• <tr id="yyy80"></tr>
  • <sup id="yyy80"></sup>
  • <tfoot id="yyy80"><noscript id="yyy80"></noscript></tfoot>
  • 99热精品在线国产_美女午夜性视频免费_国产精品国产高清国产av_av欧美777_自拍偷自拍亚洲精品老妇_亚洲熟女精品中文字幕_www日本黄色视频网_国产精品野战在线观看 ?

    Effects of Mixed Solvents on the High-Rate Performance of Li3V2(PO4)3/C Prepared by Sol-Gel Method

    2014-10-14 03:45:02TANGYanZHONGBenHeGUOXiaoDongLIUHengZHONGYanJunNIEXiangTANGHong
    物理化學(xué)學(xué)報(bào) 2014年5期
    關(guān)鍵詞:溶膠倍率電化學(xué)

    TANG Yan ZHONG Ben-He,* GUO Xiao-Dong LIU Heng ZHONG Yan-JunNIE Xiang TANG Hong

    (1College of Chemical Engineering,Sichuan University,Chengdu 610065,P.R.China;2College of Materials Science and Engineering,Sichuan University,Chengdu 610065,P.R.China)

    Effects of Mixed Solvents on the High-Rate Performance of Li3V2(PO4)3/C Prepared by Sol-Gel Method

    TANG Yan1ZHONG Ben-He1,*GUO Xiao-Dong1LIU Heng2ZHONG Yan-Jun1NIE Xiang1TANG Hong1

    (1College of Chemical Engineering,Sichuan University,Chengdu 610065,P.R.China;2College of Materials Science and Engineering,Sichuan University,Chengdu 610065,P.R.China)

    Abstract: A Li3V2(PO4)3/C composite cathode material was obtained by a sol-gel method using deionized water and organic solvents as mixed solvents.Ethanol,ethylene glycol,and 1,2-propylene glycol were used as the organic solvents and polyacrylic acid(PAA)was used as the chelating agent and carbon source.The structure,morphology,and electrochemical performance of the synthesized materials were studied by X-ray diffraction(XRD),scanning electron microscopy(SEM),charge-discharge tests,and cyclic voltammetry.XRD analysis showed that all the materials were well crystallized and that the addition of organic solvents did not affect the crystal structure of Li3V2(PO4)3.The results of galvanostatic cycling showed that the electrochemical performance of the products was improved by the addition of organic solvents.The material synthesized using 1,2-propylene glycol had the best electrochemical performance.It exhibited an initial discharge capacity of 132.89 mAh·g-1at 0.1C(1C=150 mA·g-1)in the voltage range of 3.0-4.5 V.The initial discharge capacity was as high as 125.42 mAh·g-1upon discharging at 10C,and it had a capacity retention of 95.79%after 700 cycles.These results indicate a good rate and cycling performance in the voltage range of 3.0-4.5 V;while in the voltage range of 3.0-4.8 V,it exhibits a bad rate performance.SEM images indicated that the sample prepared using the mixed solvents had a flake-like and needle-like shape,which facilitates the interface ion-transfer process and thus improves the overall electrochemical properties.

    Key Words:Lithium ion battery;Cathode material;Li3V2(PO4)3;Sol-gel method;Mixed solvents

    1 Introduction

    Lithium ion batteries have become the most promising energy storage devices for portable electronics.Some poly-anionic phosphate materials,such as the olivine-type LiFePO41-3and monoclinic Li3V2(PO4)3(LVP)4-10,have attracted much interest in the past decade.The reversible cycling of all three lithium ions from LVP would correspond to a theoretical capacity of 197 mAh·g-1,which is the highest for all phosphate that have been reported11-13.Owing to good ion mobility,high lithium capacity,and a high operating voltage,LVP has been proposed to be a potential candidate of cathode materials for Li-ion batteries.LVP has good high-rate performance and good cycling stability.14,15It may play an important role in the expanding demand of electric vehicles(EVs)and hybrid electric vehicles(HEVs)in the future.

    In the literature,carbon-coated LVP powders have been synthesized via various methods such as solid-state reaction,16-18sol-gel process,19-21and microwave solid-state reaction.22,23Among them,the solid-state reaction is simple,environment friendly,and reaction efficient,but the particle size of the material is non-uniform.By using microwave,the reaction time can be greatly shortened;however,the preparation condition is difficult to control.Although the sol-gel process is complex,this method allows reactants to mix at the atomic or molecular level,thus reducing the calcination temperature and time of the products.Therefore,the sol-gel process is a promising method to synthesize higher purity material with uniform particle size.

    So far,nearly all the LVP synthesized by the sol-gel method used pure deionized water as solvent.A few studies have been reported to use some organic solvents,but paper16did not specify the role of organic solvent.Surface tension of an organic solvent is smaller than that of water.Therefore,the organic solvent is not only used as solvent,but also would play the role of surfactant,which has an impact on the growth of the particle.Also,during the drying process,the gel is not easy to reunite,thereby reducing the particle size.In this work,LVP precursor was synthesized by the sol-gel method with an organic solvent in water.Ethanol,ethylene glycol,and 1,2-propylene glycol were used as organic solvents.The effects of different organic solvents on the performance of LVP samples were evaluated.

    2 Experimental

    The LVP/C composites were prepared by a sol-gel method.The stoichiometric ratio of LiOH·H2O(99%(w,mass fraction)),NH4VO3(99%),H3PO4(85%)were used as raw materials.Polyacrylic acid(PAA)(30%)was used as carbon source and chelating reagent.Organic solvents(in this work,ethanol,ethylene glycol,and 1,2-propylene glycol were chosen as organic solvents)and deionized water were mixed in proportion of 40:60(volume ratio).First,LiOH·H2O and NH4VO3were dissolved in deionized water at room temperature.Then organic solvent and 10%(w)of PAA were added into the solution.Finally,H3PO4was added to the mixture.This solution was constantly stirred for 2 h at 80°C,and then the excess solvent was removed by vacuum distillation.The resulting gel precursor was dried in a vacuum oven at 90°C for 15 h.After drying,the precursors were decomposed in tube furnace at 350°C for 4 h,then heated at 700°C for 6 h under flowing argon.The final product was a black powder.

    The carbon content was verified by CS-902 analytical instrument(Wanlianda Xinke,Beijing,China).The crystalline structure of each product was analyzed by X-ray diffraction(XRD,D/max-rB,Rigaku,Cu Kαradiation)(λ=0.15046 nm)operated at 40 kV and 40 mA.The particle morphology and particle size of the LVP powders were observed by scanning electron microscopy(SEM,SPA400 Seiko Instruments).

    The specific surface areas(SSA)were measured with Brunauer-Emmett-Teller(BET)method by N2physisorption at 77 K on Quanachrome automated surface area&pore size analysizer(Autosorb SI).The samples were pretreated at 300°C for 3 h prior to the measurement.

    The cathode was fabricated by pressing a mixture of 80%(w)LVP/C,13%(w)acetylene black(conducting additive),and 7%(w)PVDF(binder)onto an Al foil.The anode was lithium foil and the electrolyte was 1 mol·L-1LiPF6solution in ethylene carbonate:propylene carbonate:diethyl carbonate[1:1:1(volume ratio)].Galvanostatic charging/discharging tests were operated in the voltage range of 3.0-4.5 V and 3.0-4.8 V at room temperature(25°C)with a battery test system(Neware BTS-610).Cyclic voltammetry(CV)was performed on the positive electrode in the cells described above by a CHI 660C electrochemical work station.CV tests were carried out in voltage ranges 3.0-4.5 V and 3.0-4.8 V at a scanning rate of 0.10 mV·s-1.

    3 Results and discussion

    Fig.1 shows the X-ray diffraction patterns of the LVP/C composites synthesized with different organic solvents;they are similar to those reported by Rui24and Saidi25et al.The characteristic peaks of all the LVP/C samples are sharp and without any impurity peaks.The carbon left in the LVP can not be detected because the residual carbon is only about 3%and in amorphous form.It can be concluded that the samples with all solvents have produced a single phase of LVP/C with monoclinic structure.Table 1 shows the cell parameters of LVP/C samples,and it can be seen that the cell volumes of the four samples are close to each other.It indicates that different solvents do not have significant effects on the cell parameters of the products.In addition,the mean coherent domain sizes of the samples were calculated by Jada 5.0 software which takesaccount of all the major diffraction peaks in the XRD pattern.It can be seen that the mean coherent domain sizes of the samples synthesized by mixed solvents are smaller than that using pure deionized water;and the grain size of sample D is the smallest one,which may facilitate the electron transport and ions diffusion.

    Fig.2 shows the first charge/discharge curves of LVP/C samples in the voltage range of 3.0-4.5 V at 0.1C.It can be seen that all the initial charge curves of the samples exhibit three stable voltage plateaus at 3.57,3.65,and 4.08 V.These plateaus correspond to the two-phase transitions between the single phases of LixV2(PO4)3(x=2.5,2.0,1.0).The initial discharge capacities of samples A,B,C,and D are 123.59,127.60,130.51,and 132.89 mAh·g-1,respectively.Compared with sample A,samples B,C and D,which are synthesized with mixed solvents,have higher discharge capacity.Fig.3 displays the average discharge capacity of samples A,B,C,and D at 0.1C,0.2C,0.5C,1C,3C,5C,10C,and 20Crates,respectively.It can be seen that the capacity of the samples basically possesses better retention,only fading faster at higher rates for sample A.The discharge capacities of samples A,B,C,and D at 20Crates are 95.92,110.85,116.92,and 119.99 mAh·g-1,which are 77.61%,86.87%,89.30%,and 90.29%of the capacity at 0.1Crate,respectively.Obviously,the electrochemical performance of products can be improved by adding organic solvents during the reaction of precursors,especially at high discharge rate.

    In order to explain why the samples obtained by adding organic solvents have better electrochemical performance,the SEM images of samplesAand D in Fig.4 are compared carefully.As shown in Fig.4(a,b),the sample synthesized by pure deionized water presents an irregularity of shape with particle size of 1-3 μm.This kind of shape with a small specific surface area does not favor lithium-ion diffusion.When the current increases,the diffusion of lithium ion is blocked and the capacity decreases.The sample synthesized in the mixed solvent by adding some 1,2-propylene glycol,to some extent,is part of the particle agglomerate,but the original particle size is small and most of the particles are distributed in the range of 1-2 μm(Fig.4(c,d)).Most of the particles have a flake-like shape,as mentioned previously;26the morphology of flake-like shape has a large specific surface area and results in good electrochemical performance.There are also particles in needlelike shape that are about 0.1 μm in diameter and 1 μm in length;meanwhile these particles also have a large specific surface area.We believe that the flake-like and needle-like shape leads to the better performance of sample D.It can be concluded that the existence of organic solvent can affect the shape ofthe particle.The surface tension of organic solvents is smaller than that of water;the solvent can selectively control the surface energy of different particle faces in the process of gel formation.PAA is a long-chain molecule,so that the LVP precursor particle can grow along its long-chain direction to give flake-like and needle-like particles.

    Table 1 Cell parameters of the samples

    A confirmation,quite valuable being quantitative,of the positive influence of the solvent on the grain characteristics comes from specific surface area measurements with the BET method.The data reported in Table 2 show that 1,2-propylene glycolwater mixed solvents markedly enhance the specific surface area of the powders.The sample D shows a specific surface area almost 1.5 times that of the sample prepared by pure deionized water.Therefore,it can be concluded that the solvents have great effects on the specific surface area of the samples.

    Among the samples,sample D gave the best performance.Fig.5 demonstrates the cycle and rate performance of sample D at various discharge rates.It can be seen that its cycling stability is excellent at each rate.The discharge capacity does not decrease at each rate after several cycles.As the rate increases,the discharge capacity decreases only a little;when the current comes to 20C,the specific capacity is still as high as 119.99 mAh·g-1.The discharge voltage decreases as the rate increases since the polarization becomes heavier with increasing the rate.From Fig.6,we can clearly see that sample D shows a good cycling stability at 10Crate.The initial specific capacity is 125.42 mAh·g-1and decreases to 120.14 mAh·g-1after 700 cycles(the ratio of 95.79%of the initial capacity).The good performance of LVP/C obtained in this experiment,combined with its high safety,implies that it can be a candidate cathode material for the lithium ion battery of HEVs and EVs in the future.

    Table 2 Specific surface area(S)of the sample synthesized with different solvents

    Monoclinic lithium vanadium phosphate contains three independent lithium sites with a theoretical discharge capacity of 197 mAh·g-1,while three Li ions are completely released from the cathode.Fig.7 shows the electrochemical performance of sample D in the voltage range of 3.0-4.8 V.Sample D presents an initial charge specific capacity of 196.14 mAh·g-1at 0.1C,equivalent to the theoretical capacity(Fig.7(a)).The initial discharge capacity is 165.96 mAh·g-1,which is only 84.61%ofthe initial charge capacity.When keeping the charge rate at 1C rate and increasing the discharge rate,the polarization becomes heavy and the voltage decreases a lot.The discharge specific capacity decreases from 117.80 to 105.06 mAh·g-1when discharge rate increasing from 10C to 20C rate.It can be seen from Fig.7(b)that the fading seems to be unavoidable since the capacity of sample D is 139.69 mAh·g-1after six cycles at 0.1C and 0.2C rates,respectively,a capacity decrease of about 26.27 mAh·g-1.However,it is obvious that the major decay exists in the first 12 cycles with a fading rate of 2.19 mAh·g-1per cycle.With the increase of discharge rate,the latter 60 cycles remain stable,especially at 10Cand 20Crate.The initial specific capacity is 117.80 mAh·g-1and is also as high as 116.21 mAh·g-1after 20 cycles at 10Crate.Compared with the stable cycle ability presented in LVP samples in the voltage range of 3.0-4.5 V(Fig.5),there is a significant fading of capacity in the voltage range of 3.0-4.8 V,which might be due to the following reasons.One is the oxidation of electrolyte in this high electrochemical window(3.0-4.8 V).The other is that the crystal structures of LVP is distorted during the phase transition process at the high voltage(>4.6 V).The resistance of Li3V2(PO4)3sample might be increased during the extraction/reinsertion process,which results in the poor cycle ability.

    In order to compare the behavior of LVP at different voltage ranges,the CV curve obtained in the voltage ranges of 3.0-4.5 V and 3.0-4.8 V are shown in Fig.8.Fig.8(A)shows the CV curves of sample D from 3.0 to 4.5 V.The voltage range to 4.5 V exhibits typical oxidative peaks near 3.63,3.72,and 4.14 V(vs Li/Li+)as well as reductive peaks 3.53,3.60,and 3.99 V(vs Li/Li+),respectively.It corresponds to lithium extraction and insertion in the stoichiometric ranges:x=0.0-0.5,0.5-1.0,1.0-2.0 in Li3-xV2(PO4)3,respectively.Among the three CV curves,the first cycle has the weakest peak intensities;as the cycle number increases,the peak intensities become stronger and the oxidative/reductive peaks are approaching to each other,promising a good cycle stability.The CV profile of LVP in the voltage range of 3.0-4.8 V is shown in Fig.8(B).There are four oxidation and three reduction peaks present in the CV curve.The oxidation peak at 4.58 V is the extraction of the third Li+ion associated with the phase transition process from LiV2(PO4)3to V2(PO4)3.From Fig.8(B),it can be seen that peakintensities gradually decrease with increasing cycle number,especially from the first to the second cycle.This change corresponds to a significant capacity fading charging to 4.8 V.

    4 Conclusions

    In this work,the electrochemical performance of the LVP/C cathode material,especially the high-rate performance,was greatly improved by using an organic/water as mixture solvent.The precursor of LVPwas prepared by a sol-gel method using PAA as the chelating agent and carbon source.Electrochemical tests show that the discharge capacity of the samples is increased by adding the organic solvents.The sample with adding 1,2-propylene glycol gave the best electrochemical performance.In the voltage range of 3.0-4.5 V,the discharge capacity is 132.89,128.59,125.07,119.99 mAh·g-1at 0.1C,1C,10C,20C,respectively.The specific capacity of sample D is as high as 120.14 mAh·g-1after 700 cycles at 10C rate.In the voltage range of 3.0-4.8 V,the capacity of the materials has a significant fading and poor cycle stability.

    (1)Guo,X.D.;Zhong,B.H.;Liu,H.;Wu,D.Q.;Tang,Y.;Tang,H.J.Electrochem.Soc.2009,156,A787.

    (2)Tang,Y.;Guo,X.D.;Zhong,B.H.;Liu,H.Inorganic Chemicals Industry 2010,42,12.[唐 艷,郭孝東,鐘本和,劉 恒.無機(jī)鹽工業(yè),2010,42,12.]

    (3)Wu,D.Q.;Zhong,B.H.;Xu,R.;Guo,X.D.;Liu,H.;Song,Y.;Tang,Y.New Chemical Materials 2010,38,37.[吳德橋,鐘本和,徐 瑞,郭孝東,劉 恒,宋 楊,唐 艷.化工新型材料,2010,38,37.]

    (4) Li,Y.Z.;Zhou,Z.;Gao,X.P.;Yan,J.Electrochimica Acta 2007,52,4922.

    (5)Jiang,T.;Wei,Y.J.;Pan,W.C.;Li,Z.;Ming,X.;Chen,G.;Wang,C.Z.J.Alloy.Compd.2009,488,L26.

    (6)Li,L.J.;Li,X.H.;Wang,Z.X.;Guo,H.J.;Wu,L.;Hao,Y.;Zheng,J.C.J.Alloy.Compd.2010,497,176.

    (7)Guo,X.D.;Zhong,B.H.;Tang,Y.;Liu,H.;Wu,D.Q.;Yang,H.L.J.Chem.Eng.Chin.Univ.2009,23,701.[郭孝東,鐘本和,唐 艷,劉 恒,吳德橋,楊海蘭.高校化學(xué)工程學(xué)報(bào),2009,23,701.]

    (8)Guo,X.D.;Zhong,B.H.;Tang,Y.;Liao,W.H.;Wu,D.Q.Chemical Research and Application 2008,20,625. [郭孝東,鐘本和,唐 艷,廖文華,吳德橋.化學(xué)研究與應(yīng)用,2008,20,625.]

    (9) Hou,C.P.;Yue,M.Acta Phys.-Chim.Sin.2007,23,1954.[侯春平,岳 敏.物理化學(xué)學(xué)報(bào),2007,23,1954.]

    (10) Zheng,J.C.;Li,X.H.;Wang,Z.X.;Li,J.H.;Wu,L.;Li,L.J.;Guo,H.J.Acta Phys.-Chim.Sin.2009,25,1916.[鄭俊超,李新海,王志興,李金輝,伍 凌,李靈均,郭華軍.物理化學(xué)學(xué)報(bào),2009,25,1916.]

    (11)Chen,Q.Q.;Wang,J.M.;Tang,Z.;He,W.C.;Shao,H.B.;Zhang,J.Q.Electrochimica Acta 2007,52,5251.

    (12)Tan,L.;Luo,Z.M.;Liu,H.W.;Yu,Y.J.Alloy.Compd.2010,502,407.

    (13) Jang,I.C.;Lim,H.H.;Lee,S.B.;Karthikeyan,K.;Aravindan,V.;Kang,K.S.;Yoon,W.S.;Cho,W.I.;Lee,Y.S.J.Alloy.Compd.2010,497,321.

    (14)Wang,L.;Zhang,L.C.;Lieberwirth,L.;Xu,H.W.;Chen,C.H.Electrochem.Commun.2010,12,52.

    (15)Wang,J.W.;Zhang,X.F.;Liu,J.;Yang,G.L.;Ge,Y.C.;Yu,Z.J.;Wang,R.S.;Pan,X.M.Electrochimica Acta 2010,55,6879.(16)Wang,L.J.;Zhou,X.C.;Guo,Y.L.J.Power Sources 2010,195,2844.

    (17)Fu,P.;Zhao,Y.M.;Dong,Y.Z.;Hou,X.M.J.Phys.Chem.Solid 2010,71,394.

    (18) Zhou,X.C.;Liu,Y.M.;Guo,Y.L.Electrochimica Acta 2009,54,2253.

    (19) Jiang,T.;Pan,W.C.;Wang,J.;Bie,X.F.;Du,F.;Wei,Y.J.Electrochimica Acta 2010,55,3864.

    (20) Huang,J.S.;Yang,L.;Liu,K.Y.;Tang,Y.F.J.Power Sources 2010,195,5013.

    (21) Dai,C.S.;Wang,F.P.;Liu,J.T.;Wang,D.L.;Hu,X.G.Chin.J.Inorg.Chem.2008,24,381.[戴長(zhǎng)松,王福平,劉靜濤,王殿龍,胡信國(guó).無機(jī)化學(xué)學(xué)報(bào),2008,24,381.]

    (22)Yang,G.;Liu,H.D.;Ji,H.M.;Chen,Z.Z.;Jiang,X.F.J.Power Sources 2010,195,5374.

    (23)Yang,G.;Liu,H.D.;Ji,H.M.;Chen,Z.Z.;Jiang,X.F.Electrochimica Acta 2010,55,2951.

    (24) Rui,X.H.;Li,C.;Chen,C.H.Electrochimica Acta 2009,54,3374.

    (25) Saidi,M.Y.;Barker,J.;Huang,H.;Swoyer,J.L.;Adamson,G.J.Power Sources 2003,119-121,266.

    (26)Fu,P.;Zhao,Y.;Dong,Y.;An,X.;Shen,G.Electrochimica Acta 2006,52,1003.

    混合溶劑對(duì)溶膠-凝膠法制備的Li3V2(PO4)3/C高倍率性能的影響

    唐 艷1鐘本和1,*郭孝東1劉 恒2鐘艷君1聶 翔1唐 紅1

    (1四川大學(xué)化學(xué)工程學(xué)院,成都610065;2四川大學(xué)材料科學(xué)與工程學(xué)院,成都610065)

    以有機(jī)-水為混合溶劑,采用溶膠-凝膠法制備鋰離子電池正極材料Li3V2(PO4)3/C,選取乙醇、乙二醇和1,2-丙二醇為有機(jī)溶劑,聚丙烯酸(PAA)為碳源和螯合劑.通過X射線衍射(XRD)、掃描電鏡(SEM)、恒流充放電以及循環(huán)伏安測(cè)試等方法,研究了產(chǎn)物的結(jié)構(gòu)形貌及電化學(xué)性能.XRD測(cè)試結(jié)果表明所有溶劑制備的樣品結(jié)晶良好,有機(jī)溶劑的加入不影響Li3V2(PO4)3材料的晶型結(jié)構(gòu).恒流充放電結(jié)果表明有機(jī)溶劑的加入改善了材料的電化學(xué)性能.以1,2-丙二醇-水為溶劑的樣品電化學(xué)性能最好,在3.0-4.5 V電壓范圍內(nèi),0.1C(1C=150 mA·g-1)倍率首次放電比容量為132.89 mAh·g-1,10C倍率首次放電比容量達(dá)125.42 mAh·g-1,循環(huán)700周后容量保持率為95.79%,具有良好的倍率性能與循環(huán)性能;在3.0-4.8 V電壓范圍內(nèi)倍率性能較差.掃描電鏡結(jié)果表明混合溶劑制備的樣品呈片狀和針狀,這種形狀有利于鋰離子的擴(kuò)散,因此提高了材料的電化學(xué)性能.

    鋰離子電池; 正極材料;Li3V2(PO4)3; 溶膠-凝膠法; 混合溶劑

    O646;O614.1;TM912.9

    Received:January 3,2011;Revised:February 14,2011;Published on Web:March 7,2011.

    ?Corresponding author.Email:Zhongbenhe@hotmail.com;Tel:+86-28-85406702;Fax:+86-28-85405517.

    The project was supported by the National Science&Technology Pillar Program of China(2007BAQ01055).

    國(guó)家科技支撐計(jì)劃(2007BAQ01055)資助項(xiàng)目

    猜你喜歡
    溶膠倍率電化學(xué)
    大型桅桿起重機(jī)起升變倍率方法及其應(yīng)用
    電化學(xué)中的防護(hù)墻——離子交換膜
    溶膠-凝膠法制備高性能ZrO2納濾膜
    關(guān)于量子電化學(xué)
    FANUC0iD系統(tǒng)速度倍率PMC控制方法
    電化學(xué)在廢水處理中的應(yīng)用
    Na摻雜Li3V2(PO4)3/C的合成及電化學(xué)性能
    一種智能加工系統(tǒng)中的機(jī)床倍率控制方法
    拉伸倍率對(duì)BOPP薄膜性能的影響
    溶膠-凝膠微波加熱合成PbZr0.52Ti0.48O3前驅(qū)體
    欧美xxxx黑人xx丫x性爽| 欧美xxxx性猛交bbbb| 免费观看无遮挡的男女| 久久人人爽人人片av| 欧美97在线视频| 高清午夜精品一区二区三区| 亚洲一级一片aⅴ在线观看| 久久韩国三级中文字幕| 99久久人妻综合| 九草在线视频观看| 久久久成人免费电影| 69人妻影院| 国产视频内射| 不卡视频在线观看欧美| 欧美bdsm另类| 免费观看性生交大片5| 99热这里只有是精品在线观看| 成人午夜精彩视频在线观看| 午夜福利高清视频| 欧美另类一区| 简卡轻食公司| 日韩成人伦理影院| 日本午夜av视频| 18禁在线播放成人免费| 晚上一个人看的免费电影| 欧美+日韩+精品| 2021天堂中文幕一二区在线观| 成人特级av手机在线观看| 成年人午夜在线观看视频| 久久久久久久亚洲中文字幕| 日韩欧美 国产精品| 国产男人的电影天堂91| 黄色视频在线播放观看不卡| kizo精华| 国产精品偷伦视频观看了| 国产亚洲最大av| 男人和女人高潮做爰伦理| 乱码一卡2卡4卡精品| 国产成人精品福利久久| 99久久九九国产精品国产免费| 国产探花在线观看一区二区| 午夜免费观看性视频| 97超碰精品成人国产| 特级一级黄色大片| 在线天堂最新版资源| 天天一区二区日本电影三级| 国产精品不卡视频一区二区| 九草在线视频观看| 日本-黄色视频高清免费观看| 婷婷色麻豆天堂久久| 亚洲综合色惰| 五月天丁香电影| 国产日韩欧美在线精品| 亚洲精品亚洲一区二区| 国产精品精品国产色婷婷| 久久精品国产亚洲网站| 九草在线视频观看| 中国三级夫妇交换| 日韩 亚洲 欧美在线| 亚洲av中文字字幕乱码综合| 国产精品福利在线免费观看| 91精品伊人久久大香线蕉| 亚洲人成网站在线播| 国产精品.久久久| 精品国产三级普通话版| 国产亚洲av嫩草精品影院| 亚洲av成人精品一区久久| 肉色欧美久久久久久久蜜桃 | 尤物成人国产欧美一区二区三区| 亚洲av日韩在线播放| 久久人人爽人人爽人人片va| 秋霞在线观看毛片| 老师上课跳d突然被开到最大视频| 男人爽女人下面视频在线观看| 九九在线视频观看精品| 一个人看的www免费观看视频| 亚洲欧美精品自产自拍| 欧美日韩在线观看h| 亚洲自偷自拍三级| 亚洲婷婷狠狠爱综合网| 一级黄片播放器| 亚洲av成人精品一区久久| 一级爰片在线观看| 嫩草影院新地址| 久久久久九九精品影院| 国产精品女同一区二区软件| a级毛色黄片| 成人午夜精彩视频在线观看| 大陆偷拍与自拍| 午夜日本视频在线| 哪个播放器可以免费观看大片| 日本wwww免费看| 日韩强制内射视频| 一级毛片我不卡| 嘟嘟电影网在线观看| 99久久人妻综合| 夜夜看夜夜爽夜夜摸| 啦啦啦在线观看免费高清www| 国产老妇伦熟女老妇高清| 秋霞伦理黄片| 少妇被粗大猛烈的视频| 啦啦啦在线观看免费高清www| 91精品伊人久久大香线蕉| 极品少妇高潮喷水抽搐| 日韩av不卡免费在线播放| 听说在线观看完整版免费高清| 99热这里只有是精品在线观看| 在线精品无人区一区二区三 | 精品一区二区免费观看| 国产精品99久久99久久久不卡 | 波野结衣二区三区在线| 亚洲av国产av综合av卡| 亚洲精品成人久久久久久| 男女边吃奶边做爰视频| 成人无遮挡网站| 蜜桃亚洲精品一区二区三区| 国产在线男女| 亚洲成人av在线免费| 亚洲激情五月婷婷啪啪| 视频区图区小说| 大片免费播放器 马上看| 中文在线观看免费www的网站| 午夜福利在线观看免费完整高清在| 中文精品一卡2卡3卡4更新| 日韩免费高清中文字幕av| 免费看日本二区| av线在线观看网站| 国产伦理片在线播放av一区| 永久免费av网站大全| 99久久精品热视频| 亚洲,一卡二卡三卡| 免费在线观看成人毛片| av福利片在线观看| 国国产精品蜜臀av免费| 免费看日本二区| 网址你懂的国产日韩在线| 久久久久久久久大av| 99久国产av精品国产电影| 秋霞伦理黄片| 少妇被粗大猛烈的视频| 丰满少妇做爰视频| 亚洲精华国产精华液的使用体验| 一区二区av电影网| 亚洲综合精品二区| 国产伦理片在线播放av一区| 亚洲av.av天堂| 成年人午夜在线观看视频| 午夜免费男女啪啪视频观看| 国产精品秋霞免费鲁丝片| 69av精品久久久久久| 乱码一卡2卡4卡精品| 纵有疾风起免费观看全集完整版| 午夜免费鲁丝| 日韩视频在线欧美| 日本色播在线视频| 久久久久网色| 免费大片黄手机在线观看| www.色视频.com| 99久国产av精品国产电影| 亚洲av中文字字幕乱码综合| 一区二区av电影网| 久久精品夜色国产| .国产精品久久| 777米奇影视久久| 99热全是精品| 你懂的网址亚洲精品在线观看| 国产精品三级大全| 亚洲精品中文字幕在线视频 | 亚洲精品一区蜜桃| 日日啪夜夜撸| 校园人妻丝袜中文字幕| 晚上一个人看的免费电影| 欧美区成人在线视频| 免费观看a级毛片全部| 国产av国产精品国产| 国产成人精品一,二区| 国产精品福利在线免费观看| 男人爽女人下面视频在线观看| 高清视频免费观看一区二区| 久久人人爽人人爽人人片va| 直男gayav资源| 国内少妇人妻偷人精品xxx网站| 免费观看性生交大片5| 男女那种视频在线观看| 精品人妻视频免费看| 午夜福利视频1000在线观看| 大香蕉久久网| 精品一区二区免费观看| 69人妻影院| 日本爱情动作片www.在线观看| 一本一本综合久久| 国产成人精品一,二区| 99久久九九国产精品国产免费| av在线观看视频网站免费| 久久久精品94久久精品| 国产精品久久久久久精品电影小说 | 下体分泌物呈黄色| 亚洲成人久久爱视频| 国产黄片视频在线免费观看| av在线观看视频网站免费| 黑人高潮一二区| 美女内射精品一级片tv| 欧美日韩亚洲高清精品| 亚洲国产日韩一区二区| 夫妻午夜视频| 欧美成人午夜免费资源| 国产精品无大码| 国产亚洲精品久久久com| 在线播放无遮挡| 日日撸夜夜添| 中文字幕亚洲精品专区| 久久久午夜欧美精品| 国产免费一区二区三区四区乱码| 日韩国内少妇激情av| 国产欧美另类精品又又久久亚洲欧美| 内地一区二区视频在线| 亚洲精品久久久久久婷婷小说| 王馨瑶露胸无遮挡在线观看| 久久精品国产亚洲av涩爱| 亚洲av福利一区| 特大巨黑吊av在线直播| 免费看a级黄色片| 插阴视频在线观看视频| 黄色一级大片看看| 久久影院123| av在线老鸭窝| 国产精品av视频在线免费观看| 乱系列少妇在线播放| 白带黄色成豆腐渣| 午夜免费鲁丝| 亚洲欧美成人精品一区二区| 日韩大片免费观看网站| 久久精品国产亚洲av天美| 午夜福利在线在线| 人妻少妇偷人精品九色| 亚洲精品日本国产第一区| www.av在线官网国产| 国国产精品蜜臀av免费| 夜夜爽夜夜爽视频| 免费av毛片视频| 精品人妻熟女av久视频| 成年女人看的毛片在线观看| 18禁在线无遮挡免费观看视频| 欧美日本视频| 欧美国产精品一级二级三级 | 日本欧美国产在线视频| 老司机影院毛片| 18禁在线播放成人免费| 另类亚洲欧美激情| 亚洲内射少妇av| 国产在线一区二区三区精| 2021天堂中文幕一二区在线观| 日本欧美国产在线视频| 99视频精品全部免费 在线| 日韩成人av中文字幕在线观看| 国产淫语在线视频| 国产欧美另类精品又又久久亚洲欧美| 久久久久久久久久久丰满| 日本与韩国留学比较| 日韩亚洲欧美综合| 亚洲电影在线观看av| 国产高清有码在线观看视频| 欧美人与善性xxx| 男女边吃奶边做爰视频| 国产探花在线观看一区二区| 黑人高潮一二区| 国产爽快片一区二区三区| 亚洲精品视频女| 日韩免费高清中文字幕av| www.av在线官网国产| 搡老乐熟女国产| 免费少妇av软件| 草草在线视频免费看| 国产乱来视频区| 亚洲第一区二区三区不卡| 丝袜美腿在线中文| 亚洲在久久综合| 一级毛片电影观看| 美女被艹到高潮喷水动态| 国产精品久久久久久精品电影| 又爽又黄无遮挡网站| 国产永久视频网站| 国产亚洲精品久久久com| 久久久久久久久久久免费av| 欧美zozozo另类| 日日摸夜夜添夜夜添av毛片| 亚洲精品国产成人久久av| 亚洲人成网站高清观看| 18禁裸乳无遮挡动漫免费视频 | 国产成人精品婷婷| 精品久久久噜噜| 国产成人91sexporn| 欧美日韩亚洲高清精品| 婷婷色综合大香蕉| 久久精品久久久久久久性| 天天躁夜夜躁狠狠久久av| 亚洲欧美清纯卡通| 你懂的网址亚洲精品在线观看| 久久韩国三级中文字幕| 色综合色国产| 卡戴珊不雅视频在线播放| 欧美激情国产日韩精品一区| 综合色丁香网| 一个人看视频在线观看www免费| 欧美少妇被猛烈插入视频| 精品久久久噜噜| 国产成人免费观看mmmm| 涩涩av久久男人的天堂| 一级毛片 在线播放| 九九爱精品视频在线观看| av播播在线观看一区| 国产人妻一区二区三区在| 夜夜看夜夜爽夜夜摸| 亚洲精品影视一区二区三区av| 久久精品国产亚洲av涩爱| 舔av片在线| 人妻 亚洲 视频| 国产一区亚洲一区在线观看| 老女人水多毛片| 国内揄拍国产精品人妻在线| 欧美成人午夜免费资源| 亚洲av成人精品一二三区| 晚上一个人看的免费电影| 国产午夜精品久久久久久一区二区三区| 国产 精品1| 两个人的视频大全免费| 久久国内精品自在自线图片| 制服丝袜香蕉在线| 国产淫片久久久久久久久| 夜夜看夜夜爽夜夜摸| 18禁在线无遮挡免费观看视频| 国产精品一区二区三区四区免费观看| 丝袜美腿在线中文| 亚洲av二区三区四区| 91久久精品国产一区二区成人| 亚洲最大成人中文| 国产免费视频播放在线视频| 国产精品一区二区在线观看99| 国产av国产精品国产| 不卡视频在线观看欧美| 免费观看无遮挡的男女| 一个人看的www免费观看视频| 欧美激情在线99| 精品少妇黑人巨大在线播放| 91在线精品国自产拍蜜月| 在线精品无人区一区二区三 | 国产v大片淫在线免费观看| 中文欧美无线码| 天堂俺去俺来也www色官网| 婷婷色麻豆天堂久久| 久久久久国产精品人妻一区二区| 亚洲精品日韩在线中文字幕| 日本黄色片子视频| 免费观看a级毛片全部| 国产精品久久久久久精品古装| 黄片无遮挡物在线观看| 婷婷色av中文字幕| 亚洲精品成人久久久久久| 亚洲精品456在线播放app| 国产一区二区三区av在线| 女人被狂操c到高潮| 国产精品无大码| 婷婷色av中文字幕| 少妇丰满av| 国产欧美日韩一区二区三区在线 | 国产日韩欧美在线精品| 国产黄a三级三级三级人| 国产大屁股一区二区在线视频| 婷婷色麻豆天堂久久| videossex国产| 国产日韩欧美亚洲二区| 国内少妇人妻偷人精品xxx网站| 少妇裸体淫交视频免费看高清| 伊人久久国产一区二区| 亚洲精品自拍成人| 嫩草影院入口| 国产精品国产av在线观看| 国产伦精品一区二区三区视频9| 欧美xxxx性猛交bbbb| 最近中文字幕2019免费版| av在线天堂中文字幕| 国产成人a区在线观看| 26uuu在线亚洲综合色| 一级黄片播放器| 插逼视频在线观看| 99九九线精品视频在线观看视频| 久久久a久久爽久久v久久| 亚洲精品成人久久久久久| 国产人妻一区二区三区在| 免费av不卡在线播放| 欧美一区二区亚洲| 国产欧美日韩精品一区二区| 日韩大片免费观看网站| 欧美高清性xxxxhd video| 日日啪夜夜撸| 日本欧美国产在线视频| 岛国毛片在线播放| 少妇的逼好多水| 久久久久久久国产电影| 国产亚洲5aaaaa淫片| 国产69精品久久久久777片| 日本与韩国留学比较| 一级av片app| 日韩一本色道免费dvd| 免费观看的影片在线观看| 国产精品不卡视频一区二区| 又粗又硬又长又爽又黄的视频| 国产精品久久久久久精品古装| 99精国产麻豆久久婷婷| 91久久精品国产一区二区三区| 中文字幕人妻熟人妻熟丝袜美| 一区二区三区四区激情视频| 国产日韩欧美亚洲二区| 亚洲成人中文字幕在线播放| 国产精品99久久99久久久不卡 | 九九在线视频观看精品| 一区二区三区四区激情视频| 人人妻人人看人人澡| 国产男人的电影天堂91| 涩涩av久久男人的天堂| 久久久久精品久久久久真实原创| 久久精品久久久久久久性| 男女边摸边吃奶| 中文乱码字字幕精品一区二区三区| 三级男女做爰猛烈吃奶摸视频| 午夜亚洲福利在线播放| 80岁老熟妇乱子伦牲交| www.色视频.com| 如何舔出高潮| 国产成人freesex在线| 日日啪夜夜爽| 自拍偷自拍亚洲精品老妇| 51国产日韩欧美| 99视频精品全部免费 在线| 69av精品久久久久久| 日韩成人伦理影院| 丰满乱子伦码专区| 久久久精品免费免费高清| 国产亚洲91精品色在线| 久久精品国产亚洲av天美| 欧美日韩精品成人综合77777| 国产人妻一区二区三区在| .国产精品久久| 黄色怎么调成土黄色| 久久精品国产亚洲av天美| 国内少妇人妻偷人精品xxx网站| 大香蕉97超碰在线| 美女脱内裤让男人舔精品视频| 超碰av人人做人人爽久久| 男人和女人高潮做爰伦理| 制服丝袜香蕉在线| 免费在线观看成人毛片| 最新中文字幕久久久久| 欧美一级a爱片免费观看看| 亚洲精品国产成人久久av| 亚洲最大成人中文| 久久久久九九精品影院| 亚洲av中文av极速乱| 欧美成人精品欧美一级黄| 国产精品一及| 国产成人午夜福利电影在线观看| 女人十人毛片免费观看3o分钟| 在线天堂最新版资源| 狂野欧美激情性bbbbbb| 看非洲黑人一级黄片| 免费黄频网站在线观看国产| 久久久久久久午夜电影| 九草在线视频观看| 热99国产精品久久久久久7| 久久久午夜欧美精品| 欧美极品一区二区三区四区| 亚洲av福利一区| 中国美白少妇内射xxxbb| 久久韩国三级中文字幕| 亚洲精品aⅴ在线观看| 欧美3d第一页| 中国三级夫妇交换| 熟女av电影| 国产精品久久久久久av不卡| 欧美精品一区二区大全| 久热久热在线精品观看| 国产精品人妻久久久影院| 国产精品人妻久久久久久| 在线观看免费高清a一片| 三级国产精品欧美在线观看| 国产精品久久久久久精品古装| 99热网站在线观看| 人人妻人人看人人澡| 亚洲国产精品成人综合色| 身体一侧抽搐| 国产一级毛片在线| 爱豆传媒免费全集在线观看| 91狼人影院| 精品久久久久久久末码| 男女边摸边吃奶| 中文字幕免费在线视频6| 在线观看三级黄色| 亚洲,欧美,日韩| 亚洲va在线va天堂va国产| 婷婷色麻豆天堂久久| 欧美成人午夜免费资源| 男女边吃奶边做爰视频| 伦理电影大哥的女人| 男人爽女人下面视频在线观看| 深夜a级毛片| 国产色爽女视频免费观看| 国产av不卡久久| 在线精品无人区一区二区三 | 久久99热6这里只有精品| 九九久久精品国产亚洲av麻豆| 秋霞伦理黄片| 色播亚洲综合网| 亚洲av欧美aⅴ国产| 久久久久久久大尺度免费视频| 在线观看三级黄色| 国产一区二区三区综合在线观看 | 精品一区二区三卡| 国产黄片视频在线免费观看| 亚洲av日韩在线播放| 亚洲精品456在线播放app| 亚洲av免费在线观看| 日日摸夜夜添夜夜添av毛片| 一本久久精品| 国产黄频视频在线观看| 国产精品麻豆人妻色哟哟久久| 久久人人爽av亚洲精品天堂 | 亚洲av福利一区| 国产探花极品一区二区| 成年人午夜在线观看视频| 婷婷色综合大香蕉| 成年女人在线观看亚洲视频 | 午夜福利网站1000一区二区三区| 美女视频免费永久观看网站| xxx大片免费视频| 亚洲最大成人中文| 国产片特级美女逼逼视频| eeuss影院久久| 可以在线观看毛片的网站| 国产免费视频播放在线视频| 国产乱人视频| 又爽又黄a免费视频| 久久影院123| 日本免费在线观看一区| 免费看日本二区| 久久人人爽人人爽人人片va| 99久久九九国产精品国产免费| 国产精品99久久99久久久不卡 | 国产又色又爽无遮挡免| 最后的刺客免费高清国语| 一区二区三区精品91| 国产一区有黄有色的免费视频| 一级毛片久久久久久久久女| 国内精品美女久久久久久| 香蕉精品网在线| 2018国产大陆天天弄谢| 五月开心婷婷网| 国产黄色视频一区二区在线观看| 亚洲精品成人久久久久久| 美女被艹到高潮喷水动态| 国产精品久久久久久av不卡| 午夜福利在线在线| 国产精品麻豆人妻色哟哟久久| 久久99热这里只频精品6学生| 午夜福利网站1000一区二区三区| 熟妇人妻不卡中文字幕| 狂野欧美激情性xxxx在线观看| 全区人妻精品视频| 国产精品久久久久久久久免| 少妇的逼好多水| 国产精品一区二区在线观看99| 人妻系列 视频| 国产精品人妻久久久影院| 黄色一级大片看看| 亚洲欧美日韩另类电影网站 | 欧美性猛交╳xxx乱大交人| 成年女人看的毛片在线观看| 国产欧美日韩一区二区三区在线 | 国产精品一区二区在线观看99| 国产精品国产三级国产专区5o| 亚洲精品色激情综合| 岛国毛片在线播放| 亚洲精品成人av观看孕妇| 各种免费的搞黄视频| 九草在线视频观看| 久久精品夜色国产| 一本色道久久久久久精品综合| 亚洲国产日韩一区二区| 久久久久国产精品人妻一区二区| 日韩大片免费观看网站| 人妻制服诱惑在线中文字幕| 免费黄色在线免费观看| 我的女老师完整版在线观看| 日韩,欧美,国产一区二区三区| 久久久久国产精品人妻一区二区| 色吧在线观看| 九草在线视频观看| 99热全是精品| 国产男人的电影天堂91| 人人妻人人澡人人爽人人夜夜| 性色av一级| 有码 亚洲区| 熟女电影av网| 欧美极品一区二区三区四区| 久久久精品欧美日韩精品| 大话2 男鬼变身卡| 久久精品国产a三级三级三级| 视频中文字幕在线观看| 日韩人妻高清精品专区| 丝袜喷水一区| 久久韩国三级中文字幕| 中文欧美无线码| 久热这里只有精品99| 99久久精品国产国产毛片| 在线观看一区二区三区| 中国美白少妇内射xxxbb|