JP2006172991A - Negative electrode active material, method for producing the same, and nonaqueous electrolyte secondary battery using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress a side reaction in the first charge in the case where tungsten oxide is used as a negative electrode active material, and to have a negative charge active material which is excellent in the first charge / discharge efficiency and can realize a high capacity non-aqueous electrolyte secondary battery. provide.
SOLUTION: Fluorinated tungsten oxide is used as a negative electrode active material.
[Selection] Figure 2

Description

  The present invention relates to a negative electrode active material for a battery for realizing a high-capacity non-aqueous electrolyte secondary battery, a method for producing the same, and a non-aqueous electrolyte secondary using the same.

A lithium ion battery used as a main power source for mobile communication devices and portable electronic devices has a high electromotive force and a high energy density. Examples of the positive electrode active material used in such a lithium ion battery include lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), manganese spinel (LiMn ₂ O ₄ ), and mixtures thereof. These positive electrode active materials have a voltage of 4 V or more with respect to lithium. One report, a carbon material is generally used for the negative electrode, and a 4V class lithium ion battery is configured by combining with the above-mentioned positive electrode.

Further, as the negative electrode active material, tungsten oxide (Patent Documents 1 and 2), a mixture of tungsten oxide and spinel titanium oxide (Patent Document 3), tungsten composite oxide (see Patent Document 4), and the like are known. However, when tungsten oxide is used as the negative electrode active material, there is a problem that the irreversible capacity (charge / discharge efficiency) in the first charge / discharge is reduced. It has been proposed to perform heat treatment in a reduced-pressure atmosphere (see Patent Document 5).
JP-A-61-116756 JP-A-61-206167 Japanese Unexamined Patent Publication No. 07-302587 Japanese Unexamined Patent Publication No. 63-285871 Japanese Unexamined Patent Publication No. 06-223831

  Here, when tungsten oxide is used as the negative electrode active material as described above, the initial charge / discharge efficiency is reduced because part of lithium transferred during charging is accompanied by irreversible side reactions, and positive electrode during discharge. The reason is that it does not return. However, it has been difficult to sufficiently solve this problem even by the means proposed in Patent Document 5.

  Therefore, the present invention provides a negative electrode capable of suppressing a side reaction in the initial charge, excellent in the initial charge / discharge efficiency, and realizing a high-capacity nonaqueous electrolyte secondary battery when tungsten oxide is used as the negative electrode active material. The purpose is to provide an active material.

  It is another object of the present invention to provide a high-capacity nonaqueous electrolyte secondary battery that is excellent in initial charge / discharge efficiency when tungsten oxide is used as a negative electrode active material.

  In order to solve the above-mentioned problems, the present inventors have conducted intensive studies. As a result, if fluorine atoms are introduced into conventionally used tungsten oxide and the obtained fluorinated tungsten oxide is used as a negative electrode active material, Thus, the inventors have found that the problem that the initial charge / discharge efficiency is reduced can be solved, and the present invention has been completed. That is, this invention provides the negative electrode active material for batteries containing a fluorinated tungsten oxide.

  Here, the “initial charge / discharge efficiency” means that the non-aqueous electrolyte secondary battery immediately after being prepared using the negative electrode active material of the present invention is charged, and the initial charge electric charge and the initial discharge electric charge are measured. , A value obtained by calculating the ratio (initial discharge electricity amount / initial charge electricity amount:%). At this time, lithium metal is used for the counter electrode as described later. Since most of the irreversible reaction, which is a side reaction during the first charge, is completed, the irreversible capacity can be evaluated as the first charge / discharge efficiency.

The fluorinated tungsten oxide preferably contains lithium.
The fluorinated tungsten oxide (hereinafter referred to as “lithium-containing fluorinated tungsten oxide”) has a composition formula: Li _x WO _3-y F _z (0 ≦ x <0.8, 0 <y <2, 0 <z <0.8).

  The negative electrode active material for a battery includes primary particles having an average particle size of 0.6 μm or less of the fluorinated tungsten oxide and secondary particles having an average particle size of 10 μm or less formed by aggregation of the primary particles. Preferably, the fluorinated tungsten oxide may contain at least one additive element selected from the group consisting of a transition metal element, a group II element, and a group IIIB.

  The present invention also relates to a method for producing the above negative electrode active material. The negative electrode active material of the present invention comprises at least one lithium compound selected from the group consisting of lithium carbonate, lithium hydroxide, lithium nitrate and lithium oxide, and a group consisting of lithium fluoride, sodium fluoride and potassium fluoride. It can be produced by mixing at least one selected fluorine compound and tungsten oxide and firing the resulting mixture. In the said manufacturing method, it is preferable to bake the said mixture at the temperature of 600 to 1200 degreeC.

  ADVANTAGE OF THE INVENTION According to this invention, the negative electrode active material which consists of a fluorinated tungsten oxide which suppresses the side reaction in the first charge, is excellent in the first charge / discharge efficiency, and can implement | achieve a high capacity | capacitance nonaqueous electrolyte secondary battery is provided. be able to. Furthermore, according to the present invention, by using the negative electrode active material made of the fluorinated tungsten oxide of the present invention, it is possible to provide a high-capacity non-aqueous electrolyte secondary battery with excellent initial charge / discharge efficiency.

(1) Negative electrode active material of the present invention The fluorinated tungsten oxide constituting the negative electrode active material for a battery of the present invention can be obtained by fluorinating tungsten oxide. By introducing fluorine atoms in this way, it is possible to suppress a reduction in the initial charge / discharge efficiency of the tungsten oxide. Such a fluorinated tungsten oxide is represented by a composition formula: Li _x WO _3-y F _z (0 ≦ x <0.8, 0 <y <2, 0 <z <0.8).

  Here, when determining the range of x, y, and z in the said compositional formula, the present inventors considered as follows. That is, it is considered that the fluorinated tungsten oxide in the present invention is synthesized in a form in which a part of oxygen atoms is replaced by fluorine atoms. Originally, from the viewpoint of capacity, it is preferable that the number of oxygen atoms is large, but since the irreversible capacity in the first charge / discharge is reduced and the first charge / discharge efficiency is increased, in the present invention, as described above. Fluorine atoms are introduced into the tungsten oxide.

  Then, as described above, by introducing fluorine atoms or lithium atoms into the tungsten oxide, the initial charge and discharge efficiency when the tungsten oxide is used as the negative electrode active material is improved. This is considered to be because the production of lithium oxide, which causes a decrease in irreversible capacity, is suppressed by the introduction of.

  Since the charge / discharge capacity of the fluorinated tungsten oxide of the present invention is derived from the change in the valence of the tungsten oxide ion, if too many fluorine atoms and lithium atoms are introduced, the charge / discharge capacity per unit weight decreases. Therefore, it is not preferable.

In particular, when the fluorinated tungsten oxide contains lithium atoms, it is considered that oxygen atoms are extracted from the surface of the fluorinated tungsten oxide to become lithium oxide. The range of the amount x of lithium atoms in the composition formula may be determined.

  From the above viewpoint, the composition of the fluorinated tungsten oxide of the present invention is premised on the battery design in consideration of the reduction of the irreversible capacity and the securing of the charge / discharge capacity in the first charge / discharge which are in a trade-off relationship with each other. Is preferably determined.

  And, as a result of experiments conducted with the primary focus on the first charge / discharge efficiency in particular, the present inventors have found that, in the above composition formula, the value of x exceeds 0.8 when it is 0.8 or more. Since charging / discharging efficiency falls, it discovered that it should be less than 0.8. The range of y and z is preferably 0 <y <2 and 0 <z <0.8, because it is considered that the normal charge / discharge reaction of tungsten oxide is inhibited when fluorination proceeds excessively. It was decided.

  In addition, since the fluorinated tungsten oxide of the present invention is considered to be oxygenated by extracting oxygen atoms from the surface during charge and discharge, the surface of the fluorinated tungsten oxide particles is particularly fluorinated. preferable. That is, in the particles of fluorinated tungsten oxide in the present invention, fluorine atoms may be introduced at least on the surface, and the inside may be composed of tungsten oxide.

  The electrochemical characteristics of the negative electrode active material of the present invention comprising the fluorinated tungsten oxide having the above composition can be measured by preparing an electrochemical characteristic measurement cell as follows. That is, 80 parts by weight of a negative electrode active material (fluorinated tungsten oxide of the present invention), 10 parts by weight of acetylene black as a conductive agent, and 10 parts by weight of polyvinylidene fluoride (PVdF) as a binder are mixed, It is diluted with N-methyl-2-pyrrolidone (NMP) and applied onto a current collector made of aluminum foil.

The coated current collector is dried in vacuum at 60 ° C. for 30 minutes, then cut to 15 × 20 mm ² dimensions, and further dried in vacuum at 150 ° C. for 14 hours to obtain an electrode having a thickness of 120 μm to 190 μm. On the other hand, a counter electrode made by pressing a lithium metal sheet on a stainless steel plate, a separator made of a polyethylene porous film, and ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed at a volume ratio of 3 to 7. Using an electrolytic solution in which 1.0 M LiPF ₆ is dissolved in a solvent, charge and discharge are repeated between predetermined voltage regions at a current density of 0.17 mA / cm ² , for example.

  The fluorinated tungsten oxide in the present invention preferably contains at least one additive element selected from the group consisting of a transition metal element, a group II element and a group IIIB. This is because the physical properties of the fluorinated tungsten oxide can be changed by doping the fluorinated tungsten oxide with the above additive elements.

  For example, if the transition metal is doped as an additive element, the stability of the fluorinated tungsten oxide crystal can be increased. If magnesium or aluminum is doped as an additive element, the electron conductivity can be increased, or the reaction (side reaction) with the electrolytic solution on the surface of the fluorinated tungsten oxide particles can be suppressed. Further, the formation of extra products at the reaction interface due to such side reactions is suppressed and the life is extended, and further, the exothermic reaction with the electrolytic solution is suppressed even during high-temperature heating, and the safety is improved.

  Here, the negative electrode active material of the present invention comprises primary particles having an average particle size of 0.6 μm or less of fluorinated tungsten oxide and secondary particles having an average particle size of 10 μm or less formed by aggregating the primary particles. It is preferable to include. When submicron particles become powder alone, the bulk density is small and handling is difficult. From such a viewpoint, by making secondary particles in which primary particles are aggregated, charge / discharge characteristics can be ensured and handling can be facilitated at the same time.

Further, in relation to the ease of charge / discharge reaction, it is preferable that the primary particles are small because the diffusion of lithium into the crystal is smooth. Judging from actual electrochemical characteristics, if it is 0.6 μm or less, charge / discharge characteristics having no practical problem can be obtained. On the other hand, when manufacturing the electrode plate, a paste using the negative electrode active material of the present invention is prepared and applied. When the average particle size of the secondary particles exceeds 10 μm, the dispersibility during the paste preparation is This is unsuitable because it tends to be damaged and the coating tends to be uneven. For these reasons, it is preferable to include primary particles having an average particle diameter of 0.6 μm or less and secondary particles having an average particle diameter of 10 μm or less formed by aggregating the primary particles.
(2) Method for Producing Negative Electrode Active Material of the Present Invention Composition formula constituting the negative electrode active material of the present invention: Li _x WO _3-y F _z (0 ≦ x <0.8, 0 <y <2, 0 <z The fluorinated tungsten oxide represented by <0.8) is at least one lithium compound selected from the group consisting of lithium carbonate, lithium hydroxide, lithium nitrate and lithium oxide, lithium fluoride, sodium fluoride And at least one fluorine compound selected from the group consisting of potassium fluoride and tungsten oxide, and the resultant mixture can be synthesized by firing. That is, the negative electrode active material of the present invention can be produced by a so-called dry method using the above powdery raw material.

  As the lithium source, at least one lithium compound selected from the group consisting of lithium carbonate, lithium hydroxide, lithium nitrate, and lithium oxide can be used. Among them, the initial charge / discharge efficiency is slightly higher as a result. In addition, it is preferable to use at least one of lithium carbonate and lithium hydroxide because the product gas during the reaction does not contain harmful substances (NOx) and the reactivity with tungsten oxide is good.

  Further, as the fluorine compound, at least one selected from the group consisting of lithium fluoride, sodium fluoride, and potassium fluoride can be used, but lithium fluoride is included because it does not contain impurities such as potassium and sodium. Is preferably used.

Furthermore, as tungsten oxide, for example, WO ₂ or WO ₃ can be used. In order to adjust the oxygen atomic ratio in the obtained fluorinated tungsten oxide, the ratio of both of the mixture of WO ₂ and WO ₃ is changed. Can also be used.

  Regarding the firing temperature, firing is preferably performed in the region of 600 ° C to 1200 ° C. If the temperature is lower than 600 ° C., the reaction is insufficient, and a high temperature exceeding 1200 ° C. is not necessary, and the production cost becomes expensive. In order to sufficiently develop the crystal structure of the resulting fluorinated tungsten oxide, a firing temperature of 800 ° C. or higher is preferable.

  Here, in order to control the average particle size of the secondary particles formed by aggregating the primary particles to 10 μm or less, with the average particle size of the primary particles of the fluorinated tungsten oxide being 0.6 μm or less as described above. In this case, a material obtained by previously synthesizing such a particle with a starting material which is tungsten oxide may be used. Tungsten oxide can be easily synthesized by oxidizing metallic tungsten, but tungsten oxide particles can be prepared by adjusting metallic tungsten to suitable particles.

(3) Non-aqueous electrolyte secondary battery of the present invention The present invention provides a non-aqueous electrolyte secondary battery having a negative electrode containing the fluorinated tungsten oxide as a negative electrode active material, a positive electrode, a separator, and an electrolytic solution. Also related.

In a general LiCoO ₂ / carbon material non-aqueous electrolyte secondary battery, oxidation resistance that does not oxidize to about 4.5 V, which is the charging potential of cobalt, and reduction resistance, which does not reduce to about 0 V, which is the charging potential of graphite. Therefore, organic solvents that cannot satisfy these potential windows have been excluded from the electrolyte for non-aqueous electrolyte secondary batteries.

  For example, lactone organic solvents, propylene carbonate, trimethyl phosphate, triethyl phosphate, and other solvents are inexpensive and have a large dielectric constant, so they have the ability to sufficiently dissolve electrolytes (salts) and are resistant to oxidation. Therefore, it is a useful solvent.

  However, when graphite is used for the negative electrode, reduction resistance becomes a problem, and lactone organic solvents are difficult to use. Propylene carbonate is also difficult to use because it is simultaneously decomposed during charging and discharging of graphite. Trimethyl phosphate and triethyl phosphate, which have a fire extinguishing action and excellent safety, are difficult to use for the same reason.

  On the other hand, in the nonaqueous electrolyte secondary battery of the present invention, since the above fluorinated tungsten oxide is used as the negative electrode active material instead of graphite, the potential on the negative electrode side is increased, so that the reduction resistance required for the solvent is dramatically increased. Alleviated. Therefore, in addition to the conventionally used ethylene carbonate (ECC), dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), diethyl carbonate (DEC), etc., the above lactone organic solvents, propylene carbonate, trimethyl phosphate and A solvent such as triethyl phosphate can also be used effectively.

  When nickel manganese spinel oxide or the like is used as the positive electrode active material, the potential of the positive electrode rises to 4.7 V or higher, but the above-mentioned solvent does not oxidize even at 5 V or higher, so that it can be used without any problem with respect to oxidation resistance. In addition, sulfolane, methyl diglyme, fluorinated ethylene carbonate, and the like having excellent oxidation resistance are also considered to be suitable solvents for the nonaqueous electrolyte secondary battery of the present invention.

  The dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), and diethyl carbonate (DEC) can be used as a diluent for a highly viscous solvent.

  In addition, the use of ionic liquids, which are very useful if they can be used alone, as solvents, is limited or difficult when graphite is used in the negative electrode as described above. However, it can be used in the nonaqueous electrolyte secondary battery of the present invention.

  However, it is preferable to use an ionic liquid alone from the viewpoint of safety and the like. However, since there are solid ones and high viscosity ones, the above-mentioned solvents are considered in consideration of using conventional production equipment. It is considered that the superiority can be ensured to some extent even when used in combination.

  Examples of the ionic liquid include the following. Cationic species include, for example, 1, 2 and 3 substituted imidazolium, pyridinium, phosphonium, ammonium, pyrrolidinium, guanidinium and isouronium. Examples of the anionic species include halogen, sulfate, amide, imide, methane species, borate, phosphate, antimonate, decanate and cobalt tetracarbonyl.

The electrolyte that can be used in the non-aqueous electrolyte secondary battery of the present invention is not particularly limited, and LiPF ₆ and LiBF ₄ that are conventionally used in non-aqueous electrolyte secondary batteries, and further lithium salts of organic anions Can also be used.

  As the separator, any separator that has been conventionally used in non-aqueous electrolyte secondary batteries can be used without particular limitation. For example, a microporous membrane or non-woven fabric of polyolefin can be used. Examples of the material constituting the nonwoven fabric include polyester.

  As the current collector contained in the positive electrode and the negative electrode, generally, a thin film such as an aluminum or aluminum alloy foil is used as the current collector for the positive electrode, and a copper foil is used as the current collector for the negative electrode. On the other hand, in the non-aqueous electrolyte secondary battery of the present invention, the fluorinated tungsten oxide is used as the negative electrode active material. Therefore, it is possible to use an aluminum or aluminum alloy foil for the negative electrode current collector. is there. As the binder, polyvinylidene fluoride or styrene butadiene rubber can be used.

  The shape of the nonaqueous electrolyte secondary battery of the present invention can be applied to any of coin type, button type, sheet type, cylindrical type, flat type, square type, and the like. When the shape of the battery is a coin type or a button type, the mixture of the positive electrode active material and the negative electrode material is mainly compressed into a pellet shape and used. The thickness and diameter of the pellet may be determined depending on the size of the battery. In addition, the wound body of the electrode in the present invention does not necessarily have a true cylindrical shape, and may have a prismatic shape such as a long cylindrical shape or a rectangular shape whose cross section is an ellipse.

  FIG. 2 is a side view showing a cross section of a part of a cylindrical battery which is an example of the nonaqueous electrolyte secondary battery according to the present invention. In the cylindrical battery shown in FIG. 2, an electrode plate group 4 obtained by winding a positive electrode and a negative electrode in a spiral shape through a separator is housed in a battery case 1. A positive electrode lead 5 is drawn from the positive electrode and connected to the sealing plate 2, and a negative electrode lead 6 is drawn from the negative electrode and connected to the bottom of the battery case 1.

  For the battery case and the lead plate, a metal or alloy having an organic electrolyte resistance and an electron conductivity can be used. For example, a metal such as iron, nickel, titanium, chromium, molybdenum, copper, aluminum, or an alloy thereof is used. In particular, the battery case is preferably made of a stainless steel plate or an Al—Mn alloy plate, and the positive electrode lead is preferably aluminum. The negative electrode lead is preferably nickel or aluminum. In addition, various engineering plastics and a combination of these and a metal can be used for the battery case in order to reduce the weight.

  Insulating rings 7 are respectively provided at the upper and lower portions of the electrode plate group. And electrolyte solution is inject | poured and a battery case is sealed using a sealing board. At this time, a safety valve can be provided on the sealing plate. In addition to the safety valve, various conventionally known safety elements may be provided. For example, a fuse, bimetal, PTC element, or the like is used as the overcurrent prevention element.

  In addition to the safety valve, as a countermeasure against an increase in the internal pressure of the battery case, a method of cutting the battery case, a method of cracking the gasket, a method of cracking the sealing plate, or a method of cutting the lead plate can be used. Further, the charger may be provided with a protection circuit incorporating measures against overcharge and overdischarge, or may be connected independently. As a method for welding the cap, the battery case, the sheet, and the lead plate, a known method (for example, direct current or alternating current electric welding, laser welding, or ultrasonic welding) can be used. As the sealing agent for sealing, conventionally known compounds and mixtures such as asphalt can be used.

  Hereinafter, the present invention will be described by way of representative examples, but the present invention is not limited thereto.

Example 1
Lithium carbonate as a lithium compound, lithium fluoride as a fluorine compound, and tungsten oxide are mixed and baked at 950 ° C. for 10 hours to form a fluorinated tungsten oxide (negative electrode active material) constituting the negative electrode active material of the present invention. Substance 1: Sample number A-1) was synthesized. During mixing, the ratio of fluorine atom / tungsten atom (F / W) in the mixture is 0.2, and the ratio of lithium atom / tungsten atom (Li / W) is 0.2. So that each raw material was charged.

[Particle morphology observation]
Here, an SEM photograph of the obtained fluorinated tungsten oxide particles was taken. FIG. 1 is an SEM photograph of the fluorinated tungsten oxide particles obtained in this example. FIG. 1 was analyzed. As a result, primary particles having an average particle size of approximately 0.6 μm or less were aggregated to obtain average particles. It was found that secondary particles having a diameter of about 1 μm were formed.

[Electrochemical properties]
Moreover, the electrochemical characteristics of the negative electrode active material of the present invention comprising the fluorinated tungsten oxide obtained here were measured by preparing a cell for measuring electrochemical characteristics. 80 parts by weight of the fluorinated tungsten oxide, 10 parts by weight of acetylene black as a conductive agent, and 10 parts by weight of PVdF as a binder are mixed, diluted with NMP, and placed on a current collector made of aluminum foil. Applied. The coated current collector was dried in vacuum at 60 ° C. for 30 minutes, then cut to 15 × 20 mm ² dimensions, and further dried in vacuum at 150 ° C. for 14 hours to obtain a negative electrode having a thickness of 120 μm to 190 μm. .

On the other hand, a lithium metal sheet is pressure-bonded to a stainless steel plate to produce a counter electrode having the same dimensions as the negative electrode, a separator made of a polyethylene porous film, and EC (ethylene carbonate) and DMC (dimethyl carbonate). ) Was mixed in a volume ratio of 3 to 7 to prepare a cell for measuring electrochemical characteristics using an electrolytic solution in which 1.0 M LiPF ₆ was dissolved.

The charging / discharging of this cell was repeated at a current density of 0.17 mA / cm ² between the voltage range of 0.5 V to 2.5 V with respect to the counter electrode (that is, lithium metal), The amount of discharge electricity was measured, and the ratio (initial discharge electricity amount / initial charge electricity amount:%) was calculated. The results are shown in Table 1. Table 1 also shows the raw materials used and the firing temperature.

<< Examples 2 to 14 >>
The fluorinated tungsten oxide of the present invention (negative electrode active materials 2 to 14: sample number) except that any one of the lithium compound, the fluorine compound and the firing temperature was replaced with that shown in Table 1 in the same manner as in Example 1. A-2 to A-4, Sample Nos. B-1 to B-2 and Sample Nos. C-1 to C-8) were synthesized, and a cell for measuring electrochemical characteristics was prepared to measure electrochemical characteristics. The results are shown in Table 1.

<< Examples 15 to 21 >>
In this example, the amount of lithium atoms in the fluorinated tungsten oxide was examined. The fluorinated tungsten oxide of the present invention having various amounts of lithium (negative electrode active materials 15 to 21: sample) in the same manner as in Example 1 (sample number A-1) except that the amount of lithium carbonate mixed was changed. Nos. D-1 to D-7) were synthesized, a cell for measuring electrochemical characteristics was prepared, and the electrochemical characteristics were measured. The results are shown in Table 2. In addition, the result of Examples 1-14 is also shown.

  However, in this embodiment, lithium carbonate is charged in such an amount that Li / W is 0.05, 0.1, 0.2, 0.5, 0.7, 0.8, or 1.0. It is. Note that F / W was 0.2.

<< Examples 22 to 26 >>
In this example, the additive elements were examined. A book containing various additive elements in the same manner as in Example 1 (Sample No. A-1) except that cobalt, manganese, nickel, magnesium, or aluminum was added as an additional element in addition to other raw materials when mixing the raw materials. The fluorinated tungsten oxides of the invention (negative electrode active materials 22 to 26: sample numbers E-1 to E-5) were synthesized, and electrochemical characteristics measuring cells were prepared to measure the electrochemical characteristics. The results are shown in Table 2. However, the F / W ratio was 0.2, and the amount of additive element was 0.05 with respect to W.

<< Examples 27-33 >>
In this example, the content of fluorine atoms was examined. The tungsten oxides WO ₂ , WO ₃ , lithium carbonate, and lithium fluoride are mixed in various amounts, and the F / W ratio is 0.06, 0.1, 0.3, 0.5, 0.00. The fluorinated tungsten oxide (negative electrode active material 27) of the present invention having various fluorine atom contents was the same as in Example 1 (Sample No. A-1) except that 7, 0.8 or 1.0 was used. ~ 33: Sample numbers F-1 to F-7) were synthesized, and electrochemical characteristics measurement cells were prepared to measure electrochemical characteristics. The results are shown in Table 2.

As described above, it is advantageous that the oxygen atom ratio is larger than W from the viewpoint of charge / discharge capacity. However, fluorination is performed by fluorinating a part of oxygen on the surface of the fluorinated tungsten oxide particles. It seemed that it would not lead to a reduction in irreversible capacity unless it proceeded in the form of substitution. Further, in the fluorinated tungsten oxides of sample numbers F-1 to F-7, when converted to WO3 _-y , the values of y are 0.01, 0.25, 0 in the order of F-1 to F-7, respectively. .66, 1.2, 1.63, 2.0 and 2.2.

<< Comparative Examples 1 and 2 >>
As a comparative example of the present invention, a cell for measuring electrochemical characteristics was prepared in the same manner as in Example 1 except that commercially available WO ₃ (Comparative Example 1) and WO ₂ (Comparative Example 2) were used. The chemical properties were measured. The results are shown in Table 2.

  Table 2 shows that the firing temperature is preferably 600 ° C to 1200 ° C. In addition, it is preferable to use lithium fluoride as the fluorine compound because the amount of impurities is reduced and efficiency is increased as a negative electrode for a lithium battery. On the other hand, the F / W ratio is preferably 0.8 or less as the addition amount of fluorine atoms. In relation to this, the oxygen ratio is preferably 2.0 or less.

<< Examples 34 to 39 and Comparative Example 3 >>
In this example, a negative electrode was prepared using the negative electrode active materials of Sample Nos. A-1, B-1, C-5, D-3, E-1, F-2 and Comparative Example 1, and the negative electrode was A cylindrical battery having the structure shown in FIG. 2 was produced.

  10 parts by weight of carbon powder as a conductive agent and 5 parts by weight of polyvinylidene fluoride resin as a binder were mixed with 85 parts by weight of the negative electrode active material powder. The obtained mixture was dispersed in dehydrated N-methylpyrrolidinone to obtain a slurry, which was applied onto a current collector made of aluminum foil, dried and rolled, and then cut into a predetermined size to produce a negative electrode.

A positive electrode was produced in the same manner as the negative electrode except that the negative electrode active material was replaced with a positive electrode active material (Li _{1 ± x} Ni _1/2 Mn _1/2 O ₂ (x ≦ 0.1)). In addition, a polypropylene non-woven fabric is used as a separator, and LiPF ₆ is dissolved in a mixed solvent having a volume ratio of 1: 1 of ethylene carbonate (EC) and propylene carbonate (PC) as an organic electrolyte. We used what we did. The dimensions of the produced cylindrical battery were 14.1 mm in diameter and 50.0 mm in height.

The cylindrical battery thus produced was charged at a constant voltage of 3.0V, and discharged at a constant current of 100 mA up to 1V. The discharge capacity obtained at this time is shown in Table 3.

  As is apparent from Table 3, when the fluorinated tungsten oxide of the present invention is used, it can be seen that the battery capacity is increased by reducing the irreversible capacity. As described above, this reduction in irreversible capacity is due to the phenomenon that oxygen on the surface of the negative electrode active material particles reacts with lithium to become lithium oxide and does not return to the positive electrode by discharge, so that oxygen exists in the active material due to the presence of fluorine on the surface. It is considered that the reaction with lithium was suppressed.

  ADVANTAGE OF THE INVENTION According to this invention, the high capacity | capacitance nonaqueous electrolyte secondary battery which reduced the first irreversible capacity | capacitance which is the subject in the case of using a tungsten oxide for a negative electrode can be provided.

It is a SEM photograph which shows the particle | grain form of the fluorinated tungsten oxide of this invention. It is the side view which made a part of cylindrical battery the section which is an example of the nonaqueous electrolyte secondary battery concerning the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Battery case 2 Sealing plate 3 Insulation packing 4 Electrode plate group 5 Positive electrode lead 6 Negative electrode lead 7 Insulation ring

Claims (8)

  A negative electrode active material comprising a fluorinated tungsten oxide.   The negative electrode active material according to claim 1, wherein the fluorinated tungsten oxide contains lithium. The fluorinated tungsten oxide is represented by a composition formula: Li _x WO _3-y F _z (0 ≦ x <0.8, 0 <y <2, 0 <z <0.8). 2. The negative electrode active material according to 2.   The fluorinated tungsten oxide includes primary particles having an average particle size of 0.6 μm or less and secondary particles having an average particle size of 10 μm or less formed by the aggregation of the primary particles. The negative electrode active material as described.   The negative electrode active material according to any one of claims 1 to 4, wherein the fluorinated tungsten oxide contains at least one additional element selected from the group consisting of a transition metal element, a group II element, and a group IIIB. At least one lithium compound selected from the group consisting of lithium carbonate, lithium hydroxide, lithium nitrate and lithium oxide; and at least one fluorine selected from the group consisting of lithium fluoride, sodium fluoride and potassium fluoride A compound and tungsten oxide are mixed, and the obtained mixture is fired to obtain a composition formula: Li _x WO _3-y F _z (0 ≦ x <0.8, 0 <y <2, 0 <z < 0.8). A method for producing a negative electrode active material, comprising obtaining a tungsten oxide represented by 0.8).   The method for producing a negative electrode active material according to claim 6, wherein the mixture is fired at a temperature of 600 ° C. to 1200 ° C.   The nonaqueous electrolyte secondary battery which has a negative electrode containing the negative electrode active material in any one of Claims 1-5.