JP6291479B2 - Negative electrode active material, negative electrode sheet and power storage device using the same - Google Patents

Description

  The present invention relates to an alloy-based negative electrode active material capable of occluding and releasing lithium having high capacity and excellent cycle characteristics and charge storage characteristics, and a negative electrode sheet and an electricity storage device using the same.

In recent years, power storage devices, particularly lithium secondary batteries, have been widely used in small electronic devices such as mobile phones and laptop computers, electric vehicles, and power storage applications. Electronic devices equipped with lithium secondary batteries, such as smartphones and tablets, are becoming increasingly multifunctional and power consumption is increasing. For electric vehicles, in order to improve convenience, how to extend the cruising distance, that is, improvement of the energy density of the power storage device is the key to popularization.
In the present specification, the term lithium secondary battery is used as a concept including so-called lithium ion secondary batteries.

  In order to improve the energy density of energy storage devices, the theoretical capacity capable of occluding and releasing lithium includes silicon, tin, etc., which are much larger than the theoretical capacity of graphite, which is currently the most widely used negative electrode active material. Alloy-based negative electrode active materials have been actively studied. However, these alloy-based materials have a problem that the volume of the material greatly expands when lithium is occluded, and the active material is cracked and pulverized, so that the current collecting property is lowered and the electrode is easily expanded. Moreover, since the non-aqueous electrolyte is easily decomposed on the active new surface generated by the cracking of the active material, the decomposition product of the non-aqueous electrolyte is deposited on the surface of the active material to increase resistance, There is a problem that the battery tends to swell.

For such a problem, Patent Document 1 discloses that silicon (Si) synthesized by a single roll method or an atomizing method and copper (Cu), nickel (Ni), and cobalt (Co) are selected from the group consisting of It has been shown that the capacity retention rate after 50 cycles at 20 ° C. is improved by using a silicon alloy containing at least one metal element as a constituent element as the negative electrode material. Patent Document 2 discloses a powder composed of a composite phase of an Si phase and an Si _x Cu _y phase composed of an Si _x Cu _y alloy which is an intermetallic compound of Si and Cu, and an Si _x Cu _y phase. a composition of x <y, by using a Si alloy average hardness of the intermetallic compound phase consisting of Si _x Cu _y phase is equal to or less than 800HV a negative electrode material, 20 cycles at 25 ° C. It has been shown that the capacity retention after the improvement is improved.

JP 2004-362895 A Japanese Patent No. 4865105

  An object of the present invention is to provide an alloy-based negative electrode active material that has a high capacity and is capable of occluding and releasing lithium, which is excellent in cycle characteristics and charge storage characteristics, and a negative electrode sheet and an electricity storage device using the same.

The present inventors have studied in detail the performance of the above-described conventional silicon alloy negative electrode. As a result, it was found that the silicon alloy negative electrodes of Patent Documents 1 and 2 do not necessarily have sufficient cycle characteristics, and further, a large amount of gas is generated when stored at a high temperature in a charged state, which poses a practical problem.
Therefore, as a result of intensive studies to solve the above problems, the inventors have improved the cycle characteristics by including a very small amount of oxygen in an alloy containing at least silicon and copper as main components. The present inventors have found that the charge storage characteristics at high temperature can be improved, particularly that gas generation can be remarkably suppressed.

That is, the present invention provides the following (1) to (4).
(1) The following general formula (I)

_{Si p Cu q M r O s} (I)
(In the formula, p + q + r + s = 100, s = 0.01-5, q = 5-50, r = 0-10, M is Be, B, Al, P, Zn, Ga, Ge, In, Sn, Sb. And represents at least one element selected from Y, Zr, Nb, Mo, and W.)
A silicon-copper alloy negative electrode active material containing a trace amount of oxygen represented by :
A silicon-copper alloy negative electrode active material in which a diffraction peak corresponding to the diffraction peak position of silicon simple substance and SiCu ₃ is detected by XRD measurement .

(2) A negative electrode sheet in which a negative electrode mixture comprising a negative electrode active material represented by the general formula (I), a carbon material, and a binder is applied to the surface of a copper current collector.
(3) In an electricity storage device including a positive electrode, a negative electrode, and a nonaqueous electrolytic solution in which an electrolyte salt is dissolved in a nonaqueous solvent, the negative electrode includes at least a negative electrode active material represented by the general formula (I). A power storage device characterized.
(4) An electricity storage device including a positive electrode, a negative electrode, and a nonaqueous electrolytic solution in which an electrolyte salt is dissolved in a nonaqueous solvent, wherein the negative electrode uses at least the negative electrode sheet represented by (2) above. Power storage device.

  ADVANTAGE OF THE INVENTION According to this invention, the alloy type negative electrode active material which can occlude and discharge | release lithium which was high capacity | capacitance and excellent in cycling characteristics and charge storage characteristics, and a negative electrode sheet and an electrical storage device using the same can be provided.

It is a figure which shows the image of a structure of the negative electrode active material of this invention.

[Aspect 1; Negative electrode active material]
The negative electrode active material of the present invention is a silicon-copper alloy negative electrode active material represented by the following general formula (I).

_{Si p Cu q M r O s} (I)
(In the formula, p + q + r + s = 100, s = 0.01-5, q = 5-50, r = 0-10, M is Be, B, Al, P, Zn, Ga, Ge, In, Sn, Sb. And represents at least one element selected from Y, Zr, Nb, Mo, and W.)

FIG. 1 shows an image diagram relating to one embodiment of the structure of the silicon-copper alloy negative electrode active material of the present invention. Particle phase composed mainly of SiO _x (A) of the SiCu ₃ O _y having the same crystal structure as SiCu ₃ in a matrix phase as a main component (B) having the same crystal structure as silicon simple substance is embedded Is in a state. However, x / y (hereinafter referred to as oxygen distribution parameter) is 0.5 or less. When the negative electrode active material represented by the general formula (I) includes the element M, the element M is included in either the phase (A) or the phase (B), or the phase (A) , And may be included as another phase other than phase (B).

The reason why the silicon-copper alloy negative electrode active material of the present invention is excellent in cycle characteristics and charge storage characteristics is not clear, but is considered as follows. Conventionally, in producing a silicon-copper alloy negative electrode active material, the influence of oxidation of the negative electrode active material, in particular, the metal copper blended in anticipation of electronic conductivity is oxidized, Concerned that the electronic conductivity of the corners will be lost, it is common to process in a state where there is no oxygen in the atmosphere in the manufacturing process performed at a high temperature using a single roll method or an atomizing method. there were. Therefore, conventionally, the oxygen concentration in an alloy containing at least silicon and copper as main components obtained by manufacturing has been below the detection limit. On the other hand, in the present invention, an alloy containing silicon and copper at least as main components by focusing attention on oxygen that may impair characteristics in common sense and introducing a very small amount of oxygen into the production process. A very small amount of oxygen can be contained therein, and as a result, the obtained negative electrode active material has the same crystal structure as SiCu ₃ and the phase (A) mainly composed of SiO _x having the same crystal structure as that of silicon alone. And having a structure composed of a phase (B) containing SiCu ₃ O _y as a main component. In particular, according to the present invention, this slight oxygen atom is introduced to form a structure having such a phase (A) and a phase (B). It is considered that the cycle characteristics are remarkably improved because the bonding strength between the phase (A) and the phase (B) can be increased without lowering the electronic conductivity. Furthermore, since these slight oxygen atoms can suppress an electrochemical reaction with the non-aqueous electrolyte, it is considered that gas generation in a charged state can be remarkably suppressed.

(Silicon-copper alloy negative electrode active material represented by general formula (I))

_{Si p Cu q M r O s} (I)
In the formula, p + q + r + s = 100, s = 0.01-5, q = 5-50, r = 0-10, M is Be, B, Al, P, Zn, Ga, Ge, In, Sn, Sb, It represents at least one element selected from Y, Zr, Nb, Mo, and W.

If s representing the oxygen content (unit: atomic%) is 5 atomic% or less, the electronic conductivity of the active material and the electric capacity capable of inserting and extracting lithium are less likely to decrease, and 0.01 atomic% If it is above, since the intensity | strength with respect to the expansion | swelling and shrinkage | contraction of an active material will increase and reaction with a non-aqueous electrolyte will be suppressed, cycling characteristics and charge storage characteristics will improve, and it is preferable. The value of s is preferably 0.02 atomic% or more, more preferably 0.05 atomic% or more, still more preferably 0.1 atomic% or more, and the upper limit thereof is preferably 3 atomic% or less, more preferably 2 atomic% or less, and 1 atomic% or more. % Or less is more preferable.
The oxygen content in the negative electrode active material can be analyzed by a method such as an inert gas melting-infrared absorption method.

  If q (unit: atomic%) representing the copper content is 50 atomic% or less, the electric capacity capable of occluding and releasing lithium is less likely to decrease, and if it is 5 atomic% or more, the electronic conductivity of the active material is reduced. And the strength against expansion and contraction inside the active material are increased, and further, the reaction with the non-aqueous electrolyte is suppressed, so that the cycle characteristics and the charge storage characteristics are improved, which is preferable. The value of q is more preferably 8 atomic% or more, more preferably 15 atomic% or more, particularly preferably 20 atomic% or more, and the upper limit thereof is more preferably 45 atomic% or less, still more preferably 40 atomic% or less, and particularly preferably 35 atomic% or less. preferable.

The silicon-copper alloy negative electrode active material of the present invention preferably contains an element M other than silicon, copper, and oxygen. Examples of M include Be of Group IIA, Y of Group IIIA to VIA, Zr, Nb, Mo, Inclusion of at least one element selected from W, IIB to VB group B, Al, P, Zn, Ga, Ge, In, Sn, Sb increases the strength against expansion and contraction inside the active material. This is preferable because the characteristics and charge storage characteristics are improved. Among these, at least one element selected from Be, Y, Zr, Nb, Zn, B, Al, P, Ge, In, and Sb is more preferable. From Be, Zr, Zn, B, Al, In, and Sb Particularly preferred are at least one element selected. Among these, it is most preferable that two or more elements selected from Be, Zr, Zn, B, Al, In, and Sb are included.
When the negative electrode active material represented by the general formula (I) includes the element M, it is included in either the phase (A) or the phase (B), or the phase (A) or the phase (B). It may be included as another phase other than.

When the negative electrode active material represented by the general formula (I) forms a powder, the average particle diameter of secondary particles of the powder is preferably 1 to 40 μm. If it is 40 μm or less, it can be applied uniformly when applied to the electrode, so there is no risk of failure such as peeling of the electrode sheet, and if it is 1 μm or more, the specific surface area of the powder is small. Therefore, the reaction with the non-aqueous electrolyte can be suppressed, and the cycle characteristics and the charge storage characteristics are improved. The average particle diameter is more preferably 3 μm or more, further preferably 15 μm or more, particularly preferably 20 μm or more, and the upper limit thereof is more preferably 35 μm or less, further preferably 30 μm or less.
In addition, the average particle diameter of the secondary particles of the negative electrode active material powder can be measured with a particle size distribution meter using a laser diffraction / scattering method. The average particle diameter can be measured as the 50% diameter of the volume cumulative particle size distribution, that is, the median diameter (D50).

Moreover, it is preferable that the 5% diameter (D5) of the volume cumulative particle size distribution of the secondary particles is 0.2 μm or more. If 0.2μm or more, the phase mainly composed of SiO _x having the same crystal structure as the electrochemically active elemental silicon (A) is mainly composed of SiCu ₃ O _y having the same crystal structure as SiCu ₃ Is sufficiently covered with the phase (B), which is preferable because the reaction with the non-aqueous electrolyte can be suppressed and the cycle characteristics and the charge storage characteristics are improved. The 5% diameter (D5) of the volume cumulative particle size distribution is more preferably 1 μm or more, further preferably 5 μm or more, and particularly preferably 10 μm or more.

Moreover, it is preferable that the average crystal grain diameter of a phase (A) is 0.1-10 micrometers. An average crystal grain size of the phase (A) of 10 μm or less is preferable because distortion due to volume change accompanying insertion and extraction of lithium is small, and cycle characteristics are improved. Moreover, if the average crystal grain size of the phase (A) is 0.1 μm or more, the reaction with the non-aqueous electrolyte is suppressed, so that the cycle characteristics and the charge storage characteristics are improved, which is preferable. The average crystal grain size of the phase (A) is more preferably 0.3 to 5 μm, and particularly preferably 1 to 4 μm.
The average crystal grain size of the phase (A) is determined from, for example, a photograph in which a cross-sectional sample is prepared by embedding a negative electrode active material in a resin and polishing, and observed with a scanning electron microscope (SEM). It can be obtained by performing image analysis.

Negative electrode active material represented by the general formula (I), composed mainly of SiCu ₃ O _y having the same crystal structure phase mainly composed of SiO _x having the same crystal structure as elemental silicon (A) and SiCu ₃ When the oxygen atom in the negative electrode active material represented by the general formula (I) is contained in the phase (B) more than the phase (A), Bond strength at the interface with the phase (A) is increased, strength against expansion and contraction inside the active material is increased, and further, reaction with the non-aqueous electrolyte is suppressed, so that cycle characteristics and charge storage characteristics are improved. This is preferable. That is, the value of y is preferably larger than the value of x, and the oxygen distribution parameter x / y is more preferably 0.5 or less, and further preferably 0.1 or less.
For the values of x and y, for example, a negative electrode active material is prepared using a focused ion beam (FIB) apparatus or the like, and a thin sample is prepared, and energy dispersive X-ray spectroscopy attached to a transmission electron microscope (TEM) is used. It can be measured using an analyzer (EDS).

  This negative electrode active material can be manufactured using, for example, a single roll method or an atomizing method as follows.

  In the case of producing by a single roll method, for example, first, a raw material ingot of a silicon alloy is mixed at a predetermined ratio, and after being dissolved by high frequency induction heating in an atmosphere in which oxygen is slightly introduced into argon gas, It is sprayed on a rotating roll to obtain a silicon-copper alloy flake. Next, after pulverizing the silicon-copper alloy flakes, the negative active material can be obtained by classification as necessary.

In the case of producing by the atomizing method, first, for example, a raw material ingot of a silicon-copper alloy is mixed at a predetermined ratio, and this is mixed in an argon gas atmosphere or an atmosphere in which oxygen is slightly introduced into the argon gas. The molten metal is obtained by melting by high frequency induction heating. Next, the molten metal is injected into a tank under an argon gas atmosphere or an atmosphere in which oxygen is slightly introduced into the argon gas, while argon gas or argon gas into which oxygen is slightly introduced is sprayed toward the sample being sprayed. A silicon-copper alloy powder is obtained. Then, a negative electrode active material can be obtained by classifying as needed. The atomizing method is not limited to the gas atomizing method described here. Oxygen can be introduced in any step, and it may be introduced in at least one of the steps, but the oxygen concentration is preferably about 1 ppm to 3000 ppm, more preferably 100 ppm to 2000 ppm. Among them, in order to increase the oxygen concentration contained in the phase (B), it is particularly preferable that the argon gas ejected toward the sample being sprayed contains about 1 ppm to 3000 ppm of oxygen. The oxygen distribution parameter x / y can be adjusted by introducing oxygen in two or more steps of each step and adding light / dark to the oxygen concentration in each step. For example, in a process that mainly affects the formation of the phase (A), such as a process of injecting molten metal into a tank, a process of injecting argon gas toward the sample being sprayed while making the oxygen concentration relatively low In the step that mainly affects the formation of the phase (B), the oxygen distribution parameter x / y can be adjusted by making the oxygen concentration relatively high.
Also, the average particle diameter of the secondary particles of the negative electrode active material powder can be adjusted by adjusting the diameter of the atomizing nozzle, the pressure of argon gas jetted toward the sample being sprayed, or by adjusting the oxygen concentration as appropriate. And the average crystal grain size of phase (A) can be controlled. In addition, pulverization and classification can be performed to adjust the secondary particle diameter, but it is preferable not to perform pulverization because cycle characteristics and charge storage characteristics are improved.

[Aspect 2; negative electrode sheet]
The negative electrode sheet of the present invention is a sheet-like formed body formed of a negative electrode mixture comprising the silicon-copper alloy negative electrode active material, the carbon material, and the binder according to aspect 1, and the silicon-copper alloy according to aspect 1 A negative electrode active material, a carbon material, a binder, and a high boiling point solvent such as 1-methyl-2-pyrrolidone are kneaded to form a slurry, which is then applied to a copper foil of a current collector and dried. After pressure molding, it can be produced by heat treatment at a temperature of about 50 ° C. to 350 ° C. for about 2 hours under reduced pressure or in an inert atmosphere. In the negative electrode sheet of the present invention, the carbon material acts as a conductive agent or an active material.

  The amount of the silicon-copper alloy negative electrode active material is preferably 1% by mass or more, more preferably 5% by mass or more, still more preferably 10% by mass or more, in order to increase the capacity of the negative electrode mixture. From the viewpoint of improving characteristics, it is preferably 80% by mass or less, more preferably 65% by mass or less, and further preferably 45% by mass or less.

  When a silicon-copper alloy negative electrode active material and a carbon material used as a conductive agent or an active material are mixed and used, the ratio of the silicon-copper alloy negative electrode active material and the carbon material is an electron generated by mixing the carbon material. From the viewpoint of improving cycle characteristics based on the conductivity improving effect, the ratio of the total mass of the carbon material to the total mass of the silicon-copper alloy negative electrode active material in the negative electrode mixture is preferably 0.2 or more, preferably 1 or more. More preferably, it is more preferably 5 or more. Moreover, when there is too much ratio of the carbon material mixed with a silicon-copper alloy negative electrode active material, the amount of the silicon-copper alloy negative electrode active material in a negative electrode mixture layer falls, and there exists a possibility that the effect of high capacity | capacitance may become small. Therefore, the ratio of the total mass of the carbon material to the total mass of the silicon-copper alloy negative electrode active material is preferably 95 or less, more preferably 70 or less, and even more preferably 45 or less. The silicon-copper alloy negative electrode active material of the present invention has a specific surface area in order to ensure good electrical contact with the carbon material due to the effect of the high electronic conductivity of the phase (B) and to ensure conductivity. There is an effect that the use of a large conductive auxiliary agent can be reduced.

  Examples of the carbon material include carbon materials that can occlude and release lithium [graphitizable carbon, non-graphitizable carbon with a (002) plane spacing of 0.37 nm or more, and (002) plane spacing. Graphite of 0.34 nm or less] and carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, etc. can be used as the conductive auxiliary agent. Therefore, the amount of the conductive aid used can be 20% by mass or less, more preferably 10% by mass or less, based on the mass of the negative electrode mixture.

This effect is noticeable when fibrous carbon powder is used as a conductive additive. In particular, the fibrous carbon powder has a graphite mesh surface composed of only carbon atoms, forming a bell-shaped structural unit having a closed top portion and a trunk portion having an open bottom, and the bell-shaped structural unit is In some cases, 2-30 pieces are stacked by sharing the central axis to form an aggregate, and the aggregate is composed of fine carbon fibers that are connected to form a fiber in a head-to-tail manner. Particularly preferred.
The bell-shaped structure body portion gradually spreads toward the open end, and as a result, the busbar of the body portion is slightly inclined with respect to the central axis of the bell-shaped structure unit, and the angle θ formed by both is from 15 °. It is small, more preferably 1 ° <θ <15 °, and further preferably 2 ° <θ <10 °. If θ is too large, fine fibers composed of the structural unit exhibit a fishbone-like carbon fiber-like structure, and the conductivity in the fiber axis direction is impaired. On the other hand, when θ is small, the structure is close to a cylindrical tube shape, and the frequency at which the open end of the graphite mesh surface constituting the body of the structural unit is exposed to the outer peripheral surface of the fiber becomes low, so the conductivity between adjacent fibers deteriorates. .
The number of bell-shaped structural unit laminations is preferably 2 to 25, and more preferably 2 to 15.
The outer diameter D of the trunk portion of the aggregate is 5 to 40 nm, preferably 5 to 30 nm, and more preferably 5 to 20 nm. If D is 40 nm or less, the fiber diameter is not too large, and an excessive addition amount is not required to form a conductive path with the negative electrode active material, which is preferable. On the other hand, if D is 5 nm or more, it is preferable because the fiber diameter becomes thin and the aggregation of fibers becomes strong and it is not difficult to disperse in the negative electrode mixture.
The inner diameter d of the aggregate body is 3 to 30 nm, preferably 3 to 20 nm, more preferably 3 to 10 nm.
The aspect ratio (L / D) calculated from the length L of the aggregate and the body outer diameter D is 2 to 150, preferably 2 to 50, more preferably 2 to 30, and still more preferably 2 to 20. . When the aspect ratio is large, the structure of the formed fiber approaches a cylindrical tube shape, and the conductivity in the fiber axis direction of one fiber is improved. However, the open end of the graphite network surface constituting the structural unit body is a fiber. Since the frequency of exposure to the outer peripheral surface is reduced, the conductivity between adjacent fibers is deteriorated. On the other hand, when the aspect ratio is small, the open end of the graphite mesh surface constituting the structural unit body portion is more frequently exposed to the outer peripheral surface of the fiber, so that the conductivity between adjacent fibers is improved. Since many short graphite mesh surfaces are connected in the axial direction, conductivity in the fiber axial direction of one fiber is impaired.
As a quantity of fibrous carbon powder, it is preferable to contain 1-10 mass% as a mass in a negative mix, and it is more preferable to contain 2-5 mass%.

As the carbon material capable of inserting and extracting lithium, graphite having a specific surface area of 0.5 to 10 m ² / g and d002 of 0.335 to 0.337 nm is particularly preferable. A mechanical action such as compression force, friction force, shear force, etc. is repeatedly applied to artificial graphite particles having a massive structure in which a plurality of flat graphite fine particles are assembled or bonded non-parallel to each other, for example, scaly natural graphite particles, By using the spheroidized graphite particles, the peak intensity I (110) of the (110) plane and the peak intensity I (004) of the (004) plane of the graphite crystal obtained from the X-ray diffraction measurement of the negative electrode sheet are obtained. When the ratio I (110) / I (004) is 0.01 or more, cycle characteristics and charge storage characteristics are improved, more preferably 0.05 or more, and further preferably 0.1 or more. preferable. Moreover, since it may process too much and crystallinity may fall and the discharge capacity of a battery may fall, 0.5 or less is preferable and the upper limit of I (110) / I (004) is 0.3 or less more preferable.
When a highly crystalline carbon material (core material) is used, if the core material is coated with a carbon material having a lower crystallinity than the core material, the silicon-copper alloy negative electrode active material of the present invention is By virtue of the high electronic conductivity of the phase (B), the reaction between the non-aqueous electrolyte and the negative electrode sheet is suppressed without impairing the electrical contact between the silicon-copper alloy negative electrode active material and the carbon material. Therefore, the cycle characteristics and the charge storage characteristics are further improved, which is preferable.
The crystallinity of the carbon material for covering the core material can be confirmed by TEM.
The average particle diameter of graphite, that is, the 50% diameter (D50) of the volume cumulative particle size distribution is preferably 10 μm to 50 μm, more preferably 10 μm to 30 μm, and still more preferably 15 μm to 25 μm. If D50 is 10 μm or more, the bulk density does not become too low and the specific surface area does not become too high. Therefore, when the negative electrode sheet is formed by a coating method, its coatability is lowered or charge / discharge efficiency is lowered. There is no fear. On the other hand, if D50 is 50 μm or less, there is no possibility that streaking occurs during electrode coating, which is preferable.
When the ratio of the average particle diameter of graphite to the average particle diameter of the silicon-copper alloy is 0.6 to 1.9, the electrical contact is good even during the charge / discharge cycle and the cycle characteristics are improved. 0.8 to 1.4 is more preferable.
The amount of graphite is preferably 5% by mass or more, more preferably 20% by mass or more, still more preferably 55% by mass or more from the viewpoint of improving cycle characteristics, as the mass in the negative electrode mixture. 95 mass% or less is preferable, 85 mass% or less is more preferable, and 70 mass% or less is still more preferable.

  Moreover, in addition to the carbon material, a conductive auxiliary other than the carbon material may be blended in the negative electrode mixture, and as such a conductive auxiliary, a metal such as copper, nickel, titanium or the like should be used. Can do. For example, after producing an electrode sheet, these metals can be imparted with conductivity using plating or vapor deposition.

  Binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene / butadiene copolymer (SBR), acrylonitrile / butadiene copolymer (NBR), carboxymethylcellulose (CMC), ethylene Polyimide, aromatic tetracarboxylic acid and / or derivative thereof and diamine compound obtained from propylene diene terpolymer, polyvinyl pyrrolidone, polyacrylic acid, sodium polyacrylate, aromatic tetracarboxylic acid and / or derivative thereof and diamine compound And polyamide imide obtained from diisocyanate are preferable. Among them, polyvinyl pyrrolidone, polyacrylic acid, sodium polyacrylate, aromatic which is a polymer containing any of carboxyl group, amide group and imide group At least one selected from a polyimide obtained from tracarboxylic acid and / or a derivative thereof and a diamine compound, and a polyamideimide obtained from an aromatic tetracarboxylic acid and / or a derivative thereof, a diamine compound and a diisocyanate is silicon of the present invention. -It is preferable since the affinity with the phase (B) present on the surface of the copper alloy negative electrode active material is high, the binding force is increased, and the cycle characteristics and the storage characteristics are further enhanced. In particular, a polyimide obtained from an aromatic tetracarboxylic acid and / or a derivative thereof and a diamine compound is preferable.

  The content of the binder is preferably 0.5% by mass to 50% by mass with respect to the total mass of the negative electrode active material, the carbon material, and the binder. If the content of the binder is 0.5% by mass or more, there is no fear that the moldability of the electrode is lowered, and if it is 50% by mass or less, the decrease in the energy density of the electrode is small, which is preferable. The content of the binder is more preferably 2% by mass to 15% by mass.

The density of the portion excluding the current collector of the negative electrode is usually 0.8 g / cm ³ or more, and is preferably 1.0 g / cm ³ or more, more preferably 1.2 g in order to further increase the capacity of the battery. / Cm ³ or more, more preferably 1.5 g / cm ³ or more. The upper limit is 6 g / cm ³ or less, more preferably 5 g / cm ³ or less, and still more preferably 4 g / cm ³ or less.

From here [Aspect 3: Power storage device]
An electricity storage device of the present invention includes a positive electrode, a negative electrode, and a non-aqueous electrolyte solution in which an electrolyte salt is dissolved in a non-aqueous solvent. The negative electrode includes at least the negative electrode active material of Aspect 1, or the negative electrode of Aspect 2 A sheet is used.

[Non-aqueous electrolyte]
In the electricity storage device of the present invention, by combining the negative electrode active material of aspect 1 or the negative electrode sheet of aspect 2 with the nonaqueous electrolyte described below, the electricity storage device cycle characteristics and charge storage characteristics can be improved, and gas It exhibits a unique effect of suppressing the occurrence.

[Nonaqueous solvent]
Examples of the nonaqueous solvent used in the nonaqueous electrolytic solution of the present invention include cyclic carbonates, chain esters, lactones, ethers, and amides, and it is preferable that both cyclic carbonates and chain esters are included.
The term chain ester is used as a concept including chain carbonate and chain carboxylic acid ester.
Examples of the cyclic carbonate include ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 4-fluoro-1,3-dioxolan-2-one (FEC), trans or Cis-4,5-difluoro-1,3-dioxolan-2-one (hereinafter collectively referred to as “DFEC”), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), and 4-ethynyl-1 , 3-dioxolan-2-one (EEC) or two or more selected from ethylene carbonate, propylene carbonate, 4-fluoro-1,3-dioxolan-2-one, vinylene carbonate and 4-ethynyl- One selected from 1,3-dioxolan-2-one (EEC) Or two or more is more preferable.
Further, among the cyclic carbonates, when at least one of unsaturated carbonates such as carbon-carbon double bonds and carbon-carbon triple bonds or cyclic carbonates having a fluorine atom is used, the cycle characteristics and charge storage characteristics of the electricity storage device are further improved. Preferably, the cyclic carbonate having an unsaturated bond such as a carbon-carbon double bond or carbon-carbon triple bond is more preferably VC, VEC or EEC, and the cyclic carbonate having a fluorine atom is FEC, DFEC is more preferable, and it is more preferable to include both a cyclic carbonate having an unsaturated bond such as a carbon-carbon double bond and a carbon-carbon triple bond and a cyclic carbonate having a fluorine atom.
The content of the cyclic carbonate having an unsaturated bond such as a carbon-carbon double bond or a carbon-carbon triple bond is preferably 0.07% by volume or more, more preferably 0.8%, based on the total volume of the nonaqueous solvent. 2 vol% or more, more preferably 0.7 vol% or more, and the upper limit thereof is preferably 7 vol% or less, more preferably 4 vol% or less, further preferably 2.5 vol% or less. And the stability of the coating is increased, and the cycle characteristics and charge storage characteristics of the electricity storage device are improved.
The content of the cyclic carbonate having a fluorine atom is preferably 0.07% by volume or more, more preferably 4% by volume or more, still more preferably 7% by volume or more, based on the total volume of the nonaqueous solvent. The upper limit is preferably 35% by volume or less, more preferably 25% by volume or less, and still more preferably 15% by volume or less, because the stability of the coating increases and the cycle characteristics and charge storage characteristics of the electricity storage device are improved. preferable.
When the non-aqueous solvent contains both a cyclic carbonate having an unsaturated bond such as a carbon-carbon double bond and a carbon-carbon triple bond and a cyclic carbonate having a fluorine atom, the carbon to the content of the cyclic carbonate having a fluorine atom The content ratio of the cyclic carbonate having an unsaturated bond such as a carbon double bond or a carbon-carbon triple bond is preferably 0.2% or more, more preferably 3% or more, still more preferably 7% or more, and the upper limit thereof. Is preferably 40% or less, more preferably 30% or less, and even more preferably 15% or less, because the stability of the coating is increased and the cycle characteristics and charge storage characteristics of the electricity storage device are improved.
Further, when the non-aqueous solvent contains ethylene carbonate and / or propylene carbonate, the resistance of the film formed on the electrode is reduced, and the content of ethylene carbonate and / or propylene carbonate is preferably equal to the total volume of the non-aqueous solvent. On the other hand, it is preferably 3% by volume or more, more preferably 5% by volume or more, further preferably 7% by volume or more, and the upper limit thereof is preferably 45% by volume or less, more preferably 35% by volume or less, further Preferably it is 25 volume% or less.

  These solvents may be used alone, and when two or more types are used in combination, the cycle characteristics and charge storage characteristics of the electricity storage device are further improved, and three or more types should be used in combination. Is particularly preferred. Preferred combinations of these cyclic carbonates include EC and PC, EC and VC, PC and VC, VC and FEC, EC and FEC, PC and FEC, FEC and DFEC, EC and DFEC, PC and DFEC, VC and DFEC , VEC and DFEC, VC and EEC, EC and EEC, EC and PC and VC, EC and PC and FEC, EC and VC and FEC, EC and VC and VEC, EC and VC and EEC, EC and EEC and FEC, PC And VC and FEC, EC and VC and DFEC, PC and VC and DFEC, EC and PC and VC and FEC, EC and PC and VC and DFEC, and the like are preferable. Of the above combinations, EC and VC, EC and FEC, PC and FEC, EC and PC and VC, EC and PC and FEC, EC and VC and FEC, EC and VC and EEC, EC and EEC and FEC, PC and A combination of VC and FEC, EC and PC, VC and FEC is more preferable.

Examples of chain esters include asymmetric chain carbonates such as methyl ethyl carbonate (MEC), methyl propyl carbonate (MPC), methyl isopropyl carbonate (MIPC), methyl butyl carbonate, and ethyl propyl carbonate, dimethyl carbonate (DMC), and diethyl carbonate ( DEC), symmetrical linear carbonates such as dipropyl carbonate and dibutyl carbonate, pivalate esters (MPV) such as methyl pivalate, ethyl pivalate, propyl pivalate, methyl propionate (MP), ethyl propionate (EP), Preferable examples include chain carboxylic acid esters such as methyl acetate (MA), ethyl acetate (EA), and n-propyl acetate (PA). In particular, the inclusion of asymmetric chain carbonate is preferable because the cycle characteristics and charge storage characteristics of the electricity storage device are improved and the amount of gas generation tends to be reduced.
These solvents may be used alone or in combination of two or more, since the cycle characteristics and charge storage characteristics of the electricity storage device are improved and the amount of gas generated is reduced.

  The content of the chain ester is not particularly limited, but it is preferably used in the range of 60 to 90% by volume with respect to the total volume of the nonaqueous solvent. If the content is 60% by volume or more, the effect of reducing the viscosity of the non-aqueous electrolyte is sufficiently obtained, and if it is 90% by volume or less, the electrical conductivity of the non-aqueous electrolyte is sufficiently increased, and the cycle of the electricity storage device The above range is preferable because the characteristics and the charge storage characteristics are improved.

Moreover, when using chain carbonate, it is preferable to use 2 or more types. Further, it is more preferable that both a symmetric chain carbonate and an asymmetric chain carbonate are contained, and it is more preferable that the content of the symmetric chain carbonate is more than that of the asymmetric chain carbonate.
The volume ratio of the symmetric chain carbonate in the chain carbonate is preferably 51% by volume or more, and more preferably 55% by volume or more. As an upper limit, 95 volume% or less is more preferable, and it is still more preferable in it being 85 volume% or less. It is particularly preferable that diethyl carbonate is contained in the symmetric chain carbonate. Moreover, it is especially preferable that the asymmetric chain carbonate includes methyl ethyl carbonate.
The above case is preferable because the cycle characteristics and charge storage characteristics of the electricity storage device are further improved.

  The ratio between the cyclic carbonate and the chain carbonate is preferably 10:90 to 45:55 in terms of the cyclic carbonate: chain carbonate (volume ratio) from the viewpoint of improving electrochemical characteristics when the electricity storage device is used at a high temperature. 15: 85-40: 60 is more preferable, and 20: 80-35: 65 is particularly preferable.

In order to further improve the cycle characteristics and charge storage characteristics of the electricity storage device, it is preferable to add other additives to the non-aqueous electrolyte.
Specific examples of other additives include
(A) Trimethyl phosphate, triethyl phosphate, tris (2,2,2-trifluoroethyl) phosphate, ethyl 2- (diethoxyphosphoryl) acetate, 2-propynyl 2- (diethoxyphosphoryl) acetate, etc. Phosphate ester,
(B) Nitriles such as acetonitrile, propionitrile, succinonitrile, 2-ethylsuccinonitrile, glutaronitrile, 2-methylglutaronitrile, adiponitrile, pimelonitrile, and sebacononitrile,
(C) 1,3-propane sultone, 1,3-butane sultone, 2,4-butane sultone, 1,4-butane sultone, 2,2-dioxido-1,2-oxathiolan-4-yl acetate, 5,5-dimethyl -1,2-oxathiolane-4-one Sultone compounds such as 2,2-dioxide, butane-2,3-diyl dimethanesulfonate, butane-1,4-diyl dimethanesulfonate, methylenemethane disulfonate, dimethylmethanedi S═O bond selected from sulfonic acid ester compounds such as sulfonates, divinyl sulfone, 1,2-bis (vinylsulfonyl) ethane, bis (2-vinylsulfonylethyl) ether, vinylsulfone compounds such as vinylsulfonyl fluoride, and the like. Containing compounds,
(D) a chain carboxylic acid anhydride such as acetic anhydride and propionic anhydride, a cyclic acid anhydride such as succinic anhydride, maleic anhydride, glutaric anhydride, itaconic anhydride, 3-sulfo-propionic anhydride,
(E) Diisocyanate compounds such as 1,4-diisocyanatobutane, 1,5-diisocyanatopentane, 1,6-diisocyanatohexane, 1,7-diisocyanatoheptane,
One type or two or more types selected from among these are preferably mentioned.

  The content of the additives (a) to (e) is preferably 0.001 to 5% by mass in the non-aqueous electrolyte. In this range, the coating film is sufficiently formed without becoming too thick, and the effect of improving the cycle characteristics and charge storage characteristics of the electricity storage device is enhanced. The content is more preferably 0.005% by mass or more, more preferably 0.01% by mass or more, particularly preferably 0.03% by mass or more in the non-aqueous electrolyte, and the upper limit is 3% by mass or less. More preferred is 2% by mass or less, and particularly preferred is 1.5% by mass or less.

  Among the above, it is preferable to include at least one of a phosphate ester, a nitrile, and a diisocyanate compound because the cycle characteristics and charge storage characteristics of the electricity storage device are further improved. Among phosphate esters, one or more selected from ethyl 2- (diethoxyphosphoryl) acetate and 2-propynyl 2- (diethoxyphosphoryl) acetate are more preferable. Among nitriles, one or more selected from succinonitrile, 2-ethylsuccinonitrile, glutaronitrile, 3-methylglutaronitrile, adiponitrile, and pimelonitrile are more preferable. Among the diisocyanate compounds, 1,5-diisocyanatopentane, 1,6-diisocyanatohexane, and 1,7-diisocyanatoheptane are more preferable.

[Electrolyte salt]
Preferred examples of the electrolyte salt used in the present invention include the following lithium salts.

(Lithium salt)
Examples of the lithium salt include inorganic lithium salts such as LiPF ₆ , LiBF ₄ , and LiClO ₄ , LiN (SO ₂ F) ₂ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiCF ₃ SO ₃ , LiC (SO ₂ CF ₃ ) ₃ , LiPF ₄ (CF ₃ ) ₂ , LiPF ₃ (C ₂ F ₅ ) ₃ , LiPF ₃ (CF ₃ ) ₃ , LiPF ₃ (iso-C ₃ F ₇ ) ₃ , LiPF ₅ (iso-C ₃ F ₇ ) and other lithium salts containing a chain-like fluorinated alkyl group, (CF ₂ ) ₂ (SO ₂ ) ₂ NLi, (CF ₂ ) ₃ (SO ₂ ) ₂ NLi, etc. A lithium salt having a cyclic fluorinated alkylene chain, lithium bis (oxalato) borate (LiBOB), lithium tetrafluoro (oxalato) phosphate (LiTFOP), and Lithium salts having at least one oxalic acid skeleton selected from lithium difluoro (oxalato) phosphate (LiDFOP), lithium having at least one phosphate backbone selected from LiPO ₂ F ₂ and _Li 2 PO ₃ F, etc. Lithium salt having at least one sulfonic acid skeleton selected from a salt, lithium trifluoro ((methanesulfonyl) oxy) borate (LiTFMSB), lithium pentafluoro ((methanesulfonyl) oxy) phosphate (LiPFMSP), and FSO ₃ Li Preferably, at least one lithium salt selected from these is preferably used, and one or two or more of these can be mixed and used.
Among these, LiPF ₆ , LiBF ₄ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiN (SO ₂ F) ₂ , lithium bis (oxalato) borate (LiBOB), lithium tetra Fluoro (oxalato) phosphate (LiTFOP), Lithium difluorobis (oxalato) phosphate (LiDFOP), LiPO ₂ F ₂ , Li ₂ PO ₃ F, Lithium trifluoro ((methanesulfonyl) oxy) borate (LiTFMSB), Lithium pentafluoro ( One or more selected from (methanesulfonyl) oxy) phosphate (LiPFMSP) and FSO ₃ Li are preferred, and LiPF ₆ , LiBF ₄ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ F) ₂ , lithium Screw (Oxalato) borate (LiBOB), lithium tetrafluoro (oxalato) phosphate (LiTFOP), lithium difluorobis (oxalato) phosphate (LiDFOP), LiPO ₂ F ₂ , lithium trifluoro ((methanesulfonyl) oxy) borate (LiTFMSB), One or more selected from lithium pentafluoro ((methanesulfonyl) oxy) phosphate (LiPFMSP) and FSO ₃ Li are more preferable, and LiPF ₆ is most preferable. The concentration of the lithium salt is usually preferably 0.3 M or more, more preferably 0.7 M or more, and further preferably 1.1 M or more with respect to the non-aqueous solvent. Moreover, the upper limit is preferably 2.5M or less, more preferably 2.0M or less, and still more preferably 1.6M or less.
Moreover, as a suitable combination of these lithium salts, LiPF ₆ is included, and LiBF ₄ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ F) ₂ , lithium bis (oxalato) borate (LiBOB), lithium Tetrafluoro (oxalato) phosphate (LiTFOP), lithium difluorobis (oxalato) phosphate (LiDFOP), LiPO ₂ F ₂ , lithium trifluoro ((methanesulfonyl) oxy) borate (LiTFMSB), lithium pentafluoro ((methanesulfonyl) oxy ) It is preferable that at least one lithium salt selected from phosphate (LiPFMSP) and FSO ₃ Li is contained in the non-aqueous electrolyte, and the proportion of the lithium salt other than LiPF _{6 in the} non-aqueous solvent is 0. When it is 001 M or more, the effect of improving the cycle characteristics and charge storage characteristics of the electricity storage device is easily exhibited, and when it is 0.005 M or less, there is less concern that the effect of improving the cycle characteristics and charge storage characteristics of the electricity storage device is reduced. Preferably it is 0.01M or more, Especially preferably, it is 0.03M or more, Most preferably, it is 0.04M or more. The upper limit is preferably 0.4M or less, particularly preferably 0.2M or less.

[Production of non-aqueous electrolyte]
The non-aqueous electrolyte used in the present invention can be obtained, for example, by mixing the non-aqueous solvent and adding a predetermined additive to the electrolyte salt and the non-aqueous electrolyte. .
At this time, it is preferable that the compound added to the non-aqueous solvent and the non-aqueous electrolyte to be used is one that is purified in advance and has as few impurities as possible within a range that does not significantly reduce the productivity.

  The non-aqueous electrolyte used in the present invention can be used in the following first and second electricity storage devices, and as the non-aqueous electrolyte, not only a liquid but also a gelled one is used. obtain. Furthermore, the non-aqueous electrolyte used in the present invention can also be used for a solid polymer electrolyte. In particular, it is preferably used for a first electricity storage device (ie, for a lithium battery) or a second electricity storage device (ie, for a lithium ion capacitor) using a lithium salt as an electrolyte salt, and is used for a lithium battery. More preferably, it is most suitable for use as a lithium secondary battery.

[First power storage device (lithium battery)]
The lithium battery of the present invention is a generic term for a lithium primary battery and a lithium secondary battery. In this specification, the term lithium secondary battery is used as a concept including a so-called lithium ion secondary battery. A lithium battery according to the present invention includes a positive electrode, a negative electrode, and the non-aqueous electrolyte solution in which an electrolyte salt is dissolved in a non-aqueous solvent. The negative electrode includes at least the negative electrode active material of Aspect 1, or Aspect 2 A negative electrode sheet is used.
For example, as the positive electrode active material for a lithium secondary battery, a composite metal oxide with lithium containing one or more selected from cobalt, manganese and nickel is used. These positive electrode active materials can be used individually by 1 type or in combination of 2 or more types.
Examples of such a lithium composite metal oxide include LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiCo _1-x Ni _x O ₂ (0.01 <x <1), LiCo _1/3 Ni _1/3. One type or two or more types selected from Mn _1/3 O ₂ , LiNi _1/2 Mn _3/2 O ₄ , and LiCo _0.98 Mg _0.02 O ₂ may be mentioned. Moreover, LiCoO ₂ and LiMn ₂ O _4, LiCoO ₂ and LiNiO _2, may be used in combination as LiMn ₂ O ₄ and LiNiO _2.

In addition, in order to improve safety and cycle characteristics during overcharge, and to enable use at a charging potential of 4.3 V or higher with respect to Li, a part of the lithium composite metal oxide is replaced with another element. May be. For example, a part of cobalt, manganese, nickel is replaced with at least one element such as Sn, Mg, Fe, Ti, Al, Zr, Cr, V, Ga, Zn, Cu, Bi, Mo, La, A part of O can be substituted with S or F, or a compound containing these other elements can be coated.
Among these, lithium composite metal oxides such as LiCoO ₂ , LiMn ₂ O ₄ , and LiNiO ₂ that can be used at a charged potential of the positive electrode in a fully charged state of 4.3 V or more on the basis of Li are preferable, and LiCo _1-x M _x O ₂ (where M is one or more elements selected from Sn, Mg, Fe, Ti, Al, Zr, Cr, V, Ga, Zn, and Cu, 0.001 ≦ x ≦ 0. 05), LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ , LiNi _0.5 Mn _0.3 Co _0.2 O ₂ , LiNi _0.85 Co _0.10 Al _0.05 O ₂ , LiNi _{1 / 2} Mn _3/2 O ₄ , Li ₂ MnO ₃ and LiMO ₂ (M is a transition metal such as Co, Ni, Mn, Fe, etc.) Lithium composite metal oxide usable at 4.4 V or higher like a solid solution Things are more preferred . When a lithium composite metal oxide that operates at a high charging voltage is used, cycle characteristics and charge storage characteristics are likely to deteriorate due to reaction with the electrolyte during charging, but the lithium secondary battery according to the present invention has these electrochemical characteristics. Can be suppressed.
In particular, in the case of a positive electrode containing Mn, since the battery resistance tends to increase with the elution of Mn ions from the positive electrode, the cycle characteristics and the charge storage characteristics tend to be deteriorated. The secondary battery is preferable because it can suppress the deterioration of the electrochemical characteristics.

Furthermore, lithium-containing olivine-type phosphate can also be used as the positive electrode active material. In particular, lithium-containing olivine-type phosphate containing one or more selected from iron, cobalt, nickel and manganese is preferable. Specific examples thereof include one or more selected from LiFePO ₄ , LiCoPO ₄ , LiNiPO ₄ , and LiMnPO ₄ .
Some of these lithium-containing olivine-type phosphates may be substituted with other elements, and some of iron, cobalt, nickel, and manganese are replaced with Co, Mn, Ni, Mg, Al, B, Ti, V, and Nb. , Cu, Zn, Mo, Ca, Sr, W, Zr and the like, or may be substituted with one or two or more elements selected from these, or may be coated with a compound or carbon material containing these other elements. Among these, LiFePO ₄ or LiMnPO ₄ is preferable.
Moreover, lithium containing olivine type | mold phosphate can also be mixed with the said positive electrode active material, for example, and can be used.

As the positive electrode for lithium primary _{battery, CuO, Cu 2 O, Ag} 2 O, Ag 2 CrO 4, CuS, CuSO 4, TiO 2, TiS 2, SiO 2, SnO, V 2 O 5, V 6 O 12 , VO _x , Nb ₂ O ₅ , Bi ₂ O ₃ , Bi ₂ Pb ₂ O ₅ , Sb ₂ O ₃ , CrO ₃ , Cr ₂ O ₃ , MoO ₃ , WO ₃ , SeO ₂ , MnO ₂ , Mn ₂ O ₃ , Fe ₂ O ₃ , FeO, Fe ₃ O ₄ , Ni ₂ O ₃ , NiO, CoO ₃ , or CoO, one or more metal element oxides or chalcogen compounds, SO ₂ , SOCl _2, etc. Examples thereof include sulfur compounds, and fluorocarbons (fluorinated graphite) represented by the general formula (CF _x ) _n . Among _{these, MnO 2, V 2 O 5} , fluorinated graphite and the like are preferable.

The pH of the supernatant liquid when 10 g of the positive electrode active material is dispersed in 100 ml of distilled water is preferably 10.0 to 12.5 because the effect of improving the cycle characteristics and the charge storage characteristics can be easily obtained. Furthermore, the case where it is 10.5-12.0 is preferable.
Further, when Ni is contained as an element in the positive electrode, since there is a tendency that impurities such as LiOH in the positive electrode active material tend to increase, the effect of improving the cycle characteristics and the charge storage characteristics is more easily obtained. The case where the atomic concentration of Ni is 5 to 25 atomic% is more preferable, and the case where it is 8 to 21 atomic% is particularly preferable.

  The conductive agent for the positive electrode is not particularly limited as long as it is an electron conductive material that does not cause a chemical change. For example, graphite such as natural graphite (scaly graphite, etc.), graphite such as artificial graphite, acetylene black, ketjen black, channel black, furnace black, lamp black, and one or more carbon blacks selected from thermal black It is done. Further, graphite and carbon black may be appropriately mixed and used. 1-10 mass% is preferable and, as for the addition amount to the positive mix of a electrically conductive agent, 2-5 mass% is especially preferable.

The positive electrode is composed of a conductive agent such as acetylene black and carbon black, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), a copolymer of styrene and butadiene (SBR), acrylonitrile and butadiene. Mixing with a binder such as copolymer (NBR), carboxymethyl cellulose (CMC), ethylene propylene diene terpolymer, etc., and adding a high boiling point solvent such as 1-methyl-2-pyrrolidone to knead and mix Then, this positive electrode mixture was applied to a current collector aluminum foil, a stainless steel lath plate, etc., dried and pressure-molded, and then subjected to vacuum at a temperature of about 50 ° C. to 250 ° C. for about 2 hours. It can be manufactured by heat treatment.
The density of the part except the collector of the positive electrode is usually at 1.5 g / cm ³ or more, for further increasing the capacity of the battery, is preferably 2 g / cm ³ or more, more preferably 3 g / cm ³ or more More preferably, it is 3.6 g / cm ³ or more. The upper limit is preferably 4 g / cm ³ or less.

The structure of the lithium battery is not particularly limited, and a coin-type battery, a cylindrical battery, a square battery, a laminated battery, or the like having a single-layer or multi-layer separator can be applied.
Although it does not restrict | limit especially as a separator for batteries, The single layer or laminated | stacked microporous film, woven fabric, a nonwoven fabric, etc. of polyolefin, such as a polypropylene and polyethylene, can be used.

  The lithium secondary battery according to the present invention has excellent electrochemical characteristics even when the end-of-charge voltage of the positive electrode with respect to lithium metal is 4.2 V or higher, particularly 4.3 V or higher, and further has excellent characteristics even at 4.4 V or higher. is there. Although it does not specifically limit about an electric current value, Usually, it uses in the range of 0.1-30C. Moreover, the lithium battery in this invention can be charged / discharged at -40-100 degreeC, Preferably it is -10-80 degreeC.

  In the present invention, as a countermeasure against an increase in the internal pressure of the lithium battery, a method of providing a safety valve on the battery lid or cutting a member such as a battery can or a gasket can be employed. Further, as a safety measure for preventing overcharge, the battery lid can be provided with a current interruption mechanism that senses the internal pressure of the battery and interrupts the current.

[Second power storage device (lithium ion capacitor)]
A 2nd electrical storage device is an electrical storage device which stores energy using the lithium ion intercalation to carbon materials, such as a graphite which is a negative electrode. It is called a lithium ion capacitor (LIC). The 2nd electrical storage device of this invention contains the negative electrode active material of aspect 1 in this negative electrode. Examples of the positive electrode include those using an electric double layer between an activated carbon electrode and an electrolytic solution, and those using a π-conjugated polymer electrode doping / dedoping reaction. The electrolyte contains at least a lithium salt such as LiPF ₆ .

Examples 1-25, Comparative Examples 1-2
[Production of silicon-copper alloy negative electrode active material]
The silicon-copper alloys (A-1 to A-25, C-1, and C-2) used in Examples 1 to 25 and Comparative Examples 1 and 2 were prepared by mixing raw material ingots of silicon-copper alloys at a predetermined ratio. Then, it is melted by high frequency induction heating in an argon gas atmosphere (oxygen concentration of less than 1 ppm) or in an atmosphere in which oxygen is slightly introduced into the argon gas (oxygen concentration of about 1 ppm to 3000 ppm) to obtain a molten metal. Next, this molten metal is injected into a tank under an argon gas atmosphere (oxygen concentration of less than 1 ppm) or an atmosphere in which oxygen is slightly introduced into the argon gas (oxygen concentration of about 1 ppm to 3000 ppm), while argon is directed toward the sample being sprayed. Gas (oxygen concentration less than 1 ppm) or argon gas (oxygen concentration of about 1 ppm to 3000 ppm) into which oxygen is slightly introduced is ejected to obtain silicon-copper alloy powder. Then, it produced by classifying as needed.
The oxygen distribution parameter x / y was adjusted by adding light and shade to the oxygen concentration in each step. Specifically, mainly by appropriately adjusting the oxygen concentration in the gas gas introduced in the step of injecting the molten metal into the tank and the oxygen concentration in the gas gas injected toward the sample being sprayed, The oxygen partition parameter x / y was adjusted. In addition, by adjusting the diameter of the atomizing nozzle and the pressure of argon gas ejected toward the sample being sprayed, adjusting the oxygen concentration, screening appropriately after atomization, or crushing appropriately The average particle diameter of the secondary particles of the negative electrode active material powder and the average particle diameter of the phase (A) were controlled. Table 1 shows the physical properties of each silicon-copper alloy after fabrication.
As a result of measuring these silicon-copper alloys by XRD, they all had diffraction peaks that coincided with the diffraction peak positions of silicon simple substance and SiCu ₃ .
[Production of lithium ion secondary battery]
LiNi _1/3 Mn _1/3 Co _1/3 O ₂ (the positive electrode active material, the pH of the supernatant liquid when 10 g of the positive electrode active material is dispersed in 100 ml of distilled water is 10.8); 94% by mass, acetylene black ( Conductive agent); 3% by mass was mixed, and PVDF (binder); 3% by mass was added to and mixed with a solution in which 3% by mass was previously dissolved in 1-methyl-2-pyrrolidone to prepare a positive electrode mixture paste. . This positive electrode mixture paste was applied to one side of an aluminum foil (current collector), dried and pressurized, punched out to a predetermined size, and a positive electrode sheet was produced. The density of the portion excluding the current collector of the positive electrode was 3.6 g / cm ³ .
Further, the silicon-copper alloy produced by the above method: 15% by mass, artificial graphite (d ₀₀₂ = 0.335 nm, D50 = 19 μm); 70% by mass, acetylene black (conductive agent); (Binder) 5% by mass was added to a solution dissolved in 1-methyl-2-pyrrolidone and mixed to prepare a negative electrode mixture paste. This negative electrode mixture paste was applied to one side of a copper foil (current collector), dried and pressurized, and punched into a predetermined size to produce a negative electrode sheet. As a result of X-ray diffraction measurement using this electrode sheet, the ratio of the peak intensity I (110) of the (110) plane of the graphite crystal to the peak intensity I (004) of the (004) plane [I (110) / I (004) )] Was 0.1.
Then, EC / FEC / VC / MEC / DEC (25/3/2/30/40 volume) obtained by laminating a positive electrode sheet, a microporous polyethylene film separator, and a negative electrode sheet in this order and dissolving 1M LiPF ₆ as an electrolytic solution. Ratio) non-aqueous electrolyte was added to prepare a 2032 type coin battery. The power storage device characteristics are shown in Table 1.

[Measurement of electrical storage device characteristics]
<First charge / discharge efficiency>
Using the coin battery produced by the above method, in a constant temperature bath at 25 ° C., charge at a constant current of 1C and a constant voltage for 3 hours to a final voltage of 4.2V, and to a final voltage of 2.75V under a constant current of 1C. After discharging, the initial charge / discharge efficiency was determined from the following equation.
Initial charge / discharge efficiency (%) = initial discharge capacity / initial charge capacity x 100

<Capacity maintenance rate after 100 cycles>
Subsequently, the coin battery is charged in a constant temperature bath at 25 ° C. with a constant current and a constant voltage of 1 C for 3 hours to a final voltage of 4.2 V, and then discharged to a final voltage of 2.75 V under a constant current of 1 C. This was repeated until 100 cycles were reached. And the capacity | capacitance maintenance factor after 100 cycles was calculated | required with the following formula | equation.
Capacity retention rate (%) = (discharge capacity at 100th cycle / initial discharge capacity) × 100

<Gas generation after charge storage>
Using another coin battery produced by the same method as described above, in a constant temperature bath at 25 ° C., charging at a constant current of 1 C and a constant voltage for 3 hours to a final voltage of 4.2 V, the coin battery is in an open circuit state. It preserve | saved for 10 days in a 60 degreeC thermostat. Thereafter, after discharging to a final voltage of 2.75 V under a constant current of 1 C, the amount of gas generated was measured by the Archimedes method. The relative amount of gas generated was examined on the basis of the amount of gas generated in Comparative Example 1 as 100%.
Table 1 shows the measurement results of the measurement of the electricity storage device characteristics.

  From Examples 1 to 25, which are examples relating to the negative electrode active material of the invention of aspect 1, the negative electrode active materials (A-1 to A-25) of the present invention correspond to silicon-copper alloy negative electrode active materials of the prior art. First-time charge / discharge of the electricity storage device produced using these negative electrode active materials rather than the negative electrode active material (C-1) which does not substantially contain oxygen and the negative electrode active material (C-2) which is excessively oxidized and has a high oxygen content The efficiency (that is, a measure that does not waste charging energy), the capacity maintenance rate after 100 cycles, and the gas suppression effect after storage after charging are all significantly improved, and it is considered preferable to eliminate oxygen as much as possible. It has been found that the technical idea for the conventional negative electrode active material of silicon-copper alloy exhibits an unexpected effect.

Examples 26 to 31 and Comparative Examples 3 and 4
A coin battery was manufactured in the same manner as in Example 3 except that the negative electrode active material A-3 was used and the contents of the silicon-copper alloy and the artificial graphite in the negative electrode mixture were changed as shown in Table 2 ( Example 26 to Example 28), instead of artificial graphite (d ₀₀₂ = 0.335 nm, D50 = 19 μm) used in Example 3, artificial graphite having different average particle diameters (d ₀₀₂ = 0.335 nm, D50 = 19 μm) except that a coin battery was manufactured in the same manner as in Example 3 (Example 29). Instead of the conductive agent acetylene black, a graphite mesh surface composed only of carbon atoms was closed head. Forming a bell-shaped structural unit having a top portion and a body portion having an open bottom; the bell-shaped structural unit is stacked by sharing 2 to 30 pieces sharing a central axis; Head-to-Tai Fine carbon fiber powder AMC (registered trademark, manufactured by Ube Industries, Ltd., d002 of graphite structure by XRD measurement is 0.3437 nm, fine carbon fiber by TEM image analysis) Parameters relating to the size of the bell-shaped structural unit and its assembly are D = 12 nm, d = 7 nm, L = 114 nm, L / D = 9.5, the average value of θ is about 3 °, and an assembly is formed. A coin battery was prepared in the same manner as in Example 3 except that the number of bell-shaped structural units was about 10) (Example 30). Instead of PVDF as a binder, aromatic tetracarboxylic acid and U-Varnish-A (registered trademark, manufactured by Ube Industries, Ltd.) which is a 1-methyl-2-pyrrolidone solution of polyamic acid obtained from a diamine compound (a precursor of polyimide) A coin battery was prepared in the same manner as in Example 30 (Example 31) except that the negative electrode active material C-1 was used instead of the negative electrode active material A-3. Table 2 shows the results of measuring power storage device characteristics using coin batteries that were produced in the same manner (Comparative Example 3 and Comparative Example 4). In Table 2, the results of Example 3 and Comparative Examples 1 and 2 described above are also shown.

  Electricity storage using the negative electrode sheet of Examples 3 and 26 to 31 of the present invention from Examples 3 and 26 to 31 which are examples relating to the negative electrode sheet of the invention of aspect 2 and the electricity storage device of the invention of aspect 3 using the same The device uses a negative electrode active material (C-1) substantially free of oxygen corresponding to the silicon-copper alloy negative electrode active material of the prior art or a negative electrode active material (C-2) that is excessively oxidized and has a high oxygen content. Compared with the electricity storage device using the produced negative electrode sheet, the initial charge / discharge efficiency of the electricity storage device (that is, a measure that does not waste the charging energy), the capacity retention rate after 100 cycles, and the gas suppression effect after charge storage are all significant. It has been improved, and it turned out that a remarkable synergistic effect that is not seen in the negative electrode sheet using the conventional silicon-copper alloy, which was thought to be preferable to eliminate oxygen as much as possible, was exhibited. It was.

Examples 32-39
Table 3 also shows the results of producing a coin battery and measuring the characteristics of the electricity storage device in the same manner as in Example 3 except that the nonaqueous electrolytic solution shown in Table 3 was used. In Table 3, the results of Example 3 and Comparative Examples 1 and 2 are also shown.

  From Examples 32-39 which are examples relating to the electricity storage device of the invention of aspect 3, the electricity storage device using the non-aqueous electrolyte of various compositions using the silicon-copper alloy of the present invention is a silicon-copper alloy of the prior art. Compared to the negative electrode active material (C-1) which does not substantially contain oxygen corresponding to the negative electrode active material and the negative electrode active material (C-2) which is excessively oxidized and has a high oxygen content, The initial charge / discharge efficiency (that is, a measure that does not waste charge energy), the capacity retention rate after 100 cycles, and the gas suppression effect after charge storage are all significantly improved, and it is preferable to eliminate oxygen as much as possible. It was found that a remarkable synergistic effect that is not seen in the conventional silicon-copper alloy negative electrode active material that was considered to be

  The lithium secondary battery using the non-aqueous electrolyte of the present invention is useful as an electricity storage device such as a lithium secondary battery having excellent electrochemical characteristics in a wide temperature range.

Claims (16)

The following general formula (I)
_{Si p Cu q M r O s} (I)
(However, p + q + r + s = 100, s = 0.01-5, q = 5-50, r = 0-10, M is Be, B, Al, P, Zn, Ga, Ge, In, Sn, Sb, It represents at least one element selected from Y, Zr, Nb, Mo, and W.)
A silicon-copper alloy negative electrode active material containing a trace amount of oxygen represented by :
A silicon-copper alloy negative electrode active material in which a diffraction peak corresponding to the diffraction peak position of silicon simple substance and SiCu ₃ is detected by XRD measurement .   The negative electrode active material represented by the general formula (I) forms a powder, and an average particle diameter (D50) of secondary particles of the powder is 1 to 40 µm. The negative electrode active material according to 1.   In the said general formula (I), it is s = 0.2-2, The negative electrode active material of Claim 1 or 2 characterized by the above-mentioned. Negative electrode active material represented by the general formula (I), composed mainly of SiCu ₃ O _y having the same crystal structure phase mainly composed of SiO _x having the same crystal structure as elemental silicon (A) and SiCu ₃ The negative electrode active material according to claim 3, wherein the negative electrode active material comprises a phase (B).
(However, the oxygen distribution parameter x / y is 0.5 or less. In addition, when the negative electrode active material represented by the general formula (I) includes the element M, the atom M includes the phase (A), the phase (It may be included in any of (B), or may be included as a phase other than phase (A) and phase (B).)   5. The negative electrode active material according to claim 4, wherein the average crystal grain size of the phase (A) is 0.1 to 10 μm. The negative electrode active material according to claim 2 , wherein a 5% diameter (D5) of a volume cumulative particle size distribution of secondary particles of the powder is 0.2 μm or more.   A negative electrode sheet, wherein the negative electrode mixture comprising the negative electrode active material according to claim 1, a carbon material, and a binder is applied to the surface of a copper current collector. The carbon material includes at least graphite powder, the specific surface area of the graphite powder is 0.5 to 10 m ² / g, d002 is 0.335 to 0.337 nm, and the negative electrode mixture of the graphite powder Content in the inside is 55-95 mass%, The negative electrode sheet of Claim 7 characterized by the above-mentioned.   The negative electrode sheet according to claim 7 or 8, wherein the carbon material includes at least fibrous carbon powder.   In the fibrous carbon powder, a graphite mesh surface composed of only carbon atoms forms a bell-shaped structural unit having a closed top portion and a trunk portion having an open lower portion, and the bell-shaped structural unit is a center. 2-30 pieces are stacked by sharing an axis to form an aggregate, and the aggregate is composed of fine carbon fibers that are connected to form a fiber in a head-to-tail manner at intervals. The negative electrode sheet according to claim 9.   11. The negative electrode sheet according to claim 9, wherein 1 to 10% by mass of the fibrous carbon powder is contained in the negative electrode mixture.   The negative electrode sheet according to any one of claims 7 to 11, wherein the binder contains at least a polyimide obtained from an aromatic tetracarboxylic acid and / or a derivative thereof and a diamine compound.   An electricity storage device comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte in which an electrolyte salt is dissolved in a non-aqueous solvent, wherein the negative electrode includes at least the negative electrode active material according to any one of claims 1 to 6. Power storage device.   An electricity storage device including a positive electrode, a negative electrode, and a nonaqueous electrolytic solution in which an electrolyte salt is dissolved in a nonaqueous solvent, wherein the negative electrode uses the negative electrode sheet according to any one of claims 7 to 12. Power storage device.   A cyclic carbonate containing a carbon-carbon double bond and / or a carbon-carbon triple bond selected from vinylene carbonate, vinyl ethylene carbonate, and 4-ethynyl-1,3-dioxolan-2-one in the non-aqueous electrolyte Any one or more of cyclic carbonates having a fluorine atom selected from 4-fluoro-1,3-dioxolan-2-one, trans or cis-4,5-difluoro-1,3-dioxolan-2-one The power storage device according to claim 13 or 14, characterized in that:   In the non-aqueous electrolyte, ethyl 2- (diethoxyphosphoryl) acetate, 2-propynyl 2- (diethoxyphosphoryl) acetate, 1,5-diisocyanatopentane, 1,6-diisocyanatohexane, 1, It contains 0.001% to 5% by mass of at least one selected from 7-diisocyanatoheptane, succinonitrile, 2-ethylsuccinonitrile, glutaronitrile, 3-methylglutaronitrile, adiponitrile, and pimelonitrile. The electrical storage device in any one of Claims 13-15 characterized by these.

Images