介電電容器是一種重要的電子器件[1] 聚合物介電電容器易加工、擊穿場(chǎng)強(qiáng)高、儲(chǔ)能性能高和損耗較低，得到了廣泛的應(yīng)用[2~4] 目前制造商用介電薄膜電容器的主要材料，是雙軸拉伸聚丙烯(BOPP)材料 這種材料的擊穿場(chǎng)強(qiáng)高達(dá)700 MV·m-1，但是其可釋放能量密度只約為2 J·cm-3，難以滿足使用要求[5,6] 因此，提高介電聚合物薄膜的儲(chǔ)能性能是當(dāng)前的研究重點(diǎn)

高分子聚合物具有優(yōu)異的可加工性、良好的柔韌性、較高的擊穿場(chǎng)強(qiáng)和較低的介電損耗，且能大面積成膜[7,8] 高分子聚合物，主要有聚丙烯(PP)，聚乙烯(PE)，聚甲基丙烯酸甲酯(PMMA)，聚碳酸酯(PC)，聚酰亞胺(PI)以及聚偏氟乙烯(PVDF)[9,10] 電介質(zhì)薄膜的儲(chǔ)能密度可表示為[11]

Ue=∫DrDmaxEDd

(1)

此式表明，電介質(zhì)材料的擊穿場(chǎng)強(qiáng)(Eb)、剩余電位移強(qiáng)度(Dr)和最大電位移(Dmax)是影響電介質(zhì)薄膜儲(chǔ)能密度的關(guān)鍵因素 因此，提高電介質(zhì)材料儲(chǔ)能密度的關(guān)鍵，是降低Dr和提高其擊穿場(chǎng)強(qiáng)和Dmax PP、PC等線性介電聚合物雖然具有較大的擊穿場(chǎng)強(qiáng)和較大的充放電速率，但是其非極性本質(zhì)使其極化值較低、Dmax小和可釋放儲(chǔ)能密度較低 以PVDF為代表的鐵電聚合物極化值較高，能提供較高的可釋放能量密度[12,13] 但是，PVDF固有的高介電損耗使其充放電效率較低 這意味著，在能量轉(zhuǎn)換過程中很大一部分轉(zhuǎn)換為熱能，使電容器升溫和失效，不利于電容器的安全運(yùn)行[14] 減少PVDF能量損失的方法，包括納米復(fù)合、化學(xué)改性和聚合物共混等[15~17] 其中聚合物共混策略是一種既簡(jiǎn)單又經(jīng)濟(jì)有效的方法，能在不犧牲PVDF基聚合物可釋放儲(chǔ)能密度的情況下降低其能量損失[18] 線性介電聚合物/PVDF二元共混物受到了極大的關(guān)注 這種二元共混物，在理論上是一種低損耗線性聚合物 此外，線性介電聚合物能減弱相鄰PVDF鐵電體之間的耦合域，最大限度地減少鐵電損失和能量損失 Yang等[18]將ABS與PVDF共混制備出均勻的復(fù)合薄膜，實(shí)現(xiàn)了性能的優(yōu)化 本文選用具有優(yōu)異的機(jī)械性、耐化學(xué)性、熱穩(wěn)定性的聚酰亞胺(PI)，將共沉淀法和熱壓法相結(jié)合制備PI/PVDF全有機(jī)復(fù)合薄膜，研究其儲(chǔ)能性能

1 實(shí)驗(yàn)方法1.1 薄膜的制備

圖1給出了全有機(jī)復(fù)合薄膜的制備流程 制備步驟：(1)將一定量的聚偏氟乙烯(PVDF)粉末和熱塑型聚酰亞胺(PI)加入容積為4 mL的N,N-二甲基甲酰胺(DMF，分析純)中，將其置于65℃的加熱臺(tái)上使其完全溶解；(2) 在500 mL燒杯中倒入200 mL純水及200 mL無(wú)水乙醇，用磁力攪拌器攪拌，轉(zhuǎn)速為550 r/min；(3) 將步驟(1)中的混合溶液緩慢滴加入步驟(2)的燒杯中，收集析出的絮狀物；(4) 將絮狀物抽濾(SHZ-D(III)循環(huán)水式多用真空泵)、烘干(烘箱，DZF-6020)后熱壓(熱壓機(jī)，YLJ-HP300)，烘干溫度為60℃，時(shí)間為12 h，熱壓溫度為155℃，熱壓時(shí)間為2 h 熱壓后得到全有機(jī)復(fù)合薄膜

圖1



圖1PI/PVDF復(fù)合薄膜的制備流程

Fig.1Preparation of PI/PVDF composite film

改變PI的加入量，可制備出不同配比的全有機(jī)復(fù)合薄膜 PI的加入量(質(zhì)量分?jǐn)?shù))分別為PVDF的0%，5%，10%，15%，20%，100%，將制備出的樣品分別標(biāo)記為0/100，5/95，10/90，15/85，20/80，100/0

1.2 性能表征

用場(chǎng)發(fā)射掃描電子顯微鏡(SEM，Hitachi SU8010)分析復(fù)合薄膜的截面；用X-射線衍射(XRD)儀表征不同薄膜的晶體結(jié)構(gòu)，測(cè)試條件為：Cu-Kα靶，波長(zhǎng)0.154 nm，掃描角2θ的變化范圍為5°~60°，掃描速率為0.1 (°)·s-1 用差示掃描量熱法(DSC7020)記錄復(fù)合材料的熔融與結(jié)晶行為，溫度測(cè)試范圍為90℃~190℃，加熱速率為10℃·min-1 用阻抗分析儀(HP4294，Agilent)測(cè)試復(fù)合材料的室溫介電性能 用介電耐壓測(cè)試儀測(cè)試復(fù)合材料的擊穿場(chǎng)強(qiáng) 用鐵電測(cè)試系統(tǒng)(TF2000，Trek 10/10B-HS)測(cè)試位移-電場(chǎng)(D-E)回線

2 結(jié)果和討論2.1 全有機(jī)復(fù)合薄膜的微觀結(jié)構(gòu)

圖2給出了PI/PVDF全有機(jī)復(fù)合薄膜的截面SEM照片 從圖2a~e可見，用該方法制備的全有機(jī)薄膜的厚度約為18 μm 與純PVDF薄膜的截面(圖2a)相比，PI的加入沒有產(chǎn)生明顯的空隙和孔洞(圖2b~e)，復(fù)合薄膜的結(jié)構(gòu)依舊比較致密，驗(yàn)證了共沉淀法與熱壓法相結(jié)合的優(yōu)越性 增大PI的添加量則PI線性介電材料的特征更加明顯，可釋放儲(chǔ)能密度急劇降低，因此只討論P(yáng)I在低添加量時(shí)的情況 圖2f~i給出了20/80組分的SEM元素映射圖，C元素和F元素屬于PVDF，O元素和N元素屬于PI 與預(yù)期的一樣，O元素和N元素在20/80復(fù)合材料的斷口處的分散相當(dāng)均勻 綜上所述，SEM測(cè)試結(jié)果表明，共沉淀法與熱壓法相結(jié)合制備的全有機(jī)復(fù)合薄膜結(jié)構(gòu)均勻、致密

圖2



圖2PI/PVDF復(fù)合薄膜截面的SEM形貌和(f-i)20/80組分的SEM元素映射圖

Fig.2Cross-sectional SEM of PI/PVDF composite film (a~e) and SEM element mapping of the 20/80 component (f~i)

PVDF薄膜的性能與其晶相結(jié)構(gòu)緊密相關(guān)，PVDF 主要有α、β與γ相，其中α和γ相極性較小，鐵電損耗較小，適用于儲(chǔ)能領(lǐng)域[19~21] 全有機(jī)復(fù)合薄膜的晶相結(jié)構(gòu)，如圖3所示 可以看出，在純PVDF衍射譜的18.4°和19.8°處出現(xiàn)了兩個(gè)衍射強(qiáng)峰，分別對(duì)應(yīng)(020)晶面和(021)晶面的α相，說(shuō)明純PVDF具有以α相為主的相結(jié)構(gòu) 由PI/PVDF共混膜的XRD譜可見，PI的加入使18.4°處的衍射峰分裂成17.7°和18.5°這兩個(gè)小衍射峰，分別歸屬于(100)晶面的α相衍射和(020)晶面的γ相衍射 PI的加入對(duì)PVDF薄膜的相結(jié)構(gòu)沒有較大影響，復(fù)合薄膜依舊是α相為主導(dǎo)，意味著復(fù)合薄膜應(yīng)該較好的儲(chǔ)能性能

圖3



圖3PI/PVDF復(fù)合薄膜的XRD譜

Fig.3XRD patterns of PI/PVDF composite film

為了進(jìn)一步分析樣品的結(jié)晶性能，DSC測(cè)試結(jié)果如圖4a所示 從DSC曲線可觀察到全有機(jī)復(fù)合薄膜的熔融峰(Tc)約為167℃ α-PVDF和β-PVDF的Tc均約為167℃，可見DSC測(cè)試不能完全區(qū)分PVDF薄膜的晶相，只能作為XRD測(cè)試的輔助[22,23] 結(jié)合上述XRD測(cè)試，可見全有機(jī)復(fù)合薄膜均是以α相為主導(dǎo) 隨著PI加入量的增加共混物的Tc呈略微單調(diào)的上升趨勢(shì)，表明PI在PVDF內(nèi)部的相互作用促進(jìn)了PVDF的成核，分子鏈的纏結(jié)作用使Tc的略微上升 分子鏈相互作用引起的阻礙效應(yīng)，也反映在結(jié)晶度值上

圖4



圖4PI/PVDF復(fù)合薄膜的DSC曲線和結(jié)晶度

Fig.4DSC curve and crystallinity of PI/PVDF composite film (a) The melting DSC traces of samples, (b) Crystallinity of samples

根據(jù)DSC測(cè)試結(jié)果，可計(jì)算材料的結(jié)晶度[24]

Xc=?HC?H×100%

(2)

其中?HC為DSC測(cè)試中獲得的材料的熔融熱焓值，?H為100%結(jié)晶的PVDF的熔融熱焓值(此處為純?chǔ)?PVDF的熔融熱焓值93.07 J·g-1) 如圖4b所示，隨著PI含量的提高全有機(jī)復(fù)合薄膜的結(jié)晶度呈明顯降低的趨勢(shì) 例如，純PVDF的結(jié)晶度為41.8%，20/80復(fù)合薄膜的結(jié)晶度僅為36.8%

2.2 全有機(jī)復(fù)合薄膜的電學(xué)性能

圖5a給出了PI/PVDF復(fù)合薄膜的室溫相對(duì)介電常數(shù)(εr)和介電損耗正切角(tanδ)隨頻率的變化曲線 用該方法制備的純PVDF薄膜其室溫介電常數(shù)約為13(@1k Hz)，隨著PI添加量的增加復(fù)合薄膜的介電常數(shù)略降低 其原因是，PI的介電常數(shù)較低而PVDF的介電常數(shù)主要受晶相與結(jié)晶度影響，結(jié)晶度的降低使對(duì)應(yīng)的介電常數(shù)降低 PI的加入對(duì)tanδ 的影響微弱，因?yàn)檫@種全有機(jī)薄膜具有較為致密的結(jié)構(gòu) 圖5b給出了用Weibull分布法計(jì)算的PI/PVDF全有機(jī)復(fù)合薄膜的擊穿場(chǎng)強(qiáng) Weibull分布反映薄膜發(fā)生介電擊穿的概率，其計(jì)算方法為[25]

圖5



圖5PI/PVDF復(fù)合薄膜的介電和鐵電性能

Fig.5Dielectric and ferroelectric performance of PI/PVDF composite film (a) room temperature dielectric constant εr and dielectric loss tanδ versus frequency, (b) weibull distribution, (c) D-E loops, (d) discharged energy density and charge-discharge efficiencies

PE=1-e-(EEb)β

(3)

其中E為測(cè)試時(shí)薄膜的擊穿強(qiáng)度，P為在E下發(fā)生擊穿的概率，Eb為擊穿概率為63.2%時(shí)電場(chǎng)強(qiáng)度的大小，β為擬合直線斜率 由圖5b可見，純PVDF的擊穿場(chǎng)強(qiáng)Eb為354 MV·m-1，PI的加入略微降低了薄膜的擊穿場(chǎng)強(qiáng)，但是影響不大，因?yàn)榈吞砑恿繒r(shí)PI與PVDF良好的結(jié)合性，材料的致密度較高

圖5c給出了PI/PVDF全有機(jī)復(fù)合薄膜在300 MV·m-1電場(chǎng)下的D-E曲線 可以看出，PI的加入使剩余電位移降低，最大電位移增大，且在PI/PVDF為5/95時(shí)達(dá)到飽和最大電位移 在300 MV·m-1電場(chǎng)下5/95全有機(jī)復(fù)合薄膜的Dr為1.3 μC·cm-2，Dmax為7.2 μC·cm-2，而在相同情況下純PVDF薄膜的Dr為2.4 μC·cm-2，Dmax為6.5 μC·cm-2 Dr的減小反映了全有機(jī)復(fù)合薄膜內(nèi)部較低的鐵電損耗和電導(dǎo)損耗，因?yàn)镻I和PVDF之間強(qiáng)的相互作用和PI較低的鐵電損耗 XRD測(cè)試結(jié)果表明，復(fù)合薄膜中還有少量的γ相結(jié)構(gòu)，有利于抑制薄膜的鐵電損耗 因此，添加PI使Dr明顯減小[22] 同時(shí)，PI的加入提高了Dmax 根據(jù)單極D-E曲線計(jì)算出PI/PVDF全有機(jī)薄膜的儲(chǔ)能密度、可釋放儲(chǔ)能密度及充放電效率，結(jié)果在圖5d中給出 純PVDF在300 MV·m-1時(shí)可釋放儲(chǔ)能密度約為4.67 J·cm-3，5/95復(fù)合薄膜在300 MV·m-1時(shí)可釋放儲(chǔ)能密度可達(dá)6.52 J·cm-3，是純PVDF的1.4倍 同時(shí)，PI/PVDF全有機(jī)復(fù)合薄膜的放電效率優(yōu)于純PVDF，在300 MV·m-1內(nèi)PI/PVDF全有機(jī)復(fù)合薄膜的充放電效率可保持在50%以上，而純PVDF的充放電效率在200 MV·m-1就急劇下降到50% 例如，在300 MV·m-1時(shí)5/95復(fù)合薄膜的充放電效率為50.4%，而純PVDF的充放電效率僅為38.21% PI/PVDF全有機(jī)復(fù)合薄膜的高充放電效率，伴隨著較高的放電能量密度

3 結(jié)論

(1) 將共沉淀法與熱壓法相結(jié)合制備的PI/PVDF薄膜，具有致密的結(jié)構(gòu)

(2) 添加量較低的PI分散性良好且具有界面極化效應(yīng)，加入PI使薄膜的εr略微降低、tanδ的變化較小

(3) PI的加入提高了PVDF薄膜的可釋放儲(chǔ)能密度，PI添加量為5%的復(fù)合薄膜在300 MV·m-1電場(chǎng)下可釋放儲(chǔ)能密度達(dá)到6.52 J·cm-3 在300 MV·m-1條件下5/95復(fù)合薄膜的充放電效率為50.4%

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DOIPMID [本文引用: 1] " />

This review provides a detailed overview on the latest developments in the design and control of the interface in polymer based composite dielectrics for energy storage applications. The methods employed for interface design in composite systems are described for a variety of filler types and morphologies, along with novel approaches employed to build hierarchical interfaces for multi-scale control of properties. Efforts to achieve a close control of interfacial properties and geometry are then described, which includes the creation of either flexible or rigid polymer interfaces, the use of liquid crystals and developing ceramic and carbon-based interfaces with tailored electrical properties. The impact of the variety of interface structures on composite polarization and energy storage capability are described, along with an overview of existing models to understand the polarization mechanisms and quantitatively assess the potential benefits of different structures for energy storage. The applications and properties of such interface-controlled materials are then explored, along with an overview of existing challenges and practical limitations. Finally, a summary and future perspectives are provided to highlight future directions of research in this growing and important area.

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Zhu L.

Exploring strategies for high dielectric constant and low loss polymer dielectrics

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DOIPMID [本文引用: 1] class="outline_tb" " />

This review provides a detailed overview on the latest developments in the design and control of the interface in polymer based composite dielectrics for energy storage applications. The methods employed for interface design in composite systems are described for a variety of filler types and morphologies, along with novel approaches employed to build hierarchical interfaces for multi-scale control of properties. Efforts to achieve a close control of interfacial properties and geometry are then described, which includes the creation of either flexible or rigid polymer interfaces, the use of liquid crystals and developing ceramic and carbon-based interfaces with tailored electrical properties. The impact of the variety of interface structures on composite polarization and energy storage capability are described, along with an overview of existing models to understand the polarization mechanisms and quantitatively assess the potential benefits of different structures for energy storage. The applications and properties of such interface-controlled materials are then explored, along with an overview of existing challenges and practical limitations. Finally, a summary and future perspectives are provided to highlight future directions of research in this growing and important area.

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Martins P, Lopes A C, Lanceros-Mendez S.

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Zhu L.

Exploring strategies for high dielectric constant and low loss polymer dielectrics

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PMID

Polymer dielectrics having high dielectric constant, high temperature capability, and low loss are attractive for a broad range of applications such as film capacitors, gate dielectrics, artificial muscles, and electrocaloric cooling. Unfortunately, it is generally observed that higher polarization or dielectric constant tends to cause significantly enhanced dielectric loss. It is therefore highly desired that the fundamental physics of all types of polarization and loss mechanisms be thoroughly understood for dielectric polymers. In this Perspective, we intend to explore advantages and disadvantages for different types of polarization. Among a number of approaches, dipolar polarization is promising for high dielectric constant and low loss polymer dielectrics, if the dipolar relaxation peak can be pushed to above the gigahertz range. In particular, dipolar glass, paraelectric, and relaxor ferroelectric polymers are discussed for the dipolar polarization approach.

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Nanjing University of Aeronautics and Astronautics, 2017

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核殼結(jié)構(gòu)納米纖維摻雜PMMA/PVDF基復(fù)合介質(zhì)的儲(chǔ)能特性研究

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2021