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1 Carbn Letters Vl. 8, N. 4 December 2007 pp Electrchemical Perfrmance f Carbn/Silicn Cmpsite as Ande Materials fr High Capacity Lithium In Secndary Battery Taek-Rae Kim, Jing-Yu Wu, Quan-Li Hu and Myung-S Kim Department f Chemical Engineering, Myngji University, Yngin, Gynggi-d , Krea myungkim@mju.ac.kr (Received Octber 29, 2007; Accepted December 5, 2007) Abstract Carbn/silicn cmpsites were synthesized by mixing silicn pwders with petrleum pitch and subsequent heattreatment. The resultant cmpsites were cmpsed f carbn and nan-size crystalline silicn identified by XRD and EDX. FIB images and SEM images were taken respectively t detect the existence f silicn impregnated in carbn and the distributin f silicn n the carbn surface. The btained carbn/silicn materials were assembled as half cell andes fr lithium in secndary battery and their electrchemical prperties were tested. The pitch/silicn cmpsite (3 : 1 wt. rati) heat treated at 1000 C and mixed with 55.5 wt.% f graphite shwed relatively gd electrchemical prperties such as the initial efficiency f 78%, the initial discharge capacity f 605 mah/g, and the discharge capacity f 500 mah/g after 20 cycles. Keywrds : carbn, silicn, pitch, lithium in secndary battery, ande materials p rq l r e lp rp, p rq p p l v tp r rp v p. p rq p r t n pd q p p rq p p l vp p. pm l q p rq p l vp n p p rvp l p n p n p. p n l q rv p r p l v ˆ pm rv n pp rvp p eˆ q p l p lv p. q n lp pm p rvp p v l p ˆ q pn pp lp n p r n l pl t n 372 mah/g ~r n 818 mah/ccp r l n p p rv l n p n p v p n [1-3]. pp q ( q) n p p ˆ p p l p lv pv p p p l n p, r vp r t 3~4 p Ž}p l, r vp rl p l vr p k l, ˆ qm p p p lp ll. ql p l p p p n q kv p. p p vp v/ v p l r p ˆ ˆ p lr pp, p Ž}p m e r p l r e t rp p p. q Si Si p q l nan-si (80 nm), nan-si/c, Mg 2 Si[4]} v m t p v p lv (active/inactive cmpsite material)p l l. Si Li p p r Si p Lip p eˆ pl 4200 mah/gm 3p 9320 mah/cm t ln p v, rp 1412 C k Sn p rl pv p ˆ v kp, l n p qk p rvp p q n vp. Si p k l pm p /ˆ e Ž}p pq r Si pqm r vr~m p r r r r l p p r rr p p. l nan p Si pq n l p p p re r ps n p ˆ Si pn p vp p re l [5-8]. Sip Ž}p m e t p m l p t v p p. ˆ q rv vp v l free vlumep sq l Ž}e p free vlumep Ž}p m r l p, amrphus v l grain bundary sq v kp stress/strain lp Ž} p d m e t pl r l pl v

2 336 Taek-Rae Kim et al. / Carbn Letters Vl. 8, N. 4 (2007) Table 1. Cntents f Si, carbn, and graphite used in different ande materials Si (wt.%) Carbn (wt.%) Graphite (wt.%) AB (wt.%) PVDF (wt.%) Ttal (wt.%) S S S S S S S S S S S S s p. Datta[9], Kim[10], Yshi[11] Wang[12]p Sip Ž }l p pq Ž l carbnp Si pq p l catingp buffer l p m. r n ~800mAh/gp llp, 30 p l ~540mAh/gp v m. l l pitchm Sip l v s, 1000 Cl l}, l pr s e pm 2 rvp p v n m. rs yrv rr p r d l ˆ -e - l p r pp r q m. x $BSCPOTJMJDPODPNQPTJUF Carbn/silicn cmpsite rs l THF (tetrahydrfuran, 99.0%)l pitch(l r 250 C, t )m silicn pwder (APS 50 nm)p 1 : 1, 2 : 1, 3 : 1 4:1p p 1000 C m l l} m. l pitch:silicnp 1 : 1, 2 : 1, 3 : 1 4:1l l} l lp e S-1, S-2, S-3 S-4 e. l} v l v mp dm 10 C/minp 5h k l} m. l} carbn/silicn cmpsite, 325 mesh ~ vp n m. Carbn/ silicn cmpsitep r s r p p l l} p EDX (energy dispersive X-ray spectrmeter) XRD (X-ray diffractin) p mp, ˆ Si p l l pitch p free vlumep ˆ kk l SEM (scanning electrn micrscpy) FIB (fcused in beam) p m.»yw p sƒ p vp rs carbn/silicn cmpsitel l pq ( d(t), APS 15 ump Ž l) l v p l n mp, rq acetylene black, r plyvinylidene fluride(pvdf) n l 1-methyl-2- pyrrdidinne(nmp)l n e slurry m. v : rq : r = 85.5 : 7.5 : 7.0 wt.%p p NMPl slurry l Cu fill, 100 Cl 24 h k v s m. vp Table 1l e p l v Si s l carbn/silicn cmpsitep p 20%, 30% 40% eˆ e p v m. l l S-1-n l 2, 3, 4 S-1p 20%, 30%, 40% n mp, S- 2-n, S-3-n, S-4-nl v 20%, 30%, 40% n mp. r p r test cellp k Žn yrvp rq mp cunter electrde Li fil, r vp EC(ethylene carbnate), EMC(ethyl methyl carbnate) DMC(dimethyl carbnate) 1:1:1p n l 1Mp LiPF 6 r mp n l p p n mp, p PP (plyprpylene)p n m. rq cellp 30 C m dl C-rate 0.2 C, cut-ff rkp V rr r e p m. š Fig. 1p carbn/silicn cmpsitep r p s EDX p r p p XRD p ˆ p. XRD p l rm ˆ p pitch mr r p p v m p p pp EDX p l carbn : silicnp

3 Electrchemical Perfrmance f Carbn/Silicn Cmpsite as Ande Materials fr High Capacity Lithium In Secndary Battery 337 Fig. 1. EDX and XRD analysis f carbn/silicn cmpsite (S-3). Fig. 2. SEM and FIB image f S-3. 이 원래의 pitch : silicn 3 : 1로부터 7 : 3의 비로 변화되었다는 것을 알 수 있다. 이 것은 열처리 과정을 통한 pitch의 탄화수 율에 따른 것이다. Table 2는 열처리 전후의 pitch : silicn의 조성비를 표시한 도표이다. Fig. 2는 S-3의 표면특성을 나타내기 위한 SEM 사진과 내 부구조를 관찰하기 위한 FIB 사진이다. FIB사진에서 Si이 carbn에 함침이 되어있다는 것을 확인할 수 있었으며, SEM 사진을 통하여 carbn의 외부 표면에도 Si이 분산이 되어 있 다는 것을 알 수 있었다. Carbn의 외부 표면에 Si이 분산이 되어 있다는 것은 사이클이 경과할수록 brittle한 Si이 리튬 이 온의 삽입/탈리시의 큰 부피 팽창에 의하여 dead vlume이 증 가할 것으로 예상 된다.

4 338 Taek-Rae Kim et al. / Carbn Letters Vl. 8, N. 4 (2007) Fig. 3. Cycle perfrmance f different cntents f silicn, carbn, and graphite. Fig. 4. Charge/discharge curves f S-3-2, S-3-3, and S-3-4. Fig. 3 p lp p reˆ carbn/silicn cmpsite p s eˆ p v n mp ˆ p p. lp p pr Sip cating p pitchp p v n p p kr Table 2. The weight change f pitch/silicn cmpsites after heat treatment at 1000 C Befre heat treatment (pitch : silicn wt. rati) After heat treatment (carbn : silicn wt. rati) S-1 1 : 1 44 : 56 S-2 2 : 1 61 : 39 S-3 3 : 1 70 : 30 S-4 4 : 1 76 : 24 p skv p k pl. pitchp p pr kl l pitchp p v p kr p n p p k pl. S-3 l (pitch:silicn 3 : 1, 1000 Cl l} )p e l v s l l p v n mp, p kr p n l rp n ˆ l. Fig. 4p l pmp l l ˆ r r 0.12 ~ 0.23 V l p p plp, carbn/silicn p r r 0.4 ~ 0.5 V l p p k pl. Li in p p p p l 0.4 ~ 0.5 V pl Sip ˆr p l lrp kl Li Sip p p k pl. Carbn/silicn cmpsitep p

5 Electrchemical Perfrmance f Carbn/Silicn Cmpsite as Ande Materials fr High Capacity Lithium In Secndary Battery 339 Fig. 5. Cycle perfrmance f S-3 with different cntents f graphite Table 3. charge capacity and initial efficiency Initial efficiency 1 st discharge 20 st discharge Samples (%) capacity (mah/g) capacity (mah/g) S S S v 0.4 ~ 0.5 V p ˆr p v p rr v p p p. p p pitchp l p l p silicn pq pmp p/ˆ ep Ž}l p l dead vlumep v l pm Sip pp p Ž m. Carbn/silicn cmpsite v p l p p l lp ˆr rr Fig. 4p l p pl. S-3 lp e m lp pl r n Fig. 5l ˆ p l p Table 3l ˆ l. S-3-3 (pitch/silicn cmpsite 3 : 1p 1000 C l l} 30% l 55.5%)p p v n p, pp 78%, rn p 605 mah/g, 20 p rn p 500 mah/gp n p k r l r sp ˆ l. sp pm p rv p q n p eˆ p q l vp l q l Sip p m. Sip Ž}p m e t l pitch l e p, Sip p r r p m l rq acetylene blackp ~ m. l lv q p pm p rvn p q v n l r r r p s l p p p lp pl. 1. Carbn/silicn cmpsite p v ~ mpe n rk p l Li inp p p p l 0.4 ~ 0.5 V pl Sip ˆr p l lrp kl Li Sip p p k pl. r v ˆr rr v, p p pitchp l p l p silicn pq pmp p/ˆ ep Ž}l p l dead vlumep v l pm Sip pp p Ž m. 2. lp p r carbn/silicn cmpsitep s eˆ p v n mp e Sip cating p pitchp p v n p p kr p skv p k pl. pitchp p pr kl l pitchp p v p kr p n p p k pl. 3. S-3 l (pitch : silicn 3 : 1, 1000 Cl l} ) e l v s l l p v n mp, S-3-3 e (pitch/silicn cmpsite 3 : C l l} v 30%, l 55.5%) p 78%, rn 605 mah/g 20 cycle rn 500 mah/g r n r r p ˆ l. 3FGFSFODFT [1] Sat, K.; Nguchi, M.; Demachi, A.; Oki, N.; End, E. Science 1994, 264, 556. [2] Dahn, J. R.; Zheng, T.; Liu, Y. H.; Xue, J. S. Science 1995, 270, 590. [3] Yazami, R. Electrchimica Acta 1999, 45, 87. [4] Kim, H. S.; Chi, H. J.; Shn, H. J.; Kang, T. J. Electrchem. Sciety 1991, 146, [5] Li, H.; Huang, X.; Chen, L.; Wu, Z.; Liang, Y. Electrchem. Slid-State Lett. 1999, 2, 547. [6] Niu, J.; Lee, J. Y. Extended Abstracts 10th Internatinal Meeting n Lithium Batteries, Cm, Italy, May [7] Hwang, S. M.; Lee, H. Y.; Jang, S. W.; Lee, S. M.; Lee, S. J.; Baik, H. K.; Lee, J. Y. Electrchem. Slid-state Lett. 2001, 4, A97. [8]Lee, H. Y.; Jang, S. W.; Lee, S. M. J. Industrial Technlgy 2001, 21. [9] Taka, N.; Tanaka, I.; Adachi, H. Intermetallics 1996, [10] Li, J.; Murphy, E.; Winnick, J.; Khl, P. A. J. Pwer Surce 2001, 102, 294. [11] Bittihn, R.; Herr, R.; Hge, D. J. Pwer Surces 1993, 43, 223. [12] Scaken, U. V.; Ndwell, E.; Sundher, A.; Dahn, J. R. Slid State Inics 1994, 69, 284.