JP2005310479A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery with a large charge/discharge capacity and high Coulomb efficiency. <P>SOLUTION: The nonaqueous electrolyte secondary battery is equipped with a positive electrode, a negative electrode containing amorphous carbon, and a nonaqueous electrolyte containing a phosphazene compound and a supporting electrolyte. The amorphous carbon preferably has an average space of (002) planes (d<SB>002</SB>) as determined by an X-ray diffraction of 0.350-0.390 nm, and a crystallite size (L<SB>c</SB>) in the direction of a c-axis of 70 nm or less. The content of the phosphazene compound in the nonaqueous electrolyte is preferably 2 vol.% or more. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to a non-aqueous electrolyte secondary battery with improved charge / discharge capacity.

  Conventionally, nickel-cadmium batteries have been mainly used as secondary batteries for memory backup of AV and information devices such as personal computers and VTRs, and driving power sources thereof. In recent years, non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries have been very popular as alternatives to nickel-cadmium batteries because they have the advantages of high voltage and high energy density and exhibit excellent self-discharge characteristics. Attention has been paid and various developments have been attempted, and some of them have been commercialized. For example, more than half of notebook computers and mobile phones are driven by non-aqueous electrolyte secondary batteries.

  In these non-aqueous electrolyte secondary batteries, a lithium-containing composite oxide is used as a material for forming a positive electrode, and a carbon material is frequently used as a material for forming a negative electrode. An aprotic organic solvent such as an ester organic solvent is used as the electrolytic solution for the purpose of reducing the risk of this and increasing the driving voltage.

Further, as the carbon material used for the negative electrode, graphitizable carbon, graphite, and the like are frequently used. However, when these carbon materials are used, lithium ions are intercalated into the carbon material and LiC ₆ is formed. Once formed, no more lithium can be inserted. Therefore, when graphitizable carbon or graphite is used, the charge / discharge capacity is limited to the theoretical capacity of 372 mAh / g.

  On the other hand, when amorphous carbon such as non-graphitizable carbon is used for the negative electrode, the negative electrode can accommodate lithium exceeding the theoretical capacity of 372 mAh / g. It is preferable to use crystalline carbon. However, when amorphous carbon is used for the negative electrode, there are problems that the irreversible capacity is large and the Coulomb efficiency is poor.

JP-A-8-279358 Material integration, vol. 17, no. 1, (2004), p. 45

  Accordingly, an object of the present invention is to provide a non-aqueous electrolyte secondary battery that solves the above-described problems of the prior art, has a high charge / discharge capacity, and is excellent in coulomb efficiency.

  As a result of intensive studies to achieve the above object, the present inventors have used amorphous carbon for the negative electrode and added a phosphazene compound to the non-aqueous electrolyte so that the coulomb of the non-aqueous electrolyte secondary battery can be obtained. The inventors have found that the charge / discharge capacity can be significantly improved while maintaining the efficiency, and have completed the present invention.

  That is, the non-aqueous electrolyte secondary battery of the present invention includes a positive electrode, a negative electrode containing amorphous carbon, and a non-aqueous electrolyte containing a phosphazene compound and a supporting salt.

In a preferable embodiment of the non-aqueous electrolyte secondary battery of the present invention, the amorphous carbon, the average spacing d ₀₀₂ of the X-ray diffraction (002) plane is 0.350～0.390Nm.

In another preferred embodiment of the non-aqueous electrolyte secondary battery of the present invention, the amorphous carbon has a crystallite size L _c (002) in the c-axis direction of 70 nm or less.

（式中、Ｒ¹は、それぞれ独立して一価の置換基又はハロゲン元素を表し；Ｙ¹は、それぞれ独立して２価の連結基、２価の元素又は単結合を表し；Ｘは、炭素、ケイ素、ゲルマニウム、スズ、窒素、リン、ヒ素、アンチモン、ビスマス、酸素、硫黄、セレン、テルル及びポロニウムからなる群から選ばれる元素の少なくとも１種を含む置換基を表す）又は下記式(II)：
(ＮＰＲ² ₂)_n ・・・ (II)
（式中、Ｒ²はそれぞれ独立して一価の置換基又はハロゲン元素を表し；ｎは３〜１５を表す）で表される。 In another preferred embodiment of the non-aqueous electrolyte secondary battery of the present invention, the phosphazene compound is represented by the following formula (I):

(In the formula, each R ¹ independently represents a monovalent substituent or a halogen element; Y ¹ each independently represents a divalent linking group, a divalent element, or a single bond; Represents a substituent containing at least one element selected from the group consisting of carbon, silicon, germanium, tin, nitrogen, phosphorus, arsenic, antimony, bismuth, oxygen, sulfur, selenium, tellurium and polonium) or the following formula (II ):
(NPR ² ₂ ) _n ... (II)
(In the formula, each R ² independently represents a monovalent substituent or a halogen element; n represents 3 to 15).

In another preferred embodiment of the non-aqueous electrolyte secondary battery of the present invention, at least one lithium-containing composite oxide wherein the positive electrode active material is selected from the group consisting of LiCoO ₂ , LiNiO ₂ and LiMn ₂ O ₄ . It is.

  In another preferred embodiment of the non-aqueous electrolyte secondary battery of the present invention, the non-aqueous electrolyte further contains an aprotic organic solvent.

  In another preferable example of the non-aqueous electrolyte secondary battery of the present invention, the content of the phosphazene compound in the non-aqueous electrolyte is 2% by volume or more.

  According to the present invention, the non-aqueous electrolyte secondary that has substantially improved charge / discharge capacity while maintaining coulomb efficiency by using amorphous carbon for the negative electrode and adding a phosphazene compound to the non-aqueous electrolyte. A battery can be provided.

  The present invention is described in detail below. The non-aqueous electrolyte secondary battery of the present invention includes a positive electrode, a negative electrode containing amorphous carbon, and a non-aqueous electrolyte containing a phosphazene compound and a supporting salt, and, if necessary, non-aqueous electrolysis such as a separator. Other members that are usually used in the technical field of liquid secondary batteries are provided. In the non-aqueous electrolyte secondary battery of the present invention, by using amorphous carbon as the negative electrode active material and further adding a phosphazene compound to the non-aqueous electrolyte, the charge / discharge capacity is maintained while maintaining the coulomb efficiency of the battery. To improve. Therefore, the nonaqueous electrolyte secondary battery of the present invention has a high charge / discharge capacity that has been difficult to achieve in the past and excellent coulomb efficiency.

As the positive electrode active material used for the positive electrode of the non-aqueous electrolyte secondary battery of the present invention, lithium-containing composite oxides such as LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiFeO ₂ and LiFePO ₄ , V ₂ O ₅ , V Preferable examples include metal oxides such as ₆ O ₁₃ , MnO ₂ and MnO ₃ , metal sulfides such as TiS ₂ and MoS ₂ , and conductive polymers such as polyaniline. The lithium-containing composite oxide may be a composite oxide containing two or three transition metals selected from the group consisting of Fe, Mn, Co, and Ni. In this case, the composite oxide includes: LiFe _x Co _y Ni (wherein, 0 ≦ x <1,0 ≦ y <1,0 <x + y ≦ 1) (1-xy) O 2, or represented by LiMn _x Fe _y O _2-xy like. Among these, LiCoO ₂ , LiNiO ₂ , and LiMn ₂ O ₄ are particularly preferable in terms of high capacity, high safety, and excellent electrolyte wettability. These positive electrode active materials may be used individually by 1 type, and may use 2 or more types together.

The negative electrode active material used for the negative electrode of the non-aqueous electrolyte secondary battery of the present invention contains amorphous carbon. Examples of the amorphous carbon include non-graphitizable carbon. Amorphous carbon preferably has an average spacing d ₀₀₂ of the X-ray diffraction (002) plane is 0.350～0.390Nm, and even more preferably 0.360～0.380Nm. The amorphous carbon preferably has a crystallite size L _c (002) in the c-axis direction of 70 nm or less, and more preferably 35 nm or less. Furthermore, amorphous carbon is preferably surface area of 0.5~5.0m ² / g, more preferably in the range of 0.8~4.0m ² / g, that density of 1.40~2.00g / cm ³ Preferably, it is 1.45 to 1.70 g / cm ³ . The negative electrode active material may partially include carbon materials other than amorphous carbon, such as graphitizable carbon, graphite, mesophase carbon microbeads (MCMB), and the like. The content of amorphous carbon in the negative electrode active material is preferably 20% by mass or more, more preferably 40% by mass or more, and still more preferably 80% by mass or more. When the content of amorphous carbon in the negative electrode active material is 20% by mass or more, the charge / discharge capacity of the non-aqueous electrolyte secondary battery can be improved.

  The positive electrode and the negative electrode can be mixed with a conductive agent and a binder as necessary. Examples of the conductive agent include acetylene black. Examples of the binder include polyvinylidene fluoride (PVDF) and polytetrafluoro. Examples include ethylene (PTFE), styrene / butadiene rubber (SBR), carboxymethylcellulose (CMC), and the like. These additives can be used at a blending ratio similar to the conventional one.

  Moreover, there is no restriction | limiting in particular as a shape of the said positive electrode and a negative electrode, It can select suitably from well-known shapes as an electrode. For example, a sheet shape, a columnar shape, a plate shape, a spiral shape, and the like can be given.

  The non-aqueous electrolyte of the non-aqueous electrolyte secondary battery of the present invention contains a phosphazene compound and a supporting salt, and may contain an aprotic organic solvent and the like as necessary. By adding the phosphazene compound to the non-aqueous electrolyte, the charge / discharge capacity and coulomb efficiency of the battery can be improved, and the safety of the non-aqueous electrolyte can also be improved. In other words, an aprotic organic solvent is usually used for the non-aqueous electrolyte, and when the battery becomes high temperature due to a short circuit or the like, the aprotic organic solvent in the electrolyte may ignite and ignite. In the non-aqueous electrolyte to which the phosphazene compound is added, the risk of ignition and ignition of the aprotic organic solvent is reduced by the action of nitrogen gas derived from the phosphazene compound. In addition, phosphorus, which constitutes phosphazene compounds, acts to suppress chain decomposition of polymer materials constituting the battery by generating phosphate esters, etc., effectively reducing the risk of battery ignition and ignition. can do. Furthermore, when the phosphazene compound contains a halogen, the halogen functions as an active radical scavenger in the unlikely event of combustion, further reducing the risk of the electrolyte burning.

  Preferred examples of the phosphazene compound used in the non-aqueous electrolyte include a chain phosphazene compound represented by the above formula (I) and a cyclic phosphazene compound represented by the above formula (II). Of the phosphazene compounds represented by formula (I) or formula (II), those which are liquid at 25 ° C. (room temperature) are preferred. The viscosity at 25 ° C. of the liquid phosphazene compound is preferably 300 mPa · s (300 cP) or less, more preferably 20 mPa · s (20 cP) or less, and particularly preferably 5 mPa · s (5 cP) or less. In the present invention, the viscosity is measured at 1 rpm, 2 rpm, 3 rpm, 5 rpm, 7 rpm, 10 rpm, 20 rpm and 50 rpm using a viscometer [R-type viscometer Model RE500-SL, manufactured by Toki Sangyo Co., Ltd.] The measurement was performed at a speed of 120 seconds, and the rotation speed when the indicated value reached 50 to 60% was set as an analysis condition, and the viscosity was measured at that time. If the viscosity of the phosphazene compound at 25 ° C exceeds 300 mPa · s (300 cP), the supporting salt becomes difficult to dissolve, the wettability to the positive electrode material, the negative electrode material, the separator, etc. decreases, and the viscosity resistance of the electrolyte increases. The ionic conductivity is remarkably lowered, and the performance becomes insufficient particularly when used under low temperature conditions such as below the freezing point. In addition, since these phosphazene compounds are in a liquid state, they have the same conductivity as that of a normal liquid electrolyte, and can exhibit excellent cycle characteristics when used in an electrolytic solution.

R ^{1 in} formula (I) is not particularly limited as long as it is a monovalent substituent or a halogen element, and each R ¹ may be the same or different. Here, examples of the monovalent substituent include an alkoxy group, an alkyl group, a carboxyl group, an acyl group, and an aryl group. Among these, an alkoxy group is preferable in that the phosphazene compound has low viscosity. On the other hand, preferred examples of the halogen element include fluorine, chlorine, bromine and the like. Examples of the alkoxy group include methoxy group, ethoxy group, propoxy group, butoxy group, and alkoxy-substituted alkoxy groups such as methoxyethoxy group and methoxyethoxyethoxy group. Among these, methoxy group, ethoxy group, methoxy group, etc. An ethoxy group and a methoxyethoxyethoxy group are preferable, and a methoxy group and an ethoxy group are more preferable from the viewpoint of low viscosity and high dielectric constant. Examples of the alkyl group include a methyl group, an ethyl group, a propyl group, a butyl group, and a pentyl group. Examples of the acyl group include a formyl group, an acetyl group, a propionyl group, a butyryl group, an isobutyryl group, and a valeryl group. Examples of the aryl group include a phenyl group, a tolyl group, and a naphthyl group. The hydrogen element in these monovalent substituents is preferably substituted with a halogen element. As the halogen element, fluorine, chlorine and bromine are preferred, fluorine is most preferred, and chlorine is then preferred.

Y ^{1 in} formula (I) is not particularly limited as long as it is a divalent linking group, a divalent element, or a single bond, and each Y ¹ may be the same or different. Here, as the divalent linking group, in addition to the CH ₂ group, oxygen, sulfur, selenium, nitrogen, boron, aluminum, scandium, gallium, yttrium, indium, lanthanum, thallium, carbon, silicon, titanium, tin, germanium Divalent containing at least one element selected from the group consisting of zirconium, lead, phosphorus, vanadium, arsenic, niobium, antimony, tantalum, bismuth, chromium, molybdenum, tellurium, polonium, tungsten, iron, cobalt, nickel A divalent element includes oxygen, sulfur, selenium and the like. Among these, Y ¹ in the formula (I) is preferably a divalent linking group containing a CH ₂ group and at least one element selected from the group consisting of oxygen, sulfur, selenium, and nitrogen. In particular, a divalent linking group containing sulfur and / or selenium is preferable because the risk of ignition and ignition of the electrolyte is remarkably reduced.

［式(III)、式(IV)及び式(V)中、Ｒ³、Ｒ⁴及びＲ⁵は、それぞれ独立に一価の置換基又はハロゲン元素を表し；Ｙ³、Ｙ⁴及びＹ⁵は、それぞれ独立に２価の連結基、２価の元素又は単結合を表し；Ｚは２価の基又は２価の元素を表す］で表される置換基が更に好ましい。 X in formula (I) is a substituent containing at least one element selected from the group consisting of carbon, silicon, germanium, tin, nitrogen, phosphorus, arsenic, antimony, bismuth, oxygen, sulfur, selenium, tellurium and polonium. There is no particular limitation as long as it is. From the viewpoint of consideration for toxicity, environment, etc., X in formula (I) is preferably a substituent containing at least one element selected from the group consisting of carbon, silicon, nitrogen, phosphorus, oxygen and sulfur, The following formula (III), formula (IV) or formula (V):

[In Formula (III), Formula (IV) and Formula (V), R ³ , R ⁴ and R ⁵ each independently represents a monovalent substituent or a halogen element; Y ³ , Y ⁴ and Y ⁵ are And each independently represents a divalent linking group, a divalent element or a single bond; and Z represents a divalent group or a divalent element].

R ³ of formula (III), R ⁵ of formula (IV) R ⁴ and formula (V), substituent or a halogen element similar monovalent to that described in R ¹ of formula (I) is either Are also preferred. Further, two R ^{3 s} in the formula (III) and two R ^{5 s in} the formula (V) may be the same or different, and may be bonded to each other to form a ring.

Y ³ of the formula (III), Y ⁴ and Y ⁵ of formula (V) of the formula (IV), the divalent linking group or bivalent element similar to that described by Y ¹ in the formula (I) Are preferably mentioned. Similarly, in the case of a divalent linking group containing sulfur and / or selenium elements, the risk of ignition and ignition of the electrolyte is greatly reduced, which is particularly preferable. Y ³ , Y ⁴ and Y ⁵ are also preferably single bonds. Two Y ^{3 in} the formula (III) and two Y ^{5 in} the formula (V) may be the same or different.

Z in the formula (III) is not particularly limited as long as it is a divalent group or a divalent element. Here, as the divalent group, CH ₂ group, CHR group (where R represents an alkyl group, alkoxy group, phenyl group, etc.), NR group, oxygen, sulfur, selenium, boron, aluminum , Scandium, gallium, yttrium, indium, lanthanum, thallium, carbon, silicon, titanium, tin, germanium, zirconium, lead, phosphorus, vanadium, arsenic, niobium, antimony, tantalum, bismuth, chromium, molybdenum, tellurium, polonium, tungsten , A divalent group containing at least one element selected from the group consisting of iron, cobalt, and nickel; and examples of the divalent element include oxygen, sulfur, and selenium. Among these, Z in the formula (III) is preferably a divalent group containing at least one element selected from the group consisting of oxygen, sulfur and selenium in addition to the CH ₂ group, CHR group and NR group. In particular, a divalent group containing an element of sulfur and / or selenium is preferable because the risk of ignition and ignition of the electrolyte is greatly reduced.

  As these substituents, a substituent containing phosphorus as represented by the formula (III) is particularly preferable in that the risk of ignition / flammability can be particularly effectively reduced. Further, when the substituent is a substituent containing sulfur as represented by the formula (IV), it is particularly preferable in terms of reducing the interface resistance of the electrolytic solution.

R ^{2 in} formula (II) is not particularly limited as long as it is a monovalent substituent or a halogen element. Here, examples of the monovalent substituent include an alkoxy group, an alkyl group, a carboxyl group, an acyl group, and an aryl group. Among these, an alkoxy group is preferable in that the phosphazene compound has low viscosity. On the other hand, preferred examples of the halogen element include fluorine, chlorine, bromine and the like, and among these, fluorine is particularly preferred. Examples of the alkoxy group include a methoxy group, an ethoxy group, a methoxyethoxy group, a propoxy group, and a phenoxy group. Among these, a methoxy group, an ethoxy group, a methoxyethoxy group, and a phenoxy group are particularly preferable. Examples of the alkyl group include a methyl group, an ethyl group, a propyl group, a butyl group, and a pentyl group; examples of the acyl group include a formyl group, an acetyl group, a propionyl group, a butyryl group, an isobutyryl group, and a valeryl group. Examples of the aryl group include a phenyl group, a tolyl group, and a naphthyl group. The hydrogen element in these monovalent substituents is preferably substituted with a halogen element. Preferred examples of the halogen element include fluorine, chlorine, bromine, and the like. And a trifluoroethoxy group.

A phosphazene compound having more suitable viscosity, solubility suitable for addition and mixing, etc., by appropriately selecting R ^{1 to} R ⁵ , Y ¹ , Y ^{3 to} Y ⁵ , and Z in formulas (I) to (V) Is obtained. These phosphazene compounds may be used alone or in combination of two or more.

The supporting salt used for the non-aqueous electrolyte is preferably a supporting salt that serves as a lithium ion source. The supporting salt is not particularly limited, and for example, LiClO ₄ , LiBF ₄ , LiPF ₆ , LiCF ₃ SO ₃ , LiAsF ₆ , LiC ₄ F ₉ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N and Li ( Preferable examples include lithium salts such as C ₂ F ₅ SO ₂ ) ₂ N. These supporting salts may be used alone or in combination of two or more.

  The concentration of the supporting salt in the non-aqueous electrolyte is preferably 0.2 to 1.5 mol / L (M), more preferably 0.5 to 1 mol / L (M). If the concentration of the supporting salt is less than 0.2 mol / L, the conductivity of the electrolyte cannot be sufficiently ensured, and the discharge characteristics and charging characteristics of the battery may be hindered. Since the viscosity of the electrolytic solution increases and the mobility of lithium ions cannot be ensured sufficiently, the conductivity of the electrolytic solution cannot be sufficiently ensured in the same manner as described above, which may hinder battery discharge characteristics and charge characteristics. .

  The aprotic organic solvent that can be used for the non-aqueous electrolyte does not react with the negative electrode, and can further suppress the viscosity of the non-aqueous electrolyte. Specific examples of the aprotic organic solvent include dimethyl carbonate (DMC), diethyl carbonate (DEC), diphenyl carbonate, ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone ( Preferable examples include esters such as GBL), γ-valerolactone, and methyl formate (MF), and ethers such as 1,2-dimethoxyethane (DME) and tetrahydrofuran (THF). Among these, ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, and methyl formate are preferable. Cyclic esters are preferred in that they have a high relative dielectric constant and excellent solubility of the supporting salt, while chain esters and chain ethers have low viscosity, so It is suitable in terms of lowering the viscosity. These aprotic organic solvents may be used alone or in combination of two or more.

  The content of the phosphazene compound in the non-aqueous electrolyte is preferably 2% by volume or more, and more preferably 5% by volume or more, from the viewpoint of improving the charge / discharge capacity while sufficiently suppressing the decrease in the Coulomb efficiency of the battery. From the viewpoint of improving the safety of the non-aqueous electrolyte, the content of the phosphazene compound in the non-aqueous electrolyte is preferably 3% by volume or more, and more preferably 5% by volume or more.

  Other members that can be used in the non-aqueous electrolyte secondary battery of the present invention include a separator that is interposed between positive and negative electrodes in a role of preventing current short-circuit due to contact between both electrodes. As the material of the separator, it is possible to reliably prevent contact between the two electrodes and to allow the electrolyte to pass through or to contain, for example, synthesis of polytetrafluoroethylene, polypropylene, polyethylene, cellulose, polybutylene terephthalate, polyethylene terephthalate, etc. Preferred examples include resin non-woven fabrics and thin layer films. Of these, polypropylene or polyethylene microporous films having a thickness of about 20 to 50 μm, cellulose-based films, polybutylene terephthalate, polyethylene terephthalate, and the like are particularly suitable. In the present invention, in addition to the separators described above, known members that are normally used in batteries can be suitably used.

  The form of the non-aqueous electrolyte secondary battery of the present invention described above is not particularly limited, and various known forms such as a coin type, a button type, a paper type, a square type or a spiral type cylindrical battery are available. Preferably mentioned. In the case of the button type, a non-aqueous electrolyte battery can be produced by preparing a sheet-like positive electrode and negative electrode and sandwiching a separator between the positive electrode and the negative electrode. In the case of a spiral structure, for example, a non-aqueous electrolyte battery can be manufactured by preparing a sheet-like positive electrode, sandwiching a current collector, and stacking and winding up a sheet-like negative electrode on the current collector. it can.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples.

(Example 1)
Cyclic phosphazene compound in which ethylene carbonate (EC) 27% by volume, ethyl methyl carbonate (EMC) 63% by volume, and in the above formula (II), n is 3, 1 of 6 R ² , 1 is an ethoxy group and 5 is fluorine LiPF ₆ (supporting salt) was dissolved in a mixed solution consisting of 10% by volume of A [viscosity at 25 ° C .: 1.2 mPa · s] to 1 mol / L (M) to prepare a nonaqueous electrolytic solution.

Amorphous carbon [manufactured by Kureha Chemical Co., Ltd., average interplanar spacing d ₀₀₂ = 0.379 nm, c-axis direction crystallite size L _c (002) = 1.2 nm, surface area = 3.5 m ² / g, density = 1.52 g / cm ³ ] For 94 parts by mass, add 3 parts by mass of acetylene black (conductive agent) and 3 parts by mass of polyvinylidene fluoride (binder), and add 50/50% by mass of organic solvent (ethyl acetate and ethanol). After kneading with a mixed solvent), the kneaded product was applied to a 25 μm thick aluminum foil (current collector) with a doctor blade, and then dried with hot air (100 to 120 ° C.) to form a 150 μm thick negative electrode sheet. Produced.

Next, 3 parts by mass of acetylene black (conductive agent) and 3 parts by mass of polyvinylidene fluoride (binder) are added to 94 parts by mass of LiMn ₂ O ₄ (positive electrode active material), and an organic solvent (acetic acid (50/50 mass% mixed solvent of ethyl and ethanol), and then the kneaded product is applied to a 25 μm thick aluminum foil (current collector) with a doctor blade and further dried with hot air (100 to 120 ° C.) Thus, a positive electrode sheet having a thickness of 80 μm was produced.

  The negative electrode sheet prepared as described above was overlapped and wound up on the obtained positive electrode sheet through a separator (microporous film: made of polypropylene) having a thickness of 25 μm to prepare a cylindrical electrode. The positive electrode length of the cylindrical electrode was about 260 mm. The above electrolytic solution was injected into the cylindrical electrode and sealed to produce an AA lithium ion battery (non-aqueous electrolyte secondary battery). The obtained battery was charged and discharged up to 20 cycles under the conditions of an upper limit voltage of 4.5 V, a lower limit voltage of 3.0 V, a discharge current of 100 mA, and a charge current of 50 mA in an atmosphere of 25 ° C. Further, the coulomb efficiency was calculated by dividing the discharge capacity in each cycle by the charge capacity, and the results shown in FIG. 1 were obtained.

(Comparative Example 1)
A nonaqueous electrolytic solution in which LiPF ₆ (supporting salt) is dissolved to 1 mol / L (M) in a mixed solution composed of 30% by volume of ethylene carbonate (EC) and 70% by volume of ethyl methyl carbonate (EMC) is used. Except for the above, a lithium ion battery was produced in the same manner as in Example 1, the charge / discharge capacity of the battery was measured up to 20 cycles, and the results shown in FIG. 1 were obtained.

(Comparative Examples 2 and 3)
A negative electrode sheet was produced in the same manner as in Example 1 except that graphite [manufactured by Sumitomo Metals] was used instead of amorphous carbon. A lithium ion battery of Comparative Example 2 was produced using the negative electrode sheet and the same non-aqueous electrolyte as Comparative Example 1. Moreover, the lithium ion battery of the comparative example 3 was produced using the same non-aqueous electrolyte as Example 1 using this negative electrode sheet. The discharge capacity and coulomb efficiency of these batteries are shown in FIG.

(Comparative Examples 4 and 5)
A negative electrode sheet was produced in the same manner as in Example 1 except that mesophase carbon micro beads [MCMB, manufactured by Osaka Gas] were used instead of amorphous carbon. A lithium ion battery of Comparative Example 4 was produced using the negative electrode sheet and the same nonaqueous electrolytic solution as Comparative Example 1. Moreover, the lithium ion battery of the comparative example 5 was produced using the same non-aqueous electrolyte as Example 1 using this negative electrode sheet. The discharge capacity and coulomb efficiency of these batteries are shown in FIG.

  As is apparent from FIG. 1, by using amorphous carbon for the negative electrode and adding a phosphazene compound to the non-aqueous electrolyte, the discharge capacity can be significantly increased while maintaining the Coulomb efficiency. From the comparison of FIGS. 1 to 3, when amorphous carbon is used for the negative electrode, the effect of improving the discharge capacity of the battery at a low cycle number by adding a phosphazene compound to the non-aqueous electrolyte is particularly large. I understand.

It is a graph which shows the discharge capacity and coulomb efficiency of the battery of Example 1 and the battery of Comparative Example 1. It is a graph which shows the discharge capacity of the battery of the comparative example 2, and the battery of the comparative example 3, and coulomb efficiency. It is a graph which shows the discharge capacity and the Coulomb efficiency of the battery of Comparative Example 4 and the battery of Comparative Example 5.

Claims (7)

  A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode containing amorphous carbon, and a non-aqueous electrolyte containing a phosphazene compound and a supporting salt. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the amorphous carbon has an (002) plane average plane distance d ₀₀₂ of 0.350 to 0.390 nm according to an X-ray diffraction method. The non-aqueous electrolyte secondary battery according to claim 1, wherein the amorphous carbon has a crystallite size L _c (002) in a c-axis direction of 70 nm or less. The phosphazene compound has the following formula (I):

(In the formula, each R ¹ independently represents a monovalent substituent or a halogen element; Y ¹ each independently represents a divalent linking group, a divalent element, or a single bond; Represents a substituent containing at least one element selected from the group consisting of carbon, silicon, germanium, tin, nitrogen, phosphorus, arsenic, antimony, bismuth, oxygen, sulfur, selenium, tellurium and polonium) or the following formula (II ):
(NPR ² ₂ ) _n ... (II)
^2. The nonaqueous electrolyte solution 2 according to claim 1, wherein each R ² independently represents a monovalent substituent or a halogen element; n represents 3 to 15. Next battery. _2. The non-aqueous electrolyte 2 according to claim 1, wherein the positive electrode active material is at least one lithium-containing composite oxide selected from the group consisting of LiCoO ₂ , LiNiO _2, and LiMn ₂ O _4. Next battery.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte further contains an aprotic organic solvent.   2. The non-aqueous electrolyte secondary battery according to claim 1, wherein a content of the phosphazene compound in the non-aqueous electrolyte is 2% by volume or more.

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