JP5556252B2 - Nonaqueous electrolyte secondary battery and electrode for nonaqueous electrolyte secondary battery - Google Patents

Nonaqueous electrolyte secondary battery and electrode for nonaqueous electrolyte secondary battery Download PDF

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JP5556252B2
JP5556252B2 JP2010052560A JP2010052560A JP5556252B2 JP 5556252 B2 JP5556252 B2 JP 5556252B2 JP 2010052560 A JP2010052560 A JP 2010052560A JP 2010052560 A JP2010052560 A JP 2010052560A JP 5556252 B2 JP5556252 B2 JP 5556252B2
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弥生 勝
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Description

本発明は、非水電解質二次電池および非水電解質二次電池用電極に関し、さらに詳しくは、高温環境下でのサイクル特性の低下を抑えた非水電解質二次電池および非水電解質二次電池用電極に関する。   The present invention relates to a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery electrode, and more specifically, a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery in which deterioration of cycle characteristics in a high temperature environment is suppressed. The present invention relates to an electrode.

携帯電話やノート型パソコンなど種々の分野において、リチウムイオン二次電池に代表される、非水電解質二次電池が電源に使用されている。   In various fields such as mobile phones and notebook computers, non-aqueous electrolyte secondary batteries represented by lithium ion secondary batteries are used as power sources.

この非水電解質二次電池において、電極活物質にスピネル型リチウムマンガン複合酸化物を用いた場合、高温環境下、たとえば５０℃以上で充放電サイクルを繰り返すことにより充放電容量が低下してしまい、サイクル特性が劣化するという問題がある。このサイクル特性の劣化の原因としては、スピネル型リチウムマンガン複合酸化物からマンガンが溶出してしまうことが考えられている。   In this non-aqueous electrolyte secondary battery, when a spinel type lithium manganese composite oxide is used as the electrode active material, the charge / discharge capacity is reduced by repeating the charge / discharge cycle at a high temperature environment, for example, 50 ° C. or more, There is a problem that the cycle characteristics deteriorate. As a cause of the deterioration of the cycle characteristics, it is considered that manganese is eluted from the spinel type lithium manganese composite oxide.

この問題に対しては、種々の対策がなされており、たとえば特許文献１では、正極活物質を構成するスピネル型リチウムマンガン複合酸化物中のマンガンの一部に他の金属を均一に固溶させている。   Various countermeasures have been taken for this problem. For example, in Patent Document 1, another metal is uniformly dissolved in a part of manganese in the spinel type lithium manganese composite oxide constituting the positive electrode active material. ing.

また、非特許文献１では、スピネル型リチウムマンガン複合酸化物中のマンガンの一部をＦおよびＬｉで置換し、さらにＺｎＯをコーティングしている。   In Non-Patent Document 1, a part of manganese in the spinel type lithium manganese composite oxide is substituted with F and Li, and further coated with ZnO.

さらに、非特許文献２では、スピネル型リチウムマンガン複合酸化物にＺｒＯ2、Ａｌ2Ｏ3、ＳｉＯ2のいずれかをコーティングしている。 Furthermore, in Non-Patent Document 2, any of ZrO 2 , Al 2 O 3 , and SiO 2 is coated on a spinel type lithium manganese composite oxide.

特開平１１−２４０７２１号公報JP-A-11-240721

Jung-Min Han, Seung-Taek Myung, and Yang-Kook Sun, J.Electrochem.Soc.,153(7), A1290-1295(2006)Jung-Min Han, Seung-Taek Myung, and Yang-Kook Sun, J. Electrochem. Soc., 153 (7), A1290-1295 (2006) J.S.Kim, C.S.Johnson, and M.M.Thackeray, J.Electrochem.Soc.,151(10), A1755-1761 (2004)J.S.Kim, C.S.Johnson, and M.M.Thackeray, J. Electrochem.Soc., 151 (10), A1755-1761 (2004)

上述したように、電極活物質にスピネル型リチウムマンガン複合酸化物を用いた非水電解質二次電池において、高温環境下におけるサイクル特性を向上させるために、電極活物質を構成するスピネル型リチウムマンガン複合酸化物中のマンガンの一部を他の元素に置換したり、電極表面を種々の酸化物でコーティングするといった報告は多数なされている。しかしながら、これまでのところ、サイクル特性の劣化を十分に抑制したものは未だ得られていない。   As described above, in a non-aqueous electrolyte secondary battery using a spinel type lithium manganese composite oxide as an electrode active material, in order to improve cycle characteristics under a high temperature environment, the spinel type lithium manganese composite constituting the electrode active material There have been many reports on replacing a part of manganese in oxides with other elements and coating electrode surfaces with various oxides. However, there has not yet been obtained a product that sufficiently suppresses deterioration of cycle characteristics.

本発明は、この問題を改善するためになされたものであり、高温環境下における充放電サイクル特性を向上させ、充放電容量の低下を十分に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 was made to improve this problem, and provides a non-aqueous electrolyte secondary battery that improves charge / discharge cycle characteristics in a high-temperature environment and sufficiently suppresses a decrease in charge / discharge capacity. Objective.

その手段として本発明の非水電解質二次電池は、正極と負極の少なくとも一方の電極に、スピネル型リチウムマンガン複合酸化物を含有する電極活物質層を備え、その電極活物質層が、対向する他方の電極側の表面近傍において、スピネル型リチウムマンガン複合酸化物のマンガン濃度より高いマンガン濃度を有する柱状化合物を含有するようにした。 As the means, the nonaqueous electrolyte secondary battery of the present invention includes an electrode active material layer containing a spinel type lithium manganese composite oxide on at least one of the positive electrode and the negative electrode, and the electrode active material layers face each other. In the vicinity of the surface on the other electrode side, a columnar compound having a manganese concentration higher than the manganese concentration of the spinel type lithium manganese composite oxide was contained .

なお、電極は、表面近傍のマンガン濃度の高い柱状化合物を含有する層と、内部のマンガン濃度の低いスピネル型リチウムマンガン複合酸化物を含有する層とからなる層状に形成されても良いし、内部から表面近傍に向って、次第にマンガン濃度が高くなるように形成されても良い。 In addition, the electrode may be formed in a layer shape including a layer containing a columnar compound having a high manganese concentration near the surface and a layer containing a spinel-type lithium manganese composite oxide having a low internal manganese concentration. To the vicinity of the surface, the manganese concentration may be gradually increased.

また、本発明の非水電解質二次電池用電極は、集電体と、集電体上に形成されるスピネル型リチウムマンガン複合酸化物を含有する電極活物質層とを備え、その電極活物質層が、集電体側と反対側の表面近傍において、スピネル型リチウムマンガン複合酸化物のマンガン濃度より高いマンガン濃度を有する柱状化合物を含有するようにした。 The electrode for a non-aqueous electrolyte secondary battery of the present invention includes a current collector and an electrode active material layer containing a spinel-type lithium manganese composite oxide formed on the current collector , and the electrode active material The layer contained a columnar compound having a manganese concentration higher than that of the spinel type lithium manganese composite oxide in the vicinity of the surface opposite to the current collector side .

上述した構成とすることにより、本発明の非水電解質二次電池は、高温環境下で充放電を繰り返しても、電極活物質であるスピネル型リチウムマンガン複合酸化物からのマンガンの溶出を、電極の表面近傍のマンガン濃度の高い柱状化合物を含有する部分により抑制することができるため、サイクル特性の劣化を十分に抑制することができる。また、本発明の非水電解質二次電池用電極は、マンガンの溶出を、電極の表面近傍のマンガン濃度の高い柱状化合物を含有する部分により抑制することができるため、これを使用した非水電解質二次電池の、サイクル特性の劣化を十分に抑制することができる。
By adopting the above-described configuration, the nonaqueous electrolyte secondary battery of the present invention can elute manganese from the spinel-type lithium manganese composite oxide, which is an electrode active material, even if charging and discharging are repeated in a high temperature environment. Since it can suppress by the part containing the columnar compound with high manganese concentration of the surface vicinity, deterioration of cycling characteristics can fully be suppressed. The electrode for a non-aqueous electrolyte secondary battery of the present invention can suppress elution of manganese by a portion containing a columnar compound having a high manganese concentration in the vicinity of the surface of the electrode. Therefore, the non-aqueous electrolyte using this The deterioration of the cycle characteristics of the secondary battery can be sufficiently suppressed.

本発明の実施例１にかかる非水電解質二次電池の正極のマンガン濃度を示すＷＤＸ像である。It is a WDX image which shows the manganese density | concentration of the positive electrode of the nonaqueous electrolyte secondary battery concerning Example 1 of this invention. 本発明の実施例１にかかる非水電解質二次電池の正極を示すＳＥＭ像である。It is a SEM image which shows the positive electrode of the nonaqueous electrolyte secondary battery concerning Example 1 of this invention. 本発明の実施例１にかかる非水電解質二次電池、および比較例にかかる非水電解質二次電池の、高温環境下での充放電サイクル特性（容量維持率）を示すグラフである。It is a graph which shows the charging / discharging cycling characteristics (capacity maintenance factor) in the high temperature environment of the nonaqueous electrolyte secondary battery concerning Example 1 of this invention, and the nonaqueous electrolyte secondary battery concerning a comparative example. 比較例にかかる非水電解質二次電池の正極のマンガン濃度を示すＷＤＸ像である。It is a WDX image which shows the manganese concentration of the positive electrode of the nonaqueous electrolyte secondary battery concerning a comparative example. 比較例にかかる非水電解質二次電池の正極を示すＳＥＭ像である。It is a SEM image which shows the positive electrode of the nonaqueous electrolyte secondary battery concerning a comparative example.

以下、図面を参照しつつ、本発明を実施するための形態について説明する。
［実施例１］
スピネル型リチウムマンガン複合酸化物と、炭素材料から成る導電助剤と、ポリフッ化ビニリデン（ＰＶＤＦ）とを、質量比で８５：７：８になるように秤量し、Ｎ-メチル-２-ピロリドン中に分散させて正極用スラリーを作製した。 Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.
[Example 1]
A spinel-type lithium manganese composite oxide, a conductive aid made of a carbon material, and polyvinylidene fluoride (PVDF) are weighed so as to have a mass ratio of 85: 7: 8, and in N-methyl-2-pyrrolidone. A slurry for positive electrode was prepared by dispersing in a slurry.

次に、この正極用スラリーを、厚さ２０μｍのアルミ箔上に、乾燥後のスピネル型リチウムマンガン複合酸化物と炭素材料からなる導電助剤の重量が、片面当たり１２.０〜１３.０ｍｇ／ｃｍ2となるように塗布し、１３０℃で乾燥後、８.６ＭＰａの圧力でプレスして正極シートを作製した。 Next, the weight of the conductive assistant composed of the spinel-type lithium manganese composite oxide and the carbon material after drying on the 20 μm-thick aluminum foil on the positive electrode slurry is 12.0 to 13.0 mg / side. the coating is cm 2, and dried at 130 ° C., to produce a positive electrode sheet was pressed at a pressure of 8.6 MPa.

次に、作製した正極シートを、トムソン刃で４０ｍｍ×４５ｍｍの大きさに打ち抜き、正極活物質が正極集電体上に形成された正極を得た。   Next, the produced positive electrode sheet was punched into a size of 40 mm × 45 mm with a Thomson blade to obtain a positive electrode in which the positive electrode active material was formed on the positive electrode current collector.

同様に、黒鉛化メソフェーズ小球体と、ハードカーボンと、ポリフッ化ビニリデンとを、質量比で３６.８：５５.２：８.０になるように秤量し、Ｎ-メチル-2-ピロリドン中に分散させて負極用スラリーを作製した。   Similarly, graphitized mesophase spherules, hard carbon, and polyvinylidene fluoride were weighed so as to have a mass ratio of 36.8: 55.2: 8.0, and placed in N-methyl-2-pyrrolidone. A slurry for negative electrode was prepared by dispersing.

次に、この負極用スラリーを、厚さ２０μｍの銅箔上に塗布し、１３０℃で乾燥後、８.６ＭＰａの圧力でプレスして負極シートを作製した。   Next, this negative electrode slurry was applied onto a copper foil having a thickness of 20 μm, dried at 130 ° C., and then pressed at a pressure of 8.6 MPa to prepare a negative electrode sheet.

次に、作製した負極シートを、トムソン刃で４０ｍｍ×４５ｍｍの大きさに打ち抜き、負極活物質が負極集電体上に形成された負極を得た。   Next, the produced negative electrode sheet was punched out into a size of 40 mm × 45 mm with a Thomson blade to obtain a negative electrode in which the negative electrode active material was formed on the negative electrode current collector.

次に、正極と負極とを、電極活物質を形成した面が向かい合うようにカプトンテープを用いてセパレータに貼り付けたうえ、正極、セパレータおよび負極の積層体を作製した。作製した積層体に金属ニッケルからなる正極接続端子および負極接続端子をそれぞれ超音波で溶着し電池要素を作製した。   Next, the positive electrode and the negative electrode were attached to the separator using a Kapton tape so that the surfaces on which the electrode active material was formed faced, and a laminate of the positive electrode, the separator, and the negative electrode was produced. A positive electrode connection terminal and a negative electrode connection terminal made of metallic nickel were each welded to the prepared laminate with ultrasonic waves to produce a battery element.

次に、この電池要素を、長方形のアルミニウムラミネートフィルムに封入し、三方辺を温度８０℃で熱融着した後、電解液をアルミニウムラミネートフィルムの開口部から注入してアルミラミネートフィルムの開口部を熱融着することにより、ラミネート電池を作製した。なお、電解液には、１Ｍ ＬｉＰＦ6 ＰＣ（プロピレンカーボネート）：ＥＣ（エチレンカーボネート）：ＤＥＣ（ジエチレンカーボネート）＝２：２：６を使用し、正極電極面積に対して０.８×１０-4ｇ／ｍｍ2注入したうえで密封した。 Next, this battery element is sealed in a rectangular aluminum laminate film, and the three sides are heat-sealed at a temperature of 80 ° C., and then an electrolyte is injected from the opening of the aluminum laminate film to open the opening of the aluminum laminate film. A laminate battery was produced by heat sealing. The electrolyte used was 1M LiPF 6 PC (propylene carbonate): EC (ethylene carbonate): DEC (diethylene carbonate) = 2: 2: 6, and 0.8 × 10 −4 with respect to the positive electrode area. It sealed after inject | pouring g / mm < 2 >.

さらに、次の手順でラミネート電池に充放電を行った。   Further, the laminate battery was charged and discharged by the following procedure.

ラミネート電池に０.０７ＭＰａの圧力を加えて、２５℃にて１１時間放置し、４.２Ｖまで正極活物質量当たり２１.８ｍＡ／ｇ の電流で定電流充電し、さらに５時間定電圧充電を行った。   Apply a pressure of 0.07 MPa to the laminate battery, leave it at 25 ° C. for 11 hours, charge at a constant current of 21.8 mA / g per positive electrode active material up to 4.2 V, and then charge at a constant voltage for 5 hours. went.

次に、ラミネート電池の正極接続端子および負極接続端子が導出していない一辺部分を一部切り取り、ガス抜きを行った。再び密封し、０.０７ＭＰａの圧力をラミネート電池に加え、２５℃にて正極活物質量当たり１０９.２ｍＡ／ｇの電流で２.７Ｖまで放電し、さらに５４.６ｍＡ／ｇの電流にて２.７〜４.２Ｖの間で定電流充放電を行った。   Next, a part of one side where the positive electrode connection terminal and the negative electrode connection terminal of the laminate battery were not led out was cut out and degassed. Sealed again, a pressure of 0.07 MPa was applied to the laminated battery, and the battery was discharged to 2.7 V at a current of 109.2 mA / g per positive electrode active material at 25 ° C., and 2 at a current of 54.6 mA / g. The constant current charging / discharging was performed between 0.7-4.2V.

次に、０.０７ＭＰａの圧力を電池要素に加えた状態で、５０℃の高温下で１０９.２ｍＡ／ｇの電流で２.７〜４.２Ｖの定電流充放電を２回繰り返し、表面近傍のマンガン濃度を、内部のマンガン濃度よりも高くした電極を作製した。   Next, with a pressure of 0.07 MPa applied to the battery element, a constant current charge / discharge of 2.7 to 4.2 V was repeated twice at a high temperature of 50 ° C. with a current of 109.2 mA / g, and the vicinity of the surface An electrode having a manganese concentration higher than the internal manganese concentration was prepared.

この非水電解質二次電池においては、上述したとおり、正極の表面に、マンガン濃度の高い表面層が形成されている。表面層は、上述した製造方法において、主に、５０℃の高温下で定電流充放電を２回繰り返した際に形成されたと考えられる。正極の表面に表面層が形成されるメカニズムについては厳密に解明されてはいないが、５０℃という高温下で定電流充放電を行うことにより、正極の表面に、マンガン濃度の高い柱状化合物が形成されたものと考えられる。   In this nonaqueous electrolyte secondary battery, as described above, a surface layer having a high manganese concentration is formed on the surface of the positive electrode. It is considered that the surface layer was formed when the constant current charge / discharge was repeated twice at a high temperature of 50 ° C. in the manufacturing method described above. Although the mechanism by which the surface layer is formed on the surface of the positive electrode has not been clarified precisely, a columnar compound with a high manganese concentration is formed on the surface of the positive electrode by performing constant current charge / discharge at a high temperature of 50 ° C. It is thought that it was done.

正極の状態を確認するために、上述した製造方法において、５０℃の高温下での２回の定電流充放電を経た後の、ラミネート電池をドライルーム内にて解体し正極を取り出し、取り出した正極をＤＭＣ（ジメチルカーボネート）で洗浄し、ドライルーム内にて１２時間乾燥させたのち、断面加工を行い、断面状態をＷＤＸ、ＳＥＭ、ラマン分光で観察した。   In order to confirm the state of the positive electrode, in the manufacturing method described above, the laminate battery after being subjected to two constant current charging and discharging at a high temperature of 50 ° C. was disassembled in a dry room, and the positive electrode was taken out and taken out. The positive electrode was washed with DMC (dimethyl carbonate), dried in a dry room for 12 hours, then subjected to cross-section processing, and the cross-sectional state was observed by WDX, SEM, and Raman spectroscopy.

図１は、正極のマンガン濃度を示すＷＤＸ像である。正極の表面に、マンガン濃度の高い表面層１ａが形成されているのが確認できた。   FIG. 1 is a WDX image showing the manganese concentration of the positive electrode. It was confirmed that the surface layer 1a having a high manganese concentration was formed on the surface of the positive electrode.

図２は、正極のＳＥＭ像である。表面層１ａが、これに続く内部層１ｂよりも、空隙率が小さく、緻密になっているのが確認できた。   FIG. 2 is an SEM image of the positive electrode. It was confirmed that the surface layer 1a had a smaller porosity and became denser than the subsequent inner layer 1b.

なお、ラマン分光を測定した結果、５９０ｃｍ-1に存在するピークの強度が、内部層１ｂと表面層１ａとにおいて、ほぼ３：１の強度比であることが確認できた。なお、本実施例では５０℃で定電流充放電を２回繰り返したが、２回以上繰り返しても、ラマン分光のピーク強度比が変化するものの、同様の効果を得ることができる。２回以上定電流充放電を繰り返した場合、表面層１ａが厚くなると考えられる。また、定電流充放電の繰り返しにより、表面層１ａのＭｎ濃度も変化する。 As a result of measuring Raman spectroscopy, it was confirmed that the intensity of the peak existing at 590 cm −1 was an intensity ratio of about 3: 1 between the inner layer 1b and the surface layer 1a. In the present example, constant current charging / discharging was repeated twice at 50 ° C., but the same effect can be obtained even if the peak intensity ratio of Raman spectroscopy is changed even if it is repeated twice or more. When constant current charging / discharging is repeated twice or more, it is considered that the surface layer 1a becomes thick. Further, the Mn concentration of the surface layer 1a also changes due to repetition of constant current charge / discharge.

本発明の非水電解質二次電池は、正極と負極の少なくとも一方の電極に、内部層よりもマンガン濃度の高い表面層が形成されているため、高温環境下で充放電サイクルを繰り返しても、サイクル特性の劣化が抑制されている。このサイクル特性の劣化を抑制するメカニズムについても厳密に解明されてはいないが、マンガン濃度の高い表面層は、空隙率が小さく、緻密であるため、マンガンの溶出を抑制でき、この結果としてサイクル特性の劣化を抑制できるのではないかと考えられている。   In the nonaqueous electrolyte secondary battery of the present invention, since a surface layer having a higher manganese concentration than the internal layer is formed on at least one of the positive electrode and the negative electrode, even if the charge / discharge cycle is repeated in a high temperature environment, Deterioration of cycle characteristics is suppressed. Although the mechanism for suppressing the deterioration of the cycle characteristics has not been clarified, the surface layer with a high manganese concentration has a small porosity and is dense, so that the elution of manganese can be suppressed. As a result, the cycle characteristics It is thought that the deterioration of the can be suppressed.

本発明の効果を確認するために、上述した方法で作製した非水電解質二次電池を用いて、次の実験をおこなった。   In order to confirm the effect of the present invention, the following experiment was performed using the nonaqueous electrolyte secondary battery produced by the above-described method.

上述の方法で作製した非水電解質二次電池を、５０℃の高温環境下において、正極活物質量当たり１０９.２ｍＡ／ｇの電流で、２.７〜４.２Ｖの間で定電流充放電を１００サイクル繰り返した。そして、各充放電サイクル後に容量を測定し、初期容量との比較により容量維持率を調べた。すなわち、容量維持率＝充放電サイクル後の容量／初期容量×１００（％）となり、容量維持率が高いほど容量の低下は抑制されている。   The non-aqueous electrolyte secondary battery produced by the above method is charged and discharged at a constant current of 2.7 to 4.2 V at a current of 109.2 mA / g per positive electrode active material in a high temperature environment of 50 ° C. Was repeated 100 cycles. And capacity | capacitance was measured after each charging / discharging cycle, and the capacity | capacitance maintenance factor was investigated by the comparison with an initial stage capacity | capacitance. That is, capacity retention rate = capacity after charge / discharge cycle / initial capacity × 100 (%), and the higher the capacity retention rate, the lower the capacity decrease.

図３に、各サイクル後の容量維持率を示す（図３中の上側のグラフ）。１００サイクル後の容量維持率は９３％であり、極めて良好な、高温下でのサイクル特性を示した。正極の表面層１ａがマンガンの溶出を抑制し、容量の低下を抑制できたものと考えられる。
［比較例］
次の手順で、比較例にかかる非水電解質二次電池を作製した。 FIG. 3 shows the capacity retention rate after each cycle (upper graph in FIG. 3). The capacity retention rate after 100 cycles was 93%, which showed very good cycle characteristics at high temperatures. It is considered that the surface layer 1a of the positive electrode suppressed elution of manganese and suppressed the decrease in capacity.
[Comparative example]
The non-aqueous electrolyte secondary battery according to the comparative example was manufactured by the following procedure.

まず、実施例１と同様の原料、製造方法を用いて正極および負極を作製し、さらにこれらをセパレータを介して対向配置して積層体を作製し、積層体に金属ニッケルからなる正極接続端子および負極接続端子を超音波で溶着させ電池要素を作製した。作製した電池要素をアルミニウムラミネートフィルムに入れ、実施例１と同様にしてラミネート電池を作製した。   First, a positive electrode and a negative electrode were produced using the same raw materials and production method as in Example 1, and these were further arranged facing each other via a separator to produce a laminate, and a positive electrode connection terminal made of metallic nickel on the laminate and The negative electrode connection terminal was welded with ultrasonic waves to produce a battery element. The produced battery element was put into an aluminum laminate film, and a laminate battery was produced in the same manner as in Example 1.

次に、このラミネート電池に対し、これも実施例１と同様の方法で、２５℃において、充電、ガス抜き、放電、定電流充放電１回を行い非水電解質二次電池を作製した。しかしながら、比較例においては、実施例１において行った、５０℃の高温下における２サイクルの充放電は行わなかった。   Next, a non-aqueous electrolyte secondary battery was manufactured by performing charging, degassing, discharging, and constant current charging / discharging once for this laminated battery in the same manner as in Example 1 at 25 ° C. However, in the comparative example, the charge / discharge of 2 cycles at a high temperature of 50 ° C. performed in Example 1 was not performed.

比較例にかかる非水電解質二次電池の正極の状態を確認するために、上述した２５℃の環境下における、充電、ガス抜き、放電、定電流充放電１回を行った後のラミネート電池をドライルーム内にて解体し正極を取り出し、取り出した正極をＤＭＣで洗浄し、ドライルーム内にて１２時間乾燥させたのち、断面加工を行い、断面状態をＷＤＸ、ＳＥＭで観察した。   In order to confirm the state of the positive electrode of the non-aqueous electrolyte secondary battery according to the comparative example, the laminate battery after performing charging, degassing, discharging, and constant current charging / discharging once in the environment of 25 ° C. described above. After disassembling in a dry room and taking out the positive electrode, the taken out positive electrode was washed with DMC, dried in the dry room for 12 hours, then subjected to cross-section processing, and the cross-sectional state was observed with WDX and SEM.

図４は、比較例の正極のマンガン濃度を示すＷＤＸ像である。正極の表面には、マンガン濃度の高い部分は確認できなかった。   FIG. 4 is a WDX image showing the manganese concentration of the positive electrode of the comparative example. On the surface of the positive electrode, a portion with a high manganese concentration could not be confirmed.

図５は、比較例の正極のＳＥＭ像である。正極の表面には、空隙率が小さく、緻密になっている部分は確認できなかった。   FIG. 5 is an SEM image of the positive electrode of the comparative example. On the surface of the positive electrode, a portion having a small porosity and being dense could not be confirmed.

このように、比較例にかかる非水電解質二次電池の正極においては、マンガン濃度の高い表面層は形成されなかった。   Thus, in the positive electrode of the nonaqueous electrolyte secondary battery according to the comparative example, a surface layer having a high manganese concentration was not formed.

比較例にかかる非水電解質二次電池に対し、実施例１と同様に、５０℃の高温環境下において、正極活物質量当たり１０９.２ｍＡ／ｇの電流で、２.７〜４.２Ｖの間で定電流充放電を１００サイクル繰り返し、各充放電サイクル後の容量維持率を調べた。   As in Example 1, the nonaqueous electrolyte secondary battery according to the comparative example was 2.7 to 4.2 V at a current of 109.2 mA / g per positive electrode active material in a high temperature environment of 50 ° C. The constant current charging / discharging was repeated 100 cycles, and the capacity retention rate after each charging / discharging cycle was examined.

図３に、各サイクル後の容量維持率を示す（図３中の下側のグラフ）。比較例の１００サイクル後の容量維持率は７６.０％であり、実施例１に比較して大幅に低下した。正極に表面層が存在しないことにより、正極からマンガンが溶出し、容量が低下したものと考えられる。
［実施例２］
次の手順で、実施例２にかかる非水電解質二次電池を作製した。 FIG. 3 shows the capacity retention rate after each cycle (lower graph in FIG. 3). The capacity retention rate after 100 cycles of the comparative example was 76.0%, which was significantly lower than that of Example 1. It is considered that the absence of the surface layer on the positive electrode caused manganese to elute from the positive electrode, resulting in a decrease in capacity.
[Example 2]
A non-aqueous electrolyte secondary battery according to Example 2 was produced by the following procedure.

まず、実施例１と同様の原料、製造方法を用いて正極および負極を作製し、さらにこれらをセパレータを介して対向配置して積層体を作製し、正極接続端子および負極接続端子を超音波で溶着し電池要素を作製した。   First, a positive electrode and a negative electrode are produced using the same raw materials and production method as in Example 1, and further, these are arranged oppositely via a separator to produce a laminate, and the positive electrode connecting terminal and the negative electrode connecting terminal are ultrasonically connected. A battery element was fabricated by welding.

次に、実施例１と同様にしてラミネート電池を作製した。このラミネート電池に対し、これも実施例１と同様の方法で、２５℃において、充電、ガス抜き、放電、定電流充放電１回を行った。   Next, a laminated battery was produced in the same manner as in Example 1. The laminate battery was charged, degassed, discharged, and charged / discharged at a constant current once at 25 ° C. in the same manner as in Example 1.

次に、ラミネート電池に０.０７ＭＰａの圧力を加えた状態で、６０℃の高温環境下において正極活物質量当たり２１.８×１０-2ｍＡ／ｇの電流で２.７〜４.４Ｖの定電流充放電を1回行った。 Next, in a state where a pressure of 0.07 MPa was applied to the laminated battery, 2.7 to 4.4 V at a current of 21.8 × 10 −2 mA / g per positive electrode active material amount in a high temperature environment of 60 ° C. Constant current charge / discharge was performed once.

最後に、これも実施例１と同様にして、実施例２にかかる非水電解質二次電池を完成させた。   Finally, in the same manner as in Example 1, the nonaqueous electrolyte secondary battery according to Example 2 was completed.

実施例２にかかる非水電解質二次電池の正極の状態を確認するために、実施例１と同様の方法で、正極の断面状態をＷＤＸ、ＳＥＭで観察した。図示はしないが、正極の表面側に、マンガン濃度が高く、空隙率が小さく緻密な表面層を確認することができた。   In order to confirm the state of the positive electrode of the nonaqueous electrolyte secondary battery according to Example 2, the cross-sectional state of the positive electrode was observed with WDX and SEM in the same manner as in Example 1. Although not shown, a dense surface layer having a high manganese concentration and a small porosity was confirmed on the surface side of the positive electrode.

実施例２にかかる非水電解質二次電池に対し、実施例１と同様に、５０℃の高温環境下において、正極活物質量当たり１０９.２ｍＡ／ｇの電流で、２.７〜４.２Ｖの間で定電流充放電を１００サイクル繰り返し、各充放電サイクル後の容量維持率を調べた。１００サイクル後の容量維持率の劣化は１０％程度であり、極めて良好な、高温下での充放電サイクル特性を示した。
［実施例３］
次の手順で、実施例３にかかる非水電解質二次電池を作製した。 In the same manner as in Example 1, the nonaqueous electrolyte secondary battery according to Example 2 was 2.7 to 4.2 V at a current of 109.2 mA / g per positive electrode active material in a high temperature environment of 50 ° C. The constant current charging / discharging was repeated 100 cycles, and the capacity retention rate after each charging / discharging cycle was examined. Deterioration of the capacity retention rate after 100 cycles was about 10%, indicating extremely good charge / discharge cycle characteristics at high temperatures.
[Example 3]
A non-aqueous electrolyte secondary battery according to Example 3 was produced by the following procedure.

まず、実施例１と同様の原料、製造方法を用いて正極および負極を作製し、さらにこれらをセパレータを介して対向配置して積層体を作製し、正極接続端子および負極接続端子を超音波で溶着し電池要素を作製した。   First, a positive electrode and a negative electrode are produced using the same raw materials and production method as in Example 1, and further, these are arranged oppositely via a separator to produce a laminate, and the positive electrode connecting terminal and the negative electrode connecting terminal are ultrasonically connected. A battery element was fabricated by welding.

次に、これも実施例１と同様の方法でラミネート電池を作製し、２５℃において、充電、ガス抜き、放電、定電流充放電１回を行った。   Next, a laminated battery was produced in the same manner as in Example 1, and charging, degassing, discharging, and constant current charging / discharging were performed once at 25 ° C.

次に、ラミネート電池に０.０７ＭＰａの圧力を加えた状態で、６０℃の高温環境下において４.４Ｖまで正極活物質量当たり２１.８×１０-2ｍＡ／ｇの電流で定電流充電し、さらに１００時間定電圧充電を行った。 Next, with a pressure of 0.07 MPa applied to the laminated battery, constant current charging was performed at a current of 21.8 × 10 −2 mA / g per positive electrode active material up to 4.4 V in a high temperature environment of 60 ° C. Further, constant voltage charging was performed for 100 hours.

次に、実施例１と同様に、ガス抜きを行ったうえ、再び密封し、０.０７ＭＰａの圧力を電池要素に加え、２５℃にて正極活物質量当たり１０９.２ｍＡ／ｇの電流で２.７Ｖまで放電し、さらに５４.６ｍＡ／ｇの電流にて２.７〜４.２Ｖの間で定電流充放電を行った。   Next, after degassing and sealing again in the same manner as in Example 1, a pressure of 0.07 MPa was applied to the battery element, and a current of 109.2 mA / g per positive electrode active material amount was 2 at 25 ° C. The battery was discharged to 0.7 V, and further charged and discharged at a constant current of 2.7 to 4.2 V at a current of 54.6 mA / g.

最後に、これも実施例１と同様にして実施例３にかかる非水電解質二次電池を完成させた。   Finally, the nonaqueous electrolyte secondary battery according to Example 3 was completed in the same manner as in Example 1.

実施例３にかかる非水電解質二次電池の正極の状態を確認するために、実施例１と同様の方法で、正極の断面状態をＷＤＸ、ＳＥＭで観察した。図示はしないが、正極の表面側に、マンガン濃度が高く、空隙率が小さく緻密な表面層を確認することができた。   In order to confirm the state of the positive electrode of the nonaqueous electrolyte secondary battery according to Example 3, the cross-sectional state of the positive electrode was observed with WDX and SEM in the same manner as in Example 1. Although not shown, a dense surface layer having a high manganese concentration and a small porosity was confirmed on the surface side of the positive electrode.

実施例３にかかる非水電解質二次電池に対し、実施例１と同様に、５０℃の高温環境下において、正極活物質量当たり１０９.２ｍＡ／ｇの電流で、２.７〜４.２Ｖの間で定電流充放電を１００サイクル繰り返し、各充放電サイクル後の容量維持率を調べた。実施例３の１００サイクル後の容量維持率の劣化は１０％程度であり、極めて良好な、高温下での充放電サイクル特性を示した。   In the same manner as in Example 1, the nonaqueous electrolyte secondary battery according to Example 3 was 2.7 to 4.2 V at a current of 109.2 mA / g per positive electrode active material in a high temperature environment of 50 ° C. The constant current charging / discharging was repeated 100 cycles, and the capacity retention rate after each charging / discharging cycle was examined. The capacity retention rate after 100 cycles of Example 3 was about 10%, showing very good charge / discharge cycle characteristics at high temperatures.

なお、マンガン濃度の高い表面近傍または表面層を作製する方法は上記に記載した方法に限定されない。具体的には、集電体上にマンガン濃度の低い層を形成し、その上にマンガン濃度の高い表面層を形成する方法でも本発明と同様の効果が得られると考えられる。   In addition, the method of producing the surface vicinity or surface layer with high manganese concentration is not limited to the method described above. Specifically, it is considered that the same effect as in the present invention can be obtained by forming a layer having a low manganese concentration on the current collector and forming a surface layer having a high manganese concentration thereon.

１ａ：表面層
１ｂ：内部層 1a: surface layer 1b: inner layer

Claims (5)

正極と負極とを備えた非水電解質二次電池において、
前記正極と前記負極の少なくとも一方の電極が、スピネル型リチウムマンガン複合酸化物を含有する電極活物質層を備え、当該電極活物質層が、対向する他方の電極側の表面近傍において、前記スピネル型リチウムマンガン複合酸化物のマンガン濃度より高いマンガン濃度を有する柱状化合物を含有することを特徴とする非水電解質二次電池。 In a non-aqueous electrolyte secondary battery comprising a positive electrode and a negative electrode,
At least one of the positive electrode and the negative electrode includes an electrode active material layer containing a spinel-type lithium manganese composite oxide, and the electrode active material layer is in the vicinity of the surface on the other electrode side facing the spinel type. A non-aqueous electrolyte secondary battery comprising a columnar compound having a manganese concentration higher than that of the lithium manganese composite oxide . 前記電極活物質層が、対向する他方の電極側の表面近傍の表面層と、当該表面層の内側に位置する内部層との層状に形成されており、前記表面層が前記柱状化合物を含有し、前記内部層が前記スピネル型リチウムマンガン複合酸化物を含有することを特徴とする、請求項１に記載された非水電解質二次電池。 The electrode active material layer is formed in a layer form of a surface layer in the vicinity of the surface on the opposite electrode side and an inner layer located inside the surface layer, and the surface layer contains the columnar compound. The non-aqueous electrolyte secondary battery according to claim 1 , wherein the inner layer contains the spinel type lithium manganese composite oxide . 前記表面層の空隙率が、前記内部層の空隙率よりも小さいことを特徴とする、請求項２に記載された非水電解質二次電池。   The nonaqueous electrolyte secondary battery according to claim 2, wherein the porosity of the surface layer is smaller than the porosity of the inner layer. 前記電極活物質層が、前記正極の正極活物質層であることを特徴とする、請求項１ないし３のいずれか１項に記載された非水電解質二次電池。 The non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the electrode active material layer is a positive electrode active material layer of the positive electrode. 集電体と、当該集電体上に形成されるスピネル型リチウムマンガン複合酸化物を含有する電極活物質層とを備え、当該電極活物質層が、前記集電体側と反対側の表面近傍において、前記スピネル型リチウムマンガン複合酸化物のマンガン濃度より高いマンガン濃度を有する柱状化合物を含有することを特徴とする非水電解質二次電池用電極。 A current collector and an electrode active material layer containing a spinel-type lithium manganese oxide formed on the current collector , the electrode active material layer being in the vicinity of the surface opposite to the current collector side An electrode for a non-aqueous electrolyte secondary battery comprising a columnar compound having a manganese concentration higher than that of the spinel type lithium manganese composite oxide .
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JP2017224498A (en) * 2016-06-15 2017-12-21 旭化成株式会社 Manufacturing method of power storage module, and power storage module

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