TWI625887B - Positive electrode for lithium-ion secondary battery and lithium-ion secondary battery - Google Patents
Positive electrode for lithium-ion secondary battery and lithium-ion secondary battery Download PDFInfo
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Abstract
本發明的目標是提供一種新穎正電極及由所述正電極構成的鋰離子二次電池,所述正電極是使用作爲廉價材料的橡膠來生產且能夠增強鋰離子二次電池的充電及放電容量以及循環利用性。在鋰離子二次電池中,正電極包括集電器及形成在集電器的表面上的電極層,電極層包含活性材料、導電添加劑及經歷熱固化的熱固性樹脂黏結劑,且活性材料包含藉由在非氧化氣氛下對包含橡膠及硫的起始材料進行熱處理所製備的硫系正電極活性材料。An object of the present invention is to provide a novel positive electrode and a lithium ion secondary battery composed of the positive electrode, the positive electrode being produced using rubber as an inexpensive material and capable of enhancing the charging and discharging capacity of the lithium ion secondary battery. And recycling. In a lithium ion secondary battery, the positive electrode includes a current collector and an electrode layer formed on a surface of the current collector. The electrode layer includes an active material, a conductive additive, and a thermosetting resin binder that undergoes thermal curing. A sulfur-based positive electrode active material prepared by heat-treating a starting material containing rubber and sulfur in a non-oxidizing atmosphere.
Description
本發明涉及一種用於鋰離子二次電池的正電極及使用所述正電極製成的鋰離子二次電池。The invention relates to a positive electrode for a lithium ion secondary battery and a lithium ion secondary battery made using the positive electrode.
由於鋰離子二次電池(一種類型的非水電解質二次電池)重量輕且具有大的充電及放電容量,因此所述鋰離子二次電池已主要用作便携式電子裝置的電池。此外,期望鋰離子二次電池作爲用於例如電動汽車等機動車的電池的實際使用。一般來說,包含例如鈷或鎳等稀有金屬的材料用作鋰離子二次電池的正電極活性材料。然而,由於稀有金屬的分布量小、不總是容易購得、及另外昂貴的事實,一直需要使用取代稀有金屬的材料的正電極活性材料。Since a lithium ion secondary battery (a type of non-aqueous electrolyte secondary battery) is lightweight and has a large charging and discharging capacity, the lithium ion secondary battery has been mainly used as a battery for portable electronic devices. Further, practical use of a lithium ion secondary battery as a battery for an automobile such as an electric automobile is expected. Generally, a material containing a rare metal such as cobalt or nickel is used as a positive electrode active material of a lithium ion secondary battery. However, due to the fact that the amount of rare metal distribution is small, it is not always easily available, and it is also expensive, there has been a need to use a positive electrode active material instead of a rare metal material.
已知一種使用元素硫作爲正電極活性材料的技術。也就是,硫與稀有金屬相比容易購得且價格低廉,並且具有進一步的優勢:可使鋰離子二次電池的充電及放電容量比當前狀態更大。舉例來說,已知使用硫作爲正電極活性材料的鋰離子二次電池可實現比使用作爲一般正電極材料的鋰鈷氧化物的鋰離子二次電池大約6倍的充電及放電容量。A technique using elemental sulfur as a positive electrode active material is known. That is, sulfur is easier to buy and less expensive than rare metals, and has a further advantage: it can make the lithium ion secondary battery have a larger charge and discharge capacity than the current state. For example, it is known that a lithium ion secondary battery using sulfur as a positive electrode active material can achieve a charge and discharge capacity of about 6 times that of a lithium ion secondary battery using lithium cobalt oxide as a general positive electrode material.
然而,使用元素硫作爲正電極活性材料的鋰離子二次電池具有電池容量經過重複充電及放電而劣化的問題。也就是,元素硫可能會在放電時產生具有鋰的化合物,且由於所產生的化合物可溶於鋰離子二次電池的非水電解質(例如,碳酸伸乙酯及碳酸二甲酯等)中,因此充電及放電容量因流出至所述電解質的硫而在經過重複充電及放電時逐漸減小。However, a lithium ion secondary battery using elemental sulfur as a positive electrode active material has a problem that the battery capacity is deteriorated by repeated charging and discharging. That is, elemental sulfur may generate lithium-containing compounds during discharge, and since the generated compounds are soluble in non-aqueous electrolytes of lithium ion secondary batteries (eg, ethylene carbonate and dimethyl carbonate, etc.), Therefore, the charge and discharge capacity gradually decreases due to the sulfur flowing out of the electrolyte when it is repeatedly charged and discharged.
存在一種使用聚丙烯腈作爲用於硫系正電極活性材料的起始材料的技術。然而,聚丙烯腈是相對昂貴的材料。此外,在使用用於正電極的這種正電極活性材料的鋰離子二次電池中,例如充電及放電容量以及循環利用性等電池性能顯著取決於起始聚丙烯腈粉末的品質(尤其粒徑)。具有良好品質的聚丙烯腈更爲昂貴。因此,難以提供一種具有大的充電及放電容量以及優異循環利用性的廉價鋰離子二次電池。There is a technology using polyacrylonitrile as a starting material for a sulfur-based positive electrode active material. However, polyacrylonitrile is a relatively expensive material. In addition, in a lithium ion secondary battery using such a positive electrode active material for a positive electrode, battery performance such as charge and discharge capacity, and recyclability depend significantly on the quality of the starting polyacrylonitrile powder (especially particle size) ). Polyacrylonitrile with good quality is more expensive. Therefore, it is difficult to provide an inexpensive lithium-ion secondary battery having a large charge and discharge capacity and excellent cycleability.
已知爲藉由防止硫流出至電解質中來提高循環利用性,將藉由對硫及二烯橡膠一起進行熱處理而製備的硫系正電極活性材料與作爲黏結劑的含氟樹脂混合,且將所述混合物用作正電極材料(WO 2015/050086)。然而,尚未獲得充足的循環利用性。It is known to improve the recycling efficiency by preventing sulfur from flowing into the electrolyte. A sulfur-based positive electrode active material prepared by heat-treating sulfur and a diene rubber together is mixed with a fluorine-containing resin as a binder, and The mixture is used as a positive electrode material (WO 2015/050086). However, sufficient recycling has not been achieved.
在使用藉由將硫系正電極活性材料與作爲黏結劑的含氟樹脂混合而製備的正電極材料的鋰離子二次電池中,當重複進行充電及放電時,循環利用性降低,此被認爲是因活性材料的膨脹而造成活性材料從集電器剝離或解吸附或者由導電添加劑形成的傳導路徑的切斷所引起。本發明的目標是提供一種用於鋰離子二次電池的正電極及使用所述正電極的鋰離子二次電池,所述鋰離子二次電池無以上所提及的此種缺點且展現出優異的充電及放電容量以及循環利用性。In a lithium ion secondary battery using a positive electrode material prepared by mixing a sulfur-based positive electrode active material with a fluorine-containing resin as a binder, it is recognized that when the charge and discharge are repeatedly performed, the recyclability decreases. It is caused by the active material being peeled or desorbed from the current collector due to the expansion of the active material, or the conductive path formed by the conductive additive is cut off. An object of the present invention is to provide a positive electrode for a lithium ion secondary battery and a lithium ion secondary battery using the same, which does not have the above-mentioned disadvantages and exhibits excellent Charge and discharge capacity and recycling.
本發明者已進行了深入研究以解決以上所提及的問題,且因此已發現藉由以下方式所獲得的硫系正電極活性材料提供一種用於展現出優異特性的鋰離子二次電池的正電極:對橡膠及硫進行熱處理,其中所述熱處理是使用熱固性樹脂作爲黏結劑以及使所述樹脂固化來執行。本發明者已進行了進一步研究且已完成了本發明。The present inventors have conducted intensive studies to solve the above-mentioned problems, and have therefore found that the sulfur-based positive electrode active material obtained by the following method provides a positive electrode for a lithium ion secondary battery exhibiting excellent characteristics. Electrode: heat treatment of rubber and sulfur, wherein the heat treatment is performed using a thermosetting resin as a binder and curing the resin. The present inventors have conducted further research and have completed the present invention.
也就是,本發明涉及:That is, the invention relates to:
[1]一種用於鋰離子二次電池的正電極,所述鋰離子二次電池包括集電器及形成在所述集電器的表面上的電極層, 其中所述電極層包含活性材料、導電添加劑及經歷熱固化的熱固性樹脂黏結劑,且 所述活性材料包含硫系正電極活性材料,所述硫系正電極活性材料是藉由在非氧化氣氛下對包含橡膠及硫的起始材料進行熱處理來製備。[1] A positive electrode for a lithium ion secondary battery, the lithium ion secondary battery including a current collector and an electrode layer formed on a surface of the current collector, wherein the electrode layer includes an active material and a conductive additive And a thermosetting resin binder undergoing thermal curing, and the active material includes a sulfur-based positive electrode active material, and the sulfur-based positive electrode active material is heat-treated by starting materials including rubber and sulfur in a non-oxidizing atmosphere To prepare.
[2]根據以上[1]所述的用於鋰離子二次電池的正電極,其中所述熱固性樹脂黏結劑包含聚醯亞胺樹脂及聚醯胺-醯亞胺樹脂中的至少一者。[2] The positive electrode for a lithium ion secondary battery according to the above [1], wherein the thermosetting resin binder includes at least one of a polyimide resin and a polyimide-fluorimide resin.
[3]根據以上[1]或[2]所述的用於鋰離子二次電池的正電極,其中以所述活性材料、所述導電添加劑及所述熱固性樹脂黏結劑的總混配量計,在所述電極層中所述活性材料、所述導電添加劑及所述熱固性樹脂黏結劑的混配比分別爲按質量計30%至95%、按質量計2%至40%、及按質量計3%至30%。[3] The positive electrode for a lithium ion secondary battery according to the above [1] or [2], wherein the total amount of the active material, the conductive additive, and the thermosetting resin binder is calculated The mixing ratio of the active material, the conductive additive, and the thermosetting resin binder in the electrode layer is 30% to 95% by mass, 2% to 40% by mass, and by mass, respectively. 3% to 30%.
[4]根據以上[1]至[3]中任一項所述的用於鋰離子二次電池的正電極,其中在製備所述硫系正電極活性材料時的熱處理溫度是250℃至550℃。[4] The positive electrode for a lithium ion secondary battery according to any one of [1] to [3] above, wherein a heat treatment temperature when preparing the sulfur-based positive electrode active material is 250 ° C. to 550 ℃.
[5]根據以上[1]至[4]中任一項所述的用於鋰離子二次電池的正電極,其中所述硫系正電極活性材料的所述起始材料還包含硫化促進劑。[5] The positive electrode for a lithium ion secondary battery according to any one of the above [1] to [4], wherein the starting material of the sulfur-based positive electrode active material further contains a vulcanization accelerator .
[6]根據以上[1]至[5]中任一項所述的用於鋰離子二次電池的正電極,其中所述硫系正電極活性材料的所述起始材料還包含導電碳材料。[6] The positive electrode for a lithium ion secondary battery according to any one of [1] to [5] above, wherein the starting material of the sulfur-based positive electrode active material further includes a conductive carbon material .
[7]根據以上[6]所述的用於鋰離子二次電池的正電極,其中所述導電碳材料是具有石墨結構的碳材料。[7] The positive electrode for a lithium ion secondary battery according to the above [6], wherein the conductive carbon material is a carbon material having a graphite structure.
[8]根據以上[6]或[7]所述的用於鋰離子二次電池的正電極,其中以所述橡膠的100質量份(part by mass)計,所述硫系正電極活性材料的所述起始材料包含250質量份至1500質量份的硫、3質量份至250質量份的硫化促進劑、以及5質量份至50質量份的導電碳材料。[8] The positive electrode for a lithium ion secondary battery according to the above [6] or [7], wherein the sulfur-based positive electrode active material is based on 100 parts by mass of the rubber The starting material includes 250 to 1500 parts by mass of sulfur, 3 to 250 parts by mass of a vulcanization accelerator, and 5 to 50 parts by mass of a conductive carbon material.
[9]根據以上[1]至[8]中任一項所述的用於鋰離子二次電池的正電極,其中在所述硫系正電極活性材料中硫的總含量按質量計不少於50%,以及[9] The positive electrode for a lithium ion secondary battery according to any one of [1] to [8] above, wherein a total content of sulfur in the sulfur-based positive electrode active material is not less by mass At 50%, and
[10]一種鋰離子二次電池,包括根據以上[1]至[9]中任一項所述的用於鋰離子二次電池的正電極。[10] A lithium ion secondary battery including the positive electrode for a lithium ion secondary battery according to any one of the above [1] to [9].
根據本發明,可提供一種新穎正電極及使用所述正電極製成的鋰離子二次電池,所述正電極是使用作爲廉價材料的橡膠來生產且能夠增強鋰離子二次電池的充電及放電容量以及循環利用性。According to the present invention, a novel positive electrode and a lithium ion secondary battery made using the same can be provided. The positive electrode is produced using rubber as an inexpensive material and can enhance the charging and discharging of the lithium ion secondary battery. Capacity and recycling.
下文詳細地解釋根據本發明的實施例的用於鋰離子二次電池的正電極及鋰離子二次電池。Hereinafter, a positive electrode for a lithium ion secondary battery and a lithium ion secondary battery according to embodiments of the present invention are explained in detail.
<用於鋰離子二次電池的正電極>< Positive electrode for lithium ion secondary battery >
用於鋰離子二次電池的正電極包括集電器及形成在所述集電器的表面上的電極層。A positive electrode for a lithium ion secondary battery includes a current collector and an electrode layer formed on a surface of the current collector.
[集電器] 可使用用於鋰離子二次電池的正電極通常所用的集電器。此類集電器的實例包括鋁箔、鋁網、穿孔鋁板、鋁膨脹板(aluminum expanded sheet)、不銹鋼箔、不銹鋼網、穿孔不銹鋼板、不銹鋼膨脹板、發泡鎳、無紡鎳織物、銅箔、銅網、穿孔銅板、銅膨脹板、鈦箔、鈦網、無紡碳織物等。[Current Collector] A current collector generally used for a positive electrode of a lithium ion secondary battery can be used. Examples of such current collectors include aluminum foil, aluminum mesh, perforated aluminum sheet, aluminum expanded sheet, stainless steel foil, stainless steel mesh, perforated stainless steel sheet, stainless steel expansion sheet, foamed nickel, non-woven nickel fabric, copper foil, Copper mesh, perforated copper plate, copper expansion plate, titanium foil, titanium mesh, non-woven carbon fabric, etc.
尤其由無紡碳織物及/或由具有高石墨化度的碳形成的編織碳織物製成的集電器可適合用作用於硫系正電極活性材料的集電器,因爲不含氫且與硫的反應性低。用於具有高石墨化度的碳纖維的起始材料的實例包括作爲用於碳纖維的材料的各種瀝青(即,石油、煤、煤焦油等的副產物)、聚丙烯腈纖維(PAN)等。In particular, a current collector made of a non-woven carbon fabric and / or a woven carbon fabric formed of carbon having a high degree of graphitization can be suitably used as a current collector for a sulfur-based positive electrode active material because hydrogen-free and sulfur-containing Low reactivity. Examples of the starting material for carbon fibers having a high degree of graphitization include various pitches (ie, by-products of petroleum, coal, coal tar, etc.) as materials for carbon fibers, polyacrylonitrile fibers (PAN), and the like.
[電極層] 電極層是藉由以下方式形成在集電器的表面上的電極層:在非氧化氣氛下在比熱固性樹脂黏結劑的固化溫度高的溫度下對用於電極層的包含活性材料、導電添加劑、及熱固性樹脂黏結劑的混合物進行熱處理。[Electrode layer] An electrode layer is an electrode layer formed on the surface of a current collector in such a manner that, in a non-oxidizing atmosphere, at a temperature higher than the curing temperature of the thermosetting resin binder, the active material for the electrode layer is contained, The mixture of the conductive additive and the thermosetting resin binder is heat-treated.
(活性材料) 活性材料包含硫系正電極活性材料,所述硫系正電極活性材料是藉由在非氧化氣氛下對包含橡膠及硫的起始材料進行熱處理來製備。活性材料優選爲包含硫系正電極活性材料的活性材料。(Active Material) The active material includes a sulfur-based positive electrode active material, which is prepared by heat-treating a starting material containing rubber and sulfur in a non-oxidizing atmosphere. The active material is preferably an active material containing a sulfur-based positive electrode active material.
假定硫系正電極活性材料具有長鏈聚合物形式的二噻吩並噻吩(thienoacene)結構,所述長鏈聚合物藉由噻吩環的縮合及連接形成且由以下式(i)表示。 It is assumed that the sulfur-based positive electrode active material has a dithienoacene structure in the form of a long-chain polymer that is formed by condensation and connection of a thiophene ring and is represented by the following formula (i).
也就是,作爲在激發波長λ=532 nm、光栅爲600 gr/mm、及分辨率爲2 cm-1 的條件下,以可購自奈米光子公司(Nanophoton Corporation)的激光拉曼顯微鏡(laser Raman microscope)RAMAN-11對硫系正電極活性材料進行拉曼光譜分析的結果,在拉曼位移爲500 cm-1 、1250 cm-1 、及1450 cm-1 左右處觀察到峰值。儘管這些光譜與在6員環的石墨結構中所見的1350 cm-1 左右的被稱爲D頻帶及1590 cm-1 左右的被稱爲G頻帶的光譜不同,但當將這些光譜與在文獻(化學物理化學,2009, 10, 3069-3076)中所述的二噻吩並噻吩光譜進行比較時,認爲500 cm-1 左右的峰值是衍生自噻吩的面內變形,1250 cm-1 左右的峰值是衍生自噻吩環的C-C面內變形,且1450 cm-1 左右的峰值是衍生自噻吩的C-C伸縮。That is, under the conditions of an excitation wavelength λ = 532 nm, a grating of 600 gr / mm, and a resolution of 2 cm -1 , a laser Raman microscope (laser) commercially available from Nanophoton Corporation was used. (Raman microscope) The results of Raman-11 analysis of sulfur-based positive electrode active materials by Raman-11 showed peaks around Raman shifts of 500 cm -1 , 1250 cm -1 , and 1450 cm -1 . Although these spectra are different from those in the 6-membered graphite structure called the D-band around 1350 cm -1 and called the G-band around 1590 cm -1 , when comparing these spectra with those in the literature ( Chemical Physical Chemistry, 2009, 10, 3069-3076) When comparing the dithienothiophene spectra described above, the peak around 500 cm -1 is considered to be derived from the in-plane deformation of thiophene, and the peak around 1250 cm -1 It is the in-plane deformation of the CC derived from the thiophene ring, and the peak around 1450 cm -1 is the CC stretching derived from the thiophene.
認爲硫系正電極活性材料優選符合以下特徵。也就是,在FT-IR光譜(在以下條件下,使用可購自島津公司(Shimadzu Corporation)的傅立葉變換紅外分光光度計(Fourier transform infrared spectrophotometer)IR Affinity-1,藉由漫反射法測得:分辨率:4 cm-1 、累積數目:100次、及測量範圍:400 cm-1 至4000 cm-1 )中,優選地在917 cm-1 左右、約1042 cm-1 、1149 cm-1 左右、1214 cm-1 左右、1388 cm-1 左右、1415 cm-1 左右、及1439 cm-1 左右處存在峰值。It is considered that the sulfur-based positive electrode active material preferably meets the following characteristics. That is, in the FT-IR spectrum (under the following conditions, a Fourier transform infrared spectrophotometer, IR Affinity-1, commercially available from Shimadzu Corporation, was measured by a diffuse reflection method: Resolution: 4 cm -1 , cumulative number: 100 times, and measurement range: 400 cm -1 to 4000 cm -1 ), preferably about 917 cm -1 , about 1042 cm -1 , 1149 cm -1 There are peaks at around 1214 cm -1, around 1388 cm -1, around 1415 cm -1 , and around 1439 cm -1 .
<<橡膠>> 橡膠的實例包括二烯橡膠,例如天然橡膠、異戊二烯橡膠、及丁二烯橡膠。所述橡膠可單獨或以其兩者或更多者的組合形式使用。其中,天然橡膠及高順式聚丁二烯橡膠是尤其優選的。所述兩種橡膠易於具有包含彎曲分子鏈的不規則結構,且相鄰分子鏈之間的分子間力可相對較小,因而幾乎不會造成結晶化。因此,不僅式(i)的結構主體而且硫系正電極活性材料的靈活性及可加工性可得以增強。<<< Rubber >> Examples of the rubber include diene rubber such as natural rubber, isoprene rubber, and butadiene rubber. The rubber may be used alone or in a combination of two or more thereof. Among them, natural rubber and high-cis polybutadiene rubber are particularly preferred. The two rubbers are apt to have an irregular structure including a curved molecular chain, and the intermolecular force between adjacent molecular chains may be relatively small, and thus hardly cause crystallization. Therefore, not only the structural body of the formula (i), but also the flexibility and processability of the sulfur-based positive electrode active material can be enhanced.
可以認爲使用尤其例如高順式聚丁二烯橡膠等丁二烯橡膠對於使二噻吩並噻吩主體的結構更加均質化來說是優選的。此處,高順式聚丁二烯橡膠是按質量計順式-1,4鍵含量不少於95%的聚丁二烯橡膠。由此種高順式聚丁二烯橡膠形成的硫系正電極活性材料特徵在於:在拉曼光譜中,也存在拉曼位移爲1940 cm-1 左右的峰值,而與衍生自天然橡膠的硫系正電極活性材料不同,1400 cm-1 左右的峰值及1550 cm-1 左右的峰值非常小。It is considered that the use of a butadiene rubber such as a high-cis polybutadiene rubber is particularly preferable for making the structure of the dithienothiophene body more homogeneous. Here, the high-cis polybutadiene rubber is a polybutadiene rubber having a cis-1,4 bond content of not less than 95% by mass. The sulfur-based positive electrode active material formed by this kind of high-cis polybutadiene rubber is characterized in that a Raman shift also has a peak with a Raman shift of about 1940 cm -1 , and is similar to sulfur derived from natural rubber. The positive electrode active materials are different. The peaks around 1400 cm -1 and the peaks around 1550 cm -1 are very small.
衍生自天然橡膠的硫系正電極活性材料可被認爲在二噻吩並噻吩結構的一部分中包含石墨結構,且因此所述結構的一部分可被認爲是不均質的。與此同時,可以認爲衍生自丁二烯橡膠的硫系正電極活性材料不包含此種石墨結構,且其結構被認爲是均質的,且因此以上所提及的效果尤爲優異。The sulfur-based positive electrode active material derived from natural rubber may be considered to include a graphite structure in a part of a dithienothiophene structure, and thus a part of the structure may be considered to be heterogeneous. At the same time, it can be considered that the sulfur-based positive electrode active material derived from butadiene rubber does not contain such a graphite structure, and its structure is considered to be homogeneous, and therefore the effects mentioned above are particularly excellent.
在實施例中,以非硫化狀態提供所述橡膠作爲用於硫系正電極活性材料的起始材料。In an example, the rubber is provided in a non-vulcanized state as a starting material for a sulfur-based positive electrode active material.
<<硫>> 可使用各種形式的硫,例如粉狀硫、沉澱硫、不可溶性硫、膠態硫等。從硫向橡膠均勻擴散的角度看,適合使用精細顆粒的膠態硫。<< Sulfur> Various forms of sulfur can be used, such as powdered sulfur, precipitated sulfur, insoluble sulfur, colloidal sulfur, and the like. From the perspective of uniform diffusion of sulfur into rubber, it is suitable to use colloidal sulfur with fine particles.
以橡膠的100質量份計,硫的混配比優選爲不少於250質量份、更優選不少於300質量份。另一方面,儘管不存在硫的混配比的上限,但所述混配比通常不多於1500質量份、優選地不多於1000質量份。由於所述混配比處於以上所提及的範圍內,因此存在充電及放電容量以及循環利用性能夠完全增加的趨勢。即使所述比率超過1500質量份,仍難以充分提高充電及放電容量或循環利用性,且存在不多於1500質量份的比率從成本的角度看爲有利的趨勢。The compounding ratio of sulfur is preferably not less than 250 parts by mass, and more preferably not less than 300 parts by mass based on 100 parts by mass of the rubber. On the other hand, although there is no upper limit of the compounding ratio of sulfur, the compounding ratio is usually not more than 1500 parts by mass, and preferably not more than 1,000 parts by mass. Since the compounding ratio is within the above-mentioned range, there is a tendency that the charging and discharging capacity and the recyclability can be completely increased. Even if the ratio exceeds 1500 parts by mass, it is difficult to sufficiently improve the charging and discharging capacity or the recyclability, and there is a tendency that a ratio of not more than 1500 parts by mass is advantageous from a cost perspective.
<<硫化促進劑>><< Vulcanization accelerator >>
優選地,用於硫系正電極活性材料的起始材料還包含硫化促進劑。這是因爲硫化促進劑可用於增強鋰離子二次電池的循環利用性。Preferably, the starting material for the sulfur-based positive electrode active material further includes a vulcanization accelerator. This is because a vulcanization accelerator can be used to enhance the recycleability of a lithium ion secondary battery.
硫化促進劑的實例包括硫脲系硫化促進劑、胍系硫化促進劑、噻唑系硫化促進劑、亞磺醯胺系硫化促進劑、秋蘭姆系硫化促進劑、二硫代氨基甲酸酯系(dithiocarbamate-based)硫化促進劑、及黃原酸酯系硫化促進劑中的一者或多者。其中,秋蘭姆化合物(thiuram compound)的實例包括二硫化四甲基秋蘭姆(tetramethylthiuram disulfide,TT)、二硫化四乙基秋蘭姆(tetraethylthiuram disulfide,TET)、二硫化四丁基秋蘭姆(tetrabutylthiuram disulfide,TBT)、二硫化四(2-乙基己基)秋蘭姆(tetrakis(2-ethylhexyl)thiuram disulfide,TOT-N)、一硫化四甲基秋蘭姆(tetramethylthiuram monosulfide,TS)、四硫化雙五亞甲基秋蘭姆(dipentamethylenethiuram tetrasulfide,TRA)等中的一者或多者。Examples of the vulcanization accelerator include a thiourea-based vulcanization accelerator, a guanidine-based vulcanization accelerator, a thiazole-based vulcanization accelerator, a sulfenimide-based vulcanization accelerator, a thiuram-based vulcanization accelerator, and a dithiocarbamate-based (Dithiocarbamate-based) one or more of a vulcanization accelerator and a xanthate-based vulcanization accelerator. Examples of the thiuram compound include tetramethylthiuram disulfide (TT), tetraethylthiuram disulfide (TET), and tetrabutylthiuram disulfide Tetrabutylthiuram disulfide (TBT), tetrakis (2-ethylhexyl) thiuram disulfide (TOT-N), tetramethylthiuram monosulfide (TS) Or dipentamethylenethiuram tetrasulfide (TRA), etc.
尤其優選作爲秋蘭姆化合物的是其中末端取代基中的任一者爲直鏈烷基的二硫化四甲基秋蘭姆、二硫化四乙基秋蘭姆、二硫化四丁基秋蘭姆、一硫化四甲基秋蘭姆等。優選的二硫代氨基甲酸酯化合物是其鋅鹽。二硫代氨基甲酸的鋅鹽的實例包括二乙基二硫代氨基甲酸鋅(zinc diethyldithiocarbamate,EZ)、二丁基二硫代氨基甲酸鋅(zinc dibutyldithiocarbamate,BZ)、二甲基二硫代氨基甲酸鋅(zinc dimethyldithiocarbamate,PZ)、N-乙基-N-苯基二硫代氨基甲酸鋅(zinc N-ethyl-N-phenyldithiocarbamate,PX)等中的一者或多者。Particularly preferred as the thiuram compound are tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetrabutylthiuram disulfide in which any of the terminal substituents is a linear alkyl group. , Tetramethylthiuram monosulfide, etc. A preferred dithiocarbamate compound is its zinc salt. Examples of the zinc salt of dithiocarbamic acid include zinc diethyldithiocarbamate (EZ), zinc dibutyldithiocarbamate (BZ), dimethyldithioamino One or more of zinc dimethyldithiocarbamate (PZ), zinc N-ethyl-N-phenyldithiocarbamate (PX), and the like.
當這些化合物被選擇並用作硫化促進劑時,可形成優異地展現出不僅增強充電及放電容量且增強循環利用性的效果的硫系正電極活性材料。When these compounds are selected and used as a vulcanization accelerator, a sulfur-based positive electrode active material that exhibits an effect that not only enhances the charge and discharge capacity but also enhances the recycleability can be formed.
當混配有硫化促進劑時,以橡膠的100質量份計,硫化促進劑的混配比優選不少於3質量份、更優選不少於10質量份。另一方面,所述混配比優選不多於250質量份、更優選不多於50質量份。當硫化促進劑的混配比處於以上所提及的範圍內時,趨於增強鋰離子二次電池的循環利用性。When the vulcanization accelerator is mixed, the compounding ratio of the vulcanization accelerator is preferably not less than 3 parts by mass, and more preferably not less than 10 parts by mass based on 100 parts by mass of the rubber. On the other hand, the compounding ratio is preferably not more than 250 parts by mass, and more preferably not more than 50 parts by mass. When the compounding ratio of the vulcanization accelerator is within the above-mentioned range, the recycling efficiency of the lithium ion secondary battery tends to be enhanced.
<<導電碳材料>> 用於硫系正電極活性材料的起始材料還可包含導電碳材料。這是因爲藉由混配導電碳材料,可增強電導率。用於增強鋰離子二次電池的循環利用性的各種導電碳材料中的任一者可用作導電碳材料。<< Conductive carbon material> The starting material for the sulfur-based positive electrode active material may further include a conductive carbon material. This is because the electrical conductivity can be enhanced by mixing a conductive carbon material. Any of various conductive carbon materials for enhancing the recycling of lithium ion secondary batteries can be used as the conductive carbon material.
導電碳材料的實例包括具有稠和芳香環結構的一種或多種碳材料,例如碳黑、石墨、碳奈米管(carbon nanotube,CNT)、碳纖維(carbon fiber,CF)、石墨烯、富勒烯等。此外,具有含氮雜環環結構的導電碳材料也可用作導電碳材料。尤其優選作爲導電碳材料的是具有石墨結構的碳材料,且其實例包括以上所提及的具有稠和芳香環結構的碳材料。Examples of the conductive carbon material include one or more carbon materials having a thick and aromatic ring structure, such as carbon black, graphite, carbon nanotube (CNT), carbon fiber (CF), graphene, fullerene Wait. In addition, a conductive carbon material having a nitrogen-containing heterocyclic ring structure can also be used as the conductive carbon material. Particularly preferred as the conductive carbon material are carbon materials having a graphite structure, and examples thereof include the above-mentioned carbon materials having a thick and aromatic ring structure.
其中,碳黑是優選的,因爲碳黑價格低廉且可擴散性優異。而且,少量的碳奈米管或石墨烯可與碳黑組合。根據此種組合,鋰離子二次電池的循環利用性可在不大幅增加成本的情况下進一步提高。以導電碳材料的總量計,碳奈米管或石墨烯的組合量優選按質量計不少於8%且按質量計不多於12%。Among them, carbon black is preferable because carbon black is inexpensive and excellent in diffusibility. Moreover, a small amount of carbon nanotubes or graphene can be combined with carbon black. According to such a combination, the recyclability of the lithium ion secondary battery can be further improved without significantly increasing the cost. The combined amount of carbon nanotubes or graphene is preferably not less than 8% by mass and not more than 12% by mass based on the total amount of the conductive carbon material.
當混配導電碳材料時,以橡膠的100質量份計,所述導電碳材料的混配比優選不少於5質量份、更優選不少於10質量份。另一方面,導電碳材料的混配比優選不多於50質量份、更優選不多於30質量份。當所述混配比處於所提及的範圍內時,趨於實現藉由混配導電碳材料來增強循環利用性,同時充分增強鋰離子二次電池的充電及放電容量。When the conductive carbon material is compounded, the compounding ratio of the conductive carbon material is preferably not less than 5 parts by mass, and more preferably not less than 10 parts by mass based on 100 parts by mass of the rubber. On the other hand, the compounding ratio of the conductive carbon material is preferably not more than 50 parts by mass, and more preferably not more than 30 parts by mass. When the compounding ratio is within the mentioned range, it tends to achieve enhanced recycling efficiency by compounding conductive carbon materials, and at the same time sufficiently enhance the charging and discharging capacity of the lithium ion secondary battery.
此外,可以認爲硫化促進劑用於藉由將大量硫混入橡膠中以及防止在放電時切斷聚合物來增強鋰離子二次電池的循環利用性。另一方面,可以認爲導電碳材料用於藉由增強硫系正電極活性材料的電導率、從而提高與鋰離子的反應性來增強鋰離子二次電池的循環利用性。In addition, it is considered that a vulcanization accelerator is used to enhance the recycleability of a lithium ion secondary battery by mixing a large amount of sulfur into the rubber and preventing the polymer from being cut off during discharge. On the other hand, it can be considered that the conductive carbon material is used to enhance the recyclability of the lithium ion secondary battery by enhancing the conductivity of the sulfur-based positive electrode active material, thereby improving the reactivity with lithium ions.
<<硫系正電極活性材料的製備>> 橡膠用於各種用途,容易購得且價格低廉,並且與硫的反應性高,且具有高含量的用於將硫混入其中的雙鍵。因此,可以認爲藉由在比慣常硫化的溫度高的溫度下對橡膠及硫進行熱處理,可製備其中大量硫混入其分子中的硫系正電極活性材料。此外,假定當硫系正電極活性材料具有上式(i)的結構時,所述結構形成三維網絡,從而將元素硫密封及固定。〈〈 Preparation of sulfur-based positive electrode active material 〉〉 Rubber is used in various applications, is easily available and inexpensive, has high reactivity with sulfur, and has a high content of double bonds for mixing sulfur therein. Therefore, it can be considered that a sulfur-based positive electrode active material in which a large amount of sulfur is mixed into its molecule can be prepared by heat-treating rubber and sulfur at a temperature higher than a temperature at which vulcanization is conventionally performed. In addition, it is assumed that when the sulfur-based positive electrode active material has a structure of the above formula (i), the structure forms a three-dimensional network, thereby sealing and fixing elemental sulfur.
硫系正電極活性材料可藉由以下方式來製備:將橡膠、硫、及視需要硫化促進劑與導電碳材料以給定混合比混合以產生起始材料,以及在比慣常硫化的溫度高的溫度下對起始材料進行熱處理。Sulfur-based positive electrode active materials can be prepared by mixing rubber, sulfur, and, if necessary, a vulcanization accelerator with a conductive carbon material at a given mixing ratio to produce a starting material, and at a temperature higher than a conventional vulcanization temperature. The starting material is heat-treated at a temperature.
<<熱處理>> 優選地,藉由在非氧化氣氛下進行熱處理從而使得能夠防止氧化劣化或所述組分的過度熱分解來執行熱處理。因此,可形成增強鋰離子二次電池的充電及放電容量以及循環利用性的效果優異的硫系正電極活性材料。非氧化氣氛意指實質上不含氧氣的氣氛。在非氧化氣氛下進行加熱的實例包括在填充有例如氮氣或氬氣等惰性氣體的二氧化矽管中在惰性氣氛下進行熱處理。熱處理的溫度優選不少於250℃、更優選不少於300℃。另一方面,熱處理溫度優選不多於550℃、更優選不多於450℃。當熱處理溫度處於所提及的範圍內時,存在在實施充分硫化反應的同時可防止起始化合物分解的趨勢,此在實現鋰離子二次電池的充足的充電及放電容量方面爲有利的。<< Heat Treatment> It is preferable to perform heat treatment by performing heat treatment in a non-oxidizing atmosphere so as to prevent oxidative degradation or excessive thermal decomposition of the components. Therefore, a sulfur-based positive electrode active material having excellent effects of enhancing the charge and discharge capacity and the recyclability of the lithium ion secondary battery can be formed. A non-oxidizing atmosphere means an atmosphere that is substantially free of oxygen. Examples of heating under a non-oxidizing atmosphere include performing a heat treatment in an inert atmosphere in a silicon dioxide tube filled with an inert gas such as nitrogen or argon. The temperature of the heat treatment is preferably not less than 250 ° C, and more preferably not less than 300 ° C. On the other hand, the heat treatment temperature is preferably not more than 550 ° C, and more preferably not more than 450 ° C. When the heat treatment temperature is within the mentioned range, there is a tendency to prevent decomposition of the starting compound while performing a sufficient sulfurization reaction, which is advantageous in achieving sufficient charge and discharge capacity of the lithium ion secondary battery.
用於熱處理的時間段優選爲2小時至6小時。當熱處理時間處於所提及的範圍內時,存在可充分推進熱處理且可防止所述組分過度熱分解的趨勢。The time period for the heat treatment is preferably 2 hours to 6 hours. When the heat treatment time is within the mentioned range, there is a tendency that the heat treatment can be sufficiently advanced and the component can be prevented from being excessively thermally decomposed.
起始材料的混合及熱處理也可藉由在例如雙螺杆擠出機等連續設備中對橡膠、硫等進行捏合的同時進行熱處理來實施。Mixing and heat treatment of the starting materials can also be performed by performing heat treatment while kneading rubber, sulfur, and the like in a continuous device such as a twin-screw extruder.
<<未反應的硫的移除>> 由於對熱處理時升華的硫進行冷却而導致的沉積所引起的所謂未反應的硫可能會殘留在所製備的硫系正電極活性材料中。移除此種未反應的硫是合意的,因爲所述未反應的硫會導致循環利用性劣化。一種用於移除未反應的硫的方法的實例包括通過在減壓下進行熱處理來移除、通過暖風來移除、通過以溶劑進行洗滌來移除等。<< Removal of Unreacted Sulfur >> The so-called unreacted sulfur caused by the deposition caused by cooling the sublimed sulfur during heat treatment may remain in the prepared sulfur-based positive electrode active material. It is desirable to remove such unreacted sulfur because the unreacted sulfur can cause deterioration in recycling. Examples of a method for removing unreacted sulfur include removal by performing heat treatment under reduced pressure, removal by warm air, removal by washing with a solvent, and the like.
(粉碎及分類) 將硫系正電極活性材料粉碎成預定微粒大小,並將所述硫系正電極活性材料分類爲適合用於生產正電極的顆粒。所述顆粒的優選粒徑分布的中值粒徑爲約5 μm至25 μm。注意在以上所解釋的使用雙螺杆擠出機的熱處理方法中,由於在捏合時進行剪切,因此也可同時將所生產的硫系正電極活性材料粉碎。(Crushing and Classification) The sulfur-based positive electrode active material is pulverized into a predetermined particle size, and the sulfur-based positive electrode active material is classified into particles suitable for producing a positive electrode. A preferred median size of the particles is about 5 μm to 25 μm. Note that in the heat treatment method using the twin-screw extruder explained above, since the shearing is performed at the time of kneading, the produced sulfur-based positive electrode active material can also be pulverized at the same time.
<<硫系正電極活性材料>> 在通過以上所提及的熱處理而製備的硫系正電極活性材料中,當硫的總含量增加時,鋰離子二次電池的循環利用性趨於提高。因此,盡可能大的硫的總含量爲優選的。通過元素分析而得的硫的總含量優選按質量計不少於50%、更優選按質量計不少於51%、進一步優選按質量計不少於53%、更進一步優選按質量計不少於55%。此外,優選地,氫的含量按質量計不多於1.6%、尤其按質量計不多於1.0%。<<< Sulfur-based positive electrode active material> In the sulfur-based positive electrode active material prepared by the heat treatment mentioned above, when the total content of sulfur is increased, the recycling efficiency of the lithium ion secondary battery tends to be improved. Therefore, as large a total content of sulfur as possible is preferable. The total content of sulfur obtained by elemental analysis is preferably not less than 50% by mass, more preferably not less than 51% by mass, further preferably not less than 53% by mass, and still more preferably not less than mass At 55%. Furthermore, preferably, the content of hydrogen is not more than 1.6% by mass, especially not more than 1.0% by mass.
在其中將具有石墨結構的碳材料混配爲導電碳材料的系統中,存在其中因構成碳材料的碳的影響而硫含量低於所提及範圍的情况。然而,仍可展現出增強鋰離子二次電池的循環利用性的效果。在此種情况下,硫含量優選按質量計不少於45%,以維持增強鋰離子二次電池的循環利用性的效果。In a system in which a carbon material having a graphite structure is compounded as a conductive carbon material, there are cases where the sulfur content is lower than the mentioned range due to the influence of the carbon constituting the carbon material. However, the effect of enhancing the recyclability of the lithium ion secondary battery can still be exhibited. In this case, the sulfur content is preferably not less than 45% by mass in order to maintain the effect of enhancing the recyclability of the lithium ion secondary battery.
<<導電添加劑>> 導電添加劑的實例包括氣相生長碳纖維(vapor grown carbon fiber,VGCF)、碳粉末、碳黑(carbon black,CB)、乙炔黑(acetylene black,AB)、科琴黑(KETJENBLACK,KB)、石墨、在正電極電位下穩定的金屬(例如鋁及鈦)的精細粉末等。以上所述者中的一者或多者可用作導電添加劑。<< Conductive Additives> Examples of the conductive additives include vapor grown carbon fiber (VGCF), carbon powder, carbon black (CB), acetylene black (AB), and Ketjen Black ( KETJENBLACK, KB), graphite, fine powders of metals (such as aluminum and titanium) that are stable at the positive electrode potential. One or more of the above may be used as a conductive additive.
(黏結劑) 黏結劑用作用於將活性材料及導電添加劑固定至集電器的黏結試劑,且在本發明的實施例中,使用熱固性樹脂。通過使用熱固性樹脂作爲黏結劑,不僅將活性材料及導電添加劑牢固地固定至集電器,且可防止活性材料因活性材料的膨脹而從集電器剝離並與集電器分離,並且防止由導電添加劑形成的導電路徑被切斷。(Binder) The binder is used as a binding agent for fixing an active material and a conductive additive to a current collector, and in the embodiment of the present invention, a thermosetting resin is used. By using a thermosetting resin as a binder, not only the active material and the conductive additive are firmly fixed to the current collector, but also the active material can be prevented from being peeled from the current collector and separated from the current collector due to the expansion of the active material, and the conductive additive can be prevented from forming. The conductive path is cut off.
黏結劑是包含聚醯亞胺樹脂及聚醯胺-醯亞胺樹脂中的至少一者的黏結劑。聚醯亞胺樹脂及聚醯胺-醯亞胺樹脂耐熱性高且黏結特性高。因此,當所述黏結劑中包含聚醯亞胺樹脂及聚醯胺-醯亞胺樹脂時,可生產具有高耐熱性及長使用壽命的正電極。聚醯亞胺樹脂具有比聚醯胺-醯亞胺樹脂高的耐熱性及黏結特性,且因此優選地,所述黏結劑包含聚醯亞胺樹脂。The binder is a binder containing at least one of polyimide resin and polyamido-imide resin. Polyimide resins and polyamido-imide resins have high heat resistance and high adhesive properties. Therefore, when a polyfluorene resin and a polyfluorene-fluorene resin are contained in the binder, a positive electrode having high heat resistance and a long service life can be produced. A polyimide resin has higher heat resistance and adhesion characteristics than a polyimide-amibide resin, and therefore, it is preferable that the binder includes a polyimide resin.
如果所述黏結劑中包含即使爲少量的聚醯亞胺樹脂及聚醯胺-醯亞胺樹脂中的至少一者,則依據其含量而展現出以上所提及的效果。以整個黏結劑計,聚醯亞胺樹脂及聚醯胺-醯亞胺樹脂中的至少一者的含量優選按質量計不少於50%、更優選按質量計不少於70%、進一步優選按質量計不少於80%、更進一步優選按質量計不少於90%。從黏結特性的角度看,優選地,所述黏結劑是由聚醯亞胺樹脂及聚醯胺-醯亞胺樹脂中的至少一者組成的黏結劑。If the binder contains at least one of a polyamidoimide resin and a polyamido-amimine resin even in a small amount, the above-mentioned effects are exhibited depending on the content thereof. The content of at least one of the polyfluorene resin and the polyfluorene-fluorene resin based on the entire binder is preferably not less than 50% by mass, more preferably not less than 70% by mass, and even more preferably Not less than 80% by mass, more preferably not less than 90% by mass. From the standpoint of adhesive properties, preferably, the adhesive is an adhesive composed of at least one of a polyimide resin and a polyimide-fluorimide resin.
(正電極的生產) 一種生產正電極的方法包括塗布步驟及固化步驟。(Production of Positive Electrode) A method of producing a positive electrode includes a coating step and a curing step.
塗布步驟是以下步驟:將活性材料、導電添加劑及黏結劑混合以及視需要向其中添加溶劑等以產生漿料形式的用於電極層的混合物,以及將所述混合物施加在集電器的表面上。生產用於鋰離子二次電池的電極通常所用的塗布方法中的任一者可適合用作塗布方法。此種塗布方法的實例包括輥塗法、浸塗法、刮刀塗布法、噴塗法、簾塗法等。The coating step is a step of mixing an active material, a conductive additive, and a binder and adding a solvent or the like thereto as necessary to produce a mixture for an electrode layer in the form of a slurry, and applying the mixture on a surface of a current collector. Any one of the coating methods generally used for producing an electrode for a lithium ion secondary battery can be suitably used as the coating method. Examples of such a coating method include a roll coating method, a dip coating method, a doctor blade coating method, a spray coating method, a curtain coating method, and the like.
溶劑的實例包括N-甲基-2-吡咯烷酮、N,N-二甲基甲醛、醇、水等中的一者或多者。Examples of the solvent include one or more of N-methyl-2-pyrrolidone, N, N-dimethylformaldehyde, alcohol, water, and the like.
關於活性材料、導電添加劑、及黏結劑的混配比,優選地,相對於活性材料、導電添加劑、及黏結劑這三種組分的總含量計,混配按質量計30%至95%的活性材料、按質量計2%至40%的導電添加劑、及按質量計3%至30%的黏結劑。活性材料的混配比更優選按質量計50%至95%、尤其按質量計70%至95%,導電添加劑的混配比更優選按質量計2%至30%、尤其按質量計2%至15%,且黏結劑的混配比更優選按質量計3%至20%、尤其按質量計3%至15%。Regarding the mixing ratio of the active material, the conductive additive, and the binder, it is preferable to mix 30% to 95% of the activity by mass relative to the total content of the three components of the active material, the conductive additive, and the binder. Materials, 2% to 40% by mass of conductive additives, and 3% to 30% by mass of binders. The mixing ratio of the active material is more preferably 50% to 95% by mass, especially 70% to 95% by mass, and the mixing ratio of the conductive additive is more preferably 2% to 30% by mass, especially 2% by mass. 15%, and the compounding ratio of the binder is more preferably 3% to 20% by mass, especially 3% to 15% by mass.
電極層的塗布厚度優選爲10 μm至150 μm。The coating thickness of the electrode layer is preferably 10 μm to 150 μm.
固化步驟是以下步驟:在比熱固化樹脂的固化溫度高的溫度下對用於電極層的混合物進行熱處理,所述混合物施加在集電器的表面上。熱固性樹脂黏結劑的固化可藉由在比欲使用的熱固性樹脂的固化溫度高的溫度下施行熱處理來實現。此種溫度的代表性範圍爲例如120℃至350℃。此外,優選地,在非氧化氣氛下實施熱處理。非氧化氣氛是實質上不包含氧氣的氣氛,例如在使氧氣的分壓降低爲低至不會導致氧化反應的推進下的氣氛、或例如氮氣及氬氣等惰性氣體氣氛。The curing step is a step of heat-treating a mixture for an electrode layer at a temperature higher than a curing temperature of a thermosetting resin, and the mixture is applied on a surface of a current collector. The curing of the thermosetting resin adhesive can be achieved by performing a heat treatment at a temperature higher than the curing temperature of the thermosetting resin to be used. A typical range of such a temperature is, for example, 120 ° C to 350 ° C. Further, it is preferable to perform the heat treatment in a non-oxidizing atmosphere. The non-oxidizing atmosphere is an atmosphere that does not substantially contain oxygen, and is, for example, an atmosphere in which the partial pressure of oxygen is reduced to such an extent that it does not cause an oxidation reaction to progress, or an inert gas atmosphere such as nitrogen and argon.
生產正電極的另一方法的實例是以下方法:在研鉢等中將硫系正電極活性材料與導電添加劑、熱固性樹脂黏結劑、及少量的溶劑捏合;將所捏合產物模製成膜形式;以壓力機等將所述膜壓力黏結至集電器上;且,然後在比熱固性樹脂的固化溫度高的溫度下進行熱處理。An example of another method for producing a positive electrode is the following method: kneading a sulfur-based positive electrode active material with a conductive additive, a thermosetting resin binder, and a small amount of a solvent in a mortar or the like; molding the kneaded product into a film form; The film is pressure-bonded to a current collector with a press or the like; and then, a heat treatment is performed at a temperature higher than the curing temperature of the thermosetting resin.
如此獲得的正電極包括集電器及形成在所述集電器的表面上的電極層,且所述電極層是由活性材料、導電添加劑、及熱定形熱固性樹脂黏結劑構成的電極層。在此正電極中,活性材料呈粉末形式,且藉由黏結劑而被固定在集電器的表面上。活性材料粉末的粒徑的中值粒徑不多於25 μm。The positive electrode thus obtained includes a current collector and an electrode layer formed on a surface of the current collector, and the electrode layer is an electrode layer composed of an active material, a conductive additive, and a thermosetting thermosetting resin binder. In this positive electrode, the active material is in the form of a powder and is fixed on the surface of the current collector by a binder. The median diameter of the particle diameter of the active material powder is not more than 25 μm.
<鋰離子二次電池> 在本發明的實施例中,鋰離子二次電池是使用以上所提及的正電極製備的鋰離子二次電池,且可藉由常用方法,除使用正電極外還使用在此領域中常用的構件(即,使用負電極、電解質、及視需要還使用分隔物)來生產。鋰離子二次電池的形狀並不受特別限制,且鋰離子二次電池可呈各種形狀,例如圓柱形、層疊層型、硬幣形、及按鈕形。鋰離子二次電池具有大的充電及放電容量,且循環利用性優異。<Lithium-ion secondary battery> In the embodiment of the present invention, the lithium-ion secondary battery is a lithium-ion secondary battery prepared using the above-mentioned positive electrode, and can be used in addition to the positive electrode by a common method. It is produced using components commonly used in this field (ie, using a negative electrode, an electrolyte, and optionally a separator). The shape of the lithium ion secondary battery is not particularly limited, and the lithium ion secondary battery may have various shapes, such as a cylindrical shape, a laminated type, a coin shape, and a button shape. Lithium-ion secondary batteries have large charge and discharge capacities and are excellent in recyclability.
(負電極) 負電極材料的實例包括已知的金屬鋰、例如石墨等碳系材料、例如矽薄膜等矽系材料、例如銅-錫或鈷-錫等合金系材料等。在以上所提及的負電極材料中,在其中使用不包含鋰的碳系材料、矽系材料、合金系材料等的情况下,從以下方面來看是有利的:較少可能發生由枝晶的產生而引起的正電極與負電極之間的短路。(Negative Electrode) Examples of the negative electrode material include known metal lithium, carbon-based materials such as graphite, silicon-based materials such as silicon thin films, alloy-based materials such as copper-tin or cobalt-tin, and the like. Among the above-mentioned negative electrode materials, in the case where a carbon-based material, a silicon-based material, an alloy-based material, etc. which do not contain lithium is used, it is advantageous from the following points: it is less likely that a The resulting short circuit between the positive and negative electrodes.
然而,在其中結合本發明實施例的正電極而使用不包含鋰的負電極材料的情况下,正電極及負電極均不包含鋰,且因此其中將鋰插添至負電極或正電極兩者中的任一者或插添至負電極及正電極兩者中的預摻雜處理變得必要。對於一種預先摻雜鋰的方法,可使用公知的方法。舉例來說,在其中使負電極摻雜有鋰的情况下,可給出插添鋰的以下方法:以電解方式進行摻雜的方法,其中使用金屬鋰作爲對電極且然後以電化學方式摻雜鋰來組裝半電池;以及應用預摻雜方法,其中藉由將金屬鋰箔施加至電極上且然後使具有所施加金屬鋰箔的電極留置於電解溶液中而使鋰擴散至所述電極來進行摻雜。此外,同樣地在其中使正電極摻雜有鋰的另一種情况下,可利用前面所提及的以電解方式進行摻雜的方法。However, in the case where a negative electrode material not containing lithium is used in combination with the positive electrode of the embodiment of the present invention, neither the positive electrode nor the negative electrode contains lithium, and therefore lithium is added to both the negative electrode or the positive electrode Either one or a pre-doping process inserted into both the negative electrode and the positive electrode becomes necessary. For a method of pre-doping lithium, a known method can be used. For example, in the case where the negative electrode is doped with lithium, the following method of inserting lithium can be given: a method of doping electrolytically, in which metallic lithium is used as a counter electrode and then electrochemically doped To assemble a half-cell with hybrid lithium; and to apply a pre-doping method in which lithium is diffused to the electrode by applying a metal lithium foil to the electrode and then leaving the electrode with the applied metal lithium foil in an electrolytic solution Doping. Further, also in the other case where the positive electrode is doped with lithium, the aforementioned method of electrolytically doping may be used.
作爲高容量負電極材料的矽系材料優選作爲不包含鋰的負電極材料。其中,可使所述電極的厚度更薄且在每一體積的容量方面爲有利的矽薄膜爲特別優選的。A silicon-based material as a high-capacity negative electrode material is preferable as a negative electrode material not containing lithium. Among them, a silicon thin film that can make the thickness of the electrode thinner and is advantageous in terms of capacity per volume is particularly preferable.
(電解質) 關於欲用於鋰離子二次電池上的電解質,可使用其中用作電解質的鹼金屬鹽溶解於有機溶劑中的那些電解質。優選有機溶劑的實例包括選自非水溶劑中的至少一者,例如碳酸伸乙酯、碳酸伸丙酯、碳酸二甲酯、碳酸二乙酯、碳酸甲乙酯、二甲醚、γ-丁內酯、及乙腈。可用電解質的實例包括LiPF6 、LiBF4 、LiAsF6 、LiCF3 SO3 、LiI、LiClO4 等。電解質的濃度可爲約0.5莫耳/升至1.7莫耳/升。注意所述電解質並不僅限於液體形式。舉例來說,在其中鋰離子二次電池爲鋰聚合物二次電池的情况下,所述電解質爲固體形式(例如,聚合物凝膠的形式)(Electrolyte) As the electrolyte to be used on the lithium ion secondary battery, those electrolytes in which an alkali metal salt used as the electrolyte is dissolved in an organic solvent can be used. Examples of preferred organic solvents include at least one selected from non-aqueous solvents, such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dimethyl ether, γ-butane Lactone and acetonitrile. Examples of usable electrolytes include LiPF 6 , LiBF 4 , LiAsF 6 , LiCF 3 SO 3 , LiI, LiClO 4 and the like. The concentration of the electrolyte may be about 0.5 mol / liter to 1.7 mol / liter. Note that the electrolyte is not limited to a liquid form. For example, in the case where the lithium ion secondary battery is a lithium polymer secondary battery, the electrolyte is in a solid form (for example, in the form of a polymer gel)
(分隔物) 除以上所述的負電極、正電極、及電解質外,鋰離子二次電池同樣還可配備有其他構件,例如分隔物。分隔物介於正電極與負電極之間,從而不僅使得離子能夠在正電極與負電極之間移動且用於防止正電極與負電極在內部使彼此短路。當鋰離子二次電池爲氣密封閉型時,分隔物需要具有保存電解溶液的功能。關於分隔物,優選使用由以下材料製成的厚度薄且多微孔或無紡形膜:例如聚乙烯、聚丙烯、聚丙烯腈、芳族聚醯胺、聚醯亞胺、纖維素、玻璃等。(Separator) In addition to the negative electrode, the positive electrode, and the electrolyte described above, the lithium ion secondary battery may also be equipped with other members, such as a separator. The separator is interposed between the positive electrode and the negative electrode, thereby not only enabling ions to move between the positive electrode and the negative electrode, but also for preventing the positive electrode and the negative electrode from shorting each other internally. When the lithium ion secondary battery is hermetically sealed, the separator needs to have a function of storing an electrolytic solution. As for the separator, it is preferable to use a thin and microporous or non-woven film made of a material such as polyethylene, polypropylene, polyacrylonitrile, aromatic polyimide, polyimide, cellulose, glass Wait.
<用語的解釋> 循環利用性是鋰離子二次電池的其中充電及放電容量隨著重複充電及放電而減小的特性。充電及放電容量減小程度小的鋰離子二次電池的循環利用性優異,且充電及放電容量減小程度大的鋰離子二次電池的循環利用性差。<Explanation of Terms> Recyclability is a characteristic in which the charge and discharge capacity of a lithium ion secondary battery decreases with repeated charge and discharge. A lithium ion secondary battery with a small degree of reduction in charge and discharge capacity is excellent in recycling, and a lithium ion secondary battery with a large degree of reduction in charge and discharge capacity has poor cycleability.
DSC代表差示掃描量熱法(differential scanning calorimetry)。DSC stands for differential scanning calorimetry.
丁二烯橡膠的順式-1,4鍵含量爲整個丁二烯橡膠中的順式-1,4鍵單元的量(質量%),且可藉由13C-NMR光譜來獲得。The cis-1,4 bond content of the butadiene rubber is the amount (mass%) of the cis-1,4 bond unit in the entire butadiene rubber, and can be obtained by 13C-NMR spectrum.
實例Examples
<用於測試的材料>< Materials for testing >
橡膠:高順式丁二烯橡膠(宇部波爾(UBEPOL)(注册商標)BR150L,可購自宇部興產有限公司(Ube Industries, Ltd.),順式-1,4鍵含量:按質量計98%)Rubber: High cis-butadiene rubber (UBEPOL (registered trademark) BR150L, available from Ube Industries, Ltd.), cis-1,4 bond content: by mass 98%)
硫:膠態硫,可購自鶴見化學工業有限公司(Tsurumi Chemical Industry Co., Ltd.)Sulfur: colloidal sulfur, available from Tsurumi Chemical Industry Co., Ltd.
導電碳材料:乙炔黑(電化黑(Denka Black),可購自電氣化學工業股份有限公司(Denki Kagaku Kogyo Kabushiki Kaisha))Conductive carbon material: acetylene black (Denka Black, available from Denki Kagaku Kogyo Kabushiki Kaisha)
硫化促進劑:諾賽勞(NOCCELOR) TS(一硫化四甲基秋蘭姆,可購自大內新光化工有限公司(OUCHI SHINKO CHEMICAL INDUSTRIAL CO., LTD.))Vulcanization accelerator: NOCCELOR TS (tetramethylthiuram monosulfide, available from OUCHI SHINKO CHEMICAL INDUSTRIAL CO., LTD.)
導電添加劑:乙炔黑(電化黑(Denka Black),可購自電氣化學工業股份有限公司)Conductive additive: Acetylene black (Denka Black, available from Denka Chemical Co., Ltd.)
黏結劑1(熱固性樹脂):聚醯亞胺樹脂(固化溫度:200℃至250℃(DSC))Binder 1 (thermosetting resin): polyimide resin (curing temperature: 200 ° C to 250 ° C (DSC))
黏結劑2(熱塑性樹脂):聚偏二氟乙烯(可購自和光純藥工業有限公司(Wako Pure Chemical Industries, Ltd.))Binder 2 (thermoplastic resin): polyvinylidene fluoride (available from Wako Pure Chemical Industries, Ltd.)
實例1 Example 1
<硫系正電極活性材料的製備><Preparation of sulfur-based positive electrode active material>
向100質量份丁二烯橡膠中混配1000質量份硫、25質量份硫化促進劑、及20質量份導電碳材料,且使用捏合測試裝置[MIX-LABO,由本森山有限公司(Moriyama Company, Ltd.)製造]對所混配的混合物進行捏合以製備經捏合產物。將如此獲得的經捏合產物手工切成不多於3 mm的小片,以製備欲經歷熱處理的起始化合物。To 100 parts by mass of butadiene rubber, 1,000 parts by mass of sulfur, 25 parts by mass of a vulcanization accelerator, and 20 parts by mass of a conductive carbon material were used, and a kneading tester [MIX-LABO, by Moriyama Company, Ltd. .) Manufacturing] The kneaded mixture is kneaded to prepare a kneaded product. The kneaded product thus obtained was manually cut into small pieces of not more than 3 mm to prepare a starting compound to be subjected to a heat treatment.
(反應設備)(Reaction equipment)
使用如圖1所說明的反應設備1對起始化合物進行熱處理。反應設備1 包括:反應容器3,反應容器3具有60 mm的外徑、50 mm的內徑、及300 mm的高度,且由石英玻璃製成,所述石英玻璃被形成爲平底圓柱形以對起始化合物2進行容納及熱處理;矽酮塞4,用於封閉反應容器3的上部開口;一個氧化鋁保護管5(“氧化鋁SSA-S”,可購自日陶(NIKKATO)公司,外徑爲4 mm、內徑爲2 mm、且長度爲250 mm)及氣體引入管6及排氣管7(兩者均爲“氧化鋁SSA-S”,可購自日陶(NIKKATO)公司,外徑爲6 mm、內徑爲4 mm、且長度爲150 mm)的兩個管,這三個管穿透塞4;以及電爐8(坩堝爐,開口寬度:80 mm的直徑,加熱高度:100 mm),用於從底面加熱反應容器3。The starting compound is heat-treated using a reaction apparatus 1 as illustrated in FIG. 1. The reaction device 1 includes a reaction container 3 having an outer diameter of 60 mm, an inner diameter of 50 mm, and a height of 300 mm, and is made of quartz glass, which is formed into a flat-bottomed cylindrical shape to face The starting compound 2 is contained and heat-treated; a silicone plug 4 is used to close the upper opening of the reaction vessel 3; an alumina protective tube 5 ("alumina SSA-S", available from Nikkota Corporation, outside Diameter 4 mm, inner diameter 2 mm, and length 250 mm) and gas introduction pipe 6 and exhaust pipe 7 (both of which are "alumina SSA-S", available from NIKKATO), Two tubes with an outer diameter of 6 mm, an inner diameter of 4 mm, and a length of 150 mm), these three tubes penetrate the plug 4; and the electric furnace 8 (crucible furnace, opening width: 80 mm in diameter, heating height: 100 mm) for heating the reaction vessel 3 from the bottom surface.
氧化鋁保護管5被形成爲此種長度以使得其下部從塞4觸及容納在反應容器3的底部中的起始化合物2,且熱電偶9插入貫穿氧化鋁保護管5的內部。氧化鋁保護管5用作熱電偶9的保護管。熱電偶9的前端在由氧化鋁保護管5的封閉前端加以保護的同時插入至起始化合物2中,且用於測量起始化合物2的溫度。熱電偶9的輸出如由圖式中的實線箭頭所示被輸入電爐8的溫度控制器10中,且溫度控制器10用於基於來自熱電偶9的輸入控制電爐8的加熱溫度。The alumina protection tube 5 is formed in such a length that its lower portion touches the starting compound 2 contained in the bottom of the reaction container 3 from the plug 4, and a thermocouple 9 is inserted through the inside of the alumina protection tube 5. The alumina protection tube 5 is used as a protection tube for the thermocouple 9. The front end of the thermocouple 9 is inserted into the starting compound 2 while being protected by the closed front end of the alumina protection tube 5, and is used to measure the temperature of the starting compound 2. The output of the thermocouple 9 is input to the temperature controller 10 of the electric furnace 8 as indicated by the solid line arrows in the figure, and the temperature controller 10 is used to control the heating temperature of the electric furnace 8 based on the input from the thermocouple 9.
氣體引入管6及排氣管7被形成爲使得其底端從塞4向下突出3 mm。此外,反應容器3的上部從電爐8突出以暴露至大氣。因此,由於反應容器3的加熱而從起始化合物產生的硫的蒸汽如由圖式中的長短虛線箭頭所示上升至反應容器3的上部,且在被冷却的同時轉變成液滴以如圖式中的斷線箭頭所示滴下及回流。因此,反應系統中的硫不通過排氣管7而泄漏至外部。The gas introduction pipe 6 and the exhaust pipe 7 are formed so that the bottom ends thereof protrude downward from the plug 4 by 3 mm. In addition, the upper part of the reaction vessel 3 protrudes from the electric furnace 8 to be exposed to the atmosphere. Therefore, the steam of sulfur generated from the starting compound due to the heating of the reaction vessel 3 rises to the upper part of the reaction vessel 3 as shown by the long and short dashed arrows in the figure, and is transformed into droplets while being cooled as shown in the figure. Dropping and reflow are indicated by broken arrows in the formula. Therefore, the sulfur in the reaction system does not leak to the outside through the exhaust pipe 7.
從未被示出的氣體供應系統對氣體引入管6連續供以氬氣。排氣管7連接至容納氫氧化鈉的水溶液11的捕集溶池12。從反應容器3通過排氣管7朝外部移動的排氣在穿過捕集溶池12中的氫氧化鈉的水溶液11之後釋放至外部。因此,即使排氣中包含由硫化反應產生的硫化氫氣體,也能藉由與氫氧化鈉的水溶液發生中和而從排氣中移除所述硫化氫氣體。The gas introduction pipe 6 is continuously supplied with argon gas from a gas supply system not shown. The exhaust pipe 7 is connected to a trapping tank 12 containing an aqueous solution 11 of sodium hydroxide. The exhaust gas that has moved from the reaction vessel 3 to the outside through the exhaust pipe 7 passes through the aqueous solution 11 of sodium hydroxide in the trap solution tank 12 and is released to the outside. Therefore, even if the exhaust gas contains hydrogen sulfide gas generated by the sulfurization reaction, the hydrogen sulfide gas can be removed from the exhaust gas by neutralization with an aqueous solution of sodium hydroxide.
[熱處理步驟] 在從氣體供應系統以80 ml/min的流速開始連續供應氬(Ar)氣至在其底部中容置起始化合物2的反應容器3達30分鐘之後,以電爐8開始進行加熱。溫度上升速率爲5℃/min。由於在起始化合物的溫度變爲200℃時開始產生氣體,因此連續進行加熱同時調整氬氣的流速以使得排氣的流速變得盡可能恒定。當起始化合物2的溫度達到450℃時,在維持溫度爲450℃的同時施行熱處理兩小時。然後,在氬氣氣氛下使反應產物自然冷却至25℃同時調整氬氣的流速,且從反應容器3中取出反應產物。[Heat treatment step] After continuously supplying argon (Ar) gas from the gas supply system at a flow rate of 80 ml / min to the reaction vessel 3 containing the starting compound 2 in the bottom thereof for 30 minutes, heating was started in the electric furnace 8 . The temperature rise rate was 5 ° C / min. Since gas starts to be generated when the temperature of the starting compound becomes 200 ° C, heating is continuously performed while adjusting the flow rate of argon so that the flow rate of the exhaust gas becomes as constant as possible. When the temperature of the starting compound 2 reached 450 ° C, heat treatment was performed for two hours while maintaining the temperature at 450 ° C. Then, the reaction product was naturally cooled to 25 ° C. under an argon atmosphere while adjusting the flow rate of the argon gas, and the reaction product was taken out from the reaction container 3.
[未反應的硫的移除] 爲了在熱處理步驟之後移除殘留在產物中的未反應的硫(自由元素硫),實施以下步驟。也就是,在研鉢中粉碎反應產物,且將2 g經粉碎產物放入玻璃管烘箱中並在250℃下加熱三小時,同時施行真空抽吸以生產其中未反應的硫被移除(或僅含有痕量未反應的硫)的硫系正電極活性材料。溫度上升速率爲10℃/min。[Removal of Unreacted Sulfur] In order to remove unreacted sulfur (free element sulfur) remaining in the product after the heat treatment step, the following steps were performed. That is, the reaction product is pulverized in a mortar, and 2 g of the pulverized product is put into a glass tube oven and heated at 250 ° C. for three hours while performing vacuum suction to produce unreacted sulfur in which is removed (or A sulfur-based positive electrode active material containing only trace amounts of unreacted sulfur). The temperature rise rate was 10 ° C / min.
<正電極> 對以上所生產的硫系正電極活性材料、導電添加劑(乙炔黑)、及黏結劑(聚醯亞胺樹脂)進行測量以使得其混配比變爲硫系正電極活性材料:導電添加劑:黏結劑=87:3:10(%按質量計),並將硫系正電極活性材料、導電添加劑、及黏結劑放入容器中。在使用N-甲基-2-吡咯烷酮(可購自岸田化學有限公司(Kishida Chemical Co., Ltd.),電池級)作爲擴散劑來調整混合物的黏度時,對混合物進行攪拌並以自轉/公轉混合機(ARE-250,可購自新基(Thinky)公司)進行混合以製備均勻的漿料。以施料器(以60 μm的厚度)將所製備漿料施加至20 μm厚的鋁箔(集電器)上,然後以乾燥器在250℃下進行3小時的加熱以對黏結劑進行熱固化。因此,獲得實例1的正電極。<Positive electrode> The sulfur-based positive electrode active material, conductive additive (acetylene black), and binder (polyimide resin) produced above are measured so that the mixing ratio becomes a sulfur-based positive electrode active material: Conductive additive: binder = 87: 3: 10 (% by mass), and put the sulfur-based positive electrode active material, conductive additive, and binder into the container. When using N-methyl-2-pyrrolidone (commercially available from Kishida Chemical Co., Ltd., battery grade) as a diffusing agent to adjust the viscosity of the mixture, the mixture is stirred and rotated / revolved. A mixer (ARE-250, commercially available from Thinky) was mixed to prepare a uniform slurry. The prepared slurry was applied to a 20 μm-thick aluminum foil (current collector) with an applicator (at a thickness of 60 μm), and then heated at 250 ° C. for 3 hours with a dryer to thermally cure the adhesive. Thus, a positive electrode of Example 1 was obtained.
<負電極> 將厚度爲500 μm的金屬鋰箔(由本城金屬有限公司(Honjo Metal Co., Ltd.)製造)打孔成直徑爲14 mm的圓以製備負電極。<Negative electrode> A metal lithium foil (manufactured by Honjo Metal Co., Ltd.) having a thickness of 500 μm was punched into a circle having a diameter of 14 mm to prepare a negative electrode.
<電解質> 使用其中LiPF6 已溶解於碳酸伸乙酯與碳酸二乙酯的混合溶劑中的非水電解質作爲電解質。碳酸伸乙酯與碳酸二乙酯的體積比爲1:1。LiPF6 的濃度爲1.0莫耳/升。<Electrolyte> As the electrolyte, a nonaqueous electrolyte in which LiPF 6 has been dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate is used. The volume ratio of ethylene carbonate to diethyl carbonate was 1: 1. The concentration of LiPF 6 was 1.0 mol / liter.
<鋰離子二次電池> 通過由具有25 μm厚度的聚丙烯多微孔膜及具有500 μm厚度的玻璃無紡過濾器組成的分隔物[卡爾格德(Celgard)(注册商標)2400,由卡爾格德公司製造],將以上正電極及負電極層疊在由不銹鋼容器製成的電池殼體(例如,用於CR2032型硬幣電池(荷森有限公司(HOSEN Co., Ltd.)的產品)的構件)中,且向其中添加電解質溶液,然後以折邊機進行氣密密封,從而獲得CR2032硬幣型鋰離子二次電池。所有操作均在乾燥空間中執行。<Lithium-ion secondary battery> A separator composed of a polypropylene microporous membrane having a thickness of 25 μm and a glass nonwoven filter having a thickness of 500 μm [Celgard (registered trademark) 2400, by Carl Made by Gede Company], the above positive electrode and negative electrode are laminated in a battery case made of a stainless steel container (for example, for a CR2032 coin cell (a product of HOSEN Co., Ltd.) Component), and an electrolyte solution was added thereto, followed by hermetically sealing with a folding machine to obtain a CR2032 coin-type lithium ion secondary battery. All operations are performed in a dry space.
實例 2 除不使用導電碳材料及硫化促進劑外,以與實例1中相同的方式來製備實例2的正電極及使用所述正電極的鋰離子二次電池。 Example 2 A positive electrode of Example 2 and a lithium ion secondary battery using the same were prepared in the same manner as in Example 1 except that a conductive carbon material and a vulcanization accelerator were not used.
比較例 1 除使用聚偏二氟乙烯作爲黏結劑外,以與實例1中相同的方式來製備比較例1的正電極及使用所述正電極的鋰離子二次電池。應注意,由於聚偏二氟乙烯爲熱塑性樹脂,因此在製備正電極的最終階段進行加熱時,將“在250℃下進行3小時的加熱”變爲“在150℃下進行10小時的加熱”。 Comparative Example 1 A positive electrode of Comparative Example 1 and a lithium ion secondary battery using the same were prepared in the same manner as in Example 1, except that polyvinylidene fluoride was used as a binder. It should be noted that since polyvinylidene fluoride is a thermoplastic resin, when heating is performed in the final stage of preparing the positive electrode, "heating at 250 ° C for 3 hours" is changed to "heating at 150 ° C for 10 hours" .
比較例 2 除在對用於硫系正電極活性材料的起始材料進行熱處理的步驟中將其最終溫度變爲600℃外,以與實例1中相同的方式來製備比較例2的正電極及使用所述正電極的鋰離子二次電池。 Comparative Example 2 A positive electrode of Comparative Example 2 and a positive electrode of Comparative Example 2 were prepared in the same manner as in Example 1 except that the final temperature of the starting material for the sulfur-based positive electrode active material was changed to 600 ° C. A lithium ion secondary battery using the positive electrode.
比較例 3 除在對用於硫系正電極活性材料的起始材料進行熱處理的步驟中將其最終溫度變爲200℃外,以與實例1中相同的方式來製備比較例3的正電極及使用所述正電極的鋰離子二次電池。 Comparative Example 3 A positive electrode of Comparative Example 3 and a positive electrode of Comparative Example 3 were prepared in the same manner as in Example 1, except that the final temperature of the starting material for the sulfur-based positive electrode active material was changed to 200 ° C. A lithium ion secondary battery using the positive electrode.
<充電及放電容量以及容量保持率的測量> 關於在實例1及實例2以及比較例1中製備的每一鋰離子二次電池,對其充電及放電容量進行測量。具體來說,在測試溫度爲30℃的條件下,在每1 g正電極活性材料等於250 mA(對應於0.5 C)的電流值下重複實施充電及放電。放電端電壓爲1.0 V且充電端電壓爲3.0 V。測量每一放電容量(mAh/g)。在圖2中示出結果。<Measurement of charge and discharge capacity and capacity retention rate> Regarding each lithium ion secondary battery prepared in Examples 1 and 2 and Comparative Example 1, the charge and discharge capacity thereof were measured. Specifically, under the condition of a test temperature of 30 ° C, charging and discharging were repeatedly performed at a current value equal to 250 mA (corresponding to 0.5 C) per 1 g of the positive electrode active material. The discharge terminal voltage is 1.0 V and the charging terminal voltage is 3.0 V. Measure each discharge capacity (mAh / g). The results are shown in FIG. 2.
第二次放電時的放電容量(mAh/g)被視爲初始容量。初始容量越大,鋰離子二次電池的充電及放電容量越大,此被評估爲優選的。此外,根據第十次放電時的放電容量DC10 (mAh/g)及第二十次放電時的放電容量DC20 (mAh/g),藉由式(a)來計算容量保持率(%)。 容量保持率(%)=(DC20 (mAh/g)/ DC10 (mAh/g))´ 100 (a)The discharge capacity (mAh / g) at the second discharge is regarded as the initial capacity. The larger the initial capacity, the larger the charge and discharge capacity of the lithium ion secondary battery, and this was evaluated as preferable. Further, according to the discharge capacity at the tenth discharge DC 10 (mAh / g) and a discharge capacity at the twentieth discharge DC 20 (mAh / g), by the formula (a) to calculate the capacity retention rate (%) . Capacity retention rate (%) = (DC 20 (mAh / g) / DC 10 (mAh / g)) ´ 100 (a)
可以說容量保持率越高,鋰離子二次電池的循環利用性越優異。不少於90%的容量保持率被視爲令人滿意的。此外,容量保持率優選不少於95%。It can be said that the higher the capacity retention rate, the more excellent the lithium ion secondary battery's recyclability. A capacity retention rate of not less than 90% is considered satisfactory. In addition, the capacity retention ratio is preferably not less than 95%.
<元素分析> 對在實例及比較例中生產的硫系正電極活性材料實施元素分析。關於碳、氫、氮、及硫,根據以可構自艾利蒙塔日本有限公司(Elementar Japan K.K)的全自動元素分析裝置瓦裏奧微立方(vario MICRO cube)測量的質量數量來計算以硫系正電極活性材料的總量計的質量比(%)。<Elemental analysis> Elemental analysis was performed on the sulfur-based positive electrode active materials produced in the examples and comparative examples. Regarding carbon, hydrogen, nitrogen, and sulfur, it is calculated based on the mass quantities measured with the vario MICRO cube, a fully automatic elemental analysis device that can be constructed from Elementar Japan KK. Mass ratio (%) of the total amount of the sulfur-based positive electrode active material.
在表1中示出結果。 [表1]
如從表1可以看出,在使用作爲熱固性樹脂的聚醯亞胺樹脂作爲黏結劑的實例1的鋰離子二次電池中,第20次(循環數目:20)時的放電容量維持爲466 mAh/g。與此同時,在使用作爲熱塑性樹脂的聚偏二氟乙烯作爲黏結劑的比較例1的鋰離子二次電池中,放電容量從初始階段劣化,且在第20次(循環數目:20)時幾乎無剩餘。As can be seen from Table 1, in the lithium ion secondary battery of Example 1 using a polyimide resin as a thermosetting resin as a binder, the discharge capacity at the 20th time (number of cycles: 20) was maintained at 466 mAh / g. At the same time, in the lithium ion secondary battery of Comparative Example 1 using polyvinylidene fluoride as a thermoplastic resin as a binder, the discharge capacity deteriorated from the initial stage, and it was almost at the 20th time (number of cycles: 20). Nothing left.
因此,實例1的鋰離子二次電池與比較例1的鋰離子二次電池相比具有顯著改善的循環利用性。此外,實例1的放電容量及循環利用性兩者均比實例2的放電容量及循環利用性更令人滿意。可以認爲,這是因爲由於在製備正電極活性材料時添加硫化促進劑而將更多硫混入活性材料中,且還因爲活性材料的電導率由於導電碳材料的添加而提高。Therefore, the lithium-ion secondary battery of Example 1 has significantly improved cycleability compared with the lithium-ion secondary battery of Comparative Example 1. In addition, both the discharge capacity and the recyclability of Example 1 were more satisfactory than the discharge capacity and the recyclability of Example 2. It can be considered that this is because more sulfur is mixed into the active material due to the addition of a vulcanization accelerator when the positive electrode active material is prepared, and also because the conductivity of the active material is improved due to the addition of a conductive carbon material.
實例1的硫的質量比爲55.8%,而實例2的硫的質量比爲53.7%。在比較例2中,在第20次(循環數目:20)時幾乎未展現出放電容量,而比較例3的放電容量在第20次(循環數目:20)時爲155 mAh/g。因此,比較例2及比較例3的放電容量與實例1相比在很大程度上劣化。可以認爲,這是因爲在比較例2中,橡膠與硫的反應未充分進行,且所混入硫的量少,而在比較例3中,正電極活性材料被分解。The mass ratio of sulfur in Example 1 was 55.8%, while the mass ratio of sulfur in Example 2 was 53.7%. In Comparative Example 2, the discharge capacity was hardly exhibited at the 20th time (number of cycles: 20), while the discharge capacity of Comparative Example 3 was 155 mAh / g at the 20th time (number of cycles: 20). Therefore, the discharge capacity of Comparative Example 2 and Comparative Example 3 was largely deteriorated compared to Example 1. It is considered that this is because in Comparative Example 2, the reaction between rubber and sulfur did not proceed sufficiently, and the amount of sulfur incorporated was small, while in Comparative Example 3, the positive electrode active material was decomposed.
1‧‧‧反應設備
2‧‧‧起始化合物
3‧‧‧反應容器
4‧‧‧塞
5‧‧‧氧化鋁保護管
6‧‧‧氣體引入管
7‧‧‧排氣管
8‧‧‧電爐
9‧‧‧熱電偶
10‧‧‧溫度控制器
11‧‧‧氫氧化鈉的水溶液
12‧‧‧捕集溶池1‧‧‧ reaction equipment
2‧‧‧ starting compounds
3‧‧‧ reaction container
4‧‧‧ stop
5‧‧‧ alumina protection tube
6‧‧‧Gas introduction pipe
7‧‧‧ exhaust pipe
8‧‧‧ Electric stove
9‧‧‧ Thermocouple
10‧‧‧Temperature Controller
11‧‧‧Sodium hydroxide in water
12‧‧‧Capturing tank
圖1是示意性地說明用於生產實例中的硫系正電極活性材料的反應設備的剖視圖。 圖2是示出在實例1及實例2以及比較例1中進行循環充電及放電的結果的曲線圖。FIG. 1 is a cross-sectional view schematically illustrating a reaction apparatus used for the production of a sulfur-based positive electrode active material in an example. FIG. 2 is a graph showing the results of cycle charging and discharging in Examples 1 and 2 and Comparative Example 1. FIG.
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