JP3631185B2 - Non-aqueous electrolyte secondary battery and manufacturing method thereof - Google Patents

Description

【００５３】
４．試験結果の検討
（１）コバルト酸リチウムを正極活物質として用いた場合の炭酸ガス溶存の効果コバルト酸リチウムを正極活物質として用い、電解液中に炭酸ガスを溶存しない比較例１の電池Ｒと、電解液中に炭酸ガスを溶存した比較例２の電池Ｓを比較すると、いずれの電池も６００ｍＡｈの設計容量に対して、電池作製上の誤差（例えば、合剤塗布時の質量誤差等）程度しか差異が生じていないことが分かる。このことは、電解液中の炭酸ガスの溶存の有無に関わらず、即ち、電極表面に炭酸リチウムの皮膜が形成されているか否かに関わらず、電池性能を充分に引き出していることを示している。解体した負極においては、ポリマーも均一に硬化されていて、均一に充電されていることが分かった。
【００５４】
これは、電解液中にわずかに存在する水分がＬｉＰＦ_６等のリチウム塩と反応してＨＦなどの酸を発生し、これが正極活物質と反応して電解液の分解を促進するが、コバルト酸リチウムは酸に対してそれほど敏感ではないため、電解液の分解を促進しないためと考えられる。これらのことから、コバルト酸リチウムを正極活物質として用いた場合には、電解液中に炭酸ガスを溶存させても、電極表面に炭酸リチウムの皮膜を形成させる効果を発揮することはないということができる。
【００５５】
（２）低沸点溶媒種（鎖状カーボネート系溶媒）の必要性
コバルト酸リチウムを正極活物質として用い、環状カーボネートと鎖状カーボネートの混合溶媒（ＥＣ＋ＤＥＣ）を用いた比較例１の電池Ｒと、環状カーボネート同士の混合溶媒（ＥＣ＋ＰＣ）を用いた比較例３の電池Ｔを比較すると、初期の放電容量が電池Ｔの方が、電池Ｒより４７ｍＡｈ低くなっていることが分かる。また、マンガン酸リチウムを正極活物質として用い、環状カーボネートと鎖状カーボネートの混合溶媒（ＥＣ＋ＤＥＣ）を用いた比較例４の電池Ｕと、環状カーボネート同士の混合溶媒（ＥＣ＋ＰＣ）を用いた比較例５の電池Ｖを比較すると、初期の放電容量が電池Ｖの方が、電池Ｕより４４ｍＡｈ低くなっていることが分かる。
【００５６】
これは、環状カーボネートは極性が強いためにイオン伝導性が優れているが、環状という構造上、自由度が少ないために分子間力が高くなる傾向が強く、粘度が非常に高い。このため、環状カーボネート同士の混合溶媒（ＥＣ＋ＰＣ）を用いた比較例３の電池Ｔおよび比較例５の電池Ｖにおいては、高充填された電極（正極１１及び負極１２）内に電解液を充分に浸透させることが難しく、初期放電容量が低下した結果になったと考えられる。なお、電解液を電極内に浸透させやすくするために、電池内に界面活性剤を添加することが有効であるが、電池性能に悪影響を与えたり、界面活性剤自体が環境上好ましくないため、有効な手段であるとはいえない。
【００５７】
一方、鎖状カーボネートは、極性が環状カーボネートほど高くないため、導電性の補助的効果は少ないが、鎖状という構造上、自由度が大きいために分子間力が小さく、粘度が低い。このため、環状カーボネートと鎖状カーボネートの混合溶媒（ＥＣ＋ＤＥＣ）を用いた比較例１の電池Ｒおよび比較例４の電池Ｕにおいては、高充填された電極（正極１１及び負極１２）内に電解液を充分に浸透させることができるようになって、初期放電容量の低下を抑制できたと考えられる。しかしながら、電解液注液直後の電池内部は非常に還元性が高いため、還元されやすい鎖状カーボネートは容易に分解されてガスを発生する。
【００５８】
このことは、コバルト酸リチウムを正極活物質とした場合には、上述したようにガス発生を生じないが、マンガン酸リチウムを正極活物質とした場合には、ガスを発生するため重大な問題なる。これは、電解液中にわずかに存在する水分がＬｉＰＦ_６等のリチウム塩と反応してＨＦなどの酸を発生し、これが正極活物質のマンガン酸リチウムと反応して電解液の分解を促進するためである。このため、マンガン酸リチウムを正極活物質として用い、環状カーボネートと鎖状カーボネートの混合溶媒（ＥＣ＋ＤＥＣ）を用いた比較例４の電池Ｕにおいては、初期放電容量が設計容量よりも２９ｍＡｈだけ低下した結果になったと考えられる。
【００５９】
これらのことから、以下の事項が明らかになる。即ち、電池内で熱重合させて電解液をゲル化した非水電解質電池においては、環状カーボネートと鎖状カーボネートの混合溶媒を用いることが必須になる。しかしながら、マンガン酸リチウムを正極活物質に用いた場合には、鎖状カーボネートが分解されてガスを発生し、放電容量が低下する。このため、鎖状カーボネートの分解を抑制することが必要になる。そこで、本発明の効果を以下において、詳細に検討する。
【００６０】
（３）マンガン酸リチウムを正極活物質として用いた場合の炭酸ガス溶存の効果まず、窒素ガスあるいはアルゴンガスの雰囲気中で電解液の注液を行って、電解液中に炭酸ガスが溶存していない比較例４の電池Ｕと、炭酸ガスの雰囲気中で電解液の注液を行って、電解液中に炭酸ガスを溶存させた実施例１の電池Ａとを比較する。窒素ガスあるいはアルゴンガスの雰囲気中で電解液の注液を行った比較例４の電池Ｕにおいては、設計容量に対して２９ｍＡｈだけ初期放電容量が低下していることが分かる。また、比較例４の電池Ｕにおいては、図３に示すように、負極１２の至る所に「ガス噛み」に起因する硬化むら１２ａが発生していることが分かった。
【００６１】
これは、溶質として用いたＬｉＰＦ_６が電解液中にわずかに存在する水分と反応してＨＦなどの強酸を発生させる。すると、酸に特に敏感なマンガン酸リチウムが、発生した酸と反応してマンガンイオンを電解液中に溶出させる。この溶出したマンガンイオンが、負極表面上に点在する−ＣＯＯＨ，−ＮＨ，−ＯＨなどの活性官能基と電解液を絡めて反応して多量のガスを発生する。そして、電解液中には熱重合性のモノマー材料が存在しているので、粘度が高い状態にある。このため、発生したガスが電極間に滞留して、この状態でモノマーが熱重合して電解液はゲル化することとなる。この結果、正極１１−セパレータ１３−負極１２間に充分に電解液が充填されない状態となって、初期放電容量が低下したと考えられる。
【００６２】
一方、炭酸ガスの雰囲気中で電解液の注液を行って、電解液中に炭酸ガスを溶存させた実施例１の電池Ａにおいては、ほぼ設計容量通りの初期放電容量が得られた。また、図３に示すような「ガス噛み」に起因する硬化むら１２ａの発生も認められなく、均一に充電されたものとなった。このような結果になった理由は、今のところ、充分には把握できていないが、以下のように推測できる。即ち、電解液中に溶存した炭酸ガスは、溶質であるＬｉＰＦ_６のリチウム塩が解離したリチウムイオン（Ｌｉ^＋）と反応して、正極１１の表面や負極１２の表面に薄い炭酸リチウムの無機質皮膜を形成する。すると、この皮膜は負極表面上に点在する−ＣＯＯＨ，−ＮＨ，−ＯＨなどの活性官能基をコーティングするように包み込み、炭酸ガスを溶存させなかった場合のような副反応の進行を阻害し、「ガス噛み」に起因する硬化むら１２ａの発生を抑制できたと考えられる。
【００６３】
ここで、図３に示すように、「ガス噛み」に起因する硬化むら１２ａが形成されると、硬化むら１２ａの部分は電解液が存在しにくい状態にあるため、この硬化むら１２ａの周辺にリチウムが析出しやすくなる。そして、析出したリチウムは電解液と副反応してガスを発生させ、正規の充放電反応を阻害して充放電不良が発生する。そして、この状態で充放電サイクルを繰り返すと、充放電不良の箇所が拡大して、充放電サイクル中に急激な劣化が引き起こされる。また、析出したリチウムは１００℃付近の温度で異常発熱を引き起こすため、内部燃焼などの異常を引き起こす場合もある。
【００６４】
このことは、図４の結果が明瞭に示しているということができる。即ち、ポリマーの硬化不良が認められる比較例４の電池Ｕにおいては、充放電サイクルの経過に伴い、充放電不良の箇所が拡大して急激にサイクル特性が劣化している。これに対して、硬化不良が認められない実施例１の電池Ａにおいては、均一に重合されているために異常な反応が生じず、単調なサイクル特性劣化の挙動をしている。このことから、マンガン酸リチウムを正極活物質として用いた場合には、電解液中に炭酸ガスを溶存させることは、ポリマーの均一な重合性を確保する上で非常に有効な手段になるということができる。
【００６５】
（４）ＬｉＰＦ_６をリチウム塩として用いた場合の炭酸ガス溶存の効果
ＬｉＰＦ_６を電解液の溶質とする比較例４の電池Ｕと、ＬｉＮ（ＳＯ_２Ｃ_２Ｆ_５）_２を電解液の溶質とする比較例６の電池Ｗとを比較すると、初期放電容量が電池Ｗの方が高いことが分かる。これは、ＬｉＮ（ＳＯ_２Ｃ_２Ｆ_５）_２はＬｉＰＦ_６のようにＨＦのような強酸を発生しないために、比較例４の電池Ｕのような「ガス噛み」に起因する硬化むら１２ａの発生を緩和できたためと考えられる。しかしながら、ＬｉＮ（ＳＯ_２Ｃ_２Ｆ_５）_２を電解液の溶質を用いて電解液に炭酸ガスを溶存させた実施例２の電池Ｂ、およびＬｉＰＦ_６とＬｉＮ（ＳＯ_２Ｃ_２Ｆ_５）_２の混合溶質を用いて電解液に炭酸ガスを溶存させた実施例３の電池Ｃと、比較例６の電池Ｗとを比較すると、電池Ｂ，Ｃの方が初期放電容量が高いことが分かる。
【００６６】
これは、ＬｉＮ（ＳＯ_２Ｃ_２Ｆ_５）_２はＬｉＰＦ_６のようにＨＦのような強酸を発生しないが、ＨＦよりも弱い酸を発生することが知られており、この弱い酸により鎖状カーボネートの分解が起こってガスを発生する。このため、電池Ｗにおいては、「ガス噛み」に起因する硬化むら１２ａを発生して、初期放電容量が低下したと考えられる。一方、電池Ｂ，Ｃにおいては、上述した理由により「ガス噛み」に起因する硬化むら１２ａの発生が防止されて、初期放電容量が低下しなかったと考えられる。
このことから、特に、ＨＦのような強酸を発生させる頻度が高いＬｉＰＦ_６を溶質として用いる電解液に炭酸ガスを溶存させると、硬化むらを防止する効果を充分に発揮させることが可能となって、有効であるということができる。
【００６７】
（５）熱重合性高分子材料の必要性
ポリマー材料としてＰＶｄＦを用いた、比較例７の電池Ｘと比較例８の電池Ｙにおいては、いずれの電池も６００ｍＡｈの設計容量に対して、電池作製上の誤差程度しか差異が生じていないことが分かる。このことは、電解液中に炭酸ガスが溶存してるか否に関わらず、即ち、電極表面に炭酸リチウムの皮膜が形成されているか否かに関わらず、電池性能を充分に引き出していることを示している。解体した負極においては、ポリマーも均一に硬化されていて、均一に充電されていることが分った。
【００６８】
これは、ＰＶｄＦは熱重合性の高分子材料でないため、電解液中にＰＶｄＦを添加すると電解液の粘度が上昇する。しかしながら、粘度が上昇しても流動性を維持しているため、ゲル化の過程でガスが発生しても、発生したガスは電極間に留まることなく、完全にゲル化するまでには電極間から抜け出るようになる。このため、電解液中に炭酸ガスが溶存していなくても、溶存しても同じような結果になったと考えられる。このことから、電解液中に炭酸ガスを溶存させる効果を発揮させるためには、熱重合性のモノマー材料を用いた場合において、有効であるということができる。なお、熱重合性のモノマー材料としては、末端基がアクリレートであるものが好ましい。
【００６９】
（６）マンガン酸リチウムにコバルト酸リチウムを混合した混合正極活物質を用いた場合の炭酸ガス溶存の効果
マンガン酸リチウムにコバルト酸リチウムを混合した混合正極活物質（質量比で１：１）を用いた、実施例４の電池Ｄと比較例９の電池Ｚとを比較すると、初期放電容量は電池Ｄの方が電池Ｚよりも１６ｍＡｈだけ向上していることが分かる。このことは、正極中に酸分に対して敏感に反応するマンガン酸リチウムが含有されていると、このマンガン酸リチウムが電解液の分解に関与するため、電解液中に炭酸ガスを溶存させる効果を発揮したためと考えられる。なお、マンガン酸リチウムの含有量が少なすぎると、炭酸ガスを溶存させる効果を発揮させることができないため、マンガン酸リチウムの含有量は、混合正極活物質の質量に対して１０質量％以上、好ましくは３０質量％以上とするのが望ましい。
【００７０】
（７）炭酸ガスの電解液中への溶存方法の差異
さらに、炭酸ガスの雰囲気で注液した後、窒素ガスあるいはアルゴンガスの雰囲気で含浸した実施例１の電池Ａと、窒素ガスあるいはアルゴンガスの雰囲気で注液した後、炭酸ガスの雰囲気で含浸した実施例５の電池Ｅと、予め炭酸ガスを溶存させた電解液を窒素ガスあるいはアルゴンガスの雰囲気で注液、含浸した実施例６の電池Ｆとを比較すると、いずれの電池も６００ｍＡｈの設計容量に対して、電池作製上の誤差程度しか差異が生じていないことが分かる。このことは、炭酸ガスを注液時あるい含浸時もしくは予め電解液中に溶存させても、どのような方法によっても、炭酸ガスの導入効果を奏することができるようになる。
【００７１】
【発明の効果】
上述したように、本発明においては、スピネル型マンガン酸リチウムを正極活物質として含む正極と、環状カーボネートと鎖状カーボネートの混合溶媒と溶質からなる電解液と、熱重合性モノマーとの組み合わせで懸案となっていた発生ガスによる重合の不均一性を、炭酸ガスを電解液に溶存させることで改善している。この結果、優れた電池性能を有する非水電解質電池を提供できるようになる。
【００７２】
また、本発明においては、電解液に溶存した炭酸ガスは、電解液中の極性溶媒になどに溶存していた酸素を追い出して熱重合するため、均一な熱重合が可能になって、均一性に優れたポリマー電解質が得られる。これは、電解液中の極性溶媒に配位した酸素が、酸素よりは配位力が強い炭酸ガスにより置換されたためと考えられる。そして、均一性に優れたポリマー電解質を備えることにより、エネルギー密度、サイクル特性、負荷特性、温度特性が向上した非水電解質二次電池が得られるとともに、安全性に優れ、かつ高温保存時においてもガス発生が減少した非水電解質二次電池が得られるようになる。
【図面の簡単な説明】
【図１】本発明の非水電解質電池の一例を模式的に示す図であり、図１（ａ）は外形形状を模式的に示す斜視図であり、図１（ｂ）は、図１（ａ）のＡ−Ａ断面を示す断面図である。
【図２】本発明の非水電解質二次電池を作製するための工程手順の概略を示す工程図である。
【図３】負極の表面に形成された重合むらを模式的に示す図である。
【図４】実施例の電池と比較例の電池の充放電サイクルと放電容量の関係を示す図である。
【符号の説明】
１０…非水電解質二次電池、１１…正極、１２…負極、１３…セパレータ、１４…外装体、１５…正極端子、１６…負極端子[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a positive electrode containing spinel type lithium manganate as a positive electrode active material, a negative electrode containing a negative electrode active material capable of inserting and removing lithium ions, a separator separating these positive electrode and negative electrode, The present invention relates to a non-aqueous electrolyte secondary battery including an electrolyte in an exterior body and a method for manufacturing the same.
[0002]
[Prior art]
In recent years, lithium cobalt oxide (LiCoO) has been used as a negative electrode active material for alloys used in portable electronic / communication equipment such as small video cameras, mobile phones, laptop computers, etc. ₂ ), Lithium nickelate (LiNiO) ₂ ), Lithium manganate (LiMn) ₂ O ₄ Non-aqueous electrolyte secondary batteries (lithium secondary batteries) represented by lithium-ion batteries using lithium-containing composite oxides as positive electrode materials have been put into practical use as batteries that are small, lightweight, and capable of charging and discharging with high capacity. It is also marketed.
[0003]
Recently, there has been a demand for a lithium secondary battery having a large degree of freedom in the form of use in equipment used while maintaining excellent discharge characteristics. In particular, there has been a demand for a compact lithium secondary battery that can be thinned, does not leak, is lightweight, and has an excellent mass energy density. Against this background, a lithium secondary battery equipped with a polymer electrolyte in which an electrolytic solution is gelled (cured) by heating a thermopolymerizable monomer material, a so-called lithium polymer secondary battery has been put into practical use. It became so. This type of lithium polymer secondary battery is different from conventional lithium secondary batteries only in that the monomer material is contained in the electrolyte and the monomer material is thermally cured. The material to be used is almost similar to a conventional lithium secondary battery.
[0004]
[Problems to be solved by the invention]
Generally, it is essential to use a cyclic carbonate that is difficult to be reductively decomposed in the battery, has a high polarity, and easily ensures ionic conductivity as a solvent used in the electrolyte solution for a lithium secondary battery. Yes. However, the cyclic carbonate has a drawback that it has a low degree of freedom due to the cyclic structure and has a strong intermolecular force, and therefore has a very high viscosity and is difficult to contain liquid inside the electrode group. For this reason, a mixed solvent in which chain (acyclic) carbonate having low intermolecular force and low viscosity is mixed is used. Since this chain carbonate is not higher in polarity than the cyclic carbonate, ionic conductivity cannot be ensured, but since the degree of freedom is large due to the chain structure, the intermolecular force is weak and the viscosity is small. Has advantages.
[0005]
However, in a lithium polymer secondary battery, since the polymer material is contained in the electrolytic solution, the viscosity of the electrolytic solution increases, so that the electrolytic solution is less likely to be contained in the electrode group compared to the lithium secondary battery. There was a problem. For this reason, it is necessary to contain many chain carbonate type low boiling-point solvent species with a low viscosity in the structure of electrolyte solution. However, the low boiling point solvent species represented by the chain carbonate system has a problem that the solvent species itself is easily reductively decomposed and gas is easily generated in the battery.
[0006]
Further, it is known that a lithium secondary battery generates a gas due to a side reaction corresponding to the irreversible efficiency of a battery material (mainly a negative electrode material) at the initial stage of charging. In this case, in a lithium secondary battery in which a hard case such as an iron can or an aluminum can is used for the exterior body that houses the power generation element, it is relatively difficult to cause a problem that the battery swells. However, in a lithium polymer secondary battery, since a soft case such as an aluminum laminate film is used, the pressure of the generated gas causes the battery to swell, causing a problem of adversely affecting the equipment used.
[0007]
In particular, in a lithium polymer secondary battery using lithium manganate as a positive electrode active material, not only the negative electrode material, but also the lithium manganate of the positive electrode material is involved in the decomposition of the electrolytic solution, and a large amount of gas is generated. There was a problem. This is because, since lithium manganate is vulnerable to acid, the moisture present in the electrolyte is slightly LiPF. ₆ This is because it reacts with a strong acid such as HF generated by reacting with a solute such as HF. For this reason, it is presumed that gas is generated by dissolving manganese from the lithium manganate crystal and reacting with the dissolved manganese entangled with the electrolytic solution on the negative electrode.
[0008]
In this case, in the lithium secondary battery, since the electrolytic solution has fluidity, even if gas is generated in the battery, the gas does not stay between the electrodes. However, in the lithium polymer secondary battery, since the electrolytic solution is cured and solidified by gelation, the generated gas is fixed between the electrodes, which causes a serious problem such as causing a charge / discharge failure. This is because a so-called “gas biting” phenomenon occurs in which a gas generated in a high-viscosity solvent before curing cures (gels) in a state where it exists between the electrodes. For this reason, a portion where no electrolytic solution (in this case, a gelled electrolytic solution) exists between the positive electrode and the separator or between the separator and the negative electrode is generated. Then, even if it charges / discharges after that, it is because a uniform battery reaction cannot be performed, charging / discharging defect produced, and the battery characteristic fell.
[0009]
Accordingly, the present invention has been made to solve the above-described problems, and includes an electrolytic solution that includes lithium manganate as a positive electrode active material and has a solute dissolved in a mixed solvent containing a cyclic carbonate and a chain carbonate. It is an object of the present invention to provide a non-aqueous electrolyte secondary battery in which non-uniformity of thermal polymerization does not occur even when gelled (cured) with a thermopolymerizable monomer material.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, a nonaqueous electrolyte secondary battery of the present invention includes a positive electrode containing spinel type lithium manganate as a positive electrode active material, and a negative electrode containing a negative electrode active material capable of inserting and removing lithium ions. A separator that separates the positive electrode and the negative electrode and a gel electrolyte are provided in the outer package. The gel electrolyte is formed by polymerizing an electrolyte solution in which a solute composed of a lithium salt is dissolved in a mixed solvent containing a cyclic carbonate and a chain carbonate with a heat-polymerizable monomer material to form a gel. Alternatively, at least one surface of the negative electrode is formed with a lithium carbonate film formed by a reaction between a carbon dioxide gas dissolved in the electrolytic solution and the electrolytic solution.
[0011]
Here, the carbon dioxide gas dissolved in the electrolytic solution reacts with lithium ions from which the lithium salt that is the solute of the electrolytic solution is dissociated to form a thin lithium carbonate inorganic coating on the surface of the positive electrode or the negative electrode. Since this lithium carbonate coating coats active functional groups (-COOH, -NH, -OH, etc.) on the negative electrode, the chain carbonate of one solvent can be prevented from being decomposed by the active functional groups. It becomes like this. As a result, it is possible to prevent a “gas biting” phenomenon from occurring during the thermal polymerization of the monomer material, and it is possible to obtain a nonaqueous electrolyte secondary battery in which nonuniformity of thermal polymerization does not occur.
[0012]
In addition, carbon dioxide dissolved in the electrolyte solution is thermally polymerized by expelling oxygen dissolved in the polar solvent in the electrolyte solution, enabling uniform thermal polymerization and a gel electrolyte with excellent uniformity. (Polymer electrolyte) is obtained. This is presumably because oxygen coordinated with the polar solvent in the electrolyte was replaced by carbon dioxide gas having higher coordinating power than oxygen. By providing a gel electrolyte (polymer electrolyte) with excellent uniformity, a non-aqueous electrolyte secondary battery with improved energy density, cycle characteristics, load characteristics, and temperature characteristics can be obtained, and safety is excellent. A nonaqueous electrolyte secondary battery in which gas generation is suppressed even during high temperature storage can be obtained.
[0013]
In this case, LiPF ₆ LiPF as an electrolyte solute, LiPF ₆ Generates a strong acid such as HF. Then, HF reacts with a chain carbonate that is weak against acid, and decomposes the chain carbonate to generate gas, resulting in uneven curing due to “gas biting”. However, when a thin lithium carbonate inorganic coating is formed on the surface of the positive electrode or the negative electrode, the chain carbonate can be prevented from being decomposed. Therefore, in particular, LiPF, which has a high frequency of generating a strong acid such as HF, is used. ₆ It is preferable to dissolve carbon dioxide gas in the electrolytic solution using as a solute because the effect of preventing unevenness of curing can be sufficiently exhibited.
[0014]
In addition, as spinel type lithium manganate used for the positive electrode active material, A part of lithium manganate was substituted with at least one element selected from magnesium (Mg), aluminum (Al), cobalt (Co), zirconium (Zr), titanium (Ti), nickel (Ni), Alternatively, it is substituted and added with at least one element selected from boron (B) and fluorine (F) It is preferable to use spinel type lithium manganate.
[0015]
Further, it is essential to use a mixed solvent of a cyclic carbonate and a chain carbonate as a solvent for the electrolytic solution. However, the solvent species of the cyclic carbonate and the chain carbonate are not particularly limited, but the cyclic carbonate is preferably selected from at least one of propylene carbonate, ethylene carbonate, and butylene carbonate. The chain carbonate is preferably selected from at least one of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.
[0016]
Furthermore, as the thermopolymerizable monomer material, it is particularly preferable to use a monomer material such as polypropylene glycol diacrylate whose terminal group is an acrylate. Polymers obtained by polymerizing thermopolymerizable monomer materials are polyether solid polymers, polycarbonate solid polymers, polyacrylonitrile solid polymers, copolymers of these two or more, or crosslinked high polymers. It is desirable to use molecules.
[0017]
And in order to obtain the nonaqueous electrolyte secondary battery of the structure mentioned above, the manufacturing method of the nonaqueous electrolyte secondary battery of this invention is, after forming an electrode group by interposing a separator between a positive electrode and a negative electrode, Electrode group housing step for housing the electrode group in the exterior body, and electrolyte solution preparation by dissolving an electrolyte composed of lithium salt and a thermopolymerizable monomer material in a mixed solvent containing cyclic carbonate and chain carbonate A step of injecting an electrolyte solution in an atmosphere of carbon dioxide gas into an exterior body in which the electrode group is housed, and a pressure reduction impregnation step of impregnating the electrode group in a reduced pressure atmosphere with the electrolyte solution injected into the exterior body And a gelling step of gelling and polymerizing the thermopolymerizable monomer material dissolved in the electrolytic solution by heating.
[0018]
Thus, when the liquid injection process of injecting the electrolytic solution in an atmosphere of carbon dioxide gas is provided, the carbon dioxide gas is dissolved in the electrolytic solution. Thus, when the electrode group is impregnated in the reduced pressure impregnation step in an atmosphere of reduced pressure, a lithium carbonate film is formed on the surface of the positive electrode, the surface of the negative electrode, or the surfaces of both electrodes. For this reason, even if the thermopolymerizable monomer material is heated and cured in the subsequent curing step, it is possible to prevent uneven curing due to “gas biting”.
[0019]
In this case, instead of performing the liquid injection process in an atmosphere of carbon dioxide gas, even if the vacuum impregnation process is performed in an atmosphere of carbon dioxide gas, a lithium carbonate film can be formed on at least one of both electrodes, Similar effects can be achieved. In addition, a film of lithium carbonate can be formed on at least one of both electrodes even if carbon dioxide gas is dissolved in the electrolyte solution by bubbling in advance and then the electrolyte solution is injected and impregnated. The same effect can be achieved.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Next, an embodiment of the present invention will be described below with reference to FIG. 1. However, the present invention is not limited to this embodiment, and can be appropriately implemented without changing the object of the present invention. is there. 1 is a diagram schematically showing an example of the nonaqueous electrolyte battery of the present invention, FIG. 1 (a) is a perspective view schematically showing an outer shape, and FIG. 1 (b) is a diagram in FIG. It is sectional drawing which shows the AA cross section of (a).
[0021]
1. Nonaqueous electrolyte secondary battery
As shown in FIG. 1, a nonaqueous electrolyte secondary battery 10 of the present invention includes a positive electrode 11 using spinel type lithium manganate as a positive electrode active material, a negative electrode 12 using graphite as a negative electrode active material, and a gap between these two electrodes. Are provided with an electrode group having a separator 13 made of a polyethylene microporous film interposed therebetween. And the electrode group crushed flat is accommodated in the exterior body 14 made of an aluminum laminate film. A positive electrode lead (not shown) extending from the positive electrode 11 is connected to the positive electrode terminal 15, and a negative electrode lead (not shown) extending from the negative electrode 12 is connected to the negative electrode terminal 16. The upper opening of 14 is liquid-tightly sealed.
[0022]
The exterior body 14 is filled with a gelled electrolytic solution. As an electrolytic solution, a mixed solvent obtained by mixing ethylene carbonate (EC: cyclic carbonate) and diethyl carbonate (DEC: chain carbonate) at a volume ratio of 3: 7, and LiPF as a solute. ₆ Is used at a rate of 1 mol / l. In addition, polypropylene glycol diacrylate (having a molecular weight of about 300) as a thermopolymerizable monomer material and t-hexyl peroxypivalate as a polymerization initiator are added to the electrolyte (addition amount is 5000 ppm). ing. And after filling this electrolyte solution in the exterior body 14, it heats at 50 degreeC for 3 hours, heat-polymerizes polypropylene glycol diacrylate, and is gelatinized (hardened).
[0023]
Here, an important feature of the present invention is that it is generated on the surface of the negative electrode 12, the surface of the positive electrode 11, or the surfaces of these two electrodes 11, 12 by the reaction of carbon dioxide dissolved in the electrolytic solution and the electrolytic solution as will be described later. That is, the formed lithium carbonate film is formed. When a lithium carbonate film is formed on the surface of the electrode, this film coats active functional groups (—COOH, —NH, —OH, etc.) on the negative electrode. For this reason, it becomes possible to prevent the solvent of the electrolytic solution from being decomposed by the active functional group, thereby preventing the generation of gas. As a result, it is possible to prevent the “gas biting” phenomenon from occurring during the thermal polymerization of the monomer material, and the thermal polymerization is performed uniformly.
[0024]
In addition, as a spinel type lithium manganate used with a positive electrode active material, A part of lithium manganate was substituted with at least one element selected from magnesium (Mg), aluminum (Al), cobalt (Co), zirconium (Zr), titanium (Ti), nickel (Ni), Alternatively, it is substituted and added with at least one element selected from boron (B) and fluorine (F) It is desirable to use spinel type lithium manganate. As the negative electrode active material, graphite, coke, tin oxide, metallic lithium, silicon, and a mixture thereof can be used in addition to the above-described graphite, and any material that can insert and desorb lithium ions is particularly limited. There is no.
[0025]
Moreover, as a solvent of electrolyte solution, it is necessary to use the mixed solvent with which the cyclic carbonate and the chain carbonate were mixed. The cyclic carbonate may be selected from at least one of propylene carbonate (PC) and butylene carbonate (BC) in addition to the above-described ethylene carbonate (EC). The chain carbonate may be selected from at least one of dimethyl carbonate (DMC) and ethyl methyl carbonate in addition to the above-described diethyl carbonate (DEC).
[0026]
Further, as the solute of the electrolytic solution, the above-mentioned LiPF ₆ In addition, LiClO ₄ , LiBF ₄ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiPF _6-x (C _n F _{2n + 1} ) _x (However, 1 ≦ x ≦ 6, n = 1 or 2) and the like can be used, and one or more of these can be used in combination. In addition, as addition amount of lithium salt, 0.2-1.5 mol (0.2-1.5 mol / l) per liter of electrolyte solution is desirable.
[0027]
Furthermore, as the thermopolymerizable monomer material, it is particularly preferable to use a monomer material whose terminal group is an acrylate, such as polypropylene glycol diacrylate. Polymers obtained by polymerizing thermopolymerizable monomer materials are polyether solid polymers, polycarbonate solid polymers, polyacrylonitrile solid polymers, copolymers of these two or more, or crosslinked high polymers. It is desirable to use molecules. Note that the mass ratio of the thermopolymerizable polymer material and the electrolytic solution is desirably in the range of 1: 6 to 1:25 in view of ion conductivity and liquid retention of the electrolytic solution. In addition to the thin shape described above, the shape of the battery may be any shape, such as a square shape or a cylindrical shape, and the size is not particularly limited.
[0028]
2. Preparation of non-aqueous electrolyte secondary battery
The production procedure of the nonaqueous electrolyte secondary battery 10 configured as described above will be described in detail below. FIG. 2 shows an outline of a process procedure for producing the nonaqueous electrolyte secondary battery 10 of the present invention. In FIG. 2, the nonaqueous electrolyte secondary battery 10 according to the present invention is first wound by interposing a separator 13 between the electrodes 11 and 12 after performing an electrode manufacturing process for manufacturing the positive electrode 11 and the negative electrode 12. Then, after performing the winding process to make the electrode group, a drying process for drying the electrode group is performed. Next, the exterior body that houses the electrode group is placed in the dry box. Thereafter, in the dry box, a liquid injection process for injecting the electrolyte solution into the exterior body, an impregnation process for impregnating the injected electrolyte solution into the electrode group in a reduced pressure atmosphere, and an opening of the exterior body are temporarily sealed. A temporary sealing step for stopping is performed.
[0029]
Next, a heat-curing / aging process is performed in which the temporarily sealed outer package is heated to gel the thermopolymerizable monomer material present in the electrolytic solution and thermoset, followed by aging. Finally, a completed battery is obtained through a main sealing step of main sealing the exterior body. In the present invention, as means for dissolving carbon dioxide gas in the electrolytic solution, a method of performing the liquid injection step in a carbon dioxide atmosphere, a method of performing the impregnation step in a carbon dioxide atmosphere, or bubbling in advance. The method of dissolving in the electrolyte is adopted. In the following, some specific examples of the nonaqueous electrolyte battery of the present invention will be described, but various comparative examples will also be described in order to clarify the effects of the present invention.
[0030]
(1) Example 1
Spinel type lithium manganate (Li) in which a part of manganese as a positive electrode active material is substituted with magnesium (Mg) and boron (B) is added _1.06 Mn _1.88 Mg _0.04 O ₄ B _0.01 ) And graphite powder as a carbon conductive agent were mixed (for example, 92: 5 by mass ratio) to obtain a positive electrode mixture powder. Subsequently, the obtained positive electrode mixture powder was filled into a mixing apparatus (for example, a meso-fusion apparatus (AM-15F) manufactured by Hosokawa Micron Corporation). This was operated for 10 minutes at 1500 revolutions per minute (1500 rpm) to cause compression, impact and shearing action and mixing.
[0031]
Thereafter, the fluororesin binder was mixed at a constant ratio (for example, 97: 3 by mass ratio) to obtain a positive electrode mixture. Next, this positive electrode mixture was applied to both surfaces of a positive electrode current collector made of aluminum foil, dried, rolled to a predetermined thickness, cut into a predetermined shape, and the positive electrode 11 was produced. In mixing the positive electrode mixture powder, the positive electrode mixture powder may be used as it is and mixed in a slurry state without using a mechanofusion device. Moreover, you may make it mix by another method.
[0032]
On the other hand, the negative electrode active material (002) plane spacing (d ₀₀₂ ) Is 0.336 nm, the crystallite size (Lc) in the c-axis direction is 200 nm, and the average particle size is 20 μm. The powder of massive graphite (artificial graphite fired at 2950 ° C.) is used. This graphite powder and a styrene-based binder were mixed at a constant ratio (for example, 98: 2 in terms of mass ratio), and water was added and mixed to obtain a negative electrode mixture. Thereafter, this negative electrode mixture was applied to both surfaces of a negative electrode current collector made of copper foil, dried, rolled to a predetermined thickness, cut into a predetermined shape, and negative electrode 12 was produced.
[0033]
In addition, 1 mol / l lithium hexafluorophosphate (LiPF) was added to a mixed solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 3: 7. ₆ ) To dissolve the electrolyte (LiPF ₆ / EC: DEC = 3: 7). Next, polypropylene glycol diacrylate (having a molecular weight of about 300) as a thermopolymerizable monomer material is added to the electrolytic solution so that the mass ratio with respect to the electrolytic solution is 15: 1, and as a polymerization initiator. A mixed electrolyte was prepared by adding 5000 ppm of t-hexylperoxypivalate. In addition, the addition amount of the monomer material added to the electrolytic solution should be added so that the mass ratio with respect to the electrolytic solution is in the range of 6: 1 to 25: 1 in consideration of ion conductivity and liquid retention. desirable.
[0034]
Subsequently, the positive electrode 11 and the negative electrode 12 produced as described above were used, and a separator 13 made of a polyethylene microporous film was interposed between them to be wound in a spiral shape. Next, this was crushed so as to be flat to produce a flat electrode group, and then this electrode group was dried for a predetermined time. Next, after the electrode group was accommodated in the outer package 14 made of an aluminum laminate film, it was placed in a dry box. Thereafter, the inside of the dry box was filled with an atmosphere of carbon dioxide gas, and the electrolyte prepared as described above was poured into the outer package 14. Thereby, the carbon dioxide gas is dissolved in the electrolytic solution.
[0035]
Next, the inside of the dry box was replaced with nitrogen gas or argon gas, the inside of the dry box was made into an atmosphere of nitrogen gas or argon gas, and the inside of the dry box was sucked with a vacuum pump to make a reduced pressure atmosphere. As a result, the electrolyte injected into the exterior body 14 is impregnated in the electrode group, and a lithium carbonate coating is formed on the surface of the positive electrode 11, the surface of the negative electrode 12, or the surfaces of these electrodes 11 and 12. It becomes. Then, the opening part of the exterior body 14 was temporarily sealed and taken out from the dry box. Subsequently, after arrange | positioning this in a heating apparatus, the inside of a heating apparatus was maintained at the temperature of 50 degreeC, and was heated for 3 hours. Thereby, the polypropylene glycol diacrylate which is a thermopolymerizable monomer material is polymerized, and the electrolytic solution is cured by gelation. Subsequently, the non-aqueous electrolyte battery A of Example 1 having a design capacity of 600 mAh was manufactured by finally sealing the opening of the outer package 14.
[0036]
(2) Example 2
To a mixed solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 3: 7, 1 mol / l lithium imide salt (LiN (SO ₂ C ₂ F ₅ ) ₂ ) Is dissolved in an electrolyte solution (LiN (SO ₂ C ₂ F ₅ ) ₂ / EC: DEC = 3: 7) A nonaqueous electrolyte battery was produced in the same manner as in Example 1 described above except that it was prepared as nonaqueous electrolyte battery B in Example 2.
[0037]
(3) Example 3
To a mixed solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 3: 7, 0.5 mol / l lithium hexafluorophosphate (LiPF) was added. ₆ ) And 0.5 mol / l lithium imide salt (LiN (SO ₂ C ₂ F ₅ ) ₂ ) To dissolve the electrolyte (LiPF ₆ + LiN (SO ₂ C ₂ F ₅ ) ₂ / EC: DEC = 3: 7) A nonaqueous electrolyte battery was produced in the same manner as in Example 1 described above except that the nonaqueous electrolyte battery C of Example 3 was prepared.
[0038]
(4) Example 4
Spinel type lithium manganate (Li _1.06 Mn _1.88 Mg _0.04 O ₄ B _0.01 ) And lithium cobaltate (1: 1 by mass ratio), except that a mixed positive electrode active material was used, as in Example 1 described above. ₆ / EC: DEC = 3: 7), a nonaqueous electrolyte battery was produced in the same manner as in Example 1 described above, and this was designated as nonaqueous electrolyte battery D in Example 4.
[0039]
(5) Example 5
The electrode group produced in the same manner as in Example 1 was accommodated in the outer package 14, placed in a dry box, and then the inside of the dry box was placed in an atmosphere of nitrogen gas or argon gas to perform the same electrolysis as in Example 1 described above. Liquid (LiPF ₆ / EC: DEC = 3: 7) was injected into the outer package 14. Subsequently, the inside of the dry box was replaced with carbon dioxide gas, and the inside of the dry box was made to have an atmosphere of carbon dioxide gas, and the inside of the dry box was sucked with a vacuum pump to form a reduced pressure atmosphere. As a result, the electrolytic solution injected into the outer package 14 is impregnated in the electrode group, and the carbon dioxide gas is dissolved in the electrolytic solution, so that the surface of the positive electrode 11 or the surface of the negative electrode 12 or both of these electrodes 11 and 12 are dissolved. A lithium carbonate film is formed on the surface. Subsequently, a nonaqueous electrolyte battery was produced in the same manner as in Example 1 described above, and this was designated as a nonaqueous electrolyte battery E in Example 5.
[0040]
(6) Example 6
As in Example 1 described above, the electrolyte (LiPF ₆ / EC: DEC = 3: 7), a polymer material and a polymerization initiator were added in the same manner as in Example 1 to obtain a mixed electrolyte. Carbon dioxide gas was blown into this under normal pressure at room temperature (bubbling), so that the carbon dioxide gas was dissolved in the electrolyte until it was saturated. Next, after the electrode group produced in the same manner as in Example 1 was accommodated in the outer package 14 and placed in the dry box, the inside of the dry box was made an atmosphere of nitrogen gas or argon gas, and the carbon dioxide gas was dissolved. The electrolyte solution thus prepared was poured into the outer package 14.
As a result, a lithium carbonate film is formed on the surface of the positive electrode 11, the surface of the negative electrode 12, or the surfaces of both the electrodes 11 and 12. Next, after reducing the pressure in the dry box in an atmosphere of nitrogen gas or argon gas and impregnating the electrolyte solution injected into the outer package 14 into the electrode group, the non-aqueous electrolyte battery is the same as in Example 1 described above. This was used as the nonaqueous electrolyte battery F of Example 6.
[0041]
(7) Comparative Example 1
Electrolytic solution (LiPF) prepared in the same manner as in Example 1 above, using lithium cobaltate as the positive electrode active material ₆ / EC: DEC = 3: 7) In the same manner as in Example 1 described above, except that the pouring step and the impregnation step were performed in an atmosphere of nitrogen gas or argon gas, and carbon dioxide gas was not dissolved in the electrolytic solution. A nonaqueous electrolyte battery was produced, and this was designated as the nonaqueous electrolyte battery R of Comparative Example 1.
[0042]
(8) Comparative Example 2
The electrolyte solution (LiPF) was the same as in Example 1 described above except that lithium cobaltate was used as the positive electrode active material. ₆ After preparing / EC: DEC = 3: 7), a nonaqueous electrolyte battery was produced in the same manner as in Example 1 described above, and this was designated as Nonaqueous Electrolyte Battery S of Comparative Example 2.
[0043]
(9) Comparative Example 3
1 mol / l hexafluoride in a mixed solvent in which lithium cobaltate is used as a positive electrode active material and ethylene carbonate (EC: cyclic carbonate) and propylene carbonate (PC: cyclic carbonate) are mixed at a volume ratio of 3: 7 Lithium phosphate (LiPF ₆ ) To dissolve the electrolyte (LiPF ₆ / EC: PC = 3: 7) and the electrolyte solution injection and impregnation steps were performed in an atmosphere of nitrogen gas or argon gas, and carbon dioxide gas was not dissolved in the electrolyte solution. A nonaqueous electrolyte battery was produced in the same manner as in Example 1 described above, and this was designated as a nonaqueous electrolyte battery T of Comparative Example 3.
[0044]
(10) Comparative Example 4
Electrolyte prepared in the same manner as in Example 1 (LiPF ₆ / EC: DEC = 3: 7) In the same manner as in Example 1 described above, except that the pouring step and the impregnation step were performed in an atmosphere of nitrogen gas or argon gas, and carbon dioxide gas was not dissolved in the electrolytic solution. A non-aqueous electrolyte battery was produced and used as a non-aqueous electrolyte battery U of Comparative Example 4.
[0045]
(11) Comparative Example 5
Electrolytic solution (LiPF prepared in the same manner as in Comparative Example 3 ₆ / EC + PC), and the step of injecting and impregnating the electrolyte solution β4 was performed in an atmosphere of nitrogen gas or argon gas, and the carbon dioxide gas was not dissolved in the electrolyte solution β4. A nonaqueous electrolyte battery was produced in the same manner as described above, and this was designated as a nonaqueous electrolyte battery V of Comparative Example 5.
[0046]
(12) Comparative Example 6
Electrolytic solution (LiN (SON ₂ C ₂ F ₅ ) ₂ / EC: DEC = 3: 7), and the electrolytic solution pouring step and the impregnation step were performed in an atmosphere of nitrogen gas or argon gas, and carbon dioxide gas was not dissolved in the electrolytic solution. A nonaqueous electrolyte battery was produced in the same manner as in Example 1, and this was designated as a nonaqueous electrolyte battery W of Comparative Example 6.
[0047]
(13) Comparative Example 7
An electrolytic solution (LiPF) prepared using polyvinylidene fluoride (PVdF) as the polymer material and prepared in the same manner as in Example 1. ₆ / EC: DEC = 3: 7) In the same manner as in Example 1 described above, except that the pouring step and the impregnation step were performed in an atmosphere of nitrogen gas or argon gas, and carbon dioxide gas was not dissolved in the electrolytic solution. A nonaqueous electrolyte battery was produced, and this was designated as nonaqueous electrolyte battery X of Comparative Example 7. Polyvinylidene fluoride (PVdF) has already been polymerized, but it absorbs the liquid and swells to form a gel, and it melts with the electrolytic solution at high temperature and cools to form a polymer network. There are two types in which the electrolyte is taken in, but in this example, the latter is used.
[0048]
(14) Comparative Example 8
An electrolyte solution (LiPF) prepared in the same manner as in Example 1 except that polyvinylidene fluoride (PVdF) was used as the polymer material. ₆ / EC: DEC = 3: 7) and a non-aqueous electrolyte battery was produced in the same manner as in Example 1, and this was designated as non-aqueous electrolyte battery Y of Comparative Example 8. In addition, about the polyvinylidene fluoride (PVdF), the thing of the type which takes in electrolyte solution in a polymer network is melted with electrolyte solution at the same high temperature as the above, and it cools.
[0049]
(15) Comparative Example 9
The same positive electrode active material (Li as in Example 4) _1.06 Mn _1.88 Mg _0.04 O ₄ B _0.01 + Lithium cobaltate) and an electrolyte solution (LiPF) prepared in the same manner as in Example 1. ₆ / EC: DEC = 3: 7) In the same manner as in Example 1 described above, except that the pouring step and the impregnation step were performed in an atmosphere of nitrogen gas or argon gas, and carbon dioxide gas was not dissolved in the electrolytic solution. A nonaqueous electrolyte battery was produced, and this was designated as a nonaqueous electrolyte battery Z of Comparative Example 9.
[0050]
3. Charge / discharge test
Next, using each of the batteries A to F of Examples 1 to 6 and the batteries R to Z of Comparative Examples 1 to 9 having a design capacity of 600 mAh produced as described above, each of these batteries was placed at room temperature (about 25 ° C. The battery was charged at a constant current until the battery voltage reached 4.2 V at a charging current of 600 mA, and after reaching 4.2 V, the battery was charged at a constant voltage until the current value became 30 mA or less. Next, after 10 minutes of rest at room temperature (about 25 ° C.), this time, discharge was performed at room temperature (about 25 ° C.) with a discharge current of 600 mA until the battery voltage reached 2.75 V, and the initial discharge capacity was determined from the discharge time. As a result, the results shown in Table 1 below were obtained.
[0051]
In addition, after charging, each of these batteries was disassembled, the surface state of the negative electrode 12 was observed, and when the unevenness in curing of the negative electrode surface was confirmed by visual observation, the results shown in Table 1 below were obtained. Furthermore, using the battery A of Example 1 and the battery U of Comparative Example 4, the above-described charging / discharging cycle was repeated. When the discharge capacity for each cycle was determined and the ratio between the calculated discharge capacity and the initial discharge capacity was determined, the results shown in FIG. 4 were obtained. In addition, in the negative electrode curing unevenness in Table 1, the “*” mark with “Yes” indicates that a large amount of uneven curing occurred.
[0052]
[Table 1]

[0053]
4). Examination of test results
(1) Effect of dissolution of carbon dioxide when lithium cobaltate is used as the positive electrode active material Battery R of Comparative Example 1 in which lithium cobaltate is used as the positive electrode active material and carbon dioxide is not dissolved in the electrolyte, and in the electrolyte When comparing the battery S of Comparative Example 2 in which carbon dioxide gas was dissolved, the difference between the batteries was about the difference in battery production (for example, mass error during mixture application) with respect to the design capacity of 600 mAh. I understand that it is not. This indicates that the battery performance is sufficiently drawn regardless of the presence or absence of carbon dioxide in the electrolyte solution, that is, whether or not a lithium carbonate film is formed on the electrode surface. Yes. It was found that in the disassembled negative electrode, the polymer was also uniformly cured and charged uniformly.
[0054]
This is because the slightly present moisture in the electrolyte is LiPF. ₆ It reacts with a lithium salt such as HF to generate an acid such as HF, which reacts with the positive electrode active material to promote the decomposition of the electrolyte, but lithium cobaltate is not very sensitive to acid, so This is probably because it does not promote decomposition. From these facts, when lithium cobaltate is used as the positive electrode active material, the effect of forming a film of lithium carbonate on the electrode surface is not exhibited even if carbon dioxide gas is dissolved in the electrolyte. Can do.
[0055]
(2) Necessity of low boiling point solvent species (chain carbonate solvent)
Battery R of Comparative Example 1 using lithium cobaltate as a positive electrode active material and a mixed solvent of cyclic carbonate and chain carbonate (EC + DEC), and Battery of Comparative Example 3 using a mixed solvent of cyclic carbonates (EC + PC) Comparing T, it can be seen that the initial discharge capacity of the battery T is 47 mAh lower than that of the battery R. Moreover, the battery U of the comparative example 4 using the mixed solvent (EC + DEC) of cyclic carbonate and a chain carbonate using lithium manganate as a positive electrode active material, and the comparative example 5 using the mixed solvent (EC + PC) of cyclic carbonates. When comparing the battery V, it can be seen that the initial discharge capacity of the battery V is 44 mAh lower than that of the battery U.
[0056]
This is because cyclic carbonate has excellent ion conductivity due to its strong polarity, but due to its cyclic structure, it has a high tendency to increase intermolecular force due to its low degree of freedom, and its viscosity is very high. For this reason, in the battery T of the comparative example 3 and the battery V of the comparative example 5 using the mixed solvent (EC + PC) of cyclic carbonate, electrolyte solution is fully filled in the highly filled electrode (the positive electrode 11 and the negative electrode 12). It is difficult to infiltrate, and it seems that the initial discharge capacity was reduced. In order to facilitate the penetration of the electrolyte into the electrode, it is effective to add a surfactant in the battery, but the battery performance is adversely affected or the surfactant itself is not environmentally preferable. It is not an effective means.
[0057]
On the other hand, chain carbonates are not as high in polarity as cyclic carbonates, so there are few auxiliary effects of conductivity. However, because of the chain structure, the degree of freedom is large and the intermolecular force is small and the viscosity is low. For this reason, in the battery R of Comparative Example 1 and the battery U of Comparative Example 4 using a mixed solvent of cyclic carbonate and chain carbonate (EC + DEC), the electrolyte solution is contained in the highly filled electrodes (the positive electrode 11 and the negative electrode 12). It is considered that the decrease in the initial discharge capacity could be suppressed by sufficiently permeating the liquid. However, since the inside of the battery immediately after the electrolyte injection is very reducible, the chain carbonate that is easily reduced is easily decomposed to generate gas.
[0058]
When lithium cobaltate is used as the positive electrode active material, gas generation does not occur as described above. However, when lithium manganate is used as the positive electrode active material, gas is generated, which is a serious problem. . This is because the slightly present moisture in the electrolyte is LiPF. ₆ This is because it reacts with a lithium salt such as HF to generate an acid such as HF, which reacts with the positive electrode active material lithium manganate and promotes the decomposition of the electrolyte. Therefore, in the battery U of Comparative Example 4 using lithium manganate as the positive electrode active material and using a mixed solvent of cyclic carbonate and chain carbonate (EC + DEC), the result of the initial discharge capacity being reduced by 29 mAh from the designed capacity It is thought that it became.
[0059]
From these, the following matters become clear. That is, in a non-aqueous electrolyte battery in which an electrolytic solution is gelled by thermal polymerization in the battery, it is essential to use a mixed solvent of a cyclic carbonate and a chain carbonate. However, when lithium manganate is used as the positive electrode active material, the chain carbonate is decomposed to generate gas, and the discharge capacity is reduced. For this reason, it is necessary to suppress the decomposition of the chain carbonate. Therefore, the effects of the present invention will be examined in detail below.
[0060]
(3) Effect of dissolution of carbon dioxide gas when lithium manganate is used as the positive electrode active material First, an electrolyte solution is injected in an atmosphere of nitrogen gas or argon gas, and carbon dioxide gas is dissolved in the electrolyte solution. The battery U of Comparative Example 4 that is not present is compared with the battery A of Example 1 in which the electrolytic solution is injected in an atmosphere of carbon dioxide gas and the carbon dioxide gas is dissolved in the electrolytic solution. It can be seen that in the battery U of Comparative Example 4 in which the electrolyte was injected in an atmosphere of nitrogen gas or argon gas, the initial discharge capacity was reduced by 29 mAh relative to the design capacity. Further, in the battery U of Comparative Example 4, as shown in FIG. 3, it was found that uneven curing 12 a caused by “gas biting” occurred throughout the negative electrode 12.
[0061]
This is because LiPF used as a solute ₆ Reacts with moisture slightly present in the electrolyte to generate a strong acid such as HF. Then, lithium manganate particularly sensitive to acid reacts with the generated acid to elute manganese ions into the electrolyte. This eluted manganese ion reacts with the electrolytic solution and an active functional group such as —COOH, —NH, and —OH scattered on the negative electrode surface to generate a large amount of gas. And since the thermopolymerizable monomer material exists in electrolyte solution, it exists in a state with a high viscosity. For this reason, the generated gas stays between the electrodes, the monomer is thermally polymerized in this state, and the electrolytic solution is gelled. As a result, the electrolyte solution is not sufficiently filled between the positive electrode 11 -the separator 13 -the negative electrode 12, and the initial discharge capacity is considered to be reduced.
[0062]
On the other hand, in the battery A of Example 1 in which the electrolyte solution was injected in an atmosphere of carbon dioxide gas and the carbon dioxide gas was dissolved in the electrolyte solution, an initial discharge capacity almost as designed capacity was obtained. In addition, the occurrence of uneven curing 12a due to “gas biting” as shown in FIG. 3 was not recognized, and the battery was uniformly charged. The reason for such a result is not fully understood at present, but can be estimated as follows. That is, carbon dioxide dissolved in the electrolyte is LiPF, which is a solute. ₆ Lithium ions (Li ⁺ ) To form a thin lithium carbonate inorganic film on the surface of the positive electrode 11 and the surface of the negative electrode 12. Then, this coating wraps so as to coat active functional groups such as —COOH, —NH, and —OH scattered on the negative electrode surface, and inhibits the progress of side reactions as in the case where carbon dioxide gas is not dissolved. It is considered that the generation of unevenness in curing 12a due to “gas biting” could be suppressed.
[0063]
Here, as shown in FIG. 3, when the uneven curing 12a due to "gas biting" is formed, the portion of the uneven curing 12a is in a state where it is difficult for the electrolyte to exist. Lithium tends to precipitate. Then, the deposited lithium side-reacts with the electrolytic solution to generate gas, which inhibits regular charge / discharge reaction and causes charge / discharge failure. And if a charging / discharging cycle is repeated in this state, the location of charging / discharging failure will expand and a rapid deterioration will be caused during a charging / discharging cycle. Further, the deposited lithium causes abnormal heat generation at a temperature around 100 ° C., and thus may cause abnormalities such as internal combustion.
[0064]
This can be said that the result of FIG. 4 clearly shows. In other words, in the battery U of Comparative Example 4 in which defective curing of the polymer is recognized, with the progress of the charge / discharge cycle, the location of the charge / discharge failure is enlarged and the cycle characteristics are rapidly deteriorated. On the other hand, in the battery A of Example 1 in which no curing failure is observed, since the polymerization is uniformly performed, an abnormal reaction does not occur and the behavior of monotonous cycle characteristics deteriorates. From this, when lithium manganate is used as the positive electrode active material, dissolving carbon dioxide gas in the electrolytic solution is a very effective means for ensuring uniform polymerizability of the polymer. Can do.
[0065]
(4) LiPF ₆ Of Carbon Dioxide Dissolution in the Use of Lithium as Lithium Salt
LiPF ₆ And the battery U of Comparative Example 4 using LiN (SO ₂ C ₂ F ₅ ) ₂ Is compared with the battery W of Comparative Example 6 in which the electrolyte solution is the solute of the electrolyte solution, it can be seen that the battery W has a higher initial discharge capacity. This is because LiN (SO ₂ C ₂ F ₅ ) ₂ Is LiPF ₆ This is considered to be because the generation of the unevenness of curing 12a caused by the “gas biting” as in the battery U of Comparative Example 4 can be mitigated because the strong acid such as HF is not generated as in FIG. However, LiN (SO ₂ C ₂ F ₅ ) ₂ Battery B of Example 2 in which carbon dioxide gas was dissolved in the electrolyte using the electrolyte solute, and LiPF ₆ And LiN (SO ₂ C ₂ F ₅ ) ₂ When the battery C of Example 3 in which carbon dioxide gas was dissolved in the electrolytic solution using the mixed solute of No. 6 and the battery W of Comparative Example 6 were compared, it was found that the batteries B and C had higher initial discharge capacities.
[0066]
This is because LiN (SO ₂ C ₂ F ₅ ) ₂ Is LiPF ₆ It is known that a strong acid such as HF is not generated as in the case of HF, but an acid weaker than HF is generated. This weak acid causes the decomposition of the chain carbonate and generates a gas. For this reason, in the battery W, it is considered that the uneven curing 12a due to “gas biting” occurs and the initial discharge capacity is reduced. On the other hand, in the batteries B and C, it is considered that the occurrence of the uneven curing 12a due to the “gas biting” is prevented and the initial discharge capacity is not reduced for the reason described above.
Therefore, in particular, LiPF, which has a high frequency of generating a strong acid such as HF, is used. ₆ If carbon dioxide gas is dissolved in the electrolyte solution using as a solute, the effect of preventing unevenness of curing can be sufficiently exhibited, which can be said to be effective.
[0067]
(5) Necessity of thermopolymerizable polymer material
In the battery X of Comparative Example 7 and the battery Y of Comparative Example 8 that use PVdF as the polymer material, there is a difference between the batteries in Comparative Example 7 and the design capacity of 600 mAh, only in the degree of error in battery fabrication. I understand. This means that the battery performance is sufficiently drawn regardless of whether or not carbon dioxide gas is dissolved in the electrolyte solution, that is, whether or not a lithium carbonate film is formed on the electrode surface. Show. It was found that in the disassembled negative electrode, the polymer was also uniformly cured and charged uniformly.
[0068]
This is because PVdF is not a heat-polymerizable polymer material, so when PVdF is added to the electrolyte, the viscosity of the electrolyte increases. However, since the fluidity is maintained even if the viscosity rises, even if gas is generated during the gelation process, the generated gas does not stay between the electrodes, and it does not stay between the electrodes. Get out of it. For this reason, even if carbon dioxide gas is not dissolved in the electrolytic solution, it is considered that the same result was obtained even if it was dissolved. From this, it can be said that in order to exert the effect of dissolving the carbon dioxide gas in the electrolytic solution, it is effective when the thermopolymerizable monomer material is used. In addition, as a thermopolymerizable monomer material, the terminal group is preferably an acrylate.
[0069]
(6) Effect of carbon dioxide gas dissolution when a mixed positive electrode active material in which lithium cobaltate is mixed with lithium manganate is used
When the battery D of Example 4 and the battery Z of Comparative Example 9 using a mixed positive electrode active material (mass ratio of 1: 1) in which lithium cobaltate was mixed with lithium manganate were compared, the initial discharge capacity was the battery D. It can be seen that is improved by 16 mAh over battery Z. This is because when lithium manganate that reacts sensitively to acid content is contained in the positive electrode, this lithium manganate is involved in the decomposition of the electrolyte solution, so the effect of dissolving carbon dioxide gas in the electrolyte solution This is thought to be due to the fact that If the content of lithium manganate is too small, the effect of dissolving carbon dioxide gas cannot be exhibited. Therefore, the content of lithium manganate is preferably 10% by mass or more based on the mass of the mixed positive electrode active material, preferably Is preferably 30% by mass or more.
[0070]
(7) Differences in the method of dissolving carbon dioxide in the electrolyte
Furthermore, after pouring in an atmosphere of carbon dioxide gas, the battery A of Example 1 impregnated in an atmosphere of nitrogen gas or argon gas, and after pouring in an atmosphere of nitrogen gas or argon gas, it was impregnated in an atmosphere of carbon dioxide gas. When comparing the battery E of Example 5 with the battery F of Example 6 in which an electrolytic solution in which carbon dioxide gas was previously dissolved was injected and impregnated in an atmosphere of nitrogen gas or argon gas, the design capacity of each battery was 600 mAh. On the other hand, it can be seen that there is a difference only in the degree of error in battery fabrication. This means that the carbon dioxide gas can be introduced by any method regardless of whether carbon dioxide is injected or impregnated, or previously dissolved in the electrolyte.
[0071]
【The invention's effect】
As described above, in the present invention, a combination of a positive electrode containing spinel type lithium manganate as a positive electrode active material, a mixed solvent of a cyclic carbonate and a chain carbonate and a solute, and a thermopolymerizable monomer is a concern. The heterogeneity of polymerization caused by the generated gas is improved by dissolving carbon dioxide in the electrolyte. As a result, a non-aqueous electrolyte battery having excellent battery performance can be provided.
[0072]
In the present invention, the carbon dioxide gas dissolved in the electrolytic solution is thermally polymerized by expelling oxygen dissolved in the polar solvent in the electrolytic solution, so that uniform thermal polymerization is possible. An excellent polymer electrolyte can be obtained. This is presumably because oxygen coordinated with the polar solvent in the electrolyte was replaced by carbon dioxide gas having higher coordinating power than oxygen. By providing a polymer electrolyte with excellent uniformity, a non-aqueous electrolyte secondary battery with improved energy density, cycle characteristics, load characteristics, and temperature characteristics can be obtained, as well as excellent safety and storage at high temperatures. A non-aqueous electrolyte secondary battery with reduced gas generation can be obtained.
[Brief description of the drawings]
FIG. 1 is a diagram schematically showing an example of a non-aqueous electrolyte battery of the present invention, FIG. 1 (a) is a perspective view schematically showing an outer shape, and FIG. 1 (b) is a diagram in FIG. It is sectional drawing which shows the AA cross section of a).
FIG. 2 is a process diagram showing an outline of a process procedure for producing a nonaqueous electrolyte secondary battery of the present invention.
FIG. 3 is a diagram schematically showing uneven polymerization formed on the surface of a negative electrode.
FIG. 4 is a diagram showing the relationship between the charge / discharge cycle and the discharge capacity of the batteries of Examples and Comparative Examples.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Nonaqueous electrolyte secondary battery, 11 ... Positive electrode, 12 ... Negative electrode, 13 ... Separator, 14 ... Exterior body, 15 ... Positive electrode terminal, 16 ... Negative electrode terminal

Claims (12)

A positive electrode containing spinel type lithium manganate as a positive electrode active material, a negative electrode containing a negative electrode active material capable of inserting and removing lithium ions, a separator separating these positive electrode and negative electrode, and a gel electrolyte A non-aqueous electrolyte secondary battery provided in the body,
The gel electrolyte is formed by polymerizing an electrolyte solution in which a solute composed of a lithium salt is dissolved in a mixed solvent containing a cyclic carbonate and a chain carbonate with a thermally polymerizable monomer material, and gelling.
At least one surface of the positive electrode or the negative electrode is formed with a lithium carbonate film formed by a reaction between the carbon dioxide gas dissolved in the electrolyte and the electrolyte. battery. 2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the solute made of a lithium salt dissolved in the electrolytic solution contains at least LiPF _6. 3. In the spinel type lithium manganate, at least one kind of manganese is substituted with at least one element selected from magnesium, aluminum, cobalt, zirconium, titanium and nickel, or at least one selected from boron and fluorine The nonaqueous electrolyte secondary battery according to claim 1, wherein the nonaqueous electrolyte secondary battery is a spinel type lithium manganate substituted and added with any of the above elements. The cyclic carbonate is selected from at least one of propylene carbonate, ethylene carbonate, butylene carbonate,
The non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the chain carbonate is selected from at least one of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. The polymer obtained by polymerizing the thermopolymerizable monomer material is a polyether solid polymer, a polycarbonate solid polymer, a polyacrylonitrile solid polymer, a copolymer of these two or more, or a crosslinked polymer. The nonaqueous electrolyte secondary battery according to claim 1, wherein the nonaqueous electrolyte secondary battery is provided. The non-aqueous electrolyte secondary battery according to claim 1, wherein the monomer is polypropylene glycol diacrylate. A positive electrode containing spinel type lithium manganate as a positive electrode active material, a negative electrode containing a negative electrode active material capable of inserting and removing lithium ions, a separator separating these positive electrode and negative electrode, and a gel electrolyte A method for producing a non-aqueous electrolyte secondary battery provided in the body,
After forming the electrode group with the separator interposed between the positive electrode and the negative electrode, an electrode group housing step of housing the electrode group in an exterior body;
An electrolytic solution preparation step of preparing an electrolytic solution by dissolving a solute composed of a lithium salt and a thermopolymerizable monomer material in a mixed solvent containing a cyclic carbonate and a chain carbonate;
A liquid injecting step of injecting the electrolytic solution in an atmosphere of carbon dioxide gas into the exterior body containing the electrode group;
A reduced pressure impregnation step of impregnating the electrode group with an electrolyte injected into the exterior body in a reduced pressure atmosphere;
A method for producing a non-aqueous electrolyte secondary battery, comprising: a gelling step of polymerizing and gelling the thermopolymerizable monomer material dissolved in the electrolytic solution by heating. The method for producing a nonaqueous electrolyte secondary battery according to claim 7, wherein the decompression impregnation step is performed in an inert gas atmosphere. A positive electrode containing spinel type lithium manganate as a positive electrode active material, a negative electrode containing a negative electrode active material capable of inserting and removing lithium ions, a separator separating these positive electrode and negative electrode, and a gel electrolyte A method for producing a non-aqueous electrolyte secondary battery provided in the body,
After forming the electrode group with the separator interposed between the positive electrode and the negative electrode, an electrode group housing step of housing the electrode group in an exterior body;
An electrolytic solution preparation step of preparing an electrolytic solution by dissolving a solute composed of a lithium salt and a thermopolymerizable monomer material in a mixed solvent containing a cyclic carbonate and a chain carbonate;
An injecting step of injecting the electrolyte into the exterior body containing the electrode group;
A reduced pressure impregnation step of impregnating the electrode group in an atmosphere of carbon dioxide gas under reduced pressure with an electrolyte injected into the exterior body;
A method for producing a non-aqueous electrolyte secondary battery, comprising: a gelling step of polymerizing and gelling the thermopolymerizable monomer material dissolved in the electrolytic solution by heating. The method for producing a non-aqueous electrolyte secondary battery according to claim 9, wherein the liquid injection step is performed in an inert gas atmosphere. A positive electrode containing spinel type lithium manganate as a positive electrode active material, a negative electrode containing a negative electrode active material capable of inserting and removing lithium ions, a separator separating these positive electrode and negative electrode, and a gel electrolyte A method for producing a non-aqueous electrolyte secondary battery provided in the body,
After forming the electrode group with the separator interposed between the positive electrode and the negative electrode, an electrode group housing step of housing the electrode group in an exterior body;
An electrolytic solution preparation step of preparing an electrolytic solution by dissolving a solute composed of a lithium salt, a thermopolymerizable monomer material, and carbon dioxide in a mixed solvent containing a cyclic carbonate and a chain carbonate;
A liquid injecting step of injecting an electrolytic solution in which the carbon dioxide gas is dissolved in an exterior body containing the electrode group;
A reduced pressure impregnation step of impregnating the electrode group with an electrolyte injected into the exterior body in a reduced pressure atmosphere;
A method for producing a non-aqueous electrolyte secondary battery, comprising: a gelling step of polymerizing and gelling the thermopolymerizable monomer material dissolved in the electrolytic solution by heating. The method for producing a non-aqueous electrolyte secondary battery according to claim 11, wherein the liquid injection step and the reduced pressure impregnation step are performed in an inert gas atmosphere.

Images