USOO95091.48B2
(12) United States Patent (10) Patent No.: US 9,509,148 B2 Kako et al. (45) Date of Patent: *Nov. 29, 2016
(54) ELECTRIC STORAGE DEVICE (56) References Cited (71) Applicant: GS Yuasa International Ltd., U.S. PATENT DOCUMENTS Kyoto-shi, Kyoto (JP) 5,188,395 A 2, 1993 Kawahara et al. 2004/0259000 A1 12/2004 Adachi et al. 2008. O138714 A1 6/2008 Ihara et al. (72) Inventors: Tomonori Kako, Kyoto (JP); Hidefumi 2009/0111025 A1 4/2009 Lee et al. Hasegawa, Kyoto (JP); Katsushi 2009,0286155 A1 11/2009 Takehara Nishie, Kyoto (JP); Sumio Mori, Kyoto 2009,0286164 A1 11/2009 Wada et al. (JP) 2010. O155659 A1 6/2010 Yang et al. 2011/0111288 A1 5, 2011 Nishida et al. (73) Assignee: GS Yuasa International Ltd., Kyoto 2012/0208070 A1 8/2012 Nakashima et al. (JP) FOREIGN PATENT DOCUMENTS (*) Notice: Subject to any disclaimer, the term of this CN 1610.174 A 4/2005 patent is extended or adjusted under 35 EP 2618418 A1 T 2013 JP 2167746. A 6, 1990 U.S.C. 154(b) by 143 days. JP 38966 A 1, 1991 This patent is Subject to a terminal dis JP 11329505. A * 11, 1999 claimer. JP 2004111349 A 4/2004 JP 2005285491 A 10/2005 JP 3974O12 B2 9, 2007 (21) Appl. No.: 14/060,670 JP 2007 280781 A 10/2007 JP 2007534122. A 11/2007 JP 2007335143 A 12/2007 (22) Filed: Oct. 23, 2013 JP 2008O10183 A 1, 2008 JP 2008198432 A 8, 2008 (65) Prior Publication Data JP 2008210573. A 9, 2008 JP 2008226807. A 9, 2008 US 2014/0176O74 A1 Jun. 26, 2014 JP 2009 129541 A 6, 2009 JP 2009 199960. A 9, 2009 JP 2009245828 A 10/2009 JP 20092.77597 A 11/2009 Related U.S. Application Data JP 2010287512 A 12/2010 JP 2011049153. A 3, 2011 (63) Continuation of application No. 13/468,114, filed on JP 2011077052 A 4, 2011 May 10, 2012, now Pat. No. 8,597,827. JP 2011082033. A 4, 2011 WO WO9852244 A1 * 11, 1998 WO 201OO67549 A1 6, 2010 (30) Foreign Application Priority Data WO WO 2010O79565 A1 * T 2010 WO 20101471.06 A1 12/2010 May 11, 2011 (JP) ...... 2011-106195 WO 2011021644 A1 2, 2011 Apr. 4, 2012 (JP) ...... 2012-085291 OTHER PUBLICATIONS (51) Int. Cl. HOLM 4/3 (2010.01) J-PlatPat Machine Translation of the Detailed Description of JP HOLM 4/36 (2006.01) 2009-277597A (Nov. 26, 2009).* HOLM 4/62 (2006.01) Sheng Shui Zhang, "An Unique Lithium Salt for the Improved HOLM 2/6 (2006.01) Electrolyte of Li-ion Battery'. Electrochemistry Communications, HIM IO/0525 (2010.01) Aug. 1, 2006, pp. 1423-1428, vol. 8. HIM IO/0567 (2010.01) HIM ID/242 (2006.01) * cited by examiner H02. 700 (2006.01) HOIG II/60 (2013.01) Primary Examiner — Gregg Cantelmo (52) U.S. Cl. (74) Attorney, Agent, or Firm — The Webb Law Firm CPC ...... H02J 700 (2013.01); H0IG II/60 (2013.01); H0 IM 2/166 (2013.01); H0IM (57) ABSTRACT 2/1646 (2013.01); H0IM 2/1686 (2013.01); H01 M 4/13 (2013.01); H0 IM 4/366 Provided is an electric storage device including a positive (2013.01); H0 IM 4/62 (2013.01); HOLM electrode, a negative electrode, a separator disposed between 10/0525 (2013.01); H0IM 10/0567 (2013.01); the positive electrode and the negative electrode, a nonaque H0IM 10/4235 (2013.01); Y02E 60/122 ous electrolyte solution in which an electrolyte is dissolved (2013.01); Y02E 60/13 (2013.01); Y02P 70/54 in a nonaqueous solvent, wherein an inorganic filler layer is (2015.11); Y02T 10/7011 (2013.01); Y02T disposed between the positive electrode and the negative 10/7022 (2013.01); Y10T 29/49115 (2015.01) electrode and the nonaqueous electrolyte Solution contains (58) Field of Classification Search lithium difluorobis(oxalato)phosphate. None See application file for complete search history. 7 Claims, No Drawings US 9,509,148 B2 1. 2 ELECTRIC STORAGE DEVICE Patent Application Laid-Open No. 2009-199960 and Japa nese Patent Application Laid-Open No. 2009-277597, for CROSS-REFERENCE TO RELATED example. APPLICATION The insulating layer provided on the separator inhibits decomposition of the electrolyte in the electrolyte solution This application is a continuation of U.S. patent applica near the insulating layer and therefore is believed to inhibit tion Ser. No. 13/468,114, filed May 10, 2012, entitled generation of gas. “Electric Storage Device', now U.S. Pat. No. 8,597,827, However, while the insulating layers described in Japa which claims the benefit of Japanese Patent Application nese Patent Application Laid-Open No. 2009-199960 and Nos. 2011-106.195 and 2012-085291. The disclosure of the 10 Japanese Patent Application Laid-Open No. 2009.277597 foregoing applications are all incorporated herein by refer can inhibit generation of gas during a cycle and storage, the CCC. effect of the insulating layers is not great enough to inhibit generation of gas during initial charge. Especially when BACKGROUND OF THE INVENTION lithium difluorobis(oxalato)phosphate is added to a non 15 aqueous electrolyte solution, it is difficult to adequately 1. Field of the Invention inhibit Swelling that can be caused by gas generation during The present invention relates to an electric storage device the initial charge. including a nonaqueous electrolyte solution in which an That is, there has been a problem that a sufficient amount electrolyte is dissolved in a nonaqueous solvent. of lithium difluorobis(oxalato)phosphate cannot be added 2. Background Art because lithium difluorobis(oxalato)phosphate generates gas In recent years, rechargeable electric storage devices during reductive decomposition and, if added to a nonaque including nonaqueous electrolyte cells represented by ous electrolyte solution, swelling of the cell may be lithium ion cells and capacitors such as electric double layer increased by gas generation after initial charge and dis capacitors and the like have been used as power sources for 25 charge. electronic equipment, power sources for power storage, power sources for electric vehicles and the like, whose SUMMARY OF THE INVENTION performance enhancement and downsizing have been pro gressed. In light of the problem with the related art described The nonaqueous electrolyte cell is a cell in which a 30 above, an object of the present invention is to provide an negative electrode and a positive electrode prepared by electric storage device. Such as a nonaqueous electrolyte providing a negative electrode active material layer and a cell, in which lithium difluorobis(oxalato)phosphate is positive electrode active material layer on a current collector added to a nonaqueous electrolyte solution and which is composed of a metal foil, respectively, are arranged to face capable of inhibiting Swelling due to gas generation after each other through a separator electrically separating the 35 initial charge and discharge. According to the present invention, an electric storage electrodes, and ions are accepted and donated between the device includes: positive electrode and negative electrode in a nonaqueous a positive electrode: electrolyte solution, in which an electrolyte is dissolved in a a negative electrode: nonaqueous solvent, to charge and discharge the cell. 40 a separator disposed between the positive electrode and Known examples of the nonaqueous electrolyte Solution the negative electrode; include Solutions that contain a lithium phosphate derivative a nonaqueous electrolyte solution in which an electrolyte such as lithium difluorobis(oxalato)phosphate (Patent Docu is dissolved in a nonaqueous solvent; and ment 1: Japanese Patent No. 3974.012 and Patent Document an inorganic filler layer disposed between the positive 2: Japanese Patent Application Laid-Open No. 2007 45 electrode and the negative electrode: 335143). wherein the nonaqueous electrolyte solution contains Adding lithium difluorobis(oxalato)phosphate to a non lithium difluorobis(oxalato)phosphate. aqueous electrolyte solution increases the cycle performance of the cell and enhances the high-temperature storageability DETAILED DESCRIPTION OF THE of the cell. Accordingly, the nonaqueous electrolyte Solution 50 PREFERRED EMBODIMENTS to which lithium difluorobis(oxalato)phosphate is added can have great effects as the nonaqueous electrolyte solution for A cell which is one embodiment of the electric storage nonaqueous electrolyte cells Such as lithium ion cells. The device according to the present invention will be described greater the additive amount of lithium difluorobis(oxalato) below. The cell according to this embodiment is a nonaque phosphate, the greater the effect is. 55 ous electrolyte secondary cell, more specifically, a lithium However, lithium difluorobis(oxalato)phosphate added to ion secondary cell. the nonaqueous electrolyte solution of a cell can be reduc (First Embodiment) tively decomposed to generate gas during initial charge. As A cell of this embodiment includes a positive electrode, a a result, the cell can swell. When gas is generated between negative electrode, a separator disposed between the posi the negative and positive electrodes, current applied con 60 tive electrode and the negative electrode, and a nonaqueous centrates on that location, reducing the life of the cell. electrolyte solution in which an electrolyte is dissolved in a Therefore, there is a problem that a sufficient amount of nonaqueous solvent. The cell of this embodiment is a cell in lithium difluorobis(oxalato)phosphate cannot be added. which an inorganic filler layer is disposed between the A known approach to preventing Swelling of a typical cell positive electrode and the negative electrode, the nonaque that uses an electrolyte containing a lithium salt is to provide 65 ous electrolyte solution contains lithium difluorobis(ox an insulating inorganic oxide layer (hereinafter referred to as alato)phosphate, and the inorganic filler layer is disposed on the insulating layer) on a separator as described in Japanese the separator. US 9,509,148 B2 3 4 In particular, the cell of this embodiment includes a An inorganic filler that has an SiO2-equivalent mass ratio negative electrode including a negative-electrode active in the inorganic filler within these ranges can effectively material layer and a positive electrode including a positive inhibit initial cell swelling. electrode active material layer. The active material layers are The term SiO-equivalent mass ratio of an Si element as arranged to face each other with a separator therebetween. used herein refers to the ratio of the mass of SiO in oxides The electrodes are contained in a case together with a contained in the inorganic filler layer, which is determined nonaqueous electrolyte Solution. by extracting element species, K, Na, Ca, Ba, Rb, Cs, Al. As the separator, woven fabric, nonwoven fabric, or a Mg, Fe, Ti, Mn, Cr, Zn, V. Be, B. Si, Zr, Ce, and Y contained synthetic resin microporous membrane that is insoluble in in the inorganic filler layer and calculating the mass of each organic solvent may be used, among which a synthetic resin 10 element, on the assumption that all of these element species microporous membrane is preferable. exist in the form of oxides, K-O, NaO, CaO, BaO, Rb2O, Among various synthetic resin microporous membranes, Cs-O, Al-O, MgO, FeO, TiO, MnO, CrO, ZnO, VOs, especially polyethylene and polypropylene microporous BeO. B.O. SiO, ZrO2. CeO, and Y.O. respectively. membranes, microporous membranes of polyethylene and If two or more inorganic fillers are used, the SiO polypropylene combined with aramid or polyimide, or a 15 equivalent mass ratio in the inorganic fillers is calculated polyolefin microporous membrane Such as a microporous from the sum of the masses of SiO, and other oxides in the membrane of a composite of any of these resins are prefer inorganic fillers. able in terms of factors such as thickness, membrane Methods for measuring the SiO2-equivalent mass ratio in strength, and membrane resistance. the inorganic filler layer include quantitative analysis of the The separator has a thickness in the range of 6 um to 40 elements using a system Such as an X-ray fluorescence um, preferably in the range of 12 um to 25 Jum. spectrometer, an EPMA (electron probe microanalyzer), an The porosity of the separator is preferably in the range of NMR (nuclear magnetic resonator), and an ICP-OES (induc 30 volume % to 60 volume 96 because a porosity in this tively coupled plasma optical emission spectrometer). range can maintain the strength and provide good charge The inorganic filler may be of any shape that can be mixed discharge performance. 25 with the binder and applied to the separator, such as par The term porosity of the separator as used herein refers to ticulate or fibrous, and is not limited to a particular shape. a value calculated according to Equation (3) given below. For a particulate inorganic filler, the average diameter of the particles is preferably in the range of approximately 0.1 porosity of separator (volume %)={volume (mass-membrane density)--volume)x100 um to approximately 3.0 um because of ease of mixing with (3) 30 the binder and ease of application. The mass and the Volume are the mass (mg) and the The binder to mix with the inorganic filler is preferably volume (mm) of a separator having a predetermined size one that can bind the inorganic filler to the separator, is (the predetermined size is a size that can be accurately insoluble in the electrolyte solution, and electrochemically measured, for example 100 mmx100 mm in the case of a stable in the range of use of the lithium ion secondary cell. sheet-shaped separator material). The membrane density is 35 For example, the binder is preferably a fluorine-contain the membrane density (g/cm) of the separator. ing resin such as polyvinylidene fluoride (PVdF) or poly In this embodiment, the inorganic filler layer is disposed tetrafluoroethylene, styrene-butadiene rubber (SBR), acrylic on a surface of the separator. resin, polyolefin resin, polyvinyl alcohol, or a nitrogen Specifically, the inorganic filler layer is formed on at least containing resin Such as polyamide, polyimide, or poly one side of the separator. 40 amide-imide, or a cross-linked polymer of cellulose and The inorganic filler layer is formed, for example, by acrylamide, a cross-linked polymer of cellulose and chitosan coating at least one side of the separator with a paste of a pyrrolidone carboxylic acid, or polysaccharide macromo mixture of an inorganic filler and a binder. lecular polymer Such as chitosan or chitin cross-linked by a The inorganic filler is preferably made of a material that cross-linker. has a melting point higher than or equal to 200° C., has a 45 The content of the binder can be adjusted to be appropri high electrical insulation, and is electrochemically stable in ate for biding the inorganic filler to the separator without the range of use of the lithium ion secondary cell. reducing the permeability of the separator and the retention Examples of the inorganic filler includes: oxide ceramics ability of the electrolyte solution. The content is preferably Such as silica, alumina, titania, Zirconia, magnesia, ceria, approximately 1 to 20 weight % of the inorganic filler. yttria, Zinc oxide, and iron oxide; nitride ceramics Such as 50 To form the inorganic filler layer on the separator, one side silicon nitride, titanium nitride, and boron nitride; ceramics of the separator is coated with a mixture of the inorganic Such as silicon carbide, calcium carbonate, aluminum Sul filler and the binder and the coating is dried appropriately. fate, aluminum hydroxide, potassium titanate, talc, kaolin The thickness of the dried coating is preferably greater clay, kaolinite, halloysite, pyrophyllite, montmorillonite, than or equal to 3 um and less than or equal to the thickness sericite, mica, amesite, bentonite, asbestos, aluminosilicate, 55 of the separator. calcium silicate, magnesium silicate, diatomaceous earth, The thickness of the dried coating is preferably in the and silica sand; and glass fiber. range of 5 um to 12 um, and more preferably in the range of Any one of these inorganic fillers or a mixture of two or approximately 5 um to approximately 10 um, provided that more of these may be used. the thickness is less than or equal to the thickness of the Among these inorganic fillers, especially silica, alumino 60 separator. silicate and the like are preferable because they are inorganic If the thickness of the inorganic filler layer is 3 um or Substances predominantly composed of SiO. greater, Swelling during the initial charge can be more If an inorganic filler that is predominantly composed of effectively inhibited. At the same time, a thickness less than SiO is used, the SiO-equivalent mass ratio of the Si the thickness of the separator cannot prevent penetration of element is preferably greater than or equal to 40%, more 65 the electrolyte solution to the positive and negative electrode preferably greater than or equal to 50% and less than or plates through the inorganic filler layer during the manufac equal to 80%. turing of the cell. US 9,509,148 B2 5 6 The porosity of the inorganic filler layer is less than or ene glycol dipropionate, propylene glycol dipropionate, equal to 70 volume 96, preferably in the range of 50 volume methyl acetate, ethyl acetate, propyl acetate, butyl acetate, % to 70 volume 96, more preferably in the range of 60 methyl propionate, ethyl propionate, propyl propionate, volume 9/6 to 70 volume 96. dimethyl carbonate, diethyl carbonate, ethyl methyl carbon Furthermore, the porosity of the inorganic filler layer is ate, methyl propyl carbonate, ethyl-propyl carbonate, dipro preferably in these ranges and greater than or equal to the pyl carbonate, methyl isopropyl carbonate, ethyl isopropyl porosity of the separator. carbonate, diisopropyl carbonate, dibutyl carbonate, If the porosity of the inorganic filler layer is less than the acetonitrile, fluoroacetonitrile, alkoxy-substituted and halo porosity of the separator, the inorganic filler layer tends to gen-substituted cyclic phosphaZenes or chain phosphaZenes clog, which can result in a high internal resistance of the 10 Such aS ethoxy pentafluorocyclotriphosphaZene, separator. diethoxytetra fluorocyclotriphosphaZene, and phenoxy pen Limiting the thickness to the ranges stated above can tafluorocyclotriphosphaZene, phosphoric esters such as tri reduce a decrease in the energy density and power density of ethyl phosphate, trimethyl phosphate, and trioctyl phos the cell due to an increase in the weight of the cell. phate, boric acid esters such as triethyl borate and tributyl Furthermore, limiting the thickness to the ranges stated 15 borate, and N-methyl oxazolidinone and N-ethyl oxazolidi above can inhibit a decrease in power due to an increase in OC. the diffusion resistance of lithium ions in the inorganic filler The nonaqueous solvent may be any one of these or any layer which can occur if the inorganic filler layer is exces mixture of these. sively thick. The nonaqueous electrolyte solution contains one or more Limiting the porosity of the inorganic filler layer in the of the well-known electrolytic salts enumerated above. ranges stated above in this embodiment can be made by, for Examples include ionic compounds such as LiClO. example, adjusting the mixture ratio of the inorganic filler LiBF LiAsF LiPF LiCFSO, LiN(SOCF), LiN and the binder or the thickness of the coating of the inorganic (SOCF), LiN(SOCF)(SOCF), LiSCN, LiBr, LiI, filler. LiSO, Li BioClo, NaClO, NaI, NaSCN, NaBr. KClO The term porosity of the inorganic filler layer as used 25 and KSCN and mixtures of two or more of these com herein refers to a value calculated according to Equations (1) pounds. and (2) given below if the inorganic filler layer is disposed Furthermore, the nonaqueous electrolyte Solution can on the separator. contain any amount of other compounds as necessary in addition to the electrolytic salt(s) and the nonaqueous sol porosity of inorganic filler layer (volume %)=100-{ 30 vent to a degree that does not impair the advantageous (coating density+true density)x100 (1) effects of the present invention. coating density coating mass of inorganic filler Examples of such compound include: carbonates such as (g/cm)+thickness of separator (m) (2) lithium difluorophosphate, vinylene carbonate, methyl vinylene carbonate, ethyl vinylene carbonate, propyl If a binder is included, the coating mass and true density 35 vinylene carbonate, phenyl vinylene carbonate, vinyl ethyl of the inorganic filler are the Sums of coating masses and true ene carbonate, divinyl ethylene carbonate, dimethyl densities, respectively, of the inorganic filler and the binder. vinylene carbonate, diethyl vinylene carbonate, and fluoro The nonaqueous electrolyte solution of this embodiment ethylene carbonate; Vinyl esters such as vinyl acetate and is a solution in which lithium difluorobis(oxalato)phosphate vinyl propionate; sulfides such as diallyl sulfide, allyl phenyl having the following chemical structural formula is dis 40 sulfide, allyl vinyl sulfide, allyl ethyl sulfide, propyl sulfide, Solved in a nonaqueous solvent. diallyl disulfide, allyl ethyl disulfide, allyl propyl disulfide, and allyl phenyl disulfide; cyclic Sulfonic esters such as 1,3-propane Sultone, 1,4-butane Sultone, 1,3-propene Sul Chemical formula 1 tone, and 1,4-butene Sultone; chain Sulfonic esters such as 45 methyl methanesulfonate, ethyl methanesulfonate, propyl O methanesulfonate, methyl ethanesulfonate, ethyl ethanesul O 'Ndaf fonate, propyl ethanesulfonate, methyl benzenesulfonate, /WYOS ethyl benzenesulfonate, propyl benzenesulfonate, phenyl O F methanesulfonate, phenyl ethanesulfonate, phenyl propane 50 sulphonate, methyl benzylsulfonate, ethyl benzylsulfonate, propyl benzylsulfonate, benzyl methanesulfonate, benzyl ethanesulfonate, and benzyl propanesulfonate; sulfite esters The concentration of lithium difluorobis(oxalate)phos such as dimethyl sulfite, diethyl sulfite, ethyl methyl sulfite, phate in the nonaqueous solution is preferably greater than methyl propyl sulfite, ethyl propyl sulfite, diphenyl sulfite, or equal to 0.2 mass % and less than or equal to 1 mass % 55 methyl phenyl sulfite, ethyl methyl sulfite, ethylene sulfite, (greater than or equal to 0.008 mol/kg and less than or equal vinyl ethylene sulfite, divinyl ethylene sulfite, propylene to 0.04 mol/kg). A concentration in this range can effectively sulfite, vinyl propylene sulfite, butylene sulfite, vinyl buty inhibit swelling. lene sulfite, vinylene sulfite, and phenyl ethylene sulfite: The nonaqueous solvent can be selected from well-known sulfate esters such as dimethyl sulfate, diethyl sulfate, diiso nonaqueous solvents as appropriate. 60 propyl sulfate, dibutyl sulfate, ethylene glycol sulfate ester, Examples of the nonaqueous solvent include nonaqueous propylene glycol Sulfate ester, butylene glycol sulfate ester, Solvents of ethylene carbonate, propylene carbonate, buty and pentene glycol Sulfate ester; aromatic compounds Such lene carbonate, trifluoropropylene carbonate, Y-butyrolac as benzene, toluene, Xylene, fluorobenzene, biphenyl, cyclo tone, Y-Valerolactone, Sulfolane, 1,2-dimethoxyethane, 1.2- hexylbenzene, 2-fluorobiphenyl, 4-fluorobiphenyl, diphenyl diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 65 ether, tert-butylbenzene, orthoterphenyl, metaterphenyl, 2-methyl-1,3-dioxolan, dioxolan, fluoroethyl methyl ether, naphthalene, fluoronaphthalene, cumene, fluorobenzene, ethylene glycol diacetate, propylene glycol diacetate, ethyl and 2,4-difluoroanisole; halogen-substituted alkanes such as US 9,509,148 B2 7 8 perfluorooctane; and silyl esters such as boric acid tristrim The same specifics in the second embodiment as those in ethylsilyl, bistrimethylsilyl sulphate, and tristrimethylsilyl the first embodiment will not be repeatedly described. phosphate. The inorganic filler layer on the active material layer may Any one of these compounds or any mixture of two or be formed for example by coating a Surface of a current more of these compounds may be used. collector with a material for the positive-electrode active The negative-electrode active material of the nonaqueous material layer or the negative-electrode active material layer electrolyte cell (lithium ion cell) of this embodiment may be and, immediately thereafter, by coating with a mixture of the any of appropriate well-known materials that can occlude inorganic filler and the binder, then drying and pressing the and release lithium ions. Examples of Such material include whole structure as described in the first embodiment. lithium metals, lithium alloys (lithium-containing alloys 10 Alternatively, the surface of each current collector may be Such as lithium-aluminum, lithium-lead, lithium-tin, coated with a material for the positive-electrode active lithium-aluminum-tin, lithium-gallium, and wood's metal), material layer or the negative-electrode active material layer, and alloys, carbon materials (such as graphite, hard carbon, and the material may be dried, and then the mixture of the low temperature fired carbon, Soft carbon, and amorphous 15 inorganic filler and the binder may be applied before press carbon), metal oxides, lithium metal oxides (such as ing the whole structure. Li TiO2), and polyphosphate compounds that can occlude Alternatively, the surface of each current collector may be and release lithium ions. coated with a material for the positive-electrode active The positive-electrode active material may be any of material layer or the negative-electrode active material layer, appropriate well-known materials that can occlude and the material may be dried and pressed, then the mixture of release lithium ions. For example, such material can be the inorganic filler and the binder may be applied to form the selected from the group consisting of composite oxides inorganic filler layer on the active material layer. represented by Li, MO, (M. represents at least one transition If the inorganic filler layer is provided on at least one of metal) Such as LiCoO, LiNiO, Li MnO, Li MnO, the positive electrode and the negative electrode in the Li, Ni, Co-O2, Li, Ni,Mn. Co-O, and Li, Ni,Mn2. 25 second embodiment, the porosity of the inorganic filler layer Oa, and polyanion compounds represented by LiMe, (X- is preferably less than or equal to 70 volume %, preferably O.). (Me represents at least one transition metal and X is for in the range of 50 volume % to 70 volume '%, more example P. Si, B, or V) such as LiFePO, LiMnPO, preferably in the range of 60 volume '% to 70 volume %. LiNiPO, LiCoPO, LiV (PO). LiMnSiO, and The porosity of the inorganic filler layer is more prefer LiCoPO.F. Some of the elements or polyanions in these 30 ably in the ranges stated above and greater than or equal to compounds may be substituted by other elements or anion species. The surface may be coated with a conductive the porosity of the separator. material such as a carbon or a metal oxide such as ZrO. If the porosity of the inorganic filler layer is less than the WO, MgO, or Al-O. Other examples include, but not porosity of the separator, clogging tends to occur between limited to, conductive polymer compounds such as disulfide, 35 the separator and the inorganic filler layer which is formed polypyrrole, polyaniline, polyparastyrene, polyacethylene, on the surface of the active material layer of at least one of and polyacene materials and pseudo-graphite-structure car the positive and negative electrodes so as to face the bonaceous materials. Any one of these compounds or any separator, for example. As a result, the internal resistance of mixture of two or more of these compounds may be used. the separator is likely to increase. Each of the positive and negative electrode active mate 40 Choosing the porosity in the ranges stated above can rials are mixed with a binder or the like, is applied to a inhibit reduction of the energy density and power density of surface of the current collector, is pressed and dried to form the cell due to an increase in the weight of the cell. the positive electrode and the negative electrode. Furthermore, choosing the porosity in the ranges stated The current collectors may be made of any of copper, above can inhibit a reduction in power output due to increase nickel, iron, stainless steel, titanium, aluminum, low tem 45 in the diffusion resistance of lithium ions in the inorganic perature fired carbon, soft carbon, conductive polymers, filler layer which can occur if the inorganic filler layer is conductive glasses, Al-Cd alloys and the like. Further excessively thick. more, the surface of the current collectors made of any of The term porosity of the inorganic filler layer as used these materials may be treated with a material Such as herein refers to a value calculated according to Equation (4) chitosan or chitin, which are polysaccharide macromolecu 50 given below if the inorganic filler layer is disposed on the lar polymers, the material being cross-linked by a cross surface of the active material layer of at least one of the linker, or may be treated with carbon, nickel, titanium, or positive electrode and the negative electrode. silver for the purpose of enhancing adhesiveness, conduc tivity, and resistance against reduction. porosity of inorganic filler layer (volume %)=100 (Second Embodiment) 55 A cell of this embodiment is a cell that includes a positive where electrode, a negative electrode, a separator disposed between W: the weight of the inorganic filler layer per unit area the positive electrode and the negative electrode, and a (g/cm), nonaqueous electrolyte solution in which an electrolyte is d: the thickness of the inorganic filler layer (cm) dissolved in a nonaqueous solvent, wherein an inorganic 60 p: the average density of the inorganic filler layer (g/cm) filler layer is disposed between the positive electrode and the The weight of the inorganic filler layer per unit area, W. negative electrode and the nonaqueous electrolyte Solution (g/cm), the thickness of the inorganic filler layer, d. (cm), contains lithium difluorobis(oxalato)phosphate. Each of the and the average density of the inorganic filler layer, p. positive and negative electrodes includes an active material (g/cm), can be calculated according to Equations (5) to (7) layer and the inorganic filler layer is disposed on a Surface 65 given below. of the active material layer of at least one of the positive electrode and the negative electrode. US 9,509,148 B2 9 10 where Example 1 W: the weight of the positive or negative electrode per unit area (g/cm) before formation of the inorganic filler layer (Formation of Separator) W: the weight of the positive or negative electrode per unit A polypropylene resin sheet (12 um thick) with a weight area (g/cm) after formation of the inorganic filler layer average molecular weight of 300,000 was biaxially stretched to form a separator. d=d-d (6) (Formation of Inorganic Filler Layer) One side of the separator is coated with a solution where containing aluminosilicate, as inorganic filler, to form an d: the thickness of the positive or negative electrode (cm) inorganic filler layer. before formation of the inorganic filler layer 10 Aluminosilicate used was prepared as follows. Sodium d: the thickness of the positive or negative electrode (cm) silicate and Sodium aluminate were mixed at a molar ratio of after formation of the inorganic filler layer 1:1 in purified water. The mixture was heated at 80°C., then cleaned with purified water to a pH level of 9 and dried. The aluminosilicate solution was prepared by uniformly where 15 distributing the aluminosilicate and polyvinyl alcohol (with p: the true density of the inorganic filler (g/cm) an average degree of polymerization of 1700 and a degree of p: the true density of the binder (g/cm) saponification greater than or equal to 99%) in water. The X: the composition ratio of the binder (mass %) Surface of the separator was coated with this inorganic filler 100-X: the composition ratio of the inorganic filler (mass %) aqueous solution by means of a gravure coater and was dried In this embodiment, the thickness of the inorganic filler at 60° C. to remove water, thereby forming a separator layer after drying is preferably greater than or equal to 3 um having an inorganic filler layer formed on it. and less than the thickness of the separator. The thickness of the inorganic filler layer was determined The thickness is preferably in the range of 5 um to 12 um, by subtracting the thickness of the separator from the more preferably in the range of approximately 5 um to thickness of the separator coated with the inorganic filler 25 layer. The determined thickness was 5 um. approximately 10um, provided that the thickness is less than (Determination of Porosities of Separator and Inorganic the thickness of the separator. Filler Layer) The inorganic filler layer may be formed on one of the A 10-cm-square sample was cut from the separator before positive and the negative electrodes or on both of the being coated with the inorganic filler layer and the porosity positive and negative electrodes. was calculated from the Volume and mass of the sample However, it is preferable that the inorganic filler layer be 30 according to Equation (3) given earlier. The calculated formed on only one of the positive and negative electrodes porosity of the separator formed was 34.7%. in terms of the energy density and power density of the Then, a 10-cm-square sample was cut from the separator electric storage device. coated with the inorganic filler layer and the porosity of the According to the embodiments described above, in an inorganic filler layer was calculated from the mass and electric storage device in which lithium difluorobis(oxalato) 35 thickness of the sample according to Equations (1) and (2) phosphate is added to the nonaqueous electrolyte solution, given earlier. The calculated porosity of the inorganic filler Swelling of the electric storage device due to gas generation layer was 64.7%. after the initial charge and discharge can be inhibited. (Determination of SiO-Equivalent Mass Ratio of Inorganic Specifically, the electric storage device according to any Filler Layer) of the embodiments described above includes a positive 40 X-ray fluorescence spectrometer XRF-1800 from Shi electrode, a negative electrode, a separator disposed between madzu Corporation was used to perform measurement of the positive and negative electrodes, and a nonaqueous element species observed at the surface of the inorganic filler electrolyte solution in which an electrolyte is dissolved in a layer. nonaqueous solvent, wherein an inorganic filler layer is K, Na, Ca, Ba, Rb, Cs, Al, Mg, Fe, Ti, Mn, Cr, Zn, V. Be, disposed between the positive and negative electrodes and 45 B, Si, Zr, Ce, and Y were extracted from among the the nonaqueous electrolyte Solution contains lithium difluo measured element species and were assumed to be the robis(oxalato)phosphate. With this configuration, the inor following oxides: KO, NaO, CaO, BaO, Rb O. Cs-O, ganic filler can inhibit generation of gas and thus can inhibit Al-O, MgO, FeO, TiO, MnO, CrO, ZnO, VO, BeO. swelling of the cell even when lithium difluorobis(oxalato) BO, SiO, ZrO. CeO, and Y.O. respectively, to calculate phosphate is reductively decomposed during initial charge. 50 the SiO2-equivalent mass ratio. The calculated content was While the electric storage devices according to the 54%. embodiments have been described above, it should be under (Preparation of Nonacqueous Electrolyte Solution) stood that the embodiments disclosed herein are illustrative A nonaqueous electrolyte solution was prepared. and not limitative. The scope of the present invention is 1 mol/l of LiPF was dissolved in a solvent prepared by defined by the claims rather than by the preceding descrip 55 mixing ethylene carbonate, dimethyl carbonate, and ethyl tion, and all changes that fall within meets and bounds of the methyl carbonate at a ratio of 30:35:35 (volume '%), so that claims or equivalence of Such meets and bounds are the concentration of lithium difluorobis(oxalato)phosphate intended to be embraced by the claims. was 1 mass %. (Fabrication of Cell) EXAMPLES 60 The negative electrode used was fabricated as follows. One side of a 10-um-thick copper foil acting as a current The present invention will be described below in further collector was coated with a mixture serving as the material detail with examples. However, the present invention is not of the negative-electrode active material layer containing 92 limited to the examples. mass % of amorphous carbon as a negative-electrode active
INORGANICFILLER
MIXTURE RATIO OF SiO-EQUIVALENT MATERIAL 1. THICKNESS POROSITY WEIGHT RATIO MATERIAL 1 MATERIAL 2 MATERIAL 2 (IM) (VOL.9%) (WT9%)
EX. 1 ALUMINOSILICATE 5 65.3 S4 EX. 2 ALUMINOSILICATE 5 S1.O S4 EX. 3 ALUMINOSILICATE 6 61.3 S4 EX. 4 ALUMINOSILICATE 6 69.6 S4 EX.5 SILICA 6 64.3 1OO EX. 6 ALUMINA 5 65.2 O EX. 7 ALUMINOSILICATE 6 66.6 69 EX. 8 ALUMINOSILICATE 6 65.5 78 EX.9 ALUMINOSILICATE 6 67.8 84 EX. 10 ALUMINOSILICATE ALUMINA 1 5 64.2 26 EX 11 ALUMINOSILICATE ALUMINA 2 6 65.9 39 EX. 12 ALUMINOSILICATE ALUMINA 3 6 64.1 42 EX. 13 ALUMINOSILICATE 2 66.3 S4 EX. 14 ALUMINOSILICATE 3 66.2 S4 EX. 15 ALUMINOSILICATE 7 64.5 S4 EX. 16 ALUMINOSILICATE 9 65.8 S4 EX. 17 ALUMINOSILICATE 10 66.3 S4 EX. 18 ALUMINOSILICATE 12 64.9 S4 EX. 19 ALUMINOSILICATE 13 66.8 S4 EX. 20 ALUMINOSILICATE 15 64.1 S4 EX. 21 ALUMINOSILICATE 2O 65.6 S4 EX. 22 ALUMINOSILICATE 25 66.4 S4 EX. 23 ALUMINOSILICATE 6 64.3 S4 EX. 24 ALUMINOSILICATE 5 65.3 S4 EX. 25 ALUMINOSILICATE 5 65.3 S4 EX. 26 ALUMINOSIL 6 64.3 S4 EX. 27 ALUMINOSILICATE 6 64.3 S4 COMP. NONE O EX. 1 EX. 28 ALUMINOSILICATE 5 30.2 S4 EX. 29 ALUMINOSIL E 6 75.8 S4 EX. 30 ALUMINOSIL E 6 80.4 S4 COMP. NONE O EX. 2 COMP. NONE O EX 3 COMP. NONE O EX. 4 COMP. NONE O EX.5 COMP. NONE O EX. 6 COMP. ALUMINOSILICATE 5 65.3 S4 EX. 7 COMP. ALUMINOSILICATE 25 66.4 S4 EX. 8 US 9,509,148 B2 15 16 TABLE 1-continued ADDITIVE AGENT CAPACITY
SEPARATOR ADDITIVE CELL RETENTION
THICKNESS POROSITY ADDITIVE AMOUNT SWELLING AFTER CYCLES (IM) (VOL.9%) AGENT (MASS 9%) (mm) (%) EX. 1 2 34.7 LFOP O.3 86.3 EX. 2 2 34.7 LFOP 0.4 EX 3 2 34.7 LFOP O.3 EX. 4 2 34.7 LFOP 0.4 EX.5 2 34.7 LFOP O.S EX. 6 2 34.7 LFOP 1.O EX. 7 2 34.7 LFOP 0.4 EX. 8 2 34.7 LFOP O.3 EX. 9 2 34.7 LFOP O.S EX. 10 2 34.7 LFOP O.9 EX 11 2 34.7 LFOP 0.7 EX. 12 2 34.7 LFOP O.S EX. 13 2 34.7 LFOP O.9 EX. 14 2 34.7 LFOP O.6 EX. 15 2 34.7 LFOP 0.4 EX. 16 2 34.7 LFOP O.3 EX. 17 2 34.7 LFOP 0.4 EX. 18 2 34.7 LFOP O.S EX. 19 2 34.7 LFOP O.8 EX. 20 2 34.7 LFOP 0.7 EX. 21 2 34.7 LFOP O.8 EX. 22 2 34.7 LFOP O.8 EX. 23 2 34.7 LFOP O.1 0.7 76.8 EX. 24 2 34.7 LFOP O2 O.2 78.9 EX. 25 2 34.7 LFOP O.S O.3 EX. 26 2 34.7 LFOP .2 O.9 EX. 27 2 34.7 LFOP .5 1.O COMP. 2 34.7 LFOP 1.6 77.5 EX. 1 EX. 28 2 34.7 LFOP 1.3 EX. 29 2 34.7 LFOP 1.1 EX. 30 2 34.7 LFOP 1.2 COMP. 2 34.7 LFOP O.1 O.8 72.5 EX. 2 COMP. 2 34.7 LFOP O2 1.2 74.3 EX 3 COMP. 2 34.7 LFOP 1.2 1.O EX. 4 COMP. 2 34.7 LFOP 1.5 2.4 EX.5 COMP. 2 34.7 LiB(Ox)2 1 O EX. 6 COMP. 2 34.7 LiB(Ox)2 1 O.1 EX. 7 COMP. 2 34.7 LiB(Ox)2 1 O EX. 8
When examples 1 to 30 are compared with comparative less of lithium difluorobis(oxalato)phosphate exhibit cell example 1, the cells that use a nonaqueous electrolyte Swelling. On the other hand, the cells of the examples using Solution containing lithium difluorobis(oxalato)phosphate 50 a separator with an inorganic filler layer exhibited reduced and include a separator with an inorganic filler layer exhibit cell swelling at all concentrations of lithium difluorobis reduced cell Swelling. (oxalato)phosphate. Examples 1 to 27 shows that especially the cells in which The cells in which the nonaqueous electrolyte solution the inorganic filler layer has a porosity greater than or equal contains 1.0 mass % or more of lithium difluorobis(oxalato) to the porosity of the separator and less than or equal to 70 55 phosphate exhibit reduced swelling because of the provision volume '% have a great effect of inhibiting cell swelling. of the separator with inorganic filler layer (examples 26 and The examples including aluminosilicate or silica as the 27 and comparative examples 4 and 5). inorganic filler has a great effect of inhibiting cell Swelling. Note that comparative examples 6 to 8, in which the Among those examples, especially the examples in which nonaqueous electrolyte solution does not contain lithium the SiO2-equivalent mass ratio is greater than 40% have a 60 difluorobis(oxalato)phosphate, exhibit no cell swelling. great effect. Furthermore, as examples 1, 23 and 24 show, the cells in Examples 1 to 12, 14 to 18, and 23 to 30, in which the which the nonaqueous electrolyte solution contains lithium thickness of the inorganic filler layer is greater than or equal difluorobis(oxalato)phosphate and the separator with inor to 3 um and less than or equal to the thickness of the ganic filler layer is provided exhibit improved capacity separator, show remarkably Small cell Swelling. 65 retention after the cycles. As comparative examples 2 and 3 show, the cells in which The degree of improvement in capacity retention after the the nonaqueous electrolyte solution contain 1.0 mass % or cycles with the increase of the additive amount of lithium US 9,509,148 B2 17 18 difluorobis(oxalato)phosphate is more remarkable in the Examples 43 to 45 cells including the separator with an inorganic filler layer. These results demonstrate that the cells of the examples 400 mAh prismatic cells of examples 43 to 45 were fabricated in the same way as examples 28 to 30, respec exhibit smaller cell swelling and have excellent cycle per tively, except that the inorganic filler layer was formed on formance. the positive-electrode active material layer in the same way MIXTURE RATIO OF SiO-EQUIVALENT MATERIAL 1. THICKNESS POROSITY WEIGHT RATIO MATERIAL 1 MATERIAL 2 MATERIAL 2 (IM) (VOL.9%) (WT9%) EX. 31 ALUMINOSILICATE 5 65.3 S4 EX. 32 ALUMINOSILICATE 5 S1.O S4 EX. 33 ALUMINOSILICATE 6 61.3 S4 EX. 34 ALUMINOSILICATE 6 69.6 S4 EX. 35 SILICA 6 64.3 1OO EX. 36 ALUMINA 5 65.2 O EX. 37 ALUMINOSILICATE 6 66.6 69 EX. 38 ALUMINOSILICATE 6 65.5 78 EX. 39 ALUMINOSILICATE 6 67.8 84 EX. 40 ALUMINOSILICATE ALUMINA 1 5 642 26 EX. 41 ALUMINOSILICATE ALUMINA 2 6 65.9 39 EX. 42 ALUMINOSILICATE ALUMINA 3 6 64.1 42 COMP. NONE O EX. 1 EX. 43 ALUMINOSILICATE 5 30.2 S4 EX. 44 ALUMINOSILICATE 6 75.8 S4 EX.45 ALUMINOSILICATE 6 80.4 S4 EX. 46 ALUMINOSILICATE 5 65.3 S4 EX. 47 ALUMINOSILICATE 5 S1.O S4 EX. 48 ALUMINOSILICATE 6 61.3 S4 EX. 49 ALUMINOSILICATE 6 69.6 S4 EX. SO SILICA 6 64.3 1OO US 9,509,148 B2 19 20 TABLE 2-continued EX. S1 ALUMINA 5 65.2 O EX. S2 ALUMINOSILICATE 6 66.6 69 EX. S3 ALUMINOSILICATE 6 65.5 78 EX. S4 ALUMINOSILICATE 6 67.8 84 EX. SS ALUMINOSILICATE ALUMINA 1 5 642 26 EX. S6 ALUMINOSILICATE ALUMINA 2 6 65.9 39 EX. S7 ALUMINOSILICATE ALUMINA 3 6 64.1 42 COMP. NONE O EX. 1 EX. S8 ALUMINOSILICATE 5 30.2 S4 EX. S9 ALUMINOSILICATE 6 75.8 S4 EX. 60 ALUMINOSILICATE 6 804 S4 ADDITIVE AGENT CAPACITY SEPARATOR ADDITIVE CELL RETENTION COATE THICKNESS POROSITY ADDITIVE AMOUNT SWELLING AFTER CYCLES SURFACE (IM) (VOL.9%) AGENT (MASS 9%) (mm) (%) EX. 31 POSITIVE 2 34.7 LFOP O.2 85.2 ELECTRODE EX. 32 POSITIVE 2 34.7 LFOP O.3 ELECTRODE EX. 33 POSITIVE 2 34.7 LFOP 0.4 ELECTRODE EX. 34 POSITIVE 2 34.7 LFOP O.3 ELECTRODE EX. 35 POSITIVE 2 34.7 LFOP O.6 ELECTRODE EX. 36 POSITIVE 2 34.7 LFOP O.9 ELECTRODE EX. 37 POSITIVE 2 34.7 LFOP O.3 ELECTRODE EX. 38 POSITIVE 2 34.7 LFOP 0.4 ELECTRODE EX. 39 POSITIVE 2 34.7 LFOP 0.4 ELECTRODE EX. 40 POSITIVE 2 34.7 LFOP 1.O ELECTRODE EX. 41 POSITIVE 2 34.7 LFOP O.8 ELECTRODE EX. 42 POSITIVE 2 34.7 LFOP 0.4 ELECTRODE COMP. POSITIVE 2 34.7 LFOP 1.6 77.5 EX. 1 ELECTRODE EX. 43 POSITIVE 2 34.7 LFOP 1.2 ELECTRODE EX. 44 POSITIVE 2 34.7 LFOP 1.2 ELECTRODE EX. 45 POSITIVE 2 34.7 LFOP 1.1 RODE EX. 46 VE 2 34.7 LFOP O.2 86.7 ODE EX. 47 VE 2 34.7 LFOP 0.4 ODE EX. 48 VE 2 34.7 LFOP 0.4 ODE EX. 49 TIVE 2 34.7 LFOP O.3 ODE EX. SO TIVE 2 34.7 LFOP O.S ODE EX. S1 VE 2 34.7 LFOP 1.O DE EX. 52 VE 2 34.7 LFOP 0.4 DE EX. 53 VE 2 34.7 LFOP 0.4 DE EX. S4 VE 2 34.7 LFOP O.S DE EX. 55 VE 2 34.7 LFOP 1.O DE EX. S6 VE 2 34.7 LFOP O.9 DE EX. 57 VE 2 34.7 LFOP 0.4 DE COMP. VE 2 34.7 LFOP 1.6 77.5 EX. 1 DE US 9,509,148 B2 21 22 TABLE 2-continued EX. S8 NEGATIVE 12 34.7 LFOP 1.3 ELECTRODE EX. S9 NEGATIVE 12 34.7 LFOP 1.2 ELECTRODE EX. 60 NEGATIVE 12 34.7 LFOP 1.2 ELECTRODE As shown in Table 2, the cells in which the inorganic filler 10 injecting a nonaqueous electrolyte solution in the case, layer is formed on the positive- or negative-electrode active wherein the nonaqueous electrolyte Solution contains material layer and the nonaqueous electrolyte solution con electrolyte, nonaqueous solvent, and lithium difluoro tains lithium difluorobis(oxalato)phosphate exhibit reduced bis(oxalato)phosphate, and cell swelling, like the cells in which the inorganic filler layer sealing the injection port of the case after charging, the is formed on the separator. 15 charging causing lithium difluorobis(oxalato)phos Especially, the cells in which the porosity of the inorganic phate to be reductively decomposed and thereby the filler layer is greater than or equal to the porosity of the nonaqueous electrolyte solution to generate gas. separator and less than or equal to 70 Volume 96 have a great effect of inhibiting cell swelling. 2. The method for manufacturing an electric storage The cells containing aluminosilicate or silica as the inor device according to claim 1, wherein the inorganic filler ganic filler have a great effect of inhibiting cell Swelling. layer is disposed on a Surface of the separator. Especially, the cells of the examples in which the SiO 3. The method for manufacturing an electric storage equivalent mass ratio is greater than or equal to 40% have a device according to claim 1, wherein: remarkably greater effect. each of the positive electrode and the negative electrode The cells in which the thickness of the inorganic filler 25 comprises an active material layer, and layer is greater than or equal to 3 um and less than the the inorganic filler layer is disposed on a Surface of the thickness of the separator exhibit remarkably small cell active material layer of at least one of the positive Swelling. electrode and the negative electrode. The cells in which the nonaqueous electrolyte solution 4. The method for manufacturing an electric storage contains lithium difluorobis(oxalato)phosphate and the inor 30 device according to claim 1, wherein a porosity of the ganic filler layer is formed on the positive- or negative inorganic filler layer is greater than or equal to a porosity of electrode active material layer show improved capacity the separator and less than or equal to 70 volume '%. retention after the cycles as compared with the cells of 5. The method for manufacturing an electric storage comparative example 1 in which no inorganic filler layer is device according to claim 1, wherein a thickness of the provided. 35 inorganic filler layer is greater than or equal to 3Lum and less These results demonstrate that the cells of the examples in than or equal to a thickness of the separator. which the inorganic filler layer is formed on the positive- or 6. The method for manufacturing an electric storage negative-electrode active material layer exhibit reduced cell device according to claim 1, wherein a content of the lithium Swelling and have excellent cycle performance. difluorobis(Oxalato)phosphate in the nonaqueous electrolyte What is claimed is: 40 1. A method for manufacturing an electric storage device Solution is greater than or equal to 0.2 mass % and less than comprising: or equal to 1 mass %. placing a layered electrode structure in which negative 7. The method for manufacturing an electric storage and positive electrodes are stacked with a separator and device according to claim 1, wherein a SiO-equivalent an inorganic filler layer therebetween in a case having 45 mass ratio of a Si element in the inorganic filler layer is an injection port, wherein the inorganic filler layer greater than or equal to 40%. contains aluminosilicate, k k k k k