Short communication
Graphene-coated plastic film as current collector for lithium/sulfur batteries
最难吃的食物Li Wang a ,Xiangming He a ,b ,*,Jianjun Li a ,Jian Gao a ,Mou Fang a ,Guangyu Tian b ,Jianlong Wang a ,Shoushan Fan c
a
Institute of Nuclear and New Energy Technology,Tsinghua University,Beijing 100084,PR China
b
State Key Laboratory of Automotive Safety and Energy,Tsinghua University,Beijing 100084,PR China c
Department of Physics,Tsinghua-Foxconn Nanotechnology Rearch Center,Tsinghua University,Beijing 100084,PR China
h i g h l i g h t s
<A metal free cathode of sulfurized polyacrylonitrile is attempted.
<Using graphene coated polyethylene terephthalate film as current collector.
<110mAh prototype lithium sulfur cells are asmbled with energy density of 452Wh kg À1.<The capacity retention is 96.8%after 30cycles at 100%depth of discharge.
<The lf-discharge is less than 1%after 30days of storage at room temperature.
a r t i c l e i n f o
Article history:
Received 3October 2012Received in revid form 29January 2013
Accepted 1February 2013Available online xxx Keywords:
Sulfurized polyacrylonitrile Self-discharge Current collector Graphene
Polyethylene terephthalate
a b s t r a c t
A metal-free battery is of great practical signi ficance in terms of high energy density,low cost,high safety,eco-friendly and sustainability.Here a metal-free cathode,using graphene-coated polyethylene terephthalate (G-PET)film (Commercial-Off-The-Shelf)as current collector and sulfurized poly-acrylonitrile (SPAN)as active material,is aiming at low cost and high energy density battery.110mAh prototype lithium sulfur cells are asmbled using SPAN/G-PET cathode,showing energy density of 452Wh kg À1excluding the weight of package and capacity retention of 96.8%after 30cycles at 100%depth of discharge.The lf-discharge characteristics of prototype cells are tested.After 30days of storage at room temperature,the discharge capacity has decread less than 1%,indicative of low lf-discharge of the SPAN-bad Li/S batteries.This paper shows that G-PET can be a potential promising current collector for lithium ion batteries.
Ó2013Elvier B.V.All rights rerved.
1.Introduction
Safe,low-cost,high-energy-density and long-lasting recharge-able batteries are in high demand to address environmental and energy needs for energy storage systems that can be coupled to renewable sources [1,2].Due to their large speci fic capacity,abun-dant resources and low cost [3,4],t
he sulfur-bad cathode mate-rials are of great potential for the next generation of high performance lithium batteries.However,lithium/sulfur (Li/S)cells in liquid electrolytes suffer from critical drawbacks in terms of
cycling life,rate capability,and sulfur utilization.It is reported that the sulfurized polyacrylonitrile composite (SPAN)cathode material,which is structurally highly disperd nano-sulfur embedded in a conductive matrix,shows novel performances compared to con-ventional elemental sulfur-bad cathode by avoiding shuttle effect that is the main drawback of conventional elemental sulfur com-posite [5e 12].Afterward,the cycling characteristics and rate capability of SPAN cathode material are investigated for recharge-able lithium batteries [13].Furthermore,the charge/discharge characteristics with different voltage windows,kinetics of SPAN materials,expansion and shrinkage of SPAN electrode,the elec-trochemical characteristics of SPAN cathode on different charge/discharge manner,the compaction strength of the electrode and safety of overcharge of SPAN cathode in rechargeable lithium bat-teries are further studied [14e 18],and the electrolyte effect on the performance of SPAN is investigated as well [19].A rechargeable cell system with an electrochemically prelithiated SPAN as cathode
*Corresponding author.Institute of Nuclear and New Energy Technology,Tsinghua University,Beijing 1
00084,PR China.Tel.:þ861089796073;fax:þ861089796031.
E-mail address:hexm@tsinghua.edu ,hexiangming@tsinghua (X.
He).
Contents lists available at SciVer ScienceDirect
Journal of Power Sources
journal h omepage: m/lo cate/jp owsou
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0378-7753/$e e front matter Ó2013Elvier B.V.All rights rerved.dx.doi/10.1016/j.jpowsour.2013.02.008
沙岛Journal of Power Sources xxx (2013)1e 5
and graphite as anode is studied to address the safety concerns of metallic Li negative electrodes [17,18].The previous investigations have shown promising of SPAN for high capacity cathode with good reversibility in high capacity rechargeable batteries.Self-discharge behavior is one of the important factors for commercialization of lithium batteries [20e 22],but there has been no reports of the lf-discharge of SPAN cathode bad Li e S cells.
In addition,current collector may be considered as inactive material and reduces the gravimetric and volumetric energy den-sities of the battery.Current collectors,typically aluminum foil and copper foil,account for about 15e 20%by weight and 10e 15%by cost of a battery [23].Therefore,thinner,lighter foils would be preferred.However,due to easy creasing and tearing,thinner foils tend to be more expensive according to the method of preparation and harder to work with.It is clear that the current collectors must be electrochemically stable in contact with the cel
l components over the operating potential window of the electrode.In practice,continued corrosion of the current collectors will lead to a gradual increa in the internal resistance of the battery,with corre-sponding loss of the apparent capacity,at a given rate [24].Not only that,oxidation of metal current collectors may be one of the greatest exothermic reactions in thermal runaway.Accordingly,current collector is crucially important for cost,weight and per-formance of batteries.
In this study,graphene-coated plastic film (Commercial-Off-The-Shelf)is attempted to be ud as current collector for SPAN batteries due to its low cost and low weight.The lf-discharge characteristics of SPAN electrode in rechargeable lithium batteries using graphene-coated PET film as current collectors are investi-gated particularly.2.Experimental
Graphene-coated polyethylene terephthalate (G-PET)film is prepared as follows.PET (108N type,Hangzhou Dahua Plastics In-dustry Co.,Ltd,China)is purchad from market.The thickness of the film is 12m m.Graphene (SS-1)is provided by Ningbo Small-sheet Company,China.The graphene slurry with solid content of 0.25wt.%is prepared using DMF (N ,N -dimethylformamide)as dispersing agent,and cast on the PET film using a scalpel,succes-sively dried at 80 C for 8h before further processing.
SPAN is prepared as reported [3,7].The sulfur content is opti-mized to be 42%[3].SPAN is thoroughly mixed with acetylene black and PVdF (polyvinylidene di fluoride)binder (Kynar Ò761),using DMF as solvent.The weight ratio of SPAN,acetylene black and PVdF in the final dry cathode was 7:2:1.The resulting slurry is cast on G-PET film using a scalpel.The electrode is then obtained.The mass loading of active material of the resulting electrodes is around 5mg cm À2.The electrodes are then dried at 120 C under vacuum for 24h.The plastic packaged cells are asmbled in a glove box (M.Braun GmbH,Germany)with H 2O and O 2content below 1ppm.
Lithium foil is ud as anode and Celgard 2400microporous film is ud as parator.The electrolyte is 1.0M LiPF 6dissolved in a mixture of ethylene carbonate (EC)and diethyl carbonate (DEC)(1:1,v/v).The cells are asmbled by stack process with laminated soft package.The charge and discharge performance of the cells is tested at 30 C.The normal charge procedure is compod of a constant-current of 5.0mA up to 3.0V.The normal discharge procedure is compod of a constant-current of 5.0mA until the voltage dropped to 1.0V.The cell is rested for 1h before it begins to be discharged.The formation process,cycling 3times at 2mA current,is done before the cycling performance is tested.
The lf-discharge rate test is carried out as follows.A cell after formation is charged to 3.0V,and the
n stored at 30 C.After a designed period,it is discharged to 1.0V.3.Results and discussion
PET film is easily available Commercial-Off-The-Shelf (COTS)product.The PET films are ud in a variety of printing,labeling,decorating etc.PET film has a good balance of properties,which allows larger operating windows for temperature and tension controls.The properties of typical plastic film are listed in Table 1.PET film has properties such as it can withstand high processing temperature,excellent for high-tension conversion process,highly durable usage and the highest rvice tempera-ture,lf-extinguishing flammability,and fully functional to À70 C.PET also has good chemical resistance against acids,ethanol,ketones,carbonate,DMF,N -methyl-pyrrolidone [25].The above mentioned properties of PET film are encouraging for its application as structural material in lithium batteries.
Current materials for current collector in lithium batteries are aluminum and copper.The properties of the two metals are listed in Table 2.The current collectors,namely aluminum foil and copper foil,take roughly about 15e 20%by weight and 10e 15%by cost of a lithium battery [23].Graphene is from Ningbo Smallsheet Com-pany,its price is $100per kilogram.The content of graphene is 2g m À2.The weight and cost will decrea by using graphene-coated PET film as current collectors in lithium ion batteries.Fig.1a shows photo of PET film COTS product.It is very easily available.Fig.1b s
hows photo of a sheet of PET film,it is a trans-parent film.Fig.1c and d shows photo and SEM image of G-PET film,respectively.The graphene is uniformly coated on the surface of PET film.
Fig.2shows the SAPN electrode with G-PET film current col-lector and stack cell with laminated soft package.The electrode looks smooth and flat,as shown in Fig.2a.It becomes a little bit curl after compaction due to one side coating,as shown in Fig.2b.One layer stack cell with lithium foil anode is asmbled using lami-nated soft package,as shown in Fig.2c,capacity of which is about 110mAh.This prototype battery,using SPAN cathode,G-PET cur-rent collector and 1M LiPF 6/EC þDEC electrolyte,shows the energy
Table 1
Comparative data of typical plastic films.Property
Unit
PET BOPP PE PVC Nylon PC
Speci fic gravity g cm À3
1.400.910.92 1.40 1.15 1.15Elongation %12011040050100140Melting point C
260170135180223240Tensile strength kgf mm À222192102210Tear strength
kgf 2215282010Insulation breakdown kV
6.5 6.0 4.0 4.0 3.0 5.0Dielectric constant
0.1kHz,25 C 3.2
2.1
2.3
3.0
3.8
3.0
Service temperature range
C
À70to 150
À40to 120
À50to 75qcy蓝牙耳机怎么配对
瑞格之灯À20to 80
À70to 130
À100to 130
Note:PET e Polyethylene terephthalate;PE e Polyethylene;PVC e Polyvinyl chloride;PC e Polycarbonate;BOPP e Biaxially-oriented polypropylene;Nylon-Polyamide.Data sources:/chart.html .
L.Wang et al./Journal of Power Sources xxx (2013)1e 5
2
density of452Wh kgÀ1excluding the package weight.Though lithium ud in this prototype cell is ove
r ca.80wt%,the calculated energy density is more than420Wh kgÀ1if battery capacity is 10Ah.
Fig.3shows electrochemical performance of this100mAh battery after the formation.Fig.3a shows the charge/discharge performance between3.0V and1.0V in the electrolyte of1M LiPF6/ ECþDEC.The average charge and discharge voltage gradually stabilize at2.24and1.95V,respectively,less than0.3V voltage difference lies between charge and discharge process,as shown in Fig.3a.Fig.3b shows the cycling performance.The cell shows ca-pacity of114.3mAh at thefirst discharge process.Afterward,the capacities stabilize at ca.110mAh in the following cycles.After30 cycles at100%DOD(depth of discharge),the capacity remains over 110mAh,equivalent capacity retention of96.8%and an average capacity degradation rate of less than0.11%per cycle,which is much better than the cell using aluminum current collector,where an average capacity degradation rate is ca.0.32%per cycle[19].This indicates that the SPAN cathode with graphene-coated PETfilm current collector in the electrolyte of1M LiPF6/ECþDEC is a promising candidate cell for sulfur bad batteries in practical u.
The variation of the discharge curve with storage time is pre-nted in Fig.4a.The original cell displays the typical discharge curve of SPAN bad cell as previously reported[14e19].The discharge capacity was113mAh.As the storage time increas,the discharge capacity gradually decr
eas.After5days,the discharge curve is almost the same as the initial one.After10days storage,
the
Fig.1.(a)Photo of two roll of PETfilm of COTS product;(b)photo of a sheet of PETfilm;(c)photo of a sheet of G-PETfilm;(d)SEM image of G-PETfilm.The coating thickness is 1m m.
Table2
Comparative data of different current collector materials.
Property Unit G-PET Aluminum foil Copper foil
Thickness m m121212
Tensile strength kgf mmÀ222425
Elongation%120 1.0 2.5
Weight g mÀ215.632.4106.8
Cost$mÀ20.230.32
1.1
Fig.2.(a)Photo of a sheet of electrode before compaction;(b)photo of an electrode with tape after compaction;(c)photo of stack cell with laminated soft package.
L.Wang et al./Journal of Power Sources xxx(2013)1e53
处事cell shows only a little capacity decrea.The change in the discharge curve after 30days storage is also very weak.Its voltage and capacity are slightly lower than original one,as shown in Fig.4a.As shown in Fig.4b,the discharge capacity gradually de-creas with the increa of storage time,and the cell delivers only 0.8%lf-discharge after 30days storage at 30 C.The lf-discharge rate of 0.8%per month is acceptable in practical applications.The lf discharge property of this SPAN ba
d cell is much better than the previously reported [26],where a Li/S cell suffers lf discharge of 17%after 30days storage at room temperature.This further in-dicates that the SPAN cathode with graphene-coated PET film current collector cell in the electrolyte of 1M LiPF 6/EC þDEC is a promising candidate cell of sulfur bad batteries in practical u.4.Conclusions
Plastic current collectors bad on G-PET film substrates are successfully prepared.Due to its low cost,reduced metal con-sumption,low weight and chemical stability,plastic current col-lectors greatly improve the performance of lithium sulfur battery.Light weight cell with improved energy density can be designed becau of the density of G-PET film is only 1.37g cm À3,much less than one sixth of copper (8.94g cm À3).A prototype battery with G-PET current collector shows the energy density of 452Wh kg À1excluding the package weight.The capacity retention of this battery is 96.8%after 30cycles at 100%DOD,indicative of average capacity degradation rate of 0.11%per cycle.The lf-discharge test dem-onstrates that the SPAN bad cell only suffers 0.8%of lf-discharge after 30days storage at 30 C,which is acceptable in practical applications.In addition,stability against organic elec-trolytes is a critical criterion of the plastic polymeric substrates for
lithium battery application.Bad on our result,the rearch on the plastic current collector,which is inert to organic electrolytes,yet has good adhesion with graphene thin film,is underway.Acknowledg
ment
The authors highly appreciate the comments for the revision from the anonymous reviewers.This work is supported by the MOST (Grant No.2011CB935902,No.2010DFA72760,No.2013AA050903,No.2011CB711202,No.2011AA11A257and No.2013CB934000),the NSFC (Grand No.20901046and No.20903061),the Tsinghua University Initiative Scienti fic Rearch Program (Grand No.2010THZ08116,No.2011THZ08139,No.2011THZ01004and No.2012THZ08129)and State Key Laboratory of Automotive Safety and Energy (Grand No.ZZ2012-011).The authors also highly appreciate the assistance of experiments from Ms.Caixia Chang.References
[1]N.Petr,M.Klaus,K.S.V.Santhanam,H.Otto,Chem.Rev.97(1997)265.
[2]L.Wang,X.M.He,W.T.Sun,J.W.Guo,J.J.Li,J.Gao,C.Y.Jiang,Angew.Chem.Int.
Ed.51(2012)9034.
[3]L.Wang,X.M.He,J.W.Guo,J.J.Li,J.Gao,C.Y.Jiang,C.R.Wan,J.Mater.Chem.22
(2012)22077.
[4]X.L.Ji,L.F.Nazar,J.Mater.Chem.20(2010)9821.
[5]J.L.Wang,L.Liu,Z.J.Ling,J.Yang,C.R.Wan,C.Y.Jiang,Electrochim.Acta 48
(2003)1861.
[6]J.L.Wang,J.Yang,C.R.Wan,K.Du,J.Y.Xie,N.X.Xu,Adv.Funct.Mater.13
(2003)487.
[7]J.L.Wang,J.Yang,J.Y.Xie,N.X.Xu,Adv.Mater.14(2002)963.
[8]J.L.Wang,J.Yang,J.Y.Xie,N.X.Xu,Y.Li,Electrochem.Commun.4(2002)499.[9]J.Yang,B.F.Wang,K.Wang,Y.Liu,J.Y.Xie,Z.S.Wen,Electrochem.Solid State
Lett.6(2003)A154.
20
40
60考核管理办法
80
考研英语阅读时间100
120
1.01.5
2.02.5
3.0
capacity / mAh
P o t e n t i a l / V v s . L i /L i +
b a
b a
a: 1st cycle b: 30th cycle
(a)
20
406080100120
140C a p a c i t y / m A h
cycle number
Fig.3.Charge/discharge of cell between 3.0V and 1.0V in 1M LiPF6/EC þDEC at the current of 5mA.(a)1st and 30th cycles;(b)cyclability.
20
40
60
80
100
120
1.01.5
2.02.5
3.0
capacity / mAh
P o t e n t i a l / V v s . L i /L i +
b a
a: original cell
b: storage for 30 days
(a)
90
92949698100102104C a p a c i t y r e t e n t i o n / %
Time / day
Fig.4.(a)Changes in discharge pro files as function of storage time;(b)discharge capacity retention as function of storage time.
L.Wang et al./Journal of Power Sources xxx (2013)1e 5
4
巨乌贼
[10]X.G.Yu,J.Y.Xie,J.Yang,H.J.Huang,K.Wang,Z.S.Wen,J.Electroanal.Chem.
573(2004)121.
[11]X.G.Yu,J.Y.Xie,J.Yang,K.Wang,J.Power Sources132(2004)181.
[12]X.U.Yu,J.Y.Xie,Y.Li,H.J.Huang,C.Y.Lai,K.Wang,J.Power Sources146
(2005)335.
[13]J.L.Wang,Y.W.Wang,X.M.He,J.G.Ren,C.Y.Jiang,C.R.Wan,J.Power Sources
138(2004)271.
[14]X.M.He,W.H.Pu,J.G.Ren,L.Wang,J.L.Wang,C.Y.Jiang,C.R.Wan,Electro-
chim.Acta52(2007)7372.
[15]L.Wang,J.S.Zhao,X.M.He,C.R.Wan,Electrochim.Acta56(2011)5252.
[16]L.Wang,X.M.He,J.G.Ren,W.H.Pu,J.J.Li,J.Gao,Ionics16(2010)689.
[17]X.M.He,J.G.Ren,L.Wang,W.H.Pu,C.R.Wan,C.Y.Jiang,Ionics15(2009)477.[18]X.M.He,J.G.Ren,L.Wang,W.H.Pu,C.Y.Jiang,C.R.Wan,J.Power Sources190
(2009)154.
[19]L.Wang,X.M.He,J.J.Li,M.Chen,J.Gao,C.Y.Jiang,Electrochim.Acta72(2012)114.
[20]R.Yazami,Y.F.Reynier,Electrochim.Acta47(2002)1217.
[21]S.Zhang,M.S.Ding,T.R.Jow,J.Power Sources102(2001)16.
[22]H.S.Ryu,H.J.Ahn,K.W.Kim,J.H.Ahn,J.Y.Lee,E.J.Cairns,J.Power Sources140
(2005)365.
[23]L.Gaines,R.Cuenca,ANL/v/.
[24] A.H.Whitehead,M.Schreiber,J.Electrochem.Soc.152(2005)A2105.
[/.
[26]H.S.Ryu,H.J.Ahn,K.W.Kim,J.H.Ahn,K.K.Cho,T.H.Nam,Electrochim.Acta52
(2006)1563.
L.Wang et al./Journal of Power Sources xxx(2013)1e55
