殷志剛，王 靜，曹敏花

高能量密度鋰離子電芯設(shè)計(jì)開(kāi)發(fā)策略*

殷志剛1,2?，王 靜1，曹敏花2

（1. 北京智行鴻遠(yuǎn)汽車有限公司，北京 102202；2. 北京理工大學(xué)，北京 100081）

提高單體電芯能量密度是鋰離子電池重要的發(fā)展方向。提高鋰離子電芯能量密度的主要途徑包括開(kāi)發(fā)高比容量和高放電電壓平臺(tái)正極材料、高比容量負(fù)極材料、高適用性電解液、選擇合適的電芯類型、開(kāi)發(fā)具有高黏結(jié)性的黏結(jié)劑及優(yōu)良的導(dǎo)電劑等。另外也可通過(guò)適當(dāng)?shù)馗纳普?fù)極配方來(lái)提高活性材料的有效占比以達(dá)到提高電芯能量密度的目的。本文概括總結(jié)了高能量密度鋰離子電芯正負(fù)極材料的研究方向，電解液的研究思路，以及導(dǎo)電劑、黏結(jié)劑、結(jié)構(gòu)和工藝路線的選擇。

高能量密度；鋰離子電芯；開(kāi)發(fā)策略

0 引 言

電動(dòng)汽車及其他可再生能源發(fā)電技術(shù)的廣泛應(yīng)用為新能源推廣帶來(lái)了巨大的商業(yè)機(jī)遇，同時(shí)也面臨能源儲(chǔ)存領(lǐng)域的挑戰(zhàn)，特別是可充電二次電池[1-7]。電動(dòng)汽車取代傳統(tǒng)化石燃料汽車進(jìn)入了發(fā)展快軌道。電動(dòng)汽車產(chǎn)業(yè)的發(fā)展壯大，要求電池包的續(xù)航里程達(dá)到500 km以上，具有更長(zhǎng)的循環(huán)壽命，更高的安全性等[8-9]。目前制約電動(dòng)汽車發(fā)展的關(guān)鍵因素是動(dòng)力鋰離子電池不能滿足電動(dòng)汽車發(fā)展所需的高能量密度、高功率密度和快充要求[10-12]。解決電動(dòng)汽車?yán)锍探箲]問(wèn)題最為有效的方法之一是采用具有更高能量密度的電芯。本文將分別從高容量和高電壓正極材料的開(kāi)發(fā)、石墨及其他高容量負(fù)極材料開(kāi)發(fā)、適合不同體系要求的電解液、正負(fù)極配比的優(yōu)化、結(jié)構(gòu)及工藝設(shè)計(jì)等方面對(duì)高能量密度鋰離子電芯開(kāi)發(fā)進(jìn)行簡(jiǎn)要概述。

1 鋰離子電芯能量密度的估算

當(dāng)前鋰離子電芯采用負(fù)極過(guò)量的設(shè)計(jì)原則。設(shè)計(jì)過(guò)程中以負(fù)/正電極容量比（negative/positive capacity ratio, NP比）作為負(fù)極過(guò)量系數(shù)。因此考慮最終電芯的容量或能量時(shí)要根據(jù)正極的實(shí)際容量作為基準(zhǔn)。假設(shè)正極質(zhì)量為p，正極的克容量發(fā)揮是p，負(fù)極的克容量發(fā)揮為n，設(shè)定所需的負(fù)極質(zhì)量為n。依據(jù)鋰離子產(chǎn)生等于鋰離子消耗即鋰離子守恒規(guī)則可得式（1）：

上式為理想化公式，鋰離子電芯必然包括銅箔、鋁箔、隔膜、電解液、導(dǎo)電劑、黏結(jié)劑、鋁殼鋼殼或鋁塑膜等密封保護(hù)部件以及輔助配件。因此實(shí)際電芯的克容量要在理論基礎(chǔ)上考慮相應(yīng)的質(zhì)量系數(shù)。以國(guó)內(nèi)某動(dòng)力三元?石墨電池為例，其電芯參數(shù)如表1所示。

表1 電芯參數(shù)表

正負(fù)極活性主材質(zhì)量分?jǐn)?shù)為= 60%，bc= 111.08 A?h/kg，則電芯質(zhì)量能量密度=bc××= 111.08 × 60% × 3.67 = 244.6 W?h/kg。計(jì)算結(jié)果與電芯測(cè)算結(jié)果十分吻合。

2 正極材料體系開(kāi)發(fā)

通過(guò)上述鋰離子電芯能量密度的計(jì)算公式可知，鋰離子電芯正負(fù)極材料的比容量直接與電芯能量密度相關(guān)，當(dāng)正極材料比容量逐漸增加時(shí)，電池的能量密度也逐漸增大[13-14]。當(dāng)前電池負(fù)極材料以石墨占比最高，負(fù)極石墨材料的比容量在360 mA?h/g左右，而正極材料的比容量要明顯低于負(fù)極的比容量[15-16]，因此提高正極材料比容量是提高電芯能量密度比較理想的選擇。

2.1 高鎳正極材料

當(dāng)前已經(jīng)成熟且應(yīng)用于車載動(dòng)力電芯上的正極材料有LiNi0.6Co0.2Al0.2O2（NCA622）及LiNi0.6Co0.2Mn0.2O2（NCM 622），該類材料配合石墨負(fù)極可以實(shí)現(xiàn)240 ～ 250 W?h/kg的能量密度，上述表1計(jì)算實(shí)例即為NCM 622正極材料。材料廠商和電池企業(yè)協(xié)同正在開(kāi)發(fā)的另一類正極材料為L(zhǎng)iNi0.8Co0.1Al0.1O2（NCA811）及LiNi0.8Co0.1Mn0.1O2（NCM 811），該類材料搭配石墨負(fù)極，以上述參數(shù)為參考，正極有效克容量發(fā)揮為197 mA?h/g，可以實(shí)現(xiàn)265 ～ 275 W?h/kg的電芯能量密度。當(dāng)前高鎳低鈷四元正極材料也引起了人們的廣泛關(guān)注，有進(jìn)一步工業(yè)化的趨勢(shì)。這類材料中鈷的含量通常在6%左右，而鎳的含量要不低于88%，因此這類材料具有更高的正極容量，電芯的能量密度也能進(jìn)一步提高[17-21]。然而高鎳正極材料有其本身的制約因素，材料容易發(fā)生相轉(zhuǎn)變、氧氣及相關(guān)氣體產(chǎn)生、陽(yáng)離子混排、離子表面致密層的形成、過(guò)渡金屬溶出、微裂紋等[22-26]。因此需要對(duì)材料進(jìn)行修飾改性。高鎳材料通過(guò)材料表面包覆、摻雜和合成穩(wěn)定的單晶材料[27-32]，是正極材料開(kāi)發(fā)的主要方向。合理調(diào)控材料包覆層能夠有效緩解正極材料的微裂紋、產(chǎn)氧、鋰鎳混排等危害材料性能的問(wèn)題。NCM（A）811材料由于鎳含量增加導(dǎo)致材料在更低的充電截止電壓發(fā)生危害材料性能的問(wèn)題，采用單晶類包覆材料能夠有效緩解上述問(wèn)題，提高設(shè)計(jì)電芯的常溫和高溫循環(huán)性能。

2.2 高鎳正極材料上限電壓提高

對(duì)于當(dāng)前已經(jīng)工業(yè)化的穩(wěn)定正極材料，提高正極材料的脫嵌鋰電位也能夠?qū)崿F(xiàn)電芯更高的能量密度[33-36]。同一電芯，充電截止電壓為4.3 V電芯與充電截止電壓4.2 V比較，電芯的能量密度可以提升5% ～ 10%；同樣的，充電截止電壓為4.4 V電芯的能量密度比充電截止電壓為4.35 V的電芯能量密度提升5% ～ 10%。當(dāng)前較高電壓電芯還處于研究階段，主要原因在于鋰鎳鈷猛（LiNiCoMn1??O2）三元體系和鈷酸鋰（LiCoO2）體系電池的穩(wěn)定電壓極限值在4.5 V左右，過(guò)高電壓將導(dǎo)致材料穩(wěn)定結(jié)構(gòu)的破壞進(jìn)而導(dǎo)致電芯在循環(huán)過(guò)程中快速衰減。本公司開(kāi)發(fā)270 W?h/kg能量密度電芯另一個(gè)方案是提高NCM622與人造石墨負(fù)極電芯體系的上限充電截止電壓，然而上限截止電壓的提高需開(kāi)發(fā)與之匹配的電解液。

2.3 新型高電壓正極材料

正極材料Li[Ni0.5Mn1.5]O4、Li[Co,Mn]O4、Li[V,Ni]O4（尖晶石結(jié)構(gòu)）和LiCoPO4雖然電壓高達(dá)5 V[37-41]，但其成熟量產(chǎn)還需要克服許多問(wèn)題。而且電壓上限值已經(jīng)接近或超過(guò)了現(xiàn)今商品化電解液的電壓窗口范圍[42]。因此需要同步開(kāi)發(fā)高電壓電解液。

2.4 小結(jié)

根據(jù)正極材料廠商的技術(shù)成熟性，當(dāng)前高能量密度電芯設(shè)計(jì)主要是對(duì)高鎳正極NCM（622和811）體系開(kāi)展設(shè)計(jì)工作。其中比較成熟的正極材料為單晶NCM622，材料具有較高的熱穩(wěn)定性和安全性?，F(xiàn)有的單晶NCM811正極材料也取得技術(shù)上的突破，其鎳含量已經(jīng)超過(guò)83%，并且實(shí)現(xiàn)了大批量的生產(chǎn)供貨。對(duì)于300 W?h/kg及以上電芯的設(shè)計(jì)開(kāi)發(fā)，主要是采用上述NCM（622和811）材料配合具有更高克容量的負(fù)極材料。

3 負(fù)極材料體系開(kāi)發(fā)

3.1 碳基材料

當(dāng)前車載動(dòng)力鋰離子電芯通常采用石墨作為負(fù)極材料，包括人造石墨、天然石墨、硬碳、軟碳以及中間相碳球等[43-45]。石墨負(fù)極材料的容量已提升至360 mA?h/g左右，接近其理論容量372 mA?h/g，因此靠提高石墨實(shí)際容量來(lái)提升電芯能量密度的策略實(shí)際意義不是很大。表2是國(guó)內(nèi)某一負(fù)極材料廠商生產(chǎn)的人造石墨物理化學(xué)性能。

表2 人造石墨材料參數(shù)

當(dāng)前的改進(jìn)主要是從提高材料的壓實(shí)密度、高低溫性能及改善材料的加工特性等方面著手。人造石墨又分為一次顆粒石墨和二次顆粒石墨。通常一次顆粒石墨循環(huán)性能不佳，因此要進(jìn)行二次造粒成二次顆粒石墨，二次顆粒石墨又難于加工。因此一次顆粒石墨和二次顆粒石墨混合使用有利于提高材料的循環(huán)性能和加工性能。人造石墨以其可靠性和安全性成為了負(fù)極材料的首選。天然石墨負(fù)極材料具有高的各向異性特點(diǎn)，且吸液和循環(huán)性能不佳。天然石墨雖然克容量高、壓實(shí)密度高、價(jià)格低廉，但是由于顆粒大小不一，表面缺陷較多，在與人造石墨的競(jìng)爭(zhēng)中處于劣勢(shì)。改善天然石墨性能思路是實(shí)現(xiàn)顆粒表面均勻包覆，降低包覆層厚度和電化學(xué)阻抗，但材料的優(yōu)化需要一些理論和工程上的技術(shù)突破。中間相碳球具有良好的倍率性能，主要用作對(duì)能量密度要求不高而對(duì)倍率性能嚴(yán)格要求的電芯負(fù)極。軟碳的壓實(shí)密度和克容量低，主要用作包覆材料來(lái)改善人造石墨和天然石墨的某些性能。硬碳由于放電電壓高，與其他材料的吻合度不高，因此很少用作動(dòng)力電芯負(fù)極。

3.2 硅基材料

單質(zhì)硅、硅的氧化物、硅的金屬化合物及硅碳復(fù)合材料[46-49]等是目前研究最多的高容量負(fù)極材料。在獲得材料高克容量的同時(shí)如何提高硅基材料的長(zhǎng)期循環(huán)性能，是這些材料需要解決的主要問(wèn)題。目前措施是對(duì)材料結(jié)構(gòu)以及復(fù)合方式進(jìn)行優(yōu)化，例如將單質(zhì)硅或硅的氧化物與具有較小體積效應(yīng)的材料進(jìn)行復(fù)合，達(dá)到緩沖硅在脫嵌鋰過(guò)程中的巨大體積效應(yīng)，從而實(shí)現(xiàn)高容量材料的可應(yīng)用性[50-53]。如硅?碳復(fù)合負(fù)極材料中，結(jié)合硅主要作為活性物質(zhì)，用于脫嵌鋰，而商用石墨類負(fù)極在脫嵌鋰過(guò)程中具有較小的體積變化和優(yōu)良的長(zhǎng)期循環(huán)性能，主要用作緩沖層，因此制備與碳類負(fù)極材料復(fù)合的硅/碳（Si/C）材料具有現(xiàn)實(shí)的意義。以硅碳負(fù)極（550 mA?h/g）與NCM811正極（197 mA?h/g）做成電芯后的能量密度能夠達(dá)到307 W?h/kg。當(dāng)前多家電芯企業(yè)開(kāi)發(fā)的300 W?h/kg能量密度的電芯均是采用富鎳正極匹配硅碳負(fù)極。然而電芯距離達(dá)到設(shè)定的電化學(xué)性能還需進(jìn)行技術(shù)及配方的改進(jìn)。

3.3 錫基和金屬氧化物材料

錫氧化物、錫鹽、錫基合金等均可以作為負(fù)極材料。錫材料理論容量（990 mA?h/g）較高、導(dǎo)電率較高、對(duì)環(huán)境敏感程度較低，但也具有明顯的體積效應(yīng)問(wèn)題。同樣，錫基材料也要與其他材料復(fù)合來(lái)應(yīng)用[54-56]。但錫基材料的實(shí)際應(yīng)用還需要科研工作者努力改進(jìn)其缺陷。具有氧化還原反應(yīng)特性的金屬氧化物在Li儲(chǔ)存和循環(huán)過(guò)程中顯示出不同于插入?脫嵌和合金化過(guò)程的特點(diǎn)。金屬氧化物的可逆容量比石墨高約2 ～ 3倍，然而首次庫(kù)倫效率低、形成的固體電解質(zhì)界面（solid electrolyte interphase, SEI）膜不穩(wěn)定、存在電壓滯后現(xiàn)象、循環(huán)穩(wěn)定性差等是該類材料需要重點(diǎn)解決的問(wèn)題。當(dāng)前，許多研究者選擇過(guò)渡金屬（Mo、Fe、Cu等）氧化物作為鋰離子電池的負(fù)極材料，主要是利用材料的低維度、多孔性結(jié)構(gòu)特性，達(dá)到實(shí)現(xiàn)鋰離子快速遷移的目的[57-60]。但是過(guò)高的比表面積也會(huì)導(dǎo)致電極材料與電解液過(guò)高的副反應(yīng)以及較低的材料壓實(shí)密度。這些缺點(diǎn)也會(huì)制約相關(guān)材料進(jìn)一步在產(chǎn)品中應(yīng)用。

3.4 小結(jié)

高能量密度電芯負(fù)極材料的選擇主要集中在硅碳復(fù)合負(fù)極材料，較成熟的含硅材料的克容量達(dá)到600 mA?h/g左右。該硅碳復(fù)合材料和富鎳NCM正極材料構(gòu)成的體系是研究的熱點(diǎn)。

4 電解液體系開(kāi)發(fā)

在電芯的性能和穩(wěn)定性方面，電解液一直居于主要位置。目前電芯能量密度的提高要求對(duì)新型鋰鹽和溶劑等進(jìn)行持續(xù)深入地研究，科研人員提出了許多改善電芯性能和安全性的方法。向電解液中加入添加劑能夠彌補(bǔ)電解液某些方面的不足，特別是在正極和負(fù)極表面形成保護(hù)膜（SEI膜）領(lǐng)域，已經(jīng)取得了顯著成果[61-65]。電解液需要與電芯體系相適應(yīng)，因此電解液配方的設(shè)計(jì)和研究必須圍繞不同的電芯體系展開(kāi)。

4.1 熱穩(wěn)定性電解液

目前動(dòng)力鋰離子電芯的電解液一般包括有機(jī)溶劑、鋰鹽和添加劑。其中甲基乙基碳酸酯（ethyl methyl carbonate, EMC）、碳酸乙烯酯（ethylene carbonate, EC）、碳酸丙烯酯（propylene carbonate, PC）、二甲基碳酸酯（dimethyl carbonate, DMC）、二乙基碳酸酯（diethyl carbonate, DEC）為常見(jiàn)的幾種有機(jī)溶劑，鋰鹽是LiPF6。研究表明，電解液中的EMC能和H2O共同作用，降低LiPF6的熱穩(wěn)定性[66]。當(dāng)電芯應(yīng)用于高溫條件，或者應(yīng)用于熱安全性較高環(huán)境時(shí)，要盡可能采用具有較低EMC含量的電解液。EC具有高的雙電常數(shù)和良好的導(dǎo)電性，能形成穩(wěn)定高質(zhì)量的SEI膜，提高電池壽命，但是常溫下EC為固態(tài)，因此高EC含量適合作為高溫電解液。PC具有好的雙電常數(shù)和低的熔點(diǎn)，是低溫電解液溶劑的首選。其缺點(diǎn)是形成的SEI膜質(zhì)量不佳，另外PC也容易在嵌鋰過(guò)程中與鋰一起發(fā)生共嵌入，導(dǎo)致石墨剝離和石墨顆粒的破裂[67-71]。因此電芯設(shè)計(jì)開(kāi)發(fā)要考慮溶劑的選擇及配比以達(dá)到電解液的熱穩(wěn)定性。研究指出電解液中添加碳酸亞乙烯酯（vinylene carbonate, VC）能在正負(fù)極表面形成致密的保護(hù)膜，改善高溫性能。另外有機(jī)硅化合物R4Si添加劑會(huì)與電解液中的無(wú)機(jī)小分子H2O和HF發(fā)生反應(yīng)，阻止H2O和HF與SEI膜發(fā)生危害負(fù)極性能的副反應(yīng)，從而改善電芯的熱穩(wěn)定性。電解液廠家根據(jù)客戶需要可以通過(guò)添加1,3-丙烷磺內(nèi)酯（1,3-propane sultone, PS）、硫酸乙烯酯（1,3,2-dioxathiolane 2,2-dioxide, DTD）、雙氟代磺酰亞胺鋰［lithium bis(fluorosulfonyl)imide, LiFSI］等不同添加劑[72-81]，改善電解液性能以滿足相關(guān)產(chǎn)品需要。

4.2 高壓電解液

高壓電解液應(yīng)具有較高的電化學(xué)窗口，通常在4.5 V以上。砜類電解液電化學(xué)窗口超過(guò)5 V，是鋰離子電芯潛在的高電壓電解液之一。這類電解液通常是碳酸酯類與砜類一起作為共溶劑，目的是優(yōu)化砜類與正極材料的兼容性[82-84]。另一類電解液是腈類電解液，其優(yōu)點(diǎn)是電化學(xué)窗口寬，如單腈類抗氧化穩(wěn)定性可達(dá)到7 V，應(yīng)用于5 V高電壓鋰離子電芯中不易發(fā)生分解。腈類電解液與碳酸酯類電解液相比，在高電壓下更加穩(wěn)定，在低溫下具有更出色的性能[85-87]。氟原子具有大的電負(fù)性，弱的極性，氟代溶劑的化學(xué)穩(wěn)定性也較好，在高電壓電解液應(yīng)用方面具有很大的潛力[88-90]。具有低揮發(fā)性、優(yōu)異阻燃性、較寬電化學(xué)窗口的離子液體是最近的研究熱點(diǎn)[91]。但這些高電壓電解液還沒(méi)有大量應(yīng)用于工業(yè)生產(chǎn)中。

4.3 小結(jié)

當(dāng)前商業(yè)化電解液開(kāi)發(fā)以常規(guī)EC、DEC、EMC溶劑進(jìn)行適當(dāng)比例混合，主要研究方向是向電解液中添加電解液添加劑以滿足不同體系的需要。高容量體系電解液添加劑有VC、LiPO2F2、FEC、PS等。電解液廠商根據(jù)客戶需求設(shè)計(jì)并由客戶進(jìn)行驗(yàn)證。

5 正負(fù)極輔材及配比選擇

鋰離子電芯正極混料主要采用油性N-甲基吡咯烷酮（N-methylpyrrolidone, NMP）體系，負(fù)極主要采用水性體系。因此，對(duì)正負(fù)極要分別選擇合適的導(dǎo)電劑、黏結(jié)劑以最大化提高正負(fù)極配比中活性物質(zhì)含量，進(jìn)而提高電芯整體容量，是當(dāng)前高能量密度電芯研究的方向。

5.1 導(dǎo)電劑的選擇

導(dǎo)電劑的作用是在活性物質(zhì)之間、活性物質(zhì)與集流體之間起到收集微電流，減小電極的接觸電阻，加快電子的移動(dòng)速率，同時(shí)導(dǎo)電劑也應(yīng)該能夠提高鋰離子在電極材料中的遷移速率，達(dá)到提高電極充放電效率的目的[92-93]。目前導(dǎo)電劑主要分為纖維狀和顆粒狀兩種。纖維狀導(dǎo)電劑的典型代表是碳納米纖維和碳納米管，這兩種材料普遍具有較大的長(zhǎng)徑比，有利于形成導(dǎo)電網(wǎng)格，也具有一定的黏結(jié)作用，這有利于提高活性物質(zhì)與導(dǎo)電劑之間的黏結(jié)性。纖維狀導(dǎo)電劑應(yīng)用于三元材料體系，既可以減少導(dǎo)電劑添加量又能減少黏結(jié)劑的使用量，能夠進(jìn)一步提高電池的能量密度[94-97]。顆粒狀導(dǎo)電劑的代表是乙炔黑、炭黑及石墨等，這些材料的成本低并且易分散，是鋰離子電池正負(fù)極材料導(dǎo)電劑的不錯(cuò)選擇。然而顆粒狀導(dǎo)電劑與活性物質(zhì)之間是點(diǎn)對(duì)點(diǎn)接觸，導(dǎo)電性不如鏈狀導(dǎo)電劑，因此添加量要在2.5% ～ 4%之間，使得活性物質(zhì)含量相對(duì)較低[92-93]?？梢酝ㄟ^(guò)添加纖維狀和顆粒狀混合導(dǎo)電劑改變電極的導(dǎo)電網(wǎng)絡(luò)來(lái)改善電極的性能[94,98-101]。負(fù)極材料通常采用炭黑作為導(dǎo)電劑，正極材料通常采用碳納米管及炭黑為導(dǎo)電劑。在導(dǎo)電劑選擇時(shí)可以對(duì)極片通過(guò)極片電阻儀測(cè)試分析，儀器測(cè)量的體電阻用于分析極片導(dǎo)電劑配比和導(dǎo)電劑添加類型是否為最佳選擇。

5.2 黏結(jié)劑的選擇

黏結(jié)劑通常是一類高分子化合物，是電極片中的非活性組分，是制備鋰離子電芯必備的重要材料之一。鋰離子電芯專用黏結(jié)劑需要具備黏結(jié)性和導(dǎo)電性特點(diǎn)。通常狀況下，對(duì)鋰離子電芯專用黏結(jié)劑的要求體現(xiàn)在黏結(jié)力、柔韌性、耐堿性、親水性、電導(dǎo)率等方面[102-104]。當(dāng)前廣泛應(yīng)用的鋰離子電芯黏結(jié)劑主要有三大類：聚偏氟乙烯（polyvinylidene fluoride，PVDF）、丁苯橡膠（styrene butadiene rubber，SBR）乳液和羧甲基纖維素（carboxymethyl cellulose，CMC）[105-107]。另外，聚丙烯腈（polyacrylonitrile，PAN）、聚丙烯酸（polyacrylic acid，PAA）等作為主要成分的黏結(jié)劑也占有一定市場(chǎng)份額[108-110]。好的黏結(jié)劑不僅有利于鋰離子電芯能量密度的提高，對(duì)鋰離子電芯內(nèi)阻也有明顯的降低作用，對(duì)電芯的電化學(xué)性能也具有重要的影響。石墨負(fù)極材料通常采用CMC+SBR組合水性黏結(jié)劑，其中CMC的主要作用是增稠劑，SBR起黏結(jié)劑作用。正極材料通常采用PVDF黏結(jié)劑。應(yīng)用研究發(fā)現(xiàn)，水溶性黏結(jié)劑的添加量在2%左右為宜，油性黏結(jié)劑的添加量在1.5% ～ 3%之間。在黏結(jié)劑選擇時(shí)會(huì)通過(guò)極片電阻儀對(duì)極片進(jìn)行測(cè)試分析，儀器測(cè)量的面電阻用于分析極片黏結(jié)劑配比是否為最佳選擇。

5.3 小結(jié)

高能量密度電芯的設(shè)計(jì)過(guò)程中導(dǎo)電劑的選擇主要在碳納米管和超導(dǎo)炭黑（super P, SP）領(lǐng)域。碳納米管的使用需要注意提高其分散性以避免在漿料制備過(guò)程中再次團(tuán)聚。當(dāng)前碳納米管需要生產(chǎn)廠家事先分散到水性或油性溶劑中并且需要加入分散劑保持納米管的分散性。在保證分散效果的前提下，少加入或不加入分散劑能夠提高電芯能量密度。而石墨類黏結(jié)劑主要以SBR配合CMC使用，硅碳類可選用PAA作為黏結(jié)劑。

6 結(jié)構(gòu)及工藝設(shè)計(jì)

電芯的外觀結(jié)構(gòu)設(shè)計(jì)直接關(guān)系到電芯的空間有效利用率，進(jìn)而影響到電芯的能量密度。從結(jié)構(gòu)的角度要提高電芯的能量密度，應(yīng)該選擇薄而輕的軟包鋁塑膜作為電芯外殼。從電芯內(nèi)部的制作方式考慮，隔膜往復(fù)Z字折疊式比卷繞多極耳方式要好。在不改變混料配方的前提下（即降低電芯無(wú)效重量）可以從以下幾點(diǎn)提高電芯的能量密度：①提高正、負(fù)極極片的面密度，減少裸電芯的疊片層數(shù)或卷繞層數(shù)，避免因?qū)訑?shù)過(guò)多導(dǎo)致隔膜和導(dǎo)電箔材使用量增加；②使用更薄的銅鋁箔材、隔膜和膠紙等；③減小軟包電芯的頂側(cè)封邊寬或縮短其他電芯蓋帽和裸電芯間的距離；④減小正負(fù)極片寬度差和隔膜與極片間的寬度差；⑤盡量縮短極片的非敷料區(qū)長(zhǎng)度；⑥設(shè)計(jì)電芯外殼幾何尺寸，使得充分利用電芯外殼空間，提高電芯外殼的空間利用率等[111-112]。本公司開(kāi)發(fā)的電芯采用Z字折疊式軟包方式，最大程度提高電芯能量密度。

7 總 結(jié)

開(kāi)發(fā)具有高容量的正負(fù)極材料已成為提高電芯能量密度的最有效方法，研究開(kāi)發(fā)高鎳正極材料及新型寬工作電壓窗口的電極材料是提高電芯能量密度的有效途徑。碳基材料主要是在提高材料壓實(shí)和改善加工性等方面入手。具有大克容量的硅系、錫系、過(guò)渡金屬氧化物負(fù)極材料，需要尋找能有效緩解體積膨脹的方法和策略。尋找穩(wěn)定可靠的新型高電壓電解液是鋰離子電芯材料領(lǐng)域的重要發(fā)展方向。正負(fù)極材料配比的進(jìn)一步改進(jìn)也能適當(dāng)提高電芯的容量或性能。設(shè)計(jì)研究更加合理的結(jié)構(gòu)及工藝也是提高電芯能量密度可選方法。根據(jù)以上設(shè)計(jì)思想，本公司已經(jīng)成功完成能量密度為240 W?h/kg電芯開(kāi)發(fā)工作，產(chǎn)品已經(jīng)在電動(dòng)汽車上使用。能量密度為270 W?h/kg的電芯也已經(jīng)到中試階段，樣品也已經(jīng)在相關(guān)企業(yè)進(jìn)行測(cè)試，結(jié)果表明電芯能量密度處于領(lǐng)先水平。對(duì)于300 W?h/kg電芯開(kāi)發(fā)應(yīng)選擇高鎳（811）正極材料配合碳納米管導(dǎo)電劑、PVDF黏結(jié)劑作為正極體系，面密度控制在390 g/m2左右。選擇硅碳復(fù)合負(fù)極材料配合SP導(dǎo)電劑和PAA黏結(jié)劑作為負(fù)極體系，面密度控制在155 g/m2左右。采用軟包疊片電芯設(shè)計(jì)思路。采用EC + EMC溶劑含有LiPO2F2、FEC添加劑的電解液。電芯長(zhǎng)×寬×高尺寸應(yīng)該不小于320mm×100 mm×10mm。應(yīng)選擇具有陶瓷涂層的隔膜；考慮加工性，鋁箔材應(yīng)該在12 μm左右；銅箔材在6 μm左右。

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Design and Development Strategy of High Energy Density Lithium-Ion Cell

YIN Zhi-gang1,2, WANG Jing1, CAO Min-hua2

(1. Beijing Idrive Automotive Co, Ltd., Beijing 102202, China; 2. Beijing Institute of Technology, Beijing 100081, China)

Increasing the energy density of single cell is an important development direction of lithium-ion battery. In summary, the main ways to improve the energy density of lithium-ion cell are development of high specific capacity and high discharge voltage platform cathode materials, high specific capacity anode materials, high applicability electrolyte, selection of appropriate cell types, development of binders with high adhesive properties and excellent conductive agents. In addition, the effective proportion of active materials can be increased by appropriately improving the formula of positive and negative electrodes to achieve the purpose of increasing the energy density of the cell. In this paper, the research directions of cathode materials and anode materials for high energy density lithium-ion cell, the research ideas of electrolyte, the reasonable selection of conductive agent and binder agent, the selection of cell structure and process route, were briefly summarized.

energy density; lithium-ion cell; development strategy

TK02；TM912

A

10.3969/j.issn.2095-560X.2021.03.010

2095-560X（2021）03-0248-10

2021-01-25

2021-03-23

國(guó)家自然科學(xué)基金面上項(xiàng)目（21872008）

殷志剛，E-mail：hbtsyzg@163.com

殷志剛（1978-），男，博士，高級(jí)工程師，主要從事高能量密度電池的開(kāi)發(fā)和相關(guān)機(jī)理研究。

曹敏花（1969-），女，教授，博士生導(dǎo)師，主要從事鋰離子電池和燃料電池中材料制備與電化學(xué)問(wèn)題研究。