- 學位論文
高分子材料作為鋰離子電池膜材及矽電極黏著劑開發之研究
Preparation and Development of Polymeric Materials Applications for Membranes and Binder of Silicon Anode in Lithium Ion Batteries
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摘要
本研究以具傳導離子能力之高分子材料為主軸，並探討其應用於鋰離子電池之膜材與矽電極黏著劑的性能和潛力。鋰離子電池的性能的表現主要取決於充放電速率與電容量兩部分。前者須設計良好的鋰離子傳遞媒介，能夠快速於正負兩極之間快速傳遞鋰離子，才可以實現快速的充放電性能。後者主要取決於電極活性材料的電容量，高理論電容量的材料能夠儲存更多的鋰於其材料結構內。這兩個性能再加上穩定的電池安全性將可以滿足人類日益增加的儲能需求。 而本實驗室擅長製備多孔膜並廣泛將多孔膜應用於過濾技術上，包含油水分離、蛋白質過濾及有機溶劑的分離，對於多孔膜有非常深入的了解，再結合一電池的技術，期望能將本實驗室的專業融入鋰電池膜材開發中。 因此本研究第一部分為使用交聯的聚醯亞胺(PI)來製作高熱穩定性隔離膜，在這部分利用了四種不同的製模程序製備出型態不同的多孔膜，其中利用非溶劑誘導相轉換法(NIPS)的方式可以製備出非對稱結構多孔膜，中間具有巨大孔洞表面具有相對緻密的緻密層，緻密層上具有奈米級孔洞。此緻密層可以防止枝晶鋰的生長及透過物理阻擋的方式阻擋枝晶鋰生長穿破隔離膜。而緻密層上的奈米孔洞能讓離子通過並且提供均勻的離子流，將此種隔離膜組入鋰金屬電池可以在極高的速率下充放電(10 C)並且有很好的循環穩定性，本研究證實了使用NIPS所製作出隔離膜可以擁有優異的電池充放電表現及很好的枝晶鋰抑制能力。 第二部分為利用非溶劑誘導相轉換法製作高離子傳導率的凝膠態高分子電解質，以聚乙烯醇縮丁醛 (Polyvinyl butyral, PVB)為材料，並使用聚乙二醇(PEG)進行化學改質。以此交聯聚乙烯醇縮丁醛多孔膜為基材製作出凝膠態高分子電解質，其室溫下鋰離子傳導率及鋰離子遷移數分別為1.13 mS/cm及0.67，並且於160 ℃下維持穩定的形狀。於磷酸鋰鐵半電池測試裡，可以在10 C高充放電速率下保有72 mAh/g的電容量，證明了此凝膠態高分子電解質能提升裡電池的安全性並能夠符合高速充放電的需求。 本研究第三部分為製作含離子傳遞通道高分子電解質(SPE)，透過ATRP法改質PVDF相轉換多孔膜，將具有傳導鋰離子能力的sulfonic acid改質上PVDF，形成離子傳導通道，再利用vinylene carbonate(VC)與poly(ethylene glycol) methacrylate (PEGMMA)單體配置前驅液，將前驅液注入改質完的PVDF多孔膜內組入電池內再透過in-situ聚合法形成含離子傳遞通道的SPE。其中NIPS製膜法所製出NIPS SPE因PVDF膜具有巨大孔洞，因此可含入較多前驅液，更能幫助離子傳遞，NIPS SPE再60 ℃下有優異的離子傳導率4.0×10-4 S cm-1及鋰離子傳導數0.42。將之組入LFP電池內60 ℃下可以在2 C速率下運作且具有32.1 mAh g-1的電容量。本實驗成功製成了含有離子通道的SPE並且利用in-situ聚合法增加電解質與電極界面相容性。 本研究第四部分為將高分子材料進一步延伸致矽電極黏著劑應用上，利用含有米氏酸之聚氨酯高分子作為矽電極黏著劑之研究，矽電極因其高理論電容量(4200 mAh/g)，被期待作為高容量鋰電池之負極材料，但矽容易於充放電過程中產生體積膨脹，設計適合的黏著劑可以承受矽體積膨脹產生的應力以延長電池之壽命。因此本研究利用含有米氏酸之聚胺酯高分子作為黏著劑，藉由熱處理使米氏酸產生烯酮官能基行二聚合反應以交聯或與矽產生共價鍵結再加上高分子鏈能與矽產生氫鍵藉此承受矽的體積膨脹來穩定矽電極。且因分子鏈內具有PEG鏈段能夠增加鋰離子的傳導能力，使得利用此黏著劑之矽電極能夠在0.8 C相對高充放電速率下擁有1785 mAh/g的電容量，並且於600圈後仍保要58 %的電容量。本研究成功設計了多功能的黏著劑穩定矽電極避免其電容量衰退並且提升了電極內傳遞鋰離子的能力。
並列摘要
This research focuses on the ion-conducting polymers application for the membrane materials and binder of silicon anode in lithium ion battery. The performance of lithium ion batteries mainly depends on the two parts of charge and discharge rate and capacity. The former must design a good lithium ion transfer medium, which can quickly transfer lithium ions between the positive and negative electrode to achieve fast rate performance. The latter mainly depends on the capacity of active material in the electrode. A suitable material with high theoretical capacity can store more lithium ion in the material structure. Meet these two factors and with high battery safety, will satisfy the increasing energy storage needs of human. The first part of this research is using crosslinkd polyimide to prepare thermally-stable separator. In this part, there are four porous membrane-formation methods employed to fabricate porous membranes with different morphology. The separator made with non-solvent induced separation (NIPS) has an asymmetric structure possessing a macro-void matrix and a relatively dense top layer containing nanoscale pores. This dense layer play as a barrier layer to prevent the lithium dendrite formation and penetration. The nanoscale pores on the top layer provide high ionic conductivity and homogeneous lithium ion flux. The lithium batteries employing this separator can operate at high C rate (10 C) and show high cycling stability. This thermally-stability separator has high ionic conductivity and the inhibition of lithium dendrite formation has been demonstrated. The second part of this research demonstrates the creation of lithium-ion-conducting channels in gel polymer electrolyte made of porous membranes prepared by a non-solvent-induced phase separation process. Poly (ethylene glycol)-grafted-poly(vinyl butyral) (PVB-g-PEG) is used as the raw material for preparing the porous membrane. The PEG segment appear at the pore walls create a lithium-ion-conducting channels. The PVB-g-PEG based gel polymer electrolyte exhibit high lithium ion conductivity and lithium ion transference number of 1.13 mS/cm and 0.67. Also, the discharge capacity of 72 mAh/g has been recorded for the battery employing the prepared gel polymer electrolyte at the rate of 10C. The safety issue and high charge/discharge rate ability of the PVB-g-PEG based gel polymer electrolyte have been demonstrated. Solid polymer electrolytes (SPEs) have great potential in the field of energy storage. But the SPEs usually fail to low ionic conductivity and poor interfacial contact with electrode. In the third part of this research is a novel SPE designed with ion-conducting channel is prepared via in-situ polymerization of supported membrane soaked into precursor solution (vinylene carbonate and poly(ethylene glycol) methyl ether methacrylate). The supported membrane is prepared by phase separation and modified by styrene-4-sulfonic acid to form ion-conductivy channel. The PVC-PEG polymerized by vinylene carbonate and poly(ethylene glycol) methacrylate endow ionic transportation. It is revealed that in-situ polymerization improves interfacial compatibility due to the precursor solution filled into the electrode to form a continus interface of SPE and electrode. The NIPS SPE shows high ionic conductivity of 4.0×10-4 S cm-1 at 60 ℃ as well as wide electrochemical window up to 4.5 V. The LiFePO4/SPE/Li delivers a discharge capacity of 147.3 mAh g-1 at 0.1 C and 32.1 mAh g-1 at 2 C. The cell also maintains a capacity of 125 mAh g-1 at 0.5 C with 99% coulombic efficiency after 100 cycles. The excellent performance demonstated that this novel SPE is a promosing candidate electrolyte for solid-state lithium metal battery. The fourth part of this research is using Meldrum’s acid functionalized polyurethanes as silicon anode binder. Due to the high theoretical capacity of silicon (4200 mAh/g), silicon is expected to be the anode material of high capacity lithium ion battery. But silicon suffur from the large volume expansion in lithiation/delithiation process, it may let the capacity decay. To address this issue, a crosslinkable polyurethane containing Meldrum’s acid moieties MA-PU has been prepared and utilized as the three dimensional binder for silicon anode. The ketene groups generated from the thermolysis reaction of Meldrum’s acid moieties can undergo dimerization to form crosslinked network and form chemical bonding between silicon powder and the polymer binder matrix. Due to the unique chemical structure of polyurethane, which consists of hard and soft segment, the polymer binder can buffer volume change of silicon. This network structure with strong covalent bond can also effectively restrict the volume change of silicon and maintain the capacity of silicon anode. Moreover, the polyethylene glycol (PEG) incorporate into the crosslinked binder, enhancing the lithium ion conductivity within the silicon anode. The electrode using CR_MA-PU binder retains capacity of 1371 mAh/g after 300 cycles at the current density of 755 mA/g, which is superior than using commercial poly(acrylic acid) binder (1047 mAh/g). Also, electrode using CR_MA-PU binder maintain 58% of initial capacity after 600 cycles at high current density of 3000 mA/g.
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