス）、Ｌｉ０．３４Ｌａ０．５１ＴｉＯ２．９４（ペロブスカイト型）、Ｌｉ７Ｌａ３Ｚｒ２Ｏ１２（ガーネット型）、Ｌｉ２．９ＰＯ３．３Ｎ０．４６（アモルファス、ＬＩＰＯＮ）、５０Ｌｉ４ＳｉＯ４・５０Ｌｉ２ＢＯ３（ガラス）、９０Ｌｉ３ＢＯ３・１０Ｌｉ２ＳＯ４（ガラスセラミックス）といった酸化物系固体電解質、Ｌｉ３．２５Ｇｅ０．２５Ｐ０．７５Ｓ４（結晶）、Ｌｉ１０ＧｅＰ２Ｓ１２（結晶、ＬＧＰＳ）、Ｌｉ６ＰＳ５Ｃｌ（結晶、アルジロダイト型）、Ｌｉ９．５４Ｓｉ１．７４Ｐ１．４４Ｓ１１．７Ｃｌ０．３（結晶）、Ｌｉ３．２５Ｐ０．９５Ｓ４（ガラスセラミックス）、Ｌｉ７Ｐ３Ｓ１１（ガラスセラミックス）、７０Ｌｉ２Ｓ・３０Ｐ２Ｓ５（ガラス）、３０Ｌｉ２Ｓ・２６Ｂ２Ｓ３・４４ＬｉＩ（ガラス）、５０Ｌｉ２Ｓ・１７Ｐ２Ｓ５・３３ＬｉＢＨ４（ガラス）、６３Ｌｉ２Ｓ・３６ＳｉＳ２・Ｌｉ３ＰＯ４（ガラス）、５７Ｌｉ２Ｓ・３８ＳｉＳ２・５Ｌｉ４ＳｉＯ４（ガラス）といった硫化物系固体電解質が挙げられる。 A well-known thing can be used for a solid electrolyte. For example, a solid polymer electrolyte in which an alkali metal salt is dissolved in a polyethylene oxide polymer, Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 (Nasicon type), Li 1.07 Al 0. 69 Ti 1.46 (PO 4 ) 3 (glass ceramics), Li 0.34 La 0.51 TiO 2.94 (perovskite type), Li 7 La 3 Zr 2 O 12 (garnet type), Li 2.9 PO 3.3 N 0.46 (amorphous, LIPON), 50Li 4 SiO 4 .50Li 2 BO 3 (glass), 90Li 3 BO 3 .10Li 2 SO 4 (glass ceramics) oxide-based solid electrolyte, Li 3.25 Ge 0.25 P 0.75 S 4 (crystals), Li 10 GeP 2 S 12 ( crystals, LGPS), Li 6 PS 5 Cl ( Crystals Arujirodaito type), Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 ( crystals), Li 3.25 P 0.95 S 4 ( glass ceramic), Li 7 P 3 S 11 (glass ceramics), 70Li 2 S · 30P 2 S 5 ( glass), 30Li 2 S · 26B 2 S 3 · 44LiI ( glass), 50Li 2 S · 17P 2 S 5 · 33LiBH 4 ( glass), 63Li 2 S · 36SiS 2 · Li 3 PO 4 ( glass) include 57Li 2 S · 38SiS 2 · 5Li 4 SiO 4 ( glass) such as sulfide-based solid electrolyte.
＜正極＞
正極２０は、板状（膜状）の正極集電体２２と正極活物質層２４とを有する。正極活物質層２４は、正極集電体２２の少なくとも一面に形成されている。
<Positive electrode>
The positive electrode 20 includes a plate-like (film-like) positive electrode current collector 22 and a positive electrode active material layer 24. The positive electrode active material layer 24 is formed on at least one surface of the positive electrode current collector 22.
［正極集電体］
正極集電体２２は、導電性の板材であればよく、例えば、アルミニウム箔、銅箔、ニッケル箔等の金属薄板を用いることができる。
[Positive electrode current collector]
The positive electrode current collector 22 may be a conductive plate material, and for example, a thin metal plate such as an aluminum foil, a copper foil, or a nickel foil can be used.
［正極活物質層］
図２は、正極の一部の三次元像である。図２に示す三次元像は、ＦＩＢ（Focused Ion Beam）−ＳＥＭ（走査型電子顕微鏡）を用いて測定された積層方向の断面画像を合計２００枚組あわせて、画像解析ソフトウェアＩｍａｇｅＪを用いて三次元化して得た。ＦＩＢ−ＳＥＭ像は、加速電圧３０ｋＶ、電流値４ｎＡ、加工幅８０μｍ、加工奥行き５０μｍ、奥行ピッチ０．２５μｍの条件で２００枚撮影した。
[Positive electrode active material layer]
FIG. 2 is a three-dimensional image of a part of the positive electrode. The three-dimensional image shown in FIG. 2 is obtained by combining a total of 200 cross-sectional images in the stacking direction measured using a FIB (Focused Ion Beam) -SEM (scanning electron microscope), and using the image analysis software ImageJ. Obtained by normalization. 200 FIB-SEM images were taken under the conditions of an acceleration voltage of 30 kV, a current value of 4 nA, a processing width of 80 μm, a processing depth of 50 μm, and a depth pitch of 0.25 μm.
図３は、図２に示す正極活物質の三次元像を積層方向と直交する面で切断した切断面の画像である。図３に示すように、正極活物質層２４は、活物質粒子２４Ａを有する。また図３に示すように、正極活物質層２４以外の部分として、コントラストの低い第１領域２４Ｂがある。第１領域２４Ｂは、導電助剤、バインダー、空隙等からなる。また活物質粒子２４Ａには割れ２４Ｃが生じており、割れ２４Ｃはコントラストの高い部分として確認できる。 FIG. 3 is an image of a cut surface obtained by cutting the three-dimensional image of the positive electrode active material shown in FIG. 2 along a plane orthogonal to the stacking direction. As shown in FIG. 3, the positive electrode active material layer 24 has active material particles 24A. As shown in FIG. 3, there is a first region 24 </ b> B having a low contrast as a portion other than the positive electrode active material layer 24. The first region 24B includes a conductive additive, a binder, a void, and the like. The active material particles 24A have cracks 24C, and the cracks 24C can be confirmed as high contrast portions.
本実施形態にかかる正極活物質層２４は、活物質粒子２４Ａの割れ２４Ｃが少ない。具体的には、正極活物質層２４を積層方向と直交する切断面で１０等分した際に、活物質粒子２４Ａの割れ率が最も低い切断面における活物質粒子２４Ａの割れ率は１．５％未満である。また活物質粒子２４Ａの割れ率が最も低い切断面における活物質粒子２４Ａの割れ率は１．０％以下であることが好ましく、０．５％以下であることがより好ましい。 The positive electrode active material layer 24 according to the present embodiment has few cracks 24C of the active material particles 24A. Specifically, when the positive electrode active material layer 24 is divided into 10 equal parts by a cut surface orthogonal to the stacking direction, the crack rate of the active material particles 24A at the cut surface with the lowest crack rate of the active material particles 24A is 1.5. %. Further, the cracking rate of the active material particles 24A at the cut surface having the lowest cracking rate of the active material particles 24A is preferably 1.0% or less, and more preferably 0.5% or less.
活物質粒子２４Ａは設計して作製されている。活物質粒子２４Ａの割れ率が多いと、活物質粒子２４Ａが予定された性能を充分発揮することができない。特に活物質粒子２４Ａの組成又は組成比が中央部と外周部とで異なる場合、活物質粒子２４Ａの表面がコーティング層で覆われている場合等は、活物質粒子２４Ａが割れると粒子設計が崩壊するため、その影響は顕著となる。また活物質粒子２４Ａが一様な場合でも、割れにより予期せぬ活性面が露出すると、電解液と副反応を起こす場合がある。また活物質粒子２４Ａの割れ率が多いと、割れによって特性が低下した活物質粒子２４Ａが正極活物質層２４内に点在することになる。この場合、特性に優れる活物質粒子２４Ａ（即ち割れていない活物質粒子２４Ａ）に反応が集中し、その活物質粒子２４Ａが早く劣化してしまうため、非水電解液二次電池１００のサイクル特性が低下する。 The active material particles 24A are designed and manufactured. When the cracking rate of the active material particles 24A is large, the performance of the active material particles 24A cannot be exhibited sufficiently. In particular, when the composition or composition ratio of the active material particles 24A is different between the central portion and the outer peripheral portion, or when the surface of the active material particles 24A is covered with a coating layer, the particle design collapses when the active material particles 24A are cracked. Therefore, the effect becomes remarkable. Even when the active material particles 24A are uniform, if an unexpected active surface is exposed due to cracking, a side reaction with the electrolytic solution may occur. Further, when the cracking rate of the active material particles 24 </ b> A is large, the active material particles 24 </ b> A whose characteristics are deteriorated due to cracking are scattered in the positive electrode active material layer 24. In this case, the reaction concentrates on the active material particles 24A having excellent characteristics (that is, the active material particles 24A that are not cracked), and the active material particles 24A deteriorate quickly, so the cycle characteristics of the nonaqueous electrolyte secondary battery 100 Decreases.
これに対し、活物質粒子２４Ａの割れ率が少ない本実施形態にかかる正極活物質層２４は、活物質粒子２４Ａが予定された性能を発揮する。また正極活物質層２４内における活物質粒子２４Ａの性能の不均一が解消されるため、非水電解液二次電池１００のサイクル特性を高めることができる。 On the other hand, the positive electrode active material layer 24 according to the present embodiment having a low cracking rate of the active material particles 24A exhibits the performance for which the active material particles 24A are planned. Moreover, since the non-uniformity of the performance of the active material particles 24A in the positive electrode active material layer 24 is eliminated, the cycle characteristics of the nonaqueous electrolyte secondary battery 100 can be improved.
ここで本明細書における活物質粒子２４Ａの割れ率とは、切断面において割れ２４Ｃが占める面積率を意味する。割れ率は、以下のような手順で求められる。 Here, the cracking rate of the active material particles 24 </ b> A in this specification means an area ratio occupied by the cracks 24 </ b> C in the cut surface. The cracking rate is obtained by the following procedure.
まず図２に示すような三次元像をＦＩＢ−ＳＥＭを用いた積層方向の断面画像から作成する。作成した三次元像を正極活物質層２４の積層方向と直交する（正極活物質層２４の表面と平行）な９つの切断面Ｃ１〜Ｃ９（図２参照）で切断し、１０等分する。１０等分することで、三次元像は第１層Ｌ１〜第１０層Ｌ１０に分割される。 First, a three-dimensional image as shown in FIG. 2 is created from a cross-sectional image in the stacking direction using FIB-SEM. The created three-dimensional image is cut at nine cut planes C1 to C9 (see FIG. 2) perpendicular to the stacking direction of the positive electrode active material layer 24 (parallel to the surface of the positive electrode active material layer 24), and divided into 10 equal parts. By dividing into ten equal parts, the three-dimensional image is divided into the first layer L1 to the tenth layer L10.
そして正極活物質層２４の積層方向の二次元画像を１画素のピッチで複数再合成して、９つの切断面Ｃ１〜Ｃ９における断面画像を抽出する。そして、得られた画像のコントラストを調整して、２５６諧調のグレースケール画像を得る。コントラスト調整を行うと、画像が白とび又は黒潰れすることが避けられ、画像上で割れ２４Ｃが観察されない等の恣意的な要素が除かれる。 Then, a plurality of two-dimensional images in the stacking direction of the positive electrode active material layer 24 are recombined at a pitch of one pixel, and cross-sectional images at nine cut planes C1 to C9 are extracted. Then, the contrast of the obtained image is adjusted to obtain a 256-tone gray scale image. When contrast adjustment is performed, it is possible to avoid overexposure or blackout of the image, and to remove arbitrary elements such as a crack 24C not being observed on the image.
コントラスト調整は、活物質粒子２４Ａの階調の中央値が２２５以下であり、かつ、活物質粒子２４Ａの階調の中央値と活物質粒子以外の第１領域２４Ｂの階調の中央値との差が３０以上１１０以下となるようにコントラスト調整する。図３はコントラスト調整後のグレースケール画像に対応し、図４は図３の階調分布図である。図４において、最も高いピークは活物質粒子２４Ａによるものであり、ピークの左肩の部分は第１領域２４Ｂによるものである。図４における階調分布図は、上記の条件を満たす。 In contrast adjustment, the median of the gradation of the active material particles 24A is 225 or less, and the median of the gradation of the active material particles 24A and the median of the gradation of the first region 24B other than the active material particles The contrast is adjusted so that the difference is 30 or more and 110 or less. FIG. 3 corresponds to the grayscale image after contrast adjustment, and FIG. 4 is a gradation distribution diagram of FIG. In FIG. 4, the highest peak is due to the active material particles 24A, and the left shoulder portion of the peak is due to the first region 24B. The gradation distribution diagram in FIG. 4 satisfies the above conditions.
そしてグレースケール画像における割れ２４Ｃをより明確に得るために、グレースケール画像から活物質粒子２４Ａの部分を抽出する。活物質粒子２４Ａの抽出は、第１領域２４Ｂの階調をゼロ（黒色）に設定し直すことでできる。図５は、図３に示すグレースケール画像から正極活物質を抽出し直した第２グレースケール画像である。また図６は、第２グレースケール画像における階調分布図である。 Then, in order to more clearly obtain the crack 24C in the gray scale image, the portion of the active material particles 24A is extracted from the gray scale image. The extraction of the active material particles 24A can be performed by resetting the gradation of the first region 24B to zero (black). FIG. 5 is a second grayscale image obtained by re-extracting the positive electrode active material from the grayscale image shown in FIG. 3. FIG. 6 is a gradation distribution diagram in the second grayscale image.
得られた階調分布図における計測頻度の最大頻度を１００％とし、この最大頻度に対して計測頻度が２０％以下となる所定の閾値階調Ｔｈを求める。閾値階調Ｔｈ以上の階調を示す部分は図５における画像において特に白い部分である。図７は、閾値階調Ｔｈを閾値として画像を２値化した図である。図７において白い部分が割れ２４Ｃに対応し、画像から割れ２４Ｃを抽出できる。そして抽出された割れ２４Ｃの面積を、画像の全体面積で割ることで活物質粒子２４Ａの割れ率が求められる。活物質粒子２４Ａの割れ率は、複数枚（１０枚）の画像で同様の作業を行い、各画像で求められた割れ率の平均値として求められる。 The maximum frequency of the measurement frequency in the obtained gradation distribution map is set to 100%, and a predetermined threshold gradation Th is obtained at which the measurement frequency is 20% or less with respect to this maximum frequency. The part showing the gradation above the threshold gradation Th is a white part in the image in FIG. FIG. 7 is a diagram in which an image is binarized using the threshold gradation Th as a threshold. In FIG. 7, the white portion corresponds to the crack 24C, and the crack 24C can be extracted from the image. Then, the cracking rate of the active material particles 24A is obtained by dividing the area of the extracted crack 24C by the entire area of the image. The cracking rate of the active material particles 24A is obtained as an average value of the cracking rates obtained for each image by performing the same operation on a plurality of (10) images.
活物質粒子２４Ａの割れ率が最も低い切断面は、正極活物質層２４の積層方向の中央に位置することが好ましい。すなわち、活物質粒子２４Ａの割れ率が最も低い切断面は、第４層Ｌ４と第５層Ｌ５の境界である切断面Ｃ４又は第５層Ｌ５と第６層Ｌ６の境界である切断面Ｃ５であることが好ましい。 The cut surface with the lowest cracking rate of the active material particles 24 </ b> A is preferably located at the center of the positive electrode active material layer 24 in the stacking direction. That is, the cut surface with the lowest cracking rate of the active material particles 24A is the cut surface C4 that is the boundary between the fourth layer L4 and the fifth layer L5 or the cut surface C5 that is the boundary between the fifth layer L5 and the sixth layer L6. Preferably there is.
活物質粒子２４Ａは、原則として割れていないことが好ましい。一方で、正極活物質層２４の積層方向の中央における活物質粒子２４Ａが割れることより、正極活物質層２４の表面における活物質粒子２４Ａが割れることの方が、充放電し始めた際の反応のし易さが向上するという点において許容しうる。表層の活物質粒子２４Ａは割れていると、電解液と接触する活物質粒子２４Ａの表面積が大きくなる。つまり、非水電界二次電池１００の充放電し始めにおける反応のし易さが向上し、非水電界二次電池１００を短時間で充電することができる。 In principle, the active material particles 24A are preferably not cracked. On the other hand, the active material particles 24A on the surface of the positive electrode active material layer 24 are more broken than the active material particles 24A in the center in the stacking direction of the positive electrode active material layer 24. It is acceptable in terms of improving ease of handling. If the active material particles 24A in the surface layer are cracked, the surface area of the active material particles 24A that come into contact with the electrolyte increases. That is, the ease of reaction at the start of charging / discharging of the nonaqueous electric field secondary battery 100 is improved, and the nonaqueous electric field secondary battery 100 can be charged in a short time.
また活物質粒子２４Ａの割れ率が最も高い切断面における活物質粒子２４Ａの割れ率は１０％以下であることが好ましく、５％以下であることがより好ましく、３％以下であることがさらに好ましい。活物質粒子２４Ａの割れ率が、正極活物質層２４全体に渡って少ないことで、活物質粒子２４Ａの特性を十分発揮することができる。また特定の活物質粒子２４Ａに反応が集中することを避けることができ、非水電解液二次電池１００のサイクル特性を向上させることができる。 Further, the cracking rate of the active material particles 24A at the cut surface where the cracking rate of the active material particles 24A is the highest is preferably 10% or less, more preferably 5% or less, and even more preferably 3% or less. . Since the cracking rate of the active material particles 24A is small throughout the positive electrode active material layer 24, the characteristics of the active material particles 24A can be sufficiently exhibited. Further, it is possible to avoid the reaction from being concentrated on the specific active material particles 24 </ b> A, and to improve the cycle characteristics of the non-aqueous electrolyte secondary battery 100.
正極活物質層２４に用いる活物質粒子２４Ａは、イオンの吸蔵及び放出、イオンの脱離及び挿入（インターカレーション）、又は、イオンとカウンターアニオンのドープ及び脱ドープを可逆的に進行させることが可能な電極活物質を用いることができる。イオンには、例えば、リチウムイオン、ナトリウムイオン、マグネシウムイオン等を用いることができ、リチウムイオンを用いることが特に好ましい。 The active material particles 24A used for the positive electrode active material layer 24 can reversibly advance ion storage and release, ion desorption and insertion (intercalation), or ion and counteranion doping and dedoping. Possible electrode active materials can be used. As the ions, for example, lithium ions, sodium ions, magnesium ions and the like can be used, and it is particularly preferable to use lithium ions.
例えばリチウムイオン二次電池の場合、コバルト酸リチウム（ＬｉＣｏＯ２）、ニッケル酸リチウム（ＬｉＮｉＯ２）、マンガン酸リチウム（ＬｉＭｎＯ２）、リチウムマンガンスピネル（ＬｉＭｎ２Ｏ４）、及び、一般式：ＬｉＮｉｘＣｏｙＭｎｚＭａＯ２（ｘ＋ｙ＋ｚ＋ａ＝１、０≦ｘ＜１、０≦ｙ＜１、０≦ｚ＜１、０≦ａ＜１、ＭはＡｌ、Ｍｇ、Ｎｂ、Ｔｉ、Ｃｕ、Ｚｎ、Ｃｒより選ばれる１種類以上の元素）で表される複合金属酸化物、リチウムバナジウム化合物（ＬｉＶ２Ｏ５）、オリビン型ＬｉＭＰＯ４（ただし、Ｍは、Ｃｏ、Ｎｉ、Ｍｎ、Ｆｅ、Ｍｇ、Ｎｂ、Ｔｉ、Ａｌ、Ｚｒより選ばれる１種類以上の元素又はＶＯを示す）、チタン酸リチウム（Ｌｉ４Ｔｉ５Ｏ１２）、ＬｉＮｉｘＣｏｙＡｌｚＯ２（０．９＜ｘ＋ｙ＋ｚ＜１．１）等の複合金属酸化物、ポリアセチレン、ポリアニリン、ポリピロール、ポリチオフェン、ポリアセン等を、活物質粒子２４Ａとして用いることができる。 For example, in the case of a lithium ion secondary battery, lithium cobalt oxide (LiCoO 2), lithium nickelate (LiNiO 2), lithium manganate (LiMnO 2), lithium manganese spinel (LiMn 2 O 4), and the general formula: LiNi x Co y Mn z M a O 2 (x + y + z + a = 1, 0 ≦ x <1, 0 ≦ y <1, 0 ≦ z <1, 0 ≦ a <1, M is Al, Mg, Nb, Ti, Cu, Zn , One or more elements selected from Cr), lithium vanadium compound (LiV 2 O 5 ), olivine-type LiMPO 4 (where M is Co, Ni, Mn, Fe, Mg, One or more elements selected from Nb, Ti, Al, and Zr, or VO), lithium titanate (Li 4 Ti 5 O 12 ), LiNi x Co y Al z A composite metal oxide such as O 2 (0.9 <x + y + z <1.1), polyacetylene, polyaniline, polypyrrole, polythiophene, polyacene, or the like can be used as the active material particles 24A.
活物質粒子２４Ａは、上記に例示されるものの中でも、一般式ＬｉｘＭ１ｙＭ２１−ｙＯ２で表記される材料であることが好ましい。一般式において、Ｍ１はＮｉ、Ｃｏ及びＭｎからなる群から選択される少なくとも１種の金属元素であり、Ｍ２はＡｌ、Ｆｅ、Ｔｉ、Ｃｒ、Ｍｇ、Ｃｕ、Ｇａ、Ｚｎ、Ｓｎ、Ｂ、Ｖ、Ｃａ及びＳｒからなる群から選択される少なくとも１種の金属元素であり、ｘは０．０５≦ｘ≦１．２を満たし、ｙは０．３≦ｙ≦１．０を満たす。当該材料は、高いエネルギー密度を実現できる。 The active material particles 24A are preferably materials represented by the general formula Li x M1 y M2 1-y O 2 among those exemplified above. In the general formula, M1 is at least one metal element selected from the group consisting of Ni, Co, and Mn, and M2 is Al, Fe, Ti, Cr, Mg, Cu, Ga, Zn, Sn, B, V , Ca and Sr. At least one metal element selected from the group consisting of Ca and Sr, x satisfies 0.05 ≦ x ≦ 1.2, and y satisfies 0.3 ≦ y ≦ 1.0. The material can achieve a high energy density.
活物質粒子２４Ａは、中央部と外周部との間で構成する元素の組成又は組成比が異なっていることが好ましい。電解液と直接接触する外周部と中央部とでは求められる性能が異なる。例えば、外周部の反応性に優れた材料を用い、中央部に高容量材料を用いることで、充放電特性に優れ、高容量の活物質粒子２４Ａを得ることができる。また本実施形態にかかる正極活物質層２４内において、活物質粒子２４Ａの多くは割れずに存在するため、設計された特性を十分発揮できる。 The active material particles 24 </ b> A preferably have different compositions or composition ratios of elements constituting the central portion and the outer peripheral portion. The required performance differs between the outer peripheral portion and the central portion that are in direct contact with the electrolytic solution. For example, by using a material having excellent reactivity at the outer peripheral portion and using a high-capacity material at the central portion, the active material particles 24A having excellent charge / discharge characteristics and high capacity can be obtained. Further, in the positive electrode active material layer 24 according to the present embodiment, many of the active material particles 24A exist without being cracked, so that the designed characteristics can be sufficiently exhibited.
活物質粒子２４Ａは、表面にコーティング層を有していることが好ましい。コーティング層としては、例えばＺｒフルオロ錯体、グラフェン等を用いることができる。コーティング層を活物質粒子２４Ａと異なる材料で作製することで、上述のように部分ごとに求められる性能を実現することができる。またコーティング層は、活物質粒子２４Ａが割れることを抑制する。 The active material particles 24A preferably have a coating layer on the surface. As the coating layer, for example, a Zr fluoro complex, graphene, or the like can be used. By producing the coating layer with a material different from that of the active material particles 24A, the performance required for each portion as described above can be realized. In addition, the coating layer prevents the active material particles 24A from cracking.
正極活物質層２４は、活物質粒子２４Ａの他に、導電助剤、バインダー、固体電解質を含んでもよい。導電助剤として、例えば、カーボンブラック類等のカーボン粉末、カーボンナノチューブ、炭素材料、銅、ニッケル、ステンレス、鉄等の金属微粉、炭素材料及び金属微粉の混合物、ＩＴＯ等の導電性酸化物等を用いることができる。これらの中でも、カーボンブラック等の炭素材料が好ましい。活物質材料のみで十分な導電性を確保できる場合は、導電助剤を含んでいなくてもよい。 The positive electrode active material layer 24 may include a conductive additive, a binder, and a solid electrolyte in addition to the active material particles 24A. Examples of conductive assistants include carbon powders such as carbon blacks, carbon nanotubes, carbon materials, metal fine powders such as copper, nickel, stainless steel, and iron, a mixture of carbon materials and metal fine powders, and conductive oxides such as ITO. Can be used. Among these, carbon materials such as carbon black are preferable. In the case where sufficient conductivity can be ensured with only the active material, the conductive additive may not be included.
バインダーは、公知のものを用いることができる。例えば、ポリフッ化ビニリデン（ＰＶＤＦ）、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−ヘキサフルオロプロピレン共重合体（ＦＥＰ）、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合体（ＰＦＡ）、エチレン−テトラフルオロエチレン共重合体（ＥＴＦＥ）、ポリクロロトリフルオロエチレン（ＰＣＴＦＥ）、エチレン−クロロトリフルオロエチレン共重合体（ＥＣＴＦＥ）、ポリフッ化ビニル（ＰＶＦ）等のフッ素樹脂、が挙げられる。 A well-known thing can be used for a binder. For example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), ethylene-tetrafluoro Fluorine resins such as ethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), and polyvinyl fluoride (PVF).
上記の他に、バインダーとして、例えば、ビニリデンフルオライド−ヘキサフルオロプロピレン系フッ素ゴム（ＶＤＦ−ＨＦＰ系フッ素ゴム）、ビニリデンフルオライド−ヘキサフルオロプロピレン−テトラフルオロエチレン系フッ素ゴム（ＶＤＦ−ＨＦＰ−ＴＦＥ系フッ素ゴム）、ビニリデンフルオライド−ペンタフルオロプロピレン系フッ素ゴム（ＶＤＦ−ＰＦＰ系フッ素ゴム）、ビニリデンフルオライド−ペンタフルオロプロピレン−テトラフルオロエチレン系フッ素ゴム（ＶＤＦ−ＰＦＰ−ＴＦＥ系フッ素ゴム）、ビニリデンフルオライド−パーフルオロメチルビニルエーテル−テトラフルオロエチレン系フッ素ゴム（ＶＤＦ−ＰＦＭＶＥ−ＴＦＥ系フッ素ゴム）、ビニリデンフルオライド−クロロトリフルオロエチレン系フッ素ゴム（ＶＤＦ−ＣＴＦＥ系フッ素ゴム）等のビニリデンフルオライド系フッ素ゴムを用いてもよい。 In addition to the above, as the binder, for example, vinylidene fluoride-hexafluoropropylene-based fluororubber (VDF-HFP-based fluororubber), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-HFP-TFE-based) Fluororubber), vinylidene fluoride-pentafluoropropylene-based fluororubber (VDF-PFP-based fluororubber), vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-PFP-TFE-based fluororubber), vinylidene fluoride Ride-perfluoromethyl vinyl ether-tetrafluoroethylene fluorine rubber (VDF-PFMVE-TFE fluorine rubber), vinylidene fluoride-chlorotrifluoroethylene fluorine rubber (VDF-CTFE-based fluorine rubber) may be used vinylidene fluoride-based fluorine rubbers such.
固体電解質は、セパレータで挙げたものと同様のものを用いることができる。 As the solid electrolyte, the same materials as those mentioned for the separator can be used.
正極活物質層２４の密度は、２．９ｇ／ｃｍ３以上であることが好ましく、３．２ｇ／ｃｍ３以上であることがより好ましく、３．５ｇ／ｃｍ３以上であることがさらに好ましい。正極活物質層２４の密度が高密度であることで、非水電解液二次電池１００が高エネルギー密度化する。 The density of the positive electrode active material layer 24 is preferably 2.9 g / cm 3 or more, more preferably 3.2 g / cm 3 or more, and further preferably 3.5 g / cm 3 or more. Since the density of the positive electrode active material layer 24 is high, the non-aqueous electrolyte secondary battery 100 has a high energy density.
正極集電体２２と正極活物質層２４との間には、アンダーコート層を設けることが好ましい。アンダーコート層には、導電材とバインダーとを混合したものを用いることができる。アンダーコート層は、正極活物質層２４をプレスする際に緩衝剤として機能し、活物質粒子２４Ａが割れることを抑制する。 It is preferable to provide an undercoat layer between the positive electrode current collector 22 and the positive electrode active material layer 24. As the undercoat layer, a mixture of a conductive material and a binder can be used. The undercoat layer functions as a buffer when the positive electrode active material layer 24 is pressed, and prevents the active material particles 24A from cracking.
＜負極＞
負極３０は、板状（膜状）の負極集電体３２と負極活物質層３４とを有する。負極活物質層３４は、負極集電体３２の少なくとも一面に形成されている。
<Negative electrode>
The negative electrode 30 includes a plate-like (film-like) negative electrode current collector 32 and a negative electrode active material layer 34. The negative electrode active material layer 34 is formed on at least one surface of the negative electrode current collector 32.
［負極集電体］
負極集電体３２は、導電性の板材であればよく、正極集電体２２と同様のものを用いることができる。
[Negative electrode current collector]
The negative electrode current collector 32 may be any conductive plate material, and the same material as the positive electrode current collector 22 can be used.
［負極活物質層］
負極活物質層３４は、負極活物質を含む。また必要に応じて、導電材、バインダー、固体電解質を含んでもよい。
[Negative electrode active material layer]
The negative electrode active material layer 34 includes a negative electrode active material. Moreover, you may contain a electrically conductive material, a binder, and a solid electrolyte as needed.
負極活物質は、イオンを吸蔵・放出可能な化合物であればよく、公知の非水電解液二次電池に用いられる負極活物質を使用できる。負極活物質としては、例えば、金属リチウム等のアルカリ又はアルカリ土類金属、イオンを吸蔵・放出可能な黒鉛（天然黒鉛、人造黒鉛）、カーボンナノチューブ、難黒鉛化炭素、易黒鉛化炭素、低温度焼成炭素等の炭素材料、アルミニウム、シリコン、スズ等のリチウム等の金属と化合することのできる金属、ＳｉＯｘ（０＜ｘ＜２）、二酸化スズ等の酸化物を主体とする非晶質の化合物、チタン酸リチウム（Ｌｉ４Ｔｉ５Ｏ１２）等を含む粒子が挙げられる。 The negative electrode active material should just be a compound which can occlude / release ion, and the negative electrode active material used for a well-known non-aqueous-electrolyte secondary battery can be used. Examples of the negative electrode active material include alkali or alkaline earth metals such as lithium metal, graphite capable of occluding and releasing ions (natural graphite, artificial graphite), carbon nanotube, non-graphitizable carbon, graphitizable carbon, low temperature Carbon materials such as calcined carbon, metals that can be combined with metals such as lithium such as aluminum, silicon, and tin, amorphous materials mainly composed of oxides such as SiO x (0 <x <2) and tin dioxide Examples thereof include particles containing a compound, lithium titanate (Li 4 Ti 5 O 12 ), and the like.
負極活物質層に負極活物質を含まずに、集電体のみであってもよい。この場合、充電時に、金属リチウム等のアルカリ又はアルカリ土類金属が析出し、負極活物質が形成される。 The negative electrode active material layer may contain only the current collector without including the negative electrode active material. In this case, at the time of charging, an alkali or alkaline earth metal such as metallic lithium is deposited, and a negative electrode active material is formed.
導電材及びバインダーは、正極２０と同様のものを用いることができる。負極に用いるバインダーは正極に挙げたものの他に、例えば、セルロース、スチレン・ブタジエンゴム、エチレン・プロピレンゴム、ポリイミド樹脂、ポリアミドイミド樹脂、アクリル樹脂等を用いてもよい。 As the conductive material and the binder, the same materials as those for the positive electrode 20 can be used. The binder used for the negative electrode may be, for example, cellulose, styrene / butadiene rubber, ethylene / propylene rubber, polyimide resin, polyamideimide resin, acrylic resin, etc. in addition to those listed for the positive electrode.
固体電解質は、セパレータで挙げたものと同様のものを用いることができる。 As the solid electrolyte, the same materials as those mentioned for the separator can be used.
（端子）
端子６０、６２は、それぞれ正極２０と負極３０とに接続されている。正極２０に接続された端子６０は正極端子であり、負極３０に接続された端子６２は負極端子である。端子６０、６２は、外部との電気的接続を担う。端子６０、６２は、アルミニウム、ニッケル、銅等の導電材料から形成されている。接続方法は、溶接でもネジ止めでもよい。端子６０、６２は短絡を防ぐために、絶縁テープで保護することが好ましい。
(Terminal)
The terminals 60 and 62 are connected to the positive electrode 20 and the negative electrode 30, respectively. The terminal 60 connected to the positive electrode 20 is a positive electrode terminal, and the terminal 62 connected to the negative electrode 30 is a negative electrode terminal. The terminals 60 and 62 are responsible for electrical connection with the outside. The terminals 60 and 62 are made of a conductive material such as aluminum, nickel, or copper. The connection method may be welding or screwing. The terminals 60 and 62 are preferably protected with an insulating tape in order to prevent a short circuit.
（外装体）
外装体５０は、その内部に発電素子４０及び電解液を密封する。外装体５０は、電解液の外部への漏出や、外部からの非水電解液二次電池１００内部への水分等の侵入等を抑止できる物であれば特に限定されない。
(Exterior body)
The exterior body 50 seals the power generating element 40 and the electrolytic solution therein. The outer package 50 is not particularly limited as long as it can prevent leakage of the electrolytic solution to the outside and entry of moisture or the like into the nonaqueous electrolyte secondary battery 100 from the outside.
例えば図１に示すように、外装体５０として金属箔を高分子膜で両側からコーティングした金属ラミネートフィルムを用いてもよい。図１に示す外装体５０は、金属箔５２と、金属箔５２の各面に積層された樹脂層５４と、を有する。 For example, as shown in FIG. 1, a metal laminate film in which a metal foil is coated with a polymer film from both sides may be used as the exterior body 50. An exterior body 50 illustrated in FIG. 1 includes a metal foil 52 and a resin layer 54 laminated on each surface of the metal foil 52.
金属箔５２としては例えばアルミ箔を用いることができる。樹脂層５４には、ポリプロピレン等の高分子膜を利用できる。樹脂層５４を構成する材料は、内側と外側とで異なっていてもよい。例えば、外側の材料としては融点の高い高分子、例えば、ポリエチレンテレフタレート（ＰＥＴ）、ポリアミド（ＰＡ）等を用い、内側の高分子膜の材料としてはポリエチレン（ＰＥ）、ポリプロピレン（ＰＰ）等を用いることができる。 As the metal foil 52, for example, an aluminum foil can be used. A polymer film such as polypropylene can be used for the resin layer 54. The material constituting the resin layer 54 may be different between the inside and the outside. For example, a polymer having a high melting point such as polyethylene terephthalate (PET) or polyamide (PA) is used as the outer material, and polyethylene (PE) or polypropylene (PP) is used as the material of the inner polymer film. be able to.
（電解液）
電解液は、外装体５０内に封入され、発電素子４０に含浸する。
電解液には、リチウム塩等を含む電解質溶液（電解質水溶液、有機溶媒を使用する電解質溶液） を使用することができる。ただし、電解質水溶液は電気化学的に分解電圧が低いため、充電時の耐用電圧が低く制限される。そのため、有機溶媒を使用する電解質溶液（非水電解液）であることが好ましい。
(Electrolyte)
The electrolytic solution is enclosed in the outer package 50 and impregnated in the power generation element 40.
As the electrolytic solution, an electrolyte solution containing lithium salt or the like (electrolyte aqueous solution, electrolyte solution using an organic solvent) can be used. However, since the electrolytic aqueous solution has a low decomposition voltage electrochemically, the withstand voltage during charging is limited to be low. Therefore, an electrolyte solution (nonaqueous electrolyte) using an organic solvent is preferable.
非水電解液は、非水溶媒に電解質が溶解されており、非水溶媒として環状カーボネートと、鎖状カーボネートと、を含有してもよい。 The nonaqueous electrolytic solution has an electrolyte dissolved in a nonaqueous solvent, and may contain a cyclic carbonate and a chain carbonate as a nonaqueous solvent.
環状カーボネートとしては、電解質を溶媒和することができるものを用いることができる。例えば、エチレンカーボネート、プロピレンカーボネート及びブチレンカーボネート等を用いることができる。環状カーボネートは、プロピレンカーボネートを少なくとも含むことが好ましい。 As cyclic carbonate, what can solvate electrolyte can be used. For example, ethylene carbonate, propylene carbonate, butylene carbonate, or the like can be used. The cyclic carbonate preferably contains at least propylene carbonate.
鎖状カーボネートは、環状カーボネートの粘性を低下させることができる。例えば、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が挙げられる。その他、酢酸メチル、酢酸エチル、プロピオン酸メチル、プロピオン酸エチル、プロピオン酸プロピル、γ−ブチロラクトン、１，２−ジメトキシエタン、１，２−ジエトキシエタン等を混合して使用してもよい。 The chain carbonate can reduce the viscosity of the cyclic carbonate. Examples thereof include diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate. In addition, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, 1,2-dimethoxyethane, 1,2-diethoxyethane and the like may be used in combination.
非水溶媒中の環状カーボネートと鎖状カーボネートの割合は体積にして１：９〜１：１にすることが好ましい。 The ratio of the cyclic carbonate and the chain carbonate in the non-aqueous solvent is preferably 1: 9 to 1: 1 by volume.
電解質としては、金属塩を用いることができる。例えば、ＬｉＰＦ６、ＬｉＣｌＯ４、ＬｉＢＦ４、ＬｉＣＦ３ＳＯ３、ＬｉＣＦ３ＣＦ２ＳＯ３、ＬｉＣ（ＣＦ３ＳＯ２）３、ＬｉＮ（ＣＦ３ＳＯ２）２、ＬｉＮ（ＣＦ３ＣＦ２ＳＯ２）２、ＬｉＮ（ＣＦ３ＳＯ２）（Ｃ４Ｆ９ＳＯ２）、ＬｉＮ（ＣＦ３ＣＦ２ＣＯ）２、ＬｉＢＯＢ等のリチウム塩が使用できる。なお、これらのリチウム塩は１種を単独で使用してもよく、２種以上を併用してもよい。特に、電離度の観点から、電解質としてＬｉＰＦ６を含むことが好ましい。 As the electrolyte, a metal salt can be used. For example, LiPF 6 , LiClO 4 , LiBF 4 , LiCF 3 SO 3 , LiCF 3 CF 2 SO 3 , LiC (CF 3 SO 2 ) 3 , LiN (CF 3 SO 2 ) 2 , LiN (CF 3 CF 2 SO 2 ) 2 , LiN (CF 3 SO 2 ) (C 4 F 9 SO 2 ), LiN (CF 3 CF 2 CO) 2 , lithium salts such as LiBOB can be used. In addition, these lithium salts may be used individually by 1 type, and may use 2 or more types together. In particular, from the viewpoint of the degree of ionization, it is preferable to include LiPF 6 as the electrolyte.
ＬｉＰＦ６を非水溶媒に溶解する際は、非水電解液中の電解質の濃度を、０．５〜２．０ｍｏｌ／Ｌに調整することが好ましい。電解質の濃度が０．５ｍｏｌ／Ｌ以上であると、非水電解液のリチウムイオン濃度を充分に確保することができ、充放電時に十分な容量が得られやすい。また、電解質の濃度が２．０ｍｏｌ／Ｌ以内に抑えることで、非水電解液の粘度上昇を抑え、リチウムイオンの移動度を充分に確保することができ、充放電時に十分な容量が得られやすくなる。 When LiPF 6 is dissolved in a non-aqueous solvent, the concentration of the electrolyte in the non-aqueous electrolyte is preferably adjusted to 0.5 to 2.0 mol / L. When the concentration of the electrolyte is 0.5 mol / L or more, the lithium ion concentration of the nonaqueous electrolytic solution can be sufficiently secured, and a sufficient capacity can be easily obtained during charging and discharging. Moreover, by suppressing the electrolyte concentration to within 2.0 mol / L, it is possible to suppress an increase in the viscosity of the non-aqueous electrolyte, to sufficiently secure the mobility of lithium ions, and to obtain a sufficient capacity during charging and discharging. It becomes easy.
ＬｉＰＦ６をその他の電解質と混合する場合にも、非水電解液中のリチウムイオン濃度が０．５〜２．０ｍｏｌ／Ｌに調整することが好ましく、ＬｉＰＦ６からのリチウムイオン濃度がその５０ｍｏｌ％以上含まれることがさらに好ましい。 Even when LiPF 6 is mixed with another electrolyte, the lithium ion concentration in the non-aqueous electrolyte is preferably adjusted to 0.5 to 2.0 mol / L, and the lithium ion concentration from LiPF 6 is 50 mol%. More preferably, it is contained.
非水溶媒の代わりに、アルカリ金属塩を溶解するイオン液体を用いてもよい。 Instead of the non-aqueous solvent, an ionic liquid that dissolves the alkali metal salt may be used.
イオン液体は、例えば、カチオンに、イミダゾリウム塩類・ピリジニウム塩類等のアンモニウム系カチオンやホスホニウム系カチオン等を、アニオンに、臭化物イオンやトリフラート等のハロゲン系アニオン、テトラフェニルボレート等のホウ素系アニオン、ヘキサフルオロホスフェート等のリン系アニオンを用いたものが挙げられる。 The ionic liquid includes, for example, ammonium cations such as imidazolium salts and pyridinium salts and phosphonium cations as cations, halogen anions such as bromide ions and triflate, boron anions such as tetraphenylborate, hexa The thing using phosphorus-type anions, such as a fluorophosphate, is mentioned.
セパレータ、正極、負極に電解液を含侵させる代わりに、セパレータの代わりに固体電解質を用い、正極、負極に固体電解質を添加することにより、固体電解質電池としてもよい。 Instead of impregnating the separator, the positive electrode, and the negative electrode with the electrolytic solution, a solid electrolyte may be used by using a solid electrolyte instead of the separator and adding the solid electrolyte to the positive electrode and the negative electrode.
「非水電解液二次電池の製造方法」
まず正極２０を作製する。活物質粒子２４Ａ、バインダー及び溶媒を混合して、ペースト状の正極スラリーを作製する。必要に応じ導電助剤を更に加えても良い。溶媒としては例えば、水、Ｎ−メチル−２−ピロリドン、Ｎ，Ｎ−ジメチルホルムアミド等を用いることができる。
"Method for manufacturing non-aqueous electrolyte secondary battery"
First, the positive electrode 20 is produced. Active material particles 24A, a binder, and a solvent are mixed to produce a paste-like positive electrode slurry. You may add a conductive support agent further as needed. As the solvent, for example, water, N-methyl-2-pyrrolidone, N, N-dimethylformamide or the like can be used.
活物質粒子２４Ａの粒径は揃えることが好ましい。例えば、篩等に欠けて粒度分布の範囲を狭める。活物質粒子２４Ａの粒径が揃うことで、プレス時に局所的に圧力が加わることを抑制し、活物質粒子２４Ａの割れを抑制できる。 The particle diameters of the active material particles 24A are preferably uniform. For example, the range of the particle size distribution is narrowed by lacking a sieve or the like. When the particle diameters of the active material particles 24A are uniform, it is possible to suppress local pressure from being applied during pressing, and to suppress cracking of the active material particles 24A.
また活物質粒子２４Ａの表面には、コーティングを施すことが好ましい。表面コートは、コーティング液中に活物質粒子２４Ａを投入し、熱処理することで得ることができる。活物質粒子２４Ａの表面にコーティング層が形成されることで、活物質粒子２４Ａの割れを抑制できる。 Moreover, it is preferable to coat the surface of the active material particles 24A. The surface coat can be obtained by introducing the active material particles 24A into the coating liquid and performing a heat treatment. By forming the coating layer on the surface of the active material particles 24A, the active material particles 24A can be prevented from cracking.
正極スラリーを構成するこれらの成分の混合方法は特に制限されず、混合順序もまた特に制限されない。上記塗料を、正極集電体１Ａに塗布する。塗布方法としては、特に制限はなく、通常電極を作製する場合に採用される方法を用いることができる。例えば、スリットダイコート法、ドクターブレード法が挙げられる。 The mixing method of these components constituting the positive electrode slurry is not particularly limited, and the mixing order is not particularly limited. The paint is applied to the positive electrode current collector 1A. There is no restriction | limiting in particular as an application | coating method, The method employ | adopted when producing an electrode normally can be used. Examples thereof include a slit die coating method and a doctor blade method.
続いて、正極集電体２２上に塗布された正極スラリー中の溶媒を除去する。除去方法は特に限定されない。例えば、正極スラリーが塗布された正極集電体２２を、８０℃〜１５０℃の雰囲気下で乾燥させればよい。 Subsequently, the solvent in the positive electrode slurry applied on the positive electrode current collector 22 is removed. The removal method is not particularly limited. For example, the positive electrode current collector 22 coated with the positive electrode slurry may be dried in an atmosphere of 80 ° C. to 150 ° C.
得られた塗膜をプレスして、正極活物質層２４を高密度化する。プレスの手段は、例えばロールプレス機、静水圧プレス機等を用いることができる。静水圧プレス機を用いると、正極活物質層２４に等方的な圧力が加わるため、活物質粒子２４Ａが割れにくくなる。 The obtained coating film is pressed to increase the density of the positive electrode active material layer 24. As a pressing means, for example, a roll press machine, an isostatic press machine or the like can be used. When an isostatic press is used, isotropic pressure is applied to the positive electrode active material layer 24, so that the active material particles 24A are difficult to break.
プレスは、複数回に分けて行うことが好ましい。正極活物質層２４に一度に大きな力が加わることを避けることができ、活物質粒子２４Ａの割れを抑制できる。 The pressing is preferably performed in a plurality of times. It is possible to avoid applying a large force to the positive electrode active material layer 24 at a time, and it is possible to suppress cracking of the active material particles 24A.
また正極活物質層２４は、重層塗布してもよい。重層塗布とは、正極スラリーの塗布、乾燥、プレスの工程を複数回に分けて行うことを意味する。正極活物質層２４を重層塗布すると、活物質粒子２４Ａの割れを抑制できる。 Further, the positive electrode active material layer 24 may be applied in multiple layers. The multilayer coating means that the positive electrode slurry coating, drying, and pressing steps are performed in multiple steps. When the positive electrode active material layer 24 is applied in multiple layers, cracking of the active material particles 24A can be suppressed.
また正極集電体２２上に正極活物質層２４を形成する前に、アンダーコート層を積層してもよい。アンダーコート層を設けることで、活物質粒子２４Ａの割れを抑制できる。アンダーコート層は、導電助剤とバインダーとを溶媒に混合して、ペースト状のスラリーを作製し、乾燥させることで作製できる。溶媒としては例えば、水、Ｎ−メチル−２−ピロリドン、Ｎ，Ｎ−ジメチルホルムアミド等を用いることができる。 Further, an undercoat layer may be laminated before forming the positive electrode active material layer 24 on the positive electrode current collector 22. By providing the undercoat layer, cracking of the active material particles 24A can be suppressed. The undercoat layer can be produced by mixing a conductive additive and a binder in a solvent to produce a paste-like slurry and drying it. As the solvent, for example, water, N-methyl-2-pyrrolidone, N, N-dimethylformamide or the like can be used.
次いで、負極３０を作製する。負極３０は、正極２０と同様に作製できる。負極３０は、負極用の活物質粒子、バインダー及び溶媒を混合して、ペースト状の負極スラリーを作製し、負極スラリーを負極集電体３２に塗布し、乾燥することで得られる。 Next, the negative electrode 30 is produced. The negative electrode 30 can be produced in the same manner as the positive electrode 20. The negative electrode 30 is obtained by mixing negative electrode active material particles, a binder, and a solvent to prepare a paste-like negative electrode slurry, applying the negative electrode slurry to the negative electrode current collector 32, and drying.
次いで、作製した正極２０及び負極３０の間にセパレータ１０が位置するようにこれらを積層して、発電素子４０を作製する。発電素子４０が捲回体の場合は、正極２０、負極３０及びセパレータ１０の一端側を軸として、これらを捲回する。 Next, these are laminated so that the separator 10 is positioned between the produced positive electrode 20 and negative electrode 30, and the power generating element 40 is produced. When the power generating element 40 is a wound body, the positive electrode 20, the negative electrode 30, and the separator 10 are wound around one end side as an axis.
最後に、発電素子４０を外装体５０に封入する。非水電解液は外装体５０内に注入する。非水電解液を注入後に減圧、加熱等を行うことで、発電素子４０内に非水電解液が含浸する。外装体５０は、熱等を加えて封止する。 Finally, the power generation element 40 is sealed in the exterior body 50. The nonaqueous electrolytic solution is injected into the outer package 50. The power generation element 40 is impregnated with the nonaqueous electrolytic solution by performing decompression, heating, or the like after injecting the nonaqueous electrolytic solution. The exterior body 50 is sealed by applying heat or the like.
上述のように、本実施形態にかかる正極２０は、正極活物質層２４内の活物質粒子２４Ａの割れ率が少ない。そのため活物質粒子２４Ａは、設計された性能を十分発揮する。また活物質粒子２４Ａが割れないことで、正極活物質層２４内における活物質粒子２４Ａの性能が均質化され、特定の活物質粒子２４Ａに反応が集中することを避けることができ、非水電解液二次電池１００のサイクル特性を向上することができる。 As described above, the positive electrode 20 according to this embodiment has a low cracking rate of the active material particles 24 </ b> A in the positive electrode active material layer 24. Therefore, the active material particles 24A sufficiently exhibit the designed performance. Further, since the active material particles 24A are not cracked, the performance of the active material particles 24A in the positive electrode active material layer 24 is homogenized, and the reaction can be prevented from concentrating on the specific active material particles 24A. The cycle characteristics of the liquid secondary battery 100 can be improved.
以上、本発明の実施形態について図面を参照して詳述したが、各実施形態における各構成及びそれらの組み合わせ等は一例であり、本発明の趣旨から逸脱しない範囲内で、構成の付加、省略、置換、及びその他の変更が可能である。 Although the embodiments of the present invention have been described in detail with reference to the drawings, the configurations and combinations of the embodiments in the embodiments are examples, and the addition and omission of configurations are within the scope not departing from the gist of the present invention. , Substitutions, and other changes are possible.
「実施例１」
実施例１では、正極を重層塗布により作製した。
"Example 1"
In Example 1, the positive electrode was produced by multilayer coating.
（スラリーの作製）
まず下層用正極スラリーとして、９６重量％のＬｉＮｉ０．８５Ｃｏ０．１０Ａｌ０．０５Ｏ２（活物質粒子）と、２重量％のカーボンブラック（導電助剤）と、０．５重量％のグラファイト（導電助剤）と、１．５重量％のポリフッ化ビニリデン（ＰＶＤＦ：バインダー）と、Ｎ−メチル−２−ピロリドン（溶媒）とを混合分散させて、ペースト状の正極スラリーを作製した。
(Preparation of slurry)
First, as a positive electrode slurry for the lower layer, 96% by weight of LiNi 0.85 Co 0.10 Al 0.05 O 2 (active material particles), 2% by weight of carbon black (conductive aid), 0.5% by weight Graphite (conducting aid), 1.5% by weight of polyvinylidene fluoride (PVDF: binder), and N-methyl-2-pyrrolidone (solvent) were mixed and dispersed to prepare a paste-like positive electrode slurry. .
また上層用正極スラリーとして、９４重量％のＬｉＮｉ０．８５Ｃｏ０．１０Ａｌ０．０５Ｏ２（活物質粒子）と、３重量％のカーボンブラック（導電助剤）と、０．７５重量％のグラファイト（導電助剤）と、２．２５重量％のＰＶＤＦ（バインダー）と、Ｎ−メチル−２−ピロリドン（溶媒）とを混合分散させて、ペースト状の正極スラリーを作製した。 Further, as the positive electrode slurry for the upper layer, 94 wt% LiNi 0.85 Co 0.10 Al 0.05 O 2 (active material particles), 3 wt% carbon black (conducting aid), and 0.75 wt% Graphite (conducting aid), 2.25 wt% PVDF (binder), and N-methyl-2-pyrrolidone (solvent) were mixed and dispersed to prepare a paste-like positive electrode slurry.
（正極の作製）
得られた下層用正極スラリーを厚さ２０μｍのアルミニウム箔の両面に、活物質粒子の塗布量が１１．０ｍｇ／ｃｍ２となるように、コンマロールコーターを用いて均一に塗布した。次いで、乾燥炉内にて、１１０℃の大気雰囲気下でＮ−メチル−２−ピロリドンを乾燥させた。そして、得られた下層をロールプレス機によってプレスし、下層を正極集電体の両面に圧着させた。下層の密度は、４．２ｇ／ｃｍ３であった。
(Preparation of positive electrode)
The obtained lower layer positive electrode slurry was uniformly applied to both surfaces of an aluminum foil having a thickness of 20 μm using a comma roll coater so that the amount of active material particles applied was 11.0 mg / cm 2 . Next, N-methyl-2-pyrrolidone was dried in an air atmosphere at 110 ° C. in a drying furnace. And the obtained lower layer was pressed with the roll press machine, and the lower layer was crimped | bonded to both surfaces of the positive electrode electrical power collector. The density of the lower layer was 4.2 g / cm 3 .
次いで、得られた上層用正極スラリーを下層上に、活物質粒子の塗布量が１１．０ｍｇ／ｃｍ２となるように、コンマロールコーターを用いて均一に塗布した。次いで、乾燥炉内にて、１１０℃の大気雰囲気下でＮ−メチル−２−ピロリドン溶媒を乾燥させた。得られた上層をロールプレス機によってプレスし、上層を下層の両面に圧着させた。上層を積層後の正極活物質層の平均密度は、３．６ｇ／ｃｍ３となった。 Next, the obtained positive electrode slurry for the upper layer was uniformly applied on the lower layer using a comma roll coater so that the amount of active material particles applied was 11.0 mg / cm 2 . Next, the N-methyl-2-pyrrolidone solvent was dried in an air atmosphere at 110 ° C. in a drying furnace. The obtained upper layer was pressed by a roll press, and the upper layer was pressure-bonded to both surfaces of the lower layer. The average density of the positive electrode active material layer after the upper layer was laminated was 3.6 g / cm 3 .
（負極の作製）
９４重量％のリチウムイオン電池グレードの黒鉛（負極活物質）と、２重量％のアセチレンブラック（導電助剤）と、４重量％のＰＶＤＦ（バインダー）と、Ｎ−メチル−２−ピロリドン（溶媒）とを混合分散させて、ペースト状の負極スラリーを作製した。負極スラリーを厚さ１０μｍの電界銅箔の両面に塗布した。塗布量は、正極の活物質粒子の塗布量とバランスがとれるように、充電時のリチウムイオンの受け取り量を考慮した。塗布後に、１００℃で乾燥させ、溶媒を除去し、ロールプレスにより加圧成形した。
(Preparation of negative electrode)
94% by weight of lithium ion battery grade graphite (negative electrode active material), 2% by weight of acetylene black (conductive aid), 4% by weight of PVDF (binder), and N-methyl-2-pyrrolidone (solvent) Were mixed and dispersed to prepare a paste-like negative electrode slurry. The negative electrode slurry was applied to both sides of a 10 μm thick electrolytic copper foil. The amount of coating was determined in consideration of the amount of lithium ions received during charging so as to balance the amount of coating of the positive electrode active material particles. After coating, the film was dried at 100 ° C., the solvent was removed, and pressure molding was performed by a roll press.
（セルの作製）
作製した負極と正極とを、所定の形状に打ち抜き、厚さ１６μｍのポリプロピレン製のセパレータを介して交互に積層し、負極３枚と正極２枚とを積層することで積層体を作製した。ニッケル製の負極端子は、積層体の負極において、負極活物質層を設けていない銅箔の突起端部に取り付けた。またアルミニウム製の正極端子は、積層体の正極においては、正極活物質層を設けていないアルミニウム箔の突起端部に取り付けた。負極端子及び正極端子は、超音波溶接機によって取付けた。
(Manufacture of cells)
The produced negative electrode and positive electrode were punched into a predetermined shape, laminated alternately via a polypropylene separator having a thickness of 16 μm, and a laminate was produced by laminating three negative electrodes and two positive electrodes. The negative electrode terminal made from nickel was attached to the protrusion edge part of the copper foil which is not providing the negative electrode active material layer in the negative electrode of a laminated body. Moreover, the positive electrode terminal made from aluminum was attached to the protrusion edge part of the aluminum foil which is not providing the positive electrode active material layer in the positive electrode of a laminated body. The negative electrode terminal and the positive electrode terminal were attached by an ultrasonic welding machine.
積層体を、アルミラミネートフィルムの外装体内に挿入して周囲の１箇所を除いてヒートシールすることにより開口部を形成した。外装体内には、ＥＣとＥＭＣとＤＥＣとが体積比３：５：２の割合で配合された溶媒と、リチウム塩として１．５Ｍ（ｍｏｌ／Ｌ）のＬｉＰＦ６が添加された非水電解液と、を注入した。そして、残りの１箇所を真空シール機によって減圧しながらヒートシールで密封し、実施例１に係るリチウムイオン二次電池を作製した。 The laminated body was inserted into the outer body of the aluminum laminated film and heat sealed with the exception of one surrounding area to form an opening. A nonaqueous electrolyte solution in which EC, EMC, and DEC are mixed in a volume ratio of 3: 5: 2 and 1.5 M (mol / L) LiPF 6 as a lithium salt is added to the exterior body. And injected. And the remaining 1 place was sealed by heat sealing, reducing pressure with a vacuum sealer, and the lithium ion secondary battery which concerns on Example 1 was produced.
（電池の構造解析と評価）
作製したリチウムイオン電池は、初期特性評価後に、サイクル特性評価と正極の構造解析に供した。サイクル特性評価は、１Ｃ／１Ｃの充放電サイクルで評価を行った。
(Battery structure analysis and evaluation)
The prepared lithium ion battery was subjected to cycle characteristic evaluation and positive electrode structural analysis after initial characteristic evaluation. The cycle characteristics were evaluated with a charge / discharge cycle of 1C / 1C.
（充放電サイクル特性の測定）
サイクル特性は、二次電池充放電試験装置を用いて行った。電圧範囲は、４．３Ｖから３．０Ｖまでとした。初回の充電のみ０．２Ｃ定電流充電にて行い、放電は１Ｃで行った。充電は定電流定電圧で行った。１．０Ｃの電流値で充電し、４．３Ｖに到達後、１Ｃ電流値の５％の電流値になったときに充電を終了した。その後、１．０Ｃでの電流値で放電する条件においてサイクル特性を測定した。なお、充放電サイクル特性は容量維持率（％）として評価した。容量維持率（％）は、１サイクル目の放電容量を初期放電容量とし、初期放電容量に対する各サイクル数における放電容量の割合である。容量維持率（％）は、以下の数式（１）で表される。
容量維持率（％）＝（「１サイクル目の放電容量」／「各サイクル数における放電容量」）×１００ ・・・（１）
(Measurement of charge / discharge cycle characteristics)
The cycle characteristics were measured using a secondary battery charge / discharge test apparatus. The voltage range was 4.3V to 3.0V. Only the first charge was performed by constant current charging at 0.2 C, and discharging was performed at 1 C. Charging was performed at a constant current and a constant voltage. The battery was charged at a current value of 1.0 C, and after reaching 4.3 V, charging was terminated when the current value reached 5% of the 1 C current value. Thereafter, the cycle characteristics were measured under the condition of discharging at a current value of 1.0 C. The charge / discharge cycle characteristics were evaluated as capacity retention rate (%). The capacity retention rate (%) is the ratio of the discharge capacity at each cycle number to the initial discharge capacity, where the discharge capacity at the first cycle is the initial discharge capacity. The capacity retention rate (%) is expressed by the following mathematical formula (1).
Capacity maintenance rate (%) = (“discharge capacity at the first cycle” / “discharge capacity at each cycle number”) × 100 (1)
なお１Ｃとは公称容量値の容量を有する電池セルを定電流充電、または定電流放電して、ちょうど１時間で充放電が終了となる電流値のことである。容量維持率が高いほど、充放電サイクル特性が良好であることを意味する。 Note that 1C is a current value at which charging / discharging is completed in exactly one hour after a constant current charge or constant current discharge is performed on a battery cell having a nominal capacity value. A higher capacity retention rate means better charge / discharge cycle characteristics.
実施例１で作製したリチウムイオン二次電池は、上記の条件によって充放電を繰り返し、５００サイクル後の容量維持率を充放電サイクル特性として評価した。この結果を表１にまとめた。 The lithium ion secondary battery produced in Example 1 was repeatedly charged and discharged under the above conditions, and the capacity retention rate after 500 cycles was evaluated as charge / discharge cycle characteristics. The results are summarized in Table 1.
（正極の構造解析）
正極の構造解析は、充放電を行った後の完全放電状態のリチウムイオン電池を乾燥Ａｒ雰囲気下のグローブボックスで、分解し、正極を分離した。そして、ＤＭＣ（ジメチルカーボネート）で十分洗浄後、真空乾燥した。乾燥した正極を所定のサイズに切り出した後、ＦＩＢ−ＳＥＭ（ＦＥＩ社製Ｖｅｒｓａ３Ｄ）を用いて積層方向の断面を２００枚撮影した。ＦＩＢ−ＳＥＭ像は、加速電圧３０ｋＶ、電流値４ｎＡ、加工幅８０μｍ、加工奥行き５０μｍ、奥行ピッチ０．２５μｍの条件で撮影した。
(Structural analysis of positive electrode)
In the structural analysis of the positive electrode, the lithium ion battery in a fully discharged state after charge / discharge was disassembled in a glove box in a dry Ar atmosphere to separate the positive electrode. Then, it was sufficiently washed with DMC (dimethyl carbonate) and then vacuum-dried. After the dried positive electrode was cut into a predetermined size, 200 cross-sections in the stacking direction were photographed using FIB-SEM (Versa3D manufactured by FEI). The FIB-SEM image was taken under the conditions of an acceleration voltage of 30 kV, a current value of 4 nA, a processing width of 80 μm, a processing depth of 50 μm, and a depth pitch of 0.25 μm.
そして撮影した画像を、画像解析ソフトＩｍａｇｅＪで三次元化し、上述の手順に従って、各切断面Ｃ１〜Ｃ９における割れ率を測定した。割れ率が最大を示す切断面は、第５層Ｌ５と第６層Ｌ６との境界の切断面Ｃ５であり、その切断面における割れ率は２．１％であった。また割れ率が最小を示す切断面は、第３層Ｌ３と第４層Ｌ４との境界の切断面Ｃ３であり、その切断面における割れ率は０．４％であった。この結果を表１にまとめた。 Then, the photographed image was three-dimensionalized with image analysis software ImageJ, and the crack rate at each of the cut surfaces C1 to C9 was measured according to the above-described procedure. The cut surface having the maximum crack rate was the cut surface C5 at the boundary between the fifth layer L5 and the sixth layer L6, and the crack rate at the cut surface was 2.1%. The cut surface with the smallest crack rate was the cut surface C3 at the boundary between the third layer L3 and the fourth layer L4, and the crack rate at the cut surface was 0.4%. The results are summarized in Table 1.
「実施例２」
実施例２は、正極を重層塗布せずに、正極集電体２２と正極活物質層２４との間にアンダーコート層を設けた点が実施例１と異なる。
"Example 2"
Example 2 is different from Example 1 in that an undercoat layer was provided between the positive electrode current collector 22 and the positive electrode active material layer 24 without applying a positive electrode to the multilayer.
（アンダーコートの作製）
カーボンブラック（導電助剤）とＰＶＤＦ（バインダー）とを質量比で２：４として、Ｎ−メチル−２−ピロリドンに分散させてアンダーコートスラリーを作製した。得られたアンダーコートスラリーを厚さ２０μｍのアルミニウム箔の両面に、コンマロールコーターを用いて塗布した。そして、乾燥炉内にて１１０℃の大気雰囲気下でアンダーコートスラリーを乾燥させ、アンダーコート層を形成した。アンダーコート層の乾燥後の厚さは２μｍであった。
(Preparation of undercoat)
An undercoat slurry was prepared by dispersing carbon black (conducting aid) and PVDF (binder) in N-methyl-2-pyrrolidone in a mass ratio of 2: 4. The obtained undercoat slurry was applied to both sides of an aluminum foil having a thickness of 20 μm using a comma roll coater. Then, the undercoat slurry was dried in an air atmosphere at 110 ° C. in a drying furnace to form an undercoat layer. The thickness of the undercoat layer after drying was 2 μm.
（正極の作製）
実施例１における下層と同じ条件でペースト状の正極スラリーを作製した。アンダーコート層を有するアルミニウム箔の両面に、活物質の塗布量が２２．０ｍｇ／ｃｍ２となるように、コンマロールコーターを用いて、正極スラリーを均一に塗布した。次いで、乾燥炉内にて、１１０℃の大気雰囲気下で正極スラリーを乾燥させた。ロールプレス機によって、正極活物質層を正極集電体の両面に圧着させた。正極活物質層の密度は３．６ｇ／ｃｍ３だった。
(Preparation of positive electrode)
A paste-like positive electrode slurry was produced under the same conditions as in the lower layer in Example 1. The positive electrode slurry was uniformly applied to both surfaces of the aluminum foil having an undercoat layer using a comma roll coater so that the active material application amount was 22.0 mg / cm 2 . Next, the positive electrode slurry was dried in an air atmosphere at 110 ° C. in a drying furnace. The positive electrode active material layer was pressed onto both sides of the positive electrode current collector by a roll press. The density of the positive electrode active material layer was 3.6 g / cm 3 .
負極の作製、セルの作製、電池のサイクル特性の評価及び正極の構造解析は、実施例１と同様に行った。割れ率が最大を示す切断面は、第１層Ｌ１と第２層Ｌ２との境界の切断面Ｃ１であり、その切断面における割れ率は２．９％であった。また割れ率が最小を示す切断面は、第６層Ｌ６と第７層Ｌ７との境界の切断面Ｃ６であり、その切断面における割れ率は０．７％であった。その結果を表１に示す。 Production of the negative electrode, production of the cell, evaluation of the cycle characteristics of the battery, and structural analysis of the positive electrode were performed in the same manner as in Example 1. The cut surface having the maximum crack rate was the cut surface C1 at the boundary between the first layer L1 and the second layer L2, and the crack rate at the cut surface was 2.9%. The cut surface with the smallest crack rate was the cut surface C6 at the boundary between the sixth layer L6 and the seventh layer L7, and the crack rate at the cut surface was 0.7%. The results are shown in Table 1.
「実施例３」
実施例３は、アンダーコート層を設けずに、活物質粒子の表面にコーティング層を設けた点が実施例２と異なる。
"Example 3"
Example 3 differs from Example 2 in that a coating layer was provided on the surface of the active material particles without providing an undercoat layer.
（コーティング層の作製）
水にＫ２ＺｒＦ６（純正化学製）とＨ３ＢＯ３（関東化学製）とを、それぞれ０．０１Ｍ、０．０５Ｍとなるように溶解させた。この溶液８００ｍｌに活物質粒子としてＬｉＮｉ０．８５Ｃｏ０．１０Ａｌ０．０５Ｏ２を１２０ｇ投入し、４０℃に加温しながら２４時間攪拌して分散させた。
(Preparation of coating layer)
K 2 ZrF 6 (manufactured by Junsei Chemical Co., Ltd.) and H 3 BO 3 (manufactured by Kanto Chemical Co., Ltd.) were dissolved in water so as to be 0.01M and 0.05M, respectively. In 800 ml of this solution, 120 g of LiNi 0.85 Co 0.10 Al 0.05 O 2 as active material particles was added, and the mixture was stirred and dispersed for 24 hours while heating to 40 ° C.
分散液をろ過し、粒子群を取り出した。この粒子群を水洗し８０℃で乾燥し、さらに大気中で７００℃、２時間熱処理した。その結果、活物質粒子の表面にＺｒＯ２が被覆したコーティング粒子が得られた。 The dispersion was filtered to take out the particles. This particle group was washed with water, dried at 80 ° C., and further heat-treated in the atmosphere at 700 ° C. for 2 hours. As a result, coating particles in which the surface of the active material particles was coated with ZrO 2 were obtained.
活物質粒子が表面コーティングされている点以外は、実施例２と同様に正極を作製した。負極の作製、セルの作製、電池のサイクル特性の評価及び正極の構造解析は、実施例１と同様に行った。割れ率が最大を示す切断面は、第１層Ｌ１と第２層Ｌ２との境界の切断面Ｃ１であり、その切断面における割れ率は２．４％であった。また割れ率が最小を示す切断面は、第５層Ｌ５と第６層Ｌ６との境界の切断面Ｃ５であり、その切断面における割れ率は０．３％であった。その結果を表１に示す。 A positive electrode was produced in the same manner as in Example 2 except that the surface of the active material particles was coated. Production of the negative electrode, production of the cell, evaluation of the cycle characteristics of the battery, and structural analysis of the positive electrode were performed in the same manner as in Example 1. The cut surface having the maximum crack rate was the cut surface C1 at the boundary between the first layer L1 and the second layer L2, and the crack rate at the cut surface was 2.4%. The cut surface with the smallest crack rate was the cut surface C5 at the boundary between the fifth layer L5 and the sixth layer L6, and the crack rate at the cut surface was 0.3%. The results are shown in Table 1.
「実施例４」
実施例４は、アンダーコート層を設けずに、プレスを静水圧プレス機によって行った点が実施例２と異なる。その他の点は、実施例２と同様に行った。
Example 4
Example 4 differs from Example 2 in that pressing was performed by a hydrostatic press without providing an undercoat layer. Other points were the same as in Example 2.
割れ率が最大を示す切断面は、第９層Ｌ９と第１０層Ｌ１０との境界の切断面Ｃ９であり、その切断面における割れ率は３．４％であった。また割れ率が最小を示す切断面は、第６層Ｌ６と第７層Ｌ７との境界の切断面Ｃ７であり、その切断面における割れ率は０．４％であった。その結果を表１に示す。 The cut surface having the maximum crack rate was the cut surface C9 at the boundary between the ninth layer L9 and the tenth layer L10, and the crack rate at the cut surface was 3.4%. The cut surface with the smallest crack rate was the cut surface C7 at the boundary between the sixth layer L6 and the seventh layer L7, and the crack rate at the cut surface was 0.4%. The results are shown in Table 1.
「実施例５」
実施例５は、重層塗布、アンダーコート層の形成、コーティング層の被覆、静水圧プレス機によるプレスを全て行った。実施例２におけるアンダーコート層の形成工程、実施例３におけるコーティング層の被覆工程を実施例１に加え、プレスを静水圧プレスで行った点以外は、実施例１と同様とした。
"Example 5"
In Example 5, multilayer coating, undercoat layer formation, coating layer coating, and pressing with an isostatic press were all performed. The undercoat layer forming step in Example 2 and the coating layer covering step in Example 3 were added to Example 1, and the same procedure as in Example 1 was performed except that the pressing was performed by an isostatic press.
割れ率が最大を示す切断面は、第９層Ｌ９と第１０層Ｌ１０との境界の切断面Ｃ９であり、その切断面における割れ率は１．２％であった。また割れ率が最小を示す切断面は、第３層Ｌ３と第４層Ｌ４との境界の切断面Ｃ３であり、その切断面における割れ率は０．４％であった。その結果を表１に示す。 The cut surface having the maximum crack rate was the cut surface C9 at the boundary between the ninth layer L9 and the tenth layer L10, and the crack rate at the cut surface was 1.2%. The cut surface with the smallest crack rate was the cut surface C3 at the boundary between the third layer L3 and the fourth layer L4, and the crack rate at the cut surface was 0.4%. The results are shown in Table 1.
「比較例１」
比較例１は、アンダーコート層を形成しなかった点が実施例２と異なる。その他の条件は、実施例１と同じとした。
"Comparative Example 1"
Comparative Example 1 is different from Example 2 in that no undercoat layer was formed. Other conditions were the same as in Example 1.
割れ率が最大を示す切断面は、第１層Ｌ１と第２層Ｌ２との境界の切断面Ｃ１であり、その切断面における割れ率は１７．４％であった。また割れ率が最小を示す切断面は、第６層Ｌ６と第７層Ｌ７との境界の切断面Ｃ７であり、その切断面における割れ率は１．５％であった。その結果を表１に示す。 The cut surface having the maximum crack rate was the cut surface C1 at the boundary between the first layer L1 and the second layer L2, and the crack rate at the cut surface was 17.4%. The cut surface with the smallest crack rate was the cut surface C7 at the boundary between the sixth layer L6 and the seventh layer L7, and the crack rate at the cut surface was 1.5%. The results are shown in Table 1.
１０ セパレータ
２０ 正極
２２ 正極集電体
２４ 正極活物質層
２４Ａ 活物質粒子
２４Ｂ 第１領域
２４Ｃ 割れ
３０ 負極
３２ 負極集電体
３４ 負極活物質層
４０ 発電素子
５０ 外装体
５２ 金属箔
５４ 樹脂層
６０、６２ 端子
１００ 非水電解液二次電池
DESCRIPTION OF SYMBOLS 10 Separator 20 Positive electrode 22 Positive electrode collector 24 Positive electrode active material layer 24A Active material particle 24B 1st area | region 24C Crack 30 Negative electrode 32 Negative electrode collector 34 Negative electrode active material layer 40 Power generation element 50 Exterior body 52 Metal foil 54 Resin layer 60, 62 Terminal 100 Non-aqueous electrolyte secondary battery
Claims (8)
前記正極集電体の少なくとも一面に塗布され、活物質粒子を有する正極活物質層と、を備え、
前記正極活物質層において、前記正極活物質層を積層方向と直交する切断面で１０等分した際に、前記活物質粒子の割れ率が最も低い切断面における前記活物質粒子の割れ率が１．５％未満であり、
前記割れ率は、前記切断面における画像を、前記活物質粒子の階調の中央値が２２５以下、かつ、前記活物質粒子の階調の中央値と前記活物質粒子以外の部分の階調の中央値との差が３０以上１１０以下となるようにコントラスト調整した２５６諧調のグレースケール画像から前記活物質粒子を抽出し直した第２グレースケール画像において、計測頻度が最大頻度の２０％以下となる所定の閾値階調以上の階調を示す割れ部の面積を、前記画像の全体面積で割って求められる、正極。 A positive electrode current collector;
A positive electrode active material layer coated on at least one surface of the positive electrode current collector and having active material particles;
In the positive electrode active material layer, when the positive electrode active material layer is divided into 10 equal parts by a cut surface orthogonal to the stacking direction, the active material particle has a crack rate of 1 at the cut surface with the lowest crack rate of the active material particles. Less than 5%,
The crack rate is determined by comparing the image of the cut surface with a median gradation of the active material particles of 225 or less, and a gradation value of a portion other than the active material particles and the median gradation of the active material particles. In the second gray scale image obtained by re-extracting the active material particles from a 256-tone gray scale image whose contrast is adjusted so that the difference from the median is 30 or more and 110 or less, the measurement frequency is 20% or less of the maximum frequency. A positive electrode obtained by dividing an area of a crack portion showing a gradation equal to or higher than a predetermined threshold gradation by an entire area of the image.
前記リチウム複合酸化物は、一般式ＬｉｘＭ１ｙＭ２１−ｙＯ２で表記され、
前記一般式において、Ｍ１はＮｉ、Ｃｏ及びＭｎからなる群から選択される少なくとも１種の金属元素であり、Ｍ２はＡｌ、Ｆｅ、Ｔｉ、Ｃｒ、Ｍｇ、Ｃｕ、Ｇａ、Ｚｎ、Ｓｎ、Ｂ、Ｖ、Ｃａ及びＳｒからなる群から選択される少なくとも１種の金属元素であり、ｘは０．０５≦ｘ≦１．２を満たし、ｙは０．３≦ｙ≦１．０を満たす、請求項１〜３のいずれか一項に記載の正極。 The active material particles are a lithium composite oxide,
The lithium composite oxide is expressed by a general formula Li x M1 y M2 1-y O 2,
In the general formula, M1 is at least one metal element selected from the group consisting of Ni, Co and Mn, and M2 is Al, Fe, Ti, Cr, Mg, Cu, Ga, Zn, Sn, B, It is at least one metal element selected from the group consisting of V, Ca and Sr, x satisfies 0.05 ≦ x ≦ 1.2, and y satisfies 0.3 ≦ y ≦ 1.0. Item 4. The positive electrode according to any one of Items 1 to 3.
前記正極と対向する負極と、
前記正極と前記負極との間に配設されたセパレータと、備える、非水電解液二次電池。 The positive electrode according to any one of claims 1 to 7,
A negative electrode facing the positive electrode;
A non-aqueous electrolyte secondary battery comprising a separator disposed between the positive electrode and the negative electrode.
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