JP6004275B2 - Alkali metal-sulfur secondary battery - Google Patents
Alkali metal-sulfur secondary battery Download PDFInfo
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- JP6004275B2 JP6004275B2 JP2013048583A JP2013048583A JP6004275B2 JP 6004275 B2 JP6004275 B2 JP 6004275B2 JP 2013048583 A JP2013048583 A JP 2013048583A JP 2013048583 A JP2013048583 A JP 2013048583A JP 6004275 B2 JP6004275 B2 JP 6004275B2
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- Prior art keywords
- alkali metal
- sulfur
- lithium
- group
- secondary battery
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- 229910052710 silicon Inorganic materials 0.000 description 1
- 239000010703 silicon Substances 0.000 description 1
- 239000002356 single layer Substances 0.000 description 1
- UAZMXAXHGIZMSU-UHFFFAOYSA-N sodium tin Chemical compound [Na].[Sn] UAZMXAXHGIZMSU-UHFFFAOYSA-N 0.000 description 1
- 229910021384 soft carbon Inorganic materials 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 229920003048 styrene butadiene rubber Polymers 0.000 description 1
- 150000003463 sulfur Chemical class 0.000 description 1
- 238000005979 thermal decomposition reaction Methods 0.000 description 1
- 229910052718 tin Inorganic materials 0.000 description 1
- 229910052719 titanium Inorganic materials 0.000 description 1
- NSBGJRFJIJFMGW-UHFFFAOYSA-N trisodium;stiborate Chemical compound [Na+].[Na+].[Na+].[O-][Sb]([O-])([O-])=O NSBGJRFJIJFMGW-UHFFFAOYSA-N 0.000 description 1
- 239000013585 weight reducing agent Substances 0.000 description 1
Classifications
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Landscapes
- Secondary Cells (AREA)
- Battery Electrode And Active Subsutance (AREA)
Description
本発明は、リチウム−硫黄電池等の正極又は負極に硫黄を用いた二次電池に関する。 The present invention relates to a secondary battery using sulfur for a positive electrode or a negative electrode such as a lithium-sulfur battery.
近年、携帯電話端末の普及や、環境問題に対応した電気自動車やハイブリッド電気自動車の研究開発に伴い、高容量の二次電池が要望されている。このような二次電池としては、既にリチウムイオン二次電池が広く普及しているが、車載用に安全性を確保するため、電解液として難燃性のグライム類を用いる技術が提案されている(例えば、非特許文献1)。又、リチウム二次電池の電解液として、グライムに対するLi塩の混合比をモル換算で0.70〜1.25に調製したものを用い、これらの一部に錯体を形成させて電気化学的安定性を向上させた技術が提案されている(例えば、特許文献1)。 In recent years, with the widespread use of mobile phone terminals and the research and development of electric vehicles and hybrid electric vehicles that respond to environmental problems, high-capacity secondary batteries have been demanded. As such a secondary battery, a lithium ion secondary battery has already been widely used. However, in order to ensure safety for in-vehicle use, a technique using a flame-retardant glyme as an electrolytic solution has been proposed. (For example, Non-Patent Document 1). In addition, as an electrolyte for a lithium secondary battery, a lithium salt with a mixing ratio of Li salt to glyme adjusted to 0.70 to 1.25 in terms of mole is used. A technique with improved performance has been proposed (for example, Patent Document 1).
一方、リチウム二次電池よりさらに高容量の二次電池として、リチウム−硫黄電池が着目されている(例えば、特許文献2,3)。硫黄は理論容量が1670mAh/g程度であり、リチウム電池の正極活物質であるLiCoO2(約140mAh/g)より理論容量が10倍程度高いと共に、低コストで資源が豊富であるという利点がある。
リチウム−硫黄電池については、テトラグライムに対するLi塩(LiCF3SO3)の混合比を、モル換算で約0.12〜0.25(LiCF3SO3が0.5〜1mol/L)に調製した電解液を用いる技術(例えば、非特許文献2,3)、及び本発明者らによる、グライムに対するアルカリ金属塩(LiTFSA等)の混合比を、モル換算で0.50以上に調製した電解液を用いる技術(特許文献4)等が開示されている。
On the other hand, lithium-sulfur batteries are attracting attention as secondary batteries having a higher capacity than lithium secondary batteries (for example, Patent Documents 2 and 3). Sulfur has a theoretical capacity of about 1670 mAh / g, and has an advantage that the theoretical capacity is about 10 times higher than LiCoO 2 (about 140 mAh / g), which is a positive electrode active material of a lithium battery, and is low in cost and rich in resources. .
For a lithium-sulfur battery, an electrolysis was prepared in which the mixing ratio of Li salt (LiCF 3 SO 3 ) to tetraglyme was adjusted to about 0.12 to 0.25 (LiCF 3 SO 3 was 0.5 to 1 mol / L) in terms of mole. A technique using a liquid (for example, Non-Patent Documents 2 and 3) and an electrolyte prepared by the present inventors using a mixed ratio of alkali metal salt (LiTFSA, etc.) to glyme to 0.50 or more in terms of moles are used. Technology (Patent Document 4) and the like are disclosed.
しかしながら、本発明者が検討したところ、リチウム−硫黄電池において、テトラグライムとLi塩とを電解液として用いた場合、充放電時に副反応が生じてクーロン効率(放電容量/充電容量)が低下すると共に、充放電の繰り返しによって放電容量が大幅に低下し、電池寿命が短いことが判明した。この副反応は、充放電時に生成するリチウムポリスルフィド(Li2Sn; 1 ≦ n ≦ 8) の電解液への溶出であると考えられる。又、リチウム−硫黄電池の入出力密度の向上も課題である。
従って、本発明の目的は、充放電時の副反応を抑制してクーロン効率を向上させると共に、充放電の繰り返しによる放電容量の低下を抑制し、電池寿命が長く、入出力密度が向上したアルカリ金属−硫黄系二次電池を提供することにある。
However, as a result of investigation by the present inventors, in a lithium-sulfur battery, when tetraglyme and Li salt are used as an electrolyte, a side reaction occurs during charge and discharge, and coulomb efficiency (discharge capacity / charge capacity) decreases. At the same time, it has been found that the discharge capacity is significantly reduced by repeated charging and discharging, and the battery life is short. This side reaction is considered to be the elution of lithium polysulfide (Li 2 S n ; 1 ≦ n ≦ 8) produced during charging and discharging into the electrolyte. In addition, improvement of the input / output density of the lithium-sulfur battery is also a problem.
Accordingly, an object of the present invention is to improve the coulomb efficiency by suppressing side reactions during charge and discharge, and suppress the decrease in discharge capacity due to repeated charge and discharge, thereby increasing the battery life and improving the input / output density. The object is to provide a metal-sulfur secondary battery.
本発明者らは、特定比のエーテル化合物及びアルカリ金属塩、並びにF3CH2C−O−CF2CF2Hで表されるフッ素系溶媒を含む電解質を用いることにより上記課題を解決できることを見出し、本発明を完成させるに至った。
即ち、本発明は、単体硫黄、金属硫化物、金属多硫化物、及び有機硫黄化合物からなる群から選択される少なくとも一つを含む硫黄系電極活物質を含有する正極又は負極と、下記式
該正極又は負極の対極であって、該アルカリ金属、該アルカリ金属を含む合金、炭素、又はアルカリ金属イオンを吸蔵脱離する活物質を有する対極と、
を備えたアルカリ金属−硫黄系二次電池である。
The present inventors can solve the above-mentioned problems by using an electrolyte containing a specific ratio of an ether compound and an alkali metal salt and a fluorine-based solvent represented by F 3 CH 2 C—O—CF 2 CF 2 H. The headline and the present invention have been completed.
That is, the present invention includes a positive electrode or a negative electrode containing a sulfur-based electrode active material containing at least one selected from the group consisting of elemental sulfur, metal sulfides, metal polysulfides, and organic sulfur compounds, and the following formula:
A counter electrode of the positive electrode or the negative electrode, the counter electrode having an active material that absorbs and desorbs the alkali metal, an alloy containing the alkali metal, carbon, or alkali metal ions;
Is an alkaline metal-sulfur secondary battery.
本発明によれば、充放電時の副反応を抑制してクーロン効率を向上させると共に、充放電の繰り返しによる放電容量の低下を抑制し、電池寿命が長く、入出力密度が向上したアルカリ金属−硫黄系二次電池を得ることができる。 According to the present invention, the side reaction during charging and discharging is suppressed to improve coulomb efficiency, and the decrease in discharge capacity due to repeated charging and discharging is suppressed, the battery life is long, and the input / output density is improved. A sulfur-based secondary battery can be obtained.
以下、本発明の実施形態について説明する。本発明に係るアルカリ金属−硫黄系二次電池は、硫黄系電極活物質を有する正極又は負極と、下記のエーテル化合物とアルカリ金属塩とを含む電解液と、この正極又は負極の対極とを備える。
なお、本発明に係るアルカリ金属−硫黄系二次電池としては、正極が硫黄系電極活物質を有する電池であるリチウム−硫黄電池、ナトリウム−硫黄電池;負極が硫黄系電極活物質を有する電池である硫黄−LiCoO2電池、硫黄−LiMn2O4電池が例示されるがこれらに限られない。
Hereinafter, embodiments of the present invention will be described. An alkali metal-sulfur secondary battery according to the present invention includes a positive electrode or a negative electrode having a sulfur-based electrode active material, an electrolytic solution containing the following ether compound and an alkali metal salt, and a counter electrode of the positive electrode or the negative electrode. .
The alkali metal-sulfur secondary battery according to the present invention includes a lithium-sulfur battery, a sodium-sulfur battery in which the positive electrode has a sulfur-based electrode active material, and a battery in which the negative electrode has a sulfur-based electrode active material. there sulfur -LiCoO 2 batteries, sulfur -LiMn 2 is O 4 cell is illustrated but not limited thereto.
本発明に係るアルカリ金属−硫黄系二次電池は、例えば、上記した正極又は負極と対極とをセパレータを介して離間して配置し、セパレータ内に電解液を含ませてセルを構成し、このセルを複数個積層又は巻回してケースに収容した構造になっている。正極又は負極と、対極との集電体は、それぞれケース外部に引き出され、タブ(端子)に電気的に接続される。なお、電解液をゲル電解質としてもよい。
アルカリ金属−硫黄系二次電池は、従来公知の方法で製造することができる。
In the alkali metal-sulfur secondary battery according to the present invention, for example, the above-described positive electrode or negative electrode and a counter electrode are arranged apart from each other via a separator, and an electrolyte is included in the separator to constitute a cell. A plurality of cells are stacked or wound and accommodated in a case. Current collectors of the positive electrode or the negative electrode and the counter electrode are each drawn out of the case and electrically connected to a tab (terminal). The electrolytic solution may be a gel electrolyte.
The alkali metal-sulfur secondary battery can be manufactured by a conventionally known method.
<硫黄系電極活物質を有する正極又は負極>
正極又は負極は、単体硫黄、金属硫化物、金属多硫化物、及び有機硫黄化合物からなる群から選択される少なくとも一つを含む硫黄系電極活物質を有する。硫黄系金属硫化物としては、リチウム多硫化物;Li2Sn(1≦n≦8)が挙げられ、硫黄系金属多硫化物としては、MSn (M=Ni, Co, Cu, Fe, Mo, Ti、1≦n≦4) が挙げられる。又、有機硫黄化合物としては、有機ジスルフィド化合物、カーボンスルフィド化合物が挙げられる。
上記した正極又は負極は、上記した硫黄系電極活物質と結着剤と導電剤とを含んでもよい。そして、これら電極材料のスラリー(ペースト)を、導電性の担体(集電体)に塗布して乾燥することにより、電極材料を担体に担持させて正極又は負極を製造することができる。集電体としては、アルミニウム、ニッケル、銅、ステンレス鋼などの導電性の金属を、箔、メッシュ、エキスパンドグリッド(エキスパンドメタル)、パンチドメタルなどに形成したものが挙げられる。また、導電性を有する樹脂又は導電性フィラーを含有させた樹脂を集電体として使用してもよい。集電体の厚さは、例えば5〜30μmであるが、この範囲に限定されない。
<Positive electrode or negative electrode having a sulfur-based electrode active material>
The positive electrode or the negative electrode has a sulfur-based electrode active material containing at least one selected from the group consisting of elemental sulfur, metal sulfides, metal polysulfides, and organic sulfur compounds. Examples of the sulfur-based metal sulfide include lithium polysulfide; Li 2 Sn (1 ≦ n ≦ 8), and examples of the sulfur-based metal polysulfide include MS n (M = Ni, Co, Cu, Fe, Mo, Ti, 1 ≦ n ≦ 4). Examples of organic sulfur compounds include organic disulfide compounds and carbon sulfide compounds.
The above-described positive electrode or negative electrode may include the above-described sulfur-based electrode active material, a binder, and a conductive agent. Then, a slurry (paste) of these electrode materials is applied to a conductive carrier (current collector) and dried, whereby the electrode material is supported on the carrier and a positive electrode or a negative electrode can be produced. Examples of the current collector include those in which a conductive metal such as aluminum, nickel, copper, and stainless steel is formed on a foil, a mesh, an expanded grid (expanded metal), a punched metal, or the like. Further, a resin having conductivity or a resin containing a conductive filler may be used as the current collector. The thickness of the current collector is, for example, 5 to 30 μm, but is not limited to this range.
上記した電極材料(硫黄系電極活物質と他の成分との合計量、集電体を除く)のうち、硫黄系電極活物質の含有量は、好ましくは50〜98質量%であり、より好ましくは80〜98質量%である。活物質の含有量が前記範囲であれば、エネルギー密度を高くすることができるため好適である。
電極材料の厚さ(塗布層の片面の厚さ)は、好ましくは、10〜500μmであり、より好ましくは20〜300μmであり、さらに好ましくは20〜150μmである。
Among the electrode materials described above (total amount of sulfur-based electrode active material and other components, excluding current collector), the content of sulfur-based electrode active material is preferably 50 to 98 mass%, more preferably. Is 80-98 mass%. If the content of the active material is within the above range, it is preferable because the energy density can be increased.
The thickness of the electrode material (the thickness of one surface of the coating layer) is preferably 10 to 500 μm, more preferably 20 to 300 μm, and still more preferably 20 to 150 μm.
結着剤としては、ポリエチレン(PE)、ポリプロピレン(PP)、ポリエチレンテレフタレート(PET)、ポリエーテルニトリル(PEN)、ポリイミド(PI)、ポリアミド(PA)、ポリテトラフルオロエチレン(PTFE)、スチレンブタジエンゴム(SBR)、ポリアクリロニトリル(PAN)、ポリメチルアクリレート(PMA)、ポリメチルメタクリレート(PMMA)、ポリ塩化ビニル(PVC)、ポリフッ化ビニリデン(PVDF)、ポリビニルアルコール(PVA)、ポリアクリル酸(PAA)、ポリアクリル酸リチウム(PAALi)、エチレンオキシド若しくは一置換エポキサイドの開環重合物などのポリアルキレンオキサイド、又はこれらの混合物が挙げられる。
導電剤は、導電性を向上させるために配合される添加物であり、黒鉛、ケッチェンブラック、逆オパール炭素、アセチレンブラックなどのカーボン粉末や、気相成長炭素繊維(VGCF)、カーボンナノチューブ(CNT)などの種々の炭素繊維などが挙げられる。又、電極材料が支持塩(下記電解液に含まれる成分)を含んでもよい。
As binders, polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polyether nitrile (PEN), polyimide (PI), polyamide (PA), polytetrafluoroethylene (PTFE), styrene butadiene rubber (SBR), polyacrylonitrile (PAN), polymethyl acrylate (PMA), polymethyl methacrylate (PMMA), polyvinyl chloride (PVC), polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), polyacrylic acid (PAA) , Polyalkylene oxides such as polyacrylic acid lithium (PAALi), ring-opening polymer of ethylene oxide or monosubstituted epoxide, or a mixture thereof.
The conductive agent is an additive blended to improve conductivity. Carbon powder such as graphite, ketjen black, inverse opal carbon, acetylene black, vapor grown carbon fiber (VGCF), carbon nanotube (CNT) ) And the like. Further, the electrode material may contain a supporting salt (a component contained in the following electrolytic solution).
<対極>
正極が上記した硫黄系電極活物質を有する場合、その対極となる負極としては、リチウム、ナトリウム、リチウム合金、ナトリウム合金、リチウム/ 不活性硫黄の複合物からなる群から選択される1又は2以上の負極活物質を含む。負極に含まれる負極活物質は、アルカリ金属イオンを吸蔵脱離するよう作用する。負極活物質としては、リチウム、ナトリウム、炭素、ケイ素、アルミニウム、スズ、アンチモン及びマグネシウムからなる群から選択される少なくとも一種が好ましい。より具体的には、チタン酸リチウム、リチウム金属、ナトリウム金属、リチウムアルミ合金、ナトリウムアルミ合金、リチウムスズ合金、ナトリウムスズ合金、リチウムケイ素合金、ナトリウムケイ素合金、リチウムアンチモン合金、ナトリウムアンチモン合金等の金属材料、天然黒鉛、人造黒鉛、カーボンブラック、アセチレンブラック、グラファイト、活性炭、カーボンファイバー、コークス、ソフトカーボン、ハードカーボンなどの結晶性炭素材や非結晶性炭素材等の炭素材料といった従来公知の負極材料を用いることができる。このうち、容量、入出力特性に優れた電池を構成できることから、炭素材料もしくはリチウム、リチウム遷移金属複合酸化物を用いるのが望ましい。場合によっては、2種以上の負極活物質が併用されてもよい。
<Counter electrode>
When the positive electrode has the above-described sulfur-based electrode active material, the negative electrode serving as the counter electrode is one or more selected from the group consisting of lithium, sodium, lithium alloys, sodium alloys, and lithium / inert sulfur composites. Negative electrode active material. The negative electrode active material contained in the negative electrode acts to occlude and desorb alkali metal ions. The negative electrode active material is preferably at least one selected from the group consisting of lithium, sodium, carbon, silicon, aluminum, tin, antimony and magnesium. More specifically, metals such as lithium titanate, lithium metal, sodium metal, lithium aluminum alloy, sodium aluminum alloy, lithium tin alloy, sodium tin alloy, lithium silicon alloy, sodium silicon alloy, lithium antimony alloy, sodium antimony alloy, etc. Conventionally known negative electrode materials such as crystalline carbon materials such as materials, natural graphite, artificial graphite, carbon black, acetylene black, graphite, activated carbon, carbon fiber, coke, soft carbon, hard carbon, and amorphous carbon materials Can be used. Among these, it is desirable to use a carbon material or lithium or a lithium transition metal composite oxide because a battery having excellent capacity and input / output characteristics can be configured. In some cases, two or more negative electrode active materials may be used in combination.
負極が上記した硫黄系電極活物質を有する場合、その対極となる正極としては、アルカリ金属イオンを吸蔵脱離する正極活物質を含むものを用いることができる。正極活物質としては、リチウム遷移金属複合酸化物が好ましく、例えば、LiMn2O4などのLi−Mn系複合酸化物やLiNiO2などのLi−Ni系複合酸化物が挙げられる。より具体的には、LiMn2O4、LiCoO2、LiNiO2、LiFePO4、LiMnPO4、LiCo0.5Ni0.5O2、LiNi0.7Co0.2Mn0.1O2が好ましく挙げられる。またリチウム以外にも、アルカリ金属イオンを電気化学的に挿入、脱離する物質であれば、制限なく用いることができ、例えば、ナトリウムなどが挙げられる。2種以上の正極活物質が併用されてもよい。
対極も、上記した活物質と結着剤と導電剤とを含んでもよい。そして、これら電極材料を、導電性の担体(集電体)に担持して対極を製造することができる。集電体としては上記と同様のものを使用できる。
なお、負極が上記した硫黄系電極活物質を含有する場合も、電解液としては、下記のものを用いることができる。
When the negative electrode has the above-described sulfur-based electrode active material, as the positive electrode serving as the counter electrode, a material containing a positive electrode active material that occludes and desorbs alkali metal ions can be used. As the positive electrode active material, a lithium transition metal composite oxide is preferable, and examples thereof include a Li—Mn composite oxide such as LiMn 2 O 4 and a Li—Ni composite oxide such as LiNiO 2 . More specifically, LiMn 2 O 4 , LiCoO 2 , LiNiO 2 , LiFePO 4 , LiMnPO 4 , LiCo 0.5 Ni 0.5 O 2 , LiNi 0.7 Co 0.2 Mn 0.1 O 2 are preferable. Can be mentioned. In addition to lithium, any substance that electrochemically inserts and desorbs alkali metal ions can be used without limitation, and examples thereof include sodium. Two or more positive electrode active materials may be used in combination.
The counter electrode may also contain the above-described active material, binder, and conductive agent. These electrode materials can be carried on a conductive carrier (current collector) to produce a counter electrode. A current collector similar to the above can be used.
In addition, also when a negative electrode contains the above-mentioned sulfur type electrode active material, the following can be used as electrolyte solution.
正極と負極の間にはセパレータが配置されている。セパレータとしては、例えば、後述する電解液を吸収保持するガラス繊維製セパレータ、ポリマーからなる多孔性シート及び不織布を挙げることができる。多孔性シートは、例えば、微多孔質のポリマーで構成される。このような多孔性シートを構成するポリマーとしては、例えば、ポリエチレン(PE)、ポリプロピレン(PP)などのポリオレフィン;PP/PE/PPの3層構造をした積層体、ポリイミド、アラミドが挙げられる。特にポリオレフィン系微多孔質セパレータ及びガラス繊維製セパレータは、有機溶媒に対して化学的に安定であるという性質があり、電解液との反応性を低く抑えることができることから好ましい。多孔性シートからなるセパレータの厚みは限定されないが、車両のモータ駆動用二次電池の用途においては、単層又は多層で全体の厚み4〜60μmであることが好ましい。また、多孔性シートからなるセパレータの微細孔径は、最大で10μm以下(通常、10〜100nm程度)、空孔率は20〜80%であることが好ましい。
不織布としては、綿、レーヨン、アセテート、ナイロン(登録商標)、ポリエステル;PP、PEなどのポリオレフィン;ポリイミド、アラミドなど従来公知のものを、単独又は混合して用いる。不織布セパレータの空孔率は50〜90%であることが好ましい。さらに、不織布セパレータの厚さは、好ましくは5〜200μmであり、特に好ましくは10〜100μmである。厚さが5μm未満では電解質の保持性が悪化し、200μmを超える場合には抵抗が増大する場合がある。
A separator is disposed between the positive electrode and the negative electrode. Examples of the separator include a glass fiber separator that absorbs and holds an electrolyte solution described later, a porous sheet made of a polymer, and a nonwoven fabric. The porous sheet is composed of, for example, a microporous polymer. Examples of the polymer constituting such a porous sheet include polyolefins such as polyethylene (PE) and polypropylene (PP); laminates having a three-layer structure of PP / PE / PP, polyimide, and aramid. In particular, a polyolefin-based microporous separator and a glass fiber separator are preferable because they have a property of being chemically stable with respect to an organic solvent and can keep the reactivity with an electrolytic solution low. The thickness of the separator made of a porous sheet is not limited, but in the use of a secondary battery for driving a motor of a vehicle, the total thickness is preferably 4 to 60 μm with a single layer or multiple layers. Moreover, it is preferable that the fine pore diameter of the separator made of a porous sheet is 10 μm or less (usually about 10 to 100 nm) and the porosity is 20 to 80%.
As the nonwoven fabric, cotton, rayon, acetate, nylon (registered trademark), polyester; polyolefins such as PP and PE; conventionally known materials such as polyimide and aramid are used alone or in combination. The porosity of the nonwoven fabric separator is preferably 50 to 90%. Furthermore, the thickness of the nonwoven fabric separator is preferably 5 to 200 μm, particularly preferably 10 to 100 μm. When the thickness is less than 5 μm, the electrolyte retainability deteriorates, and when it exceeds 200 μm, the resistance may increase.
<電解液>
本願の電解液は、エーテル化合物、アルカリ金属塩、及びF3CH2C−O−CF2CF2Hで表されるフッ素系溶媒を含む。
このエーテル化合物は下式で表される。
The electrolytic solution of the present application includes an ether compound, an alkali metal salt, and a fluorine-based solvent represented by F 3 CH 2 C—O—CF 2 CF 2 H.
This ether compound is represented by the following formula.
上記式中のアルキル基としては、メチル基、エチル基、プロピル基、イソプロピル基、ブチル基、イソブチル基、ペンチル基、イソペンチル基、ヘキシル基、ヘプチル基、オクチル基、ノニル基等が挙げられる。これらのアルキル基は、任意の位置がフッ素で置換されていてもよい。アルキル基の炭素数が9を超えると、エーテル化合物の極性が弱くなるため、アルカリ金属塩の溶解性が低下する傾向がある。そのため、アルキル基の炭素数は少ない方が好ましく、好ましくはメチル基及びエチル基であり、最も好ましくはメチル基である。 Examples of the alkyl group in the above formula include methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, pentyl group, isopentyl group, hexyl group, heptyl group, octyl group, and nonyl group. These alkyl groups may be substituted at any position with fluorine. When the carbon number of the alkyl group exceeds 9, the polarity of the ether compound becomes weak, so that the solubility of the alkali metal salt tends to decrease. For this reason, the alkyl group preferably has a smaller number of carbon atoms, preferably a methyl group or an ethyl group, and most preferably a methyl group.
ハロゲン原子で置換されていてもよいフェニル基としては、特に制限はないが、2−クロロフェニル基、3−クロロフェニル基、4−クロロフェニル基、2,4−ジクロロフェニル基、2−ブロモフェニル基、3−ブロモフェニル基、4−ブロモフェニル基、2,4−ジブロモフェニル基、2−ヨードフェニル基、3−ヨードフェニル基、4−ヨードフェニル基、2,4−ヨードフェニル基等が挙げられる。 The phenyl group which may be substituted with a halogen atom is not particularly limited, but 2-chlorophenyl group, 3-chlorophenyl group, 4-chlorophenyl group, 2,4-dichlorophenyl group, 2-bromophenyl group, 3- Examples include bromophenyl group, 4-bromophenyl group, 2,4-dibromophenyl group, 2-iodophenyl group, 3-iodophenyl group, 4-iodophenyl group, 2,4-iodophenyl group and the like.
ハロゲン原子で置換されていてもよいシクロヘキシル基としては、特に制限はないが、2−クロロシクロヘキシル基、3−クロロシクロヘキシル基、4−クロロシクロヘキシル基、2,4−ジクロロシクロヘキシル基、2−ブロモシクロヘキシル基、3−ブロモシクロヘキシル基、4−ブロモシクロヘキシル基、2,4−ジブロモシクロヘキシル基、2−ヨードシクロヘキシル基、3−ヨードシクロヘキシル基、4−ヨードシクロヘキシル基、2,4−ジヨードシクロヘキシル基等が挙げられる。 The cyclohexyl group which may be substituted with a halogen atom is not particularly limited, but 2-chlorocyclohexyl group, 3-chlorocyclohexyl group, 4-chlorocyclohexyl group, 2,4-dichlorocyclohexyl group, 2-bromocyclohexyl group. Group, 3-bromocyclohexyl group, 4-bromocyclohexyl group, 2,4-dibromocyclohexyl group, 2-iodocyclohexyl group, 3-iodocyclohexyl group, 4-iodocyclohexyl group, 2,4-diiodocyclohexyl group and the like. Can be mentioned.
R3は、H又はCH3を表し、xが2以上の場合には、それぞれ互いに独立する。
xは、0〜10を表し、エチレンオキシド単位の繰り返し数を表わす。xは好ましくは1〜6、より好ましくは2〜5、最も好ましくは3又は4である。
R 3 represents H or CH 3, and when x is 2 or more, they are independent of each other.
x represents 0 to 10 and represents the number of repeating ethylene oxide units. x is preferably 1 to 6, more preferably 2 to 5, and most preferably 3 or 4.
このエーテル化合物は、例えば、テトラヒドロフラン(THF)、1,3−ジオキソラン、1,4−ジオキサン若しくはグライム又はその誘導体である。
上記一般式(化1)で表されるエーテル化合物は共に環を形成してもよく、この環状化合物としては、xが0の場合には、テトラヒドロフラン(THF)やその誘導体である2−メチルテトラヒドロフランが挙げられ、xが1の場合には、1,3−ジオキソランや1,4−ジオキサンが挙げられる。
グライムは、上記一般式(化1)(但し、R3はHを表し、xは1以上を表し、直鎖化合物である。)で表され、モノグライム(G1、x=1)、ジグライム(G2、x=2)、トリグライム(G3、x=3)及びテトラグライム(G4、x=4)等が挙げられる。モノグライム(G1)としては、メチルモノグライム、エチルモノグライム等が挙げられ、ジグライム(G2)としては、エチリジグライム、ブチルジグライム等が挙げられる。
This ether compound is, for example, tetrahydrofuran (THF), 1,3-dioxolane, 1,4-dioxane, glyme or a derivative thereof.
The ether compound represented by the above general formula (Formula 1) may form a ring together, and as this cyclic compound, when x is 0, tetrahydrofuran (THF) or 2-methyltetrahydrofuran which is a derivative thereof is used. And when x is 1, 1,3-dioxolane and 1,4-dioxane are exemplified.
Glyme is represented by the above general formula (Formula 1) (wherein R 3 represents H, x represents 1 or more and is a linear compound), monoglyme (G1, x = 1), diglyme (G2 X = 2), triglyme (G3, x = 3) and tetraglyme (G4, x = 4). Examples of monoglyme (G1) include methyl monoglyme and ethyl monoglyme, and examples of diglyme (G2) include ethyl diglyme and butyl diglyme.
このエーテル化合物として、xが1〜10であるグライムを使用すると、電解液の熱安定性、イオン伝導性、電気化学的安定性をより向上でき、高電圧に耐え得る電解液となる。
電解液に用いるエーテル化合物は、一種が単独で使用されても、二種以上の混合物の形態で使用されてもよい。
エーテル化合物の種類によっても電解液の酸化電位は変化する。そのため、二次電池に適用することを考慮すると、酸化電位が3.5〜5.3V vs Li/Li+になるように混合比等を調整することが好ましい。酸化電位はより好ましくは4.0〜5.3Vvs Li/Li+である。
本発明のエーテル化合物としては、トリグライム(G3)及びテトラグライム(G4)が好ましい。
When glyme having x of 1 to 10 is used as this ether compound, the thermal stability, ionic conductivity, and electrochemical stability of the electrolytic solution can be further improved, and the electrolytic solution can withstand high voltages.
The ether compound used for the electrolytic solution may be used singly or in the form of a mixture of two or more.
The oxidation potential of the electrolyte also varies depending on the type of ether compound. Therefore, considering application to a secondary battery, it is preferable to adjust the mixing ratio and the like so that the oxidation potential becomes 3.5 to 5.3 V vs. Li / Li + . The oxidation potential is more preferably 4.0 to 5.3 V vs Li / Li + .
As the ether compound of the present invention, triglyme (G3) and tetraglyme (G4) are preferable.
アルカリ金属塩はMXで表すことができ、Mはアルカリ金属、Xは対の陰イオンとなる物質である。上記アルカリ金属塩は、一種を単独で使用してもよいし、二種以上を混合物の形態で使用してもよい。
Mとしては特に制限はなく、通常の電池に支持塩や活物質として使用されているアルカリ金属がいずれも使用可能である。具体的には、Li、Na、K、Rb及びCsが挙げられる。より好ましくはLi、Na及びKであり、汎用性の点から最も好ましくはLiである。
Xとしては、特に制限はないが、Cl、Br、I、BF4、PF6、CF3SO3、ClO4、CF3CO2、AsF6、SbF6、AlCl4、N(CF3SO2)2、N(CF3CF2SO2)2、PF3(C2F5)3、N(FSO2)2、N(FSO2)(CF3SO2)、N(CF3CF2SO2)2、N(C2F4S2O4)、N(C3F6S2O4)、N(CN)2、N(CF3SO2)(CF3CO)、R4FBF3(但し、R4F=n-CmF2m+1、m=1〜4の自然数、nはノルマル)及びR5BF3(但し、R5=n−CpH2p+1、p=1〜5の自然数、nはノルマル)からなる群から選択される少なくとも一種であると好ましい。エーテル化合物に対する溶解性や、錯構造の形成しやすさの点から、より好ましくはN(CF3SO2)2、N(CF3CF2SO2)2、及びPF6である。
The alkali metal salt can be represented by MX, where M is an alkali metal and X is a substance that becomes a counter anion. The said alkali metal salt may be used individually by 1 type, and may be used in the form of a mixture of 2 or more types.
There is no restriction | limiting in particular as M, The alkali metal currently used as a supporting salt and an active material in a normal battery can be used. Specific examples include Li, Na, K, Rb, and Cs. Li, Na and K are more preferable, and Li is most preferable from the viewpoint of versatility.
X is not particularly limited, but Cl, Br, I, BF 4 , PF 6 , CF 3 SO 3 , ClO 4 , CF 3 CO 2 , AsF 6 , SbF 6 , AlCl 4 , N (CF 3 SO 2 ) 2 , N (CF 3 CF 2 SO 2 ) 2 , PF 3 (C 2 F 5 ) 3 , N (FSO 2 ) 2 , N (FSO 2 ) (CF 3 SO 2 ), N (CF 3 CF 2 SO 2) 2, N (C 2 F 4 S 2 O 4), N (C 3 F 6 S 2 O 4), N (CN) 2, N (CF 3 SO 2) (CF 3 CO), R 4 FBF 3 (where R 4 F = n-C m F 2m + 1 , m = 1 to 4 is a natural number, n is normal) and R 5 BF 3 (where R 5 = n−C p H 2p + 1 , p = 1-5) The natural number of n is preferably at least one selected from the group consisting of n). N (CF 3 SO 2 ) 2 , N (CF 3 CF 2 SO 2 ) 2 , and PF 6 are more preferable from the viewpoint of solubility in ether compounds and ease of forming a complex structure.
ここで、前記エーテル化合物の、エーテル酸素を[O]としたとき、[O]/前記アルカリ金属塩(モル比)は、好ましくは2〜10、より好ましくは2〜6、さらに好ましくは3〜5である。 Here, when the ether oxygen of the ether compound is [O], [O] / the alkali metal salt (molar ratio) is preferably 2 to 10, more preferably 2 to 6, and further preferably 3 to 3. 5.
上記のエーテル化合物とアルカリ金属塩との少なくとも一部が錯体を形成していることは、これらを混合した電解液の熱重量測定で判定することができる。つまり、錯形成しているエーテル化合物は、錯形成していないエーテル化合物に比べて揮発しにくい。このため、エーテル化合物のみの熱重量測定による重量減少をベースとし、温度による重量減少がこのベースより少ない電解液は、エーテル化合物とアルカリ金属塩との少なくとも一部が錯体を形成しているとみなす。
図2は、それぞれエーテル化合物としてトリグライム(G3)及びテトラグライム(G4)(上記化学式1においてRがメチル基、xがそれぞれ3及び4)を用い、アルカリ金属塩として後述するLiTFSA(LiN(CF3SO2)2)を用いた電解液の熱重量測定の結果(温度上昇と重量減少の関係)のグラフを示す。なお、各グライムとLiTFSAの混合比(モル換算)を変えた電解液を調製し、電解液の温度を室温から550℃まで、10℃min-1の昇温速度で上昇させて熱重量測定を行った。又、測定装置として、示唆熱熱重量同時測定装置(セイコーインスツル社製のTG/DTA 6200)を用いた。
なお、図2のLiTFSA/G3=1は、グライムに対するLiTFSAの混合比(モル換算)が1であることを示す。又、図2のG3の示す曲線は、トリグライムのみからなる電解液の熱重量測定を示す。
Whether at least a part of the ether compound and the alkali metal salt forms a complex can be determined by thermogravimetric measurement of an electrolytic solution obtained by mixing them. That is, a complexed ether compound is less likely to volatilize than a non-complexed ether compound. For this reason, electrolyte solutions based on thermogravimetric weight loss of ether compounds alone and with less weight loss due to temperature than this base are considered that at least a portion of the ether compound and alkali metal salt form a complex. .
FIG. 2 shows triglyme (G3) and tetraglyme (G4) (wherein R is a methyl group and x is 3 and 4 respectively) as ether compounds, and LiTFSA (LiN (CF 3 SO 2) shows a graph of 2) result of the electrolyte thermogravimetry of using (relationship between the temperature rise and weight loss). In addition, we prepared electrolytes with different mixing ratios (molar conversion) of each glyme and LiTFSA, and raised the temperature of the electrolyte from room temperature to 550 ° C at a heating rate of 10 ° C min -1 for thermogravimetry. went. In addition, as a measuring device, a suggested thermothermogravimetric simultaneous measuring device (TG / DTA 6200 manufactured by Seiko Instruments Inc.) was used.
Note that LiTFSA / G3 = 1 in FIG. 2 indicates that the mixing ratio of LiTFSA to glyme (in terms of mole) is 1. Also, the curve indicated by G3 in FIG.
図2のように、重量減少の過程は、以下の(1)-(3)の3段階で進行することがわかる。
(1)100〜200℃までの重量減少は、錯形成していないグライムの蒸発に由来する
(2)200〜400℃までの重量減少は、錯形成しているグライムの蒸発に由来する
(3)400℃以上での重量減少は、アルカリ金属塩(LiTFSA)の熱分解に由来する
従って、上記 (2)のプロセスが熱重量測定の結果から確認できる場合、グライムが錯形成していると考えることができる。
なお、グライムに対するLiTFSAの混合比(モル換算)が1より大きい系では、すべてのグライムが錯体を形成しているため、(1)のプロセスがなく、200℃以上から重量減少が始まることがわかる。
As shown in FIG. 2, it can be seen that the process of weight reduction proceeds in the following three stages (1) to (3).
(1) The weight loss from 100 to 200 ° C is due to the evaporation of uncomplexed glyme
(2) Weight loss from 200 to 400 ° C is due to the evaporation of complexed glyme
(3) The weight loss at 400 ° C or higher is derived from the thermal decomposition of alkali metal salt (LiTFSA) .Therefore, when the process of (2) above can be confirmed from the results of thermogravimetry, glyme is complexed. Can be considered.
In addition, in the system where the mixing ratio of LiTFSA to glyme (molar conversion) is larger than 1, since all glyme forms a complex, there is no process of (1), and weight loss starts from 200 ° C or higher. .
本発明において、アルカリ金属塩に対する、フッ素系溶媒の混合比{(フッ素系溶媒)/(アルカリ金属塩)}が、モル換算で0.50〜6.0であることが好ましい。
(フッ素系溶媒)/(アルカリ金属塩)で表される比がモル換算で0.50未満であると、フッ素系溶媒が少なくて上述した効果が生じず、入出力密度が向上しない場合がある。一方、上記比が6.0を超えてもフッ素系溶媒による効果が飽和し、コストアップとなる。
In the present invention, the mixing ratio {(fluorinated solvent) / (alkali metal salt)} of the fluorinated solvent to the alkali metal salt is preferably 0.50 to 6.0 in terms of mole.
When the ratio represented by (fluorine-based solvent) / (alkali metal salt) is less than 0.50 in terms of mole, the above-mentioned effect does not occur because the fluorine-based solvent is small, and the input / output density may not be improved. . On the other hand, even if the ratio exceeds 6.0, the effect of the fluorinated solvent is saturated and the cost is increased.
本発明において、エーテル化合物に対する上記アルカリ金属塩の混合比が、モル換算で0.50以上、上記エーテル化合物中の上記アルカリ金属塩の飽和濃度で決まる値以下であることが好ましい。
上記した非特許文献2,3に記載されているように、従来、リチウム−硫黄電池において、テトラエーテル化合物に対するLi塩(LiCF3SO3)の混合比を、モル換算で0.25以下(LiCF3SO3が1mol/ L以下)に調製した電解液を用いることが知られている。ところが、本発明者が検討したところ、このようなリチウム−硫黄電池の充放電を繰り返すと、充電時に副反応が生じてクーロン効率(放電容量/充電容量)が低下すると共に、充放電の繰り返しによって放電容量が大幅に低下し、電池寿命が短いことが判明した。
In this invention, it is preferable that the mixing ratio of the said alkali metal salt with respect to an ether compound is 0.50 or more in molar conversion, and below the value decided by the saturated density | concentration of the said alkali metal salt in the said ether compound.
As described in Non-Patent Documents 2 and 3 above, conventionally, in a lithium-sulfur battery, the mixing ratio of Li salt (LiCF 3 SO 3 ) to the tetraether compound is 0.25 or less (LiCF It is known to use an electrolyte prepared with 3 SO 3 of 1 mol / L or less. However, when the present inventor examined, when charging / discharging of such a lithium-sulfur battery was repeated, a side reaction occurred during charging, and the coulomb efficiency (discharge capacity / charge capacity) was lowered. It was found that the discharge capacity was significantly reduced and the battery life was short.
図3は、グライム(G4)に対するLi塩(LiTFSA)の混合比とクーロン効率との関係を示し、図4は、グライム(G4)に対するLi塩(LiTFSA)の混合比と放電容量維持率との関係を示す。
上記混合比が0.50以上であると、充電時の副反応が抑制されクーロン効率が95%以上に向上すると共に、充放電の繰り返しによる放電容量の低下が抑制され放電容量維持率が向上し、電池寿命が長くなる。なお、上記混合比が高いほど、クーロン効率及び放電容量維持率が向上するが、混合比が上記エーテル化合物中の上記アルカリ金属塩の飽和濃度で決まる値を超えて高くなるとアルカリ金属塩がエーテル化合物に溶解しなくなる。
以上のことより、上記混合比をモル換算で0.50以上、上記エーテル化合物中の上記アルカリ金属塩の飽和濃度で決まる値以下に規定すると好ましい。
FIG. 3 shows the relationship between the mixing ratio of Li salt (LiTFSA) to glyme (G4) and Coulomb efficiency, and FIG. 4 shows the mixing ratio of Li salt (LiTFSA) to glyme (G4) and the discharge capacity maintenance ratio. Show the relationship.
When the mixing ratio is 0.50 or more, side reactions during charging are suppressed and coulomb efficiency is improved to 95% or more, and a decrease in discharge capacity due to repeated charge and discharge is suppressed, and a discharge capacity maintenance ratio is improved. Battery life will be longer. The higher the mixing ratio, the better the Coulomb efficiency and the discharge capacity retention ratio. However, when the mixing ratio becomes higher than the value determined by the saturation concentration of the alkali metal salt in the ether compound, the alkali metal salt becomes an ether compound. It will not dissolve in.
From the above, it is preferable that the mixing ratio is specified to be 0.50 or more in terms of mole, and below a value determined by the saturated concentration of the alkali metal salt in the ether compound.
なお、エーテル化合物中のアルカリ金属塩の飽和濃度は、30℃のエーテル化合物にアルカリ金属塩を溶解させたとき、アルカリ金属塩の固形分が目視で確認できたときの濃度とする。
エーテル化合物としてG3(トリエチレングリコールジメチルエーテル(トリグライムともいう))を用い、アルカリ金属塩をLi塩とした場合、G3中のLi塩の飽和濃度によって決まる上記混合比は、モル換算で1.67である。
エーテル化合物としてテトラグライム(G4)を用い、アルカリ金属塩をLi塩とした場合、G4中のLi塩の飽和濃度によって決まる上記混合比は、モル換算で2.00である。
In addition, let the saturation density | concentration of the alkali metal salt in an ether compound be a density | concentration when solid content of an alkali metal salt can be visually confirmed when an alkali metal salt is dissolved in an ether compound of 30 degreeC.
When G3 (triethylene glycol dimethyl ether (also referred to as triglyme)) is used as the ether compound and the alkali metal salt is Li salt, the mixing ratio determined by the saturation concentration of Li salt in G3 is 1.67 in terms of mole. is there.
When tetraglyme (G4) is used as the ether compound and the alkali metal salt is Li salt, the mixing ratio determined by the saturated concentration of Li salt in G4 is 2.00 in terms of mole.
電解液をゲル状のゲル電解質としてもよい。ゲル電解質は、イオン伝導性ポリマーからなるマトリックスポリマーに、電解液が注入されてなる構成を有する。この電解液として、上記の本発明の電解液を使用する。マトリックスポリマーとして用いられるイオン伝導性ポリマーとしては、例えば、ポリエチレンオキシド(PEO)、ポリプロピレンオキシド(PPO)、ポリエチレングリコール(PEG)、ポリアクリロニトリル(PAN)、フッ化ビニリデン−ヘキサフルオロプロピレン(VDF−HEP)の共重合体、ポリ(メチルメタクリレート(PMMA)及びこれらの共重合体等が挙げられる。ポリアルキレンオキシド系高分子には、リチウム塩などの電解質塩がよく溶解しうる。 The electrolytic solution may be a gel gel electrolyte. The gel electrolyte has a configuration in which an electrolytic solution is injected into a matrix polymer made of an ion conductive polymer. As the electrolytic solution, the above-described electrolytic solution of the present invention is used. Examples of the ion conductive polymer used as the matrix polymer include polyethylene oxide (PEO), polypropylene oxide (PPO), polyethylene glycol (PEG), polyacrylonitrile (PAN), and vinylidene fluoride-hexafluoropropylene (VDF-HEP). And poly (methyl methacrylate (PMMA) and their copolymers, etc. Electrolytic salts such as lithium salts can be well dissolved in the polyalkylene oxide polymer.
以下、実施例によって本発明を更に具体的に説明するが、本発明は以下の実施例に限定されるものではない。なお、特に断らない限り、%は質量%を示す。 EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not limited to a following example. In addition, unless otherwise indicated,% shows the mass%.
<電解液の調製>
グライムとして、トリグライム(以下「G3」という)(キシダ化学社製)を用いた。
又、アルカリ金属塩として、以下の式2で示すリチウムビス(トリフルオロメタンスルフォニル)アミド (以下「LiTFSA」と称する) (森田化学工業社製)を用いた。
As the glyme, triglyme (hereinafter referred to as “G3”) (manufactured by Kishida Chemical Co., Ltd.) was used.
Further, as the alkali metal salt, lithium bis (trifluoromethanesulfonyl) amide (hereinafter referred to as “LiTFSA”) represented by the following formula 2 (made by Morita Chemical Co., Ltd.) was used.
G3と、LiTFSAとをアルゴン雰囲気下のグローブボックス内で、混合比(LiTFSA)/(G3)=1.00(モル換算)で混合した。さらに、この混合物に、F3CH2C−O−CF2CF2H(フッ素系溶媒;2,2,2-トリフルオロエチル(1,1,2,2-テトラフルオロエチル)エーテル))(旭硝子社製)を所定の割合で加えて電解液を調製した。 G3 and LiTFSA were mixed at a mixing ratio (LiTFSA) / (G3) = 1.00 (molar conversion) in a glove box under an argon atmosphere. Further, F 3 CH 2 C—O—CF 2 CF 2 H (fluorinated solvent; 2,2,2-trifluoroethyl (1,1,2,2-tetrafluoroethyl) ether)) ( Asahi Glass Co., Ltd.) was added at a predetermined ratio to prepare an electrolytic solution.
<リチウム−硫黄電池の作製>
単体硫黄(S8)を硫黄系電極活物質とし、単体硫黄を60 wt%、導電剤としてケッチェンブラックを30 wt%、結着剤としてPVA (ポリビニルアルコール)を10 wt%の割合で混合し、正極の電極材料2a(図1参照)を調製した。まず、単体硫黄とケッチェンブラックを混合後、155℃で加熱することで単体硫黄とケッチェンブラックを複合化した。この混合物に対し、さらにPVAを溶解した適量のNMP (N-メチルピロリドン)を加えスラリー状に混錬した。得られたスラリーを厚さ10μmのアルミニウム箔(集電体)2bに塗布した後、80℃で12時間乾燥してNMPを蒸発させた後、プレスして正極2(図1参照)を得た。厚さ200μmのリチウム金属板を厚さ0.5mmのステンレスディスクに貼り付けて負極を作製した。
<Production of lithium-sulfur battery>
Single sulfur (S 8 ) is used as a sulfur-based electrode active material, 60 wt% of single sulfur, 30 wt% of ketjen black as a conductive agent, and 10 wt% of PVA (polyvinyl alcohol) as a binder. A positive electrode material 2a (see FIG. 1) was prepared. First, simple sulfur and ketjen black were mixed, and then heated at 155 ° C. to compound simple sulfur and ketjen black. To this mixture, an appropriate amount of NMP (N-methylpyrrolidone) in which PVA was dissolved was further added and kneaded into a slurry. The obtained slurry was applied to an aluminum foil (current collector) 2b having a thickness of 10 μm, dried at 80 ° C. for 12 hours to evaporate NMP, and then pressed to obtain a positive electrode 2 (see FIG. 1). . A lithium metal plate having a thickness of 200 μm was attached to a stainless steel disk having a thickness of 0.5 mm to produce a negative electrode.
アルゴン雰囲気下のグローブボックス内で、正極2に上記電解液を適量加え、60℃で60分間、電解液を正極2に浸漬させた。正極2と負極(対極)4とを、セパレータ6(厚さ200μmの東洋濾紙社製のガラス製セパレータ(商品名GA-55))を介して積層し、さらに上記電解液を注入した後、2032型のコインセルケース20(SUS304製の厚さ3.2mm)に封入し、負極(対極)4の上にスペーサ12を載置した。スペーサ12の上にスプリング14を配置した。スプリング14の上から蓋22でコインセルケース20を封止し、図1に示す構造のリチウム−硫黄電池50を作製した。なお、コインセルケース20の側壁にはガスケット10が介装されている。 An appropriate amount of the electrolyte solution was added to the positive electrode 2 in a glove box under an argon atmosphere, and the electrolyte solution was immersed in the positive electrode 2 at 60 ° C. for 60 minutes. The positive electrode 2 and the negative electrode (counter electrode) 4 were laminated through a separator 6 (a glass separator manufactured by Toyo Roshi Kaisha Co., Ltd. having a thickness of 200 μm (trade name: GA-55)), and the electrolyte was further injected. A coin cell case 20 (thickness: 3.2 mm made of SUS304) was sealed, and a spacer 12 was placed on the negative electrode (counter electrode) 4. A spring 14 is disposed on the spacer 12. The coin cell case 20 was sealed from above the spring 14 with a lid 22 to produce a lithium-sulfur battery 50 having the structure shown in FIG. A gasket 10 is interposed on the side wall of the coin cell case 20.
<評価>
(1)充電レート特性
上記のようにして得られた二次電池について、放電電流密度を1/12 C (12 時間率、電極活物質の理論容量をn (時間) で放電する電流値を1/n のC レートと表す)として定電流放電した後、種々の充電電流密度にて充電レート特性(充電容量)を評価した。電圧は1.5−3.3Vの範囲とし、30℃一定に保持された恒温槽中で実施した。
特に、充電電流密度を1/3 Cレート(3時間率)に設定したときの充電容量を、「1/3 Cレートの時の充電容量」とし、入力特性の指標とした。なお、1/3 Cレートの時の充電容量が大きいほど、急速充電が可能になるため、好ましい。
(2)放電レート特性
上記のようにして得られた二次電池について、充電電流密度を1/12 Cとして定電流充電した後、種々の放電電流密度にて放電レート特性(放電容量)を評価した。電圧は1.5−3.3Vの範囲とし、30℃一定に保持された恒温槽中で実施した。
特に、放電密度を1/5 Cレート(5時間率)に設定したときの放電容量を、「1/5 Cレートの時放電容量」とし、出力特性の指標とした。なお、1/5 Cレートの時放電容量が大きいほど、急速放電が可能になるため、好ましい。
<Evaluation>
(1) Charging rate characteristics For the secondary battery obtained as described above, the discharge current density is 1/12 C (12 hour rate, the theoretical capacity of the electrode active material is n (hours), and the current value for discharging is 1 The charge rate characteristics (charge capacity) were evaluated at various charge current densities. The voltage was in the range of 1.5-3.3 V, and the test was carried out in a thermostatic chamber maintained at 30 ° C.
In particular, the charge capacity when the charge current density was set to 1/3 C rate (3 hour rate) was defined as “charge capacity at 1/3 C rate”, which was used as an indicator of input characteristics. A larger charge capacity at the 1/3 C rate is preferable because quick charge is possible.
(2) Discharge rate characteristics The secondary battery obtained as described above was charged at a constant current with a charge current density of 1/12 C, and then evaluated for discharge rate characteristics (discharge capacity) at various discharge current densities. did. The voltage was in the range of 1.5-3.3 V, and the test was carried out in a thermostatic chamber maintained at 30 ° C.
In particular, the discharge capacity when the discharge density was set to 1/5 C rate (5 hour rate) was defined as “discharge capacity at 1/5 C rate”, which was used as an indicator of output characteristics. A larger discharge capacity at the 1/5 C rate is preferable because rapid discharge becomes possible.
(2)クーロン効率、充放電容量及び放電容量維持率
得られた充電容量と放電容量(mAh/g:gは単体硫黄の質量当り)から、充放電サイクルの各サイクルで、クーロン効率(%)=放電容量/充電容量を求めた。クーロン効率は、充電した電気量を放電でどれだけ取りだせるかを示す値であり、値が100(%)に近いほど良い。
又、放電容量維持率(%)=nサイクル目の放電容量/2サイクル目の放電容量を求めた。放電容量維持率は、充放電の繰り返しの安定性を示す値であり、値が100(%)に近いほど良い。
なお、正極(硫黄電極)は充電状態で作製されるため、充放電サイクルの第1サイクルは放電過程のみ進行し、第2サイクル目以降は充電と放電過程が進行する。したがって、充放電の順序は、第1サイクルの放電→第2サイクルの充電→第2サイクルの放電→第3サイクルの充電→第3サイクルの放電となる。充放電サイクルは20サイクル行った。なお、図8の「充放電容量」は、各充放電サイクルにおけるそれぞれ充電容量と放電容量の別に表示した。
又、10cycle目の放電容量維持率(%) = (10cycle目の放電容量)/(2cycle目の放電容量)で求めた。
(2) Coulomb efficiency, charge / discharge capacity and discharge capacity maintenance rate From the obtained charge capacity and discharge capacity (mAh / g: g is per mass of elemental sulfur), the Coulomb efficiency (%) in each charge / discharge cycle. = Discharge capacity / charge capacity was determined. The coulomb efficiency is a value indicating how much the charged amount of electricity can be taken out by discharging, and the closer the value is to 100 (%), the better.
Further, discharge capacity retention ratio (%) = discharge capacity at the nth cycle / discharge capacity at the second cycle was determined. The discharge capacity retention ratio is a value indicating the stability of repeated charge and discharge, and the value is preferably closer to 100 (%).
In addition, since the positive electrode (sulfur electrode) is manufactured in a charged state, the first cycle of the charge / discharge cycle proceeds only in the discharge process, and the charge and discharge processes proceed in the second and subsequent cycles. Therefore, the order of charge / discharge is as follows: first cycle discharge → second cycle charge → second cycle discharge → third cycle charge → third cycle discharge. The charge / discharge cycle was 20 cycles. In addition, “charge / discharge capacity” in FIG. 8 is displayed separately for each charge capacity and discharge capacity in each charge / discharge cycle.
Further, the discharge capacity retention rate at 10th cycle (%) = (discharge capacity at 10th cycle) / (discharge capacity at 2nd cycle).
(3)イオン伝導率
イオン伝導率は複素インピーダンス法により測定した。測定機器としてPrinceton Applied Research社の型番:VMP2 を用い、周波数範囲を500 kHz から1 Hzとし、印加電圧を10 mV とした。サンプルとなる電解液をグローブボックス中で白金黒電極セル(東亜ディーケーケー社のCG-511B)に投入し、セルを密封して測定した。尚、白金黒電極セルは、測定前に予め標準KCl水溶液を用いてセル定数を算出した。測定温度は30℃とした。
また、表1,2に示すように、トリグライム(G3)の代わりに他のグライム(G1、G2、G4)(キシダ化学社製)又はTHF(和光純薬工業社製)を用いて、同様にして実験を行った。
得られた結果を表1、2及び図5〜図9に示す。
(3) Ionic conductivity Ionic conductivity was measured by the complex impedance method. Princeton Applied Research's model number: VMP2 was used as a measuring instrument, the frequency range was 500 kHz to 1 Hz, and the applied voltage was 10 mV. The electrolyte solution as a sample was placed in a platinum black electrode cell (CG-511B manufactured by Toa DKK Corporation) in a glove box, and the cell was sealed and measured. For the platinum black electrode cell, the cell constant was calculated in advance using a standard KCl aqueous solution before measurement. The measurement temperature was 30 ° C.
In addition, as shown in Tables 1 and 2, other glyme (G1, G2, G4) (manufactured by Kishida Chemical Co., Ltd.) or THF (manufactured by Wako Pure Chemical Industries, Ltd.) is used in the same manner instead of triglyme (G3). The experiment was conducted.
The obtained results are shown in Tables 1 and 2 and FIGS.
図5、図6に示すように、(フッ素系溶媒)/(LiTFSA)で表される混合比が、モル換算で0.50〜6.0である実施例1〜18の場合、フッ素系溶媒を添加しなかった比較例1〜16に比べて、電流密度が大きくしても充電容量及び放電容量の低下が少なく、入出力密度(取り出せる電力)が向上することがわかる。
又、図7〜図9に示すように、各実施例1〜8の場合、クーロン効率、サイクル特性、放電容量維持率が比較例1、2よりやや劣るレベルであるが、実用上は問題ないことがわかる。
As shown in FIGS. 5 and 6, in the case of Examples 1 to 18 in which the mixing ratio represented by (fluorinated solvent) / (LiTFSA) is 0.50 to 6.0 in terms of mole, the fluorinated solvent. Compared to Comparative Examples 1 to 16 in which no is added, even when the current density is increased, the charge capacity and the discharge capacity are hardly decreased, and the input / output density (power that can be extracted) is improved.
Further, as shown in FIGS. 7 to 9, in each of Examples 1 to 8, the Coulomb efficiency, cycle characteristics, and discharge capacity retention rate are slightly inferior to those of Comparative Examples 1 and 2, but there is no problem in practical use. I understand that.
2 正極
4 負極(対極)
50 リチウム−硫黄電池(アルカリ金属−硫黄系二次電池)
2 Positive electrode 4 Negative electrode (counter electrode)
50 Lithium-sulfur battery (alkali metal-sulfur secondary battery)
Claims (6)
該正極又は負極の対極であって、該アルカリ金属、該アルカリ金属を含む合金、炭素、又はアルカリ金属イオンを吸蔵脱離する活物質を有する対極と、を備え、
前記アルカリ金属塩に対する前記フッ素系溶媒の混合比(モル比)が、0.50〜5.0であるアルカリ金属−硫黄系二次電池。 Elemental sulfur, lithium polysulphides; and Li 2 S n (1 ≦ n ≦ 8), and a positive electrode containing a sulfur-based electrode active material containing at least one selected from the group consisting of organic sulfur compound or the negative electrode, the following formula
A counter electrode of the positive electrode or the negative electrode, comprising the alkali metal, an alloy containing the alkali metal, carbon, or an active material that absorbs and desorbs alkali metal ions ,
An alkali metal-sulfur secondary battery in which a mixing ratio (molar ratio) of the fluorine-based solvent to the alkali metal salt is 0.50 to 5.0 .
グライムと、リチウム塩と、F Glime, lithium salt, F 33 CHCH 22 C−O−CFC-O-CF 22 CFCF 22 Hで表されるフッ素系溶媒とを含み、グライムに対するリチウム塩の混合比が0.50以上で、グライムとリチウム塩とが錯体を形成している、イオン伝導率が1.8mScmAn ion conductivity of 1.8 mScm in which the mixing ratio of lithium salt to glyme is 0.50 or more and glyme and lithium salt form a complex. −1-1 以上の電解液と、The above electrolyte,
前記正極又は前記負極の対極であって、リチウム、リチウムを含む合金、炭素、又はリチウムイオンを吸蔵脱離する活物質を有する対極と、を備え、 A counter electrode of the positive electrode or the negative electrode, comprising lithium, an alloy containing lithium, carbon, or an active material that absorbs and desorbs lithium ions,
前記リチウム塩に対する前記フッ素系溶媒の混合比(モル比)が、0.50〜5.0であるアルカリ金属−硫黄系二次電池。 An alkali metal-sulfur secondary battery in which a mixing ratio (molar ratio) of the fluorine-based solvent to the lithium salt is 0.50 to 5.0.
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