JP5279567B2 - Nonaqueous electrolyte secondary battery - Google Patents

Nonaqueous electrolyte secondary battery Download PDF

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JP5279567B2
JP5279567B2 JP2009070082A JP2009070082A JP5279567B2 JP 5279567 B2 JP5279567 B2 JP 5279567B2 JP 2009070082 A JP2009070082 A JP 2009070082A JP 2009070082 A JP2009070082 A JP 2009070082A JP 5279567 B2 JP5279567 B2 JP 5279567B2
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porosity
positive electrode
secondary battery
electrolyte secondary
nonaqueous electrolyte
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安展 岩見
宏宜 白方
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Sanyo Electric Co Ltd
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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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    • Y02E60/00Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10Energy storage using batteries
    • 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
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
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Abstract

<P>PROBLEM TO BE SOLVED: To inexpensively provide a nonaqueous electrolyte secondary battery excellent in cycle characteristics in high rate discharge and safety. <P>SOLUTION: The porosity of a positive electrode including a positive active material containing a lithium transition metal phosphate represented by general formula Li<SB>x</SB>MPO<SB>4</SB>having olivine structure (0&lt;x&lt;1.3; M is at least one element selected from the group consisting of Co, Ni, Mn and Fe) and a conductive agent made of acetylene black having a specific surface area of 35-45 m<SP>2</SP>/g is made 30-50%, and the porosity of a negative electrode is made 20-30%. Preferably, the porosity of the positive electrode is 1.3 times or more of that of the negative electrode. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

本発明は、非水電解質二次電池に関し、より詳しくは、ハイレート放電でのサイクル特性の向上を目的とした非水電解質二次電池の改良に関する。   The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to an improvement of a non-aqueous electrolyte secondary battery for the purpose of improving cycle characteristics in high-rate discharge.

近年、携帯電話、ノートパソコン等の移動情報端末の高機能化・小型化および軽量化が急速に進展しており、その駆動電源として、高いエネルギー密度を有し、高容量である非水電解質二次電池が広く利用されている。   In recent years, mobile information terminals such as mobile phones and laptop computers have been rapidly advanced in function, size, and weight. As a driving power source, non-aqueous electrolytes having high energy density and high capacity are used. Secondary batteries are widely used.

従来、非水電解質二次電池用の正極活物質としては、放電特性に優れるコバルト酸リチウムが用いられていた。しかし、コバルト酸リチウムは、資源量が少なく高価なコバルトを用いる必要がある。また、ハイレート放電等によって電池が異常な高温にさらされた場合に、コバルト酸リチウムの結晶中から酸素が脱離しやすく、これにより結晶構造が不安定となって、熱暴走する危険性があるという問題があった。   Conventionally, lithium cobalt oxide having excellent discharge characteristics has been used as a positive electrode active material for a non-aqueous electrolyte secondary battery. However, lithium cobaltate needs to use expensive cobalt with a small amount of resources. In addition, when the battery is exposed to an abnormally high temperature due to high-rate discharge or the like, oxygen is easily desorbed from the lithium cobaltate crystal, which may cause the crystal structure to become unstable and cause a risk of thermal runaway. There was a problem.

このような中、資源量が豊富で安価な鉄を用いた、オリビン構造を有するリン酸鉄リチウムに対する注目が高まっている。オリビン構造を有するリン酸鉄リチウムは、放電容量がコバルト酸リチウムよりも低いものの、高温時における結晶構造が安定であるため、安全性に優れる。しかしながら、オリビン構造を有するリン酸鉄リチウムは、コバルト酸リチウムよりも導電性が悪いため、ハイレート放電を行う場合の放電特性が十分ではないという問題がある。   Under such circumstances, attention has been paid to lithium iron phosphate having an olivine structure using iron which is rich in resources and inexpensive. Although lithium iron phosphate having an olivine structure has a discharge capacity lower than that of lithium cobaltate, the crystal structure at high temperature is stable, so that it is excellent in safety. However, since lithium iron phosphate having an olivine structure has lower conductivity than lithium cobaltate, there is a problem that discharge characteristics when performing high-rate discharge are not sufficient.

この問題を解決するため、コバルト酸リチウムよりも小粒径のものを用いたり、導電剤をより多く加えたりすることが行われているが、ハイレート放電を繰り返し行うサイクル特性については、十分に改善されていない。   In order to solve this problem, it is possible to use a material with a smaller particle size than lithium cobaltate or to add more conductive agent, but the cycle characteristics for repeated high-rate discharge are sufficiently improved. It has not been.

ところで、非水電解質二次電池に関する技術としては、下記特許文献1が挙げられる。   By the way, the following patent document 1 is mentioned as a technique regarding a nonaqueous electrolyte secondary battery.

特開2005-259708号公報JP 2005-259708 A

特許文献1は、合計15体積%以上90体積%未満のジメチルカーボネート、エチルメチルカーボネート、プロピオン酸メチル、プロピオン酸エチルからなる群から選ばれる少なくとも1種のエステル類および10体積%以上55体積%未満のエチレンカーボネートを少なくとも含有する混合溶媒に、濃度が0.6M以上1.5M以下となるようにLiPF6及びLiBF4を溶解した非水電解質を用い、正極の空隙率を18%以上35%以下とし、負極の空隙率を18%以上35%以下とする技術である。この技術によると、大電流での使用に適した電池が得られるとされる。 Patent Document 1 describes a total of 15% by volume or more and less than 90% by volume of at least one ester selected from the group consisting of dimethyl carbonate, ethyl methyl carbonate, methyl propionate, and ethyl propionate, and 10% by volume to less than 55% by volume. A non-aqueous electrolyte in which LiPF 6 and LiBF 4 are dissolved so that the concentration is 0.6 M or more and 1.5 M or less is used in a mixed solvent containing at least ethylene carbonate, and the porosity of the positive electrode is 18% or more and 35% or less. And the porosity of the negative electrode is 18% or more and 35% or less. According to this technology, a battery suitable for use with a large current is obtained.

しかしながら、この技術では、正極活物質として、コバルト酸リチウムやニッケル酸リチウムを用いているため、コスト高であるという問題がある。   However, this technique has a problem of high cost because lithium cobaltate or lithium nickelate is used as the positive electrode active material.

本発明は、上記に鑑みなされたものであって、オリビン構造を有するリチウム遷移金属リン酸塩を正極活物質に用いた非水電解質二次電池のハイレート放電でのサイクル特性の向上を目的とする。   The present invention has been made in view of the above, and an object of the present invention is to improve cycle characteristics at high rate discharge of a nonaqueous electrolyte secondary battery using a lithium transition metal phosphate having an olivine structure as a positive electrode active material. .

上記課題を解決するための本発明は、正極活物質と導電剤とを有する正極と、負極活物質を有する負極と、を有する電極体と、非水溶媒と電解質塩とを有する非水電解質と、を備える非水電解質二次電池において、前記正極活物質は、オリビン構造を有する一般式LixMPO4(0<x<1.3、MはCo,Ni,Mn,Feからなる群より選択される少なくとも一種の元素)で示されるリチウム遷移金属リン酸塩を含み、前記正極の空隙率が30〜50%であり、且つ前記負極の空隙率が20〜30%であることを特徴とする。 The present invention for solving the above problems includes an electrode body having a positive electrode having a positive electrode active material and a conductive agent, a negative electrode having a negative electrode active material, and a nonaqueous electrolyte having a nonaqueous solvent and an electrolyte salt. The positive electrode active material is selected from the group consisting of a general formula Li x MPO 4 having an olivine structure (0 <x <1.3, M is Co, Ni, Mn, Fe) At least one element), wherein the positive electrode has a porosity of 30 to 50%, and the negative electrode has a porosity of 20 to 30%. .

本発明者らが鋭意研究を行った結果、リチウム遷移金属リン酸塩を正極活物質として用いる非水電解質二次電池には、次のような問題があることを知った。   As a result of intensive studies by the present inventors, it has been found that a nonaqueous electrolyte secondary battery using lithium transition metal phosphate as a positive electrode active material has the following problems.

正極の導電性を高めるために、リチウム遷移金属リン酸塩の粒径を小さくすると、正極活物質と非水電解質との接触面積が大きくなるので、その分正極が必要とする非水電解質量が増加する。また、ハイレート放電を行うと、リチウムイオンの吸蔵・脱離によって、正極及び負極の体積が急激に変化し、これに伴い正負極板の空隙に浸透した非水電解質が移動するため、ハイレート放電でのサイクル中には、正負極の活物質に供給される非水電解質量が不十分となりやすい。特にハイレート放電中の正極側で電解液が不足した場合、放電時に活物質に挿入されるLiイオンが不足することになり、ハイレート放電での特性が低下する。   If the particle size of the lithium transition metal phosphate is reduced in order to increase the conductivity of the positive electrode, the contact area between the positive electrode active material and the nonaqueous electrolyte increases. To increase. In addition, when high-rate discharge is performed, the volume of the positive electrode and the negative electrode rapidly changes due to insertion and extraction of lithium ions, and the nonaqueous electrolyte that has permeated into the gaps of the positive and negative electrode plates moves accordingly. During this cycle, the non-aqueous electrolytic mass supplied to the positive and negative active materials tends to be insufficient. In particular, when the electrolyte is insufficient on the positive electrode side during high-rate discharge, Li ions inserted into the active material at the time of discharge are insufficient, and the characteristics at high-rate discharge are degraded.

ここで、上記本発明のように、正極の空隙率を30%以上とし、且つ、負極の空隙率を20%以上とすると、正極活物質周囲に存在するリチウムイオン(非水電解質)量が十分となり、且つ負極活物質周囲に存在する非水電解質量が十分となる。このため、正負極の体積変化が急激なハイレート放電時においても、正負極に十分な非水電解質が供給され続けるので、ハイレート放電でのサイクル特性が高まる。なお、空隙率が大きすぎると、その分活物質量が減少するので、空隙率の上限は、正極側で50%、負極側で30%とする。   Here, when the porosity of the positive electrode is 30% or more and the porosity of the negative electrode is 20% or more as in the present invention, the amount of lithium ions (nonaqueous electrolyte) present around the positive electrode active material is sufficient. And the nonaqueous electrolytic mass present around the negative electrode active material is sufficient. For this reason, even during high-rate discharge where the volume change of the positive and negative electrodes is abrupt, sufficient non-aqueous electrolyte continues to be supplied to the positive and negative electrodes, so that the cycle characteristics in high-rate discharge are enhanced. Note that if the porosity is too large, the amount of the active material decreases, so the upper limit of the porosity is 50% on the positive electrode side and 30% on the negative electrode side.

上記構成において、前記正極の空隙率が、前記負極の空隙率の1.3倍以上である構成とすることができる。   The said structure WHEREIN: The porosity of the said positive electrode can be set as the structure which is 1.3 times or more of the porosity of the said negative electrode.

上記構成を採用すると、ハイレート放電時にさらに十分な非水電解質が正負極板に供給されるので、ハイレート放電でのサイクル特性がさらに高まる。   If the said structure is employ | adopted, since sufficient nonaqueous electrolyte is supplied to a positive / negative electrode plate at the time of high-rate discharge, the cycling characteristics in high-rate discharge further improve.

上記構成において、前記導電剤は、比表面積が35〜45m2/gのアセチレンブラックである構成とすることができる。 The said structure WHEREIN: The said electrically conductive agent can be set as the structure which is acetylene black whose specific surface area is 35-45 m < 2 > / g.

導電剤の比表面積が35m2/g未満であると、導電剤の粒径が大きいために、正極の導電性向上効果が若干低下し、他方、導電剤の比表面積が45m2/gより大きいと、導電剤の粒径が小さいために導電剤が凝集しやすくなるので、この場合もまた、正極の導電性向上効果が若干低下する。よって、導電剤の比表面積は、35〜45m2/gであることが好ましい。また、導電剤としては、炭素粒子の鎖状構造が発達しており、導電性に優れたアセチレンブラックを用いることが好ましい。 When the specific surface area of the conductive agent is less than 35 m 2 / g, since the particle size of the conductive agent is large, the effect of improving the conductivity of the positive electrode is slightly reduced. On the other hand, the specific surface area of the conductive agent is greater than 45 m 2 / g. In addition, since the conductive agent easily aggregates due to the small particle size of the conductive agent, the conductivity improvement effect of the positive electrode is slightly reduced in this case as well. Therefore, the specific surface area of the conductive agent is preferably 35 to 45 m 2 / g. As the conductive agent, it is preferable to use acetylene black having a chain structure of carbon particles and excellent conductivity.

ここで、オリビン構造を有する一般式LixMPO4(0<x<1.3、Mは、Co,Ni,Mn及びFeから選択される少なくとも1種の元素)で表されるリチウム遷移金属リン酸塩は、リチウムの拡散経路を短くして良好な出力特性が得られるようにするため、平均粒径が10μm以下のものを用いることが好ましく、平均粒径が5μm以下のものを用いることがより好ましい。 Here, a lithium transition metal phosphorus represented by the general formula Li x MPO 4 having an olivine structure (0 <x <1.3, M is at least one element selected from Co, Ni, Mn, and Fe) In order to shorten the lithium diffusion path and obtain good output characteristics, it is preferable to use an acid salt having an average particle diameter of 10 μm or less, and an average particle diameter of 5 μm or less. More preferred.

以上に説明したように、上記本発明によると、リチウム遷移金属リン酸塩を用いた電池のハイレート放電特性を向上させることができる。   As described above, according to the present invention, the high rate discharge characteristics of a battery using a lithium transition metal phosphate can be improved.

本発明を実施するための最良の形態を、実施例を用いて詳細に説明する。   The best mode for carrying out the present invention will be described in detail with reference to examples.

(実施例1)
〈正極の作製〉
正極活物質としての平均粒径が100nmのオリビン構造を有するリン酸鉄リチウム(LiFePO4)80質量部と、導電剤としての比表面積が40m2/gのアセチレンブラック10質量部と、結着剤としてのポリフッ化ビニリデン10質量部と、N−メチル−2−ピロリドン(NMP)と、を混合して正極活物質スラリーを調製した。
Example 1
<Preparation of positive electrode>
80 parts by mass of lithium iron phosphate (LiFePO 4 ) having an olivine structure with an average particle size of 100 nm as a positive electrode active material, 10 parts by mass of acetylene black having a specific surface area of 40 m 2 / g as a conductive agent, and a binder A positive electrode active material slurry was prepared by mixing 10 parts by mass of polyvinylidene fluoride and N-methyl-2-pyrrolidone (NMP).

このスラリーを、ドクターブレード法により、正極集電体としてのアルミ箔の両面に塗布し、正極活物質層を形成した。この後、乾燥し、その後圧縮ローラーで圧縮し、55mm×700mmのサイズに裁断して、正極を作製した。この正極の空隙率は、30%であった。   This slurry was applied to both surfaces of an aluminum foil as a positive electrode current collector by a doctor blade method to form a positive electrode active material layer. Then, it dried, after that, it compressed with the compression roller, and cut | judged to the size of 55 mm x 700 mm, and produced the positive electrode. The porosity of this positive electrode was 30%.

〈負極の作製〉
負極活物質としての天然黒鉛粉末95質量部と、結着剤としてのポリフッ化ビニリデン5質量部と、N−メチル−2−ピロリドン(NMP)と、を混合して負極活物質スラリーを調製した。
<Preparation of negative electrode>
A negative electrode active material slurry was prepared by mixing 95 parts by mass of natural graphite powder as a negative electrode active material, 5 parts by mass of polyvinylidene fluoride as a binder, and N-methyl-2-pyrrolidone (NMP).

このスラリーを、ドクターブレード法により、負極集電体としての銅箔の両面に塗布し、負極活物質層を形成した。この後、乾燥し、その後圧縮ローラーで圧縮し、57mm×750mmのサイズに裁断して、負極を作製した。この負極の空隙率は、25%であった。よって、空隙率比率(正極空隙率/負極空隙率)は、1.2となる。   This slurry was applied to both surfaces of a copper foil as a negative electrode current collector by a doctor blade method to form a negative electrode active material layer. Then, it dried, after that, it compressed with the compression roller, and cut | judged to the size of 57 mm x 750 mm, and produced the negative electrode. The porosity of this negative electrode was 25%. Therefore, the porosity ratio (positive electrode porosity / negative electrode porosity) is 1.2.

なお、正極及び負極の空隙率は、次の式により算出した。
空隙率(%)=100×(1−(活物質層の密度)÷(活物質層の真密度))
In addition, the porosity of the positive electrode and the negative electrode was calculated by the following formula.
Porosity (%) = 100 × (1− (density of active material layer) ÷ (true density of active material layer))

ここで、活物質層の密度は、実際に作製した極板の密度を意味し、活物質層の真密度は、下記数式1により算出した。   Here, the density of the active material layer means the density of the actually produced electrode plate, and the true density of the active material layer was calculated by the following formula 1.

Figure 0005279567
Figure 0005279567

〈電極体の作製〉
上記正極及び負極を、ポリプロピレン製微多孔膜からなるセパレータを介して巻回し、渦巻状の電極体を作製した。
<Production of electrode body>
The positive electrode and the negative electrode were wound through a separator made of a polypropylene microporous film to produce a spiral electrode body.

〈非水電解質の調整〉
エチレンカーボネート(EC)と、ジエチルカーボネート(DEC)と、を体積比50:50(25℃、1気圧)で混合した混合溶媒に、LiPF6を1モル/リットルとなるように溶かして、非水電解質となした。
<Adjustment of non-aqueous electrolyte>
LiPF 6 was dissolved in a mixed solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 50:50 (25 ° C., 1 atm) to a concentration of 1 mol / liter, and non-aqueous It became an electrolyte.

〈電池の組み立て〉
上記電極体及び上記非水電解質を有底円筒状の外装缶内に収容し、外装缶の開口部を封口板により封口して、直径18mm、高さ650mm、設計容量が1000mAhである実施例1にかかる非水電解質二次電池を作製した。
<Assembly of battery>
Example 1 in which the electrode body and the non-aqueous electrolyte are accommodated in a bottomed cylindrical outer can, the opening of the outer can is sealed with a sealing plate, the diameter is 18 mm, the height is 650 mm, and the design capacity is 1000 mAh. A non-aqueous electrolyte secondary battery was produced.

(実施例2)
正極の空隙率を32.5%としたこと以外は、上記実施例1と同様にして、実施例2に係る非水電解質二次電池を作製した。
(Example 2)
A nonaqueous electrolyte secondary battery according to Example 2 was fabricated in the same manner as in Example 1 except that the porosity of the positive electrode was 32.5%.

(実施例3)
正極の空隙率を35%としたこと以外は、上記実施例1と同様にして、実施例3に係る非水電解質二次電池を作製した。
(Example 3)
A nonaqueous electrolyte secondary battery according to Example 3 was produced in the same manner as in Example 1 except that the porosity of the positive electrode was set to 35%.

(実施例4)
正極の空隙率を40%としたこと以外は、上記実施例1と同様にして、実施例4に係る非水電解質二次電池を作製した。
Example 4
A nonaqueous electrolyte secondary battery according to Example 4 was produced in the same manner as in Example 1 except that the porosity of the positive electrode was 40%.

(実施例5)
正極の空隙率を50%としたこと以外は、上記実施例1と同様にして、実施例5に係る非水電解質二次電池を作製した。
(Example 5)
A nonaqueous electrolyte secondary battery according to Example 5 was produced in the same manner as in Example 1 except that the porosity of the positive electrode was 50%.

(実施例6)
正極の空隙率を40%とし、負極の空隙率を20%としたこと以外は、上記実施例1と同様にして、実施例6に係る非水電解質二次電池を作製した。
(Example 6)
A nonaqueous electrolyte secondary battery according to Example 6 was fabricated in the same manner as in Example 1 except that the porosity of the positive electrode was 40% and the porosity of the negative electrode was 20%.

(実施例7)
正極の空隙率を40%とし、負極の空隙率を30%としたこと以外は、上記実施例1と同様にして、実施例7に係る非水電解質二次電池を作製した。
(Example 7)
A nonaqueous electrolyte secondary battery according to Example 7 was fabricated in the same manner as in Example 1 except that the porosity of the positive electrode was 40% and the porosity of the negative electrode was 30%.

(実施例8)
正極の空隙率を30%とし、負極の空隙率を20%としたこと以外は、上記実施例1と同様にして、実施例8に係る非水電解質二次電池を作製した。
(Example 8)
A nonaqueous electrolyte secondary battery according to Example 8 was fabricated in the same manner as in Example 1 except that the porosity of the positive electrode was 30% and the porosity of the negative electrode was 20%.

(実施例9)
正極の空隙率を30%とし、負極の空隙率を30%としたこと以外は、上記実施例1と同様にして、実施例9に係る非水電解質二次電池を作製した。
Example 9
A nonaqueous electrolyte secondary battery according to Example 9 was produced in the same manner as in Example 1 except that the porosity of the positive electrode was 30% and the porosity of the negative electrode was 30%.

(比較例1)
正極の空隙率を25%としたこと以外は、上記実施の形態と同様にして、比較例1に係る非水電解質二次電池を作製した。
(Comparative Example 1)
A nonaqueous electrolyte secondary battery according to Comparative Example 1 was fabricated in the same manner as in the above embodiment, except that the porosity of the positive electrode was 25%.

(比較例2)
正極の空隙率を55%としたこと以外は、上記実施例1と同様にして、比較例2に係る非水電解質二次電池を作製した。
(Comparative Example 2)
A nonaqueous electrolyte secondary battery according to Comparative Example 2 was fabricated in the same manner as in Example 1 except that the porosity of the positive electrode was 55%.

(比較例3)
正極の空隙率を40%とし、負極の空隙率を15%としたこと以外は、上記実施例1と同様にして、比較例3に係る非水電解質二次電池を作製した。
(Comparative Example 3)
A nonaqueous electrolyte secondary battery according to Comparative Example 3 was produced in the same manner as in Example 1 except that the porosity of the positive electrode was 40% and the porosity of the negative electrode was 15%.

(比較例4)
正極の空隙率を40%とし、負極の空隙率を35%としたこと以外は、上記実施例1と同様にして、比較例4に係る非水電解質二次電池を作製した。
(Comparative Example 4)
A nonaqueous electrolyte secondary battery according to Comparative Example 4 was produced in the same manner as in Example 1 except that the porosity of the positive electrode was 40% and the porosity of the negative electrode was 35%.

(参考例1)
正極作製に用いる正極活物質スラリーを次のようにして調製したこと以外は、上記実施例1と同様にして、参考例1に係る非水電解質二次電池を作製した。なお、正極の空隙率は25%、負極の空隙率は25%、設計容量は1500mAhである。
(Reference Example 1)
A nonaqueous electrolyte secondary battery according to Reference Example 1 was produced in the same manner as in Example 1 except that the positive electrode active material slurry used for producing the positive electrode was prepared as follows. The porosity of the positive electrode is 25%, the porosity of the negative electrode is 25%, and the design capacity is 1500 mAh.

〈参考例1にかかる正極活物質スラリーの調製〉
正極活物質としての平均粒径が8μmのコバルト酸リチウム(LiCoO2)90質量部と、導電剤としての比表面積が40m2/gのアセチレンブラック5質量部と、結着剤としてのポリフッ化ビニリデン5質量部と、N−メチル−2−ピロリドン(NMP)と、を混合して正極活物質スラリーを調製した。
<Preparation of positive electrode active material slurry according to Reference Example 1>
90 parts by mass of lithium cobalt oxide (LiCoO 2 ) having an average particle diameter of 8 μm as a positive electrode active material, 5 parts by mass of acetylene black having a specific surface area of 40 m 2 / g as a conductive agent, and polyvinylidene fluoride as a binder 5 parts by mass and N-methyl-2-pyrrolidone (NMP) were mixed to prepare a positive electrode active material slurry.

(参考例2)
正極の空隙率を30%としたこと以外は、上記参考例1と同様にして、参考例2に係る非水電解質二次電池を作製した。
(Reference Example 2)
A nonaqueous electrolyte secondary battery according to Reference Example 2 was produced in the same manner as Reference Example 1 except that the porosity of the positive electrode was 30%.

(参考例3)
正極の空隙率を35%としたこと以外は、上記参考例1と同様にして、参考例3に係る非水電解質二次電池を作製した。
(Reference Example 3)
A nonaqueous electrolyte secondary battery according to Reference Example 3 was produced in the same manner as in Reference Example 1 except that the porosity of the positive electrode was set to 35%.

(参考例4)
正極の空隙率を40%としたこと以外は、上記参考例1と同様にして、参考例4に係る非水電解質二次電池を作製した。
(Reference Example 4)
A nonaqueous electrolyte secondary battery according to Reference Example 4 was produced in the same manner as in Reference Example 1 except that the porosity of the positive electrode was 40%.

(参考例5)
正極の空隙率を40%とし、負極の空隙率を15%としたこと以外は、上記参考例1と同様にして、参考例5に係る非水電解質二次電池を作製した。
(Reference Example 5)
A nonaqueous electrolyte secondary battery according to Reference Example 5 was produced in the same manner as Reference Example 1 except that the porosity of the positive electrode was 40% and the porosity of the negative electrode was 15%.

(参考例6)
正極の空隙率を40%とし、負極の空隙率を20%としたこと以外は、上記参考例1と同様にして、参考例6に係る非水電解質二次電池を作製した。
(Reference Example 6)
A nonaqueous electrolyte secondary battery according to Reference Example 6 was produced in the same manner as in Reference Example 1 except that the porosity of the positive electrode was 40% and the porosity of the negative electrode was 20%.

(参考例7)
正極の空隙率を40%とし、負極の空隙率を30%としたこと以外は、上記参考例1と同様にして、参考例7に係る非水電解質二次電池を作製した。
(Reference Example 7)
A nonaqueous electrolyte secondary battery according to Reference Example 7 was produced in the same manner as in Reference Example 1 except that the porosity of the positive electrode was 40% and the porosity of the negative electrode was 30%.

(参考例8)
正極の空隙率を40%とし、負極の空隙率を35%としたこと以外は、上記参考例1と同様にして、参考例8に係る非水電解質二次電池を作製した。
(Reference Example 8)
A nonaqueous electrolyte secondary battery according to Reference Example 8 was produced in the same manner as in Reference Example 1 except that the porosity of the positive electrode was 40% and the porosity of the negative electrode was 35%.

なお、上記実施例1〜9、比較例1〜4、参考例1〜8において、正極及び負極の空隙率は、圧縮ローラーの圧縮条件を変更することにより調整した。   In Examples 1 to 9, Comparative Examples 1 to 4, and Reference Examples 1 to 8, the porosity of the positive electrode and the negative electrode was adjusted by changing the compression conditions of the compression roller.

(ハイレート放電サイクル特性の測定)
実施例1〜9、比較例1〜4、参考例1〜8と同一の条件で電池を作製し、以下の条件で充放電サイクルを行った。下記式によりサイクル特性を算出し、この結果を、下記表1に示す。
(Measurement of high-rate discharge cycle characteristics)
Batteries were produced under the same conditions as in Examples 1 to 9, Comparative Examples 1 to 4, and Reference Examples 1 to 8, and a charge / discharge cycle was performed under the following conditions. The cycle characteristics were calculated by the following formula, and the results are shown in Table 1 below.

(実施例及び比較例の充放電条件)
充電条件:定電流1It(1000mA)で電圧が4.2Vまで、その後定電圧4.2Vで電流が0.02It(20mA)となるまで
放電条件:定電流5It(5000mA)で電圧が2.0Vまで
(参考例の充放電条件)
充電条件:定電流1It(1500mA)で電圧が4.2Vまで、その後定電圧4.2Vで電流が0.02It(30mA)となるまで
放電条件:定電流5It(7500mA)で電圧が2.75Vまで
なお、充放電はすべて25℃条件で行った。
(Charge / discharge conditions of Examples and Comparative Examples)
Charging condition: constant current 1 It (1000 mA) until voltage is 4.2 V, then constant voltage 4.2 V until current is 0.02 It (20 mA) discharging condition: constant current 5 It (5000 mA), voltage is 2.0 V (Charging / discharging conditions in the reference example)
Charging condition: constant current 1 It (1500 mA) at voltage up to 4.2 V, then constant voltage 4.2 V until current reaches 0.02 It (30 mA) discharging condition: constant current 5 It (7500 mA) at voltage 2.75 V Until all, charging / discharging was performed on 25 degreeC conditions.

ハイレート放電サイクル特性(%)=500サイクル目放電容量÷1サイクル目放電容量×100 High rate discharge cycle characteristics (%) = 500th cycle discharge capacity / first cycle discharge capacity × 100

Figure 0005279567
Figure 0005279567

上記表1から、正極活物質としてオリビン構造を有するリン酸鉄リチウム(LiFePO4)を用い、正極の空隙率が30〜50%且つ負極の空隙率が20〜30%である実施例1〜9は、5Itサイクル特性が83〜95%であるのに対し、正極活物質としてオリビン構造を有するリン酸鉄リチウム(LiFePO4)を用い、正極の空隙率あるいは負極の空隙率が上記範囲を満たさない比較例1〜4は、ハイレート放電サイクル特性が71〜77%と、劣っていることがわかる。 From Table 1, using the lithium iron phosphate (LiFePO 4) having an olivine structure as a positive active material, Examples 1-9 porosity of the positive electrode 30 to 50 percent and the negative electrode of a porosity of 20-30% Uses a lithium iron phosphate (LiFePO 4 ) having an olivine structure as the positive electrode active material, and the positive electrode porosity or the negative electrode porosity does not satisfy the above range, while the 5 It cycle characteristic is 83 to 95%. It can be seen that Comparative Examples 1 to 4 have inferior high-rate discharge cycle characteristics of 71 to 77%.

このことは、次のように考えられる。正極の導電性を高めるために、小粒径(平均粒径100nm)のリン酸鉄リチウムを用いると、正極活物質と非水電解質との接触面積が大きくなるので、その分正極が必要とする非水電解質量が増加する。また、ハイレート放電(5It放電)を行うと、リチウムイオンの吸蔵・脱離によって、正極及び負極の体積が急激に変化し、これに伴い正負極板の空隙に浸透した非水電解質が移動するため、ハイレート放電中に正負極の活物質に供給される非水電解質量が不十分となりやすい。
ここで、正極の空隙率を30〜50%、且つ、負極の空隙率を20〜30%に規制すると、正極活物質周囲に存在するリチウムイオン量が十分となり、且つ負極活物質周囲に存在する非水電解質量が十分となる。このため、正負極の膨張収縮が大きいハイレート放電時を行っても、正負極に十分な非水電解質が供給され続ける。これにより、ハイレート放電サイクル特性が高まる。上記範囲を外れる場合、正負極に十分な非水電解質が供給されないので、ハイレート放電サイクル特性が高まらない。
This is considered as follows. If lithium iron phosphate having a small particle size (average particle size of 100 nm) is used to increase the conductivity of the positive electrode, the contact area between the positive electrode active material and the non-aqueous electrolyte is increased, so that the positive electrode is required accordingly. Non-aqueous electrolytic mass increases. In addition, when high-rate discharge (5 It discharge) is performed, the volume of the positive electrode and the negative electrode changes suddenly due to insertion and extraction of lithium ions, and the nonaqueous electrolyte that has permeated into the gaps of the positive and negative electrode plates moves accordingly. In addition, the non-aqueous electrolytic mass supplied to the positive and negative active materials during high-rate discharge tends to be insufficient.
Here, when the porosity of the positive electrode is regulated to 30 to 50% and the porosity of the negative electrode is regulated to 20 to 30%, the amount of lithium ions existing around the positive electrode active material becomes sufficient and exists around the negative electrode active material. Non-aqueous electrolytic mass is sufficient. For this reason, even when performing high-rate discharge in which the positive and negative electrodes are large in expansion and contraction, a sufficient nonaqueous electrolyte is continuously supplied to the positive and negative electrodes. Thereby, the high rate discharge cycle characteristics are enhanced. When outside the above range, sufficient non-aqueous electrolyte is not supplied to the positive and negative electrodes, so the high rate discharge cycle characteristics do not increase.

また、上記表1から、空隙率比率(正極空隙率/負極空隙率)が1.3以上である実施例2〜8は、5Itサイクル特性が88〜95%と、空隙率比率が1.3未満である実施例1,9の、5Itサイクル特性が84%,83%よりも、優れていることがわかる。このことは、ハイレート放電時にさらに十分な非水電解質が正負極板に供給されるためと考えられる。よって、空隙率比率(正極空隙率/負極空隙率)を1.3以上とすることがより好ましい。   From Table 1 above, Examples 2 to 8 in which the porosity ratio (positive electrode porosity / negative electrode porosity) is 1.3 or more have a 5It cycle characteristic of 88 to 95% and a porosity ratio of 1.3. It can be seen that the 5It cycle characteristics of Examples 1 and 9, which are less than those, are superior to 84% and 83%. This is considered to be because more sufficient non-aqueous electrolyte is supplied to the positive and negative electrode plates during high-rate discharge. Therefore, the porosity ratio (positive electrode porosity / negative electrode porosity) is more preferably 1.3 or more.

この一方、正極活物質としてコバルト酸リチウム(LiCoO2)を用いた参考例1〜8は、ハイレート放電サイクル特性が75〜78%と、正極空隙率及び負極空隙率による影響がほとんどないことがわかる。 On the other hand, in Reference Examples 1 to 8 using lithium cobalt oxide (LiCoO 2 ) as the positive electrode active material, the high rate discharge cycle characteristics are 75 to 78%, and it is understood that there is almost no influence due to the positive electrode porosity and the negative electrode porosity. .

(実施例10)
導電剤として、比表面積が30m2/gのアセチレンブラックを用いたこと以外は、上記実施例4と同様にして、実施例10に係る非水電解質二次電池を作製した。
(Example 10)
A nonaqueous electrolyte secondary battery according to Example 10 was produced in the same manner as in Example 4 except that acetylene black having a specific surface area of 30 m 2 / g was used as the conductive agent.

(実施例11)
導電剤として、比表面積が35m2/gのアセチレンブラックを用いたこと以外は、上記実施例4と同様にして、実施例11に係る非水電解質二次電池を作製した。
(Example 11)
A nonaqueous electrolyte secondary battery according to Example 11 was produced in the same manner as in Example 4 except that acetylene black having a specific surface area of 35 m 2 / g was used as the conductive agent.

(実施例12)
導電剤として、比表面積が45m2/gのアセチレンブラックを用いたこと以外は、上記実施例4と同様にして、実施例12に係る非水電解質二次電池を作製した。
(Example 12)
A nonaqueous electrolyte secondary battery according to Example 12 was produced in the same manner as in Example 4 except that acetylene black having a specific surface area of 45 m 2 / g was used as the conductive agent.

(実施例13)
導電剤として、比表面積が55m2/gのアセチレンブラックを用いたこと以外は、上記実施例4と同様にして、実施例13に係る非水電解質二次電池を作製した。
(Example 13)
A nonaqueous electrolyte secondary battery according to Example 13 was produced in the same manner as in Example 4 except that acetylene black having a specific surface area of 55 m 2 / g was used as the conductive agent.

上記実施例10〜13と同一の条件で電池を作製し、上記と同様にしてサイクル特性を測定した。この結果を、実施例4と合わせて下記表2に示す。   Batteries were produced under the same conditions as in Examples 10 to 13, and cycle characteristics were measured in the same manner as described above. The results are shown in Table 2 below together with Example 4.

Figure 0005279567
Figure 0005279567

上記表2から、導電剤の比表面積が35〜45m2/gである実施例4,11,12は、ハイレート放電サイクル特性が92〜95%と、導電剤の比表面積が上記範囲外である実施例10,13の86%,87%よりも優れていることがわかる。 From Table 2 above, in Examples 4, 11 and 12 where the specific surface area of the conductive agent is 35 to 45 m 2 / g, the high rate discharge cycle characteristics are 92 to 95% and the specific surface area of the conductive agent is outside the above range. It turns out that it is superior to 86% and 87% of Example 10,13.

このことは、次のように考えられる。導電剤の比表面積が35m2/g未満であると、導電剤の粒径が大きくなるため、導電作用が若干低下する。他方、導電剤の比表面積が45m2/gより大きいと、導電剤が凝集しやすくなるので、この場合もまた、導電作用が若干低下する。これにより、正極の導電性が若干低下するので、実施例10,13では、ハイレート放電サイクル特性がわずかに低下する。 This is considered as follows. When the specific surface area of the conductive agent is less than 35 m 2 / g, the particle size of the conductive agent is increased, and the conductive action is slightly reduced. On the other hand, if the specific surface area of the conductive agent is larger than 45 m 2 / g, the conductive agent is likely to aggregate, and in this case also, the conductive action is slightly reduced. Thereby, since the electroconductivity of a positive electrode falls a little, in Example 10, 13, the high rate discharge cycle characteristic falls slightly.

(追加事項)
上記実施例では、正極活物質としてオリビン構造を有するリン酸鉄リチウム(LiFePO4)を用いたが、その他のオリビン構造を有する一般式LixMPO4(0<x<1.3、MはCo,Ni,Mn,Feからなる群より選択される少なくとも一種の元素)で示されるリチウム遷移金属リン酸塩を用いてもよい。中でも、資源量豊富で安価な鉄を含んだ一般式LixFey1-yPO4(0<x<1.3、0<y≦1、MはCo,Ni,Mnからなる群より選択される少なくとも一種の元素)で示されるオリビン構造を有する鉄含有リチウム遷移金属リン酸塩を正極活物質に含ませることが好ましい。
(Additions)
In the above examples, lithium iron phosphate (LiFePO 4 ) having an olivine structure was used as the positive electrode active material, but other general formula Li x MPO 4 (0 <x <1.3, where M is Co , Ni, Mn, Fe, or at least one element selected from the group consisting of Fe may be used. Among them, the general formula Li x Fe y M 1-y PO 4 (0 <x <1.3, 0 <y ≦ 1, M is a group consisting of Co, Ni, and Mn, including abundant and inexpensive resources) It is preferable that the positive electrode active material contains an iron-containing lithium transition metal phosphate having an olivine structure represented by at least one selected element.

また、上記オリビン構造を有するリチウム遷移金属リン酸塩に、公知の正極活物質材料(一般式LixMO2(0<x≦1.1、MはCo,Ni,Mn,Feからなる群より選択される少なくとも一種の元素)で示されるリチウム遷移金属複合酸化物やスピネル型マンガン酸リチウム、これらの化合物に異種元素(Zr,Ti,Mg,Al等)を添加したもの)を混合して用いてもよい。 The lithium transition metal phosphate having the olivine structure may be added to a known positive electrode active material (general formula Li x MO 2 (0 <x ≦ 1.1, M is a group consisting of Co, Ni, Mn, Fe). Selected from at least one element selected from the group consisting of lithium transition metal composite oxides, spinel type lithium manganates, and other compounds (Zr, Ti, Mg, Al, etc.) added to these compounds) May be.

オリビン構造を有するリチウム遷移金属リン酸塩は、正極活物質全質量に対して50質量%以上であることが好ましく、70質量%以上であることがより好ましく、90質量%以上であることがさらに好ましい。   The lithium transition metal phosphate having an olivine structure is preferably 50% by mass or more, more preferably 70% by mass or more, and further preferably 90% by mass or more based on the total mass of the positive electrode active material. preferable.

以上に説明したように、本発明によれば、ハイレート放電でのサイクル特性及び安全性に優れた非水電解質二次電池を安価に提供することができる。したがって、産業上の利用可能性は大きい。   As described above, according to the present invention, a non-aqueous electrolyte secondary battery excellent in cycle characteristics and safety in high rate discharge can be provided at low cost. Therefore, industrial applicability is great.

Claims (3)

正極活物質と導電剤とを有する正極と、負極活物質を有する負極と、を有する電極体と、非水溶媒と電解質塩とを有する非水電解質と、を備える非水電解質二次電池において、
前記正極活物質は、オリビン構造を有する一般式LixMPO4(0<x<1.3、MはCo,Ni,Mn,Feからなる群より選択される少なくとも一種の元素)で示されるリチウム遷移金属リン酸塩を含み、
前記正極の空隙率が30〜50%であり、且つ前記負極の空隙率が20〜30%である、
ことを特徴とする非水電解質二次電池。
In a nonaqueous electrolyte secondary battery comprising: a positive electrode having a positive electrode active material and a conductive agent; an electrode body having a negative electrode having a negative electrode active material; and a nonaqueous electrolyte having a nonaqueous solvent and an electrolyte salt.
The positive electrode active material is lithium represented by the general formula Li x MPO 4 having an olivine structure (0 <x <1.3, M is at least one element selected from the group consisting of Co, Ni, Mn, and Fe). Including transition metal phosphates,
The porosity of the positive electrode is 30 to 50%, and the porosity of the negative electrode is 20 to 30%.
A non-aqueous electrolyte secondary battery.
請求項1に記載の非水電解質二次電池において、
前記正極の空隙率が、前記負極の空隙率の1.3倍以上であることを特徴とする非水電解質二次電池。
The nonaqueous electrolyte secondary battery according to claim 1,
A nonaqueous electrolyte secondary battery, wherein the porosity of the positive electrode is 1.3 times or more of the porosity of the negative electrode.
請求項1又は2に記載の非水電解質二次電池において、
前記導電剤は、比表面積が35〜45m2/gのアセチレンブラックであることを特徴とする非水電解質二次電池。
The nonaqueous electrolyte secondary battery according to claim 1 or 2,
The non-aqueous electrolyte secondary battery, wherein the conductive agent is acetylene black having a specific surface area of 35 to 45 m 2 / g.
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