Lithium secondary batteries and nonaqueous electrolyte for use in the same

Abstract

Provided is a lithium secondary battery having a nonaqueous electrolyte which contains at least one compound selected from the group consisting of monofluorophosphoric acid salts, and difluorophosphoric acid salts, in an amount of 10 ppm or more of the whole nonaqueous electrolyte, and a negative electrode selected from [1], [2], [3] and [6]: [1]: a negative electrode containing two or more carbonaceous substances differing in crystallinity; [2]: a negative electrode containing an amorphous carbonaceous substance which, when examined by wide-angle X-ray diffractometry, has an interplanar spacing (d002) for the (002) planes of 0.337 nm or larger and a crystallite size (Lc) of 80 nm or smaller and which, in an examination by argon ion laser Raman spectroscopy, has a Raman. R value of 0.2 or higher defined as the ratio of the peak intensity at 1,360 cm −1 to the peak intensity at 1,580 cm −1 ; [3]: a negative-electrode active material a titanium-containing metal oxide capable of occluding and releasing lithium; [6]: as a negative-electrode active material, graphitic carbon particles which have a roundness of 0.85 or higher and an interplanar spacing (d002) for the (002) planes of smaller than 0.337 nm as determined by wide-angle X-ray diffractometry and which, in an examination by argon ion laser Raman spectroscopy, have a Raman R value of from 0.12 to 0.8 defined as the ratio of the peak intensity at 1,360 cm −1 to the peak intensity at 1,580 cm −1 .

1 . (canceled) 
     
     
         2 . A lithium secondary battery comprising: an electrode group comprising:
 a positive electrode,   a negative electrode,   a microporous film separator interposed between the electrodes; and   a nonaqueous electrolyte comprising a nonaqueous solvent and a lithium salt, wherein the electrode group and the nonaqueous electrolyte are held in a battery case, and the positive electrode and the negative electrode each comprising a current collector and, formed thereon, an active-material layer containing an active material capable of occluding and releasing a lithium ion, wherein the nonaqueous electrolyte is a nonaqueous electrolyte which contains at least one compound selected from the group consisting of monofluorophosphoric acid salts, and difluorophosphoric acid salts, in an amount of 10 ppm or more of the whole nonaqueous electrolyte, and   the negative electrode is any negative electrode selected from the group consisting of the following negative electrodes [1], [2], [3] and [6]:   negative electrode [1]: a negative electrode containing as a negative-electrode active material two or more carbonaceous substances differing in crystallinity;   negative electrode [2]: a negative electrode containing as a negative-electrode active material an amorphous carbonaceous substance which, when examined by wide-angle X-ray diffractometry, has an interplanar spacing (d002) for the (002) planes of 0.337 nm or larger and a crystallite size (Lc) of 80 nm or smaller and which, in an examination by argon ion laser Raman spectroscopy, has a Raman R value of 0.2 or higher defined as the ratio of the peak intensity at 1,360 cm −1  to the peak intensity at 1,580 cm −1 ;   negative electrode [3]: a negative electrode containing as a negative-electrode active material a titanium-containing metal oxide capable of occluding and releasing lithium;   negative electrode [6]: a negative electrode containing, as a negative-electrode active material, graphitic carbon particles which have a roundness of 0.85 or higher and an interplanar spacing (d002) for the (002) planes of smaller than 0.337 nm as determined by wide-angle X-ray diffractometry and which, in an examination by argon ion laser Raman spectroscopy, have a Raman R value of from 0.12 to 0.8 defined as the ratio of the peak intensity at 1,360 cm −1  to the peak intensity at 1,580 cm −1 .   
     
     
         3 . The lithium secondary battery according to  claim 2 , wherein the nonaqueous electrolyte comprises the at least one compound selected from the group consisting of monofluorophosphoric acid salts and difluorophosphoric acid salts, in an amount of from 0.01% by mass to 5% by mass. 
     
     
         4 . The lithium secondary battery according to  claim 2 , wherein the negative electrode [1] contains as a negative-electrode active material a composite carbonaceous material comprising two or more carbonaceous substances differing in crystallinity. 
     
     
         5 . The lithium secondary battery according to  claim 4 , wherein the composite carbonaceous material comprises a particulate carbonaceous substance and has an interface where the particulate carbonaceous substance is covered with and/or bonded to a carbonaceous substance differing in crystallinity from the particulate carbonaceous substance, the interface changing in crystallinity discontinuously and/or continuously. 
     
     
         6 . The lithium secondary battery according to  claim 5 , wherein the particulate carbonaceous substance is a graphitic carbonaceous substance comprising a natural graphite and/or an artificial graphite. 
     
     
         7 . The lithium secondary battery according to  claim 5 , wherein the particulate carbonaceous substance comprises at least one member selected from the group consisting of the following (a), (b), and (c): (a) a product of organic-substance pyrolysis selected from the group consisting of coal coke, petroleum coke, furnace black, acetylene black, and pitch-derived carbon fibers; (b) a product of the carbonization of the gas of an organic substance; and (c) a carbonaceous substance obtained by partly or wholly graphitizing (a) or (b). 
     
     
         8 . The lithium secondary battery according to  claim 5 , wherein the carbonaceous substance differing in crystallinity from the particulate carbonaceous substance is a lowly crystalline carbonaceous substance having lower crystallinity than the particulate carbonaceous substance. 
     
     
         9 . The lithium secondary battery according to  claim 5 , wherein the carbonaceous substance differing in crystallinity from the particulate carbonaceous substance is a product of the carbonization of the following (d) or (e): (d) an organic substance capable of carbonization which is selected from the group consisting of coal-derived heavy oil, straight-run heavy oil, petroleum-derived cracked heavy oil, aromatic hydrocarbons, nitrogen-ring compounds, sulfur-ring compounds, polyphenylenes, organic synthetic polymers, natural polymers, thermoplastic resins, and thermosetting resins; and (e) a solution obtained by dissolving the organic substance capable of carbonization (d) in a low-molecular organic solvent. 
     
     
         10 . The lithium secondary battery according to  claim 4 , wherein the composite carbonaceous material comprises a graphitic carbonaceous substance and a lowly crystalline carbonaceous substance, and the content of the graphitic carbonaceous substance is 50% by mass or higher based on the whole composite carbonaceous material. 
     
     
         11 . The lithium secondary battery according to  claim 4 , wherein the composite carbonaceous material has a roundness of 0.85 or higher. 
     
     
         12 . The lithium secondary battery according to  claim 4 , wherein the composite carbonaceous material is obtained by a method comprising mixing a particulate carbonaceous substance with an organic substance capable of carbonization and heat-treating the resultant mixture at 400° C.-3,200° C. one or more times. 
     
     
         13 . The lithium secondary battery according to  claim 12 , wherein the organic substance capable of carbonization is heat-treated via a liquid-phase state. 
     
     
         14 . The lithium secondary battery according to  claim 2 , wherein the amorphous carbonaceous substance contained as a negative-electrode active material in the negative electrode [2] has a true density of 2.22 g/cm 3  or lower. 
     
     
         15 . The lithium secondary battery according to  claim 2 , wherein the amorphous carbonaceous substance contained as a negative-electrode active material in the negative electrode [2] has an atomic amount ratio O/C value of from 0 to 0.15. 
     
     
         16 . The lithium secondary battery according to  claim 2 , wherein the amorphous carbonaceous substance contained as a negative-electrode active material in the negative electrode [2] has an atomic amount ratio H/C value of from 0.01 to 0.3. 
     
     
         17 . The lithium secondary battery according to  claim 2 , wherein the amorphous carbonaceous substance contained as a negative-electrode active material in the negative electrode [2] has a tap density of 0.1 g/cm 3  or higher. 
     
     
         18 . The lithium secondary battery according to  claim 2 , wherein the amorphous carbonaceous substance contained as a negative-electrode active material in the negative electrode [2] has a BET specific surface area of from 0.1 m 2 /g to 100 m 2 /g. 
     
     
         19 . The lithium secondary battery according to  claim 2 , wherein the amorphous carbonaceous substance contained as a negative-electrode active material in the negative electrode [2] has a volume-average particle diameter of from 1 μm to 50 μm. 
     
     
         20 . The lithium secondary battery according to  claim 2 , wherein the amorphous carbonaceous substance contained as a negative-electrode active material in the negative electrode [2] has a pore volume, in terms of the volume of particle pores corresponding to the diameter range of from 0.01 μm to 1 μm as determined by mercury porosimetry, of 0.01 mL/g or larger. 
     
     
         21 . The lithium secondary battery according to  claim 2 , wherein the amorphous carbonaceous substance contained as a negative-electrode active material in the negative electrode [2] has an ash content of from 1 ppm to 1% by mass. 
     
     
         22 . The lithium secondary battery according to  claim 2 , wherein at least one of the amorphous carbonaceous substances contained as a negative-electrode active material in the negative electrode [2] is an amorphous carbonaceous substance selected from the group consisting of (1) to (4):
 (1) one obtained by further heat-treating a carbonization product selected from the group consisting of coal coke, petroleum coke, furnace black, acetylene black, and pitch-derived carbon fibers,   (2) an organic substance selected from the group consisting of pitch materials, aromatic hydrocarbons, nitrogen-ring compounds, sulfur-ring compounds, polyphenylenes, organic synthetic polymers, natural polymers, thermoplastic resins, and thermosetting resins and/or a product of the pyrolysis of the organic substance and/or one obtained by further heat-treating the pyrolysis product;   (3) a product of the pyrolysis of a solution obtained by dissolving the organic substance (2) in a low-molecular organic solvent and/or one obtained by further heat-treating the pyrolysis product; and   (4) a product of the carbonization of a gas containing an organic substance.   
     
     
         23 . The lithium secondary battery according to  claim 2 , wherein the amorphous carbonaceous substance contained as a negative-electrode active material in the negative electrode [2] is one which has undergone a heat treatment at from 600° C. to 2,500° C. one or more times. 
     
     
         24 . The lithium secondary battery according to  claim 23 , wherein the amorphous carbonaceous substance underwent a pulverization treatment before and/or after the heat treatment. 
     
     
         25 . The lithium secondary battery according to  claim 2 , wherein the metal oxide contained as a negative-electrode active material in the negative electrode [3] is a lithium composite oxide. 
     
     
         26 . The lithium secondary battery according to  claim 2 , wherein the metal oxide contained as a negative-electrode active material in the negative electrode [3] is one having a spinel structure. 
     
     
         27 . The lithium secondary battery according to  claim 2 , wherein the metal oxide contained as a negative-electrode active material in the negative electrode [3] is a lithium-titanium composite oxide of composition formula (1): Li x Ti y M z O 4  composition formula (1) wherein M is at least one element selected from the group consisting of Na, K, Co, Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn, and Nb], and 0.7≤x≤1.5, 1.5≤y≤2.3, and 0≤z≤1.6. 
     
     
         28 . The lithium secondary battery according to  claim 27 , wherein 1.2≤x≤1.4, 1.5≤y≤1.7, and z=0. 
     
     
         29 . The lithium secondary battery according to  claim 27 , wherein 0.9≤x≤1.1, 1.9≤y≤2.1, and z=0. 
     
     
         30 . The lithium secondary battery according to  claim 27 , wherein 0.7≤x≤0.9, 2.1≤y≤2.3, and z=0. 
     
     
         31 . The lithium secondary battery according to  claim 2 , wherein the metal oxide contained as a negative-electrode active material in the negative electrode [3] has a BET specific surface area of from 0.5 m 2 /g to 200 m 2 /g. 
     
     
         32 . The lithium secondary battery according to  claim 2 , wherein the metal oxide contained as a negative-electrode active material in the negative electrode [3] has a volume-average particle diameter of from 0.1 μm to 50 μm. 
     
     
         33 . The lithium secondary battery according to  claim 2 , wherein the metal oxide contained as a negative-electrode active material in the negative electrode [3] has an average primary-particle diameter of from 0.01 μm to 2 μm. 
     
     
         34 . The lithium secondary battery according to  claim 2 , wherein the current collector of the lithium secondary battery is a metal foil film comprising Cu and/or Al. 
     
     
         35 . The lithium secondary battery according to  claim 2 , wherein the graphitic carbon particles contained as a negative-electrode active material in the negative electrode [6] have a tap density of 0.55 or higher. 
     
     
         36 . The lithium secondary battery according to  claim 2 , wherein the graphitic carbon particles contained as a negative-electrode active material in the negative electrode [6] have a BET specific area of from 0.1 m 2 /g to 100 m 2 /g. 
     
     
         37 . The lithium secondary battery according to  claim 2 , wherein the graphitic carbon particles contained as a negative-electrode active material in the negative electrode [6] have a volume-average particle diameter of from 1 μm to 50 μm. 
     
     
         38 . The lithium secondary battery according to  claim 2 , wherein the graphitic carbon particles contained as a negative-electrode active material in the negative electrode [6] have a pore volume, in terms of the volume of pores in the range of from 0.01 μm to 1 μm as determined by mercury porosimetry, of 0.01 mL/g or larger. 
     
     
         39 . The lithium secondary battery according to  claim 2 , wherein the graphitic carbon particles contained as a negative-electrode active material in the negative electrode [6] have an ash content of from 1 ppm to 1% by mass. 
     
     
         40 . The lithium secondary battery according to  claim 2 , wherein the graphitic carbon particles contained as a negative-electrode active material in the negative electrode [6] are ones comprising a natural graphite. 
     
     
         41 . The lithium secondary battery according to  claim 2 , wherein the negative-electrode active material contained in the negative electrode [6] is graphitic carbon particles obtained by subjecting carbonaceous particles to one or more treatments comprising a mechanical energy treatment, the mechanical energy treatment being one which reduces the particle diameter so that the ratio of the volume-average particle diameter after the treatment to that before the treatment is less than 1 and which heightens the tap density and increases the Raman R value, i.e., the ratio of the peak intensity at 1,360 cm −1  to the peak intensity at 1,580 cm −1  in an argon ion laser Raman spectrum, at least 1.1-fold. 
     
     
         42 . The lithium secondary battery according to  claim 41 , wherein the carbonaceous particles comprise a natural graphite. 
     
     
         43 . The lithium secondary battery according to  claim 41 , wherein the mechanical energy treatment is conducted in an apparatus comprising a casing and disposed therein a rotor equipped with blades, the treatment being conducted by rotating the rotor at a high speed.