JP5547591B2 - Selection method - Google Patents

Description

  The present invention relates to a lithium secondary battery.

Conventionally, lithium secondary batteries are known. For example, it has been proposed that the electrolytic solution contains a cyclic carbonate derivative having a halogen atom and a light metal salt, thereby suppressing the decomposition reaction of the solvent in the negative electrode and improving the cycle characteristics (for example, Patent Document 1). In addition, for example, in a case having a negative electrode using graphitic carbon and a non-aqueous electrolyte, the concentration of transition metal ions in the non-aqueous electrolyte is A (ppm), and the electrode area of the negative electrode is B (m ² ). In this case, it has been proposed to suppress the deterioration of the lifetime by, for example, forming a coating film through which lithium ions can pass by setting the A / B value within a predetermined range (for example, Patent Document 2).

JP 2006-190635 A JP 2005-85545 A

  By the way, in the thing of patent document 1, the electrolyte solution is made into a predetermined thing, and in the thing described in patent document 2, the ion concentration in an electrolyte solution and the electrode area of a negative electrode are made into a predetermined thing. As a result, the cycle characteristics can be improved, but the output characteristics may be inferior. Therefore, it has been desired to improve the output characteristics.

  The present invention has been made to solve such a problem, and a main object of the present invention is to provide a lithium secondary battery capable of further improving output characteristics.

  In order to achieve the above-described object, the inventors of the present invention, in a lithium secondary battery, the content of a predetermined anion compound contained in a non-aqueous ion conductive medium and the crystallite side surface of the carbon material used for the negative electrode active material As a result, it was found that the output characteristics can be enhanced, and the present invention has been completed.

That is, the lithium secondary battery of the present invention is
A positive electrode having a positive electrode active material;
A negative electrode having a carbon material as a negative electrode active material;
A non-aqueous ion conductive medium that is interposed between the positive electrode and the negative electrode, has an electrolyte compound containing a cation and an anion compound represented by the general formula (1), and conducts lithium ions;
With
The content of the anionic compound is A (μmol), the surface area of the carbon material is B (m ² ), the crystallite size in the c-axis direction of the carbon material is Lc (nm), When the size of the crystallite in the a-axis direction is La (nm), the relational expression (1) is satisfied.
The selection method of the present invention is as follows.
A positive electrode having a positive electrode active material; a negative electrode having a carbon material as a negative electrode active material; and an electrolyte compound including a cation and an anion compound represented by the general formula (1) interposed between the positive electrode and the negative electrode. In a lithium secondary battery comprising a non-aqueous ion conductive medium that conducts lithium ions, a method for selecting the negative electrode and the non-aqueous ion conductive medium,
The content of the anionic compound is A (μmol), the surface area of the carbon material is B (m ² ), the crystallite size in the c-axis direction of the carbon material is Lc (nm), When the crystallite size in the a-axis direction is La (nm), the negative electrode and the non-aqueous ion conductive medium are selected so as to satisfy the relational expression (1).

(However, M represents a transition element, a group 13, 14 or 15 element of the periodic table; b is an integer of 1 to 3, m is an integer of 1 to 4, n is an integer of 0 to 8, q is R ¹ represents alkylene having 1 to 10 carbon atoms, halogenated alkylene having 1 to 10 carbon atoms, arylene having 6 to 20 carbon atoms or halogenated arylene having 6 to 20 carbon atoms (these alkylene and Arylene may have a substituent or a hetero atom in the structure, and when q is 1 and m is 2 to 4, m R ^{1 s} may be bonded to each other); R ² Is a halogen, an alkyl having 1 to 10 carbon atoms, an alkyl halide having 1 to 10 carbon atoms, an aryl having 6 to 20 carbon atoms, an aryl halide having 6 to 20 carbon atoms (these alkyl and aryl are in the structure) May have substituents, heteroatoms And n represents the n number of R ² may be each bonded to form a ring) or -X ³ R ³ at the time of 2~8; X ^1, X ² and X ³ are each independently in represents O, S or NR ^4; R ³ and R ⁴ are each hydrogen independently alkyl having 1 to 10 carbon atoms, a halogenated alkyl having 1 to 10 carbon atoms, 6 to 20 carbon atoms aryl, carbon A number 6 to 20 aryl halide (These alkyls and aryls may have a substituent or a heteroatom in the structure, and when a plurality of R ³ or R ⁴ are present, they are bonded to form a ring. May represent))

In the present invention, the crystallite size Lc (nm) in the c-axis direction of the carbon material, the crystallite size La (nm) in the a-axis direction of the carbon material, and the lattice constant a in the basal plane of the carbon material ₀ (m), lattice constant c ₀ of the stacking direction (m), the interlayer distance of the basal plane of carbon materials d ₀₀₂ (m), for, by using a standard silicon powder as an internal standard, the diffraction peak position, the half The value obtained by a method based on the Japan Science and Technology Act (method determined by the Japan Society for the Promotion of Science 117), characterized by correcting the price range.

  In this lithium secondary battery, output characteristics can be improved. The reason why such an effect is obtained is not clear, but the anionic compound represented by the general formula (1) is partially decomposed on the negative electrode to form a stable film on the surface of the negative electrode active material. It is considered that the output characteristics are improved to facilitate occlusion and release. In particular, it is considered that when the compound of the general formula (1) and the carbon material satisfy a predetermined relationship, the surface state of the negative electrode active material becomes more suitable for occlusion / release of lithium ions, and the output characteristics can be further improved. It is done.

It is a schematic diagram which shows an example of the crystal structure of a carbon material. 1 is a schematic diagram illustrating an example of a lithium secondary battery 10.

  Next, an embodiment embodying the present invention will be described. The lithium secondary battery of the present invention includes a positive electrode having a positive electrode active material, a negative electrode having a carbon material as a negative electrode active material, and a nonaqueous ion conductive medium that is interposed between the positive electrode and the negative electrode and conducts lithium ions. It is a thing.

  In the lithium secondary battery of the present invention, the positive electrode is applied to the surface of the positive electrode current collector by mixing a positive electrode active material with a conductive material and a binder and adding a suitable solvent to form a paste-like positive electrode mixture. It can be dried and compressed to increase the electrode density as needed. The positive electrode current collector is not particularly limited as long as it is formed of a conductive material. For example, a foil or mesh formed of a metal such as aluminum, copper, stainless steel, or nickel-plated steel may be used. it can. As the positive electrode active material, an oxide containing lithium and a transition metal element or a polyanionic compound can be used. Specifically, for example, lithium cobalt composite oxide, lithium nickel composite oxide, lithium manganese composite oxide, lithium iron composite phosphorus oxide, and the like can be given. The conductive material is for ensuring the electrical conductivity of the positive electrode, and for example, a material obtained by mixing one or more carbon materials such as carbon black, acetylene black, natural graphite, artificial graphite, and cokes is used. be able to. The binder plays a role of connecting the active material particles and the conductive material particles. For example, a fluorine-containing resin such as polytetrafluoroethylene, polyvinylidene fluoride, or fluororubber, or a thermoplastic resin such as polypropylene or polyethylene is used. be able to. As the solvent for dispersing the positive electrode active material, the conductive material, and the binder, for example, an organic solvent such as N-methyl-2-pyrrolidone can be used.

  In the lithium secondary battery of the present invention, the negative electrode has a carbon material as a negative electrode active material. This negative electrode is prepared by, for example, mixing a binder with a negative electrode active material, adding a suitable solvent to form a paste-like positive electrode mixture, applying and drying on the surface of the negative electrode current collector, and increasing the electrode density as necessary. It can be formed as compressed as possible. The negative electrode current collector is not particularly limited as long as it is formed of a conductive material. For example, a foil or mesh formed of a metal such as copper, stainless steel, or nickel-plated steel can be used. The negative electrode active material may be a carbon material, but is preferably graphite, more preferably artificial graphite, and more preferably high graphitization degree. As the binder, for example, fluorine-containing resins such as polytetrafluoroethylene, polyvinylidene fluoride, and fluororubber, or thermoplastic resins such as polypropylene and polyethylene can be used. As the solvent for dispersing the negative electrode active material and the binder, for example, an organic solvent such as N-methyl-2-pyrrolidone can be used.

  In the lithium secondary battery of the present invention, the non-aqueous ion conductive medium is interposed between the positive electrode and the negative electrode, has an electrolyte compound containing a cation and an anion compound represented by the general formula (1), and contains lithium ions. It conducts. In the general formula (1), M is a transition element, a group 13, 14 or 15 element of the periodic table, among which Al, B, V, Ti, Si, Zr, Ge, Sn, Cu, Y, It is preferably at least one of Zn, Ga, Nb, Ta, Bi, P, As, Sc, Hf, and Sb, and more preferably at least one of Al, B, and P. In the case where M is Al, B or P, the synthesis of the anionic compound becomes relatively easy, and the production cost can be suppressed. The valence b of the anion is 1 to 3, of which 1 is preferable. When the valence b is larger than 3, it is not preferable because the salt of the anion compound tends to be hardly dissolved in the mixed organic solvent. The constants m and n are values related to the number of ligands and are determined by the type of M. m is an integer of 1 to 4, and n is an integer of 0 to 8. The constant q is 0 or 1. When q is 0, the chelating ring is a five-membered ring, and when q is 1, the chelating ring is a six-membered ring.

R ¹ represents alkylene having 1 to 10 carbons, halogenated alkylene having 1 to 10 carbons, arylene having 6 to 20 carbons, or halogenated arylene having 6 to 20 carbons. These alkylene and arylene may have a substituent or a hetero atom in the structure. Specifically, instead of hydrogen on alkylene and arylene, halogen, chain or cyclic alkyl group, aryl group, alkenyl group, alkoxy group, aryloxy group, sulfonyl group, amino group, cyano group, carbonyl group, acyl It may have a group, an amide group or a hydroxyl group as a substituent, or may have a structure in which nitrogen, sulfur or oxygen is introduced instead of carbon on alkylene and arylene. When q is 1 and m is 2 to 4, m R ^{1 s} may be bonded to each other. Examples thereof include a ligand such as ethylenediaminetetraacetic acid.

R ² is halogen, alkyl having 1 to 10 carbon atoms, alkyl halide having 1 to 10 carbon atoms, aryl having 6 to 20 carbon atoms, aryl halide having 6 to 20 carbon atoms, or —X ³ R ³ (X ³ , R ³ will be described later. Alkyl and aryl here may also have a substituent or a hetero atom in the structure in the same manner as R ^1, and when n is 2 to 8, n R ² are bonded to each other to form a ring. May be formed. R ² is preferably an electron-withdrawing group, particularly preferably a fluorine atom. This is because in the case of a fluorine atom, the solubility and dissociation degree of the salt of the anion compound are improved, and the ionic conductivity is improved accordingly. Moreover, it is because oxidation resistance improves and generation | occurrence | production of a side reaction can be suppressed by this.

X ¹ , X ² and X ³ each independently represent O, S or NR ⁴ . That is, the ligand is bonded to M through these heteroatoms.

R ³ and R ⁴ each independently represent hydrogen, an alkyl having 1 to 10 carbon atoms, an alkyl halide having 1 to 10 carbon atoms, an aryl having 6 to 20 carbon atoms, or an aryl halide having 6 to 20 carbon atoms. . Similarly to R ¹ , these alkyls and aryls may have a substituent or a hetero atom in the structure. Further, when a plurality of R ³ or R ⁴ are present, they may be bonded to each other to form a ring.

Examples of the cation paired with the anionic compound include lithium, sodium, potassium, magnesium, calcium, barium, cesium, rubidium, silver, zinc, copper, cobalt, iron, nickel, manganese, titanium, lead, chromium, vanadium, and ruthenium. In addition to cations such as yttrium, lanthanoid, and actinoid, tetraalkylammonium (alkyl is methyl, ethyl, butyl, etc.), ammonium cation such as triethylammonium, pyridinium, imidazolium, protons, and the like. Of these, lithium (Li ⁺ ), sodium (Na ⁺ ), or potassium (K ⁺ ) is preferable.

  These anionic compounds are obtained by charging a lithium secondary battery at least once, so that all or part of the anionic compound is decomposed, and both the positive electrode and the negative electrode or both surfaces, and both the positive electrode active material and the negative electrode active material. Or it is thought that one surface is coat | covered and a film is formed. This coating can be detected by, for example, X-ray photoelectron spectroscopy (XPS) or IR analysis. Such an anionic compound is preferably at least one of BFO, PTFO, PFO, and PO represented by chemical formulas (2) to (5). The reason is that the solubility and dissociation degree of the salt of the anion compound are improved, so that the ionic conductivity of the non-aqueous ion conductive medium is improved and the oxidation resistance is improved. In particular, when the lithium-containing transition metal nitride containing Co is used as the positive electrode active material and the additive compound contains PFO as an anion, a higher effect of maintaining the discharge capacity can be obtained even if overdischarge occurs. .

As a method for synthesizing such an anionic compound, for example, in the case of BFO, LiBF ₄ and 2-fold moles of lithium alkoxide are reacted in a non-aqueous solvent, and then oxalic acid is added to bind to boron. There is a method of substituting alkoxide with oxalic acid. In the case of PFO, a method of reacting LiPF ₆ with 4 times moles of lithium alkoxide in a non-aqueous solvent and then adding oxalic acid to replace the alkoxide bonded to phosphorus with oxalic acid. Etc. In these cases, a lithium salt of an anionic compound can be obtained.

  In the lithium secondary battery of the present invention, the non-aqueous ion conductive medium may be a non-aqueous electrolyte solution in which an electrolyte compound containing a cation and an anion compound represented by the general formula (1) and a supporting salt are dissolved. Examples of the solvent for the nonaqueous electrolytic solution include carbonates, esters, ethers, nitriles, furans, sulfolanes and dioxolanes, and these can be used alone or in combination. Specifically, as carbonates, cyclic carbonates such as ethylene carbonate, propylene carbonate, vinylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl-n-butyl carbonate, methyl-t-butyl carbonate, di- chain carbonates such as i-propyl carbonate and t-butyl-i-propyl carbonate, cyclic esters such as γ-butyllactone and γ-valerolactone, chain esters such as methyl formate and ethyl acetate, dimethoxyethane, Ethers such as ethoxymethoxyethane, nitriles such as acetonitrile and benzonitrile, furans such as tetrahydrofuran and methyltetrahydrofuran, sulfolanes such as sulfolane and tetramethylsulfolane Examples include holanes, dioxolanes such as 1,3-dioxolane and methyldioxolane. Among these, the combination of cyclic carbonates and chain carbonates is preferable. According to this combination, not only the cycle characteristics representing the battery characteristics in repeated charge and discharge are excellent, but also the viscosity of the electrolyte, the electric capacity of the obtained battery, the battery output, etc. should be balanced. it can. The cyclic carbonates are considered to have a relatively high relative dielectric constant and increase the dielectric constant of the electrolytic solution, and the chain carbonates are considered to suppress the viscosity of the electrolytic solution. Also, instead of a liquid non-aqueous electrolyte, a solid ion conductive polymer, an inorganic solid electrolyte, a mixed material of an organic polymer electrolyte and an inorganic solid electrolyte, or an inorganic solid powder bound by an organic binder is used. be able to.

Examples of the supporting salt include LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiSbF ₆ , LiSiF ₆ , LiAlF ₄ , LiSCN, Examples include LiClO ₄ , LiCl, LiF, LiBr, LiI, and LiAlCl ₄ . Among these, from the group consisting of inorganic salts such as LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiSbF ₆ and organic salts such as LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) _3. It is preferable from the viewpoint of electrical characteristics to use a combination of one or two or more selected salts. Of these, LiPF ₆ is preferred. The supporting salt does not include an electrolyte compound containing the anion compound represented by the general formula (1). The concentration of the electrolyte compound containing the anion compound represented by the general formula (1) and the supporting salt in the entire non-aqueous ion conductive medium is preferably 0.1 mol / L or more and 5 mol / L or less, and 0.5 mol More preferably, it is / L or more and 2 mol / L or less. If it is 0.1 mol / L or more, a sufficient current density can be obtained, and if it is 5 mol / L or less, the electrolytic solution can be made more stable. Moreover, you may add flame retardants, such as a phosphorus type and a halogen type, to this non-aqueous ion conduction medium.

In the lithium secondary battery of the present invention, the content of the anion compound represented by the general formula (1) is A (μmol), the surface area of the carbon material is B (m ² ), and the crystal of the carbon material in the c-axis direction. When the size of the child is Lc (nm) and the size of the crystallite in the a-axis direction of the carbon material is La (nm), the relational expression (1) is satisfied.

Hereinafter, the relational expression (1) will be described. FIG. 1 shows an example of the crystal structure of the carbon material. This carbon material has a crystal structure in which carbons having SP ² hybrid orbitals are regularly arranged in a plane and laminated. In this carbon material, a covalent bond spreads in a plane by the SP ² hybrid orbital and forms a basal plane of a hexagonal network. The basal planes are stacked in the order of ABABAB... To form a crystal structure belonging to the hexagonal system. Here, a direction perpendicular to the basal plane is referred to as a c-axis, and an arbitrary direction within the basal plane is referred to as an a-axis. In this crystal structure, a unit cell is a solid having a rhombus of one side length a ₀ (m) connecting carbons in the basal plane and having a height of c _{0 in} the stacking direction of the basal plane. Here, a ₀ (m) is a lattice constant in the basal plane, c ₀ (m) is a lattice constant in the stacking direction, and a typical value at room temperature is a ₀ = 2.462 × 10 ^-10 (m), c ₀ = 6.708 × 10 ^-10 (m). As the typical value at room temperature of the interlayer distance d ₀₀₂ of the base ^{_{plane, d 002 = 3.354 × 10 -10}} (m) can be given. One or more such unit cells are aggregated to form a crystallite. This crystallite has a height Lc (nm) with a rhombus having a side length La (nm) and an acute angle of 60 ° as a bottom surface, for example. ). In this case, in the relational expression (1), (√3 × La ² ) represents the area of two rhombuses with La as one side, that is, the sum of the upper and lower base areas of the crystallite. Further, (4 × Lc × La) indicates the area of four rectangular surfaces having the lengths of two orthogonal sides as Lc and La, that is, the sum of the areas of the side surfaces (hereinafter also referred to as edge surfaces) of the crystallites. . Therefore, (4 × Lc × La) / (√3 × La ² + 4 × Lc × La) in the relational expression (1) indicates the ratio of the area of the edge surface to the surface area of the crystallite. And B × (4 × Lc × La) / (√3 × La ² + 4 × Lc × La), which is a value obtained by multiplying this by the surface area B (m ² ) of the carbon material, is the edge of the crystallite of the carbon material It represents the area of the surface. The surface area B (m ² ) of the carbon material is a value obtained by multiplying the weight (g) of the carbon material by the specific surface area (m ² / g) of the carbon material obtained by the BET method. By the way, occlusion / release of lithium ions to / from the carbon material is performed through the edge surface, and occlusion / release of lithium ions is not performed on the basal plane. Therefore, it is considered that the state of the film formed on the edge surface due to the decomposition of the electrolytic solution or the like affects the output characteristics. That is, if the thickness of the coating formed on the edge surface is appropriate, it is considered that the insertion and release of lithium ions performed smoothly through the edge surface can be performed and the output characteristics at a large current can be improved. . When the value Z obtained by dividing the content A (μmol) of the anion compound represented by the general formula (1) in the ion conductive medium by the area of the edge surface of the crystallite is within a predetermined range, output characteristics can be improved. . This Z is represented by Z = A / {B × (4 × Lc × La) / (√3 × La ² + Lc × La)}, and 0.010 × 10 ² ≦ Z ≦ 2.5 × 10 ² When satisfying, the output characteristics can be enhanced. Among ^{them, 0.010 × 10 2 <Z <} 0.060 × 10 2, or, more preferably ^{0.060 × 10 2 <Z <2.5} × 10 2. If it is this range, an output characteristic can be improved more.

In the lithium secondary battery of the present invention, the Avogadro constant is N _A (mol ⁻¹ ), the lattice constant in the basal plane of the carbon material is a ₀ (m), and the interlayer distance between the basal planes of the carbon material is d. ₀₀₂ (m), where the number of molecules of the anion compound is the number of molecules N _L, and the number of active sites involved in the occlusion and release of lithium in the carbon material is the number of active points n _L , the relational expression (2) It is preferable that the number of molecules N _L and the number of active sites n _L represented by the relational expression (3) satisfy the relational expression (4).

Below, relational expression (2) is demonstrated. The number of active points n _L indicates the number of carbon atoms existing on the edge surface of the carbon material, and is a value determined based on the following assumptions. It is assumed that when all the edge surfaces of the crystallite are connected, a square plane including the c-axis and the a-axis is obtained. In this case, if the area of the edge surface of the crystallite is S (= B × (4 × Lc × La) / (√3 × La ² + Lc × La)), √S / a _{0 in the} a-axis direction, c By arranging √S / d ₀₀₂ carbon atoms in the axial direction, (√S / a ₀ ) × (√S / d ₀₀₂ ) carbon atoms exist in the edge plane. Then, the number of active points n _L can be expressed by n _L = (√S / a ₀ ) × (√S / d ₀₀₂ ). That is, it can be expressed by the relational expression (3). When the number of active sites n _L and the number of molecules N _L of the anionic compound satisfy the relational expression (4), it is possible to form a film with a more preferable quality and quantity on the edge surface, and to further improve the output characteristics. Can be considered. Among these, 0.05 ≦ N _L / n _L ≦ 10 is preferable, 0.59 ≦ N _L / n _L ≦ 9.91 is more preferable, and 2.52 ≦ N _L / n _L ≦. More preferably, it is 2.97. If it is this range, an output characteristic can be improved more.

  The lithium secondary battery of the present invention may include a separator between the positive electrode and the negative electrode. The separator is not particularly limited as long as it has a composition that can withstand the range of use of the secondary battery. Is mentioned. These may be used alone or in combination.

  The shape of the lithium secondary battery of the present invention is not particularly limited, and examples thereof include a coin type, a button type, a sheet type, a laminated type, a cylindrical type, a flat type, and a square type. Moreover, you may apply to the large sized thing etc. which are used for an electric vehicle etc. FIG. 2 is a schematic view showing an example of the lithium secondary battery 10 of the present invention. The lithium secondary battery 10 includes a positive electrode sheet 13 in which a positive electrode active material 12 is formed on a current collector 11, a negative electrode sheet 18 in which a negative electrode active material 17 is formed on the surface of the current collector 14, and the positive electrode sheet 13 and the negative electrode sheet. 18 and a non-aqueous ion conductive medium 20 that fills between the positive electrode sheet 13 and the negative electrode sheet 18. In this lithium secondary battery 10, the separator 19 is sandwiched between the positive electrode sheet 13 and the negative electrode sheet 18, and these are wound and inserted into the cylindrical case 22, and the positive electrode terminal 24 connected to the positive electrode sheet 13 and the negative electrode sheet are connected. A connected negative electrode terminal 26 is provided.

  It should be noted that the present invention is not limited to the above-described embodiment, and it goes without saying that the present invention can be implemented in various modes as long as it belongs to the technical scope of the present invention.

  Below, the example which produced the lithium secondary battery of this invention concretely is demonstrated as an Example.

Example 1
(Production of battery)
LiNi _0.8 Co _0.15 Al _0.05 O ₂ as a positive electrode active material was synthesized by a known coprecipitation method using nitrates of the respective metals as raw materials. 85 parts by weight of the positive electrode active material, 10 parts by weight of carbon black (made by Tokai Carbon Co., Ltd., TB5500) as a conductive material, and 5 parts by weight of polyvinylidene fluoride (manufactured by Kureha Chemical Industry, KF polymer) as a binder Mixed. Then, an appropriate amount of N-methyl-2-pyrrolidone (NMP) as a dispersing agent was added and dispersed to obtain a paste-like positive electrode mixture. This paste-like positive electrode mixture was uniformly applied on both sides of an aluminum foil current collector having a thickness of 20 μm and dried by heating to prepare a coated sheet. Thereafter, the coated sheet was passed through a roll press to be densified and cut into a width of 54 mm and a length of 450 mm to obtain a positive electrode sheet (positive electrode).

As the negative electrode active material, the crystallite size Lc in the c-axis direction is 50 nm, the crystallite size La in the a-axis direction is 50 nm, the lattice constant a ₀ in the basal plane is 2.4 × 10 ⁻¹⁰ m, graphite interlayer distance d ₀₀₂ in the stacking direction 3.35 × 10 ^-10 m, the specific surface area was used artificial graphite of 1 m ² / g. The crystallite size (Lc, La) was determined according to the method (Michio Inagaki, Carbon, 1963 [26], 25) defined by the 117th Committee of the Japan Society for the Promotion of Science. 95 parts by weight of this negative electrode active material, 5 parts by weight of polyvinylidene fluoride as a binder (manufactured by Kureha Chemical Industry Co., Ltd., KF polymer) are mixed, and N-methyl-2-pyrrolidone (NMP) is added as a dispersion material. An appropriate amount was added and dispersed to obtain a slurry-like composite material. These slurry composites were uniformly applied on both sides of a 10 μm thick copper foil current collector and dried by heating to prepare a coated sheet. Thereafter, the coated sheet was passed through a roll press to be densified and cut into a width of 56 mm and a length of 500 mm to obtain a negative electrode sheet (negative electrode). At this time, the weight of graphite contained in the negative electrode was 2.8 g.

The positive electrode sheet and the negative electrode sheet prepared as described above were wound around a 25 μm thick polyethylene separator to prepare a roll-shaped electrode body, which was inserted into a 18650 type cylindrical case. Next, a nonaqueous electrolytic solution was prepared as follows. First, LiPF ₆ as a main component electrolyte (supporting salt) is added to an organic solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed at a volume ratio of 3: 7 so as to have a concentration of 1 mol / L. A main component electrolyte solution was prepared. Further, in an organic solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed at a volume ratio of 3: 7, b = 1, n = 2, q = 0, and R ² in Formula (1) are F. , X ¹ and X ² are O, and M is P. An anionic compound (PFO, see chemical formula (4)) and LPFO, which is a compound composed of Li ⁺ , are added so as to have a concentration of 1 mol / L, and a secondary component electrolyte solution Was made. Next, the main component electrolyte solution and the subcomponent electrolyte solution were added to the battery so that the subcomponent electrolyte was 24 μmol. The prepared non-aqueous electrolyte was impregnated in the above-mentioned 18650 type cylindrical case and sealed to produce a cylindrical battery. Thus, the battery of Example 1 was obtained.

(Examples 2 to 5)
As the negative electrode active material, 3.2 g of artificial graphite having a crystallite size Lc in the c-axis direction of 200 nm, a crystallite size La in the a-axis direction of 50 nm, and a specific surface area of 8 m ² / g was used, and a secondary component electrolyte was used. A battery of Example 2 was made in the same manner as Example 1 except that the amount was 24 μmol. As the negative electrode active material, 2.8 g of artificial graphite having a c-axis direction crystallite size Lc of 100 nm, an a-axis direction crystallite size La of 50 nm, and a specific surface area of 1 m ² / g was used. A battery of Example 3 was made in the same manner as Example 1 except that the component electrolyte was 120 μmol LiBF ₂ (C ₂ O ₄ ). As the negative electrode active material, 2.8 g of artificial graphite having a crystallite size Lc in the c-axis direction of 50 nm, a crystallite size La in the a-axis direction of 50 nm, and a specific surface area of 1 m ² / g was used. A battery of Example 4 was made in the same manner as Example 1 except that the component electrolyte was 120 μmol. Further, 2.8 g of artificial graphite having a crystallite size Lc of 50 nm in the c-axis direction, a crystallite size La in the a-axis direction of 50 nm, and a specific surface area of 1 m ² / g as a negative electrode active material is used as a secondary component. A battery of Example 5 was made in the same manner as Example 1 except that the electrolyte was 400 μmol.

(Comparative Examples 1-3)
A battery of Comparative Example 1 was produced in the same manner as Example 1 except that the subcomponent electrolyte was not added. Further, 3.2 g of artificial graphite having a crystallite size Lc in the c-axis direction of 250 nm, a crystallite size La in the a-axis direction of 20 nm, and a specific surface area of 8 m ² / g is used as the negative electrode active material. A battery of Comparative Example 2 was produced in the same manner as Example 1 except that the electrolyte was 24 μmol. As the negative electrode active material, 2.8 g of artificial graphite having a crystallite size Lc in the c-axis direction of 50 nm, a crystallite size La in the a-axis direction of 100 nm, and a specific surface area of 1 m ² / g was used. A battery of Comparative Example 3 was produced in the same manner as Example 1 except that the component electrolyte was 400 μmol.

[Charge / discharge test]
The capacity of the produced battery was confirmed under a temperature condition of 20 ° C. First, the battery is charged to a charge upper limit voltage of 4.1 V at a constant current of 0.5 mA / cm ² and then discharged to a discharge lower limit voltage of 3 V at a constant current of 0.2 mA / cm ² to measure the discharge capacity. did.

[Charge / discharge cycle test]
Under a temperature condition of 60 ° C., which is considered to be the upper limit of the actual use temperature range of the battery, the battery is charged to a charging upper limit voltage of 4.1 V with a constant current of 2.0 mA / cm ² and then a current density of 2.0 mA / cm. Charging / discharging for discharging to a discharge lower limit voltage of 3 V at a constant current of ² was defined as one cycle, and this cycle was performed for a total of 500 cycles. After the end of the cycle, the discharge capacity after the cycle was measured in the same manner as the charge / discharge test described above.

[IV resistance measurement]
Each battery after the cycle was adjusted to 50% of the battery capacity (SOC = 5%), and 0.5 A, 1 A, 2 A, 3 A, and 5 A currents were passed to measure the battery voltage after 10 seconds. The applied current and voltage were linearly approximated, and IV resistance (mΩ) was obtained from the slope.

[Experimental result]
Table 1 shows the results of IV resistance measurement of Examples 1 to 5 and Comparative Examples 1 to 3. In addition to this, in Table 1, the crystallite size Lc (nm) and La (nm), the surface area of graphite (m ² ), the weight of graphite (g), the type and amount of subcomponent electrolyte (μmol), general formula The value of A / {B × (4 × Lc × La) / (√3 × La ² + Lc × La)} in (1) (= Z (μmol / m ² )), and the value of N _L / n _L Indicated. Table 2 shows the discharge capacities before and after the cycles of Examples 1 to 5 and Comparative Examples 1 to 3, and the capacity retention rate. From Tables 1 and 2, it was found that in Examples 1 to 5 satisfying the relational expression (1), the IV resistance value can be reduced and the output characteristics are improved. In particular, it was found that the IV resistance was smaller when 0.010 × 10 ² <Z <0.060 × 10 ² or 0.060 × 10 ² <Z <2.5 × 10 ² . . Further, in Examples 1 to 5 satisfying the relational expression (4), it was found that the IV resistance value can be reduced and the output characteristics are improved. In particular, it was found that the IV resistance becomes smaller when 0.59 ≦ N _L / n _L ≦ 9.91, particularly 2.52 ≦ N _L / n _L ≦ 2.97. In addition, since the output characteristics are good regardless of whether PFO or BFO is used as the anion compound represented by the general formula (1), the output characteristics are also good even if the anion compound is PTFO or PO. I guess it can be done. Further, it was presumed that the output characteristics of the anion compound and the cation paired with Na ⁺ and K ⁺ , which are not limited to lithium, can be improved.

  DESCRIPTION OF SYMBOLS 10 Lithium secondary battery, 11 Current collector, 12 Positive electrode active material, 13 Positive electrode sheet, 14 Current collector, 17 Negative electrode active material, 18 Negative electrode sheet, 19 Separator, 20 Nonaqueous ion conduction medium, 22 Cylindrical case, 24 Positive electrode Terminal, 26 Negative terminal.

Claims (3)

A positive electrode having a positive electrode active material, a negative electrode having a carbon material as an anode active material, before Symbol interposed between the positive electrode and the negative electrode, electrolyte compound comprising an anion compound represented by the cation and the general formula (1) the a, a nonaqueous ion conductive medium that conducts lithium ions, a lithium secondary battery having a a method of selecting the negative electrode and the nonaqueous ionic conductive medium,
The content of the anionic compound is A (μmol), the surface area of the carbon material is B (m ² ), the crystallite size in the c-axis direction of the carbon material is Lc (nm), A selection method in which the negative electrode and the non-aqueous ion conductive medium are selected so as to satisfy the relational expression (1), where La (nm) is the size of the crystallite in the a-axis direction.

(However, M represents a transition element, a group 13, 14 or 15 element of the periodic table; b is an integer of 1 to 3, m is an integer of 1 to 4, n is an integer of 0 to 8, q is R ¹ represents alkylene having 1 to 10 carbon atoms, halogenated alkylene having 1 to 10 carbon atoms, arylene having 6 to 20 carbon atoms or halogenated arylene having 6 to 20 carbon atoms (these alkylene and Arylene may have a substituent or a hetero atom in the structure, and when q is 1 and m is 2 to 4, m R ^{1 s} may be bonded to each other); R ² Is a halogen, an alkyl having 1 to 10 carbon atoms, an alkyl halide having 1 to 10 carbon atoms, an aryl having 6 to 20 carbon atoms, an aryl halide having 6 to 20 carbon atoms (these alkyl and aryl are in the structure) May have substituents, heteroatoms And n represents the n number of R ² may be each bonded to form a ring) or -X ³ R ³ at the time of 2~8; X ^1, X ² and X ³ are each independently in represents O, S or NR ^4; R ³ and R ⁴ are each hydrogen independently alkyl having 1 to 10 carbon atoms, a halogenated alkyl having 1 to 10 carbon atoms, 6 to 20 carbon atoms aryl, carbon A number 6 to 20 aryl halide (These alkyls and aryls may have a substituent or a heteroatom in the structure, and when a plurality of R ³ or R ⁴ are present, they are bonded to form a ring. May represent))

BFO represented by the chemical formula as a pre-Symbol anion compound (2) ~ (5), PTFO, in a lithium secondary battery comprising the nonaqueous ion conductive medium which is dissolved at least one member selected from the group consisting of PFO and PO The selection method according to claim 1 , wherein the negative electrode and the non-aqueous ion conductive medium are selected .

Avogadro constant is N _A (mol ⁻¹ ), lattice constant in the basal plane of the carbon material is a ₀ (m), interlayer distance of the basal plane of the carbon material is d ₀₀₂ (m), and the anionic compound and the number of molecules with molecular number n _L, when the number of active sites involved in the storage and release of lithium and the active number n _L in the carbon material, the number of molecules n _L represented by equation (2), equation The negative electrode and the non-aqueous ion conductive medium are selected so that the active site number n _L represented by (3) satisfies the relational expression (4) .
The selection method according to claim 1 or 2.

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