1、鋰離子電池負(fù)極材料 碳包覆二氧化錫,報(bào)告人：張飛虎 專(zhuān)業(yè)：無(wú)機(jī)化學(xué),SnO2/C新成果,鋰離子電池的特點(diǎn),鋰離子電池具有以下特點(diǎn): (1) 工作電壓高。鋰離子電池的電壓一般在3.6 V ,是鎳鎘、鎳氫電池工作電壓的3 倍。 (2) 能量密度高。鋰離子電池的能量密度應(yīng)達(dá)到180 Wh/kg ,是同等質(zhì)量下鎳鎘電池的3 倍,鎳氫電池的1.5 倍。 (3) 循環(huán)壽命長(zhǎng)。鋰離子電池通常具有1 000多次的循環(huán)壽命,是鎳鎘、鎳氫電池的2 倍。 (4) 自放電率小。鋰離子電池在首次充電的過(guò)程中會(huì)在碳負(fù)極上形成一層固體電解質(zhì)鈍化膜(SEI) ,它只允許離子通過(guò)而不允許電子通過(guò),因此可以較好地防止自放電,使得

2、貯存壽命增長(zhǎng),容量衰減減小。一般其月自放電率為2 %3 % ,遠(yuǎn)低于鎳鎘電池(25 %30 %) 及鎳氫電池(20 %) 。,(5) 允許溫度范圍寬,具有優(yōu)良的高低溫放電性能,可在- 20 + 60 之間工作。 (6) 無(wú)環(huán)境污染。鋰離子電池中不含有鉛、鎘等有毒、有害物質(zhì),是真正的綠色環(huán)保電池。 (7) 無(wú)記憶效應(yīng)。記憶效應(yīng)指電池用電未完時(shí)再充電時(shí)充電量會(huì)下降,而鋰離子電池不存在鎳鎘、鎳氫電池的記憶效應(yīng),可隨時(shí)充放電,而不影響其容量和循環(huán)壽命。 由于鋰離子電池具有以上優(yōu)良的性能,因此它在便攜式電子設(shè)備、電動(dòng)汽車(chē)、空間技術(shù)、國(guó)防工業(yè)等多方面均展示了廣闊的應(yīng)用前景和潛在的巨大經(jīng)濟(jì)效益,被稱(chēng)為21

3、世紀(jì)的理想電源。,鋰離子電池與其他電池的參數(shù)對(duì)比,應(yīng)用領(lǐng)域,鋰離子電池因其具有優(yōu)良的特性而成為目前綜合性能較好的電池體系，并廣泛地應(yīng)用于許多高能便攜式電子設(shè)備上。民用領(lǐng)域已從信息產(chǎn)業(yè)(移動(dòng)電話、筆記本電腦等)擴(kuò)展到能源交通(電動(dòng)汽車(chē)等)。而在國(guó)防軍事領(lǐng)域，鋰離子電池則涵蓋了海(潛艇、水下機(jī)器人)、陸(單兵系統(tǒng)、陸軍戰(zhàn)車(chē)、軍用通信設(shè)備)、空(無(wú)人機(jī))、天(衛(wèi)星、飛船)等諸多兵種，成為現(xiàn)代和未來(lái)軍事裝備不可缺少的重要能源。隨著各國(guó)軍隊(duì)向信息化、自動(dòng)化和遠(yuǎn)程控制的作戰(zhàn)方向轉(zhuǎn)變，未來(lái)鋰離子動(dòng)力電池也將獲得更大規(guī)模的使用。,近年來(lái)，多功能便攜式和高能量電子設(shè)備的消費(fèi)量逐年劇增(手機(jī)、隨身聽(tīng)、筆記本電腦、

4、攝像機(jī)等)。據(jù)中國(guó)信息產(chǎn)業(yè)部統(tǒng)計(jì)，截至2005年1O月底，中國(guó)移動(dòng)電話用戶已經(jīng)超過(guò)383億，每部手機(jī)一般都配有兩塊電池，即具有超過(guò)76億塊電池的市場(chǎng)，如若每塊電池使用負(fù)極材料6 g來(lái)估算，則需要負(fù)極材料約4600 t。目前，小型鋰離子電池市場(chǎng)還處于持續(xù)快速增長(zhǎng)階段，1994年鋰離子電池的全球產(chǎn)量為012億顆，到2005年則上升為2555億顆(在過(guò)去12年中增加了200多倍)，預(yù)計(jì)2010年全球年需求量將達(dá)到35億顆以上。由此可見(jiàn)鋰離子電池的市場(chǎng)前景非常廣闊。,鋰離子電池簡(jiǎn)介,鋰離子二次電池于20 世紀(jì)90 年代初由日本SONY公司率先研制成功并實(shí)現(xiàn)商品化。所謂鋰離子電池是指分別用兩個(gè)能可逆地嵌

5、入和脫嵌鋰離子的化合物作為正負(fù)極構(gòu)成的二次電池。電池在充電時(shí),Li + 從正極中脫出,通過(guò)電解液和隔膜,嵌入到負(fù)極中。反之,電池放電時(shí),Li +由負(fù)極中脫嵌,通過(guò)電解液和隔膜,重新嵌入到正極中。由于Li +在正負(fù)極中有相對(duì)固定的空間和位置,因此電池充放電反應(yīng)的可逆性很好,從而保證了電池的長(zhǎng)循環(huán)壽命和工作的安全性。,鋰離子電池工作原理圖,鋰離子電池的結(jié)構(gòu),（1）正極活性物質(zhì)一般為錳酸鋰或者鈷酸鋰，現(xiàn)在又出現(xiàn)了鎳鈷錳酸鋰材料，電動(dòng)自行車(chē)則用磷酸鐵鋰，導(dǎo)電集流體使用厚度10-20微米的電解鋁箔 （2）隔膜一種特殊的復(fù)合膜，可以讓離子通過(guò)，但卻是電子的絕緣體 （3）負(fù)極活性物質(zhì)為石墨，或近似石墨結(jié)構(gòu)的

6、碳，導(dǎo)電集流體使用厚度7-15微米的電解銅箔 （4）有機(jī)電解液溶解有六氟磷酸鋰的碳酸酯類(lèi)溶劑，聚合物的則使用凝膠狀電解液 （5）電池外殼分為鋼殼（現(xiàn)在方型很少使用）、鋁殼、鍍鎳鐵殼（圓柱電池使用）、鋁塑膜（軟包裝）等，還有電池的蓋帽，也是電池的正負(fù)極引出端,鋰離子負(fù)極材料,負(fù)極材料是決定鋰離子電池綜合性能優(yōu)劣的關(guān)鍵因素之一。目前，商業(yè)化碳負(fù)極材料存在的主要問(wèn)題是：實(shí)際比容量低(約為300330 mAhg，理論比容量為372 mAhg)、首次不可逆損失大、倍率放電性能差等，其組裝電池已遠(yuǎn)遠(yuǎn)不能滿足實(shí)際需求。盡管人們對(duì)碳材料進(jìn)行了摻雜改性或表面處理，但是碳材料儲(chǔ)鋰能力低是導(dǎo)致其實(shí)際比容量難以提高的

7、根本原因。因此，積極探索比容量高、容量衰減率小、安全性能好的新型鋰離子電池負(fù)極材料體系，已為國(guó)際上研究的熱點(diǎn)。文章對(duì)鋰離子電池的工作原理和應(yīng)用領(lǐng)域作了簡(jiǎn)要概述，并對(duì)其負(fù)極材料的研究概況進(jìn)行了綜述。,負(fù)極材料的研究進(jìn)展,下面對(duì)包括 碳材料 氧化物負(fù)極材料 金屬及合金類(lèi)負(fù)極材料 復(fù)合負(fù)極材料,碳材料,碳材料(理論比容量372 mAg)是目前商品化的鋰離子電池所使用的負(fù)極材料。由于其電極電位低(95)、循環(huán)壽命長(zhǎng)和安全性能好等優(yōu)點(diǎn)，確保了其在商業(yè)電池應(yīng)用中成為第一選擇對(duì)象。用于鋰離子電池的碳負(fù)極材料包括了石墨、無(wú)定型碳，其中石墨又分為天然石墨、人造石墨和石墨化碳；無(wú)定型碳分為硬碳和軟碳。石墨是鋰離子

8、電池碳材料中應(yīng)用最早、研究最多的一種，其具有完整的層狀晶體結(jié)構(gòu)，石墨晶體的片層結(jié)構(gòu)中碳原子以sP2雜化方式結(jié)合成六角網(wǎng)狀平面，理想石墨的層間距為03354 nm，層與層之間以范德華力結(jié)合。石墨的層狀結(jié)構(gòu)，有利于鋰離子的脫嵌，能與鋰形成鋰-石墨層間化合物，其理論容量為372 mAhg，充放電效率通常在90以上。鋰在石墨中的脫嵌反應(yīng)主要發(fā)生在0025 V之間(相對(duì)于LiLi+)，具有良好的充放電電壓平臺(tái)，與提供鋰源的正極材料匹配性較好，所組成的電池平均輸出電壓高，是一種性能較好的鋰離子電池負(fù)極材料。,氧化物負(fù)極材料,氧化物是當(dāng)前人們研究的另一種負(fù)極材料體系，包括金屬氧化物、金屬基復(fù)合氧化物和其它氧

9、化物。前兩者雖具有較高理論比容量，但因從氧化物中置換金屬單質(zhì)消耗了大量鋰而導(dǎo)致巨大容量損失，抵消了高容量的優(yōu)點(diǎn)；LixMoO2、Li WO2等其它氧化物負(fù)極材料具有較好的循環(huán)性能，但由于其比容量低， 目前為止并沒(méi)有獲得廣泛深入的研究。Li4Ti5Ol2具有尖晶石結(jié)構(gòu)，充放電曲線平坦，放電容量為150 mAhg，具有非常好的耐過(guò)充、過(guò)放特征，充放電過(guò)程中晶體結(jié)構(gòu)幾乎無(wú)變化，循環(huán)壽命長(zhǎng)，充放電效率近100。采用化學(xué)方法合成鋰鈦復(fù)合氧化物，用X射線衍射分析其物相結(jié)構(gòu)，并測(cè)試了其電化學(xué)性能，結(jié)果表明： 由Li2Co03、TiO2高溫合成的鋰鈦復(fù)合氧化物為尖晶石結(jié)構(gòu)的Li4Ti5O12，以0.3 mAc

10、m2的電流充放電時(shí)，首次嵌鋰比容量達(dá)300 mAhg，可逆比容量為100 mAhg，多次充放電循環(huán)后其結(jié)構(gòu)穩(wěn)定不變。,SnO2負(fù)極材料,SnO2 offers a high theoretical capacity of 790 mAh/g and exhibits low reactivity with the electrolyte due to a higher operating voltage compared to that of carbon.,缺點(diǎn),如首次充放電過(guò)程中體積膨脹高達(dá)50%以上,循環(huán)期間鋰離子的反復(fù)嵌入與脫出過(guò)程中易出現(xiàn)“粉化”和“團(tuán)聚”現(xiàn)象,這些都導(dǎo)致錫的氧化物電

11、化學(xué)性能迅速下降,從而限制了它在鋰離子電池中的廣泛應(yīng)用.,金屬及合金類(lèi)負(fù)極材料,金屬鋰是最先采用的負(fù)極材料，理論比容量3860 mAhg，原子量6.94，電化學(xué)還原電位-3.045 V，20世紀(jì)70年代中期金屬鋰在商業(yè)化電池中得到應(yīng)用。但因充電時(shí)，負(fù)極表面形成枝晶，造成電池短路，于是人們開(kāi)始尋找一種能替代金屬鋰的負(fù)極材料。合金負(fù)極材料是研究得較多的新型負(fù)極材料體系，有關(guān)鋰合金的研究工作最早始于1958年。據(jù)報(bào)道，鋰能與許多金屬M(fèi)(M =A1、Si、Ge、Sn、Pb、As、Sb、Bi、Ag、Au、Zn等)在室溫下形成金屬間化合物，由于鋰合金形成反應(yīng)通常為可逆，因此能夠與鋰形成合金的金屬理論上都能

12、夠作為鋰離子電池負(fù)極材料。金屬合金最大的優(yōu)勢(shì)，就是能夠形成含鋰很高的鋰合金，具有很高的比容量；相比碳材料，合金較大的密度使得其理論體積比容量也較大。同時(shí)，合金材料由于加工性能好、導(dǎo)電性好等優(yōu)點(diǎn)，因此被認(rèn)為是極有發(fā)展?jié)摿Φ囊环N負(fù)極材料。目前研究主要集中在Sn基、Si基、sb基和Al基合金材料 。,復(fù)合負(fù)極材料,隨著電子產(chǎn)品的日益普及，對(duì)高比能量電池的需要越來(lái)越迫切。目前看來(lái)，單獨(dú)的某種材料都不能完全滿足這個(gè)要求。碳材料雖然有很好的循環(huán)性能，但比容量低；比容量稍高的碳材料其他電化學(xué)性能又無(wú)法滿足要求。合金材料具有很高的比能量，但由于嵌脫鋰過(guò)程中巨大體積變化導(dǎo)致其循環(huán)性能遠(yuǎn)遠(yuǎn)滿足不了使用的需要。錫基

13、復(fù)合氧化物具有很好的循環(huán)特性，但首次不可逆容量損失一直沒(méi)辦法解決。因此，綜合各種材料的優(yōu)點(diǎn)，有目的的將各種材料復(fù)合形成復(fù)合負(fù)極材料，避免各自存在的不足，已經(jīng)引起了廣泛的關(guān)注。,碳包覆的二氧化錫負(fù)極材料,目前商業(yè)鋰離子電池主要采用碳材料作為負(fù)極活性物質(zhì). 人們對(duì)碳材料做了比較多的研究工作,從無(wú)定形碳到天然石墨,都進(jìn)行了制備方法、表面修飾等多方面研究,但由于受到理論比容量( 372mAh /g)的限制,碳負(fù)極材料的比容量很難進(jìn)一步提高. 金屬氧化物與合金具有較高的容量,已引起研究人員的極大興趣,如SnO2、CoO、CuO、SnCu、SnNi、SnCo等.其中,錫的氧化物因?yàn)榫哂懈弑热萘亢偷颓朵囯妱?shì)

14、而倍受關(guān)注,曾被認(rèn)為是碳負(fù)極材料最有希望的代替物 ,但它也存在一些缺點(diǎn),如首次充放電過(guò)程中體積膨脹高達(dá)50%以上,循環(huán)期間鋰離子的反復(fù)嵌入與脫出過(guò)程中易出現(xiàn)“粉化”和“團(tuán)聚”現(xiàn)象,這些都導(dǎo)致錫的氧化物電化學(xué)性能迅速下降,從而限制了它在鋰離子電池中的廣泛應(yīng)用.,錫氧化物的制備方法和晶粒尺寸對(duì)材料的性能有明顯的影響，小顆粒的納米氧化錫具有更大比表面積和更多的活性位置。采用碳包覆的方法可以緩沖氧化錫材料的體積變化，并阻止氧化錫顆粒在鋰離子嵌脫過(guò)程中的團(tuán)聚。,SnO2C材料電化學(xué)性能調(diào)查表,Dense coreshell structured SnO2/C composites as high per

15、formanceanodes for lithium ion batteries,Jun Liu, Wen Li and Arumugam Manthiram*,ChemComm,2010,Introduction,Lithium ion batteries have made a significant impact in portable electronics and communication devices. There is now tremendous interest in adopting lithium ion battery technology in the autom

16、obile industry to develop plug-in hybrid electric vehicles (PHEV) and electric vehicles (EV). However, significant improvement in both energy and power densities is needed to meet the full requirements of PHEV and EV. In this regard,(i) increasing the operating voltage of the positive electrode such

17、 as the stabilized 5 V spinel athodes (ii) increasing the capacity of the cathode materials such as the high capacity layered oxides, (iii) increasing the capacity of the anode materials such as the high capacity alloy anodes, (iv) improving the rate capability by decreasing the particle size10 or c

18、oating with conductive agents like carbon11 have become appealing in recent years.,SnO2 is a promising anode material. Unfortunately, the huge volume change (300%) occurring during the chargedischarge process of SnO2 poses serious problems. The large volume change leads to pulverization and loss of

19、electrical contact between particles, resulting in severe capacity fade and poor rate capability. A few strategies have been pursued in the literature to alleviate this problem, which include (i) hollow structures to partially accommodate the large volume change (ii) nano-sized materials to reduce t

20、he volume variation, (iii) nano-composites based on an active/inactive concept in which the inactive material serves as a confining buffer for the volume changes; normally, carbon is used as the inactive buffer material due to its soft nature and good electronic conductivity.,However, the hollow str

21、ucture alone could not improve the cycling performance significantly due to the lack of a supporting matrix that can prevent the breaking down of the metastable hollow structure. Similarly, use of nano-sized materials may not be an ultimate solution as they can lower the energy density due to low ta

22、p density, aggravatecapacity fade due to aggregation, and magnify safety issues due to high surface reactivity. Comparatively, the active/inactive nanocomposite strategy is more promising, but the capacity value is compromised by the inactive component. More recently, Lou et al. have applied this st

23、rategy to synthesize dense C shell SnO2 core spheres with improved electrochemical performance.,Combining the nanostructure design of the electrode materials and the active/inactive nanocomposite concept SnO2/C composite anode with a dense coreshell sphere structure. In this structure, the SnO2/C ac

24、tive/inactive nanocomposite shell with a thickness of 100 nm is intimately attached onto a carbon sphere core with a diameter of a few micrometres. This specific configuration results in micrometre-size particles, which helps to realize higher tap density and improved safety, while still taking adva

25、ntage of the nanodimensions in suppressing the mechanical strain. The carbon core serves simultaneously as a physical buffer and an electronically connecting matrix, which helps to realize the full potential of the SnO2/C composite anodes.,Synthesis of SnO2/C composites,8.76 g of SnCl4.5H2O and 8.56

26、 g of sucrose(蔗糖) were dissolved in 100 mL of a mixed solvent consisting of ethylene glycol (EG乙二醇) and de-ionized water in 1 : 1 volume ratio. The solution was then transferred into a 120 mL Teflon-lined stainless steel autoclave, sealed, and kept at 190 for 24 h in an oven before cooling down to r

27、oom temperature. The black sediment formed was washed with de-ionized water and ethanol, dried in a vacuum oven at 100 overnight, and divided into three parts.,The first part was calcined at 600 in air for 3 h to obtain SnO2 hollow spheres; The second and the third parts were calcined at 600 in flow

28、ing argon for 3 h to obtain the traditional coreshell SnO2/C composite where the carbon core and the SnO2 shell are detached with empty space between them. To prepare the dense coreshell SnO2/C composite, the traditional coreshell SnO2/C composite obtained by the above process and a proper amount of

29、 glucose (glucose : SnO2/C weight ratio=1 : 1) were put into the Teflon-lined stainless steel autoclave containing 1 : 1 EG/de-ionized water mixed solvent, sealed, and kept at 180 for 20h in an oven. During this process, the dissolved glucose penetrates into the empty space between the SnO2 shell an

30、d the carbon core and the polymerization and carbonization of glucose fills the empty space fully with carbon. The resultin g sediment was washed and calcined at 600 in argon for 3 h to make the carbon core more conductive.,Process,SnCl4.5H2O,sucrose,dissolving,EG:Water 1：1,Teflon-lined stainless st

31、eel autoclave,190 ,24h,black sediment formed,Washed,Dried,intermediate product,Calcined in air,600 3h,SnO2 hollow spheres,traditional coreshell SnO2/C composite,calcined in flowing Argon 600 3h,The synthesis process involved in obtaining the SnO2 /C composite with the dense coreshell structure is sc

32、hematically shown in Fig. 1. The synthesis of just solid SnO2 spheres could also be realized by a similar process, but without having glucose in the reaction mixture.,Materials Characterization,It is interesting to note that the SnO2 shell is in close contact with the carbon core spheres in the dens

33、e coreshell SnO2/C composite unlike in the traditional coreshell SnO2/C composite where the SnO2 shell is not in contact with the carbon core.,The SEM images given here also clearly show the microstructural differences between the hollow SnO2 sphere and the dense coreshell SnO2/C sphere.,The EDS dat

34、a collected near the boundary between the SnO2/C shell (region 1) and the carbon core (region 2) reveal significant differences in carbon content, confirming further that the SnO2 shell is in close contact with the carbon core.,Fig. 3(a) compares the X-ray diffraction (XRD) patterns of the various m

35、icrostructures, and they all exhibit similar XRD patterns. In Fig. 3(b) and (c). Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) plots recorded in air with a heating rate of 5 min- are compared,While no weight loss is observed in the cases of both solid and hollow SnO2 s

36、pheres, weight losses of 30 and 40% are found, respectively, with the traditional and the dense coreshell SnO2/C spheres. The larger weight loss observed with the dense coreshell SnO2/C sphere compared to that with the traditional coreshell SnO2/C sphere is due to the additional carbon filling in th

37、e space between the carbon core and the SnO2 shell. The DSC plots of both the traditional and the dense coreshell SnO2/C spheres show two major exothermic reaction peaks, indicating two different combustion kinetics for the carbon in the SnO2/C composites. While the exotherm below 500 is due to the

38、combustion of carbon in the shell ，that at 500 is due to the combustion of carbon in the core. The first exothermic peak of the dense coreshell SnO2/C sphere occurs at a lower temperature (426 ) compared to that of the traditional coreshell SnO2/C sphere (448 ), implying that most of the carbon of t

39、he shell is on the surface in the former case while it exists possibly between the SnO2 nano-particles in the shell in the latter case.,Fig. 3(a) compares the X-ray diffraction (XRD) patterns of the various microstructures, and they all exhibit similar XRD patterns. In Fig. 3(b) and (c). Thermogravi

40、metric analysis (TGA) and differential scanning calorimetry (DSC) plots recorded in air with a heating rate of 5 min- are compared,In Fig. 3(d) Clearly, the coreshell SnO2/C anodes exhibit lower irreversible capacity (IRC) loss in the first cycle compared to the solid and hollow SnO2. Specifically,

41、the dense coreshell SnO2/C anode delivers a capacity of 1331 mAh/g in the first charge and 890 mAh/g in the first discharge, while the solid SnO2 anode displays 1612 mAh/g in the first charge and 871 mAh/g in the first discharge. The reduced IRC is possibly due to the small amount of Sn formed at th

42、e interface between SnO2 and carbon via the carbothermic reduction reaction during thecalcination process, and the slightly increased discharge capacity could be attributed to the improved electronic contact between the SnO2 particles.,Electrochemical Measurement,Fig. 4(a) and (b) show that both the cycling performance and the coulombic efficiency at a current density of 100 mA g- increase in the order solid SnO2 anode hollow SnO2 anode traditional coreshell SnO2/C anode dense coreshell SnO2/C anode. The dense coreshell SnO2/C anode delivers a high capacity of 630 mAh/g even after 50 cycle