锂电池电极与无机电解质间的界面剂

Society Chem.Mater.2010,22,949–956949 DOI:10.1021/cm901819cInterfacial Observation between LiCoO2Electrode and Li2S-P2S5Solid Electrolytes of All-Solid-State Lithium Secondary Batteries UsingTransmission Electron Microscopy†Atsushi Sakuda,Akitoshi Hayashi,*and Masahiro Tatsumisago Department of Applied Chemistry,Graduate School of Engineering,Osaka Prefecture University,1-1,Gakuen-cho,Naka-ku,Sakai,Osaka599-8531,JapanReceived June26,2009.Revised Manuscript Received September8,2009In all-solid-state lithium secondary batteries,both the electrode and electrolyte materials are solid. The electrode and solid electrolyte interface’s structure and morphology affect a battery’s electro-chemical performance.Observation of the interface between LiCoO2positive electrode and highly lithium-ion-conducting Li2S-P2S5solid electrolyte was conducted using transmission electron microscopy.An interfacial layer was formed at the interface between LiCoO2electrode and Li2S-P2S5solid electrolyte after the battery’s initial charge.Furthermore,mutual diffusions of Co,P,and S at the interface between LiCoO2and Li2S-P2S5were observed.The mutual diffusion and the formation of the interfacial layer were suppressed using LiCoO2particles coated with Li2SiO3 thin film.Results showed that all-solid-state cells using Li2SiO3-coated LiCoO2had better electro-chemical performance than those using noncoated LiCoO2.The all-solid-state cells functioned at -30°C.Moreover,the all-solid-state cell using Li2SiO3-coated LiCoO2was charged and discharged under a high current density of40mA cm-2at100°C.IntroductionLithium ion secondary batteries offer large energy den-sities.They have been used as power sources of various portable devices.1Commercially produced lithium ion secondary batteries consist mainly of LiCoO2as a positive electrode,carbon as a negative electrode,and an organic electrolyte solution.As an effective approach to improve the batteries’electrochemical performance,interfacial modifications between the positive electrode and electro-lyte by coatings of Al2O3,ZrO2,SiO2,AlPO4,and AlF3on the LiCoO2positive electrode have been studied.2-7That modification efficiently improves the batteries’cycle per-formance,rate capability,and thermal stability.The effects of the modification are(i)suppression of structural change caused by phase transition of LiCoO2,(ii)decrease of cobalt dissolution from LiCoO2to liquid electrolyte,and (iii)suppression of side reactions between the electrode and electrolyte.For application to electric vehicles(EV)and hybrid electric vehicles(HEV),development of large-scale lithium secondary batteries with high safety has been strongly desired.Conventional lithium ion secondary batteries entail risks of fire or explosion because of the use of flammable organic electrolyte solutions.From the per-spective of safety,all-solid-state batteries using inorganic solid electrolytes represent a superior battery.8To con-struct high-performance all-solid-state batteries,highly lithium-ion-conducting solid electrolytes are required.Sul-fide-based solid electrolytes show remarkably high lithium-ion conductivity.9-11Among them,Li2S-P2S5 glass ceramics show high lithium-ion conductivity of more than1Â10-3S cm-1at room temperature,along with a wide electrochemical window over5V.11,12We reported that the all-solid-state batteries using LiCoO2electrode and80Li2S320P2S5(mol%)glass-ceramic solid electrolyte exhibited long cycle performance.13However,all-solid-state batteries have generally been difficult to operate at high current densities of more than several milliamperes†Accepted as part of the2010“Materials Chemistry of Energy Conversion Special Issue”.*Corresponding author.Tel.:þ81-72-254-9334.Fax:þ81-72-9334. E-mail:hayashi@chem.osakafu-u.ac.jp.(1)Tarascon,J.-M.;Armand,M.Nature2001,414,359–367.(2)Cho,J.;Kim,Y.-J.;Park,B.Chem.Mater.2000,12,3788–3791.(3)Cho,J.;Kim,Y.J.;Kim,J.-T.;Park,B.Angew.Chem.,Int.Ed.2001,40,3367–3369.(4)Cho,J.;Kim,B.;Lee,J.-G.;Kim,Y.-W.;Park,B.J.Electrochem.Soc.2005,152,A32–A36.(5)Chen,Z.;Dahn,J.R.Electrochem.Solid-State Lett.2003,6,A221–A224.(6)Chen,Z.;Dahn,J.R.Electrochim.Acta2004,49,1079–1090.(7)Sun,Y.-K.;Cho,S.-W.;Myung,S.-T.;Amine,K.;Prakash,J.Electrochim.Acta2007,53,1013–1019.(8)Minami,T.Solid State Ionics for Batteries;Springer-Verlag:Tokyo,2005.(9)Kanno,R.;Murayama,M.J.Electrochem.Soc.2001,148,A742–A746.(10)Hayashi,A.;Hama,S.;Minami,T.;Tatsumisago,M.Electrochem.Commun.2003,5,111–114.(11)Mizuno,F.;Hayashi,A.;Tadanaga,K.;Tatsumisago,M.Adv.Mater.2005,17,918–921.(12)Hayashi,A.;Hama,S.;Mizuno,F.;Tadanaga,K.;Minami,T.;Tatsumisago,M.Solid State Ionics2004,175,683–686.(13)Minami,T;Hayashi,A;Tatsumisago,M Solid State Ionics2006,177,2715–2720./cmPublished on Web09/25/2009 r2009American Chemical950Chem.Mater.,Vol.22,No.3,2010Sakuda et al.per square centimeter despite the use of highly conducting solid electrolytes.The interface between the electrode and electrolyte in the all-solid-state batteries differs from that in conven-tional batteries using liquid electrolytes.Both electrode and electrolyte materials are solid;electrochemical reac-tions occur through the solid-solid interface between the electrode and solid electrolyte materials.Therefore,for-mation of a effective electrode-electrolyte interface is important for all-solid-state batteries to achieve high performance.8Many studies have been conducted to form an effective electrode-electrolyte interface in all-solid-state batteries.14-21Among them,interfacial mod-ification between electrode and solid electrolyte has been an effective technique to improve battery performance,as has been reported for batteries using liquid electrolytes. All-solid-state batteries using LiCoO2positive electrodes and sulfide solid electrolytes have shown large interfacial resistance between LiCoO2and solid electrolytes.The interfacial resistances have been decreased greatly through the use of coatings using LiNbO3,Li4Ti5O12, LiTaO3,and Li2O-SiO2on LiCoO2.17-21The reason for the decreased interfacial resistance remains unclear. Observation and structural analysis of the interfacebetween LiCoO2and sulfide solid electrolyte is beneficialto reveal the reasons for the large interfacial resistance ofthe all-solid-state batteries and for the decrease of theinterfacial resistance by the coatings.Electrochemicalimpedance measurements have so far been used mainlyto analyze the electrode-electrolyte interface of the all-solid-state batteries using sulfide-based solid electrolytes.On the other hand,transmission electron microscopy(TEM)is a powerful tool to obtain information of theelectrode-electrolyte interface.Brazier et al.reportedTEM observation of the electrode-electrolyte interfaceon the thin film batteries using oxide-based solid electro-lyte(amorphous Li2O-V2O5-SiO2).Their TEM obser-vations suggested that the deterioration of the interfaceupon cycling was caused by the migration of the chemicalelements between stacked layers.22Information about theinterface between electrode and electrolyte particles isnecessary to construct an ideal electrode-electrolyteinterface in all-solid-state batteries.The morphology,structure,and elemental distribution at the interfacial region directly affect the electrochemical performanceof the all-solid-state batteries;their investigation enablesus to obtain guidelines for the development of all-solid-state batteries with high performance.As describedabove,it is readily apparent that the interfacial observa-tion between positive electrode and sulfide solid electro-lyte is important.Therefore,we have conducted TEMobservations of the interface between LiCoO2and asulfide solid electrolyte.In the present work,samples for TEM observation wereprepared using a focused ion beam(FIB).The interfacebetween the LiCoO2electrode and80Li2S320P2S5glass-ceramic solid electrolyte of all-solid-state cells was studiedusing TEM and scanning TEM(STEM)with energydispersive X-ray spectroscopy(EDX).Additionally,weprepared all-solid-state cells using Li2SiO3-coated LiCoO2and compared the electrode-electrolyte interface of thecell using Li2SiO3-coated LiCoO2with that using non-coated LiCoO2to clarify the coating effect from theperspective of structural changes.Finally,the electroche-mical performances of the all-solid-state batteries usingnoncooated and Li2SiO3-coated LiCoO2were demon-strated.The charge-discharge performance of the all-solid-state batteries using sulfide-based solid electrolyteshas been investigated mainly at room temperature to date.As described in this paper,we demonstrate the charge-discharge performance of the batteries in a wide tempera-ture range of-30to100°C.It is difficult for conventionalbatteries using liquid electrolyte to operate at a tempera-ture of100°C because of safety issues;nevertheless,operation at that temperature is beneficial for describingfeatures of all-solid-state batteries.Experimental Section1.Preparation of All-Solid-State Cells.The LiCoO2particles (Toda Kogyo Corp.)used for a positive electrode material were dried at350°C before fabricating the all-solid-state cells.The Li2SiO3-coated LiCoO2particles were prepared using the sol-gel method.Lithium ethoxide(LiOEt)and tetraethoxysilane [Si(OEt)4]were diluted to1wt%with dry ethanol.Subsequently, the diluted sols were mixed with LiCoO2particles.After drying at room temperature,the mixture was heated at350°C for30min. The weight ratio of Li2SiO3coatings to LiCoO2particles was 0.6/100.Figures6-8show cross-sectional TEM images of 0.6wt%Li2SiO3-coated LiCoO2particles.The Li2SiO3coating layer on the LiCoO2particles was confirmed by cross-sectional TEM and SEM-EDX;the thickness was ca.10nm.20More details are described in previous reports.18,20In this study,an80Li2S320P2S5(mol%)glass ceramic among Li2S-P2S5solid electrolytes was used as a solid electrolyte;the 80Li2S320P2S5glass ceramic is described as a Li2S-P2S5solid electrolyte in this paper.An80Li2S320P2S5(mol%)glass-ceramic for solid electrolytes was prepared using mechanical milling and subsequent heat treatment.10For preparation of the 80Li2S320P2S5glass,Li2S(99.9%;Idemitsu Kosan Co.Ltd.) and P2S5(99%;Aldrich Chemical Co.Inc.)were used as starting materials.These materials were mechanically milled at510rpm for10h at room temperature using a planetary ball mill (Pulverisette7;Fritsch GmbH)with a zirconia pot(45mL volume)and160zirconia balls(5mm diameter).The obtained(14)Mizuno, F.;Hayashi, A.;Tadanaga,K.;Tatsumisago,M.J.Electrochem.Soc.2005,152,A1499–A1503.(15)Hayashi,A;Nishio,Y.;Kitaura,H.;Tatsumisago,M.Electro-mun.2008,10,1860–1863.(16)Ohta,N.;Takada,K.;Zhang,L.;Ma,R.;Osada,M.;Sasaki,T.Adv.Mater.2006,18,2226–2229.(17)Ohta,N.;Takada,K.;Sakaguchi,I.;Zhang,L.;Ma,R.;Fukuda,K.;Osada,M.;Sasaki,mun.2007,9,1486–1490.(18)Sakuda,A.;Kitaura,H.;Hayashi,A.;Tadanaga,K.;Tatsumisago,M.Electrochem.Solid-State lett.2008,11,A1–A3.(19)Takada,K.;Ohta,N.;Zhang,L.;Fukuda,K.;Sakaguchi,I.;Ma,R.;Osada,M.;Sasaki,T.Solid State Ionics2008,179,1333–1337.(20)Sakuda,A.;Kitaura,H.;Hayashi,A.;Tadanaga,K.;Tatsumisago,M.J.Electrochem.Soc.2009,156,A27–A32.(21)Sakuda,A.;Kitaura,H.;Hayashi,A.;Tadanaga,K.;Tatsumisago,M.J.Power Sources2009,189,527–530.(22)Brazier, A.;Dupont,L.;Dantras-Laffont,L.;Kuwata,N.;Kawamura,J.;Tarascon,J-M.Chem.Mater.2008,20,2352–2359.Article Chem.Mater.,Vol.22,No.3,2010951 glassy powder was heated at210°C for4h to yield highlyconductive80Li2S320P2S5glass-ceramic.All-solid-state cellswere constructed as follows.The LiCoO2and the glass-ceramicelectrolyte with a weight ratio of70:30were mixed using anagate mortar to prepare composite positive electrodes.Indiumfoil(99.999%;Furuuchi Chemical Corp.)was used as a negativeelectrode.A bilayer pellet consisting of the composite positiveelectrode(10mg)and glass-ceramic solid electrolytes(80mg)was obtained by pressing under360MPa(φ=10mm);indiumfoil was then attached to the bilayer pellet by pressing under240MPa.The pellet was pressed using two stainless steel rods;thestainless steel rods were used as current collectors for bothpositive and negative electrodes.All the processes for preparationof solid electrolytes and fabrication of all-solid-state batterieswere performed in a dry Ar-filled glovebox([H2O]<1ppm).2.Electrochemical Measurements.Electrochemical impe-dance spectroscopy measurements of the all-solid-state cellsusing noncoated and Li2SiO3-coated LiCoO2were performedusing an impedance analyzer(SI1260;Solartron)after chargingthem to3.6V vs Li-In under0.13mA cm-2at room tempera-ture.The applied voltage was50mV and the frequency rangewas from10mHz to1MHz.The cells were charged anddischarged using a charge-discharge measuring device(BTS-2004;Nagano Co.Ltd.).The measurements were conducted attemperatures between-30and100°C.The charge-dischargemeasurement at100°C was conducted at a high current densityof40mA cm-2.3.Cross-Sectional Observation of Electrode-ElectrolyteInterface.After charging,the layered pellets of In/80Li2S320P2S5/LiCoO2were obtained by removing of stainless steel current collector from the all-solid-state cells.Samples of the LiCoO2/solid electrolyte cross section for TEM observations were obtained using focused ion beam(FIB)milling of the positive electrode layer.The electrode-electrolyte interface was analyzed using TEM (JEM2100F;JEOL).An elemental mapping analysis for the cross-section of the positive electrode layer was conducted using STEM equipped with EDX(JED-2300T;JEOL).The samples were transferred in Ar atmosphere from a globe box to the equipments for FIB and TEM.Results and Discussion1.Electrochemical Impedance Spectroscopy on the All-Solid-State Cells Using LiCoO2Electrode and Li2S-P2S5 Solid Electrolytes.Figure1shows impedance profiles of the all-solid-state cells using(a,c)noncoated and(b,d) 0.6wt%Li2SiO3-coated LiCoO2.Panels a and b in Figure1show impedance profiles of the as-prepared all-solid-state cells with noncoated and0.6wt%Li2SiO3-coated LiCoO2.No remarkable difference was apparent between the noncoated cell and the cell using Li2SiO3-coated LiCoO2in the impedance profiles before the charge-discharge measurements.Figures1(c,d)show impedance profiles of the cells after charging to3.6V vs Li-In at the current density of0.13mA cm-2.Two semicircles are visible in the impedance profiles;their peak top frequencies are about500and1Hz.The identification of the impedance components has been reported as follows:the resistance observed at the high-frequency region(>100kHz)is the resistance of the solid electrolyte layer;the semicircles observed in the medium-frequency(the peak top frequency of about500Hz)and low-frequency regions(the peak top frequency of about 1Hz)are,respectively,the resistances in the positive electrode layer(interfacial resistance between LiCoO2 and Li2S-P2S5solid electrolyte)and the negative elec-trode layer.20As presented in Figure1c,a large interfacial resistance(the resistance observed at500Hz)is observed in the cell using noncoated LiCoO2;the resistance de-creases because of the Li2SiO3-coated LiCoO2.We as-sume that the large interfacial resistance results from formation of the high-resistance interface between Li-CoO2and sulfide electrolyte.202.Interfacial Observation between LiCoO2Electrode and Li2S-P2S5Solid Electrolyte.To obtain information about the interface between LiCoO2electrode and Li2S-P2S5solid electrolyte,we conducted TEM observa-tions of the positive electrode layer of the all-solid-state cells.The all-solid-state cell using noncoated LiCoO2after charging to3.6V vs Li-In at the current density of 0.13mA cm-2was used for observations.Figure2shows cross-sectional high-angle annular dark field(HAADF) TEM images near the interface between noncoated Li-CoO2and Li2S-P2S5solid electrolyte.Figure2b shows a magnified image of LiCoO2/Li2S-P2S5interface pre-sented as a square in Figure2a.The TEM images show that LiCoO2electrode and Li2S-P2S5solid electrolyte retains a smooth contact after charging.An interfacial layer is visible at the interface between LiCoO2electrode and Li2S-P2S5solid electrolyte in Figure2b.The layer thickness is ca.10nm.Figure3shows a HAADF-STEM image and EDX mapping for the Co element near the LiCoO2electrode/Li2S-P2S5solid electrolyte interface. Existence of a Co element of LiCoO2electrode isobserved Figure1.Impedance profiles of the all-solid-state cells In/Li2S-P2S5solid electrolyte/(a,c)noncoated and(b,d)Li2SiO3-coated LiCoO2.Measure-ments were conducted(a,b)before and(c,d)after charging to3.6V vs Li-In at the current density of0.13mA cm-2.952Chem.Mater.,Vol.22,No.3,2010Sakuda et al.in Li 2S -P 2S 5solid electrolyte,indicating Co diffusion from LiCoO 2to Li 2S -P 2S 5.More details are available from EDX line profiles at the region near the LiCoO 2electrode/Li 2S -P 2S 5solid electrolyte interface.Figure 4a shows the HAADF -STEM image of the LiCoO 2/Li 2S -P 2S 5interface.Figure 4b presents the EDX line profiles of the existence ratio for Co,S,and P elements at the position indicated by the arrow in Figure 4a.The coexistence of Co,S,and P elements is observed at the interfacial layer,indicating that the elements of LiCoO 2and Li 2S -P 2S 5solid electrolyte mutually diffuse.In parti-cular,the Co diffusion from LiCoO 2to Li 2S -P 2S 5is outstanding;the Co element is observed even at a distance of 50nm from the interface.Moreover,the EDX line profile shows small S diffusion into LiCoO 2.The mutual diffusion of Co,S,and P is related to the formation of the interfacial layer.The interfacial region nanostructure is observed using nanoarea electron diffraction (n-ED),which selectively analyzes the interfacial materials.Figure 5presents a cross-sectional HAADF -STEM image and the n-ED pattern of the Li 2S -P 2S 5solid electrolyte,interfaciallayer,and LiCoO 2electrode.The n-ED pattern of the solid electrolyte (position 1)shows that the solid electrolyte is amorphous.The n-ED patterns of LiCoO 2electrode show the same diffraction patterns from inside to the surface (position 4and 5),indicating that the LiCoO 2is a single crystal and that large degradation does not occur.On the other hand,the n-ED patterns of the interface layer (position 2and 3)show patterns suggesting the presence of a nanosize polycrystal.The EDX analysis shows that the interfacial layer mainly comprises Co and S.Uchimoto et al.reported from X-ray absorption spectroscopy that a compound whose electronic state resembles that of CoS is produced at the interface between LiCoO 2and sulfide electrolyte during charge -discharge cycling.23Conse-quently,it is assumed that nanosize polycrystalline cobalt sulfides exist at the interfacial layer.However,identifica-tion of the polycrystals is difficult because there are no remarkable spots in the n-ED pattern.Further analysesareFigure 2.(a)Cross-sectional high-angle annular dark field (HAADF)TEM images of the interface between the LiCoO 2electrode and the Li 2S -P 2S 5solid electrolyte.(b)Magnified image of the area described by the square in a.Observations were conducted after initial charging to 3.6V vs Li -In.Figure 3.(a)Cross-sectional HAADF -STEM image and (b)the corresponding EDX mapping for the Co element near the LiCoO 2electrode/Li 2S -P 2S 5solid electrolyte interface after initial charging.(23)Uchimoto,Y.;Wakihara,M.In Solid State Ionics for Batteries ;Minami,T.Ed.;Springer-Verlag:Tokyo,2005;p 126.Article Chem.Mater.,Vol.22,No.3,2010953necessary to clarify the interfacial structure in greater detail.The interfacial TEM observation revealed that the inter-facial layer was formed at the interface between LiCoO 2and Li 2S -P 2S 5solid electrolyte.Moreover,mutual diffusion ofCo,P,and S was observed at the interface.The formation of the interfacial layer and the mutual diffusion indicates the degradation of the LiCoO 2electrode and Li 2S -P 2S 5solid electrolyte near the interface.Degradation of the interface is inferred as one cause of the large interfacial resistance of the electrode -electrolyte interface of the all-solid-state batteries using LiCoO 2electrode and Li 2S -P 2S 5solid electrolytes.Suppression of both the formation of the interfacial layer and the diffusion is expected to be effective in decreasing the interfacial resistance and bringing about improvement of the elec-trochemical performance of all-solid-state cells.3.Interfacial Observation between Li 2SiO 3-Coated LiCoO 2Electrode and Li 2S -P 2S 5Solid Electrolyte.Here,it has been revealed that the interfacial layer was formed and that the elements of Co,P,and S mutually diffused at the interface between LiCoO 2and the Li 2S -P 2S 5solid electrolyte.These results suggest interfacial structural changes,which would cause the high interfacial resistance for lithium-ion conduction between LiCoO 2and solid electrolyte.Oxide coatings have been reported as an effec-tive means to decrease the interfacial resistance of the all-solid-state cells using sulfide solid electrolyte,as pre-sented in Figure 1.In this section,we specifically examine the electrode -solid electrolyte interface of the cell using Li 2SiO 3-coated LiCoO 2particles as a positive electrode material.The Li 2SiO 3coating is effective in decreasing the interfacial resistance (Figure 1)and improving the high rate performance of the all-solid-state cells using LiCoO 2electrode and Li 2S -P 2S 5solid electrolyte.18,20We specifi-cally investigated the LiCoO 2/Li 2S -P 2S 5interface oftheFigure 4.(a)Cross-sectional HAADF -STEM image of LiCoO 2elec-trode/Li 2S -P 2S 5solid electrolyte interface after initial charging and (b)cross-sectional EDX line profiles for Co,P,and S elements.The arrow in a presents the positions at which EDX measurements weretaken.Figure 5.Cross-sectional HAADF -STEM image and the n-ED patterns of the Li 2S -P 2S 5solid electrolyte,the interfacial layer,and the LiCoO 2electrode after initial charging.The numbered points in the HAADF-STEM image correspond to the positions of n-ED measurements.954Chem.Mater.,Vol.22,No.3,2010Sakuda et al.cell using Li 2SiO 3-coated LiCoO 2after charging to 3.6V vs Li -In.Images a and b in Figure 6show the HAADF -STEM image and (c)the EDX mapping for Co element near the Li 2SiO 3-coated LiCoO 2electrode/Li 2S -P 2S 5solid elec-trolyte interface.The LiCoO 2and Li 2S -P 2S 5solid elec-trolyte retain their smooth contact (Figure 6a).The EDX mapping shows that the Co diffusion from LiCoO 2to Li 2S -P 2S 5is suppressed by Li 2SiO 3coatings.Figure 7a shows the HAADF -STEM image;Figure 7b shows EDX line profiles of the existence ratio for Co,P,S,and Si elements at the position indicated by the arrow in Figure 7a.In the STEM image,the interfacial layer is visible.The EDX line profile shows that the Si element of the Li 2SiO 3coating is visible at the interface.The EDX line profile also shows coexistence of Co,P,and S elements at the interfacial region.The Co diffusion is observed between about 30nm.Figure 8presents the cross-sectional HAADF -STEM image and the n-ED patterns of the interface between Li 2SiO 3-coated LiCoO 2electrode and Li 2S -P 2S 5solid electrolyte.The n-ED pattern of Li 2S -P 2S 5solid electrolyte (position 5)shows that the solid electrolyte is amorphous.The n-ED pattern of the interfacial layer (position 4)shows that the inter-facial layer is amorphous.The n-ED patterns of LiCoO 2(positions 1-3)show the same patterns,indicatingthatFigure 6.(a)Cross-sectional HAADF -STEM image near the Li 2SiO 3-coated LiCoO 2electrode/Li 2S -P 2S 5solid electrolyte interface after initial charging.(b)Magnified image of cross-sectional HAADF-STEM image.(c)EDX mapping for the Co element in the area corresponding tob.Figure 7.(a)Cross-sectional HAADF -STEM image of the Li 2SiO 3-coated LiCoO 2/Li 2S -P 2S 5interface after initial charging and (b)cross-sectional EDX line profiles for Co,P,S,and Si ele-ments.The arrow in a indicates the positions of the EDX measure-ments.Article Chem.Mater.,Vol.22,No.3,2010955the LiCoO 2particle is single-crystal and that large de-gradation does not occur.The Co and S exist at the interfacial layer also in the presence of Li 2SiO 3thin films;cobalt sulfides would form partially at the interfacial layer.However,the Co diffusion at the interface in the presence of the Li 2SiO 3thin film decreases compared to that at the interface without Li 2SiO 3thin film (Figures 3and 4).The Co diffusion is suppressed by the Li 2SiO 3coating layer.The Li 2SiO 3acts as a buffer layer prevent-ing Co diffusion from the LiCoO 2electrode to Li 2S -P 2S 5solid electrolyte.Nanocrystalline materials are not ob-served in the n-ED patterns when using Li 2SiO 3-coated LiCoO 2.The interfacial layer in this case is considered as an amorphous Li 2SiO 3coating layer.The Li 2SiO 3coatings suppress formation of the polycrystalline interfacial pro-ducts.The interfacial Li 2SiO 3coating is effective in pre-venting the direct contact between LiCoO 2and Li 2S -P 2S 5and suppressing degradation of the interface such as the mutual elemental diffusion and the interfacial layer formation.Ohta et al.proposed a “space -charge layer model”to explain the large interfacial resistance between LiCoO 2and the sulfide solid electrolytes in all-solid-state bat-teries using Li 3.25Ge 0.25P 0.75S 4(thio -LISICON)as a solid electrolyte.16,17,19In the model,the reason for the large interfacial resistance is considered to be formation of a lithium-deficient layer (space -charge layer)at the interface.The space -charge layer results from lithium-ion transfer from the sulfide electrolyte to LiCoO 2because of the large difference in electrochemical poten-tials in these materials.The coatings of Li 4Ti 5O 12,LiNbO 3,and LiTaO 3on the LiCoO 2electrode yielded a low interfacial resistance in the all-solid-state batteries,and Ohta et al.suggested that the oxide coatings act as a buffer layer to suppress the formation of the space--charge layer.16,17,19In this study,we identified structural changes caused by the diffusion of Co,P,and S elements and the formation of new interfacial layers mainly composed of Co and S at the LiCoO 2/Li 2S -P 2S 5interface.These phenomena are one reason for the large interfacial resistance of the all-solid-state batteries.The coating of Li 2SiO 3on LiCoO 2was effective in suppressing the interfacial layers.We thus believe that the suppression of the interfacial layers is the main reason for the reduction of interfacial resistance between LiCoO 2electrode and Li 2S -P 2S 5solid electrolyte.4.Electrochemical Performance of the All-Solid-State Cells Using LiCoO 2Electrode and Li 2S -P 2S 5Solid Elec-trolyte.All-solid-state batteries using Li 2SiO 3-coated Li-CoO 2particles reportedly show good electrochemical performance at room temperature.18,20We demonstrate herein the all-solid-state batteries using LiCoO 2electrode and Li 2S -P 2S 5solid electrolytes at extremely low and high temperatures.Panels a and b in Figure 9show impedance profiles of the all-solid-state cells using noncoated and Li 2SiO 3-coated LiCoO 2at -30°C after charging to 3.6V vs Li -In,which corresponds to 4.2V vs Li.The internal resistance of the cells at the low temperature of -30°C is much larger than that at room temperature,as presented in Figure 1.The resistances attributed to a solid electrolyte layer(theFigure 8.Cross-sectional HAADF -STEM image and the n-ED patterns of the interface between Li 2SiO 3-coated LiCoO 2electrode and Li 2S -P 2S 5solid electrolyte after initial charging.The numbered points in the HAADF -STEM image correspond to the positions of n-ED measurements.。

锂离子电池电解液1 锂离子电解液概况电解液是锂离子电池四大关键材料(正极、负极、隔膜、电解液）之一，号称锂离子电池的“血液”，在电池中正负极之间起到传导电子的作用，是锂离子电池获得高电压、高比能等优点的保证.电解液一般由高纯度的有机溶剂、电解质锂盐(六氟磷酸锂，LiFL6）、必要的添加剂等原料，在一定条件下,按一定比例配制而成的。

有机溶剂是电解液的主体部分，与电解液的性能密切相关，一般用高介电常数溶剂与低粘度溶剂混合使用；常用电解质锂盐有高氯酸锂、六氟磷酸锂、四氟硼酸锂等,但从成本、安全性等多方面考虑，六氟磷酸锂是商业化锂离子电池采用的主要电解质；添加剂的使用尚未商品化，但一直是有机电解液的研究热点之一.自1991年锂离子电池电解液开发成功，锂离子电池很快进入了笔记本电脑、手机等电子信息产品市场,并且逐步占据主导地位。

目前锂离子电池电解液产品技术也正处于进一步发展中。

在锂离子电池电解液研究和生产方面，国际上从事锂离子电池专用电解液的研制与开发的公司主要集中在日本、德国、韩国、美国、加拿大等国，以日本的电解液发展最快，市场份额最大.国内常用电解液体系有EC+DMC、EC+DEC、EC+DMC+EMC、EC+DMC+DEC等。

不同的电解液的使用条件不同,与电池正负极的相容性不同,分解电压也不同。

电解液组成为lmol/LLiPF6/EC+DMC+DEC+EMC，在性能上比普通电解液有更好的循环寿命、低温性能和安全性能，能有效减少气体产生，防止电池鼓胀.EC/DEC、EC/DMC电解液体系的分解电压分别是4。

25V、5.10V.据Bellcore研究，LiPF6/EC+DMC与碳负极有良好的相容性，例如在LixC6/LiMnO4电池中,以LiPF6/EC+DMC为电解液, 室温下可稳定到4。

9V，55℃可稳定到4.8V，其液相区为-20℃～130℃，突出优点是使用温度范围广，与碳负极的相容性好，安全指数高,有好的循环寿命与放电特性。

锂离子电池常用的粘结剂的种类、作用及性能锂离子电池粘结剂一般都是高分子化合物，电池中常用的粘结剂有；(1)PVA(聚乙烯醇)PVA的分子式为卡CH2CHOH手JJ，聚合度”一般为700—2000，PVA是一种亲水性高聚物白色粉末，密度为1，24—1．34g•cm-3。

PVA 可与其他水溶性高聚物混溶，如与淀粉、CMC、海藻钠等都有较好的混溶性。

(2)聚四氟乙烯(PTFE)PTFE俗称“塑料王”，是一种白色粉末，密度为2．1—2．3g•CITI+，热分解温度为415℃。

PTFE电绝缘性能好，耐酸，耐碱，耐氧化。

PTFE的分子式为卡CF2一CF2头。

，是由四氟乙烯聚合而成的。

nCF2＝CF、2一卡CF2＝CF2于。

常用60％的PTFE乳液作电极粘结剂。

(3)羧甲基纤维素钠(CMC)CMC为白色粉末，易溶于水，并形成透明的溶液，具有良好的分散能力和结合力，并有吸水和保持水分的能力。

(4)聚烯烃类(PP，PE以及其他的共聚物)；(5)(PVDF／NMP)或其他的溶剂体系；(6)粘接性能良好的改性SBR橡胶；(7)氟化橡胶；(8)聚胺酯。

锂电池用粘接剂；锂离子电池中，由于使用电导率低的有机电解液，因而要求电极的面积大，而且电池装配采用卷式结构，电池的性能的提高不仅对电极材料提出了新的要求，而且对电极制造过程中使用的粘接剂也提出了新的要求。

1、粘接剂的作用及性能；(1)保证活性物质制浆时的均匀性和安全性；(2)对活性物质颗粒间起到粘接作用；(3)将活性物质粘接在集流体上；(4)保持活性物质间以及和集流体间的粘接作用；(5)有利于在碳材料(石墨)表面上形成SEI膜。

2、对粘接剂的性能要求；(1)在干燥和除水过程中加热到130—180~C情况下能保持热稳定性；(2)能被有机电解液所润湿；(3)具有良好的加工性能；(4)不易燃烧；(5)对电解液中的I．iClQ，I．iPP、6等以及副产物I．iOH，㈠2C03等稳定；(6)具有比较高的电子离子导电性；(7)用量少，价格低廉；以往的镍镉、镍氢电池，使用的电解液是水溶液体系，粘接剂可以使用PVA，CMC等水溶性高分子材料，或PTFE的水分散乳液。

技术丨5大锂电池粘结剂性能分析解码粘结剂是浆料中重要的组分，粘结剂将各种颗粒粘接在一起，形成了具有粘附性的浆料，将其与金属箔紧密粘接在一起。

好的粘结剂，不仅有利于电池能量密度的提高，对于电池内阻也有明显的降低作用，对电池的电化学性能也具有重要的影响。

锂电池浆料是一个复杂的多相混合非牛顿型流体。

正极浆料由活物质、导电剂、粘结剂及溶剂组成。

目前市场化的锂电池正极材料包括钴酸锂、锰酸锂、磷酸铁锂和三元材料等产品，导电剂主要有炭黑、碳纳米管、导电石墨等，粘结剂分为水系和油系粘结剂，对应的溶剂有水系的去离子水和油系的NMP溶剂。

负极浆料由活物质、导电剂、粘结剂、增稠剂及溶剂去离子水等多相物质混合制成。

负极活物质主要是各类型的石墨、硅碳负极，导电剂和正极导电剂种类差不多（炭黑、CNT、VGCF等），目前市场上负极粘结剂一般选择对环境无污染的水系粘结剂如CMC、SBR、LA132等。

当负极材料采用钛酸锂时，粘结剂一般选择油系的PVDF，用NMP来作溶剂。

活物质、导电剂、溶剂对金属电极没有粘附性，故无法做成极片用于制备锂电池。

粘结剂是浆料中重要的组分，粘结剂将各种颗粒粘接在一起，形成了具有粘附性的浆料，将其与金属箔紧密粘接在一起。

好的粘结剂，不仅有利于电池能量密度的提高，对于电池内阻也有明显的降低作用，对电池的电化学性能也具有重要的影响。

从极片加工角度对粘结剂的性能要求主要有以下几点：1.能够长时间维持浆料粘度保持不变。

不会因为浆料放置导致其沉降，失效。

2.可溶解形成高浓度溶液，所需的汽化热较低。

3.碾压时容易成型且不会反弹。

4.具有柔性，在电极破裂时不会形成碎片。

粘结剂不仅关乎锂电池的制造工艺，而且对锂电池的电化学性能有着重要的影响，从电池性能角度来讲需要粘结剂具有这样的特点：1.能够很好的保持活物质的状态。

2.与金属箔具有良好的粘结性，不会因为电解液和充放电使用而剥离金属箔。

3.在较宽的电压范围内有良好的电化学稳定性。

锂电池电极芯的助溶剂
锂电池电极芯的助溶剂是指在电极制备过程中添加的一种溶剂，用于提高电极材料的溶解性和分散性，促进电极材料的均匀分散和涂覆。

常用的锂电池电极芯助溶剂包括以下几种：
1. 丁二酮（MEK）：丁二酮是一种有机溶剂，具有良好的溶解性和挥发性，常用于溶解聚合物粘结剂和电解质添加剂，以促进电极材料的分散和涂覆。

2. 二甲基亚砜（DMSO）：二甲基亚砜是一种极性有机溶剂，具有良好的溶解性和溶解度，常用于溶解锂盐和聚合物粘结剂，以提高电极材料的溶解性和电导率。

3. 乙二醇二甲醚（EGDME）：乙二醇二甲醚是一种低粘度的有机溶剂，具有良好的溶解性和挥发性，常用于溶解锂盐和聚合物粘结剂，以促进电极材料的分散和涂覆。

4. 甲醇（MeOH）：甲醇是一种常用的溶剂，具有较好的溶解性和挥发性，常用于溶解锂盐和聚合物粘结剂，以促进电极材料的分散和涂覆。

需要注意的是，助溶剂的选择应根据具体的电极材料和制备工艺来确定，以确保最佳的溶解性和分散性。

同时，助溶剂的使用量和溶解温度等因素也需要进行合理控制，以避免对电池性能产生不利影响。

锂离子电池电极界面化学与碳负极/电解液的相容性研究进展摘要：综述了目前锂离子电池碳负极/电解液相容性的研究概况，系统地阐述了固体电解质相界面（SEI）膜的组成、织构、稳定性与碳负极/电解液相容性的关系，并从电极界面和电解液组成两方面阐述了电极界面SEI膜的内涵特征等内容。

关键词：锂离子蓄电池；碳负极；电解液；界面化学；相容性在电化学体系中，研究的是影响电荷在化学相界面之间迁移的过程和因素。

电极界面SEI 膜的组成、形态、结构和稳定性对电极电化学性能有很大影响，本文从电极界面和电解液组成两方面阐述了电极界面SEI膜的内涵特征等内容。

一、碳负极/电解液相容性的基本内涵用于锂离子蓄电池的极性非质子溶剂，在电池首次充电过程中不可避免地都要在碳负极与电解液的相界面上反应，形成覆盖在碳电极表面的钝化薄层，人们称之为固体电解质相界面或称SEI膜。

SEI膜的形成一方面消耗了电池中有限的锂离子，例如，石墨电极在PC等许多电解液中的首次充放电过程中，不可逆容量损失高达50%以上［1］，石油焦等其它碳材料也达25%左右［2］，致使电池的质量比能量和体积比能量下降，这就需要使用更多的含锂正极材料来补偿初次充电过程中的锂消耗；另一方面也增加了电极/电解液界面的电阻，造成一定的电压滞后。

但优良的SEI膜具有有机溶剂不溶性，允许Li+比较自由地进出电极而溶剂分子却无法穿越，从而阻止了溶剂分子共插对电极的破坏，大大提高了电极循环寿命。

因此，如何优化电极的微细结构，改善界面状况，如何选择适当的电解液，保证电解液各组分与Li+在电极/电解液相界面形成优良的、稳定的、Li+可导的SEI膜是实现碳负极/电解液相容性的关键。

SEI膜机制的基本内容可归纳为：1、在一定的负极电位下，到达电极/电解液相界面的锂离子与电解液中的溶剂分子、电解质阴离子、添加剂分子、甚至是杂质分子在电极/电解液相界面发生不可逆反应；2、不可逆反应主要发生在电池首次充电过程中；3、电极表面完全被SEI膜覆盖后，不可逆反应即停止；4、一旦形成稳定的SEI膜，充放电过程可多次循环进行。

究集中在各种添加剂的使用方面，即进行少量加入就能有效的提高锂离子电池电化学性能的添加剂的研究。

1、SEI成膜促进剂主要指电解液在负极表面还原形成的SEI（solid electrolyte interface固体电解质界面）。

主要由Li2CO3，烷基锂，烷氧基锂和其他锂盐组成。

SEI膜主要分成两层，即嵌锂前形成的多孔层和嵌锂时形成的紧密层，后者电导率较高。

以EC基电解液为例，其反应机理为：其中机理1主要产物为Li2CO3及其他气体；机理2主要产物为烷氧基锂，形成的SEI膜较致密且产气量少。

两种反应机理在成膜过程中同时存在，并受石墨表面形态和化学性质影响。

如通过石墨的掺杂或表面包覆可减少嵌锂过程中的产气量并有助于SEI膜的形成。

可分为还原型、反应型及SEI修饰作用三种。

1.1 还原型SEI成膜促进剂具有较溶剂高的还原电位，充电时优先形成难溶固体产物覆盖在石墨表面。

包括电化学聚合和吸附两种；该类添加剂减少了气体产生量且增加了SEI的稳定性。

包括可聚合单体和还原剂两种。

如VC，VEC，AEC，VA等可进行电化学聚合成膜。

a.电化学聚合反应原理其中机理1主要产物为Li2CO3及其他气体；机理2主要产物为烷氧基锂，形成的SEI膜较致密且产气量少。

两种反应机理在成膜过程中同时存在，并受石墨表面形态和化学性质影响。

如通过石墨的掺杂或表面包覆可减少嵌锂过程中的产气量并有助于SEI膜的形成。

可分为还原型、反应型及SEI修饰作用三种。

1.1 还原型SEI成膜促进剂具有较溶剂高的还原电位，充电时优先形成难溶固体产物覆盖在石墨表面。

包括电化学聚合和吸附两种；该类添加剂减少了气体产生量且增加了SEI的稳定性。

包括可聚合单体和还原剂两种。

如VC，VEC，AEC，VA等可进行电化学聚合成膜。

a.电化学聚合反应原理b.应用实例c. 吸附：通过还原产物在石墨表面催化活性点吸附辅助SEI成型。

主要为S基，N基化合物，如SO2、CS2、SX2-、ES、PS及硝酸盐，该类添加剂由于S自身的氧化－还原穿梭作用引起一定程度的电池自放电。

锂离子电极电解质界面层调控【最新版】目录一、锂离子电极电解质界面层的概述二、锂离子电极电解质界面层的调控方法三、锂离子电极电解质界面层调控的重要性四、锂离子电极电解质界面层调控的研究进展五、锂离子电极电解质界面层调控的未来发展方向正文锂离子电池作为一种重要的能源存储设备，广泛应用于各类电子产品中。

然而，随着锂离子电池在各个领域的应用越来越广泛，人们对于锂离子电池性能的要求也越来越高。

其中，锂离子电极电解质界面层的调控成为提高锂离子电池性能的重要研究方向。

一、锂离子电极电解质界面层的概述锂离子电极电解质界面层是指电极材料与电解质之间的界面，它对锂离子电池的电化学性能具有重要影响。

锂离子在电极与电解质之间的传输过程中，会在界面层形成锂离子浓度梯度，这种梯度会影响到锂离子电池的容量、循环寿命等性能。

二、锂离子电极电解质界面层的调控方法锂离子电极电解质界面层的调控方法主要包括以下几种：1.界面修饰：通过在电极表面修饰一层功能性材料，如金属纳米颗粒、碳纳米管等，以提高界面层的电子传导性能和锂离子传输速率。

2.电解质优化：通过改变电解质的组成和结构，如添加界面稳定剂、使用新型电解质材料等，以降低界面电阻，提高锂离子传输速率。

3.电极材料改性：通过改变电极材料的结构和组成，如制备多孔电极、添加硅基材料等，以提高电极的锂离子存储容量和循环寿命。

三、锂离子电极电解质界面层调控的重要性锂离子电极电解质界面层的调控对于提高锂离子电池的电化学性能具有重要意义。

通过优化界面层，可以降低界面电阻，提高锂离子传输速率，从而提升电池的容量、循环寿命等性能。

此外，界面层的调控还能够提高电池的安全性能，降低电池的热失控风险。

四、锂离子电极电解质界面层调控的研究进展近年来，关于锂离子电极电解质界面层调控的研究取得了显著进展。

研究人员通过多种调控方法，如界面修饰、电解质优化、电极材料改性等，成功降低了界面电阻，提高了锂离子传输速率，从而提升了锂离子电池的性能。