JP2009123473A - Nonaqueous electrolyte battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte battery capable of obtaining enough cycle characteristics, even in case a positive electrode material with an olivine structure is used. <P>SOLUTION: A negative electrode active material layer 22B contains a negative electrode active material capable of doping and dedoping lithium. The negative electrode active material is to contain a carbon material with chemical shift values on the basis of lithium chloride having spectra resulting from a plurality of peaks within a range of 0 ppm to 100 ppm, in case NMR (nuclear magnetic resonance) of<SP>7</SP>Li is measured in a fully charged state, with peak positions at the time of peak separation existing in at least 1 ppm, 31 ppm, 44 ppm, and 58 ppm. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a non-aqueous electrolyte battery. More specifically, the present invention relates to a non-aqueous electrolyte battery including a lithium phosphate compound having an olivine structure in a positive electrode.

  In recent years, many portable electronic devices such as a camera-type VTR (Video Tape Recorder), a mobile phone, and a laptop computer have appeared, and their size and weight have been reduced. As portable power sources for these electronic devices, research and development for improving the energy density of batteries, particularly secondary batteries, are being actively promoted.

  Batteries using non-aqueous electrolytes, especially lithium ion secondary batteries, are expected to have higher energy density than lead batteries and nickel cadmium batteries, which are conventional aqueous electrolyte secondary batteries. The market is growing and the market is growing significantly.

  In particular, since the characteristics of lithium ion secondary batteries such as light weight and high energy density are suitable for use in electric vehicles and hybrid electric vehicles, studies aiming to increase the size and output of the batteries have become active.

In a nonaqueous secondary battery represented by a lithium ion secondary battery, an oxide positive electrode such as LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ is generally used as a positive electrode active material. This is because a high capacity, a high voltage can be obtained, and a high filling property can be obtained, which is advantageous for reducing the size and weight of portable devices.

  However, these positive electrodes start releasing oxygen at 200 ° C. to 300 ° C. when heated in a charged state. When oxygen release starts, the flammable organic electrolyte solution is used as the electrolyte solution, so there is a risk that the battery will run out of heat. Therefore, when an oxide positive electrode is used, it is not easy to ensure safety particularly in a large battery.

  In contrast, A. K. It has been shown that the positive electrode material having an olivine structure reported by Padhi et al. Does not release oxygen even when the temperature exceeds 350 ° C. and is extremely excellent in safety. (See Non-Patent Document 1)

J. et al. Electrochem. Soc. , Vol. 144, p. 1188

In the positive electrode material having this olivine structure, charge / discharge proceeds in a two-layer coexistence state of LiFePO ₄ and FePO ₄ , so that the potential flatness is very high. For this reason, when performing constant current / constant voltage charging, which is a charging method of a normal lithium ion battery, there is a feature that charging is performed almost in a constant current charging state. Therefore, in a battery using a positive electrode material having an olivine structure, charging time can be shortened when charged at the same charge rate as compared with conventional positive electrode materials such as LiCoO ₂ , LiNiO ₂ , and LiMn ₂ O ₄ .

  However, in a battery using a positive electrode material having an olivine structure, since charging at a high current value continues for a relatively long time, the movement of Li ions in the negative electrode does not follow, and Li at the interface between the negative electrode and the electrolyte solution The ion concentration increases and Li metal is likely to be deposited on the negative electrode. As a result, when a conventional negative electrode carbon material was used, sufficient cycle characteristics could not be obtained in a battery using a positive electrode material having an olivine structure.

  Accordingly, an object of the present invention is to provide a nonaqueous electrolyte battery that can obtain sufficient cycle characteristics even when a positive electrode material having an olivine structure is used.

In order to solve the above-mentioned problems,
The present invention includes a positive electrode including a lithium phosphate compound having an olivine structure, a negative electrode including a negative electrode active material that can be doped and dedoped with lithium, and a nonaqueous electrolyte. The negative electrode active material is in a fully charged state. When measuring ⁷ Li NMR, the chemical shift value based on lithium chloride has a spectrum caused by a plurality of peaks in the range of 0 ppm to 100 ppm, and the peak position is at least 1 ppm, 31 ppm, 44 ppm when the peaks are separated. And a carbon material present at 58 ppm.

In this invention, the negative electrode material has a spectrum caused by a plurality of peaks in the range of 0 ppm to 100 ppm of chemical shift value based on lithium chloride when ⁷ Li NMR is measured in a fully charged state, and peak separation In this case, the carbon material having peak positions of at least 1 ppm, 31 ppm, 44 ppm and 58 ppm is included, so that even when a lithium phosphate compound having an olivine structure is used, sufficient cycle characteristics can be obtained.

  According to the present invention, sufficient cycle characteristics can be obtained even when a positive electrode material having an olivine structure is used.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a cross-sectional structure of a nonaqueous electrolyte battery according to an embodiment of the present invention. This battery is, for example, a non-aqueous electrolyte secondary battery, for example, a lithium ion secondary battery.

  As shown in FIG. 1, this secondary battery is a so-called cylindrical type, and a strip-shaped positive electrode 21 and a strip-shaped negative electrode 22 are interposed in a substantially hollow cylindrical battery can 11 via a separator 23. The wound electrode body 20 is wound. The battery can 11 is made of, for example, iron (Fe) plated with nickel (Ni), and has one end closed and the other end open. Inside the battery can 11, a pair of insulating plates 12 and 13 are arranged perpendicular to the winding peripheral surface so as to sandwich the winding electrode body 20.

  At the open end of the battery can 11, a battery lid 14, a safety valve mechanism 15 provided inside the battery lid 14 and a heat sensitive resistance element (Positive Temperature Coefficient; PTC element) 16 are interposed via a gasket 17. It is attached by caulking, and the inside of the battery can 11 is sealed. The battery lid 14 is made of, for example, the same material as the battery can 11.

  The safety valve mechanism 15 is electrically connected to the battery lid 14 via the heat sensitive resistance element 16, and the disk plate 15A is reversed when the internal pressure of the battery exceeds a certain level due to an internal short circuit or external heating. Thus, the electrical connection between the battery lid 14 and the wound electrode body 20 is cut off. When the temperature rises, the heat sensitive resistance element 16 limits the current by increasing the resistance value and prevents abnormal heat generation due to a large current. The gasket 17 is made of, for example, an insulating material, and asphalt is applied to the surface.

  The wound electrode body 20 is wound around a center pin 24, for example. A positive electrode lead 25 made of aluminum (Al) or the like is connected to the positive electrode 21 of the spirally wound electrode body 20, and a negative electrode lead 26 made of nickel (Ni) or the like is connected to the negative electrode 22. The positive electrode lead 25 is electrically connected to the battery lid 14 by being welded to the safety valve mechanism 15, and the negative electrode lead 26 is welded to and electrically connected to the battery can 11.

  FIG. 2 shows an enlarged part of the spirally wound electrode body 20 shown in FIG. The positive electrode 21 includes, for example, a positive electrode current collector 21A having a pair of opposed surfaces, and a positive electrode active material layer 21B provided on both surfaces of the positive electrode current collector 21A. In addition, you may make it have the area | region where the positive electrode active material layer 21B exists only in the single side | surface of 21 A of positive electrode collectors. The positive electrode current collector 21A is made of, for example, a metal foil such as an aluminum (Al) foil.

  The positive electrode active material layer 21B includes, for example, a positive electrode active material, and may include a conductive agent such as carbon black or graphite and a binder such as polyvinylidene fluoride as necessary. As the positive electrode active material, for example, a lithium phosphate compound having an olivine structure is used.

Examples of the lithium phosphate compound having an olivine structure include a compound represented by Formula I.
(Chemical I)
LiFe _1-y M _y PO ₄
Wherein M is selected from the group consisting of manganese (Mn), cobalt (Co), nickel (Ni), magnesium (Mg), zinc (Zn), chromium (Cr), titanium (Ti), and vanadium (V). Y is 0 ≦ y ≦ 0.8.)

  The negative electrode 22 includes, for example, a negative electrode current collector 22A having a pair of opposed surfaces and a negative electrode active material layer 22B provided on both surfaces of the negative electrode current collector 22A. In addition, you may make it have the area | region where the negative electrode active material layer 22B exists only in the single side | surface of 22 A of negative electrode collectors. The anode current collector 22A is made of a metal foil such as a copper (Cu) foil.

  The negative electrode active material layer 22B contains a negative electrode active material that can be doped and dedoped with lithium, and may contain a binder such as polyvinylidene fluoride as necessary.

The negative electrode active material has a spectrum caused by a plurality of peaks in the range of 0 to 100 ppm in chemical shift value based on lithium chloride when ⁷ Li NMR (Nuclear magnetic resonance) is measured in a fully charged state. It includes carbon materials having peak positions at least 1 ppm, 31 ppm, 44 ppm and 58 ppm when separated.

  This carbon material can be obtained, for example, by subjecting an organic material such as coal tar pitch to high-temperature heat treatment, pulverization and classification. The high-temperature heat treatment is performed, for example, by maintaining the temperature in the range of 1800 ° C. to 2400 ° C. for an appropriate time in an inert gas atmosphere such as argon gas.

  The negative electrode active material may include other carbon materials having different physical properties from the carbon material. The content of the carbon material at that time is preferably in the range of 7 wt% to 50 wt% with respect to the negative electrode active material layer 22 </ b> B in consideration of the effect of improving cycle characteristics and the effect of reducing DC resistance. Other carbon materials having different physical properties can be obtained, for example, by subjecting an organic material such as coal tar pitch to heat treatment at a temperature of less than 1800 ° C. or higher than 2400 ° C. in an inert gas atmosphere, and pulverizing and classifying.

  As the separator 23, for example, a polyethylene porous film, a polypropylene porous film, a synthetic resin nonwoven fabric, or the like can be used. The separator 23 is impregnated with an electrolytic solution that is a liquid electrolyte.

  The electrolytic solution includes a liquid solvent, for example, a nonaqueous solvent such as an organic solvent, and an electrolyte salt dissolved in the nonaqueous solvent.

  The non-aqueous solvent preferably contains at least one of cyclic carbonates such as ethylene carbonate and propylene carbonate. This is because the cycle characteristics can be improved. In particular, it is preferable to mix and contain ethylene carbonate and propylene carbonate because cycle characteristics can be further improved.

  The non-aqueous solvent preferably contains at least one of chain carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, and methyl propyl carbonate. This is because the cycle characteristics can be further improved.

  The non-aqueous solvent preferably further contains at least one of 2,4-difluoroanisole and vinylene carbonate. This is because 2,4-difluoroanisole can improve discharge capacity, and vinylene carbonate can further improve cycle characteristics. In particular, it is more preferable that they are mixed and contained because both the discharge capacity and the cycle characteristics can be improved.

  Nonaqueous solvents further include butylene carbonate, γ-butyrolactone, γ-valerolactone, those in which part or all of the hydrogen groups of these compounds are substituted with fluorine groups, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran. 1,3-dioxolane, 4-methyl-1,3-dioxolane, methyl acetate, methyl propionate, acetonitrile, glutaronitrile, adiponitrile, methoxyacetonitrile, 3-methoxypropyronitrile, N, N-dimethylformamide, N-methylpyrrolidinone, N-methyloxazolidinone, N, N-dimethylimidazolidinone, nitromethane, nitroethane, sulfolane, dimethyl sulfoxide, or trimethyl phosphate may be included.

  Depending on the electrode to be combined, the reversibility of the electrode reaction may be improved by using a material in which part or all of the hydrogen atoms of the substance contained in the non-aqueous solvent group are substituted with fluorine atoms. Therefore, these substances can be used as appropriate.

A lithium salt can be used as the electrolyte salt. Examples of the lithium salt include LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiSbF ₆ , LiClO ₄ , LiB (C ₆ H ₅ ) ₄ , LiCH ₃ SO ₃ , LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiC (SO ₂ CF ₃ ) ₃ , LiAlCl ₄ , LiSiF ₆ , LiCl, LiBF ₂ (ox) [lithium difluorooxalate borate], LiBOB (lithium bisoxalate borate), LiBr, etc. are suitable, and among these, Any one kind or a mixture of two or more kinds is used. Among them, LiPF ₆ is preferable because it can obtain high ion conductivity and can improve cycle characteristics.

  This secondary battery can be manufactured, for example, as described below. First, for example, a positive electrode active material, a conductive agent, and a binder are mixed to prepare a positive electrode mixture, and the positive electrode mixture is dispersed in a solvent such as N-methylpyrrolidone to obtain a positive electrode mixture slurry. . Subsequently, the positive electrode mixture slurry is applied to the positive electrode current collector 21A and the solvent is dried. Then, the positive electrode active material layer 21B is formed by compression molding using a roll press or the like, and the positive electrode 21 is manufactured.

  Further, for example, a negative electrode active material and a binder are mixed to prepare a negative electrode mixture, and the negative electrode mixture is dispersed in a solvent such as N-methylpyrrolidone to obtain a negative electrode mixture slurry. Subsequently, the negative electrode mixture slurry is applied to the negative electrode current collector 22A, and the solvent is dried. Then, the negative electrode active material layer 22B is formed by compression molding using a roll press or the like, and the negative electrode 22 is manufactured.

  Next, the positive electrode lead 25 is attached to the positive electrode current collector 21 by welding or the like, and the negative electrode lead 26 is attached to the negative electrode current collector 22 by welding or the like. After that, the positive electrode 21 and the negative electrode 22 are wound through the separator 23, and the tip of the positive electrode lead 25 is welded to the safety valve mechanism 15, and the tip of the negative electrode lead 26 is welded to the battery can 11. The positive electrode 21 and the negative electrode 22 are sandwiched between a pair of insulating plates 12 and 13 and stored in the battery can 11.

  After the positive electrode 21 and the negative electrode 22 are accommodated in the battery can 11, the electrolyte solution described above is injected into the battery can 11 and impregnated in the separator 23. After that, the battery lid 14, the safety valve mechanism 15, and the heat sensitive resistance element 16 are fixed to the opening end of the battery can 11 by caulking through the gasket 17. As described above, the secondary battery shown in FIG. 1 can be manufactured.

  In this secondary battery, when charged, for example, lithium ions are released from the positive electrode 21 and inserted in the negative electrode 22 through the electrolytic solution. When discharging is performed, for example, lithium ions are released from the negative electrode 22 and are inserted in the positive electrode 21 through the electrolytic solution.

  Specific embodiments of the present invention will be described in detail. However, the present invention is not limited to these examples.

<Example 1>

[Production of carbon material (I)]
The coal tar pitch was heat-treated at 1900 ° C. in an inert gas atmosphere to obtain a carbon material (I).

[Production of cylindrical cell]
92 parts by mass of carbon material (I), 8 parts by mass of polyvinylidene fluoride, and N-methyl-2-pyrrolidone out of the quantity were kneaded to obtain a negative electrode mixture paint. This negative electrode mixture paint was applied to both sides of a copper foil having a thickness of 15 μm, dried and pressed to prepare a strip-like negative electrode.

A predetermined amount of LiCO ₃ , FeSO ₄ .7H ₂ O, and NH ₄ H ₂ PO ₄ is mixed, and the mixed powder and carbon black are mixed at a weight ratio of 97: 3. And dry mixing for 10 hours. The mixed powder was baked at 550 ° C. in a nitrogen atmosphere to obtain a lithium phosphate compound having an olivine structure represented by LiFePO ₄ coated with carbon.

  85 parts by mass of this lithium phosphate compound, 10 parts by mass of polyvinylidene fluoride, 5 parts by mass of artificial graphite, and N-methyl-2-pyrrolidone outside the amount were kneaded to obtain a positive electrode mixture paint. This positive electrode mixture paint was applied to both sides of an aluminum foil having a thickness of 15 μm, dried and pressed to produce a strip-like positive electrode.

A polypropylene microporous film having a thickness of 25 μm was wound between the positive electrode and the negative electrode, and LiPF ₆ 1 mol / l was dissolved in a mixed solvent in which ethylene carbonate and dimethyl carbonate were mixed in an equal volume. A cylindrical cell of Example 1 having a capacity of 1 Ah and 18650 size was prepared together with a water electrolyte in a metal case having a diameter of 18 mm and a height of 65 mm.

<Example 2>
[Production of carbon material (II)]
The coal tar pitch was heat-treated at 2800 ° C. in an inert gas atmosphere to obtain a carbon material (II).

[Production of cylindrical cell]
7 parts by mass of carbon material (I), 85 parts by mass of carbon material (II), 8 parts by mass of polyvinylidene fluoride, and N-methyl-2-pyrrolidone out of the quantity were kneaded to obtain a negative electrode mixture paint. . Except for the above, a cylindrical cell of Example 2 was produced in the same manner as Example 1.

<Example 3>
[Production of cylindrical cell]
42 parts by mass of carbon material (I), 50 parts by mass of carbon material (II), 8 parts by mass of polyvinylidene fluoride, and N-methyl-2-pyrrolidone out of the quantity were kneaded to obtain a negative electrode mixture paint. . Except for the above, a cylindrical cell of Example 3 was produced in the same manner as Example 1.

<Example 4>
[Production of cylindrical cell]
52 parts by mass of carbon material (I), 40 parts by mass of carbon material (II), 8 parts by mass of polyvinylidene fluoride, and N-methyl-2-pyrrolidone out of the quantity were kneaded to obtain a negative electrode mixture paint. A cylindrical cell of Example 4 was produced in the same manner as Example 1 except for the points.

<Example 5>
[Production of cylindrical cell]
5 parts by mass of carbon material (I), 87 parts by mass of carbon material (II), 5 parts by mass of polyvinylidene fluoride, and N-methyl-2-pyrrolidone outside the amount were kneaded to obtain a negative electrode mixture paint. . Except for the above, a cylindrical cell of Example 5 was produced in the same manner as Example 1.

<Example 6>
[Production of cylindrical cell]
A predetermined amount of Li ₂ Co ₃ , MnCO ₃ , FeSO ₄ .7H ₂ O and NH ₄ H ₂ PO ₄ is mixed, and the mixed powder and carbon black are mixed at a weight ratio of 97: 3. After mixing, dry mixing was performed for 10 hours in a ball mill. This mixed powder was baked at 550 ° C. in a nitrogen atmosphere to obtain a MnFe olivine positive electrode active material represented by LiMn _0.7 Fe _0.3 PO ₄ . 85 parts by mass of this MnFe olivine positive electrode active material, 10 parts by mass of polyvinylidene fluoride, 5 parts by mass of artificial graphite, and N-methyl-2-pyrrolidone out of the amount were kneaded to obtain a positive electrode mixture paint. Except for the above, a cylindrical cell of Example 6 was produced in the same manner as Example 1.

<Comparative Example 1>
[Production of cylindrical cell]
92 parts by mass of carbon material (II), 8 parts by mass of polyvinylidene fluoride, and N-methyl-2-pyrrolidone out of the quantity were kneaded to obtain a negative electrode mixture paint. Except for the above, a cylindrical cell of Comparative Example 1 was produced in the same manner as Example 1.
<Comparative example 2>
[Production of cylindrical cell]
85 parts by mass of lithium cobaltate, 10 parts by mass of polyvinylidene fluoride, 5 parts by mass of artificial graphite, and N-methyl-2-pyrrolidone outside the quantity were kneaded to obtain a positive electrode mixture paint. Except for the above, a cylindrical cell of Comparative Example 2 was produced in the same manner as Comparative Example 1.

<Comparative Example 3>
85 parts by mass of lithium cobaltate, 10 parts by mass of polyvinylidene fluoride, 5 parts by mass of artificial graphite, and N-methyl-2-pyrrolidone outside the quantity were kneaded to obtain a positive electrode mixture paint. Except for the above, a cylindrical cell of Comparative Example 3 was produced in the same manner as Example 1.

<Comparative example 4>
[Production of cylindrical cell]
92 parts by mass of carbon material (II), 8 parts by mass of polyvinylidene fluoride, and N-methyl-2-pyrrolidone out of the quantity were kneaded to obtain a negative electrode mixture paint. Except for the above, a cylindrical cell of Comparative Example 4 was produced in the same manner as in Example 6.

(Evaluation)
For Examples 1 to 6 and Comparative Examples 1 to 4, the following (I) to (IV) were evaluated.

(I) ⁷ Li-NMR measurement in a fully charged state 92 parts by mass of carbon material (I), 8 parts by mass of polyvinylidene fluoride, and N-methyl-2-pyrrolidone out of the quantity were kneaded, and Example 1 A similar negative electrode mixture paint was obtained. This negative electrode mixture paint was applied only to one side of a 15 μm thick copper foil, dried and pressed, and punched to 15 mmφ to produce a coin cell electrode. Incidentally, the powder coating amount, since it is desirable that the ^{5mg / cm 2 ~10mg / cm 2} ( one side) was adjusted to the powder coating amount within this range.

  A coin cell was produced using a microporous film made of polypropylene having a thickness of 25 μm sandwiched between the produced coin cell and a Li metal as a counter electrode, and the electrolytic solution having the same composition as in Example 1. The coin cell was charged and discharged for one cycle by constant current and constant voltage charging (0.1C-0V-15h) and discharging (0.1C 2V), and then charged again under the same charging conditions.

In this state, the coin cell was disassembled, the negative electrode was taken out, washed with DMC (dimethyl carbonate), the negative electrode powder was scraped off from the copper foil, and ⁷ Li-NMR measurement was performed under the following conditions. As for Comparative Example 1, to prepare a coin cell using the same negative electrode mixture coating in Comparative Example 1 was subjected to the same ⁷ Li-NMR measurement.
Equipment: Bruker Nuclear Magnetic Resonance Equipment AVANCE400 (with 2.5mm MAS probe)
Temperature: Room temperature Measurement nucleus: ⁷ Li
Sample rotation speed: 30 kHz (magic angle spinning method)
Reference material: 1M LiCl aq

FIG. 3 shows ⁷ Li-NMR spectra of the carbon material (I) and the carbon material (II) obtained by ⁷ Li-NMR measurement.

In FIG. 3, the solid line indicates the measurement result of the ⁷ Li-NMR measurement of the carbon material (I), and the upward arrow indicates the peak position when the peaks are separated. The dotted line indicates the ⁷ Li-NMR measurement result of the carbon material (II), and the downward arrow indicates the peak position.

As shown in FIG. 3, in the ⁷ Li-NMR spectrum of the carbon material (I), 4 peaks were confirmed at 0 to 100 ppm, and the peak positions were 1 ppm, 31 ppm, 44 ppm, and 58 ppm, respectively. In the ⁷ Li-NMR spectrum of the carbon material (II), two peaks were confirmed at 0 to 100 ppm, and the peak positions were 5 ppm and 44 ppm, respectively.

(II) Evaluation of cycle characteristics For the cylindrical cells of Examples 1 to 6 and Comparative Examples 1 to 4, constant current and constant voltage charging (1A 3.6V 0.1 Acut) and constant current discharging (7A 2. 0V) was repeated, and the capacity retention rate of the discharge capacity at 500 cycles with respect to the discharge capacity at 1 cycle was determined, and the capacity retention rates of the examples and comparative examples were summarized in a bar graph. FIG. 4 shows a graph summarizing the cycle capacity retention rates of Examples 1 to 6 and Comparative Examples 1 to 4.

As shown in FIG. 4, in Examples 1 to 5, when LiFePO ₄ having an olivine structure is used for the positive electrode, the carbon material (I) is included in the negative electrode. Obtained.

Further, according to the comparison between Comparative Example 2 and Comparative Example 3 in which the positive electrode active material was LiCoO ₂ , no difference was observed in the cycle characteristics. This is thought to be because the constant current region during charging was shorter than that of LiFePO ₄ , so that the influence on the cycle characteristics due to the difference in the negative electrode was small. As can be seen from the comparison between Comparative Example 4 Similarly to Example 6, as the positive electrode active material, there is improvement in the cycle properties when using the LiMn _0.7 Fe _0.3 PO _4, as the positive electrode active material, as LiFePO ₄ It was found that no improvement effect was obtained.

(III) Negative electrode capacity comparison Using the negative electrode mixture paints obtained in Examples 1 to 5 and Comparative Example 1, coin cells were prepared in the same manner as in the evaluation (I), and constant current constant voltage charging (0.1 C -0V-15h), 1 cycle charge / discharge was performed with discharge (0.1C 2V), 0.1C discharge capacity was measured, and the discharge capacity per weight of the negative electrode active material was determined.

(IV) DC resistance measurement For the cylindrical cells of Examples 1 to 5 and Comparative Example 1, 10 A discharge was performed from the fully charged state, and the DC resistance was measured using the voltage V1 after 1 second and the voltage V0 immediately before the discharge. Was calculated by (Equation 1).
DC resistance = (V0−V1) / 10 (Expression 1)

  The measurement results of (III) to (IV) are shown in Table 1. Note that (IV) is a summary of comparative values when the DC resistance value of Comparative Example 1 is 100%.

  As shown in Table 1, the carbon material (II) can obtain a high capacity because the graphite structure has developed, but the carbon material (I) has a relatively low capacity because the graphite structure is relatively undeveloped. all right.

  Further, according to Examples 2 to 3 and Comparative Example 1, it was found that the carbon material (I) had a greater effect of reducing the direct current resistance than the carbon material (II). However, if the mixing amount of the carbon material (I) is too large, the capacity at the negative electrode becomes low, and it becomes necessary to increase the coating amount of the negative electrode. Therefore, there is an adverse effect that the direct current resistance of the battery is too large as in Example 1. Will occur.

  As described above, in consideration of the effect of improving the cycle characteristics and the effect of reducing the direct current resistance, the content of the carbon material (I) contained in the negative electrode active material layer is within the range of 7 wt% or more and 50 wt% or less. I found it desirable.

  The present invention is not limited to the above-described embodiments of the present invention, and various modifications and applications are possible without departing from the spirit of the present invention. For example, in the above-described embodiment, a cylindrical battery has been described as an example. However, the present invention is not limited to this, and for example, a metal for an exterior material such as a square battery, a coin battery, a button battery, or the like. Various shapes and sizes, such as a battery using a container or the like, a battery using a laminate film or the like as an exterior material such as a thin battery, can be used.

  For example, instead of the electrolytic solution, another electrolyte, for example, a gel electrolyte in which the electrolytic solution is held in a polymer compound may be used. The electrolyte solution (that is, liquid solvent, electrolyte salt, and additive) is as described above. Examples of the polymer compound include polyacrylonitrile, polyvinylidene fluoride, and a copolymer of polyvinylidene fluoride and polyhexafluoropropylene. , Polytetrafluoroethylene, polyhexafluoropropylene, polyethylene oxide, polypropylene oxide, polyphosphazene, polysiloxane, polyvinyl acetate, polyvinyl alcohol, polymethyl methacrylate, polyacrylic acid, polymethacrylic acid, styrene-butadiene rubber, nitrile -Butadiene rubber, polystyrene, polycarbonate. In particular, in consideration of electrochemical stability, polyacrylonitrile, polyvinylidene fluoride, polyhexafluoropropylene, polyethylene oxide, and the like are preferable.

  Examples of other electrolytes include solid polymer electrolytes using ion conductive polymers, and inorganic solid electrolytes using ion conductive inorganic materials. These can be used alone or in combination with other electrolytes. Also good. Examples of the polymer compound that can be used for the polymer solid electrolyte include polyether, polyester, polyphosphazene, and polysiloxane. Examples of the inorganic solid electrolyte include ion conductive ceramics, ion conductive crystals, and ion conductive glass.

It is sectional drawing showing the structure of the nonaqueous electrolyte battery by one Embodiment of this invention. It is sectional drawing which expands and represents a part of winding electrode body shown in FIG. It is a ⁷ Li-NMR spectrum measured in the evaluation. It is the graph which put together the capacity | capacitance maintenance factor at the time of 500 cycles of Example 1- Example 6 and Comparative Example 1- Comparative Example 4. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Battery can 12, 13 ... Insulating plate 14 ... Battery cover 15 ... Safety valve mechanism 16 ... Thermal resistance element 17 ... Gasket 20 ... Winding electrode body 21 ... Positive electrode 21A ... Positive electrode current collector 21B ... Positive electrode active material layer 22 ... Negative electrode 22A ... Negative electrode current collector 22B ... Negative electrode active material layer 23 ... Separator 24 ... Center pin 25 ... Positive electrode lead 26 ... Negative electrode lead

Claims (3)

A positive electrode including a lithium phosphate compound having an olivine structure, a negative electrode including a negative electrode active material capable of doping and dedoping lithium, and a non-aqueous electrolyte,
The negative electrode active material has a spectrum derived from a plurality of peaks in the range of 0 to 100 ppm in terms of the chemical shift value based on lithium chloride when ⁷ Li NMR is measured in a fully charged state, and when the peak is separated And a carbon material having a peak position of at least 1 ppm, 31 ppm, 44 ppm and 58 ppm. The nonaqueous electrolyte battery according to claim 1, wherein the content of the carbon material contained in the negative electrode active material layer is within a range of 7 wt% to 50 wt%. The nonaqueous electrolyte battery according to claim 1, wherein the lithium phosphate compound having an olivine structure is a compound represented by LiFePO ₄ .

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