JP2005005024A - Woven fabric for solid electrolyte carrier and solid electrolyte sheet for lithium battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a woven fabric for solid electrolyte carrier which has a large aperture ratio with a thin thickness and has a sufficient strength when solid electrolyte is carried, and a solid electrolyte sheet which carries a powder containing lithium ion conductive solid electrolyte on this woven fabric, hardly brings about the occurrence of a short circuit, and is superior in load characteristics irrespective of temperature environment and capable of making the thickness of the solid electrolyte layer thin, and excellent in electrical conductivity. <P>SOLUTION: In the solid electrolyte sheet, a material containing a polymer is coated on the surface of a fabric component yarn as a binder for carrying a solid electrolyte at the opening part of a woven fabric 2 which is plain woven using a high strength, high elasticity monofilament fiber having heat resistance, and the woven fabric is continuously rolled by a nip process or the like using a roll, and thereby the thickness of the woven fabric is made thin and arranged uniform. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０１００】
ここで、ｍは、平均の繰り返し数を示し、１〜１０００の実数を示す。また、ｎは、平均の繰り返し数を示し、１〜２０の実数を示す。
【０１０１】
比較例１，２，３：
コーティング樹脂を用いなかった場合及びコーティング樹脂としてポリエチレンテレフタレート樹脂の溶液濃度を１０ｍａｓｓ％および５０ｍａｓｓ％とした以外は、それぞれ実施例１と同様の方法により固体電解質担持用織布および固体電解質シートを得た。
【０１０２】
比較例４：
合成繊維モノフィラメントとしてポリアリレート繊維の４５μｍ糸を用いて経糸、緯糸共に９０メッシュの密度で平織り製織した織布を使用して実施例１と同様の方法により固体電解質担持用織布および固体電解質シートを得た。
【０１０３】
比較例５：
合成繊維モノフィラメントとしてポリアリレート繊維の２３μｍ糸を用いて経糸、緯糸共に１５０メッシュの密度で平織り製織した織布を使用して、実施例１と同様の方法により固体電解質担持用織布および固体電解質シートを得た。
【０１０４】
比較例６：
合成繊維モノフィラメントとしてポリエチレンテレフタレート繊維の２７μｍ糸を用いて経糸、緯糸共に１３０メッシュの密度で平織り製織し、加熱圧延加工の条件を８０℃、３．０ＭＰｓとした以外は実施例１と同様の方法により固体電解質担時用織布および固体電解質シートを得た。
【０１０５】
織布の評価項目としては、コーティング前の織布として強度、熱収縮性、開口率を、樹脂コーティング後の織布として樹脂付着量、織布厚さ、開口率を、電解質シートとして粉体担持性および電気伝導度を測定し、その結果を表１に示した。
【０１０６】
【表１】

【０１０７】
なお、各評価項目の測定は、下記の方法により行った。
【０１０８】
＜樹脂の付着量＞
樹脂付着量については、樹脂コーティング前後での重量変化を測定して算出した。
【０１０９】
＜織布の厚み＞
コーティング後の織布につき、マイクロメーターで測定した。
【０１１０】
＜開口率＞
織布の開口率については、「網状体単位面積当たりの総開口面積の割合」で定義され、コーティング前及び後の各々につき、顕微鏡写真撮影にて測定した。
【０１１１】
＜強度＞
織布を５ｃｍ巾に調整し、強伸度試験機により測定した。
【０１１２】
＜熱収縮＞
熱収縮性については、一辺２０ｃｍの正方形に裁断した織布の各辺の中央部で縦および横方向寸法を、加熱前と２００℃恒温槽中に１０分間放置後に測定し、寸法変化の有無により評価した。ここで、表１に示す○の評価は、熱収縮率が０．０５％未満に収まった場合である。表１に示すように、耐熱性樹脂であるポリアリレートを用いた実施例１〜４、比較例１〜５では、熱収縮は発生せず、高温環境下においても担持体として安定した形態を維持できることが確認された。一方、比較例６では、織糸の素材にポリアリレートに比して熱安定性の低いＰＥＴを用いているため、大幅な熱収縮が生じた。
【０１１３】
＜粉体担持性＞
粉体担持性については、固体電解質シートを金型から離型した際の充填度合いで評価した。ここでの評価方法は、固体電解質シートを１００枚作成し、織布開口部での無機固体電解質粉末の脱離の有無を目視により判定し、脱落の無いシートの比率を担持率として表示した。脱離部は電池を構成したときの短絡点となる極めて重大な欠陥である。本発明の織布並びに固体電解質シートは、応用分野の一つとして大型の固体リチウム電池を考慮しており、３０ｍｍ四方の試料で粉末の脱離が生ずる技術では大型の実用化は難しいと判断される。しかしながら、本評価は、生産技術の向上によってもある程度結果が変わりうることを考慮し、担持率が１００〜５０％程度までならば、担持性は良好とした。担持率が５０％未満の構成については担持性を不良とし、使用に耐えないと判断した。
【０１１４】
次に、担持性が良好と判断した構成（すなわち実施例１〜４及び比較例２〜６）について、該固体電解質シートの構成を用いて試験用の固体電池を組み上げて、充放電試験を行った。以下、この固体電池の構成及び試験内容について、図１を参照して説明する。
【０１１５】
試験用の固体電池は、図１に示すように、ポリエチレンテレフタレート管１（内径１０ｍｍφ）に、負極層４と、正極層５と、各層４，５の間に位置する固体電解質シート（すなわち固体電解質３及び織布２）と、からなる素子を充填し、充填した素子の両端に電極端子６，６を取り付けた構成とした。ここで、素子のうち正極層５には、活物質としての銅シュブレル化合物Ｃｕ_２Ｍｏ_６Ｓ_８と、電解質としてのリチウムゲルマニウムチオ−ホスフェートＬｉ_３．２５Ｇｅ_０．２５Ｐ_０．７５Ｓ_４と、導電助材としてのアセチレンブラックと、を重量比７０：３０：３．５で混合した合材を、１０ｍｇ用いた。また、電解質層となる固体電解質３には、リチウムゲルマニウムチオ−ホスフェートＬｉ_３．２５Ｇｅ_０．２５Ｐ_０．７５Ｓ_４粉末を７０ｍｇ用い、該粉末層の中央に織布２が位置するように成型した。このときの固体電解質層（シート）の厚みは５０μｍとした。一方、負極層４にはＬｉ金属を用いた。そして、このようにして得られた試験用の固体電池に電流密度１ｍＡ／ｃｍ^２で直流を印加し、定電流充放電を３サイクル行った。本系は正極が充放電前にＬｉを含まないので、試験は放電から開始した。
【０１１６】
充放電後に電池を解体したところ、担持性良好の検体では、固体電解質３の電解質粉末ペレットと織布２は十分に接合していたが、担持率がやや低かった検体（比較例２及び比較例４）の場合には、電解質粉末ペレットと織布２とが担持率９１％以上の検体に比べて容易に離脱した。
【０１１７】
なお、本充放電試験では、電解質層（固体電解質３）の厚みを上記のように５０μｍと厚くしたので、織布２から電解質ペレットが脱離した場合でも、このペレット自身が十分な機械強度を持っており、ペレットがひび割れるようなことはなく、短絡を起こすこともなかった。しかしながら、本発明を将来的に薄型のシート状の電池に応用することを考えると、従来のリチウムイオン電池に採用されているセパレーターを固体電解質層で置き換えると見立てた場合に、該セパレーターの厚みが２０μｍ程度と薄いために、電解質粉末シートをさらに薄くした構成において、該シートが織布２と離脱してその機械的支持が得られなくなれば、電解質粉末シートはひび割れるなどして、電池の短絡を引き起こす可能性がある。したがって、担持性の評価については、充放電試験の結果を踏まえて、表１の総合判定欄を、良好、やや不良、不良に区分して示した。
【０１１８】
＜電気伝導度持性＞
上述の総合判定において粉体担持性が良好であった構成（すなわち実施例１〜４、及び比較例３，５，６）について、イオン伝導度の測定を下記の方法で行った。
【０１１９】
１０ｍｍφの検体の両主面にＬｉＴｉＳ_２を塗布し、印加電圧を１０ｍＶ、周波数を１ＭＨｚから０．１Ｈｚの範囲とした交流インピーダンス法により測定した。その結果を表１に示す。
【０１２０】
表１に示すように、実施例１〜４では、高開口を維持しつつ担持体の厚みを薄くすることが可能で、かつ充分な強度を保つことが確認された。また、熱可塑性樹脂または高輸率高分子でコートした織布に固体電解質粉を担持した電解質シートは、固体付着強度が、樹脂コートの無い比較例１と比べ、著しく優れていることが確認された。
【０１２１】
高輸率高分子を用いた実施例４では、電解質粉体の脱落した検体は一枚もなかったが、これは該高分子の粘度が他に比して低いこと、および分極性の強い分子構造であるため無機固体電解質粉末との濡れ性が良好という理由が考えられる。また、他のコート材より高い伝導度を示しているのは、コート層自体がイオン伝導性を有するためと考えられる。
【０１２２】
コート材を必要以上に過剰に付着させた場合にも伝導度が低くなるが（比較例３）、これは、コート材により織布の開口部が狭められたり、電解質シート形成時の加熱により軟化した樹脂が電解質粉体間に浸入し、イオンの伝導度を低下させるためと考えられる。
【０１２３】
糸径が太く、織布の厚さが厚い場合（比較例４）には、電解質粉末の脱落が多く粉体の担持性は不良であった。高メッシュ織布で開口率が小さい比較例５では、粉体担持性は問題ないものの、電解質シートとしての伝導度は低くなった。これは、リチウムイオンの導電経路が狭くなるためと考えられる。
【０１２４】
織糸の素材にポリアリレートに比して熱安定性の低いＰＥＴを用いた比較例６では、経糸、緯糸方向とも約５％の熱収縮が生じ、粉体担持性は比較的良好であったものの伝導度が低くなった。
【０１２５】
表１に示す結果より、本発明の織布は、高開口を維持しつつ、厚みが薄くとも充分な強度を兼ね備え、また担持体として耐熱性が高く、固体電解質を強固に担持することができ、その結果として優れた電気伝導性を有することが分かる。
【０１２６】
【発明の効果】
以上説明したように、本発明によれば、織布の厚みが薄く高強度かつ高い開口率を有する粉体担持用織布を得ることができる。得られた担持体は、耐熱性が高く、また固体電解質を強固に担持することができるので、外的応力に対しても優れた安定性を兼ね備えている。従って、この粉体担持用織布を用いた固体電解質シートは、電気伝導性に優れ、薄型で大面積の二次電池用固体電解質シートとして好適に用いることができる。
【図面の簡単な説明】
【図１】固体電解質シートを用いた試験用の固体電池の断面図である。
【符号の説明】
１ ポリエチレンテレフタレート管
２ 固体電解質担持用織布
３ 固体電解質
４ 負極層
５ 正極層
６ 電極端子[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a woven fabric for supporting a solid electrolyte that supports a solid electrolyte, and also relates to a lithium battery using a lithium ion conductive solid electrolyte whose movable ion species is lithium ion, and more specifically, a material including a polymer. The present invention relates to a woven fabric for supporting a solid electrolyte having a small thickness and a high aperture ratio, and a lithium ion conductive solid electrolyte sheet using the woven fabric, which is suitable as a coated structure for supporting a solid electrolyte powder and the like.
[0002]
[Prior art]
In recent years, technological progress in the electronic industry has been remarkable, and the demand for batteries as a power source for the equipment has become very large. In particular, lithium secondary batteries are materials that have a low atomic weight of lithium and a large ionization energy. Therefore, lithium secondary batteries have been actively researched as batteries that can obtain a high energy density, and are now widely used as power sources for portable devices. It is used for.
[0003]
Recently, as the performance of devices using lithium secondary batteries has increased, not only battery capacity and charge / discharge cycle life, but also demands for shape diversity have become apparent. For example, a thinner cell structure is required. ing. In addition, demand for large-sized lithium secondary batteries is expected as a stationary power source or a vehicle-mounted power source such as an electric vehicle or a hybrid car. In particular, in the case of a hybrid car application where the load fluctuation is severe and a high output is required, the thinning of the cell structure is regarded as an important factor.
[0004]
On the other hand, due to an increase in internal energy due to an increase in the amount of active material, and an increase in the content of organic solvents, which are flammable substances used in electrolytes, problems related to dangers such as battery ignition have been highlighted in recent years. Therefore, it is difficult to increase the size of the battery.
[0005]
In view of the above, there is an increasing demand for lithium secondary batteries that are thin and, more desirably, all solid types that do not contain an organic solvent. Therefore, as a lithium secondary battery that is rich in shape processability and / or high in safety, all-solid-state batteries using a solid electrolyte in which the organic solvent electrolyte is replaced with a solid are actively researched. Yes. Among these types of solid electrolytes, research on polymer gel electrolytes confined in a three-dimensional network structure of polymers, polymer electrolytes that do not contain any organic solvent, and inorganic solid electrolytes is actively promoted. It has been.
[0006]
However, among these materials, the polymer gel electrolyte still contains an organic solvent, so that the safety is not perfect. Moreover, in the polymer electrolyte which does not contain an organic solvent at all, since the lithium ion conductivity is low and / or the lithium ion transport number is low, practical conductive characteristics have not yet been obtained. In terms of conduction characteristics, an inorganic solid electrolyte is considered most suitable.
[0007]
Regardless of which electrolyte is employed, these electrolytes have both the role of an electrolyte in a conventional lithium ion battery and the role of a separator that separates the electrode from the positive and negative electrodes. Therefore, the basic structure of a solid battery is a laminated structure in which a solid electrolyte is provided between a pair of positive and negative electrodes. When the positive and negative electrodes are powder molded bodies, the solid electrolyte is also included in the molded body. It is common that
[0008]
In the process of thinning the solid battery, the lamination of the electrode and the electrolyte becomes extremely difficult as the thickness of each decreases. For this reason, as a specific problem that arises, for example, if there is a hole in the electrolyte layer during the operation of the battery, a short circuit occurs immediately between the positive and negative electrodes. Since a large current flows in the case of a short circuit, severe heat generation occurs and is extremely dangerous. In the case of a system including an electrolytic solution, such heat generation may cause the battery temperature to rise to a region exceeding the ignition point of the electrolytic solution.
[0009]
Even in a polymer electrolyte that does not contain an electrolytic solution, the high temperature at the time of a short circuit may cause the polymer to decompose or melt, leading to an increase in internal pressure. If it is an inorganic solid electrolyte, some materials are stable up to about 600 ° C., and there is no danger as described above. Therefore, from the viewpoint of avoiding such danger, originally, the solid electrolyte should also have a separator function, but measures such as introducing an extra separator material are required.
[0010]
However, conventional nonwoven fabric separators can still be applied to polymer gel electrolyte systems containing organic solvents, but they are electrolyte systems with a focus on fundamental safety, that is, polymers that do not contain organic solvents. When applied to an electrolyte or an inorganic solid electrolyte, it can be a high resistance layer. Therefore, in order to prevent such a short circuit without relying on the separator, it is desirable to take a method of stably forming an electrolyte directly on a smooth electrode layer.
[0011]
In the case of applying an inorganic solid electrolyte having the highest safety and high ionic conductivity among solid electrolytes to an all-solid lithium secondary battery, for example, a sulfide glass electrolyte (see Non-Patent Document 1) is representative. Thus, the ion conduction activation energies of the powder molded body and the bulk body are almost equal, and the influence of the grain boundary can be ignored in the ion conduction. Therefore, when an electrolyte product form such as pellets or sheets of the electrolyte is imaged, there is an advantage that it can be used as it is without being subjected to heat treatment such as sintering or melting again.
[0012]
However, since the inorganic solid electrolyte is generally hard and brittle, it is difficult to obtain a large powder molded sheet. In order to stabilize the production process of such a sheet and to obtain uniform quality, compounding of polymer materials has been studied. For example, a novel solid electrolyte named “polymer in salt” made of a high concentration of lithium ion conductive inorganic salt and a rubbery polymer has been proposed (Non-patent Document). 2).
[0013]
In addition, a technique is known in which a woven fabric is introduced as an electrolyte sheet core material and an electrolyte is supported on the woven fabric. That is, a solid electrolyte sheet obtained by filling a mixture of a solid electrolyte powder uniformly dispersed in a polymer elastic body into an opening of a non-conductive network, or an electrode active material powder and, if necessary, further a solid electrolyte powder An electrode active material sheet has been developed in which a mixture in which polymer is uniformly dispersed in a polymer elastic body is filled in a non-conductive network or an opening of a conductive network (see Patent Document 1). In addition, a method for producing a woven fabric for a support as a non-conductive network used when producing a solid electrolyte sheet or an electrode active material sheet is known (see Patent Document 2).
[0014]
These woven fabrics for the solid electrolyte support ensure high yield and maintain uniform quality in the battery manufacturing process, as well as heat generation due to electrochemical reaction during use as a battery, external pressure and It is necessary to have a strength capable of stably maintaining the solid electrolyte layer against impact, and it is desirable that the opening ratio of the woven fabric is high from the viewpoint of battery performance.
[0015]
However, in the conventional woven fabric, since the fiber yarn strength of the woven fabric material is not sufficiently strong, there is a restriction on the opening ratio, specifically, 60% to 65% is the limit. It was difficult to obtain a woven fabric with a small thickness. In addition, the conventional woven fabric is not sufficient in heat resistance, and the woven fabric undergoes thermal shrinkage at the time of hot pressing for pelletizing the solid electrolyte, so that it functions as a support for the solid electrolyte. There were problems such as inability to complete.
[0016]
On the other hand, when a general-purpose polymer exemplified in Patent Documents 1 and 2 is used, since the polymer is ion-insulating, the surface of the electrolyte particles can be simply dispersed in the inorganic solid electrolyte. Is covered with a polymer film which is an ionic insulating layer, which reduces the ionic conductivity of the electrolyte sheet and raises the internal impedance of the all-solid lithium secondary battery using the sheet. Actually, with respect to the dispersion state of the polymer binder, the obtained composite electrolyte is obtained in a case where the polymer is arranged uniformly in the inorganic solid electrolyte matrix by a wet method and a case where the polymer is arranged in a granular manner, that is, non-uniformly in a dry method. When comparing the ionic conductivities of the samples, it has been reported that the samples arranged uniformly have a significantly lower ionic conductivity (see Non-Patent Document 3).
[0017]
Also, when the polymer is dispersed in the inorganic solid electrolyte matrix, whether uniform or non-uniform, when the woven fabric is introduced as a core material, the opening of the woven fabric is easily formed by the polymer. In some cases, the ionic conduction is blocked and the ion conduction is hindered.
[0018]
[Patent Document 1]
Japanese Patent No. 1887667
[Patent Document 2]
Japanese Patent No. 2928551
[Non-Patent Document 1]
N. Aotani, K .; Iwamoto, K .; Takada, andS. Kondo, Solid State Ionics, vol. 68 (1994), p. 35
[Non-Patent Document 2]
C. A. Angel, C.I. Liu, and E.J. Sanchez, Nature, vol. 632 (1993), p. 137
[Non-Patent Document 3]
T.A. Inada, K .; Takada, A .; Kajiyama, M .; Kouguchi, H .; Sasaki, S .; Kondo, W .; Watanabe, M.A. Murayama, and R.M. Kanno, Solid State Ionics, vol. 158 (2003), p. 275
[0019]
[Problems to be solved by the invention]
The present invention solves the problems in the prior art of the solid electrolyte supporting woven fabric used in the above-described solid electrolyte secondary battery and the solid electrolyte sheet using the woven fabric as a core material, and reduces internal resistance and improves load characteristics. It is thin and has sufficient strength, has excellent ion conductivity and thermal form stability, and is suitable for solid electrolyte secondary batteries, that is, it has a thin polymer with a high aperture ratio. It is an object of the present invention to provide a solid electrolyte supporting woven fabric coated with a material and a solid electrolyte sheet for a lithium battery using the woven fabric.
[0020]
[Means for Solving the Problems]
The above problems have been solved by the present invention having the following configuration.
[0021]
(1) A woven fabric for supporting a solid electrolyte, wherein a surface layer of a single yarn composed of a woven fabric woven with monofilament synthetic fiber yarns is coated with a material containing a polymer.
[0022]
(2) The monofilament synthetic fiber yarn is a solid electrolyte-supporting woven fabric according to the above (1), wherein the tensile strength according to a test method according to JIS L 1013 is 10 cN / dtex or more.
[0023]
(3) The above (1), wherein the material constituting the monofilament synthetic fiber yarn comprises one or more materials selected from aramid, polyarylate, and polyparaphenylenebenzobisoxazole (PBO). ) Or a woven fabric for supporting a solid electrolyte according to (2).
[0024]
(4) Any of the above (1) to (3), wherein the coating material of the surface layer of the single yarn constituting the woven fabric woven with the synthetic filament yarn of monofilament contains at least one kind of thermoplastic resin 2. A woven fabric for supporting a solid electrolyte according to 1.
[0025]
(5) Constitution of woven fabric woven with monofilament synthetic fiber yarn The coating material of the single yarn surface layer contains at least one material selected from polyethylene, polyethylene terephthalate, polyethylene naphthalate, polypropylene, terpene phenol copolymer The woven fabric for supporting a solid electrolyte according to any one of (1) to (4) above, wherein
[0026]
(6) Structure of woven fabric woven with monofilament synthetic fiber yarn The coating material of the single yarn surface layer has lithium ion permeability and has a lithium ion transport number of 0.7 or higher. The woven fabric for supporting a solid electrolyte according to any one of (1) to (5) above, comprising at least one kind of molecule.
[0027]
(7) The solid electrolyte according to any one of (1) to (6) above, wherein the coating material of the single yarn surface layer of the woven fabric woven with monofilament synthetic fiber yarn does not contain lithium salt Supporting woven fabric.
[0028]
(8) Composition of woven fabric woven with monofilament synthetic fiber yarn The coating material of the surface layer of the single yarn contains a chemically crosslinked precursor, and the polymer is chemically crosslinked by a chemical crosslinking reaction using the precursor as one of the raw materials. The solid electrolyte supporting woven fabric according to any one of (1) to (7) above, wherein a body is produced.
[0029]
(9) Composition of woven fabric woven with monofilament synthetic fiber yarn The coating material of the single yarn surface layer contains a chemical cross-linked precursor, and the chemical cross-linking of the polymer by chemical cross-linking reaction using the precursor as one of the raw materials The solid electrolyte-supporting woven fabric according to any one of (1) to (8) above, wherein a body is formed and the chemical crosslinking reaction is an addition reaction.
[0030]
(10) A single yarn surface layer of a woven fabric woven with monofilament synthetic fiber yarns is coated with a material containing a polymer, and the coat mass relative to the mass of the woven fabric after coating is 0.3% or more and 10% or less. The woven fabric for carrying a solid electrolyte according to any one of (1) to (9) above, wherein
[0031]
(11) From the above (1), wherein the thickness of the woven fabric is 10 μm or more and 50 μm or less and the opening ratio is 60% or more and 90% or less after the coating of the surface layer of the single yarn constituting the woven fabric. (10) The woven fabric for supporting a solid electrolyte according to any one of (10).
[0032]
(12) The body electrolyte-supporting woven fabric according to any one of (1) to (11) above, wherein the solid electrolyte is a powder comprising a lithium ion conductive inorganic solid electrolyte.
[0033]
(13) The solid electrolyte is a powder comprising a lithium ion conductive inorganic solid electrolyte, and a polymer is not dispersed in the powder, wherein the solid electrolyte is any one of (1) to (12) Woven fabric for supporting solid electrolyte.
[0034]
(14) A powder comprising a lithium ion conductive inorganic solid electrolyte is supported on a woven fabric for supporting a solid electrolyte coated with a material comprising the polymer according to any one of (1) to (13). Solid electrolyte sheet.
[0035]
(15) The solid electrolyte sheet as described in (14) above, wherein sulfur is included as one of the constituent elements in at least one solid electrolyte component of the powder comprising the lithium ion conductive inorganic solid electrolyte.
[0036]
(16) The at least one solid electrolyte component of the powder comprising the lithium ion conductive inorganic solid electrolyte contains sulfur as one of the constituent elements, and the solid electrolyte component is crystalline. The solid electrolyte sheet according to the above (14) or (15).
[0037]
DETAILED DESCRIPTION OF THE INVENTION
As a preferred embodiment of the present invention, a woven fabric for supporting a solid powder is woven by plain weaving using heat-resistant, high-strength, high-elastic monofilament fibers, and the solid powder is bound to the opening. Therefore, the surface of the woven fabric constituting single yarn is coated with a material containing a polymer, and is continuously rolled in the woven fabric warp direction by a nip process using a roll before or after the coating. A thin woven fabric for supporting a solid electrolyte powder having a desired strength with a high aperture ratio and excellent thermal stability by making the fabric thickness thin and uniform, and a solid electrolyte for a lithium secondary battery on the woven fabric Can be obtained.
[0038]
The supporting woven fabric that is the carrier for the solid electrolyte powder is preferably one having sufficient strength even at a high aperture ratio, and such a woven fabric can be obtained by weaving monofilament synthetic fiber yarns. Is possible. Here, as the weaving method of the woven fabric, there are various methods such as plain weave, twill weave, satin weave, tatami mat weave, twist weave, etc., but in order to obtain thinness as a carrier and flatness of the surface, plain weave Weaving by is preferred.
[0039]
Examples of the material of the woven fabric monofilament yarn used for the carrier include, for example, aramid, polyarylate, ultrahigh molecular weight polyethylene, polyparaphenylene benzobisoxazole (PBO), polyparaphenylene benzobisthiazole (PBT), and polyparaphenylene. Benzobisimidazole (PBI), fluorine-based fiber, polyethylene terephthalate, polypropylene, 6-nylon, 66-nylon, polyethylene, ethylene-vinyl acetate copolymer, polycarbonate, polyphenylene sulfide (PPS), polyethylene naphthalate, polyether ether ketone , Modified polyphenylene ether (PPE), other liquid crystal polymers, and mixtures using two or more of these, for example, core-sheath type composite fibers can be used for weaving.
[0040]
In the weaving step, weaving may be performed by adopting synthetic fiber yarns of different materials for warp and weft. However, in order to stably produce a high-opening woven fabric in the weaving process, the adopted synthetic fiber yarn preferably has a tensile strength of 10 cN / dtex or more according to a test method according to JIS L 1013. When the tensile strength of the synthetic fiber yarn does not reach 10 cN / dtex, the yarn breakage frequently occurs during weaving due to insufficient strength, and weaving becomes difficult and a woven fabric may not be obtained.
[0041]
In addition, as the electrolyte-supporting woven fabric, it is preferable to weave monofilament fiber yarns of a material having a high thermal deformation temperature in order to maintain a stable form without causing thermal contraction even during hot pressing described later. A woven fabric using monofilament fiber yarn having high heat resistance and high tensile strength has high strength, so that high strength can be secured even if the aperture ratio is increased and the thickness is reduced. When this woven fabric is used as a support for the solid electrolyte layer, the form can be sufficiently maintained, and safety and reliability are ensured without causing a short circuit between the electrodes. In addition, since the thickness is thin and the aperture ratio is high, the electrical resistance can be lowered and the performance can be improved, and the battery can be made thinner. In particular, application to a large and thin battery can be expected.
[0042]
From the viewpoint of such strength and heat distortion temperature, the material of the monofilament fiber yarn constituting the electrolyte carrier woven fabric has a tensile strength as high as 15 cN / dtex or higher in a test method according to JIS L 1013, and Aramid, polyarylate, and polyparaphenylene benzobisoxazole (PBO) having a heat distortion temperature of 250 ° C. or higher are particularly suitable.
[0043]
Conventionally, a technique is known in which a woven fabric is loaded with a mixture in which a polymer elastic body or the like serving as a binder is dispersed in an inorganic solid electrolyte powder. In this case, when the ratio of the electrolyte in the solid decreases, the surface of the solid electrolyte powder cannot sufficiently function, and a decrease in conductivity cannot be avoided.
[0044]
On the other hand, the inventors of the present invention dare to mix a binder such as a polymer elastic body by coating the surface layer of the woven fabric constituting single yarn with a material containing a polymer during or after weaving. The present inventors have found that an electrolyte sheet excellent in flexibility can be obtained by firmly supporting solid electrolyte powder on a woven fabric without any problems, and the present invention has been completed based on such findings.
[0045]
Coating of the material comprising the polymer on the woven fabric can be performed by a known method such as impregnation treatment, spray coating, roll coating in which the woven fabric is passed over a roll impregnated with the solution.
[0046]
Here, the polymer may be electronically insulating, and various polymers such as rubber-based, acrylic-based, polyester-based, or mixtures may be used in the category to obtain a uniform and stable coating on the woven fabric opening. I can do things. Specifically, the polymer material includes a thermoplastic resin such as polyethylene, polyethylene terephthalate, polyethylene naphthalate, polypropylene, and terpene phenol copolymer, or a copolymer thereof, or a rubber such as a thermoplastic elastomer. Examples thereof include materials having elasticity.
[0047]
Of these, thermoplastic elastomers with smaller compression set and closer to vulcanized rubber are desirable because they exhibit the ability to follow the thermal volume change of the battery and the volume change during charge / discharge. Here, examples of the material having a small compression set include styrenes such as a styrene butadiene block copolymer having a high styrene content.
[0048]
The general-purpose polymer materials exemplified in Patent Documents 1 and 2 are inexpensive and excellent in electrochemical stability. However, since they are ionic insulating, the woven yarn surface coat layer does not contribute to ionic conduction. Since the surface coat layer is an extremely thin layer, the influence of conductivity is not great, but it is more desirable to apply a polymer having ion permeability to the surface coat layer. The following points are mentioned as characteristics that the polymer exhibiting ion permeability should have.
[0049]
First, a wet process is suitable for uniformly covering the yarn. Therefore, it is necessary that the polymer is soluble in a solvent.
[0050]
Second, in order to employ the system of the present invention in a practical lithium battery, electrochemical stability up to about 5 V is required.
[0051]
Thirdly, it is necessary that the polymer has ion permeability and high selectivity for lithium ions in its ionic conduction.
[0052]
The above points will be described next.
[0053]
The solubility of the polymer in the solvent can be tested in any solvent. That is, it is possible to visually determine the state in which a uniform solution is obtained, while on the other hand, as a case where the polymer does not dissolve, a state where the polymer is separated in the solvent or a swollen state is observed. Easy to judge.
[0054]
Electrochemical stability is also known as a potential window. For example, a cell in which a lithium ion conductive inorganic solid electrolyte and polymer composite is sandwiched between stainless steel and lithium foil is assembled and evaluated by cyclic voltammetry. can do.
[0055]
The ion permeability of a polymer can be judged by examining the ionic conductivity of a sample obtained by forming a polymer into a film by a casting method or the like. Here, the ionic conductivity can be evaluated by measuring the electrical conductivity by the alternating current impedance method or the like and confirming that the electron conduction does not appear by the direct current polarization method.
[0056]
A polymer is generally insulative to ionic conduction by itself. In addition, a group of substances called ion conductive polymers is known, but ion permeability is a narrower concept than ion conductivity. For example, the polymer disclosed in Japanese Patent Application Laid-Open No. 10-3818 is limited in ionic conductivity to the contact interface with the inorganic solid electrolyte, and has ionic conductivity only at the interface. In such a polymer, the inorganic solid electrolyte is not dissolved and mixed in the polymer film that is not in contact with the inorganic solid electrolyte, and lithium ions as ion carriers are not present in the polymer matrix. Cannot flow. Therefore, such polymers are not ion permeable.
[0057]
On the other hand, a polymer can be made ion permeable by adding a specific auxiliary agent to the polymer having no ion permeability. That is, since a polymer having a specific structure such as a polyether does not have lithium as an ion carrier inside, for example, a layer of a lithium ion conductive inorganic solid electrolyte and the polymer between a pair of positive and negative electrodes Even when a single layer is sandwiched, a high impedance is exhibited in the electrolyte layer. However, it is known that high lithium ion conductivity can be obtained by adding a lithium salt that dissociates and uniformly mixes in such a matrix to such a polymer, and has been widely studied. (For example, A. Nishimoto, M. Watanabe, Y. Ikeda, and S. Kohjiya, Electrochim. Acta, 43, (1998), p. 117, etc.).
[0058]
This lithium salt is also called a supporting electrolyte (Hashimoto, the latest technology of new secondary battery materials, supervised by Kokumi, CMC (1997), p. 152). For example, the anion is ClO.₄ ⁻, BF₄ ⁻, PF₆ ⁻, AsF₆ ⁻, SbF₆ ⁻, CF₃SO₃ ⁻, (CF₃SO₂) N⁻Or (C₂F₅SO₂) N⁻And lithium cations alone, which do not exhibit ionic conduction alone, but when formed into a composite polymer film that is compatible with the polymer, lithium ions are generated inside the polymer film by ion dissociation, and Since the polymer membrane serves as a route for ion transport, the composite polymer membrane exhibits ion permeability.
[0059]
By the way, although this lithium salt is an inorganic lithium compound, it is clearly distinguished from the lithium ion conductive inorganic solid electrolyte used in the present invention. That is, the former does not exhibit ionic conductivity in the single state without ion dissociation as described above, whereas the latter exhibits ionic conductivity alone in the latter. This is because the lithium ion conductive inorganic solid electrolyte used in the present invention has lithium ions and a matrix through which lithium ions flow at the same time. For ionic conduction, the former lithium salt and polymer are combined. It is thought that it has both functions of lithium salt and polymer membrane in the body.
[0060]
As described above, the ion-permeable polymer needs to have lithium ions in the polymer, and as one of the methods, a method for dissociating a lithium salt into the polymer has been described. However, in such a system, not only lithium ions move in the polymer matrix, but also the counter anion derived from the lithium salt as described above may move. The ion transport number will decrease.
[0061]
On the other hand, in the lithium ion conductive inorganic solid electrolyte used in the present invention, only lithium ions can be selectively conducted. Such conduction characteristics are generally referred to as single ion conductivity, and the expression that the lithium ion transport number is 1 is used. Therefore, the polymer used in the present invention preferably has a high lithium ion transport number as well as a high ion conductivity.
[0062]
In general, the ionic conductivity is calculated from a value obtained by measuring an impedance by applying an alternating current. Therefore, even if the ion conductivity shows a high value, if ions other than lithium, especially anions, are mixed in the species responsible for the ion conduction, the battery reaction is a direct current reaction, causing polarization and increasing internal resistance. sell. That is, when the battery is charged, in the electrolyte layer, lithium ions move from the electrolyte particles close to the positive electrode to the adjacent electrolyte particles close to the negative electrode through the polymer binder. At this time, when the lithium ion transport number of the binder is low, the anion moves toward the positive electrode, and the inside of the binder matrix is polarized. As a result, since the ion insulating layer is formed in the binder matrix, the resistance is increased.
[0063]
There is a concern that the effect of such polarization on the battery reaction becomes more pronounced as the charge / discharge rate of the battery increases. When a polymer with a low lithium ion transport number is used, not only does polarization occur in the binder matrix due to the above-mentioned reasons, but there is a concern that the presence of anionic species may induce side reactions, both of which reduce the charge / discharge performance of the battery. It is feared to let you. In fact, when the present inventors conducted a charge / discharge test of a lithium battery element using a sulfide-based inorganic solid electrolyte, it was confirmed that when the lithium ion transport number is lower than 0.7, the discharge performance is lowered. The details of this test are disclosed in Japanese Patent Application No. 2002-135173.
[0064]
As a means for improving the lithium ion transport number of the polymer, the most effective means is to suppress the movement of anion species. Specific examples of the method include a method of chemically supplementing an anion derived from a lithium salt added to a polymer with an additive, or a method of drastically not adding a lithium salt. . When the lithium salt is not added, a polymer in which a lithium cation is contained in the molecular structure as an anion site and its counter ion can be used. In the polymer, since anions are fixed in the molecule, only lithium is likely to move.
[0065]
For methods of chemically supplementing with additives, see, for example, A. Metha, T .; Fujinami, S .; Inoue, K .; Matsushita, T .; Miwa, and T.M. Inoue, Electrochim. Acta, 45 (2000), p. 1175, etc. are known. In this document, by adding a boroxine compound to a composite ion conduction system in which a lithium salt is dissolved in a polyether polymer, an anion of the lithium salt is captured, and only lithium as a cation is more removed. A technique for selectively permeating a polymer matrix is disclosed. Here, boroxine is a compound containing a cyclic structure in which boron and oxygen are alternately linked. Hereinafter, this cyclic structure portion is referred to as a boroxine ring. By introducing a polyether as a substituent on the boron of the boroxine ring, compatibility with the polyether polymer is developed. In addition, it is possible to construct a network structure of a polyether containing a boroxine ring in a matrix by bonding both ends of the polyether chain onto boron of different boroxine rings.
[0066]
With respect to a method in which no lithium salt is added, a method for obtaining a polymer using a lithium compound as a raw material (for example, T. Fujijinami, K. Sugie, K. Mori, and MA Metha, Chem. Lett. (1998), p.619) is known. This document discloses, for example, a method for obtaining a polymer having a structure as shown in Chemical Formula 1 described later, and that the polymer system exhibits a high lithium ion transport number of about 1. That is, by using the lithium metal hydride such as lithium aluminum hydride, which is a reducing agent system generally used in organic synthesis, as a starting material, the polymer system is built to have a lithium cation derived from the starting material. In addition, a molecular structure in which the counter anion site is fixed in the molecule is obtained. Therefore, lithium is permeated through the polymer matrix without adding a lithium salt, and an anion is fixed to the polymer, so that a high transport number is exhibited. Moreover, according to the method like this system, the raw material conversion rate is also high. Furthermore, a high-selectivity, high-lithium ion conductor can be simply constructed from metal hydrides by simply passing through a few synthesis steps. Therefore, this method is considered to be extremely useful industrially.
[0067]
As another method in which the addition of the lithium salt is not performed, not only a method using lithium as a counter cation but also having an anion site in the molecule, a method that ion-polarizes the molecular structure (for example, mesoionic structure) may be used.
[0068]
The ion-permeable polymer having a high lithium ion transport number used in the present invention (hereinafter referred to as “high transport number polymer”) is not limited to the above examples. Polymers that exhibit high lithium ion transport selectivity are fields that have been intensively studied in recent years, and how to improve the lithium ion transport number of ion-conductive polymers and further improve ionic conductivity. Research has focused on the question of whether or not to squeeze, and various proposals have also been reported regarding molecular design.
That is, as the high transport number polymer used in the present invention, the solvent used in the wet process, that is, the solvent that dissolves or uniformly disperses the polymer does not deteriorate the woven fabric of the present invention and is electrochemically stable. Any material that matches the properties can be included in the surface coating material of the woven fabric. In the present invention, the high transport number polymer may be used singly or in combination, and furthermore, a polymer material compatible with the polymer, such as polyethylene oxide and poly ( A polyether polymer such as propylene oxide-ethylene oxide may be added and used.
[0069]
Such a polymer blend is applicable not only to the high transport number polymer but also to all polymer materials that can be included in the woven yarn surface coating material in the present invention. In particular, when the polymer material is oily, it has an effect of suppressing bleeding. Further, the coat is prevented from peeling off from the weaving yarn due to outflow or the like. Such peeling can occur by being pushed out by the inorganic solid electrolyte, for example, when filling the woven yarn opening with the inorganic solid electrolyte. In view of the purpose of improving the strength, it is possible to add an inorganic filler to the coating material. However, the filler material must be electronically insulating. One kind or two or more kinds of inorganic fillers may be used.
[0070]
As a method for avoiding the bleeding of the polymer, a method using a precursor that forms a polymer by a chemical crosslinking reaction or that the polymer has a crosslinking point of a chemical crosslinking reaction is useful. The cross-linking reaction may be performed in any step from the surface coating of the woven yarn to the point of filling the opening of the woven fabric with the inorganic solid electrolyte, or may be performed after the filling. However, when the viscosity of the precursor is low, the coating may be peeled off when the inorganic solid electrolyte is filled as described above. Therefore, the crosslinking reaction is preferably before filling the inorganic solid electrolyte. However, cross-linking after filling improves bondability to an inorganic solid electrolyte and exhibits excellent binder performance. The crosslinking point of the crosslinking reaction is generally a functional group, but when a by-product is generated in the crosslinking reaction, and the by-product stays in the battery system, the material is deteriorated or the battery reaction is hindered. Therefore, it is desirable to select a system that does not generate by-products in the crosslinking reaction.
[0071]
As a specific crosslinking reaction, an addition reaction is desirable. For example, a molecule having a vinyl group and a molecule having a SiH group can coexist and a crosslinked product can be formed by a hydrosilylation reaction. Silicone is a commercially available material such as this, but the reaction proceeds between a compound having a vinyl group and a compound having a SiH group. In this reaction, heating may be necessary, but the temperature is usually 150 ° C. or lower, and the electrolyte is not deteriorated and lithium is not melted. Moreover, although a very small amount of a transition metal complex such as a platinum complex is used as a catalyst for the reaction, the catalyst residue does not inhibit the battery reaction. Furthermore, although it is generally said that this reaction is poisoned in the presence of a sulfur compound, no poisoning occurs in the presence of a sulfide-based inorganic solid electrolyte.
[0072]
Regarding the presence form of a functional group that causes a crosslinking reaction, all of the functional groups are contained in only one type of compound, and the functional group may be crosslinked in only two or more types of compounds. It may be cross-linked between the compounds. The compound to be a crosslinked precursor may be a polymer or a low molecule, but at least one kind of precursor is already a polymer in order to combine appropriate flexibility as a binder and sufficient strength. It is desirable. Moreover, the smaller the number of crosslinking points of the precursor and the larger the molecular weight between the crosslinking points, the more flexible the crosslinked body.
[0073]
To summarize the above, the polymer material included in the material coated on the surface of the woven yarn is electronically insulating and can be used as a general-purpose material typified by a thermoplastic resin or a special material such as an ion-permeable polymer. The viscosity is arbitrary, but when using a low-viscosity material, a blend with another polymer material or a chemical crosslinking reaction can be applied. An inorganic filler may be added. Both polymer materials and inorganic fillers can be used alone or in combination of two or more.
[0074]
About the thickness of the thread | yarn which comprises a woven fabric, it is preferable to use the thing of 10-50 micrometers of linear warp as a warp and a weft in the case of plain weaving, respectively. If the thickness is less than 10 μm, stable weaving is difficult, and if it is thicker than 50 μm, the battery may not be thinned when used as a solid electrolyte carrying woven fabric. It is preferable to use the same warp for the warp and the weft in terms of the flatness of the woven fabric, but different warps may be used.
[0075]
The woven density of the woven fabric is preferably 50 mesh or more and 150 mesh or less. If it is less than 50 mesh, the uniformity of the opening cannot be maintained, and the strength as a carrying cloth becomes insufficient. On the other hand, when the value is larger than 150 mesh, it is difficult to obtain an aperture ratio of 60% or more, and it is difficult to achieve high performance in terms of battery performance such as conductivity.
[0076]
The woven fabric used as the solid electrolyte support preferably has an opening ratio of 60% or more and 90% or less after coating with a material containing a polymer. When the aperture ratio is less than 60%, the amount of solid electrolyte per volume decreases, so that the ionic conductivity decreases, and the solid electrolyte secondary battery manufactured using such a solid electrolyte layer has good characteristics. Is difficult to obtain. On the other hand, if the opening ratio exceeds 90%, the uniformity of the opening at the time of weaving the woven fabric cannot be obtained, and sufficient physical strength cannot be obtained. In addition, there are problems such as difficulty in handling during battery assembly and / or increased risk of internal short circuit. Therefore, the opening ratio of the woven fabric used as the solid electrolyte support is suitably 60 to 90%. Furthermore, from the viewpoint of characteristics and physical strength as a solid electrolyte sheet, the opening ratio is preferably in the range of 70 to 85%. Here, the aperture ratio is defined as the ratio of the total aperture area per mesh unit area.
[0077]
Conventionally, the coating of a resin on a woven fabric has been performed for the purpose of improving the surface of the woven fabric and the flexibility, or bonding the intersections of warps and wefts to prevent misalignment. For these purposes, it is sufficient if the surface of the fibers constituting the woven fabric is coated with a thin film or a small amount of resin is attached so that the intersections can be bound.
[0078]
The adhesion amount of the coating with the material (resin) comprising the polymer in the present invention is 0.3 to 10.0%, preferably 1.0 to 5.0% with respect to the mass of the woven fabric after coating. It is. When the resin adhesion amount is less than 0.3%, sufficient binding properties with the electrolyte powder filling the opening cannot be obtained, and when the resin adhesion amount exceeds 10.0%, the opening area decreases and When the coating resin is a thermoplastic resin, the conductivity decreases due to the influence of the softened resin entering between the electrolyte powders.
[0079]
Coating may be performed before winding on a roll as a post-process at the time of plain weaving, or after winding on a roll after weaving, and performed as a pre-process for continuous heating and rolling in a nip between two rolls. May be. Moreover, after passing through the woven fabric manufacturing process, it may be performed before filling with the inorganic solid electrolyte. The coating material applied by a known method such as dipping or spray coating is subjected to removal removal of the resin solution and evaporation of the solvent by a known method such as air blow or far infrared irradiation, and is dried to fix the resin. In particular, when coating on the woven fabric during weaving, in the process before winding it on the roll after weft driving, spray or roll coating, and securing the opening by blowing air, and the solvent removal process by drying Is included. Further, the coating on the woven fabric after weaving is performed by an impregnation treatment as a method for obtaining a uniform resin layer on the surface layer of the single yarn constituting the woven fabric, and then by adjusting the amount of the adhered resin and drying with a far infrared dryer.
[0080]
The carrier woven fabric according to the present invention has a uniform adhesion of the resin by, for example, coating the plain weave woven fabric with a predetermined amount of coating material and then continuously heating and rolling in the warp direction through the nip of two rolls. In addition, the unevenness at the intersections of the constituent single yarns is reduced, and a thin and uniform woven fabric surface can be obtained. The roll nip is not limited to one stage, and can be realized by passing through two or more stages or roll nip processes having different pressures. In addition, the roll rolling process may be performed more than once on the second floor. As a rolling method instead of the roll nip, the same effect can be obtained by a press method.
[0081]
The thickness of the solid electrolyte layer carrier woven fabric is preferably 10 to 50 μm. If the thickness of the woven fabric is less than 10 μm, the strength suitable for the solid electrolyte support cannot be maintained and the occurrence of short circuit cannot be prevented. On the other hand, if it is thicker than 50 μm, the load characteristics and energy density are good. It cannot be kept within the proper range, and the original performance cannot be achieved. The thickness of the solid electrolyte layer carrier woven fabric is particularly preferably 15 to 30 μm.
[0082]
The lithium ion conductive inorganic solid electrolyte filled in the coated woven fabric opening can be used alone or in combination of two or more, and among them, a sulfide having high lithium ion conductivity and high decomposition potential. Based inorganic solid electrolytes are desirable. Sulfide-based inorganic solid electrolytes contain sulfur as one of the constituent elements.₂S and P₂S₅, GeS₂, SiS₂, B₂S₃It is synthesized by combining at least one kind of sulfide selected from the above. Li₃PO₄Materials containing a small amount of ortho acid such as Li, and materials containing lithium halide such as LiI are also known. These may be used alone or in combination.
[0083]
More specifically, 0.01Li₃PO₄・ 0.63Li₂S ・ 0.36SiS₂(N. Aotani, K. Iwamoto, K. Takada, and S. Kondo, Solid State Ionics, 68, (1994), p. 35), 0.45 LiI.0.55 (0.69 Li₂S ・ 0.31P₂S₅(R. Mercier, JP Malugani, B. Fahys, and G. Robert, Solid State Ionics, 5, (1981), p. 663), or 0.45 LiI · 0.55 (0.69 Li)₂S ・ 0.31B₂S₃(H. Wada, M. Menetrier, A. Levasseur, and P. Hagentmuller, Mat. Res. Bill, 18 (1983), p. 189.), Li_3.25Ge_0.25P_0.75S₄Lithium germanium thio-phosphate (R. Kannoand M. Murayama, J. Electrochemical Soc., 148 (2001) p. A742) and the like.
[0084]
The inorganic solid electrolyte is roughly classified into an amorphous one and a crystalline one. Amorphous materials have lower ionic conductivity due to heating, but crystalline electrolytes have high thermal stability without such deterioration. It is more desirable because it is positioned as having a wide allowable range. Among the above, Li_3.25Ge_0.25P_0.75S₄Is a crystalline material, which is 2 × 10 at room temperature^-3It has high conductivity reaching S / cm and is stable up to about 600 ° C. The material is expected to have low conduction activation energy and good low-temperature characteristics.
[0085]
The electrolyte is pulverized to about 1 to 5 μm. When the electrolyte is a sulfide-based material, it is highly hydrolyzable, so it is pulverized in an atmosphere such as dry argon. Examples of the grinding method include a vibration mill and a planetary ball mill. The present inventor performed the visual observation by SEM observation with respect to the particle diameter, but it is also possible to evaluate the particle diameter by a technique of classification using an electroform sieve or a mesh sieve, or an optical technique such as laser scattering.
[0086]
Next, a method for filling the coated woven fabric with the electrolyte will be described.
[0087]
First, the inorganic solid electrolyte to be filled may be used alone or in combination of two or more.
[0088]
Further, in the present invention, the polymer is not dispersed particularly in the inorganic solid electrolyte powder, and the function of the binder is caused by the coat layer containing the polymer on the surface of the woven fabric, thereby stabilizing the solid electrolyte sheet. Although the purpose of ensuring the ion conduction is large, if attention is paid to the function of the present coating layer as a binder, even if a polymer is dispersed in the inorganic solid electrolyte, the binder function of the coating layer is not affected. . In addition, whether the polymer is dispersed or not dispersed in the inorganic solid electrolyte powder, the solid electrolyte exhibits a certain degree of flexibility due to the coating of the surface of the woven yarn. It is also possible to wind on a cylinder. At this time, if there is no coating, the solid electrolyte filled in the opening of the woven fabric tends to fall off the woven fabric.
[0089]
The solid electrolyte powder can be charged into the coated woven fabric by directly feeding the woven fabric with a solventless powder or a moistened with a small amount of solvent and granulating it as necessary, or pouring a slurry. A method is mentioned. As a method for charging the slurry, for example, a general-purpose coating method such as screen printing, doctor blade, or dipping can be used.
[0090]
The injection of the solid electrolyte may be performed from one side of the woven fabric or may be performed from both sides. The installation location of the woven fabric at the time of charging may be on the substrate, in the air, or in the liquid. When charged on the substrate, the sheet filled with the solid electrolyte in the woven fabric and the substrate can be detached. As for the method of supplying the solid electrolyte, when it is performed on the substrate or in the air, it is possible to supply the solid electrolyte regardless of whether it is dry or wet using a nozzle or the like. This is a process in which the woven fabric is dipped in the solid electrolyte slurry and pulled up.
[0091]
The charged solid electrolyte is desirably sufficiently filled in the woven fabric by pressurization. Examples of the filling method include a uniaxial pressure press and a roller. Further, in order to smooth the charging surface, a squeegee may be applied before filling, and the effect of filling the solid electrolyte can also be obtained by this squeegee.
[0092]
When the coating material contains a thermoplastic resin, after filling the woven fabric opening with the inorganic solid electrolyte, the obtained electrolyte sheet is heated and pressurized above the melting point or softening point of the resin, and then cooled. The coating material and the inorganic solid electrolyte are firmly bound. In such heating, pressurization or cooling and depressurization steps, the profile of each load is arbitrary. That is, when it comes to pressurization, the molding pressure may be increased discontinuously or continuously. The heating temperature rise / fall is the same, and the rate thereof may be constant or may change in the middle, but it is desirable that the heating start be performed at least under pressure. The temperature drop may be natural cooling. In addition, the holding time at the maximum setting of the heating temperature is arbitrary, but it does not have to be particularly long because melting and softening of the polymer occur instantaneously.
[0093]
Further, the pressure load may be increased or decreased in order to suppress or reduce the change in the generated pressure accompanying the change in the volume of the sheet in the process of raising and lowering the temperature. When pressurizing the sheet, the periphery of the sheet may or may not be surrounded by a jig. This is desirable because deformation is reduced or suppressed.
[0094]
According to the solid electrolyte sheet obtained by the method as described above, mechanical strength is imparted by the woven fabric, and since it shows self-supporting and flexible, it can be easily overlapped with the electrode sheet. A lithium battery element can be obtained.
[0095]
【Example】
Next, the present invention will be described more specifically with reference to examples. However, the present invention is not limited only to the following examples. In the following description, examples and comparative examples will be described in which the woven fabrics having different synthetic fiber yarn materials, yarn diameters, and meshes are used as the carrier for the solid electrolyte layer, and the resin coating material and the amount of adhesion are changed.
[0096]
Example 1:
A core-sheath composite comprising a core component composed of polyarylate (melted liquid crystalline polyester) as a synthetic fiber monofilament, and a sheath component composed of a thermoplastic polymer as a sea component and polyarylate (melted liquid crystalline polyester) as an island component. Using a yarn diameter of 23 μm of fibers (manufactured by Kuraray Co., Ltd., product name Vecry), both warp and weft were woven in a plain weave at a density of 60 mesh. Thereafter, the film was immersed in a solution of 30% by mass of a polyethylene terephthalate resin, which is a thermoplastic resin using water as a solvent, and then air was blown with an air gun to secure an opening. And it was made to dry for 5 minutes in a thermostat, and the resin coat layer was formed in the woven fabric surface layer surface. Further, in the hot rolling process, the woven fabric thickness is reduced by passing between two metal rolls under the conditions of 70 ° C. and 1.0 MPs, and the resin coat layer is uniformly fixed. I got a cloth.
The filling of the inorganic solid electrolyte powder into the woven fabric thus obtained will be described. First, the woven fabric is cut into 30 mm × 30 mm by laser processing. Next, in an argon-substituted glove box (dew point of −70 to −75 ° C.), a composition Li is charged as an inorganic solid electrolyte powder into a mold made of carbon tool steel S45C._3.25Ge_0.25P_0.75S₄After adding 1.5 g of lithium germanium thio-phosphate, the surface was smoothed and the cut woven fabric was placed thereon. Furthermore, after pressurizing these to 32.3 MPa with a uniaxial press, it was heated to 140 ° C. while being pressurized to obtain a solid electrolyte sheet.
[0097]
Example 2:
A solid electrolyte supporting woven fabric and a solid electrolyte sheet were obtained in the same manner as in Example 1 except that the woven density of the woven fabric was 90 mesh.
[0098]
Examples 3 and 4:
A solid electrolyte supporting woven fabric and a solid electrolyte sheet were obtained in the same manner as in Example 1 except that polypropylene and a high transport number polymer were used as the coating resin. Here, in Example 4, a material described in the following chemical formula 1, which is a high transport number polymer, was obtained from a literature (T. Fujinami, K. Sugie, K. Mori, and MA Metha, Chem. Lett., ( 1998), p.619.). Here, the polymer is polyethylene glycol monomethyl ether CH 1 mol equivalent to 1 mol equivalent of lithium aluminum hydride in the first stage.₃O (CH₂CH₂O)_nIt is obtained by reacting 2 mole equivalents of H and reacting with 1 mole equivalent of phenylboric acid as the second stage without isolating the product of the first stage. In this example, an Aldrich reagent having an average molecular weight of about 350 was used for the polyethylene glycol monomethyl ether. In this reagent, n indicating the glycol repeat unit length corresponds to n = 7.2 described in the above literature. Since this synthesis reaction is a dehydrogenative condensation in both steps and no reaction occurs within the glycol repeating unit, n in the obtained polymer (Chemical Formula 1) also reflects the raw material polyethylene glycol monomethyl ether 7.2. It is considerable. The obtained polymer coating was prepared by immersing an uncoated woven fabric rolled by the above-described method in a polymer tetrahydrofuran solution at room temperature in an argon-substituted glove box (dew point -70 to -75 ° C), followed by a blower. The opening was secured.
[0099]
[Chemical 1]

[0100]
Here, m shows the average number of repetitions, and shows a real number of 1-1000. Moreover, n shows the average number of repetitions and shows a real number of 1-20.
[0101]
Comparative examples 1, 2 and 3:
A solid electrolyte supporting woven fabric and a solid electrolyte sheet were obtained in the same manner as in Example 1 except that the coating resin was not used and the polyethylene terephthalate resin solution concentration was 10 mass% and 50 mass% as the coating resin. .
[0102]
Comparative Example 4:
A woven fabric for supporting a solid electrolyte and a solid electrolyte sheet were prepared in the same manner as in Example 1 using a woven fabric obtained by weaving plain weave with a density of 90 mesh for both warp and weft using 45 μm polyarylate fiber as a synthetic monofilament. Obtained.
[0103]
Comparative Example 5:
Using a woven fabric obtained by weaving plain weave with a density of 150 mesh for both warp and weft using a 23 μm polyarylate fiber as a synthetic monofilament, a solid electrolyte supporting woven fabric and a solid electrolyte sheet are produced in the same manner as in Example 1. Got.
[0104]
Comparative Example 6:
Using the same method as in Example 1 except that a 27 μm yarn of polyethylene terephthalate fiber is used as a synthetic fiber monofilament, and both the warp and weft are woven in plain weave at a density of 130 mesh, and the conditions of the hot rolling process are 80 ° C. and 3.0 MPs A woven fabric for carrying a solid electrolyte and a solid electrolyte sheet were obtained.
[0105]
The evaluation items of the woven fabric include strength, heat shrinkability, and aperture ratio as a woven fabric before coating, resin adhesion amount, woven fabric thickness, and aperture ratio as a woven fabric after resin coating, and powder support as an electrolyte sheet The results are shown in Table 1.
[0106]
[Table 1]

[0107]
In addition, the measurement of each evaluation item was performed by the following method.
[0108]
<Amount of resin attached>
The resin adhesion amount was calculated by measuring the weight change before and after resin coating.
[0109]
<Thickness of woven fabric>
The woven fabric after coating was measured with a micrometer.
[0110]
<Opening ratio>
The opening ratio of the woven fabric is defined by “ratio of the total opening area per unit area of the mesh body”, and was measured by taking a microphotograph before and after coating.
[0111]
<Strength>
The woven fabric was adjusted to a width of 5 cm and measured with a strong elongation tester.
[0112]
<Heat shrinkage>
For heat shrinkability, the vertical and horizontal dimensions were measured at the center of each side of the woven fabric cut into a square of 20 cm on each side before heating and after standing in a 200 ° C. constant temperature bath for 10 minutes. evaluated. Here, the evaluation of “◯” shown in Table 1 is when the thermal shrinkage rate falls below 0.05%. As shown in Table 1, in Examples 1 to 4 and Comparative Examples 1 to 5 using polyarylate, which is a heat resistant resin, heat shrinkage does not occur, and a stable form is maintained as a carrier even in a high temperature environment. It was confirmed that it was possible. On the other hand, in Comparative Example 6, since heat-stable PET was used as a material for the weaving yarn compared to polyarylate, significant heat shrinkage occurred.
[0113]
<Powder supportability>
About powder supportability, it evaluated by the filling degree at the time of releasing a solid electrolyte sheet from a metal mold | die. In this evaluation method, 100 solid electrolyte sheets were prepared, the presence / absence of detachment of the inorganic solid electrolyte powder at the opening of the woven fabric was visually determined, and the ratio of the sheets without detachment was displayed as the loading rate. The detachment part is a very serious defect that becomes a short circuit point when a battery is constructed. The woven fabric and the solid electrolyte sheet of the present invention are considered to be a large solid lithium battery as one of the application fields, and it is judged that it is difficult to put the large-scale practical use into the technology in which powder detachment occurs in a 30 mm square sample. The However, in this evaluation, considering that the result can be changed to some extent by improving the production technology, the carrying property is considered good if the carrying rate is up to about 100 to 50%. With respect to the structure having a supporting rate of less than 50%, the supporting property was considered to be poor, and it was determined that the supporting rate could not be used.
[0114]
Next, for the configurations judged to have good supportability (that is, Examples 1 to 4 and Comparative Examples 2 to 6), a solid battery for testing was assembled using the configuration of the solid electrolyte sheet, and a charge / discharge test was performed. It was. Hereinafter, the configuration and test contents of the solid state battery will be described with reference to FIG.
[0115]
As shown in FIG. 1, a solid battery for testing includes a polyethylene terephthalate tube 1 (inner diameter 10 mmφ), a negative electrode layer 4, a positive electrode layer 5, and a solid electrolyte sheet (that is, a solid electrolyte) positioned between the layers 4 and 5. 3 and the woven fabric 2), and the electrode terminals 6 and 6 were attached to both ends of the filled element. Here, in the positive electrode layer 5 of the element, a copper subrrel compound Cu as an active material is used.₂Mo₆S₈Lithium germanium thio-phosphate Li as electrolyte_3.25Ge_0.25P_0.75S₄10 mg of a mixture of acetylene black as a conductive additive and a weight ratio of 70: 30: 3.5 was used. In addition, the solid electrolyte 3 serving as the electrolyte layer includes lithium germanium thio-phosphate Li._3.25Ge_0.25P_0.75S₄70 mg of the powder was used and molded so that the woven fabric 2 was positioned at the center of the powder layer. The thickness of the solid electrolyte layer (sheet) at this time was 50 μm. On the other hand, Li metal was used for the negative electrode layer 4. And the current density of 1 mA / cm was applied to the solid battery for test thus obtained.²A direct current was applied and constant current charge / discharge was performed for 3 cycles. In this system, since the positive electrode did not contain Li before charge and discharge, the test started from discharge.
[0116]
When the battery was disassembled after charging / discharging, in the specimen having good supportability, the electrolyte powder pellet of the solid electrolyte 3 and the woven fabric 2 were sufficiently bonded, but the specimen having a slightly low support rate (Comparative Example 2 and Comparative Example) In the case of 4), the electrolyte powder pellet and the woven fabric 2 were easily detached from the specimen having a loading rate of 91% or more.
[0117]
In this charge / discharge test, the thickness of the electrolyte layer (solid electrolyte 3) was increased to 50 μm as described above, so that even when the electrolyte pellet was detached from the woven fabric 2, the pellet itself had sufficient mechanical strength. The pellets did not crack and did not cause a short circuit. However, considering that the present invention will be applied to a thin sheet-like battery in the future, when it is assumed that the separator employed in the conventional lithium ion battery is replaced with a solid electrolyte layer, the thickness of the separator is Since the electrolyte powder sheet is further thinned because it is as thin as about 20 μm, if the sheet is detached from the woven fabric 2 and its mechanical support cannot be obtained, the electrolyte powder sheet will crack and short circuit of the battery will occur. May cause. Therefore, for the evaluation of the supportability, based on the result of the charge / discharge test, the comprehensive judgment column of Table 1 is classified into good, slightly defective, and defective.
[0118]
<Electrical conductivity>
Ion conductivity was measured by the following method for the configurations (that is, Examples 1 to 4 and Comparative Examples 3, 5, and 6) that had good powder supportability in the above comprehensive determination.
[0119]
LiTiS on both main surfaces of 10mmφ specimen₂Was measured by an AC impedance method with an applied voltage of 10 mV and a frequency in the range of 1 MHz to 0.1 Hz. The results are shown in Table 1.
[0120]
As shown in Table 1, in Examples 1 to 4, it was confirmed that it was possible to reduce the thickness of the carrier while maintaining a high opening and to maintain sufficient strength. In addition, it was confirmed that the electrolyte sheet in which the solid electrolyte powder is supported on the woven cloth coated with the thermoplastic resin or the high transport number polymer has the solid adhesion strength remarkably superior to that of Comparative Example 1 without the resin coat. It was.
[0121]
In Example 4 using the high transport number polymer, there was no specimen from which the electrolyte powder was dropped. This was because the viscosity of the polymer was lower than the others, and a highly polarizable molecule. The reason is that the wettability with the inorganic solid electrolyte powder is good because of the structure. The reason why the conductivity is higher than that of other coating materials is considered to be because the coating layer itself has ionic conductivity.
[0122]
Even if the coating material is excessively adhered, the conductivity is lowered (Comparative Example 3). This is because the opening of the woven fabric is narrowed by the coating material or softened by heating at the time of forming the electrolyte sheet. This is thought to be due to the intruded resin permeating between the electrolyte powders and reducing the ionic conductivity.
[0123]
When the yarn diameter was large and the thickness of the woven fabric was thick (Comparative Example 4), the electrolyte powder was largely removed and the powder supportability was poor. In Comparative Example 5 having a high mesh woven fabric and a small opening ratio, the powder supportability was not a problem, but the conductivity as an electrolyte sheet was low. This is thought to be because the conductive path of lithium ions becomes narrow.
[0124]
In Comparative Example 6 in which PET, which is less thermally stable than polyarylate, was used as the material for the weaving yarn, thermal shrinkage of about 5% occurred in the warp and weft directions, and the powder supportability was relatively good. The conductivity of things became low.
[0125]
From the results shown in Table 1, the woven fabric of the present invention has sufficient strength even if it is thin while maintaining a high opening, has high heat resistance as a carrier, and can firmly support a solid electrolyte. As a result, it can be seen that it has excellent electrical conductivity.
[0126]
【The invention's effect】
As described above, according to the present invention, it is possible to obtain a powder-supporting woven fabric having a thin woven fabric with a high strength and a high aperture ratio. The obtained support has high heat resistance and can firmly support the solid electrolyte, and thus has excellent stability against external stress. Therefore, the solid electrolyte sheet using the powder-supporting woven fabric is excellent in electrical conductivity, and can be suitably used as a thin and large area solid electrolyte sheet for a secondary battery.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a test solid battery using a solid electrolyte sheet.
[Explanation of symbols]
1 Polyethylene terephthalate tube
2 Woven fabric for supporting solid electrolyte
3 Solid electrolyte
4 Negative electrode layer
5 Positive electrode layer
6 Electrode terminal

Claims (16)

A woven fabric for supporting a solid electrolyte, characterized in that a single yarn surface layer of a woven fabric woven with a monofilament synthetic fiber yarn is coated with a material containing a polymer. The woven fabric for carrying a solid electrolyte according to claim 1, wherein the monofilament synthetic fiber yarn is a yarn having a tensile strength of 10 cN / dtex or more according to a test method according to JIS L 1013. The material constituting the fiber yarn of the monofilament synthetic fiber yarn comprises one or more materials selected from aramid, polyarylate, and polyparaphenylenebenzobisoxazole (PBO). The woven fabric for supporting a solid electrolyte according to 1 or 2. The solid electrolyte support according to any one of claims 1 to 3, wherein the coating material of the surface layer of the single yarn constituting the woven fabric woven with the monofilament synthetic fiber yarn comprises at least one thermoplastic resin. Woven fabric. The composition of the woven fabric woven with monofilament synthetic fiber yarn, the coating material of the single yarn surface layer comprises at least one material selected from polyethylene, polyethylene terephthalate, polyethylene naphthalate, polypropylene, terpene phenol copolymer The woven fabric for supporting a solid electrolyte according to any one of claims 1 to 4. The coating material of the single yarn surface layer comprising a woven fabric woven with monofilament synthetic fiber yarns comprises at least one polymer having lithium ion permeability and a lithium ion transport number of 0.7 or more. A woven fabric for supporting a solid electrolyte according to any one of claims 1 to 5. The solid electrolyte supporting woven fabric according to any one of claims 1 to 6, wherein the coating material of the surface layer of the single yarn constituting the woven fabric woven with the monofilament synthetic fiber yarn does not contain lithium salt. Composition of woven fabric woven with monofilament synthetic fiber yarn The coating material of the single yarn surface layer contains a chemical cross-linked precursor, and a chemical cross-linked polymer is produced by a chemical cross-linking reaction using the precursor as one of the raw materials The woven fabric for supporting a solid electrolyte according to any one of claims 1 to 7, wherein Composition of woven fabric woven with monofilament synthetic fiber yarn The coating material of the single yarn surface layer contains a chemical cross-linked precursor, and a chemical cross-linked polymer is produced by a chemical cross-linking reaction using the precursor as one of the raw materials The woven fabric for carrying a solid electrolyte according to any one of claims 1 to 8, characterized in that the chemical crosslinking reaction is an addition reaction. A single yarn surface layer of a woven fabric woven with monofilament synthetic fiber yarns is coated with a material containing a polymer, and the coat mass relative to the mass of the woven fabric after coating is 0.3% or more and 10.0% or less. The woven fabric for supporting a solid electrolyte according to any one of claims 1 to 9, wherein the woven fabric is for supporting a solid electrolyte. The thickness of the woven fabric woven is 10 μm or more and 50 μm or less after coating the surface layer of the single yarn constituting the woven fabric, and the opening ratio is 60% or more and 90% or less. 2. A woven fabric for supporting a solid electrolyte according to 1. The solid electrolyte carrying woven fabric according to any one of claims 1 to 11, wherein the solid electrolyte is a powder comprising a lithium ion conductive inorganic solid electrolyte. The woven fabric for supporting a solid electrolyte according to any one of claims 1 to 12, wherein the solid electrolyte is a powder comprising a lithium ion conductive inorganic solid electrolyte, and no polymer is dispersed in the powder. . A solid electrolyte sheet in which a powder comprising a lithium ion conductive inorganic solid electrolyte is supported on a woven fabric for supporting a solid electrolyte coated with a material comprising the polymer according to any one of claims 1 to 13. The solid electrolyte sheet according to claim 14, wherein sulfur is included as one of the constituent elements in at least one solid electrolyte component of the powder comprising the lithium ion conductive inorganic solid electrolyte. 15. At least one solid electrolyte component of a powder comprising a lithium ion conductive inorganic solid electrolyte contains sulfur as one of the constituent elements, and the solid electrolyte component is crystalline. Or the solid electrolyte sheet of 15.

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