JP2013062089A - Lithium ion secondary battery - Google Patents

Lithium ion secondary battery Download PDF

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JP2013062089A
JP2013062089A JP2011198829A JP2011198829A JP2013062089A JP 2013062089 A JP2013062089 A JP 2013062089A JP 2011198829 A JP2011198829 A JP 2011198829A JP 2011198829 A JP2011198829 A JP 2011198829A JP 2013062089 A JP2013062089 A JP 2013062089A
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positive electrode
secondary battery
ion secondary
lithium ion
lithium
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Yoshitomo Takebayashi
義友 竹林
Takeshi Abe
武志 阿部
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Toyota Motor Corp
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    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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    • Y02EREDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10Energy storage using batteries

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery capable of preventing deterioration of battery performance due to decomposition of an electrolyte by suppressing oxidative decomposition of the electrolyte during charging/discharging, in a lithium ion secondary battery having high battery voltage by using a positive electrode active material with high potential.SOLUTION: In a lithium ion secondary battery provided by the present invention, a positive electrode 64 comprises: a positive electrode collector 62; and a positive electrode mixture layer 66 formed on the collector and including at least a positive electrode active material 70. The positive electrode active material is a compound containing high-potential lithium and having a discharge potential of 4.5 V or more at a metal lithium electrode standard. A surface of the compound containing high-potential lithium is covered with a carbon material 72, and the carbon material has an average particle size of 50 nm or less.

Description

本発明は、リチウムイオン二次電池に関する。詳しくは、該電池の正極の構造に関する。   The present invention relates to a lithium ion secondary battery. In detail, it is related with the structure of the positive electrode of this battery.

リチウムイオンが正極と負極との間を行き来することにより充電及び放電するリチウムイオン二次電池は、軽量で高エネルギー密度が得られることから、例えば、電気を駆動源として利用する車両に搭載される電源、或いはパソコンや携帯端末その他の電気製品等に用いられる電源として好ましく用いられている。特にハイレートで充放電を行う車両用駆動源としての重要性が高まっている。   A lithium ion secondary battery that is charged and discharged by moving lithium ions back and forth between a positive electrode and a negative electrode can be mounted on a vehicle that uses electricity as a drive source, for example, because it is lightweight and has a high energy density. It is preferably used as a power source or a power source used for personal computers, portable terminals, and other electrical products. In particular, the importance as a vehicle drive source that charges and discharges at a high rate is increasing.

リチウムイオン二次電池の正極は、典型的には、正極集電体(導電性部材)と、該集電体上にリチウムイオンを可逆的に吸蔵および放出し得る物質(正極活物質)を主体とする電極材料が層状に形成された正極合材層とによって構成されている。
一般的なリチウムイオン二次電池の満充電時の電圧は約4Vであり、かかるリチウムイオン二次電池の性能(高電圧及び高容量)の更なる向上が望まれている。該二次電池の性能の向上のために、例えば、金属リチウム電極基準で4.5V以上の電位を有する高電位な正極活物質に関する研究が行われるようになってきた。
The positive electrode of a lithium ion secondary battery typically comprises a positive electrode current collector (conductive member) and a substance capable of reversibly occluding and releasing lithium ions (positive electrode active material) on the current collector. And a positive electrode mixture layer formed in layers.
The voltage at the time of full charge of a general lithium ion secondary battery is about 4V, and the further improvement of the performance (high voltage and high capacity) of such a lithium ion secondary battery is desired. In order to improve the performance of the secondary battery, for example, research on a high potential positive electrode active material having a potential of 4.5 V or more with respect to a metal lithium electrode has been conducted.

特開平11−283623号公報JP-A-11-283623 特開2003−157836号公報Japanese Patent Laid-Open No. 2003-155786 特開2009−152188号公報JP 2009-152188 A 特開2009−245808号公報JP 2009-245808 A 特開2003−292308号公報JP 2003-292308 A

しかしながら、正極活物質として上記のような高電位な正極活物質を使用する場合、リチウムイオン二次電池の満充電時において高い電池電圧(例えば4.3V以上)を得ることができるものの、かかる高電圧下では電解液と正極活物質との界面(表面)において、電解液の酸化分解反応が発生する虞がある。かかるリチウムイオン二次電池の充放電を繰り返し行うことで、該二次電池中の電解液の分解が進行してリチウムイオン二次電池の電池性能(例えばサイクル特性)が低下してしまう虞があるため、高電圧下でも電解液の酸化分解を抑制する技術が望まれていた。
そこで、本発明は上述した従来の課題を解決すべく創出されたものであり、その目的は高電位な正極活物質を用いることによって高い電池電圧を有するリチウムイオン二次電池において、充放電時の電解液の酸化分解を抑制して該電解液の分解に伴う電池性能の低下を防止し得るリチウムイオン二次電池を提供することである。
However, when a positive electrode active material having a high potential as described above is used as the positive electrode active material, a high battery voltage (for example, 4.3 V or more) can be obtained when the lithium ion secondary battery is fully charged. Under voltage, there is a possibility that an oxidative decomposition reaction of the electrolytic solution occurs at the interface (surface) between the electrolytic solution and the positive electrode active material. By repeatedly charging and discharging the lithium ion secondary battery, the electrolyte solution in the secondary battery may be decomposed to deteriorate the battery performance (for example, cycle characteristics) of the lithium ion secondary battery. Therefore, a technique for suppressing the oxidative decomposition of the electrolyte even under a high voltage has been desired.
Therefore, the present invention has been created to solve the above-described conventional problems, and the purpose of the present invention is to use a high potential positive electrode active material in a lithium ion secondary battery having a high battery voltage. It is an object of the present invention to provide a lithium ion secondary battery capable of suppressing the oxidative decomposition of the electrolytic solution and preventing the deterioration of the battery performance accompanying the decomposition of the electrolytic solution.

本発明者は種々検討した結果、高電位な正極活物質(リチウム含有化合物)を炭素材料で被覆するのみならず、炭素材料の平均粒径を規定することによって上記課題を解決することを見出して本発明を完成するに至った。なお、上記特許文献1〜特許文献5には、従来の正極活物質の表面を炭素材料で被覆するという技術が開示されているが、これらは本発明のように高電位の正極活物質に適用するような技術ではない。   As a result of various studies, the present inventor has found that the above problem can be solved not only by coating a high potential positive electrode active material (lithium-containing compound) with a carbon material but also by defining the average particle diameter of the carbon material. The present invention has been completed. In addition, the above Patent Documents 1 to 5 disclose techniques for coating the surface of a conventional positive electrode active material with a carbon material, but these are applied to a high potential positive electrode active material as in the present invention. It's not a technology to do.

本発明により提供されるリチウムイオン二次電池は、正極と、負極と、電解液と、を備えるリチウムイオン二次電池であって、典型的には、充電終止電圧(充電上限電圧)が4.3V以上(即ち極間電圧が4.3V以上)のリチウムイオン二次電池が提供される。即ちここで開示されるリチウムイオン二次電池において、上記正極は、正極集電体と、該集電体上に形成された少なくとも正極活物質を含む正極合材層とを備えている。上記正極活物質は、金属リチウム電極基準で4.5V以上の放電電位を有する高電位リチウム含有化合物である。上記高電位リチウム含有化合物の表面は、炭素材料によって被覆されている。そして、上記炭素材料の平均粒径は50nm以下であることを特徴とする。
なお、本明細書において「平均粒径」は、メジアン径(d50)をいい、市販されている種々のレーザー回折・散乱法に基づく粒度分布測定装置によって容易に測定することができる。
The lithium ion secondary battery provided by the present invention is a lithium ion secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, and typically has a charge end voltage (charge upper limit voltage) of 4. A lithium ion secondary battery having 3 V or more (that is, a voltage between electrodes of 4.3 V or more) is provided. That is, in the lithium ion secondary battery disclosed herein, the positive electrode includes a positive electrode current collector and a positive electrode mixture layer including at least a positive electrode active material formed on the current collector. The positive electrode active material is a high-potential lithium-containing compound having a discharge potential of 4.5 V or higher with respect to a metal lithium electrode. The surface of the high potential lithium-containing compound is covered with a carbon material. And the average particle diameter of the said carbon material is 50 nm or less, It is characterized by the above-mentioned.
In the present specification, the “average particle diameter” refers to a median diameter (d50) and can be easily measured by a commercially available particle size distribution measuring apparatus based on various laser diffraction / scattering methods.

このように、正極活物質としての高電位リチウム含有化合物の表面が平均粒径50nm以下の炭素材料によって被覆されていることにより、高電位リチウム含有化合物(正極活物質)と電解液との接触が抑制され、充電終止電圧(充電上限電圧)が4.3V以上の高電圧下であっても、該高電位リチウム含有化合物の表面における電解液の(過度な)分解を防止することができる。従って、本発明のリチウムイオン二次電池は、高い電池電圧が得られると共に、かかる高電圧下でも電解液の酸化分解反応に基づくリチウムイオンの消費を伴う不可逆容量を低減することができるためサイクル特性に優れる(即ち高い容量維持率を備える)リチウムイオン二次電池となり得る。   Thus, since the surface of the high potential lithium-containing compound as the positive electrode active material is coated with the carbon material having an average particle size of 50 nm or less, the contact between the high potential lithium-containing compound (positive electrode active material) and the electrolyte is prevented. Even if the charge end voltage (charge upper limit voltage) is under a high voltage of 4.3 V or higher, (excessive) decomposition of the electrolyte solution on the surface of the high potential lithium-containing compound can be prevented. Therefore, the lithium ion secondary battery of the present invention can obtain a high battery voltage and can reduce the irreversible capacity accompanying the consumption of lithium ions based on the oxidative decomposition reaction of the electrolytic solution even under such a high voltage. (Ie, having a high capacity retention rate) lithium ion secondary battery.

ここで開示されるリチウムイオン二次電池の好適な一態様では、上記炭素材料の被覆量は、上記高電位リチウム含有化合物を100質量%としたときに1質量%〜8質量%であることを特徴とする。
かかる構成によると、高電位リチウム含有化合物の表面が適当な量の炭素材料で被覆されているため、高電圧下における電解液の分解を効果的に防止することができる。
好ましくは、上記炭素材料の被覆量は、上記高電位リチウム含有化合物を100質量%としたときに3質量%〜5質量%である。かかる構成によると、高電圧下における電解液の分解をより効果的に防止することができるため、より高い容量維持率が得られる。
In a preferred aspect of the lithium ion secondary battery disclosed herein, the amount of the carbon material coated is 1% by mass to 8% by mass when the high potential lithium-containing compound is 100% by mass. Features.
According to this configuration, since the surface of the high potential lithium-containing compound is coated with an appropriate amount of carbon material, it is possible to effectively prevent the electrolytic solution from being decomposed under a high voltage.
Preferably, the coating amount of the carbon material is 3% by mass to 5% by mass when the high potential lithium-containing compound is 100% by mass. According to such a configuration, decomposition of the electrolytic solution under a high voltage can be more effectively prevented, and thus a higher capacity maintenance rate can be obtained.

ここで開示されるリチウムイオン二次電池の好適な他の一態様では、上記高電位リチウム含有化合物は、LiNi0.5Mn1.5であることを特徴とする。
LiNi0.5Mn1.5は、金属リチウム電極基準で高い放電電位を有するためリチウムイオン二次電池において高い電池電圧を得られ得る一方、かかる高電圧下(例えば4.3V以上の電圧下)ではLiNi0.5Mn1.5と電解液との界面において、電解液が酸化分解しやすい傾向にある。従って、正極活物質として高電位リチウム含有化合物であるLiNi0.5Mn1.5を用いたリチウムイオン二次電池では、高電位リチウム含有化合物の表面が所定の平均粒径を有する炭素材料によって被覆されているという本発明の構成を採用することによる効果が特に発揮され得る。
In another preferred embodiment of the lithium ion secondary battery disclosed herein, the high potential lithium-containing compound is LiNi 0.5 Mn 1.5 O 4 .
Since LiNi 0.5 Mn 1.5 O 4 has a high discharge potential with respect to a metal lithium electrode, a high battery voltage can be obtained in a lithium ion secondary battery, while under such a high voltage (eg, a voltage of 4.3 V or more). Below), the electrolyte solution tends to be oxidatively decomposed at the interface between LiNi 0.5 Mn 1.5 O 4 and the electrolyte solution. Accordingly, in a lithium ion secondary battery using LiNi 0.5 Mn 1.5 O 4 which is a high potential lithium-containing compound as a positive electrode active material, a carbon material having a predetermined average particle size on the surface of the high potential lithium-containing compound The effect of adopting the configuration of the present invention that is covered with can be particularly exhibited.

ここで開示されるリチウムイオン二次電池の好適な他の一態様では、上記炭素材料は、平均粒径が30nm〜40nmのアセチレンブラックであることを特徴とする。
かかる構成によると、高電位リチウム含有化合物と電解液との接触を抑制すると共に、リチウムイオン二次電池の直流抵抗の増加を抑制することができる。
In another preferred embodiment of the lithium ion secondary battery disclosed herein, the carbon material is acetylene black having an average particle diameter of 30 nm to 40 nm.
According to this configuration, it is possible to suppress the contact between the high-potential lithium-containing compound and the electrolytic solution, and it is possible to suppress an increase in DC resistance of the lithium ion secondary battery.

ここで開示されるリチウムイオン二次電池の好適な一態様では、上記負極は、負極集電体と、該集電体上に形成された少なくとも負極活物質を含む負極合材層とを備えており、上記負極活物質は、黒鉛材料であることを特徴とする。
このように、負極活物質として黒鉛材料を用い、正極活物質として上記高電位リチウム含有化合物を用いることによって高い電池電圧を有するリチウムイオン二次電池が得られる。
In a preferred aspect of the lithium ion secondary battery disclosed herein, the negative electrode includes a negative electrode current collector and a negative electrode mixture layer including at least a negative electrode active material formed on the current collector. The negative electrode active material is a graphite material.
Thus, a lithium ion secondary battery having a high battery voltage can be obtained by using a graphite material as the negative electrode active material and using the high potential lithium-containing compound as the positive electrode active material.

上述のように、ここで開示されるいずれかのリチウムイオン二次電池は、高い電池電圧(即ち高容量)と高い容量維持率を有するリチウムイオン二次電池となり得るため、かかるリチウムイオン二次電池を複数個(例えば10個以上、好ましくは10〜30個程度)直列に接続された組電池の形態で車両(典型的には自動車、特にハイブリッド自動車、電気自動車、燃料電池自動車のような電動機を備える自動車)の駆動電源として好ましく用いることができる。   As described above, any of the lithium ion secondary batteries disclosed herein can be a lithium ion secondary battery having a high battery voltage (that is, high capacity) and a high capacity retention rate. A plurality of (for example, 10 or more, preferably about 10 to 30) vehicles in the form of battery packs connected in series (typically motors such as automobiles, particularly hybrid cars, electric cars, fuel cell cars, etc.) It can be preferably used as a drive power source for an automobile equipped with the vehicle.

本発明の一実施形態に係るリチウムイオン二次電池の外形を模式的に示す斜視図である。It is a perspective view which shows typically the external shape of the lithium ion secondary battery which concerns on one Embodiment of this invention. 図1中のII‐II線に沿う断面図である。It is sectional drawing which follows the II-II line | wire in FIG. 本発明の一実施形態に係る正極の構造を模式的に示す図である。It is a figure which shows typically the structure of the positive electrode which concerns on one Embodiment of this invention. 炭素材料の平均粒径と容量維持率との関係を示すグラフである。It is a graph which shows the relationship between the average particle diameter of a carbon material, and a capacity | capacitance maintenance factor. 炭素材料の平均粒径と直流抵抗との関係を示すグラフである。It is a graph which shows the relationship between the average particle diameter of a carbon material, and direct current | flow resistance. 炭素材料の被覆量と容量維持率との関係を示すグラフである。It is a graph which shows the relationship between the coating amount of a carbon material, and a capacity | capacitance maintenance factor. 炭素材料の被覆量と直流抵抗との関係を示すグラフである。It is a graph which shows the relationship between the coating amount of a carbon material, and direct current | flow resistance. 本発明に係るリチウムイオン二次電池を備えた車両(自動車)を模式的に示す側面図である。It is a side view which shows typically the vehicle (automobile) provided with the lithium ion secondary battery which concerns on this invention.

以下、本発明の好適な実施形態を説明する。なお、本明細書において特に言及している事項以外の事柄であって本発明の実施に必要な事項は、当該分野における従来技術に基づく当業者の設計事項として把握され得る。本発明は、本明細書に開示されている内容と当該分野における技術常識に基づいて実施することができる。   Hereinafter, preferred embodiments of the present invention will be described. It should be noted that matters other than matters specifically mentioned in the present specification and necessary for carrying out the present invention can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

本発明によって提供されるリチウムイオン二次電池は、上述の通り充電終止電圧(充電上限電圧)が4.3V以上のリチウムイオン二次電池であって、正極と負極と電解液とを備えており、該正極に含まれる金属リチウム電極基準で4.5V以上の放電電位を有する高電位リチウム含有化合物(正極活物質)の表面が平均粒径50nm以下の炭素材料によって被覆されていることによって特徴づけられる。以下、ここで開示されるリチウムイオン二次電池について詳細に説明する。   The lithium ion secondary battery provided by the present invention is a lithium ion secondary battery having a charge end voltage (charge upper limit voltage) of 4.3 V or higher as described above, and includes a positive electrode, a negative electrode, and an electrolyte. The surface of a high-potential lithium-containing compound (positive electrode active material) having a discharge potential of 4.5 V or higher with respect to the metal lithium electrode contained in the positive electrode is characterized by being coated with a carbon material having an average particle size of 50 nm or less. It is done. Hereinafter, the lithium ion secondary battery disclosed herein will be described in detail.

まず、本発明によって提供されるリチウムイオン二次電池の正極について説明する。ここで開示される正極は、正極集電体と、該正極集電体上に形成された少なくとも正極活物質を含む正極合材層とを備えている。
ここで開示されるリチウムイオン二次電池の正極で用いられる正極集電体としては、従来のリチウムイオン二次電池の正極に用いられている正極集電体と同様、アルミニウム又はアルミニウムを主体とするアルミニウム合金が用いられる。正極集電体の形状は、リチウムイオン二次電池の形状等に応じて異なり得るため、特に制限はなく、箔状、シート状、棒状、板状等の種々の形態であり得る。
First, the positive electrode of the lithium ion secondary battery provided by the present invention will be described. The positive electrode disclosed here includes a positive electrode current collector and a positive electrode mixture layer including at least a positive electrode active material formed on the positive electrode current collector.
The positive electrode current collector used in the positive electrode of the lithium ion secondary battery disclosed here is mainly composed of aluminum or aluminum, as in the positive electrode current collector used in the positive electrode of a conventional lithium ion secondary battery. An aluminum alloy is used. The shape of the positive electrode current collector may vary depending on the shape or the like of the lithium ion secondary battery, and is not particularly limited, and may be various forms such as a foil shape, a sheet shape, a rod shape, and a plate shape.

ここで開示されるリチウムイオン二次電池の正極で用いられる正極活物質は、リチウム元素と一種または二種以上の遷移金属元素とを含む化合物であって、金属リチウム電極基準で4.5V以上の放電電位を有する高電位リチウム含有化合物である。かかる高電位リチウム含有化合物は、リチウムイオンを吸蔵及び放出可能な化合物であり、例えば、LiMn2−x(ここで、0≦x<2、典型的には0≦x≦1。M=Ni,Co,Cr等の一種以上の金属元素(典型的には遷移金属元素))、LiMO(M=Mn,Fe等の一種以上の金属元素(典型的には遷移金属元素))、LiMPO(M=Ni,CO等の一種以上の金属元素(典型的には遷移金属元素))、LiMPOF(M=Ni,Co等の一種以上の金属元素(典型的には遷移金属元素))等が挙げられる。上記正極活物質(高電位リチウム含有化合物)は、後述する負極活物質と組み合わせた際に、リチウムイオン二次電池の充電終止電圧が4.3V以上(即ち極間電圧が4.3V以上)となるように適宜決定することができる。 The positive electrode active material used in the positive electrode of the lithium ion secondary battery disclosed herein is a compound containing a lithium element and one or more transition metal elements, and is 4.5 V or more based on a metal lithium electrode It is a high potential lithium-containing compound having a discharge potential. Such a high-potential lithium-containing compound is a compound capable of inserting and extracting lithium ions, for example, LiMn 2−x M x O 4 (where 0 ≦ x <2, typically 0 ≦ x ≦ 1. M = one or more metal elements (typically transition metal elements) such as Ni, Co, Cr, etc., Li 2 MO 3 (M = one or more metal elements such as Mn, Fe (typically transition metal elements) )), LiMPO 4 (one or more metal elements such as M = Ni, CO (typically transition metal elements)), Li 2 MPO 4 F (one or more metal elements such as M = Ni, Co (typical) Includes transition metal elements)) and the like. When the positive electrode active material (high potential lithium-containing compound) is combined with a negative electrode active material described later, the charge end voltage of the lithium ion secondary battery is 4.3 V or higher (that is, the interelectrode voltage is 4.3 V or higher). It can be determined as appropriate.

上記高電位リチウム含有化合物(正極活物質)の表面を被覆する炭素材料としては、例えば、天然黒鉛粒子、人工黒鉛(人造黒鉛)粒子、カーボン粒子等が挙げられる。カーボン粒子としては、種々のカーボンブラック(例えば、アセチレンブラック、ケッチェンブラック、ファーネスブラック等)を用いることができる。これらのうち一種又は二種以上を併用してもよい。
上記粒子状の炭素材料(典型的には一次粒子)の平均粒径(メジアン径d50)は、例えば、50nm以下(通常は10nm〜50nm。例えば20nm〜40nm。好ましくは30nm〜40nm)である。上記炭素材料の平均粒径が50nmよりも大きすぎる場合には、上記高電位リチウム含有化合物の表面を十分に被覆することができず、高電位リチウム含有化合物と電解液との接触を防止することができない虞がある。
上記高電位リチウム含有化合物(正極活物質)の表面を被覆する上記炭素材料の被覆量は、上記高電位リチウム含有化合物を100質量%としたときに凡そ1質量%〜8質量%(例えば、1.5質量%〜7質量%。好ましくは3質量%〜5質量%)である。高電位リチウム含有化合物の表面を被覆する炭素材料の被覆量が、1質量%よりも小さすぎる場合や8質量%よりも大きすぎる場合には、高電位リチウム含有化合物と電解液との接触を十分に抑制することができず、電解液の酸化分解反応が進行する虞がある。
また、上記炭素材料の被覆量が、上記高電位リチウム含有化合物を100質量%としたときに凡そ1質量%〜6質量%(例えば、1.5質量%〜5質量%。好ましくは1.5質量%〜3質量%。)の場合には、高電位リチウム含有化合物の表面が適切な量の炭素材料に被覆されているため、かかる炭素材料で被覆された高電位リチウム含有化合物(被覆正極活物質)を含むリチウムイオン二次電池では充放電の際の直流抵抗を低く抑えることができる。
上記炭素材料の被覆量が、上記高電位リチウム含有化合物を100質量%としたときに凡そ2質量%〜4質量%(例えば、3質量%〜4質量%。)の場合には、より高い容量維持率とより低い直流抵抗を有する優れたリチウムイオン二次電池となり得る。
Examples of the carbon material that covers the surface of the high potential lithium-containing compound (positive electrode active material) include natural graphite particles, artificial graphite (artificial graphite) particles, and carbon particles. As the carbon particles, various carbon blacks (for example, acetylene black, ketjen black, furnace black, etc.) can be used. Among these, you may use together 1 type, or 2 or more types.
The average particle diameter (median diameter d50) of the particulate carbon material (typically primary particles) is, for example, 50 nm or less (usually 10 nm to 50 nm, for example, 20 nm to 40 nm, preferably 30 nm to 40 nm). When the average particle size of the carbon material is too larger than 50 nm, the surface of the high-potential lithium-containing compound cannot be sufficiently covered, and contact between the high-potential lithium-containing compound and the electrolytic solution is prevented. There is a possibility of not being able to.
The coating amount of the carbon material covering the surface of the high potential lithium-containing compound (positive electrode active material) is about 1% by mass to 8% by mass (for example, 1%) when the high potential lithium-containing compound is 100% by mass. 0.5 mass% to 7 mass%, preferably 3 mass% to 5 mass%). When the coating amount of the carbon material that coats the surface of the high potential lithium-containing compound is too smaller than 1% by mass or larger than 8% by mass, sufficient contact between the high potential lithium-containing compound and the electrolytic solution is sufficient. There is a risk that the oxidative decomposition reaction of the electrolytic solution proceeds.
Further, the coating amount of the carbon material is about 1% by mass to 6% by mass (for example, 1.5% by mass to 5% by mass, preferably 1.5% when the high potential lithium-containing compound is 100% by mass). Mass% to 3 mass%), since the surface of the high potential lithium-containing compound is coated with an appropriate amount of carbon material, the high potential lithium-containing compound coated with the carbon material (coated positive electrode active In a lithium ion secondary battery containing a substance, direct current resistance during charging and discharging can be kept low.
When the coating amount of the carbon material is about 2% by mass to 4% by mass (for example, 3% by mass to 4% by mass) when the high potential lithium-containing compound is 100% by mass, a higher capacity is obtained. It can be an excellent lithium ion secondary battery having a maintenance rate and a lower DC resistance.

上記高電位リチウム含有化合物(正極活物質)の表面を上記所定の平均粒径を有する炭素材料で被覆する方法としては、該化合物の表面を炭素材料で被覆できる限り特に制限はなく従来公知の方法を用いることができる。例えば、ビーズミル、ボールミル又は遊星ミル等の粉体処理装置を用いて高電位リチウム含有化合物及び炭素材料にメカノケミカル処理を施し、高電位リチウム含有化合物の表面を炭素材料で被覆する方法が挙げられる。ここで、「メカノケミカル処理」とは、被処理物(本実施形態では、上記高電位リチウム含有化合物と炭素材料)に圧縮力、剪断力、摩擦力等の機械的エネルギーを加えることにより、被処理物同士を物理的(機械的)に結合(複合化)させることをいう。   The method of coating the surface of the high potential lithium-containing compound (positive electrode active material) with the carbon material having the predetermined average particle diameter is not particularly limited as long as the surface of the compound can be coated with the carbon material, and is a conventionally known method. Can be used. For example, a high potential lithium-containing compound and a carbon material are subjected to mechanochemical treatment using a powder processing apparatus such as a bead mill, a ball mill, or a planetary mill, and the surface of the high potential lithium-containing compound is coated with the carbon material. Here, the “mechanochemical treatment” refers to an object to be treated (in this embodiment, the high-potential lithium-containing compound and the carbon material) by applying mechanical energy such as compressive force, shearing force, and frictional force. This means that the processed products are physically (mechanically) bonded (composited).

上記正極合材層は、上記炭素材料で表面を被覆された高電位リチウム含有化合物(被覆正極活物質)の他に、導電材、結着材(バインダ)等の任意の成分を必要に応じて含有し得る。
上記導電材としては、従来この種のリチウムイオン二次電池の正極で用いられているものであればよく、特定の導電材に限定されない。例えば、カーボン粉末やカーボンファイバー等のカーボン材料を用いることができる。カーボン粉末としては、種々のカーボンブラック(例えば、アセチレンブラック、ファーネスブラック、ケッチェンブラック等)、グラファイト粉末等のカーボン粉末を用いることができる。これらのうち一種又は二種以上を併用してもよい。導電材の使用量については特に限定されるものではないが、例えば、上記被覆正極活物質100質量%に対して1質量%〜20質量%(好ましくは5質量%〜15質量%)とすることが例示される。
In addition to the high-potential lithium-containing compound (coated positive electrode active material) whose surface is coated with the carbon material, the positive electrode mixture layer may contain any component such as a conductive material and a binder (binder) as necessary. May be contained.
The conductive material is not limited to a specific conductive material as long as it is conventionally used in the positive electrode of this type of lithium ion secondary battery. For example, carbon materials such as carbon powder and carbon fiber can be used. As the carbon powder, various carbon blacks (for example, acetylene black, furnace black, ketjen black, etc.), carbon powders such as graphite powder can be used. Among these, you may use together 1 type, or 2 or more types. The amount of the conductive material used is not particularly limited. For example, the amount is 1% by mass to 20% by mass (preferably 5% by mass to 15% by mass) with respect to 100% by mass of the coated positive electrode active material. Is exemplified.

上記結着材(バインダ)としては、一般的なリチウムイオン二次電池の正極に使用される結着材と同様のものを適宜採用することができる。例えば、上記正極合材層を形成する組成物として溶剤系のペーストを用いる場合には、ポリフッ化ビニリデン(PVDF)、ポリ塩化ビニリデン(PVDC)等の、有機溶媒(非水溶媒)に溶解するポリマー材料を用いることができる。あるいは、水系のペースト状組成物(ペースト状組成物には、スラリー状組成物及びインク状組成物が包含される。)を用いる場合には、水に溶解または分散するポリマー材料を好ましく採用し得る。例えば、ポリテトラフルオロエチレン(PTFE)、カルボキシメチルセルロース(CMC)等が挙げられる。なお、上記で例示したポリマー材料は、結着材として用いられる他に、上記組成物の増粘剤その他の添加剤として使用されることもあり得る。結着材の使用量は特に限定されるものではないが、例えば、上記被覆正極活物質100質量%に対して0.5質量%〜10質量%とすることができる。   As said binder (binder), the thing similar to the binder used for the positive electrode of a common lithium ion secondary battery can be employ | adopted suitably. For example, when a solvent-based paste is used as the composition for forming the positive electrode mixture layer, a polymer that dissolves in an organic solvent (non-aqueous solvent) such as polyvinylidene fluoride (PVDF) or polyvinylidene chloride (PVDC). Materials can be used. Alternatively, when an aqueous paste-like composition (a paste-like composition includes a slurry-like composition and an ink-like composition) is used, a polymer material that dissolves or disperses in water can be preferably used. . For example, polytetrafluoroethylene (PTFE), carboxymethyl cellulose (CMC) and the like can be mentioned. In addition, the polymer material illustrated above may be used as a thickener and other additives in the above composition in addition to being used as a binder. Although the usage-amount of a binder is not specifically limited, For example, it can be 0.5 mass%-10 mass% with respect to 100 mass% of the said covering positive electrode active materials.

ここで、「溶剤系のペースト状組成物」とは、正極活物質(高電位リチウム含有化合物)の分散媒が主として有機溶媒である組成物を指す概念である。有機溶媒としては、例えば、N‐メチルピロリドン(NMP)等を用いることができる。「水系のペースト状組成物」とは、正極活物質の分散媒として水または水を主体とする混合溶媒を用いた組成物を指す概念である。かかる混合溶媒を構成する水以外の溶媒としては、水と均一に混合し得る有機溶媒(低級アルコール、低級ケトン等)の一種または二種以上を適宜選択して用いることができる。   Here, the “solvent-based paste-like composition” is a concept indicating a composition in which the dispersion medium of the positive electrode active material (high potential lithium-containing compound) is mainly an organic solvent. As the organic solvent, for example, N-methylpyrrolidone (NMP) can be used. The “aqueous paste-like composition” is a concept indicating a composition using water or a mixed solvent mainly containing water as a dispersion medium of the positive electrode active material. As a solvent other than water constituting such a mixed solvent, one or more organic solvents (lower alcohol, lower ketone, etc.) that can be uniformly mixed with water can be appropriately selected and used.

ここで開示されるリチウムイオン二次電池の正極は、例えば、以下のようにして作製することができる。上記炭素材料で表面を被覆された高電位リチウム含有化合物(被覆正極活物質)と他の任意成分(上記導電材、結着材等)とを適当な溶媒に分散したペースト状の正極合材層形成用組成物を用意(調製、購入等)する。そして、該用意した組成物を正極集電体の表面に塗布(付与)して該組成物を乾燥させて正極合材層を形成した後、必要に応じて圧縮(プレス)する。これにより、正極集電体と、該正極集電体上に形成された正極合材層とを備える正極を作製することができる。
なお、上記組成物を正極集電体上に塗布する方法としては、従来公知の方法と同様の技法を適宜採用することができる。例えば、ダイコーター、スリットコーター、グラビアコーター等の適当な塗布装置を使用することにより、正極集電体に上記組成物を好適に塗布することができる。また、圧縮(プレス)方法としては、従来公知のロールプレス法、平板プレス法等の圧縮方法を採用することができる。
The positive electrode of the lithium ion secondary battery disclosed here can be produced as follows, for example. A paste-like positive electrode mixture layer in which a high-potential lithium-containing compound (coated positive electrode active material) whose surface is coated with the carbon material and other optional components (the conductive material, binder, etc.) are dispersed in an appropriate solvent. A forming composition is prepared (prepared, purchased, etc.). Then, the prepared composition is applied (applied) to the surface of the positive electrode current collector, the composition is dried to form a positive electrode mixture layer, and then compressed (pressed) as necessary. Thereby, a positive electrode provided with a positive electrode current collector and a positive electrode mixture layer formed on the positive electrode current collector can be produced.
In addition, as a method of apply | coating the said composition on a positive electrode electrical power collector, the technique similar to a conventionally well-known method is employable suitably. For example, the composition can be suitably applied to the positive electrode current collector by using an appropriate application device such as a die coater, a slit coater, or a gravure coater. Moreover, as a compression (pressing) method, conventionally known compression methods such as a roll press method and a flat plate press method can be employed.

図3に示すように、上記のようにして作製された正極(正極シート)64は、正極集電体62と、該集電体62上に形成された少なくとも正極活物質(高電位リチウム含有化合物)70を含む正極合材層66とを備えている。正極合材層66中の正極活物質70は、その表面が所定の平均粒径(50nm以下)を有する炭素材料72で被覆されているため、正極活物質70と電解液との接触が抑制される。従って、正極活物質として金属リチウム電極基準で4.5V以上の放電電位を有する高電位リチウム含有化合物を用いることにより充電終止電圧(充電上限電圧)が4.3V以上の高電圧を有するリチウムイオン二次電池であっても、該正極活物質(高電位リチウム含有化合物)の表面における電解液の過度な分解を防止することができる。なお、図3において導電材、結着材等の図示は省略している。   As shown in FIG. 3, the positive electrode (positive electrode sheet) 64 manufactured as described above includes a positive electrode current collector 62 and at least a positive electrode active material (high potential lithium-containing compound) formed on the current collector 62. ) And a positive electrode mixture layer 66 including 70. Since the surface of the positive electrode active material 70 in the positive electrode mixture layer 66 is coated with a carbon material 72 having a predetermined average particle size (50 nm or less), contact between the positive electrode active material 70 and the electrolytic solution is suppressed. The Therefore, by using a high-potential lithium-containing compound having a discharge potential of 4.5 V or higher with respect to the metal lithium electrode as the positive electrode active material, Even in the secondary battery, excessive decomposition of the electrolytic solution on the surface of the positive electrode active material (high potential lithium-containing compound) can be prevented. In addition, illustration of a conductive material, a binder, etc. is abbreviate | omitted in FIG.

次に、ここで開示されるリチウムイオン二次電池に備えられる負極について説明する。かかる負極は、負極集電体と、該負極集電体上に形成された少なくとも負極活物質を含む負極合材層とを備えている。
上記負極活物質としては、従来からリチウムイオン二次電池の負極に用いられる材料の一種または二種以上を特に限定なく使用することができる。例えば、黒鉛(グラファイト)等のカーボン材料、リチウム・チタン酸化物(LiTi12)等の酸化物材料、スズ、アルミニウム(Al)、亜鉛(Zn)、ケイ素(Si)等の金属若しくはこれらの金属元素を主体とする金属合金からなる金属材料、等が挙げられる。
特に充電終止電圧が4.3V以上のリチウムイオン二次電池を作製するために、金属リチウム電極基準で凡そ0.1V〜0.2Vの低い放電電位を有する黒鉛材料(典型的には天然黒鉛や人造黒鉛等)を好適に使用することができる。さらに、かかる黒鉛材料の表面を非晶質炭素膜で被覆してもよい。
Next, the negative electrode provided in the lithium ion secondary battery disclosed here will be described. The negative electrode includes a negative electrode current collector and a negative electrode mixture layer including at least a negative electrode active material formed on the negative electrode current collector.
As the negative electrode active material, one or more materials conventionally used for negative electrodes of lithium ion secondary batteries can be used without particular limitation. For example, carbon materials such as graphite (graphite), oxide materials such as lithium titanium oxide (Li 4 Ti 5 O 12 ), metals such as tin, aluminum (Al), zinc (Zn), silicon (Si), or Examples thereof include metal materials composed of metal alloys mainly composed of these metal elements.
In particular, in order to produce a lithium ion secondary battery having a charge end voltage of 4.3 V or more, a graphite material having a low discharge potential of about 0.1 V to 0.2 V with respect to a metal lithium electrode (typically natural graphite or Artificial graphite or the like) can be preferably used. Further, the surface of the graphite material may be covered with an amorphous carbon film.

上記負極合材層は、上記負極活物質の他に、結着材(バインダ)、増粘材等の任意の成分を必要に応じて含有し得る。
上記結着材としては、一般的なリチウムイオン二次電池の負極に使用される結着材と同様のものを適宜採用することができる。例えば、負極合材層を形成するために水系のペースト状組成物を用いる場合には、水に溶解または分散するポリマー材料を好ましく採用し得る。水に分散する(水分散性の)ポリマー材料としては、スチレンブタジエンゴム(SBR)、フッ素ゴム等のゴム類;ポリエチレンオキサイド(PEO)、ポリテトラフルオロエチレン(PTFE)等のフッ素系樹脂;酢酸ビニル共重合体等が例示される。
The negative electrode mixture layer may contain any component such as a binder (binder) and a thickener as necessary in addition to the negative electrode active material.
As said binder, the thing similar to the binder used for the negative electrode of a general lithium ion secondary battery can be employ | adopted suitably. For example, when an aqueous paste composition is used to form the negative electrode mixture layer, a polymer material that is dissolved or dispersed in water can be preferably used. Polymer materials that disperse in water (water dispersible) include rubbers such as styrene butadiene rubber (SBR) and fluorine rubber; fluorine resins such as polyethylene oxide (PEO) and polytetrafluoroethylene (PTFE); vinyl acetate Examples thereof include copolymers.

また、上記増粘材としては、水若しくは溶剤(有機溶媒)に溶解又は分散するポリマー材料を採用し得る。水に溶解する(水溶性の)ポリマー材料としては、例えば、カルボキシメチルセルロース(CMC)、メチルセルロース(MC)、酢酸フタル酸セルロース(CAP)、ヒドロキシプロピルメチルセルロース(HPMC)等のセルロース系ポリマー;ポリビニルアルコール(PVA);等が挙げられる。   Moreover, as the thickener, a polymer material that is dissolved or dispersed in water or a solvent (organic solvent) can be employed. Examples of water-soluble (water-soluble) polymer materials include cellulose polymers such as carboxymethyl cellulose (CMC), methyl cellulose (MC), cellulose acetate phthalate (CAP), and hydroxypropylmethyl cellulose (HPMC); polyvinyl alcohol ( PVA); and the like.

上記負極合材層は、例えば、上記負極活物質と、他の任意成分(結着材、増粘材等)とを適当な溶媒(例えば水)に分散したペースト状の負極合材層形成用組成物を用意(調製、購入等)し、該組成物を負極集電体の表面に塗布(付与)して該組成物を乾燥させた後に、必要に応じてプレス(圧縮)することによって負極合材層が形成される。これにより、負極集電体と、負極合材層を備える負極を作製することができる。   The negative electrode mixture layer is, for example, for forming a paste-like negative electrode mixture layer in which the negative electrode active material and other optional components (binder, thickener, etc.) are dispersed in an appropriate solvent (for example, water). Prepare the composition (preparation, purchase, etc.), apply (apply) the composition to the surface of the negative electrode current collector, dry the composition, and then press (compress) the negative electrode as necessary. A composite layer is formed. Thereby, a negative electrode provided with a negative electrode current collector and a negative electrode mixture layer can be produced.

以下、ここで開示される正極を備えるリチウムイオン二次電池の一形態を図面を参照しつつ説明するが、本発明をかかる実施形態に限定することを意図したものではない。即ち、上記正極が採用される限りにおいて、作製されるリチウムイオン二次電池の形状(外形やサイズ)には特に制限はない。以下の実施形態では、捲回電極体および電解液を角型形状の電池ケースに収容した構成のリチウムイオン二次電池を例にして説明する。
なお、以下の図面において、同じ作用を奏する部材・部位には同じ符号を付し、重複する説明は省略することがある。また、各図における寸法関係(長さ、幅、厚さ等)は、必ずしも実際の寸法関係を反映するものではない。
Hereinafter, although one form of a lithium ion secondary battery provided with the positive electrode disclosed here is demonstrated with reference to drawings, it is not intending to limit this invention to this embodiment. That is, as long as the positive electrode is employed, the shape (outer shape and size) of the manufactured lithium ion secondary battery is not particularly limited. In the following embodiment, a lithium ion secondary battery having a configuration in which a wound electrode body and an electrolytic solution are housed in a rectangular battery case will be described as an example.
In addition, in the following drawings, the same code | symbol is attached | subjected to the member and site | part which show | plays the same effect | action, and the overlapping description may be abbreviate | omitted. Moreover, the dimensional relationship (length, width, thickness, etc.) in each drawing does not necessarily reflect the actual dimensional relationship.

図1は、本実施形態に係るリチウムイオン二次電池(二次電池)10を模式的に示す斜視図である。図2は、図1中のII−II線に沿う縦断面図である。
図1に示すように、本実施形態に係るリチウムイオン二次電池10は、金属製(樹脂製又はラミネートフィルム製も好適である。)の電池ケース15を備える。このケース(外容器)15は、上端が開放された扁平な直方体状のケース本体30と、その開口部20を塞ぐ蓋体25とを備える。溶接等により蓋体25は、ケース本体30の開口部20を封止している。ケース15の上面(すなわち蓋体25)には、捲回電極体50の正極(正極シート)64と電気的に接続する正極端子60および該電極体の負極(負極シート)84と電気的に接続する負極端子80が設けられている。また、蓋体25には、従来のリチウムイオン二次電池のケースと同様に、電池異常の際にケース15内部で発生したガスをケース15の外部に排出するための安全弁40が設けられている。ケース15の内部には、正極シート64および負極シート84を計二枚のセパレータシート95とともに積層して捲回し、次いで得られた捲回体を側面方向から押しつぶして拉げさせることによって作製される扁平形状の捲回電極体50及び電解液(電解質)が収容されている。
FIG. 1 is a perspective view schematically showing a lithium ion secondary battery (secondary battery) 10 according to the present embodiment. FIG. 2 is a longitudinal sectional view taken along line II-II in FIG.
As shown in FIG. 1, the lithium ion secondary battery 10 according to this embodiment includes a battery case 15 made of metal (a resin or a laminate film is also suitable). The case (outer container) 15 includes a flat cuboid case main body 30 having an open upper end, and a lid body 25 that closes the opening 20. The lid body 25 seals the opening 20 of the case main body 30 by welding or the like. The upper surface of the case 15 (that is, the lid body 25) is electrically connected to the positive electrode terminal 60 electrically connected to the positive electrode (positive electrode sheet) 64 of the wound electrode body 50 and the negative electrode (negative electrode sheet) 84 of the electrode body. A negative electrode terminal 80 is provided. In addition, the lid 25 is provided with a safety valve 40 for discharging the gas generated inside the case 15 to the outside of the case 15 when the battery is abnormal, as in the case of the conventional lithium ion secondary battery. . In the case 15, the positive electrode sheet 64 and the negative electrode sheet 84 are laminated together with a total of two separator sheets 95 and wound, and then the obtained wound body is crushed from the side direction and ablated. A flat wound electrode body 50 and an electrolytic solution (electrolyte) are accommodated.

上記積層の際には、図2に示すように、正極シート64の正極合材層非形成部分(即ち正極合材層66が形成されずに正極集電体62が露出した部分)と負極シート84の負極合材層非形成部分(即ち負極合材層90が形成されずに負極集電体82が露出した部分)とがセパレータシート95の幅方向の両側からそれぞれはみ出すように、正極シート64と負極シート84とを幅方向にややずらして重ね合わせる。その結果、捲回電極体50の捲回方向に対する横方向において、正極シート64および負極シート84の電極合材層非形成部分がそれぞれ捲回コア部分(すなわち正極シート64の正極合材層形成部分と負極シート84の負極合材層形成部分と二枚のセパレータシート95とが密に捲回された部分)から外方にはみ出ている。かかる正極側はみ出し部分に正極端子60を接合して、上記扁平形状に形成された捲回電極体50の正極シート64と正極端子60とを電気的に接続する。同様に負極側はみ出し部分に負極端子80を接合して、負極シート84と負極端子80とを電気的に接続する。なお、正負極端子60,80と正負極集電体62,82とは、例えば、超音波溶接、抵抗溶接等によりそれぞれ接合することができる。   At the time of the above lamination, as shown in FIG. 2, the positive electrode mixture layer non-formed portion of the positive electrode sheet 64 (that is, the portion where the positive electrode current collector 62 is exposed without forming the positive electrode mixture layer 66) and the negative electrode sheet The negative electrode composite material layer non-formed portion 84 (that is, the portion where the negative electrode current collector 82 is exposed without forming the negative electrode composite material layer 90) protrudes from both sides in the width direction of the separator sheet 95. And the negative electrode sheet 84 are overlapped with a slight shift in the width direction. As a result, in the lateral direction with respect to the winding direction of the wound electrode body 50, the electrode mixture layer non-forming portions of the positive electrode sheet 64 and the negative electrode sheet 84 are respectively wound core portions (that is, the positive electrode mixture layer forming portion of the positive electrode sheet 64. And a portion where the negative electrode mixture layer forming portion of the negative electrode sheet 84 and the two separator sheets 95 are wound tightly) protrude outward. The positive electrode terminal 60 is joined to the protruding portion on the positive electrode side, and the positive electrode sheet 64 and the positive electrode terminal 60 of the wound electrode body 50 formed in the flat shape are electrically connected. Similarly, the negative electrode terminal 80 is joined to the negative electrode side protruding portion, and the negative electrode sheet 84 and the negative electrode terminal 80 are electrically connected. The positive and negative electrode terminals 60 and 80 and the positive and negative electrode current collectors 62 and 82 can be joined by, for example, ultrasonic welding, resistance welding, or the like.

上記電解液としては、従来からリチウムイオン二次電池に用いられる非水電解液と同様のものを特に限定なく使用することができる。かかる非水電解液は、典型的には、適当な非水溶媒(有機溶媒)に支持塩を含有させた組成を有する。上記非水溶媒としては、例えば、エチレンカーボネート(EC)、プロピレンカーボネート(PC)、ジメチルカーボネート(DMC)、ジエチルカーボネート(DEC)、エチルメチルカーボネート(EMC)等から選択される一種又は二種以上を用いることができる。また、上記支持塩(支持電解質)としては、例えば、LiPF,LiBF等のリチウム塩を用いることができる。さらに上記非水電解液に、ジフルオロリン酸塩(LiPO)やリチウムビスオキサレートボレート(LiBOB)を溶解させてもよい。
また、上記セパレータシートとしては、従来公知のものを特に制限なく使用することができる。例えば、樹脂からなる多孔性シート(微多孔質樹脂シート)を好ましく用いることができる。ポリエチレン(PE)、ポリプロピレン(PP)、ポリスチレン(PS)等の多孔質ポリオレフィン系樹脂シートが好ましい。
As said electrolyte solution, the thing similar to the nonaqueous electrolyte solution conventionally used for a lithium ion secondary battery can be used without limitation. Such a nonaqueous electrolytic solution typically has a composition in which a supporting salt is contained in a suitable nonaqueous solvent (organic solvent). Examples of the non-aqueous solvent include one or more selected from ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and the like. Can be used. Further, as the supporting salt (supporting electrolyte), for example, it can be used lithium salts such as LiPF 6, LiBF 4. Further, difluorophosphate (LiPO 2 F 2 ) or lithium bisoxalate borate (LiBOB) may be dissolved in the non-aqueous electrolyte.
Moreover, as said separator sheet, a conventionally well-known thing can be especially used without a restriction | limiting. For example, a porous sheet made of resin (a microporous resin sheet) can be preferably used. Porous polyolefin resin sheets such as polyethylene (PE), polypropylene (PP), and polystyrene (PS) are preferred.

以下、本発明に関する実施例を説明するが、本発明をかかる実施例に示すものに限定することを意図したものではない。   EXAMPLES Examples relating to the present invention will be described below, but the present invention is not intended to be limited to those shown in the examples.

[試験例1]
<例1>
正極活物質としてのLiNi0.5Mn1.5と、炭素材料としての平均粒径31nmのABとを、質量比が100:3となるように秤量し、これら材料を粉体処理装置(ホソカワミクロン社製、商品名「ノビルタNOB」)に投入し、5000rpmで10分間処理を行った。かかる処理により、LiNi0.5Mn1.5の表面が平均粒径31nmのアセチレンブラックで被覆された例1に係る炭素材料で被覆された正極活物質(被覆正極活物質)を得た。
次に、上記例1に係る被覆正極活物質と、導電材としてのABと、結着材としてのポリフッ化ビニリデン(PVDF)との質量比が89:8:3となるように秤量し、これら材料をNMPに分散させて例1に係るペースト状の正極合材層形成用組成物を調製した。そして、例1に係る組成物を厚さ15μmの正極集電体(アルミニウム箔)上に塗布して乾燥させた後、ロールプレス処理を行い正極集電体上に正極合材層が形成された例1に係る正極シートを作製した。
また、黒鉛化度0.9以上の天然黒鉛(平均粒径20μm)と、結着材としてのSBRと、増粘材としてのCMCとの質量比が98:1:1となるように秤量し、これら材料を水に分散させてペースト状の負極合材層形成用組成物を調製した。そして、該組成物を厚さ10μmの負極集電体(銅箔)上に塗布して乾燥させた後、ロールプレス処理を行い負極集電体上に負極合材層が形成された例1に係る負極シートを作製した。正極の理論容量と負極の理論容量との比率が1:1.5となるように上記各組成物の塗布量を調整した。
そして、上記作製した正極シート及び負極シートをセパレータシート(ポリプロピレン/ポリエチレン複合体多孔質膜)を挟んで対向配置させ(積層させ)、これを電解液と共にラミネート型のケース(ラミネートフィルム)に収容することにより例1に係るリチウムイオン二次電池(以下、単に「二次電池」とすることもある。)を作製した。電解液としては、エチレンカーボネート(EC)とエチルメチルカーボネート(EMC)との体積比3:7の混合溶媒に1mol/LのLiPFを溶解させたものを使用した。
[Test Example 1]
<Example 1>
LiNi 0.5 Mn 1.5 O 4 as a positive electrode active material and AB with an average particle diameter of 31 nm as a carbon material are weighed so that the mass ratio is 100: 3, and these materials are processed by a powder processing apparatus. (Trade name “Nobilta NOB” manufactured by Hosokawa Micron Corporation) and treated at 5000 rpm for 10 minutes. By this treatment, a positive electrode active material (coated positive electrode active material) coated with the carbon material according to Example 1 in which the surface of LiNi 0.5 Mn 1.5 O 4 was coated with acetylene black having an average particle diameter of 31 nm was obtained. .
Next, the coated positive electrode active material according to Example 1 above, AB as a conductive material, and polyvinylidene fluoride (PVDF) as a binder are weighed so that the mass ratio is 89: 8: 3. The material was dispersed in NMP to prepare a paste-like composition for forming a positive electrode mixture layer according to Example 1. And after apply | coating the composition which concerns on Example 1 on the positive electrode electrical power collector (aluminum foil) with a thickness of 15 micrometers, and drying it, the roll press process was performed and the positive electrode compound-material layer was formed on the positive electrode electrical power collector. A positive electrode sheet according to Example 1 was produced.
Also, weigh so that the mass ratio of natural graphite (average particle size 20 μm) having a graphitization degree of 0.9 or more, SBR as a binder, and CMC as a thickener is 98: 1: 1. These materials were dispersed in water to prepare a paste-like composition for forming a negative electrode mixture layer. And after applying this composition on a 10-micrometer-thick negative electrode collector (copper foil) and making it dry, the roll press process was performed and the negative mix layer was formed on the negative electrode collector in Example 1 Such a negative electrode sheet was prepared. The coating amount of each composition was adjusted so that the ratio between the theoretical capacity of the positive electrode and the theoretical capacity of the negative electrode was 1: 1.5.
Then, the prepared positive electrode sheet and negative electrode sheet are placed opposite to each other with a separator sheet (polypropylene / polyethylene composite porous membrane) interposed therebetween (laminated), and this is accommodated in a laminate type case (laminate film) together with the electrolyte. Thus, a lithium ion secondary battery according to Example 1 (hereinafter sometimes simply referred to as “secondary battery”) was produced. As the electrolytic solution, a solution obtained by dissolving 1 mol / L LiPF 6 in a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3: 7 was used.

<例2>
炭素材料として平均粒径31nmのABの代わりに平均粒径35nmのABを用いた他は例1と同様にして、例2に係るリチウムイオン二次電池を作製した。
<例3>
炭素材料として平均粒径31nmのABの代わりに平均粒径46nmのABを用いた他は例1と同様にして、例3に係るリチウムイオン二次電池を作製した。
<例4>
炭素材料として平均粒径31nmのABの代わりに平均粒径53nmのABを用いた他は例1と同様にして、例4に係るリチウムイオン二次電池を作製した。
<例5>
正極活物質としてのLiNi0.5Mn1.5と、導電材としてのABと、結着材としてのPVDFとの質量比が89:8:3となるように秤量し、これら材料をNMPに分散させて例5に係るペースト状の正極合材層形成用組成物を調製した。例5に係る組成物を用いた他は例1と同様にして、例5に係るリチウムイオン二次電池を作製した。例1〜例5に係るリチウムイオン二次電池の負極の組成を表1に示す。
<Example 2>
A lithium ion secondary battery according to Example 2 was fabricated in the same manner as in Example 1 except that AB having an average particle diameter of 35 nm was used as the carbon material instead of AB having an average particle diameter of 31 nm.
<Example 3>
A lithium ion secondary battery according to Example 3 was fabricated in the same manner as in Example 1 except that AB having an average particle diameter of 46 nm was used as the carbon material instead of AB having an average particle diameter of 31 nm.
<Example 4>
A lithium ion secondary battery according to Example 4 was produced in the same manner as in Example 1 except that AB having an average particle diameter of 53 nm was used instead of AB having an average particle diameter of 31 nm as the carbon material.
<Example 5>
LiNi 0.5 Mn 1.5 O 4 as the positive electrode active material, AB as the conductive material, and PVDF as the binder are weighed so that the mass ratio is 89: 8: 3. A paste-like composition for forming a positive electrode mixture layer according to Example 5 was prepared by dispersing in NMP. A lithium ion secondary battery according to Example 5 was produced in the same manner as in Example 1 except that the composition according to Example 5 was used. Table 1 shows the compositions of the negative electrodes of the lithium ion secondary batteries according to Examples 1 to 5.

Figure 2013062089
Figure 2013062089

[容量維持率測定]
上記作製した例1〜例5に係るリチウムイオン二次電池について、3日間保存後の容量維持率[%]を測定した。まず、各リチウムイオン二次電池に対して定電流‐定電圧方式(CCCV方式)によって充放電を行い初期容量を測定した。即ち、25℃の温度条件下、C/5の定電流で4.9Vまで定電流充電を行い、定電圧充電時の電流値がC/50になる点まで定電圧充電を行うことによって満充電(SOC(State of Charge)100%)とした。その後、定電流方式(CC方式)によって、C/5の定電流で3.5Vまで放電した。このときに得られた容量を初期容量とした。
次に、上記初期容量測定後の各リチウムイオン二次電池を上記初期容量測定と同様にして、満充電とし、満充電後の各二次電池を60℃の温度条件下で3日間保存した。保存後、25℃の温度条件下にて5時間放置することで温度を安定させ、充電することなく定電流方式(CC方式)によって、C/5の定電流で3.5Vまで放電した。このときに得られた容量を保存後容量とした。(保存後容量)/(初期容量)×100を、3日間保存後の容量維持率[%]とした。各例の容量維持率の測定結果を表1及び図4に示す。
[Capacity maintenance rate measurement]
About the lithium ion secondary battery which concerns on the produced said Example 1-Example 5, the capacity | capacitance maintenance factor [%] after storage for 3 days was measured. First, each lithium ion secondary battery was charged and discharged by a constant current-constant voltage method (CCCV method), and the initial capacity was measured. In other words, under a temperature condition of 25 ° C., a constant current charge is performed up to 4.9 V with a constant current of C / 5, and the battery is fully charged by performing a constant voltage charge until the current value during constant voltage charge becomes C / 50. (SOC (State of Charge) 100%). Then, it discharged to 3.5V with the constant current of C / 5 by the constant current system (CC system). The capacity obtained at this time was used as the initial capacity.
Next, each lithium ion secondary battery after the initial capacity measurement was fully charged in the same manner as the initial capacity measurement, and each secondary battery after the full charge was stored under a temperature condition of 60 ° C. for 3 days. After storage, the temperature was stabilized by allowing it to stand for 5 hours under a temperature condition of 25 ° C., and it was discharged to 3.5 V at a constant current of C / 5 by a constant current method (CC method) without charging. The capacity obtained at this time was taken as the capacity after storage. (Capacity after storage) / (initial capacity) × 100 was defined as a capacity retention rate [%] after storage for 3 days. The measurement results of the capacity retention rate of each example are shown in Table 1 and FIG.

表1及び図4に示すように、例5に係る二次電池と比較して、例1〜例3に係る二次電池では容量維持率が増大していた。一方、例4に係る二次電池でも容量維持率は増加していたがその増加率は例1〜例3と比べて小さいものであった。この結果より、正極活物質の表面を被覆する炭素材料(AB)の平均粒径は50nm以下(例えば46nm以下、好ましくは30nm〜40nm)であることが好ましいことが確認された。   As shown in Table 1 and FIG. 4, the capacity retention rate was increased in the secondary batteries according to Examples 1 to 3 as compared with the secondary battery according to Example 5. On the other hand, the capacity retention rate of the secondary battery according to Example 4 also increased, but the increase rate was smaller than those of Examples 1 to 3. From this result, it was confirmed that the average particle diameter of the carbon material (AB) covering the surface of the positive electrode active material is preferably 50 nm or less (for example, 46 nm or less, preferably 30 nm to 40 nm).

[直流抵抗測定]
上記例1〜例5に係るリチウムイオン二次電池に対して、25℃の温度条件下、C/5で定電流充電を行いSOC60%の充電状態に調整した。SOC60%の充電状態において、C/3、C、3Cの定電流を5秒間流すことで充電時及び放電時の過電圧を測定し、それらの値を上記電流値で除することで算出した抵抗の平均値を直流抵抗とした。測定結果を表1及び図5に示す。
[DC resistance measurement]
The lithium ion secondary batteries according to Examples 1 to 5 were adjusted to a SOC of 60% by performing constant current charging at C / 5 under a temperature condition of 25 ° C. In an SOC 60% state of charge, a constant current of C / 3, C, 3C was passed for 5 seconds to measure the overvoltage during charging and discharging, and the resistance calculated by dividing those values by the above current value The average value was defined as DC resistance. The measurement results are shown in Table 1 and FIG.

表1及び図5に示すように、正極活物質を炭素材料で被覆していない例5に係る二次電池と比較して、例1〜例3に係る二次電池は同等の直流抵抗を示していた。一方、例4に係る二次電池では直流抵抗が大きく増加していることが確認された。この結果からも、正極活物質の表面を被覆する炭素材料(AB)の平均粒径は50nm以下(例えば46nm以下、好ましくは30nm〜40nm)であることが好ましいことが確認された。   As shown in Table 1 and FIG. 5, the secondary batteries according to Examples 1 to 3 exhibit equivalent direct current resistance as compared with the secondary battery according to Example 5 in which the positive electrode active material is not coated with the carbon material. It was. On the other hand, in the secondary battery according to Example 4, it was confirmed that the DC resistance was greatly increased. Also from this result, it was confirmed that the average particle diameter of the carbon material (AB) covering the surface of the positive electrode active material is preferably 50 nm or less (for example, 46 nm or less, preferably 30 nm to 40 nm).

[試験例2]
上記例1〜例4に係るリチウムイオン二次電池では、正極活物質の表面を被覆する炭素材料の被覆量を一定(正極活物質100質量%に対して炭素材料の被覆量が3質量%)としていたが、炭素材料の被覆量によってリチウムイオン二次電池の容量維持率及び直流抵抗がどのように変化するのかを測定した。以下、例6〜例8に係るリチウムイオン二次電池を新たに作製した。なお、上記試験例1に係る例1及び例5に係るリチウムイオン二次電池の測定結果を合わせて比較した。
[Test Example 2]
In the lithium ion secondary batteries according to Examples 1 to 4, the coating amount of the carbon material covering the surface of the positive electrode active material is constant (the coating amount of the carbon material is 3% by mass with respect to 100% by mass of the positive electrode active material). However, it was measured how the capacity retention ratio and the direct current resistance of the lithium ion secondary battery change depending on the coating amount of the carbon material. Hereinafter, lithium ion secondary batteries according to Examples 6 to 8 were newly produced. In addition, the measurement result of the lithium ion secondary battery which concerns on Example 1 and Example 5 which concerns on the said test example 1 was combined, and compared.

<例6>
LiNi0.5Mn1.5と、平均粒径31nmのAB(炭素材料)との質量比が100:1.5となるように秤量し、これら材料を粉体処理装置(ホソカワミクロン社製、商品名「ノビルタNOB」)に投入し、5000rpmで10分間処理を行った。かかる処理により、LiNi0.5Mn1.5の表面が平均粒径31nmのABで被覆された例6に係る被覆正極活物質を得た。例6に係る被覆正極活物質を用いた他は例1と同様にして、例6に係るリチウムイオン二次電池を作製した。
<Example 6>
Weighed so that the mass ratio of LiNi 0.5 Mn 1.5 O 4 and AB (carbon material) having an average particle diameter of 31 nm was 100: 1.5, and these materials were processed by a powder processing apparatus (manufactured by Hosokawa Micron Corporation). , Trade name “Nobilta NOB”) and processed at 5000 rpm for 10 minutes. By this treatment, a coated positive electrode active material according to Example 6 in which the surface of LiNi 0.5 Mn 1.5 O 4 was coated with AB having an average particle diameter of 31 nm was obtained. A lithium ion secondary battery according to Example 6 was produced in the same manner as in Example 1 except that the coated positive electrode active material according to Example 6 was used.

<例7>
LiNi0.5Mn1.5と、平均粒径31nmのAB(炭素材料)との質量比が100:5となるように秤量し、これら材料を粉体処理装置(ホソカワミクロン社製、商品名「ノビルタNOB」)に投入し、5000rpmで10分間処理を行った。かかる処理により、LiNi0.5Mn1.5の表面が平均粒径31nmのABで被覆された例7に係る被覆正極活物質を得た。例7に係る被覆正極活物質を用いた他は例1と同様にして、例7に係るリチウムイオン二次電池を作製した。
<Example 7>
Weighed so that the mass ratio of LiNi 0.5 Mn 1.5 O 4 and AB (carbon material) with an average particle diameter of 31 nm was 100: 5, and these materials were processed into powder processing equipment (manufactured by Hosokawa Micron Co., Ltd. Name “Nobilta NOB”) and treated at 5000 rpm for 10 minutes. By this treatment, a coated positive electrode active material according to Example 7 in which the surface of LiNi 0.5 Mn 1.5 O 4 was coated with AB having an average particle diameter of 31 nm was obtained. A lithium ion secondary battery according to Example 7 was produced in the same manner as in Example 1 except that the coated positive electrode active material according to Example 7 was used.

<例8>
LiNi0.5Mn1.5と、平均粒径31nmのAB(炭素材料)との質量比が100:7となるように秤量し、これら材料を粉体処理装置(ホソカワミクロン社製、商品名「ノビルタNOB」)に投入し、5000rpmで10分間処理を行った。かかる処理により、LiNi0.5Mn1.5の表面が平均粒径31nmのABで被覆された例8に係る被覆正極活物質を得た。例8に係る被覆正極活物質を用いた他は例1と同様にして、例8に係るリチウムイオン二次電池を作製した。上記試験例1で作成した例1、例5および例6〜例8に係るリチウムイオン二次電池の負極の組成を表2に示す。
<Example 8>
Weighed so that the mass ratio of LiNi 0.5 Mn 1.5 O 4 and AB (carbon material) with an average particle diameter of 31 nm was 100: 7, and these materials were processed into powder processing equipment (manufactured by Hosokawa Micron Co., Ltd. Name “Nobilta NOB”) and treated at 5000 rpm for 10 minutes. By this treatment, a coated positive electrode active material according to Example 8 in which the surface of LiNi 0.5 Mn 1.5 O 4 was coated with AB having an average particle diameter of 31 nm was obtained. A lithium ion secondary battery according to Example 8 was produced in the same manner as Example 1 except that the coated positive electrode active material according to Example 8 was used. Table 2 shows the composition of the negative electrode of the lithium ion secondary battery according to Examples 1, 5 and 6 to 8 created in Test Example 1.

Figure 2013062089
Figure 2013062089

[容量維持率測定]
上記作製した例6〜例8に係るリチウムイオン二次電池について容量維持率[%]を測定した。なお、測定条件は上記試験例1における容量維持率測定と同様の条件である。各例の容量維持率の測定結果を表2及び図6に示す。
表2及び図6に示すように、例5に係る二次電池と比較して、例1及び例6〜例8に係る二次電池では容量維持率が増大していた。特に例1及び例7に係る二次電池は高い容量維持率を示した。この結果より、炭素材料の被覆量は、正極活物質を100質量%としたときに1質量%〜8質量%(例えば1.5質量%〜7質量%。好ましくは3質量%〜5質量%)が好ましいことが確認された。
[Capacity maintenance rate measurement]
About the lithium ion secondary battery which concerns on the produced said Example 6-8, capacity | capacitance maintenance factor [%] was measured. The measurement conditions are the same as the capacity maintenance ratio measurement in Test Example 1. The measurement results of the capacity retention ratio of each example are shown in Table 2 and FIG.
As shown in Table 2 and FIG. 6, compared with the secondary battery according to Example 5, the capacity retention rate of the secondary batteries according to Example 1 and Examples 6 to 8 was increased. In particular, the secondary batteries according to Examples 1 and 7 showed a high capacity retention rate. From this result, the coating amount of the carbon material is 1% by mass to 8% by mass (for example, 1.5% by mass to 7% by mass, preferably 3% by mass to 5% by mass) when the positive electrode active material is 100% by mass. ) Was confirmed to be preferable.

[直流抵抗測定]
上記例6〜例8に係るリチウムイオン二次電池について直流抵抗[Ω]を測定した。なお、測定条件は上記試験例1における直流抵抗測定と同様の条件である。各例の直流抵抗の測定結果を表2及び図7に示す。
表2及び図7に示すように、炭素材料の被覆量が7質量%以上のときに直流抵抗が大きく増加していることが確認された(例8)。一方、例1、例6及び例7に係る二次電池は、例5に係る二次電池と同等の直流抵抗を示していることが確認された。この結果より、炭素材料の被覆量は、正極活物質を100質量%としたときに1質量%〜6質量%(例えば、1.5質量%〜5質量%。好ましくは1.5質量%〜3質量%。)であることが好ましいことが確認された。
上記容量維持率測定及び直流抵抗測定の結果から、炭素材料の被覆量は、正極活物質を100質量%としたときに2質量%〜4質量%(例えば、3質量%〜4質量%。)がより好ましいことが確認された。
[DC resistance measurement]
The direct current resistance [Ω] of the lithium ion secondary batteries according to Examples 6 to 8 was measured. The measurement conditions are the same as the DC resistance measurement in Test Example 1. The measurement results of DC resistance in each example are shown in Table 2 and FIG.
As shown in Table 2 and FIG. 7, it was confirmed that the DC resistance was greatly increased when the coating amount of the carbon material was 7% by mass or more (Example 8). On the other hand, it was confirmed that the secondary batteries according to Example 1, Example 6 and Example 7 showed the same DC resistance as the secondary battery according to Example 5. From this result, the coating amount of the carbon material is 1% by mass to 6% by mass (for example, 1.5% by mass to 5% by mass, preferably 1.5% by mass to 100% by mass when the positive electrode active material is 100% by mass). 3% by mass) was confirmed to be preferable.
From the results of the capacity retention rate measurement and the DC resistance measurement, the coating amount of the carbon material is 2% by mass to 4% by mass (for example, 3% by mass to 4% by mass) when the positive electrode active material is 100% by mass. Was confirmed to be more preferable.

以上、本発明を好適な実施形態により説明してきたが、こうした記述は限定事項ではなく、勿論、種々の改変が可能である。   As mentioned above, although this invention was demonstrated by suitable embodiment, such description is not a limitation matter and of course various modifications are possible.

本発明に係るリチウムイオン二次電池は高い電池電圧を有しており、上述の通りかかる高電圧下でのサイクル特性に優れているため、各種用途向けのリチウムイオン二次電池として利用可能である。例えば、図8に示すように、自動車等の車両100に搭載される車両駆動用モーターの電源(駆動電源)として好適に利用することができる。車両100に使用されるリチウムイオン二次電池10は、単独で使用されてもよく、直列及び/又は並列に複数接続されてなる組電池の形態で使用されてもよい。   Since the lithium ion secondary battery according to the present invention has a high battery voltage and is excellent in cycle characteristics under such a high voltage as described above, it can be used as a lithium ion secondary battery for various applications. . For example, as shown in FIG. 8, it can be suitably used as a power source (drive power source) for a vehicle drive motor mounted on a vehicle 100 such as an automobile. The lithium ion secondary battery 10 used for the vehicle 100 may be used alone, or may be used in the form of an assembled battery that is connected in series and / or in parallel.

10 リチウムイオン二次電池(二次電池)
15 電池ケース
20 開口部
25 蓋体
30 ケース本体
40 安全弁
50 捲回電極体
60 正極端子
62 正極集電体
64 正極(正極シート)
66 正極合材層
70 正極活物質
72 炭素材料
80 負極端子
82 負極集電体
84 負極(負極シート)
90 負極合材層
95 セパレータシート
100 車両(自動車)
10 Lithium ion secondary battery (secondary battery)
15 Battery Case 20 Opening 25 Lid 30 Case Body 40 Safety Valve 50 Winding Electrode Body 60 Positive Terminal 62 Positive Electrode Current Collector 64 Positive Electrode (Positive Electrode Sheet)
66 Positive electrode mixture layer 70 Positive electrode active material 72 Carbon material 80 Negative electrode terminal 82 Negative electrode current collector 84 Negative electrode (negative electrode sheet)
90 Negative electrode composite material layer 95 Separator sheet 100 Vehicle (automobile)

Claims (5)

正極と、負極と、電解液と、を備えるリチウムイオン二次電池であって、
前記正極は、正極集電体と、該集電体上に形成された少なくとも正極活物質を含む正極合材層とを備えており、
前記正極活物質は、金属リチウム電極基準で4.5V以上の放電電位を有する高電位リチウム含有化合物であり、
前記高電位リチウム含有化合物の表面は、炭素材料によって被覆されており、
前記炭素材料の平均粒径は50nm以下であることを特徴とする、リチウムイオン二次電池。
A lithium ion secondary battery comprising a positive electrode, a negative electrode, and an electrolyte solution,
The positive electrode includes a positive electrode current collector, and a positive electrode mixture layer including at least a positive electrode active material formed on the current collector,
The positive electrode active material is a high-potential lithium-containing compound having a discharge potential of 4.5 V or more based on a metal lithium electrode.
The surface of the high potential lithium-containing compound is coated with a carbon material,
The lithium ion secondary battery, wherein the carbon material has an average particle size of 50 nm or less.
前記炭素材料の被覆量は、前記高電位リチウム含有化合物を100質量%としたときに1質量%〜8質量%であることを特徴とする、請求項1に記載のリチウムイオン二次電池。   2. The lithium ion secondary battery according to claim 1, wherein a coating amount of the carbon material is 1% by mass to 8% by mass when the high potential lithium-containing compound is 100% by mass. 前記高電位リチウム含有化合物は、LiNi0.5Mn1.5であることを特徴とする、請求項1又は2に記載のリチウムイオン二次電池。 3. The lithium ion secondary battery according to claim 1, wherein the high potential lithium-containing compound is LiNi 0.5 Mn 1.5 O 4. 4 . 前記炭素材料は、平均粒径が30nm〜40nmのアセチレンブラックであることを特徴とする、請求項1から3のいずれか一項に記載のリチウムイオン二次電池。   4. The lithium ion secondary battery according to claim 1, wherein the carbon material is acetylene black having an average particle diameter of 30 nm to 40 nm. 5. 前記負極は、負極集電体と、該集電体上に形成された少なくとも負極活物質を含む負極合材層とを備えており、前記負極活物質は、黒鉛材料であることを特徴とする、請求項1から4のいずれか一項に記載のリチウムイオン二次電池。   The negative electrode includes a negative electrode current collector and a negative electrode mixture layer including at least a negative electrode active material formed on the current collector, and the negative electrode active material is a graphite material. The lithium ion secondary battery according to any one of claims 1 to 4.
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